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2.
Stud Fam Plann ; 52(3): 383-393, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34268743

RESUMO

The global family planning community has made significant progress towards enabling 120 million more women and girls to use contraceptives by 2020, though we enter the decade ahead with a long road yet to travel. While investment in strong health systems and supply chains is still needed, the supply-driven approach dominant in family planning fails to address the individual, relational, and social barriers faced by women and couples in achieving their reproductive intentions and desired family size. Overcoming these barriers will require a better understanding of behavioral drivers and the social environment in which family planning decisions are made, and an increased investment in the proven, yet underutilized, approach of social and behavior change (SBC). We make the case that a more intentional focus on the science of human behavior in family planning can help advance the achievement of global, regional, and national goals while also calling for strategic and sustained investment that reflects the critical importance and proven impact of SBC approaches.


Assuntos
Anticoncepcionais , Serviços de Planejamento Familiar , Países em Desenvolvimento , Feminino , Humanos , Intenção , Masculino , Educação Sexual
3.
Lancet ; 391(10123): 870-882, 2018 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-29217374

RESUMO

BACKGROUND: The London Summit on Family Planning in 2012 inspired the Family Planning 2020 (FP2020) initiative and the 120×20 goal of having an additional 120 million women and adolescent girls become users of modern contraceptives in 69 of the world's poorest countries by the year 2020. Working towards achieving 120 × 20 is crucial for ultimately achieving the Sustainable Development Goals of universal access and satisfying demand for reproductive health. Thus, a performance assessment is required to determine countries' progress. METHODS: An updated version of the Family Planning Estimation Tool (FPET) was used to construct estimates and projections of the modern contraceptive prevalence rate (mCPR), unmet need for, and demand satisfied with modern methods of contraception among women of reproductive age who are married or in a union in the focus countries of the FP2020 initiative. We assessed current levels of family planning indicators and changes between 2012 and 2017. A counterfactual analysis was used to assess if recent levels of mCPR exceeded pre-FP2020 expectations. FINDINGS: In 2017, the mCPR among women of reproductive age who are married or in a union in the FP2020 focus countries was 45·7% (95% uncertainty interval [UI] 42·4-49·1), unmet need for modern methods was 21·6% (19·7-23·9), and the demand satisfied with modern methods was 67·9% (64·4-71·1). Between 2012 and 2017 the number of women of reproductive age who are married or in a union who use modern methods increased by 28·8 million (95% UI 5·8-52·5). At the regional level, Asia has seen the mCPR among women of reproductive age who are married or in a union grow from 51·0% (95% UI 48·5-53·4) to 51·8% (47·3-56·5) between 2012 and 2017, which is slow growth, particularly when compared with a change from 23·9% (22·9-25·0) to 28·5% (26·8-30·2) across Africa. At the country level, based on a counterfactual analysis, we found that 61% of the countries that have made a commitment to FP2020 exceeded pre-FP2020 expectations for modern contraceptive use. Country success stories include rapid increases in Kenya, Mozambique, Malawi, Lesotho, Sierra Leone, Liberia, and Chad relative to what was expected in 2012. INTERPRETATION: Whereas the estimate of additional users up to 2017 for women of reproductive age who are married or in a union would suggest that the 120 × 20 goal for all women is overly ambitious, the aggregate outcomes mask the diversity in progress at the country level. We identified countries with accelerated progress, that provide inspiration and guidance on how to increase the use of family planning and inform future efforts, especially in countries where progress has been poor. FUNDING: The Bill & Melinda Gates Foundation, through grant support to the University of Massachusetts Amherst and Avenir Health.


