Agricolaite, a new mineral of uranium from J��chymov, Czech Republic     

Roman Sk��la  Petr Ondru?  Franti?ek Veselovsky  Ivana C��sa?ov��  Jan Hlou?ek 《Mineralogy and Petrology》2011,103(1-4):169-175

The new mineral agricolaite, a potassium uranyl carbonate with ideal formula K₄(UO₂)(CO₃)₃, occurs in vugs of ankerite gangue in gneisses in the abandoned Giftkiesstollen adit at Jáchymov, Czech Republic. The name is after Georgius Agricola (1494?C1555), German scholar and scientist. Agricolaite occurs as isolated equant irregular translucent grains to 0.3?mm with yellow color, pale yellow streak, and vitreous luster. It is brittle with uneven fracture and displays neither cleavage nor parting. Agricolaite is non-fluorescent. Mohs hardness is ~4. It is associated with aragonite, brochantite, posnjakite, malachite, rutherfordine, and ??pseudo-voglite??. Experimental density is higher than 3.3?g.cm^?3, Dcalc is 3.531?g.?cm^?3. The mineral is monoclinic, space group C2/c, with a 10.2380(2), b 9.1930(2), c 12.2110(3) ?, ?? 95.108(2)°, V 1144.71(4) ?³, Z?=?4. The strongest lines in the powder X-ray diffraction pattern are d(I)(hkl): 6.061(55)(002), 5.087(57)(200), 3.740(100)(202), 3.393(43)(113), 2.281(52)(402). Average composition based on ten electron microprobe analyses corresponds to (in wt.%) UO₃ 48.53, K₂O 31.49, CO₂(calc) 22.04 which gives the empirical formula K_3.98(UO₂)_1.01(CO₃)_3.00. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R ₁?=?0.0184 on the basis of the 1,308 unique reflections with F _o?>?4??F _o. The structure of agricolaite is identical to that of synthetic K₄(UO₂)(CO₃)₃ and consists of separate UO₂(CO₃)₃ groups organized into layers parallel to (100) and two crystallographically non-equivalent sites occupied by K⁺ cations. Both the mineral and its name were approved by the IMA-CNMNC.  相似文献   

Radar and optical observations and physical modeling of near-Earth Asteroid 10115 (1992 SK)     

Michael W. Busch  Steven J. Ostro  Jon D. Giorgini  Randy Rose  Petr Pravec  Stephen B. Broschart 《Icarus》2006,181(1):145-155

We estimate Asteroid 1992 SK's physical properties from delay-Doppler images and Doppler-only echo spectra obtained during March 22-27, 1999, at Goldstone and from optical lightcurves obtained during February-March 1999 at Ond?ejov Observatory. The images span only about 15° of sky motion and are not strong, but they place up to twenty 40 m by 160 m pixels on the asteroid and have complete rotational phase coverage. Our analysis establishes that the radar observations are confined to subradar latitudes between −20° and −40°. The echo spectra and optical lightcurves span ∼80° of sky motion, which provides important geometric leverage on the pole direction. The lightcurves are essential for accurate estimation of the asteroid's shape and spin state. We estimate the asteroid's period to be 7.3182±0.0003 h and its pole direction to be at ecliptic longitude, latitude=(99°±5°,−3°±5°). The asteroid is about 1.4 km in maximum extent and mildly asymmetric, with an elongation of about 1.5 and relatively subdued topography. The OC radar albedo is 0.11±0.02 and the SC/OC ratio is 0.34±0.05. The current orbital solution permits accurate identification of planetary close approaches during 826-2690. We use our model to predict salient characteristics of radar images and optical lightcurves obtainable during the asteroid's March 2006 approach.  相似文献   

Photometry and models of eight near-Earth asteroids     

Mikko Kaasalainen  Petr Pravec  Lenka Šarounová  Jenni Virtanen  Anders Erikson  Josef ?urech  Johan S.V. Lagerros  Claes-Ingvar Lagerkvist  John Davies  Peter Kušnirák  Vasilij G. Shevchenko  Irina N. Belskaya 《Icarus》2004,167(1):178-196

We present new observations and models of the shapes and rotational states of the eight near-Earth Asteroids (1580) Betulia, (1627) Ivar, (1980) Tezcatlipoca, (2100) Ra-Shalom, (3199) Nefertiti, (3908) Nyx, (4957) Brucemurray, and (5587) 1990 SB. We also outline some of their solar phase curves, corrected to common reference geometry with the models. Some of the targets may feature sizable global nonconvexities, but the observable solar phase angles were not sufficiently high for confirming these. None is likely to have a very densely cratered surface. We discuss the role of the intermediate topographic scale range in photometry, and surmise that this scale range is less important than large or small scale lengths.  相似文献   

Five centuries of Southern Moravian drought variations revealed from living and historic tree rings     

Ulf B��ntgen  Rudolf Br��zdil  Petr Dobrovolny  Mirek Trnka  Tom��? Kyncl 《Theoretical and Applied Climatology》2011,105(1-2):167-180

