Extensive radiative transfer calculations to fit the more significant average spectral features displayed in measured reflectance spectra by cuticles of Chrysina resplendes scarabs have been carried out. A simulated annealing approach is the starting point to optimize the values of the spatial average uric acid volume fraction, the thickness of the retarder layer located between the two left-handed chiral structures in the cuticle, and the slope of the parameter describing the variation with depth of the uric acid volume fraction through the retarder layer. Both twisted arrangements are characterized in terms of their photonic behaviors to display the variation with depth of the photonic band gaps, effective refractive index and birefringence, wave numbers and relative densities of states.

Background Río Celeste (“Sky-Blue River”) is a river located in the Tenorio National Park (Costa Rica) that has become an important hotspot for eco-tourism due to its striking sky-blue color. A previous study indicated that this color is not caused by dissolved chemical species, but by formation of light-scattering aluminosilicate particles at the mixing point of two colorless streams, the acidic Quebrada Agria and the neutral Río Buenavista. Results We now present microbiological information on Río Celeste and its two tributaries, as well as a more detailed characterization of the particles that occur at the mixing point. Our results overturn the previous belief that the light scattering particles are formed by the aggregation of smaller particles coming from Río Buenavista, and rather point to chemical formation of hydroxyaluminosilicate colloids when Quebrada Agria is partially neutralized by Río Buenavista, which also contributes silica to the reaction. The process is mediated by the activities of different microorganisms in both streams. In Quebrada Agria, sulfur-oxidizing bacteria generate an acidic environment, which in turn cause dissolution and mobilization of aluminum and other metals. In Río Buenavista, the growth of diatoms transforms dissolved silicon into colloidal biogenic forms which may facilitate particle precipitation. Conclusions We show how the sky-blue color of Río Celeste arises from the tight interaction between chemical and biological processes, in what constitutes a textbook example of emergent behavior in environmental microbiology.

Measured reflectance spectra by cuticles of C. resplendens scarabs, in the spectral range 300 to 1000 nm, show high variability depending on the magnitude of the illuminated area, the position of the illuminated section, the elytron, a single specimen, and on the different specimens considered. This fact suggests variability in the depth dependence of the pitch and of the average uric acid concentration, and on the thickness of the retarder layer located between the two helicoidal structures characterizing the cuticle of these beetles.

Aquatic environments of volcanic origin provide an exceptional opportunity to study the adaptations of microorganisms to early planet life conditions. Here, we characterized the prokaryotic communities and physicochemical properties of seepage sites at the bottom of the Poas Volcano crater and the Agrio River, two geologically related extremely acidic environments located in Costa Rica. Both locations hold a low pH (1.79–2.20) and have high sulfate and iron concentrations (Fe = 47–206 mg/L, SO 4 2− = 1170–2460 mg/L), but significant differences in their temperature (90.0–95.0 ºC in the seepages at Poas Volcano, 19.1–26.6 ºC in Agrio River) and in the elemental sulfur content. Based on the analysis of 16S rRNA gene sequences, we determined that Sulfobacillus spp . represented more than half of the sequences in Poas Volcano seepage sites, while Agrio River was dominated by Leptospirillum and members of the archaeal order Thermoplasmatales . Both environments share some chemical characteristics and part of their microbiota, however, the temperature and the reduced sulfur are likely the main distinguishing features, ultimately shaping their microbial communities. Our data suggest that in the Poas Volcano–Agrio River system there is a common metabolism but with specialization of species that adapt to the physicochemical conditions of each environment.

