Incidence and Reproduction Numbers of Pertussis: Estimates from Serological and Social Contact Data in Five European Countries

Background

Despite large-scale vaccination programmes, pertussis has remained endemic in all European countries and has been on the rise in many countries in the last decade. One of the reasons that have been discussed for the failure of vaccination to eliminate the disease is continued circulation of the pathogen Bordetella pertussis by mostly asymptomatic and mild infections in adolescents and adults. To understand the impact of asymptomatic and undiagnosed infection on the transmission dynamics of pertussis we analysed serological data from five European countries in combination with information about social contact patterns from five of those countries to estimate incidence and reproduction numbers.

Methods and Findings

We compared two different methods for estimating incidence from individual data on IgG pertussis toxin (PT) titres. One method combines the cross-sectional surveys of titres with longitudinal information about the distribution of amplitude and decay rate of titres in a back-calculation approach. The second method uses age-dependent contact matrices and cross-sectional surveys of IgG PT titres to estimate a next generation matrix for pertussis transmission among age groups. The next generation approach allows for computation of basic reproduction numbers for five European countries. Our main findings are that the seroincidence of infections as estimated with the first method in all countries lies between 1% and 6% per annum with a peak in the adolescent age groups and a second lower peak in young adults. The incidence of infections as estimated by the second method lies slightly lower with ranges between 1% and 4% per annum. There is a remarkably good agreement of the results obtained with the two methods. The basic reproduction numbers are similar across countries at around 5.5.

Conclusions

Vaccination with currently used vaccines cannot prevent continued circulation and reinfection with pertussis, but has shifted the bulk of infections to adolescents and adults. If a vaccine conferring lifelong protection against clinical and subclinical infection were available pertussis could be eliminated. Currently, continuing circulation of the pathogen at a subclinical level provides a refuge for the pathogen in which it can evolve and adjust to infect vaccinated populations. Please see later in the article for the Editors'' Summary     

Estimates of a Treatment Effect Based on Censored Data Rank Tests

Linear rank test statistics are applied to the problem of estimating a treatment effect if two sets of censored failure time data are compared and the distributions of the log-failure times of the two samples are assumed to differ only in location. Rank tests for this accelerated failure time model are reviewed and Hodges-Lehmann type estimates for the shift parameter are proposed. Properties of these estimates are investigated, computational aspects are discussed and an example is presented.     

无线传感器网络中基于缠绕多路径的ReInforM路由

对缠绕多路径算法技术的基本构建方法和ReInforM路由算法技术的基本过程进行了讨论,分析了其在无线传感器网络应用中的发展方向,提出了基于缠绕多路径的ReInforM路由。     

Contact Patterns in a High School: A Comparison between Data Collected Using Wearable Sensors,Contact Diaries and Friendship Surveys

Given their importance in shaping social networks and determining how information or transmissible diseases propagate in a population, interactions between individuals are the subject of many data collection efforts. To this aim, different methods are commonly used, ranging from diaries and surveys to decentralised infrastructures based on wearable sensors. These methods have each advantages and limitations but are rarely compared in a given setting. Moreover, as surveys targeting friendship relations might suffer less from memory biases than contact diaries, it is interesting to explore how actual contact patterns occurring in day-to-day life compare with friendship relations and with online social links. Here we make progresses in these directions by leveraging data collected in a French high school and concerning (i) face-to-face contacts measured by two concurrent methods, namely wearable sensors and contact diaries, (ii) self-reported friendship surveys, and (iii) online social links. We compare the resulting data sets and find that most short contacts are not reported in diaries while long contacts have a large reporting probability, and that the durations of contacts tend to be overestimated in the diaries. Moreover, measured contacts corresponding to reported friendship can have durations of any length but all long contacts do correspond to a reported friendship. On the contrary, online links that are not also reported in the friendship survey correspond to short face-to-face contacts, highlighting the difference of nature between reported friendships and online links. Diaries and surveys suffer moreover from a low sampling rate, as many students did not fill them, showing that the sensor-based platform had a higher acceptability. We also show that, despite the biases of diaries and surveys, the overall structure of the contact network, as quantified by the mixing patterns between classes, is correctly captured by both networks of self-reported contacts and of friendships, and we investigate the correlations between the number of neighbors of individuals in the three networks. Overall, diaries and surveys tend to yield a correct picture of the global structural organization of the contact network, albeit with much less links, and give access to a sort of backbone of the contact network corresponding to the strongest links, i.e., the contacts of longest cumulative durations.     

