UV-induced Coulomb crystallization of dust grains in high-pressuregas

A scheme for forming a Coulomb lattice of positively charged dust grains in a high-pressure (P>torr) gas is discussed theoretically. The grains are charged positively by photoemission in the presence of a flux of ultraviolet (UV) photons with energy larger than the work function of the grains, but lower than the ionization potential of the background gas. Methods for levitating and containing the dust using photophoretic forces (both UV and non-UV), gas drag, and electrostatic forces are considered     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

Nature of subpicosecond terahertz pulse propagation in practical dielectric-filled parallel-plate waveguides

It is analytically shown that the presence of submicrometer-sized air gaps between the dielectric and metal contact surfaces in a dielectric-filled metallic parallel-plate waveguide can have a dramatic effect on the guided-wave propagation of subpicosecond terahertz pulses. Through the use of metal-evaporated dielectric surfaces to overcome the imperfect contact problem, and a special air-dielectric-air cascaded waveguide geometry to avoid multimode excitation, undistorted subpicosecond terahertz pulse propagation via the single-TEM mode is demonstrated, for what is believed to be the first time, in a silicon-filled PPWG.     

WRAO and OWA learning using Levenberg–Marquardt and genetic algorithms

The generalized Weighted Relevance Aggregation Operator (WRAO) is a non-additive aggregation function. The Ordered Weighted Aggregation Operator (OWA) (or its generalized form: Generalized Ordered Weighted Aggregation Operator (GOWA)) is more restricted with the additivity constraint in its weights. In addition, it has an extra weights reordering step making it hard to learn automatically from data. Our intension here is to compare the efficiency (or effectiveness) of learning these two types of aggregation functions from empirical data. We employed two methods to learn WRAO and GOWA: Levenberg–Marquardt (LM) and a Genetic Algorithm (GA) based method. We use UCI (University of California Irvine) benchmark data to compare the aggregation performance of non-additive WRAO and additive GOWA. We found that the non-constrained aggregation function WRAO was learnt well automatically and produced consistent results, while GOWA was learnt less well and quite inconsistently.     

Secondary emission from small dust grains at high electron energies

A previous model for secondary electron emission from small grains is modified to calculate yields for micron sized grains, both spherical and cylindrical, when the primary electrons constitute a high energy parallel beam. It is found that, in general, the secondary electron yield is significantly higher than for the case of normal incidence. Moreover, the equilibrium potentials of the grain are always positive due to this enhanced secondary emission. These results are compared with experimental data recently available for micron sized glass particles, and equilibrium potentials, calculated based on the model presented here, and are found to be in reasonably good agreement with their measured potentials     

Latin Squares with a Unique Intercalate

Suppose that and . We construct a Latin square of order n with the following properties:

• has no proper subsquares of order 3 or more .
• has exactly one intercalate (subsquare of order 2) .
• When the intercalate is replaced by the other possible subsquare on the same symbols, the resulting Latin square is in the same species as .

Hence generalizes the square that Sade famously found to complete Norton's enumeration of Latin squares of order 7. In particular, is what is known as a self‐switching Latin square and possesses a near‐autoparatopism.     

UV-induced Coulomb crystallization in a dusty gas

Conditions are investigated for forming a Coulomb lattice of dust grains which are charged positively by the ultraviolet induced photoemission of electrons     

Evolution of the premartensitic state in the NiAl phase of a NiCoCrAlY bond coat during thermal cycling

Transmission electron microscopy (TEM) is used to investigate the evolution of the premartensitic state in the NiAl-based β-phase in NiCoCrAlY bond coats during thermal cycling. Bright-field imaging and diffraction analysis confirm that the lattice modulation is in the form of {110} ?110? transverse displacement waves. High resolution electron microscopy (HREM) revealed an increase in modulation wavelength during thermal cycling due to the β-phase becoming progressively richer in Ni through superalloy–bond coat interdiffusion. Transverse modulations extending over large regions of the crystal were observed in the HREM images, inconsistent with previous theories attributing the origin of the premartensitic state to point defects that couple to the dynamic instability of the lattice.     

Autoparatopisms of Quasigroups and Latin Squares

Paratopism is a well‐known action of the wreath product on Latin squares of order n. A paratopism that maps a Latin square to itself is an autoparatopism of that Latin square. Let Par(n) denote the set of paratopisms that are an autoparatopism of at least one Latin square of order n. We prove a number of general properties of autoparatopisms. Applying these results, we determine Par(n) for . We also study the proportion of all paratopisms that are in Par(n) as .