Overlay Configuration Research Articles

Comparative Studies on In-Plane Shear Behavior of Masonry Wallettes Retrofitted with Mortar, UHPC, and ECC Ferrocement: Shotcrete and Prefabricated Panels

Masonry walls, prevalent in many historical and contemporary structures, often require retrofitting to meet modern safety and performance standards. Motivated by the need for efficient and reliable retrofitting solutions, this research investigates the potential of various types of ferrocement, reinforced with high-strength steel meshes, to enhance the in-plane shear behavior of brick masonry walls. Through rigorous diagonal compression tests on nine masonry wallettes, the study evaluated the performance of ferrocement overlays in terms of overlay configuration (asymmetric or symmetric), cementitious material type (mortar, ECC, or UHPC), the presence or absence of steel mesh, and construction method (shotcrete or prefabricated panels). The results indicated that UHPC and ECC overlays significantly enhanced post-cracking deformation capacity. Compared to the asymmetric retrofit, the symmetric retrofit led to more uniform deformation in the retrofitted wallette, effectively improving the maximum shear by up to 119 %. While UHPC shotcrete was more effective in improving the shear strength, ECC shotcrete led to the highest rupture shear strain and pseudo-ductility for the retrofitted wallette, reaching 0.83 % and 17.2, respectively. Moreover, although steel mesh inclusion in the ferrocement overlay was crucial in enhancing post-peak ductility, its impact on shear strength of the retrofitted wallettes was minimal. The test results also demonstrated that the developed prefabricated UHPC panels emerged as an effective retrofitting solution to simultaneously improve the strength, deformation capacity, and ductility for masonry wallettes. In addition to the experimental investigation, a new strength model, accounting for various key design variables, was developed, offering reliable shear strength predictions for the retrofitted wallettes.

Validated Finite-Element Model for Predicting Asphalt Concrete Overlay Reflective Cracking Potential

The reflective cracking potential of overlay systems is often studied through large-scale testing, which is time-consuming and expensive. Therefore, a generalized 3D finite-element model was developed to simulate a large-scale test setup to predict the reflective cracking potential. Crack propagation was modeled, and fracture parameters, such as stress intensity factor (SIF) and J-integral, were obtained. Mode I cracking dominated the model’s crack propagation, while in-plane shear cracking was insignificant. The model was validated with large-scale testing results; the average Mode I SIF was found to be a valid measure to assess the overlays’ reflective cracking potential. The model could be used qualitatively to compare different overlay configurations. A database of 128 cases was generated to compute fracture parameters for extreme scenarios or a combination of inputs. A data-driven surrogate model that predicts reflective cracking potential was developed to allow easy application by agencies. Shapley Additive Explanations (SHAP) analysis confirmed the model’s robustness. The surrogate model may be used by engineers to select asphalt concrete mixtures and design overlay thicknesses to control reflective cracking potential.

Development of a full-Scale approach to predict overlay reflective crack

ABSTRACT Resurfacing a moderately deteriorated Portland cement concrete (PCC) pavement with asphalt concrete (AC) layers is considered an efficient rehabilitation practice. However, reflective cracks may develop shortly after resurfacing because of discontinuities (e.g. joints and cracks) in existing PCC pavement. In this paper, a new accelerated full-scale testing approach was developed to study reflective crack growth in AC overlays. Two hydraulic actuators were used to simulate a moving dual-tire assembly with a loading rate of more than five-thousand-wheel passes per hour. A load cycle consists of three steps, simulating a tire approaching, moving across, and leaving a PCC discontinuity. Experiments were conducted to compare the reflective crack behaviour of two overlay configurations. Both test sections were fully cracked in less than an hour. The initiation and propagation of reflective cracks were explicitly documented using crack detectors in conjunction with a camera. The proposed full-scale testing protocol offers a repeatable and efficient approach to systematically investigate the effects of various overlay configurations, thus enabling the identification of optimal design against reflective cracking.

