Physical Geometry Research Articles

Heterogeneity-controlled uncertain optimization of pump-and-treat systems explained through geological entropy

Pump-and-treat (P&T) is a widely-adopted solution for the containment of solute plumes in contaminated aquifers. A cost-effective design of P&T systems requires optimizing (minimizing) the overall pumping rates (Q). This optimization is a stochastic process, as Q is a random variable linked to the randomness of the aquifer hydraulic conductivity (K). Previously presented stochastic approaches to minimize Q adopted two-dimensional (2D) Gaussian random spatial fields (r.s.f.) of log-transformed K. Recent studies based on geological entropy have demonstrated the limited ability of Gaussian r.s.f. to reproduce extreme K patterns, which mostly control transport in heterogeneous aquifers, when compared to non-Gaussian r.s.f. Moreover, 2D models generate different flow and transport connectivity than three-dimensional (3D) models. On these premises, this work aimed at extending previous works on P&T optimization in heterogeneous aquifers through Monte-Carlo groundwater simulations of 2D and 3D Gaussian and non-Gaussian r.s.f. The results indicated that the mean ( $$ \bar{Q}_{n} $$ ) and variance ( $$ \sigma_{Qn}^{2} $$ ) of the optimal Q distribution depend strictly on the chosen model dimensionality and r.s.f. generator. In particular, 2D models and models embedding indicator-based (i.e. non-Gaussian) r.s.f. tended to generate higher $$ \bar{Q}_{n} $$ and $$ \sigma_{Qn}^{2} $$ than 3D models with increasing number of model layers (KL) and Gaussian models. This behavior can be explained considering the spatial ordering of K clusters in the simulated aquifers, which is measured through metrics derived from the concept of geological entropy. It was found that 2D models and models embedding non-Gaussian r.s.f. displayed more spatially-persistent ordered K structures than 3D models and Gaussian models, resulting in higher $$ \bar{Q}_{n} $$ and $$ \sigma_{Qn}^{2} $$ . This is attributed to the relative amount of heterogeneity sampled by the solute source and the increased likelihood of more ordered K clusters to generate preferential flow and solute transport channeling than more disordered and chaotic systems, which enhance solute mixing. Combining P&T with physical barriers (i.e. cut-off walls) was helpful to reduce both $$ \bar{Q}_{n} $$ and $$ \sigma_{Qn}^{2} $$ in all tested scenarios, corroborating previous findings. However, the relative efficacy of a specific physical barrier geometry to reduce $$ \bar{Q}_{n} $$ and $$ \sigma_{Qn}^{2} $$ also depends on the chosen model dimensionality and r.s.f. generator.

PMMA-TiO2 Fibers for the Photocatalytic Degradation of Water Pollutants.

Titanium dioxide (TiO2) is a promising photocatalyst that possesses a redox potential suitable for environmental remediation applications. A low photocatalytic yield and high cost have thus far limited the commercial adoption of TiO2-based fixed-bed reactors. One solution is to engineer the physical geometry or chemical composition of the substrate to overcome these limitations. In this work, porous polymethyl methacrylate (PMMA) substrates with immobilized TiO2 nanoparticles in fiber forms were fabricated and analyzed to demonstrate the influence of contaminant transport and light accessibility on the overall photocatalytic performance. The influences of (i) fiber porosity and (ii) fiber architecture on the overall photocatalytic performance were investigated. The porous structure was fabricated using wet phase inversion. The core-shell-structured fibers exhibited much higher mechanical properties than the porous fibers (7.52 GPa vs. non-testability) and maintained the same degradation rates as porous structures (0.059 vs. 0.053/min) in removing methylene blue with comparable specific surface areas. The highest methylene blue (MB) degradation rate (kMB) of 0.116 min−1 was observed due to increases of the exposed surface area, pointing to more efficient photocatalysis by optimizing core-shell dimensions. This research provides an easy-to-manufacture and cost-efficient method for producing PMMA/TiO2 core-shell fibers with a broad application in water treatment, air purification, and volatile sensors.

