A Biased Resistor Network Model for Electromigration Failure and Related Phenomena in Metallic Lines

Electromigration phenomena in metallic lines are studied by using a biased resistor network model. The void formation induced by the electron wind is simulated by a stochastic process of resistor breaking, while the growth of mechanical stress inside the line is described by an antagonist process of recovery of the broken resistors. The model accounts for the existence of temperature gradients due to current crowding and Joule heating. Alloying effects are also accounted for. Monte Carlo simulations allow the study within a unified theoretical framework of a variety of relevant features related to the electromigration. The predictions of the model are in excellent agreement with the experiments and in particular with the degradation towards electrical breakdown of stressed Al-Cu thin metallic lines. Detailed investigations refer to the damage pattern, the distribution of the times to failure (TTFs), the generalized Black's law, the time evolution of the resistance, including the early-stage change due to alloying effects and the electromigration saturation appearing at low current densities or for short line lengths. The dependence of the TTFs on the length and width of the metallic line is also well reproduced. Finally, the model successfully describes the resistance noise properties under steady state conditions.Comment: 39 pages + 17 figure

Historic records and GIS applications for flood risk analysis in the Salento peninsula (southern Italy)

International audienceThe occurrence of calamitous meteoric events represents a current problem of the Salento peninsula (Southern Italy). In fact, flash floods, generated by very intense rainfall, occur not only in autumn and winter, but at the end of summer as well. These calamities are amplified by peculiar geological and geomorphological characteristics of Salento and by the pollution of sinkholes. Floodings affect often large areas, especially in the impermeable lowering zones. These events cause warnings and emergency states, involving people as well as socio-economic goods. A methodical investigation based on the historic flood records and an analysis of the geoenvironmental factors have been performed, using a Geographic Information System (GIS) methodology for database processing in order to identify the distribution of areas with different risk degrees. The data, referring to events that occurred from 1968 to 2004, have been collected in a database, the so-called IPHAS (Salento Alluvial PHenomena Inventory), extracted in an easily consultable table. The final goal is the development of a risk map where the areas that are affected by floodings are included between small ridges, the so-called "Serre". More than 50% of the Salento peninsula shows high or very high risk values. The numerous maps that were utilized and generated represent an important basis in order to quantify the flood risk, according to the model using historic records

Tuning the Correlation Decay in the Resistance Fluctuations of Multi-Species Networks

A new network model is proposed to describe the $1/f^\alpha$ resistance noise in disordered materials for a wide range of $\alpha$ values ($0< \alpha < 2$). More precisely, we have considered the resistance fluctuations of a thin resistor with granular structure in different stationary states: from nearly equilibrium up to far from equilibrium conditions. This system has been modelled as a network made by different species of resistors, distinguished by their resistances, temperature coefficients and by the energies associated with thermally activated processes of breaking and recovery. The correlation behavior of the resistance fluctuations is analyzed as a function of the temperature and applied current, in both the frequency and time domains. For the noise frequency exponent, the model provides $0< \alpha < 1$ at low currents, in the Ohmic regime, with $\alpha$ decreasing inversely with the temperature, and $1< \alpha <2$ at high currents, in the non-Ohmic regime. Since the threshold current associated with the onset of nonlinearity also depends on the temperature, the proposed model qualitatively accounts for the complicate behavior of $\alpha$ versus temperature and current observed in many experiments. Correspondingly, in the time domain, the auto-correlation function of the resistance fluctuations displays a variety of behaviors which are tuned by the external conditions.Comment: 26 pages, 16 figures, Submitted to JSTAT - Special issue SigmaPhi200

ARCHAEOLOGICAL MATERIALS FROM GABII (CENTRAL ITALY): KNOWLEDGE OF OFFERINGS AND RITUALS AT THE INFANT BURIALS THROUGH AN INTEGRATED APPROACH

The ancient Latin city of Gabii is situated 18 km (11.2 miles) to the east of Rome (Central Italy) along the modern Via Prenestina. Gabii was a renowned city in Roman times, particularly during the Republican period and there are various influences in the site that can be identified in Roman culture itself. Gabii is also one of the most significant and important archaeological sites in the territory of the Municipality of Rome and due to its characteristics, it represents today an extraordinary research context. From the excavations carried out in the past it is possible to see how, under the soil, the main structures and buildings of the ancient city are still largely preserved. Among the various testimonies of the past, the tombs, and the micro and macro remains that these contain, represent an opportunity to investigate such practices in the context of Early Iron Age and Orientalizing Latium. In particular, the finds from the Area D baby burials of Gabii enriched the existing dataset so far significantly, allowing us to explore funerary ritual behavior in a more systematic way. This work reports the results of the detailed examination of four tombs (Tombs 30, 50, 51 and 52) of archaeological site. The field strategy for the excavation of the tombs was geared from the start towards both the systematic retrieval of archaeobotanical and zooarchaeological remains and the sampling for organic residue analysis. Aiming for total recovery, the sediments from the tomb fills were sifted in their entirety as their stratigraphic excavation progressed, and samples were taken for flotation. This careful screening allowed for the detection of concentrations of organic material that represent plant and/or animal depositions. The excavation and removal of the grave goods was carried out following strict protocols for residue sampling, minimizing the risk of organic contamination. Samples were analysed by High Temperature Gas Chromatography/Mass Spectrometry (HTGC/MS) and Gas chromatography/Combustion/Isotope ratio mass spectrometry (GC-C-IRMS). For each burial, a subset of vessels including both closed and open shapes was selected, such as cups, open bowl without foot, amphoretta, amphora with dots, Kantharos, plate on a foot, olla, and olpe in bucchero. The results demonstrate the still largely unexploited potential of this sort of integrated studies, encouraging us to expand the application of chemical methods to contexts from other well–controlled excavations

