SiO2 nanoparticle-regulated crystallization of lead halide perovskite and improved efficiency of carbon-electrode-based low-temperature planar perovskite solar cells

SiO2 nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method,which was used in the low-temperature-processed,carbon-electrode-basing,hole-conductor-free planar perovskite solar cells.It was observed that,after adding small amount of SiO2 precursor(1 vol%)into the lead iodide solution,performance parameters of open-circuit voltage,short-circuit current and fill factor were all upgraded,which helped to increase the power conversion efficiency(reverse scan)from 11.44(±1.83)%(optimized at 12.42%)to 14.01(±2.14)%(optimized at 15.28%,AM 1.5G,100 mW/cm^2).Transient photocurrent decay curve measurements showed that,after the incorporation of SiO2 nanoparticles,charge extraction was accelerated,while transient photovoltage decay and dark current curve tests both showed that recombination was retarded.The improvement is due to the improved crystallinity of the perovskite film.X-ray diffraction and scanning electron microscopy studies observed that,with incorporation of amorphous SiO2 nanoparticles,smaller crystallites were obtained in lead iodide films,while larger crystallites were achieved in the final perovskite film.This study implies that amorphous SiO2 nanoparticles could regulate the coarsening process of the perovskite film,which provides an effective method in obtaining high quality perovskite film.

The influence of turbulent mixing on the subsurface chlorophyll maximum layer in the northern South China Sea

We present observations from deployments of turbulent microstructure instrument and CTD package in the northern South China Sea from April to May 2010.From them we determined the turbulent mixing(dissipation rateεand diapycnal diffusivityκ),nutrients(phosphate,nitrate,and nitrite),nutrient fluxes,and chlorophyll a in two transects(A and B).Transect A was located in the region where turbulent mixing in the upper 100 m was weak(κ~10-6-10-4 m^(2)/s).Transect B was located in the region where the turbulent mixing in the upper 100 m was strong(κ~10-5-10-3 m^(2)/s)due to the influence of internal waves originating from the Luzon Strait and water intrusion from the Western Pacific.In both transects,there was a thin subsurface chlorophyll maximum layer(SCML)(>0.25 mg/m^(3))nested in the upper 100 m.The observations indicate that the effects of turbulent mixing on the distributions of nutrients and chlorophyll a were different in the two transects.In the transect A with weak turbulent mixing,nutrient fluxes induced by turbulent mixing transported nutrients to the SCML but not to the upper water.Nutrients were sufficient to support a local SCML phytoplankton population and the SCML remained compact.In the transect B with strong turbulent mixing,nutrient fluxes induced by turbulent mixing transported nutrients not only to the SCML but also to the upper water,which scatters the nutrients in the water column and diffuses the SCML.

Interfaces between MoO x and Mo X2(X=S,Se,and Te)

In the past decades there have been many breakthroughs in low-dimensional materials,especially in two-dimensional(2D)atomically thin crystals like graphene.As structural analogues of graphene but with a sizeable band gap,monolayers of atomically thin transition metal dichalcogenides(with formula of MX2,M=Mo,W;X=S,Se,Te,etc.)have emerged as the ideal 2D prototypes for exploring fundamentals in physics such as valleytronics due to the quantum confinement effects,and for engineering a wide range of nanoelectronic,optoelectronic,and photocatalytic applications.Transition metal trioxides as promising materials with low evaporation temperature,high work function,and inertness to air have been widely used in the fabrication and modification of MX2.In this review,we reported the fabrications of one-dimensional MoS2 wrapped MoO2 single crystals with varied crystal direction via atmospheric pressure chemical vapor deposition method and of 2D MoOx covered MoX2 by means of exposing MoX2 to ultraviolet ozone.The prototype devices show good performances.The approaches are common to other transition metal dichalcogenides and transition metal oxides.

