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1.
BJOG ; 128(8): 1364-1372, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33528862

RESUMO

OBJECTIVE: To compare the effect of inhaled nitrous oxide (INO) on pain control during in-office hysteroscopy with 1% lidocaine paracervical infiltration and no analgesic. DESIGN: Single-blind stratified randomised clinical trial with masked assessment by a third party. SETTING: Department of Obstetrics and Gynaecology in a Spanish hospital. POPULATION: Women who underwent hysteroscopy. METHODS: Patients were stratified into three groups according to the purpose of the hysteroscopy (biopsy, polypectomy or tubal sterilisation) and then assigned to different treatment groups through a permuted-blocks randomisation within strata. Pain scale was provided by a gynaecologist totally blinded to procedures and treatments. Effects were assessed using a one-way analysis of variance following an intention-to-treat approach. MAIN OUTCOME MEASURES: Visual analogue scale (VAS) from 0 to 100 mm. RESULTS: A total of 314 women were included: 105 to INO, 104 to 1% lidocaine and 105 to no analgesic. Baseline characteristics were comparable. Mean VAS score after the procedure was 34.7 ± 25.8 mm, 36.1 ± 22.9 mm (P = 1.0) and 47.3 ± 28.2 mm (P = 0.001) for INO, 1% lidocaine and no analgesic, respectively. No adverse events were reported in 91 (86.7%) patients in the INO group compared with 79 (76%) in the 1%-lidocaine group (P = 0.04) and 85 (81%) in the no-analgesic group (P = 0.26). CONCLUSION: INO was as effective as 1% lidocaine in pain control for in-office hysteroscopy and was better tolerated. The no-analgesic group presented the poorer results, so was the least recommended clinical option.


Assuntos
Assistência Ambulatorial , Anestésicos Inalatórios/administração & dosagem , Anestésicos Locais/administração & dosagem , Histeroscopia , Lidocaína/administração & dosagem , Óxido Nitroso/administração & dosagem , Manejo da Dor/métodos , Adulto , Anestésicos Inalatórios/efeitos adversos , Anestésicos Locais/efeitos adversos , Biópsia , Feminino , Humanos , Lidocaína/efeitos adversos , Pessoa de Meia-Idade , Óxido Nitroso/efeitos adversos , Pólipos/cirurgia , Método Simples-Cego , Esterilização Tubária , Neoplasias Uterinas/cirurgia
3.
Rev Neurol ; 66(8): 268-270, 2018 Apr 16.
Artigo em Espanhol | MEDLINE | ID: mdl-29645070

RESUMO

INTRODUCTION: The differential diagnosis of diseases that are accompanied by adult-onset girdle weakness is broad and includes motor neurone, neuromuscular junction or muscular diseases. The 8344A>G mutation of the MTTK gene of mitochondrial DNA usually presents with involvement of multiple organs associated (or not) with girdle weakness. To date no cases of isolated girdle weakness have been reported as the presenting symptom of this mutation. CASE REPORT: A 57-year-old male, with a four-year history of isolated clinical signs of progressive girdle weakness. He is the brother of a 59-year-old woman with the same clinical features. Muscular biopsy played a decisive role in the diagnosis and was characteristic of mitochondrial myopathy. The genetic analysis revealed the 8344A>G mutation of the MTTK gene of mitochondrial DNA. CONCLUSIONS: The 8344A>G mutation of mitochondrial DNA can be associated with clinical signs and symptoms of adult-onset girdle weakness, and must therefore be included as part of its differential diagnosis.


TITLE: Debilidad aislada de cinturas: ampliacion del espectro fenotipico de la mutacion MERRF 8344A>G del ADN mitocondrial.Introduccion. El diagnostico diferencial de los trastornos que cursan con debilidad de cinturas de inicio en la edad adulta es amplio e incluye enfermedades de neurona motora, union neuromuscular o musculo. La mutacion m.8344A>G del gen MTTK del ADN mitocondrial suele presentarse con afectacion de multiples organos asociada o no a una debilidad de cinturas. No se han descrito hasta el momento casos de debilidad de cinturas aislada como sintoma de presentacion de esta mutacion. Caso clinico. Varon de 57 años, con clinica aislada de debilidad progresiva de cinturas, de cuatro años de evolucion. Hermano de una mujer de 59 años con la misma sintomatologia. La biopsia muscular fue decisiva en el diagnostico y es caracteristica de una miopatia mitocondrial. El analisis genetico objetivo la mutacion m.8344A>G del gen MTTK del ADN mitocondrial. Conclusiones. La mutacion 8344A>G del ADN mitocondrial puede cursar con un cuadro aislado de debilidad de cinturas de inicio en el adulto, por lo que debe de formar parte del diagnostico diferencial de este.


