Changes In Boundary Conditions Research Articles

Thermo‐Kinematic Evolution of the Eastern European Alps Along the TRANSALP Transect

AbstractThe eastern European Alps are shaped by the indentation of Adria into Europe. Recent tomography, depicting detached slab fragments, has been interpreted as evidence of continuous southward subduction of European lithosphere, contrary to an often‐invoked subduction polarity reversal. Orogen‐scale exhumation, driven by rock displacement along active faults, may reflect subduction polarity within the framework of doubly‐vergent Coulomb wedge theory, provided the absence of rheological contrasts across the colliding plates. Low‐temperature thermochronology can evaluate crustal cooling in response to changes in tectonic and erosional boundary conditions. This study investigates the consistency of observed crustal re‐organization, exhumation, and mantle processes in the Eastern Alps. Thermo‐kinematic forward models driven by reconstructions of crustal shortening along the TRANSALP geophysical transect were subjected to variations in shortening rates, thermophysical parameters, and topographic evolution, supplemented by new fission‐track data. The thermo‐kinematic models reproduce: (a) the orogen‐scale structural geometry, (b) the distribution of thermochronometer ages, (c) observed time‐temperature paths, and (f) the present‐day surface heat flux. Results suggest that exhumation is driven by rock displacement along active faults without the need to involve mantle‐driven buoyancy forces. Taken together, the results identify two possible scenarios: if the Tauern Ramp is a retro‐thrust and the southward shift of deformation in the Southern Alps is a response to new Coulomb‐wedge conditions, then our results support a Mid‐Miocene reversal of the subduction polarity. Alternatively, crustal deformation does not reflect mantle processes entailing a high degree of inter‐plate decoupling.

Effect of antisiphon devices on ventriculoperitoneal shunt drainage dynamics in growing children.

Infants and small children face changing boundary conditions when treated with a ventriculoperitoneal shunt (VPS) for hydrocephalus. There are no systematic data describing shunt drainage behavior and changes over time in a growing child. Using a child-adapted patient simulator, the authors investigated the drainage behaviors of fixed differential pressure (DP) valves and adjustable valves with devices for preventing overdrainage in children of different ages. Three miniNAV DP valves with a 10-cm H2O medium-pressure setting (MN10) and three adjustable proGAV2.0 valves with a 25-cm H2O gravitational unit (GU) at low 5-cm H2O opening pressure (PG5) and medium 10-cm H2O opening pressure (PG10) settings were each investigated with a hardware-in-the-loop test bed. This test bed consisted of a posture motion mechanism and two pressure compartments that mimicked intracranial and abdominal pressures and was used to test the VPS under realistic in vitro conditions. Body orientation and length were physically set according to the child's age. The software simulated the physiological situations of children aged 1, 5, and 10 years. All valves were tested according to these specifications, with 5 runs for 1 hour each in the horizontal, vertical, and horizontal positions. Intracranial pressure (ICP) and VPS flow were measured, and the respective cerebrospinal fluid volume changes and ICP set value were computed. The drainage parameters increased with age in all valves in the vertical position, with that of MN10 being pronounced in the 1-year-old simulation. The GU values in PG5 and PG10 substantially reduced drainage compared with MN10. PG10 prevented drainage in the 1-year-old and 5-year-old setups, but there was some drainage at physiological ICP in the 10-year-old setup. In contrast, MN10 produced the largest decreases in ICP across all ages and positions, and overdrainage resulted in insufficient ICP recovery in the subsequent horizontal position. ICP levels were mostly constant with PG10 at all ages. This study shows that unprotected DP valves may lead to overdrainage in infants, whereas low-pressure GU valves can prevent overdrainage through 5 years and medium-pressure GU valves admit physiological ICP through at least 10 years. Therefore, devices for preventing overdrainage should be included in the first implanted shunt, and opening pressure should be adjusted as the child grows.