Tuning the alignment of pentacene on copper substrate by annealing-assistant surface functionalization

Controlling the alignment and packing structure of organic molecules on solid substrate surfaces at molecule level is essential to develop high-performance organic thin film(OTF)devices.Pentacene,which is a typical p-type semiconductor material usually adopts lying-down geometry on metal substrates owning toπ-d coupling between pentacene and metal substrates.However,in this study,we found that pentacene molecules can be adsorbed on an anneal-treated Cu(111)surface with their long axis perpendicular to substrate surface.Highly ordered single-layer pentacene film with stand-up molecular geometry was achieved on this substrate.It was found that the functionalization of Cu surface with C=O groups due to annealing treatment should be accounted for standing-up geometry of pentacene on Cu substrate.This observation shed light on the tuning of the alignment and packing structure of organic molecules.

中国石笋生长速率时空变化特征的初步分析

近年来,随着现代监测研究以及铀系定年技术的发展,石笋生长速率研究日趋得到了重视。本研究主要收集了我国内地地区已发表的17个洞穴的70支石笋的年代数据,计算并分析了冰期/间冰期尺度和全新世期间石笋生长速率的时空变化特征,发现规律如下:1)内陆干旱区科桑洞和东部季风区长江以北的3个洞穴(分别为珍珠洞、Buddha洞和三宝洞)的石笋呈现间冰期生长速率快,冰期生长速率较慢,甚至出现沉积间断;2)我国北方的琉璃洞、马沟洞、莲花洞(山西)、乌鸦洞、九仙洞和南方的莲花洞(湖南)、Dark洞和董哥洞表现为中全新世石笋生长速率较快,而早/晚全新世相对较慢;长江中下游地区的三宝洞和落水洞在早全新世期间生长速率较快,中/晚全新世较稳定;3)大多数洞穴石笋生长速率在近2ka B.P.以来呈现上升趋势,这些特征可能暗示了气候条件对石笋生长速率的影响。同时也发现:1)我国南部湿润区以及沿海地区的洞穴石笋生长速率在冰期/间冰期尺度呈现复杂多变的特征;2)不同洞穴之间或同一洞穴不同石笋之间,石笋生长速率均存在一定差异;这些结果表明洞穴系统内部的差异性会对石笋生长产生复杂影响。上述分析结果为认识我国石笋生长速率时空变化特征提供了一些基础性证据,但目前条件下,不建议将其作为单独的气候环境变化指标,而建议将其与其它石笋指标结合,开展多指标综合分析和验证。对于具体洞穴而言,现代监测对于理解石笋生长速率控制机制仍是必不可少的。

The biological effect of recombinant humanized collagen on damaged skin induced by UV-photoaging:An in vivo study

The application of medical devices to repair skin damage is clinically accepted and natural polymer enjoys an important role in this field,such as collagen or hyaluronic acid,etc.However,the biosafety and efficacy of these implants are still challenged.In this study,a skin damage animal model was prepared by UV-photoaging and recombinant humanized type Ⅲ collagen(rhCol Ⅲ)was applied as a bioactive material to implant in vivo to study its biological effect,comparing with saline and uncrosslinked hyaluronic acid(HA).Animal skin conditions were non-invasively and dynamically monitored during the 8 weeks experiment.Histological observation,specific gene expression and other molecular biological methods were applied by the end of the animal experiment.The results indicated that rhCol Ⅲ could alleviate the skin photoaging caused by UV radiation,including reduce the thickening of epidermis and dermis,increase the secretion of Collagen Ⅰ(Col Ⅰ)and Collagen Ⅲ(Col Ⅲ)and remodel of extracellular matrix(ECM).Although the cell-material interaction and mechanism need more investigation,the effect of rhCol Ⅲ on damaged skin was discussed from influence on cells,reconstruction of ECM,and stimulus of small biological molecules based on current results.In conclusion,our findings provided rigorous biosafety information of rhCol Ⅲ and approved its potential in skin repair and regeneration.Although enormous efforts still need to be made to achieve successful translation from bench to clinic,the recombinant humanized collagen showed superiorities from both safety and efficacy aspects.

