Epitaxial stabilization and phase instability of VO2 polymorphs

NASA Astrophysics Data System (ADS)

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

2016-01-01

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

Epitaxial stabilization and phase instability of VO2 polymorphs.

PubMed

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

2016-01-20

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

Epitaxial stabilization and phase instability of VO2 polymorphs

PubMed Central

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

2016-01-01

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

Epitaxial stabilization and phase instability of VO 2 polymorphs

DOE PAGES

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

2016-01-20

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

VoCATS User Guide. [Draft.

ERIC Educational Resources Information Center

North Carolina State Dept. of Public Instruction, Raleigh. Div. of Vocational Education Services.

This guide focuses on use of the North Carolina Vocational Competency Achievement Tracking System (VoCATS)-designated software in the instructional management process. (VoCATS is a competency-based, computer-based instructional management system that allows the collection of data on student performance achievement prior to, during, and following…

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.

UkrVO astronomical WEB services

NASA Astrophysics Data System (ADS)

Mazhaev, A.

2017-02-01

Ukraine Virtual Observatory (UkrVO) has been a member of the International Virtual Observatory Alliance (IVOA) since 2011. The virtual observatory (VO) is not a magic solution to all problems of data storing and processing, but it provides certain standards for building infrastructure of astronomical data center. The astronomical databases help data mining and offer to users an easy access to observation metadata, images within celestial sphere and results of image processing. The astronomical web services (AWS) of UkrVO give to users handy tools for data selection from large astronomical catalogues for a relatively small region of interest in the sky. Examples of the AWS usage are showed.

Metamaterials based on the phase transition of VO2

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

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.

VoIP to the Rescue

ERIC Educational Resources Information Center

Milner, Jacob

2005-01-01

Voice over Internet Protocol (VoIP) is everywhere. The technology lets users make and receive phone calls over the Internet, transporting voice traffic alongside data traffic such as instant messages (IMs) and e-mail. While the number of consumer customers using VoIP increases every week, the technology is finding its way into K-12 education as…

Security Research on VoIP with Watermarking

NASA Astrophysics Data System (ADS)

Hu, Dong; Lee, Ping

2008-11-01

With the wide application of VoIP, many problems have occurred. One of the problems is security. The problems with securing VoIP systems, insufficient standardization and lack of security mechanisms emerged the need for new approaches and solutions. In this paper, we propose a new security architecture for VoIP which is based on digital watermarking which is a new, flexible and powerful technology that is increasingly gaining more and more attentions. Besides known applications e.g. to solve copyright protection problems, we propose to use digital watermarking to secure not only transmitted audio but also signaling protocol that VoIP is based on.

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.

Tunable VO{sub 2}/Au hyperbolic metamaterial

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

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

2016-08-08

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

Spectroscopic analysis in the virtual observatory environment with SPLAT-VO

NASA Astrophysics Data System (ADS)

Škoda, P.; Draper, P. W.; Neves, M. C.; Andrešič, D.; Jenness, T.

2014-11-01

SPLAT-VO is a powerful graphical tool for displaying, comparing, modifying and analysing astronomical spectra, as well as searching and retrieving spectra from services around the world using Virtual Observatory (VO) protocols and services. The development of SPLAT-VO started in 1999, as part of the Starlink StarJava initiative, sometime before that of the VO, so initial support for the VO was necessarily added once VO standards and services became available. Further developments were supported by the Joint Astronomy Centre, Hawaii until 2009. Since end of 2011 development of SPLAT-VO has been continued by the German Astrophysical Virtual Observatory, and the Astronomical Institute of the Academy of Sciences of the Czech Republic. From this time several new features have been added, including support for the latest VO protocols, along with new visualization and spectra storing capabilities. This paper presents the history of SPLAT-VO, its capabilities, recent additions and future plans, as well as a discussion on the motivations and lessons learned up to now.

Triclinic-monoclinic-orthorhombic (T-M-O) structural transitions in phase diagram of FeVO4-CrVO4 solid solutions

NASA Astrophysics Data System (ADS)

Bera, Ganesh; Reddy, V. R.; Rambabu, P.; Mal, P.; Das, Pradip; Mohapatra, N.; Padmaja, G.; Turpu, G. R.

2017-09-01

Phase diagram of FeVO4-CrVO4 solid solutions pertinent with structural and magnetic phases is presented with unambiguous experimental evidences. Solid solutions Fe1-xCrxVO4 (0 ≤ x ≤ 1.0) were synthesized through the standard solid state route and studied by X-ray diffraction, scanning electron microscopy, energy dispersive spectra of X-rays, Raman spectroscopy, d.c. magnetization, and 57Fe Mössbauer spectroscopic studies. FeVO4 and CrVO4 were found to be in triclinic (P-1 space group) and orthorhombic structures (Cmcm space group), respectively. Cr incorporation into the FeVO4 lattice leads to the emergence of a new monoclinic phase dissimilar to the both end members of the solid solutions. In Fe1-xCrxVO4 up to x = 0.10, no discernible changes in the triclinic structure were found. A new structural monoclinic phase (C2/m space group) emerges within the triclinic phase at x = 0.125, and with the increase in Cr content, it gets stabilized with clear single phase signatures in the range of x = 0.175-0.25 as evidenced by the Rietveld analysis of the structures. Beyond x = 0.33, orthorhombic phase similar to CrVO4 (Cmcm space group) emerges and coexists with a monoclinic structure up to x = 0.85, which finally tends to stabilize in the range of x = 0.90-1.00. The Raman spectroscopic studies also confirm the structural transition. FeVO4 Raman spectra show the modes related to three nonequivalent V ions in the triclinic structure, where up to 42 Raman modes are observed in the present study. With the stabilization of structures having higher symmetry, the number of Raman modes decreases and the modes related to symmetry inequivalent sites collate into singular modes from the doublet structure. A systematic crossover from two magnetic transitions in FeVO4, at 21.5 K and 15.4 K to single magnetic transition in CrVO4, at 71 K (antiferromagnetic transition), is observed in magnetization studies. The intermediate solid solution with x = 0.15 shows two magnetic transitions

Oxidizing annealing effects on VO2 films with different microstructures

NASA Astrophysics Data System (ADS)

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

2015-08-01

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

Williams with VO2max

NASA Image and Video Library

2012-08-08

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

BiVO4 microstructures with various morphologies: Synthesis and characterization

NASA Astrophysics Data System (ADS)

Wu, Min; Jing, Qifeng; Feng, Xinyan; Chen, Limiao

2018-01-01

Bismuth vanadate (BiVO4) microstructures with dumbbell, rod, ellipsoid, sphere, and cake-like morphologies have been successfully fabricated by using a surfactant-free hydrothermal method, in which the morphology of the BiVO4 microstructures can be tuned by simply varying the molar ratio of Bi(NO)3·5H2O to NaVO3 in the starting materials. Based on a series of contrast experiments, the probable formation mechanism of the BiVO4 microstructures with multiple shapes have been proposed. The photocatalytic performances of the as-prepared BiVO4 microstructures have been evaluated by studying the degradation of Rhodamine B solutions under visible light irradiation. The results reveal that the cake-like BiVO4 microstructures exhibit the higher photocatalytic activity than other BiVO4 microstructures due to its high surface area and unique morphology.

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

PubMed

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

2013-06-25

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

Audio CAPTCHA for SIP-Based VoIP

NASA Astrophysics Data System (ADS)

Soupionis, Yannis; Tountas, George; Gritzalis, Dimitris

Voice over IP (VoIP) introduces new ways of communication, while utilizing existing data networks to provide inexpensive voice communications worldwide as a promising alternative to the traditional PSTN telephony. SPam over Internet Telephony (SPIT) is one potential source of future annoyance in VoIP. A common way to launch a SPIT attack is the use of an automated procedure (bot), which generates calls and produces audio advertisements. In this paper, our goal is to design appropriate CAPTCHA to fight such bots. We focus on and develop audio CAPTCHA, as the audio format is more suitable for VoIP environments and we implement it in a SIP-based VoIP environment. Furthermore, we suggest and evaluate the specific attributes that audio CAPTCHA should incorporate in order to be effective, and test it against an open source bot implementation.

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

PubMed Central

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

2014-01-01

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

Origin of phase transition in VO2

NASA Astrophysics Data System (ADS)

Basu, Raktima; Sardar, Manas; Dhara, Sandip

2018-04-01

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

The structural conversion from α-AgVO3 to β-AgVO3: Ag nanoparticle decorated nanowires with application as cathode materials for Li-ion batteries.

PubMed

McNulty, David; Ramasse, Quentin; O'Dwyer, Colm

2016-09-15

The majority of electrode materials in batteries and related electrochemical energy storage devices are fashioned into slurries via the addition of a conductive additive and a binder. However, aggregation of smaller diameter nanoparticles in current generation electrode compositions can result in non-homogeneous active materials. Inconsistent slurry formulation may lead to inconsistent electrical conductivity throughout the material, local variations in electrochemical response, and the overall cell performance. Here we demonstrate the hydrothermal preparation of Ag nanoparticle (NP) decorated α-AgVO 3 nanowires (NWs) and their conversion to tunnel structured β-AgVO 3 NWs by annealing to form a uniform blend of intercalation materials that are well connected electrically. The synthesis of nanostructures with chemically bound conductive nanoparticles is an elegant means to overcome the intrinsic issues associated with electrode slurry production, as wire-to-wire conductive pathways are formed within the overall electrode active mass of NWs. The conversion from α-AgVO 3 to β-AgVO 3 is explained in detail through a comprehensive structural characterization. Meticulous EELS analysis of β-AgVO 3 NWs offers insight into the true β-AgVO 3 structure and how the annealing process facilitates a higher surface coverage of Ag NPs directly from ionic Ag content within the α-AgVO 3 NWs. Variations in vanadium oxidation state across the surface of the nanowires indicate that the β-AgVO 3 NWs have a core-shell oxidation state structure, and that the vanadium oxidation state under the Ag NP confirms a chemically bound NP from reduction of diffused ionic silver from the α-AgVO 3 NWs core material. Electrochemical comparison of α-AgVO 3 and β-AgVO 3 NWs confirms that β-AgVO 3 offers improved electrochemical performance. An ex situ structural characterization of β-AgVO 3 NWs after the first galvanostatic discharge and charge offers new insight into the Li + reaction

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

Electronic structure and insulating gap in epitaxial VO 2 polymorphs

DOE PAGES

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

2015-12-24

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

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

PubMed

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

2018-04-25

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

Using VoIP to compete.

PubMed

Werbach, Kevin

2005-09-01

Internet telephony, or VoIP, is rapidly replacing the conventional kind. This year, for the first time, U.S. companies bought more new Internet-phone connections than standard lines. The major driver behind this change is cost. But VoIP isn't just a new technology for making old-fashioned calls cheaper, says consultant Kevin Werbach. It is fundamentally changing how companies use voice communications. What makes VoIP so powerful is that it turns voice into digital data packets that can be stored, copied, combined with other data, and distributed to virtually any device that connects to the Internet. And it makes it simple to provide all the functionality of a corporate phone-call features, directories, security-to anyone anywhere there's broadband access. That fosters new kinds of businesses such as virtual call centers, where widely dispersed agents work at all hours from their homes. The most successful early adopters, says Werbach, will focus more on achieving business objectives than on saving money. They will also consider how to push VoIP capabilities out to the extended organization, making use of everyone as a resource. Deployment may be incremental, but companies should be thinking about where VoIP could take them. Executives should ask what they could do if, on demand, they could bring all their employees, customers, suppliers, and partners together in a virtual room, with shared access to every modern communications and computing channel. They should take a fresh look at their business processes to find points at which richer and more customizable communications could eliminate bottlenecks and enhance quality. The important dividing line won't be between those who deploy Vol P and those who don't, or even between early adopters and laggards. It will be between those who see Vol P as just a new way to do the same old things and those who use itto rethink their entire businesses.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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.

Integrating the IA2 Astronomical Archive in the VO: The VO-Dance Engine

NASA Astrophysics Data System (ADS)

Molinaro, M.; Laurino, O.; Smareglia, R.

2012-09-01

Virtual Observatory (VO) protocols and standards are getting mature and the astronomical community asks for astrophysical data to be easily reachable. This means data centers have to intensify their efforts to provide the data they manage not only through proprietary portals and services but also through interoperable resources developed on the basis of the IVOA (International Virtual Observatory Alliance) recommendations. Here we present the work and ideas developed at the IA2 (Italian Astronomical Archive) data center hosted by the INAF-OATs (Italian Institute for Astrophysics - Trieste Astronomical Observatory) to reach this goal. The core point is the development of an application that from existing DB and archive structures can translate their content to VO compliant resources: VO-Dance (written in Java). This application, in turn, relies on a database (potentially DBMS independent) to store the translation layer information of each resource and auxiliary content (UCDs, field names, authorizations, policies, etc.). The last token is an administrative interface (currently developed using the Django python framework) to allow the data center administrators to set up and maintain resources. This deployment, platform independent, with database and administrative interface highly customizable, means the package, when stable and easily distributable, can be also used by single astronomers or groups to set up their own resources from their public datasets.

Current Status of VO Compliant Data Service in Japanese Virtual Observatory

NASA Astrophysics Data System (ADS)

Shirasaki, Y.; Komiya, Y.; Ohishi, M.; Mizumoto, Y.; Ishihara, Y.; Tsutsumi, J.; Hiyama, T.; Nakamoto, H.; Sakamoto, M.

2012-09-01

In these years, standards to build a Virtual Observatory (VO) data service have been established with the efforts in the International Virtual Observatory Alliance (IVOA). We applied these newly established standards (SSAP, TAP) to our VO service toolkit which was developed to implement earlier VO standards SIAP and (deprecated) SkyNode. The toolkit can be easily installed and provides a GUI interface to construct and manage VO service. In this paper, we describes the architecture of our toolkit and how it is used to start hosting VO service.

The preparation of a plasmonically resonant VO2 thermochromic pigment.

PubMed

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

2009-02-25

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

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.

Mobile telephones: a comparison of radiated power between 3G VoIP calls and 3G VoCS calls.

PubMed

Jovanovic, Dragan; Bragard, Guillaume; Picard, Dominique; Chauvin, Sébastien

2015-01-01

The purpose of this study is to assess the mean RF power radiated by mobile telephones during voice calls in 3G VoIP (Voice over Internet Protocol) using an application well known to mobile Internet users, and to compare it with the mean power radiated during voice calls in 3G VoCS (Voice over Circuit Switch) on a traditional network. Knowing that the specific absorption rate (SAR) is proportional to the mean radiated power, the user's exposure could be clearly identified at the same time. Three 3G (High Speed Packet Access) smartphones from three different manufacturers, all dual-band for GSM (900 MHz, 1800 MHz) and dual-band for UMTS (900 MHz, 1950 MHz), were used between 28 July and 04 August 2011 in Paris (France) to make 220 two-minute calls on a mobile telephone network with national coverage. The places where the calls were made were selected in such a way as to describe the whole range of usage situations of the mobile telephone. The measuring equipment, called "SYRPOM", recorded the radiation power levels and the frequency bands used during the calls with a sampling rate of 20,000 per second. In the framework of this study, the mean normalised power radiated by a telephone in 3G VoIP calls was evaluated at 0.75% maximum power of the smartphone, compared with 0.22% in 3G VoCS calls. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR.

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.

CT enterography: Mannitol versus VoLumen.

PubMed

Wong, Jessica; Moore, Helen; Roger, Mark; McKee, Chris

2016-10-01

Several different neutral oral contrast agents have been trialled in magnetic resonance and CT enterography (CTE). In the Auckland region, Mannitol 2.5% and VoLumen are both used in CTE. This study compares the performance of these two neutral oral contrast agents in CTE. Computed tomography enterography data were collected from 25 consecutive studies that used either Mannitol or VoLumen in 2014. All images were reviewed by three radiologists blinded to the type of oral contrast. Each quadrant was assessed for maximum distension, proportion of bowel loops distended, presence of inhomogeneous content and bowel wall visibility. Assessment also included whether the contrast agent reached the caecum and an overall subjective quality assessment. Patients were invited to answer a questionnaire regarding tolerability of the preparations. Mannitol achieves better wall visibility in the right upper quadrant, left upper quadrant and left lower quadrant (P < 0.01). Overall differences in study quality favours Mannitol (P < 0.01) with 48% of the Mannitol studies being considered excellent compared with 4% of the VoLumen studies. There was no difference in maximal distension or proportion of loops distended. Mannitol in CTE achieves studies of a better quality than and is a viable alternative to VoLumen. © 2016 The Royal Australian and New Zealand College of Radiologists.

Research progress of VO2 thin film as laser protecting material

NASA Astrophysics Data System (ADS)

Liu, Zhiwei; Lu, Yuan; Hou, Dianxin

2018-03-01

With the development of laser technology, the battlefield threat of directional laser weapons is becoming more and more serious. The blinding and destruction caused by laser weapons on the photoelectric equipment is an important part of the current photo-electronic warfare. The research on the defense technology of directional laser weapons based on the phase transition characteristics of VO2 thin films is an important subject. The researches of VO2 thin films are summarized based on review these points: the preparation methods of VO2 thin films, phase transition mechanism, phase transition temperature regulating, interaction between VO2 thin films and laser, and the application prospect of vo2 thin film as laser protecting material. This paper has some guiding significance for further research on the VO2 thin films in the field of defense directional laser weapons.

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.

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.

Electronic structure of HxVO2 probed with in-situ spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Kim, So Yeun; Sandilands, Luke J.; Kang, Taedong; Son, Jaeseok; Sohn, C. H.; Yoon, Hyojin; Son, Junwoo; Moon, S. J.; Noh, T. W.

Vanadium dioxide (VO2) undergoes a metal-to-insulator transition (MIT) near 340K. Despite extensive studies on this material, the role of electron-electron correlation and electron-lattice interactions in driving this MIT is still under debate. Recently, it was demonstrated that hydrogen can be reversibly absorbed into VO2 thin film without destroying the lattice framework. This H-doping allows systematic control of the electron density and lattice structure which in turn leads to a insulator (VO2) - metal (HxVO2) - insulator (HVO2) phase modulation. To better understand the phase modulation of HxVO2, we used in-situ spectroscopic ellipsometry to monitor the electronic structure during the hydrogenization process, i.e. we measured the optical conductivity of HxVO2 while varying x. Starting in the high temperature rutile metallic phase of VO2, we observed a large change in the electronic structure upon annealing in H gas at 370K: the low energy conductivity is continuously suppressed, consistent with reported DC resistivity data, while the conductivity peaks at high energy show strong changes in energy and spectral weight. The implications of our results for the MIT in HxVO2 will be discussed.

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

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.

Persistent electrochemical performance in epitaxial VO 2(B)

DOE PAGES

Lee, Shinbuhm; Sun, Xiao -Guang; Lubimtsev, Andrew A.; ...

2017-03-07

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 [VO 2(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 VO 2(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 scanningmore » transmission electron microscopy and density functional theory calculations also reveal that the unique open pathways in VO 2(B) provide the most stable sites for Li adsorption and diffusion. Furthermore, this work ultimately demonstrates that VO 2(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.« less

A VO-Driven Astronomical Data Grid in China

NASA Astrophysics Data System (ADS)

Cui, C.; He, B.; Yang, Y.; Zhao, Y.

2010-12-01

With the implementation of many ambitious observation projects, including LAMOST, FAST, and Antarctic observatory at Doom A, observational astronomy in China is stepping into a brand new era with emerging data avalanche. In the era of e-Science, both these cutting-edge projects and traditional astronomy research need much more powerful data management, sharing and interoperability. Based on data-grid concept, taking advantages of the IVOA interoperability technologies, China-VO is developing a VO-driven astronomical data grid environment to enable multi-wavelength science and large database science. In the paper, latest progress and data flow of the LAMOST, architecture of the data grid, and its supports to the VO are discussed.

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

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

Zhang, Yifu; Huang, Yanfen; Zhang, Juecheng

2012-08-15

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

Determining the role of TiO/VO in hot exoplanet atmospheres

NASA Astrophysics Data System (ADS)

Evans, Thomas

2016-10-01

The role of TiO and VO in ultra hot (>2000K) gas giant atmospheres is a major unresolved issue in the exoplanet field. At these temperatures, TiO and VO are known to be important absorbers in the atmospheres of M/L dwarfs and have been theorized to play an important role in irradiated gas giants. To date, however, TiO/VO has not been securely detected in a planetary atmosphere, despite numerous searches. One possibility is that the upper atmospheres of highly irradiated planets are typically depleted of TiO/VO by cold-trapping at lower altitudes or rain-out on the relatively cool nightside. Using WFC3 G141 and ground-based photometry, we have recently published a transmission spectrum for WASP-121b (T~2400K) showing new evidence for absorption by TiO/VO. Our observations also yielded a high confidence (5.4 sigma) detection of the 1.4 micron H2O absorption band. The TiO/VO claim, however, remains tentative, as it currently hinges upon broadband photometry measurements obtained from the ground at relatively low signal-to-noise. If TiO/VO is present it will have significant implications for the overall physics and chemistry of the atmosphere, including the likely production of a strong thermal inversion in the upper atmosphere. I will describe the follow-up observations we are currently pursuing in order to confirm or rule out TiO/VO in the atmosphere of WASP-121b and in doing so address a long-standing mystery of exoplanet atmospheres.

Proposal of Secure VoIP System Using Attribute Certificate

NASA Astrophysics Data System (ADS)

Kim, Jin-Mook; Jeong, Young-Ae; Hong, Seong-Sik

VoIP is a service that changes the analogue audio signal into a digital signal and then transfers the audio information to the users after configuring it as a packet; and it has an advantage of lower price than the existing voice call service and better extensibility. However, VoIP service has a system structure that, compared to the existing PSTN (Public Switched Telephone Network), has poor call quality and is vulnerable in the security aspect. To make up these problems, TLS service was introduced to enhance the security. In practical system, however, since QoS problem occurs, it is necessary to develop the VoIP security system that can satisfy QoS at the same time in the security aspect. In this paper, a user authentication VoIP system that can provide a service according to the security and the user through providing a differential service according to the approach of the users by adding AA server at the step of configuring the existing VoIP session is suggested. It was found that the proposed system of this study provides a quicker QoS than the TLS-added system at a similar level of security. Also, it is able to provide a variety of additional services by the different users.

Pacing strategy and VO2 kinetics during a 1500-m race.

PubMed

Hanon, C; Leveque, J-M; Thomas, C; Vivier, L

2008-03-01

We investigated the oxygen uptake response (V.O (2)) to a 1500-m test conducted using a competition race strategy. On an outdoor track, eleven middle-distance runners performed a test to determine V.O (2max), velocity associated with V.O (2max) (v-V.O (2max)) and a supramaximal 1500-m running test (each test at least two days apart). V.O (2max) response was measured with the use of a miniaturised telemetric gas exchange system (Cosmed, K4, Roma, Italy). The 1500-m running test was performed at a mean velocity of 107. 6 + 2 % v-V.O (2max). The maximal value of oxygen uptake recorded during the 1500-m test (V.O (2peak)) was reached by subjects at 75.9 + 7.5 s (mean + SD) (i.e., 459 +/- 59 m). The time to reach V.O (2max) (TV.O (2peak)) and the start velocity (200- to 400-m after the onset of the 1500 m) expressed in % v-V.O (2max) were negatively and significantly correlated (p < 0.05), but our results indicate that a fast start does not necessarily induce a good performance. These results suggest that V.O (2max) is reached by all the subjects at the onset of a simulated 1500-m running event and are therefore in contrast with previous results obtained during treadmill running.

Thermal hysteresis measurement of the VO2 emissivity and its application in thermal rectification.

PubMed

Gomez-Heredia, C L; Ramirez-Rincon, J A; Ordonez-Miranda, J; Ares, O; Alvarado-Gil, J J; Champeaux, C; Dumas-Bouchiat, F; Ezzahri, Y; Joulain, K

2018-05-31

Hysteresis loops in the emissivity of VO 2 thin films grown on sapphire and silicon substrates by a pulsed laser deposition process are experimentally measured through the thermal-wave resonant cavity technique. Remarkable variations of about 43% are observed in the emissivity of both VO 2 films, within their insulator-to-metal and metal-to-insulator transitions. It is shown that: i) The principal hysteresis width (maximum slope) in the VO 2 emissivity of the VO 2  + silicon sample is around 3 times higher (lower) than the corresponding one of the VO 2  + sapphire sample. VO 2 synthesized on silicon thus exhibits a wider principal hysteresis loop with slower MIT than VO 2 on sapphire, as a result of the significant differences on the VO 2 film microstructures induced by the silicon or sapphire substrates. ii) The hysteresis width along with the rate of change of the VO 2 emissivity in a VO 2  + substrate sample can be tuned with its secondary hysteresis loop. iii) VO 2 samples can be used to build a radiative thermal diode able to operate with a rectification factor as high as 87%, when the temperature difference of its two terminals is around 17 °C. This record-breaking rectification constitutes the highest one reported in literature, for a relatively small temperature change of diode terminals.

A novel magneto-optical crystal Yb:TbVO4

NASA Astrophysics Data System (ADS)

Zhu, Xianchao; Tu, Heng; Hu, Zhanggui

2018-04-01

Highly transparent Yb:TbVO4 single crystal with dimensions of Ø27 × 41 mm3 alomost without scattering defects has been successfully grown by Czochralski technique. The spectra, thermal properties and laser-induced damage threshold were investigated in detailed. The Faraday rotation (FR) measurement was carried out by means of extinction method. The Verdet constant comes up to 80 rad m-1 T-1 at 1064 nm, significantly larger than TbVO4 (58 rad m-1 T-1) and TGG (40 rad m-1 T-1) reported. Meanwhile, the as-grown crystal presents lower absorption coefficient and higher magneto-optical figure of merit at measured wavelength in comparison with TGG. Moreover, the crystal exhibits a substantially improved extinction ratio (42 dB) in contrast with TbVO4 (29 dB), and exceeds the highest value of TGG (40 dB). These advantages make Yb:TbVO4 a highly promising magneto-optical material candidate for optical isolators in the visible-near infrared region.

BiVO4 thin film photoanodes grown by chemical vapor deposition.

PubMed

Alarcón-Lladó, Esther; Chen, Le; Hettick, Mark; Mashouf, Neeka; Lin, Yongjing; Javey, Ali; Ager, Joel W

2014-01-28

BiVO4 thin film photoanodes were grown by vapor transport chemical deposition on FTO/glass substrates. By controlling the flow rate, the temperatures of the Bi and V sources (Bi metal and V2O5 powder, respectively), and the temperature of the deposition zone in a two-zone furnace, single-phase monoclinic BiVO4 thin films can be obtained. The CVD-grown films produce global AM1.5 photocurrent densities up to 1 mA cm(-2) in aqueous conditions in the presence of a sacrificial reagent. Front illuminated photocatalytic performance can be improved by inserting either a SnO2 hole blocking layer and/or a thin, extrinsically Mo doped BiVO4 layer between the FTO and the CVD-grown layer. The incident photon to current efficiency (IPCE), measured under front illumination, for BiVO4 grown directly on FTO/glass is about 10% for wavelengths below 450 nm at a bias of +0.6 V vs. Ag/AgCl. For BiVO4 grown on a 40 nm SnO2/20 nm Mo-doped BiVO4 back contact, the IPCE is increased to over 40% at wavelengths below 420 nm.

Magnetic structures and magnetocaloric effect in R VO4 (R =Gd , Nd )

NASA Astrophysics Data System (ADS)

Palacios, E.; Evangelisti, M.; Sáez-Puche, R.; Dos Santos-García, A. J.; Fernández-Martínez, F.; Cascales, C.; Castro, M.; Burriel, R.; Fabelo, O.; Rodríguez-Velamazán, J. A.

2018-06-01

We report the magnetic properties and magnetic structure of the zircon-type compound GdVO4, together with the magnetic structure of the isostructural NdVO4. At T ≃2.5 K, GdVO4 undergoes a phase transition to antiferromagnetic Gz, driven mainly by the exchange interactions, while the magnetic anisotropy and dipolar interactions are minor contributions. Near the liquid-helium boiling temperature, the magnetocaloric effect of GdVO4 is nearly as large as that of the structurally closely related GdPO4. It is noteworthy that GdVO4 has been recently proposed as a good passive regenerator in Gifford-McMahon cryocoolers, since adding a magnetization-demagnetization stage to the cryocooler refrigeration cycle would increase its efficiency for liquefying helium. NdVO4 is a canted Gz-type antiferromagnet and shows enhancement of the magnetic reflections in neutron diffraction below ca. 500 mK, due to the polarization of the Nd nuclei by the hyperfine field.

Time to Exhaustion at the VO2max Velocity in Swimming: A Review

PubMed Central

Fernandes, Ricardo J.; Vilas-Boas, J. Paulo

2012-01-01

The aim of this study was to present a review on the time to exhaustion at the minimum swimming velocity corresponding to maximal oxygen consumption (TLim-vVO2max). This parameter is critical both for the aerobic power and the lactate tolerance bioenergetical training intensity zones, being fundamental to characterize it, and to point out its main determinants. The few number of studies conducted in this topic observed that swimmers were able to maintain an exercise intensity corresponding to maximal aerobic power during 215 to 260 s (elite swimmers), 230 to 260 s (high level swimmers) and 310 to 325 s (low level swimmers), and no differences between genders were reported. TLim-vVO2max main bioenergetic and functional determinants were swimming economy and VO2 slow component (direct relationship), and vVO2max, velocity at anaerobic threshold and blood lactate production (inverse relationship); when more homogeneous groups of swimmers were analysed, the inverse correlation value between TLim-vVO2max and vVO2max was not so evident. In general, TLim-vVO2max was not related to VO2max. TLim-vVO2max seems also to be influenced by stroking parameters, with a direct relationship to stroke length and stroke index, and an inverse correlation with stroke rate. Assessing TLim-vVO2max, together with the anaerobic threshold and the biomechanical general parameters, will allow a larger spectrum of testing protocols application, helping to build more objective and efficient training programs. PMID:23486651

VO2 /TiN Plasmonic Thermochromic Smart Coatings for Room-Temperature Applications.

PubMed

Hao, Qi; Li, Wan; Xu, Huiyan; Wang, Jiawei; Yin, Yin; Wang, Huaiyu; Ma, Libo; Ma, Fei; Jiang, Xuchuan; Schmidt, Oliver G; Chu, Paul K

2018-03-01

Vanadium dioxide/titanium nitride (VO 2 /TiN) smart coatings are prepared by hybridizing thermochromic VO 2 with plasmonic TiN nanoparticles. The VO 2 /TiN coatings can control infrared (IR) radiation dynamically in accordance with the ambient temperature and illumination intensity. It blocks IR light under strong illumination at 28 °C but is IR transparent under weak irradiation conditions or at a low temperature of 20 °C. The VO 2 /TiN coatings exhibit a good integral visible transmittance of up to 51% and excellent IR switching efficiency of 48% at 2000 nm. These unique advantages make VO 2 /TiN promising as smart energy-saving windows. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The VO-Dance web application at the IA2 data center

NASA Astrophysics Data System (ADS)

Molinaro, Marco; Knapic, Cristina; Smareglia, Riccardo

2012-09-01

Italian center for Astronomical Archives (IA2, http://ia2.oats.inaf.it) is a national infrastructure project of the Italian National Institute for Astrophysics (Istituto Nazionale di AstroFisica, INAF) that provides services for the astronomical community. Besides data hosting for the Large Binocular Telescope (LBT) Corporation, the Galileo National Telescope (Telescopio Nazionale Galileo, TNG) Consortium and other telescopes and instruments, IA2 offers proprietary and public data access through user portals (both developed and mirrored) and deploys resources complying the Virtual Observatory (VO) standards. Archiving systems and web interfaces are developed to be extremely flexible about adding new instruments from other telescopes. VO resources publishing, along with data access portals, implements the International Virtual Observatory Alliance (IVOA) protocols providing astronomers with new ways of analyzing data. Given the large variety of data flavours and IVOA standards, the need for tools to easily accomplish data ingestion and data publishing arises. This paper describes the VO-Dance tool, that IA2 started developing to address VO resources publishing in a dynamical way from already existent database tables or views. The tool consists in a Java web application, potentially DBMS and platform independent, that stores internally the services' metadata and information, exposes restful endpoints to accept VO queries for these services and dynamically translates calls to these endpoints to SQL queries coherent with the published table or view. In response to the call VO-Dance translates back the database answer in a VO compliant way.

Kyiv UkrVO glass archives: new life

NASA Astrophysics Data System (ADS)

Pakuliak, L.; Golovnya, V.; Andruk, V.; Shatokhina, S.; Yizhakevych, O.; Kazantseva, L.; Lukianchuk, V.

In the framework of UkrVO national project the new methods of plate digital image processing are developed. The photographic material of the UkrVO Joint Digital Archive (JDA) is used for the solution of classic astrometric problem - positional and photometric determinations of objects registered on the plates. The results of tested methods show that the positional rms errors are better than ±150 mas for both coordinates and photometric ones are better than ±0.20m with the Tycho-2 catalogue as reference.

Spectroscopic characterisation of Er-doped LuVO4 single crystals

NASA Astrophysics Data System (ADS)

Lisiecki, R.; Dominiak-Dzik, G.; Solarz, P.; Strzęp, A.; Ryba-Romanowski, W.; Łukasiewicz, T.

2010-12-01

The LuVO4:Er single crystals were grown by the Czochralski technique. The crystal-field split energy levels of Er3+ ion were derived experimentally employing absorption and emission spectra measured at T=10 K. The Judd-Ofelt phenomenological method was used to estimate intensity parameters, radiative lifetimes and branching ratios of luminescence. The excited state dynamics of the LuVO4:Er systems was investigated and experimental lifetimes of emitting levels were measured. The emission cross section of the 4I13/2→4I15/2 transition in the infrared was calculated by the Füchtbauer-Ladenburg method. The gain cross section, estimated for several inverse-population parameters, allowed us to evaluate a potential laser activity of the LuVO4:Er system at 1.6 μm. Also, the potential range of the optical pumping was assessed based on absorption spectra achieved at the room temperature. The optical losses related to the green up-converted emission, encountered under the 978 nm excitation between 300 and 670 K were indicated and discussed. Spectroscopic peculiarities of the Er3+-doped LuVO4 crystal were discussed in relation to optical properties of the YVO4:Er and GdVO4:Er crystals. Taking into account the high quantum efficiency of the 4I13/2 level, and satisfactory absorption and emission features, the LuVO4:Er crystal can be considered as a promising active material for laser operation near 1.6 μm.

Voltage switching of a VO{sub 2} memory metasurface using ionic gel

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

Goldflam, M. D.; Liu, M. K.; Chapler, B. C.

2014-07-28

We demonstrate an electrolyte-based voltage tunable vanadium dioxide (VO{sub 2}) memory metasurface. Large spatial scale, low voltage, non-volatile switching of terahertz (THz) metasurface resonances is achieved through voltage application using an ionic gel to drive the insulator-to-metal transition in an underlying VO{sub 2} layer. Positive and negative voltage application can selectively tune the metasurface resonance into the “off” or “on” state by pushing the VO{sub 2} into a more conductive or insulating regime respectively. Compared to graphene based control devices, the relatively long saturation time of resonance modification in VO{sub 2} based devices suggests that this voltage-induced switching originates primarilymore » from electrochemical effects related to oxygen migration across the electrolyte–VO{sub 2} interface.« less

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

PubMed

Billat, L V; Koralsztein, J P

1996-08-01

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

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

PubMed

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

2014-09-07

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

Structures, physicochemical and cytoprotective properties of new oxidovanadium(IV) complexes -[VO(mIDA)(dmbipy)]·1.5H2O and [VO(IDA)(dmbipy)]·2H2O

NASA Astrophysics Data System (ADS)

Drzeżdżon, Joanna; Jacewicz, Dagmara; Wyrzykowski, Dariusz; Inkielewicz-Stępniak, Iwona; Sikorski, Artur; Tesmar, Aleksandra; Chmurzyński, Lech

2017-09-01

New oxidovanadium(IV) complexes with a modification of the ligand in the VO2+ coordination sphere were synthesized. [VO(mIDA)(dmbipy)]•1.5H2O and [VO(IDA)(dmbipy)]•2H2O were obtained as dark green crystals and grey-green powder, respectively (mIDA = N-methyliminodiacetic anion, IDA = iminodiacetic anion, dmbipy = 4,4‧-dimethoxy-2,2‧-dipyridyl). The crystal structure of [VO(mIDA)(dmbipy)]·1.5H2O has been determined by the X-ray diffraction method. The studies of structure of [VO(mIDA)(dmbipy)]•1.5H2O have shown that this compound occurs in the crystal as two rotational conformers. Furthermore, the stability constants of [VO(mIDA)(dmbipy)]•1.5H2O and [VO(IDA)(dmbipy)]•2H2O complexes in aqueous solutions were studied by using the potentiometric titration method and, consequently, determined using the Hyperquad2008 program. Moreover, the title complexes were investigated as antioxidant substances. The impact of the structure modification in the VO2+ complexes on the radical scavenging activity has been studied. The ability to scavenge the superoxide radical by two complexes - [VO(mIDA)(dmbipy)]·1.5H2O and [VO(IDA)(dmbipy)]·2H2O was studied by cyclic voltammetry (CV) and nitrobluetetrazolium (NBT) methods. The title complexes were also examined by the spectrophotometric method as scavengers of neutral organic radical - 1,1-diphenyl-2-picrylhydrazyl (DPPH•) and radical cation - 2,2'-azinobis-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS•+). Furthermore, the biological properties of two oxidovanadium(IV) complexes were investigated in relation to its cytoprotective properties by the MTT and LDH tests based on the hippocampal HT22 neuronal cell line during the oxidative damage induced by hydrogen peroxide. Finally, the results presented in this paper have shown that the both new oxidovanadium(IV) complexes with the 4,4‧-dimethoxy-2,2‧-dipyridyl ligand can be treated as the cytoprotective substances.

Synthesis, Characterization and Antibacterial Activity of BiVO4 Microstructure

NASA Astrophysics Data System (ADS)

Ekthammathat, Nuengruethai; Phuruangrat, Anukorn; Thongtem, Somchai; Thongtem, Titipun

2018-05-01

Hyperbranched BiVO4 microstructure were successfully synthesized by a hydrothermal method. Upon characterization the products by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, selected area electron diffraction (SAED) and photoluminescence (PL) spectroscopy, pure monoclinic hyperbranched BiVO4 with dominant vibration peak at 810 cm-1 and strong photoemission peak at 360 nm was synthesized in the solution with pH 1. In the solution with pH 2, tetragonal BiVO4 phase was also detected. In this research, antibacterial activity against S. aureus and E. coli was investigated by counting the colony forming unit (CFU). At 37°C within 24 h, the monoclinic BiVO4 phase can play the role in inhibiting S. aureus growth (350 CFU/mL remaining bacteria) better than that against E. coli (a large number of remaining bacteria).

BiVO4 Photoanode with Exposed (040) Facets for Enhanced Photoelectrochemical Performance

NASA Astrophysics Data System (ADS)

Xia, Ligang; Li, Jinhua; Bai, Jing; Li, Linsen; Chen, Shuai; Zhou, Baoxue

2018-03-01

A BiVO4 photoanode with exposed (040) facets was prepared to enhance its photoelectrochemical performance. The exposure of the (040) crystal planes of the BiVO4 film was induced by adding NaCl to the precursor solution. The as-prepared BiVO4 photoanode exhibits higher solar-light absorption and charge-separation efficiency compared to those of an anode prepared without adding NaCl. To our knowledge, the photocurrent density (1.26 mA cm-2 at 1.23 V vs. RHE) of as-prepared BiVO4 photoanode is the highest according to the reports for bare BiVO4 films under simulated AM1.5G solar light, and the incident photon-to-current conversion efficiency is above 35% at 400 nm. The photoelectrochemical (PEC) water-splitting performance was also dramatically improved with a hydrogen evolution rate of 9.11 μmol cm-2 h-1, which is five times compared with the BiVO4 photoanode prepared without NaCl (1.82 μmol cm-2 h-1). Intensity-modulated photocurrent spectroscopy and transient photocurrent measurements show a higher charge-carrier-transfer rate for this photoanode. These results demonstrate a promising approach for the development of high-performance BiVO4 photoanodes which can be used for efficient PEC water splitting and degradation of organic pollutants. [Figure not available: see fulltext.

