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Sample records for gps wo mochiita

  1. GPS

    NASA Technical Reports Server (NTRS)

    Webb, Frank H.

    2006-01-01

    Geodetic networks support the TRF requirements of NASA ESE missions. Each of SLR, VLBI, GPS substantially and uniquely contributes to TRF determination. NASA's SLR, VLBI, and GPS groups collaborate toward wide-ranging improvements in the next 5 years. NASA leverages considerable resources through its significant activity in international services. NASA faces certain challenges in continuing and advancing these activities. The Terrestrial Reference Frame (TRF) is an accurate, stable set of positions and velocities. The TRF provides the stable coordinate system that allows us to link measurements over space and time. The geodetic networks provide data for determination of the TRF as well as direct science observations.

  2. GPS Interferometry

    NASA Technical Reports Server (NTRS)

    Vangrass, Frank

    1992-01-01

    This semi-annual progress report provides an overview of the work performed during the first six months of Grant NAG 1 1423, titled 'GPS Interferometry'. The Global Positioning System (GPS) is a satellite-based positioning and timing system. Through the use of interferometric processing techniques, it is feasible to obtain sub-decimeter position accuracies for an aircraft in flight. The proposed duration of this Grant is three years. During the first year of the Grant, the efforts are focussed on two topics: (1) continued development of GPS Interferometry core technology; and (2) rapid technology demonstration of GPS interferometry through the design and implementation of a flight reference/autoland system. Multipath error has been the emphasis of the continued development of GPS Interferometry core technology. The results have been documented in a Doctoral Dissertation and a conference paper. The design and implementation of the flight reference/autoland system is nearing completion. The remainder of this progress report summarizes the architecture of this system.

  3. GPS Status and Modernization

    DTIC Science & Technology

    2010-03-10

    11 GPS IIA • 12 GPS IIR • 7 GPS IIR-M • 4 additional satellites in residual status • 1 additional IIR-M waiting to be set healthy • Global GPS ...AEP) Next Generation Control Segment (OCX) Legacy Control System 7 GPS Modernization – Ground • Architecture Evolution Plan (AEP) • Transitioned in 2007...Modern distributed system replaced 1970’s mainframes • Increased capacity for monitoring of GPS signals • Increased worldwide commanding

  4. Improved visible light photocatalytic activity of WO3 through CuWO4 for phenol degradation

    NASA Astrophysics Data System (ADS)

    Chen, Haihang; Xiong, Xianqiang; Hao, Linlin; Zhang, Xiao; Xu, Yiming

    2016-12-01

    Development of a visible light photocatalyst is challenging. Herein, we report a significant activity enhancement of WO3 upon addition of CuWO4. Reaction was carried out under visible light for phenol degradation in aqueous suspension in the presence of H2O2. A maximum reaction rate was observed at 1.0 wt% CuWO4, which was 2.1 and 4.3 times those measured with WO3 and CuWO4, respectively. Similar results were also obtained from the photocatalytic formation of OH radicals, and from the electrochemical reduction of O2. A possible mechanism responsible for the improved activity of WO3 is proposed, involving the electron transfer from CuWO4 to WO3, followed by the reduction of H2O2 over WO3.

  5. Improved Charge Separation in WO3/CuWO4 Composite Photoanodes for Photoelectrochemical Water Oxidation

    PubMed Central

    Wang, Danping; Bassi, Prince Saurabh; Qi, Huan; Zhao, Xin; Gurudayal; Wong, Lydia Helena; Xu, Rong; Sritharan, Thirumany; Chen, Zhong

    2016-01-01

    Porous tungsten oxide/copper tungstate (WO3/CuWO4) composite thin films were fabricated via a facile in situ conversion method, with a polymer templating strategy. Copper nitrate (Cu(NO3)2) solution with the copolymer surfactant Pluronic®F-127 (Sigma-Aldrich, St. Louis, MO, USA, generic name, poloxamer 407) was loaded onto WO3 substrates by programmed dip coating, followed by heat treatment in air at 550 °C. The Cu2+ reacted with the WO3 substrate to form the CuWO4 compound. The composite WO3/CuWO4 thin films demonstrated improved photoelectrochemical (PEC) performance over WO3 and CuWO4 single phase photoanodes. The factors of light absorption and charge separation efficiency of the composite and two single phase films were investigated to understand the reasons for the PEC enhancement of WO3/CuWO4 composite thin films. The photocurrent was generated from water splitting as confirmed by hydrogen and oxygen gas evolution, and Faradic efficiency was calculated based on the amount of H2 produced. This work provides a low-cost and controllable method to prepare WO3-metal tungstate composite thin films, and also helps to deepen the understanding of charge transfer in WO3/CuWO4 heterojunction. PMID:28773473

  6. GPS Control Segment Improvements

    DTIC Science & Technology

    2015-04-29

    Systems Center GPS Control Segment Improvements Mr. Tim McIntyre GPS Product Support Manager GPS Ops Support and Sustainment Division Peterson...hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...DATE 29 APR 2015 2. REPORT TYPE 3. DATES COVERED 00-00-2015 to 00-00-2015 4. TITLE AND SUBTITLE GPS Control Segment Improvements 5a. CONTRACT

  7. GPS Scintillation Analysis.

    DTIC Science & Technology

    2007-11-02

    Rev. 2-89) Prescribed by ANSI Std. Z39-1 298-102 TABLE OF CONTENTS 1. INTRODUCTION 1 2. GPS COMPARISON WITH ALL-SKY IMAGES OVER AGUA VERDE...Depletions from 1 October 1994 2 3. GPS data from Agua Verde, Chile on the night of 1 October 1994 3 4. PL-SCINDA display of GPS ionospheric...comparison of GPS measurements with GOES8 L-band scintillation data, are discussed. 2. GPS COMPARISON WITH ALL-SKY IMAGES OVER AGUA VERDE, CHILE As

  8. On "GPS weeknumber rollover".

    NASA Astrophysics Data System (ADS)

    Chen, Hongqing

    1998-12-01

    The relation between GPS system time and weeknumber is introduced, and it is explained that the limited number of (10 bits) used in the GPS navigation message causes the problem of GPS weeknumber rollover which is similar to that the millennium problem will occur when the year number becomes 00 from 99. The GPS weeknumber has the maximum of 1023 so that it will rollover from 1023 to 0 at the midnight of August 21 - 22, 1999. The GPS users should check if the receivers can work correctly once the "rollover" occurs. If the equipments or softwares for the GPS receiver are not perfect. The receiver will interpret the new week 0 as January 6, 1980, and some receivers may display wrong information or wrong locating results, even stop tracking any satellite. The GPS users should contact the manufacturer of the GPS receiver to determine if the GPS receiver will be affected by the GPS weeknumber rollover. It should be noted that the problem of time rollover often occurs for timing service.

  9. Environmental applications of GPS

    SciTech Connect

    Vigil, S.A.; Zueck, D.

    1999-07-01

    The use of the Global Positioning System (GPS) has revolutionized air travel, ocean navigation, land navigation, and the collection of environmental data. Although a basic civilian GPS receiver can be purchased for as little as $100, the receiver is only the tip of a 12 billion dollar iceberg. This paper will discuss the history and basic operation of the Global Positioning System, a satellite-based precision positioning and timing service developed and operated by the Department of Defense. It will also describe the accuracy limitations of the civil GPS service and how accuracy can be enhanced by the use of differential GPS (DGPS), using either the free National Differential GPS system, or commercial differential monitor stations. Finally, the paper will discuss the future accuracy upgrades of civil GPS as a result of recent federal policy decisions.

  10. GPS Measurement Of Attitude

    NASA Technical Reports Server (NTRS)

    Dinardo, S. J.; Hushbeck, E. L.; Meehan, T. K.; Munson, T. N.; Purcell, G. H.; Srinivasan, J. M.; Young, L. E.; Yunck, T. P.

    1992-01-01

    Signals transmitted by satellites of Global Positioning System (GPS) measure orientation of baseline on ship, aircraft, or other vehicle with accuracy. Two GPS antennas and receivers placed at well separated points on platform. Receivers measure positions of ends of baseline as functions of time. Output processor computes vector difference between two positions and determines orientation of baseline. Combined with conventional GPS data, orientation data allows more precise navigation and mapping and enhances calculations related to performance and control of vehicle.

  11. GPS Decision Analysis Process

    DTIC Science & Technology

    2005-06-23

    712 A/B: GPS Decision Analysis Process Revised title:___________________________________________________________________ Presented in (input and Bold...JUN 2005 2. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE GPS Decision Analysis Process 5a. CONTRACT NUMBER 5b. GRANT NUMBER...Prescribed by ANSI Std Z39-18 GPS Decision Analysis Process Nisha Shah The Boeing Company 73rd MORS Symposium US Military Academy – West Point 21-23

  12. USNO GPS program

    NASA Technical Reports Server (NTRS)

    Putkovich, K.

    1981-01-01

    Initial test results indicated that the Global Positioning System/Time Transfer Unit (GPS/TTU) performed well within the + or - 100 nanosecond range required by the original system specification. Subsequent testing involved the verification of GPS time at the master control site via portable clocks and the acquisition and tracking of as many passes of the space vehicles currently in operation as possible. A description and discussion of the testing, system modifications, test results obtained, and an evaluation of both GPS and the GPS/TTU are presented.

  13. Integrated Inertial/gps

    NASA Technical Reports Server (NTRS)

    Kline, Paul; Vangraas, Frank

    1990-01-01

    The presence of failures in navigation sensors can cause the determination of an erroneous aircraft state estimate, which includes position, attitude, and their derivatives. Aircraft flight control systems rely on sensor inputs to determine the aircraft state. In the case of integrated Inertial/NAVSTAR Global Positioning System (GPS), sensor failures could occur in the on-board inertial sensors or in the GPS measurements. The synergistic use of both GPS and the Inertial Navigation System (INS) allows for highly reliable fault detection and isolation of sensor failures. Integrated Inertial/GPS is a promising technology for the High Speed Civil Transport (HSCT) and the return and landing of a manned space vehicle.

  14. GPS Modernization Update

    DTIC Science & Technology

    2014-06-01

    Navigation Satellite System ( GNSS ) performance Spectrum Allocation and Sharing Initiatives Fully support the allocation and sharing of spectrum through...reallocation or sharing with IMT • Various US agencies and international GNSS providers share this interest to help protect GPS International Spectrum...domestically, internationally and with Industry to simultaneously protect GNSS services and release spectrum for mobile services GPS Summary

  15. Crop Dusting Using GPS

    USDA-ARS?s Scientific Manuscript database

    Global Positioning System (GPS) receivers and GPS-based swath guidance systems are used on agricultural aircraft for remote sensing, airplane guidance, and to support variable-rate aerial application of crop inputs such as insecticides, cotton growth regulators, and defoliants. Agricultural aircraf...

  16. How GPs learn.

    PubMed

    MacLeod, Sheona

    2009-07-01

    As the requirements for the revalidation of general practitioners (GPs) unfold, there is an increasing emphasis on demonstrating effective continued medical education (CME) based on identified learning needs. This qualitative study aimed to promote understanding of how GPs currently approach their learning. The behaviour of one group of GPs was studied to explore how they assessed and met individual learning needs. The GPs studied showed a pragmatic approach, valuing learning that gave them practical advice and instant access to information for patient-specific problems. The main driver for the GPs' learning was discomfort during their daily work if a possible lack of knowledge or skills was perceived. However, some learning benchmarked current good practice or ensured continued expertise. Learning purely for interest was also described. The GPs in this study all demonstrated a commitment to personal learning, although they were not yet thinking about demonstrating the effectiveness of this for revalidation. The GPs prioritised their learning needs and were beginning to use some objective assessment methods to do this and the GP appraisal process was found to have a mainly positive effect on learning.

  17. Progress on GPS standardization

    NASA Technical Reports Server (NTRS)

    Thomas, C.

    1993-01-01

    It has been clear for some time that a desirable and necessary step for improvement of the accuracy of GPS time comparisons is to establish GPS standards which may be adopted by receiver designers and users. For this reason, a formal body, the CCDS Group on GPS Time Transfer Standards (CGGTTS), was created in 1991. It operates under the auspices of the permanent CCDS Working Group on TAI, with the objective of recommending procedures and models for operational time transfer by the GPS common-view method. It works in close cooperation with the Subcommittee on Time of the Civil GPS Service Interface Committee. The members of the CGGTTS have met in December 1991 and in June 1992. Following these two formal meetings, a number of decisions were taken for unifying the treatment of GPS short-term data and for standardizing the format of GPS data files. A formal CGGTTS Recommendation is now being written concerning these points. This paper relates on the work carried out by the CGGTTS.

  18. Progress on GPS standardization

    NASA Technical Reports Server (NTRS)

    Thomas, C.

    1993-01-01

    It has been clear for some time that a desirable and necessary step for improvement of the accuracy of GPS time comparisons is to establish GPS standards which may be adopted by receiver designers and users. For this reason, a formal body, the CCDS Group on GPS Time Transfer Standards (CGGTTS), was created in 1991. It operates under the auspices of the permanent CCDS Working Group on TAI, with the objective of recommending procedures and models for operational time transfer by the GPS common-view method. It works in close cooperation with the Subcommittee on Time of the Civil GPS Service Interface Committee. The members of the CGGTTS have met in December 1991 and in June 1992. Following these two formal meetings, a number of decisions were taken for unifying the treatment of GPS short-term data and for standardizing the format of GPS data files. A formal CGGTTS Recommendation is now being written concerning these points. This paper relates on the work carried out by the CGGTTS.

  19. GPS Activities at SLAC

    SciTech Connect

    Behrend, Dirk

    2002-11-19

    The Alignment Engineering Group of the Stanford Linear Accelerator Center (SLAC) started to use RTK (real-time kinematic) GPS equipment in order to perform structure mapping and GIS-related tasks on the SLAC campus. In a first step a continuously observing GPS station (SLAC M40) was set up. This station serves as master control station for all differential GPS activities on site and its coordinates have been determined in the well-defined global geodetic datum ITRF2000 at a given reference epoch. Some trials have been performed to test the RTK method. The tests have proven RTK to be very fast and efficient.

  20. Advanced GPS Technologies (AGT)

    DTIC Science & Technology

    2015-05-01

    AND ADDRESS(ES) Air Force Research Laboratory,Space Vehicles Directorate,3550 Aberdeen Avenue SE , Kirtland AFB,NM,87117 8. PERFORMING ORGANIZATION...Inform Partnership Council about AFRL technology investments to improve affordability and performance of the GPS Space Segment Summary • Working in...development Exploring/opening paths to the future! Distribution A 2 \\.J ••• • AFRL Investments Supporting GPS Space Segment • AFRL is investigating

  1. GPS Control Segment

    DTIC Science & Technology

    2015-04-29

    AND MISSILE SYSTEMS CENTER • Provides GPS Ill SV command and control • NAV capability equivalent to GPS IIF (legacy and modern signals) - No L 1 ...Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions...information if it does not display a currently valid OMB control number 1 . REPORT DATE 29 APR 2015 2. REPORT TYPE 3. DATES COVERED 00-00-2015 to 00

  2. Metastable superconductivity of W/WO3 interface

    NASA Astrophysics Data System (ADS)

    Palnichenko, A. V.; Vyaselev, O. M.; Mazilkin, A. A.; Zver`kova, I. I.; Khasanov, S. S.

    2017-03-01

    Metastable W/WO3 interface has been formed at the surface of a tungsten metal bar using a solid state redox reaction of W with powdered WO3. Superconductivity at 35 ≤ T ≤ 75 K in the W/WO3 interfacial layer has been observed by means of the ac magnetic susceptibility and electrical resistance measurements. Comparative analysis of the experimental results infers that the W/WO3 interfacial layer consists of weakly linked superconducting regions.

  3. GPS Metric Tracking Unit

    NASA Technical Reports Server (NTRS)

    2008-01-01

    As Global Positioning Satellite (GPS) applications become more prevalent for land- and air-based vehicles, GPS applications for space vehicles will also increase. The Applied Technology Directorate of Kennedy Space Center (KSC) has developed a lightweight, low-cost GPS Metric Tracking Unit (GMTU), the first of two steps in developing a lightweight, low-cost Space-Based Tracking and Command Subsystem (STACS) designed to meet Range Safety's link margin and latency requirements for vehicle command and telemetry data. The goals of STACS are to improve Range Safety operations and expand tracking capabilities for space vehicles. STACS will track the vehicle, receive commands, and send telemetry data through the space-based asset, which will dramatically reduce dependence on ground-based assets. The other step was the Low-Cost Tracking and Data Relay Satellite System (TDRSS) Transceiver (LCT2), developed by the Wallops Flight Facility (WFF), which allows the vehicle to communicate with a geosynchronous relay satellite. Although the GMTU and LCT2 were independently implemented and tested, the design collaboration of KSC and WFF engineers allowed GMTU and LCT2 to be integrated into one enclosure, leading to the final STACS. In operation, GMTU needs only a radio frequency (RF) input from a GPS antenna and outputs position and velocity data to the vehicle through a serial or pulse code modulation (PCM) interface. GMTU includes one commercial GPS receiver board and a custom board, the Command and Telemetry Processor (CTP) developed by KSC. The CTP design is based on a field-programmable gate array (FPGA) with embedded processors to support GPS functions.

  4. GPS Spectrum Management (Briefing Charts)

    DTIC Science & Technology

    2015-04-29

    Maintenance/Security Spectrum 39 Satellites /31 Set Healthy Baseline Constellation : 24 Satellites • All Level l and Level II - Worldwide...of Transportation • Federal Aviation Administration Satellite Block GPS IIA GPS IIR GPS IIR-M GPS IIF Constellation Department of Homeland...Authorized Nation 11 Mar 14 SPACE AND MISSILE SYSTEMS CENTER 4 UNCLASSIFIED/APPROVED FOR PUBLIC RELEASE GNSS Deployed or Planned • Global Constellations

  5. Update on GPS Modernization Efforts

    DTIC Science & Technology

    2015-06-11

    Security Spectrum 38 Satellites I 31 Set Healthy Baseline Constellation : 24 Satellites • All Level l and Level II - Worldwide Infrastructure...GPS IIA GPS IIR GPS IIR-M GPS IIF Constellation Department of Homeland Security • U.S. Coast Guard Quantity Average Age Oldest 3 21 .5 24.4...OCS) - Flying the G PS constellation with both the Architecture Evolution Plan (AEP) and the Launch & Early Orbit, Anomaly Resolution , and Disposal

  6. High Precision GPS Measurements

    DTIC Science & Technology

    2010-02-28

    GNSS Service (IGS) database, and magnetic field vectors from the International Geomagnetic Reference Field (IGRF) model [9]. These combined...Additonal correlations between the higher order range error and geomagnetic activity and seasonal variations are also obtained. Fig. 4 shows...clear correlation between the geomagnetic activity and enhanced higher order error at both sites. High Precision GPS Final Report Page 5 Fig.3

  7. Positioning With GPS: 1985

    NASA Astrophysics Data System (ADS)

    Remondi, Benjamin W.; Hothem, Larry D.

    The First International Symposium on Precise Positioning With the Global Positioning System (GPS) was held in Rockville, Maryland from April 15 to April 19, 1985; 600 participants from 31 countries attended. Sponsors included the International Union of Geodesy and Geophysics, the International Association of Geodesy, the Defense Mapping Agency (DMA), and the National Oceanic and Atmospheric Administration (NOAA) in cooperation with the American Society of Civil Engineers. GPS uses the NAVSTAR (an acronym for Navigation and Satellite Timing and Ranging) satellite system developed by the Department of Defense (DOD).Although this symposium was limited to precise positioning with GPS, the scope of precise positioning was left open. Without a doubt, precise relative positioning with L band carrier phase measurements was the most important topic. Also included were certain high-accuracy applications of pseudorange measurements, such as orbit determination, time transfer, and navigation. Administration, policy, hardware, software, processing, and applications in these areas were also covered. Intentionally left out were areas in which high positional accuracy was not important (e.g., commercial aviation). Attendees presented 89 papers, which were organized into 15 sessions covering nine subject areas: overview, status, and policy; GPS time and orbits; user equipment; user equipment testing; modeling and processing; applications; survey positioning results; practical aspects of geodesy; and dynamic positioning.

  8. Networked differential GPS system

    NASA Technical Reports Server (NTRS)

    Mueller, K. Tysen (Inventor); Loomis, Peter V. W. (Inventor); Kalafus, Rudolph M. (Inventor); Sheynblat, Leonid (Inventor)

    1994-01-01

    An embodiment of the present invention relates to a worldwide network of differential GPS reference stations (NDGPS) that continually track the entire GPS satellite constellation and provide interpolations of reference station corrections tailored for particular user locations between the reference stations Each reference station takes real-time ionospheric measurements with codeless cross-correlating dual-frequency carrier GPS receivers and computes real-time orbit ephemerides independently. An absolute pseudorange correction (PRC) is defined for each satellite as a function of a particular user's location. A map of the function is constructed, with iso-PRC contours. The network measures the PRCs at a few points, so-called reference stations and constructs an iso-PRC map for each satellite. Corrections are interpolated for each user's site on a subscription basis. The data bandwidths are kept to a minimum by transmitting information that cannot be obtained directly by the user and by updating information by classes and according to how quickly each class of data goes stale given the realities of the GPS system. Sub-decimeter-level kinematic accuracy over a given area is accomplished by establishing a mini-fiducial network.

  9. Growth of BaWO4 fishbone-like nanostructures in w/o microemulsion.

    PubMed

    Zhang, Xu; Xie, Yi; Xu, Fen; Tian, Xiaobo

    2004-06-01

    BaWO(4) fishbone-like nanostructures with fourfold structural symmetry have been successfully grown in w/o microemulsion. The BaWO(4) fishbone-like nanostructures have four rows of nanorods, epitaxially grown on the stem and perpendicular to the stem. The obtained samples are characterized by means of XRD, TEM, HRTEM, and SEM. It is found that the water content has a large influence on the size of the product and the molar ratio between cations and anions plays an important role in the morphology of the product. It is assumed that site-selective surfactant adsorption may be responsible for the formation of the BaWO(4) fishbone-like nanostructures.

  10. Structural stability and phase transitions in WO3 thin films.

    PubMed

    Ramana, C V; Utsunomiya, S; Ewing, R C; Julien, C M; Becker, U

    2006-06-01

    Tungsten oxide (WO3) thin films have been produced by KrF excimer laser (lambda = 248 nm) ablation of bulk ceramic WO3 targets. The crystal structure, surface morphology, chemical composition, and structural stability of the WO3 thin films have been studied in detail. Characterization of freshly grown WO3 thin films has been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurements. The results indicate that the freshly grown WO3 thin films are nearly stoichiometric and well crystallized as monoclinic WO3. The surface morphology of the resulting WO3 thin film has grains of approximately 60 nm in size with a root-mean-square (rms) surface roughness of 10 nm. The phase transformations in the WO3 thin films were investigated by annealing in the TEM column at 30-500 degrees C. The phase transitions in the WO3 thin films occur in sequence as the temperature is increased: monoclinic --> orthorhombic --> hexagonal. Distortion and tilting of the WO6 octahedra occurs with the phase transitions and significantly affects the electronic properties and, hence, the electrochemical device applications of WO3.

  11. The GPS Space Service Volume

    NASA Technical Reports Server (NTRS)

    Bauer, F. H.; Moreau, M. C.; Dahle-Melsaether, M. E.; Petrofski, W. P.; Stanton, B. J.; Thomason, S.; Harris, G. A.; Sena, R. P.; Temple, L. Parker, III

    2006-01-01

    Prior to the advent of artificial satellites, the concept of navigating in space and the desire to understand and validate the laws of planetary and satellite motion dates back centuries. At the initiation of orbital flight in 1957, space navigation was dominated by inertial and groundbased tracking methods, underpinned by the laws of planetary motion. It was early in the 1980s that GPS was first explored as a system useful for refining the position, velocity, and timing (PVT) of other spacecraft equipped with GPS receivers. As a result, an entirely new GPS utility was developed beyond its original purpose of providing PVT services for land, maritime, and air applications. Spacecraft both above and below the GPS constellation now receive the GPS signals, including the signals that spill over the limb of the Earth. The use of radionavigation satellite services for space navigation in High Earth Orbits is in fact a capability unique to GPS. Support to GPS space applications is being studied and planned as an important improvement to GPS. This paper discusses the formalization of PVT services in space as part of an overall GPS improvement effort. It describes the GPS Space Service Volume (SSV) and compares it to the Terrestrial Service Volume (TSV). It also discusses SSV coverage with the current GPS constellation, coverage characteristics as a function of altitude, expected power levels, and coverage figures of merit.

  12. GPS Quasars as Special Blazars

    NASA Astrophysics Data System (ADS)

    Bai, J. M.; Lee, Myung Gyong

    2005-06-01

    In this paper, we argue that the gigahertz peaked spectrum (GPS) quasars are special blazars, blazars in dense and dusty gas enviornment. The ROSAT detection rate of GPS quasars is similar to that of flat spectrum radio quasars (FSRQs), suggesting that the relativistic jets in GPS quasars are oriented at small angle to the line of sight. Due to strong inverse Compton scattering off infrared photons from dense and dusty nuclear interstellar media in GPS quasars, most of them may have significant soft gamma-ray and X-ray emission, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than that in FSRQs, synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust, hence most GPS quasars show low optical polarization and small variability, consistent with observations. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. Whether GPS quasars are special blazars can be tested by gamma-ray observations with GLAST in the near future, with the detection rate of GPS quasars being similar to that of FSRQs.

  13. GPS Timing Performance

    DTIC Science & Technology

    2014-01-01

    U.S. Naval Observatory (USNO) [1]. Interoperability with Galileo, and perhaps someday with other Global Navigation Satellite Systems ( GNSS ), is to...be established through transmission of the differences between the GNSS system times. This paper describes the performance of the GPS system, which...interoperable GNSS systems will benefit from the additional satellites, and in certain situations markedly so. 2. Current Performance Under Optimal

  14. GPS lessons learned

    NASA Technical Reports Server (NTRS)

    Heflin, Michael B.

    2003-01-01

    Global geodesy has improved dramatically over the past decade starting with the GPS for IERS and Geodynamics demonstration campaign in 1991 (GIG 91). At the time it took over a week of CPU time to process a network solution based on 21 global receivers and orbit overlaps were in the 40 cm range. Today it is possible to process a network solution based on 80 global receivers in less then one day of CPU time and orbit overlaps are in the 4 cm range. Special methods are under development for efficient processing of increasingly large regional networks which may contain hundreds or thousands of GPS receivers. Along the way there have been many lessons learned about GPS satellites, receivers, monuments, antennas, radomes, analysis, reference frames, error sources, and interpretation. A wide range of scientific disciplines have been impacted including studies of plate motion, post-glacial rebound, seasonal loading, deformation in plate boundary zones, coseismic displacements due to major earthquakes, postseiemic relaxation, and interseismic strain accumulation related to assessment of seismic hazards. Lessons learned will be presented in the context of new dense networks such as the Plate Boundary Observation (PBO).

  15. Interference to GPS

    NASA Astrophysics Data System (ADS)

    Blanchard, Walter

    I read Captain Gyldeń's account of failure of his GPS set (Vol. 50, 328, May 1997) withsome interest. A few days earlier we had had a few thunderstorms while I had my personal hand-held GPS running, using its own built-in antenna and a 12 volt battery. It was lying on a bench inside a wooden hut where I keep some of my amateur radio equipment. After one particularly close flash and bang, which produced a one-inch spark from my transceiver antenna, the transceiver locked up and stopped responding to keyboard commands. Then I noticed the GPS set had also stopped working, showing only random symbols on its readout. I feared the worst but, after switching them both off, leaving them for a few minutes, and then back on again, they worked perfectly.Microprocessors locking up in strong local electrostatic fields, perhaps? Maybe if I had simply left them alone they would have started working again after the charge had leaked away. Next time I nearly get hit by lightning I'll try it.

  16. GPS lessons learned

    NASA Technical Reports Server (NTRS)

    Heflin, Michael B.

    2003-01-01

    Global geodesy has improved dramatically over the past decade starting with the GPS for IERS and Geodynamics demonstration campaign in 1991 (GIG 91). At the time it took over a week of CPU time to process a network solution based on 21 global receivers and orbit overlaps were in the 40 cm range. Today it is possible to process a network solution based on 80 global receivers in less then one day of CPU time and orbit overlaps are in the 4 cm range. Special methods are under development for efficient processing of increasingly large regional networks which may contain hundreds or thousands of GPS receivers. Along the way there have been many lessons learned about GPS satellites, receivers, monuments, antennas, radomes, analysis, reference frames, error sources, and interpretation. A wide range of scientific disciplines have been impacted including studies of plate motion, post-glacial rebound, seasonal loading, deformation in plate boundary zones, coseismic displacements due to major earthquakes, postseiemic relaxation, and interseismic strain accumulation related to assessment of seismic hazards. Lessons learned will be presented in the context of new dense networks such as the Plate Boundary Observation (PBO).

  17. Detection and phylogenetic analysis of bacteriophage WO in spiders (Araneae).

    PubMed

    Yan, Qian; Qiao, Huping; Gao, Jin; Yun, Yueli; Liu, Fengxiang; Peng, Yu

    2015-11-01

    Phage WO is a bacteriophage found in Wolbachia. Herein, we represent the first phylogenetic study of WOs that infect spiders (Araneae). Seven species of spiders (Araneus alternidens, Nephila clavata, Hylyphantes graminicola, Prosoponoides sinensis, Pholcus crypticolens, Coleosoma octomaculatum, and Nurscia albofasciata) from six families were infected by Wolbachia and WO, followed by comprehensive sequence analysis. Interestingly, WO could be only detected Wolbachia-infected spiders. The relative infection rates of those seven species of spiders were 75, 100, 88.9, 100, 62.5, 72.7, and 100 %, respectively. Our results indicated that both Wolbachia and WO were found in three different body parts of N. clavata, and WO could be passed to the next generation of H. graminicola by vertical transmission. There were three different sequences for WO infected in A. alternidens and two different WO sequences from C. octomaculatum. Only one sequence of WO was found for the other five species of spiders. The discovered sequence of WO ranged from 239 to 311 bp. Phylogenetic tree was generated using maximum likelihood (ML) based on the orf7 gene sequences. According to the phylogenetic tree, WOs in N. clavata and H. graminicola were clustered in the same group. WOs from A. alternidens (WAlt1) and C. octomaculatum (WOct2) were closely related to another clade, whereas WO in P. sinensis was classified as a sole cluster.

  18. Reactivity of Hydrogen and Methanol on (001) Surfaces of WO3, ReO3, WO3/ReO3 and ReO3/WO3

    SciTech Connect

    Ling, Sanliang; Mei, Donghai; Gutowski, Maciej S.

    2011-05-16

    Bulk tungsten trioxide (WO3) and rhenium trioxide (ReO3) share very similar structures but display different electronic properties. WO3 is a wide bandgap semiconductor while ReO3 is an electronic conductor. With the advanced molecular beam epitaxy techniques, it is possible to make heterostructures comprised of layers of WO3 and ReO3. These heterostructures might display reactivity different than pure WO3 and ReO3. The interactions of two probe molecules (hydrogen and methanol) with the (001) surfaces of WO3, ReO3, and two heterostructures ReO3/WO3 and WO3/ReO3 were investigated at the density functional theory level. Atomic hydrogen prefers to adsorb at the terminal O1C sites forming a surface hydroxyl on four surfaces. Dissociative adsorption of a hydrogen molecule at the O1C site leads to formation of a water molecule adsorbed at the surface M5C site. This is thermodynamically the most stable state. A thermodynamically less stable dissociative state involves two surface hydroxyl groups O1CH and O2CH. The interaction of molecular hydrogen and methanol with pure ReO3 is stronger than with pure WO3 and the strength of the interaction substantially changes on the WO3/ReO3 and ReO3/WO3 heterostructures. The reaction barriers for decomposition and recombination reactions are sensitive to the nature of heterostructure. The calculated adsorption energy of methanol on WO3(001) of -65.6 kJ/mol is consistent with the previous experimental estimation of -67 kJ/mol. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

  19. GPS navigation experiment using high precision GPS timing receivers

    NASA Technical Reports Server (NTRS)

    Buisson, J. A.; Oaks, O. J.; Lister, M. J.; Wardrip, S. C.; Leschiutta, S.; Galliano, P. G.; Cordara, D.; Pettiti, V.; Detoma, E.; Dachel, P.

    1985-01-01

    Global Positioning System (GPS) Time Transfer receivers were developed by the Naval Research Laboratory (NRL) to provide synchronization for the NASA Global Laser Tracking Network (GLTN). The capabilities of the receiver are being expanded mainly through software modification to: Demonstrate the position location capabilities of a single channel receiver unsign the GPS C/A code; and Demonstrate the time/navigation capability of the receiver onboard a moving platform, by sequential tracking of GPS satellites.

  20. Photoelectrocatalytic degradation of oxalic acid using WO3 and stratified WO3/TiO2 photocatalysts under sunlight illumination.

    PubMed

    Hunge, Y M; Mahadik, M A; Moholkar, A V; Bhosale, C H

    2017-03-01

    The WO3 and stratified WO3/TiO2 thin films are successfully prepared by the spray pyrolysis method. The structural, morphological, compositional and photoelectrocatalytic properties of WO3 and stratified WO3/TiO2 thin films are studied. XRD analysis confirms that films are polycrystalline with monoclinic and tetragonal crystal structures for WO3 and TiO2 respectively. The SEM images clearly show 3D sheeted porous structure of the as-prepared TiO2 forms on WO3 in stratified WO3/TiO2 samples. The synthesized photoelectrodes was used as catalyst for photoelectrocatalytic degradation of oxalic acid in aqueous medium. The rate constant (k) was evaluated as a function of the initial concentration of species. A significant decrease in concentrations of organic species was observed from COD analysis. The photoelectrocatalytic degradation effect is relatively higher in the case of the stratified WO3/TiO2 than WO3 thin film photoelectrode in the degradation of oxalic acid and 83% removal efficiency of oxalic acid is obtained after 180min. Based on the obtained experimental data, the possible photoelectrocatalytic reaction mechanism was proposed. The photoelectrocatalytic experimental results indicate that stratified WO3/TiO2 photoelectrode is the promising material for removing of water pollutants. Copyright © 2016 Elsevier B.V. All rights reserved.

  1. Sensing Human Activity: GPS Tracking

    PubMed Central

    van der Spek, Stefan; van Schaick, Jeroen; de Bois, Peter; de Haan, Remco

    2009-01-01

    The enhancement of GPS technology enables the use of GPS devices not only as navigation and orientation tools, but also as instruments used to capture travelled routes: as sensors that measure activity on a city scale or the regional scale. TU Delft developed a process and database architecture for collecting data on pedestrian movement in three European city centres, Norwich, Rouen and Koblenz, and in another experiment for collecting activity data of 13 families in Almere (The Netherlands) for one week. The question posed in this paper is: what is the value of GPS as ‘sensor technology’ measuring activities of people? The conclusion is that GPS offers a widely useable instrument to collect invaluable spatial-temporal data on different scales and in different settings adding new layers of knowledge to urban studies, but the use of GPS-technology and deployment of GPS-devices still offers significant challenges for future research. PMID:22574061

  2. Update on GPS Modernization Efforts

    DTIC Science & Technology

    2015-06-02

    SPACE AND MISSILE SYSTEMS CENTER , GPS constellation consists of 24+ satellites orbiting the earth at - 10,900 nautical miles (Medium Earth Orbit , MEO...estimates instantaneous state of GPS constellation PUBLICALL Y RELEASABLE 4 Civil Cooperation • 1 + Bill ion civil & commercial users worldwide...Observatory • PNT EXCOMS • GPS Partnership Council Maintenance/Security Spectrum 38 Satellites I 31 Set Healthy Baseline Constellation : 24 Satellites

  3. Global Positioning System (GPS) Modernization

    DTIC Science & Technology

    2001-01-01

    GLOBAL POSITIONING SYSTEM ( GPS ) MODERNIZATION Lt. Col. C. McGinn, Capt. S...CA 90501, USA Abstract The Global Positioning System ( GPS ) signal is now the primary means of obtaining precise time to an internationally accepted...number. 1. REPORT DATE NOV 2000 2. REPORT TYPE 3. DATES COVERED 00-00-2000 to 00-00-2000 4. TITLE AND SUBTITLE Global Positioning System ( GPS

  4. H2O Adsorption on WO3 and WO3-x (001) Surfaces.

    PubMed

    Albanese, Elisa; Di Valentin, Cristiana; Pacchioni, Gianfranco

    2017-07-12

    The nature of the interaction of water with the WO3 surface is of crucial importance for the use of this semiconductor oxide in photocatalysis. In this work, we investigate water adsorption and dissociation on both clean and O-deficient (001) WO3 surfaces by means of an accurate DFT approach. The O vacancy formation energy (computed with respect to O2) has been evaluated for all possible surface configurations, and the removal of the terminal O atom along the c axis is found to be preferred, costing about half the corresponding energy in the bulk. The presence of oxygen vacancies leads to a semiconductor to metal transition, confirming the experimental evidence of n-type conductivity in defective WO3 films. H2O preferably adsorbs on WO3 in a molecular undissociated form, due to the presence of W ions at the surface that act as Lewis acid sites. This interaction, about -1 eV per H2O molecule, is not very strong. Contrary to what is usually expected, the presence of oxygen vacancies does not significantly affect H2O adsorption. Finally, we investigated the H2O desorption from a hydroxylated surface. This suggests that the exposure of WO3 to H2 directly results in a hydroxylated surface and the corresponding H2O desorption turns out to be a very efficient mechanism to generate a reduced oxide surface, with important consequences on the electronic structure of this oxide.

  5. A GPS coverage model

    NASA Technical Reports Server (NTRS)

    Skidmore, Trent A.

    1994-01-01

    The results of several case studies using the Global Positioning System coverage model developed at Ohio University are summarized. Presented are results pertaining to outage area, outage dynamics, and availability. Input parameters to the model include the satellite orbit data, service area of interest, geometry requirements, and horizon and antenna mask angles. It is shown for precision-landing Category 1 requirements that the planned GPS 21 Primary Satellite Constellation produces significant outage area and unavailability. It is also shown that a decrease in the user equivalent range error dramatically decreases outage area and improves the service availability.

  6. GPS Sounding Rocket Developments

    NASA Technical Reports Server (NTRS)

    Bull, Barton

    1999-01-01

    Sounding rockets are suborbital launch vehicles capable of carrying scientific payloads several hundred miles in altitude. These missions return a variety of scientific data including; chemical makeup and physical processes taking place in the atmosphere, natural radiation surrounding the Earth, data on the Sun, stars, galaxies and many other phenomena. In addition, sounding rockets provide a reasonably economical means of conducting engineering tests for instruments and devices used on satellites and other spacecraft prior to their use in more expensive activities. This paper addresses the NASA Wallops Island history of GPS Sounding Rocket experience since 1994 and the development of highly accurate and useful system.

  7. GPS Sounding Rocket Developments

    NASA Technical Reports Server (NTRS)

    Bull, Barton

    1999-01-01

    Sounding rockets are suborbital launch vehicles capable of carrying scientific payloads several hundred miles in altitude. These missions return a variety of scientific data including; chemical makeup and physical processes taking place in the atmosphere, natural radiation surrounding the Earth, data on the Sun, stars, galaxies and many other phenomena. In addition, sounding rockets provide a reasonably economical means of conducting engineering tests for instruments and devices used on satellites and other spacecraft prior to their use in more expensive activities. This paper addresses the NASA Wallops Island history of GPS Sounding Rocket experience since 1994 and the development of highly accurate and useful system.

  8. Thermoluminescence of PbWO4 irradiated with UV light.

    PubMed

    Kim, T; Song, K; Woo, J; Kim, T; Whang, C

    2002-01-01

    PbWO4 single crystals were grown by the Czochralski method in argon and air. The glow curves induced by UV light and the absorption spectra of PbWO4 annealed at various temperatures were measured. The glow curves of PbWO4 were strongly dependent on the growing atmospheres. The activation energies of the 110 K peak of PbWO4 grown in argon and the 122 K peak of PbWO4 grown in air were calculated to be 0.23 eV and 0.29 eV, respectively. The ratio of the 2.76 eV emission band to the 2.48 eV or 2.26 eV emission bands of the PbWO4 grown in air was smaller than that of the PbWO4 grown in argon. The glow curve of PbWO4 grown in argon was similar to that of PbWO4 grown in air when the annealing temperatures were increased.

  9. Polarized Raman spectra of the oriented NaY(WO 4) 2 and KY(WO 4) 2 single crystals

    NASA Astrophysics Data System (ADS)

    Macalik, L.; Hanuza, J.; Kaminskii, A. A.

    2000-11-01

    Polarized Raman scattering spectra of the NaY(WO 4) 2 (NYW) single crystal have been measured. Its structure is described in the tetragonal space group isomorphic to CaWO 4 scheelite. The A g, B g and E g spectra were made and discussed in terms of factor group analysis. These spectra are compared to those of monoclinic KY(WO 4) 2 (KYW) single crystals whose structure differs from the other crystal. The NYW unit cell comprises of the isolated WO 4 tetrahedra whereas the KYW structure is built from the WO 6 octahedra joined by WO 2W double bonds and WOW single bridges. The vibrational characteristics of the bridge bond systems are proposed. On this basis, the role of the vibronic transitions for the KYW crystal doped with Eu 3+ ions is discussed.

  10. GPS Moving Vehicle Experiment

    NASA Technical Reports Server (NTRS)

    Oaks, O. J.; Reid, Wilson; Wright, James; Duffey, Christopher; Williams, Charles; Warren, Hugh; Zeh, Tom; Buisson, James

    1996-01-01

    The Naval Research Laboratory (NRL) in the development of timing systems for remote locations, had a technical requirement for a Y code (SA/AS) Global Positioning System (GPS) precise time transfer receiver (TTR) which could be used both in a stationary mode or mobile mode. A contract was awarded to the Stanford Telecommunication Corporation (STEL) to build such a device. The Eastern Range (ER) als had a requirement for such a receiver and entered into the contract with NRL for the procurement of additional receivers. The Moving Vehicle Experiment (MVE) described in this paper is the first in situ test of the STEL Model 5401C Time Transfer System in both stationary and mobile operations. The primary objective of the MVE was to test the timing accuracy of the newly developed GPS TTR aboard a moving vessel. To accomplish this objective, a joint experiment was performed with personnel from NRL and the er at the Atlantic Undersea Test and Evaluation Center (AUTEC) test range at Andros Island. Results and discussion of the test are presented in this paper.

  11. GPS Sounding Rocket Developments

    NASA Technical Reports Server (NTRS)

    Bull, Barton

    1999-01-01

    Sounding rockets are suborbital launch vehicles capable of carrying scientific payloads several hundred miles in altitude. These missions return a variety of scientific data including; chemical makeup and physical processes taking place In the atmosphere, natural radiation surrounding the Earth, data on the Sun, stars, galaxies and many other phenomena. In addition, sounding rockets provide a reasonably economical means of conducting engineering tests for instruments and devices used on satellites and other spacecraft prior to their use in more expensive activities. The NASA Sounding Rocket Program is managed by personnel from Goddard Space Flight Center Wallops Flight Facility (GSFC/WFF) in Virginia. Typically around thirty of these rockets are launched each year, either from established ranges at Wallops Island, Virginia, Poker Flat Research Range, Alaska; White Sands Missile Range, New Mexico or from Canada, Norway and Sweden. Many times launches are conducted from temporary launch ranges in remote parts of the world requi6ng considerable expense to transport and operate tracking radars. An inverse differential GPS system has been developed for Sounding Rocket. This paper addresses the NASA Wallops Island history of GPS Sounding Rocket experience since 1994 and the development of a high accurate and useful system.

  12. GPS Sounding Rocket Developments

    NASA Technical Reports Server (NTRS)

    Bull, Barton

    1999-01-01

    Sounding rockets are suborbital launch vehicles capable of carrying scientific payloads several hundred miles in altitude. These missions return a variety of scientific data including; chemical makeup and physical processes taking place In the atmosphere, natural radiation surrounding the Earth, data on the Sun, stars, galaxies and many other phenomena. In addition, sounding rockets provide a reasonably economical means of conducting engineering tests for instruments and devices used on satellites and other spacecraft prior to their use in more expensive activities. The NASA Sounding Rocket Program is managed by personnel from Goddard Space Flight Center Wallops Flight Facility (GSFC/WFF) in Virginia. Typically around thirty of these rockets are launched each year, either from established ranges at Wallops Island, Virginia, Poker Flat Research Range, Alaska; White Sands Missile Range, New Mexico or from Canada, Norway and Sweden. Many times launches are conducted from temporary launch ranges in remote parts of the world requi6ng considerable expense to transport and operate tracking radars. An inverse differential GPS system has been developed for Sounding Rocket. This paper addresses the NASA Wallops Island history of GPS Sounding Rocket experience since 1994 and the development of a high accurate and useful system.

  13. Ionospheric Profiling using GPS/MET Data

    NASA Technical Reports Server (NTRS)

    Hajj, George; Romans, Larry

    1996-01-01

    A report on ionospheric profiling using GPS and MET data is presented. A description of the GPS occultation technique, some examples of GPS/MET data products, the data processing system and a preliminary validation of ionospheric profiles is discussed.

  14. Position, Navigation, and Timing: GPS Scientific Applications

    NASA Technical Reports Server (NTRS)

    Neilan, Ruth E.

    2008-01-01

    This slide presentation reviews the development and deployment of the Global Positioning System (GPS). This presentation also includes measuring space and time, GPS as a tool for science, development of high precision JPL GPS receivers, and technology and applications developments.

  15. In situ synthesis of CdS/CdWO4/WO3 heterojunction films with enhanced photoelectrochemical properties

    NASA Astrophysics Data System (ADS)

    Zhan, Faqi; Li, Jie; Li, Wenzhang; Yang, Yahui; Liu, Wenhua; Li, Yaomin

    2016-09-01

    CdS/CdWO4/WO3 heterojunction films on fluorine-doped tin oxide (FTO) substrates are for the first time prepared as an efficient photoanode for photoelectrochemical (PEC) hydrogen generation by an in situ conversion process. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet visible spectrometry (UV-vis) and X-ray photoelectron spectroscopy (XPS). The CdS hollow spheres (∼80 nm) sensitized WO3 plate film with a CdWO4 buffer-layer exhibits increased visible light absorption and a significantly improved photoelectrochemical performance. The photocurrent density at 0 V (vs. Ag/AgCl) of the CdS/CdWO4/WO3 anode is ∼3 times higher than that of the CdWO4/WO3 anode, and ∼9 times higher than that of pure WO3 under illumination. The highest incident-photon-to-current-efficiency (IPCE) value increased from 16% to 63% when the ternary heterojunction was formed. This study demonstrates that the synthesis of ternary composite photocatalysts by the in situ conversion process may be a promising approach to achieve high photoelectric conversion efficiency.

  16. Determining GPS average performance metrics

    NASA Technical Reports Server (NTRS)

    Moore, G. V.

    1995-01-01

    Analytic and semi-analytic methods are used to show that users of the GPS constellation can expect performance variations based on their location. Specifically, performance is shown to be a function of both altitude and latitude. These results stem from the fact that the GPS constellation is itself non-uniform. For example, GPS satellites are over four times as likely to be directly over Tierra del Fuego than over Hawaii or Singapore. Inevitable performance variations due to user location occur for ground, sea, air and space GPS users. These performance variations can be studied in an average relative sense. A semi-analytic tool which symmetrically allocates GPS satellite latitude belt dwell times among longitude points is used to compute average performance metrics. These metrics include average number of GPS vehicles visible, relative average accuracies in the radial, intrack and crosstrack (or radial, north/south, east/west) directions, and relative average PDOP or GDOP. The tool can be quickly changed to incorporate various user antenna obscuration models and various GPS constellation designs. Among other applications, tool results can be used in studies to: predict locations and geometries of best/worst case performance, design GPS constellations, determine optimal user antenna location and understand performance trends among various users.

  17. Determining GPS average performance metrics

    NASA Technical Reports Server (NTRS)

    Moore, G. V.

    1995-01-01

    Analytic and semi-analytic methods are used to show that users of the GPS constellation can expect performance variations based on their location. Specifically, performance is shown to be a function of both altitude and latitude. These results stem from the fact that the GPS constellation is itself non-uniform. For example, GPS satellites are over four times as likely to be directly over Tierra del Fuego than over Hawaii or Singapore. Inevitable performance variations due to user location occur for ground, sea, air and space GPS users. These performance variations can be studied in an average relative sense. A semi-analytic tool which symmetrically allocates GPS satellite latitude belt dwell times among longitude points is used to compute average performance metrics. These metrics include average number of GPS vehicles visible, relative average accuracies in the radial, intrack and crosstrack (or radial, north/south, east/west) directions, and relative average PDOP or GDOP. The tool can be quickly changed to incorporate various user antenna obscuration models and various GPS constellation designs. Among other applications, tool results can be used in studies to: predict locations and geometries of best/worst case performance, design GPS constellations, determine optimal user antenna location and understand performance trends among various users.

  18. Optimal Preprocessing Of GPS Data

    NASA Technical Reports Server (NTRS)

    Wu, Sien-Chong; Melbourne, William G.

    1994-01-01

    Improved technique for preprocessing data from Global Positioning System (GPS) receiver reduces processing time and number of data to be stored. Technique optimal in sense it maintains strength of data. Also sometimes increases ability to resolve ambiguities in numbers of cycles of received GPS carrier signals.

  19. GPS Position Time Series @ JPL

    NASA Technical Reports Server (NTRS)

    Owen, Susan; Moore, Angelyn; Kedar, Sharon; Liu, Zhen; Webb, Frank; Heflin, Mike; Desai, Shailen

    2013-01-01

    Different flavors of GPS time series analysis at JPL - Use same GPS Precise Point Positioning Analysis raw time series - Variations in time series analysis/post-processing driven by different users. center dot JPL Global Time Series/Velocities - researchers studying reference frame, combining with VLBI/SLR/DORIS center dot JPL/SOPAC Combined Time Series/Velocities - crustal deformation for tectonic, volcanic, ground water studies center dot ARIA Time Series/Coseismic Data Products - Hazard monitoring and response focused center dot ARIA data system designed to integrate GPS and InSAR - GPS tropospheric delay used for correcting InSAR - Caltech's GIANT time series analysis uses GPS to correct orbital errors in InSAR - Zhen Liu's talking tomorrow on InSAR Time Series analysis

  20. GPS Position Time Series @ JPL

    NASA Technical Reports Server (NTRS)

    Owen, Susan; Moore, Angelyn; Kedar, Sharon; Liu, Zhen; Webb, Frank; Heflin, Mike; Desai, Shailen

    2013-01-01

    Different flavors of GPS time series analysis at JPL - Use same GPS Precise Point Positioning Analysis raw time series - Variations in time series analysis/post-processing driven by different users. center dot JPL Global Time Series/Velocities - researchers studying reference frame, combining with VLBI/SLR/DORIS center dot JPL/SOPAC Combined Time Series/Velocities - crustal deformation for tectonic, volcanic, ground water studies center dot ARIA Time Series/Coseismic Data Products - Hazard monitoring and response focused center dot ARIA data system designed to integrate GPS and InSAR - GPS tropospheric delay used for correcting InSAR - Caltech's GIANT time series analysis uses GPS to correct orbital errors in InSAR - Zhen Liu's talking tomorrow on InSAR Time Series analysis

  1. Fabrication and characterization of WO3/Ag/WO3 multilayer transparent anode with solution-processed WO3 for polymer light-emitting diodes

    PubMed Central

    2012-01-01

    The dielectric/metal/dielectric multilayer is suitable for a transparent electrode because of its high-optical and high-electrical properties; however, it is fabricated by an expensive and inefficient multistep vacuum process. We present a WO3/Ag/WO3 (WAW) multilayer transparent anode with solution-processed WO3 for polymer light-emitting diodes (PLEDs). This WAW multilayer not only has high transmittance and low resistance but also can be easily and rapidly fabricated. We devised a novel method to deposit a thin WO3 layer by a solution process in an air environment. A tungstic acid solution was prepared from an aqueous solution of Na2WO4 and then converted to WO3 nanoparticles (NPs) by a thermal treatment. Thin WO3 NP layers form WAW multilayer with a thermal-evaporated Ag layer, and they improve the transmittance of the WAW multilayer because of its high transmittance and refractive index. Moreover, the surface of the WO3 layer is homogeneous and flat with low roughness because of the WO3 NP generation from the tungstic acid solution without aggregation. We performed optical simulation and experiments, and the optimized WAW multilayer had a high transmittance of 85% with a sheet resistance of 4 Ω/sq. Finally, PLEDs based on the WAW multilayer anode achieved a maximum luminance of 35,550 cd/m2 at 8 V, and this result implies that the solution-processed WAW multilayer is appropriate for use as a transparent anode in PLEDs. PMID:22587669

  2. Nd:SrWO 4 and Nd:BaWO 4 Raman lasers

    NASA Astrophysics Data System (ADS)

    Šulc, J.; Jelínková, H.; Basiev, T. T.; Doroschenko, M. E.; Ivleva, L. I.; Osiko, V. V.; Zverev, P. G.

    2007-09-01

    Properties of the laser operation and simultaneously stimulated Raman scattering in the SRS-active neodymium doped SrWO4 and BaWO4 crystals coherently end-pumped at wavelength 752 nm by pulsed free-running alexandrite laser radiation were investigated. The Nd3+ ion emission at wavelength λNd ˜ 1.06 μm was corresponding to 4F3/2 → 4I11/2 transition. To reach the SRS-self-conversion threshold inside Raman crystal the Nd3+ lasers were operating in a Q-switching regime. For Q-switching LiF:F2- crystal as a saturable absorber was used. Raman self-conversion at wavelength ˜1.17 μm was successfully reached with both tungstate crystals. The shortest generated pulse (1.3 ns FWHM) and highest peak power (615 kW) was obtained with Nd:BaWO4 Raman laser Q-switched by LiF:F2- crystal with initial transmission T0 = 60%. Up to 0.8 mJ was registered at the first Stokes wavelength 1169 nm. Using Q-switched Nd:SrWO4 laser higher energy in Raman emission was obtained (1.23 mJ) but generated pulse was longer (2.9 ns FWHM) resulting in lower peak power (430 kW).

  3. Dye-sensitized solar cells based on WO3.

    PubMed

    Zheng, Haidong; Tachibana, Yasuhiro; Kalantar-Zadeh, Kourosh

    2010-12-21

    In research on alternative photoanode materials for dye-sensitized solar cells (DSCs), there is rarely any report on WO(3), probably due to its acidic surface and more positive (vs NHE) conduction band edge position compared to TiO(2) and ZnO. For the first time, dye-sensitized solar cells based on porous WO(3) nanoparticle films were successfully fabricated with efficiency of up to 0.75%. The multicrystalline structure of WO(3) was examined by Raman spectroscopy and X-ray diffraction analysis. It was found that significant performance enhancement can be obtained from treating the WO(3) nanoparticle film with TiCl(4); the TiCl(4)-treated WO(3) DSCs were recorded with efficiency reaching 1.46%.

  4. The need for GPS standardization

    NASA Technical Reports Server (NTRS)

    Lewandowski, Wlodzimierz W.; Petit, Gerard; Thomas, Claudine

    1992-01-01

    A desirable and necessary step for improvement of the accuracy of Global Positioning System (GPS) time comparisons is the establishment of common GPS standards. For this reason, the CCDS proposed the creation of a special group of experts with the objective of recommending procedures and models for operational time transfer by GPS common-view method. Since the announcement of the implementation of Selective Availability at the end of last spring, action has become much more urgent and this CCDS Group on GPS Time Transfer Standards has now been set up. It operates under the auspices of the permanent CCDS Working Group on TAI and works in close cooperation with the Sub-Committee on Time of the Civil GPS Service Interface Committee (CGSIC). Taking as an example the implementation of SA during the first week of July 1991, this paper illustrates the need to develop urgently at least two standardized procedures in GPS receiver software: monitoring GPS tracks with a common time scale and retaining broadcast ephemeris parameters throughout the duration of a track. Other matters requiring action are the adoption of common models for atmospheric delay, a common approach to hardware design and agreement about short-term data processing. Several examples of such deficiencies in standardization are presented.

  5. Nd:SrWO4 Raman laser

    NASA Astrophysics Data System (ADS)

    Jelinkova, Helena; Sulc, Jan; Doroschenko, Maxim E.; Skornyakov, Vadim V.; Kravtsov, Sergey B.; Basiev, Tasoltan T.; Zverev, Peter G.

    2004-09-01

    Properties of the laser operation and simultaneously stimulated Raman scattering in the new SRS-active neodymium doped SrWO4 crystal coherently end-pumped by alexandrite 752 nm laser radiation were investigated. The maximum generated energy 90 mJ from the free-running Nd3+:SrWO4 laser at 1057 nm wavelength was obtained with the output coupler reflectivity 52%. The slope efficiency reached s = 0.52, the beam characteristic parameters M2 and divergence q were 2.5 +/- 0.1, and 1.5 +/- 0.1 mrad, respectively. Maximal output energy of 1.46 mJ for the fundamental wavelength was obtained for Q-switched Nd3+:SrWO4 oscillator with a double Fabry-Perrot as the output coupler (R = 48%), and with the 5% initial transmission of LiF:F2- saturable absorber. Up to 0.74 mJ energy was registered at the first Stokes frequency. The pulse duration was 5 ns and 2.4 ns for the fundamental and Stokes radiation, respectively. The energy of 1.25 mJ at 1170 nm was obtained for closed Raman resonator with special mirrors. For the case of mode-locking, two dye saturable absorbers (ML51 dye in dichlorethan and 3955 dye in ethanol) were used and SRS radiation in the form of pulse train was observed. The influence of the various Raman laser output couplers reflectivity as well as the initial transmissions of passive absorbers were investigated with the goal of the output energy maximization at the Stokes wavelength. In the output, the total measured energy was 1.8 mJ (for ML51 dye) and 2.4 mJ (for 3955 dye). The SRS output at 1170 nm was approximately 20% of total energy.

  6. Visible-Near-Infrared-Light-Driven Oxygen Evolution Reaction with Noble-Metal-Free WO2-WO3 Hybrid Nanorods.

    PubMed

    Wang, Song Ling; Mak, Yan Lin; Wang, Shijie; Chai, Jianwei; Pan, Feng; Foo, Maw Lin; Chen, Wei; Wu, Kai; Xu, Guo Qin

    2016-12-13

    Understanding and manipulating the one half-reaction of photoinduced hole-oxidation to oxygen are of fundamental importance to design and develop an efficient water-splitting process. To date, extensive studies on oxygen evolution from water splitting have focused on visible-light harvesting. However, capturing low-energy photons for oxygen evolution, such as near-infrared (NIR) light, is challenging and not well-understood. This report presents new insights into photocatalytic water oxidation using visible and NIR light. WO2-WO3 hybrid nanorods were in situ fabricated using a wet-chemistry route. The presence of metallic WO2 strengthens light absorption and promotes the charge-carrier separation of WO3. The efficiency of the oxygen evolution reaction over noble-metal-free WO2-WO3 hybrids was found to be significantly promoted. More importantly, NIR light (≥700 nm) can be effectively trapped to cause the photocatalytic water oxidation reaction. The oxygen evolution rates are even up to around 220 (λ = 700 nm) and 200 (λ = 800 nm) mmol g(-1) h(-1). These results demonstrate that the WO2-WO3 material is highly active for water oxidation with low-energy photons and opens new opportunities for multichannel solar energy conversion.

  7. Orbital problems in GPS interferometry

    NASA Astrophysics Data System (ADS)

    Zielinski, Janusz B.

    The GPS orbits and the influence of the orbital errors on the geodetic determination were investigated during the last few years. In the paper, the summary of some analyses is presented concerning the nature of the interferometric observations, the propagation of the orbital errors, and the correlations and covariances in geodetic GPS solutions. One of the results was a proof that, in relative determinations by GPS, the error propagation factor is close to b/10 h, that is almost one order smaller than previously supposed.

  8. Precise GPS orbits for geodesy

    NASA Technical Reports Server (NTRS)

    Colombo, Oscar L.

    1994-01-01

    The Global Positioning System (GPS) has become, in recent years, the main space-based system for surveying and navigation in many military, commercial, cadastral, mapping, and scientific applications. Better receivers, interferometric techniques (DGPS), and advances in post-processing methods have made possible to position fixed or moving receivers with sub-decimeter accuracies in a global reference frame. Improved methods for obtaining the orbits of the GPS satellites have played a major role in these achievements; this paper gives a personal view of the main developments in GPS orbit determination.

  9. Compensating For GPS Ephemeris Error

    NASA Technical Reports Server (NTRS)

    Wu, Jiun-Tsong

    1992-01-01

    Method of computing position of user station receiving signals from Global Positioning System (GPS) of navigational satellites compensates for most of GPS ephemeris error. Present method enables user station to reduce error in its computed position substantially. User station must have access to two or more reference stations at precisely known positions several hundred kilometers apart and must be in neighborhood of reference stations. Based on fact that when GPS data used to compute baseline between reference station and user station, vector error in computed baseline is proportional ephemeris error and length of baseline.

  10. Remote Clock Calibration Via GPS

    DTIC Science & Technology

    1986-12-01

    cesium clocks and a Global Positioning System ( GPS ) receiver. The f i rs t purpose was t o ca l ibra te t h e propagation delays and timing... positions in t h e vicinity of each t r ansmi t t e r could be obtained f rom survey markers in the a r e a or determined by t h e GPS receiver a...t any desired location. While t h e GPS receiver was used to obtain positions f o r t h e LORAN par t of t h e experiment, i t was also

  11. Phase transformations upon doping in WO3

    NASA Astrophysics Data System (ADS)

    Wang, Wennie; Janotti, Anderson; Van de Walle, Chris G.

    2017-06-01

    High levels of doping in WO3 have been experimentally observed to lead to structural transformation towards higher symmetry phases. We explore the structural phase diagram with charge doping through first-principles methods based on hybrid density functional theory, as a function of doping the room-temperature monoclinic phase transitions to the orthorhombic, tetragonal, and finally cubic phase. Based on a decomposition of energies into electronic and strain contributions, we attribute the transformation to a gain in energy resulting from a lowering of the conduction band on an absolute energy scale.

  12. Sustainable Rejuvenation of Electrochromic WO3 Films.

    PubMed

    Wen, Rui-Tao; Niklasson, Gunnar A; Granqvist, Claes G

    2015-12-30

    Devices relying on ion transport normally suffer from a decline of their long-term performance due to irreversible ion accumulation in the host material, and this effect may severely curtail the operational lifetime of the device. In this work, we demonstrate that degraded electrochromic WO3 films can sustainably regain their initial performance through galvanostatic detrapping of Li(+) ions. The rejuvenated films displayed degradation features similar to those of the as-prepared films, thus indicating that the detrapping process is effectively reversible so that long-term performance degradation can be successfully avoided. Detrapping did not occur in the absence of an electric current.

  13. Evaluating elk habitat interactions with GPS collars

    Treesearch

    Mark A. Rumble; Lakhdar Benkobi; Fredrick Lindzey; R. Scott Gamo

    2001-01-01

    Global positioning systems (GPS) are likely to revolutionize animal telemetry studies. GPS collars allow biologists to collect systematically scheduled data when VHF telemetry data is difficult or impossible to collect. Past studies have shown that the success of GPS telemetry is greater when animals are standing, or in open habitats. To make effective use of GPS...

