Theoretical-computational Approach Research Articles

Designing an Optimal Ion Adsorber at the Nanoscale: The Unusual Nucleation of AgNP/Co2+–Ni2+ Binary Mixtures

Selective removal of heavy metals from water is a complex topic. We present a theoretical–computational approach, supported by experimental evidences, to design a functionalized nanomaterial that i...

Thermal-hydraulic optimisation of the DEMO divertor cassette body cooling circuit equipped with a liner

Within the framework of the Work Package DIV 1 - “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by University of Palermo and ENEA to investigate the thermal-hydraulic performances of the DEMO divertor cassette cooling system. The research activity has been focused onto the most recent design of the Cassette Body (CB) cooling circuit equipped with a Liner, whose main function is to protect the underlying vacuum pump hole from the radiation arising from the plasma. The research campaign has been carried out following a theoretical-computational approach based on the Finite Volume Method and adopting the commercial Computational Fluid-Dynamic code ANSYS-CFX.The CB thermal-hydraulic performances have been assessed in terms of coolant and structure temperature, coolant overall pressure drop, flow velocity distribution and mass flow rate fed to the Liner cooling circuit, mainly in order to check coolant aptitude to provide a uniform and effective cooling to both CB and Liner structures.The outcomes of the study have shown some major criticalities, mainly in terms of water coolant vaporization as well as non-symmetric coolant distribution between the two Liner inlets. As a consequence, the following potential solutions have been successfully explored in order to allow the CB to safely operate while complying with its design constraints:•revising the CB design layout in order to increase the coolant mass flow rate fed to Liner;•increasing coolant inlet pressure to rise water saturation temperature and, hence, its margin against vaporization;•increasing coolant mass flow rate to reduce its overall thermal rise.The main results and the achieved optimized model are herewith described and critically discussed.

Challenging the Limits of Nanoscale Simulations: Modeling Joule Effect and Piezoresistivity in Carbon Nanotubes Enforced Polymers

The unique electric properties of carbon nanotubes (CNT)1, have opened new scientific and technological fields2 based on the investigation and optimization of CNT filled polymers3. CNTs, when added to polymer matrices (such as epoxy, bitumen, concrete) make them conductive once they overcome a specific (so-called percolative) concentration4. When this percolative threshold is reached, a CNT electric circuit is formed and the composite materials become conductors. Based on such peculiar behavior, smart materials able to monitor their own conditions could be realized and employed for several applications ranging from automotive and aeronautics to civil engineering infrastructures. The main goal of this work is to understand, through a theoretical-computational approach, the electric behavior of CNT based composites5 and help in improving their performances. In particular, the Joule effect, i.e. the heat dissipation of the conductive CNTs is simulated. The CNTs Joule effect can be employed to build smart materials able to have specific properties (i.e. self-deicing under certain temperatures) or to repair their own cracks (self-healing). The piezoresistivity, i.e. the change in the electric resistance of the CNTs due to an applied strain or stress, is also investigated. This feature allows these composites to be sensitive to an external stress or damage (self-sensing), in this way an immediate and efficient repair can be performed. A computational protocol to understand the behavior, the sensitivity and the limits of such materials at the nanoscale is proposed. This will improve the materials performances and efficiency on larger scales. For the first time, a computational modeling strategy along with preliminary results is built and presented to simulate at the nanoscale the Joule effect and the piezoresistivity of CNTs filled polymers. Obtaining a widely applicable strategy to model electric properties of CNTs and characteristic behavior trends of such materials is the final goal of this project. [1] Iijima, Nature, 1991, 354, 56-58. [2] W. Nan, Y. Shen, J. Ma, Annu.Rev.Mater.Res., 2010, 40, 131-151. [3] M. Ajayan, O. Stephan, C. Colliex, D. Trauth, Science, 1994, 265, 1212-1214. [4] M. Mutiso, K. I. Winey, Prog. Polym. Sci., 2015, 40, 63.84. [5] Zhao, M. Byshkin, Y. Cong, T. Kawakatsu, L. Guadagno, A. De Nicola, N. Yu, G. Milano, B. Dong, Nanoscale, 2016, 8, 15538-15552.