We describe the geochemistry and microbial diversity of a pristine environment that resembles an acid rock drainage (ARD) but it is actually the result of hydrothermal and volcanic influences. We designate this environment, and other comparable sites, as volcanic influenced acid rock drainage (VARD) systems. The metal content and sulfuric acid in this ecosystem stem from the volcanic milieu and not from the product of pyrite oxidation. Based on the analysis of 16S rRNA gene amplicons, we report the microbial community structure in the pristine San Cayetano Costa Rican VARD environment (pH = 2.94–3.06, sulfate ~ 0.87–1.19 g L−1, iron ~ 35–61 mg L−1 (waters), and ~ 8–293 g kg−1 (sediments)). San Cayetano was found to be dominated by microorganisms involved in the geochemical cycling of iron, sulfur, and nitrogen; however, the identity and abundance of the species changed with the oxygen content (0.40–6.06 mg L−1) along the river course. The hypoxic source of San Cayetano is dominated by a putative anaerobic sulfate-reducing Deltaproteobacterium. Sulfur-oxidizing bacteria such as Acidithiobacillus or Sulfobacillus are found in smaller proportions with respect to typical ARD. In the oxic downstream, we identified aerobic iron-oxidizers (Leptospirillum, Acidithrix, Ferrovum) and heterotrophic bacteria (Burkholderiaceae bacterium, Trichococcus, Acidocella). Thermoplasmatales archaea closely related to environmental phylotypes found in other ARD niches were also observed throughout the entire ecosystem. Overall, our study shows the differences and similarities in the diversity and distribution of the microbial communities between an ARD and a VARD system at the source and along the oxygen gradient that establishes on the course of the river.

In this work, we characterize the geochemistry and microbial community of Bajo las Peñas, a neutral (pH 6.5-7.4), hot spring (T = 62.0-68.0°C) located near Turrialba Volcano, Costa Rica. The microbiota at its two sources belongs mainly to the family Aquificae, comprising OTUs closely related to the genera Sulfurihydrogenibium , Thermosulfidibacter , Thermodesulfovibrio and Thermocrinis which is consistent with the presence of moderate levels of sulfate (243-284 mg/L) along the stream. We determined a dramatic shift in the microbial community just a few meters downstream of the sources of the hot spring (15-20 meters), with a change from sulfur related chemoautotrophic (e.g. Sulfurihydrogenibium and an OTU closely related to Thermodesulfovibrio ) to chemoheterotrophic prokaryotes (e.g. Meiothermus , Nitrososphaera , Thermoflexus , Thermus ). Thus, in this neutral hot spring, the first level of the trophic chain is associated with photosynthesis as well other anaerobic CO 2 fixing bacteria. Then, thermotolerant chemoheterotrophic bacteria colonize the environment to degrade organic matter and use fermentative products from the first level of the trophic chain. Our data demonstrate how quickly the microbial community of an ecosystem can change in response to environmental variables and sheds light on the microbial ecology of less common circumneutral pH hot springs.

Establishing and understanding large format paintings are key to provide accurate information about the artist’s palette and developing conservation strategies. Therefore, investigating the artworks of a population offers insight into its culture, history and origins which reveals individual and collective identity through cultural heritage worldwide. Particularly, the ceiling of the Foyer at the National Theatre of Costa Rica (Central America) is decorated with three large format paintings from the nineteenth century made by the Italian painter Vespasiano Bignami. The paintings are known as La Poesía, La Música and La Danza (The Poetry, the Music and The Dance) and have undergone restorations in the past. However, their state of conservation is unknown and thus demands accurate scientific examination in order to document their status and the extent of undocumented previous restoration work. To overcome those issues, we propose the application of a combination of non-invasive and in-situ techniques to carry out a qualitative assessment of the pigments and actual state of conservation. Here, we employed technical photography in the visible and near infrared regions, using panoramic stitching techniques in order to obtain high resolution images of the very large artworks. Several conservation problems were observed such as: detachment of pigments, cracks, stains, and sections with undocumented restorations. In the IR and False Colour Infrared images we observed a very conspicuous behaviour of the red pigment used in the three paintings. Particular areas with the red pigment were fluorescent, and by means of ultraviolet fluorescence imaging we identified the pigment as through its red-coral fluorescence as Madder Lake, by comparison to a historical pigments reference palette. Measurements in five different red pigmented zones using UV–Vis spectroscopy in The Music show bands in the (550–650) nm region. A Lorentz Model nonlinear curve fit to the bands allowed us to correlate the fluorescent pigment in the paintings of Vespasiano Bignami with Madder Lake.

