Weak Cores Research Articles

Resonance Structure of 8Be within the Two-Cluster Resonating Group Method

A microscopic two-cluster model is applied to study the elastic alpha-alpha scattering and the resonance structure of 8Be. The model is an algebraic version of the Resonating Group Method (RGM), which involves the complete set of oscillator functions to expand the wave function of a two-cluster system. The interaction of nucleons inside each cluster and the interaction between clusters are determined by the well-known semirealistic nucleon-nucleon potentials which are employed in calculations. They differ by a size of the core at small distances between nucleons and realize the strong, moderate, and weak cores. They allow us to study dependence of calculated quantities on the shape of a nucleon-nucleon potential. The detailed analysis of resonance wave functions is carried out in the oscillator, coordinate, and momentum spaces. Effects of the Pauli principle on the wave functions of the 8Be continuous spectrum states are thoroughly studied.

Enhanced flexural properties of bionic carbon fiber sandwiches inspired by the coconut shell

Carbon fiber reinforced plastics (CFRP)/metal foam sandwiches with high strength-to-weight ratios are in growing demand for applications in architecture, automobile, and aerospace. However, most of the sandwiches have low mechanical properties due to the weak metal foam cores and the low interfacial bond strength between cores and skins. In this study, inspired by the natural coconut shell, novel sandwich structures containing magnesium syntactic foam (MSF) cores were designed to improve flexural properties. The CFRP skins were selected to mimic the high strength and multilayer structure of the exocarp and mesocarp, and two types of MSF cores (PMSF with low density and SMSF with high density) were used to mimic the hierarchical cellular structure of the endocarp. The cores with different structures will significantly affect the failure mechanisms and flexural properties of the corresponding sandwich structures. Compared with conventional CFRP/MF, the peak load and flexural stiffness of bionic CFRP/PMSF and CFRP/SMSF are significantly improved due to the hierarchical cellular structure of MSF cores. The enhanced skin-core debonding resistance allows bionic CFRP/PMSF to have better structural integrity under bending loads. Therefore, the CFRP/PMSF exhibits the highest specific flexural strength and specific energy absorption capacity, though the PMSF core has the lowest specific flexural properties. This result confirms that the reasonable matching between the PMSF core and the CFRP skin transfers the load more effectively and improves the strength-to-weight ratio of the sandwich structure. The proposed bio-inspired design method is expected to supply an effective way to enhance the mechanical properties of conventional CFRP/MF sandwich structures in a wide range of engineering applications.

Effect of wettability on oil and water distribution and production performance in a tight sandstone reservoir

Wettability is an important factor that dominates the micro-distribution of initial oil and water, residual oil, and subsequent oil recovery in a tight oil reservoir. In this paper, integrated experimental techniques have been developed to examine the effect of wettability on oil and water micro-distribution together with production performance in a tight reservoir. Wettability alteration indicated by contact angles during the aging process was firstly monitored and measured continuously. Then, nuclear magnetic resonance (NMR) measurements were integrated with rate-controlled mercury injection (RMI) tests to determine pore and throat size distribution. Subsequently, NMR measurements were performed to not only characterize the oil and water distribution in the process of wettability change, but also evaluate the production performance and recovery potential. Furthermore, displacement experiments were carried out to visually observe the microscopic distribution of residual oil under different wettability conditions. For a strong water-wetting rock, oil is separated from the surface of a pore/throat on which a thin water film is adsorbed, and then fills the center of the pore in the form of oil droplets. The displacement experiments show that water saturation of a two-phase flow zone on relative permeability curves ranges from 22.5% to 55.1% and that water saturation at the isotonic point is 43.6% with its waterflooding oil recovery of 42.1%. For a weak oil-wetting rock, oil is mainly distributed in porous media in the form of an oil film. The water saturation of a two-phase flow zone ranges from 22.3% to 48.1%, while that of the isotonic point is 38.1% with waterflooding oil recovery of 33.2%. With wettability altering from strong water-wetting to weak oil-wetting, oil either is adsorbed on the pore and throat surface or migrates from the center of a larger pore to a smaller pore and/or throat. It is more unfavorable to the seepage of oil due to the fact that the two-phase flow zone is narrowed and a decrease in water saturation at the isotonic point, leading to a lower waterflooding oil recovery. After waterflooding, oil droplets caused by the Jamin effect, oil clusters resulted from heterogeneity, and small oil droplets dispersed at the corner of a pore are visually observed in cores with strong water-wetting. Within weak oil-wetting cores, residual oil is mainly distributed in a membrane-like form due to adsorption and oil clusters resulted from heterogeneity.

