Showing 621 - 630 of 733 Items
Lake water chemistry and local adaptation shape NaCl toxicity in Daphnia ambigua
Date: 2024-01-01
Creator: Mary Alta Rogalski, Elizabeth S Baker, Clara M Benadon
Access: Open access
- Increasing application of road deicing agents (e.g., NaCl) has caused widespread salinization of freshwater environments. Chronic exposure to toxic NaCl levels can impact freshwater biota at genome to ecosystem scales, yet the degree of harm caused by road salt pollution is likely to vary among habitats and populations. The background ion chemistry of freshwater environments may strongly impact NaCl toxicity, with greater harm occurring in ion-poor, soft water conditions. In addition, populations exposed to salinization may evolve increased NaCl tolerance. Notably, if organisms are adapted to their natal lake water chemistry, toxicity responses may also vary among populations in a given test medium. We examined how this evolutionary and environmental context may interact in shaping NaCl toxicity with a pair of laboratory reciprocal transplant toxicity experiments, using natural populations of the water flea Daphnia ambigua from three lakes differing in ion availability. The lake water environment strongly influenced NaCl toxicity in both trials. NaCl greatly reduced reproduction and r in lake water from a low-ion/ calcium-poor environment compared with water from both a calcium-rich lake and an ion-rich coastal lake. Daphnia from this coastal lake were most robust to the effects of NaCl. A significant population x environment interaction shaped survival in both trials, suggesting that local adaptation to the test waters used contributed to toxicity responses. Our findings that the lake water environment, adaptation to that environment, and adaptation to a focal contaminant may shape toxicity demonstrate the importance of considering environmental and biological complexity in mitigating pollution impacts.
Narrative-inspired generation of ambient music
Date: 2017-01-01
Creator: Sarah Harmon
Access: Open access
- An author might read other written works to polish their own writing skill, just as a painter might analyze other paintings to hone their own craft. Yet, either might also visit the theatre, listen to a piece of music, or otherwise experience the world outside their particular discipline in search of creative insight. This paper explores one example of how a computational system might rely on what they have learned from analyzing another distinct form of expression to produce creative work. Specifically, the system presented here extracts semantic meaning from an input text and uses this knowledge to generate ambient music. An independent measures experiment was conducted to provide a preliminary assessment of the system and direct future work.
GREEN-PSO: Conserving function evaluations in Particle Swarm Optimization
Date: 2013-11-18
Creator: Stephen M. Majercik
Access: Open access
- In the Particle Swarm Optimization (PSO) algorithm, the expense of evaluating the objective function can make it difficult, or impossible, to use this approach effectively; reducing the number of necessary function evaluations would make it possible to apply the PSO algorithm more widely. Many function approximation techniques have been developed that address this issue, but an alternative to function approximation is function conservation. We describe GREEN-PSO (GR-PSO), an algorithm that, given a fixed number of function evaluations, conserves those function evaluations by probabilistically choosing a subset of particles smaller than the entire swarm on each iteration and allowing only those particles to perform function evaluations. The "surplus" of function evaluations thus created allows a greater number of particles and/or iterations. In spite of the loss of information resulting from this more parsimonious use of function evaluations, GR-PSO performs as well as, or better than, the standard PSO algorithm on a set of six benchmark functions, both in terms of the rate of error reduction and the quality of the final solution.
Galileo, poetry, and patronage: Iulio strozzi's venetia edificata and the lace of galileo in seventeenth-century talian poetry
Date: 2013-12-01
Creator: Crystal Hall
Access: Open access
- The Venetian poet and librettist Giulio Strozzi (1583 -1652) spent much of his career glorifying he Serenissima through a series of theatrical pieces. His only epic poem, the Venetia edificata (1621, 1624), while ostensibly a celebration of the republic, shows a level of commitment to alileo Galilei (1564 -1643) and to Galileo's science that is unique among poets of the time, enetian or otherwise. It is the apex of Strozzi's artistic project to incorporate Galileo's discoveries nd texts into poetic works. The Venetia edificata also represents the culmination of a fifteen-year ffort to gain patronage from the Medici Grand Dukes in Florence. While the first, incomplete ersion is dedicated to the Venetian Doge, the second, finished version is dedicated to Grand DukeFerdinando II de' Medici of Florence. More than a decade after Galileo's departure from the eneto to Florence, Strozzi cites from Galileo's early works, creates a character inspired by Galileo, ncorporates the principles of Galileo's science into the organizing structure of the poem, and nswers one of Galileo's loudest complaints about Torquato Tasso's Jerusalem Delivered (1581). trozzi's strategies both in writing the Venetia edificata and in seeking patronage for it underscore he ambivalent response to Galileo in contemporary poetry.