Rotator Cuff Repair and Overlay Augmentation by Direct Interlocking of a Nonwoven Polyethylene Terephthalate Patch Into the Tendon: Evaluation in an Ovine Model

Background: Arthroscopic repair of large rotator cuff tendon tears is associated with high rates of retear. Construct failure often occurs at the suture-tendon interface. Patch augmentation can improve mechanical strength and healing at this interface. Purpose: To introduce a novel technique for suture-free attachment of an overlaid patch and evaluate its biomechanical strength and biological performance. Study Design: Descriptive and controlled laboratory studies. Methods: An established ovine model of partial infraspinatus tendon resection and immediate repair was used. After a nonwoven polyethylene terephthalate patch was overlaid to the resected tendon, a barbed microblade was used to draw fibers of the patch directly into the underlying tissue. In vivo histological assessment of healing was performed at 6 and 13 weeks after implantation. Ex vivo models were used to characterize primary repair strength of the suture-free patch fixation to tendon. Additional ex vivo testing assessed the potential of the technique for patch overlay augmentation of suture-based repair. Results: The in vivo study revealed no macroscopic evidence of adverse tissue reactions to the interlocked patch fibers. Histological testing indicated a normal host healing response with minimal fibrosis. Uniform and aligned tissue ingrowth to the core of the patch was observed from both the tendon and the bone interfaces to the patch. There was no evident retraction of the infraspinatus muscle, lengthening of the tendon, or tendon gap formation over 13 weeks. Ex vivo testing revealed that direct patch interlocking yielded tendon purchase equivalent to a Mason-Allen suture (150 ± 58 vs 154 ± 49 N, respectively; P = .25). In an overlay configuration, fiber interlocked patch augmentation increased Mason-Allen suture retention strength by 88% (from 221 ± 43 N to 417 ± 86 N; P < .01) with no detectable difference in repair stiffness. Conclusion: Testing in an ovine model of rotator cuff tendon repair suggested that surgical interlocking of a nonwoven medical textile can provide effective biomechanical performance, support functional tissue ingrowth, and help avoid musculotendinous retraction after surgical tendon repair. Clinical Relevance: The novel technique may facilitate patch augmentation of rotator cuff repairs.

RC beams strengthened in shear with FRP-Reinforced UHPC overlay: An experimental and numerical study

In this study, a hybrid strengthening technique consisting of ultra-high performance concrete (UHPC) overlay reinforced by fiber reinforced polymer (FRP) bars is proposed to strengthen reinforced concrete (RC) beams in shear. Eleven beams, five of which are physical samples tested under static load, and the other six are virtual ones derived from a robust finite element (FE) analysis, are used to assess the effectiveness of this retrofitting technique. Several parameters are examined, namely overlay thickness, overlay configuration (continuous vs. discontinuous), FRP reinforcement ratio in the overlay, and type of FRP rebar (Glass-FRP vs. Carbon-FRP). Results showed that the system was very effective in increasing the beam capacity (Pu) and altering the failure mode from shear to flexure. Increasing the overlay thickness (toverlay) from 0 to 30 mm for plain and FRP-reinforced overlays results in a significant increase in Pu of 76–117%, compared to the control beam. Using discontinuous UHPC strips, although does not alter the shear failure, results in 89% increase in Pu. Reinforcing the overlay with GFRP and CFRP bars results in reducing the overlay thickness needed to shift the failure mode from shear to flexure. The energy absorption index, which is a measure of ductility, of the strengthened specimens was 4.0 to 6.9 times that of the control beam. FRP bars resulted in 11–25% increase in energy absorption compared to plain overlays, with GFRP showing more ductility than CFRP. An analytical procedure is also included and used to predict Pu from modifying existing code equations to include the contribution of UHPC overlay to shear.