Threonine-Based Stimuli-Responsive Nanoparticles with Aggregation-Induced Emission-Type Fixed Cores for Detection of Amines in Aqueous Solutions.

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection.

Estudo do ciclo de vida do ciclone subtropical Arani ocorrido no Atlântico Sul em março de 2011 através das reanálises ERA-Interim e CFSR

O ciclone Arani ocorreu em março de 2011 no oceano Atlântico Sul e foi classificado inicialmente como depressão subtropical. Ao atingir ventos superiores a 34 nós, passou à categoria de tempestade subtropical, sendo nomeado pela Marinha do Brasil como Arani, que significa tempo furioso em Tupi Guarani. O objetivo deste trabalho foi analisar o ciclone Arani através do Espaço de Fase de Ciclones, construído com dados da reanálise ERA-Interim do European Centre for Medium-Range Weather Forecasts (ECMWF), com 0,7º de resolução espacial, e, também, utilizando campos sinóticos e cortes verticais com os dados da reanálise do Climate Forecast System Reanalisys (CFSR), com 0,5º de resolução. Através dos diagramas de fase foi possível identificar a estrutura subtropical do ciclone Arani e o indício de uma transição de fase extratropical no final de seu ciclo de vida. Os resultados indicaram, também, que a qualidade dos diagramas de fase para ciclones com fraco núcleo quente e pequenas dimensões depende de modelos atmosféricos adequados e, por isso, os valores obtidos devem ser analisados com cautela quando se trata do uso de modelos globais. Neste caso, o estudo qualitativo dos diagramas se mostrou mais útil do que a análise puramente quantitativa. Apesar de discordar da informação de uma transição de fase extratropical no final do ciclo de vida do ciclone Arani, contida nos diagramas de fase empregados no estudo, a análise dos campos e dos perfis sinóticos contribuiu para o entendimento do desenvolvimento do ciclone e para a interpretação dos próprios diagramas de fase.

A Novel Flux Reversal Claw Pole Machine With Soft Magnetic Composite Cores

This paper proposes a novel flux reversal claw pole machine (FRCPM) with soft magnetic composite (SMC) cores, the proposed FRCPM has both the advantages of flux reversal permanent magnet machine (FRPMM) and claw pole machine (CPM). Specifically, with the permanent magnets (PMs) are surface mounted on the surface of stator claw pole teeth with a determined pattern, the FRCPM can operate based on flux reversal principle. As the adopted winding is global ring winding and 3D magnetic flux stator core structure is similar to the CPM's, the FRCPM is operated based on magnetic flux characteristic of the CPM as well. Therefore, the FRCPM can be operated under relatively high rotate speed since there is no winding or PMs on rotor, and the weak PMs, ring winding and SMC stator cores are encapsulated together as a whole part. Moreover the adopted 3D magnetic flux path can bring FRCPM with relatively high torque ability, and the adopted SMC cores can bring FRCPM with low core loss at the high speed operation. The operation principle of FRCPM is explained, the power equation is deduced for obtaining the initial design, and the main dimensions are optimized to ensure the developed FRCPM can have good performance. The main electromagnetic parameters and performance of FRCPM are obtained based on using the 3D finite element method (FEM).

Secondary buckling and failure behaviors of composite sandwich panels with weak and strong cores under in-plane shear loading

The secondary buckling and failure behaviors of composite sandwich panels (CSPs) subjected to in-plane shear loading are studied via a self-developed quasi-conforming finite element method. The influences of key material and geometry parameters on postbuckling and failure behaviors are investigated. Numerical results show that (1) postbuckling failure is dominated by the ratio of two strengths, i.e. the through-thickness shear strength of the core and the transverse tensile strength of the lamina. In addition, two constant thresholds for this strength ratio exist in the relationship between the load bearing capacity of CSPs and the ratio, which can be used to define “weak” or “strong” core and the status of postbuckling load bearing capacity (PLBC); (2) local failures of the core and face sheets (FSs) can lead to a drastic decrease in the local stiffness of CSPs, a singularity of the tangent stiffness matrix and the occurrence of secondary bucklings of CSPs; (3) secondary bifurcation identification, branch switching and convergence improvement are all necessary to obtain reasonable paths during the path-following.

