CuO nanoparticles and microaggregates: an experimental and computational study of structure and electronic properties

The link between morphology and properties is well-established in the nanoparticle literature. In this report, we show that different approaches in the synthesis of copper oxide can lead to nanoparticles (NPs) of different size and morphology. The structure and properties of the synthesized NPs are investigated with powder X-ray diffraction, scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS). Through detailed SEM analyses, we were able to correlate the synthetic pathways with the particles’ shape and aggregation, pointing out that bare hydrothermal pathways yield mainly spheroidal dandelion-like aggregates, whereas, if surfactants are added, the growth of the nanostructures along a preferential direction is promoted. The effect of the morphology on the electronic properties was evaluated through DRS, which allowed us to obtain the electron bandgap in every system synthesized, and to find that the rearrangement of threaded particles into more compact structures leads to a reduction in the energy difference. The latter result was compared with Density Functional Theory (DFT) computational models of small centrosymmetric CuO clusters, cut from the tenorite crystal structure. The computed UV-Vis absorption spectra obtained from the clusters are in good agreement with experimental findings

Inter-block Filtering and Downsampling in DCT Domain

The extensive use of discrete cosine transform (DCT) techniques in image coding suggests the investigation on filtering and downsampling methods directly acting on the DCT domain. As DCT image transforms usually operate on blocks, it is useful that the DCT filtering techniques preserve the block dimension. In this context the present paper first revises the intra-block filtering techniques to enlighten the limitations implied by small block dimensions. To overcome the artefacts introduced by this method and to satisfy the filtering design constraints which are usually defined in the Fourier domain, inter-block techniques are developed starting from the implementation of FIR filtering. Inter-block schemes do not exhibit any limitation but their computational cost has to be taken into account. In addition, hybrid techniques, using variable length FIR filters after the discard of low order DCT coefficients, are introduced to increase the computational efficiency; in this case, the introduced aliasing has to be kept at tolerable values. The amount of the tolerable aliasing strictly depends on the subsequent operations applied to the filtered and downsampled image. The numerical examples reported could form a basis for error estimation and evaluation of trade-off between performance and computational complexity. © 1994

Three-dimensional-DCT pipe coding

The paper reports on a video sequence coding method taking advantage of the generic video- communication layout: some moving objects on a still background. The algorithm operates on groups of frames in which the whole digital video sequence is divided, that implies the synchronization requirements' satisfaction and an acceptable level of compatibility with standard video coding (H.261, MPEG, etc.). An analysis of the spatial-temporal continuum, represented by each group of frames, is performed, in order to detect a tridimensional segmentation that identifies the moving objects by means of spatial regions. These regions can spread, as a sort of `pipes,' through the whole group of frames in the temporal direction. Various pipes' construction and coding strategies, including techniques based on object recognition and coding, are allowed. In this work a pipes' identification method based on fixed size moving blocks and their coding by means of a 3D-DCT transform is reported. The above method allows adjacent starting pipes to part themselves, leaving uncoded stripes at their boundaries. The proposed method does not imply the stripes coding, while it minimizes their number and the amount of the artifacts generated by their presentation. As a final topic, the paper reports some considerations on the coding efficiency related to the quality of the reconstructed sequences and on the compatibility characteristics

Spinel Iron Oxide by the Co-Precipitation Method: Effect of the Reaction Atmosphere

Synthesis atmosphere (i.e., air and nitrogen) effects on the physical properties and formation mechanism of spinel iron oxide nanoparticles prepared via the co-precipitation method have been investigated using a multi-technique approach. The obtained magnetic nanoparticles (MNPs) were characterized using the X-ray diffraction, transmission electron microscopy (TEM), SQUID magnetometry, M\uf6ssbauer spectroscopy and X-ray absorption near-edge Structure spectroscopy techniques. The synthesis procedure leads to the formation of a spinel structure with an average crys-tallite size of 9.0(9) nm. The morphology of the particles synthetized under an inert atmosphere was quasi-spherical, while the nanoparticles prepared in air present a faceted shape. The small differences observed in morphological properties are explained by the influence of the reaction atmosphere on the formation mechanism of the MNPs. The magnetic characterization indicates that both samples exhibit superparamagnetic behavior at 300 K. The investigation by means of the Langevin approach at 300 K also leads to equal values for the mean size of the magnetic cores (Dm). Additionally, the analysis of the M\uf6ssbauer spectra revealed the lack of spin disorder for both samples, resulting in a high saturation magnetization. The fit of XANES spectrum suggests that about 2/3 of the iron ions reside in a local environment close to that of \u3b3-Fe2O3 and about 1/3 close to that of Fe3O4 for the sample synthetized in inert atmosphere

Co-doped MnFe2O4 nanoparticles: magnetic anisotropy and interparticle interactions