Impact of VoIP and QoS on Open and Distance Learning

ERIC Educational Resources Information Center

Saxena, P. C.; Jasola, Sanjay; Sharma, Ramesh C.

2006-01-01

Voice over Internet Protocol (VoIP) is becoming a reality in many organizations. The potential for mobility in voice over wi-fi networks will derive demand for the technology. Wireless VoIP is poised to rival VoIP as an alternative telephony tool. Internet has been used to transport data in the form of packet. In the past, Internet did not support…

Compare the phase transition properties of VO2 films from infrared to terahertz range

NASA Astrophysics Data System (ADS)

Liang, Shan; Shi, Qiwu; Huang, Wanxia; Peng, Bo; Mao, Zhenya; Zhu, Hongfu

2018-06-01

VO2 with reversible semiconductor-metal phase transition properties is particularly available for the application in smart opto-electrical devices. However, there are rare reports on comparing its phase transition properties at different ranges. In this study, the VO2 films are designed with the similar crystalline structure and stoichiometry, but different morphologies by inorganic and organic sol-gel methods, and their phase transition characteristics are compared both at infrared and terahertz range. The results indicate that the VO2 film prepared by inorganic sol-gel method shows more compact nanostructure. It results in larger resistivity change, infrared and terahertz switching ratio in the VO2 film. Moreover, it presents that the phase transition intensity of VO2 film in terahertz range is more sensitive to its microstructure. This work is helpful for understanding the susceptibility of terahertz switching properties of VO2 to its microstructure. And it can provide insights for the applications of VO2 in terahertz smart devices.

Crystal growth of the quasi-one dimensional spin-magnet LiCuVO 4

NASA Astrophysics Data System (ADS)

Prokofiev, A. V.; Wichert, D.; Assmus, W.

2000-12-01

The phase relationships in the Li-Cu-V-O and Li-Cu-V-O-Cl systems were investigated and the phase diagrams determined. Based on these diagrams single crystals of the low-dimensional spin compound LiCuVO 4 with maximal dimensions up to 12×3×3 mm 3 were grown from a solution of LiCuVO 4 in a LiVO 3 or a LiVO 3-LiCl melt. The stoichiometry of the grown crystals is discussed.

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

PubMed

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

2003-01-01

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

FTIR spectra of the solid solutions (Na0.88K0.12)VO3, (Na0.5K0.5)VO3, and Na(V0.66P0.34)O3

NASA Astrophysics Data System (ADS)

de Waal, D.; Heyns, A. M.

1992-03-01

It is known that three different solid solutions, (Na0.88K0.12)VO3, (Na0.5K0.5)VO3 and Na(V0.66P0.34)O3, form in the (Na,K)(V,P)O3 system. These compounds all have monoclinic crystal structures similar to the pure alkali metal metavanadates containing small cations, e.g. Li+ and Na+ (Space group C2/c). Metavanadates with large cations like K+, Rb+, C+s and NH+4 form orthorhombic crystals, space group Pbcm. All those are structurally related to the silicate pyroxenes. Na(V0.66P0.34)O3 and (Na0.88K0.12)VO3 have the same modified diopside structure as (alpha) - NaVO3 while (Na0.5K0.5)VO3 adopts the true diopside structure. The infrared spectra of the three solid solutions are reported here in comparison with those of (alpha) -NaVO3 and KVO3. The results are also correlated with those obtained in two independent high pressure Raman studies of NH4VO3 and RbVO3 as the introduction of a larger cation like K+ should increase the pressure in the structure.

VO2 nanorods for efficient performance in thermal fluids and sensors

NASA Astrophysics Data System (ADS)

Dey, Kajal Kumar; Bhatnagar, Divyanshu; Srivastava, Avanish Kumar; Wan, Meher; Singh, Satyendra; Yadav, Raja Ram; Yadav, Bal Chandra; Deepa, Melepurath

2015-03-01

VO2 (B) nanorods with average width ranging between 50-100 nm are synthesized via a hydrothermal method and the post hydrothermal treatment drying temperature is found to be influential in their overall phase and growth morphology evolution. The nanorods with unusually high optical bandgap for a VO2 material are effective in enhancing the thermal performance of ethylene glycol nanofluids over a wide temperature range as is indicated by the temperature dependent thermal conductivity measurements. Humidity and LPG sensors fabricated using the VO2 (B) nanorods bear testament to their efficient sensing performance, which can be partially attributed to the mesoporous nature of the nanorods.VO2 (B) nanorods with average width ranging between 50-100 nm are synthesized via a hydrothermal method and the post hydrothermal treatment drying temperature is found to be influential in their overall phase and growth morphology evolution. The nanorods with unusually high optical bandgap for a VO2 material are effective in enhancing the thermal performance of ethylene glycol nanofluids over a wide temperature range as is indicated by the temperature dependent thermal conductivity measurements. Humidity and LPG sensors fabricated using the VO2 (B) nanorods bear testament to their efficient sensing performance, which can be partially attributed to the mesoporous nature of the nanorods. Electronic supplementary information (ESI) available: Plots representing the actual ratio Knf/KEG (Knf is the thermal conductivity of the nanofluid and KEG being thermal conductivity of the base fluid) across the entire experimental temperature range of 20 to 80 °C, table representing a comparison of performance of the VO2 sensor towards different gases. See DOI: 10.1039/c4nr06032f

Wavelength-dependent ultrafast charge carrier separation in the WO 3/BiVO 4 coupled system

DOE PAGES

Grigioni, Ivan; Stamplecoskie, Kevin G.; Jara, Danilo H.; ...

2017-05-08

Due to its ~2.4 eV band gap, BiVO 4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO 3/BiVO 4 heterojunction films, the electrons photoexcited in BiVO 4 are injected into WO 3, overcoming the lower charge carriers’ diffusion properties limiting the PEC performance of BiVO 4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO 4 excitation, a favorable electron transfermore » from photoexcited BiVO 4 to WO 3 occurs immediately after excitation and leads to an increase of the trapped holes’ lifetime in BiVO4. However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO 4. As a result, PEC measurements reveal the implication of these wavelength-dependent ultrafast interactions on the performances of the WO 3/BiVO 4 heterojunction.« less

Wavelength-dependent ultrafast charge carrier separation in the WO 3/BiVO 4 coupled system

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

Grigioni, Ivan; Stamplecoskie, Kevin G.; Jara, Danilo H.

Due to its ~2.4 eV band gap, BiVO 4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO 3/BiVO 4 heterojunction films, the electrons photoexcited in BiVO 4 are injected into WO 3, overcoming the lower charge carriers’ diffusion properties limiting the PEC performance of BiVO 4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO 4 excitation, a favorable electron transfermore » from photoexcited BiVO 4 to WO 3 occurs immediately after excitation and leads to an increase of the trapped holes’ lifetime in BiVO4. However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO 4. As a result, PEC measurements reveal the implication of these wavelength-dependent ultrafast interactions on the performances of the WO 3/BiVO 4 heterojunction.« less

VoIP for Telerehabilitation: A Pilot Usability Study for HIPAA Compliance

PubMed Central

Watzlaf, Valerie R.; Ondich, Briana

2012-01-01

Consumer-based, free Voice and video over the Internet Protocol (VoIP) software systems such as Skype and others are used by health care providers to deliver telerehabilitation and other health-related services to clients. Privacy and security applications as well as HIPAA compliance within these protocols have been questioned by practitioners, health information managers, and other healthcare entities. This pilot usability study examined whether four respondents who used the top three, free consumer-based, VoIP software systems perceived these VoIP technologies to be private, secure, and HIPAA compliant; most did not. While the pilot study limitations include the number of respondents and systems assessed, the protocol can be applied to future research and replicated for instructional purposes. Recommendations are provided for VoIP companies, providers, and clients/consumers. PMID:25945194

Thermally tunable VO2-SiO2 nanocomposite thin-film capacitors

NASA Astrophysics Data System (ADS)

Sun, Yifei; Narayanachari, K. V. L. V.; Wan, Chenghao; Sun, Xing; Wang, Haiyan; Cooley, Kayla A.; Mohney, Suzanne E.; White, Doug; Duwel, Amy; Kats, Mikhail A.; Ramanathan, Shriram

2018-03-01

We present a study of co-sputtered VO2-SiO2 nanocomposite dielectric thin-film media possessing continuous temperature tunability of the dielectric constant. The smooth thermal tunability is a result of the insulator-metal transition in the VO2 inclusions dispersed within an insulating matrix. We present a detailed comparison of the dielectric characteristics of this nanocomposite with those of a VO2 control layer and of VO2/SiO2 laminate multilayers of comparable overall thickness. We demonstrated a nanocomposite capacitor that has a thermal capacitance tunability of ˜60% between 25 °C and 100 °C at 1 MHz, with low leakage current. Such thermally tunable capacitors could find potential use in applications such as sensing, thermal cloaks, and phase-change energy storage devices.

Modular VO oriented Java EE service deployer

NASA Astrophysics Data System (ADS)

Molinaro, Marco; Cepparo, Francesco; De Marco, Marco; Knapic, Cristina; Apollo, Pietro; Smareglia, Riccardo

2014-07-01

The International Virtual Observatory Alliance (IVOA) has produced many standards and recommendations whose aim is to generate an architecture that starts from astrophysical resources, in a general sense, and ends up in deployed consumable services (that are themselves astrophysical resources). Focusing on the Data Access Layer (DAL) system architecture, that these standards define, in the last years a web based application has been developed and maintained at INAF-OATs IA2 (Italian National institute for Astrophysics - Astronomical Observatory of Trieste, Italian center of Astronomical Archives) to try to deploy and manage multiple VO (Virtual Observatory) services in a uniform way: VO-Dance. However a set of criticalities have arisen since when the VO-Dance idea has been produced, plus some major changes underwent and are undergoing at the IVOA DAL layer (and related standards): this urged IA2 to identify a new solution for its own service layer. Keeping on the basic ideas from VO-Dance (simple service configuration, service instantiation at call time and modularity) while switching to different software technologies (e.g. dismissing Java Reflection in favour of Enterprise Java Bean, EJB, based solution), the new solution has been sketched out and tested for feasibility. Here we present the results originating from this test study. The main constraints for this new project come from various fields. A better homogenized solution rising from IVOA DAL standards: for example the new DALI (Data Access Layer Interface) specification that acts as a common interface system for previous and oncoming access protocols. The need for a modular system where each component is based upon a single VO specification allowing services to rely on common capabilities instead of homogenizing them inside service components directly. The search for a scalable system that takes advantage from distributed systems. The constraints find answer in the adopted solutions hereafter sketched. The

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.

Direct and continuous synthesis of VO2 nanoparticles.

PubMed

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

2015-11-28

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.

Magnetic and Ferroelectric Anisotropy in Multiferroic FeVO4

NASA Astrophysics Data System (ADS)

Abdelhamid, Ehab; Dixit, Ambesh; Kimura, Kenta; Kimura, Tsuyoshi; Jayakumar, Onattu; Naik, Vaman; Naik, Ratna; Lawes, Gavin; Nadgorny, Boris

FeVO4 has been studied as a model system for understanding the magnetoelectric interaction mechanisms in low symmetry multiferroics. Triclinic FeVO4 is characterized by two antiferromagnetic phase transitions, occurring at TN 1 = 22 K and TN 2 = 15 K, with the latter transition signaling a break in the space inversion symmetry, accompanied by the development of a non-collinear magnetic order which induces ferroelectricity. Earlier measurements on polycrystalline FeVO4 doped with magnetic (Cr and Mn) as well as non magnetic (Zn) dopants indicate the stability of the two antiferromagnetic transition temperatures. In this work, single crystals of both undoped and doped FeVO4 were grown from flux. To track the changes in lattice parameters induced by changing the doping concentration (measured by EDAX), XRD and Raman spectra were obtained. By recording the magnetization along two different crystal orientations, we were able to confirm the easy magnetic axis in this structure. Finally, we obtain the crystal's ferroelectric polarization along two different directions in an attempt to further understand the mechanism responsible for the ferroelectric transition. This work is supported by the NSF under DMR-1306449.

Ion beam modification of single crystalline BiVO4

NASA Astrophysics Data System (ADS)

Wendler, Elke; Bischoff, Marie; Schmidt, Emanuel; Schrempel, F.; Ellmer, Klaus; Kanis, Michael; van de Krol, Roel

2017-10-01

A single crystalline BiVO4 sample was investigated. Angular resolved Rutherford backscattering spectrometry (arRBS) was performed as a function of two orthogonal angles perpendicular to the surface. The crystal planes appearing in the angular charts are compared with the crystal structure of monoclinic BiVO4. By this comparison the crystal axis being almost normal to the surface was identified to be 〈0 0 1〉. These measurements support the control of orientation and quality of the grown BiVO4 crystal. Additionally it is found that during prolonged analysis the He ions produce a considerable amount of damage. As the nuclear energy loss of the He ions is negligibly low within the corresponding depth region, the damage is mainly caused by the electronic energy loss of the ions. For studying radiation resistance and damage formation, the BiVO4 single crystal was implanted with 200 keV Ar ions. The damage production in the Bi sublattice was analysed by RBS applying 1.8 MeV He ions in channelling configuration. The damage profiles determined from the channelling RBS spectra can be well represented by the electronic energy loss of the implanted Ar ions. From this it is concluded that, in agreement with the finding mentioned above, this energy mainly triggers damage formation in ion irradiated BiVO4. The energy for producing one displaced Bi atom as seen by RBS decreases with increasing damage concentration and varies between 33 and 3.4 eV.

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

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

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

2016-03-15

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

Improved photoelectrochemical performance of BiVO4/MoO3 heterostructure thin films

NASA Astrophysics Data System (ADS)

Kodan, Nisha; Mehta, B. R.

2018-05-01

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

Efficient solar-driven water splitting by nanocone BiVO4-perovskite tandem cells

PubMed Central

Qiu, Yongcai; Liu, Wei; Chen, Wei; Chen, Wei; Zhou, Guangmin; Hsu, Po-Chun; Zhang, Rufan; Liang, Zheng; Fan, Shoushan; Zhang, Yuegang; Cui, Yi

2016-01-01

Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm−2 at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%. PMID:27386565

Switchable vanadium dioxide (VO2) metamaterials fabricated from tungsten doped vanadia-based colloidal nanocrystals

NASA Astrophysics Data System (ADS)

Paik, Taejong; Hong, Sung-Hoon; Gordon, Thomas; Gaulding, Ashley; Kagan, Cherie; Murray, Christopher

2013-03-01

We report the fabrication of thermochromic VO2-based metamaterials using solution-processable colloidal nanocrystals. Vanadium-based nanoparticles are prepared through a non-hydrolytic reaction, resulting in stable colloidal dispersions in solution. Thermochromic nanocrystalline VO2 thin-films are prepared via rapid thermal annealing of colloidal nanoparticles coated on a variety of substrates. Nanostructured VO2 can be patterned over large areas by nanoimprint lithography. Precise control of tungsten (W) doping concentration in colloidal nanoparticles enables tuning of the phase transition temperature of the nanocrystalline VO2 thin-films. W-doped VO2 films display a sharp temperature dependent phase transition, similar to the undoped VO2 film, but at lower temperatures tunable with the doping level. By sequential coating of doped VO2 with different doping concentrations, we fabricate ?smart? multi-layered VO2 films displaying multiple phase transition temperatures within a single structure, allowing for dynamic modulation of the metal-dielectric layered structure. The optical properties programmed into the layered structure are switchable with temperature, which provides additional degrees of freedom to design tunable optical metamaterials. This work is supported by the US Office of Naval Research Multidisciplinary University Research Initiative (MURI) program grant number ONR-N00014-10-1-0942.

Unraveling Metal-insulator Transition Mechanism of VO2 Triggered by Tungsten Doping

PubMed Central

Tan, Xiaogang; Yao, Tao; Long, Ran; Sun, Zhihu; Feng, Yajuan; Cheng, Hao; Yuan, Xun; Zhang, Wenqing; Liu, Qinghua; Wu, Changzheng; Xie, Yi; Wei, Shiqiang

2012-01-01

Understanding the mechanism of W-doping induced reduction of critical temperature (TC) for VO2 metal-insulator transition (MIT) is crucial for both fundamental study and technological application. Here, using synchrotron radiation X-ray absorption spectroscopy combined with first-principles calculations, we unveil the atomic structure evolutions of W dopant and its role in tailoring the TC of VO2 MIT. We find that the local structure around W atom is intrinsically symmetric with a tetragonal-like structure, exhibiting a concentration-dependent evolution involving the initial distortion, further repulsion, and final stabilization due to the strong interaction between doped W atoms and VO2 lattices across the MIT. These results directly give the experimental evidence that the symmetric W core drives the detwisting of the nearby asymmetric monoclinic VO2 lattice to form rutile-like VO2 nuclei, and the propagations of these W-encampassed nuclei through the matrix lower the thermal energy barrier for phase transition. PMID:22737402

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Preparation and enhanced infrared response properties of ordered W-doped VO2 nanowire array

NASA Astrophysics Data System (ADS)

Xie, Bing He; Fu, Wen Biao; Fei, Guang Tao; Xu, Shao Hui; Gao, Xu Dong; Zhang, Li De

2018-04-01

In this article, pure and tungsten-doped (W-doped) highly ordered two-dimensional (2D) vanadium dioxide (VO2) nanowire arrays were successfully prepared by a hydrothermal treatment, followed by a self-assembly progress and the in-situ high temperature treatment. The infrared photodetector devices based on monoclinic VO2 (VO2(M)) and W-doped VO2(M) nanowires were comparatively studied . It was found that the device based on W-doped VO2(M) nanowires exhibits a rapid infrared response and an enhanced photoelectric responsivity of 21.4 mA/W under the incident infrared light intensity of 280 mW/cm2, which is nearly two orders of magnitude superior to pure VO2(M) nanowire array. Our experimental results provided a direct and convenient path for design of future high-performance photodetector devices.

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

DTIC Science & Technology

2014-06-09

Voltage-controlled switching and thermal effects in VO2 nano-gap junctions Arash Joushaghani,1 Junho Jeong,1 Suzanne Paradis,2 David Alain,2 J...2014) Voltage-controlled switching in lateral VO2 nano-gap junctions with different gap lengths and thermal properties was investigated. The effect of...indicate that the VO2 phase transition was likely initiated electroni- cally, which was sometimes followed by a secondary thermally-induced transition

Optimizing highly noncoplanar VMAT trajectories: the NoVo method.

PubMed

Langhans, Marco; Unkelbach, Jan; Bortfeld, Thomas; Craft, David

2018-01-16

We introduce a new method called NoVo (Noncoplanar VMAT Optimization) to produce volumetric modulated arc therapy (VMAT) treatment plans with noncoplanar trajectories. While the use of noncoplanar beam arrangements for intensity modulated radiation therapy (IMRT), and in particular high fraction stereotactic radiosurgery (SRS), is common, noncoplanar beam trajectories for VMAT are less common as the availability of treatment machines handling these is limited. For both IMRT and VMAT, the beam angle selection problem is highly nonconvex in nature, which is why automated beam angle selection procedures have not entered mainstream clinical usage. NoVo determines a noncoplanar VMAT solution (i.e. the simultaneous trajectories of the gantry and the couch) by first computing a [Formula: see text] solution (beams from every possible direction, suitably discretized) and then eliminating beams by examing fluence contributions. Also all beam angles are scored via geometrical considerations only to find out the usefulness of the whole beam space in a very short time. A custom path finding algorithm is applied to find an optimized, continuous trajectory through the most promising beam angles using the calculated score of the beam space. Finally, using this trajectory a VMAT plan is optimized. For three clinical cases, a lung, brain, and liver case, we compare NoVo to the ideal [Formula: see text] solution, nine beam noncoplanar IMRT, coplanar VMAT, and a recently published noncoplanar VMAT algorithm. NoVo comes closest to the [Formula: see text] solution considering the lung case (brain and liver case: second), as well as improving the solution time by using geometrical considerations, followed by a time effective iterative process reducing the [Formula: see text] solution. Compared to a recently published noncoplanar VMAT algorithm, using NoVo the computation time is reduced by a factor of 2-3 (depending on the case). Compared to coplanar VMAT, NoVo reduces the objective

Optimizing highly noncoplanar VMAT trajectories: the NoVo method

NASA Astrophysics Data System (ADS)

Langhans, Marco; Unkelbach, Jan; Bortfeld, Thomas; Craft, David

2018-01-01

We introduce a new method called NoVo (Noncoplanar VMAT Optimization) to produce volumetric modulated arc therapy (VMAT) treatment plans with noncoplanar trajectories. While the use of noncoplanar beam arrangements for intensity modulated radiation therapy (IMRT), and in particular high fraction stereotactic radiosurgery (SRS), is common, noncoplanar beam trajectories for VMAT are less common as the availability of treatment machines handling these is limited. For both IMRT and VMAT, the beam angle selection problem is highly nonconvex in nature, which is why automated beam angle selection procedures have not entered mainstream clinical usage. NoVo determines a noncoplanar VMAT solution (i.e. the simultaneous trajectories of the gantry and the couch) by first computing a 4π solution (beams from every possible direction, suitably discretized) and then eliminating beams by examing fluence contributions. Also all beam angles are scored via geometrical considerations only to find out the usefulness of the whole beam space in a very short time. A custom path finding algorithm is applied to find an optimized, continuous trajectory through the most promising beam angles using the calculated score of the beam space. Finally, using this trajectory a VMAT plan is optimized. For three clinical cases, a lung, brain, and liver case, we compare NoVo to the ideal 4π solution, nine beam noncoplanar IMRT, coplanar VMAT, and a recently published noncoplanar VMAT algorithm. NoVo comes closest to the 4π solution considering the lung case (brain and liver case: second), as well as improving the solution time by using geometrical considerations, followed by a time effective iterative process reducing the 4π solution. Compared to a recently published noncoplanar VMAT algorithm, using NoVo the computation time is reduced by a factor of 2-3 (depending on the case). Compared to coplanar VMAT, NoVo reduces the objective function value by 24%, 49% and 6% for the lung, brain and liver

Infrared spectra of the ammonium ion in ammonium metavanadate NH 4VO 3

NASA Astrophysics Data System (ADS)

de Waal, D.; Heyns, A. M.; Range, K.-J.; Eglmeier, C.

The ND stretching modes of isotopically dilute NH 3D + ions in NH 4VO 3 are in agreement with the predicted splitting into C s, C s and C1(2) components under C s site symmetry for the NH +4 ion. The three bands observed represent the three NH bonding distances in the crystal, and the position, shape and low temperature behaviour of each band confirms the existence of two types of hydrogen bonding in NH 4VO 3. The low temperature infrared modes of NH +4 and ND +4 in NH 4VO 3 and ND 4VO 3, respectively, can be assigned under space group Pbcm. Temperature dependence of these modes also reflects the presence of both normal and bifurcated hydrogen bonds in NH 4VO 3.

DynAstVO : a Europlanet database of NEA orbits

NASA Astrophysics Data System (ADS)

Desmars, J.; Thuillot, W.; Hestroffer, D.; David, P.; Le Sidaner, P.

2017-09-01

DynAstVO is a new orbital database developed within the Europlanet 2020 RI and the Virtual European Solar and Planetary Access (VESPA) frameworks. The database is dedicated to Near-Earth asteroids and provide parameters related to orbits: osculating elements, observational information, ephemeris through SPICE kernel, and in particular, orbit uncertainty and associated covariance matrix. DynAstVO is daily updated on a automatic process of orbit determination on the basis of the Minor Planet Electronic Circulars that reports new observations or the discover of a new asteroid. This database conforms to EPN-TAP environment and is accessible through VO protocols and on the VESPA portal web access (http://vespa.obspm.fr/). A comparison with other classical databases such as Astorb, MPCORB, NEODyS and JPL is also presented.

Synthesis, crystal structure and optical properties of BiMgVO 5

NASA Astrophysics Data System (ADS)

Benmokhtar, S.; El Jazouli, A.; Chaminade, J. P.; Gravereau, P.; Guillen, F.; de Waal, D.

2004-11-01

The new vanadate BiMgVO 5 has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P21/n, a=7.542(6) Å, b=11.615(5) Å, c=5.305(3) Å, β=107.38(5)°, wR2=0.0447, R=0.0255. The structure consists of [Mg 2O 10] and [Bi 2O 10] dimers sharing their corners with [VO 4] tetrahedra. The ranges of bond lengths are 2.129-2.814 Å for Bi-O; 2.035-2.167 Å for Mg-O and 1.684-1.745 Å for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 Å. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.

Frequency tunable near-infrared metamaterials based on VO2 phase transition.

PubMed

Dicken, Matthew J; Aydin, Koray; Pryce, Imogen M; Sweatlock, Luke A; Boyd, Elizabeth M; Walavalkar, Sameer; Ma, James; Atwater, Harry A

2009-09-28

Engineering metamaterials with tunable resonances from mid-infrared to near-infrared wavelengths could have far-reaching consequences for chip based optical devices, active filters, modulators, and sensors. Utilizing the metal-insulator phase transition in vanadium oxide (VO(2)), we demonstrate frequency-tunable metamaterials in the near-IR range, from 1.5 - 5 microns. Arrays of Ag split ring resonators (SRRs) are patterned with e-beam lithography onto planar VO(2) and etched via reactive ion etching to yield Ag/VO(2) hybrid SRRs. FTIR reflection data and FDTD simulation results show the resonant peak position red shifts upon heating above the phase transition temperature. We also show that, by including coupling elements in the design of these hybrid Ag/VO(2) bi-layer structures, we can achieve resonant peak position tuning of up to 110 nm.

Controlled Synthesis and Photocatalytic Antifouling Properties of BiVO4 with Tunable Morphologies

NASA Astrophysics Data System (ADS)

Xiang, Zhenbo; Wang, Yi; Ju, Peng; Zhang, Dun

2017-02-01

Monoclinic BiVO4 with different nanostructures were prepared via a facile and rapid route by adding different surfactants. Ethylenediaminetetraacetic acid, polyvinylpyrrolidone, and sodium dodecyl sulfate surfactants were selected as morphology controlling agents. The crystal phase, morphology, and diffuse reflectance spectra of BiVO4 were characterized by x-ray diffraction, scanning electron microscopy, and UV-visible diffuse reflectance spectra techniques, respectively. The photocatalytic activities of BiVO4 were investigated by killing the typical marine fouling bacteria Pseudomonas aeruginosa ( P. aeruginosa) under visible light irradiation. BiVO4 with grape-like nanostructure exhibited the best photocatalytic bactericidal activity. The sterilization rate of P. aeruginosa could reach up to 99.9% in 120 min. The photocatalytic mechanism was studied by captive species trapping experiments. The result revealed that photogenerated hole (h+) is the main reactive specie for killing P. aeruginosa under visible light irradiation. In addition, after five recycles, BiVO4 does not exhibit significant loss of photocatalytic sterilization activity. The results confirm that the synthesized BiVO4 photocatalyst has long-time reusability and good photocatalytic stability.

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

PubMed

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

2018-01-22

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

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.

Open porous BiVO{sub 4} nanomaterials: Electronspinning fabrication and enhanced visible light photocatalytic activity

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

Wang, Mengyan; Xi, Xin; Gong, Cairong, E-mail: gcr@tju.edu.cn

2016-02-15

Highlights: • BiVO{sub 4} nanofibers were successfully fabricated by electrospinning method. • PVP was used to adjust the viscosity and increase spinnability of the electrospinning sol. • BiVO{sub 4} nanofibers were used for the degradation of MB. • Compared to the submicron sized BiVO4, BiVO{sub 4} nanofibers show superior photocatalytic activity. - Abstract: Witnessed by X-ray powder diffraction (XRD), Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies, BiVO{sub 4} nanofibers and porous nanostructures were successfully fabricated by electrospinning method using NH{sub 4}VO{sub 3} and Bi(NO{sub 3}){sub 3} as starting materials. Polyvinylpyrrolidinone (PVP) was used to tune themore » viscosity and spinnability of the electrospinning sol. The slow decomposition and combustion of PVP matrix prevented rapid crystal growth of BiVO{sub 4} nanostructures leading to considerably small crystallite size (approximately 19.1–28.3 nm) with less surface defects after two hours calcination at varying temperatures. This paid great tributes to the superior visible light photocatalytic activity when compared to the submicron sized BiVO{sub 4} prepared in the absence of PVP.« less

Fern-like rGO/BiVO4 Hybrid Nanostructures for High-Energy Symmetric Supercapacitor.

PubMed

Patil, Santosh S; Dubal, Deepak P; Deonikar, Virendrakumar G; Tamboli, Mohaseen S; Ambekar, Jalindar D; Gomez-Romero, Pedro; Kolekar, Sanjay S; Kale, Bharat B; Patil, Deepak R

2016-11-23

Herein, we demonstrate the synthesis of rGO/BiVO 4 hybrid nanostructures by facile hydrothermal method. Morphological studies reveal that rGO sheets are embedded in the special dendritic fern-like structures of BiVO 4 . The rGO/BiVO 4 hybrid architecture shows the way to a rational design of supercapacitor, since these structures enable easy access of electrolyte ions by reducing internal resistance. Considering the unique morphological features of rGO/BiVO 4 hybrid nanostructures, their supercapacitive properties were investigated. The rGO/BiVO 4 electrode exhibits a specific capacitance of 151 F/g at the current density of 0.15 mA/cm 2 . Furthermore, we have constructed rGO/BiVO 4 symmetric cell which exhibits outstanding volumetric energy density of 1.6 mW h/cm 3 (33.7 W h/kg) and ensures rapid energy delivery with power density of 391 mW/cm 3 (8.0 kW/kg). The superior properties of symmetric supercapacitor can be attributed to the special dendritic fern-like BiVO 4 morphology and intriguing physicochemical properties of rGO.

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

PubMed

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

1998-06-01

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

o-Iminobenzosemiquinonate and o-imino-p-methylbenzosemiquinonate anion radicals coupled VO2+ stabilization.

PubMed

Roy, Amit Saha; Saha, Pinaki; Adhikary, Nirmal Das; Ghosh, Prasanta

2011-03-21

The diamagnetic VO(2+)-iminobenzosemiquinonate anion radical (L(R)(IS)(•-), R = H, Me) complexes, (L(-))(VO(2+))(L(R)(IS)(•-)): (L(1)(-))(VO(2+))(L(H)(IS)(•-))•3/2MeOH (1•3/2MeOH), (L(2)(-))(VO(2+))(L(H)(IS)(•-)) (2), and (L(2)(-))(VO(2+))(L(Me)(IS)(•-))•1/2 L(Me)(AP) (3•1/2 L(Me)(AP)), incorporating tridentate monoanionic NNO-donor ligands {L = L(1)(-) or L(2)(-), L(1)H = (2-[(phenylpyridin-2-yl-methylene)amino]phenol; L(2)H = 1-(2-pyridylazo)-2-naphthol; L(H)(IS)(•-) = o-iminobenzosemiquinonate anion radical; L(Me)(IS)(•-) = o-imino-p-methylbenzosemiquinonate anion radical; and L(Me)(AP) = o-amino-p-methylphenol} have been isolated and characterized by elemental analyses, IR, mass, NMR, and UV-vis spectra, including the single-crystal X-ray structure determinations of 1•3/2MeOH and 3•1/2 L(Me)(AP). Complexes 1•3/2MeOH, 2, and 3•1/2 L(Me)(AP) absorb strongly in the visible region because of intraligand (IL) and ligand-to-metal charge transfers (LMCT). 1•3/2MeOH is luminescent (λ(ext), 333 nm; λ(em), 522, 553 nm) in frozen dichloromethane-toluene glass at 77 K due to π(diimine→)π(diimine)* transition. The V-O(phenolato) (cis to the V═O) lengths, 1.940(2) and 1.984(2) Å, respectively, in 1•3/2MeOH and 3•1/2 L(Me)(AP) are consistent with the VO(2+) description. The V-O(iminosemiquinonate) (trans to the V═O) lengths, 2.1324(19) in 1•3/2MeOH and 2.083(2) Å in 3•1/2 L(Me)(AP), are expectedly ∼0.20 Å longer due to the trans influence of the V═O bond. Because of the stronger affinity of the paramagnetic VO(2+) ion to the L(H)(IS)(•-) or L(Me)(IS)(•-), the V-N(iminosemiquinonate) lengths, 1.908(2) and 1.921(2) Å, respectively, in 1•3/2MeOH and 3•1/2 L(Me)(AP), are unexpectedly shorter. Density functional theory (DFT) calculations using B3LYP, B3PW91, and PBE1PBE functionals on 1 and 2 have established that the closed shell singlet (CSS) solutions (VO(3+)-amidophenolato (L(R)(AP)(2-)) coordination) of these

Tailoring of the thermomechanical performance of VO2 nanowire bimorph actuators by ion implantation

NASA Astrophysics Data System (ADS)

Karl, H.; Peyinghaus, S. C.

2015-12-01

Vanadium dioxide VO2 nanowire bimorph actuators work on the basis of the large abrupt length change at the metal-insulator phase transition (MIT). A key parameter for the bimorph performance and efficiency is the bending curvature and the width of the temperature hysteresis of the MIT which is inherently large for single domain VO2 metal side coated nanowires. In this work we present single-clamped Ir side coated VO2 bimorphs which show unprecedented high bending curvatures of up to 105 m-1 and new type of side ion-implanted VO2 nanowire bimorph actuators with a nearly completely suppressed temperature hysteresis. It is assumed that ion-beam induced radiation defects in the VO2 crystal structure act as nucleation sites for the MIT. Moreover it will be shown that mechanical strain intentionally built-in during VO2 nanowire bimorph fabrication allows to direct phase transformation via a strain stabilized metastable phase and thus allows to control bending response on temperature change.

First finding of impact melt in the IIE Netschaëvo meteorite

NASA Astrophysics Data System (ADS)

Roosbroek, N.; Pittarello, L.; Greshake, A.; Debaille, V.; Claeys, P.

2016-02-01

About half of the IIE nonmagmatic iron meteorites contain silicate inclusions with a primitive to differentiated nature. The presence of preserved chondrules has been reported for two IIE meteorites so far, Netschaëvo and Mont Dieu, which represent the most primitive silicate material within this group. In this study, silicate inclusions from two samples of Netschaëvo were examined. Both silicate inclusions are characterized by a porphyritic texture dominated by clusters of coarse-grained olivine and pyroxene, set in a fine-grained groundmass that consists of new crystals of olivine and a glassy appearing matrix. This texture does not correspond to the description of the previously examined pieces of Netschaëvo, which consist of primitive chondrule-bearing angular clasts. Detailed petrographic observations and geochemical analyses suggest that the investigated samples of Netschaëvo consist of quenched impact melt. This implies that Netschaëvo is a breccia containing metamorphosed and impact-melt rock (IMR) clasts and that collisions played a major role in the formation of the IIE group.

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”.

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)

Laminarin-induced apoptosis in human colon cancer LoVo cells

PubMed Central

JI, CHEN-FENG; JI, YU-BIN

2014-01-01

A number of scientific studies have revealed that laminarin has antitumor effects. Therefore, the aim of the present study was to investigate the apoptosis of LoVo cells and the underlying mechanisms induced by laminarin. LoVo cells were treated with various concentrations of laminarin and fluorescence-inverted microscopy was used to observe the morphology of LoVo cells treated with laminarin. In addition, western blotting was performed to analyze the expression levels of death receptor (DR)4, DR5, TNF-related apoptosis-inducing ligand (TRAIL), Fas-associated protein with death domain (FADD), caspase-8, caspase-3, Bid and tBid. Flow cytometry was conducted to analyze the expressions of Bcl-2 and Bax, and spectrophotometry was performed to quantify the activity of caspases-8, -3, -6 and -7. Following the treatment of LoVo cells with laminarin for 24 h, the expression levels of DR4, DR5, TRAIL, FADD, Bid, tBid and Bax were observed to be upregulated, whereas the expression levels of pro-caspase-8, pro-caspase-3 and Bcl-2 were downregulated. In addition, the activities of casapse-8, -3, -6 and -7 were observed to increase, which was a significant difference when compared with those of the control group. Therefore, laminarin is considered to induce the apoptosis of LoVo cells, which may occur via a DR pathway, suggesting that laminarin may be a potent agent for cancer treatment. PMID:24765209

Laminarin-induced apoptosis in human colon cancer LoVo cells.

PubMed

Ji, Chen-Feng; Ji, Yu-Bin

2014-05-01

A number of scientific studies have revealed that laminarin has antitumor effects. Therefore, the aim of the present study was to investigate the apoptosis of LoVo cells and the underlying mechanisms induced by laminarin. LoVo cells were treated with various concentrations of laminarin and fluorescence-inverted microscopy was used to observe the morphology of LoVo cells treated with laminarin. In addition, western blotting was performed to analyze the expression levels of death receptor (DR)4, DR5, TNF-related apoptosis-inducing ligand (TRAIL), Fas-associated protein with death domain (FADD), caspase-8, caspase-3, Bid and tBid. Flow cytometry was conducted to analyze the expressions of Bcl-2 and Bax, and spectrophotometry was performed to quantify the activity of caspases-8, -3, -6 and -7. Following the treatment of LoVo cells with laminarin for 24 h, the expression levels of DR4, DR5, TRAIL, FADD, Bid, tBid and Bax were observed to be upregulated, whereas the expression levels of pro-caspase-8, pro-caspase-3 and Bcl-2 were downregulated. In addition, the activities of casapse-8, -3, -6 and -7 were observed to increase, which was a significant difference when compared with those of the control group. Therefore, laminarin is considered to induce the apoptosis of LoVo cells, which may occur via a DR pathway, suggesting that laminarin may be a potent agent for cancer treatment.

VO(2max) and Microgravity Exposure: Convective versus Diffusive O(2) Transport.

PubMed

Ade, Carl J; Broxterman, Ryan M; Barstow, Thomas J

2015-07-01

Exposure to a microgravity environment decreases the maximal rate of O2 uptake (VO(2max)) in healthy individuals returning to a gravitational environment. The magnitude of this decrease in VO(2max) is, in part, dependent on the duration of microgravity exposure, such that long exposure may result in up to a 38% decrease in VO(2max). This review identifies the components within the O(2) transport pathway that determine the decrease in postmicrogravity VO(2max) and highlights the potential contributing physiological mechanisms. A retrospective analysis revealed that the decline in VO(2max) is initially mediated by a decrease in convective and diffusive O(2) transport that occurs as the duration of microgravity exposure is extended. Mechanistically, the attenuation of O(2) transport is the combined result of a deconditioning across multiple organ systems including decreases in total blood volume, red blood cell mass, cardiac function and mass, vascular function, skeletal muscle mass, and, potentially, capillary hemodynamics, which become evident during exercise upon re-exposure to the head-to-foot gravitational forces of upright posture on Earth. In summary, VO(2max) is determined by the integration of central and peripheral O(2) transport mechanisms, which, if not maintained during microgravity, will have a substantial long-term detrimental impact on space mission performance and astronaut health.

Validation of the firefighter WFI treadmill protocol for predicting VO2 max.

