Membrane-type acoustic metamaterials were fabricated, characterized, and analyzed to understand their acoustic response. Thin plates which obey the acoustic mass law have low transmission loss (TL) at low frequencies. Acoustic metamaterials with negative dynamic mass density have been shown to demonstrate a significant (5×) increase in TL over mass law predictions for a narrow band (100 Hz) at low frequencies (100-1000 Hz). The peak TL frequency can be tuned to specific values by varying the membrane and mass properties. In this work, TL magnitude as a function of frequency was measured for variations in the mass magnitude and membrane tension using an impedance tube setup. The dynamic properties of membranes constructed from different materials were measured and compared to the results of coupled field acoustic-structural finite element analysis modeling to understand the role of tension and element quality factor. To better comprehend the mechanism(s) responsible for the TL peak, a laser vibrometer was used to map the out-of-plane dynamic response of the structure under acoustic loading at discrete frequencies. Negative dynamic mass was experimentally demonstrated at the peak TL frequency.

Abstract. Seven specific-pathogen-free (SPF) ponies, 1-5 years old, were exposed to Borrelia burgdorferiinfected adult ticks while being treated with dexamethasone over 5 consecutive days. One SPF pony (pony No. 178) was first exposed to laboratory-reared nymphs without B. burgdorferi infection and 3 weeks later was exposed to B. burgdorferi-infected adult ticks with concurrent dexamethasone treatment for 5 consecutive days. Four uninfected ponies treated with dexamethasone, exposed to laboratory-reared ticks without B. burgdorferi infection served as uninfected controls. Clinical signs, bacteriologic culture, polymerase chain reaction (PCR) for bacterial DNA, immunologic responses, and gross lesions and histopathologic changes were investigated during the experiment or at necropsy 9 months after tick exposure. In all of the seven challenged ponies, infection with B. burgdorferi was detected from monthly skin biopsies and various tissues at postmortem examination by culture and by PCR. However, pony No. 178 exposed to laboratory-reared nymphs (without B. burgdorferi infection) and challenged with B. burgdorferi-infected adult ticks 2 months later did not develop a B. burgdorferi infection. All of the infected ponies seroconverted. Control ponies and pony No. 178 were negative by culture, PCR, and serology. Except for skin lesions, we failed to induce any significant histopathologic changes in this study. This is the first report of successful tick-induced experimental infection in ponies by exposure to B. burgdorferi-infected ticks. This Lyme disease model will be very useful to evaluate efficacy of vaccines against the Lyme agent and the effect of antibiotic therapy on horses infected with B. burgdorferi.

Enhancing the specific strength and specific stiffness of phenolic microsphere syntactic foams reinforced with carbon fibers,

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