Analog Model Research Articles

Hemodynamic aspects of the Budd–Chiari syndrome of the liver: A computational model study

Budd–Chiari syndrome (BCS) is a rare liver disease characterised by the obstruction of draining hepatic veins, and subsequent reduced blood return to the heart. Although many clinical BCS studies have been reported, few studies have quantified the associated changes that occur in the entire hepatic circulation. In this communication, we present an electrical analog model of the hepatic circulation that incorporates the Hepatic Arterial Buffer Response (HABR) mechanism in both the left and right lobes. Using this model we can simulate the hepatic flow under both normal and acute BCS conditions. The model can capture subtle features in the hepatic circulation, such as reduced total portal flow but increased arterial flow under BCS. This observation was previously reported in literature and may have clinical implications. As such, we suggest the presented model could be used for the analysis of systematic haemodynamic changes of BCS and therefore may be useful in supporting clinical interventions.

Characterization of heat transfer and its effect on solidification in water cooled LPDC of wheels

Computational process modelling has become an important engineering tool in the casting industry to predict the solidification sequence in complex castings. Used properly, this tool can help reduce manufacturing costs. One of the challenging issues in developing casting simulations of the low pressure die casting (LPDC) process for automotive wheels is to quantify the heat transfer coefficients (HTC) within the cooling channels in a die. When water is used as the cooling media, the HTCs exhibit a complex, non-linear behaviour due to the boiling phenomena that occur making it possible to extract a significant amount of heat from the die in a short period of time and influence the solidification of a wheel. Primarily, constant heat transfer coefficients have been used to describe this heat transfer in casting models up until now, but an opportunity exists to improve the transient description of heat transfer in channels cooled with water. In this paper, HTC’s in a lab-scale physical analogue model of die cooling will be characterized as a function of initial die temperatures.

Data-Driven Interpolation of Sea Level Anomalies Using Analog Data Assimilation

From the recent developments of data-driven methods as a means to better exploit large-scale observation, simulation and reanalysis datasets for solving inverse problems, this study addresses the improvement of the reconstruction of higher-resolution Sea Level Anomaly (SLA) fields using analog strategies. This reconstruction is stated as an analog data assimilation issue, where the analog models rely on patch-based and Empirical Orthogonal Functions (EOF)-based representations to circumvent the curse of dimensionality. We implement an Observation System Simulation Experiment (OSSE) in the South China Sea. The reported results show the relevance of the proposed framework with a significant gain in terms of Root Mean Square Error (RMSE) for scales below 100 km. We further discuss the usefulness of the proposed analog model as a means to exploit high-resolution model simulations for the processing and analysis of current and future satellite-derived altimetric data with regard to conventional interpolation schemes, especially optimal interpolation.

Huygens’ envelope principle in Finsler spaces and analogue gravity

We extend to the n-dimensional case a recent theorem establishing the validity of the Huygens’ envelope principle for wavefronts in Finsler spaces. Our results have direct applications in analogue gravity models, for which the Fermat’s principle of least time naturally gives origin to an underlying Finslerian geometry. For the sake of illustration, we consider two explicit examples motivated by recent experimental results: surface waves in flumes and vortices. For both examples, we have distinctive directional spacetime structures, namely horizons and ergospheres, respectively. We show that both structures are associated with certain directional divergences in the underlying Finslerian (Randers) geometry. Our results show that Finsler geometry may provide a fresh view on the causal structure of spacetime, not only in analogue models but also for general relativity.

Deformation Patterns and Surface Settlement Trough in Stratified Jointed Rock in Tunnel Excavation

The special mechanics of inclined stratified jointed rock may cause unexpectedly surface settlement. This paper studies the special rock condition with analyses of discrete element method (DEM) numerical analysis, field monitoring data and physical model testing results. Numerical models with different internal friction angles, different thicknesses and different inclination angles were analyzed. The surrounding rock deformation patterns can be divided into three categories — shear deformation pattern, mixed deformation pattern and normal deformation pattern — based on different dominant deformation behaviors. The beam analogue model and combined beam analogue model were discussed in different stratum thickness conditions to understand the surrounding deformation patterns. It was found that the settlement trough consisted of two diverging dissymmetrical Gaussian curves by comparing the settlement troughs for different inclination angles, which is unique for excavation in ordinary rock conditions. In this paper, the approximated formulas to verifying the settlement trough position were provided to secure the safety of the upper structures during tunnel excavation.

