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1
Беликов, А. В., А. М. Загорулько, С. Н. Смирнов, А. Н. Сергеев, А. А. Михайлова e А. А. Шимко. "Оптические свойства in vitro катарактальных хрусталиков глаза человека в видимом и ближнем ИК диапазонах-=SUP=-*-=/SUP=-". Журнал технической физики 126, n. 5 (2019): 656. http://dx.doi.org/10.21883/os.2019.05.47667.16-19.
Testo completoAbstract (sommario):
Spectral dependences of absorption coefficient, scattering coefficient, anisotropy factor and reduced scattering coefficient for in vitro human eye lenses of different cataract type are investigated. The spectra of absorption coefficient and reduced scattering coefficient were obtained for the spectral range 400-2300 nm, and the spectra of scattering coefficient and scattering anisotropy factor - for the spectral range 400-1800 nm. The regions of wavelengths within which the spectra of the studied optical characteristics of the human eye lens are not statistically significantly different for samples with different stages of cataract maturity and, conversely, within which they are statistically significantly different, are determined.
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Dumont, M., O. Brissaud, G. Picard, B. Schmitt, J. C. Gallet e Y. Arnaud. "High-accuracy measurements of snow Bidirectional Reflectance Distribution Function at visible and NIR wavelengths – comparison with modelling results". Atmospheric Chemistry and Physics Discussions 9, n. 5 (16 settembre 2009): 19279–311. http://dx.doi.org/10.5194/acpd-9-19279-2009.
Testo completoAbstract (sommario):
Abstract. High-accuracy measurements of snow Bidirectional Reflectance Distribution Function (BRDF) were performed for four natural snow samples with a spectrogonio-radiometer in the 500–2600 nm wavelength range. These measurements are one of the first set of direct snow BRDF values over a wide range of lighting and viewing geometry. They were compared to BRDF calculated with two optical models. Variations of the snow anisotropy factor with lighting geometry, wavelength and snow physical properties were investigated. Results show that at wavelengths with small penetration depth, scattering mainly occurs in the very top layers and the anisotropy factor is controlled by the phase function. In this condition, forward scattering peak or double scattering peak is observed. In constrast at shorter wavelengths, the penetration of the radiation is much deeper and the number of scattering events increases. The anisotropy factor is thus nearly constant and decreases at grazing observation angles.
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Dumont, M., O. Brissaud, G. Picard, B. Schmitt, J. C. Gallet e Y. Arnaud. "High-accuracy measurements of snow Bidirectional Reflectance Distribution Function at visible and NIR wavelengths – comparison with modelling results". Atmospheric Chemistry and Physics 10, n. 5 (11 marzo 2010): 2507–20. http://dx.doi.org/10.5194/acp-10-2507-2010.
Testo completoAbstract (sommario):
Abstract. High-accuracy measurements of snow Bidirectional Reflectance Distribution Function (BRDF) were performed for four natural snow samples with a spectrogonio-radiometer in the 500–2600 nm wavelength range. These measurements are one of the first sets of direct snow BRDF values over a wide range of lighting and viewing geometry. They were compared to BRDF calculated with two optical models. Variations of the snow anisotropy factor with lighting geometry, wavelength and snow physical properties were investigated. Results show that at wavelengths with small penetration depth, scattering mainly occurs in the very top layers and the anisotropy factor is controlled by the phase function. In this condition, forward scattering peak or double scattering peak is observed. In contrast at shorter wavelengths, the penetration of the radiation is much deeper and the number of scattering events increases. The anisotropy factor is thus nearly constant and decreases at grazing observation angles. The whole dataset is available on demand from the corresponding author.
4
Kao, Meng-Chun, Che-Yen Kung, Chun-Li Lin e Wen-Chuan Kuo. "Simultaneous Measurement of Multiple Scattering Coefficient and Scattering Anisotropy Factor in Dental Demineralization". Journal of Medical Imaging and Health Informatics 5, n. 8 (1 dicembre 2015): 1859–63. http://dx.doi.org/10.1166/jmihi.2015.1659.
Testo completo
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Popescu, Dan P., e Michael G. Sowa. "In Vitro Assessment of Optical Properties of Blood by Applying the Extended Huygens-Fresnel Principle to Time-Domain Optical Coherence Tomography Signal at 1300 nm". International Journal of Biomedical Imaging 2008 (2008): 1–6. http://dx.doi.org/10.1155/2008/591618.
Testo completoAbstract (sommario):
A direct method for the measurement of the optical attenuation coefficient and the scattering anisotropy parameter based on applying the extended Huygens-Fresnel principle to optical coherence tomography images of blood is demonstrated. The images are acquired with a low-power probing beam at the wavelength of 1300 nm. Values of 12.15 mm−1and 0.95 are found for the total attenuation coefficient and the scattering anisotropy factor, respectively. Also, as a preliminary step, the optical refraction index is determined with a precision of two decimal numbers directly from optical coherence images. The total attenuation coefficient and the scattering anisotropy factor are determined with precisions within experimental error margins of 5% and 2%, respectively. Readable OCT signal is obtained for a maximum propagation of light into blood of 0.25 mm. At the maximum probed depth, the measured signal is almost103smaller than its initial intensity when entering the sample.
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Buchen, Johannes, Wolfgang Sturhahn, Takayuki Ishii e Jennifer M. Jackson. "Vibrational anisotropy of <i>δ</i>-(Al,Fe)OOH single crystals as probed by nuclear resonant inelastic X-ray scattering". European Journal of Mineralogy 33, n. 4 (17 agosto 2021): 485–502. http://dx.doi.org/10.5194/ejm-33-485-2021.
Testo completoAbstract (sommario):
Abstract. The formation of high-pressure oxyhydroxide phases spanned by the components AlOOH–FeOOH–MgSiO2(OH)2 in experiments suggests their capability to retain hydrogen in Earth's lower mantle. Understanding the vibrational properties of high-pressure phases provides the basis for assessing their thermal properties, which are required to compute phase diagrams and physical properties. Vibrational properties can be highly anisotropic, in particular for materials with crystal structures of low symmetry that contain directed structural groups or components. We used nuclear resonant inelastic X-ray scattering (NRIXS) to probe lattice vibrations that involve motions of 57Fe atoms in δ-(Al0.87Fe0.13)OOH single crystals. From the recorded single-crystal NRIXS spectra, we calculated projections of the partial phonon density of states along different crystallographic directions. To describe the anisotropy of central vibrational properties, we define and derive tensors for the partial phonon density of states, the Lamb–Mössbauer factor, the mean kinetic energy per vibrational mode, and the mean force constant of 57Fe atoms. We further show how the anisotropy of the Lamb–Mössbauer factor can be translated into anisotropic displacement parameters for 57Fe atoms and relate our findings on vibrational anisotropy to the crystal structure of δ-(Al,Fe)OOH. As a potential application of single-crystal NRIXS at high pressures, we discuss the evaluation of anisotropic thermal stresses in the context of elastic geobarometry for mineral inclusions. Our results on single crystals of δ-(Al,Fe)OOH demonstrate the sensitivity of NRIXS to vibrational anisotropy and provide an in-depth description of the vibrational behavior of Fe3+ cations in a crystal structure that may motivate future applications of NRIXS to study anisotropic vibrational properties of minerals.
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Tong, S. Y., C. W. Mok, Huasheng Wu e L. Z. Xin. "Role of scattering-factor anisotropy in electron, positron, and photon holography". Physical Review B 58, n. 16 (15 ottobre 1998): 10815–22. http://dx.doi.org/10.1103/physrevb.58.10815.
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Baranyai, László, e Manuela Zude. "Analysis of laser light migration in apple tissue by Monte Carlo simulation". Progress in Agricultural Engineering Sciences 4, n. 1 (1 dicembre 2008): 45–59. http://dx.doi.org/10.1556/progress.4.2008.3.
Testo completoAbstract (sommario):
The distribution of laser light in the tissue of Golden Delicious and Idared apples was measured with backscattering imaging and simulated with Monte Carlo (MC) method. The settings of the vision system (sensitivity and resolution) and the parameters of the laser modules (wavelength, power and beam diameter) were used in a time resolved MC model to optimize the computation. The 1 ns pulse containing 1.42 × 10 7 (at 670 nm) and 2.49 × 10 8 (at 785 nm) photons was selected for the simulation of backscattering on the fruit surface. The statistical effect of the scattering coefficient (µ s ), absorption coefficient (μ a ), and anisotropy factor ( g ) on photon flux and shape of the backscattering profile was evaluated within ±20 % range relative to expected mean values for apple tissue (µ a = 0.63 cm −1 , µ s = 30.0 cm −1 and g = 0.8). The multi-factor ANOVA test pointed out the highest importance (p<0.001) of the anisotropy factor compared to the scattering and absorption coefficients. Decreasing value of anisotropy factor enhanced the maximum intensity and increased the decline of the gradient resulting in a rotation of the intensity profiles. The measured backscattering profiles for Golden Delicious apples responded to bruising (p<0.05) already after one day storage.
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Stocker, Sabrina, Florian Foschum e Alwin Kienle. "Spatially Resolved Lateral Transmission Measurements to Characterize Changes in the Scattering Coefficient and the Anisotropy Factor". Applied Spectroscopy 72, n. 5 (21 febbraio 2018): 757–64. http://dx.doi.org/10.1177/0003702818757520.
Testo completoAbstract (sommario):
A new setup is described to characterize the scattering coefficient and the scattering phase function of liquid media. The setup utilizes the basic idea of a spatially resolved reflectance measurement combined with a sophisticated illumination geometry. The sample is illuminated parallel and close to the interface of the sample and a glass window to get information from single scattered and multiple scattered light. By illuminating the sample with a fiber orientated with the axis parallel to the glass surface, small distances to the source can be examined unimpeded by the illumination beam. The derived information is, for example, not only sensitive to the concentration of the scatterers but also to the size of the scattering particles. We present the setup including the theory to describe the light propagation in the whole configuration using Monte Carlo simulations. The validation has been done with polystyrene microsphere dispersions with different scattering coefficients. As application for the developed setup, we show measurements of different milk samples which vary in concentration of fat, protein, and in fat droplet size during homogenization process. By measuring milk, we show the ability of the sensor to determine information about the scattering phase function without diluting the sample. For sensors in the dairy industry, a measurement with no pre-processing and no diluting of the sample is worthwhile, because this can be used to determine the fat and protein concentration on-line.