The role of susceptibility, exposure and vulnerability as drivers of flood disaster risk at the parish level

Fluvial flooding continues to be a process that has a major impact on society, the environment and the economy. Although its natural triggering factors, the spatial configuration of exposure and vulnerability is expected to play a relevant role in explaining the damage records. The starting point of this research is the use of existing flood susceptibility, exposure and social vulnerability mapping, produced at the parish level, as input data in a Classification and Regression Trees’ (CART) model. Two models were ran, autonomously, that use two databases of flood damage as dependent variables: one including the human damages (fatalities, missing, injured, displaced and evacuated people) from flood events—the DISASTER database; another one that sums the DISASTER cases and the lower impact damages (damages to roads, railroads and buildings). The results show a quite distinct classification of parishes, whether one database is used or the other. The DISASTER database reveals susceptibility as the most relevant flood risk driver in explaining the damage patterns, while the database with all the flood cases identifies exposure as the more relevant driver. In the end, the degree of damages as documented in databases is conditioned by the geographical distribution and overlay configuration of the three flood risk drivers. Finally, the CART classification groups are analyzed at the light of the European Union’s Floods Directive areas of significant potential flood risk. This analysis showed that the Directive’s parishes are interpreted differently—in terms of their positioning in face of the risk drivers—which is explained by the use of distinct impacting-criteria in the construction of the flood damage databases.

Multi-grain reconfigurable and scalable overlays for hardware accelerator composition

In this paper, the reconfigurable nature of SRAM-based FPGAs is exploited to build a dynamically multi-grain reconfigurable and scalable overlay architecture. The composition of the overlay can be reconfigured on the fly to map applications with different requirements, change the size of the overlay to free up resources for other accelerators, or to deal with run-time variable computation demands. The overlay has been implemented by combining two different dynamic partial reconfiguration granularities. First, medium grain is used to compose the overlay by stitching together different processing elements, while fine grain reconfiguration is used to map applications onto the overlay by configuring the interconnections of the processing elements. The overlay has been coupled with a multiport memory and integrated into a System-on-Chip (SoC). Finally, a fully automated toolchain is proposed to transform code segments with one or two nested loops into the appropriate overlay configuration and the required control routines, enabling the transparent offloading of the computing-intensive parts of the application from the embedded SoC processor to hardware. The proposed overlay has been implemented in a Xilinx Zynq-7000 device and tested using the benchmark proposed in the CGRA-ME framework, obtaining up to 2 × speed-up.

Assessment of heuristics for self-stabilisation in real-time interactive communication overlays

Self-stabilisation is an autonomic behaviour closely related to self-healing. In multimedia communication overlays, self-stabilisation copes with network disruptions by dynamically restoring data links and communication paths. The restoration of links may require reorganisation of the overlay by establishing new connections among members or by modifying existing ones. Selfstabilisation techniques are usually triggered asynchronously, either on use (during reorganisation of the overlay) or on event (as a response to a failure), and several heuristics may be used when selecting link peers. This work assesses several heuristics to perform on event self-stabilisation in multimedia communication overlays. A real-time communication overlay deployed following a fullmesh topology interconnecting a set of multicast islands is used as the assessment framework to evaluate the proposed heuristics. Intensive tests have been carried out to compare and assess heuristics with several overlay configurations and network conditions.

Assessment of heuristics for self-stabilization in real-time interactive communication overlays

Self-stabilisation is an autonomic behaviour closely related to self-healing. In multimedia communication overlays, self-stabilisation copes with network disruptions by dynamically restoring data links and communication paths. The restoration of links may require reorganisation of the overlay by establishing new connections among members or by modifying existing ones. Selfstabilisation techniques are usually triggered asynchronously, either on use (during reorganisation of the overlay) or on event (as a response to a failure), and several heuristics may be used when selecting link peers. This work assesses several heuristics to perform on event self-stabilisation in multimedia communication overlays. A real-time communication overlay deployed following a fullmesh topology interconnecting a set of multicast islands is used as the assessment framework to evaluate the proposed heuristics. Intensive tests have been carried out to compare and assess heuristics with several overlay configurations and network conditions.