Exact Maximum Likelihood Estimates of Cox's Regression Parameters Based on Categorized Factorial Data

This paper describes how Cox's Proportional Hazards model may be used to analyze dichotomized factorial data obtained from a right-censored epidemiological study where time to response is of interest. Exact maximum likelihood estimates of the relative mortality rates are obtained for any number of prognostic factors, as well as their joint asymptotic sampling distribution. These rates represent excess mortality due to the various levels of the prognostic factors. The results are used to discuss the effect of the factors on the survival probability distribution of a cohort of industrial workers who have been exposed to a carcinogen. Kaplan-Meier estimates of the survival function of the internal control population are used to determine the expected number of deaths in the study population. This method differs from the usual lite-table procedure. Asymptotic tests are proposed for some simultaneous and conditional statistical hypotheses.     

Inverted Social Reward: Associations between Psychopathic Traits and Self-Report and Experimental Measures of Social Reward

Individuals with high levels of psychopathic traits tend to undervalue long-term, affiliative relationships, but it remains unclear what motivates them to engage in social interactions at all. Their experience of social reward may provide an important clue. In Study 1 of this paper, a large sample of participants (N = 505) completed a measure of psychopathic traits (Self-Report Psychopathy Scale Short-Form) and a measure of social reward value (Social Reward Questionnaire) to explore what aspects of social reward are associated with psychopathic traits. In Study 2 (N = 110), the same measures were administered to a new group of participants along with two experimental tasks investigating monetary and social reward value. Psychopathic traits were found to be positively correlated with the enjoyment of callous treatment of others and negatively associated with the enjoyment of positive social interactions. This indicates a pattern of ‘inverted’ social reward in which being cruel is enjoyable and being kind is not. Interpersonal psychopathic traits were also positively associated with the difference between mean reaction times (RTs) in the monetary and social experimental reward tasks; individuals with high levels of these traits responded comparatively faster to social than monetary reward. We speculate that this may be because social approval/admiration has particular value for these individuals, who have a tendency to use and manipulate others. Together, these studies provide evidence that the self-serving and cruel social behaviour seen in psychopathy may in part be explained by what these individuals find rewarding.     

H3N2v and Other Influenza Epidemic Risk Based on Age-Specific Estimates of Sero-Protection and Contact Network Interactions

Cases of a novel swine-origin influenza A(H3N2) variant (H3N2v) have recently been identified in the US, primarily among children. We estimated potential epidemic attack rates (ARs) based on age-specific estimates of sero-susceptibility and social interactions. A contact network model previously established for the Greater Vancouver Area (GVA), Canada was used to estimate average epidemic (infection) ARs for the emerging H3N2v and comparator viruses (H1N1pdm09 and an extinguished H3N2 seasonal strain) based on typical influenza characteristics, basic reproduction number (R₀), and effective contacts taking into account age-specific sero-protection rates (SPRs). SPRs were assessed in sera collected from the GVA in 2009 or earlier (pre-H1N1pdm09) and fall 2010 (post-H1N1pdm09, seasonal A/Brisbane/10/2007(H3N2), and H3N2v) by hemagglutination inhibition (HI) assay. SPR was assigned per convention based on proportion with HI antibody titre ≥40 (SPR40). Recognizing that the HI titre ≥40 was established as the 50%sero-protective threshold we also explored for ½SPR40, SPR80 and a blended gradient defined as: ¼SPR20, ½SPR40, ¾SPR80, SPR160. Base case analysis assumed R₀ = 1.40, but we also explored R₀ as high as 1.80. With R₀ = 1.40 and SPR40, simulated ARs were well aligned with field observations for H1N1pdm09 incidence (AR: 32%), sporadic detections without a third epidemic wave post-H1N1pdm09 (negligible AR<0.1%) as well as A/Brisbane/10/2007(H3N2) seasonal strain extinction and antigenic drift replacement (negligible AR<0.1%). Simulated AR for the novel swine-origin H3N2v was 6%, highest in children 6–11years (16%). However, with modification to SPR thresholds per above, H3N2v AR ≥20% became possible. At SPR40, H3N2v AR ≥10%, ≥15% or ≥30%, occur if R₀≥1.48, ≥1.56 or ≥1.86, respectively. Based on conventional assumptions, the novel swine-origin H3N2v does not currently pose a substantial pandemic threat. If H3N2v epidemics do occur, overall community ARs are unlikely to exceed typical seasonal influenza experience. However risk assessment may change with time and depends crucially upon the validation of epidemiological features of influenza, notably the serologic correlate of protection and R₀.     

