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2.
Nat Commun ; 15(1): 1859, 2024 Feb 29.
Artigo em Inglês | MEDLINE | ID: mdl-38424099

RESUMO

Studies suggest that inducing gut microbiota changes may alter both muscle physiology and cognitive behaviour. Gut microbiota may play a role in both anabolic resistance of older muscle, and cognition. In this placebo controlled double blinded randomised controlled trial of 36 twin pairs (72 individuals), aged ≥60, each twin pair are block randomised to receive either placebo or prebiotic daily for 12 weeks. Resistance exercise and branched chain amino acid (BCAA) supplementation is prescribed to all participants. Outcomes are physical function and cognition. The trial is carried out remotely using video visits, online questionnaires and cognitive testing, and posting of equipment and biological samples. The prebiotic supplement is well tolerated and results in a changed gut microbiome [e.g., increased relative Bifidobacterium abundance]. There is no significant difference between prebiotic and placebo for the primary outcome of chair rise time (ß = 0.579; 95% CI -1.080-2.239 p = 0.494). The prebiotic improves cognition (factor score versus placebo (ß = -0.482; 95% CI,-0.813, -0.141; p = 0.014)). Our results demonstrate that cheap and readily available gut microbiome interventions may improve cognition in our ageing population. We illustrate the feasibility of remotely delivered trials for older people, which could reduce under-representation of older people in clinical trials. ClinicalTrials.gov registration: NCT04309292.


Assuntos
Microbioma Gastrointestinal , Doenças Musculares , Idoso , Humanos , Envelhecimento , Cognição , Suplementos Nutricionais , Método Duplo-Cego , Microbioma Gastrointestinal/fisiologia , Músculos , Pessoa de Meia-Idade
3.
Elife ; 122023 01 24.
Artigo em Inglês | MEDLINE | ID: mdl-36692910

RESUMO

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody levels can be used to assess humoral immune responses following SARS-CoV-2 infection or vaccination, and may predict risk of future infection. Higher levels of SARS-CoV-2 anti-Spike antibodies are known to be associated with increased protection against future SARS-CoV-2 infection. However, variation in antibody levels and risk factors for lower antibody levels following each round of SARS-CoV-2 vaccination have not been explored across a wide range of socio-demographic, SARS-CoV-2 infection and vaccination, and health factors within population-based cohorts. Methods: Samples were collected from 9361 individuals from TwinsUK and ALSPAC UK population-based longitudinal studies and tested for SARS-CoV-2 antibodies. Cross-sectional sampling was undertaken jointly in April-May 2021 (TwinsUK, N=4256; ALSPAC, N=4622), and in TwinsUK only in November 2021-January 2022 (N=3575). Variation in antibody levels after first, second, and third SARS-CoV-2 vaccination with health, socio-demographic, SARS-CoV-2 infection, and SARS-CoV-2 vaccination variables were analysed. Using multivariable logistic regression models, we tested associations between antibody levels following vaccination and: (1) SARS-CoV-2 infection following vaccination(s); (2) health, socio-demographic, SARS-CoV-2 infection, and SARS-CoV-2 vaccination variables. Results: Within TwinsUK, single-vaccinated individuals with the lowest 20% of anti-Spike antibody levels at initial testing had threefold greater odds of SARS-CoV-2 infection over the next 6-9 months (OR = 2.9, 95% CI: 1.4, 6.0), compared to the top 20%. In TwinsUK and ALSPAC, individuals identified as at increased risk of COVID-19 complication through the UK 'Shielded Patient List' had consistently greater odds (two- to fourfold) of having antibody levels in the lowest 10%. Third vaccination increased absolute antibody levels for almost all individuals, and reduced relative disparities compared with earlier vaccinations. Conclusions: These findings quantify the association between antibody level and risk of subsequent infection, and support a policy of triple vaccination for the generation of protective antibodies. Funding: Antibody testing was funded by UK Health Security Agency. The National Core Studies program is funded by COVID-19 Longitudinal Health and Wellbeing - National Core Study (LHW-NCS) HMT/UKRI/MRC ([MC_PC_20030] and [MC_PC_20059]). Related funding was also provided by the NIHR 606 (CONVALESCENCE grant [COV-LT-0009]). TwinsUK is funded by the Wellcome Trust, Medical Research Council, Versus Arthritis, European Union Horizon 2020, Chronic Disease Research Foundation (CDRF), Zoe Ltd and the National Institute for Health Research (NIHR) Clinical Research Network (CRN) and Biomedical Research Centre based at Guy's and St Thomas' NHS Foundation Trust in partnership with King's College London. The UK Medical Research Council and Wellcome (Grant ref: [217065/Z/19/Z]) and the University of Bristol provide core support for ALSPAC.