Intracoronary Optical Coherence Tomography and Histology of Overlapping Everolimus-Eluting Bioresorbable Vascular Scaffolds in a Porcine Coronary Artery Model: The Potential Implications for Clinical Practice

This study sought to assess the vascular response of overlapping Absorb stents compared with overlapping newer-generation everolimus-eluting metallic platform stents (Xience V [XV]) in a porcine coronary artery model. The everolimus-eluting bioresorbable vascular scaffold (Absorb) is a novel approach to treating coronary lesions. A persistent inflammatory response, fibrin deposition, and delayed endothelialization have been reported with overlapping first-generation drug-eluting stents. Forty-one overlapping Absorb and overlapping Xience V (XV) devices (3.0 × 12 mm) were implanted in the main coronary arteries of 17 nonatherosclerotic pigs with 10% overstretch. Implanted coronary arteries were evaluated by optical coherence tomography (OCT) at 28 days (Absorb n = 11, XV n = 7) and 90 days (Absorb n = 11, XV n = 8), with immediate histological evaluation following euthanasia at the same time points. One animal from each time point was evaluated with scanning electron microscopy alone. A total of 1,407 cross sections were analyzed by OCT and 148 cross sections analyzed histologically. At 28 days in the overlap, OCT analyses indicated 80.1% of Absorb struts and 99.4% of XV struts to be covered (p < 0.0001), corresponding to histological observations of struts with cellular coverage of 75.4% and 99.6%, respectively (p < 0.001). Uncovered struts were almost exclusively related to the presence of "stacked" Absorb struts, that is, with a direct overlay configuration. At 90 days, overlapping Absorb and overlapping XV struts demonstrated >99% strut coverage by OCT and histology, with no evidence of a significant inflammatory process, and comparable % volume obstructions. In porcine coronary arteries implanted with overlapping Absorb or overlapping XV struts, strut coverage is delayed at 28 days in overlapping Absorb, dependent on the overlay configuration of the thicker Absorb struts. At 90 days, both overlapping Absorb and overlapping XV have comparable strut coverage. The implications of increased strut thickness may have important clinical and design considerations for bioresorbable platforms.

PSON

Predictable Service Overlay Networks (PSON) improve the predictability of Internet communication by providing an estimate of the upper bound on message latency for each path of the overlay. The upper bound serves as an assurance of synchrony and enables applications to order events or make inferences based on non-receipt of a message. For improved performance, PSON also employs overlay routing and overlay configuration. Messages are routed either through the direct overlay path or via a one-hop overlay path such that the selected path is stable and promotes synchrony, while the overlay configuration mechanisms are utilized in order to select nodes that promote predictable communication. The expected impact of PSON is that by utilizing intelligent techniques such as upper bound estimation, routing and configuration, it can harness the unexpected and unreliable Internet substrate to provide a predictable communication overlay for applications.

Distributed Hierarchical Multicast Tree Algorithms for Application Layer Mesh Networks

This paper proposes a set of novel distributed algorithms on m-D mesh overlay configurations for short delay and low resource consumption application layer multicast. In contrast to previous approaches, our application layer multicast adopts two-layer tree architecture and the novelty and contribution are: (1) cluster formation algorithm assigns the closest group members into the same cluster that greatly decreases the multicast delay and resource consumption caused by the message transmission among the members with long distances; (2) optimal core selection algorithm seeks the cluster member who has the minimum sum of static delay distances to other cluster members as the optimal cores (i.e. cluster cores) that guarantees the short multicast delay; (3) weighted shortest path tree generation algorithm constructs a shortest path tree rooted at the optimal core for each cluster. The shortest path tree utilizes the minimum sum of links that are on the shortest paths among the cluster members; and (4) distributed multicast routing algorithm directs the multicast messages to be efficiently distributed along the two-layer multicast architecture in parallel without a global control. The extended simulation results indicate that the application layer multicast constructed by our algorithms is efficient in terms of short multicast delay and low network resource consumption as compared with other well-known existing multicast solutions.