Computational thermofluid-dynamic analysis of DEMO divertor cassette body cooling circuit

Within the framework of the Work Package Divertor, Subproject: Cassette Design and Integration (WPDIV-Cassette) of the EUROfusion action, a research campaign has been jointly carried out by ENEA and University of Palermo to investigate the thermal-hydraulic performances of the DEMO divertor cassette cooling system.The research activity has been carried out following a theoretical-computational approach based on the finite volume method and adopting a qualified Computational Fluid-Dynamic (CFD) code.Fully-coupled fluid-structure CFD analyses have been carried out for the recently-revised cassette body cooling circuit under nominal steady state conditions, imposing a non-uniform spatial distribution of nuclear-deposited heat power volumetric density drawn from the most recent neutron transport analysis. The pertaining thermal-hydraulic performances have been assessed in terms of coolant flow velocity and total pressure distributions as well as of coolant and structure temperature distributions to check whether they comply with the corresponding prescribed limits. Results obtained are reported and critically discussed.

Dynamics and structural stability effects of germline PTEN mutations associated with cancer versus autism phenotypes

Individuals with germline mutations in the tumor suppressor gene phosphatase and tensin homolog (PTEN), irrespective of clinical presentation, are diagnosed with PTEN hamartoma tumor syndrome (PHTS). PHTS confers a high risk of breast, thyroid, and other cancers or autism spectrum disorder (ASD) with macrocephaly. It remains unclear why mutations in one gene can lead to seemingly disparate phenotypes. Thus, we sought to identify differences in ASD vs. cancer-associated germline PTEN missense mutations by investigating putative structural effects induced by each mutation. We utilized a theoretical computational approach combining in silico structural analysis and molecular dynamics (MD) to interrogate 17 selected mutations from our patient population: six mutations were observed in patients with ASD (only), six mutations in patients with PHTS-associated cancer (only), four mutations shared across both phenotypes, and one mutation with both ASD and cancer. We demonstrate structural stability changes where all six cancer-associated mutations showed a global decrease in structural stability and increased dynamics across the domain interface with a proclivity to unfold, mediating a closed (inactive) active site. In contrast, five of the six ASD-associated mutations showed localized destabilization that contribute to the partial opening of the active site. Our results lend insight into distinctive structural effects of germline PTEN mutations associated with PTEN-ASD vs. those associated with PTEN-cancer, potentially aiding in identification of the shared and separate molecular features that contribute to autism or cancer, thus, providing a deeper understanding of genotype–phenotype relationships for germline PTEN mutations.

Thermal-hydraulic behaviour of the DEMO divertor plasma facing components cooling circuit

Within the framework of the Work Package DIV 1 – “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by ENEA and University of Palermo to investigate the thermal-hydraulic performances of the DEMO divertor cassette cooling system.A comparative evaluation study has been performed considering three different options for the cooling circuit layout of the divertor Plasma Facing Components (PFCs). The potential improvement in the thermal-hydraulic performance of the cooling system, to be achieved by modifying cooling circuit layout, has been also assessed and discussed in terms of optimization strategy. The research activity has been carried out following a theoretical-computational approach based on the finite volume method and adopting a qualified Computational Fluid-Dynamic (CFD) code. Results obtained are reported and critically discussed.

Recent Progress in Computational Materials Science for Semiconductor Epitaxial Growth

Recent progress in computational materials science in the area of semiconductor epitaxial growth is reviewed. Reliable prediction can now be made for a wide range of problems, such as surface reconstructions, adsorption-desorption behavior, and growth processes at realistic growth conditions, using our ab initio-based chemical potential approach incorporating temperature and beam equivalent pressure. Applications are examined by investigating the novel behavior during the hetero-epitaxial growth of InAs on GaAs including strain relaxation and resultant growth mode depending growth orientations such as (111)A and (001). Moreover, nanowire formation is also exemplified for adsorption-desorption behaviors of InP nanowire facets during selective-area growth. An overview of these issues is provided and the latest achievement are presented to illustrate the capability of the theoretical-computational approach by comparing experimental results. These successful applications lead to future prospects for the computational materials design in the fabrication of epitaxially grown semiconductor materials.