Dimension Confinement Effect Boosted Ultrasensitive Colorimetric Signal Concentrating

AbstractTo understand the underlying fundamental mechanism affecting the optical sensitivity of a paper‐based substrate, a layered polyvinyl alcohol (PVA) network paper is proposed considering the physical geometry and chemical composition required to enhance the sensitivity. It is verified both theoretically and experimentally that the dimension confinement effect introduced by the Steiner network, layered and pore structures, as well as massive hydroxyl groups, play an essential role in enhancing the concentration signal on the surface. Trace chlorate droplets and particles are considered representative examples to prove the excellent structural design‐induced performance of the PVA network paper. A practical mass detection from potassium chlorate solution and particles could be as low as 9.9 pg and 0.34 fg, respectively, and the corresponding naked‐eye observation limit could reach 0.69 ng and 1.6 pg, respectively, assuming the distinguishable size for human eyes is 100 µm. Further, the detection time could be far less than 2 s, which is remarkably superior than the detection performance of the parallel filter paper counterpart. The dimension confinement effect demonstrated here is expected to be of great importance for advancing the development of paper‐based trace detection.

Graphene-based THz tunable ultra-wideband polarization converter

This paper presents the design and simulation of two distinct reflection-mode graphene cross-polarization converters (CPCs), which operate in the THz region. The first is a tri-band converter capable of converting linear and circular to cross-polarized waves at 6.0, 9.0, and 13.3 THz, with a polarization converter ratio (PCR) greater than 0.98. Also it converts linear to circular-polarized waves at 5.0 and 11.0 THz. The designed converter is stable over incidence angles from 0∘ to 60∘, with a slight degradation in bandwidth near 60∘. The second is an ultra-wideband (3.75 to 11.35 THz) linear to cross- and circular to cross-polarization converter with a PCR ratio of 0.85. The bandwidth of the second converter has been enhanced by using the same structure as the first, but with dual-layered graphene. Furthermore, the proposed structures can be dynamically tuned by varying the chemical energy of the graphene, without needing to modify the physical geometry.

Mechanics of transiently cross-linked nematic networks

Polymeric networks are ubiquitous in biology and are vital components to some of the key functions of life. Composite networks of stiff and flexible polymers such as the actin-filamin network of the cytoskeleton posses novel mechanical properties that arise from physical interactions, geometry and topology of the network. Particularly, (a) the cross-linking chains in these networks dynamically break and reform in time that drive their rheological properties, and (b) stiff rod-like polymers have been found to show liquid crystalline phases including nematic alignment. Models of such transient nematic networks are either phenomenological or computational thereby lacking the simplicity of physics-based models in elucidating the key physical mechanisms. We present here a modelling framework using the statistically-based transient network theory to describe the rate-dependent mechanics of nematic networks. The model bridges continuum mechanics quantities to statistical measures of chain distribution in the network such as the conformation tensor. We show that the model degenerates to classical theories of anisotropic solids when the bonds are permanent and to anisotropic fluids when the bond exchange is rapid. The effect of the interplay between the bond dynamics and geometry of the network on its emergent mechanics is explored and illustrated using the example of a thin-walled tube under pressure. The generality of the framework and its potential to describe continuum level mechanics based on a variety of local physical interactions and network geometries is discussed.

Versatile Cross‐Polarization Conversion Chiral Metasurface for Linear and Circular Polarizations

AbstractIn this work, first the necessary conditions for a versatile cross‐polarization conversion meta‐atom that operates both for linear and circular cross polarizations are discussed. Based on these, a versatile chiral metasurface cross‐polarization converter is proposed. The correspondence between its physical geometry and polarization domain characteristics is studied. To verify the design concept, a prototype is fabricated and measured. An effective vertical and horizontal linear cross‐polarization conversion is achieved from 29.3 to 38.8 GHz (27.90%) and from 34.0 to 36.6 GHz (7.36%), respectively. Furthermore, the proposed converter also achieves circular polarization handedness rotation from 34.5 to 36.6 GHz (5.91%).

