Core Compaction Research Articles

FINITE ELEMENT MODELING OF CIRCULAR REINFORCED CONCRETE COLUMN CONFINED WITH CFRP UNDER ECCENTRIC LOADING

This paper presents nonlinear finite element analysis of eccentrically loaded circular Reinforced Concrete (RC) column confined with Carbon Fiber Reinforced Polymer (CFRP) wraps. The concrete constitutive model uses a plasticity-fracture model which is restraint sensitive, utilize a non-constant plastic dilation rate, and is able to simulate the plastic volumetric compaction of concrete core under high confining pressure. For validation of the models, two available specimens from the literature are used in the validations. Excellent agreement between the numerical models and the available test results are obtained in this study. A detailed investigation on the confinement effectiveness of both external and internal confining devices are presented and discussed. This discussion of the confinement effectiveness is important to be included in the design formula.

Stability and acidic pH-mediated leakage of guest molecules from self-assembly of poly(amidoamine)-graft-alkyl copolymers

Self-assembly of a copolymer with compact hydrophobic core, good stability at physiological condition and responsive nature towards stimuli is beneficial for sustained release application. Diffusion mediated release from a self-assembly at normal physiological conditions limits its application. Herein, extremely simple self-assemblies of poly(amidoamine)-graft-alkyl (PAMAM-g-alkyl) copolymers have been designed based on the N-alkylation (alkyl = C-8, C-10, C12, and C-18) of linear PAMAM to elucidate the differences in properties of the hydrophobic core and to select the appropriate self-assembly for triggered release application. The synthesis of PAMAM-g-alkyl copolymers allows us to assess the influence of alkyl chain length on the critical micelle concentration, stability, core hydrophobicity, core compactness, and encapsulation-release performance of the self-assemblies. The C18 chains facilitate the formation of compact micellar core with higher hydrophobicity, higher encapsulation property, and extended stability at pH 7.4. The C18 bearing micelles showed lowest (20–26% w/w) release of guest molecules at pH 7.4 while triggered the release (65–80% w/w) at pH 5. The triggered release behavior of the self-assembly is attributed to the leakage of guest molecules through partial dissociation of the copolymer chains followed by the creation of release channel. The effect of alkyl chain length on the micellar stability was further probed by Förster Resonance Energy Transfer (FRET) between two hydrophobic chromophores. The design of this type of simple self-assembly is beneficial to encapsulate hydrophobic guest molecules for sustained release application.

Preparation and characterization of nano-SiO2/paraffin/PE wax composite shell microcapsules containing TDI for self-healing of cementitious materials

Cement concrete materials are prone to form internal micro-cracks during service, which can be self-healed via microcapsule method. In this paper, self-healing microcapsules were prepared through melt condensation method with nano-SiO2/paraffin/PE wax composite shell and toluene-di-isocyanate (TDI) healing agent. The core fraction and compactness of microcapsules were measured. Particle size distributions, morphologies, micromechanical properties and chemical structure of microcapsules were characterized by laser particle size analyzer, scanning electron microscopy (SEM), nanoindentation test and Fourier transform infrared spectroscopy (FTIR), respectively. Self-healing capability of mortars containing microcapsules was investigated. The results depicted that core fraction of nano-SiO2/paraffin/PE wax composite shell microcapsule was 72.6%, and the size of the microcapsules was mainly between 400 and 600 µm. Since nano-SiO2 was added to the shell material, the elastic modulus and hardness of the microcapsule reached 1.87 GPA and 61.67 MPa respectively, and the weight loss rate decreased by only 2.6% within 60 d. SEM showed that nano-SiO2/paraffin/PE wax composite shell microcapsules were regular spherical with rough surface, and the shell thickness was about 1/20 of the diameter. The result of FTIR indicated that TDI was encapsulated into the nano-SiO2/paraffin/PE wax composite shell successfully. The compressive strength recovery rate of the mortar containing nano-SiO2/paraffin/PE wax composite shell microcapsules was 87.8% after 60% fc0 pre-load for 10 d self-healing in air. Moreover, the nano-SiO2/paraffin/PE wax composite shell microcapsule could completely self-heal the surface crack of mortar with a maximum width of 0.48 mm within 4 h, which showed that it had good self-healing capability for cracks in cementitious materials.

