Penetration of solar radiation into the waters of Messina Strait (Italy)

The optical properties of the waters of five different stations, three located in the Messina Strait and two near the Strait (open sea), were analysed. Direct spectral measurements of the downward solar irradiance (290 - 800 nm) at different depths (0.5 m, 7 m, 10 m, 13 m, 20 m) were made using a cosine sensor connected to a spectroradiometer. Water samples were collected in the surface layer and their absorption spectra were analysed. The natural fluorescence profiles, along the water column, were determined using a fluorometer (SBE 911plus - Sea Teach). The spectral attenuation coefficient (K(lambda)), the variation of K(lambda) in different wavelength ranges (deltaK(deltalambda)), the wavelength corresponding to minimum value of K(lambda), the spectral depths of penetration of both 1% and 10% of the sub-surface irradiance values (P(lambda)), the depths of 1% of penetration of UVB, UVA and PAR, the depth ranges of the maxim concentration of Chl a and superficial CDOM were measured at each station. The maximum solar UVB penetration was about 65% of the photic zone and the maximum UVA penetration was nearly 100% (data of the Ionic sea station). Thus, a large part of the photic zone was exposed to UV radiation sufficient to cause a possible reduction in the photosynthetic activity of phytoplankton. The spectral penetration of solar radiation, especially UVB radiation, was significantly different in the three stations of the Strait with respect to the two stations studied in the open sea. This shows that variations in the spectral attenuation along the water column can be used as an indicator of properties of the water body.     

What anions do inside a receptor's cavity: a trifurcate anion receptor providing both electrostatic and hydrogen-bonding interactions

The trifurcate receptor 1(3+) forms stable 1:1 complexes with halide and oxo anions in MeCN solution, as shown by spectrophotometric and 1H NMR experiments, and selectively recognizes chloride (lg K(ass) > 7) in the presence of fluoride and bromide. The high stability reflects the receptor's ability to donate up to six hydrogen bonds (from three pyrrole N-H and three C-H fragments, polarized by the proximate positive charge) to the included anion. Addition of an excess of more basic anions (F- and CH3COO-) induces stepwise deprotonation of the N-H groups, an event signalled by the appearance of a bright yellow color. Crystal and molecular structures are reported for the complex with NO3(-) and a capsule consisting of two interconnected trifurcate subunits, one of which includes an H-bound Br- ion, while the other is doubly deprotonated and includes an H-bound water molecule. Finally, evidence is given for the formation in solution of an authentic complex of OH-, in which H-bound hydroxide is included within the cavity of 1(3+).     

Evidence of correlation in spin excitations of few-electron quantum dots

We report inelastic light scattering measurements of spin and charge excitations in nanofabricated AlGaAs/GaAs quantum dots with few electrons. A narrow spin excitation peak is observed and assigned to the intershell triplet-to-singlet monopole mode of dots with four electrons. Configuration-interaction theory provides precise quantitative interpretations that uncover large correlation effects that are comparable to exchange Coulomb interactions.     

Ab initio valence bond calculations. X. Vertical valence ionization potentials of allene and butatriene

The ground and vertical valence ionized states of allene and butatriene have been studied in the ab initio valence bond framework using the 6–31G basis set after contraction and introducing the core–valence shell separation. The final wave functions have been analyzed in terms of VB structures by means of population analysis.     

A theoretical study of electrophilic aromatic substitution

To study the electrophilic reactant in the nitration reaction,ab initio molecular orbital calculations of the nitronium ion and its protonated derivative, as well as of the corresponding isoelectronic CO₂ and CO₂H⁺ systems, have been performed, with special reference to the stiffness of NO ₂ ⁺ and CO₂ to a bending of the \(\widehat{OXO}\) angle. According to these calculations, the nitronium ion and carbon dioxide have comparable bending constants.     

Phytochemical and pharmacological properties of essential oils from Cedrus species

Natural products frequently exert pharmacological activities. The present review gives an overview of the ethnobotany, phytochemistry and pharmacology of the Cedrus genus, e.g. cytotoxic, spasmolytic immunomodulatory, antiallergic, anti-inflammatory and analgesic activities. Cancer patients frequently seek remedies from traditional medicinal plants that are believed to exert less side effects than conventional therapy with synthetic drugs. A long-lasting goal of anti-cancer and anti-microbial therapy research is to find compounds with reduced side effects compared to currently approved drugs. In this respect, Cedrus species might be of interest. The essential oil isolated from Cedrus libani leaves may bear potential for drug development due to its high concentrations of germacrene D and β-caryophyllene. The essential oils from Cedrus species also show bioactivity against bacteria and viruses. More preclinical analyses (e.g. in vivo experiments) as well as clinical trials are required to evaluate the potential of essential oils from Cedrus species for drug development.     

Simultaneous determination of specific heat,thermal conductivity and thermal diffusivity at low temperature via the photopyroelectric technique

The photopyroelectric effect has been used to measure simultaneously specific heat (c), thermal conductivity (k) and thermal diffusivity () at low temperatures. A calibration procedure which allows the use of a pyroelectric transducer at low temperatures is described. Simultaneous measurements of c, k, and over a high T _c superconducting phase transition are reported.     

Singularity of the density of states for one-dimensional chains with random couplings

We prove that the density of states for the tight-binding model with off-diagonal disorder under general conditions diverges forR0 at least as . This result is established through the study of the recurrence properties of an associated Markov chain.Partial financial support by GNAFA (CNR)Partial financial support by CNPq, grant n.303795-77FA