Terahertz Bessel Beam Applied to Thickness Measurement of Ellipsometry Methods

This paper introduces a Terahertz (THz) ellipsometer thickness measurement method based on Bessel beams. The ellipsometry method is used to measure the thickness of film in the THz band. And the thickness of film could be measured in the range of hundreds of microns which the measurement of film thickness by ellipsometer is usually only a few hundred nm in visible light. In addition, the photon energy of the THz-wave is very low and has little damage to the film. The THz Bessel beam has the characteristics of self-healing and diffraction-free. It can make the film thickness measurement within the diffraction-free distance, which is conducive to the flexibility of the ellipsometer system. We use a multi-frequency method to measure film with two-dimensional finite different time domain (FDTD) to numerical simulation analysis of light intensity successfully.

BMP7 expression in mammalian cortical radial glial cells increases the length of the neurogenic period

The seat of human intelligence is the human cerebral cortex,which is responsible for our exceptional cognitive abilities.Identifying principles that lead to the development of the large-sized human cerebral cortex will shed light on what makes the human brain and species so special.The remarkable increase in the number of human cortical pyramidal neurons and the size of the human cerebral cortex is mainly because human cortical radial glial cells,primary neural stem cells in the cortex,generate cortical pyramidal neurons for more than 130 days,whereas the same process takes only about 7 days in mice.The molecular mechanisms underlying this difference are largely unknown.Here,we found that bone morphogenic protein 7(BMP7)is expressed by increasing the number of corti-cal radial glial cells during mammalian evolution(mouse,ferret,monkey,and human).BMP7 expression in cortical radial glial cells promotes neurogenesis,inhibits gliogenesis,and thereby increases the length of the neurogenic period,whereas Sonic Hedgehog(SHH)signaling promotes cortical gliogenesis.We demonstrate that BMP7 sign-aling and SHH signaling mutually inhibit each other through regulation of GLI3 repressor formation.We propose that BMP7 drives the evolutionary expansion of the mammalian cortex by increasing the length of the neurogenic period.

Developmental Origins of Human Cortical Oligodendrocytes and Astrocytes

Human cortical radial glial cells are primary neural stem cells that give rise to cortical glutaminergic projection pyramidal neurons, glial cells (oligodendrocytes and astrocytes) and olfactory bulb GABAergic interneurons. One of prominent features of the human cortex is enriched with glial cells, but there are major gaps in understanding how these glial cells are generated. Herein, by integrating analysis of published human cortical single-cell RNA-Seq datasets with our immunohistochemistical analyses, we show that around gestational week 18, EGFR-expressing human cortical truncated radial glial cells (tRGs) give rise to basal multipotent intermediate progenitors (bMIPCs) that express EGFR, ASCL1, OLIG2 and OLIG1. These bMIPCs undergo several rounds of mitosis and generate cortical oligodendrocytes, astrocytes and olfactory bulb interneurons. We also characterized molecular features of the cortical tRG. Integration of our findings suggests a general picture of the lineage progression of cortical radial glial cells, a fundamental process of the developing human cerebral cortex.

Programmed Death Ligand-1 on Microglia Regulates Th1 Differentiation via Nitric Oxide in Experimental Autoimmune Encephalomyelitis

Microglia are considered to be potential anti- gen-presenting cells and have the ability to present antigen under pathological conditions. Nevertheless, whether and how microglia are involved in immune regulation are lar- gely unknown. Here, we investigated the suppressive activity of microglia during experimental autoimmune encephalomyelitis （EAE） induced by myelin oligodendro- cyte glycoprotein, with the goal of understanding their role in regulating the T cell reaction. Using flow cytometric analysis, we found that microglia were characterized by increased cell number and up-regulated programmed death ligand-1 （PD-L1） at the peak phase of EAE. Meanwhile, both the CD4＋ T cells and microglia that infiltrated the central nervous system expressed higher levels of PD1, the receptor for PD-L1, accompanied by a decline of Thl cells. In an ex vivo co-culture system, microglia from EAE mice inhibited the proliferation of antigen-specific CD4＋ T cells and the differentiation of Thl cells, and this was significantly inhibited by PD-L 1 blockade. Further, microglia suppressed Thl cells via nitric oxide （NO）, the production of which was dependent on PD-L1. Thus, these data suggest a scenario in which microglia are involved in the regulation of EAE by suppressing Thl-cell differenti- ation via the PD-L1-NO pathway.

Decoding Cortical Glial Cell Development

Mouse cortical radial glial cells(RGCs)are primary neural stem cells that give rise to cortical oligodendrocytes,astrocytes,and olfactory bulb(OB)GABAergic interneurons in late embryogenesis.There are fundamental gaps in understanding how these diverse cell subtypes are generated.Here,by combining single-cell RNA-Seq with intersectional lineage analyses,we show that beginning at around E16.5,neocortical RGCs start to generate ASCL1^(+)EGFR^(+)apical multipotent intermediate progenitors(MIPCs),which then differentiate into basal MIPCs that express ASCL1,EGFR,OLIG2,and MKI67.These basal MIPCs undergo several rounds of divisions to generate most of the cortical oligodendrocytes and astrocytes and a subpopulation of OB interneurons.Finally,single-cell ATAC-Seq supported our model for the genetic logic underlying the specification and differentiation of cortical glial cells and OB interneurons.Taken together,this work reveals the process of cortical radial glial cell lineage progression and the developmental origins of cortical astrocytes and oligodendrocytes.

