Chemical and structural characterization of fibrous richterite with high environmental and health relevance from Libby, Montana (USA)

This study reports new structural and spectroscopic data of a sample of fibrous richterite from Libby, Montana (USA). The OH-stretching region was investigated by FT-IR. The spectrum showed, except for the typical absorption band at 3671 cm-1 assigned to the vibration of the O-H dipole bonded to three [6]Mg cations, a well developed band at 3658 cm-1 attributed to the M(1)+M(3)Fe2+ environment. The M(1)+M(3)Fe2+ occupancy calculated using the FT-IR data is in very good agreement with that obtained combining Mössbauer and EMP data. Fe3+ was only assigned at M(2) owing to the absence in FT-IR spectrum of absorption bands at Δ=-50 cm-1 from the tremolite reference band. Structural investigation was done by X-ray powder-diffraction using the Rietveld method. Cell parameters, fractional coordinates for all non-hydrogen atoms, and site scattering for M(1), M(2), M(3), M(4) and A were refined. The most relevant difference with respect to prismatic winchite is a general reduction of the cell parameters that is ascribed mainly to the higher fluorine content of fibrous richterite. Possible site occupancies were obtained by combining chemical data and Rietveld refinement results

A nonexistence result for sign-changing solutions of the Brezis-Nirenberg problem in low dimensions

We consider the Brezis-Nirenberg problem: \begin{equation*} \begin{cases} -\Delta u = \lambda u + |u|^{2^* -2}u & \hbox{in}\ \Omega\\ u=0 & \hbox{on}\ \partial \Omega, \end{cases} \end{equation*} where $\Omega$ is a smooth bounded domain in $\mathbb{R}^N$, $N\geq 3$, $2^{*}=\frac{2N}{N-2}$ is the critical Sobolev exponent and $\lambda>0$ a positive parameter. The main result of the paper shows that if $N=4,5,6$ and $\lambda$ is close to zero there are no sign-changing solutions of the form $$u_\lambda=PU_{\delta_1,\xi}-PU_{\delta_2,\xi}+w_\lambda,$$ where $PU_{\delta_i}$ is the projection on $H_0^1(\Omega)$ of the regular positive solution of the critical problem in $\mathbb{R}^N$, centered at a point $\xi \in \Omega$ and $w_\lambda$ is a remainder term. Some additional results on norm estimates of $w_\lambda$ and about the concentrations speeds of tower of bubbles in higher dimensions are also presented.Comment: 21 page

Neurovisual training (TRIGRAM) in young patients with visual-perceptive dyslexia

Dyslexia is a language-based learning disability. Although this condition is characterized by anatomical malformation of the brain, it seems that the typical reading pattern of dyslexic may be also related to more complex sensory deficits. Among them, visual- perceptive deficits have been described in a subtype of dyslexia, called visual-perceptive dyslexia. The distinctive feature of a patient suffering from visual-perceptive dyslexia form is marked by effortlessly recognize the characteristics of each individual stimulus. The Tetra protocol is a visual-perceptual evaluation protocol that was introduced for the diagnostic phase and the rehabilitation of visual-perceptive dyslexia. The diagnostic tests include: the eidomorphometry test, designed to evaluate the perception of spatial relationships; the contrast sensitivity threshold test, especially at low spatial frequencies; and the REPORT TEST words, to assess the speed and the reading efficiency. In addition, the rehabilitation phase is carried out with the visual neuro-enhancement program TRIGRAM, a visual training proposal designed to reduce the lateral masking phenomenon in visual-perceptive dyslexic. Thus, in this study we used the diagnostic tests of TETRA® Protocol to determine presence of visual-perceptual abnormalities in children with dyslexia. Proven time the presence of these visual-perceptual alterations, the patients were also subjected to the rehabilitation sessions of TRIGRAM, in order to investigate whether this visual training may improve the pattern of reading. At the end of the program (t1) and after three months (t2), the same subjects underwent the same diagnostic tests of TETRA® Protocol to evaluate and confirm the results obtained during rehabilitation program. The results showed a significant increase in contrast sensitivity at low and high spatial frequencies. Moreover, the same improvements in the visual system's ability to discriminate the contours of an object within the field of view, have been maintained three months after the end of treatment. We also observed a significant improvement in the perception of spatial relationships, with reduction of SRA value. In conclusion, this study demonstrates that the visual rehabilitation training (TRIGRAM) is able to improve the perception of spatial relationships, and increase contrast sensitivity in young patients affected by "visual dyslexia". Nonetheless, these data need to be confirmed in larger cohort of subjects in order to establish whether these effects can also increase lexical ability (increased reading speed and reduce errors during the lexical task)

Surface reactivity of amphibole asbestos. A comparison between crocidolite and tremolite

