1,721,107 research outputs found
Small ribosomal subunits associate with nuclear myosin and actin in transit to the nuclear pores.
No full textWe have followed at high resolution theribosomal protein S6 entering the nucleus of HeLacells, stopping in some (not all) interchromatin granulesclusters and reaching, via Cajal bodies, the nucleolus.There, S6 is assembled with other proteins andrRNA into small ribosomal subunit (SSU), released inthe nucleoplasm, and exported through the nuclearpores. We show for the first time the spatial associationof nuclear myosin I (NMI) and actin with the SSUalready at the nucleolar periphery to the nuclear pore.A blockade of NMI or actin induces an upstreamaccumulation of the S6 protein en route to the nucleolus,and a temperature lower than normal influencesRNA export. Our data strongly suggest a functionalrelationship of SSU with NMI and actin. In our hypothesis,an active, myosin-driven movement of the smallribosomal subunit can be responsible for the exportof 10% of SSUs. This hypothesis is supported byultrastructural, immunofluorescence, and biochemicalanalyses. The currently accepted model for the subunitrelease suggests a diffusive, temperature-independentmechanism. However, the advantage of the doublemechanism would assure that the movement of a partof the subunits could be modulated, increased, ordecreased according to the needs of the cell at a specificmoment in the cell cycle.—Cisterna, B., Necchi, D.,Prosperi, E., Biggiogera, M. Small ribosomal subunitsassociate with nuclear myosin and actin in transit to thenuclear pores
Analysis of different reclaimed asphalt pavements to assess the potentiality of RILEM cohesion test
No full textIn the last years, RILEM Technical Committee 237-SIB proposed a new test protocol for reclaimed asphalt pavement (RAP) characterization, the cohesion test, with the goal to facilitate the identification of the most suitable solution for the recycling within new pavement layers. However, this procedure actually allows discriminating between different RAP sources but it does not exactly indicate the effective “activity” of the binder in the RAP.The present paper deals with the analysis of different RAP materials through the RILEM cohesion test. In particular, two “young” RAPs, different in composition and milled immediately after being laid, were aged in the laboratory and tested at different ageing levels. Moreover, an in-site aged RAP was tested as reference, either in neat conditions or after being sprayed with a rejuvenator. The results showed that the actual cohesion test approach, based on the evaluation of the indirect tensile strength (ITS), is not able to distinguish between RAP binders with stiff-brittle behaviour or good residual binding properties (despite the first is an unwanted condition while the second is a desired condition, both of them determine an increase in ITS). Differently, the Cracking Tolerance Index (CT Index) defined by ASTM D8225-19 can emphasize the RAP bitumen ductility and highlight any residual binding and adhesive properties. For this reason, a RILEM cohesion test improvement is proposed by including the CT Index calculation in the analysis
Recycling of reclaimed fibers from end-of-life tires in hot mix asphalt
No full textNowadays, the disposal of end-of-life tires (ELT) is worldwide one of the major concerns for the environment as well as for public health. Crumb rubber and steel wires, the main by-products (in terms of weight) deriving from the ELT processing, can be recycled in several ways. However, the textile fiber, representing about 10% of the waste by weight, is typically not reused and ends up in landfills or incinerators. The present paper deals with the use of reclaimed fibers from ELT in hot mix asphalt (HMA), with the aim to improve its performance. The study included the preliminary characterization of the fiber through microscope observation and Fourier trans form infrared (FTIR) spectroscopy and then the investigation of the mechanical properties of HMA containing ELT fibers, in comparison with an ordinary HMA with no fibers. In particular, indirect tensile strength (ITS), indirect tensile stiffness modulus (ITSM), semi-circular bending (SCB), three point bending (3PB) and indirect tensile fatigue (ITF) tests were carried out. The results showed that the use of ELT fibers does not reflect in a significant improvement in terms of strength and stiffness properties. However, the ELT fibers determine a noticeable increase of the HMA resistance to fatigue, probably related to the ability of the fibers in sewing the micro-crack edges and contrasting the macro-crack opening
Effect of Bitumen Production Process and Mix Heating Temperature on the Rheological Properties of Hot Recycled Mix Asphalt
No full textHeavy traffic loads require the replacement of damaged pavements, so a huge amount of reclaimed asphalt pavement (RAP) material is now available and must be recycled in order to avoid landfill and to achieve both environmental and economic benefits. The most common and profitable solution to reuse RAP is associated with the hot recycling technique, as it allows recovering both solid and binding components of RAP. Several factors influence the performance of hot recycled mix asphalt (HRMA). Among those, this paper focuses on the role played by the origin of the virgin bitumen, i.e. the oil-distillation process, and by the mixing temperature adopted during HRMA production. The objective was to evaluate the rheological properties of mixtures produced using a high amount of RAP (50%), two different rejuvenators, two mixing temperatures (140 degrees C or 170 degrees C) and two neat bitumen types derived from different distillation processes (visbreaker and straight-run). The results showed that the addition of RAP led to an increase in the dynamic modulus and a decrease in the phase angle, while the use of rejuvenators partly tended to rebalance these characteristics. The visbreaker bitumen showed a higher sensitivity to short-term aging than the straight-run, determining higher mix stiffness and lower viscous features. The higher mixing temperature also determined an increase in the complex modulus and a reduction in the phase angle as a result of the higher mobilization of the aged bitumen from the RAP
