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1.
Psychiatry Res ; 336: 115897, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38636333

RESUMO

Interoception is defined as the sense of the internal state of the body. Dysfunctions in interoception are found in several mental disorders, including trauma-related conditions. Mindfulness-Based Interventions (MBIs) have been shown to influence interoceptive processes. Randomised controlled trials (RCTs) have investigated whether MBIs impact symptoms and interoception in patients with trauma-related disorders. We undertook a systematic review and meta-analysis to synthesize these data. We included RCTs with an MBI arm which enrolled adult patients with trauma related-disorders or exposure to a traumatic experience, and addressed changes in interoception and trauma-related symptoms. A random-effects multivariate meta-analytic model was performed to quantify group differences in score change from baseline to follow-up. Twelve studies were included in the systematic review, and eleven in the meta-analysis. Overall, MBIs showed small to moderate positive effects on both interoception and symptoms. Despite a high heterogeneity in results, sensitivity analyses confirmed the robustness of the findings. We conclude that the efficacy of MBIs on trauma-related symptoms and interoception is supported by randomised evidence. However, further research is needed to understand whether changes in interoception might underpin the effectiveness of MBIs in trauma-related disorders.


Assuntos
Interocepção , Atenção Plena , Humanos , Atenção Plena/métodos , Interocepção/fisiologia , Transtornos de Estresse Pós-Traumáticos/terapia , Transtornos de Estresse Pós-Traumáticos/fisiopatologia
2.
Sci Total Environ ; 915: 170111, 2024 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-38232837

RESUMO

Mediterranean forest ecosystems will be increasingly affected by hotter drought and more frequent and severe wildfire events in the future. However, little is known about the longer-term responses of these forests to multiple disturbances and the forests' capacity to maintain ecosystem function. This is particularly so for below-ground organisms, which have received less attention than those above-ground, despite their essential contributions to forest function. We investigated rhizosphere microbial communities in a resprouting Eucalyptus marginata forest, southwestern Australia, that had experienced a severe wildfire four years previously, and a hotter drought eight years previously. Our aim was to understand how microbial communities are affected over longer-term trajectories by hotter drought and wildfire, singularly, and in combination. Fungal and bacterial DNA was extracted from soil samples, amplified, and subjected to high throughput sequencing. Richness, diversity, composition, and putative functional groups were then examined. We found a monotonic decrease in fungal, but not bacterial, richness and diversity with increasing disturbance with the greatest changes resulting from the combination of drought and wildfire. Overall fungal and bacterial community composition reflected a stronger effect of fire than drought, but the combination of both produced the greatest number of indicator taxa for fungi, and a significant negative effect on the abundance of several fungal functional groups. Key mycorrhizal fungi, fungal saprotrophs and fungal pathogens were found at lower proportions in sites affected by drought plus wildfire. Wildfire had a positive effect on bacterial hydrogen and bacterial nitrogen recyclers. Fungal community composition was positively correlated with live tree height. These results suggest that microbial communities, in particular key fungal functional groups, are highly responsive to wildfire following drought. Thus, a legacy of past climate conditions such as hotter drought can be important for mediating the responses of soil microbial communities to subsequent disturbance like wildfire.


Assuntos
Microbiota , Incêndios Florestais , Ecossistema , Secas , Solo , Florestas , Bactérias , Microbiologia do Solo , Fungos
3.
Arch Dermatol Res ; 315(7): 2139-2143, 2023 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-36369596

RESUMO

Skin and soft tissue infections (SSTIs) have high rates of morbidity and mortality worldwide but lack reliable standards for diagnostic workup. As a result, atypical infections, more prevalent among immunocompromised patients, can be missed due to deviance from classic features only to be revealed later through inconsistently performed ancillary studies. Our objectives included to evaluate the sensitivities of clinical impression, histopathology, tissue culture, and molecular and non-molecular ancillary tests in diagnosing inpatient SSTIs, as well as to qualitatively discuss the unusual features making a subset of infections "atypical." To do so, we retrospectively reviewed the histopathologic reports and charts of inpatient dermatologic consults at a single tertiary care institution over a 3-year period. We identified a total of 111 cases of SSTIs evaluated by the inpatient dermatology consultation service with concurrent skin or soft tissue biopsy, with 32.4% representing atypical infections. Among these, clinical impression suggested infection in 9(25.0%), routine histopathology in 21(58.3%), specialized stains for microorganisms in 22(68.8%), and tissue culture in 15(68.2%). Due to incomplete picture that each modality by itself creates, we conclude that clinicians and pathologists should carry a low threshold for including SSTIs in their differential diagnoses and should evaluate with skin biopsy, special stains for microorganisms, and ancillary studies, particularly in critically ill individuals who necessitate timely diagnoses.

