The photoelectron-hole recombination in silver halide crystals is the major process responsible for the lack of conversion of light into the latent image. In order to favor the escape of electrons from recombination and to enhance the effective quantum yield, photographic emulsions are doped with Chini-type platinum carbonyl clusters [Pt3(CO)6]n2–(n = 6 − 9) which are known to behave as electron donors or acceptors. An increase in sensitivity of silver bromide of Δlog(I × texp) = 0.5 without fogging compared to undoped crystals is obtained through this process for a relative concentration of 5 × 10–5 Pt atoms per silver ion and an intermediate intensity. The attenuation of HIRF (Δlog(I × texp) = 0.6 at high intensity) and mostly of LIRF (Δlog(I × texp) = 1.0 at low intensity) confirms that the doping contributes to lowering the electron-hole recombination and indicates that clusters act mainly as hole scavengers. The doping by clusters induces a sensitivity increase of Δlog(I × texp) = 0.26 for (S + Au) sensitized emulsions but causes no change in ultrasensitive formate doped emulsions. Similar results are obtained in AgCl crystals.
The force needed to detach spherical toner particles having a number average radius of 7.1 μm from an organic photoconductor was determined by ultracentrifugation. In the absence of any release agents applied to the photoconductor, it was found that only a small fraction of the toner particles could be removed from the photoconductor, even at the highest centrifugal accelerations (354,000 g). However, when the photoconductor was coated with a thin layer of zinc stearate, the release force was reduced substantially and detachment was readily achieved, the remaining release force varying with the square of the toner charge-to-mass ratio. Hence, the residual detachment force varied as the square of the particle charge. These results suggest that electrostatic forces become dominant when van der Waals forces are greatly reduced. Conversely, the large increase in toner adhesion to a photoconductor observed in the absence of a good release agent suggests that van der Waals forces may often dominate toner adhesion for this size particle.
The tribocharging behavior of toners in the toner/carrier system dictates the final output results of the electrophotographic system. However, the available theoretical models describe only the charging results in the equilibrium state and leave the charging during the transient state almost untouched. Therefore, in this paper the charging behavior of a toner-carrier development system were carefully examined and a dynamic model that could account for the charging process of both the transient and equilibrium states was constructed. The influences on charging due to the physical parameters of charging time, toner sizes, and toner concentration were studied by measuring the charge-to-mass ratio (Qt/Mt). The relationship between charges and charging surface was also studied. The predicted dynamic results from the model are in good agreement with the observed data.
This article details a simulation effort from first principles to evaluate the feasibility of using ink aerosols in a direct marking technology based on the ElectroPrint concept. This technology, called Acoustic Mist Imaging (AMI), uses acoustic or other nebulizer mechanisms to create a fine mist of droplets, which are then charged and directed onto a print medium to record the image. Drop charging is modeled using two approximations: a very rapid ballistic impact scheme; and by tracking individual ion trajectories with a more compute intensive self-consistent drift attachment model. Charged drops are then individually tracked to deposit on a print medium, producing virtual pixels. Results are generated for square and circular apertures at 600 spi, and for combinations of stationary and moving aperture-print media configurations to quantify image smearing. Preliminary data indicates that the technology is capable of 600 spi and higher print resolutions. Even higher resolution is achievable by synchronizing the velocities of both the print aperture and print medium, and by electrostatic focusing of the ion beam. Numerical experiments to duplicate the ElectroPrint images indicate that image smearing can be significantly reduced through a combination of uniform airflow velocity profile (slug flow) and increasing the deposition electric field.
A color gamut compression algorithm has been developed based on analysis of observer judgements in a previous interactive gamut mapping experiment. The new algorithm preserves the color relationships between the original and reproduced images, by matching the local conformations of the source and destination gamut boundaries. A core gamut is constructed inside the destination gamut boundary, within which no compression occurs, i.e., color is preserved unchanged. Colors outside the destination gamut are mapped into the region between the core and destination gamut boundaries in a reversible manner. The results of an experiment are reported, indicating that the new algorithm performed well but that scope remains for further improvement.
This study aims at modeling ink spreading in order to improve the prediction of the reflection spectra of three ink color prints. Ink spreading is a kind of dot gain which causes significant color deviations in ink jet printing. We have developed an ink spreading model which requires the consideration of only a limited number of cases. Using a combinatorial approach based on Pólya's counting theory, we determine a small set of ink drop configurations which allows us to deduce the ink spreading in all other cases. This improves the estimation of the area covered by each ink combination that is crucial in color prediction models. In a previous study, we developed a unified color prediction model. This model, augmented by the ink spreading model, predicts accurately the reflection spectra of halftoned samples printed on various ink jet printers. For each printer, the reflection spectra of 125 samples uniformly distributed in the CMY color cube were computed. The average prediction error between measured and predicted spectra is about ΔE = 2.5 in CIELAB. Such a model simplifies the calibration of ink jet printers, as well as their recalibrations when ink or paper is changed.
In this article an improvement to a current methodology for testing iterative reconstruction methods is presented. This improvement consists in the use of a multidimensional global optimization algorithm for the best estimate of the free parameters of the reconstruction process. This algorithm is based on a probabilistic random search method. The global optimization algorithms allow us to achieve the best performance of the reconstruction algorithms in order to compare them under the optimal conditions. This methodology has been applied for the testing of a MART (Multiplicative Algebraic Reconstruction Technique) algorithm performance using the classical cubic-shaped voxels and spherical symmetric basis functions, also known as blobs, as the basis functions for the image representation in 3D X-ray cone-beam transmission tomography.
The title compound (BP-DPP), known as a red pigment as well as a photoconductor for photoreceptors, is characterized by an extremely large bathochromic shift upon crystallization, as compared with other DPP analogues. The electronic structure of BP-DPP has therefore been investigated from the standpoint of crystal structure and exciton coupling effects. BP-DPP is found to crystallize in the “bricks in a brick wall” fashion, just like J-aggregates in cyanine dyestuffs. On the molecular plane of BP-DPP, there are chains of intermolecular hydrogen bonds between the NH group of one molecule and the O atom of the neighboring one. The hydrogen bond aligns the transition dipoles in a fashion “head-to-tail”, leading to a bathochromic displacement of the absorption maximum. Additionally, there are diagonal pairs of the brick wall structure whose exciton coupling again induces a bathochromic shift. Both the hydrogen bond in the molecular plane and the brick wall structure along the molecular stack are found to displace significantly the absorption band toward longer wavelengths on going from solution to the solid state.
We observed sulfur sensitization centers, which were formed on octahedral silver bromide grains in emulsions and decorated with silver clusters by means of an amplification treatment with a special physical developer. The concentration of the centers increased with increasing the amount of the sensitizer, and reached a plateau with the amount that gave the maximum sensitivity. The concentration of the centers, which gave the maximum sensitivity, was as many as 3200 per μm2, and the same as the concentration of fog centers formed with excessive amount of the sensitizer. The comparison of the concentration of the observed centers with the amount of silver sulfide formed by sulfur sensitization revealed that each sulfur sensitization center contained two sulfide ions in the emulsion with the maximum sensitivity. This result supported the idea that the sulfur sensitization centers were dimers of silver sulfide, as proposed by Keevert and Gokhale,1 Kanzaki and Tadakuma,2 and Tani.3