鹤岗市中小学生性健康教育现状的调查研究

目的:了解鹤岗市中小学生性健康教育现状,为进一步开展青春期性健康教育提供依据。方法:分层随机整群抽取鹤岗市1735名中小学生进行无记名问卷调查。结果:被调查的学生已具备一定的青春期性知识,但其知晓率仍偏低;性知识获取途径以社会媒体为主。大多数被调查者性生理发育状况良好,对青少年中发生的恋爱行为持宽容和理解的态度,而对婚前性行为持谨慎和保守态度。结论:今后应加大对性健康教育的宣传和投入,加强对中小学生的性道德教育。     

Using a Polygraph System for Evaluation of the Social Desirability Response Bias in Self-Report Measures of Aggression

Empirical evidence suggests that respondents systematically overreport socially desirable behaviors and systematically underreport socially undesirable behaviors. This “social desirability response bias (SDRB)” presents significant challenges for research that relies on self-report measures to assess behaviors that adhere to or violate social norms. The present study used a state-of-the-art polygraph system to examine SDRB in widely used aggression questionnaires, including the Buss–Perry Aggression Questionnaire-Short Form, the Indirect Aggression subscale of the Aggression Questionnaire by Western Psychological Services, and the Reactive–Proactive Questionnaire. Sixteen college students with no criminal record, no known prior history of aggressive behavior, and no reported drug abuse, responded to verbally administered forms of the instruments. Indirect aggression items produced the largest, statistically significant physiological response across the sampled channels. The magnitude of this response was negatively and significantly correlated with the self-report ratings of the frequency of such behaviors. The mean separation between physiological (skin conductance) and self-report responses for indirect aggression remained significant and consistent with correlational analyses when both types of responses were converted to the same scale and compared directly. Finally, the relative magnitude of skin conductance response for items assessing indirect aggression was significantly greater than the relative magnitude of skin conductance response for direct aggression. Overall, the study suggests that the use of automated state-of-the art polygraph systems may potentially identify sensitive items on self-report instruments where social responsibility response bias is possible. Implications for the use of this procedure with such instruments are discussed.     

Energy and QoS Aware Routing in Wireless Sensor Networks

Many new routing protocols have been proposed for wireless sensor networks in recent years. Almost all of the routing protocols considered energy efficiency as the ultimate objective since energy is a very scarce resource for sensor nodes. However, the introduction imaging sensors has posed additional challenges. Transmission of imaging data requires both energy and QoS aware routing in order to ensure efficient usage of the sensors and effective access to the gathered measurements. In this paper, we propose an energy-aware QoS routing protocol for sensor networks which can also run efficiently with best-effort traffic. The protocol finds a least-cost, delay-constrained path for real-time data in terms of link cost that captures nodes energy reserve, transmission energy, error rate and other communication parameters. Moreover, the throughput for non-real-time data is maximized by adjusting the service rate for both real-time and non-real-time data at the sensor nodes. Such adjustment of service rate is done by using two different mechanisms. Simulation results have demonstrated the effectiveness of our approach for different metrics with respect to the baseline approach where same link cost function is used without any service differentiation mechanism.Kemal Akkaya received his B.S. degree in Computer Science from Bilkent University, Ankara, Turkey in 1997 and MS degree in Computer Science from Ortadogu Technical University (ODTU), Ankara, Turkey in 1999. He worked as a software developer at an automation project of Siemens and World Bank in Ankara, Turkey in 2000. He is currently a Ph.D. candidate at University of Maryland, Baltimore County (UMBC), Baltimore, MD. His research interests include energy aware routing, security and quality of service issues in ad hoc wireless networks.Mohamed F. Younis received B.S. degree in computer science and M.S. in engineering mathematics from Alexandria University in Egypt in 1987 and 1992, respectively. In 1996, he received his Ph.D. in computer science from New Jersey Institute of Technology. He is currently an assistant professor in the department of computer science and electrical engineering at the university of Maryland Baltimore County (UMBC). Before joining UMBC, he was with the Advanced Systems Technology Group, an Aerospace Electronic Systems R&D organization of Honeywell International Inc. While at Honeywell he led multiple projects for building integrated fault tolerant avionics, in which a novel architecture and an operating system were developed. This new technology has been incorporated by Honeywell in multiple products and has received worldwide recognition by both the research and the engineering communities. He also participated in the development the Redundancy Management System, which is a key component of the Vehicle and Mission Computer for NASAs X-33 space launch vehicle. Dr. Younis technical interest includes network architectures and protocols, embedded systems, fault tolerant computing and distributed real-time systems. Dr. Younis has four granted and three pending patents. He served on multiple technical committees and published over 40 technical papers in refereed conferences and journals.     

