首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
Abstract: Some gynodloecious species present not only hermaphrodite and female individuals but also gynomonoecious individuals that produce both female and perfect flowers. In a study of natural populations of Silene italica , we found that gynomonoecious individuals were common in all populations (from 13 to 39%) and that their frequency was independent of the frequency of females. No relationship was found between the number of flowers a plant produced and its sex. The majority of gynomonoecious individuals showed a low proportion of female flowers but all proportions were found. Female flowers of these individuals were well-developed flowers that set fruit as often as female flowers on pure females. The percentage fruit set was characteristic of the type of flowers (around 56% for perfect flowers and 76% for female flowers) whatever the sex of the individual plant. The determination of sex is not known but data indicate that environmental conditions could be responsible for a shift between the hermaphrodite and the gynomonoecious states rather than between the female and the gynomonoecious states.  相似文献   

3.
Genetic variation of Rana pirica , an east Asian brown frog of the R. temporaria group, was elucidated by analysing 140 specimens from 11 populations from Hokkaido and Sakhalin, both locating near the eastern coasts of the Asian continent, and 12 specimens of R. ornativentris from Honshu, Japan mainland, as an outgroup, through horizontal starch gel electrophoresis. Rana pirica shows relatively low genetic differentiation, and high genetic affinities are found between Hokkaido and Sakhalin populations. Populations from these islands are morphologically somewhat differentiated but should be regarded as conspecific. Degree of genetic divergence among populations of amphibian species from Hokkaido, including R. pirica , is not so extensive as that reported for species from Japan mainland and relatively recent formation of amphibian fauna in Hokkaido is suggested.  相似文献   

4.
Abstract Examinations of chromosome number voucher specimens show that sexual diploid and agamospermous polyploid plants of Eupatorium in Asia can be distinguished by morphology, fertility, and stainability of pollen grains. Using these criteria, reproductive systems (sexual vs. agamospermous) were estimated for 558 herbarium specimens of Eupatorium in East Asia. Of 22 taxa examined, six included both sexual and agamospermous specimens; those of one taxon were all agamospermous; and those of 15 taxa were all sexual. This result shows that 21 taxa are not agamospermous microspecies but are differentiated at the diploid level. Sexual populations of most taxa had restricted geographical distributions. Eupatorium chinense var. chinense and var. oppositifolium consisted of both sexual and agamospermous populations. Sexual populations of these two varieties were allopatric and distinct in external morphology, suggesting differentiation at the species level. The specimens of E. heterophyllum s. str. were all agamospermous, while those of E. mairel , often treated as synonymous with E. heterophyllum , were sexual.
In comparing East Asian and North American Eupatorium for the distributional patterns of sexual and agamospermous populations, three differences can be pointed out: (1) Agamospermous plants of autopolyploid origin have evolved in eight species and are widespread in North America; while most agamospermous plants in East Asia may be of allopolyploid origin, have relatively restricted ranges, and are less frequent than the diploid plants with the exception of in E. chinense var. oppositifolium , (2) The number of sexual species with wide range is greater in North America than in East Asia. (3) The number of sexual species with restricted ranges is greater in East Asia than in North America. The results obtained suggest that speciation among the plants of Eupatorium has occurred more recently in East Asia than in North America.  相似文献   

5.
6.

Background

Global efforts in response to the increased prevalence of the human immunodeficiency virus (HIV) are mainly aimed at reducing high risk sexual behaviors among young people. However, knowledge regarding intentions of young people to engage in protective sexual behaviors is still lacking in many countries around the world, especially in Sub-Saharan Africa where prevalence of human immunodeficiency virus is the highest. The objective of this study was to test the theory of planned behavior (TPB) for predicting factors associated with protective sexual behaviors, including sexual abstinence and condom use, among in-school youths aged between 15 and 19 years in Swaziland.

Methods

This cross-sectional survey was conducted using a anonymous questionnaire. A two-stage stratified and cluster random sampling method was used. Approximately one hundred pupils from each of four schools agreed to participate in the study, providing a total sample size of 403 pupils of which 369 were ultimately included for data analysis. The response rate was 98%. Structural equation modeling was used to analyse hypothesized paths.

