UV-blocking Filter Research Articles

Physiological responses of maca (Lepidium meyenii Walp.) plants to UV radiation in its high-altitude mountain ecosystem

Ultraviolet (UV) radiation is a small fraction of the solar spectrum, which acts as a key environmental modulator of plant function affecting metabolic regulation and growth. Plant species endemic to the Andes are well adapted to the harsh features of high-altitude climate, including high UV radiation. Maca (Lepidium meyenii Walpers) is a member of Brassicaceae family native to the central Andes of Peru, which grows between 3500 and 4500 m of altitude, where only highland grasses and few hardy bushes can survive. Even though maca has been the focus of recent researches, mainly due to its nutraceutical properties, knowledge regarding its adaptation mechanisms to these particular natural environmental conditions is scarce. In this study, we manipulated solar UV radiation by using UV-transmitting (Control) or blocking (UV-block) filters under field conditions (4138 m above the sea level) in order to understand the impact of UV on morphological and physiological parameters of maca crops over a complete growing season. Compared to the UV-blocking filter, under control condition a significant increase of hypocotyl weight was observed during the vegetative phase together with a marked leaf turnover. Although parameters conferring photosynthetic performance were not altered by UV, carbohydrate allocation between above and underground organs was affected. Control condition did not influence the content of secondary metabolites such as glucosinolates and phenolic compounds in hypocotyls, while some differences were observed in the rosettes. These differences were mainly related to leaf turnover and the protection of new young leaves in control plants. Altogether, the data suggest that maca plants respond to strong UV radiation at high altitudes by a coordinated remobilization and relocation of metabolites between source and sink organs via a possible UV signaling pathway.

The role of ultraviolet coloration in intrasexual interactions in a colonial fish

Ultraviolet (UV) coloration varies drastically across species and likely plays fundamentally different roles in facilitating social communication depending on the ecological or social context. While it is well known that UV coloration serves important social functions in species that school and flock, far less is known about the role of UV coloration in group-territorial and colonial species, where individuals have long-lasting and potentially cooperative relationships with many neighbours. We measured spectral reflectance in Neolamprologus pulcher, a group-living, colonial Tanganyikan cichlid fish, and found prominent UV coloration on both sexes. We manipulated the visibility of this UV coloration using a clear UV-blocking filter or a UV-transparent filter during behavioural contests across a barrier. We found that trials between similarly sized same-sex opponents involved significantly lower frequencies of aggression when opponents' UV coloration was obscured compared to when opponents' UV coloration was visible. As aggression is typically high between similarly sized same-sex individuals in N. pulcher, this reduction in aggression suggests that UV coloration aids in motivating individuals to engage in conspecific intrasexual interactions. We found no difference in aggression in trials between familiar and unfamiliar opponents in female–female and male–female trials, regardless of the presence of UV coloration. In male–male trials, we found significantly higher frequencies of aggression in contests between familiar male opponents than in contests between unfamiliar male opponents, but only when UV coloration was visible. Collectively, these results suggest that UV coloration is important for intrasexual interactions and prompts further investigation as to the benefits of having visual signals of communication extend into the ultraviolet spectrum.

Clean water photovoltaic sensor for solar disinfection in developing countries

One of the limitations for the widespread use of solar water disinfection technologies in developing regions is the lack of low-cost clean water sensors. A new type of low-cost sensors using photovoltaic solar cells that provide information about received irradiance, temperature, UV irradiance and sunshine duration is presented. A key aspect of the design is the UV irradiance measurement. Two identical cells are used, one of them with a low-cost UV-blocking filter on top, so the total UV irradiance can be calculated as the difference between the two solar cells outputs. The first cell would be measuring UV–vis–NIR and the second only vis–NIR. The UV filter material was explored and a low-cost architectural film was selected. Materials costs for the first prototype were of approximately 4€ excluding labour. Initial testing also included experiments with real polluted water and Escherichia coli, showing the feasibility of the new design.

TiO2–carbon nanotube composites for visible photocatalysts – Influence of TiO2 crystal structure

We investigated the influence of the crystal structure of TiO2 and the use of different TiO2 precursors on the properties and photocatalytic activity of carbon nanotube (CNTs)–titania composites. We found that the crystal structure and properties of starting TiO2 nanomaterial significantly affected the effect of CNTs incorporation on the photocatalytic activity under simulated solar and visible light illumination (simulated solar illumination with UV-blocking filter). In case of significant photocatalytic activity under visible light illumination (anatase TiO2), likely due to the presence of native defects, composites exhibited lower activity under visible illumination only, but higher activity under simulated solar illumination. The opposite trends were observed for P25 (anatase + rutile) and rutile TiO2, where incorporation of CNTs resulted in a significant increase of photocatalytic activity under visible illumination. Thus, control over crystal structure and native defects is essential for the development of efficient visible light activated photocatalysts.

