Electrically-driven ultrafast out-of-equilibrium light emission from hot electrons in suspended graphene/hBN heterostructures

Nanoscale light sources with high speed of electrical modulation and low energy consumption are key components for nanophotonics and optoelectronics.The record-high carrier mobility and ultrafast carrier dynamics of graphene make it promising as an atomically thin light emitter which can be further integrated into arbitrary platforms by van der Waals forces.However,due to the zero bandgap,graphene is difficult to emit light through the interband recombination of carriers like conventional semiconductors.Here,we demonstrate ultrafast thermal light emitters based on suspended graphene/hexagonal boron nitride(Gr/hBN)heterostructures.Electrons in biased graphene are significantly heated up to 2800 K at modest electric fields,emitting bright photons from the near-infrared to the visible spectral range.By eliminating the heat dissipation channel of the substrate,the radiation efficiency of the suspended Gr/hBN device is about two orders of magnitude greater than that of graphene devices supported on SiO2or hBN.Wefurther demonstrate that hot electrons and low-energy acoustic phonons in graphene are weakly coupled to each other and are not in full thermal equilibrium.Direct cooling ofhigh-temperature hot electrons to low-temperature acoustic phonons is enabled by the significant near-field heat transfer at the highly localized Gr/hBN interface,resulting in ultrafast thermal emission with up to 1 GHz bandwidth under electrical excitation.It is found thatsuspending the Gr/hBN heterostructures on the SiO2trenches significantly modifies the light emission due to the formation of the optical cavity and showed a~440%enhancement inintensity at the peak wavelength of 940 nm compared to the black-body thermal radiation.The demonstration of electrically driven ultrafast light emission from suspended Gr/hBNheterostructures sheds the light on applications of graphene heterostructures in photonicintegrated circuits,such as broadband light sources and ultrafast thermo-optic phase modulators.

Intrinsic polarization conversion and avoided-mode crossing in X-cut lithium niobate microrings

Compared with well-developed free space polarization converters, polarization conversion between TE and TM modes in the waveguide is generally considered to be caused by shape birefringence, like curvature, morphology of waveguide cross section and scattering. Here, we study the polarization conversion mechanism in 1-THz-FSR X-cut lithium niobate microrings with multiple-resonance condition, that is the conversion can be implemented by birefringence of waveguides,which will also introduce an avoided-mode crossing. In the experiment, we find that this mode crossing results in severe suppression of one sideband in local nondegenerate four-wave mixing and disrupts the cascaded four-wave mixing on this side. Simultaneously, we propose one two-dimensional method to simulate the eigenmodes(TE and TM) in X-cut microrings, and the mode crossing point. This work will provide one approach to the design of polarization converters and simulation for monolithic photonics integrated circuits, and may be helpful to the studies of missed temporal dissipative soliton formation in X-cut lithium niobate rings.

CPS Modeling of CNC Machine Tool Work Processes Using an Instruction-Domain Based Approach

Building cyber-physical system(CPS) models of machine tools is a key technology for intelligent manufacturing. The massive electronic data from a computer numerical control(CNC) system during the work processes of a CNC machine tool is the main source of the big data on which a CPS model is established. In this work-process model, a method based on instruction domain is applied to analyze the electronic big data, and a quantitative description of the numerical control(NC) processes is built according to the G code of the processes. Utilizing the instruction domain, a work-process CPS model is established on the basis of the accurate, real-time mapping of the manufacturing tasks, resources, and status of the CNC machine tool. Using such models, case studies are conducted on intelligent-machining applications, such as the optimization of NC processing parameters and the health assurance of CNC machine tools.

