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1.
Proc Natl Acad Sci U S A ; 119(38): e2208814119, 2022 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-36095186

RESUMO

Ureilite meteorites are arguably our only large suite of samples from the mantle of a dwarf planet and typically contain greater abundances of diamond than any known rock. Some also contain lonsdaleite, which may be harder than diamond. Here, we use electron microscopy to map the relative distribution of coexisting lonsdaleite, diamond, and graphite in ureilites. These maps show that lonsdaleite tends to occur as polycrystalline grains, sometimes with distinctive fold morphologies, partially replaced by diamond + graphite in rims and cross-cutting veins. These observations provide strong evidence for how the carbon phases formed in ureilites, which, despite much conjecture and seemingly conflicting observations, has not been resolved. We suggest that lonsdaleite formed by pseudomorphic replacement of primary graphite shapes, facilitated by a supercritical C-H-O-S fluid during rapid decompression and cooling. Diamond + graphite formed after lonsdaleite via ongoing reaction with C-H-O-S gas. This graphite > lonsdaleite > diamond + graphite formation process is akin to industrial chemical vapor deposition but operates at higher pressure (∼1-100 bar) and provides a pathway toward manufacture of shaped lonsdaleite for industrial application. It also provides a unique model for ureilites that can reconcile all conflicting observations relating to diamond formation.

2.
Immunol Cell Biol ; 102(1): 8-11, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-37982351

RESUMO

The advent and clinical success of immune checkpoint inhibitors Ipilimumab, Nivolumab and Pembrolizumab has had a seismic impact on our drug discovery focus and rationale. Novel extrinsic targets that enhance immune responses to cancer are actively being pursued, while tumor intrinsic targets that render cancer cells more sensitive to the immune system have joined traditional intrinsic targets (e.g. directly cytotoxic) in the drug discovery pipeline. The phosphatase PTPN2 (TC-PTP) and its paralog PTPN1 (PTP-1B) are negative regulators of several cytokine signaling pathways and T cell receptor (TCR) signaling. In a recent publication, Baumgartner et al. demonstrate the pre-clinical efficacy of a first-in-class dual PTPN1/N2 active site inhibitor (ABBV-CLS-484/AC484) in cancer models.


Assuntos
Anticorpos Monoclonais , Neoplasias , Humanos , Anticorpos Monoclonais/uso terapêutico , Nivolumabe/uso terapêutico , Ipilimumab/uso terapêutico , Neoplasias/tratamento farmacológico , Imunoterapia , Biologia
3.
Am J Otolaryngol ; 45(2): 104143, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38101130

RESUMO

BACKGROUND: Invasive fungal sinusitis (IFS) is a rare infection with high mortality, mainly impacting immunocompromised patients. Given its significant mortality, timely recognition and treatment is crucial. This study aims to highlight the differences in presentation of IFS between pediatric and adult patients to aid in prompt diagnosis and treatment of this condition. METHODS: A comprehensive literature search of PubMed, EMBASE, Web of Science, Global Index Medicus, Global Health (EBSCO) and Cochrane Database of Systematic Reviews was conducted to identify articles relating to IFS. Patient demographics, comorbidities, presentation, disease characteristics, treatments and outcomes were extracted from the studies, and statistical analyses were conducted to compare these variables between pediatric and adult patients. RESULTS: 111 studies identified 22 pediatric and 132 adult patients worldwide. Children were more likely to have hematologic malignancies compared to adults (59.1 % vs. 15.2 %, p < 0.001). Facial symptoms such as pain, edema, and numbness were the most common symptoms for both age groups. In the pediatric population, fever and nasal or oral mucosal lesions were more common presenting symptoms (both p < 0.001). Pediatric patients were more likely to present without disease extension beyond the sinuses (p < 0.001). There was no significant difference in either medication treatment or mortality between the two cohorts. CONCLUSION: IFS often presents with non-specific symptoms and a unique presentation in pediatric and adult populations. Clinical awareness of the varying presentations in both populations is important to treat in a timely manner given the rapid progression and high mortality rates of IFS.


