The stability of xenotime in high Ca and Ca-Na systems, under experimental conditions of 250-350°C and 200-400 MPa : the implications for fluid-mediated low-temperature processes in granitic rocks

The stability of xenotime was tested by experiments in the presence of a silicate mineral assemblage and two different fluids, 2M Ca(OH)_2 or Na_2Si_2O_5 + H_2O, under P-T conditions of 200-400 MPa and 250-350°C. The xenotime was stable in runs with 2M Ca(OH)_2, replicating the low-temperature metasomatic alterations of granitic rocks, except in experiment at 350°C and 400 MPa, where some (Y,REE)-rich fluorapatite formed. Experiments with Na_2Si_2O_5 + H_2O resulted in significant xenotime alteration and partial replacement by an unknown (Y,HREE)-rich silicate, and in the formation of minor amounts of (Y,REE)-rich fluorapatite. The latter indicate preferential partitioning of Y and REE into silicates over phosphates during low-temperature, metasomatic processes in a high Na-Ca system, similar to peralkaline granitic rocks

Stability of monazite and disturbance of the Th-U-Pb system under experimental conditions of 250-350^{\circ}C and 200-400 MPa

This experimental study provides important data filling the gap in our knowledge on monazite stability under conditions of fluid-mediated low-temperature metamorphic alteration and post-magmatic hydrothermal alterations. The stability of monazite and maintenance of original Th-U-total Pb ages were tested experimentally under P-T conditions of 250-350 ^{\circ}C and 200-400 MPa over 20-40 days. The starting materials included the Burnet monazite + K-feldspar ± albite ± labradorite + muscovite + biotite + SiO_2 + CaF_2 and 2M Ca(OH)_2 or Na_2Si_2O_5 + H_2O fluid. In the runs with 2M Ca(OH)_2, monazite was unaltered. REE-enriched apatite formed at 350 ^{\circ}C and 400 MPa. The presence of the Na_2Si_2O_5 + H_2O fluid promoted the strong alteration of monazite, the formation of secondary REE-enriched apatite to fluorcalciobritholite, and the formation of REE-rich steacyite. Monazite alteration included the newly developed porosity, patchy zoning, and partial replacement by REE-rich steacyite. The unaltered domains of monazite maintained the composition of the Burnet monazite and its age of (or close to) ca. 1072 Ma, while the altered domains showed random dates in the intervals of 375-771 Ma (250 ^{\circ}C, 200 MPa run), 82-253 Ma (350 ^{\circ}C, 200 MPa), and 95-635 Ma (350 ^{\circ}C, 400 MPa). The compositional alteration and disturbance of the Th-U-Pb system resulted from fluid-mediated coupled dissolution-reprecipitation. In nature, such age disturbance in monazite can be attributed to post-magmatic alteration in granitic rocks or to metasomatic alteration during metamorphism. Recognition of potentially altered domains (dark patches in high-contrast BSE-imaging, developed porosity or inclusions of secondary minerals) is crucial to the application of Th-U-Pb geochronology

New School, the Same Old Rut? Action Research of Unsuccessful First-year Students in a High School

Action research is one of the tools that a reflective teacher may use in order to solve specific problems they encounter in their daily teaching practice. The article describes action research carried out in a high school to investigate some of the reasons behind the poor performance of some first-year students. It has been observed that students’ lack of success during the first semester corresponds directly to their low results in the end-of-middle school exam, despite the fact that they were allocated to groups on the basis of a placement test. In a questionnaire survey, students reflected upon their motivation, attitude, classroom anxiety, and assessed their performance against other group members. This article offers an analysis of the questionnaire results and attempts at presenting certain ways in which teachers could help students who did not manage to wipe the slate clean avoid some learning barriers

Ochrona informacji niejawnych w świetle krajowych aktów prawnych

Publikacja recenzowana / Peer-reviewed publicationArtykuł omawia uwarunkowania bezpieczeństwa informacyjnego, a przede wszystkim ochrony informacji niejawnych w Polsce, zarówno w sferze cywilnej, jak i wojskowej. Autor interpretując polskie akty prawne ukazuje najważniejsze czynniki oraz rozwiązania techniczno-organizacyjne zabezpieczenia treści chronionych. Z uwagi na rangę tematu, za punkt wyjścia przyjęto przesłanki wolności informacyjnej zawarte w ustawie zasadniczej, czynniki opisane w Strategii Bezpieczeństwa Narodowego RP z 2014 r., czy ustawie o ochronie informacji niejawnej i licznych rozporządzeniach oraz w rozdziale związanym z tą problematyką, w Kodeksie Karnym. Autor podkreśla ważność dostępu do informacji, jako składową strategicznych uwarunkowań funkcjonowania organizacji państwa.The thesis analyzes the conditions of information safety/security with the special emphasis on classified information protection in Poland, taking into consideration both civilian and military spheres. The Author presents the interpretation of respective legal acts thereby emphasizing crucial factors, technical-organizational solutions to the protection of classified contents/information. Considering the importance of the subject matter, the Author begins by discussing the freedom of information premises included in the constitution, then moving to factors included in the National Security Strategy, the protection of classified information act and numerous regulations as well as reformatory/ remedial character of the issues in question as presented in the respective chapter of the penal code. The Author emphasizes the importance of information access as a thread of strategic conditions of the functioning of state organization.В статье рассмотрены условия информационной безопасности, прежде всего, связан- ные с защитой гражданской и военной секретной информации в Польше. Автор ин- терпретируя польские правовые акты, указывает наиболее весомые факторы и тех- ническо-организационные решения по защите секретной информации. Имея ввиду важность тематики, в качестве отправной точки, рассмотрено правовые решения связанные со свободой информации, содержащиеся в Основном законе, факторы, описанные в «Стратегии национальной безопасности Республики Польша» от 2014 года, в «Законе о защите секретной информации», во многочисленных распоряже- ний, а также во главе Уголовного кодекса, рассматривающей этот вопрос. Автор под- черкивает важность доступа к информации – как компоненту стратегических условий функционирования организации государства

