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1.
Pediatr Int ; 64(1): e15231, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-35831247

RESUMO

BACKGROUND: We evaluated the significance of perinatal plasma natriuretic peptide (NP) levels in neonates with congenital heart defects (CHDs) or arrhythmias and determined whether measurement of perinatal plasma NP levels and echocardiographic assessment in utero could predict heart failure after birth. METHODS: The study was conducted between 2012 and 2016 to evaluate the correlation of perinatal atrial NP (ANP) and brain NP (BNP) levels at birth with the modified Ross score after birth and the cardiovascular profile (CVP) score before birth. RESULTS: A total of 122 singletons with CHDs or arrhythmias and 27 controls were analyzed. Neonatal blood sampling was performed at a median of 0.7 h (range, 0.1-1.5) after birth. The neonatal plasma ANP and BNP levels shortly after birth were significantly higher than those in the umbilical artery (UA) plasma. The ANP and BNP levels in UA and neonatal blood were correlated with the modified Ross score. The neonatal plasma ANP and BNP levels and the modified Ross scores were inversely correlated with the CVP score in neonates with CHDs or arrhythmias. The area under the receiver operating characteristic curve of UA ANP levels for predicting neonatal heart failure was highest among those for the CVP score, perinatal plasma ANP and BNP levels, and their combinations. CONCLUSIONS: The plasma ANP and BNP levels increased markedly shortly after birth. Assessment of the UA plasma ANP level at birth and the CVP score in utero may be utilized to predict neonatal heart failure.


Assuntos
Cardiopatias Congênitas , Insuficiência Cardíaca , Arritmias Cardíacas , Fator Natriurético Atrial , Feminino , Cardiopatias Congênitas/diagnóstico , Insuficiência Cardíaca/diagnóstico , Humanos , Recém-Nascido , Peptídeo Natriurético Encefálico , Peptídeos Natriuréticos , Gravidez , Vasodilatadores
2.
Mem Cognit ; 49(6): 1247-1266, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-33890247

RESUMO

This study investigated what academic traits, attitudes, and habits predict individual differences in task-unrelated thought (TUT) during lectures, and whether this TUT propensity mediates associations between academic individual differences and course outcomes (final grade and situational interest evoked by material). Undergraduates (N = 851) from ten psychology classes at two US universities responded to thought probes presented during two early-course lectures; they also indicated sitting in the front, middle, or back of the classroom. At each probe, students categorized their thought content, such as indicating on-task thought or TUT. Students also completed online, academic-self-report questionnaires at the beginning of the course and a situational interest questionnaire at the end. Average TUT rate was 24% but individuals' rates varied widely (SD = 18%). TUT rates also increased substantially from the front to back of the classroom, and modestly from the first to second half of class periods. Multiple-group analyses (with ten classroom groups) indicated that: (a) classroom media-multitasking habits, initial interest in the course topic, and everyday propensity for mind-wandering and boredom accounted for unique variance in TUT rate (beyond other predictors); (b) TUT rate accounted for unique (modest) variance in course grades and situational interest; and (c) classroom media multitasking and propensity for mind-wandering and boredom had indirect associations with course grades via TUT rate, and these predictor variables, along with initial interest, had indirect associations with end-of-term situational interest via TUT rate. Some academic traits and behaviors predict course outcomes in part because they predict off-task thought during class.


Assuntos
Individualidade , Universidades , Atenção , Cognição , Humanos , Pensamento
3.
Pediatr Cardiol ; 40(6): 1322, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31218372

RESUMO

The authors have retracted this article [1] because, contrary to the statement in the article, this research did not obtain ethics approval from the National Cerebral and Cardiovascular Center Institutional Review Board prior to submission of the manuscript to Pediatric Cardiology. All authors agree to this retraction.