Numerical Study Of Structural Joints ReinforcedWith Composite Fabrics

The structural application of composite materials such as fiber reinforced plastics (FRP) has increased in recent years. The FRP products can be used in the initial construction or for repair and structural enhancement. FRP materials have several advantages over steel including, light weight, corrosion resistance, and the ability to mold FRP overlays to concrete surfaces. FRP overlays have been used to strengthen/repair both concrete beam and column elements. Limited studies have been performed on the use of FRP overlays at beam-column connections. Joints that are reinforced with FRP overlays have a different failure mode than FRP plated beams or wrapped columns. At the beam-column connection the interface is subjected to prying or peeling stresses. This investigation involves parametric studies of the application of FRP overlays to exterior beam-column connections for enhancement of structural performance. Different composite materials and different overlay configurations are used. The choice of the composite materials affects the structural performance. Materials that are considered are E-glass, kevlar, and graphite. Configurations studied include overlays bonded to the tensile faces with and without wraps. Numerical analysis shows that the bond stress perpendicular to the overlay/concrete interface at the beam-column junction can easily exceed the tensile strength of the underlying concrete. Therefore, the configuration of the FRP overlay plays an important role in the prevention of peeling. Transactions on Engineering Sciences vol 21, © 1998 WIT Press, www.witpress.com, ISSN 1743-3533

Evaluation of a capture zone overlay method for designing groundwater remediation systems

Simplified approaches are often used to model the removal of groundwater contamination. These approaches can yield poor remediation schemes because they incorrectly portray the effects of multiple pumping wells. In this study, a pumping configuration designed by graphically overlaying capture zones having an identical, quasi-elliptical shape was evaluated with a numerical mass transport model. After a 3-year period (within which the hypothetical aquifer was to be remediated) the contaminant mass had been reduced by 77%. Due to stagnation zones which developed between extraction wells, approximately 15 years of pumping was required to remediate the aquifer with the overlay configuration. An alternative design, consisting of an extraction well between two injection wells along the long axis of the plume, removed the contaminant within the 3-year design period.

Epitaxial interactions between molecular overlayers and ordered substrates.

Abstract : A framework for evaluating the epitaxy of ordered organic overlayers of generic symmetry on ordered substrates is described that combines a computationally efficient method for explicit determination of the type of epitaxy (i.e., commensurism, coincidence, or incommensurism) and overlayer azimuthal orientation with an analysis of the elastic properties of the overlayer and the overlayer-substrate interface. The azimuthal orientations predicted by this function agree with values predicted by semi-empirical potential energy calculations and observed experimentally for previously reported organic overlayers which are demonstrated here to be coincident, including electrochemically grown overlayers of molecular conductors. Calculations based on this analytical approach are much less computationally intensive than potential energy calculations as the number of computational operations is independent of the overlayer size chosen for analysis. This enables analyses to be performed for the large overlayer basis sets common for molecular overlayers. Furthermore, this facilitates the analysis of coincident overlayers, for which the overlayer size needs to be large enough to establish the phasing relationship between the substrate and large non-primitie overlays supercell so that the global minimum with respect to azimuthal angle can be determined. The computational efficiency of this method also enables convenient examination of numerous possible reconstructed overlayer configurations in which the lattice parameters are bracketed around those of the native overlayer, thereby allowing examination of possible epitaxy-driven overlayer reconstructions. When combined with calculated intralayer and overlayer-substrate elastic constants this method provides a strategy for the design of heteroepitaxial molecular films.