Assuntos
DNA Mitocondrial/genética , Síndrome MERRF/genética , Debilidade Muscular/genética , Mutação de Sentido Incorreto , Mutação Puntual , RNA de Transferência de Lisina/genética , Idade de Início , Diagnóstico Diferencial , Estudos de Associação Genética , Humanos , Síndrome MERRF/diagnóstico , Síndrome MERRF/diagnóstico por imagem , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Debilidade Muscular/diagnóstico , Debilidade Muscular/diagnóstico por imagem , Músculo Esquelético/diagnóstico por imagem , Músculo Esquelético/ultraestrutura , Fenótipo
4.
Nanotechnology ; 28(50): 505704, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29160238

RESUMO

We report on structural, compositional, and thermal characterization of self-assembled in-plane epitaxial Si1-x Ge x alloy nanowires grown by molecular beam epitaxy on Si (001) substrates. The thermal properties were studied by means of scanning thermal microscopy (SThM), while the microstructural characteristics, the spatial distribution of the elemental composition of the alloy nanowires and the sample surface were investigated by transmission electron microscopy and energy dispersive x-ray microanalysis. We provide new insights regarding the morphology of the in-plane nanostructures, their size-dependent gradient chemical composition, and the formation of a 5 nm thick wetting layer on the Si substrate surface. In addition, we directly probe heat transfer between a heated scanning probe sensor and Si1-x Ge x alloy nanowires of different morphological characteristics and we quantify their thermal resistance variations. We correlate the variations of the thermal signal to the dependence of the heat spreading with the cross-sectional geometry of the nanowires using finite element method simulations. With this method we determine the thermal conductivity of the nanowires with values in the range of 2-3 W m-1 K-1. These results provide valuable information in growth processes and show the great capability of the SThM technique in ambient environment for nanoscale thermal studies, otherwise not possible using conventional techniques.

5.
Soft Matter ; 11(38): 7606-16, 2015 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-26291429

RESUMO

We have used low-field (1)H nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments of water protons, depending on the local strength of the field gradients. Hence, the spatial redistribution of the magnetic particles in the ferrofluid caused by the presence of an external magnetic field in a time scale of minutes can be monitored in real time, following the changes in the features of the NMR spectra during a period of about an hour. As previously reported [Heinrich et al., Phys. Rev. Lett., 2011, 106, 208301], in the homogeneous magnetic field of a NMR spectrometer, the aggregation of the particles of the IFF proceeds in two stages. The first stage corresponds to the gradual aggregation of monomers prior to and during the formation of chain-like structures. The second stage proceeds after the chains have reached a critical average length, favoring lateral association of the strings into hexagonal zipped-chain superstructures or bundles. In this work, we focus on the influence of a strongly inhomogeneous magnetic field on the aforementioned aggregation dynamics. The main observation is that, as the sample is immersed in a certain magnetic field gradient and kept there for a time τinh, magnetophoresis rapidly converts the ferrofluid into an aggregation state which finds its correspondence to a state on the evolution curve of the pristine sample in a homogeneous field. From the degree of aggregation reached at the time τinh, the IFF sample just evolves thereafter in the homogeneous field of the NMR spectrometer in exactly the same way as the pristine sample. The final equilibrium state always consists of a colloidal suspension of zipped-chain bundles with the chain axes aligned along the magnetic field direction.


