Presence Of Illumination Research Articles

Photolytic color bleaching of cationic dyes in presence of selenious acid in aqueous and micellar environments

Photodecolorization of three cationic dyes in aqueous and micellar solution are reported under UV illumination in presence of selenious acid. Selenious acid (H 2SeO 3) has been used for the first time as a reagent for dye decolorization reaction. Micellar media have been found to influence the rate of decolorization reaction through electrostatic, hydrophobic and charge transfer interaction. It has also been shown that strong charge transfer and electrostatic interaction lead to an appreciable enhancement of the reaction rate in micelle, whereas, weak hydrophobic interaction is of marginal importance. In depth kinetic studies have been carried out to realize the interaction of the dyes with selenious acid and micelles. Kinetic studies have revealed that the reaction is first order with respect to H 2SeO 3 and zero order with respect to dye. ‘Salting-in’ and ‘salting-out’ agents were successfully employed for the real time application of the dye decolorization process.

Safety testing of indocyanine green and trypan blue using retinal pigment epithelium and glial cell cultures.

Indocyanine green (ICG) and trypan blue have been advocated as vital stains for use during macular surgery. The safety of these agents was tested using a cell culture model. Human retinal pigment epithelium (RPE) and Müller cell lines were exposed to ICG over a range of concentrations up to 0.5%, and trypan blue up to 0.2%. Cells were exposed to each dye for 5, 15, or 30 minutes, rinsed, and incubated 24 hours. Cell viability was measured using a mitochondrial dehydrogenase-assay and fluorescent live-dead probe. Experiments were repeated using 0.5% and 1% ICG and 0.06% and 0.12% trypan blue, with follow-up at 0, 1, 5, and 15 days. ICG experiments were repeated in the presence of illumination from a xenon light-source channeled through a surgical endolight, and using reduced osmolarity solutions of 0.1%, 0.5%, and 1% (185 vs. 275 mOsM). There was no clear relationship between cell viability and the concentration of the agent or duration of follow-up, except in RPE cells exposed to 1% ICG. These showed a linear (R(2) 0.9952) decline in viability with time, with a significant reduction by day 15 (P = 0.016). RPE cells exposed to ICG and illumination were not significantly different from the negative control, but when illumination was combined with low osmolarity, viability was reduced (P = 0.0016). ICG and illumination reduced Müller cell viability (P < 0.0001 for both 185 and 275 mOsM). Müller cells incubated with 185 mOsM 1% ICG showed a significant reduction in viability (P < 0.0001) not seen with the 185 mOsM 0.5% or 0.1% solutions or in the low-osmolarity RPE groups. The combination of exposure to 0.5% ICG and the newer endoillumination light-sources can damage cultured Müller cells. Although the preparations of ICG most commonly used clinically did not produce significant damage, relatively small changes in ICG osmolarity and concentration did. This suggests that safety margins are not large. Trypan blue is safe in a cell culture model.

FIRE: fractal indexing with robust extensions for image databases

As already documented in the literature, fractal image encoding is a family of techniques that achieves a good compromise between compression and perceived quality by exploiting the self-similarities present in an image. Furthermore, because of its compactness and stability, the fractal approach can be used to produce a unique signature, thus obtaining a practical image indexing system. Since fractal-based indexing systems are able to deal with the images in compressed form, they are suitable for use with large databases. We propose a system called FIRE, which is then proven to be invariant under three classes of pixel intensity transformations and under geometrical isometries such as rotations by multiples of /spl pi//2 and reflections. This property makes the system robust with respect to a large class of image transformations that can happen in practical applications: the images can be retrieved even in the presence of illumination and/or color alterations. Additionally, the experimental results show the effectiveness of FIRE in terms of both compression and retrieval accuracy.

Solid state electrochemical reaction in photocells made using conducting polyaniline and sensitized with methylene blue

The effect of small concentration of methylene blue (MB) on photocurrents was studied in solid state photoelectrochemical cells fabricated using conducting polyaniline (PANI) coated electrodes sandwiched with a solid polymer electrolyte, viz. poly(vinyl alcohol) (PVA) with phosphoric acid. These exhibit good photoresponse to visible light (maximum photosensitivity factor of the order of 10). The current-voltage (I-V) characteristics in such cells reveal that the charge transport is ohmic. Also, an electrochemical reaction (motion of Cl– from SPE+MB to PANI) is observed at 1.2–1.3 V, which gives rise to a sudden increase of current at this particular voltage. The presence of illumination enhances this electrochemical reaction. The combined effect, i.e. ohmic charge transport and an electrochemical reaction, is observed in the I-V characteristics. Along with the dye concentration, the photosensitivity is observed to be field/voltage dependent. The sensitization effects are due to lowering of the potential barrier formed at the PANI/SPE+MB interface under illumination.