Double-layered osmotic pump controlled release tablets of actarit: In vitro and in vivo evaluation

The aim of the study was to develop actarit double-layered osmotic pump tablets to overcome the weak points of actarit common tablets, such as short half-life and large plasma concentration fluctuations. Single factor experiment and orthogonal test were applied to optimize the formulation;the pharmacokinetic study was performed in beagle dogs adopting actarit common tablets as reference tablets. The optimal formulation was as follows: drug layer: 150 mg actarit, 240 mg PEO-N80, 50 mg NaCl;push layer: 140 mg PEO-WSR303, 20 mg NaCl;coating solution: 30 g cellulose acetate and 6 g PEG 4000 in 1000 ml 94% acetone solution, 60 mg coating weight gain. The pharmacokinetic study showed that T max was prolonged by the contrast of commercial common tablets with constant drug release rate, but the bioavailability was equivalent. And a good in vivo –in vitro correlation of the actarit osmotic pump tablets was also established. The designed actarit osmotic pump tablets can be applied for rheumatoid arthritis, proposing a promising replacement for the marked common products.

Characterize and optimize the four-wave mixing in dual-interferometer coupled silicon microrings

By designing and fabricating a series of dual-interferometer coupled silicon microrings, the coupling condition of the pump, signal, and idler beams can be engineered independently and then we carried out both the continuous-wave and pulse pumped four-wave mixing experiments to verify the dependence of conversion efficiency on the coupling conditions of the four interacting beams, respectively. Under the continuous-wave pump, the four-wave mixing efficiency gets maximized when both the pump and signal/idler beams are closely operated at the critical coupling point, while for the pulse pump case, the efficiency can be enhanced greatly when the pump and converted idler beams are all overcoupled. These experiment results agree well with our theoretical calculations. Our design provides a platform for explicitly characterizing the four-wave mixing under different pumping conditions, and offers a method to optimize the four-wave mixing, which will facilitate the development of on-chip all-optical signal processing with a higher efficiency or reduced pump power.

Solar radiation effects on leaf nitrogen and phosphorus stoichiometry of Chinese fir across subtropical China

Background:Solar radiation(SR)plays critical roles in plant physiological processes and ecosystems functions.However,the exploration of SR influences on the biogeochemical cycles of forest ecosystems is still in a slow progress,and has important implications for the understanding of plant adaption strategy under future environmental changes.Herein,this research was aimed to explore the influences of SR on plant nutrient characteristics,and provided theoretical basis for introducing SR into the establishment of biochemical models of forest ecosystems in the future researches.Methods:We measured leaf nitrogen(N)and phosphorus(P)stoichiometry in 19 Chinese fir plantations across subtropical China by a field investigation.The direct and indirect effects of SR,including global radiation(Global R),direct radiation(Direct R)and diffuse radiation(Diffuse R)on the leaf N and P stoichiometry were investigated.Results:The linear regression analysis showed that leaf N concentration had no association with SR,while leaf P concentration and N:P ratio were negatively and positively related to SR,respectively.Partial least squares path model(PLS-PM)demonstrated that SR(e.g.Direct R and Diffuse R),as a latent variable,exhibited direct correlations with leaf N and P stoichiometry as well as the indirect correlation mediated by soil P content.The direct associations(path coefficient=−0.518)were markedly greater than indirect associations(path coefficient=−0.087).The covariance-based structural equation modeling(CB-SEM)indicated that SR had direct effects on leaf P concentration(path coefficient=−0.481),and weak effects on leaf N concentration.The high SR level elevated two temperature indexes(mean annual temperature,MAT;≥10°C annual accumulated temperature,≥10℃ AAT)and one hydrological index(mean annual evapotranspiration,MAE),but lowered the soil P content.MAT,MAE and soil P content could affect the leaf P concentration,which cause the indirect effect of SR on leaf P concentration(path coefficient=0.004).Soil N content had positive effect on the leaf N concentration,which was positively and negatively regulated by MAP and≥10℃ AAT,respectively.Conclusions:These results confirmed that SR had negatively direct and indirect impacts on plant nutrient status of Chinese fir based on a regional investigation,and the direct associations were greater than the indirect associations.Such findings shed light on the guideline of taking SR into account for the establishment of global biogeochemical models of forest ecosystems in the future studies.

