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1.
J Imaging ; 7(4)2021 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-34460517

RESUMO

Skin lesion segmentation is a primary step for skin lesion analysis, which can benefit the subsequent classification task. It is a challenging task since the boundaries of pigment regions may be fuzzy and the entire lesion may share a similar color. Prevalent deep learning methods for skin lesion segmentation make predictions by ensembling different convolutional neural networks (CNN), aggregating multi-scale information, or by multi-task learning framework. The main purpose of doing so is trying to make use of as much information as possible so as to make robust predictions. A multi-task learning framework has been proved to be beneficial for the skin lesion segmentation task, which is usually incorporated with the skin lesion classification task. However, multi-task learning requires extra labeling information which may not be available for the skin lesion images. In this paper, a novel CNN architecture using auxiliary information is proposed. Edge prediction, as an auxiliary task, is performed simultaneously with the segmentation task. A cross-connection layer module is proposed, where the intermediate feature maps of each task are fed into the subblocks of the other task which can implicitly guide the neural network to focus on the boundary region of the segmentation task. In addition, a multi-scale feature aggregation module is proposed, which makes use of features of different scales and enhances the performance of the proposed method. Experimental results show that the proposed method obtains a better performance compared with the state-of-the-art methods with a Jaccard Index (JA) of 79.46, Accuracy (ACC) of 94.32, SEN of 88.76 with only one integrated model, which can be learned in an end-to-end manner.

2.
J Environ Qual ; 50(3): 580-588, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33751608

RESUMO

This study presents the concept of an economic in situ light-scattering sensor for real-time measurement of the solid content in tailings facilities. An experimental setup using a blue (405 nm wavelength) laser diode and silicon photodiodes was constructed to measure the angular distribution of the intensity of scattered light. It was found that the angular intensity of scattered light for tailing samples follows a cosn (θ) relation with n ≈ 1.5, where θ is the angle between the laser beam and the photodiode. An angular value of θ = 20° was chosen for the sensor design based on a high signal-to-noise ratio. The setup was used to determine the relation between scattered light intensity and solids content using a thickened tailings underflow from an oil sands facility and Kaolin as a model material. It was observed that the intensity of scattered light tends to increase with an increase in solids content, with qualitatively similar settling behavior for the two materials but at largely different time scales. An insertion-based prototype was built and tested in a large (2.7 m height) settling column with treated mature fine tailings, and the light-scattering data were verified by standard gravimetric method and gamma-ray measurements. In general, good agreement was established between these measurements in the absence of optical fouling, which demonstrates the potential of the sensor as an effective tool for tailings management.


Assuntos
Caulim , Campos de Petróleo e Gás
3.
J Food Sci ; 85(4): 1203-1212, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32118300

RESUMO

Listeria monocytogenes is often responsible for postprocessing contamination of ready-to-eat (RTE) products including cooked ham. As an emerging technology, atmospheric cold plasma (ACP) has the potential to inactivate L. monocytogenes in packaged RTE meats. The objectives of this study were to evaluate the effect of treatment time, modified atmosphere gas compositions (MAP), ham formulation, and post-treatment storage (1 and 7 days at 4 °C) on the reduction of a five-strain cocktail of L. monocytogenes and quality changes in ham subjected to in-package ACP treatment. Initial average cells population on ham surfaces were 8 log CFU/cm2 . The ACP treatment time and gas composition significantly (P < 0.05) influenced the inactivation of L. monocytogenes, irrespective of ham formulations. When MAP1 (20% O2 + 40% CO2 + 40% N2 ) was used, there was a significantly higher log reduction (>2 log reduction) in L. monocytogenes on ham in comparison to MAP2 (50% CO2 + 50% N2 ) and MAP3 (100% CO2 ), irrespective of ham formulation. Addition of preservatives (that is, 0.1% sodium diacetate and 1.4% sodium lactate) or bacteriocins (that is, 0.05% of a partially purified culture ferment from Carnobacterium maltaromaticum UAL 307) did not significantly reduce cell counts of L. monocytogenes after ACP treatment. Regardless of type of ham, storage of 24 hr after ACP treatment significantly reduced cells counts of L. monocytogenes to approximately 4 log CFU/cm2 . Following 7 days of storage after ACP treatment, L. monocytogenes counts were below the detection limit (>6 log reduction) when samples were stored in MAP1. However, there were significant changes in lipid oxidation and color after post-treatment storage. In conclusion, the antimicrobial efficacy of ACP is strongly influenced by gas composition inside the package and post-treatment storage. PRACTICAL APPLICATION: Surface contamination of RTE ham with L. monocytogenes may occur during processing steps such as slicing and packaging. In-package ACP is an emerging nonthermal technology, which can be used as a postpackaging decontamination step in industrial settings. This study demonstrated the influence of in-package gas composition, treatment time, post-treatment storage, and ham formulation on L. monocytogenes inactivation efficacy of ACP. Results of present study will be helpful to optimize in-package ACP treatment and storage conditions to reduce L. monocytogenes, while maintaining the quality of ham.


