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  • 2020-2024  (3)
  • 1980-1984  (4)
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  • 1
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    Cardiac myosin subfragment 1 modification by carbodiimide in the presence of a nucleophile (1982)
    Elsevier
    Details
    Publikationsdatum: 1982-04-01
    Print ISSN: 0006-291X
    Digitale ISSN: 1090-2104
    Thema: Biologie , Chemie und Pharmazie , Physik
    Publiziert von Elsevier
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    AKTUELLE ARTIKEL
  • 2
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    Doppler System Phase Transfer Functions for a System with an X-band Uplink and X-band and S-band Downlinks (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-10
    Beschreibung: A new DSN RF system is being developed that transmits at X-band and receive at both X-band and S-band. End-to-end tests are planned to measure the phase stability of this system. Equations for the phase transfer functions between the error sources in the system and the X-band and S-band Doppler extractor outputs are derived. This analysis considers both test modes, using a test translator, and actual spacecraft tracking where the spacecraft is at some distance from the DSN station. The results indicate that the proposed end-to-end tests will not accurately reflect the error that occurs during actual spacecraft tracking.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: The Telecommun. and Data Acquisition Rept.; p 58-69
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    NASA TECHNICAL REPORTS
  • 3
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    Effect of RF Filtering on the Performance of Uncoded PCM/PM Telemetry Channels (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: A method for calculating the increase in received telemetry signal power required to compensate for the use of a radio frequency interference (RFI) filter in front of the DSN receiving system low-noise amplifier is described. The telemetry system for which the degradation is calculated is an uncoded PCM/PM system in which the NRZ data directly modulates the carrier at a modulation level which leaves a discrete carrier. A phase-locked loop in the RF receiver tracks the discrete carrier and coherently demodulates the PCM data. The RFI filter may be a series of Butterworth, Tchebychev, or Bessel low-pass, high-pass, band-pass, or band-reject filters, each with arbitrary bandwidth, number of poles, and, for band-pass or band-reject filters, resonant frequency. The only restriction is that the RFI filter must have only simple poles. Numerical results are presented for the RFI filters the DSN plans to place in front of the S-band FET, S-band maser, and X-band maser low noise amplifiers. The main conclusion is that the filters will produce negligible degradation at data rates below 4 Mbps.
    Schlagwort(e): SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Materialart: The Telecommun. and Data Acquisition Rept.; p 104-125
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    NASA TECHNICAL REPORTS
  • 4
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    Starprobe - Coronal plasma turbulence effects on tracking and telemetry (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The telemetry and tracking problems expected for Starprobe, a solar flyby with a perihelion of 4 solar radii, are discussed. The Starprobe is intended to obtain measurements of the solar quadrupole moment within an accuracy of 1/100,000,000, allowing more accurate modelling of the solar interior. Obstacles are perceived for Doppler velocity measurements due to RF signal amplitude and phase scintillations created by the solar corona. Model calculations are presented for the propagation effects in the maximum disturbance area, and an open loop two-way Doppler system is described. The system comprises X-band and S-band uplinks and downlinks to eliminate the plasma-induced phase scintillations, means of correcting unfolding errors caused by S-band amplitude scintillations, and a new method of estimating the Doppler frequency.
    Schlagwort(e): SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Materialart: AIAA PAPER 82-0044 , Aerospace Sciences Meeting; Jan 11, 1982 - Jan 14, 1982; Orlando, FL
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    NASA TECHNICAL REPORTS
  • 5
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    Unique southern African terrestrial and oceanic biomes and their relation to steep environmental gradients (2024)
    Springer
    Details
    Publikationsdatum: 2024-01-07
    Beschreibung: The southern African subcontinent and its surrounding oceans accommodate globally unique ecoregions, characterized by exceptional biodiversity and endemism. This diversity is shaped by extended and steep physical gradients or environmental discontinuities found in both ocean and terrestrial biomes. The region’s biodiversity has historically been the basis of life for indigenous cultures and continues to support countless economic activities, many of them unsustainable, ranging from natural resource exploitation, an extensive fisheries industry and various forms of land use to nature-based tourism. Being at the continent’s southern tip, terrestrial species have limited opportunities for adaptive range shifts under climate change, while warming is occurring at an unprecedented rate. Marine climate change effects are complex, as warming may strengthen thermal stratification, while shifts in regional wind regimes influence ocean currents and the intensity of nutrient-enriching upwelling. The flora and fauna of marine and terrestrial southern African biomes are of vital importance for global biodiversity conservation and carbon sequestration. They thus deserve special attention in further research on the impacts of anthropogenic pressures including climate change. Excellent preconditions exist in the form of long-term data sets of high quality to support scientific advice for future sustainable management of these vulnerable biomes.
