On the space group of threadgoldite

Summary It is shown that the crystal structure of the autunite group mineral threadgoldite, Al(UO₂)₂(PO₄)₂(OH)·8H₂O, recently determined byPiret et al. (1979) in the acentric space groupCc, can be better described and refined in the centrosymmetric space groupC2/c. The bond distances thus obtained are more reasonable than the previous ones.

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Zur Raumgruppe des Minerals Threadgoldit

Zusammenfassung Es wird gezeigt, daß die Kristallstruktur des Uranglimmer-Minerals Threadgoldit, Al(UO₂)₂(PO₄)₂(OH)·8H₂O, die kürzlich vonPiret et al. (1979) unter Verwendung der nichtzentrosymmetrischen RaumgruppeCc bestimmt wurde, besser in der zentrosymmetrischen RaumgruppeC2/c zu beschreiben und verfeinern ist. Die so erhaltenen Bindungslängen sind kristallchemisch plausibler als die zuvor gefundenen Werte.

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A shrinking particle—shrinking core model for leaching of a zinc ore containing silica

A new mathematical model was developed for leaching of zinc ores containing silicates such as hemimorphite which produce a gel during leaching with sulfuric acid. This model is based on the shrinking core model in which the particle size and the reacting core shrink simultaneously. It was shown that the actual dissolution time of the ore particles is longer than the time corresponding to the dissolution of chemical zinc oxide itself. It was suggested that because of the existence of silicates in the ore, a gelatinous layer was formed around the reacting core. Since the gel product is soft, it breaks apart when the particles collide and as a result, the particles shrink. However, a thin gelatinous layer always covers the reacting core which increases the mass transfer resistance and increases the leaching time. This model was applied to leaching of a zinc-rich tailing containing hemimorphite and the thickness of the gelatinous layer as well as the diffusion coefficient in this layer was determined.     

Shear velocity estimates in rough‐bed open‐channel flow

Shear velocity u_* is an important parameter in geophysical flows, in particular with respect to sediment transport dynamics. In this study, we investigate the feasibility of applying five standard methods [the logarithmic mean velocity profile, the Reynolds stress profile, the turbulent kinetic energy (TKE) profile, the wall similarity and spectral methods] that were initially developed to estimate shear velocity in smooth bed flow to turbulent flow over a loose bed of coarse gravel (D₅₀ = 1·5 cm) under sub‐threshold conditions. The analysis is based on quasi‐instantaneous three‐dimensional (3D) full depth velocity profiles with high spatial and temporal resolution that were measured with an Acoustic Doppler Velocity Profiler (ADVP) in an open channel. The results of the analysis confirm the importance of detailed velocity profile measurements for the determination of shear velocity in rough‐bed flows. Results from all methods fall into a range of ± 20% variability and no systematic trend between methods was observed. Local and temporal variation in the loose bed roughness may contribute to the variability of the logarithmic profile method results. Estimates obtained from the TKE and Reynolds stress methods reasonably agree. Most results from the wall similarity method are within 10% of those obtained by the TKE and Reynolds stress methods. The spectral method was difficult to use since the spectral energy of the vertical velocity component strongly increased with distance from the bed in the inner layer. This made the choice of the reference level problematic. Mean shear stress for all experiments follows a quadratic relationship with the mean velocity in the flow. The wall similarity method appears to be a promising tool for estimating shear velocity under rough‐bed flow conditions and in field studies where other methods may be difficult to apply. This method allows for the determination of u_* from a single point measurement at one level in the intermediate range (0·3 < h < 0·6). Copyright © 2013 John Wiley & Sons, Ltd.     

The biostratigraphy of the uppermost calcareous nannofossils of Cretaceous deposit in both Shahdar and Namazgah sections (NE Iran)

A moderately various calcareous nannofossil assemblage of 44 species assigned to 24 genera is identified in samples collected from the Shahdar section and 18 genera and 43 species in Namazgah section. Testing of calcareous nannofossil has permitted recognition of few important coccolith events in stratigraphic interval occupied by the uppermost layers of Cretaceous in the Shahdar and Namazgah sections. These events are correlated to the CC24–CC26 of Sissingh (Geol Minjbouw 56: 37–65, 1977) in two sections. According to these biozones, the age of the studied sections in Shahdar and Namazgah is Early Maastrichtian–Late Maastrichtian. On the basis of paleoecological interpretation, the last layers related to the Cretaceous deposits in two sections were deposited in shallow marine environment in relatively low latitude, and the depth of the basin from the Cretaceous deposits toward Fajan Formation is minimized.     