Analysis of steady state thermal-hydraulic behaviour of the DEMO divertor cassette body cooling circuit

Within the framework of the Work Package DIV 1 – “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by ENEA and University of Palermo to investigate the thermal-hydraulic performances of the DEMO divertor cassette cooling system. A comparative evaluation study has been performed considering the two different options under consideration for the divertor cassette body coolant, namely subcooled pressurized water and helium.The research activity has been carried out following a theoretical-computational approach based on the finite volume method and adopting a qualified Computational Fluid-Dynamic (CFD) code.CFD analyses have been carried out for the considered options of cassette body cooling circuit under nominal steady state conditions and the pertaining thermal-hydraulic performances have been assessed in terms of overall coolant thermal rise, coolant total pressure drop, flow velocity and pumping power, to check whether they comply with the corresponding limits. Results obtained are reported and critically discussed.

Quantum Optimal Control for Particles at Cross-Section in Nucleus

In this work, a novel concept abstract surface (cross-section at nucleus) is proposed firstly. Quantum optimal control is interested in taking particles at Yukawa interaction of cross-section σ in the nucleus as target for controlling by external force. In the nucleus, as intersecting surface full of particles can be considered for applying control theory and numerical simulation using a stable semi-discrete algorithm. Theoretical investigation, computational approach and experimental demonstration had accomplished.

Computation of Dielectric Response in Molecular Solids for High Capacitance Organic Dielectrics.

The dielectric response of a material is central to numerous processes spanning the fields of chemistry, materials science, biology, and physics. Despite this broad importance across these disciplines, describing the dielectric environment of a molecular system at the level of first-principles theory and computation remains a great challenge and is of importance to understand the behavior of existing systems as well as to guide the design and synthetic realization of new ones. Furthermore, with recent advances in molecular electronics, nanotechnology, and molecular biology, it has become necessary to predict the dielectric properties of molecular systems that are often difficult or impossible to measure experimentally. In these scenarios, it is would be highly desirable to be able to determine dielectric response through efficient, accurate, and chemically informative calculations. A good example of where theoretical modeling of dielectric response would be valuable is in the development of high-capacitance organic gate dielectrics for unconventional electronics such as those that could be fabricated by high-throughput printing techniques. Gate dielectrics are fundamental components of all transistor-based logic circuitry, and the combination high dielectric constant and nanoscopic thickness (i.e., high capacitance) is essential to achieving high switching speeds and low power consumption. Molecule-based dielectrics offer the promise of cheap, flexible, and mass producible electronics when used in conjunction with unconventional organic or inorganic semiconducting materials to fabricate organic field effect transistors (OFETs). The molecular dielectrics developed to date typically have limited dielectric response, which results in low capacitances, translating into poor performance of the resulting OFETs. Furthermore, the development of better performing dielectric materials has been hindered by the current highly empirical and labor-intensive pace of synthetic progress. An accurate and efficient theoretical computational approach could drastically decrease this time by screening potential dielectric materials and providing reliable design rules for future molecular dielectrics. Until recently, accurate calculation of dielectric responses in molecular materials was difficult and highly approximate. Most previous modeling efforts relied on classical formalisms to relate molecular polarizability to macroscopic dielectric properties. These efforts often vastly overestimated polarizability in the subject materials and ignored crucial material properties that can affect dielectric response. Recent advances in first-principles calculations via density functional theory (DFT) with periodic boundary conditions have allowed accurate computation of dielectric properties in molecular materials. In this Account, we outline the methodology used to calculate dielectric properties of molecular materials. We demonstrate the validity of this approach on model systems, capturing the frequency dependence of the dielectric response and achieving quantitative accuracy compared with experiment. This method is then used as a guide to new high-capacitance molecular dielectrics by determining what materials and chemical properties are important in maximizing dielectric response in self-assembled monolayers (SAMs). It will be seen that this technique is a powerful tool for understanding and designing new molecular dielectric systems, the properties of which are fundamental to many scientific areas.

Theoretical-computational characterization of the temperature-dependent folding thermodynamics of a [formula omitted]-hairpin peptide

A theoretical-computational approach is presented to characterize the temperature-dependent thermodynamics of protein folding. Making use of the Quasi-Gaussian Entropy (QGE) theory and temperature exchanged molecular dynamics (TREMD) simulations, a complete picture of the folding thermodynamics can be obtained. The strategy is applied to analyze the folding thermodynamics of a β-hairpin peptide, Peptide 1, the folding process of which was experimentally characterized by means of infrared spectroscopy. The results provided by the approach here presented very well reproduce the experimental results, showing that the methodology can be successfully utilized to investigate the thermodynamics of folding processes in a wide temperature range.

