Schiume metalliche: recenti risultati e sviluppi futuri

In questa rassegna vengono presentati e discussi i risultati degli studi condotti dagli autori negli ultimianni riguardo la produzione e caratterizzazione di materiali metallici porosi. Dopo le prime esperienzenella produzione di schiume di Al a porosità chiusa, partendo da polveri e con l’aggiunta di TiH2 comeagente soffiante, si è passati alla produzione di schiume di diversi metalli a porosità aperta mediante latecnica “SDP” (sintering and dissolution process) modificata. Un’altra via percorsa per la produzione dischiume a basso costo è la cosiddetta “RP” (replication process), anch’essa sottoposta ad alcune variantirispetto alla tecnica classica a seconda del metallo o della lega che si intende schiumare. Un importanteaspetto di questo filone di ricerca ha riguardato la produzione di schiume partendo da materiale diriciclo, truciolo tal quale per quanto riguarda Al e sue leghe, griglie e pasta recuperate da batterie esausteper le schiume di piombo. Questa rappresenta un’interessante prospettiva, anche sotto il profilo energeticoe ambientale, per la conversione diretta del materiale, prodotto di scarto di lavorazioni, in schiume di Al ePb rispettivamente. Vengono quindi presentati i risultati sperimentali e le problematiche emerse durante ilprocesso di ottenimento della schiuma utilizzando il materiale recuperato. Un ulteriore aspetto hariguardato la produzione di schiume di Fe che combinano un buon mix tra proprietà meccaniche erequisiti di leggerezza. Infine l’ultimo punto della rassegna illustra i principali risultati della ricerca piùrecente che riguarda la produzione di elettrodi porosi realizzati in schiume di Pb. Una possibileapplicazione potrebbe essere la realizzazione di lamierini in piombo da impiegare come elettrodimicroporosi in accumulatori al piombo acido con l’obiettivo di ridurne il peso e migliorarne le prestazioni.Critico da questo punto di vista si presenta il problema del controllo della dimensione della porosità. Atale proposito alcune problematiche devono ancora essere superate e sono tuttora oggetto disperimentazione. Per tutte le tipologie di schiume prodotte è stata effettuata una caratterizzazionemorfologica e meccanica

Mechanical characterization of aisi 316 tubes filled with Al alloy foams

In tubular elements filled with metal foams the structural collapse is delayed in comparison with the empty tubes,consequently compression strength and absorbed energy increase. Production methods of foams are crucial, asthey determine cellular morphology and bonds formation with tube wall. In this work AISI 316 steel tubes filledwith foam of commercially pure Al and Al-Si alloys with hypoeutectic compositions were produced. The processparameters were optimized to obtain closed cells foams with an acceptable morphology of porosity and goodmechanical properties. Foams were characterized by optical and scanning electron microscopy and by computertomography; mechanical properties were investigated by axial compression tests (performed on foam samplesand on Cu tubes, empty or filled with foams) and radial compression “Brazilian test” (carried out on AISI 316tubes, empty or filled with foams)

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe

Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV

The Lambda(b) differential production cross section and the cross section ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Lambda(b) decays reconstructed in the exclusive final state J/Psi Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and Lambda to proton pion, using a data sample corresponding to an integrated luminosity of 1.9 inverse femtobarns. The product of the cross section times the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls faster than that of b mesons. The measured value of the cross section times the branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06 +/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are statistical and systematic, respectively.Comment: Submitted to Physics Letters

Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV

A search is presented for physics beyond the standard model (BSM) in final states with a pair of opposite-sign isolated leptons accompanied by jets and missing transverse energy. The search uses LHC data recorded at a center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to an integrated luminosity of approximately 5 inverse femtobarns. Two complementary search strategies are employed. The first probes models with a specific dilepton production mechanism that leads to a characteristic kinematic edge in the dilepton mass distribution. The second strategy probes models of dilepton production with heavy, colored objects that decay to final states including invisible particles, leading to very large hadronic activity and missing transverse energy. No evidence for an event yield in excess of the standard model expectations is found. Upper limits on the BSM contributions to the signal regions are deduced from the results, which are used to exclude a region of the parameter space of the constrained minimal supersymmetric extension of the standard model. Additional information related to detector efficiencies and response is provided to allow testing specific models of BSM physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO

Search for leptophobic Z ' bosons decaying into four-lepton final states in proton-proton collisions at root s=8 TeV

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Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at root s=13 TeV

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Measurements of differential production cross sections for a Z boson in association with jets in pp collisions at root s=8 TeV

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