Activation of MHD reconnection on ideal timescales

Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number $S$, up to $10^7$. Results confirm that when the critical aspect ratio of $S^{1/3}$ is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfv\'enic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be robust, as the predicted scaling is measured both in inviscid simulations and when using a Prandtl number $P=1$ in the viscous regime.Comment: Accepted for publication in Plasma Physics and Controlled Fusio

The virtuous cycle of stakeholder engagement in developing a sustainability culture: Salcheto winery

Stakeholder engagement in sustainability represents a powerful driver for value creation. Drawing from stakeholder theory, this paper explores how a firm with a proactive sustainable behaviour engages stakeholders in developing innovation and creating value. A longitudinal, single case study of the Salcheto winery was carried out. Since the late 1990s, Salcheto has been at the forefront of wine eco-innovation and it has played a key role in the development of Montepulciano (Tuscany, Italy) as one of the first sustainable wine clusters worldwide. The development of a sustainable wine culture is one of the firm's various innovations. In doing so, the firm has had to face three challenges - identity creation, legitimization and enhancement - and has engaged its stakeholders through three specific mechanisms (adoption and development; co-creation and diffusion; exploitation and contamination). This virtuous cycle of stakeholder engagement has resulted in value creation at a firm, stakeholder and local level

Majorana: from atomic and molecular, to nuclear physics

In the centennial of Ettore Majorana's birth (1906-1938?), we re-examine some aspects of his fundamental scientific production in atomic and molecular physics, including a not well known short communication. There, Majorana critically discusses Fermi's solution of the celebrated Thomas-Fermi equation for electron screening in atoms and positive ions. We argue that some of Majorana's seminal contributions in molecular physics already prelude to the idea of exchange interactions (or Heisenberg-Majorana forces) in his later workson theoretical nuclear physics. In all his papers, he tended to emphasize the symmetries at the basis of a physical problem, as well as the limitations, rather than the advantages, of the approximations of the method employed.Comment: to appear in Found. Phy

One-step functionalization of mildly and strongly reduced graphene oxide with maleimide: An experimental and theoretical investigation of the Diels-Alder [4+2] cycloaddition reaction

For large-scale graphene applications, such as the production of polymer-graphene nanocomposites, exfoliated graphene oxide (GO) and its reduced form (rGO) are presently considered to be very suitable starting materials, showing enhanced chemical reactivity with respect to pristine graphene, in addition to suitable electronic properties (i.e., tunable band gap). Among other chemical processes, a suitable way to obtain surface decoration of graphene is through a direct one-step Diels-Alder (DA) reaction, e.g. through the use of dienophile or diene moieties. However, the feasibility and extent of decoration largely depends on the specific graphene microstructure that in the case of rGO sheets is not easy to control and generally presents a high degree of inhomogeneity owing to various on-plane functionalization (e.g., epoxide and hydroxyl groups) or in-plane lattice defects. In an effort to gain some insights into the covalent functionalization of variably reduced GO samples, we present a combined experimental and theoretical study on the DA cycloaddition reaction of maleimide, a dienophile functional unit well-suited for chemical conjugation of polymers and macromolecules. In particular, we considered both mildly and strongly reduced GOs. Using thermogravimetry, Raman and X-Ray photoelectron spectroscopy, and elemental analysis we show evidence of variable chemical reactivity of rGO as a function of the residual oxygen content. Moreover, from quantum mechanical calculations carried out at the DFT level on different graphene reaction sites, we provide a more detailed molecular view to interpret experimental findings and to assess the reactivity series of different graphene modifications. This journal i

Geology of the lower Belice River valley, epicentral area of the M > 5 1968 seismic sequence (south-western Sicily, Italy)

We present a new 1:25,000-scale geological map of the lower Belice River valley, the area struck by the M > 5.0 devastating 1968 seismic sequence, whose seismic source and seismotectonic framework are still controversial. The map, utilizing dating methods and traditional field survey approaches integrated by high-resolution topography, provides an unprecedented detail and precision on the spatial distribution and on the compressional growth geometries of the prominent sedimentary sequence. This map, supported by the first recognition of an on-shore Chibanian-Calabrian deposition and by identifying a flight of marine terraces, offers new insights on the long-lasting syn-depositional tectonic forces up to late-Pleistocene-Holocene times. Such tectonic forces may take part in the regional ongoing deformational phase, prompting detailed studies on the potential seismic sources affecting the area

A Novel Approach for an Integrated Straw tube-Microstrip Detector

We report on a novel concept of silicon microstrips and straw tubes detector, where integration is accomplished by a straw module with straws not subjected to mechanical tension in a Rohacell $^{\circledR}$ lattice and carbon fiber reinforced plastic shell. Results on mechanical and test beam performances are reported on as well.Comment: Accepted by Transactions on Nuclear Science (2005). 11 pages, 9 figures, uses lnfprep.st

Environment-man relationships in historical times: the balance between urban development and natural forces at Leptis Magna (Libya).