4.
Br Dent J ; 233(1): 4-5, 2022 07.
Artigo em Inglês | MEDLINE | ID: mdl-35804105
5.
Br Dent J ; 232(6): 355, 2022 03.
Artigo em Inglês | MEDLINE | ID: mdl-35338270
6.
Mater Today Bio ; 9: 100092, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33554105

RESUMO

Anaerobes are a major constituent of the gut microbiome and profoundly influence the overall health of humans. However, the lack of a simple, cost-effective, and scalable system that mimics the anaerobic conditions of the human gut is hindering research on the gut microbiome and the development of therapeutics. Here, we address this gap by using glucose oxidase and catalase containing gelatin microparticles (GOx-CAT-GMPs) to precisely regulate dissolved oxygen concentration [O2] via GOx-mediated consumption of oxygen. Fluorescence images generated using conjugated polymer afterglow nanoparticles showed that [O2] can be tuned from 257.9 â€‹± â€‹6.2 to 0.0 â€‹± â€‹4.0 â€‹µM using GOx-CAT-GMPs. Moreover, when the obligate anaerobe Bacteroides thetaiotaomicron was inoculated in media containing GOx-CAT-GMPs, bacterial growth under ambient oxygen was comparable to control conditions in an anaerobic chamber (5.4 â€‹× â€‹105 and 8.8 â€‹× â€‹105 colony forming units mL-1, respectively). Finally, incorporating GOx-CAT-GMPs into a bioreactor that permitted continuous radial diffusion of oxygen and glucose generated a gut-mimetic [O2] gradient of 132.4 â€‹± â€‹2.6 â€‹µM in the outer ring of the reactor to 7.9 â€‹± â€‹1.7 â€‹µM at the core. Collectively, these results indicate that GOx-CAT-GMPs are highly effective oxygen-regulating materials. These materials can potentially be leveraged to advance gut microbiome research and fecal microbiota transplantation, particularly in low-resource settings.

7.
Rev Sci Instrum ; 87(8): 084703, 2016 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-27587143

RESUMO

A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approaches the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement "meta-metallic." In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz.

8.
Curr Trends Neurol ; 10: 53-64, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-28690375

RESUMO

Recent discoveries on the nature of the activity generated by the reticular activating system (RAS) suggest that arousal is much more involved in perception and movement than previously thought. The RAS is not simply an amorphous, unspecific region but rather a distinct group of nuclei with specific cell and transmitter types that control waking and modulate such processes as perception and movement. Thus, disturbances in the RAS will affect a number of neurological disorders. The discovery of gamma band activity in the RAS determined that high threshold calcium channels are responsible for generating gamma band activity in the RAS. Results showing that waking is mediated by CaMKII modulation of P/Q-type channels and REM sleep is modulated by cAMP/PK modulation of N-type channels points to different intracellular pathways influencing each state. Few studies address these important breakthroughs. Novel findings also show that the same primate RAS neurons exhibiting activity in relation to arousal are also involved in locomotion. Moreover, deep brain stimulation of this region, specifically the pedunculopontine nucleus (PPN DBS), in Parkinson's disease has salutary effects on movement, sleep, and cognition. Gamma oscillations appear to participate in sensory perception, problem solving, and memory, and coherence at these frequencies may occur at cortical or thalamocortical levels. However, rather than participating in the temporal binding of sensory events, gamma band activity generated in the RAS may help stabilize coherence related to arousal, providing a stable activation state during waking, and relay such activation to the cortex. Continuous sensory input will thus induce gamma band activity in the RAS to participate in the processes of preconscious awareness, and provide the essential stream of information for the formulation of many of our perceptions and actions. Such a role has received little attention but promises to help understand and treat a number of neurological disorders.