Experimental study on fragmentation characteristics of molten aluminum/copper jet penetrating in sodium pool

Under Hypothetical Core Disruptive Accidents (HCDA) in Sodium-cooled Fast Reactor (SFR), Molten Fuel-Coolant Interaction (MFCI) will cause intensive fragmentation of molten fuel materials and violent sodium boiling, possibly resulting in recriticality due to sodium void effect and reactor core compaction. And the formation and sufficient cooling of core debris bed are significantly affected by the fragmentation of molten fuel materials in sodium pool. Due to approximate ambient Weber Number (Wea) with molten metallic fuel, kilogram-level molten copper jet is dropped into sodium pool to study the fragmentation characteristics under varied experimental parameters in the present experiments. The nucleate boiling of liquid sodium is estimated to occur at the instantaneous contact interface between molten copper and liquid sodium. The molten copper jet suffers from intensive fragmentation and solidification to produce many fragments under thermodynamic and hydrodynamic effects. Besides, experiment with molten aluminum jet injected into sodium pool is conducted without occurrence of sodium boiling to independently study the effect of hydrodynamic interaction on interphase penetration and fragmentation. During the experiments, temperature variations and dynamic pressure change in sodium pool are monitored to evaluate energy release. The resultant fragments are recorded and measured for morphology analysis and size distribution to examine the fragmentation characteristics. Based on experimental results, the fragmentation mechanism is discussed against hydraulic and thermal factors. The present findings contribute to further understanding the fragmentation characteristics of molten corium in sodium pool and optimization of mitigation systems against MFCI for SFR.

Effect of Polymer Chain Density on Protein-Polymer Conjugate Conformation.

Many biomedical applications employ covalent attachment to synthetic polymers to enhance the efficiency of proteins or other therapeutically active molecules. We report here the impact of polymer conjugation on the structural and thermal stability of a protein model, the bovine serum albumin, using a variable number of linear biodegradable polyphosphoesters, which were covalently tethered to the protein. We observed that BSA's secondary structure measured by circular dichroism is independent of the conjugation. Small-angle neutron scattering, however, reveals a change from ellipsoid to globular shape of the whole complex arising from a slight compaction of the protein core and an increase of the polymer's radius of gyration as a function of the grafting polymer density. In particular, we highlight a gradual change of the polymer conformation around the protein and elongation of the semimajor dimension of the ellipsoidal protein. Our results will contribute to the description of biophysical characteristics of a new class of biologically relevant protein-polymer conjugates.

Component design and accident analysis of fuel assembly for prototype GEN-IV sodium-cooled fast reactor

Abstract The Korea 150 MWe Prototype GEN-IV Sodium cooled Fast Reactor (PGSFR) project has reached the middle of its preliminary safety analysis report (SAR) design phase. The core design studies are being conducted by KAERI. Some design features for the core have been made to comply with the GEN-IV reactor objectives. The main objective to improve the safety of the core design. A negative sodium void worth was achieved thanks to a new fuel assembly design including U-Zr and U-TRU-Zr axially heterogeneous fuel rods, a large cladding/small spacer wire bundle, a sodium bonding between metal slug and cladding, and upper gas plenum above the active core region, and upper/lower reflectors. Finite element calculations were performed to increase the stiffness of the above core load pad and top load pad in order to analyze their effect on the core mechanical behavior during hypothetical radial core flowering and compaction events. More generally, all design choices for the PGSFR have been made with the permanent objective of minimizing the fuel assembly height to decrease the overall costs of the reactor and the fuel cycle. This paper describes the fuel assembly design for the GEN-IV core at the end of the preliminary SAR design phase and studies performed to optimize the performances. The basic design and fuel assembly analysis results were described in this work. In specially, the design analysis results under the accident condition is focused in this paper. As the results of that, the structural integrity of a fuel assembly was satisfied for the PGSFR fuel assembly mechanical design criteria.