  14. GPS (Global Positioning System) Range Applications Study.

    DTIC Science & Technology

    1982-12-31

    Global Positioning System ( GPS ) as a source of Time i. Space Position ...THE ANALYTIC SCIENCES CORPORATION 2. GPS OVERVIEW This chapter provides a short, general introduction to the Global Positioning System ( GPS ) and...chapters. 2.1 SYSTEM OPERATION The NAVSTAR Global Positioning System ( GPS ) is a space- based radio navigation system designed to provide users with

  15. The green emission and local structure of the scintillator PbWO 4

    NASA Astrophysics Data System (ADS)

    Qi, Zeming; Shi, Chaoshu; Zhou, Dongfang; Tang, Honggao; Liu, Tao; Hu, Tiandou

    2001-12-01

    The green emission of lead tungstate (PbWO 4 ) is closely related to structure defects. For studying the mechanism of the green emission, the local structure of PbWO 4 has been first investigated by extended X-ray absorption fine structure using synchrotron radiation. The results indicate that the excess oxygen in air-annealed PbWO 4 exists and forms “WO 4+O i” centers. The green emission of PbWO 4 is not caused by (WO 3+F) centers, but probably originates from the centers of “WO 4+O i”.

  16. Synthesis of S-doped WO3 nanowires with enhanced photocatalytic performance towards dye degradation

    NASA Astrophysics Data System (ADS)

    Han, Fugui; Li, Heping; Fu, Li; Yang, Jun; Liu, Zhong

    2016-05-01

    In this letter, S-doped WO3 nanowires (S-WO3) were prepared using a hydrothermal method followed by a low-temperature solid-state annealing treatment. The synthesized S-WO3 was characterized by SEM, EDX, XRD, XPS, Raman spectroscopy, UV-vis DRS and photocurrent responses. The results indicated that S could enhance the light harvesting capacity of WO3 nanowires. The photocatalytic performance of the S-WO3 was investigated by photodegradation of methyl orange (MO) under visible light irradiation. Results demonstrated that the photocatalytic activity of the S-WO3 nanowires is much higher than that of pure WO3 nanowires.

  17. Scintillation-Hardened GPS Receiver

    NASA Technical Reports Server (NTRS)

    Stephens, Donald R.

    2015-01-01

    CommLargo, Inc., has developed a scintillation-hardened Global Positioning System (GPS) receiver that improves reliability for low-orbit missions and complies with NASA's Space Telecommunications Radio System (STRS) architecture standards. A software-defined radio (SDR) implementation allows a single hardware element to function as either a conventional radio or as a GPS receiver, providing backup and redundancy for platforms such as the International Space Station (ISS) and high-value remote sensing platforms. The innovation's flexible SDR implementation reduces cost, weight, and power requirements. Scintillation hardening improves mission reliability and variability. In Phase I, CommLargo refactored an open-source GPS software package with Kalman filter-based tracking loops to improve performance during scintillation and also demonstrated improved navigation during a geomagnetic storm. In Phase II, the company generated a new field-programmable gate array (FPGA)-based GPS waveform to demonstrate on NASA's Space Communication and Navigation (SCaN) test bed.

  18. High Rate GPS on Volcanoes

    NASA Astrophysics Data System (ADS)

    Mattia, M.

    2005-12-01

    The high rate GPS data processing can be considered as the "new deal" in geodetic monitoring of active volcanoes. Before an eruption, infact, transient episodes of ground displacements related to the dynamics of magmatic fluids can be revealed through a careful analysis of high rate GPS data. In the very first phases of an eruption the real time processing of high rate GPS data can be used by the authorities of Civil Protection to follow the opening of fractures field on the slopes of the volcanoes. During an eruption large explosions, opening of vents, migration of fractures fields, landslides and other dangerous phenomena can be followed and their potential of damage estimated by authorities. Examples from the recent eruption of Stromboli volcano and from the current activities of high rate GPS monitoring on Mt. Etna are reported, with the aim to show the great potential and the perspectives of this technique.

  19. Efficient GPS Position Determination Algorithms

    DTIC Science & Technology

    2007-06-01

    Dilution of Precision ( GDOP ) conditions. The novel differential GPS algorithm for a network of users that has been developed in this research uses a...performance is achieved, even under high Geometric Dilution of Precision ( GDOP ) conditions. The second part of this research investigates a...respect to the receiver produces high Geometric Dilution of Precision ( GDOP ), which can adversely affect GPS position solutions [1]. Four

  20. GPS Modernization and Program Update

    DTIC Science & Technology

    2011-03-02

    2 March 2011 Colonel Bernie Gruber Director Global Positioning Systems Directorate 2011 03 03 Munich Summit v8 GPS Modernization and Program Update...Munich Summit v8 Global Positioning Systems Directorate Mission: Deliver sustained, reliable GPS capabilities to America’s warfighters, our allies...5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Air Force Space Command,Space & Missile Systems Center, Global Positioning

  1. Alternative Timing Networks with GPS

    DTIC Science & Technology

    1989-11-01

    receiving stations has been investigated. The xnethods of llsirlg tht: Global P~s i t~ iun- ing System ( GPS ) for transferring time in previolis work has...planes established by the positions of the other stations used to range to six SV’s. Tn this coordinate system the number of observations (24) will...ALTERNATIVE TIMING NETWORKS WITH GPS G.P. Landis, S. Stebbins, and ILL. Heard Naval ltesearch Laboratory Washington, D.C. and H.F. Pliegel The

  2. Global Positioning Systems Directorate: GPS Update

    DTIC Science & Technology

    2015-04-29

    Council Maintenance/Security Spectrum 39 Satellites /31 Set Healthy Baseline Constellation : 24 Satellites • All Level l and Level II...Department of Transportation • Federal Aviation Administration Satellite Block GPS IIA GPS IIR GPS IIR-M GPS IIF Constellation Department of...segment - India- IRNSS UNCLASSIFIED/APPROVED FOR PUBLIC RELEASE 3 UNCLASSIFIED/APPROVED FOR PUBLIC RELEASE GPS Constellation Status SPACE AND

  3. Locating The Geocenter From GPS Measurements

    NASA Technical Reports Server (NTRS)

    Vigue, Yvonne; Lichten, Stephen M.; Blewitt, Geoffrey; Heflin, Michael B.; Malla, Rajendra P.

    1994-01-01

    Report presents analysis of Global Positioning System (GPS) measurements taken during 3-week geodetic experiment in early 1991. Involved constellation of 15 GPS satellites operational at that time, plus 21 GPS receiving stations at widely distributed sites, all but 4 of which in Northern Hemisphere. Analysis consisted principally of estimation of location of center of mass of Earth relative to GPS receiving stations. As part of analysis, GPS estimates of geocenter compared with estimates obtained by satellite laser ranging (SLR).

  4. Kinetics and mechanism of dye adsorption on WO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Adhikari, Sangeeta; Mandal, Sandip; Sarkar, Debasish; Kim, Do-Heyoung; Madras, Giridhar

    2017-10-01

    Monoclinic WO3 nanoparticles were synthesized by a simple acid catalyzed co-precipitation reaction. Spherical particles with average size ∼55 nm were confirmed from electron microscopy followed by functional, structural and optical characterizations. The adsorption of methylene blue was examined by using WO3 nanoparticles and the capacity was higher than most of the reported studies. The effect of pH and material loading on adsorption was determined. The mechanism of adsorption was examined by XPS and a detailed explanation of surface phenomena was proposed. Regeneration study was carried and a high stability of heat treated WO3 towards adsorption of methylene blue was observed.

  5. WO3 nanopaticles and PEDOT:PSS/WO3 composite thin films studied for photocatalytic and electrochromic applications

    NASA Astrophysics Data System (ADS)

    Ivanov Boyadjiev, Stefan; Manduca, Bruno; Szűcs, Júlia; Miklós Szilágyi, Imre

    2016-03-01

    WO3 is a widely studied material for electrochromic and photocatalytic applications. In the present study, WO3 nanoparticles with a controlled structure (monoclinic or hexagonal) were obtained by controlled thermal decomposition of hexagonal ammonium tungsten bronze in air at 500 °C and 600 °C, respectively. The formation, morphology, structure and composition of the as-prepared nanoparticles were studied by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX). The photocatalytic activity of the monoclinic and hexagonal WO3 nanoparticles was studied by decomposing methyl orange in aqueous solution under UV light irradiation. In order to study the electrochromic properties of the WO3 nanoparticles, as well to introduce them for self-cleaning photocatalytic surface applications, thin films were prepared from the WO3 particles together with a conductive polymer. For this, PEDOT:PSS was used, which gives excellent opportunities for obtaining transparent and conductive thin films, suitable for both electrochromic and photocatalytic applications. By spin-coating, transparent PEDOT:PSS/WO3 composite thin films were prepared, on which cyclic voltammetry measurements were performed, and the coloring and bleaching states were studied. Our initial results for the PEDOT:PSS/WO3 composite thin films are promising, suggesting that such composites, after further development, might be successfully used in electrochromic devices and photocatalysis.

  6. Wakeshield WSF-02 GPS Experiment

    NASA Technical Reports Server (NTRS)

    Schutz, B. E.; Abusali, P. A. M.; Schroeder, Christine; Tapley, Byron; Exner, Michael; Mccloskey, rick; Carpenter, Russell; Cooke, Michael; Mcdonald, samantha; Combs, Nick; Duncan, Courtney; Dunn, Charles; Meehan, Tom

    1995-01-01

    Shuttle mission STS-69 was launched on September 7, 1995, 10:09 CDT, carrying the Wake Shield Facility (WSF-02). The WSF-02 spacecraft included a set of payloads provided by the Texas Space Grant Consortium, known as TexasSat. One of the TexasSat payloads was a GPS TurboRogue receiver loaned by the University Corporation for Atmospheric Research. On September 11, the WSF-02 was unberthed from the Endeavour payload bay using the remote manipulator system. The GPS receiver was powered on prior to release and the WSF-02 remained in free-flight for three days before being retrieved on September 14. All WSF-02 GPS data, which includes dual frequency pseudorange and carrier phase, were stored in an on-board recorder for post-flight analysis, but "snap- shots" of data were transmitted for 2-3 minutes at intervals of several hours, when permitted by the telemetry band- widdl The GPS experiment goals were: (1) an evaluation of precision orbit determination in a low altitude environment (400 km) where perturbations due to atmospheric drag and the Earth's gravity field are more pronounced than for higher altitude satellites with high precision orbit requirements, such as TOPEX/POSEIDON; (2) an assessment of relative positioning using the WSF GPS receiver and the Endeavour Collins receiver; and (3) determination of atmospheric temperature profiles using GPS signals passing through the atmosphere. Analysis of snap-shot telemetry data indicate that 24 hours of continuous data were stored on board, which includes high rate (50 Hz) data for atmosphere temperature profiles. Examination of the limited number of real-time navigation solutions show that at least 7 GPS satellites were tracked simultaneously and the on-board clock corrections were at the microsec level, as expected. Furthermore, a dynamical consistency test provided a further validation of the on-board navigation solutions. Complete analysis will be conducted in post-flight using the data recorded on-board.

  7. GPS/INS Sensor Fusion Using GPS Wind up Model

    NASA Technical Reports Server (NTRS)

    Williamson, Walton R. (Inventor)

    2013-01-01

    A method of stabilizing an inertial navigation system (INS), includes the steps of: receiving data from an inertial navigation system; and receiving a finite number of carrier phase observables using at least one GPS receiver from a plurality of GPS satellites; calculating a phase wind up correction; correcting at least one of the finite number of carrier phase observables using the phase wind up correction; and calculating a corrected IMU attitude or velocity or position using the corrected at least one of the finite number of carrier phase observables; and performing a step selected from the steps consisting of recording, reporting, or providing the corrected IMU attitude or velocity or position to another process that uses the corrected IMU attitude or velocity or position. A GPS stabilized inertial navigation system apparatus is also described.

  8. Precision GPS ephemerides and baselines

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The required knowledge of the Global Positioning System (GPS) satellite position accuracy can vary depending on a particular application. Application to relative positioning of receiver locations on the ground to infer Earth's tectonic plate motion requires the most accurate knowledge of the GPS satellite orbits. Research directed towards improving and evaluating the accuracy of GPS satellite orbits was conducted at the University of Texas Center for Space Research (CSR). Understanding and modeling the forces acting on the satellites was a major focus of the research. Other aspects of orbit determination, such as the reference frame, time system, measurement modeling, and parameterization, were also investigated. Gravitational forces were modeled by truncated versions of extant gravity fields such as, Goddard Earth Model (GEM-L2), GEM-T1, TEG-2, and third body perturbations due to the Sun and Moon. Nongravitational forces considered were the solar radiation pressure, and perturbations due to thermal venting and thermal imbalance. At the GPS satellite orbit accuracy level required for crustal dynamic applications, models for the nongravitational perturbation play a critical role, since the gravitational forces are well understood and are modeled adequately for GPS satellite orbits.

  9. Hydrothermally grown nanostructured WO3 films and their electrochromic characteristics

    NASA Astrophysics Data System (ADS)

    Jiao, Zhihui; Sun, Xiao Wei; Wang, Jinmin; Ke, Lin; Demir, Hilmi Volkan

    2010-07-01

    We report the synthesis of nanostructured tungsten trioxide (WO3) films and their electrochromic characteristics. Plate-like monoclinic WO3 nanostructures were grown directly on fluorine-doped tin oxide glass substrates by a simple and low-cost crystal-seed-assisted hydrothermal method. The growth mechanism of the film is investigated. HRTEM analysis reveals the single crystalline quality of the WO3 nanostructure. The film exhibits tunable transmittance modulation under different voltages and repetitive cycling between the clear and blue states has no deleterious effect on its electrochromic performance after 3000 cycles. The electrochromic device composed of the WO3 film has high electrochromic stability, colour contrast and reasonable switching response with a colouration efficiency of 38.2 cm2 C-1 at 632.8 nm.

  10. Electrochromic device based on electrospun WO{sub 3} nanofibers

    SciTech Connect

    Dulgerbaki, Cigdem; Maslakci, Neslihan Nohut; Komur, Ali Ihsan; Oksuz, Aysegul Uygun

    2015-12-15

    Highlights: • WO{sub 3} electrochromic nanofibers were prepared by electrospinning technique. • WO{sub 3} nanofibers switched reversibly from transparent to blue color. • Electrochromic device was assembled using ionic liquid based gel electrolyte. • Significant optical modulation and excellent cycling stability were achieved for ECD. - Abstract: The tungsten oxide (WO{sub 3}) nanofibers were grown directly onto an ITO-coated glass via an electrospinning method for electrochromic applications. The electrochromic properties of WO{sub 3} nanofibers were investigated in the presence of different electrolytes including a series of ionic liquids and classic LiClO{sub 4}-PC system. A significant optical modulation of 20.82% at 760 nm, reversible coloration with efficiency of 64.58 cm{sup 2}/C and excellent cycling stability were achieved for the nanofiber electrochromic device (ECD) with ionic liquid based gel electrolyte.

  11. Insight into Charge Separation in WO3/BiVO4 Heterojunction for Solar Water Splitting.

    PubMed

    Chae, Sang Youn; Lee, Chang Soo; Jung, Hyejin; Joo, Oh-Shim; Min, Byoung Koun; Kim, Jong Hak; Hwang, Yun Jeong

    2017-06-14

    Recently, the WO3/BiVO4 heterojunction has shown promising photoelectrochemical (PEC) water splitting activity based on its charge transfer and light absorption capability, and notable enhancement of the photocurrent has been achieved via morphological modification of WO3. We developed a graft copolymer-assisted protocol for the synthesis of WO3 mesoporous thin films on a transparent conducting electrode, wherein the particle size, particle shape, and thickness of the WO3 layer were controlled by tuning the interactions in the polymer/sol-gel hybrid. The PEC performance of the WO3 mesoporous photoanodes with various morphologies and the individual heterojunctions with BiVO4 (WO3/BiVO4) were characterized by measuring the photocurrents in the absence/presence of hole scavengers using light absorption spectroscopy and intensity-modulated photocurrent spectroscopy. The morphology of the WO3 photoanode directly influenced the charge separation efficiency within the WO3 layer and concomitant charge collection efficiency in the WO3/BiVO4 heterojunction, showing the smaller sized nanosphere WO3 layer showed higher values than did the plate-like or rod-like one. Notably, we observed that photocurrent density of WO3/BiVO4 was not dependent on the thickness of WO3 film or its charge collection time, implying slow charge flow from BiVO4 to WO3 can be a crucial issue in determining the photocurrent, rather than the charge separation within the nanosphere WO3 layer.

  12. Driving Force for the WO3(001) Surface Relaxation

    SciTech Connect

    Yakovkin, Ivan N.; Gutowski, Maciej S.

    2007-03-15

    The optimized structure of the WO3(001) surface with various types of termination ((1x1)O, (1x1) WO2, and c(2x2)O) has been simulated using density functional theory with the Perdew-Wang 91 gradient-corrected exchange correlation functional. While energy of bulk WO3 depends weakly on the distortions and tilting of the WO6 octahedra, relaxation the (001) surface results in a significant decrease of surface energy (from 10.2x10-2 eV/Å2 for bulk-extracted, ReO3-like, c(2x2)O-terminated surface to 2.2x10-2 eV/Å2 for the relaxed surface). This feature illustrates important role of surface in formation of crystalline nano-size clusters of WO3. The surface relaxation is accompanied by a dramatic redistribution of density of states near the Fermi level, in particular the transformations of surface electronic states. This redistribution is responsible for the decrease of electronic energy and therefore is suggested to be the driving force for surface relaxation of the WO3(001) surface and, presumably, similar surfaces of other transition metal oxides. Battelle operates PNNL for the USDOE.

  13. GPS test range mission planning

    NASA Astrophysics Data System (ADS)

    Roberts, Iris P.; Hancock, Thomas P.

    The principal features of the Test Range User Mission Planner (TRUMP), a PC-resident tool designed to aid in deploying and utilizing GPS-based test range assets, are reviewed. TRUMP features time history plots of time-space-position information (TSPI); performance based on a dynamic GPS/inertial system simulation; time history plots of TSPI data link connectivity; digital terrain elevation data maps with user-defined cultural features; and two-dimensional coverage plots of ground-based test range assets. Some functions to be added during the next development phase are discussed.

  14. Photoluminescence in solid solutions and thin films of tungstates CaWO{sub 4}-CdWO{sub 4}

    SciTech Connect

    Taoufyq, A.; Mauroy, V.; Guinneton, F.; Valmalette, J-C.; Fiorido, T.; Benlhachemi, A.; Lyoussi, A.; Nolibe, G.; Gavarri, J-R.

    2015-07-01

    In this study, we present two types of studies on the luminescence properties under UV and X-ray excitations of solid solutions Ca{sub 1-x}Cd{sub x}WO{sub 4} and of thin layers of CaWO{sub 4} and CdWO{sub 4}. These tungstate based solid solutions are susceptible to be integrated into new radiation sensors, in order to be used in different fields of applications such as reactor measurements, safeguards, homeland security, nuclear nondestructive assays, LINAC emission radiation measurement. However these complex materials were rarely investigated in the literature. One first objective of our studies was to establish correlations between luminescence efficiency, chemical substitution and the degree of crystallization resulting from elaboration conditions. A second objective will be to determine the efficiency of luminescence properties of thin layers of these materials. In the present work, we focus our attention on the role of chemical substitution on photon emissions under UV and X-ray irradiations. The luminescence spectra of Ca{sub 1-x}Cd{sub x}WO{sub 4} polycrystalline materials have been investigated at room temperature as a function of composition (0≤x≤1). In addition, we present a preliminary study of the luminescence of CaWO{sub 4} and CdWO{sub 4} thin layers: oscillations observed in the case of X-ray excitations in the luminescence spectra are discussed. (authors)

  15. In-situ transmission electron microscopy imaging of formation and evolution of Li{sub x}WO{sub 3} during lithiation of WO{sub 3} nanowires

    SciTech Connect

    Qi, Kuo; Li, Xiaomin; Sun, Muhua; Huang, Qianming; Wei, Jiake; Xu, Zhi E-mail: xdbai@iphy.ac.cn; Wang, Wenlong; Bai, Xuedong E-mail: xdbai@iphy.ac.cn; Wang, Enge

    2016-06-06

    The phase transition from monoclinic WO{sub 3} to cubic Li{sub x}WO{sub 3} during lithiation of WO{sub 3} is one of the key features for tungsten oxide as the most used electrochromic material. Conventionally, the lithium intercalation of WO{sub 3} has been studied by building generic layered electrochromic device combining with structural characterization and electrochemistry measurement at macro scale. In-situ transmission electron microscopy (in-situ TEM) has been proposed as a method for revealing the detailed mechanism of structural, physical, and chemical properties. Here, we use in-situ TEM method to investigate the formation and evolution of Li{sub x}WO{sub 3} in real-time during the electrochemical lithiation of WO{sub 3} nanowires. The dynamic lithiation process is recorded by TEM imaging, diffraction, and electron energy loss spectroscopy. The WO{sub 3}-Li{sub x}WO{sub 3} phase boundary of reaction front has been observed at high resolution. The timeliness of crystallinity of Li{sub x}WO{sub 3} and the intercalation channels for Li ions are also identified. Moreover, the co-existence of both polycrystalline Li-poor area and amorphous Li-rich phases of Li{sub x}WO{sub 3} was found. Our results provide an insight into the basic lithiation process of WO{sub 3}, which is significantly important for understanding the electrochromic mechanism of tungsten oxide.

  16. In-situ transmission electron microscopy imaging of formation and evolution of LixWO3 during lithiation of WO3 nanowires

    NASA Astrophysics Data System (ADS)

    Qi, Kuo; Li, Xiaomin; Sun, Muhua; Huang, Qianming; Wei, Jiake; Xu, Zhi; Wang, Wenlong; Bai, Xuedong; Wang, Enge

    2016-06-01

    The phase transition from monoclinic WO3 to cubic LixWO3 during lithiation of WO3 is one of the key features for tungsten oxide as the most used electrochromic material. Conventionally, the lithium intercalation of WO3 has been studied by building generic layered electrochromic device combining with structural characterization and electrochemistry measurement at macro scale. In-situ transmission electron microscopy (in-situ TEM) has been proposed as a method for revealing the detailed mechanism of structural, physical, and chemical properties. Here, we use in-situ TEM method to investigate the formation and evolution of LixWO3 in real-time during the electrochemical lithiation of WO3 nanowires. The dynamic lithiation process is recorded by TEM imaging, diffraction, and electron energy loss spectroscopy. The WO3-LixWO3 phase boundary of reaction front has been observed at high resolution. The timeliness of crystallinity of LixWO3 and the intercalation channels for Li ions are also identified. Moreover, the co-existence of both polycrystalline Li-poor area and amorphous Li-rich phases of LixWO3 was found. Our results provide an insight into the basic lithiation process of WO3, which is significantly important for understanding the electrochromic mechanism of tungsten oxide.

  17. Saved by Iridium? An Alternative to GPS

    DTIC Science & Technology

    2012-05-17

    there is not an alternative to GPS for ground, air, sea, or space operations. The methods of operating with a degradation or loss of GPS are contingent...The methods of operating with a degradation or loss of GPS are contingent on the type of operation, whether it is land, sea, air, or space; as the...posits the following research question: How should the joint force continue battlefield operations in the event of degradation or loss of GPS? In

  18. GPS: Public Utility or Software Platform

    DTIC Science & Technology

    2016-09-01

    of charge ,22 And anyone who has a GPS receiver can utilize the GPS signal. It has made many of GPS civil specifications publicly available.23...Verizon) and public utilities (e.g., electricity companies) use GPS’s timing signals to help manage and route the flow of transmission through their...hopes to achieve by providing GPS globally and free of charge . Through GPS’s design and operations, the United States has determined who can use the

  19. Photocatalytic properties of h-WO3 nanoparticles obtained by annealing and h-WO3 nanorods prepared by hydrothermal method

    NASA Astrophysics Data System (ADS)

    Boyadjiev, Stefan I.; Nagy-Kovács, Teodóra; Lukács, István; Szilágyi, Imre M.

    2016-03-01

    In the present study, two different methods for preparing hexagonal WO3 (h-WO3) photocatalysts were used - controlled thermal decomposition and hydrothermal synthesis. WO3 nanoparticles with hexagonal structure were obtained by annealing (NH4)xWO3-y at 500 °C in air. WO3 nanorods were prepared by a hydrothermal method using sodium tungstate Na2WO4, HCl, (COOH)2 and NaSO4 precursors at 200 °C. The formation, morphology, structure and composition of the as-prepared nanoparticles and nanorods were studied by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX). The photocatalytic activity of the h-WO3 nanoparticles and nanorods was studied by decomposing methyl orange in aqueous solution under UV light irradiation.

  20. Global Positioning System III (GPS III)

    DTIC Science & Technology

    2015-12-01

    modernization of the constellation . GPS III complies with 10 United States Code (USC) § 2281, ensuring the continued sustainment and operation of GPS for... constellations , further increasing the accuracy and availability of user PNT solutions. GPS III December 2015 SAR March 23, 2016 16:15:29 UNCLASSIFIED

  1. Accuracy of Tracking Forest Machines with GPS

    Treesearch

    M.W. Veal; S.E. Taylor; T.P. McDonald; D.K. McLemore; M.R. Dunn

    2001-01-01

    This paper describes the results of a study that measured the accuracy of using GPS to track movement offorest machines. Two different commercially available GPS receivers (Trimble ProXR and GeoExplorer II) were used to track wheeled skidders under three different canopy conditions at two different vehicle speeds. Dynamic GPS data were compared to position data...

  2. Aiding GPS With Additional Satellite Navigation Services

    DTIC Science & Technology

    2010-03-01

    10 FDMA Frequency Division Multiple Access . . . . . . . . . . . . . 10 GBCC Ground Based Control Complex . . . . . . . . . . . . . . . 11...Precision Service (HPS), which is like PPS in GPS. GLONASS uses Frequency Division Multiple Access ( FDMA ) unlike the CDMA used in GPS. Every GLONASS...GLONASS uses FDMA , its receiver design is more costly compared to GPS. The GLONASS user segment is small and located primarily in Russia. There are

  3. A Test Of Precision GPS Clock Synchronization

    NASA Technical Reports Server (NTRS)

    Jefferson, D. C.; Lichten, S. M.; Young, L. E.

    1996-01-01

    This paper will describe tests of precision GPS time transfer using geodetic-quality TurboRogue receivers. The GPS data are processed with the GIPSY-OASIS II software, which simultaneously estimates the GPS satellite orbits and clocks, receiver locations and clock offsets, as well as other parameters such as earth orientation.

  4. GPS Block IIF Atomic Frequency Standard Analysis

    DTIC Science & Technology

    2010-11-01

    Frequency stability of GPS constellation for October 2010 (NGA products). REFERENCES [1] “ Rubidium Atomic Frequency Standard (RAFS) GPS...Block IIR Rubidium Atomic Frequency Standard Life Test,” in Proceedings of the 30 th Annual Precise Time and Time Interval (PTTI) Applications and...42 nd Annual Precise Time and Time Interval (PTTI) Meeting 181 GPS BLOCK IIF ATOMIC FREQUENCY STANDARD ANALYSIS

  5. Detection of VHF lightning from GPS orbit

    SciTech Connect

    Suszcynsky, D. M.

    2003-01-01

    Satellite-based VHF' lightning detection is characterized at GPS orbit by using a VHF receiver system recently launched on the GPS SVN 54 satellite. Collected lightning triggers consist of Narrow Bipolar Events (80%) and strong negative return strokes (20%). The results are used to evaluate the performance of a future GPS-satellite-based VHF global lightning monitor.

  6. Global Positioning System III (GPS III)

    DTIC Science & Technology

    2013-12-01

    Global Positioning System III ( GPS III) As of FY 2015 President’s Budget...00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE Global Positioning System III ( GPS III) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...Responsible Office References Program Name Global Positioning System III ( GPS III) DoD Component Air Force

  7. Ekofisk automatic GPS subsidence measurements

    SciTech Connect

    Mes, M.J.; Landau, H.; Luttenberger, C.

    1996-10-01

    A fully automatic GPS satellite-based procedure for the reliable measurement of subsidence of several platforms in almost real time is described. Measurements are made continuously on platforms in the North Sea Ekofisk Field area. The procedure also yields rate measurements, which are also essential for confirming platform safety, planning of remedial work, and verification of subsidence models. GPS measurements are more attractive than seabed pressure-gauge-based platform subsidence measurements-they are much cheaper to install and maintain and not subject to gauge drift. GPS measurements were coupled to oceanographic quantities such as the platform deck clearance, which leads to less complex offshore survey procedures. Ekofisk is an oil and gas field in the southern portion of the Norwegian North Sea. Late in 1984, it was noticed that the Ekofisk platform decks were closer to the sea surface than when the platforms were installed-subsidence was the only logical explanation. After the subsidence phenomenon was recognized, an accurate measurement method was needed to measure progression of subsidence and the associated subsidence rate. One available system for which no further development was needed, was the NAVSTAR GPS-measurements started in March 1985.

  8. Optimal Preprocessing Of GPS Data

    NASA Technical Reports Server (NTRS)

    Wu, Sien-Chong; Melbourne, William G.

    1994-01-01

    Improved technique for preprocessing data from Global Positioning System receiver reduces processing time and number of data to be stored. Optimal in sense that it maintains strength of data. Also increases ability to resolve ambiguities in numbers of cycles of received GPS carrier signals.

  9. Precision GPS ephemerides and baselines

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The emphasis of this grant was focused on precision ephemerides for the Global Positioning System (GPS) satellites for geodynamics applications. During the period of this grant, major activities were in the areas of thermal force modeling, numerical integration accuracy improvement for eclipsing satellites, analysis of GIG '91 campaign data, and the Southwest Pacific campaign data analysis.

  10. Recent GPS Results at SLAC

    SciTech Connect

    Behrend, Dirk; Imfeld, Hans L.; /SLAC

    2005-08-17

    The Alignment Engineering Group (AEG) makes use of GPS technology for fulfilling part of its above ground surveying tasks at SLAC since early 2002. A base station (SLAC M40) has been set up at a central location of the SLAC campus serving both as master station for real-time kinematic (RTK) operations and as datum point for local GPS campaigns. The Leica RS500 system is running continuously and the GPS data are collected both externally (logging PC) and internally (receiver flashcard). The external logging is facilitated by a serial to Ethernet converter and an Ethernet connection at the station. Internal logging (ring buffer) is done for data security purposes. The weatherproof boxes for the instrumentation are excellent shelters against rain and wind, but do heat up considerably in sun light. Whereas the GPS receiver showed no problems, the Pacific Crest PDL 35 radio shut down several times due to overheating disrupting the RTK operations. In order to prevent heat-induced shutdowns, a protection against direct sun exposure (shading) and a constant air circulation system (ventilation) were installed. As no further shutdowns have occurred so far, it appears that the two measures successfully mended the heat problem.

  11. Animal Tracking ARGOS vs GPS

    NASA Astrophysics Data System (ADS)

    Robinson, P. W.; Costa, D.; Arnould, J.; Weise, M.; Kuhn, C.; Simmons, S. E.; Villegas, S.; Tremblay, Y.

    2006-12-01

    ARGOS satellite tracking technology has enabled a tremendous increase in our understanding of the movement patterns of a diverse array of marine vertebrates from Sharks to marine mammals. Our current understanding has moved from simple descriptions of large scale migratory patterns to much more sophisticated comparisons of animal movements and behavior relative to oceanic features. Further, animals are increasingly used to carry sensors that can acquire water column temperature and salinity profiles. However, a major limitation of this work is the spatial precision of ARGOS locations. ARGOS provides 7 location qualities that range from 3,2,1,0,A,B,Z and correspond to locations with a precision of 150m to tens of kilometers. Until recently, GPS technology could not be effectively used with marine mammals because they did not spend sufficient time at the surface to allow complete acquisition of satellite information. The recent development of Fastloc technology has allowed the development of GPS tags that can be deployed on marine mammals. Here we compare the location quality and frequency derived from standard ARGOS PTTs to Fastloc GPS locations acquired from 11 northern elephant seals, 5 California and 5 Galapagos sea lions and 1 Cape and 3 Australian fur seals. Our results indicate that GPS technology will greatly enhance our ability to understand the movement patterns of marine vertebrates and the in-situ oceanographic data they collect.

  12. Contents of GPS Data Files

    SciTech Connect

    Sullivan, John P.; Carver, Matthew Robert; Norman, Benjamin

    2016-12-09

    There are no very detailed descriptions of most of these instruments in the literature – we will attempt to fix that problem in the future. The BDD instruments are described in [1]. One of the dosimeter instruments on CXD boxes is described in [2]. These documents (or web links to them) and a few others are in this directory tree. The cross calibration of the CXD electron data with RBSP is described in [3]. Each row in the data file contains the data from one time bin from a CXD or BDD instrument along with a variety of parameters derived from the data. Time steps are commandable but 4 minutes is a typical setting. These instruments are on many (but not all) GPS satellites which are currently in operation. The data come from either BDD instruments on GPS Block IIR satellites (SVN41 and 48), or else CXD-IIR instruments on GPS Block IIR and IIR-M satellites (SVN53-61) or CXD-IIF instruments on GPS block IIF satellites (SVN62-73). The CXD-IIR instruments on block IIR and IIR(M) satellites use the same design.

  13. Integrated navigation of aerial robot for GPS and GPS-denied environment

    NASA Astrophysics Data System (ADS)

    Suzuki, Satoshi; Min, Hongkyu; Wada, Tetsuya; Nonami, Kenzo

    2016-09-01

    In this study, novel robust navigation system for aerial robot in GPS and GPS- denied environments is proposed. Generally, the aerial robot uses position and velocity information from Global Positioning System (GPS) for guidance and control. However, GPS could not be used in several environments, for example, GPS has huge error near buildings and trees, indoor, and so on. In such GPS-denied environment, Laser Detection and Ranging (LIDER) sensor based navigation system have generally been used. However, LIDER sensor also has an weakness, and it could not be used in the open outdoor environment where GPS could be used. Therefore, it is desired to develop the integrated navigation system which is seamlessly applied to GPS and GPS-denied environments. In this paper, the integrated navigation system for aerial robot using GPS and LIDER is developed. The navigation system is designed based on Extended Kalman Filter, and the effectiveness of the developed system is verified by numerical simulation and experiment.

  14. The application of NAVSTAR Differential GPS to civil helicopter operations

    NASA Technical Reports Server (NTRS)

    Beser, J.; Parkinson, B. W.

    1981-01-01

    Principles concerning the operation of the NAVSTAR Global Positioning Systems (GPS) are discussed. Selective availability issues concerning NAVSTAR GPS and differential GPS concepts are analyzed. Civil support and market potential for differential GPS are outlined. It is concluded that differential GPS provides a variation on the baseline GPS system, and gives an assured, uninterrupted level of accuracy for the civilian community.

  15. Improved red emission by codoping Li+ in ZnWO4:Eu3+ phosphors

    NASA Astrophysics Data System (ADS)

    Chen, Guiqiang; Wang, Fengli; Yu, Jie; Zhang, Haisheng; Zhang, Xiao

    2017-01-01

    ZnWO4:Eu3+ and ZnWO4:Eu3+/Li+ phosphors have been synthesized successfully by a microwave-assist hydrothermal process. The phase, morphology and luminescent properties are investigated carefully. The XRD and FTIR results indicate that ZnWO4:Eu3+ and ZnWO4:Eu3+/Li+ phosphors have the monoclinic phase. The SEM images indicate that ZnWO4:Eu3+ and ZnWO4:Eu3+/Li+ phosphors are cubes with average particle size about 1 μm. Under the excitation at 395 nm, ZnWO4:Eu3+ and ZnWO4:Eu3+/Li+ phosphors show emission bands originating from the 5D0 → 7Fj (j = 0, 1, 2 and 3) transitions of Eu3+ ions. The Li+ ion acts as charge compensator and results in the enhancement of emission intensity.

  16. Large single crystal growth of MnWO4-type materials from high-temperature solutions

    NASA Astrophysics Data System (ADS)

    Gattermann, U.; Röska, B.; Paulmann, C.; Park, S.-H.

    2016-11-01

    A simple high-temperature growth apparatus was constructed to obtain large crystals of chemically gradient (In, Na)-doped MnWO4solid-solutions. This paper presents the crystal growth and characterisation of both MnWO4and epitaxially grown (In, Na): MnWO4crystals on MnWO4. These large monolithic crystals were made in two steps: A MnWO4 crystal was grown in the crystallographic main direction [001] applying the Czochralski method, followed by the top seeded growth of (In, Na): MnWO4 solid-solutions with an oriented seed crystal of MnWO4. Such a monolithic crystal will serve to fundamental investigation of coupling properties at boundaries between various multiferroic MnWO4-typesolid-solutions.

  17. Altimetry Using GPS-Reflection/Occultation Interferometry

    NASA Technical Reports Server (NTRS)

    Cardellach, Estel; DeLaTorre, Manuel; Hajj, George A.; Ao, Chi

    2008-01-01

    A Global Positioning System (GPS)- reflection/occultation interferometry was examined as a means of altimetry of water and ice surfaces in polar regions. In GPS-reflection/occultation interferometry, a GPS receiver aboard a satellite in a low orbit around the Earth is used to determine the temporally varying carrier- phase delay between (1) one component of a signal from a GPS transmitter propagating directly through the atmosphere just as the GPS transmitter falls below the horizon and (2) another component of the same signal, propagating along a slightly different path, reflected at glancing incidence upon the water or ice surface.

  18. Optical Properties and Aging of Gasochromic WO3

    NASA Astrophysics Data System (ADS)

    Ghosh, Rudresh; Baker, Matthew B.; Lopez, Rene

    2008-10-01

    WO3 as a possible optical gas sensor has gained increasing importance with H2 becoming a major fuel of the future. This has led to efforts to understand the theoretical and practical aspects of the gasochromic behavior of WO3. WO3 films were fabricated using pulsed laser deposition (PLD). Morphological and stoichiometric ratios of films obtained were observed as functions of deposition parameters. We present the optical constants induced by 2% H2:Ar in WO3 films. This allows us to obtain the limits of the gasochromic change in comparison to ion injection. It was found using Langmuir's adsorption equation that at low H2 concentrations a high sensitivity is predicted but the coloration could saturate at 57.9 % of the material's maximum ion adsorption. Poisoning of the films was also addressed by coating with a permeable polydimethylsiloxane layer. It is shown that gasochromic degradation is prevented thus eliminating common atmospheric gases as possible contaminants. Our studies suggest WO3 thin films as highly sensitive and stable optical hydrogen sensors.

  19. Optical Properties and Aging of Gasochromic WO3

    NASA Astrophysics Data System (ADS)

    Ghosh, Rudresh; Baker, Matthew B.; Lopez, Rene

    2009-03-01

    WO3 as a possible optical gas sensor has gained increasing importance with H2 becoming a major fuel of the future. This has led to efforts to understand the theoretical and practical aspects of the gasochromic behavior of WO3. WO3 films were fabricated using pulsed laser deposition (PLD). Morphological and stoichiometric ratios of films obtained were observed as functions of deposition parameters. We present the optical constants induced by 2% H2:Ar in WO3 films. This allows us to obtain the limits of the gasochromic change in comparison to ion injection. It was found using Langmuir's adsorption equation that at low H2 concentrations a high sensitivity is predicted but the coloration could saturate at 57.9 % of the material's maximum ion adsorption. Poisoning of the films was also addressed by coating with a permeable polydimethylsiloxane layer. It is shown that gasochromic degradation is prevented thus eliminating common atmospheric gases as possible contaminants. Our studies suggest WO3 thin films as highly sensitive and stable optical hydrogen sensors. .

  20. Preparation and physical properties of CuxWO3

    NASA Astrophysics Data System (ADS)

    Koriche, N.; Bessekhouad, Y.; Bouguelia, A.; Trari, M.

    2012-04-01

    We report on the study of WO3 doped with Cu using sol-gel (CuxWO3d) and impregnation (CuxWO3i) methods. All materials are well crystallized and exhibit single phases whose crystallite size ranges from 17 to 100 nm depending on Cu amount and the preparation technique. The conductivity dependence on temperature demonstrates semiconductor behavior and follows the Arrhenius model, with activation energies, Eσ, commonly in the range 0.4-0.6 eV. Moreover, the thermopower study shows that CuxWO3d is mainly of p-type conductivity, whereas CuxWO3i is n-type. The mechanism of conduction is attributed to a small polaron hopping. The doping process is found to decrease the interband transition down to 520 nm depending on the preparation conditions. The photoelectrochemical characterization confirms the conductivity type and demonstrates that the photocurrent Jph increases with Cu-doping. Taking into consideration the activation energy, the flat band potential and the band gap energy, the band positions of each material are proposed according to the preparation method and Cu amount.

  1. Synthesis of high aspect ratio WO2 nanostructures

    NASA Astrophysics Data System (ADS)

    Coşkun, Selim; Koziol, Krzysztof K. K.

    2016-02-01

    Tungsten oxide (WO2) nanorods and nanowires were prepared by the heat treatment of WO2 nanocrystalline powders in the presence of Ar. Nanocrystalline powders produced by a simple water-assisted route at the room temperature were annealed at different temperatures for different durations, which yielded orthorhombic and monoclinic WO2 crystals. Annealing the powders at 700 °C and above resulted in orthorhombic WO2 nanorods/nanowires with an average diameter of 60-70 nm beside the monoclinic WO2 nanocrystalline powders with a diameter of 5 nm. The lengths of the nanorods increased from several 100 nm up to several 10 µm with increasing temperature while their diameters did not change. With increased length, nanowires became more elastic in nature having a cotton-like fabric. The prepared nanostructures have been characterized by X-ray powder diffraction measurements, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. An oriented attachment mechanism leading to root growth from a parent structure was proposed.

  2. Optimization of the effective GPS data rate

    NASA Technical Reports Server (NTRS)

    Mcintyre, David S.

    1990-01-01

    Ohio University's Avionics Engineering Center is performing research directed towards the integration of the NAVSTAR Global Positioning System (GPS) and the Inertial Navigation System (INS) for attitude and heading determination. The integration of GPS/INS offers synergistic benefits. INS gyro drift error can be compensated by the long-term stability of GPS by means of an in-flight data monitoring algorithm. Using GPS data as a reference is more advantageous than implementing an additional INS since GPS offers a dissimilar redundancy to the attitude and heading determination configuration. In converse, the short-term stability of the INS can be used to correct or substitute for faulty GPS data due to tracking loop phase lag or data gaps because of satellite shielding. The optimization of the effective GPS data rate is essential for the proper execution of an integrated GPS/INS in-flight algorithm. GPS attitude and heading information must be consistently available during INS outages. Present research efforts involve the development of an in-flight algorithm that maximizes the potential of integrated GPS/INS. This algorithm determines the acceptable limits of phase lag that the GPS tracking loop introduces to the flight control system (FCS) during the transmission of information. Once these calculated limits are exceeded, INS data are used to insure the continuous availability of attitude and heading information to the flight control system.

  3. GPS instrumentation for the Trident weapon system

    NASA Astrophysics Data System (ADS)

    Grossman, J.; Jacobson, L.; Wells, L.

    With the planned full operational deployment of the Navstar Global Positioning System (GPS), many applications for the system are beginning to be developed. This paper discusses the concept of GPS instrumentation for the Trident II (D-5) program as well as the background for the Navy's use of existing GPS assets for test evaluation of the Trident I (C-4) Weapon System. Included are the concepts of translated GPS used for real-time tracking for missile range safety as well as for posttest performance evaluation (metric tracking) of the Trident guidance system. The use of GPS pseudosatellite signals to enhance the robustness of the tracking system to provide range safety information is presented. GPS time transfer capabilities are to be used to ensure efficient time synchronization operation for all stations. The unique design features associated with using GPS for range instrumentation are highlighted.

  4. GPS - The versatile tool for range instrumentation

    NASA Astrophysics Data System (ADS)

    Hoefener, Carl; Richardson, William

    The GPS has made significant contributions in range instrumentation. It was the prime tracking method for both realtime range safety and metric tracking for the Trident II. Because of its many advantages, GPS will become the primary source of time, space, and position information (TSPI) on the ranges. Many activities requiring precision TSPI have already committed to GPS and others are planning on the application of GPS in the future for use on the ranges. GPS is also an extremely accurate time source, with timing accuracies of 10 nanoseconds obtainable worldwide. The range interoperability problem is solvable through the use of GPS as the TSPI source. There is little doubt that GPS will become the standard TSPI source for all test and training ranges.

  5. Spaceborne GPS: Current Status and Future Visions

    NASA Technical Reports Server (NTRS)

    Bauer, Frank H.; Hartman, Kate; Lightsey, E. Glenn

    1998-01-01

    The Global Positioning System (GPS), developed by the Department of Defense is quickly revolutionizing the architecture of future spacecraft and spacecraft systems. Significant savings in spacecraft life cycle cost, in power, and in mass can be realized by exploiting GPS technology in spaceborne vehicles. These savings are realized because GPS is a systems sensor--it combines the ability to sense space vehicle trajectory, attitude, time, and relative ranging between vehicles into one package. As a result, a reduced spacecraft sensor complement can be employed and significant reductions in space vehicle operations cost can be realized through enhanced on-board autonomy. This paper provides an overview of the current status of spaceborne GPS, a description of spaceborne GPS receivers available now and in the near future, a description of the 1997-2000 GPS flight experiments, and the spaceborne GPS team's vision for the future.

  6. Spaceborne GPS Current Status and Future Visions

    NASA Technical Reports Server (NTRS)

    Bauer, Frank H.; Hartman, Kate; Lightsey, E. Glenn

    1998-01-01

    The Global Positioning System (GPS), developed by the Department of Defense, is quickly revolutionizing the architecture of future spacecraft and spacecraft systems. Significant savings in spacecraft life cycle cost, in power, and in mass can be realized by exploiting Global Positioning System (GPS) technology in spaceborne vehicles. These savings are realized because GPS is a systems sensor-it combines the ability to sense space vehicle trajectory, attitude, time, and relative ranging between vehicles into one package. As a result, a reduced spacecraft sensor complement can be employed on spacecraft and significant reductions in space vehicle operations cost can be realized through enhanced on- board autonomy. This paper provides an overview of the current status of spaceborne GPS, a description of spaceborne GPS receivers available now and in the near future, a description of the 1997-1999 GPS flight experiments and the spaceborne GPS team's vision for the future.

  7. Integrated Global Positioning Systems (GPS) Laboratory

    NASA Technical Reports Server (NTRS)

    Brown, Dewayne Randolph

    2002-01-01

    The purpose of this research is to develop a user-friendly Integrated GPS lab manual. This manual will help range engineers at NASA to integrate the use of GPS Simulators, GPS receivers, computers, MATLAB software, FUGAWI software and SATELLITE TOOL KIT software. The lab manual will be used in an effort to help NASA engineers predict GPS Coverage of planned operations and analyze GPS coverage of operation post mission. The Integrated GPS Laboratory was used to do GPS Coverage for two extensive case studies. The first scenario was an airplane trajectory in which an aircraft flew from Cape Canaveral to Los Angeles, California. In the second scenario, a rocket trajectory was done whereas a rocket was launched from Cape Canaveral to one thousand kilometers due east in the Atlantic Ocean.

  8. Photocatalytic activity of Bi2WO6/Bi2S3 heterojunctions: the facilitation of exposed facets of Bi2WO6 substrate

    NASA Astrophysics Data System (ADS)

    Yan, Long; Wang, Yufei; Shen, Huidong; Zhang, Yu; Li, Jian; Wang, Danjun

    2017-01-01

    Bi2S3/Bi2WO6 hybrid architectures with exposed (020) Bi2WO6 facets have been synthesized via a controlled anion exchange approach. X-ray photoelectron spectroscopy (XPS) reveals that a small amount of Bi2S3 was formed on the surface of Bi2WO6 during the anion exchange process, thus leading to the transformation from the Bi2WO6 to Bi2S3/Bi2WO6. A rhodamine B (RhB) aqueous solution was chosen as model organic pollutants to evaluate the photocatalytic activities of the Bi2S3/Bi2WO6 catalysts. Under visible light irradiation, the Bi2S3/Bi2WO6-TAA displayed the excellent visible light photoactivities compared with pure Bi2S3, Bi2WO6 and other composite photocatalysts. The efficient photocatalytic activity of the Bi2S3/Bi2WO6-TAA composite microspheres was ascribed to the constructed heterojunctions and the inner electric field caused by the exposed (020) Bi2WO6 facets. Active species trapping experiments revealed that h+ and O2rad - are the main active species in the photocatalytic process. Furthermore, the as-obtained photocatalysts showed good photocatalytic activity after four recycles. The results presented in this study provide a new concept for the rational design and development of highly efficient photocatalysts.

  9. AgBi(WO4)2 : A New Modification Material to Bi2 WO6 for Enhanced and Stable Visible-Light Photocatalyic Performance.

    PubMed

    Feng, Cuiyun; Dong, Yuming; Jiang, Pingping; Wang, Guangli; Zhang, Jingjing; Wu, Xiuming; Zhang, Chi

    2015-09-01

    In this work, we report a novel AgBi(WO4 )2 -Bi2 WO6 heterostructure, which was designed and synthesized by using a simple hydrothermal method. Methyl orange was used as a representative dye indicator to evaluate the visible-light catalytic activity and the catalytic mechanism was investigated. The as-synthesized AgBi(WO4 )2 -Bi2 WO6 composite displayed a 43 times higher photocatalytic activity than Bi2 WO6 . Owing to the matched band gap and distinctive heterostructure, AgBi(WO4 )2 -Bi2 WO6 reveals a high visible-light response and high-efficiency utilization of both photogenerated electrons and holes. AgBi(WO4 )2 reveals a similar energy level to and good lattice match with Bi2 WO6 , which are favorable qualities for band bending and fluent electron transfer. Furthermore, the photoexcited electrons can produce oxygen to generate (.) O2 (-) radicals, which is vital for the overall utilization of both holes and electrons. This is the first example of AgBi(WO4 )2 being used as photocatalytic material. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Photoelectrochemical water oxidation on photoanodes fabricated with hexagonal nanoflower and nanoblock WO3.

    PubMed

    Wang, Nan; Wang, Donge; Li, Mingrun; Shi, Jingying; Li, Can

    2014-02-21

    Hexagonal nanoflower WO3 arrays have been prepared by using RCOO(-) as the structure directing agent in the microwave-assisted hydrothermal synthesis process. The photoelectrochemical performance of the synthesized hexagonal flower-like WO3 electrode was enhanced compared with the block-like WO3 film.

  11. Biomimetic fabrication of WO3 for water splitting under visible light with high performance

    NASA Astrophysics Data System (ADS)

    Yin, Chao; Zhu, Shenmin; Yao, Fan; Gu, Jiajun; Zhang, Wang; Chen, Zhixin; Zhang, Di

    2013-08-01

    Inspired by the high light-harvesting properties of typical butterfly wings, ceramic WO3 butterfly wings with hierarchical structures of bio-butterfly wings was fabricated using a template of PapilioParis butterfly wings through a sol-gel method. The effect of calcination temperatures on the structures of the ceramic butterfly wings was investigated and the results showed that the WO3 butterfly wing replica calcined at 550 °C (WO3 replica-550) is a single phase and has a high crystallinity and relatively fine hierarchical structure. The average grain size of WO3 replica-550 and WO3 powder are around 32.6 and 42.2 nm, respectively. Compared with pure WO3 powder, WO3 replica-550 demonstrated a higher light-harvesting capability in the region from 460 to 700 nm and more importantly the higher charge separation rate, as evidenced by electron paramagnetic resonance measurements. Photocatalytic O2 evolutions from water were investigated on the ceramic butterfly wings and pure WO3 powder under visible light ( λ > 420 nm). The results showed that the amount of O2 produced from WO3 replica-550 is 50 % higher than that of the pure WO3 powder. The improved photocatalytic performance of WO3 replica-550 is attributed to the quasi-honeycomb structure inherited from the PapilioParis butterfly wings, providing both high light-harvesting efficiency and efficient charge transport through the WO3.

  12. International GPS Service for Geodynamics

    NASA Technical Reports Server (NTRS)

    Zumberge, J. F. (Editor); Urban, M. P. (Editor); Liu, R. (Editor); Neilan, R. E. (Editor)

    1996-01-01

    This 1995 annual report of the IGS International GPS (Global Positioning System) Service for Geodynamics - describes the second operational year of the service. It provides the many IGS contributing agencies and the rapidly growing user community with essential information on current organizational and technical matters promoting the IGS standards and products (including organizational framework, data processing strategies, and statistics showing the remarkable expansion of the GPS monitoring network, the improvement of IGS performance, and product quality). It also introduces important practical concepts for network densification by integration of regional stations and the combination of station coordinate solutions. There are groups of articles describing general aspects of the IGS, the Associate Analysis Centers (AACs), Data Centers, and IGS stations.

  13. Pre-Flight Testing of Spaceborne GPS Receivers Using a GPS Constellation Simulator

    NASA Technical Reports Server (NTRS)

    Kizhner, Semion; Davis, Edward; Alonso, Roberto

    1999-01-01

    The NASA Goddard Space Flight Center (GSFC) Global Positioning System (GPS) applications test facility has been established within the GSFC Guidance Navigation and Control Center. The GPS test facility is currently housing the Global Simulation Systems Inc. (GSSI) STR2760 GPS satellite 40-channel attitude simulator and a STR4760 12-channel navigation simulator. The facility also contains a few other resources such as an atomic time standard test bed, a rooftop antenna platform and a radome. It provides a new capability for high dynamics GPS simulations of space flight that is unique within the aerospace community. The GPS facility provides a critical element for the development and testing of GPS based technologies i.e. position, attitude and precise time determination used on-board a spacecraft, suborbital rocket or balloon. The GPS simulator system is configured in a transportable rack and is available for GPS component development as well as for component, spacecraft subsystem and system level testing at spacecraft integration and test sites. The GPS facility has been operational since early 1996 and has been utilized by space flight projects carrying GPS experiments, such as the OrbView-2 and the Argentine SAC-A spacecrafts. The SAC-A pre-flight test data obtained by using the STR2760 simulator and the comparison with preliminary analysis of the GPS data from SAC-A telemetry are summarized. This paper describes pre-flight tests and simulations used to support a unique spaceborne GPS experiment. The GPS experiment mission objectives and the test program are described, as well as the GPS test facility configuration needed to verify experiment feasibility. Some operational and critical issues inherent in GPS receiver pre-flight tests and simulations using this GPS simulator, and test methodology are described. Simulation and flight data are presented. A complete program of pre-flight testing of spaceborne GPS receivers using a GPS constellation simulator is

  14. Pre-Flight Testing of Spaceborne GPS Receivers using a GPS Constellation Simulator

    NASA Technical Reports Server (NTRS)

    Kizhner, Semion; Davis, Edward; Alonso, R.

    1999-01-01

    The NASA Goddard Space Flight Center (GSFC) Global Positioning System (GPS) applications test facility has been established within the GSFC Guidance Navigation and Control Center. The GPS test facility is currently housing the Global Simulation Systems Inc. (GSSI) STR2760 GPS satellite 40-channel attitude simulator and a STR4760 12-channel navigation simulator. The facility also contains a few other resources such as an atomic time standard test bed, a rooftop antenna platform and a radome. It provides a new capability for high dynamics GPS simulations of space flight that is unique within the aerospace community. The GPS facility provides a critical element for the development and testing of GPS based technologies i.e. position, attitude and precise time determination used on-board a spacecraft, suborbital rocket balloon. The GPS simulation system is configured in a transportable rack and is available for GPS component development as well as for component, spacecraft subsystem and system level testing at spacecraft integration and tests sites. The GPS facility has been operational since early 1996 and has utilized by space flight projects carrying GPS experiments, such as the OrbView-2 and the Argentine SAC-A spacecrafts. The SAC-A pre-flight test data obtained by using the STR2760 simulator and the comparison with preliminary analysis of the GPS data from SAC-A telemetry are summarized. This paper describes pre-flight tests and simulations used to support a unique spaceborne GPS experiment. The GPS experiment mission objectives and the test program are described, as well as the GPS test facility configuration needed to verify experiment feasibility. Some operational and critical issues inherent in GPS receiver pre-flight tests and simulations using this GPS simulation, and test methodology are described. Simulation and flight data are presented. A complete program of pre-flight testing of spaceborne GPS receivers using a GPS constellation simulator is detailed.

  15. Military GPS User Equipment (MGUE)

    DTIC Science & Technology

    2015-04-29

    Incremental Acquisition effort to develop form factors - Increment 1 (Inc 1 ): Ground (GB- GRAM -M) and Aviation/Maritime ( GRAM -S/M) - Inc 1 form factors...since 2005 GPS Receiver Application Module (GB- GRAM ) 100,000 units, since 2005 MGUE Next Step in Long History 2015 04 29 _MGUE Partnership...Availability ========---========== SPACE AND MISSILE SYSTEMS CENTER User Equipment DAGR (SAASM) GB- GRAM (SAASM) Projected M-Code Receivers (FY17

  16. GPS Multipath in Urban Environments

    NASA Astrophysics Data System (ADS)

    Bilich, A.; Sella, G.

    2008-12-01

    Multipath, where a GNSS signal arrives by more than one path, is considered one of the last unmodeled errors remaining in GNSS. Multipath is of great concern because the additional path length traveled by the incoming signal biases the satellite-receiver range and therefore determination of position. Siting a GNSS station in an urban area, in the immediate vicinity of large reflecting objects such as rooftops, buildings, asphalt and concrete parking lots, grassy fields, and chainlink fences, is both a multipath nightmare and a necessary evil. We note that continuously-operating GNSS stations are becoming increasingly common in urban areas, which makes sense as these stations are often installed in support of civil infrastructure (e.g. departments of transportation, strong motion monitoring of buildings in earthquake-prone areas, surveying networks). Urban stations are well represented in geodetic networks such as the CORS (United States) and GeoNet (Japan) networks, with more stations likely to be installed in the coming years. What sources and types of urban multipath are the most detrimental to geodetic GPS positioning? Which reflecting objects are assumed to be a major source of multipath error, but the GPS data show otherwise? Are certain reflecting environments worse for specific applications, i.e. kinematic vs. static positioning? If forced to install a GNSS station in a highly reflective environment, is it possible to rank objects for their multipath severity? To answer these questions, we provide multipath examples taken from continuously- operating GNSS stations sited in urban environments. We concentrate on some of the most common obstacles and reflecting objects for urban sites - rooftops, parking lots, and fences. We analyze the multipath signature of these objects as manifested in the GPS phase, pseudorange, and signal-to-noise ratio (SNR) observables, and also examine multipath impacts on the precision and accuracy of GPS-derived positions.

  17. A GPS Disciplined Rubidium Clock

    DTIC Science & Technology

    1989-11-01

    A GPS DISCIPLINED RUBIDIUM CLOCK .Wayne Dewey. Kincmctrics/TrueTime 3243 Sarita Rosa Ave. Santa Rosa, CA 95407 Abstract Sub-microsecond timing ...accuracy during periods when no satellites are visible, a highly sta1,lc local time base is required. For those cases which require Cesililll oscillat...tcrxxr stability. INTRODUCTION In recerlt years, time syr~chronization requirements between rer-note sites has becorrie rrlora clr:rriiir~tilr

  18. Precision GPS ephemerides and baselines

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Based on the research, the area of precise ephemerides for GPS satellites, the following observations can be made pertaining to the status and future work needed regarding orbit accuracy. There are several aspects which need to be addressed in discussing determination of precise orbits, such as force models, kinematic models, measurement models, data reduction/estimation methods, etc. Although each one of these aspects was studied at CSR in research efforts, only points pertaining to the force modeling aspect are addressed.

  19. Degradation of methylene blue using porous WO3, SiO2-WO3, and their Au-loaded analogs: adsorption and photocatalytic studies.

    PubMed

    DePuccio, Daniel P; Botella, Pablo; O'Rourke, Bruce; Landry, Christopher C

    2015-01-28

    A facile sonochemical approach was used to deposit 3-5 nm monodisperse gold nanoparticles on porous SiO2-WO3 composite spheres, as confirmed by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). High-resolution TEM (HR-TEM) and energy dispersive X-ray spectroscopy (EDS) further characterized the supported Au nanoparticles within the Au-SiO2-WO3 composite. These analyses showed isolated Au nanoparticles within both SiO2- and WO3-containing regions. Selective etching of the SiO2 matrix from Au-SiO2-WO3 yielded a pure Au-WO3 material with well-dispersed 10 nm Au nanoparticles and moderate porosity. This combined sonochemical-nanocasting technique has not been previously used to synthesize Au-WO3 photocatalysts. Methylene blue (MB) served as a probe for the adsorption capacity and visible light photocatalytic activity of these WO3-containing catalysts. Extensive MB demethylation (azures A, B, C, and thionine) and polymerization of these products occurred over WO3 under dark conditions, as confirmed by electrospray ionization mass spectrometry (ESI-MS). Photoirradiation of these suspensions led to further degradation primarily through demethylation and polymerization pathways, regardless of the presence of Au nanoparticles. Ring-opening sulfur oxidation to the sulfone was a secondary photocatalytic pathway. According to UV-vis spectroscopy, pure WO3 materials showed superior MB adsorption compared to SiO2-WO3 composites. Compared to their respective nonloaded catalysts, Au-SiO2-WO3 and Au-WO3 catalysts exhibited enhanced visible light photocatalytic activity toward the degradation of MB. Specifically, the rates of MB degradation over Au-WO3 and Au-SiO2-WO3 during 300 min of irradiation were faster than those over their nonloaded counterparts (WO3 and SiO2-WO3). These studies highlight the ability of Au-WO3 to serve as an excellent adsorbant and photodegradation catalyst toward MB.

  20. Applications of GPS technologies to field sports.

    PubMed

    Aughey, Robert J

    2011-09-01

    Global positioning system (GPS) technology was made possible after the invention of the atomic clock. The first suggestion that GPS could be used to assess the physical activity of humans followed some 40 y later. There was a rapid uptake of GPS technology, with the literature concentrating on validation studies and the measurement of steady-state movement. The first attempts were made to validate GPS for field sport applications in 2006. While GPS has been validated for applications for team sports, some doubts continue to exist on the appropriateness of GPS for measuring short high-velocity movements. Thus, GPS has been applied extensively in Australian football, cricket, hockey, rugby union and league, and soccer. There is extensive information on the activity profile of athletes from field sports in the literature stemming from GPS, and this includes total distance covered by players and distance in velocity bands. Global positioning systems have also been applied to detect fatigue in matches, identify periods of most intense play, different activity profiles by position, competition level, and sport. More recent research has integrated GPS data with the physical capacity or fitness test score of athletes, game-specific tasks, or tactical or strategic information. The future of GPS analysis will involve further miniaturization of devices, longer battery life, and integration of other inertial sensor data to more effectively quantify the effort of athletes.

  1. Intrinsic Defects and H Doping in WO3

    PubMed Central

    Zhu, Jiajie; Vasilopoulou, Maria; Davazoglou, Dimitris; Kennou, Stella; Chroneos, Alexander; Schwingenschlögl, Udo

    2017-01-01

    WO3 is widely used as industrial catalyst. Intrinsic and/or extrinsic defects can tune the electronic properties and extend applications to gas sensors and optoelectonics. However, H doping is a challenge to WO3, the relevant mechanisms being hardly understood. In this context, we investigate intrinsic defects and H doping by density functional theory and experiments. Formation energies are calculated to determine the lowest energy defect states. O vacancies turn out to be stable in O-poor environment, in agreement with X-ray photoelectron spectroscopy, and O-H bond formation of H interstitial defects is predicted and confirmed by Fourier transform infrared spectroscopy. PMID:28098210

  2. Symmetry driven control of optical properties in WO3 films

    NASA Astrophysics Data System (ADS)

    Herklotz, A.; Rus, S. F.; KC, S.; Cooper, V. R.; Huon, A.; Guo, E.-J.; Ward, T. Z.

    2017-06-01

    In this work, we demonstrate that the optical bandgap of WO3 films can be continuously controlled through uniaxial strain induced by low-energy helium implantation. The insertion of He into epitaxially grown and coherently strained WO3 films can be used to induce single axis out-of-plane lattice expansion of up to 2%. Ellipsometric spectroscopy reveals that the optical bandgap is reduced by about 0.18 eV per percent expansion of the out-of-plane unit cell length. Density functional theory calculations show that this response is a direct result of changes in orbital degeneracy driven by changes in the octahedral rotations and tilts.