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Mettus, Denis, e Andreas Michels. "Small-angle neutron scattering correlation functions of bulk magnetic materials". Journal of Applied Crystallography 48, n. 5 (29 agosto 2015): 1437–50. http://dx.doi.org/10.1107/s1600576715013187.
Testo completoAbstract (sommario):
On the basis of the continuum theory of micromagnetics, the correlation function of the spin-misalignment small-angle neutron scattering cross section of bulk ferromagnets (e.g.elemental polycrystalline ferromagnets, soft and hard magnetic nanocomposites, nanoporous ferromagnets, or magnetic steels) is computed. For such materials, the spin disorder which is related to spatial variations in the saturation magnetization and magnetic anisotropy field results in strong spin-misalignment scattering dΣM/dΩ along the forward direction. When the applied magnetic field is perpendicular to the incoming neutron beam, the characteristics of dΣM/dΩ (e.g.the angular anisotropy on a two-dimensional detector or the asymptotic power-law exponent) are determined by the ratio of magnetic anisotropy field strengthHpto the jump ΔMin the saturation magnetization at internal interfaces. Here, the corresponding one- and two-dimensional real-space correlations are analyzed as a function of applied magnetic field, the ratioHp/ΔM, the single-particle form factor and the particle volume fraction. Finally, the theoretical results for the correlation function are compared with experimental data on nanocrystalline cobalt and nickel.
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Asllanaj, Fatmir, e Ahmad Addoum. "Simultaneous reconstruction of absorption, scattering and anisotropy factor distributions in quantitative photoacoustic tomography". Biomedical Physics & Engineering Express 6, n. 4 (14 maggio 2020): 045010. http://dx.doi.org/10.1088/2057-1976/ab90a0.
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Lorente, Alba, K. Folkert Boersma, Piet Stammes, L. Gijsbert Tilstra, Andreas Richter, Huan Yu, Said Kharbouche e Jan-Peter Muller. "The importance of surface reflectance anisotropy for cloud and NO<sub>2</sub> retrievals from GOME-2 and OMI". Atmospheric Measurement Techniques 11, n. 7 (27 luglio 2018): 4509–29. http://dx.doi.org/10.5194/amt-11-4509-2018.
Testo completoAbstract (sommario):
Abstract. The angular distribution of the light reflected by the Earth's surface influences top-of-atmosphere (TOA) reflectance values. This surface reflectance anisotropy has implications for UV/Vis satellite retrievals of albedo, clouds, and trace gases such as nitrogen dioxide (NO2). These retrievals routinely assume the surface to reflect light isotropically. Here we show that cloud fractions retrieved from GOME-2A and OMI with the FRESCO and OMCLDO2 algorithms have an east–west bias of 10 % to 50 %, which are highest over vegetation and forested areas, and that this bias originates from the assumption of isotropic surface reflection. To interpret the across-track bias with the DAK radiative transfer model, we implement the bidirectional reflectance distribution function (BRDF) from the Ross–Li semi-empirical model. Testing our implementation against state-of-the-art RTMs LIDORT and SCIATRAN, we find that simulated TOA reflectance generally agrees to within 1 %. We replace the assumption of isotropic surface reflection in the equations used to retrieve cloud fractions over forested scenes with scattering kernels and corresponding BRDF parameters from a daily high-resolution database derived from 16 years' worth of MODIS measurements. By doing this, the east–west bias in the simulated cloud fractions largely vanishes. We conclude that across-track biases in cloud fractions can be explained by cloud algorithms that do not adequately account for the effects of surface reflectance anisotropy. The implications for NO2 air mass factor (AMF) calculations are substantial. Under moderately polluted NO2 and backward-scattering conditions, clear-sky AMFs are up to 20 % higher and cloud radiance fractions up to 40 % lower if surface anisotropic reflection is accounted for. The combined effect of these changes is that NO2 total AMFs increase by up to 30 % for backward-scattering geometries (and decrease by up to 35 % for forward-scattering geometries), which is stronger than the effect of either contribution alone. In an unpolluted troposphere, surface BRDF effects on cloud fraction counteract (and largely cancel) the effect on the clear-sky AMF. Our results emphasise that surface reflectance anisotropy needs to be taken into account in a coherent manner for more realistic and accurate retrievals of clouds and NO2 from UV/Vis satellite sensors. These improvements will be beneficial for current sensors, in particular for the recently launched TROPOMI instrument with a high spatial resolution.
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GIRAEV, K. M., N. A. ASHURBEKOV e O. V. KOBSEV. "OPTICAL SPECTRA OF SOME PATHOLOGICAL CONDITIONS OF STOMACH TISSUES". International Journal of Modern Physics B 20, n. 01 (10 gennaio 2006): 25–36. http://dx.doi.org/10.1142/s021797920603295x.
Testo completoAbstract (sommario):
Diffuse reflection spectra, diffuse and collimated transmittance spectra of the mucous tissue of stomach anthrus in norm and at a low-differential form of stomach cancer are measured in 300–800 nm spectrum range. The optical coefficients of absorption (μa), scattering (μs) and anisotropy factor (g) for tissues with pathological changes have been calculated by the three-flux model and diffusion approximation methods. It has been determined that the magnitude of optical parameters grows with the development of malignant processes in stomach tissues which indicates the prevalence of forward light scattering and the increase in Mi scatter contribution to the total scattering coefficient of malignant tissues. It has also been shown that the application of two independent theories as methods of tissues' optical parameters determination (μa,μs,g) gives satisfactorily similar results.
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Schuch, Luiz Alexandre, e Ivanor Antonio Sachett. "Calibração do Long Counter de De Pangher com o padrão secundário destinado a calibração de monitores de nêutrons com moderadores". Ciência e Natura 7, n. 7 (10 dicembre 1985): 19. http://dx.doi.org/10.5902/2179460x25403.
Testo completoAbstract (sommario):
In this work a De Pangher Long Counter used as a secondary standard for calibration of neutron moderador detectors was calibrated.A 5 Ci Am-Be standard source calibrated for neutron emission rate by the manganese sulfate bath method was used as a primary standard. Due to the cylindrical shape of the standard source an anisotropy factor was determined. The scattering effects were experimentally determined using the shadow cone method and reproducibility tests were also donne.
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Wang, H. S., e Qi Li. "Strain, Anisotropy and Low Field Magnetoresistance Effect in Ultrathin Manganite Films". International Journal of Modern Physics B 12, n. 29n31 (20 dicembre 1998): 3372–75. http://dx.doi.org/10.1142/s0217979298002672.
Testo completoAbstract (sommario):
We report low-field magnetoresistance (LFMR) of strained ultrathin Pr0.67Sr0.33MnO3 (PSMO) films. We observed very large LFMR, a factor of 7 of resistance change in zero-field-cooled sample at 80 K and 2000 Oe, in ultrathin PSMO films on LaAlO3 (LAO) (100). Samples with compressive (on (LAO), tensile (on SrTiO 3 (100)) and very small strain (on NdGaO 3 (110)) have been studied systematically and remarkable differences were observed. We also observed large LFMR anisotropy between magnetic fields applied parallel and perpendicular to the film surface. Our results demonstrated that strain and strain-induced spin scattering can result in large LFMR effect.
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Kienle, Alwin, Michael S. Patterson, Lutz Ott e Rudolf Steiner. "Determination of the scattering coefficient and the anisotropy factor from laser Doppler spectra of liquids including blood". Applied Optics 35, n. 19 (1 luglio 1996): 3404. http://dx.doi.org/10.1364/ao.35.003404.
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Cheng, Juan, Jianguang Wen, Qing Xiao, Shengbiao Wu, Dalei Hao e Qinhuo Liu. "Extending the GOSAILT Model to Simulate Sparse Woodland Bi-Directional Reflectance with Soil Reflectance Anisotropy Consideration". Remote Sensing 14, n. 4 (18 febbraio 2022): 1001. http://dx.doi.org/10.3390/rs14041001.
Testo completoAbstract (sommario):
Anisotropic canopy reflectance plays a crucial role in estimating vegetation biophysical parameters, whereas soil reflectance anisotropy affects canopy reflectance. However, woodland canopy bidirectional reflectance distribution function (BRDF) models considering soil anisotropy are far from universal, especially for the BRDF models of mountain forest. In this study, a mountain forest canopy model, named geometric-optical and mutual shadowing and scattering from arbitrarily inclined-leaves model coupled with topography (GOSAILT), was extended to consider the soil anisotropic reflectance characteristics by introducing the simple soil directional (SSD) reflectance model. The modified GOSAILT model (named GOSAILT-SSD) was evaluated using unmanned aerial vehicle (UAV) field observations and discrete anisotropic radiative transfer (DART) simulations. Then, the effects of Lambertian soil assumption on simulating the vi-directional reflectance factor (BRF) were evaluated across different fractions of vegetation cover (Cv), view zenith angles (VZA), solar zenith angles (SZA), and spectral bands with the GOSAILT-SSD model. The evaluation results, with the DART simulations, show that the performance of the GOSAILT-SSD model in simulating canopy BRF is significantly improved, with decreasing RMSE, from 0.027 to 0.017 for the red band and 0.051 to 0.037 for the near-infrared (NIR) band. Meanwhile, the GOSAILT-SSD simulations show high consistency with UAV multi-angular observations (R2 = 0.97). Besides, it is also found that the BRF simulation errors caused by Lambertian soil assumption are too large to be neglected, with a maximum relative bias of about 45% for the red band. This inappropriate assumption results in a remarkable BRF underestimation near the hot spot direction and an obvious BRF overestimation for large VZA in the solar principal plane (PP). Meanwhile, this simulation bias decreases with the increase of fraction of vegetation cover. This study provides an effective technique to improve the capability of the mountain forest canopy BRDF model by considering the soil anisotropic characteristics for advancing the modeling of radiative transfer (RT) processes over rugged terrain.
