Monotonic Regime Research Articles

Conventional-, bulk-fill- or flowable-resin composites as prosthetic core build-up: Influence on the load-bearing capacity under fatigue of bonded leucite-reinforced glass-ceramic

This study aimed to evaluate the fatigue performance of simplified ceramic restorations (leucite-reinforced glass ceramic) adhesively cemented onto substrates of different resin composites. Three options from the same commercial line were selected (Tetric N-Line, Ivoclar), classified as Conventional (CRC), Bulk-fill (BRC) and Flowable (FRC), which were used to make discs using a cylindrical metallic device (n = 19; Ø = 10 mm, thickness = 2.0 mm). A total of 57 discs (Ø = 10 mm, thickness = 1.0 mm) were made from CAD/CAM prefabricated blocks of a leucite reinforced glass-ceramic (Empress CAD, Ivoclar) to simulate a monolithic restoration, then were randomly distributed to be bonded on 19 discs of each three different resin composite substrates (CRC; BRC; or FRC) with a dual resin cement (Multilink N; Ivoclar). The samples were subjected to a compression test with a hemispherical stainless-steel piston (Ø = 40 mm) at a monotonic regimen (n = 4; 1 mm/min loading rate and 500 kgf loading cell until fracture). The cyclic fatigue test was performed underwater at a frequency of 20 Hz (n = 15). The first step was applied using 200N for 5000 cycles, followed by increments of 50N at each step of 10,000 until failure. The outcome considered for both tests was the occurrence of radial crack. Specific statistical tests (α = 0.05) were performed for monotonic (One-way ANOVA; Tukey's test) and fatigue data (Kaplan-Meier test; Log-rank test). Fractography of fractured samples were also performed. The FRC group had the lowest failure load in both test regimes (p < 0.05; monotonic: 726.64N; fatigue: 716.67N). There were no differences between the CRC and BRC groups (p > 0.05; monotonic: 989.30 and 990.11N; fatigue: 810.00 and 833.33N, respectively). The same result was obtained considering cycles for fatigue failure (FRC < CRC=BRC). Leucite glass-ceramic bonded to substrates made of flowable resin composite behaves worse mechanically than bonding to conventional or bulk-fill resin composite substrates.

Sectional analysis of the flexural creep of cracked fiber reinforced concrete

AbstractThis paper presents a sectional analysis of cracked fiber reinforced concrete (FRC) under flexural loading. The approach considers three separate loading conditions: monotonic, cyclic, and creep bending loads. Different parts of the approach are experimentally calibrated and validated with tests on polypropylene FRC. In the monotonic regime, numerical optimization is used to find the optimal stress–strain relation of FRC to capture the experimental bending behavior as closely as possible, while satisfying the horizontal force and bending moment equilibrium. To model the cyclic behavior, the constitutive law is extended by introducing a tension‐only scalar damage function. The agreement between the predicted and measured response is again very good, and the measured upwards shift of the neutral axis during unloading is predicted as well. Finally, the flexural creep response of a cracked FRC beam is simulated by using uniaxial creep data. The approach predicts the time‐dependent crack widening under sustained flexural loading and can be used to check SLS criteria in the design of FRC elements.

RETROSPECTIVE ANALYSIS OF WATERNESS CHANGE IN THE DON RIVER

Water resources are one of the most important problems of our time. Population growth, industrial and agricultural development all over the world entail an ever-increasing demand for clean fresh water. These circumstances induce hydrologists to actively and thoroughly study the problem of studying water resources, changing their quantitative and qualitative characteristics in time and space, and the peculiarities of changes in the water regime of river runoff under conditions of climatic changes. In this work, we performed a retrospective analysis and assessment of changes in the water content of the Upper Don basin over a long 126-year period of hydrometric observational data (1881/1882–2006/2007). To study the change in the water content of the Upper Don River, we used the difference integral curves of the annual and seasonal (spring flood, summerautumn and winter low-water periods) runoff. Regularities of long-term cyclical fluctuations in the water content of the annual and seasonal runoff of the Upper Don are obtained. A retrospective analysis of long-term data of hydrometric observations made it possible to distinguish long phases of high-water, medium-water-content and low-water years on the differential integral curves of river runoff. Each phase, which is long in terms of water content, contains groups of years of shorter duration, for example, 2–3-year and 4–5-year phases of increased and decreased water content in a river. The analysis of the differential integral curves of the annual and seasonal runoff made it possible to establish that the long-term fluctuations in the annual runoff of the Upper Don are rhythmic, in contrast to the runoff of the spring flood, summer-autumn and winter low-water periods, which are characterized by a monotonic regime.