Th-U-total Pb timing constraints on the emplacement of the granitoid pluton of Stolpen, Germany

Monazite from the Stolpen monzogranite (SE Germany) was studied to constrain the Th-U-total Pb age of pluton formation. Monazite grains demonstrate subtle to distinct patchy zoning related to slight compositional variations. Textural and compositional characteristics indicate that the monazite formed in a single magmatic event in a slightly heterogeneous system, and was only weakly affected by secondary alteration, which did not disturb the Th-U-Pb system. Chemical dating of the monazite gave a consistent age of 299 ± 1.7 Ma. The current study presents the first geochronological data for the Stolpen granite. It provides evidence that Stolpen is the youngest Variscan granitic intrusion in the Lusatian Granodiorite Complex and indicates that magmatic activity related to post-collisional extension in this region lasted at least 5my longer than previously assumed

Implicit lunar dust mitigation technology: compliant mechanisms

The finest fraction of the lunar regolith, namely the lunar dust, poses a challenge for hardware design and lunar operations. The Apollo missions experienced equipment malfunctions and failures due to dust interactions with hardware. In this work we focus on the problems related to the clogging of rigid body mechanisms. We explain the causes of the problem and propose a solution consisting of replacing traditional mechanisms with compliant mechanisms. There are multiple methods for synthesizing compliant mechanisms, but two approaches are most commonly used: analytical design and topology optimization. In this paper using a compliant gripper as an example, the suitability of these methods to design compliant mechanisms used in extra-vehicular activities is investigated. In doing so, the feasibility of using complaint mechanisms in the lunar equipment as part of dust mitigation strategies for surface projects is also demonstrated

Topology Optimization of Compliant Mechanisms as a Design Method to Improve Hardware Performance in Lunar Dust Environment

The experience from the Apollo missions showed that Lunar regolith particles are exceptionally sharp, electrostatically charged, adhesive, and pose a significant risk to mission hardware by entering gaps between the elements of mechanisms and can cause damage especially where rigid body relative displacements occur. The present work presents an alternative approach for the design of hardware that will operate on the Lunar surface. The authors propose the use of compliant mechanisms to produce monolithic mechanisms that are intrinsically resilient to Lunar dust. To support the design of compliant mechanisms topology-optimisation based design methods are here proposed. Topology optimization focuses on optimizing material distribution for a given design space and boundary conditions with the goal of maximizing the performance of the design. Achieving topologically optimized compliant mechanisms, so far, has proven to be challenging, especially when compared to static structures, and the use of commercial software does not automatically translate in ease of use. In this work, several MATLAB routines that can support topology optimisation of compliant mechanisms are explored. The advantages and disadvantages of each routine are highlighted and their application to a compliant force inverter is presented

Detrital zircon U-Pb and Hf constraints on provenance and timing of deposition of the Mesoproterozoic to Cambrian sedimentary cover of the East European Craton, Belarus

International audienceThe sedimentary cover of the East European Craton (EEC) is unique because of its low degree of diagenetic alteration that allows preservation of the original “source to sink” relationships. The present study provides U-Pb and Hf zircon data for the entire Proterozoic sedimentary section of the EEC based on samples from five boreholes in Belarus within the Volyn-Orsha Basin, one of the most important sedimentary basins of the craton. Twenty-one samples of mudstones and sandstones were selected for detrital zircon U-Pb geochronology, supplemented by the Hf isotope analyses of zircons from 6 samples representing different U-Pb age spectra and bulk rock XRD mineralogy of all mudstone samples collected from the studied boreholes. Five clastic successions in the Volyn-Orsha Basin are characterized by different sources of detrital material: (1) The Mesoproterozoic Pinsk Suite with a narrow population of c. 2.0 Ga zircons, (2) The Orsha Suite with a broad 1.3–3.2 Ga zircon age distribution, (3) Glacial sediments of the Vilchitsy Series with an age spectra similar to the Orsha Suite, except for a c. 1.0 and 1.2 Ga cluster, (4) The Volyn and Valdai Series, including lowermost Cambrian, with a narrow trimodal population of 0.5, 1.5, and 1.8 Ga zircons, and (5) lower Cambrian (?) sediments with a diffused zircon age spectrum, including a 500–700 Ma cluster. Maximum depositional ages were constrained for the Vilchitsy Series at 977 ± 6 Ma and for the Volyn Series at 579–545 ± 4 Ma. Combined Hf zircon data indicate four episodes of new continental crust generation at 3.3, 2.8, 2.1–2.3 and 1.8 Ga, suggestive of source terrains within the crust of the present-day EEC. These sources experienced subsequent reworking of crust at c. 1.8 Ga and 550–600 Ma. Only a lower Cambrian sample lacks any trend or clustering within the Hf data probably due to mixing of zircons from exotic and local sources. Paleogeographic models explaining these provenance signals in terms of intracratonic erosion and sediment transport are presented