Hydrodynamical Neutron-star Kicks in Electron-capture Supernovae and Implications for the CRAB Supernova

Abstract Neutron stars (NSs) obtain kicks, typically of several 100 km s−1, at birth. The gravitational tugboat mechanism can explain these kicks as consequences of asymmetric mass ejection during the supernova (SN) explosion. Support for this hydrodynamic explanation is provided by observations of SN remnants with associated NSs, which confirm the prediction that the bulk of the explosion ejecta, particularly the chemical elements between silicon and the iron group, are dominantly expelled in the hemisphere opposite to the direction of the NS kick. Here, we present a large set of two- and three-dimensional explosion simulations of electron-capture SNe, considering explosion energies between ∼3 × 1049 erg and ∼1.6 × 1050 erg. We find that the fast acceleration of the SN shock in the steep density gradient delimiting the O–Ne–Mg core of the progenitor enables such a rapid expansion of neutrino-heated matter that the growth of neutrino-driven convection freezes out quickly in a high-mode spherical harmonics pattern. Because the corresponding momentum asymmetry of the ejecta is very small and the gravitational acceleration by the fast-expanding ejecta abates rapidly, the NS kick velocities are a few km s−1, at most. The extremely low core compactness of O–Ne–Mg-core progenitors therefore favors hydrodynamic NS kicks much below the ∼160 km s−1 measured for the Crab pulsar. This suggests either that the Crab Nebula is not the remnant of an electron-capture SN, but rather of a low-mass iron-core progenitor; or that the Crab pulsar was not accelerated by the gravitational tugboat mechanism, but instead received its kick by a non-hydrodynamic mechanism such as, e.g., anisotropic neutrino emission.

The Npa1p complex chaperones the assembly of the earliest eukaryotic large ribosomal subunit precursor.

The early steps of the production of the large ribosomal subunit are probably the least understood stages of eukaryotic ribosome biogenesis. The first specific precursor to the yeast large ribosomal subunit, the first pre-60S particle, contains 30 assembly factors (AFs), including 8 RNA helicases. These helicases, presumed to drive conformational rearrangements, usually lack substrate specificity in vitro. The mechanisms by which they are targeted to their correct substrate within pre-ribosomal particles and their precise molecular roles remain largely unknown. We demonstrate that the Dbp6p helicase, essential for the normal accumulation of the first pre-60S pre-ribosomal particle in S. cerevisiae, associates with a complex of four AFs, namely Npa1p, Npa2p, Nop8p and Rsa3p, prior to their incorporation into the 90S pre-ribosomal particles. By tandem affinity purifications using yeast extracts depleted of one component of the complex, we show that Npa1p forms the backbone of the complex. We provide evidence that Npa1p and Npa2p directly bind Dbp6p and we demonstrate that Npa1p is essential for the insertion of the Dbp6p helicase within 90S pre-ribosomal particles. In addition, by an in vivo cross-linking analysis (CRAC), we map Npa1p rRNA binding sites on 25S rRNA adjacent to the root helices of the first and last secondary structure domains of 25S rRNA. This finding supports the notion that Npa1p and Dbp6p function in the formation and/or clustering of root helices of large subunit rRNAs which creates the core of the large ribosomal subunit RNA structure. Npa1p also crosslinks to snoRNAs involved in decoding center and peptidyl transferase center modifications and in the immediate vicinity of the binding sites of these snoRNAs on 25S rRNA. Our data suggest that the Dbp6p helicase and the Npa1p complex play key roles in the compaction of the central core of 25S rRNA and the control of snoRNA-pre-rRNA interactions.