  3. Intrinsic Defects and H Doping in WO3

    NASA Astrophysics Data System (ADS)

    Zhu, Jiajie; Vasilopoulou, Maria; Davazoglou, Dimitris; Kennou, Stella; Chroneos, Alexander; Schwingenschlögl, Udo

    2017-01-01

    WO3 is widely used as industrial catalyst. Intrinsic and/or extrinsic defects can tune the electronic properties and extend applications to gas sensors and optoelectonics. However, H doping is a challenge to WO3, the relevant mechanisms being hardly understood. In this context, we investigate intrinsic defects and H doping by density functional theory and experiments. Formation energies are calculated to determine the lowest energy defect states. O vacancies turn out to be stable in O-poor environment, in agreement with X-ray photoelectron spectroscopy, and O-H bond formation of H interstitial defects is predicted and confirmed by Fourier transform infrared spectroscopy.

  4. Facile Hydrogen Evolution Reaction on WO3Nanorods

    PubMed Central

    2007-01-01

    Tungsten trioxide nanorods have been generated by the thermal decomposition (450 °C) of tetrabutylammonium decatungstate. The synthesized tungsten trioxide (WO3) nanorods have been characterized by XRD, Raman, SEM, TEM, HRTEM and cyclic voltammetry. High resolution transmission electron microscopy and X-ray diffraction analysis showed that the synthesized WO3nanorods are crystalline in nature with monoclinic structure. The electrochemical experiments showed that they constitute a better electrocatalytic system for hydrogen evolution reaction in acid medium compared to their bulk counterpart.

  5. Phase behaviour of 2D MnWO x and FeWO x ternary oxide layers on Pd(1 0 0)

    NASA Astrophysics Data System (ADS)

    Doudin, N.; Kuhness, D.; Blatnik, M.; Netzer, F. P.; Surnev, S.

    2017-06-01

    The structure and properties of ternary oxide materials at the nanoscale are poorly explored both on experimental and theoretical levels. With this work we demonstrate the successful on-surface synthesis of two-dimensional (2D) ternary oxide, MnWO x and FeWO x , nanolayers on a Pd(1 0 0) surface and the understanding of their new structure and phase behaviour with the help of state-of-art surface structure and spectroscopy techniques. We find that the 2D MnWO x and FeWO x phases, prepared under identical thermodynamic conditions, exhibit similar structural properties, reflecting the similarity of the bulk MnWO4 and FeWO4 phases with the wolframite structure. Structure models of prototypical 2D ternary oxide phases are proposed and discussed in the light of new structure architecture concepts which have no analogues in the bulk.

  6. Synthesis of Shape-Tailored WO3 Micro-/Nanocrystals and the Photocatalytic Activity of WO3/TiO2 Composites

    PubMed Central

    Székely, István; Kovács, Gábor; Baia, Lucian; Danciu, Virginia; Pap, Zsolt

    2016-01-01

    A traditional semiconductor (WO3) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO3 microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). These methods contributed to the detailed analysis of the crystal morphology and structural features. The synthesized bare WO3 photocatalysts were totally inactive, while the P25/WO3 composites were efficient under UV light radiation. Furthermore, the maximum achieved activity was even higher than the bare P25’s photocatalytic performance. A correlation was established between the shape of the WO3 crystallites and the observed photocatalytic activity registered during the degradation of different substrates by using P25/WO3 composites. PMID:28773386

  7. Reactive Sputter Deposition of WO3/Ag/WO3 Film for Indium Tin Oxide (ITO)-Free Electrochromic Devices.

    PubMed

    Yin, Yi; Lan, Changyong; Guo, Huayang; Li, Chun

    2016-02-17

    Functioning both as electrochromic (EC) and transparent-conductive (TC) coatings, WO3/Ag/WO3 (WAW) trilayer film shows promising potential application for ITO-free electrochromic devices. Reports on thermal-evaporated WAW films revealed that these bifunctional WAW films have distinct EC characteristics; however, their poor adhesive property leads to rapid degradation of coloring-bleaching cycling. Here, we show that WAW film with improved EC durability can be prepared by reactive sputtering using metal targets. We find that, by introducing an ultrathin tungsten (W) sacrificial layer before the deposition of external WO3, the oxidation of silver, which leads to film insulation and apparent optical haze, can be effectively avoided. We also find that the luminous transmittance and sheet resistance were sensitive to the thicknesses of tungsten and silver layers. The optimized structure for TC coating was obtained to be WO3 (45 nm)/Ag (10 nm)/W (2 nm)/WO3 (45 nm) with a sheet resistance of 16.3 Ω/□ and a luminous transmittance of 73.7%. Such film exhibits compelling EC performance with decent luminous transmittance modulation ΔTlum of 29.5%, fast switching time (6.6 s for coloring and 15.9 s for bleaching time), and long-term cycling stability (2000 cycles) with an applied potential of ±1.2 V. Thicker external WO3 layer (45/10/2/100 nm) leads to larger modulation with maximum ΔTlum of 46.4%, but at the cost of significantly increasing the sheet resistance. The strategy of introducing ultrathin metal sacrificial layer to avoid silver oxidation could be extended to fabricating other oxide-Ag-oxide transparent electrodes via low-cost reactive sputtering.

  8. Accuracy of GPS velocities from repeated GPS surveys: results from a denser network and verification by continuous GPS

    NASA Astrophysics Data System (ADS)

    Tekic, Simge; Ugur Sanli, D.; Arslan, Ersoy

    2017-04-01

    The quality of GPS velocities derived from repeated (campaign) GPS surveys is under investigation today because we still need them due to various constraints affecting the design of geophysical experiments. On this basis, the IGS network developed for scientific purposes play a great role for the assessment of the solutions of GPS campaigns. With about 20 years of contunious GPS data and positioning solutions, today the time series of the IGS network serve as a large population for statistical analysis. From this population it is possible to make random samples of repeated GPS surveys. Thus, the sisgnificancy of the velocities derived from repeated GPS surveys can be investigated using statistical hypothesis testing. Generating repeated GPS surveys from the population and then processing the data using the PPP module of NASA JPL's GIPSY/OASIS II, we tried to quantify the velocities derived from these surveys. Previously the significance of the velocities derived from repeated GPS measurements of 8-12 h sessions were tested against those of the repeated surveys derived from 24 h sessions. However, the sampling for the vertical component was very poor. Here we use a larger sample and repeat the same experiment. In addition, we compare monthly sampled 24 h campain solutions with JPL continuous time series. The significancy of the repeated measurement velocity estimated is tested against the velocity derived from continuous JPL time series. Here, the velocity and its error estimated from continuous GPS time series are taken as the population parameters.

  9. Multiple Horizontal Transfers of Bacteriophage WO and Host Wolbachia in Fig Wasps in a Closed Community.

    PubMed

    Wang, Ningxin; Jia, Sisi; Xu, Heng; Liu, Yong; Huang, Dawei

    2016-01-01

    Wolbachia-bacteriophage WO is a good model system for studying interactions between bacteria and viruses. Previous surveys of insect hosts have been conducted via sampling from open or semi-open communities; however, no studies have reported the infection patterns of phage WO of insects living in a closed community. Figs and fig wasps form a peculiar closed community in which the Ficus tree provides a compact syconium habitat for a variety of fig wasp. Therefore, in this study, we performed a thorough survey of Wolbachia and bacteriophage WO infection patterns in a total of 1406 individuals from 23 fig wasps species living on three different fig tree species. The infection rates of Wolbachia and phage WO were 82.6% (19/23) and 39.1% (9/23), respectively. Additionally, phage WO from fig wasps showed strong insect host specificity based on orf7 sequences from fig wasps and 21 other insect species. Probably due to the physical barrier of fig syconium, most phage WO from fig wasps form a specific clade. Phylogenetic analysis showed the absence of congruence between WO and host Wolbachia, WO and insect host, as well as Wolbachia and fig wasps, suggesting that both Wolbachia and phage WO exchanged frequently and independently within the closed syconium. Thus, the infection pattern of bacteriophage WO from fig wasps appeared quite different from that in other insects living outside, although the effect and the transfer routes of phage WO are unclear, which need to be investigated in the future.

  10. Multiple Horizontal Transfers of Bacteriophage WO and Host Wolbachia in Fig Wasps in a Closed Community

    PubMed Central

    Wang, Ningxin; Jia, Sisi; Xu, Heng; Liu, Yong; Huang, Dawei

    2016-01-01

    Wolbachia-bacteriophage WO is a good model system for studying interactions between bacteria and viruses. Previous surveys of insect hosts have been conducted via sampling from open or semi-open communities; however, no studies have reported the infection patterns of phage WO of insects living in a closed community. Figs and fig wasps form a peculiar closed community in which the Ficus tree provides a compact syconium habitat for a variety of fig wasp. Therefore, in this study, we performed a thorough survey of Wolbachia and bacteriophage WO infection patterns in a total of 1406 individuals from 23 fig wasps species living on three different fig tree species. The infection rates of Wolbachia and phage WO were 82.6% (19/23) and 39.1% (9/23), respectively. Additionally, phage WO from fig wasps showed strong insect host specificity based on orf7 sequences from fig wasps and 21 other insect species. Probably due to the physical barrier of fig syconium, most phage WO from fig wasps form a specific clade. Phylogenetic analysis showed the absence of congruence between WO and host Wolbachia, WO and insect host, as well as Wolbachia and fig wasps, suggesting that both Wolbachia and phage WO exchanged frequently and independently within the closed syconium. Thus, the infection pattern of bacteriophage WO from fig wasps appeared quite different from that in other insects living outside, although the effect and the transfer routes of phage WO are unclear, which need to be investigated in the future. PMID:26913026

  11. Tunable luminescence and enhanced photocatalytic activity for Eu(III) doped Bi2WO6 nanoparticles

    NASA Astrophysics Data System (ADS)

    Gu, Haidong; Yu, Lei; Wang, Juan; Ni, Min; Liu, Tingting; Chen, Feng

    2017-04-01

    A series of Eu(III) doped Bi2WO6 nanoparticles were synthesized by a hydrothermal process. The obtained Bi2WO6:Eu(III) nanoparticles were characterized by XRD, SEM, luminescence spectrophotometer and DRS. The XRD and TEM results indicate that the Eu(III) doping concentration has no influence on the phase and morphology. However, the Eu(III) doping can tune the luminescence and enhance the photocatalytic activity of Bi2WO6. With the increases of Eu3 + doping concentrations, the emission intensity of WO66 - group decreases nut the photocatalytic activity increases. The tunable luminescence of Bi2WO6:Eu(III) nanoparticles results from the energy transfer from WO66 - group to Eu(III) ion. The enhanced performance can be ascribed to efficient separation of electron and hole pairs after doping Eu(III) into the Bi2WO6 lattice.

  12. Tunable luminescence and enhanced photocatalytic activity for Eu(III) doped Bi2WO6 nanoparticles.

    PubMed

    Gu, Haidong; Yu, Lei; Wang, Juan; Ni, Min; Liu, Tingting; Chen, Feng

    2017-04-15

    A series of Eu(III) doped Bi2WO6 nanoparticles were synthesized by a hydrothermal process. The obtained Bi2WO6:Eu(III) nanoparticles were characterized by XRD, SEM, luminescence spectrophotometer and DRS. The XRD and TEM results indicate that the Eu(III) doping concentration has no influence on the phase and morphology. However, the Eu(III) doping can tune the luminescence and enhance the photocatalytic activity of Bi2WO6. With the increases of Eu(3+) doping concentrations, the emission intensity of WO6(6-) group decreases nut the photocatalytic activity increases. The tunable luminescence of Bi2WO6:Eu(III) nanoparticles results from the energy transfer from WO6(6-) group to Eu(III) ion. The enhanced performance can be ascribed to efficient separation of electron and hole pairs after doping Eu(III) into the Bi2WO6 lattice.

  13. Tripartite associations among bacteriophage WO, Wolbachia, and host affected by temperature and age in Tetranychus urticae.

    PubMed

    Lu, Ming-Hong; Zhang, Kai-Jun; Hong, Xiao-Yue

    2012-11-01

    A phage density model of cytoplasmic incompatibility (CI), which means lytic phages reduce bacterial density associated with CI, significantly enhances our understanding of the tripartite associations among bacteriophage WO, Wolbachia and host. However, WO may alternate between lytic and lysogenic life cycles or change phage production under certain conditions including temperature, host age and host species background. Here, extreme temperatures can induce an alteration in the life cycle of WO and change the tripartite associations among WO, Wolbachia and CI. Based on the accumulation of the WO load, WO can transform into the lytic life cycle with increasing age. These findings confirmed that the environment plays an important role in the associations among WO, Wolbachia and host.

  14. Synthesis of a highly reactive form of WO2Cl2, its conversion into nanocrystalline mono-hydrated WO3 and coordination compounds with tetramethylurea.

    PubMed

    Bortoluzzi, Marco; Evangelisti, Claudio; Marchetti, Fabio; Pampaloni, Guido; Piccinelli, Fabio; Zacchini, Stefano

    2016-10-21

    A new form of WO2Cl2 was obtained by modification of a literature procedure. Both the newly prepared WO2Cl2 and the commercial yellow WO2Cl2 exhibited an orthorhombic structure (powder X-ray diffraction, P-XRD), and their air exposure at room temperature afforded light green and lemon yellow WO3·H2O (orthorhombic phase), respectively. These materials were characterized by P-XRD, high-resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (S-TEM). The analyses revealed the nanocrystalline nature of light green WO3·H2O, and the prevalent amorphism of lemon yellow WO3·H2O. The reactions of grey WO2Cl2 with one and two equivalents of tetramethylurea (tmu), in CH2Cl2 at room temperature, led to the isolation of the trinuclear complex [WO2Cl2(tmu)]3, 1 (45% yield), and the mononuclear one WO2Cl2(tmu)2, 2 (64%), respectively. Compounds 1 and 2 were fully characterized by analytical and spectroscopic methods, single crystal X-ray diffraction (SC-XRD) and DFT calculations.

  15. Advanced GPS Technology For Automated/Autonomous Shuttle Missions

    NASA Technical Reports Server (NTRS)

    Goodman, John L.

    2004-01-01

    Test flights of a GPS receiver to replace TACAN began in 1996. Each orbiter has one GPS receiver. After RTF, ramp-up to single string GPS use will commence. Endeavour is undergoing TACAN removal and upgrade to three string GPS. GPS is not used for ascent and is powered on prelaunch to support an emergency landing. GPS has limited use for orbital operations and is not used for Rendezvous and docking. GPS will supplement or replace TACAN, but cannot be used as an MLS replacement. GPS enhances Shuttle navigation and improves safety. State-of-the-art GPS receivers have capabilities that would be useful in supporting automated/autonomous missions.

  16. Miniaturized GPS/MEMS IMU integrated board

    NASA Technical Reports Server (NTRS)

    Lin, Ching-Fang (Inventor)

    2012-01-01

    This invention documents the efforts on the research and development of a miniaturized GPS/MEMS IMU integrated navigation system. A miniaturized GPS/MEMS IMU integrated navigation system is presented; Laser Dynamic Range Imager (LDRI) based alignment algorithm for space applications is discussed. Two navigation cameras are also included to measure the range and range rate which can be integrated into the GPS/MEMS IMU system to enhance the navigation solution.

  17. Holes: Ionospheric Scintillation, GPS and Imputation

    DTIC Science & Technology

    2007-03-01

    HOLES: IONOSPHERIC SCINTILLATION GPS AND IMPUTATION THESIS Robert A. Steenburgh, Senior Master Sergeant, USAF AFIT/GAP/ENP/07-06 DEPARTMENT OF THE...of Defense, or the United States Government. AFIT/GAP/ENP/07-06 HOLES: IONOSPHERIC SCINTILLATION GPS AND IMPUTATION THESIS Presented to the Faculty...Master Sergeant, USAF March 2007 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT/GAP/ENP/07-06 HOLES: IONOSPHERIC SCINTILLATION GPS AND

  18. Global Positioning System (GPS) Geodetic Receivers,

    DTIC Science & Technology

    1982-02-08

    Subti.) S. TYPE OF REPORT A PERFo COVERED Global Positioning System ( GPS ) Geodetic N/A Receivers S. PERFORMING OrG. REPORT NUMBER I N/A AUTNORf*) S...i N meueaed idautfy b block nmAr) The NAVSTAR Global Positioning System ( GPS ) when fully developed will pro- vide world-wide, all weather, continuous... Global Positioning System ( GPS ) when fully developed will provide world-wide, all weather, continuous, highly accurate radio navigation support to

  19. GPS Synchronized Disciplined Rubidium Frequency Standard

    DTIC Science & Technology

    1989-11-01

    GPS SYNCHRONIZED DISCIPLINED RUBIDIUM FREQUENCY STANDARD D. Earl Fossler TRAK Systems Div. of TRAK Microwave Tampa, Florida Abstract A...disciplined rubidium freqllency standard steered by the corrected 1 PPS output from a GPS timing receiver or other stable 1 PPS source can provide a low...used for many timing applications, disciplined rubidium frcqucncy standards arc rtot, in wide use. GPS timing receivers have bcen used for several

  20. Determination of GPS orbits to submeter accuracy

    NASA Technical Reports Server (NTRS)

    Bertiger, W. I.; Lichten, S. M.; Katsigris, E. C.

    1988-01-01

    Orbits for satellites of the Global Positioning System (GPS) were determined with submeter accuracy. Tests used to assess orbital accuracy include orbit comparisons from independent data sets, orbit prediction, ground baseline determination, and formal errors. One satellite tracked 8 hours each day shows rms error below 1 m even when predicted more than 3 days outside of a 1-week data arc. Differential tracking of the GPS satellites in high Earth orbit provides a powerful relative positioning capability, even when a relatively small continental U.S. fiducial tracking network is used with less than one-third of the full GPS constellation. To demonstrate this capability, baselines of up to 2000 km in North America were also determined with the GPS orbits. The 2000 km baselines show rms daily repeatability of 0.3 to 2 parts in 10 to the 8th power and agree with very long base interferometry (VLBI) solutions at the level of 1.5 parts in 10 to the 8th power. This GPS demonstration provides an opportunity to test different techniques for high-accuracy orbit determination for high Earth orbiters. The best GPS orbit strategies included data arcs of at least 1 week, process noise models for tropospheric fluctuations, estimation of GPS solar pressure coefficients, and combine processing of GPS carrier phase and pseudorange data. For data arc of 2 weeks, constrained process noise models for GPS dynamic parameters significantly improved the situation.

  1. GPS data exploration for seismologists and geodesists

    NASA Astrophysics Data System (ADS)

    Webb, F.; Bock, Y.; Kedar, S.; Dong, D.; Jamason, P.; Chang, R.; Prawirodirdjo, L.; MacLeod, I.; Wadsworth, G.

    2007-12-01

    Over the past decade, GPS and seismic networks spanning the western US plate boundaries have produced vast amounts of data that need to be made accessible to both the geodesy and seismology communities. Unlike seismic data, raw geodetic data requires significant processing before geophysical interpretations can be made. This requires the generation of data-products (time series, velocities and strain maps) and dissemination strategies to bridge these differences and assure efficient use of data across traditionally separate communities. "GPS DATA PRODUCTS FOR SOLID EARTH SCIENCE" (GDPSES) is a multi-year NASA funded project, designed to produce and deliver high quality GPS time series, velocities, and strain fields, derived from multiple GPS networks along the western US plate boundary, and to make these products easily accessible to geophysicists. Our GPS product dissemination is through modern web-based IT methodology. Product browsing is facilitated through a web tool known as GPS Explorer and continuous streams of GPS time series are provided using web services to the seismic archive, where it can be accessed by seismologists using traditional seismic data viewing and manipulation tools. GPS-Explorer enables users to efficiently browse several layers of data products from raw data through time series, velocities and strain by providing the user with a web interface, which seamlessly interacts with a continuously updated database of these data products through the use of web-services. The current archive contains GDPSES data products beginning in 1995, and includes observations from GPS stations in EarthScope's Plate Boundary Observatory (PBO), as well as from real-time real-time CGPS stations. The generic, standards-based approach used in this project enables GDPSES to seamlessly expand indefinitely to include other space-time-dependent data products from additional GPS networks. The prototype GPS-Explorer provides users with a personalized working environment

  2. The GPS Laser Retroreflector Array Project

    NASA Technical Reports Server (NTRS)

    Merkowitz, Stephen M.

    2012-01-01

    Systematic co-location in space through the precision orbit determination of GPS satellites via satellite laser ranging will contribute significantly towards improving the accuracy and stability of the international terrestrial reference frame. NASA recently formed the GPS Laser Retroreflector Array Project to develop and deliver retroreflectors for integration on the next generation of GPS satellites. These retroreflectors will be an important contributor to achieving a global accuracy of 1.0 mm and 0.1 mm/year stability in the international terrestrial reference frame. We report here the current status of the GPS Laser Retroreflector Array Project.

  3. The Te-ni-wo-ha: An Etymological Study.

    ERIC Educational Resources Information Center

    Jolly, Yukiko S.

    1972-01-01

    The designation of the Japanese word class "joshi" (in English known as particles, post-positional case markers, or relationals) by the term te-ni-wo-ha can be traced to the early superimposition of the Chinese writing system on Japanese speech. Because of the structural differences between the two languages and the existence of elements in…

  4. Characterisation and application of WO3 films for electrochromic devices

    NASA Astrophysics Data System (ADS)

    Stapinski, Thomas; Marszalek, Konstanty; Swatowska, Barbara; Stanco, Agnieszka

    2013-07-01

    Electrochromic system is the one of the most popular devices using color memory effect under the influence of an applied voltage. The electrochromic system was produced based on the thin WO3 electrochromic films. Films were prepared by RF magnetron sputtering from tungsten targets in a reactive Ar+O2 gas atmosphere of various Ar/O2 ratios. The technological gas mixture pressure was 3 Pa and process temperature 30°C. Structural and optical properties of WO3 films were investigated for as-deposited and heat treated samples at temperature range from 350°C to 450°C in air. The material revealed the dependence of properties on preparation conditions and on post-deposition heat treatment. Main parameters of thin WO3 films: thickness d, refractive index n, extinction coefficient k and energy gap Eg were determined and optimized for application in electrochromic system. The main components of the system were glass plate with transparent conducting oxides, electrolyte, and glass plate with transparent conducting oxides and WO3 layer. The optical properties of the system were investigated when a voltage was applied across it. The electrochromic cell revealed the controllable transmittance depended on the operation voltage.

  5. Morphologically different WO3 nanocrystals in photoelectrochemical water oxidation

    NASA Astrophysics Data System (ADS)

    Biswas, Soumya Kanti; Baeg, Jin-Ook; Moon, Sang-Jin; Kong, Ki-jeong; So, Won-Wook

    2012-01-01

    Different morphologies of WO3 nanocrystals such as nanorods and nanoplates have been obtained under hydrothermal conditions using ammonium metatungstate as the precursor in presence of different organic acids such as citric, oxalic, and tartaric acid in the reaction medium. Detailed characterization of the crystal structure, particle morphology, and optical band gap of the synthesized powders have been done by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and solid-state UV-visible spectroscopy study. The as-synthesized materials are WO3 hydrates with orthorhombic phase which transform to the hexagonal WO3 through dehydration upon heating at 350 °C. The resultant products are crystalline with nanoscale dimensions. Finally, the photoactivity of the synthesized materials annealed at 500 °C has been compared employing in photoelectrochemical water oxidation under the illumination of AM 1.5G simulated solar light (100 mWcm-2). The photocurrent measurements upon irradiation of light exhibit obvious photocatalytic activity with a photocurrent of about 0.77, 0.61, and 0.65 mAcm-2 for the WO3 film derived with the oxalic acid, tartaric, and citric acid assisting agents, respectively, at 1.8 V versus Ag/AgCl electrode.

  6. Enhanced photocatalytic properties in well-ordered mesoporous WO3.

    PubMed

    Li, Li; Krissanasaeranee, Methira; Pattinson, Sebastian W; Stefik, Morgan; Wiesner, Ulrich; Steiner, Ullrich; Eder, Dominik

    2010-10-28

    We used polyisoprene-block-ethyleneoxide copolymers as structure-directing agents to synthesise well-ordered and highly-crystalline mesoporous WO(3) architectures that possess improved photocatalytic properties due to enhanced dye-adsorption in absence of diffusion limitation.

  7. Current and voltage noise in WO3 nanoparticle films

    NASA Astrophysics Data System (ADS)

    Hoel, A.; Vandamme, L. K. J.; Kish, L. B.; Olsson, E.

    2002-04-01

    Current and voltage noise measurements have been carried out on nanoparticle WO3 films. The fluctuation dissipation theorem holds, which indicates that the observed noise is an equilibrium phenomenon. Results on the thinnest films show that noise measurements can be used for quality assessment of nanocrystalline insulating films.

  8. The International GPS Service: A Global Resource for GPS Applications and Research

    NASA Technical Reports Server (NTRS)

    Neilan, Ruth E.; Zumberge, James F.; Beutler, Gerhard; Kouba, Jan

    1997-01-01

    Since June, 1992, the International GPS service has been coordinating a global civilian GPS infrastructure in order to support numerous GPS applications and research activities. A key aspect of the IGS is the reliability and quality of the analysis products that have been made available over the past five years through the IGS Analysis Centers and the Analysis Center Coordinator.

  9. The International GPS Service: A Global Resource for GPS Applications and Research

    NASA Technical Reports Server (NTRS)

    Neilan, Ruth E.; Zumberge, James F.; Beutler, Gerhard; Kouba, Jan

    1997-01-01

    Since June, 1992, the International GPS service has been coordinating a global civilian GPS infrastructure in order to support numerous GPS applications and research activities. A key aspect of the IGS is the reliability and quality of the analysis products that have been made available over the past five years through the IGS Analysis Centers and the Analysis Center Coordinator.

  10. Tungsten-based nanomaterials (WO3 & Bi2WO6): Modifications related to charge carrier transfer mechanisms and photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Girish Kumar, S.; Koteswara Rao, K. S. R.

    2015-11-01

    Heterogeneous photocatalysis is an ideal green energy technology for the purification of wastewater. Although titania dominates as the reference photocatalyst, its wide band gap is a bottleneck for extended utility. Thus, search for non-TiO2 based nanomaterials has become an active area of research in recent years. In this regard, visible light absorbing polycrystalline WO3 (2.4-2.8 eV) and Bi2WO6 (2.8 eV) with versatile structure-electronic properties has gained considerable interest to promote the photocatalytic reactions. These materials are also explored in selective functional group transformation in organic reactions, because of low reduction and oxidation potential of WO3 CB and Bi2WO6 VB, respectively. In this focused review, various strategies such as foreign ion doping, noble metal deposition and heterostructuring with other semiconductors designed for efficient photocatalysis is discussed. These modifications not only extend the optical response to longer wavelengths, but also prolong the life-time of the charge carriers and strengthen the photocatalyst stability. The changes in the surface-bulk properties and the charge carrier transfer dynamics associated with each modification correlating to the high activity are emphasized. The presence of oxidizing agents, surface modification with Cu2+ ions and synthesis of exposed facets to promote the degradation rate is highlighted. In depth study on these nanomaterials is likely to sustain interest in wastewater remediation and envisaged to signify in various green energy applications.

  11. Photoelectrochemical Properties and Behavior of α-SnWO4 Photoanodes Synthesized by Hydrothermal Conversion of WO3 Films.

    PubMed

    Zhu, Zhehao; Sarker, Pranab; Zhao, Chenqi; Zhou, Lite; Grimm, Ronald L; Huda, Muhammad N; Rao, Pratap M

    2017-01-18

    Metal oxides with moderate band gaps are desired for efficient production of hydrogen from sunlight and water via photoelectrochemical (PEC) water splitting. Here, we report an α-SnWO4 photoanode synthesized by hydrothermal conversion of WO3 films that achieves photon to current conversion at wavelengths up to 700 nm (1.78 eV). This photoanode is promising for overall PEC water-splitting because the flat-band potential and voltage of photocurrent onset are more negative than the potential of hydrogen evolution. Furthermore, the photoanode utilizes a large portion of the solar spectrum. However, the photocurrent density reaches only a small fraction of that which is theoretically possible. Density functional theory based thermodynamic and electronic structure calculations were performed to elucidate the nature and impact of defects in α-SnWO4 prepared by this synthetic route, from which hole localization at Sn-at-W antisite defects was determined to be a likely cause for the poor photocurrent. Measurements further showed that the photocurrent decreases over time due to surface oxidation, which was suppressed by improving the kinetics of hole transfer at the semiconductor/electrolyte interface. Alternative synthetic methods and the addition of protective coatings and/or oxygen evolution catalysts are suggested to improve the PEC performance and stability of this promising α-SnWO4 material.

  12. Mass balance assessment using GPS

    NASA Technical Reports Server (NTRS)

    Hulbe, Christina L.

    1993-01-01

    Mass balance is an integral part of any comprehensive glaciological investigation. Unfortunately, it is hard to determine at remote locations where there is no fixed reference. The Global Positioning System (GPS) offers a solution. Simultaneous GPS observations at a known location and the remote field site, processed differentially, will accurately position the camp site. From there, a monument planted in the firn atop the ice can also be accurately positioned. Change in the monument's vertical position is a direct indicator of ice thickness change. Because the monument is not connected to the ice, its motion is due to both mass balance change and to the settling of firn as it densifies into ice. Observations of relative position change between the monument and anchors at various depths within the firn are used to remove the settling effect. An experiment to test this method has begun at Byrd Station on the West Antarctic Ice Sheet and the first epoch of observations was made. Analysis indicates that positioning errors will be very small. It appears likely that the largest errors involved with this technique will arise from ancillary data needed to determine firn settling.

  13. WO{sub 3} nanoplates, hierarchical flower-like assemblies and their photocatalytic properties

    SciTech Connect

    Huang, Jianhua Xiao, Liang; Yang, Xiaolong

    2013-08-01

    Graphical abstract: WO{sub 3} nanoplates, hierarchical flower-like assemblies and their visible light-driven photocatalytic properties for degradation of rhodamine B. - Highlights: • Preparation of monoclinic WO{sub 3} by a hydrothermal reaction of PbWO{sub 4} in the presence of HNO{sub 3}. • Single-crystalline WO{sub 3} nanoplates were formed when 4 M HNO{sub 3} solution was used. • WO{sub 3} flowers were assembled by nanoplates when 15 M HNO{sub 3} solution was used. • The products showed excellent visible light-driven photodegradation of rhodamine B. - Abstract: Monoclinic WO{sub 3} was prepared by a hydrothermal reaction of PbWO{sub 4} in the presence of HNO{sub 3}. WO{sub 3} rectangular nanoplates with a side length of 50–150 nm and a thickness of about 25 nm were obtained at 4 M HNO{sub 3} solution. And the single crystal nature was confirmed by the selected area electron diffraction. Whereas WO{sub 3} hierarchical flower-like assemblies with 3–5 μm in diameter were self-organized by nanoplates in the presence of 15 M HNO{sub 3} solution. Compared with commercial WO{sub 3} particles, our products showed an enhancement of photocatalytic properties for the degradation of rhodamine B under visible light irradiation.

  14. Microwave Intercalation Synthesis of WO3 Nanoplates and Their NO-Sensing Properties

    NASA Astrophysics Data System (ADS)

    Tu, Yue; Li, Qiang; Jiang, Danyu; Wang, Qi; Feng, Tao

    2015-01-01

    Tungsten(VI) oxide (WO3) nanoplates were successfully synthesized by microwave intercalation. Through microwave processing, an intermediate product H2W2O7· xH2O was prepared quickly to greatly decrease the time used to prepare WO3 nanoplates. The crystal structure and morphology of WO3 were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The morphology of WO3 changed with an increase in calcining temperature. A mixed-potential NO x sensor using planar yttria-stabilized zirconia and WO3 as the sensing electrode (SE) was fabricated, and its performance in NO x detection at high temperature was examined. It was determined that at 500 °C, the sensor with the WO3-nanoplate SE had higher sensitivity to NO than the sensor with a SE consisting of WO3 microparticles. The response of the NO sensor with a WO3-nanoplate SE was linear with the logarithm of NO concentration in the range of 100-1000 ppm. The electrochemical impedance measurements indicate that the electrode reaction that occurred at the triple-phase boundary (TPB) of the sensor with WO3-nanoplate SE was stronger than the reaction that occurred at the TPB of the sensor with WO3-microparticle sensing electrode.

  15. Ideas for Future GPS Timing Improvements

    NASA Technical Reports Server (NTRS)

    Hutsell, Steven T.

    1996-01-01

    Having recently met stringent criteria for full operational capability (FOC) certification, the Global Positioning System (GPS) now has higher customer expectations than ever before. In order to maintain customer satisfaction, and the meet the even high customer demands of the future, the GPS Master Control Station (MCS) must play a critical role in the process of carefully refining the performance and integrity of the GPS constellation, particularly in the area of timing. This paper will present an operational perspective on several ideas for improving timing in GPS. These ideas include the desire for improving MCS - US Naval Observatory (USNO) data connectivity, an improved GPS-Coordinated Universal Time (UTC) prediction algorithm, a more robust Kalman Filter, and more features in the GPS reference time algorithm (the GPS composite clock), including frequency step resolution, a more explicit use of the basic time scale equation, and dynamic clock weighting. Current MCS software meets the exceptional challenge of managing an extremely complex constellation of 24 navigation satellites. The GPS community will, however, always seek to improve upon this performance and integrity.

  16. Accuracy of tracking forest machines with GPS

    Treesearch

    M.W. Veal; S.E. Taylor; T.P. McDonald; D.K. McLemore; M.R. Dunn

    2001-01-01

    This paper describes the results of a study that measured the accuracy of using GPS to track movement of forest machines. Two different commercially available GPS receivers (Trimble ProXR and GeoExplorer II) were used to track\\r\

  17. External Review of GPS LifePlan

    ERIC Educational Resources Information Center

    Arendale, David R.

    2008-01-01

    The GPS LifePlan is an interactive resource that helps students succeed in reaching their career, education and personal goals. GPS stands for "GOALS + PLANS = SUCCESS". http://gpslifeplan.org This holistic academic and student development program provides a structure for students to define their goals and helps them establish plans to…

  18. Wave measurements using GPS velocity signals.

    PubMed

    Doong, Dong-Jiing; Lee, Beng-Chun; Kao, Chia Chuen

    2011-01-01

    This study presents the idea of using GPS-output velocity signals to obtain wave measurement data. The application of the transformation from a velocity spectrum to a displacement spectrum in conjunction with the directional wave spectral theory are the core concepts in this study. Laboratory experiments were conducted to verify the accuracy of the inversed displacement of the surface of the sea. A GPS device was installed on a moored accelerometer buoy to verify the GPS-derived wave parameters. It was determined that loss or drifting of the GPS signal, as well as energy spikes occurring in the low frequency band led to erroneous measurements. Through the application of moving average skill and a process of frequency cut-off to the GPS output velocity, correlations between GPS-derived, and accelerometer buoy-measured significant wave heights and periods were both improved to 0.95. The GPS-derived one-dimensional and directional wave spectra were in agreement with the measurements. Despite the direction verification showing a 10° bias, this exercise still provided useful information with sufficient accuracy for a number of specific purposes. The results presented in this study indicate that using GPS output velocity is a reasonable alternative for the measurement of ocean waves.

  19. Wave Measurements Using GPS Velocity Signals

    PubMed Central

    Doong, Dong-Jiing; Lee, Beng-Chun; Kao, Chia Chuen

    2011-01-01

    This study presents the idea of using GPS-output velocity signals to obtain wave measurement data. The application of the transformation from a velocity spectrum to a displacement spectrum in conjunction with the directional wave spectral theory are the core concepts in this study. Laboratory experiments were conducted to verify the accuracy of the inversed displacement of the surface of the sea. A GPS device was installed on a moored accelerometer buoy to verify the GPS-derived wave parameters. It was determined that loss or drifting of the GPS signal, as well as energy spikes occurring in the low frequency band led to erroneous measurements. Through the application of moving average skill and a process of frequency cut-off to the GPS output velocity, correlations between GPS-derived, and accelerometer buoy-measured significant wave heights and periods were both improved to 0.95. The GPS-derived one-dimensional and directional wave spectra were in agreement with the measurements. Despite the direction verification showing a 10° bias, this exercise still provided useful information with sufficient accuracy for a number of specific purposes. The results presented in this study indicate that using GPS output velocity is a reasonable alternative for the measurement of ocean waves. PMID:22346618

  20. Doppler Test Results of Experimental GPS Receiver.

    DTIC Science & Technology

    1982-01-01

    Global Positioning System ( GPS ) which is intended to supplant the Navy system for navigation. (An...Bossler, John D., Clyde C. Good and Peter L. Bender, "Using the Global Positioning System ( GPS ) for Geodetic Positioning ", Bulletin Geodesique, 54 (4), 553...necessary and identify by block number) Geodesy Satellite Positioning Global Positioning System Surveying 20. ABSTRACT (Continue on ,eovoera~ldo

  1. Space Shuttle Navigation in the GPS Era

    NASA Technical Reports Server (NTRS)

    Goodman, John L.

    2001-01-01

    The Space Shuttle navigation architecture was originally designed in the 1970s. A variety of on-board and ground based navigation sensors and computers are used during the ascent, orbit coast, rendezvous, (including proximity operations and docking) and entry flight phases. With the advent of GPS navigation and tightly coupled GPS/INS Units employing strapdown sensors, opportunities to improve and streamline the Shuttle navigation process are being pursued. These improvements can potentially result in increased safety, reliability, and cost savings in maintenance through the replacement of older technologies and elimination of ground support systems (such as Tactical Air Control and Navigation (TACAN), Microwave Landing System (MLS) and ground radar). Selection and missionization of "off the shelf" GPS and GPS/INS units pose a unique challenge since the units in question were not originally designed for the Space Shuttle application. Various options for integrating GPS and GPS/INS units with the existing orbiter avionics system were considered in light of budget constraints, software quality concerns, and schedule limitations. An overview of Shuttle navigation methodology from 1981 to the present is given, along with how GPS and GPS/INS technology will change, or not change, the way Space Shuttle navigation is performed in the 21 5 century.

  2. Monitoring beach changes using GPS surveying techniques

    USGS Publications Warehouse

    Morton, Robert; Leach, Mark P.; Paine, Jeffrey G.; Cardoza, Michael A.

    1993-01-01

    The adaptation of Global Positioning System (GPS) surveying techniques to beach monitoring activities is a promising response to this challenge. An experiment that employed both GPS and conventional beach surveying was conducted, and a new beach monitoring method employing kinematic GPS surveys was devised. This new method involves the collection of precise shore-parallel and shore-normal GPS positions from a moving vehicle so that an accurate two-dimensional beach surface can be generated. Results show that the GPS measurements agree with conventional shore-normal surveys at the 1 cm level, and repeated GPS measurements employing the moving vehicle demonstrate a precision of better than 1 cm. In addition, the nearly continuous sampling and increased resolution provided by the GPS surveying technique reveals alongshore changes in beach morphology that are undetected by conventional shore-normal profiles. The application of GPS surveying techniques combined with the refinement of appropriate methods for data collection and analysis provides a better understanding of beach changes, sediment transport, and storm impacts.

  3. Expected Position Error for an Onboard Satellite GPS Receiver

    DTIC Science & Technology

    2015-03-01

    The Global Positioning System (GPS) constellation provides ranging information that delivers inexpensive, high precision positioning for terrestrial...altitude approaches that of the GPS constellation . Above the GPS constellation , the available GPS signals for ranging will originate from satellites on the...Concerns about the GPS coverage environment increase when the receiver’s altitude approaches or surpasses the orbital altitude of the GPS constellation

  4. 75 FR 8928 - Announcement of IS-GPS-200, IS-GPS-705, IS-GPS-800 Interface Control Working Group (ICWG...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-26

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF DEFENSE Department of the Air Force Announcement of IS-GPS-200, IS-GPS-705, IS-GPS-800Interface Control Working Group... an Interface Control Working Group (ICWG) teleconference meeting for document/s IS-GPS-200E (NAVSTAR...

  5. Pre-Flight Testing of Spaceborne GPS Receivers Using a GPS Constellation Simulator

    NASA Technical Reports Server (NTRS)

    Kizhner, Semion; Alonso, Roberto

    1999-01-01

    The NASA Goddard Space Flight Center (GSFC) Global Positioning System (GPS) test facility has been established within the GSFC Guidance Navigation and Control Center. The GPS test facility is currently housing the STR2760 GPS satellite 40-channel attitude simulator and an STR4760 12-channel navigation simulator. The facility also contains a few other Goddard resources such as an atomic time standard test bed, a rooftop antenna platform and a radome. It provides a new capability of high dynamics GPS simulations for space flight that is unique within the aerospace community. The GPS facility gives a significant advantage in the development and support of GPS based technologies for position, attitude and precise time determination on-board a spacecraft, sounding rocket or balloon. The GPS simulator system is configured in a transportable rack and is available for GPS applications' component development as well as for spacecraft subsystem and system level testing at spacecraft integration and test sites. The GPS facility has been operational since early 1996 and has been already utilized by a few successful flight projects carrying GPS experiments, such as USA Seastar satellite and the first Argentine satellite SAC-A. The experience in the SAC-A pre-flight testing using the STR2760 simulator is summarized as well as the comparison with preliminary analysis of the GPS data from SAC-A telemetry.

  6. Using GPS Reflections for Satellite Remote Sensing

    NASA Technical Reports Server (NTRS)

    Mickler, David

    2000-01-01

    GPS signals that have reflected off of the ocean's surface have shown potential for use in oceanographic and atmospheric studies. The research described here investigates the possible deployment of a GPS reflection receiver onboard a remote sensing satellite in low Earth orbit (LEO). The coverage and resolution characteristics of this receiver are calculated and estimated. This mission analysis examines using reflected GPS signals for several remote sensing missions. These include measurement of the total electron content in the ionosphere, sea surface height, and ocean wind speed and direction. Also discussed is the potential test deployment of such a GPS receiver on the space shuttle. Constellations of satellites are proposed to provide adequate spatial and temporal resolution for the aforementioned remote sensing missions. These results provide a starting point for research into the feasibility of augmenting or replacing existing remote sensing satellites with spaceborne GPS reflection-detecting receivers.

  7. Fault tolerant GPS/Inertial System design

    NASA Astrophysics Data System (ADS)

    Brown, Alison K.; Sturza, Mark A.; Deangelis, Franco; Lukaszewski, David A.

    The use of a GPS/Inertial integrated system in future launch vehicles motivates the described design of the present fault-tolerant system. The robustness of the navigation system is enhanced by integrating the GPS with an inertial fault-tolerant system. Three layers of failure detection and isolation are incorporated to determine the nature of flaws in the inertial instruments, the GPS receivers, or the integrated navigation solution. The layers are based on: (1) a high-rate parity algorithm for instrument failures; (2) a similar parity algorithm for GPS satellite or receiver failures; and (3) a GPS navigation solution to monitor inertial navigation failures. Dual failures of any system component can occur in any system component without affecting the performance of launch-vehicle navigation or guidance.

  8. GPS studies during the ENIGMA era

    NASA Astrophysics Data System (ADS)

    Torniainen, I.; Tornikoski, M.; Lähteenmäki, A.; Aller, M. F.; Aller, H. D.; Mingaliev, M. G.

    2006-10-01

    We have studied two samples of gigahertz-peaked spectrum sources, one consisting of mostly quasars and the other consisting of galaxy-type objects. Among both samples most of the GPS sources lost their GPS status because with competent data sets the shape of the spectrum was not in compliance with a GPS spectrum. Instead a remarkable share of the quasars were actually flat-spectrum sources caught in a flare of which the spectrum is inverted. Also many of the galaxies did not have enough data for solid classifications so, with more observations at different frequencies, they can turn out to be anything from genuine GPS sources to flaring blazars with more observations at different frequencies. This implicates a complicated situation for ESA's Planck mission. In order to study the anisotropies of the cosmic microwave background, the contribution of the foreground emission must be known. The different possibilities instead of classical invariable GPS sources will make predictions complex.

  9. Inappropriate circumcision referrals by GPs.

    PubMed Central

    Griffiths, D; Frank, J D

    1992-01-01

    One hundred and twenty boys were referred by GPs over a 12-month period to a paediatric urologist for circumcision. The reasons for referral were: ballooning in 36, non-retraction in 28, balanoposthitis in 36 or a combination in 15. On examination 53% had a retractile, 21% a partially retractile and 21% a non-retractile foreskin. Six patients had obvious balanitis xerotica obliterans. Only one quarter of the patients required a circumcision. The penis was not examined by the referring doctor in 15 patients. The implications of this survey are that a large proportion of general practitioners have difficulty in discriminating between a true phimosis and a developmentally non-retractile foreskin. This diagnostic inaccuracy was greatest when the referring doctor did not examine the patient. PMID:1625262

  10. HRTEM Microstructural Characterization of β-WO3 Thin Films Deposited by Reactive RF Magnetron Sputtering

    PubMed Central

    Faudoa-Arzate, A.; Arteaga-Durán, A.; Saenz-Hernández, R.J.; Botello-Zubiate, M.E.; Realyvazquez-Guevara, P.R.; Matutes-Aquino, J.A.

    2017-01-01

    Though tungsten trioxide (WO3) in bulk, nanosphere, and thin film samples has been extensively studied, few studies have been dedicated to the crystallographic structure of WO3 thin films. In this work, the evolution from amorphous WO3 thin films to crystalline WO3 thin films is discussed. WO3 thin films were fabricated on silicon substrates (Si/SiO2) by RF reactive magnetron sputtering. Once a thin film was deposited, two successive annealing treatments were made: an initial annealing at 400 °C for 6 h was followed by a second annealing at 350 °C for 1 h. Film characterization was carried out by X-ray diffraction (XRD), high-resolution electron transmission microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The β-WO3 final phase grew in form of columnar crystals and its growth plane was determined by HRTEM. PMID:28772559

  11. Photocatalytic Removal of Microcystin-LR by Advanced WO3-Based Nanoparticles under Simulated Solar Light

    PubMed Central

    Zhao, Chao; Li, Dawei; Feng, Chuanping; Zhang, Zhenya; Sugiura, Norio; Yang, Yingnan

    2015-01-01

    A series of advanced WO3-based photocatalysts including CuO/WO3, Pd/WO3, and Pt/WO3 were synthesized for the photocatalytic removal of microcystin-LR (MC-LR) under simulated solar light. In the present study, Pt/WO3 exhibited the best performance for the photocatalytic degradation of MC-LR. The MC-LR degradation can be described by pseudo-first-order kinetic model. Chloride ion (Cl−) with proper concentration could enhance the MC-LR degradation. The presence of metal cations (Cu2+ and Fe3+) improved the photocatalytic degradation of MC-LR. This study suggests that Pt/WO3 photocatalytic oxidation under solar light is a promising option for the purification of water containing MC-LR. PMID:25884038

  12. Nanoarchitectonics of a Au nanoprism array on WO3 film for synergistic optoelectronic response

    PubMed Central

    Chen, Xiaoqing; Li, Peng; Tong, Hua; Kako, Tetsuya; Ye, Jinhua

    2011-01-01

    A layered photoelectrode consisting of a conductive indium tin oxide substrate, a WO3 nanocrystalline film and an array of Au nanoprisms was fabricated via a multistep process. Scanning electron microscopy and atomic force microscopy showed that the Au nanoprisms had a uniform size and shape and formed periodic hexagonal patterns on the WO3 film. The optical absorption of the photoelectrode combined the intrinsic absorption of WO3 and plasmonic absorption of Au. Using this photoelectrode, we investigated the effect of the Au nanoprism array on the optoelectronic conversion performance of the WO3 film. Photoelectrochemical measurement indicated that the array substantially enhanced the photocurrent in the WO3 film. Electrochemical impedance measurements revealed that the Schottky junctions formed between Au and WO3 can facilitate the separation of photogenerated carriers as well as the interfacial carrier transfer. In this study, we demonstrate that covering a semiconductor with plasmonic noble metal nanoparticles can improve its optoelectronic conversion efficiency. PMID:27877412

  13. HRTEM Microstructural Characterization of β-WO3 Thin Films Deposited by Reactive RF Magnetron Sputtering.

    PubMed

    Faudoa-Arzate, A; Arteaga-Durán, A; Saenz-Hernández, R J; Botello-Zubiate, M E; Realyvazquez-Guevara, P R; Matutes-Aquino, J A

    2017-02-17

    Though tungsten trioxide (WO3) in bulk, nanosphere, and thin film samples has been extensively studied, few studies have been dedicated to the crystallographic structure of WO3 thin films. In this work, the evolution from amorphous WO3 thin films to crystalline WO3 thin films is discussed. WO3 thin films were fabricated on silicon substrates (Si/SiO2) by RF reactive magnetron sputtering. Once a thin film was deposited, two successive annealing treatments were made: an initial annealing at 400 °C for 6 h was followed by a second annealing at 350 °C for 1 h. Film characterization was carried out by X-ray diffraction (XRD), high-resolution electron transmission microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The β-WO3 final phase grew in form of columnar crystals and its growth plane was determined by HRTEM.

  14. Facile synthesis of hierarchical double-shell WO3 microspheres with enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Wang, Zhenfeng; Chu, Deqing; Wang, Limin; Wang, Lipeng; Hu, Wenhui; Chen, Xiangyu; Yang, Huifang; Sun, Jingjing

    2017-02-01

    Hierarchical double-shell WO3 microspheres (HDS-WO3) have been successfully obtained through the thermal decomposition of WO3·H2O formed by metal salts as the templates. The products were characterized by X-ray diffraction (XRD), and the morphology was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, the HDS-WO3 microspheres were analyzed by the Thermogravimetric (TG) and Brunauer-Emmett-Teller (BET) analysis. The synthetic mechanism of the products with hierarchical structures was proposed. The obtained HDS-WO3 exhibits excellent photocatalytic efficiency (84.9%), which is much higher than other WO3 sample under visible light illumination.

  15. WO3 nanorods created by self-assembly of highly crystalline nanowires under hydrothermal conditions.

    PubMed

    Navarro, Julien R G; Mayence, Arnaud; Andrade, Juliana; Lerouge, Frédéric; Chaput, Frédéric; Oleynikov, Peter; Bergström, Lennart; Parola, Stephane; Pawlicka, Agnieszka

    2014-09-02

    WO3 nanorods and wires were obtained via hydrothermal synthesis using sodium tungstate as a precursor and either oxalic acid, citric acid, or poly(methacrylic acid) as a stabilizing agent. Transmission electron microscopy images showed that the organic acids with different numbers of carboxylic groups per molecule influence the final sizes and stacking nanostructures of WO3 wires. Three-dimensional electron diffraction tomography of a single nanocrystal revealed a hexagonal WO3 structure with preferential growth along the c-axis, which was confirmed by high-resolution transmission electron microscopy. WO3 nanowires were also spin-coated onto an indium tin oxide/glass conducting substrate, resulting in the formation of a film that was characterized by scanning electron microscopy. Finally, cyclic voltammetry measurements performed on the WO3 thin film showed voltammograms typical for the WO3 redox process.

  16. NixWO2.72 nanorods as an efficient electrocatalyst for oxygen evolution reaction

    DOE PAGES

    Xi, Zheng; Mendoza-Garcia, Adriana; Zhu, Huiyuan; ...

    2017-01-13

    NixWO2.72 nanorods (NRs) are synthesized by a one-pot reaction of Ni(acac)2 and WCl4. In the rod structure, Ni(II) intercalates in the defective perovskite-type WO2.72 and is stabilized. The NixWO2.72 NRs show the x-dependent electrocatalysis for the oxygen evolution reaction (OER) in 0.1M KOH with Ni0.78WO2.72 being the most efficient, even outperforming the commercial Ir-catalyst. Lastly, the synthesis is not limited to NixWO2.72 but can be extended to MxWO2.72 (M = Co, Fe) as well, providing a new class of oxide-based catalysts for efficient OER and other energy conversion reactions.

  17. Tailoring surface states in WO3 photoanodes for efficient photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Singh, Trilok; Müller, Ralf; Singh, Jai; Mathur, Sanjay

    2015-08-01

    The dynamics of photo-induced charge carriers are significantly influenced by the surface states of WO3 thin films, which were synthesized by reactive sputtering of tungsten substrates in oxygen plasma. Tailoring the surface properties by (i) hydrogen plasma treatment and (ii) anchoring plasmonic nanoparticles (Au and Ag) altered the light harvesting and charge separation/transport processes of WO3 photoanodes. Upon hydrogen plasma-treatment and coating of noble metal clusters, WO3 films showed enhanced visible light absorption and consequently higher photocurrent density (1.4 mA cm-2) compared to pristine WO3 (0.2 mA cm-2). Enhancement in hydrogen treated WO3 sample was found to be due to the reduction of W(VI) into W(V) centers, which produced substoichiometric WO3-x phases, whereas noble metal particles contributed towards both resonant and non-resonant scattering of incident light thereby increasing photon-to-current conversion efficiency.

  18. Fungus mediated biosynthesis of WO3 nanoparticles using Fusarium solani extract

    NASA Astrophysics Data System (ADS)

    Kavitha, N. S.; Venkatesh, K. S.; Palani, N. S.; Ilangovan, R.

    2017-05-01

    Currently nanoparticles were synthesized by emphasis bioremediation process due to less hazardous, eco-friendly and imperative applications on biogenic process. Fungus mediated biosynthesis strategy has been developed to prepare tungsten oxide nanoflakes (WO3, NFs) using the plant pathogenic fungus F.solani. The powder XRD pattern revealed the monoclinic crystal structure with improved crystalline nature of the synthesized WO3 nanoparticles. FESEM images showed the flake-like morphology of WO3, with average thickness and length around 40 nm and 300 nm respectively. The Raman spectrum of WO3 NFs showed their characteristic vibration modes that revealed the defect free nature of the WO3 NFs. Further, the elemental analysis indicated the stoichiometric composition of WO3 phase.

  19. Enhancement of the photocatalytic activity and electrochemical property of graphene-SrWO4 nanocomposite

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoyan; Nie, Yu; Yang, Hongxun; Sun, Shengnan; Chen, Yingying; Yang, Tongyi; Lin, Shengling

    2016-05-01

    SrWO4 is a promising candidate as not only photocatalyst for the removal of organic pollutants from water, but also electrode material for energy storage devices. However, the drawbacks of its poor adsorptive performance, low electrical conductivity, and high recombination rate of photogenerated electron-hole pair impede its practical applications. In this work, we have developed a new graphene/SrWO4 nanocomposite synthesized via a facile chemical precipitation method. Characterizations show that SrWO4 nanoparticles with 80 nm or so deposited on the surface of graphene nanosheets. Graphene nanosheets in the graphene-SrWO4 hybrid could increase adsorptive property, improve the electrical conductivity of hybrid, and reduce the recombination of electron-hole pairs. As a kind of photocatalyst or electrode material for supercapacitor, the binary graphene-SrWO4 hybrid presents enhanced photocatalytic activity and electrochemical property compared to pure SrWO4.

  20. Preparation and characterization of WO3 nanoparticles, WO3/TiO2 core/shell nanocomposites and PEDOT:PSS/WO3 composite thin films for photocatalytic and electrochromic applications

    NASA Astrophysics Data System (ADS)

    Boyadjiev, Stefan I.; Santos, Gustavo dos Lopes; Szżcs, Júlia; Szilágyi, Imre M.

    2016-03-01

    In this study, monoclinic WO3 nanoparticles were obtained by thermal decomposition of (NH4)xWO3 in air at 600 °C. On them by atomic layer deposition (ALD) TiO2 films were deposited, and thus core/shell WO3/TiO2 nanocomposites were prepared. We prepared composites of WO3 nanoparticles with conductive polymer as PEDOT:PSS, and deposited thin films of them on glass and ITO substrates by spin coating. The formation, morphology, composition and structure of the as-prepared pure and composite nanoparticles, as well thin films, were studied by TEM, SEM-EDX and XRD. The photocatalytic activity of both the WO3 and core/shell WO3/TiO2 nanoparticles was studied by decomposing methyl orange in aqueous solution under UV light irradiation. Cyclic voltammetry measurements were performed on the composite PEDOT:PSS/WO3 thin films, and the coloring and bleaching states were studied.

  1. Preparation and characterization of WO{sub 3} nanoparticles, WO{sub 3}/TiO{sub 2} core/shell nanocomposites and PEDOT:PSS/WO{sub 3} composite thin films for photocatalytic and electrochromic applications

    SciTech Connect

    Boyadjiev, Stefan I.; Santos, Gustavo dos Lopes; Szűcs, Júlia; Szilágyi, Imre M.

    2016-03-25

    In this study, monoclinic WO{sub 3} nanoparticles were obtained by thermal decomposition of (NH{sub 4}){sub x}WO{sub 3} in air at 600 °C. On them by atomic layer deposition (ALD) TiO{sub 2} films were deposited, and thus core/shell WO{sub 3}/TiO{sub 2} nanocomposites were prepared. We prepared composites of WO{sub 3} nanoparticles with conductive polymer as PEDOT:PSS, and deposited thin films of them on glass and ITO substrates by spin coating. The formation, morphology, composition and structure of the as-prepared pure and composite nanoparticles, as well thin films, were studied by TEM, SEM-EDX and XRD. The photocatalytic activity of both the WO{sub 3} and core/shell WO{sub 3}/TiO{sub 2} nanoparticles was studied by decomposing methyl orange in aqueous solution under UV light irradiation. Cyclic voltammetry measurements were performed on the composite PEDOT:PSS/WO{sub 3} thin films, and the coloring and bleaching states were studied.

  2. GPS Radio Occultation as Part of the Global Observing System for Atmosphere

    NASA Technical Reports Server (NTRS)

    Mannucci, Anthony J.; Ao, C. O.; Iijima, B. A.; Wilson, B. D.; Yunck, T. P.; Kursinski, E. R.

    2008-01-01

    Topics include: The Measurement (Physical retrievals based on time standards), GPS Retrieval Products, Retrievals and Radiances: CLARREO Mission, GPS RO and AIRS, GPS RO and Microwave, GPS RO and Radiosondes, GPS/GNSS Science, and Conclusions.

  3. Phage WO of Wolbachia: lambda of the endosymbiont world

    PubMed Central

    Kent, Bethany N.; Bordenstein, Seth R.

    2010-01-01

    The discovery of an extraordinarily high level of mobile elements in the genome of Wolbachia, a widespread arthropod and nematode endosymbiont, suggests that this bacterium could be an excellent model for assessing the evolution and function of mobile DNA in specialized bacteria. Here, we discuss how studies on the temperate bacteriophage WO of Wolbachia have revealed unexpected levels of genomic flux and are challenging previously held views about the clonality of obligate intracellular bacteria. We also discuss the roles that this phage might play in the Wolbachia-arthropod symbiosis, and infer how this research can be translated to combating human diseases vectored by arthropods. We expect that this temperate phage will be a preeminent model system to understand phage genetics, evolution, and ecology in obligate intracellular bacteria. In this sense, phage WO might be likened to phage λ of the endosymbiont world. PMID:20083406

  4. Symmetry driven control of optical properties in WO3 films

    DOE PAGES

    Herklotz, A.; Rus, S. F.; KC, S.; ...

    2017-06-23

    Optical band gap control of semiconducting thin films is critical for the optimization of photoelectronic and photochemical applications. In this work, we demonstrate that the optical band gap of WO3 films can be continuously controlled through uniaxial strain induced by low-energy helium implantation. We show that the implantation of He into epitaxially grown and coherently strained WO3 films can be used to induce single axis out-of-plane lattice expansion of up to 2%. Ellipsometric spectroscopy reveals that this lattice expansion shifts the absorption spectrum to lower energies and effectively reduces the optical band gap by about 0.18 eV per percent expansionmore » of the out-of-plane unit cell length. Furthermore, density functional calculations show that this response is a direct result of changes in orbital degeneracy driven by changes in the octahedral rotations and tilts.« less

  5. Snake River Plain FORGE Well Data for WO-2

    DOE Data Explorer

    Robert Podgorney

    1991-07-29

    Well data for the WO-2 well located in eastern Snake River Plain, Idaho. This data collection includes lithology reports, borehole logs, temperature at depth data, neutron density and gamma data, and rock strength parameters for the WO-2 well. This collection of data has been assembled as part of the site characterization data used to develop the conceptual geologic model for the Snake River Plain site in Idaho, as part of phase 1 of the Frontier Observatory for Research in Geothermal Energy (FORGE) initiative. They were assembled by the Snake River Geothermal Consortium (SRGC), a team of collaborators that includes members from national laboratories, universities, industry, and federal agencies, lead by the Idaho National Laboratory (INL).

  6. Invasion noise in nanoparticle WO3/Au thin film devices

    NASA Astrophysics Data System (ADS)

    Hoel, Anders; Ederth, Jesper; Heszler, Peter; Kish, Laszlo B.; Olsson, Eva; Granqvist, Claes-Goeran

    2001-11-01

    Conduction noise measurements were carried out in the 0.3 to 45 Hz frequency range on Au films covered by a thin layer of tungsten trioxide (WO3) nanoparticles. Exposing the films to alcohol vapor resulted in a gradually increased noise intensity which went through a maximum after an exposure time of the order of 15 min. The maximum noise intensity could increase by several orders of magnitude above the initial level. Longer exposure times made the noise decrease and approach its original value. This effect was not observed in the absence of WO3 nanoparticles. The phenomenon is discussed in terms of a new invasion noise model in which the noise is related to the insertion and extraction of mobile chemical species.

  7. GPS Position and Heading Circuitry for Ships

    NASA Technical Reports Server (NTRS)

    Cooke, Michael P.; Yim, Hester J.; Gomez, Susan F.

    2003-01-01

    Circuit boards that contain radio-frequency (RF) and digital circuitry have been developed by NASA to satisfy a requirement of the Port of Houston Authority for relatively inexpensive Global Positioning System (GPS) receivers that indicate the azimuthal headings as well as the positions of ships. The receiver design utilizes the unique architecture of the Mitel commercial chip-set, which provides for an accurate GPS-based heading-determination device. The major components include two RF front ends (each connected to a separate antenna), a surface-acoustic-wave intermediate-frequency filter between second- and third-stage mixers, a correlator, and a reduced-instruction- set computer. One of the RF front ends operates as a master, the other as a slave. Both RF front ends share a 10-MHz sinusoidal clock oscillator, which provides for more accurate carrier phase measurements between the two antennas. The outputs of the RF front ends are subjected to conventional GPS processing. The commercial-based chip-set design approach provides an inexpensive open architecture GPS platform, which can be used in developing and implementing unique GPS-heading and attitude-determination algorithms for specific applications. The heading is estimated from the GPS position solutions of the two antennas by an algorithm developed specifically for this application. If a third (and preferably a fourth) antenna were added, it would be possible to estimate the attitude of the GPS receiver in three dimensions instead of only its heading in a horizontal plane.

  8. Think GPS offers high security? Think again.

    SciTech Connect

    Johnston, R. G.; Warner, J. S.

    2004-01-01

    The Global Positioning System (GPS) is being increasingly used for a variety of important applications. These include public safety services (police, fire, rescue, and ambulance), marine and aircraft navigation, vehicle theft monitoring, cargo tracking, and critical time synchronization for utility, telecommunications, banking, and computer industries. Civilian GPS signals-the only ones available to business and to most of the federal government-are high-tech, but not high-security. They were never meant for critical or security applications. Unlike the military GPS signals, civilian GPS satellite signals are unencrypted and unauthenticated. This makes it easy for even relatively unsophisticated adversaries to jam or counterfeit them. Counterfeiting ('spoofing') of civilian GPS signals is particularly troublesome because it is totally surreptitious, and (as we have demonstrated) surprisingly simple. The U.S. Department of Transportation (DOT) has warned of vulnerabilities and looming problems associated with over-reliance and over-confidence in civilian GPS. Few GPS users appear to be paying attention.