Application of Avaatech X-ray fluorescence core-scanning in Sr/Ca analysis of speleothems

Application of X-ray fluorescence core-scanning(XRF-CS) on both marine and lake sediments has achieved remarkable results. However, its application has not been widely extended to the research on speleothems. In this study, we measure the Sr abundance and the Sr/Ca ratios of three stalagmites(two aragonite stalagmites, one calcite stalagmite) using the state-of-the-art fourth-generation Avaatech high-resolution XRF core scanner. Through comparisons among different scan paths and among different scan resolutions, as well as comparisons with inductively coupled plasma optical emission spectrometer(ICP-OES), Itrax XRF, and Artax XRF results, we confirm that the Avaatech XRF core scanner could precisely, quickly, and nondestructively analyze the high-resolution Sr abundance of speleothems. Furthermore, we combine the stalagmite δ^(18)O records to explore the paleoclimatic significance of the measured stalagmite Sr/Ca.

Solution-processed ultra-flexible C8-BTBT organic thin-film transistors with the corrected mobility over 18 cm^2/(V s)

Organic thin film transistors(OTFTs)show great potential for applications in low-cost,light-weight flexible electronics.OTFTs were first reported in 1986 with polythiophene as the active layer material with a mobility of^105 cm2/(V s)[1].Since then,OTFTs have shown impressive improvements in device performance parameters,e.g.,mobility improved by over 4 orders of magnitude.These advances followed discoveries of new materials and improvements in device engineering,as well as in morphology and interface engineering[2–4].Flexible OTFTs(f-OTFTs)as a very important electronic component in flexible electronics are attracting a great deal of attention from both academic and industrial communities.Presently,f-OTFTs are potentially used for electronic skin[5],flexible organic integrated circuits[6],flexible active matrix displays[7]and neuromorphic devices[8].

Enormous enhancement in electrical performance of few-layered MoTe2 due to Schottky barrier reduction induced by ultraviolet ozone treatment

Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically investigated a convenient and effective method,ultraviolet ozone treatment,for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance.The resulted hole concentration and mobility are near 100 times enhanced to be〜1.0×10^13 cm^-2 and 101.4 cm^2/(V·s),respectively,and the conductivity is improved by 5 orders of magnitude.These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature.Compared with the pristine one,the photoresponsivity(522 mA/W)is enhanced approximately 100 times.Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx(x<3),as proved by photoemission spectroscopy.Additionally,the p-doped devices exhibit excellent stability in ambient air.Our findings show significant potential in future nanoelectronic and optoelectronic applications.

The effect of collagen hydrogels on chondrocyte behaviors through restricting the contraction of cell/hydrogel constructs

Collagen is a promising material for tissue engineering,but the poor mechanical properties of collagen hydrogels,which tend to cause contraction under the action of cellular activity,make its application challengeable.In this study,the amino group of type I collagen(Col I)was modified with methacrylic anhydride(MA)and the photo-crosslinkable methacrylate anhydride modified type I collagen(CM)with three different degrees of substitution(DS)was prepared.The physical properties of CM and Col I hydrogels were tested,including micromorphology,mechanical properties and degradation properties.The results showed that the storage modulus and degradation rate of hydrogels could be adjusted by changing the DS of CM.In vitro,chondrocytes were seeded into these four groups of hydrogels and subjected to fluorescein diacetate/propidium iodide(FDA/PI)staining,cell counting kit-8(CCK-8)test,histological staining and cartilage-related gene expression analysis.In vivo,these hydrogels encapsulating chondrocytes were implanted subcutaneously into nude mice,then histological staining and sulfated glycosaminoglycan(sGAG)/DNA assays were performed.The results demonstrated that contraction of hydrogels affected behaviors of chondrocytes,and CM hydrogels with suitable DS could resist contraction of hydrogels and promote the secretion of cartilage-specific matrix in vitro and in vivo.

