1,198 research outputs found
3D modelling of geomaterials accounting for an unconventional plasticity approach
The coupled hydro-mechanical state in geomaterials undergoing plasticity phenomena is here evaluated by means of the subloading surface model . The most important feature of this theory is the abolition of the distinction between the elastic and plastic domain, as it happens in conventional elastoplastic models. This means that plastic deformations are generated whenever there is a change in stress and a smoother elasto-plastic transition is produced. The subloading surface takes the role of a loading surface which always passes through the current stress point Ï and keeps a shape similar to that of the normal yield surface
and a similar orientation with respect to the origin of stress space. Additionally, the model allows for giving a smooth response in a smooth monotonic loading process and the stress is automatically drawn back to the normal-yield surface even if it goes out from that surface, leading to a more stable and robust calculation even for large loading steps. The plasticity algorithm has been implemented within the FE PLASCON3D research code, coupling hydro-(thermo)-mechanical fields within a saturated porous medium (locally partially saturated) subjected to external loads. Applications to soils allow e.g. for assessing subsidence evolution at regional scale
Measuring performances of linux hypervisors
Virtualization is a now proven software technology that is rapidly transforming the IT landscape and fundamentally changing the way people make computations and implement services. Recently, all major software producers (e.g.,
Microsoft and RedHat) developed or acquired virtualization technologies. Our institute (http://www.cnaf.infn.it) is a Tier1 for experiments carried on at the Large Hadron Collider at CERN (http://lhc.web.cern.ch/lhc/) and is experiencing several benefits from virtualization technologies, like improving fault tolerance, providing efficient hardware resource usage and increasing security. Currently, the virtualization solution we adopted is xen, which is well supported by the Scientific Linux distribution, widely used by the High-Energy Physics (HEP) community. Since Scientific Linux is based on RedHat ES, we felt the need to investigate performances and usability differences with the new kvm technology, recently acquired
by RedHat. The case study of this work is the Tier2 site for the LHCb experiment hosted at our institute; all major grid elements for this Tier2 run on xen virtual machines smoothly. We will investigate the impact on performance and stability that a migration to kvm would entail on the Tier2 site, as well as the effort required by a system administrator to deploy the migration
Subloading surface plasticity model algorithm for 3D subsidence analyses above gas reservoirs
The coupled hydro-mechanical state in soils coming from
consolidation/subsidence processes and undergoing plasticity phenomena is here evaluated by
means of the subloading surface model. The most important feature of this theory is the
abolition of the distinction between the elastic and plastic domain, as it happens in
conventional elastoplastic models. This means that plastic deformations are generated
whenever there is a change in stress and a smoother elasto-plastic transition is produced.The
plasticity algorithm has been implemented in the PLASCON3D FE code (on the basis of a
previous 2D version), coupling hydro-(thermo)-mechanical fields within a saturated porous
medium (locally partially saturated at reservoir level due to the possible presence of a gas
phase) subjected to external loads and water/gas withdrawals from deep layers
(aquifers/reservoirs). The 3D model has been first calibrated and validated against examples
taken from literature, and then subsidence analyses at regional scales due to gas extractions
have been developed to predict the evolution of settlements and pore pressure in soils for
long-term scenarios
Feno e silagem como volumoso para confinamento de bovinos de corte.
bitstream/item/67190/1/CT-49-2001.pd
Effect of aggregates and ITZ on visco-damaged response of concrete at the meso scale level
A deep knowledge on the behavior of concrete materials at the mesoscale level
requires, as a fundamental aspect, to characterize aggregates and specifically, their thermal
properties if fire hazards (e.g. spalling) are accounted for. The assessment of aggregates
performance (and, correspondingly, concrete materials made of aggregates, cement paste and
ITZ âinterfacial transition zone-) is crucial for defining a realistic structural response as well
as damage scenarios. Particularly, it is assumed that concrete creep is associated to cement
paste only and that creep obeys to the B3 model proposed by Bazant and Baweja since it
shows good compatibility with experimental results and it is properly justified theoretically.