  9. NASA's GPS tracking system for Aristoteles

    NASA Astrophysics Data System (ADS)

    Davis, E. S.; Hajj, G.; Kursinski, E. R.; Kyriacou, C.; Meehan, T. K.; Melbourne, William G.; Neilan, R. E.; Young, L. E.; Yunck, Thomas P.

    1991-12-01

    NASA 's Global Positioning System (GPS) tracking system for Artistoteles receivers and a GPS flight receiver aboard Aristoteles is described. It will include a global network of GPS ground receivers and a GPS flight receiver aboard Aristoteles. The flight receiver will operate autonomously; it will provide real time navigation solutions for Aristoteles and tracking data needed by ESOC for operational control of the satellite. The GPS flight and ground receivers will currently and continuously track all visible GPS satellites. These observations will yield high accuracy differential positions and velocities of Aristoteles in a terrestrial frame defined by the locations of the globally distributed ground work. The precise orbits and tracking data will be made available to science investigators as part of the geophysical data record. The characteristics of the GPS receivers, both flight and ground based, that NASA will be using to support Aristoteles are described. The operational aspects of the overall tracking system, including the data functions and the resulting data products are summarized. The expected performance of the tracking system is compared to Aristoteles requirements and the need to control key error sources such as multipath is identified.

  10. PiVoT GPS Receiver

    NASA Technical Reports Server (NTRS)

    Wennersten, Miriam Dvorak; Banes, Anthony Vince; Boegner, Gregory J.; Dougherty, Lamar; Edwards, Bernard L.; Roman, Joseph; Bauer, Frank H. (Technical Monitor)

    2001-01-01

    NASA Goddard Space Flight Center has built an open architecture, 24 channel space flight GPS receiver. The CompactPCI PiVoT GPS receiver card is based on the Mitel/GEC Plessey Builder-2 board. PiVoT uses two Plessey 2021 correlators to allow tracking of up to 24 separate GPS SV's on unique channels. Its four front ends can support four independent antennas, making it a useful card for hosting GPS attitude determination algorithms. It has been built using space quality, radiation tolerant parts. The PiVoT card will track a weaker signal than the original Builder 2 board. It also hosts an improved clock oscillator. The PiVoT software is based on the original Plessey Builder 2 software ported to the Linux operating system. The software is POSIX complaint and can easily be converted to other POSIX operating systems. The software is open source to anyone with a licensing agreement with Plessey. Additional tasks can be added to the software to support GPS science experiments or attitude determination algorithms. The next generation PiVoT receiver will be a single radiation hardened CompactPCI card containing the microprocessor and the GPS receiver optimized for use above the GPS constellation. PiVoT was flown successfully on a balloon in July, 2001, for its first non-simulated flight.

  11. Briefing highlights space weather risks to GPS

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-07-01

    Solar storms, which are expected to increase as the Sun nears the most active phase of the solar cycle, can disrupt a variety of technologies on which society relies. Speakers at a 22 June briefing on Capitol Hill in Washington, D. C., focused on how space weather can affect the Global Positioning System (GPS), which is used in a wide range of industries, including commercial air travel, agriculture, national security, and emergency response. Rocky Stone, chief technical pilot for United Airlines, noted that GPS allows more aircraft to be in airspace, saves fuel, and helps aircraft move safely on runways. “Improvements in space weather forecasting need to be pursued,” he said. Precision GPS has also “changed the whole nature of farming,” said Ron Hatch, Director of Navigation Systems, NavCom Technology/John Deere. GPS makes it possible for tractors to be driven in the most efficient paths and for fertilizer and water to be applied precisely to the areas that most need them. Space weather-induced degradation of GPS signals can cause significant loss to farms that rely on GPS. Elizabeth Zimmerman, Deputy Associate Administrator for the Office of Response and Recovery at the Federal Emergency Management Agency (FEMA), described how FEMA relies on GPS for disaster recovery. The agency is developing an operations plan for dealing with space weather, she said.

  12. Seasonal Effects on GPS PPP Accuracy

    NASA Astrophysics Data System (ADS)

    Saracoglu, Aziz; Ugur Sanli, D.

    2016-04-01

    GPS Precise Point Positioning (PPP) is now routinely used in many geophysical applications. Static positioning and 24 h data are requested for high precision results however real life situations do not always let us collect 24 h data. Thus repeated GPS surveys of 8-10 h observation sessions are still used by some research groups. Positioning solutions from shorter data spans are subject to various systematic influences, and the positioning quality as well as the estimated velocity is degraded. Researchers pay attention to the accuracy of GPS positions and of the estimated velocities derived from short observation sessions. Recently some research groups turned their attention to the study of seasonal effects (i.e. meteorological seasons) on GPS solutions. Up to now usually regional studies have been reported. In this study, we adopt a global approach and study the various seasonal effects (including the effect of the annual signal) on GPS solutions produced from short observation sessions. We use the PPP module of the NASA/JPL's GIPSY/OASIS II software and globally distributed GPS stations' data of the International GNSS Service. Accuracy studies previously performed with 10-30 consecutive days of continuous data. Here, data from each month of a year, incorporating two years in succession, is used in the analysis. Our major conclusion is that a reformulation for the GPS positioning accuracy is necessary when taking into account the seasonal effects, and typical one term accuracy formulation is expanded to a two-term one.

  13. Stigma and GPs' perceptions of dementia.

    PubMed

    Gove, D; Downs, M; Vernooij-Dassen, M; Small, N

    2016-01-01

    General practitioners (GPs) are crucial to improving timely diagnosis, but little is reported about how they perceive dementia, and whether their perceptions display any elements of stigma. The aim of this study was to explore how GPs' perceptions of dementia map onto current conceptualizations of stigma and whether GPs feel that stigma affects timely diagnosis. Twenty-three GPs from England were interviewed by telephone. Data were analyzed by means of content analysis. This involved open coding followed by the application of a coding framework derived from the literature to explore how and to what extent their perceptions relate to stigma as well as the unique nature of their perceptions. Three themes emerged from the analysis: (1) 'making sense of dementia', (2) 'relating perceptions of dementia to oneself' and (3) 'considering the consequences of dementia'. GPs' perceptions of dementia mapped onto current conceptualizations of stigma. Perceptions about dementia that were linked to their own existential anxiety and to a perceived similarity between people with dementia and themselves were particularly salient. GPs perceived dementia as a stigma which was gradually being overcome but that stigma still hindered timely diagnosis. They provided examples of structural discrimination within the health service, including lack of time for patients and shortcomings in training that were to the detriment of people with dementia. Measures to involve GPs in tackling stigma should include training and opportunities to explore how they perceive dementia, as well as support to address structural discrimination.

  14. Operational Single-Frequency GPS Error Maps

    NASA Astrophysics Data System (ADS)

    Bishop, G. J.; Doherty, P.; Decker, D.; Delay, S.; Sexton, E.; Citrone, P.; Scro, K.; Wilkes, R.

    2001-12-01

    The Air Force Research Laboratory and Detachment 11, Space & Missile Systems Center have implemented a new system of graphical products that provide easy-to-visualize displays of space weather effects on theater-based radio systems operating through the ionosphere. This system, the Operational Space Environment Network Display (OpSEND), is now producing its first four products at 55th Space Weather Squadron (55SWXS) in Colorado Springs. One of these products, the OpSEND Estimated GPS Single-Frequency Error Map, provides a current specification (nowcast) and one-hour forecast of estimated positioning errors that result from inaccurate ionospheric correction and GPS constellation geometry. Two-frequency GPS receivers can measure ionospheric range errors due to ionospheric total electron content (TEC), but single-frequency receivers depend on a built-in Ionospheric Correction Algorithm (ICA) for ionospheric error mitigation. The ICA, developed at AFRL in the 1970's corrects for roughly half of the ionospheric error. In the OpSEND GPS Single-Frequency Error Map, position error due to the ionosphere is based on the differences between ionospheric estimates from ICA and those generated by more accurate global ionospheric specification from the PRISM model, updated by real-time TEC data from a global set of monitor stations. Details and examples of the OpSEND system and the GPS Error Map will be presented, as well as results of initial GPS Error Map validation studies, comparing GPS error predictions and PRISM TEC specifications with observational data.

  15. Synthesis and ionic liquid gating of hexagonal WO3 thin films

    NASA Astrophysics Data System (ADS)

    Wu, Phillip M.; Ishii, Satoshi; Tanabe, Kenji; Munakata, Ko; Hammond, R. H.; Tokiwa, Kazuyasu; Geballe, T. H.; Beasley, M. R.

    2015-01-01

    Via thin film deposition techniques, the meta-stable in bulk crystal hexagonal phase of tungsten oxide (hex-WO3) is stabilized as a thin film. The hex-WO3 structure is potentially promising for numerous applications and is related to the structure for superconducting compounds found in WO3. Utilizing ionic liquid gating, carriers were electrostatically induced in the films and an insulator-to-metal transition is observed. These results show that ionic liquid gating is a viable technique to alter the electrical transport properties of WO3.

  16. Photocatalysis and photoinduced hydrophilicity of WO3 thin films with underlying Pt nanoparticles.

    PubMed

    Miyauchi, Masahiro

    2008-11-07

    The photocatalytic oxidation and photoinduced hydrophilicity of thin tungsten trioxide (WO(3)) films coupled with platinum (Pt) nanoparticles were investigated. WO(3) films with underlying Pt nanoparticles (WO(3)/Pt/substrate) and those with overlying Pt nanoparticles (Pt/WO(3)/substrate) were synthesized by sputtering and sol-gel methods. Between these films, underlying Pt nanoparticles greatly enhanced the photocatalytic oxidation activity of WO(3) without decreasing the photoinduced hydrophilic conversion. However, overlying Pt nanoparticles deteriorated the hydrophilicity of WO(3) because the Pt nanoparticle surface was hydrophobic. The enhanced photocatalytic reaction by the Pt nanoparticles was attributed to the multi-electron reduction in Pt, which is caused by the injected electrons from the conduction band of WO(3). The relationship between photocatalytic activity and thin film structure, including the size of Pt nanoparticles, the thickness and porosity of the WO(3) layer, were investigated. Consequently, the optimum structure for high performance in both photocatalysis and photoinduced hydrophilicity was WO(3) (50 nm)/Pt(1.5 nm)/substrate, and this film exhibited a significant self-cleaning property even under visible light irradiation.

  17. Formation of Monodisperse (WO3)3 Clusters on Ti02(110)

    SciTech Connect

    Bondarchuk, Olexsandr; Huang, Xin; Kim, Jooho; Kay, Bruce D.; Wang, Lai S.; White, J. M.; Dohnalek, Zdenek

    2006-07-01

    Monodisperse, adsorbed cyclic trimers of WO3 have been prepared and characterized. Powdered WO3 was sublimed onto TiO2(110) at 300 K. After annealing to 600 K, scanning tunneling microscopy (STM) images indicated monodispersity, X-ray photoelectron spectroscopy indicated fully oxidized W6+, and mass microbalance, coupled with STM, indicated that each nanocluster was (WO3)3. Within the STM image of each adsorbed nanocluster, there was structure ascribed, on the basis of density functional theory, to characteristic low-lying unoccupied molecular orbitals of the cyclic isomer of (WO3)3.

  18. Ag Nanoparticle-Sensitized WO3 Hollow Nanosphere for Localized Surface Plasmon Enhanced Gas Sensors.

    PubMed

    Yao, Yao; Ji, Fangxu; Yin, Mingli; Ren, Xianpei; Ma, Qiang; Yan, Junqing; Liu, Shengzhong Frank

    2016-07-20

    Ag nanoparticle (NP)-sensitized WO3 hollow nanospheres (Ag-WO3-HNSs) are fabricated via a simple sonochemical synthesis route. It is found that the Ag-WO3-HNS shows remarkable performance in gas sensors. Field-emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) images reveal that the Agx-WO3 adopts the HNS structure in which WO3 forms the outer shell framework and the Ag NPs are grown on the inner wall of the WO3 hollow sphere. The size of the Ag NPs can be controlled by adjusting the addition amount of WCl6 during the reaction. The sensor Agx-WO3 exhibits extremely high sensitivity and selectivity toward alcohol vapor. In particular, the Ag(15nm)-WO3 sensor shows significantly lower operating temperature (230 °C), superior detection limits as low as 0.09 ppb, and faster response (7 s). Light illumination was found to boost the sensor performance effectively, especially at 405 and 900 nm, where the light wavelength resonates with the absorption of Ag NPs and the surface oxygen vacancies of WO3, respectively. The improved sensor performance is attributed to the localized surface plasmon resonance (LSPR) effect.

  19. Surface oxygen vacancies on WO3 contributed to enhanced photothermo-synergistic effect

    NASA Astrophysics Data System (ADS)

    Li, Yingying; Wang, Changhua; Zheng, Han; Wan, Fangxu; Yu, Fei; Zhang, Xintong; Liu, Yichun

    2017-01-01

    Photothermooxidation has demonstrated a high efficiency in the removal of volatile organic compounds in air. Among photothermocatalysts, attention is presently focused on composites of noble metal/metal oxide or metal oxide/metal oxide. Instead, in this work, we present a case of single oxide WO3 subjected to hydrogen treatment as photothermocatalyst. With the increase of hydrogen treatment temperature, the color of WO3 changes from yellow to blue to dark blue and a phase transition from WO3 to WO2.72 to WO2 is accompanied, suggesting an increase of concentration of oxygen vacancy. Photothermocatalytic test against degradation of gaseous acetaldehyde at 60 °C under UV light shows that WO3-x sample with low concentration of oxygen vacancy displays the most significant synergetic effect between photocatalysis and thermocatalysis. Its photothermocatalytic activity in terms of CO2 evolution rate is 5.2 times higher than that of photocatalytic activity. However, WO3-WO2.72 and WO2 with high degree of oxygen deficiency show insignificant synergetic effect between photocatalysis and thermocatalysis. The reason for the different synergistic effect over above samples is believed to lie in balance between decreased activation energy of lattice oxygen and recombination of photogenerated electrons and holes induced by oxygen deficiency.

  20. Metastable Tetragonal CdWO4 Nanoparticles Synthesized with a Solvothermal Method

    SciTech Connect

    Rondinone, Adam Justin; Travaglini, Dustin H; Pawel, Michelle D; Mahurin, Shannon Mark; Dai, Sheng

    2007-01-01

    CdWO{sub 4} has only previously been reported in the monoclinic, or wolframite, phase. Here we report the first metastable, tetragonal or scheelite, CdWO4 nanopowder. The tetragonal CdWO{sub 4} was synthesized by a propylene glycol solvothermal method. The scheelite phase is stabilized by a combination of high surface area and surface complexation by the propylene glycol. The CdWO{sub 4} is stable at 1 bar to 300 C, and converts back to the monoclinic wolframite phase between 300 and 500 C. The nanopowder exhibits cubic morphology and the average particle size of the nanopowder is around 50 nm.

  1. Light-controlled resistive switching of ZnWO{sub 4} nanowires array

    SciTech Connect

    Zhao, W. X.; Sun, B.; Liu, Y. H.; Wei, L. J.; Li, H. W.; Chen, P.

    2014-07-15

    ZnWO{sub 4} nanowires array was prepared on the titanium substrate by a facile hydrothermal synthesis, in which the average length of ZnWO{sub 4} nanowires is about 2um and the diameter of individual ZnWO{sub 4} nanowire ranges from 50 to 70 nm. The bipolar resistive switching effect of ZnWO{sub 4} nanowires array was observed. Moreover, the performance of the resistive switching device is greatly improved under white light irradiation compared with that in the dark.

  2. Synthesis and ionic liquid gating of hexagonal WO{sub 3} thin films

    SciTech Connect

    Wu, Phillip M. E-mail: beasley@stanford.edu; Munakata, Ko; Hammond, R. H.; Geballe, T. H.; Beasley, M. R. E-mail: beasley@stanford.edu; Ishii, Satoshi; Tanabe, Kenji; Tokiwa, Kazuyasu

    2015-01-26

    Via thin film deposition techniques, the meta-stable in bulk crystal hexagonal phase of tungsten oxide (hex-WO{sub 3}) is stabilized as a thin film. The hex-WO{sub 3} structure is potentially promising for numerous applications and is related to the structure for superconducting compounds found in WO{sub 3}. Utilizing ionic liquid gating, carriers were electrostatically induced in the films and an insulator-to-metal transition is observed. These results show that ionic liquid gating is a viable technique to alter the electrical transport properties of WO{sub 3}.

  3. Eukaryotic association module in phage WO genomes from Wolbachia

    PubMed Central

    Bordenstein, Sarah R.; Bordenstein, Seth R.

    2016-01-01

    Viruses are trifurcated into eukaryotic, archaeal and bacterial categories. This domain-specific ecology underscores why eukaryotic viruses typically co-opt eukaryotic genes and bacteriophages commonly harbour bacterial genes. However, the presence of bacteriophages in obligate intracellular bacteria of eukaryotes may promote DNA transfers between eukaryotes and bacteriophages. Here we report a metagenomic analysis of purified bacteriophage WO particles of Wolbachia and uncover a eukaryotic association module in the complete WO genome. It harbours predicted domains, such as the black widow latrotoxin C-terminal domain, that are uninterrupted in bacteriophage genomes, enriched with eukaryotic protease cleavage sites and combined with additional domains to forge one of the largest bacteriophage genes to date (14,256 bp). To the best of our knowledge, these eukaryotic-like domains have never before been reported in packaged bacteriophages and their phylogeny, distribution and sequence diversity imply lateral transfers between bacteriophage/prophage and animal genomes. Finally, the WO genome sequences and identification of attachment sites will potentially advance genetic manipulation of Wolbachia. PMID:27727237

  4. Eukaryotic association module in phage WO genomes from Wolbachia.

    PubMed

    Bordenstein, Sarah R; Bordenstein, Seth R

    2016-10-11

    Viruses are trifurcated into eukaryotic, archaeal and bacterial categories. This domain-specific ecology underscores why eukaryotic viruses typically co-opt eukaryotic genes and bacteriophages commonly harbour bacterial genes. However, the presence of bacteriophages in obligate intracellular bacteria of eukaryotes may promote DNA transfers between eukaryotes and bacteriophages. Here we report a metagenomic analysis of purified bacteriophage WO particles of Wolbachia and uncover a eukaryotic association module in the complete WO genome. It harbours predicted domains, such as the black widow latrotoxin C-terminal domain, that are uninterrupted in bacteriophage genomes, enriched with eukaryotic protease cleavage sites and combined with additional domains to forge one of the largest bacteriophage genes to date (14,256 bp). To the best of our knowledge, these eukaryotic-like domains have never before been reported in packaged bacteriophages and their phylogeny, distribution and sequence diversity imply lateral transfers between bacteriophage/prophage and animal genomes. Finally, the WO genome sequences and identification of attachment sites will potentially advance genetic manipulation of Wolbachia.

  5. First-principles reinvestigation of bulk WO3

    NASA Astrophysics Data System (ADS)

    Hamdi, Hanen; Salje, Ekhard K. H.; Ghosez, Philippe; Bousquet, Eric

    2016-12-01

    Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO3. Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which provides very good agreement with experimental data. We show that the hypothetical high-symmetry cubic reference structure combines several ferroelectric and antiferrodistortive (antipolar cation motions, rotations, and tilts of oxygen octahedra) structural instabilities. Although the ferroelectric instability is the largest, the instability related to antipolar W motions combines with those associated to oxygen rotations and tilts to produce the biggest energy reduction, yielding a P 21/c ground state. This nonpolar P 21/c phase is only different from the experimentally reported P c ground state by the absence of a very tiny additional ferroelectric distortion. The calculations performed on a stoichiometric compound so suggest that the low-temperature phase of WO3 is not intrinsically ferroelectric and that the experimentally observed ferroelectric character might arise from extrinsic defects such as oxygen vacancies. Independently, we also identify never observed R 3 m and R 3 c ferroelectric metastable phases with large polarizations and low energies close to the P 21/c ground state, which makes WO3 a potential antiferroelectric material. The relative stability of various phases is discussed in terms of the anharmonic couplings between different structural distortions, highlighting a very complex interplay.

  6. Electrochromism in sputtered WO{sub 3} thin films

    SciTech Connect

    Batchelor, R.A.; Burdis, M.S.; Siddle, J.R.

    1996-03-01

    There are large variations in the properties of WO{sub 3} sputtered under different conditions and two samples sputtered from an oxide target and reactively sputtered from a metal target were compared in detail. The thin film sputtered from an oxide target was found to color and bleach rapidly in 1 M LiClO{sub 4} in propylene carbonate, while the thin film reactively sputtered from a metal target could be colored deeply, but bleached only slowly. By calculating the rate of change of optical density during cyclic voltammetry, it was possible to directly compare the coloration response with the current/voltage behavior of the electrodes. In both cases at least two lithium insertion reactions appear to occur. The distinction between the two reactions was especially clear in the sample sputtered from a metal target, in which an insertion of high electrochromic efficiency occurred up to Li{sub 0.2}WO{sub 3} and then an insertion of considerably lower electrochromic efficiency up to Li{sub 0.5}WO{sub 3}. Although a small amount of coloration and bleaching continued to occur after switching the reactively sputtered sample to open circuit during the coloration and bleaching cycles; transmission change was largely halted by disconnecting the external current supply. The slow end to the bleach of the reactively sputtered sample corresponded to a reaction of high electrochromic efficiency.

  7. Disciplined rubidium oscillator with GPS selective availability

    NASA Technical Reports Server (NTRS)

    Dewey, Wayne P.

    1993-01-01

    A U.S. Department of Defense decision for continuous implementation of GPS Selective Availability (S/A) has made it necessary to modify Rubidium oscillator disciplining methods. One such method for reducing the effects of S/A on the oscillator disciplining process was developed which achieves results approaching pre-S/A GPS. The Satellite Hopping algorithm used in minimizing the effects of S/A on the oscillator disciplining process is described, and the results of using this process to those obtained prior to the implementation of S/A are compared. Test results are from a TrueTime Rubidium based Model GPS-DC timing receiver.

  8. Disciplined rubidium oscillator with GPS selective availability

    NASA Technical Reports Server (NTRS)

    Dewey, Wayne P.

    1993-01-01

    A U.S. Department of Defense decision for continuous implementation of GPS Selective Availability (S/A) has made it necessary to modify Rubidium oscillator disciplining methods. One such method for reducing the effects of S/A on the oscillator disciplining process was developed which achieves results approaching pre-S/A GPS. The Satellite Hopping algorithm used in minimizing the effects of S/A on the oscillator disciplining process is described, and the results of using this process to those obtained prior to the implementation of S/A are compared. Test results are from a TrueTime Rubidium based Model GPS-DC timing receiver.

  9. The Promise of GPS in Atmospheric Monitoring.

    NASA Astrophysics Data System (ADS)

    Businger, Steven; Chiswell, Steven R.; Bevis, Michael; Duan, Jingping; Anthes, Richard A.; Rocken, Christian; Ware, Randolph H.; Exner, Michael; Vanhove, T.; Solheim, Fredrick S.

    1996-01-01

    This paper provides an overview of applications of the Global Positioning System (GPS) for active measurement of the Earth's atmosphere. Microwave radio signals transmitted by GPS satellites are delayed (refracted) by the atmosphere as they propagate to Earth-based GPS receivers or GPS receivers carried on low Earth orbit satellites.The delay in GPS signals reaching Earth-based receivers due to the presence of water vapor is nearly proportional to the quantity of water vapor integrated along the signal path. Measurement of atmospheric water vapor by Earth-based GPS receivers was demonstrated during the GPS/STORM field project to be comparable and in some respects superior to measurements by ground-based water vapor radiometers. Increased spatial and temporal resolution of the water vapor distribution provided by the GPS/STORM network proved useful in monitoring the moisture-flux convergence along a dryline and the decrease in integrated water vapor associated with the passage of a midtropospheric cold front, both of which triggered severe weather over the area during the course of the experiment.Given the rapid growth in regional networks of continuously operating Earth-based GPS receivers currently being implemented, an opportunity exists to observe the distribution of water vapor with increased spatial and temporal coverage, which could prove valuable in a range of operational and research applications in the atmospheric sciences.The first space-based GPS receiver designed for sensing the Earth's atmosphere was launched in April 1995. Phase measurements of GPS signals as they are occluded by the atmosphere provide refractivity profiles (see the companion article by Ware et al. on page 19 of this issue). Water vapor limits the accuracy of temperature recovery below the tropopause because of uncertainty in the water vapor distribution. The sensitivity of atmospheric refractivity to water vapor pressure, however, means that refractivity profiles can in principle

  10. Space Station GPS Multipath Analysis and Validation

    NASA Technical Reports Server (NTRS)

    Hwu, Shian U.; Loh, Y. C.

    1999-01-01

    To investigate the multipath effects on the International Space Station (ISS) Global Positioning System (GPS) measurement accuracy, experimental and computational investigations were performed to estimate the carrier phase errors due to multipath. A new modeling approach is used to reduce the required computing time by separating the dynamic structure elements from the static structure elements in the multipath computations. This study confirmed that the multipath is a major error source to the ISS GPS performance and can possibly degrade the attitude determination solution. It is demonstrated that the GPS antenna carrier phase errors due to multipath can be analyzed using the electromagnetic modeling technique such as the Uniform Geometrical Theory of Diffraction (UTD).

  11. Improvement of radiopurity level of enriched 116CdWO4 and ZnWO4 crystal scintillators by recrystallization

    NASA Astrophysics Data System (ADS)

    Barabash, A. S.; Belli, P.; Bernabei, R.; Borovlev, Yu. A.; Cappella, F.; Caracciolo, V.; Cerulli, R.; Danevich, F. A.; Incicchitti, A.; Kobychev, V. V.; Konovalov, S. I.; Laubenstein, M.; Mokina, V. M.; Polischuk, O. G.; Safonova, O. E.; Shlegel, V. N.; Tretyak, V. I.; Tupitsyna, I. A.; Umatov, V. I.; Zhdankov, V. N.

    2016-10-01

    As low as possible radioactive contamination of a detector plays a crucial role to improve sensitivity of a double beta decay experiment. The radioactive contamination of a sample of 116CdWO4 crystal scintillator by thorium was reduced by a factor ≈10, down to the level 0.01 mBq/kg (228Th), by exploiting the recrystallization procedure. The total alpha activity of uranium and thorium daughters was reduced by a factor ≈3, down to 1.6 mBq/kg. No change in the specific activity (the total α activity and 228Th) was observed in a sample of ZnWO4 crystal produced by recrystallization after removing ≈0.4 mm surface layer of the crystal.

  12. Photocatalytic properties of h-WO{sub 3} nanoparticles obtained by annealing and h-WO{sub 3} nanorods prepared by hydrothermal method

    SciTech Connect

    Boyadjiev, Stefan I.; Nagy-Kovács, Teodóra; Lukács, István; Szilágyi, Imre M.

    2016-03-25

    In the present study, two different methods for preparing hexagonal WO{sub 3} (h-WO{sub 3}) photocatalysts were used - controlled thermal decomposition and hydrothermal synthesis. WO{sub 3} nanoparticles with hexagonal structure were obtained by annealing (NH{sub 4}){sub x}WO{sub 3-y} at 500 °C in air. WO{sub 3} nanorods were prepared by a hydrothermal method using sodium tungstate Na{sub 2}WO{sub 4}, HCl, (COOH){sub 2} and NaSO{sub 4} precursors at 200 °C. The formation, morphology, structure and composition of the as-prepared nanoparticles and nanorods were studied by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX). The photocatalytic activity of the h-WO{sub 3} nanoparticles and nanorods was studied by decomposing methyl orange in aqueous solution under UV light irradiation.

  13. Navstar Global Positioning System (GPS) clock program: Present and future

    NASA Technical Reports Server (NTRS)

    Tennant, D. M.

    1981-01-01

    Global Positioning System (GPS) program status are discussed and plans for ensuring the long term continuation of the program are presented. Performance of GPS clocks is presented in terms of on orbit data as portrayed by GPS master control station kalman filter processing. The GPS Clock reliability program is reviewed in depth and future plans fo the overall clock program are published.

  14. Soil Moisture Sensing Using Reflected GPS Signals: Description of the GPS Soil Moisture Product.

    NASA Astrophysics Data System (ADS)

    Larson, Kristine; Small, Eric; Chew, Clara

    2015-04-01

    As first demonstrated by the GPS reflections group in 2008, data from GPS networks can be used to monitor multiple parameters of the terrestrial water cycle. The GPS L-band signals take two paths: (1) the "direct" signal travels from the satellite to the antenna, which is typically located 2-3 meters above the ground; (2) the reflected signal interacts with the Earth's surface before traveling to the antenna. The direct signal is used by geophysicists and surveyors to measure the position of the antenna, while the effects of reflected signals are a source of error. If one focuses on the reflected signal rather than the positioning observables, one has a method that is sensitive to surface soil moisture (top 5 cm), vegetation water content, and snow depth. This method - known as GPS Interferometric Reflectometry (GPS-IR) - has a footprint of ~1000 m2 for most GPS sites. This is intermediate in scale to most in situ and satellite observations. A significant advantage of GPS-IR is that data from existing GPS networks can be used without any changes to the instrumentation. This means that there is a new source of cost-effective instrumentation for satellite validation and climate studies. This presentation will provide an overview of the GPS-IR methodology with an emphasis on the soil moisture product. GPS water cycle products are currently produced on a daily basis for a network of ~500 sites in the western United States; results are freely available at http://xenon.colorado.edu/portal. Plans to expand the GPS-IR method to the network of international GPS sites will also be discussed.

  15. Temperature and acidity effects on WO{sub 3} nanostructures and gas-sensing properties of WO{sub 3} nanoplates

    SciTech Connect

    Zhang, Huili; Liu, Zhifang; Yang, Jiaqin; Guo, Wei; Zhu, Lianjie; Zheng, Wenjun

    2014-09-15

    Graphical abstract: Generally, large acid quantity and high temperature are beneficial to the formation of anhydrous WO3, but the acidity effect on the crystal phase is weaker than that of temperature. Large acid quantity is found helpful to the oriented growth of tungsten oxides, forming a nanoplate-like product. - Highlights: • Large acid quantity is propitious to the oriented growth of a WO{sub 3} nanoplate. • Effect of acid quantity on crystal phases of products is weaker than that of temperature. • One step hydrothermal synthesis of WO{sub 3} is facile and can be easily scaled up. • A WO{sub 3} nanoplate shows a fast response and distinct sensing selectivity to acetone gas. - Abstract: WO{sub 3} nanostructures were successfully synthesized by a facile hydrothermal method using Na{sub 2}WO{sub 4}·2H{sub 2}O and HNO{sub 3} as raw materials. They are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The specific surface area was obtained from N{sub 2} adsorption–desorption isotherm. The effects of the amount of HNO{sub 3}, hydrothermal temperature and reaction time on the crystal phases and morphologies of the WO{sub 3} nanostructures were investigated in detail, and the reaction mechanism was discussed. Large amount of acid is found for the first time to be helpful to the oriented growth of tungsten oxides, forming nanoplate-like products, while hydrothermal temperature has more influence on the crystal phase of the product. Gas-sensing properties of the series of as-prepared WO{sub 3} nanoplates were tested by means of acetone, ethanol, formaldehyde and ammonia. One of the WO{sub 3} nanoplates with high specific surface area and high crystallinity displays high sensitivity, fast response and distinct sensing selectivity to acetone gas.

  16. Shuttle Global Positioning System (GPS) system design study

    NASA Technical Reports Server (NTRS)

    Nilsen, P. W.

    1979-01-01

    The various integration problems in the Shuttle GPS system were investigated. The analysis of the Shuttle GPS link was studied. A preamplifier was designed since the Shuttle GPS antennas must be located remotely from the receiver. Several GPS receiver architecture trade-offs were discussed. The Shuttle RF harmonics and intermode that fall within the GPS receiver bandwidth were analyzed. The GPS PN code acquisition was examined. Since the receiver clock strongly affects both GPS carrier and code acquisition performance, a clock model was developed.

  17. Qualification of TAOS satellite GPS receiver

    NASA Astrophysics Data System (ADS)

    Weninger, Roger M.; Sfeir, Richard; Forgette, Tom T.; Kelton, Phil T.; Najarian, Richard J.

    1992-03-01

    A light-weight, compact GPS receiver developed for a Technology for Autonomous Operational Survivability (TAOS) satellite planned for launch in 1993 is described. The receiver is capable of continuously tracking four primary GPS satellites and sequentially acquiring and tracking other visible satellites with its six channels. Using an eight-state extended Kalman filter it performs pseudo-range and continuous-carrier, delta-range measurements and estimates time-tagged, 3D user position and velocity. Results of qualification testing obtained from a multichannel GPS spaceborne simulation and evaluation system show that with a GPS constellation of 18 satellites and over a period where GDOP is less than 6, the receiver's rms spherical position and per axis velocity errors are less than 14.5 meters and 0.05 m/sec, respectively.

  18. ScienceCast 218: Twinkle Twinkle GPS

    NASA Image and Video Library

    2016-06-14

    Dynamic bubbles of ionization in Earth's upper atmosphere can cause GPS signals to "twinkle" like stars, affecting the quality of navigation on Earth below. NASA recently conducted a mission called CINDI to investigate this phenomenon.

  19. CASA Central and South America GPS geodesy

    NASA Astrophysics Data System (ADS)

    Kellogg, James; Dixon, Timothy; Neilan, Ruth

    In January 1988, scientists from over 25 organizations in 13 countries and territories cooperated in the largest Global Positioning System (GPS) campaign in the world to date (Table 1) [Neilan et al., 1988]. From January 18 to February 5, 1988, 43 GPS receivers collected about 590 station-days of data in American Samoa, Australia, Canada, Colombia, Costa Rica, Ecuador, New Zealand, Norway, Panama, Sweden, United States, West Germany, and Venezuela. The experiment was entitled CASA UNO, an acronym for Central and South America—and “uno” is Spanish for “one,” designating first-epoch measurements. The CASA UNO experiment was the first civilian effort at implementing an extended GPS satellite-tracking network and established the first major GPS network in the northern Andean margin and the western Caribbean.

  20. Using Evolutionary Computation on GPS Position Correction

    PubMed Central

    2014-01-01

    More and more devices are equipped with global positioning system (GPS). However, those handheld devices with consumer-grade GPS receivers usually have low accuracy in positioning. A position correction algorithm is therefore useful in this case. In this paper, we proposed an evolutionary computation based technique to generate a correction function by two GPS receivers and a known reference location. Locating one GPS receiver on the known location and combining its longitude and latitude information and exact poisoning information, the proposed technique is capable of evolving a correction function by such. The proposed technique can be implemented and executed on handheld devices without hardware reconfiguration. Experiments are conducted to demonstrate performance of the proposed technique. Positioning error could be significantly reduced from the order of 10 m to the order of 1 m. PMID:24578657

  1. Absolute Time Error Calibration of GPS Receivers Using Advanced GPS Simulators

    DTIC Science & Technology

    1997-12-01

    29th Annual Precise Time a d Time Interval (PTTI) Meeting ABSOLUTE TIME ERROR CALIBRATION OF GPS RECEIVERS USING ADVANCED GPS SIMULATORS E.D...DC 20375 USA Abstract Preche time transfer eq)er&nen& using GPS with t h e stabd?v’s under ten nanoseconh are common& being reported willrbr the... time transfer communily. Relarive calibrations are done by naeasurhg the time error of one GPS receiver versus a “known master refmence receiver.” Z?t

  2. Permanent GPS Geodetic Array in Southern California

    NASA Technical Reports Server (NTRS)

    Green, Cecil H.; Green, Ida M.

    1998-01-01

    The southern California Permanent GPS Geodetic Array (PGGA) was established in the spring of 1990 to evaluate continuous Global Positioning System (GPS) measurements as a new too] for monitoring crustal deformation. Southern California is an ideal location because of the relatively high rate of tectonic deformation, the high probability of intense seismicity, the long history of conventional and space geodetic measurements, and the availability of a well developed infrastructure to support continuous operations. Within several months of the start of regular operations, the PGGA recorded far-field coseismic displacements induced by the June 28, 1992 (M(sub w)=7.3), Landers earthquake, the largest magnitude earthquake in California in the past 40 years and the first one to be recorded by a continuous GPS array. Only nineteen months later, on 17 January 1994, the PGGA recorded coseismic displacements for the strongest earthquake to strike the Los Angeles basin in two decades, the (M(sub e)=6.7) Northridge earthquake. At the time of the Landers earthquake, only seven continuous GPS sites were operating in southern California; by the beginning of 1994, three more sites had been added to the array. However, only a pair of sites were situated in the Los Angeles basin. The destruction caused by the Northridge earthquake spurred a fourfold increase in the number of continuous GPS sites in southern California within 2 years of this event. The PGGA is now the regional component of the Southern California Integrated GPS Network (SCIGN), a major ongoing densification of continuous GPS sites, with a concentration in the Los Angeles metropolitan region. Continuous GPS provides temporally dense measurements of surface displacements induced by crustal deformation processes including interseismic, coseismic, postseismic, and aseismic deformation and the potential for detecting anomalous events such as preseismic deformation and interseismic strain variations. Although strain meters

  3. Comparison of three retrievals of COSMIC GPS radio occultation results in the tropical upper troposphere and lower stratosphere

    NASA Astrophysics Data System (ADS)

    Noersomadi; Tsuda, Toshitaka

    2017-09-01

    Combining geometrical optics (GO) and wave optics (WO), the COSMIC data analysis and archive center (CDAAC) retrieved two sets of dry atmosphere temperatures ( T) from COSMIC GPS radio occultation (GPS-RO), which are called atmPrf2010 and atmPrf2013. In atmPrf2010, the sewing height between WO and GO varies between 10 and 20 km, but is fixed at 20 km for atmPrf2013. The height resolution of the atmPrf2010 depends on the sewing height, while the T profiles by atmPrf2013 are smoothed over 500 m. We also derived T by applying WO throughout the troposphere and the stratosphere up to a 30-km altitude, which is called rishfsi2013. The three retrievals have different characteristics in the height resolution around the tropopause. Therefore, we aim to examine a possible discrepancy in the statistical results of the cold-point tropopause (CPT) and the lapse rate tropopause (LRT) among the three datasets, conducting their inter-comparisons as well as the comparison between GPS-RO and the simultaneous radiosonde dataset. We investigate the T variations in the upper troposphere and lower stratosphere (UTLS) over the tropics from October 1, 2011, to March 31, 2012, when radiosonde soundings were conducted as the CINDY-DYNAMO 2011 campaign. The mean T profiles are consistent between atmPrf2010 and atmPrf2013, but rishfsi2013 results are colder (warmer) than the CDAAC retrievals below (above) the tropopause. The mean T difference between atmPrf2013 and atmPrf2010 is 0.17 K at the cold-point tropopause (CPT) and -0.38 K at the lapse rate tropopause (LRT). On the other hand, rishfsi2013 shows a colder T at CPT by -0.77 and -0.59 K relative to atmPrf2013 and atmPrf2010, respectively, and the warmer T by 0.60 and 0.20 Kd at LRT. During CINDY-DYNAMO, we found 134 radiosonde soundings that coincide with GPS-RO within ±3 h and are collocated within 200 km from GPS-RO. The mean T difference at CPT from the radiosondes is 0.32, 0.49 and -0.24 K for atmPrf2010, atmPrf2013 and rishfsi2013

  4. Annealing dynamics of WO{sub 3} by in situ XRD

    SciTech Connect

    Righettoni, Marco; Pratsinis, Sotiris E.

    2014-11-15

    Highlights: • Flame-made WO{sub 3} nanoparticles with closely controlled crystal and grain size. • Dynamic phase transition of annealing of pure and Si-doped WO{sub 3} by in situ XRD. • Irreversible evolution of WO{sub 3} crystallinity by heating/cooling during its annealing. • Si-doping alters the WO{sub 3} crystallinity dynamics and stabilizes nanosized WO{sub 3}. • Flame-made nano-WO{sub 3} can sense NO at the ppb level. - Abstract: Tungsten trioxide is a semiconductor with distinct applications in gas sensors, catalysis, batteries and pigments. As such the transition between its different crystal structures during its annealing are of interest, especially for sensor applications. Here, WO{sub 3} nanoparticles with closely controlled crystal and grain size (9–15 nm) and phase composition are made by flame spray pyrolysis and the formation of different WO{sub 3} phases during annealing is investigated. Most notably, the dynamic phase transition and crystal size evolution of WO{sub 3} during heating and cooling is monitored by in situ X-ray diffraction revealing how metastable WO{sub 3} phases can be captured stably. The effect of Si-doping is studied since it is used in practise to control crystal growth and phase transition during metal oxide synthesis and processing. Finally the influence of annealing on the WO{sub 3} sensing performance of NO, a lung inflammation tracer in the human breath, is explored at the ppb-level.

  5. GPs have central role in managing IBD.

    PubMed

    Orchard, Tim

    2008-10-01

    Ulcerative colitis and Crohn's disease are extremely variable in their presentation and course, and treatment can be difficult. It is important that GPs have a high index of suspicion of IBD and initiate appropriate treatment for patients undergoing relapse of the disease. GPs also have a vital role in the monitoring of patients, often in collaboration with gastroenterologists, particularly for those patients on immunosuppressant therapy.

  6. Scintillation Effects on Space Shuttle GPS Data

    NASA Technical Reports Server (NTRS)

    Goodman, John L.; Kramer, Leonard

    2001-01-01

    Irregularities in ionospheric electron density result in variation in amplitude and phase of Global Positioning System (GPS) signals, or scintillation. GPS receivers tracking scintillated signals may lose carrier phase or frequency lock in the case of phase sc intillation. Amplitude scintillation can cause "enhancement" or "fading" of GPS signals and result in loss of lock. Scintillation can occur over the equatorial and polar regions and is a function of location, time of day, season, and solar and geomagnetic activity. Mid latitude regions are affected only very rarely, resulting from highly disturbed auroral events. In the spring of 1998, due to increasing concern about scintillation of GPS signals during the upcoming solar maximum, the Space Shuttle Program began to assess the impact of scintillation on Collins Miniaturized Airborne GPS Receiver (MAGR) units that are to replace Tactical Air Control and Navigation (TACAN) units on the Space Shuttle orbiters. The Shuttle Program must determine if scintillation effects pose a threat to safety of flight and mission success or require procedural and flight rule changes. Flight controllers in Mission Control must understand scintillation effects on GPS to properly diagnose "off nominal" GPS receiver performance. GPS data from recent Space Shuttle missions indicate that the signals tracked by the Shuttle MAGR manifest scintillation. Scintillation is observed as anomalous noise in velocity measurements lasting for up to 20 minutes on Shuttle orbit passes and are not accounted for in the error budget of the MAGR accuracy parameters. These events are typically coincident with latitude and local time occurrence of previously identified equatorial spread F within about 20 degrees of the magnetic equator. The geographic and seasonal history of these events from ground-based observations and a simple theoretical model, which have potential for predicting events for operational purposes, are reviewed.

  7. Assisting with GPS in geoscience research

    NASA Astrophysics Data System (ADS)

    Ware, Randolph

    The University Navstar Consortium (UNAVCO) helps university researchers use Global Positioning System (GPS) technology in Earth sciences applications. Providing GPS equipment and technical support assists scientists in the study of plate tectonics, earthquakes, crustal motion, volcanos, sea level, ocean currents, ice dynamics, and atmospheric sensing.More than fifty universities and research institutions participate as members of UNAVCO, a national program governed by universities and funded by the National Science Foundation.

  8. Offset detection in GPS coordinate time series

    NASA Astrophysics Data System (ADS)

    Gazeaux, J.; King, M. A.; Williams, S. D.

    2013-12-01

    Global Positioning System (GPS) time series are commonly affected by offsets of unknown magnitude and the large volume of data globally warrants investigation of automated detection approaches. The Detection of Offsets in GPS Experiment (DOGEx) showed that accuracy of Global Positioning System (GPS) time series can be significantly improved by applying statistical offset detection methods (see Gazeaux et al. (2013)). However, the best of these approaches did not perform as well as manual detection by expert analysts. Many of the features of GPS coordinates time series have not yet been fully taken into account in existing methods. Here, we apply Bayesian theory in order to make use of prior knowledge of the site noise characteristics and metadata in an attempt to make the offset detection more accurate. In the past decades, Bayesian theory has shown relevant results for a widespread range of applications, but has not yet been applied to GPS coordinates time series. Such methods incorporate different inputs such as a dynamic model (linear trend, periodic signal..) and a-priori information in a process that provides the best estimate of parameters (velocity, phase and amplitude of periodic signals...) based on all the available information. We test the new method on the DOGEx simulated dataset and compare it to previous solutions, and to Monte-Carlo method to test the accuracy of the procedure. We make a preliminary extension of the DOGEx dataset to introduce metadata information, allowing us to test the value of this data type in detecting offsets. The flexibility, robustness and limitations of the new approach are discussed. Gazeaux, J. Williams, S., King, M., Bos, M., Dach, R., Deo, M.,Moore, A.W., Ostini, L., Petrie, E., Roggero, M., Teferle, F.N., Olivares, G.,Webb, F.H. 2013. Detecting offsets in GPS time series: First results from the detection of offsets in GPS experiment. Journal of Geophysical Research: Solid Earth 118. 5. pp:2169-9356. Keywords : GPS

  9. GPS antenna multipath rejection performance

    NASA Astrophysics Data System (ADS)

    Dinius, A. M.

    1995-08-01

    A GPS antenna multipath rejection performance evaluation was conducted. Ground reference station antennas and aviation patches were tested for their ability to reject a multipath signal. Different types of ground plane structures were used such as choke rings, ground planes, and mock sections of fuselage. Frequencies transmitted were L1 (1575 MHz), L2 (1227 MHz), and the median GLONASS frequency (1609 MHz). Receive amplitude and phase were measured on each antenna. Subsequently, these data were converted to absolute gain for a right hand and left hand circularly polarized signal as a function of satellite elevation angle. Two types of multipath signals were considered: ground bounce multipath and building or structure bounce multipath. Ground bounce multipath typically occurs at low satellite elevation angles while structure bounce multipath can occur at any satellite elevation angle. Separate analysis methods were used to assess an antenna's ability to reject either type of multipath. This report describes the data collection methods, data reduction and analysis, and the results.

  10. Front end for GPS receivers

    NASA Technical Reports Server (NTRS)

    Thomas, Jr., Jess Brooks (Inventor)

    1999-01-01

    The front end in GPS receivers has the functions of amplifying, down-converting, filtering and sampling the received signals. In the preferred embodiment, only two operations, A/D conversion and a sum, bring the signal from RF to filtered quadrature baseband samples. After amplification and filtering at RF, the L1 and L2 signals are each sampled at RF at a high selected subharmonic rate. The subharmonic sample rates are approximately 900 MHz for L1 and 982 MHz for L2. With the selected subharmonic sampling, the A/D conversion effectively down-converts the signal from RF to quadrature components at baseband. The resulting sample streams for L1 and L2 are each reduced to a lower rate with a digital filter, which becomes a straight sum in the simplest embodiment. The frequency subsystem can be very simple, only requiring the generation of a single reference frequency (e.g. 20.46 MHz minus a small offset) and the simple multiplication of this reference up to the subharmonic sample rates for L1 and L2. The small offset in the reference frequency serves the dual purpose of providing an advantageous offset in the down-converted carrier frequency and in the final baseband sample rate.

  11. Benefits of Software GPS Receivers for Enhanced Signal Processing

    DTIC Science & Technology

    2000-01-01

    1 Published in GPS SOLUTIONS 4(1) Summer, 2000, pages 56-66. Benefits of Software GPS Receivers for Enhanced Signal Processing Alison Brown...Diego, CA 92110-3127 Number of Pages: 24 Number of Figures: 20 ABSTRACT In this paper the architecture of a software GPS receiver is described...and an analysis is included of the performance of a software GPS receiver when tracking the GPS signals in challenging environments. Results are

  12. GPS as an orbit determination subsystems

    NASA Technical Reports Server (NTRS)

    Fennessey, Richard; Roberts, Pat; Knight, Robin; Vanvolkinburg, Bart

    1995-01-01

    This paper evaluates the use of Global Positioning System (GPS) receivers as a primary source of tracking data for low-Earth orbit satellites. GPS data is an alternative to using range, azimuth, elevation, and range-rate (RAER) data from the Air Force Satellite Control Network antennas, the Space Ground Link System (SGLS). This evaluation is applicable to missions such as Skipper, a joint U.S. and Russian atmosphere research mission, that will rely on a GPS receiver as a primary tracking data source. The Detachment 2, Space and Missile Systems Center's Test Support Complex (TSC) conducted the evaluation based on receiver data from the Space Test Experiment Platform Mission O (STEP-O) and Advanced Photovoltaic and Electronics Experiments (APEX) satellites. The TSC performed orbit reconstruction and prediction on the STEP-0 and APEX vehicles using GPS receiver navigation solution data, SGLS RAER data, and SGLS anglesonly (azimuth and elevation) data. For the STEP-O case, the navigation solution based orbits proved to be more accurate than SGLS RAER based orbits. For the APEX case, navigation solution based orbits proved to be less accurate than SGLS RAER based orbits for orbit prediction, and results for orbit reconstruction were inconclusive due to the lack of a precise truth orbit. After evaluating several different GPS data processing methods, the TSC concluded that using GPS navigation solution data is a viable alternative to using SGLS RAER data.

  13. Jammers in the commercial world of GPS

    SciTech Connect

    Wollschlager, B.

    1994-12-31

    The military world of electronic countermeasures is an enviromnent where receivers are designed to perform in a high level of interference or jamming. The electronic battlefield is full of radio frequency interference, both intentional and unintentional, which disrupts communications, fools radar, overloads guidance systems, and in general causes havoc with sensitive electronic systems such as GPS receivers. The commercial radio world is also becoming more electronically hazardous. The FCC has adopted certain emission standards which attempt to control how much ``noise`` electronic devices give off; however, these standards are much less stringent than their military counterparts. For GPS signals with typical power levels of {minus}125 dBm the interfering signals can pose a large in-band or near-band problem. Because the spread spectrum signal exists below thermal noise, any in-band noise also poses a large challenge to GPS reception. Harmonics from a cellular phone, a UHF radio, or a personal computer can cause a GPS receiver to be unable to navigate. Recognition of this problem is causing filter performance profiles such as ARINC 743A and others to become popular for GPS receiver interference rejection. This paper is based on Rockwell`s experience on Navstar GPS programs such as PLGR.

  14. Combined GPS/GLONASS precise point positioning with fixed GPS ambiguities.

    PubMed

    Pan, Lin; Cai, Changsheng; Santerre, Rock; Zhu, Jianjun

    2014-09-18

    Precise point positioning (PPP) technology is mostly implemented with an ambiguity-float solution. Its performance may be further improved by performing ambiguity-fixed resolution. Currently, the PPP integer ambiguity resolutions (IARs) are mainly based on GPS-only measurements. The integration of GPS and GLONASS can speed up the convergence and increase the accuracy of float ambiguity estimates, which contributes to enhancing the success rate and reliability of fixing ambiguities. This paper presents an approach of combined GPS/GLONASS PPP with fixed GPS ambiguities (GGPPP-FGA) in which GPS ambiguities are fixed into integers, while all GLONASS ambiguities are kept as float values. An improved minimum constellation method (MCM) is proposed to enhance the efficiency of GPS ambiguity fixing. Datasets from 20 globally distributed stations on two consecutive days are employed to investigate the performance of the GGPPP-FGA, including the positioning accuracy, convergence time and the time to first fix (TTFF). All datasets are processed for a time span of three hours in three scenarios, i.e., the GPS ambiguity-float solution, the GPS ambiguity-fixed resolution and the GGPPP-FGA resolution. The results indicate that the performance of the GPS ambiguity-fixed resolutions is significantly better than that of the GPS ambiguity-float solutions. In addition, the GGPPP-FGA improves the positioning accuracy by 38%, 25% and 44% and reduces the convergence time by 36%, 36% and 29% in the east, north and up coordinate components over the GPS-only ambiguity-fixed resolutions, respectively. Moreover, the TTFF is reduced by 27% after adding GLONASS observations. Wilcoxon rank sum tests and chi-square two-sample tests are made to examine the significance of the improvement on the positioning accuracy, convergence time and TTFF.

  15. Combined GPS/GLONASS Precise Point Positioning with Fixed GPS Ambiguities

    PubMed Central

    Pan, Lin; Cai, Changsheng; Santerre, Rock; Zhu, Jianjun

    2014-01-01

    Precise point positioning (PPP) technology is mostly implemented with an ambiguity-float solution. Its performance may be further improved by performing ambiguity-fixed resolution. Currently, the PPP integer ambiguity resolutions (IARs) are mainly based on GPS-only measurements. The integration of GPS and GLONASS can speed up the convergence and increase the accuracy of float ambiguity estimates, which contributes to enhancing the success rate and reliability of fixing ambiguities. This paper presents an approach of combined GPS/GLONASS PPP with fixed GPS ambiguities (GGPPP-FGA) in which GPS ambiguities are fixed into integers, while all GLONASS ambiguities are kept as float values. An improved minimum constellation method (MCM) is proposed to enhance the efficiency of GPS ambiguity fixing. Datasets from 20 globally distributed stations on two consecutive days are employed to investigate the performance of the GGPPP-FGA, including the positioning accuracy, convergence time and the time to first fix (TTFF). All datasets are processed for a time span of three hours in three scenarios, i.e., the GPS ambiguity-float solution, the GPS ambiguity-fixed resolution and the GGPPP-FGA resolution. The results indicate that the performance of the GPS ambiguity-fixed resolutions is significantly better than that of the GPS ambiguity-float solutions. In addition, the GGPPP-FGA improves the positioning accuracy by 38%, 25% and 44% and reduces the convergence time by 36%, 36% and 29% in the east, north and up coordinate components over the GPS-only ambiguity-fixed resolutions, respectively. Moreover, the TTFF is reduced by 27% after adding GLONASS observations. Wilcoxon rank sum tests and chi-square two-sample tests are made to examine the significance of the improvement on the positioning accuracy, convergence time and TTFF. PMID:25237901

  16. Evaluation of solar radio bursts' effect on GPS receiver signal tracking within International GPS Service network

    NASA Astrophysics Data System (ADS)

    Chen, Zhiyu; Gao, Yang; Liu, Zhizhao

    2005-06-01

    The direct interference from solar radio bursts (SRB) has not usually been considered as a potential threat to global positioning system (GPS) signal tracking, since the flux densities of most bursts are below 40,000 solar flux units (sfu), a threat threshold to GPS L1 frequency proposed by Klobuchar et al. (1999). Recent analysis indicated that a much lower threshold should be adopted for codeless or semicodeless dual-frequency GPS receivers. In this investigation, severe signal corruptions were found at dayside International GPS Service GPS receiver stations during a large solar radio burst that accompanied the super flare of 28 October 2003. Almost no GPS L2 signals were tracked during the solar flux peak time for areas near the subsolar point. Correlation analysis was performed between the rate of loss of lock on GPS L2 frequency and solar radio flux density at different bands, and a correlation index as high as 0.75 is revealed in the 1415 MHz solar radiation band, which is located between the two GPS operating frequencies L2 (1227.60 MHz) and L1 (1575.42 MHz). The correlation analysis indicates that GPS signal losses of lock were primarily caused by microwave in-band interference and that the threat threshold of SRB effects on the GPS system should be re-evaluated, since the flux density of the burst at 1415 MHz was just 4,000-12,000 sfu, which is far below the previously proposed threat threshold. The signal-tracking performance of different types of GPS receivers during such a super flare event is also presented.

  17. Hydrogen-treated commercial WO3 as an efficient electrocatalyst for triiodide reduction in dye-sensitized solar cells.

    PubMed

    Cheng, Ling; Hou, Yu; Zhang, Bo; Yang, Shuang; Guo, Jian Wei; Wu, Long; Yang, Hua Gui

    2013-07-07

    The electrocatalytically inactive commercial WO3 can be transformed into an efficient counter electrode (CE) material for dye-sensitized solar cells (DSCs) via facile hydrogen treatment. The energy conversion efficiency of the DSCs with the hydrogen-treated WO3 CE was 5.43%, while the corresponding value for commercial WO3 with the stoichiometric surface was only 0.63%.

  18. Effect of crystallization water on the structural and electrical properties of CuWO{sub 4} under high pressure

    SciTech Connect

    Wang, Li; Yan, Jiejuan; Liu, Cailong; Liu, Xizhe; Han, Yonghao E-mail: cc060109@qq.com; Gao, Chunxiao E-mail: cc060109@qq.com; Ke, Feng; Wang, Qinglin; Li, Yanchun; Ma, Yanzhang

    2015-11-16

    The effect of crystallization water on the structural and electrical properties of CuWO{sub 4} under high pressure has been investigated by in situ X-ray diffraction and alternating current impedance spectra measurements. The crystallization water was found to be a key role in modulating the structural stability of CuWO{sub 4} at high pressures. The anhydrous CuWO{sub 4} undergoes two pressure-induced structural transitions at 8.8 and 18.5 GPa, respectively, while CuWO{sub 4}·2H{sub 2}O keeps its original structure up to 40.5 GPa. Besides, the crystallization water makes the electrical transport behavior of anhydrous CuWO{sub 4} and CuWO{sub 4}·2H{sub 2}O quite different. The charge carrier transportation is always isotropic in CuWO{sub 4}·2H{sub 2}O, but anisotropic in the triclinic and the third phase of anhydrous CuWO{sub 4}. The grain resistance of CuWO{sub 4}·2H{sub 2}O is always larger than that of anhydrous CuWO{sub 4} in the entire pressure range. By analyzing the relaxation response, we found that the large number of hydrogen bonds can soften the grain characteristic frequency of CuWO{sub 4}·2H{sub 2}O over CuWO{sub 4} by one order of magnitude.

  19. Lithium-titanate-nanotube-supported WO3 for enhancing transmittance contrast in electrochromics.

    PubMed

    Dong, Yunbing; Xiong, Chunrong; Zhang, Yilu; Xing, Shuai; Jiang, Hong

    2016-03-11

    Lithium titanate nanotubes (Li-TNTs) have been successfully synthesized. The inner and outer diameters of the nanotubes are 5 nm and 8 nm with an interlayer spacing of 0.83 nm. The nanotubes were in accordance with the Li1.81H0.19Ti2O5 · xH2O phase. The chemical component was Li0.9H1.1Ti2O5 · H2O as determined by ICP-AES. The Li-TNT-supported WO3 nanoparticle (WO3/Li-TNTs) thin film was prepared onto ITO glass via spin-coating and then fabricated with an electrochromic device. The Li ion diffusion coefficient in the WO3/Li-TNT film was 6.1 × 10(-10) cm(2) s(-1), which is eight times higher than that for the pure WO3 film. The transmittance contrast of the pure WO3-based ECD was 53.3% at 600 nm. However, this increased to 74.1% for the WO3/Li-TNT-based ECD. Meanwhile, the color-switching times of the WO3/Li-TNT-based ECD were apparently shorter than the ones for the WO3-based ECD.

  20. Lithium-titanate-nanotube-supported WO3 for enhancing transmittance contrast in electrochromics

    NASA Astrophysics Data System (ADS)

    Dong, Yunbing; Xiong, Chunrong; Zhang, Yilu; Xing, Shuai; Jiang, Hong

    2016-03-01

    Lithium titanate nanotubes (Li-TNTs) have been successfully synthesized. The inner and outer diameters of the nanotubes are 5 nm and 8 nm with an interlayer spacing of 0.83 nm. The nanotubes were in accordance with the Li1.81H0.19Ti2O5 · xH2O phase. The chemical component was Li0.9H1.1Ti2O5 · H2O as determined by ICP-AES. The Li-TNT-supported WO3 nanoparticle (WO3/Li-TNTs) thin film was prepared onto ITO glass via spin-coating and then fabricated with an electrochromic device. The Li ion diffusion coefficient in the WO3/Li-TNT film was 6.1 × 10-10 cm2 s-1, which is eight times higher than that for the pure WO3 film. The transmittance contrast of the pure WO3-based ECD was 53.3% at 600 nm. However, this increased to 74.1% for the WO3/Li-TNT-based ECD. Meanwhile, the color-switching times of the WO3/Li-TNT-based ECD were apparently shorter than the ones for the WO3-based ECD.

  1. Optical properties of WO{sub 3} thin films using surface plasmon resonance technique

    SciTech Connect

    Paliwal, Ayushi; Sharma, Anjali; Gupta, Vinay E-mail: vgupta@physics.du.ac.in; Tomar, Monika

    2014-01-28

    Indigenously assembled surface plasmon resonance (SPR) technique has been exploited to study the thickness dependent dielectric properties of WO{sub 3} thin films. WO{sub 3} thin films (80 nm to 200 nm) have been deposited onto gold (Au) coated glass prism by sputtering technique. The structural, optical properties and surface morphology of the deposited WO{sub 3} thin films were studied using X-ray diffraction, UV-visible spectrophotometer, Raman spectroscopy, and Scanning electron microscopy (SEM). XRD analysis shows that all the deposited WO{sub 3} thin films are exhibiting preferred (020) orientation and Raman data indicates that the films possess single phase monoclinic structure. SEM images reveal the variation in grain size with increase in thickness. The SPR reflectance curves of the WO{sub 3}/Au/prism structure were utilized to estimate the dielectric properties of WO{sub 3} thin films at optical frequency (λ = 633 nm). As the thickness of WO{sub 3} thin film increases from 80 nm to 200 nm, the dielectric constant is seen to be decreasing from 5.76 to 3.42, while the dielectric loss reduces from 0.098 to 0.01. The estimated value of refractive index of WO{sub 3} film is in agreement to that obtained from UV-visible spectroscopy studies. The strong dispersion in refractive index is observed with wavelength of incident laser light.

  2. Detecting hydrogen using graphene quantum dots/WO3 thin films

    NASA Astrophysics Data System (ADS)

    Fardindoost, Somayeh; Iraji zad, Azam; Sadat Hosseini, Zahra; Hatamie, Shadie

    2016-11-01

    In the present work we report an approach to resistive hydrogen sensing based on graphene quantum dots (GQDs)/WO3 thin films that work reproducibly at low temperatures. GQDs were chemically synthesized and evenly dispersed in WO3 solution with 1:1 molar ratio. The structural evaluation and crystallization of the prepared films was studied by x-ray diffraction, Raman and scanning electron microscopy (SEM) techniques. The SEM images showed uniform distribution of the GQDs in WO3 films with sizes around 50 nm. Raman experiment showed the GQDs are partially reduced with high edge defects as hydroxyl and carboxyl groups which involve both in bridging between WO3 grains via bindings as well as interacting with target gas molecules. GQDs can develop an electron conductive network and shorten the current transport paths inside the sensitive films. As a result, they improved the poor electrical properties and charge transfer of pure WO3. Resistive hydrogen sensing showed significant decrease in the working temperature for GQDs/WO3 films compared to pure WO3 films. The working temperature of about 150 °C with 15 and 40 s response and recovery times are significant characteristics of the introduced sensing structure. Then palladium (Pd) was added as a catalyst in GQDs/WO3 film to make the sensing materials selective to hydrogen. Pd doped film worked at temperature of 120 °C with high selectivity and improved response magnitude to hydrogen gas.

  3. Congruence of Behavioral Symptomatology in Children with ADD/H, ADD/WO, and Learning Disabilities.

    ERIC Educational Resources Information Center

    Stanford, Lisa D.; Hynd, George W.

    1994-01-01

    This study compared parent and teacher behavioral ratings for 77 children (ages 5-16) diagnosed as having attention deficit disorder with hyperactivity (ADD/H), attention deficit disorder without hyperactivity (ADD/WO), or learning disabilities (LD). ADD/WO and LD children were rated similarly on symptoms of withdrawal and impulsivity but differed…

  4. Correlation between surface chemistry, density and band gap in nanocrystalline WO3 thin films

    SciTech Connect

    Vemuri, Venkata Rama Ses; Engelhard, Mark H.; Ramana, C.V.

