Jana Ryckaert

Route of entry and tissue distribution of Yersinia ruckeri in experimentally infected rainbow trout Oncorhynchus mykiss

Yersinia ruckeri is the causative agent of enteric redmouth disease, which leads to significant losses in salmonid aquaculture worldwide. Despite the significance of the disease, little information is available on the pathogenesis. In this study, the portal of entry was investigated using a contact-exposure infection method in rainbow trout Oncorhynchus mykiss with 4 different Y. ruckeri strains. Bacteriological and histological examination revealed the presence of high numbers of bacteria in the gills immediately after infection resulting in a rapid spread of Y. ruckeri in the internal organs. However, only a virulent strain was able to survive and multiply in the host, causing septicaemia and death several days after infection. These findings indicate that gills may be an important site of entry and that Y. ruckeri virulence is related to immune evasion.

Heat shock proteins protect platyfish (Xiphophorus maculatus) from Yersinia ruckeri induced mortality.

The significant disadvantages accompanied with the use of antibiotics in aquaculture, emphasize the need for developing alternative disease control strategies, like novel vaccine approaches and immunostimulating measures. Several studies have already pointed out the ability of heat shock proteins (HSPs) to modulate innate and adaptive immune responses, what makes them potent candidates for the development of a new disease prevention method. In this study, the use of self and non-self heat shock proteins as a new prophylactic treatment against bacterial diseases in freshwater aquaculture was investigated. Therefore, an infection model was developed with platyfish as a host for Yersinia ruckeri infections. In this infection model, the effect of different treatments with HSPs on the survival of the fish after bacterial infection was tested: non-lethal heat shock, intracoelomal injection with two recombinant bacterial HSPs, GroEL and DnaK, and a combination of a non-lethal heat shock and an injection with bacterial HSPs. The results show that a non-lethal heat shock could not protect fish against a subsequent infection with Y. ruckeri. However, when the fish received an injection with bacterial HSPs, Y. ruckeri induced mortality was reduced. This effect became significant when the administration of bacterial HSPs was combined with a non-lethal heat shock. These data suggest a possible role for heat shock proteins as an immunostimulating treatment in fish against bacterial infections.

Persistence of Yersinia ruckeri in trout macrophages.

Yersinia ruckeri is the etiological agent of enteric redmouth disease, a systemic infection which mainly affects salmonids. Although this important freshwater pathogen was discovered in 1966, little is known about its virulence mechanisms. In the present study, the interactions with rainbow trout head kidney macrophages were investigated. In vitro experiments were performed to measure uptake, intracellular survival, respiratory burst response and macrophage viability after exposure to Y. ruckeri. Additionally, the fate of Y. ruckeri in the head kidney after immersion infection was studied in vivo. Results show that Y. ruckeri induced the production of reactive oxygen species and that this response peaked at around 3 h after exposure. Despite these toxic substances, Y. ruckeri is able to survive in vitro inside trout macrophages for at least 24 h. Transmission electron microscopy demonstrated that Y. ruckeri bacteria are sequestered in autophagocytic compartments without fusion with primary lysosomes. Inside these compartments, bacteria were capable of replicating. Immersion infection of juvenile rainbow trout resulted in steadily increasing numbers of bacteria in the head kidney over time. As the infection progressed, Y. ruckeri shifted from a predominantly extracellular phase during the first week after infection to an intracellular phase inside the host macrophages from day 7 onwards. In conclusion, this study clearly demonstrates the capacity of Y. ruckeri to survive in rainbow trout macrophages in vitro as well as in vivo, confirming its facultative intracellular nature.

Determination of the optimal amount of scattering in a wavelength conversion plate for white LEDs

Luminescent materials are widely used in white LEDs to convert part of the blue LED light into light with a longer wavelength, resulting in white light when both colors are well mixed. One way to integrate the luminescent material in the LED package is to deposit a thin luminescent layer on a planar carrier or disperse luminescent particles in the carrier material and then position the resulting wavelength conversion plate above one or more LEDs. It is very important that these wavelength conversion plates have the right properties to ensure homogeneous white light with a high efficiency and desired correlated color temperature (CCT). Key properties are the absorption and emission spectrum and the scattering and absorption coefficients. These properties strongly influence the color of the resulting light, but also the efficiency and the angular uniformity. This work describes an extensive study of the effect of the scattering and absorption coefficients in terms of the desired CCT. A computationally efficient extended Adding-Doubling method is used for the simulation of the light distribution and conversion in the planar wavelength conversion element. Ultimately an optimal combination with a high efficiency and low angular color deviation is desired. Different systems are investigated and optimal coefficients are found. With these findings a more targeted approach can be used in the manufacturing of wavelength conversion plates for white LEDs. The addition of scatterers or non-scattering luminescent particles can be used to obtain optimal scattering properties of the wavelength conversion plate.

A hybrid tool for spectral ray tracing simulations of luminescent cascade systems

To perform adequate simulations of luminescent cascade systems, a hybrid method combining a commercial ray tracer and a programming tool is presented. True Monte Carlo algorithms for luminescent materials, treating each ray individually, are adapted to allow wavelength conversion of ray sets. Two solutions for the wavelength conversion of ray sets are discussed: a random approach, where absorption events are randomly selected to create emission events, and a combined approach, where information from multiple absorption events is combined to create emission events. Both methods are applied to simulate the performance of a virtual remote phosphor light-emitting diode module. When using the combined approach, the required computation time to achieve sufficient accuracy is a factor 2 lower, compared to the time required when applying the random approach.