Assuntos
Coloides/química , Nanopartículas de Magnetita/química , Dimerização , Íons/química , Campos Magnéticos , Espectroscopia de Ressonância Magnética , Simulação de Dinâmica Molecular
6.
An Sist Sanit Navar ; 38(1): 9-20, 2015.
Artigo em Espanhol | MEDLINE | ID: mdl-25963454

RESUMO

OBJECTIVE: To determine the number of suicides and the main social and demographic characteristics, time frames and methods involved during the period 2010-2013 in Navarra by gender. METHODS: A study of the Electronic Clinical Records provided by Navarra's Healthcare Service in which suicides in Navarra are detailed. RESULTS: One hundred and eighty individuals committed suicide. The number of suicides remained stable: 41 in 2010, 51 in 2011 and 44 in 2012 and 2013. Seventy-five point four percent were males (n=136) and 24.6 % (n=44) were females. In the 13 to 26 age group, 12 (92.3%) out of 13 suicides were committed by males. In terms of employment status, 49.3% (n=70) were pensioners. The highest rate of suicides was reached in summer (n=71) and spring (n=39). Monday was the day with the highest rate of suicides (n=37) and the time period between 8:00 and 12:00 hours was when the highest number of suicides (n=80) took place. The most usual ways of committing suicide were hanging (n=80), falling from a height (n=41) and pharmacological overdose (n=23). Males used violent methods more frequently. It is necessary to highlight the fact that in some of the sociodemographic characteristics there was up to 60% of cases without enough information. CONCLUSION: The results obtained show some specific features of the phenomenon of suicide in Navarra that should be considered for its prevention. Furthermore, the implementation of effective protocols of data collection is recommended to develop prevention strategies.


Assuntos
Distribuição por Sexo , Suicídio/estatística & dados numéricos , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Espanha/epidemiologia , Adulto Jovem
7.
Inorg Chem ; 54(11): 5239-48, 2015 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-25985317

RESUMO

Nanoparticulate Fe2O3 and Fe2O3/C composites with different carbon proportions have been prepared for anode application in lithium ion batteries (LIBs). Morphological studies revealed that particles of Fe2O3 in the composites were well-dispersed in the matrix of amorphous carbon. The properties of the γ-Fe2O3 nanoparticles and the correlation with the particle size and connectivity were studied by electron paramagnetic resonance, magnetic, and Mössbauer measurements. The electrochemical study revealed that composites with carbon have promising electrochemical performances. These samples yielded specific discharge capacities of 1200 mAh/g after operating for 100 cycles at 1C. These excellent results could be explained by the homogeneity of particle size and structure as well as the uniform distribution of γ-Fe2O3 nanoparticles in the in situ generated amorphous carbon matrix.

8.
Methods Inf Med ; 54(2): 145-55, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25301322

RESUMO

BACKGROUND: An aging population and people's higher survival to diseases and traumas that leave physical consequences are challenging aspects in the context of an efficient health management. This is why telerehabilitation systems are being developed, to allow monitoring and support of physiotherapy sessions at home, which could reduce healthcare costs while also improving the quality of life of the users. OBJECTIVES: Our goal is the development of a Kinect-based algorithm that provides a very accurate real-time monitoring of physical rehabilitation exercises and that also provides a friendly interface oriented both to users and physiotherapists. METHODS: The two main constituents of our algorithm are the posture classification method and the exercises recognition method. The exercises consist of series of movements. Each movement is composed of an initial posture, a final posture and the angular trajectories of the limbs involved in the movement. The algorithm was designed and tested with datasets of real movements performed by volunteers. We also explain in the paper how we obtained the optimal values for the trade-off values for posture and trajectory recognition. RESULTS: Two relevant aspects of the algorithm were evaluated in our tests, classification accuracy and real-time data processing. We achieved 91.9% accuracy in posture classification and 93.75% accuracy in trajectory recognition. We also checked whether the algorithm was able to process the data in real-time. We found that our algorithm could process more than 20,000 postures per second and all the required trajectory data-series in real-time, which in practice guarantees no perceptible delays. Later on, we carried out two clinical trials with real patients that suffered shoulder disorders. We obtained an exercise monitoring accuracy of 95.16%. CONCLUSIONS: We present an exercise recognition algorithm that handles the data provided by Kinect efficiently. The algorithm has been validated in a real scenario where we have verified its suitability. Moreover, we have received a positive feedback from both users and the physiotherapists who took part in the tests.