The fully coupled 3D F.E. code NEWCON3D has been adopted to perform meso-scale
analyses of concrete characterized by aggregates of different types and different thermal
conductivities. Damage maps allows for defining an appropriate concrete mixture for
responding to spalling and for characterizing the coupled behaviour of ITZ as well
Numerical modelling of ellipsoidal inclusions
Within the framework of numerical algorithms for the threedimensional
random packing of granular materials this work presents an
innovative formulation for polydispersed ellipsoidal particles, including
an overlapping detection algorithm for an optimized simulation of the
mesostructure of geomaterials, particularly concrete.
Granular composite cement-based materials can be so reconstructed with
adequate precision in terms of grain size distribution. Specifically, the
algorithm performance towards the assumed inclusion shape (ellipsoidal or
spheric) and degree of regularity (round or irregular) is here discussed.
Examples on real grading curves prove that this approach is effective.
The advantages of the proposed method for computational mechanics
purposes are also disclosed when properly interfaced with visualization
CAD (Computer Aided Design) tools
Celecoxib inhibits proliferation and survival of chronic myelogeous leukemia (CML) cells via AMPK-dependent regulation of ÎČ-catenin and mTORC1/2.
CML is effectively treated with tyrosine kinase inhibitors (TKIs). However, the efficacy of these drugs is confined to the chronic phase of the disease and development of resistance to TKIs remains a pressing issue. The anti-inflammatory COX2 inhibitor celecoxib has been utilized as anti-tumour drug due to its anti-proliferative activity. However, its effects in hematological malignancies, in particular CML, have not been investigated yet. Thus, we tested biological effects and mechanisms of action of celecoxib in Philadelphia-positive (Ph+) CML and ALL cells.We show here that celecoxib suppresses the growth of Ph+ cell lines by increasing G1-phase and apoptotic cells and reducing S- and G2-phase cells. These effects were independent of COX2 inhibition but required the rapid activation of AMP-activated protein kinase (AMPK) and the consequent inhibition mTORC1 and 2. Treatment with celecoxib also restored GSK3ÎČ function and led to down-regulation of ÎČ-catenin activity through transcriptional and post-translational mechanisms, two effects likely to contribute to Ph+ cell growth suppression by celecoxib.Celecoxib inhibited colony formation of TKI-resistant Ph+ cell lines including those with the T315I BCR-ABL mutation and acted synergistically with imatinib in suppressing colony formation of TKI-sensitive Ph+ cell lines. Finally, it suppressed colony formation of CD34+ cells from CML patients, while sparing most CD34+ progenitors from healthy donors, and induced apoptosis of primary Ph+ ALL cells.Together, these findings indicate that celecoxib may serve as a COX2-independent lead compound to simultaneously target the mTOR and ÎČ-catenin pathways, key players in the resistance of CML stem cells to TKIs
Investigation of stress-strain behaviour in concrete materials through the aid of 3D advanced measurement techniques
This work deals with the investigation of the mechanical behaviour of cementitious materials, following a mesoscopic approach where aggregates, grains and cement paste are explicitly represented, and the strict comparison between the numerical results and the experimental results from uniaxial tests is carried out.
For this purpose, solid models are created with the support of advanced techniques of measurement and detection, such as laser scanners or computer tomography (CT). The 3D laser- scanning technique in fact allows to acquire the exact shape of the grains added to the concrete mix design while, through the adoption of an ad-hoc random distribution algorithm, a realistic disposition of the inclusions is guaranteed. The industrial CT instead, is able to reproduce exactly the tested specimens; the geometry of the inclusions and their placement.
Once reconstructed realistic geometries for the models, the mechanical behaviour of concrete under uniaxial compression tests is numerically studied. A specific constitutive behaviour is assigned to each component; an elasto-plastic law with damage is assumed for the cement matrix while the aggregates are conceived to behave elastically.
The implemented damage-plasticity model consists in the combination of the non-associated plasticity model by Men\ue9trey-Willam, where the yield surface is described in function of the second and the third invariant of the deviatoric stress tensor and the scalar isotropic damage model by Mazars.
