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1.
PLoS One ; 14(9): e0222584, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31527915

RESUMO

The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m, VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five-class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m2 area) nested within larger ones (of hundreds of km2). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.

2.
J Nanosci Nanotechnol ; 19(1): 593-601, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30327074

RESUMO

The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow angular range defined by the Bragg angle. We also show that excitation can be done by using photons (X-rays), electrons or protons (or charged particles), under near normal or grazing incident geometries, which makes the method relatively easy to implement. The main constraint comes from the angular resolution necessary for the detection of the emitted radiation. This leads to small solid angles of detection and long acquisition times to collect data with sufficient statistical significance. Provided this difficulty is overcome, the comparison or fit of the experimental Kossel curves, i.e., the angular distributions of the intensity of an emitted radiation of one of the element of the periodic stack, with the simulated curves enables getting information on the depth distribution of the elements throughout the multilayer. Thus the same kind of information obtained from the more widespread method of X-ray standing wave induced fluorescence used to characterize stacks of nanometer period, can be obtained using the Kossel effect.

3.
Rev Sci Instrum ; 89(9): 096109, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30278717

RESUMO

We present the observation of the angular distribution of a characteristic x-ray emission through a periodic multilayer. The emission coming from the substrate on which the multilayer is deposited is used for this purpose. It is generated upon proton irradiation through the multilayer and detected with an energy sensitive CCD camera. The observed distribution in the low detection angle range presents a clear dip at a position characteristic of the emitting element. Thus, such a device can be envisaged as a spectrometer without mechanical displacement and using various ionizing sources (electrons, x-rays, and ions), their incident direction being irrelevant.

4.
Struct Dyn ; 4(5): 054306, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28852688

RESUMO

Stimulated emission is a fundamental process in nature that deserves to be investigated and understood in the extreme ultra-violet (EUV) and x-ray regimes. Today, this is definitely possible through high energy density free electron laser (FEL) beams. In this context, we give evidence for soft-x-ray stimulated emission from a magnesium oxide solid target pumped by EUV FEL pulses formed in the regime of travelling-wave amplified spontaneous emission in backward geometry. Our results combine two effects separately reported in previous works: emission in a privileged direction and existence of a material-dependent threshold for the stimulated emission. We develop a novel theoretical framework, based on coupled rate and transport equations taking into account the solid-density plasma state of the target. Our model accounts for both observed mechanisms that are the privileged direction for the stimulated emission of the Mg L2,3 characteristic emission and the pumping threshold.

5.
J Synchrotron Radiat ; 24(Pt 2): 376-385, 2017 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-28244430

RESUMO

The propagation within a one-dimensional photonic crystal of a single ultra-short and ultra-intense pulse delivered by an X-ray free-electron laser is analysed with the framework of the time-dependent coupled-wave theory in non-linear media. It is shown that the reflection and the transmission of an ultra-short pulse present a transient period conditioned by the extinction length and also the thickness of the structure for transmission. For ultra-intense pulses, non-linear effects are expected: they could give rise to numerous phenomena, bi-stability, self-induced transparency, gap solitons, switching, etc., which have been previously shown in the optical domain.

6.
J Synchrotron Radiat ; 22(6): 1419-25, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26524307

RESUMO

The characterization of Mg-Co-Zr tri-layer stacks using X-ray fluorescence induced by X-ray standing waves, in both the grazing-incidence (GI) and the grazing-exit (GE) modes, is presented. The introduction of a slit in the direction of the detector improves the angular resolution by a factor of two and significantly improves the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kα and Co Lα characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, it is shown that the interfaces of the Si/[Mg/Co/Zr] × 30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co] × 30 multilayer a strong intermixing occurs at the Co-on-Zr interfaces. An explanation of this opposite behavior of the Co-on-Zr and Zr-on-Co interfaces is given by the calculation of the mixing enthalpies of the Co-Mg, Co-Zr and Mg-Zr systems, which shows that the Co-Zr system presents a negative value and the other two systems present positive values. Together with the difference of the surface free energies of Zr and Co, this leads to the Mg/Zr/Co system being considered as a Mg/CoxZry bi-layer stack, with x/y estimated around 3.5.

