Influence of knots on the modulus of elasticity of wooden foundation piles

openLe città fondate su suoli di tipo paludoso, come Amsterdam e Venezia, sono caratterizzate da terreni con scarsa capacità portante, motivo per il quale vengono utilizzati pali di fondazione in legno. Essendo quest’ultimo un materiale naturale, le proprietà meccaniche dei pali vengono alterate dalla presenza di difetti strutturali, come possono essere i nodi. Al fine di comprendere questo aspetto, questa ricerca studia l’influenza dei nodi sul modulo di elasticità in direzione longitudinale dei pali di fondazione in legno. Sono stati considerati 27 pali di abete rosso e pino (provenienti da Germania e Paesi Bassi), successivamente suddivisi in 110 segmenti ed analizzati. In particolare, sono stati considerati due principali parametri che più influiscono sulla rigidezza, quali la dimensione dei nodi e la disposizione di essi. Lo studio dei segmenti è stato condotto tramite test meccanici a grande scala che comprendono test a compressione e test di misurazione della risposta dinamica. L’analisi globale è stata validata testando dischi ottenuti da sezioni dei pali con e senza nodi, per analizzare ulteriormente, con test locali, l’influenza dei nodi sulla rigidezza longitudinale. Un Overall Knots Ratio (OKR) è stato definito analizzando la disposizione dei nodi di ogni palo di fondazione, e valutando come il modulo di elasticità è influenzato dalla dimensione, numero e disposizione di essi. L’influenza dei nodi è stata anche studiata creando un modello numerico per riprodurre la risposta dinamica dei segmenti di palo. Il modello conferma ancora che i nodi sono un fattore rilevante nella variazione di rigidezza dei pali di fondazione in legno. Infine, si è sviluppato un modello predittivo in grado di stimare il modulo di elasticità di un palo conoscendo la densità e la quantità di nodi nello stesso. L’analisi dei dati ottenuti mostra che i nodi influiscono sulla deviazione delle fibre longitudinali e il modulo di elasticità. Quindi, le sezioni con nodi risultano avere una rigidezza molto bassa in direzione assiale di un palo che, per questo motivo, non è stata considerata nell’analisi. Inoltre, è stato stimato che la rigidezza dell’area attorno ad un nodo, dove le fibre sono deviate, sia leggermente più elevata del nodo stesso, ma ancora molto bassa. Infine, la larghezza di influenza equivalente è stata stimata approsimativamente come 1.5 volte la dimensione del nodo stesso. Questi risultati sono stati studiati nel dettaglio con test di Digital Image Correlation (DIC). Questa tecnica è stata usata per meglio indagare il comportamento dei nodi nella variazione del MOE. Il test DIC è stato usato durante l’esecuzione di un test a compressione per analizzare le deformazioni di una piccola area attorno ad un nodo su due segmenti di palo. I risultati confermano che la sezione con nodi ha una rigidezza più bassa della sezione senza nodi.Cities build on marshy undergrounds, such as Amsterdam and Venice, are based on timber foundation piles due to the low bearing capacity of the soil. Since wood is a natural material, the mechanical properties of timber piles are affected by structural defects like knots. With the aim to understand this aspect, this research studies the influence of knots on the modulus of elasticity in the longitudinal direction of wooden foundation piles. The research analyzed 27 spruce and pine piles (from Germany and The Netherlands), that were divided in 110 segments. In particular, two main parameters that influence the stiffness of timber piles were considered: the knots size and layout. The study of segments was performed with large-scale mechanical testing that involved compression tests and frequency response measurement. The global analysis was validated by testing also wooden disks sawn from a section of the pile with and without knots, to further analyze the influence of knots on stiffness with local tests, besides the large-scale ones. A good correlation was observed between the MOE of pile segments and disks, and confirming that section with knots governs the stiffness when loading a pile in compression. An Overall Knots Ratio (OKR) was defined considering the layout of knots in each foundation pile and evaluating how the modulus of elasticity is influenced by dimension, number and layout of knots. The influence of knots was studied also performing a numerical model to predict the dynamic response of the segments. The model confirms again that knots are a relevant factor in the variation of the MOE of wooden foundation piles. Finally, a prediction model was performed. The model can predict the modulus of elasticity of a pile, by knowing density and knots layout. The analysis of the obtained data showed that knots influence the deviation of longitudinal fibers and subsequently the modulus of elasticity. Therefore, the cross-section with knots in the axial direction of a pile, due to fiber deviation around a knot, resulted to have very low stiffness, that was neglected in the analysis. In addition, it was estimated that the zone around the knot, where the fibers in longitudinal direction deviate, has a slightly higher stiffness than the knot itself, but still very low. In conclusion, the equivalent size of influence was estimated approximately as 1.5 times the diameter of the knot itself. These results were studied in detail with Digital Image Correlation (DIC) test. This technique was used to better investigate the behaviour of knots on the variation of the MOE. DIC was used to analyze the deformations on a small area around a knot, during a compression test of two pile segments. The results confirmed that the section with knots has a lower stiffness than the section without knots