Assuntos
Comportamento Contraceptivo/estatística & dados numéricos , Anticoncepção/estatística & dados numéricos , Inquéritos sobre o Uso de Métodos Contraceptivos/métodos , Países em Desenvolvimento/estatística & dados numéricos , Serviços de Planejamento Familiar/métodos , Adolescente , Adulto , Anticoncepção/economia , Comportamento Contraceptivo/tendências , Feminino , Acessibilidade aos Serviços de Saúde/estatística & dados numéricos , Necessidades e Demandas de Serviços de Saúde/tendências , Humanos , Masculino , Pessoa de Meia-Idade , Satisfação Pessoal , Adulto Jovem
4.
Stud Fam Plann ; 50(4): 289-316, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31793671

RESUMO

When designing a family planning (FP) strategy, decision-makers can choose from a wide range of interventions designed to expand access to and develop demand for FP. However, not all interventions will have the same impact on increasing modern contraceptive prevalence (mCP). Understanding the existing evidence is critical to planning successful and cost-effective programs. The Impact Matrix is the first comprehensive summary of the impact of a full range of FP interventions on increasing mCP using a single comparable metric. It was developed through an extensive literature review with input from the wider FP community, and includes 138 impact factors highlighting the range of effectiveness observed across categories and subcategories of FP interventions. The Impact Matrix is central to the FP Goals model, used to project scenarios of mCP growth that help decision-makers set realistic goals and prioritize investments. Development of the Impact Matrix, evidence gaps identified, and the contribution to FP Goals are discussed.


Assuntos
Comportamento Contraceptivo , Serviços de Planejamento Familiar/organização & administração , Saúde Global , Avaliação de Programas e Projetos de Saúde/métodos , Agentes Comunitários de Saúde/organização & administração , Serviços de Planejamento Familiar/normas , Objetivos , Promoção da Saúde/organização & administração , Humanos , Avaliação de Programas e Projetos de Saúde/normas
5.
BMC Public Health ; 13 Suppl 2: S5, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23902699

RESUMO

BACKGROUND: Individual family planning service delivery organisations currently rely on service provision data and couple-years of protection as health impact measures. Due to the substitution effect and the continuation of users of long-term methods, these metrics cannot estimate an organisation's contribution to the national modern contraceptive prevalence rate (CPR), the standard metric for measuring family planning programme impacts. Increasing CPR is essential for addressing the unmet need for family planning, a recognized global health priority. Current health impact estimation models cannot isolate the impact of an organisation in these efforts. Marie Stopes International designed the Impact 2 model to measure an organisation's contribution to increases in national CPR, as well as resulting health and demographic impacts. This paper aims to describe the methodology for modelling increasing national-level CPR as well as to discuss its benefits and limitations. METHODS: Impact 2 converts service provision data into estimates of the number of family planning users, accounting for continuation among users of long-term methods and addressing the challenges of converting commodity distribution data of short-term methods into user numbers. These estimates, combined with the client profile and data on the organisation's previous year's CPR contribution, enable Impact 2 to estimate which clients maintain an organisation's baseline contribution, which ones fulfil population growth offsets, and ultimately, which ones increase CPR. RESULTS: Illustrative results from Marie Stopes Madagascar show how Impact 2 can be used to estimate an organisation's contribution to national changes in the CPR. CONCLUSIONS: Impact 2 is a useful tool for service delivery organisations to move beyond cruder output measures to a better understanding of their role in meeting the global unmet need for family planning. By considering health impact from the perspective of an individual organisation, Impact 2 addresses gaps not met by other models for family planning service outcomes. Further, the model helps organisations improve service delivery by demonstrating that increases in the national CPR are not simply about expanding user numbers; rather, the type of user (e.g. adopters, provider changers) must be considered. Impact 2 can be downloaded at http://www.mariestopes.org/impact-2.