7.
Opt Express ; 21(12): 14399-408, 2013 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-23787628

RESUMO

The reflectivity of Al/Zr multilayers is enhanced by the use of a novel structure. The Al layers are divided by insertion of Si layers. In addition, Si barrier layers are inserted at the Al/Zr interfaces (Zr-on-Al and Al-on-Zr). As a result, crystallization of the Al layer is inhibited and that of Zr is enhanced. In grazing incidence x-ray reflectometry, x-ray diffraction, and extreme ultraviolet measurements, the novel multilayers exhibit lower interfacial roughness compared with traditional multilayer structures, and their reflectivity is increased from 48.2% to 50.0% at a 5° angle of incidence. These novel multilayers also have potential applications in other multilayer systems and the semiconductor industry.


Assuntos
Alumínio/química , Fotometria/métodos , Refratometria/métodos , Silício/química , Zircônio/química , Luz , Teste de Materiais , Espalhamento de Radiação
8.
Opt Express ; 20(10): 10692-700, 2012 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-22565694

RESUMO

Two kinds of Al/Zr (Al(1%wtSi)/Zr and Al(Pure)/Zr) multilayers for extreme ultraviolet (EUV) optics were deposited on fluorine doped tin oxide coated glass by using direct-current magnetron sputtering technology. The comparison of the two systems shows that the Al(1%wtSi)/Zr multilayers have the lowest interfacial roughness and highest reflectivity. Based on the X-ray diffraction, the performance of the two systems is determined by the crystallization of Al layer. To fully understand the Al(1%wtSi)/Zr multilayer, we built up a two-layer model to fit situation of the AFM images, and simulate the grazing incident x-ray reflection-measurements of multilayers with various periods (N = 10, 40, 60, 80). Below 40 periods, the roughness components are lowered. After 40 periods, both surface and interfacial roughness increase with the period number, and decrease the reflectance. According to transmission electron microscope images, the model can represent the variable structure of the system.


Assuntos
Alumínio/química , Óptica e Fotônica , Zircônio/química , Cristalização/métodos , Desenho de Equipamento , Magnetismo , Teste de Materiais , Microscopia de Força Atômica/métodos , Microscopia Eletrônica de Transmissão/métodos , Propriedades de Superfície , Difração de Raios X , Raios X
9.
Opt Express ; 19(22): 21849-54, 2011 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-22109036

RESUMO

The efficiency of B(4)C, Mo and Zr barrier layers to improve thermal stability of Mg/Co multilayer up to 400 °C is investigated. Multilayers were deposited by direct current magnetron sputtering and characterized using X-ray and extreme ultraviolet reflection. The results suggest that B(4)C barrier layer is not effective due to drastic diffusion at Mg-B(4)C interface. Although introducing Mo barriers improves the thermal stability from 200 to 300 °C, it increases the interface roughness and thus degrades the optical performances. On the contrary, Zr barriers can significantly increase the thermal stability of Mg/Co up to 400 °C without optical performance degradation. Thus, Mg/Zr/Co/Zr is suitable for EUV applications requiring both optimal optical performances and heat resistance.

10.
Opt Express ; 18(19): 20019-28, 2010 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-20940893

RESUMO

We present the results of an optical and chemical, depth and surface study of Al/Mo/SiC periodic multilayers, designed as high reflectivity coatings for the extreme ultra-violet (EUV) range. In comparison to the previously studied Al/SiC system, the introduction of Mo as a third material in the multilayer structure allows us to decrease In comparison to the previously studied Al/SiC system with a reflectance of 37% at near normal incidence around 17 nm, the introduction of Mo as a third material in the multilayer structure allows us to decrease the interfacial roughness and achieve an EUV reflectivity of 53.4%, measured with synchrotron radiation. This is the first report of a reflectivity higher than 50% around 17 nm. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) measurements are performed on the Al/Mo/SiC system in order to analyze the individual layers within the stack. ToF-SIMS and XPS results give evidence that the first SiC layer is partially oxidized, but the O atoms do not reach the first Mo and Al layers. We use these results to properly describe the multilayer stack and discuss the possible reasons for the difference between the measured and simulated EUV reflectivity values.


