Effect of excess iron on oxidative dehydrogenation of 1-butene over a series of zinc ferrite catalysts

The influence of excess Fe3+ in ZnFe2O4 for the catalytic oxidative dehydrogenation of 1-butene to 1, 3-butadiene was investigated to try to clarify inconsistencies in the existing literature. A series of nanoscale zinc ferrite powders were produced with increasing Fe: Zn ratios. The materials were characterized by a range of techniques, which showed the presence of α-Fe2O3 as a distinct phase with an increasing excess of Fe3+ and SEM highlighted the increased presence of surface structures on the ferrites at higher Fe: Zn ratios. Reaction testing showed α-Fe2O3to be virtually inactive for the oxidative dehydrogenation of 1-butene. Results for the ferrite catalysts showed a significant decrease in both conversion and yield with an increasing excess of Fe3+. Therefore an excess of Fe3+ has a negative effect on catalytic activity and selectivity of zinc ferrite for the oxidative dehydrogenation of 1-butene, but acts as a promoter for competing hydrogenation and combustion side reactions

A refined estimate for the topological degree

We sharpen an estimate of Bourgain, Brezis, and Nguyen for the topological degree of continuous maps from a sphere $\mathbb{S}^d$ into itself in the case $d \ge 2$. This provides the answer for $d \ge 2$ to a question raised by Brezis. The problem is still open for $d=1$

Documented AIDS Cases as the Basis for Projections of Adolescence HIV Infections in the US

Twenty percent of AIDS cases in the U.S. occur in individuals in the age range 20 to 29. The mean incubation time, the time from infection to the onset of AIDS, is in the order of 8 years. Therefore, most of these AIDS cases represent HIV infections that occurred during mid- to late-adolescence. About 800 officially reported cases in the age group 13 to 19 have occurred in the U.S. This low occurrence of AIDS should not be a source of complacency in assessing the need to provide education and behavioral alternatives to this age group. As the predominate mode of transmission of HIV infection shifts from gay-male behaviors and intravenous drug abuse (IVDA) to heterosexual intercourse, adolescents may be at significantly increased risk. The occurrence of STDs and early pregnancies indicate a significant rate of high-risk sexual behaviors in adolescents in the U.S. The rate of adolescent HIV infections can be projected by extrapolation from historical data and by epidemiological modeling and computer simulation. The rates of infection projected by these methods are sufficiently congruent to lend credibility to them. A rate of new HIV infections, in individuals in the age range of 13 to 19, in the order of 300,000 annually should be anticipated within the next 10 years

Homoclinic orbits and chaos in a pair of parametrically-driven coupled nonlinear resonators

We study the dynamics of a pair of parametrically-driven coupled nonlinear mechanical resonators of the kind that is typically encountered in applications involving microelectromechanical and nanoelectromechanical systems (MEMS & NEMS). We take advantage of the weak damping that characterizes these systems to perform a multiple-scales analysis and obtain amplitude equations, describing the slow dynamics of the system. This picture allows us to expose the existence of homoclinic orbits in the dynamics of the integrable part of the slow equations of motion. Using a version of the high-dimensional Melnikov approach, developed by Kovacic and Wiggins [Physica D, 57, 185 (1992)], we are able to obtain explicit parameter values for which these orbits persist in the full system, consisting of both Hamiltonian and non-Hamiltonian perturbations, to form so-called Shilnikov orbits, indicating a loss of integrability and the existence of chaos. Our analytical calculations of Shilnikov orbits are confirmed numerically

Coherent Diffusion of Polaritons in Atomic Media

Coherent diffusion pertains to the motion of atomic dipoles experiencing frequent collisions in vapor while maintaining their coherence. Recent theoretical and experimental studies on the effect of coherent diffusion on key Raman processes, namely Raman spectroscopy, slow polariton propagation, and stored light, are reviewed in this Colloquium.Comment: Submitted to Review of Modern Physic

MAMS: High resolution atmospheric moisture/surface properties

Multispectral Atmospheric Mapping Sensor (MAMS) data collected from a number of U2/ER2 aircraft flights were used to investigate atmospheric and surface (land) components of the hydrologic cycle. Algorithms were developed to retrieve surface and atmospheric geophysical parameters which describe the variability of atmospheric moisture, its role in cloud and storm development, and the influence of surface moisture and heat sources on convective activity. Techniques derived with MAMS data are being applied to existing satellite measurements to show their applicability to regional and large process studies and their impact on operational forecasting

Signal Amplification by Sensitive Control of Bifurcation Topology

We describe a novel amplification scheme based on inducing dynamical changes to the topology of a bifurcation diagram of a simple nonlinear dynamical system. We have implemented a first bifurcation-topology amplifier using a coupled pair of parametrically driven high-frequency nanoelectromechanical systems resonators, demonstrating robust small-signal amplification. The principles that underlie bifurcation-topology amplification are simple and generic, suggesting its applicability to a wide variety of physical, chemical, and biological systems

Mammals of Spanish Peaks State Wildlife Area, Colorado

Habitats and relative abundance of small mammals in the Spanish Peaks State Wildlife Area in western Las Animas Co., Colorado, were assessed. A total of 821 mammals of 20 species was collected in 2750 trapnights between 31 May and 19 August of 1981. Eight additional species of mammals were observed on the wildlife area but not documented. The deer mouse (Peromyscus maniculatus) and rock mouse (P. difficilis) were the most abundant small mammals, accounting for 63 and 16%, respectively, of the total catch. The deer mouse was the only species caught in every habitat sampled. Abert\u27s squirrel (Sciurus abert,) previously has not been recorded in Colorado from as far southeast as the Spanish Peaks State Wildlife Area. The mammalian fauna of Colorado has been the subject of numerous studies since the late 1800s. Early studies were by Cockerell (1890), Warren (1906), Cary (1911), and Warren (1942, published posthumously). More recent investigations include the book by Lechleitner (1969), the exhaustive compilation by Armstrong (1972), and the latilong surveys by Bissell (1978, 1982). In spite of these studies, several regions of Colorado remain poorly represented in collections. Armstrong (1972) noted that certain poorly surveyed parts of the western two-thirds of the state appear to me to be ... significant from the standpoint of zoogeography. Western Las Animas County--the Park Plateau and Culebra Range [of the Sangre de Cristo Mountains]--is such an area. In a later publication, Armstrong et al. (1973) noted that additional field investigations were needed in the vicinity of the Wet Mountains, a biogeographically important region where several species of grassland mammals reach altitudinal extremes and certain southern species reach northern limits. With this in mind, the Colorado Division of Wildlife initiated fieldwork in the Spanish Peaks State Wildlife Area to sample the vertebrate fauna in general and to assess habitat associations and relative abundance of small mammals in particular. This report documents the mammals collected and observed in the Spanish Peaks State Wildlife Area during summer of 1981 and summarizes biological data on mammals obtained at that time.https://scholars.fhsu.edu/fort_hays_studies_series/1067/thumbnail.jp