A classical limit of Grover’s algorithm induced by dephasing: Coherence versus entanglement

A new approach to the classical limit of Grover’s algorithm is discussed by assuming a very rapid dephasing of a system between consecutive Grover’s unitary operations, which drives pure quantum states to decohered mixed states. One can identify a specific element among [Formula: see text] unsorted elements by a probability of the order of unity after [Formula: see text] steps of classical amplification, which is realized by a combination of Grover’s unitary operation and rapid dephasing, in contrast to [Formula: see text] steps in quantum mechanical amplification. The initial two-state system with enormously unbalanced existence probabilities, which is realized by a chosen specific state and a superposition of all the rest of the states among [Formula: see text] unsorted states, is crucial in the present analysis of classical amplification. This analysis illustrates Grover’s algorithm in extremely noisy circumstances. A similar increase from [Formula: see text] to [Formula: see text] steps due to the loss of quantum coherence takes place in the analog model of Farhi and Gutmann where the entanglement does not play an obvious role. This supports a view that entanglement is crucial in quantum computation to describe quantum states by a set of qubits, but the actual speedup of the quantum computation is based on quantum coherence.

Deterministic Parameter Change Models in Continuous and Discrete Time

We consider a model of deterministic one‐time parameter change in a continuous time autoregressive model around a deterministic trend function. The exact discrete time analogue model is detailed and compared to corresponding parameter change models adopted in the discrete time literature. The relationships between the parameters in the continuous time model and the discrete time analogue model are also explored. Our results show that the discrete time models used in the literature can be justified by the corresponding continuous time model, with a only a minor modification needed for the (most likely) case where the changepoint does not coincide with one of the discrete time observation points. The implications of our results for a number of extant discrete time models and testing procedures are discussed.

Analisis Multi Raster SRTM, Radarsat dan Landsat untuk Karakterisisasi Morfo-struktur dari Geometri Sesar di Daerah Binuang, Kalimantan Selatan

The Binuang area and its surroundings are genetically structural landforms which characterized by cuesta ridge line with curve lineaments pattern on northeast-southwest direction. Geomorphological approach were carried out to determine structural geometry of geological surface using qualitative and quantitative approach on multiple map analysis of remote sensing data. The result of quantitative analysis on elevation data are used to classify heights, slope shape and steepness, lineaments, drainage, and slope aspect. Optical images were classified to determine lithological pattern and boundaries through analysis of band ratios, decorrelation stretch, principal component, and spatial enhancement. The research area are classified into eight class of structural landforms, depicting deformations that occured in western flank of Meratus Mountains. The surface pattern indicates the influence of compressional stress, shown by fold belt with longitudinal characteristic and fault-bounded anticlines on northeast-southwest axis. The formation of main structure pattern on research area was compared with that on strike-slip fault analog model. The resulting correlation factor, R=0.932, shows that both of them are highly correlated. In conclusion, surface structure can possibly form another variation of thrusted mountain belt, such as thrust-dominated restraining bends.Keywords: landsat, SRTM, morphostructure, morphometry, rhomboidal pattern, Meratus.