Based on the analysis of 16S rRNA gene metabarcoding, here we report the shift in the microbial community structure along a horizontal oxygen gradient (0.40-6.06 mg L −1 ) in a volcanic influenced acid rock drainage (VARD) environment, known as San Cayetano (Cartago, Costa Rica; pH =2.94-3.06, sulfate ~0.87-1.19 g L −1 , iron ~35-61 mg L −1 ). This VARD is dominated by microorganisms involved in the geochemical cycling of iron, sulfur and nitrogen; however, the identity of the species changes with the oxygen gradient along the river course. The anoxic spring of San Cayetano is dominated by a putative anaerobic sulfate-reducing Deltaproteobacterium as well as sulfur-oxidizing bacteria (such as Acidithiobacillus or Sulfobacillus ), which favor the process of dissolution of sulfide minerals and oxidation of H2S. In oxic conditions, aerobic iron-oxidizers ( Leptospirillum, Acidithrix, Ferritrophicum, Ferrovum ) and heterotrophic bacteria (Burkholderiaceae Betaproteobacterium, Trichococcus, Acidocella ) were identified among others. Thermoplasmatales archaea closely related to environmental phylotypes found in other ARD/AMD niches were also found throughout the entire ecosystem. This work describes the changes in bacterial diversity, and possible metabolic activities occurring along a horizontal oxygen gradient in a volcanic influenced acid rock drainage system.

A unified description involving structural morphology and composition, dispersion of optical constants, modeled and measured reflection spectra and photonic crystal characterization is devised. Light reflection spectra by the cuticles of scarab beetles (Chrysina chrysargyrea and Chrysina optima), measured in the wavelength range 300–1000 nm, show spectrally structured broad bands. Scanning electron microscopy analysis shows that the pitches of the twisted structures responsible for the left-handed circularly polarized reflected light change monotonically with depth through the cuticles, making it possible to obtain the explicit depth-dependence for each cuticle arrangement considered. This variation is a key aspect, and it will be introduced in the context of Berreman’s formalism, which allows us to evaluate reflection spectra whose main features coincide in those displayed in measurements. Through the dispersion relation obtained from the Helmholtz’s equation satisfied by the circular components of the propagating fields, the presence of a photonic band gap is established for each case considered. These band gaps depend on depth through the cuticle, and their spectral positions change with depth. This explains the presence of broad bands in the reflection spectra, and their spectral features correlate with details in the variation of the pitch with depth. The twisted structures consist of chitin nanofibrils whose optical anisotropy is not large enough so as to be approached from modeling the measured reflection spectra. The presence of a high birefringence substance embedded in the chitin matrix is required. In this sense, the presence of uric acid crystallites through the cuticle is strongly suggested by frustrated attenuated total reflection and Raman spectroscopy analysis. The complete optical modeling is performed incorporating the wavelength-dependent optical constants of chitin and uric acid.

Cuticles of some Chrysina scarabs are characterized by flat, graded, and twisted structures of nanosized chitin fibrils. As inferred from SEM images, each species has its own spatial period or pitch P which is dependent on the depth z through the cuticle. From Berreman’s formalism, taking into account the corresponding P(z) dependence, we evaluate reflection spectra of C. aurigans and C. chrysargyrea scarabs. The spectra display the main spectral features observed in the measured ones when small sections of the cuticles are illuminated with non-polarized light, for wavelengths between 300 and 1100 nm. By considering these twisted structures as 1D photonic crystals, an approach is developed to show how the broad band characterizing the reflection spectra arises from a narrow intrinsic photonic band width, whose spectral position moves through visible and near infrared wavelengths. The role of the epicuticle that covers the twisted structures is analyzed in terms of a waxy layer acting as an anti-reflecting coating that also shows low levels of light scattering.

Whether the extreme conditions of acidity and heavy metal pollution of streams and rivers originating in pyritic formations are caused primarily by mining activities or by natural activities of metal-oxidizing microbes living within the geological formations is a subject of considerable controversy. Most microbiological studies of such waters have so far focused on acid mine drainage sites, which are heavily human-impacted environments, so it has been problematic to eliminate the human factor in the question of the origin of the key metal compounds. We have studied the physico-chemistry and microbiology of the Río Sucio in the Braulio Carrillo National Park of Costa Rica, 22 km from its volcanic rock origin. Neither the remote origin, nor the length of the river to the sampling site, have experienced human activity and are thus pristine. The river water had a characteristic brownish-yellow color due to high iron-dominated minerals, was slightly acidic, and rich in chemolithoautotrophic iron- and sulfur-oxidizing bacteria, dominated by Gallionella spp. Río Sucio is thus a natural acid-rock drainage system whose metal-containing components are derived primarily from microbial activities.

Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

Under normal incidence of non-polarized light, reflection spectra from the cuticle of golden-like C. aurigans scarabs shows a broad band displayed from 525 to 950nm, with a spectral ripple structure that consists of a uniform sequence of peaks superimposed on the main reflection band. Cross sectional Scanning Electron Microscope (SEM) images of the cuticle initially suggest the presence of a multilayered structure. A radiative transfer matrix formalism is first applied to describe as much as possible the main features of coherent reflection spectra, by assuming optically homogenous layers distributed through the exocuticle, with chitin as the major constituent material. Additional non-coherent multiple reflections due to layers in the endocuticle are also evaluated from this approach. The presence of a pigmented micron sized structure beneath the procuticle requires the evaluation of a diffuse light contribution to the reflection. This was carried out from a four-flux radiative transfer model. Optical anisotropy is introduced by interpreting the SEM images in terms of a twisted Bouligand-type structure, and reflection spectra are evaluated from an implementation of the so-called 4×4 Berreman׳s formalism. We have been able to approach the main features characterizing the reflection spectra of C. aurigans׳ elytra following this progressive way.

Measured reflection spectra from elytra of C. aurigans scarabs are reported for wavelengths between 300 and 1100 nm. They show a broad reflection band for wavelengths from 525 to 950 nm with a ripple structure consisting of a sequence of maxima and minima reflection values superimposed on a mean value of around 30% of the reflection band. To our knowledge, this is one the first reports on measurements of a natural broad band reflector in which the spectral features of the band are completely contained in the measuring range, including the mentioned ripple structure. What seems to be a multilayer structure of the cuticle of the C. aurigans is displayed from SEM analysis showing a layer’s thickness dependence with the perpendicular depth through the procuticle. Additional optical measurements are carried out to establish the polarization of the reflected light which is circularly polarized to the left, with lower contributions of diffuse and non-coherent light. These findings require an interpretation of the structure displayed by the SEM images, in terms of a Bouligand-type (twisted helical) structure characterized by a depth-dependent spatial period distribution more complex than those previously reported in the literature for others biological systems.

Measured reflection spectra from elytra of Chrysina aurigans scarabs are reported. They show a broad reflection band for wavelengths from 0.525 to 1.0 mu m with a sequence of maxima and minima reflection values superimposed on a mean value of around 40% for the high reflection band. Different mechanisms contributing to the reflection spectra have been considered, with the dominant effect, reflection of left handed circularly polarized light, being produced by a laminated left handed twisted structure whose pitch changes with depth through the procuticle in a more complex way than that characterizing broad band circular polarizers based on cholesteric liquid crystals.

Resumen es: Se describen las reacciones quimicas involucradas en el grabado de placas de hierro y de aluminio tratadas con sulfato salino como mordente. En ambos cas...

The chemical reactions involved in the etching process of iron and aluminum plates treated with saline sulfate mordant are described. In both cases, the cupric ions of the mordant are reduced to atomic copper, that precipitates as a reddish sediment, while the metal of the plate is ionized and dissolved, so etching the plate. Therefore, the metal ions extracted from the plates of iron or aluminum, reacting with the chloride in the solution, producing ferrous chloride (FeCl2) or aluminum chloride (AlCl3), respectively. The former is the chemical precursor of the mordant for etching copper plates, which only needs an additional oxidizing process to be transformed in ferric chloride (FeCl3). Meanwhile, the aluminum chloride is a precursor of alumina, a common component of the ceramic pastes.

This chapter contains sections titled: Tetraaquabis(1,2-Benzisothiazol-3(2H)-one 1,l-dioxidato)-vanadium(II) Dihydrate Bis(1,2-benzisothiazol-3(2H)-one 1,1-dioxidato)tetrakis-(pyridine)vanadium(II)-Dipyridine Tetraaquabis(l,2-benzisothiazol-3(2H)-one 1,l-dioxidato)-chromium(II) Dihydrate.