Phase Transformations in Binary Colloidal Monolayers

Phase transformations can be difficult to characterize at the microscopic level due to the inability to directly observe individual atomic motions. Model colloidal systems, by contrast, permit the direct observation of individual particle dynamics and of collective rearrangements, which allows for real-space characterization of phase transitions. Here, we study a quasi-two-dimensional, binary colloidal alloy that exhibits liquid-solid and solid-solid phase transitions, focusing on the kinetics of a diffusionless transformation between two crystal phases. Experiments are conducted on a monolayer of magnetic and nonmagnetic spheres suspended in a thin layer of ferrofluid and exposed to a tunable magnetic field. A theoretical model of hard spheres with point dipoles at their centers is used to guide the choice of experimental parameters and characterize the underlying materials physics. When the applied field is normal to the fluid layer, a checkerboard crystal forms; when the angle between the field and the normal is sufficiently large, a striped crystal assembles. As the field is slowly tilted away from the normal, we find that the transformation pathway between the two phases depends strongly on crystal orientation, field strength, and degree of confinement of the monolayer. In some cases, the pathway occurs by smooth magnetostrictive shear, while in others it involves the sudden formation of martensitic plates.Comment: 13 pages, 7 figures. Soft Matter Latex template was used. Published online in Soft Matter, 201

Emergence of limit-periodic order in tiling models

A 2D lattice model defined on a triangular lattice with nearest- and next-nearest-neighbor interactions based on the Taylor-Socolar monotile is known to have a limit-periodic ground state. The system reaches that state during a slow quench through an infinite sequence of phase transitions. We study the model as a function of the strength of the next-nearest-neighbor interactions, and introduce closely related 3D models with only nearest-neighbor interactions that exhibit limit-periodic phases. For models with no next-nearest-neighbor interactions of the Taylor-Socolar type, there is a large degenerate classes of ground states, including crystalline patterns and limit-periodic ones, but a slow quench still yields the limit-periodic state. For the Taylor-Socolar lattice model, we present calculations of the diffraction pattern for a particular decoration of the tile that permits exact expressions for the amplitudes, and identify domain walls that slow the relaxation times in the ordered phases. For one of the 3D models, we show that the phase transitions are first order, with equilibrium structures that can be more complex than in the 2D case, and we include a proof of aperiodicity for a geometrically simple tile with only nearest-neighbor matching rules.Comment: 25 pages, 28 figures; To appear in Physical Review

Geology and wall rock alteration at the Hercynian Draa Sfar Zn–Pb–Cu massive sulphide deposit, Morocco

International audienceDraa Sfar is a siliciclastic–felsic, volcanogenic massive sulphide (VMS) Zn–Pb–Cu deposit located 15 km north of Marrakesh within the Jebilet massif of the western Moroccan Meseta. The Draa Sfar deposit occurs within the Sarhlef series, a volcano-sedimentary succession that hosts other massive sulphide deposits (e.g., Hajar, Kettara) within the dominantly siliciclastic sedimentary succession of the lower Central Jebilet. At Draa Sfar, the footwall lithofacies are dominated by grey to black argillite, carbonaceous argillite and intercalated siltstone with localized rhyodacitic flows and domes, associated in situ and transported autoclastic deposits, and lesser dykes of aphanitic basalt and gabbro. Thin- to thick-bedded, black carbonaceous argillite, minor intercalated siltstone, and a large gabbro sill dominate the hanging wall lithofacies. The main lithologies strike NNE–SSW, parallel to a pronounced S1 foliation, and have a low-grade, chlorite–muscovite–quartz–albite–oligoclase metamorphic assemblage. The Draa Sfar deposit consists of two stratabound sulphide orebodies, Tazakourt to the south and Sidi M'Barek to the north. Both orebodies are hosted by argillite in the upper part of the lower volcano-sedimentary unit. The Tazakourt and Sidi M'Barek orebodies are highly deformed, sheet-like bodies of massive pyrrhotite (up to 95% pyrrhotite) with lesser sphalerite, galena, chalcopyrite, and pyrite. The Draa Sfar deposit formed within a restricted, sediment-starved, fault-controlled, anoxic, volcano-sedimentary rift basin. The deposit formed at and below the seafloor within anoxic, pelagic muds. The argillaceous sedimentary rocks that surround the Draa Sfar orebodies are characterized by a pronounced zonation of alteration assemblages and geochemical patterns. In the more proximal volcanic area to the south, the abundance of medium to dark green chlorite progressively increases within the argillite toward the base of the Tazakourt orebody. Chlorite alteration is manifested by the replacement of feldspar and a decrease in muscovite abundance related to a net addition of Fe and Mg and a loss of K and Na. In the volcanically distal and northern Sidi M'Barek orebody alteration within the footwall argillite is characterized by a modal increase of sericite relative to chlorite. A calcite–quartz–muscovite assemblage and a pronounced decrease in chlorite characterize argillite within the immediate hanging wall to the entire Draa Sfar deposit. The sympathetic lateral change from predominantly sericite to chlorite alteration within the footwall argillite with increasing volcanic proximity suggests that the higher temperature part of the hydrothermal system is coincident with a volcanic vent defined by localized rhyodacitic flow/domes within the footwall succession