Analisis Multi Raster SRTM, Radarsat dan Landsat untuk Karakterisisasi Morfo-struktur dari Geometri Sesar di Daerah Binuang, Kalimantan Selatan

The Binuang area and its surroundings are genetically structural landforms which characterized by cuesta ridge line with curve lineaments pattern on northeast-southwest direction. Geomorphological approach were carried out to determine structural geometry of geological surface using qualitative and quantitative approach on multiple map analysis of remote sensing data. The result of quantitative analysis on elevation data are used to classify heights, slope shape and steepness, lineaments, drainage, and slope aspect. Optical images were classified to determine lithological pattern and boundaries through analysis of band ratios, decorrelation stretch, principal component, and spatial enhancement. The research area are classified into eight class of structural landforms, depicting deformations that occured in western flank of Meratus Mountains. The surface pattern indicates the influence of compressional stress, shown by fold belt with longitudinal characteristic and fault-bounded anticlines on northeast-southwest axis. The formation of main structure pattern on research area was compared with that on strike-slip fault analog model. The resulting correlation factor, R=0.932, shows that both of them are highly correlated. In conclusion, surface structure can possibly form another variation of thrusted mountain belt, such as thrust-dominated restraining bends.Keywords: landsat, SRTM, morphostructure, morphometry, rhomboidal pattern, Meratus.

Analisis Multi Raster SRTM, Radarsat dan Landsat untuk Karakterisisasi Morfo-struktur dari Geometri Sesar di Daerah Binuang, Kalimantan Selatan

The Binuang area and its surroundings are genetically structural landforms which characterized by cuesta ridge line with curve lineaments pattern on northeast-southwest direction. Geomorphological approach were carried out to determine structural geometry of geological surface using qualitative and quantitative approach on multiple map analysis of remote sensing data. The result of quantitative analysis on elevation data are used to classify heights, slope shape and steepness, lineaments, drainage, and slope aspect. Optical images were classified to determine lithological pattern and boundaries through analysis of band ratios, decorrelation stretch, principal component, and spatial enhancement. The research area are classified into eight class of structural landforms, depicting deformations that occured in western flank of Meratus Mountains. The surface pattern indicates the influence of compressional stress, shown by fold belt with longitudinal characteristic and fault-bounded anticlines on northeast-southwest axis. The formation of main structure pattern on research area was compared with that on strike-slip fault analog model. The resulting correlation factor, R=0.932, shows that both of them are highly correlated. In conclusion, surface structure can possibly form another variation of thrusted mountain belt, such as thrust-dominated restraining bends.Keywords: landsat, SRTM, morphostructure, morphometry, rhomboidal pattern, Meratus.

Tustin's technique based digital decentralized load frequency control in a realistic multi power system considering wind farms and communications delays

Abstract This paper presents a digital model of decentralized Load Frequency Control (LFC) using an optimal PID controller-based Particle Swarm Optimization (PSO) in Egyptian Power System (EPS) considering communication delays. The EPS includes both conventional generation units (i.e., non-reheat, reheat, and hydraulic power plants) with inherent non-linearities and wind power, which extracted from Zafarana wind farm, location in Egypt. Thus, the optimal digital controller-based Tustin’s technique is designed for every subsystem of the EPS separately to guarantee the stability of the overall closed-loop system. The performance of the proposed digital model is tested and compared with the analog model under variation in loading patterns, loading conditions, system parameters, wind farm penetration, and communication delays. Results approved that, the proposed digital model can effectively regulate the system frequency and guarantee robust performance under different conditions. Also, it gives a reliable performance at large sampling times, which means a reduction of implementation cost.

Stochastic ensemble climate forecast with an analogue model

Abstract. This paper presents a system to perform large-ensemble climate stochastic forecasts. The system is based on random analogue sampling of sea-level pressure data from the NCEP reanalysis. It is tested to forecast a North Atlantic Oscillation (NAO) index and the daily average temperature in five European stations. We simulated 100-member ensembles of averages over lead times from 5 days to 80 days in a hindcast mode, i.e., from a meteorological to a seasonal forecast. We tested the hindcast simulations with the usual forecast skill scores (CRPS or correlation) against persistence and climatology. We find significantly positive skill scores for all timescales. Although this model cannot outperform numerical weather prediction, it presents an interesting benchmark that could complement climatology or persistence forecast.