Assuntos
Anticoncepção/estatística & dados numéricos , Serviços de Planejamento Familiar/organização & administração , Agências Internacionais/organização & administração , Modelos Estatísticos , Avaliação de Programas e Projetos de Saúde/métodos , Adulto , Estudos de Coortes , Feminino , Humanos , Madagáscar , Masculino , Pessoa de Meia-Idade , Prevalência
6.
PLOS Glob Public Health ; 3(10): e0002347, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37851610

RESUMO

Around half of adolescent pregnancies in low- and middle-income countries are unintended, contributing to millions of unsafe abortions per year. Adolescents 360 (A360), a girl-centred initiative, aimed to increase voluntary uptake of modern contraceptives among adolescents in Nigeria, Ethiopia and Tanzania. We evaluated the effectiveness and cost-effectiveness of A360 in increasing modern contraceptive use in selected geographies. We used before-and-after cross-sectional studies of adolescent girls in four settings. Two Nigerian settings had purposefully selected comparison areas. Baseline and endline household surveys were conducted. The primary study outcome was modern contraceptive prevalence rate (mCPR). Secondary outcomes mapped onto the A360 Theory of Change. Interpretation was aided by a process evaluation along with secular mCPR trends and self-reported A360 exposure data. Incremental design and implementation costs were calculated from implementer systems, site visits, surveys, and interviews. mCPR change was modelled into maternal disability-adjusted life years (DALY) averted to calculate incremental cost-effectiveness ratios. In Oromia, Ethiopia, mCPR increased by 5% points (95% CI 1-10; n = 1,697). In Nigeria, there was no evidence of an effect of A360 on mCPR in Nasarawa (risk ratio: 0·96, 95% CI: 0·76-1·21; n = 5,414) or in Ogun (risk ratio: 1·08, 95% CI: 0·92-1·26; n = 3,230). In Mwanza, Tanzania, mCPR decreased by 9% points (-17 to -0.3; n = 1,973). Incremental cost per DALY averted were $30,855 in Oromia, $111,416 in Nasarawa, $30,114 in Ogun, and $25,579 in Mwanza. Costs per DALY averted were 14-53 times gross domestic product per capita. A360 did not lead to increased adolescent use of modern contraceptives at a population level, except in Oromia, and was not cost-effective. This novel adolescent-centred design approach showed some promise in addressing the reproductive health needs of adolescents, but must be accompanied by efforts to address the contextual drivers of low modern contraceptive use.

7.
BMJ Glob Health ; 6(4)2021 04.
Artigo em Inglês | MEDLINE | ID: mdl-33846142

RESUMO

INTRODUCTION: The role of the private sector in family planning (FP) is well studied; however, few efforts have been made to quantify the role of private out-of-pocket (OOP) expenditures on FP commodities across low-and-middle-income countries (LMICs). Calculating OOP expenditures is important to illuminate the magnitude of these contributions and to inform discussions on how financial burdens can be reduced. METHODS: Estimates of FP users and commodities consumed by women getting their FP methods from the private sector were made for 132 LMICs. Next, unit price data were compiled from to estimate the average price of commodities in the private sector at both a commercial and subsidised price point. These unit prices were applied to commodity consumption estimates to calculate total private OOP expenditures. Sensitivity testing was conducted. RESULTS: Total estimated private OOP expenditures for FP commodities in 2019 was $2.73 billion across 132 LMICs. Spending on contraceptive pills accounted for 80% of this total, and just over three-quarters of expenditure came from upper-middle-income countries. OOP expenditures on subsidised commodities were small but accounted for 20% of expenditures in low-income countries. Non-subsidised unit prices were found to be between 5 and 20 times higher in upper-middle-income countries compared with low-income countries, although wide variation exists. For low-income and lower-middle-income countries, subsidies appear to be greatest for intrauterine devices (IUDs) and pills. CONCLUSION: Large OOP expenditures across all income levels highlight a need for financing approaches that ensure that a wide range of contraceptives are both accessible and affordable.


