Communication Subsystems for Emerging Wireless Technologies

The paper describes a multi-disciplinary design of modern communication systems. The design starts with the analysis of a system in order to define requirements on its individual components. The design exploits proper models of communication channels to adapt the systems to expected transmission conditions. Input filtering of signals both in the frequency domain and in the spatial domain is ensured by a properly designed antenna. Further signal processing (amplification and further filtering) is done by electronics circuits. Finally, signal processing techniques are applied to yield information about current properties of frequency spectrum and to distribute the transmission over free subcarrier channels

New insights into the outflows from R Aquarii

R Aquarii is a symbiotic binary surrounded by a large and complex nebula with a prominent curved jet. It is one of the closest known symbiotic systems, and therefore offers a unique opportunity to study the central regions of these systems and the formation and evolution of astrophysical jets. We studied the evolution of the central jet and outer nebula of R Aqr taking advantage of a long term monitoring campaign of optical imaging, as well as of high-resolution integral field spectroscopy. Narrow-band images acquired over a period of more than 21 years are compared in order to study the expansion and evolution of all components of the R Aqr nebula. The magnification method is used to derive the kinematic ages of the features that appear to expand radially. Integral field spectroscopy of the OIII 5007A emission is used to study the velocity structure of the central regions of the jet. New extended features, further out than the previously known hourglass nebula, are detected. The kinematic distance to R Aqr is calculated to be 178 pc using the expansion of the large hourglass nebula. This nebula of R Aqr is found to be roughly 650 years old, while the inner regions have ages ranging from 125 to 290 years. The outer nebula is found to be well described by a ballistic expansion, while for most components of the jet strong deviations from such behaviour are found. We find that the Northern jet is mostly red-shifted while its Southern part is blue-shifted, apparently at odds with findings from previous studies but almost certainly a consequence of the complex nature of the jet and variations in ionisation and illumination between observations.Comment: 13 pages, 8 figures, accepted for publication in A&

The hypergiant HR 8752 evolving through the yellow evolutionary void

Context. We study the time history of the yellow hypergiant HR 8752 based on high-resolution spectra (1973-2005), the observed MK spectral classification data, B - V- and V-observations (1918-1996) and yet earlier V-observations (1840-1918).<br>Aims. Our local thermal equilibrium analysis of the spectra yields accurate values of the effective temperature (T-eff), the acceleration of gravity (g), and the turbulent velocity (v(t)) for 26 spectra. The standard deviations average are 82 K for T-eff, 0.23 for log g, and 1.1 km s(-1) for v(t).<br>Methods. A comparison of B-V observations, MK spectral types, and T-eff-data yields E(B-V), "intrinsic" B-V, T-eff, absorption A(V), and the bolometric correction BC. With the additional information from simultaneous values of B-V, V, and an estimated value of R, the ratio of specific absorption to the interstellar absorption parameter E(B - V), the "unreddened" bolometric magnitude m(bol),(0) can be determined. With Hipparcos distance measurements of HR 8752, the absolute bolometric magnitude M-bol,M-0 can be determined.<br>Results. Over the period of our study, the value of T-eff gradually increased during a number of downward excursions that were observable over the period of sufficient time coverage. These observations, together with those of the effective acceleration g and the turbulent velocity v(t), suggest that the star underwent a number of successive gas ejections. During each ejection, a pseudo photosphere was produced of increasingly smaller g and higher v(t) values. After the dispersion into space of the ejected shells and after the restructuring of the star's atmosphere, a hotter and more compact photosphere became visible. From the B - V and V observations, the basic stellar parameters, T-eff, log M/M-circle dot, log L/L-circle dot, and log R/R-circle dot are determined for each of the observational points. The results show the variation in these basic stellar parameters over the past near-century.<br>Conclusions. We show that the atmospheric instability region in the HR-diagram that we baptize the yellow evolutionary void actually consists of two parts. We claim that the present observations show that HR 8752 is presently climbing out of the "first" instability region and that it is on its way to stability, but in the course of its future evolution it still has to go through the second potential unstable region

