spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models

The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site complete graph extended with on-site repulsion is obtained from the underlying spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic ground state is realized for 1 and N+1 electrons only. We identify the large density of states to be responsible for the suppression of the ferromagnetic state and argue that a similar situation is encountered in the Kagome, pyrochlore, and other lattices with flat bands in their one-particle density of states.Comment: 7 pages, 1 figur

Climate change-driven losses in ecosystem services of coastal wetlands: A case study in the West coast of Bangladesh

© 2018 The Authors Climate change is globally recognized as one of the key drivers of degradation of coastal wetland ecosystems, causing considerable alteration of services provided by these habitats. Quantifying the physical impacts of climate change on these services is therefore of utmost importance. Yet, practical work in this field is fragmented and scarce in current literature, especially in developing countries which are likely to suffer most from the adverse climate change impacts. Using a coherent scenario-based approach that combines assessment of physical impacts with economic valuation techniques, here we quantify potential climate change driven losses in the value of wetland ecosystems services due to relative sea-level rise (RSLR)-induced inundation in the vulnerable Western coastal area of Bangladesh in 2100. The results show a small inundation area in 2100 under the three IPCC climate scenarios of RCP2.6 (with 0.25 m of RSLR), RCP6.0 (with 1.18 m of RSLR), and RCP8.5 (with 1.77 m of RSLR) for the coastal wetland ecosystems including the Sundarbans mangrove forest, neritic system and aquaculture ponds. In all scenarios, RSLR will drive a loss in the total value of ecosystem services such as provision of raw materials, and food provision, ranging from US$0–1 million to US$ 16.5–20 million, respectively. The outcomes of this study reveal that RSLR-induced inundation on its own, is unlikely to be a major threat to the wetland ecosystems in Western coast of Bangladesh. This would suggest that other climate change impacts such as coastal erosion, increase in frequency of cyclone events, and sea temperature rise might be the likely primary drivers of change in the value of wetland ecosystems services in this area

Revisiting Implicit and Explicit Averaging for Noisy Optimization

Explicit and implicit averaging are two well-known strategies for noisy optimization. Both strategies can counteract the disruptive effect of noise; however, a critical question remains: which one is more efficient? This question has been raised in many studies, with conflicting preferences and, in some cases, findings. Nevertheless, theoretical findings on the noisy sphere problem with additive Gaussian noise supports the superiority of implicit averaging, which may have had a strong impact on the preference of implicit averaging in more recent evolutionary methods for noisy optimization. This study speculates that the analytically supported superiority of implicit averaging relies on specific features of the noisy sphere problem with additive noise, which cannot be generalized to other problems. It enumerates these features and designs controlled numerical experiments to investigate this potential reliance. Each experiment gradually suppresses one specific feature, and the progress rate is numerically calculated for different values of the sample size given a fixed evaluation budget. Our empirical results indicate that for a wide range of noise strength and evaluation budget per iteration, the more these specific features are suppressed, the more the optimal averaging strategy deviates from implicit toward explicit averaging, which confirms our speculations. Consequently, the optimal sample size, which is regarded as the tradeoff between implicit and explicit averaging, depends on the problem characteristics and should be learned during optimization for maximum efficiency

Static and Dynamic Multimodal Optimization by Improved Covariance Matrix Self-Adaptation Evolution Strategy with Repelling Subpopulations

The covariance matrix self-adaptation evolution strategy with repelling subpopulations (RS-CMSA-ES) is one of the most successful multimodal optimization (MMO) methods currently available. However, some of its components may become inefficient in certain situations. This study introduces the second variant of this method, called RS-CMSA-ESII. It improves the adaptation schemes for the normalized taboo distances of the archived solutions and the covariance matrix of the subpopulation, the termination criteria for the subpopulations, and the way in which the infeasible solutions are treated. It also improves the time complexity of RS-CMSA-ES by updating the initialization procedure of a subpopulation and developing a more accurate metric for determining critical taboo regions. The effects of these modifications are illustrated by designing controlled numerical simulations. RS-CMSA-ESII is then compared with the most successful and recent niching methods for MMO on a widely adopted test suite. The results obtained reveal the superiority of RS-CMSA-ESII over these methods, including the winners of the competition on niching methods for MMO in previous years. Besides, this study extends RS-CMSA-ESII to dynamic MMO and compares it with a few recently proposed methods on the modified moving peak benchmark functions

PyDDRBG: A Python framework for benchmarking and evaluating static and dynamic multimodal optimization methods

PyDDRBG is a Python framework for generating tunable test problems for static and dynamic multimodal optimization. It allows for quick and simple generation of a set of predefined problems for non-experienced users, as well as highly customized problems for more experienced users. It easily integrates with an arbitrary optimization method. It can calculate the optimization performance when measured according to the robust mean peak ratio. PyDDRBG is expected to advance the fields of static and dynamic multimodal optimization by providing a common platform to facilitate the numerical analysis, evaluation, and comparison in these fields

Comparative Study of Monosex Tilapia (Oreochromis niloticus) Production under Different Stocking Density in Ponds

A field experiment was conducted to study the effect of stocking density on the growth and production of monosex male tilapia (Oreochromis niloticus L.) conducted in six ponds commencing from 7th July to 4th November, 2012. Feeding frequency were two times in a day. The mean initial weight of fry in all the treatments were 5.7±0.04 g and after completion of the experiment the mean final weight of tilapia was 321.62±1.11 g for T1, 300.12±0.87 g for T2 and 256.25±2.38 g for T3. The mean weight gain of 315.92±1.11, 294.42±0.87  and 250.552.38g and mean percent weight gain of 5542.40, 5165.20 and 4395.61% and mean FCR was 1.41±0.00, 1.46±0.01 and 1.59±0.00and mean SGRof 3.36, 3.30 and 3.17% and the survival rate was 97.67, 94.25 and 93.40% were recorded in T1, T2 and T3, respectively. The highest weight gain, percent weight gain, SGR and survival rate were found in T1 and lowest were found in T3. The production was observed to be 47.12±0.52, 56.57±0.80 and 59.84±1.10 kg/dec/4 months in T1, T2 and T3, respectively. The significant (P?0.01) highest fish production and FCR was obtained 59.84 kg/dec/4 months and 1.59 respectively in T3 under stocking density was 250 fish/decimal and production, FCR was found to be decreased significantly with the decrease in stocking density. The lowest fish production 47.12 kg/dec/4 months were observed in T1. Although higher production was obtained in T3 but individually growth performance of monosex tilapia was higher in T1. Keywords: Monosex tilapia, growth performance, stocking density, tilapia production

Complexes of stationary domain walls in the resonantly forced Ginsburg-Landau equation

The parametrically driven Ginsburg-Landau equation has well-known stationary solutions -- the so-called Bloch and Neel, or Ising, walls. In this paper, we construct an explicit stationary solution describing a bound state of two walls. We also demonstrate that stationary complexes of more than two walls do not exist.Comment: 10 pages, 2 figures, to appear in Physical Review