360 Intrusions in a Miniature Volcano: Birth, Growth, and Evolution of an Analog Edifice

Volcanoes throughout the world have been monitored with complete geophysical data for no more than three decades, a relatively short time compared to their overall life. The consequence is that we lack a long observation of volcanic growth and behavior to get a more complete picture of the interaction between edifice stress state and magma transfer. Here we present the birth and evolution of a 83x83 cm analog model, where we reproduce for the first time volcanic growth over 360 successive intrusions (15 mL every half hour, at a rate of 3 mL/min) in an analog elasticity-dominated material (pigskin gelatine). Our model volcano started as a flat topography and ended 3.82 cm in height at the summit. It displayed cyclic eruptive patterns with alternating phases of eruptive and purely intrusive behavior. Alike to many intraplate volcanoes in nature, main dyke swarms produced in the experiment were disposed in a three-branched star pattern centered above the injection source (“volcanic rift zones”). Two radial sill networks, at source depth and edifice base, surrounded them. The interaction of edifice growth and magma transfer was dominated by long-term radial compressive stress building during dyke swarming and radial compressive stress release/compensation during sill emplacement. Near-surface stresses, deduced from the main orientation eruptive fissures and “dry” fractures, became more localised as the volcano grew. At the end of the experiment, the shallow stress field was interpreted as generally extensional radial at the summit, extensional tangential on the flanks, and compressive radial in distal areas.

Using computer simulation to explore mechanisms of right ventriculo-arterial uncoupling after lung resection

Right ventriculo-arterial (RV-VA) coupling expressed as a ratio of ventricular contractility to afterload (Ees/Ea) provides an integrated assessment of the efficiency of the pulmonary vascular—right ventricular unit. In previous work our group has demonstrated deterioration in cardiovascular magnetic resonance (CMR)-derived indices of VA coupling in patients undergoing lung resection. In patients, however, exploration of the mechanisms underlying uncoupling (i.e. the relative contributions of changes in contractility and afterload) is challenging, requiring expensive, invasive techniques. In this study we sought to use the Aplysia CardioVascular Lab haemodynamic simulator1 to explore in silico the mechanisms of uncoupling observed after lung resection. Demographic and haemodynamic data [including stroke volume (SV) and end-systolic volume (ESV)] were obtained from 15 patients enrolled in a CMR study examining RV-VA function before and on Day 2 after lung resection. Coupling was derived as the ratio of SV to ESV.2 Physiological adaptations were run for each patient within the simulator both before and after simulated lung resection (simulated by reducing the number of pulmonary blood vessels in the simulated patients in proportion to the volume of lung resected according to a 19-segment model of the pulmonary tree). The ratio of SV/ESV fell after both real and simulated lung resection implying deterioration in RV-VA coupling. The median SV/ESV fell by –0.14 [inter-quartile range (IQR), –0.34 to 0.01; P=0.02] in vivo and by –0.10 (IQR, –0.29 to –0.08; P<0.01) in silico; bias for the difference 0.01 (LOA –0.62 to 0.62), concordance 81.8%. Within the simulation this was attributable to a significant increase in Ea (P<0.01 for change; association between change in Ea and SV/ESV r=–0.9, P<0.01). There was, however, no association between changes in SV/ESV in real and simulated patients (r=0.32, P=0.24), and no association between simulated changes in Ea after lung resection and observed changes in SV/ESV in patients (r=–0.11, P=0.69). The mechanism of postoperative RV dysfunction after lung resection is widely believed to be the result of increased afterload, although this has not been demonstrated in clinical studies. The lack of association observed between simulated changes in Ea and changes in coupling seen in patients suggests that the mechanism of postoperative un-coupling is not simply related to the mechanical effect of a reduced pulmonary vasculature as would have been simulated according to the electrical analogue model within Aplysia. We hypothesise that an acute inflammatory injury to the RV impairs RV contractility and contributes to postoperative RV dysfunction, a mechanism which would not have been demonstrated by the computational model. 1.Broome M, Maksuti E, Bjallmark, et al. Biomed Eng Online 2013; 12: 692.Sanz J, Garcia-Alvarez A, Fernandez-Friere L. Heart 2012; 98: 238–43