Contributions of Visible and Ultraviolet Parts of Sunlight to Photoinhibition

Photoinhibition is light-induced inactivation of PSII, and action spectrum measurements have shown that UV light causes photoinhibition much more efficiently than visible light. In the present study, we quantified the contribution of the UV part of sunlight in photoinhibition of PSII in leaves. Greenhouse-grown pumpkin leaves were pretreated with lincomycin to block the repair of photoinhibited PSII, and exposed to sunlight behind a UV-permeable or UV-blocking filter. Oxygen evolution and Chl fluorescence measurements showed that photoinhibition proceeds 35% more slowly under the UV-blocking than under the UV-permeable filter. Experiments with a filter that blocks UV-B but transmits UV-A and visible light revealed that UV-A light is almost fully responsible for the UV effect. The difference between leaves illuminated through a UV-blocking and UV-transparent filter disappeared when leaves of field-grown pumpkin plants were used. Thylakoids isolated from field-grown and greenhouse-grown plants were equally sensitive to UV light, and measurements of UV-induced fluorescence from leaves indicated that the protection of the field-grown plants was caused by substances that block the passage of UV light to the chloroplasts. Thus, the UV part of sunlight, especially the UV-A part, is potentially highly important in photoinhibition of PSII but the UV-screening compounds of plant leaves may offer almost complete protection against UV-induced photoinhibition.

Highly Stable Molecular Layers on Nanocrystalline Anatase TiO2 through Photochemical Grafting

Well-defined molecular layers can be formed on the surface of nanocrystalline anatase TiO2 by photochemically grafting organic molecules bearing a terminal vinyl group. The molecular layers produced are shown to have minimal oxidation and are able to be patterned and uniformly grafted through optically thick nanocrystalline films. Stability tests show that the layers have excellent stability in deionized water at 80 degrees C, aqueous solutions at pH=1.0 and pH=10.3 at 65 degrees C, and acetonitrile for time scales approaching 1200 h. Degradation of the films in deionized water occurs using a AM1.5 full-spectrum solar simulator as an illumination source but is partially suppressed by filtering with a 400 nm UV blocking filter which blocks the above-bandgap light. A mechanism is proposed for the grafting reaction in which the surface hydroxyl groups trap photoexcited holes, facilitating reaction with the vinyl group.

Ultraviolet reflectance and female mating preferences in the common kestrel (Falco tinnunculus)

Previous studies revealed the importance of plumage brightness (considering only the visible spectral range) in female mate choice of common kestrels ( Falco tinnunculus L., 1758). Our study focuses on the effect of UV reflectance on female preference; we hypothesize that common kestrel females prefer males with UV-reflecting plumage and refuse, or are not attracted to, males whose plumage UV reflectance is prevented. We tested the preference of 20 captive females who were given a choice between two males, one behind a UV-transmitting (UV+) filter and another one behind a UV-blocking (UV–) filter. Female preference was measured as frequency and duration of visits to either male, specifically by sitting on the perch or hanging on to the partition wall. Females visited the male behind the UV+ filter more often than the male behind the UV– filter, indicating that females prefer males with UV-reflecting plumage than males without UV reflection. UV plumage and skin reflectance could provide females with information regarding current male conditions more so than other colours and other morphological parameters.

Effect of UV-reflecting markings on female mate-choice decisions in Cosmophasis umbratica, a jumping spider from Singapore

Earlier studies have shown that Cosmophasis umbratica, a jumping spider from Singapore, is sexually dimorphic in the reflectance of ultraviolet (UV) (males, but not females, have UV-reflecting markings). Here we present the first experimental evidence that the male's UV markings influence mate choice of C. umbratica females. When presented with males whose appearance was manipulated by the use of a UV-blocking filter, females spent more time watching UV+ males (i.e., males with UV present) and less time watching UV− males (UV absent). We also manipulated the levels of male brightness by using 2 UV-transmitting neutral density filters and showed that UV reflectance was used specifically for hue discrimination instead of being used for detecting differences in brightness alone. This is not only the first strong evidence of UV influence on female mate-choice decisions for a spider but also the best experimental demonstration of color vision, whatever the wavelength.

Reverse biased annealing: Effective post treatment tool for polymer/nano-composite solar cells

Hybrid organic solar cells using nano-porous TiO2 infiltrated with MEH-PPV were made and characterized under standard AM 1.5 G solar illumination. Reverse biased annealing was performed on the fabricated cells as a post treatment and origin of the counter-diode was investigated by illuminating the cells through a UV-blocking filter. Treated devices deliver increased open circuit voltage and short circuit current density values, leading to significant increase in cell performances.

Innate and learned aspects of vole urine UV‐reflectance use in the hunting behaviour of the common kestrel Falco tinnunculus

Some birds are known to use the UV reflectance in their feeding strategy. Knowing that the common kestrel Falco tinnunculus is able to recognise vole trails by perceiving the UV reflectance of their scent marks, this study was designed to investigate whether the use of scent marks in the UV range has an innate component, or if it is only acquired with experience. We tested the preference of 44 experienced adult and 49 naïve juvenile common kestrels in four types of arenas: (1) scent‐marked and covered with a UV transmitting filter (UV+SC), (2) scent‐marked and covered with a UV blocking filter (UV‐SC), (3) sprinkled with water and covered with a UV transmitting filter (UV+W), and (4) sprinkled with water and covered with a UV blocking filter (UV‐W). We assessed the birds’ preference by counting the number of visual scans and visits to each arena. The distribution of scans differed from random in both adults and juveniles. The birds scanned the UV+SC arena more often than the others. Since naïve individuals showed the same preference as experienced ones, we hypothesised that the association between vole scent UV reflectance and vole presence has an innate component in the common kestrel. Nevertheless, adults differed from juveniles because they perceived the scented arenas from the water sprinkled ones, in fact, adults scanned the UV‐SC arena more frequently than both UV+W and UV‐W arenas. This result suggests that the ability of detecting UV cues has a learned component.