Vaccination against the virus that causes COVID-19 triggers the body to produce antibodies that help fight future infections. But some people generate more antibodies after vaccination than others. People with lower levels of antibodies are more likely to get COVID-19 in the future. Identifying people with low antibody levels after COVID-19 vaccination is important. It could help decide who receives priority for future vaccination. Previous studies show that people with certain health conditions produce fewer antibodies after one or two doses of a COVID-19 vaccine. For example, people with weakened immune systems. Now that third booster doses are available, it is vital to determine if they increase antibody levels for those most at risk of severe COVID-19. Cheetham et al. show that a third booster dose of a COVID-19 vaccine boosts antibodies to high levels in 90% of individuals, including those at increased risk. In the experiments, Cheetham et al. measured antibodies against the virus that causes COVID-19 in 9,361 individuals participating in two large long-term health studies in the United Kingdom. The experiments found that UK individuals advised to shield from the virus because they were at increased risk of complications had lower levels of antibodies after one or two vaccine doses than individuals without such risk factors. This difference was also seen after a third booster dose, but overall antibody levels had large increases. People who received the Oxford/AstraZeneca vaccine as their first dose also had lower antibody levels after one or two doses than those who received the Pfizer/BioNTech vaccine first. Positively, this difference in antibody levels was no longer seen after a third booster dose. Individuals with lower antibody levels after their first dose were also more likely to have a case of COVID-19 in the following months. Antibody levels were high in most individuals after the third dose. The results may help governments and public health officials identify individuals who may need extra protection after the first two vaccine doses. They also support current policies promoting booster doses of the vaccine and may support prioritizing booster doses for those at the highest risk from COVID-19 in future vaccination campaigns.


Assuntos
COVID-19 , SARS-CoV-2 , Humanos , COVID-19/epidemiologia , COVID-19/prevenção & controle , Vacinas contra COVID-19 , Estudos Transversais , Fatores de Risco , Anticorpos Antivirais , Londres , Estudos Longitudinais , Vacinação
4.
BMC Med ; 21(1): 25, 2023 01 19.
Artigo em Inglês | MEDLINE | ID: mdl-36658548

RESUMO

BACKGROUND: Predicting the likely size of future SARS-CoV-2 waves is necessary for public health planning. In England, voluntary "plan B" mitigation measures were introduced in December 2021 including increased home working and face coverings in shops but stopped short of restrictions on social contacts. The impact of voluntary risk mitigation behaviours on future SARS-CoV-2 burden is unknown. METHODS: We developed a rapid online survey of risk mitigation behaviours ahead of the winter 2021 festive period and deployed in two longitudinal cohort studies in the UK (Avon Longitudinal Study of Parents and Children (ALSPAC) and TwinsUK/COVID Symptom Study (CSS) Biobank) in December 2021. Using an individual-based, probabilistic model of COVID-19 transmission between social contacts with SARS-CoV-2 Omicron variant parameters and realistic vaccine coverage in England, we predicted the potential impact of the SARS-CoV-2 Omicron wave in England in terms of the effective reproduction number and cumulative infections, hospital admissions and deaths. Using survey results, we estimated in real-time the impact of voluntary risk mitigation behaviours on the Omicron wave in England, if implemented for the entire epidemic wave. RESULTS: Over 95% of survey respondents (NALSPAC = 2686 and NTwins = 6155) reported some risk mitigation behaviours, with vaccination and using home testing kits reported most frequently. Less than half of those respondents reported that their behaviour was due to "plan B". We estimate that without risk mitigation behaviours, the Omicron variant is consistent with an effective reproduction number between 2.5 and 3.5. Due to the reduced vaccine effectiveness against infection with the Omicron variant, our modelled estimates suggest that between 55% and 60% of the English population could be infected during the current wave, translating into between 12,000 and 46,000 cumulative deaths, depending on assumptions about severity and vaccine effectiveness. The actual number of deaths was 15,208 (26 November 2021-1 March 2022). We estimate that voluntary risk reduction measures could reduce the effective reproduction number to between 1.8 and 2.2 and reduce the cumulative number of deaths by up to 24%. CONCLUSIONS: Predicting future infection burden is affected by uncertainty in disease severity and vaccine effectiveness estimates. In addition to biological uncertainty, we show that voluntary measures substantially reduce the projected impact of the SARS-CoV-2 Omicron variant but that voluntary measures alone would be unlikely to completely control transmission.