Taking the spectral overlap between excitation and emission spectra of fluorescent materials into account with Monte Carlo simulations

Monte Carlo ray tracing is an important simulation tool in applications where fluorescence is present, e.g. in bio-medical applications and in the design of luminaires and luminescent solar concentrators. A frequently used ray tracing procedure for fluorescence is the ‘dual stage’ approach. In this approach, first, all sources are traced through the system and the rays absorbed in the fluorescent components are stored. Next, the emission from the fluorescent components is traced. This approach does not allow for subsequent re-absorption and re-emission effects in fluorescent materials with a spectral overlap between excitation and emission spectra. In this work, a ‘multi stage’ ray tracing procedure for the simulation of luminescence is presented. Herein, wavelengths are traced from short to long separately and no distinction is made regarding the origin of emission (either a fluorescent component or a source). The presented approach can be easily implemented in existing commercial ray tracing software thus reducing the programming efforts for the new ray tracing algorithm and taking advantage of the strength of the selected ray tracing package concerning the modelling of complex geometrical systems. Both techniques are compared to investigate the influence of the selected ray tracing approach on the efficiency and colour prediction of a remote phosphor LED module.

Spot phosphor concept applied to the remote phosphor configuration of a white phosphor-converted LED

Although the remote phosphor technology outperforms the conformal phosphor technology for mid-power applications, one of the limiting factors is the amount of phosphor required and its impact on the total cost. Besides, an important loss mechanisms in remote phosphor LED technology is the re-absorption of converted light. An obvious solution to this issue is enabling a light path for the converted light, such that further interactions with the phosphor element are avoided. In order to explore such a configuration, a simulation model of a phosphor element is devised and validated based on experimental data and the application of the inverse adding-doubling method. The resulting configuration, denoted as spot concept, along with a long-pass filter is shown to be a potential solution to reduce the phosphor usage. Since the moderate change in the light extraction ratio when applying the spot concept is partly attributed to the losses in the secondary optics needed to narrow the LED beam, the application of the spot concept configuration with a directional light source such as a laser diode could be a powerful combination for the enhancement of the light extraction ratio.

Searching for the optimal synthesis parameters of InP/Cd x Zn 1-x Se quantum dots when combined with a broad band phosphor to optimize color rendering and efficacy of a hybrid remote phosphor white LED

Combining traditional phosphors with a broad emission spectrum and non-scattering quantum dots with a narrow emission spectrum can have multiple advantages for white LEDs. It allows to reduce the amount of scattering in the wavelength conversion element, increasing the efficiency of the complete system. Furthermore, the unique possibility to tune the emission spectrum of quantum dots allows to optimize the resulting LED spectrum in order to achieve optimal color rendering properties for the light source. However, finding the optimal quantum dot properties to achieve optimal efficacy and color rendering is a non-trivial task. Instead of simply summing up the emission spectra of the blue LED, phosphor and quantum dots, we propose a complete simulation tool that allows an accurate analysis of the final performance for a range of different quantum dot synthesis parameters. The recycling of the reflected light from the wavelength conversion element by the LED package is taken into account, as well as the re-absorption and the associated red-shift. This simulation tool is used to vary two synthesis parameters (core size and cadmium fraction) of InP/CdxZn1-xSe quantum dots. We find general trends for the ideal quantum dot that should be combined with a specific YAG:Ce broad band phosphor to obtain optimal efficiency and color rendering for a white LED with a specific pumping LED and recycling cavity, with a desired CCT of 3500K.

Simulation of white LEDs with a planar luminescent layer using the extended Adding-Doubling method

The most common method to create white light with LEDs is the use of a luminescent material (e.g. phosphor) in combination with one or more blue LEDs. Different configurations can be used (intimate phosphor, remote phosphor, phosphor layer on top of a chip-on-board LED array). To design high quality LED sources it is important that these systems can be optimized. The Monte Carlo ray-tracing method is the traditional algorithm to simulate these systems. A disadvantage of the Monte Carlo method however is the large computation time which makes it less suitable for system optimization. We present a new simulation method to predict the performance of various white LED packages with a planar phosphor layer using the extended Adding-Doubling method. In a phosphor converted white LED part of the incident and converted light is back-scattered from the phosphor layer towards the LED package. This light will be partly reflected back onto the phosphor layer by the LED package. When simulating the LED source with the extended Adding-Doubling method, the behavior of the LED package can be approximated by a reflection matrix. This matrix includes the directions in which the light is scattered from the LED package, as well as the efficiencies. We found that, by using the extended Adding-Doubling method with the appropriate reflection matrix, it is possible to predict the total flux and the spectral angular intensity distribution of the light emitted from white LED packages with a planar luminescent layer. With this method we present a fast technique to predict the performance of phosphor converted white LEDs and optimize the optical parameters of the luminescent layer to obtain the best overall performance.