A multiple-proxy stalagmite record reveals historical deforestation in central Shandong, northern China

Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models.In this study,we analyzed stable isotopes(δ^18O,δ^13C)and trace elements(Mg/Ca,Sr/Ca)of a stalagmite from Huangchao Cave in central Shandong,northern China.230Th and AMS14C dating results indicate the stalagmite deposited during 174BC and AD1810,with a hiatus between AD638 and 1102.Broad similarities of theδ^18O and trace elements in the stalagmite suggest they are reliable precipitation indexes.Theδ^13C of the stalagmite,a proxy of vegetation change,was generally consistent with local precipitation and temperature variations on a centennial-scale before the 15th century.It typically varied from–9.6‰to–6.3‰,indicating climate controlled C3 type vegetation during this period.However,a persistent and marked increasing trend in theδ^13C record was observed since the 15th century,resulting inδ^13C values from–7.7‰to–1.6‰in the next four centuries.This unprecedentedδ^13C change caused by vegetation deterioration cannot be explained by climate change but is fairly consistent with the dramatically increasing population and farmland in Shandong.We suggest that the increasing deforestation and reclamation in central Shandong began to affect vegetation in the mountain region of central Shandong since the 15th century and severely destroyed or even cleared the forest during the 16th–18th century.

Characterization of recombinant humanized collagen type III and its influence on cell behavior and phenotype

Collagen made a tremendous impact in the field of regenerative medicine as a bioactive material.For decades,collagen has been used not only as a scaffolding material but also as an active component in regulating cells’biological behavior and phenotype.However,animal-derived collagen as a major source suffered from problems of immunogenicity,risk of viral infection,and the unclear relationship between bioactive sequence and function.Recombinant humanized collagen(rhCol)provided alternatives for regenerative medicine with more controllable risks.However,the characterization of rhCol and the interaction between rhCol and cells still need further investigation,including cell behavior and phenotype.The current study preliminarily demonstrated that recombinant humanized collagen type III(rhCol III)conformed to the theoretical amino acid sequence and had an advanced structure resembling bovine collagen.Furthermore,rhCol III could facilitate basal biological behaviors of human skin fibroblasts,such as adhesion,proliferation and migration.rhCol III was beneficial for some extracellular matrix-expressing cell phenotypes.The study would shed light on the mechanism research of rhCol and cell interactions and further understanding of effectiveness in tissue regeneration.

Characterization of tub_4^(P287L), a β-tubulin mutant,revealed new aspects of microtubule regulation in shade

When sun plants, such as Arabidopsis thaliana, are under canopy shade, elongation of stems/petioles will be induced as one of the most prominent responses. Plant hormones mediate the elongation growth. However, how environmental and hormonal signals are translated into cell expansion activity that leads to the elongation growth remains elusive. Through forward genetic study, we identi-fied shade avoidance2 (sav2) mutant, which contains a P287L mutation in b-TUBULIN 4. Cortical microtubules (cMTs) play a key role in anisotropic cell growth. Hypocotyls of sav2 are wild type-like in white light, but are short and highly swollen in shade and dark. We showed that shade not only induces cMT rearrangement, but also affects cMT stability and dynamics of plus ends. Even though auxin and brassinosteroids are required for shade-induced hypocotyl elongation, they had little effect on shade-induced rearrangement of cMTs. Blocking auxin transport suppressed dark phenotypes of sav2, while overexpressing EB1b-GFP, a microtubule plus-end binding protein, rescued sav2 in both shade and dark,&nbsp;suggesting that tub4P287L represents a unique type of tubulin mutation that does not affect cMT function in supporting cell elongation, but may affect the ability of cMTs to respond properly to growth promoting stimuli.

Large-scale roll-to-roll printed,flexible and stable organic bulk heterojunction photodetector