Assuntos
COVID-19 , SARS-CoV-2 , Estados Unidos , Criança , Humanos , Estudos Longitudinais , COVID-19/epidemiologia , COVID-19/prevenção & controle , Inglaterra/epidemiologia
5.
Nanomaterials (Basel) ; 12(15)2022 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-35893512

RESUMO

The interest in magnetic nanostructures exhibiting perpendicular magnetic anisotropy and exchange bias (EB) effect has increased in recent years owing to their applications in a new generation of spintronic devices that combine several functionalities. We present a nanofabrication process used to induce a significant out-of-plane component of the magnetic easy axis and EB. In this study, 30 nm thick CoO/Co multilayers were deposited on nanostructured alumina templates with a broad range of pore diameters, 34 nm ≤ Dp ≤ 96 nm, maintaining the hexagonal lattice parameter at 107 nm. Increase of the exchange bias field (HEB) and the coercivity (HC) (12 times and 27 times, respectively) was observed in the nanostructured films compared to the non-patterned film. The marked dependence of HEB and HC with antidot hole diameters pinpoints an in-plane to out-of-plane changeover of the magnetic anisotropy at a nanohole diameter of ∼75 nm. Micromagnetic simulation shows the existence of antiferromagnetic layers that generate an exceptional magnetic configuration around the holes, named as antivortex-state. This configuration induces extra high-energy superdomain walls for edge-to-edge distance >27 nm and high-energy stripe magnetic domains below 27 nm, which could play an important role in the change of the magnetic easy axis towards the perpendicular direction.

6.
Wellcome Open Res ; 7: 19, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-37811312

RESUMO

Background: Twins offer social scientists a unique opportunity to understand the interplay of social factors and physical and mental well-being. TwinsUK is the largest UK registry of adult mono- and dy-zygotic twins, but most of the research that utilises the cohorts' data to date has focused on the genetic underpinnings of complex disease. Methods: Following formal unstructured discussions with social scientists we identified key areas of research interest and annotated the historical data collections in TwinsUK where they could be applied to these research aims. Results: We present a summary of variables identified as of key interest to researchers from the social science sphere, spanning the following domains: 1: Parenting, child rearing and pregnancies; 2: Working habits and patterns; 3: Sleeping habits and patterns; 4: Social support; 5: Negative life events; 6: Spousal relationships. Conclusions: TwinsUK has a wide range of genetic and health data that would allow investigation of research questions focusing on these domains.

7.
BMC Geriatr ; 21(1): 407, 2021 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-34210274

RESUMO

BACKGROUND: Loss of skeletal muscle mass and strength occurs with increasing age and is associated with loss of function, disability, and the development of sarcopenia and frailty. Dietary protein is essential for skeletal muscle function, but older adults do not anabolise muscle in response to protein supplementation as well as younger people, so called 'anabolic resistance'. The aetiology and molecular mechanisms for this are not understood, however the gut microbiome is known to play a key role in several of the proposed mechanisms. Thus, we hypothesise that the gut microbiome may mediate anabolic resistance and therefore represent an exciting new target for ameliorating muscle loss in older adults. This study aims to test whether modulation of the gut microbiome using a prebiotic, in addition to protein supplementation, can improve muscle strength (as measured by chair-rise time) versus protein supplementation alone. METHODS: The study is a randomised, double-blinded, placebo-controlled trial, with two parallel arms; one will receive prebiotic and protein supplementation, and the other will receive placebo (maltodextrin) and protein supplementation. Participants will be randomised as twin pairs, with one twin from each pair in each arm. Participants will be asked to take supplementation once daily for 12 weeks in addition to resistance exercises. Every participant will receive a postal box, containing their supplements, and the necessary equipment to return faecal, urine, saliva and capillary blood samples, via post. A virtual visit will be performed using online platform at the beginning and end of the study, with measures taken over video. Questionnaires, food diary and cognitive testing will be sent out via email at the beginning and end of the study. DISCUSSION: This study aims to provide evidence for the role of the gut microbiome in anabolic resistance to dietary protein. If those who take the prebiotic and protein supplementation have a greater improvement in muscle strength compared with those who take protein supplementation alone, this would suggest that strategies to modify the gut microbiome may reduce anabolic resistance, and therefore potentially mitigate sarcopenia and frailty in older adults. TRIAL REGISTRATION: Clinicaltrials.gov: NCT04309292 . Registered on the 2nd May 2020.