4.
Pediatr Cardiol ; 40(4): 865-870, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30830281

RESUMO

The frequency of newborns with congenital heart disease (CHD) is approximately 1% in the general population; however, the recurrence rate of CHD in mothers with CHD differs in ethnicity and reports. We therefore aimed to determine the prevalence of CHD among neonates born to mothers with CHD in our institute in Japan. We reviewed the medical charts of 803 neonates delivered by 529 women with CHD at the National Cerebral and Cardiovascular Center from 1982 to 2016. They included isolated ventricular septal defect (VSD,31.4%), isolated atrial septal defect (ASD, 23.3%), tetralogy of Fallot (TOF,10.6%). We defined CHD in neonates as being diagnosed within 1 month of birth. We estimated that the average rate of the CHD recurrence was 3.1%. The recurrence ratios in each maternal CHD were 8.6%, 7.1%, 6.2%, 4.8%, 3.6%, and 1.5% for PS, CoA, TOF, atrioventricular septal defect, VSD, and ASD, respectively. The rate of CHD in offsprings whose mothers have CHD was 3 times greater than that of mothers with healthy hearts. Almost half of neonates with CHD had the same phenotype as their mother in our series. Especially, PS and CoA were closely related to the type of maternal CHD.


Assuntos
Cardiopatias Congênitas/epidemiologia , Adolescente , Adulto , Criança , Feminino , Cardiopatias Congênitas/etiologia , Humanos , Recém-Nascido , Japão , Masculino , Pessoa de Meia-Idade , Mães/estatística & dados numéricos , Prevalência , Recidiva , Estudos Retrospectivos , Adulto Jovem
5.
Pediatr Cardiol ; 39(7): 1355-1365, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-29777280

RESUMO

For neonates with right atrial isomerism (RAI), functional single ventricle (f-SV), and obstructive total anomalous pulmonary venous connection (TAPVC), primary TAPVC repair (TAPVCR) has a poor outcome. At our hospital, the survival rate at 1 year of such neonates undergoing primary TAPVCR between 1999 and 2010 (TAPVCR group) was 30% (3/10). Most deceased cases suffered from capillary leak syndrome and unstable pulmonary resistance after the surgeries. We sought to determine whether less invasive primary draining vein stenting (DVS) improved the outcome of these neonates. We investigated outcomes in consecutive nine such neonates (median gestational age 38 weeks, birth weight 2.8 kg, females 4) who underwent primary DVS with 6-mm-diameter Palmaz® Genesis® stents at our hospital between 2007 and 2017 (DVS group). Eight patients underwent subsequent surgeries to adjust the pulmonary flow after decreased pulmonary resistance. The survival rate at 1 year after the first interventions in the DVS group improved to 77% (7/9), although there was a difference between the interventional eras of the two groups. Of the seven patients who underwent multiple stent redilations with a larger balloon or additional stenting in other sites until the next stage of surgery at a median age of 8 months, four received a bidirectional Glenn (BDG) shunt and TAPVCR and three underwent TAPVCR, with two of those cases reaching BDG. Less invasive primary DVS improved the outcome of neonates with RAI, f-SV, and obstructive TAPVC, with many reaching BDG. Patient selection to advance toward Fontan is thought to further improve the outcome.


Assuntos
Procedimentos Cirúrgicos Cardiovasculares/métodos , Síndrome de Heterotaxia/cirurgia , Síndrome do Coração Esquerdo Hipoplásico/cirurgia , Síndrome de Cimitarra/cirurgia , Stents/efeitos adversos , Procedimentos Cirúrgicos Cardiovasculares/efeitos adversos , Drenagem , Feminino , Ventrículos do Coração/anormalidades , Síndrome de Heterotaxia/complicações , Síndrome de Heterotaxia/mortalidade , Humanos , Lactente , Recém-Nascido , Masculino , Complicações Pós-Operatórias/epidemiologia , Complicações Pós-Operatórias/etiologia , Veias Pulmonares/anormalidades , Estudos Retrospectivos , Síndrome de Cimitarra/complicações , Síndrome de Cimitarra/mortalidade , Taxa de Sobrevida , Resultado do Tratamento
6.
Learn Individ Differ ; 54: 160-172, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28943742

RESUMO

This study examined the relationship between academic procrastination and goal accomplishment in two novel ways. First, we experimentally tested whether undergraduate students (N = 177) could reduce their academic procrastination over a course of three weeks after performing goal-related exercises to set so-called SMART goals and/or to prepare those students with specific strategies to resist their temptations (forming implementation intentions). Second, we conducted systematic regression analyses to examine whether academic procrastination at baseline uniquely predicts later goal-related outcomes, controlling for various correlated variables, including personality traits (e.g., impulsivity), motivational factors (e.g., motivation for the generated goals), and situational factors (e.g., memory for the goals). Results indicated that neither the SMART-goal nor implementation-intention intervention significantly reduced academic procrastination in the three-week interval, even when relevant moderating variables were examined. Initial levels of academic procrastination, however, were predictive of the success of accomplishing the goals generated during the initial exercises, above and beyond a wide range of other candidate correlates. These results provided new correlational evidence for the association between academic procrastination and goal accomplishment, but suggest a need for further research to understand what interventions are effective at reducing academic procrastination.

