Control and optical mapping of mechanical transitions in polymer networks and DNA-based soft materials

Complex mechanical changes in response to an external trigger are pervasive in natural soft materials and often sought for applications. Be it the reversible stiffening of sea cucumber, the failure of a polymeric or colloidal gel under load, or the dissolution of a biosensing hydrogel upon target binding, mechanical transitions are typically enabled, and critically affected, by heterogeneous structures and reversible bonds. New possibilities to monitor evolving properties and to gain access to stress propagation with temporal and spatial resolution are being disclosed by mechanochromic molecules and molecular complexes, which transduce a mechanical stress into a light signal and act as built-in stress reporters. I will review recent strategies and identify future directions for the design of mechanically responsive soft networks and for their optical mapping, focusing particular attention on the emerging class of hydrogels based on DNA self-assembly

Precollisional development and Cenozoic evolution of the Southalpine retrobelt (European Alps)

The retrobelts of doubly vergent collisional orogens are classically interpreted as late-stage postcollisional features. Here, we integrate literature data with new structural and thermochronological evidence from the European Alps in order to document the precollisional development of the retrobelt segment exposed in the central southern Alps. During the Late Cretaceous, by inversion of inherited extensional faults of Permian age, the Variscan basement of the central southern Alps was stacked southward onto the Permian-Mesozoic cover sequences of the Adria margin. These thrust systems were first deformed within regional-scale antiforms (the "Orobic anticlines") and then cut by Eocene magmatic bodies. Our apatite fission-track data show that these units were largely structured and exhumed to shallow crustal levels before the intrusion of the Eocene magmatic rocks. Therefore, thrusting and folding in the Alpine retrobelt took place before the final closure of the Alpine Tethys and subsequent continental collision between Adria and Europe. Final exhumation and uplift in the northern part of the Southalpine retrobelt took place under a dextral transpressional regime largely coeval with the right-lateral strike-slip activity along the Insubric fault. In Neogene times, deformation propagated southward, leading to the formation of a frontal thrust belt that is largely buried beneath the Po Plain

Environmental change within the Balkan region during the past ca. 50 ka recorded in the sediments from lakes Prespa and Ohrid

Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15 m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5 m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth

Liquid crystalline phases in oligonucleotide solutions

In this thesis, we investigate the behavior of short complementary B-form DNA oligomers, 6 to 20 base pairs in length, exhibiting chiral nematic and columnar liquid crystal phases, even though such duplexes lack the shape anisotropy required for liquid crystal ordering. Structural characterization reveals that these phases are produced by the end-to-end stacking of the duplex oligomers into polydisperse anisotropic rod-shaped aggregates, which can order into liquid crystals. By use of polarized optical microscopy, X-ray micro-di raction and optical interferometry, we determine the phase diagram of DNA oligomers and we estimate the stacking energy to be 4-6 KBT. We also nd that upon cooling mixed solutions of short DNA oligomers, in which only a small fraction of the present DNA is complementary, the duplex-forming oligomers phase-separate into liquid crystal droplets, leaving the unpaired single strands in isotropic solution. This spontaneous partitioning is the combined result of the free energy gain from the end-to-end stacking and LC ordering of duplexes and of depletion-type interactions favoring the segregation of the more rigid duplexes from the flexible single strands. In a chemical environment where oligomer ligation is possible, such ordering and condensation would provide an autocatalytic link whereby complementarity promotes the extended polymerization of complementary oligomers. The possible relevance of these observations for prebiotic synthesis of nucleic acids is discussed