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Bezugla, Natalia, Serhii Poluectov, Vladyslav Chornyi e Mikhail Bezuglyi. "MONTE CARLO SIMULATION OF LIGHT SCATTERING IN HUMAN SKIN LAYERS BY SPATIAL PHOTOMETRY METHODS". Bulletin of Kyiv Polytechnic Institute. Series Instrument Making, n. 61(1) (30 giugno 2021): 91–100. http://dx.doi.org/10.20535/1970.61(1).2021.237112.
Testo completoAbstract (sommario):
The ability to register and analyze the spatial distribution of light scattered within the full solid angle is the basis for the development and improvement of information-measuring systems and software and hardware complexes for problems of optical biomedical diagnostics. The greatest contribution to light scattering at non-invasive methods of biomedical research are made by the layers of human skin, affecting the depth of probing and the resolution of diagnostic systems. The significant individual variability of the optical properties of biological tissues does not allow practically (clinically) assessing their effect on the light scattering characteristics; therefore, the use of methods for modeling the optical radiation propagation in media in the measuring tools functioning context makes it possible to provide such a prognostic analysis. The goal of this work is a comparative evaluation of the results of the light propagation in human skin layers by Monte Carlo simulation using information-measuring systems of a biomedical photometer with ellipsoidal reflectors and a goniophotometer.
The Monte Carlo simulation results of light scattering in dermis and epidermis at a wavelength of 632.8 nm using spatial photometry methods and the "BT_Mod" software, as well as coordinates, direction, and statistical weight of photons, allows the ray-tracing in a biomedical photometer with ellipsoidal reflectors are presented in this work.
As a result of modeling, graphs of the dependence of optical coefficients (transmission T, diffuse reflection Rd, and absorption A) for the studied tissues of various thicknesses on the value of the scattering anisotropy factor were obtained, as well as photometric images of the second focal plane of ellipsoidal reflectors when receiving a scattering spot in reflected and transmitted light. Diagrams of the averaged scattering indicatrix at three thicknesses of the epidermis and dermis were obtained for a set of biophysically significant values of the scattering anisotropy factor, based on which the integral distribution of the photons statistical weight in diffuse scattered light was analyzed. A quantitative assessment of the illuminance level of images is carried out according to the zone analysis principles in photometry by ellipsoidal reflectors. The resulting graphs of the illuminance dependence the external and middle rings of photometric images in reflected and transmitted light.
The results of the research make it possible to analyze the spatial distribution of light scattered by the human skin layers (epidermis and dermis) within the full solid angle, which can be used in problems of optical dosimetry and medical imaging in diagnostic, endoscopic, and therapeutic methods of biophotonics.
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HU, GUANGXIA, ZHIYU QIAN, TIANMING YANG, WEITAO LI e JIERU XIE. "FUNDAMENTAL RESEARCH ON RADIOFREQUENCY ABLATION OF RAT BRAIN TISSUE BASED ON NEAR-INFRARED SPECTROSCOPY AND MIE THEORY". Journal of Innovative Optical Health Sciences 03, n. 03 (luglio 2010): 213–19. http://dx.doi.org/10.1142/s1793545810001040.
Testo completoAbstract (sommario):
Near-infrared spectroscopy (NIRS) technology and Mie theory are utilized for fundamental research on radiofrequency ablation of biological tissue. Firstly, NIRS is utilized to monitor rats undergoing radiofrequency ablation surgery in real time so as to explore the relationship between reduced scattering coefficient ([Formula: see text]) and the degree of thermally induced tissue coagulation. Then, Mie theory is utilized to analyze the morphological structure change of biological tissue so as to explore the basic mechanism of the change of optical parameters caused by thermally induced tissue coagulation. Results show that there is a close relationship between [Formula: see text] and the degree of thermally induced tissue coagulation; the degree of thermal coagulation can be obtained by the value of [Formula: see text]; when biological tissue thermally coagulates, the average equivalent scattering particle decreases, the particle density increases, and the anisotropy factor decreases.
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Fujii, Hiroyuki, Iori Terabayashi, Toshiaki Aoki, Yuki Inoue, Hyeonwoo Na, Kazumichi Kobayashi e Masao Watanabe. "Numerical Study of Near-Infrared Light Propagation in Aqueous Alumina Suspensions Using the Steady-State Radiative Transfer Equation and Dependent Scattering Theory". Applied Sciences 12, n. 3 (24 gennaio 2022): 1190. http://dx.doi.org/10.3390/app12031190.
Testo completoAbstract (sommario):
Understanding light propagation in liquid phantoms, such as colloidal suspensions, involves fundamental research of near-infrared optical imaging and spectroscopy for biological tissues. Our objective is to numerically investigate light propagation in the alumina colloidal suspensions with the mean alumina particle diameter of 55 nm at the volume fraction range 1–20%. We calculated the light scattering properties using the dependent scattering theory (DST) on a length scale comparable to the optical wavelength. We calculated the steady-state radiative transfer and photon diffusion equations (RTE and PDE) using the DST results based on the finite difference method in a length scale of the mean free path. The DST calculations showed that the scattering and reduced scattering coefficients become more prominent at a higher volume fraction. The anisotropy factor is almost zero at all the volume fractions, meaning the scattering is isotropic. The comparative study of the RTE with the PDE showed that the diffusion approximation holds at the internal region with all the volume fractions and the boundary region with the volume fraction higher than 1%. Our findings suggest the usefulness of the PDE as a light propagation model for the alumina suspensions rather than the RTE, which provides accurate but complicated computation.
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Carlsen, Tim, Gerit Birnbaum, André Ehrlich, Veit Helm, Evelyn Jäkel, Michael Schäfer e Manfred Wendisch. "Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica". Cryosphere 14, n. 11 (12 novembre 2020): 3959–78. http://dx.doi.org/10.5194/tc-14-3959-2020.
Testo completoAbstract (sommario):
Abstract. The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase function of the snow crystals. The characterization of this surface reflection anisotropy is essential for satellite remote sensing over both the Arctic and Antarctica. To quantify the angular snow reflection properties, the hemispherical-directional reflectance factor (HDRF) of snow surfaces was derived from airborne measurements in Antarctica during austral summer in 2013/14. For this purpose, a digital 180∘ fish-eye camera (green channel, 490–585 nm wavelength band) was used. The HDRF was measured for different surface roughness conditions, optical-equivalent snow grain sizes, and solar zenith angles. The airborne observations covered an area of around 1000 km × 1000 km in the vicinity of Kohnen Station (75∘0′ S, 0∘4′ E) at the outer part of the East Antarctic Plateau. The observations include regions with higher (coastal areas) and lower (inner Antarctica) precipitation amounts and frequencies. The digital camera provided upward, angular-dependent radiance measurements from the lower hemisphere. The comparison of the measured HDRF derived for smooth and rough snow surfaces (sastrugi) showed significant differences, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven bidirectional reflectance distribution function (BRDF) model, the measured HDRF of snow surfaces was parameterized as a function of solar zenith angle, surface roughness, and optical-equivalent snow grain size. This allows a direct comparison of the HDRF measurements with the BRDF derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite product MCD43. For the analyzed cases, MODIS observations (545–565 nm wavelength band) generally underestimated the anisotropy of the surface reflection. The largest deviations were found for the volumetric model weight fvol (average underestimation by a factor of 10). These deviations are likely linked to short-term changes in snow properties.
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Fukutomi, Daichi, Katsunori Ishii e Kunio Awazu. "Determination of the scattering coefficient of biological tissue considering the wavelength and absorption dependence of the anisotropy factor". Optical Review 23, n. 2 (15 dicembre 2015): 291–98. http://dx.doi.org/10.1007/s10043-015-0161-y.
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Fukushige, T., J. Makino e T. Ebisuzaki. "Effect of Multiple Gravitational Lensing on the Anisotropy of the Cosmic Background Radiation". Symposium - International Astronomical Union 173 (1996): 95–96. http://dx.doi.org/10.1017/s007418090023101x.
Testo completoAbstract (sommario):
We investigated smoothing of the cosmic background radiation (CBR) by multiple gravitational lensing. The CBR is gravitationally scattered by galaxies, clusters of galaxies, and superclusters during the travel from the last scattering surface. Although the effect of the gravitational lensing was thought to be unimportant, we found that the multiple gravitational lensing by clusters of galaxies or by superclusters can reduced by a large factor. This result is explained by the fact that the distance between two light rays grows exponentially though multiple gravitational lensing. If such structures were formed at z = 2–5 and contain a large fraction of the mass of the universe (Ωs > 0.5), then multiple gravitational lensing can reduce the temperature anisotropy of the CBR by 40-60%, approximately up to a degree scale.
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McElhinny, Kyle M., Gokul Gopalakrishnan, Donald E. Savage, David A. Czaplewski, Max G. Lagally, Martin V. Holt e Paul G. Evans. "Synchrotron x-ray thermal diffuse scattering probes for phonons in Si/SiGe/Si trilayer nanomembranes". MRS Advances 1, n. 48 (2016): 3263–68. http://dx.doi.org/10.1557/adv.2016.352.
