An Assessment of Geographic and Taxonomic Biases in Research on Climate Change-Related Range Shifts

Geographic and taxonomic biases in ecological literature inhibit the ability of research to be generalized or translated to other systems. This is particularly true with research on climate change-related range shifts, where a diverse and representative set of observations is needed to understand the significant heterogeneity of range shifts and improve models. A literature review was conducted and biases were assessed by examining the geographic location of study areas, the taxonomic makeup of study species, and the location of study areas within species ranges. A substantial geographic skew towards terrestrial, mid-latitude North America and Europe was observed. However, taxonomic coverage was even and representative within plants and animals. At the level of individual species ranges, the vast majority of study areas were not representative and study areas failed to effectively include range extremes. Based on these results, scientists must more strategically design studies to include diverse geographic regions and to representatively capture range shifts throughout a species range

Evidence from Escalera al Cielo: Abandonment of a Terminal Classic Puuc Maya Hill Complex in Yucatán, Mexico

This is a postprint (author's final draft) version of an article published in Journal of Field Arhcaeology in 2012. The final version of this article may be found at http://dx.doi.org/10.1179/0093469012Z.00000000025 (login may be required). The version made available in OpenBU was supplied by the author.Excavations at the hilltop site of Escalera al Cielo, located in the Puuc Maya region of Yucatán, Mexico, have uncovered evidence of a planned abandonment at the end of the Terminal Classic period (A.D. 800–950). Six buildings investigated among three residential groups contain rich floor assemblages similar to those known from only a few rapidly abandoned sites in the Maya area. Through an analysis of de facto refuse—most of which was recovered in locations of storage and provisional discard—and midden refuse, this paper illustrates how the assemblages represent an example of household-level abandonment with anticipated return. We also consider Escalera al Cielo in light of our present understanding of the political and environmental history of the Puuc region during the late 9th century A.D

Terrace grading of SiGe for high-quality virtual substrates

Silicon germanium (SiGe) virtual substrates of final germanium composition x = 0.50 have been fabricated using solid-source molecular beam epitaxy with a thickness of 2 µm. A layer structure that helps limit the size of dislocation pileups associated with the modified Frank–Read dislocation multiplication mechanism has been studied. It is shown that this structure can produce lower threading dislocation densities than conventional linearly graded virtual substrates. Cross-sectional transmission electron microscopy shows the superior quality of the dislocation network in the graded regions with a lower rms roughness shown by atomic force microscopy. X-ray diffractometry shows these layers to be highly relaxed. This method of Ge grading suggests that high-quality virtual substrates can be grown considerably thinner than with conventional grading methods

Institutional analysis of standard setting in the United States : a preliminary exploration

This paper, one of a series resulting from institutional analysis of photovoltaic (PV) acceptance, discusses standards and the standard setting process in the United States. Standards, and the manner in which standards are established, can play a significant role in facilitating or impeding the acceptance of solar technologies. The objective of this paper is to provide an overview of standards for those concerned with ensuring the timely and appropriate acceptance of needed new energy sources in diverse economic and geographic sectors. The paper has three sections. The first provides a conceptual framework for understanding standards. The second section discusses a number of approaches for categorizing standards. Finally, the third section identifies the processes employed and the persons and organizations involved in the standards development process in the US.Prepared under Dept. of Energy Contract no. EX-76-A-01-2295, Task order no. 37

Hall mobility enhancement caused by annealing of Si0.2Ge0.8/Si0.7Ge0.3/Si(001) p-type modulation-doped heterostructures

The effect of post-growth furnace thermal annealing (FTA) on the Hall mobility and sheet carrier density measured at 9–300 K in the Si0.2Ge0.8/Si0.7Ge0.3/Si(001) p-type modulation-doped heterostructures was studied. FTA treatments in the temperature range of 600–900 °C for 30 min were performed on similar heterostructures but with two Si0.2Ge0.8 channel thicknesses. The annealing at 600 °C is seen to have a negligible effect on the Hall mobility as well as on the sheet carrier density. Increases in the annealing temperature resulted in pronounced successive increases of the mobility. For both samples the maximum Hall mobility was observed after FTA at 750 °C. Further increases of the annealing temperature resulted in a decrease in mobility. The sheet carrier density showed the opposite behavior with an increase in annealing temperature. The mechanism causing this behavior is discussed. Structural characterization of as-grown and annealed samples was done by cross-sectional transmission electron microscopy

Severe Convective Wind Environments

Nontornadic thunderstorm winds from long-lived, widespread convective windstorms can have a tremendous impact on human lives and property. To examine environments that support damaging wind producing convection, sounding parameters from Rapid Update Cycle model analyses (at 3-hourly intervals) from 2003 were compared with 7055 reports of damaging winds and 377 081 occurrences of lightning. Ground- relative wind velocity was the most effective at discriminating between damaging and nondamaging wind convective environments. Steep surface-based lapse rates (a traditional damaging wind parameter) gener- ally did not discriminate between damaging and nondamaging wind convective environments. Other pa- rameters, such as convective available potential energy, humidity aloft, and lapse rates aloft were moder- ately discriminating. This paper presents a composite damaging wind algorithm in which the two most discriminatory parameters were combined, yielding more skill than any individual parameter. Damaging wind environments are then examined further through a selection of cases that highlight common severe wind ingredients and failure modes. A primary result is that, even in seemingly favorable environments, when the winds at the top of the inflow layer were either parallel to the convective line or blowing from warm to cold over a front, damaging winds were less likely. In the former case, it appears that the downdraft winds and the cold pool’s gust-front-normal flow are not additive. In the latter case, it appears that convection becomes elevated and does not produce downdrafts that reach the surface. Combining the most discriminatory severe wind parameters with knowledge of these severe wind failure modes may help to improve the situational awareness of forecasters

Energy loss rates of two-dimensional hole gases in inverted Si/Si0.8Ge0.2 heterostructures

We have investigated the energy loss rate of hot holes as a function of carrier temperature TC in p-type inverted modulation-doped (MD) Si/SiGe heterostructures over the carrier sheet density range (3.5–13)×1011 cm–2, at lattice temperatures of 0.34 and 1.8 K. It is found that the energy loss rate (ELR) depends significantly upon the carrier sheet density, n2D. Such an n2D dependence of ELR has not been observed previously in p-type SiGe MD structures. The extracted effective mass decreases as n2D increases, which is in agreement with recent measurements on a gated inverted sample. It is shown that the energy relaxation of the two-dimensional hole gases is dominated by unscreened acoustic phonon scattering and a deformation potential of 3.0±0.4 eV is deduced

Misfit strain relaxation and dislocation formation in supercritical strained silicon on virtual substrates

Relaxation of strained silicon on 20% linear graded virtual substrates was quantified using high resolution x-ray diffraction and a defect etching technique. The thickness of strained silicon was varied between 10 and 180 nm. Relaxation was observed in layers below the critical thickness but increased to only 2% relaxation in the thickest layers even with annealings up to 950 °C. Cross-sectional transmission electron microscopy revealed stacking faults present in layers thicker than 25 nm, and nucleated 90° Shockley partial dislocations forming microtwins in the thickest layer. These features are implicated in the impediment of the relaxation process