171,768 research outputs found
Recent results on rare charm decays at LHCb
No full textRare decays of charmed hadrons are a powerful tool to search New Physics in the up-quark sector, complementary to searches in the strange and bottom hadron systems. In particular, anomalies in the transitions, highly suppressed in the Standard Model, can be investigated in the decays with leptons of opposite charge in the final state. Given the high forward charm-anticharm production crosssection, LHCb is the ideal experiment for this type of studies. Two recent results on the semileptonic decays of the meson and the baryon are presented
Release of lead from Pb-clinoptilolite: managing the fate of an exhausted exchanger
No full textThe selectivity of clinoptilolite toward Pb2+ has stimulated many studies aimed to evaluate the metal uptake. Conversely, the management of a Pb-bearing clinoptilolite has not received the same attention, although it can release a harmful metal. This work aims to evaluate the possibility to control, through thermal treatments, the release of lead from a Pb-clinoptilolite, prepared to simulate the condition of highest dangerousness of an exhausted exchanger. A zeolite-rich rock from Sardinia (Italy) has been processed, obtaining a powder with almost 90 % (wt.) of clinoptilolite. This material has been initially Na- and then Pb-exchanged, reaching a Pb2+ content of 2.28 meq/g. The lead release has been tested before and after 2-h heating at eight different temperatures from 200 to 900 °C. The unheated material releases 64 % of the lead. Heating weakly affects lead release up to 400 °C (54 %), but higher temperatures determine an abrupt reduction from 44 % at 500 °C to 1 % at 700 °C, when the zeolite breakdown occurs. At 800 °C the nucleation of Pb-feldspar and silica polymorphs begins. Basically, the material heated at 900 °C does not release lead (0.03 %), because the metal is trapped in the lead feldspar, whose content attains 42 % (wt.). This solid-state transformation does not involve the emission of lead vapors, another significant environmental aspect
Solid-state transformations of Zn-clinoptilolite through heating
No full textZn-clinoptilolite was heated and analyzed ex-situ. Breakdown occurred between 400-700 °C. After 2 h at 850 °C gahnite and Zn-β-quartz nucleated. Exolution of zinc and aluminum from Zn-β-quartz determined Zn-α-quartz formation after 8 h. An increase in temperature and/or heating time determined exolution also in Zn-α-quartz, that progressively turned into cristobalite. Zn-β-quartz decreased over time at 1000 °C and disappeared after 100
h, whereas at 900 °C the quantitative ratio β-quartz/α-quartz asymptotically stabilized at ≈2.5. Rietveld refinements evidenced that at 900 °C the decrease of zinc occupancy followed an almost asymptotic path in both quartz phases. Considering the formula ZnxAl2xSi3-2xO6, if x < 0.173 ± 0.008 Zn-β-quartz is not stable at room temperature. Treatments of 2 h at 1100 and 1200 °C produced the same quantities of gahnite (≈20.6%) and glass (≈11.6%), and slight differences for cristobalite (56 vs. 63%) and quartz (8.4 vs. 1.5%). Basically, gahnite incorporated all Zn2+ contained in clinoptilolite
Assessing the risks to Mediterranean islands ecosystems from non-native plant introductions
No full textThe islands of the Mediterranean Basin probably represent some of the ecosystems globally most at
risk from invasive species. Compared to neighbouring mainland areas, island floras have a significantly
higher proportion of alien plant species. Yet the circumstances that have led to this situation
and the subsequent consequences of plant invasions remain poorly understood. This knowledge
deficit is addressed in this paper through a comprehensive review of recent research findings. Most
alien plants occurring on Mediterranean islands have been introduced intentionally for economic
purposes although there still exists a sizeable proportion that arrives by accident. A wide range of
alien plant functional types have colonized Mediterranean islands. While certain traits appear
important, e.g. reproductive strategies, species characteristics are closely allied to the habitats invaded.
Large-scale biogeographic studies have highlighted a strong correlation between local and
regional abundance suggesting a common driver of both small and large-scale invasion. Species
with non-European origins appeared more successful at both spatial scales. These findings highlight
the importance of estimating invasion success across a wide region thus minimizing local idiosyncrasies.
Since the importance of different biological attributes may change along the dispersal, colonization
and establishment phases of invasion, analyses of what makes a species invasive should
also focus on specific invasion stages. For example, reproductive traits may be expected to be more
relevant for long-distance colonization, while vegetative traits would prevail in achieving local dominance.