Assuntos
Infecções Fúngicas Invasivas , Seios Paranasais , Sinusite , Adulto , Criança , Humanos , Infecções Fúngicas Invasivas/diagnóstico , Infecções Fúngicas Invasivas/tratamento farmacológico , Infecções Fúngicas Invasivas/epidemiologia , Nariz , Sinusite/terapia , Sinusite/tratamento farmacológico , Revisões Sistemáticas como Assunto
4.
Am J Otolaryngol ; 45(1): 104077, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-39382965

RESUMO

This study examines how patient demographics impact pediatric sensorineural hearing loss (SNHL) prevalence using the 2016 Kids' Inpatient Database (KID). By analyzing age, gender, race, income, insurance, and region, the study provides insights for early intervention and diagnosis. Multivariate regression analysis reveals associations between these factors and SNHL occurrence. OBJECTIVE: This study aims to assess the influence of patient demographics on pediatric SNHL prevalence, offering guidance for early detection and intervention strategies. STUDY DESIGN: Using 2016 KID data, this retrospective analysis investigates how patient factors like age, gender, race, income, insurance, and region relate to SNHL prevalence. Multivariate regression is employed to control for potential confounders. METHODS: Data from 6,266,285 patient discharges, including 9997 hearing loss cases, are analyzed. SNHL prevalence is calculated, and demographic variables are examined. Weighted odds ratios and multivariate regression are used to assess associations. RESULTS: The study finds an overall SNHL prevalence of 101.67 cases per 100,000 discharges in 2016. Non-Hispanic White patients show the highest prevalence. Black patients are more likely to be diagnosed, while Hispanic patients are less likely. Multivariate analysis highlights race, income, insurance, region, age, and sex as significant confounders. CONCLUSION: This study underscores the impact of patient demographics on pediatric SNHL prevalence. Factors like race, income, insurance, and region play a role. These findings aid in risk assessment, early identification, and tailored interventions. Further research can uncover socioeconomic disparities and underlying mechanisms.


Assuntos
Bases de Dados Factuais , Perda Auditiva Neurossensorial , Pacientes Internados , Humanos , Perda Auditiva Neurossensorial/epidemiologia , Perda Auditiva Neurossensorial/diagnóstico , Masculino , Feminino , Criança , Pré-Escolar , Estudos Retrospectivos , Adolescente , Lactente , Prevalência , Estados Unidos/epidemiologia , Pacientes Internados/estatística & dados numéricos , Fatores Etários , Fatores Sexuais , Recém-Nascido , Análise Multivariada , Renda/estatística & dados numéricos
5.
Am J Otolaryngol ; 45(6): 104447, 2024 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-39216170

RESUMO

OBJECTIVE: Hearing loss is a common sensory impairment in children that affects quality of life and development. Early intervention, such as hearing aids and communication therapies, can help children overcome these challenges and lessen the impact on their development. The objective of this study was to identify specific patient demographic factors correlated with the prevalence of pediatric conductive hearing loss. STUDY DESIGN: The study utilized the Kids' Inpatient Database (KID) by the Agency for Healthcare Research and Quality which collects inpatient information from hospitals for patients under 21 years old. We included all patients discharged in 2016 diagnosed with conductive hearing loss, and excluded neonatal patients discharged within 28 days of birth. METHODS: Statistical analyses were performed using R Studio and IBM SPSS Statistics. Weighted odds ratios were calculated for conductive hearing loss in relation to race and income, and a multivariate regression analysis examined associations between demographic variables and race categories in conductive hearing loss. RESULTS: The prevalence of conductive hearing loss (CHL) in pediatric patients in 2016 was 51.62 cases per 100,000 patients. Non-Hispanic White patients had the highest prevalence, while Black patients had the highest likelihood of CHL compared to the overall population. Lower income levels were associated with a decreased probability of CHL diagnosis. After adjusting for age, sex, hospital region, insurance, and income on multivariate analysis, White and Black patients were less likely to be diagnosed with CHL. Furthermore, patients in specific income quartiles also had lower CHL likelihood compared to the general population. CONCLUSION: While Black patients had a higher likelihood of being diagnosed with CHL than the general population, socioeconomic factors such as income greatly influenced the likelihood of CHL diagnosis. Other significant factors included income, region of the country, sex, and age. Further research is needed to better understand and address healthcare disparities related to pediatric hearing loss.

