Advances in Optical Based Turbidity Sensing Using LED Photometry (PEDD)

Turbidity is one of the primary metrics to determine water quality in terms of health and environmental concerns, however analysis typically takes place in centralized facilities, with samples periodically collected and transported there. Large scale autonomous deployments (WSNs) are impeded by both initial and per measurement costs. In this study we employ a Paired Emitter-Detector Diode (PEDD) technique to quantitatively measure turbidity using analytical grade calibration standards. Our PEDD approach compares favorably against more conventional photodiode-LED arrangements in terms of spectral sensitivity, cost, power use, sensitivity, limit of detection, and physical arrangement as per the ISO 7027 turbidity sensing standard. The findings show that the PEDD technique was superior in all aforementioned aspects. It is therefore more ideal for low-cost, low-power, IoT deployed sensors. The significance of these findings can lead to environmental deployments that greatly lower the device and per-measurement costs.

COLOURIMETRIC CALIBRATION FOR PHOTOGRAPHY, PHOTOGRAMMETRY, AND PHOTOMODELLING WITHIN ARCHITECTURAL SURVEY

In accordance with the “Declaration of Rome on architectural survey”, we can affirm that recording and interpretation of colour information in photographic surveying, in photogrammetric surveying and in photomodelling requires careful planning of Colour Imaging processes. Information acquired by an optical sensor is influenced not just by the actual photographed scene, but also by the spectral sensitivity of the sensor. We have adopted, from the field of Cultural Heritage, a method of colourimetric calibration for digital photographs and have proposed some adjustments to finalise this process for the purposes of Architectural Survey. With the use of a colourimetric target and a non-linear transformation algorithm, our Colour Imaging method statistically reconstructs colours conventionally unrecordable by a commercial camera. In addition, this method reconstructs colours as if the photographed object were exposed to a standard illuminant, assessing a colour error parameter value for each photo. By including the colourimetric target in every shot and by applying the calibration algorithm to all photographs taken, the process correlates all data sets to a single standard illuminant: regarding photomodelling, this leads to a more uniform and detailed representation of the surfaces of virtual models. We present two successful examples of application: one focused on a design object with physioplastic decoration and another regarding a circular fountain in a historic villa.

Can the Fe K-alpha Line Reliably Predict Supernova Remnant Progenitors?

The centroid energy of the Fe Kα line has been used to identify the progenitors of supernova remnants (SNRs). These investigations generally considered the energy of the centroid derived from the spectrum of the entire remnant. Here we use XMM-Newton data to investigate the Fe Kα centroid in 6 SNRs: 3C 397, N132D, W49B, DEM L71, 1E 0102.2-7219, and Kes 73. In Kes 73 and 1E 0102.2-7219, we fail to detect any Fe Kα emission. We report a tentative first detection of Fe Kα emission in SNR DEM L71 with a centroid energy consistent with its Type Ia designation. In the remaining remnants, the spatial and spectral sensitivity is sufficient to investigate spatial variations of the Fe Kα centroid. We find in N132D and W49B that the centroids in different regions are consistent with those derived from the overall spectrum, although not necessarily with the remnant type identified via other means. However, in SNR 3C 397, we find statistically significant variation in the centroid of up to 100 eV, aligning with the variation in the density structure around the remnant. These variations span the intermediate space between centroid energies signifying core-collapse (CC) and Type Ia remnants. Shifting the dividing line downwards by 50 eV can place all the centroids in the CC region, but contradicts the remnant type obtained via other means. Our results show that caution must be used when employing the Fe Kα centroid of the entire remnant as the sole diagnostic for typing a remnant.

Red-green opponency in the long visual fibre photoreceptors of brushfoot butterflies (Nymphalidae)

In many butterflies, the ancestral trichromatic insect colour vision, based on UV-, blue- and green-sensitive photoreceptors, is extended with red-sensitive cells. Physiological evidence for red receptors has been missing in nymphalid butterflies, although some species can discriminate red hues well. In eight species from genera Archaeoprepona, Argynnis, Charaxes, Danaus, Melitaea, Morpho, Heliconius and Speyeria , we found a novel class of green-sensitive photoreceptors that have hyperpolarizing responses to stimulation with red light. These green-positive, red-negative (G+R–) cells are allocated to positions R1/2, normally occupied by UV and blue-sensitive cells. Spectral sensitivity, polarization sensitivity and temporal dynamics suggest that the red opponent units (R–) are the basal photoreceptors R9, interacting with R1/2 in the same ommatidia via direct inhibitory synapses. We found the G+R– cells exclusively in butterflies with red-shining ommatidia, which contain longitudinal screening pigments. The implementation of the red colour channel with R9 is different from pierid and papilionid butterflies, where cells R5–8 are the red receptors. The nymphalid red-green opponent channel and the potential for tetrachromacy seem to have been switched on several times during evolution, balancing between the cost of neural processing and the value of extended colour information.

