Changes in the Period of Negative Superhumps of Type SU UMa Dwarf Novae. II. NY Her (2017 and 2020)

Astrophysics - Photometric studies of the type SU UMa dwarf nova NY Her were made during 2017 and 2020 at the Crimean Astrophysical Observatory and at the Sanglokh Observatory over a total of 77...     

Trace element mobility during sub-seafloor alteration of basaltic glass from Ocean Drilling Program site 953 (off Gran Canaria)

Trace element concentrations of altered basaltic glass shards (layer silicates) and zeolites in volcaniclastic sediments drilled in the volcanic apron northeast of Gran Canaria during Ocean Drilling Program (ODP) leg 157 document variable element mobilities during low-temperature alteration processes in a marine environment. Clay minerals (saponite, montmorillonite, smectite) replacing volcanic glass particles are enriched in transition metals and rare earth elements (REE). The degree of retention of REE within the alteration products of the basaltic glass is correlated with the field strength of the cations. The high field-strength elements are preferentially retained or enriched in the alteration products by sorption through clay minerals. Most trace elements are enriched in a boundary layer close to the interface mineral-altered glass. This boundary layer has a key function for the physico-chemical conditions of the subsequent alteration process by providing a large reactive surface and by lowering the fluid permeability. The release of most elements is buffered by incorporation into secondary precipitates (sodium-rich zeolites, phillipsite, Fe- and Mn-oxides) as shown by calculated distribution coefficients between altered glasses and authigenic minerals. Chemical fluxes change from an open to a closed system behavior during prograde low-temperature alteration of volcaniclastic sediments with no significant trace metal flux from the sediment to the water column.     

Polycyclic aromatic hydrocarbons in sediments,mussels and crustacea around a former gasworks site in Shoreham-by-Sea,UK

Concentrations of polycyclic aromatic hydrocarbons have been determined in sediments, mussels and crustacea in the vicinity of a former gasworks site by Shoreham Harbour, UK. Very high concentrations of PAH were found in the substrate, an ash-like material deposited on the former gasworks site, which exhibited a profile consistent with the major source of contamination being coal or coke tar produced during the period of gas production at the site. Elevated PAH concentrations were also found in mussels both from the beach below the former gasworks site, and from sites further to the east in Portslade and Hove. The significance of these concentrations were assessed using an approach which involved the calculation of benzo[a]pyrene equivalent conoentrations (BaPEs), summing concentrations of individual PAH on the basis of their comparative potency as carcinogens. BaPE ranged from values of, or close to, zero for crustacea, to 336 microg kg(-1) wet weight in mussels from Southwick Beach. The contaminated mussels are not exploited commercially but may be taken by casual gatherers, and notices have been posted to warn potential consumers.     

The impact of vertebrate herbivores on wetland vegetation in Atchafalaya Bay, Louisiana

Delta islands in the Atchafalaya and Wax Lake deltas in Atchafalaya Bay, Louisiana, are in an extremely dynamic successional phase. These islands initially supported large marshes dominated by the pioneering plant species Sagittaria latifolia and Sagittaria platyphylla. A general decrease in vegetated areas has occurred in the delta island marshes in the Atchafalaya Delta since about 1980, while in the Wax Lake Delta portion of the complex the vegetation still flourished. The Atchafalaya Delta provides an interesting setting for the study of herbivory because of the complex interaction of biotic and physical factors operating in this delta. We hypothesized that grazing by herbivores has a marked effect on vegetation in these developing marshes. To test this hypothesis, exclosures were erected on islands in both deltas in September 1985 and January 1986. Each set of exclosure treatments included an openly-grazed control area, an ungrazed area, an area allowing nutria grazing, and one allowing waterfowl grazing in each site. Results of the experiment, based on field sampling of vegetation, indicated decreases in plant biomass and changes in plant species composition in grazed treatments. Waterfowl and nutria reduced biomass aboul equally, but there was a more marked effect in the openly grazed areas. These findings may be extrapolated to sediment diversion areas along the Mississippi River.     

Zur Tektonik des mittleren Südwestafrika

Zusammenfassung Der Gesteinsuntergrund des mittleren Südwestafrika weist eine NO-SW gerichtete Struktur auf. Nahezu sämtliche Bewegungs-Vorgänge vom ältesten Archäikum abwärts sind dieser Grundrichtung gefolgt.Die ältesten Faltungsvorgänge im Präkambrium stehen im Zusammenhang mit gewaltigen Intrusionen vorwiegend granitischer Gesteine. Nachdem der Kontinent durch diese Vorgänge bereits am Ende des Archäikums in NO-SW-Richtung konsolidiert war, erfolgten in postarchäischer Zeit Krustenbewegungen, die sich ebenfalls dieser Richtung anpassen. Auffällig ist die randliche Aufwulstung des Kontinents in diesem Abschnitt und deren NO-SW gerichtete Querverbiegung, die stellenweise von großen Brüchen begleitet wird. Diese Bruchtektonik scheint jedoch wenigstens im mittleren Südwestafrika nicht das vonStahl angenommene Ausmaß erreicht zu haben. Die vonKrenkel angenommene große Überschiebungslinie am Südrande des Khomas-Hochlandes konnte als nicht vorhanden nachgewiesen werden.Das durch die Vergitterung der randlichen Aufwulstung und der NO-SW gerichteten Querverbiegung am höchsten herausgehobene Gebiet ist das Khomas-Hochland, dessen Anlage als Resistenzscholle bis ins älteste Archäikum zurückzuverfolgen ist.     

SOME URALIAN CORALS FROM NORTHERN KUANGSI COLLECTED BY DR.V.K.TING IN 1930

The specimens described in the present contribution were collected byDr.V.K.Ting in 1930 at the fort of Kungchishan,Nantanhsien,Kuangsi Pro-vince,Loc.T241 (广西南丹县公鸡山) The containing rock is a lightgrey limestone full of Funsulinoids,which,according to Mr.S Chen of Shang-hai,include the following species:     

Analysis of decade-long time series of GPS-based polar motion estimates at 15-min temporal resolution

We present results from the generation of 10-year-long continuous time series of the Earth’s polar motion at 15-min temporal resolution using Global Positioning System ground data. From our results, we infer an overall noise level in our high-rate polar motion time series of 60 \(\upmu \hbox {as}\) (RMS). However, a spectral decomposition of our estimates indicates a noise floor of 4 \(\upmu \hbox {as}\) at periods shorter than 2 days, which enables recovery of diurnal and semidiurnal tidally induced polar motion. We deliberately place no constraints on retrograde diurnal polar motion despite its inherent ambiguity with long-period nutation. With this approach, we are able to resolve damped manifestations of the effects of the diurnal ocean tides on retrograde polar motion. As such, our approach is at least capable of discriminating between a historical background nutation model that excludes the effects of the diurnal ocean tides and modern models that include those effects. To assess the quality of our polar motion solution outside of the retrograde diurnal frequency band, we focus on its capability to recover tidally driven and non-tidal variations manifesting at the ultra-rapid (intra-daily) and rapid (characterized by periods ranging from 2 to 20 days) periods. We find that our best estimates of diurnal and semidiurnal tidally induced polar motion result from an approach that adopts, at the observation level, a reasonable background model of these effects. We also demonstrate that our high-rate polar motion estimates yield similar results to daily-resolved polar motion estimates, and therefore do not compromise the ability to resolve polar motion at periods of 2–20 days.