616,482 research outputs found
Light intensity, photoperiod duration, daily light flux and coral growth of Galaxea fascicularis in an aquarium setting: a matter of photons?
No full textLight is one of the most important abiotic factors influencing the (skeletal) growth of scleractinian corals. Light stimulates coral growth by the process of light-enhanced calcification, which is mediated by zooxanthellar photosynthesis. However, the quantity of light that is available for daily coral growth is not only determined by light intensity (i.e. irradiance), but also by photoperiod (i.e. the light duration time). Understanding and optimizing conditions for coral growth is essential for sustainable coral aquaculture. Therefore, in this study, the question was explored whether more light (i.e. more photons), presented either as irradiance or as light duration, would result in more growth. A series of nine genetically identical coral colonies of Galaxea fascicularis L. were cultured for a period of 18 weeks at different light duration times (8 hours 150 µE m-2 s-1:16 hours dark, 12 hours 150 µE m-2 s-1:12 hours dark, 16 hours 150 µE m-2 s-1:8 hours dark, 24 hours 150 µE m-2 s-1:0 hours dark) and different irradiance levels (8 hours 150 µE m-2 s-1:16 hours dark, 8 hours 225 µE m-2 s-1:16 hours dark and 8 hours 300 µE m-2 s-1:16 hours dark). Growth was determined every two weeks by measuring buoyant weight. Temperature, salinity and feeding levels were kept constant during the experiment. To detect possible acclimation of the corals to an increased light duration, rates of net photosynthesis and dark respiration were measured, hereby comparing coral colonies grown under an 8:16 hours light (150 µE m-2 s-1):dark cycle with corals grown under a 16:8 hours light (150 µE m-2 s-1):dark cycle. No increase in growth was detected with either increasing photoperiod or irradiance. Continuous lighting (24 hours 150 µE m-2 s-1:0 hours dark) resulted in immediate bleaching and the corals died after 14 weeks. Hourly photosynthetic rates were significantly reduced in the 16 hour light treatment compared to the 8 hour light treatment. As a result, daily net photosynthetic rates were not significantly different, which may explain the observed specific growth rates. Acclimation to photoperiod duration appeared neither to be mediated by changes in chlorophyll-a concentration nor zooxanthellae density. Based on the results of this study, we can conclude that the enhancing effect of light on coral growth is not only a matter of photons. Obviously, the availability of light was not limiting growth in these experiments and was probably in excess (i.e. stressful amounts). Other factors are discussed that play a role in determining growth rates and might explain our results
Light Focusing and Additive Manufacturing Through Highly Scattering Media Using Upconversion Nanoparticles
No full textLight-based additive manufacturing holds great potential in the field of bioprinting due to its exceptional spatial resolution, enabling the reconstruction of intricate tissue structures. However, printing through biological tissues is severely limited due to the strong optical scattering within the tissues. The propagation of light is scrambled to form random speckle patterns, making it impossible to print features at the diffraction-limited size with conventional printing approaches. The poor tissue penetration depth of ultra-violet or blue light, which is commonly used to trigger photopolymerization, further limits the fabrication of high cell-density tissue constructs. Recently, several strategies based on wavefront shaping have been developed to manipulate the light and refocus it inside scattering media to a diffraction-limited spot. In this study, we present a high-resolution additive manufacturing technique using upconversion nanoparticles and a wavefront shaping method that does not require measurement from an invasive detector, i.e., it is a non-invasive technique. Upconversion nanoparticles convert near-infrared light to ultraviolet and visible light. The ultraviolet light serves as a light source for photopolymerization and the visible light as a guide star for digital light shaping. The incident light pattern is manipulated using the feedback information of the guide star to focus light through the tissue. In this way, we experimentally demonstrate that near-infrared light can be non-invasively focused through a strongly scattering medium. By exploiting the optical memory effect, we further demonstrate micro-meter resolution additive manufacturing through highly scattering media such as a 300-mu m-thick chicken breast. This study provides a concept of high-resolution additive manufacturing through turbid media with potential application in tissue engineering.LAP
Light-dependent magnetoreception in birds : increasing intensity of monochromatic light changes the nature of the response
