Pure Configuration Research Articles

Entanglement negativity, holography and black holes

We investigate the application of our recent holographic entanglement negativity conjecture for higher dimensional conformal field theories to specific examples which serve as crucial consistency checks. In this context we compute the holographic entanglement negativity for bipartite pure and finite temperature mixed state configurations in d-dimensional conformal field theories dual to bulk pure AdS_{d+1} geometry and AdS_{d+1}-Schwarzschild black holes respectively. It is observed that the holographic entanglement negativity characterizes the distillable entanglement for the finite temperature mixed states through the elimination of the thermal contributions. Significantly our examples correctly reproduce universal features of the entanglement negativity for corresponding two dimensional conformal field theories, in higher dimensions.

Differential diagnosis of gastrointestinal stromal tumor by histopathology and immunohistochemistry.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the gastrointestinal (GI) tract. GISTs account for approximately 80% of the clinically relevant GI mesenchymal tumors. Although most GISTs show spindle cell morphology, 10-15% of GISTs show pure epithelioid configuration. Therefore, not only spindle cell tumors but also epithelioid cell ones developing in the GI tract are subject to the differential diagnoses of GISTs. GISTs are basically positive for KIT, a receptor tyrosine kinase (RTK) encoded by protooncogene c-kit, by immunohistochemistry, but approximately 5% of GISTs are only weakly or barely positive for KIT. Since almost all spindle cell type GISTs are strongly and diffusely positive for KIT regardless of different genetic subtypes, diagnosis of the spindle cell type GISTs is not difficult. On the other hand, epithelioid cell type GISTs show different staining patterns of KIT in different genetic backgrounds. Approximately half of the epithelioid cell type GISTs with platelet-derived growth factor receptor alpha (PDGFRA) gene mutation might show weak or undetectable staining of KIT. On the other hand, almost all GISTs are negative for desmin, which is a positive marker for mature smooth muscle cells, and S100 protein, which is a Schwann cell marker. Smooth muscle tumors such as leiomyomas and leiomyosarcomas, which usually show the spindle cell morphology, consist of approximately 10% of the clinically relevant GI mesenchymal tumors and are almost positive for desmin and negative for KIT and S100 protein. Schwannomas which nearly always show the spindle cell pattern, comprise up to 5% of the GI mesenchymal tumors, and almost all of them are positive for S100 protein and negative for KIT and desmin. Thus, most GI mesenchymal tumors are differentially diagnosed by immunohistochemistry (IHC) of KIT, desmin and S100 protein. However, mesenchymal tumors such as desmoids, solitary fibrous tumors (SFTs), inflammatory myofibroblastic tumors (IMTs), perivascular epithelioid cell tumors (PEComas), inflammatory fibroid polyps (IFPs), rarely develop in the GI tract, and have to be correctly diagnosed through detection of specific immunohistochemical markers and/or unique genetic aberrations.

Study of the Mechanism of the 13C(d, p)14C Reaction at E d = 15.3 MeV

The angular dependences of the differential cross sections of the 13C(d, p)14C reaction at the deuteron energy of 15.3MeV are presented according tomeasurements for the cases where the final nucleus is produced in the ground state (0+) and in the 1− excited state at 6.094 MeV. The angular distribution of protons corresponding to the sum 0+ (6.589 MeV) + 3− (6.728 MeV) + 0− (6.903 MeV) of states of the 14C nucleus that were not separated experimentally is also obtained. These experimental results are compared with their counterparts calculated by means of the FRESCO code for the mechanisms of neutron stripping and sequential neutron and dineutron transfer. The neutron and dineutron spectroscopic amplitudes are calculated for pure and mixed shell configurations. The best set of optical-potential parameters is determined for the entrance and exit reaction channels. It is shown that the neutron-stripping mechanismpermits describing themeasured angular distributions for all states of the 14C nucleus that were investigated here.