Large-Scale Integration of Nanoelectromechanical Systems for Gas Sensing Applications

We have developed arrays of nanomechanical systems (NEMS) by large-scale integration, comprising thousands of individual nanoresonators with densities of up to 6 million NEMS per square centimeter. The individual NEMS devices are electrically coupled using a combined series-parallel configuration that is extremely robust with respect to lithographical defects and mechanical or electrostatic-discharge damage. Given the large number of connected nanoresonators, the arrays are able to handle extremely high input powers (>1 W per array, corresponding to <1 mW per nanoresonator) without excessive heating or deterioration of resonance response. We demonstrate the utility of integrated NEMS arrays as high-performance chemical vapor sensors, detecting a part-per-billion concentration of a chemical warfare simulant within only a 2 s exposure period

Piezoelectric nanoelectromechanical resonators based on aluminum nitride thin films

We demonstrate piezoelectrically actuated, electrically tunable nanomechanical resonators based on multilayers containing a 100-nm-thin aluminum nitride (AlN) layer. Efficient piezoelectric actuation of very high frequency fundamental flexural modes up to ~80 MHz is demonstrated at room temperature. Thermomechanical fluctuations of AlN cantilevers measured by optical interferometry enable calibration of the transduction responsivity and displacement sensitivities of the resonators. Measurements and analyses show that the 100 nm AlN layer employed has an excellent piezoelectric coefficient, d_(31)=2.4 pm/V. Doubly clamped AlN beams exhibit significant frequency tuning behavior with applied dc voltage

Permo-Triassic Deposits: from shallow water to base of slope

Conference on the Geology of Oman, Muscat, Oman, Field Guidebook A0

HCI as a means to prosociality in the economy

HCI research often involves intervening in the economic lives of people, but researchers only rarely give explicit consideration to what actually constitutes prosociality in the economy. Much has been said previously regarding sustainability but this has largely focused on environmental rather than interpersonal relations. This paper provides an analysis of how prosocial HCI has been discussed and continues to be defined as a research field. Based on a corpus of published works, we describe a variety of genres of work relating to prosocial HCI. Key intellectual differences are explored, including the epistemological and ethical positions involved in designing for prosocial outcomes as well as how HCI researchers posit economic decision-making. Finally, emerging issues and opportunities for further debate and collaboration are discussed in turn

A specific nanobody prevents amyloidogenesis of D76N β2-microglobulin in vitro and modifies its tissue distribution in vivo

Systemic amyloidosis is caused by misfolding and aggregation of globular proteins in vivo for which effective treatments are urgently needed. Inhibition of protein self-aggregation represents an attractive therapeutic strategy. Studies on the amyloidogenic variant of β2-microglobulin, D76N, causing hereditary systemic amyloidosis, have become particularly relevant since fibrils are formed in vitro in physiologically relevant conditions. Here we compare the potency of two previously described inhibitors of wild type β2-microglobulin fibrillogenesis, doxycycline and single domain antibodies (nanobodies). The β2-microglobulin -binding nanobody, Nb24, more potently inhibits D76N β2-microglobulin fibrillogenesis than doxycycline with complete abrogation of fibril formation. In β2-microglobulin knock out mice, the D76N β2-microglobulin/ Nb24 pre-formed complex, is cleared from the circulation at the same rate as the uncomplexed protein; however, the analysis of tissue distribution reveals that the interaction with the antibody reduces the concentration of the variant protein in the heart but does not modify the tissue distribution of wild type β2-microglobulin. These findings strongly support the potential therapeutic use of this antibody in the treatment of systemic amyloidosis