Inter-annual variability in atmospheric input and partitioning of heavy metals in the Lagoon of Venice

Atmospheric bulk deposition of major and trace elements was measured at Venice from November 1995 to October 1997. Collection was carried out using polyethylene bulk passive samplers, samples being collected bi-weekly. In order to highlight the contribution of the atmosphere to water chemistry and particle budgets in the Lagoon of Venice, the geochemical composition (Si, Al, Ca, Mg, K, Na, Mn, Cr, Zn, Pb, Cd, Cu, As) of dissolved and insoluble bulk fractions was determined by AAS + ICP mass spectrometry. Great sample variability was found, with almost two orders of magnitude between maximum and minimum values for several metals. All fluxes in 1995/96 were 30% lower than in 1996/97, ranging from -3% (Ca) to -57% (Li), except for Zn, Cd and As. On the contrary, the solubility of all elements decreased during 1996/97. Partitioning between soluble and insoluble phases shows that Al, Cr, Fe and Si are mainly in the insoluble form, whereas for As, Ca, Cu, Mg, Na, Ni, K, Pb and Zn the dissolved fraction represents 50-90% of total input. The amount of particle load affects partitioning between dissolved and particulate, especially for Al and Pb. Seasonal variability was evident. The lowest pH values (approximately 5.2) were recorded in winter, causing an increase of solubility for all metals except for As, which showed the highest solubility in summer.     

B-MWW Zeolite: The Case Against Single-Site Catalysis

Boron-containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron-containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B₂(OH)_xO_(3−x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM-22 isomorphously substituted with boron (B-MWW). Using ¹¹B solid-state NMR spectroscopy, we show that the majority of boron species in B-MWW exist as isolated BO₃ units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B-MWW for ODH of propane falsifies the hypothesis that site-isolated BO₃ units are the active site in boron-based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium-based catalysts and provides an important piece of the mechanistic puzzle.     

B‐MWW Zeolite: The Case Against Single‐Site Catalysis

Boron‐containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron‐containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B₂(OH)_xO_(3?x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM‐22 isomorphously substituted with boron (B‐MWW). Using ¹¹B solid‐state NMR spectroscopy, we show that the majority of boron species in B‐MWW exist as isolated BO₃ units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B‐MWW for ODH of propane falsifies the hypothesis that site‐isolated BO₃ units are the active site in boron‐based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium‐based catalysts and provides an important piece of the mechanistic puzzle.     

Approximate Entropy of Brain Network in the Study of Hemispheric Differences

Human brain, a dynamic complex system, can be studied with different approaches, including linear and nonlinear ones. One of the nonlinear approaches widely used in electroencephalographic (EEG) analyses is the entropy, the measurement of disorder in a system. The present study investigates brain networks applying approximate entropy (ApEn) measure for assessing the hemispheric EEG differences; reproducibility and stability of ApEn data across separate recording sessions were evaluated. Twenty healthy adult volunteers were submitted to eyes-closed resting EEG recordings, for 80 recordings. Significant differences in the occipital region, with higher values of entropy in the left hemisphere than in the right one, show that the hemispheres become active with different intensities according to the performed function. Besides, the present methodology proved to be reproducible and stable, when carried out on relatively brief EEG epochs but also at a 1-week distance in a group of 36 subjects. Nonlinear approaches represent an interesting probe to study the dynamics of brain networks. ApEn technique might provide more insight into the pathophysiological processes underlying age-related brain disconnection as well as for monitoring the impact of pharmacological and rehabilitation treatments.     

Fate of the resonating valence bond in graphene

We apply a variational wave function capable of describing qualitatively and quantitatively the so-called "resonating valence bond" (RVB) in realistic materials, by improving standard ab initio calculations by means of quantum Monte Carlo methods. In this framework we clearly identify the Kekulé and Dewar contributions to the chemical bond of the benzene molecule and establish the corresponding RVB energy of these structures (?0.01 eV/atom). We apply this method to unveil the nature of the chemical bond in undoped graphene, providing an estimate of the RVB energy gain, and show that this picture remains only within a small "resonance length" of a few atomic units.     

Optimal lower exponent for the higher gradient integrability of solutions to two-phase elliptic equations in two dimensions

We study the higher gradient integrability of distributional solutions u to the equation \({{\mathrm{div}}}(\sigma \nabla u) = 0\) in dimension two, in the case when the essential range of \(\sigma \) consists of only two elliptic matrices, i.e., \(\sigma \in \{\sigma _1, \sigma _2\}\) a.e. in \(\Omega \). In Nesi et al. (Ann Inst H Poincaré Anal Non Linéaire 31(3):615–638, 2014), for every pair of elliptic matrices \(\sigma _1\) and \(\sigma _2\), exponents \(p_{\sigma _1,\sigma _2}\in (2,+\infty )\) and \(q_{\sigma _1,\sigma _2}\in (1,2)\) have been found so that if \(u\in W^{1,q_{\sigma _1,\sigma _2}}(\Omega )\) is solution to the elliptic equation then \(\nabla u\in L^{p_{\sigma _1,\sigma _2}}_{\mathrm{weak}}(\Omega )\) and the optimality of the upper exponent \(p_{\sigma _1,\sigma _2}\) has been proved. In this paper we complement the above result by proving the optimality of the lower exponent \(q_{\sigma _1,\sigma _2}\). Precisely, we show that for every arbitrarily small \(\delta \), one can find a particular microgeometry, i.e., an arrangement of the sets \(\sigma ^{-1}(\sigma _1)\) and \(\sigma ^{-1}(\sigma _2)\), for which there exists a solution u to the corresponding elliptic equation such that \(\nabla u \in L^{q_{\sigma _1,\sigma _2}-\delta }\), but \(\nabla u \notin L^{q_{\sigma _1,\sigma _2}}\). The existence of such optimal microgeometries is achieved by convex integration methods, adapting to the present setting the geometric constructions provided in Astala et al. (Ann Scuola Norm Sup Pisa Cl Sci 5(7):1–50, 2008) for the isotropic case.     

First results on diffraction dissociation of neutrons at the ISR

Neutron diffraction dissociation has been measured at the ISR in proton-neutron interactions at 37 GeV c.m. energy. The data were taken with the Split Field Magnet detector, during a short deuteron storage test run with colliding p-d beams. Differential mass and momentum transfer distributions are reported; the value of the total cross-section shows a weak s-dependence when compared to lower energy data.     

Objective bayesian analysis of the Yule–Simon distribution with applications

The Yule–Simon distribution is usually employed in the analysis of frequency data. As the Bayesian literature, so far, has ignored this distribution, here we show the derivation of two objective priors for the parameter of the Yule–Simon distribution. In particular, we discuss the Jeffreys prior and a loss-based prior, which has recently appeared in the literature. We illustrate the performance of the derived priors through a simulation study and the analysis of real datasets.     

Decomposition and reconstruction of multidimensional signals by radial functions with tension parameters

The aim of the paper is to construct a multiresolution analysis of L²(IR^d) based on generalized kernels which are fundamental solutions of differential operators of the form \(\boldsymbol {\prod }_{\ell =?1}^{m}(-{\Delta }+\kappa _{\ell }^{2}\,I)\). We study its properties and provide a set of pre-wavelets associated with it, as well as the filters which are indispensable to perform decomposition and reconstruction of a given signal, being very useful in applied problems thanks to the presence of the tension parameters κ_?.