Maximizing utilization of reactivated and left-over catalysts in heavy gas oil hydrotreater: A case study of ADNOC Refining

Recently, ADNOC Refining Research Center (ARRC) has studied the possibility to maximize the reutilization of left-overs and reactivated hydrodesulfurization catalysts for one of its hydrotreater producing Ultra Low Sulfur Diesel (ULSD) from Heavy Gas Oil (HGO). Based on the refinery inventory, several catalyst configurations composed of different amounts of reactivated and fresh CoMo catalyst, including a full reactivated configuration having a stacked CoMo/NiMo/CoMo combination (50/25/25), have been tested in a pilot-plant reactor under commercially-relevant conditions. Experimental results in terms of reactor bed temperature, H2 consumption, aromatics and diesel yields have been analyzed and compared to the current commercial hydrotreater load and catalyst supplier forecasts for the studied configurations. Results show excellent performances of reactivated catalysts and a strong effect of the NiMo layer in the case of the stacked configuration. In a pure CoMo configuration, up to 75% reactor volume of reactivated catalyst could be utilized without impacting the product quality and cycle length, compared to a full fresh CoMo catalyst load. The full reactivated stacked configuration performed even better than the full fresh CoMo catalyst, without impacting product quality and diesel yield. Potential effect of the reactivated catalysts on the reaction selectivity and the role of the NiMo layer in the stacked configuration are discussed. Pilot-plant experimental data were in strong accordance with catalyst supplier commercial forecasts, emphasizing the quality of the pilot-plant study. Implementation of one of the studied configuration by the refinery could lead to between 30% and 55% savings on the cost of catalyst for the next load.

Learning as a Necessary but Not Sufficient Condition for Major Health Policy Change: A Qualitative Comparative Analysis Combining ACF and MSF

ABSTRACTFollowing the financial crisis, Bismarckian health systems underwent some major reforms. This article analyzes under which conditions major reforms occurred. To do so, it theoretically combines conditions from the Advocacy Coalition Framework (ACF) and the Multiple Streams Framework (MSF) to emphasize the added value of merging them to explain major policy change. By combining these two approaches, it is possible to present a more comprehensive picture of the reform processes, relying on the significance of both policy learning within actor coalitions (as particularly important in the ACF) and the role of ambiguity and timing (as particularly important in the MSF). Empirically, the article focuses on the health care reform packages from 2009 to 2013 in the four traditional European Bismarckian countries, Austria, Belgium, France and Germany. The analysis reveals learning as a necessary condition for major policy change. Consequently, a major reform only happens as a result of learning processes, either combined with a negotiated agreement, which presents a pure ACF-related configuration, or combined with a window of opportunity opening in the problem stream. The latter configuration thus confirms the need for integrating a condition from the MSF into the ACF to explain major policy change.

Influence of the pinch-point-temperature difference on the performance of the Preheat-parallel configuration for a low-temperature geothermally-fed CHP

In this work, we investigate the performance of the so-called Preheat-parallel CHP configuration, for the connection to a thermal network (TN). A low-temperature geothermal source (130°C), and the connection to a 75°C/50°C and a 75°C/35°C thermal network are considered. For a pure parallel CHP configuration, the brine delivers heat to the ORC and the thermal network in parallel. However, after having delivered heat to the ORC, the brine in the ORC branch still contains some energy which is not used. The Preheat-parallel configuration utilizes this heat to preheat the TN water before it enters the parallel branch, where the TN water is heated to the required supply temperature. The Preheat-parallel configuration is especially favorable when connected to a thermal network with a low return temperature, a large temperature difference between supply and return temperatures—thereby exploiting the preheating-effect—and for high heat demands.In this paper, we focus on the effect of the pinch-point-temperature difference (∆Tpinch) on the plant performance. ∆Tpinch is directly related with the size and cost of the heat exchangers and strongly influences the preheating-effect, which is the most characteristic feature of the Preheat-parallel configuration. First, we present the results of a detailed sensitivity analysis of ∆Tpinch. A higher ∆Tpinch results in a lower preheating-effect, a lower net power output and, correspondingly, lower plant efficiency. Furthermore, we compare the performance of the Preheat-parallel configuration with the convenient parallel and series CHP configurations. For all three configurations, the performance decreases with an increase of ∆Tpinch. For the considered thermal network requirements, the net power generation is the highest for the Preheat-parallel configuration. With respect to the parallel configuration, the gain in net power generation stays approximately constant (75°C/35°C TN) or decreases (75°C/50°C TN) with the imposed pinch-point-temperature difference. With respect to the series configuration, the gain in net power generation increases for a higher value of ∆Tpinch. This means that the impact of ∆Tpinch is the biggest for the series configuration, followed by the Preheat-parallel configuration, and that the impact on the performance of the parallel configuration is the smallest.