The Influence of Bitumen Nature and Production Conditions on the Mechanical and Chemical Properties of Asphalt Mixtures Containing Reclaimed Asphalt Pavement
No full text: Several variables influence the performance of hot asphalt mixtures including reclaimed asphalt pavement (RAP). Among these, the virgin bitumen's origin, the mix production temperature and the time the mix is kept at a high temperature between mixing and compaction play a fundamental role but are often neglected. This study aimed to quantify the negative effects associated with the improper choice of these variables. Therefore, their influence on the mechanical (indirect tensile stiffness modulus and strength, Cracking Tolerance Index) and chemical (Fourier Transform Infra-Red spectroscopy) characteristics of asphalt mixtures containing 50% RA were investigated. In particular, two rejuvenators, two types of virgin bitumen (visbreaker and straight-run), two production temperatures (140 °C and 170 °C) and three conditioning times in the oven (30 min, 90 min and 180 min) were analyzed. The results showed interesting findings that allow us to recommend selecting the virgin bitumen type carefully and to avoid excessively stressing the binder during the production of the mix
A review on bitumen aging and rejuvenation chemistry: Processes, materials and analyses
No full textDuring the last decades, extensive research has been carried out on using reclaimed asphalt pavement (RAP) material in the production of hot recycled mix asphalt. Unfortunately, the aged, stiff, and brittle binder in the RAP typically increases the mixture stiffness and can therefore cause fatigue and low-temperature damages. In the scientific literature, there are many studies concerning the aging and rejuvenation of bitumen, but there is a lack of up-to-date reviews that bring them together, especially those facing the phenomena from a chemical point of view. In this paper, a recap of the chemical aspects of virgin, aged, and rejuvenated bitumen is proposed in order to provide a useful summary of the state of the art, with the aim of both encouraging the use of an increasing quantity of RAP in hot mix asphalt and trying to give indications for further research
Evaluation of the rejuvenating effect of different additives on bituminous mixtures including hot-recycled RA as a function of the production temperature
No full textThe increasing bitumen cost, the growth of the traffic loads and the need to find more sustainable paving practices are forcing agencies to identify new ways to maximise the re-use of Reclaimed Asphalt (RA). If RA could theoretically be 100% recycled, its content in bituminous layers is still restricted in most countries mainly due to legislation limitations and technical issues. In particular, the stiffer and more brittle mixes, usually resulting from RA addition, have raised concerns about the long-term properties of the pavement. In order to further increase the amount of usable RA, rejuvenating additives can be included in the mixtures. The paper deals with the analysis of seven additives, with particular focus on their ability in mitigating the effects of the presence of RA in the mix as a function of production temperature. In particular, FTIR analysis was carried out on the additives to evaluate the differences in their chemical composition. Moreover, the mechanical properties of the mixtures including 50% RA and produced at 140°C or 170°C were investigated. The results showed the reduction of the mixing temperature from 170°C to 140°C determined a slight increase of the air voids content but also allowed a significant decrease of mix stiffness and strength with a contemporary increase of ductility. The mixtures containing 50% RA and the additive had an intermediate behaviour between the mix without RA and the mix with 50% RA and no additive. The additives investigated in this research showed, in most cases, different chemical structures, which reflected in their rejuvenating performance. The comparative analysis of the results from mechanical and chemical tests provided remarkable information about the characteristic properties of a good rejuvenator, particularly the presence of esters and the high flashpoint
Flow cytometric analysis of DNA sensitivity to nuclease S1 in UVC-irradiated human fibroblasts
No full textThe sensitivity of human fibroblast DNA towards the activity of nuclease S1 was investigated in situ after irradiation of the cells with UVC light. DNA digestion was assessed using flow cytometry by staining the nuclease-resistant DNA fraction with the specific fluorochrome propidium iodide (PI). The results showed a non-linear dependence of DNA digestion on the UVC irradiation dose between 0 and 20 J m-2. About 70% of the UVC-induced DNA sensitivity to nuclease S1 was lost after 30 min of repair. These results suggest that flow cytometry may be useful for assessing the heterogeneity of cell response to UV damage
Influence of the Hot-Mix Asphalt Production Temperature on the Effectiveness of the Reclaimed Asphalt Rejuvenation Process
No full textHot recycling of reclaimed asphalt pavement (RAP) into new hot-mix asphalt (HMA) is a complex process that must be precisely calibrated in the asphalt plants. In particular, temperature is a key parameter that, if inadequately set, can affect the final mix performance as it influences the RAP binder mobilization rate and the severity of bitumen short-term aging. The present paper aims at evaluating the effect of HMA production temperature on the behavior of mixtures including 50% of RAP and two types of rejuvenating agents. In particular, volumetric, mechanical, chemical, and rheological properties of the mixes and binder-aggregate adhesion have been investigated on the HMA produced in the laboratory at 140 °C or 170 °C. The results showed that the adoption of a lower production temperature did not significantly influence the air voids content in the mix, but determined a less stiff, brittle and cracking-prone behavior. Moreover, the decrease of the HMA production temperature was profitable for the increase of bitumen-aggregate adhesion
- …