“Fanny Buitrago: La magia de contar historias”. A Body of One’s Own: Conversations with Caribbean and Latina Writers
Date: 2007-01-01
Creator: Nadia V. Celis Salgado, Fanny Buitrago
Access: Open access
Breathers and other time-periodic solutions in an array of cantilevers decorated with magnetsy
Date: 2019-01-01
Creator: Christopher Chong, Andre Foehr, Efstathios G. Charalampidis, Panayotis G. Kevrekidis, Chiara, Daraio
Access: Open access
- In this article, the existence, stability and bifurcation structure of time-periodic solutions (including ones that also have the property of spatial localization, i.e., breathers) are studied in an array of cantilevers that have magnetic tips. The repelling magnetic tips are responsible for the intersite nonlinearity of the system, whereas the cantilevers are responsible for the onsite (potentially nonlinear) force. The relevant model is of the mixed Fermi-Pasta-Ulam-Tsingou and Klein-Gordon type with both damping and driving. In the case of base excitation, we provide experimental results to validate the model. In particular, we identify regions of bistability in the model and in the experiment, which agree with minimal tuning of the system parameters. We carry out additional numerical explorations in order to contrast the base excitation problem with the boundary excitation problem and the problem with a single mass defect. We find that the base excitation problem is more stable than the boundary excitation problem and that breathers are possible in the defect system. The effect of an onsite nonlinearity is also considered, where it is shown that bistability is possible for both softening and hardening cubic nonlinearities.
Nontranscribed spacer sequences promote in vitro transcription of Drosophila ribosomal DNA
Date: 1982-11-11
Creator: Bruce D. Kohorn, Peter M.m. Rae
Access: Open access
- Tandem repeats of ribosomal RNA transcription units in Drosophila melanogaster are separated by a nontranscribed spacer that is comprised in part of serial repeats of a 0.24 kb sequence. DNA sequence analysis shows that such repeats are imperfect copies of a region that includes the site of in vivo rRNA transcription initiation (ca. -240 to +30). Subclones of the rDNA spacer that are copies of the sequence extending from -34 through the initiation site support detectable in vitro transcription in a mixture involving a Drosophila cell-free extract, but accurate in vitro transcription is considerably enhanced when a nontranscribed spacer template includes a copy of the sequence extending upstream of -34. From a comparison of the sequence and transcription template-effectiveness of various rDNA subclones, we infer that a major promoter of RNA polymerase I activity lies between -150 and -30 in the rDNA nontranscribed spacer. The nontranscribed spacer copies of the initiation region are less effective templates for transcription than is the region of in vivo initiation and there are differences between spacer repeates and the authentic sequence downstream of -240 that may account for this. © 1982 IRL Press Limited.
Highly nonlinear wave propagation in elastic woodpile periodic structures
Date: 2015-03-17
Creator: E. Kim, F. Li, C. Chong, G. Theocharis, J., Yang, P. G. Kevrekidis
Access: Open access
- In the present work, we experimentally implement, numerically compute with, and theoretically analyze a configuration in the form of a single column woodpile periodic structure. Our main finding is that a Hertzian, locally resonant, woodpile lattice offers a test bed for the formation of genuinely traveling waves composed of a strongly localized solitary wave on top of a small amplitude oscillatory tail. This type of wave, called a nanopteron, is not only motivated theoretically and numerically, but is also visualized experimentally by means of a laser Doppler vibrometer. This system can also be useful for manipulating stress waves at will, for example, to achieve strong attenuation and modulation of high-amplitude impacts without relying on damping in the system.
Damped-driven granular chains: An ideal playground for dark breathers and multibreathers
Date: 2014-03-31
Creator: C. Chong, F. Li, J. Yang, M. O. Williams, I. G., Kevrekidis, P. G. Kevrekidis
Access: Open access
- By applying an out-of-phase actuation at the boundaries of a uniform chain of granular particles, we demonstrate experimentally that time-periodic and spatially localized structures with a nonzero background (so-called dark breathers) emerge for a wide range of parameter values and initial conditions. We demonstrate a remarkable control over the number of breathers within the multibreather pattern that can be "dialed in" by varying the frequency or amplitude of the actuation. The values of the frequency (or amplitude) where the transition between different multibreather states occurs are predicted accurately by the proposed theoretical model, which is numerically shown to support exact dark breather and multibreather solutions. Moreover, we visualize detailed temporal and spatial profiles of breathers and, especially, of multibreathers using a full-field probing technology and enable a systematic favorable comparison among theory, computation, and experiments. A detailed bifurcation analysis reveals that the dark and multibreather families are connected in a "snaking" pattern, providing a roadmap for the identification of such fundamental states and their bistability in the laboratory. © 2014 American Physical Society.
Discord between the phylogenies inferred from molecular versus functional data: Uneven rates of functional evolution or low levels of gene flow?
Date: 1996-11-20
Creator: Michael F. Palopoli, Andrew W. Davis, Chung I. Wu
Access: Open access
- According to measures of molecular divergence, the three species of the Drosophila simulans clade are closely related to and essentially equidistant from each other. We introgressed 10% of the D. sechellia X chromosome into a pure D. simulans genetic background and found that males carrying this introgressed region were consistently fertile; in contrast, males carrying the same segment from D. mauritiana are sterile and suffer from incompatibilities at a minimum of four loci. Together with other recent results, these data suggest that D. simulans and D. sechellia are much more closely related to each other than either is to D. mauritiana. How can we reconcile the phylogeny inferred from the density of hybrid sterility genes with that inferred from molecular divergence? If the molecular phylogeny is correct, the discrepancy might be explained by uneven rates of functional evolution, resulting in the uneven accumulation of substitutions with corresponding negative effects in hybrids. If the functional phylogeny is correct, then low levels of gene flow across nascent species boundaries, particularly for loci not tightly linked to a hybrid sterility gene, may have erased the original pattern of lineage splitting. We propose tests that will allow us to discriminate between the hypotheses.