INTRODUCTION

The use of dental ceramics is now increasing for restoring damaged,decayed,or missing teeth due to improvements in the physical properties of ceramics and advances in computer-aided design and computer-aided manufacturing(CAD/CAM)technology.1–3Dental ceramics for all-ceramic restorations can be classified into two main categories by their compositions:glassbased and crystalline-based.4Crystalline-based ceramics such as zirconia and alumina have stronger physical properties but poorer esthetic and bonding properties compared with glass-based ceramics.5,6Glass-based ceramics show relatively better esthetics and bonding with resin cement,and therefore,they are mainly applied for reconstructing anterior teeth such as crowns and laminates and for intracoronal restorations in posterior teeth such as inlays and onlays.4,7Feldspathic ceramic,a traditional glassbased ceramic,has been used for decades with good esthetic properties7.In the meantime,a leucite-reinforced glass ceramic,Empress®1,was introduced in the late 1980s through many researchers’and manufacturers’efforts to develop a ceramic that was more resistant to crack propagation.8A lithium disilicatereinforced glass ceramic(IPS Empress®II,now called IPS e.max®),another enhanced glass-based ceramic,has now gained popularity as a material for restoring anterior and posterior teeth from laminates,inlays,and onlays to single crowns due to its superior physical properties.9,10Monolithic ceramic blocks of all these glass-based ceramics are now available as CAD/CAM restorative materialsforcliniciansto choose based on theirdesired restorations and mechanical and optical properties.

Although lithium disilicate ceramic,e.max,has better mechanical strength than leucite-reinforced ceramic,Empress,and thus clinicians tend to prefer e.max to Empress,4a ceramic with higher mechanical strength might not necessarily ensure better clinical performance.The clinical performance of ceramic restorations depends on adequate cementation to dental hard tissue with resin cement as well as the good mechanical properties of ceramic materials.3,11The polymerization of resin cement under ceramic restorations is one of the most important factors in obtaining its optimal physical properties.Inadequate polymerization can yield poorer physical properties and faster degradation of cement finish line by acid,ultimately causing the de-bonding of restorations.12,13 Many previous studies reported that sufficient light curing is essential for achieving high polymerization even in dual-cured resin cements.12–16

The amount of light transmitted through ceramic restorations depends on the light intensity of the light curing unit and the thickness,type,and translucency of the ceramic materials.17,18 Although a number of studies have shown that increased thickness and darker shades of ceramic materials act as optical barriers to light reaching the cement,19–21the level of light transmittance through dental ceramics and the consequent effects on the polymerization of resin cement have not yet been fully investigated.In particular,few studies have investigated the effects of different ceramic compositions(feldspathic,leucitereinforced,and lithium disilicate-reinforced)and translucency(high and low)with identical shades on the light transmittance and degree of polymerization of resin cement.

Therefore,the objective of this study was to investigate the light transmittance through glass-based ceramics of identical shades with different compositions,translucency values,and thicknesses and to compare the degrees of polymerization of resin cement under those ceramic materials.The null hypothesis was that the light transmittance and degree of conversion(DC)of the resin cement through glass-based ceramics of identical shades would not be influenced by composition,translucency,or thickness.

RESULTS

Translucency parameter

Translucency parameter.We evaluated the translucency of the ceramicplatesemploying thetranslucencyparameter.We measured each plate’s color with white and black backings using a colorimeter(Minolta Chroma Meter CR-321,Minolta Co.,Ltd.,Osaka,Japan)in triplicate.For each color measurement,the values were expressed as CIELAB parameters(L*,a*,and b*).L*is lightness,where 100 is completely white and 0 is completely black,and a*and b*are red-green and yellow-blue chromatic coordinates,respectively.A positive a*or b*value represents a red or yellow shade,respectively.36Light source illumination corresponded to average daylight(D65).The colorimeter was calibrated before each measurement period using the white calibrating sample supplied by the manufacturer.The white and black backgrounds used in this study were white(L*=91.53,a*=0.87,b*=3.47)and black(L*=3.92,a*=1.50,b*=−0.57)ceramic tile.