Wearable Conformal Metasurfaces for Polarization Division Multiplexing

AbstractIn practice, there is a strong requirement for modulating the performance of existing bulk devices without changing their physical geometry. In this study, by attaching a flexible metasurface on a cylindrical lens, a wearable conformal metasurface for terahertz polarization division multiplexing is demonstrated, which could be used in wireless communications, detection, and imaging. The integrated metasurface/lens can achieve the control functions of spot focusing, generation of Bessel beams, and phase holograms, respectively, for crosspolarized waves and line focusing for copolarized waves. A total modulation efficiency of up to 87% is experimentally obtained. Notably, the metasurfaces can be attached on/removed from existing bulk devices multiple times, without reducing the performances of both metasurface and conventional devices. As the flexible samples are fabricated using the cost‐effective standard flexible printed circuit technique, a multilayer conformal metasurface can be easily obtained for an efficient control. Furthermore, the same bulk device can be integrated with different flexible metasurfaces for various controls. Thus, the proposed metasurface can provide a promising flexible platform for various integrated applications and contribute to the development of wearable functional devices.

Mechanophysical Cues in Extracellular Matrix Regulation of Cell Behavior.

The extracellular matrix (ECM) is a macromolecular network that can provide biochemical and structural support for cell adhesion and formation. It regulates cell behavior by influencing biochemical and physical cues. It is a dynamic structure whose components are modified, degraded, or deposited during connective tissue development, giving tissues strength and structural integrity. The physical properties of the natural ECM environment control the design of naturally or synthetically derived biomaterials to guide cell function in tissue engineering. Tissue engineering is an important field that explores physical cues of the ECM to produce new viable tissue for medical applications, such as in organ transplant and organ recovery. Understanding how the ECM exerts physical effects on cell behavior, when cells are seeded in synthetic ECM scaffolds, is of utmost importance. Herein we review recent findings in this area that report on cell behaviors in a variety of ECMs with different physical properties, i.e., topology, geometry, dimensionality, stiffness, and tension.

Porphyrin-Armored Gold Nanospheres Modulate the Secondary Structure of α-Synuclein and Arrest Its Fibrillation

The gold nanoparticle exhibits strong absorption and emission due to its unique physical geometry and surface plasmon resonance phenomena. The current investigation illustrates a unique preparation...

A method for modelling compressor bleed in gas turbine analysis software

The modelling of compressor interstage bleed in a gas turbine is required at all phases of the engine design cycle. The effect of the physical geometry of the bleed offtake on compressor flow is an important consideration, but of equal importance is the analysis of the effect of bleed air on compressor work requirements and overall gas turbine cycle efficiency. Knowledge of bleed air properties (temperature, pressure, work) is of paramount importance to carry out a reliable preliminary cycle analysis.While interstage bleed modelling may be regarded as a small detail in the overall gas turbine cycle, it is of increasing importance in modern engine design due to the requirement to obtain performance optimisation in engines that have already had significant development. Consequently, even small improvements to the modelling process can yield beneficial improvements to the engine cycle.Current methods to identify these effects vary in terms of complexity and accuracy; in this paper, a novel method is proposed, which offers an innovative -yet simple- way to simulate any number of interstage bleeds within a compressor, without the need to compromise on model accuracy. This is achieved through implementation of two methods - 1) properties of the bleed air are calculated by utilising the polytropic relationship between pressure and temperature, and 2) compressor work requirements are calculated by use of the “superposition principle” by implementing the work requirements of the bleed into an initial ‘no bleed’ calculation. This method has been implemented in the Cranfield modelling software Turbomatch, and validated against test data from an industrial gas turbine. Analyses so far show that the method is quick, accurate, and compares extremely well to the test data.This novel, ‘integrated’ method has been shown to calculate interstage bleed properties in a gas turbine compressor without the need for complex modelling or artificial ‘splitting’ of components. This method is partially dependent on the assumption that stage pressure ratio can be estimated using constant stage temperature rise and compressor overall polytropic efficiency (although the use of overall isentropic efficiency was also investigated). Case studies performed on a number of Siemens industrial gas turbines suggest this is indeed the case, with calculated stage inlet/outlet pressure typically within 3% of the real engine comparison, although older technology compressors tend to be modelled less accurately than newer ones.For compressor work and overall cycle calculation, comparison of this method against test data shows that accuracies between 0.5% and 1% can be obtained down to low load conditions. Compared to compressor ‘splitting’ methods, which demonstrated relatively poor accuracy levels (above 20%), likely due to inaccurate compressor map selection, the alternative method is shown to be a suitable method to model bleed without the need for extensive manual model adjustment. It is also shown how this method can be used to quickly assess the effect of bleed stage and mass flow on the compressor running line, as well as on the surge margin.It should be noted that, while the engines used in the case study represent different engine designs and technology levels, they are from the same engine manufacturer and represent a gradual evolution of compressor technology using a similar design philosophy.