Assuntos
Microbioma Gastrointestinal , Sarcopenia , Idoso , Suplementos Nutricionais , Método Duplo-Cego , Humanos , Força Muscular , Prebióticos , Ensaios Clínicos Controlados Aleatórios como Assunto , Sarcopenia/tratamento farmacológico , Sarcopenia/prevenção & controle
8.
Enferm. clín. (Ed. impr.) ; 30(6): 404-410, nov.-dic. 2020. tab
Artigo em Espanhol | IBECS | ID: ibc-197670

RESUMO

OBJETIVO: Describir el nivel de satisfacción de los estudiantes de Enfermería con la simulación clínica en su formación de Grado. MÉTODO: Se realizó un estudio observacional descriptivo de corte transversal retrospectivo en estudiantes del Grado en Enfermería durante los cursos académicos 2016-2017 y 2017-2018. El instrumento utilizado fue la escala de satisfacción en SC de alta fidelidad en estudiantes (ESSAF), un cuestionario validado, anónimo y autoadministrado (alfa de Cronbach 0,857) para medir el grado de satisfacción tras las prácticas en simulación clínica de alta fidelidad. RESULTADOS: Participaron un total de 269 estudiantes, de los cuales el 63,3% fueron mujeres y la edad media ± desviación estándar de la muestra fue de 21,68 ± 13,46 años. El análisis de frecuencias muestra resultados del nivel de satisfacción superiores al 89%, especialmente en la toma de decisiones, la capacidad de priorizar y el aprendizaje de procedimientos. El 87% de las respuestas superaban una media de 4 sobre 5. Las preguntas del cuestionario con respuestas superiores al 4,6 fueron el realismo de los casos (4,71), el profesor hace retroalimentación constructiva después de cada sesión (4,65), la simulación relaciona la teoría con la practica (4,72), el análisis (debriefing) al final de la sesión ayuda a la reflexión de los casos (4,65) y utilidad práctica (4,69). CONCLUSIONES: Los estudiantes del Grado en Enfermería de la Universidad de Cantabria (España) refieren una elevada satisfacción con la simulación clínica de alta fidelidad, confirmando su utilidad en el proceso de aprendizaje


OBJECTIVE: To describe the level of satisfaction of nursing students with clinical simulation in their undergraduate training. METHOD: a descriptive observational study of a retrospective cross section was conducted in undergraduate students in Nursing during the academic years 2016-17 and 2017-18. The instrument used was the High Fidelity Clinical Simulation satisfaction scale in students (ESSAF), a validated, anonymous and self-administered questionnaire (alpha .857) to measure the level of satisfaction after high-fidelity clinical simulation practices. RESULTS: Data were collected from a total of 269 students, of which 63.3% were women and the average age of the sample was 21.68±13.46 years. The analysis of frequencies shows results of the grade of satisfaction over 89%, especially in decision-making, the ability to prioritize and learning procedures. Of the answers, 87% exceeded an average of 4 out of 5. The questions in the questionnaire with answers higher than 4.6 were the realism of the cases (4.71), the teacher provides constructive feedback after each session (4.65), the simulation relates theory to practice (4.72), the analysis (debriefing) at the end of the session helps reflection on the cases (4.65) and practical utility (4.69). CONCLUSIONS: Nursing students from the University of Cantabria (Spain) report high satisfaction in high fidelity clinical simulation, confirming its usefulness in the learning process