9.
Transplant Proc ; 47(7): 2301-3, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26361705

RESUMO

BACKGROUND: Post-transplant lymphoproliferative disease is a serious complication of renal transplantation. Major risk factors include Epstein-Barr virus (EBV) seronegativity and induction immunosuppression with lymphocyte-depleting agents. RESULTS: We present a case of a 50-year year-old woman with very early onset PTLD confined to the donor ureter. Phenotypic studies on the tumor material reveal that the lymphoma was most likely of donor origin. A complete staging workup including the kidney allograft was negative for any other sites of involvement. CONCLUSIONS: This case, which had a fatal outcome, emphasizes the risk of renal transplantation in BV-negative individuals when given induction with lymphocyte-depleting drugs.


Assuntos
Transplante de Rim , Transtornos Linfoproliferativos/etiologia , Doadores de Tecidos , Ureter/patologia , Doenças Ureterais/etiologia , Feminino , Humanos , Transtornos Linfoproliferativos/diagnóstico , Pessoa de Meia-Idade , Fatores de Tempo , Doenças Ureterais/diagnóstico
10.
Ultramicroscopy ; 159 Pt 2: 292-8, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26051655

RESUMO

To understand the contribution of long term thermal ageing to Reactor Pressure Vessel (RPV) embrittlement two high Cu steel welds with different Ni contents were thermally aged for times up to 100,000 h at 330 °C and 365 °C. Microstructural characterisation using Atom Probe Tomography was performed. Thermal ageing produced a high number density of nano-scale Cu-enriched precipitates. The precipitate-matrix interfaces were enriched in Ni, Mn and Si. The characterisation of these interfaces using a double cluster search approach is the subject of this work. The interface region around thermally-induced precipitates was found to be wider in steels with higher bulk Ni contents and where precipitates had larger core radii. The effect of ageing temperature on interface width was small when comparing precipitates of equal core radius. The narrower interface width in the lower Ni steels is reflected in the composition of the interface, which has a lower Ni content than in the higher Ni material. The reduction in interfacial energy due to the segregation of Ni, Mn and Si has been calculated and shows enhanced reductions in interfacial energy with increasing precipitate size, but no obvious effect of temperature.

11.
J Neural Transm (Vienna) ; 122(2): 225-35, 2015 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24880787

RESUMO

This brief review resolves a number of persistent conflicts regarding the location and characteristics of the mesencephalic locomotor region, which has in the past been described as not locomotion-specific and is more likely the pedunculopontine nucleus (PPN). The parameters of stimulation used to elicit changes in posture and locomotion we now know are ideally suited to match the intrinsic membrane properties of PPN neurons. The physiology of these cells is important not only because it is a major element of the reticular activating system, but also because it is a novel target for the treatment of gait and postural deficits in Parkinson's disease (PD). The discussion explains many of the effects reported following deep brain stimulation (DBS) of the PPN by different groups and provides guidelines for the determination of long-term assessment and effects of PPN DBS. A greater understanding of the physiology of the target nuclei within the brainstem and basal ganglia, amassed over the past decades, has enabled increasingly better patient outcomes from DBS for movement disorders. Despite these improvements, there remains a great opportunity for further understanding of the mechanisms through which DBS has its effects and for further development of appropriate technology to effect these treatments. We review the scientific basis for one of the newest targets, the PPN, in the treatment of PD and other movement disorders, and address the needs for further investigation.


Assuntos
Estimulação Encefálica Profunda , Núcleo Tegmental Pedunculopontino/fisiologia , Animais , Humanos , Transtornos dos Movimentos/terapia
12.
Exp Brain Res ; 232(5): 1509-22, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24309750