Testo completoAbstract (sommario):
ABSTRACTNanostructures offer the opportunity to control the vibrational properties of via the scattering of phonons due to boundaries and mass disorder as well as through changes in the phonon dispersion due to spatial confinement. Advances in understanding these effects have the potential to lead to thermoelectrics with an improved figure of merit by lowering the thermal conductivity and to provide insight into electron-phonon scattering rates in nanoelectronics. Characterizing the phonon population in nanomaterials has been challenging because of their small volume and because optical techniques probe only a small fraction of reciprocal space. Recent developments in x-ray scattering now allow the phonon population to be evaluated across all of reciprocal space in samples with volumes as small as several cubic micrometers. We apply this approach, synchrotron x-ray thermal diffuse scattering (TDS), to probe the population of phonons within a Si/SiGe/Si trilayer nanomembrane. The distributions of scattered intensity from Si/SiGe/Si trilayer nanomembranes and Si nanomembranes with uniform composition are qualitatively similar, with features arising from the elastic anisotropy of the diamond structure. The TDS signal for the Si/SiGe/Si nanomembrane, however, has higher intensity than the Si membrane of the same total thickness by approximately 3.75%. Possible origins of the enhancement in scattering from SiGe in comparison with Si include the larger atomic scattering factor of Ge atoms within the SiGe layer or reduced phonon frequencies due to alloying.
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Chremos, Alexandros, Ferenc Horkay e Jack F. Douglas. "Influence of network defects on the conformational structure of nanogel particles: From “closed compact” to “open fractal” nanogel particles". Journal of Chemical Physics 156, n. 9 (7 marzo 2022): 094903. http://dx.doi.org/10.1063/5.0072274.
Testo completoAbstract (sommario):
We propose an approach to generate a wide range of randomly branched polymeric structures to gain general insights into how polymer topology encodes a configurational structure in solution. Nanogel particles can take forms ranging from relatively symmetric sponge-like compact structures to relatively anisotropic open fractal structures observed in some nanogel clusters and in some self-associating polymers in solutions, such as aggrecan solutions under physiologically relevant conditions. We hypothesize that this broad “spectrum” of branched polymer structures derives from the degree of regularity of bonding in the network defining these structures. Accordingly, we systematically introduce bonding defects in an initially perfect network having a lattice structure in three and two topological dimensions corresponding to “sponge” and “sheet” structures, respectively. The introduction of bonding defects causes these “closed” and relatively compact nanogel particles to transform near a well-defined bond percolation threshold into “open” fractal objects with the inherent anisotropy of randomly branched polymers. Moreover, with increasing network decimation, the network structure of these polymers acquires other configurational properties similar to those of randomly branched polymers. In particular, the mass scaling of the radius of gyration and its eigenvalues, as well as hydrodynamic radius, intrinsic viscosity, and form factor for scattering, all undergo abrupt changes that accompany these topological transitions. Our findings support the idea that randomly branched polymers can be considered to be equivalent to perforated sheets from a “universality class” standpoint. We utilize our model to gain insight into scattering measurements made on aggrecan solutions.
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Hamdy, Omnia, e Haitham S. Mohammed. "Variations in tissue optical parameters with the incident power of an infrared laser". PLOS ONE 17, n. 1 (31 gennaio 2022): e0263164. http://dx.doi.org/10.1371/journal.pone.0263164.
Testo completoAbstract (sommario):
Infrared (IR) lasers are extensively utilized as an effective tool in many medical practices. Nevertheless, light penetration into the inspected tissue, which is highly affected by tissue optical properties, is a crucial factor for successful optical procedures. Although the optical properties are highly wavelength-dependent, they can be affected by the power of the incident laser. The present study demonstrates a considerable change in the scattering and absorption coefficients as a result of varying the incident laser power probing into biological samples at a constant laser wavelength (808 nm). The optical parameters were investigated using an integrating sphere and Kubelka-Munk model. Additionally, fluence distribution at the sample’s surface was modeled using COMSOL-multiphysics software. The experimental results were validated using Receiver Operating Characteristic (ROC) curves and Monte-Carlo simulation. The results showed that tissue scattering coefficient decreases as the incident laser power increases while the absorption coefficient experienced a slight change. Moreover, the penetration depth increases with the optical parameters. The reduction in the scattering coefficients leads to wider and more diffusive fluence rate distribution at the tissue surface. The simulation results showed a good agreement with the experimental data and revealed that tissue anisotropy may be responsible for this scattering reduction. The present findings could be considered in order for the specialists to accurately specify the laser optical dose in various biomedical applications.
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SAMATHAM, RAVIKANT, KEVIN G. PHILLIPS e STEVEN L. JACQUES. "ASSESSMENT OF OPTICAL CLEARING AGENTS USING REFLECTANCE-MODE CONFOCAL SCANNING LASER MICROSCOPY". Journal of Innovative Optical Health Sciences 03, n. 03 (luglio 2010): 183–88. http://dx.doi.org/10.1142/s1793545810001064.
Testo completoAbstract (sommario):
The mechanism of action of clearing agents to improve optical imaging of mouse skin during reflectance-mode confocal microscopy was tested. The dermal side of excised dorsal mouse skin was exposed for one hour to saline, glycerin, or 80% DMSO, then the clearing agent was removed and the dermis placed against a glass cover slip through which a confocal microscope measured reflectance at 488 nm wavelength. An untreated control was also measured. The axial attenuation of reflectance signal, R(zf) versus increasing depth of focus zf behaved as R = ρ exp (-μzf2G), where ρ is tissue reflectivity and μ is attenuation [cm-1]. The factor 2G accounts for the in/out path of photons, and the numerical aperture of the lens. The ρ, μ data were mapped to values of scattering coefficient (μs [cm-1]) and anisotropy of scattering (g). Images showed that glycerin significantly increased the g of dermis from about 0.7 to about 0.99, with little change in the μs of dermis at about 300 cm-1. DMSO and saline had only slight and inconsistent effects on g and μs.
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Yang, Li, Jian Hua Sun e Ai Qing Wu. "Measurements of Optical Parameters of the Fat Emulsion ". Advanced Materials Research 510 (aprile 2012): 822–26. http://dx.doi.org/10.4028/www.scientific.net/amr.510.822.
Testo completoAbstract (sommario):
The rules that optical parameters of the biological tissue simulating liquid ( Intralipid-20% diluents ) were changed along with the change of temperature were investigated by CCD imaging and photograph analyzing system, based on the diffusion approximation and extensive boundary conditions. It was found that the absorption coefficient is gradually increasing and the reduced scattering coefficient is gradually decreasing along with the increase of temperature. And by measurements of diffusing reflection light and the transmission light by CCD, the anisotropy factor of Intralipid-20% diluents was obtained experimentally. The measured value by CCD was compared with the theoretical value. The results were approximately consistent. It was shown the measuring method by CCD not only is easy operation but also has a high accuracy.
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Kaewboonrueng, Gamoltip, Yiğiter Özmen, Sarai Lekchaum e Kitsakorn Locharoenrat. "Monte Carlo Simulation of Photon-Skeletal Muscle Interaction in Human Tissue Model". Advanced Materials Research 1147 (maggio 2018): 12–17. http://dx.doi.org/10.4028/www.scientific.net/amr.1147.12.
Testo completoAbstract (sommario):
We have investigated a possibility of photon propagation into the human tissue model (skin, fat, and skeletal muscle) by Monte Carlo method using Matlab program. There were some parameters of each tissue layer effecting on the light packet, for instance the absorption coefficient, scattering coefficient, anisotropy factor and thickness. It was found that the photon distribution on the surface of the human tissue and photon penetration into the human tissue under the propagation of 100,000 photons were - 0.8580 cm to + 0.7030 cm (served as two detection points) and 0.7220 cm respectively. Therefore, the simulation result gave the photon penetration depth of 0.2220 cm at the skeletal muscle. These numbers could be primarily used as a standard for design and construction of the tissue diagnostic instrument.
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Vorobiev, Andrei, e Spartak Gevorgian. "Enhanced tunable performance of high Q-factor BaxSr1−xTiO3 film bulk acoustic wave resonators". International Journal of Microwave and Wireless Technologies 5, n. 3 (15 aprile 2013): 361–69. http://dx.doi.org/10.1017/s1759078713000317.
Testo completoAbstract (sommario):
Emerging intrinsically tunable film bulk acoustic wave(BAW) resonators allow the development of new generation reconfigurable and agile microwave circuits. In this paper, we demonstrate the enhancement of tunable performance of the high Q-factor BaxSr1−xTiO3 BAW – solidly mounted resonators (BAW–SMR) by varying Ba concentration. The Ba0.5Sr0.5TiO3 BAW–SMR reveal tunability of series resonance frequency up to 2.4%, electromechanical coupling coefficient up to 7.5% and rather high Q-factor, up to 250 at 5.3 GHz. Correlations between the measured electroacoustic parameters are analyzed using the theory of dc field-induced piezoelectric effect in paraelectric phase ferroelectrics. Higher coupling coefficient and tunability of resonance frequency of the Ba0.5Sr0.5TiO3 BAW–SMR are associated with higher tunability of permittivity. Strong anisotropy in field-induced piezoelectric effect is predicted with highest coupling coefficient in (001) direction of the BaxSr1−xTiO3 films. It is also shown that the tunability of series resonance frequency of Ba0.5Sr0.5TiO3 BAW–SMR is limited by relatively high and negative nonlinear electrostriction coefficient which is found to be m ≈ −4·1010 m/F. The BAW–SMR Q-factor is limited significantly by extrinsic acoustic loss associated with wave scattering at reflection from relatively rough top interface. The results of analysis show possible ways of further improvement of the performance of tunable BAW–SMR.
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Durkin, A. J., S. Jaikumar e R. Richards-Kortum. "Optically Dilute, Absorbing, and Turbid Phantoms for Fluorescence Spectroscopy of Homogeneous and Inhomogeneous Samples". Applied Spectroscopy 47, n. 12 (dicembre 1993): 2114–21. http://dx.doi.org/10.1366/0003702934066244.