Assuntos
Embalagem de Alimentos/métodos , Conservação de Alimentos/métodos , Produtos da Carne/microbiologia , Gases em Plasma/farmacologia , Animais , Bacteriocinas/farmacologia , Contagem de Colônia Microbiana , Contaminação de Alimentos/análise , Embalagem de Alimentos/instrumentação , Conservação de Alimentos/instrumentação , Conservantes de Alimentos/farmacologia , Armazenamento de Alimentos , Listeria monocytogenes/efeitos dos fármacos , Listeria monocytogenes/crescimento & desenvolvimento , Produtos da Carne/análise , Lactato de Sódio/farmacologia , Suínos
4.
Food Res Int ; 123: 276-285, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31284978

RESUMO

Ready-to-eat (RTE) deli meat has been linked to several Listeria monocytogenes associated recalls. Recent studies demonstrated the potential antimicrobial effects of atmospheric cold plasma treatment on various food surfaces including RTE meat products. However, the influence of intrinsic and extrinsic factors, determining the efficacy of cold plasma to reduce Listeria has not been reported. This study investigated the influence of rosemary extract, salt (% NaCl), and treatment temperature on the efficacy of plasma to reduce numbers of L. innocua on RTE ham. The effect of post-treatment storage on L. innocua inactivation was also investigated. When the cold plasma treatment temperature was 4 °C, we observed a significant reduction in L. innocua of 1.75 and 1.51 log CFU/cm2 on 1% and 3% NaCl ham surface without rosemary extract respectively, after 180 s treatment. At a treatment temperature of 23 °C, the L. innocua cells were reduced by 1.78 and 1.43 log CFU/cm2, respectively on these surfaces after 180 s. No significant effects of salt concentration and treatment temperature were observed on L. innocua inactivation during cold plasma treatment of ham. The post treatment storage at 4 °C for 6 h after 180 s of plasma treatment enhanced further reduction of L. innocua on 1% NaCl ham without rosemary. We also observed the increased concentration of malondialdehyde (MDA) equivalent lipid oxidation of plasma treated samples and was significantly higher (1.53 MDA mg/ kg ham) compared to untreated samples (0.92 MDA mg/kg ham). However, no significant differences in surface color parameters, L* and b* values were observed after plasma treatment, except a significant increase in a* values. The water content of plasma exposed samples decreased significantly for all treatment conditions whereas the water activity values were not changed significantly. In conclusion, the atmospheric cold plasma could be applied as a means for surface decontamination of RTE ham. However, the drying and oxidation of ham should be controlled in an open atmospheric plasma treatment condition.


Assuntos
Armazenamento de Alimentos , Listeria monocytogenes/efeitos dos fármacos , Listeria/efeitos dos fármacos , Produtos da Carne/microbiologia , Gases em Plasma/farmacologia , Temperatura Baixa , Contagem de Colônia Microbiana , Cor , Qualidade de Produtos para o Consumidor , Contaminação de Alimentos/prevenção & controle , Microbiologia de Alimentos , Embalagem de Alimentos , Peróxido de Hidrogênio/análise , Metabolismo dos Lipídeos/efeitos dos fármacos , Listeria/isolamento & purificação , Listeria monocytogenes/isolamento & purificação , Óxido Nitroso/análise , Ozônio/análise , Cloreto de Sódio/análise , Substâncias Reativas com Ácido Tiobarbitúrico/análise , Água/análise
5.
Opt Express ; 25(14): 16140-16150, 2017 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-28789123