6.
J Cancer Educ ; 2024 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-39448411

RESUMO

This qualitative study delves into the facilitators and barriers surrounding cervical cancer prevention among Latina women in Georgia, with a specific focus on the impact of community-based organizations (CBOs). Employing semi-structured interviews with healthcare providers and representatives from CBOs, faith-based organizations, and other key stakeholders, the study uncovers key themes and subthemes shaping cervical cancer disparities. Themes such as challenges in cross-cultural healthcare access, difficulties due to lack of US citizenship, and limited mobility emerge as significant barriers, while community and family support stand out as crucial facilitators to cancer prevention. Additionally, the study examines community intervention methods from CBOs to target cervical cancer disparity, highlighting the importance of public awareness campaigns, building trust within the Latina community, and providing medical support tailored to immigrant populations. Through this comprehensive examination, the study not only offers invaluable insights into the intricate web of issues surrounding cervical cancer prevention but also endeavors to serve as a catalyst for targeted interventions and evidence-based policies aimed at ameliorating cervical cancer disparities among immigrant Latinas in Georgia and beyond.

7.
Ann Surg ; 277(2): 238-245, 2023 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-34102667

RESUMO

OBJECTIVE: To develop a COS, an agreed minimum set of outcomes to measure and report in all studies evaluating the introduction and evaluation of novel surgical techniques. SUMMARY OF BACKGROUND DATA: Agreement on the key outcomes to measure and report for safe and efficient surgical innovation is lacking, hindering transparency and risking patient harm. METHODS: (I) Generation of a list of outcome domains from published innovation-specific literature, policy/regulatory body documents, and surgeon interviews; (II) Prioritization of identified outcome domains using an international, multi-stakeholder Delphi survey; (III) Consensus meeting to agree the final COS. Participants were international stakeholders, including patients/public, surgeons, device manufacturers, regulators, trialists, methodologists, and journal editors. RESULTS: A total of 7972 verbatim outcomes were identified, categorized into 32 domains, and formatted into survey items/questions. Four hundred ten international participants (220 professionals, 190 patients/public) completed at least one round 1 survey item, of which 153 (69.5%) professionals and 116 (61.1%) patients completed at least one round 2 item. Twelve outcomes were scored "consensus in" ("very important" by ≥70% of patients and professionals) and 20 "no consensus." A consensus meeting, involvingcontext: modifications, unexpected disadvantages, device problems, technical procedure completion success, patients' experience relating to the procedure being innovative, surgeons'/operators' experience. Other domains relate to intended benefits, whether the overall desired effect was achieved and expected disadvantages. CONCLUSIONS: The COS is recommended for use in all studies before definitive randomized controlled trial evaluation to promote safe, transparent, and efficient surgical innovation.


Assuntos
Projetos de Pesquisa , Cirurgiões , Humanos , Técnica Delphi , Consenso , Avaliação de Resultados em Cuidados de Saúde/métodos
8.
Am J Bot ; 110(2): e16112, 2023 02.
Artigo em Inglês | MEDLINE | ID: mdl-36478327