Testo completoAbstract (sommario):
This paper presents a phantom which simulates the optical properties of tissue. The phantom absorption coefficient, scattering coefficient, anisotropy factor, and fluorescence quantum yield can be independently varied to investigate the effects of these parameters on fluorescence excitation and emission spectra from 300 to 650 nm. Phantom fluorophores include Flavin Adenine Dinucleotide (FAD) and Rhodamine B. Absorption is controlled by adjusting phantom hemoglobin concentration. On the basis of their smoothly varying scattering coefficient and the relatively low amount of fluorescence contributed to the mixture in comparison to other available scatterers, 1.05-µm-diameter polystyrene microspheres were selected as a scatterer. Sample inhomogeneities are simulated by preparing the phantom in a gelatin substrate. The optical properties of turbid phantoms determined with the use of indirect techniques agree well with known values as long as µs(l – g) > µa. Data are presented from dilute, absorbing, and turbid phantoms and inhomogeneous phantoms to qualitatively illustrate the effects of optical properties and sample geometry on fluorescence spectra. The phantom provides the framework for detailed quantitative investigations of the effects of optical properties, sample size, shape, and structure, boundary conditions, and collection geometry on fluorescence spectra.
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Bezuglaya, N. V., A. A. Haponiuk, D. V. Bondariev, S. A. Poluectov, V. A. Chornyi e M. A. Bezuglyi. "Rationale for the Choice of the Ellipsoidal Reflector Parameters for Biomedical Photometers". Devices and Methods of Measurements 12, n. 4 (22 dicembre 2021): 259–71. http://dx.doi.org/10.21122/2220-9506-2021-12-4-259-271.
Testo completoAbstract (sommario):
Biomedical photometersʼ information-measuring systems with ellipsoidal reflectors have acceptable results in determining of biological tissues optical properties in the visible and near-infrared spectral range. These photometers make it possible to study the optical radiation propagation in turbid media for direct and inverse problems of light-scattering optics. The purpose of this work is to study the influence of the ellipsoidal reflectors design parameters on the results of biomedical photometry when simulating the optical radiation propagation in a system of biological tissue and reflectors in transmitted and reflected light.The paper substantiates the choice of the ellipsoidal reflectors’ focal parameter for efficient registration of forward and backscattered light. The methodology of the process is illustrated by the results of a model experiment using the Monte Carlo simulation for samples of human brain white and gray matter at the visible range of 405 nm, 532 nm, and 650 nm. The total transmittance, diffuse reflectance, and absorption graphs depending on the sample thickness were obtained. Based on the introduced concepts of the ellipsoidal reflector efficiency index and its efficiency factor, the expediency of choosing the ellipsoidal reflectors focal parameter is analyzed to ensure the registration of the maximum amount of scattered light. The graphs of efficiency index in reflected and transmitted light for different thickness samples of white and gray matter and efficiency factors depending on the sample thickness were obtained.The influence of the reflectors ellipticity on the illuminance of various zones of photometric images using the example of an absorbing biological medium – pig liver tissue – at wavelength of 405 nm with a Monte Carlo simulation was analyzed.The optical properties of biological media (scattering and absorption coefficients, scattering anisotropy factor, refractive index) and the samples’ geometric dimensions, particularly the thickness, are predetermined when choosing the ellipsoidal reflectors parameters for registration of the scattered light. Coordinates of the output of photons and their statistical weight obtained in the Monte Carlo simulation of light propagation in biological tissue have a physical effect on a characteristic scattering spot formation in the receiving plane of a biomedical photometer with ellipsoidal reflectors.
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Brot, Claude. "Liquides de toupies symétriques: leur tenseur de polarisabilité optique intrinsèque via deux expériences sous champ statique: CH3CN". Canadian Journal of Chemistry 68, n. 9 (1 settembre 1990): 1490–93. http://dx.doi.org/10.1139/v90-228.
Testo completoAbstract (sommario):
NMR line splitting under a strong static electric field (EF-NMR) allows one to measure the average alignment (second spherical harmonic) of the molecule studied under the influence of the field. This average alignment (per unit squared field) can be formulated theoretically by an expression involving the permanent dipole moment, the anisotropy of the static polarizability, etc. and possibly orientational intercorrelations within the liquid. On the other hand the Kerr constant per molecule can be represented by the same expression, multiplified by a factor that is independent of any static electrical property of the molecule (for a gas this factor would be simply proportional to the anisotropy of the optical polarizability). Consequently the ratio of the above experimental results contains information bearing only on the optical properties. The formalism of the "tensor of polarizability increment" developed by the author for liquids made up of ellipsoidal molecules is employed. It is shown that by combining the above ratio with the constitutive equation for the refractivity of the liquid, the two distinct principal elements of the tensor of polarizability increment of the symmetric top molecules constituting the liquid are immediately obtained. Using then the molecular volume, a van der Waals estimate for the elongation of the molecule, and the index of refraction of the liquid, one can calculate the elements of the optical polarizability tensor invacuo. The method is illustrated by neat acetonitrile for which the necessary experimental data exist in the literature. One finds, in units 1040 C2 m2 J−1 5.06 for the mean polarizability and 2.52 for its anisotropy. A published experimental study using depolarized light scattering in the gas phase indicates that the corresponding figures are 4.96 and 2.49 respectively at λ = 633 nm. Finally and accessorily, it is suggested that dipolar intercorrelations are weak in acetonitrile. Indeed, using an analogous formalism for the static permittivity of the liquid, a value for the permanent moment of the molecule is deduced. This value is within 1% of the experimental gas value. Keywords: polarizability tensors, liquids, Kerr constant, NMR.
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Liang, Yuxuan, Chuang Niu, Chen Wei, Shenghan Ren, Wenxiang Cong e Ge Wang. "Phase function estimation from a diffuse optical image via deep learning". Physics in Medicine & Biology 67, n. 7 (25 marzo 2022): 074001. http://dx.doi.org/10.1088/1361-6560/ac5b21.
Testo completoAbstract (sommario):
Abstract Objective. The phase function is a key element of a light propagation model for Monte Carlo (MC) simulation, which is usually fitted with an analytic function with associated parameters. In recent years, machine learning methods were reported to estimate the parameters of the phase function of a particular form such as the Henyey–Greenstein phase function but, to our knowledge, no studies have been performed to determine the form of the phase function. Approach. Here we design a convolutional neural network (CNN) to estimate the phase function from a diffuse optical image without any explicit assumption on the form of the phase function. Specifically, we use a Gaussian mixture model (GMM) as an example to represent the phase function generally and learn the model parameters accurately. The GMM is selected because it provides the analytic expression of phase function to facilitate deflection angle sampling in MC simulation, and does not significantly increase the number of free parameters. Main Results. Our proposed method is validated on MC-simulated reflectance images of typical biological tissues using the Henyey–Greenstein phase function with different anisotropy factors. The mean squared error of the phase function is 0.01 and the relative error of the anisotropy factor is 3.28%. Significance. We propose the first data-driven CNN-based inverse MC model to estimate the form of scattering phase function. The effects of field of view and spatial resolution are analyzed and the findings provide guidelines for optimizing the experimental protocol in practical applications.
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GABOR, M. S., M. BELMEGUENAI, F. ZIGHEM, S. M. CHERIF, T. PETRISOR, T. PETRISOR, C. TIUSAN e M. HEHN. "ELECTRONIC, STRUCTURAL AND MAGNETIC PROPERTIES OF Co2FeAl THIN FILMS FOR POTENTIAL SPINTRONIC APPLICATIONS". SPIN 04, n. 04 (dicembre 2014): 1440022. http://dx.doi.org/10.1142/s2010324714400220.
Testo completoAbstract (sommario):
This paper presents an overview concerning the electronic, structural and magnetic properties of Co 2 FeAl (CFA) thin films. We first used ab initio calculations of the electronic structure in order to discuss the half-metallicity of this compound. Involving a correlated structural-magnetic analysis, we then illustrate, experimentally, the effect of the thickness as well as the annealing temperature on the magnetic and structural properties of CFA films epitaxially grown on MgO (001) single crystal substrates. The X-ray diffraction shows that in our samples having the CFA(001)[110]// MgO (001)[100] epitaxial relation, the chemical order is enhanced as the thickness and the annealing temperature (T a ) are increased. Ferromagnetic resonance measurements reveal further dynamic magnetic properties. The gyromagnetic factor, estimated at 29.2 GHz/T, is both thickness and annealing temperature independent. The in-plane anisotropy results from the superposition between a dominant fourfold symmetry term, as expected for cubic crystal symmetry of the alloy, and a small uniaxial term. The fourfold anisotropy decreases with increasing thickness and annealing temperature. The exchange stiffness constant is thickness independent but increases with T a . In addition, the effective magnetization varies linearly with T a and with the inverse CFA thickness. This is due to the presence of perpendicular uniaxial anisotropy, estimated around -1.8 erg/cm2 at T a = 600°C and 1.05 erg/cm2 at T a = 265°C, respectively. Frequency and angular dependences of the FMR linewidth show two magnon scattering and mosaicity contributions which depend on the CFA thickness and T a . A Gilbert damping coefficient as low as 0.0011 is found for samples annealed at 600°C. Finally, we illustrate that these films can be used as ferromagnetic electrodes in sputtered epitaxial magnetic tunnel junctions (MTJ) based on MgO (001) tunnel barriers. These MTJs show an improvable TMR ratio around 95% at room temperature.
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Sasaki, Yo, Maki Okube, Satoshi Sasaki e Takeshi Toyoda. "Resonant X-ray magnetic scattering study of Ti-Mn-doped Ba ferrites". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 agosto 2014): C1465. http://dx.doi.org/10.1107/s2053273314085349.