Influence of Gravity on Passively Cooled Heat Sink Using Experimental Data and Finite Element Analysis

This paper studies the effect of gravity orientation on a heat sink, used to passively cool a thick film resistor, by changing the assembly orientation. Using the same geometry and boundary conditions as in the experimental setup, finite element simulations were conducted to evaluate the accuracy of Siemens Flotherm XT 2021.2 simulation software. In order to determine the influence of heat sink orientation, experimental measurements were performed on the resistor and heat sink temperature using thermocouples. Siemens Simcenter Flotherm XT 2021.2 software (Siemens, Munich, Germany) was used to perform finite element simulation. The influence of the heat sink position was evaluated on two setups, one where the resistor is placed directly on the heat sink using screws, and the second one, where a thermal pad was placed between the resistor and the heat sink. Screws were to clamp the parts in both cases. In total, four experiments and simulations were performed with two assemblies with two different gravity orientations for each assembly. In all the cases, the heat sink was placed on a wooden structure to prevent heat transfer through conduction, due to poor thermal conductivity of wood, and to allow unrestricted air flow underneath and around the heat sink. The first simulation was then calibrated for the first scenario, and the rest of the simulations were made using the calibrated one. No other changes in boundary conditions were made. Temperature measurements show an improved cooling when the air speed between the heat sink fins is enhanced due to natural hot air movement generated by the gravity. Gravity has an influence on the cooling regardless of the presence or absence of a thermal interface material. Measured temperatures were reduced up to 8.2 °C due to the rotation of the heatsink. Finite element analysis shows similar temperature values to the measured ones in all the scenarios.

Prediction of acoustical behavior of granular material stacks as measured in a standing wave tube by using a Biot theory-based model

The acoustical behavior of granular materials, such as activated carbon and silica gel, has drawn attention in recent studies, due to their favorable properties such as good low frequency sound absorption. Like other more traditional porous materials, granular materials can also be tested in a standing wave tube for a convenient assessment of their acoustical properties. However, the behavior of granular materials stacked in a standing tube is more complex than that of traditional materials. For example, the response of lightweight glass bubbles reveals a clear dependence on the sound pressure level of the input signal. Also, when tested in standing wave tubes of different diameters, the same type of granular materials displays differences in their behavior. The apparent stiffness of granule pack is also related to the depth of the stack. In the present work, a model based on Biot theory is proposed, together with a consideration of the effect of the change of boundary conditions and the granule stack stiffness in different test configurations. The model is realized by using a finite difference method, and the simulation results are compared with measurements of different types of granular materials.

Scaling of convection in high-pressure ice layers of large icy moons and implications for habitability

The existence of a high-pressure (HP) ice layer between the silicate core and the liquid ocean in large icy moons and ocean worlds is usually seen as a barrier to habitability, preventing a direct contact and therefore transfer of nutrients from the core to the liquid ocean. More recently, several studies challenged that hypothesis and showed that exchanges were possible under specific conditions, allowing transport of salts toward the ocean. In our study, we consider an effect not taken into account in the previous works, which is the dynamical implications of the phase equilibrium at the ice–ocean interface allowing a non-zero vertical velocity at the surface of the HP ice layer. This effect, which can be modeled as a phase change boundary condition for the ice layer, has a significant impact on the flow dynamics and enables exchanges with the ocean by fusion and crystallization at the top interface of the HP ice layer, even without partial melting in the bulk of the ice layer. For the same conditions as standard convective systems, it also leads to faster mass transfer in the bulk. These exchanges are directly linked to the melting capacity of the ice at the interface between the HP ice layer and the core, depending on the efficiency of convection in the liquid ocean. This is controlled by a dimensionless parameter noted Φ. Considering this boundary condition at the interface between the HP ice layer and the liquid ocean, we propose a scaling of the bottom temperature and the top vertical velocity as function of the Rayleigh number, in the case of a fixed heat flux from the core, a rigid or free-slip bottom boundary and various values of Φ.

