Ehlers K.M.,Truckee Meadows Community College
Mathematical and Computer Modelling | Year: 2011
Sir James Lighthill proposed in 1992 that acoustic streaming (AS) within the mammalian cochlea could play a role in the transmission of acoustic signals to the auditory sensory cells. Microelectromechanical devices for mixing and pumping, based on the acoustic streaming effect were introduced in the mid 1990s. Nature may have preceded this invention by 2.7. Gyr. We believe that acoustic streaming produced by nanometer scale membrane vibrations is widespread in cell biology. Flows generated by acoustic streaming could be produced along the "raphes" (central channels) of silica coated diatoms. Other possible instances are yeast cells and erythrocytes whose membranes generate nanoscale vibrations. We hypothesize that some of the most ancient organisms use acoustic streaming not only for self-propulsion but also to enhance their nutrient uptake. In this paper we focus on a motile strain of Synechococcus, a cyanobacterium whose mechanism for self-propulsion is not known. The calculations presented here show that a traveling surface acoustic wave (SAW) could account for the observed velocities. These SAWs would also produce a non-negligible Stokes layer surrounding the cell, motion within this region being essentially chaotic. Therefore, an AS mechanism would be biologically advantageous, enhancing localized diffusion processes and consequently, chemical reactions. Finally, we discuss possible experiments to support (or rule out) the AS model vs. other contending explanations for Synechococcus locomotion. © 2010 Elsevier Ltd.
Ehlers K.,Truckee Meadows Community College |
Ehlers K.,Desert Research Institute |
Chakrabarty R.,Desert Research Institute |
Moosmuller H.,Desert Research Institute
Applied Optics | Year: 2014
The familiar yellow or orange disks of the moon and sun, especially when they are low in the sky, and brilliant red sunsets are a result of the selective extinction (scattering plus absorption) of blue light by atmospheric gas molecules and small aerosols, a phenomenon explainable using the Rayleigh scattering approximation. On rare occasions, dust or smoke aerosols can cause the extinction of red light to exceed that for blue, resulting in the disks of the sun and moon to appear as blue. Unlike Earth, the atmosphere of Mars is dominated by micron-size dust aerosols, and the sky during sunset takes on a bluish glow. Here we investigate the role of dust aerosols in the blue Martian sunsets and the occasional blue moons and suns on Earth. We use the Mie theory and the Debye seriesto calculate the wavelength-dependent optical properties of dust aerosols most commonly found on Mars. Our findings show that while wavelength selective extinction can cause the sun's disk to appear blue, the color of the glow surrounding the sun as observed from Mars is due to the dominance of near-forward scattering of blue light by dust particles and cannot be explained by a simple, Rayleigh-like selective extinction explanation. © 2014 Optical Society of America.
Moosmuller H.,Desert Research Institute |
Chakrabarty R.K.,Desert Research Institute |
Ehlers K.M.,Truckee Meadows Community College |
Arnott W.P.,University of Nevada, Reno
Atmospheric Chemistry and Physics | Year: 2011
The concept of wavelength-dependent absorption Ångström coefficients (AACs) is discussed and clarified for both single and two-wavelengths AACs and guidance for their implementation with noisy absorption spectra is provided. This discussion is followed by application of the concept to models for brown carbon bulk absorption spectra including the damped simple harmonic oscillator model, its Lorentzian approximation, and the band-gap model with and without Urbach tail. We show that the band-gap model with Urbach tail always has an unphysical discontinuity in the first derivative of the AAC at the band-gap - Urbach-tail matching wavelength. Complex refractive indices obtained from the bulk damped simple harmonic oscillator model are used to calculate absorption spectra for spherical particles, followed by a discussion of their features. For bulk material and small particles, this model predicts a monotonic decrease of the AAC with wavelength well above the resonance wavelength; the model predicts a monotonic increase for large particles. © 2011 Author(s).
Cameron E.Z.,University of Tasmania |
White A.M.,U.S. Department of Agriculture |
Gray M.E.,Truckee Meadows Community College
BioScience | Year: 2016
The attrition of women from science with increasing career stage continues, suggesting that current strategies are unsuccessful. Research evaluation using unbiased metrics could be important for the retention of women, because other factors such as implicit bias are unlikely to quickly change. We compare the publishing patterns of men and women within the discipline of ecology and show sexual dimorphism in self-citation leading to higher h-index scores for men despite lower citations per paper, which is exacerbated by more career absences by women. However, if self-citations and non-research active years are excluded, there are no gender differences in research performance. The pattern is consistent across disciplines and may contribute to current geographic disparities in research performance, rewarding confident behavior and traditional career paths rather than research impact. Importantly, these changes would not disadvantage anyone, because self-citation does not indicate broader impact, and researchers should only be judged on their research-active career. © 2016 The Author(s) 2016. Published by Oxford University Press on behalf of the American Institute of Biological Sciences. All rights reserved.
Branson D.,Truckee Meadows Community College |
Demchak M.,University of Nevada, Reno
Topics in Early Childhood Special Education | Year: 2011
Effective strategies to promote social-emotional development and prevent occurrence of challenging behaviors in young children is critical. The Teaching Pyramid, a framework for supporting social-emotional development and preventing and addressing challenging behaviors, was developed for preschool children. This mixed methods study investigated toddler teachers' use of Teaching Pyramid practices and the relationship between these practices and classroom quality. Results indicated that toddler teachers used practices associated with the universal level of the Pyramid (e.g., positive relationships with children and parents). At this level, however, it was also evident that some preventive practices were missing (e.g., posted visual schedules and rules). Missing across classrooms was evidence of practices associated with the secondary level (e.g., explicitly teaching behavior expectations) and tertiary level (e.g., participating in developing behavior support plans). Implementation of Pyramid practices appeared to be associated with classrooms rated as being high quality. © 2011 Hammill Institute on Disabilities.