RESUMO

We demonstrate a self-referencing method to reduce noise in a single-shot terahertz detection scheme. By splitting a single terahertz pulse and using a reflective echelon, both the signal and reference terahertz time-domain waveforms were measured using one laser pulse. Simultaneous acquisition of these waveforms significantly reduces noise originating from shot-to-shot fluctuations. We show that correlation function based referencing, which is not limited to polarization dependent measurements, can achieve a noise floor that is comparable to state-of-the-art polarization-gated balanced detection. Lastly, we extract the DC conductivity of a 30 nm free-standing gold film using a single THz pulse. The measured value of σ0 = 1.3 ± 0.4 × 107 S m-1 is in good agreement with the value measured by four-point probe, indicating the viability of this method for measuring dynamical changes and small signals.

6.
Opt Express ; 24(25): 28877-28888, 2016 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-27958553

RESUMO

An experimental setup capable of measuring simultaneous 2D scattered light angular distribution from two directions to study cell morphology without the use of bio-labels was developed. Experiments with hematopoietic stem cells (CD34+ cells) show good agreement with detailed numerical simulations of light scattering. Numerical simulations and computer models of cells are used to identify physical features of cells with the largest scattering cross sections. This allows for determination of size, geometry of the nucleus and distribution of mitochondria in hematopoietic stem cells by means of our label-free method.


Assuntos
Células-Tronco Hematopoéticas/fisiologia , Óptica e Fotônica , Contagem de Células , Núcleo Celular , Células-Tronco Hematopoéticas/classificação , Luz
7.
Ultrasound Med Biol ; 40(6): 1187-96, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24613212

RESUMO

We investigated the effect of low-intensity pulsed ultrasound (LIPUS) on orthodontically induced inflammatory root resorption in vivo. Ten beagle dogs were treated with an orthodontic appliance to move the mandibular fourth premolars bodily. The orthodontic movement was carried out for 4 wk with a continuous force of 1 N/side; using a split-mouth model, LIPUS was applied daily for 20 min. Fourth premolar and surrounding periodontal tissue were evaluated with micro-computed tomography and hematoxylin and eosin and tartrate-resistant acid phosphatase staining. We calculated the number, volume and distribution of root resorption lacunae and their percentage relative to total root volume, orthodontic tooth movement and periodontal ligament space. There was no significant difference in orthodontic tooth movement between the two sides. LIPUS significantly reduced the number of orthodontically induced inflammatory root resorption initiation areas by 71%, reduced their total volume by 68% and reduced their volume relative to the affected root total volume by 70%. LIPUS induced the formation of a precementum layer, thicker cementum and reparative cellular cementum.


Assuntos
Cemento Dentário/fisiologia , Aparelhos Ortodônticos , Reabsorção da Raiz/prevenção & controle , Técnicas de Movimentação Dentária , Ultrassom , Animais , Dente Pré-Molar/diagnóstico por imagem , Cães , Imuno-Histoquímica , Masculino , Mandíbula/diagnóstico por imagem , Reabsorção da Raiz/diagnóstico por imagem , Microtomografia por Raio-X
8.
Opt Express ; 21(15): 18525-31, 2013 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-23938724

RESUMO

The effect of donor film thickness and laser beam fluence on the size of laser-induced forward transfer (LIFT) spots is studied to achieve sub-100 nm features. A 130 fs, 800 nm laser is focused on ultrathin Cr films, and the transfer and ablation thresholds of these films at various thicknesses are determined. The minimum transfer spot size decreases with decreasing donor film thickness and incident laser fluence. Minimum LIFT spots of 70-450 nm diameter are obtained from films of 20-80 nm thickness, respectively. The 70 nm diameter transfer spots obtained from sputtered continuous films are the smallest to date.


Assuntos
Cromo/química , Cromo/efeitos da radiação , Lasers , Membranas Artificiais , Nanopartículas/química , Nanopartículas/ultraestrutura , Teste de Materiais , Nanopartículas/efeitos da radiação , Tamanho da Partícula , Doses de Radiação
9.
Opt Express ; 21(9): 11048-56, 2013 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-23669961

RESUMO

We demonstrate the fine tuning capability of femtosecond laser surface modification as a permanent trimming mechanism for silicon photonic components. Silicon microring resonators with a 15 µm radius were irradiated with single 400 nm wavelength laser pulses at varying fluences. Below the laser ablation threshold, surface amorphization of the crystalline silicon waveguides yielded a tuning rate of 20 ± 2 nm/J · cm(-2)with a minimum resonance wavelength shift of 0.10nm. Above that threshold, ablation yielded a minimum resonance shift of -1.7 nm. There was some increase in waveguide loss for both trimming mechanisms. We also demonstrated the application of the method by using it to permanently correct the resonance mismatch of a second-order microring filter.