Three visits to Montevidisco: Spanish enrichment with interactive videodisc

Montevidisco is an interactive videodisc application intended for intermediate Spanish students. It combines language enrichment with elements of role-playing games as the student plays the role of someone visiting a hypothetical city in Mexico, interacting with native Spanish speakers in native situations via videodisc. The concept originated at Brigham Young University in the early eighties, with the video filming done at that time. More recently, the BYU Humanities Research Center has adapted the original material to run on standard microcomputer platforms.There are three implementations of Montevidisco in various stages of development. The first is a side-by-side version that uses a HyperCard stack on a Macintosh to control a separate videodisc player and monitor. The second version uses a video overlay configuration with ToolBook and Windows on an IBM platform. Both of these versions are 'finished' to the extent that they are being used in intermediate Spanish classes at BYU and elsewhere. General marketing arrangements are expected to be finalized this summer. The most recent implementation uses QuickTime on a Macintosh to display digitized video directly from the computer's hard disk.This paper begins with an explanation of the general features of Montevidisco that are common to all three implementations. It outlines some of the design considerations faced and explains how the choice of metaphor influenced those decisions. Some questions that have been raised during the testing and review process are also addressed. The paper then categorizes the significant differences between the three implementations and discusses the technological and pedagogical reasons for them. It concludes with a status report on the QuickTime version and gives an assessment of this new digital video technology in an instructional environment.

Surface diffusion in temporally and spatially inhomogeneous systems

Non-equilibrium processes in an overlayer with the system evolving between two different states (i.e., ordering, disordering, adsorption) can be used to study surface diffusion. Diffraction experiments on O W(110) at high coverage measure an activation energy E d = 0.6 ± 0.05 eV during ordering and E d = 1 ± 0.05 eV during disordering. These results are consistent with other diffusion experiments carried out with the fluctuation and Boltzmann-Matano methods. The difference between the measured activation energies can be accounted for in terms of the interactions which contribute differently in different overlayer configurations. Computer simulations on lattice gas models illustrate the dependence on the configuration, by comparing diffusion coefficients obtained with different methods.

Method-dependent diffusion coefficients on interactive systems

Diffusion coefficients are examined in interactive models by using different methods and different overlayer configurations. Comparison between the fluctuation and laser-induced-desorption method on well-equilibrated overlayers can lead to large differences depending on the ordered structures formed. If comparison is made between well-equilibrated and faraway-from-equilibrium configurations different diffusion coefficients and activation energies are obtained. Finally, the activation energy ΔEc obtained from growth rates in coarsening experiments is shown to verify ΔEc=xΔEd, where x is the growth exponent and ΔEd the activation energy of diffusion.

Ab initio cluster study of the chemisorption of oxygen on an aluminium (111) surface

The results of an ab initio all-electron Hartree-Fock study of the interaction of oxygen with Al10 and Al3 clusters are reported. These clusters model the close-packed Al(111) surface. The Al10 cluster has seven atoms in the first layer and three in the second; the Al3 cluster has only three atoms in the first layer. The chemisorption of atomic oxygen at the f.c.c. sites of Al(111) has been studied by means of calculations on Al10O3, Al10O and Al3O. The Al10O3 cluster was chosen to provide the opportunity of incorporating part of the possible influence of oxygen-oxygen interactions on the chemisorption properties. A stable phase of oxygen has been found to be chemisorbed just outside the surface, with a vertical distance between oxygen and the first Al plane of ~0.6 A. The calculated vibrational energy of the oxygen motion in a direction normal to the surface in the harmonic approximation is ~50 meV. The results are consistent with the coexistence of oxygen in overlayer and underlayer configurations. No significant influence of oxygen-oxygen interaction on the calculated properties has been found. Finally, the calculation of the chemical shift of surface Al(2p) ionization is discussed.

Plural concentric moving coil speaker with push-pull voltage follower direct coupling

A loudspeaker with an overlay voice coil and directly coupled push-pull audio amplifier circuit is disclosed. The overlay configuration compensates for increased input impedance at high frequencies by introducing a transformer coupling between two co-axial voice coils. The resultant input impedance remains fairly constant over a large frequency range, thereby insuring uniform power transfer to the speaker.