OPEX: (Olympus Propagation EXperiment)

The Olympus-1 satellite carries four distinct payloads for experimental utilization and research in the field of satellite communications: (1) the Direct Broadcasting Service (DBS) payload; (2) the Specialized Services Payload; (3) the 20/30 GHz Advanced Communications Payload; and (4) the Propagation Payload. Experimental utilization of the first three payloads involves ground transmissions to the satellite and hence sharing of available satellite time among experimenters. This is coordinated through the Olympus Utilization Program

The role of the Dotson Ice Shelf and Circumpolar Deep Water as driver and source of dissolved and particulate iron and manganese in the Amundsen Sea polynya, Southern Ocean

Coastal areas around Antarctica such as the Amundsen Sea are important sources of trace metals and biological hotspots, but are also experiencing the effects of climate change, including the rapid thinning of ice sheets. In the central Amundsen Sea Polynya (ASP), both bio-essential dissolved Fe (DFe) and dissolved Mn (DMn) were found to be depleted at the surface, indicating substantial biological uptake and/or precipitation. Close to the Dotson Ice Shelf (DIS) there were elevated surface concentrations of DMn (>3 nM) but surprisingly not for DFe (100 m depth). We compared different uptake ratios, underlining that uptake ratio estimates do not necessarily capture natural variability and it is likely better to use a range of values. In the future, climate change may increase the heat flux of mCDW and thereby the melting of the DIS. This will most likely cause an increased input of Fe and Mn into the ASP, which may fuel increased levels of primary productivity in the ASP

Erlang capacity of ATM-based CDMA satellite system

The capacity and throughput of an ATM-based CDMA system offering flexible access rates on demand are analysed. Extending the existing analysis of traffic capacity of a power-controlled CDMA cellular system, it is shown that offering multiple access rates may result in higher throughput efficiency. An example given of a satellite system shows that the gain in capacity may be some 10

COST TIST – European Research Cooperation in Telecommunications and

European countries the possibility of cooperation in the field of scientific and technical research, by formally establishing the framework of COST (COopération Scientifique et Technique). Until the mid-eighties, COST was th

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The Galileo Reference Troposphere Model of ESA [1] defines the algorithms for the calculation of zenith tropospheric delay and the mapping functions, to be implemented in navigation receivers. The model describes the dependence of delay on position, season, elevation angle and surface meteorological data. A critical analysis has been carried out of the model and the procedures to extract vertical and slant delay values, in particular with respect to consistency and scientific soundness. The main results of this study are discussed. ZENITH DELAY Refractivity model The classical model for refractivity, formulated by Smith and Weintraub [6] is: with where ( ) dry vapour N N

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The Galileo Reference Troposphere Model of ESA defines the algorithms for the calculation of zenith tropospheric delay and the mapping functions, to be implemented in navigation receivers. The model describes the dependence of delay on position, season, elevation angle and surface meteorological data. A critical analysis has been carried out of the model and the procedures to extract vertical and slant delay values, in particular with respect to consistency and scientific soundness. The main results of this study are discussed. ZENITH DELAY Refractivity model The classical model for refractivity, formulated by Smith and Weintraub (7) is: with where ( ) dry vapour N N

Analysis of Propagation Loss in Urban Microcells at 1.9 GHz and 5.8 GHz

Continuous Wave (CW) measurements carried out in downtown Ottawa were used as the basis for comparisons between propagation loss at frequencies near 2 GHz and 6 GHz in urban microcellular environments. The difference (dB) was found to have a Gaussian distribution over urban microcellular coverage areas. To provide physical explanations for measured results, modelling was carried out at 2 GHz. During this process, low complexity models reported for other parts of the world were evaluated against the measurements, which were made in an urban area, which is typical of North America. Comparison of selected models with measurement data resulted in median root mean square (rms) modelling errors that ranged between 4 dB and 7 dB

Addendum: Mapping electron dynamics in highly transient EUV photon-induced plasmas: a novel diagnostic approach using multi-mode microwave cavity resonance spectroscopy (2018 J PHYS D APPL PHYS 52 034004)