Assuntos
Lasers , Silício/química , Silício/efeitos da radiação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Propriedades de Superfície/efeitos da radiação
10.
Ultrasound Med Biol ; 39(6): 1066-74, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23499341

RESUMO

We investigated the short-term effect of LIPUS on human dentin-pulp complex in vitro. We collected sixty-three premolars from patients who needed the extraction. The premolars were sectioned transversely into 600-µm-thick slices, and then divided into five groups according to LIPUS application time (control, 5, 10, 15 and 20 min). LIPUS transducer produced an incident intensity of 30 mW/cm(2). After 24 h, tissue was harvested for histomorphometrical analysis and RT-PCR (Genes of interest: Collagen I, DMP1, DSPP, TGF ß1, RANKL and OPG). Histomorphometric analysis showed no significant difference among the five groups in the odontoblast count and predentin thickness. RT-PCR demonstrated no expression of TGF ß1, low amounts of DSPP, a twofold increase in collagen I expression in the 5- and 10-minute LIPUS groups and a threefold increase in DMP1 expression in the 10-minute LIPUS group. LIPUS application was stimulatory to the dentin-pulp complex in vitro and increased the expression of collagen I and DMP1.


Assuntos
Dente Pré-Molar/fisiologia , Dente Pré-Molar/efeitos da radiação , Polpa Dentária/fisiologia , Polpa Dentária/efeitos da radiação , Dentina/fisiologia , Dentina/efeitos da radiação , Terapia por Ultrassom/métodos , Dente Pré-Molar/citologia , Criança , Colágeno Tipo I/metabolismo , Polpa Dentária/citologia , Relação Dose-Resposta à Radiação , Proteínas da Matriz Extracelular/metabolismo , Feminino , Ondas de Choque de Alta Energia , Humanos , Masculino , Técnicas de Cultura de Órgãos , Fosfoproteínas/metabolismo , Doses de Radiação
11.
ACS Appl Mater Interfaces ; 4(3): 1423-8, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22387678

RESUMO

Solution-processed ZnO thin films are attractive as active materials in thin film transistors (TFTs) for low-cost electronic device applications. However, the lack of true enhancement mode operation, low mobility, and unreliability in transistor characteristics due to the high density of traps and other defects present challenges in using such TFTs in circuits. We demonstrate in this report that the electrical characteristics of such TFTs can be improved by source injection barriers. Asymmetrical Schottky source metal-oxide-semiconductor field-effect transistors (MOSFETs) have been fabricated by utilizing heavily doped solution-processed ZnO as the active layer. n(+)-ZnO was obtained by using triethylamine as the stabilizer in the solution process instead of the more commonly used monoethanolamine. Au was chosen for source metallization to create a Schottky contact to the ZnO and an Al ohmic contact was chosen as the drain. Voltage applied to the gate induced field emission through the Schottky barrier and allowed modulation of the drain current by varying the width of the barrier. By operating the asymmetrical MOSFET when the Schottky contact is reverse biased, effective control over the transistor characteristics was obtained.