Dark and photoreactions of acetates on TiO 2( [formula omitted]) single crystal surface

The surface reaction of acetates on TiO 2(1 1 0) single crystal has been monitored in dark and under UV by XPS. XPS O(1s) data indicated that surface saturation is obtained at ≈0.5 monolayer coverage consistent with STM results [J. Chem. Phys., 106 (1997) 2924, Surf. Sci. 433–435 (1999) 322]. Annealing the surface results in a steady decrease of surface acetates that disappeared by ≈600 K. UV illumination at room temperature, and in the absence of diatomic oxygen in the gas phase, did not decrease the intensity of the XPS C(1s) and O(1s) signals attributed to surface acetates. On the other hand, UV illumination in presence of oxygen (≈10 −7–10 −6 Torr of diatomic oxygen) has resulted in a noticeable decrease of surface acetates. These combined results indicate that both the two-fold bridging oxygen and the three fold lattice oxygen atoms are not directly involved in the photooxidation reaction of acetates on TiO 2(1 1 0) single crystal. The cross-section of the photodepletion of acetates was estimated equal to 0.6–0.8×10 −17 cm 2.

Photoelectrodeposition of patterned cobalt films on silicon substrates

Cobalt films have been electrodeposited directly onto p-type (1 0 0) silicon substrates. Since electrons were required for reduction of the cobalt in solution, deposition only occurred in the presence of illumination. Projection of an optical grating onto the substrate during deposition demonstrated direct patterning of the Co which could lead to novel methods of defining magnetic structures on semiconductor substrates.

The catalytic and photocatalytic autoxidation of S x2− to SO 42− by water-soluble cobalt porphyrin

The catalytic and photocatalytic transformation of S 4 2−, S 3 2−, S 2 2− and S 2− to SO 4 2− by water-soluble cobalt tetrakis ( N-methyl-4-pyridyl) porphyrin (Co(4-TMPyP)) was performed by a two-step process. The catalytic autoxidation of S x 2− ( x=2, 3 and 4) to S 2O 3 2− by Co(4-TMPyP) in the presence of oxygen was followed by the photocatalytic oxidation of S 2O 3 2− by Co(4-TMPyP) under illumination in presence of oxygen at a strong basic solution. The direct transformation of S x 2− to SO 4 2− was also performed. The catalytic activity of Co(4-TMPyP) was compared to Fe(2-TMPyP) and Mn(4-TMPyP). All three catalysts have activity towards autoxidation of S 4 2− to S 2O 3 2−. The trend in photocatalytic oxidation activity of the porphyrin complexes is Co(4-TMPyP)>Fe(2-TMPyP)>Mn(4-TMPyP). The electrocatalytic reactions of S x 2− by Co(4-TMPyP) were also observed.

Frequency Response of Trap States in an AlxGa1−xN/GaN Heterostructure Field-Effect Transistor Measured at the Nanoscale by dC/dV Spectroscopy

ABSTRACTScanning capacitance spectroscopy has been used to characterize, at the nanoscale, the frequency-dependent response of surface charge and of charge in the two-dimensional electron gas of an AlxGa1−xN/GaN heterostructure field-effect transistor structure. dC/dV spectra were measured in a scanning capacitance microscope with a voltage signal consisting of a triangle wave at frequencies of 1 – 50 Hz applied to the sample. The spectra were obtained in the dark (except for 600 nm laser light from the scanning capacitance apparatus) and under illumination. Measurements were performed in the vicinity of and away from charged threading dislocations visible in scanning capacitance images. In the absence of illumination, the dC/dV data indicate that electrons are trapped at or near the AlxGa1−xN surface, consistent with suggestions in the literature that a high density of surface states exists on the free AlxGa1−xN surface. Frequency-dependent measurements show that emission times for these traps can be as long as several hundred ms. In the presence of illumination, reduced electron trapping is observed. The nature and behavior of trap states in the vicinity of threading dislocations is found to differ significantly from that in regions between dislocations for measurements in the dark, and suggest that the electrostatic potential due to the charged threading dislocation is negligible at the surface.