Hellmann–Feynman theorem and internal pressure for atoms, molecules and plasmas under pressure

Since the beginning of the twentieth century, confinement of atoms, molecules and plasma inside impenetrable sharp (hard) and smooth (soft) cavities has been studied with utmost interest. Physically, such situations introduce the trapping of a quantum system under high pressure. The internal pressure () of the system under multi-megabar external pressure has not yet been explored. Also, there is a lack of Hellmann–Feynman theorem (HFT) in such a scenario, which is essential to derive a concrete analytical expression of under stressed condition. Here using a scaling concept we provide a general HFT in terms of expectation values of total energy, potential and kinetic energy of a given confined system. A change in boundary condition (from smooth to sharp and vice versa) does not affect this. Applying this proposed HFT, a closed-form expression of and has been obtained for confined and shell-confined quantum systems. Based on this , several virial-like equations are also modeled. This HFT and are demonstrated for one- and many-electron atoms, plasmas and molecules using both analytical and numerical methods. Their applicability in several other confined systems is discussed from simple arguments.

Monitoring of Damage in Composite Structures Using an Optimized Sensor Network: A Data-Driven Experimental Approach.

Due to the complexity of the fracture mechanisms in composites, monitoring damage using a vibration-based structural response remains a challenging task. This is also complex when considering the physical implementation of a health monitoring system with its numerous uncertainties and constraints, including the presence of measurement noise, changes in boundary and environmental conditions of a tested object, etc. Finally, to balance such a system in terms of efficiency and cost, the sensor network needs to be optimized. The main aim of this study is to develop a cost- and performance-effective data-driven approach to monitor damage in composite structures and validate this approach through tests performed on a physically implemented structural health monitoring (SHM) system. In this study, we combined the mentioned research problems to develop and implement an SHM system to monitor delamination in composite plates using data combined from finite element models and laboratory experiments to ensure robustness to measurement noise with a simultaneous lack of necessity to perform multiple physical experiments. The developed approach allows the implementation of a cost-effective SHM system with validated predictive performance.

Energy futures of representative Swiss communities under the influence of urban development, building retrofit, and climate change

Reducing energy demand in buildings is an integral part of many climate change mitigation strategies. Yet, the prospected development of communities is often overlooked when estimating future energy demand. Here, we investigate the future energy demand in representative Swiss communities, considering climate change projections, building retrofit and urban development. Following a scenario-based approach we model urban, suburban and rural community archetypes under changing boundary conditions and different time scales using the City Energy Analyst an open-source computational framework. The results demonstrate that the future energy demand of Swiss communities is highly dependant on their development trajectories regarding population growth, occupant density and building use-types. For the urban archetype, the most significant result is the increase of annual space cooling which by 2060 could be comparable to space heating. For the sub-urban, increases in energy demand due to urban development were observed despite retrofit measures, whereas the rural archetype displays high space heating demand across all scenarios. Consequently, predictions for future energy demand at the community scale without considering urban development trajectories are likely to be incomplete. The results demonstrate the relevance of increasing the modelling scale from national to community scale to support decision making on different levels of governance.

Controlling the freezing process of nano-enhanced phase change materials with internal fins in the latent thermal energy storage system

In this article, the freezing process of phase change material (PCM) in a latent energy thermal storage system with new internal fins was numerically discussed. Two PCMs: RT35 and RT50 are used. The finite volume method and the enthalpy-porosity model are employed. The effects of seven new internal fins, the addition of aluminum oxide nanoparticles in two volume fractions of 2.5 % and 5 %, and changes in the temperature boundary condition on the freezing process of the PCM are explored and the results were compared with the case without fins. The outcomes determine that with the addition of nanoparticles, the freezing time decreases for all states with fins compared to the state without fins, and the percentage of these changes is around 29–62 %. Also, the outcomes show that the reduction in freezing time compared to the case without fins for case C3 is about 69.43 % and 71.82 % for RT35 and RT50, respectively, and this mode performed best among the considered cases. The spatial changes in the temperature of the active walls of the chamber along the y, and z-directions affect the freezing rate and increase the freezing rate compared to the constant temperature boundary condition.