RESUMO

Gamma band activity participates in sensory perception, problem solving, and memory. This review considers recent evidence showing that cells in the reticular activating system (RAS) exhibit gamma band activity, and describes the intrinsic membrane properties behind such manifestation. Specifically, we discuss how cells in the mesopontine pedunculopontine nucleus, intralaminar parafascicular nucleus, and pontine SubCoeruleus nucleus dorsalis all fire in the gamma band range when maximally activated, but no higher. The mechanisms involve high-threshold, voltage-dependent P/Q-type calcium channels, or sodium-dependent subthreshold oscillations. Rather than participating in the temporal binding of sensory events as in the cortex, gamma band activity in the RAS may participate in the processes of preconscious awareness and provide the essential stream of information for the formulation of many of our actions. We address three necessary next steps resulting from these discoveries: an intracellular mechanism responsible for maintaining gamma band activity based on persistent G-protein activation, separate intracellular pathways that differentiate between gamma band activity during waking versus during REM sleep, and an intracellular mechanism responsible for the dysregulation in gamma band activity in schizophrenia. These findings open several promising research avenues that have not been thoroughly explored. What are the effects of sleep or REM sleep deprivation on these RAS mechanisms? Are these mechanisms involved in memory processing during waking and/or during REM sleep? Does gamma band processing differ during waking versus REM sleep after sleep or REM sleep deprivation?


Assuntos
Ritmo Gama/fisiologia , Formação Reticular Mesencefálica/citologia , Neurônios/fisiologia , Sono REM/fisiologia , Animais , Canais de Cálcio Tipo N/fisiologia , Córtex Cerebral/citologia , Córtex Cerebral/fisiologia , Humanos , Formação Reticular Mesencefálica/fisiologia , Modelos Biológicos
14.
Mol Ecol Resour ; 12(2): 233-7, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22067369

RESUMO

Here we describe the application of new and existing multiplex PCR methodologies for shark species molecular identification. Four multiplex systems (group ID, thresher sharks, hammerhead sharks and miscellaneous shark) were employed with primers previously described and some designed in this study, which allow for species identification after running PCR products through an agarose gel. This system was implemented for samples (bodies and fins) collected from unidentified sharks landed in the port of Buenaventura and from confiscated tissues obtained from illegal fishing around the Malpelo Island Marine Protected Area, Pacific Coast of Colombia. This method has allowed reliable identification, to date, of 407 samples to the genus and/or species levels, most of them (380) identified as the pelagic thresher shark (Alopias pelagicus). Another seven samples were identified as scalloped hammerhead sharks (Sphyrna lewini). This is an easy-to-implement and reliable identification method that could even be used locally to monitor shark captures in the main fishing ports of developed and developing countries.


Assuntos
Reação em Cadeia da Polimerase Multiplex/métodos , Tubarões/classificação , Tubarões/genética , Animais , Conservação dos Recursos Naturais , Complexo IV da Cadeia de Transporte de Elétrons/genética , Proteínas de Peixes/genética , Pesqueiros , Dados de Sequência Molecular , Oceanos e Mares , Especificidade da Espécie
15.
Rev Sci Instrum ; 82(7): 074704, 2011 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21806211

RESUMO

The two-way insertion loss of a 1 m length of waveguide was reduced by nearly 5 dB over a 4% bandwidth at W-band (94 GHz) for an electron paramagnetic resonance (EPR) spectrometer relative to WR10 waveguide. The waveguide has an oversize section of commercially available rectangular WR28 and a novel pair of tapers that vary in cross section with axial position according to a hyperbolic-cosine (HC) function. The tapers connect conventional rectangular WR10 waveguide to the WR28. For minimum loss, the main mode electric field is parallel to the long side of the WR28. Using mode coupling theory, the position of maximum flare (inflection point) in the taper was optimized with respect to the coupling to higher order modes and the reflection of the main mode. The optimum inflection point position is about one-tenth of the taper length from the small end of the taper. Reflection and coupling were reduced by about 20 dB relative to a pyramidal (linear) taper of the same length. Comb-like dips in the transmission coefficient produced by resonances of the higher order modes in the oversize section were about 0.03 dB. Specially designed high-precision, adjustable WR28 flanges with alignment to about 5 µm were required to keep higher order mode amplitudes arising from the flanges comparable to those from the HC tapers. Minimum return loss was about 30 dB. This paper provides a foundation for further optimization, if needed. Methods are not specific to EPR or the microwave frequency band.


Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Eletricidade , Espectroscopia de Ressonância de Spin Eletrônica/instrumentação , Análise de Elementos Finitos , Modelos Teóricos
16.
Int J Clin Pract ; 65(6): 658-63, 2011 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-21564437

RESUMO

INTRODUCTION: Percutaneous coronary intervention (PCI) activity has increased more than 6 fold in the last 15 years. Increased demand has been met by PCI centres without on-site surgical facilities. To improve communication between cardiologists and surgeons at a remote centre, we have developed a video conferencing system using standard internet links. The effect of this video data link (VDL) on referral pattern and patient selection for revascularisation was assessed prospectively after introduction of a joint cardiology conference (JCC) using the system. METHODS: Between 1st October 2005 and 31st March 2007, 1346 patients underwent diagnostic coronary angiography (CA). Of these, 114 patients were discussed at a cardiology conference (CC) attended by three consultant cardiologists (pre-VDL). In April 2007, the VDL system was introduced. Between 1st April 2007 and 30th September 2008, 1428 patients underwent diagnostic CA. Of these, 120 patients were discussed at a JCC attended by four consultant cardiologists and two consultant cardiothoracic surgeons (post-VDL). Following case-matching for patient demographics and coronary artery disease (CAD) severity and distribution, we assessed the effect upon management decisions arising from both the pre- and post-VDL JCC meetings. RESULTS: When comparing decision-making outcomes of post-VDL JCC with pre-VDL CC, significantly fewer patients were recommended for PCI (36.8% vs. 17.2% respectively, p = 0.001) and significantly more patients were recommended for surgery (21.1% vs. 48.4% respectively, p < 0.001). There were no significant differences in waiting times for PCI following JCC discussion; however, waiting times for surgical revascularisation were significantly reduced (140.9 ± 71.8 days vs. 99.4 ± 56.6 days respectively, p = 0.045). CONCLUSIONS: The VDL system provides a highly practical method for PCI centres without onsite surgical cover to discuss complex patients requiring coronary revascularisation and significantly increases the number of patients referred for surgical revascularisation rather than PCI.


Assuntos
Angiografia Coronária/métodos , Doença das Coronárias/terapia , Revascularização Miocárdica/métodos , Comunicação por Videoconferência , Idoso , Angioplastia Coronária com Balão/métodos , Angioplastia Coronária com Balão/estatística & dados numéricos , Tomada de Decisões , Feminino , Humanos , Relações Interprofissionais , Masculino , Pessoa de Meia-Idade , Revascularização Miocárdica/estatística & dados numéricos , Equipe de Assistência ao Paciente/organização & administração , Seleção de Pacientes , Padrões de Prática Médica/estatística & dados numéricos , Estudos Prospectivos , Encaminhamento e Consulta
17.
J Magn Reson ; 209(2): 142-8, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21277814

RESUMO

Spin-lattice relaxation times (T1s) of small water-soluble spin-labels in the aqueous phase as well as lipid-type spin-labels in membranes increase when the microwave frequency increases from 2 to 35 GHz (Hyde, et al., J. Phys. Chem. B 108 (2004) 9524-9529). The T1s measured at W-band (94 GHz) for the water-soluble spin-labels CTPO and TEMPONE (Froncisz, et al., J. Magn. Reson. 193 (2008) 297-304) are, however, shorter than when measured at Q-band (35 GHz). In this paper, the decreasing trends at W-band have been confirmed for commonly used lipid-type spin-labels in model membranes. It is concluded that the longest values of T1 will generally be found at Q-band, noting that long values are advantageous for measurement of bimolecular collisions with oxygen. The contribution of dissolved molecular oxygen to the relaxation rate was found to be independent of microwave frequency up to 94 GHz for lipid-type spin-labels in membranes. This contribution is expressed in terms of the oxygen transport parameter W=T1⁻¹(Air)-T1⁻¹(N2), which is a function of both concentration and translational diffusion of oxygen in the local environment of a spin-label. The new capabilities in measurement of the oxygen transport parameter using saturation-recovery (SR) EPR at Q- and W-band have been demonstrated in saturated (DMPC) and unsaturated (POPC) lipid bilayer membranes with the use of stearic acid (n-SASL) and phosphatidylcholine (n-PC) spin-labels, and compared with results obtained earlier at X-band. SR EPR spin-label oximetry at Q- and W-band has the potential to be a powerful tool for studying samples of small volume, ~30 nL. These benefits, together with other factors such as a higher resonator efficiency parameter and a new technique for canceling free induction decay signals, are discussed.