How to Properly Measure a Current-Voltage Relation?-Interpolation vs. Ramp Methods Applied to Studies of GABAA Receptors.

The relation between current and voltage, I-V relation, is central to functional analysis of membrane ion channels. A commonly used method, since the introduction of the voltage-clamp technique, to establish the I-V relation depends on the interpolation of current amplitudes recorded at different steady voltages. By a theoretical computational approach as well as by experimental recordings from GABAA-receptor mediated currents in mammalian central neurons, we here show that this interpolation method may give reversal potentials and conductances that do not reflect the properties of the channels studied under conditions when ion flux may give rise to concentration changes. Therefore, changes in ion concentrations may remain undetected and conclusions on changes in conductance, such as during desensitization, may be mistaken. In contrast, an alternative experimental approach, using rapid voltage ramps, enable I-V relations that much better reflect the properties of the studied ion channels.

Analysis of the steady state hydraulic behaviour of the ITER blanket cooling system

The blanket system is the ITER reactor component devoted to providing a physical boundary for plasma transients and contributing to thermal and nuclear shielding of vacuum vessel, magnets and external components. It is expected to be subjected to significant heat loads under nominal conditions and its cooling system has to ensure an adequate cooling, preventing any risk of critical heat flux occurrence while complying with pressure drop limits.At the University of Palermo a study has been performed, in cooperation with the ITER Organization, to investigate the steady state hydraulic behaviour of the ITER blanket standard sector cooling system. A theoretical–computational approach based on the finite volume method has been followed, adopting the RELAP5 system code. Finite volume models of the most critical blanket cooling circuits have been set-up, realistically simulating the coolant flow domain. The steady state hydraulic behaviour of each cooling circuit has been investigated, determining its hydraulic characteristic function and assessing the spatial distribution of coolant mass flow rates, velocities and pressure drops under reference nominal conditions.Results obtained have indicated that the investigated cooling circuits are able to provide an effective cooling to blanket modules, generally meeting ITER requirements in term of pressure drop and velocity distribution, except for a couple of circuits that are being revised.

A computational procedure for the investigation of whipping effect on ITER High Energy Piping and its application to the ITER divertor primary heat transfer system

The Tokamak Cooling Water System of nuclear facility has the function to remove heat from plasma facing components maintaining coolant temperatures, pressures and flow rates as required and, depending on thermal-hydraulic requirements, its systems are defined as High Energy Piping (HEP) because they contain fluids, such as water or steam, at a pressure greater than or equal to 2.0MPa and/or at a temperature greater than or equal to 100°C, or even gas at pressure above the atmospheric one. The French standards contemplate the need to consider the whipping effect on HEP design. This effect happens when, after a double ended guillotine break, the reaction force could create a displacement of the piping which might affect adjacent components.A research campaign has been performed, in cooperation by ITER Organization and University of Palermo, to outline the procedure to check whether whipping effect might occur and assess its potential damage effects so to allow their mitigation. This procedure is based on the guidelines issued by U.S. Nuclear Regulatory Commission. The proposed procedure has been applied to the analysis of the whipping effect of divertor primary heat transfer system HEP, using a theoretical–computational approach based on the finite element method.

Analysis of the thermo-mechanical behaviour of the DEMO Water-Cooled Lithium Lead breeding blanket module under normal operation steady state conditions

Within the framework of DEMO R&D activities, a research cooperation has been launched between ENEA, the University of Palermo and CEA to investigate the thermo-mechanical behaviour of the outboard equatorial module of the DEMO1 Water-Cooled Lithium Lead (WCLL) blanket under normal operation steady state scenario. The research campaign has been carried out following a theoretical–computational approach based on the Finite Element Method (FEM) and adopting a qualified commercial FEM code. In particular, two different 3D FEM models (Model 1 and Model 2), reproducing respectively the central and the lateral poloidal–radial slices of the WCLL blanket module, have been set up. A particular attention has been paid to the modelling of water flow domain, within both the segment box channels and the breeder zone tubes, to simulate realistically the coolant-box thermal coupling. Results obtained are herewith reported and critically discussed.

