A Self-Adapting and Efficient Dandelion Algorithm and Its Application to Feature Selection for Credit Card Fraud Detection

A dandelion algorithm(DA) is a recently developed intelligent optimization algorithm for function optimization problems. Many of its parameters need to be set by experience in DA,which might not be appropriate for all optimization problems. A self-adapting and efficient dandelion algorithm is proposed in this work to lower the number of DA's parameters and simplify DA's structure. Only the normal sowing operator is retained;while the other operators are discarded. An adaptive seeding radius strategy is designed for the core dandelion. The results show that the proposed algorithm achieves better performance on the standard test functions with less time consumption than its competitive peers. In addition, the proposed algorithm is applied to feature selection for credit card fraud detection(CCFD), and the results indicate that it can obtain higher classification and detection performance than the-state-of-the-art methods.

Mechanism of Herbal Medicine and Food Dandelion Effects May be Related to RNA or DNA Regulation: A Review

Background: A dandelion is a common plant with a global growth distribution that has been used as a medicinal and food with no adverse effects. Purpose: In this article, the products and effects of dandelions are reviewed to help further in-depth studies and develop more products derived from dandelions in the future. Method: The literature about dandelion in various databases such as Pubmed is searched. Results: Dandelions have many effects, such as virus inhibition, anti-tumor activity, nutritional value, anti-aging, potential as a vaccine and alleviation of heat stress. The mechanism underlying these effects is analyzed and it was found that dandelions were regulated by RNA or DNA. Conclusion: As a medicinal and food, dandelions are safe and have many effects. Many products derived from dandelions have been developed. The metabolic regulation is related with ribonucleic acid or possibly deoxynucleic acid. Further in-depth studies should be conducted on the regulation of dandelions through RNA or DNA. There will likely be more products derived from dandelions in the future.

Effect of Dandelion(Taraxacum mongolicum Hand.-Mazz.)Intercropping with Different Plant Spacing on Blight and Growth of Pepper(Capsicum annuum L.)

Intercropping of crops that can secrete bacteriostatic active substances can not only inhibit the occurrence of disease but also have an important effect on plant growth.However,the effects of dandelion intercropping on pepper blight control and pepper growth remain unclear.In this study,the control effect of dandelion on pepper blight was studied by inoculating the pepper leaves with Phytophthora infestans,and it also discusses the correlation of the occurrence of pepper epidemic disease with the pepper canopy environment,soil environment,pepper photo-synthesis,and yield index.The results showed that best plant distance for dandelion intercropping was 20 cm(P20),and the control effect reached 43.31%.As compared to the CK,SOD enzyme,POD enzyme,and PAL enzyme were significantly up-regulated during the growth of pepper;chlorophyll content in pepper leaves was significantly increased;photosynthetic characteristics were significantly increased;stem diameter and yield of crop pepper were effectively improved;and the quality of the pepper product was better,but intercropping dandelion resulted in a significant decrease of nutrients in the soil environment of pepper,so a reasonable intercropping distance was needed.The correlation analysis shows that the incidence of pepper blight(A)was significantly positively correlated with soil temperature(Q),intercellular carbon dioxide(L),and canopy air temperature(O).The incidence of capsicum blight(A)was significantly negatively correlated with chlorophyll content(F),net photo-synthetic rate(K),stomatal conductance(M),ww rate(N),soil sucrase activity(W),vitamin C(AB),and leaf PAL enzyme(J).Finally,it was deduced that intercropping dandelion could effectively control the occurrence of pepper blight while also demonstrating a complex interaction with the pepper growing environment.

Effective anti-inflammatory phenolic compounds from dandelion:identification and mechanistic insights using UHPLC-ESI-MS/MS,fluorescence quenching and anisotropy,molecular docking and dynamics simulation

