Push-out Research Articles

Aspects of glass and hybridization protocols for bonding of fiber posts to root dentine.

This study evaluated bond strength of glass fiber posts to root dentin using push-out (PO) and diametral compression (DC), testing glycolic acid as a conditioner and varying dentin moisture. An additional aim was to test whether DC can be an alternative test to PO for bond strength assessment. Eighty bovine teeth were divided into eight groups (n=10) defined by the use of either 37% glycolic acid or 37% phosphoric acid (PA) on moist or wet dentin before bonding with either Adapter SingleBond/RelyX ARC or One Step Plus/Duo-Link Bisco. Each tooth provided discs with an internal diameter of 2mm, external diameter of 5mm, and height of 2mm, which underwent PO and DC. Finite element analysis (FEA) was carried out on 3D models. When analyzing PO results through linear regression, the highest values of bond strength were observed using glycolic acid on wet dentin in the cervical and middle thirds of the teeth. Analyzing DC results, the only statistical influence on values was the dental thirds. The scatterplot of the DC results and the PO bond strength values indicated no relationship between the results of the two tests (r=0.03; p=0.64). PO test detected more sensitive changes in bond strength values than DC.

Correlation approach for the Push-Out and full-size bending short-term performances of timber-to-timber slabs with Self-Tapping Screws

Self-Tapping Screws (STSs) are commonly used to realize many geometrical configurations for connections that are characterized by enhanced stiffness and load-carrying capacity. The analysis of STS joints and composite systems, however, usually requires designers to account for several aspects in their actual load transfer mechanisms, and most of them require refined calculation tools.In this paper, an extended Finite Element (FE) investigation is proposed for timber-to-timber slabs with STS joints, based on full 3D brick models inclusive of Cohesive Zone Modelling (CZM) techniques and damage constitutive laws for the materials in use. The final goal of the study takes advantage of the global and local performance assessment of a selection of STS joints, with careful consideration for their response under a conventional Push-Out (PO) test setup or a full-size bending configuration. As shown, major FE outcomes are discussed to elaborate a design procedure that can be developed on the base of correlation coefficients for maximum force and stiffness calculations in a given slab and loading condition. Major effects due to variable loading configurations are in fact explored at the screw level. Further, geometrically simplified spring-based FE models, that hardly capture the complex behaviour of the examined systems but are largely used in design practice, are presented in comparison to refined FE approaches and literature efforts. As shown, the variation of maximum force and stiffness parameters for STSs is emphasized in the paper for a selection of configurations, and fitting curves are proposed to estimate the STS performance along a given full-size slab, thus suggesting the feasibility and possible generalization of the procedure.

Mechanical Characterization of Timber-to-Timber Composite (TTC) Joints with Self-Tapping Screws in a Standard Push-Out Setup

Self-tapping screws (STSs) can be efficiently used in various fastening solutions for timber constructions and are notoriously able to offer high stiffness and load-carrying capacity, compared to other timber-to-timber composite (TTC) joint typologies. The geometrical and mechanical characterization of TTC joints, however, is often hard and uncertain, due to a combination of various influencing parameters and mechanical aspects. Among others, the effects of friction phenomena between the system components and their reciprocal interaction under the imposed design loads can remarkably influence the final estimates on structural capacity, in the same way of possible variations in the boundary conditions. The use of Finite Element (FE) numerical models is well-known to represent a robust tool and a valid alternative to costly and time consuming experiments and allows one to further explore the selected load-bearing components at a more refined level. Based on previous research efforts, this paper presents an extended FE investigation based on full three-dimensional (3D) brick models and surface-based cohesive zone modelling (CZM) techniques. The attention is focused on the mechanical characterization of small-scale TTC specimens with inclined STSs having variable configurations, under a standard push-out (PO) setup. Based on experimental data and analytical models of literature, an extended parametric investigation is presented and correlation formulae are proposed for the analysis of maximum resistance and stiffness variations. The attention is then focused on the load-bearing role of the steel screws, as an active component of TTC joints, based on the analysis of sustained resultant force contributions. The sensitivity of PO numerical estimates to few key input parameters of technical interest, including boundaries, friction and basic damage parameters, is thus discussed in the paper.