Laboratory study heterogeneity impact on microscopic residual oil distribution in tight sandstone cores during CO2 immiscible flooding

ABSTRACTWe use physical simulation experiment and nuclear magnetic resonance methods to investigate crude oil distribution after immiscible CO2 flooding schemes in tight sandstone cores. Experimental results indicate that water-wet cores lead to the highest final recovery factor in comparison with intermediate wet cores and weak oil-wet cores, and the recovery oil difference in clay micropore is mainly because of the heterogeneity, and the difference in medium pore and large pore is affected by asphaltene precipitation phenomenon. Therefore, it is important to enhance the recovery in the clay micropores and reduce the impact of cores permeability reduction caused by asphaltene precipitation. Based on this investigation on the residual oil saturation in pore throats, immiscible CO2 flooding can be a potential method to improve recovery efficiency in tight oil reservoir.

Laboratory research of wettability and heterogeneity effect on microscopic residual oil distribution in tight sandstone cores during CO2 flooding

Based on physical simulation experiment and nuclear magnetic resonance (NMR) measurements, the effect of wettability and pore throat heterogeneity upon oil recovery efficiency during CO2 flooding, were conducted to investigate how crude oil residing in different sized pore are produced by immiscible CO2 flooding schemes in tight sandstone cores. Experimental results indicate that water wet cores lead to the highest final recovery factor in comparison with intermediate wet cores and weak oil wet cores. The recovery factor difference in clay micro pore is mainly because of the heterogeneity, while the difference in medium pore and large pore is affected by asphaltene precipitation phenomenon. Therefore, it is important to enhance the recovery in the clay micro pores, and focus on the cores permeability reduction caused by asphaltene precipitation. Based on this investigation on the residual oil saturation in pore throats subjected to immiscible CO2 flooding, it is possible to design an optimum flood scheme which suits for the microscope pore throat characteristics for a given tight oil reservoir.

LeMMINGs – I. The eMERLIN legacy survey of nearby galaxies. 1.5-GHz parsec-scale radio structures and cores

We present the first data release of high-resolution ($\leq0.2$ arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the LeMMINGs survey. This sample includes galaxies which are active (LINER and Seyfert) and quiescent (HII galaxies and Absorption line galaxies, ALG), which are reclassified based upon revised emission-line diagrams. We detect radio emission $\gtrsim$ 0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for HII galaxies and 5/14 for ALGs) with radio sizes typically of $\lesssim$100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 10$^{32}$ to 10$^{40}$ erg s$^{-1}$: LINERs and HII galaxies show the highest and the lowest radio powers respectively, while ALGs and Seyferts have intermediate luminosities. We find that radio core luminosities correlate with black hole (BH) mass down to $\sim$10$^{7}$ M$_{\odot}$, but a break emerges at lower masses. Using [O III] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted HII galaxies follow an optical fundamental plane of BH activity, suggesting a common disc-jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; HII galaxies may host weak active BHs and/or nuclear star-forming cores; and recurrent BH activity may account for ALG properties.

Investigation effect of wettability and heterogeneity in water flooding and on microscopic residual oil distribution in tight sandstone cores with NMR technique

Abstract In order to explore the effect of wettability and pore throat heterogeneity on oil recovery efficiency in porous media, physical simulation experiment and nuclear magnetic resonance (NMR) measurements were conducted to investigate how crude oil residing in different sized pores are recovered by water flooding. Experimental results indicate that the recovery factor of water flooding is governed by spontaneous imbibition and also pore throat heterogeneity. It is found that intermediate wetting cores lead to the highest final recovery factor in comparison with water wet cores and weak oil wet cores, and the recovery oil difference in clay micro pore is mainly because of the wettability, the difference in medium pore and large pore is affected by pore throat heterogeneity. Water wet core has a lower recovery factor in medium and large pore due to its poor heterogeneity, in spite of the spontaneous imbibition effect is very satisfying. Intermediate wetting cores has significant result in different sized pore and throat, the difference in medium pore and large pore is affected by pore throat heterogeneity.

Computing Least Cores of Supermodular Cooperative Games

One of the goals of a cooperative game is to compute a valuedivision to the players from which they have no incentive todeviate. This concept is formalized as the notion of the core.To obtain a value division that motivates players to cooperate to a greater extent or that is more robust under noise, the notions of the strong least core and the weak least core have been considered. In this paper, we characterize the strong and the weak least cores of supermodular cooperative games using the theory of minimizing crossing submodular functions. We then apply our characterizations to two representative supermodular cooperative games, namely, the induced subgraph game generalized to hypergraphs and the airport game. For these games, we derive explicit forms of the strong and weak least core values, and provide polynomial-time algorithms that compute value divisions in the strong and weak least cores.

