This article presents a method for estimating and interpreting total, direct, and indirect effects in logit or probit models. The method extends the decomposition properties of linear models to these ...models; it closes the much-discussed gap between results based on the “difference in coefficients” method and the “product of coefficients” method in mediation analysis involving nonlinear probability models models; it reports effects measured on both the logit or probit scale and the probability scale; and it identifies causal mediation effects under the sequential ignorability assumption. We also show that while our method is computationally simpler than other methods, it always performs as well as, or better than, these methods. Further derivations suggest a hitherto unrecognized issue in identifying heterogeneous mediation effects in nonlinear probability models. We conclude the article with an application of our method to data from the National Educational Longitudinal Study of 1988.
We calculate the accurate spectrum of the stochastic gravitational-wave background from U(1) gauge fields produced by axion dark matter. The explosive production of gauge fields soon invalidates the ...applicability of the linear analysis and one needs nonlinear schemes. We make use of numerical lattice simulations to properly follow the nonlinear dynamics such as backreaction and rescattering which gives important contributions to the emission of gravitational waves. It turns out that the axion with the decay constant f∼10^{16} GeV and the mass m∼10^{-14} eV which gives the correct dark matter abundance predicts the circularly polarized gravitational-wave signature detectable by SKA. We also show that the resulting gravitational-wave spectrum has a potential to explain NANOGrav 12.5 yr data.
The paper discusses the implications of ductility in design of timber structures under static and dynamic loading including earthquakes. Timber is a material inherently brittle in bending and in ...tension, unless reinforced adequately. However connections between timber members can exhibit significant ductility, if designed and detailed properly to avoid splitting. Hence it is possible to construct statically indeterminate systems made of brittle timber members connected with ductile connections that behave in a ductile fashion. The brittle members, however, must be designed for the overstrength related to the strength of the ductile connections to ensure the ductile failure mechanism will take place before the failure of the brittle members. The overstrength ratio, defined as the ratio between the 95th percentile of the connection strength distribution and the analytical prediction of the characteristic connection strength, was calculated for multiple doweled connections loaded parallel to the grain based on the results of an extensive experimental programme carried out on timber splice connections with 10.65 and 11.75 mm diameter steel dowels grade 4.6. In this particular case the overstrength ratio was found to range from 1.2 to 2.1, and a value of 1.6 is recommended for ductile design. The paper illustrates the use of the elastic–perfectly plastic analysis with ductility control for a simple statically indeterminate structure and compares this approach to the fully non-linear analysis and with the more traditional linear elastic analysis. It is highlighted that plastic design should not be used for timber bridges since fatigue may lead to significant damage accumulation in the connections if plastic deformations have developed. The paper also shows that the current relative definitions of ductility, as a ratio between an ultimate deformation/displacement and the corresponding yield quantity, should be replaced by absolute definitions of ductility, for example the ultimate deformation/displacement, as the latter ones better represent the ductile structural behavior.
► Ductility in timber structures can be achieved mainly by designing ductile connections. ► Timber members, however, must be designed for the overstrength of the connections. ► Overstrength is the ratio between the 95th percentile and the analytical design strength. ► An overstrength ratio of 1.6 is recommended for doweled timber splice connections. ► Absolute definitions like the ultimate deformation should be used to measure ductility.
The evaluation of performance in endurance athletes and the subsequent individualisation of training is based on the determination of individual physiological thresholds during incremental tests. Gas ...exchange or blood lactate analysis are usually implemented for this purpose, but these methodologies are expensive and invasive. The short-term scaling exponent alpha 1 of detrended Fluctuation Analysis (DFA-α1) of the Heart Rate Variability (HRV) has been proposed as a non-invasive methodology to detect intensity thresholds.
The aim of this study is to analyse the validity of DFA-α1 HRV analysis to determine the individual training thresholds in elite cyclists and to compare them against the lactate thresholds.
38 male elite cyclists performed a graded exercise test to determine their individual thresholds. HRV and blood lactate were monitored during the test. The first (LT1 and DFA-α1-0.75, for lactate and HRV, respectively) and second (LT2 and DFA-α1-0.5, for lactate and HRV, respectively) training intensity thresholds were calculated. Then, these points were matched to their respective power output (PO) and heart rate (HR).
There were no significant differences (
> 0.05) between the DFA-α1-0.75 and LT1 with significant positive correlations in PO (r = 0.85) and HR (r = 0.66). The DFA-α1-0.5 was different against LT2 in PO (
= 0.04) and HR (
= 0.02), but it showed significant positive correlation in PO (r = 0.93) and HR (r = 0.71).
The DFA1-a-0.75 can be used to estimate LT1 non-invasively in elite cyclists. Further research should explore the validity of DFA-α1-0.5.