Assuntos
Países em Desenvolvimento , Gastos em Saúde , Serviços de Planejamento Familiar , Feminino , Humanos , Pobreza , Setor Privado
8.
Gates Open Res ; 5: 152, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34934906

RESUMO

Background: Despite a wide range of contraceptive methods, unmet need persists. New contraceptive technologies (CTs) have the potential to improve uptake and continuation. CT development has a long-time horizon; products will be introduced into markets that look very different than today. Identifying viable investments requires an understanding of these future markets. For this work the 2040 potential contraceptive market is described utilizing seven market segments based on marital status, fertility preferences, and patterns of sexual activity outside of marriage.  Methods: Market size estimates are developed by country for all countries in the world for a current market (2020) and a future market (2040). United Nation's (UN) population projections of the number of women of reproductive age (WRA) form the basis of this work. WRA are then segmented into market segments based on marital status, fertility intentions, and patterns of sexual activity outside of marriage.  Each segment is further subdivided by contraceptive use versus non-use.  Segmentation draws from UN projections, household surveys, census data, and modeling techniques developed for this work. Results: The largest market increases will be seen in Africa; most notably among the segment of married women wanting no more children. By contrast, Asia will see declines across all three married segments, coupled with increases among sexually active unmarried segments.  Levels of contraceptive use are projected to vary widely by segment, with differential patters across regions. Conclusions: This analysis projects the impact of demographic changes, evolving fertility preferences, shifts in sexual activity outside of marriage and increased utilization of contraceptives in shaping the contraceptive market of 2040. Results show that there is not one global market, but distinct markets that vary in size and shape across the world. This diversity suggests that a range of different new CTs could have potential for uptake.

9.
Gates Open Res ; 4: 113, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33117964

RESUMO

Background: Sustainable Development Goal 3.7 aims to ensure universal access to sexual and reproductive health services. One suggested benchmark is to have at least 75% of the demand for contraception satisfied with modern methods (DS) in all countries by 2030. The translation of DS-based targets into targets for the modern contraceptive prevalence rate (mCPR) is needed to make targets actionable. Methods: We propose the Accelerated Transition (AT) method for determining the mCPR needed to reach demand-satisfied targets by 2030. The starting point for this method is the projection of DS under "business as usual" using the one-country implementation of the Family Planning Estimation Model (FPEMcountry). For countries in which the DS target is projected to be later than 2030, the AT method assumes that meeting the DS target by 2030 requires an acceleration of the contraceptive use transition such that the DS target, and its associated mCPR, will be reached in 2030 as opposed to the later year. The DS-target-associated mCPR becomes the mCPR target for the year 2030. Results: We apply the AT method to assess progress needed for attaining the 75% DS target for married or in-union women in the world's poorest countries. For 50 out of 68 countries, we estimate that accelerations are needed, with required mCPR increases ranging from 4.3 to 50.8 percentage points. Conclusions: The AT method quantifies the acceleration needed - as compared to business as usual projections - for a country to meet a family planning target. The method can be used to determine the mCPR needed to reach demand-satisfied targets.

10.
BMJ Glob Health ; 5(9)2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32928799

RESUMO

Family planning market segmentation approaches typically include analysis by wealth, particularly when considering whether individuals can afford out-of-pocket expenses in the private sector. Most commonly, this is done using the Demographic and Health Survey (DHS) wealth index, which uses a relative approach by summing household asset questions and categorising respondents into five groups from poorest to wealthiest within a country. In addition, the use of absolute measures, such as segmenting populations based on whether one lives below or above the International Poverty line, defined by the World Bank as US$1.90 per person per day, may provide further useful insights when designing strategies to ensure access to family planning. While such measures are not readily available in the DHS, a simple approach can be used to combine the wealth index and World Bank poverty lines to generate an absolute measure for an additional perspective when conducting family planning market segmentation. Family planning market size estimates were made for 24 low-income countries using wealth quintiles and World Bank poverty lines. The results show large variations in market size based on what measure is used, particularly for countries with a high density of poverty. Looking at both types of measures and understanding the reasons for the differences in market size estimates between the approaches can help lend a more nuanced understanding of the distribution of wealth and income in a country, leading to improved family planning market segmentation and ultimately to ensure more women have access to a method of their choice.