Results

The TPB model used in this study was effective in predicting protective sexual behavior among Swazi in-school youths, as shown by model fit indices. All hypothesized constructs significantly predicted intentions for abstinence and condom use, except perceived abstinence controls. Subjective norms were the strongest predictors of intention for premarital sexual abstinence; however, perceived controls for condom use were the strongest predictors of intention for condom use.

Conclusions

Our findings support application of the model in predicting determinants of condom use and abstinence intentions among Swazi in-school youths.  相似文献   

7.

Background

Identifying the economic value assigned by users to a particular health service is of principal interest in planning the service. The aim of this study was to evaluate the perception of economic value of nursing consultation in primary care (PC) by its users.

Methods and Results

Economic study using contingent valuation methodology. A total of 662 users of nursing consultation from 23 health centers were included. Data on demographic and socioeconomic characteristics, health needs, pattern of usage, and satisfaction with provided service were compiled. The validity of the response was evaluated by an explanatory mixed-effects multilevel model in order to assess the factors associated with the response according to the welfare theory. Response reliability was also evaluated. Subjects included in the study indicated an average Willingness to Pay (WTP) of €14.4 (CI 95%: €13.2–15.5; median €10) and an average Willingness to Accept [Compensation] (WTA) of €20.9 (CI 95%: €19.6–22.2; median €20). Average area income, personal income, consultation duration, home visit, and education level correlated with greater WTP. Women and older subjects showed lower WTP. Fixed parameters explained 8.41% of the residual variability, and response clustering in different health centers explained 4–6% of the total variability. The influence of income on WTP was different in each center. The responses for WTP and WTA in a subgroup of subjects were consistent when reassessed after 2 weeks (intraclass correlation coefficients 0.952 and 0.893, respectively).

Conclusions

The economic value of nursing services provided within PC in a public health system is clearly perceived by its user. The perception of this value is influenced by socioeconomic and demographic characteristics of the subjects and their environment, and by the unique characteristics of the evaluated service. The method of contingent valuation is useful for making explicit this perception of value of health services.  相似文献   

8.
The distribution pattern of mtDNA haplotypes in distinct populations of the glacial relict crustacean Saduria entomon was examined to assess phylogeographic relationships among them. Populations from the Baltic, the White Sea and the Barents Sea were screened for mtDNA variation using PCR‐based RFLP analysis of a 1150 bp fragment containing part of the CO I and CO II genes. Five mtDNA haplotypes were recorded. An analysis of geographical heterogeneity in haplotype frequency distributions revealed significant differences among populations. The isolated populations of S. entomon have diverged since the retreat of the last glaciation. The geographical pattern of variation is most likely the result of stochastic (founder effect, genetic drift) mechanisms and suggests that the haplotype differentiation observed is probably older than the isolation of the Baltic and Arctic seas.  相似文献   

9.
The problem of selecting a “best” (largest mean, or smallest mean) population from a collection of k independent populations was formulated and solved by Bechhofer (1954). Gupta (1965) solved another important problem, that of selecting a subset of populations containing the “best” population from the original collection of populations. Since then many variations of the problem have been considered. Tong (1969) and Lewis (1980) have investigated the problem of selecting extreme populations (populations with a largest, and populations with a smallest, mean) with respect to one and two standard populations, respectively. In this paper we study the selection of extreme populations in absence of any standard population. We formulate subset-selection procedures when variances are known and equal, and also in the most general case when they are unknown and unequal. Nonexistence of a single-stage procedure is noted for this latter case (even if variances are equal). A two-stage procedure and some of its associated properties are discussed. Tables needed for application are provided, as is a worked example.  相似文献   

10.

Objectives

Estimate the prevalence of functional dentition among Brazilian adults using four different definitions and identify associated factors.