Assuntos
Algoritmos , Pessoas com Deficiência/reabilitação , Telerreabilitação/métodos , Idoso , Sistemas Computacionais , Terapia por Exercício , Humanos , Postura , Interface Usuário-Computador
9.
Nanotechnology ; 25(18): 185402, 2014 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-24737220

RESUMO

We measure the thermal conductivity of a 17.5-nm-thick single crystalline Si layer by using a suspended structure developed from a silicon-on-insulator wafer, in which the Si layer bridges the suspended platforms. The obtained value of 19 Wm(-1) K(-1) at room temperature represents a tenfold reduction with respect to bulk Si. This design paves the way for subsequent lateral nanostructuration of the layer with lithographic techniques, to define different geometries such as Si nanowires, nanostrips or phononic grids. As a proof of concept, nanostrips of 0.5 × 10 µm have been defined by focused ion beam (FIB) in the ultrathin Si layer. After the FIB cutting process with Ga ions at 30 kV and 100 pA, the measured thermal conductivity dramatically decreased to 1.7 Wm(-1) K(-1), indicating that the structure became severely damaged (amorphous). Re-crystallization of the structure was promoted by laser annealing while monitoring the Raman spectra. The thermal conductivity of the layer increased again to a value of 9.5 Wm(-1) K(-1) at room temperature, below that of the single crystalline material due to phonon scattering at the grain boundaries.

10.
Nanotechnology ; 24(18): 185704, 2013 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-23579463

RESUMO

Local strain and Ge content distribution in self-assembled, in-plane Ge/Si nanowires grown by combining molecular beam epitaxy and the metal-catalyst assisted-growth method were investigated by tip-enhanced Raman scattering. We show that this technique is essential to study variations of physical properties of single wires at the nanoscale, a task which cannot be achieved with conventional micro-Raman scattering. As two major findings, we report that (i) the Ge distribution in the (001) crystallographic direction is inhomogeneous, displaying a gradient with a higher Ge content close to the top surface, and (ii) in contrast, the (uncapped) wires exhibit essentially the same small residual compressive strain everywhere along the wire.

11.
Langmuir ; 28(24): 9010-20, 2012 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-22594822

RESUMO

Coupling magnetic materials to plasmonic structures provides a pathway to dramatically increase the magneto-optical response of the resulting composite architecture. Although such optical enhancement has been demonstrated in a variety of systems, some basic aspects are scarcely known. In particular, reflectance/transmission modulations and electromagnetic field intensification, both triggered by plasmon excitations, can contribute to the magneto-optical enhancement. However, a quantitative evaluation of the impact of both factors on the magneto-optical response is lacking. To address this issue, we have measured magneto-optical Kerr spectra on corrugated gold/dielectric interfaces with magnetic (nickel and iron oxide) nanoparticles. We find that the magneto-optical activity is enhanced by up to an order of magnitude for wavelengths that are correlated to the excitation of propagating or localized surface plasmons. Our work sheds light on the fundamental principles for the observed optical response and demonstrates that the outstanding magneto-optical performance is originated by the increase of the polarization conversion efficiency, whereas the contribution of reflectance modulations is negligible.

12.
Microb Pathog ; 52(1): 85-91, 2012 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-22079896

RESUMO

Histotoxic strains of Clostridium perfringens cause human gas gangrene, a devastating infection during which potent tissue-degrading toxins are produced and secreted. Although this pathogen only grows in anaerobic-nutrient-rich habitats such as deep wounds, very little is known regarding how nutritional signals influence gas gangrene-related toxin production. We hypothesize that sugars, which have been used throughout history to prevent wound infection, may represent a nutritional signal against gas gangrene development. Here we demonstrate, for the first time, that sugars (sucrose, glucose) inhibited the production of the main protein toxins, PLC (alpha-toxin) and PFO (theta-toxin), responsible for the onset and progression of gas gangrene. Transcription analysis experiments using plc-gusA and pfoA-gusA reporter fusions as well as RT-PCR analysis of mRNA transcripts confirmed that sugar represses plc and pfoA expression. In contrast an isogenic C. perfringens strain that is defective in CcpA, the master transcription factor involved in carbon catabolite response, was completely resistant to the sugar-mediated inhibition of PLC and PFO toxin production. Furthermore, the production of PLC and PFO toxins in the ccpA mutant strain was several-fold higher than the toxin production found in the wild type strain. Therefore, CcpA is the primary or unique regulatory protein responsible for the carbon catabolite (sugar) repression of toxin production of this pathogen. The present results are analyzed in the context of the role of CcpA for the development and aggressiveness of clostridial gas gangrene and the well-known, although poorly understood, anti-infective and wound healing effects of sugars and related substances.


