The de novo genome assembly of Tapiscia sinensis and the transcriptomic and developmental bases of androdioecy

Tapiscia sinensis(Tapisciaceae)possesses an unusual androdioecious breeding system that has attracted considerable interest from evolutionary biologists.Key aspects of T.sinensis biology,including its biogeography,genomics,and sexlinked genes,are unknown.Here,we report the first de novo assembly of the genome of T.sinensis.The genome size was 410 Mb,with 22,251 predicted genes.Based on whole-genome resequencing of 55 trees from 10 locations,an analysis of population genetic structure indicated that T.sinensis has fragmented into five lineages,with low intrapopulation genetic diversity and little gene flow among populations.By comparing whole-genome scans of male versus hermaphroditic pools,we identified 303 candidate sex-linked genes,79 of which(25.9%)were located on scaffold 25.A 24-kb region was absent in hermaphroditic individuals,and five genes in that region,TsF-box4,TsF-box10,TsF-box13,TsSUT1,and TsSUT4,showed expression differences between mature male and hermaphroditic flowers.The results of this study shed light on the breeding system evolution and conservation genetics of the Tapisciaceae.

Diffractive neural networks with improved expressive power for gray-scale image classification

In order to harness diffractive neural networks(DNNs)for tasks that better align with real-world computer vision requirements,the incorporation of gray scale is essential.Currently,DNNs are not powerful enough to accomplish gray-scale image processing tasks due to limitations in their expressive power.In our work,we elucidate the relationship between the improvement in the expressive power of DNNs and the increase in the number of phase modulation layers,as well as the optimization of the Fresnel number,which can describe the diffraction process.To demonstrate this point,we numerically trained a double-layer DNN,addressing the prerequisites for intensitybased gray-scale image processing.Furthermore,we experimentally constructed this double-layer DNN based on digital micromirror devices and spatial light modulators,achieving eight-level intensity-based gray-scale image classification for the MNIST and Fashion-MNIST data sets.This optical system achieved the maximum accuracies of 95.10%and 80.61%,respectively.

走出歌德的阴影:迈向更加科学的植物系统学

传统的植物学理论中,被子植物雌蕊的基本单位心皮被认为是变态的叶(即大孢子叶)通过纵向对折和内卷演化而来。该理论造成了被子植物和裸子植物之间不可逾越的鸿沟。近年来提出的一统理论认为被子植物的心皮由长胚珠的枝和包裹这个枝的叶共同组成,从而弥合了被子植物与裸子植物之间的鸿沟。最近,当代植物学界两大权威人物Peter R.Crane和PeterK.Endress分别撰文,发表了不同于传统理论的观点。Endress认为,心皮由胚珠和叶性器官组成;而Crane认为,所有的胚珠都长在枝上。结合二者的结论,不难得出"心皮实际上等同于一个长胚珠的枝加上一个叶"的论断。这在某种意义上等于认同了一统理论的观点。两位权威人物观点的转变预示着植物学理论将很快发生根本性的转变。该文向国内植物学同行通报这一最新动态,以期让我国学者能够了解最新理论。

Phase characterisation of metalenses

Metalenses have emerged as a new optical element or system in recent years,showing superior performance and abundant applications.However,the phase distribution of a metalens has not been measured directly up to now,hindering further quantitative evaluation of its performance.We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern.Based on the measured phase distribution,we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses.Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment.Furthermore,through phase distribution analysis,it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture,even though the metalens is ideal without any fabrication error.We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens.Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process,which will pave the way for metalenses in industrial applications.

Routing valley exciton emission of a WS_(2) monolayer via delocalized Bloch modes of in-plane inversion-symmetry-broken photonic crystal slabs

The valleys of two-dimensional transition metal dichalcogenides(TMDCs)offer a new degree of freedom for information processing.To take advantage of this valley degree of freedom,on the one hand,it is feasible to control valleys by utilizing different external stimuli,such as optical and electric fields.On the other hand,nanostructures are also used to separate the valleys by near-field coupling.However,for both of the above methods,either the required low-temperature environment or low degree of coherence properties limit their further applications.Here,we demonstrate that all-dielectric photonic crystal(PhC)slabs without in-plane inversion symmetry(C_(2) symmetry)can separate and route valley exciton emission of a WS2 monolayer at room temperature.Coupling with circularly polarized photonic Bloch modes of such PhC slabs,valley photons emitted by a WS_(2) monolayer are routed directionally and are efficiently separated in the far field.In addition,far-field emissions are directionally enhanced and have long-distance spatial coherence properties.

Momentum-space imaging spectroscopy for the study of nanophotonic materials

The novel phenomena in nanophotonic materials, such as the angle-dependent reflection and negative refraction effect, are closely related to the photonic dispersions EepT. EepT describes the relation between energy E and momentum p of photonic eigenmodes, and essentially determines the optical properties of materials. As EepT is defined in momentum space(k-space), the experimental method to detect the energy distribution, that is the spectrum, in a momentum-resolved manner is highly required. In this review, the momentum-space imaging spectroscopy(MSIS) system is presented, which can directly study the spectral information in momentum space. Using the MSIS system, the photonic dispersion can be captured in one shot with high energy and momentum resolution. From the experimental momentumresolved spectrum data, other key features of photonic eigenmodes, such as quality factors and polarization states, can also be extracted through the post-processing algorithm based on the coupled mode theory. In addition, the interference configurations of the MSIS system enable the measurement of coherence properties and phase information of nanophotonic materials, which is important for the study of light-matter interaction and beam shaping with nanostructures. The MSIS system can give the comprehensive information of nanophotonic materials, and is greatly useful for the study of novel photonic phenomena and the development of nanophotonic technologies.