12.
Arch Oral Biol ; 57(6): 760-8, 2012 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-22138259

RESUMO

OBJECTIVE: Investigate the effect of therapeutic Low Intensity Pulsed Ultrasound (LIPUS) on human dentine-pulp complex in an in vitro model. DESIGN: 92 premolars were extracted from 23 adolescent orthodontic patients. The premolars were sectioned transversely into 600 µm thick slices. The slices were divided into two main groups according to how often the LIPUS was applied (single or daily application), and then subdivided into five subgroups each (5, 10, 15 and 20 min and one control group). The tooth slices were cultured at (37 °C/5% CO(2)) in a humidified incubator where medium was changed every 48 h. LIPUS was applied using a 3.9 cm(2) transducer that produces an incident intensity of 30 mW/cm(2). After five days, tissue was harvested for histomorphometrical analysis and real time PCR to investigate expression of genes of interest (Collagen I, DMP1, DSPP, TGF-ß1, RANKL and OPG). RESULTS: Histomorphometric analyses revealed that odontoblast cell count was higher in the single application groups (5, 10 and 15 min, respectively) than in the control and other treatment groups. Predentin thickness was higher in the single application group (10, 5 and 15 min) respectively than in the daily application group and the control groups, however they were not significantly different from each other. Real time PCR demonstrated no statistically significant difference between the groups in the expression of Collagen I, DMP1, TGF-ß1, DSPP, RANKL and OPG. CONCLUSION: Reproducible responses from cultured dentine-pulp complex were observed in groups with single application of LIPUS for 5, 10 and 15 min.


Assuntos
Dente Pré-Molar/anatomia & histologia , Polpa Dentária/crescimento & desenvolvimento , Dentina/crescimento & desenvolvimento , Odontoblastos , Técnicas de Cultura de Órgãos , Terapia por Ultrassom , Adolescente , Biomarcadores/análise , Feminino , Humanos , Masculino , Reação em Cadeia da Polimerase em Tempo Real , Reprodutibilidade dos Testes , Estatísticas não Paramétricas
13.
Opt Lett ; 36(23): 4695-7, 2011 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-22139287

RESUMO

Femtosecond laser modification is demonstrated as a possible method for postfabrication tuning of silicon microring resonators. Single 400 nm femtosecond laser pulses were used to modify the effective index of crystalline silicon microring waveguides by either amorphization or surface nanomilling depending on the laser fluence. Both blue- and redshifts in the microring resonance could be achieved without imparting significant degradation to the device quality factor.

14.
J Biomed Opt ; 16(6): 067003, 2011 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-21721824

RESUMO

A microfluidic flow cytometric technique capable of obtaining information on nanometer-sized organelles in single cells in a label-free, noninvasive optical manner was developed. Experimental two-dimensional (2D) light scattering patterns from malignant lymphoid cells (Jurkat cell line) and normal hematopoietic stem cells (cord blood CD34+ cells) were compared with those obtained from finite-difference time-domain simulations. In the simulations, we assumed that the mitochondria were randomly distributed throughout a Jurkat cell, and aggregated in a CD34+ cell. Comparison of the experimental and simulated light scattering patterns led us to conclude that distinction from these two types of cells may be due to different mitochondrial distributions. This observation was confirmed by conventional confocal fluorescence microscopy. A method for potential cell discrimination was developed based on analysis of the 2D light scattering patterns. Potential clinical applications using mitochondria as intrinsic biological markers in single cells were discussed in terms of normal cells (CD34+ cell and lymphocytes) versus malignant cells (THP-1 and Jurkat cell lines).


Assuntos
Citometria de Fluxo/métodos , Processamento de Imagem Assistida por Computador/métodos , Técnicas Analíticas Microfluídicas/métodos , Mitocôndrias/química , Espalhamento de Radiação , Análise de Célula Única/métodos , Células-Tronco Hematopoéticas/ultraestrutura , Humanos , Células Jurkat/ultraestrutura , Luz , Microscopia Confocal , Reconhecimento Automatizado de Padrão
15.
Opt Express ; 19(1): 387-98, 2011 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-21263578

RESUMO

A microscope-based label-free microfluidic cytometer capable of acquiring two dimensional light scatter patterns from single cells, pattern analysis of which determines cellular information such as cell size, orientation and inner nanostructure, was developed. Finite-difference time-domain numerical simulations compared favorably with experimental scatter patterns from micrometer-sized beads and cells. The device was capable of obtaining light scattering patterns from the smallest mature blood cells (platelets) and cord blood hematopoietic stem/progenitor cells (CD34 + cells) and myeloid precursor cells. The potential for evaluation of cells using this label-free microfluidic cytometric technique was discussed.