Biodegradation of a nonylphenol ethoxylate by the autochthonous microflora in lake water with observations on the influence of light

Alkylphenol polyethoxylates (APE) are routinely used as additives in pesticide formulations. Biodegradation of APEs results in the accumulation of persistent short chain mono-, di- and tri-ethoxylates (AP1EO, AP2EO AP3EO) that are more toxic than the parent compounds and potentially oestrogenic. Accumulation of persistent APE metabolites in shallow or ephemeral waters may pose a hazard to aquatic fauna. This study has followed the degradation and formation of individual oligomers in freshwater in static die-away tests with and without illumination. Over 33 days in darkness there was a progressive and complete loss of long chain oligomers (NP8-17EO), transient increases and subsequent loss of short to medium chain oligomers (NP4-7EO), and large persistent increases (∼1000%) in short chain oligomers (NP1-3EO). In the presence of illumination, biodegradation was retarded and heterotrophic bacterial proliferation was inhibited. After 33 days there was complete loss of long chain oligomers (NP9-17EO), incomplete loss of medium chain oligomers (NP6-8EO) and increases in short chain oligomers (NP1-5EO).

A reverse bias, tip-insulator-semiconductor tunnel diode model accounting for the delineation of a p/p+ junction using scanning tunneling microscopy

In this article, a tunneling-generation-avalanche model has been proposed to explain the reverse bias current–voltage behavior observed at a tip/air/p-type silicon junction. Based on this model, under conditions where the applied bias is more negative than the flat band voltage, the current will be dominated by generation processes, which has significant doping density dependence. Since mechanically cut tips, used in this work, can have complicated geometries, geometric effects, such as extended gates and concentration of the electrical field must be taken into account. By taking these factors into account, good agreement between theory and experiments can be achieved. Finally, in the presence of illumination, p/p+ junctions can be delineated successfully by taking advantage of the generation process. These results demonstrate that scanning tunneling microscopy can be used as a powerful tool for characterizing semiconductor devices.

Impact of light illumination and passivation layer on silicon finite-ground coplanar-waveguide transmission-line properties

The modeling of silicon finite-ground coplanar-waveguide (FGCPW) transmission lines is presented in this paper. It is shown that the effective substrate conductivity increases in the presence of illumination and in the presence of a passivation layer in the slot regions independently. As a result, the losses of trenched FGCPW are lower than conventional FGCPW transmission lines. The strong dependence of the substrate conductivity on illumination suggests that optically controlled attenuators can be implemented with FGCPW transmission lines exhibiting practically no phase change between the different attenuation states. A new contrast ratio for optically controlled transmission lines is derived.

Photoemission measurements on aluminium and amorphous silicon by pulsed laser illumination in presence of a plasma

In this paper the effect of the illumination of a surface by a pulsed laser beam was studied. Al layers and intrinsic and doped amorphous silicon films were illuminated in vacuum, in the presence of different gases and under a DC plasma. The wavelength of the pulsed beam ranged from 308 to 348 nm. Applied bias influenced strongly the measured signal when performing experiments in a gas atmosphere. While no photoemission was detected on both intrinsic and p-type amorphous Si:H, a signal was obtained on n-type a-Si:H if a gas atmosphere is present.

Empirical investigation of the signal performance of a high‐resolution, indirect detection, active matrix flat‐panel imager (AMFPI) for fluoroscopic and radiographic operation