Primary radiation damage of Zr-0.5%Nb binary alloy: atomistic simulation by molecular dynamics method

Ab initio calculations predict high positive binding energy (∼1 eV) between niobium atoms and self-interstitial configurations in hcp zirconium. It allows the expectation of increased niobium fraction in self-interstitials formed under neutron irradiation in atomic displacement cascades. In this paper, we report the results of molecular dynamics simulation of atomic displacement cascades in Zr-0.5%Nb binary alloy and pure Zr at the temperature of 300 K. Two sets of n-body interatomic potentials have been used for the Zr-Nb system. We consider a cascade energy range of 2–20 keV. Calculations show close estimations of the average number of produced Frenkel pairs in the alloy and pure Zr. A high fraction of Nb is observed in the self-interstitial configurations. Nb is mainly detected in single self-interstitial configurations, where its fraction reaches tens of percent, i.e. more than its tenfold concentration in the matrix. The basic mechanism of this phenomenon is the trapping of mobile self-interstitial configurations by niobium. The diffusion of pure zirconium and mixed zirconium-niobium self-interstitial configurations in the zirconium matrix at 300 K has been simulated. We observe a strong dependence of the estimated diffusion coefficients and fractions of Nb in self-interstitials produced in displacement cascades on the potential.

Isolable Bis(triarylamine) Dications: Analogues of Thiele's, Chichibabin's, and Müller's Hydrocarbons.

Since the pioneering work by Thiele and Chichibabin, who synthesized the first diradicals bridged by phenylene and biphenylene groups in 1904 and 1907, respectively, numerous efforts have been devoted to synthesizing stable diradicals during the last few decades, and several strategies have been developed to stabilize these highly reactive diradicals. In this Account, we describe the synthesis and characterization of isolable bis(triarylamine) dications, nitrogen analogues of Thiele's, Chichibabin's, and Müller's hydrocarbons, which represent facilely accessible, stable diradicals by replacing carbinyl centers with isoelectronic aminium centers. Along with discussing the molecular structures and electronic structures of the isolated bis(triarylamine) dications, their spectroscopic and magnetic properties are also introduced. Since 2011, we have reported the stabilization of a variety of radical cations bearing the weakly coordinating anion Al(ORF)4- (RF = polyfluorinated alkyl group), which we have recently successfully applied for the stabilization and crystallization of bis(triarylamine) dications, analogues of Thiele's, Chichibabin's, and Müller's hydrocarbons. Prior to our and Kamada's work, there have been only three stable bis(triarylamine) dications isolated in the solid state. The facile access of bis(triarylamine) dications in their crystalline forms allowed us to pursue a deep investigation of their solid-state structures, electronic structures, and physical properties. Similar to their hydrocarbon analogues, bis(triarylamine) dications possess characteristic resonance structures between open-shell singlet (OS) diradicals and closed-shell (CS) quinoidal forms. The combination of single-crystal X-ray diffraction (XRD) analysis and density functional theory (DFT) calculations has proved to be a robust strategy to gain a better understanding of the electronic structures of the obtained diradicals. The structural parameters obtained from XRD analysis reflect the overall contribution of each resonance structure to the crystal structure. The comparison of the parameters from the crystal structures with those from DFT calculations for the pure electronic configurations (CS, OS, and triplet states) affords an overview of the ground-state structures of the diradicals. To justify the "degree" of singlet diradical character, the diradical parameter y is applied, which is estimated by the occupancy of the lowest unoccupied natural orbital (LUNO) having antibonding nature (y = 0 for the closed-shell and y = 1 for the pure singlet diradical). In addition, magnetic susceptibility measurements serve as a practical experimental method to determine the singlet-triplet energy gaps of the isolable diradical dications. Through detailed studies on isolable bis(triarylamine) dications, magnetic bistability caused by intramolecular electron-exchange interactions was observed. Moreover, we also found that the singlet-triplet energy gaps of the diradicals could be thermally controlled. These investigations highlight the potential of bis(triarylamine) dications as building blocks for functional materials.