乙肝疫苗对中小学生的保护效果

为进一步了解中小学生乙肝病毒的感染率及乙肝疫苗的保护效果,用固相放免方法检测1 134名小学生和358名中学生的HBsAg和抗-HBs。判定:S/N≥2.1;以≥10 mIU/mL为阳性。乙肝疫苗接种率,市区小学生高于郊区学生(χ2=54.58,P<0.01),HBsAg的阳性率呈下降趋势,检测到的1 134名小学生中,抗-HBs阳性率平均在89.2%。HBsAg阳性率随乙肝疫苗接种率的增高而下降,但市区学生(2.65%)与郊区学生(2.76%)差异无显著意义(χ2=1.35,P>0.05)。近期加强接种了重组乙肝疫苗的中学生,抗HBS-抗体阳性率97.7%。随着乙肝疫苗接种率和抗-HBs阳性率的增高,HBsAg阳性率呈下降趋势。在乙肝高发区,尽管推行了乙肝疫苗全程免疫规划,但从长远的免疫策略考虑,有必要制定加强免疫计划。     

A Plethora of Fungi: Teaching a Middle School Unit on Fungi

Abstract

While fungi play a vital role in Earth's ecosystems, they are not highlighted in the Next Generation Science Standards (NGSS). This article contains a unit plan to introduce students to the fungal kingdom, characteristics of fungi, and their role as decomposers. The unit plan is written in a 5E model format and can be adjusted for any type of lesson planning format. Students explore fungi through hands-on activities, a jigsaw activity that makes use of collaborative learning, and analysis of case studies. Teachers can use this unit without a strong background in mycology, the study of fungi, or costly materials. A summative assessment is included at the end of the unit plan.     

Age Estimates for the Buckwheat Family Polygonaceae Based on Sequence Data Calibrated by Fossils and with a Focus on the Amphi-Pacific Muehlenbeckia

The buckwheat family Polygonaceae is a diverse group of plants and is a good model for investigating biogeography, breeding systems, coevolution with symbionts such as ants and fungi, functional trait evolution, hybridization, invasiveness, morphological plasticity, pollen morphology and wood anatomy. The main goal of this study was to obtain age estimates for Polygonaceae by calibrating a Bayesian phylogenetic analysis, using a relaxed molecular clock with fossil data. Based on the age estimates, we also develop hypotheses about the historical biogeography of the Southern Hemisphere group Muehlenbeckia. We are interested in addressing whether vicariance or dispersal could account for the diversification of Muehlenbeckia, which has a “Gondwanan” distribution.Eighty-one species of Polygonaceae were analysed with MrBayes to infer species relationships. One nuclear (nrITS) and three chloroplast markers (the trnL-trnF spacer region, matK and ndhF genes) were used. The molecular data were also analysed with Beast to estimate divergence times. Seven calibration points including fossil pollen and a leaf fossil of Muehlenbeckia were used to infer node ages.Results of the Beast analyses indicate an age of 110.9 (exponential/lognormal priors)/118.7 (uniform priors) million years (Myr) with an uncertainty interval of (90.7–125.0) Myr for the stem age of Polygonaceae. This age is older than previously thought (Maastrichtian, approximately 65.5–70.6 Myr). The estimated divergence time for Muehlenbeckia is 41.0/41.6 (39.6–47.8) Myr and its crown clade is 20.5/22.3 (14.2–33.5) Myr old. Because the breakup of Gondwana occurred from 95–30 Myr ago, diversification of Muehlenbeckia is best explained by oceanic long-distance and maybe stepping-stone dispersal rather than vicariance. This study is the first to give age estimates for clades of Polygonaceae and functions as a jumping-off point for future studies on the historical biogeography of the family.     