Testo completoAbstract (sommario):
BaFe12O19 has M-type hexaferrite structure, giving strong uniaxial anisotropy of the magnetization along c axis. In doped BaTixMnxFe12-2xO19, the substitution of Fe3+ by a pair of Ti4+ and Mn2+ results in a weakening of the magnetic interactions due to the canting of magnetic moments. The crystal structure has a sequence of (Fe6O8) spinel and (BaFe6O11) hcp blocks, associated with five independent Fe sites: tetrahedral 4f1, bipyramidal 2b, and octahedral 2a, 4f2 and 12k sites. Single crystals synthesized by a flux method have cell dimensions of a = 5.8953(2) and c = 23.1887(8) Å and a = 5.9039(2) and c = 23.2047(8) Å for samples of x = 0.5 and 1.0, respectively. Each crystal was mounted with short glass fiber on rare-earth magnet and goniometer head. Conventional intensity measurements were made using a Rigaku AFC7 four-circle diffractometer with a graphite (002) monochromator for Mo Kα radiation. Site-occupancy experiments were performed by using a vertical-type four-circle diffractometer at PF-BL-10A. In this study the magnetic structure has been examined to use resonant X-ray magnetic scattering (RXMS) at the Fe K absorption edge in PF-BL-6C. Circularly polarized X rays produced by a diamond phase retarder were switched between right-handed (helicity=+1) and left-handed polarizations. An AFC-5u four-circle diffractometer was used in the geometry of horizontal scattering plane. Intensity measurements were made to collect as many as possible of Bragg reflections. Based on an asymmetrical ratio of the intensities between right- and left- handed circular polarizations, the intensity difference in the RXMS was estimated for each of reflections. A set of observed asymmetrical ratios was fitted to a model of spin orientation in crystal-structure calculations with the resonant magnetic scattering factors. A residual function in the least-squares fitting is useful to evaluate magnetic moments for individual sites, which is a multiplicity parameter refined in terms of atomic scattering factor. It gives a minimum in plot between site-multiplicity and residual function, assigning the multiplicity related to the canting of magnetic moment in the Fe sites. The magnetic structure obtained in this study is compared with those of M-type BaFe12O19 and BaTiCoFe10O19.
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Zhao, Zhili, Xinzhong Wang, Kaidong Yang, Fang Fan, Dan Wu, Sheng Liu e Kai Wang. "Analysis of Factors Affecting Optical Performance of GaN-Based Micro-LEDs with Quantum Dots Films". Crystals 10, n. 3 (14 marzo 2020): 203. http://dx.doi.org/10.3390/cryst10030203.
Testo completoAbstract (sommario):
Optical performance in terms of light efficiency, color crosstalk and ambient contrast ratio were analyzed for blue GaN-based micro-light emitting diodes (micro-LEDs) combined with red/green quantum dots (QDs)-polymethyl methacrylate (PMMA) films. The thickness and mass ratio of QDs films are two critical factors in affecting the performance of micro-LEDs. Firstly, the precise optical modeling of QDs-PMMA films is established based on the double integrating sphere (DIS) testing system and inverse adding doubling algorithm (IADA) theory. Red and green QDs-PMMA films are composed of ZnCdSe/ZnS QDs and green ZnCdSeS/ZnS QDs, respectively. The fundamental optical parameters of QDs-PMMA films, including scattering, absorption and anisotropy coefficients, are obtained successfully. Secondly, based on these optical parameters, the Monte Carlo ray tracing method is applied to analyze the effect of a QDs-PMMA film’s thickness and mass ratio on the optical performance of micro-LEDs. Results reveal that the light efficiency first increases and then decreases with the increase of a QDs film’s thickness or mass ratio, owing to the scattering characteristics of QDs. Different from the variation tendencies of light efficiency, the crosstalk between adjacent pixels increases as the QDs-PMMA film’s thickness or mass ratio increases, and the ambient contrast ratio is kept stable when the thickness increases. The mass ratio variation of QDs film can change the optical performance of micro-LEDs more effectively than thickness, which demonstrates that mass ratio is a more important factor affecting the optical performance of micro-LEDs.
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Letu, Husi, Hiroshi Ishimoto, Jerome Riedi, Takashi Y. Nakajima, Laurent C.-Labonnote, Anthony J. Baran, Takashi M. Nagao e Miho Sekiguchi. "Investigation of ice particle habits to be used for ice cloud remote sensing for the GCOM-C satellite mission". Atmospheric Chemistry and Physics 16, n. 18 (29 settembre 2016): 12287–303. http://dx.doi.org/10.5194/acp-16-12287-2016.
Testo completoAbstract (sommario):
Abstract. In this study, various ice particle habits are investigated in conjunction with inferring the optical properties of ice clouds for use in the Global Change Observation Mission-Climate (GCOM-C) satellite programme. We develop a database of the single-scattering properties of five ice habit models: plates, columns, droxtals, bullet rosettes, and Voronoi. The database is based on the specification of the Second Generation Global Imager (SGLI) sensor on board the GCOM-C satellite, which is scheduled to be launched in 2017 by the Japan Aerospace Exploration Agency. A combination of the finite-difference time-domain method, the geometric optics integral equation technique, and the geometric optics method is applied to compute the single-scattering properties of the selected ice particle habits at 36 wavelengths, from the visible to the infrared spectral regions. This covers the SGLI channels for the size parameter, which is defined as a single-particle radius of an equivalent volume sphere, ranging between 6 and 9000 µm. The database includes the extinction efficiency, absorption efficiency, average geometrical cross section, single-scattering albedo, asymmetry factor, size parameter of a volume-equivalent sphere, maximum distance from the centre of mass, particle volume, and six nonzero elements of the scattering phase matrix. The characteristics of calculated extinction efficiency, single-scattering albedo, and asymmetry factor of the five ice particle habits are compared. Furthermore, size-integrated bulk scattering properties for the five ice particle habit models are calculated from the single-scattering database and microphysical data. Using the five ice particle habit models, the optical thickness and spherical albedo of ice clouds are retrieved from the Polarization and Directionality of the Earth's Reflectances-3 (POLDER-3) measurements, recorded on board the Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL) satellite. The optimal ice particle habit for retrieving the SGLI ice cloud properties is investigated by adopting the spherical albedo difference (SAD) method. It is found that the SAD is distributed stably due to the scattering angle increases for bullet rosettes with an effective diameter (Deff) of 10 µm and Voronoi particles with Deff values of 10, 60, and 100 µm. It is confirmed that the SAD of small bullet-rosette particles and all sizes of Voronoi particles has a low angular dependence, indicating that a combination of the bullet-rosette and Voronoi models is sufficient for retrieval of the ice cloud's spherical albedo and optical thickness as effective habit models for the SGLI sensor. Finally, SAD analysis based on the Voronoi habit model with moderate particle size (Deff = 60 µm) is compared with the conventional general habit mixture model, inhomogeneous hexagonal monocrystal model, five-plate aggregate model, and ensemble ice particle model. The Voronoi habit model is found to have an effect similar to that found in some conventional models for the retrieval of ice cloud properties from space-borne radiometric observations.
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Letu, H., H. Ishimoto, J. Riedi, T. Y. Nakajima, L. C.-Labonnote, A. J. Baran, T. M. Nagao e M. Skiguchi. "Investigation of ice particle habits to be used for ice cloud remote sensing for the GCOM-C satellite mission". Atmospheric Chemistry and Physics Discussions 15, n. 21 (11 novembre 2015): 31665–703. http://dx.doi.org/10.5194/acpd-15-31665-2015.
Testo completoAbstract (sommario):
Abstract. Various ice particle habits are investigated in conjunction with inferring the optical properties of ice cloud for the Global Change Observation Mission-Climate (GCOM-C) satellite program. A database of the single-scattering properties of five ice particle habits, namely, plates, columns, droxtals, bullet-rosettes, and Voronoi, is developed. The database is based on the specification of the Second Generation Global Imager (SGLI) sensor onboard the GCOM-C satellite, which is scheduled to be launched in 2017 by Japan Aerospace Exploration Agency (JAXA). A combination of the finite-difference time-domain (FDTD) method, Geometric Optics Integral Equation (GOIE) technique, and geometric optics method (GOM) are applied to compute the single-scattering properties of the selected ice particle habits at 36 wavelengths, from the visible-to-infrared spectral region, covering the SGLI channels for the size parameter, which is defined with respect to the equivalent-volume radius sphere, which ranges between 6 and 9000. The database includes the extinction efficiency, absorption efficiency, average geometrical cross-section, single-scattering albedo, asymmetry factor, size parameter of an equivalent volume sphere, maximum distance from the center of mass, particle volume, and six non-zero elements of the scattering phase matrix. The characteristics of the calculated extinction efficiency, single-scattering albedo, and asymmetry factor of the five ice particle habits are compared. Furthermore, the optical thickness and spherical albedo of ice clouds using the five ice particle habit models are retrieved from the Polarization and Directionality of the Earth's Reflectances-3 (POLDER-3) measurements on board the Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL). The optimal ice particle habit for retrieving the SGLI ice cloud properties was investigated by adopting the spherical albedo difference (SAD) method. It is found that the SAD, for bullet-rosette particle, with radii of equivalent volume spheres (r~) ranging between 6 to 10 μm, and the Voronoi particle, with r~ ranging between 28 to 38 μm, and 70 to 100 μm, is distributed stably as the scattering angle increases. It is confirmed that the SAD of small bullet rosette and all sizes of voronoi particles has a low angular dependence, indicating that the combination of the bullet-rosette and Voronoi models are sufficient for retrieval of the ice cloud spherical albedo and optical thickness as an effective habit models of the SGLI sensor. Finally, SAD analysis based on the Voronoi habit model with moderate particles (r~ = 30 μm) is compared to the conventional General Habit Mixture (GHM), Inhomogeneous Hexagonal Monocrystal (IHM), 5-plate aggregate and ensemble ice particle model. It is confirmed that the Voronoi habit model has an effect similar to the counterparts of some conventional models on the retrieval of ice cloud properties from space-borne radiometric observations.
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Satsukawa, T., B. Ildefonse, D. Mainprice, L. F. G. Morales, K. Michibayashi e F. Barou. "A database of plagioclase crystal preferred orientations (CPO) and microstructures – implications for CPO origin, strength, symmetry and seismic anisotropy in gabbroic rocks". Solid Earth 4, n. 2 (18 dicembre 2013): 511–42. http://dx.doi.org/10.5194/se-4-511-2013.