PubMed

Dolezal, B A; Barr, D; Boland, D M; Smith, D L; Cooper, C B

2015-03-01

The Wellness-Fitness Initiative submaximal treadmill exercise test (WFI-TM) is recommended by the US National Fire Protection Agency to assess aerobic capacity (VO2 max) in firefighters. However, predicting VO2 max from submaximal tests can result in errors leading to erroneous conclusions about fitness. To investigate the level of agreement between VO2 max predicted from the WFI-TM against its direct measurement using exhaled gas analysis. The WFI-TM was performed to volitional fatigue. Differences between estimated VO2 max (derived from the WFI-TM equation) and direct measurement (exhaled gas analysis) were compared by paired t-test and agreement was determined using Pearson Product-Moment correlation and Bland-Altman analysis. Statistical significance was set at P < 0.05. Fifty-nine men performed the WFI-TM. Mean (standard deviation) values for estimated and measured VO2 max were 44.6 (3.4) and 43.6 (7.9) ml/kg/min, respectively (P < 0.01). The mean bias by which WFI-TM overestimated VO2 max was 0.9ml/kg/min with a 95% prediction interval of ±13.1. Prediction errors for 22% of subjects were within ±5%; 36% had errors greater than or equal to ±15% and 7% had greater than ±30% errors. The correlation between predicted and measured VO2 max was r = 0.55 (standard error of the estimate = 2.8ml/kg/min). WFI-TM predicts VO2 max with 11% error. There is a tendency to overestimate aerobic capacity in less fit individuals and to underestimate it in more fit individuals leading to a clustering of values around 42ml/kg/min, a criterion used by some fire departments to assess fitness for duty. © The Author 2015. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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.

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

PubMed Central

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

2015-01-01

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

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.

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

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

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

2014-05-01

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

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

PubMed

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

2009-01-28

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

Is VoIP Worth It?

ERIC Educational Resources Information Center

Schaffhauser, Dian

2008-01-01

School districts have by and large had great results implementing VoIP, which has become the conduit for delivering expanded functionality, achieving greater internal control, and gaining freedom from onerous monthly phone bills. But demonstrating a financial return on what is a substantial investment can be an elusive effort. The goal of…

Evolution of Structural and Electrical Properties of Oxygen-Deficient VO2 under Low Temperature Heating Process.

PubMed

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

2017-08-16

Structural stability and functional performances of vanadium dioxide (VO 2 ) are strongly influenced by oxygen vacancies. However, the mechanism of metal-insulator transition (MIT) influenced by defects is still under debate. Here, we study the evolution of structure and electrical property of oxygen-deficient VO 2 by a low temperature annealing process (LTP) based on a truss-structured VO 2 nanonet. The oxygenation process of the oxygen-deficient VO 2 is greatly prolonged, which enables us to probe the gradual change of properties of the oxygen-deficient VO 2 . A continuous lattice reduction is observed during LTP. No recrystallization and structural collapse of the VO 2 nanonet can be found after LTP. The valence-band X-ray photoelectron spectroscopy (XPS) measurements indicate that the oxygen deficiency strongly affects the energy level of the valence band edge. Correspondingly, the resistance changes of the VO 2 films from 1 to 4.5 orders of magnitude are achieved by LTP. The effect of oxygen vacancy on the electric field driven MIT is investigated. The threshold value of voltage triggering the MIT decreases with increasing the oxygen vacancy concentration. This work demonstrates a novel and effective way to control the content of oxygen vacancies in VO 2 and the obvious impact of oxygen vacancy on MIT, facilitating further research on the role of oxygen vacancy in structure and MIT of VO 2 , which is important for the deep understanding of MIT and exploiting innovative functional application of VO 2 .

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.

Nanoscale thermal imaging of VO2 via Poole-Frenkel conduction

NASA Astrophysics Data System (ADS)

Spitzig, Alyson; Hoffman, Jason D.; Pivonka, Adam E.; Mickalide, Harry; Frenzel, Alex; Kim, Jeehoon; Ko, Changhyun; Zhou, You; O'Connor, Kevin; Hudson, Eric W.; Ramanathan, Shriram; Hoffman, Jennifer E.

We present a novel method for nanoscale thermal imaging of insulating thin films. We demonstrate this method on VO2, which undergoes a sharp insulator-to-metal transition at 340 K. We sweep the voltage applied to a conducting atomic force microscope tip in contact mode at room temperature and measure the resultant current through a VO2 film. The Poole-Frenkel (PF) conduction mechanism, which dominates in the insulating state of VO2, is fit to extract the local temperature of the film using fundamental constants and known film properties. We measure the local electric field and temperature immediately preceding the insulator-to-metal transition in VO2 to determine whether the transition can be triggered by an applied electric field alone. We calculate an average temperature of 334 +/- 5 K, implying that Joule heating has locally warmed the sample very close to the transition temperature. Our thermometry technique opens up the possibility to measure the local temperature of any film dominated by the PF conduction mechanism, and presents the opportunity to extend our technique to other conduction mechanisms. Canada Excellence Research Chair program and NSERC - CGSM.

Relationship between inflammatory markers of cardiovascular disease and VO2peak in asymptomatic females.

PubMed

Omran Simin, F; Narges, Z; Sajad, A; Parisa, Y; Omrani Vahid, F

2013-04-01

The objective of this study was to investigate the relationship between inflammatory markers of cardiovascular disease (IL-6 and acute-phase reactants) and VO2peak in asymptomatic females. Study subjects were females not affected by coronary heart diseases. Forty healthy female subjects (age, 45±4.2 years; height, 161±3.5 cm; weight, 65±3.1 kg; history of regular physical activity, 5.2±0.45 years) participated in this study Analysis of data was carried out by Pearson's correlation. Statistical analysis of data indicated a negative significant relationship between IL-6 and VO2peak (r=-0.48, r2=0.23, P<0.048), CRP and VO2peak (r=-0.40, r2= 0.16, P<0.002), fibrinogen and VO2peak (r=-0.42, r2=0.17, P<0.001), and WBC and VO2peak (r=-0.22, r2=0.04, P<0.044). In conclusion higher circulating levels of IL-6, CRP and fibrinogen are associated with lower VO2peak in females.

Building a VO-compliant Radio Astronomical DAta Model for Single-dish radio telescopes (RADAMS)

NASA Astrophysics Data System (ADS)

Santander-Vela, Juan de Dios; García, Emilio; Leon, Stephane; Espigares, Victor; Ruiz, José Enrique; Verdes-Montenegro, Lourdes; Solano, Enrique

2012-11-01

The Virtual Observatory (VO) is becoming the de-facto standard for astronomical data publication. However, the number of radio astronomical archives is still low in general, and even lower is the number of radio astronomical data available through the VO. In order to facilitate the building of new radio astronomical archives, easing at the same time their interoperability with VO framework, we have developed a VO-compliant data model which provides interoperable data semantics for radio data. That model, which we call the Radio Astronomical DAta Model for Single-dish (RADAMS) has been built using standards of (and recommendations from) the International Virtual Observatory Alliance (IVOA). This article describes the RADAMS and its components, including archived entities and their relationships to VO metadata. We show that by using IVOA principles and concepts, the effort needed for both the development of the archives and their VO compatibility has been lowered, and the joint development of two radio astronomical archives have been possible. We plan to adapt RADAMS to be able to deal with interferometry data in the future.

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

PubMed

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

2018-04-01

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

VO2 estimation using 6-axis motion sensor with sports activity classification.

PubMed

Nagata, Takashi; Nakamura, Naoteru; Miyatake, Masato; Yuuki, Akira; Yomo, Hiroyuki; Kawabata, Takashi; Hara, Shinsuke

2016-08-01

In this paper, we focus on oxygen consumption (VO2) estimation using 6-axis motion sensor (3-axis accelerometer and 3-axis gyroscope) for people playing sports with diverse intensities. The VO2 estimated with a small motion sensor can be used to calculate the energy expenditure, however, its accuracy depends on the intensities of various types of activities. In order to achieve high accuracy over a wide range of intensities, we employ an estimation framework that first classifies activities with a simple machine-learning based classification algorithm. We prepare different coefficients of linear regression model for different types of activities, which are determined with training data obtained by experiments. The best-suited model is used for each type of activity when VO2 is estimated. The accuracy of the employed framework depends on the trade-off between the degradation due to classification errors and improvement brought by applying separate, optimum model to VO2 estimation. Taking this trade-off into account, we evaluate the accuracy of the employed estimation framework by using a set of experimental data consisting of VO2 and motion data of people with a wide range of intensities of exercises, which were measured by a VO2 meter and motion sensor, respectively. Our numerical results show that the employed framework can improve the estimation accuracy in comparison to a reference method that uses a common regression model for all types of activities.

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

PubMed

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

2002-12-01

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

Carbon quantum dots coated BiVO{sub 4} inverse opals for enhanced photoelectrochemical hydrogen generation

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

Nan, Feng; Shen, Mingrong; Fang, Liang, E-mail: zhkang@suda.edu.cn, E-mail: lfang@suda.edu.cn

Carbon quantum dots (CQDs) coated BiVO{sub 4} inverse opal (io-BiVO{sub 4}) structure that shows dramatic improvement of photoelectrochemical hydrogen generation has been fabricated using electrodeposition with a template. The io-BiVO{sub 4} maximizes photon trapping through slow light effect, while maintaining adequate surface area for effective redox reactions. CQDs are then incorporated to the io-BiVO{sub 4} to further improve the photoconversion efficiency. Due to the strong visible light absorption property of CQDs and enhanced separation of the photoexcited electrons, the CQDs coated io-BiVO{sub 4} exhibit a maximum photo-to-hydrogen conversion efficiency of 0.35%, which is 6 times higher than that of themore » pure BiVO{sub 4} thin films. This work is a good example of designing composite photoelectrode by combining quantum dots and photonic crystal.« less

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

PubMed

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

2010-03-01

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

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

PubMed

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

2016-09-28

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

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

PubMed

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

2007-11-15

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

Infrared characteristics of VO2 thin films for smart window and laser protection applications

NASA Astrophysics Data System (ADS)

Huang, Zhangli; Chen, Sihai; Lv, Chaohong; Huang, Ying; Lai, Jianjun

2012-11-01

Vanadium dioxide (VO2) films with a low semiconductor-to-metal transition temperature of 45 °C were fabricated through direct current magnetron sputtering followed by a post-annealing. Atomic force microscopy measurements show that the VO2 grain size is about one hundred of nanometers. Infrared (IR) characteristic is well investigated by applying a He-Ne laser power intensity measurement, and the result reveals that the VO2 film exhibits excellent IR switching property. Furthermore, solar smart window and laser protection experiments demonstrate that the obtained VO2 thin film is a promising material for the application in related fields.

VO 2 thin films synthesis for collaborators and various applications.

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

Johnson, Raegan Lynn; Clem, Paul G.

2016-11-01

Vanadium dioxide (VO 2) is an attractive material for a variety of applications due to its metal-to-insulator transition (MIT) observed at modest temperatures. This transition takes VO 2 from its low temperature insulating monoclinic phase to a high temperature (above 68°C) metallic rutile phase. This transition gives rise to a change in resistivity up to 5 orders of magnitude and a change in complex refractive index (especially at IR wavelengths), which is of interest for radar circuit protection and tunable control of infrared signature. Recently, collaborations have been initiated between CINT scientists and external university programs. The Enhanced Surveillance fundsmore » help fund this work which enabled synthesis of VO 2 films for several collaborations with internal and external researchers.« less

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

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.

Non-catalytic hydrogenation of VO2 in acid solution.

PubMed

Chen, Yuliang; Wang, Zhaowu; Chen, Shi; Ren, Hui; Wang, Liangxin; Zhang, Guobin; Lu, Yalin; Jiang, Jun; Zou, Chongwen; Luo, Yi

2018-02-26

Hydrogenation is an effective way to tune the property of metal oxides. It can conventionally be performed by doping hydrogen into solid materials with noble-metal catalysis, high-temperature/pressure annealing treatment, or high-energy proton implantation in vacuum condition. Acid solution naturally provides a rich proton source, but it should cause corrosion rather than hydrogenation to metal oxides. Here we report a facile approach to hydrogenate monoclinic vanadium dioxide (VO 2 ) in acid solution at ambient condition by placing a small piece of low workfunction metal (Al, Cu, Ag, Zn, or Fe) on VO 2 surface. It is found that the attachment of a tiny metal particle (~1.0 mm) can lead to the complete hydrogenation of an entire wafer-size VO 2 (>2 inch). Moreover, with the right choice of the metal a two-step insulator-metal-insulator phase modulation can even be achieved. An electron-proton co-doping mechanism has been proposed and verified by the first-principles calculations.

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

Predictors of VO2Peak in children age 6- to 7-years-old.

PubMed

Dencker, Magnus; Hermansen, Bianca; Bugge, Anna; Froberg, Karsten; Andersen, Lars B

2011-02-01

This study investigated the predictors of aerobic fitness (VO2PEAK) in young children on a population-base. Participants were 436 children (229 boys and 207 girls) aged 6.7 ± 0.4 yrs. VO2PEAK was measured during a maximal treadmill exercise test. Physical activity was assessed by accelerometers. Total body fat and total fat free mass were estimated from skinfold measurements. Regression analyses indicated that significant predictors for VO2PEAK per kilogram body mass were total body fat, maximal heart rate, sex, and age. Physical activity explained an additional 4-7%. Further analyses showed the main contributing factors for absolute values of VO2PEAK were fat free mass, maximal heart rate, sex, and age. Physical activity explained an additional 3-6%.

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

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

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 changemore » 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.« less

VO2 microcrystals as an advanced smart window material at semiconductor to metal transition

NASA Astrophysics Data System (ADS)

Basu, Raktima; Magudapathy, P.; Sardar, Manas; Pandian, Ramanathaswamy; Dhara, Sandip

2017-11-01

Textured VO2(0 1 1) microcrystals are grown in the monoclinic, M1 phase which undergoes a reversible first order semiconductor to metal transition (SMT) accompanied by a structural phase transition to rutile tetragonal, R phase. Around the phase transition, VO2 also experiences noticeable change in its optical and electrical properties. A change in color of the VO2 micro crystals from white to cyan around the transition temperature is observed, which is further understood by absorption of red light using temperature dependent ultraviolet-visible spectroscopic analysis and photoluminescence studies. The absorption of light in the red region is explained by the optical transition between Hubbard states, confirming the electronic correlation as the driving force for SMT in VO2. The thermochromism in VO2 has been studied for smart window applications so far in the IR region, which supports the opening of the band gap in semiconducting phase; whereas there is hardly any report in the management of visible light. The filtering of blue light along with reflection of infrared above the semiconductor to metal transition temperature make VO2 applicable as advanced smart windows for overall heat management of a closure.

The ROI of VoIP: Everybody Says VoIP Saves Big Bucks. But Does It?

ERIC Educational Resources Information Center

Villano, Matt

2006-01-01

Advocates of Voice over Internet Protocol (VoIP) say it saves money on long distance calls by sending them over the Internet, improves communication by eliminating the Private Branch Exchange (PBX), and offers a host of neat features such as call forwarding, e-mail accessible voicemail, and more. When it comes to measuring the dollars-and-cents…

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

PubMed

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

2007-06-01

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

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.

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

PubMed

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

2015-11-04

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.

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

PubMed Central

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

1990-01-01

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

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

Two-Dimensional VO2 Mesoporous Microarrays for High-Performance Supercapacitor

NASA Astrophysics Data System (ADS)

Fan, Yuqi; Ouyang, Delong; Li, Bao-Wen; Dang, Feng; Ren, Zongming

2018-05-01

Two-dimensional (2D) mesoporous VO2 microarrays have been prepared using an organic-inorganic liquid interface. The units of microarrays consist of needle-like VO2 particles with a mesoporous structure, in which crack-like pores with a pore size of about 2 nm and depth of 20-100 nm are distributed on the particle surface. The liquid interface acts as a template for the formation of the 2D microarrays, as identified from the kinetic observation. Due to the mesoporous structure of the units and high conductivity of the microarray, such 2D VO2 microarrays exhibit a high specific capacitance of 265 F/g at 1 A/g and excellent rate capability (182 F/g at 10 A/g) and cycling stability, suggesting the effect of unique microstructure for improving the electrochemical performance.

Strain effect in epitaxial VO2 thin films grown on sapphire substrates using SnO2 buffer layers

NASA Astrophysics Data System (ADS)

Kim, Heungsoo; Bingham, Nicholas S.; Charipar, Nicholas A.; Piqué, Alberto

2017-10-01

Epitaxial VO2/SnO2 thin film heterostructures were deposited on m-cut sapphire substrates via pulsed laser deposition. By adjusting SnO2 (150 nm) growth conditions, we are able to control the interfacial strain between the VO2 film and SnO2 buffer layer such that the semiconductor-to-metal transition temperature (TC) of VO2 films can be tuned without diminishing the magnitude of the transition. It is shown that in-plane tensile strain and out-of-plane compressive strain of the VO2 film leads to a decrease of Tc. Interestingly, VO2 films on SnO2 buffer layers exhibit a structural phase transition from tetragonal-like VO2 to tetragonal-VO2 during the semiconductor-to-metal transition. These results suggest that the strain generated by SnO2 buffer provides an effective way for tuning the TC of VO2 films.

Metal-Insulator Transition in W-doped VO2 Nanowires

NASA Astrophysics Data System (ADS)

Long, Gen; Parry, James; Whittaker, Luisa; Banerjee, Sarbajit; Zeng, Hao

2010-03-01

We report a systematic study of the metal-insulator transition in W-doped VO2 nanowires. Magnetic susceptibility were measured for a bulk amount of VO2 nanowire powder. The susceptibility shows a sharp drop with decreasing temperature corresponding to the metal-insulator transition. The transition shows large temperature hysteresis for cooling and heating. With increasing doping concentration, the transition temperatures decreases systematically from 320 K to 275K. Charge transport measurements on the same nanowires showed similar behavior. XRD and TEM measurements were taken to further determine the structure of the materials in study.

BiVO4 Fern Architectures: A Competitive Anode for Lithium-Ion Batteries.

PubMed

Dubal, Deepak P; Patil, Deepak R; Patil, Santosh S; Munirathnam, N R; Gomez-Romero, Pedro

2017-09-21

The development of high-performance anode materials for lithium-ion batteries (LIBs) is currently subject to much interest. In this study, BiVO 4 fern architectures are introduced as a new anode material for LIBs. The BiVO 4 fern shows an excellent reversible capacity of 769 mAh g -1 (ultrahigh volumetric capacity of 3984 mAh cm -3 ) at 0.12 A g -1 with large capacity retention. A LIB full cell is then assembled with a BiVO 4 fern anode and LiFePO 4 (LFP, commercial) as cathode material. The device can achieve a capacity of 140 mAh g -1 at 1C rate, that is, 81 % of the capacity of the cathode and maintained to 104 mAh g -1 at a high rate of 8C, which makes BiVO 4 a promising candidate as a high-energy anode material for LIBs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of respiratory muscle work on VO(2) and leg blood flow during submaximal exercise.

PubMed

Wetter, T J; Harms, C A; Nelson, W B; Pegelow, D F; Dempsey, J A

1999-08-01

The work of breathing (W(b)) normally incurred during maximal exercise not only requires substantial cardiac output and O(2) consumption (VO(2)) but also causes vasoconstriction in locomotor muscles and compromises leg blood flow (Q(leg)). We wondered whether the W(b) normally incurred during submaximal exercise would also reduce Q(leg). Therefore, we investigated the effects of changing the W(b) on Q(leg) via thermodilution in 10 healthy trained male cyclists [maximal VO(2) (VO(2 max)) = 59 +/- 9 ml. kg(-1). min(-1)] during repeated bouts of cycle exercise at work rates corresponding to 50 and 75% of VO(2 max). Inspiratory muscle work was 1) reduced 40 +/- 6% via a proportional-assist ventilator, 2) not manipulated (control), or 3) increased 61 +/- 8% by addition of inspiratory resistive loads. Increasing the W(b) during submaximal exercise caused VO(2) to increase; decreasing the W(b) was associated with lower VO(2) (DeltaVO(2) = 0.12 and 0.21 l/min at 50 and 75% of VO(2 max), respectively, for approximately 100% change in W(b)). There were no significant changes in leg vascular resistance (LVR), norepinephrine spillover, arterial pressure, or Q(leg) when W(b) was reduced or increased. Why are LVR, norepinephrine spillover, and Q(leg) influenced by the W(b) at maximal but not submaximal exercise? We postulate that at submaximal work rates and ventilation rates the normal W(b) required makes insufficient demands for VO(2) and cardiac output to require any cardiovascular adjustment and is too small to activate sympathetic vasoconstrictor efferent output. Furthermore, even a 50-70% increase in W(b) during submaximal exercise, as might be encountered in conditions where ventilation rates and/or inspiratory flow resistive forces are higher than normal, also does not elicit changes in LVR or Q(leg).

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.

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

Supercritical temperature synthesis of fluorine-doped VO2(M) nanoparticle with improved thermochromic property

NASA Astrophysics Data System (ADS)

Riapanitra, Anung; Asakura, Yusuke; Cao, Wenbin; Noda, Yasuto; Yin, Shu

2018-06-01

Fluorine-doped VO2(M) nanoparticles have been successfully synthesized using the hydrothermal method at a supercritical temperature of 490 °C. The pristine VO2(M) has the critical phase transformation temperature of 64 °C. The morphology and homogeneity of the monoclinic structure VO2(M) were adopted by the fluorine-doped system. The obtained particle size of the samples is smaller at the higher concentration of anion doping. The best reduction of critical temperature was achieved by fluorine doping of 0.13% up to 48 °C. The thin films of the fluorine-doped VO2(M) showed pronounced thermochromic property and therefore are suitable for smart window applications.

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

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

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..

How To: Be VoIP-Savvy

ERIC Educational Resources Information Center

Branzburg, Jeffrey

2005-01-01

Cablevision, Comcast, Verizon, and many other high-speed broadband Internet providers are now also offering telephone services through "Voice over Internet Protocol" (VoIP). This technology sends ordinary telephone calls over the Internet rather than over telephone lines. While impractical without the use of a broadband Internet connection, with…

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. Copyright © 2015 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Enhanced photocatalytic performance of BiVO4 in aqueous AgNO3 solution under visible light irradiation

NASA Astrophysics Data System (ADS)

Huang, Chien-Kai; Wu, Tsunghsueh; Huang, Chang-Wei; Lai, Chi-Yung; Wu, Mei-Yao; Lin, Yang-Wei

2017-03-01

Monoclinic-phase bismuth vanadate (BiVO4) with a 2.468 eV band gap exhibited enhanced synergic photodegradation activity toward methylene blue (MB) when combined with silver ions (Ag+) in an aqueous solution under visible light irradiation. The mass ratio of AgNO3 to BiVO4 and the calcination temperature were discovered to considerably affect the degradation activity of BiVO4/Ag+. Superior photocatalytic performance was obtained when BiVO4 was mixed with 0.01%(w/v) AgNO3 solution, and complete degradation of MB was achieved after 25 min visible light irradiation, outperforming BiVO4 or AgNO3 solution alone. The enhanced photodegradation was investigated using systematic luminescence measurements, electrochemical impedance spectroscopy, and scavenger addition, after which a photocatalytic mechanism for MB degradation under visible light irradiation was identified that involved oxygen radicals and holes. This study also discovered the two dominating processes involved in enhancing the electron-hole separation efficiency and reducing their recombination rate, namely photoreduction of Ag+ and the formation of a BiVO4/Ag heterojunction. The synergic effect between BiVO4 and Ag+ was discovered to be unique. BiVO4/Ag+ was successfully used to degrade two other dyes and disinfect Escherichia Coli. A unique fluorescent technique using BiVO4 and a R6G solution to detect Ag+ ions in water was discovered.

Inelastic Neutron Scattering studies of pure and Mo doped VO2

NASA Astrophysics Data System (ADS)

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

2014-03-01

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

VO2-based radiative thermal transistor with a semi-transparent base

NASA Astrophysics Data System (ADS)

Prod'homme, Hugo; Ordonez-Miranda, Jose; Ezzahri, Younès; Drévillon, Jérémie; Joulain, Karl

2018-05-01

We study a radiative thermal transistor analogous to an electronic one made of a VO2 base placed between two silica semi-infinite plates playing the roles of the transistor collector and emitter. The fact that VO2 exhibits an insulator to metal transition is exploited to modulate and/or amplify heat fluxes between the emitter and the collector, by applying a thermal current on the VO2 base. We extend the work of precedent studies considering the case where the base can be semi-transparent so that heat can be exchanged directly between the collector and the emitter. Both near and far field cases are considered leading to 4 typical regimes resulting from the fact that the emitter-base and base-collector separation distances can be larger or smaller than the thermal wavelength for a VO2 layer opaque or semi-transparent. Thermal currents variations with the base temperatures are calculated and analyzed. It is found that the transistor can operate in an amplification mode as already stated in [1] or in a switching mode as seen in [2]. An optimum configuration for the base thickness and separation distance maximizing the thermal transistor modulation factor is found.

Correlation between surface morphology and electrical properties of VO2 films grown by direct thermal oxidation method

NASA Astrophysics Data System (ADS)

Yoon, Joonseok; Park, Changwoo; Park, Sungkyun; Mun, Bongjin Simon; Ju, Honglyoul

2015-10-01

We investigate surface morphology and electrical properties of VO2 films fabricated by direct thermal oxidation method. The VO2 film prepared with oxidation temperature at 580 °C exhibits excellent qualities of VO2 characteristics, e.g. a metal-insulator transition (MIT) near 67 °C, a resistivity ratio of ∼2.3 × 104, and a bandgap of 0.7 eV. The analysis of surface morphology with electrical resistivity of VO2 films reveals that the transport properties of VO2 films are closely related to the grain size and surface roughness that vary with oxidation annealing temperatures.

Epitaxial growth of VO2 by periodic annealing

NASA Astrophysics Data System (ADS)

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

2014-02-01

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

Naturally formed ultrathin V2O5 heteroepitaxial layer on VO2/sapphire(001) film

NASA Astrophysics Data System (ADS)

Littlejohn, Aaron J.; Yang, Yunbo; Lu, Zonghuan; Shin, Eunsung; Pan, KuanChang; Subramanyam, Guru; Vasilyev, Vladimir; Leedy, Kevin; Quach, Tony; Lu, Toh-Ming; Wang, Gwo-Ching

2017-10-01

Vanadium dioxide (VO2) and vanadium pentoxide (V2O5) thin films change their properties in response to external stimuli such as photons, temperature, electric field and magnetic field and have applications in electronics, optical devices, and sensors. Due to the multiple valence states of V and non-stoichiometry in thin films, it is challenging to grow epitaxial, single-phase V-oxide on a substrate, or a heterostructure of two epitaxial V-oxides. We report the formation of a heterostructure consisting of a few nm thick ultrathin V2O5 epitaxial layer on pulsed laser deposited tens of nm thick epitaxial VO2 thin films grown on single crystal Al2O3(001) substrates without post annealing of the VO2 film. The simultaneous observation of the ultrathin epitaxial V2O5 layer and VO2 epitaxial film is only possible by our unique reflection high energy electron diffraction pole figure analysis. The out-of-plane and in-plane epitaxial relationships are V2O5[100]||VO2[010]||Al2O3[001] and V2O5[03 2 bar ]||VO2[100]||Al2O3[1 1 bar 0], respectively. The existence of the V2O5 layer on the surface of the VO2 film is also supported by X-ray photoelectron spectroscopy and Raman spectroscopy.

Solar water oxidation using nickel-borate coupled BiVO4 photoelectrodes.

PubMed

Choi, Sung Kyu; Choi, Wonyong; Park, Hyunwoong

2013-05-07

A naturally abundant nickel-borate (Ni-Bi) complex is demonstrated to successfully catalyze the photoelectrochemical (PEC) water oxidation of BiVO4 electrodes at 1.23 VRHE with nearly 100% faradaic efficiency for oxygen evolution. Ni-Bi is electrodeposited (ED) and photodeposited (PD) for varying times on BiVO4 electrodes in the 0.1 M borate electrolyte with 1 mM Ni(2+) at pH 9.2. Surprisingly, optimally deposited Ni-Bi films (ED-10 s and PD-30 min) display the same layer thickness of ca. 40 nm. Both Ni-Bi films enhance the photocurrent generation of BiVO4 at 1.23 VRHE by a factor of 3-4 under AM 1.5-light irradiation (100 mW cm(-2)) along with ca. 250% increase in the incident and absorbed photon-to-current efficiencies. Impedance analysis further reveals that the charge transfer resistance at BiVO4 is markedly decreased by Ni-Bi deposits. The primary role of Ni-Bi has been suggested to be a hole-conductor making photogenerated electrons more mobile and catalyzing a four-hole transfer to water through cyclic changes between the lower and higher Ni oxidation states. However, thick Ni-Bi films (>~40 nm) significantly reduce the PEC performance of BiVO4 due to the kinetic bottleneck and charge recombination. Under identical PEC conditions (0.1 M, pH 9.2), the borate electrolyte (good proton acceptor) is found to be better than nitrate (poor proton acceptor), indicative of a proton-coupled electron transfer pathway in PEC water oxidation.

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.

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.

Near-zero IR transmission of VO2 thin films deposited on Si substrate

NASA Astrophysics Data System (ADS)

Zhang, Chunzi; Koughia, Cyril; Li, Yuanshi; Cui, Xiaoyu; Ye, Fan; Shiri, Sheida; Sanayei, Mohsen; Wen, Shi-Jie; Yang, Qiaoqin; Kasap, Safa

2018-05-01

Vanadium dioxide (VO2) thin films of different thickness have been deposited on Si substrates by using DC magnetron sputtering. The effects of substrate pre-treatment by means of seeding (spin coating and ultrasonic bathing) and biasing on the structure and optical properties were investigated. Seeding results in a smaller grain size in the oxide film, whereas biasing results in square-textured crystals. VO2 thin films of 150 nm thick show a near-zero IR transmission in switched state. Especially, the 150 nm thick VO2 thin film with seeding treatment shows an enhanced switching efficiency.

Enhanced photoelectrochemical performance of inorganic-organic hybrid consisting of BiVO4 and PEDOT:PSS

NASA Astrophysics Data System (ADS)

Trzciński, K.; Szkoda, M.; Siuzdak, K.; Sawczak, M.; Lisowska-Oleksiak, A.

2016-12-01

The PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) was electrodeposited on a thin layer of bismuth vanadate (BiVO4) prepared using the pulsed laser deposition technique onto FTO. The inorganic-organic junction was characterized by Raman spectroscopy, UV-vis spectroscopy and scanning electron microscopy. Chronoamperometry curves, recorded under simulated solar light illumination, were performed to determine generated photocurrent during water and hydroquinone oxidation at the electrode surface. Experiments were performed for three types of electrode materials: (i) FTO/BiVO4, (ii) FTO/PEDOT:PSS and (iii) FTO/BiVO4/PEDOT:PSS in aqueous electrolyte. Almost 5 times higher photocurrent in electrolyte containing hole scavenger was generated after modification of BiVO4 photoanode with electrodeposited polymer. It is noteworthy that anodic photocurrent was stable even after 4 h of illumination. Cyclic voltammetry curves of FTO/BiVO4/PEDOT:PSS recorded before and after experiments performed under electrode illumination indicated that the organic part in tested junction is photo-corrosion resistant.

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

NASA Astrophysics Data System (ADS)

Song, Shaokun; Huang, Qiwei; Zhu, Wanting

2017-10-01

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

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

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

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

PubMed

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

2017-01-01

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

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

PubMed

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

2004-02-01

To test the hypotheses that: 1) the time constant for the fast component of .VO2 kinetics (tau1) at exercise onset would be faster in trained than in untrained subjects for both moderate and heavy exercise, and that 2) tau1 would become progressively slower in untrained subjects at higher power outputs but be invariant in trained subjects. Eight untrained subjects (.VO2peak: 42.9 +/- 5.1 mL.kg-1.min-1) and seven trained cyclists (.VO2peak: 66.6 +/- 2.5 mL.kg-1.min-1) completed square-wave transitions to power outputs requiring 60% and 80% of gas exchange threshold (GET), and 50% of the difference between GET and .VO2 peak (50%Delta) from a baseline of "unloaded" cycling. .VO2 was measured breath-by-breath and individual responses were modeled using nonlinear regression techniques. A repeated measures ANOVA revealed that the tau1 was significantly smaller (i.e., the kinetics were faster) in the trained compared with the untrained subjects and that tau1 became significantly greater (i.e., the kinetics were slowed) at higher power outputs both in the untrained (60%GET: 17.8 +/- 3.8 s, 80%GET: 21.5 +/- 6.6 s, and 50%Delta: 23.5 +/- 2.8 s) and the trained (60%GET: 8.9 +/- 1.3 s, 80%GET: 11.7 +/- 2.5 s, and 50%Delta: 15.2 +/- 2.0 s) subjects (P < 0.05). Phase II .VO2 kinetics became progressively slower at higher power outputs in both trained and untrained subjects. That a greater tau1 was evident at a higher power output within the moderate exercise intensity domain (VO2 kinetics may be attributed to other factors besides O2 availability such as the recruitment of higher threshold motor units.

Metal-Insulator Transitions in Epitaxial LaVO(3) and LaTiO(3) Films

DTIC Science & Technology

2012-08-01

epitaxial films of LaVO3 and LaTiO3 can exhibit metallicity though their bulk counterparts are Mott insulators. When LaTiO3 films are compressively...secondarily to interface electronic reconstruction at the LaTiO3 /SrTiO3 interface. However, when LaVO3 films are compressively strained on SrTiO3...ABSTRACT We have demonstrated that epitaxial films of LaVO3 and LaTiO3 can exhibit metallicity though their bulk counterparts are Mott insulators. When

Gate-tunable gigantic lattice deformation in VO{sub 2}

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

Okuyama, D., E-mail: okuyama@riken.jp, E-mail: nakano@imr.tohoku.ac.jp, E-mail: iwasa@ap.t.u-tokyo.ac.jp; Hatano, T.; Nakano, M., E-mail: okuyama@riken.jp, E-mail: nakano@imr.tohoku.ac.jp, E-mail: iwasa@ap.t.u-tokyo.ac.jp

2014-01-13

We examined the impact of electric field on crystal lattice of vanadium dioxide (VO{sub 2}) in a field-effect transistor geometry by in-situ synchrotron x-ray diffraction measurements. Whereas the c-axis lattice parameter of VO{sub 2} decreases through the thermally induced insulator-to-metal phase transition, the gate-induced metallization was found to result in a significant increase of the c-axis length by almost 1% from that of the thermally stabilized insulating state. We also found that this gate-induced gigantic lattice deformation occurs even at the thermally stabilized metallic state, enabling dynamic control of c-axis lattice parameter by more than 1% at room temperature.

VoIP in a Campus Environment

ERIC Educational Resources Information Center

Young, Dan

2005-01-01

Internet Protocol (IP) Telephony, or voice-over IP (VoIP), has proved to be a wise decision for many organizations. This technology crosses the boundaries of public and private networks, enterprise and residential markets, voice and data technologies, as well as local and long-distance services. The convergence of voice and data into a single,…

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

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.

Facile fabrication of an efficient BiVO4 thin film electrode for water splitting under visible light irradiation.

PubMed

Jia, Qingxin; Iwashina, Katsuya; Kudo, Akihiko

2012-07-17

An efficient BiVO(4) thin film electrode for overall water splitting was prepared by dipping an F-doped SnO(2) (FTO) substrate electrode in an aqueous nitric acid solution of Bi(NO(3))(3) and NH(4)VO(3), and subsequently calcining it. X-ray diffraction of the BiVO(4) thin film revealed that a photocatalytically active phase of scheelite-monoclinic BiVO(4) was obtained. Scanning electron microscopy images showed that the surface of an FTO substrate was uniformly coated with the BiVO(4) film with 300-400 nm of the thickness. The BiVO(4) thin film electrode gave an excellent anodic photocurrent with 73% of an IPCE at 420 nm at 1.0 V vs. Ag/AgCl. Modification with CoO on the BiVO(4) electrode improved the photoelectrochemical property. A photoelectrochemical cell consisting of the BiVO(4) thin film electrode with and without CoO, and a Pt counter electrode was constructed for water splitting under visible light irradiation and simulated sunlight irradiation. Photocurrent due to water splitting to form H(2) and O(2) was confirmed with applying an external bias smaller than 1.23 V that is a theoretical voltage for electrolysis of water. Water splitting without applying external bias under visible light irradiation was demonstrated using a SrTiO(3)Rh photocathode and the BiVO(4) photoanode.

Study of the thermal-induced intensity balanced Nd:GdVO4 microchip dual-frequency laser

NASA Astrophysics Data System (ADS)

Cai, Meiling; Hu, Miao; Zhou, Xuefang; Lu, Yang; Zeng, Ran; Li, Qiliang; Wei, Yizhen

2018-01-01

The intensity balance ratio (IBR) tuning mechanism of Nd:GdVO4 monolithic microchip dual-frequency laser (DFL) is presented. The intensity balanced DFL signals are obtained by precisely controlling the heat sink temperature of the Nd:GdVO4 crystal. In experiments, the DFL signal with frequency separation at 64 GHz and IBR above 0.99 is realized with the temperature at 47.6 °C. The other balanced intensity distribution can be reached at -0.9 °C before mode hopping. Moreover, utilizing the fluorescence spectrum and the intensity balance points of Nd:GdVO4 DFL, we obtain the temperature difference between internal and external of Nd:GdVO4 crystal ΔT = 24.0 °C.

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.

Li2.97Mg0.03VO4: High rate capability and cyclability performances anode material for rechargeable Li-ion batteries

NASA Astrophysics Data System (ADS)

Dong, Youzhong; Zhao, Yanming; Duan, He; Singh, Preetam; Kuang, Quan; Peng, Hongjian

2016-07-01

Mg-doped composite, Li2.97Mg0.03VO4, with an orthorhombic structure was prepared by a sol-gel method. The effects of the Mg doping on the structure and electrochemical performance of Li3VO4 were investigated. The X-ray diffraction pattern shows that the Mg doping does not change the crystal structure of Li3VO4. The EDS mappings indicated the fairly uniform distribution of Mg throughout the grains of Li2.97Mg0.03VO4. Electronic conductivity of Mg-doped Li3VO4 increased by two orders of magnitude compared to that of pure Li3VO4. CV and EIS measurement confirms that the Li2.97Mg0.03VO4 sample exhibits a smaller polarization and transfer resistance and a higher lithium diffusion coefficient compared with the pure Li3VO4. Due to the better electrochemical kinetics properties, Mg-doped Li3VO4 showed a significant improved performance compared to the pure Li3VO4, especially for the high rate capability. At the higher discharge/charge rate (2C), the discharge and charge capacities of 415.5 and 406.1 mAh/g have been obtained for the Li2.97Mg0.03VO4 which is more than three times higher the discharge/charge capacities of Li3VO4. The discharge and charge capacities of pure Li3VO4 are only 126.4 and 125.8 mAh/g respectively. The excellent electrochemical performance of Li2.97Mg0.03VO4 enables it as a promising anode material for rechargeable lithium-ion batteries.

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

PubMed

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

1999-09-01

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

Investigations on structural and giant magneto impedance properties of Zn3(VO4)2 nanorods

NASA Astrophysics Data System (ADS)

Malaidurai, M.; Bulusu, Venkat; De, Sourodeep; Thangavel, R.

2018-05-01

In this paper, we successfully synthesized Zn3(VO4)2 novel nanorods by hydrothermal method. As mixed phase of Zn3(VO4)2 structural and phase transformations were monitored in crystal lattice with different ionic strength by X-ray diffraction(XRD). The Zn3(VO4)2 thin film formation validated through qualitative and quantitative analysis by FESEM and it is clearly depicted the formation of the Zn3(VO4)2 nanorods varied from ˜100nm in lengths and ˜30 nm in widths. The Zn precursor's anions directly influence the composition and shape of the resultant hydrated Zn3(VO4)2. Impedance analysis were closely studied with Impedance-Frequency characterization, which was then followed by a dielectric measurement. The analysis of GMI effect was carried out with the help of the model equivalent circuit at low frequencies, constant phase element (CPE). GMI effect and the sensitivity are calculated for the sample by appling magnetic field and driving frequency in order to analyze the giant magnetoimpedance resistance of grain boundaries for spintronics applications.

Surface charge sensing by altering the phase transition in VO2

NASA Astrophysics Data System (ADS)

Kumar, S.; Esfandyarpour, R.; Davis, R.; Nishi, Y.

