Identical Apertures Research Articles

Investigating mechanical properties of 3D printed porous titanium scaffolds for bone tissue engineering

Objective. Three-dimensional (3D) printed porous titanium scaffolds serve as a bone tissue engineering technology that offers a promising solution for addressing bone defects. The scaffold’s pore structure offers structural support and facilitates the proliferation of bone cells. Therefore, investigating the aperture and pore shape is of crucial for the development of 3D printed porous titanium scaffolds. Methods. Ti6Al4V scaffolds with the specified structure were fabricated using selective laser melting (SLM) technology. The scaffolds comprised fifteen cylindrical models measuring 20 mm in diameter and 20 mm in height. These models featured five scaffold shapes: imitation diamond-60°, imitation diamond-90°, imitation diamond-120°, regular tetrahedron and regular hexahedron. Each of these structural shapes was characterized by three different aperture sizes (400 μm, 600 μm and 800 μm). The porosity and mechanical properties of Ti6Al4V scaffolds were examined. Results. The measured porosity of Ti6Al4V scaffolds varied between 56.50% and 95.28%. The porosity increased with the size of the aperture. The mechanical properties tests revealed that, for identical apertures, the compressive strength and torsional strength were influenced by the configuration of the unit structure. Furthermore, the positive and lateral compressive strength as well as torsional strength of various unit structures exhibited distinct advantages and disadvantages. Within a uniform unit structure shape, the compressive strength and torsional strength were found to be correlated with the size of apertures, indicating that larger apertures result in decreased compressive and torsional strength. Conclusion. The configuration of the aperture and the shape of the pore were identified as significant factors that influenced the compressive strength. The compressive strength of Ti6Al4V scaffolds with various unit structure shapes exhibited both advantages and disadvantages when subjected to positive, lateral, and torsional forces. The enlarged aperture augmented the scaffold’s porosity while diminishing its compressive and torsional strength.

Effect of pore size polydispersity on the acoustic properties of high-porosity solid foams

This study investigates the influence of pore size polydispersity on the acoustic behavior of high-porosity solid foams using numerical simulations. The effect of the size of the periodic unit cell (PUC) on the transport parameters is first examined. It is found that the size of the PUC required for properly estimating the acoustic properties of random foams depends on both the analyzed transport parameter(s) and level of polydispersity. Assuming identical and constant aperture ratio of membranes, the results indicate that (i) the viscous permeability is a reliable indicator regarding the size of the PUC (a more constraining property than the other transport parameters), and (ii) high-polydispersity foams require a larger number of pores in the PUC to achieve convergence with respect to morphological characteristics and acoustic properties. The influence of polydispersity on dimensionless transport parameters is then analyzed. It is found that polydispersity has a negligible effect on the high-frequency tortuosity but induces substantial variations in the remaining macroscopic parameters. Simulations further show that the ratio of the dimensionless transport parameters does not depend on membrane aperture ratio. This important result allows us to propose a fast method to estimate the acoustic properties of a random foam from the transport parameters of monodisperse foams with different pore sizes, for each studied transport parameter. The proposed method is finally employed to characterize the pore size and polydispersity in two real foams (with and without membranes), solving an inverse problem.

Quantum limits of parameter estimation in long-baseline imaging

Telescope systems with distributed apertures are a well-established approach for boosting resolution in astronomical imaging. However, theoretical limits on quantitative imaging precision, and the fundamentally best possible mode-sorting, beam-combining, and detection schemes to use with such arrays, remain largely unexplored. Using mathematical tools of the quantum and classical Crámer-Rao bounds, we perform analyses showing the fundamental origins of the enhancement provided by distributed imaging systems, over and above a single monolithic telescope, and consider the precision with which one can estimate any desired parameter embedded in a scene's incoherent radiation with a multi-aperture imaging system. We show how quantum-optimal measurements can be realized via beam-combination strategies of two classes: (1) , where light from different apertures is directed to a common focal plane, e.g., of a segmented-aperture telescope; and (2) , where light collected at each aperture, e.g., telescope sites of a long-baseline array, is routed to an optical interferometer. As an example, we show an explicit calculation of the quantum Fisher information (QFI) for estimating the angular separation between two-point emitters using two identical apertures separated by a baseline distance. We show that this QFI splits instructively into additive contributions from the single apertures and from the baseline. We quantify the relative benefits of intratelescope (e.g., spatial-mode) optical processing and intertelescope beam combination. We show how both receiver designs can be used to capture both sources of information and discuss how similar methods could be extended to more general imaging tasks. We discuss translating QFI-attaining measurements to explicit receiver designs, and the use of preshared entanglement to achieve the QFI when it is impractical to colocate and combine light collected by the apertures. Published by the American Physical Society 2024