Assuntos
Humanos , Treinamento com Simulação de Alta Fidelidade/métodos , Satisfação Pessoal , Estudantes de Enfermagem/estatística & dados numéricos , Treinamento com Simulação de Alta Fidelidade/estatística & dados numéricos , Estudos Transversais , Estudos Retrospectivos , Inquéritos e Questionários
9.
Enferm Clin (Engl Ed) ; 30(6): 404-410, 2020.
Artigo em Inglês, Espanhol | MEDLINE | ID: mdl-31443936

RESUMO

OBJECTIVE: To describe the level of satisfaction of nursing students with clinical simulation in their undergraduate training. METHOD: a descriptive observational study of a retrospective cross section was conducted in undergraduate students in Nursing during the academic years 2016-17 and 2017-18. The instrument used was the High Fidelity Clinical Simulation satisfaction scale in students (ESSAF), a validated, anonymous and self-administered questionnaire (alpha .857) to measure the level of satisfaction after high-fidelity clinical simulation practices. RESULTS: Data were collected from a total of 269 students, of which 63.3% were women and the average age of the sample was 21.68±13.46 years. The analysis of frequencies shows results of the grade of satisfaction over 89%, especially in decision-making, the ability to prioritize and learning procedures. Of the answers, 87% exceeded an average of 4 out of 5. The questions in the questionnaire with answers higher than 4.6 were the realism of the cases (4.71), the teacher provides constructive feedback after each session (4.65), the simulation relates theory to practice (4.72), the analysis (debriefing) at the end of the session helps reflection on the cases (4.65) and practical utility (4.69). CONCLUSIONS: Nursing students from the University of Cantabria (Spain) report high satisfaction in high fidelity clinical simulation, confirming its usefulness in the learning process.


Assuntos
Bacharelado em Enfermagem , Estudantes de Enfermagem , Adolescente , Adulto , Criança , Competência Clínica , Feminino , Humanos , Masculino , Satisfação Pessoal , Estudos Retrospectivos , Espanha , Adulto Jovem
10.
Metas enferm ; 22(2): 56-61, mar. 2019.
Artigo em Espanhol | IBECS | ID: ibc-183519

RESUMO

El tema de la innovación es uno de los aspectos recurrentes en el mundo actual y, en consecuencia, de enorme interés en el ámbito de la atención sanitaria y quizás, muy especialmente, en el de los cuidados enfermeros. Basta ver cualquier periódico profesional o sanitario en los que se encuentran multitud de noticias genéricas o específicas sobre este tema y sus implicaciones en la gestión o los resultados, o simplemente en la reputación de una determinada organización. También aparece frecuentemente en los medios de difusión general, si bien ligada más con la actividad médica u organizativa. Como toda palabra de moda, produce un cierto temor a su mal uso o banalización, cosa que ocurre a menudo. Así pues, se presenta una reflexión sobre su significado, su realidad y sus consecuencias para la gestión enfermera


The topic of innovation is one of the recurring aspects in the world today, and consequently it causes a huge interest in the healthcare setting and maybe particularly in the nursing care setting. In any professional or healthcare newspaper, there are plenty of general or specific news about this matter and its consequences in management or results, or simply in the reputation of a specific organization. It also appears frequently in the general media, but in this case more linked to medical or organizational activities. Just like any trendy word, it causes some fear in terms of its incorrect use or trivialization, which will frequently happen. Therefore, we present here some reflections on its meaning, its reality, and its consequences for nursing management


Assuntos
Humanos , Inovação Organizacional , Gestão em Saúde , Serviços de Enfermagem/organização & administração , Cuidados de Enfermagem/organização & administração , Autonomia Profissional
11.
Magn Reson Med ; 76(5): 1400-1409, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-26588040