Testo completoAbstract (sommario):
Abstract. This study presents a unique database of 172 plagioclase Crystallographic Preferred Orientations (CPO) of variously deformed gabbroic rocks. The CPO characteristics as a function of the deformation regime (magmatic or crystal-plastic) are outlined and discussed. The studied samples are dominantly from slow- and fast-spread present-day ocean crust, as well as from the Oman ophiolite. Plagioclase is the dominant mineral phase in the studied samples. Plagioclase CPOs are grouped into three main categories: Axial-B, a strong point alignment of (010) with a girdle distribution of [100]; Axial-A, a strong point maximum concentration of [100] with parallel girdle distributions of (010) and (001); and P-type, point maxima of [100], (010), and (001). A majority of CPO patterns are Axial-B and P-type, in samples showing either magmatic or crystal-plastic deformation textures. Axial-A CPOs are less common; they represent 21% of the samples deformed by crystal-plastic flow. Although fabric strength (ODF J index) does not show any consistent variation as a function of the CPO patterns, there is a significant difference in the relationship between the ODF and pole figures J indices; the magmatic type microstructures have high (010) pole figures J indices, which increase linearly with ODF J index, whereas the high [100] pole figures J indices of plastically deformed samples vary in a more scattered manner with ODF J index. The multistage nature of plastic deformation superposed on a magmatic structure compared with magmatic flow, and the large number of possible slip-systems in plagioclase probably account for these differences. Calculated seismic properties (P wave and S wave velocities and anisotropies) of plagioclase aggregates show that anisotropy (up to 12% for P wave and 14% for S wave) tends to increase as a function of ODF J index. In comparison with the olivine 1998 CPO database, the magnitude of P wave anisotropy for a given J index is much less than olivine, whereas it is similar for S wave anisotropy. Despite a large variation of fabric patterns and geodynamic setting, seismic properties of plagioclase-rich rocks have similar magnitudes of anisotropy. There is a small difference in the aggregate elastic symmetry, with magmatic microstructures having higher orthorhombic and hexagonal components, whereas plastic deformation microstructures have a slightly higher monoclinic component, possibly correlated with predominant monoclinic simple shear flow in plastically deformed samples. Overall, plots for CPO strength (ODF J index), pole figure strength, CPO symmetry and seismic anisotropy show significant scattering. This could be related to sampling statistics, although our database is a factor of ten higher than the olivine database of 1998, or it could be related to the low symmetry (triclinic) structure of plagioclase resulting in the addition of degrees of freedom in the processes creating the CPOs.
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Satsukawa, T., B. Ildefonse, D. Mainprice, L. F. G. Morales, K. Michibayashi e F. Barou. "A database of plagioclase crystal preferred orientations (CPO) and microstructures – implications for CPO origin, strength, symmetry and seismic anisotropy". Solid Earth Discussions 5, n. 2 (14 agosto 2013): 1191–257. http://dx.doi.org/10.5194/sed-5-1191-2013.
Testo completoAbstract (sommario):
Abstract. This study presents a unique database of 170 plagioclase Crystallographic Preferred Orientations (CPO) of variously deformed gabbroic rocks. The CPO characteristics as a function of the deformation regime (magmatic or crystal-plastic) are outlined and discussed. The studied samples are dominantly from slow- and fast-spread present-day ocean crust, as well as from the Oman ophiolite. Plagioclase is the dominant mineral phase in the studied samples. Plagioclase CPOs are grouped in three main categories: Axial-B, a strong point alignment of (010) with a girdle distribution of [100]; Axial-A, a strong point maximum concentration of [100] with parallel girdle distributions of (010) and (001); and P-type, point maxima of [100], (010), and (001). A majority of CPO patterns are Axial-B and P-type, in samples showing either magmatic or crystal-plastic deformation textures. Axial-A CPOs are less common; they represent 21% of the samples deformed by crystal-plastic flow. Although fabric strength (ODF J-index) does not show any consistent variation as a function of the CPO patterns, there is a significant difference in the relationship between the ODF and pole figures J-indices; the magmatic type microstructures have high (010) pole figures J-indices, which increase linearly with ODF J-index, whereas the high [100] pole figures J-indices of plastically deformed samples vary in a more scattered manner with ODF J-index. The multistage nature of plastic deformation superposed on a magmatic structure compared with magmatic flow, and the large number of possible slip-systems in plagioclase probably account for these differences. Calculated seismic properties (P wave and S wave velocities and anisotropies) of plagioclase aggregates show that anisotropy (up to 12% for P wave and 14% for S wave) tends to increase as a function of ODF J-index. In comparison with the olivine 1998 CPO database, the magnitude of P wave anisotropy for a given J-index is much less than olivine, whereas it is similar for S wave anisotropy. Despite a large variation of fabric patterns and geodynamic setting, seismic properties of plagioclase-rich rocks have similar magnitudes of anisotropy. There is a small difference in the aggregate elastic symmetry, with magmatic microstructures having higher orthorhombic and hexagonal components, whereas plastic deformation microstructures have a slightly higher monoclinic component, possibly correlated with predominant monoclinic simple shear flow in plastically-deformed samples. Overall, plots for CPO strength (ODF J-index), pole figure strength, CPO symmetry and seismic anisotropy show significant scattering. This could be related to sampling statistics, although our database is a factor of ten higher than the olivine database of 1998, or it could be related to the low symmetry (triclinic) structure of plagioclase resulting in the addition of degrees of freedom in the processes creating the CPOs.
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Ren, Ren, Fei Liang Chen, Jing Jing Chen, L. Zhang e Yu Jun Liu. "Local Dipole Field Enhancement Along the Surface of Metal-Dielectric Au/Pd Core-Shell Nanostructure". Advanced Materials Research 347-353 (ottobre 2011): 582–86. http://dx.doi.org/10.4028/www.scientific.net/amr.347-353.582.
Testo completoAbstract (sommario):
The nanostructure of bimetallic Au/Pd particles was fabricated to investigate their surface plasmon (SP) dynamics and local field factor. The SP dynamics was detected according to the structure, electric dipole and multipole electrical quadrupole moment. It was found that the symmetric coupling red shifts decreased obviously with the increase of the shell thickness and the nanoparticle size, and the absorption efficiencies of the nanostructure depended on the SP resonance frequency. The waves of surface plasmon Pd/Au are achieved by gradient of electrons density between interface and shell layer. The dipole couple and electrical quadrupole moment make the plasmonic anisotropy related to transition of electron energy band. The FWHM under collective plasmonic enhancement has been found to enlarge with rise of radius ratio.Moreover, the SP resonance and the local field were measured with annular limited optical distribution in terms of dipole resonance mode and resonance frequency. The resonance scattering has been changed inspite of the Au/Pd deformation and the collective plasmon enhancement. Besides, the single particle in Z direction went up with the particle dimension. The solid structures of the Au/Pd Core/shell nanoparticles were measured by TEM and EDS
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Zherebtsov, Dmitry, Dilyus Chukov, Isabelle Royaud, Marc Ponçot, Ilya Larin, Eugene S. Statnik, Taisia Drozdova et al. "On the Structural Peculiarities of Self-Reinforced Composite Materials Based on UHMWPE Fibers". Polymers 13, n. 9 (27 aprile 2021): 1408. http://dx.doi.org/10.3390/polym13091408.
Testo completoAbstract (sommario):
The structure of self-reinforced composites (SRCs) based on ultra-high molecular weight polyethylene (UHMWPE) was studied by means of Wide-Angle X-ray Scattering (WAXS), X-ray tomography, Raman spectroscopy, Scanning Electron Microscopy (SEM) and in situ tensile testing in combination with advanced processing tools to determine the correlation between the processing conditions, on one hand, and the molecular structure and mechanical properties, on the other. SRCs were fabricated by hot compaction of UHMWPE fibers at different pressure and temperature combinations without addition of polymer matrix or softener. It was found by WAXS that higher compaction temperatures led to more extensive melting of fibers with the corresponding reduction of the Herman’s factor reflecting the degree of molecular orientation, while the increase of hot compaction pressure suppressed the melting of fibers within SRCs at a given temperature. X-ray tomography proved the absence of porosity while polarized light Raman spectroscopy measurements for both longitudinal and perpendicular fiber orientations showed qualitatively the anisotropy of SRC samples. SEM revealed that the matrix was formed by interlayers of molten polymer entrapped between fibers in SRCs. Moreover, in situ tensile tests demonstrated the increase of Young’s modulus and tensile strength with increasing temperature.
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Ganoza-Quintana, José Luis, Félix Fanjul-Vélez e José Luis Arce-Diego. "Digital Histology by Phase Imaging Specific Biomarkers for Human Tumoral Tissues Discrimination". Applied Sciences 11, n. 13 (1 luglio 2021): 6142. http://dx.doi.org/10.3390/app11136142.
Testo completoAbstract (sommario):
Histology is the diagnosis gold standard. Conventional biopsy presents artifacts, delays, or human bias. Digital histology includes automation and improved diagnosis. It digitalizes microscopic images of histological samples and analyzes similar parameters. The present approach proposes the novel use of phase contrast in clinical digital histology to improve diagnosis. The use of label-free fresh tissue slices prevents processing artifacts and reduces processing time. Phase contrast parameters are implemented and calculated: the external scale, the fractal dimension, the anisotropy factor, the scattering coefficient, and the refractive index variance. Images of healthy and tumoral samples of liver, colon, and kidney are employed. A total of 252 images with 10×, 20×, and 40× magnifications are measured. Discrimination significance between healthy and tumoral tissues is assessed statistically with ANOVA (p-value < 0.005). The analysis is made for each tissue type and for different magnifications. It shows a dependence on tissue type and image magnification. The p-value of the most significant parameters is below 10−5. Liver and colon tissues present a great overlap in significant phase contrast parameters. The 10× fractal dimension is significant for all tissue types under analysis. These results are promising for the use of phase contrast in digital histology clinical praxis.
