Knickpoint analysis of streams in North Dakota, South Dakota, and Nebraska

Analysis of stream profiles, seismic reflection studies, engineering studies, and historical earthquakes indicates uplift in south-central South Dakota and north-central Nebraska over the last 5-10 ma. The purpose of this study was to determine if this uplift could be detected by constructing topographic profiles along, and in close proximity to several streams in this region. The Cannonball River, ND, was used to compare the streams in South Dakota and Nebraska to a stream beyond the affected area. Data for the profiles were collected from 7 .5 minute topographic maps as well as GPS surveys. Abrupt changes in slope (irregularities) were determined along the profiles based on visual inspection and spreadsheet calculation. The use of spreadsheet calculation assured consistency in identification of irregularities among profiles. Profiles constructed along and in close proximity to streams in the study area contain numerous irregularities. In general, the profiles in close proximity to the streams (land surface profiles) show more irregularities than stream profiles. This is partly related to the method of construction of land surface profiles. Examination of the profiles has shown that some of the identified irregularities are the result of lithologic changes while others are the result of tributary streams. However, the reasons for many of the irregularities, which may include recent uplift, are not apparent and need to be field checked. Future work should also involve collection of more data through GPS surveying, which would increase the data base from which profiles can be constructed

Acoustic phonon dynamics in thin-films of the topological insulator Bi2Se3

Transient reflectivity traces measured for nanometer-sized films of the topological insulator Bi2Se3 revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ~35 to ~70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40 nm. The amplitude of oscillations decays rapidly for films below 15 nm thick when the indirect intersurface coupling in Bi2Se3 films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi2Se3

Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Transient reflectivity measurements of thin films, ranging from 6 to 40 nm in thickness, of the topological insulator Bi2Se3 revealed a strong dependence of the carrier relaxation time on the film thickness. For thicker films the relaxation dynamics are similar to those of bulk Bi2Se3, where the contribution of the bulk insulating phase dominates over that of the surface metallic phase. The carrier relaxation time shortens with decreasing film thickness, reaching values comparable to those of noble metals. This effect may result from the hybridization of Dirac cone states at the opposite surfaces for the thinnest films

Manipulation of prenatal hormones and dietary phytoestrogens during adulthood alter the sexually dimorphic expression of visual spatial memory

BACKGROUND: In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit higher performance levels compared to females (a difference attributed to sex steroid hormonal influences). Based upon the results from our companion investigation, this study examined the influence of prenatal sex steroid hormone manipulations on VSM in adulthood, as assessed in the radial arm maze. Additionally, the influence of dietary soy phytoestrogens (i.e., the presence of high or low estrogen-like compounds present in the animal's diet) on VSM was examined in combination with the prenatal hormonal manipulations. RESULTS: Radial arm maze performance on a phytoestrogen-rich diet: 1) females treated prenatally with testosterone were masculinized and acquired/performed in a manner similar to control or oil-treated males and 2) males treated prenatally with an androgen receptor blocker (flutamide) were feminized and acquired/performed in a fashion typical of control or flutamide-treated females. When a diet change was initiated in adulthood, control phytoestrogen-rich fed females outperformed control females switched to a phytoestrogen-free diet. Whereas, in control males the opposite diet effect was identified. Furthermore, flutamide-treated males fed a phytoestrogen-rich diet outperformed flutamide-treated males switched to a phytoestrogen-free diet. CONCLUSIONS: These results suggest that prenatal hormonal manipulations significantly sex-reverse the normal sexually dimorphic expression of VSM. Specifically, VSM was enhanced in females treated with testosterone and inhibited in males treated with flutamide. Finally, dietary soy phytoestrogens set a bias on learning and memory in these hormonally manipulated animals in a predictable manner and these data confirm and extend the findings in our companion paper (see Lund etal, BMC Neuroscience 2001 2:20)

Finding Respondents in the Forest: A Comparison of Logistic Regression and Random Forest Models for Response Propensity Weighting and Stratification

Survey response rates for modern surveys using many different modes are trending downward leaving the potential for nonresponse biases in estimates derived from using only the respondents. The reasons for nonresponse may be complex functions of known auxiliary variables or unknown latent variables not measured by practitioners. The degree to which the propensity to respond is associated with survey outcomes casts light on the overall potential for nonresponse biases for estimates of means and totals. The most common method for nonresponse adjustments to compensate for the potential bias in estimates has been logistic and probit regression models. However, for more complex nonresponse mechanisms that may be nonlinear or involve many interaction effects, these methods may fail to converge and thus fail to generate nonresponse adjustments for the sampling weights. In this paper we compare these traditional techniques to a relatively new data mining technique- random forests – under a simple and complex nonresponse propensity population model using both direct and propensity stratification nonresponse adjustments. Random forests appear to offer marginal improvements for the complex response model over logistic regression in direct propensity adjustment, but have some surprising results for propensity stratification across both response models

Germination responses of a dry sclerophyll forest soil-stored seedbank to fire related cues

Fire is an integral component of many ecosystems worldwide. Many plant species require fire-related cues, primarily heat and smoke, to trigger germination. Despite the importance of this process, the responses of many Australian species to these cues are unknown. Without this knowledge fire management strategies may be developed that are inappropriate for individual species and vegetation communities. In this study we examined the responses of a dry sclerophyll forest seed bank to heat and smoke germination cues. Analysis was possible for 48 taxa within the soil seedbank with 34 of these showing a response to one or both of the germination cues. 10 species responded to the heat treatment, 11 species responded to the smoke treatment and 13 species responded to both the heat and smoke treatments. Germination cues acted independently for all species considered. Results in this study were consistent with published reports for most species, although some differences were seen at the species and genus level. The study highlights the importance of fire-related cues in enhancing germination of a large proportion of the species occurring in dry sclerophyll forests

Wolff's Theorem on Ideals for Matrices

We extend Wolff's theorem concerning ideals on H-infinity(D) to the matrix case, giving conditions under which an H-infinity solution G to the equation FG = H exists for all z in D, where F is an m-by-infinity matrix of functions in H-infinity (D), and H is an m-by-1 vector of such functions. We then examine several useful results