University of Colorado Boulder

About: University of Colorado Boulder is a education organization based out in Boulder, Colorado, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 48794 authors who have published 115151 publications receiving 5387328 citations. The organization is also known as: CU Boulder & UCB.

Artificial neural networks for RF and microwave design - from theory to practice

Abstract: Neural-network computational modules have recently gained recognition as an unconventional and useful tool for RF and microwave modeling and design. Neural networks can be trained to learn the behavior of passive/active components/circuits. A trained neural network can be used for high-level design, providing fast and accurate answers to the task it has learned. Neural networks are attractive alternatives to conventional methods such as numerical modeling methods, which could be computationally expensive, or analytical methods which could be difficult to obtain for new devices, or empirical modeling solutions whose range and accuracy may be limited. This tutorial describes fundamental concepts in this emerging area aimed at teaching RF/microwave engineers what neural networks are, why they are useful, when they can be used, and how to use them. Neural-network structures and their training methods are described from the RF/microwave designer's perspective. Electromagnetics-based training for passive component models and physics-based training for active device models are illustrated. Circuit design and yield optimization using passive/active neural models are also presented. A multimedia slide presentation along with narrative audio clips is included in the electronic version of this paper. A hyperlink to the NeuroModeler demonstration software is provided to allow readers practice neural-network-based design concepts.

Digging deeper to find unique microbial communities: The strong effect of depth on the structure of bacterial and archaeal communities in soil

Abstract: Microorganisms exist throughout the soil profile and those microorganisms living in sub-surface horizons likely play key roles in nutrient cycling and soil formation However, the distributions of microbes through the soil profile remain poorly understood, as most studies focus only on those communities found in near-surface horizons Here we examined how microbial community structure changes within soil profiles, whether these changes are similar across soils from different landscape positions, and how the community-level variation within individual soil depth profiles compares to the variation across surface soils from a wide range of biomes We characterized changes in bacterial and archaeal community composition and diversity with depth through nine soil profiles located in a forested montane watershed in Colorado, USA Microbial community composition was determined by barcoded pyrosequencing of the 16S rRNA gene employing a primer set that captures both bacteria and archaea Relative microbial biomass and soil carbon concentrations decreased exponentially with depth while soil pH increased in nearly all of the profiles examined Bacterial diversity was typically highest in the top 10 cm of the profile; diversity typically dropped by 20–40% from the surface horizons to the deepest horizons sampled Community composition was significantly affected by soil depth in all profiles, driven primarily by a decline in the relative abundance of Bacteroidetes with depth and the peak in the relative abundance of Verrucomicrobia between 10 and 50 cm Microbial community composition across the nine pits was most variable in the surface horizons; communities at deeper soil depths were relatively similar regardless of landscape position When compared to the microbial communities from 54 previously-analyzed surface soils collected across a wide range of biome types, we found that there was as much variation within individual soil pits as across surface soils from different biomes, emphasizing the importance of soil depth as an environmental gradient structuring soil microbial communities

Measurement of an excess of B̄→D(*) τ-ν̄τ decays and implications for charged Higgs bosons

Abstract: The concept for this analysis is to a large degree based on earlier BABAR work and we acknowledge the guidance provided by M. Mazur. The authors consulted with theorists A. Datta, S. Westhoff, S. Fajfer, J. Kamenik, and I. Nisandzic on the calculations of the charged Higgs contributions to the decay rates. We are grateful for the extraordinary contributions of our PEP-II colleagues in achieving the excellent luminosity and machine conditions that have made this work possible. The success of this project also relied critically on the expertise and dedication of the computing organizations that support BABAR. The collaborating institutions wish to thank SLAC for its support and the kind hospitality extended to them. This work is supported by the U.S. Department of Energy and National Science Foundation, the Natural Sciences and Engineering Research Council (Canada), the Commissariat a l'Energie Atomique and Institut National de Physique Nucleaire et de Physique des Particules (France), the Bundesministerium fur Bildung und Forschung and Deutsche Forschungsgemeinschaft (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), the Foundation for Fundamental Research on Matter (Netherlands), the Research Council of Norway, the Ministry of Education and Science of the Russian Federation, Ministerio de Economia y Competitividad (Spain), and the Science and Technology Facilities Council (United Kingdom). Individuals have received support from the Marie-Curie IEF program (European Union) and the A. P. Sloan Foundation (USA).

Averaged transition conditions for electromagnetic fields at a metafilm

Abstract: This paper derives generalized sheet transition conditions (GSTCs) for the average electromagnetic fields across a surface distribution of electrically small scatterers characterized by electric and magnetic polarization densities. We call such an arrangement of scatterers a metafilm-the two-dimensional (2-D) equivalent of a metamaterial. The derivation is based on a replacement of the discrete distribution of scatterers by a continuous one, resulting in a continuous distribution of electric and magnetic polarization densities in the surface. This is done in a manner analogous to the Clausius-Mossotti-Lorenz-Lorentz procedure for determining the dielectric constant of a volume distribution of small scatterers. The result contains as special cases many particular ones found throughout the literature. The GSTCs are expected to have wide application to the design and analysis of antennas, reflectors, and other devices where controllable scatterers are used to form a "smart" surface.

Coefficients of Determination for Multiple Logistic Regression Analysis

Abstract: Coefficients of determination for continuous predicted values (R 2 analogs) in logistic regression are examined for their conceptual and mathematical similarity to the familiar R 2 statistic from ordinary least squares regression, and compared to coefficients of determination for discrete predicted values (indexes of predictive efficiency). An example motivated by substantive concerns and using empirical data from a national household probability sample is presented to illustrate the behavior of the different coefficients of determination in the evaluation of models including dependent variables with different base rates—that is, different proportions of cases or observations with “positive” outcomes. One R 2 analog appears to be preferable to the others both in terms of conceptual similarity to the ordinary least squares coefficient of determination, and in terms of its relative independence from the base rate. In addition, base rate should also be considered when selecting an index of predictiv...