RESUMO

PREMISE: Phenological variation among individuals within populations is common and has a variety of ecological and evolutionary consequences, including forming the basis for population-level responses to environmental change. Although the timing of life-cycle events has genetic underpinnings, whether intraspecific variation in the duration of life-cycle events reflects genetic differences among individuals is poorly understood. METHODS: We used a common garden experiment with 10 genotypes of Salix hookeriana (coastal willow) from northern California, United States to investigate the extent to which genetic variation explains intraspecific variation in the timing and duration of multiple, sequential life-cycle events: flowering, leaf budbreak, leaf expansion, fruiting, and fall leaf coloration. We used seven clones of each genotype, for a total of 70 individual trees. RESULTS: Genotype affected each sequential life-cycle event independently and explained on average 62% of the variation in the timing and duration of vegetative and reproductive life-cycle events. All events were significantly heritable. A single genotype tended to be "early" or "late" across life-cycle events, but for event durations, there was no consistent response within genotypes. CONCLUSIONS: This research demonstrates that genetic variation can be a major component underlying intraspecific variation in the timing and duration of life-cycle events. It is often assumed that the environment affects durations, but we show that genetic factors also play a role. Because the timing and duration of events are independent of one another, our results suggest that the effects of environmental change on one event will not necessarily cascade to subsequent events.


Assuntos
Salix , Animais , Estações do Ano , Salix/fisiologia , Estágios do Ciclo de Vida , Folhas de Planta , Genótipo
9.
Ann Emerg Med ; 81(6): 691-698, 2023 06.
Artigo em Inglês | MEDLINE | ID: mdl-36841661

RESUMO

STUDY OBJECTIVE: Bystander cardiopulmonary resuscitation increases the likelihood of out-of-hospital cardiac arrest survival by more than two-fold. A common barrier to the prompt initiation of compressions is moving victims to the floor, but compression quality on a "floor" versus a "mattress" has not been tested among lay bystanders. METHODS: We conducted a prospective, randomized, cross-over trial comparing lay bystander compression quality using a manikin on a bed versus the floor. Participants included adults without professional health care training. We randomized participants to the order of manikin placement, either on a mattress or on the floor. For both, participants were instructed to perform 2 minutes of chest compressions on a cardiopulmonary resuscitation Simon manikin Gaumard (Gaumard Scientific, Miami, FL). The primary outcome was mean compression depth (cm) over 2 minutes. We fit a linear regression model adjusted for scenario order, age, sex, and body mass index with robust standard errors to account for repeated measures and reported mean differences with 95% confidence intervals (CIs). RESULTS: Our sample of 80 adults was 66% female with a mean age of 50.5 years (SD 18.2). The mean compression depth on the mattress was 2.9 cm (SD 2.3) and 3.5 cm (SD 2.2) on the floor, a mean difference of 0.58 cm (95% CI 0.18, 0.98). Compression depth fell below the 5 to 6 cm depth recommended by the American Heart Association on both surfaces. In the adjusted model, the mean depth was greater when the manikin was on the floor than the mattress (adjusted mean difference 0.62 cm; 95% CI 0.23 to 1.01), and mean depth was less for females than males (adjusted mean difference -1.42 cm, 95% CI -2.59, -0.25). In addition, the difference in compression depth was larger for female participants (mean difference 0.94 cm; 95% CI 0.54, 1.34) than for male participants (mean difference -0.01 cm; 95% CI -0.80, 0.78), and the interaction was statistically significant (P = .04). CONCLUSION: The mean compression depth was significantly smaller on the mattress and with female bystanders. Further research is needed to understand the benefit of moving out-of-hospital cardiac arrest victims to the floor relative to the detrimental effect of delaying chest compressions.


Assuntos
Reanimação Cardiopulmonar , Parada Cardíaca Extra-Hospitalar , Adulto , Humanos , Masculino , Feminino , Pessoa de Meia-Idade , Parada Cardíaca Extra-Hospitalar/terapia , Estudos Cross-Over , Estudos Prospectivos , Reanimação Cardiopulmonar/educação , Mãos , Manequins
10.
Am Sociol ; : 1-13, 2023 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-36855521

RESUMO

In this review essay, we probe three main elements of Laura Ford's Intellectual Property of Nations: her discussion of the structure of moral obligation and its materialization via writing and the institutions of the law; reflections on how the book intersects with questions of textual epistemology (especially the question of inferring intent from texts); and, finally, a self-consciously "presentist" discussion of how the book's findings intersect with our modern world of global legal regimes.