    2012-03-01

    Nanocrystalline WO3 thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteristics, and optical properties of nanocrystalline WO3 films were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray reflectivity (XRR), and spectrophotometric measurements. The effect of ultra-microstructure was significant on the optical properties of WO3 films. The XPS analyses indicate the formation of stoichiometric WO3 with tungsten existing in fully oxidized valence state (W6+). However, WO3 films grown at high oxygen concentration (>60%) in the sputtering gas mixture were over stoichiometric with excess oxygen. XRR simulations, which are based on isotropic WO3 film - SiO2 interface - Si substrate model, indicate that the density of WO3 films is sensitive to the oxygen content in the sputtering gas. The spectral transmission of the films increased with the increasing oxygen. The band gap of these films increases from 2.78 eV to 3.25 eV with increasing oxygen. A direct correlation between the film-density and band gap in nanocrystalline WO3 films is established based on the observed results.

  5. Strain Accommodation By Facile WO6 Octahedral Distortion and Tilting During WO3 Heteroepitaxy on SrTiO3(001)

    SciTech Connect

    Du, Yingge; Gu, Meng; Varga, Tamas; Wang, Chong M.; Bowden, Mark E.; Chambers, Scott A.

    2014-08-27

    In this paper, we show that compared to other BO6 octahedra in ABO3 structured perovskite oxides, the WO6 octahedra in tungsten trioxide (WO3) can withstand a much larger degree of distortion and tilting to accommodate interfacial strain, which in turn strongly impact the nucleation, structure, and defect formation during the epitaxial growth of WO3 on SrTiO3(001). A meta-stable tetragonal phase can be stabilized by epitaxy and a thickness dependent phase transition (tetragonal to monoclinic) is observed. In contrast to misfit dislocations to accommodate the interfacial stain, the facial WO6 octahedral distortion and tilting give rise to three types of planar defects that affect more than 15 monolayers from the interface. These atomically resolved, unusual interfacial defects may significantly alter the electronic, electrochromic, and mechanical properties of the epitaxial films.

  6. Microwave-assisted synthesis and photocatalytic properties of flower-like Bi2WO6 and Bi2O3-Bi2WO6 composite.

    PubMed

    Li, Zhao-Qian; Chen, Xue-Tai; Xue, Zi-Ling

    2013-03-15

    Flower-like Bi(2)WO(6) and Bi(2)O(3)-Bi(2)WO(6) composite microstructures have been synthesized via a facile and rapid microwave-assisted hydrothermal method through controlling the experimental parameters. The phases and morphologies of the products are characterized by powder X-ray diffraction (XRD), energy dispersion X-ray analysis (EDX), high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Photocatalytic experiments indicate that such Bi(2)O(3)-Bi(2)WO(6) composite possesses higher photocatalytic activity for RhB degradation under visible-light irradiation in comparison with pure Bi(2)O(3) and Bi(2)WO(6). On the basis of the calculated energy band positions, the enhanced photocatalytic activity is attributed to the effective separation of electron-hole pairs between the two semiconductors. The present study provides a new strategy to design composite materials with enhanced photocatalytic activity.

  7. Electrochromic properties of WO3 thin film onto gold nanoparticles modified indium tin oxide electrodes

    NASA Astrophysics Data System (ADS)

    Deng, Jiajia; Gu, Ming; Di, Junwei

    2011-04-01

    Gold nanoparticles (GNPs) thin films, electrochemically deposited from hydrogen tetrachloroaurate onto transparent indium tin oxide (ITO) thin film coated glass, have different color prepared by variation of the deposition condition. The color of GNP film can vary from pale red to blue due to different particle size and their interaction. The characteristic of GNPs modified ITO electrodes was studied by UV-vis spectroscopy, scanning electron microscope (SEM) images and cyclic voltammetry. WO3 thin films were fabricated by sol-gel method onto the surface of GNPs modified electrode to form the WO3/GNPs composite films. The electrochromic properties of WO3/GNPs composite modified ITO electrode were investigated by UV-vis spectroscopy and cyclic voltammetry. It was found that the electrochromic performance of WO3/GNPs composite films was improved in comparison with a single component system of WO3.

  8. High photocatalytic capability of self-assembled nanoporous WO3 with preferential orientation of (002) planes.

    PubMed

    Guo, Yafeng; Quan, Xie; Lu, Na; Zhao, Huimin; Chen, Shuo

    2007-06-15

    Self-assembled nanoporous tungsten oxide (WO3) with preferential orientation (002) planes was successfully synthesized on the tungsten sheet by anodization in a 0.2 wt % NaF and 0.3% (V/V) HF mixture solution in a 1:1 ratio. The pores, of a highly ordered self-assembled structure, had an average size of approximately 70 nm. X-ray diffraction identified a monoclinic WO3 structure and fine preferential orientation of (002) planes. A maximum photoconversion efficiency of 17.2% was obtained for the self-assembled nanoporous WO3 under high-pressure mercury lamp illumination. The photocatalytic (PC) degradation of pentachlorophenol (PCP) in aqueous solution using the self-assembled nanoporous WO3 photocatalyst, performed under both high-pressure mercury lamp and Xe lamp illumination, showed more excellent PC capability than WO3 film and TiO2 nanotube arrays.

  9. Characterization of MAPLE deposited WO3 thin films for electrochromic applications

    NASA Astrophysics Data System (ADS)

    Boyadjiev, S. I.; Stefan, N.; Szilágyi, I. M.; Mihailescu, N.; Visan, A.; Mihailescu, I. N.; Stan, G. E.; Besleaga, C.; Iliev, M. T.; Gesheva, K. A.

    2017-01-01

    Tungsten trioxide (WO3) is a widely studied material for electrochromic applications. The structure, morphology and optical properties of WO3 thin films, grown by matrix assisted pulsed laser evaporation (MAPLE) from monoclinic WO3 nano-sized particles, were investigated for their possible application as electrochromic layers. A KrF* excimer (λ=248 nm, ζFWHM=25 ns) laser source was used in all experiments. The MAPLE deposited WO3 thin films were studied by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry measurements were also performed, and the coloring and bleaching were observed. The morpho-structural investigations disclosed the synthesis of single-phase monoclinic WO3 films consisting of crystalline nano-grains embedded in an amorphous matrix. All thin films showed good electrochromic properties, thus validating application of the MAPLE deposition technique for the further development of electrochromic devices.

  10. Gamma-ray irradiation induced bulk photochromism in WO3-P2O5 glass

    NASA Astrophysics Data System (ADS)

    Shen, Wei; Baccaro, Stefania; Cemmi, Alessia; Xu, Xiaoqing; Chen, Guorong

    2015-11-01

    In the present work, photochromism of WO3-P2O5 glass under gamma-ray irradiation was reported. As-prepared glass samples with different WO3 content are all optically transparent in the visible wavelength range thanks to the addition of a small amount of oxidizing couple Sb2O3-NaNO3. The photochromic properties are identified by transmission spectra of the glasses before and after irradiation. The results show that the irradiation induced darkening results from the reduction of W6+ to W5+ or W4+. The existence of WO6 clusters in glasses of high WO3 content is proved by XPS, which is the main reason for the obvious photochromic effects. The WO3-P2O5 glass is a promising candidate in gamma-ray sensitive detector.

  11. Photoactivity and stability of Ag2WO4 for organic degradation in aqueous suspensions

    NASA Astrophysics Data System (ADS)

    Chen, Haihang; Xu, Yiming

    2014-11-01

    Silver tungstate as photocatalyst for water splitting and dye degradation has been reported, but the catalyst stability is not known. In this work, we find that both α- and β-Ag2WO4 are not stable under UV light for the photocatalytic degradation of phenol and azo-dye X3B in aqueous solutions. Comparatively, β-Ag2WO4 was more photoactive, but less stable than α-Ag2WO4. Solid characterization with X-ray diffraction and scanning electron microscope showed that metallic silver particles were produced with the two catalysts, consequently resulting into decrease in the activity for organic degradation. Measurement of photoluminescence revealed that β-Ag2WO4 had a weaker band gap emission and higher portion of structural defects than α-Ag2WO4. A possible mechanism responsible for the observed difference in photoactivity and stability between the two tungstates is proposed.

  12. Photoelectron spectromicroscopy study of metal-insulator transition in NaxWO3

    NASA Astrophysics Data System (ADS)

    Paul, Sanhita; Ghosh, Anirudha; Dudin, Pavel; Barinov, Alexei; Chakraborty, Anirban; Ray, Sugata; Sarma, D. D.; Oishi, Shuji; Raj, Satyabrata

    2013-07-01

    We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, NaxWO3 by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of NaxWO3 reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in NaxWO3. The possible origin of insulating phase in NaxWO3 is due to the Anderson localization of all the states near EF. The localization occurs because of the strong disorder arising from random distribution of Na+ ions in the WO3 lattice.

  13. US Coast Guard GPS Information Center (GPSIC) and its function within the Civil GPS Service (CGS)

    NASA Technical Reports Server (NTRS)

    1993-01-01

    In 1987, the U.S. Department of Defense (DOD) formally requested that the U.S. Department of Transportation (DOT) take responsibility for providing an office that would respond to nonmilitary user needs for GPS information, data, and assistance. DOT accepted this responsibility and in February 1989, named the Coast Guard as their lead agency for the project. Since that time, the U.S. Coast Guard has worked with the U.S. Space Command to develop requirements and implement a plan for providing the requested interface with the civil GPS community. The Civil GPS Service (CGS) consists of four main elements: GPS Information Center (GPSIC) - provides GPS status information to civilian users of the system: Civil GPS Service Interface Committee (CGSIC) - established to identify civil GPS user technical information needs in support of the CGS program; Differential GPS (DGPS) - Coast Guard Research and Development Project; and PPS Program Office (PPSPO) - (Under development) will administer the program allowing qualified civil users to have access to the PPS signal. Details about the services these organizations provide are described.

  14. The International GPS Service (IGS) as a Continuous Reference System for Precise GPS Positioning

    NASA Technical Reports Server (NTRS)

    Neilan, Ruth; Heflin, Michael; Watkins, Michael; Zumberge, James

    1996-01-01

    The International GPS Service for Geodynamics (IGS) is an organization which operates under the auspices of the International Association of Geodesy (IAG) and has been operational since January 1994. The primary objective of the IGS is to provide precise GPS data and data products to support geodetic and geophysical research activities.

  15. GPS Space Service Volume: Ensuring Consistent Utility Across GPS Design Builds for Space Users

    NASA Technical Reports Server (NTRS)

    Bauer, Frank H.; Parker, Joel Jefferson Konkl; Valdez, Jennifer Ellen

    2015-01-01

    GPS availability and signal strength originally specified for users on or near surface of Earth with transmitted power levels specified at edge-of-Earth, 14.3 degrees. Prior to the SSV specification, on-orbit performance of GPS varied from block build to block build (IIA, IIRM, IIF) due to antenna gain and beam width variances. Unstable on-orbit performance results in significant risk to space users. Side-lobe signals, although not specified, were expected to significantly boost GPS signal availability for users above the constellation. During GPS III Phase A, NASA noted significant discrepancies in power levels specified in GPS III specification documents, and measured on-orbit performance. To stabilize the signal for high altitude space users, NASA DoD team in 2003-2005 led the creation of new Space Service Volume (SSV) definition and specifications.

  16. Catalytic activities of noble metal atoms on WO3 (001): nitric oxide adsorption.

    PubMed

    Ren, Xiaoyan; Zhang, Shuai; Li, Chong; Li, Shunfang; Jia, Yu; Cho, Jun-Hyung

    2015-01-01

    Using first-principles density functional theory calculations within the generalized gradient approximation, we investigate the adsorption of NO molecule on a clean WO3(001) surface as well as on the noble metal atom (Cu, Ag, and Au)-deposited WO3(001) surfaces. We find that on a clean WO3 (001) surface, the NO molecule binds to the W atom with an adsorption energy (E ads) of -0.48 eV. On the Cu- and Ag-deposited WO3(001) surface where such noble metal atoms prefer to adsorb on the hollow site, the NO molecule also binds to the W atom with E ads = -1.69 and -1.41 eV, respectively. This relatively stronger bonding of NO to the W atom is found to be associated with the larger charge transfer of 0.43 e (Cu) and 0.33 e (Ag) from the surface to adsorbed NO. However, unlike the cases of Cu-WO3(001) and Ag-WO3(001), Au atoms prefer to adsorb on the top of W atom. On such an Au-WO3(001) complex, the NO molecule is found to form a bond to the Au atom with E ads = -1.32 eV. Because of a large electronegativity of Au atom, the adsorbed NO molecule captures the less electrons (0.04 e) from the surface compared to the Cu and Ag catalysts. Our findings not only provide useful information about the NO adsorption on a clean WO3(001) surface as well as on the noble metal atoms deposited WO3(001) surfaces but also shed light on a higher sensitive WO3 sensor for NO detection employing noble metal catalysts.

  17. MWCNT/WO{sub 3} nanocomposite photoanode for visible light induced water splitting

    SciTech Connect

    Yousefzadeh, Samira; Reyhani, Ali; Naseri, Naimeh; Moshfegh, Alireza Z.

    2013-08-15

    The Multi-walled carbon nanotube (MWCNT)/WO{sub 3} nanocomposite thin films with different MWCNT’s weight percentages were prepared by sol–gel method as visible light induced photoanode in water splitting reaction. Weight percentage of MWCNT in the all nanocomposite thin films was confirmed by TGA/DSC analysis. According to XPS analysis, oxygenated groups at the surface of the MWCNT and stoichiometric formation of WO{sub 3} thin films were determined, while the crystalline structure of the nanocomposite samples was studied by XRD indicating (0 0 2) peak of MWCNT in the monoclinic phase of WO{sub 3}. The influence of different weight percentage (wt%) of MWCNT on WO{sub 3} photoactivity showed that the electron conductivity, charge transfer and electron life time had improved as compared with the pure WO{sub 3}. Based on linear sweep voltammetry and chronoamperometry measurements, the (1 wt%) MWCNT/WO{sub 3} nanocomposite thin films photoanode has a maximum photocurrent density of ∼4.5 A/m{sup 2} and electron life time of about 57 s. - Graphical abstract: Photocurrent density versus time at constant potential (0.7 V) for the WO{sub 3} films containing different MWCNT weight percentages annealed at 400 °C under 1000 Wm{sup −2} visible photo-illumination. Display Omitted - Highlights: • MWCNT/ WO{sub 3} nanocomposite thin films were synthesized using sol–gel derived method. • TGA/DSC confirmed the weight percentage of MWCNT in the all nanocomposite thin films. • XPS analysis revealed that WO{sub 3} was attached on the oxygenated group of MWCNT surface. • The Highest Photoelectrochemical activity is achieved for (1 wt%)MWCNT/WO{sub 3} thin film.

  18. The enhanced alcohol-sensing response of ultrathin WO3 nanoplates

    NASA Astrophysics Data System (ADS)

    Chen, Deliang; Hou, Xianxiang; Wen, Hejing; Wang, Yu; Wang, Hailong; Li, Xinjian; Zhang, Rui; Lu, Hongxia; Xu, Hongliang; Guan, Shaokang; Sun, Jing; Gao, Lian

    2010-01-01

    Chemical sensors based on semiconducting metal oxide nanocrystals are of academic and practical significance in industrial processing and environment-related applications. Novel alcohol response sensors using two-dimensional WO3 nanoplates as active elements have been investigated in this paper. Single-crystalline WO3 nanoplates were synthesized through a topochemical approach on the basis of intercalation chemistry (Chen et al 2008 Small 4 1813). The as-obtained WO3 nanoplate pastes were coated on the surface of an Al2O3 ceramic microtube with four Pt electrodes to measure their alcohol-sensing properties. The results show that the WO3 nanoplate sensors are highly sensitive to alcohols (e.g., methanol, ethanol, isopropanol and butanol) at moderate operating temperatures (260-360 °C). For butanol, the WO3 nanoplate sensors have a sensitivity of 31 at 2 ppm and 161 at 100 ppm, operating at 300 °C. For other alcohols, WO3 nanoplate sensors also show high sensitivities: 33 for methanol at 300 ppm, 70 for ethanol at 200 ppm, and 75 for isopropanol at 200 ppm. The response and recovery times of the WO3 nanoplate sensors are less than 15 s for all the test alcohols. A good linear relationship between the sensitivity and alcohol concentrations has been observed in the range of 2-300 ppm, whereas the WO3 nanoparticle sensors have not shown such a linear relationship. The sensitivities of the WO3 nanoplate sensors decrease and their response times become short when the operating temperatures increase. The enhanced alcohol-sensing performance could be attributed to the ultrathin platelike morphology, the high crystallinity and the loosely assembling structure of the WO3 nanoplates, due to the advantages of the effective adsorption and rapid diffusion of the alcohol molecules.

  19. The enhanced alcohol-sensing response of ultrathin WO3 nanoplates.

    PubMed

    Chen, Deliang; Hou, Xianxiang; Wen, Hejing; Wang, Yu; Wang, Hailong; Li, Xinjian; Zhang, Rui; Lu, Hongxia; Xu, Hongliang; Guan, Shaokang; Sun, Jing; Gao, Lian

    2010-01-22

    Chemical sensors based on semiconducting metal oxide nanocrystals are of academic and practical significance in industrial processing and environment-related applications. Novel alcohol response sensors using two-dimensional WO(3) nanoplates as active elements have been investigated in this paper. Single-crystalline WO(3) nanoplates were synthesized through a topochemical approach on the basis of intercalation chemistry (Chen et al 2008 Small 4 1813). The as-obtained WO(3) nanoplate pastes were coated on the surface of an Al(2)O(3) ceramic microtube with four Pt electrodes to measure their alcohol-sensing properties. The results show that the WO(3) nanoplate sensors are highly sensitive to alcohols (e.g., methanol, ethanol, isopropanol and butanol) at moderate operating temperatures (260-360 degrees C). For butanol, the WO(3) nanoplate sensors have a sensitivity of 31 at 2 ppm and 161 at 100 ppm, operating at 300 degrees C. For other alcohols, WO(3) nanoplate sensors also show high sensitivities: 33 for methanol at 300 ppm, 70 for ethanol at 200 ppm, and 75 for isopropanol at 200 ppm. The response and recovery times of the WO(3) nanoplate sensors are less than 15 s for all the test alcohols. A good linear relationship between the sensitivity and alcohol concentrations has been observed in the range of 2-300 ppm, whereas the WO(3) nanoparticle sensors have not shown such a linear relationship. The sensitivities of the WO(3) nanoplate sensors decrease and their response times become short when the operating temperatures increase. The enhanced alcohol-sensing performance could be attributed to the ultrathin platelike morphology, the high crystallinity and the loosely assembling structure of the WO(3) nanoplates, due to the advantages of the effective adsorption and rapid diffusion of the alcohol molecules.

  20. Revival of "dead" memristive devices: case of WO3-x.

    PubMed

    Tan, Zheng-Hua; Yang, Rui; Terabe, Kazuya; Yin, Xue-Bing; Guo, Xin

    2016-01-21

    Inappropriate operation could make a memristive device "dead" and cause the loss of resistive switching performance. In this study, the revival of "dead" devices was investigated in the case of WO3-x-based memristive devices. It is believed that inappropriate operation with a high-voltage pulse creates an ordered structure of oxygen vacancies and such an ordered structure makes the normal reset process fail. By precisely controlled voltage sweeping at certain compliance currents, a "dead" device can be revived. The revival operation disrupts the ordered structure by Joule heating and recovers Schottky-like barrier modulation-based switching.

  1. Ion doping effects in multiferroic MnWO4

    NASA Astrophysics Data System (ADS)

    Bahoosh, Safa Golrokh; Wesselinowa, J. M.

    2012-04-01

    We have studied the ion doping effects in multiferroic MnWO4 proposing a microscopic model. It is shown that the exchange interaction constants can be changed due to the different ion doping radii. This leads to reduction of the magnetic phase transition temperature TN by doping with non-magnetic ions, such as Zn, Mg, whereas TN is enhanced by doping with transition metal ions, such as Fe, Co. The different behavior of the temperature T1 (where up-up-down-down collinear spin structure appears) by Fe and Co doping could be explained taking into account the single-ion anisotropy.

  2. Small polaron formation in porous WO3-x nanoparticle films

    NASA Astrophysics Data System (ADS)

    Ederth, J.; Hoel, A.; Niklasson, G. A.; Granqvist, C. G.

    2004-11-01

    Porous tungsten oxide nanoparticle films were prepared by reactive gas evaporation. The structure was studied by x-ray diffraction and scanning electron microscopy, and the oxygen nonstoichiometry was inferred by x-ray photoelectron spectroscopy, elastic recoil detection analysis, and neutron scattering. Specifically, the films consisted of WO3-x with 0.25

  3. Epitaxial growth of high quality WO3 thin films

    DOE PAGES

    Leng, X.; Pereiro, J.; Strle, J.; ...

    2015-09-09

    We have grown epitaxial WO3 films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

  4. Photoinduced (WO4)3--La3+ center in PbWO4: Electron spin resonance and thermally stimulated luminescence study

    NASA Astrophysics Data System (ADS)

    Laguta, V. V.; Martini, M.; Meinardi, F.; Vedda, A.; Hofstaetter, A.; Meyer, B. K.; Nikl, M.; Mihóková, E.; Rosa, J.; Usuki, Y.

    2000-10-01

    The localization of electrons at W6+ sites perturbed by lanthanum in PbWO4 is studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL) measurements. The (WO4)3--La3+ centers are created at the W6+ sites close to La3+ in two different ways: (i) direct trapping of electrons from the conduction band under ultraviolet or x-ray irradiation at T=60 K (ii) retrapping of electrons freed from unperturbed (WO4)3- centers after irradiation at T<40 K followed by heating up to T around 60 K. Electron transfer from La3+-perturbed to unperturbed W6+ sites stimulated by red light illumination is also observed. The proposed mechanism of electron localization at one of four equivalent tungstate ions close to La3+ is based on the pseudo-Jahn-Teller effect, which gives rise to a rhombic distortion of (WO4)3- complex. At T~95-98 K the (WO4)3--La3+ centers are thermally ionized giving rise to a TSL glow peak due to the recombination of detrapped electrons with localized holes. The emission spectrum of the TSL features one band peaking at 2.8 eV. The temperature dependence of both TSL and ESR intensity is analyzed in the frame of a general order recombination model. The thermal ionization energy of (WO4)3--La3+ centers has been calculated to be approximately 0.27 eV.

  5. Luminescence of CaWO4, CaMoO4, and ZnWO4 scintillating crystals under different excitations

    NASA Astrophysics Data System (ADS)

    Mikhailik, V. B.; Kraus, H.; Miller, G.; Mykhaylyk, M. S.; Wahl, D.

    2005-04-01

    The luminescence spectra of CaWO4, CaMoO4, and ZnWO4 scintillating crystals were investigated in the temperature range 8-400K. The excitation photon energy was varied from the ultraviolet (4.5eV ) to the hard x-ray region (35keV). It is found that as the excitation energy decreases the relative intensity of the low-energy luminescence band, attributed to the extrinsic emission of defect centers in CaWO4 and CaMoO4 crystals, increases. This observation is interpreted in terms of the total absorption of incident radiation, i.e., the variation of the mean penetration depth of the photons with their energy. It indicates that the centers responsible for the extrinsic emission in the crystals with scheelite structure are mainly localized in a thin (˜100nm ) surface layer. On the other hand no noticeable changes with the excitation energy were found in the emission spectra of ZnWO4 crystals with wolframite structure. The possible implication of this finding is discussed. The light yield of the crystals is compared at low temperature using monochromatic x-ray excitation and it is shown that ZnWO4 has ˜10% higher light yield than CaWO4, while this parameter has a factor of 4 lower in CaMoO4.

  6. Very long-period GPS waveforms. What can GPS bring to Earth seismic velocity models?

    NASA Astrophysics Data System (ADS)

    Kelevitz, K.; Houlie, N.; Nissen-Meyer, T.; Boschi, L.; Giardini, D.; Rothacher, M.

    2014-12-01

    It is now admitted that high rate GPS observations can provide reliable surface displacement waveforms. For long-period (T > 5s) transients, it was shown that GPS and seismometer (STS-1) displacements are in agreement at least for vertical component [Houlié et al., 2011]. We propose here to supplement existing long-period seismic networks with high rate (>= 1Hz) GPS data in order to improve the resolution of global seismic velocity models. We aim at extending the use of GPS measurements beyond the range of STS-1 in the low frequency end (T>1000s). We present the results of the processing of 1Hz GPS records of the Hokkaido, Sumatra and Tohoku earthquakes (25th of September, 2003, Mw = 8.3; 26th of December, 2004, Mw = 8.9; 11th of March, 2011, Mw = 9.1, respectively). 3D waveforms phase time-series have been used to recover the ground motion histories at the GPS sites. Through the better resolution of inversion of the GPS phase observations, we determine displacement waveforms of periods ranging from 30 seconds to 1300 seconds for a selection of sites. We compare inverted GPS waveforms with STS-1 waveforms, superconducting gravity waveforms and synthetic waveforms computed using 3D global wave propagation with SPECFEM. We find that the GPS waveforms are in agreement with the SPECFEM synthetic data and are able to fill the period-gap between the broadband seismometer STS-1 data and the normal mode period range detected by the superconducting gravimeters. References: Houlié, N., G. Occhipinti, T. Blanchard, N. Shapiro, P. Lognonne, and M. Murakami (2011), New approach to detect seismic surface waves in 1Hz-sampled GPS time series, Scientific reports, 1, 44.

  7. Spectral Character of Repeated GPS Measurements

    NASA Astrophysics Data System (ADS)

    Turen, Yener; Ugur Sanli, D.

    2017-04-01

    We need GPS campaigns because we are not always able to monitor natural hazards using CORS. Prime examples in regard to the above statement are landslides and local subsidence. For instance, we are reluctant to install permanent GPS equipment in a landslide area because the equipment might be destroyed due to the sudden flow of the ground. Similarly, the CORS might not be covering the area in which a local subsidence happening. Obviously more examples can be given. We take repeated (campaign) GPS to such case study areas. Therefore, similar to the continuous GPS, we also need to study the properties of the repeated GPS. Upto now, the positioning accuracy and the accuracy of velocity estimation have been documented well for the repeated measurements. The spectral character is one such issue that we desire to look along with the other investigations. Thanks to the IGS and its data and analysis center SOPAC, we are able to simulate possible campaign senarios and apply variety of statistics using their products. Thanks also to NASA, JPL; using the PPP module of GIPSY/OASIS II software, we are able to study the direct absolute deformations of the earth at the mm level. These investigations should shed light into multi-GNSS experiments. We generate monthly sampled GPS campaigns from the continuous IGS data and estimate station velocities from repeated GPS measurements. Then, we test the statistical significancy of the estimated trends against SOPAC derived station velocities. The analysis procedure includes the computation of periodograms for the campaign solutions and determine significant periodicities in the data. We ceheck the obtained periodicities with those of the SOPAC time series analysis of the continuous GPS data. As might be expected, the spectral character of the campaign solutions differ from those of the daily sampled continuous GPS solutions implemented by SOPAC. For instance, the typical annual signal on the vertical componenet might disappear at some

  8. Synthesis of chemically bonded BiOCl@Bi2WO6 microspheres with exposed (0 2 0) Bi2WO6 facets and their enhanced photocatalytic activities under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Ma, Yongchao; Chen, Zhiwei; Qu, Dan; Shi, Jinsheng

    2016-01-01

    Bi2WO6 photocatalysts has been extensively studied for its photocatalytic activity. However, few works have been conducted on hierarchical Bi2WO6 composite photocatalysts with specifically exposed facets. In this work, we report a facile method to synthesize BiOCl@Bi2WO6 hierarchical composite microspheres. Bi2WO6 nanosheets with specifically exposed (0 2 0) facet were directly formed on the surface of BiOCl precursor microspheres via a controlled anion exchange route between BiOCl and Na2WO4. The visible-light photocatalytic activity of the BiOCl@Bi2WO6 heterojunction with exposed (0 2 0) facets (denoted as BiOCl@Bi2WO6) was investigated by degradation of Rhodamine B (RhB) and ciprofloxacin (CIP) aqueous solution under visible light irradiation. The experimental results indicated that the BiOCl@Bi2WO6 composite microsphere with intimate interfacial contacts exhibited improved efficiency for RhB photodegradation in comparison with pure BiOCl and Bi2WO6. The BiOCl@Bi2WO6 composite microsphere also shows high photocatalytic activity for degradation of CIP under visible light irradiation. The enhanced photocatalytic performance of BiOCl@Bi2WO6-020 hierarchical microspheres can be ascribed to the improved visible light harvesting ability, high charge separation and transfer. This work will make significant contributions toward the exploration of novel heterostructures with high potential in photocatalytic applications.

  9. Physical applications of GPS geodesy: a review.

    PubMed

    Bock, Yehuda; Melgar, Diego

    2016-10-01

    Geodesy, the oldest science, has become an important discipline in the geosciences, in large part by enhancing Global Positioning System (GPS) capabilities over the last 35 years well beyond the satellite constellation's original design. The ability of GPS geodesy to estimate 3D positions with millimeter-level precision with respect to a global terrestrial reference frame has contributed to significant advances in geophysics, seismology, atmospheric science, hydrology, and natural hazard science. Monitoring the changes in the positions or trajectories of GPS instruments on the Earth's land and water surfaces, in the atmosphere, or in space, is important for both theory and applications, from an improved understanding of tectonic and magmatic processes to developing systems for mitigating the impact of natural hazards on society and the environment. Besides accurate positioning, all disturbances in the propagation of the transmitted GPS radio signals from satellite to receiver are mined for information, from troposphere and ionosphere delays for weather, climate, and natural hazard applications, to disturbances in the signals due to multipath reflections from the solid ground, water, and ice for environmental applications. We review the relevant concepts of geodetic theory, data analysis, and physical modeling for a myriad of processes at multiple spatial and temporal scales, and discuss the extensive global infrastructure that has been built to support GPS geodesy consisting of thousands of continuously operating stations. We also discuss the integration of heterogeneous and complementary data sets from geodesy, seismology, and geology, focusing on crustal deformation applications and early warning systems for natural hazards.

  10. Countering GPS jamming and EW threat

    NASA Astrophysics Data System (ADS)

    Pereira, Carlos M.; Rastegar, J.; McLain, Clifford E.; Alanson, T.; McMullan, Charles; Nguyen, H.-L.

    2007-09-01

    Efforts at the U.S. Army Research, Development and Engineering Center (ARDEC) at Picatinny, New Jersey are focused on developing methods to counter GPS jamming and electronic warfare (EW) threat by eliminating GPS dependency entirely. In addition, the need for munitions cost reduction requires alternatives to expensive high-grade inertia components. Efforts at ARDEC include investigations of novel methods for onboard measurement of munitions full position and angular orientation independent of GPS signals or high-grade inertia components. Currently, two types of direct angular measurement sensors are being investigated. A first sensor, Radio Frequency Polarized Sensor (RFPS), uses an electromagnetic field as a reference. A second sensor is based on magnetometers, using the Earth magnetic field for orientation measurement. Magnetometers, however, can only provide two independent orientation measurements. The RFPS may also be used to make full object position and angular orientation measurement relative to a reference coordinate system, which may be moving or stationary. The potential applications of novel RFPS sensors is in providing highly effective inexpensive replacement for GPS, which could be used in a "Layered Navigation" scheme employing alternate referencing methods and reduce the current dependency on GPS as a primary reference for guided gun-fired munitions. Other potential applications of RFPSs is in UAVs, UGVs, and robotic platforms.

  11. Prompt GPS TEC response to magnetospheric compression

    NASA Astrophysics Data System (ADS)

    Hao, Yongqiang; Huang, Jianping; Liu, Wenlong; Zhang, Donghe; Xiao, Zuo

    2017-04-01

    A new type of total electron content (TEC) variation was observed when an interplanetary shock impacted on the Earth's magnetosphere on 17 March 2015. With hundreds of ground-based Global Positioning System (GPS) receivers, instantaneous TEC impulses were detected in the signals from four GPS satellites cruising in the dayside equatorial magnetosphere. Despite the small amplitude (0.3 TECU), the impulses were synchronously registered by receivers spreading from low to middle latitudes on the ground; they lasted for several minutes, during which period the interplanetary magnetic field (IMF) kept northward. The TEC impulses therefore discriminate themselves from usual traveling ionospheric disturbances and exclude possible effects from the southward IMF-driven magnetic storm. We suggest that the TEC variation is caused by shock-induced magnetospheric compression, which moves plasma earthward in the dayside plasmasphere. As a result, some plasma outside of GPS orbit (4.2 RE) is moved to the inside and contributes to the plasma content traversed by GPS raypath. The GPS TEC technique thus exhibits an unprecedented capability to capture small tremor of the magnetosphere, and with the dense receiver network on the ground it can be a feasible tool for remote sensing of the plasma dynamics around 4.2 RE.

  12. GPS Remote Sensing Measurements Using Aerosonde UAV

    NASA Technical Reports Server (NTRS)

    Grant, Michael S.; Katzberg, Stephen J.; Lawrence, R. W.

    2005-01-01

    In February 2004, a NASA-Langley GPS Remote Sensor (GPSRS) unit was flown on an Aerosonde unmanned aerial vehicle (UAV) from the Wallops Flight Facility (WFF) in Virginia. Using direct and surface-reflected 1.575 GHz coarse acquisition (C/A) coded GPS signals, remote sensing measurements were obtained over land and portions of open water. The strength of the surface-reflected GPS signal is proportional to the amount of moisture in the surface, and is also influenced by surface roughness. Amplitude and other characteristics of the reflected signal allow an estimate of wind speed over open water. In this paper we provide a synopsis of the instrument accommodation requirements, installation procedures, and preliminary results from what is likely the first-ever flight of a GPS remote sensing instrument on a UAV. The correct operation of the GPSRS unit on this flight indicates that Aerosonde-like UAV's can serve as platforms for future GPS remote sensing science missions.

  13. Soil moisture monitoring with GPS reflected signals.

    NASA Astrophysics Data System (ADS)

    Van Baelen, Joël; Presset, Benoît; Arnaudet, Emilien; Morel, Laurent

    2017-04-01

    In the context of necessary reductions of inputs in agricultural practices (fertilizers, sanitary treatments, irrigation), monitoring of low level atmospheric water vapor and soil moisture has become a major issue. Nowadays, it is well known that GPS positioning with a network of receivers can also yield estimates of tropospheric parameters which in turn provide reliable estimates of atmospheric water vapor. Furthermore, when a dense network of GPS stations exists, GPS signals can be used to perform tomography in order to retrieve the three dimensional distribution of water vapour density. A more recent aspect of the GPS applications is also to investigate the technique of reflectivity (i.e., the monitoring of ground reflected rays) to monitor and retrieve the soil moisture variations. In this work, we will present preliminary results of a dedicated campaign to study low level water vapour retrieval and, more particularily, soil moisture variation identification and estimation as demonstrated in the figure below. A strong correlation exists between soil humidity and GPS reflected signal phase variations, while we also pursue ways to investigate the most influential factors which help determine the most suited satellite passage to potentially provide ways to estimate the soil moisture content fluctuations. PIC

  14. Extended x-ray absorption fine structure spectroscopy and first-principles study of SnWO4

    NASA Astrophysics Data System (ADS)

    Kuzmin, A.; Anspoks, A.; Kalinko, A.; Timoshenko, J.; Kalendarev, R.

    2014-04-01

    The local atomic structure in α- and β-SnWO4 was studied by synchrotron radiation W L3-edge x-ray absorption spectroscopy at 10 and 300 K. Strongly distorted WO6 octahedra were found in α-SnWO4, whereas nearly regular WO4 tetrahedra were observed in β-SnWO4, confirming previous results. The structural results obtained were supported by the first-principles calculations, suggesting that the second-order Jahn-Teller effect is responsible for octahedral distortion.

  15. Enhancement of visible-light photocatalytic activity of silver and mesoporous carbon co-modified Bi2WO6

    NASA Astrophysics Data System (ADS)

    Zhao, Qian; Gong, Ming; Liu, Wangping; Mao, Yulin; Le, Shukun; Ju, Shang; Long, Fei; Liu, Xiufang; Liu, Kai; Jiang, Tingshun

    2015-03-01

    Ordered mesoporous carbon CMK-3 was prepared by hard template method using SBA-15 as template, sucrose as carbon source. Flower/sphere-like Bi2WO6 and CMK-3/Bi2WO6 photocatalysts were synthesized by hydrothermal method, and then Ag/Bi2WO6 and Ag/Bi2WO6/CMK-3 composite photocatalysts were prepared via a photoreduction process. The samples were characterized by XRD, UV-vis, TEM (HR-TEM), SEM, N2 physical adsorption and PL and their photocatalytic activities were evaluated by the photocatalytic degradation of methylene blue (MB) under visible light irradiation. The results show that both incorporating of CMK-3 and Ag loading greatly improved the photocatalytic activity of Bi2WO6, and the content of CMK-3 and silver have an impact on the photocatalytic activity of Bi2WO6. The photocatalytic activity of Ag/Bi2WO6/CMK-3 photocatalyst is superior to the activities of CMK-3/Bi2WO6 and Ag/Bi2WO6 under comparable conditions, and Ag/Bi2WO6/CMK-3 photocatalyst has high stability and is easy to be recycled. Also, the mechanism for the enhancement of the photocatalytic activity of CMK-3 and Ag co-modified Bi2WO6 was also investigated.

  16. Ag loaded WO3 nanoplates for efficient photocatalytic degradation of sulfanilamide and their bactericidal effect under visible light irradiation.

    PubMed

    Zhu, Wenyu; Liu, Jincheng; Yu, Shuyan; Zhou, Yan; Yan, Xiaoli

    2016-11-15

    Sulfonamides (SAs) are extensively used antibiotics and their residues in the water bodies propose potential threat to the public. In this study, degradation efficiency of sulfanilamide (SAM), which is the precursor of SAs, using WO3 nanoplates and their Ag heterogeneous as photocatalysts was investigated. WO3 nanoplates with uniform size were synthesized by a facile one step hydrothermal method. Different amount of Ag nanoparticles (Ag NPs) were loaded onto WO3 nanoplates using a photo-reduction method to generate WO3/Ag composites. The physio-chemical properties of synthesized nanomaterials were systematically characterized. Photodegradation of SAM by WO3 and WO3/Ag composites was conducted under visible light irradiation. The results show that WO3/Ag composites performed much better than pure WO3 where the highest removal rate was 96.2% in 5h. Ag as excellent antibacterial agent also endows certain antibacterial efficiency to WO3, and 100% removal efficiency against Escherichia Coli and Bacillus subtilis could be achieved in 2h under visible light irradiation for all three WO3/Ag composites synthesized. The improved performance in terms of SAM degradation and antibacterial activity of WO3/Ag can be attributed to the improved electron-hole pair separation rate where Ag NPs act as effective electron trapper during the photocatalytic process.

  17. Hierarchically plasmonic photocatalysts of Ag/AgCl nanocrystals coupled with single-crystalline WO3 nanoplates

    NASA Astrophysics Data System (ADS)

    Chen, Deliang; Li, Tao; Chen, Qianqian; Gao, Jiabing; Fan, Bingbing; Li, Jian; Li, Xinjian; Zhang, Rui; Sun, Jing; Gao, Lian

    2012-08-01

    The hierarchical photocatalysts of Ag/AgCl@plate-WO3 have been synthesized by anchoring Ag/AgCl nanocrystals on the surfaces of single-crystalline WO3 nanoplates that were obtained via an intercalation and topochemical approach. The heterogeneous precipitation process of the PVP-Ag+-WO3 suspensions with a Cl- solution added drop-wise was developed to synthesize AgCl@WO3 composites, which were then photoreduced to form Ag/AgCl@WO3 nanostructures in situ. WO3 nanocrystals with various shapes (i.e., nanoplates, nanorods, and nanoparticles) were used as the substrates to synthesize Ag/AgCl@WO3 photocatalysts, and the effects of the WO3 contents and photoreduction times on their visible-light-driven photocatalytic performance were investigated. The techniques of TEM, SEM, XPS, EDS, XRD, N2 adsorption-desorption and UV-vis DR spectra were used to characterize the compositions, phases and microstructures of the samples. The RhB aqueous solutions were used as the model system to estimate the photocatalytic performance of the as-obtained Ag/AgCl@WO3 nanostructures under visible light (λ >= 420 nm) and sunlight. The results indicated that the hierarchical Ag/AgCl@plate-WO3 photocatalyst has a higher photodegradation rate than Ag/AgCl, AgCl, AgCl@WO3 and TiO2 (P25). The contents and morphologies of the WO3 substrates in the Ag/AgCl@plate-WO3 photocatalysts have important effects on their photocatalytic performance. The related mechanisms for the enhancement in visible-light-driven photodegradation of RhB molecules were analyzed.The hierarchical photocatalysts of Ag/AgCl@plate-WO3 have been synthesized by anchoring Ag/AgCl nanocrystals on the surfaces of single-crystalline WO3 nanoplates that were obtained via an intercalation and topochemical approach. The heterogeneous precipitation process of the PVP-Ag+-WO3 suspensions with a Cl- solution added drop-wise was developed to synthesize AgCl@WO3 composites, which were then photoreduced to form Ag/AgCl@WO3 nanostructures in

  18. US Coast Guard differential GPS network

    SciTech Connect

    Alsip, D.H.; Butler, J.M.; Radice, J.T.

    1993-03-01

    In order to aid navigation and to prevent disasters such as oil spills, collisions, and wrecks of vessels and aircraft, the US Coast Guard is charged with establishing, maintaining, and operating electronic aids to navigation. In a technological advance developed and operated by the Department of Defense, the global positioning system (GPS) provides all-weather global coverage, 24 hours/day at unprecedented accuracies. GPS provides standard positioning service (SPS) and precise positioning service (PPS). By applying differential techniques to GPS, navigational accuracies of better than 10 meters can be achieved. For the first time, an all-weather system is possible to meet all the marine navigator's needs including harbor and harbor approach navigation. This should revolutionize navigation safety and efficiency, surveying operations, search and rescue operations, and underwater mine disposal efficiency and safety.

  19. International GPS Service 2001 - 2002 Technical Reports

    NASA Technical Reports Server (NTRS)

    Gowey, Ken (Editor); Neilan, Ruth (Editor); Moore, Angelyn (Editor)

    2004-01-01

    Applications of the Global Positioning System (GPS) to Earth Science are numerous. The International GPS Service (IGS), a federation of government agencies and universities, plays an increasingly critical role in support of GPS-related research and engineering activities. Contributions from the IGS Governing Board and Central Bureau, analysis and data centers, station operators, and others constitute the 2001 / 2002 Technical Reports. Hard copies of each volume can be obtained by contacting the IGS Central Bureau at the Jet Propulsion Laboratory. This report is published in black and white. To view graphs or plots that use color to represent data trends or information, please refer to the online PDF version at http://igscb.jpl.nasa.gov/overview/pubs.html.

  20. Testing Rtk GPS System In Urban Areas

    NASA Astrophysics Data System (ADS)

    Pirti, A.; Ata, E.

    RTK GPS is provided with cm accuracy and real time surveying system. For providing this conditions, the reference is necessary for high accuracy position. Because this sta- tion is transmitted the corrections to the other receivers. At the some time this system is required common satellites on the receiver to compute integer ambiguity solution. In addition to the conditions, the data transmission device's range is very important. Although RTK GPS technique has a lot of advantages, many problems meet in prac- tice. One of the most important problem in RTK system, which is very useful and reliable in the rural areas, uses in the urban areas. We search this article, how influence RTK GPS applications on satellite numbers, multipath, data transmission device's range capability and etc. in the urban areas.

  1. GPS common-view time transfer

    NASA Technical Reports Server (NTRS)

    Lewandowski, W.

    1994-01-01

    The introduction of the GPS common-view method at the beginning of the 1980's led to an immediate and dramatic improvement of international time comparisons. Since then, further progress brought the precision and accuracy of GPS common-view intercontinental time transfer from tens of nanoseconds to a few nanoseconds, even with SA activated. This achievement was made possible by the use of the following: ultra-precise ground antenna coordinates, post-processed precise ephemerides, double-frequency measurements of ionosphere, and appropriate international coordination and standardization. This paper reviews developments and applications of the GPS common-view method during the last decade and comments on possible future improvements whose objective is to attain sub-nanosecond uncertainty.

  2. Airborne gravimetry, altimetry, and GPS navigation errors

    NASA Technical Reports Server (NTRS)

    Colombo, Oscar L.

    1992-01-01

    Proper interpretation of airborne gravimetry and altimetry requires good knowledge of aircraft trajectory. Recent advances in precise navigation with differential GPS have made it possible to measure gravity from the air with accuracies of a few milligals, and to obtain altimeter profiles of terrain or sea surface correct to one decimeter. These developments are opening otherwise inaccessible regions to detailed geophysical mapping. Navigation with GPS presents some problems that grow worse with increasing distance from a fixed receiver: the effect of errors in tropospheric refraction correction, GPS ephemerides, and the coordinates of the fixed receivers. Ionospheric refraction and orbit error complicate ambiguity resolution. Optimal navigation should treat all error sources as unknowns, together with the instantaneous vehicle position. To do so, fast and reliable numerical techniques are needed: efficient and stable Kalman filter-smoother algorithms, together with data compression and, sometimes, the use of simplified dynamics.

  3. An optimal GPS data processing technique

    NASA Technical Reports Server (NTRS)

    Wu, S. C.; Melbourne, W. G.

    1992-01-01

    A formula is derived to optimally combine dual-frequency GPS (Global Positioning System) pseudorange and carrier phase data streams into a single equivalent data stream, reducing the data volume and computing time in the filtering process for parameter estimation by a factor of four. The resulting single data stream is that of carrier phase measurements with both data noise and bias uncertainty strictly defined. With this analytical formula the single stream of equivalent GPS measurements can be efficiently formed by simple numerical calculations without any degradation in data strength. The formulation for the optimally combined GPS data and their covariances are given in closed form. Carrier phase ambiguity resolution, when feasible, is improved due to the preservation of the full data strength with the optimal data combining process.

  4. TOPEX/POSEIDON GPS Demonstration Experiment Data

    NASA Technical Reports Server (NTRS)

    Guinn, J. R.; Jee, J.; Lindqwister, U.; Starr, D.

    1993-01-01

    Global Positioning Satellite (GPS) measurements obtained from the on-board TOPEX/POSEIDON demonstration flight receiver and a global network of ground receivers are available from the GPS Data Handling Facility (GDHF) archive. Ground receiver observations are derived from a six station subset of the GPS global tracking network. The six TOPEX ground stations yielded 95 percent of the expected data during the six month demonstration phase from November, 1992 to April, 1993. For the same period, 98 percent of the available P-code tracking from the TOPEX flight receiver was obtained. Raw carrier phase and P-code pseudorange measurements are provided for the ground and flight receivers along with an additional file of calibrated and compressed flight receiver data...

  5. Global periodic effects of GPS time series

    NASA Astrophysics Data System (ADS)

    Poutanen, M.; Jokela, J.; Bilker, M.; Ollikainen, M.; Koivula, H.

    2003-04-01

    We have analysed time series of permanent GPS stations of the IGS network. Data used are the daily station coordinates of the IGS official solutions. Lomb periodograms show in most cases a statistically significant annual period in station height, which can be addressed to the periodic vertical motion of the site. We determined the amplitude and phase of the variation, and confirmed the phase shift between the Northern and Southern hemisphere. A similar behaviour can be seen in DORIS time series. In a regional network, the Finnish permanent GPS network, FinnRef, we have discovered an annual scale variation which can be explained as a loading effect of the crust. For the global network, a similar analysis will be made. We discuss on the geophysical reasons of the annual periods, and their consequences on the high-precision GPS observations. Additonal constraints, e.g. time series from a superconducting gravimeter are also discussed.

  6. Differential GPS for air transport: Status

    NASA Technical Reports Server (NTRS)

    Hueschen, Richard M.

    1993-01-01

    The presentation presents background on what the Global Navigation Satellite System (GNSS) is, desired target dates for initial GNSS capabilities for aircraft operations, and a description of differential GPS (Global Positioning System). The presentation also presents an overview of joint flight tests conducted by LaRC and Honeywell on an integrated differential GPS/inertial reference unit (IRU) navigation system. The overview describes the system tested and the results of the flight tests. The last item presented is an overview of a current grant with Ohio University from LaRC which has the goal of developing a precision DGPS navigation system based on interferometry techniques. The fundamentals of GPS interferometry are presented and its application to determine attitude and heading and precision positioning are shown. The presentation concludes with the current status of the grant.

  7. Giant Born effective charges in cubic WO_3.

    NASA Astrophysics Data System (ADS)

    Detraux, Francois; Ghosez, Philippe; Gonze, Xavier

    1997-03-01

    WO3 crystallizes in many different phases. It is also sometimes considered in a reference idealized simple cubic structure (defect-perovskite) where the tungsten is at the center of the cell and the oxygens at the middle of each face. Using a variational formulation of the density functional perturbation theory and a planewave-pseudopotential approach, we compute the Born effective charges for this idealized cubic structure, with an optimized lattice parameter of 3.73 ÅThe values obtained are anomalously large with respect to the nominal ionic charge (+6 on W and -2 on O). For the tungsten atom, the effective charge tensor is isotropic and Z_W= +12.43. For the oxygen, we must consider two different elements corresponding respectively to a displacement of the atom parallel or perpendicular to the W-O bond: Z^*O allel= -9.07 and Z^*O ⊥= -1.66. The giant anomalous contributions to Z^*W and Z^*O allel can be explained by transfer of charge produced by dynamic changes of hybridization between the O-2p and W-5d orbitals.

  8. Luminescence in trilanthanumtrichlorotungstate (La 3WO 6Cl 3)

    NASA Astrophysics Data System (ADS)

    Blasse, G.; Dirksen, G. J.; Brixner, L. H.

    1983-03-01

    The luminescence properties of La 3WO 6Cl 3 are reported and discussed. The tungstate group occurs as a trigonal prismatic WO 6-6 complex. The blue luminescence is, for the greater part, quenched at room temperature. No energy migration occurs in this lattice. The decay times are discussed in terms of a simple molecular-orbital (MO) scheme. The luminescence of the following activating ions was studied: Mo 6+, Bi 3+, Eu 3+, Sm 3+, Ce 3+, and Tb 3+. The molybdate group produces a red emission with low efficiency. The Bi 3+ ion induces a narrow band emission with small Stokes shift. This is interpreted using a Bi 3+O 2-W 6+ charge-transfer state. Except for Ce 3+, the rare earth activators show luminescence, but the total transfer efficiency from tungstate to the rare-earth ions is low. This is not due to the one-step tungstate-rare-earth transfer (which is efficient), but to the localized nature of the tungstate excitation. The Eu 3+ charge-transfer band is at very low energies.

  9. Combustion synthesis and characterization of nanocrystalline WO3.

    PubMed

    Morales, Walter; Cason, Michael; Aina, Olawunmi; de Tacconi, Norma R; Rajeshwar, Krishnan

    2008-05-21

    The energy payback time associated with the semiconductor active material is an important parameter in a photovoltaic solar cell device. Thus lowering the energy requirements for the semiconductor synthesis step or making it more energy-efficient is critical toward making the overall device economics more competitive relative to other nonpolluting energy options. In this communication, combustion synthesis is demonstrated to be a versatile and energy-efficient method for preparing inorganic oxide semiconductors such as tungsten trioxide (WO3) for photovoltaic or photocatalytic solar energy conversion. The energy efficiency of combustion synthesis accrues from the fact that high process temperatures are self-sustained by the exothermicity of the combustion process, and the only external thermal energy input needed is for dehydration of the fuel/oxidizer precursor mixture and bringing it to ignition. Importantly, we show that, in this approach, it is also possible to tune the optical characteristics of the oxide semiconductor (i.e., shift its response toward the visible range of the electromagnetic spectrum) in situ by doping the host semiconductor during the formative stage itself. As a bonus, the resultant material shows enhanced surface properties such as markedly improved organic dye uptake relative to benchmark samples obtained from commercial sources. Finally, this synthesis approach requires only very simple equipment, a feature that it shares with other "mild" inorganic semiconductor synthesis routes such as sol-gel chemistry, chemical bath deposition, and electrodeposition. The present study constitutes the first use of combustion synthesis for preparing WO3 powder comprising nanosized particles.

  10. Pickering w/o emulsions: drug release and topical delivery.

    PubMed

    Frelichowska, Justyna; Bolzinger, Marie-Alexandrine; Valour, Jean-Pierre; Mouaziz, Hanna; Pelletier, Jocelyne; Chevalier, Yves

    2009-02-23

    The skin absorption from Pickering emulsions as a new dosage form was investigated for the first time. Pickering emulsions are stabilized by adsorbed solid particles instead of emulsifier molecules. They are promising dosage forms that significantly differ from classical emulsions within several features. The skin permeation of a hydrophilic model penetrant (caffeine) was investigated from a w/o Pickering emulsion and compared to a w/o classical emulsion stabilized with an emulsifier. Both emulsions had the same composition and physicochemical properties in order to focus on the effect of the interfacial layer on the drug release and skin absorption processes. The highest permeation rates were obtained from the Pickering emulsion with a pseudo-steady state flux of 25 microg cm(-2)h(-1), threefold higher than from a classical emulsion (9.7 microg cm(-2)h(-1)). After 24h exposure, caffeine was mostly in the receptor fluid and in the dermis; cumulated amounts of caffeine were higher for the Pickering emulsion. Several physicochemical phenomena were investigated for clearing up the mechanisms of enhanced permeation from the Pickering emulsion. Among them, higher adhesion of Pickering emulsion droplets to skin surface was disclosed. The transport of caffeine adsorbed on silica particles was also considered relevant since skin stripping showed that aggregates of silica particles entered deeply the stratum corneum.

  11. GPS-SNO: Computational Prediction of Protein S-Nitrosylation Sites with a Modified GPS Algorithm

    PubMed Central

    Xue, Yu; Liu, Zexian; Gao, Xinjiao; Jin, Changjiang; Wen, Longping; Yao, Xuebiao; Ren, Jian

    2010-01-01

    As one of the most important and ubiquitous post-translational modifications (PTMs) of proteins, S-nitrosylation plays important roles in a variety of biological processes, including the regulation of cellular dynamics and plasticity. Identification of S-nitrosylated substrates with their exact sites is crucial for understanding the molecular mechanisms of S-nitrosylation. In contrast with labor-intensive and time-consuming experimental approaches, prediction of S-nitrosylation sites using computational methods could provide convenience and increased speed. In this work, we developed a novel software of GPS-SNO 1.0 for the prediction of S-nitrosylation sites. We greatly improved our previously developed algorithm and released the GPS 3.0 algorithm for GPS-SNO. By comparison, the prediction performance of GPS 3.0 algorithm was better than other methods, with an accuracy of 75.80%, a sensitivity of 53.57% and a specificity of 80.14%. As an application of GPS-SNO 1.0, we predicted putative S-nitrosylation sites for hundreds of potentially S-nitrosylated substrates for which the exact S-nitrosylation sites had not been experimentally determined. In this regard, GPS-SNO 1.0 should prove to be a useful tool for experimentalists. The online service and local packages of GPS-SNO were implemented in JAVA and are freely available at: http://sno.biocuckoo.org/. PMID:20585580

  12. GPS-SNO: computational prediction of protein S-nitrosylation sites with a modified GPS algorithm.

    PubMed

    Xue, Yu; Liu, Zexian; Gao, Xinjiao; Jin, Changjiang; Wen, Longping; Yao, Xuebiao; Ren, Jian

    2010-06-24

    As one of the most important and ubiquitous post-translational modifications (PTMs) of proteins, S-nitrosylation plays important roles in a variety of biological processes, including the regulation of cellular dynamics and plasticity. Identification of S-nitrosylated substrates with their exact sites is crucial for understanding the molecular mechanisms of S-nitrosylation. In contrast with labor-intensive and time-consuming experimental approaches, prediction of S-nitrosylation sites using computational methods could provide convenience and increased speed. In this work, we developed a novel software of GPS-SNO 1.0 for the prediction of S-nitrosylation sites. We greatly improved our previously developed algorithm and released the GPS 3.0 algorithm for GPS-SNO. By comparison, the prediction performance of GPS 3.0 algorithm was better than other methods, with an accuracy of 75.80%, a sensitivity of 53.57% and a specificity of 80.14%. As an application of GPS-SNO 1.0, we predicted putative S-nitrosylation sites for hundreds of potentially S-nitrosylated substrates for which the exact S-nitrosylation sites had not been experimentally determined. In this regard, GPS-SNO 1.0 should prove to be a useful tool for experimentalists. The online service and local packages of GPS-SNO were implemented in JAVA and are freely available at: http://sno.biocuckoo.org/.

  13. A GPS Receiver for Lunar Missions

    NASA Technical Reports Server (NTRS)

    Bamford, William A.; Heckler, Gregory W.; Holt, Greg N.; Moreau, Michael C.

    2008-01-01

    Beginning with the launch of the Lunar Reconnaissance Orbiter (LRO) in October of 2008, NASA will once again begin its quest to land humans on the Moon. This effort will require the development of new spacecraft which will safely transport people from the Earth to the Moon and back again, as well as robotic probes tagged with science, re-supply, and communication duties. In addition to the next-generation spacecraft currently under construction, including the Orion capsule, NASA is also investigating and developing cutting edge navigation sensors which will allow for autonomous state estimation in low Earth orbit (LEO) and cislunar space. Such instruments could provide an extra layer of redundancy in avionics systems and reduce the reliance on support and on the Deep Space Network (DSN). One such sensor is the weak-signal Global Positioning System (GPS) receiver "Navigator" being developed at NASA's Goddard Space Flight Center (GSFC). At the heart of the Navigator is a Field Programmable Gate Array (FPGA) based acquisition engine. This engine allows for the rapid acquisition/reacquisition of strong GPS signals, enabling the receiver to quickly recover from outages due to blocked satellites or atmospheric entry. Additionally, the acquisition algorithm provides significantly lower sensitivities than a conventional space-based GPS receiver, permitting it to acquire satellites well above the GPS constellation. This paper assesses the performance of the Navigator receiver based upon three of the major flight regimes of a manned lunar mission: Earth ascent, cislunar navigation, and entry. Representative trajectories for each of these segments were provided by NASA. The Navigator receiver was connected to a Spirent GPS signal generator, to allow for the collection of real-time, hardware-in-the-loop results for each phase of the flight. For each of the flight segments, the Navigator was tested on its ability to acquire and track GPS satellites under the dynamical

  14. Single-Receiver GPS Phase Bias Resolution

    NASA Technical Reports Server (NTRS)

    Bertiger, William I.; Haines, Bruce J.; Weiss, Jan P.; Harvey, Nathaniel E.

    2010-01-01

    Existing software has been modified to yield the benefits of integer fixed double-differenced GPS-phased ambiguities when processing data from a single GPS receiver with no access to any other GPS receiver data. When the double-differenced combination of phase biases can be fixed reliably, a significant improvement in solution accuracy is obtained. This innovation uses a large global set of GPS receivers (40 to 80 receivers) to solve for the GPS satellite orbits and clocks (along with any other parameters). In this process, integer ambiguities are fixed and information on the ambiguity constraints is saved. For each GPS transmitter/receiver pair, the process saves the arc start and stop times, the wide-lane average value for the arc, the standard deviation of the wide lane, and the dual-frequency phase bias after bias fixing for the arc. The second step of the process uses the orbit and clock information, the bias information from the global solution, and only data from the single receiver to resolve double-differenced phase combinations. It is called "resolved" instead of "fixed" because constraints are introduced into the problem with a finite data weight to better account for possible errors. A receiver in orbit has much shorter continuous passes of data than a receiver fixed to the Earth. The method has parameters to account for this. In particular, differences in drifting wide-lane values must be handled differently. The first step of the process is automated, using two JPL software sets, Longarc and Gipsy-Oasis. The resulting orbit/clock and bias information files are posted on anonymous ftp for use by any licensed Gipsy-Oasis user. The second step is implemented in the Gipsy-Oasis executable, gd2p.pl, which automates the entire process, including fetching the information from anonymous ftp

  15. Guidance accuracy considerations for realtime GPS interferometry

    NASA Technical Reports Server (NTRS)

    Braasch, Michael S.; Van Graas, Frank

    1991-01-01

    During April and May of 1991, the Avionics Engineering Center at Ohio University completed the first set of realtime flight tests of a GPS interferometric attitude and heading determination system. This technique has myriad applications for aircraft and spacecraft guidance and control. However, before these applications can be further developed, a number of guidance accuracy issues must be considered. Among these are: signal derogation due to multipath and shadowing, effects of structural flexures, and system robustness during loss of phase lock. This paper addresses these issues with special emphasis on the information content of the GPS signal, and characterization and mitigation of multipath encountered while in flight.

  16. GPS synchronized power system phase angle measurements

    NASA Astrophysics Data System (ADS)

    Wilson, Robert E.; Sterlina, Patrick S.

    1994-09-01

    This paper discusses the use of Global Positioning System (GPS) synchronized equipment for the measurement and analysis of key power system quantities. Two GPS synchronized phasor measurement units (PMU) were installed before testing. It was indicated that PMUs recorded the dynamic response of the power system phase angles when the northern California power grid was excited by the artificial short circuits. Power system planning engineers perform detailed computer generated simulations of the dynamic response of the power system to naturally occurring short circuits. The computer simulations use models of transmission lines, transformers, circuit breakers, and other high voltage components. This work will compare computer simulations of the same event with field measurement.

  17. Dual RF Astrodynamic GPS Orbital Navigator Satellite

    NASA Technical Reports Server (NTRS)

    Kanipe, David B.; Provence, Robert Steve; Straube, Timothy M.; Reed, Helen; Bishop, Robert; Lightsey, Glenn

    2009-01-01

    Dual RF Astrodynamic GPS Orbital Navigator Satellite (DRAGONSat) will demonstrate autonomous rendezvous and docking (ARD) in low Earth orbit (LEO) and gather flight data with a global positioning system (GPS) receiver strictly designed for space applications. ARD is the capability of two independent spacecraft to rendezvous in orbit and dock without crew intervention. DRAGONSat consists of two picosatellites (one built by the University of Texas and one built by Texas A and M University) and the Space Shuttle Payload Launcher (SSPL); this project will ultimately demonstrate ARD in LEO.

  18. Capturing Depolarization Information in GPS Reflections

    NASA Technical Reports Server (NTRS)

    Kelly, Kenneth C.

    2000-01-01

    The state of the surface of the ocean has a prominent effect on the depolarization of the circularly polarized emissions of the GPS satellites. The system designers election to capture the important information carries with it the need to implement the data extraction in a cost efficient manner. Antenna components, and associated networks for deriving depolarization information are described. For typical sea states the polarization characteristics of the reflected GPS signal vary rapidly with time so various methods for recording the changes are discussed.