Pubblicita' e new media. Social e digital al servizio della comunicazione.

La tesi tratta dell'avvento dei nuovi media all'interno del mondo della pubblicità; di come ha modificato il mestiere del pubblicitario e di come le imprese si sono adattate ai nuovi metodi di comunicazione. L'elaborato riporta esempi specifici per ogni caso discusso e riporta i lavori dell'autore durante il periodo di tirocinio presso l'agenzia pubblicitaria C.O.W. di Torino

NuSTAR and XMM-Newton observations of the Arches cluster in 2015: fading hard X-ray emission from the molecular cloud

We present results of long NuSTAR (200 ks) and XMM-Newton (100 ks) observations of the Arches stellar cluster, a source of bright thermal (kT~2 keV) X-rays with prominent Fe XXV K_alpha 6.7 keV line emission and a nearby molecular cloud, characterized by an extended non-thermal hard X-ray continuum and fluorescent Fe K_alpha 6.4 keV line of a neutral or low ionization state material around the cluster. Our analysis demonstrates that the non-thermal emission of the Arches cloud underwent a dramatic change, with its homogeneous morphology, traced by fluorescent Fe K_alpha line emission, vanishing after 2012, revealing three bright clumps. The declining trend of the cloud emission, if linearly fitted, is consistent with half-life decay time of ~8 years. Such strong variations have been observed in several other molecular clouds in the Galactic Centre, including the giant molecular cloud Sgr B2, and point toward a similar propagation of illuminating fronts, presumably induced by the past flaring activity of Sgr A*.Comment: 15 pages, 14 figures, 7 tables, submitted to MNRAS; comments welcom

No association between candidate genes for color determination and color phenotype in Hierophis viridiflavus, and characterization of a contact zone

Genetic and phenotypic differentiation in allopatric conditions can be explained either by neutral phenomena or adaptative processes driven by selection. In reptiles, coloration can affect aspects directly related to their survival, representing a classical character under selection. In this context, secondary contact areas are natural laboratory to understand evolutionary processes underlying genetic permeability, especially when populations differ in phenotypic traits such as coloration. The western whip snake Hierophis viridiflavus presents two divergent mitochondrial clades, characterized by the presence of one of two main color phenotypes, namely one with black and yellow stripes and a fully melanic one. Here, we investigated whether melanogenesis-linked genes are determinant of the chromatic differences observed across the phenotypic variation of the species. In addition, we used a multilocus dataset, including 134 original ND4 sequences, to better define the overall genetic structure and to provide a characterization of a contact zone identified in Central Italy by estimating the amount of nuclear gene exchange. While we found no evidence supporting a direct association between target genes and coloration, a non-synonymous substitution polymorphism, at high frequency, was detected in the β melanocyte-stimulating hormone whose possible function has been discussed. Concerning the genetic structure, both mtDNA and nuDNA were partly concordant indicating introgression events occurring at the contact zone. When we measured the nuclear gene flow, we found a significant amount of gene exchange, mainly guided from one clade to the other, that is, asymmetric. These results might suggest the presence of ecological and/or behavioral processes driving the observed directional gene flow

