A surge of late-occurring meiotic double-strand breaks rescues synapsis abnormalities in spermatocytes of mice with hypomorphic expression of SPO11

Meiosis is the biological process that, after a cycle of DNA replication, halves the cellular chromosome complement, leading to the formation of haploid gametes. Haploidization is achieved via two successive rounds of chromosome segregation, meiosis I and II. In mammals, during prophase of meiosis I, homologous chromosomes align and synapse through a recombination-mediated mechanism initiated by the introduction of DNA double-strand breaks (DSBs) by the SPO11 protein. In male mice, if SPO11 expression and DSB number are reduced below heterozygosity levels, chromosome synapsis is delayed, chromosome tangles form at pachynema, and defective cells are eliminated by apoptosis at epithelial stage IV at a spermatogenesis-specific endpoint. Whether DSB levels produced in Spo11 (+/-) spermatocytes represent, or approximate, the threshold level required to guarantee successful homologous chromosome pairing is unknown. Using a mouse model that expresses Spo11 from a bacterial artificial chromosome, within a Spo11 (-/-) background, we demonstrate that when SPO11 expression is reduced and DSBs at zygonema are decreased (approximately 40 % below wild-type level), meiotic chromosome pairing is normal. Conversely, DMC1 foci number is increased at pachynema, suggesting that under these experimental conditions, DSBs are likely made with delayed kinetics at zygonema. In addition, we provide evidences that when zygotene-like cells receive enough DSBs before chromosome tangles develop, chromosome synapsis can be completed in most cells, preventing their apoptotic elimination

Produzione di spugne di acciaio tramite metallurgia delle polveri

I materiali cellulari sono caratterizzati da un’interessante combinazione di proprietà fisiche e meccaniche. Inquesto contesto, le schiume metalliche in acciaio possono essere impiegate come alternativa alle leghe leggerein tutte quelle applicazioni dove si necessita un buon compromesso tra leggerezza e resistenza meccanica. Inquesto studio viene presentato un nuovo approccio per la realizzazione di spugne in acciaio tramite metallurgiadelle polveri utilizzando sfere di SiC come riempitivo. Terminato il processo produttivo le particelle ceramichesono state rimosse tramite lisciviazione e le spugne sono state caratterizzate dal punto di vista morfologico,microstrutturale e meccanico. Il risultato della caratterizzazione ha dimostrato la fattibilità del processoproduttivo per l’ottenimento di spugne metalliche in acciaio

New perspective in steelmaking activity to increase competitiveness and reduce enviromental impact

The competitiveness of the European steel industry is strictly related to the introduction of high performanceproducts and to the increase in process efficiency and to the reduction in environmental impact. Thesechallenges can be faced to ensure a future to the area’s important industrial assets and some actions need to beidentified. Several aspects about steelmaking plants, processes and steel products have been highlighted andnowadays, they may become the object of innovative action and efforts in order to achieve and maintain a highlevel of competitiveness and to solve this serious industrial crisis

Study on the microstructure influence in ultrasonic test in duplex forged components

Ultrasonic tests are fundamental to grant the integrity of the metal products, especially after forgingoperations. Due to the high attenuation of duplex stainless steel (DSS), the efficiency of ultrasonic test (UT)performed on DSS components could decrease and make the inspection difficult.The interaction between the ultrasonic acoustic radiation and the microstructure of 2205 duplex stainlesssteel was studied. The specimens were treated at 780 °C for different soacking times to promote theprecipitation of intermetallic phases. The UT response of each specimen was measured and associated to thecorresponding microstructural features.Electron Back Scatter Diffraction (EBSD) was performed to analyze the grains orientation and to relate therevealed crystallographic texture with the acoustic signal attenuation.Tensile test were performed to determine the variation of the main mechanical parameters (yield strength,ultimate tensile strength, elongation and Young modulus) induced by the presence of the secondary phases.The variation of ultrasound velocity can be associated to the modification of the volume fraction of theprecipitated intermetallic phases (sigma (s) and chi (?) phases) and to the morphology of the structuralconstituents observed within the material