Analysis-oriented stress–strain model of CRFP-confined circular concrete columns with applied preload

The compressive behavior of FRP-confined concrete is a current issue in the field of structural retrofitting. The available models well predict the stress–strain behavior under monotonic and cyclic loads. However, in the practical applications, columns that need an increasing of bearing capacity are often strengthened under serviceability load conditions, with a stress and strain state that could change the response of the reinforced systems with respect to the case of the unloaded state. In this paper, the compressive behavior of circular FRP-confined concrete columns with preload is analyzed with the introduction of a modified analysis-oriented model. Differently from the classical formulations in which stress–strain model is aimed to the evaluation of the confinement capacity of non-preloaded elements in monotonic regime, the proposed model is also suitable for the determination of the combined response of unconfined and confined concrete subjected to an established stress/strain state in the unconfined state. The proposed model is also compared with the experimental results available in the literature under different assigned preloading levels.

Convection of a stratified colloidal suspension

The convection of a colloidal suspension, which is a binary mixture of a carrier medium with an admixture of nanoparticles having a large positive thermal diffusion parameter, has been studied for the case of the heating of a horizontal cell from below and periodic conditions at the vertical boundaries corresponding to the experimental situation of ring channels. Bifurcation diagrams have been constructed for vibrational and monotonic regimes of the convection of the colloidal mixture. The time dependences of the maximum stream function and the stream function at a fixed point of the cell, as well as the spatial distributions of the concentration field of the colloid admixture, have been obtained. It has been shown that a stable regime of traveling waves exists in a certain region of the parameters of the problem (Boltzmann and Rayleigh numbers characterizing the gravitational stratification and intensity of the thermal effect, respectively).

A Bayesian autoregressive three-state hidden Markov model for identifying switching monotonic regimes in Microarray time course data

When modeling time course microarray data special interest may reside in identifying time frames in which gene expression levels follow a monotonic (increasing or decreasing) trend. A trajectory may change its regime because of the reaction to treatment or of a natural developmental phase, as in our motivating example about identification of genes involved in embryo development of mice with the 22q11 deletion. To this aim we propose a new flexible Bayesian autoregressive hidden Markov model based on three latent states, corresponding to stationarity, to an increasing and to a decreasing trend. In order to select a list of genes, we propose decision criteria based on the posterior distribution of the parameters of interest, taking into account the uncertainty in parameter estimates. We also compare the proposed model with two simpler models based on constrained formulations of the probability transition matrix.

Comparative Analysis of Plastic Flow and Grain Refinement in Pure Aluminium Subjected to Simple Shear-Based Severe Plastic Deformation Processing

In the present work, effects of loading scheme and strain reversal on structure and hardness evolution have been studied by using high pressure torsion (HPT) and twist extrusion (TE) techniques. High purity aluminium (99.99%) was processed at room temperature up to a maximum total equivalent strain of εmax ≈ 8 by TE, and HPT in monotonic and reversal deformation modes with strain increment Δεmax = 1. Minimum subgrain sizes reached in this study were 1.6 µm for TE and 1.1 µm for HPT. It was revealed that microstructural change with straining was a common consequence of severe plastic deformation (SPD) processing and was not affected significantly by the loading scheme. Among the SPD methods used in this study, HPT in monotonic regime produced the smallest grain size, while the most homogeneous microstructure was obtained by TE due to specific vortex-like flow field imposed by the tool geometry.