7.
Cogn Emot ; 30(7): 1289-303, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-26208534

RESUMO

The current study investigated the effects of trait worry, a subcomponent of trait anxiety, on the process of updating information in working memory (WM). A leading theory on anxiety and executive functions, attentional control theory (ACT), states that anxiety is not related to WM updating in emotionally neutral situations. Previous research, however, has focused almost exclusively on WM span tasks that primarily emphasised storage, rather than the updating of WM representations. Moreover, few studies have directly examined the effects of trait worry. In this study, 116 subjects performed a WM updating task that required the memorisation of short lists of words and the within-trial removal of some of these items from WM. Results indicated that levels of trait worry were not related to word-span performance, but were related to performance on trials that required subjects to effectively update WM. Moreover, these effects were observed only for trait worry, not for levels of anxious arousal or comorbid levels of dysphoria. These results support the hypothesis that trait worry is related to WM updating performance and thereby extend ACT in new directions.


Assuntos
Ansiedade/psicologia , Memória de Curto Prazo , Ansiedade/complicações , Nível de Alerta , Depressão/complicações , Depressão/psicologia , Feminino , Humanos , Masculino , Teoria Psicológica , Tempo de Reação
8.
Psychol Sci ; 25(6): 1178-88, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24705635

RESUMO

Previous research has revealed a moderate and positive correlation between procrastination and impulsivity. However, little is known about why these two constructs are related. In the present study, we used behavior-genetics methodology to test three predictions derived from an evolutionary account that postulates that procrastination arose as a by-product of impulsivity: (a) Procrastination is heritable, (b) the two traits share considerable genetic variation, and (c) goal-management ability is an important component of this shared variation. These predictions were confirmed. First, both procrastination and impulsivity were moderately heritable (46% and 49%, respectively). Second, although the two traits were separable at the phenotypic level (r = .65), they were not separable at the genetic level (r genetic = 1.0). Finally, variation in goal-management ability accounted for much of this shared genetic variation. These results suggest that procrastination and impulsivity are linked primarily through genetic influences on the ability to use high-priority goals to effectively regulate actions.


Assuntos
Objetivos , Comportamento Impulsivo/fisiologia , Motivação/genética , Gêmeos/genética , Gêmeos/psicologia , Adulto , Cognição/fisiologia , Feminino , Humanos , Individualidade , Estudos Longitudinais , Masculino , Modelos Genéticos , Análise Multivariada , Fenótipo , Inquéritos e Questionários , Adulto Jovem
9.
Circ J ; 78(8): 1974-9, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24871449

RESUMO

BACKGROUND: Genetic testing for long QT syndrome (LQTS) is now in clinical practice. We conducted molecular genetic analyses to definitively diagnose LQTS and to determine its subtypes for gene-specific treatment. We conducted a retrospective study to determine the characteristics of schoolchildren with LQTS living on the Okinawa Islands. METHODS AND RESULTS: The study population included children identified in a school-based electrocardiographic (ECG) screening program for cardiovascular diseases who were referred to Okinawa Children's Medical Center between 2007 and 2012; 23 children met the diagnostic criteria for LQTS. Of them, 17 were genotype-positive and 14 were found to harbor theSCN5AE1784K mutation exclusively among the LQTS genotype-positive children. The children were divided into genotype-positive and -negative groups. Clinical characteristics and ECG data were analyzed and compared. The median Schwartz score was 3. The median QT interval was 521 ms. CONCLUSIONS: The major finding is that the prevalent subtype of LQTS in Okinawa is discordant with other cohorts living in other regions of Japan or overseas. We cannot exclude the possibility of the presence of a specific founder mutation in this geographically clustered population, particularly considering that the hospital is the only tertiary heart center for children in Okinawa. However, this uniquely high prevalence of theSCN5AE1784K mutation serves as a compelling justification to conduct a larger study.