  19. Volcano deformation and subdaily GPS products

    NASA Astrophysics Data System (ADS)

    Grapenthin, Ronni

    Volcanic unrest is often accompanied by hours to months of deformation of the ground that is measurable with high-precision GPS. Although GPS receivers are capable of near continuous operation, positions are generally estimated for daily intervals, which I use to infer characteristics of a volcano’s plumbing system. However, GPS based volcano geodesy will not be useful in early warning scenarios unless positions are estimated at high rates and in real time. Visualization and analysis of dynamic and static deformation during the 2011 Tohokuoki earthquake in Japan motivates the application of high-rate GPS from a GPS seismology perspective. I give examples of dynamic seismic signals and their evolution to the final static offset in 30 s and 1 s intervals, which demonstrates the enhancement of subtle rupture dynamics through increased temporal resolution. This stresses the importance of processing data at recording intervals to minimize signal loss. Deformation during the 2009 eruption of Redoubt Volcano, Alaska, suggested net deflation by 0.05 km³ in three distinct phases. Mid-crustal aseismic precursory inflation began in May 2008 and was detected by a single continuous GPS station about 28 km NE of Redoubt. Deflation during the explosive and effusive phases was sourced from a vertical ellipsoidal reservoir at about 7-11.5 km. From this I infer a model for the temporal evolution of a complex plumbing system of at least 2 sources during the eruption. Using subdaily GPS positioning solutions I demonstrate that plumes can be detected and localized by utilizing information on phase residuals. The GPS network at Bezymianny Volcano, Kamchatka, records network wide subsidence at rapid rates between 8 and 12 mm/yr from 2005-2010. I hypothesize this to be caused by continuous deflation of a ˜30 km deep sill under Kluchevskoy Volcano. Interestingly, 1-2 explosive events per year cause little to no deformation at any site other than the summit site closest to the vent. I

  20. Enhanced photocatalytic activity of cadmium-doped Bi2WO6 nanoparticles under simulated solar light

    NASA Astrophysics Data System (ADS)

    Song, Xu Chun; Li, Wen Ting; Huang, Wan Zhen; Zhou, Huan; Yin, Hao Yong; Zheng, Yi Fan

    2015-03-01

    Novel cadmium-doped Bi2WO6 nanoparticles with different Cd contents have been synthesized by a one-step route using ethylene glycol and water as solvents at 180 °C for 12 h. The as-synthesized samples were characterized in detailed by SEM, XRD, EDS, HRTEM, UV-Vis DRS, BET techniques, and so on. The results shown that with the increase of the Cd2+ addition, the crystal structure, lattice space, and absorption edge were not significantly changed and the calculated band gap value was 2.58 eV. However, the flower-like Bi2WO6 sphere was gradually destroyed. Simultaneously, the surface area and photocurrent responses of the catalysts were greatly increased. Photocatalytic activity of the Cd-doped Bi2WO6 samples was determined by monitoring the change of RhB concentration under simulated solar light. The results revealed that cadmium doping greatly improved the photocatalytic efficiency of Bi2WO6. The Bi2WO6 sample with R Cd = 0.05 displayed the highest photocatalytic activity, and the degradation rate is about two times greater than pure Bi2WO6. Moreover, the Cd-Bi2WO6 photocatalyst remained stable even after five consecutive cycles. A possible mechanism of photocatalytic activity enhancement on basis of the experimental results was proposed.

  1. Structural and gasochromic properties of WO3 films prepared by reactive sputtering deposition

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.; Hakoda, T.; Miyashita, A.; Yoshikawa, M.

    2015-02-01

    The effects of deposition temperature and film thickness on the structural and gasochromic properties of tungsten trioxide (WO3) films used for the optical detection of diluted cyclohexane gas have been investigated. The WO3 films were prepared on SiO2 substrates by magnetron sputtering, with the deposition temperature ranging from 300 to 550 °C in an Ar and O2 gas mixture. The films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and Rutherford backscattering spectroscopy (RBS). The gasochromic properties of the WO3 films, coated with a catalytic Pt layer, were examined by exposing them to up to 5% cyclohexane in N2 gas. It was found that (001)-oriented monoclinic WO3 films, with a columnar structure, grew at deposition temperatures between 400 and 450 °C. Furthermore, (010)-oriented WO3 films were preferably formed at deposition temperatures higher than 500 °C. The gasochromic characterization of the Pt/WO3 films revealed that (001)-oriented WO3 films, with cauliflower-like surface morphology, were appropriate for the optical detection of cyclohexane gas.

  2. Material and sensing properties of Pd-deposited WO3 thin films.

    PubMed

    Choi, Gwangpyo; Jin, Guanghu; Park, Si-Hyun; Lee, Woonyoung; Park, Jinseong

    2007-11-01

    The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.

  3. Ultrahigh-efficiency photocatalysts based on mesoporous Pt-WO3 nanohybrids.

    PubMed

    Wen, Zhenhai; Wu, Wei; Liu, Zhuang; Zhang, Hao; Li, Jinghong; Chen, Junhong

    2013-05-14

    A reliable nanocasting method has been developed to synthesize mesoporous hybrids of platinum (Pt) nanoparticles decorating tungsten trioxide (WO3). The process began with modification of the SBA-15 template with carbon polymers and Pt nanoparticles accompanied by adsorption of W(6+), which was then converted into m-Pt-WO3 composites by heat treatment and subsequent template removal. The synthetic strategy can be easily extended to prepare other mesoporous nanohybrids with metal oxide loaded precious metal composites. Comprehensive characterizations suggest that the as-developed m-Pt-WO3 nanohybrid exhibits unique properties with mesoporous structure, excellent crystalline structure, and high surface area. When the photocatalytic properties of m-Pt-WO3 nanohybrids were systematically investigated, it was revealed that the m-Pt-WO3 nanohybrids showed great promise for degrading the organic dye under visible light irradiation, which shows an excellent photocatalytic activity that far exceeded those of pure phase mesoporous WO3 and commercial TiO2 (P25), and was 10-fold more active than that of the bulk Pt-WO3 catalyst. The as-developed synthetic route opens up a new avenue for designing mesoporous hybrid materials for various applications benefiting from the unique porous structure, high surface area, and synergistic effects among constituents.

  4. Superconducting phase diagram of InxWO3 synthesized by indium deintercalation

    NASA Astrophysics Data System (ADS)

    Bocarsly, Joshua D.; Hirai, Daigorou; Ali, M. N.; Cava, R. J.

    2013-07-01

    We report the superconducting phase diagram of the hexagonal tungsten bronze (HTB) InxWO3. The InxWO3 samples were prepared by indium deintercalation of the thermodynamically stable parent phase In0.33WO3. By employing this technique, a lowest indium content in the HTB phase of x \\sim 0.07 was achieved, which cannot be obtained by conventional solid-state reaction. In addition, accurately and reproducibly controlled indium content and homogeneous samples enable us to perform a systematic study of the physical properties of InxWO3. Most of the InxWO3 samples exhibit a superconducting transition and the highest transition temperature T_{\\text{c}} = 4.2\\text{K} in InxWO3 was observed at x= 0.11 . The indium content dependence of T_{\\text{c}}(x) shows remarkable similarities to other MxWO3 (M=\\text{K} and Rb) HTBs. Our results reveal the universality of physical properties in the HTB family and give a strategy to achieve higher T_{\\text{c}} in HTBs.

  5. Preparation, structures and photoluminescent enhancement of CdWO 4-TiO 2 composite nanofilms

    NASA Astrophysics Data System (ADS)

    Jia, Runping; Zhang, Guoxin; Wu, Qingsheng; Ding, Yaping

    2006-12-01

    For the first time, Cadmium tungstate (CdWO4)-TiO2 composite nanofilms on a glass substrate were prepared by means of the dip-coating technique, in which collodion was used as a dispersant and film-forming agent. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo gravimetric and thermal analyses (TG/DTA), FTIR and photoluminescence (PL) methods, respectively. SEM and XRD characterization of these films indicated that CdWO4 particles crystallized in a monoclinic wolframite-type structure whereas TiO2 particles were Anatase phase; and both of them were well distributed in the nanofilms. FTIR spectra proved the presence of CdWO4 on the nanofilms. Photoluminescent results showed that the emitting peak of CdWO4 films blue shifted slightly relative to that of CdWO4 crystal. Moreover, the PL intensity of CdWO4-TiO2 composite nanofilm was much higher than that of CdWO4 nanofilm. We ascribed that the introduction of TiO2 should be responsible for the PL enhancement.

  6. Dual preparation of hydrophobic and hydrophilic BaWO{sub 4}:Eu phosphors

    SciTech Connect

    Cho, Young-Sik; Huh, Young-Duk

    2016-06-15

    Highlights: • Red-emitting BaWO{sub 4}:Eu phosphors were prepared in hexane-water bilayer system. • The hydrophobic nanometer-sized BaWO{sub 4}:Eu phosphors were obtained in hexane. • The hydrophilic micrometer-sized BaWO{sub 4}:Eu dendrites were obtained in water. - Abstract: BaWO{sub 4}:Eu phosphors were prepared by performing a solvothermal reaction in a water–hexane bilayer system. A barium oleate (and europium oleate) complex was obtained in hexane via a phase transfer reaction involving Ba{sup 2+} (and Eu{sup 3+}) ions in an aqueous solution of sodium oleate. The outer surfaces of the nanometer-sized BaWO{sub 4}:Eu phosphors were capped by the long alkyl chain of oleate; therefore, the hydrophobic nanometer-sized BaWO{sub 4}:Eu phosphors preferentially dissolved in the hexane layer. The micrometer-sized BaWO{sub 4}:Eu phosphors were obtained in the water layer. The BaWO{sub 4}:Eu phosphors prepared in hexane and water yielded sharp strong absorption and emission peaks at 464 and 615 nm, respectively, due to the {sup 7}F{sub 0} → {sup 5}D{sub 2} and the {sup 5}D{sub 0} →{sup 7} F{sub 2} transitions of the Eu{sup 3+} ions. The BaWO{sub 4}:Eu phosphors are good candidate red-emitting phosphors for use in InGaN blue-emitting diodes, which have an emission wavelength of 465 nm.

  7. WO3 nanorolls self-assembled as thin films by hydrothermal synthesis

    NASA Astrophysics Data System (ADS)

    Vankova, S.; Zanarini, S.; Amici, J.; Cámara, F.; Arletti, R.; Bodoardo, S.; Penazzi, N.

    2015-04-01

    We report a novel type of WO3 nanostructure, i.e. nanorolls obtained as a self-assembled thin film on a transparent conductive substrate. The mild conditions of preparation, avoiding the use of HCl, result in an eco-friendly hydrothermal method with reduced crystallization time. FESEM and HR-TEM show that WO3 nanocrystals are made of rolled nanoflakes with a telescope-like appearance at their tip. For their nano-porosity, electrochemical accessibility, good adhesion to substrates and the envisaged presence of nanocavities between the WO3 layers, these materials hold tremendous promise in nano-electronics, electrochromic devices, water photo-splitting cells, Li-ion batteries and nano-templated filters for UV radiation.We report a novel type of WO3 nanostructure, i.e. nanorolls obtained as a self-assembled thin film on a transparent conductive substrate. The mild conditions of preparation, avoiding the use of HCl, result in an eco-friendly hydrothermal method with reduced crystallization time. FESEM and HR-TEM show that WO3 nanocrystals are made of rolled nanoflakes with a telescope-like appearance at their tip. For their nano-porosity, electrochemical accessibility, good adhesion to substrates and the envisaged presence of nanocavities between the WO3 layers, these materials hold tremendous promise in nano-electronics, electrochromic devices, water photo-splitting cells, Li-ion batteries and nano-templated filters for UV radiation. Electronic supplementary information (ESI) available: Characterization techniques; additional FESEM micrographs; typical XRD pattern of WO3 nanoroll thin film; typical Nyquist plots at ambient temperature; indicative diameter and length of WO3 NR by varying the PVA chain length; effect of 2000 cycles of electrochemical switching on the STB, STC and ΔT% coloration efficiency of the WO3 NR. See DOI: 10.1039/c4nr07290a

  8. A research on SLAM aided INS/GPS navigation system

    NASA Astrophysics Data System (ADS)

    Cao, Menglong; Cui, Pingyuan

    2007-11-01

    Simultaneous Localization and Mapping (SLAM) aided INS/GPS navigation system is a landmark based terrain aided autonomous integrated system that has the capability for online map building and simultaneously utilizing the generated map to bind the errors in the Inertial Navigation System (INS) when GPS is not available. If GPS information is available, the SLAM integrated system builds a landmark-based map using an INS/GPS solution. If GPS is not available, the previously newly generated map is used to constrain the INS errors. The SLAM augmented INS/GPS system shows two capabilities of landmark tracking and mapping using GPS information and more importantly, aiding the INS under GPS denied situation. The validity of the proposed method is demonstrated by computer simulation.

  9. Enhanced field-emission from SnO2:WO(2.72) nanowire heterostructures.

    PubMed

    Shinde, Deodatta R; Chavan, Padmakar G; Sen, Shashwati; Joag, Dilip S; More, Mahendra A; Gadkari, S C; Gupta, S K

    2011-12-01

    The field-emission properties of SnO(2):WO(2.72) hierarchical nanowire heterostructure have been investigated. Nanoheterostructure consisting of SnO(2) nanowires as stem and WO(2.72) nanothorns as branches are synthesized in two steps by physical vapor deposition technique. Their field emission properties were recorded. A low turn-on field of ~0.82 V/μm (to draw an emission current density ~10 μA/cm(2)) is achieved along with stable emission for 4 h duration. The emission characteristic shows the SnO(2):WO(2.72) nanoheterostructures are extremely suitable for field-emission applications.

  10. CTAB-assisted ultrasonic synthesis, characterization and photocatalytic properties of WO{sub 3}

    SciTech Connect

    Sánchez-Martínez, D. Gomez-Solis, C.; Torres-Martinez, Leticia M.

    2015-01-15

    Highlights: • WO{sub 3} 2D nanostructures were synthesized by ultrasound method assisted with CTAB. • WO{sub 3} morphology was mainly of rectangular nanoplates with a thickness of ∼50 nm. • The highest surface area value of WO{sub 3} was obtained to lowest concentration of CTAB. • WO{sub 3} activity was attributed to morphology, surface area and the addition of CTAB. • WO{sub 3} nanoplates were able to causing almost complete mineralization of rhB and IC. - Abstract: WO{sub 3} 2D nanostructures have been prepared by ultrasound synthesis method assisted with CTAB using different molar ratios. The formation of monoclinic crystal structure of WO{sub 3} was confirmed by X-ray powder diffraction (XRD). The characterization of the WO{sub 3} samples was complemented by analysis of scanning electron microscopy (SEM), which revealed morphology mainly of rectangular nanoplates with a thickness of around 50 nm and length of 100–500 nm. Infrared spectroscopy (FT-IR) was used to confirm the elimination of the CTAB in the synthesized samples. The specific surface area was determinate by the BET method and by means of diffuse reflectance spectroscopy (DRS) it was determinate the band-gap energy (E{sub g}) of the WO{sub 3} samples. The photocatalytic activity of the WO{sub 3} oxide was evaluated in the degradation reactions of rhodamine B (rhB) and indigo carmine (IC) under Xenon lamp irradiation. The highest photocatalytic activity was observed in the samples containing low concentration of CTAB with morphology of rectangular nanoplates and with higher surface area value than commercial WO{sub 3}. Photodegradation of rhB and IC were followed by means of UV–vis absorption spectra. The mineralization degree of organic dyes by WO{sub 3} photocatalyst was determined by total organic carbon analysis (TOC) reaching percentages of mineralization of 92% for rhB and 50% for IC after 96 h of lamp irradiation.

  11. Nanostructured photoelectrodes based on WO3: applications to photooxidation of aqueous electrolytes.

    PubMed

    Bignozzi, Carlo Alberto; Caramori, Stefano; Cristino, Vito; Argazzi, Roberto; Meda, Laura; Tacca, Alessandra

    2013-03-21

    Some recent studies mainly addressing the preparation and the modification of nanostructured thin films based on WO(3) and their application to photoelectrolysis of aqueous electrolytes are reviewed with the aim of rationalizing the main factors at the basis of an efficient photoanodic response. WO(3) represents one of the few materials which can achieve efficient water photo-oxidation under visible illumination, stably operating under strongly oxidizing conditions; thus the discussion of the structure-related photoelectrochemical properties of WO(3) thin films and their optimization for achieving almost quantitative photon to electron conversion constitutes the core of this contribution.

  12. Scheelite (CaWO4)-type microphosphors: Facile synthesis, structural characterization and photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Han, Yuanyuan; Wang, Dan; Liang, Danyang; Wang, Shiqi; Lu, Guoxin; Wang, Xiaoyu; Pei, Nana

    2016-11-01

    Scheelite (CaWO4)-type microphosphors were synthesized by the precipitation method assisted with cetyltrimethyl ammonium bromide (CTAB). All compounds crystallized in the tetragonal structure with space group I41/a (No. 88). FE-SEM micrographs illustrate the spherical-like morphologies and rough surface. PL spectra indicate the broad emission peak maximum at 613 nm under UV excitation. Luminescence decay curves monitored by 5D 6 -7F 0 transition (λex = 394 nm) of Eu3+ in doped CaWO4 are presented, the curves exhibit a single-exponential feature and the lifetime for doped CaWO4 is 0.61 ms.

  13. Electrodeposition of WO3 nanoparticles into surface mounted metal-organic framework HKUST-1 thin films

    NASA Astrophysics Data System (ADS)

    Yoo, Hyeonseok; Welle, Alexander; Guo, Wei; Choi, Jinsub; Redel, Engelbert

    2017-03-01

    We describe a novel procedure to fabricate WO3@surface-mounted metal-organic framework (SURMOF) hybrid materials by electrodeposition of WO3 nanoparticles into HKUST-1, also termed Cu3(BTC)2 SURMOFs. These materials have been characterized using x-ray diffraction, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, x-ray photoelectron spectroscopy as well as linear sweep voltammetry. The WO3 semiconductor/SURMOF heterostructures were further tested as hybrid electrodes in their performance for hydrogen evolution reaction from water.

  14. High photocurrent conversion efficiency in self-organized porous WO{sub 3}

    SciTech Connect

    Berger, S.; Tsuchiya, H.; Ghicov, A.; Schmuki, P.

    2006-05-15

    Self-organized porous structures of WO{sub 3} were grown on tungsten by an anodic oxidation, and their photoelectrochemical properties were characterized. The porous WO{sub 3} layers show a regular morphology with average pore sizes of approximately 70 nm and a pore wall thickness of approximately 10 nm. As formed layers show an amorphous structure but the layers can be altered to a crystalline monoclinic structure by thermal annealing. The annealed porous WO{sub 3} layers show a very high specific photocurrent conversion efficiency.

  15. Electrodeposition of WO3 nanoparticles into surface mounted metal-organic framework HKUST-1 thin films.

    PubMed

    Yoo, Hyeonseok; Welle, Alexander; Guo, Wei; Choi, Jinsub; Redel, Engelbert

    2017-03-17

    We describe a novel procedure to fabricate WO3@surface-mounted metal-organic framework (SURMOF) hybrid materials by electrodeposition of WO3 nanoparticles into HKUST-1, also termed Cu3(BTC)2 SURMOFs. These materials have been characterized using x-ray diffraction, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, x-ray photoelectron spectroscopy as well as linear sweep voltammetry. The WO3 semiconductor/SURMOF heterostructures were further tested as hybrid electrodes in their performance for hydrogen evolution reaction from water.

  16. Metal-insulator transition in NaxWO3: Photoemission spectromicroscopy study

    NASA Astrophysics Data System (ADS)

    Paul, Sanhita; Ghosh, Anirudha; Raj, Satyabrata

    2014-04-01

    We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, NaxWO3 by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of NaxWO3 reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in NaxWO3.

  17. Fabrication and photocatalysis of mesoporous ZnWO{sub 4} with PAMAM as a template

    SciTech Connect

    Lin Shen Chen Jiebo; Weng Xiulan; Yang Liuyi; Chen Xinqin

    2009-05-06

    Mesoporous ZnWO{sub 4} was prepared with the template of PAMAM. The as-formed samples were characterized by X-ray diffraction (XRD), nitrogen absorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy (DRS). It is found that the size of pore is in the range of 5-22 nm and that the porosity of ZnWO{sub 4} is composed of aggregated ZnWO{sub 4} nanoparticles. The photocatalytic activities towards degradation of rhodamine B (RhB) and malachite green (MG) under UV light has been investigated. The formation mechanism of mesoporous structures is proposed.

  18. Synthesis of WC powder through microwave heating of WO3-C mixture

    NASA Astrophysics Data System (ADS)

    Behnami, Amir Karimzadeh; Hoseinpur, Arman; Sakaki, Masoud; Bafghi, Mohammad Sh.; Yanagisawa, Kazumichi

    2017-02-01

    A simple, easy, and low-cost process for the fabrication of tungsten carbide (WC) powder through microwave heating of WO3-C mixtures was developed. Thermodynamic calculations and experimental investigations were carried out for WO3-C and W-C systems, and a formation mechanism was proposed. In the results, for the synthesis of WC, the use of over stoichiometric amount of C together with a specially assembled experimental setup (which effectively retains heat in the system) is necessary. The WC powder is successfully obtained by heating WO3:5C mixture for 900 s in a domestic microwave oven.

  19. Fine tuning GPS clock estimation in the MCS

    NASA Technical Reports Server (NTRS)

    Hutsell, Steven T.

    1995-01-01

    With the completion of a 24 operational satellite constellation, GPS is fast approaching the critical milestone, Full Operational Capability (FOC). Although GPS is well capable of providing the timing accuracy and stability figures required by system specifications, the GPS community will continue to strive for further improvements in performance. The GPS Master Control Station (MCS) recently demonstrated that timing improvements are always composite Clock, and hence, Kalman Filter state estimation, providing a small improvement to user accuracy.

  20. Using crystallographic shear to reduce lattice thermal conductivity: high temperature thermoelectric characterization of the spark plasma sintered Magnéli phases WO2.90 and WO2.722.

    PubMed

    Kieslich, Gregor; Veremchuk, Igor; Antonyshyn, Iryna; Zeier, Wolfgang G; Birkel, Christina S; Weldert, Kai; Heinrich, Christophe P; Visnow, Eduard; Panthöfer, Martin; Burkhardt, Ulrich; Grin, Yuri; Tremel, Wolfgang

    2013-10-07

    Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require a conflicting combination of low thermal conductivity and low electrical resistivity. We report the thermoelectric properties of spark plasma sintered Magnéli phases WO2.90 and WO2.722. The crystallographic shear planes, which are a typical feature of the crystal structures of Magnéli-type metal oxides, lead to a remarkably low thermal conductivity for WO2.90. The figures of merit (ZT = 0.13 at 1100 K for WO2.90 and 0.07 at 1100 K for WO2.722) are relatively high for tungsten-oxygen compounds and metal oxides in general. The electrical resistivity of WO2.722 shows a metallic behaviour with temperature, while WO2.90 has the characteristics of a heavily doped semiconductor. The low thermopower of 80 μV K(-1) at 1100 K for WO2.90 is attributed to its high charge carrier concentration. The enhanced thermoelectric performance for WO2.90 compared to WO2.722 originates from its much lower thermal conductivity, due to the presence of crystallographic shear and dislocations in the crystal structure. Our study is a proof of principle for the development of efficient and low-cost thermoelectric materials based on the use of intrinsically nanostructured materials rather than artificially structured layered systems to reduce lattice thermal conductivity.

  1. Applications of GPS Provided Time and Frequency and Future

    DTIC Science & Technology

    2012-08-14

    Provided Timing Service – History of UTC and GPS – Accuracy of GPS timing service • Precise Time Requirements – Communication Networks – Power Grid...Very Long Baseline Interferometry (VLBI) needs very stable frequency and uses MASER clocks and carrier phase GPS to link various sites. • CERN

  2. The Evolution of Global Positioning System (GPS) Technology.

    ERIC Educational Resources Information Center

    Kumar, Sameer; Moore, Kevin B.

    2002-01-01

    Describes technological advances in the Global Positioning System (GPS), which is also known as the NAVSTAR GPS satellite constellation program developed in 1937, and changes in the nature of our world by GPS in the areas of agriculture, health, military, transportation, environment, wildlife biology, surveying and mapping, space applications, and…

  3. The Evolution of Global Positioning System (GPS) Technology.

    ERIC Educational Resources Information Center

    Kumar, Sameer; Moore, Kevin B.

    2002-01-01

    Describes technological advances in the Global Positioning System (GPS), which is also known as the NAVSTAR GPS satellite constellation program developed in 1937, and changes in the nature of our world by GPS in the areas of agriculture, health, military, transportation, environment, wildlife biology, surveying and mapping, space applications, and…

  4. Broadcast vs Precise GPS Ephemerides: A Historical Perspective

    DTIC Science & Technology

    2002-03-01

    software used varies between analysis centres and includes Bernese GPS 32 software V4.1, ESOC BAHN, GPSOBS and BATUSI, GFZ EPOS.P.V2, NOAA page 5, MIT...Rothacher, and S. Schaer, Bernese GPS Software Introduction Course – Orbit Part, October 2001. “Boeing: Products – GPS – General Data”, Boeing

  5. Interferometric Determination of GPS (Global Positioning System) Satellite Orbits.

    DTIC Science & Technology

    1985-04-23

    Global Positioning System ,’ GPS interferometrv...INTRODUCTION If the NAVSTAR Global Positioning System ( GPS ) is to be useful for crustal motion monitoring, the orbits of the GPS satellites 7will need to be... Global Position . * ing System , April 15-19, 1985, Rockville, MD 19. KEY WORDS (Continue on rev’erse side if necessary and Identity by block

  6. Texas Instruments 4100 GPS (Global Positioning System) Positioning Software

    DTIC Science & Technology

    1986-09-01

    Global Positioning System ( GPS ). To meet...solutions as correct before accepting them. 9 II, BACKGROUND A. GLOBAL POSITIONING SYSTEM GPS is a universal satellite poitioning system that is...ABBREVIATIONS AND ACRONYMS GPS = Global Positioning System NPS = Naval Postgraduate School Montcrey CA DMA Defense Mapping Agency NOAA = National Oceanic

  7. Improvements in Dynamic GPS Positions Using Track Averaging

    DTIC Science & Technology

    1999-08-01

    Global Positioning System ( GPS ), Precise Positioning System (PPS) solution under dynamic...SUBJECT TERMS 15. NUMBER OF GPS , Global Positioning System , Dynamic Positioning PAGES 31 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY... Global Positioning System ( GPS ), Precise Positioning System (PPS) solution under dynamic conditions through averaging is investigated. Static

  8. Engineering and Design: Using Differential GPS Positioning for Elevation Determination

    DTIC Science & Technology

    1998-04-01

    Global Positioning System ( GPS ) surveying...Surveying Techniques Directorate of Civil Works NAVSTAR Global Positioning System Surveying. Survey (NGS) using several different GPS surveying 7701...NAVD88 Transformation NAVSTAR Global Positioning System Surveying, for Techniques assistance in setting up a network. a. The GPS relative positioning

  9. A Novel Use of GPS for Determining the Orbit of a Geosynchronous Satellite: The TDRS/GPS Demonstration

    NASA Technical Reports Server (NTRS)

    Haines, B. J.; Lichten, S. M.; Muellerschoen, R. J.; Spitzmesser, D. J.; Srinivasan, J. M.; Stephens, S. A.; Sweeney, D.; Young, L. E.

    1994-01-01

    New GPS-based techniques for tracking high Earth orbiters are under evaluation at the Jet Propulsion Laboratory (JPL). One promising approach dispenses with the GPS flight receiver, employing instead a simple beacon on the user spacecraft.

  10. Processing GPS Occultation Data To Characterize Atmosphere

    NASA Technical Reports Server (NTRS)

    Hajj, George; Kursinski, Emil; Leroy, Stephen; Lijima, Byron; de la Torre Juarez, Manuel; Romans, Larry; Ao, Chi

    2005-01-01

    GOAS [Global Positioning System (GPS) Occultation Analysis System] is a computer program that accepts signal-occultation data from GPS receivers aboard low-Earth-orbiting satellites and processes the data to characterize the terrestrial atmosphere and, in somewhat less comprehensive fashion, the ionosphere. GOAS is very robust and can be run in an unattended semi-operational processing mode. It features sophisticated retrieval algorithms that utilize the amplitudes and phases of the GPS signals. It incorporates a module that, using an assumed atmospheric refractivity profile, simulates the effects of the retrieval processing system, including the GPS receiver. GOAS utilizes the GIPSY software for precise determination of orbits as needed for calibration. The GOAS output for the Earth s troposphere and mid-to-lower stratosphere consists of high-resolution (<1 km) profiles of density, temperature, pressure, atmospheric refractivity, bending angles of signals, and water-vapor content versus altitude from the Earth s surface to an altitude of 30 km. The GOAS output for the ionosphere consists of electron-density profiles from an altitude of about 50 km to the altitude of a satellite, plus parameters related to the rapidly varying structure of the electron density, particularly in the E layer of the ionosphere.

  11. Discovering Hidden Treasures with GPS Technology

    ERIC Educational Resources Information Center

    Nagel, Paul; Palmer, Roger

    2014-01-01

    "I found it!" Addison proudly proclaimed, as she used an iPhone and Global Positioning System (GPS) software to find the hidden geocache along the riverbank. Others in Lisa Bostick's fourth grade class were jealous, but there would be other geocaches to find. With the excitement of movies like "Pirates of the Caribbean" and…

  12. Using Unmanned Aerial Vehicles and GPS Receivers

    NASA Technical Reports Server (NTRS)

    Gary, B.

    1995-01-01

    It is proposed that a small fleet of unmanned aerial vehicles (UAVs) be used over a period of years to monitor the rise of pressure surfaces caused by the hypothesized rise in average temperature of the troposphere due to global warming. Global Positioning Satellite System (GPS) receivers would be used for the precise tracking required.

  13. The MARCOR GPS mobile data system

    NASA Technical Reports Server (NTRS)

    Rothblatt, Martin

    1991-01-01

    Market research revealed several key demands for an Automatic Vehicle Location (AVL) Global Positioning System (GPS) radio. The demands were for minimization of urban building blockage, easy programmability to minimize mobile data transmission costs, high accuracy for street map level coordination, interface capability with non-digital Specialized Mobile Radios (SMR), and a selling price close to that of alternatives such as Signposts and Loran-C. A team of experts was assembled to surmount these challenges and deliver a GPS radio for $500 to $1000, which operates at high accuracy in an urban environment and is plug-compatible with nearly all vehicle radios. Among the engineering and production breakthroughs described here are a unique Simultrac (Trademark) approach to satellite tracking, enabling up to eight GPS satellites to be used for position determination with a 2-channel receiver, and a receiver-in-a-microphone design. A powerful Application Specific Integrated Circuit (ASIC) allowed GPS to be brought within easy reach of millions of AVL users such as bus, taxi, and delivery vehicle fleets.

  14. GPS pseudolites: Theory, design, and applications

    NASA Astrophysics Data System (ADS)

    Cobb, H. Stewart

    Pseudolites (ground-based pseudo-satellite transmitters) can initialize carrier-phase differential GPS (CDGPS) navigation systems in seconds to perform real-time dynamic positioning with one-sigma errors as low as 1 cm. Previous CDGPS systems were rarely used due to cumbersome initialization procedures requiring up to 30 minutes; initialization of the carrier-phase integer ambiguities via pseudolite removes these constraints. This work describes pseudolites optimized for this application which cost two orders of magnitude less than previous pseudolites. Synchrolites (synchronized pseudolites) which derive their timing from individual Global Positioning System (GPS) satellites are also described. Synchrolites can replace the CDGPS reference station and datalink, while simultaneously serving to initialize CDGPS navigation. A cluster of well-placed synchrolites could enable CDGPS navigation even if only one GPS satellite signal is available. A prototype CDGPS system initialized by pseudolites and synchrolites was designed and tested. The goal of this system, known as the Integrity Beacon Landing System (IBLS), was to provide navigation accurate and reliable enough to land aircraft in bad weather. Flight test results for prototype pseudolite and synchrolite systems, including results from 110 fully automatic landings of a Boeing 737 airliner controlled by IBLS, are presented. Existing pseudolite applications are described, including simulation of the GPS constellation for indoor navigation experiments. Synchrolite navigation algorithms are developed and analyzed. New applications for pseudolites and synchrolites are proposed. Theoretical and practical work on the near/far problem is presented.

  15. Differential GPS Terminal Area Test Results

    DTIC Science & Technology

    1990-11-01

    being occupied by the DGPS data input. The two tap lines connected to an RS232 port on a Compaq SLT/286 lap top computer. The Compaq utilized Smart Term...more satellites and a Position Dilution of Precision (PDOP) of 6 or Less. The GPS antenn employed in thence tests was configured for a mask angle 5

  16. Global geodesy using GPS without fiducial sites

    NASA Technical Reports Server (NTRS)

    Heflin, Michael; Bertiger, Willy; Blewitt, Geoff; Freedman, Adam; Hurst, Ken; Lichten, Steve; Lindqwister, Ulf; Vigue, Yvonne; Webb, Frank; Yunck, Tom

    1992-01-01

    Baseline lengths and geocentric radii have been determined from GPS data without the use of fiducial sites. Data from the first GPS experiment for the IERS and Geodynamics (GIG '91) have been analyzed with a no-fiducial strategy. A baseline length daily repeatability of 2 mm + 4 parts per billion was obtained for baselines in the Northern Hemisphere. Comparison of baseline lengths from GPS and the global VLBI solution GLB659 (Caprette et al. 1990) show rms agreement of 2.1 parts per billion. The geocentric radius mean daily repeatability for all sites was 15 cm. Comparison of geocentric radii from GPS and SV5 (Murray et al. 1990) show rms agreement of 3.8 cm. Given n globally distributed stations, the n(n - 1)/2 baseline lengths and n geocentric radii uniquely define a rigid closed polyhedron with a well-defined center of mass. Geodetic information can be obtained by examining the structure of the polyhedron and its change with time.

  17. Periodic Effects In GPS Time Series

    NASA Astrophysics Data System (ADS)

    Koivula, H.; Ollikainen, M.; Poutanen, M.

    We have computed the Lomb periodograms of GPS time series in the Finnish per- manent GPS network FinnRef. We can distinguish an annual period but also a diur- nal period in all vector components between any two stations, including the baseline length. The amplitude of the annual period is a function of the baseline length, thus behaving like a scale error. We have also analysed the diurnal period, which is most clearly visible between neighbouring stations. The FinnRef network is used e.g. for studying the Fennoscandian postglacial rebound. The periodic terms may be cancelled out in the solution of the height components of the stations by including seasonal terms in the solution. The method can be used when long series of observations are available, but in episodic campaigns the periodicity will degrade the accuracy. A geophysical interpretation of the annual variations in the height component of the GPS time series must be done with caution because the reason can be computational, not a physical one. We discuss on the effect and possible reasons for periods and tests made for studying the periodicity. We also discuss on the loading effect and their causes on the crustal deformation that can explain the observed scale variation in GPS time series.

  18. GPS LifePlan--Leading Campus Change

    ERIC Educational Resources Information Center

    Litecky, Larry; Bruner, Mike; Hageman, Kristin

    2009-01-01

    The Goals + Plans = Success (GPS) LifePlan is a new and innovative approach to assist and support students in answering critical questions that give direction to their pursuit of success. The program has brought impressive cultural changes to Century College. It benefited new students by establishing a framework for critical decision making that…

  19. Is GPS telemetry location error screening beneficial?

    USGS Publications Warehouse

    Ironside, Kirsten E.; Mattson, David J.; Arundel, Terry; Hansen, Jered R.

    2017-01-01

    The accuracy of global positioning system (GPS) locations obtained from study animals tagged with GPS monitoring devices has been a concern as to the degree it influences assessments of movement patterns, space use, and resource selection estimates. Many methods have been proposed for screening data to retain the most accurate positions for analysis, based on dilution of precision (DOP) measures, and whether the position is a two dimensional or three dimensional fix. Here we further explore the utility of these measures, by testing a Telonics GEN3 GPS collar's positional accuracy across a wide range of environmental conditions. We found the relationship between location error and fix dimension and DOP metrics extremely weak (r2adj ∼ 0.01) in our study area. Environmental factors such as topographic exposure, canopy cover, and vegetation height explained more of the variance (r2adj = 15.08%). Our field testing covered sites where sky-view was so limited it affected GPS performance to the degree fix attempts failed frequently (fix success rates ranged 0.00–100.00% over 67 sites). Screening data using PDOP did not effectively reduce the location error in the remaining dataset. Removing two dimensional fixes reduced the mean location error by 10.95 meters, but also resulted in a 54.50% data reduction. Therefore screening data under the range of conditions sampled here would reduce information on animal movement with minor improvements in accuracy and potentially introduce bias towards more open terrain and vegetation.

  20. Using Unmanned Aerial Vehicles and GPS Receivers

    NASA Technical Reports Server (NTRS)

    Gary, B.

    1995-01-01

    It is proposed that a small fleet of unmanned aerial vehicles (UAVs) be used over a period of years to monitor the rise of pressure surfaces caused by the hypothesized rise in average temperature of the troposphere due to global warming. Global Positioning Satellite System (GPS) receivers would be used for the precise tracking required.

  1. Global geodesy using GPS without fiducial sites

    NASA Technical Reports Server (NTRS)

    Heflin, Michael; Bertiger, Willy; Blewitt, Geoff; Freedman, Adam; Hurst, Ken; Lichten, Steve; Lindqwister, Ulf; Vigue, Yvonne; Webb, Frank; Yunck, Tom

    1992-01-01

    Baseline lengths and geocentric radii have been determined from GPS data without the use of fiducial sites. Data from the first GPS experiment for the IERS and Geodynamics (GIG '91) have been analyzed with a no-fiducial strategy. A baseline length daily repeatability of 2 mm + 4 parts per billion was obtained for baselines in the Northern Hemisphere. Comparison of baseline lengths from GPS and the global VLBI solution GLB659 (Caprette et al. 1990) show rms agreement of 2.1 parts per billion. The geocentric radius mean daily repeatability for all sites was 15 cm. Comparison of geocentric radii from GPS and SV5 (Murray et al. 1990) show rms agreement of 3.8 cm. Given n globally distributed stations, the n(n - 1)/2 baseline lengths and n geocentric radii uniquely define a rigid closed polyhedron with a well-defined center of mass. Geodetic information can be obtained by examining the structure of the polyhedron and its change with time.

  2. The MARCOR GPS mobile data system

    NASA Technical Reports Server (NTRS)

    Rothblatt, Martin

    1991-01-01

    Market research revealed several key demands for an Automatic Vehicle Location (AVL) Global Positioning System (GPS) radio. The demands were for minimization of urban building blockage, easy programmability to minimize mobile data transmission costs, high accuracy for street map level coordination, interface capability with non-digital Specialized Mobile Radios (SMR), and a selling price close to that of alternatives such as Signposts and Loran-C. A team of experts was assembled to surmount these challenges and deliver a GPS radio for $500 to $1000, which operates at high accuracy in an urban environment and is plug-compatible with nearly all vehicle radios. Among the engineering and production breakthroughs described here are a unique Simultrac (Trademark) approach to satellite tracking, enabling up to eight GPS satellites to be used for position determination with a 2-channel receiver, and a receiver-in-a-microphone design. A powerful Application Specific Integrated Circuit (ASIC) allowed GPS to be brought within easy reach of millions of AVL users such as bus, taxi, and delivery vehicle fleets.

  3. Discovering Hidden Treasures with GPS Technology

    ERIC Educational Resources Information Center

    Nagel, Paul; Palmer, Roger

    2014-01-01

    "I found it!" Addison proudly proclaimed, as she used an iPhone and Global Positioning System (GPS) software to find the hidden geocache along the riverbank. Others in Lisa Bostick's fourth grade class were jealous, but there would be other geocaches to find. With the excitement of movies like "Pirates of the Caribbean" and…

  4. GPS LifePlan--Leading Campus Change

    ERIC Educational Resources Information Center

    Litecky, Larry; Bruner, Mike; Hageman, Kristin

    2009-01-01

    The Goals + Plans = Success (GPS) LifePlan is a new and innovative approach to assist and support students in answering critical questions that give direction to their pursuit of success. The program has brought impressive cultural changes to Century College. It benefited new students by establishing a framework for critical decision making that…

  5. IRI-vTEC versus GPS-vTEC for Nigerian SCINDA GPS stations

    NASA Astrophysics Data System (ADS)

    Okoh, Daniel; McKinnell, Lee-Anne; Cilliers, Pierre; Okere, Bonaventure; Okonkwo, Chinelo; Rabiu, Babatunde

    2015-04-01

    Following the recent proliferation of dual-frequency GPS (Global Positioning System) receiver systems across the African continent, there is a growing number of papers that compare vertical Total Electron Content (vTEC) values derived from the International Reference Ionosphere (IRI) model with those obtained from the GPS receiver measurements. In this work we report an investigation of IRI-vTEC versus GPS-vTEC comparisons for three Nigerian SCINDAGPS stations (Nsukka, Ilorin, and Lagos) for which data are available in the year 2012, and present a further review of the differences/similarities observed between them. Since a major interest in this work is to use the GPS measurements to improve the predictions of the IRI model for the region, we present a detailed regression analysis of differences between the two sources in a manner that will benefit this application.

  6. Coastal GPS Altimetry for Eddy Monitoring

    NASA Astrophysics Data System (ADS)

    Cardellach, E.; Treuhaft, R. N.; Chao, Y.; Lowe, S. T.; Young, L. E.; Zuffada, C.

    2003-04-01

    Coastal zones (within approximately 20-30 km of the coast) are dominated by fast-changing (on the order of days) and small-scale (on the order of km or less) processes. The dynamics and thermodynamics associated with these coastal processes influence the physics, biogeochemistry and the associated carbon cycling in the coastal zones. To monitor these important processes at the highest possible resolution (both spatial and temporal) is therefore an integrated component of the Earth's observing system. Coastal processes are currently not adequately monitored from existing spaceborne observations. The infrared instruments can measure the sea surface temperature in coastal zones with a resolution of approximately 1km daily, but are heavily contaminated by clouds usually found in the land-sea boundaries. The conventional radar altimetry, even with the wide-swath (e.g., OSTM) configuration, can only provide measurements every 10 days, too long to resolve the fast-changing coastal processes, not mentioning the land contamination within the first few footprints (on the order of 20 km) away from the coast. Coastal GPS altimetry from cliffs or structures near the coastline provides a complementary way to measure these coastal processes. The precision of such ground-based grazing angle GPS measurements has been proven to be 2-cm over the smooth surface at Crater Lake [Treuhaft et al., 2001]. Nevertheless, the accuracy of the GPS altimetry over the open sea, significantly affected by roughness, has yet to be assessed. This poster aims to present a set of experiments and analyses to prove the coastal GPS altimetry concept with a few-cm accuracy goal. It includes the analysis of data gathered over the ocean from an oil platform, Platform Harvest, as well as simulations of the GPS reflected signal to identify and correct the effects of the sea roughness. The results of this research are planned to feed the design, execution and processing of an eddy monitoring experiment. It will

  7. Signal quality monitoring for GPS augmentation systems

    NASA Astrophysics Data System (ADS)

    Mitelman, Alexander Michael

    Civilian applications of the Global Positioning System have grown rapidly over the past decade. One of the most significant examples is guidance for aviation. In conjunction with specially designed equipment on the ground, GPS can provide precision approach and landing capability for aircraft. As with other safety-critical aviation applications, GPS-based landing systems must meet stringent accuracy, safety, and availability requirements set by the Federal Aviation Administration. Currently, compliance with FAA requirements is ensured by a host of monitors including the Signal Quality Monitor, a module specifically tasked with continuously observing raw GPS signals for interference and distortion. This dissertation focuses on several theoretical and practical aspects of SQM design. The discussion begins with in-depth analysis of the seminal event in SQM, a significant anomaly on GPS space vehicle 19 initially observed in 1993. At the time, a tenfold increase in vertical position error was reported when this satellite was in view. Little consensus was initially reached about the exact origin, nature, or magnitude of the distortion; this section considers these effects in detail. The analysis is then extended to compute a rigorous upper bound for differential error. Starting with the architecture of a basic landing system, a theoretical worst-case is derived that maximizes user error while defying detection by the ground station. A simplified distortion model, adopted by the International Civil Aviation Organization in response to the worst-case analysis, is also described. The discussion then describes the design and construction of an arbitrary GPS generator. Essential features include architecture, shielding, independent signal and noise levels, and fast switching between two input channels. Two example applications are presented to illustrate the instrument's utility. A theoretical analysis of the ICAO model is validated by measuring the spectra of generated

  8. GPS Ocean Reflection Experiment on Spartan 251

    NASA Technical Reports Server (NTRS)

    Garrison, James L; Russo, Angela; Mickler, Dave; Armatys, Michael; Ferebee, Melvin J.

    1999-01-01

    It has recently been demonstrated that the GPS signal which has reflected from the ocean surface contains useful geophysical data from which the sea surface wind speed and other parameters can be extracted. This can be used for remote sensing, similar to present day use of radar altimeters or scatterometers, but with significantly smaller instrumentation because of the utilization of the existing GPS broadcast signal for illumination. Several campaigns of aircraft experimentation have been completed demonstrating this technique and reflected GPS data has been reliably collected from 25 km altitude on a balloon. However, there has not yet been a demonstration that the reflected GPS signal can be detected from orbit with sufficient signal to noise ratio (SNR) to make useful remote sensing measurements. A technology demonstration experiment was planned for a Space Shuttle flight in the late 2000 using the Spartan 251 recoverable carrier. This experiment would also have been the first flight validation of the PiVoT GPS receiver developed in house at the Goddard Space Flight Center. The "open-architecture" design of this receiver would allow the software modifications to be made which control code-correlator spacing to map out the shape of the reflected signal waveform, which is the most basic data product generated by this instrumentation. A moderate gain left-hand circularly polarized antenna, constructed from an array of off-the-shelf hemispherical antennas was to be used to give approximately 3 to 6 dB of additional gain. Preliminary SNR predictions have been done indicating that this antenna would offer sufficient gain to record waveform measurements. A system level description of the experiment instrumentation, including the receiver, antenna and data storage and retrieval will be given. The visibility of GPS reflections over the mission duration of several hours will be studied, including the effects of the limited beamwidth of the antenna. Spartan 251 has now

  9. 76 FR 67019 - Eighty-Seventh: RTCA Special Committee 159: Global Positioning System (GPS)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-28

    ...--Working Group 2C, GPS/Inertial November 15--Working Group 2, GPS/WAAS November 16--Working Group 2, GPS...-2A) GPS/Inertial (WG-2C) GPS/Precision Landing Guidance (WG-4) GPS/Airport Surface Surveillance...

  10. How does the workload and work activities of procedural GPs compare to non-procedural GPs?

    PubMed

    Russell, Deborah J; McGrail, Matthew R

    2017-08-01

    To investigate patterns of Australian GP procedural activity and associations with: geographical remoteness and population size hours worked in hospitals and in total; and availability for on-call DESIGN AND PARTICIPANTS: National annual panel survey (Medicine in Australia: Balancing Employment and Life) of Australian GPs, 2011-2013. Self-reported geographical work location, hours worked in different settings, and on-call availability per usual week, were analysed against GP procedural activity in anaesthetics, obstetrics, surgery or emergency medicine. Analysis of 9301 survey responses from 4638 individual GPs revealed significantly increased odds of GP procedural activity in anaesthetics, obstetrics or emergency medicine as geographical remoteness increased and community population size decreased, albeit with plateauing of the effect-size from medium-sized (population 5000-15 000) rural communities. After adjusting for confounders, procedural GPs work more hospital and more total hours each week than non-procedural GPs. In 2011 this equated to GPs practising anaesthetics, obstetrics, surgery, and emergency medicine providing 8% (95%CI 0, 16), 13% (95%CI 8, 19), 8% (95%CI 2, 15) and 18% (95%CI 13, 23) more total hours each week, respectively. The extra hours are attributable to longer hours worked in hospital settings, with no reduction in private consultation hours. Procedural GPs also carry a significantly higher burden of on-call. The longer working hours and higher on-call demands experienced by rural and remote procedural GPs demand improved solutions, such as changes to service delivery models, so that long-term procedural GP careers are increasingly attractive to current and aspiring rural GPs. © 2016 National Rural Health Alliance Inc.

  11. Precipitable Water Vapor from GPS in Antarctica: Opportunities from the TAMDEF GPS Network, Victoria Land.

    NASA Astrophysics Data System (ADS)

    Vazquez, G. E.; Grejner, D. A.

    2005-12-01

    An experiment was carried out in order to estimate Precipitable Water Vapor (PWV) using the Global Positioning System (GPS) data collected by the Trans Antarctic Mountain Deformation Network, Victoria Land in Antarctica. TAMDEF is the OSU and US Geological Survey joint project sponsored by National Science Foundation (NSF). Estimation of PWV from the GPS data could play a crucial role in weather and climate study for Antarctica, by increasing the spatial and temporal resolutions of PWV estimates that can be used together with traditional meteorological data (such as ground meteorological stations and radiosonde) in the numerical weather prediction models. The basic observation used in this experiment is the ion-free, double-difference phase observations. Data collected by the TAMDEF network were processed using the PAGES software (Program for the Adjustment of GPS Ephemerides) with a 30-s sampling rate and 15-degree cutoff angle, using precise GPS orbits disseminated by the IGS (International GPS Service). PAGES is a production and research tool employed for a variety of NGS products (Mader et al. 1995). Optimal data reduction strategy was developed based on three different models tested. The Niell Mapping Functions and CfA 2.2 mapping functions with the Saastamoinen model, and the Marini model were used to estimate the wet delay (step Piece-Wise Linear strategy), which later was transformed to PWV via Bevis et al. (1992). The GPS PWV estimates are currently being compared to the radiosonde data in order to assess the quality of the GPS PWV solutions. The preliminary results are very promising, indicating a good match between the two methods. In summary, introducing GPS-derived PWV to weather/climate models will improve the model's predictive capability, and will allow a better understanding of the Antarctic weather conditions (and climate). Furthermore, more exact forecast of storm systems will recover surface, coastal, and air travel safety across the Antarctic

  12. Electrochemical lithium insertion in the solid solution Bi{sub 2}WO{sub 6}-Sb{sub 2}WO{sub 6} with Aurivillius framework

    SciTech Connect

    Martinez-de la Cruz, A. Longoria Rodriguez, F.E.

    2007-10-02

    Following the structural evolution of the Aurivillius crystalline framework in the solid solution Bi{sub 2}WO{sub 6}-Sb{sub 2}WO{sub 6} we have carried out an electrochemical lithium insertion study in this system. A slight loss of the specific capacity of the electrochemical cell was observed as amount of Sb was increased. In general, the different compositions within solid solution Bi{sub 2-x}Sb{sub x}WO{sub 6} (0.25 {<=} x {<=} 0.75) exhibited a similar behaviour featured mainly by two semiconstant potential regions located at 1.7 and 0.8 V versus Li{sup +}/Li{sup o}. The oxide Sb{sub 2}WO{sub 6} with Autivillius structure but without Bi was tested as cathode too. The maximum amount of lithium inserted, 13.5 lithium atoms per formula, is the same amount inserted in its homologous bismuth oxide Bi{sub 2}WO{sub 6}.

  13. Growth and crystallographic characterization of molecular beam epitaxial WO3 and MoO3/WO3 thin films on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Yano, Mitsuaki; Koike, Kazuto; Matsuo, Masayuki; Murayama, Takayuki; Harada, Yoshiyuki; Inaba, Katsuhiko

    2016-09-01

    Molecular beam epitaxy of tungsten trioxide (WO3) on (01 1 bar 2)-oriented (r-plane) sapphire substrates and molybdenum trioxide (MoO3) on the WO3 was studied by focusing on their crystallogrhaphic properties. Although polycrystalline monoclinic (γ-phase) WO3 films were grown at 500 °C and they became single-crystalline (0 0 1)-oriented γ-phase at 700 °C, the latter films were oxygen-deficient from stoichiometry and contained dense and deep thermal etchpits. By using a two-step growth method where only the initial 15 nm was grown at 700 °C and the rest part was grown at 500 °C, (0 0 1)-oriented γ-phase single-crystalline WO3 films with stoichiometric composition and smooth surface were obtained. On top of the 15-nm-thick WO3 initiation layer, (1 1 0)-oriented orthorhombic (α-phase) MoO3 films with smooth surface were obtained.

  14. Software Defined GPS API: Development and Implementation of GPS Correlator Architectures Using MATLAB with Focus on SDR Implementations

    DTIC Science & Technology

    2014-05-18

    and Implementation of GPS Correlator Architectures Using MATLAB with Focus on SDR Implementations The Software Defined GPS API was created with the...documentation. 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS (ES) U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 SDR ...Implementation of GPS Correlator Architectures Using MATLAB with Focus on SDR Implementations Report Title The Software Defined GPS API was created

  15. U.S. Coast Guard GPS Information Center (GPSIC) and Its Function Within the Civil GPS Service (CGS)

    DTIC Science & Technology

    1991-12-01

    GPSIC) was created to provide civil wers of the Global Positioning System with timely @ern status and other GPS satellite idormation. The GPSIC...ANSI Std Z39-18 timely GPS status information to civil users of the global positioning satellite navigation system . Specifically, the functions to...entity of the (:GS whicll provides GPS status information t o civilian users of the Global Positioning System based on input fro111 the: * GPS

  16. Photoreduction of non-noble metal Bi on the surface of Bi2WO6 for enhanced visible light photocatalysis

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojing; Yu, Shan; Liu, Yang; Zhang, Qian; Zhou, Ying

    2017-02-01

    In this report, Bi2WO6-Bi composite was prepared through an in situ photoreduction method and was characterized systematically by X-Ray diffraction, transmission electron microscopy, X-Ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The as-prepared Bi2WO6-Bi maintains the same crystal structure with the pristine Bi2WO6 regardless of some surface defects. Nevertheless, these surface defects result in the change of surface oxygen adsorption mode from hydroxyl to molecular oxygen on Bi2WO6. Photocatalytic activity over Bi2WO6-Bi is 2.4 times higher than that of Bi2WO6 towards the degradation of organic dye Rhodamine B (RhB) under visible light irradiation (λ > 420 nm). A deep study shows that cleavage of benzene ring is the main pathway for RhB degradation over Bi2WO6, but both the benzene cleavage and de-ethylation pathway coexist for RhB decomposition in the presence of Bi2WO6-Bi as the photocatalyst. Photoelectrochemical study including transient photocurrent tests and electrochemical impedance spectroscopy measurements shows that Bi2WO6-Bi could facilitate the charge transfer process compared to Bi2WO6. These data above has indicated a new insight into the promotion mechanism based on Bi related heterostructures.

  17. Experimental and theoretical investigation on photocatalytic activities of 1D Ag/Ag2WO4 nanostructures.

    PubMed

    Liu, Danqing; Huang, Weicheng; Li, Long; Liu, Lu; Sun, Xiaojun; Liu, Bo; Yang, Bin; Guo, Chongshen

    2017-09-20

    Ag2WO4 is a significant photocatalyst that responds to UV light irradiation only, which greatly hinders it for further practical application for solar light. To address this problem, herein, 1D plasmonic Ag/Ag2WO4 photocatalysts have been fabricated by a successive process including hydrothermal synthesis to obtain Ag2WO4 followed by an additional in situ chemical-reduction process for Ag decoration. Then, the structural features, optical properties, and electronic structures of Ag2WO4 and Ag/Ag2WO4 nanowires were systematically investigated via a combination of theoretical calculations and experimental evidence. The plasmon-enhanced Ag/Ag2WO4 nanowires exhibited higher visible-light-driven photocatalytic activity, which performed a desired photodestruction ratio of 91.2% on methylene blue within 60 min and good stability in five cycles. The Ag decoration greatly facilitates visible-light harvesting and thus promotes photogenerated radical oxidation to dye, which is evidenced by the higher hydroxyl radical level of Ag/Ag2WO4 detected in the ESR test during the photocatalytic process. The theoretical calculation based on density functional theory indicates that Ag nanoparticles formed on the surface of Ag2WO4 could narrow the band gap of Ag2WO4. In addition, the surface plasmon resonance absorption effect and fast charge transfer effect in the metal-semiconductor system contribute to the photocatalytic performance of Ag/Ag2WO4.

  18. Experimental and theoretical investigation on photocatalytic activities of 1D Ag/Ag2WO4 nanostructures

    NASA Astrophysics Data System (ADS)

    Liu, Danqing; Huang, Weicheng; Li, Long; Liu, Lu; Sun, Xiaojun; Liu, Bo; Yang, Bin; Guo, Chongshen

    2017-09-01

    Ag2WO4 is a significant photocatalyst that responds to UV light irradiation only, which greatly hinders it for further practical application for solar light. To address this problem, herein, 1D plasmonic Ag/Ag2WO4 photocatalysts have been fabricated by a successive process including hydrothermal synthesis to obtain Ag2WO4 followed by an additional in situ chemical-reduction process for Ag decoration. Then, the structural features, optical properties, and electronic structures of Ag2WO4 and Ag/Ag2WO4 nanowires were systematically investigated via a combination of theoretical calculations and experimental evidence. The plasmon-enhanced Ag/Ag2WO4 nanowires exhibited higher visible-light-driven photocatalytic activity, which performed a desired photodestruction ratio of 91.2% on methylene blue within 60 min and good stability in five cycles. The Ag decoration greatly facilitates visible-light harvesting and thus promotes photogenerated radical oxidation to dye, which is evidenced by the higher hydroxyl radical level of Ag/Ag2WO4 detected in the ESR test during the photocatalytic process. The theoretical calculation based on density functional theory indicates that Ag nanoparticles formed on the surface of Ag2WO4 could narrow the band gap of Ag2WO4. In addition, the surface plasmon resonance absorption effect and fast charge transfer effect in the metal-semiconductor system contribute to the photocatalytic performance of Ag/Ag2WO4.

  19. Influence of molybdenum doping on the structural, optical and electronic properties of WO3 for improved solar water splitting.

    PubMed

    Kalanur, Shankara S; Seo, Hyungtak

    2017-09-08

    Doping WO3 with foreign atoms is a very efficient strategy to modify the structural, optical and electronic properties which could influence its photoelectrochemical (PEC) water splitting activity. In this study, we report a simple and efficient single-step strategy for the fabrication of molybdenum (Mo)-doped WO3 thin films. The characterization results show that doping Mo into WO3 leads to a significant change in the morphology without changing its crystal structure. Elemental mapping and EDS analysis revealed that Mo was homogeneously doped into the crystal lattice of WO3 in the at.% range of 0-10.31. The incorporation of Mo into WO3 reduced the band-gap of WO3 and increased its light absorption ability. Notably, X-ray photoelectron spectroscopic valence band-edge analysis confirmed that substitution of Mo into WO3 led to a downward shift in the conduction band minimum without any significant change in the valence band maximum with respect to Fermi level. The fabricated Mo-doped WO3 electrodes exhibited a higher photocurrent compared to undoped WO3 samples under simulated 1.5AM sunlight without the addition of a water oxidation catalyst. The procedure proposed herein provides a simple and systematic approach for the fabrication of band-gap-tailored WO3 photoanodes by Mo doping for efficient PEC water splitting. Copyright © 2017. Published by Elsevier Inc.

  20. Physical applications of GPS geodesy: a review

    NASA Astrophysics Data System (ADS)

    Bock, Yehuda; Melgar, Diego

    2016-10-01

    Geodesy, the oldest science, has become an important discipline in the geosciences, in large part by enhancing Global Positioning System (GPS) capabilities over the last 35 years well beyond the satellite constellation’s original design. The ability of GPS geodesy to estimate 3D positions with millimeter-level precision with respect to a global terrestrial reference frame has contributed to significant advances in geophysics, seismology, atmospheric science, hydrology, and natural hazard science. Monitoring the changes in the positions or trajectories of GPS instruments on the Earth’s land and water surfaces, in the atmosphere, or in space, is important for both theory and applications, from an improved understanding of tectonic and magmatic processes to developing systems for mitigating the impact of natural hazards on society and the environment. Besides accurate positioning, all disturbances in the propagation of the transmitted GPS radio signals from satellite to receiver are mined for information, from troposphere and ionosphere delays for weather, climate, and natural hazard applications, to disturbances in the signals due to multipath reflections from the solid ground, water, and ice for environmental applications. We review the relevant concepts of geodetic theory, data analysis, and physical modeling for a myriad of processes at multiple spatial and temporal scales, and discuss the extensive global infrastructure that has been built to support GPS geodesy consisting of thousands of continuously operating stations. We also discuss the integration of heterogeneous and complementary data sets from geodesy, seismology, and geology, focusing on crustal deformation applications and early warning systems for natural hazards.

  1. Subdaily Earth rotation model and GPS solutions

    NASA Astrophysics Data System (ADS)

    Panafidina, Natalia; Hugentobler, Urs; Seitz, Manuela

    2014-05-01

    In this contribution we study the influence of the subdaily Earth rotation model on the GPS solution including station coordinates, satellite orbits and daily Earth rotation parameters (ERPs). The approach used is based on the transformation of GPS normal equation systems: free daily normal equations containing ERPs with 1-hour resolution are used as input data, in this case the high-frequency ERPs can be transformed into tidal terms which then can be fixed to new a priori values, thus changing implicitly the underlying subdaily Earth rotation model. To study the influence of individual tidal terms on the solution we successively changed a priori values for one tidal term in polar motion and compared the resulting solutions for GPS orbits, station coordinates and daily ERPs for a time interval of 13 years. The comparison reveals periodic changes in all estimated parameters with periods depending on the periods of the changed tidal terms. The dynamical reference frame realized by the GPS orbits is also affected: the whole satellite constellation shows periodic orientation variations, and each individual satellite shows periodic changes in the position of the orbit origin. We present a mechanism showing how errors in the subdaily Earth rotation model are propagated into the dynamical reference frame and the estimated parameters. Our model represents a change in one tidal term over one day as the sum of a prograde diurnal wave, a retrograde diurnal wave and an offset and linear drift in x- and y-pole. We demonstrate that this simple model, in conjunction with appropriate constraints, can explain well the observed variations in a one day GPS solution as well as in daily pole rates caused by changes in the subdaily Earth rotation model.

  2. Mutual Information Between GPS Measurements and Earthquakes

    NASA Astrophysics Data System (ADS)

    Wang, T.; Bebbington, M. S.

    2009-12-01

    Prior to the wide deployment of Continuous GPS stations in the early 1990s, there were a number of well-documented deformation rate changes observed before large earthquakes. GPS measurements provide the opportunity for systematic investigation of pre-, co- and post-seismic deformation anomalies, but contain much noise that needs to be filtered out of the observations. Assuming the existence of an earthquake cycle (for example, mainshock--aftershock--quiescence--precursory seismicity), a hidden Markov model (HMM) provides a natural framework for analyzing the observed GPS data. For two case studies of a) deep earthquakes in the central North Island, New Zealand, and b) shallow earthquakes in Southern California, an HMM fitted to the trend ranges of the GPS measurements can classify the deformation data into different patterns which form proxies for states of the earthquake cycle. Mutual information can be used to examine whether there is any relation between these patterns, in particular the Viterbi path, and subsequent (or previous) earthquakes. One class of GPS movements (identified by the HMM as having the largest range of deformation rate changes) appears to have some precursory character for earthquakes with minimum magnitude 5.1 (central North Island, New Zealand, 26 earthquakes in 1747 days) and 4.5 (Southern California, 50 earthquakes in 3815 days). We define a ``Time of Increased Probability'' (TIP) as being a 10-day interval (central North Island, New Zealand) or a 20-day interval (Southern California) following entry (as identified by the Viterbi algorithm) to the `precursory' hidden state, and examine the performance of this in probabilistically forecasting subsequent earthquakes.

  3. The GPS Tide Gauge Problem Revisited

    NASA Astrophysics Data System (ADS)

    Larson, K. M.; Löfgren, J. S.; Haas, R.

    2011-12-01

    It is well-known that GPS instruments can be used to measure local sea level. In most experiments, two antennas are deployed at a coastal site. A geodetic antenna - optimized for RHCP signals - is used in the traditional orientation and tracks the direct signal. The second antenna is optimized for reflected signals - which are primarily LHCP - and is pointed towards the ocean. The sea surface can then be estimated by analyzing the carrier phase data. While the data from the "up" antenna are dominated by the direct signal, the effects of signals reflected from the ocean are also present in its data. Thus in principle, one might be able to estimate sea level using only data from the "up" antenna. This is similar in concept to recent multipath studies where geodetic GPS installations are being used to measure soil moisture variations and snow depth. We have analyzed GPS data for a three-month period from a GPS tide gauge installation at the Onsala Space Observatory. It is located on the western coast of Sweden. We used the SNR data from the "up" antenna only. The data were windowed by azimuth for ocean-reflections and elevation angles from 18-40 degrees. This provides hourly sea level measurements. Comparisons were made to an average for tide gauge records 18 km south and 33 km north of Onsala. The standard deviation of the residual between our solutions and the tide gauges is 4.9 cm. This is less precise than the combined up-down antenna system of 2.6 cm. These precision values include errors associated with real tidal motion at the GPS site. While the "down" antenna performs poorly in high-wind conditions (> 8 m/s), we found that the "up" antenna performs significantly better at these times.

