200,769 research outputs found
Strategie per la rigenerazione dell'Albergheria
No full textIl saggio esplica l'importanza di azioni di 'partecipazione' attiva per la rigenerazione di un quartiere complesso del centro storico di Palermo, caratterizzato da una forte multiculturalità
Indirectly-supported one-way R/C slabs: Durability and safety issues
No full textSimply-supported one-way R/C slabs are commonly used in the covers of small and medium underground facilities, where durability is the main issue face with rather limited service loads and short spans (2-4 m [6.5-13.0 ft]). The structural performance, however, should not be underrated, as being the slab in a roundabout does not prevent a heavy truck from straying off the right lane! To have fresh information on durability and cracking (working loads), and on the bearing capacity and failure mode (ultimate loads), displacement-controlled tests have been recently performed in Milan on four typical rectangular R/C slabs suspended along their short sides via corbels (dapped ends; size: 1.3×2.2×0.15 m [51×87×6 in.]). A transversely-distributed or concentrated load was applied either at mid-span (in the bending tests), or at 1/10 of the span (in the shear tests). The two slabs Type A are provided with longitudinal bent-up bars in the main body and hooks in the corbels. On the contrary, the slabs type B are reinforced via two continuous layers of longitudinal straight bars. Under the working loads, cracking never occurred, neither in bending nor in shear - to the advantage of durability - while above the working loads rather complex crack patterns formed in the D zones close to the corbels, particularly under the concentrated load, which brought in 3-D effects, with a limited reduction in the bearing capacity. Refining the reinforcement layout is shown - once more - to markedly improve slab performance, with little or no extra cost
Progress in the understanding of drug-receptor interactions, Part 1 : Experimental charge-density study of an angiotensin II receptor antagonist (C30H30N6O3S) at T=17K
No full textAn experimental study of the electron-density distribution rho(r) in an angiotensin II receptor antagonist 1 has been made on the basis of single-crystal X-ray diffraction data collected at a low temperature. The crystal structure of 1 consists of infinite ribbons in which molecules are connected by an N-H center dot center dot center dot N hydrogen bond and several interactions of the CH center dot center dot center dot O, C-H center dot center dot center dot N, and C-H center dot center dot center dot S type. The molecular conformation, characterized by the syn orientation of a tetrazole and a pyrimidinone ring with respect to a phenyl spacer group, is stabilized by two short S center dot center dot center dot O and S center dot center dot center dot N intramolecular contacts between a substituted thiophene fragment and the other two heterocycles of 1. The electrostatic nature of these teractions is documented. Furthermore, the Laplacian of rho(r) in the plane defined by the sulfur, oxygen, and nitrogen atoms involved in these interactions shows their strongly directional character as the regions of charge concentration on the valence shell of the nitrogen and oxygen atoms directly face the regions of charge depletion on the valence shell of the sulfur atom. All the chemical bonds and the relevant intra- and intermolecular interactions of 1 have been quantitatively described by the topological analysis of rho(r). Simple relationships between the bond path lengths (R-b) and the values of rho at the bond critical points (rho(hcp)) have been obtained for the 28 C-C bonds, the seven N-C bonds, and the four O-C bonds. For the first two classes of bonds the relationship is in the form of a straight line, whose parameters, for the C-C bonds, agree, within experimental uncertainty, with those previously derived in our laboratory from a 19 K X-ray diffraction study of crystals of a different compound. Maps of the molecular electrostatic potential phi(r) derived from the experimental charge density display features that are important for the drug-receptor recognition of 1
Application of methods for assessing the geno- and cytotoxicity of Triclosan to C. ehrenbergii
No full textThe toxic effects of Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) on morphology and sexual and asexual reproduction of C. ehrenbergii were examined. In addition, the genotoxic effects of Triclosan were evaluated on the same alga using the microgel electrophoresis test, also-called Comet assay. Increasing Triclosan concentrations in the range 0.125-5 mg L-1 did not affect size and shape of the cells but had relevant effects on both chloroplast morphology and dimension. Triclosan inhibited the vegetative growth of C. ehrenbergii at 0.5 mg L-1. The effects on sexual reproduction indicate that the number of C. ehrenbergii zygospores was significantly reduced by the application of 0.937 mg L-1. The Comet assay showed that Triclosan treatments led to a dose-dependent DNA damage of C. ehrenbergii; 0.25 mg L-1 caused significant genotoxic effects and higher concentrations irreversibly altered the DNA strands. These results suggest that C. ehrenbergii could represent a useful organism to evaluate the whole toxicity of pharmaceuticals and personal care products (PPCPs), giving valuable information for a risk assessmen
Recovering quantum correlations in classical environments without backaction: observation and interpretation
No full textQuantum correlations (entanglement, discord, nonlo-cality) present in a composite quantum system are essential resources for quantum information processing [1, 2]. However, the exploitation of these quantum resources is jeopardized by the detrimental effects of the environment surrounding the quantum system. For instance under Markovian noise, they decay asymptotically or disappear at a finite time [3, 4]. This drawback leads one to look for conditions where quantum correlations can be recovered during the evolution. To this aim non-Markovian noise, arising from strong couplings or structured environments, has been shown to be fundamental because of its memory effects. In fact, in the case of qubits in independent non-Markovian quantum environments, quantum corre- lations exhibit a combination of asymptotic decay with disappearance and revival [2, 5, 6], permitting their partial recovery and thus an extension of their use.
