SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Diffuse reflection

5

Specular reflection appears as a bright spot or highlight on any smooth glossy convex surface and is caused by a near mirror-like reflectance off the surface. Convex shapes always provide the ideal geometry for highlights, areas of very strong reflectance, regardless of the orientation of the surface or position of the receiver. Despite highlights and glossy appearance being common in chemically defended insects, their potential signalling function is unknown. We tested the role of highlights in warning colouration of a chemically defended, alpine leaf beetle, Oreina cacaliae. We reduced the beetles' glossiness, hence their highlights, by applying a clear matt finish varnish on their elytra. We used blue tits as predators to examine whether the manipulation affected their initial latency to attack, avoidance learning and generalization of warning colouration. The birds learned to avoid both dull and glossy beetles but they initially avoided glossy prey more than dull prey. Interestingly, avoidance learning was generalized asymmetrically: birds that initially learned to avoid dull beetles avoided glossy beetles equally strongly, but not vice versa. We conclude that specular reflectance and glossiness can amplify the warning signal of O. cacaliae, augmenting avoidance learning, even if it is not critical for it.

Concepts: Insect, Predation, Signal, Beetle, Reflection, Aposematism, Glossmeter, Diffuse reflection

3

A galvanic-displacement-reaction-based, room-temperature “dip-and-dry” technique is demonstrated for fabricating selectively solar-absorbing plasmonic-nanoparticle-coated foils (PNFs). The technique, which allows for facile tuning of the PNFs' spectral reflectance to suit different radiative and thermal environments, yields PNFs which exhibit excellent, wide-angle solar absorptance (0.96 at 15°, to 0.97 at 35°, to 0.79 at 80°), and low hemispherical thermal emittance (0.10) without the aid of antireflection coatings. The thermal emittance is on par with those of notable selective solar absorbers (SSAs) in the literature, while the wide-angle solar absorptance surpasses those of previously reported SSAs with comparable optical selectivities. In addition, the PNFs show promising mechanical and thermal stabilities at temperatures of up to 200 °C. Along with the performance of the PNFs, the simplicity, inexpensiveness, and environmental friendliness of the “dip-and-dry” technique makes it an appealing alternative to current methods for fabricating selective solar absorbers.

Concepts: Energy, Temperature, Thermodynamics, Diffuse reflection, Emissivity, Solar thermal collector

2

We demonstrate wide-angle, broadband and efficient reflection holography by utilizing coupled dipole-patch nano-antenna cells to impose an arbitrary phase profile on of the reflected light. High fidelity images were projected at angles of 450 and 200 with respect to the impinging light with efficiencies ranging between 40%-50% over an optical bandwidth exceeding 180nm. Excellent agreement with the theoretical predictions was found at a wide spectral range. The demonstration of such reflectarrays opens new avenues towards expanding the limits of large angle holography.

Concepts: Light, Snell's law, Refraction, Sound, Reflection, Total internal reflection, Diffuse reflection, Ripple tank

1

There are neurons localized in the lower bank of the superior temporal sulcus (STS) in the inferior temporal (IT) cortex of the monkey that selectively respond to specific ranges of gloss characterized by combinations of three physical reflectance parameters: specular reflectance (ρs), diffuse reflectance (ρd), and spread of specular reflection (α; Nishio et al., 2012). In the present study, we examined how the activities of these gloss-selective IT neurons are related to perceived gloss. In an earlier psychophysical study, Ferwerda et al. (2001) identified a perceptually uniform gloss space defined by two axes where the c-axis corresponds to a nonlinear combination of ρs and ρd and the d-axis corresponds to 1 - α. In the present study, we tested the responses of gloss-selective neurons to stimuli in the perceptual gloss space defined by the c- and d-axes. We found that gloss-selective neurons systematically changed their responses in the perceptual gloss space, and the distribution of the tuning directions of the population of gloss-selective neurons is biased toward directions in which perceived gloss increases. We also found that a set of perceptual gloss parameters as well as surface albedo can be well explained by the population activities of gloss-selective neurons, and that these parameters are likely encoded by the gloss-selective neurons in this area of the STS to represent various glosses. These results thus provide evidence that the IT cortex represents perceptual gloss space.

Concepts: Time, Cerebral cortex, Temporal lobe, Hippocampus, Reflection, Albedo, Glossmeter, Diffuse reflection

1

Hierarchical micro- and nano-structured surfaces have previously been made using a variety of materials and methods, including particle deposition, polymer molding, and the like. These surfaces have attracted a wide variety of interest for applications including reduced specular reflection and super-hydrophobic surfaces. In this paper we report the first monolithic, hierarchically structured glass surface that combines micron-scale and nano-scale surface features to simultaneously generate antiglare (AG), antireflection (AR), and superhydrophobic properties. The AG microstructure mechanically protects the AR nanostructure during wiping and smudging while the uniform composition of the substrate and the micro-nano-structured surface enables ion exchange through the surface, so that both the substrate and the structured surface can be simultaneously chemically strengthened.