    Materialart: Book chapter , NonPeerReviewed
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    ARTIKEL (OCEANREP)
  • 6
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    Seasonal cycle of mixing and upward nutrient supply in the equatorial Atlantic cold tongue (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publikationsdatum: 2023-06-05
    Beschreibung: The eastern equatorial Atlantic hosts a productive marine ecosystem that depends on the upward supply of nutrients. The main process that transports nutrients into the surface mixed layer is turbulent mixing induced in the shear zone between the surface mixed layer and the core of the Equatorial Undercurrent (EUC). Here we present experimental data from two trans-Atlantic cruises along the equator as well as moored observations allowing to characterize the seasonal cycle of velocity shear and turbulence. These data in combination with hydrographic data allow the analysis of the seasonal cycle of equatorial mixing and upward nitrate flux. The core of the EUC migrates vertically following an annual cycle. It reaches its shallowest position in boreal spring and its deepest position in boreal fall. The seasonal cycle of the maximum nitrate gradient instead shows a primary upward movement during boreal summer and a secondary upward movement in boreal winter bringing the nitrate gradient into the region of enhanced shear and turbulent mixing. During boreal spring, the nitrate gradient is located below the EUC core that is characterized by a minimum of turbulence. It prevents an upward supply of nitrate into the surface mixed layer and results in low productivity. The dynamic behavior of the shear zone is driven by a resonant equatorial basin mode associated with the east- and westward propagation of equatorial Kelvin and Rossby waves making the seasonal cycle of upward nutrient supply and productivity in the equatorial Atlantic distinct from that in the Pacific Ocean.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/conferenceObject
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    ARTIKEL (OA)
  • 7
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    How can coastal trapped waves and mixing explain the productivity season in the tropical Angolan upwelling system? (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publikationsdatum: 2023-08-02
    Beschreibung: The tropical Angolan upwelling system (tAUS) is a highly productive ecosystem with a distinct seasonal variability with productivity peaking in austral winter. The tAUS is connected to equatorial dynamics via the propagation of equatorial and coastal trapped waves (CTWs). We use hydrographic, ocean turbulence and satellite data to investigate the role of CTWs in controlling the seasonal cycle of productivity in the tAUS. During austral winter associated with the passage of an upwelling CTW, the nitracline is displaced upward by about 50 m. Through this vertical advection nitrate-rich waters passes onto the shelf. Due to the elevated mixing rates on the shelf, this movement of the nitracline results an increased vertical nitrate flux into the ocean mixed layer. Our analysis further shows that interannual variability in the strength of the austral winter net primary production correlates with the amplitude of the seal level anomaly signal of the corresponding upwelling CTW. The signal of sea level depression leads the maximum productivity signal by about 40 days. It is suggested that this time lag arises, among other factors, from the vertical structure of the CTWs arriving in the tAUS. While the sea level anomaly is dominated by the faster low-baroclinic mode CTWs, the displacement of the nitracline is mainly influenced by the slower high-baroclinic mode CTWs that arrive later in the tAUS. Our results highlight the crucial role CTWs play for the productivity in the tAUS. The strong connection between equatorial dynamics and productivity further introduces a possibility for predicting interannual variability.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/conferenceObject
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    ARTIKEL (OA)
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