Nascita ed evoluzione del linguaggio chimico

Il linguaggio chimico \ue8 nato e si \ue8 sviluppato come linguaggio simbolico, in paral-lelo con quello esteso. Il primitivo simbolismo chimico si basava su significati magici e criptici, per poi evolvere fino ad assumere il valore di linguaggio compatto, molto simile a quello algebrico. Sebbene convenzionale, il linguaggio chimico pu\uf2 essere considerato naturale, perch\ue9, nei suoi termini e nei suoi simboli, esso cerca di dar conto della natura e delle propriet\ue0 degli oggetti. Per questo, la storia della sua origine e del suo sviluppo pu\uf2 essere presa a modello dello sviluppo degli altri linguaggi delle scienze naturali

Progettazione efficiente di Biocompositi Rinforzati con fibre di Agave

La crescente sensibilit\ue0 nei riguardi dell'inquinamento ambientale e le nuove disposizioni legislative in materia di protezione dell'ambiente, hanno portato negli ultimi anni ad una crescente attenzione verso i cosiddetti biocompositi, cio\ue8 verso materiali compositi ecocompatibili e/o rinnovabili, ottenuti da biopolimeri rinforzati da fibre naturali come lino, kenaf, agave ecc. Il presente lavoro intende dare un contributo alla comprensione del comportamento meccanico ed alla efficiente progettazione di performanti biocompositi, ottenuti attraverso una oculata scelta di matrici termoindurenti e termoplastiche, rinforzate con fibre di agave. Dopo avere indagato sulle peculiari propriet\ue0 delle fibre di agave, attraverso prove di trazione e prove di pull-out su singola fibra, nonch\ue9 sulle effettive propriet\ue0 delle matrici selezionate, si propongono modelli teorici e di micromeccanica che descrivono correttamente il comportamento meccanico di tali biocompositi. Verifiche sperimentali, eseguite su biocompositi a fibre corte e lunghe hanno consentito di correlare le propriet\ue0 meccaniche ai particolari meccanismi di danneggiamento, confermando la bont\ue0 dei modelli teorici proposti

Multidisciplinary learning at the University scientific museums: the Bunsen burner

Nell'articolo riportiamo un'attività di laboratorio svolta insieme a studenti di scuole superiori, al fine di aumentare l’interesse dei giovani studenti verso gli strumenti scientifici di interesse storico e stimolare il loro approccio agli studi scientifici. Viene proposta un'attività "hands on" che può essere facilmente condotta presso i musei scientifici universitari. Un gruppo di studenti selezionati ha frequentato, sotto la guida di ricercatori universitari, uno Stage estivo di una settimana organizzato presso la Collezione Storica degli Strumenti di Fisica e il Museo di Chimica dell'Università di Palermo. È stato proposto lo studio del becco Bunsen, di come funziona e come viene usato nei laboratori di chimica. In particolare, sono stati presi in considerazione alcuni esemplari appartenenti alle collezioni, che saranno illustrati nell'articolo. Alla fine dello Stage, gli studenti hanno descritto ai visitatori gli strumenti e illustrato le attività svolte.We report on a laboratory activity carried out together with secondary school (high-school) students, with the aim of increasing their interest toward historical scientific instruments and stimulate their approach to scientific knowledge. To this purpose, we propose a hands-on activity that can be fruitfully performed at the University scientific museums. We organized a one-week summer stage at the Historical Collection of Physics Instruments and at the Museum of Chemistry of the University of Palermo. A group of selected students attended it, under the tutoring of university researchers. They were showed some Bunsen burners belonging to the collections, how they are restored, how they work and how they were used in the chemical laboratories. At the end of the stage, students introduced museum visitors to these instruments, describing them and referring about the activities they had carried out

The Silver Voltameter: An Essential Instrument for the Definition of the Unit of Electric Current

We discuss the restoration of a silver voltameter belonging lo the Historical Collection of Physics Instruments of the University of Palermo. We stress the essential role this instrument had in the definition of the unit of electric current

Trypanosoma cruzi mitochondrial maxicircles display species- and strain-specific variation and a conserved element in the non-coding region