Assuntos
Países em Desenvolvimento , Serviços de Planejamento Familiar , Características da Família , Feminino , Inquéritos Epidemiológicos , Humanos , Renda
11.
Gates Open Res ; 3: 1472, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31363715

RESUMO

Adolescents 360 (A360) is a four-year initiative (2016-2020) to increase 15-19-year-old girls' use of modern contraception in Nigeria, Ethiopia and Tanzania. The innovative A360 approach is led by human-centred design (HCD), combined with social marketing, developmental neuroscience, public health, sociocultural anthropology and youth engagement 'lenses', and aims to create context-specific, youth-driven solutions that respond to the needs of adolescent girls. The A360 external evaluation includes a process evaluation, quasi-experimental outcome evaluation, and a cost-effectiveness study. We reflect on evaluation opportunities and challenges associated with measuring the application and impact of this novel HCD-led design approach. For the process evaluation, participant observations were key to capturing the depth of the fast-paced, highly-iterative HCD process, and to understand decision-making within the design process. The evaluation team had to be flexible and align closely with the work plan of the implementers. The HCD process meant that key information such as intervention components, settings, and eligible populations were unclear and changed over outcome evaluation and cost-effectiveness protocol development. This resulted in a more time-consuming and resource-intensive study design process. As much time and resources went into the creation of a new design approach, separating one-off "creation" costs versus those costs associated with actually implementing the programme was challenging. Opportunities included the potential to inform programmatic decision-making in real-time to ensure that interventions adequately met the contextualized needs in targeted areas. Robust evaluation of interventions designed using HCD, a promising and increasingly popular approach, is warranted yet challenging. Future HCD-based initiatives should consider a phased evaluation, focusing initially on programme theory refinement and process evaluation, and then, when the intervention program details are clearer, following with outcome evaluation and cost-effectiveness analysis. A phased approach would delay the availability of evaluation findings but would allow for a more appropriate and tailored evaluation design.

12.
Glob Health Sci Pract ; 6(1): 93-102, 2018 03 21.
Artigo em Inglês | MEDLINE | ID: mdl-29467167

RESUMO

The need for annual family planning program tracking data under the Family Planning 2020 (FP2020) initiative has contributed to renewed interest in family planning service statistics as a potential data source for annual estimates of the modern contraceptive prevalence rate (mCPR). We sought to assess (1) how well a set of commonly recorded data elements in routine service statistics systems could, with some fairly simple adjustments, track key population-level outcome indicators, and (2) whether some data elements performed better than others. We used data from 22 countries in Africa and Asia to analyze 3 data elements collected from service statistics: (1) number of contraceptive commodities distributed to clients, (2) number of family planning service visits, and (3) number of current contraceptive users. Data quality was assessed via analysis of mean square errors, using the United Nations Population Division World Contraceptive Use annual mCPR estimates as the "gold standard." We also examined the magnitude of several components of measurement error: (1) variance, (2) level bias, and (3) slope (or trend) bias. Our results indicate modest levels of tracking error for data on commodities to clients (7%) and service visits (10%), and somewhat higher error rates for data on current users (19%). Variance and slope bias were relatively small for all data elements. Level bias was by far the largest contributor to tracking error. Paired comparisons of data elements in countries that collected at least 2 of the 3 data elements indicated a modest advantage of data on commodities to clients. None of the data elements considered was sufficiently accurate to be used to produce reliable stand-alone annual estimates of mCPR. However, the relatively low levels of variance and slope bias indicate that trends calculated from these 3 data elements can be productively used in conjunction with the Family Planning Estimation Tool (FPET) currently used to produce annual mCPR tracking estimates for FP2020.