11.
J Environ Manage ; 302(Pt A): 114011, 2022 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-34735830

RESUMO

CONTEXT: Logging and wildfire can reduce the height of the forest canopy and the distance to the understorey vegetation below. These conditions may increase the likelihood of high severity wildfire (canopy scorch or consumption), which may explain the greater prevalence of high severity wildfire in some recently logged or burnt forests. However, the effects of these structural characteristics on wildfire severity have not clearly been demonstrated. OBJECTIVES: We aimed to assess how the structure of forests affected by logging and wildfire influence the probability of high severity wildfire. METHODS: We used terrestrial laser scanning to measure the connectivity of canopy and understorey vegetation in forests at various stages of recovery after logging and wildfire (approximately 0-80 years since disturbance). These sites were subsequently burnt by mixed severity wildfire during the 2019-20 'Black Summer' fire season in south-eastern Australia. We assessed how these forest structure metrics affected the probability of high severity wildfire. RESULTS: The probability of high severity fire decreased as the canopy base height increased, and the distance between the canopy base and understorey increased. High severity wildfire was less likely in forests with taller understoreys and greater canopy or understorey cover, but these effects were not considered causal. Fire weather was the strongest driver of wildfire severity, which was also affected by topography. CONCLUSIONS: These findings demonstrate a link between forest structure characteristics, that are strongly shaped by antecedent logging and fire, and fire severity. They also indicate that vertical fuel structure should be incorporated into assessments of fire risk.


Assuntos
Queimaduras , Incêndios , Incêndios Florestais , Florestas , Humanos , Lasers
12.
Nat Immunol ; 10(4): 348-55, 2009 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19295631

RESUMO

Death receptors (DRs) are members of the tumor necrosis factor receptor superfamily that possess a cytoplasmic death domain (DD). DRs regulate important operational and homeostatic aspects of the immune system. They transmit signals through apical protein complexes, which are nucleated by the DD adaptors FADD and TRADD, to control cellular outcomes that range from apoptosis to gene activation. FADD and TRADD also nucleate several distal signaling complexes, which mediate cross-talk between distinct DR signaling pathways. Moreover, together with other DR signal transducers, FADD and TRADD participate in functional complexes assembled by certain non-DR immune cell receptors, such as pattern-recognition receptors. Thus, DR signal transducers may provide important nodes of coordination in immune signaling networks.


Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Proteína de Domínio de Morte Associada a Fas/fisiologia , Receptores de Morte Celular/fisiologia , Transdução de Sinais/fisiologia , Proteína de Domínio de Morte Associada a Receptor de TNF/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/imunologia , Animais , Apoptose/fisiologia , Proteína de Domínio de Morte Associada a Fas/imunologia , Humanos , Imunidade Ativa , Imunidade Inata , Receptores de Morte Celular/imunologia , Receptores do Fator de Necrose Tumoral/imunologia , Receptores do Fator de Necrose Tumoral/fisiologia , Proteína de Domínio de Morte Associada a Receptor de TNF/imunologia
13.
BMC Public Health ; 21(1): 405, 2021 02 25.
Artigo em Inglês | MEDLINE | ID: mdl-33632170

RESUMO

BACKGROUND: High rates of maternal mortality and intimate partner violence (IPV) are both major worldwide health challenges. Evidence from single-country samples suggests that IPV may be an important risk factor for low utilization of maternal health services, but there is little large-scale evidence on this association. This paper evaluates whether IPV is a risk factor for low utilization of maternal health services in a large cross-country sample, and also compiles evidence on the relative effects of different forms of IPV. METHODS: We analyze the association between intimate partner violence and utilization of maternal health care, using a dataset compiling all Demographic and Health Surveys that report data on intimate partner violence. Using data on 166,685 women observed in 36 countries between 2005 and 2016, we estimate logistic regression models to analyze the relationship between lifetime experience of IPV and utilization of antenatal care (ANC), facility delivery care, and postnatal care. We estimate both unadjusted models and models adjusted for geographic and sociodemographic characteristics that are generally correlated with utilization of maternal health care (including age, education, number of children, wealth status, marital status, and urbanity). RESULTS: Lifetime experience of any IPV is associated with decreased use of maternal health services in a broad sample of births observed in lower and middle-income countries: in particular, the utilization of four or more ANC visits, the number of ANC visits, and the utilization of facility care at birth. This association remains statistically significant even after adjusting for country of residence, subnational region of residence, and additional individual-level covariates; however, there is no statistically significant association between experience of any IPV and postnatal care. The only form of IPV significantly associated with care utilization is physical IPV. CONCLUSIONS: Women experiencing physical intimate partner violence show lower levels of utilization of maternal health services in a large sample of developing and middle-income countries. Given that reduced utilization of maternal health services is correlated with maternal and neonatal health outcomes, this pattern suggests that IPV prevention may be an important component of interventions targeting enhanced maternal and neonatal health.


