A military perspective on small unmanned aerial vehicles

In recent years, advancements in three technology areas, microelectronics, MEMS sensors, and GPS receivers, have allowed small UAVs to overcome critical deficiencies and become practical for insertion into the military mainstream. The maturation and commercialization of these technologies have resulted in readily available components that have decreased in both size and cost, to the point where truly low-cost, highly capable, small UAVs are possible. In particular, inertial devices such as MEMS accelerometers and angular rate sensors, pressure sensors, and magnetometers have reached the point where they are reliable, accurate, and affordable. These devices allow the determination of vehicle state with the precision required to enable autonomous flight. In addition, advanced microelectronic devices, such as digital signal processors, field programmable gate arrays, and microcontrollers have enabled sophisticated flight control functions, including fully autonomous flight using GPS waypoints. In combination, these advances have allowed small UAVs such as Pointer, Raven, and Dragon Eye to move into full-scale production and continue to allow the progression of UAVs into smaller and smaller packages. To address several of the deployment issues connected with small UAVs, a gun-launched version, along with the underpinning technologies, is under development. This device represents a clear departure from conventional UAVs with several clear advantages; however, it also contains severe design challenges, as well as test and evaluation dilemmas. An option of this type is envisioned not as a replacement for conventional small UAVs but rather as an augmenting capability.     

Observation of Mode Patterns for High Purity Mode Operation in the Submillimeter Wave Gyrotron FU VA

Operation tests of a cavity designed for high purity mode operation of the submillimeter wave gyrotron FU VA has been carried out successfully. The observed emission patterns of several cavity modes appear very pure and are compared with calculated results. High purity mode operation has the advantage of making the conversion to Gaussian-like beams more efficient.     

Electronic payment systems

Trusted electronic payment systems are a key enabler for mass acceptance of electronic commerce over insecure networks such as the Internet. This paper classifies the currently available payment systems on the Internet, and looks at likely payment systems for the future. The need for micropayments is also discussed.     

Surface photoabsorption monitoring of the growth of GaAs and InGaAs at 650°C by MOCVD

By monitoring the cyclic behavior of surface photoabsorption (SPA) reflectance changes during the growth of GaAs at 650°C and with sufficient H₂ purging time between the supply of trimethylgallium and AsH₃, we have been able to achieve controlled growth of GaAs down to a monolayer. Our results show, as confirmed by photoluminescence (PL) measurements, the possibility of growing highly accurate quantum well heterostructures by metalorganic chemical vapor deposition at conventional growth temperatures. We also present our PL measurements on the InGaAs single quantum wells grown at this temperature by monitoring the SPA signal.     

Structural properties of ZnSy Se1−yZnSe/GaAs (001) heterostructures grown by photoassisted metalorganic vapor phase epitaxy

ZnS_ySe_1−yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSy_ySe_1−y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is h_c ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnS_ySe_1−y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnS_ySe_1−y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ∼ 5.9%), rather than growth temperature lattice matching (y ∼ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by the near-band edge/deep level emission peak intensity ratio and the near band edge absolute peak intensity from 300K photoluminescence measurements.     

A design of experiment analysis of serial EEPROM endurance

The results of a study using a design of experiments approach to examine the effects of environmental operating conditions on serial EEPROM endurance are presented. The conditions studied in the experiment were operating temperature, applied voltage, device type, array usage, write cycles per day, data pattern, and write pulse width. An ANOVA table showing the significant effects and an estimation of the value of the effects using an error minimization technique is presented. While the techniques presented are relatively simple, they may be useful as a quick check of acceleration effects in EEPROM endurance cycling, without the use of extensive factorial experiments. The results show temperature, array size and voltage to be the most important effects on EEPROM endurance cycling. The temperature effect matches other published data.     

An anomalous acoustic effect during martensite transformations in NiTi-based alloys

Martensite transformations proceeding in mechanically loaded TiNi-based alloys account for an “anomalous” character of the acoustic emission from the material, whereby cyclic transformations during the growth of mechanical stress in the course of the direct transition is accompanied by an increase, rather than by a decrease, in the acoustic emission energy. This behavior of the acoustic emission is evidence of a significant influence of the external stresses on the martensite transformations and the related energy dissipation process.     

Membrane-based hybrid processes for high water recovery and selective inorganic pollutant separation

The removal of heavy metals (e.g. Pb(II), Cd(II), Cu(II), etc.) and oxyanions (e.g. nitrate, As(III, V), Cr(VI), etc.) is of immense interest for treatment of groundwater and other dilute aqueous systems. However, the presence of non-toxic components, such as hardness (Ca, Mg) and sulfate, can interfere with the separation of toxic species. For example, pressure-driven membrane processes, such as reverse osmosis (RO), have been limited for water treatment due to problems that these extraneous components cause with water recovery and ionic strength (osmotic pressure) of the retentate. In addition, nitrate rejection by RO is considerably lower than NaCl rejection, resulting in permeate concentrations that may be too high for groundwater recharging. Other separation systems that rely solely on sorption of toxic species (e.g. ion exchange resins) may not have sufficient selectivity for efficient use in the presence of competing ions. Hence, implementation of pressure-driven membrane separations and high capacity sorbents in hybrid processes shows much promise for remedying these difficulties. For example, selective separation of nitrate may be achieved by combining nanofiltration (NF) for sulfate removal, followed by RO or ion exchange for nitrate removal (see example 1). When small concentrations of toxic metals are present, the large retentate volumes of RO processes may be reduced by selective removal of toxic species with a high capacity sorbent, thus permitting disposal of a lower volume, non-toxic stream (see example 2). The use of microfiltration membrane-based sorbents containing multiple polymeric functional groups is a novel technique to achieve high metal sorption capacity under convective flow conditions. These sorbents are formed by the attachment of various polyamino acids (MW: 2500-10,000), such as polyaspartic acid (cation sorption), polyarginine (oxyanion sorption), and polycysteine (chelation exchange), directly on the membrane pore surfaces. Since these sorbents have also been found to have high selectivity over non-toxic metals, such as calcium, they are ideal candidates for hybrid processing with RO/NF.     

Visualizing chemical compositions and kinetics of sol-gel by near-infrared multispectral imaging technique

Kinetics of sol-gel formation were studied using the recently developed near-infrared (NIR) multispectral imaging instrument. This imaging spectrometer possesses all the advantages of conventional spectrometers. It also has additional features that NIR spectrometers cannot offer, namely, its ability to provide kinetic information at different positions within a sample. The high spatial resolution and sensitivity of the InSb camera make it possible for the imaging spectrometer to determine the kinetic from data recorded by a single pixel. Kinetics of sol-gel reactions, determined by this multispectral imaging instrument, show that the initial hydrolysis of the TEOS, MTES, or a mixture of these two alkoxysilanes is relatively inhomogeneous. The inhomogeneity is dependent on the number of pixels used to calculate the spectrum for each spot. Data calculated from a single pixel provide the largest inhomogeneity. No inhomogeneity was observed when an average of a large number of pixels (e.g., 10 x 10) is used for calculation. The inhomogeneities observed for TEOS sol-gels are different from those for the MTES sol-gels, and those for sol-gels prepared from a mixture of TEOS and MTES are relatively larger and more similar to those of the MTES sol-gels. A variety of reasons might account for the observed inhomogeneities including differences in the structure of the TEOS sol-gels and MTES sol-gels and the inability of the TEOS to mix well with MTES with the latter being more hydrophobic.