Assuntos
Comportamento Contraceptivo/estatística & dados numéricos , Serviços de Planejamento Familiar/estatística & dados numéricos , Avaliação de Programas e Projetos de Saúde/métodos , África , Ásia , Humanos , Inquéritos e Questionários
13.
Gates Open Res ; 1: 15, 2017 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-29355228

RESUMO

Most frameworks for family planning include both access and demand interventions. Understanding how these two are linked and when each should be prioritized is difficult. The maximum contraceptive prevalence 'demand curve' was created based on a relationship between the modern contraceptive prevalence rate (mCPR) and mean ideal number of children to allow for a quantitative assessment of the balance between access and demand interventions. The curve represents the maximum mCPR that is likely to be seen given fertility intentions and related norms and constructs that influence contraceptive use. The gap between a country's mCPR and this maximum is referred to as the 'potential use gap.' This concept can be used by countries to prioritize access investments where the gap is large, and discuss implications for future contraceptive use where the gap is small. It is also used within the FP Goals model to ensure mCPR growth from access interventions does not exceed available demand.

14.
Glob Health Sci Pract ; 5(4): 658-667, 2017 12 28.
Artigo em Inglês | MEDLINE | ID: mdl-29217695

RESUMO

Estimates of the potential impacts of contraceptive use on averting unintended pregnancies, total and unsafe abortions, maternal deaths, and newborn, infant, and child deaths provide evidence of the value of investments in family planning programs and thus are critically important for policy makers, donors, and advocates alike. Several research teams have independently developed mathematical models that estimate the number of adverse health outcomes averted due to contraceptive use. However, each modeling approach was designed for different purposes, and as such the methodological assumptions, data inputs, and mathematical algorithms initially used in each model differed; consequently, the models did not produce comparable estimates for the same outcome indicators. To address this, a series of expert group meetings took place in which 5 models-Adding it Up, Impact 2, ImpactNow, Reality Check, and FamPlan/Lives Saved Tool (LiST)-were reviewed and harmonized where possible. The group identified the main reasons for the inconsistencies in the estimates generated by the models for each of the adverse health outcome indicators. The group then worked together to align the methodologies for estimating numbers of unintended pregnancies, abortions, and maternal deaths averted due to contraceptive use, and reviewed the challenges with estimating the impact of contraceptive use on newborn, infant, and child deaths, including the lack of a conceptually clear pathway and rigorous evidence. The assumption that most influenced harmonization was the comparison pregnancy rate used by the models to estimate the counterfactual scenario-that is, if women who are currently using contraception were not using a method, how many would become pregnant? All the models now base this on the number of unintended pregnancies among women with unmet contraceptive need, bringing the estimates for unintended pregnancies, total and unsafe abortion, and maternal deaths much closer together. The agreed approaches have already been adopted by the Family Planning 2020 (FP2020) initiative and Track20, a project that supports FP2020. The experts will continue to update their models collaboratively to ensure that the most current estimation methodologies and data available are used. Valid and reliable methodologies for estimating these impacts from family planning are critically important, not only for advocacy to sustain resource allocation commitments but also to enable measurement and tracking of global development indicators. Conflicting estimates can be counterproductive to generating support for family planning programs, and this harmonization process has created a more unified voice for quantifying the benefits of family planning.


Assuntos
Aborto Induzido/estatística & dados numéricos , Anticoncepção/estatística & dados numéricos , Serviços de Planejamento Familiar , Morte Materna/prevenção & controle , Saúde Materna/estatística & dados numéricos , Gravidez não Planejada , Avaliação de Programas e Projetos de Saúde/métodos , Feminino , Humanos , Modelos Teóricos , Gravidez
16.
Glob Health Sci Pract ; 2(1): 72-92, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-25276564