Effects of Topological Properties with Local Variable Apertures on Solute Transport through Three-Dimensional Discrete Fracture Networks

In this study, the effects of topological properties with local variable apertures on fluid flow and solute transport through three-dimensional (3D) discrete fracture networks (DFNs) were investigated. A series of 3D DFNs with different fracture density, length, and aperture distribution were generated. The fluid flow and solute transport through the models were simulated by combining the MATLAB code and COMSOL Multiphysics. The effects of network topology and aperture heterogeneity on fluid flow and transport process were analyzed. The results show that the fluid flow and solute transport exhibit a strong channeling effect even in the DFNs with identical aperture, in which the areas of fast and slow migration fit well with the high- and low-flow regions, respectively. More obvious preferential paths of flow and migration are observed in individual fractures for the DFN with heterogeneous aperture than the model with identical aperture. Increasing the fracture length exponent reduces the available flow and transport paths for sparse fracture networks but does not significantly change the flow and transport channels for dense fracture networks. The breakthrough curves (BTCs) shift towards the right and slightly lag behind as the fracture density decreases or the aperture heterogeneity increases. The advection–diffusion equation (ADE) model cannot properly capture the evolution of BTCs for 3D DFNs, especially the long tails of BTCs. Compared to the ADE model, the mobile-immobile model (MIM) model separating the liquid phase into flowing and stagnate regions is proven to better fit the BTCs of 3D DFNs with heterogeneous aperture.

A simple experiment to study the array theorem using Fraunhofer diffraction of a two-dimensional grating

A transmission electron microscopy (TEM) grid comprises an array of identical square apertures. In this study, the Fraunhofer diffraction pattern of a TEM grid was obtained by a 532 nm wavelength diode laser. It was compared with the Fraunhofer diffraction pattern computed by using the array theorem and employed to estimate the mesh size of the TEM grid.

Enhanced Forward-Looking Missile-Borne Bistatic SAR Imaging With Electromagnetic Vortex

Bistatic radar possesses the forward-looking imaging performance that conventional synthetic aperture radar (SAR) lacks. Nevertheless, bistatic forward-looking imaging is seriously limited by the motion of the transmitter and receiver, resulting in a restrained resolution. In this work, the method for vortex missile-borne bistatic SAR (BSAR) is proposed, which combines the orbital angular momentum (OAM) beam with the traditional missile-borne BSAR technique to obtain a larger Doppler bandwidth. Higher azimuth resolution is achieved by compensating large spatial range cell migration (RCM) and serious range-azimuth coupling. First, the imaging scene of vortex missile-borne BSAR and the OAM-based echo model are established and deduced. Second, the preprocessing method for amplitude compensation is proposed with the design of the transmitted OAM beam, which improves the uncorrelation between different pulse echoes. Then, the improved range Doppler (RD) algorithm with azimuth compensation factor is proposed for vortex missile-borne BSAR to obtain the super-resolution 2-D reconstruction for the target. Simulation results show that compared with conventional missile-borne BSAR, the proposed vortex missile-borne BSAR possessing the extending Doppler bandwidth can obtain superior azimuth resolution performance with the identical synthetic aperture length situation. Furthermore, this work will contribute to the application for OAM-carrying in the field of radar forward-looking imaging and the development for high-resolution missile-borne BSAR imaging technology.