Influence of system boundary conditions on the life cycle cost and carbon emissions of CO2 transport

One of the critical stages in carbon capture and storage (CCS) is the transport of CO2 from the point of capture to the storage site. Besides pipeline transport, the present proposition of marine CO2 transport is to make use of vessels that transport chemicals of similar physical properties to CO2 such as liquefied propane gas (LPG) and liquefied natural gas. Through a life cycle analysis, this study examines the influence of system boundary conditions on the total cost and benefits of CO2 transport using a reference LPG tanker. While the levelized cost of transport (i.e. shipping) can be intuitively obtained at 31.65–47.05$/t when LPG and CO2 are assumed to be transported as cargos between two fixed ports, the total system-level CO2 emission is contentious when the greater “interconnected” systems including LPG and a fictitious power plant life cycle are considered. Base on the analysis of the proposed most reasonable boundary condition, a break-even carbon price is further examined and found to be ranging from 39.37 to 22.32$/t-CO2. While the boundary conditions can influence the break-even price of CO2, such variations and the associated change in boundary conditions can be used to facilitate policy debate on the right carbon price for international shipping.

Constrained Design of Potentiometric RFID Sensors Based on Auto-Tuning ICs

Auto-tuning integrated circuits (ICs), interconnected with radio-frequency identification (RFID) antennas in the UHF band, can provide digital information about the changes in the local boundary conditions in the proximity of the device. This feature, in conjunction with a varactor diode, can be used to create a general-purpose framework for the controlled wireless sensing of chemical agents. The varactor works as a transducer converting the potentiometric output of a chemical sensor into a capacitance change, which in turn is detected by the IC. A constrained optimization method is here introduced to maximize the sensitivity of the above transduction mechanism by deriving closed-form expressions that relate the digital output of the IC to the chemical variation. In this way, said variation will be optimally mapped within the retuning dynamic range of the IC. The method is demonstrated with reference to a pH sensor and is capable of providing a sensitivity of 30 units per unitary pH variation with stable communication performance. Moreover, the application to an on-body plaster-like antenna, namely when there are not fully controllable boundary conditions, demonstrated that the sensing performance is practically unaffected by the placement region over the human body as well as by the inter-user variability.

Quasi-optimal control of a solar thermal system via neural networks

The optimal control of complex thermal energy systems is a challenge due to their dynamic behavior and constantly changing boundary conditions. To maximize the energy efficiency of such a dynamic system, optimal trajectories for the controlled variables are needed. Extensive system knowledge is required to model the system accurately enough to be able to compute optimal trajectories. The high computational cost of computing optimal control solutions with traditional approaches, especially with changing boundary conditions, often makes this approach unusable for applications with limited computational power, such as real-time applications on electronic control units (ECUs). This study investigates a possible solution to this challenge using a simplified example system. Optimal control solutions for different boundary and initial conditions are generated for the selected solar thermal system using a direct multiple shooting algorithm. Based on Bellman’s optimality principle, the generated solutions are transformed into a data set of optimal state–action pairs. On this basis, different types of neural networks are trained, specifically a feed-forward, a recurrent, and a radial basis function network. Thus, data generation and training can be performed offline, and the required online computations are significantly reduced since the evaluation of a trained neural network requires comparatively low central processing unit (CPU) power. The trained neural network controllers are tested for their ability to output near-optimal control actions based on the current system state. The feed-forward and recurrent neural networks show promising initial results in this regard. Open questions and the need for improvements are discussed.

Geothermal heat flux is the dominant source of uncertainty in englacial-temperature-based dating of ice rise formation