The power and heart rate values derived from the DFA-α1-0.75 threshold showed high levels of validity and agreement when they were compared against the first lactate threshold.The second lactate threshold and the DFA-α1-0.5 were different (
< 0.05) but showed high levels of correlation.The detrended fluctuation analysis is a valid method to estimate the first lactate threshold and more studies are needed to verify its validity with the second lactate threshold.
The development of precise medicine requires diagnostic probes to simultaneously satisfy an excellent detection limit and a wide linear analysis range because of enormous individual-discrepancy of ...disease biomarker concentrations, yet it remains challenging. Herein, an upconverison nanoprobe with a luminescence ratio flexibly tailored was designed for ultrasensitive monitoring exhaled nitric oxide to indicate the clinical course of asthma. Two independent emissions from the same nanoprobe can be discretionarily modulated to vary their intensity ratios for adapting different analysis requirements. Delightfully, this novel nanoprobe demonstrated a 100-fold lower detection limit compared with the traditional ratiometric fluorescence manner and a more broad linear detection range from the subpart per billion (ppb) level to hundreds of ppb. This ratio-adjustable fluorescence detection strategy holds great potential for miscellaneous disease diagnosis applications.
•Discretised composite failure surfaces for line and planar interfaces.•Suitable to simulate local cracking, crushing and shearing failures in masonry.•Suitable to load-unload (total) and incremental ...sequentially linear methods.•Helps capture localised brittle collapse mechanisms in a robust manner.
In the finite element modelling of masonry structures, the micro-modelling technique of differentiating the continuum into a linear elastic bulk, and interfaces representing non-linear joints is common. However, this approach of simulating cracking-crushing-shearing failure possibilities in interfaces, typical of damage in masonry, also poses numerical stability issues due to the quasi-brittle nature of the failure. In this regard, the article proposes the use of numerically robust sequentially linear procedures and a suitable discretised tension-shear-compression failure model for interfaces. Sequentially linear solution procedures describe the nonlinear response of a specimen/structure through a sequence of scaled linear analyses, each of which represents locally applied damage increments, using secant-stiffness based discretised constitutive relations called saw-tooth laws. The constitutive formulation proposed herein includes a tension cut-off criterion combined with a uniaxial discretised softening law, a Coulomb friction criterion with a discretised cohesion softening law, and a compression cut-off criterion combined with a uniaxial discretised hardening–softening law. It is presented for both two-dimensional (2D) line interfaces and three-dimensional (3D) planar interfaces. The applicability of these formulations are illustrated using 2D and 3D models of a pushover analysis on a squat unreinforced masonry wall. The simulations are made using Sequentially Linear Analysis (SLA) and the Force-Release method, which are total (load-unload) and incremental sequentially linear methods respectively. The clear global softening in the force–displacement evolution and the localised brittle shear failure observed in the experiment are reproduced well and in a stable manner.
The role of reliable Carbon emission measures and relevant climate policy is imperative in realizing Sustainable Development Goals. A large extent of the literature concludes the emissions-mitigating ...effect of green innovations in a linear framework and ignored structural changes, technological revolutions, and socio-economic reforms that create non-linearity. Apart from that, there is a murky relationship between emissions and green innovation, where two-way links exist between both variables. Therefore, this study draws the inter-linkages between green technology innovation (GI) and carbon emissions (consumption-based and terrestrial emissions) in BRICS countries using monthly data from 1990 to 2017. Our preliminary findings strictly reject the preposition of data normality and highlight that the observed relationship is quantile-dependent. Therefore, a complete set of non-linear modeling is employed that included; Quantile unit root, Quantile cointegration, Quantile causality, and Quantile on Quantile regression to unveil hidden unit root, cointegration, causality, and association between variables. The results exhibit that the emissions-mitigating effect of GI is only pronounced at higher emissions quantiles in Brazil, China, India, and Russia, whereas at lower emissions quantile, GI is weekly or positively linked with carbon emissions. On the flipside, higher carbon emissions instigate GI across medium to higher emissions quantiles in Brazil, China, and India. Unlike them, Russia produces different outcomes, where higher emissions are associated with lower GI across all quantiles. The overall results suggest that GI (carbon emissions) mitigate (instigate) carbon emissions (GI) when a country is embodied with higher level of emissions.
•Asymmetric and murky relationship exists between carbon emissions and green innovation (GI).•GI mitigate carbon emissions only at higher levels of emissions.•Carbon emissions instigate GI only at higher emissions quantiles.•Direction and magnitude of the above relationship significantly varied across BRICS countries.
Traction-separation relationship is an important material characteristic describing the fracture behaviour of quasi-brittle solids. A new numerical scheme for identification of the ...traction-separation relation by inverse analysis of data obtained from various types of fracture tests is proposed. Due to employing the concept of sequentially linear analysis, the method exhibits a superior numerical stability and versatility. The applicability and effectiveness of the proposed method is demonstrated on examples involving identification of the traction-separation relationship using experimental data from various test configurations.
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