Charge screening strategy for domain pattern control in nano-scale ferroelectric systems

Strain engineering is a widespread strategy used to enhance performance of devices based on semiconductor thin films. In ferroelectrics strain engineering is used to control the domain pattern: When an epitaxial film is biaxially compressed, e.g. due to lattice mismatch with the substrate, the film displays out-of-plane, often strongly enhanced polarization, while stretching the film on the substrate results in in-plane polarization. However, this strategy is of a limited applicability in nanorods because of the small rod/substrate contact area. Here we demonstrate another strategy, in which the polar axis direction is controlled by charge screening. When charge screening is maintained by bottom and top metallization, the nanorods display an almost pure c-domain configuration (polarization perpendicular to the substrate); when the sidewalls of the nanorods are metallized too, a-domain formation prevails (polarization parallel to the substrate). Simulations of the depolarization fields under various boundary conditions support the experimental observations. The employed approach can be expanded to other low-dimensional nano-scale ferroelectric systems.

Simplified stress analysis of hybrid (bolted/bonded) joints

The load transfer in hybrid (bolted/bonded) – denoted HBB – single-lap joints is complicated due to the association of two different transfer modes (discrete and continuous) through elements with different stiffnesses. The Finite Element (FE) method can be used to address the stress analysis of those joints. However, analyses based on FE models are computationally expensive and it would be profitable to use simplified approaches enabling extensive parametric studies. Two among the authors of this paper participated in the development of a dedicated 1D-beam approach [25]. This paper presents an extension of this framework enabling (i) the analysis of HBB joints made of dissimilar laminated or monolithic adherends, and (ii) the introduction of non linear material behaviour for both the adhesive layer and the fasteners. The output data are the distributions of displacements and forces in the adherends and fasteners, as well as those of adhesive shear and peeling stresses, allowing for a fast assessment of the material behaviour and strength prediction of HBB joints. The use of this model is illustrated in the identification of the failure mechanisms of HBB joints under quasistatic loadings, based on experimental and numerical tests on single-lap HBB joint. It is worth mentioning that the model can support pure bonded and pure bolted configurations. It can be used during the presizing phase at the design office (possibly independently on commercial software), to obtain quickly mechanical performances and to help in decision making. Moreover, it was shown that the judicious choice of the adhesive material allows for a significant increase of the static and fatigue strength compared to pure bolted or bonded corresponding configurations [17,24]. The model can then be used to formulate at best adhesive materials to optimize the mechanical performance of HBB joints according to work specifications.

Enforcing causality in nonrelativistic equations of state at finite temperature

We present a thermodynamically consistent method by which equations of state based on nonrelativistic potential models can be modified so that they respect causality at high densities, both at zero and finite temperature (entropy). We illustrate the application of the method using the high density phase parametrization of the well known APR model in its pure neutron matter configuration as an example. We also show that, for models with only contact interactions, the adiabatic speed of sound is independent of the temperature in the limit of very large temperature. This feature is approximately valid for models with finite-range interactions as well, insofar as the temperature dependence they introduce to the Landau effective mass is weak. In addition, our study reveals that in first principle nonrelativistic models of hot and dense matter, contributions from higher than two-body interactions must be screened at high density to preserve causality.