This novel study identifi es the effective anti-inflammatory phenolic compounds in dandelion and provides mechanistic insights into their interactions with receptor proteins(toll-like receptor 4,TLR4;co-receptor myeloid differentiation protein-2,MD-2)using UHPLC-ESI-MS/MS,lipopolysaccharide(LPS)-stimulated THP-1 cell line,fluorescence quenching and anisotropy,molecular docking(single ligand and multi-ligand docking)and molecular dynamics simulation.A 50%aqueous methanol extract had a greater anti-inflammatory effect and higher chicoric acid content,compared with the 100%water and 100%methanol extracts.Chicoric acid,chlorogenic acid,methylophiopogonone A,caffeic acid,gallic acid monohydrate and 4’-O-demethylbroussonin A had relatively high binding energies and contents in all extracts.Chicoric acid competed with chlorogenic acid,4’-O-demethylbroussonin A and quercetin for MD-2.Among dandelion’s phenolics,chicoric acid most effectively hindered TLR4-MD-2 complex formation,with a quenching constant of 0.62×10^(6) L/mol for MD-2 or TLR4 at 320 K,and binding energies of-6.87 and-5.97 kcal/mol,respectively,for MD-2 and TLR4.

Hepatoprotection by dandelion (Taraxacum officinale) and mechanisms

The protection of the liver as an essential organ in the body against oxidative stress and deleterious compounds has been the subject of recent investigations.Among different compounds,medicinal plants play an important role due to their hepatoprotective effects.Taraxacum officinale or"common dandelion"is a popular plant that has been traditionally used for its hepatoprotective effects.Currently,there are limited clinical studies on its hepatoprotective effects.The aim of this review article is to evaluate the hepatoprotective effects of dandelion and its mechanism of action.We reviewed literature up to July 2019 on"Taraxacum officinale"or"dandelion"and hepatoprotection.Currently available pharmacological studies indicate that dandelion extracts have hepatoprotective effects against chemical agents due to its antioxidant and antiinflammatory activities.The anti-inflammatory effects of dandelion,the prebiotic effects of its oligofructans,inhibitory effects against the release of lipopolysaccharides and fasting induced adipose factor,digestive enzymes,and enhancing effects of lipogenesis,reduce lipid accumulation and liver inflammation,which directly or indirectly improve the liver functions.Given emerging evidence on hepatoprotective effects of dandelion,designing large human clinical studies is essential.

Dandelion格网：一种新型立体格网设计方案

随着空间探索技术和数据获取手段的飞速发展，对地球的研究已经不仅仅局限于地表，而是趋向于海陆空地下一体化发展。因此，全球离散格网开始由球面格网发展到球体格网。然而，现阶段球体格网单元与单元之间的联系比较复杂。于是，一种新的三维立体剖分格网——Dandelion格网的设计方案经探讨提出。Dandelion格网仿蒲公英结构，从中心点发射线构成球面单元部分，从球心发射线截取它的径向距离，从而构成一个单元结构体。由于其特殊构造，单元之间的联系相对其他格网更加明朗简单。本文重点对Dandelion格网的构建方案进行了深入研究。

基于Dandelion编码生成有界树宽CP-nets

针对条件偏好网络(CP-nets)图模型在进行推理运算时的高时间复杂度的问题,提出了一种基于Dandelion编码生成有界树宽的CP-nets(BTW-CP-nets Gen)算法。首先,通过Dandelion编码与树宽为k的树结构(ktree)之间的双向映射原理推导出Dandelion编码与k-tree之间的解码与编码算法,实现编码与树结构的一对一映射;其次,利用k-tree来约束CP-nets结构的树宽,并利用k-tree的特征树得到了CP-nets的有向无环图结构;最后,利用离散多值函数的双射计算出各CP-nets结构节点的条件偏好表,然后针对生成的有界树宽CP-nets进行占优查询检测。理论分析和实验数据表明,与Pruffer编码生成k-tree(Pruffer code)算法相比,BTW-CP-nets Gen算法的运行时间在生成简单结构和复杂结构时的下降幅度分别为21.1%和30.5%;而BTW-CP-nets Gen算法所生成的图模型在进行占优查询时的节点遍历比在简单结构和复杂结构上分别提高了18.48%和29.03%。BTW-CP-nets Gen算法在更短的时间内,占优查询时遍历的节点率更高。可见,BTW-CP-nets Gen算法在图模型的推理中能够有效提高算法效率。

Research Progress of Anti-tumor Active Ingredients in Dandelion

As a traditional Chinese herb,dandelion,containing complicated active ingredients which includes polysaccharide,flavonoid,terpene,pigment,phytosterol,coumarin,organic acid and etc,plays significant roles in various physiological activities in organisms.The active ingredients generally interfere in signal transduction of cancer cells,regulate cell cycle and apoptotic protein expression,inhibit cancer cells proliferation and migration and etc,which effectively restrains tumor development and deterioration.This article summarizes the anti-tumor mechanism of five active ingredients in dandelion through paper reading which provides thoughts and references for anti-tumor research.

