Passively mode-locked diode-pumped Nd:YVO4 oscillator operating at ultra-low repetition rate

We demonstrate the operation of an ultra low repetition rate, high peak power, picosecond diode pumped Nd:YVO4 passively mode locked laser oscillator. Repetition rates even below 1 MHz were achieved with the use of a new design multiple-pass cavity and a semiconductor saturable absorber. Long term stable operation at 1.2 MHz, pulse duration of 16.3 ps and average output power of 470 mW corresponding to 24 KW peak power pulses is reported. This is, to our knowledge, the lowest repetition rate high peak power pulses ever generated directly from a picosecond laser resonator without cavity dumping

Cluster Control in Oligouranyl Complexes of p-t-Butylcalix[8]arene

Formation of uranyl ion complexes of p-t-butylcalix[8]arene by reaction of the calixarene with [UO2(dmso)5]2+ in the presence of various bases leads to the crystallisation of solids with interestingly different stoichiometry, involving both di- and tri-uranate oligomers bound to the calixarene in anionic species. In all, the calixarene hexa-anion is present in a virtually identical conformation, suggesting that conformational preferences of the ligand must be a major factor controlling the form of the bound oxo-metal complex. Hydrogen bonding to the anions does not appear to be prominent even in the presence of protonated amines and this may explain the formation of some remarkable cation/solvent/simple anion clusters found within the lattices

Deprotonation of large calixarenes-cation binding and conformations

© 2016 CSIRO. Single crystal X-ray studies of p-t-butylcalix[10]arene·2dmso·7H2O (1) and [NMe4][p-t-butylcalix[9]arene-H]·2dmso·H2O (2), provide new data on these large macrocycles and their conformations, that of 2 being the first where an encapsulated [NMe4]+ cation is present, while 1 contains the neutral ligand. Both were obtained as crystalline products of the reactions of the calixarenes with tetramethylammonium hydroxide after prolonged standing. The structure of [NEt4][calix[4]arene-H], in which the cation approaches inclusion in the shallow cone of the anion, is also defined and compared with various other alkylammonium derivatives of calixarenes as well as that of p-t-butylcalix[9]arene

Laboratory Observation of the Buffering Effect of Aragonite Dissolution at the Seafloor

Carbon dioxide entering and acidifying the ocean can be neutralized by the dissolution of calcium carbonate, which is mainly found in two mineral forms. Calcite is the more stable form and is often found in deep-sea sediments, whilst aragonite is more soluble and therefore rarely preserved. Recent research shows aragonite may account for a much larger portion of marine calcium carbonate export to the ocean interior via the biological pump than previously thought, and that aragonite does reach the deep sea and seafloor despite rarely being buried. If aragonite is present and dissolving at the seafloor it will raise local pH and calcium and carbonate concentrations, potentially enough to inhibit calcite dissolution, representing a deep-sea, carbonate version of galvanization. Here, we test this hypothesis by simulating aragonite dissolution at the sediment-water interface in the laboratory and measuring its effects on pH using microsensors. We show that the addition of aragonite to calcite sediment, overlain by seawater undersaturated with respect to both minerals, results in an unchanged alkalinity flux out of the dissolving sediment, suggesting a decrease the net dissolution rate of calcite. In combination with a diagenetic model, we show that aragonite dissolution can suppress calcite dissolution in the top millimeters of the seabed, locally leading to calcite precipitation within 1 day. Future research efforts should quantify this galvanization effect in situ, as this process may represent an important component of the marine carbon cycle, assigning a key role to aragonite producers in controlling ocean alkalinity and preserving climatic archives

Physicochemical behaviour of a dinuclear uranyl complex formed with an octaphosphinoylated para-tert-butylcalix[8]arene. Spectroscopic studies in solution and in the solid state

Spectrophotometric titrations of an octaphosphinoylated para-tert-butylcalix[8]arene (B8bL8) by uranyl nitrate and vice versa in anhydrous ethanol indicate that the species with 2:1 (uranyl:calixarene) stoichiometry is the major complex in solution. Based on these results, a synthesis route was designed to isolate this complex. The latter is an orange, non-hygroscopic polycrystalline powder, with chemical formula [(UO2)2(NO3)4(B8bL8) 2H2O]2(H2O). (Compd. 1), as ascertained by elemental analysis. Spectroscopic characterization of Compd. 1 in the solid and liquid states suggests that a neutral dinuclear uranyl calixarene complex was formed. MIR and FIR spectra indicate that, four phosphinoyl arms of the calixarene and two monodentate nitrates are bound to each 6-coordinate uranyl ion in the complex because no vibrational frequencies from un-coordinated O@P groups or from ionic nitrates are present; in addition the spectra reveal that water molecules form intramolecular hydrogen bonding with monodentate nitrates. The de-convoluted luminescence and XPS spectra obtained in the solid state point to a similar chemical environment around each uranyl ion, as confirmed by the mono-exponential decay of the luminescence. The more rigid conformation acquired by the calixarene in the complex and the non-symmetrical arrangement of the coordinated nitrates result in a particular feature of the emission spectra at 77 K. No evidence of cation-cation interaction was found. A rough approach to the molecular structure of the complex by molecular modelling based on the experimental findings yielded a molecule that was useful for understanding the physicochemical behaviour of Compd. 1.This work was supported by CONACYT [grant Nr. 36689-E], Mexico; and the Swiss National Science Foundation [grant SCOPES 2000–2002: No. 7BUPJ062293.00/1], Switzerland