Concepts: Structure, Atom, Materials science, Reflection, Fresnel equations, Specular reflection, Diffuse reflection, Anti-reflective coating

0

We present a sequential fitting-and-separating algorithm for surface reflectance components that separates individual dominant reflectance components and simultaneously estimates the corresponding bidirectional reflectance distribution function (BRDF) parameters from the separated reflectance values. We tackle the estimation of a Lafortune BRDF model, which combines a nonLambertian diffuse reflection and multiple specular reflectance components with a different specular lobe. Our proposed method infers the appropriate number of BRDF lobes and their parameters by separating and estimating each of the reflectance components using an interval analysis-based branch-and-bound method in conjunction with iterative K-ordered scale estimation. The focus of this paper is the estimation of the Lafortune BRDF model. Nevertheless, our proposed method can be applied to other analytical BRDF models such as the Cook-Torrance and Ward models. Experiments were carried out to validate the proposed method using isotropic materials from the Mitsubishi Electric Research Laboratories-Massachusetts Institute of Technology (MERL-MIT) BRDF database, and the results show that our method is superior to a conventional minimization algorithm.

Concepts: Mathematics, Estimation, Reflection, Object-oriented programming, Specular reflection, Diffuse reflection, Reflectivity, Bidirectional reflectance distribution function

0

The Fitzpatrick classification for skin phototyping is widely used, but its usefulness in dark-skinned populations has been questioned by some researchers. Recently, skin colour measurement has been proposed for phototyping skin colour objectively.

Concepts: Population, Human skin color, Diffuse reflection

0

Liver thermal ablation techniques have been widely used for the treatment of liver cancer. Kinetic model of damage propagation play an important role for ablation prediction and real-time efficacy assessment. However, practical methods for modeling liver thermal damage are rare. A minimally invasive optical method especially adequate for in situ liver thermal damage modeling is introduced in this paper. Porcine liver tissue was heated by water bath under different temperatures. During thermal treatment, diffuse reflectance spectrum (DRS) of liver was measured by optical fiber and used to deduce reduced scattering coefficient (μ’s ). Arrhenius parameters was obtained through non-isothermal heating approach with damage marker of μ’s . Activation energy (Ea ) and frequency factor (A) was deduced from these experiments. A pair of averaged value is 1.200×105 J mol-1 and 4.016×1017 s-1 . The results were verified for their reasonableness and practicality. Therefore, it is feasible to modeling liver thermal damage based on minimally invasive measurement of optical property and in situ kinetic analysis of damage progress with Arrhenius model. These parameters and this method are beneficial for preoperative planning and real-time efficacy assessment of liver ablation therapy.

Concepts: Cancer, Energy, Temperature, Heat, Minimally invasive, Chemical kinetics, Arrhenius equation, Diffuse reflection

0

This paper shows that it is possible to exploit the modulated metasurface concept to control the unwanted coupling between antennas that are installed on the same satellite. The metasurface is combined with a Multi-Layer thermal Insulation blanket to reduce its specular reflection by spreading the energy incoherently in the surrounding space. In the design, sub-wavelength radiating elements printed on thin substrate have been used to make the metasurface response azimuthally independent, and to keep the weight of blanket down. The comparison between simulations and measurements confirms the validity of the idea.

Concepts: Sun, Carbon, Heat, Concept, Reflection, Fresnel equations, Specular reflection, Diffuse reflection

0

The bottom-up fabrication of regular nanowires (NWs) arrays on a masked substrate is technologically relevant but the growth dynamic is rather complex due to the superposition of severe shadowing effects that vary with array pitch, NW diameter, NW height and growth duration. By inserting GaAsP marker layers at a regular time interval during the growth of a self-catalyzed GaP NW array, we are able to retrieve precisely the time evolution of the diameter and height of a single NW. We then propose a simple numerical scheme which fully computes shadowing effects at play in infinite arrays of NWs. By confronting the simulated and experimental results, we infer that re-emission of Ga from the mask is necessary to sustain the NW growth while Ga migration on the mask must be negligible. When compared to random cosine or random uniform re-emission from the mask, the simple case of specular reflection on the mask gives the most accurate account of the Ga balance during the growth.

Concepts: Time, Reflection, Array, Complex number, Fresnel equations, Calendar, Specular reflection, Diffuse reflection