Biocompatibility of Porous Spherical Calcium Carbonate Microparticles on Hela Cells

Recently there has been a wide concern on inorganic nanoparticles as drug delivery carriers. CaCO3 particles have shown promising potential for the development of carriers for drugs, but little research had been performed regarding their safe dosage for maximizing the therapeutic activity without harming biosystems. In this study, we assessed the biological safety of porous spherical CaCO3 microparticles on Hela cells. The reactive oxygen species (ROS), glutathione (GSH), carbonyl content in proteins (CCP), DNA-protein crosslinks (DPC) and cell viability were measured. Results showed that with the exposure concentration increase, ROS and CCP in Hela cells presented a significant increase but GSH contents in Hela cells and cell viability showed a significant decrease respectively compared with the control. DPC coefficient ascended, but no statistically significant changes were observed. The results indicated that porous spherical CaCO3 microparticles may induce oxidative damage to Hela cells. But compared with other nanomaterials, porous spherical CaCO3 appeared to have good biocompatibility. The results implied that porous spherical calcium carbonate microparticles could be applied as relatively safe drug vehicles, but with the caveat that the effect of high dosages should not be ignored when attempting to maximize therapeutic activity by increasing the concentration.

A systematic in vitro investigation on poly-arginine modified nanostructured lipid carrier: Pharmaceutical characteristics, cellular uptake, mechanisms and cytotoxicity

The aim of the present study was to develop a poly-arginine modified nanostructured lipid carrier(R-NLC) by fusion-emulsification method and to test its pharmaceutical characteristics. The influence of R-NLC on A549 cells like cellular uptake and cytotoxicity was also appraised using unmodified NLC as the controlled group. As the results revealed, R-NLC had an average diameter of about 40 nm and a positive zeta potential of about +17 mv, the entrapment efficiency decreased apparently, and no significant difference on the in vitro drug release was found after R8-modification. The cellular uptake and cytotoxicity increased obviously compared with unmodified NLC. The cellular uptake mechanisms of R-NLC involved energy, macropinocytosis, clathrin-mediated endocytosis, and caveolin-mediated endocytosis. The outcomes of the present study strongly support the theory that cell penetrating peptides have the ability of enhancing the cellular uptake of nanocarriers.

Bandwidth-tunable silicon nitride microring resonators

We designed a reconfigurable dual-interferometer coupled silicon nitride microring resonator.By tuning the integrated heater on interferometer's arms,the"critical coupling"bandwidth of resonant mode is continuously adjustable whose quality factor varies from 7.9×10^(4) to 1.9×10^(5) with the extinction ratio keeping higher than 25 dB.Also a variety of coupling spanning from"under-coupling"to"over-coupling"were achieved,showing the ability to tune the quality factor from 6.0×10^(3) to 2.3×10^(5).Our design can provide an adjustable filtering method on silicon nitride photonic chip and contribute to optimize the nonlinear process for quantum photonics and all-optical signal processing.

拓扑半导体激光器研究进展

受凝聚态物理中拓扑相概念的启发,拓扑光子学这一研究领域应运而生.它提供了一种新颖的光场调控机制:缺陷免疫且背散射抑制的边界输运、自旋轨道依赖的选择性传输、高维度光场调控等.同时,拓扑边界态、拓扑角态和拓扑缺陷态的发现推动着拓扑半导体激光器的产生和发展.本文回顾了拓扑半导体激光器的研究进展,分析了各种拓扑半导体激光器的原理和结构,以及拓扑边界态、角态和缺陷态的物理基础.相比拓扑边界态和拓扑角态,基于拓扑缺陷态的谐振腔具有大自由光谱范围、小远场发散角以及矢量光场输出等特性,对应的拓扑半导体激光器功率更高,鲁棒性更好.拓扑半导体激光器对激光雷达、激光打印、光子集成等应用具有深远的影响.