RESUMO

Contraceptive implants offer promising opportunities for addressing the high and growing unmet need for modern contraceptives in sub-Saharan Africa. Marie Stopes International (MSI) offers implants as one of many family planning options. Between 2008 and 2012, MSI scaled up voluntary access to implants in 15 sub-Saharan African countries, from 80,041 implants in 2008 to 754,329 implants in 2012. This 9-fold increase amounted to more than 1.7 million implants delivered cumulatively over the 5-year period. High levels of client satisfaction were attained alongside service provision scale up by using existing MSI service delivery channels-mobile outreach, social franchising, and clinics-to implement strategies that broadened access for underserved clients and maintained service quality. Use of adaptive and context-specific service delivery models and attention to key operational components, including sufficient numbers of trained providers, strong supply chains, diverse financing mechanisms, and implant removal services, underpinned our service delivery efforts. Accounting for 70% of the implants delivered by MSI in 2012, mobile outreach services through dedicated MSI provider teams played a central role in scale-up efforts, fueled in part by the provision of free or heavily subsidized services. Social franchising also demonstrated promise for future program growth, along with MSI clinics. Continued high growth in implant provision between 2011 and 2012 in all sub-Saharan African countries indicates the region's capacity for further service delivery expansion. Meeting the expected rising demand for implants and ensuring long-term sustainable access to the method, as part of a comprehensive method mix, will require continued use of appropriate service delivery models, effective operations, and ongoing collaboration between the private, public, and nongovernmental sectors. MSI's experience can be instructive for future efforts to ensure contraceptive access and choice in sub-Saharan Africa, especially as the global health community works to achieve its Family Planning 2020 (FP2020) commitments to expand family planning access to 120 million new users.


Assuntos
Anticoncepcionais Femininos , Atenção à Saúde/organização & administração , Implantes de Medicamento , África Subsaariana , Humanos , Modelos Organizacionais , Garantia da Qualidade dos Cuidados de Saúde , População Urbana
18.
Phys Rev Lett ; 100(4): 045506, 2008 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-18352299

RESUMO

Interest in osmium as an ultra-incompressible material and as an analog for the behavior of iron at high pressure has inspired recent studies of its mechanical properties. We have measured elastic and plastic deformation of Os metal at high pressures using in situ high pressure x-ray diffraction in the radial geometry. We show that Os has the highest yield strength observed for any pure metal, supporting up to 10 GPa at a pressure of 26 GPa. Furthermore, our data indicate changes in the nonhydrostatic apparent c/a ratio and clear lattice preferred orientation effects at pressures above 15 GPa.

19.
Science ; 316(5823): 436-9, 2007 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-17446399

RESUMO

The quest to create superhard materials rarely strays from the use of high-pressure synthetic methods, which typically require gigapascals of applied pressure. We report that rhenium diboride (ReB2), synthesized in bulk quantities via arc-melting under ambient pressure, rivals materials produced with high-pressure methods. Microindentation measurements on ReB2 indicated an average hardness of 48 gigapascals under an applied load of 0.49 newton, and scratch marks left on a diamond surface confirmed its superhard nature. Its incompressibility along the c axis was equal in magnitude to the linear incompressibility of diamond. In situ high-pressure x-ray diffraction measurements yielded a bulk modulus of 360 gigapascals, and radial diffraction indicated that ReB2 is able to support a remarkably high differential stress. This combination of properties suggests that this material may find applications in cutting when the formation of carbides prevents the use of traditional materials such as diamond.


Assuntos
Compostos de Boro/química , Compostos de Boro/síntese química , Rênio/química , Anisotropia , Força Compressiva , Dureza , Pressão , Estresse Mecânico , Difração de Raios X
20.
J Am Chem Soc ; 127(20): 7264-5, 2005 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-15898746

RESUMO

The need for wear- and scratch-resistant materials drives the quest for new superhard materials. In this work, we apply two design parameters to identify ultra-incompressible, superhard materials-high valence electron density and high bond covalency. Our first example of such a material is OsB2. The bulk modulus of OsB2 was measured using in situ high-pressure X-ray diffraction and was determined to be in the range of 365-395 GPa. While this value is slightly less than that of the bulk modulus of diamond, due to the anisotropic crystal structure of OsB2, the axis compressibility in the orthorhombic c-direction is less than the axis compressibility found in diamond. OsB2 also scratches the surface of a sapphire window, indicating that the hardness of OsB2 exceeds 2000 kg/mm2.

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