Abstract. Ice rises are areas of locally grounded, slow-moving ice adjacent to floating ice shelves. Temperature profiles measured through ice rises contain information regarding changes to their dynamic evolution and external forcings, such as past surface temperatures, past accumulation rates and geothermal heat flux. While previous work has used borehole temperature–depth measurements to infer one or two such parameters, there has been no systematic investigation of parameter sensitivity to the interplay of multiple external forcings and dynamic changes. A one-dimensional vertical heat flow forward model developed here examines how changing forcings affect temperature profiles. Further, using both synthetic data and previous measurements from the Crary Ice Rise in Antarctica, we use our model in a Markov chain Monte Carlo inversion to demonstrate that this method has potential as a useful dating technique that can be implemented at ice rises across Antarctica. However, we also highlight the non-uniqueness of previous ice rise formation dating based on temperature profiles, showing that using nominal values for forcing parameters, without taking into account their realistic uncertainties, can lead to underestimation of dating uncertainty. In particular, geothermal heat flux represents the dominant source of uncertainty in ice rise age estimation. For instance, in Crary Ice Rise higher heat flux values (i.e. about 90 mW m−2) yield grounding timing of 1400 ± 800 years, whereas lower heat flux of around 60 mW m−2 implies earlier ice rise formation and lower uncertainties in the ice rise age estimations (500 ± 250 years). We discuss the utility of this method in choosing future ice drilling sites and conclude that integrating this technique with other indirect dating methods can provide useful constraints on past forcings and changing boundary conditions from in situ temperature–depth measurements.

Hygrothermal Performance Evaluation of Internally Insulated Historic Stone Building in a Cold Climate

In most cases, internal insulation is the only solution to improve the energy efficiency of historic buildings. However, it is one of the most challenging and complex energy efficiency measures due to changes in boundary conditions and hygrothermal behavior of the wall, particularly in cold climates. This study presents the long-term monitoring of the hygrothermal performance of an internally insulated historic stone wall building. The study aimed to assess the hygrothermal behavior of the dolomite wall if mineral wool insulation is applied internally on the north-east wall in the rooms with and without high internal moisture load. The measurements included temperature, relative humidity, water content, and heat flux. Monitoring results are compared with 1D hygrothermal simulations and a building energy consumption simulation. The in situ measurement results and hygrothermal assessment shows energy consumption decreased by 55% with relative humidity under the insulation staying belove 60% for most of the time, with short periods of increase over 80%. Energy consumption simulation shows an energy saving potential of up to 72% in the case of proper energy management.

Comment on “Confined Klein–Gordon oscillators in Minkowski spacetime and a pseudo-Minkowski spacetime with a space-like dislocation: PDM KG-oscillators, isospectrality and invariance”

We argue that the analytical energies obtained recently in Mustafa (2022) from a radial eigenvalue equation are incorrect because the truncation method used by the author forces a relationship between two model parameters. This relationship (overlooked by the author) depends on the truncation number and as a result the exact analytical energies do not correspond to a single model but are solutions to different physical models. The reason is that the radial eigenvalue equation is not exactly solvable but conditionally solvable so that one can only obtain some particular exact solutions. We also show that the exact eigenvalues obtained for a particular simpler case are also incorrect because the author overlooked that the shift of the radial coordinate leads to a change in the left boundary condition.

ESTIMATING THE QUALITY FUNCTIONAL IN OPTIMAL CONTROL VARIATIONAL CALCULUS TASKS UNDER THE CHANGES OF THE LEFT-HAND ARGUMENT OF BOUNDARY CONDITION

Estimating the quality functional in optimal control variational calculus tasks under the changes of boundary condition is considered. In control systems, there is a certain permissible change of the controlled parameter based on which the control system is designed. Unlike ordinary control systems, in optimal control systems, there is another indicator - the quality functional (optimality criteria), which also depends on the controlled parameters. Therefore, the permissible range of changes of controlled parameters in optimal control systems should be determined based on the quality functional value’s tolerances. Therefore, estimating the quality functional under the changes of boundary conditions has theoretical and practical importance. It is particularly important for problems solved by numerical methods because it is quite simple for problems solved analytically. In this article, the estimation methods of the quality functional under the changes of left-hand argument of boundary condition in the form of Taylor series with an accuracy of the second member in optimal control variational calculus tasks solved by the indirect nu-merical method are developed. According to the developed method, both the optimization function and the quality functional are functions of the left-hand argument of boundary condition. In other words, the boundary condition parameter is an argument of the optimi-zation function. The mathematical apparatus for determining the specified series coeffi-cients has been developed. These coefficients depend on the partial derivatives of the op-timization function by boundary parameter. The boundary conditions for partial deriva-tive functions of the optimal function by boundary parameters, and the determination methods for these functions using the known optimal function are studied. The truth of the Taylor series coefficients, and the algorithm for their determination are shown experimen-tally.