The effect of cobalt doping on the magnetic properties of Mn1−xCoxFe2O4 nanoparticles was investigated. All samples consist of ensembles of nanoparticles with a spherical shape and average diameter of about 10 nm, showing small structural changes due to the substitution. Besides having the same morpho-structural properties, the effect of the chemical composition, i.e., the amount of Co doping, produces marked differences on the magnetic properties, especially on the magnetic anisotropy, with evident large changes in the coercive field. Moreover, Co substitution has a profound effect on the interparticle interactions, too. A dipolar-based interaction regime is detected for all samples; in addition, the intensity of the interactions shows a possible relation with the single particle anisotropy. Finally, the sample with the strongest interaction regime shows a superspin glass state confirmed by memory effect dynamics

Morpho-Structural and Magnetic Properties of CoFe₂O₄/SiO₂ Nanocomposites: The Effect of the Molecular Coating

The use of magnetic nanoarchitecture in several applications is often limited by the lack of noninteracting particles, due to the frequent presence of clusters and aggregates of particles. Here, we report an investigation of the interparticle interactions by changing the molecular coating on ∼5 nm CoFe2O4 nanoparticles embedded in a silica structure. The magnetic investigation at a low temperature allows revealing the key role of organic ligands in tuning the morpho-structural properties of hybrid materials. Cobalt ferrite-coated nanoparticles were prepared by the polyol method using triethylene glycol as a co-reagent (CFOT) and by the exchange ligand process using dihydroxyhydrocinnamic acid (CFOH). Then, magnetic mesoporous silica nanocomposites have been prepared starting from CFOT (CFOTS) and CFOH (CFOHS). For the CFOTS sample, the interparticle distance did not change after coating, whereas the CFOHS sample showed an increase in the interparticle distance by 23%. This value has been obtained by investigating interparticle interactions by remanence techniques, which represent a good approach to determine the approximated values of interparticle distances in complex systems. The measurements showed that the silica coating produces a reduction of 47% in the dipolar interaction strength for the CFOHS sample, whereas no significant change was observed for the CFOTS sample. The differences in magnetic response upon varying the molecular coating of nanoparticles are due to the different interactions of the molecular ligands with silica, resulting in a change of interparticle distances and then magnetic interactions

A multi-scale approach to the recent activity of the Stradella thrust in the seismotectonic context of the Emilia Arc (northwestern Italy)

The frontal thrusts and folds of the northern Apennines - Italy - are mainly covered under the alluvial deposits of the Po Plain. Some of these structures show geological evidence of Late Quaternary activity, thus posing the need for an accurate seismic hazard assessment due to widespread housing settlements, industries, lifeline infrastructures, and large towns. We present new morphostructural, geophysical, and seismological data to discuss the recent activity of the Broni-Sarmato fault, an 18 km-long outcropping section of the north-verging Stradella thrust, located 50 km south of Milan, along the Pede-Apennine thrust front (PTF) in the rear of the Emilia Arc thrust system. The new geoelectrical surveys across the fault scarp show deformation of the shallow deposits. The outcropping deformations, with a fault scarp ranging up to 25.8 m, are investigated within the seismotectonic framework of the PTF and the Emilia Arc. The analysis of the associated seismicity and new focal mechanisms highlight two seismogenic contractional volumes dipping at low-angle southwest-ward, at upper (<12 km) and lower crustal depths (~20–30 km). The shallow seismicity partially illuminates the Stradella thrust and its along-strike southeastward prosecution along the extent of the Stradella-Salsomaggiore Arc. Subordinately, it also illuminates some of the Emilia Arc thrust planes. The deeper seismogenic volume shows large patches of the basal thrust of the Emilia Arc fault system. We interpret the above multi-scale data as evidence of ongoing tectonic activity of the outer fronts of the Emilia Arc under a regional NNE-oriented compressional stress field, with some evidence of thrust involvement along the Pede-Apennine front. In our 3D fault-model reconstruction, all the analyzed thrust structures appear as expressions of a thick-skinned deformation that controls earthquake release at different structural levels

Composite Peptide-Agarose Hydrogels for Robust and High-Sensitivity 3D Immunoassays

Canonical immunoassays rely on highly sensitive and specific capturing of circulating biomarkers by interacting biomolecular baits. In this frame, bioprobe immobilization in spatially discrete three-dimensional (3D) spots onto analytical surfaces by hydrogel encapsulation was shown to provide relevant advantages over conventional two-dimensional (2D) platforms. Yet, the broad application of 3D systems is still hampered by hurdles in matching their straightforward fabrication with optimal functional properties. Herein, we report on a composite hydrogel obtained by combining a self-assembling peptide (namely, Q3 peptide) with low-temperature gelling agarose that is proved to have simple and robust application in the fabrication of microdroplet arrays, overcoming hurdles and limitations commonly associated with 3D hydrogel assays. We demonstrate the real-case scenario feasibility of our 3D system in the profiling of Covid-19 patients' serum IgG immunoreactivity, which showed remarkably improved signal-to-noise ratio over canonical assays in the 2D format and exquisite specificity. Overall, the new two-component hydrogel widens the perspectives of hydrogel-based arrays and represents a step forward towards their routine use in analytical practices