An equivalent analysis of non-linear flow along rough-walled fractures based on power spectrum and wavelet transform

The classical cubic law deviates from the estimation of the flow rate because of the surface roughness distributed along the fracture surface, which can be decomposed as the primary and the secondary roughness. A piecewise equivalent model is developed to characterise the relationship between primary and secondary roughness and flow rate inside the fracture, setting the fractal dimension 2.0 as the piecewise point. The rough-walled fracture influenced by the primary and secondary roughness is quantitatively evaluated based on the wavelet transform and the power spectrum method. A classification criterion is then proposed to accurately capture the secondary roughness by investigating the non-linear flow behavior along rough-walled fractures using the lattice Boltzmann method. The results found that secondary roughness greatly enhances the flow non-linearity when the fracture fractal dimension exceeds 2.0, while secondary roughness has little effect on non-linear flow behavior with the fracture fractal dimension less than 2.0. The developed piecewise equivalent model shows that the non-linear flow pattern is affected by both fracture primary and secondary roughness. The flow variation along fractures with identical fracture apertures and primary roughness is greatly related to the influence of the secondary roughness. The increase of secondary roughness greatly decreases the hydraulic aperture and the permeability. This work provides an improved equivalent model which can be potentially used in field practices to precisely predict the non-linear flow property by emphasising the great impacts of the secondary roughness.

Large-area homoporous membranes (HOMEs) enabled by multiple annealing

Homoporous membranes (HOMEs) featuring through pores with almost identical apertures, are highly desired for high-precision separations. It remains a major challenge to produce large-area HOMEs because the microstructure control and defect annihilation become increasingly difficult when membrane sizes are dramatically increased. Herein, we propose a multiple annealing strategy to fabricate large-area HOMEs. Polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) films are first coated on smooth and large substrates. Being annealed by chloroform vapor, perpendicularly aligned P2VP cylinders are formed within the films, and further converted into through pores via the mechanism of selective swelling-induced pore generation. It is shown that the conventional single-time annealing is inadequate to create the ordered through pores, because P2VP chains may have no sufficient time to locomote to the right position as required for the ideal hexagonally arranged ordering. By virtue of the multiple annealing, well-defined through pores can be generated after consecutive annealing for three times, as more P2VP chains aggregate into the ideally ordering position. The films are transferred and composited onto macroporous substrates, producing composite membranes with an effective area of up to ∼100 cm2. The resultant membranes exhibit excellent separation performances. Importantly, HOMEs can be fabricated on low-cost substrates via this strategy, highlighting their great promise in real-world applications of high-precision separations.

A Lubrication‐Based Solver for Shear‐Thinning Flow in Rough Fractures

AbstractThe depth‐averaged (2D) lubrication theory is often adopted to simulate Newtonian flow in rough fractures. This approach, which is computationally much less expensive than using 3D CFD solvers, allows addressing large ensembles of stochastic fracture realizations. For creeping flow, the degree of approximation introduced is limited as long as the apertures vary relatively smoothly. We propose the first generalization of this approach addressing the flow of fluids whose rheology, described by the Ellis model, is shear‐thinning (ST) above a crossover shear stress and Newtonian (of viscosity μ0) below. The resulting nonlinear Reynolds equation for pressures is solved for a vast range of realistic rheological parameter values using a novel and specifically designed finite volume‐based numerical model. The spatial discretization takes inspiration from the graph p‐Laplacian to yield a symmetric Newton Jacobian, allowing for a highly efficient inexact implementation of the preconditioned conjugate gradient‐based Newton‐Krylov method. This is combined with a parameter continuation strategy to increase code robustness and ensure global convergence for flow indices as low as 0.1 with an excellent efficiency. This original solver is used to investigate realistic synthetic rough fracture geometries, which exhibits both self‐affinity and a correlation length. The results show that the ST rheology mitigates the effects of aperture heterogeneities, increasing fracture transmissivity by several orders of magnitudes as compared to the Newtonian flow of viscosity μ0 if the imposed macroscopic gradient is sufficiently large, and even rendering the rough fracture up to 10 times more permeable than a smooth fracture of identical mean aperture.