Methods

A cross-sectional study was conducted involving 9564 Brazilian adults aged 35–44 years who participated in the 2010 National Oral Health Survey. Data collection involved oral examinations and the administration of questionnaires. The following definitions were used: 1—WHO Functional Dentition (FDWHO: ≥ 20 teeth present); 2—well-distributed teeth (WDT: ≥ 10 teeth in each arch); 3 –Functional dentition classified by esthetics and occlusion (FDClass5: dentitions that sequentially exhibit at least one tooth in each arch, at least 10 teeth in each arch, all maxillary and mandibular anterior teeth, three or four premolar posterior occluding pairs [POPs], and at least one molar POP bilaterally); 4—Functional dentition classified by esthetics, occlusion and periodontal status (FDClass6: corresponds to FDClass5 with the addition of periodontal status of all sextants in the oral cavity with, at most, shallow pockets and/or clinical attachment level of 5 mm (CPI ≤ 3 and/or CAL ≤ 1). The independent variables were individual factors (gender, self-declared skin color, schooling, monthly household income, age group, self-rated treatment need, dental pain, dental appointment in the previous 12 months and dental services) and contextual factors (Municipal Human Development Index [MHDI]), Gini coefficient, fluoridated water supply and oral health coverage). Multilevel mixed-effect Poisson regression analyses were performed.

Results

The prevalence of functional dentition based on the FDWHO, WDT, FDClass5 and FDClass6 definitions was 77.9%, 72.9%, 42.6% and 40.3%, respectively. Adults with ≥12 years of schooling and monthly household income from US$ 853 to 2557 had higher prevalence rates of FDWHO (PR: 1.41 and 1.10, respectively), WDT (PR: 1.58 and 1.14, respectively), FDClass5 (PR: 2.03 and 1.27, respectively) and FDClass6 (PR: 2.15 and 1.35, respectively). These values in the final models were adjusted for gender, self-declared skin color (FDClass5), age group, self-rated treatment need (FDWHO, FDClass5 and FDClass6), dental appointment in the previous 12 months (FDWHO and WDT), dental services (FDWHO and WDT) and contextual factors. A very high MHDI and presence of fluoridated water supply were associated with higher prevalence rates of the four outcomes.

Conclusions

The incorporation of the criteria of new definitions of functional dentition led to a lower prevalence rate among Brazilian adults. Striking individual and contextual inequalities were identified with regard to the four definitions analyzed, which need to be addressed through inter-sector efforts.  相似文献   

11.
We develop a mathematical framework to model the dynamics of the effect of antimicrobial agents on heterogeneous microbial populations of distributed antimicrobial resistance. Our framework uses the concept of cumulants of a distribution. Simplifications that result in easily usable approximation tools are presented. A case study on experimental data exemplifies shortcomings of standard methods and the usefulness of the proposed approach. Suggestions for future development are made. Author to whom all correspondence should be addressed  相似文献   

12.
Pieter W.  Kat 《Journal of Zoology》1983,201(3):395-416
Simultaneous hermaphroditism is an infrequent mode of reproduction among bivalves of the family Unionidae: only five of the 220 North American species are simultaneous hermaphrodites. However, hermaphroditic individuals of otherwise predominantly dioecious species have been encountered in 30 of I01 species examined. These hermaphroditic individuals as well as simultaneous hermaphrodites can exhibit considerable variability in the ratio of spermatogenic: oogenic tissue within the gonad, and the purposes of this paper are to determine the underlying causes of both this variability and the occurrence of occasional hermaphroditic individuals among dioecious species. Results indicate that the ratio of male: female gonodal tissue of a simultaneous hermaphrodite is bimodally distributed, and several hypotheses to account for this observation are presented. It is proposed that populations occurring in different habitats and under conditions of different individual density are subject to fundamentally different sexual selection pressures acting on ratios of allocation to male and female gametes. Occasional hermaphroditism among otherwise predominantly dioecious species was in this study associated with infection of the gonads by digenean trematodes. A model of sexual determination among unionids presented in this paper proposes that sex is determined by genetically controlled hormone levels: occasional hermaphrodites result from alterations in these hormone levels caused by developmental errors and trematodal infections which mimic the results of such errors. Predictions of this model are consistent with observed levels of variability in male: females gonadal tissue among occasional hermaphrodites.  相似文献   

13.

Background

There is currently limited information as to which conditions are most prevalent in communities in developing countries. This makes effective planning of eye services difficult.