Ordered and Disordered Hybrid Tunnel Structured Manganese Oxides for Na-Ion Batteries

Through modification of previously developed hydrothermal techniques, we synthesize two tunnel structured manganese oxides with novel hybrid tunnel configurations and investigate their behavior in Na-ion batteries. Tunnel manganese oxides represent a promising class of materials for Na-ion batteries due to their low cost, low toxicity, and high electrochemical activity. The two materials studied in this work contain unique combinations of structural tunnels composed of varying amounts of MnO6 octahedra surrounding stabilizing Na+ ions, resulting in numerous different tunnel dimensions within individual nanostructures. Through cross-sectional TEM analysis, the ordered phase was found to consist of a systematic combination of 2x2, 2x3, and 2x4 octahedra tunnels. The disordered phase, on the other hand, was found to consist of a more random and nonuniform distribution of not only 2xn (n=2, 3, 4, 5, 6) tunnels, but also larger 3x3 octahedra tunnels. Moreover, although both materials were synthesized with a nanowire morphology, the disordered phase is found to be composed of nanowires with smaller diameter. We investigate these two materials as cathodes for Na-ion batteries and find that upon first discharge, the ordered phase exhibits a capacity nearly 300 mAh g-1, while the disordered phase exhibits a capacity of just below 200 mAh g-1. Upon further cycling, however, the disordered phase maintains a greater amount of its initial capacity, indicating that although the better defined tunnel structure may be advantageous for greater initial ion intercalation capacity, the disordered phase shows a greater degree of electrochemical stability. The rate performance of these two materials is discussed in relationship to the different diffusion pathways present in the materials, as well as the structural stability of the two phases upon repeated ions insertion and deinsertion. The performance of these materials is also compared to tunnel manganese oxides with pure tunnel configurations, and the advantage of having such a hybrid tunnel configuration is also emphasized. This work highlights the performance of two similar novel cathode materials for Na-ion batteries, as well as the relationship between the degree of structural order in manganese oxides and their electrochemical behavior in Na-ion batteries.

誘電性エラストマーによる発電に関する研究

The purpose of this research is to increase energy density and efficiency of electric generator made by dielectric elastomer (DE). With pure shear loading configuration, the energy density and efficiency was compared by controlling constant voltage and constant current. It was found that the energy density and efficiency with constant current method was higher than those with constant voltage method. Moreover, it was indicated that both the energy density and the efficiency increase with an increase in charging voltage.

Cyanide-bridged mixed-valence copper(II/I) coordination polymers: Unique 7-connected sev-type 3D network versus anionic 2D host network encapsulated with cationic complex

Reactions of CuCl2, K2[Ni(CN)4]/K3[Co(CN)6], and 5-amino-1H-tetrazole led to cyanide-bridged mixed-valence Cu(II/I) complexes, [Cu(H2O)3Cu3(CN)5] (1) and [Cu(H2O)4][Cu4(CN)6] (2).The uncommon semi-closed {Cu2(CN)3} dimmers in 1 are bridged by μ3-C,C,N cyanide ligands to afford rare 1D centipedal-like chain motifs, which are further bridged by μ2-C,N and metalloligand “CN–Cu(4)–CN” to finish sophisticated zeolite-like 3-D structure. Topologically, 1 is the first example of uninodal 7-connected sev-like cyanide-bridged network. Compound 2 consists of two-dimensional honeycomb-related anionic layers [Cu4(CN)6]2−, within which the [Cu(H2O)4]2+ cations are intercalated into alternate interlamellar space. Compound 1 shows antiferromagnetic couple arising from pure ground-state configuration of Cu(II) mediated by diamagnetic bridges –CN–CuI–CN−. The inclusion compound 2 shows blue photoluminescence originated from Cu(I) center to the unoccupied π* orbital of the cyanide ligand (MLCT) charge transfer.