Social and Individual Components of Animal Contact in Preschool Children

ABSTRACT

Humans are generally biophilic. Still, for unknown reasons, interest in animals varies substantially among individuals. Our goal was to investigate how differential interest of children towards animals might be related to social competence and personality. We proposed two alternatives: 1) Children may compensate for potential deficits in social competence by resorting to animals, and 2) Socially well-connected children may show a particular interest in animals. We focused on relationships between age, gender, family background, play behavior, personality components, and contact with rabbits in 50 children (22 boys/28 girls; 3 to 7 years of age) at a preschool in Krems/Austria. Data were analyzed using GLM. We found that each one of these variables had significant impact on intensity of engagement with the rabbits. In general, girls, children with siblings, and children without pets were more oriented towards the rabbits than were boys, children without siblings, or pet-owning children. The older the children, the less frequently they occupied themselves with the rabbits but the longer they remained when they did engage them. Furthermore, we found that the more “Confident/Respected” (PCA factor 1) and less “Patient/Calm,” “Cheerful/Sociable,” and “Solitary” (PCA factors 2–4) the children, the more time they spent in direct occupation with rabbits. Most effects of the investigated variables varied between boys and girls. By and large, our findings support the hypothesis that the “socially competent” children were particularly interested in the animals. Also, children's social styles, as evinced in interactions with peers, were generally reflected in how they interacted with the rabbits.     

Estimation of 24-Hour Intraocular Pressure Peak Timing and Variation Using a Contact Lens Sensor

Purpose

To compare estimates of 24-hour intraocular pressure (IOP) peak timing and variation obtained using a contact lens sensor (CLS) and using a pneumatonometer.

Methods

Laboratory data collected from 30 healthy volunteers (ages, 20-66 years) in a randomized, controlled clinical trial were analyzed. Participants were housed for 24 hours in a sleep laboratory. One randomly selected right or left eye was fitted with a CLS that monitored circumferential curvature in the corneoscleral region related to the change of IOP. Electronic output signals of 30 seconds were averaged and recorded every 5 minutes. In the contralateral eye, habitual IOP measurements were taken using a pneumatonometer once every two hours. Simulated 24-hour rhythms in both eyes were determined by cosinor fitting. Simulated peak timings (acrophases) and simulated data variations (amplitudes) were compared between the paired eyes.

Results

Bilateral change patterns of average 24-hour data for the group were in parallel. The simulated peak timing in the CLS fitted eye occurred at 4:44 AM ± 210 min (mean ± SD) and the IOP peak timing in the contralateral eye at 4:11 AM ± 120 min (P=0.256, Wilcoxon signed-rank test). There was no significant correlation between the simulated data variations in the paired eyes (P=0.820, linear regression).

Conclusions

The 24-hour CLS data showed a simulated peak timing close to the 24-hour IOP peak timing obtained using the pneumatonometer. However, the simulated variations of 24-hour data in the paired eyes were not correlated. Estimated 24-hour IOP rhythms using the two devices should not be considered interchangeable.     

Spread of Academic Success in a High School Social Network

Application of social network analysis to education has revealed how social network positions of K-12 students correlate with their behavior and academic achievements. However, no study has been conducted on how their social network influences their academic progress over time. Here we investigated correlations between high school students’ academic progress over one year and the social environment that surrounds them in their friendship network. We found that students whose friends’ average GPA (Grade Point Average) was greater (or less) than their own had a higher tendency toward increasing (or decreasing) their academic ranking over time, indicating social contagion of academic success taking place in their social network.     

Efficacy of a Contact Lens Sensor for Monitoring 24-H Intraocular Pressure Related Patterns

Purpose

To study performance of a contact lens sensor (CLS) for 24-hour monitoring of IOP-related short-term patterns and compare with IOP obtained by pneumatonometry.

