Phase and Microstructure Selection During Directional Solidification of Peritectic Alloy Under Convection Condition

A phase and microstructure selection map used for peritectic alloy directionally solidified under convection condition was presented,which is based on the nucleation,constitutional undercooling criterion（NCU criterion）,and the highest interface temperature criterion.This selection map shows the relationships between the phase/microstructure,the G/V ratio（G is the temperature gradient,V is the growth velocity）,and the alloy composition under different convection intensities and nucleation undercoolings.Comparing with the results from directional solidification experiments of Sn–Cd peritectic alloys,this selection map was generally in agreement with the experimental results.

Visual response characteristics of neurons in the second visual area of marmosets

The physiological characteristics of the marmoset second visual area(V2) are poorly understood compared with those of the primary visual area(V1). In this study, we observed the physiological response characteristics of V2 neurons in four healthy adult marmosets using intracortical tungsten microelectrodes. We recorded 110 neurons in area V2, with receptive fields located between 8° and 15° eccentricity. Most(88.2%) of these neurons were orientation selective, with half-bandwidths typically ranging between 10° and 30°. A significant proportion of neurons(28.2%) with direction selectivity had a direction index greater than 0.5. The vast majority of V2 neurons had separable spatial frequency and temporal frequency curves and, according to this criterion, they were not speed selective. The basic functional response characteristics of neurons in area V2 resemble those found in area V1. Our findings show that area V2 together with V1 are important in primate visual processing, especially in locating objects in space and in detecting an object's direction of motion. The methods used in this study were approved by the Monash University Animal Ethics Committee, Australia(MARP 2009-2011) in 2009.

An Empirical Study of Using Imitation-Based Error Correction to Reduce Repeated Errors in English Writing of Rural Junior High School Students

Junior high school students in rural areas constitute a particular group of English learners, for whom English writing is not only important, but also difficult. In order to find out an effective means to help them enhance English writing proficiency. To this end, after carefully analyzing the writing characteristics of this group of English learners, one intact class in Grade 8 of No. 14 junior middle school in Wuwei was given an experimental treatment which required them to imitate the correct examples of expressions provided by their teacher where they used to make errors. Results revealed that students in experimental class outperform their peers in control class significantly.

Demographic Processes Linked to Genetic Diversity and Positive Selection across a Species’ Range

Demography determines the strength of genetic drift,which generally reduces genetic variation and the efficacy of selection.Here,we disentangled the importance of demographic processes at a local scale(census size and mating system)and at a species-range scale(old split between population clusters,recolonization after the last glaciation cycle,and admixture)in determining within-population genomic diversity and genomic signatures of positive selection.Analyses were based on re-sequence data from 52 populations of North American Arabidopsis lyrata collected across its entire distribution.The mating system and range dynamics since the last glaciation cycle explained around 60%of the variation in genomic diversity among populations and 52%of the variation in the signature of positive selection.Diversity was lowest in selfing compared with outcrossing populations and in areas further away from glacial refugia.In parallel,reduced positive selectionwas found in selfing populations and in populations with a longer route of postglacial range expansion.The signature of positive selection was also reduced in populations without admixture.We conclude that recent range expansion can have a profound influence on diversity in coding and non-coding DNA,similar in magnitude to the shift toward selfing.Distribution limits may in fact be caused by reduced effective population size and compromised positive selection in recently colonized parts of the range.

Directional tunings independent of orientation in the primary visual cortex of the cat

A family of moving ‘random-line' patterns was developed and used to study the directional tuning of 91 single units in cat primary visual cortex (V1). The results suggest that, in addition to the well-known orientation-dependent mechanism, there is also some kind of orientation-independent mechanism underlying the direction selectivity. The directional tuning of the neurons varies in accordance with the increase of orientation or non-orientation element in the stimulus.

Direction Selectivityof TmY Neurites in Drosophila

The perception of motion is an important func-tion of vision.Neural wiring diagrams for extracting direc-tional information have been obtained by connectome recon-struction.Direction selectivity in Drosophila is thought to originate in T4/T5 neurons through integrating inputs with different temporal filtering properties.Through genetic screening based on synaptic distribution,we isolated a new type of TmY neuron,termed TmY-ds,that form recipro-cal synaptic connections with T4/T5 neurons.Its neurites responded to grating motion along the four cardinal direc-tions and showed a variety of direction selectivity.Intrigu-ingly,its direction selectivity originated from temporal filtering neurons rather than T4/T5.Genetic silencing and activation experiments showed that TmY-ds neurons are functionally upstream of T4/T5.Our results suggest that direction selectivity is generated in a tripartite circuit formed among these three neurons—temporal filtering,TmY-ds,and T4/T5 neurons,in which TmY-ds plays a role in the enhancement of direction selectivity in T4/T5 neurons.

Direct manufacturing of Cu-based alloy parts by selective laser melting

The frequent defects of the metal parts, such as non-fully melting, thermal strain, and balling, which are produced by selective laser melting （SLM） that is a novel method of one-step manufacturing, are analyzed theoretically and experimentally. The processing parameters significantly affect the quality of the final parts, and simultaneously, the appropriate laser mode and the special scanning strategy assure a satisfying quality of the final parts. The SLM experiment is carried out using Cu-based powder. The metal part is divided into several scanned regions, each of which is scanned twice at the cross direction with different scanning speeds. The microstructure is analyzed on microscope. The results show that the part is metallurgically bonded entity with a relative density of 95%, and the microstructure is composed of equiaxial crystal and dendritic crystal whose distributions are mainly decided by the scanning strategy.

Pollinator-dependent evolution of floral trait combinations in an orchid herb

Aims As one of the most important agents driving floral evolution,pollinators shape the diversity of flowers in angiosperms.However,most previous studies have only quantified pollinators driving the evolution of a single floral trait,and experimental estimates of the potential role of pollinators in shaping the evolution of floral trait associations are relatively rare.Methods We experimentally identified and estimated the pollinator-mediated directional and correlational selection on single floral traits and trait combinations across 2 years in an orchid species,Spiranthes sinensis.Important Findings Pollinators mediated directional selection for an earlier flowering start date and larger corolla size.Pollinators mediated positive correlational selection on the combinations of floral display traits and negative correlational selection on the combinations of flowering phenology and floral display traits.In addition,the strength of selection differed over time.Our results highlight the potential role of pollinators in driving the evolution of floral trait combinations and suggest that it is necessary to consider floral character functional associations when seeking to understand and predict the evolutionary trajectory of flowers in angiosperms.

Selectivity of Crystal Growth Direction in Layered Double Hydroxides

Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.