Illusory rotations in the haptic perception of moving spheres and planes

Recently, we have shown that a translating bar on which blindfolded participants position their hand is perceived as also rotating. Here, we investigated whether such an illusory rotation would also be found if a sphere or a plane (i.e. a stimulus without a clear orientation) was used as translating stimulus. We indeed found similar rotation biases: on average a stimulus that translates over a distance of 60cm has to rotate 25 degrees to be perceived as non-rotating. An additional research question was whether the biases were caused by the same underlying biasing egocentric reference frame. To our surprise, the correlations between the sizes of the biases of the individual participants in the various conditions were not high and mostly not even significant. This was possibly due to day-to-day variations, but clearly, more research is needed to answer this second research question

Carrier localization mechanisms in InGaN/GaN quantum wells

Localization lengths of the electrons and holes in InGaN/GaN quantum wells have been calculated using numerical solutions of the effective mass Schr\"odinger equation. We have treated the distribution of indium atoms as random and found that the resultant fluctuations in alloy concentration can localize the carriers. By using a locally varying indium concentration function we have calculated the contribution to the potential energy of the carriers from band gap fluctuations, the deformation potential and the spontaneous and piezoelectric fields. We have considered the effect of well width fluctuations and found that these contribute to electron localization, but not to hole localization. We also simulate low temperature photoluminescence spectra and find good agreement with experiment.Comment: 7 pages, 7 figure

Composition and luminescence studies of InGaN epilayers grown at different hydrogen flow rates

Indium gallium nitride (In(x)Ga(1-x)N) is a technologically important material for many optoelectronic devices, including LEDs and solar cells, but it remains a challenge to incorporate high levels of InN into the alloy while maintaining sample quality. A series of InGaN epilayers was grown with different hydrogen flow rates (0-200 sccm) and growth temperatures (680-750 °C) to obtain various InN fractions and bright emission in the range 390-480 nm. These 160-nm thick epilayers were characterized through several compositional techniques (wavelength dispersive x-ray spectroscopy, x-ray diffraction, Rutherford backscattering spectrometry) and cathodoluminescence hyperspectral imaging. The compositional analysis with the different techniques shows good agreement when taking into account compositional gradients evidenced in these layers. The addition of small amounts of hydrogen to the gas flow at lower growth temperatures is shown to maintain a high surface quality and luminescence homogeneity. This allowed InN fractions of up to ~16% to be incorporated with minimal peak energy variations over a mapped area while keeping a high material quality

Comparison of the haptic and visual deviations in a parallelity task

Deviations in both haptic and visual spatial experiments are thought to be caused by a biasing influence of an egocentric reference frame. The strength of this influence is strongly participant-dependent. By using a parallelity test, it is studied whether this strength is modality-independent. In both haptic and visual conditions, large, systematic and participant-dependent deviations were found. However, although the correlation between the haptic and visual deviations was significant, the explained variance due to a common factor was only 20%. Therefore, the degree to which a participant is “egocentric” depends on modality and possibly even more generally, on experimental condition

Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN

We combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black–white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component (i.e., screw and mixed dislocations) act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated

Terpene synthases in cucumber (<i>Cucumis sativus</i>) and their contribution to herbivore-induced volatile terpenoid emission

Terpenoids play important roles in flavour, pollinator attraction and defence of plants. In cucumber (Cucumis sativus) they are important components of the herbivore‐induced plant volatile blend that attracts natural enemies of herbivores. We annotated the cucumber TERPENE SYNTHASE gene (CsTPS) family and characterized their involvement in the response towards herbivores with different feeding guilds using a combined molecular and biochemical approach. Transcripts of multiple CsTPS genes were upregulated in leaves upon herbivory and the products generated by the expressed proteins match the terpenoids recorded in the volatile blend released by herbivore‐damaged leaves. Spatial and temporal analysis of the promoter activity of CsTPS genes showed that cell content‐feeding spider mites (Tetranychus urticae) and thrips (Frankliniella occidentalis) induced promoter activity of CsTPS9 and CsTPS19 within hours after initiation of infestation, while phloem‐feeding aphids (Myzus persicae) induced CsTPS2 promoter activity. Our findings offer detailed insights into the involvement of the TPS gene family in the dynamics and fine‐tuning of the emission of herbivore‐induced plant volatiles in cucumber, and open a new avenue to understand molecular mechanisms that affect plant–herbivore interactions

Carrier distribution in InGaN/GaN tricolor multiple quantum well light emitting diodes

Carrier transport in InGaN light emitting diodes has been studied by comparing the electroluminescence (EL) from a set of triple quantum well structures with different indium content in each well, leading to multicolor emission. Both the sequence and width of the quantum wells have been varied. Comparison of the EL spectra reveals the current dependent carrier transport between the quantum wells, with a net carrier flow toward the deepest quantum well. (C) 2009 American Institute of Physics. (doi:10.1063/1.3244203