Methods

Prospective clinical trial. Thirty-one healthy volunteers and 2 glaucoma patients were housed for 24 hours in a sleep laboratory. One randomly selected eye was fitted with a CLS (Triggerfish, Sensimed, Switzerland), which measures changes in ocular circumference. In the contralateral eye, IOP measurements were taken using a pneumatonometer every two hours with subjects in the habitual body positions. Heart rate (HR) was measured 3 times during the night for periods of 6 minutes separated by 2 hours. Performance of CLS was defined in two ways: 1) recording the known pattern of IOP increase going from awake (sitting position) to sleep (recumbent), defined as the wake/sleep (W/S) slope and 2) accuracy of the ocular pulse frequency (OPF) concurrent to that of the HR interval. Strength of association between overall CLS and pneumatonometer curves was assessed using coefficients of determination (R²).

Results

The W/S slope was statistically significantly positive in both eyes of each subject (CLS, 57.0 ± 40.5 mVeq/h, p<0.001 and 1.6 ± 0.9 mmHg/h, p<0.05 in the contralateral eye). In all, 87 CLS plots concurrent to the HR interval were evaluated. Graders agreed on evaluability for OPF in 83.9% of CLS plots. Accuracy of the CLS to detect the OPF was 86.5%. Coefficient of correlation between CLS and pneumatonometer for the mean 24-h curve was R² = 0.914.

Conclusions

CLS measurements compare well to the pneumatonometer and may be of practical use for detection of sleep-induced IOP changes. The CLS also is able to detect ocular pulsations with good accuracy in a majority of eyes.

Trial Registration

ClinicalTrials.gov NCT01390779     

Ultrasensitive and Tunable Sensor Based on Plasmon-Induced Transparency in a Black Phosphorus Metasurface

We propose an ultrasensitive and tunable mid-infrared sensor based on plasmon-induced transparency (PIT) in a monolayer black phosphorus metasurface. Results show that there are two PIT windows, each of which occurs when the long axis of the metasurface is placed along the MBP’s armchair and zigzag crystal directions, respectively. The corresponding sensors based on these PIT effects show high sensitivities of 7.62 THz/RIU and 7.36 THz/RIU. Both PIT frequencies can be tuned statically by varying the geometric parameters or dynamically by changing the electron doping of monolayer black phosphorus, making the sensors adaptable to tackle with a variety of scenarios. We expect that this work will advance the engineering of metasurfaces based on monolayer black phosphorus and promote their sensing applications.

     

Influence of Design Parameters on the Performance of a Surface Plasmon Sensor Based Fiber Optic Sensor

In the present work, the influence of two key design parameters, namely, fiber core diameter and sensing region length on the performance of a fiber optic surface plasmon resonance sensor, was experimentally observed. The sensor was designed with a multimode optical fiber of numerical aperture 0.40 and a thin silver layer of 50 nm thickness. The performance evaluation was carried out in terms of three performance parameters: sensitivity, signal-to-noise ratio and resolution. It was found that performance of the sensor tends to improve if fiber of large core diameter is used. Further, sensing region length should be taken as small as possible to attain highly sensitive and accurate sensing procedure. The experimental results are explained in terms of related physical background and mathematical expressions.     

广州市公园对比评价研究——基于社交媒体数据的文本分析

传统公园评价的研究大多集中在单个公园使用满意度方面,存在问卷样本量小、采集时间较集中等缺陷。大数据相关研究的快速发展为公园系统评价提供了新的契机。基于对社交媒体数据的文本分析,研究对比广州市 50 个公园的评价结果,同时探究公园评价与人口统计学特征、地理区位、评价时间以及公园属性之间的关系。研究发现, 1）公园正面评价主要集中在免费设施、环境和特色等方面,而负面评价多集中于公园卫生、交通成本、停车等管理服务方面,广州公园的管理服务水平亟待提升。 2）女性较男性更关注公园能否满足其对社交场所的需求,本地游客较外地游客更关注公园本身的服务质量而非公园的外部属性。 3）基干公园应更侧重其可达性和基本的服务功能,承担大众日常活动;特色公园应更注重满足特定人群的需求及特色打造;自然公园应更关注公园生态质量并能够承担需要较大场地的活动。 4） 2010—2018 年,人们越来越关注公园特色的打造,在公园中的活动类型也越来越多样,现代公园建设更应着力于文化服务质量的提升。研究突破传统公园研究方法的局限,将大数据的手段运用到多个公园的整体评价当中,有助于建立更普适、更有针对性的公园评价指标体系,具有较高的实践价值。