Typically, for composite quantum systems within inde- pendent quantum environments, revivals of quantum cor- relations are interpreted as due to correlation exchanges induced by the back-action of non-Markovian quantum environments on the system (flows of quantum informa- tion back and forth from systems to quantum environments) [8-11]. Recently, it has been shown that revivals of quantum correlations may also occur when the envi- ronment is classical, thus unable to store quantum corre- lations, and forbids system-environment back-action [12- 18]. This fact naturally leads to basic issues on the in- terpretation of back-action-free quantum revivals, in par- ticular about: (i) the role of a classical environment in reviving quantum correlations, for instance if it may act as a control system for what operation is applied to the qubits; (ii) the role of collective effects of the environ- ment on the qubits; (iii) the role of the memory effects; (iv) the role of possible system-environment correlations.
In this presentation, I first make a brief overview of some theoretical results about revivals of entanglement in classical environments. I describe a model of two nonin- teracting qubits, initially entangled, where only one qubit is subject to a random external classical field (a laser with two random phases) with inhomogeneous broadening in its amplitude [18]. I then report the results of an all- optical experiment that simulates this model and allows us to observe and control revivals of quantum correlations without system-environment back-action [18]. Finally, I
discuss about non-Markovianity and provide a possible interpretation showing the role of the classical environ- ment in this phenomenon.
The findings so far reveal that the revivals of quantum correlations are a dynamical feature of composite open systems irrespective of the nature, classical or quantum, of the environment. These results introduce the possibil- ity to recover and control, against decoherence, quantum resources even in absence of back-action, without resort- ing to demanding quantum structured environments or quantum error correction procedures and open the way to further studies concerning quantum correlation dynamics in classical environments.
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G. Falci, Phys. Scr. T153, 014014 (2013).
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pagno, Phys. Rev. A 85, 032318 (2012).
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Explosive spalling in R/C structures exposed to fire: key aspects in experimental testing
No full textExplosive spalling in R/C members exposed to fire consists in the violent expulsion of the hottest layers of concrete, due to the combination of compressive stress and vapour pressure, with the consequent reduction of the bearing cross-section and of the structural fire resistance. Experimental tests aimed at assessing concrete spalling sensitivity can be performed at dif-ferent scales, namely small, intermediate and real scale, with increasing time and cost of testing. The correct level of investi-gation must be defined as the right compromise between efficiency and representativeness of the real case. Starting from the comparison among different test setups at different scales, the main parameters to be considered in planning the experi-mental investigations will be described. On the other hand, with regards to the definition of the mix design, it will be shown how the use of different types of fibre can bring remarkable benefits against spalling
Source function applied to experimental densities reveals subtle electron delocalization effects and appraises their transferability properties in crystals
No full textThe Source Function (SF) [1] enables the electron density (ED) to be seen at a point as determined by source contributions from the atoms of a system, and it is therefore well linked to the chemist’s awareness that any local property and chemical behaviour is to some degree influenced by all the remaining parts of a system [1-3]. The key feature of the SF is that its evaluation requires only knowledge of the ED of a system, enabling a comparison of ab initio and X-ray diffraction derived ED properties on a common, rigorous basis. We here apply the SF descriptor to X-ray derived EDs as a mean to reveal electron-delocalization effects (EDEs) in crystals. Use of the SF to detect them has been firmly assessed for isolated molecules and for theoretically-derived EDs [2,4-5], but extending to crystals and experimental EDs, although being reported at two conferences [6-7] and in two papers discussing heteroaromaticity in a benzothiazol-substituted phosphane [8] or antiaromaticity in cyclopentadienone derivatives [9] needs to be fully demonstrated. Still unanswered questions are whether the EDs from X-ray data may be accurate enough to reveal the subtle features caused by electron pairing and whether these are not only detectable, but also reproducible and transferable, whenever appropriate. To provide an answer we analyse the experimental SF patterns in benzene (BZ), naphthalene (NT) and (+/-)-8’-benzhydrylideneamino-1,1’-binaphtyl-2-ol (BAB) molecular crystals. We find that the SF tool recovers the characteristic SF% patterns caused by pi-electron conjugation in the first two paradigmatic aromatic molecules in almost perfect quantitative accord with those from ab initio periodic calculations [10]. Moreover, the effect of chemical substitution on the transferability of such patterns to the BZ- and NT-like moieties of BAB is neatly spotted by the observed systematic deviations, relative to BZ and NT, of only those SF contributions from the substituted C atoms [10]. The capability of the SF to reveal EDEs by using a promolecule ED (PED), rather than the “true” ED, is then tested; the PED seems unable to reproduce the SF trends anticipated by the increase of electron delocalization [10].
The SF has wider applications than those related to the nature of chemical bonds in more or less conventional situations [2-3]. Detection of EDEs is one such new direction, another being the extension of the SF machinery to retrieve the atomic sources of the spin ED [5,11].