2014-08-01

Detection of surface charges has various applications in medicine, electronics, biotechnology, etc. The source of surface charge induction may range from simple charge-polarized molecules like water to complicated proteins. It was recently discovered that surface charge accumulation can alter the temperature at which VO2 undergoes a Mott transition. Here, we deposited polar molecules onto the surface of two-terminal thin-film VO2 lateral devices and monitored the joule-heating-driven Mott transition, or conductance switching. We observed that the power required to induce the conductance switching reduced upon treatment with polar molecules and, using in-situ blackbody-emission direct measurement of local temperature, we show that this reduction in power was accompanied by reduction in the Mott transition temperature. Further evidence suggested that this effect has specificity to the nature of the species used to induce surface charges. Using x-ray absorption spectroscopy, we also show that there is no detectable change in oxidation state of vanadium or structural phase in the bulk of the 40 nm VO2 thin-film even as the phase transition temperature is reduced by up to 20 K by the polar molecules. The ability to alter the phase transition parameters by depositing polar molecules suggests a potential application in sensing surface charges of different origins and this set of results also highlights interesting aspects of the phase transition in VO2.

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

PubMed

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

2015-01-05

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

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

PubMed

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

2017-06-14

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

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.

The Volcanism Ontology (VO): a model of the volcanic system

NASA Astrophysics Data System (ADS)

Myer, J.; Babaie, H. A.

2017-12-01

We have modeled a part of the complex material and process entities and properties of the volcanic system in the Volcanism Ontology (VO) applying several top-level ontologies such as Basic Formal Ontology (BFO), SWEET, and Ontology of Physics for Biology (OPB) within a single framework. The continuant concepts in BFO describe features with instances that persist as wholes through time and have qualities (attributes) that may change (e.g., state, composition, and location). In VO, the continuants include lava, volcanic rock, and volcano. The occurrent concepts in BFO include processes, their temporal boundaries, and the spatio-temporal regions within which they occur. In VO, these include eruption (process), the onset of pyroclastic flow (temporal boundary), and the space and time span of the crystallization of lava in a lava tube (spatio-temporal region). These processes can be of physical (e.g., debris flow, crystallization, injection), atmospheric (e.g., vapor emission, ash particles blocking solar radiation), hydrological (e.g., diffusion of water vapor, hot spring), thermal (e.g., cooling of lava) and other types. The properties (predicates) relate continuants to other continuants, occurrents to continuants, and occurrents to occurrents. The ontology also models other concepts such as laboratory and field procedures by volcanologists, sampling by sensors, and the type of instruments applied in monitoring volcanic activity. When deployed on the web, VO will be used to explicitly and formally annotate data and information collected by volcanologists based on domain knowledge. This will enable the integration of global volcanic data and improve the interoperability of software that deal with such data.

Photoinduced surface plasmon switching at VO2/Au interface.

PubMed

Kumar, Nardeep; Rúa, Armando; Aldama, Jennifer; Echeverría, Karla; Fernández, Félix E; Lysenko, Sergiy

2018-05-28

Angle-resolved reflection, light scattering and ultrafast pump-probe spectroscopy combined with a surface plasmon-polariton (SPP) resonance technique in attenuated total reflection geometry was used to investigate the light-induced plasmonic switching in a photorefractive VO 2 /Au hybrid structure. Measurements of SPP scattering and reflection shows that the optically-induced formation of metallic state in a vanadium dioxide layer deposited on a gold film significantly alters the electromagnetic field enhancement and SPP propagation length at the VO 2 /Au interface. The ultrafast optical manipulation of SPP resonance is shown on a picosecond timescale. Obtained results demonstrate high potential of photorefractive vanadium oxides as efficient plasmonic modulating materials for ultrafast optoelectronic devices.

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.

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

PubMed

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

2015-01-01

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

Visible-light-induced Ag/BiVO4 semiconductor with enhanced photocatalytic and antibacterial performance

NASA Astrophysics Data System (ADS)

Regmi, Chhabilal; Dhakal, Dipesh; Wohn Lee, Soo

2018-02-01

An Ag-loaded BiVO4 visible-light-driven photocatalyst was synthesized by the microwave hydrothermal method followed by photodeposition. The photocatalytic performance of the synthesized samples was evaluated on a mixed dye (methylene blue and rhodamine B), as well as bisphenol A in aqueous solution. Similarly, the disinfection activities of synthesized samples towards the Gram-negative Escherichia coli (E. coli) in a model cell were investigated under irradiation with visible light (λ ≥ 420 nm). The synthesized samples have monoclinic scheelite structure. Photocatalytic results showed that all Ag-loaded BiVO4 samples exhibited greater degradation and a higher mineralization rate than the pure BiVO4, probably due to the presence of surface plasmon absorption that arises due to the loading of Ag on the BiVO4 surface. The optimum Ag loading of 5 wt% has the highest photocatalytic performance and greatest stability with pseudo-first-order rate constants of 0.031 min-1 and 0.023 min-1 for the degradation of methylene blue and rhodamine B respectively in a mixture with an equal volume and concentration of each dye. The photocatalytic degradation of bisphenol A reaches 76.2% with 5 wt% Ag-doped BiVO4 within 180 min irradiation time. Similarly, the Ag-loaded BiVO4 could completely inactivate E. coli cells within 30 min under visible light irradiation. The disruption of the cell membrane as well as degradation of protein and DNA exhibited constituted evidence for antibacterial activity towards E. coli. Moreover, the bactericidal mechanisms involved in the photocatalytic disinfection process were systematically investigated.

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

PubMed

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

2017-07-01

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

Gate-tunable gigantic changes in lattice parameters and optical properties in VO2

NASA Astrophysics Data System (ADS)

Nakano, Masaki; Okuyama, Daisuke; Shibuya, Keisuke; Ogawa, Naoki; Hatano, Takafumi; Kawasaki, Masashi; Arima, Taka-Hisa; Iwasa, Yoshihiro; Tokura, Yoshinori

2014-03-01

The field-effect transistor provides an electrical switching function of current flowing through a channel surface by external gate voltage (VG). We recently reported that an electric-double-layer transistor (EDLT) based on vanadium dioxide (VO2) enables electrical switching of the metal-insulator phase transition, where the low-temperature insulating state can be completely switched to the metallic state by application of VG. Here we demonstrate that VO2-EDLT enables electrical switching of lattice parameters and optical properties as well as electrical current. We performed in-situ x-ray diffraction and optical transmission spectroscopy measurements, and found that the c-axis length and the infrared transmittance of VO2 can be significantly modulated by more than 1% and 40%, respectively, by application of VG. We emphasize that these distinguished features originate from the electric-field induced bulk phase transition available with VO2-EDLT. This work was supported by the Japan Society for the Promotion of Science (JSPS) through its ``Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program).''

Deposition of GdVO4:Eu3+ nanoparticles on silica nanospheres by a simple sol gel method

NASA Astrophysics Data System (ADS)

Liu, Guixia; Hong, Guangyan; Wang, Jinxian; Dong, Xiangting

2006-07-01

The deposition and coating of GdVO4:Eu3+ nanoparticles on spherical silica was carried out using a simple sol-gel method at low temperature. The GdVO4:Eu3+-coated silica composites obtained were characterized by differential thermal analysis (DTA), thermogravimetric (TG) analysis, x-ray diffraction (XRD), Fourier-transform IR spectroscopy (FT-IR), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), photoluminescence spectra, and kinetic decay. It is found that the ~5 nm GdVO4:Eu3+ nanoparticles coating the silica spheres are crystal in the as-prepared samples and the crystallinity increases with increasing annealing temperature. The composites obtained are spherical in shape with an average size of 100 nm. The GdVO4:Eu3+ nanoparticles are linked with silica cores by a chemical bond. The photoluminescence spectra of the obtained GdVO4:Eu3+-coated silica composites are similar to those of the bulk GdVO4:Eu3+ phosphors. The strongest peak is near 617 nm, which indicates that Eu3+ is located in the low symmetry site with non-inversion centre.

Enhancing long-term photostability of BiVO4 photoanodes for solar water splitting by tuning electrolyte composition

NASA Astrophysics Data System (ADS)

Lee, Dong Ki; Choi, Kyoung-Shin

2018-01-01

As the performance of photoelectrodes used for solar water splitting continues to improve, enhancing the long-term stability of the photoelectrodes becomes an increasingly crucial issue. In this study, we report that tuning the composition of the electrolyte can be used as a strategy to suppress photocorrosion during solar water splitting. Anodic photocorrosion of BiVO4 photoanodes involves the loss of V5+ from the BiVO4 lattice by dissolution. We demonstrate that the use of a V5+-saturated electrolyte, which inhibits the photooxidation-coupled dissolution of BiVO4, can serve as a simple yet effective method to suppress anodic photocorrosion of BiVO4. The V5+ species in the solution can also incorporate into the FeOOH/NiOOH oxygen-evolution catalyst layer present on the BiVO4 surface during water oxidation, further enhancing water-oxidation kinetics. The effect of the V5+ species in the electrolyte on both the long-term photostability of BiVO4 and the performance of the FeOOH/NiOOH oxygen-evolution catalyst layer is systematically elucidated.

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

PubMed Central

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

2008-01-01

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

Mg-doped VO2 nanoparticles: hydrothermal synthesis, enhanced visible transmittance and decreased metal-insulator transition temperature.

PubMed

Zhou, Jiadong; Gao, Yanfeng; Liu, Xinling; Chen, Zhang; Dai, Lei; Cao, Chuanxiang; Luo, Hongjie; Kanahira, Minoru; Sun, Chao; Yan, Liuming

2013-05-28

This paper reports the successful preparation of Mg-doped VO2 nanoparticles via hydrothermal synthesis. The metal-insulator transition temperature (T(c)) decreased by approximately 2 K per at% Mg. The Tc decreased to 54 °C with 7.0 at% dopant. The composite foils made from Mg-doped VO2 particles displayed excellent visible transmittance (up to 54.2%) and solar modulation ability (up to 10.6%). In addition, the absorption edge blue-shifted from 490 nm to 440 nm at a Mg content of 3.8 at%, representing a widened optical band gap from 2.0 eV for pure VO2 to 2.4 eV at 3.8 at% doping. As a result, the colour of the Mg-doped films was modified to increase their brightness and lighten the yellow colour over that of the undoped-VO2 film. A first principle calculation was conducted to understand how dopants affect the optical, Mott phase transition and structural properties of VO2.

Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows.

PubMed

Li, Ming; Magdassi, Shlomo; Gao, Yanfeng; Long, Yi

2017-09-01

Vanadium dioxide (VO 2 ) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τ c ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO 2 a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long-standing issues that hindered its application in energy efficient windows: high τ c , low luminous transmittance (T lum ), and undesirable solar modulation ability (ΔT sol ). Many approaches, including nano-thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach-nano-thermochromism-which is to integrate VO 2 nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high-quality VO 2 nanoparticles, and has its own advantages of large-scale synthesis and precise phase control of VO 2 . This Review focuses on hydrothermal synthesis, physical properties of VO 2 polymorphs, and their transformation to thermochromic VO 2 (M), and discusses the advantages, challenges, and prospects of VO 2 (M) in energy-efficient smart windows application. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic transport in VO 2 —Experimentally calibrated Boltzmann transport modeling

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

Kinaci, Alper; Kado, Motohisa; Rosenmann, Daniel

2015-12-28

Materials that undergo metal-insulator transitions (MITs) are under intense study because the transition is scientifically fascinating and technologically promising for various applications. Among these materials, VO2 has served as a prototype due to its favorable transition temperature. While the physical underpinnings of the transition have been heavily investigated experimentally and computationally, quantitative modeling of electronic transport in the two phases has yet to be undertaken. In this work, we establish a density-functional-theory (DFT)-based approach to model electronic transport properties in VO2 in the semiconducting and metallic regimes, focusing on band transport using the Boltzmann transport equations. We synthesized high qualitymore » VO2 films and measured the transport quantities across the transition, in order to calibrate the free parameters in the model. We find that the experimental calibration of the Hubbard correction term can efficiently and adequately model the metallic and semiconducting phases, allowing for further computational design of MIT materials for desirable transport properties.« less

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Influence of VO2 Nanoparticle Morphology on the Colorimetric Assay of H2O2 and Glucose

PubMed Central

Tian, Rui; Sun, Jiaheng; Qi, Yanfei; Zhang, Boyu; Guo, Shuanli; Zhao, Mingming

2017-01-01

Nanozyme-based colorimetric sensors have received considerable attention due to their unique properties. The size, shape, and surface chemistry of these nanozymes could dramatically influence their sensing behaviors. Herein, a comparative study of VO2 nanoparticles with different morphologies (nanofibers, nanosheets, and nanorods) was conducted and applied to the sensitive colorimetric detection of H2O2 and glucose. The peroxidase-like activities and mechanisms of VO2 nanoparticles were analyzed. Among the VO2 nanoparticles, VO2 nanofibers exhibited the best peroxidase-like activity. Finally, a comparative quantitative detections of H2O2 and glucose were done on fiber, sheet, and rod nanoparticles. Under the optimal reaction conditions, the lower limit of detection (LOD) of the VO2 nanofibers, nanosheets, and nanorods for H2O2 are found to be 0.018, 0.266, and 0.41 mM, respectively. The VO2 nanofibers, nanosheets, and nanorods show the linear response for H2O2 from 0.025–10, 0.488–62.5, and 0.488–15.625 mM, respectively. The lower limit of detection (LOD) of the VO2 nanofibers, nanosheets, and nanorods for glucose are found to be 0.009, 0.348, and 0.437 mM, respectively. The VO2 nanofibers, nanosheets, and nanorods show the linear response for glucose from 0.01–10, 0.625–15, and 0.625–10 mM, respectively. The proposed work will contribute to the nanozyme-based colorimetric assay. PMID:29068412

BiVO{sub 4} photoanodes for water splitting with high injection efficiency, deposited by reactive magnetron co-sputtering

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

Gong, Haibo; Institute for Solar Fuels, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin; Freudenberg, Norman

2016-04-15

Photoactive bismuth vanadate (BiVO{sub 4}) thin films were deposited by reactive co-magnetron sputtering from metallic Bi and V targets. The effects of the V-to-Bi ratio, molybdenum doping and post-annealing on the crystallographic and photoelectrochemical (PEC) properties of the BiVO{sub 4} films were investigated. Phase-pure monoclinic BiVO{sub 4} films, which are more photoactive than the tetragonal BiVO{sub 4} phase, were obtained under slightly vanadium-rich conditions. After annealing of the Mo-doped BiVO{sub 4} films, the photocurrent increased 2.6 times compared to undoped films. After optimization of the BiVO{sub 4} film thickness, the photocurrent densities (without a catalyst or a blocking layer ormore » a hole scavenger) exceeded 1.2 mA/cm{sup 2} at a potential of 1.23 V{sub RHE} under solar AM1.5 irradiation. The surprisingly high injection efficiency of holes into the electrolyte is attributed to the highly porous film morphology. This co-magnetron sputtering preparation route for photoactive BiVO{sub 4} films opens new possibilities for the fabrication of large-scale devices for water splitting.« less

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

PubMed

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

2017-08-09

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

Effect of a prior intermittent run at vVO2max on oxygen kinetics during an all-out severe run in humans.

PubMed

Billat, V L; Bocquet, V; Slawinski, J; Laffite, L; Demarle, A; Chassaing, P; Koralsztein, J P

2000-09-01

The purpose of this study was to examine the influence of prior intermittent running at VO2max on oxygen kinetics during a continuous severe intensity run and the time spent at VO2max. Eight long-distance runners performed three maximal tests on a synthetic track (400 m) whilst breathing through the COSMED K4 portable telemetric metabolic analyser: i) an incremental test which determined velocity at the lactate threshold (vLT), VO2max and velocity associated with VO2max (vVO2max), ii) a continuous severe intensity run at vLT+50% (vdelta50) of the difference between vLT and vVO2max (91.3+/-1.6% VO2max)preceded by a light continuous 20 minute run at 50% of vVO2max (light warm-up), iii) the same continuous severe intensity run at vdelta50 with a prior interval training exercise (hard warm-up) of repeated hard running bouts performed at 100% of vVO2max and light running at 50% of vVO2max (of 30 seconds each) performed until exhaustion (on average 19+/-5 min with 19+/-5 interval repetitions). This hard warm-up speeded the VO2 kinetics: the time constant was reduced by 45% (28+/-7 sec vs 51+/-37 sec) and the slow component of VO2 (deltaVO2 6-3 min) was deleted (-143+/-271 ml x min(-1) vs 291+/-153 ml x min(-1)). In conclusion, despite a significantly lower total run time at vdelta50 (6 min 19+/-0) min 17 vs 8 min 20+/-1 min 45, p=0.02) after the intermittent warm-up at VO2max, the time spent specifically at VO2max in the severe continuous run at vdelta50 was not significantly different.

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

Performance improvement of high repetition rate electro-optical cavity-dumped Nd:GdVO4 laser

NASA Astrophysics Data System (ADS)

Yu, X.; Wang, C.; Ma, Y. F.; Chen, F.; Yan, R. P.; Li, X. D.

2012-02-01

We improved the electro-optical cavity-dumped Nd:GdVO4 laser performance at high repetition rates by employing continuous-grown GdVO4/Nd:GdVO4 composite crystal under 879 nm diode-laser pumping. A constant 3.8 ns duration pulsed laser was obtained and the repetition rate could reach up to 100 kHz with a maximum average output power of 13.1 W and a slope efficiency of 56.4%, corresponding to a peak power of 34.4 kW.

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

PubMed

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

2014-09-01

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

Non-Congruence of Thermally Induced Structural and Electronic Transitions in VO2

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

Nag, Joyeeta; HaglundJr., Richard F; Payzant, E Andrew

2012-01-01

The multifunctional properties of vanadium dioxide (VO2) arise from coupled first-order phase transitions: an insulator-to-metal transition (IMT) and a structural phase transition (SPT) from monoclinic to tetragonal. The characteristic signatures of the IMT and SPT are the hysteresis loops that track the phase transition from nucleation to stabilization of a new phase and back. A long-standing question about the mechanism of the VO2 phase transition is whether and how the almost-simultaneous electronic and structural transitions are related. Here we report independent measurements of the IMT and SPT hystereses in epitaxial VO2 films with differing morphologies. We show that, in bothmore » cases, the hystereses are not congruent, that the structural change requires more energy to reach completion. This result is independent of nanoscale morphology, so that the non- congruence is an intrinsic property of the VO2 phase transition. Our conclusion is supported by effective-medium calculations of the dielectric function incorporating the measured volume fractions of the monoclinic and tetragonal states. The results are consistent with the existence of an monoclinic correlated metallic state in which the electron- electron correlations characteristic of the monoclinic state begin to disappear before the transition to the tetragonal structural state.« less

A cost-effective process to prepare VO{sub 2} (M) powder and films with superior thermochromic properties

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

Xiao, Xiudi; Zhang, Hua; Chai, Guanqi

2014-03-01

Graphical abstract: Combining codeposition and short time post annealing, VO{sub 2} (M) with high quality and excellent phase transition performance is obtained. After mixing the VO{sub 2} powder with acrylic resin, the composite films deposited on glass show superior visible transmission and solar modulation, which can be used as an excellent candidate of low cost smart window in energy saving field. - Highlights: • The VO{sub 2} powder obtained by short time thermolysis method is high purity and crystallinity with superior phase transition performance. • The maximum decreasing efficiency of phase transition temperature is about −30 K/at% with w =more » 0.4 at%. • After mixing VO{sub 2} powder with acrylic resin, the maximal visible transmission of the composite films is 48% and the transmission modulation at 2000 nm is 37.3% with phase transition temperature of 66.2 °C. • Though the phase transition performance is weakened by tungsten doping, the film prepared by 1.3 at% tungsten doped VO{sub 2} still show superior transmission modulation about 26.4%, which means that it is a potential candidate as smart windows. - Abstract: VO{sub 2} powder with superior phase transition performance was prepared by convenient thermolysis method. The results illustrated that VO{sub 2} powder show high purity and crystallinity. VO{sub 2} particles are transformed from cluster to quasi-sphere with the increase of annealing temperature. The DSC analysis proves that VO{sub 2} show superior phase transition performance around 68 °C. The phase transition temperature can be reduced to 33.5 °C by 1.8 at% tungsten doping. The maximum decreasing efficiency of phase transition temperature is about −30 K/at% with w = 0.4 at%. After mixing VO{sub 2} powder with acrylic resin, the maximal visible transmission of the composite thin films on glass is 48% and the transmission modulation at 2000 nm is 37.3% with phase transition temperature of 66.2 °C. Though the phase transition

Observation of reduced phase transition temperature in N-doped thermochromic film of monoclinic VO2

NASA Astrophysics Data System (ADS)

Wan, Meinan; Xiong, Mo; Li, Neng; Liu, Baoshun; Wang, Shuo; Ching, Wai-Yim; Zhao, Xiujian

2017-07-01

Research on monoclinic (M1) phase of VO2 has attracted a great of interest for smart coating applications due to its exceptional thermochromic property. Herein, we report the results using a novel approach to synthesize N-doped VO2(M1) thin films with high purity by heat treatment in NH3 atmosphere. The N dopant in the film can be regulated by varying NH3 concentration during the annealing process. We find that the N atoms are located at the interstitial sites or substitute oxygen atoms, and the V-N bonds in the VO2 thin films increase with NH3 concentration. The metal to insulator transition (MIT) temperature (τc,h) of the VO2 thin film is effectively reduced from 80.0 to 62.9 °C, while the solar modulation efficiency (ΔTsol) and the modulation efficiency at 2000 nm (ΔT2000nm) are 7.36% and 55.6% respectively. The band gap of N-doped VO2 thin films related to MIT (Eg1) is estimated to be as low as 0.18-0.25 eV whereas the band gap associated with the visible transparency (Eg2) is about 1.50-1.58 eV. Based on the highly accurate first-principles calculations, the Eg1 of VO2 (M1) is reduced after substituted or interstitial N-doping, while the Eg2 alters with the mode of N-doping, which is excellent agreement with experimental measurement.

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 VO 2 (B) has been carried out by a facile hydrothermal process, and the compact and locally ordered VO 2 (B) raft-like nanobelt arrays have been prepared. The synthesis route provides a new approach to elaborate a VO 2 (B) nanostructure under a mild environment condition. It is found that the growth mechanism of VO 2 (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 VO 2 (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 VO 2 (B) raft-like nanobelt arrays have great potential applications as cathode materials for lithium ion batteries.

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.

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

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

PubMed

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

2011-12-01

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

Influence of Nb doping on the phase transition properties of VO2 thin films prepared by ion beam co-sputtering deposition

NASA Astrophysics Data System (ADS)

Zhu, Huiqun; Li, Pengfei; Zhao, Lite; Liu, Jiahuan

2016-03-01

The Nb-doped VO2 thin films were successfully prepared on the glass substrates by ion beam co-sputtering at room temperature and post annealing under the air condition. The effects of the preparation processing and Nb doping on the thermal hysteresis loop and phase transition temperature of the VO2 thin films were analyzed by resistancetemperature measurement. The results show that Nb doping significantly changes the surface morphologies of VO2 thin films, and Nb-doped VO2 thin films exhibit VO2(002) preferred orientation growth with greatly improved crystallinity and orientation. Compared with pure VO2, the phase transition temperature of Nb-doped VO2 thin films drops to 40 ºC, and the width of thermal hysteresis loop narrows to 8 ºC. It is demonstrated that Nb-doped VO2 thin films prepared by ion beam co-sputtered at room temperature have an obvious thermal sensitive effect, and keep a good characteristic from metal to semiconductor phase transition.

Submaximal Treadmill Exercise Test to Predict VO[subscript 2]max in Fit Adults

ERIC Educational Resources Information Center

Vehrs, Pat R.; George, James D.; Fellingham, Gilbert W.; Plowman, Sharon A.; Dustman-Allen, Kymberli

2007-01-01

This study was designed to develop a single-stage submaximal treadmill jogging (TMJ) test to predict VO[subscript 2]max in fit adults. Participants (N = 400; men = 250 and women = 150), ages 18 to 40 years, successfully completed a maximal graded exercise test (GXT) at 1 of 3 laboratories to determine VO[subscript 2]max. The TMJ test was completed…

Spatial Databases for CalVO Volcanoes: Current Status and Future Directions

NASA Astrophysics Data System (ADS)

Ramsey, D. W.

2013-12-01

The U.S. Geological Survey (USGS) California Volcano Observatory (CalVO) aims to advance scientific understanding of volcanic processes and to lessen harmful impacts of volcanic activity in California and Nevada. Within CalVO's area of responsibility, ten volcanoes or volcanic centers have been identified by a national volcanic threat assessment in support of developing the U.S. National Volcano Early Warning System (NVEWS) as posing moderate, high, or very high threats to surrounding communities based on their recent eruptive histories and their proximity to vulnerable people, property, and infrastructure. To better understand the extent of potential hazards at these and other volcanoes and volcanic centers, the USGS Volcano Science Center (VSC) is continually compiling spatial databases of volcano information, including: geologic mapping, hazards assessment maps, locations of geochemical and geochronological samples, and the distribution of volcanic vents. This digital mapping effort has been ongoing for over 15 years and early databases are being converted to match recent datasets compiled with new data models designed for use in: 1) generating hazard zones, 2) evaluating risk to population and infrastructure, 3) numerical hazard modeling, and 4) display and query on the CalVO as well as other VSC and USGS websites. In these capacities, spatial databases of CalVO volcanoes and their derivative map products provide an integrated and readily accessible framework of VSC hazards science to colleagues, emergency managers, and the general public.

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

NASA Astrophysics Data System (ADS)

Chaison, Jindaporn; Wetchakun, Khatcharin; Wetchakun, Natda

2017-12-01

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

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

PubMed

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

2018-05-02

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

Morphological effect of BiVO4 catalysts on degradation of aqueous paracetamol under visible light irradiation.

PubMed

Hu, Changying; Xu, Jie; Zhu, Yaqi; Chen, Acong; Bian, Zhaoyong; Wang, Hui

2016-09-01

Morphological effect of bismuth vanadate (BiVO4) on visible light-driven catalytic degradation of aqueous paracetamol was carefully investigated using four monoclinic BiVO4 catalysts. The catalysts with different morphologies were controllably prepared by a hydrothermal method without any additions. The prepared catalysts were fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy (DRS). Under the visible light irradiation, these catalysts with different morphology were investigated to degrade aqueous paracetamol contaminant. The degradation effects were evaluated based on the catalyst morphology, solution pH, initial paracetamol concentration, and catalyst dosage. Cube-like BiVO4 powders exhibited excellent photocatalytic performance. The optimal photocatalytic performance of the cube-like BiVO4 in degrading paracetamol was achieved.

Sapphire substrate-induced effects in VO2 thin films grown by oxygen plasma-assisted pulsed laser deposition

NASA Astrophysics Data System (ADS)

Skuza, J. R.; Scott, D. W.; Pradhan, A. K.

2015-11-01

We investigate the structural and electronic properties of VO2 thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO2 film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO2, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO2 film growth with SMTs that can be easily tailored for device applications.

Nd:GdVO4 ring laser pumped by laser diodes

NASA Astrophysics Data System (ADS)

Hao, E. J.; Li, T.; Wang, Z. D.; Zhang, Y.

2013-02-01

The design and operation of a laser diode-pumped Nd:GdVO4 ring laser is described. A composite crystal (Nd:GdVO4/YVO4) with undoped ends is single-end pumped by a fiber-coupled laser diode (LD) at 808 nm. A four-mirror ring cavity is designed to keep the laser operating unidirectionally, which eliminates spatial hole burning in the standing-wave cavity. This laser can operate either as continuous wave (CW) or Q-switched. The single-frequency power obtained was 9.1 W at 1063 nm. Q-switched operation produced 0.23 mJ/pulse at 20 kHz in the fundamental laser.

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

VO-compliant libraries of high resolution spectra of cool stars

NASA Astrophysics Data System (ADS)

Montes, D.

2008-10-01

In this contribution we describe a Virtual Observatory (VO) compliant version of the libraries of high resolution spectra of cool stars described by Montes et al. (1997; 1998; and 1999). Since their publication the fully reduced spectra in FITS format have been available via ftp and in the World Wide Web. However, in the VO all the spectra will be accessible using a common web interface following the standards of the International Virtual Observatory Alliance (IVOA). These libraries include F, G, K and M field stars, from dwarfs to giants. The spectral coverage is from 3800 to 10000 Å, with spectral resolution ranging from 0.09 to 3.0 Å.

Microwave assisted synthesis of sheet-like Cu/BiVO{sub 4} and its activities of various photocatalytic conditions

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

Chen, Xi; College of Chemistry and Chemical Engineering, Qiqihar University, Qiqihar 161006; Li, Li, E-mail: qqhrll@163.com

2015-09-15

The Cu/BiVO{sub 4} photocatalyst with visible-light responsivity was prepared by the microwave-assisted hydrothermal method. The phase structures, chemical composition and surface physicochemical properties were well-characterized via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance absorption (UV–vis/DRS), scanning electron microscopy (SEM), and N{sub 2} adsorption–desorption tests. Results indicate that the crystal structure of synthetic composite materials is mainly monoclinic scheelite BiVO{sub 4}, which is not changed with the increasing doping amount of Cu. In addition, the presence of Cu not only enlarges the range of the composite materials under the visible-light response, but also increases the BET value significantly.more » Compared to pure BiVO{sub 4}, 1% Cu/BiVO{sub 4}-160 performs the highest photocatalytic activity to degrade methylene blue under the irradiation of ultraviolet, visible and simulated sunlight. In addition, the capture experiments prove that the main active species was superoxide radicals during photocatalytic reaction. Moreover, the 1% Cu/BiVO{sub 4}-160 composite shows good photocatalytic stability after three times of recycling. - Graphical abstract: A series of BiVO{sub 4} with different amounts of Cu doping were prepared by the microwave-assisted method, moreover, which performed the high photocatalytic activities to degrade methylene blue under multi-mode. - Highlights: • A series of Cu/BiVO{sub 4} with different amounts of Cu doping were prepared by microwave-assisted synthesis. • The morphologies of as-samples were different with the amount of Cu doping increased. • Compared with pure BiVO{sub 4}, as-Cu/BiVO{sub 4} showed stronger absorption in the visible light region obviously. • 1% Cu/BiVO{sub 4}-160 performed the high photocatalytic activities to degrade methylene blue under multi-mode. • OH{sup •} and h{sup +} both play important roles in the photocatalytic

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

NASA Astrophysics Data System (ADS)

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

1997-02-01

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

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

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

NASA Astrophysics Data System (ADS)

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

2016-11-01

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.

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

PubMed

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

2016-11-16

Designing materials with a negative feedback function is beneficial for achieving temperature regulation inside a greenhouse. VO 2 has been studied extensively because of its low insulator-to-metal transition temperature (IMT). In this study, reflection changes during a VO 2 phase transition were investigated. Glass fiber cloth was used as a substrate, as it is stable and soft. A VO 2 thin film on a glass fiber cloth whose surface contained 96% V 4+ and 4% V 5+ 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 V 5+ , which causes destabilization of the monoclinic phase of VO 2 . When the greenhouse temperature was increased from 30 °C to 40 °C, the reflected intensity of VO 2 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 VO 2 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.

Influence of Security Mechanisms on the Quality of Service of VoIP

NASA Astrophysics Data System (ADS)

Backs, Peter; Pohlmann, Norbert

While Voice over IP (VoIP) is advancing rapidly in the telecommunications market, the interest to protect the data transmitted by this new service is also rising. However, in contrast to other internet services such as email or HTTP, VoIP is real-time media, and therefore must meet a special requirement referred to as Quality-of-Service to provide a comfortable flow of speech. Speech quality is worsened when transmitted over the network due to delays in transmission or loss of packets. Often, voice quality is at a level that even prevents comprehensive dialog. Therefore, an administrator who is to setup a VoIP infrastructure might consider avoiding additional decreases in voice quality resulting from security mechanisms, and might leave internet telephony unprotected as a result. The inspiration for this paper is to illustrate that security mechanisms have negligible impact on speech quality and should in fact be encouraged.

CeVO4 nanofibers hybridized with g-C3N4 nanosheets with enhanced visible-light-driven photocatalytic activity

NASA Astrophysics Data System (ADS)

Li, Li; Wang, Haoran; Wang, Xiong

2018-01-01

The g-C3N4/CeVO4 composites were successfully synthesized by hybridizing CeVO4 nanofibers with g-C3N4 nanosheets. The photocatalytic activity of g-C3N4/CeVO4 composites was evaluated for the photodegradation of methylene blue under visible light irradiation. Among them, the 50 wt% g-C3N4/CeVO4 composites presented the highest photocatalytic activity, about 2 and 3.2 times higher than those of CeVO4 and g-C3N4, respectively. The improved catalytic activity was owed to the hybridization, which facilitated the rapid separation of photoinduced carriers and enhanced the visible light harvesting. A possible photocatalytic mechanism was proposed.

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

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

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.

Optical bistability and optical response of an infrared quantum dot hybridized to VO2 nanoparticle

NASA Astrophysics Data System (ADS)

Zamani, Naser; Hatef, Ali; Nadgaran, Hamid; Keshavarz, Alireza

2017-08-01

In this work, we theoretically investigate optical bistability and optical response of a hybrid system consisting of semiconductor quantum dot (SQD) coupled with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) regime. The VO2 material exists in semiconductor and metallic phases below and above the critical temperature, respectively where the particle optical properties dramatically change during this phase transition. In our calculations a filling fraction factor controls the VO2NP phase transition when the hybrid system interacts with a laser field. We demonstrate that the switch-up threshold for optical bistability is strongly controlled by filling fraction without changing the structure of the hybrid system. Also, it is shown that, the threshold of optical bistability increases when the VO2NP phases changes from semiconductor to metallic phase. The presented results have the potential to be applied in designing optical switching and optical storage.

Highly efficient photocatalytic conversion of solar energy to hydrogen by WO3/BiVO4 core-shell heterojunction nanorods

NASA Astrophysics Data System (ADS)

Kosar, Sonya; Pihosh, Yuriy; Bekarevich, Raman; Mitsuishi, Kazutaka; Mawatari, Kazuma; Kazoe, Yutaka; Kitamori, Takehiko; Tosa, Masahiro; Tarasov, Alexey B.; Goodilin, Eugene A.; Struk, Yaroslav M.; Kondo, Michio; Turkevych, Ivan

2018-04-01

Photocatalytic splitting of water under solar light has proved itself to be a promising approach toward the utilization of solar energy and the generation of environmentally friendly fuel in a form of hydrogen. In this work, we demonstrate highly efficient solar-to-hydrogen conversion efficiency of 7.7% by photovoltaic-photoelectrochemical (PV-PEC) device based on hybrid MAPbI3 perovskite PV cell and WO3/BiVO4 core-shell nanorods PEC cell tandem that utilizes spectral splitting approach. Although BiVO4 is characterized by intrinsically high recombination rate of photogenerated carriers, this is not an issue for WO3/BiVO4 core-shell nanorods, where highly conductive WO3 cores are combined with extremely thin absorber BiVO4 shell layer. Since the BiVO4 layer is thinner than the characteristic carrier diffusion length, the photogenerated charge carriers are separated at the WO3/BiVO4 heterojunction before their recombination. Also, such architecture provides sufficient optical thickness even for extremely thin BiVO4 layer due to efficient light trapping in the core-shell WO3/BiVO4 nanorods with high aspect ratio. We also demonstrate that the concept of fill factor can be used to compare I-V characteristics of different photoanodes regarding their optimization for PV/PEC tandem devices.

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.

Luminescence study of Eu3+ doped GdVO4 nanoparticles: Concentration, particle size, and core/shell effects

NASA Astrophysics Data System (ADS)

Singh, N. Shanta; Ningthoujam, R. S.; Devi, L. Romila; Yaiphaba, N.; Sudarsan, V.; Singh, S. Dorendrajit; Vatsa, R. K.; Tewari, R.

2008-11-01

Nanoparticles of GdVO4 doped with Eu3+ and core/shell of GdVO4:Eu3+/GdVO4 are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130 °C. Unit cell volume increases when GdVO4 is doped with Eu3+ indicating the substitution of Gd3+ lattice sites by Eu3+. From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu3+. Optimum luminescence intensity is found to be in 5-10 at. % Eu3+. Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu3+ surroundings by bonding to GdVO4 shell. The lifetime for D50 level increases with annealing and core/shell formation.

Does arterial health affect VO2peak and muscle oxygenation in a sedentary cohort?

PubMed

Lizamore, Catherine Anne; Stoner, Lee; Lucas, Samuel John Edwin; Lucero, Adam; Hamlin, Michael John

2015-02-01

An association between arterial health and peak oxygen consumption (VO2peak) has been demonstrated; however, little is known about how arterial health influences muscular oxygenation during exercise. The aim of this study was to gain insight into the relations between arterial health, VO2peak, and muscle oxygenation in a middle-age sedentary population. Radial augmentation index (AIx) (via pulse wave analysis) of 21 sedentary middle-age participants (15 females and six males; age, 54.7 ± 5.4; body mass index, 29.0 ± 4.7 kg·m; mean ± SD) was assessed, and on another day ( < 7 d), participants completed a modified Bruce protocol (MBP). Using near-infrared spectroscopy, total oxygenation index (TOI) of the left flexor carpi ulnaris and the left vastus lateralis were monitored throughout the MBP. Independent and average (arm + leg) percentage decrease in TOI between stage 1 of the MBP and maximal exertion (TOIdiff) during MBP was calculated. Changes between dependent variables were correlated using Pearson product-moment correlations and were interpreted as follows: r > 0.5, strong; 0.5 > r > 0.3, moderate; and r < 0.3, weak. We observed moderate negative correlation between AIx and VO2peak (r = -0.34, -0.63 to -0.03; Pearson correlation, 90% confidence limits) and strong negative correlation between AIx and average TOIdiff (r = -0.58, -0.78 to -0.27). The VO2peak and average TOIdiff were strongly correlated (r = 0.55, 0.23-0.77). Arterial health seems to be an important determinant of muscle oxygenation during exercise. In turn, muscle oxygenation during exercise is strongly related to VO2peak. Developing training modalities to prioritize arterial health outcomes may be a useful way of improving VO2peak in this population.

Voice Over Internet Protocol (VoIP) in a Control Center Environment

NASA Technical Reports Server (NTRS)

Pirani, Joseph; Calvelage, Steven

2010-01-01

The technology of transmitting voice over data networks has been available for over 10 years. Mass market VoIP services for consumers to make and receive standard telephone calls over broadband Internet networks have grown in the last 5 years. While operational costs are less with VoIP implementations as opposed to time division multiplexing (TDM) based voice switches, is it still advantageous to convert a mission control center s voice system to this newer technology? Marshall Space Flight Center (MSFC) Huntsville Operations Support Center (HOSC) has converted its mission voice services to a commercial product that utilizes VoIP technology. Results from this testing, design, and installation have shown unique considerations that must be addressed before user operations. There are many factors to consider for a control center voice design. Technology advantages and disadvantages were investigated as they refer to cost. There were integration concerns which could lead to complex failure scenarios but simpler integration for the mission infrastructure. MSFC HOSC will benefit from this voice conversion with less product replacement cost, less operations cost and a more integrated mission services environment.

High-Quality LaVO3 Films as Solar Energy Conversion Material.

PubMed

Zhang, Hai-Tian; Brahlek, Matthew; Ji, Xiaoyu; Lei, Shiming; Lapano, Jason; Freeland, John W; Gopalan, Venkatraman; Engel-Herbert, Roman

2017-04-12

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron-hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron-electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO 3 films were grown with defect densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO 3 bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO 3 films compared to their nonstoichiometric counterparts. This work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.

VO2 film temperature dynamics at low-frequency current self-oscillations

NASA Astrophysics Data System (ADS)

Bortnikov, S. G.; Aliev, V. Sh.; Badmaeva, I. A.; Mzhelskiy, I. V.