2. 45 Ga break-up of the Archaean continent in Northern Fennoscandia: Rifting dynamics and the role of inherited structures within the Archaean basement

Constraints from restoration of minor rift-related faults preserved from subsequent Palaeoproterozoic overprint along the southern margin of the Peräpohja Belt, northern Fennoscandia indicate local NE-SW extension directions prevailed at the time of 2.44 Ga rifting of the Archaean continent. This palaeostress field is attributed to pull-apart setting of the Peräpohja Belt at a left overstepping zone of major sinistral N-S trending deformation zones. Consequently, the variably overprinted NW-SE trending structures of the Peräpohja Belt, including the NW-SE central graben were originally generated as normal faults. The proposed setting is compatible with a conducted reconnaissance sandbox analogue model where the orientation of the major normal faults was controlled by the ambient stress field within the step-over zone between strike-slip faults. By contrast, the faults bounding E-W to ENE-WSW trending basement horsts are the result of reactivation of older basement structures underlying the pull-apart basin. Based on the results, we infer that the final break-up of the Archaean continent in northern Fennoscandia utilized the 2.44 Ga rift-related NW-SE trending crustal anisotropy (parallel with dyke swarms), with pre-existing Archaean N-S trending structures reactivated as second-order shear zones in-between. The voluminous syn-rift 2.5–2.4 Ga and later pulses of mafic magmatism (2.32–1.98 Ga) are considered indicative of active-type rifting which onset was controlled by a mantle plume centred within a supercraton formed by the Superior, Hearne and Karelian (-Kola) cratons. The presented model supports the continuity of the Archaean craton beyond the Caledonian Orogen towards north-west and explains its segmentation, suggesting a model for the localization of the Palaeoproterozoic supracrustal belts of Northern Fennoscandia. Moreover, this paper provides an approach to understand the basement-cover relationships and the structural signatures within these relatively shallow supracrustal belts which are highly prospective for mineral deposits.

Dynamical equations and Lagrange–Ricci flow evolution on prolongation Lie algebroids

The approach to nonholonomic Ricci flows and geometric evolution of regular Lagrange systems (S. Vacaru. J. Math. Phys. 49, 043504 (2008); Ibid. Rep. Math. Phys. 63, 95 (2009)) is extended to include geometric mechanics and gravity models on Lie algebroids. We prove that such evolution scenarios of geometric mechanics and analogous gravity can be modeled as gradient flows characterized by generalized Perelman functionals if an equivalent geometrization of Lagrange mechanics (J. Kern. Arch. Math. (Basel), 25, 438 (1974)) is considered. The Hamilton equations on Lie algebroids describing Lagrange–Ricci flows are derived. Finally, we show that geometric evolution models on Lie algebroids are described by effective thermodynamical values derived from statistical functionals on prolongation Lie algebroids.

Propagation and coalescence of en-echelon cracks under a far-field tensile stress regime: An experimental study

Experiments were carried out to observe the variation in propagation and linkage of parallel en-echelon cracks with varying orientation of the crack array and different relative position of the cracks within the array in an extensional regime. Two-layered analogue model, with a basal layer of pitch overlain by a layer of kaolin paste was used in the experiments. En-echelon cracks were pre-cut within the kaolin layer maintaining specific geometrical parameters of the cracks (e.g., length, centre spacing, separation) in such a manner that there was a weak (though not negligible) local tip-induced stress favouring curvature of adjacent crack tips towards one another. The results obtained were matched with natural pattern of linkage of veins, rift basins and spreading ridges, as described in the relevant literature. The experimental results showed that the final pattern of linkage between the cracks was a result of initial deflection of crack tip from its plane due to combined effect of local and far-field stress. When the deflection of tip from the crack plane was between \(0{^{\circ }}\) to \(45{^{\circ }}\), a ‘tip to wall’ linkage took place between adjacent cracks isolating a rhombohedral area in the interaction zone. The resultant structure could be geometrically comparable to a micro-plate-like structure isolated due to linkage of ridge segments initially forming an overlapping spreading centre (OSC). When the deflection of tip from the crack plane was greater than \(45{^{\circ }}\), a ‘tip to tip’ linkage between adjacent cracks took place resulting in a structure similar to a transform fault between spreading ridges and or rift basins. When effect of the remote stress opposed the tip induced stress, no linkage took place between the adjacent cracks, and finally the tips propagated straight along a plane perpendicular to the remote extension direction.