Efficacy of Concomitant Intratympanic Steroid Injection for Sudden Deafness According to Initial Hearing Loss.

We identified the efficacy and appropriate target group for intratympanic steroid injections (ITS) in patients with idiopathic sudden sensorineural hearing loss (ISSNHL). Retrospective case-control study. Fifty-five ears treated with concomitant ITS and systemic steroids and 165 ears without ITS treatment were identified. Each case had three controls matched according to the age, sex, and the presence of vertigo. Patients were divided into subgroups according to pure tone audiometric configuration and the levels of initial hearing loss. Hearing results and frequency-related hearing gain were investigated. Additional ITS was effective for patients with an ascending type audiogram or patients with Grade 3 (60-90 dB) initial hearing loss. Concomitant ITS, however, resulted in a negative effect on hearing in patients with Grades 1 and 2 (<60 dB). ITS resulted in significant (p < 0.05) hearing improvement at 250 Hz in the Grade 3 (60-90 dB) and Grade 4 (>90 dB) ITS subgroups. The efficacy of additional ITS for ISSNHL was different among subgroups with various levels of initial hearing loss or audiogram configuration.

$ \beta^{-}$ transitions of 16 7N9 $\rightarrow$ 16 8O8 with optimized SDI residual interaction using pnTDA and TDA approximations

Within a developed particle-hole approach, a systematic study of the $\beta^{-}$ transition from the ground state of the 16N nucleus to the ground and some exited states of the 16O nucleus has been carried out. The energy spectrum and the wave functions of pure configuration of the 16N and 16O nuclei are numerically obtained using the mean-field shell model with respect to the Woods-Saxon nuclear potential accompanying spin-orbit and Coulomb interaction. Considering SDI residual interaction, mixed configuration of ground and excited pnTDA and TDA states are extracted for the aforementioned nucleus. These energy spectra and corresponding eigenstates are highly correspondent to the experimental energy spectrum and eigenstates after adjusting the residual potential parameters using the Nelder-Mead (NM) algorithm. In this approach, the endpoint energy, log ft and the partial half-lives of some possible transitions are calculated. The obtained results using the optimized SDI approach are reasonably close to the available experimental data.

Energy consumption and cost analysis of hybrid electric powertrain configurations for two wheelers

The development of hybrid electric two wheelers in recent years has targeted the reduction of on road emissions produced by these vehicles. However, added cost and complexity have resulted in the failure of these systems to meet consumer expectations. This paper presents a comparative study of the energy economy and essential costs of alternative forms of small two wheelers such as scooters or low capacity motorcycles. This includes conventional, hybrid, plug-in hybrid and electric variants. Through simulations of vehicle driving range using two popular driving cycles it is demonstrated that there is considerable benefit in fuel economy realised by hybridising such vehicles. However, the added costs associated with electrification, i.e. motor/generator, power electronics, and energy storage provide a significant cost obstacle to the purchase of such vehicles. Only the pure electric configuration is demonstrated to be cost effective over its life in comparison to conventional two wheelers. Both the hybrid electric and plug-in equivalents must overcome significant upfront costs to be cost competitive with conventional vehicles. This is demonstrated to be achieved if the annual driving range of the vehicle is increased substantially from the assumed mean. Given the shorter distances travelled by most two wheeler drivers it can therefore be concluded that the development of similar hybrid electric vehicles are unlikely to achieve the desired acceptance that pure electric or conventional equivalents currently achieve.

Noninvasive fetal electrocardiography: an overview of the signal electrophysiological meaning, recording procedures, and processing techniques.

