Two-dimensional modulation transfer function: a new perspective

One-dimensional templates, such as the U.S. Air Force resolution target or the circular spoke target, are commonly used for the characterization of imaging systems via the modulation transfer function response. It is shown in this paper that one needs a new family of templates for a true characterization of imaging systems that acquire two-dimensional (2D) high-density images or handle 2D information, such as 2D bar code detection and identification. The contrast provided by the newly defined 2D templates is the "true" contrast of the acquired image that the electronic processors are challenged with.     

Dispersions of Surface‐Modified Carbon Nanotubes in Water‐Soluble and Water‐Insoluble Polymers

Microscale aggregate formation, resulting from high intrinsic filler attractions, is one of the major issues in nanocomposite preparation and processing. Herein, the dispersive effects achieved by a wide range of surface‐active agents, as well as surface oxidation and functionalization, are investigated. The aim of our research is to form a uniform, multiwalled carbon nanotube (MWNT) distribution in water‐soluble (poly(ethylene glycol)) and water‐insoluble (polypropylene) polymers. In order to understand the surface‐charge‐related stability of the treated nanotubes solutions, zeta‐potential measurements are applied. Quantification of the state of the MWNT dispersion is derived from particle‐size analysis, while visual characterization is based on optical and electron microscopy. To estimate the nucleating ability of the surface‐modified carbon nanotubes, the temperature of crystallization and the degree of crystallinity are calculated from differential scanning thermograms. Finally, we suggest general guidelines to produce uniform MWNT dispersions using a dispersive agent and/or surface treatment in water‐soluble and water‐insoluble polymers.     

Scanning tunneling microscopy measurements of the initial erosion of graphite by hyperthermal atomic oxygen and neon

Highly ordered pyrolitic graphite (HOPG) was bombarded by low-energy (30eV) O⁺ and Ne⁺ at fluxes in the range of 10¹⁵–10¹⁶ ions cm⁻². The initial erosion of a few monolayers was studied with the aid of scanning tunneling microscopy (STM). Damage consisting of hillocks was observed for both O⁺ and Ne⁺, and the damage density increased with dose. O⁺-bombarded surfaces exhibited partial exfoliation of one to two monoatomic layers (propably as a result of chemical erosion), which was absent for Ne⁺ bombardment. Surface reconstruction of damaged areas was observed. The present work is the first step in an STM study of the effects of atomic oxygen erosion of graphite/epoxy composites in space.     

Wavelength-multiplexing system for single-mode image transmission

The expanding use of optical communication by means of optical fibers and the situation of drastically increasing amounts of data to be transmitted urge the exploration of novel systems permitting the transmission of large amounts of spatial information by fiber with smaller spatial resolution. An optical encoding and decoding system is suggested for transmitting one- or two-dimensional images by means of a single-mode fiber. The superresolving system is based on wavelength multiplexing of the input spatial information, which is achieved with diffractive optical elements. Preliminary experimental results demonstrate the capabilities of the suggested method for the one- and two-dimensional cases.     

Respiratory function in poultry workers and pharmacologic characterization of poultry dust extract

The Sj?bring system of personality dimensions measuring intellectual capacity, activity, impulsivity and sociability was used to study possible "salutogenic" (i.e. causes of health) effects. The study comprised 590 subjects investigated in 1947, 1957, 1972 and 1988-1989 in the Lundby project, an epidemiological study in Sweden. Psychiatric diagnoses were made in 1947, 1957 and 1972. Mental health was estimated in 1988-1989 using the concept "love well, work well, play well and expect well". The Sj?bring dimensions were clinically assessed in 1972. Both in the concurrent study in 1972 and in the prospective study in 1988-1989 "super capacity" (high intellectual function), "super validity" (high activity level) and "super solidity" (low impulsivity) were statistically associated with lower frequencies of certain psychiatric diagnoses and a higher frequency of positive mental health. These variables are proposed to increase coping capacity, and therefore increase stress resilience.     

High-efficiency arbitrary array generator

Implementation of a beam-shaping system, whereby an arbitrary array of spots is generated, is proposed. The suggested beam-shaping generator, which is based on the Gerchberg-Saxton algorithm, contains two phase-only filters and thus yields a very-high-power throughput. The flexibility of the suggested approach is demonstrated with some computer simulations.     

Polyethylene fibers-polyethylene matrix composites: Preparation and physical properties

Drawing on the difference in melting points of UHMPE fiber (150°C) and HDPE matrix (130°C), single-polymer composites were fabricated under various processing conditions. Because of the chemical similarity of the composite components, good bonding at the fiber-matrix interface could be expected. The matrix, the fiber, and unidirectional composite laminae were studied using TMA and DSC analyses, a hot-stage crystallization unit attached to a polarizing microscope, and an universal tensile testing machine. The TMA showed negative thermal expansion of the fiber over the complete temperature range of the experiment. Three regimes of contraction according to the values of the thermal expansion coefficient were detected. DSC analyses of either the fiber or the composite specimens did not show any appreciable changes after various thermal treatments. They also showed no evidence of fiber relaxation during manufacture, probably because of the pressure-related transverse constraint. The tensile strength and modulus values of the composite appeared to be fairly high and close to those reported for other composites reinforced with polyethylene (PE) fibers. An apparent maximum on the temperature dependencies of tensile properties was observed. A study of the matrix microstructure did not give any proof of transcrystalline growth at the fiber-matrix interface even for chemical or plasma surface-treated fibers. © 1993 John Wiley & Sons, Inc.     

Br treated graphite nanoplatelets for improved electrical conductivity of polymer composites

The graphite nanoplatelets (GNP) were treated by vapor-phase bromination. The increase in weight and atomic concentration of Br indicated the bromine uptake. The intercalation of Br between graphene layers of GNP was confirmed by the X-ray diffraction result, showing an increase in the interlayer spacing from 3.342 Å to 3.361 Å. Two types of bonds between C and Br were introduced simultaneously, ionic and covalent bonds, both of them increased with bromination duration. The fraction of ionic bond reached the highest value by 3 h Br exposure, which corresponded to the highest electrical conductivity of GNP. Although the bromination treatment did not change the percolation threshold of composites, it increased the absolute value of electrical conductivity of composites when the filler content was higher than the percolation threshold.     

Real-time spatial-temporal signal processing with opticalnonlinearities

The instantaneous response time of parametric optical nonlinearitics enable real-time processing of, and interaction between, spatial and temporal optical waveforms. We review the various signal-processing alternatives based on three- and four-wave-mixing arrangements among spatial and temporal information carrying waveforms. The fast response time of the interaction permits information exchange between the time and space domains, providing the ability to correlate and convolve signals from the two domains. We demonstrate the usefulness of real-time signal processing with optical nonlinearities with the following experiments: converting waveforms from the time to space domain as well as from the space to time domain, spectral phase conjugation and spectral inversion of ultrafast waveforms, transmission of the spatial correlation function on an ultrafast waveform, and a suggestion for a single-shot triple autocorrelation measurement