Assuntos
Eletrocardiografia , Síndrome do QT Longo/genética , Síndrome do QT Longo/fisiopatologia , Canal de Sódio Disparado por Voltagem NAV1.5/genética , Adolescente , Povo Asiático , Criança , Feminino , Humanos , Japão/epidemiologia , Síndrome do QT Longo/epidemiologia , Masculino , Mutação de Sentido Incorreto , Prevalência , Estudos Retrospectivos
10.
Pediatr Int ; 56(3): 422-4, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24894929

RESUMO

Chromosomal abnormalities as well as non-cardiac anomalies have been identified as independent risk factors for surgical morbidity and mortality in Fontan palliation. The combination of malformations consisting of pulmonary hypoplasia, agonadism (sex reversal), omphalocele, and diaphragmatic defect is compatible with pulmonary artery and lung hypoplasia, agonadism, omphalocele, and diaphragmatic defect (PAGOD). Most cases have been associated with cardiac disease, particularly hypoplastic left heart syndrome (HLHS) that is potentially destined for Fontan palliation. Reported herein is the case of a Japanese female infant diagnosed with PAGOD syndrome along with HLHS (mitral atresia and aortic atresia), in whom intractable respiratory failure manifested as bilateral eventration of the diaphragm and presumed right lung hypoplasia. These characteristic pulmonary lesions associated with the syndrome precluded use of the Fontan pathway.


Assuntos
Dextrocardia/complicações , Genitália Feminina/anormalidades , Hérnias Diafragmáticas Congênitas/complicações , Síndrome do Coração Esquerdo Hipoplásico/complicações , Feminino , Humanos , Recém-Nascido , Pulmão/anormalidades
11.
Cortex ; 177: 130-149, 2024 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-38852224

RESUMO

Although event-related potential (ERP) research on language processing has capitalized on key, theoretically influential components such as the N400 and P600, their measurement properties-especially the variability in their temporal and spatial parameters-have rarely been examined. The current study examined the measurement properties of the N400 and P600 effects elicited by semantic and syntactic anomalies, respectively, during sentence processing. We used a bootstrap resampling procedure to randomly draw many thousands of resamples varying in sample size and stimulus count from a larger sample of 187 participants and 40 stimulus sentences of each type per condition. Our resampling investigation focused on three issues: (a) statistical power; (b) variability in the magnitudes of the effects; and (c) variability in the temporal and spatial profiles of the effects. At the level of grand averages, the N400 and P600 effects were both robust and substantial. However, across resamples, there was a high degree of variability in effect magnitudes, onset times, and scalp distributions, which may be greater than is currently appreciated in the literature, especially for the P600 effects. These results provide a useful basis for designing future studies using these two well-established ERP components. At the same time, the results also highlight challenges that need to be addressed in future research (e.g., how best to analyze the ERP data without engaging in such questionable research practices as p-hacking).

12.
Ind Health ; 2024 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-38522926

RESUMO

Librarians at a university had planned to check the collection prior to the library renovations that began in 2015. They had previous knowledge of the presence of a light greyish-white powder with an unpleasant odour (hereinafter referred to as 'powder') sprinkled between the pages of antiquarian books in the library archive. The purpose of this study was to identify this powder with the help of experts from both inside and outside the university. The powder was qualitatively analysed using gas chromatography with mass spectrometry after hexane extraction. The powder was examined under a polarised light microscope and a field-emission scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. Benzene hexachloride (BHC) was detected in the powder. Talc was the most abundant particle in the powder. The powder also contained 0.52 wt% asbestos, which belonged to the tremolite-actinolite series. No other types of asbestos were detected. The powder was presumed to be a bulking agent for BHC, and its major constituent was talc. This is the first report on asbestos-containing insecticides.

13.
Sci Adv ; 10(3): eadi7203, 2024 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-38241366

RESUMO

The Hayabusa2 spacecraft delivered samples of the carbonaceous asteroid Ryugu to Earth. Some of the sample particles show evidence of micrometeoroid impacts, which occurred on the asteroid surface. Among those, particles A0067 and A0094 have flat surfaces on which a large number of microcraters and impact melt splashes are observed. Two impact melt splashes and one microcrater were analyzed to unveil the nature of the objects that impacted the asteroid surface. The melt splashes consist mainly of Mg-Fe-rich glassy silicates and Fe-Ni sulfides. The microcrater trapped an impact melt consisting mainly of Mg-Fe-rich glassy silicate, Fe-Ni sulfides, and minor silica-rich glass. These impact melts show a single compositional trend indicating mixing of Ryugu surface materials and impactors having chondritic chemical compositions. The relict impactor in one of the melt splashes shows mineralogical similarity with anhydrous chondritic interplanetary dust particles having a probable cometary origin. The chondritic micrometeoroids probably impacted the Ryugu surface during its residence in a near-Earth orbit.