  4. GPS, GNSS, and Ionospheric Density Gradients

    NASA Astrophysics Data System (ADS)

    Kintner, P. M.; O'Hanlon, B.; Humphreys, T. E.

    2009-12-01

    Ionospheric density and density gradients affect GNSS signals in two ways. They can introduce ranging errors or irregularities that form on the density gradients producing scintillation. Here we focus on the issue of ranging errors. There are two approaches to mitigating ranging errors produced by ionospheric density gradients which can be 20-30 m during major magnetic storms. The first approach is to use a reference receiver(s) to determine the ionospheric contribution to ranging errors. The ranging error is then transmitted to the user for correction within the mobile receiver. This approach is frequently referred to as differential GPS and, when multiple reference receivers are used, the system is referred to as an augmentation system. This approach is vulnerable to ionospheric gradients depending on the reference receiver spacing(s) and latency in applying the correction within the mobile receiver. The second approach is to transmit navigation signals at two frequencies and then use the relative delay between the two signals to both estimate the ranging error and calculate the correct range. Currently the dual frequency technique is used by US military receivers with an encryption key and some civilian receivers which must be stationary and average over times long compared to those required for navigation. However, the technology of space based radio navigation is changing. GPS will soon be a system with three frequencies and multiple codes. Furthermore Europe, Russia, and China are developing independent systems to complement and compete with GPS while India and Japan are developing local systems to enhance GPS performance in their regions. In this talk we address two questions. How do density gradients affect augmentation systems including the social consequences and will the new GPS/GNSS systems with multiple civilian frequencies be able to remove ionospheric errors. The answers are not at all clear.

  5. Preparation of WO3/g-C3N4 composites and their application in oxidative desulfurization

    NASA Astrophysics Data System (ADS)

    Zhao, Rongxiang; Li, Xiuping; Su, Jianxun; Gao, Xiaohan

    2017-01-01

    WO3/graphitic carbon nitride (g-C3N4) composites were successfully synthesized through direct calcining of a mixture of WO3 and g-C3N4 at 400 °C for 2 h. The WO3 was prepared by calcination of phosphotungstic acid at 550 °C for 4 h, and the g-C3N4 was obtained by calcination of melamine at 520 °C for 4 h. The WO3/g-C3N4 composites were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and Brunner-Emmett-Teller analysis (BET). The WO3/g-C3N4 composites exhibited stronger XRD peaks of WO3 and g-C3N4 than the WO3 and pure g-C3N4. In addition, two WO3 peaks at 25.7° and 26.6° emerged for the 36% -WO3/g-C3N4 composite. This finding indicated that WO3 was highly dispersed on the surface of the g-C3N4 nanosheets and interacted with the nanosheets, which resulted in the appearance of (012) and (022) planes of WO3. The WO3/g-C3N4 composite also exhibited a larger specific surface area and higher degree of crystallization than WO3 or pure g-C3N4, which resulted in high catalytic activity of the catalyst. Desulfurization experiments demonstrated that the desulfurization rate of dibenzothiophene (DBT) in model oil reached 91.2% under optimal conditions. Moreover, the activity of the catalyst was not significantly decreased after five recycles.

  6. US Coast Guard GPS Information Center (GPSIC) and its function within the Civil GPS Service (CGS)

    NASA Technical Reports Server (NTRS)

    Barndt, Luann

    1992-01-01

    The Global Positioning System Information Center (GPSIC) was created to provide civil users of the Global Positioning System with timely system status and other GPS satellite information. The GPSIC began providing basic services on a test and evaluation basis in March 1990. Since then we have improved these services, formalized the information gathering processes, and expanded GPSIC operations to meet GPS user needs. The GPSIC serves as a central point of contact for civil users to make their interests and needs known to the system operator, the Department of Defense (DOD) under the management of the U.S. Air Force. The GPSIC provides GPS information to civil users through Operational Advisory Broadcasts (OAB) containing GPS performance data. The OABs are disseminated through numerous sources including 24 hour access to a voice telephone recording and a computer bulletin board system (BBS). The GPSIC staff also responds to individual user inquiries, comments, or concerns about civil access to and use of the GPS during normal working hours. This paper provides an overview of the Civil GPS Service as well as the details of the type of information and services that are available through the GPSIC and how they can be obtained. It will also address the future expansion of GPSIC responsibilities.

  7. Anomalously large Born effective charges in cubic WO3

    NASA Astrophysics Data System (ADS)

    Detraux, F.; Ghosez, Ph.; Gonze, X.

    1997-07-01

    Within density-functional theory, we compute the Born effective charges of tungsten trioxyde in its reference cubic phase (defect-perovskite structure). For the tungsten atom, the effective charge tensor is isotropic, with Z*W=+12.51. For the oxygen atoms, the two independent components of the tensor, corresponding, respectively, to a displacement of the atom parallel or perpendicular to the W-O bond, have the values Z*O||=-9.13 and Z*O⊥=-1.68. Z*W and Z*O|| are anomalously large with respect to the nominal ionic charges (+6 on W and -2 on O), but compatible with the Born effective charges found in related ABO3-perovskite compounds.

  8. Efficient photoelectrochemical water splitting by anodically grown WO3 electrodes.

    PubMed

    Cristino, Vito; Caramori, Stefano; Argazzi, Roberto; Meda, Laura; Marra, Gian Luigi; Bignozzi, Carlo Alberto

    2011-06-07

    The potentiostatic anodization of metallic tungsten has been investigated in different solvent/electrolyte compositions with the aim of improving the water oxidation ability of the tungsten oxide layer. In the NMF/H(2)O/NH(4)F solvent mixture, the anodization leads to highly efficient WO(3) photoanodes, which, combining spectral sensitivity, an electrochemically active surface, and improved charge-transfer kinetics, outperform, under simulated solar illumination, most of the reported nanocrystalline substrates produced by anodization in aqueous electrolytes and by sol-gel methods. The use of such electrodes results in high water electrolysis yields of between 70 and 90% in 1 M H(2)SO(4) under a potential bias of 1 V versus SCE and close to 100% in the presence of methanol.

  9. Sonochromic effect in WO{sup 3} colloidal suspensions

    SciTech Connect

    Kamat, P.V.; Vinodgopal, K.

    1996-11-13

    In recent years there has been a burst of activities in investigating sonolytic reactions. The usefulness of this technique in synthesizing colloidal semiconductors and metals and dissolution of MnO{sup 2} colloids has also been demonstrated. We have now employed semiconductor colloids to investigate the radical reactions in sonolytic processes. In this study we present our preliminary results from the reaction of WO{sup 3} colloids with sonolytically generated H atoms. Sodium tungstate, oxalic acid, and Acid Orange 7 were obtained from Aldrich. Acid Orange 7 was purified by column chromatography. All other chemicals were analytical reagents of highest available purity. The analysis experiments were carried out with a 640 kHz sonolysis setup of Ultrasonic Energy Systems (Panama City, FL). 24 refs., 4 figs.

  10. Piezo-optic coefficients of CaWO4 crystals

    NASA Astrophysics Data System (ADS)

    Mytsyk, B. G.; Kost', Ya. P.; Demyanyshyn, N. M.; Andrushchak, A. S.; Solskii, I. M.

    2015-01-01

    All components of the piezo-optic coefficient matrix of calcium tungstate crystals, belonging to the 4/ m symmetry class, are determined. The reliability of the piezo-optic effect measurements in CaWO4 crystals is achieved by determining each piezo-optic coefficient from several experimental geometries and is also based on the correlation of the absolute piezo-electric coefficients and the path-difference coefficients. The rotation-shear diagonal coefficients π44 and π66 and three principal piezo-optic coefficients π11, π13, and π31 are refined by the polarization-optical method. It is confirmed that both the interferometric and polarization-optical methods should be used to study the piezo-optic effect with high accuracy. The results show that calcium tungstate is a promising material for acousto-optical and photoelastic modulation.

  11. Characterization of Nanoporous WO3 Films Grown via Ballistic Deposition

    SciTech Connect

    Smid, Bretislav; Li, Zhenjun; Dohnalkova, Alice; Arey, Bruce W.; Smith, R. Scott; Matolin, Vladimir; Kay, Bruce D.; Dohnalek, Zdenek

    2012-05-17

    We report on the preparation and characterization of high surface area, supported nanoporous tungsten oxide films prepared under different conditions on polished polycrystalline Ta and Pt(111) substrates via direct sublimation of monodispersed gas phase of cyclic (WO3)3 clusters. Scanning Electron Microscopy and Transmission Electron Microscopy were used to investigate the film morphology on a nanometer scale. The films consist of arrays of separated filaments that are amorphous. The chemical composition and the thermal stability of the films were investigated by means of X-ray Photoelectron Spectroscopy. The surface area and the distribution of binding sites on the films are measured as functions of growth temperature, deposition angle, and annealing conditions using temperature programmed desorption of Kr. Films deposited at 20 K and at an incident angle of 65{sup o} from substrate normal display the greatest specific surface area of {approx}560 m2/g.

  12. Composite WO3/TiO2 nanostructures for high electrochromic activity.

    PubMed

    Reyes-Gil, Karla R; Stephens, Zachary D; Stavila, Vitalie; Robinson, David B

    2015-02-04

    A composite material consisting of TiO2 nanotubes (NT) with WO3 electrodeposited on its surface has been fabricated, detached from its Ti substrate, and attached to a fluorine-doped tin oxide (FTO) film on glass for application to electrochromic (EC) reactions. Several adhesion layers were tested, finding that a paste of TiO2 made from commercially available TiO2 nanoparticles creates an interface for the TiO2 NT film to attach to the FTO glass, which is conductive and does not cause solution-phase ions in an electrolyte to bind irreversibly with the material. The effect of NT length and WO3 concentration on the EC performance were studied. The composite WO3/TiO2 nanostructures showed higher ion storage capacity, better stability, enhanced EC contrast, and longer memory time compared with the pure WO3 and TiO2 materials.

  13. Reflectance modulation with electrochromic Li sub x WO sub 3 films

    SciTech Connect

    Goldner, R.B.; Berera, G.; Arntz, F.O.; Haas, T.E.; Morel, B.; Wong, K.K.

    1989-01-01

    Reflectance-modulated Smart Glass Windows (or smart windows) is a potentially important application for electrochromic thin films. The question addressed in this paper is, what is the upper bound for the near infrared reflectivity modulation in Li{sub x}WO{sub 3} films Based upon recent research on bulk crystals of Na{sub x}WO{sub 3} and bulk crystals and thin films of polycrystalline Li{sub x}WO{sub 3}, it is concluded that the upper bound is probably close to that of bulk crystals of Na{sub x}WO{sub 3} (x > 0.5) for which near infrared reflectance >90% has been reported. 9 refs., 7 figs.

  14. Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films

    PubMed Central

    Wen, Rui-Tao; Granqvist, Claes G.; Niklasson, Gunnar A.

    2015-01-01

    Amorphous WO3 thin films are of keen interest as cathodic electrodes in transmittance-modulating electrochromic devices. However, these films suffer from ion-trapping-induced degradation of optical modulation and reversibility upon extended Li+-ion exchange. Here, we demonstrate that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-trapping, i.e., WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance. Pronounced ion-trapping occurs when x exceeds ~0.65 in LixWO3 during ion insertion. We find two main kinds of Li+-ion trapping sites (intermediate and deep) in WO3, where the intermediate ones are most prevalent. Li+-ions can be completely removed from intermediate traps but are irreversibly bound in deep traps. Our results provide a general framework for developing and designing superior electrochromic materials and devices. PMID:26259104

  15. Synthesis of NiWO4 powder crystals of polyhedron for photocatalytic degradation of Rhodamine

    NASA Astrophysics Data System (ADS)

    Hao, Meifeng; Meng, Xiangrui; Miao, Yuqing

    2017-10-01

    The NiWO4 powder crystals were synthesized by a simple hydrothermal method. It is found that the morphologies of most of NiWO4 particles are the polyhedron including cube, decahedron and dodecahedron et al. The typical cubic structures show the side length around 3 μm. SEM, TEM, XRD, FTIR and UV-vis were employed to characterize the NiWO4 powder crystals. The band gap value of 1.48 eV was calculated according to UV-vis. The NiWO4 powder crystals exhibit high photocatalytic activity toward the degradation of Rh B under both UV and visible irradiations. Especially, under UV, only 17% Rh B remains after 40 min UV photodegradation and only 80 min is needed for the complete degradation.

  16. Composition control of InN/WO3 nanocomposite by in-situ reactive plasma annealing

    NASA Astrophysics Data System (ADS)

    Saroni, Azianty; Goh, Boon Tong; Alizadeh, Mahdi; Rahman, Saadah Abdul

    2016-05-01

    A composition control and formation of InN/WO3 nanocomposite on the as-grown In2O3 by in-situ reactive plasma annealing was investigated. The reactive plasma annealing changes the facets crystalline In2O3 structure to nanograin structure of InN/WO3 nanocomposite with the grain size of 100-200 nm. X-ray photoelectron spectroscopy (XPS) reveals the formation of In2O3, InN and WO3 nanostructures in the nanocomposite. In-situ reactive plasma annealing enhances the removing of In2O3 and facilitates the formation of InN/WO3 nanocomposite. Furthermore, the reduction of oxygen in In2O3 leads to a decreasing in optical energy gap from 2.91 to 2.63 eV.

  17. Nitrogen doping of nanoporous WO3 layers by NH3 treatment for increased visible light photoresponse.

    PubMed

    Nah, Yoon-Chae; Paramasivam, Indhumati; Hahn, Robert; Shrestha, Nabeen K; Schmuki, Patrik

    2010-03-12

    Nanoporous WO(3) layers were grown by electrochemical anodization of W in a fluoride containing electrolyte. These layers were exposed to a thermal treatment in NH(3) to achieve nitrogen doping of the material. The morphology, crystal structure, composition and photoresponse of pure and nitrogen doped WO(3) were compared using scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and photoelectrochemical measurements. The results clearly show that successful nitrogen doping into WO(3) layers can be achieved by controlling the temperature and time during the NH(3) treatment. Most importantly, it is demonstrated that for the nitrogen doped WO(3) layers the photocurrent is significantly enhanced in the visible light region.

  18. Visible-light active photocatalytic WO3 films loaded with Pt nanoparticles deposited by sputtering.

    PubMed

    Murata, Akiyo; Oka, Nobuto; Nakamura, Shinichi; Shigesato, Yuzo

    2012-06-01

    Visible-Light active photocatalytic tungsten trioxide (WO3) films were deposited at a substrate temperature of 800 degrees C by dc reactive magnetron sputtering using a W metal target. In addition, Platinum (Pt) was deposited on the WO3 film surfaces at room temperature, also by sputtering. In the early stages of Pt growth, formation of Pt nanoparticles could be expected because of the island structure observed in Volmer-Weber-type growth mode. The surface coverage of Pt on the WO3 films was estimated quantitatively by X-ray photoelectron spectroscopy and was found to be approximately 60% after 7 s deposition. High resolution electron microscopy (HREM) demonstrated that Pt nanoparticles with a diameter of about 2.5 nm were generated and dispersed uniformly on the entire surface area of the columnar polycrystalline WO3 films. These Pt-loaded films exhibited high photocatalytic activity in the decomposition of acetaldehyde (CH3CHO) under visible light irradiation.

  19. High capacity WO3 film as efficient charge collection electrode for solar rechargeable batteries

    NASA Astrophysics Data System (ADS)

    Zhao, Wenjie; Wang, Xiao-Feng; Zheng, Enqiang; Wei, Yingjin; Sanehira, Yoshitaka; Chen, Gang

    2017-05-01

    In this work, we demonstrated the dye-sensitized solar rechargeable batteries devices sharing a structure of Dye-TiO2/electrolyte/Ni/WO3. The WO3 film was prepared by a simple sol-gel process exhibit high cavities and large surface area allowing efficient chemical/electrical reactions. The WO3 films with 2 ± 0.5 μm in thickness as charge collection electrodes exhibited a high energy density over other materials reported thus far. Under irradiation energy of 7.5 mWcm-2 in the photo-charging, the discharging time sustained 1758 s at the current density of 0.05 mA cm-2 in dark, the first specific discharge capacities of WO3 nano-film reach 40.6 mAh g-1 (0.0244 mAh cm-2). This work substantially pushes forward the easy processing solar rechargeable batteries for future potential applications.

  20. Hydrothermal Fabrication of WO3 Hierarchical Architectures: Structure, Growth and Response

    PubMed Central

    Wu, Chuan-Sheng

    2015-01-01

    Recently hierarchical architectures, consisting of two-dimensional (2D) nanostructures, are of great interest for potential applications in energy and environmental. Here, novel rose-like WO3 hierarchical architectures were successfully synthesized via a facile hydrothermal method. The as-prepared WO3 hierarchical architectures were in fact assembled by numerous nanosheets with an average thickness of ~30 nm. We found that the oxalic acid played a significant role in governing morphologies of WO3 during hydrothermal process. Based on comparative studies, a possible formation mechanism was also proposed in detail. Furthermore, gas-sensing measurement showed that the well-defined 3D WO3 hierarchical architectures exhibited the excellent gas sensing properties towards CO. PMID:28347062

  1. Sonochemically prepared PbWO4 tetragonal-bipyramidal microcrystals and their photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Kannan, S.; Mohanraj, K.; Sivakumar, G.

    2015-03-01

    Lead tungstate (PbWO4) microcrystals were synthesized for the first time, via different concentrations of PVA assisted sonochemical process. The concentration of PVA acts as a structure directing agent and played an important role in the morphological control of resulting PbWO4 microcrystals. The product PbWO4 composing of Pb, W and O and Wsbnd O stretching vibration band of WO4 tetrahedrons were confirmed through XRD, FTIR, FESEM and EDS. The TG/DTA curves showed that the particles are crystallized at room temperature itself and the thermal stability of the product is really good. The optical properties of the product shows extraordinarily high room temperature photoluminescence intensity compared to without PVA assisted product.

  2. Pd Nanoparticles Coupled to WO2.72 Nanorods for Enhanced Electrochemical Oxidation of Formic Acid.

    PubMed

    Xi, Zheng; Erdosy, Daniel P; Mendoza-Garcia, Adriana; Duchesne, Paul N; Li, Junrui; Muzzio, Michelle; Li, Qing; Zhang, Peng; Sun, Shouheng

    2017-04-12

    We synthesize a new type of hybrid Pd/WO2.72 structure with 5 nm Pd nanoparticles (NPs) anchored on 50 × 5 nm WO2.72 nanorods. The strong Pd/WO2.72 coupling results in the lattice expansion of Pd from 0.23 to 0.27 nm and the decrease of Pd surface electron density. As a result, the Pd/WO2.72 shows much enhanced catalysis toward electrochemical oxidation of formic acid in 0.1 M HClO4; it has a mass activity of ∼1600 mA/mgPd in a broad potential range of 0.4-0.85 V (vs RHE) and shows no obvious activity loss after a 12 h chronoamperometry test at 0.4 V. Our work demonstrates an important strategy to enhance Pd NP catalyst efficiency for energy conversion reactions.

  3. Bacteriophage WO Can Mediate Horizontal Gene Transfer in Endosymbiotic Wolbachia Genomes

    PubMed Central

    Wang, Guan H.; Sun, Bao F.; Xiong, Tuan L.; Wang, Yan K.; Murfin, Kristen E.; Xiao, Jin H.; Huang, Da W.

    2016-01-01

    Phage-mediated horizontal gene transfer (HGT) is common in free-living bacteria, and many transferred genes can play a significant role in their new bacterial hosts. However, there are few reports concerning phage-mediated HGT in endosymbionts (obligate intracellular bacteria within animal or plant hosts), such as Wolbachia. The Wolbachia-infecting temperate phage WO can actively shift among Wolbachia genomes and has the potential to mediate HGT between Wolbachia strains. In the present study, we extend previous findings by validating that the phage WO can mediate transfer of non-phage genes. To do so, we utilized bioinformatic, phylogenetic, and molecular analyses based on all sequenced Wolbachia and phage WO genomes. Our results show that the phage WO can mediate HGT between Wolbachia strains, regardless of whether the transferred genes originate from Wolbachia or other unrelated bacteria. PMID:27965627

  4. Hydrothermal synthesis of Bi2WO6 hierarchical flowers with their photonic and photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Dumrongrojthanath, Phattharanit; Thongtem, Titipun; Phuruangrat, Anukorn; Thongtem, Somchai

    2013-02-01

    Bi2WO6 hierarchical multi-layered flower-like assemblies were synthesized by a hydrothermal method at 180 °C for 24 h. XRD patterns were specified as pure orthorhombic well-crystallized Bi2WO6 phase. Their FTIR spectra show main absorption bands at 400-1000 cm-1, assigned as the stretching modes of the Bi-O and W-O, and W-O-W bridging stretching modes. SEM analysis shows that the product was 3D hierarchical flower-like assemblies, constructed by orderly arranged 2D layers of nanoplates. The UV-visible absorption shows an absorbance in the ultraviolet region with 3.4 eV band gap. Photocatalytic activity of Bi2WO6 hierarchical flowers was determined from the degradation of rhodamine-B by Xe light at 88% for 360 min irradiation.

  5. Enhanced electrochemical performance of monoclinic WO3 thin film with redox additive aqueous electrolyte.

    PubMed

    Shinde, Pragati A; Lokhande, Vaibhav C; Chodankar, Nilesh R; Ji, Taeksoo; Kim, Jin Hyeok; Lokhande, Chandrakant D

    2016-12-01

    To achieve the highest electrochemical performance for supercapacitor, it is very essential to find out a suitable pair of an active electrode material and an electrolyte. In the present work, a simple approach is employed to enhance the supercapacitor performance of WO3 thin film. The WO3 thin film is prepared by a simple and cost effective chemical bath deposition method and its electrochemical performance is tested in conventional (H2SO4) and redox additive [H2SO4+hydroquinone (HQ)] electrolytes. Two-fold increment in electrochemical performance for WO3 thin film is observed in redox additive aqueous electrolyte compared to conventional electrolyte. WO3 thin film showed maximum specific capacitance of 725Fg(-1), energy density of 25.18Whkg(-1) at current density of 7mAcm(-2) with better cycling stability in redox electrolyte. This strategy provides the versatile way for designing the high performance energy storage devices.

  6. Fabrication of luminescent SrWO{sub 4} thin films by a novel electrochemical method

    SciTech Connect

    Chen Lianping Gao Yuanhong

    2007-10-02

    Highly crystallized SrWO{sub 4} thin films with single scheelite structure were prepared within 60 min by a cell electrochemical method. X-ray diffraction analysis shows that SrWO{sub 4} thin films have a tetragonal structure. Scanning electron microscopy examinations reveal that SrWO{sub 4} grains grow well in tetragonal tapers and grains like flowers or bunches, which can usually form by using the electrolysis electrochemical method, have disappeared under cell electrochemical conditions. X-ray photoelectron spectra and energy dispersive X-ray microanalysis examinations demonstrate that the composition of the film is consistent with its stoichiometry. These SrWO{sub 4} films show a single blue emission peak (located at 460 nm) using an excitation wave of 230 nm. The speed of cell electrochemical method can be controlled by changing temperature. The optimum treatment temperature is about 50-60 deg. C.

  7. Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films.

    PubMed

    Wen, Rui-Tao; Granqvist, Claes G; Niklasson, Gunnar A

    2015-10-01

    There is keen interest in the use of amorphous WO3 thin films as cathodic electrodes in transmittance-modulating electrochromic devices. However, these films suffer from ion-trapping-induced degradation of optical modulation and reversibility on extended Li(+)-ion exchange. Here, we demonstrate that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-trapping; that is, WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance. Pronounced ion trapping occurs when x exceeds ∼0.65 in LixWO3 during ion insertion. We find two main kinds of Li(+)-ion-trapping site (intermediate and deep) in WO3, where the intermediate ones are most prevalent. Li(+) ions can be completely removed from intermediate traps but are irreversibly bound in deep traps. Our results provide a general framework for developing and designing superior electrochromic materials and devices.

  8. Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films

    NASA Astrophysics Data System (ADS)

    Wen, Rui-Tao; Granqvist, Claes G.; Niklasson, Gunnar A.

    2015-10-01

    There is keen interest in the use of amorphous WO3 thin films as cathodic electrodes in transmittance-modulating electrochromic devices. However, these films suffer from ion-trapping-induced degradation of optical modulation and reversibility on extended Li+-ion exchange. Here, we demonstrate that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-trapping; that is, WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance. Pronounced ion trapping occurs when x exceeds ~0.65 in LixWO3 during ion insertion. We find two main kinds of Li+-ion-trapping site (intermediate and deep) in WO3, where the intermediate ones are most prevalent. Li+ ions can be completely removed from intermediate traps but are irreversibly bound in deep traps. Our results provide a general framework for developing and designing superior electrochromic materials and devices.

  9. Evaluation of a Mobile Phone for Aircraft GPS Interference

    NASA Technical Reports Server (NTRS)

    Nguyen, Truong X.

    2004-01-01

    Measurements of spurious emissions from a mobile phone are conducted in a reverberation chamber for the Global Positioning System (GPS) radio frequency band. This phone model was previously determined to have caused interference to several aircraft GPS receivers. Interference path loss (IPL) factors are applied to the emission data, and the outcome compared against GPS receiver susceptibility. The resulting negative safety margins indicate there are risks to aircraft GPS systems. The maximum emission level from the phone is also shown to be comparable with some laptop computer's emissions, implying that laptop computers can provide similar risks to aircraft GPS receivers.

  10. Measuring Postglacial Rebound with GPS and Absolute Gravity

    NASA Technical Reports Server (NTRS)

    Larson, Kristine M.; vanDam, Tonie

    2000-01-01

    We compare vertical rates of deformation derived from continuous Global Positioning System (GPS) observations and episodic measurements of absolute gravity. We concentrate on four sites in a region of North America experiencing postglacial rebound. The rates of uplift from gravity and GPS agree within one standard deviation for all sites. The GPS vertical deformation rates are significantly more precise than the gravity rates, primarily because of the denser temporal spacing provided by continuous GPS tracking. We conclude that continuous GPS observations are more cost efficient and provide more precise estimates of vertical deformation rates than campaign style gravity observations where systematic errors are difficult to quantify.

  11. Application of GPS tracking techniques to orbit determination for TDRS

    NASA Technical Reports Server (NTRS)

    Haines, B. J.; Lichten, S. M.; Malla, R. P.; Wu, S. C.

    1993-01-01

    In this paper, we evaluate two fundamentally different approaches to TDRS orbit determination utilizing Global Positioning System (GPS) technology and GPS-related techniques. In the first, a GPS flight receiver is deployed on the TDRSS spacecraft. The TDRS ephemerides are determined using direct ranging to the GPS spacecraft, and no ground network is required. In the second approach, the TDRSS spacecraft broadcast a suitable beacon signal, permitting the simultaneous tracking of GPS and TDRSS satellites from a small ground network. Both strategies can be designed to meet future operational requirements for TDRS-2 orbit determination.

  12. Synthesis and evaluation of α-Ag2WO4 as novel antifungal agent

    NASA Astrophysics Data System (ADS)

    Foggi, Camila C.; Fabbro, Maria T.; Santos, Luís P. S.; de Santana, Yuri V. B.; Vergani, Carlos E.; Machado, Ana L.; Cordoncillo, Eloisa; Andrés, Juan; Longo, Elson

    2017-04-01

    Because of the need for new antifungal materials with greater potency, microcrystals of α-Ag2WO4, a complex metal oxide, have been synthetized by a simple co-precipitation method, and their antifungal activity against Candida albicans has been investigated. A theoretical model based on clusters that are building blocks of α-Ag2WO4 has been proposed to explain the experimental results.

  13. Light-Driven Au-WO3@C Janus Micromotors for Rapid Photodegradation of Dye Pollutants.

    PubMed

    Zhang, Qilu; Dong, Renfeng; Wu, Yefei; Gao, Wei; He, Zihan; Ren, Biye

    2017-02-08

    A novel light-driven Au-WO3@C Janus micromotor based on colloidal carbon WO3 nanoparticle composite spheres (WO3@C) prepared by one-step hydrothermal treatment is described. The Janus micromotors can move in aqueous media at a speed of 16 μm/s under 40 mW/cm(2) UV light due to diffusiophoretic effects. The propulsion of such Au-WO3@C Janus micromotors (diameter ∼ 1.0 μm) can be generated by UV light in pure water without any external chemical fuels and readily modulated by light intensity. After depositing a paramagnetic Ni layer between the Au layer and WO3, the motion direction of the micromotor can be precisely controlled by an external magnetic field. Such magnetic micromotors not only facilitate recycling of motors but also promise more possibility of practical applications in the future. Moreover, the Au-WO3@C Janus micromotors show high sensitivity toward extremely low concentrations of sodium-2,6-dichloroindophenol (DCIP) and Rhodamine B (RhB). The moving speed of motors can be significantly accelerated to 26 and 29 μm/s in 5 × 10(-4) wt % DCIP and 5 × 10(-7) wt % RhB aqueous solutions, respectively, due to the enhanced diffusiophoretic effect, which results from the rapid photocatalytic degradation of DCIP and RhB by WO3. This photocatalytic acceleration of the Au-WO3@C Janus micromotors confirms the self-diffusiophoretic mechanism and opens an opportunity to tune the motility of the motors. This work also offers the light-driven micromotors a considerable potential for detection and rapid photodegradation of dye pollutants in water.

  14. Study of electrochromic APCVD WO3-V2O5 films

    NASA Astrophysics Data System (ADS)

    Bodurov, G.; Ivanova, T.; Abrashev, M.; Gesheva, K. A.

    2012-12-01

    WO3-V2O5 thin films were deposited by atmospheric pressure chemical vapour deposition (APCVD). WO3-V2O5 thin films are investigated related to their potential use as primary electrochromic layers (working electrodes) in Electrochromic Devices. A typical EC Device is a sandwich like structure with two conductive glasses and an electrolyte with working electrodes that possess electrochromic properties. APCVD has the advantages of scalability to large areas with uniform thickness and potentially low cost.

  15. Synthesis and structure of Na+-intercalated WO3(4,4-bipyridyl)0.5.

    PubMed

    Islah-u-din; Fox, Matthew R; Martin, Hélène; Gainsford, Graeme J; Kennedy, John; Markwitz, Andreas; Telfer, Shane G; Jameson, Geoffrey B; Tallon, Jeffery L

    2010-06-28

    WO3(4,4-bipyridyl)0.5 was doped with Na+ by ion implantation so as to alter the electronic structure. Single-crystal X-ray diffraction reveals layers of corner-shared WO5N octahedra linked by bipyridine. In the observed space group of Pbca, the fully-ordered bipyridyls form cages with Na+ disordered bimodally about the cage centre.

  16. Facile and controlled synthesis of aligned WO3 nanorods and nanosheets as an efficient photocatalyst material.

    PubMed

    Ahmed, Bilal; Kumar, Sumeet; Ojha, Animesh K; Donfack, P; Materny, A

    2017-03-15

    In this work, we have performed a facile and controlled synthesis of WO3 nanorods and sheets in different crystal phases (triclinic, orthorhombic and monoclinic) of WO3 using the sol-gel method. The detailed structures of the synthesized materials were examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy measurements. The shapes and crystal phases of the WO3 nanostructures were found to be highly dependent on the calcination temperature. The variation in crystalline phases and shapes is modified the electronic structure of the samples, which causes a variation in the value of optical band gap. The value of the Raman line intensity ratio I264/I320 has been successfully used to identify the structural transition from the triclinic to the orthorhombic phase of WO3. The PL spectra of the synthesized products excited at wavelengths 380, 400, and 420nm exhibit intense emission peaks that cover the complete visible range (blue-green-red). The emission peaks at ~460 and ~486nm were caused by the near band-edge and band to band transition, respectively. The peaks in spectral range 500-600nm might be originated from the presence of oxygen vacancies lying within the energy band gap. The synthesized WO3 nanostructures showed improved photocatalytic activity for the photodegradation of MB dye. The enhanced photocatalytic activity of WO3 nanosheets compared to WO3 nanorods for photodegradation of methylene blue (MB) dye could be due to the shape of the nanostructured WO3. The sheet type of structure provides more active surface for the interaction of dye molecules compared to the rods, which results in a more efficient degradation of the dye molecules. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Facile and controlled synthesis of aligned WO3 nanorods and nanosheets as an efficient photocatalyst material

    NASA Astrophysics Data System (ADS)

    Ahmed, Bilal; Kumar, Sumeet; Ojha, Animesh K.; Donfack, P.; Materny, A.

    2017-03-01

    In this work, we have performed a facile and controlled synthesis of WO3 nanorods and sheets in different crystal phases (triclinic, orthorhombic and monoclinic) of WO3 using the sol-gel method. The detailed structures of the synthesized materials were examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy measurements. The shapes and crystal phases of the WO3 nanostructures were found to be highly dependent on the calcination temperature. The variation in crystalline phases and shapes is modified the electronic structure of the samples, which causes a variation in the value of optical band gap. The value of the Raman line intensity ratio I264/I320 has been successfully used to identify the structural transition from the triclinic to the orthorhombic phase of WO3. The PL spectra of the synthesized products excited at wavelengths 380, 400, and 420 nm exhibit intense emission peaks that cover the complete visible range (blue-green-red). The emission peaks at 460 and 486 nm were caused by the near band-edge and band to band transition, respectively. The peaks in spectral range 500-600 nm might be originated from the presence of oxygen vacancies lying within the energy band gap. The synthesized WO3 nanostructures showed improved photocatalytic activity for the photodegradation of MB dye. The enhanced photocatalytic activity of WO3 nanosheets compared to WO3 nanorods for photodegradation of methylene blue (MB) dye could be due to the shape of the nanostructured WO3. The sheet type of structure provides more active surface for the interaction of dye molecules compared to the rods, which results in a more efficient degradation of the dye molecules.

  18. Temperature Dependence of the Luminescence Decay Time of a PbWO4 Scintillator

    NASA Astrophysics Data System (ADS)

    Shi, Chao-shu; Deng, Jie; Han, Zheng-fu; Xie, Zhi-jian; Liao, Jing-ying; G, Zimmerer; J, Beker; M, Kamada; M, Runne; A, Schröder

    1998-06-01

    Experimental results are given for the temperature dependence of the decay time of the emission at 430 nm from PbWO4 crystal under vacuum-ultraviolet (82 nm) photon excitation in the temperature range of 80-300 K. The structures in the curve are interpreted for the first time by studying the thermoluminescence of PbWO4, which originates from the traps in the crystal.

  19. UV-VUV synchrotron radiation spectroscopy of NiWO4

    NASA Astrophysics Data System (ADS)

    Kuzmin, A.; Pankratov, V.; Kalinko, A.; Kotlov, A.; Shirmane, L.; Popov, A. I.

    2016-07-01

    Photoluminescence and excitation spectra of microcrystalline and nanocrystalline nickel tungstate (NiWO4) were measured using UV-VUV synchrotron radiation source. The origin of the bands is interpreted using comparative analysis with isostructural ZnWO4 tungstate and based on the results of recent first-principles band structure calculations. The influence of the local atomic structure relaxation and of Ni2+ intra-ion d-d transitions on the photoluminescence band intensity are discussed.

  20. [Doctor's degree thesis of Tomasz Adolf Wołkowiński "Carditidis rheumaticae historia"].

    PubMed

    Stembrowicz, W

    2001-01-01

    In 1817 on the University of Vilnius Faculty of Medicine, T. A. Wołkowiński, a student of the eminent clinician Józef Frank, defended his doctor's degree thesis about a direct relation between rheumatic disease and cardiomegaly. It was probably the first paper in Poland describing with details the rheumatic heart disease. Unfortunately we don't know much about T. A. Wołkowiński's life.

  1. Impact of GPS tracking data of LEO satellites on global GPS solutions

    NASA Astrophysics Data System (ADS)

    Rothacher, M.; Svehla, D.

    Already at present quite a few Low Earth Orbiting (LEO) satellites (SAC-C, CHAMP, JASON-1, GRACE-1 and GRACE-2) are equipped with one or more GPS receivers for precise orbit determination or other applications (atmospheric sounding, gravity field recovery, . . . ). This trend will continue in the near future (e.g., with the GOCE and COSMIC missions) and we will soon have an entire "constellation" of LEO satellites tracked by GPS at our disposal. In this contribution we want to study the impact of LEO GPS measurements (from a single LEO satellite or from a LEO constellation) on global GPS solutions, where GPS satellite orbits and clocks, Earth rotation parameters (ERPs), station coordinates and troposphere zenith delays are determined simultaneously using the data of the global network of the International GPS Service (IGS). In order to assess the impact of the LEO GPS data on global IGS results, we have to perform a combined analysis of the space-borne and the ground-based GPS data. Such a combination may benefit on one hand from the differences between a ground station and a LEO, e.g., (1) the different tracking geometry (coverage of isolated geographical areas by LEOs, rapidly changing geometry, . . . ), (2) that LEOs connect all ground stations within 1-2 hours, (3) that baselines between LEO and ground stations may be longer than station-station baselines, (4) that no tropospheric delays have to be estimated for LEOs, and (5) that LEOs orbit the Earth within the ionosphere and may therefore contribute to global ionosphere models. On the other hand we have to deal with difficult aspects of precise orbit determination for the LEOs: only if we succeed to obtain very accurate dynamic or reduced-dynamic orbits for the LEOs, we will have a chance at all to improve the global GPS results. We present first results concerning the influence of LEO data on GPS orbits, ERPs, site coordinates, and troposphere zenith delays using both, variance-covariance analyses based on

  2. Controllable synthesis of hierarchical nanostructures of CaWO{sub 4} and SrWO{sub 4} via a facile low-temperature route

    SciTech Connect

    Chen, Z.; Gong, Q.; Zhu, J.; Yuan, Y.P.; Qian, L.W.; Qian, X.F.

    2009-01-08

    CaWO{sub 4} and SrWO{sub 4} nanostructures have been synthesized via a simple microemulsion-mediated route. With careful control of the fundamental experimental parameters including the concentration of reactants, the reaction time and the temperature, the products with different morphologies of dumbbell, coral, rod and dendrite have been obtained, respectively. The possible formation mechanism of these unique morphologies has been proposed based on surfactant self-assembly under different experimental conditions. The as-synthesized CaWO{sub 4} samples with various morphologies exhibit different photoluminescence properties. X-ray powder diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and luminescence spectroscopy were used to characterize these products.

  3. The First Experiment with VLBI-GPS Hybrid System

    NASA Technical Reports Server (NTRS)

    Kwak, Younghee; Kondo, Tetsuro; Gotoh, Tadahiro; Amagai, Jun; Takiguchi, Hiroshi; Sekido, Mamoru; Ichikawa, Ryuichi; Sasao, Tetsuo; Cho, Jungho; Kim, Tuhwan

    2010-01-01

    In this paper, we introduce our GPS-VLBI hybrid system and show the results of the first experiment which is now under way. In this hybrid system, GPS signals are captured by a normal GPS antenna, down-converted to IF signals, and then sampled by the VLBI sampler VSSP32 developed by NICT. The sampled GPS data are recorded and correlated in the same way as VLBI observation data. The correlator outputs are the group delay and the delay rate. Since the whole system uses the same frequency standard, many sources of systematic errors are common between the VLBI system and the GPS system. In this hybrid system, the GPS antenna can be regarded as an additional VLBI antenna having multiple beams towards GPS satellites. Therefore, we expect that this approach will provide enough data to improve zenith delay estimates and geodetic results.

  4. WO3/TiO2 nanotube photoanodes for solar water splitting with simultaneous wastewater treatment.

    SciTech Connect

    Reyes, Karla Rosa; Robinson, David B.

    2013-05-01

    Nanostructured WO3/TiO2 nanotubes with properties that enhance solar photoconversion reactions were developed, characterized and tested. The TiO2 nanotubes were prepared by anodization of Ti foil, and WO3 was electrodeposited on top of the nanotubes. SEM images show that these materials have the same ordered structure as TiO2 nanotubes, with an external nanostructured WO3 layer. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare TiO2 nanotubes, and in the UV absorption relative to bare WO3 films. Incident simulated solar photon-to-current efficiency increased from 30% (for bare WO3) to 50% (for WO3/TiO2 composites). With the addition of diverse organic pollutants, the photocurrent densities exhibited more than a 5-fold increase. Chemical oxygen demand measurements showed the simultaneous photodegradation of organic pollutants. The results of this work indicate that the unique structure and composition of these composite materials enhance the charge carrier transport and optical properties compared with the parent materials.

  5. Memristive properties of hexagonal WO3 nanowires induced by oxygen vacancy migration

    PubMed Central

    2013-01-01

    Tungsten trioxide (WO3) is always oxygen-deficient or non-stoichiometric under atmospheric conditions. Positively charged oxygen vacancies prefer to drift as well as electrons when the electric field is strong enough, which will alter the distribution of oxygen vacancies and then endow WO3 with memristive properties. In Au/WO3 nanowire/Au sandwich structures with two ohmic contacts, the axial distribution of oxygen vacancies and then the electrical transport properties can be more easily modulated by bias voltage. The threshold electric field for oxygen vacancy drifting in single-crystal hexagonal WO3 nanowire is about 106 V/m, one order of magnitude less than that in its granular film. At elevated temperatures, the oxygen vacancy drifts and then the memristive effect can be enhanced remarkably. When the two metallic contacts are asymmetric, the WO3 nanowire devices even demonstrate good rectifying characteristic at elevated temperatures. Based on the drift of oxygen vacancies, nanoelectronic devices such as memristor, rectifier, and two-terminal resistive random access memory can be fabricated on individual WO3 nanowires. PMID:23347429

  6. Influence of annealing temperature of WO3 in photoelectrochemical conversion and energy storage for water splitting.

    PubMed

    Ng, Charlene; Ng, Yun Hau; Iwase, Akihide; Amal, Rose

    2013-06-12

    The current work demonstrates the importance of WO3 crystallinity in governing both photoenergy conversion efficiency and storage capacity of the flower structured WO3 electrode. The degree of crystallinity of the WO3 electrodes was varied by altering the calcination temperature from 200 to 600 °C. For the self-photochargeability phenomenon, the prevailing flexibility of the short-range order structure at low calcination temperature of 200 °C favors the intercalation of the positive cations, enabling more photoexcited electrons to be stored within WO3 framework. This leads to a larger amount of stored charges that can be discharged in an on-demand manner under the absence of irradiation for H2 generation. The stability of the electrodes calcined at 200 °C, however, is compromised because of the structural instability caused by the abundance insertion of cations. On the other hand, films that were calcined at 400 °C displayed the highest stability toward both intercalation of the cations and photoelectrochemical water splitting performance. Although crystallinty of WO3 was furthered improved at 600 °C heat treatment, the worsened contact between the WO3 platelets and the conducting substrate as induced by the significant sintering has been more detrimental toward the charge transport.

  7. Modulating memristive performance of hexagonal WO3 nanowire by water-oxidized hydrogen ion implantation

    PubMed Central

    Zhou, Yong; Peng, Yuehua; Yin, Yanling; Zhou, Fang; Liu, Chang; Ling, Jing; Lei, Le; Zhou, Weichang; Tang, Dongsheng

    2016-01-01

    In a two-terminal Au/hexagonal WO3 nanowire/Au device, ions drifting or carriers self-trapping under external electrical field will modulate the Schottky barriers between the nanowire and electrodes, and then result in memristive effect. When there are water molecules adsorbed on the surface of WO3 nanowire, hydrogen ions will generate near the positively-charged electrode and transport in the condensed water film, which will enhance the memristive performance characterized by analogic resistive switching remarkably. When the bias voltage is swept repeatedly under high relative humidity level, hydrogen ions will accumulate on the surface and then implant into the lattice of the WO3 nanowire, which leads to a transition from semiconducting WO3 nanowire to metallic HxWO3 nanowire. This insulator-metal transition can be realized more easily after enough electron-hole pairs being excited by laser illumination. The concentration of hydrogen ions in HxWO3 nanowire will decrease when the device is exposed to oxygen atmosphere or the bias voltage is swept in atmosphere with low relative humidity. By modulating the concentration of hydrogen ions, conductive hydrogen tungsten bronze filament might form or rupture near electrodes when the polarity of applied voltage changes, which will endow the device with memristive performance characterized by digital resistive switching. PMID:27600368

  8. Epitaxial NiWO4 films on Ni(110): Experimental and theoretical study of surface stability

    NASA Astrophysics Data System (ADS)

    Doudin, N.; Pomp, S.; Blatnik, M.; Resel, R.; Vorokhta, M.; Goniakowski, J.; Noguera, C.; Netzer, F. P.; Surnev, S.

    2017-05-01

    Despite the application potential of nickel tungstate (NiWO4) in heterogeneous catalysis, humidity and gas sensing, etc, its surfaces have essentially remained unexplored. In this work, NiWO4 nanoparticles and films with the wolframite structure have been grown via a solid-state reaction of (WO3)3 clusters and a NiO(100) film on a Ni(110) crystal surface and characterized by a variety of experimental techniques, including x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM) and x-ray diffraction (XRD), combined with ab-initio density functional theory (DFT) calculations. NiWO4 grows initially as three-dimensional (3D) crystalline nanoparticles displaying mainly two crystalline facets vicinal to the (100) surface, which merge with increasing the (WO3)3 coverage into a quasi-continuous epitaxial film. The DFT results provide an account of the energetics of NiWO4 low index surfaces and highlight the role of faceting in the stabilization of extended polar (100) terraces. These combined experimental and theoretical results show that interaction with a metal substrate and vertical confinement may stabilize oxide nano-objects with high energy facets, able to enhance their reactivity.

  9. Highly sensitive and selective trimethylamine sensors based on WO3 nanorods decorated with Au nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Lu; Song, Peng; Yang, Zhongxi; Wang, Qi

    2017-06-01

    One-dimensional tungsten oxide (WO3) gas sensing materials have been widely used for the detection of trimethylamine (TMA) gas. Furthermore, it is believed that an effective method to improve the gas sensing performance is to introduce noble metals into sensing materials. In this work, a novel gas sensing material was prepared by decorating Au nanoparticles on WO3 nanorods. Based on field emission scanning electron microscopy (FESEM/EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the morphology and microstructure of as-prepared samples were characterized. Results show that Au nanoparticles with diameter of 13-15 nm are loaded on the surface of WO3 nanorods with length of about 1-2 μm and width of 50-80 nm. Gas sensing tests reveal that the Au@WO3 sensor has remarkably enhanced response to TMA gas compared with pure WO3 nanorods. In addition, and the gas sensing mechanism has been investigated based on the experimental results. The superior sensing features indicate the present Au@WO3 nanocomposites are promising for gas sensors, which can be used in the detection of the trimethylamine gas and this work provides insights and strategies for the fabrication of sensing materials.

  10. Modulating memristive performance of hexagonal WO3 nanowire by water-oxidized hydrogen ion implantation.

    PubMed

    Zhou, Yong; Peng, Yuehua; Yin, Yanling; Zhou, Fang; Liu, Chang; Ling, Jing; Lei, Le; Zhou, Weichang; Tang, Dongsheng

    2016-09-07

    In a two-terminal Au/hexagonal WO3 nanowire/Au device, ions drifting or carriers self-trapping under external electrical field will modulate the Schottky barriers between the nanowire and electrodes, and then result in memristive effect. When there are water molecules adsorbed on the surface of WO3 nanowire, hydrogen ions will generate near the positively-charged electrode and transport in the condensed water film, which will enhance the memristive performance characterized by analogic resistive switching remarkably. When the bias voltage is swept repeatedly under high relative humidity level, hydrogen ions will accumulate on the surface and then implant into the lattice of the WO3 nanowire, which leads to a transition from semiconducting WO3 nanowire to metallic HxWO3 nanowire. This insulator-metal transition can be realized more easily after enough electron-hole pairs being excited by laser illumination. The concentration of hydrogen ions in HxWO3 nanowire will decrease when the device is exposed to oxygen atmosphere or the bias voltage is swept in atmosphere with low relative humidity. By modulating the concentration of hydrogen ions, conductive hydrogen tungsten bronze filament might form or rupture near electrodes when the polarity of applied voltage changes, which will endow the device with memristive performance characterized by digital resistive switching.

  11. Modulating memristive performance of hexagonal WO3 nanowire by water-oxidized hydrogen ion implantation

    NASA Astrophysics Data System (ADS)

    Zhou, Yong; Peng, Yuehua; Yin, Yanling; Zhou, Fang; Liu, Chang; Ling, Jing; Lei, Le; Zhou, Weichang; Tang, Dongsheng

    2016-09-01

    In a two-terminal Au/hexagonal WO3 nanowire/Au device, ions drifting or carriers self-trapping under external electrical field will modulate the Schottky barriers between the nanowire and electrodes, and then result in memristive effect. When there are water molecules adsorbed on the surface of WO3 nanowire, hydrogen ions will generate near the positively-charged electrode and transport in the condensed water film, which will enhance the memristive performance characterized by analogic resistive switching remarkably. When the bias voltage is swept repeatedly under high relative humidity level, hydrogen ions will accumulate on the surface and then implant into the lattice of the WO3 nanowire, which leads to a transition from semiconducting WO3 nanowire to metallic HxWO3 nanowire. This insulator-metal transition can be realized more easily after enough electron-hole pairs being excited by laser illumination. The concentration of hydrogen ions in HxWO3 nanowire will decrease when the device is exposed to oxygen atmosphere or the bias voltage is swept in atmosphere with low relative humidity. By modulating the concentration of hydrogen ions, conductive hydrogen tungsten bronze filament might form or rupture near electrodes when the polarity of applied voltage changes, which will endow the device with memristive performance characterized by digital resistive switching.

  12. Phonon properties of nanosized MnWO{sub 4} with different size and morphology

    SciTech Connect

    Maczka, MirosLaw; Ptak, Maciej; Kurnatowska, Michalina; Kepinski, Leszek; Tomaszewski, PaweL; Hanuza, Jerzy

    2011-09-15

    Highly hierarchical barlike and flowerlike MnWO{sub 4} microcrystals have been synthesized for the first time by a hydrothermal method, where ethanolamine (EA) and cetyltrimethylamonnium bromide (CTAB) play important roles in directing growth and self-assembly of these structures. The possible formation process has been proposed. In addition, platelike nanosized MnWO{sub 4} was also synthesized by annealing of a precursor obtained by coprecipitation method. The obtained samples were characterized by XRD, SEM, TEM, Raman and IR methods. Raman spectra showed relatively weak dependence on particle size and morphology of the particles. In contrast to this behavior, IR-active bands showed pronounced shifts and changes in relative intensities on particle size and the morphology. Origin of this behavior is discussed. - Graphical Abstract: SEM images of MnWO{sub 4} particles prepared by hydrothermal process at 150 deg. C (left panel) and 200 deg. C (right panel). Highlights: > Hydrothermal synthesis with ethanolamine enables growth of hierarchical nanosized MnWO{sub 4} particles. > Annealing of a precursor obtained by coprecipitation method enables growth of platelike MnWO{sub 4} nanoparticles. > Raman and IR spectra of MnWO{sub 4} nanoparticles depend on both size and morphology of the nanoparticles. > We discuss origin of this behavior.

  13. MWCNT/WO3 nanocomposite photoanode for visible light induced water splitting

    NASA Astrophysics Data System (ADS)

    Yousefzadeh, Samira; Reyhani, Ali; Naseri, Naimeh; Moshfegh, Alireza Z.

    2013-08-01

    The Multi-walled carbon nanotube (MWCNT)/WO3 nanocomposite thin films with different MWCNT’s weight percentages were prepared by sol-gel method as visible light induced photoanode in water splitting reaction. Weight percentage of MWCNT in the all nanocomposite thin films was confirmed by TGA/DSC analysis. According to XPS analysis, oxygenated groups at the surface of the MWCNT and stoichiometric formation of WO3 thin films were determined, while the crystalline structure of the nanocomposite samples was studied by XRD indicating (0 0 2) peak of MWCNT in the monoclinic phase of WO3. The influence of different weight percentage (wt%) of MWCNT on WO3 photoactivity showed that the electron conductivity, charge transfer and electron life time had improved as compared with the pure WO3. Based on linear sweep voltammetry and chronoamperometry measurements, the (1 wt%) MWCNT/WO3 nanocomposite thin films photoanode has a maximum photocurrent density of ~4.5 A/m2 and electron life time of about 57 s.

  14. Investigation of x-ray photoelectron spectroscopic (XPS), cyclic voltammetric analyses of WO3 films and their electrochromic response in FTO/WO3/electrolyte/FTO cells

    NASA Astrophysics Data System (ADS)

    Sivakumar, R.; Gopalakrishnan, R.; Jayachandran, M.; Sanjeeviraja, C.

    2006-06-01

    Electrochromic thin films of tungsten oxide (WO3) were prepared on transparent conducting oxide substrates, i.e., fluorine doped tin oxide coated (FTO or SnO2:F) glass and microscopic glass substrates by the electron beam evaporation technique using pure WO3 (99.99%) pellets at various substrate temperatures (i.e., Tsub = room temperature (RT, 30 °C), 100 °C and 200 °C). The films were prepared under vacuum of the order of 1 × 10-5 mbar. The room temperature prepared films were further post-heat-treated (Tanne) at 200 and 300 °C for about 1 h in the vacuum environment. The prepared films are in monoclinic phase. The chemical composition has been characterized by using the XPS technique. The W 4f and O 1s core levels of WO3 films have been studied on the samples. The obtained core level binding energies revealed the WO3 films contained six-valent tungsten (W6+). The electrochemical nature of the films was studied by a three-electrode electrochemical cell in the configuration of FTO/WO3/H2SO4/Pt, SCE, using the cyclic voltammetry (CV) technique. Electrochromic devices (ECDs) of the general type FTO/WO3/electrolyte/FTO were studied. The films produced at higher substrate temperature show smaller modulation of the visible spectrum, compared with the films produced at lower temperatures. The significant chemical bonding nature associated with the coloring/bleaching process which follows the H+ ion incorporation in the film is studied by FTIR analysis. The W-O-W framework peak was observed at 563 cm-1 and confirms the stability of the films in the electrochemical analysis. The results obtained from cyclic voltammetry technique and ECD cell characterization are used to emphasize the suitability for some applications of the solar control systems.

  15. Reloading Continuous GPS in Northwest Mexico

    NASA Astrophysics Data System (ADS)

    Gonzalez-Garcia, J. J.; Suarez-Vidal, F.; Gonzalez-Ortega, J. A.

    2007-05-01

    For more than 10 years we try to follow the steps of the Southern California Integrated GPS Network (SCIGN) and the Plate Boundary Observatory (PBO) in USA, this gives us the opportunity to be in position to contribute to develop a modern GPS Network in Mexico. During 1998 and 2001, three stations were deployed in Northwest Mexico in concert with the development of SCIGN: SPMX in north central Baja California state at the National Astronomical Observatory, UNAM in the Sierra San Pedro Martir; CORX in Isla Coronados Sur, offshore San Diego, Ca./Tijuana, Mexico and GUAX in Guadalupe island 150 miles offshore Baja California peninsula, which provide a unique site on the Pacific plate in the Northamerica/Pacific boundary zone in Las Californias. The former IGS station in CICESE, Ensenada, CICE installed in 1995, was replaced by CIC1 in 1999. In 2004 and 2005 with partial support from SCIGN and UNAVCO to University of Arizona a volunteer team from UNAVCO, Caltech, U.S. Geological Survey, Universidad de la Sierra at Moctezuma Sonora and CICESE built two new shallow-braced GPS sites in northwest Mexico. The first site USMX is located at east-central Sonora and the second YESX is located high in the Sierra Madre Occidental at Yecora near the southern border of Sonora and Chihuahua. All data is openly available at SOPAC and/or UNAVCO. The existing information has been valuable to resolve the "total" plate motion between the Pacific plate (GUAX) and the Northamerica plate (USMX and YESX) in the north- central Gulf of California. Since the last year we have the capability of GPS data processing using GAMIT/GLOBK, and after gain some practice with survey mode data processing we can convert us in a GPS processing center in Mexico. Currently only 2 sites are operational: CIC1 and USMX. With new energy we are ready to contribute to the establishment of a modern GPS network in Mexico for science, hazard monitoring and infrastructure.

  16. Monitoring of D-layer using GPS

    NASA Astrophysics Data System (ADS)

    Golubkov, Maxim; Bessarab, Fedor; Karpov, Ivan; Golubkov, Gennady; Manzheliy, Mikhail; Borchevkina, Olga; Kuverova, Veronika; Malyshev, Nikolay; Ozerov, Georgy

    2016-07-01

    Changes in D layer of ionosphere during the periods of high solar activity lead to non-equilibrium two-temperature plasma parameter variations. Accordingly, the population of orbital degenerate states of Rydberg complexes changes in a fraction of a microsecond. In turn, this affects the operation of any of the systems based on the use of GPS radio signals passing through this layer. It is well known that GPS signals undergo the greatest distortion in the altitude range of 60-110 km. Therefore, the analysis of changes in signal intensity can be useful for plasma diagnosis in these altitudes. In particular, it is useful to determine the vertical temperature profiles and electron density. For this purpose, one can use the satellite radio occultation method. This method is widely used in recent years to solve problems of the electron concentration profile recovery in the F-region of the ionosphere, and also for climate problem solutions. This method allows to define the altitude profiles of the GPS signal propagation delays and to obtain from the inverse problem solution qualitatively high-altitude profiles of the quantities using relative measurements. To ensure the authenticity of the found distributions of electron density and temperature in the D region of the ionosphere, the results should be complemented by measurements of the own atmospheric radiation power at frequencies of 1.4 and 5.0 GHz. This ensures control of the reliability of the results obtained using the "Rydberg" code. Monitoring of the state changes in the D layer by repeatedly following at regular intervals GPS satellite measurements are also of great interest and can provide valuable information on the macroscopic dynamics of D layer containing Rydberg complexes and free electrons. For example, one can monitor changes in the thickness of the emitting layer in time. Such changes lead to an additional contribution to the formation of satellite GPS system errors. It should also be noted that the

  17. Tectonics of Western Canada From GPS Observations

    NASA Astrophysics Data System (ADS)

    Mazzotti, S.; Flueck, P.; Hyndman, R. D.; Dragert, H.; Craymer, M.; Schmidt, M.

    2002-12-01

    Western Canada can be divided into three main current tectonic domains: The Cascadia subduction zone, the Queen Charlotte transform margin, and the Yukon intraplate deformation region. Well-developed GPS monitoring of present-day deformation has contributed substantially to our knowledge of the dynamics of the Cascadia margin. To the north, although seismicity and plate tectonics model indicate significant deformation, our understanding of the detailed tectonics is still sparse. We present a summary of GPS measurements obtained in western Canada and adjacent regions over the last 10 years that allow us to better apprehend these three tectonic systems. Along the Cascadia margin, the Juan de Fuca (JF) plate subducts beneath North America (NA). The crustal velocity field is well constrained by continuous and campaign GPS data that show a northeastward motion that decreases landward from ~10 to ~5 mm/yr. This deformation pattern indicates significant elastic shortening of the forearc due to the locking of the subduction thrust. The northernmost Cascadia region corresponds to a transition between subduction and transform regimes. GPS campaign data suggest that this transition is accommodated by internal deformation and underthrusting of the Explorer plate beneath the NA margin. Further to the north, the Queen Charlotte Fault (QCF) accommodates the strike-slip motion between the Pacific (PA) and the NA plates. The slight obliquity of the PA/NA motion relative to the QCF direction implies some convergence along this margin. GPS campaign data in the Queen Charlotte Islands indicate velocities of 5-15 mm/yr northward with respect to NA. These results suggest a complex interaction between strain loading along the locked QCF, strain loading along a subduction thrust just offshore, and potential long-term deformation of the NA margin up to the Alaska Panhandle. The PA/NA transform margin changes to a convergence system in the Gulf of Alaska, where the Yakutat Terrane is

  18. Comparative studies of monoclinic and orthorhombic WO3 films used for hydrogen sensor fabrication on SiC crystal

    NASA Astrophysics Data System (ADS)

    Zuev, V. V.; Grigoriev, S. N.; Romanov, R. I.; Fominski, V. Y.; Volosova, M. A.; Demin, M. V.

    2016-09-01

    Amorphous WOx films were prepared on the SiC crystal by using two different methods, namely, reactive pulsed laser deposition (RPLD) and reactive deposition by ion sputtering (RDIS). After deposition, the WOx films were annealed in an air. The RISD film possessed a m-WO3 structure and consisted of closely packed microcrystals. Localized swelling of the films and micro-hills growth did not destroy dense crystal packing. RPLD film had layered β-WO3 structure with relatively smooth surface. Smoothness of the films were destroyed by localized swelling and the micro-openings formation was observed. Comparative study of m-WO3/SiC, Pt/m-WO3/SiC, and P-WO3/SiC samples shows that structural characteristics of the WO3 films strongly influence on the voltage/current response as well as on the rate of current growth during H2 detection at elevated temperatures.

  19. Preparation, characterization and photocatalytic behavior of WO3-fullerene/TiO2 catalysts under visible light

    PubMed Central

    2011-01-01

    WO3-treated fullerene/TiO2 composites (WO3-fullerene/TiO2) were prepared using a sol-gel method. The composite obtained was characterized by BET surface area measurements, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and UV-vis analysis. A methyl orange (MO) solution under visible light irradiation was used to determine the photocatalytic activity. Excellent photocatalytic degradation of a MO solution was observed using the WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 composites under visible light. An increase in photocatalytic activity was observed, and WO3-fullerene/TiO2 has the best photocatalytic activity; it may attribute to the increase of the photo-absorption effect by the fullerene and the cooperative effect of the WO3. PMID:21774800

  20. DFT study of CO sensing mechanism on hexagonal WO3 (0 0 1) surface: The role of oxygen vacancy

    NASA Astrophysics Data System (ADS)

    Tian, FengHui; Zhao, Linghuan; Xue, Xu-Yan; Shen, Yaoyao; Jia, Xiangfeng; Chen, Shougang; Wang, Zonghua

    2014-08-01

    In this work, density functional theory (DFT) calculations have been used to study the adsorption of CO on the oxygen deficient hexagonal WO3 (h-WO3) (0 0 1) surface. Two different situations including the O- and WO-terminated h-WO3 (0 0 1) surfaces are considered. The influence of surface defect density is also concerned. Calculations proposed that the oxygen vacancy exert negative effects on the sensing ability of the h-WO3 material. Under relatively higher defect density, the presence of the oxygen vacancy on both of the O and WO-terminated (0 0 1) surfaces all decreases their sensitivity to CO gas to some extent, while they are still sensitive enough to detect CO gas with the charge transfers of 0.498 and 0.129 e, respectively. Whereas, under lower defect density, calculations indicated that the sensitivity of the material can be lowered largely.

  1. Constructing TiO2 decorated Bi2WO6 architectures with enhanced visible-light-driven photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Yang, Zhiyuan; Chen, Lu; Yang, Yun; Wang, Junjie; Huang, Yongkui; Liu, Xiaoxia; Yang, Shuijin

    2017-06-01

    TiO2 nanoparticles modified Bi2WO6 photocatalysts were prepared via a facile hydrothermal process. The photocatalytic activity of as-prepared TiO2/Bi2WO6 composites was investigated sufficiently by the photodegradation of rhodamine B (RhB), tetracycline hydrochloride (TC) and ciprofloxacin (CIP). The TiO2/Bi2WO6 composites, in which the molar ratio of TiO2 to Bi2WO6 is 1:1, exhibited optimum photocatalytic activity, which is found to increase by about 2.4 times more than that of pristine Bi2WO6 for the photodegradation of TC. The enhanced photocatalytic activity may be attributed to the higher surface area and the highly efficient charge separation between Bi2WO6 nanosheets and TiO2 nanoparticles. The mechanism of the photocatalysts is investigated by the determination of reactive species in the photocatalytic reactions, the photoluminescence measurement and photoelectrochemical analyses.