Assuntos
Alumínio/química , Compostos Inorgânicos de Carbono/química , Lentes , Membranas Artificiais , Molibdênio/química , Fotometria/instrumentação , Refratometria/instrumentação , Compostos de Silício/química , Desenho de Equipamento , Análise de Falha de Equipamento , Teste de Materiais , Raios Ultravioleta
11.
Appl Opt ; 49(20): 3922-5, 2010 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-20648167

RESUMO

Mg-based multilayers, including SiC/Mg, Co/Mg, B(4)C/Mg, and Si/Mg, are investigated for solar imaging and a He II calibration lamp at a 30.4 nm wavelength. These multilayers were fabricated by a magnetron sputtering method and characterized by x-ray reflection. The reflectivities of these multilayers were measured by synchrotron radiation. Near-normal-incidence reflectivities of Co/Mg and SiC/Mg multilayer mirrors are as high as 40.3% and 44.6%, respectively, while those of B(4)C/Mg and Si/Mg mirrors are too low for application. The measured results suggest that SiC/Mg, Co/Mg multilayers are promising for a 30.4 nm wavelength.

12.
Atherosclerosis ; 190(1): 150-5, 2007 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-16510148

RESUMO

BACKGROUND: Tuberculosis is a chronic recurrent infection and inflammation is part of the disease which may remain undiagnosed for months. Furthermore immunization with recombinant heat shock protein-65-rich mycobacterium tuberculosis increased atherogenesis in hypercholesterolemic animal models. OBJECTIVE: To investigate the potential interrelationships between past tuberculosis with carotid and femoral atherosclerosis in hypercholesterolemic patients. DESIGN AND SETTING: Case control study in a university hospital. PATIENTS: Two groups of hypercholesterolemic patient group (n=147) studied in a cardiovascular prevention unit during the same quarter, age (+/-1 year) and sex-matched. The first group presented a history of tuberculosis in the past and the second group never. METHODS: Atherosclerosis was assessed by carotid and femoral external echography. Measurements of maximum plaque diameter were done in longitudinal planes, and the extent of atherosclerosis was graded according to the most severe visible changes on the scanned arteries. RESULTS: The frequency and the distribution of atherosclerosis was similar in the two groups, whatever the arterial site explored, carotid or femoral. None of the clinical and biological studied variables were different between the two groups of patients. CONCLUSION: Past tuberculosis is not associated with increased frequency of atherosclerotic lesions in hypercholesterolemic patients.


Assuntos
Doenças das Artérias Carótidas/epidemiologia , Doenças das Artérias Carótidas/microbiologia , Hipercolesterolemia/epidemiologia , Tuberculose Pulmonar/epidemiologia , Doenças das Artérias Carótidas/diagnóstico por imagem , Estudos de Casos e Controles , Feminino , Artéria Femoral/diagnóstico por imagem , Humanos , Masculino , Pessoa de Meia-Idade , Fatores de Risco , Ultrassonografia
13.
Appl Opt ; 43(20): 4041-54, 2004 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-15285096

RESUMO

A neural network is developed to retrieve chlorophyll a concentration from marine reflectance by use of the five visible spectral bands of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The network, dedicated to the western equatorial Pacific Ocean, is calibrated with synthetic data that vary in terms of atmospheric content, solar zenith angle, and secondary pigments. Pigment variability is based on in situ data collected in the study region and is introduced through nonlinear modeling of phytoplankton absorption as a function of chlorophyll a, b, and c and photosynthetic and photoprotectant carotenoids. Tests performed on simulated yet realistic data show that chlorophyll a retrievals are substantially improved by use of the neural network instead of classical algorithms, which are sensitive to spectrally uncorrelated effects. The methodology is general, i.e., is applicable to regions other than the western equatorial Pacific Ocean.


Assuntos
Clorofila/análise , Colorimetria/métodos , Monitoramento Ambiental/métodos , Fitoplâncton/metabolismo , Água do Mar/análise , Análise Espectral/métodos , Algoritmos , Clorofila/metabolismo , Clorofila A , Biologia Marinha/métodos , Modelos Biológicos , Oceano Pacífico , Pigmentos Biológicos/análise , Pigmentos Biológicos/metabolismo , Controle de Qualidade , Reprodutibilidade dos Testes , Água do Mar/microbiologia , Sensibilidade e Especificidade
14.
Appl Opt ; 41(1): 239-44, 2002 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-11900440

RESUMO

An x-ray multilayer monochromator with improved resolution and a low specular background is presented. The monochromator consists of a lamellar multilayer amplitude grating with appropriate parameters used at the zeroth diffraction order. The device is fabricated by means of combining deposition of thin films on a nanometer scale, UV lithography, and reactive ion etching. The performance of this new monochromator at photon energies near 1500 eV is shown.

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