Endovascular Management of Juxtarenal and Pararenal Abdominal Aortic Aneurysms: Role of Chimney Technique

The use of chimney technique in endovascular repair of abdominal aortic aneurysms (ChEVAR) has had a secondary role. Although it was first developed in an emergent/urgent setting, the publication of various important studies has helped overcome scepticism towards this technique in elective procedures. This paper reviews current evidence about ChEVAR, focusing on clinical results, technical notes and comparisons with other techniques. The new ChEVAR findings show favourable mid- and long-term clinical outcomes, even in elective patients. These results, comparable to those related to fenestrated endografts, have been achieved through standardisation in planning and materials. An adequate endograft oversizing associated to the right aortic neck length is fundamental to avoid ChEVAR-related complications, such as type 1a endoleaks. These data indicate that ChEVAR, compared to other complex endovascular treatments, has comparable outcomes along with features that could make it an essential option in every clinical settin

Generalised extreme value statistics and sum of correlated variables

We show that generalised extreme value statistics -the statistics of the k-th largest value among a large set of random variables- can be mapped onto a problem of random sums. This allows us to identify classes of non-identical and (generally) correlated random variables with a sum distributed according to one of the three (k-dependent) asymptotic distributions of extreme value statistics, namely the Gumbel, Frechet and Weibull distributions. These classes, as well as the limit distributions, are naturally extended to real values of k, thus providing a clear interpretation to the onset of Gumbel distributions with non-integer index k in the statistics of global observables. This is one of the very few known generalisations of the central limit theorem to non-independent random variables. Finally, in the context of a simple physical model, we relate the index k to the ratio of the correlation length to the system size, which remains finite in strongly correlated systems.Comment: To appear in J.Phys.

Interplay between non-coding rna transcription, stringent/relaxed phenotype and antibiotic production in streptomyces ambofaciens

While in recent years the key role of non-coding RNAs (ncRNAs) in the regulation of gene expression has become increasingly evident, their interaction with the global regulatory circuits is still obscure. Here we analyzed the structure and organization of the transcriptome of Streptomyces ambofaciens, the producer of spiramycin. We identified ncRNAs including 45 small-RNAs (sRNAs) and 119 antisense-RNAs (asRNAs I) that appear transcribed from dedicated promoters. Some sRNAs and asRNAs are unprecedented in Streptomyces and were predicted to target mRNAs encoding proteins involved in transcription, translation, ribosomal structure and biogenesis, and regulation of morphological and biochemical differentiation. We then compared ncRNA expression in three strains: (i) the wild-type strain; (ii) an isogenic pirA-defective mutant with central carbon metabolism imbalance, “relaxed” phenotype, and repression of antibiotic production; and (iii) a pirA-derivative strain harboring a “stringent” RNA polymerase that suppresses pirA-associated phenotypes. Data indicated that the expression of most ncRNAs was correlated to the stringent/relaxed phenotype suggesting novel effector mechanisms of the stringent response

Sideroflexin 3 is an α-synuclein-dependent mitochondrial protein that regulates synaptic morphology.

α-Synuclein plays a central role in Parkinson's disease, where it contributes to the vulnerability of synapses to degeneration. However, the downstream mechanisms through which α-synuclein controls synaptic stability and degeneration are not fully understood. Here, comparative proteomics on synapses isolated from α-synuclein-/- mouse brain identified mitochondrial proteins as primary targets of α-synuclein, revealing 37 mitochondrial proteins not previously linked to α-synuclein or neurodegeneration pathways. Of these, sideroflexin 3 (SFXN3) was found to be a mitochondrial protein localized to the inner mitochondrial membrane. Loss of SFXN3 did not disturb mitochondrial electron transport chain function in mouse synapses, suggesting that its function in mitochondria is likely to be independent of canonical bioenergetic pathways. In contrast, experimental manipulation of SFXN3 levels disrupted synaptic morphology at the Drosophila neuromuscular junction. These results provide novel insights into α-synuclein-dependent pathways, highlighting an important influence on mitochondrial proteins at the synapse, including SFXN3. We also identify SFXN3 as a new mitochondrial protein capable of regulating synaptic morphology in vivo

Sideroflexin 3 is an α-synuclein-dependent mitochondrial protein that regulates synaptic morphology.

α-Synuclein plays a central role in Parkinson's disease, where it contributes to the vulnerability of synapses to degeneration. However, the downstream mechanisms through which α-synuclein controls synaptic stability and degeneration are not fully understood. Here, comparative proteomics on synapses isolated from α-synuclein-/- mouse brain identified mitochondrial proteins as primary targets of α-synuclein, revealing 37 mitochondrial proteins not previously linked to α-synuclein or neurodegeneration pathways. Of these, sideroflexin 3 (SFXN3) was found to be a mitochondrial protein localized to the inner mitochondrial membrane. Loss of SFXN3 did not disturb mitochondrial electron transport chain function in mouse synapses, suggesting that its function in mitochondria is likely to be independent of canonical bioenergetic pathways. In contrast, experimental manipulation of SFXN3 levels disrupted synaptic morphology at the Drosophila neuromuscular junction. These results provide novel insights into α-synuclein-dependent pathways, highlighting an important influence on mitochondrial proteins at the synapse, including SFXN3. We also identify SFXN3 as a new mitochondrial protein capable of regulating synaptic morphology in vivo