ABSTRACT
An application of active noise control (ANC) is the active headrest, using actuators (loadspeakers), sensors (microphones), and a controller to create a local zone of quiet around the occupants head. In this paper, the attenuation performance of various ANC-algorithms for active headrests known from literature is evaluated considering non-stationary broadband disturbances and head movement. Numerical studies are performed to determine the optimal plant models and parameters for the ANC-algorithms. Based on the findings of the numerical studies, several real-time experiments are conducted with and without head tracking examining the distribution of the 10 dB zone of quiet and the attenuation at the occupants ear using either a head mounted microphone technique, the remote microphone technique, the virtual microphone technique, or the virtual microphone control method. It is found that none of the algorithms using a virtual sensing technique can produce a 10 dB zone of quiet for all considered non-stationary broadband disturbances and head movement. For the algorithm using a head mounted microphone, it is possible to form a 10 dB zone of quiet, but placing a microphone at the ear is not feasible in most situations.
Subject(s)
Acoustic Stimulation/standards , Algorithms , Computer Simulation/standards , Head Movements/physiology , Noise , Acoustic Stimulation/methods , HumansABSTRACT
Oropharyngeal tularemia was identified as the cause of a die-off in captured wild prairie dogs at a commercial exotic animal facility in Texas. From this point source, Francisella tularensis-infected prairie dogs were traced to animals distributed to the Czech Republic and to a Texas pet shop. F. tularensis culture isolates were recovered tissue specimens from 63 prairie dogs, including one each from the secondary distribution sites. Molecular and biochemical subtyping indicated that all isolates were F. tularensis subsp. holarctica (Type B). Microagglutination assays detected antibodies against F. tularensis, with titers as great as 1:4,096 in some live animals. All seropositive animals remained culture positive, suggesting that prairie dogs may act as chronic carriers of F. tularensis. These findings demonstrate the need for additional studies of tularemia in prairie dogs, given the seriousness of the resulting disease, the fact that prairie dogs are sold commercially as pets, and the risk for pet-to-human transmission.
Subject(s)
Disease Outbreaks/veterinary , Francisella tularensis/isolation & purification , Sciuridae , Tularemia/veterinary , Animals , Antibodies, Bacterial/isolation & purification , Fluorescent Antibody Technique, Direct , Francisella tularensis/classification , Francisella tularensis/immunology , Humans , Texas/epidemiology , Tularemia/epidemiology , Tularemia/physiopathologyABSTRACT
A tularemia outbreak, caused by Francisella tularensis type B, occurred among wild-caught, commercially traded prairie dogs. F. tularensis microagglutination titers in one exposed person indicated recent infection. These findings represent the first evidence for prairie-dog-to-human tularemia transmission and demonstrate potential human health risks of the exotic pet trade.