Design a continuous microfluidic flow cell for turbidimetric-flow injection technology: A new approach for routine analysis of active pharmaceutical formulations

In this study, a new flow injection analysis (FIA) based on a microfluidic flow cell (MFC) with a sample capacity of 40 µL is described. A Tungsten lamp directs light from a typical 2100P Portable Turbidimeter apparatus into a quartz flow cell through a round sidewall aperture of 2.0 mm and emerges through the identical aperture on the opposite side of the flow cell, where a photodiode array (light detector) detects the passing light. When compared to a traditional cuvette (25 mm x 60 mm round) with the same nominal route length, this technique improves sensitivity by around 4.0. This improvement is due to the use of a short, narrow internal diameter microfluid as the flow cell, which reduces physical dispersion. The designed flow cell has been evaluated by developing a turbidimetric method for the detection of promethazine in pure form or pharmaceutical dosages. The developed method is based on forming of a yellowish ion-pair association complex due to the reaction of promethazine and sodium tetraphenylborate (STPB) in an acidic medium. At the flow optimum conditions, the calibration curve (CC) and the LOD for promethazine were obtained 0.5-90 µg mL-1 and 0.35 µg mL-1, respectively (R2 = 0.9955).

부배열 TRM이 적용된 능동위상배열 안테나의 Field of View 분석

In this paper, we describe a field of view (FOV) analysis of active phased array antennas with transmitter and receiver modules (TRM) applied to each subarray stage. First, the subarray design and amplitude-tapering optimization methods are introduced. Second, a comparative analysis of the sidelobe level (SLL) and half-power beamwidth (HPBW) according to the change in the distance between the radiation elements and number of subarrays is presented. Finally, the beam characteristics according to the change in the distance between the radiation elements are analyzed under the condition of identical aperture size and number of subarrays. The beam steering angles were analyzed for boresights at 7°, 12°, and 15°. As the number of subarrays increased and the distance between the radiation elements narrowed, a lower SLL was secured during beam steering. It was confirmed that the distance between phase centers between the subarrays was dominant in the phased array antenna with subarrays.

A fast numerical method and optimization of 3D discrete fracture network considering fracture aperture heterogeneity

A novel numerical method was developed to evaluate the effect of the aperture heterogeneity of individual fractures on fluid flow through three-dimensional discrete fracture networks (DFNs). First, the rock fractures are modelled as circular discs with sizes, orientations, and positions following exponential, Fisher, and uniform distributions, respectively. Isolated fractures (clusters) that make no contribution to fluid flow through the DFN were then removed by optimization programming using breadth optimization and deep optimization algorithms. Subsequently, individual fractures with heterogeneous apertures were developed using successive random addition algorithms. After that, fracture networks were triangulated, and the Reynolds equations were solved for fluid dynamics computations. The verification showed that the developed method provides advantages in computational accuracy and efficiency. Finally, the influence of the aperture heterogeneity of individual fractures on fluid flow through a DFN was evaluated with the proposed method. For comparison, DFN models with identical mechanical apertures (DFN-I) and another model with heterogeneous apertures (DFNH) were developed. The results show that a preferential flow phenomenon appeared in both the DFN-I and DFNH models. However, owing to the aperture heterogeneity of the individual fractures, the results of the DFNH model were more substantial than those of the DFN-I model. This preferential flow phenomenon would be weakened by an increase in either the mechanical aperture or the fracture density. The results also showed that the permeability difference between the DFN-I and DFNH models was obvious for DFN models with small apertures and low fracture densities, but this permeability discrepancy decreased with increasing mechanical aperture or fracture density. Therefore, a critical mechanical aperture exists for a DFN model with a specified fracture density. Beyond this threshold, the influence of aperture heterogeneity within individual fractures on fluid flow can be neglected, and the DFN-I model can be selected to replace the DFNH model for efficient modelling and computation.

Permeability of polydisperse solid foams.