2018-02-01

Low-frequency (˜2 Hz) current self-oscillations were first obtained in a millimeter-sized two-terminal planar device with a vanadium dioxide (VO2) film. The film temperature distribution dynamics was investigated within one oscillation period. It was established that the formation and disappearance of a conductive channel occur in a film in less than 60 ms with oscillation period 560 ms. The experimentally observed temperature in the channel region reached 413 K, being understated due to a low infrared microscope performance (integration time 10 ms). The VO2 film temperature distribution dynamics was simulated by solving a 2D problem of the electric current flow and heat transfer in the film. The calculation showed that the thermally initiated resistance switching in the film occurs in less than 4 ms at a channel temperature reaching ˜1000 K. The experimental results and simulation are consistent with the current self-oscillation mechanism based on the current pinching and dielectric relaxation in the VO2 film at the metal-insulator phase transition.

Colossal Negative Thermal Expansion in Electron-Doped PbVO3 Perovskites.

PubMed

Yamamoto, Hajime; Imai, Takashi; Sakai, Yuki; Azuma, Masaki

2018-07-02

Colossal negative thermal expansion (NTE) with a volume contraction of about 8 %, the largest value reported so far for NTE materials, was observed in an electron-doped giant tetragonal perovskite compound Pb 1-x Bi x VO 3 (x=0.2 and 0.3). A polar tetragonal (P4mm) to non-polar cubic structural transition took place upon heating. The coefficient of thermal expansion (CTE) and the working temperature could be tuned by changing the Bi content, and La substitution decreased the transition temperature to room temperature. Pb 0.76 La 0.04 Bi 0.20 VO 3 exhibited a unit cell volume contraction of 6.7 % from 200 K to 420 K. Interestingly, further gigantic NTE of about 8.5 % was observed in a dilametric measurement of a Pb 0.76 La 0.04 Bi 0.20 VO 3 polycrystalline sample. The pronounced NTE in the sintered body should be attributed to an anisotropic lattice parameter change. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chapter 11: Web-based Tools - VO Region Inventory Service

NASA Astrophysics Data System (ADS)

Good, J. C.

As the size and number of datasets available through the VO grows, it becomes increasingly critical to have services that aid in locating and characterizing data pertinent to a particular scientific problem. At the same time, this same increase makes that goal more and more difficult to achieve. With a small number of datasets, it is feasible to simply retrieve the data itself (as the NVO DataScope service does). At intermediate scales, "count" DBMS searches (searches of the actual datasets which return record counts rather than full data subsets) sent to each data provider will work. However, neither of these approaches scale as the number of datasets expands into the hundreds or thousands. Dealing with the same problem internally, IRSA developed a compact and extremely fast scheme for determining source counts for positional catalogs (and in some cases image metadata) over arbitrarily large regions for multiple catalogs in a fraction of a second. To show applicability to the VO in general, this service has been extended with indices for all 4000+ catalogs in CDS Vizier (essentially all published catalogs and source tables). In this chapter, we will briefly describe the architecture of this service, and then describe how this can be used in a distributed system to retrieve rapid inventories of all VO holdings in a way that places an insignificant load on any data supplier. Further, we show and this tool can be used in conjunction with VO Registries and catalog services to zero in on those datasets that are appropriate to the user's needs. The initial implementation of this service consolidates custom binary index file structures (external to any DBMS and therefore portable) at a single site to minimize search times and implements the search interface as a simple CGI program. However, the architecture is amenable to distribution. The next phase of development will focus on metadata harvesting from data archives through a standard program interface and distribution

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.

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

NASA Astrophysics Data System (ADS)

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

2012-06-01

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

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.

Synergy Between Archives, VO, and the Grid at ESAC

NASA Astrophysics Data System (ADS)

Arviset, C.; Alvarez, R.; Gabriel, C.; Osuna, P.; Ott, S.

2011-07-01

Over the years, in support to the Science Operations Centers at ESAC, we have set up two Grid infrastructures. These have been built: 1) to facilitate daily research for scientists at ESAC, 2) to provide high computing capabilities for project data processing pipelines (e.g., Herschel), 3) to support science operations activities (e.g., calibration monitoring). Furthermore, closer collaboration between the science archives, the Virtual Observatory (VO) and data processing activities has led to an other Grid use case: the Remote Interface to XMM-Newton SAS Analysis (RISA). This web service-based system allows users to launch SAS tasks transparently to the GRID, save results on http-based storage and visualize them through VO tools. This paper presents real and operational use cases of Grid usages in these contexts

Design and Implement of Astronomical Cloud Computing Environment In China-VO

NASA Astrophysics Data System (ADS)

Li, Changhua; Cui, Chenzhou; Mi, Linying; He, Boliang; Fan, Dongwei; Li, Shanshan; Yang, Sisi; Xu, Yunfei; Han, Jun; Chen, Junyi; Zhang, Hailong; Yu, Ce; Xiao, Jian; Wang, Chuanjun; Cao, Zihuang; Fan, Yufeng; Liu, Liang; Chen, Xiao; Song, Wenming; Du, Kangyu

2017-06-01

Astronomy cloud computing environment is a cyber-Infrastructure for Astronomy Research initiated by Chinese Virtual Observatory (China-VO) under funding support from NDRC (National Development and Reform commission) and CAS (Chinese Academy of Sciences). Based on virtualization technology, astronomy cloud computing environment was designed and implemented by China-VO team. It consists of five distributed nodes across the mainland of China. Astronomer can get compuitng and storage resource in this cloud computing environment. Through this environments, astronomer can easily search and analyze astronomical data collected by different telescopes and data centers , and avoid the large scale dataset transportation.

Controlled synthesis of BiVO{sub 4} with multiple morphologies via an ethylenediamine-assisted hydrothermal method

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

Qi, Xuemei, E-mail: qixuemei@shiep.edu.cn; School of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090; Zhu, Xinyuan

2014-11-15

Graphical abstract: BiVO{sub 4} samples with various morphologies were synthesized via a simple ethylenediamine (EN) assisted hydrothermal route. One of the mixed crystal phase with spherical and porous morphology showed excellent photocatalytic activity and about 90% Rhodamine B was degraded after 140 min visible light irradiation. - Highlights: • BiVO{sub 4} samples with various morphologies were synthesized by hydrothermal method. • Ethylenediamine mainly acts as alkaline source to adjust pH values of precursor. • BiVO{sub 4} with spherical morphology has excellent photocatalytic activity. - Abstract: In this work, BiVO{sub 4} particles with different crystal structures and morphologies including hexahedral, sphericalmore » porous and hyperbranched ones were fabricated in the presence of ethylenediamine by hydrothermal process. The as-fabricated samples were well characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and ultraviolet–visible absorption spectroscopy. The results showed that the morphology and crystal structure of BiVO{sub 4} particles could be well controlled by only changing the ethylenediamine content in the deionized water solution. Photocatalytic activity of the samples was evaluated by the degradation of Rhodamine B under visible-light irradiation. It was shown that BiVO{sub 4} sample with spherical porous morphology and mixed crystal phase exhibited the best photocatalytic performance after optimizing the ethylenediamine content. The best degradation ratio of Rhodamine B could reach about 87% after 140 min visible-light irradiation.« less

Photocatalytic degradation and removal mechanism of ibuprofen via monoclinic BiVO4 under simulated solar light.

PubMed

Li, Fuhua; Kang, Yapu; Chen, Min; Liu, Guoguang; Lv, Wenying; Yao, Kun; Chen, Ping; Huang, Haoping

2016-05-01

Characterized as by X-ray diffraction, scanning electron microscopy and UV-vis diffuse reflectance spectra techniques, BiVO4 photocatalyst was hydrothermally synthesized. The photocatalytic degradation mechanisms of ibuprofen (IBP) were evaluated in aqueous media via BiVO4. Results demonstrated that the prepared photocatalyst corresponded to phase-pure monoclinic scheelite BiVO4. The synthesized BiVO4 showed superior photocatalytic properties under the irradiation of visible-light. The photocatalytic degradation rate of IBP decreased with an increase in the initial IBP concentration. The degradation process followed first-order kinetics model. At an IBP concentration of 10 mg L(-1), while a BiVO4 concentration of 5.0 g L(-1) with pH value of 4.5, the rate of IBP degradation was obtained as 90% after 25 min. The photocatalytic degradation of IBP was primarily accomplished via the generation of superoxide radical (O2(•-)) and hydroxyl radicals ((•)OH). During the process of degradation, part of the (•)OH was converted from the O2(•-). The direct oxidation of holes (h(+)) made a minimal contribution to the degradation of IBP. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fourier transform infrared study of the phase transitions in (NH4)3VO2FO4

NASA Astrophysics Data System (ADS)

de Waal, D.; Heyns, A. M.

1994-01-01

Ammonium oxofluorovanadate compounds are known to show some potential as ferroelectric materials. The whole series of ammonium and sodium oxofluorovanadate compounds including Na3VO2F4 have already been prepared and investigated by means of various techniques including x-ray diffraction, EPR, and vibrational spectroscopy. It was established that the pure ammonium compound shows the two above mentioned transitions from phase A (below 200 K) to phase B (between 200 and 400 K) and phase C (above 400 K) while Na(NH4)2VO2F4 has only one transition from phase A to phase B around 400 K4. In the present study various aspects regarding the nature of the structures of (NH4)3VO2F3 and Na(NH4)2VO2F4 and its influence on the phase transitions have been investigated.

Dissociation and purification of the endogenous membrane-bound Vo complex from Pichia pastoris.

PubMed

Li, Sumei; Hong, Tao; Wang, Kun; Lu, Yinghong; Zhou, Min

2017-10-01

Most proteins occur and function in complexes rather than as isolated entities in membranes. In most cases macromolecules with multiple subunits are purified from endogenous sources. In this study, an endogenous membrane-protein complex was obtained from Pichia pastoris, which can be grown at high densities to significantly improve the membrane protein yield. We successfully isolated the membrane-bound Vo complex of V-ATPase from P. pastoris using a fusion FLAG tag attached to the C-terminus of subunit a to generate the vph-tag strain, which was used for dissociation and purification. After FLAG affinity and size exclusion chromatography purification, the production quantity and purity of the membrane-bound Vo complex was 20 μg l -1 and >98%, respectively. The subunits of the endogenous membrane-bound Vo complex observed in P. pastoris were similar to those obtained from S. cerevisiae, as demonstrated by liquid chromatography-tandem mass spectrometry (LC-MS-MS). Therefore, successful dissociation and purification of the membrane-bound Vo complex at a high purity and sufficient quantity was achieved via a rapid and simple procedure that can be used to obtain the endogenous membrane-protein complexes from P. pastoris. Copyright © 2017 Elsevier Inc. All rights reserved.

Local probing of thermal energy transfer and conversion processes in VO2 nanostructures

NASA Astrophysics Data System (ADS)

Menges, Fabian

Nanostructures of strongly correlated materials, such as metal-insulator transition (MIT) oxides, enable unusual coupling of charge and heat transport. Hence, they provide an interesting pathway to the development of non-linear thermal devices for active heat flux control. Here, we will report the characterization of local thermal non-equilibrium processes in vanadium dioxide (VO2) thin films and single-crystalline nanobeams. Using a scanning thermal microscope and calorimetric MEMS platforms, we studied the MIT triggered by electrical currents, electrical fields, near-field thermal radiation and thermal conduction. Based on out recently introduced scanning probe thermometry method, which enables direct imaging of local Joule and Peltier effects, we quantified self-heating processes in VO2 memristors using the tip of a resistively heated scanning probe both as local sensor and nanoscopic heat source. Finally, we will report on recent approaches to build radiative thermal switches and oscillators using VO2 nanostructures. We quantified variations of near-field radiative thermal transport between silicon dioxide and VO2 down to nanoscopic gap sizes, and will discuss its implications for the development of phonon polariton based radiative thermal devices. Funding of the Swiss Federal Office of Energy under Grant Agreement No. SI/501093-01 is gratefully acknowledged.

Controlling the Temperature and Speed of the Phase Transition of VO 2 Microcrystals

DOE PAGES

Yoon, Joonseok; Kim, Howon; Chen, Xian; ...

2015-12-29

Here, we investigated the control of two important parameters of vanadium dioxide (VO 2 ) microcrystals, the phase transition temperature and speed, by varying microcrystal width. By using the reflectivity change between insulating and metallic phases, phase transition temperature is measured by optical microscopy. As the width of square cylinder-shaped microcrystals decreases from ~70 to ~1 μm, the phase transition temperature (67 °C for bulk) varied as much as 26.1 °C (19.7 °C) during heating (cooling). In addition, the propagation speed of phase boundary in the microcrystal, i.e., phase transition speed, is monitored at the onset of phase transition bymore » using the high-speed resistance measurement. The phase transition speed increases from 4.6 × 10 2 to 1.7 × 10 4 μm/s as the width decreases from ~50 to ~2 μm. While the statistical description for a heterogeneous nucleation process explains the size dependence on phase transition temperature of VO 2 , the increase of effective thermal exchange process is responsible for the enhancement of phase transition speed of small VO 2 microcrystals. These findings not only enhance the understanding of VO 2 intrinsic properties but also contribute to the development of innovative electronic devices.« less

Controlling the Temperature and Speed of the Phase Transition of VO 2 Microcrystals

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

Yoon, Joonseok; Kim, Howon; Chen, Xian

Here, we investigated the control of two important parameters of vanadium dioxide (VO 2 ) microcrystals, the phase transition temperature and speed, by varying microcrystal width. By using the reflectivity change between insulating and metallic phases, phase transition temperature is measured by optical microscopy. As the width of square cylinder-shaped microcrystals decreases from ~70 to ~1 μm, the phase transition temperature (67 °C for bulk) varied as much as 26.1 °C (19.7 °C) during heating (cooling). In addition, the propagation speed of phase boundary in the microcrystal, i.e., phase transition speed, is monitored at the onset of phase transition bymore » using the high-speed resistance measurement. The phase transition speed increases from 4.6 × 10 2 to 1.7 × 10 4 μm/s as the width decreases from ~50 to ~2 μm. While the statistical description for a heterogeneous nucleation process explains the size dependence on phase transition temperature of VO 2 , the increase of effective thermal exchange process is responsible for the enhancement of phase transition speed of small VO 2 microcrystals. These findings not only enhance the understanding of VO 2 intrinsic properties but also contribute to the development of innovative electronic devices.« less

A comparison of VO2max and metabolic variables between treadmill running and treadmill skating.

PubMed

Koepp, Kriston K; Janot, Jeffrey M

2008-03-01

The purpose of this study was to determine differences in VO2max and metabolic variables between treadmill running and treadmill skating. This study also examined VO2max responses during a continuous skating treadmill protocol and a discontinuous skating treadmill protocol. Sixteen male high school hockey players, who had a mean age of 16 +/- 1 years and were of an above-average fitness level, participated in this study. All subjects completed 4 exercise trials: a 1-hour skating treadmill familiarization trial, a treadmill running trial, and 2 randomized skating treadmill trials. Minute ventilation (VE), oxygen consumption VO2), carbon dioxide production VCO2), respiratory exchange ratio (RER), and heart rate were averaged every 15 seconds up to VO2max for each exercise test. The results showed that there was a significant difference (P < 0.05) for VO2max (mL.kg.min) and maximal VCO2 (L.min) between the running treadmill protocol and discontinuous skating treadmill protocol. There was also a significant difference for maximal RER between the discontinuous and continuous skating treadmill protocol and between the discontinuous skating treadmill protocol and running treadmill protocol. In conclusion, the running treadmill elicited a greater VO2max (mL.kg.min) than the skating treadmill did, but when it comes to specificity of ice skating, the skating treadmill may be ideal. Also, there was no significant difference between the discontinuous and continuous skating treadmill protocols. Therefore, a continuous protocol is possible on the skating treadmill without compromising correct skating position and physiologic responses. However, the continuous skating treadmill protocol should undergo validation before other scientists, coaches, and strength and conditioning professionals can apply it correctly.

47 CFR 52.34 - Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS...

Code of Federal Regulations, 2010 CFR

2010-10-01

... and from interconnected VoIP or Internet-based TRS providers. 52.34 Section 52.34 Telecommunication... Portability § 52.34 Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS providers. (a) An interconnected VoIP or VRS or IP Relay provider must facilitate an end-user...

47 CFR 52.34 - Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS...

Code of Federal Regulations, 2011 CFR

2011-10-01

... and from interconnected VoIP or Internet-based TRS providers. 52.34 Section 52.34 Telecommunication... Portability § 52.34 Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS providers. (a) An interconnected VoIP or VRS or IP Relay provider must facilitate an end-user...

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

NASA Astrophysics Data System (ADS)

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

2017-08-01

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

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

DOE PAGES

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

2016-10-06

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

Selective Oxidation of Alcohols Using Photoactive VO@g??C3N4

EPA Pesticide Factsheets

A photoactive VO@g-C3N4 catalyst has been developed for the selective oxidation of alcohols to the corresponding aldehydes and ketones. The visible light mediated activity of the catalyst could be attributed to photoactive graphitic carbon nitrides surface.This dataset is associated with the following publication:Verma, S., R.B. Nasir Baig, M. Nadagouda , and R. Varma. Selective oxidation of alcohols using photoactive VO@g-C3N4.. ACS Sustainable Chemistry & Engineering. American Chemical Society, Washington, DC, USA, 4(3): 1094-1098, (2015).

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

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.

Graphene-Nanowall-Decorated Carbon Felt with Excellent Electrochemical Activity Toward VO2+/VO2+ 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 VO 2 + /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.

Equivalent circuit for VO{sub 2} phase change material film in reconfigurable frequency selective surfaces

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

Sanphuang, Varittha; Ghalichechian, Nima; Nahar, Niru K.

We developed equivalent circuits of phase change materials based on vanadium dioxide (VO{sub 2}) thin films. These circuits are used to model VO{sub 2} thin films for reconfigurable frequency selective surfaces (FSSs). This is important as it provides a way for designing complex structures. A reconfigurable FSS filter using VO{sub 2} ON/OFF switches is designed demonstrating −60 dB isolation between the states. This filter is used to provide the transmission and reflection responses of the FSS in the frequency range of 0.1–0.6 THz. The comparison between equivalent circuit and full-wave simulation shows excellent agreement.

The effect of Iron Supplying on VO2 MAX and Haematology Parameter on Menstrual Woman

NASA Astrophysics Data System (ADS)

Nailuvar Sinaga, Rika; Sari Harahap, Novita; Mediyana Sari, Rima

2018-03-01

One of the supporting factors to have good aerobic endurance requires high VO2 max levels supported by good quality and quantity level of Haematology parameter especially such as erythrocytes, hematocrit and hemoglobin. One of the components in hemoglobin is iron which functions as theoxygen transport to parts of all body required in the process of metabolism. The objective of this research was to find out the difference between VO2 Max and Haematology parameter between iron supplying and no iron supplyingonmenstrual woman. The type of this research is quasi experimental research with non-randomized control group Pretest-Postest Design. The subjectsarethe studentsat faculty of Sports Sciences, Medan State University with the criteria of female gender, monthly regular menstrual cycle, having the level of health and the level of training, willing to be a sample by filling out informed consent. The total number of research subjectsis twenty students, divided into two groups namely the treatment group and the control group. The hematology parameter was measuredby Haemotology analyzer and VO2 Max was measured by multi-stage run. The result showed that there was a significant effect of iron supplyingon the increase of erythrocyte level on menstrual women, hemotocrit, haemoglobin and an increase in VO2 Max. Iron supplying on menstrual woman has the effect on the increase of erythrocyte, hematocrit, hemoglobin level and VO2 Max

Thermal tuning of infrared resonant absorbers based on hybrid gold-VO{sub 2} nanostructures

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

Kocer, Hasan; Department of Electrical Engineering, Turkish Military Academy, 06654 Ankara; Butun, Serkan

2015-04-20

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 (VO{sub 2}) nanostructure arrays. Absorption intensity is tuned from 90% to 20%more » and 96% to 32% using hybrid gold-VO{sub 2} nanowire and nanodisc arrays, respectively, by heating up the absorbers above the phase transition temperature of VO{sub 2} (68 °C). Phase change materials such as VO{sub 2} 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.« less

VO2 nanoparticles on edge orientated graphene foam for high rate lithium ion batteries and supercapacitors

NASA Astrophysics Data System (ADS)

Ren, Guofeng; Zhang, Ruibo; Fan, Zhaoyang

2018-05-01

With the fully exposed graphene edges, high conductivity and large surface area, edge oriented graphene foam (EOGF), prepared by deposition of perpendicular graphene network encircling the struts of Ni foam, is a superior scaffold to support active materials for electrochemical applications. With VO2 as an example, EOGF loaded VO2 nanoparticle (VO2/EOGF) electrode has high rate performance as cathode in lithium ion batteries (LIBs). In addition to the Li+ intercalation into the lattice, contribution of non-diffusion-limited pseudocapacitance to the capacity is prominent at high rates. VO2/EOGF based supercapacitor also exhibits fast response, with a characteristic frequency of 15 Hz when the phase angle reaches -45°, or a relaxation time constant of 66.7 ms. These results suggest the promising potential of EOGF as a scaffold in supporting active nanomaterials for electrochemical energy storage and other applications.

Enhanced photoelectrochemical and photocatalytic activity in visible-light-driven Ag/BiVO{sub 4} inverse opals

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

Fang, Liang, E-mail: lfang@suda.edu.cn, E-mail: dawei.cao@tu-ilmenau.de; Nan, Feng; Yang, Ying

2016-02-29

BiVO{sub 4} photonic crystal inverse opals (io-BiVO{sub 4}) with highly dispersed Ag nanoparticles (NPs) were prepared by the nanosphere lithography method combining the pulsed current deposition method. The incorporation of the Ag NPs can significantly improve the photoelectrochemical and photocatalytic activity of BiVO{sub 4} inverse opals in the visible light region. The photocurrent density of the Ag/io-BiVO{sub 4} sample is 4.7 times higher than that of the disordered sample without the Ag NPs, while the enhancement factor of the corresponding kinetic constant in photocatalytic experiment is approximately 3. The improved photoelectrochemical and photocatalytic activity is benefited from two reasons: onemore » is the enhanced light harvesting owing to the coupling between the slow light and localized surface plasmon resonance effect; the other is the efficient separation of charge carriers due to the Schottky barriers.« less

High-quality LaVO 3 films as solar energy conversion material

DOE PAGES

Zhang, Hai -Tian; Brahlek, Matthew; Ji, Xiaoyu; ...

2017-03-21

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO 3 films were grown withmore » defect densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO 3 bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO 3 films compared to their nonstoichiometric counterparts. Furthermore, this work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.« less

High pressure spectroscopic studies of phase transition in VO2

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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

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).

Sapphire substrate-induced effects in VO{sub 2} thin films grown by oxygen plasma-assisted pulsed laser deposition

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

Skuza, J. R., E-mail: jrskuza@nsu.edu, E-mail: apradhan@nsu.edu; Scott, D. W.; Pradhan, A. K., E-mail: jrskuza@nsu.edu, E-mail: apradhan@nsu.edu

2015-11-21

We investigate the structural and electronic properties of VO{sub 2} thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO{sub 2} film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO{sub 2}, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO{sub 2} film growth with SMTs that can bemore » easily tailored for device applications.« less

Microwave-assisted synthesis and electrochemical evaluation of VO 2 (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 VO 2 (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 batterymore » operation.« less

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

PubMed

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

2017-01-01

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

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

DTIC Science & Technology

2014-11-27

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

Luminescent LuVO4:Ln3+ (Ln = Eu, Sm, Dy, Er) hollow porous spheres for encapsulation of biomolecules

NASA Astrophysics Data System (ADS)

Li, Dan; Liu, Chunlei; Jiang, Lianzhou

2015-10-01

In this study, LuVO4:Ln3+ (Ln = Eu, Sm, Dy, Er) hollow porous spheres, synthesized via self-sacrificing templated route, are developed for enzyme immobilization and protein adsorption. The four LuVO4 hollow spheres with diameter of 180 nm, 280 nm, 370 nm and 480 nm were obtained. The size of LuVO4 hollow sphere is dependent on Lu(OH)CO3 template. Upon excitation by UV light, hollow LuVO4:Ln3+ (Ln = Eu, Sm, Dy, Er) spheres exhibit red (Eu3+), orange (Sm3+), yellow-green (Dy3+), and green (Er3+) emissions. The good biocompatibility of sample is validated by MTT assay. Due to structure feature and size of obtained sample, the rapid encapsulation of biomolecules within samples has been achieved. Furthermore, the hollow spheres show different biomolecules adsorption capacities at different buffer solution pH values. The release behaviors of two kinds of biomolecules (lysozyme and bovine serum albumin) are also investigated. LuVO4 hollow spheres are suitable carriers for biomolecules. The emission intensity of Eu3+ in the LuVO4:Eu3+ varies with the released amount of LYZ. This enables the monitoring of release process by the change in the luminescence intensity.

Thermal aging effect of vanadyl acetylacetonate precursor for deposition of VO{sub 2} thin films with thermochromic properties

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

Yu, Jung-Hoon; Nam, Sang-Hun; Kim, Donguk

Highlights: • 7 day aged VO(acac){sub 2} sol shows enhanced adhesivity on the SiO{sub 2} compared with non-aged sol. • The aging process has significantly affected the morphologies of VO{sub 2} films. • From the FT-IR spectra, thermal aging process provides the deformation of precursor. • The metal insulator transition (MIT) efficiency (ΔT{sub at2000} {sub nm}) reached a maximum value of 51% at 7 day aging. • Thermal aging process could shorten the aging time of sol solution. - Abstract: Thermochromic properties of vanadium dioxide (VO{sub 2}) have been studied extensively due to their IR reflection applications in energy smartmore » windows. In this paper, we studied the optical switching property of VO{sub 2} thin film, depending on the thermal aging time of the vanadyl acetylacetonate (VO(acac){sub 2}) precursor. We found the alteration of the IR spectra of the precursor by tuning the aging time as well as heat treatments of the precursor. An aging effect of vanadium precursor directly affects the morphologies, optical switching property and crystallinity of VO{sub 2} films. The optimum condition was achieved at the 7 day aging time with metal insulator transition (MIT) efficiency of 50%.« less

Synthesis and thermochromic property studies on W doped VO2 films fabricated by sol-gel method.

PubMed

Pan, Guoping; Yin, Jinhua; Ji, Keli; Li, Xiang; Cheng, Xingwang; Jin, Haibo; Liu, Jiping

2017-07-21

Tungsten-doped VO 2 thin films have been synthesized by a modified sol-gel process and followed by a post annealing. Vanadium pentoxide and tungstic acid as raw materials with the addition of hydrogen peroxide, concentrated hydrochloric acid (catalyst) and oxalic acid used as reducing agent were reacted in isobutanol. Finally, the uniform sol of vanadyl oxalate in isobutanol solvent was obtained as precursor. Detailed study suggested that W doped in VO 2 introduces additional electron carriers and induces the formation of V 3+ . Post annealing under vacuum promotes the releasing of chemical stress and generates oxygen vacancies in the samples. Temperature dependent transmittance study revealed that the releasing of chemical stress and deliberately introducing oxygen vacancies in W-doped VO 2 films have positive effects on enhancing its switching ability in the infrared transmittance as the metal-insulator transition (MIT) occurs. The largest switching of transmittance was obtained about 48% in the infrared range at 43 °C in 1.5%W doped VO 2 films, which is significantly larger than the reported ones. The findings in this work open a new way to synthesize the novel and thermochromic W doped VO 2 films with facility and low cost. Therefore, it has extensive application to construct smart windows and electronic devices.

Comprehensive studies of interfacial strain and oxygen vacancy on metal-insulator transition of VO2 film

NASA Astrophysics Data System (ADS)

Fan, L. L.; Chen, S.; Liao, G. M.; Chen, Y. L.; Ren, H.; Zou, C. W.

2016-06-01

As a typical strong correlation material, vanadium dioxide (VO2) has attracted wide interest due to its particular metal-insulator transition (MIT) property. However, the relatively high critical temperature (T c) of ~68 °C seriously hinders its practical applications. Thus modulating the phase transition process and decreasing the T c close to room temperature have been hot topics for VO2 study. In the current work, we conducted a multi-approach strategy to control the phase transition of VO2 films, including the interfacial tensile/compressive strain and oxygen vacancies. A synchrotron radiation reciprocal space mapping technique was used to directly record the interfacial strain evolution and variations of lattice parameters. The effects of interfacial strain and oxygen vacancies in the MIT process were systematically investigated based on band structure and d-orbital electron occupation. It was suggested that the MIT behavior can be modulated through the combined effects of the interfacial strain and oxygen vacancies, achieving the distinct phase transition close to room temperature. The current findings not only provide better understanding for strain engineering and oxygen vacancies controlling phase transition behavior, but also supply a combined way to control the phase transition of VO2 film, which is essential for VO2 film based device applications in the future.

Comprehensive studies of interfacial strain and oxygen vacancy on metal-insulator transition of VO2 film.

PubMed

Fan, L L; Chen, S; Liao, G M; Chen, Y L; Ren, H; Zou, C W

2016-06-29

As a typical strong correlation material, vanadium dioxide (VO2) has attracted wide interest due to its particular metal-insulator transition (MIT) property. However, the relatively high critical temperature (T c) of ~68 °C seriously hinders its practical applications. Thus modulating the phase transition process and decreasing the T c close to room temperature have been hot topics for VO2 study. In the current work, we conducted a multi-approach strategy to control the phase transition of VO2 films, including the interfacial tensile/compressive strain and oxygen vacancies. A synchrotron radiation reciprocal space mapping technique was used to directly record the interfacial strain evolution and variations of lattice parameters. The effects of interfacial strain and oxygen vacancies in the MIT process were systematically investigated based on band structure and d-orbital electron occupation. It was suggested that the MIT behavior can be modulated through the combined effects of the interfacial strain and oxygen vacancies, achieving the distinct phase transition close to room temperature. The current findings not only provide better understanding for strain engineering and oxygen vacancies controlling phase transition behavior, but also supply a combined way to control the phase transition of VO2 film, which is essential for VO2 film based device applications in the future.

Phase-field model of insulator-to-metal transition in VO2 under an electric field

NASA Astrophysics Data System (ADS)

Shi, Yin; Chen, Long-Qing

2018-05-01

The roles of an electric field and electronic doping in insulator-to-metal transitions are still not well understood. Here we formulated a phase-field model of insulator-to-metal transitions by taking into account both structural and electronic instabilities as well as free electrons and holes in VO2, a strongly correlated transition-metal oxide. Our phase-field simulations demonstrate that in a VO2 slab under a uniform electric field, an abrupt universal resistive transition occurs inside the supercooling region, in sharp contrast to the conventional Landau-Zener smooth electric breakdown. We also show that hole doping may decouple the structural and electronic phase transitions in VO2, leading to a metastable metallic monoclinic phase which could be stabilized through a geometrical confinement and the size effect. This work provides a general mesoscale thermodynamic framework for understanding the influences of electric field, electronic doping, and stress and strain on insulator-to-metal transitions and the corresponding mesoscale domain structure evolution in VO2 and related strongly correlated systems.

The Effectiveness of Volition Support (VoS) in Promoting Students' Effort Regulation and Performance in an Online Mathematics Course

ERIC Educational Resources Information Center

Kim, ChanMin; Bennekin, Kimberly N.

2016-01-01

The purposes of this study were to investigate (a) the effects of volition support (VoS) on students' motivation, effort regulation, and performance as well as (b) the perceptions of students about VoS in an online mathematics course offered at a community college. VoS was developed based on the theories of and research on volition (e.g., Corno…

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

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

L Whittaker; J Velazquez; S Banerjee

2011-12-31

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

Characterisation of a LoVo subline resistant to a benzoyl mustard derivative of distamycin A (FCE 24517).

PubMed Central

Capolongo, L.; Melegaro, G.; Broggini, M.; Mongelli, N.; Grandi, M.

1993-01-01

Human colon adenocarcinoma cells (LoVo) resistant to the new antitumor agent FCE 24517 [benzoyl-mustard derivative of distamycin A] (LoVo/24517) are resistant to the selecting agent and related molecules as well as to vinblastine, with marginal or no resistance to other antitumour drugs. Treatment with verapamil, tamoxifen, nicergoline or cyclosporin A only partially restores the activity of FCE 24517 against LoVo/24517 cells. Such results suggest that resistance mechanisms possible specific for this class of compounds are operating. Images Figure 2 PMID:8105866

Dynamic electronic correlation effects in NbO 2 as compared to VO 2

DOE PAGES

Brito, W. H.; Aguiar, M. C. O.; Haule, K.; ...

2017-11-01

In this study we present a comparative investigation of the electronic structures of NbO 2 and VO 2 obtained within a combination of density functional theory and cluster-dynamical mean-field theory calculations. We investigate the role of dynamic electronic correlations on the electronic structure of the metallic and insulating phases of NbO 2 and VO 2, with a focus on the mechanism responsible for the gap opening in the insulating phases. For the rutile metallic phases of both oxides, we obtain that electronic correlations lead to a strong renormalization of the t 2g subbands, as well as the emergence of incoherentmore » Hubbard subbands, signaling that electronic correlations are also important in the metallic phase of NbO 2. Interestingly, we find that nonlocal dynamic correlations do play a role in the gap formation of the [body-centered-tetragonal (bct)] insulating phase of NbO 2, by a similar physical mechanism as that recently proposed by us in the case of the monoclinic (M 1) dimerized phase of VO 2. Finally, although the effect of nonlocal dynamic correlations in the gap opening of bct phase is less important than in the (M 1 and M 2) monoclinic phases of VO 2, their presence indicates that the former is not a purely Peierls-type insulator, as it was recently proposed.« less

Microstructure evolution determined by the crystalline phases competition in self-assembled WO3-BiVO4 hetero nanostructures

NASA Astrophysics Data System (ADS)

Song, Haili; Li, Chao; Nguyen Van, Chien; Dong, Wenxia; Qi, Ruijuan; Zhang, Yuanyuan; Huang, Rong; Chu, Ying-Hao; Duan, Chun-Gang

2018-02-01

A series of self-assembled WO3-BiVO4 nanostructured thin films were grown on the (001) yttria-stabilized zirconia (YSZ) substrate at the substrate temperatures of 400 °C, 500 °C, 550 °C, 600 °C, 650 °C and 700 °C by a pulsed laser deposition method. The microstructures including crystalline phases, epitaxial relationships, surface morphologies and interface structures were investigated by a combination of x-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The sample grown at 400 °C was amorphous due to the low driving forces for nucleation and diffusion. For the samples made at 500 °C, 550 °C and 600 °C, the monoclinic BiVO4 matrix epitaxially grew on YSZ, forming the matrix, where the WO3 nanopillars were embedded in with a specific orientation relationship among BiVO4, WO3 and YSZ. However, in thin films deposited at 650 °C and 700 °C, the WO3 grains randomly grew on the YSZ substrate, which dominated the microstructures of the resultant thin films. Quantitative analyses of the microstructures revealed that the lateral grain sizes of BiVO4 and WO3 increased and the volume fraction of BiVO4 in the thin films decreased with the increase of the deposition temperature. A three-regime growth mechanism of the WO3-BiVO4 composite thin film was proposed based on the growth dynamics determined by the competition between BiVO4 and WO3.

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

ERIC Educational Resources Information Center

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

2005-01-01

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

Tuning phase transition temperature of VO2 thin films by annealing atmosphere

NASA Astrophysics Data System (ADS)

Liu, Xingxing; Wang, Shao-Wei; Chen, Feiliang; Yu, Liming; Chen, Xiaoshuang

2015-07-01

A simple new way to tune the optical phase transition temperature of VO2 films was proposed by only controlling the pressure of oxygen during the annealing process. Vanadium films were deposited on glass by a large-scale magnetron sputtering coating system and then annealed in appropriate oxygen atmosphere to form the VO2 films. The infrared transmission change (at 2400 nm) is as high as 58% for the VO2 thin film on the glass substrate, which is very good for tuning infrared radiation and energy saving as smart windows. The phase transition temperature of the films can be easily tuned from an intrinsic temperature to 44.7 °C and 40.2 °C on glass and sapphire by annealing oxygen pressure, respectively. The mechanism is: V3+ ions form in the film when under anaerobic conditions, which can interrupt the V4+ chain and reduce the phase transition temperature. The existence of V3+ ions has been observed by x-ray photoelectron spectroscopy (XPS) experiments as proof.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Influence of a physical exercise program on VO2max in adults with cardiovascular risk factors.

PubMed

Meseguer Zafra, Marcos; García-Cantó, Eliseo; Rodríguez García, Pedro Luis; Pérez-Soto, Juan José; Tárraga López, Pedro Juan; Rosa Guillamón, Andrés; Tarraga López, M Loreto

The aim of the study was to assess the influence of a physical exercise program on VO 2 max in sedentary subjects with cardiovascular risk factors. The sample was composed of 214 patients (80 males, 134 females) with an average age of 52 years, who were referred to a physical exercise program from 2 primary care centres of Spanish southeast. It was implemented a 10 week program (3 training×1h/week) combining strength with cardiorespiratory fitness. TheVO 2 max was analyzed through the Rockport Walk Test (RWT) comparing the pre and post program measurements. The results show significant improvements on VO 2 max for both genders (p<0,05). The most pronounced increase in VO 2 max was among males in the highest age band (56-73 years). Prescribing and referral exercise programs from primary care centers must be considered as a resource for improving cardiorespiratory fitness in the population studied. Copyright © 2017. Publicado por Elsevier España, S.L.U.

Effects of Zirconium Ions Doping on the Structural and Thermochromic Properties of VO2 Thin Films

NASA Astrophysics Data System (ADS)

Li, Yuanbao; Liu, Juncheng; Wang, Danping; Dang, Yuanyuan

2017-11-01

As an inorganic functional material, VO2 thin films are expected to be used for smart windows. However, these films are not conducive to practical applications when the phase transition temperature ( Tc) of the VO2 is approximately 68°C, which is greater than room temperature. To decrease Tc, the effect of Zr4+ doping on the structure and properties of VO2 films were investigated. The films were prepared using a sol-gel process, spin-coating on quartz glasses, and annealing at 525°C in a tube furnace within a nitrogen atmosphere. The results demonstrate that these films have a highly preferential crystalline orientation on the substrate; however, the primary two x-ray diffraction pattern peaks shift slightly toward the small angle, and when 7 at.% Zr4+ was doped in the VO2 film, the deviation angle was 0.16°, and the crystallite size was approximately 98 nm. A large number of grains were found on the surface of the pure VO2 films, but all the Zr4+ doped films had a layered structure, and the thickness of the films was approximately 200 nm. The Tc of these films was characterized using differential scanning calorimetry, and the luminous and solar transmittance was characterized using a UV-Vis-NIR spectrophotometer, which demonstrated that the effect of Zr4+ doping decreased Tc by approximately 1°C per 1 at.% on average, and the Tc of the 7 at.% film was slightly greater than that of the 5 at.% film, the phase transition temperature of which was 61.4°C. The transmittance decreased as the doping concentration increased, and 1 at.% Zr4+ doping increased the luminous regulation efficiency (Δ T lum) and solar modulation efficiency (Δ T sol). The Δ T lum of the pure VO2 film and the 1 at.% Zr4+-doped VO2 films was 10.9% and 11.2%, and Δ T sol was 14.4 and 15.2%, respectively.

