Fluctuation-enhanced frequency mixing in a nonlinear micromechanical oscillator

We study noise-enhanced frequency mixing in an underdamped micromechanical torsional oscillator. The oscillator is electrostatically driven into bistability by a strong, periodic voltage at frequency $\omega_d$. A second, weak ac voltage is applied at a frequency $\omega$ close to $\omega_d$. Due to nonlinearity in the system, vibrations occur at both $\omega$ and $2\omega_d-\omega$. White noise is injected into the excitation, allowing the system to occasionally overcome the activation barrier and switch between the two states. At the primary drive frequency where the occupations of the two states are approximately equal, we observe noise-induced enhancement of the oscillation amplitudes at both $\omega$ and the down-converted frequency $2\omega_d-\omega$, in agreement with theoretical predictions. Such enhancement occurs as a result of the noise-induced interstate transitions becoming synchronous with the beating between the two driving frequencies.Comment: 4 pages 5 figure

Activation barrier scaling and crossover for noise-induced switching in a micromechanical parametric oscillator

We explore fluctuation-induced switching in a parametrically-driven micromechanical torsional oscillator. The oscillator possesses one, two or three stable attractors depending on the modulation frequency. Noise induces transitions between the coexisting attractors. Near the bifurcation points, the activation barriers are found to have a power law dependence on frequency detuning with critical exponents that are in agreement with predicted universal scaling relationships. At large detuning, we observe a crossover to a different power law dependence with an exponent that is device specific.Comment: 5 pages, 5 figure

An Environmental Control and Life Support System Concept for a Pressurized Lunar Rover

Pressurized rovers can add many attractive capabilities to a human lunar exploration campaign, most notably by extending the reach of astronauts far beyond the immediate vicinities of lunar landers and fixed assets such as habitats. Effective campaigns will depend on an efficient allocation of environmental control and life support system (ECLSS) equipment amongst mobile rovers and fixed habitats such that widespread and sustainable exploration can be achieved. This paper will describe some of the key drivers that influence the design of an ECLSS for a pressurized lunar rover and a conceptual design that has been formulated to address those drivers. Opportunities to realize programmatic and operational efficiencies through commonality of rover ECLSS and extravehicular activity (EVA) equipment have also been explored and will be described. Plans for the inclusion of ECLSS functionality in prototype lunar rovers will be summarize

Multi-scale synthesis of historical fire regimes along the south-central US prairie-forest border

dendrochronology; drought; humans; oak; prairie; woodlandBackground: Along the prairie-forest border in the south-central USA exists one of the most extensive areas of uncut forest in the nation ([greater than]323 750 hectares), providing unique potential for developing multi-century records of environmental changes through dendrochronological analyses. Twentieth century changes in vegetation, increased prescribed fire management, and recent years of elevated wildfire activity have increased interest in understanding the region's long-term fire regime characteristics. To address this need, we analyzed and compared fire intervals, seasonality, severity, and extent based on fire-scar history datasets from three new and ten existing study sites. Results: At the study sites, mean fire intervals ranged from 3 to 10 years prior to Euro-American settlement and generally became more frequent after. The majority of fires occurred in the dormant season and resulted in low percentages of trees scarred. Coinciding with Euro-American settlement (EAS), fire frequencies appear to have varied by geography. At the regional scale, fire regimes have trended towards decreased fire severity and slightly decreased fire intervals over the past 300 years. Further, fires appear to have increased in extent from circa 1770 to the mid to late 1800s, after which it began to decline, circa 1920. Conclusions: Although frequent, descriptions of fire regimes since the eighteenth century should be characterized as time-dependent and spatially variable, likely depending on local socio-ecological influences. Similar influences may explain fire frequency increases following EAS, while fire severity trended lower. c2019, The Author(s).Includes bibliographical references

Supernarrow spectral peaks near a kinetic phase transition in a driven, nonlinear micromechanical oscillator