Acknowledgements
Prof. Sine Larsen and Prof. Mark Spackman are both warmly thanked for providing us with, respectively, the 135 K X-ray diffraction dataset of naphthalene crystal and the 110 K X-ray diffraction data set of benzene. The Danish National Research Foundation is also thanked for partial funding of this work through the Center for Materials Crystallography (DNRF93).
References
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[6] Gatti, C., Saleh, G., Lo Presti, L. et al. (2012). In: Abstracts (page 42) of the Sagamore meeting XVII on Charge Spin and Momentum Densities, Daini Meisui Tei, Sapporo, Hokkaido, Japan, 15-20 July.
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Competing C═O···C═O, C–H···O, Cl···O, and Cl···Cl Interactions Governing the Structural Phase Transition of 2,6-Dichloro-p-benzoquinone at Tc=122.6 K
No full text2,6-Dichloro-p-benzoquinone (DCBQ) has been investigated by single-crystal X-ray diffraction experiments in the T range of 300−21 K and quantum-mechanical simulations. A reversible monoclinic (high-T) to triclinic
(low-T) phase transition has been detected at Tc = 122.6(5) K. The various
noncovalent interactions (NCIs) that determine the solid-state self recognition of DCBQ have been characterized as a function of T through
the quantum theory of atoms in molecules. On lowering T, carbonyl−carbonyl interactions progressively strengthen, inducing a change in the crystal structure, while the dipolar C−Cl···O=C NCIs and the relatively strong Cl···Cl halogen bonds (XBs) and CH···O hydrogen bonds play an essential, but ancillary, role. Dispersive forces cooperate with other closed-shell dipolar NCIs, and particularly with XBs, in determining their overall attractive character, even when bulky and positively charged chlorine atoms are drawn closer and closer at low temperatures. The intermolecular interaction energies have been evaluated above and below Tc as sums of electrostatic, repulsion, and dispersion contributions
Single N–C Bond Becomes Shorter than a Formally Double N═C Bond in a Thiazete-1,1-dioxide Crystal: An Experimental and Theoretical Study of Strong Crystal Field Effects
No full text3-Diethylamino-4-(4-methoxyphenyl)-1,1-dioxo-4H-1λ6,2-thiazete-4-carbonitrile (DTC) is a synthetic compound that exhibits a significant similarity with β-sultamic drugs. Its core chemical moiety is an uncommon four-membered thiazete-1,1-dioxide heterocycle. Former crystallographic investigations carried out at room temperature on different DTC polymorphs and a chemically related compound showed a very unusual structural feature: within the conjugated −N–C═N–SO2– system, the formally single N–C bond is, on average, 0.018 Å shorter than the formally double N═C bond. In this work, the charge density distribution of DTC has been explored by both single-crystal X-ray diffraction at T = 100(2) K and quantum mechanical simulations, with the aim of gaining insights into the subtle interplay between structure, electron delocalization, and crystal field polarization effects. To this end, both local and nonlocal topological descriptors provided by the Quantum Theory of Atoms in Molecules have been employed. Topological and structural changes of crystalline and in vacuo DTC have been related to the smaller or larger importance of resonance forms in the −N–C═N–SO2– moiety. A rationale for the mentioned C–N/C═N bond length inversion is found in terms of the large DTC dipole moment enhancement occurring in the crystal, which stabilizes highly polar resonant forms that exploit more favorable electrostatic interactions with neighboring molecules. In turn, this causes a significant electronic rearrangement within the molecule that results in an unusual and counterintuitive bond length alternation pattern. Possible implications from the viewpoint of the accurate in silico modeling of crystal structures are discussed
Primi studi sulla biologia e sul controllo di Cydia funebrana (Treitschke) in susineti biologici siciliani
No full textFirst studies on biology and control of Cydia funebrana (treitschke) in Sicilian organic plum orchards.
Cydia funebrana (Treitschke), considered the key pest in the Sicilian plum orchards. Few studies were carried out in
Sicily concerning C. funebrana life cycle, forecasting models and the effectiveness of some products permitted in organic
plum orchards.
In 2010 researches were carried out in three Sicilian plum orchards, two in Palermo Province (Monreale and San
Giuseppe Jato) and one in Agrigento Province (Castrofilippo), in order to monitor the population, to evaluate damage levels
caused by the plum moth and to estimate how many generations it could complete by Charmillot’s forecasting model.
In addition, in San Giuseppe Jato, the effectiveness of mineral oil and Spinosad, products permitted in organic farming,
was evaluated on three different plum cultivars, Angeleno, Friar and Stanley.
Field data showed that the plum moth completes at least three yearly generations. Moreover, clear differences have been
found among the cultivars compared in San Giuseppe Jato orchard, Angeleno being the most susceptible to the moth attack.
Local plum cultivars in Monreale were more susceptible to plum moth attack than all the other ones.
Charmillot's model about generation numbers by temperature records, provided an overestimate of the C. funebrana
generations.
The only orchard in which the infestation level was very low was that in Castrofilippo.
Field trials did not show adequate efficacy of tested products to reduce C. funebrana damages
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