Improved mitochondrial amino acid substitution models for metazoan evolutionary studies

Abstract Background Amino acid substitution models play an essential role in inferring phylogenies from mitochondrial protein data. However, only few empirical models have been estimated from restricted mitochondrial protein data of a hundred species. The existing models are unlikely to represent appropriately the amino acid substitutions from hundred thousands metazoan mitochondrial protein sequences. Results We selected 125,935 mitochondrial protein sequences from 34,448 species in the metazoan kingdom to estimate new amino acid substitution models targeting metazoa, vertebrates and invertebrate groups. The new models help to find significantly better likelihood phylogenies in comparison with the existing models. We noted remarkable distances from phylogenies with the existing models to the maximum likelihood phylogenies that indicate a considerable number of incorrect bipartitions in phylogenies with the existing models. Finally, we used the new models and mitochondrial protein data to certify that Testudines, Aves, and Crocodylia form one separated clade within amniotes. Conclusions We introduced new mitochondrial amino acid substitution models for metazoan mitochondrial proteins. The new models outperform the existing models in inferring phylogenies from metazoan mitochondrial protein data. We strongly recommend researchers to use the new models in analysing metazoan mitochondrial protein data

Effect of growth conditions on optical properties of CdSe/ZnSe single quantum dots

In this work, we have investigated the optical properties of two samples of CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect of vicinal-surface GaAs substrates on their properties has been also assessed. The thinner sample, grown on a substrate with vicinal surface, includes only dots with a diameter of less than 10 nm (type A islands). Islands of an average diameter of about 16 nm (type B islands) that are related to a phase transition via a Stranski-Krastanow growth process are also distributed in the thicker sample grown on an oriented substrate. We have studied the evolution of lineshapes of PL spectra for these two samples by improving spatial resolution that was achieved using nanoapertures or mesa structures. It was found that the use of a substrate with the vicinal surface leads to the suppression of excitonic PL emitted from a wetting layer.Comment: 2pages, 2 figures, Proceedings of International Conference On Superlattices Nano-Structures And Nano-Devices, July, Toulouse, France, to appear in the special issue of Physica

Synchronized and Desynchronized Phases of Exciton-Polariton Condensates in the Presence of Disorder

Condensation of exciton-polaritons in semiconductor microcavities takes place despite in plane disorder. Below the critical density the inhomogeneity of the potential seen by the polaritons strongly limits the spatial extension of the ground state. Above the critical density, in presence of weak disorder, this limitation is spontaneously overcome by the non linear interaction, resulting in an extended synchronized phase. This mechanism is clearly evidenced by spatial and spectral studies, coupled to interferometric measurements. In case of strong disorder, several non phase-locked (independent) condensates can be evidenced. The transition from synchronized phase to desynchronized phase is addressed considering multiple realizations of the disorder.Comment: 11 pages, 4 figures,corrected typos, added figure

AN INVESTIGATION INTO DIFFICULTIES IN ENGLISH LISTENING OF FRESHMEN MAJORING IN ENGLISH AT A UNIVERSITY IN THE MEKONG DELTA, VIETNAM

English is a very popular language in the world. However, learning a foreign language is not an easy process for learners, especially the English listening process. In fact, most learners believe that it is hard for them to master this skill. Therefore, the research “An Investigation into Difficulties in English Listening of Freshmen Majoring in English at a University in the Mekong Delta” was conducted with the purpose of helping these students to recognize clearly their own problems in English listening. Statistical data were collected from eighty-five English-majored freshmen. The main instrument of the study was a questionnaire. The findings of the research would point out the students’ difficulties in linguistics, including vocabulary, grammar, pronunciation, intonation and accent; background knowledge; and difficulties from their own minds. One more notable purpose of this research is that thanks to the results, students can now solve their own problems, so that they can study better. Article visualizations

PROBLEMS IN VIETNAMESE-ENGLISH TRANSLATION OF RELATIVE CLAUSES FOR ENGLISH-MAJORED JUNIORS AT TAY DO UNIVERSITY, VIETNAM

Realistically, Vietnamese-English translation is not easy for Vietnamese students to master, and relative clauses are not typical in Vietnamese. Therefore, learners cannot avoid mistakes in their translation practice. Concerned researchers carried out a study to identify common Vietnamese-English translation errors in terms of English relative clauses. The participants were 60 juniors from the Bachelor of English course at Tay Do University. Test papers and interviews were employed as the instruments. The collected data from the two instruments mentioned above were all analyzed carefully afterward. The results of the study showed that the students suffered from a variety of grammar and vocabulary problems hindering them from translating Vietnamese into English correctly. Article visualizations

Dynamics of long-range order in an exciton-polariton condensate

We report on time resolved measurements of the first order spatial coherence in an exciton polariton Bose-Einstein condensate. Long range spatial coherence is found to set in right at the onset of stimulated scattering, on a picosecond time scale. The coherence reaches its maximum value after the population and decays slower, staying up to a few hundreds of picoseconds. This behavior can be qualitatively reproduced, using a stochastic classical field model describing interaction between the polariton condensate and the exciton reservoir within a disordered potential.Comment: 7 pages, 4 figure

Optimization of Weld Parameters in Wire and Arc-Based Directed Energy Deposition of High Strength Low Alloy Steels

This paper aims to investigate the fabrication of high strength low alloy (HSLA) steels by wire and arc-based directed energy deposition (WADED). Firstly, the relationship between the process variables (including the travel speed-V, the current-C, and the voltage-U) and the geometrical characteristics of weld beads (including the bead height (BH), bead width (BW), and melting pool length (MPL)) was investigated. Secondly, the optimal process variables were identified using the desirability approach. The results indicate that voltage-U has the highest impact on BW and MPL, meanwhile the travel speed-V is the most impacting factor on BH. The optimal variables for the WADED process of HSAL steels are V = 0.3 m/min, C = 160 A, and U = 19 V. The component fabricated with the optimal variables is fully dense without spatters and defects, confirming the efficiency of the WADED process for HSLA steels