University of Texas at Dallas

About: University of Texas at Dallas is a education organization based out in Richardson, Texas, United States. It is known for research contribution in the topics: Population & Computer science. The organization has 14986 authors who have published 35589 publications receiving 1293714 citations. The organization is also known as: UT-Dallas & UT Dallas.

Topological negative refraction of surface acoustic waves in a Weyl phononic crystal

Abstract: Reflection and refraction of waves occur at the interface between two different media. These two fundamental interfacial wave phenomena form the basis of fabricating various wave components, such as optical lenses. Classical refraction—now referred to as positive refraction—causes the transmitted wave to appear on the opposite side of the interface normal compared to the incident wave. By contrast, negative refraction results in the transmitted wave emerging on the same side of the interface normal. It has been observed in artificial materials1–5, following its theoretical prediction6, and has stimulated many applications including super-resolution imaging7. In general, reflection is inevitable during the refraction process, but this is often undesirable in designing wave functional devices. Here we report negative refraction of topological surface waves hosted by a Weyl phononic crystal—an acoustic analogue of the recently discovered Weyl semimetals8–12. The interfaces at which this topological negative refraction occurs are one-dimensional edges separating different facets of the crystal. By tailoring the surface terminations of the Weyl phononic crystal, constant-frequency contours of surface acoustic waves can be designed to produce negative refraction at certain interfaces, while positive refraction is realized at different interfaces within the same sample. In contrast to the more familiar behaviour of waves at interfaces, unwanted reflection can be prevented in our crystal, owing to the open nature of the constant-frequency contours, which is a hallmark of the topologically protected surface states in Weyl crystals8–12. Sound waves in a specially designed crystal undergo ‘topologically protected’ negative refraction, whereby no reflection is allowed, at certain facets of the crystal and positive refraction at others.

Carbonatitic melts along the solidus of model lherzolite in the system CaO-MgO-Al2O3-SiO2-CO2 from 3 to 7 GPa

Abstract: We have experimentally determined the solidus position of model lherzolite in the system CaO-MgO-Al2O3-SiO2-CO2 (CMAS.CO2) from 3 to 7 GPa by locating isobaric invariant points where liquid coexists with olivine, orthopyroxene, clinopyroxene, garnet and carbonate. The intersection of two subsolidus reactions at the solidus involving carbonate generates two invariant points, I1A and I2A, which mark the transition from CO2-bearing to dolomite-bearing and dolomite-bearing to magnesite-bearing lherzolite respectively. In CMAS.CO2, we find I1A at 2.6 GPa/1230 °C and I2A at 4.8 GPa/1320 °C. The variation of all phase compositions along the solidus has also been determined. In the pressure range investigated, solidus melts are carbonatitic with SiO2 contents of <6 wt%, CO2 contents of ˜45 wt%, and Ca/(Ca+Mg) ratios that range from 0.59 (3 GPa) to 0.45 (7 GPa); compositionally they resemble natural magnesiocarbonatites. Volcanic magnesiocarbonatites may well be an example of the eruption of such melts directly from their mantle source region as evidenced by their diatremic style of activity and lack of associated silicate magmas. Our data in the CMAS.CO2 system show that in a carbonate-bearing mantle, solidus and near-solidus melts will be CO2-rich and silica poor. The widespread evidence for the presence of CO2 in both the oceanic and continental upper mantle implies that such low degree SiO2-poor carbonatitic melts are common in the mantle, despite the rarity of carbonatites themselves at the Earth's surface.

Are sex offenders dangerous

Abstract: Research Summary: Current legislation mandating DNA collection, civil commitment, registration, and community notification of sex offenders is predicated on the assumption that sex offenders are simply more dangerous than other types of offenders in that they inevitably re-offend. Moreover, many states are moving to expand sex offender legislation to include non-sexual offenders on the assumption that some offense types, such as burglary and robbery, serve as “gateway” offenses to sex crimes. The purpose of this research is to highlight two of the common perceptions underlying sex offender laws, and the extension thereof, and examine them in light of current empirical evidence. We employ analysis of variance techniques on Illinois arrest data from 1990 to 1997 to examine the degree to which sex offenders have higher proportions of repeat offending than other criminal categories and if some offense types serve as “gateway” or predicate offenses to sex crimes. Policy Implications: Our results suggest that the extension of sex offender laws to non-sexual offenders will likely have little effect on sexual victimization rates. More importantly, our results illustrate that policies can be founded on misconceptions, and these misconceptions not only have financial consequences, but also can affect the likelihood that the policies enacted will achieve their goals. If nothing else, this research suggests that policy makers need to become better informed on the issues they subject to far-reaching and costly legislation.

Optimal surface reconstruction from planar contours

Abstract: In many scientific and technical endeavors, a three-dimensional solid must be reconstructed from serial sections, either to aid in the comprehension of the object's structure or to facilitate its automatic manipulation and analysis. This paper presents a general solution to the problem of constructing a surface over a set of cross-sectional contours. This surface, to be composed of triangular tiles, is constructed by separately determining an optimal surface between each pair of consecutive contours. Determining such a surface is reduced to the problem of finding certain minimum cost cycles in a directed toroidal graph. A new fast algorithm for finding such cycles is utilized. Also developed is a closed-form expression, in terms of the number of contour points, for an upper bound on the number of operations required to execute the algorithm. An illustrated example which involves the construction of a minimum area surface describing a human head is included.

Model Uncertainty, Limited Market Participation and Asset Prices

Abstract: We demonstrate that limited participation can arise endogenously in the presence of model uncertainty. Our model generates novel predictions on how limited participation relates to equity premium and diversification discount. When the dispersion in investors' model uncertainty is small, full participation prevails in equilibrium. In this case, equity premium is unrelated to model uncertainty dispersion and a conglomerate trades at a price equal to the sum of its single segment counterparts. When model uncertainty dispersion is large, however, investors with relatively high uncertainty optimally choose to stay sidelined in equilibrium. In this case, equity premium can decrease with model uncertainty dispersion. This is in sharp contrast to the understanding in the existing literature that limited participation leads to higher equity premium. Moreover, when limited participation occurs, a conglomerate trades at a discount relative to its single segment counterparts. The discount increases in model uncertainty dispersion and is positively related to the proportion of investors not participating in the markets.