Effect of alkalis on the Fe oxidation state and local environment in peralkaline rhyolitic glasses

International audienceIron oxidation state and coordination geometry have been determined by Fe K-edge X-ray absorption near edge spectroscopy (XANES) for three sets of silicate glasses of peralkaline rhyolitic composition with different peralkalinity values. These compositions were chosen to investigate the effect of alkali content (and oxygen fugacity) on the Fe oxidation state. The samples were produced by means of hydrothermal vessels at 800 °C with oxygen fugacity conditions ranging from NNO-1.61 to NNO+2.96 log units. Comparison of the pre-edge peak data with those of Fe model compounds of known oxidation state and coordination number allowed determination of the Fe oxidation state and coordination number in all glasses analyzed. Within each group of samples, Fe tends to oxidize with increasing oxygen fugacity as expected. However, alkali content is shown to have a strong effect on the Fe3+/(Fe3++Fe2+) ratio at constant oxygen fugacity: this ratio varies from 0.25 to 0.55 (±0.05) for the least peralkaline series, and from 0.45 to 0.80 (±0.05) for the most peralkaline series. Moreover, pre-edge peak data clearly indicate that Fe3+ is in fourfold coordination in the most peralkaline glasses. Extrapolation of pre-edge peak data suggests the presence of both fourfold and fivefold coordination for trivalent Fe in the other two series. Divalent Fe is suggested to be mainly in fivefold coordination in all the three glass series. The presence of minor amounts of sixfold- and fourfold-coordinated Fe cannot be ruled out by XANES data alone. XANES data suggest that the amount of alkalis also affects the Fe3+ coordination environment resulting in a decrease in the average coordination numbers. Extended X-ray absorption fine structure (EXAFS) data of the most oxidized and peralkaline sample indicate that Fe3+ is in tetrahedral coordination with = 1.85 Å (±0.02). This value compares well with literature data for [4]Fe3+ in crystalline phases (e.g., in tetra-ferriphlogopite or rodolicoite) or in silicate glasses (e.g., phonolite glasses) supporting the XANES-determined coordination number obtained for the most peralkaline glasses. Calculated NBO/T ratios decrease slightly with Fe oxidation because of the higher fraction of network forming Fe, thus increasing the polymerization of the tetrahedral network

Discovery of periodicities in two highly variable intermediate polars towards the Galactic Center

We discovered Fe $K_{\alpha}$ complex emission and pulsation in two highly variable sources (4XMM J174917.7--283329, 4XMM J174954.6--294336). The equivalent widths of 6.4 and 6.7 keV lines of 4XMM J174917.7--283329 are $99^{+84}_{-72}$ and $220^{+160}_{-140}$ eV, respectively. The continuum is fitted by a partially absorbed apec model with plasma temperature of $kT=13^{+10}_{-2}$ keV. The inferred mass of the white dwarf (WD) is $0.9^{+0.3}_{-0.2}\ M_{\odot}$. We detected pulsations with a period of $1212\pm3$ s and a pulsed fraction of $26\pm6\%$. The light curves of 4XMM J174954.6--294336 display asymmetric eclipse and dipping behaviour. To date, this is only the second intermediate polar (IP) that shows a total eclipse in X-rays. The spectrum of the sources is characterized by a power-law model with photon index $\Gamma=0.4\pm0.2$. The equivalent widths of the 6.4 keV and 6.7 keV iron lines are $171^{+99}_{-79}$ and $136^{+89}_{-81}$ eV, respectively. The continuum is described by emission from optically thin plasma with a temperature of $kT\sim35$ keV. The inferred mass of the WD is $1.1^{+0.2}_{-0.3}\ M_{\odot}$. We discovered coherent pulsations from the source with a period of $1002\pm2$ s. The pulsed fraction is $66\pm15\%$. The measured spin period, hard photon index, and equivalent width of the fluorescent Fe $K_{\alpha}$ line in both sources are consistent with the values found in IP. While 4XMM J174954.6--294336 was already previously classified as an IP, we also suggest 4XMM J174917.7--283329 as a new IP. The X-ray eclipses in 4XMM J174954.6--294336 are most likely caused by a low-mass companion star obscuring the central X-ray source. The asymmetry in the eclipse is likely caused by a thick bulge that intercepts the line of sight during the ingress phase but not during the egress phase located behind the WD along the line of sight.Comment: 9 pages, six figures, accepted for publication in A&

