Issues in the implementation of an indirect adaptive control system

This work presents techniques for addressing the various issues relevant to the implementation of an indirect adaptive control system. The sufficiency of these techniques is demonstrated by implementation onboard a small autonomous underwater vehicle. The control system is organized into two layers: the standard adaptive control algorithms and the supervisory logic. Modeling and implementation issues involved in the design of the basic adaptive control loop are described. The design of supervisory logic to address insufficiency of excitation, identification under low signal-to-noise ratio conditions, and guaranteeing appropriate control actions during periods when the parameter estimates are inaccurate is discussed. Results from in-water demonstrations are presented     

Search for HD in Jupiter and Saturn

Upper limits are placed on the D/H ratio in the observed portions of the atmospheres of Jupiter and Saturn from observations at high S/N over the region of the 5-0 R(1) line of HD. The upper limits of 4 × 10^?5 and 6 × 10^?5 D/H on Jupiter and Saturn, respectively, are not inconsistent with present models for abundance ratios in the primitive solar nebula or with other estimates of this quantity from observations.     

EUREC<Superscript>4</Superscript>A: A Field Campaign to Elucidate the Couplings Between Clouds,Convection and Circulation

Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air–sea interactions and convective organization.     

Differential rotation in compact objects with hyperons and delta isobars

Neutron stars may experience differential rotation on short, dynamical timescales following extreme astrophysical events like binary neutron star mergers. In this work, the masses and radii of differentially rotating neutron star models are computed. We employ a set of equations of states for dense hypernuclear and $\mathrm{\Delta }$-admixed-hypernuclear matter obtained within the framework of CDF theory in the relativistic Hartree-Fock (RHF) approximation. Results are shown for varying meson- $\mathrm{\Delta }$ couplings, or equivalently the $\mathrm{\Delta }$-potential in nuclear matter. A comparison of our results with those obtained for nonrotating stars shows that the maximum mass difference between differentially rotating and static stars is independent of the underlying particle composition of the star. We further find that the decrease in the radii and increase in the maximum masses of stellar models when $\mathrm{\Delta }$-isobars are added to hyperonuclear matter (as initially observed for static and uniformly rotating stars) persist also in the case of differentially rotating neutron stars.     

Rapid Holocene coastal change revealed by high-resolution micropaleontological analysis, Pamlico Sound, North Carolina, USA

Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000 yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500 cal yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting.     

Sulfur K-edge XANES study of local electronic structure in ternary monosulfide solid solution [(Fe, Co, Ni)0.923S]

 Synchrotron radiation S K-edge XANES spectra and unit-cell parameters are used to investigate the local electronic structure of non-stoichiometric binary and ternary Fe-Co-Ni monosulfide solid solution (mss; M_0.923S, M = Fe, Co, Ni) quenched from 800 °C and low pressure. The prominent absorption edge feature of the XANES spectra represents transition of S 1s core level electrons to unoccupied S 3p σ* antibonding orbitals hybridized with empty metal 3d(e_g) orbitals. There is a progressive increase in area of the edge peak from Fe_0.923S to Ni_0.923S and Co_0.923S, which correlates with progressive decrease in c and a parameters for the NiAs-type subcell and increase in metallic character, and reflects increase in the number and availability of empty e_g ^β orbitals and covalence of metal-S bonds. More generally, the area of the edge peak exhibits an inverse linear correlation with a, c and unit-cell volume of binary and ternary mss. This inverse linear correlation is attributed to progressive increase in covalence and M-S-M bonding interaction in the c-axis direction, through metal-S [M 3d(e_g) - S 3p (or 3d)] π bonding. However, the area of the edge peak does not correlate very well with the average number of 3d electrons per metal atom in these solid solutions, showing that the absorption of synchrotron radiation reflects the local electronic structure of individual absorber atoms (i.e. the SM₆ cluster), and is not a group (crystal energy band) effect. Received: 21 March 2000 / Accepted: 14 July 2000     

A Review of “Environmental Modelling: An Introduction”

The purpose of this study is to answer several important questions concerning the learning of categories of geographic information from maps. Categorization is a fundamental part of both learning and communication, and learning and communication are, in turn, central to any field of study. If categorization is a fundamental part of the learning process, then how people categorize information learned from maps must be of concern to cartographers and geographers. This study examines map reader categorization by having subjects in an experimental situation learn categories of maps. The primary variables in this study are the coherence of the categories and the duration of exposure to the categories. It was found that coherent categories cause subjects to rely on prior knowledge. The ability to use prior knowledge allows subjects to learn categories quickly, but it also causes them to make inaccurate assumptions about the category membership. This finding was not altered when subjects were given longer exposures to the category membership.     

Study of solar system planetary lightning with LOFAR

Radio signatures of lightning discharges have been detected by the Voyager spacecraft near Saturn and Uranus up to 40 MHz. Corresponding flux densities at the distance of the Earth are up to 1000 Jansky (Jy) for Saturn (1 event per minute above 50 Jy, with 30–300 ms duration) and up to a few tens of Jansky for Uranus. Low Frequency ARray LOFAR will allow us to detect and monitor the lightning activity at these two planets. Imaging will allow us to locate lightning sources on Saturn's disk (even if with moderate accuracy), which could then be correlated to optical imaging of clouds. Such observations could provide new information on electrification processes, atmospheric dynamics, composition, and geographical and seasonal variations, compared to the Earth. In addition, lightning may play a role in the atmospheric chemistry, through the production of non-equilibrium trace organic constituents potentially important for biological processes. LOFAR observations can also help us to assess the existence of lightning at Neptune (marginally detected by Voyager), at Venus (where their existence is very controversial), and at Mars (possibly resulting from dust cloud charging). At Jupiter, low-altitude ionospheric layers of meteoritic origin and/or intrinsically long discharge duration seem to prevent the emission and escape of high-frequency radio waves associated with lightning. LOFAR thus presents good possibilities for the detection and study of solar system planetary lightning; we also discuss its relevance to bring new information on Terrestrial lightning-related upper atmosphere transient phenomena (sprites, TIPPs…). Instrumental constraints are outlined.