Impact of the aqueous extract of dandelion, probiotic and their synbiotic on male lamb’s testicular histopathology relative to semen characteristics

This study aimed at investigating effects of dandelion/probiotic on the testis histology and semen characteristics of male lambs. Twelve prepuberal Noemi male lambs (2 ± 0.4-month-old and 20 ± 3.5 kg B.W) were randomly allocated into four groups. Animals in group 1 were controlled, orally given normal saline as the same schedule of treated animals. In group 2 animals were given daily oral 50 ml of an aqueous extract of dandelion leaves. In group 3 animals were given a daily 50 ml of cow’s milk probiotics, and in group 4 animals were given 50 ml of a 1:1 mixture (dandelion extract: probiotic). Animals were treated for 8 consecutive weeks. At puberty, semen ejaculates were collected weekly for further 10 weeks. Thereafter, animals were sacrificed and testicles were obtained, weighed and a histopathological study was performed on the testis. Results revealed that oral administration of the dandelion aqueous extract to prepuberal lambs exhibited disturbances in the histological architecture of the testicular semeniferous tubules. Additionally, dandelion resulted in edematic interstitial tissues with evident vaculations. These deteriorations were reflected in less spermatogenesis (i.e. less sperm concentration and ejaculate volume by 10% and 20%, respectively than controlled group). Also, the percentage of sperm progressive motility was lower (P < 0.05) and dead sperm was higher (P < 0.05) in rams given dandelion than control. Administration of probiotic hasn’t revealed a change in the seminiferous tubules architecture, however, very little vaculation with rare edema was observed. Administration of the synbiotic mixture revealed intermediate histopathological appearances. The highest sperm concentration, testosterone concentration and advanced motility were obtained when probiotic was administered. In conclusion, although dandelion cures some hepatic malfunctions in human, caution must be taken into consideration of the frequent ingestion of dandelion for its harmful effect on male fertility.

Introduction and Selection of Dandelion Varieties under the Forest

[Objectives]To select dandelion varieties suitable for forest land in Beijing suburb plain.[Methods]With the local varieties in Beijing as control,four dandelion varieties,Hebei 2,Shandong 1,Anhui 1 and Henan 1 were introduced,and the growth differences,effective components and yield indexes of different varieties were analyzed.[Results]The leaf and root yield of Henan 1 dandelion was significantly higher than that of the control,and the content of caffeic acid in the root was also higher than the standard of Pharmacopoeia.[Conclusions]On the whole,the dandelion variety Henan 1 is suitable for demonstration planting under the young forest in the plains of Beijing suburb.

Comparison of DPPH Scavenging Ability of Flavonoid and Polysaccharide from Dandelion ( Taraxacum mongolicum)

The paper was to study DPPH(1,1-diphenyl-2-trinitrobenzene hydrazine) scavenging ability of different concentrations of flavonoid and polysaccharide from dandelion. Flavonoids were extracted from dandelion using alcohol precipitation ultrasonic extraction method and polysaccharide was extracted using water ultrasonic extraction method. DPPH free radical scavenging ability of flavonoid and polysaccharide was determined using ultraviolet spectrophotometer method.The difference in DPPH free radical scavenging ability between flavonoids and polysaccharide was analyzed statistically. The results showed that DPPH scavenging ability was the best when the concentration of flavonoid was 1. 6 mg/m L; the scavenge rate was up to 96. 11% and IC50(median inhibitory concentration of inhibitors) was 0. 38 mg/m L. DPPH scavenging ability was the best when the concentration of polysaccharide was 1. 4 mg/m L; the scavenge rate was 89. 33%and IC50 was 0. 51 mg/m L. Statistical results showed that there were significant differences in DPPH free radical scavenging ability between dandelion flavonoid and polysaccharide( P < 0. 05). Flavonoid had significantly higher scavenging ability than polysaccharide( P < 0. 05). The study lays a theoretical foundation for further research on dandelion flavonoid,and provides a theoretical basis for development and utilization of dandelion resources.