An eighteenth century tunnel as possible archive for palaeoclimate studies

The former Silva Lake (present “Pian del Lago”, Siena, Italy) developed during late Quaternary and formed as a poljie on the Triassic limestones. The depression, nowadays completely drained, is N-S oriented, 4.5 km wide and 12 km long. The lake never exceeded 6 m in depth, and it was mainly a grassy swamp during the dry season. The lake depression is filled with 20 to 30 m of a reddish siltyclayey succession. Starting from the Middle Age till late 18th century, the shallow waters of the lake and the humid area around acted as a swampy area infested by malaria. In 1766 a Sienese nobleman, Francesco Bindi Sergardi drained the lake excavating a drainage 2124m-long tunnel in Triassic limestones to connect the Silva Lake with the closeby Rigo Creek. However, quite often the tunnel was filled with debris and the lake swamped up again. In 1780 Pietro Leopoldo Grand Duke of Tuscany definitively reclaimed the Silva Lake and completed the construction of the drainage tunnel by paving and extending it for an additional 197 m. Since then, the tunnel is called the ”Canale del Gran Duca”. The entrance altitude of the canal is at 252 m a.s.l., and the exit is at 247 m a.s.l. The altitude difference is therefore of 5 m, and the canal floor has a slope of 0.2 %. The canal is for the most part paved but, in places, solid walls of Triassic limestone are still visible. Diffuse karst features are forming locally. Stalactites have lengths varying from 5 to 10 cm, and flowstones occur along the tunnel walls. The presence of these speleothems has allowed geochemical investigations to establish climatic variations of the last two centuries. The tunnel was probably cleaned and well maintained for sometime after its construction (1780), and it is likely that all the remaining speleothems have developed in the last two centuries with an estimated growth of a 0.5/6 mm per year. A petrographic investigation of a well laminated flowstone with a parasitic stalagmite has been undertaken to determine the growth mechanisms. Oxygen and carbon isotope data (δ18O and δ13C values) were used as indirect proxies for palaeoenvironmental reconstructions. Preliminary, data show significant variations along the axis of the flowstone possibly related to environmental and climatic variations within and above the “canale”

Environmental change within the Balkan region during the past ca. 50 ka recorded in the sediments from lakes Prespa and Ohrid

Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15 m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5 m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth

Radial force control of Multi-Sector Permanent Magnet machines considering radial rotor displacement

A mathematical model enabling to predict the electromagnetic x-y forces and torque for a given input current in a Multi-Sector Permanent Magnet Synchronous (MSPMS) machine is presented. The rotor static eccentricity is also accounted and the analytical calculations are validated by means Finite Element Analysis (FEA). Furthermore, a novel force and torque control is proposed based on input current minimization and is applied to suppress the Unbalanced Magnetic Pull (UMP) caused by the rotor eccentricity. The effective operation of the force suppression technique is verified by means of FEA

Radial force control of multi-sector permanent magnet machines for vibration suppression

Radial force control in electrical machines has been widely investigated for a variety of bearingless machines, as well as for the conventional structures featuring mechanical bearings. This paper takes advantage of the spatial distribution of the winding sets within the stator structure in a multisector permanent-magnet (MSPM) machine toward achieving a controllable radial force. An alternative force control technique for MSPM machines is presented. The mathematical model of the machine and the theoretical investigation of the force production principle are provided. A novel force control methodology based on the minimization of the copper losses is described and adopted to calculate the d–q axis current references. The predicted performances of the considered machine are benchmarked against finite-element analysis. The experimental validation of the proposed control strategy is presented, focusing on the suppression of selected vibration frequencies for different rotational speeds

Optimized design of high power density EMI filters for power electronic converters

Nowadays, power density of power converters and related EMI filters is gaining more and more attention. This severely impacts on the design constraints in several application domains. A conventional design of the EMI filter does not guarantee the selection of components/configuration leading to the best power density. For this reason, an optimized design procedure of discrete EMI filters in terms of power density is proposed in this paper. It is based on a previously developed rule-based design procedure, introducing here additional features to obtain a more effective optimization of EMI filter's power density. The proposed approach has been validated in terms of EMI filter's performance and size reduction, by a comparison between an EMI filter designed using the optimized procedure and a conventionally designed one, for two different case studies