Unipolar p-type monolayer WSe_(2) field-effect transistors with high current density and low contact resistance enabled by van der Waals contacts

High-performance field-effect transistors (FETs) based on atomically thin two-dimensional (2D) semiconductors have demonstrated great promise in post-Moore integrated circuits. However, unipolar p-type 2D semiconductor transistors yet remain challenging and suffer from low saturation current density (less than 10 µA·µm^(−1)) and high contact resistance (larger than 100 kΩ·µm), mainly limited by the Schottky barrier induced by the mismatch of the work-functions and the Fermi level pinning at the metal contact interfaces. Here, we overcome these two obstacles through van der Waals (vdW) integration of high work-function metal palladium (Pd) as the contacts onto monolayer WSe2 grown by chemical vapor deposition (CVD) method. We demonstrate unipolar p-type monolayer WSe2 FETs with superior device performance: room temperature on-state current density exceeding 100 µA·µm^(−1), contact resistance of 12 kΩ·µm, on/off ratio over 107, and field-effect hole mobility of ~ 103 cm2·V^(−1)·s^(−1). Electrical transport measurements reveal that the Fermi level pinning effect is completely effectively eliminated in monolayer WSe2 with vdW Pd contacts, leading to a Schottky barrier-free Ohmic contact at the metal-semiconductor junctions. Combining the advantages of large-scale vdW contact strategy and CVD growth, our results pave the way for wafer-scale fabrication of complementary-metal-oxide-semiconductor (CMOS) logic circuits based on atomically thin 2D semiconductors.

Machine Learning-Based Research on Tensile Strength of SiC-Reinforced Magnesium Matrix Composites via Stir Casting

SiC is the most common reinforcement in magnesium matrix composites,and the tensile strength of SiC-reinforced magnesium matrix composites is closely related to the distribution of SiC.Achieving a uniform distribution of SiC requires fine control over the parameters of SiC and the processing and preparation process.However,due to the numerous adjustable parameters,using traditional experimental methods requires a considerable amount of experimentation to obtain a uniformly distributed composite material.Therefore,this study adopts a machine learning approach to explore the tensile strength of SiC-reinforced magnesium matrix composites in the mechanical stirring casting process.By analyzing the influence of SiC parameters and processing parameters on composite material performance,we have established an effective predictive model.Furthermore,six different machine learning regression models have been developed to predict the tensile strength of SiC-reinforced magnesium matrix composites.Through validation and comparison,our models demonstrate good accuracy and reliability in predicting the tensile strength of the composite material.The research findings indicate that hot extrusion treatment,SiC content,and stirring time have a significant impact on the tensile strength.

Visible-Light-Induced[4+1]Cyclization-Aromatization of Acylsilanes andα,β-Unsaturated Ketones

Herein we report the first[4+1]cyclization-aromatization reaction of acylsilanes andα,β-unsaturated ketones.The unprecedented visible-light-induced reaction proceeded through mild conditions without addition of any catalyst or additive,affording a variety of furans with broad substrate scope and good functional-group tolerance.The synthetic utility of the method was demonstrated by various downstream transformations of the otherwise difficult-to-access sulfone-containing silyl furans.The mechanism study reveals that 1,4-diketones are not likely to be the intermediates of the reaction.

Mesoporous polydopamine nanoplatforms loaded with calcium ascorbate for amplified oxidation and photothermal combination cancer therapy

Destruction of cellular redox homeostasis to induce cancer cell apoptosis is an emerging tumor therapeutic strategy. To achieve this goal, elevating exogenous oxidative stress or impairing the antioxidant defense system of cancer cells is an effective method. Herein, we firstly report a biocompatible and versatile nanoplatform based on mesoporous polydopamine (MpDA) nanoparticles and a phase-change material (PCM) for delivering calcium ascorbate (Vc-Ca), simultaneously enabling combination therapy of hyperthermia, reactive oxygen species (ROS) generation, and suppression of tumor antioxidant capability. In this design, Vc-Ca encapsulated in MpDA using PCM is controllably released due to the melting of PCM matrix in response to photothermal heating upon near-infrared irradiation. Vc-Ca is proved to be a prooxidant that can promote the production of ROS (H2O2) in the tumor site. Remarkably, MpDA can not only act as a photothermal agent but also can break the redox balance of cancer cells through depleting the primary antioxidant glutathione, thus amplifying Vc-Ca-mediated oxidative therapy. Both in vitro and in vivo results demonstrate the significantly enhanced antitumor activity of boosted ROS combined with local hyperthermia. This study highlights the potential applications of Vc-Ca in cancer treatment, and the prepared multifunctional nanoplatform provides a novel paradigm for highefficiency oxidation-photothermal therapy.