Detection and classification of pesticide residues in dandelion(Taraxacum officinale L.)by electronic nose combined with chemometric approaches

In this study,for the first time a suitable pesticide residue detection system for dandelion(Taraxacum officinale L.)was established based on electronic nose to determine and study the concentration of pesticide residue in dandelion.Dandelions were sprayed with different concentrations of pesticides(avermectin,trichlorfon,deltamethrin,and acetamiprid),respectively.Data collection was performed by application of an electronic nose equipped with 12 metal oxide semiconductor(MOS)sensors.Data analysis was conducted using different methods including BP neural network and random forest(RF)as well as the support vector machine(SVM).The results showed the superior effectiveness of SVM in discrimination and classification of non-exceeding maximum residue limits(MRLs)and exceeding MRLs standards.Moreover,the model trained by SVM has the best performance for the classification of pesticide categories in dandelion,and the classification accuracy was 91.7%.The results of this study can provide reference for further development and construction of efficient detection technology of pesticide residues based on electronic nose for agricultural products.

蒲公英提取物对脑出血大鼠的治疗作用及机制研究

目的研究蒲公英提取物对自发性脑出血(ICH)大鼠的治疗作用及核因子E2相关因子2(Nrf2)/血红素加氧酶1(HO-1)信号通路的影响。方法通过脑定位注射Ⅳ型胶原酶诱导建立48只ICH大鼠模型,随机分为模型组、蒲公英提取物组、Nrf2抑制剂(ML385)组和蒲公英提取物+ML385组,每组12只,另选12只大鼠作为假手术组。以药物分组处理后,进行大鼠神经功能损伤评分;检测大鼠血脑屏障功能、海马神经元细胞凋亡率、血清环氧化酶2(COX-2)、白细胞介素6(IL-6)、诱导型一氧化氮合酶(iNOS)及脑组织过氧化氢酶(CAT)、谷胱甘肽过氧化物酶(GSH-Px)、活性氧、丙二醛水平和Nrf2/HO-1信号通路蛋白表达。结果与假手术组比较,模型组大鼠神经功能缺损评分、伊文思蓝渗出量、海马神经元细胞凋亡率、血清COX-2、IL-6、iNOS水平、脑组织活性氧、丙二醛水平显著升高(P<0.05),CAT、GSH-Px、Nrf2、HO-1蛋白表达水平显著降低(P<0.05)。与蒲公英提取物组比较,蒲公英提取物+ML385组大鼠神经功能评分[(2.54±0.23)分vs(1.43±0.19)分]、伊文思蓝渗出量[(22.15±3.61)ng/mg vs(6.54±1.24)ng/mg]、海马神经元细胞凋亡率[(31.97±5.26)%vs(3.51±0.94)%]、血清COX-2[(5.82±1.16)ng/ml vs(1.34±0.42)ng/ml]、IL-6[(1.47±0.31)ng/ml vs(0.43±0.14)ng/ml]、iNOS[(59.91±10.36)U/ml vs(13.94±3.78)U/ml]、脑组织活性氧[(4.70±0.45)U/kg vs(1.70±0.51)U/kg]、丙二醛水平[(3.72±0.52)nmol/mg vs(1.17±0.34)nmol/mg]显著升高(P<0.05),CAT[(2.54±0.59)U/mg vs(5.68±1.04)U/mg]、GSH-Px[(8.01±0.86)U/mg vs(16.97±3.03)U/mg]、Nrf2(0.67±0.13 vs 1.07±0.19)、HO-1(0.55±0.07 vs 0.86±0.10)蛋白表达水平显著降低(P<0.05)。结论蒲公英提取物可通过激活Nrf2/HO-1信号通路增强ICH大鼠抗氧化活性,阻止炎症和氧化应激反应进展,抑制海马神经元细胞凋亡,修复血脑屏障功能,改善大鼠神经功能。

蒲公英葡萄复合饮料的研发

为了丰富饮料的品种,本文以蒲公英、葡萄为主要原料,研制了一种新型的复合饮品。通过单因素试验和正交试验,优化蒲公英葡萄复合饮料的配方。结果表明,蒲公英汁10 g、葡萄汁30 g、白砂糖15 g、柠檬酸0.2 g、水120 mL为蒲公英葡萄复合饮料的最佳工艺配方,复合饮料口感清爽、风味独特、营养丰富,理化和微生物指标均符合国家标准。