The effect of polydispersity on foam permeability is investigated by numerical simulations. Foam structures are first generated by Laguerre tessellations via the Neper software and relaxed to minimize the surface energy via the Surface Evolver software. The fluid flow and permeability are then calculated by means of pore-network simulations, by considering either fully open-cell foams or foams with randomly selected closed windows. Different configurations of window aperture are used, including identical window aperture size, identical window aperture ratio, or random window aperture ratio. The main results are obtained for the case of foams having identical and uniform window aperture ratios. For such foams and at constant mean pore size, foam permeability is found to strongly increase with the polydispersity degree. The numerical results are employed to discuss the validity of the mean pressure field assumption used to calculate the foam permeability, the effect of small pores, and the definition of an equivalent Kelvin foam size. We show that as long as the fluctuations of the window aperture ratio remain low, foam permeability can be estimated by using the mean pressure field hypothesis. The weak effect of small pores on permeability is related to their small contribution to the overall fluid volume fraction. Finally, various estimations of the equivalent Kelvin foam size based on pore-size distribution are proposed.

Proposal and design of an 81.25 MHz interdigital H-mode dual-beam drift tube linac

A novel type dual-beam drift tube linac (DB-DTL) was proposed at the Institute of Modern Physics for ultra-high intensity heavy-ion acceleration. With two identical beam apertures located in the vertical direction with the same off-set from the cavity axis, two beams could be accelerated simultaneously by the DB-DTL and then be merged to one, thus double the current beam intensity limit, which is of great significance for ultra-high intensity heavy-ion acceleration. An 81.25 MHz proof-of-principle cavity was developed to demonstrate this new concept. Designed and optimized with the alternative phase focusing (APF) scheme, this prototype cavity was supposed to accelerate 10 mA protons beam from 0.56 MeV to 2.5 MeV in one meter with transmission efficiency more than 90%. Inter-digital H-mode (IH) structure was adopted by this DB-DTL, thus high shunt impedance could be achieved which significantly reduce the power loss. With efficient cooling, this cavity was capable to work at the pulsed mode with a maximum duty cycle of 10%. Beam dynamics simulations, electromagnetic design and optimization of the prototype cavity, and multi-physics analyses of this DB-DTL will be presented in this paper.

A Hybrid Transtibial Technique Combines the Advantages of Anteromedial Portal and Transtibial Approaches: A Prospective Randomized Controlled Trial

Background: The anteromedial (AM) portal and transtibial (TT) approaches are 2 common anterior cruciate ligament (ACL) femoral tunnel drilling techniques, each with unique benefits and disadvantages. A hybrid TT (HTT) technique using medial portal guidance of a flexible TT guide wire has recently been described that may combine the strengths of both the AM portal and the TT approaches. Hypothesis: The HTT technique will achieve anatomic femoral tunnel apertures similar to the AM portal technique, with improved femoral tunnel length and orientation. Study Design: Randomized controlled trial; Level of evidence, 2. Methods: A total of 30 consecutive patients with primary ACL tears were randomized to undergo the TT, AM portal, or HTT technique for femoral tunnel positioning at the time of reconstruction. All patients underwent 3-dimensional computed tomography of the operative knee at 6 weeks postoperatively. Femoral and tibial tunnel aperture positions and tunnel lengths, as well as graft bending angles in the sagittal and coronal planes, were measured. Results: Tibial tunnel lengths and aperture positions were identical between the 3 groups. The AM portal and HTT techniques achieved identical femoral aperture positions in regard to both height (P = .629) and depth (P = .582). By contrast, compared with the AM portal and HTT techniques, femoral apertures created with the TT technique were significantly higher (P < .001 and P < .001, respectively) and shallower (P = .014 and P = .022, respectively) in the notch. The mean femoral tunnel length varied significantly between the groups, measuring 35.2, 41.6, and 54.1 mm for the AM portal, HTT, and TT groups, respectively (P < .001). Last, there was no difference between the mean coronal (P = .190) and sagittal (P = .358) graft bending angles between the TT and HTT groups. By contrast, compared with the TT and HTT techniques, femoral tunnels created with the AM portal technique were significantly more angulated in the coronal plane (17.7° [P < .001] and 12.5° [P = .006], respectively) and sagittal plane (13.5° [P < .001] and 10.5° [P = .013], respectively). Conclusion: This prospective randomized controlled trial found that the HTT technique achieved femoral aperture positions equally as anatomic as the AM portal technique but produced longer, less angulated femoral tunnels, which may help reduce graft strain and mismatch. As such, this hybrid approach may represent a beneficial combination of both the TT and the AM portal techniques. Registration: NCT02795247 (ClinicalTrials.gov identifier)