Experimental and numerical studies on compaction of carbon fiber composite joint with variable cross‐section using thermal expansion process

For hollow composite with complex shape, thermal expansion process is usually used to ensure uniform compaction pressure and excellent processing quality. This study focused on compaction of carbon fiber/epoxy matrix composite joint with variable cross‐section using thermal expansion process. Three kinds of silicone rubber core molds were adopted and experiments were performed to study the effect of elastomer core mold on resin pressure distribution inside prepreg stack during process and processing quality of composite joint. Moreover, based on numerical analysis, thermal expansion behaviors of different core molds and compaction pressure on prepreg stack were studied. The results indicate that material properties and geometric structure of core mold significantly influence thermal expansion behavior of core mold and compaction pressure distribution on prepreg stack. Due to irregular shape of core mold, thermal expansion of core mold at the regions with different cross‐sections is obviously uneven. And core mold with large coefficient of thermal expansion and small compressive modulus is more likely to fill process gap and achieve uniform compaction pressure distribution on prepreg stack. Therefore, controlling thermal expansion behavior of core mold to improve processing quality of composite involves reasonable material properties of core mold and adjusting process gap at different cross‐sections of composite. POLYM. COMPOS., 40:E1057–E1074, 2019. © 2018 Society of Plastics Engineers

Molecular dynamics simulations of metalloproteins: A folding study of rubredoxin from <em>Pyrococcus furiosus</em>

The constant increase of computational power has made feasible to investigate the folding mechanism of small proteins using molecular dynamics (MD). Metal-binding proteins (metalloproteins) are usually complicated to model, largely due to the presence of the metal cofactor. Thus, the study of metal-coupled folding is still challenging. In this work, we addressed the folding process of Pyrococcus furiosus rubredoxin (PfRd), a 53-residue protein binding a single iron ion, using different MD methods. Starting from an extended conformation of the polypeptide chain where we preserved the coordination of the metal ion, a classical MD simulation and an extensive accelerated MD run were performed to reconstruct the folding process of the metal-bound protein. For comparison, we simulated also the dynamics of folded PfRd devoid of the metal cofactor (apo-form), starting from the folded structure. For these MD trajectories, we computed various structural and biochemical properties. In addition, we took advantage of available experimental data to quantify the degree to which our simulations sampled conformations close to the native folded state. We observed that the compaction of the hydrophobic core is the main feature driving the folding of the structure. However, we could not reach a fully folded conformation within our trajectories, because of the incomplete removal of the solvent from the core. Altogether, the various MD simulations, including that of the folded apo-form of the protein, suggest that an improvement in the accuracy of the protein force-field is still needed.

Diffuse supernova neutrino background from extensive core-collapse simulations of 8–100 M⊙ progenitors

We revisit the diffuse supernova neutrino background in light of recent systematic studies of stellar core collapse that reveal the quantitative impacts of the progenitor conditions on the collapse process. In general, the dependence of the progenitor on the core-collapse neutrino emission is not monotonic in progenitor initial mass, but we show that it can, at first order, be characterized by the core compactness. For the first time, we incorporate the detailed variations in the neutrino emission over the entire mass range $8$-$100 {\rm M}_\odot$, based on (i) a long-term simulation of the core collapse of a $8.8 {\rm M}_\odot$ O-Ne-Mg core progenitor, (ii) over 100 simulations of iron core collapse to neutron stars, and (iii) half a dozen simulations of core collapse to black holes (the "failed channel"). The fraction of massive stars that undergo the failed channel remains uncertain, but in view of recent simulations which reveal high compactness to be conducive to collapse to black holes, we characterize the failed fraction by considering a threshold compactness above which massive stars collapse to black holes and below which the final remnant is a neutron star. We predict that future detections of the diffuse supernova neutrino background may have the power to reveal this threshold compactness, if its value is relatively small as suggested by interpretations of several recent astronomical observations.