Wetland and Hydric Soils

Soil and the inherent biogeochemical processes in wetlands contrast starkly with those in upland forests and rangelands. The differences stem from extended periods of anoxia, or the lack of oxygen in the soil, that characterize wetland soils; in contrast, upland soils are nearly always oxic. As a result, wetland soil biogeochemistry is characterized by anaerobic processes, and wetland vegetation exhibits specific adaptations to grow under these conditions. However, many wetlands may also have periods during the year where the soils are unsaturated and aerated. This fluctuation between aerated and nonaerated soil conditions, along with the specialized vegetation, gives rise to a wide variety of highly valued ecosystem services

Limited Effects of Precipitation Manipulation on Soil Respiration and Inorganic N Concentrations Across Soil Drainage Classes in Northern Minnesota Aspen Forests

It is critical to gain insight into the responses of forest soils to the changing climate. We simulated future climate conditions with growing season throughfall reduction (by 50%) and winter snow removal using a paired-plot design across a soil drainage class gradient at three upland, Populus-dominated forests in northern Minnesota, USA. In situ bulk soil respiration and concentrations of extractable soil N were measured during the summers of 2020–2021. Soil respiration and N concentrations were not affected by throughfall reduction and snow removal, which was largely attributed to the limited treatment effects on soil moisture content and soil temperature. Drainage class was only a significant factor during the spring thaw period in 2021. During this period, the poorly drained plots had lower respiration rates compared to the well-drained plots, which was associated with the drainage class effects on soil temperature. The results of the companion laboratory incubation with varying levels of soil moisture also indicated no effect of the treatment on soil respiration, but effects of drainage class and moisture content on respiration were observed. Our results indicate that the combined effects of reduced summer and winter precipitation on soil respiration and N dynamics may be limited across the range of conditions that occurred in our study

Restoration of a Severely Impacted Riparian Wetland System - The Pen Branch Project

The Savannah River Swamp is a 3020 ha forested wetland on the floodplain of the Savannah River and is located on the Department of Energy’s Savannah River Site (SRS) near Aiken, SC (Fig. 1). Historically the swamp consisted ofapproximately 50% baldcypress-water tupelo stands, 40% mixed bottomland hardwood stands, and 10% shrub, marsh, and open water. Tributeries of the river were typical of Southeastern bottomland hardwood forests. The hydrology was controlled by flow from four creeks that drain into the swamp and by flooding of the Savannah River. Upstream dams on the Savannah River have caused some alteration of the water levels and timing of flooding within the floodplain(Schneider et al., 1989)

LITHOLOGY AND SEDIMENTARY GEOCHEMISTRY OF CORE CO1410 FROM LAKE IMANDRA (KOLA PENINSULA, NW RUSSIA)

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Flooding tolerance of four tropical peatland tree species in a nursery trial

In order to facilitate hydrological restoration, initiatives have been conducted to promote tree growth in degraded and rewetted peatlands in Indonesia. For these initiatives to be successful, tree seedlings need to be able to survive flooding episodes, with or without shade. We investigated the survival rates and the formation of adventitious roots in the case of four tree species exposed to combinations of different shading and water levels under controlled conditions in a nursery, with artificial rainwater and with peat soil as the medium. The research focused on the following questions (i) whether trees can grow on flooded peat soils; and (ii) which plant traits allow plants to cope with inundation, with or without shade. The four tree species compared (Shorea balangeran, Cratoxylum arborescens, Nephelium lappaceum and Durio zibethinus) include two natural pioneer and two farmer-preferred fruit trees. The experiment used a split-split plot design with 48 treatment combinations and at least 13 tree-level replicates. The study found that S. balangeran and C. arborescens had relatively high survival rates and tolerated saturated condition for 13 weeks, while N. lappaceum and D. zibethinus required non-saturated peat conditions. S. balangeran and C. arborescens developed adventitious roots to adapt to the inundated conditions. D. zibethinus, S. balangeran and N. lappaceum grew best under moderate (30%) shading levels, while C. arborescent grew best in full sunlight

Towards an understanding of the Of?p star HD 191612: optical spectroscopy

We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f?pe-O8fp). The Balmer and HeI lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. Metal lines and HeII absorptions (including many selective emission lines but excluding He II 4686A emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with P(orb) = 1542d, e=0.45. We conduct a model-atmosphere analysis of the primary, and find that the system is consistent with a O8: giant with a B1: main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying `clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint.Comment: Accepted for MNRA