Speckle characteristics of simulated deep Fresnel region under shadowing effect

2021 ◽  
Vol 19 (4) ◽  
pp. 041404
Author(s):  
Zengshun Jiang ◽  
Xingqi An ◽  
Yuqin Zhang ◽  
Xuan Liu ◽  
Xifeng Qin ◽  
...  
Author(s):  
Klaus-Ruediger Peters

Topographic ultra high resolution can now routinely be established on bulk samples in cold field emission scanning electron microscopy with a second generation of microscopes (FSEM) designed to provide 0.5 nm probe diameters. If such small probes are used for high magnification imaging, topographic contrast is so high that remarkably fine details can be imaged on 2DMSO/osmium-impregnated specimens at ribosome surfaces even without a metal coating. On TCH/osmium-impregnated specimens topographic resolution can be increased further if the SE-I imaging mode is applied. This requires that beam diameter and metal coating thickness be made smaller than the SE range of ~1 nm and background signal contributions be reduced. Subnanometer small probes can be obtained (only) at high accelerating voltages. Subnanometer thin continuous metal films can be produced under the following conditions: self-shadowing effect between metal atoms must be reduced through appropriate deposition techniques and surface mobility of metal atoms must be diminished through high energy sputtering and/or specimen cooling.


Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 380
Author(s):  
Jun-Hyun Kim ◽  
Sanghyun You ◽  
Chang-Koo Kim

Si surfaces were texturized with periodically arrayed oblique nanopillars using slanted plasma etching, and their optical reflectance was measured. The weighted mean reflectance (Rw) of the nanopillar-arrayed Si substrate decreased monotonically with increasing angles of the nanopillars. This may have resulted from the increase in the aspect ratio of the trenches between the nanopillars at oblique angles due to the shadowing effect. When the aspect ratios of the trenches between the nanopillars at 0° (vertical) and 40° (oblique) were equal, the Rw of the Si substrates arrayed with nanopillars at 40° was lower than that at 0°. This study suggests that surface texturing of Si with oblique nanopillars reduces light reflection compared to using a conventional array of vertical nanopillars.


Author(s):  
Imen Ksiaa ◽  
Safa Ben Aoun ◽  
Sourour Zina ◽  
Dhouha Nefzi ◽  
Sana Khochtali ◽  
...  

Abstract Objective To describe a case of Behçet disease (BD) uveitis manifesting with sequential bilateral neuroretinitis associated with prepapillary inflammatory vitreous exudate (PIVE). Material and methods A single case report documented with multimodal imaging. Results A 37-year-old man developed neuroretinitis with associated PIVE in the left eye. He was diagnosed with ocular toxoplasmosis and treated accordingly based on positive serologic testing and negative work-up for other entities, including BD. The disease course was favorable, but 1 year later a similar neuroretinitis developed in the right eye. Extraocular features of BD became evident only at the time of the second eye involvement, and the patient received corticosteroid and immunosuppressive therapy. Swept source (SS) OCT showed at the acute phase in both eyes a typical “mushroom-shaped” prepapillary hyperreflectivity of the PIVE. SS OCT angiography (OCTA) demonstrated a corresponding prepapillary hypointense area due to shadowing effect, decreasing in size while scanning deeper layers. It also detected peripapillary retinal hypervascularity in both eyes and a sectoral area of flow signal loss in the first involved left eye. Visual acuity improved following the resolution of the PIVE and associated acute inflammatory changes in both eyes. The left eye showed residual optic disc pallor and retinal nerve fiber layer defects. Conclusion Sequential bilateral neuroretinitis associated with PIVE may occur before other clinical features of BD become evident. SS OCT and OCTA can provide useful information for the diagnosis and management of this rare, but typical, ocular manifestation of BD uveitis.


2010 ◽  
Vol 87 (11) ◽  
pp. 2134-2138 ◽  
Author(s):  
Chang Young Jeong ◽  
Sangsul Lee ◽  
Hyun-Duck Shin ◽  
Tae Geun Kim ◽  
Jinho Ahn

2015 ◽  
Vol 336 ◽  
pp. 213-223
Author(s):  
Shuyun Teng ◽  
Junhong Wang ◽  
Wei Zhang ◽  
Yuwei Cui
Keyword(s):  

2021 ◽  
Author(s):  
Dwaipayan Deb ◽  
Pavan Chakraborty

Abstract Surfaces of solid solar system objects are covered by layers of particulate materials called regolith originated from their surface bedrock. They preserve important information about surface geological processes. Often regolith is composed of more than one type of particle in terms of composition, maturity, size, etc. Experiments and theoretical works are being carried out to constrain the result of mixing and extract the abundance of compositional end-members from regolith spectra. In this work we have studied, photometric light scattering from simulated surfaces made of two different materials – one is highly bright quartz particles ≈ 80µm and the other moderately bright sandstone particles ≈ 250µm. The samples were mixed with varying proportions and investigated at normal illumination conditions to avoid the shadowing effect. Said combinations may resemble ice mixed regolith on various solar system objects and therefore important for in situ observations. We find that the combinations show a linear trend in the corresponding reflectance data in terms of their mixing proportion and some interesting facts come out when compared to previous studies.


Sensors ◽  
2022 ◽  
Vol 22 (2) ◽  
pp. 646
Author(s):  
Pietro Tedeschi ◽  
Gabriele Oligeri ◽  
Roberto Di Pietro

Jamming is a malicious radio activity that represents a dreadful threat when employed in critical scenarios. Several techniques have been proposed to detect, locate, and mitigate jamming. Similarly, counter-counter-jamming techniques have been devised. This paper belongs to the latter thread. In particular, we propose a new jammer model: a power-modulated jammer that defies standard localization techniques. We provide several contributions: we first define a new mathematical model for the power-modulated jammer and then propose a throughout analysis of the localization error associated with the proposed power-modulated jammer, and we compare it with a standard power-constant jammer. Our results show that a power-modulated jammer can make the localization process completely ineffective—even under conservative assumptions of the shadowing process associated with the radio channel. Indeed, we prove that a constant-power jammer can be localized with high precision, even when coupled with a strong shadowing effect (σ ≈ 6 dBm). On the contrary, our power-modulated jammer, even in the presence of a very weak shadowing effect (σ < 2 dBm), presents a much wider localization error with respect to the constant-power jammer. In addition to being interesting on its own, we believe that our contribution also paves the way for further research in this area.


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