Hard X-ray Morphological and Spectral Studies of The Galactic Center Molecular Cloud Sgr B2: Constraining Past Sgr A* Flaring Activity

Galactic Center (GC) molecular cloud Sgr B2 is the best manifestation of an X-ray reflection nebula (XRN) reprocessing a past giant outburst from the supermassive black hole Sgr A*. Alternatively, Sgr B2 could be illuminated by low-energy cosmic ray electrons (LECRe) or protons (LECRp). In 2013, NuSTAR for the first time resolved Sgr B2 hard X-ray emission on sub-arcminute scales. Two prominent features are detected above 10 keV - a newly emerging cloud G0.66-0.13 and the central 90" radius region containing two compact cores Sgr B2(M) and Sgr B2(N) surrounded by diffuse emission. It is inconclusive whether the remaining level of Sgr B2 emission is still decreasing or has reached a constant background level. A decreasing Fe K$\alpha$ emission can be best explained by XRN while a constant background emission can be best explained by LECRp. In the XRN scenario, the 3-79 keV Sgr B2 spectrum can well constrain the past Sgr A* outburst, resulting in an outburst spectrum with a peak luminosity of $L_{3-79\rm~keV} \sim 5\times10^{38} \rm~erg~s^{-1}$ derived from the maximum Compton-scattered continuum and the Fe K$\alpha$ emission consistently. The XRN scenario is preferred by the fast variability of G0.66-0.13, which could be a molecular clump located in the Sgr B2 envelope reflecting the same Sgr A* outburst. In the LECRp scenario, we derived the required CR ion power $dW/dt=(1-4)\times10^{39}\rm~erg~s^{-1}$ and the CR ionization rate $\zeta_{H}=(6-10)\times 10^{-15}\rm~H^{-1}~s^{-1}$. The Sgr B2 background level X-ray emission will be a powerful tool to constrain GC CR population.Comment: 17 pages, 6 figures, submitted to Ap

Diacylated Sulfoglycolipids Are Novel Mycobacterial Antigens Stimulating CD1-restricted T Cells during Infection with Mycobacterium tuberculosis

Mycobacterial lipids comprise a heterogeneous group of molecules capable of inducing T cell responses in humans. To identify novel antigenic lipids and increase our understanding of lipid-mediated immune responses, we established a panel of T cell clones with different lipid specificities. Using this approach we characterized a novel lipid antigen belonging to the group of diacylated sulfoglycolipids purified from Mycobacterium tuberculosis. The structure of this sulfoglycolipid was identified as 2-palmitoyl or 2-stearoyl-3-hydroxyphthioceranoyl-2′-sulfate-α-α′-d-trehalose (Ac2SGL). Its immunogenicity is dependent on the presence of the sulfate group and of the two fatty acids. Ac2SGL is mainly presented by CD1b molecules after internalization in a cellular compartment with low pH. Ac2SGL-specific T cells release interferon γ, efficiently recognize M. tuberculosis–infected cells, and kill intracellular bacteria. The presence of Ac2SGL-responsive T cells in vivo is strictly dependent on previous contact with M. tuberculosis, but independent from the development of clinically overt disease. These properties identify Ac2SGL as a promising candidate to be tested in novel vaccines against tuberculosis

Synthesis of 2-Alkynoates by Palladium(II)-Catalyzed Oxidative Carbonylation of Terminal Alkynes and Alcohols

A homogeneous Pd(II) catalyst, utilizing a simple and inexpensive amine ligand (TMEDA), allows 2‐alkynoates to be prepared in high yields by an oxidative carbonylation of terminal alkynes and alcohols. The catalyst system overcomes many of the limitations of previous palladium carbonylation catalysts. It has an increased substrate scope, avoids large excesses of alcohol substrate and uses a desirable solvent. The catalyst employs oxygen as the terminal oxidant and can be operated under safer gas mixtures