Assuntos
Citometria de Fluxo/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Microscopia/instrumentação , Separação Celular , Tamanho Celular , Sangue Fetal/citologia , Humanos , Técnicas In Vitro , Recém-Nascido , Fenômenos Ópticos , Espalhamento de Radiação
16.
Cytometry A ; 77(6): 580-4, 2010 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-20301111

RESUMO

A finite-difference time-domain (FDTD) method is used to study the multiple scattering from many organelle-size particles distributed in a biological cell. Conventional flow cytometry, where the small-angle forward scatter (FSC) intensity and side scatter (SSC) intensity are used for cell characterizations, may have difficulties to differentiate the organelle distributions in biological cells. Based on the FDTD simulations, a light-scattering methodology is proposed here to overcome such a problem. This method differentiates the dense and sparse distributions of organelle-size particles in a cell, by counting the peak numbers in both large-angle FSC and wide-angle SSC, with the multiple scattering effects being considered. Implemented with a wide-angle microfluidic cytometer, the approach demonstrated in this theoretical study may find potential applications in clinics for label-free cell physiological study.


Assuntos
Citometria de Fluxo/métodos , Luz , Tamanho das Organelas , Tamanho da Partícula , Contagem de Células , Microfluídica/métodos
17.
Appl Opt ; 47(15): 2798-805, 2008 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-18493285

RESUMO

Periodic high-/low-index film stacks composed of Y(2)O(3) : Eu were grown by glancing angle deposition on silicon and fused silica substrates. Postdeposition annealing at temperatures from 600 to 1000 degrees C for 1 h in air was performed to activate photoluminescence. Absolute photoluminescence spectra were obtained as a function of observation angle. The angular emission distribution was non-Lambertian, with peak emission at angles of 50 to 60 degrees with respect to substrate normal. Spectroscopic transmittance and ellipsometry measurements were performed to characterize the films. Using this description, we were able to reproduce the angular photoluminescence patterns of the films.

18.
Anal Chem ; 80(6): 1995-2000, 2008 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-18278880

RESUMO

Laser-induced breakdown spectroscopy (LIBS) is a well-known technique for fast, stand-off, and nondestructive analysis of the elemental composition of a sample. We have been investigating micro-LIBS for the past few years and demonstrating its application to microanalysis of surfaces. Recently, we have integrated micro-LIBS with laser-induced fluorescence (LIF), and this combination, laser ablation laser-induced fluorescence (LA-LIF), allows one to achieve much higher sensitivity than traditional LIBS. In this study, we use a 170 microJ laser pulse to ablate a liquid sample in order to measure the lead content. The plasma created was re-excited by a 10 microJ laser pulse tuned to one of the lead resonant lines. Upon optimization, the 3sigma limit of detection was found to be 35 +/- 7 ppb, which is close to the EPA standard for the level of lead allowed in drinking water.

19.
Anal Bioanal Chem ; 385(2): 287-94, 2006 May.
Artigo em Inglês | MEDLINE | ID: mdl-16437203

RESUMO

The analytical performance of femtosecond laser-induced breakdown spectroscopy (LIBS) for elemental microanalysis of aluminium alloys and for mapping precipitate distribution on the sample surface has been studied in detail. A Ti-sapphire laser system producing pulses of 130 fs at 800 nm was used to generate the laser-induced plasma. Multi-element microanalysis of commercially available aluminium alloys was performed in air at atmospheric pressure. Crater characteristics such as diameter and crater morphology were characterized by optical and scanning-electron microscopy. Scaling of plasma emission and limit of detection as a function of laser pulse energy was also investigated. Current experimental results are presented and are compared with previous nanosecond microLIBS measurements.

20.
Appl Opt ; 42(30): 6138-47, 2003 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-14594076

RESUMO

Multielemental microanalysis of commercially available aluminum alloys has been performed in air by laser-induced breakdown spectroscopy (LIBS) by use of UV laser pulses with energies below 10 microJ. It is shown that the LIBS technique is capable of detecting the elemental composition of particles less than 10 microm in size, such as precipitates in an aluminum alloy matrix, by using single laser shots. Chemical mapping with a lateral resolution of approximately 10 microm of the distribution of precipitates in the surface plane of a sample was also carried out. Two main types of precipitate, namely, Mn-Fe-Cu (type I) and Mg-Cu (type II), were unambiguously distinguished in our LIBS experiments, in good agreement with x-ray microanalysis measurements. The relative standard deviations of emission of the main minor constituent elements (Cu, Mg, Mn) of the aluminum 2024 alloy range from 33% to 39% when laser shots on the precipitates are included in the analysis but decrease to a range from 5.3% to 7.4% when laser shots are taken only on the matrix material, excluding the precipitates.

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