Surface spin-glass freezing in interacting core-shell NiO nanoparticles

Magnetization and AC susceptibility measurements have been performed on ～3?nm NiO nanoparticles in powder form. The results indicate that the structure of the particles can be considered as consisting of an antiferromagnetically ordered core, with an uncompensated magnetic moment, and a magnetically disordered surface shell. The core magnetic moments block progressively with decreasing temperature, according to the distribution of their anisotropy energy barriers, as shown by a broad maximum of the low field zero-field-cooled magnetization (M(ZFC)) and in the in-phase component χ' of the AC susceptibility, centred at ～70?K. On the other hand, surface spins thermally fluctuate and freeze in a disordered spin-glass-like state at much lower temperature, as shown by a peak in M(ZFC) (at 17?K, for H = 50?Oe) and in χ'. The temperature of the high temperature χ' peak changes with frequency according to the Arrhenius law; instead, for the low temperature maximum a power law dependence of the relaxation time was found, τ = τ(0)(T(g)/(T(ν)-T(g)))(α), where α = 8, like in spin glasses, τ(0) = 10(-12)?s and T(g) = 15.9?K. The low temperature surface spin freezing is accompanied by a strong enhancement of magnetic anisotropy, as shown by the rapid increase of coercivity and high field susceptibility. Monte Carlo simulations for core/shell antiferromagnetic particles, with an antiferromagnetic core and a disordered shell, reproduce the qualitative behaviour of the temperature dependence of the coercivity. Interparticle interactions lead to a shift to a high temperature of the distribution of the core moment blocking temperature and to a reduction of magnetization dynamics.     

Sculpting nanoelectrodes with a transmission electron beam for electrical and geometrical characterization of nanoparticles

A method to produce metal electrodes with a gap of a few nanometers with a highly focused electron beam in a transmission electron microscope (TEM) is described. With this method the electrical and geometrical characterization of the same particle is possible. The I-V characteristics of a gold particle trapped between such electrodes showed the expected single-electron tunneling behavior, with a Coulomb gap corresponding to the geometry of the particle as observed with high-resolution TEM.     

Simplified AIP‐II Peptidomimetics Are Potent Inhibitors of Staphylococcus aureus AgrC Quorum Sensing Receptors

The bacterial pathogen Staphylococcus aureus controls many aspects of virulence by using the accessory gene regulator (agr) quorum sensing (QS) system. The agr system is activated by a macrocyclic peptide signal known as an autoinducing peptide (AIP). We sought to develop structurally simplified mimetics of AIPs for use as chemical tools to study QS in S. aureus. Herein, we report new peptidomimetic AgrC receptor inhibitors based on a tail‐truncated AIP‐II peptide that have almost analogous inhibitory activities to the parent peptide. Structural comparison of one of these peptidomimetics to the parent peptide and a highly potent, all‐peptide‐derived, S. aureus agr inhibitor (AIP‐III D4A) revealed a conserved hydrophobic motif and overall amphipathic nature. Our results suggest that the AIP scaffold is amenable to structural mimicry and minimization for the development of synthetic agr inhibitors.     

Studies for aluminum photoionization in hot cavity for the selective production of exotic species project

Selective production of exotic species (SPES) is an ISOL-based accelerator facility that will be built in the Legnaro INFN Laboratory (Italy), intended to provide an intense neutron-rich radioactive ion beams obtained by proton induced fission of an uranium carbide target. Beside this main target, a silicon carbide (SiC) target will the first to be used to deliver some p-rich beams. This target will validate also the functionality of the SPES facility with aluminum beam as result of hitting SiC target with protons. In the past off-line studies on laser photoionization of aluminum have performed in Pavia Spectroscopy Laboratory and in Laboratori Nazionali di Legnaro where, recently, a XeCl excimer laser was installed in order to test the laser ionization in the SPES hot cavity. Results are promising to justify further studies with this technique, aiming a better characterization of the SPES ion extraction capability under laser photoionization.     

Off-line ionization tests using the surface and the plasma ion sources of the SPES project

The development of new target ion source systems for the selective production of exotic species (SPES) facility is currently in progress at Legnaro National Laboratories. In this context, the study of ion sources and their performance in terms of ionization efficiency and transversal emittance is a crucial point in order to maximize the available yields, particularly for short-lived isotopes. In this work, preliminary off-line ionization efficiency and emittance measurements for the SPES surface and plasma ion sources are presented. The plasma source emittance measurements are supported by dedicated numerical calculations.     

Impact testing of structural biological materials

Structural biological materials must be highly impact resistant, as appendages such as antlers and horns must sustain repeated, seasonal impact loads. Determining the impact damage progression along with the impact strength is very important for understanding how nature has optimized the structure and properties of biological materials in order to guide the design of superior bio-inspired synthetic materials. A drop weight test tower based on standards for testing fiber-reinforced polymer matrix composites was designed and fabricated to accommodate the small size of biological materials. The materials tested were divided into two groups: non-mineralized and mineralized. The former demonstrated the highest impact strength and showed strong dependence on water content, while the latter were relatively brittle and demonstrated no dependence on water content. Delamination was the most common damage mode observed for all biological materials tested.     

Conversion of isopropanol and mixed alcohols to hydrocarbons using HZSM‐5 Catalyst in the MixAlco™ process

HZSM‐5 (SiO₂/Al₂O₃=280 mol/mol) is used to produce hydrocarbons from reagent‐grade isopropanol and mixed alcohols made from lignocellulosic biomass (waste office paper and chicken manure) using the MixAlco? process. All studies were performed at 101 kPa (abs). The experiments were conducted in two sets: (1) vary temperature (300–T_max°C) at weight hourly space velocity (WHSV)=1.31 h^–1, and (2) vary WHSV (0.5–11.5 h^–1) at T=370°C. For isopropanol, T_max=450°C and for mixed alcohols T_max=520°C. For isopropanol, higher temperatures produced more gaseous products and more aromatics. High WHSV gives high concentration of C6+ olefins, whereas low WHSV gives high concentrations of C9 aromatics. For mixed alcohols, changes in temperature affected the product distribution similar to isopropanol. In contrast, WHSV did not affect the concentration of reaction products; only dehydration products were observed. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2549–2557, 2013     

The Synthesis and Evaluation of Up-scalable Molybdenum Based Ultra Dispersed Catalysts: Effect of Temperature on Particle Size

Unsupported molybdenum (Mo) micro/nanoparticle size range catalysts have been synthesized via precursor salts dissolved within a water-in-oil emulsion and online injected to a decomposition zone simulating processing conditions. The particles were characterized via DLS, reactivity tests and SEM. The effect of decomposition temperature on particle sizes was studied in both a horizontal reactor and vertical reactor configuration.