An improved algorithm and a Fortran 90 module for computing the conical function [formula omitted

In this paper we describe an algorithm and a Fortran 90 module ( Conical) for the computation of the conical function P − 1 2 + i τ m ( x ) for x > − 1 , m ⩾ 0 , τ > 0 . These functions appear in the solution of Dirichlet problems for domains bounded by cones; because of this, they are involved in a large number of applications in engineering and physics. In the Fortran 90 module, the admissible parameter ranges for computing the conical functions in standard IEEE double precision arithmetic are restricted to ( x , m , τ ) ∈ ( − 1 , 1 ) × [ 0 , 40 ] × [ 0 , 100 ] and ( x , m , τ ) ∈ ( 1 , 100 ) × [ 0 , 100 ] × [ 0 , 100 ] . Based on tests of the three-term recurrence relation satisfied by these functions and direct comparison with Maple, we claim a relative accuracy close to 10 − 12 in the full parameter range, although a mild loss of accuracy can be found at some points of the oscillatory region of the conical functions. The relative accuracy increases to 10 − 13 – 10 − 14 in the region of the monotonic regime of the functions where integral representations are computed ( − 1 < x < 0 ). Program summary Program title: Conical Catalogue identifier: AELD_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AELD_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5387 No. of bytes in distributed program, including test data, etc.: 49 615 Distribution format: tar.gz Programming language: Fortran 90 Computer: Any supporting a FORTRAN compiler Operating system: Any supporting a FORTRAN compiler RAM: A few MB Classification: 4.7 Nature of problem: Conical functions appear in a large number of applications because these functions are the natural function basis for solving Dirichlet problems bounded by conical domains. Also, they are the Kernel of the Mehler–Fock transform. Solution method: The algorithm uses different methods of computation depending on the range of parameters: asymptotic expansions, quadrature methods and recurrence relations. Restrictions: In order to avoid underflow/overflow problems, the admissible parameter ranges for computing the conical functions in standard IEEE double precision arithmetic are restricted to ( x , m , τ ) ∈ ( − 1 , 1 ) × [ 0 , 40 ] × [ 0 , 100 ] and ( x , m , τ ) ∈ ( 1 , 100 ) × [ 0 , 100 ] × [ 0 , 100 ] . Additional comments: The module Conical uses a Fortran 90 version of the routine dkia (developed by the authors) for computing the modified Bessel functions K i a ( x ) and its derivative. This routine is included in the distribution file and is also available at http://toms.calgo.org. Running time: Depending on the parameter range: when numerical quadrature is used (for x < 0 ), the algorithm is 10–20 times slower than the computations made using asymptotic expansions + recurrence relations.

Vacuum fluctuations and topological Casimir effect in Friedmann–Robertson–Walker cosmologies with compact dimensions

We investigate the Wightman function, the vacuum expectation values of the field squared and the energy-momentum tensor for a massless scalar field with general curvature coupling parameter in spatially flat Friedmann-Robertson-Walker universes with an arbitrary number of toroidally compactified dimensions. The topological parts in the expectation values are explicitly extracted and in this way the renormalization is reduced to that for the model with trivial topology. In the limit when the comoving lengths of the compact dimensions are very short compared to the Hubble length, the topological parts coincide with those for a conformal coupling and they are related to the corresponding quantities in the flat spacetime by standard conformal transformation. In the opposite limit of large comoving lengths of the compact dimensions, in dependence of the curvature coupling parameter, two regimes are realized with monotonic or oscillatory behavior of the vacuum expectation values. In the monotonic regime and for nonconformally and nonminimally coupled fields the vacuum stresses are isotropic and the equation of state for the topological parts in the energy density and pressures is of barotropic type. In the oscillatory regime, the amplitude of the oscillations for the topological part in the expectation value of the field squared can be either decreasing or increasing with time, whereas for the energy-momentum tensor the oscillations are damping.