Comparisons between numerical and experimental results fairly prove the correctness of the suggested approach
Geometrical reconstruction of concrete materials through the aid of advanced measurement techniques and studies of their mechanical behavior
New Trends in Designing Parabolic trough Solar Concentrators and Heat Storage Concrete Systems in Solar Power Plants
Energy availability has always been an essential component of human civilization and the energetic consumption is directly linked to the produced wealth. In many depressed countries the level of solar radiation is considerably high and it could be the primary energy source under conditions that low cost, simple-to-be-used technologies are employed. Then, it is responsibility of the most advanced countries to develop new equipments to allow this progress for taking place. A large part of the energetic forecast, based on economic projection for the next decades, ensure us that fossil fuel supplies will be largely enough to cover the demand. The predicted and consistent increase in the energetic demand will be more and more covered by a larger use of fossil fuels, without great technology innovations. A series of worrying consequences are involved in the above scenario: important climatic changes are linked to strong CO2 emissions; sustainable development is hindered by some problems linked to certainty of oil and natural gas supply; problems of global poverty are not solved but amplified by the unavoidable increase in fossil fuel prices caused by an increase in demand. These negative aspects can be avoided only if a really innovative and more acceptable technology will be available in the next decades at a suitable level to impress a substantial effect on the society. Solar energy is the ideal candidate to break this vicious circle between economic progress and consequent greenhouse effect. The low penetration on the market shown today by the existent renewable technologies, solar energy included, is explained by well-known reasons: the still high costs of the produced energy and the \u201cdiscontinuity\u201d of both solar and wind energies. These limitations must be removed in reasonable short times, with the support of innovative technologies, in view of such an urgent scenario. On this purpose ENEA, on the basis of the Italian law n. 388/2000, has started an R&D program addressed to the development of CSP (Concentrated Solar Power) systems able to take advantage of solar energy as heat source at high temperature. One of the most relevant objectives of this research program (Rubbia, 2001) is the study of CSP systems operating in the field of medium temperatures (about 550\ub0C), directed towards the development of a new and low-cost technology to concentrate the direct radiation and efficiently convert solar energy into high temperature heat; another aspect is focused on the production of hydrogen by means of thermo-chemical processes at temperatures above 800\ub0C.
As well as cost reductions, the current innovative ENEA conception aims to introduce a set of innovations, concerning: i) The parabolic-trough solar collector: an innovative design to reduce production costs, installation and maintenance and to improve thermal efficiency is defined in collaboration with some Italian industries; ii) The heat transfer fluid: the synthetic hydrocarbon oil, which is flammable, expensive and unusable beyond 400\ub0C, is substituted by a mixture of molten salts (sodium and potassium nitrate), widely used in the industrial field and chemically stable up to 600\ub0C; iii) The thermal storage (TES): it allows for the storage of solar energy, which is then used when energy is not directly available from the sun (night and covered sky) (Pilkington, 2000). After some years of R&D activities, ENEA has built an experimental facility (defined within the Italian context as PCS, \u201cProva Collettori Solari\u201d) at the Research Centre of Casaccia in Rome (ENEA, 2003), which incorporates the main proposed innovative elements. The next step is to test these innovations at full scale by means of a demonstration plant, as envisioned by the \u201cArchimede\u201d ENEA/ENEL Project in Sicily. Such a project is designed to upgrade the ENEL thermo-electrical combined-cycle power plant by about 5 MW, using solar thermal energy from concentrating parabolic-trough collectors.
Particularly, the Chapter will focus on points i) and iii) above:
- loads, actions, and more generally, the whole design procedure for steel components of parabolic-trough solar concentrators will be considered in agreement with the Limit State method, as well as a new approach will be critically and carefully proposed to use this method in designing and testing \u201cspecial structures\u201d such as the one considered here;
- concrete tanks durability under prolonged thermal loads and temperature variations will be estimated by means of an upgraded F.E. coupled model for heat and mass transport (plus mechanical balance). The presence of a surrounding soil volume will be additionally accounted for to evaluate environmental risk scenarios.
Specific technological innovations will be considered, such as:
-higher structural safety related to the reduced settlements coming from the chosen shape of the tank (a below-grade cone shape storage);
- employment of HPC containment structures and foundations characterized by lower costs with respect to stainless steel structures;
- substitution of highly expensive corrugated steel liners with plane liners taking advantage of the geometric compensation of thermal dilations due to the conical shape of the tank;
- possibility of employing freezing passive systems for the concrete basement made of HPC, able to sustain temperature levels higher than those for OPC;
- fewer problems when the tank is located on low-strength soils
- âŠ