Excellence in Research:A Hybrid Transtibial Technique Combines the Strengths of theAnteromedial Portal and Transtibial Approaches: A Prospective Randomized Controlled Trial

Objectives:Improved biomechanical and clinical outcomes have been reported when femoral anterior cruciate ligament (ACL) tunnels are centered on the native footprint. The anteromedial (AM) portal technique achieves improved aperture position when compared to a transtibial (TT) approach but sacrifices technical ease and creates a shorter more acutely angulated tunnel. A hybrid transtibial technique (HTT) technique using medial portal guidance of a flexible transtibial guide wire without the need for knee hyperflexion may combine the strengths of both the AM and TT approaches. The authors hypothesized that this HTT technique would achieve anatomic femoral tunnel apertures similar to the AM technique, but with longer and less angulated femoral tunnels similar to a TT technique.Methods:A prospective randomized controlled trial was implemented where 30 consecutive patients with acute, primary ACL tears were randomized to receive a TT, AM or HTT technique for their reconstruction. A total of 46 patients were assessed for eligibility in the investigation (Figure 1). All patients underwent 3D CT scans of the operative knee 6 weeks postoperatively to characterize tunnel positions. Femoral and tibial tunnel aperture positions and tunnel lengths, as well as the graft bending angle in the sagittal and coronal plane were measured.Results:There were no significant differences between the patient demographics of the three groups. Tibial tunnel lengths and aperture positions were identical between the three groups. The AM portal and HTT techniques achieved identical femoral aperture positions in regards to both height (p=0.75) and depth (p=0.72). On the other hand, compared to the AM portal and HTT techniques, respectively, femoral apertures created by the TT technique were significantly higher (p<0.001 and p<0.001) and shallower (p=0.001 and p<0.001) in the notch. The average femoral tunnel lengths varied significantly between the three groups measuring 35.16 mm, 41.64 mm, and 54.13 mm for the AM, HTT and TT groups, respectively (p<0.001). Lastly, there were no differences between the average coronal (164.0 degrees versus 158.8 degrees, p=0.190) and sagittal (114.0 degrees versus 111.0 degrees, p=0.358) graft bending angles between the TT and HTT groups, respectively. By contrast, compared to the TT and HTT groups, respectively, the graft bending angles created with an AM technique were significantly more acutely angled in the coronal (146.3 degrees, p<0.001, p<0.006) and sagittal (100.5 degrees, p=0.014, p=0.013) planes.Conclusion:The HTT technique achieves femoral aperture positions equally as anatomic as an AM portal technique, but with longer and less acutely oriented grafts similar to a transtibial approach. These advantages will decrease the incidence of graft tunnel mismatch as well as reduce the amount of stress imparted onto the graft by avoiding an acute graft bending angle. As such, this hybrid approach may represent a beneficial combination of both transtibial and AM portal techniques.

Dynamics of foam flow in a rock fracture: Effects of aperture variation on apparent shear viscosity and bubble morphology

There has recently been renewed interest in understanding the physics of foam flow in permeable media. As for Newtonian flows in fractures, the heterogeneity of local apertures in natural fractures is expected to strongly impact the spatial distribution of foam flow. Although several experimental studies have been previously performed to study foam flow in fractured media, none of them has specifically addressed that impact for parallel flow in a realistic fracture geometry and its consequences for the foam’s in situ shear viscosity and bubble morphologies. To do so, a comprehensive series of single-phase experiments have been performed by injecting pre-generated foams with six different qualities at a constant flow rate through a replica of a Vosges sandstone fracture of well-characterized aperture map. These measurements were compared to measurements obtained in a Hele-Shaw (i.e., smooth) fracture of identical hydraulic aperture. The results show that fracture wall roughness strongly increases the foam’s apparent viscosity and shear rate. Moreover, foam bubbles traveling in regions of larger aperture exhibit larger velocity, size, a higher coarsening rate, and are subjected to a higher shear rate. This study also presents the first in situ measurement of foam bubbles velocities in fracture geometry, and provides hints towards measuring the in situ rheology of foam in a rough fracture from the velocity maps, for various imposed mean flow rates. These findings echo the necessity of considering fracture wall when predicting the pressure drop through the fracture and the effective viscosity, as well as in situ rheology, of the foam.