BACKGROUND: The mitochondrial DNA of kinetoplastid flagellates is distinctive in the eukaryotic world due to its massive size, complex form and large sequence content. Comprised of catenated maxicircles that contain rRNA and protein-coding genes and thousands of heterogeneous minicircles encoding small guide RNAs, the kinetoplast network has evolved along with an extreme form of mRNA processing in the form of uridine insertion and deletion RNA editing. Many maxicircle-encoded mRNAs cannot be translated without this post-transcriptional sequence modification. RESULTS: We present the complete sequence and annotation of the Trypanosoma cruzi maxicircles for the CL Brener and Esmeraldo strains. Gene order is syntenic with Trypanosoma brucei and Leishmania tarentolae maxicircles. The non-coding components have strain-specific repetitive regions and a variable region that is unique for each strain with the exception of a conserved sequence element that may serve as an origin of replication, but shows no sequence identity with L. tarentolae or T. brucei. Alternative assemblies of the variable region demonstrate intra-strain heterogeneity of the maxicircle population. The extent of mRNA editing required for particular genes approximates that seen in T. brucei. Extensively edited genes were more divergent among the genera than non-edited and rRNA genes. Esmeraldo contains a unique 236-bp deletion that removes the 5'-ends of ND4 and CR4 and the intergenic region. Esmeraldo shows additional insertions and deletions outside of areas edited in other species in ND5, MURF1, and MURF2, while CL Brener has a distinct insertion in MURF2. CONCLUSION: The CL Brener and Esmeraldo maxicircles represent two of three previously defined maxicircle clades and promise utility as taxonomic markers. Restoration of the disrupted reading frames might be accomplished by strain-specific RNA editing. Elements in the non-coding region may be important for replication, transcription, and anchoring of the maxicircle within the kinetoplast network

Multiple agency perspective, family control, and private information abuse in an emerging economy

Using a comprehensive sample of listed companies in Hong Kong this paper investigates how family control affects private information abuses and firm performance in emerging economies. We combine research on stock market microstructure with more recent studies of multiple agency perspectives and argue that family ownership and control over the board increases the risk of private information abuse. This, in turn, has a negative impact on stock market performance. Family control is associated with an incentive to distort information disclosure to minority shareholders and obtain private benefits of control. However, the multiple agency roles of controlling families may have different governance properties in terms of investors’ perceptions of private information abuse. These findings contribute to our understanding of the conflicting evidence on the governance role of family control within a multiple agency perspectiv

Who is the Ultimate Master of Contractual, Regulatory, Discretionary and Residual Cash Flows? An Answer from the Standpoint of Corporate Governance

This paper sets forth a framework of analysis that links contractual, discretionary, regulatory and residual cash flows with decision rights over them. To attain this purpose, firstly we introduce the standard incremental cash flow model, underlying its main limitations. Secondly, we move on bringing to light cash flows to senior management and directors, as well as the so-often neglected investment portfolio. Next, we settle down to what we are going to call the compact cash flow model that comprises five building blocks, namely those arising out of assets, those addressed to owners, creditors, managers and directors, and lastly the company's investment portfolio. Afterwards, contractual, discretionary, regulatory and residual cash flows are enlarged upon. Last of all, we focus on decision rights over every constituent of each building block. This issue carries weight in Corporate Governance since stakeholders who claim or exercise decision rights, also could trespass on the rules of the game, becoming better off to the expense and damage of other stakeholders

Local Charge Excesses in Metallic Alloys: a Local Field Coherent Potential Approximation Theory

Electronic structure calculations performed on very large supercells have shown that the local charge excesses in metallic alloys are related through simple linear relations to the local electrostatic field resulting from distribution of charges in the whole crystal. By including local external fields in the single site Coherent Potential Approximation theory, we develop a novel theoretical scheme in which the local charge excesses for random alloys can be obtained as the responses to local external fields. Our model maintains all the computational advantages of a single site theory but allows for full charge relaxation at the impurity sites. Through applications to CuPd and CuZn alloys, we find that, as a general rule, non linear charge rearrangements occur at the impurity site as a consequence of the complex phenomena related with the electronic screening of the external potential. This nothwithstanding, we observe that linear relations hold between charge excesses and external potentials, in quantitative agreement with the mentioned supercell calculations, and well beyond the limits of linearity for any other site property.Comment: 11 pages, 1 table, 7 figure