Analysis of air flow and heat transfer in a winding using porous medium approach

Abstract The efficient cooling of turbo-generators especially in the end-windings region directly affects the power output rating. Modeling the coolant flow passing through the stator end-winding of a high-powered generator, however, remains a challenge due to a large number of parts with irregular geometries as well as the intricacy of cooling flow paths. This paper focuses on a numerical investigation of flow and heat transfer in stator end-winding aiming at replacing the geometry of winding with a porous medium model. Using computational fluid dynamics analysis to examine the viscous and inertial contributions to the pressure drop of airflow in the stator end-winding region, a generalized porous medium model is developed for the real physical geometry of winding together with a correlation for interfacial Nusselt number. The results indicate that the inertial effect considerably prevails over the viscous effect, that is, viscous contribution becomes small and almost negligible. It is shown that not only the pressure drop characteristics match closely within both real and porous models, but also the heat transfer results agree as well which means that the replaced porous model can amply describe the macroscopic behavior of the winding.

Comparison of Experimental and Computational Heat Transfer Characterization of Water Jet Impingement Array with Interspersed Fluid Extraction

A jet impingement cooling device was designed with jet-adjacent fluid extraction ports distributed throughout the impingement array. The device was fabricated from a photopolymer material using a three-dimensional printing technique and tested for flow resistance and cooling performance using water as the working fluid. Parallel to physical experiments, computational simulations were performed using a quarter-jet repeating unit cell consistent with the physical device geometry, but independent of the manifold architecture. Pressure drop and heat transfer results from both methods were evaluated and compared. It was found that the computational and experimental pressure drop results showed excellent agreement after manifold pressure drops were properly accounted for using a reduced-order analytical model. Heat transfer results were shown to have reasonable agreement with differing trends. A discussion on possible causes for the difference is presented and suggestions are made for future accommodation. Finally, this work proposes a strategy for development of broadly applicable thermal and pressure drop correlations which span a wide range of geometries, fluid properties, heat fluxes, and flow parameters.

Performance Bounds on Passive Indoor Positioning Using Visible Light

In this article, a novel method for passive indoor localization using LED luminaires is proposed where explicit user participation is not required. This approach measures changes in the impulse response between sources and receivers and estimates a location based on optical channel sounding data. An exponential integrating-sphere model is used to represent object impulse response (OIR) from each luminaire source-receiver pair, which is obtained by subtracting impulse response (IR) of the room background (i.e., without an object) from IR when the object is present inside the room. This model is represented as a function of 3D position of the object and depends on both source and receiver parameters and the physical geometry of the room. An analytical expression of the Cramér-Rao lower bound (CRLB) on the proposed passive indoor localization method is derived. The position is also estimated by using a maximum likelihood (ML) estimator which gives the position estimate by maximizing the log-likelihood function of the received noisy OIR waveforms. The results show that the signal-to-noise ratio (SNR) and number of source-receiver pairs used in the estimation, play a crucial role in performance. Typical localization root-mean squared error is less than 10 cm over a broad range of light intensities and object locations.

Physical geometry of the quasispherical Szekeres models

The quasispherical Szekeres metric is an exact solution to Einstein's equations describing an inhomogeneous and anisotropic cosmology. Though its governing equations are well-known, there are subtle, often-overlooked details in how the model's functions relate to its physical layout, including the shapes and relative positions of structures. We present an illustrated overview of the quasispherical Szekeres models and show exactly how the model functions relate to the physical shape and distribution of matter. In particular, we describe a shell rotation effect that has not previously been fully understood. We show how this effect relates to other known properties, and lay out some mathematical tools useful for constructing models and picturing them accurately.

An overview of durability model for timber structure decay under Indonesian climate

The problem of wood durability is closely related to the degradation mechanism that can be distinguished into mechanical, physical, biological, and chemical degradation. The most affecting combination of degradation in modelling the durability of wood structures is a combination of mechanical and biological. The durability model of wood structure reviewed was based on a model developed by CSIRO (Commonwealth Scientific and Industrial Research Organization), Australia. Parameters taken into account in the model included physical wood, climate, coating paint, thickness, width, connection, and geometry parameters. The model predicted a decay rate for timber installed in-ground and timber above-ground. The results of this study were expected to provide a preliminary description of the behavior of the durability of wood structures based on several parameters adapted based on environmental conditions in Indonesia.