We analyze the relationships between human modification of the environment and natural events in the Roman city of Leptis Magna (UNESCO world heritage), western Libya. For the first time the history of Leptis Magna is tested against a high resolution geo-morphological and stratigraphical reconstruction and absolute radiocarbon dating. Historical and archaeological sources indicate the occurrence of different natural events as the cause of the town decline: earthquakes, flooding, and tsunamis. Our data indicate that Leptis Magna was tightly linked to the nearby wadi. In fact, aware of the hazards related to violent flooding, the Romans were able to cope with the threat posed by the wadi by engineering defensive hydraulic works around the town. Once economic decay began and the society could no longer guarantee the ongoing maintenance of these structures, the decline of the settlement began and the occurrence of violent floods reclaimed the populated areas. The occurrence of large earthquakes, and the tsunami event that damaged the harbor have been discarded as playing a primary role in the decline of Leptis Magna

On the relation between standard and μ\mu-symmetries for PDEs

We give a geometrical interpretation of the notion of $\mu$-prolongations of vector fields and of the related concept of $\mu$-symmetry for partial differential equations (extending to PDEs the notion of $\lambda$-symmetry for ODEs). We give in particular a result concerning the relationship between $\mu$-symmetries and standard exact symmetries. The notion is also extended to the case of conditional and partial symmetries, and we analyze the relation between local $\mu$-symmetries and nonlocal standard symmetries.Comment: 25 pages, no figures, latex. to be published in J. Phys.

Environment-human relationships in historical times: The balance between urban development and natural forces at Leptis Magna (Libya)

The relationships between human modification of the environment and natural events in the Roman city of Lepti Magna (UNESCO world heritage), western Libya, are analyzed. For the first time, the history of Leptis Magna is tested against a geomorphological and stratigraphical reconstruction and radiocarbon dating. Historical and archaeological interpretations or analyses indicate the occurrence of different extreme natural events as the cause of the town’s decline: earthquakes, flooding and tsunami. Geological and geomorphological surveys investigated the dynamics of the nearby Wadi Lebda, a major dryland stream that forms the depositional and erosional systems of the settlement area. Alluvial phases were studied by applying traditional stratigraphic analyses of outcrops and hand-cores. Additionally, the mapped flights of inset terrace surfaces provided insights into the human modifications of the natural depositional/erosional environment during historical times and the following alluvial phases affecting the Leptis Magna harbor. The results integrate the archaeological knowledge by providing some independent chronological constraints, and indicate that Leptis Magna history was tightly linked to the Wadi Lebda. Aware of the hazards related to devastating flooding, the Romans were able to cope with the threat posed by the wadi by performing engineering defensive hydraulic works around the town (dam and artificial channels). Once the economic decay began and the society could no longer guarantee the ongoing maintenance of these structures, the decline of the settlement started and the occurrence of destructive floods reclaimed the populated areas. Conversely, the occurrence of a large earthquake (365 CE), or of a tsunami that caused the disruption of the hydraulic systems and the infill of the harbor, has been discarded as primary cause of the decline of Leptis Magna

Cooperative role of thrombopoietin and vascular endothelial growth factor-a in the progression of liver cirrhosis to hepatocellular carcinoma

Primary thrombopoietic mediator thrombopoietin (THPO) is mainly produced by the liver; it may act as a growth factor for hepatic progenitors. Principal angiogenesis inducer vascular endothelial growth factor-A (VEGF-A) is critical for the complex vascular network within the liver architecture. As a cross-regulatory loop between THPO and VEGF-A has been demonstrated in the hematopoietic system, the two growth factors were hypothesized to cooperatively contribute to the progression from liver cirrhosis (LC) to hepatocellular carcinoma (HCC). The mRNA and protein expression levels of THPO, VEGF-A, and their receptors were examined, compared, and correlated in paired cancerous and LC tissues from 26 cirrhosis-related HCC patients, using qRT-PCR and immunohistochemistry. THPO and VEGF-A were alternatively silenced by small interfering RNA (siRNA) in human liver cancer cell lines Huh7 and HepG2. THPO and VEGF-A expressions significantly increased in tumor versus LC tissues. HCC and paired LC cells expressed similar levels of THPO receptor (R), whereas vascular endothelial growth factor receptor (VEGFR) -1 and VEGFR-2 levels were higher in HCC than in corresponding LC tissue samples. A significant linear correlation emerged between THPO and VEGF-A transcripts in HCC and, at the protein level, THPO and THPOR were significantly correlated with VEGF-A in tumor tissues. Both HCC and LC expressed similar levels of gene and protein hypoxia inducible factor (HIF)-1α. Positive cross-regulation occurred with the alternative administration of siRNAs targeting THPO and those targeting VEGF-A in hypoxic liver cancer cell lines. These results suggest THPO and VEGF-A might act as interdependently regulated autocrine and/or paracrine systems for cellular growth in HCC. This might be clinically interesting, since new classes of THPOR agonistic/antagonistic drugs may provide novel therapeutic options to correct the frequent hemostatic abnormality seen in HCC patients