If Human Ears Were Tuned to Bat Frequencies": Inaudible Sound and the Sciences of Bat Echolocation

This report provides draft excerpts from my PhD dissertation titled "The Inaudible Sounds of Science and Medicine: Animals and Media from the Galton Whistle to Bat Echolocation," a chapter of which explores the laboratory work of Donald R. Griffin – and especially the emergence of the concept of bat echolocation – as it contributed to a sonic history of "ultrasound" and other typologies of liminal sound vibrations. Such "inaudible sounds" repeatedly defied amplification (efforts to make them louder); their frequencies were too high or too low to vibrate the human eardrum. But humans have long suspected that insects, bats, dogs, and other animals could hear them and communicate through them. The following research on bat echolocation in the Griffin laboratory is one aspect of a much more comprehensive historical project, which platforms nonhuman listeners in 19th- and 20th-century experimental contexts as they repeatedly pushed the limitations of human hearing. Broadly speaking, the dissertation suggests that animal figures are useful vectors for exploring an expanded history of sounds, including high-pitched frequencies, in science and medicine. My objective is to better understand how scientists designed media and choreographed animal listeners in order to make meaning from the sounds they could not hear on their own. I am most invested in understanding how humans exploited, collaborated with, and coexisted with animals to make sense of the insensible – or, to understand the unheard bestial worlds of communication.  In this report, I draw on material from the Donald R. Griffin Papers, held at the Rockefeller Archive Center, which includes a vast array of Griffin's laboratory notebooks, correspondences, sound films, newspaper clippings, and publications. The analysis spans the years between Donald Griffin's first experiment on bat navigation in the dark (1938) – conducted during his early graduate training years – and his postwar research on the physical principles of bat pulses into the 1960s.  More specifically, I characterize the ways in which various forms of media were deployed in experimental settings to study bats and the inaudible sounds emitted by them for orienting their bodies in flight. Scientists and collaborators of the Griffin lab relied on an array of mixed media, from the sound transposing devices of Harvard physicist George W. Pierce, to mechanical-visual apparatuses such as cathode-ray oscillograms and sound spectrographs, through to hand-written laboratory notes and printed correspondences and – ultimately – the bats themselves, to answer their questions. Furthermore, I explore the epistemic techniques of listening for sound and silence in the Griffin laboratory, in which the ears and eyes of scientists interfaced with special acoustic media to produce certain knowledges about bats and their patterns of flight. This project also engages with the highly militarized scientific contexts that constituted Griffin's work on bat echolocation

Ion release from experimental Au-Pt-based metal-ceramic alloys

Objective. The aim of the study was to assess the effect of individual metallic elements within experimental Au-Pt-based dental alloys for porcelain veneering on ion release. Methods. A binary Au-10 at% Pt alloy (AP10) was designed as a parent alloy. Six ternary AP10-X (X = In/Fe/Sn/Zn) and four quaternary (AP10-In2)-Y (Y = Fe/Sn/Zn) alloys containing oxide-forming elements, X and Y, up to 2 at% were prepared and ion release from the experimental alloys in deionized water and commercial soft drink was examined. For ion release determination samples with size 10 mm x 10 mm x 0.5 mm were immersed in 20 ml of deionized water for 5 min. Samples were then removed and immersed in 20 ml of Sprite Light (R) for a further 5 min, and 2 h at 37 degrees C. The amounts of ions released in the test solutions were analyzed by inductively coupled plasma-mass spectrometry. Results. When looking at individual elemental ion release, the order of the amount of dissolved ions was Fe > Zn > In > Sn. Among the base metal elements examined, Fe showed significantly higher levels of ion release than the other base metal elements for all three testing conditions (P < 0.05). When looking at the effects of test solution on ion release from the alloys, Sprite Light (R) caused significantly higher level of ion release than deionized water, with the exception of In in the ternary AP10-In1.0 and AP10-In1.7 alloys and the quaternary (AP10-In2)-Sn1.0 alloy, which showed similar or slightly greater amounts of ion release into deionized water. Significance. Significant ion release was only observed from the Fe element. Sn and In elements showed less ion release than the Fe and Zn elements. Accordingly, Sn and In elements should be recommended as oxide-forming elements in Au-Pt-based metal-ceramic systems. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved

Cytotoxicity and Dentin Permeability of Carbamide Peroxide and Hydrogen Peroxide Vital Bleaching Materials, in vitro