Detailed mapping of species distribution highlighted that all habitats are to some extent at
risk, though human disturbed areas proportionally more so. Impacts were examined for three focal
species Ailanthus altissima, Carpobrotus spp. and Oxalis pes-caprae. Correlative analysis on six
islands highlighted that impacts on biodiversity and soil properties are a function of both species
and island with Ailanthus in general having the least impact while Carpobrotus reduced native plant
diversity significantly. Although impossible to extrapolate to all invasive species, these results do
highlight that significant losses in local species richness as well as ecosystem structure and function is likely to be occurring in the Mediterranean. To address this threat, mechanisms should be put
in place to limit the further spread of known problem species across the Mediterranean through
awareness-raising activities and better regulation of the import and disposal of alien plant material
On the possibility to modify the CsAlSi5O12/CsAlSi2O6 ratio during thethermal transformation of Cs-clinoptilolite
No full textClinoptilolite is a natural zeolite employed in Cs+ removal, and its cesium form transforms, by heating, into a matrix composed mainly by CsAlSi5O12 (CAS) with smaller quantities of glass and CsAlSi2O6 (pollucite). Both crystalline compounds were proposed as host for 137Cs, albeit pollucite is considered superior. This work shows how, by mixing Cs-clinoptilolite and amorphous hydrated aluminum hydroxide (L), it is possible to modify the solid-state transformation of the zeolite and favor the crystallization of pollucite over CAS. Cs-clinoptilolite, L and several mixtures of the two materials were preliminary subjected to thermal and XRD analyses. Muffle treatments of 32 h at 1200 °C and 8 h at 1300 °C, followed by Q-XRD analyses, were performed on some materials. Unlike CAS, pollucite always crystallized. The greater the quantity of L in the mixture, the lower the ratio between the quantities of CAS and pollucite formed. In the range 1200–1300 °C, the CAS/pollucite ratio decreases with temperature. Al2O3-polymorphs (mainly corundum) and glass were ubiquitous in the fired mixtures, whereas mullite was not. By varying the content of L in the mixture, the distribution of cesium among the Cs-bearing phases varied, and for some compositions most of the cesium was trapped inside pollucite
Thermal transformation of Cs-clinoptilolite to CsAlSi5O12
No full textIn this study we have investigated the protocol to produce CsAlSi5O12 (CAS), a potential host for radioactive cesium, starting from clinoptilolite, a natural zeolite employed in cesium decontamination. A clinoptilolite-rich rock sampled in Sardinia (Italy) has been subjected to a beneficiation process, to obtain a powder with a higher zeolite content. The enriched material (90 wt.% clinoptilolite) has been previously Na-, then Cs-exchanged. Both forms have been analyzed by ICP-AES and ICP-MS. Thermal treatments of 2 hours between 800 and 1250°C have been performed on different aliquots of the Cs-exchanged material. Samples heated at T≥1150°C are composed basically only by CAS, as determined by XRD analyses, and their high crystallinity has been also confirmed by SEM observations. Ideally, the nucleation of CAS follows the reaction Cs6Al6Si30O72•nH2O → nH2O↑ + 6CsAlSi5O12. DTA analyses indicate that the transformation has occurred at 1145°C. TG analyses, coupled with XRD data, lead to exclude a cesium volatilization during the synthesis of CAS
Ag- and Zn-clinoptilolite: a comparison of their in-vitro antibacterial activity against Helicobacter pylori
No full textHelicobacter pylori is a bacterium recognized as the most frequent cause of chronic gastritis and is classified as carcinogen by the World Health Organization. For the eradication of H. pylori, the use of silver and zinc was studied due to their antibacterial properties. The use of clinoptilolite was also considered, since ammonium is essential for the survival of the bacterium in the stomach and clinoptilolite is acid resistant and selective toward NH4+. This research compared the antibacterial activity against H. pylori of Ag- and Zn-clinoptilolite through in-vitro tests, aiming to exploit the zeolite simultaneously as a metal supplier and as an ammonium sequestrant. A powder containing approximately 90% of clinoptilolite was used to prepare, by cation exchange, two materials based on Zn-clinoptilolite (FA-Zn) and Ag-clinoptilolite (FA-Ag), containing 2.12 meq/g of Zn2+ and 2.28 meq/g of Ag+, respectively. In the agar cup test, both materials evinced a direct and linear relationship between their concentration and the width of the inhibition zones, but FA-Ag allowed the onset of the development of an inhibition halo already at a concentration of 12.5 mg/mL, whereas FA-Zn required 25 mg/mL to get the same result. The Minimum Inhibitory Concentration of FA-Ag resulted eight time lower than that of FA-Zn (0.5 and 4.0 mg/mL, respectively). Tests showed superior antimicrobial activity of FA-Ag, but it should be considered that Ag-clinoptilolite has some disadvantages compared to Zn-clinoptilolite, such as higher toxicity, higher cost, and instability to light
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