Assuntos
Violência por Parceiro Íntimo , Serviços de Saúde Materna , Criança , Estudos Transversais , Feminino , Inquéritos Epidemiológicos , Humanos , Recém-Nascido , Estado Civil , Aceitação pelo Paciente de Cuidados de Saúde , Gravidez , Cuidado Pré-Natal
15.
Nat Immunol ; 9(11): 1244-52, 2008 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-18849989

RESUMO

The importance of conventional dendritic cells (cDCs) in the processing and presentation of antigen is well established, but the contribution of plasmacytoid dendritic cells (pDCs) to these processes, and hence to T cell immunity, remains unclear. Here we showed that unlike cDCs, pDCs continued to synthesize major histocompatibility complex (MHC) class II molecules and the MHC class II ubiquitin ligase MARCH1 long after activation. Sustained MHC class II-peptide complex formation, ubiquitination and turnover rendered pDCs inefficient in the presentation of exogenous antigens but enabled pDCs to continuously present endogenous viral antigens in their activated state. As the antigen-presenting abilities of cDCs and pDCs are fundamentally distinct, these two cell types may activate largely nonoverlapping repertoires of CD4(+) T cells.


Assuntos
Apresentação de Antígeno , Células Dendríticas/imunologia , Antígenos de Histocompatibilidade Classe II/metabolismo , Ubiquitinação , Animais , Antígenos Virais/imunologia , Antígenos CD11/metabolismo , Linfócitos T CD4-Positivos/imunologia , Células Dendríticas/metabolismo , Antígenos de Histocompatibilidade Classe II/biossíntese , Antígenos Comuns de Leucócito/metabolismo , Ativação Linfocitária , Camundongos , Camundongos Endogâmicos , Camundongos Knockout , Ubiquitina-Proteína Ligases/biossíntese , Ubiquitina-Proteína Ligases/genética
16.
Health Econ ; 29(2): 195-208, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31766076

RESUMO

Tax-preferred health savings devices such as Flexible Spending Accounts (FSAs) and Health Savings Accounts (HSAs) offer employees potentially valuable financial instruments for directing pre-tax earnings to eligible medical expenses. Despite their increasing popularity as an employee benefit, however, there is little causal evidence around individual demand for these accounts. This paper seeks to address this gap in the literature, reporting on a randomized controlled field experiment conducted with over 11,000 U. S federal employees in 2017 in order to evaluate the effectiveness of targeted messages designed to increase FSA contributions. Our results suggest that the provision of basic information about FSAs delivered via an emailed employee newsletter did not affect the likelihood of contribution or the contribution level. The addition of statements about the absolute returns or relative returns offered by the accounts similarly had no significant effects, and these null effects are observed despite relatively high email open rates. We discuss explanations for the null results and the policy implications of findings from what appears to be the first health economics experiment analyzing tax incentives around health care savings.