A novel three-dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses

Effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated, yet the aperture variability of individual fractures in 3D discrete fracture networks (DFNs) is commonly negligible by using parallel-plate fractures. The present study proposed a 3D DFN model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow. In total, a set of 1280 3D models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code. The influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3D DFNs are estimated. The results show that the network topology provides a first-order frame of geometrical connectivity, and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures. The DFN model with identical apertures generates a large number of medium-flow rate regions whereas the DFN model with fractures having heterogeneous apertures results in extremely low- and high-flow rate regions. The permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution. The average permeability ratio increases significantly first and then approaches to 1.0 with increasing the average mechanical aperture. This allows for the definition of a critical mechanical aperture, above which the permeability can be properly predicted using the DFN model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the DFN model with fractures having heterogeneous apertures should be employed.

Influence of permeability anisotropy on heat transfer and permeability evolution in geothermal reservoir

Extracting heat energy from geothermal reservoirs essentially relies on circulating cold fluid within fractured hot rocks. The intrinsic anisotropic permeability in the reservoir directly affects the path of flow and the associated thermal drawdown from cooling procedure. Consequently, each individual component including thermal, hydraulic, and mechanical field needs to be considered, to evaluate the influence of permeability anisotropy on the thermal production and evolution of rock properties. In this work, the fully implicit coupled simulator TFReact was successfully implemented to generate results prototypical of an enhanced geothermal system. Anisotropic permeability values were generated from the variation of fracture spacing at three orthogonal principal directions, with identical initial fracture aperture. Five case scenarios of permeability anisotropy were simulated to evaluate the influence of anisotropic thermal drawdown in triggering permeability evolution. Analysis of the propagation of the thermal front from injector to producer indicated that low anisotropic permeability values will lead to late cold water breakthrough at producer, slower migration rate and wider sweep area than high anisotropic permeability values. Isotropic permeability scenario showed a lower thermal gradient profile, comparing against the scenarios of anisotropic permeability. The anisotropic value of 0.01 produced the highest power output, while isotropic permeability generated the least power output. Induced thermal stress resulted an unloading response by reducing compressive normal stress in sub-horizontal direction, and thereby increase fracture aperture in sub-horizontal direction. Invariably, the induced thermal expansion stress increased the compressive stress and reduced fracture aperture and permeability. After the same timing of injection-production cycle, the highest anisotropic permeability scenario resulted a factor of 2.5 increment in evolving fracture permeability, while lowest anisotropic permeability scenario lead to a factor of 0.35 decrease in changing fracture permeability. The generated thermal output suggested the most favorable strategy in maximizing thermal sweep across the reservoir, by prompting thermal transfer normal to direction of injector-producer.

Ku-Band Transmitarrays With Improved Feed Mechanism

Combining the advantages of lens antenna and array techniques, transmitarrays have been widespreadly concerned in recent years. In the first part of this paper, a wideband four-layer transmitarray operating at 13 GHz fed by a horn with a focus-to-diameter ratio (F/D) of unity is proposed. The employed elements composed of dual-resonance double hexagonal rings are closely arranged in the honeycomb lattice. The simulated results show that the transmitarray can achieve a 53.34% peak aperture efficiency and a 19.23% bandwidth for 1 dB gain drop, respectively. The factors with strong influences on the measured results are analyzed. In the second part, an improved feed mechanism, which is aimed at reducing the transmitarray profile, is discussed in detail. The conjugate field matching technology is utilized to realize an ideal compensation. The small-scale antenna array, which has a nearly identical aperture size to the feed horn applied in the first design, can effectively excite the transmitarray with a profile reduction of 64.5%. These prototypes confirm the feasibility of designing a wideband transmitarray and a low-profile array-fed transmitarray.