蒲公英叶提取物在盐酸中对铁片的缓蚀行为研究

通过浸提法从蒲公英叶中提取植物缓蚀剂,采用失重法、傅里叶红外光谱测试、腐蚀形貌表征法及吸附等温曲线拟合,研究了蒲公英叶提取物在1 mol/L HCl中对纯铁的缓蚀性能和机制。结果表明:蒲公英叶提取物对铁片均有显著的缓蚀效果,在35℃下,0.8 g/L的蒲公英叶提取物对铁片的缓蚀效率高达97.45%,效果最佳;蒲公英叶提取物中的活性分子官能团,以物理吸附的形式占据铁片表面反应位点来抑制铁片腐蚀。吸附等温线拟合结果显示,蒲公英叶提取物在铁片表面的吸附为单分子层吸附,吸附过程符合Langmuir吸附等温模型。

蒲公英种子与绒毛脱分机设计与试验

针对蒲公英的种子与绒毛分离困难,分离过程中劳动量大、人工成本高等问题,设计两级脱分的蒲公英种子与绒毛脱分机。整机结构由一级脱分装置、二级脱分装置、负压除杂装置、传动装置以及进料口组成。对一级脱分和二级脱分的筛网进行结构设计和计算,得出设计参数:一级锥形筛网高度为277 mm,母线长为320 mm,顶圈筛孔个数为87个,底圈筛孔的个数为185个,二级冲孔筛的直径为520 mm,筛孔数为6928个。以喂入量和毛刷转速为试验因素,以蒲公英种子的脱净率、破损率为试验指标进行试验,得到脱分机的最佳工作状态:当毛刷转速为320 r/min、喂入量为0.0037 kg/s时,脱净率为87.6%,破损率为2.8%。蒲公英种子与绒毛脱分机整体结构合理、运行状况稳定,满足设计要求。

人参与蒲公英根配伍对大鼠“上火”症状的调节作用

为改善食用人参出现的“上火”症状,提高人参的普适性,通过动物实验,分别设置正常组、2、4 g/kg人参组以及2、4 g/kg人参与蒲公英根配伍组进行灌胃19 d,测量体温、血压及血清中与“上火”相关联的5-羟色胺(5-HT)、促甲状腺激素(TSH)、皮质酮(CORT)等指标。结果表明,2、4 g/kg人参与蒲公英根配伍组体温及血压均低于人参组,其中4 g/kg配伍组效果更显著(P<0.05);与正常组比较,人参组5-HT含量下降,TSH、17-羟皮质类固醇(17-OHCS)、CORT、肿瘤坏死因子-α(TNF-α)含量升高,差异均有统计学意义(P<0.05);与人参组相比,2、4 g/kg人参与蒲公英根配伍组5-HT含量升高,TSH、17-OHCS、CORT、TNF-α含量下降,差异均有统计学意义(P<0.05)。由此表明,利用人参与蒲公英根配伍可提高人参和蒲公英根价值,调节食用人参引起的“上火”症状。

基于网络药理学和体外实验探讨蒲公英治疗卵巢早衰的作用机制

目的 通过网络药理学技术和体外实验探讨蒲公英治疗卵巢早衰的作用机制。方法 从中药系统药理学数据库与分析平台、STITCH、BATMAN-TCM、GEO、中药研究数据库、Bindingdb、DAVID数据库获取蒲公英的活性成分及卵巢早衰的潜在靶点,构建靶蛋白质-蛋白质相互作用网络、成分-靶点-疾病网络,并进行KEGG富集分析。通过卵巢颗粒细胞在不同浓度H2O2条件下培养不同时间,选择最佳造模条件构建卵巢细胞早衰模型(模型组),另采用不同浓度的蒲公英甾醇预处理细胞,选择后续干预的最佳浓度。将细胞设置空白组、模型组及蒲公英甾醇高、低剂量组。蒲公英甾醇高、低剂量组分别给予蒲公英甾醇预处理24 h后和模型组一同加入H2O2,空白组不做处理。干预结束后,采用CCK-8法测定细胞活力,DCFH-DA荧光探针检测细胞内活性氧(ROS)水平,蛋白质印迹法分别检测细胞质、细胞核中的低氧诱导因子-1α(HIF-1α)。结果 数据库共筛选出蒲公英活性成分23个,相应的作用靶点345个,卵巢早衰相关靶点基因497个,二者共同靶点基因61个,涉及的通路有HIF-1信号通路、蛋白聚糖作用等。当用600μmol/L H2O2处理细胞4 h,细胞活力最接近IC50。蒲公英甾醇浓度为7.5、15.0μmol/L时,细胞活力高于模型组(P<0.05)。模型组ROS相对荧光强度高于空白组,蒲公英甾醇高、低剂量组低于模型组(P<0.05)。四组细胞质HIF-1α蛋白表达比较,差异无统计学意义(P>0.05)。模型组细胞核HIF-1α蛋白表达高于空白组,蒲公英甾醇高、低剂量组低于模型组(P<0.05)。结论 蒲公英可通过多成分、多靶点、多通路治疗卵巢早衰,其代表性成分蒲公英甾醇可能通过抗氧化作用发挥治疗卵巢早衰的功能。