Comparison between two post-dentin bond strength measurement methods

The push-out (PO) test and the diametral compression (DC) test were performed to compare the merits of two post-dentin bond strength measurement methods. Compared with the push-out test, the disk in DC provided post-dentin bond strength measurements that were more precise. The load-displacement curves from the DC test were much smoother and more linear up to the point of fracture when compared to those from the PO test. Compared to the PO test, DC is easier to perform for determining the bond strength between posts and dentin. No specimen alignment is needed in the DC test, and it produces a smaller standard deviation in the measured bond strength. The main disadvantage of the DC test, however, is that finite element analysis (FEA) is required to calculate the bond strength. The shear bond strength given by the PO test based on the simple formula is not valid, though, and the peak failure load is dependent on friction at the post-dentin interface.

Transformation Plasticity in (GdxDy1−x)PO4 Fiber Coatings During Fiber Push Out

The reduction in fiber push‐out stress by transformation plasticity in xenotime rare‐earth orthophosphate fiber–matrix interphases was demonstrated. Processing methods for transformable xenotime coatings were explored. For conversion to xenotime during processing, (GdxDy1−x)PO4 solid solutions had to be more Dy‐rich than those for pellets. Single‐crystal alumina fibers were coated with 10–20 μm of (Gd0.4Dy0.6)PO4 xenotime and incorporated into polycrystalline alumina matrices. Coated fiber push‐out stresses were between 10 and 80 MPa, significantly lower than those for fibers with other rare‐earth orthophosphates coatings. Phase transformations and deformation mechanisms were characterized by SEM and TEM in fiber coatings after push out. Bands of deformed coating several micrometers in width formed during fiber push out. Cataclastic flow with fracture, granulation, translation, rotation, and intense plastic deformation of coating grains was observed. Three phase transformations may occur in heavily deformed particles in the deformation band: xenotime → monazite, xenotime → anhydrite, and anhydrite → monazite. Anhydrite was abundant as a fine lamellar phase on (100) planes in xenotime. Selected area electron diffraction and high‐resolution TEM confirmed formation of monazite in a variety of heavily deformed particles. Issues for use of rare‐earth orthophosphate transformation plasticity to lower fiber pull‐out stress in ceramic matrix composites are discussed.

Dynamic Detection and Expulsion Buffer Management Scheme for High-Speed Networks

In this letter, we propose a simple but effective buffer management scheme to achieve fair bandwidth sharing with a FIFO scheduling algorithm, that is, Dynamic Detection and Expulsion (DDE). The DDE scheme dynamically detects buffer occupancy and then precisely expels resided packets on demand through simple comparisons. Simulation results under various traffic conditions show that DDE can arrive at more robust and better fairness, and lower implementation complexity than that of a well-known Pushout (PO) scheme.

Measuring bond strength between fiber post and root dentin: a comparison of different tests.

the aim of this study was to evaluate the ability of bond strength tests to accurately measure the bond strength of fiber posts luted into root canals. the test methods studied were hourglass microtensile (HM), push-out (PS), modified pushout (MP), and pull-out (PL). The evaluated parameters were: bond strength values, reliability (using Weibull analysis), failure mode (using confocal microscopy), and stress distribution (using finite element analysis). Forty human intact single-rooted and endodontically treated teeth were divided into four groups. Each group was assigned one of the test methods. The samples in the HM and PS groups were 1.0 ± 0.1 mm thick; the HM samples were hourglass shaped and the PS samples were disk shaped. For the PL and MP groups, each 1-mm dentin slice was luted with a fiber post piece. Three-dimensional models of each group were made and stress was analyzed based on Von Mises criteria. PL provided the highest values of bond strength, followed by MP, both of which also had greater amounts of adhesive failures. PS showed the highest frequency of cohesive failures. MP showed a more homogeneous stress distribution and a higher Weibull modulus. the specimen design directly influences the biomechanical behavior of bond strength tests.