Assuntos
Toxinas Bacterianas/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Clostridium perfringens/metabolismo , Regulação para Baixo , Gangrena Gasosa/microbiologia , Glucose/metabolismo , Proteínas Hemolisinas/metabolismo , Sacarose/metabolismo , Fosfolipases Tipo C/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Toxinas Bacterianas/genética , Proteínas de Ligação ao Cálcio/genética , Linhagem Celular , Clostridium perfringens/enzimologia , Clostridium perfringens/genética , Regulação Bacteriana da Expressão Gênica , Proteínas Hemolisinas/genética , Humanos , Fosfolipases Tipo C/genética
13.
Phys Rev Lett ; 106(20): 208301, 2011 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-21668267

RESUMO

Combining nuclear magnetic resonance and molecular dynamics simulations, we unravel the long-time dynamics of a paradigmatic colloid with strong dipole-dipole interactions. In a homogeneous magnetic field, ionic ferrofluids exhibit a stepwise association process from ensembles of monomers over stringlike chains to bundles of hexagonal zipped-chain patches. We demonstrate that attractive van der Waals interactions due to charge-density fluctuations in the magnetic particles play the key role for the dynamical stabilization of the hexagonal superstructures against thermal dissociation. Our results give insight into the dynamics of self-organization in systems dominated by dipolar interactions.

14.
J Chem Phys ; 132(24): 244501, 2010 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-20590200

RESUMO

Hydroxyapatite is the main mineral component of bones and teeth. Fluorapatite, a bioceramic that can be obtained from hydroxyapatite by chemical substitution of the hydroxide ions with fluoride, exhibits lower mineral solubility and larger mechanical strength. Despite the widespread use of fluoride against caries, a reliable technique for unambiguous assessment of fluoridation in in vitro tests is still lacking. Here we present a method to probe fluorapatite formation in fluoridated hydroxyapatite by combining Raman scattering with thermal annealing. In synthetic minerals, we found that effectively fluoride substituted hydroxyapatite transforms into fluorapatite only after heat treatment, due to the high activation energy for this first order phase transition.

15.
An Sist Sanit Navar ; 32(2): 161-8, 2009.
Artigo em Espanhol | MEDLINE | ID: mdl-19738641

RESUMO

BACKGROUND: To analyse the diagnostic concordance between the paediatric and mental health (MH) services. MATERIALS AND METHODS: Two hundred and seven patients from 0 to 16 years referred from paediatrics to the Estella Mental Health Centre during 2006 and 2007. Concordance between global Kappa Index and specific diagnosis was calculated with Epidat 3.1. An analysis was made for each diagnostic category of the percentage of cases where the diagnosis made in paediatrics was confirmed in Mental Health. RESULTS: The global diagnostic concordance between both medical care levels has a Kappa Index of 0.58. There is a wide variability in the concordance between the different diagnoses. The concordance is weak (0.2-0.4) for specific developmental disorder, affective disorders and adaptative disorders. A moderate concordance (0.41-0.6) is obtained for mental retardation, pervasive developmental disorder, z diagnostics, and sibling rivalry disorder. Concordance is good for attention deficit disorder with hyperactivity, anxiety disorder and conduct disorder. Finally, the diagnostic concordance is very good for enuresis and encopresis and for eating disorders. CONCLUSIONS: The diagnostic concordance obtained between paediatric services and the mental health centre is moderate. A wide variability is obtained in the concordance between different diagnoses.


