Sulla determinazione polarografica delle impurezze metalliche nello zinco iperpuro

Résumé (W) On précise les conditions expérimentales les plus favorables pour l'exécution d'analyses polarographiques de zine extrêmement pur, en vue d'endéceler les impuretés, soit les éléments Cu, Bi, Pb, Cd, Tl et Fe. La méthode, très sensible, permet le dosage de ces divers métaux quand la concentration, dans le zinc, est de 0,0001% pour Pb, Bi et Tl, et de 0,00005% pour Cd, Cu et Fe.

---

Zusammenfassung Es wurden die günstigsten experimentellen Bedingungen für die polarographische Bestimmung der in äußerst reinem Zink als Verunreinigungen vorkommenden Elemente Cu, Bi, Pb, Cd, Tl und Fe ermittelt.Das sehr empfindliche Verfahren gestattet die Bestimmung dieser Metalle, selbst wenn die betreffenden Konzentrationen im Zink bloß 0,0001% Pb, Bi oder Tl und 0,00005% Cd, Cu oder Fe betragen.

---

Riassuno Vengono precisate le condizioni sperimentali più favorevoli per l'esecuzione dell'analisi polarografica dello zinco iperpuro per la determinazione delle impurezze di Cu, Bi, Pb, Cd, Tl, Fe.Il metodo, molto sensibile, permette il dosaggio dei varii metalli anche quando la concentrazione nello zinco è di 0,0001% per Pb, Bi, Tl e di 0,00005% per Cd, Cu, Fe.

---

---

A 3 figure     

Sediment metal contamination in a creek flowing from a pristine to an industrial area of Trieste Province (Italy)

The following metals: Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined by inductively coupled plasma - atomic emission spectroscopy (ICP-AES) in fluvial sediments of Rosandra Creek, using two different, strong and mild sediment decomposition methods. The purpose was to obtain information about the contamination by metals and distribution paths of pollutants in the area crossed by Rosandra Creek: this little river is the unique epigeous watercourse in the Italian Karst and very few data can be found in literature. In this area, we can find a natural park, but also agricultural activities and an industrial district that was recently defined as "polluted site of national interest". By comparing the results of the strong and mild extraction we have obtained the percentage of extraction and enrichment factors for each metal in the different sediments of the sites R2 and R3 exposed to pollution, while the site R1 was considered as a pristine one because situated in the natural park. The computed enrichment factors are generally not very high, but copper, lead and zinc have factors that require attention. The principal component analysis (PCA) shows that the typically anthropogenic metals (as Cr, Pb, Cu and Zn) constitute the first factor, while the lithogenic metals, as Fe and Ni, constitute the second one; moreover the score plots permit to classify and distinguish the 3 sites: site R3, possibly the more exposed to contamination, has high scores both for anthropogenic and lithogenic metals.     

Sulphur speciation of PM10 samples by XANES spectroscopy

Sulphur K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to identify sulphur compounds in PM10 samples collected simultaneously at two sites with different environmental situations in the province of Trieste (NE of Italy), during summer and winter seasons respectively. The first site is an industrial site located near a steel mill plant and the second is a coastal site. The sulphur speciation at the industrial site has shown the presence of the following sulphur compounds in both seasons: organic compounds (thiophenes or Polycyclic Aromatic Sulphur Heterocycles — PAHs) and sulphates while in the winter season sulphites were also present. In the coastal site organic compounds (thiophenes or PASHs) and sulphate were found during winter season, moreover bisulphates were found during summer season. Relative percentages of the different sulphur compounds have shown that sulphate is the most abundant form of sulphur in the industrial site samples during both seasons and in the coastal site sample collected during the winter season (> 98%); in the coastal site sample collected during the summer season the relative percentages of bisulphate and sulphate were around 40% and 60% respectively.      

Diastereoselective and enantioselective photoredox pinacol coupling promoted by titanium complexes with a red-absorbing organic dye

The pinacol coupling reaction, a reductive coupling of carbonyl compounds that proceeds through the formation of ketyl radicals in the presence of an electron donor, affords the corresponding 1,2-diols in one single step. The photoredox version of this transformation has been accomplished using different organic dyes or photoactive metal complexes in the presence of sacrificial donors such as tertiary amines or Hantzsch''s ester. Normally, the homo-coupling of such reactive ketyl radicals is neither diastereo- nor enantio-selective. Herein, we report a highly diastereoselective pinacol coupling reaction of aromatic aldehydes promoted by 5 mol% of the non-toxic, inexpensive and available Cp₂TiCl₂ complex. The key feature that allows the complete control of diastereoselectivity is the employment of a red-absorbing organic dye in the presence of a redox-active titanium complex. Taking advantage of the well-tailored photoredox potential of this organic dye, the selective reduction of Ti(iv) to Ti(iii) is achieved. These conditions enable the formation of the d,l (syn) diastereoisomer as the favored product of the pinacol coupling (d.r. > 20 : 1 in most of the cases). Moreover, employing a simply prepared chiral SalenTi complex, the new photoredox reaction gave a complete diastereoselection for the d,l diastereoisomer, and high enantiocontrol (up to 92% of enantiomeric excess).

A metallaphotoredox, diastereoselective and enantioselective pinacol coupling reaction promoted by titanium complexes with the use of a red-absorbing organic dye was developed.     

Solutions to the 2D Euler equations with velocity unbounded at infinity

We prove existence of solutions to the two-dimensional Euler equations with vorticity bounded and with velocity locally bounded but growing at infinity at a rate slower than a power of the logarithmic function. We place no integrability conditions on the initial vorticity. This result improves upon a result of Serfati which gives existence of a solution to the two-dimensional Euler equations with bounded velocity and vorticity.     

Vanishing viscosity in the plane for vorticity in borderline spaces of Besov type

The existence and uniqueness of solutions to the Euler equations for initial vorticity in BΓ∩Lp₀∩Lp₁ was proved by Misha Vishik, where BΓ is a borderline Besov space parameterized by the function Γ and 1<p₀<2<p₁. Vishik established short time existence and uniqueness when Γ(n)=O(logn) and global existence and uniqueness when . For initial vorticity in BΓ∩L², we establish the vanishing viscosity limit in L²(R²) of solutions of the Navier-Stokes equations to a solution of the Euler equations in the plane, convergence being uniform over short time when Γ(n)=O(logn) and uniform over any finite time when Γ(n)=O(logκn), 0?κ<1, and we give a bound on the rate of convergence. This allows us to extend the class of initial vorticities for which both global existence and uniqueness of solutions to the Euler equations can be established to include BΓ∩L² when Γ(n)=O(logκn) for 0<κ<1.