Past, present, and projected fluctuations of the hydrological cycle, associated to anthropogenic climate change, describe a pending challenge for natural ecosystems and human civilizations. Here, we compile and analyze long meteorological records from Brno, Czech Republic and nearby tree-ring measurements of living and historic firs from Southern Moravia. This unique paleoclimatic compilation together with innovative reconstruction methods and error estimates allows regional-scale May?CJune drought variability to be estimated back to ad 1500. Driest and wettest conditions occurred in 1653 and 1713, respectively. The ten wettest decades are evenly distributed throughout time, whereas the driest episodes occurred in the seventeenth century and from the 1840s onward. Discussion emphasizes agreement between the new reconstruction and documentary evidence, and stresses possible sources of reconstruction uncertainty including station inhomogeneity, limited frequency preservation, reduced climate sensitivity, and large-scale constraints.  相似文献   

An unsustainable state: Contrasting food practices and state policies in the Czech Republic   总被引：1，自引：0，他引：1  

Petr Jehli?ka 《Geoforum》2011,42(3):362-372

This paper brings together consideration of food policies and practices and of post-socialist transition to raise neglected questions about means of nurturing more sustainable food systems in the developed world. The last three decades have been marked by the growing salience of food as a political and scholarly concern. While market-based alternative food systems have been heralded for their potential to promote environmental sustainability, the benefits of non-market practices such as household food self-provisioning and barter have been assumed rather than being the focus of research. In the western context, both types of food consumption have positive connotations. Although food self-provisioning in European post-socialist societies is a more wide-spread practice than in western societies, it has been on the periphery of research. The existing literature has conceptualised them as ‘coping strategies’ or as a legacy of irregular supply of goods in the state socialist era. Drawing on empirical research in the Czech Republic, we are proposing a novel approach to the phenomenon of household food production in post-socialist societies as a practice compliant with principles of sustainability. First, we highlight the large extent and social inclusivity of food self-provisioning in Czech society to demonstrate how post-socialist societies are a repository of a rich set of sustainability-promoting consumption practices in relation to food systems. Second, we show that international and domestic policy actors in these societies have ignored these alternative, socially inclusive and environmentally effective practices in favour of far less effective market-based sustainability oriented food policy initiatives. The paper promotes a more integrated view of non-market and market approaches in the pursuit of more sustainable food systems.  相似文献   

Towards hydrological triggering mechanisms of large deep-seated landslides   总被引：3，自引：3，他引：0  

Roberta Prokešová  Alžbeta Medveďová  Petr Tábořík  Zora Snopková 《Landslides》2013,10(3):239-254

It is a widely accepted idea that hydrologically triggered deep-seated landslides are initiated by an increase in pore-water pressure on potential slip surface induced by rising groundwater level after prolonged period of intense rainfall although the process is not fully understood. In order to contribute to better understanding, the rainfall–groundwater relationships, hydrogeological monitoring and repeated geoelectrical imaging were carried out from March 2007 to April 2011 in large deep-seated landslide near ?ubietová (Western Carpathians) catastrophically reactivated at the end of February 1977. Based on our observations, groundwater level (GWL) response to precipitation differs considerably with respect to both overall hydrological conditions and GWL mean depth. While the rate of GWL increase up to 25 cm/day were measured after some rainfall events during wet periods, noticeably lower recharge rate (up to 1–2 cm/day) and delayed GWL response to rainfall (usually from 2 weeks to 2–4 months) were observed at the beginning of the wet season after considerable depression of GWLs due to previous effective rainfall deficit. Likewise, slow GWL fluctuations without short-term oscillations are typical for deeper GWLs. Thus, long-term (several seasons to several years) hydrological conditions affect markedly groundwater response to rainfall events in the studied landslide and can be crucial for its behaviour. Comparison of hydrological conditions characterising the analysed period with those that accompanied the landslide reactivation in 1977 allow us to assume that slightly above-average rainy season following the prolonged wet period can be far more responsible for movement acceleration (and possibly failure initiation) in deep landslides than the isolated season of extreme precipitation following a longer dry period. This is true especially for landslides in regions with significant seasonal temperature changes where potential effective precipitation (PEP), calculated as excess of precipitation (P) over potential evapotranspiration (PET), may be efficiently used for estimation of slope saturation condition.  相似文献   

Testing Stokes-Helmert geoid model computation on a synthetic gravity field: experiences and shortcomings     

Petr Vaníček  Robert Kingdon  Michael Kuhn  Artu Ellmann  Will E. Featherstone  Marcelo C. Santos  Zdeněk Martinec  Christian Hirt  David Avalos-Naranjo 《Studia Geophysica et Geodaetica》2013,57(3):369-400