We measure the spectral densities of fluctuations of an underdamped nonlinear micromechanical oscillator. By applying a sufficiently large periodic excitation, two stable dynamical states are obtained within a particular range of driving frequency. White noise is injected into the excitation, allowing the system to overcome the activation barrier and switch between the two states. While the oscillator predominately resides in one of the two states for most excitation frequencies, a narrow range of frequencies exist where the occupations of the two states are approximately equal. At these frequencies, the oscillator undergoes a kinetic phase transition that resembles the phase transition of thermal equilibrium systems. We observe a supernarrow peak in the power spectral densities of fluctuations of the oscillator. This peak is centered at the excitation frequency and arises as a result of noise-induced transitions between the two dynamical states.Comment: 4 pages, 4 figure

Jesse James Syndrome

Serving Gifted Students in Rural Settings is a superb set of essays that would help practitioners in rural settings develop or enhance services for gifted students. The authors are specialists in Rural Studies, Counseling, and Gifted Education. Dr. Tamra Stambaugh is an Assistant Research Professor for Special Education and the Executive of Programs for Talented Youth at Vanderbilt University. Dr. Susannah M. Wood is an associate professor at the University of Iowa in the Department of Rehabilitation and Counselor Education. The talent of the two editors created this manual for practitioners that brings much-needed guidance for building and enhancing programs to meet the needs of gifted rural students. Leadership in rural settings is a challenge. In my own experience as a rural superintendent and principal, my talent needed to be spread across multiple roles within the district, from expertise in curriculum and instruction to not-so-strong expertise for inspecting school bus routes. Teachers are required to have talent in multiple areas as well. Each day they plan and teach multiple classes and all types of students, from a special needs child to second language learner, an average learner or a very gifted child. Education should meet the needs of all students, but without layers of support, it is a challenge

Jesse James Syndrome

Serving Gifted Students in Rural Settings is a superb set of essays that would help practitioners in rural settings develop or enhance services for gifted students. The authors are specialists in Rural Studies, Counseling, and Gifted Education. Dr. Tamra Stambaugh is an Assistant Research Professor for Special Education and the Executive of Programs for Talented Youth at Vanderbilt University. Dr. Susannah M. Wood is an associate professor at the University of Iowa in the Department of Rehabilitation and Counselor Education. The talent of the two editors created this manual for practitioners that brings much-needed guidance for building and enhancing programs to meet the needs of gifted rural students. Leadership in rural settings is a challenge. In my own experience as a rural superintendent and principal, my talent needed to be spread across multiple roles within the district, from expertise in curriculum and instruction to not-so-strong expertise for inspecting school bus routes. Teachers are required to have talent in multiple areas as well. Each day they plan and teach multiple classes and all types of students, from a special needs child to second language learner, an average learner or a very gifted child. Education should meet the needs of all students, but without layers of support, it is a challenge

Paths of fluctuation induced switching

We demonstrate that the paths followed by a system in fluctuation-activated switching form a narrow tube in phase space. A theory of the path distribution is developed and its direct measurement is performed in a micromechanical oscillator. The experimental and theoretical results are in excellent agreement, with no adjustable parameters. We also demonstrate the lack of time-reversal symmetry in switching of systems far from thermal equilibrium.Comment: Accepted to Phys. Rev. Let

Effects of Practice Schedule on Wind Instrument Performance: A Preliminary Application of a Motor Learning Principle

The effects of three practice schedules on beginning instrumental achievement were explored. A total of 19 seventh-grade clarinet and saxophone students completed one 18-minute practice session using either a blocked schedule causing a low level of cognitive (contextual) interference, a hybrid schedule causing a moderate level of interference, or a serial schedule causing a high level of interference. No main effects were found at immediate acquisition testing or 24-hr delayed retention testing for technical accuracy, attitude toward practice, or musicality. A significant practice Condition × Trial interaction was found for musicality. The discussion examines the discrepancy between technical and musical achievement. Recommendations are given for future research applying motor learning principles to instrumental music contexts