Signal properties of the first large-area, high resolution, active matrix, flat-panel imager are reported. The imager is based on an array of 1536 x 1920 pixels with a pixel-to-pixel pitch of 127 microns. Each pixel consists of a discrete amorphous silicon n-i-p photodiode coupled to an amorphous silicon thin-film transistor. The imager detects incident x rays indirectly by means of an intensifying screen placed over the array. External acquisition electronics send control signals to the array and process analog imaging signals from the pixels. Considerations for operation of the imager in both fluoroscopic and radiographic modes are detailed and empirical signal performance data are presented with an emphasis on exploring similarities and differences between the two modes. Measurements which characterize the performance of the imager were performed as a function of operational parameters in the absence or presence of illumination from a light-emitting diode or x rays. These measurements include characterization of the drift and magnitude of the pixel dark signal, the size of the pixel switching transient, the temporal behavior of pixel sampling and the implied maximum frame rate, the dependence of relative pixel efficiency and pixel response on photodiode reverse bias voltage and operational mode, the degree of linearity of pixel response, and the trapping and release of charge from metastable states in the photodiodes. In addition, X-ray sensitivity as a function of energy for a variety of phosphor screens for both fluoroscopic and radiographic operation is reported. Example images of a line-pair pattern and an anthropomorphic phantom in each mode are presented along with a radiographic image of a human hand. General and specific improvements in imager design are described and anticipated developments are discussed. This represents the first systematic investigation of the operation and properties in both radiographic and fluoroscopic modes of an imager incorporating such an array.

ORIENTATION OF SWIMMING FLAGELLATES BY SIMULTANEOUSLY ACTING EXTERNAL FACTORS1

ABSTRACTThe directionality of phototaxis combined with gravitaxis was investigated experimentally for populations of the swimming alga Euglena gracilis Klebs. Two irradiances were used: a “weak” irradiance to elicit positive phototaxis and a “strong” irradiance to elicit negative phototaxis. In addition, by changing the density of cells in the suspension, the number of collisions between cells was varied to determine the effects of these collisions on the distribution of swimming directions in both the absence and the presence of illumination. We found that positive phototaxis was associated with a broader distribution of swimming directions than was negative phototaxis. In the latter case, the effect of phototaxis dominated over that of gravitaxis. Experiments on another swimming alga, Chlamydomonas nivalis Wille, showed that collisions between cells degraded the directionality of gravitaxis.

Effects of Wind and Illumination on Behavior and Metabolic Rate of American Goldfinches (Carduelis tristis)

We measured the metabolic rate of active-phase American Goldfinches (Carduelis tristis) with and without illumination at 10°C and four wind speeds. We observed the birds via closed-circuit television. Illumination alone increased metabolism 37%. Metabolic rate increased linearly with activity and wind speed. A decrease in activity as wind speed increased tended to counteract the increase in thermoregulatory metabolism caused by convection, and reduced the slope of metabolism-vs.-wind-speed plots. The increase of metabolism with activity was reduced by the presence of illumination, which suggests relatively more compensation for thermoregulatory metabolism by activity metabolism when illumination is present. Stepwise linear regression was used to correct for nonthermal effects of illumination and wind to improve estimates of their purely thermal effects.

Aspects of diamond deposition by anomalous pulsed d.c. glow-discharge-activated chemical vapor deposition

Diamond was deposited onto SiAlON substrates by glow-discharge-activated chemical vapor deposition (CVD) using hydrogen-methane gas mixtures. The formation of diamond depends strongly on the plasma parameters (current, voltage, pressure, gas mixture) and the substrates used. Diamond deposition occurred in a d.c. glow discharge at a pressure of 30 mbar, a voltage of 660 V and current density of 0.5 A cm 2, and a series of bright and dark striations in the Faraday dark space was observed. As the presence of illumination in the interelectrode space is apparently important for successful diamond deposition, its dependence on the various luminous effects, and the voltage distribution in the interelectrode space are discussed.

Stability of molten nitrate salts containing light absorbing additives as solar flux absorbers

The decomposition of molten sodium nitrite-sodium nitrate-potassium nitrate ( 40:7:53 wt% ) and sodium nitrate-potassium nitrate ( 46:54 wt% ) with release of nitrogen dioxide was studied at 320°C, 440°C and 500°C, in the absence and presence of suspensions of various additives, without or with illumination by UV and visible light. In the NaNO 2NaNO 3KNO 3 melt, TiO 2, Fe 2O 3, CuO, Co 3O 4, graphite and active charcoal formed quite stable suspensions, while MoS 2 decomposed, and Fe 3O 4 and carbon black failed to disperse. The photoinduced release of nitrogen dioxide was enhanced in the presence of TiO 2, Co 3O 4 and Fe 2O 3, but was much smaller in the presence of CuO. At 440°C, in the presence of graphite powder, the release of NO 2 in the dark and under illumination with a 150 W xenon lamp were 18 and 35 μ mol h −1, respectively. In the NaNO 3KNO 3 melt, Fe 2O 3, Co 3O 4 and CuO formed stable suspensions. With this melt in the presence of Co 3O 4 low rates of decomposition were observed, which at 440°C in the absence and presence of illumination with a 150 W Xe lamp were 0.07 and 0.1 μ mol h −1 per 50 g of the melt. In electrochemical experiments with stainless steel electrodes at 300°C–306°C, the release of nitrogen dioxide increased with applied potential. At 1.6 V cell potential and 21 mA current, the rate of NO 2 release was 42 μmol h −1. Using a polycrystalline TiO 2 electrode under illumination with a 150 W Xe lamp, versus a stainless steel cathode in a NaNO 3KNO 3 (46–54 wt%) melt at 286°C, the photocurrent amounted to 0.2 mA at an applied potential of 1.0 V.

