R. Myllylä

Inkjet printing of light emitting quantum dots

We demonstrate the fabrication of diodes having inkjet printed light emitting quantum dots layer. Close packing of printed layer is shown to be influenced by surface morphology of the underlying polymer layer and size variance of quantum dots used. We extend our approach to printing quantum dots onto a quarter video graphics array substrate (76u2009800 monochrome pixels). The purity of emitted electroluminescent spectra of resulting devices is related to coverage integrity of printed layer, which in turn is shown to be affected by the number of printed drops per pixel.

Inkjet Printed RGB Quantum Dot-Hybrid LED

We report DC driven full color inkjet printed quantum-dots light-emitting devices. The inkjet was used to print monochromatic red, green, and blue, as well as integrate red-green-blue light-emitting quantum dots unto a substrate having QVGA display. The performance of the inkjet printed monochrome devices was on the same order as that of spin coated ones. For the full color RGB devices, a video brightness of 100 cd/m2 is achieved at 9.3 V.

Optical and terahertz measurement techniques for flat-faced pharmaceutical tablets: a case study of gloss, surface roughness and bulk properties of starch acetate tablets

Surface and bulk properties of flat-faced starch acetate tablets were studied. For surface quality inspection optical coherence tomography and recently developed diffractive glossmeter were utilized. Both these optical devices together provide local information on surface roughness and gloss of a tablet over a measured area. The concepts of mean topography and mean gloss profile for surface quality of a tablet are introduced. It was observed that the surface quality of the tablet varies, and compression at high pressure may not guarantee a good surface quality of the tablet. Using novel statistical parameters for gloss and relevant surface roughness parameter, it is possible to get more comprehensive quantitative data on the surface condition of a tablet. THz spectrometer was utilized for detection of THz pulse delay in transmission measurement mode from the tablets. The delay time and thickness ratio of the tablet are consistent with the porosity of the tablet as a function of compression pressure. We suggest that the multimeasurement scheme using three different devices helps tablet makers to better assess bulk and surface quality of their products.

A Variable Delay Optical Buffer Based on Nonlinear Polarization Rotation in Semiconductor Optical Amplifier

In this letter, a variable delay optical buffer with three stage-cascaded buffer units based on nonlinear polarization rotation in semiconductor optical amplifier is demonstrated. The buffer is suitable for integration, fast reconfiguration, scalable, and easy control. With the proposed buffers, 1024-bit data are buffered more than 100 different buffering times at 2.5 Gb/s.

Doppler OCT imaging of cytoplasm shuttle flow in Physarum polycephalum

The Doppler optical coherence tomography technique was applied to image the oscillatory dynamics of protoplasm in the strands of the plasmodium of slime mould Physarum polycephalum. Radial contractions of the gel-like walls of the strands and the velocity distributions in the sol-like endoplasm streaming along the plasmodial strands are imaged. The motility inhibitor effect of carbon dioxide on the cytoplasm shuttle flow and strand-wall contraction is shown. The optical attenuation coefficient of cytoplasm is estimated.

Biophysical mechanisms of modification of skin optical properties in the UV wavelength range with nanoparticles

In this paper, by means of the Mie theory and Monte Carlo simulations we investigate modification of optical properties of the superficial layer of human skin (stratum corneum) for 310- and 400-nm ultraviolet (UV) radiation by embedding of 35–200-nm-sized particles of titanium dioxide (TiO2) and silicon (Si). Problem of skin protection against UV light is of major importance due to increased frequency of skin cancer provoked by excessive doses of accepted UV radiation. For 310-nm light, the optimal sizes of the TiO2 and Si particles are found to be 62 and 55 nm, respectively, and for 400-nm radiation, 122 and 70 nm, respectively.In this paper, by means of the Mie theory and Monte Carlo simulations we investigate modification of optical properties of the superficial layer of human skin (stratum corneum) for 310- and 400-nm ultraviolet (UV) radiation by embedding of 35–200-nm-sized particles of titanium dioxide (TiO2) and silicon (Si). Problem of skin protection against UV light is of major importance due to increased frequency of skin cancer provoked by excessive doses of accepted UV radiation. For 310-nm light, the optimal sizes of the TiO2 and Si particles are found to be 62 and 55 nm, respectively, and for 400-nm radiation, 122 and 70 nm, respectively.