A flexible and stable photodetector shows great potential applications in intelligent wearable devices,health monitoring,and biological sensing.The high-output fabrication of flexible and stable photodetector via the large-scale printing process would accelerate its commercialization.Herein,a high performance,flexible organic bulk heterojunction(BHJ)photodetector with good stability is designed and fabricated via a large-scale roll-to-roll(R2R)micro-gravure printing technique on polyethylene terephthalate(PET)or paper substrate,in which the organic BHJ active layer is structured with[6,6]-phenyl C_(61)butyric acid methyl ester(PCBM)and a donor-acceptor copolymer,i.e.,employing 4,8-bis(2-ethylhexylthiophene)benzo[1,2-b;3,4-b′]dithiophene(BDTT)as the donor unit and 5,8-bis(5-thiophen-2-yl)-6,7-difluoro-2,3-bis(4-ethylhexyloxy-1-mata-luorophenyl)quinoxaline(ffQx)as the acceptor unit(PBDTT-ffQx).The PBDTT-ffQx/PCBM BHJ photodetector shows a broad photoresponse in ultraviolet and visible light,a high detectivity(D^(*))value up to 6.19×10^(11)Jones,and an excellent Iphoto/Idark as high as 5.6×10^(2).It exhibits excellent flexibility and stability.Its performance parameters could maintain over 80%of original values after bending 10,000 cycles or exposing in ambient condition(humidity~50%,temperature~30℃)for 50 days without any encapsulation.More importantly,the R2R micro-gravure printed PBDTT-ffQx/PCBM BHJ active layer is great homogeneous,and the responsivity(R)values of photodetector arrays show a very narrow distribution.The research results show that a high-performance PBDTT-ffQx/PCBM BHJ photodetector with well reliability and reproducibility can be fabricated via the R2R micro-gravure printing technique,which provides an available strategy for fabricating large-area and flexible electronic and optoelectronic devices.

Synthesis of photo-reactive poly(vinyl alcohol)and construction of scaffold-free cartilage like pellets in vitro

Photo-reactive poly(vinyl alcohol)(PRPVA)was synthesized by introduction of phenyl azido groups into poly(vinyl alcohol)(PVA)and applied for surface modification.PRPVA was grafted onto cell culture plate surface homogeneously or in a micropattern.Human mesenchymal stem cells(hMSCs)cultured on cell culture plate surface and PVA-modified surface showed different behaviors.Cells adhered and spread well on cell culture plate surface,while they did not adhere on PVA-grafted surface at all.When hMSCs were cultured on PVA-micropatterned surface,they formed a cell micropattern.Cells formed pellets after cultured on PVA homogeneously modified surface in chondrogenic induction medium for 2 weeks.The pellets were positively stained by hematoxylin/eosin,safranin-O/fast green and toluidin blue,and they were also stained brown by Type II collagen and proteoglycan immunohistological staining.Real-time PCR analysis was conducted to investigate the expression of colI,colII,colX,aggrecan and sox9 mRNA.Results of gene expression were in agreement with those of histological and immunohistological observations.These results indicated that hMSCs cultured on PVA-modified surface performed chondrogenic differentiation,and it was possible to construct scaffold-free cartilage like pellets with PVA-modified surface in vitro.

80 years education of aerospace science and technology in Tsinghua University

The development of aerospace science and technology largely relies on the education and academic contribution of students in universities covering aerospace science and technology. The School of Aerospace Engineering of Tsinghua University, with a history of eighty years since the set-up of its Department of Aeronautical Engineering in 1938, graduated 5273 undergraduate students, 1939 master students and 931 Ph.D. students. This paper provides an overview and analysis of the data related to undergraduate, master and Ph.D. students of this school. These data include the historical evolution of number of students and the actual status of students like their various interests and academic performance. The data and information shared in this paper may be useful for comparative study and for those who need primitive data to study relevant issues such as mental health of students, promotion of gender balance and educational improvement.

Characterization of recombinant humanized collagen type Ⅲ and its influence on cell behavior and phenotype

Collagen made a tremendous impact in the field of regenerative medicine as a bioactive material.For decades,collagen has been used not only as a scaffolding material but also as an active component in regulating cells'biological behavior and phenotype.However,animal-derived collagen as a major source suffered from problems of immunogenicity,risk of viral infection,and the unclear relationship between bioactive sequence and function.Recombinant humanized collagen(rhCol)provided alternatives for regenerative medicine with more controllable risks.However,the characterization of rhCol and the interaction between rhCol and cells still need further investigation,including cell behavior and phenotype.The current study preliminarily demonstrated that recombinant humanized collagen typeⅢ(rhColⅢ)conformed to the theoretical amino acid sequence and had an advanced structure resembling bovine collagen.Furthermore,rhColⅢcould facilitate basal biological behaviors of human skin fibroblasts,such as adhesion,proliferation and migration.rhColⅢwas beneficial for some extracellular matrix-expressing cell phenotypes.The study would shed light on the mechanism research of rhCol and cell interactions and further understanding of effectiveness in tissue regeneration.