Synthesis and structural characterization of the hexagonal anti-perovskite Na{sub 2}CaVO{sub 4}F

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

Green, Robert L., E-mail: rgreen@flpoly.org; Avdeev, Maxim; School of Chemistry, The University of Sydney, Sydney, NSW 2006

The structural details of the ordered hexagonal oxyfluoride Na{sub 2}CaVO{sub 4}F prepared by solid-state synthesis using stoichiometric amounts of V{sub 2}O{sub 5}, CaCO{sub 3}, Na{sub 2}CO{sub 3} and NaF were characterized using high-resolution neutron powder diffraction. The structural changes between 25 °C and 750 °C revealed that the two structural subunits in this material behave different when heated: there is an expansion of the face-shared FNa{sub 4}Ca{sub 2} octahedra while the VO{sub 4} tetrahedra due to increased thermal disorder reveal marginal bond contractions. Bond valences and the global instability index point to significant structural disorder at 750 °C. - Graphicalmore » abstract: The structure of the novel oxyfluoride Na{sub 2}CaVO{sub 4}F is studied at room temperature and high-temperatures. The structure can be viewed as layers of compression and elongation of polyhedral subunits, which change as a function of temperature. - Highlights: • The novel oxyfluoride, Na{sub 2}CaVO{sub 4}F, is synthesized via solid-state method. • High-resolution neutron diffraction data is used to analyze the structure of Na{sub 2}CaVO{sub 4}F. • Structural subunits exhibit expansion and contraction with increasing temperature. • Higher temperatures increase instability within the structure of Na{sub 2}CaVO{sub 4}F.« less

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.

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.

Tunable photoluminescence and magnetic properties of Dy(3+) and Eu(3+) doped GdVO4 multifunctional phosphors.

PubMed

Liu, Yanxia; Liu, Guixia; Dong, Xiangting; Wang, Jinxian; Yu, Wensheng

2015-10-28

A series of Dy(3+) or/and Eu(3+) doped GdVO4 phosphors were successfully prepared by a simple hydrothermal method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectrometry (EDS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). The results indicate that the as-prepared samples are pure tetragonal phase GdVO4, taking on nanoparticles with an average size of 45 nm. Under ultraviolet (UV) light excitation, the individual Dy(3+) or Eu(3+) ion activated GdVO4 phosphors exhibit excellent emission properties in their respective regions. The mechanism of energy transfer from the VO4(3-) group and the charge transfer band (CTB) to Dy(3+) and Eu(3+) ions is proposed. Color-tunable emissions in GdVO4:Dy(3+),Eu(3+) phosphors are realized through adopting different excitation wavelengths or adjusting the appropriate concentration of Dy(3+) and Eu(3+) when excited by a single excitation wavelength. In addition, the as-prepared samples show paramagnetic properties at room temperature. This kind of multifunctional color-tunable phosphor has great potential applications in the fields of photoelectronic devices and biomedical sciences.

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

Enhancing Mo:BiVO 4 Solar Water Splitting with Patterned Au Nanospheres by Plasmon-Induced Energy Transfer [Rational Nanopositioning for BiVO 4 Solar Water Splitting by Plasmon-induced Energy Transfer

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

Kim, Jung Kyu; Shi, Xinjian; Jeong, Myung Jin

Here, plasmonic metal nanostructures have been extensively investigated to improve the performance of metal oxide photoanodes for photoelectrochemical (PEC) solar water splitting cells. Most of these studies have focused on the effects of those metal nanostructures on enhancing light absorption and enabling direct energy transfer via hot electrons. However, several recent studies have shown that plasmonic metal nanostructures can improve the PEC performance of metal oxide photoanodes via another mechanism known as plasmon–induced resonant energy transfer (PIRET). However, this PIRET effect has not yet been tested for the molybdenum–doped bismuth vanadium oxide (Mo:BiVO 4), regarded as one of the bestmore » metal oxide photoanode candidates. Here, this study constructs a hybrid Au nanosphere/Mo:BiVO 4 photoanode interwoven in a hexagonal pattern to investigate the PIRET effect on the PEC performance of Mo:BiVO 4. This study finds that the Au nanosphere array not only increases light absorption of the photoanode as expected, but also improves both its charge transport and charge transfer efficiencies via PIRET, as confirmed by time–correlated single photon counting and transient absorption studies. As a result, incorporating the Au nanosphere array increases the photocurrent density of Mo:BiVO 4 at 1.23 V versus RHE by ≈2.2–fold (2.83 mA cm –2).« less

Enhancing Mo:BiVO 4 Solar Water Splitting with Patterned Au Nanospheres by Plasmon-Induced Energy Transfer [Rational Nanopositioning for BiVO 4 Solar Water Splitting by Plasmon-induced Energy Transfer

DOE PAGES

Kim, Jung Kyu; Shi, Xinjian; Jeong, Myung Jin; ...

2017-10-04

Here, plasmonic metal nanostructures have been extensively investigated to improve the performance of metal oxide photoanodes for photoelectrochemical (PEC) solar water splitting cells. Most of these studies have focused on the effects of those metal nanostructures on enhancing light absorption and enabling direct energy transfer via hot electrons. However, several recent studies have shown that plasmonic metal nanostructures can improve the PEC performance of metal oxide photoanodes via another mechanism known as plasmon–induced resonant energy transfer (PIRET). However, this PIRET effect has not yet been tested for the molybdenum–doped bismuth vanadium oxide (Mo:BiVO 4), regarded as one of the bestmore » metal oxide photoanode candidates. Here, this study constructs a hybrid Au nanosphere/Mo:BiVO 4 photoanode interwoven in a hexagonal pattern to investigate the PIRET effect on the PEC performance of Mo:BiVO 4. This study finds that the Au nanosphere array not only increases light absorption of the photoanode as expected, but also improves both its charge transport and charge transfer efficiencies via PIRET, as confirmed by time–correlated single photon counting and transient absorption studies. As a result, incorporating the Au nanosphere array increases the photocurrent density of Mo:BiVO 4 at 1.23 V versus RHE by ≈2.2–fold (2.83 mA cm –2).« less

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.

Effects of anaesthesia on proliferation, invasion and apoptosis of LoVo colon cancer cells in vitro.

PubMed

Xu, Y J; Li, S Y; Cheng, Q; Chen, W K; Wang, S L; Ren, Y; Miao, C H

2016-02-01

Tumour cell proliferation, invasion and apoptosis are crucial steps in tumour metastasis. We evaluated the effect of serum from patients undergoing colon cancer surgery receiving thoracic epidural and propofol anaesthesia on colon cancer cell biology. Patients were randomly assigned to receive propofol anaesthesia with a concomitant thoracic epidural (PEA, n = 20) or sevoflurane anaesthesia with opioid analgesia (SGA, n = 20). Venous blood was obtained before induction of anaesthesia and 24 hours postoperatively. The LoVo colon cancer cells were cultured with patient serum from both groups and the effects on proliferation, invasion and apoptosis were measured. Twenty-four hours after surgery, the absorbance value of LoVo cells at 10% serum concentration from PEA was decreased when compared with SGA (0.302 (0.026) vs 0.391 (0.066), p = 0.005). The inhibitory rate of LoVo cells at 10% serum concentration from PEA was higher than that from SGA (p = 0.004) 24 h after surgery. The number of invasive LoVo cells at 10% serum concentration from PEA was reduced when compared with SGA (44 (4) vs 62 (4), p < 0.001). Exposure of LoVo cells to postoperative serum from patients receiving PEA led to a higher luminescence ratio (apoptosis) than those receiving SGA (0.36 (0.04) vs 0.27 (0.05), p < 0.001). Serum from patients receiving PEA for colon cancer surgery inhibited proliferation and invasion of LoVo cells and induced apoptosis in vitro more than that from patients receiving SGA. Anaesthetic technique might influence the serum milieu in a way that affects cancer cell biology and, thereby, tumour metastastasis. © 2015 The Association of Anaesthetists of Great Britain and Ireland.

Characterization of pulsed laser deposition grown V2O3 converted VO2

NASA Astrophysics Data System (ADS)

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

2016-10-01

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

Tunable subwavelength hot spot of dipole nanostructure based on VO2 phase transition.

PubMed

Park, Jun-Bum; Lee, Il-Min; Lee, Seung-Yeol; Kim, Kyuho; Choi, Dawoon; Song, Eui Young; Lee, Byoungho

2013-07-01

We propose a novel approach to generate and tune a hot spot in a dipole nanostructure of vanadium dioxide (VO2) laid on a gold (Au) substrate. By inducing a phase transition of the VO2, the spatial and spectral distributions of the hot spot generated in the feed gap of the dipole can be tuned. Our numerical simulation based on a finite-element method shows a strong intensity enhancement difference and tunability near the wavelength of 678 nm, where the hot spot shows 172-fold intensity enhancement when VO2 is in the semiconductor phase. The physical mechanisms of forming the hot spots at the two-different phases are discussed. Based on our analysis, the effects of geometric parameters in our dipole structure are investigated with an aim of enhancing the intensity and the tunability. We hope that the proposed nanostructure opens up a practical approach for the tunable near-field nano-photonic devices.

Tuning of thermally induced first-order semiconductor-to-metal transition in pulsed laser deposited VO2 epitaxial thin films

NASA Astrophysics Data System (ADS)

Behera, Makhes K.; Pradhan, Dhiren K.; Pradhan, Sangram K.; Pradhan, Aswini K.

2017-12-01

Vanadium oxide (VO2) thin films have drawn significant research and development interest in recent years because of their intriguing physical origin and wide range of functionalities useful for many potential applications, including infrared imaging, smart windows, and energy and information technologies. However, the growth of highly epitaxial films of VO2, with a sharp and distinct controllable transition, has remained a challenge. Here, we report the structural and electronic properties of high quality and reproducible epitaxial thin films of VO2, grown on c-axis oriented sapphire substrates using pulsed laser deposition at different deposition pressures and temperatures, followed by various annealing schedules. Our results demonstrate that the annealing of epitaxial VO2 films significantly enhances the Semiconductor to Metal Transition (SMT) to that of bulk VO2 transition. The effect of oxygen partial pressure during the growth of VO2 films creates a significant modulation of the SMT from around room temperature to as high as the theoretical value of 68 °C. We obtained a bulk order transition ≥104 while reducing the transition temperature close to 60 °C, which is comparatively less than the theoretical value of 68 °C, demonstrating a clear and drastic improvement in the SMT switching characteristics. The results reported here will open the door to fundamental studies of VO2, along with tuning of the transition temperatures for potential applications for multifunctional devices.

Hybrid Ag 2VO 2PO 4/CF x as a High Capacity and Energy Cathode for Primary Batteries

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

Li, Yue Ru; Bruck, Andrea M.; Brady, Alexander B.

In this report, we describe the electrochemistry of hybrid dual silver vanadium phosphorus oxide/carbon fluoride (Ag 2VO 2PO 4/CF x) cathodes with various weight ratios. Through modification of the Ag 2VO 2PO 4/CF x ratio, we can control the gravimetric and volumetric capacity, as well as mitigate the voltage drop during high current pulses. The increase in impedance caused by irreversible LiF formation in CFx was reduced by the silver reduction-displacement during electrochemical discharge of the Ag 2VO 2PO 4. Moreover, the addition of graphite was shown to reduce initial voltage delay. When Ag 2VO 2PO 4 dominates the electrodemore » mass (i.e. 75/25 Ag 2VO 2PO 4/CF x) in the hybrid cathode, pulse testing shows less voltage drop and delay, but at the expense of capacity and energy density. As the amount of CFx in the composite increases (i.e. Ag 2VO 2PO 4/CF x ratio of to 50/50 or 25/75), charge capacity and energy density increases, but at the expense of larger voltage drops and delays early in the discharge process. Thus, controlling the Ag 2VO 2PO 4/CF x ratio can be used to tune the electrochemical properties of the dual cathode, allowing for optimization of capacity and power depending on the application.« less

Hybrid Ag 2VO 2PO 4/CF x as a High Capacity and Energy Cathode for Primary Batteries

DOE PAGES

Li, Yue Ru; Bruck, Andrea M.; Brady, Alexander B.; ...

2017-08-18

In this report, we describe the electrochemistry of hybrid dual silver vanadium phosphorus oxide/carbon fluoride (Ag 2VO 2PO 4/CF x) cathodes with various weight ratios. Through modification of the Ag 2VO 2PO 4/CF x ratio, we can control the gravimetric and volumetric capacity, as well as mitigate the voltage drop during high current pulses. The increase in impedance caused by irreversible LiF formation in CFx was reduced by the silver reduction-displacement during electrochemical discharge of the Ag 2VO 2PO 4. Moreover, the addition of graphite was shown to reduce initial voltage delay. When Ag 2VO 2PO 4 dominates the electrodemore » mass (i.e. 75/25 Ag 2VO 2PO 4/CF x) in the hybrid cathode, pulse testing shows less voltage drop and delay, but at the expense of capacity and energy density. As the amount of CFx in the composite increases (i.e. Ag 2VO 2PO 4/CF x ratio of to 50/50 or 25/75), charge capacity and energy density increases, but at the expense of larger voltage drops and delays early in the discharge process. Thus, controlling the Ag 2VO 2PO 4/CF x ratio can be used to tune the electrochemical properties of the dual cathode, allowing for optimization of capacity and power depending on the application.« less

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.

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

NASA Astrophysics Data System (ADS)

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

2012-02-01

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

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

PubMed

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

2015-09-01

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

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

PubMed

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

2013-01-01

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

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

PubMed Central

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

2013-01-01

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

Combined strain and composition-induced effects in the metal-insulator transition of epitaxial VO2 films

NASA Astrophysics Data System (ADS)

Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.

2017-12-01

The role of epitaxial strain, thermal strain, and bulk (strain-free) lattice parameters in the metal-insulator transition (MIT) and the structural phase transition (SPT) of VO2 is investigated for the case of epitaxial films grown on (001)-oriented TiO2 substrates. Temperature-resolved X-ray reciprocal space mapping has been used to determine the absolute state of strain as well as the bulk lattice parameters of VO2 at 100 °C. For the thinnest film (15 nm), the state of strain is dominated by the film/substrate lattice mismatch yielding an in-plane tensile strain which, in turn, shifts both the MIT and the SPT towards lower temperatures. Conversely, for the thickest film (100 nm), the epitaxial strain is relaxed, so that the state of strain is dominated by the VO2/TiO2 thermal expansion mismatch which is responsible for a compressive in-plane strain. In all cases, a swelling of the strain-free VO2 unit-cell is observed which indicates the presence of interfacial oxygen vacancies and/or Ti diffusion into the VO2 films. The presence of oxygen vacancies stabilizes the metallic rutile phase and counterbalances the action of thermal strain on the MIT and the SPT and degrades the electric properties for the thinnest film. For the thickest film, the resistivity ratio is 6.4 × 104.

VO Access to BASECOL Database

NASA Astrophysics Data System (ADS)

Moreau, N.; Dubernet, M. L.

2006-07-01

Basecol is a combination of a website (using PHP and HTML) and a MySQL database concerning molecular ro-vibrational transitions induced by collisions with atoms or molecules. This database has been created in view of the scientific preparation of the Heterodyne Instrument for the Far-Infrared on board the Herschel Space Observatory (HSO). Basecol offers an access to numerical and bibliographic data through various output methods such as ASCII, HTML or VOTable (which is a first step towards a VO compliant system). A web service using Apache Axis has been developed in order to provide a direct access to data for external applications.

Exploring the work function variability and structural stability of VO2(1 1 0) surface upon noble metal (Ag, Au, Pt) adsorption and incorporation

NASA Astrophysics Data System (ADS)

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

2018-08-01

Vanadium dioxide (VO2) has attracted great attention, with scientific and technological advances over the past few decades due to its reversible metal-insulator transition at 340 K. However, the high phase transition temperature (Tc) of VO2 limits its practical applications. Our first-principles calculations show that VO2(1 1 0) surfaces with adsorbed noble metals (Ag, Au, Pt) exhibit a lower work function compared with the clean surface and further induces a lower Tc due to charge transfer from the noble metals to the VO2(1 1 0) surface. However, the work functions of the VO2(1 1 0) surfaces after the incorporation of noble metals are higher than that of the clean surface. In addition, the results of formation energies of various configurations show that the VO2(1 1 0) surface with the adsorption and incorporation of Ag is energetically more favorable than those with Au and Pt. Therefore, it may be concluded that the adsorption and incorporation of noble metals can not only tailor the work function of VO2, in turn realizing the rational tuning of Tc of VO2, but also stabilize the structures of VO2 thin films. These results provide guidance for further exploration of VO2-based optical switching devices and smart windows.

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.

Role of indium tin oxide electrode on the microstructure of self-assembled WO3-BiVO4 hetero nanostructures

NASA Astrophysics Data System (ADS)

Song, Haili; Li, Chao; Van, Chien Nguyen; Dong, Wenxia; Qi, Ruijuan; Zhang, Yuanyuan; Huang, Rong; Chu, Ying-Hao; Duan, Chun-Gang

2017-11-01

Self-assembled WO3-BiVO4 nanostructured thin films were grown on a (001) yttrium stabilized zirconia (YSZ) substrate by the pulsed laser deposition method with and without the indium tin oxide (ITO) bottom electrode. Their microstructures including surface morphologies, crystalline phases, epitaxial relationships, interface structures, and composition distributions were investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray energy dispersive spectroscopy. In both samples, WO3 formed nanopillars embedded into the monoclinic BiVO4 matrix with specific orientation relationships. In the sample with the ITO bottom electrode, an atomically sharp BiVO4/ITO interface was formed and the orthorhombic WO3 nanopillars were grown on a relaxed BiVO4 buffer layer with a mixed orthorhombic and hexagonal WO3 transition layer. In contrast, a thin amorphous layer appears at the interfaces between the thin film and the YSZ substrate in the sample without the ITO electrode. In addition, orthorhombic Bi2WO6 lamellar nanopillars were formed between WO3 and BiVO4 due to interdiffusion. Such a WO3-Bi2WO6-BiVO4 double heterojunction photoanode may promote the photo-generated charge separation and further improve the photoelectrochemical water splitting properties.

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

NASA Astrophysics Data System (ADS)

Molaei, Roya

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

A Real-time Spectrum Handoff Algorithm for VoIP based Cognitive Radio Networks: Design and Performance Analysis

NASA Astrophysics Data System (ADS)

Chakraborty, Tamal; Saha Misra, Iti

2016-03-01

Secondary Users (SUs) in a Cognitive Radio Network (CRN) face unpredictable interruptions in transmission due to the random arrival of Primary Users (PUs), leading to spectrum handoff or dropping instances. An efficient spectrum handoff algorithm, thus, becomes one of the indispensable components in CRN, especially for real-time communication like Voice over IP (VoIP). In this regard, this paper investigates the effects of spectrum handoff on the Quality of Service (QoS) for VoIP traffic in CRN, and proposes a real-time spectrum handoff algorithm in two phases. The first phase (VAST-VoIP based Adaptive Sensing and Transmission) adaptively varies the channel sensing and transmission durations to perform intelligent dropping decisions. The second phase (ProReact-Proactive and Reactive Handoff) deploys efficient channel selection mechanisms during spectrum handoff for resuming communication. Extensive performance analysis in analytical and simulation models confirms a decrease in spectrum handoff delay for VoIP SUs by more than 40% and 60%, compared to existing proactive and reactive algorithms, respectively and ensures a minimum 10% reduction in call-dropping probability with respect to the previous works in this domain. The effective SU transmission duration is also maximized under the proposed algorithm, thereby making it suitable for successful VoIP communication.

Electron and hole dynamics in the electronic and structural phase transitions of VO2

NASA Astrophysics Data System (ADS)

Haglund, Richard

2015-03-01

The ultrafast, optically induced insulator-to-metal transition (IMT) and the associated structural phase transition (SPT) in vanadium dioxide (VO2) have been studied for over a decade. However, only recently have effects due to the combined presence of electron-hole pairs and injected electrons been observed. Here we compare and contrast IMT dynamics when both hot electrons and optically excited electron-hole pairs are involved, in (1) thin films of VO2 overlaid by a thin gold foil, in which hot electrons are generated by 1.5 eV photons absorbed in the foil and accelerated through the VO2 by an applied electric field; (2) VO2 nanoparticles covered with a sparse mesh of gold nanoparticles averaging 20-30 nm in diameter in which hot electrons are generated by resonant excitation and decay of the localized surface plasmon; and (3) bare VO2 thin films excited by intense near-single-cycle THz pulses. In the first case, the IMT is driven by excitation of the bulk gold plasmon, and the SPT appears on a few-picosecond time scale. In the second case, density-functional calculations indicate that above a critical carrier density, the addition of a single electron to a 27-unit supercell drives the catastrophic collapse of the coherent phonon associated with, and leading to, the SPT. In the third case, sub-bandgap-energy photons (approximately 0.1 eV) initiate the IMT, but exhibit the same sub-100 femtosecond switching time and coherent phonon dynamics as observed when the IMT is initiated by 1.5 eV photons. This suggests that the underlying mechanism must be quite different, possibly THz-field induced interband tunneling of spatially separated electron-hole pairs. The implications of these findings for ultrafast switching in opto-electronic devices - such as hybrid VO2 silicon ring resonators - are briefly considered. Support from the National Science Foundation (DMR-1207407), the Office of Science, U.S. Department of Energy (DE-FG02-01ER45916) and the Defense Threat

Heart Rate and VO[subscript 2] Responses to Cycle Ergometry in White and African American Men

ERIC Educational Resources Information Center

Vehrs, Pat R.; Fellingham, Gilbert W.

2006-01-01

The validity of estimates of peak oxygen consumption (VO[subscript 2]peak) using submaximal exercise tests may be compromised when the participants being tested are not similar to the participants used to develop the test. This study compared ethnic differences in the heart rate (HR) and oxygen consumption (VO[subscript 2]) responses to submaximal…

Conditions for Productive Learning in Networked Learning Environments: A Case Study from the VO@NET Project

ERIC Educational Resources Information Center

Ryberg, Thomas; Koottatep, Suporn; Pengchai, Petch; Dirckinck-Holmfeld, Lone

2006-01-01

In this article we bring together experiences from two international research projects: the Kaleidoscope ERT research collaboration and the VO@NET project. We do this by using a shared framework identified for cross-case analyses within the Kaleidoscope ERT to analyse a particular case in the VO@NET project, a training course called "Green…

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

NASA Astrophysics Data System (ADS)

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

2015-06-01

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

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.

Preparation, Characterization and Thermo-Chromic Properties of EVA/VO2 Laminate Films for Smart Window Applications and Energy Efficiency in Building

PubMed Central

Srirodpai, Onruthai; Wootthikanokkhan, Jatuphorn; Nawalertpanya, Saiwan; Yuwawech, Kitti; Meeyoo, Vissanu

2017-01-01

Thermochromic films based on vanadium dioxide (VO2)/ethylene vinyl acetate copolymer (EVA) composite were developed. The monoclinic VO2 particles was firstly prepared via hydrothermal and calcination processes. The effects of hydrothermal time and tungsten doping agent on crystal structure and morphology of the calcined metal oxides were reported. After that, 1 wt % of the prepared VO2 powder was mixed with EVA compound, using two different mixing processes. It was found that mechanical properties of the EVA/VO2 films prepared by the melt process were superior to those of which prepared by the solution process. On the other hand, percentage visible light transmittance of the solution casted EVA/VO2 film was greater than that of the melt processed composite film. This was related to the different gel content of EVA rubber and state of dispersion and distribution of VO2 within the polymer matrix phase. Thermochromic behaviors and heat reflectance of the EVA/VO2 film were also verified. In overall, this study demonstrated that it was possible to develop a thermochromic film using the polymer composite approach. In this regard, the mixing condition was found to be one of the most important factors affecting morphology and thermo-mechanical properties of the films. PMID:28772413

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.

In situ growth of sol-gel-derived nano-VO2 film and its phase transition characteristics

NASA Astrophysics Data System (ADS)

Shi, Qiwu; Huang, Wanxia; Lu, Tiecheng; Yue, Fang; Xiao, Yang; Hu, Yanyan

2014-10-01

We reported the growth of VO2 film deposited by an inorganic sol-gel method, followed by post-annealing. An in situ evolution of the grain size in the films with different annealing temperatures (300, 500, and 700 °C for 90 min), annealing times (500 °C for 20, 40, 60, and 90 min), and film thicknesses (30, 150 and 320 nm) was observed. The results indicated that the grain size distribution in the sol-gel-derived VO2 films was mediated by the density of nucleation center, which was varied in the films with different extents of thermal deformation during the annealing. By increasing the film thickness from 30 to 320 nm, a compact nanostructure with uniform distribution of grain size could be formed. It suggested that the in situ-evolved nanostructure in the thicker VO2 film will lead to lower threshold temperature and enhanced transition intensity in the phase transition. The effect of nanoscale grain size on the lower phase transition temperature in the VO2 film was discussed.

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

NASA Astrophysics Data System (ADS)

Ouyang, Qi; Li, Zhonghua; Liu, Jiawen

2018-05-01

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

Microwave assisted growth of nanorods vanadium dioxide VO2 (R): structural and electrical properties

NASA Astrophysics Data System (ADS)

Derkaoui, I.; Khenfouch, M.; Mothudi, B. M.; Moloi, S. J.; Zorkani, I.; Jorio, A.; Maaza, M.

2018-03-01

Nanostructured metal oxides have attracted a lot of attention recently owning to their unique structural advantages and demonstrated promising chemical and physical properties for various applications. In this study, we report the structural and electrical properties of vanadium dioxide VO2 (R) prepared via a single reaction microwave (SRC) synthesis. Our results are revealing that the components of VO2 (R) films have a rod-like shape with a uniform size distribution. The nanorods with very smooth and flat surfaces have a typical length of up to 2μm and a width of about several nanometers. The structural investigations reveal the high crystallinity of VO2 (R) ensuring good electrical contact and showing a high conductivity as a function of temperature. This synthesis method provides a new simple route to fabricate one-dimensional nanostructured metal oxides which is suitable for a large field of applications especially for smart windows.

Covert Channels in SIP for VoIP Signalling

NASA Astrophysics Data System (ADS)

Mazurczyk, Wojciech; Szczypiorski, Krzysztof

In this paper, we evaluate available steganographic techniques for SIP (Session Initiation Protocol) that can be used for creating covert channels during signaling phase of VoIP (Voice over IP) call. Apart from characterizing existing steganographic methods we provide new insights by introducing new techniques. We also estimate amount of data that can be transferred in signalling messages for typical IP telephony call.

Luminescence Properties of Self-Activated Mm(VO4)2 (M = Mg, Ca, Sr, and Ba) Phosphors Synthesized by Solid-State Reaction Method.

PubMed

Min, Xin; Huang, Zhaohui; Fang, Minghao; Liu, Yan'gai; Tang, Chao; Wu, Xiaowen

2016-04-01

In this paper, M3(VO4)2 (M = Mg, Ca, Sr, and Ba) self-activated phosphors were prepared by a solid-state reaction method at 1,000 °C for 5 h. The phase formation and micrographs were analyzed by X-ray diffraction and scanning electron microscopy. The Ca3(VO4)2 phosphor does not show any emission peaks under excitation with ultraviolet (UV) light. However, the M3(VO4)2 (M = Mg, Sr, and Ba) samples are effectively excited by UV light chips ranging from 200 nm to 400 nm and exhibit broad emission bands due to the charge transfer from the oxygen 2p orbital to the vacant 3d orbital of the vanadium in the VO4. The color of these phosphors changes from yellow to light blue via blue-green with increasing ionic radius from Mg to Sr to Ba. The luminescence lifetimes and quantum yield decrease with the increasing unit cell volume and V-V distance, in the order of Mg3(VO4)2 to Sr3(VO4)2 to Ba3(VO4)2. The emission intensity decreases with the increase of temperatures, but presents no color shift. This confirms that these self-activated M3(VO4)2 phosphors can be suggested as candidates of the single-phase phosphors for light using UV light emitting diodes (LEDs).

Estradiol agonists inhibit human LoVo colorectal-cancer cell proliferation and migration through p53.

PubMed

Hsu, Hsi-Hsien; Kuo, Wei-Wen; Ju, Da-Tong; Yeh, Yu-Lan; Tu, Chuan-Chou; Tsai, Ying-Lan; Shen, Chia-Yao; Chang, Sheng-Huang; Chung, Li-Chin; Huang, Chih-Yang

2014-11-28

To investigate the effects of 17β-estradiol via estrogen receptors (ER) or direct administration of ER agonists on human colorectal cancer. LoVo cells were established from the Bioresource Collection and Research Center and cultured in phenol red-free DMEM (Sigma, United States). To investigate the effects of E2 and/or ER selective agonists on cellular proliferation, LoVo colorectal cells were treated with E2 or ER-selective agonists for 24 h and 48 h and subjected to the MTT (Sigma) assay to find the concentration. And investigate the effects of E2 and/or ER selective agonists on cell used western immunoblotting to find out the diversification of signaling pathways. In order to observe motility and migration the wound healing assay and a transwell chamber (Neuro Probe) plate were tased. For a quantitative measure, we counted the number of migrating cells to the wound area post-wounding for 24 h. We further examined the cellular migration-regulating factors urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA) and matrix metalloproteinase (MMP)-9 in human LoVo cells so gelatin zymography that we used and gelatinolytic activity was visualized by Coomassie blue staining. And these results are presented as means ± SE, and statistical comparisons were made using Student's t-test. The structure was first compared with E2 and ER agonists. We then treated the LoVo cells with E2 and ER agonists (10(-8) mol/L) for 24 h and 48 h and subsequently measured the cell viability using MTT assay. Our results showed that treatment with 17β-estradiol and/or ER agonists in human LoVo colorectal cancer cells activated p53 and then up-regulated p21 and p27 protein levels, subsequently inhibiting the downstream target gene, cyclin D1, which regulates cell proliferation. Taken together, our findings demonstrate the anti-tumorigenesis effects of 17β-estradiol and/or ER agonists and suggest that these compounds may prove to be a potential alternative

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. © Georg Thieme Verlag KG Stuttgart · New York.

EPR and optical absorption studies of paramagnetic molecular ion (VO2+) in Lithium Sodium Acid Phthalate single crystal

NASA Astrophysics Data System (ADS)

Subbulakshmi, N.; Kumar, M. Saravana; Sheela, K. Juliet; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.

2017-12-01

Electron Paramagnetic Resonance (EPR) spectroscopic studies of VO2+ ions as paramagnetic impurity in Lithium Sodium Acid Phthalate (LiNaP) single crystal have been done at room temperature on X-Band microwave frequency. The lattice parameter values are obtained for the chosen system from Single crystal X-ray diffraction study. Among the number of hyperfine lines in the EPR spectra only two sets are reported from EPR data. The principal values of g and A tensors are evaluated for the two different VO2+ sites I and II. They possess the crystalline field around the VO2+ as orthorhombic. Site II VO2+ ion is identified as substitutional in place of Na1 location and the other site I is identified as interstitial location. For both sites in LiNaP, VO2+ are identified in octahedral coordination with tetragonal distortion as seen from the spin Hamiltonian parameter values. The ground state of vanadyl ion in the LiNaP single crystal is dxy. Using optical absorption data the octahedral and tetragonal parameters are calculated. By correlating EPR and optical data, the molecular orbital bonding parameters have been discussed for both sites.

Effect of oxygen partial pressure and VO2 content on hexagonal WO3 thin films synthesized by pulsed laser deposition technique

NASA Astrophysics Data System (ADS)

Kaushal, Ajay; Kaur, Davinder

2011-06-01

We report on the effect of oxygen partial pressure and vacuum annealing on structural and optical properties of pulsed laser-deposited nanocrystalline WO3 thin films. XRD results show the hexagonal phase of deposited WO3 thin films. The crystallite size was observed to increase with increase in oxygen partial pressure. Vacuum annealing changed the transparent as-deposited WO3 thin film to deep shade of blue color which increases the optical absorption of the film. The origin of this blue color could be due to the presence of oxygen vacancies associated with tungsten ions in lower oxidation states. In addition, the effects of VO2 content on structural, electrochemical, and optical properties of (WO3)1- x (VO2) x nanocomposite thin films have also been systematically investigated. Cyclic voltammogram exhibits a modification with the appearance of an extra cathodic peak for VO2-WO3 thin film electrode with higher VO2 content ( x ≥ 0.2). Increase of VO2 content in (WO3)1- x (VO2) x films leads to red shift in optical band gap.

Enhanced photoelectrochemical water splitting of BiVO4 photonic crystal photoanode by decorating with MoS2 nanosheets

NASA Astrophysics Data System (ADS)

Nan, Feng; Cai, Tianyi; Ju, Sheng; Fang, Liang

2018-04-01

Bismuth vanadate (BiVO4) has been considered as one of the promising Photoelectrochemical (PEC) photoanode materials. However, the performances remain poorly rated due to inefficient carrier separation, short carrier diffusion length, and sluggish water oxidation kinetics. Herein, a photoanode consisting of MoS2 nanosheet coating on the three-dimensional ordered BiVO4 inverse opal is fabricated by a facile combination of nanosphere lithography and hydrothermal methods. By taking advantage of the photonic crystal and two-dimensional material, the optimized MoS2/BiVO4 inverse opal photoanode exhibits a 560% improvement of the photocurrent density and threefold enhancement of the incident photon-to-current efficiency than that of the pristine BiVO4 film photoanode. Systematic studies reveal that the excellent PEC activity should be attributed to enhanced light harvesting and charge separation efficiency.

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)

Synthesis and characterization of CoOx/BiVO4 photocatalysts for the degradation of propyl paraben.

PubMed

Petala, Athanasia; Noe, Antigoni; Frontistis, Zacharias; Drivas, Charalampos; Kennou, Stella; Mantzavinos, Dionissios; Kondarides, Dimitris I

2018-03-13

Cobalt-promoted bismuth vanadate photocatalysts of variable cobalt content (0-1.0 wt.%) were synthesized and characterized with various techniques including BET, XRD, DRS, XPS and TEM. BiVO 4 exists in the monoclinic scheelite structure, while cobalt addition improves the absorbance in the visible region although it does not affect the band gap energy of BiVO 4 . Cobalt exists in the form of well-dispersed Co 3 O 4 nanocrystallites, which are in intimate contact with the much larger BiVO 4 nanoparticles. Photocatalytic activity was evaluated for the degradation of propyl paraben (PP) under simulated solar radiation. The activity of pristine BiVO 4 is significantly improved adding small amounts of cobalt and is maximized for the catalyst containing 0.5 wt.% Co. PP degradation in ultrapure pure water increases with increasing photocatalyst loading (100 mg/L to 1.5 g/L), and decreasing PP concentration (1600-200 μg/L). Experiments in bottled water, as well as in pure water spiked with bicarbonate and chloride ions showed little effect of non-target inorganics on degradation. Conversely, degradation is severely impeded in secondary treated wastewater. The enhancement of the photocatalytic activity of the synthesized catalysts is attributed to efficient electron-hole separation, achieved at the p-n junction formed between the p-type Co 3 O 4 and the n-type BiVO 4 semiconductors. Copyright © 2018 Elsevier B.V. All rights reserved.

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

PubMed Central

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

2016-01-01

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

Near-infrared tunable multiple broadband perfect absorber base on VO2 semi-shell arrays photonic microstructure and gold reflector

NASA Astrophysics Data System (ADS)

Liang, Jiran; Li, Peng; Zhou, Liwei; Guo, Jinbang; Zhao, Yirui

2018-01-01

We proposed a metamaterial absorber which is aimed to achieve a multiple broadband absorption and tunable absorption peak in the near-infrared region. The absorber is based on VO2 semi-shell coated on the top of silica nano-particle array supported on the gold-reflective layer. Measured results show that the absorber has the multiple broadband with the absorption magnitudes more than 95% in the near infrared region. The absorption peaks can be tuned through the VO2 phase transition from metallic phase to insulator phase in the short wavelength (before λ = 1500 nm), when VO2 is at the metallic state, an absorption band appears in the long wavelength (after λ = 1500 nm). The simulation results closely match those of measured. The absorption intensity becomes stronger and absorption peaks have red shift with the increase of thickness of VO2 semi-shell. Thus, this designed tunable absorption intensity and position absorber based on VO2 can be a good choice for enhancing the performance of multiple band, this would be beneficial to the field of photo detectors, sensor and solar cell.

Astroinformatics as a New Research Field. UkrVO Astroinformation Resources: Tasks and Prospective

NASA Astrophysics Data System (ADS)

Vavilova, I. B.

The data-oriented astronomy has allowed classifying the Astroinformatics as a new academic research field, which covers various multi-disciplinary applications of the e-Astronomy. Among them are the data modeling, data mining, metadata standards development, data access, digital astronomical databases, image archives and visualization, machine learning, statistics and other computational methods and software for work with astronomical survey and catalogues with their teta- topeta-scale astroinformation resource. In this review we describe briefly the astroinformatics applications and software/services performed for different astronomical tasks in frame of the VIrtual Roentgen and Gamma Observatory (VIRGO) and Ukrainian VirtualObservatory (UkrVO). Among them there are projects based on the archival space-born data of X-ray and gamma space observatories and on the Joint Digitized Archive (JDA) database of astroplate network collections. The UkrVO JDA DR1 deals with the star catalogues (FON, Polar zone, open clusters, GRB star fields) as well as the UkrVO JDA DR2 deals with the Solar System bodies (giant and small planets, satellites, astronomical heritage images).

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

PubMed

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

2016-12-07

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

Change in VO2max and time trial performance in response to high-intensity interval training prescribed using ventilatory threshold.

PubMed

Astorino, Todd A; deRevere, Jamie; Anderson, Theodore; Kellogg, Erin; Holstrom, Patrick; Ring, Sebastian; Ghaseb, Nicholas

2018-06-19

Completion of high-intensity interval training (HIIT) leads to significant increases in maximal oxygen uptake (VO 2max ) and oxidative capacity. However, individual responses to HIIT have been identified as approximately 20-40% of individuals show no change in VO 2max , which may be due to the relatively homogeneous approach to implementing HIIT. This study tested the effects of HIIT prescribed using ventilatory threshold (VT) on changes in VO 2max and cycling performance. Fourteen active men and women (age and VO 2max  = 27 ± 8 year and 38 ± 4 mL/kg/min) underwent nine sessions of HIIT, and 14 additional men and women (age and VO 2max  = 22 ± 3 year and 40 ± 5 mL/kg/min) served as controls. Training was performed on a cycle ergometer at a work rate equal to 130%VT and consisted of eight to ten 1 min bouts interspersed with 75 s of recovery. At baseline and post-testing, they completed progressive cycling to exhaustion to determine VO 2max , and on a separate day, a 5 mile cycling time trial. Compared to the control group, HIIT led to significant increases in VO 2max (6%, p = 0.007), cycling performance (2.5%, p = 0.003), and absolute VT (9 W, p = 0.005). However, only 57% of participants revealed meaningful increases in VO 2max and cycling performance in response to training, and two showed no change in either outcome. A greater volume of HIIT may be needed to maximize the training response for all individuals.

Proliferation of metallic domains caused by inhomogeneous heating near the electrically driven transition in VO2 nanobeams

NASA Astrophysics Data System (ADS)

Singh, Sujay; Horrocks, Gregory; Marley, Peter M.; Shi, Zhenzhong; Banerjee, Sarbajit; Sambandamurthy, G.

2015-10-01

We discuss the mechanisms behind the electrically driven insulator-metal transition in single-crystalline VO2 nanobeams. Our dc and ac transport measurements and the versatile harmonic analysis method employed show that nonuniform Joule heating causes electronic inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO2. A Poole-Frenkel-like purely electric-field-induced transition is found to be absent, and the role of percolation near and away from the electrically driven transition in VO2 is also identified. The results and the harmonic analysis can be generalized to many strongly correlated materials that exhibit electrically driven transitions.

Etching Characteristics of VO2 Thin Films Using Inductively Coupled Cl2/Ar Plasma

NASA Astrophysics Data System (ADS)

Ham, Yong-Hyun; Efremov, Alexander; Min, Nam-Ki; Lee, Hyun Woo; Yun, Sun Jin; Kwon, Kwang-Ho

2009-08-01

A study on both etching characteristics and mechanism of VO2 thin films in the Cl2/Ar inductively coupled plasma was carried. The variable parameters were gas pressure (4-10 mTorr) and input power (400-700 W) at fixed bias power of 150 W and initial mixture composition of 25% Cl2 + 75% Ar. It was found that an increase in both gas pressure and input power results in increasing VO2 etch rate while the etch selectivity over photoresist keeps a near to constant values. Plasma diagnostics by Langmuir probes and zero-dimensional plasma model provided the data on plasma parameters, steady-state densities and fluxes of active species on the etched surface. The model-based analysis of the etch mechanism showed that, for the given ranges of operating conditions, the VO2 etch kinetics corresponds to the transitional regime of ion-assisted chemical reaction and is influenced by both neutral and ion fluxes with a higher sensitivity to the neutral flux.

