Grain size characterization of modern and ancient dunes within a dune field along the Pisan coast (Tuscany, Italy)

In this paper, grain size analysis on a large number of samples from a dune field within the Migliarino – San Rossore – Massaciuccoli Regional Park has been carried out in order to define the textural characterization of modern and ancient dune ridges. More than 200 samples along five transects have been collected from the backshore, the active dunes and the steady dunes up to the last recognizable dune ridge. The samples have been dry-sieved and the obtained data have been processed electronically to achieve textural parameters such as mean diameter and sorting. The results showed similar trends of the transects throughout the entire dune field. In particular, the grain size tends to decrease towards the most ancient dune ridges, showing a significant drop at the transition between active and inactive areas. The drastic decrease might be related to a possible variation of River Arno sediment discharge occurred after the XVIII century

Litho-sedimentological and morphodynamic characterization of the Pisa Province coastal area (northern Tuscany, Italy)

In this paper litho-sedimentological and morphodynamic maps of the coastal sector belonging to the Pisa Province are presented as an example of how increasing the accessibility to data on lithology, sedimentology, and morphodynamics may lead to a better approach to coastal management. The database used to build the maps includes an original rendering of remote sensing data (aerial imagery) and new field data (geologic survey), as well as data retrieved from the scientific literature (grain-size and past coastline positions). The maps show that the geometry of beach ridges is an indication of the evolution of the Arno River delta in the last 3000 years, highlighting the relationships between geological aspects and morphodynamic features. The maps represent the synthesis of different data available in the database, and they may be a useful support to coastal management as they are more easily understandable and straightforward than the database from which are created

Tuning of the characteristics of Au nanoparticles produced by solid target laser ablation into water by changing the irradiation parameters.

We report the production of Au nanoparticles with different average sizes and size distributions, by laser ablation of a solid Au target into pure deionized water. Tuning laser parameters such as pulse duration, energy, and wavelength is possible to tune the size and the size distributions of the produced nanoparticles into the liquid. We demonstrate the possibility of production of highly monodispersed colloidal solutions, in which the average nanoparticle size ranges from 3 to 10 nm, using laser pulses of ns duration. Laser ablation using fs laser pulses can also produce very small nanoparticles, although a small population of bigger nanoparticles is always present. Low and high-resolution transmission electron microscopy (TEM), in combination with UV-Vis spectroscopy have been employed for the characterization of our samples

Impressive abrasion rates of marked pebbles on a coarse-clastic beach within a 13-month timespan

In this paper the abrasion rate on a coarse-clastic beach was evaluated by calculating the volume loss recorded on indigenous pebbles within a 13-month timespan. The experiment was carried out at Marina di Pisa (Italy) on an artificial beach that was built to counteract the erosion processes affecting this sector of the coast. A total of 240 marble pebbles (120 rounded and 120 angular) were marked using the RFID technology and injected on the beach. The volume loss measured after consecutive recovery campaigns was progressively increasing, reaching the maximum value after 13 months (61% overall). The average volume loss is consistent between rounded and angular pebbles at any time (59.3% and 64.2% after 13 months respectively), meaning that the roundness is not a primary control factor on abrasion rate. The pebbles that did not reach such abrasion rates after 8 and 10 months (volume loss less than 20%) were found at heights equal or greater than 2 m above mean sea level, on the crest of the storm berm that formed during the strongest storms. This implies that the highest wearing is achieved in the lower portion of the backshore, which is also the area that underwent major topographic modifications. Here, sea water action might also exert chemical influence on the pebbles, adding to the mechanical abrasion. The main result of this research, indicating an impressive volume loss on beach pebbles in a short timespan, could be of key importance for coastal managers. The optimization of coarse sediment beach nourishments is also relevant, taking into right consideration that the volume loss due to sediment abrasion might exceed 50% of the original fill volume just after 1 year in the most dynamic portion of the beach

Formation and microscopic investigation of iron oxide aligned nanowires into polymeric nanocomposite films

We present a microscopic investigation of nanocomposite films of iron oxide (g-Fe2O3) magnetic nanowires (NWs) aligned into polymers, formed upon evaporation of solutions of acrylate polymer/magnetic nanoparticles under magnetic field (MF). The field causes the assembly of the g-Fe2O3 nanoparticles along the direction of the MF lines, resulting in magnetic NWs embedded throughout the entire volume of the polymer film. The scanning electron microscopy and the trans- mission electron microscopy studies show that the cylindrical-shaped NWs have � 15-lm average length and are isotropically distributed throughout the film. The study with the MF microscopy tech- nique not only proves that the composed NWs are magnetic but also makes possible the magnetic study of each individual NW in a nondestructive way. In this way it becomes possible for the localized study of the magnetic properties alteration after the binding of various molecules onto individual NWs, opening up the way of using these films in sensor devices applied in various fields ranging from biology to environmental purposes. Microsc. Res. Tech. 73:952-958, 2010. V C 2010 Wiley-Liss, Inc