Scaling of Star Polymers with one to 80 Arms

We present large statistics simulations of 3-dimensional star polymers with up to $f=80$ arms, and with up to 4000 monomers per arm for small values of $f$. They were done for the Domb-Joyce model on the simple cubic lattice. This is a model with soft core exclusion which allows multiple occupancy of sites but punishes each same-site pair of monomers with a Boltzmann factor $v<1$. We use this to allow all arms to be attached at the central site, and we use the `magic' value $v=0.6$ to minimize corrections to scaling. The simulations are made with a very efficient chain growth algorithm with resampling, PERM, modified to allow simultaneous growth of all arms. This allows us to measure not only the swelling (as observed from the center-to-end distances), but also the partition sum. The latter gives very precise estimates of the critical exponents $\gamma_f$. For completeness we made also extensive simulations of linear (unbranched) polymers which give the best estimates for the exponent $\gamma$.Comment: 7 pages, 7 figure

A review of Monte Carlo simulations of polymers with PERM

In this review, we describe applications of the pruned-enriched Rosenbluth method (PERM), a sequential Monte Carlo algorithm with resampling, to various problems in polymer physics. PERM produces samples according to any given prescribed weight distribution, by growing configurations step by step with controlled bias, and correcting "bad" configurations by "population control". The latter is implemented, in contrast to other population based algorithms like e.g. genetic algorithms, by depth-first recursion which avoids storing all members of the population at the same time in computer memory. The problems we discuss all concern single polymers (with one exception), but under various conditions: Homopolymers in good solvents and at the $\Theta$ point, semi-stiff polymers, polymers in confining geometries, stretched polymers undergoing a forced globule-linear transition, star polymers, bottle brushes, lattice animals as a model for randomly branched polymers, DNA melting, and finally -- as the only system at low temperatures, lattice heteropolymers as simple models for protein folding. PERM is for some of these problems the method of choice, but it can also fail. We discuss how to recognize when a result is reliable, and we discuss also some types of bias that can be crucial in guiding the growth into the right directions.Comment: 29 pages, 26 figures, to be published in J. Stat. Phys. (2011

Study about the augmented reality adoption in the maintenance in steelmaking area

In this work a study about the application of the augmented reality in steelmaking area is presented. Augmented reality systems add virtual computer-generated material to the surrounding physical world. The augmented reality systems use see-through headworn displays to overlay graphics and sounds on a person's natural vision and hearing. As the person moves about, the position and orientation of the head is tracked, allowing the overlaid material to remain tied to the physical world. An application and description of prototypes to the training and maintenance of continuous casting machine is described

Pig Iron – Direct Reduced Iron high temperature microstructural interaction

A steelmaking facility (for making products with low residual levels) is forced to use high-quality high-cost prompt scrap. The alternative is to use a combination of the polluted obsolete scrap along with what is generally referred to as clean iron units, such as Pig Iron (PI) or Direct Reduced Iron (DRI). These are raw materials containing little or no residual elements. Indeed, during the usual practice EAF-based producers use DRI, which is produced by the reaction between iron ore and reducing agents, typically from 20 up to 30 % of the charge weight, to improve the metallic charge by diluting impurities introduced by scrap. Due to this, the world’s direct reduction industry continued its solid growth setting a new record each year and it is expected to grow quite considerably over the next few decades. Since its high carbon content, the charge of PI, typically from 5% up to 60%, results in a significant increase of the carbon content of the resultant steel. Its consequent decarburization, if adequate, allows a maximum recovery energy from CO, since it is an exothermic reaction. This could result as a very important source of chemical energy within the EAF, granting power savings. Moreover, due to the still oxidized 7% volume of DRI, the carburizing environment generated by PI would grant beneficial effects on DRI yield. After the characterization of both pig iron and DRI, testing trials have been performed in order to evaluate their interaction at high temperatures, simulating their behavior within EAF

STUDY ON YIELD OF HOT BRIQUETTED IRON CHARGE INSIDE ELECTRIC ARC FURNACE

The EAF steel production process currently provides very stringent limits on emissions but the environmental impact appears to be minor, if compared to blast furnace cycle. The electric arc furnace operates as a batch process. The scrap yard operators classify and prepare buckets of scrap according to the chemical and production needs of the Electric Arc Furnace. The study about the preparation of the charge bucket is becoming an important operation, in order to ensure proper melt chemistry and good melting conditions. Actually, most of charging operations are based on buckets, where different kind of scrap is charged inside. The addition of high quantity of shredded scrap can increase the concentration of unwanted alloy elements inside the metal bath. The use of HBI can be considered a good operational practice both for increasing the melt yield and for decreasing the high quality scrap fraction used in the EAF cycle. This implies a decrease of the environmental impact, without affecting the production and it avoids the high concentration of undesired elements (e.g. Sulphur, Copper, Tin), due to the charge of low quality scrap