Assuntos
Oximetria/métodos , Oxigênio/química , Marcadores de Spin , Espectroscopia de Ressonância de Spin Eletrônica , Bicamadas Lipídicas/química , Lipídeos/química , Lipossomos/química , Membranas Artificiais , Micro-Ondas , Óxidos de Nitrogênio/química , Fosfatidilcolinas/química , Espécies Reativas de Oxigênio/química , Ácidos Esteáricos/química
18.
Ultramicroscopy ; 111(6): 676-82, 2011 May.
Artigo em Inglês | MEDLINE | ID: mdl-21232865

RESUMO

In this work, the importance of optimising experimental conditions for the analysis of reactor pressure vessel (RPV) steels using atom probe tomography is explored. The quality of the resultant atom probe data is assessed in terms of detection efficiency, noise levels and mass resolution. It is demonstrated that artefacts can exist even when experimental conditions have been optimised. In particular, it is shown that surface diffusion of some minority species, including P and Si, to major poles prior to field evaporation can be an issue. The effects were most noticeable during laser pulsing. The impact of surface migration on the characterisation of dislocations and grain boundaries is assessed. The importance of selecting appropriate regions of the reconstructed data for subsequent re-analysis is emphasised.

19.
Ultramicroscopy ; 111(6): 664-71, 2011 May.
Artigo em Inglês | MEDLINE | ID: mdl-21227587

RESUMO

Nanometre scale clusters form in Cu-containing reactor pressure vessel (RPV) steels during neutron irradiation. These clusters have a deleterious effect on mechanical properties, which can result in embrittlement and limit the reactor operating life. Thermal ageing of RPV steels can also induce the formation of solute clusters but it is not clear how similar these are to those formed during irradiation. In this work atom probe tomography, combined with detailed structural assessments of the structure of solute clusters, is used to address this issue. A series of thermal ageing heat treatments has been performed on several high- and low-Ni RPV welds to produce 1-4 nm diameter solute clusters. The same materials have also been neutron irradiated. The results show that CuMnNiSi enriched clusters formed during thermal ageing have, on average, higher Cu contents and lower Mn, Ni and Si contents than those found in irradiation-induced clusters. The effect of increasing bulk Ni is to encourage the formation of clusters with significantly higher Ni content, slightly higher Mn and Si contents and significantly lower Cu contents. At very high doses and dose rates MnNiSi enriched clusters can form even in high-Cu welds. Despite differences in the compositions of individual clusters formed during irradiation and during thermal ageing, clusters in both exhibit similar structure. In particular, well developed clusters in both materials have Cu-enriched cores whose peripheries are enriched in Ni, Mn and, in most cases, Si.

20.
Ultramicroscopy ; 111(6): 440-7, 2011 May.
Artigo em Inglês | MEDLINE | ID: mdl-21227588

RESUMO

Variants of the maximum separation method have become the de-facto methodologies for the characterisation of nanometre scale clusters in atom probe tomography (APT) data obtained from dilute solid solutions. All variants rely on a number of parameters and it is well known that the precise values for these parameters strongly influence estimates of cluster size and number density. Quantitative analyses require an improved understanding of the inter-relationship between user-defined parameters, experimental parameters such as detection efficiency and the resultant parameterisation of the microstructure. A series of simulations has been performed to generate clusters with a range of compositions (50-100%) and diameters (1.5-2.5 nm) in a dilute solid solution. The data were degraded to simulate the effects of the finite detection efficiencies and positioning uncertainties associated with the ECOPoSAP and LEAP-3000X HR. An extensive analysis of each resultant dataset, using a range of values for the maximum separation parameters was then performed. Optimum values for each material condition were identified and it is shown that it is possible to characterise cluster size, number density and matrix chemistry. However, accurate estimates of cluster compositions are more difficult and absolute measurements must be treated with caution. Furthermore, it is shown that D(MAX) must increase with decreasing detection efficiency and consequently clusters of a specific size will appear slightly larger in atom probes with a lower detection efficiency.

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