  2. Inversion of the Tohoku 2011 Earthquke Using High Rate GPS Data (cGPS)

    NASA Astrophysics Data System (ADS)

    Ruiz, S.; Madariaga, R. I.

    2011-12-01

    The Mw 9 Tohoku-oki earthquake was recorded by over 1200 continuously recording high rate GPS sensor (cGPS). We use these data to do kinematic inversions of the rupture process of this mega-earthquake. The Neighborhood algorithm and other Monte Carlo inversion methods were used to find the optimum source models comparing observed and synthetic records. The cGPS and synthetic records were filtered using variable low-pass filters from 0.04 to 0.1 Hz (25 to 10 s). The AXITRA spectral code was used to simulate wave propagation. Different approaches for the parameterisation of the source were tested like elliptical patches and splines based on a fixed rectangular mesh. At low frequencies, less than 0.04 Hz, synthetics fit the static and very low frequency near field with error reduction better than 92 %. A simple model comprising two elliptical patches fits both static and cGPS data very well. At frequencies higher than 0.04 Hz more detailed source models are required. We use a fixed rectangular mesh with piecewise continuous slip distribution although higher order spline based slip distributions may be explored. Synthetics computed with the AXITRA program fully describe the static and near, intermediate and far field seismic waves that compose cGPS records (motograms) for a flat layered structure. The best kinematic solutions from a family that has a strong trade-off between rupture velocity and slip distribution, with maximum slip values in a range of 30 to 60 meters and rupture speeds in the range of 1.5 to 3.5 km/sec. Finally, the Tohoku cGPS inversions are compared with kinematic inversions of the cGPS data for the 2010 Maule, Chile earthquake, showing remarkably similar characteristics.

  3. GPS-PWV dataset by GPS Preciptable Water Research Project (GRASP)

    NASA Astrophysics Data System (ADS)

    Fujita, M.; Wada, A.; Iwabuchi, T.; Rocken, C.

    2012-12-01

    A novel project (GPS pRecipitable wAter reSearch Project) GRASP has been launched to investigate variations of precipitable water vapor caused by the climate change. The water vapor is one of the greenhouse gases, which is more effective than CO2, so it is important to observe water vapor change for a long period. More than 1,000 points stationary data of GPS were collected globally from International GNSS Services and GPS Earth Observation Network System (GEONET) in Japan over 15 years from 1996 through 2010. Atmospheric zenith total delay (ZTD) caused by refractivity of pressure, temperature, and water vapor pressure is estimated by the GPS processing software RTNet (Rocken et al 2006, Iwabuchi et al. 2006), where fiducial coordinate of GPS position is estimated periodically in a month to absorb any un-modeled and site-specific biases. Sophisticated seamless processing is performed every month to prevent jumps of ZTD solution in day boundary as observed in historical ZTD database. The estimated ZTD is converted to precipitable water vapor by metrological data derived from Japan Meteorological Agency or reanalysis data of NOAA with high-temporal resolution (CFSR) that have been performed altitude correction. The temporal resolution of some product is relatively high with one hour, which is applicable to climate research within a day such as diurnal circulation of water vapor. The greatest advantage of GPS precipitable water includes high temporal resolution and high accuracy of absolute value, comparing with other data of water vapor (Radiosonde, water vapor radiometer, lidar, SSM/I, etc.). Furthermore, the dataset of GPS precipitable water will be released to public by WWW. It could not only be important information to understand behavior of long-term water vapor variability and circulation, but also to be helpful to further explain mechanism of heavy rainfall cases affected by the climate change with addition of the high quality precipitable water vapor

  4. Continuous-wave laser operation of Tm and Hoco-doped NaY(WO(4))(2) and NaLu(WO(4))(2) crystals.

    PubMed

    Han, X; Fusari, F; Serrano, M D; Lagatsky, A A; Cano-Torres, J M; Brown, C T A; Zaldo, C; Sibbett, W

    2010-03-15

    Tetragonal single crystals of NaT(WO(4))(2) (T = Y or Lu) co-doped with Tm(3+) and Ho(3+) ions have been employed for broadly tunable and efficient room-temperature laser operation at around 2 mum. With Ti:sapphire laser pumping at 795 nm, a slope efficiency and a maximum output power as high as 48% and 265 mW, respectively, have been achieved at 2050 nm from a Tm,Ho:NaY(WO(4))(2) crystal. Tuning from 1830 nm to 2080 nm has also been obtained using an intracavity Lyot filter.

  5. Regional Deformation Studies with GRACE and GPS

    NASA Technical Reports Server (NTRS)

    Davis, J. L.; Elosequi, P.; Tamisiea, M.; Mitrovica, J. X.

    2005-01-01

    GRACE data indicate large seasonal variations in gravity that have been shown to be to be related to climate-driven fluxes of surface water. Seasonal redistribution of surface mass deforms the Earth, and our previous study using GRACE data demonstrate that annual radial deformations of +/-13 mm in the region of Amazon River Basin were observed by both GRACE and ten GPS sites in the region. For the GRACE determinations, we estimate in a least-squares solution for each Stokes coefficient parameters that represent the amplitudes of the annual variation. We then filter these parameters based on a statistical test that uses the scatter of the postfit residuals. We demonstrate by comparison to the GPS amplitudes that this method is more accurate, for this region, than Gaussian smoothing. Our model for the temporal behavior of the gravity coefficients includes a rate term, and although the time series are noisy, the glacial isostatic adjustment signal over Hudson s Bay can be observed. .

  6. Improved thermal force modeling for GPS satellites

    NASA Technical Reports Server (NTRS)

    Vigue, Y.; Schutz, R. E.; Abusali, P. A. M.

    1993-01-01

    Geophysical applications of the Global Positioning System (GPS) require the capability to estimate and propagate satellite orbits with high precision. An accurate model of all the forces acting on a satellite is an essential part of achieving high orbit accuracy. Methods of analyzing the perturbation due to thermal radiation and determining its effects on the long-term orbital behavior of GPS satellites are presented. The thermal imbalance force, a nongravitational orbit perturbation previously considered negligible, is the focus of this article. The earth's shadowing of a satellite in orbit causes periodic changes in the satellite's thermal environment. Simulations show that neglecting thermal imbalance in the satellite force model gives orbit error larger than ten meters over several days for eclipsing satellites. This orbit mismodeling can limit accuracy in orbit determination and in estimation of baselines used for geophysical applications.

  7. Airborne Laser/GPS Mapping of Beaches

    NASA Technical Reports Server (NTRS)

    Krabill, W. B.; Swift, R. N.; Fredrick, E. B.; Manizade, S. S.; Martin, C. F.; Sonntag, J. G.; Duffy, Mark

    1999-01-01

    Results are presented from topographic surveys of the Assateague National Seashore Park using recently developed airborne laser and Global Positioning System (GPS) technology. During November, 1995, and again in May, 1996, the NASA Arctic Ice Mapping (AIM) group from the NASA Goddard Space Flight Center's Wallops Flight Facility conducted surveys as a part of technology enhancement activities or warm-up missions prior to conducting elevation measurements of the Greenland Ice Sheet as part of NASA's Global Climate Change program. The resulting data are compared to surface surveys using standard techniques. The goal of these projects is to make these measurements to an accuracy of 10 cm. The measurements were made from NASA's 4-engine P-3 Orion aircraft using the Airborne Topographic Mapper (ATM), a scanning laser system. The necessary high accuracy vertical as well as horizontal positioning are provided by Global Positioning System (GPS) receivers located both on board the aircraft and at a fixed site at Wallops Island.

  8. Using GPS to determine vehicle attitude

    NASA Astrophysics Data System (ADS)

    Kruczynski, Leonard R.; Li, Pui C.; Evans, Alan G.; Hermann, Bruce R.

    The use of Navstar GPS for static and dynamic attitude determination is discussed, summarizing the results of tests on a prototype heading and attitude system comprising a 3-antenna array of area less than 1 sq m and a compact receiver-processor unit (RPU) of volume less than 1/3 cu ft and weight about 10 pounds. The algorithms employed in the orientation computation for 4-channel and 6-channel RPUs are outlined, and the selection of baseline lengths is discussed. Results from static (rooftop) and dynamic (antenna-rotor) tests of the 6-channel RPU are presented in graphs and briefly characterized, with particular attention to the integer-ambiguity problem inherent in GPS-based orientation systems. It is shown that the 6-channel RPU can maintain track of the correct integer set but cannot recover from a loss of integer track. An 18-channel RPU with a modified RF section is being developed to correct this deficiency.

  9. Pseudolite-aided GPS - A comparison

    NASA Astrophysics Data System (ADS)

    Stein, Barry A.; Tsang, Wai L.

    The author suggests that there is strong reason to believe that variations in GPS (Global Positioning System) performance as a function of location and time can be mitigated by augmenting the GPS system wih pseudolites in pure geodetic, differential, and hybrid forms. Analysis have been performed to calculate the relative merits of these augmentations. The area of detail studied was the southwestern US to ascertain the effects on a typical test range. Simulation results show that the navigation solution accuracy of either a stationary or mobile user improves by adding pseudolites with a pure geodetic capability, and improves dramatically with a differential capability. The results demonstrate the time dependence of the navigation solution at the user location.

  10. High dynamic GPS receiver validation demonstration

    NASA Technical Reports Server (NTRS)

    Hurd, W. J.; Statman, J. I.; Vilnrotter, V. A.

    1985-01-01

    The Validation Demonstration establishes that the high dynamic Global Positioning System (GPS) receiver concept developed at JPL meets the dynamic tracking requirements for range instrumentation of missiles and drones. It was demonstrated that the receiver can track the pseudorange and pseudorange rate of vehicles with acceleration in excess of 100 g and jerk in excess of 100 g/s, dynamics ten times more severe than specified for conventional High Dynamic GPS receivers. These results and analytic extensions to a complete system configuration establish that all range instrumentation requirements can be met. The receiver can be implemented in the 100 cu in volume required by all missiles and drones, and is ideally suited for transdigitizer or translator applications.

  11. GPS-derived crustal deformation in Azerbaijan

    NASA Astrophysics Data System (ADS)

    Safarov, Rafig; Mammadov, Samir; Kadirov, Fakhraddin

    2017-04-01

    Crustal deformations of the Earth's crust in Azerbaijan were studied based on GPS measurements. The GPS velocity vectors for Azerbaijan, Iran, Georgia, and Armenia were used in order to estimate the deformation rates. It is found that compression is observable along the Greater Caucasus, in Gobustan, the Kura depression, Nakhchyvan Autonomous Republic, and adjacent areas of Iran. The axes of compression/contraction of the crust in the Greater Caucasus region are oriented in the S-NE direction. The maximum strain rate is observed in the zone of mud volcanism at the SHIK site (Shykhlar), which is marked by a sharp change in the direction of the compression axes (SW-NE). It is revealed that the deformation field also includes the zones where strain rates are very low. These zones include the Caspian-Guba and northern Gobustan areas, characterized by extensive development of mud volcanism. The extension zones are confined to the Lesser Caucasus and are revealed in the Gyadabei (GEDA) and Shusha (SHOU) areas. The analysis of GPS data for the territory of Azer baijan and neighboring countries reveals the heterogeneous patterns of strain field in the region. This fact suggests that the block model is most adequate for describing the structure of the studied region. The increase in the number of GPS stations would promote increasing the degree of detail in the reconstructions of the deformation field and identifying the microplate boundaries.It is concluded that the predominant factor responsible for the eruption of mud volcanoes is the intensity of gas generation processes in the earth's interior, while deformation processes play the role of a trig ger. The zone of the epicenters of strong earthquakes is correlated to the gradient zone in the crustal strain rates.

  12. Absolute GPS Positioning Using Genetic Algorithms

    NASA Astrophysics Data System (ADS)

    Ramillien, G.

    A new inverse approach for restoring the absolute coordinates of a ground -based station from three or four observed GPS pseudo-ranges is proposed. This stochastic method is based on simulations of natural evolution named genetic algorithms (GA). These iterative procedures provide fairly good and robust estimates of the absolute positions in the Earth's geocentric reference system. For comparison/validation, GA results are compared to the ones obtained using the classical linearized least-square scheme for the determination of the XYZ location proposed by Bancroft (1985) which is strongly limited by the number of available observations (i.e. here, the number of input pseudo-ranges must be four). The r.m.s. accuracy of the non -linear cost function reached by this latter method is typically ~10-4 m2 corresponding to ~300-500-m accuracies for each geocentric coordinate. However, GA can provide more acceptable solutions (r.m.s. errors < 10-5 m2), even when only three instantaneous pseudo-ranges are used, such as a lost of lock during a GPS survey. Tuned GA parameters used in different simulations are N=1000 starting individuals, as well as Pc=60-70% and Pm=30-40% for the crossover probability and mutation rate, respectively. Statistical tests on the ability of GA to recover acceptable coordinates in presence of important levels of noise are made simulating nearly 3000 random samples of erroneous pseudo-ranges. Here, two main sources of measurement errors are considered in the inversion: (1) typical satellite-clock errors and/or 300-metre variance atmospheric delays, and (2) Geometrical Dilution of Precision (GDOP) due to the particular GPS satellite configuration at the time of acquisition. Extracting valuable information and even from low-quality starting range observations, GA offer an interesting alternative for high -precision GPS positioning.

  13. Global Geodesy Using GPS Without Fiducial Sites

    NASA Technical Reports Server (NTRS)

    Heflin, Michael B.; Blewitt, Geoffrey

    1994-01-01

    Global Positioning System, GPS, used to make global geodetic measurements without use of fiducial site coordinates. Baseline lengths and geocentric radii for each site determined without having to fix any site coordinates. Given n globally distributed sites, n baseline lengths and n geocentric radii form polyhedron with each site at vertex and with geocenter at intersection of all radii. Geodetic information derived from structure of polyhedron and its change with time. Approach applied to any global geodetic technique.

  14. Long arc analysis of GPS orbits

    NASA Astrophysics Data System (ADS)

    Schutz, B.; Froideval, L.

    The influence of gravitational and nongravitational forces on the orbits of GPS satellites is well known. Although the gravitational forces are the dominant factors in characterizing long term orbital evolution, the uncertainties associated with modeling nongravitational forces are the dominant factors that limit the accuracy of long term predictions of GPS satellite positions. Even though the GPS satellites are in deep resonance with the gravity field of the Earth, which in turn produces secular changes in the semimajor axis, the uncertainties in the gravity field model are not limiting factors in long term prediction accuracy. In the case of nongravitational forces, a simple Lageos-like (cannonball) solar radiation pressure model produces few decimeter accuracy when used in conjunction with other forces, such as y-bias, in the determination of GPS orbits over time intervals of a few days. Furthermore, the cannonball model, with y-bias, performs as well as the ROCK42 model (with y-bias) over a one year estimation arc after solving for epoch state, y-bias and a scale factor for solar radiation pressure (8 parameters). In this case, a one year arc exhibits approximately 30 meter RMS differences with either model compared to the daily IGS orbits. On the other hand, the Berne ECOM model under the same conditions shows < 5 meters for most satellites, but some satellites are a factor of three worse. Estimation of scale parameters with higher resolution (for example, daily or less) provides some insight into the nature of the nongravitational forces and correlations with other factors, such as eclipse seasons. Further model evaluation can be obtained from predictions, but such cases are limited by the ability to choose appropriate parameters to use in the prediction. The observed characteristics may have implications for future navigation satellite systems.

  15. Comparison of LASSO and GPS time transfers

    NASA Technical Reports Server (NTRS)

    Lewandowski, W.; Petit, G.; Baumont, F.; Fridelance, P.; Gaignebet, J.; Grudler, P.; Veillet, C.; Wiant, J.; Klepczynski, W. J.

    1994-01-01

    The LASSO is a technique which should allow the comparison of remote atomic clocks with sub-nanosecond precision and accuracy. The first successful time transfer using LASSO has been carried out between the Observatoire de la Cote d'Azur in France and the McDonald Observatory in Texas, United States. This paper presents a preliminary comparison of LASSO time transfer with GPS common-view time transfer.

  16. Digital Signal Processor For GPS Receivers

    NASA Technical Reports Server (NTRS)

    Thomas, J. B.; Meehan, T. K.; Srinivasan, J. M.

    1989-01-01

    Three innovative components combined to produce all-digital signal processor with superior characteristics: outstanding accuracy, high-dynamics tracking, versatile integration times, lower loss-of-lock signal strengths, and infrequent cycle slips. Three components are digital chip advancer, digital carrier downconverter and code correlator, and digital tracking processor. All-digital signal processor intended for use in receivers of Global Positioning System (GPS) for geodesy, geodynamics, high-dynamics tracking, and ionospheric calibration.

  17. Global Geodesy Using GPS Without Fiducial Sites

    NASA Technical Reports Server (NTRS)

    Heflin, Michael B.; Blewitt, Geoffrey

    1994-01-01

    Global Positioning System, GPS, used to make global geodetic measurements without use of fiducial site coordinates. Baseline lengths and geocentric radii for each site determined without having to fix any site coordinates. Given n globally distributed sites, n baseline lengths and n geocentric radii form polyhedron with each site at vertex and with geocenter at intersection of all radii. Geodetic information derived from structure of polyhedron and its change with time. Approach applied to any global geodetic technique.

  18. The NAVSTAR GPS (Global Positioning System) System

    DTIC Science & Technology

    1988-09-01

    Block IIR satellites is the autonomous navigation of GPS satellites utilizing crosslink ranging. The Block II satellites have crosslink Lommunications...capability, but no ranging. The Block HIR satellites will be modified to enable crosslink ranging on the same crosslink frequency and, by processing the... crosslink range measurements, the CPS navigation message can be generated onboard the satellite without daily upload from the ground. Analysis has

  19. GPS and Relativity: An Engineering Overview

    DTIC Science & Technology

    1996-12-01

    System (OCS) of the Global Positioning System ( GPS ) does not include the rigorous transformations between coordinate systems that Einstein’s general... Positioning System ," in Global Positioning System : Theory and Ap- plications, Vol. I, ed. B. Parkinson and J.J. Spilker, Jr. (American Institute of...Nelson 1991, "An analysis of g e n e d ~elativity in the Global Positioning System time transfer algorithm, " report

  20. Measuring Orientation Of The Earth With GPS

    NASA Technical Reports Server (NTRS)

    Freedman, Adam P.

    1992-01-01

    Report discusses feasibility of using Global Positioning System (GPS) to resolve short-term fluctuations (days or hours) in locations of points on crust of Earth to within centimeters or millimeters. With full constellation of satellites and ground receiving stations, system provides rapid (within 12 hours) determinations of variations in orientation. Measurements used to enhance precision of spacecraft navigation and in geophysical and meteorological studies of daily exchanges of angular momentum among fluid core, crust and mantle, oceans, and atmosphere.

  1. Precise Clock Solutions Using Carrier Phase from GPS Receivers in the International GPS Service

    NASA Technical Reports Server (NTRS)

    Zumberge, J. F.; Jefferson, D. C.; Stowers, D. A.; Tjoelker, R. L.; Young, L. E.

    1999-01-01

    As one of its activities as an Analysis Center in the International GPS Service (IGS), the Jet Propulsion Laboratory (JPL) uses data from a globally distributed network of geodetic-quality GPS receivers to estimate precise clock solutions, relative to a chosen reference, for both the GPS satellites and GPS receiver internal clocks, every day. The GPS constellation and ground network provide geometrical strength resulting in formal errors of about 100 p sec for these estimates. Some of the receivers in the global IGS network contain high quality frequency references, such as hydrogen masers. The clock solutions for such receivers are smooth at the 20-p sec level on time scales of a few minutes. There are occasional (daily to weekly) shifts at the microsec level, symptomatic of receiver resets, and 200-p sec-level discontinuities at midnight due to 1-day processing boundaries. Relative clock solutions among 22 IGS sites proposed as "fiducial" in the IGS/BIPM pilot project have been examined over a recent 4-week period. This allows a quantitative measure of receiver reset frequency as a function of site. For days and-sites without resets, the Allan deviation of the relative clock solutions is also computed for subdaily values of tau..

  2. GPS phase scintillation correlated with auroral forms

    NASA Astrophysics Data System (ADS)

    Hampton, D. L.; Azeem, S. I.; Crowley, G.; Santana, J.; Reynolds, A.

    2013-12-01

    The disruption of radio wave propagation due to rapid changes in electron density caused by auroral precipitation has been observed for several decades. In a few cases the disruption of GPS signals has been attributed to distinct auroral arcs [Kintner, 2007; Garner, 2011], but surprisingly there has been no systematic study of the characteristics of the auroral forms that cause GPS scintillation. In the Fall of 2012 ASTRA deployed four CASES GPS receivers at UAF observatories in Alaska (Kaktovik, Fort Yukon, Poker Flat and Gakona) specifically to address the effects of auroral activity on the high latitude ionosphere. We have initiated an analysis that compares the phase scintillation, recorded at high cadence, with filtered digital all-sky camera data to determine the auroral morphology and electron precipitation parameters that cause scintillation. From correlation studies from a single site (Poker Flat), we find that scintillation is well correlated with discrete arcs that have high particle energy flux (power per unit area), and not as well correlated with pulsating forms which typically have high characteristic energy, but lower energy flux . This indicates that the scintillation is correlated with the magnitude of the change in total electron density as expected. We will also report on ongoing work where we correlate the scintillation from the Fort Yukon receiver with the all-sky images at Poker Flat to determine the altitude that produces the greatest disturbance. These studies are aimed at a model that can predict the expected local disturbance to navigation due to auroral activity.

  3. Time and position accuracy using codeless GPS

    NASA Technical Reports Server (NTRS)

    Dunn, C. E.; Jefferson, D. C.; Lichten, S. M.; Thomas, J. B.; Vigue, Y.; Young, L. E.

    1994-01-01

    The Global Positioning System has allowed scientists and engineers to make measurements having accuracy far beyond the original 15 meter goal of the system. Using global networks of P-Code capable receivers and extensive post-processing, geodesists have achieved baseline precision of a few parts per billion, and clock offsets have been measured at the nanosecond level over intercontinental distances. A cloud hangs over this picture, however. The Department of Defense plans to encrypt the P-Code (called Anti-Spoofing, or AS) in the fall of 1993. After this event, geodetic and time measurements will have to be made using codeless GPS receivers. However, there appears to be a silver lining to the cloud. In response to the anticipated encryption of the P-Code, the geodetic and GPS receiver community has developed some remarkably effective means of coping with AS without classified information. We will discuss various codeless techniques currently available and the data noise resulting from each. We will review some geodetic results obtained using only codeless data, and discuss the implications for time measurements. Finally, we will present the status of GPS research at JPL in relation to codeless clock measurements.

  4. GPS/GNSS reflectometry nanosatellite demonstration mission

    NASA Astrophysics Data System (ADS)

    Unwin, Martin J.; Liddle, J. Douglas; Jason, Susan J.

    2003-01-01

    Loss of life, injury and huge economic losses are incurred annually due to irregular and insufficient sea-state information. Figures indicate that, each year, the marine insurance industry pays out over $2 billion in claims for weather-related accidents, while bad weather causes one ship of over 500 t to sink somewhere on the globe every week. Accurate knowledge of local ocean conditions is therefore crucial in providing forecasts and early warnings of severe weather conditions. Space-borne systems, particularly satellites, provide the ideal platform for global monitoring of sea conditions via altimetric measurements. As an alternative to active altimetry, another concept is passively receiving reflected signals from the Global Positioning System (GPS) and other Global Navigation Satellite System (GNSS) satellites. This concept was first developed by Dr Manuel Martin-Neira at ESAESTEC. ESA's Passive Reflectometry and Interferometry System makes use of GPS/GNSS signals from satellites and their reflection off the ocean surface to derive oceanic properties such as surface height, significant wave height, wind speed and wind direction. Surrey Satellite Technology Ltd are proposing a nanosatellite demonstration mission to ascertain the feasibility of the GPS ocean reflectometry concept.

  5. Cleaning HI Spectra Contaminated by GPS RFI

    NASA Astrophysics Data System (ADS)

    Sylvia, Kamin; Hallenbeck, Gregory L.; Undergraduate ALFALFA Team

    2016-01-01

    The NUDET systems aboard GPS satellites utilize radio waves to communicate information regarding surface nuclear events. The system tests appear in spectra as RFI (radio frequency interference) at 1381MHz, which contaminates observations of extragalactic HI (atomic hydrogen) signals at 50-150 Mpc. Test durations last roughly 20-120 seconds and can occur upwards of 30 times during a single night of observing. The disruption essentially renders the corresponding HI spectra useless.We present a method that automatically removes RFI in HI spectra caused by these tests. By capitalizing on the GPS system's short test durations and predictable frequency appearance we are able to devise a method of identifying times containing compromised data records. By reevaluating the remaining data, we are able to recover clean spectra while sacrificing little in terms of sensitivity to extragalactic signals. This method has been tested on 500+ spectra taken by the Undergraduate ALFALFA Team (UAT), in which it successfully identified and removed all sources of GPS RFI. It will also be used to eliminate RFI in the upcoming Arecibo Pisces-Perseus Supercluster Survey (APPSS).This work has been supported by NSF grant AST-1211005.

  6. Inductive effect of poly(vinyl pyrrolidone) on morphology and photocatalytic performance of Bi2WO6

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Chen, Jinxing; Xie, Yunyun; Wang, Mozhen; Ge, Xuewu

    2016-04-01

    Bi2WO6 has great potential applications in the field of photocatalyst due to its excellent visible-light photocatalytic performance. This work studied the detailed morphological evolution of Bi2WO6 particles synthesized in a simple hydrothermal system induced by the stabilizer poly(vinyl pyrrolidone) (PVP). The XRD and HRTEM results show PVP would not change the crystal structure of Bi2WO6, but the distribution of PVP on the initially formed Bi2WO6 nanosheets will induce the crystal growth, resulting in a distinct morphology evolution of Bi2WO6 with the increase of the concentration of PVP. At the same time, with the increase of the molecular weight of PVP, the morphology of Bi2WO6 varied from simple sheet-like (S-BWO) to some complicated morphology, such as flower-like (F-BWO), red blood cell-like (B-BWO), and square-pillar-like (SP-BWO). The photocatalytic performances of Bi2WO6 with various morphologies on the decomposition of RhB under visible light irradiation reveal that S-BWO has the best photocatalytic performance, while SP-BWO has the worst. This work not only gives the explanation of the inductive effect of PVP molecular chains on the morphological formation of Bi2WO6 particles, but also provides the controllable way to the preparation of Bi2WO6 with various morphologies taking advantage of the stabilizer PVP.

  7. WO3-enhanced TiO2 nanotube photoanodes for solar water splitting with simultaneous wastewater treatment.

    PubMed

    Reyes-Gil, Karla R; Robinson, David B

    2013-12-11

    Composite WO3/TiO2 nanostructures with optimal properties that enhance solar photoconversion reactions were developed, characterized, and tested. The TiO2 nanotubes were prepared by anodization of Ti foil and used as substrates for WO3 electrodeposition. The WO3 electrodeposition parameters were controlled to develop unique WO3 nanostructures with enhanced photoelectrochemical properties. Scanning electron microscopy (SEM) images showed that the nanomaterials with optimal photocurrent density have the same ordered structure as TiO2 nanotubes, with an external tubular nanostructured WO3 layer. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare TiO2 nanotubes and in the UV absorption relative to bare WO3 films. Incident simulated solar photon-to-current efficiency (IPCE) increased from 30% (for bare WO3) to 50% (for tubular WO3/TiO2 composites). With the addition of diverse organic pollutants, the photocurrent densities exhibited more than a 5-fold increase. Chemical oxygen demand measurements showed the simultaneous photodegradation of organic pollutants. The results of this work showed that the unique structure and composition of these composite WO3/TiO2 materials enhance the IPCE efficiencies, optical properties, and photodegradation performance compared with the parent materials.

  8. Effect of fluorine, nitrogen, and carbon impurities on the electronic and magnetic properties of WO{sub 3}

    SciTech Connect

    Shein, I. R.; Ivanovskii, A. L.

    2013-06-15

    Within electron density functional theory with the use of the Vienna ab-initio simulation package (VASP), the effect of the sp substitutional impurities of fluorine (n-type dopant), nitrogen, and carbon (p-type dopants) on the electronic and magnetic properties of tungsten trioxide WO{sub 3} is studied. It is established that these impurities induce the transformation of tungsten trioxide (nonmagnetic semiconductor) into nonmagnetic metal (WO{sub 3}:F), magnetic semimetal (WO{sub 3}:N), or magnetic metal (WO{sub 3}:C) states.

  9. Thermal effects associated with the Raman spectroscopy of WO3 gas-sensor materials.

    PubMed

    Garcia-Sanchez, Raul F; Ahmido, Tariq; Casimir, Daniel; Baliga, Shankar; Misra, Prabhakar

    2013-12-19

    Metal oxides are suitable for detecting, through conductive measurements, a variety of reducing and oxidizing gases in environmental and sensing applications. Metal-oxide gas sensors can be developed with the goal of sensing gases under specific conditions and, as a whole, are heavily dependent on the manufacturing process. Tungsten oxide (WO3) is a promising metal-oxide material for gas-sensing applications. The purpose of this paper is to determine the existence of a correlation between thermal effects and the changes in the Raman spectra for multiple WO3 structures. We have obtained results utilizing Raman spectroscopy for three different structures of WO3 (monoclinic WO3 on Si substrate, nanopowder, and nanowires) that have been subjected to temperatures in the range of 30-160 °C. The major vibrational modes of the WO3:Si and the nanopowder samples, located at ~807, ~716, and ~271 cm(-1), correspond to the stretching of O-W-O bonds, the stretching of W-O, and the bending of O-W-O, respectively; these are consistent with a monoclinic WO3 structure. However in the nanowires sample only asymmetric stretching of the W-O bonds occurs, resulting in a 750 cm(-1) band, and the bending of the O-W-O mode (271 cm(-1)) is a stretching mode (239 cm(-1)) instead, suggesting the nanowires are not strictly monoclinic. The most notable effect of increasing the temperature of the samples is the appearance of the bending mode of W-OH bonds in the approximate range of 1550-1150 cm(-1), which is related to O-H bonding caused by humidity effects. In addition, features such as those at 750 cm(-1) for nanowires and at 492 and 670 cm(-1) for WO3:Si disappear as the temperature increases. A deeper understanding of the effect that temperature has on the Raman spectral characteristics of a metal oxide such as WO3 has helped to extend our knowledge regarding the behavior of metal oxide-gas interactions for sensing applications. This, in turn, will help to develop theoretical models for

  10. GPS deflection monitoring of the West Gate Bridge

    NASA Astrophysics Data System (ADS)

    Raziq, Noor; Collier, Philip

    2007-05-01

    The achievable precision and relatively high sampling rates of currently available GPS receivers are well suited for monitoring the movements of long-span engineering structures where the amplitude of movements is often more than a few centimetres and the frequency of vibrations is low (below 10 Hz). However, engineering structures often offer non-ideal environments for GPS data collection due to high multipath interference and obstructions causing cycle slips in the GPS observations. Also, for many engineering structures such as bridge decks, vertical movements are more pronounced and more structurally critical than horizontal movements. Accuracy of GPS determined positions in the vertical direction is typically two to three times poorer than in the horizontal component. This paper describes the results of a GPS deflection monitoring trial on the West Gate Bridge in Melbourne, Australia. The results are compared to the estimated frequencies and movements from the design of the bridge and previous accelerometer campaigns. The frequency information derived from the GPS results is also compared to frequency data extracted from an accelerometer installed close to a GPS receiver. GPS results agree closely to the historical results and recent accelerometer trials for key modal frequencies. This indicates the suitability of GPS receivers to monitor engineering structures that exhibit smaller movements due to their stiffness and in environments not ideally suited to using GPS.

  11. GPS/CAPS dual-mode software receiver

    NASA Astrophysics Data System (ADS)

    Ning, Chunlin; Shi, Huli; Hu, Chao

    2009-03-01

    The positioning of the GPS or Chinese Area Positioning System (CAPS) software receiver was developed on a software receiver platform. The structure of the GPS/CAPS dual-mode software receiver was put forward after analyzing the differences in the satellite identification, ranging code, spread spectrum, coordinate system, time system, carrier band, and navigation data between GPS and CAPS. Based on Matlab software on a personal computer, baseband signal processing and positioning procedures were completed using real GPS and CAPS radio frequency signals received by two antennas. Three kinds of experiments including GPS positioning, CAPS positioning, and GPS/CAPS positioning were carried out. Stability and precision of the results were analyzed and compared. The experimental results show that the precision of CAPS is similar to that of GPS, while the positioning precision of the GPS/CAPS dual-mode software receiver is 1-2 m higher than that of CAPS or GPS. The smallest average variance of the positioning can be obtained by using the GPS/CAPS dual-mode software receiver.

  12. NAVIGATION PERFORMANCE IN HIGH EARTH ORBITS USING NAVIGATOR GPS RECEIVER

    NASA Technical Reports Server (NTRS)

    Bamford, William; Naasz, Bo; Moreau, Michael C.

    2006-01-01

    NASA GSFC has developed a GPS receiver that can acquire and track GPS signals with sensitivity significantly lower than conventional GPS receivers. This opens up the possibility of using GPS based navigation for missions in high altitude orbit, such as Geostationary Operational Environmental Satellites (GOES) in a geostationary orbit, and the Magnetospheric MultiScale (MMS) Mission, in highly eccentric orbits extending to 12 Earth radii and higher. Indeed much research has been performed to study the feasibility of using GPS navigation in high Earth orbits and the performance achievable. Recently, GSFC has conducted a series of hardware in-the-loop tests to assess the performance of this new GPS receiver in various high Earth orbits of interest. Tracking GPS signals to down to approximately 22-25 dB-Hz, including signals from the GPS transmitter side-lobes, steady-state navigation performance in a geostationary orbit is on the order of 10 meters. This paper presents the results of these tests, as well as sensitivity analysis to such factors as ionosphere masks, use of GPS side-lobe signals, and GPS receiver sensitivity.

  13. Experimental and theoretical investigation of a mesoporous KxWO3 material having superior mechanical strength

    NASA Astrophysics Data System (ADS)

    Dey, Sonal; Anderson, Sean T.; Mayanovic, Robert A.; Sakidja, Ridwan; Landskron, Kai; Kokoszka, Berenika; Mandal, Manik; Wang, Zhongwu

    2016-01-01

    Mesoporous materials with tailored properties hold great promise for energy harvesting and industrial applications. We have synthesized a novel tungsten bronze mesoporous material (KxWO3; x ~ 0.07) having inverse FDU-12 type pore symmetry and a crystalline framework. In situ small angle X-ray scattering (SAXS) measurements of the mesoporous K0.07WO3 show persistence of a highly ordered meso-scale pore structure to high pressure conditions (~18.5 GPa) and a material with remarkable mechanical strength despite having ~35% porosity. Pressure dependent in situ SAXS measurements reveal a bulk modulus κ = 44 +/- 4 GPa for the mesoporous KxWO3 which is comparable to the corresponding value for the bulk monoclinic WO3 (γ-WO3). Evidence from middle angle (MAXS) and wide angle X-ray scattering (WAXS), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy shows that the presence of potassium leads to the formation of a K-bearing orthorhombic tungsten bronze (OTB) phase within a monoclinic WO3 host structure. Our ab initio molecular dynamics calculations show that the formation of the OTB phase provides superior strength to the mesoporous K0.07WO3.Mesoporous materials with tailored properties hold great promise for energy harvesting and industrial applications. We have synthesized a novel tungsten bronze mesoporous material (KxWO3; x ~ 0.07) having inverse FDU-12 type pore symmetry and a crystalline framework. In situ small angle X-ray scattering (SAXS) measurements of the mesoporous K0.07WO3 show persistence of a highly ordered meso-scale pore structure to high pressure conditions (~18.5 GPa) and a material with remarkable mechanical strength despite having ~35% porosity. Pressure dependent in situ SAXS measurements reveal a bulk modulus κ = 44 +/- 4 GPa for the mesoporous KxWO3 which is comparable to the corresponding value for the bulk monoclinic WO3 (γ-WO3). Evidence from middle angle (MAXS) and wide angle X-ray scattering (WAXS), high

  14. Using GPS to Detect Imminent Tsunamis

    NASA Technical Reports Server (NTRS)

    Song, Y. Tony

    2009-01-01

    A promising method of detecting imminent tsunamis and estimating their destructive potential involves the use of Global Positioning System (GPS) data in addition to seismic data. Application of the method is expected to increase the reliability of global tsunami-warning systems, making it possible to save lives while reducing the incidence of false alarms. Tsunamis kill people every year. The 2004 Indian Ocean tsunami killed about 230,000 people. The magnitude of an earthquake is not always a reliable indication of the destructive potential of a tsunami. The 2004 Indian Ocean quake generated a huge tsunami, while the 2005 Nias (Indonesia) quake did not, even though both were initially estimated to be of the similar magnitude. Between 2005 and 2007, five false tsunami alarms were issued worldwide. Such alarms result in negative societal and economic effects. GPS stations can detect ground motions of earthquakes in real time, as frequently as every few seconds. In the present method, the epicenter of an earthquake is located by use of data from seismometers, then data from coastal GPS stations near the epicenter are used to infer sea-floor displacements that precede a tsunami. The displacement data are used in conjunction with local topographical data and an advanced theory to quantify the destructive potential of a tsunami on a new tsunami scale, based on the GPS-derived tsunami energy, much like the Richter Scale used for earthquakes. An important element of the derivation of the advanced theory was recognition that horizontal sea-floor motions contribute much more to generation of tsunamis than previously believed. The method produces a reliable estimate of the destructive potential of a tsunami within minutes typically, well before the tsunami reaches coastal areas. The viability of the method was demonstrated in computational tests in which the method yielded accurate representations of three historical tsunamis for which well-documented ground

  15. Synthesis and photoactivity enhancement of Ba doped Bi{sub 2}WO{sub 6} photocatalyst

    SciTech Connect

    Li, Wen Ting; Huang, Wan Zhen; Zhou, Huan; Yin, Hao Yong; Zheng, Yi Fan; Song, Xu Chun

    2015-04-15

    Highlights: • The Ba-doped Bi{sub 2}WO{sub 6} photocatalyst have been synthesized by a hydrothermal route. • The photocatalytic activity of Bi{sub 2}WO{sub 6} was greatly enhanced by Ba-doping. • The effect of Ba on the catalytic activity of Bi{sub 2}WO{sub 6} was studied and discussed. - Abstract: In this study, Bi{sub 2}WO{sub 6} doped with different barium contents were successfully prepared by a simple hydrothermal route at 180 °C for 12 h. The as-synthesized samples were characterized in detailed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffusere flectance spectroscopy (UV–vis DRS) and Brunauer–Emmet–Teller (BET) theory. Their photocatalytic activities were evaluated by photodegradation of Rhodamine B (RhB) under simulated solar light. As a result, the photocatalytic properties were enhanced after Ba doping and the Ba-doped Bi{sub 2}WO{sub 6} with R{sub Ba} = 0.15 showed the highest photocatalytic activities of 96.3% RhB was decomposed in 50 min. Close investigation revealed that the proper Ba doped into Bi{sub 2}WO{sub 6} could not only increases its BET surface area, decrease its crystalline size, but also act as electron traps and facilitate the separation of photogenerated electron–hole pairs. The mechanism of enhanced photocatalytic activities of Ba-doped Bi{sub 2}WO{sub 6} were further investigated.

  16. Guanidine sulfate-assisted synthesis of hexagonal WO3 nanoparticles with enhanced adsorption properties.

    PubMed

    Mu, Wanjun; Li, Mei; Li, Xingliang; Ma, Zongping; Zhang, Rui; Yu, Qianhong; Lv, Kai; Xie, Xiang; He, Jiaheng; Wei, Hongyuan; Jian, Yuan

    2015-04-28

    Large surface area hexagonal phase WO3 (h-WO3) nanowires were synthesized by a hydrothermal route with the assistance of C2H12N6O4S. They were characterized by XRD, SEM, TEM, BET, FT-IR and XPS. It is shown that C2H12N6O4S not only acts as a stabilizer to facilitate the generation of a metastable hexagonal phase, but also functions as a structure directing agent to assist the construction of nanowires. The obtained h-WO3 possesses a large specific surface area and numerous adsorption functional groups such as -OH groups. These characteristics result in an excellent adsorption performance for the removal of strontium from acidic aqueous solutions. A maximum adsorption capacity of 52.93 mg g(-1) was achieved on the h-WO3 prepared in the presence of C2H12N6O4S. This value is almost two times higher than that of bare h-WO3 (no C2H12N6O4S). The effects of pH, contact time, initial Sr(2+) concentration and ion strength on Sr(2+) removal from the solution by h-WO3 were systematically investigated. The adsorption mechanism involving the combination of electrostatic attraction and ion exchange for the adsorption of Sr(2+) is proposed. Based on our results, h-WO3 with high adsorption capacity and good surface characteristics exhibits great potential for the removal of Sr(2+) from radioactive wastewater.

  17. WO-Type Wolf-Rayet Stars: the Last Hurrah of the Most Massive Stars?

    NASA Astrophysics Data System (ADS)

    Massey, Philip

    2014-10-01

    WO-type Wolf-Rayet (WR) stars are considered the final evolutionary stage of the highest mass stars, immediate precursors to Type Ic (He-poor) core-collapse supernovae. These WO stars are rare, and until recently only 6 were known. Our knowledge about their physical properties is mostly based on a single object, Sand 2 in the LMC. It was the only non-binary WO star both bright and unreddened enough that its FUV and NUV spectra could be obtained by FUSE and HST/FOS. A non-LTE analysis showed that Sand 2 is very hot and its (C+O)/He abundance ratio is higher than that found in WC-type WRs, suggesting it is indeed highly evolved. However, the O VI resonance doublet in the FUV required a considerably cooler temperature (120,000 K) model than did the optical O VI lines (170,000 K). Further, the enhanced chemical abundances did not match the predictions of stellar evolutionary models. Another non-LTE study found a 3x higher (C+O)/He abundance ratio and a cooler temperature. We have recently discovered two other bright, single, and lightly reddened WOs in the LMC, allowing us to take a fresh look at these important objects. Our newly found WOs span a range in excitation type, from WO1 (the highest) to WO4 (the lowest). Sand 2 is intermediate (WO3). We propose to use COS to obtain FUV and NUV data of all three stars for as comprehensive a study as is currently possible. These UV data will be combined with our optical Magellan spectra for a detailed analysis with CMFGEN with the latest atomic data. Knowing the degree of chemical evolution of these WO stars is crucial to determining their evolutionary status, and thus in understanding the final stages of the most massive stars.

  18. Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals.

    PubMed

    Souza, E L S; Sczancoski, J C; Nogueira, I C; Almeida, M A P; Orlandi, M O; Li, M S; Luz, R A S; Filho, M G R; Longo, E; Cavalcante, L S

    2017-09-01

    Copper tungstate (CuWO4) crystals were synthesized by the sonochemistry (SC) method, and then, heat treated in a conventional furnace at different temperatures for 1h. The structural evolution, growth mechanism and photoluminescence (PL) properties of these crystals were thoroughly investigated. X-ray diffraction patterns, micro-Raman spectra and Fourier transformed infrared spectra indicated that crystals heat treated and 100°C and 200°C have water molecules in their lattice (copper tungstate dihydrate (CuWO4·2H2O) with monoclinic structure), when the crystals are calcinated at 300°C have the presence of two phase (CuWO4·2H2O and CuWO4), while the others heat treated at 400°C and 500°C have a single CuWO4 triclinic structure. Field emission scanning electron microscopy revealed a change in the morphological features of these crystals with the increase of the heat treatment temperature. Transmission electron microscopy (TEM), high resolution-TEM images and selected area electron diffraction were employed to examine the shape, size and structure of these crystals. Ultraviolet-Visible spectra evidenced a decrease of band gap values with the increase of the temperature, which were correlated with the reduction of intermediary energy levels within the band gap. The intense photoluminescence (PL) emission was detected for the sample heat treat at 300°C for 1h, which have a mixture of CuWO4·2H2O and CuWO4 phases. Therefore, there is a synergic effect between the intermediary energy levels arising from these two phases during the electronic transitions responsible for PL emissions. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Synthesis of WO 3 nanoparticles for superthermites by the template method from silica spheres

    NASA Astrophysics Data System (ADS)

    Gibot, Pierre; Comet, Marc; Vidal, Loic; Moitrier, Florence; Lacroix, Fabrice; Suma, Yves; Schnell, Fabien; Spitzer, Denis

    2011-05-01

    Nanosized WO 3 tungsten trioxide was prepared by calcination of H 3P 4W 12O 40· xH 2O phosphotungstic acid, previously dissolved in a silica colloidal solution. The influence of the silica spheres/tungsten precursor weight ratio ( x) was investigated. The pristine oxide powders were characterized by XRD, nitrogen adsorption, SEM and TEM techniques. A specific surface area and a pore volume of 64.2 m 2 g -1 and 0.33 cm 3 g -1, respectively, were obtained for the well-crystallized WO 3 powder prepared with x = 2/3 and after the removal of the silica template. The WO 3 particles exhibit a sphere-shaped morphology with a particle size of 13 and 320 nm as function of the x ratio. The performance and the sensitivity levels of the thermites prepared from aluminium nanoparticles mixed with (i) the smallest tungsten (VI) oxide material and (ii) the microscale WO 3 were compared. The combustion of these energetic composites was investigated by time resolved cinematography (TRC). This unconventional experimental technique consists to ignite the dried compressed composites by using a CO 2 laser beam, in order to determine their ignition delay time (IDT) and their combustion rate. The downsizing WO 3 particles improves, without ambiguity, the energetic performances of the WO 3/Al thermite. For instance, the ignition delay time was greatly shortened from 54 ± 10 ms to 5.7 ± 0.2 ms and the combustion velocity was increased by a factor 50 to reach a value of 4.1 ± 0.3 m/s. In addition, the use of WO 3 nanoparticles sensitizes the mixture to mechanical stimuli but decreases the sensitivity to electrostatic discharge.

  20. Deactivation of the TiO2 photocatalyst by coupling with WO3 and the electrochemically assisted high photocatalytic activity of WO3.

    PubMed

    Tada, Hiroaki; Kokubu, Akio; Iwasaki, Mitsunobu; Ito, Seisihro

    2004-05-25

    Patterned TiO2 stripes were formed on a sol-gel crystalline WO3 film by using a chemically modified sol-gel method (pat-TiO2/WO3), and the coupling effect on the photocatalytic activity was studied. Although the photoinduced electron transfer from TiO2 to WO3 was confirmed by labeling and visualization of the reduction sites with Ag particles, the photocatalytic activities of TiO2 for both the gas-phase oxidation of CH3CHO and the liquid-phase oxidation of 2-naphthol decreased significantly with the coupling. This finding was rationalized in terms of the decrease in the rate of the electron transfer from the semiconductor-(s) to 02 with the coupling, which was estimated from the kinetic analysis of the photopotential relaxation. When the excited electrons were removed by a SnO2 underlayer, the WO3 film exhibited a high photocatalytic activity exceeding that of TiO2 for the oxidation of 2-naphthol.

  1. The Performance Analysis of a Real-Time Integrated INS/GPS Vehicle Navigation System with Abnormal GPS Measurement Elimination

    PubMed Central

    Chiang, Kai-Wei; Duong, Thanh Trung; Liao, Jhen-Kai

    2013-01-01

    The integration of an Inertial Navigation System (INS) and the Global Positioning System (GPS) is common in mobile mapping and navigation applications to seamlessly determine the position, velocity, and orientation of the mobile platform. In most INS/GPS integrated architectures, the GPS is considered to be an accurate reference with which to correct for the systematic errors of the inertial sensors, which are composed of biases, scale factors and drift. However, the GPS receiver may produce abnormal pseudo-range errors mainly caused by ionospheric delay, tropospheric delay and the multipath effect. These errors degrade the overall position accuracy of an integrated system that uses conventional INS/GPS integration strategies such as loosely coupled (LC) and tightly coupled (TC) schemes. Conventional tightly coupled INS/GPS integration schemes apply the Klobuchar model and the Hopfield model to reduce pseudo-range delays caused by ionospheric delay and tropospheric delay, respectively, but do not address the multipath problem. However, the multipath effect (from reflected GPS signals) affects the position error far more significantly in a consumer-grade GPS receiver than in an expensive, geodetic-grade GPS receiver. To avoid this problem, a new integrated INS/GPS architecture is proposed. The proposed method is described and applied in a real-time integrated system with two integration strategies, namely, loosely coupled and tightly coupled schemes, respectively. To verify the effectiveness of the proposed method, field tests with various scenarios are conducted and the results are compared with a reliable reference system. PMID:23955434

  2. The performance analysis of a real-time integrated INS/GPS vehicle navigation system with abnormal GPS measurement elimination.

    PubMed

    Chiang, Kai-Wei; Duong, Thanh Trung; Liao, Jhen-Kai

    2013-08-15

    The integration of an Inertial Navigation System (INS) and the Global Positioning System (GPS) is common in mobile mapping and navigation applications to seamlessly determine the position, velocity, and orientation of the mobile platform. In most INS/GPS integrated architectures, the GPS is considered to be an accurate reference with which to correct for the systematic errors of the inertial sensors, which are composed of biases, scale factors and drift. However, the GPS receiver may produce abnormal pseudo-range errors mainly caused by ionospheric delay, tropospheric delay and the multipath effect. These errors degrade the overall position accuracy of an integrated system that uses conventional INS/GPS integration strategies such as loosely coupled (LC) and tightly coupled (TC) schemes. Conventional tightly coupled INS/GPS integration schemes apply the Klobuchar model and the Hopfield model to reduce pseudo-range delays caused by ionospheric delay and tropospheric delay, respectively, but do not address the multipath problem. However, the multipath effect (from reflected GPS signals) affects the position error far more significantly in a consumer-grade GPS receiver than in an expensive, geodetic-grade GPS receiver. To avoid this problem, a new integrated INS/GPS architecture is proposed. The proposed method is described and applied in a real-time integrated system with two integration strategies, namely, loosely coupled and tightly coupled schemes, respectively. To verify the effectiveness of the proposed method, field tests with various scenarios are conducted and the results are compared with a reliable reference system.

  3. Specification of a NAVSTAR Global Positioning System (GPS) receiver for a differential GPS ground system

    NASA Technical Reports Server (NTRS)

    Mccall, D. L.; Turner, R. N.

    1984-01-01

    One step towards the successful completion of a functional ground unit for the Differential Global Positioning System (DGPS) will be in choosing a currently available GPS receiver that will accurately measure the propagation times of the satellite signals and have the capability to be electrically interfaced with and controlled by a Digital Equipment Corporation (DEC) PDP-11/34A computer. The minimum requirements and characteristics of a NAVSTAR Global Positioning System (GPS) receiver are described. The specific technical specifications addressed include data accuracies and resolutions, receiver interface/external control, enclosure dimensions and mounting requirements, receiver operation, and environmental specifications.

  4. GPS Modeling and Analysis. Summary of Research: GPS Satellite Axial Ratio Predictions

    NASA Technical Reports Server (NTRS)

    Axelrad, Penina; Reeh, Lisa

    2002-01-01

    This report outlines the algorithms developed at the Colorado Center for Astrodynamics Research to model yaw and predict the axial ratio as measured from a ground station. The algorithms are implemented in a collection of Matlab functions and scripts that read certain user input, such as ground station coordinates, the UTC time, and the desired GPS (Global Positioning System) satellites, and compute the above-mentioned parameters. The position information for the GPS satellites is obtained from Yuma almanac files corresponding to the prescribed date. The results are displayed graphically through time histories and azimuth-elevation plots.

  5. Structural, vibrational and luminescence properties of the (1−x)CaWO{sub 4}−xCdWO{sub 4} system

    SciTech Connect

    Taoufyq, A.; Guinneton, F.; Valmalette, J-C.; Arab, M.; Benlhachemi, A.; Bakiz, B.; Villain, S.; and others

    2014-11-15

    In the present work, we investigate the structural, microstructural, vibrational and luminescence properties of the system (1−x)CaWO{sub 4}−xCdWO{sub 4} with x ranging between 0 and 1. Polycrystalline samples were elaborated using a coprecipitation technique followed by thermal treatment at 1000 °C. The samples were then characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and luminescence analyses. X-ray diffraction profile analyses using Rietveld method showed that two kinds of solid solutions Ca{sub 1−x}Cd{sub x}WO{sub 4} having scheelite and wolframite structures, with respectively tetragonal and monoclinic crystal cells, were observed, with a biphasic system for compositions x=0.6 and 0.7. The scanning electron microscopy experiments showed a complex evolution of morphologies and crystallite sizes as x increased. The vibration modes of Raman spectra were characteristic of composition-dependent disordered solid solutions with decreasing wavenumbers as x increased. Luminescence experiments were performed under UV-laser light irradiation. The energies of emission bands increased linearly with cadmium composition x. The integrated intensity of luminescence reached a maximum value for the substituted wolframite phase with composition x=0.8. - Graphical abstract: Luminescence on UV excitation (364.5 nm) of (1−x)CaWO{sub 4−x}CdWO{sub 4} system, elaborated from coprecipitation technique at 1000 °C, with 0WO{sub 4} polycrystalline phases with 0≤x≤0.5. (b) Maximum of luminescence intensity for the composition x=0.8. - Highlights: • Solid solutions Ca{sub 1−x}Cd{sub x}WO{sub 4} are elaborated from coprecipitation technique. • The structures of two types of solid solutions are refined using Rietveld method. • A maximum of luminescence is obtained for an intermediate composition x=0.8.

  6. Precise estimation of tropospheric path delays with GPS techniques

    NASA Technical Reports Server (NTRS)

    Lichten, S. M.

    1990-01-01

    Tropospheric path delays are a major source of error in deep space tracking. However, the tropospheric-induced delay at tracking sites can be calibrated using measurements of Global Positioning System (GPS) satellites. A series of experiments has demonstrated the high sensitivity of GPS to tropospheric delays. A variety of tests and comparisons indicates that current accuracy of the GPS zenith tropospheric delay estimates is better than 1-cm root-mean-square over many hours, sampled continuously at intervals of six minutes. These results are consistent with expectations from covariance analyses. The covariance analyses also indicate that by the mid-1990s, when the GPS constellation is complete and the Deep Space Network is equipped with advanced GPS receivers, zenith tropospheric delay accuracy with GPS will improve further to 0.5 cm or better.

  7. Application of GPS attitude determination to gravity gradient stabilized spacecraft

    NASA Technical Reports Server (NTRS)

    Lightsey, E. G.; Cohen, Clark E.; Parkinson, Bradford W.

    1993-01-01

    Recent advances in the Global Positioning System (GPS) technology have initiated a new era in aerospace navigation and control. GPS receivers have become increasingly compact and affordable, and new developments have made attitude determination using subcentimeter positioning among two or more antennas feasible for real-time applications. GPS-based attitude control systems will become highly portable packages which provide time, navigation, and attitude information of sufficient accuracy for many aerospace needs. A typical spacecraft application of GPS attitude determination is a gravity gradient stabilized satellite in low Earth orbit that employs a GPS receiver and four body mounted patch antennas. The coupled, linearized equations of motion enable complete position and attitude information to be extracted from only two antennas. A discussion of the various error sources for spaceborne GPS attitude measurement systems is included. Attitude determination of better than 0.3 degrees is possible for 1 meter antenna separation. Suggestions are provided to improve the accuracy of the attitude solution.

  8. Application of GPS attitude determination to gravity gradient stabilized spacecraft

    NASA Technical Reports Server (NTRS)

    Lightsey, E. G.; Cohen, Clark E.; Parkinson, Bradford W.

    1993-01-01

    Recent advances in the Global Positioning System (GPS) technology have initiated a new era in aerospace navigation and control. GPS receivers have become increasingly compact and affordable, and new developments have made attitude determination using subcentimeter positioning among two or more antennas feasible for real-time applications. GPS-based attitude control systems will become highly portable packages which provide time, navigation, and attitude information of sufficient accuracy for many aerospace needs. A typical spacecraft application of GPS attitude determination is a gravity gradient stabilized satellite in low Earth orbit that employs a GPS receiver and four body mounted patch antennas. The coupled, linearized equations of motion enable complete position and attitude information to be extracted from only two antennas. A discussion of the various error sources for spaceborne GPS attitude measurement systems is included. Attitude determination of better than 0.3 degrees is possible for 1 meter antenna separation. Suggestions are provided to improve the accuracy of the attitude solution.

  9. The application of NAVSTAR differential GPS in the civilian community

    NASA Technical Reports Server (NTRS)

    Beser, J.; Parkinson, B. W.

    1981-01-01

    The NAVSTAR Global Positioning System (GPS), currently being developed by the DOD, is a space based navigation system that will provide the user with precise position, velocity, and time information on a 24 hour basis, in all weather conditions and at any point on the globe. The baseline GPS system will provide guaranteed high accuracy to only a limited number of users, mostly the military. The civilian community has to devise a variation of this system to allow for an assured, uninterrupted level of accuracy. Differential GPS provides such a capability. In connection with the conceived possibility of the use of GPS by an enemy, it is found to be necessary to implement a selective availability technical capability. Differential GPS provides an approach for the civilian community to have a guaranteed level of accuracy better than the 250 meters presently planned for GPS.

  10. The attitudes of GPs towards the nurse-practitioner role.

    PubMed

    Carr, J; Bethea, J; Hancock, B

    2001-09-01

    In recent years, nursing and health-care policy have promoted the advanced role of the nurse -- that of nurse practitioner. But such a role has not been integrated widely into the primary health-care team. This study investigates the knowledge and attitudes of GPs who do not employ nurse practitioners to find out what prevents them doing so. Ten GPs who did not already employ a nurse practitioner took part in semi-structured interviews. Our findings show that GPs, although confused about the role, were generally supportive of advanced nursing practice. Skills identified with the role were prescribing, disease diagnosis and minor-illness management. GPs thought that protocols and guidelines should govern practice, which differs fundamentally from the Royal College of Nursing definition. None of the GPs had encountered the role in primary care, and the lack of professional regulation and role definition for practice nurses and nurse practitioners who work in primary care may have affected GPs' perceptions.

  11. Estimating Baselines From Constrained Data On GPS Orbits

    NASA Technical Reports Server (NTRS)

    Lindqwister, Ulf J.; Lichten, Stephen M.; Blewitt, Geoffrey I.

    1991-01-01

    Method of processing measurements of signals received at terrestrial stations from satellites in Global Positioning System (GPS) increases precision of estimates of both orbits of GPS satellites and locations of stations, computed from measurement and orbital data. Involves network of fiducial GPS stations collocated with very-long-baseline-interferometry (VLBI) stations, for which independent VLBI determinations of baselines available. Locations of stations used to establish baselines for geodesy. Potential applications include measurements of seismic and volcanic displacements and movements of tectonic plates.

  12. A Report on GPS and Galileo Time Offset Coordination Efforts

    DTIC Science & Technology

    2007-01-01

    A Report on GPS and Galileo Time Offset Coordination Efforts Jörg H. Hahn Galileo Project Office ESA-ESTEC, Navigation Department Noordwijk...The Netherlands joerg.hahn@esa.int Edward D. Powers GPS Operations Division Chief USNO Time Service Department Washington D.C., USA edward.powers...usno.navy.mil Abstract - Precise timing is an inherent part of Radio Navigation Systems like GPS and Galileo. This paper will update progress on

  13. Method and apparatus for relative navigation using reflected GPS signals

    NASA Technical Reports Server (NTRS)

    Cohen, Ian R. (Inventor); Boegner, Jr., Gregory J. (Inventor)

    2010-01-01

    A method and system to passively navigate an orbiting moving body towards an orbiting target using reflected GPS signals. A pair of antennas is employed to receive both direct signals from a plurality of GPS satellites and a second antenna to receive GPS signals reflected off an orbiting target. The direct and reflected signals are processed and compared to determine the relative distance and position of the orbiting moving body relative to the orbiting target.

  14. Briefing Highlights Vulnerability of GPS to Adverse Space Weather

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2011-08-01

    Through its effects on GPS and other technologies, space weather can affect a variety of industries, including agriculture, commercial air travel, and emergency response. Speakers focused on these topics at a 22 June briefing on Capitol Hill in Washington, D. C. Solar flares can produce radio bursts that directly interfere with GPS signals. Solar activity can also cause ionospheric disturbances that produce distortions and delays in GPS signals, degrading the accuracy of positioning and navigation systems.

  15. Directional Networking in GPS Denied Environments - Time Synchronization

    DTIC Science & Technology

    2016-03-14

    Directional Networking in GPS Denied Environments—Time Synchronization Derya Cansever and Gilbert Green Army CERDEC Aberdeen Proving Ground MA...on GPS use. This paper describes a decentralized algorithm, called “Fast RTSR”, for directional networking to re-construct time and position data...when GPS is not available. We show that the Fast RTSR algorithm allows the entire network to achieve time synchronization with convergence time of

  16. Feedback from GPS Timing Users: Relayed Observations from 2 SOPS

    DTIC Science & Technology

    1999-12-01

    military systems that utilize one-way synchronization via GPS . 29 Report Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for...supports the common perception that many receiver systems don’t sample the GPS navigation message’s subframe 1 health information nearly as often as...most commonly reported problem involved a miscalculation of the GPS -UTC(USN0) correction term. In many cases, several receiver systems would mis-tag

  17. A Consistent Geodetic Reference System for GPS (Global Positioning System).

    DTIC Science & Technology

    1987-02-27

    reliable and accurate Operational Control System (OCS) is a prerequisite for successful Global Positioning System ( GPS ) navigation performance. The OCS...DDOR Doubly differenced (between station pair and Navstar pair) phase data GPS Global Positioning System MIT Massachusetts Institute of Technology...FWft SOTR4as-2 A Consistent Geodetic Reference System for GPS A. S. LIU Systems and Computer Engineering Division Engineering Group The Aerospace

  18. Terrestrial navigation based on integrated GPS and INS

    NASA Astrophysics Data System (ADS)

    Ge, Sam S.; Goh, Terence K. L.; Jiang, T. Y.; Koopman, R.; Chan, S. W.; Fong, A. M.

    1998-07-01

    The Global Positioning System (GPS) and Inertial Navigation System (INS) have complimentary features that can be exploited in an integrated system, thus resulting in improved navigation performance. The INS is able to provide accurate aiding data on short-term vehicle dynamics, while the GPS provides accurate data on long-term vehicle dynamics. In this paper, a complete solution is presented for terrestrial navigation based on integrated GPS and INS using Kalman filtering technique.

  19. GPS versus Galileo: Balancing for Position in Space

    DTIC Science & Technology

    2006-05-01

    others? –– Galileo Galilei In 1633 the Roman Catholic Church declared Galileo Galilei a heretic because his beliefs conflicted with the status quo.1 Almost...MAY 2006 2. REPORT TYPE 3. DATES COVERED 00-00-2006 to 00-00-2006 4. TITLE AND SUBTITLE GPS versus Galileo . Balancing for Position in Space 5a...lin e GPS versus Galileo Balancing for Position in Space Beidleman COLLEGE OF AEROSPACE DOCTRINE, RESEARCH AND EDUCATION AIR UNIVERSITY GPS versus

  20. Chromic mechanism in amorphous WO{sub 3} films

    SciTech Connect

    Zhang, J G; Benson, D K; Tracy, C E; Deb, S K; Czanderna, A W; Bechinger, C

    1996-11-01

    The authors propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO{sub 3{minus}y}{center_dot}nH{sub 2}O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W{sup 6+} and W{sup 4+} states and can be represented as W{sub 1{minus}y}{sup 6+} W{sub y}{sup 4+}O{sub 3{minus}y}{center_dot}nH{sub 2}O. The proposed chromic mechanism is based on the small polaron transition between the charge-induced W{sup 5+} state and the original W{sup 4+} state instead of the W{sup 5+} and W{sup 6+} states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.