Study of the viscoelastic properties of the agarose gel

Abstract Agarose is a biopolymer extracted from the red marine alga (Rhodophycees), it is widely used in agribusiness, pharmaceutical industry or as electrophoresis. The solution of this biopolymer in water gives rise to a more or less rigid solid mass called gel. This gel can be described as a matrix generating a macromolecular three-dimensional network. In this work, we exploit the experimental measurements of the stress undergone by the gel and the underlying deformation as a function of the different concentrations of the agarose to determine the creep function of this polymer in a linear regime according to the Boltzmann superposition principle. It turns out from the calculations that the gel is subjected to a delayed elasticity governed by Voigt’s analog model. This model allowed us to find the elastic modulus of the gel, and to determine the delay time and viscosity as function s of agarose concentrations.

Asymptotic normality in the problem of selfish parking

We continue in this paper to study one of the models of a discrete analog of the Renyi problem, also known as the parking problem. Suppose that n and i are integers satisfying n ≥ 0 and 0 ≤ i ≤ n – 1. We place an open interval (i, i + 1) in the segment [0, n] with i being a random variable taking values 0, 1, 2, …, n – 1 with equal probability for all n ≥ 2. If n < 2, then we say that the interval does not fit. After placing the first interval, two free segments [0, i] and [i + 1, n] are formed and independently filled with intervals of unit length according to the same rule, and so on. At the end of the process of filling the segment [0, n] with intervals of unit length, the distance between any two adjacent unit intervals does not exceed one. Suppose now that Xn is the number of unit intervals placed. In our earlier work published in 2018, we studied the asymptotic behavior of the first moments of random variable Xn. In contrast to the classical case, the exact expressions for the expectation, variance, and third central moment were obtained. The asymptotic behavior of all central moments of random variable Xn is investigated in this paper and the asymptotic normality for Xn is proved.

An Analog Model Template Library: Simplifying Chip-Level, Mixed-Signal Design Verification

Real number models, which are computationally efficient analog functional models, are now indispensable in verifying complex mixed-signal systems on chip (SoCs); yet, creating and validating these models remain difficult. To remove this problem, we created a framework for building analog functional model templates. Each template covers a class of circuits (e.g., oscillators or amplifiers) and can generate functional models for any implementation of this circuit class, regardless of pin configurations, circuit topologies, and process technologies/corners. This ability to cover many implementations with one template allows one to create a “standard model template” library that covers all the basic analog building blocks used in mixed-signal SoCs. Like a digital standard cell library, this template library only contains the low-level building blocks. Models for more complex systems, such as a phase-locked loop, are constructed using a number of these models. Our template library also contains validation routines for each of the models, measuring the key performance parameters of the modeled function. These routines can also be used to drive the circuit-level implementation of this function, making it easy to update the parameters of the functional models to match their circuit implementations. We demonstrate the utility of our template library on several mixed-signal IPs integrated into an SoC. Using the proposed framework, designers can easily generate a working model of an analog functional block in a second and thus construct a complete mixed-signal IP model for the design exploration in less than a couple of hours, while it typically needs a few days when the models are manually written. The regeneration of the models to reflect the behaviors of real implementations can be seamlessly done in less half a day from the same template library. In addition to the vast improvement in model creation speed, the generated model from the template library is less error-prone by archiving designer’s experience from previous mistakes to the template library.