Clamped sandwich beams with thick weak cores from central impact: A theoretical study

A theoretical model is obtained to predict the dynamic response of a clamped sandwich beam with thick weak core impacted centrally by a projectile. The core is weak and thick enough that only part or all of the front face sheet and the core undergo permanent plastic deformations, while the back face sheet undergoes an elastic vibration. The core is taken to be rigid-plastic and the front face sheet is treated as an individual rigid-plastic beam resting on a foundation. The back face sheet is modeled as an Euler–Bernoulli beam. Based on the rigid-perfectly theory and Galerkin method, two types of the sandwich beam response are given, i.e., intermediate strength and low strength core type responses. The critical kinetic energy of the projectile as the back face sheet reaches its elastic limit is studied. The localized indentation and response history of the sandwich beam are presented. It is found that the dynamic response of the sandwich beam is sensitive to the core strength, mass ratio, breadth and impact velocity of the projectile. The finite element (FE) simulation is also carried out to verify the analytical predictions and a good agreement is achieved.

The current system east of the Ryukyu Islands as revealed by a global ocean reanalysis

The structure and variability of the Ryukyu Current System (RCS), which forms the western boundary current along the eastern slope of the Ryukyu Islands, are studied using results from a 32-layer, 1/12.5° global HYbrid Coordinate Ocean Model (HYCOM) and Navy Coupled Ocean Data Assimilation (NCODA) reanalysis for the period 1993–2012. It is confirmed that the reanalysis realistically reproduces salient features of the observed currents at three sections southeast of Miyakojima, Okinawa and Amami-Ohshima. The mean velocity sections show well-developed subsurface velocity maxima between 700 and 900m. The current core southeast of Amami-Ohshima shows year-to-year variations with cyclonic (anticyclonic) circulation east of Amami-Ohshima generating weak (strong) velocity cores. Interaction of the RCS with an anticyclonic eddy often produces a two-core velocity structure, with a surface core in the upper 300m and a deeper core near 700–900m. The horizontal structure of the RCS at 15m depth shows a well-developed northeastward current northeast of Okinawa, which is partly fed by the southwestward extension of the anticyclonic recirculation gyre. The RCS forms a continuous northeastward current from Miyakojima to Amami-Ohshima below 500m with shoreward intensification. The circulation at 2000m shows a seasonal flow reversal, which is northeastward from December to June and southwestward from August to October with July and November being the transition months. The volume transports across these three sections have respective mean values of 0.6, 6.2 and 12.4Sv (1Sv≡106m3s−1) and standard deviations of 10.2, 7.1 and 11.3Sv. They have dominant seasonal variations with the maximum in winter and spring and the minimum in summer. The interannual variation of the transport anomaly, which co-varies with the RCS core, results from westward propagating mesoscale eddies arriving from the Pacific interior.

Localized buckling in sandwich struts with inhomogeneous deformations in both face plates

A nonlinear analytical model for investigating localized interactive buckling in simply supported thin-face plate sandwich struts with weak cores is extended to account for local deformations in both face plates, which have been observed in experiments and finite element simulations. The original model is based on potential energy principles with large displacement assumptions. It assumes Timoshenko shear deformable theory for the core and approximates the overall mode as a half-sine wave along the length of the strut while the local face plate displacements are initially unknown and are found as solutions of the governing equations. The extended model is able to capture measurable local face plate displacements in the less compressed face plate, beyond the secondary bifurcation which leads to localized interactive buckling, for the case where overall buckling is critical. Moreover, the allowance of local displacements in both face plates allows the extended model to predict the post-buckling behavior better in cases where local buckling is critical. The results from this model compare very well with nonlinear finite element simulations with respect to both the equilibrium paths and panel deformations.

Information, Uncertainty and the Core

How are contracts formed when agents face uncertainty, have asymmetric information and cannot write binding agreements? In this paper we propose a solution to this problem. Agents can discuss state-contingent allocations but cannot write binding contracts. At any stage in the contract formation phase a coalition of agents can deviate and choose to form agreements amongst themselves. However, we restrict these deviations to be credible: meaning that no sub-coalition has a further credible deviation. In this context, we propose the coarse and fine weak sequential cores as solution concepts and sufficient conditions for the non-emptiness of these solution concepts are provided.