There has been recent concern about the inadvertent exposure of dentin with patent tubules as well as gingiva to bleaching systems containing 10-15% carbamide peroxide or 2-10% hydrogen peroxide for more than a few minutes. The aims of the present study were: (1) to determine the cytotoxicity of dilutions of hydrogen peroxide in cell culture; (2) to measure hydrogen peroxide diffusion from bleaching agents through dentin in vitro; and (3) to determine the risk of hydrogen peroxide-induced cytotoxicity from exposure of dentin to these vital bleaching agents. The 50% inhibitory dose (ID50) of hydrogen peroxide to succinyl dehydrogenase activity in cultured cells was found to be 0.58 mmol/L after 1 h. All bleaching materials demonstrated diffusion of hydrogen peroxide through dentin in an "in vitro pulp chamber" device. The one- and six-hour diffusates of all bleaching agents through 0.5-mm dentin exceeded the ID50 in monolayer cultures. Inhibition of succinyl dehydrogenase activity corresponded to the amount of hydrogen peroxide that can rapidly diffuse through dentin in vitro and reach concentrations which are toxic to cultured cells in less than 1 h.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66707/2/10.1177_00220345930720051501.pd

The Effects of Cleaning on the Kinetics of in vitro Metal Release from Dental Casting Alloys

The kinetics of the release of elements from six dental casting alloys into cell-culture medium was assessed by means of atomic absorption spectroscopy. Alloys were evaluated in the polished and polished-cleaned conditions so that the effects of cleaning could be determined. Auger scanning microscopy was used for analysis of the surfaces of selected alloys before and after exposure to the cell-culture medium. Release patterns for each element were characterized by the shape of the dissolution us. time curve, concentration of the element at 12 h as a percentage of the 72-hour concentration, and the relative slope of the curve from 48 to 72 h. Three patterns of release were observed for elements in these alloys. Type I patterns had logarithmic shapes with relatively large 12-hour concentrations and low 48-72-hour slopes. Type II patterns had logarithmic shapes but with moderate 12-hour concentrations and 48-72-hour slopes. Type III patterns were polynomial in shape, had relatively low 12-hour concentrations, and had large 48-72-hour slopes. Cleaning did not change the pattern of release but did generally significantly decrease the quantities of elements released (p = 0.05). The type of dissolution vs. time curve appeared to be dependent upon the element and the composition of the alloy. When cleaning reduced dissolution, surface analyses showed that the cleaning process increased the abundance of elements such as Au and Pd and reduced the abundance of Ag and Cu. Elements which were released from the alloys were more abundant on the surface than in the bulk in both polished and polished-cleaned conditions. Auger analyses of alloy surfaces after exposure to medium showed the presence of organic films up to 50 nm thick. This study demonstrated the importance of consideration of the cleaning method and kinetic release pattern when in vitro tests which assess the cytotoxicities of these alloys are planned.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67010/2/10.1177_00220345920710071101.pd

CVD elaboration of nanostructured TiO2-Ag thin films with efficient antibacterial properties

Nanostructured TiO2-Ag composite coatings are deposited by direct liquid injection metal-organic (DLI-MO) CVD at 683K in a one-step process. Silver pivalate (AgPiv) and titanium tetra-iso-propoxide (TTIP) are used as Ag and Ti molecular precursors, respectively. Metallic silver nanoparticles are co-deposited with anatase TiO2 on stainless steel, glass, and silicon wafers. The silver particles are uniformly embedded in the oxide matrix through the entire film thickness. The influence of the growth conditions, including injection parameters, is investigated on the chemical, physical, and structural characteristics of the coatings as well as on their anti-bacterial activities. The bacterium Staphylococcus aureus is employed for anti-bacterial tests. The films are bactericidal, according to the JIS Z 2801 standard test performed in the dark, when they contain less than 1 at.-% of silver. UnderUVirradiation they exhibit a photocatalytic activity which decays by increasing the silver content. As a result of this dual functionality, the TiO2-Ag nanocomposite coatings show promising potentialities as long-term anti-bacterial surfaces since selfcleaning can be achieved periodically under UV light in order to maintain an efficient anti-bacterial activity in the dark or in visible light

The effect of cell monolayer density on the cytotoxicity metal ions which are released from dental alloys