14.
Pediatr Int ; 55(2): 251-3, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23679169

RESUMO

We describe a case of a 10-year-old girl with genetically confirmed LQTS type 3 developed recurrent episodes of loss of consciousness due to epilepsy that was diagnosed by using an implantable loop recorder (ILR).


Assuntos
Eletrodos Implantados , Eletroencefalografia/instrumentação , Epilepsia/diagnóstico , Síndrome do QT Longo/complicações , Doença do Sistema de Condução Cardíaco , Criança , Diagnóstico Diferencial , Eletrocardiografia , Epilepsia/complicações , Desenho de Equipamento , Feminino , Humanos , Síndrome do QT Longo/diagnóstico
15.
J Electrocardiol ; 46(6): 663-5, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23477893

RESUMO

Wolff-Parkinson-White (WPW) syndrome can be the cause of syncope or sudden cardiac death, which results from ventricular fibrillation (VF) degenerated from rapid anterograde conduction of atrial fibrillation (AF) to the ventricles through the accessory pathway. We present a case of WPW syndrome in which recording the actual moment of onset of the degeneration of pre-excited AF into VF. This was fortuitous and also lucky for this patient.


Assuntos
Fibrilação Atrial/diagnóstico , Fibrilação Atrial/prevenção & controle , Desfibriladores Implantáveis , Fibrilação Ventricular/diagnóstico , Fibrilação Ventricular/prevenção & controle , Síndrome de Wolff-Parkinson-White/diagnóstico , Síndrome de Wolff-Parkinson-White/prevenção & controle , Adolescente , Morte Súbita Cardíaca/prevenção & controle , Feminino , Humanos , Terapia Assistida por Computador/métodos , Resultado do Tratamento
16.
PLoS One ; 18(6): e0287911, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37384732

RESUMO

This article reports a preregistered study in which we attempted to replicate the results of an influential study on the ego-depletion effect reported by Job, Dweck, and Walton in 2010. The original Job et al. study (Study 1, N = 60) provided evidence that the ego-depletion effect-a performance decrease on a self-control task after performing another self-control task-occurs only for individuals who hold a belief that their willpower is limited. This moderation of the ego-depletion effect by one's willpower mindset (limited vs. nonlimited) has been interpreted as evidence against a prevalent limited-resource account of self-control. Although this alternative account of the ego-depletion effect has become well-known, the statistical evidence of the original study was on shaky ground. We therefore conducted a preregistered replication of the original study with some methodological improvements. As in the original study, participants (N = 187) performed a self-control task (Stroop color-word interference task) after performing the control or depletion version of a letter cancelation task. Despite extensive analyses, we failed to replicate the original results: There was neither a significant main effect of ego depletion nor a significant moderation of this ego-depletion effect by individual differences in willpower mindset. Together with other recent failures to replicate the original moderation effect, our results cast doubts on the claim that an individual's view of whether willpower is limited or not affects one's susceptibility to the ego-depletion effect.


Assuntos
Autocontrole , Humanos , Ego , Emoções , Individualidade
17.
PLoS One ; 18(10): e0292215, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37878578

RESUMO

People differ substantially in their vulnerability to distraction. Yet, many types of distractions exist, from external stimulation to internal thoughts. How should we characterize individual differences in their distractibility? Two samples of adult participants (total N = 1220) completed a large battery of questionnaires assessing different facets of real-world distractibility. Latent modeling revealed that these measures could be explained by three correlated-yet-distinct factors: external distraction, unwanted intrusive thoughts, and mind-wandering. Importantly, about 80% of the total variance in these three factors could be explained by a single higher-order factor (d) that could be construed in terms of a person's general distractibility, and this general distractibility model was replicated across the two samples. We then applied the general distractibility model to understand the nature of ADHD symptomatology and hyperfocus (an intense state of long-lasting and highly focused attention). d was substantially associated with self-reported ADHD symptoms. Interestingly, d was also positively associated with hyperfocus, suggesting that hyperfocus may, to some degree, reflect attention problems. These results also show marked consistencies across the two samples. Overall, the study provides an important step toward a comprehensive understanding of individual differences in distractibility and related constructs.