Dandelion polyphenols protect against acetaminophen-induced hepatotoxicity in mice via activation of the Nrf-2/HO-1 pathway and inhibition of the JNK signaling pathway

We investigated the liver protective activity of dandelion polyphenols(DP)against acetaminophen(APAP;Paracetamol)-induced hepatotoxicity.Mice were acclimated for 1 week and randomly divided into the following groups(n=9 per group):Control,APAP,APAP+DP(100 mg·kg^–1),APAP+DP(200 mg·kg^–1),and APAP+DP(400 mg·kg^–1)groups.Mice were pretreated with DP(100,200,and 400 mg·kg^–1)by oral gavage for 7 d before being treated with 350 mg·kg^–1 APAP for 24 h to induced hepatotoxicity.Severe liver injury was observed,and hepatotoxicity was analyzed after 24 h by evaluation of biochemical markers,protein expressions levels,and liver histopathology.Pretreatment with DP was able to restore serum liver characteristics(aspartate transaminase,AST;alanine aminotransferase,ALT;alkaline phosphatase,AKP),improve redox imbalance(superoxide dismutase,SOD;glutathione,GSH;malondialdehyde,MDA),and decrease inflammatory factors(tumor necrosis factor-α,TNF-α;interleukin-1β,IL-1β).Pretreatment with DP also significantly inhibited the expression levels of nitric oxide synthase(iNOS)and cyclooxygenase-2(COX-2).Furthermore,DP pretreatment could inhibit the apoptosis of liver cells caused by APAP through up-regulation of Bcl-2 and down-regulation of Bax and caspase-9 protein.DP also down-regulated p-JNK protein expression levels to inhibit APAP-induced mitochondrial oxidative stress and up-regulated the expression of Nrf-2 and its target gene HO-1.The histopathological staining demonstrated that DP pretreatment could inhibit APAP-induced hepatocyte infiltration,congestion,and necrosis.Our results demonstrate that DP pretreatment could protect against APAP-induced hepatic injury by activating the Nrf-2/HO-1 pathway and inhibition of the intrinsic apoptosis pathway.

外源硒对蒲公英生长、生理特性及其硒含量的影响

为研究叶面喷施外源硒对蒲公英(Taraxacum mongolicum Hand.-Mazz.)生长和品质的影响,采用盆栽试验,分析叶面喷施不同浓度亚硒酸钠溶液(0、100、200、300、400μmol/L)对蒲公英生长、生理特性及其硒含量的影响。结果表明,随着喷施硒浓度的增大,蒲公英根长和鲜重等生长指标呈先升高后降低的趋势;与对照相比,施加200μmol/L亚硒酸钠可显著提高蒲公英光合作用速率和光化学反应效率,提高光合色素含量;施加200μmol/L亚硒酸钠时蒲公英叶片SOD和CAT活性最高,施加300μmol/L亚硒酸钠时POD活性最高(P<0.05)。施硒可有效提高蒲公英绿原酸、总黄酮和总多酚的含量,施加200μmol/L亚硒酸钠时总黄酮和总多酚的含量较对照分别提高49.73%、31.34%。施硒后蒲公英各部位硒含量显著提高,叶片和根系的硒含量随硒浓度的变化符合一元二次方程。蒲公英叶片对外源硒浓度的变化较敏感,是富硒的主要部位。研究认为,叶面喷施200μmol/L亚硒酸钠是培养富硒蒲公英的最佳浓度。