RESUMO

PURPOSE: MRI can produce quantitative liver fat fraction (FF) maps noninvasively, which can help to improve diagnoses of fatty liver diseases. However, most sequences acquire several two-dimensional (2D) slices during one or more breath-holds, which may be difficult for patients with limited breath-holding capacity. A whole-liver 3D FF map could also be obtained in a single acquisition by applying a reliable breathing-motion correction method. Several correction techniques are available for 3D imaging, but they use external devices, interrupt acquisition, or jeopardize the spatial resolution. To overcome these issues, a proof-of-concept study introducing a self-navigated 3D three-point Dixon sequence is presented here. METHODS: A respiratory self-gating strategy acquiring a center k-space profile was integrated into a three-point Dixon sequence. We obtained 3D FF maps from a water-fat emulsions phantom and fifteen volunteers. This sequence was compared with multi-2D breath-hold and 3D free-breathing approaches. RESULTS: Our 3D three-point Dixon self-navigated sequence could correct for respiratory-motion artifacts and provided more precise FF measurements than breath-hold multi-2D and 3D free-breathing techniques. CONCLUSION: Our 3D respiratory self-gating fat quantification sequence could correct for respiratory motion artifacts and yield more-precise FF measurements. Magn Reson Med 76:1400-1409, 2016. © 2015 International Society for Magnetic Resonance in Medicine.


Assuntos
Tecido Adiposo/fisiologia , Adiposidade/fisiologia , Interpretação de Imagem Assistida por Computador/métodos , Fígado/fisiologia , Imageamento por Ressonância Magnética/métodos , Técnicas de Imagem de Sincronização Respiratória/métodos , Processamento de Sinais Assistido por Computador , Tecido Adiposo/anatomia & histologia , Tecido Adiposo/diagnóstico por imagem , Adulto , Humanos , Aumento da Imagem/métodos , Imageamento Tridimensional/métodos , Fígado/anatomia & histologia , Fígado/diagnóstico por imagem , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
12.
Artigo em Espanhol | LILACS, BDENF - Enfermagem | ID: biblio-1035237

RESUMO

Resumen:


Se aborda la problemática de la enfermería como ciencia, partiendo de la definición y condiciones de lo científico, propugnado para la enfermería, como ciencia emergente, el concepto de ciencia transdisciplinar, construida por el entrecruzamiento de saberes y la relación productiva entre ellos, afirmando que este tipo de construcción científica no es la suma de los conocimientos, sino más bien una nueva creación con características propias, definida teóricamente y útil socialmente. Se defiende la necesidad de aplicar el conocimiento a la práctica, haciendo a ésta más segura y a aquel más útil en el trabajo diario que llevan a cabo las enfermeras de todos los niveles.


Assuntos
Humanos , Enfermagem , Modelos de Enfermagem , Pesquisa em Enfermagem , México
13.
Hist. enferm., Rev. eletronica ; 2(1): 16-37, Jan-Jul. 2011. ilus
Artigo em Espanhol | BDENF - Enfermagem | ID: biblio-1028925

RESUMO

A lo largo del siglo XX la imagen de la mujer enfermera se ha utilizado progresivamente desde ámbitos muy diversos y con fines no siempre claros, aunque se intenten disfrazar con otros matices. Ellos serían en primer lugar el bienestar y la salud, tal como defienden algunas empresas. Otras valoraciones van en la línea del uso de la imagen enfermera para la venta de ocio y el fomento del consumo, sin olvidar la transmisión de los valores que adornan tradicionalmente a las enfermeras: paz, abnegación, caridad, eficacia, que también están siendo usados con diversas finalidades como la venta de artículos. Según el análisis de las fuentes iconográficas, podemos afirmar que están en la línea de la más pura utilización de la mujer-enfermera para los fines y los intereses más variados y tradicionales de la sociedad patriarcal en la que seguimos inmersos. Pero si esto resulta como realmente parece, debería de servir de llamada de alerta para la profesión y los profesionales y su rol en la sociedad - es


Assuntos
Enfermagem , História da Enfermagem , Identidade de Gênero
14.
Phys Chem Chem Phys ; 13(3): 927-32, 2011 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-21116550

RESUMO

We report unusual cooling field dependence of the exchange bias in oxide-coated cobalt nanoparticles embedded within the nanopores of a carbon matrix. The size-distribution of the nanoparticles and the exchange bias coupling observed up to about 200 K between the Co-oxide shell (∼3-4 nm) and the ferromagnetic Co-cores (∼4-6 nm) are the key to understand the magnetic properties of this system. The estimated values of the effective anisotropy constant and saturation magnetization obtained from the fit of the zero-field cooling and field cooling magnetization vs. temperature curves agree quite well with those of the bulk fcc-Co.