Numerical simulation of the transient thermal-hydraulic behaviour of the ITER blanket cooling system under the draining operational procedure

Within the framework of the research and development activities supported by the ITER Organization on the blanket system issues, an intense analysis campaign has been performed at the University of Palermo with the aim to investigate the thermal-hydraulic behaviour of the cooling system of a standard 20° sector of ITER blanket during the draining transient operational procedure.The analysis has been carried out following a theoretical-computational approach based on the finite volume method and adopting the RELAP5 system code. In a first phase, attention has been focused on the development and validation of the finite volume models of the cooling circuits of the most demanding modules belonging to the standard blanket sector. In later phase, attention has been put to the numerical simulation of the thermal-hydraulic transient behaviour of each cooling circuit during the draining operational procedure. The draining procedure efficiency has been assessed in terms of both transient duration and residual amount of coolant inside the circuit, observing that the former ranges typically between 40 and 120s and the latter reaches at most ∼8kg, in the case of the cooling circuit of twinned modules #6–7. Potential variations to operational parameters and/or to circuit lay-out have been proposed and investigated to optimize the circuit draining performances. In this paper, the set-up of the finite volume models is briefly described and the key results are summarized and critically discussed.

Theoretical–computational modelling of the electric field effects on protein unfolding thermodynamics

In this paper we present a general theoretical–computational approach to model the protein unfolding thermodynamics response to intense electric fields.

Assessment of the Thermo-mechanical Performances of a DEMO Water-Cooled Liquid Metal Blanket Module

Within the framework of DEMO R&D activities, a research cooperation has been launched between ENEA-Brasimone, CEA-Saclay and the University of Palermo to investigate the thermo-mechanical behaviour of the outboard equatorial module of the DEMO1 Water-Cooled Lithium Lead (WCLL) blanket, both under normal operation and over-pressurization steady state scenarios. The research campaign has been carried out following a theoretical-computational approach based on the finite element method (FEM) and adopting a qualified commercial FEM code. In particular, two different three-dimensional FEM models of the WCLL blanket module have been set-up to be used for normal operation and over-pressurization analysis, respectively. The former reproduces realistically the WCLL blanket module central poloidal–radial region, including one breeder cell in the toroidal direction and all the five cells in the radial one. The latter simulates the entire module segment box, without including the breeder and its cooling tubes. Two set of uncoupled steady state thermo-mechanical analyses have been carried out with reference to the investigated loading scenarios. In particular, under normal operation scenario (level A) the module has been supposed to undergo both 15.5 MPa coolant pressure on its cooling channels walls and thermal deformations due to the flat-top plasma operational state thermal field, while under over-pressurization scenario (level D) it has been assumed to experience 15.5 MPa coolant pressure on its segment box internal walls while operating at normal operation thermal level. Results obtained are presented and critically discussed according to the SDC IC code.

Modeling of frost build-up on parallel-plate channels under supersaturated air-frost interface conditions

Abstract The present work is aimed at studying, by means of a theoretical-computational approach, the frost formation on parallel-plate channels. A mathematical model to predict the frost growth and densification under supersaturated air-frost interface conditions was devised through the first-principles of mass, energy and momentum conservation. A semi-empirical correlation was additionally adopted to predict the time evolution of the frost porosity. The model predictions were compared with experimental data obtained in-house, when it was found that the model predictions for the frost thickness showed satisfactory agreement with the experimental data, with most errors falling within the uncertainties thresholds.

Inclusion of cybotactic effect in the theoretical modeling of absorption spectra of liquid-state systems with perturbed matrix method and molecular dynamics simulations: the UV–Vis absorption spectrum of para-nitroaniline as a case study

In this study, we present an extension of the theoretical–computational approach developed in our group and based on molecular dynamics simulations, quantum chemical calculations, perturbed matrix method, and essential dynamics analysis for taking into account the cybotactic effect in the computational modeling of absorption spectra of molecular systems in condensed phase. The low-energy UV–Vis spectra of para-nitroaniline in water, methanol, and in the presence of a zwitterionic micelle have been computationally addressed and compared to the experimental data. The approach, considering all the systematic errors deriving from the intrinsic limitations of the computational setup (force field, quantum chemical calculations, and the approximations of the method), satisfactorily reproduces the experimental spectral shifts and peaks shapes and provides a promising tool of investigation for reproducing spectral observables of very complex systems.