Light transmittance rates and light spectrum profiles through the ceramic plates

The light transmittance rates(%)for each ceramic specimen at the different thickness are also shown in Table 1.Transmitted light(%)showed significantdifferencesbyceramicplate type and thickness(P＜0.05),and the interactions between ceramic type and thickness were also statistically significant(P＜0.05)(Table 2).In general,light transmittance wasmore effective in the high-rather than low-translucency ceramics.Emp_HT showed the highest transmittance rate and Emx_LT showed the lowest.Emp_LT transmitted significantly less light than Emx_HT or VITA.The light transmittance rate was less than 30%even at 0.5mm thickness,and it decreased exponentially as the ceramic thickness increased.The lighttransmittance rate and translucency parameter had a very strong positive correlation(r=0.993).

The representative light spectrum profiles emitted through the ceramic plates are depicted in Fig.1.The peak spectrum was observed at 410 nm and 460nm.Emx_LT showed the lowest peak value,and Emp_HT showed the highest(Fig.1a),and as the ceramic thickness increased,the height of the peak decreased.When the Emp_LT was 4mm thick,the peak spectrum at 410nm was hardly observed(Fig.1b).

膨润土加工产品应用领域非常广，现大宗应用领域为冶金球团、铸造、石油钻采，其消耗原矿量占到全部膨润土开采资源量的约75%，这3大应用领域产品加工根据原矿品质，一般采用原矿直接钠化改性—粉磨等工艺，或采用配矿均化—钠化改性—粉磨等工艺，可生产出满足使用要求的产品，这些加工一般不涉及传统意义的选矿，加工过程仅有少量伴生的硅石进入产品，或磨矿过程中有少量的损失，剔除的硅石等可进一步做建材等原料也能得到利用，原矿利用率(即选矿回收率)实际值也容易达到近100%的较高值。

DC of resin cement

The DC of resin cement according to ceramic type and thickness are shown in Table 3.There were statistical differences by ceramic type and thickness(P＜0.05),and the interactions between the two were statistically significant(P＜0.05)(Table 2).Emp_HT showed the highest DC,and Emx_LT showed the lowest.Emp_HT showed no significant difference from Vita(P＜0.05)but yielded a higherDC than Emp_LT,Emx_HT,and Emx_LT(P＜0.05).Regarding the translucency type,the high-translucency types of Empress showed significantly higherDC than the lowtranslucency types(P＜0.05),but there were no significant differences between the two types in e.max(P＜0.05).Regardless of the material,DCs decreased significantly as the ceramic thickness increased(P＜0.05).

DISCUSSION

The light spectra transmitted through each ceramic plate was recorded using a spectrally resolving fiber optic spectrometer(Avaspec-3648,Avantes,Broomfield,CO,USA),and every measurement was taken 10s after the light was turned on.

In this study,Light transmittance decreased exponentially with increasing ceramic plate thickness,which is consistent withprevious studies.17–19,22–24However,the light transmittance ratio was lower than it was in previous studies;23,24in this study,the ratio was less than 30%even at 0.5mm thickness and less than 5%at 4.0mm(Fig.1b).Kilinc et al.23reported that 40%–50%of light was transmitted through 1mm thick Empress ceramic in various shades,and Moraes et al.24reported that approximately 42%of light was transmitted through 2mm thick Empress shade A3.Zhang et al.22reported that 37,14,and 9%of irradiance was transmitted through 1,2,and 3mm thick e.max ceramics,respectively.In another study,20%of the light was transmitted through 1.5mm thick lithium disilicate ceramic of shade A2.25 Considering that in this study,the light guide tip and photodetector were separated by the corresponding ceramic thickness for measuring the original light emission for each depth(0.5,1.0,2.0,4.0mm),the light transmittance through the ceramics was notably low.If the original light intensity of the light curing unit had been set as the baseline value for all the thicknesses,the transmittance levels in this study would be much lower.Although we are not clear about why transmittance was lower in our study than in previous studies,the differences might have been related to the different shades of ceramic we used and different light curing units.Our having polished one surface of the ceramic plates but leaving the other surface rough could also have caused the different light attenuation conditions in this study.The decreasing light transmittance with increasing ceramic thickness was also reflected in the light spectrum results;the peak light spectrum profiles decreased considerably with increasing ceramic thickness(Fig.1b).In particular,we rarely observed the 410nm peak—one of the light curing unit’s two light emission peaks—in the spectrum through the 4.0mm thick ceramics.The increasing ceramic thicknesses might raise concerns that sufficient polymerization will not be achieved by an additional co-initiator such as trimethylbenzoyl-diphenylphosphine oxide,which absorbs light near the 410nm peak.26As expected,the effect of light attenuation with increasing ceramic thickness was re-confirmed in the present study.Therefore,adequate polymerization of resin cement through thick ceramic plates might be difficult to achieve by lightcuring alone.Use ofdual-cure resin cementis recommended in areas where light attenuation is anticipated to enhance polymerization by chemical curing.17,23,27,28