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Lunagaria, Manoj M., e Haridas R. Patel. "Changes in reflectance anisotropy of wheat crop during different phenophases". International Agrophysics 31, n. 2 (25 aprile 2017): 203–18. http://dx.doi.org/10.1515/intag-2016-0045.
Testo completoAbstract (sommario):
Abstract The canopy structure of wheat changes significantly with growth stages and leads to changes in reflectance anisotropy. Bidirectional reflectance distribution function characterises the reflectance anisotropy of the targets, which can be approximated. Spectrodirectional reflectance measurements on wheat crop were acquired using a field goniometer system. The bidirectional reflectance spectra were acquired at 54 view angles to cover the hemispheric span up to 60° view zenith. The observations were made during early growth stages till maturity of the crop. The anisotropy was not constant for all wavelengths and anisotropic factors clearly revealed spectral dependence, which was more pronounced in near principal plane. In near infrared, wheat canopy expressed less reflectance anisotropy because of higher multiple scattering. The broad hotspot signature was noticeable in reflectance of canopy whenever view and solar angles were close. Distinct changes in bidirectional reflectance distribution function were observed during booting to flowering stages as the canopy achieves more uniformity, height and head emergence. The function clearly reveals bowl shape during heading to early milking growth stages of the crop. Late growth stages show less prominent gap and shadow effects. Anisotropy index revealed that wheat exhibits changes in reflectance anisotropy with phenological development and with spectral bands.
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Chaizy, P. A. "Cross-field gradients: general concept, importance of multi-spacecraft measurements and study at 1 AU of the source intensity gradient for E > 30 keV solar event electrons". Annales Geophysicae 18, n. 3 (31 marzo 2000): 263–76. http://dx.doi.org/10.1007/s00585-000-0263-z.
Testo completoAbstract (sommario):
Abstract. Three main physical processes (and associated properties) are currently used to describe the flux and anisotropy time profiles of solar energetic par- ticle events, called SEP profiles. They are (1) the particle scattering (due to magnetic waves), (2) the particle focusing (due to the decrease of the amplitude of the interplanetary magnetic field (IMF) with the radial distance to the Sun) and (3) the finite injection profile at the source. If their features change from one field line to another, i.e. if there is a cross IMF gradient (CFG), then the shape of the SEP profiles will depend, at onset time, on the relative position of the spacecraft to the IMF and might vary significantly on small distance scale (e.g. 106 km). One type of CFG is studied here. It is called intensity CFG and considers variations, at the solar surface, only of the intensity of the event. It is shown here that drops of about two orders of magnitude over distances of ~104 km at the Sun (1° of angular distance) can influence dramatically the SEP profiles at 1 AU. This CFG can lead to either an under or overestimation of both the parallel mean free path and of the injection parameters by factor up to, at least, ~2-3 and 18, respectively. Multi-spacecraft analysis can be used to identify CFG. Three basic requirements are proposed to identify, from the observation, the type of the CFG being measured.Key words: Solar physics, astrophysics, and astronomy (energetic particles; flares and mass ejections) - Space plasma physics (transport processes)
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Song, Yongjia, Jun Wang, Hengshan Hu e Bo Han. "Frequency-dependent anisotropy in porous rocks with aligned cracks containing compressible fluid–a model based on poroelastic spring condition and exact solution of scattering by a circular crack at oblique incidence". Geophysical Journal International 226, n. 2 (15 aprile 2021): 1105–29. http://dx.doi.org/10.1093/gji/ggab145.
Testo completoAbstract (sommario):
SUMMARY Thorough understanding of seismic signatures in cracked rocks is essential to estimate rock physical properties. Wave-induced fluid flow (or diffusion), scattering and Biot's global flow are three major mechanisms in controlling frequency-dependent attenuation and dispersion. To shed light on how those mechanisms and their interference affect the anisotropic features in cracked porous rocks, we develop an analytic model to estimate the angle-dependent attenuation and dispersion in such media. The most noteworthy feature of the model is that it is developed upon the exact solution of the problem of elastic wave scattered by a crack at oblique incidence. In particular, the poroelastic spring condition is applied to describe the influences of crack thickness and crack-filling fluid elasticity on wave scattering. Regardless of its complexity, we have showed that the model agrees with many benchmark theories under corresponding conditions, demonstrating its reasonability. It is found that the key factors that dominate anisotropic attenuation and dispersion are different in separating frequency regimes. At diffusion-dominated frequencies, the frequency-dependent anisotropic properties are mainly determined by the normal stress on the crack faces. In contrast, in Rayleigh scattering regime, they are greatly determined by the applied shear stress. At higher frequencies (Mie scattering regime), affected by the wave reflections between the crack edges, the frequency-dependent anisotropy becomes complex. The angle-dependent velocity can largely deviate from elliptic-shaped profile. As a result, the material properties cannot be described within the framework of the transversely isotropic medium model. Moreover, it is found that the attenuation is sensitive to the fluid compressibility and crack thickness, showing evidences that it is possible to invert fluid saturation and permeability from seismic attenuation. We also conclude that using a simple linear superposition of the attenuations due to wave-induced fluid flow and elastic scattering from their corresponding equivalent medium models will leads to an overestimation of the total attenuation. Our results demonstrate it is necessary to account for the mechanism interference to allow for an adequate estimation of the intrinsic attenuation of cracked porous rocks.
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Janson, Markus, Alexis Brandeker, Göran Olofsson e René Liseau. "The far reaches of the β Pictoris debris disk". Astronomy & Astrophysics 646 (febbraio 2021): A132. http://dx.doi.org/10.1051/0004-6361/202039990.
Testo completoAbstract (sommario):
The nearby young star β Pictoris hosts a rich and complex planetary system, with at least two giant planets and a nearly edge-on debris disk that contains several dynamical subpopulations of planetesimals. While the inner ranges of the debris disk have been studied extensively, less information is known about the outer, fainter parts of the disk. Here we present an analysis of archival FORS V -band imaging data from 2003–2004, which have previously not been explored scientifically because the halo substructure of the bright stellar point spread function is complex. Through a high-contrast scheme based on angular differential imaging, with a forward-modelling approach to mitigate self-subtraction, we produced the deepest imaging yet for the outer range of the β Pic disk, and extracted its morphological characteristics. A brightness asymmetry between the two arms of the edge-on disk, which was previously noted in the inner disk, is even more pronounced at larger angular separations, reaching a factor ~10 around 1000 AU. Approaching 2000 AU, the brighter arm is visible at a surface brightness of 27–28 mag arcsec−2. Much like for the brightness asymmetry, a tilt angle asymmetry exists between the two arms that becomes increasingly extreme at large separations. The outer tilt angle of 7.2 deg can only be explained if the outer disk is farther from an edge-on inclination than the inner disk, or if its dust has a stronger scattering anisotropy, or (most likely) both. The strong asymmetries imply the presence of a highly eccentric kinematic disk component, which may have been caused by a disruptive event thought to have taken place at a closer-in location in the disk.
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Lupi, Laura, Brenda Bracco, Paola Sassi, Silvia Corezzi, Assunta Morresi, Daniele Fioretto, Lucia Comez e Marco Paolantoni. "Hydration Dynamics of Model Peptides with Different Hydrophobic Character". Life 12, n. 4 (12 aprile 2022): 572. http://dx.doi.org/10.3390/life12040572.
Testo completoAbstract (sommario):
The multi-scale dynamics of aqueous solutions of the hydrophilic peptide N-acetyl-glycine-methylamide (NAGMA) have been investigated through extended frequency-range depolarized light scattering (EDLS), which enables the broad-band detection of collective polarizability anisotropy fluctuations. The results have been compared to those obtained for N-acetyl-leucinemethylamide (NALMA), an amphiphilic peptide which shares with NAGMA the same polar backbone, but also contains an apolar group. Our study indicates that the two model peptides induce similar effects on the fast translational dynamics of surrounding water. Both systems slow down the mobility of solvating water molecules by a factor 6–8, with respect to the bulk. Moreover, the two peptides cause a comparable far-reaching spatial perturbation extending to more than two hydration layers in diluted conditions. The observed concentration dependence of the hydration number is explained considering the random superposition of different hydration shells, while no indication of solute aggregation phenomena has been found. The results indicate that the effect on the dynamics of water solvating the amphiphilic peptide is dominated by the hydrophilic backbone. The minor impact of the hydrophobic moiety on hydration features is consistent with structural findings derived by Fourier transform infrared (FTIR) measurements, performed in attenuated total reflectance (ATR) configuration. Additionally, we give evidence that, for both systems, the relaxation mode in the GHz frequency range probed by EDLS is related to solute rotational dynamics. The rotation of NALMA occurs at higher timescales, with respect to the rotation of NAGMA; both processes are significantly slower than the structural dynamics of hydration water, suggesting that solute and solvent motions are uncoupled. Finally, our results do not indicate the presence of super-slow water (relaxation times in the order of tens of picoseconds) around the peptides investigated.
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Thompson, Matt. "Generalizing small-angle scattering form factors with linear transformations". Journal of Applied Crystallography 53, n. 5 (20 agosto 2020): 1387–91. http://dx.doi.org/10.1107/s1600576720010389.
Testo completoAbstract (sommario):
Nanostructure characterization using small-angle scattering is often performed by iteratively fitting a scattering model to experimental data. These scattering models are usually derived in part from the form factors of the expected shapes of the particles. Most small-angle-scattering pattern-fitting software is well equipped with form factor libraries for high-symmetry models, yet there is more limited support for distortions to these ideals that are more typically found in nature. Here, a means of generalizing high-symmetry form factors to these lower-symmetry cases via linear transformations is introduced, significantly expanding the range of form factors available to researchers. These linear transformations are composed of a series of scaling, shear, rotation and inversion operations, enabling particle distortions to be understood in a straightforward and intuitive way. This approach is expected to be especially useful for in situ studies of nanostructure growth where anisotropic structures change continuously and large data sets must be analysed.