No full textBackground The Radical Pair model proposes that magnetoreception is a light-dependent process. Under low monochromatic light from the short-wavelength part of the visual spectrum, migratory birds show orientation in their migratory direction. Under monochromatic light of higher intensity, however, they showed unusual preferences in other directions or axial preferences. To determine whether or not these responses are still controlled by the respective light regimes, European robins, Erithacus rubecula, were tested under UV, Blue, Turquoise and Green light at increasing intensities, with orientation in migratory direction serving as a criterion whether or not magnetoreception works in the normal way. Results Under low light with a quantal flux of 8 times 10 to 15 power quanta s-1 m-2, the birds were well oriented in their seasonally appropriate migratory direction under 424 nm Blue, 502 nm Turquoise and 565 nm Green light, indicating unimpaired magnetoreception. Under 373 nm UV of the same quantal flux, they were not oriented in migratory direction, showing a preference of the east-west axis instead, but they showed excellent orientation in migratory direction under UV of lower intensity. Intensities of above 36 times 10 to 15 power quanta s-1 m-2 of Blue, Turquoise and Green light elicited a variety of responses: disorientation, headings along the east-west axis, headings along the north-south axis or 'fixed' direction tendencies. These responses changed as the intensity was increased from 36 times 10 to the 15 power quanta s-1 m-2 to 54 and 72 times 10 to 15 power quanta s-1 m-2. Conclusion The specific manifestation of responses in directions other than migratory direction clearly depends on the ambient light regime. This implies that although mechanisms normally providing magnetic compass information seem disrupted, processes that are activated by light still control the behavior. It suggests complex interactions between different types of receptors, magnetic and visual. The nature of the receptors involved and details of their connections are not yet known; however, a role of the color cones in the processes mediating magnetic input is suggested
Surface plasmon polariton modification in top-emitting organic light-emitting diodes for enhanced light outcoupling
No full textWe report on the enhanced light outcoupling efficiency of monochrome top-emitting organic light-emitting diodes (OLEDs). These OLEDs incorporate a hole transport layer (HTL) material with a substantially lower refractive index (∼ 1:5) than the emitter material or the standard HTL material (∼ 1:8) of a reference device. This low-index HTL is situated between the opaque bottom metal contact (anode) and the active emission layer. Compared to an HTL with common refractive index, the dispersion relation of the surface plasmon polariton (SPP) mode from the opaque metal contact is shifted to smaller in-plane wavenumbers. This shift enhances the outcoupling efficiency as it reduces the total dissipated power of the emitter. Furthermore, the excitation of the coupled SPPs at the thin transparent metal top contact (cathode) is avoided by using an ultrathin top electrode. Hence, the coupling of the electroluminescence from the emitter molecules to all non-radiative evanescent modes, with respect to the emitter material, is reduced by at least a factor of two, additionally increasing the outcoupling efficiency. Furthermore, for sufficiently high refractive index contrast the shift of the SPP at the anode/organic interface can lead to in-plane wavenumbers smaller than the wavenumber within the organic emitter layer and outcoupling of all excited modes by high index light extraction structures, e.g. microlens, seems feasible. In accordance to optical simulations, the external quantum efficiency is enhanced by about 20% for monochrome green emitting OLEDs with low refractive index HTL compared to a reference sample
Mineral inclusions in diamonds: associations and chemical distinctions around the 670-km discontinuity
No full textThree new mineral associations have been discovered within diamonds from the Juina district of Brazil. These include a previously unrecorded NaAl-(Mg, Fe)SiO3 phase associated with ferroperidase and the tetragonal almandine pyrope phase, TAPP. Also reported are an association of corundum with aluminous-pyroxene and an olivine composition phase associated with ferroperidase. The minerals in each association often occurred within the same diamonds in addition to being recovered from individual diamonds in different combinations. High-pressure experimental data indicate that these associations formed at different depths within a region ca. 60 km on either side of the upper-mantle/lower-mantle boundary. Mineral compositions show that for the regions sampled, the deep transition zone and lower mantle are chemically distinct and inhomogeneous. Importantly, in the shallow lower mantle, Al is not solely accommodated within perovskite-structured (Mg, Fe)SiO3 as some recent experimental studies have suggested
Vortex knots in light