Assuntos
Carbono/química , Cobalto/química , Nanopartículas Metálicas/química , Óxidos/química , Magnetismo , Nanopartículas Metálicas/ultraestrutura , Porosidade , Temperatura
15.
Phys Chem Chem Phys ; 12(13): 3294-300, 2010 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-20237722

RESUMO

Rate coefficients at room temperature for the reaction of 2-ethyl-1-hexanol with OH and NO(3) radicals and with Cl atoms have been determined in a 150 L PTFE chamber using GC-FID/SPME and FTIR as detection systems. The rate coefficients k (in units of cm(3) molecule(-1) s(-1)) obtained were: (1.13 +/- 0.31) 10(-11) for the OH reaction, (2.93 +/- 0.92) 10(-15) for the NO(3) reaction and (1.88 +/- 0.25) 10(-10) for the Cl reaction. Despite the high concentrations of 2-ethyl-1-hexanol, especially in indoor air, this is the first kinetic study carried out to date for these reactions. The results are consistent with the expected reactivity given the chemical structure of 2-ethyl-1-hexanol. Calculated atmospheric lifetimes reveal that the dominant loss process for 2-ethyl-1-hexanol is clearly the daytime reaction with the hydroxyl radical.

16.
Environ Sci Pollut Res Int ; 17(3): 539-46, 2010 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19633879

RESUMO

BACKGROUND, AIM, AND SCOPE: Acrylate and methacrylate esters are alpha,beta-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon (CH(2)=CHCOO- and CH(2)=CCH(3)COO-, respectively) and are widely used in the polymer plastic and resin production. Rate coefficients for Cl reactions for most of the unsaturated esters have not been previously determined, and a good understanding is needed of all the atmospheric oxidation processes of these compounds in order to determine lifetimes in the atmosphere and to evaluate the impact of these reactions on the formation of photo-oxidants and therefore on health and environment. MATERIALS AND METHODS: The relative rate technique has been used to obtain rate coefficients for the reactions between the Cl atom and a series of unsaturated esters. The experiments have been carried out in a static Teflon reactor at room temperature and atmospheric pressure (N(2) as bath gas) using gas chromatography with flame ionization detection as detection system. RESULTS: The following rate coefficients are obtained (in cubic meter per molecule per second): methyl acrylate + Cl = 1.71 +/- 0.13 x 10(-10); methyl methacrylate + Cl = 2.30 +/- 0.18 x 10(-10); ethyl acrylate + Cl = 1.82 +/- 0.13 x 10(-10); ethyl methacrylate + Cl = 2.71 +/- 0.21 x 10(-10); butyl acrylate + Cl = 2.94 +/- 0.23 x 10(-10); butyl methacrylate + Cl = 3.83 +/- 0.30 x 10(-10); methyl 3-methyl acrylate + Cl = 2.21 +/- 0.17 x 10(-10); and methyl 3,3-dimethyl acrylate + Cl = 3.58 +/- 0.28 x 10(-10). DISCUSSION: Rate coefficients calculated for Cl reactions are around one order of magnitude higher than OH ones. The effect in the reactivity of increased substitution at the carbon-carbon double bond is analyzed and also the effect of the identity of the alkyl group R in the -C(O)OR. Atmospheric lifetimes of the compounds against the attack by the major oxidants are estimated and the atmospheric implications are discussed. CONCLUSIONS: The dominant atmospheric loss process for acrylate esters is clearly their daytime reaction with the hydroxyl radical. However, in coastal areas and in the marine boundary layer and in some industrial zones, Cl-atom-initiated degradation of the unsaturated esters considered here can be a significant if not dominant homogeneous loss process. RECOMMENDATIONS AND PERSPECTIVES: Product analysis should be necessary in order to evaluate the real environmental impact of these reactions. OH and ozone reactions of most of the considered compounds have already been studied and products determined, but kinetic and products information for NO(3) radical reactions is especially scarce.


Assuntos
Acrilatos/química , Poluentes Atmosféricos/química , Atmosfera/química , Cloro/química , Acrilatos/análise , Poluentes Atmosféricos/análise , Cloro/análise , Monitoramento Ambiental , Ésteres , Resíduos Industriais/análise , Cinética , Compostos Orgânicos Voláteis/análise , Compostos Orgânicos Voláteis/química
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