Assuntos
Marketing , Poupança para Cobertura de Despesas Médicas , Motivação , Impostos/economia , Atenção à Saúde , Planos de Assistência de Saúde para Empregados/economia , Humanos , Poupança para Cobertura de Despesas Médicas/economia , Poupança para Cobertura de Despesas Médicas/estatística & dados numéricos , Estados Unidos
17.
Health Econ ; 29(4): 489-507, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-31965689

RESUMO

Self-tests offer one approach for reducing frictions underlying low demand for preventive health inputs, yet there is little evidence on demand for self-tests. We used the Becker-DeGroot-Marschak mechanism-an incentive-compatible approach-to elicit exact willingness to pay (WTP) for HIV self-tests in a field experiment with 822 participants at 66 health clinics/pharmacies in Kenya. Our analysis reveals substantial demand at low prices and highly elastic demand at a wide range of prices above this range. We find few participants with nonpositive WTP. We examine correlates of WTP and discuss policy and research implications of our findings.


Assuntos
Motivação , Humanos
18.
Microsc Microanal ; 26(4): 821-836, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32513338

RESUMO

An Al­Cu­Li aerospace alloy has been investigated to determine the order in which corrosion at different types of sites occurs in AA2099-T83. Specifically, the sequence of galvanic attack on intermetallic (IM) particles and other sites of AA2099-T83 was determined as a function of time, in 0.1 M NaCl, through the use of scanning electron microscopy and electron backscatter diffraction characterization techniques. The earliest attack occurred at isolated grains and grain boundaries and on Li-containing dispersoids. Similarly, some constituent IM particles showed evidence of trenching in the surrounding alloy matrix. These IM particles included Al7Cu2Fe and another group of unidentified particles which displayed complete trenching within the first 10 min of exposure. Al13(Fe, Mn)4 were next most active followed by Al37Fe12Cu2 with Al6(Fe,Mn) and large TiB2 particles being the least active.

19.
Microsc Microanal ; 26(4): 768-792, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32284076

RESUMO

Alluvial mineral sands rank among the most complex subjects for mineral characterization due to the diverse range of minerals present in the sediments, which may collectively contain a daunting number of elements (>20) in major or minor concentrations (>1 wt%). To comprehensively characterize the phase abundance and chemistry of these complex mineral specimens, a method was developed using hyperspectral x-ray and cathodoluminescence mapping in an electron probe microanalyser (EPMA), coupled with automated cluster analysis and quantitative analysis of clustered x-ray spectra. This method proved successful in identifying and quantifying over 40 phases from mineral sand specimens, including unexpected phases with low modal abundance (<0.1%). The standard-based quantification method measured compositions in agreement with expected stoichiometry, with elemental detection limits in the range of <10­1,000 ppm, depending on phase abundance, and proved reliable even for challenging mineral species, such as the multi-rare earth element (REE) bearing mineral xenotime [(Y,REE)PO4] for which 24 elements were analyzed, including 12 overlapped REEs. The mineral identification procedure was also capable of characterizing mineral groups that exhibit significant compositional variability due to the substitution of multiple elements, such as garnets (Mg, Ca, Fe, Mn, Cr), pyroxenes (Mg, Ca, Fe), and amphiboles (Na, Mg, Ca, Fe, Al).

20.
Microsc Microanal ; 26(4): 814-820, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32248881

RESUMO

Hyperspectral soft X-ray emission (SXE) and cathodoluminescence (CL) spectrometry have been used to investigate a carbonaceous-rich geological deposit to understand the crystallinity and morphology of the carbon and the associated quartz. Panchromatic CL maps show both the growth of the quartz and the evidence of recrystallization. A fitted CL map reveals the distribution of Ti4+ within the grains and shows subtle growth zoning, together with radiation halos from 238U decay. The sensitivity of the SXE spectrometer to carbon, together with the anisotropic X-ray emission from highly orientated pyrolytic graphite, has enabled the C Kα peak shape to be used to measure the crystal orientation of individual graphite regions. Mapping has revealed that most grains are predominantly of a single orientation, and a number of graphite grains have been investigated to demonstrate the application of this new SXE technique. A peak fitting approach to analyzing the SXE spectra was developed to project the C Kα 2pz and 2p(x+y) orbital components of the graphite. The shape of these two end-member components is comparable to those produced by electron density of states calculations. The angular sensitivity of the SXE spectrometer has been shown to be comparable to that of electron backscatter diffraction.

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