Giant regular polyhedra from calixarene carboxylates and uranyl

Self-assembly of large multi-component systems is a common strategy for the bottom-up construction of discrete, well-defined, nanoscopic-sized cages. Icosahedral or pseudospherical viral capsids, built up from hundreds of identical proteins, constitute typical examples of the complexity attained by biological self-assembly. Chemical versions of the so-called 5 Platonic regular or 13 Archimedean semi-regular polyhedra are usually assembled combining molecular platforms with metals with commensurate coordination spheres. Here we report novel, self-assembled cages, using the conical-shaped carboxylic acid derivatives of calix[4]arene and calix[5]arene as ligands, and the uranyl cation UO22+ as a metallic counterpart, which coordinates with three carboxylates at the equatorial plane, giving rise to hexagonal bipyramidal architectures. As a result, octahedral and icosahedral anionic metallocages of nanoscopic dimensions are formed with an unusually small number of components

On the visual detection of non-natural records in streamflow time series: challenges and impacts

Large datasets of long-term streamflow measurements are widely used to infer and model hydrological processes. However, streamflow measurements may suffer from what users can consider anomalies, i.e. non-natural records that may be erroneous streamflow values or anthropogenic influences that can lead to misinterpretation of actual hydrological processes. Since identifying anomalies is time consuming for humans, no study has investigated their proportion, temporal distribution, and influence on hydrological indicators over large datasets. This study summarizes the results of a large visual inspection campaign of 674 streamflow time series in France made by 43 evaluators, who were asked to identify anomalies falling under five categories, namely, linear interpolation, drops, noise, point anomalies, and other. We examined the evaluators' individual behaviour in terms of severity and agreement with other evaluators, as well as the temporal distributions of the anomalies and their influence on commonly used hydrological indicators. We found that inter-evaluator agreement was surprisingly low, with an average of 12 % of overlapping periods reported as anomalies. These anomalies were mostly identified as linear interpolation and noise, and they were more frequently reported during the low-flow periods in summer. The impact of cleaning data from the identified anomaly values was higher on low-flow indicators than on high-flow indicators, with change rates lower than 5 % most of the time. We conclude that the identification of anomalies in streamflow time series is highly dependent on the aims and skills of each evaluator, which raises questions about the best practices to adopt for data cleaning.</p

Les villages de l'Alpujarra Alta de Grenade. De l'architecture à son histoire

L'homogénéité des villages de l'Alpujarra Alta, déterminante de leur qualité architecturale, ne provient pas uniquement de l'emploi de matériaux identiques ou de l'utilisation répétée de la toiture-terrasse, mais aussi de la pertinence des différentes adaptations de ces constantes. Il en ressort une grande richesse de solutions architecturales

Les villages de l'Alpujarra Alta de Grenade. De l'architecture à son histoire

L'homogénéité des villages de l'Alpujarra Alta, déterminante de leur qualité architecturale, ne provient pas uniquement de l'emploi de matériaux identiques ou de l'utilisation répétée de la toiture-terrasse, mais aussi de la pertinence des différentes adaptations de ces constantes. Il en ressort une grande richesse de solutions architecturales

Flexible polymer-on-polymer architecture for piezo/pyroelectric energy harvesting

An all polymer piezo/pyroelectric device was fabricated using β phase poly(vinylidene fluoride) (PVDF) as the active material and vapor phase polymerized (VPP) poly(3,4-ethylenedioxythiphene) (PEDOT) as the flexible electrode overlay material. Inherent problems usually associated with coating polymeric electrodes onto the low surface energy PVDF were overcome by air plasma treating the film in conjunction with utilizing the VPP technique to simultaneously synthesize and in situ deposit the PEDOT electrode. Strain measurements up to the breaking-strain of PVDF (approximately 35%) indicated that the change in R/Ro was significantly smaller for the PEDOT based electrodes compared to the platinum electrode. Plasma treatment of the PVDF film increased the level of surface oxygenated carbon species that contributed to increased surface energy, as confirmed by confirmed by contact angle measurement. The enhanced adhesion between the two polymers layers contributed to a significant increase in the measured piezoelectric output voltage from 0.2 to 0.5 V for the same strain conditions. Pyroelectric voltage outputs were obtained by placing the film onto and off of a hotplate, for temperatures up to 50 °C above ambient. Finally, as a proof of concept, a simple energy harvesting device (plastic tube with slots for mounting multiple piezo/pyro films) was fabricated. The device was able to generate a usable level of peak output current (>3.5 μA) from human inhalation and exhalation "waste energy".Pejman Talemi, Marine Delaigue, Peter Murphy, and Manrico Fabrett