This paper characterizes jointly optimal default and exchange-rate policy in a small open economy with limited enforcement of debt contracts and downward nominal wage rigidity. Under optimal policy, default occurs during contractions and is accompanied by large devaluations. The latter inflate away real wages thereby avoiding massive unemployment. Thus, the Twin Ds phenomenon emerges endogenously as the optimal outcome. By contrast, under fixed exchange rates, optimal default takes place in the context of large involuntary unemployment. Fixed-exchange-rate economies are shown to have stronger default incentives and therefore support less external debt than economies with optimally floating rates.
Technological advancement of measurement systems has enhanced the accuracy of power quality assessment by using a combination of measured information. This paper proposes a novel approach for estimating power quality based on information fusion technique of Dempster-Shafer (D-S) evidence theory. First, in order to accurately extract transient features regarding power quality indexes, wavelet packet transform and lifting wavelet transform are proposed to detect various disturbance signals’ measurement. By using many kinds of transformed transient indexes and steady state indexes, a novel reliability distribution function is constructed, and synthesized assessment index of power quality is drafted based on information fusion technique of D-S evidence theory. Finally, the simulation results prove that D-S evidence theory is a more effective means for evaluating the power quality.
Dasmeh, P.
Serohijos, A. W. R.
Kepp, K. P.
Shakhnovich, E. I.
Understanding the relative contributions of various evolutionary processes-purifying selection, neutral drift, and adaptation-is fundamental to evolutionary biology. A common metric to distinguish these processes is the ratio of nonsynonymous to synonymous substitutions (i.e., dN/dS) interpreted from the neutral theory as a null model. However, from biophysical considerations, mutations have non-negligible effects on the biophysical properties of proteins such as folding stability. In this work, we investigated how stability affects the rate of protein evolution in phylogenetic trees by using simulations that combine explicit protein sequences with associated stability changes. We first simulated myoglobin evolution in phylogenetic trees with a biophysically realistic approach that accounts for 3D structural information and estimates of changes in stability upon mutation. We then compared evolutionary rates inferred directly from simulation to those estimated using maximum-likelihood (ML) methods. We found that the dN/dS estimated by ML methods (omega(ML)) is highly predictive of the per gene dN/dS inferred from the simulated phylogenetic trees. This agreement is strong in the regime of high stability where protein evolution is neutral. At low folding stabilities and under mutation-selection balance, we observe deviations from neutrality (per gene dN/dS > 1 and dN/dS < 1). We showed that although per gene dN/dS is robust to these deviations, ML tests for positive selection detect statistically significant per site dN/dS > 1. Altogether, we show how protein biophysics affects the dN/dS estimations and its subsequent interpretation. These results are important for improving the current approaches for detecting positive selection.
In growing bulk crystals from the melt, impurities contained in silicon feedstock, generated due to the melt-to-crucible contact and transported by the gas flow from graphite elements strongly affect the efficiency of mono and multicrystalline silicon solar cells. The present paper is aimed at developing an advanced coupled chemical model accounting for such phenomena as oxygen and nitrogen solution at crucible wall, oxygen and carbon transport through the melt free surface, formation of Si 3N 4-, Si 2N 2O - and SiC-particles in the melt, mass transport of SiO-, CO- and Si-species in argon carrier gas and, finally, formation of parasitic deposits on the furnace units. The model is verified by simulation of DS and Cz Si-crystal growth. It is shown that the computational results agree well with available experimental data, and the model can be used for optimization of Cz and DS processes. [All rights reserved Elsevier].
The ratio of divergence at nonsynonymous and synonymous sites, dN/dS, is a widely used measure in evolutionary genetic studies to investigate the extent to which selection modulates gene sequence evolution. Originally tailored to codon sequences of distantly related lineages, dN/dS represents the ratio of fixed nonsynonymous to synonymous differences. The impact of ancestral and lineage-specific polymorphisms on dN/dS, which we here show to be substantial for closely related lineages, is generally neglected in estimation techniques of dN/dS. To address this issue, we formulate a codon model that is firmly anchored in population genetic theory, derive analytical expressions for the dN/dS measure by Poisson random field approximation in a Markovian framework and validate the derivations by simulations. In good agreement, simulations and analytical derivations demonstrate that dN/dS is biased by polymorphisms at short time scales and that it can take substantial time for the expected value to settle at its time limit where only fixed differences are considered. We further show that in any attempt to estimate the dN/dS ratio from empirical data the effect of the intrinsic fluctuations of a ratio of stochastic variables, can even under neutrality yield extreme values of dN/dS at short time scales or in regions of low mutation rate. Taken together, our results have significant implications for the interpretation of dN/dS estimates, the McDonald-Kreitman test and other related statistics, in particular for closely related lineages.
This paper characterizes jointly optimal default and exchange-rate policy in a small open economy with limited enforcement of debt contracts and downward nominal wage rigidity. Under optimal policy, default occurs during contractions and is accompanied by large devaluations. The latter inflate away real wages thereby avoiding massive unemployment. Thus, the Twin Ds phenomenon emerges endogenously as the optimal outcome. By contrast, under fixed exchange rates, optimal default takes place in the context of large involuntary unemployment. Fixed-exchange-rate economies are shown to have stronger default incentives and therefore support less external debt than economies with optimally floating rates.