An integrated fuzzy-GA approach for buffer management

This paper deals with a novel buffer management scheme based on evolutionary computing for shared-memory asynchronous transfer mode (ATM) switches. The philosophy behind it is adaptation of the threshold for each logical output queue to the real traffic conditions by means of a system of fuzzy inferences. The optimal fuzzy system is achieved using a systematic methodology, based on genetic algorithms (GAs), which allows the fuzzy system parameters to be derived for each switch size, offering a high degree of scalability to the fuzzy control system. Its performance is comparable to that of the push-out (PO) mechanism, which can be considered ideal from a performance viewpoint, and at any rate much better than that of threshold schemes based on conventional logic. In addition, the fuzzy threshold (FT) scheme is simple and cost-effective when implemented using VLSI technology

Performance analysis of threshold-based selective drop mechanism for high performance packet switches

In this paper, a simple and efficient threshold-based selective drop (TSD) buffer management scheme is proposed to improve the overall loss performance and fairness by regulating the buffer sharing in a packet switch. The key idea of TSD is to divide the output ports into active or inactive output ports by comparing their queue lengths with a fair share buffer size. When total queue length equals or exceeds the threshold value, only arrival packets destined to inactive output ports are admitted to enter the shared buffer. A transient analysis of TSD is derived to prove the fairness of buffer allocation among different output queues. We use computer simulation to compare the overall loss performance of TSD, complete sharing (CS), complete partitioning (CP), dynamic threshold (DT) and pushout (PO). The TSD method is shown to be more robust than CS, CP and DT methods under different traffic conditions.

Performance analysis of threshold-based selective drop mechanism for high performance packet switches

In this paper, a simple and efficient threshold-based selective drop (TSD) buffer management scheme is proposed to improve the overall loss performance and fairness by regulating the buffer sharing in a packet switch. The key idea of TSD is to divide the output ports into active or inactive output ports by comparing their queue lengths with a fair share buffer size. When total queue length equals or exceeds the threshold value, only arrival packets destined to inactive output ports are admitted to enter the shared buffer. A transient analysis of TSD is derived to prove the fairness of buffer allocation among different output queues. We use computer simulation to compare the overall loss performance of TSD, complete sharing (CS), complete partitioning (CP), dynamic threshold (DT) and pushout (PO). The TSD method is shown to be more robust than CS, CP and DT methods under different traffic conditions.

The economics of crowd out under mixed public/private health insurance

It is well known that public insurance sometimes crowds out private insurance. Yet, the economic theory of crowd out has remained unstudied. Here, I show that crowd out causes two countervailing effects: (a) the intensive margin effect-since high demanders are crowded out, the private market now has a larger proportion of low demanders on the intensive margin (The intensive margin are those who have already bought private insurance), and so will drop quality to lower the price to the low demanders’ liking; and (b) the extensive margin effect-before the public insurance expansion, the private sector had lowered quality to make insurance more affordable at the extensive margin (The extensive margin is the next group of people who would buy private insurance if the price decreased), but now that public insurance crowds out the extensive margin, quality can then be raised back up to the high demanders’ liking. If the extensive margin effect dominates, then a new phenomenon of push out occurs, in which crowd out causes the private sector to raise quality and to increase the number of uninsured low demanders not eligible for public insurance. If the intensive margin effect dominates, then crowd out will cause the private sector to lower quality, causing the phenomenon of crowd-in, in which the number of uninsured low demanders that take-up private insurance increases. These two countervailing effects have important implications for any government policy that desires to eradicate all uninsurance. First, if push out is dominant, then the private sector will respond to the public insurance by pushing out and leaving some people newly uninsured. If crowd-in is dominant, then all people can be insured and the government can do it at a lower-than-anticipated level of expansion due to the private sector crowding in.

Threshold-based selective drop for shared buffer packet switches

We propose a novel buffer management scheme called threshold-based selective drop (TSD) to improve the overall loss performance and fairness by regulating the buffer sharing in a packet switch. A transient analysis of TSD is derived to prove the fairness of buffer allocation. Computer simulation shows that the overall loss performance of TSD approaches to the pushout (PO) scheme, which is considered as an optimal solution with implementation difficulties in high-speed Internet. However, unlike the PO, the TSD will block the unwanted packets before they enter the queue, and does not need to pre-empty the queue for accepting new packets.

