Browsing by Subject "Threshold"

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Control and modulation of action potential initiation in principal neurons of the medial superior olive
(2015-08) Ko, Kwang Woo; Golding, Nace L.; Johnston, Daniel; Pollak, George; Raab-Graham, Kimberly F.; Zakon, Harold
The axon initial segment (AIS) serves as the site of action potential initiation in most neurons, but the technical difficulty in isolating the effects of voltage-gated ion channels in the AIS from those of the soma and dendrites has hampered understanding how AIS properties influence neural coding. Here we have combined confocal microscopy, patch-clamp recordings and light-sensitive channel blockers (“photoswitches”) in binaural auditory neurons to show that hyperpolarization and cyclic nucleotide-gated (HCN) channels are expressed in the AIS and decrease spike probability, distinct from the role of HCN channels in the soma and dendrites. We show further that control of spike threshold by HCN channels in the AIS can be altered through serotonin modulation of 5-HT₁ [subscript A] receptors, which in turn hyperpolarizes the activation range of HCN channels. As serotonin release signals differences in attention states and motivation in broad regions in the brain, the present results reveal a role for axonal HCN channels as a mechanism to translate these signals into changes in the threshold for sensory stimuli.
Energy intensity ratios as net energy measures for selected countries 1978-2010
(2013-12) Maxwell, John Paul; King, Carey Wayne, 1974-; Zarnikau, Jay William, 1959-
Stated simply, this thesis focuses on the relationship between energy and the economy. Using the foundation of King 2010, this analysis expands the scholarship from a U.S. focus to perform Energy Intensity Ratio analysis on forty-four countries for the time period 1978-2010. There are four fuels examined: coal, natural gas, crude oil and electricity. Using both the price and expenditures based Energy Intensity Ratio methods, outputs for each fuel in any applicable sector was determined. In addition, this work compiles an estimate of the total energy expenditures for the majority of the world. By examining the overall expenditures of gross domestic product spent on energy, the data showed two points in time where energy appears to become a constraint on growth. Though this thesis does not answer the question directly as to whether an increase in energy expenditures “causes” an increase in economic growth, or whether an increase in economic growth “causes” an increase in energy expenditures, the research shows that vi there may be a “threshold” effect whereby as energy expenditures become a greater share of output, the ability of economic growth to take place is affected.
A fracture mechanics approach to accelerated life testing for cathodic delamination at polymer/metal interfaces
(2013-05) Mauchien, Thomas Kevin; Liechti, K. M.
This work presents a fracture mechanics analysis of the cathodic delamination problem for the polyurethane/titanium and polyurea/steel interfaces. The nonlinear behavior of both polymers was investigated. The recent Marlow model was used to define the strain energy function of the polymers. Viscoelastic effects of the polyurea were also studied. The Marlow model was associated with a nine-term Prony series. This model was seen to represent experimental data relatively well for a wide range of strain rates both in tension and compression. The driving force for delamination, the strain energy release rate G, is presented for both interfaces. Cathodic delamination data for several temperatures are presented as crack growth rate as a function of crack driving force. The approach recognizes that both temperature and stress can be used as accelerated life testing parameters.
Memristor-based arithmetic units
(2016-12) Guckert, Lauren Elise; Swartzlander, Earl E., Jr., 1945-; John, Lizy; Schulte, Michael; Touba, Nur; Lee, Jack
The modern computer architecture community is continually pushing the limits of performance, speed, and efficiency. Recently, the ability to satisfy this endeavor with popular CMOS technology has proved difficult, and in many settings, impossible. The community has begun to explore alternatives to standard practices, researching new components such as nanoscale structures. Additional research has applied these new components and their characteristics to rethink the architecture of the latest technology, moving away from the Von Neumann architecture. A leading technology in this effort is the memristor. Memristors are a new class of circuit elements that have the ability to change their resistance value while retaining knowledge of their current and past resistances. Their small form factor, high density, and fast switching times have sparked research in their applications in modern memory hierarchies. However, their utility in arithmetic has been minimally explored. This dissertation describes the prior work in the exploration of memristor technology, fabrication, modeling, and application, followed by the completed research performed in the design and implementation of arithmetic units using memristors. Implementations of popular adders, multipliers, and dividers in the context of memristors are designed using four approaches: IMPLY, hybrid-CMOS, threshold gates, and MAD gates. Each of these approaches has different tradeoffs and benefits for memristor-based design. Although the first three approaches have been defined in prior work, MAD gates are a novel application for memristors proposed that offer lower power, area, and delay as compared to prior approaches. This work explores these benefits for arithmetic unit design. The details of each designs, simulation results, and analyses in terms of complexity and delay and power are presented. For arithmetic units which have been designed or presented in prior work, this research improves upon the design in each metric. Many of the designs are transformed and pipelined to leverage memristor characteristics and the various approaches rather than traditional CMOS and this is discussed in detail. Overall, the proposed designs offer significant improvements to traditional CMOS designs, motivating the effort to continue exploring memristors and their application to modern computer architecture design.
The perceptibility of duration in the phonetics and phonology of contrastive consonant length
(2012-05) Hansen, Benjamin Bozzell; Myers, Scott P.; Crowhurst, Megan; King, Robert; Lindblom, Björn; Sussman, Harvey
This dissertation investigates the hypothesis that the more vowel-like a consonant is, the more difficult it is for listeners to classify it as geminate or singleton. A perceptual account of this observation holds that more vowel-like consonants lack clear markers to signal the beginning and ending of the consonant, so listeners don’t perceive the precise duration and consequently the phonological contrast may be neutralized in some languages. Three experiments were performed to address these questions using data from Persian speakers. In Experiment I, four speakers produced singleton and geminate tokens of the voiced oral consonants [d,z,n,l,j] and the glottals [h] and glottal stop at three speaking rates. It was found that Persian speakers do distinguish geminate durations from singleton durations for all manners even at very fast speaking rates, and vowels preceding geminates are slightly longer than those preceding singletons. Speaking rate had more of an effect on geminates than on singletons for all segments studied: the durations of the geminates decreased more in fast speech than the durations of the singletons did. In Experiment II, listeners heard manipulated continua of consonants ranging from singletons to geminates. Subjects’ identification curves were modeled using the cumulative Gaussian model. The modeled standard deviation was interpreted as the breadth of the perceptual threshold, and a broader threshold understood to indicate a less distinct perceptual boundary between the two categories. Obstruents [d,z] had smaller breadth values than the sonorants [n,l,j], and the glottals had the largest breadth values of all. This indicates that while sonorants were more difficult for listeners to categorize than obstruents, the glottals were the most difficult to categorize of the segments tested. Experiment III tested whether the modification of a specific parameter, the formant transition duration, would affect the perceptibility of the geminate/singleton contrast. A single token containing the glide [j] was manipulated to produce three different continua, each having a distinctly different manipulated transition: short, normal or long. It was found that the longer the transition was, the broader the perceptual threshold, thus making the consonant harder to categorize.