Table 1.Mean(SD)for translucency parameter and light transmittance rates(%)of different ceramic types and thicknesses

Different superscript(upper case for rows and lower case for columns)indicate statistical significance(P＜0.05)within each dependent variable

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Table 2.Two-way ANOVA results of transmittance values,translucency parameter,and DC according to the ceramic type and thickness

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Fig.1 The representative light-spectrum profiles emitted.a Through the different ceramic types of 2.0 mm thickness and b through different thicknesses of Emp_LT

We purchased five CAD/CAM ceramic blocks in shade A2:hightranslucency and low-translucency types of IPS Empress CAD(Emp_HT and Emp_LT,Ivoclar Vivadent,Schaan,Liechtenstein)for leucite-reinforced glass;high-translucency and low-translucency types of IPS e.max CAD(Emx_HT and Emx_LT,Ivoclar Vivadent)for lithium disilicate glass;and Vita Mark II(Vita Zahnfabrik,Bad Sackingen,Germany)for feldspathic(Table 4).We cut the ceramic blocks into 10mm squares with final thicknesses of 0.5,1.0,2.0,and 4.0mm using a 3-axis cutting machine(Steptool,Harig,IL,USA).The prepared IPS e.max CAD plates were prepared to havefinal property.We polished the top surfaces of all plates with 1μm grit diamond particles with a lapping machine(SPL-15,Okamoto Corp.,Santa Fe Springs,CA,USA)in order to simulate the polished surfaces of ceramic restorations.In this way,we fabricated three ceramic plates for each thickness of each ceramic group.

Table 3.Mean(SD)for degree of conversion(%)of light-cured resin cement under different ceramic types and thicknesses

Different superscript(upper case for rows and lower case for columns)indicate statistical significance(P＜0.05)

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雷公藤内脂醇的浓度为5时，培养24 h和48 h的抑制作用差异无统计学意义(P>0.05)；雷公藤内脂醇浓度为10、20、40 nmol/L时，培养24 h和48 h的抑制作用，差异有统计学意义(P<0.05)；雷公藤内脂醇的浓度为80、160 nmol/L时，培养24 h和48 h的抑制作用差异，明显有统计学意义(P<0.05)。见表1。

从表1中数据可以得出，采用振动压路机碾压后的大粒径沥青混合料基层压实度平均值为98.6%，满足规范中要求，表明采用振动压路机对大粒径沥青混合料基层进行碾压是可行的。

In the present study,the DC of resin cement differed significantly by ceramic type and thickness;the ceramic plates that transmitted more light led higher DCs of the underlying resin cement.Emp_HT presented the greatest DC of resin cement,and Emx_LT yielded the lowest DC,indicating the different light transmittance levels.A number of studies evaluated the degree of underlying resin cement polymerization at various ceramic thicknesses and reported conflicting results.Moraes et al.24 detected no significant differences in DC of dual-cured resin cements in 0.7,1.4,and 2.0mm thick ceramics,and Passos et al.32 also reported no significant differences in hardness between 1.0 and 3.0mm thick ceramic.By contrast,Bansal et al.33reported a significant decrease in DC of resin cement in 4mm thick leucitereinforced ceramic or IPS e.max Press compared with 2 or 3mm plates.Similarly,Oliveira et al.34found that less DC of resin cement was shown under 3.0mm e.max than under 1.5mm e.max,and Runnacles et al.21found that less resin cement was polymerized under 2.0mm than 0.5mm feldspathic porcelain.These contradictory results about the effects of ceramic thickness on the degree of polymerization of underneath resin cement might be attributed to different experimental conditions such as ceramic specimen thickness,type of resin cement material,the light curing unit,and post-polymerization effects.There have been a number of studies on resin cement post-polymerization during storage after light curing.In previous studies,the DC and hardness of dualcure resin cement increased as post-irradiation time increased.24,35 We measured the DC over the course of time up to 24 h(data not shown),and we detected a slight increase in DC at 24 h in all groups that maintained the between-group differences.However,the increase in DC after light curing was insignificant,we believe,which is because polymerization was induced solely by light cure with no chemical cure.