Adult Neural Stem Cells: Constant Extension from Embryonic Ancestors

Adult neural stem cells(a NSCs)primarily exist in two regions:the subventricular zone(SVZ)of the lateral ventricle(LV)and the subgranular zone(SGZ)in the hippocampal dentate gyrus(DG)[1].It has been revealed that a NSCs in the SVZ(called type B cells)originate from embryonic NSCs mainly before embryonic day 15.5(E15.5),and are set aside for postnatal neurogenesis after diverging[2,3].

Influence of the amplitude ratio between two terahertz pulses on two-dimensional spectroscopy

The influence of the amplitude ratio between the two THz pulses on two-dimension THz spectroscopy(2DTS)has been studied theoretically via a classical method in which the expressions for the second-order nonlinearity were derived using perturbation approach,and the THz pulses were not treated as a delta function.Three types of nonlinear sources i.e.,anharmonicity,nonlinear damping,and nonlinear coupling,are considered in a single mode system.The simulation results demonstrated that the amplitude ratio had a notable influence on the 2DTSs,and different sources have different influences.This study is promising for guiding future experiments.

Litchi detection in the field using an improved YOLOv3 model

Due to the illumination,complex background,and occlusion of the litchi fruits,the accurate detection of litchi in the field is extremely challenging.In order to solve the problem of the low recognition rate of litchi-picking robots in field conditions,this study was inspired by the ideas of ResNet and dense convolution and proposed an improved feature-extraction network model named“YOLOv3_Litchi”,combining dense connections and residuals for the detection of litchis.Firstly,based on the traditional YOLOv3 deep convolution neural network and regression detection,the idea of residuals was to be put into the feature-extraction network to effectively avoid the problem of decreasing detection accuracy due to the excessive depths of the network layers.Secondly,under the premise of a good receptive field and high detection accuracy,the large convolution kernel was replaced by a small convolution kernel in the shallow layer of the network,thereby effectively reducing the model parameters.Finally,the idea of feature pyramid was used to design the network to identify the small target litchi to ensure that the shallow features were not lost and simultaneously reduced the model parameters.Experimental results show that the improved YOLOv3_Litchi model achieved better results than the classic YOLOv3_DarkNet-53 model and the YOLOv3_Tiny model.The mean average precision(mAP)score was 97.07%,which was higher than the 95.18%mAP of the YOLOv3_DarkNet-53 model and the 94.48%mAP of the YOLOv3_Tiny model.The frame frequency was 58 fps,which was higher than 29 fps of the YOLOv3_DarkNet-53 model.Compared with the classic Faster R-CNN model with the feature-extraction network VGG16,the mAP was increased by 1%,and the FPS advantage was obvious.Compared with the classic single shot multibox detector(SSD)model,both the accuracy and the running efficiency were improved.The results show that the improved YOLOv3_Litchi model had stronger robustness,higher detection accuracy,and less computational complexity for the identification of litchi in the field conditions,which should be helpful for litchi orchard precision management.

Homeobox Gene Six3 is Required for the Differentiation of D2-Type Medium Spiny Neurons

Medium spiny neurons(MSNs)in the striatum,which can be divided into D1 and D2 MSNs,originate from the lateral ganglionic eminence(LGE).Previously,we reported that Six3 is a downstream target of Sp8/Sp9 in the transcriptional regulatory cascade of D2 MSN development and that conditionally knocking out Six3 leads to a severe loss of D2 MSNs.Here,we showed that Six3 mainly functions in D2 MSN precursor cells and gradually loses its function as D2 MSNs mature.Conditional deletion of Six3 had little effect on cell proliferation but blocked the differentiation of D2 MSN precursor cells.In addition,conditional overexpression of Six3 promoted the differentiation of precursor cells in the LGE.We measured an increase of apoptosis in the postnatal striatum of conditional Six3-knockout mice.This suggests that,in the absence of Six3,abnormally differentiated D2 MSNs are eliminated by programmed cell death.These results further identify Six3 as an important regulatory element during D2 MSN differentiation.

Coupling Characteristics of DFIG-based WT Considering Reactive Power Control and Its Impact on Phase/Amplitude Transient Stability in a Rotor Speed Control Timescale

The transient stability issues caused by doubly fed induction generator(DFIG)-based wind turbines(WTs)are receiving increasing attention.The q-axis reactive power control(QCtrl),as an essential part of DFIG-based WTs,has a significant impact on its transient response.In this paper,the impact of QCtrl on the phase/amplitude transient stability of a DFIGbased WT-dominated system is analyzed from the perspective of internal voltage amplitude-phase coupling characteristics.First,an amplitude/phase dynamic model of a DFIG-based WT in rotor speed control timescale(in seconds,corresponding to traditional electromechanical timescale)is developed.Then,in comparison with familiar synchronous generators(SGs),an inherently amplitude-phase characteristic of internal voltage for a DFIG-based WT is identified.Next,taking the DFIG-based WTdominated system as an example,the impact of QCtrl on system transient stability via the internal coupling paths is analyzed.A novel phase-amplitude coupling instability mechanism is found,which is different from that in a traditional SG-dominated system.Finally,the effects of different QCtrl strategies on transient stability are discussed.

A proposed approach for detecting terahertz pulses by using double few-cycle laser pulses with opposite carrier envelope phases

Previous research shows that few-cycle laser（FCL） pulses with low energy and without a bias field can be used to coherently detect terahertz（THz） pulses. As we know, it is very difficult to stabilize the carrier envelope phase（CEP） of FCL pulses, i.e., there are some random fluctuations for the CEP. Here we theoretically investigate the influence of such instability on the accuracy of THz detection. Our results show that although there is an optimum CEP for THz detection, the fluctuations of the CEP will lead to terrible thorns on the detected THz waveform. In order to solve this problem, we propose an approach using two few-cycle laser pulses with opposite CEPs, i.e., their CEPs are differed by π.