Among asbestos minerals, fibrous riebeckite (crocidolite) and tremolite share the amphibole structure but largely differ in terms of their iron content and oxidation state. In asbestos toxicology, iron-generated free radicals are largely held as one of the causes of asbestos malignant effect. With the aim of clarifying i) the relationship between Fe occurrence and asbestos surface reactivity, and ii) how free-radical generation is modulated by surface modifications of the minerals, UICC crocidolite and fibrous tremolite from Maryland were leached from 1 day to 1 month in an oxidative medium buffered at pH 7.4 to induce redox alterations and surface rearrangements that may occur in body fluids. Structural and chemical modifications and free radical generation were monitored by HR-TEM/EDS and spin trapping/EPR spectroscopy, respectively. Free radical yield resulted to be dependent on few specific Fe2+ and Fe3+ surface sites rather than total Fe content. The evolution of reactivity with time highlighted that low-coordinated Fe ions primarily contribute to the overall reactivity of the fibre. Current findings contribute to explain the causes of the severe asbestosinduced oxidative stress at molecular level also for iron-poor amphiboles, and demonstrate that asbestos have a sustained surface radical activity even when highly altered by oxidative leaching

Existence of nonradial domains for overdetermined and isoperimetric problems in nonconvex cones

In this work we address the question of the existence of nonradial domains inside a nonconvex cone for which a mixed boundary overdetermined problem admits a solution. Our approach is variational, and consists in proving the existence of nonradial minimizers, under a volume constraint, of the associated torsional energy functional. In particular we give a condition on the domain $D$ on the sphere spanning the cone which ensures that the spherical sector is not a minimizer. Similar results are obtained for the relative isoperimetric problem in nonconvex cones

The mechanism of iron binding processes in erionite fibres

Fibrous erionite-Na from Rome (Oregon, USA) was K-exchanged and characterized from the structural point of view. In addition, the modifications experienced after contact with a Fe(II) source were investigated for evaluating if the large potassium ions, blocking off nearly all the erionite cavity openings, might prevent the Fe(II) binding process, which is currently assumed to be one of the reasons of the toxicity of erionite. The K-exchanged sample had a 95% reduction of the BET surface area indicating that it behaves as a mesoporous material. Exchanged K is segregated at K2 and at OW sites commonly occupied by H2O. The latter K cations provide a relevant contribution to the reduction of the surface area. Surprisingly, despite the collapse of its surface area the sample preserves the tendency to bind Fe(II). Therefore, yet in the case of a peculiar and potentially hostile structural environment the Fe(II) ion-exchange process has essentially the same kinetics observed in a typical erionite sample. This is a clear evidence of the very limited effect of the chemical composition of erionite on the Fe(II) binding process and reasonably it does not play a significant role in its toxicity

Energy stability for a class of semilinear elliptic problems

In this paper, we consider semilinear elliptic problems in a bounded domain $\Omega$ contained in a given unbounded Lipschitz domain $\mathcal C \subset \mathbb R^N$. Our aim is to study how the energy of a solution behaves with respect to volume-preserving variations of the domain $\Omega$ inside $\mathcal C$. Once a rigorous variational approach to this question is set, we focus on the cases when $\mathcal C$ is a cone or a cylinder and we consider spherical sectors and radial solutions or bounded cylinders and special one-dimensional solutions, respectively. In these cases, we show both stability and instability results, which have connections with related overdetermined problems

Prismatic to asbestiform offretite from Northern Italy. Occurrence, morphology and crystal-chemistry of a new potentially hazardous zeolite

A multi-methodological approach, based upon field investigation, morphological characterization, chemical analysis and structure refinement was applied to different samples of fibrous offretite, a new potentially hazardous zeolite recently discovered in northern Italy. Their morphology ranges from stocky-prismatic to asbestiform. All the investigated fibers may be considered as "inhalable", and they are well within the range of the "more carcinogenic fibers" regarding diameter. As regards the length, the main mode observed in the asbestiform samples is 20-25 mu m, and similar to 93% of the measured fibers are >5 mu m and may be significantly associated with carcinogenesis also in terms of lengths. The chemical-structural features of the investigated fibers are comparable: the extra-framework cations K+, Mg2+ and Ca2+ are present in all samples in similar proportions, and refined cell parameters are similar among the samples. Offretite occurs in 60% of the investigated sites, with an estimated amount up to 75 vol % of the associated minerals. The presence of this mineral could be of concern for risk to human health, especially if one considers the vast number of quarries and mining-related activities that are operating in the zeolite host rocks

Energy stability for a class of semilinear elliptic problems

In this paper, we consider semilinear elliptic problems in a bounded domain $\Omega$ contained in a given unbounded Lipschitz domain $\mathcal C \subset \mathbb R^N$. Our aim is to study how the energy of a solution behaves with respect to volume-preserving variations of the domain $\Omega$ inside $\mathcal C$. Once a rigorous variational approach to this question is set, we focus on the cases when $\mathcal C$ is a cone or a cylinder and we consider spherical sectors and radial solutions or bounded cylinders and special one-dimensional solutions, respectively. In these cases, we show both stability and instability results, which have connections with related overdetermined problems.Comment: 33 page