合理利用安全人机工程学的原理对设备、设施进行优化。注意设备的保养与维护，编制严格、多层次设备的维修和检修规程；尽量采用具有互锁装置的设备，以有效避免人员误操作；对于特殊作业的设备必须满足相应的安全性能，如水下设备须达到相应密封要求，临电全部采用三相五线制，用电设备有漏电保护、接地，同一水平、垂直工作面上下电源实行单向联锁供电装置；合理利用人机工程学中的视觉原理设计安全警示牌，对于特殊环境设置检测装置、联动光电报警装置等，积极探索试行安全“目视化”管理。

Although we tried to simulate the clinical surface conditions of ceramic restorations by polishing the top surface and leaving the bottom surface unpolished considering the CAD/CAM fabrication procedure,one limitation of this study is that the bottom was not treated with hydrofluoric acid and silane which might change the light penetration and the DC of resin cements.The influence of surface treatmentson thelightpenetration needsto be investigated in the future.Another limitation of this study is that the DC measurement was performed not in the body temperature but in the room temperature,which could lead a different DC results from the real clinical situation.

Within the limitations of this study,the glass ceramic type and thickness significantly influenced the light transmittance and light spectra and the DC of resin cement underneath ceramics of the same shade.It seems that the choice of a ceramic type should not be based solely on strength because the clinical performance relates not only to the ceramic’s strength but also to the physical properties of the resin cement beneath the ceramic,for which light transmittance is the main influence.Additional studies on other physical resin cement properties such as bond strength,microhardness,and fracture resistance should be conducted to confirm the effect of ceramic type on the clinical performance of ceramic restorations.Moreover,studies are needed to determine the behavior of bonded ceramic restorations in oral environments.Long-term clinical studies will eventually produce clear evidence for checking differing clinical performance by ceramic type.

MATERIALS AND METHODS

Fabrication of ceramic plates

Ceramic type was also a determining factor for both light transmittance and light spectrum profiles.Emp_HT showed the highest light transmittance and light spectrum and Emx_LT showed the lowest for each ceramic thickness.There has been little research concerning the effectsofceramictype on transmitted light,and thus,it is difficult to compare the results of this study with those of previous studies.A plausibleexplanation for the differences in light transmittance by ceramic type is the different crystalline structures of ceramics including the compositions of filler and matrix.29E.max is composed of 70%lithium disilicate by volume,which consists of many small,randomly oriented,interlocking plate-like crystals;light transmission through lithium disilicate ceramic is interrupted by the platelike crystal.4Vita Mark II is a feldspathic porcelain that contains less leucite crystal and more glass,and therefore light attenuation by a crystal component is relatively low.4Given the fact that the ceramic type can cause a significant difference in light transmittance,this difference might have to be considered when choosing ceramic types,especially in restoring deep cavities in which the light transmittance is hindered.

Table 4.Ceramic materials and resin cement used in this study

Material(code) Basic chemical structure(chemical components) Manufacturer Lot no.IPS Empress CAD HT(Emp_HT) Leucite-reinforced glass ceramic(SiO2,BaO,Al2O3,CaO,CeO2,Na2O,K2O,B2O3,TiO2)Ivoclar Vivadent,Schaan,Liechtenstein P17582 LT(Emp_LT) L41778 IPS e.max CAD HT(Emx_HT) Lithium disilicate glass ceramic(SiO2,Li2O,K2O,P2O5,ZrO2,ZnO,Al2O3,MgO)Ivoclar Vivadent,Schaan,Liechtenstein P20492 LT(Emx_LT) P43213 Vita Mark II(Vita) Fine-particle feldspathic ceramic(SiO2,Al2O3,Na2O,K2O,CaO,TiO2)Vita Zahnfabrik,Bad Säckingen,Germany 17510 Variolink N Base paste:Bis-GMA,UDMA,TEGDMA Ivoclar Vivadent,Schaan,Liechtenstein U11257

Measurement of translucency,light transmittance,and light spectra through the ceramic plates

The translucency parameters for each ceramic specimen at the different thicknesses are shown in Table 1.The translucency parameter showed significant differences by ceramic plate type and thickness(P＜0.05),and the interactions between ceramic type and thickness were statistically significant(P＜0.05)(Table 2).Emp_HT showed the highest value of translucency parameter and Emx_LT showed the lowest in every thickness.Both the hightranslucency types of Empress and e.max specimens showed higher translucency parameter values than the low-translucency types,and regardless of material,thicker specimens had lower translucency parameter values.