FM-radio and TV tower signals can cause spontaneous hand movements near moving RF reflector.

For testing human sensitivity to radio frequency (RF) standing waves a movable reflecting wall was constructed. Radio waves from the radio-TV tower reflected back and formed a standing wave near the reflector. When the reflector was moved, the position of the maximums of the standing waves changed and the electromagnetic intensity changed in the body of the standing test subject. The computer with an AD-converter registered the signals of the hand movement transducer and the RF-meter with 100MHz dipole antennas. A total of 29 adults of different ages were tested. There were 9 persons whose hand movement graphs included features like the RF-meter. Six showed responses that did not correlate with the RF-meter. There were also 14 persons who did not react at all. Sensitive persons seem to react to crossing standing waves of the FM-radio or TV broadcasting signals.

Critical behavior of phase interfaces in porous media: Analysis of scaling properties with the use of noncoherent and coherent light

Image sequences of the surface of disordered layers of porous medium (paper) obtained under noncoherent and coherent illumination during capillary rise of a liquid are analyzed. As a result, principles that govern the critical behavior of the interface between liquid and gaseous phases during its pinning are established. By a cumulant analysis of speckle-modulated images of the surface and by the statistical analysis of binarized difference images of the surface under noncoherent illumination, it is shown that the macroscopic dynamics of the interface at the stage of pinning is mainly controlled by the power law dependence of the appearance rate of local instabilities (avalanches) of the interface on the critical parameter, whereas the growth dynamics of the local instabilities is controlled by the diffusion of a liquid in a layer and weakly depends on the critical parameter. A phenomenological model is proposed for the macroscopic dynamics of the phase interface for interpreting experimental data. The values of critical indices are determined that characterize the samples under test within this model. These values are compared with the results of numerical simulation for discrete models of directed percolation corresponding to the Kardar-Parisi-Zhang equation.

Involuntary human hand movements due to FM radio waves in a moving van

Finland TRACT Involuntary movements of hands in a moving van on a public road were studied to clarify the possible role of frequency modulated radio waves on driving. The signals were measured in a direct 2 km test segment of an international road during repeated drives to both directions. Test subjects (n=4) had an ability to sense radio frequency field intensity variations of the environment. They were sitting in a minivan with arm movement detectors in their hands. A potentiometer was used to register the hand movements to a computer which simultaneously collected data on the amplitude of the RF signal of the local FM tower 30 km distance at a frequency of about 100 MHz. Involuntary hand movements of the test subjects correlated with electromagnetic field, i.e. FM radio wave intensity measured. They reacted also on the place of a geomagnetic anomaly crossing the road, which was found on the basis of these recordings and confirmed by the public geological maps of the area.In conclusion, RF irradiation seems to affect the human hand reflexes of sensitive persons in a moving van along a normal public road which may have significance in traffic safety.

Determination of optical parameters of pulp suspensions by time-resolved detection of photoacoustic signals and total diffuse reflectance measurements

Time-resolved photoacoustics were used to measure the optical parameters of pulp suspensions for the first time. Reconstructing stress distribution along the direction of the incident laser light allows the effective attenuation coefficient of these suspensions to be determined. Simultaneously, the total diffuse reflectance of the suspensions was measured by the same laser source. Based on the effective attenuation coefficient and total diffuse reflectance, the absorption and reduced scattering coefficients of pulp suspensions can be calculated. In this study, three kinds of pulp suspensions with different kappa number (2, 13, and 16), a measure of lignin content in pulp fibers, were diluted with water to make samples with a consistency range from 1% to 5%, and studied at 355 nm wavelength. The results showed that the optical coefficients were approximately proportional to pulp consistency; on the other hand, the absorption coefficient was linearly correlated with kappa number, but the reduced scattering coefficient was not. Therefore, by determining its optical parameters, it is possible to extract the consistency and kappa number of an unknown pulp suspension.