Analysis of compaction in brittle foam with multiscale indentation tests

Lightweight plasterboard is a product composed of “plaster foam” core whose porosity can reach 75 vol%, lined with two sheets of paper. To optimize the trade-off between thermal resistance and mechanical strength, it is important to understand and characterize the mechanical behavior of plasterboard. Core compaction of plasterboard is one of the prevalent degradation mechanisms. This mechanism is studied herein using in-situ indentation experiments performed at two different scales. The first test was carried out in a lab tomograph. The second test was conducted on the high resolution synchrotron ID19 beamline at ESRF. Very early damage is revealed. The basic mechanism of pore collapse and its gradual development is detected in contrast with mesoscale observations where compaction appears very abrupt.

Core geometry for recriticality prevention against CDA in sodium-cooled fast reactor

In core disruptive accident (CDA) of sodium-cooled fast reactors (SFRs), fuel and steel can melt to form a molten pool. The objective of the present work is to investigate design measures for core of SFR to prevent recriticality. This paper studied core geometry of convex cross-section shape to increase neutron leakage from core surface in case of core compaction. In order to evaluate effective neutron multiplication factor, 70-group neutron diffusion calculations were performed by changing parameters related to the convex core geometry (i.e. ratio of inner height to inner diameter). Neutron diffusion code and nuclear data library employed in those calculations are CITATION and JENDL-3.3, respectively. By optimizing core configuration, the compaction reactivity of the convex shaped core showed drastic reduction from 2.07 % of reference cylindrical core (Japan Sodium-cooled Fast Reactor) to -3.28 %.

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

We investigate the relationship between 5 GHz interstellar scintillation (ISS) and 15 GHz intrinsic variability of compact, radio-selected AGNs drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory (OVRO) blazar monitoring program. We discover that the strongest scintillators at 5 GHz (modulation index, $m_5 \geq 0.02$) all exhibit strong 15 GHz intrinsic variability ($m_{15} \geq 0.1$). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at $\sim 100\, \mu$as scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5 GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15 GHz variability amplitudes, most likely due to jet opacity effects.

Estimating the core compactness of massive stars with Galactic supernova neutrinos

We suggest the future detection of neutrinos from a Galactic core-collapse supernova can be used to infer the progenitor’s inner mass density structure. We present the results from 20 axisymmetric core-collapse supernova simulations performed with progenitors spanning initial masses in the range 11–, and focus on their connections to the progenitor compactness. The compactness is a measure of the mass density profile of the progenitor core and recent investigations have suggested its salient connections to the outcomes of core collapse. Our simulations confirm a correlation between the neutrinos emitted during the accretion phase and the progenitor’s compactness, and that the ratio of observed neutrino events during the first hundreds of milliseconds provides a promising handle on the progenitor’s inner structure. Neutrino flavor mixing during the accretion phase remains a large source of uncertainty.

Mechanical performance of CF/PEEK–PEI foam core sandwich structures

Previous work showed that thermoplastic composite sandwich structures offer great potential to meet the demands of lightweight structures for aviation applications. In this study, the influence of several processing parameters on the mechanical properties of thermoplastic sandwich components, consisting of carbon fibre reinforced polyetheretherketone skins and polyetherimide foam cores, is characterised. Sandwich specimens are manufactured with varying skin temperatures, core compaction distances and different polyetherimide concentrations at the skin–core interface. Following, sandwich samples are mechanically tested to characterise the bond strength, the core performance as well as the performance of the whole sandwich. The results show that in most cases the processing parameters significantly affect the cell structure of the sandwich core, provided that a proper fusion bond between skins and core exists. Thereby, the core performance seems to be weakened and failure predominantly occurs in the transition between affected and original cell structures.

