The growth mechanism from pentatwinned (PTW) gold nanorods into truncated quasi-decahedral particles when a gold salt (HAuCl₄) is reduced by N, N-dimethylformamide (DMF) in the presence of poly(vinylpyrrolidone), was elucidated through a combination of different techniques, including transmission and scanning electron microscopy, high resolution TEM and selected area electron diffraction. Particles with intermediate shapes between the original pentatwinned Au nanorods, used as seeds, and the final quasi-decahedral particles were obtained by simply tuning the [HAuCl₄] to [seeds] ratio. From the thorough structural analysis of all the intermediate morphologies obtained, it was concluded that gradual morphology changes are related to the preferential growth of higher energy crystallographic facets. As a result of the particle growth and concomitant decreased anisotropy, a progressive blue-shift of the surface plasmon resonance bands of the nanoparticles was registered by vis-NIR extinction spectroscopy.
Abstract While a variety of methods exist to reconstruct ancestral sequences, all of them assume that a single phylogeny underlies all the positions in the alignment and therefore that recombination has not taken place. Using computer simulations we show that recombination can severely bias ancestral sequence reconstruction (ASR), and quantify this effect. If recombination is ignored, the ancestral sequences recovered can be quite distinct from the grand most recent common ancestor (GMRCA) of the sample and better resemble the concatenate of partial most recent common ancestors (MRCAs) at each recombination fragment. When independent phylogenetic trees are assumed for the different recombinant segments, the estimation of the fragment MRCAs improves significantly. Importantly, we show that recombination can change the biological predictions derived from ASRs carried out with real data. Given that recombination is widespread on nuclear genes and in particular in RNA viruses and some bacteria, the reconstruction of ancestral sequences in these cases should consider the potential impact of recombination and ideally be carried out using approaches that accommodate recombination.
The periscope training simulation system based on VR technology is discussed. At first, the idiographic designing, the function module and the working principium are studied. Then the workflow, the hardware composition and the software designing are analyzed. And then the realization and the systemic framework are studied as a whole. The key technologies used in the simulator, including 3D model optimization, texture generation and mapping, ocean environment simulation etc., are also introduced in this paper. As a facility for training, the simulation system has advantages of high accuracy mathematical model, low training costs and display of three dimension scene of certain sea area for training. This simulation system can completely simulate the training process of the periscope and meets the requirements of training.
A coalescent model of a sample of size n is derived from a birth-death process that originates at a random time in the past from a single founder individual. Over time, the descendants of the founder evolve into a population of large (infinite) size from which a sample of size n is taken. The parameters and time of the birth-death process are scaled in N<sub>0</sub>, the size of the present-day population, while letting N<sub>0</sub>→∞, similarly to how the standard Kingman coalescent process arises from the Wright-Fisher model. The model is named the Limit Birth-Death (LBD) coalescent model. Simulations from the LBD coalescent model with sample size n are computationally slow compared to standard coalescent models. Therefore, we suggest different approximations to the LBD coalescent model assuming the population size is a deterministic function of time rather than a stochastic process. Furthermore, we introduce a hybrid LBD coalescent model, that combines the exactness of the LBD coalescent model model with the speed of the approximations.