Methods

3,899 eligible individuals were recruited and examined in a cross-sectional survey in Asa Local Government Area, Nigeria. Those who self-reported an ocular morbidity were also asked about their health-seeking behaviour. Health records of local facilities were reviewed to collect information on those presenting with ocular morbidities.

Results

25.2% (95% CI: 22.0–28.6) had an ocular morbidity in at least one eye. Leading causes were presbyopia and conditions affecting the lens and conjunctiva. The odds of having an ocular morbidity increased with age and lower educational attainment. 10.1% (7.7–13.0) self-reported ocular morbidity; 48.6% (40.4–56.8) of them reported seeking treatment. At the facility level, 344 patients presented with an ocular morbidity over one month, the most common conditions were red (26.3%) or itchy (20.8%) eyes.

Conclusion

Ocular morbidities, including many non vision impairing conditions, were prevalent with a quarter of the population affected. The delivery of eye care services needs to be tailored in order to address this need and ensure delivery in a cost-effective and sustainable manner.  相似文献   

14.
DNA sequences were determined for portions of the mitochondrial control region and 16S rRNA genes in five populations of Schistura oedipus, a troglobitic fish from northwestern Thailand. Based on variation at seven sites out of 593 sequenced, the five populations fall into three groups, apparently isolated by altitude and distance. Nucleotide diversity within groups is on the order of 1.0×10–3 while the extra increment of diversity among groups is on the order of 5.0×10–3. While the groups are distinct, the level of differentiation among them is low enough to accept provisionally that the five populations represent a single species. On the basis of 16S sequence, Schistura oedipus appears to be more closely related to S. poculi than to S. reidi, a proposed sister taxon.  相似文献   

15.
Goal, Scope and Background Incorporation of exposure and risk concepts into life cycle impact assessment (LCIA) is often impaired by the number of sources and the complexity of site-specific impact assessment, especially when input-output (I-O) analysis is used to evaluate upstream processes. This makes it difficult to interpret LCIA outputs, especially in policy contexts. In this study, we develop an LCIA tool which takes into account the geographical variability in both emissions and exposure and which can be applied to all economic sectors in I-O analysis, relying on screening-level risk calculations and methods to estimate population exposure per unit emissions from specific geographic locations. Methods We develop our analytical approach with reference to the case of increasing insulation for new single-family homes in the US. We quantify the public health costs from increasing insulation manufacturing and compare them with the benefits from energy savings, focusing on mortality and morbidity associated with exposure to primary and secondary fine particles (PM2.5) as well as cancer risk associated with exposure to toxic air pollutants. We use OpenLC to estimate the incremental economic outputs induced by increased insulation and reduced fuel consumption and calculate emissions from a sector-specific pollution intensity matrix. We calculate sector-specific intake fractions (dimensionless ratios between the amount of pollutant intake and the amount of a pollutant emitted) using previously-derived regression models and apply these values to the supply chain emissions of fiberglass and fuel sources. We refine the exposure estimates for selected emission sites and pollutants that contribute significantly to total health impacts, running site-specific air dispersion models. We estimate health impacts using concentration-response functions from the published literature and compare the costs and benefits of the program by assigning monetary values to the health risks. In the second part of this paper, we present the results of our case study and consider the implications for incorporating exposure and risk concepts into I-O LCA.  相似文献   

16.
17.
Glibenclamide (GL)-loaded microcapsules (MC) and transdermal patches (TDP) were formulated and in vitro and in vivo parameters compared to find out the best route of drug administration. The formulation TDP1 having a drug–polymer ratio 1:1 showed comparatively higher GL release and better permeation across mice skin (p < 0.05). From the comparative study, it was concluded that the transdermal system of GL produced better improvement compared to oral microcapsule administration (p < 0.05). The transdermal system exhibited comparatively slow and continuous supply of GL at a desired rate to systemic circulation avoiding metabolism, which improved day-to-day glycemic control in diabetic subjects. Transdermal system of GL exhibited better control of hyperglycemia and prolonged plasma half-life by transdermal systems (9.6 ± 1.2 h) in comparison with oral microcapsule (5.84 ± 2.1 h), indicating that the drug, when administered by transdermal systems, will remain in the body for a longer period. From the glucose tolerance test, transdermal route effectively maintained the normoglycemic levels in contrast to the oral group (MC1), which produced remarkable hypoglycemia ranging from −12.6 ± 2.1% to −18 ± 2.3%. The significantly high (p < 0.05) area under the curve values observed with transdermal system (1,346.2 ± 92.3 ng ml−1 h−1) also indicate increased bioavailability of the drug from these systems compared to the oral route (829.8 ± 76.4 ng ml−1 h−1).  相似文献   