The translucency parameters of the materials were calculated in the differing thicknesses using the following equation:30,31

郭熙《早春图》以立卷之形表现北方之景，景物多却不拖累，空间的结构，自然而有趣，构建十分有序。近处，河湖溪涧序列，松林高耸，行人悠闲岸边；中景，山山应对，林木葱茏；远景，云雾缥缈，路径曲折，画面富有纵深感。《早春图》的画面内容需要决定了其空间形式，作者为了达到万里江山尽收眼底的目的，多采用移动的角度，使图画上的事物向左右、上下方向自由发展。它突破了时间和空间，巧妙地将不同的时间、空间中的景物集中表现在一幅画里，利用这种方法的好处就是使得画面容量更宽阔，意境更加深远。郭熙创作《早春图》体现了“步步移，面面观”的空间构建方法，这也正是郭熙山水画所展现出来的空间的奥妙所在。

where the subscriptsWandBrefer to the CIELAB values for each specimen on white backing and black backing,respectively.

所以，山东省政府应在金融、财政等方面制定创新制度，着力支持设计、研发、营销、培育品牌等对结构升级优化有重大影响的核心环节，积极推动制造业企业的自主创新。通过持续推进科研经费管理改革和科技成果奖励评价，着重激励、引导创新要素汇聚于企业，加速构建围绕企业、政府、高校、科研单位等技术的创新体系，促使科技研发、经济市场更好地融合和科研成果更好更快地被转化，进而实现科研成果的产业化。

Light transmittance rate and light spectra through the ceramic plates.We measured the power(mW)of a conventional LED light-curing unit(Bluephase G2,IvoclarVivadent)using a photodetector(918D-SL-OD3,Newport Corp.,Irvine,CA,USA)attached to an optical power meter(Model 1918-C,Newport Corp.).The light intensity(mW·cm−2)was calculated as the ratio of the emitted power(mW)to the area of the light guide tip(cm2).The light intensity of the LED light-curing unit was 678 mW·cm−2.We then measured the light intensity transmitted through each ceramic plate(0.5,1.0,2.0,and 4.0mm thick)in the five different ceramic materials.The light guide tip was placed in direct contact with the ceramic plates.

The lighttransmittance rate (%)wascalculated asthe percentage ratio of the light intensity through a ceramic plate to the light intensity without the plate.When we measured the intensity without the plate,the photodetector was separated from the light guide tip by the corresponding thickness of the ceramic plate.Every measurement was taken 10 s after the light was turned on in order to obtain stable light intensity.We also took triplicate measurementsperspecimen and calculated the averages.

This study evaluated the influence of ceramic type and thickness on the light transmittance rates and assessed the DCs of the lightcured resin cements beneath the ceramics.A number of studies have investigated the effects of different shades and thicknesses on the light transmittance and the DCs of the underneath resin cement for the same ceramics;16–18,22however,researchers have rarely investigated the effects of ceramic type in same shade on the light transmittance and the polymerization of resin cement.Wespeculated thatthe cements’lighttransmittanceand polymerization might differ according to the type of dental ceramic even in the same shade.Clinically,successful ceramic restorations require optimal physical properties of resin cement through adequate polymerization as well as the mechanical strength of the ceramic materials,which is the reason that light transmittance through ceramics should be considered.In the present study,we found that both ceramic type and thickness significantly influenced the light transmittance and the DC of the resin cement through the ceramic.Therefore,the null hypothesis of this study was rejected.

Because highly translucent material is expected to have high light transmittance,we should have checked the linear relationship between the two.We obtained the light transmittance ratios by directly measuring the light irradiance,and we obtained the translucency parameters by measuring color against different backgrounds using a colorimeter.30,31To our surprise,the light transmittance and translucency parameter had a nearly perfect positive linear correlation in spite of different measuring methods(Pearson’s correlation coefficient=0.993),which has not been reported in previous studies to the best of our knowledge.Measuring light transmittance requires an expensive photo detecting machine,and it is a cumbersome procedure to obtain precise values,whereas the translucency parameter can be attained relatively quickly and easily with a simple colorimeter.Therefore,the translucency parameter appears to be an easier way of checking the light transmittance of restorative materials.