We report on testing the UNB (University of New Brunswick) software suite for accurate regional geoid model determination by use of Stokes-Helmert’s method against an Australian Synthetic Field (ASF) as “ground truth”. This testing has taken several years and has led to discoveries of several significant errors (larger than 5mm in the resulting geoid models) both in the UNB software as well as the ASF. It was our hope that, after correcting the errors in UNB software, we would be able to come up with some definite numbers as far as the achievable accuracy for a geoid model computed by the UNB software. Unfortunately, it turned out that the ASF contained errors, some of as yet unknown origin, that will have to be removed before that ultimate goal can be reached. Regardless, the testing has taught us some valuable lessons, which we describe in this paper. As matters stand now, it seems that given errorless gravity data on 1′ by 1′ grid, a digital elevation model of a reasonable accuracy and no topographical density variations, the Stokes-Helmert approach as realised in the UNB software suite is capable of delivering an accuracy of the geoid model of no constant bias, standard deviation of about 25 mm and a maximum range of about 200 mm. We note that the UNB software suite does not use any corrective measures, such as biases and tilts or surface fitting, so the resulting errors reflect only the errors in modelling the geoid.  相似文献   

Photochemical production and decomposition of particulate organic carbon in a freshwater stream     

Petr Porcal  Peter J. Dillon  Lewis A. Molot 《Aquatic Sciences - Research Across Boundaries》2013,75(4):469-482

Irradiation of dissolved organic carbon (DOC) of terrestrial origin that is freshly released to surface waters can produce particulate organic carbon (POC). Laboratory experiments with stream water were conducted to determine POC and particulate metals formation during exposure to artificial solar radiation comparable to surface intensity. The results showed that decreases in DOC concentration were accompanied initially by increasing and later by decreasing POC concentrations. Data were fit to first order kinetics models to compare rates of POC formation and loss with DOC and absorbance loss, and to better understand how metals might be involved in photochemical POC formation. This abiotic mechanism may be important for the transfer of allochthonous DOC and metals to sediments in temperate aquatic systems.  相似文献   

Buried Late Weichselian thermokarst landscape discovered in the Czech Republic,central Europe     

Jan Ho&#x;ek  Jind&#x;ich Prach  Marek K&#x;íek  Petr &#x;ída  Piotr Moska  Petr Pokorný 《Boreas: An International Journal of Quaternary Research》2019,48(4):988-1005

Pronounced climatic warming associated with the Late Weichselian Pleniglacial‐to‐Lateglacial transition caused considerable environmental changes throughout the former periglacial zones (in Europe ~53°–46°N). During permafrost degradation and subsequent ground subsidence (i.e. thermokarst processes), the landscape changed rapidly. In this study we investigated a flat mid‐altitude area in south Bohemia, Czech Republic, lying close to the southern limit of the Weichselian permafrost. We discovered palaeo‐lake basins with sedimentary infillings up to 11 m in depth. According to radiocarbon and palynostratigraphical dating, these basins were formed at the onset of the Late Pleniglacial‐to‐Lateglacial transition, whereas the smaller depressions were formed later. We suggest that the basins resulted from thermal and fluvio‐thermal erosion of the former permafrost and represent remnants of discontinuous gullies and possibly collapsed frost mounds (pingo/lithalsa scars). The formation of this a fossil thermokarst landscape was climatically driven and multiple phased, with the major phase during the climatic warming and wetting at the onset of GI‐1e (Bølling) and the minor phase during GI‐1c (Allerød). This study enhances knowledge of the palaeogeography of the former European periglacial zone by showing that Late Pleistocene thermokarst activity could have had a significant impact on the evolution of the landscape of at least some regions of central Europe along the southern limit of the continuous permafrost zone. The research also points to a similar history for the physical transformation of the landscape of the former European periglacial zone and current thermokarst landscapes and could be a valuable source of information with respect to the future transformation of the Arctic under conditions of ongoing global warming.  相似文献   

Magnetomineralogy of the cordierite gneiss from the magnetic anomaly at Humpolec,Bohemian Moldanubicum (Czech Republic)     

Václav Procházka  Marta Chlupáčová  Daniel Nižňanský  František Hrouda  Pavel Uher  Petr Rajlich 《Studia Geophysica et Geodaetica》2010,54(1):95-120

Magnetic properties as well as the magnetomineralogy were investigated in rocks underlying a 7 km long aeromagnetic anomaly situated in the Moldanubian crystalline unit of the Bohemian Massif. The anomaly is caused by highly magnetic cordierite gneiss forming a stripe of NE — SW direction east of the town of Humpolec, eastern Bohemia. Magnetic susceptibility and its anisotropy (AMS), natural remanent magnetization, field and temperature variations of susceptibility were measured. Optical study of thin sections, electron microprobe and Mössbauer studies were also used to reveal the carrier of the high susceptibility and the high NRM. There appear to be two major generations of Fe-Ti oxides: older hematite with ilmenite exsolutions (Ti-hematite) which is the dominant remanence phase, and younger magnetite, the dominant susceptibility phase, usually associated with rutile. This indicates a reaction Hematite + Ilmenite → Magnetite + + Rutile; the trace elements in magnetite, as well as texture and morphology of the oxide grains support this assertion. An additional minor portion of maghemite is revealed by Mössbauer and thermomagnetic results. The Ti-hematite belongs to the oldest mineral assemblage in the rock, despite its anhedral morphology. Inclusions in Ti-hematite, among which corundum and abundant paragonite occur, record a strongly peraluminous and probably disequilibrium association during the crystallization of the Ti-hematite.  相似文献