A robust bifunctional catalyst for rechargeable Zn-air batteries:Ultrathin NiFe-LDH nanowalls vertically anchored on soybeanderived Fe-N-C matrix

ABSTRACT NiFe layered double hydroxide(NiFe-LDH)nanosheets and metal-nitrogen-carbon materials(M-N-C,M=Ni,Fe,Co,etc.)are supreme catalysts in the oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)process,respectively.Nevertheless,the monotonic performance and insufficient stability severely hamper their practical application in rechargeable batteries.Herein,we simultaneously combine ultrathin NiFe-LDH nanowalls with renewable soybean-derived Fe-N-C matrix to obtain a hybrid materials(NiFe-LDH/FeSoy-CNSs-A),which exhibits robust catalytic activities for OER(E_(j=10)=1.53 V vs.RHE)and ORR(E_(1/2)=0.91 V vs.RHE),with a top-notch battery parameters and stability in assembled rechargeable Zn-air batteries.Intensive investigations indicate that the vertically dispersed NiFe-LDH nanosheets,Fe-N-C matrix derived from soybean and the strong synergy between them are responsible for the unprecedented OER and ORR performances.The key role of intrinsic N defects involved in the hybrid materials is firstly specified by ultrasoundassisted extraction of soy protein from soybean.The exquisite design can facilitate the utilization of sustainable biomass-derived catalysts,and the mechanism investigations of N defects and oxygenic groups on the structure-activity relationship can stimulate the progress of other functional hybrid electrocatalysts.

Photothermal/matrix metalloproteinase-2 dual-responsive gelatin nanoparticles for breast cancer treatment

The chemotherapy combined with photothermal therapy has been a favorable approach for the treatment of breast cancer.In present study,nanoparticles with the characteristics of photothermal/matrix metalloproteinase-2(MMP-2)dual-responsive,tumor targeting,and size-variability were designed for enhancing the antitumor efficacy and achieving"on-demand"drug release markedly.Based on the thermal sensitivity of gelatin,we designed a size-variable gelatin nanoparticle(GNP)to encapsulate indocyanine green(ICG)and doxorubicin(DOX).Under an 808 nm laser irradiation,GNP-DOX/ICG responded photothermally and swelled in size from 71.58?4.28 to 160.80?9.51 nm,which was beneficial for particle retention in the tumor sites and release of the loaded therapeutics.Additionally,GNP-DOX/ICG showed a size reduction of the particles to 33.24?4.11 nm and further improved drug release with the degradation of overexpressed MMP-2 in tumor.In the subsequently performed in vitro experiments,it was confirmed that GNP-DOX/ICG could provide a therapeutic effect that was enhanced and synergistic.Consequently,GNP-DOX/ICG could efficiently suppress the growth of 4 T1 tumor in vivo.In conclusion,this study may provide a promising strategy in the rational design of drug delivery nanosystems based on gelatin for chemo-photothermal therapy to achieve synergistically enhanced therapeutic efficacy against breast cancer.