Discrete Element Modeling of Southeast Asia's 3D Lithospheric Deformation During the Indian Collision

AbstractThe Indian collision has deformed the eastern Asian continent in a multifaceted way, uplifting Tibet and surrounding mountains, activating ≥1,000 km‐long strike‐slip faults, and opening Tertiary rifts and oceanic basins up to ≈3,000 km away from the Himalayas. Modeling such broad‐scale tectonics has been challenging. While continent‐scale, lithospheric deformation appears to have been primarily taken‐up by long, narrow, inter‐connected shear‐zones with large offsets, the contribution of processes such as channel‐flow, collapse, delamination, etc… has remained contentious. Here, based on increasing 4G (Geological, Geophysical, Geochronological, Geodetic) evidence including kinematic and timing constraints on the main mechanisms at play, we use Discrete Element (DE) Modeling to simulate and further understand the evolution of 3D strain across east Asia since the onset of collision, ≈55 Ma ago. The planar, 50 million km2, 125 km‐thick models are scaled for gravity. The approach permits mega‐fault generation and evolution without pre‐arranged initial settings. The results provide insight into fault birth, propagation and motion, as well as mountain building and plateau growth. They corroborate that continental crustal thickening across Tibet alternated with the extrusion of large blocks that rifted apart in the far field. Remarkably, without changes in boundary conditions or indentation rate, the DE model also vindicates slip reversal along initial strike‐slip shear zones.

Enhancing SLM Stainless Steel: Model-Based Parameter Optimization

SLM (selective laser melting) has faced challenges in ensuring consistent mechanical properties for various geometries. However, the authors have developed a system that solves this issue by calculating the optimal process parameters for each scan vector on each layer. This approach ensures consistent melt pool geometry, derived from the most robust parameters in conduction welding mode. The results from the single melt-line experiments and the presented thermal conduction solver demonstrate the effectiveness of this approach in achieving a stable melt pool geometry in stainless steel (1.4404 or 316L). Furthermore, a testing regimen has been developed to evaluate the system under different changing boundary conditions, to further demonstrate its usefulness. By utilizing this system, manufacturers will achieve consistent and high-quality mechanical properties which improves cost-effectiveness for small lot sizes, including spare and obsolescent parts.

Geometric singularities and regularity of solution of the Stokes system in nonsmooth domains

This paper deals with the geometrical singularities of the weak solution of the mixed boundary value problem governed by the stationary Stokes system in two-dimensional nonsmooth domains with corner points and points at which the type of boundary conditions changes. The presence of these points on the boundary generally generates local singularities in the solution. We will see the impact of the geometrical singularities of the boundary or the mixed boundary conditions on the qualitative properties of the solution including its regularity. Moreover, the asymptotic singular representations for the solution which inherently depend on the zeros of certain transcendental functions are presented.

Localization transitions and winding numbers for non-Hermitian Aubry-André-Harper models with off-diagonal modulations

We study localization and topological properties, as well as the fate of the critical phase, of non-Hermitian generalizations of the Aubry-Andr\'e-Harper model with both on-site and off-diagonal incommensurate modulations. Non-Hermiticity arises from nonreciprocal hopping and a complex phase in the potential. In the absence of nonreciprocal hopping, we compute analytically the localization length of single-particle states by applying Avila's global theory. The system has the same phase diagram as Hermitian cases, except that the complex phase renormalizes the strength of the potential. In the presence of nonreciprocal hopping, the phase diagram is analytically determined by a similarity transformation. Due to the presence of the skin effect, induced by nonreciprocity, the skin phase turns into extended and critical phases when the boundary condition changes from open to periodic, while states are localized asymmetrically in the boundary-independent localized phase. The nonreciprocal hopping is in favor of the critical phase under a periodic boundary condition. The spectra are complex, and loops always exist. A winding number is not a proper indicator of the presence of loops, but the topological transition is in agreement with the localization transition.