Structural modeling of sandwich structures with lightweight cellular cores

An effective single layered finite element (FE) computational model is proposed to predict the structural behavior of lightweight sandwich panels having two dimensional (2D) prismatic or three dimensional (3D) truss cores. Three different types of cellular core topology are considered: pyramidal truss core (3D), Kagome truss core (3D) and corrugated core (2D), representing three kinds of material anisotropy: orthotropic, monoclinic and general anisotropic. A homogenization technique is developed to obtain the homogenized macroscopic stiffness properties of the cellular core. In comparison with the results obtained by using detailed FE model, the single layered computational model can give acceptable predictions for both the static and dynamic behaviors of orthotropic truss core sandwich panels. However, for non-orthotropic 3D truss cores, the predictions are not so well. For both static and dynamic behaviors of a 2D corrugated core sandwich panel, the predictions derived by the single layered computational model is generally acceptable when the size of the unit cell varies within a certain range, with the predictions for moderately strong or strong corrugated cores more accurate than those for weak cores.

Haloadaptation: Insights from comparative modeling studies of halophilic archaeal DHFRs

Proteins of halophilic archaea function in high-salt concentrations that inactivate or precipitate homologous proteins from non-halophilic species. Haloadaptation and the mechanism behind the phenomenon are not yet fully understood. In order to obtain useful information, homology modeling studies of dihydrofolate reductases (DHFRs) from halophilic archaea were performed that led to the construction of structural models. These models were subjected to energy minimization, structural evaluation and analysis. Complementary approaches concerning calculations of the amino acid composition and visual inspection of the surfaces and cores of the models, as well as calculations of electrostatic surface potentials, in comparison to non-halophilic DHFRs were also performed. The results provide evidence that sheds some light on the phenomenon of haloadaptation: DHFRs from halophilic archaea may maintain their fold, in high-salt concentrations, by sharing highly negatively charged surfaces and weak hydrophobic cores.

Specific Interactions Improve the Loading Capacity of Block Copolymer Micelles in Aqueous Media

Block copolymer micelles find application in many fields as nanocarriers, especially in drug delivery. We report herein that specific interactions between hydrophobic guest molecules and core-forming segments can significantly improve the loading capacity of polymeric micelles. High loading capacities (>100% weight/weight of polymer (w/wp)) were systematically observed for the encapsulation of probes containing weak carboxylic acid groups by micellar nanoparticles having poly[2-(dialkylamino)ethyl methacrylate] cores (i.e., particles whose cargo space exhibits antagonist weak base functions), as demonstrated by the incorporation of indomethacin (IND), ibuprofen (IBPF), and trans-3,5-bis(trifluoromethyl)cinnamic acid (F-CIN) into either poly(ethylene oxide)-b-poly[2-(diisopropylamino)ethyl methacrylate] (PEO-b-PDPA) or poly(glycerol monomethacrylate)-b-PDPA (PG2MA-b-PDPA) micelles. The esterification of IND yielding to a nonionizable IND ethyl ester derivative (IND-Et) caused an abrupt decrease in the micellar loading capacity down to 10-15% w/wp. Similar results were also obtained when IND was combined with nonionizable block copolymers such as PEO-b-polycaprolactone (PEO-b-PCL) and PEO-b-poly(glycidyl methacrylate) (PEO-b-PGMA). The existence of acid-base interactions between the solubilizate and the weak polybase block forming the micelle core was confirmed by 1H NMR measurements. However, the incorporation of high numbers of hydrophobic guest molecules inside polymeric micelles can provoke not only an increase in the hydrodynamic size (2RH) of the objects but also a substantial change in the morphology (transition from spheres to cylinders). The application of the Higuchi model showed that the probe release followed a diffusion-controlled mechanism, and diffusion coefficients (D) on the order of 10-18-10-17 cm2/s were determined for IND release from 1.0 mg/mL PEO113-b-PDPA50 + 100% w/wp IND. Probe release from micelles with weak polybase-based cores can also be triggered by changes in the solution pH.

One-dimensional response of sandwich plates to underwater shock loading

The one-dimensional shock response of sandwich plates is investigated for the case of identical face sheets separated by a compressible foam core. The dynamic response of the sandwich plates is analysed for front face impulsive loading, and the effect of strain hardening of the core material is determined. For realistic ratios of core mass to face sheet mass, it is found that the strain hardening capacity of the core has a negligible effect upon the average through-thickness compressive strain developed within the core. Consequently, it suffices to model the core as an ideally plastic-locking solid. The one-dimensional response of sandwich plates subjected to an underwater pressure pulse is investigated by both a lumped parameter model and a finite element (FE) model. Unlike the monolithic plate case, cavitation does not occur at the fluid–structure interface, and the sandwich plates remain loaded by fluid until the end of the core compression phase. The momentum transmitted to the sandwich plate increases with increasing core strength, suggesting that weak sandwich cores may enhance the underwater shock resistance of sandwich plates.