18.
Modern biological and chemical studies rely on life science databases as well as sophisticated software tools (e.g., homology search tools, modeling and visualization tools). These tools often have to be combined and integrated in order to support a given study. SIBIOS (System for the Integration of Bioinformatics Services) serves this purpose. The services are both life science database search services and software tools. The task engine is the core component of SIBIOS. It supports the execution of dynamic workflows that incorporate multiple bioinformatics services. The architecture of SIBIOS, the approaches to addressing the heterogeneity as well as interoperability of bioinformatics services, including data integration are presented in this paper.  相似文献   

19.

Background

The private sector plays a large role in health services delivery in low- and middle-income countries; yet significant gaps remain in the quality and accessibility of private sector services. Clinical social franchising, which applies the commercial franchising model to achieve social goals and improve health care, is increasingly used in developing countries to respond to these limitations. Despite the growth of this approach, limited evidence documents the effect of social franchising on improving health care quality and access.

Objectives and Methods

We examined peer-reviewed and grey literature to evaluate the effect of social franchising on health care quality, equity, cost-effectiveness, and health outcomes. We included all studies of clinical social franchise programs located in low- and middle-income countries. We assessed study bias using the WHO-Johns Hopkins Rigour Scale and used narrative synthesis to evaluate the findings.

Results

Of 113 identified articles, 23 were included in this review; these evaluated a small sample of franchises globally and focused on reproductive health franchises. Results varied widely across outcomes and programs. Social franchising was positively associated with increased client volume and client satisfaction. The findings on health care utilization and health impact were mixed; some studies find that franchises significantly outperform other models of health care, while others show franchises are equivalent to or worse than other private or public clinics. In two areas, cost-effectiveness and equity, social franchises were generally found to have poorer outcomes.

Conclusions

Our review indicates that social franchising may strengthen some elements of private sector health care. However, gaps in the evidence remain. Additional research should include: further documentation of the effect of social franchising, evaluating the equity and cost-effectiveness of this intervention, and assessing the role of franchising within the context of the greater healthcare delivery system.  相似文献   

20.

Introduction

In an effort to increase understanding of formation of the community and home-based care economy in South Africa, we investigated the origin and development of non-profit organisations (NPOs) providing home- and community-based care for health and social services in a remote rural area of South Africa.

Methods

Over a three-year period (2010-12), we identified and tracked all NPOs providing health care and social services in Bushbuckridge sub-district through the use of local government records, snowballing techniques, and attendance at NPO networking meetings—recording both existing and new NPOs. NPO founders and managers were interviewed in face-to-face in-depth interviews, and their organisational records were reviewed.

Results

Forty-seven NPOs were formed prior to the study period, and 14 during the study period – six in 2010, six in 2011 and two in 2012, while four ceased operation, representing a 22% growth in the number of NPOs during the study period. Histories of NPOs showed a steady rise in the NPO formation over a 20-year period, from one (1991-1995) to 12 (1996-2000), 16 (2001-2005) and 24 (2006-2010) new organisations formed in each period. Furthermore, the histories of formation revealed three predominant milestones – loose association, formal formation and finally registration. Just over one quarter (28%) of NPOs emerged from a long-standing community based programme of ‘care groups’ of women. Founders of NPOs were mostly women (62%), with either a religious motivation or a nursing background, but occasionally had an entrepreneurial profile.

Conclusion

We observed rapid growth of the NPO sector providing community based health and social services. Women dominated the rural NPO sector, which is being seen as creating occupation and employment opportunities. The implications of this growth in the NPO sector providing community based health and social services needs to be further explored and suggests the need for greater coordination and possibly regulation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号