On the Correspondence between the Spectral Sensitivity Characteristics of Human Eye Retina Photo-Receivers and the Frequencies of the Universal Period-Tripling System

The article is devoted to the discussion of the evolutionary adjustment of the photodetectors of the human retina to the frequencies of the UPTS (the so-called universal period-tripling system). This is a new scientific direction in the study of complex systems. The article invites lighting engineers who study the issues of visual perception to get acquainted with the phenomenon of UPTS. To date, an experimental research material has been accumulated and sufficient theoretical grounds have been obtained for the formulation of the assumption that the UPTS and its main parameter Тk, m are manifested in almost all time scales. The values of Тk, m are described with great accuracy by means of the empirical Puetz’s formula. In human vision, UPTS manifests itself in the form of nine periods of Тk, m, corresponding to the cases of m = –11, –8, –5, –3, 0, 3, 5, 8, and 11, where the five central ones dominate –5, –3, 0, 3, and 5, corresponding to the rods, as well as the B- and R-cones. Some questions remain about the G-cones and the ipRGC cells that respond to the extreme, “weakened” values of the index m = –11, –8, 8, and 11. The determination of the proposed calculated values of the wavelengths of light corresponding to the maximum spectral sensitivity of retinal photodetectors is important for specialists in the field of visual perception, medicine, optics, as well as for applications in a number of technical applications.

A common computational principle for vibrotactile pitch perception in mouse and human

We live surrounded by vibrations generated by moving objects. These oscillatory stimuli propagate through solid substrates, are sensed by mechanoreceptors in our body and give rise to perceptual attributes such as vibrotactile pitch (i.e. the perception of how high or low a vibration’s frequency is). Here, we establish a mechanistic relationship between vibrotactile pitch perception and the physical properties of vibrations using behavioral tasks, in which vibratory stimuli were delivered to the human fingertip or the mouse forelimb. The resulting perceptual reports were analyzed with a model demonstrating that physically different combinations of vibration frequencies and amplitudes can produce equal pitch perception. We found that the perceptually indistinguishable but physically different stimuli follow a common computational principle in mouse and human. It dictates that vibrotactile pitch perception is shifted with increases in amplitude toward the frequency of highest vibrotactile sensitivity. These findings suggest the existence of a fundamental relationship between the seemingly unrelated concepts of spectral sensitivity and pitch perception.

Evolutionary analyses of visual opsin genes in anurans reveals diversity and positive selection suggestive of functional adaptation to distinct light environments

Among major vertebrate groups, anurans (frogs and toads) are understudied with regards to their visual systems and little is known about variation among species that differ in ecology. We sampled North American anurans representing diverse evolutionary and life histories that likely possess visual systems adapted to meet different ecological needs. Using standard molecular techniques, visual opsin genes, which encode the protein component of visual pigments, were obtained from anuran retinas. Additionally, we extracted the visual opsins from publicly available genome and transcriptome assemblies, further increasing the phylogenetic and ecological diversity of our dataset. We found that anurans consistently express four visual opsin genes (RH1, LWS, SWS1, and SWS2, but not RH2) even though reported photoreceptor complements vary widely among species. We found the first evidence of visual opsin duplication in an amphibian with the duplication of the LWS gene in the African bullfrog, which had distinct LWS copies on the sex chromosomes. The proteins encoded by these genes showed considerable sequence variation among species, including at sites known to shift the spectral sensitivity of visual pigments in other vertebrates and thus mediate dim-light and color vision. Using molecular evolutionary analyses of selection (dN/dS) we found significant evidence for positive selection at a subset of sites in the dim-light rod opsin gene RH1 and the long wavelength sensitive cone opsin gene LWS. The function of sites inferred to be under positive selection are largely unknown, but a few are likely to affect spectral sensitivity and other visual pigment functions based on proximity to previously identified sites in other vertebrates. The observed variation cannot fully be explained by evolutionary relationships among species alone. Taken together, our results suggest that other ecological factors, such as habitat and life history, as well as behaviour, may be driving changes to anuran visual systems.

Behavioural red-light sensitivity in fish according to the optomotor response

Various procedures have been adopted to investigate spectral sensitivity of animals, e.g. absorption spectra of visual pigments, electroretinography, optokinetic response, optomotor response (OMR) and phototaxis. The use of these techniques has led to various conclusions about animal vision. However, visual sensitivity should be evaluated consistently for a reliable comparison. In this study, we retrieved behavioural data of several fish species using a single OMR procedure and compared their sensitivities to near-infrared light. Besides cavefish that lack eyes, some species were not appropriate for the OMR test because they either stayed still or changed swimming direction frequently. Eight of 13 fish species tested were OMR positive. Detailed analyses using medaka, goldfish, zebrafish, guppy, stickleback and cichlid revealed that all the fish were sensitive to light at a wavelength greater than or equal to 750 nm, where the threshold wavelengths varied from 750 to 880 nm. Fish opsin repertoire affected the perception of red light. By contrast, the copy number of long-wavelength-sensitive ( LWS ) genes did not necessarily improve red-light sensitivity. While the duplication of LWS and other cone opsin genes that has occurred extensively during fish evolution might not aid increasing spectral sensitivity, it may provide some other advantageous ophthalmic function, such as enhanced spectral discrimination.