Some Equations for the External Space and Their Implications on the Inverse Cone Concept and the Geometry of the Physical Universe

In previous works, they were proposed a photonic model of the Big Bang [1] and several parameters derived from the Hubble-Lemaitre equation [2]. Since these parameters result higher than the classical ones and, otherwise, the General Theory of Relativity does not apply far away the Physical Universe, in this paper, it will be revised the adequacy of such parameters in the external Space and their influence on the relativistic concept of the cone of time. As well, it will be intended to define the Physical Universe geometry accordingly to a thermo-dynamical analysis of the Big Bang.

Topology Optimization of Disc Brake Rotor

The main purpose of this study is to analyze the thermo-mechanical behavior of the brake disc during the braking phase. Brakes must undergo through continuous use, so many issues surround their heating characteristics when it comes to their development, including contact region properties, material choice, and development of hot spots, associated physical geometry, and deformations. The coupled thermal-structural analysis is used to determine the deformation and the Von Misses stress established in the disc to enhance performance and life of the rotor disc. A comparison between analytical calculations and results obtained from Finite Element Analysis (ANSYS) is done and the values obtained from the analysis are in the range of allowable values. The experiment has been performed with different disc-geometries. Based on the experiment results we have performed ANSYS simulation for the disc-brake. Hence best suitable optimum design is suggested based on the performance, strength and rigidity criteria.

A Compact Phase Change Memory Model With Dynamic State Variables

A SPICE model for phase change memories (PCM) without relying on macro modules is developed in this work. The crystal fraction, physical geometry, and the conduction path of the amorphous region are treated as dynamic state variables to keep track of the memory cell status during SET and RESET. The memory cell resistance is calculated based on a detail 3-D resistance model to capture its transitional behavior during switching. The detail physical formulation correctly reproduced a recent observation of oscillation during the SET operation. The model has been implemented in SPICE, and the convergence of the model is demonstrated by simulations of a complete PCM array. The use of dynamic state variables also significantly reduces the number of internal nodes to one, which helps convergence and reduces the simulation time.

A Comprehensive Analysis of Windings Electrical and Mechanical Faults Using a High-Frequency Model

The measurement procedures for frequency response analysis (FRA) of power transformers are well documented in IEC and IEEE standards. However, the interpretation of FRA results is still far from reaching an accepted methodology and is limited to the analysis of the experts. The dilemma is that there are limited case studies available to understand the effect of different faults. Additionally, due to the destructive nature, it is not possible to apply the real mechanical deformations in the transformer windings to obtain the data. To solve these issues, in this contribution, the physical geometry of a three-phase transformer is simulated using 3D finite integration analysis to emulate the real transformer operation. The novelty of this model is that FRA traces are directly obtained from the 3D model of windings without estimating and solving lumped parameter circuit models. At first, the method is validated with a simple experimental setup. Afterwards, different mechanical and electrical faults are simulated, and their effects on FRA are discussed objectively. A key contribution of this paper is the winding assessment factor it introduces based on the standard deviation of difference (SDD) to detect and classify different electrical and mechanical faults. The results reveal that the proposed model provides the ability of precise and accurate fault simulation. By using SDD, different deviation patterns can be characterized for different faults, which makes fault classification possible. Thus, it provides a way forward towards the establishment of the standard algorithm for a reliable and automatic assessment of transformer FRA results.

Algebraic Fields and the Dynamical Approach to Physical Geometry

Brown and Pooley’s ‘dynamical approach’ to physical theories asserts, in opposition to the orthodox position on physical geometry, that facts about physical geometry are grounded in, or explained by, facts about dynamical fields, not the other way round. John Norton has claimed that the proponent of the dynamical approach is illicitly committed to spatiotemporal presumptions in ‘constructing’ space-time from facts about dynamical symmetries. In this article, I present an abstract, algebraic formulation of field theories and demonstrate that the proponent of the dynamical approach is not committed, in special relativity, to the illicit presumptions to which Norton refers.