Study of the effect of changing the microstructure of titania layers on composite solar cell performance

This paper reports a study of the microstructures of titania thin films fabricated by two methods; doctor blade casting and glancing angle deposition (GLAD). The microstructures were characterised by a broad range of techniques, including SEM, HRTEM, and XRD. Porous films with a three-dimensional network of interconnected TiO 2 particles were obtained using the doctor blade technique. GLAD was used to fabricate well-defined columnar structures. The power efficiency of composite solar cells (CSCs) based on doctor-bladed titanium dioxide and a spin coat MEH-PPV layer is reproducibly greater than 0.5% at 800 W/m 2, using a solar simulator and 420 nm UV blocking filter, with typical values J sc = 14.3 A/m 2, V oc = 0.79 V and FF = 36%. This performance is significantly better than that reported for similar devices by other groups [1,2]. Under the same illumination conditions, preliminary results for CSCs based on GLAD titanium dioxide gave at best efficiencies of only 0.08%, with J sc = 2.4 A/m 2, V oc = 0.61 V and FF = 43%. We discuss how the morphology, crystal structure and optical absorption properties of the two types of TiO 2 affect the overall device performance.

Egg-wrapping behaviour protects newt embryos from UV radiation

Oviparous species that do not guard their eggs during development may suffer significant embryonic mortality. However, the way females lay eggs may help prevent this. For example, females of several newt species carefully wrap single eggs into leaves of aquatic vegetation in shallow water. Wrapping behaviour may protect eggs from predators and from mechanical damage. We hypothesized that egg-wrapping behaviour also protects newt embryos from the negative effects of ultraviolet (UV) radiation. In field experiments, we tested the effects of ambient levels of UV radiation on marbled newt, Triturus marmoratus, embryos exposed to sunlight. Of these embryos 95–100% died during the first 14 days of exposure. The eggs showed loss of their round shape, skin damage, oedemas and fungal infection. In contrast, during the same period, mortality of embryos protected by UV-blocking filters was only 20%. In laboratory experiments, we exposed marbled newt embryos to an artificially elevated intensity of UV-B radiation and tested the protective effect of leaves. The mortality of eggs wrapped in leaves and exposed to UV-B radiation was low and similar to that of unwrapped eggs that were shielded from UV-B radiation with a UV-blocking filter, whereas 119 of 120 unwrapped eggs exposed to UV radiation died within 5 days.

Ultraviolet Light from the Nighttime Sky Enhances Retinal Sensitivity of Limulus.

Here we report that stimulation of the median ocelli of the horseshoe crab, Limulus polyphemus, by UV light from the nighttime sky enhances the sensitivity of the lateral eyes to visible light. At night a circadian clock in the brain of Limulus generates and transmits neural activity via efferent optic nerve fibers to the lateral eyes and median ocelli (8), significantly increasing their sensitivity (9,lO). Experiments carried out in the laboratory show that illumination of the median ocelli at night with UV light enhances the clock’s efferent output and thus further increases the sensitivity of the lateral eyes and median ocelli (11). We tested whether this occurs under natural conditions; that is, whether ocellar exposure to UV light from the nighttime sky increases visual sensitivity of the lateral eyes. We carried out our experiments in an outdoor shed located in a remote area of Woods Hole, MA, where no artificial light was detectable at night. We mounted animals securely to a platform in an aquarium so that their gills were irrigated with recirculated seawater, but their lateral eyes and median ocelli remained above water. An opaque chamber was placed over the right lateral eye of each animal to occlude the eye from ambient light. A wick electrode and light emitting diode (LED) within the chamber allowed us to record electroretinograms (ERGS) from the eye in its dark-adapted state while the animal was exposed to normal diurnal changes in illumination. A computerbased system recorded ERGS every 30 min in response to a 10 ms light flash from the LED (12). Changes in the amplitude of the ERG of the occluded right eye provided a measure of the clock’s effect on retinal sensitivity and the ocellar influence on the clock’s action. Animals (n = 7) were maintained in this apparatus for approximately one month. During this period, ERGS were monitored while the median ocelli were either fully exposed, covered by a UV blocking filter (blocks y < 420 nm), a UV bandpass filter (ymaX = 360 nm, 54 nm bandwidth at half maximum) or occluded to block all incident light. Figure 1 shows the ERG data recorded from the lateral eye of an animal during five days of a month-long experiment (1990). The amplitude of the ERG increased at night and decreased during the day. The extent of the change depended, in part, on the light incident on the median ocelli. Fully exposing the ocelli to the nighttime sky on 19