Noninvasive fetal electrocardiography (fECG), obtained positioning electrodes on the maternal abdomen, is important in safeguarding the life and the health of the unborn child. This study aims to provide a review of the state of the art of fECG, and includes a description of the parameters useful for fetus clinical evaluation; of the fECG recording procedures; and of the techniques to extract the fECG signal from the abdominal recordings. The fetus clinical status is inferred by analyzing growth parameters, supraventricular arrhythmias, ST-segment variability, and fetal-movement parameters from the fECG signal. This can be extracted from an abdominal recording obtained using one of the following two electrode-types configurations: pure-abdominal and mixed. Differently from the former, the latter also provides pure maternal ECG tracings. From a mathematical point of view, the abdominal recording is a summation of three signal components: the fECG signal (i.e., the signal of interest to be extracted), the abdominal maternal ECG (amECG), and the noise. Automatic extraction of fECG includes noise removal by abdominal signal prefiltration (0.5-45 Hz bandpass filter) and amECG cancellation. Differences among methods rely on different techniques used to extract fECG. If pure abdominal electrode configurations are used, fECG is extracted directly from the abdominal recording using independent component analysis or template subtraction. Eventually, if mixed electrode configurations are used, the fECG can be extracted using the adaptive filtering fed with the maternal ECG recorded by the electrodes located in the woman thorax or shoulder.

Dynamics of a ±1/2 defect pair in a confined geometry: A thin hybrid aligned nematic cell**Project supported by the National Natural Science Foundation of China (Grant No. 11374087) and the Key Subject Construction Project of Hebei Province University.

Confined geometry can change the defect structure and its properties. In this paper, we investigate numerically the dynamics of a dipole of ±1/2 parallel wedge disclination lines in a confined geometry: a thin hybrid aligned nematic (HAN) cell, based on the Landau–de Gennes theory. When the cell gap d is larger than a critical value of 12ξ (where ξ is the characteristic length for order-parameter change), the pair annihilates. A pure HAN configuration without defect is formed in an equilibrium state. In the confined geometry of d ≤ 12ξ, the diffusion process is discovered for the first time and an eigenvalue exchange configuration is formed in an equilibrium state. The eigenvalue exchange configuration is induced by different essential reasons. When 10ξ < d ≤ 12ξ, the two defects coalesce and annihilate. The biaxial wall is created by the inhomogeneous distortion of the director, which results in the eigenvalue exchange configuration. When d ≤ 10ξ, the defects do not collide and the eigenvalue exchange configuration originates from the biaxial seeds concentrated at the defects.

On the identifiability of Anand visco-plastic model parameters using the Virtual Fields Method

In this paper, the issue of the identification of constitutive parameters of the Anand visco-plastic model is addressed using the Virtual Fields Method (VFM) in an infinitesimal deformation framework. By using VFM, one can take advantage of heterogeneous strain fields obtained by full-field experimental techniques, such as Digital Image Correlation (DIC). Since a wide range of strains and strain rates are sampled in a typical heterogeneous strain field, the number of experiments required to reliably estimate constitutive parameters, especially of rate-dependent materials, is significantly smaller than that needed if conventional experiments (such as uniaxial tension or pure shear configurations) leading to nominally homogeneous strain states were used. However, for such an approach to be successful, the test configuration and loading program should be such that all the constitutive parameters play a significant role (are ‘activated’) in the resulting strain fields. An analysis of the Anand constitutive model shows that 4 of the 8 parameters can only be found to within a multiplicative constant from full-field kinematic data. Therefore, one of these 4 constants is arbitrarily chosen and the activation of the remaining 7 material parameters is investigated by performing a series of one-element models. Detailed sensitivities of the VFM cost function to these material parameters are derived for a variety of normal stress to shear stress ratios and loading rates. Two main conclusions are drawn based on this one-element study: (i) the VFM cost function sensitivities to the material parameters do not vary significantly with loading ratios or rates, and (ii) 2 of the 7 material parameters are not activated for any of the loading ratios or rates considered. Based on the results of the finite-element study, a modified single lap-shear test configuration is designed to yield heterogeneous strains in the joint. Deformation data from a finite-element analysis of this experiment are used as inputs to a VFM routine to compute the Anand material parameters. Our results highlight that non-uniqueness of the identified parameters is a significant issue. The effect of the choice of the cost function and the loading profile on the inverse technique is also thoroughly investigated.