The effect of cell density (number of cells per unit area of a monolayer culture) on the in vitro cytotoxicity of metal ions which are known to be released from dental materials was investigated. The effects of cell density (1) may explain previous discrepancies in in vitro tests, (2) may be important in wound healing where cell density changes over time, and (3) may help clarify the mechanisms of cytotoxicity of metal ions. Balb/c 3T3 fibroblasts were plated at cell densities ranging from 10,000-80,000 cells/cm2 and were exposed to 8 concentrations of 10 different metal ions. After 24 h, the succinic dehydrogenase activity and DNA synthesis were measured to quantify the cytotoxic effect. Higher cell densities markedly reduced the sensitivity of these fibroblasts to all metal ions except Al+3 and Zn+2, but the magnitude of the reduction was metal dependent. In addition, the DNA synthesis was inhibited more than the succinic dehydrogenase activity for all metal ions except Zn+2. The unique effect of cell density on each metal ion supported the hypothesis that the effect was not simply caused by a dilution of the number of metal ions per cell. Given these results, the effect of cell density should be carefully selected in in vitro cytotoxicity tests.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30808/1/0000466.pd

Precision of and new methods for testing in vitro alloy cytotoxicity

Previous studies have utilized in vitro alloy cytotoxicity tests to evaluate dental casting alloys. The purposes of this study were to: (1) evaluate the precision of the optical density and visual tests previously used, (2) evaluate a new test measuring absorbance of solubilized formazan dyes, and (3) test the correlation between these tests for cytotoxicity. Balb/c 3T3 cells were plated in 24-well culture trays at 25,000 cells/cm2 around ten types of dental casting alloy (six samples/alloy) and incubated for 72 h. Cells were histochemically stained with MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) succinate for 2 h, then fixed, washed, and dried. Toxicity was measured by optical densitometer (OD) scanning, visual assessment, and 560-nm absorbance of DMSO-solubilized dyes. Measurements of rings of inhibition were not used, because they did not provide precise data, and correlated poorly with the other methods. The results were analyzed by ANOVA, Tukey intervals, and coefficients of variation (CV's). MTT required shorter incubation times for adequate staining, allowed for solubilization of the monolayers, and was less expensive than NBT (2,2'-di-p-nitro-phenyl-5,5'-diphenyl-3,3'-dimethoxy-[3,3'-dimethoxy-4,4'-biphenylene] ditetrazolium chloride). Results showed that all three methods ranked alloy toxicities similarly (p = 0.05). The solubilization method was most discriminating due to lower CV's. Correlation between densitometer and solubilization methods was excellent (R2 = 0.96). Between-experiment CV's were generally less than 20%, and often less than 10%. Between-sample CV;s were generally less than 20%. CV's were consistently lower for the solubilization method. Thus, all methods were repeatable and correlated well, but the solubilization method was more precise and discriminating.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30285/1/0000687.pd

The effect of repeated stretching on the force decay and compluance of vulcanized cis-polyisoprene orthodontic elastics

Compliance measurements, used in the past to measure the viscoelastic properties of dental impression materials, were used to assess these properties in vulcanized cis-polyisoprene orthodontic elastics, and the results were compared with traditional force decay measurements. Both methods were also used to evaluate the effect of repeated stretching on these elastics. Compliance measurements successfully characterized the viscoelastic behavior of the elastics, and the results agreed with force decay measurements. Repeated stretching significantly reduced the force and the compliance of the elastics. There was no statistical difference in the force or compliance measurements after the elastics were stretched more than 200 times. Stretching for 1000 cycles of 400% extension reduced elastic force by approximately 12%.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31027/1/0000704.pd

Correlation of cytotoxicity with elemental release from mercury- and gallium-based dental alloys in vitro

Objectives. An in vitro screening test was used to compare the cytotoxicity and elemental release from mercury- and gallium-based dental restorative materials. Methods. The test employed three sequential extractions of the samples into cell-culture medium which were then used to evaluate the cytotoxicity of the samples and the release of elements from the samples. Cytotoxicity was measured by placing the extract in contact with Balb/c mouse fibroblasts for 24 h and measuring the succinic dehydrogenase activity of the cells. The release of elements was measured by means of atomic absorption spectrophotometry. Results. Samples of Tytin (Kerr) showed no cytotoxicity compared to Teflon controls. Dispersalloy (Johnson and Johnson) was severely cytotoxic initially when Zn release was greatest, but was less toxic between 48 and 72 h as Zn release decreased. Gallium Alloy GF (Tokuriki Honten) was moderately cytotoxic after 8 h, and increased in cytotoxicity thereafter, which correlated with a substantial and persistent release of Ga from this material. Significance. The results of the current study concurred with in vivo assessments of these materials, and the use of sequential extractions was useful in determining trends in the cytotoxicity and elemental release from these materials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31360/1/0000272.pd