A scaled perspective on permeability: How to get the best from what we have

The suppression and equivalence of permeability and thickness of transmissive reservoir intervals are managed by integrating data measured at different scales. Essential requirements are estimates of effective permeability from core, logs and well tests for comparison over net reservoir intervals at key wells. The starting point is a quality-assured determination of interval transmissibility from well testing. The interval thickness is refined to effective thickness through the scale-compatible application of dynamically-conditioned net-reservoir discriminators, a process that allows effective permeability to be determined at the well-test scale. Algorithms for transforming core absolute permeability to core effective permeability form the basis for comparisons of laboratory and well-test data provided that appropriate core compaction corrections have been made with data partitioning as needed. Where core sampling is comprehensive and representative over the perforated interval, the comparison with well-tests can be made directly. Otherwise core-calibrated log data constitute an essential intermediary. In the absence of formation-damage effects, the reconciliation of petrophysically- and dynamically-derived effective permeabilities over a tested interval is diagnostic of uniform reservoir character. Beyond data shortfalls, impediments to reconciliation include formation anisotropy exacerbated by natural fractures and relatively high permeability conduits possibly in the form of “super-k” layers. A deterministic workflow for achieving reconciliation is substantiated by reference to field examples, which collectively reveal further opportunities for improved permeability characterization in integrated reservoir studies.

Conceptual design of ASTRID fuel sub-assemblies

The French 600MWe Advanced Sodium Technological Reactor for Industrial Demonstration (ASTRID) project has reached the end of its Conceptual Design phase. The core design studies are being conducted by the CEA with support from AREVA and EDF. Innovative design choices for the core have been made to comply with the GEN IV reactor objectives, marking a break with the former Phénix and SuperPhénix Sodium Fast Reactors.The main objective to improve safety compared with current GEN II or III reactors led to a core design that demonstrates intrinsically safe behaviour. A negative sodium void worth is achieved thanks to a new fuel sub-assembly design including (U,Pu)O2 and UO2 axially heterogeneous fuel pins, a large cladding/small spacer wire bundle, a sodium plenum above the fuel pins, and upper neutron shielding with both enriched and natural boron carbide (B4C) which also maintain a low secondary sodium activity level. As these Na-bonded B4C pins can lead to the retention of unacceptable amounts of sodium, the whole upper neutron shielding has been made removable on-line through the sub-assembly head just before the washing operations. Finite elements calculations have been performed to increase the stiffness of the stamped spacer pads in order to analyse its effect on the core mechanical behaviour during hypothetical radial core flowering and compaction events. More generally, all design choices for ASTRID have been made with the permanent objective of minimising the sub-assembly height to decrease the overall costs of the reactor and the fuel cycle.This paper describes the fuel sub-assembly design for the ASTRID CFV v4 core at the end of the Conceptual Design phase and studies performed to optimise the performances. Focus is placed on innovations and specificities in the design compared with former French SFRs.

Failure Mechanisms of Plasterboard in Nail Pull Test Determined by X-ray Microtomography and Digital Volume Correlation

To design lightweight plasterboard and optimize the compromise between thermal resistance and mechanical strength, it is important to characterize its strength as assessed with the normative “Nail pull” test. Understanding the phenomenology of this test is the key to identifying the limiting factor in terms of load carrying capacity. In this work, the degradation mechanisms of lightweight plasterboard are analyzed via tests conducted in situ in a laboratory tomograph. Through the analysis of the kinematics by digital volume correlation, the different mechanisms at play up to failure mechanism have been identified, i.e., quasi-elastic regime, failure of the roller coating layer, core compaction and core failure. The compaction of the core by the collapse of porosity in compression is recognized as the limiting factor in terms of compressive strength and tearing resistance.

Core solidification and dynamo evolution in a mantle‐stripped planetesimal

AbstractThe physical processes active during the crystallization of a low‐pressure, low‐gravity planetesimal core are poorly understood but have implications for asteroidal magnetic fields and large‐scale asteroidal structure. We consider a core with only a thin silicate shell, which could be analogous to some M‐type asteroids including Psyche, and use a parameterized thermal model to predict a solidification timeline and the resulting chemical profile upon complete solidification. We then explore the potential strength and longevity of a dynamo in the planetesimal's early history. We find that cumulate inner core solidification would be capable of sustaining a dynamo during solidification, but less power would be available for a dynamo in an inward dendritic solidification scenario. We also model and suggest limits on crystal settling and compaction of a possible cumulate inner core.