Realized niche shift associated with Galinsoga quadriradiata(Asteraceae)invasion in China

Shifts in the realized niches of exotic species may play an important role in their invasion.Galinsoga quadriradiata has invaded China widely and occupied many climate zones that are different from its native range.We addressed the climatic niche shift of G.quadriradiata and evaluated how this could contribute to its invasion in China.We used the Maxent model to predict the potential distribution of G.quadriradiata using its native and invaded range occurrences and climatic variables.Principal component analysis was conducted to measure climatic niche shifts of G.quadriradiata during its invasion in China.The models revealed only 32.7%niche overlap between the native and invasive populations.The niche similarity of the two populations was significantly low(Schoener’s D=0.093,P<0.005),suggesting the occurrence of a niche shift.The envelop and center of the realized climatic niche in China has shifted to lower temperature and less precipitation compared to that in its native range.The majority of invaded areas in southern China are in the stabilizing zone,whereas the colonization and adaptation zones are predicted to be at the leading edge of G.quadriradiata invasion in northern China.This suggests that the regional distribution of G.quadriradiata may be in a quasi-equilibrium state,and that the species continues to invade environmentally suitable areas.Alterations in G.quadriradiata’s niche would help to explain why this species is so invasive in China.

Light-induced irreversible structural phase transition in trilayer graphene

A crystal structure has a profound influence on the physical properties of the corresponding material.By synthesizing crystals with particular symmetries,one can strongly tune their properties,even for the same chemical configuration(compare graphite and diamond,for instance).Even more interesting opportunities arise when the structural phases of crystals can be changed dynamically through external stimulations.Such abilities,though rare,lead to a number of exciting phenomena,such as phase-change memory effects.In the case of trilayer graphene,there are two common stacking configurations(ABA and ABC)that have distinct electronic band structures and exhibit very different behaviors.Domain walls exist in the trilayer graphene with both stacking orders,showing fascinating new physics such as the quantum valley Hall effect.Extensive efforts have been dedicated to the phase engineering of trilayer graphene.However,the manipulation of domain walls to achieve precise control of local structures and properties remains a considerable challenge.Here,we experimentally demonstrate that we can switch from one structural phase to another by laser irradiation,creating domains of different shapes in trilayer graphene.The ability to control the position and orientation of the domain walls leads to fine control of the local structural phases and properties of graphene,offering a simple but effective approach to create artificial two-dimensional materials with designed atomic structures and electronic and optical properties.

Bright photon-pair source based on a silicon dual-Mach-Zehnder microring

Single photons and photon pairs are typically generated by spontaneous parametric down conversion or quantum dots;however,spontaneous four-wave mixing(SFWM)in silicon microring resonators[1]is also an appealing source of entangled photons,offering a strong cavity-enhanced nonlinear interactions while maintaining features,such as compact,simple to fabricate,and allowing for thermal tuning.However,silicon ring-resonators usually suffer from a trade-off between providing a high pair generation rate(PGR)and high extraction efficiency.To achieve high PGR,devices are generally operated with the signal and idler photons in the undercoupling regime and pump photons at the critical coupling point,while high extraction rates require the converted photons to be overcoupled.Therefore,the optimal conditions for achieving maximal output photon pair flux are critical coupling for the pump photons and overcoupling for the converted photons[2,3].

Comparative study of the cytotoxicity of the nanosized and microsized tellurium powders on HeLa cells

To compare the cytotoxicity on HeLa cells induced by nanosized and microsized tellurium powders, HeLa cells were exposed to different concentrations of tellurium powders （0, 50, 100, 150 and 200 μg/mL） for 12 h. In this study, detection of a series of biomarkers, including reactive oxygen species （ROS）, glutathione （GSH）, 8-hydroxy-2＇- deoxyguanosine （8-OHdG）, in addition to DNA and protein crosslink （DPC） and MTT assay, were conducted to evaluate the cytotoxicity. It is indicated that compared with the control group, there was no significant difference in the induced cytotoxicity at concentrations lower than 50 μg/mL for both nanosized and microsized tellurium powders. While there appears a significant difference in the induced cytotoxicity for nanosized tellurium powders when the concentration is higher than 100 μg/mL as well as for microsized tellurium powders when the concentration is higher than 200 μg/mL. Moreover, it is found that the cytotoxicity induced on HeLa cells exhibits a certain dose-effect relationship with the concentration of tellurium powders. A conclusion has been reached that the toxicity on HeLa cells can be induced by both nanosized and microsized tellurium powders, and the toxicity of the nanosized tellurium powders is significantly greater than the microsized one.