Representable linear functionals on partial *-algebras

A GNS - like *-representation of a \pa\ \A defined by certain representable linear functionals on \A is constructed. The study of the interplay with the GNS construction associated with invariant positive sesquilinear forms (ips) leads to the notions of pre-core and of singular form. It is shown that a positive sesquilinear form with pre-core always decomposes into the sum of an ips form and a singular one

Induced and reduced unbounded operator algebras

The induction and reduction precesses of an O*-vector space \M obtained by means of a projection taken, respectively, in \M itself or in its weak bounded commutant \M'_\w are studied. In the case where \M is a partial GW*-algebra, sufficient conditions are given for the induced and the reduced spaces to be partial GW*-algebras again

Weak commutation relations of unbounded operators and applications

Four possible definitions of the commutation relation [S,T]=\Id of two closable unbounded operators $S,T$ are compared. The {\em weak} sense of this commutator is given in terms of the inner product of the Hilbert space \H where the operators act. Some consequences on the existence of eigenvectors of two number-like operators are derived and the partial O*-algebra generated by $S,T$ is studied. Some applications are also considered.Comment: In press in Journal of Mathematical Physic

Seismic analysis and risk mitigation of existing constructions

Following a thorough and lengthy procedure, we would like to thank all contributors for their highest calibre papers, which comprise the Special Issue on \u201cSeismic analysis and risk mitigation of existing constructions\u201d of the Open Construction and Building Technology Journal. The topic of the Special Issue encompasses a large number of issues spanning the design of special interventions for the reduction of the effects of earthquakes on civil structures and infrastructures, to the structural identification and assessment issues. The field of seismic engineering is continuously looking for new strategies and methods, which empower the designers and make them able to obtain more accurate response predictions. Researchers are involved in this process and are called to successfully encounter new challenges emerging from the increasing need for the assessment of existing constructions, especially when assuming strategic roles. As is also reflected by the papers presented in the Special Issue, the continuous advances of the research in this field moves across two basic directions. On the one hand, there is the direction of the robustness and the reliability of the recent nonlinear seismic assessment methods (static, dynamic, incremental dynamic). Several approaches can be followed to predict the response of structures to strong ground motions; however the results coming from each of them are in some cases conflicting and not always amenable to easy interpretation. On the other hand, the reliability of structural models still remains a major task of structural engineering and of seismic engineering in particular. Mathematical models have to reproduce the physics of structures and its evolution during complex damaging processes. Global and local models tend to reflect this by minimizing the loss of information. In the Special Issue, we are proud to present state-of-the-art research findings described in detail in 9 papers authored by 27 researchers of different universities in Italy, California (USA), Greece and United Kingdom. The papers deal with the seismic analysis and risk mitigation aiming to address different purposes by proposing numerical, analytical approaches and experimental tests

Weak commutation relations of unbounded operators: nonlinear extensions

We continue our analysis of the consequences of the commutation relation [S,T]=\Id, where $S$ and $T$ are two closable unbounded operators. The {\em weak} sense of this commutator is given in terms of the inner product of the Hilbert space \H where the operators act. {We also consider what we call, adopting a physical terminology}, a {\em nonlinear} extension of the above commutation relations

La Stima dei Moduli Elastici delle Murature Secondo le Norme Tecniche: il Confronto con la Sperimentazione

Nel presente lavoro viene proposto uno studio sperimentale per la caratterizzazione meccanica di diverse tipologie di muratura. Vengono in particolare valutati i moduli elastici longitudinali e tangenziali che come è noto condizionano la risposta di sistemi murari sotto carichi laterali. I valori sperimentali sono confrontati con quelli stimabili per mezzo dei modelli proposti dalle normative tecniche italiana (DM 14/01/2008) e europea (Eurocodice 6). Lo studio prende spunto dalla questio posta dalla norma americana (MSJC 2008) che, pur proponendo l’uso di tali modelli, riconosce la poca sperimentazione eseguita a supporto della loro validazione. La campagna sperimentale ha incluso prove di compressione sui componenti (malte e blocchi), prove di compressione diagonale e prove di compressione ordinaria (in direzione ortogonale ai letti di malta) su porzioni di muratura. I risultati conseguiti hanno consentito la valutazione diretta dei moduli elastici e successivamente di ottenere le grandezze meccaniche necessarie per l’utilizzo dei succitati modelli normativi

Modelling failure analysis of RC frame structures with masonry infills under sudden column losses

Abstract Robustness of structures is fundamental to limit progressive collapse of buildings in case of accidental loss of columns due to explosions, impacts or materials deterioration. Modelling of progressive collapse response of reinforced concrete (RC) frame structures needs considering extreme geometric and mechanical nonlinearities. Moreover, in the case of infilled frames the collapse mechanism becomes more complex because of the frame-infill interaction. This paper presents a numerical study aimed at proposing: a) an appropriate fiber-section modeling methodology for reinforced concrete frames under large displacement progressive collapse events; b) a new multi-strut fiber macro-element model to account for the influence of masonry infills in the progressive collapse response. Proposed numerical models are developed using the OpenSees software platform. The predictive capacity of the proposed methodology is widely validated in the paper through comparisons with experimental test results and refined numerical simulation pushdown test results. Results show that the new equivalent-strut modeling approach can be suitably employed as a simple assessment method when numerical simulation of progressive collapse scenarios is needed for bare and infilled reinforced concrete frames

Treatment of high strength industrial wastewater with membrane bioreactors for water reuse: Effect of pre-treatment with aerobic granular sludge on system performance and fouling tendency

In this study, the treatment of citrus wastewater with membrane bioreactors (MBRs) under different configurations was investigated for water reuse. In particular, one MBR and one aerobic granular sludge MBR (AGS+MBR) bench scale plants were operated for 60 days. The experimental campaign was divided into two periods. In Phase I, a conventional hollow fiber MBR was employed for the treatment of the raw high strength wastewater, whereas in Phase II a combination of in-series reactors (AGS plus MBR) was adopted for the treatment of the high strength citrus wastewater The results demonstrated that both plant configurations enabled very high COD removal, with average values close to 99%. Respirometric batch tests revealed a considerable high metabolic activity of the biomass in both plant configurations, with higher values in the AGS+MBR. It was speculated that the MBR reactor enriched in active biomass deriving from the erosion of the external granule layers in the upstream reactor. In terms of fouling tendency, higher resistance to filtration was observed in the AGS+MBR plant, also characterized by higher irremovable resistance increase compared to the MBR plant that might severely affect the membrane service life

Combination of the OSA process with thermal treatment at moderate temperature for excess sludge minimization

This study investigated the chance to couple the conventional Oxic Settling Anaerobic (OSA) process with a thermic treatment at moderate temperature (35 \ub0C). The maximum excess sludge reduction rate (80%) was achieved when the plant was operated under 3 h of hydraulic retention time (HRT). Compared with the conventional OSA system, the thermic treatment enabled a further improvement in excess sludge minimization of 35%. The observed yield coefficient decreased from 0.25 gTSS gCOD 121 to 0.10 gTSS gCOD 121 when the temperature in the anaerobic reactor was increased to 35 \ub0C, despite the lower HRT (3 h vs 6 h). Moreover, the thermic treatment enabled the decrease of filamentous bacteria, thereby improving the sludge settling properties. The thermic treatment enhanced the destruction of extracellular polymeric substances and the increase of endogenous decay rate (from 0.64 d 121 to 1.16 d 121) that reduced the biomass active fraction (from 22% to 4%)