Anthropogenic Decline of Ancient,Sustainable Water Systems: Qanats

Qanat is an ancient underground structure to abstract groundwater without the need for external energy. A recognized world heritage, Qanat has enabled civilization in arid and semi-arid regions that lack perennial surface water resources. These important structures, however, have faced significant challenges in recent decades due to increasing anthropogenic pressures. This study uses remote sensing to investigate land-use changes and the loss of 15,983 Qanat shafts in the Mashhad plain, northeast of Iran, during the past six decades. This entails obtaining a rare aerial imagery from 1961, as well as recent satellite imagery, over a region with the highest density of Qanats in Iran, the birthplace of Qanat. Results showed that only 5.59% of the Qanat shafts in 1961 remained intact in 2021. The most prominent Qanat-impacting land-use changes were agriculture and urban areas, that accounted for 42.93 and 31.81% Qanat shaft destruction in the study area, respectively. This study also showed that groundwater table decline, demographic changes, and reduction in the appeal of working in the Qanat maintenance and construction industry among the new generation are existential threats to Qanats, and may result in the demise of these ancient structures in the future. Findings of this study can be used for urban planning in arid and semi-arid areas with the aim of protecting these historic water structures.     

The crystal structure of meta-uranocircite II,Ba(UO2)2(PO4)2·6H2O

Summary The crystal structure of meta-uranocircite II, Ba(UO₂)₂(PO₄)₂·6H₂O, has been determined with a synthetic crystal using three-dimensional X-ray techniques.R=0.071 andR _w =0.064 were obtained for 1743 observed reflections. Ba(UO₂)₂(PO₄)₂·6H₂O is monoclinic, space groupP112₁/a, a=9.789,b=9.822,c=16.868 Å, =89.95° andZ=4. The structure consists of slightly corrugated UO₂PO₄ layers parallel (001). The layers are connected by Ba atoms and H₂O molecules. Uranium exhibits a (2+4)-coordination with mean U-O bond lengths of 1.78 Å for the uranyl oxygens and 2.28 Å for the phosphate oxygens. The average P-O bond length is 1.52 Å. Barium is coordinated by two uranyl oxygens. two phosphate oxygens and five water molecules. The Ba–O bond lengths vary from 2.74 to 3.11 Å. Two of the six water molecules of the formula are not bonded to barium.

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Die Kristallstruktur des Meta-Uranocircits II, Ba(UO₂)₂(PO₄)₂·6H₂O

Zusammenfassung Die Kristallstruktur des Meta-Uranocircits II, Ba(UO₂)₂(PO₄)₂·6H₂O, wurde anhand eines künstlichen Kristalls mit dreidimensionalen Röntgendaten bearbeitet und für 1743 Reflexe aufR=0,071 undR _w =0,064 verfeinert. Ba(UO₂)₂(PO₄)₂·6H₂O kristallisiert monoklin in der RaumgruppeP112₁/a, a=9,789,b=9,882,c=16,868 Å, =89,95° und einem Zellinhalt von vier Formeleinheiten. Die Struktur besteht aus schwach gewellten UO₂PO₄-Schichten parallel (001), die durch Ba-Atome und H₂O-Moleküle miteinander verknüpft sind. Uran besitzt oktaedrische (2+4)-Koordination mit mittleren U-O-Abständen von 1,78 Å für die Uranylsauerstoffatome und 2,28 Å für die Phosphatsauerstoffatome. Die P-O-Abstände der Phosphattetraeder messen im Mittel 1.52 Å. Barium ist von je zwei Uranyl- und Phosphatsauerstoffatomen sowie von fünf Wassermolekülen koordiniert. Die Ba-O-Abstände betragen 2,74–3,11 Å. Von den sechs H₂O-Molekülen der Formel sind zwei nicht an Barium gebunden.

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