Hcy属于蛋氨酸循环的中间产物，且临床上已有不少研究报道证实，血浆Hcy水平的升高可促进动脉粥样硬化，同时促进动脉以及静脉血栓形成，从而导致心脑血管疾病的发生［5-8］。

We used one ceramic plate of the three plates we prepared for each thickness of each ceramic to measure the DC of resin cement because the differences in values among the three plates in each group were statistically ignorable for the translucency parameter and light transmittance.

DC of resin cement underneath ceramic plate

The DCs for the resin cements underneath the ceramic plates were examined using Fourier transform infrared spectroscopy(FTIR)(1600 Series;PerkinElmer,Wellesley,MA,USA).We used only base paste from the base and catalyst of the Variolink N(Ivoclar Vivadent)to evaluate DC solely by light cure.We placed the base paste between two polyester strips,covered each one with a glass slide,and then pressed each firmly against another glass slide base to make a film as thin as possible;the cement film with the two polyester strips was approximately 50 μm thick in all specimens.We fabricated five resin cement films for each ceramic plate,placing each plate over a cement film with the polished surface of the plate facing upward.We placed the light guide tip of the light-curing unit directly onto the polished ceramic surface and light-cured the sample for 40 s.We performed the light curing directly on the resin cement films for the DC control group,which were not influenced by the ceramic plates.Fabrication of resin cement films and measurement of DC by FT-IR was performed in room temperatureofdarkroom to avoid theadditional polymerization progress by ambient light.All resin cement films were also kept in aluminum foil-covered petri dish until DC measurement.

Infrared spectrawere collected between 1700cm−1and 1500cm−1in transmission mode under 4cm−1resolution and 30 scans.We calculated the DC using the standard baseline method,that is,by the changes in the ratios between the absorbance peaks corresponding to the aliphatic(1637cm−1)and aromatic(1608cm−1)carbon double bonds prior to and after polymerization.We used the absorbance intensities of aromatic C=C as internal references because the intensity does not change during the polymerization reaction.The DC was determined using the following equation:

where abs(C=Caromatic)is the height of the aromatic C=C bond peak and abs(C=Caliphatic)is the height of the aliphatic C=C bond peak for both cured and uncured resin cements.

Statistical analysis

变化环境下，我国干旱应在实地观测实验以及水循环、水化学、水生态和水沙过程机制识别的基础上，构建干旱指标和模拟预测系统，形成层次化的综合应对体系。从长期宏观发展战略层次上，构建与水资源承载能力相适应的经济社会发展模式（重点种植结构和工业产业结构），可从根本上减少干旱危害；在中尺度时段上，优化水资源调配体系是干旱综合应对的重点；在短尺度时段上，需制定有效应急预案，保障应急水源。

We conducted two-way analysis of variance to evaluate the differences in the ceramics’translucency parameters and light transmittance and the DC of the resin cement according to the ceramic type and thickness.We conducted multiple comparisons using the Bonferroni test,and we also ran Pearson’s correlation tests between the translucency parameter and light transmittance rate.For all of the analyses,we used the statistical software SPSS for Windows,v23.0(IBM Corp.,Chicago,IL,USA)with a 95%level of confidence.

CLINICAL RELEVANCE

Light transmittance differs by the glass ceramic type even in the same shade,which might significantly influence the clinical performance of the resin cements underneath ceramic restorations.

油茶苗木培养中，播种育苗是其中一种育苗方式。在播种育苗中，要选择地势平坦和避风向阳以及排水良好的微酸性土壤。在播种之前做好苗床，并且在苗床中使用基肥，在播种完成之后需要在覆盖一层肥土和薄草，从而更好的提升种子发芽率。

ACKNOWLEDGEMENTS

This study was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute(KHIDI),funded by the Ministry of Health and Welfare,Republic of Korea(HI14C1817).

ADDITIONAL INFORMATION

利用无人机机动性好、操作方便、成本低廉、无人员伤亡等特点，在暴雨或者山洪等极端气候条件下，派出无人机对矿山尾矿库、堆渣场、边坡等进行监测，在发生次生地质灾害的前期及时进行观测，发出预警信号。

Conflict of interest:The authors declare that they have no conflict of interest.

一些普通高校继续教育学院并没有意识到举办社区教育的重要性、紧迫性，还停留在成人学历教育层次上，对服务社区成员的社区教育存在着轻视、歧视和无视的错误认识。一些高校继续教育学院虽然认识到社区教育的重要性，却找不到介入社区教育的合适方式、途径和模式，无场地、无师资、无经费、无课程，思想上处于观望，行动上难以向前迈进。

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