Adhesion characteristics of VO2 ink film sintered by intense pulsed light for smart window

NASA Astrophysics Data System (ADS)

Youn, Ji Won; Lee, Seok-Jae; Kim, Kwang-Seok; Kim, Dae Up

2018-05-01

Progress in the development of energy-efficient coatings on glass has led to the research of smart windows that can modulate solar energy in response to an external stimulus like light, heat, or electricity. Thermochromic smart windows have attracted great interest because they provide highly visible transparency and intelligently controllable solar heat. VO2 has been widely used as coating material for thermochromism owing to its reversible metal-to-insulator transition near room temperature. However, unstable crystalline phases and expensive fabrication processes of VO2 films limit their facile application in smart windows. To overcome these restrictions, we manufactured nanoinks based on VO2 nanoparticles and fabricated films using spin coating and intense pulsed light (IPL) sintering on a quartz substrate. We examined adhesion between the VO2 nanoink films and the quartz substrate by varying the applied voltages and the number of pulses. The average adhesion of thin films increased to 83 and 108 N/m as the applied voltage during IPL sintering increased from 1400 to 2000 V. By increasing the number of pulses from 5 to 20, the adhesive strength increased from 83 to 94 N/m at 1400 V, and decreased from 108 to 96 N/m at 2000 V voltage.

Metal-insulator transition characteristics of VO2 thin films grown on Ge(100) single crystals

NASA Astrophysics Data System (ADS)

Yang, Z.; Ko, C.; Ramanathan, S.

2010-10-01

Phase transitions exhibited by correlated oxides could be of potential relevance to the emerging field of oxide electronics. We report on the synthesis of high-quality VO2 thin films grown on single crystal Ge(100) substrates by physical vapor deposition and their metal-insulator transition (MIT) properties. Thermally triggered MIT is demonstrated with nearly three orders of magnitude resistance change across the MIT with transition temperatures of 67 °C (heating) and 61 °C (cooling). Voltage-triggered hysteretic MIT is observed at room temperature at threshold voltage of ˜2.1 V for ˜100 nm thickness VO2 films. Activation energies for electron transport in the insulating and conducting states are obtained from variable temperature resistance measurements. We further compare the properties of VO2 thin films grown under identical conditions on Si(100) single crystals. The VO2 thin films grown on Ge substrate show higher degree of crystallinity, slightly reduced compressive strain, larger resistance change across MIT compared to those grown on Si. Depth-dependent x-ray photoelectron spectroscopy measurements were performed to provide information on compositional variation trends in the two cases. These results suggest Ge could be a suitable substrate for further explorations of switching phenomena and devices for thin film functional oxides.

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

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.

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

High beam quality of a Q-switched 2-µm Tm,Ho:LuVO4 laser

NASA Astrophysics Data System (ADS)

Wang, Wei; Yang, Xining; Shen, Yingjie; Li, Linjun; Zhou, Long; Yang, Yuqiang; Bai, Yunfeng; Xie, Wenqiang; Ye, Guangchao; Yu, Xiaoyang

2018-05-01

A diode-end-pumped 2.05-µm Q-switched Tm,Ho:LuVO4 laser is reported in this paper. The cryogenic Tm3+ (5.0 at.%),Ho3+ (0.5 at.%):LuVO4 crystal was pumped by an 800-nm laser diode. At a pulse repetition frequency of 10 kHz, the maximum average output power of 3.77 W was achieved at 77 K when an incident pump power of 14.7 W was used. The slope efficiency and optical-optical conversion efficiency were 28.3 and 25.6%, respectively. The maximum per pulse energy was 2.54 mJ for a pulse duration of 69.9 ns. The beam quality factor Mx 2 was approximately 1.17 and My 2 was approximately 1.01 for the Tm,Ho:LuVO4 laser.

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.

Probabilistic Seeking Prediction in P2P VoD Systems

NASA Astrophysics Data System (ADS)

Wang, Weiwei; Xu, Tianyin; Gao, Yang; Lu, Sanglu

In P2P VoD streaming systems, user behavior modeling is critical to help optimise user experience as well as system throughput. However, it still remains a challenging task due to the dynamic characteristics of user viewing behavior. In this paper, we consider the problem of user seeking prediction which is to predict the user's next seeking position so that the system can proactively make response. We present a novel method for solving this problem. In our method, frequent sequential patterns mining is first performed to extract abstract states which are not overlapped and cover the whole video file altogether. After mapping the raw training dataset to state transitions according to the abstract states, we use a simpel probabilistic contingency table to build the prediction model. We design an experiment on the synthetic P2P VoD dataset. The results demonstrate the effectiveness of our method.

Microwave-assisted in situ synthesis of reduced graphene oxide-BiVO4 composite photocatalysts and their enhanced photocatalytic performance for the degradation of ciprofloxacin.

PubMed

Yan, Yan; Sun, Shaofang; Song, Yang; Yan, Xu; Guan, Weisheng; Liu, Xinlin; Shi, Weidong

2013-04-15

To improve the photodegradation efficiency for ciprofloxacin (CIP), a new-type microwave-assisted in situ growth method is developed for the preparation of reduced graphene oxide (RGO) -BiVO4 composite photocatalysts. The as-produced RGO-BiVO4 composite photocatalysts show extremely high enhancement of CIP degradation ratio over the pure BiVO4 photocatalyst under visible light. Specially, the 2 wt% RGO-BiVO4 composite photocatalyst exhibits the highest CIP degradation ratio (68.2%) in 60 min, which is over 3 times than that (22.7%) of the pure BiVO4 particles. The enhancement of photocatalytic activities of RGO-BiVO4 photocatalysts can be attributed to the effective separation of electron-hole pairs rather than the improvement of light absorption. Copyright © 2013 Elsevier B.V. All rights reserved.

Brave New World: Data Intensive Science with SDSS and the VO

NASA Astrophysics Data System (ADS)

Thakar, A. R.; Szalay, A. S.; O'Mullane, W.; Nieto-Santisteban, M.; Budavari, T.; Li, N.; Carliles, S.; Haridas, V.; Malik, T.; Gray, J.

2004-12-01

With the advent of digital archives and the VO, astronomy is quickly changing from a data-hungry to a data-intensive science. Local and specialized access to data will remain the most direct and efficient way to get data out of individual archives, especially if you know what you are looking for. However, the enormous sizes of the upcoming archives will preclude this type of access for most institutions, and will not allow researchers to tap the vast potential for discovery in cross-matching and comparing data between different archives. The VO makes this type of interoperability and distributed data access possible by adopting industry standards for data access (SQL) and data interchange (SOAP/XML) with platform independence (Web services). As a sneak preview of this brave new world where astronomers may need to become SQL warriors, we present a look at VO-enabled access to catalog data in the SDSS Catalog Archive Server (CAS): CasJobs - a workbench environment that allows arbitrarily complex SQL queries and your own personal database (MyDB) that you can share with collaborators; OpenSkyQuery - an IVOA (International Virtual Observatory Alliance) compliant federation of multiple archives (OpenSkyNodes) that currently links nearly 20 catalogs and allows cross-match queries (in ADQL - Astronomical Data Query Language) between them; Spectrum and Filter Profile Web services that provide access to an open database of spectra (registered users may add their own spectra); and VO-enabled Mirage - a Java visualizatiion tool developed at Bell Labs and enhanced at JHU that allows side-by-side comparison of SDSS catalog and FITS image data. Anticipating the next generation of Petabyte archives like LSST by the end of the decade, we are developing a parallel cross-match engine for all-sky cross-matches between large surveys, along with a 100-Terabyte data intensive science laboratory with high-speed parallel data access.

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

PubMed

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

2017-06-30

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

On the Design of the Peer-Assisted UGC VoD System

NASA Astrophysics Data System (ADS)

Wan, Yi; Asaka, Takuya; Takahashi, Tatsuro

User Generated Content (UGC) VoD services such as YouTube are becoming more and more popular, and their maintenance costs are growing as well. Many P2P solutions have been proposed to reduce server load in such systems, but almost all of them focus on the single-video approach, which only has limited effect on the systems serving short videos such as UGC. The purpose of this paper is to investigate the potential of an alternative approach, the multi-video approach, and we use a very simple method called collaborative caching to show that methods using the multi-video approach are generally more suitable for current UGC VoD systems. We also study the influence of the major design factors through simulations and provide guidelines for efficiently building systems with this method.

Preparation of plasmonic porous Au@AgVO3 belt-like nanocomposites with enhanced visible light photocatalytic activity.

PubMed

Fu, Haitao; Yang, Xiaohong; Zhang, Zhikui; Wang, Wenwen; An, Xizhong; Dong, Yu; Li, Xue

2018-07-20

This study reports a visible light-driven plasmonic photocatalyst of Au deposited AgVO 3 nanocomposites prepared by a hydrothermal method, and further in situ modification of Au nanoparticles by a reducing agent of NaHSO 3 in an aqueous solution at room temperature. Various characterization techniques, such as SEM, TEM, XRD, EDS, XPS, and Brunauer-Emmett-Teller, were used to reveal the morphology, composition, and related properties. The results show that belt-like AgVO 3 nanoparticles with a width of ∼100 nm were successfully synthesized, and Au nanoparticles with controlled sizes (5-20 nm) were well distributed on the surface of the nanobelts. The UV-vis absorption spectra indicate that the decoration of Au nanoparticles can modulate the optical properties of the nanocomposites, namely, red shift occurs with the increase of Au content. The photocatalytic activities were measured by monitoring the degradation of Rhodamine B (RhB) with the presence of photocatalysts under visible light irradiation. The photodegradation results show that AgVO 3 nanobelts exhibit good visible light photocatalytic activities with a degradation efficiency of 98% in 50 min and a reaction rate constant of 0.025 min -1 towards 30 ppm RhB. With the modification of Au nanoparticles, photocatalytic activity basically increases with the molar ratio of Au to V. Among the Au@AgVO 3 nanocomposites, the 3% (molar ratio) Au decorated AgVO 3 nanobelts showed the highest photocatalytic activity, and the k (0.064 min -1 ) was almost two times higher than that of the pure AgVO 3 nanobelts. This can be attributed to several factors including specific surface areas, optical properties, and the energy band structure of the composites under visible light illumination. These findings may be useful for the practical use of visible light-driven photocatalysts with enhanced photocatalytic efficiencies for environmental remediation.

Preparation of plasmonic porous Au@AgVO3 belt-like nanocomposites with enhanced visible light photocatalytic activity

NASA Astrophysics Data System (ADS)

Fu, Haitao; Yang, Xiaohong; Zhang, Zhikui; Wang, Wenwen; An, Xizhong; Dong, Yu; Li, Xue

2018-07-01

This study reports a visible light-driven plasmonic photocatalyst of Au deposited AgVO3 nanocomposites prepared by a hydrothermal method, and further in situ modification of Au nanoparticles by a reducing agent of NaHSO3 in an aqueous solution at room temperature. Various characterization techniques, such as SEM, TEM, XRD, EDS, XPS, and Brunauer–Emmett–Teller, were used to reveal the morphology, composition, and related properties. The results show that belt-like AgVO3 nanoparticles with a width of ∼100 nm were successfully synthesized, and Au nanoparticles with controlled sizes (5–20 nm) were well distributed on the surface of the nanobelts. The UV–vis absorption spectra indicate that the decoration of Au nanoparticles can modulate the optical properties of the nanocomposites, namely, red shift occurs with the increase of Au content. The photocatalytic activities were measured by monitoring the degradation of Rhodamine B (RhB) with the presence of photocatalysts under visible light irradiation. The photodegradation results show that AgVO3 nanobelts exhibit good visible light photocatalytic activities with a degradation efficiency of 98% in 50 min and a reaction rate constant of 0.025 min‑1 towards 30 ppm RhB. With the modification of Au nanoparticles, photocatalytic activity basically increases with the molar ratio of Au to V. Among the Au@AgVO3 nanocomposites, the 3% (molar ratio) Au decorated AgVO3 nanobelts showed the highest photocatalytic activity, and the k (0.064 min‑1) was almost two times higher than that of the pure AgVO3 nanobelts. This can be attributed to several factors including specific surface areas, optical properties, and the energy band structure of the composites under visible light illumination. These findings may be useful for the practical use of visible light-driven photocatalysts with enhanced photocatalytic efficiencies for environmental remediation.

Effective visible light-active boron and europium co-doped BiVO4 synthesized by sol-gel method for photodegradion of methyl orange.

PubMed

Wang, Min; Che, Yinsheng; Niu, Chao; Dang, Mingyan; Dong, Duo

2013-11-15

Eu-B co-doped BiVO4 visible-light-driven photocatalysts have been synthesized using the sol-gel method. The resulting materials were characterized by a series of joint techniques, including XPS, XRD, SEM, BET, and UV-vis DRS analyses. Compared with BiVO4 and B-BiVO4 photocatalysts, the Eu-B-BiVO4 photocatalysts exhibited much higher photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. The optimal Eu doping content is 0.8 mol%. It was revealed that boron and europium were doped into the lattice of BiVO4 and this led to more surface oxygen vacancies, high specific surface areas, small crystallite size, a narrower band gap and intense light absorbance in the visible region. The doped Eu(III) cations can help in the separation of photogenerated electrons. The synergistic effects of boron and europium in doped BiVO4 were the main reason for improving visible light photocatalytic activity. Copyright © 2013 Elsevier B.V. All rights reserved.

Near-infrared localized surface plasmon resonance of self-growing W-doped VO2 nanoparticles at room temperature

NASA Astrophysics Data System (ADS)

Nishikawa, Kazutaka; Kishida, Yoshihiro; Ito, Kota; Tamura, Shin-ichi; Takeda, Yasuhiko

2017-11-01

Nanoparticles (NPs) of vanadium dioxide (VO2) in the metal state exhibit localized surface plasmon resonance (LSPR) at 1200-1600 nm, which fills the gap between the absorption ranges of silicon and the LSPR of conventional transparent conductor NPs (ZnO:Al, In2O3:Sn, etc.). However, two issues of the lithographic process for NP formation and the metal-insulator transition temperature (69 °C) higher than room temperature have made it difficult to use VO2 NPs for applications such as energy conversion devices, near infrared (NIR) light detectors, and bio-therapy. In this study, we developed a self-growing process for tungsten (W)-doped VO2 NPs that are in the metal state at room temperature, using sputter deposition and post-lamp annealing. The changes in the LSPR peak wavelengths with the NP size were well controlled by changing the deposited film thickness and oxygen pressure during the post-annealing treatment. The presented results resolve the difficulties of using the metal-insulator transition material VO2 for practical NIR utilization.

Design and implementation of a VoIP broadcasting service over embedded systems in a heterogeneous network environment.

PubMed

Leu, Jenq-Shiou; Lin, Wei-Hsiang; Hsieh, Wen-Bin; Lo, Chien-Chih

2014-01-01

As the digitization is integrated into daily life, media including video and audio are heavily transferred over the Internet nowadays. Voice-over-Internet Protocol (VoIP), the most popular and mature technology, becomes the focus attracting many researches and investments. However, most of the existing studies focused on a one-to-one communication model in a homogeneous network, instead of one-to-many broadcasting model among diverse embedded devices in a heterogeneous network. In this paper, we present the implementation of a VoIP broadcasting service on the open source-Linphone-in a heterogeneous network environment, including WiFi, 3G, and LAN networks. The proposed system featuring VoIP broadcasting over heterogeneous networks can be integrated with heterogeneous agile devices, such as embedded devices or mobile phones. VoIP broadcasting over heterogeneous networks can be integrated into modern smartphones or other embedded devices; thus when users run in a traditional AM/FM signal unreachable area, they still can receive the broadcast voice through the IP network. Also, comprehensive evaluations are conducted to verify the effectiveness of the proposed implementation.

Design and Implementation of a VoIP Broadcasting Service over Embedded Systems in a Heterogeneous Network Environment

PubMed Central

Lin, Wei-Hsiang; Hsieh, Wen-Bin; Lo, Chien-Chih

2014-01-01

As the digitization is integrated into daily life, media including video and audio are heavily transferred over the Internet nowadays. Voice-over-Internet Protocol (VoIP), the most popular and mature technology, becomes the focus attracting many researches and investments. However, most of the existing studies focused on a one-to-one communication model in a homogeneous network, instead of one-to-many broadcasting model among diverse embedded devices in a heterogeneous network. In this paper, we present the implementation of a VoIP broadcasting service on the open source—Linphone—in a heterogeneous network environment, including WiFi, 3G, and LAN networks. The proposed system featuring VoIP broadcasting over heterogeneous networks can be integrated with heterogeneous agile devices, such as embedded devices or mobile phones. VoIP broadcasting over heterogeneous networks can be integrated into modern smartphones or other embedded devices; thus when users run in a traditional AM/FM signal unreachable area, they still can receive the broadcast voice through the IP network. Also, comprehensive evaluations are conducted to verify the effectiveness of the proposed implementation. PMID:25300280

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

PubMed

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

2018-05-07

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

Role of Hydrogen in Defining the n-Type Character of BiVO 4 Photoanodes

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

Cooper, Jason K.; Scott, Soren B.; Ling, Yichuan

The roles of hydrogen impurity and oxygen vacancy defects on defining the conductivity, and hence photoelectrochemical (PEC) performance characteristics, of monoclinic scheelite bismuth vanadate (BiVO 4) are investigated using a combination of experiment and theory. We find that elemental hydrogen is present as an impurity in as-synthesized BiVO 4 and that increasing its concentration by annealing in H 2 at temperatures up to 290°C leads to near-complete elimination of majority carrier transport limitations, a beneficial shift in the photoanodic current onset potential, and improved fill factor. Magnetic resonance measurements reveal that hydrogen can be incorporated in at least two differentmore » chemical environments, which are assigned to interstitial and substitutional sites. Incorporation of hydrogen leads to a shift of the Fermi level toward the conduction band edge, indicating that n-type character is correlated with increased hydrogen content. This finding is in agreement with theory and reveals that hydrogen acts as a donor in BiVO 4. Sub-bandgap photoluminescence is observed from as-synthesized material and is consistent with deep electronic states associated with oxygen vacancies. Hydrogen treatment leads to reduced emission from these states. These findings support the conclusion that hydrogen, rather than oxygen vacancies, is dominant in determining the n-type conductivity of BiVO 4. These findings have important implications for controlling the electronic properties and functional characteristics of this promising photoanode material.« less

Role of Hydrogen in Defining the n-Type Character of BiVO 4 Photoanodes

DOE PAGES

Cooper, Jason K.; Scott, Soren B.; Ling, Yichuan; ...

2016-07-19

The roles of hydrogen impurity and oxygen vacancy defects on defining the conductivity, and hence photoelectrochemical (PEC) performance characteristics, of monoclinic scheelite bismuth vanadate (BiVO 4) are investigated using a combination of experiment and theory. We find that elemental hydrogen is present as an impurity in as-synthesized BiVO 4 and that increasing its concentration by annealing in H 2 at temperatures up to 290°C leads to near-complete elimination of majority carrier transport limitations, a beneficial shift in the photoanodic current onset potential, and improved fill factor. Magnetic resonance measurements reveal that hydrogen can be incorporated in at least two differentmore » chemical environments, which are assigned to interstitial and substitutional sites. Incorporation of hydrogen leads to a shift of the Fermi level toward the conduction band edge, indicating that n-type character is correlated with increased hydrogen content. This finding is in agreement with theory and reveals that hydrogen acts as a donor in BiVO 4. Sub-bandgap photoluminescence is observed from as-synthesized material and is consistent with deep electronic states associated with oxygen vacancies. Hydrogen treatment leads to reduced emission from these states. These findings support the conclusion that hydrogen, rather than oxygen vacancies, is dominant in determining the n-type conductivity of BiVO 4. These findings have important implications for controlling the electronic properties and functional characteristics of this promising photoanode material.« less

Effects of three warm-up regimens of equal distance on VO2 kinetics during supramaximal exercise in Thoroughbred horses.

PubMed

Mukai, K; Hiraga, A; Takahashi, T; Ohmura, H; Jones, J H

2010-11-01

Several studies have indicated that even low-intensity warm-up increases O(2) transport kinetics and that high-intensity warm-up may not be needed in horses. However, conventional warm-up exercise for Thoroughbred races is more intense than those utilised in previous studies of equine warm-up responses. To test the hypothesis that warm-up exercise at different intensities alters the kinetics and total contribution of aerobic power to total metabolic power in subsequent supramaximal (sprint) exercise in Thoroughbred horses. Nine well-trained Thoroughbreds ran until fatigue at 115% of maximal oxygen consumption (VO2max) 10 min after warming-up under each of 3 protocols of equal running distance: 400 s at 30% VO2max (LoWU), 200 s at 60% VO2max (MoWU) and 120 s at 100% VO2max (HiWU). Variables measured during exercise were rates of O(2) and CO(2) consumption/production (VO2,VO2), respiratory exchange ratio (RER), heart rate, blood lactate concentration and accumulation rate and blood gas variables. VO2 was significantly higher in HiWU than in LoWU at the onset of the sprint exercise and HR was significantly higher in HiWU than in LoWU throughout the sprint. Accumulation of blood lactate, RER, P(a)CO(2) and PvCO2 in the first 60 s were significantly lower in HiWU than in LoWU and MoWU. There were no significant differences in stroke volume, run time or arterial-mixed venous O(2) concentration. These results suggest HiWU accelerates kinetics and reduces reliance on net anaerobic power compared with LoWU at the onset of the subsequent sprint. © 2010 EVJ Ltd.

Effects of postdeposition annealing on the metal-insulator transition of VO2-x thin films prepared by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Liu, Shiu-Jen; Su, Yu-Tai; Hsieh, Juang-Hsin

2014-03-01

We report the fabrication of textured VO2-x films on c-cut sapphire substrates by postdeposition annealing of V2O3 films prepared by RF magnetron sputtering using V2O3 as the target. Although the prepared VO2-x films are expected to be oxygen-deficient, overoxidation on the film surface was revealed by X-ray photoelectron spectroscopy. The metal-insulator transition (MIT) characteristics of the VO2-x films were investigated. MIT parameters including the transition temperature, transition sharpness, and hysteresis width of the VO2-x films were manipulated by varying the oxygen pressure during postdeposition annealing. The suppression of optical transmittance in the near-infrared region was observed by increasing the temperature through the MIT.

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

PubMed

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

2017-07-19

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

C-oriented and {010} facets exposed BiVO4 nanowall films: template-free fabrication and their enhanced photoelectrochemical properties.

PubMed

Zhou, Min; Zhang, Shudong; Sun, Yongfu; Wu, Changzheng; Wang, Mingtai; Xie, Yi

2010-12-03

Vertically aligned BiVO(4) nanowall films on indium tin oxide (ITO) glass have been fabricated through a template-free hydrothermal method for the first time. Based on the structural understanding of both BiVO(4) and ITO, the lattice matches ({020}(BiVO4) and {040}(ITO), {200}(BiVO4) and {004}(ITO), respectively) and the similarity of metal atomic arrangement parallel to {001} planes turn out to be crucial for the fabrication of the nanowalls. Consequently, the growth of a BiVO(4) film begins from heteroepitaxy and undergoes an Ostwald ripening process to form an extended network, resulting in a c-orientation and exposing {010} facets. Through this process, it is much easier to obtain a range of nanowall films with different packing densities, as the surface state of ITO glass is alterable by adjusting the concentration of acid. The films can be directly used as an electrode, which exhibits an excellent response to visible light, especially light with low intensity, allowing for the electrical interconnection, highly active surface, appropriate orientation, and a good contact with the substrate. There are great benefits in improving the technique for detecting the weak light source signals.

The preparation of Ag-BiVO4 metal composite oxides and its application in efficient photocatalytic oxidative thiophene

NASA Astrophysics Data System (ADS)

Gao, Xiao-Ming; Fu, Feng; Zhang, Li-Ping; Li, Wen-Hong

2013-06-01

A series of Ag-BiVO4 photocatalysts was synthesized by the hydrothemal synthesis method for different pH values. A strong correlation was found among the prepared processing, structure and property of the samples. With increasing pH value from 5 to 9, the crystallinity increases and the as-prepared Ag-BiVO4 sample gradually disappeared from the nanostructures. The light absorption became higher in the UV and visible range, accompanied by a bathochromic shift of the absorption edge. The competitive relations between crystallinity and surface area affecting photocatalytic activity were also discussed. Photocatalytic desulfurization on the as-prepared Ag-BiVO4 samples using thiophene dissolved in n-octane as a model organosulfur compound was performed. It showed that the photocatalytic desulfurization on the as-prepared Ag-BiVO4 sample at pH=7 can be up to 95%, which existed as various size particles and had significant high surface area of 13.768 m2 g-1.

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

Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition

PubMed Central

2014-01-01

We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data. PACS 71.30. + h; 73.21.La; 78.47.jd PMID:25404877

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

NASA Astrophysics Data System (ADS)

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

2017-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2004-08-01

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

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

PubMed

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

2015-12-01

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

Thermochromic VO2 Films Deposited by RF Magnetron Sputtering Using V2O3 or V2O5 Targets

NASA Astrophysics Data System (ADS)

Shigesato, Yuzo; Enomoto, Mikiko; Odaka, Hidehumi

2000-10-01

Thermochromic monoclinic-tetragonal VO2 films were successfully deposited on glass substrates with high reproducibility by rf magnetron sputtering using V2O3 or V2O5 targets. In the case of reactive sputtering using a V-metal target, the VO2 films could be obtained only under the very narrow deposition conditions of the “transition region” where the deposition rate decreases drastically with increasing oxygen gas flow rate. In the case of a V2O3 target, polycrystalline VO2 films with a thickness of 400 to 500 nm were obtained by the introduction of oxygen gas [O2/(Ar+O2)=1--1.5%], whereas hydrogen gas [H2/(Ar+H2)=2.5--10%] was introduced in the case of a V2O5 target. Furthermore, the VO2 films were successfully grown heteroepitaxially on a single-crystal sapphire [α-Al2O3(001)] substrate, where the epitaxial relationship was confirmed to be VO2(010)[100]\\parallelAl2O3(001)[100], [010], [\\bar{1}\\bar{1}0] by an X-ray diffraction pole figure measurement. The resistivity ratio between semiconductor and metal phases for the heteroepitaxial VO2 films was much larger than the ratio of the polycrystalline films on glass substrates under the same deposition conditions.

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.

Elevated transition temperature in Ge doped VO2 thin films

NASA Astrophysics Data System (ADS)

Krammer, Anna; Magrez, Arnaud; Vitale, Wolfgang A.; Mocny, Piotr; Jeanneret, Patrick; Guibert, Edouard; Whitlow, Harry J.; Ionescu, Adrian M.; Schüler, Andreas

2017-07-01

Thermochromic GexV1-xO2+y thin films have been deposited on Si (100) substrates by means of reactive magnetron sputtering. The films were then characterized by Rutherford backscattering spectrometry (RBS), four-point probe electrical resistivity measurements, X-ray diffraction, and atomic force microscopy. From the temperature dependent resistivity measurements, the effect of Ge doping on the semiconductor-to-metal phase transition in vanadium oxide thin films was investigated. The transition temperature was shown to increase significantly upon Ge doping (˜95 °C), while the hysteresis width and resistivity contrast gradually decreased. The precise Ge concentration and the film thickness have been determined by RBS. The crystallinity of phase-pure VO2 monoclinic films was confirmed by XRD. These findings make the use of vanadium dioxide thin films in solar and electronic device applications—where higher critical temperatures than 68 °C of pristine VO2 are needed—a viable and promising solution.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

Sharpness and intensity modulation of the metal-insulator transition in ultrathin VO2 films by interfacial structure manipulation

NASA Astrophysics Data System (ADS)

McGee, Ryan; Goswami, Ankur; Pal, Soupitak; Schofield, Kalvin; Bukhari, Syed Asad Manzoor; Thundat, Thomas

2018-03-01

Vanadium dioxide (VO2) undergoes a structural transformation from monoclinic (insulator) to tetragonal (metallic) upon heating above 340 K, accompanied by abrupt changes to its electronic, optical, and mechanical properties. Not only is this transition scientifically intriguing, but there are also numerous applications in sensing, memory, and optoelectronics. Here we investigate the effect different substrates and the processing conditions have on the characteristics metal-insulator transition (MIT), and how the properties can be tuned for specific applications. VO2 thin films were grown on c -plane sapphire (0001) and p-type silicon <100 > by pulsed laser deposition. High-resolution x-ray diffraction along with transmission electron microscopy reveals textured epitaxial growth on sapphire by domain-matching epitaxy, while the presence of a native oxide layer on silicon prevented any preferential growth resulting in a polycrystalline film. An orientation relationship of <001 > (010)VO2||<11 ¯00 > (0001)Al 2O3 was established for VO2 grown on sapphire, while no such relationship was found for VO2 grown on silicon. Surface-energy minimization is the driving force behind grain growth, as the lowest energy VO2 plane grew on silicon, while on sapphire the desire for epitaxial growth was dominant. Polycrystallinity of films grown on silicon caused a weaker and less prominent MIT than observed on sapphire, whose MIT was higher in magnitude and steeper in slope. The position of the MIT was shown to depend on the competing effects of misfit strain and grain growth. Higher deposition temperatures caused an increase in the MIT, while compressive strain resulted in a decreased MIT.

Enhancement of electrical transport modulation in epitaxial VO2 nanowire field-effect transistor

NASA Astrophysics Data System (ADS)

Tanaka, Hidekazu; Chikanari, Masashi; Kanki, Teruo

Strongly correlated system vanadium dioxide VO2 has attracted widespread concerns from researchers as an exciting electronic material, due to the many intriguing features, especially metal-insulator transition (MIT) in vicinity of room temperature. In this work, we report a diverse geometry for high sensitivity in the transport modulation. By taking advantage of nanometer scale channel, instead of thin film channels, we demonstrated the enhancement of resistance modulation by applying gate voltage. Also we designed the insulating gate, consisting of high-k material Ta2O5/organic polymer parylene-C hybrid insulator. Such as this hybrid gate dielectric would effectively reduce interface deterioration of active channel oxide and provide sufficient carrier density. Moreover, benefited from the nanometer scale channel, the VO2 nanowire-based transistor could deliver a resistance modulation ratio over 8.5%, which are about 10 folds higher than that of the film case. Furthermore, this result is explained that in spite of the stronger field distribution in the edge parts of VO2 nanowire channel yielded little carrier density, the generated mobility modulation would biquadratic increase according to Brinkman-Rice picture as new finding.

ESA Science Archives, VO tools and remote Scientific Data reduction in Grid Architectures

NASA Astrophysics Data System (ADS)

Arviset, C.; Barbarisi, I.; de La Calle, I.; Fajersztejn, N.; Freschi, M.; Gabriel, C.; Gomez, P.; Guainazzi, M.; Ibarra, A.; Laruelo, A.; Leon, I.; Micol, A.; Parrilla, E.; Ortiz, I.; Osuna, P.; Salgado, J.; Stebe, A.; Tapiador, D.

2008-08-01

This paper presents the latest functionalities of the ESA Science Archives located at ESAC, Spain, in particular, the following archives : the ISO Data Archive (IDA {http://iso.esac.esa.int/ida}), the XMM-Newton Science Archive (XSA {http://xmm.esac.esa.int/xsa}), the Integral SOC Science Data Archive (ISDA {http://integral.esac.esa.int/isda}) and the Planetary Science Archive (PSA {http://www.rssd.esa.int/psa}), both the classical and the map-based Mars Express interfaces. Furthermore, the ESA VOSpec {http://esavo.esac.esa.int/vospecapp} spectra analysis tool is described, which allows to access and display spectral information from VO resources (both real observational and theoretical spectra), including access to Lines database and recent analysis functionalities. In addition, we detail the first implementation of RISA (Remote Interface for Science Analysis), a web service providing remote users the ability to create fully configurable XMM-Newton data analysis workflows, and to deploy and run them on the ESAC Grid. RISA makes fully use of the inter-operability provided by the SIAP (Simple Image Access Protocol) services as data input, and at the same time its VO-compatible output can directly be used by general VO-tools.

Postfabrication annealing effects on insulator-metal transitions in VO2 thin-film devices.

PubMed

Rathi, Servin; Lee, In-yeal; Park, Jin-Hyung; Kim, Bong-Jun; Kim, Hyun-Tak; Kim, Gil-Ho

2014-11-26

In order to investigate the metal-insulator transition characteristics of VO2 devices annealed in reducing atmosphere after device fabrication at various temperature, electrical, chemical, and thermal characteristics are measured and analyzed. It is found that the sheet resistance and the insulator-metal transition point, induced by both voltage and thermal, decrease when the devices are annealed from 200 to 500 °C. The V 2p3/2 peak variation in X-ray photoelectron spectroscopy (XPS) characterization verifies the reduction of thin-films. A decrease of the transition temperature from voltage hysteresis measurements further endorse the reducing effects of the annealing on VO2 thin-film.

Role of interfacial transition layers in VO2/Al2O3 heterostructures

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

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

2011-01-01

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

Mesoscopic Metal-Insulator Transition at Ferroelastic Domain Walls in VO2

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

Jones, Keith M; Kalinin, Sergei V; Kolmakov, Andrei

2010-01-01

The novel phenomena induced by symmetry breaking at homointerfaces between ferroic variants in ferroelectric and ferroelastic materials have attracted recently much attention. Using variable temperature scanning microwave microscopy, we demonstrate the mesoscopic strain-induced metal-insulator phase transitions in the vicinity of ferroelastic domain walls in the semiconductive VO2 that nucleated at temperatures as much as 10-12 C below bulk transition, resulting in the formation of conductive channels in the material. Density functional theory is used to rationalize the process low activation energy. This behavior, linked to the strain inhomogeneity inherent in ferroelastic materials, can strongly affect interpretation of phase-transition studies inmore » VO2 and similar materials with symmetry-lowering transitions, and can also be used to enable new generations of electronic devices though strain engineering of conductive and semiconductive regions.« less

Structural analysis of LaVO3 thin films under epitaxial strain

NASA Astrophysics Data System (ADS)

Meley, H.; Karandeep, Oberson, L.; de Bruijckere, J.; Alexander, D. T. L.; Triscone, J.-M.; Ghosez, Ph.; Gariglio, S.

2018-04-01

Rare earth vanadate perovskites exhibit a phase diagram in which two different types of structural distortions coexist: the strongest, the rotation of the oxygen octahedra, comes from the small tolerance factor of the perovskite cell (t = 0.88 for LaVO3) and the smaller one comes from inter-site d-orbital interactions manifesting as a cooperative Jahn-Teller effect. Epitaxial strain acts on octahedral rotations and crystal field symmetry to alter this complex lattice-orbit coupling. In this study, LaVO3 thin film structures have been investigated by X-ray diffraction and scanning transmission electron microscopy. The analysis shows two different orientations of octahedral tilt patterns, as well as two distinct temperature behaviors, for compressive and tensile film strain states. Ab initio calculations capture the strain effect on the tilt pattern orientation in agreement with experimental data.

Telemedicine using free voice over internet protocol (VoIP) technology.

PubMed

Miller, David J; Miljkovic, Nikola; Chiesa, Chad; Callahan, John B; Webb, Brad; Boedeker, Ben H

2011-01-01

Though dedicated videoteleconference (VTC) systems deliver high quality, low-latency audio and video for telemedical applications, they require expensive hardware and extensive infrastructure. The purpose of this study was to investigate free commercially available Voice over Internet Protocol (VoIP) software as a low cost alternative for telemedicine.

The Effect of Background Traffic Packet Size to VoIP Speech Quality

NASA Astrophysics Data System (ADS)

Triyason, Tuul; Kanthamanon, Prasert; Warasup, Kittipong; Yamsaengsung, Siam; Supattatham, Montri

VoIP is gaining acceptance into the corporate world especially, in small and medium sized business that want to save cost for gaining advantage over their competitors. The good voice quality is one of challenging task in deployment plan because VoIP voice quality was affected by packet loss and jitter delay. In this paper, we study the effect of background traffic packet size to voice quality. The background traffic was generated by Bricks software and the speech quality was assessed by MOS. The obtained result shows an interesting relationship between the voice quality and the number of TCP packets and their size. With the same amount of data smaller packets affect the voice's quality more than the larger packet.

Stoichiometric and Oxygen-Deficient VO2 as Versatile Hole Injection Electrode for Organic Semiconductors.

PubMed

Fu, Keke; Wang, Rongbin; Katase, Takayoshi; Ohta, Hiromichi; Koch, Norbert; Duhm, Steffen

2018-03-28

Using photoemission spectroscopy, we show that the surface electronic structure of VO 2 is determined by the temperature-dependent metal-insulator phase transition and the density of oxygen vacancies, which depends on the temperature and ultrahigh vacuum (UHV) conditions. The atomically clean and stoichiometric VO 2 surface is insulating at room temperature and features an ultrahigh work function of up to 6.7 eV. Heating in UHV just above the phase transition temperature induces the expected metallic phase, which goes in hand with the formation of oxygen defects (up to 6% in this study), but a high work function >6 eV is maintained. To demonstrate the suitability of VO 2 as hole injection contact for organic semiconductors, we investigated the energy-level alignment with the prototypical organic hole transport material N, N'-di(1-naphthyl)- N, N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB). Evidence for strong Fermi-level pinning and the associated energy-level bending in NPB is found, rendering an Ohmic contact for holes.

Optical constants, dispersion energy parameters and dielectric properties of ultra-smooth nanocrystalline BiVO4 thin films prepared by rf-magnetron sputtering

NASA Astrophysics Data System (ADS)

Sarkar, S.; Das, N. S.; Chattopadhyay, K. K.

2014-07-01

BiVO4 thin films have been prepared through radio frequency (rf) magnetron sputtering of a pre-fabricated BiVO4 target on ITO coated glass (ITO-glass) substrate and bare glass substrates. BiVO4 target material was prepared through solid-state reaction method by heating Bi2O3 and V2O5 mixture at 800 °C for 8 h. The films were characterized by X-ray diffraction, UV-Vis spectroscopy, LCR meter, field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. BiVO4 thin films deposited on the ITO-glass substrate are much smoother compared to the thin films prepared on bare glass substrate. The rms surface roughness calculated from the AFM images comes out to be 0.74 nm and 4.2 nm for the films deposited on the ITO-glass substrate and bare glass substrate for the deposition time 150 min respectively. Optical constants and energy dispersion parameters of these extra-smooth BiVO4 thin films have been investigated in detail. Dielectric properties of the BiVO4 thin films on ITO-glass substrate were also investigated. The frequency dependence of dielectric constant of the BiVO4 thin films has been measured in the frequency range from 20 Hz to 2 MHz. It was found that the dielectric constant increased from 145 to 343 at 20 Hz as the film thickness increased from 90 nm to 145 nm (deposition time increased from 60 min to 150 min). It shows higher dielectric constant compared to the literature value of BiVO4.

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

PubMed

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

2002-07-01

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

Revealing mechanism responsible for structural reversibility of single-crystal VO 2 nanorods upon lithiation/delithiation

DOE PAGES

Liu, Qi; Tan, Guoqiang; Wang, Peng; ...