Assuntos
Serviços de Saúde da Criança , Transtornos Mentais/diagnóstico , Serviços de Saúde Mental , Adolescente , Criança , Pré-Escolar , Humanos , Lactente , Encaminhamento e Consulta
16.
Physiol Meas ; 30(9): 983-98, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19696464

RESUMO

We propose a new algorithm to detect and classify transient cardiac ischemia episodes, designed with the goal of providing a real-time execution without penalizing the classifier accuracy much. The algorithm is based on a novel mixture of time-domain analysis and machine learning techniques, specifically bagging of decision trees, and it has been developed using a well-recognized and freely distributed database, namely the long-term ST database. The ST episode detection sensitivity/positive predictivity using the annotation protocol A for this database is 68.26%/74.91%. The sensitivity result increases until 93.97% for the most dangerous episodes in terms of duration and magnitude (annotated according to protocol C). The test of the algorithm over the freely distributed part of the European Society of Cardiology database has shown results of sensitivity and positive predictivity of 83.33% and 77.31%, respectively. Those results are close to the results obtained by related works that present approaches to detect ischemia episodes off-line, which is remarkable if we take into account that in our real-time approach, less information is available during the classification process.


Assuntos
Eletrocardiografia/estatística & dados numéricos , Isquemia Miocárdica/fisiopatologia , Processamento de Sinais Assistido por Computador/instrumentação , Algoritmos , Área Sob a Curva , Inteligência Artificial , Interpretação Estatística de Dados , Bases de Dados Factuais , Árvores de Decisões , Reações Falso-Negativas , Frequência Cardíaca/fisiologia , Humanos
17.
Nanotechnology ; 20(31): 315701, 2009 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-19597252

RESUMO

Room-temperature photoluminescence (PL) measurements have been performed on single-crystal ZnO nanowires grown on SiO2/Si and quartz substrates by the vapor transport method using Au as a catalyst. Two emission bands are apparent, one in the UV spectral region around 380 nm (3.26 eV) associated with exciton recombination processes and a much broader structure in the visible range from 420 to 700 nm, which exhibits two distinct peak-like features around 520 and 590 nm (2.38 and 2.10 eV). Spectrally resolved scanning near-field optical microscopy (SNOM) of single ZnO nanowires have been performed for a direct imaging of the PL emission with spatial resolution below 100 nm. SNOM results provide evidence that the yellow emission band observed at 590 nm is a unique property of the ZnO nanowires, being most likely related to radiative recombination processes associated with Au impurities introduced during the catalytic growth.

18.
J Nanosci Nanotechnol ; 9(5): 3013-9, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19452963

RESUMO

By combining cross-sectional transmission and scanning electron microscopy with Raman scattering we have investigated the mechanism of nanocrystal formation in ultrathin amorphous SiO2/Ge/SiO2 trilayers grown by e-beam evaporation as a function of annealing temperature and a-Ge layer thickness. We observe that with decreasing a-Ge thickness the amorphous-to-crystalline (a-to-c) transition occurs at considerably higher temperatures, even avoiding crystallisation for very thin films below 2 nm thickness. Furthermore, we demonstrate that the formation of Ge nanocrystals by annealing at around 900 degrees C takes place driven by a liquid-mediated mechanism. As indicated by the observed microstructure, the metallic liquid film dewets from the surface forming droplets that upon cooling and under the influence of the SiO2 capping layer, solidify into barrel-type nanocrystals.

20.
J Chem Phys ; 126(12): 124701, 2007 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-17411146

RESUMO

Using Raman spectroscopy, the authors have investigated the aggregation/disgregation of magnetic nanoparticles in dense ionic ferrofluids (IFF) into clusters due to the action of an inhomogeneous external magnetic field. Evidence for changes in particle density and/or effective cluster size were obtained from the variation of the Raman intensity in a time window from 10 s to 10 min for magnetic fields up to 350 mT and at a temperature of 28 degrees C. Clustering sets in already at very low fields (>15 mT) and the IFF samples exhibit a clear hysteresis in the Raman spectra after releasing the magnetic field, which lasts for many hours at room temperature. The authors determined the characteristic times of the two competing processes, that of field-induced cluster formation and, at room temperature, that of thermal-activated dissociation, to range from 100 to 150 s.

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