Assuntos
Transtorno do Deficit de Atenção com Hiperatividade , Transtornos Cognitivos , Adulto , Humanos , Transtorno do Deficit de Atenção com Hiperatividade/diagnóstico , Atenção/fisiologia , Cognição , Individualidade
18.
Front Psychol ; 14: 1218663, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-38023046

RESUMO

Although the personality correlates of dispositional interpersonal forgiveness (forgiveness of others) have been well characterized, those of dispositional self-forgiveness are less well understood. Moreover, when the personality correlates are examined for both types of forgiveness, the comparison has been based on participants' self-report ratings on questionnaires. The current study sought to address these gaps in the literature by adopting a scenario-based approach, which has been used less frequently, especially in self-forgiveness research. A total of 160 participants read six fictional scenarios, each describing a severe transgression, from the perspective of the transgressor (self-forgiveness, n = 78) or the victim (interpersonal forgiveness, n = 82) of the transgression, and then responded to several items assessing different facets of forgiveness (avoidance, revenge, and benevolence). Participants' personality (Big Five) and explanatory style were also assessed. Consistent with prior literature, agreeableness and neuroticism generally predicted different facets of interpersonal forgiveness. These two personality traits also predicted facets of self-forgiveness, but, additionally, conscientiousness and one's tendency to internalize failure (the personal component of explanatory style) uniquely predicted self-forgiveness, especially avoidance motivations. These results point to both similarities and differences in the personality correlates of interpersonal and self-forgiveness. As a secondary, more exploratory aim, the current study compared the results from our scenario-based assessment of forgiveness to those based on a commonly used questionnaire, the Other and Self subscales of the Heartland Forgiveness Scale (HFS). As expected, the Other subscale of the HFS were associated with levels of interpersonal forgiveness assessed with our transgression scenarios, but, surprisingly, the HFS Self subscale was more strongly related to interpersonal than self-forgivess assessed with scenarios. Moreover, the Self subscale was not associated with levels of self-forgiveness assessed with transgression scenarios, except for avoidance motivations. These results suggest that scenario-based and questionnaire-based methods may capture different facts of forgiveness and cannot be used interchangeably, especially for the assessment of self-forgiveness. More generally, the current study illustrates the importance of conducting direct within-study comparisons of interpersonal and self-forgiveness as well as of different assessment methods to better understand the similarities and differences between the two types of forgiveness.

19.
Sci Rep ; 13(1): 7117, 2023 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-37160932

RESUMO

Nanometer-sized crystals (nanolites) play an important role in controlling eruptions by affecting the viscosity of magmas and inducing bubble nucleation. We present detailed microscopic and nanoscopic petrographic analyses of nanolite-bearing and nanolite-free pumice from the 2021 eruption of Fukutoku-Oka-no-Ba, Japan. The nanolite mineral assemblage includes biotite, which is absent from the phenocryst mineral assemblage, and magnetite and clinopyroxene, which are observed as phenocrysts. The boundary between the nanolite-bearing brown glass and nanolite-free colorless glass is either sharp or gradational, and the sharp boundaries also appear sharp under the transmitted electron microscope. X-ray absorption fine structure (XAFS) analysis of the volcanic glass revealed that the nanolite-free colorless glass records an oxygen fugacity of QFM + 0.98 (log units), whereas the nanolite-bearing brown glass records a higher apparent oxygen fugacity (~ QFM + 2). Thermodynamic modelling using MELTS indicates that higher oxygen fugacities increase the liquidus temperature and thus induced the crystallization of magnetite nanolites. The hydrous nanolite mineral assemblage and glass oxygen fugacity estimates suggest that an oxidizing fluid supplied by a hot mafic magma induced nanolite crystallization in the magma reservoir, before the magma fragmentation. The oxidation-induced nanolite crystallization then enhanced heterogeneous bubble nucleation, resulting in convection in the magma reservoir and triggering the eruption.

20.
Nat Astron ; 7(2): 170-181, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-36845884

RESUMO

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (-OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

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