Stressed liquid-crystal optical phased array for fast tip-tilt wavefront correction

A liquid-crystal optical phased-array technology that uses stressed liquid crystals provides a new type of tip-tilt wavefront corrector. It demonstrates a very fast time response (10 kHz) and high beam-steering efficiency (approximately 91%). The new technology presented here will allow for a nonmechanical, high-speed correction with simple device construction.     

A Queueing Model for Radio Nets--Part I: Methodology

In voice radio communication nets, digital-frequency assignment patterns and multiple-access discrete address transceivers are being studied to improve grade of service, mean access delay, and other aspects of system performance. An analytical methodology based on a calling system-outer system queueing model is presented. This model permits study of these radio communication problems and system design tradeoffs without computer simulation. In addition, the model utilizes several types of statistics (e.g., Poisson, Erlangian, or hyperexponential). In this paper, the model and the mathematical methodology are explained in detail. Formulas for equilibrium performance measures are derived from their definitions. The concept of station-busy probabilities is introduced and a matrix technique for obtaining numerical results is illustrated.     

Development of chemically engineered porous metal oxides for phosphate removal

In this study, the application of ordered mesoporous silica (OMS) doped with various metal oxides (Zr, Ti, Fe and Al) were studied for the removal of (ortho) phosphate ions from water by adsorption. The materials were characterized by means of N₂ physisorption (BET), powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). The doped materials had surface areas between 600 and 700 m² g⁻¹ and exhibited pore sizes of 44–64 Å. Phosphate adsorption was determined by measurement of the aqueous concentration of orthophosphate using ultraviolet–visible (UV–vis) spectroscopy before and after extraction. The effects of different metal oxide loading ratios, initial concentration of phosphate solution, temperature and pH effects on the efficiency of phosphate removal were investigated. The doped mesoporous materials were effective adsorbents of orthophosphate and up to 100% removal was observed under appropriate conditions. ‘Back extracting’ the phosphate from the doped silica (following water treatment) was also investigated and shown to have little adverse effect on the adsorbent.     

Large pore diameter MCM-41 and its application for lead removal from aqueous media

A room temperature method to create large pore size and pore volume ordered mesoporous silica (MCM-41) is demonstrated. Template removal was achieved with a microwave digestion procedure using a solution of nitric acid and hydrogen peroxide. The silica product exhibited an ordered hexagonal mesostructure, large pore volume (up to 0.99 cm(3)/g), and large pore size (up to 6.74 nm) indicating its potential as a high capacity adsorbent. Surface modification, to enhance the ability of the material to extract potentially toxic metals (PTMs) from water was performed using different amino- and mercapto-functional groups. This paper reports on the extraction of lead ions from aqueous solution to demonstrate the material's significant improvement in adsorption capacity (up to 1000 μmol g(-1) for lead). Moreover, methods have been developed to regenerate the sorbent allowing 100% recovery of Pb and reuse of the sorbent material in subsequent extractions. The performance of the material was also demonstrated for environmental samples containing relatively high concentrations (ppmv) of mixed metal ions reducing them to lower values (<100 ppbv) indicating that the sorbent may have applicability for environmental remediation of polluted water.     

A Queueing Model for Radio Nets--Part II: Results

In Part I of this paper an analytical methodology for quantitatively evaluating radio-communication nets was introduced and the details of the model and mathematics were explained. In this part of the paper the application of the methodology is quantitatively discussed. Results for particular net situations are presented. They are performance of single nets with multiple frequencies, nets with mutual signaling interference resulting from asynchronous signaling and a comparison of dedicated nets with a multiple access-discrete address system. The frequency spectrum savings for the latter use is also considered.     

Optical phased array technology

Optical phased arrays represent an enabling new technology that makes possible simple affordable, lightweight, optical sensors offering very precise stabilization, random-access pointing programmable multiple simultaneous beams, a dynamic focus/defocus capability, and moderate to excellent optical power handling capability. These new arrays steer or otherwise operate on an already formed beam. A phase profile is imposed on an optical beam as it is either transmitted through or reflected from the phase shifter array. The imposed phase profile steers, focuses, fans out, or corrects phase aberrations on the beam. The array of optical phase shifters is realized through lithographic patterning of an electrical addressing network on the superstrate of a liquid crystal waveplate. Refractive index changes sufficiently large to realize full-wave differential phase shifts can be effected using low (<10 V) voltages applied to the liquid crystal phase plate electrodes. High efficiency large-angle steering with phased arrays requires phase shifter spacing on the order of a wavelength or less; consequently addressing issues make 1-D optical arrays much more practical than 2-D arrays. Orthogonal oriented 1-D phased arrays are used to deflect a beam in both dimensions. Optical phased arrays with apertures on the order of 4 cm by 4 cm have been fabricated for steering green, red, 1.06 μm, and 10.6 μm radiation. System concepts that include a passive acquisition sensor as well as a laser radar are presented     

Results of an Experiment in Channel Quality Monitoring

This paper presents results of an experiment in binary error estimation in near real time for quality-monitoring purposes. Received binary data transitions are processed to give upper and lower estimation bounds for the number of errors in a sample. These bounds are compared with the recorded number of errors.     

Technical Implications of Teleconference Service

Definitions of separated-groups teleconferences, as opposed to person-to-person video telephone service, are reviewed. The teleconference facility, in terms of an audio mode, a graphics mode, and a video mode, can have an impact on the interactive, interpersonal communication process. Recent audio and audio/video teleconference experiments are summarized. Audio and video limitations of current technology have the potential of increasing transmission bandwidths and terminal complexity. For a large channel CATV network of more than 60 channels, teleconference service in the intracity context implies that CATV networks may have limited capacity for this service.