No full textOptical vortices generically arise when optical beams are combined. Recently, we reported how several laser beams containing optical vortices could be combined to form optical vortex loops, links and knots embedded in a light beam (Leach et al 2004 Nature 432 165). Here, we describe in detail the experiments in which vortex loops form these structures. The experimental construction follows a theoretical model originally proposed by Berry and Dennis, and the beams are synthesized using a programmable spatial light modulator and imaged using a CCD camera
Resonant energy transfer in light harvesting and light emitting applications
No full textThe performance of light emitting and light harvesting devices is improved by utilising resonant energy transfer. In lighting applications, the emission energy of a semiconductor heterostructure and the absorption of organic dyes or colloidal quantum dots (QDs) are engineered so that the excitations in the semiconductor heterostructure can be transferred to the light emitters by means of resonant energy transfer. The emitters subsequently emit colour-tunable light ranging from the visible to the near-infrared. As a result, a twofold enhancement of QD emission is demonstrated in a hybrid QD/semiconductor heterostructure. In light harvesting applications, a hybrid structure of colloidal QDs and a quantum well (QW) p-i-n heterostructure is investigated. After highly absorbing QDs absorb photons, the excitations are efficiently transferred to a QW p-i-n heterostructure via resonant energy transfer. The generated electron-hole pairs in the heterostructure are subsequently separated by the built-in electric held and collected by the corresponding electrodes. In order to increase the energy transfer rate, the donor-acceptor separation distance is minimised by fabricating channel structures on the heterostructure surface penetrating its active layers. Consequently, a sixfold enhancement of photocurrent conversion efficiency is demonstrated. Photocurrent of the hybrid structure is further improved by replacing the QW heterostructure with a bulk p-i-n heterostructure which has higher carrier transport efficiency. Hence, the photocurrent of the hybrid bulk heterostructure is about two orders of magnitude higher than that of the hybrid QW heterostructure. The proposed hybrid structures offer efficient light harvesting devices where high absorption of the colloidal QDs is utilised and their low charge-transfer is overcome
Revealing new properties of light-matter interaction using ultrashort light pulses: from self-assembled nanostructures to hidden anisotropy of light beam
No full textInteraction of intense ulrashort light pulses with transparent materials reveal new interesting properties and phenomena. Recent demonstrations of 3D nanoripple formation, nonreciprocal photosensitivity, ultrafast laser calligraphy and light blade effect due to hidden anisotropy of ultrafast laser beam are reviewed
Understanding the rich physics of light propagation in slow photonic crystal waveguides
No full textSelected papers. Held as part of SPIE Photonics West 2010.We study propagation losses in slow light photonic crystal waveguides and show that dispersion engineering can reduce the loss. We develop an improved understanding of why and how this occurs and develop an new approach to modeling these devices that provides new design insights
Grounded light
No full textGrounded Light was a promenade performance and installation event, staged along the thirty-minute work to a mountain summit and was commissioned by the Noosa Floating Land Festival. It featured a single performer (dancer/performer Lisa O’Neill) whose costume and parasol emanated white light (multiple LEDs) and sound. The work continued on the summit with a solar powered video installation integrated within the mountain’s lookout tower/shelter. This was accompanied by a live trombonist and hundreds of miniature white lights on flexible wire stalks quivering in the wind - set over the plateau and mountainsides. The backdrop was a dramatic 360 view of the Noosa Shire’s lights, set far below.-----\ud
Set within the context of a re-envisioned post colonial politics, the work, commented upon contemporary theories of weight and groundedness, contrasting these to the sense of personal ‘separation’ from the landscape that many Australians have once, or maybe in many cases, still do experience. The work garnered strong audience and critical responses and has become a key case study for two published, scholarly papers developing the idea of a ‘Grounded Media” form.-----\ud
The field involved developing and deepening understanding of dialogic modes and contexts of engagement between the public and non-gallery-based mediatised performance experiences. The context involved the contemporary practices of land and site-specific performance art in concert with the disciplines the Suzuki Actor Training Method and contemporary experimental Dance practices. Grounded Light drew upon the work of writer Paul Carter to examine the colonial roots of non-indigenous Australians’ enduring psychological discomfort with the Australian land through the practical invocation of Carter’s “environmentally grounded poetics”. The methodology was primarily practice-led
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