2017-04-17

A pure phase of VO 2(B) nanorods have been synthesized through an energy-efficient microwave hydrothermal reaction and used as cathode materials of lithium ion batteries, which exhibit promising specific capacity (e.g., 130 mA h g -1 even after 100 charge/discharge cycles) and rate capacity (e.g., ~130 mA h g -1 at a high current of 400 mA g -1). The excellent cyclability originates from the structural reversibility of VO 2(B) upon lithiation/delithiation that is confirmed by the in situ high-energy synchrotron X-ray diffraction (HEXRD) and in situ x-ray adsorption near-edge spectroscopy (XANES) of the VO 2 nanorods in operating batterymore » cells. As a result, the real-time results reveal that discharge forces lithium ions to insert firstly into the tunnels with the largest size along b direction followed by the second largest tunnels along c direction, which is completely reversible in the charge process.« less

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

PubMed Central

2016-01-01

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

Revealing mechanism responsible for structural reversibility of single-crystal VO 2 nanorods upon lithiation/delithiation

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

Liu, Qi; Tan, Guoqiang; Wang, Peng

A pure phase of VO 2(B) nanorods have been synthesized through an energy-efficient microwave hydrothermal reaction and used as cathode materials of lithium ion batteries, which exhibit promising specific capacity (e.g., 130 mA h g -1 even after 100 charge/discharge cycles) and rate capacity (e.g., ~130 mA h g -1 at a high current of 400 mA g -1). The excellent cyclability originates from the structural reversibility of VO 2(B) upon lithiation/delithiation that is confirmed by the in situ high-energy synchrotron X-ray diffraction (HEXRD) and in situ x-ray adsorption near-edge spectroscopy (XANES) of the VO 2 nanorods in operating batterymore » cells. As a result, the real-time results reveal that discharge forces lithium ions to insert firstly into the tunnels with the largest size along b direction followed by the second largest tunnels along c direction, which is completely reversible in the charge process.« less

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.

Photocatalytic C–H Activation of Hydrocarbons over VO@g ...

EPA Pesticide Factsheets

A highly selective and sustainable method has been developed for the oxidation of methyl arenes and their analogues. The VO@g-C3N4 catalyst is very efficient in the C–H activation and oxygen insertion reaction resulting in formation of the corresponding carbonyl compounds and phenols. Prepared for submission to American Chemical Society (ACS) journal, ACS Sustainable Chemistry & Engineering.

Green Synthesis and Characterization of SmVO4 Nanoparticles in the Presence of Carbohydrates As Capping Agents with Investigation of Visible-Light Photocatalytic Properties

NASA Astrophysics Data System (ADS)

Eghbali-Arani, Mohammad; Sobhani-Nasab, Ali; Rahimi-Nasrabadi, Mehdi; Pourmasoud, Saeid

2018-03-01

SmVO4 nanoparticles were synthesized through a fast and simple procedure (green method). The effects of three parameters including temperature, type of capping agent, and concentration on the size and morphology behavior of SmVO4 nanoparticles were explored. The analysis of SmVO4 nanoparticles was performed through some techniques including, Fourier transform infrared spectroscopy, x-ray diffraction, energy dispersive x-ray microanalysis, scanning electron microscopy, transmission electron microscopy, thermogravimetry, differential thermal analysis, ultraviolet-visible spectroscopy, and vibrating sample magnetometers. The study of photocatalytic behaviour of the SmVO4 nanoparticles in various conditions has been carried out. The impacts of different factors such as dosage, grain size, and kind of pollutant (methylene blue = MB and methyl orange = MO) on the photocatalytic property of SmVO4 nanoparticles were assessed. The photocatalytic activities of SmVO4 catalysts were studied for the degradation of dye under visible light (λ > 400 nm).

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

NASA Astrophysics Data System (ADS)

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

2016-05-01

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

Luminescent GdVO4:Eu3+ functionalized mesoporous silica nanoparticles for magnetic resonance imaging and drug delivery.

PubMed

Huang, Shanshan; Cheng, Ziyong; Ma, Ping'an; Kang, Xiaojiao; Dai, Yunlu; Lin, Jun

2013-05-14

Luminescent GdVO4:Eu(3+) nanophosphor functionalized mesoporous silica nanoparticles (MSN) were prepared (denoted as GdVO4:Eu(3+)@MSN). The in vitro cytotoxicity tests show that the sample has good biocompatibility, which indicates that the nanocomposite could be a promising candidate for drug delivery. Flow cytometry and confocal laser scanning microscopy (CLSM) confirm that the sample can be effectively taken up by SKOV3 ovarian cancer cells and A549 lung adenocarcinoma cells. It was also shown that the GdVO4:Eu(3+)@MSN brightened the T1-weighted images and enhanced the r1 relaxivity of water protons, which suggested that they could act as T1 contrast agents for magnetic resonance (MR) imaging. It was found that the carriers present a pH-dependent drug release behavior for doxorubicin (DOX). The composites show a red emission under UV irradiation due to the GdVO4:Eu(3+) nanophosphors. Furthermore, the PL intensity of the composite shows correlation with the cumulative release of DOX. These results suggest that the composite can potentially act as a multifunctional drug carrier system with luminescent tagging, MR imaging and pH-controlled release property for DOX.

Localized phase change of VO2 films grown by atomic-layer deposition on InAlN/AlN/GaN heterostructures

NASA Astrophysics Data System (ADS)

Downey, Brian P.; Wheeler, Virginia D.; Meyer, David J.

2017-06-01

We demonstrate the thermally actuated phase change of VO2 films formed by atomic layer deposition and subsequent thermal annealing on InAlN/AlN/GaN heterostructures. To locally raise the device temperature above the VO2 semiconductor-metal transition temperature, a two-dimensional electron gas formed within the InAlN/AlN/GaN heterostructure was used as an integrated resistive heater. An ON/OFF resistance ratio of nearly 103 was achieved for 50 nm VO2 films over a temperature range of 25 to 105 °C. The time required to switch the VO2 film from high- to low-resistance states was shown to depend on the applied heater power, with sub-microsecond transition times achieved.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

Flexible 3D Fe@VO2 core-shell mesh: A highly efficient and easy-recycling catalyst for the removal of organic dyes.

PubMed

Li, Jing; Wang, Ruoqi; Su, Zhen; Zhang, Dandan; Li, Heping; Yan, Youwei

2018-10-01

Nowadays, it is extremely urgent to search for efficient and effective catalysts for water purification due to the severe worldwide water-contamination crises. Here, 3D Fe@VO 2 core-shell mesh, a highly efficient catalyst toward removal of organic dyes with excellent recycling ability in the dark is designed and developed for the first time. This novel core-shell structure is actually 304 stainless steel mesh coated by VO 2 , fabricated by an electrophoretic deposition method. In such a core-shell structure, Fe as the core allows much easier separation from the water, endowing the catalyst with a flexible property for easy recycling, while VO 2 as the shell is highly efficient in degradation of organic dyes with the addition of H 2 O 2 . More intriguingly, the 3D Fe@VO 2 core-shell mesh exhibits favorable performance across a wide pH range. The 3D Fe@VO 2 core-shell mesh can decompose organic dyes both in a light-free condition and under visible irradiation. The possible catalytic oxidation mechanism of Fe@VO 2 /H 2 O 2 system is also proposed in this work. Considering its facile fabrication, remarkable catalytic efficiency across a wide pH range, and easy recycling characteristic, the 3D Fe@VO 2 core-shell mesh is a newly developed high-performance catalyst for addressing the universal water crises. Copyright © 2018 Elsevier B.V. All rights reserved.

In situ probing of doping- and stress-mediated phase transitions in a single-crystalline VO2 nanobeam by spatially resolved Raman spectroscopy

NASA Astrophysics Data System (ADS)

Chang, Sung-Jin; Park, Jong Bae; Lee, Gaehang; Kim, Hae Jin; Lee, Jin-Bae; Bae, Tae-Sung; Han, Young-Kyu; Park, Tae Jung; Huh, Yun Suk; Hong, Woong-Ki

2014-06-01

We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO2 nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO2 nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO2 nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under air. The triclinic T phase of the VO2 nanobeam upon heating under hydrogen gas transformed to the R phase and this R phase was stabilized even at room temperature in air after sample cooling. In particular, after the VO2 nanobeam with the R phase was annealed at approximately 250 °C in air, it exhibited the monoclinic M1 phase (not the T phase) at room temperature during heating and cooling cycles. These results were attributed to the interplay between hydrogen doping and stress associated with nanobeam-substrate interactions. Our study has important implications for engineering metal-insulator transition properties and developing functional devices based on VO2 nanostructures through doping and stress.We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO2 nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO2 nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO2 nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under

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. © Georg Thieme Verlag KG Stuttgart · New York.

Porous VO(x)N(y) nanoribbons supported on CNTs as efficient and stable non-noble electrocatalysts for the oxygen reduction reaction.

PubMed

Huang, K; Bi, K; Lu, Y K; Zhang, R; Liu, J; Wang, W J; Tang, H L; Wang, Y G; Lei, M

2015-11-30

Novel nanocomposites of carbon nanotubes supported porous VO(x)N(y) nonoribbons (VO(x)N(y)-CNTs) have been synthesized by the annealing of the sol-gel mixture of CNTs and V2O5 under NH3 atmosphere as well as the ageing process in air. Besides the morphological and structural characterizations revealed by TEM, SEAD, EDS, XRD and XPS measurements, typical electrochemical tests including cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry have been employed to determine the oxygen reduction reaction (ORR) performance of VO(x)N(y)-CNTs. Inspiringly, the results indicate that VO(x)N(y)-CNTs catalyst exhibits a 0.4 mA/cm(2) larger diffusion-limited current density, a 0.10  V smaller onset potential value, a 10.73% less of ORR current decay and an excellent methanol-tolerance compared with commercial Pt/C catalyst. Therefore, we have reasonable grounds to believe that this new VO(x)N(y)-CNTs nanocomposites can be regarded as a promising non-precious methanol-tolerant ORR catalyst candidate for alkaline fuel cells.

Metal-Insulator crossover in SrVO3 thin film

NASA Astrophysics Data System (ADS)

Wang, Gaomin; Wang, Zhen; Saghayezhian, Mohammad; Chen, Chen; Chen, Lina; Guo, Hangwen; Zhu, Yimei; Zhang, Jiandi

Paramagnetic metallic oxide SrVO3 (SVO) represents a prototype system for the study of the mechanism behind thickness-induced metal-to-insulator transition (MIT) or crossover due to its simple structure and itinerancy. Here SrVO3 thin films with different thicknesses were obtained through the layer-by-layer growth by laser Molecular Beam Epitaxy on SrTiO3 (001) surface. Ultraviolet Photoemission Spectroscopy and Scanning Tunneling Spectroscopy measurements confirm a MIT at the thickness of 3 unit cell, while atomically resolved Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy analysis reveal the depletion of Sr, change of V-valence and expansion of the out-of-plane lattice constant in the first three unit cell above the interface, thus different from the rest of the films. The existence of significant amount of oxygen vacancies is proposed, which is also supported by X-ray Photoelectron Spectroscopy, therefore providing a possible explanation of MIT. This work is primarily supported by U.S. DOE under Grant No. DOE DE-SC0002136. G.W. was supported by U.S. NSF under Grant No. DMR 16088865.

Effect of annealing temperature on VO2(M)/ITO film nanomaterials for thermochromic smart windows application and study its contact angle

NASA Astrophysics Data System (ADS)

Shaban, Mohamed; Rabia, Mohamed; Ezzat, Sara; Mansour, Naglaa; Saeed, Ebtisam; Sayyah, Said M.

2018-01-01

Metastable phase VO2(B) film coated ITO glass was prepared using cyclic potentiometric device utilizing VOSO4 and H2SO4 solution. The optimum conditions for the deposition of the nanostructured VO2(B) film were determined using cathodic peak current density (Ipc) values. Ipc values increase with increasing both VOSO4 and H2SO4 concentrations and then decrease with further increasing the concentrations. Also, monoclinic phase VO2(M)/ITO film was prepared from VO2(B)/ITO film under the effect of annealing temperatures from 550°C to 750°C. Different analyses have been carried out to confirm the chemical, morphological, and crystal structure of the nanostructured VO2(M)/ITO film. From the XRD analysis, the crystallinity increases with the increasing of annealing temperature from 550°C to 750°C. The optical transmittance spectrum was ˜97% for the film annealed at 650°C. Also, the critical thermochromic temperature (Tc) of the optimized film was ˜47.5°C that measured using cooling and heating modes. Finally, the wettability of the VO2(M)/ITO film at different annealing temperature (550°C to 750°C) was studied, in which the contact angle increases from 81 deg to 92 deg with increasing annealing temperatures from 550°C to 750°C, respectively.

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

VO-ESD: a virtual observatory approach to describe the geomagnetic field temporal variations with application to Swarm data

NASA Astrophysics Data System (ADS)

Saturnino, Diana; Langlais, Benoit; Amit, Hagay; Mandea, Mioara; Civet, François; Beucler, Éric

2017-04-01

A complete description of the main geomagnetic field temporal variation is crucial to understand dynamics in the core. This variation, termed secular variation (SV), is known with high accuracy at ground magnetic observatory locations. However the description of its spatial variability is hampered by the globally uneven distribution of the observatories. For the past two decades a global coverage of the field changes has been allowed by satellites. Their surveys of the geomagnetic field have been used to derive and improve global spherical harmonic (SH) models through some strict data selection schemes to minimise external field contributions. But discrepancies remain between ground measurements and field predictions by these models. Indeed, the global models do not reproduce small spatial scales of the field temporal variations. To overcome this problem we propose a modified Virtual Observatory (VO) approach by defining a globally homogeneous mesh of VOs at satellite altitude. With this approach we directly extract time series of the field and its temporal variation from satellite measurements as it is done at observatory locations. As satellite measurements are acquired at different altitudes a correction for the altitude is needed. Therefore, we apply an Equivalent Source Dipole (ESD) technique for each VO and each given time interval to reduce all measurements to a unique location, leading to time series similar to those available at ground magnetic observatories. Synthetic data is first used to validate the new VO-ESD approach. Then, we apply our scheme to measurements from the Swarm mission. For the first time, a 2.5 degrees resolution global mesh of VO times series is built. The VO-ESD derived time series are locally compared to ground observations as well as to satellite-based model predictions. The approach is able to describe detailed temporal variations of the field at local scales. The VO-ESD time series are also used to derive global SH models. Without

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

The extended TRIP supporting VoIP routing reservation with distributed QoS

NASA Astrophysics Data System (ADS)

Wang, Furong; Wu, Ye

2004-04-01

In this paper, an existing protocol, i.e. TRIP (Telephony Routing over IP) is developed to provide distributed QoS when making resource reservations for VoIP services such as H.323, SIP. Enhanced LSs (location servers) are deployed in ITADs (IP Telephony Administrative Domains) to take in charge of intra-domain routing policy because of small propagation price. It is an easy way to find an IP telephone route for intra-domain VoIP media association and simultaneously possess intra-domain load balancing features. For those routing reservations bridging domains, inter-domain routing policy is responsible for finding the shortest inter-domain route with enough resources. I propose the routing preference policy based on QoS price when the session traffic is shaped by a token bucket, related QoS messages, and message cooperation.

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.

Photocatalytic generation of hydrogen by core-shell WO3/BiVO4 nanorods with ultimate water splitting efficiency

PubMed Central

Pihosh, Yuriy; Turkevych, Ivan; Mawatari, Kazuma; Uemura, Jin; Kazoe, Yutaka; Kosar, Sonya; Makita, Kikuo; Sugaya, Takeyoshi; Matsui, Takuya; Fujita, Daisuke; Tosa, Masahiro; Kondo, Michio; Kitamori, Takehiko

2015-01-01

Efficient photocatalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Here we show that the effectiveness of each process can be separately maximized in a nanostructured heterojunction with extremely thin absorber layer. We demonstrate this concept on WO3/BiVO4+CoPi core-shell nanostructured photoanode that achieves near theoretical water splitting efficiency. BiVO4 is characterized by a high recombination rate of photogenerated carriers that have much shorter diffusion length than the thickness required for sufficient light absorption. This issue can be resolved by the combination of BiVO4 with more conductive WO3 nanorods in a form of core-shell heterojunction, where the BiVO4 absorber layer is thinner than the carrier diffusion length while it’s optical thickness is reestablished by light trapping in high aspect ratio nanostructures. Our photoanode demonstrates ultimate water splitting photocurrent of 6.72 mA cm−2 under 1 sun illumination at 1.23 VRHE that corresponds to ~90% of the theoretically possible value for BiVO4. We also demonstrate a self-biased operation of the photoanode in tandem with a double-junction GaAs/InGaAsP photovoltaic cell with stable water splitting photocurrent of 6.56 mA cm−2 that corresponds to the solar to hydrogen generation efficiency of 8.1%. PMID:26053164

Photocatalytic generation of hydrogen by core-shell WO3/BiVO4 nanorods with ultimate water splitting efficiency

NASA Astrophysics Data System (ADS)

Pihosh, Yuriy; Turkevych, Ivan; Mawatari, Kazuma; Uemura, Jin; Kazoe, Yutaka; Kosar, Sonya; Makita, Kikuo; Sugaya, Takeyoshi; Matsui, Takuya; Fujita, Daisuke; Tosa, Masahiro; Kondo, Michio; Kitamori, Takehiko

2015-06-01

Efficient photocatalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Here we show that the effectiveness of each process can be separately maximized in a nanostructured heterojunction with extremely thin absorber layer. We demonstrate this concept on WO3/BiVO4+CoPi core-shell nanostructured photoanode that achieves near theoretical water splitting efficiency. BiVO4 is characterized by a high recombination rate of photogenerated carriers that have much shorter diffusion length than the thickness required for sufficient light absorption. This issue can be resolved by the combination of BiVO4 with more conductive WO3 nanorods in a form of core-shell heterojunction, where the BiVO4 absorber layer is thinner than the carrier diffusion length while it’s optical thickness is reestablished by light trapping in high aspect ratio nanostructures. Our photoanode demonstrates ultimate water splitting photocurrent of 6.72 mA cm-2 under 1 sun illumination at 1.23 VRHE that corresponds to ~90% of the theoretically possible value for BiVO4. We also demonstrate a self-biased operation of the photoanode in tandem with a double-junction GaAs/InGaAsP photovoltaic cell with stable water splitting photocurrent of 6.56 mA cm-2 that corresponds to the solar to hydrogen generation efficiency of 8.1%.

Atomic Origins of Monoclinic-Tetragonal (Rutile) Phase Transition in Doped VO2 Nanowires.

PubMed

Asayesh-Ardakani, Hasti; Nie, Anmin; Marley, Peter M; Zhu, Yihan; Phillips, Patrick J; Singh, Sujay; Mashayek, Farzad; Sambandamurthy, Ganapathy; Low, Ke-Bin; Klie, Robert F; Banerjee, Sarbajit; Odegard, Gregory M; Shahbazian-Yassar, Reza

2015-11-11

There has been long-standing interest in tuning the metal-insulator phase transition in vanadium dioxide (VO2) via the addition of chemical dopants. However, the underlying mechanisms by which doping elements regulate the phase transition in VO2 are poorly understood. Taking advantage of aberration-corrected scanning transmission electron microscopy, we reveal the atomistic origins by which tungsten (W) dopants influence the phase transition in single crystalline WxV1-xO2 nanowires. Our atomically resolved strain maps clearly show the localized strain normal to the (122̅) lattice planes of the low W-doped monoclinic structure (insulator). These strain maps demonstrate how anisotropic localized stress created by dopants in the monoclinic structure accelerates the phase transition and lead to relaxation of structure in tetragonal form. In contrast, the strain distribution in the high W-doped VO2 structure is relatively uniform as a result of transition to tetragonal (metallic) phase. The directional strain gradients are furthermore corroborated by density functional theory calculations that show the energetic consequences of distortions to the local structure. These findings pave the roadmap for lattice-stress engineering of the MIT behavior in strongly correlated materials for specific applications such as ultrafast electronic switches and electro-optical sensors.

Roles of Bi, M and VO{sub 4} tetrahedron in photocatalytic properties of novel Bi{sub 0.5}M{sub 0.5}VO{sub 4} (M=La, Eu, Sm and Y) solid solutions for overall water splitting

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

Liu Hui; Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University, shanghai 200240; Faculty of Engineering Sciences, Kyushu University, Fukuoka 816-8580

2012-02-15

Novel Bi{sub 0.5}M{sub 0.5}VO{sub 4} (BMV; M=La, Eu, Sm and Y) solid solutions were prepared and studied in this paper. All the samples were proved to produce H{sub 2} and O{sub 2} simultaneously from pure water under the irradiation of UV light. M-O bond lengths were proved to increase with M cations by refining cell parameters and atomic positions. Besides, band gaps, energy gaps and photocatalytic activities of BMV also changed with M cations. Both of M-O and V-O bond lengths were suggested to account for this phenomenon. Inactive A{sub 0.5}Y{sub 0.5}VO{sub 4} (A=La, Ce) for water splitting proved incorporationmore » of Bi rather than distortion of VO{sub 4} tetrahedron was a critical factor for improving efficiency of overall water splitting by facilitating the generation of electron and hole with lighter effective masses. Replacement of Bi by M cations not only gave indirect effect on band structure but also raised position of conduction band minimum to meet requirement of H{sub 2} production. - Graphical abstract: Novel Bi{sub 0.5}M{sub 0.5}VO{sub 4} (M=La, Eu, Sm and Y) solid solutions showed the high and stable photocatalytic activities for overall water splitting with their crystal radii of M elements. Highlights: Black-Right-Pointing-Pointer BMV solid solutions were novel highly efficient V-based photocatalysts for overall water splitting. Black-Right-Pointing-Pointer Photocatalytic activity of BMV solid solution related to the effective ionic radii of M cations. Black-Right-Pointing-Pointer Incorporation of Bi is one of key factors for the highly efficient activity of BMV solid solution. Black-Right-Pointing-Pointer Incorporation of Y is dispensable for H{sub 2} production.« less

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.

Voice over Internet Protocol (VoIP) Technology as a Global Learning Tool: Information Systems Success and Control Belief Perspectives

ERIC Educational Resources Information Center

Chen, Charlie C.; Vannoy, Sandra

2013-01-01

Voice over Internet Protocol- (VoIP) enabled online learning service providers struggling with high attrition rates and low customer loyalty issues despite VoIP's high degree of system fit for online global learning applications. Effective solutions to this prevalent problem rely on the understanding of system quality, information quality, and…

47 CFR 52.34 - Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS...

Code of Federal Regulations, 2012 CFR

2012-10-01

... and from interconnected VoIP or Internet-based TRS providers. 52.34 Section 52.34 Telecommunication... Portability § 52.34 Obligations regarding local number porting to and from interconnected VoIP or Internet... customer's or a Registered Internet-based TRS User's valid number portability request, as it is defined in...

47 CFR 52.34 - Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS...

Code of Federal Regulations, 2013 CFR

2013-10-01

... and from interconnected VoIP or Internet-based TRS providers. 52.34 Section 52.34 Telecommunication... Portability § 52.34 Obligations regarding local number porting to and from interconnected VoIP or Internet... customer's or a Registered Internet-based TRS User's valid number portability request, as it is defined in...

47 CFR 52.34 - Obligations regarding local number porting to and from interconnected VoIP or Internet-based TRS...

Code of Federal Regulations, 2014 CFR

2014-10-01

... and from interconnected VoIP or Internet-based TRS providers. 52.34 Section 52.34 Telecommunication... Portability § 52.34 Obligations regarding local number porting to and from interconnected VoIP or Internet... customer's or a Registered Internet-based TRS User's valid number portability request, as it is defined in...

Bismuth zinc vanadate, BiZn{sub 2}VO{sub 6}: New crystal structure type and electronic structure

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

Eliziario Nunes, Sayonara; Department of Materials Engineering, Federal University of São Carlos, 13565-905 São Carlos, SP; Wang, Chun-Hai

2015-02-15

We report a combined experimental and computational study of the crystal structure and electronic properties of bismuth zinc vanadate, BiZn{sub 2}VO{sub 6}, known for its visible light photocatalytic activity. The crystal structure has been solved from laboratory powder X-ray diffraction data using the repeated minimisations from random starting values method. BiZn{sub 2}VO{sub 6} adopts a new structure type, based on the following building blocks: corner- and edge-sharing ZnO{sub 4} tetrahedra, ZnO{sub 6} octahedra and VO{sub 4} tetrahedra, and Bi{sub 2}O{sub 12} dimers. It is the only known member of the BiM{sub 2}AO{sub 6} (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu;more » A=V, P, As) family which does not appear to be structurally closely related to others. The electronic structure of BiZn{sub 2}VO{sub 6}, calculated by DFT methods, shows that it is an indirect gap semiconductor with a calculated band gap of 1.6 eV, which compares favourably to the experimentally measured value of 2.4 eV. - Graphical abstract: The crystal structure of BiZn{sub 2}VO{sub 6}, a new structure type in the BiM{sub 2}AO{sub 6} (M=Mg, Ca, Cd, Cu, Pb, Mn, Zn; A=V, P, As) family. - Highlights: • Structure solution from PXRD data by repeated minimisations from random starting values. • New structure type in the BiM{sub 2}AO{sub 6} (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family. • Electronic structure calculation.« less

Voltage- and current-activated metal-insulator transition in VO2-based electrical switches: a lifetime operation analysis.

PubMed

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 VO 2 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 VO 2 switches in both voltage- and current-controlled modes. We demonstrated enhanced lifetime operation of current-controlled VO 2 -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 VO 2 -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.

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

NASA Astrophysics Data System (ADS)

Bayati, Mohammad Reza

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

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.

Integrating a Semitransparent, Fullerene-Free Organic Solar Cell in Tandem with a BiVO4 Photoanode for Unassisted Solar Water Splitting.

PubMed

Peng, Yuelin; Govindaraju, Gokul V; Lee, Dong Ki; Choi, Kyoung-Shin; Andrew, Trisha L

2017-07-12

We report an unassisted solar water splitting system powered by a diketopyrrolopyrrole (DPP)-containing semitransparent organic solar cell. Two major merits of this fullerene-free solar cell enable its integration with a BiVO 4 photoanode. First is the high open circuit voltage and high fill factor displayed by this single junction solar cell, which yields sufficient power to effect water splitting when serially connected to an appropriate electrode/catalyst. Second, the wavelength-resolved photoaction spectrum of the DPP-based solar cell has minimal overlap with that of the BiVO 4 photoanode, thus ensuring that light collection across these two components can be optimized. The latter feature enables a new water splitting device configuration wherein the solar cell is placed first in the path of incident light, before the BiVO 4 photoanode, although BiVO 4 has a wider bandgap. This configuration is accessed by replacing the reflective top electrode of the standard DPP-based solar cell with a thin metal film and an antireflection layer, thus rendering the solar cell semitransparent. In this configuration, incident light does not travel through the aqueous electrolyte to reach the solar cell or photoanode, and therefore, photon losses due to the scattering of water are reduced. Moreover, this new configuration allows the BiVO 4 photoanode to be back-illuminated, i.e., through the BiVO 4 /back contact interface, which leads to higher photocurrents compared to front illumination. The combination of a semitransparent single-junction solar cell and a BiVO 4 photoanode coated with oxygen evolution catalysts in a new device configuration yielded an unassisted solar water splitting system with a solar-to-hydrogen conversion efficiency of 2.2% in water.

Temperature dependence of laser induced insulator-metal transition in VO2

NASA Astrophysics Data System (ADS)

Wang, Siming; Bar-Ad, Shimshon; Ramirez, Juan Gabriel; Huppert, Dan; Schuller, Ivan K.

2013-03-01

We performed optical pump-probe experiments on VO2 thin films with low laser fluence at temperatures ranging across the insulator-metal transition (IMT). At room temperature, the reflectivity of VO2 increases in the first 400-500 fs when pumped by 150 fs laser pulses. An exponential decay of the reflectivity is observed in the following 1 ps. Interestingly, as the temperature approaches the transition temperature (340 K), the reflectivity shows a second increase on an 80 ps time scale following the exponential decay, indicating an IMT. We propose that the decay of the reflectivity is due to electron-phonon thermalization, which raises the phonon temperature and causes a superheating of the lattice. This process provides the latent heat and induces the IMT on the 80 ps time scale. The coexistence of the insulating and metallic phases is observed in the reflectivity measurements for temperatures above 340 K. This work is supported by the Air Force Office of Scientific Research No. FA9550-12-1-0381.

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 (VO 2 ) 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 VO 2 . 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.

Efficient carbon dots/NiFe-layered double hydroxide/BiVO4 photoanodes for photoelectrochemical water splitting

NASA Astrophysics Data System (ADS)

Lv, Xiaowei; Xiao, Xin; Cao, Minglei; Bu, Yi; Wang, Chuanqing; Wang, Mingkui; Shen, Yan

2018-05-01

Modification of semiconductor photoanodes with oxygen evolution catalyst (OEC) is an effective approach for improving photoelectrochemical (PEC) water splitting efficiency. In the configuration, how to increase the activity of OEC is crucial to further improve PEC performance. Herein, a ternary photoanode system was designed to enhance PEC efficiency of photoelectrodes through introducing carbon dots (CDs), NiFe-layered double hydroxide (NiFe-LDH) nanosheets on BiVO4 particles. Systematic research shows that NiFe-LDH serves as an OEC which accelerates oxygen evolution kinetics, while the introduction of CDs can further reduce charge transfer resistance and overpotential for oxygen evolution. Under the synergistic effect of NiFe-LDH and CDs, the photocurrent and incident photon to current conversion efficiency (IPCE) of the resulting CDs/NiFe-LDH/BiVO4 photoanode is improved significantly than those of the NiFe-LDH/BiVO4 electrode. Consequently, such a ternary heterostructure could be an alternative way to further enhance PEC water splitting performance.

Roles of strain and domain boundaries on the phase transition stability of VO2 thin films

NASA Astrophysics Data System (ADS)

Jian, Jie; Chen, Aiping; Chen, Youxing; Zhang, Xinghang; Wang, Haiyan

2017-10-01

The fundamental phase transition mechanism and the stability of the semiconductor-to-metal phase transition properties during multiple thermal cycles have been investigated on epitaxial vanadium dioxide (VO2) thin films via both ex situ heating and in situ heating by transmission electron microscopy (TEM). VO2 thin films were deposited on c-cut sapphire substrates by pulsed laser deposition. Ex situ studies show the broadening of transition sharpness (ΔT) and the width of thermal hysteresis (ΔH) after 60 cycles. In situ TEM heating studies reveal that during thermal cycles, large strain was accumulated around the domain boundaries, which was correlated with the phase transition induced lattice constant change and the thermal expansion. It suggests that the degradation of domain boundary structures in the VO2 films not only caused the transition property reduction (e.g., the decrease in ΔT and ΔH) but also played an important role in preventing the film from fracture during thermal cycles.

A fundamental mode Nd:GdVO4 laser pumped by a large aperture 808 nm VCSEL

NASA Astrophysics Data System (ADS)

Hao, Y. Q.; Ma, J. L.; Yan, C. L.; Liu, G. J.; Ma, X. H.; Gong, J. F.; Feng, Y.; Wei, Z. P.; Wang, Y. X.; Zhao, Y. J.

2013-05-01

A fundamental mode Nd:GdVO4 laser pumped by a vertical cavity surface emitting laser (VCSEL) is experimentally demonstrated. The VCSEL has a circular output-beam which makes it easier for it to be directly coupled to a Nd:GdVO4 microcrystal. In our research, a large aperture 808 nm VCSEL, with a multi-ring-shaped aperture (MRSA) and an almost Gaussian-shaped far-field profile, is used as the pumping source. Experimental results for the Nd:GdVO4 laser pumped by the VCSEL are presented. The maximum output peak power of 0.754 W is obtained under a pump peak power of 1.3 W, and the corresponding opto-optic conversion efficiency is 58.1%. The average slope efficiency is 65.8% from the threshold pump power of 0.2 W to the pump power of 1.3 W. The laser beam quality factors are measured to be {M}x2=1.2 0 and {M}y2=1.1 5.

Strain Effects in Epitaxial VO2 Thin Films on Columnar Buffer-Layer TiO2/Al2O3 Virtual Substrates.

PubMed

Breckenfeld, Eric; Kim, Heungsoo; Burgess, Katherine; Charipar, Nicholas; Cheng, Shu-Fan; Stroud, Rhonda; Piqué, Alberto

2017-01-18

Epitaxial VO 2 /TiO 2 thin film heterostructures were grown on (100) (m-cut) Al 2 O 3 substrates via pulsed laser deposition. We have demonstrated the ability to reduce the semiconductor-metal transition (SMT) temperature of VO 2 to ∼44 °C while retaining a 4 order of magnitude SMT using the TiO 2 buffer layer. A combination of electrical transport and X-ray diffraction reciprocal space mapping studies help examine the specific strain states of VO 2 /TiO 2 /Al 2 O 3 heterostructures as a function of TiO 2 film growth temperatures. Atomic force microscopy and transmission electron microscopy analyses show that the columnar microstructure present in TiO 2 buffer films is responsible for the partially strained VO 2 film behavior and subsequently favorable transport characteristics with a lower SMT temperature. Such findings are of crucial importance for both the technological implementation of the VO 2 system, where reduction of its SMT temperature is widely sought, as well as the broader complex oxide community, where greater understanding of the evolution of microstructure, strain, and functional properties is a high priority.

A facile hydrothermal approach to synthesize rGO/BiVO4 photocatalysts for visible light induced degradation of RhB dye

NASA Astrophysics Data System (ADS)

Pal, Shreyasi; Dutta, Shibsankar; De, Sukanta

2018-05-01

RGO/BiVO4 composites were synthesized by a simple hydrothermal method. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) and surface analysis (BET). The photocatalytic activity of the as-prepared samples was evaluated by studying the degradation of model dyes rhodamine B (RhB) under visible light. The prepared rGO/BiVO4 composites exhibited higher photocatalytic activity for the degradation of RhB with a maximum removal rate of 86% under visible light irradiation under visible-light irradiation than pure BiVO4 nanoparticles (63%). This behavior could be associated to their higher specific surface area (BET), increased light absorption intensity and the degradation of electron-hole pair recombination in BiVO4 with the introduction of the rGO.

Green synthesis of BiVO4 nanorods via aqueous extracts of Callistemon viminalis

NASA Astrophysics Data System (ADS)

Mohamed, H. E. A.; Sone, B. T.; Fuku, X. G.; Dhlamini, M. S.; Maaza, M.

2018-05-01

Nowadays, the development of efficient green chemistry methods for synthesis of metal oxides nanoparticles has become a major focus of researchers. These methods are being investigated in order to find an eco-friendly technique for production of well-characterized nanoparticles. In this contribution we report for the first time, the synthesis and structural characterization of n-type Bismuth vanadate (BiVO4) nanoparticles using aqueous extracts of Callistemon viminalis as a chelating agent. To ascertain the formation of BiVO4, X-Ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Electron Dispersion X-ray Spectroscopy (EDS), Fourier Transform Infra-red Spectroscopy (FTIR), and Photoluminescence spectroscopy (PL) were carried out.

Thymoquinone suppresses migration of LoVo human colon cancer cells by reducing prostaglandin E2 induced COX-2 activation.

PubMed

Hsu, Hsi-Hsien; Chen, Ming-Cheng; Day, Cecilia Hsuan; Lin, Yueh-Min; Li, Shin-Yi; Tu, Chuan-Chou; Padma, Viswanadha Vijaya; Shih, Hui-Nung; Kuo, Wei-Wen; Huang, Chih-Yang

2017-02-21

To identify potential anti-cancer constituents in natural extracts that inhibit cancer cell growth and migration. Our experiments used high dose thymoquinone (TQ) as an inhibitor to arrest LoVo (a human colon adenocarcinoma cell line) cancer cell growth, which was detected by cell proliferation assay and immunoblotting assay. Low dose TQ did not significantly reduce LoVo cancer cell growth. Cyclooxygenase 2 (COX-2) is an enzyme that is involved in the conversion of arachidonic acid into prostaglandin E2 (PGE2) in humans. PGE2 can promote COX-2 protein expression and tumor cell proliferation and was used as a control. Our results showed that 20 μmol/L TQ significantly reduced human LoVo colon cancer cell proliferation. TQ treatment reduced the levels of p-PI3K, p-Akt, p-GSK3β, and β-catenin and thereby inhibited the downstream COX-2 expression. Results also showed that the reduction in COX-2 expression resulted in a reduction in PGE2 levels and the suppression of EP2 and EP4 activation. Further analysis showed that TG treatment inhibited the nuclear translocation of β-catenin in LoVo cancer cells. The levels of the cofactors LEF-1 and TCF-4 were also decreased in the nucleus following TQ treatment in a dose-dependent manner. Treatment with low dose TQ inhibited the COX-2 expression at the transcriptional level and the regulation of COX-2 expression efficiently reduced LoVo cell migration. The results were further verified in vivo by confirming the effects of TQ and/or PGE2 using tumor xenografts in nude mice. TQ inhibits LoVo cancer cell growth and migration, and this result highlights the therapeutic advantage of using TQ in combination therapy against colorectal cancer.

Ultrafast photo-induced dynamics across the metal-insulator transition of VO2

NASA Astrophysics Data System (ADS)

Wang, Siming; Ramírez, Juan Gabriel; Jeffet, Jonathan; Bar-Ad, Shimshon; Huppert, Dan; Schuller, Ivan K.

2017-04-01

The transient reflectivity of VO2 films across the metal-insulator transition clearly shows that with low-fluence excitation, when insulating domains are dominant, energy transfer from the optically excited electrons to the lattice is not instantaneous, but precedes the superheating-driven expansion of the metallic domains. This implies that the phase transition in the coexistence regime is lattice-, not electronically-driven, at weak laser excitation. The superheated phonons provide the latent heat required for the propagation of the optically-induced phase transition. For VO2 this transition path is significantly different from what has been reported in the strong-excitation regime. We also observe a slow-down of the superheating-driven expansion of the metallic domains around the metal-insulator transition, which is possibly due to the competition among several co-existing phases, or an emergent critical-like behavior.

Estimating the total energy demand for supra-maximal exercise using the VO2-power regression from an incremental exercise test.

PubMed

Aisbett, B; Le Rossignol, P

2003-09-01

The VO2-power regression and estimated total energy demand for a 6-minute supra-maximal exercise test was predicted from a continuous incremental exercise test. Sub-maximal VO2-power co-ordinates were established from the last 40 seconds (s) of 150-second exercise stages. The precision of the estimated total energy demand was determined using the 95% confidence interval (95% CI) of the estimated total energy demand. The linearity of the individual VO2-power regression equations was determined using Pearson's correlation coefficient. The mean 95% CI of the estimated total energy demand was 5.9 +/- 2.5 mL O2 Eq x kg(-1) x min(-1), and the mean correlation coefficient was 0.9942 +/- 0.0042. The current study contends that the sub-maximal VO2-power co-ordinates from a continuous incremental exercise test can be used to estimate supra-maximal energy demand without compromising the precision of the accumulated oxygen deficit (AOD) method.

Hierarchically porous Li3VO4/C nanocomposite as an advanced anode material for high-performance lithium-ion capacitors

NASA Astrophysics Data System (ADS)

Xu, Xuena; Niu, Feier; Zhang, Dapeng; Chu, Chenxiao; Wang, Chunsheng; Yang, Jian; Qian, Yitai

2018-04-01

Lithium-ion capacitors, as a hybrid electrochemical energy storage device, realize high specific energy and power density within one device, thus attracting extensive attention. Here, hierarchically porous Li3VO4/C nanocomposite is prepared by a solvo-thermal reaction, followed with a post-annealing process. This composite has macropores at the center and mesopores in the wall, thus effectively promoting electrolyte penetration and structure stability upon cycling simultaneously. Compared to mesoporous Li3VO4, the enhanced rate capability and specific capacity of hierarchically porous Li3VO4/C indicate the synergistic effect of mesopores and macropores. Inspired by these results, this composite is coupled with mesoporous carbon (CMK-3) for lithium-ion capacitors, generating a specific energy density of 105 Wh kg-1 at a power density of 188 W kg-1. Even if the power density increases to 9.3 kW kg-1, the energy density still remains 62 Wh kg-1. All these results demonstrate the promising potential of hierarchically porous Li3VO4 in lithium ion capacitors.

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

NASA Astrophysics Data System (ADS)

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

2017-05-01

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

Energy star compliant voice over internet protocol (VoIP) telecommunications network including energy star compliant VoIP devices

DOEpatents