Review of atom probe FIB-based specimen preparation methods.

Several FIB-based methods that have been developed to fabricate needle-shaped atom probe specimens from a variety of specimen geometries, and site-specific regions are reviewed. These methods have enabled electronic device structures to be characterized. The atom probe may be used to quantify the level and range of gallium implantation and has demonstrated that the use of low accelerating voltages during the final stages of milling can dramatically reduce the extent of gallium implantation.     

Dihydroazulene-Azobenzene-Dihydroazulene Triad Photoswitches

Photoswitch triads comprising two dihydroazulene (DHA) units in conjugation with a central trans-azobenzene (AZB) unit were prepared in stepwise protocols starting from meta- and para-disubstituted azobenzenes. The para-connected triad had significantly altered optical properties and lacked the photoactivity of the separate photochromes. In contrast, for the meta-connected triad, all three photochromes could be photoisomerized to generate an isomer with two vinylheptafulvene (VHF) units and a cis-azobenzene unit. Ultrafast spectroscopy of the photoisomerizations revealed a fast DHA-to-VHF photoisomerization and a slower trans-to-cis AZB photoisomerization. This meta triad underwent thermal VHF-to-DHA back-conversion with a similar rate of all VHFs, independent of the identity of the neighboring units, and in parallel thermal cis-to-trans AZB conversion. The experimental observations were supported by computation (excitation spectra and orbital analysis of the transitions).     

Divide-and-conquer memetic algorithm for online multi-objective test paper generation

Online test paper generation (Online-TPG) generates a test paper automatically online according to user specification based on multiple assessment criteria, and the generated test paper can then be attempted online by user. Online-TPG is challenging as it is a multi-objective optimization problem that is NP-hard, and it is also required to satisfy the online generation requirement. In this paper, we propose an efficient multi-objective optimization approach based on the divide-and-conquer memetic algorithm (DAC-MA) for Online-TPG. Instead of solving the multi-objective constraints simultaneously, the set of constraints is divided into two subsets of relevant constraints, which can then be solved separately and effectively by evolutionary computation and local search of DAC-MA. The empirical performance results have shown that the proposed approach has outperformed other TPG techniques in terms of runtime efficiency and paper quality.     

Micropipette tips--the unsung heroes of mass spectrometry

Micropipette tip (tip) pipetting accuracy and precision are functions of tip manufacture consistency, morphological variation, and retained inner tip wall particulate matter. Irregular tip inner wall surfaces and retained particulate matter cause pipetting inaccuracy. Washed and unwashed tips from seven manufacturers were compared using weight by difference (six), microscopic Luxol Fast Blue staining (seven), and matrix-assisted laser desorption/onization time-of-flight (MALDI-TOF) mass spectrometry (six). Photomicrographs revealed tip irregularity and inner wall retained particulate matter. Computer model analysis was used to identify tip irregularity and retained matter. These tests established the utility of a pipette solvent wash to increase the performance and the accuracy of tips and, thus, improve the MALDI mass spectra obtained.     

Vacuum electron acceleration by coherent dipole radiation

The validity of the concept of laser-driven vacuum acceleration has been questioned, based on an extrapolation of the well-known Lawson-Woodward theorem, which stipulates that plane electromagnetic waves cannot accelerate charged particles in vacuum. To formally demonstrate that electrons can indeed be accelerated in vacuum by focusing or diffracting electromagnetic waves, the interaction between a point charge and coherent dipole radiation is studied in detail. The corresponding four-potential exactly satisfies both Maxwell's equations and the Lorentz gauge condition everywhere, and is analytically tractable. It is found that in the far-field region, where the field distribution closely approximates that of a plane wave, we recover the Lawson-Woodward result, while net acceleration is obtained in the near-field region. The scaling of the energy gain with wave-front curvature and wave amplitude is studied systematically.     

Consequences and benefits of utilizing continuous vibro-impact representations in constrained pipeline conveying fluid systems

The effectiveness of continuous vibro-impact forcing representations for the cantilevered pipe that conveys fluid is explored and analyzed. The previously accepted forcing model utilizing a smoothened trilinear spring is estimated using three continuous forcing representations, namely, polynomial, rational polynomial, and hyperbolic tangent. The accuracy of the estimated forcing functions is investigated and analyzed by calculating the root mean square error, and bifurcation diagrams are generated and compared to the nominal system. Additionally, the dynamic response of the system is further characterized using Poincare maps, power spectra, and basins of attraction. Once all continuous forcing representations are analyzed and compared to the nominal system, the computational cost of each method is examined, and further limitations of the hyperbolic tangent method are discovered. It is proved that the hyperbolic tangent forcing representation most accurately captures the dynamic response of the pipeline, and the least accurate representation is the rational polynomial representation. Additionally, considerable computational cost is saved when employing the hyperbolic tangent representation compared to the discontinuous representation.