A new approach for an in-line beam monitor for ionizing radiation was introduced in a recent publication (Beckers, J., et al. "Mapping electron dynamics in highly transient EUV photon-induced plasmas: a novel diagnostic approach using multi-mode microwave cavity resonance spectroscopy." Journal of Physics D: Applied Physics 52.3 (2018): 034004.). Due to the recent detection and investigation of an additional third decay regime of the afterglow of an extreme ultraviolet photon-induced plasma described in a later article (Platier, B., et al. "Transition of ambipolar-to-free diffusion in the decay of an extreme ultraviolet photon-induced low-pressure argon plasma." Applied Physics Letters 116.10 (2020), 103703.) there is an additional reason for a minimum number of photons for this approach to work. Near or below this threshold, we explain that the response time of the diagnostic method is a limiting factor. Further, a second limit for the number of photons within a pulse is formalized related to the trapping of highly energetic free electrons

The biogeochemistry of zinc and cadmium in the Amundsen Sea, coastal Antarctica

The trace metals zinc (Zn) and cadmium (Cd) are both involved in the metabolic processes of marine phytoplankton, and as such, both metals play important roles in ocean biogeochemical cycles. In Antarctica, the Amundsen Sea (AS) experiences rapid ice shelf melting, and the Amundsen Sea polynya (ASP) hosts seasonal phytoplankton blooms in austral summer, with important implications for atmospheric carbon dioxide drawdown. However, the effects of ice melting and phytoplankton blooms on the biogeochemistry and distributions of Zn and Cd in the ASP remain poorly studied. Here, we present the first combined dataset of dissolved and particulate Zn and Cd in the AS (including the inflow and outflow to and from the Dotson and Getz ice shelves) collected as part of the GEOTRACES process study GPpr12. We use this dataset to assess the sources of both elements to the AS region and characterize the particle composition in the ASP. We find that the main source of both dissolved Zn and Cd in the AS is Circumpolar Deep Water (CDW), with an additional small flux of both metals from shelf sediments. By contrast, aerosol deposition, ice shelf melt, and sea ice melt are all deemed insignificant sources for either Zn or Cd in the AS. Labile particulate Zn and Cd dominate the total particulate pool in the surface layer, indicating that biological uptake is a predominant process for the cycling of both metals in the ASP, whereas sediment resuspension and ice shelf melt do not supply a significant amount of either particulate Zn or Cd. Additionally, we use two commonly used approaches to estimate biogenic and lithogenic particulate concentrations. We find high biogenic particulate concentrations at the surface, decreasing with depth, indicating remineralization plays an important role in the cycling of particulate metals. In contrast, lithogenic particulate metal concentrations remain low throughout the water column. We also show that the estimated uptake ratios of Zn and Cd relative to phosphate in the surface layer are lower than reported for the open Southern Ocean, likely related to the spatial and temporal variability of Fe in the AS. Overall, these new observations provide insight into the biogeochemistry of both Zn and Cd in the AS, a region that is subject to the influence of rapid climate change, which may have implications for the larger-scale cycling of trace metals in the Southern Ocean. Specifically, the amount of Zn and Cd supplied to the surface ASP will increase, given that the volume of CDW that flows towards the Dotson Ice Shelf is predicted to increase

The role of the Dotson Ice Shelf and Circumpolar Deep Water as driver and source of dissolved and particulate iron and manganese in the Amundsen Sea polynya, Southern Ocean

Coastal areas around Antarctica such as the Amundsen Sea are important sources of trace metals and biological hotspots, but are also experiencing the effects of climate change, including the rapid thinning of ice sheets. In the central Amundsen Sea Polynya (ASP), both bio-essential dissolved Fe (DFe) and dissolved Mn (DMn) were found to be depleted at the surface, indicating substantial biological uptake and/or precipitation. Close to the Dotson Ice Shelf (DIS) there were elevated surface concentrations of DMn (>3 nM) but surprisingly not for DFe (100 m depth). We compared different uptake ratios, underlining that uptake ratio estimates do not necessarily capture natural variability and it is likely better to use a range of values. In the future, climate change may increase the heat flux of mCDW and thereby the melting of the DIS. This will most likely cause an increased input of Fe and Mn into the ASP, which may fuel increased levels of primary productivity in the ASP