Photodissolution of coal pyrite

Coal pyrite has been polarized anodically in the presence and absence of illumination. Photodissolution experiments were also carried out at fixed anodic potentials and the total dissolved iron was determined spectrophotometrically. The experimental data indicate the presence of significant photocurrents resulting in higher dissolution rates in the presence of illumination.

The functional organization of the crayfish lamina ganglionaris. II. Large-field spiking and nonspiking cells.

The functional properties of the multicolumnar interneurons of the crayfish lamina ganglionaris were examined by intracellular recording and the cell structures were revealed with the aid of Lucifer yellow or horseradish peroxidase iontophoresis. The multicolumnar monopolar cell M5 responds to a light pulse with a depolarizing compound EPSP and a burst of action potentials. Both the EPSP amplitude and the spike rate decay toward a lower level plateau in less than 200 ms after light onset. M5 is subject to surround inhibition, which is associated with a compound IPSP and net hyperpolarization of the membrane potential. Direct depolarization of M5 may provide a weak excitatory drive to medullary sustaining fibers (SF). Tangenital-cell type 1 (Tan1) has a broad expanse of neurites in the lamina (covering 10 to 15 cartridges) and a much narrower projection in the medulla (1 to 3 cartridges). The response to a light pulse has a long latency consistent with a polysynaptic receptor to Tan1 pathway. The response consists of a nearly rectangular hyperpolarization. Light 'off' elicits a depolarization and a burst of impulses. The polarity of the 'on' response can be reversed by hyperpolarizing the membrane by 23 mV. The receptive field is broad and the intensity-response function exceeds 4 log units. Direct hyperpolarization of Tan1 provides a strong excitatory signal to medullary SFs both in the dark and in the presence of illumination. We propose that Tan1 provides the principal steady-state excitatory drive to the SFs. Tangential-cell type 2 (Tan2) is distinguished from Tan1 by the extent and shape of the lamina process, which is a vertically oriented neurite spanning most of the lamina in a single plane. Functionally, Tan2 is similar in most respects to Tan1, but the response latency is much shorter, comparable to that of monopolar cells. T-cells may exhibit spontaneous impulse activity in the dark which is inhibited by a short latency hyperpolarizing light response. The receptive field, which is about 2 X larger than that of the columnar monopolar cells, is correlated with a small but multicolumnar dendritic arbor in the lamina. Since T-cells are aminergic, it is possible that the amines are normally released in the dark. A single amacrine cell was fully characterized. It exhibited a short latency hyperpolarizing response to light onset and a strong depolarizing 'off' response.(ABSTRACT TRUNCATED AT 400 WORDS)

Superlinearity of light-current characteristics of cds films grown in an oxygen-containing atmosphere

A study is made of features of the light-current characteristics (LCC) of thin cadmium sulfide films obtained by deposition of an aerosol of the reagent solution on a heated substrate. Nonlinearity of the film LCC and photosensitivity can be effectively controlled by thermooptical processing (specimen annealing in an air atmosphere in the presence of illumination). It is established that superlinearity of the specimen LCC is caused by an increase in charge carrier mobility with increase in the intensity of photo-excitation. A relatively weak change in nonequilibrium electron lifetime with a significant increase in their mobility leads to the conclusion that in such films the recombination centers which essentially determine carrier lifetime are located outside the region of intercrystallite barriers. The calculated LCC is slightly superlinear and is found to be in good agreement with experimental characteristics obtained for specimens grown or thermoprocessed in the absence of illumination.