Nanochains Formation of Superparamagnetic Nanoparticles

We present simulations on the aggregation of nanometer sized polydispersed superparamagnetic particles under the application of an external magnetic field. We make use of a Monte Carlo method, using a cluster-moving approach, as previously used in literature for ferrofluids. van der Waals attraction and magnetic anisotropy are taken into account in the simulations. Chains elongated in the field direction are formed. The results are in good agreement with recent experimental results on nanochains made of iron oxide nanoparticles into polymer matrix, obtained with the application of a magnetic field during film deposition. The magnetization anisotropy of the nanocomposite film under dc magnetic field can be predicted within this simple model

A holographic biprism as a perfect energy filter?

a b s t r a c t It has often been stated that a holographic biprism represents a near perfect energy filter and only elastically scattered electrons can participate in the interference fringes. This is based on the assumption that the reference wave does not contain inelastically scattered electrons. In this letter we show that this is not exactly true because of the delocalised inelastic interaction of the reference wave with the sample. We experimentally and theoretically show that inelastic scattering plays a role in the fringe formation, but it is shown that this contribution is small and can usually be neglected in practice

Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals

Cu2-xTe nanocubes were used as starting seeds to access metal telluride nanocrystals by cation exchanges at room temperature. The coordination number of the entering cations was found to play an important role in dictating the reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e. with coordination number 4), such as Cd2+ or Hg2+, yielded monocrystalline CdTe or HgTe nanocrystals with Cu2-xTe/CdTe or Cu2-xTe/HgTe Janus-like heterostructures as intermediates. The formation of Janus-like architectures was attributed to the high diffusion rate of the relatively small tetrahedrally coordinated cations, which could rapidly diffuse in the Cu2-xTe NCs and nucleate the CdTe (or HgTe) phase in a preferred region of the host structure. Also, with both Cd2+ and Hg2+ ions the exchange led to wurtzite CdTe and HgTe phases rather than the more stable zinc-blende ones, indicating that the anion framework of the starting Cu2- xTe particles could be more easily deformed to match the anion framework of the metastable wurtzite structures. As hexagonal HgTe had never been reported to date, this represents another case of metastable new phases that can only be accessed by cation exchange. On the other hand, the exchanges involving octahedrally coordinated ions (i.e. with coordination number 6), such as Pb2+ or Sn2+, yielded rock-salt polycrystalline PbTe or SnTe nanocrystals with Cu2-xTe@PbTe or Cu2-xTe@SnTe core@shell architectures at the early stages of the exchange process. In this case, the octahedrally coordinated ions are probably too large to diffuse easily through the Cu2-xTe structure: their limited diffusion rate restricts their initial reaction to the surface of the nanocrystals, where cation exchange is initiated unselectively, leading to core@shell architectures.Comment: 11 pages, 7 figures in J. Am. Chem. Soc, 13 May 201

An Analytical Approach for the Design of Class-E Resonant DC-DC Converters

We present a new approach to design resonant dc-dc converters, that allows us to achieve both a more accurate implementation and a simpler architecture, by reducing the number of required passive components. The approach is applied to a class-E topology, and it is based on the analytic solution of the system of differential equations regulating the converter evolution. Our technique is also capable of taking into account the most important circuit nonidealities. This represents an important breakthrough with respect to the state of the art, where class-E circuit analysis is based on strong simplifying assumptions, and the final circuit design is achieved by means of numerical simulations after many time-consuming parametric sweeps. The developed methodology is dimensionless, and the achieved design curves can be denormalized to easily get the desired circuit design. Measurements on two different prototypes confirm an extremely high adherence to the developed mathematical approach.We present a new approach to design resonant dc-dc converters, that allows us to achieve both a more accurate implementation and a simpler architecture, by reducing the number of required passive components. The approach is applied to a class-E topology, and it is based on the analytic solution of the system of differential equations regulating the converter evolution. Our technique is also capable of taking into account the most important circuit nonidealities. This represents an important breakthrough with respect to the state of the art, where class-E circuit analysis is based on strong simplifying assumptions, and the final circuit design is achieved by means of numerical simulations after many time-consuming parametric sweeps. The developed methodology is dimensionless, and the achieved design curves can be denormalized to easily get the desired circuit design. Measurements on two different prototypes confirm an extremely high adherence to the developed mathematical approach