Threshold-based filtering buffer management scheme in a shared buffer packet switch

In this paper, an efficient threshold-based filtering (TF) buffer management scheme is proposed. The TF is capable of minimizing the overall loss performance and improving the fairness of buffer usage in a shared buffer packet switch. The TF consists of two mechanisms. One mechanism is to classify the output ports as active or inactive by comparing their queue lengths with a dedicated buffer allocation factor. The other mechanism is to filter the arrival packets of inactive output ports when the total queue length exceeds a threshold value. A theoretical queuing model of TF is formulated and resolved for the overall packet loss probability. Computer simulations are used to compare the overall loss performance of TF, dynamic threshold (DT), static threshold (ST) and pushout (PO). We find that TF scheme is more robust against dynamic traffic variations than DT and ST. Also, although the overall loss performance between TF and PO are close to each other, the implementation of TF is much simpler than the PO.

A differentiated services architecture for multimedia streaming in next generation Internet

This paper presents a Differentiated Services (Diffserv or DS) architecture for multimedia streaming applications. Specifically, we define two types of services in the context of Assured Forwarding (AF) per hop behavior (PHB) that are differentiated in terms of reliability of packet delivery: the High Reliable (HR) service and the Less Assured (LA) service. We propose a novel node mechanism called Selective Pushout with Random Early Detection (SPRED) that is capable of simultaneously achieving the following four objectives: (1) a core router does not maintain any state information for each flow (i.e., core-stateless); (2) the packet sequence within each flow is not re-ordered at a node; (3) packets from HR service are delivered more reliably than packets from LA service at a node during congestion; and (4) packets from TCP traffic are dropped randomly to avoid global synchronization during congestion. We show that SPRED is a generalized buffer management algorithm of both tail-dropping and Random Early Detection (RED), and combines the best features of pushout (PO), RED and RED with In/Out (RIO) mechanisms. Simulation results demonstrate that under the same link speed and network topology, network nodes employing our Diffserv architecture have substantial performance improvement over the current Best Effort (BE) Internet architecture for multimedia streaming applications.

Dynamic queue length thresholds for shared-memory packet switches

In shared-memory packet switches, buffer management schemes can improve overall loss performance, as well as fairness, by regulating the sharing of memory among the different output port queues. Of the conventional schemes, static threshold (ST) is simple but does not adapt to changing traffic conditions, while pushout (PO) is highly adaptive but difficult to implement. We propose a novel scheme called dynamic threshold (DT) that combines the simplicity of ST and the adaptivity of PO. The key idea is that the maximum permissible length, for any individual queue at any instant of time, is proportional to the unused buffering in the switch. A queue whose length equals or exceeds the current threshold value may accept no more arrivals. An analysis of the DT algorithm shows that a small amount of buffer space is (intentionally) left unallocated, and that the remaining buffer space becomes equally distributed among the active output queues. We use computer simulation to compare the loss performance of DT, ST, and PO. DT control is shown to be more robust to uncertainties and changes in traffic conditions than ST control.

Revenue maximization in ATM networks using the CLP capability and buffer priority management

The cell loss priority (CLP) bit in the header of the ATM cell may be used either by the network to tag noncompliant cells, or by the application to declare two levels of quality-of-service (QoS) within the same virtual circuit (VC). We study the possibility of the use of this bit by the application alone. An application can offer two types of traffic streams to the network, namely, a precious traffic stream (with stringent QoS requirements, e.g., cell loss ratio (CLR) <10/sup -9/ and identified by the CLP bit=0) and a less precious stream (CLP=1 and less stringent QoS requirements, e.g., CLR <10/sup -4/). We study the performance of an ATM multiplexer with two traffic classes with different QoS requirements. The buffer priority schemes adopted are partial buffer sharing (PBS) and PBS+push-out (PO). We first obtain the engineering trade-off curves, between CLP=0 and CLP=1 traffic. To identify an operating point, we formulate a revenue optimization problem in which the constraints are the engineering trade-off curve and a simple model of the variation of CLP=1 demand with its price.