Rotor Dynamics Modification Of An Eight Stage Compressor For Safety/Reliability Improvement.

LecturePg. 81-96The catastrophic failure of a high pressure centrifugal air compressor utilizing air-pressurized bearing housings dictated the redesign of its sister compressor. The modification of this early 1950's compressor involved elements of both practical and analytical design. The project included the design of new bearings and seals and the alteration of various support systems to permit operation with non-pressurized bearing housings. The project was undertaken as risk minimization, with all performance and reliability improvements being additional benefits. The matching of the computer model with the field data of the existing system was the key to its successful evaluation. It was found that a case seal was acting as an additional bearing during certain operating conditions. This third bearing caused the compressor to behave differently than had been predicted with the initial two-bearing models. With the system properly modeled, changes were proposed to optimize the rotor dynamics. The main objectives were to achieve reliable rotor dynamic characteristics and to maintain the integrity of the process labyrinth seals. The changes were made in April, 1982, with the normal hardware fitting considerations. The subsequent start-up and operation were without incident. The modified compressor has performed well through a number of emergency trips and subsequent restarts, exhibiting exceptional rotor stability and overall reliability

Perception of polyphony with cochlear implants for 2 and 3 simultaneous pitches

Hypothesis: It was hypothesized that cochlear implant (CI) subjects would be able to correctly identify one, two and three simultaneous pitches through direct electrical stimulation. We further hypothesized that the location on the implant array and the fundamental frequency of the pitches would have an impact on the performance. Background: "They gave me back speech but not music." is a sentence commonly heard by CI subjects. One of the reasons is that in music, multiple streams are frequently played at the same time which is an essential feature of harmony. Current CI speech processors do not allow CI users to perceive such complex polyphonic sounds. Methods: In the present study the authors assessed the ability of CI subjects to perceive simultaneous modulation frequencies based on direct electrical stimulation. Ten CI subjects were asked to identify one, two and three simultaneous pitches applied on different electrodes using sinusoidal amplitude modulation. All stimuli were loudness balanced before the actual identification task. Results: Subjects were able to identify one, two and three simultaneous pitches. The further the distance between the two electrodes, the better was the performance in the two-pitch condition. The distance between the modulation frequencies had a significant effect on the performance in the two and three pitch condition. Conclusion: Subjects are able to identify complex polyphonic stimuli based on the number of active electrodes. The additional polyphonic rate pitch cue improves performance in some conditions

Supplementary Material for: A Comparative Study on Speech in Noise Understanding with a Direct Acoustic Cochlear Implant in Subjects with Severe to Profound Mixed Hearing Loss

The aim of this study was to investigate the efficacy of a direct acoustic cochlear implant (DACI) for speech understanding in noise in patients suffering from severe to profound mixed hearing loss (MHL) due to various etiologies compared to the preoperative best-aided condition. The study was performed at five tertiary referral centers in Europe (Belgium, Germany, Poland and Spain). Nineteen adult subjects with severe to profound MHL due to (advanced) otosclerosis, ear canal fibrosis, chronic otitis media, tympanosclerosis or previous cholesteatoma were implanted with a DACI (Codacs™ Investigational Device) combined with a conventional stapes prosthesis. Unaided and aided speech reception scores in quiet and in noise, preoperative and postoperative air and bone conduction thresholds and aided and unaided sound field thresholds were measured prospectively during the study. Subjective benefit analysis was determined through the Abbreviated Profile of Hearing Aid Benefit questionnaire. Quality of life was measured by the Health Utilities Index. All subjects were fitted preoperatively with hearing aids and/or a bone conduction implant on a headband before DACI implantation. This allows direct comparison between different hearing rehabilitation solutions. The mean speech reception threshold in noise improved significantly by 7.9 dB signal-to-noise ratio (SNR) after activation of the DACI compared to the preoperative best-aided condition. For all 19 subjects, a mean postoperative aided speech reception threshold of 2.6 dB SNR (standard deviation: 8.3 dB) was measured. On average, no significant shift in the bone conduction thresholds was noted 4-5 months after implantation. A mean sound field threshold improvement of 46 and 16 dB was measured compared to the preoperative unaided and best-aided condition, respectively. Speech perception tests in quiet showed a mean improvement of the word recognition scores by 65 and 48% at 65 dB SPL compared to the preoperative unaided and best-aided condition, respectively. In summary, DACI provides an effective improvement of the speech perception in noise compared to the best-aided condition in subjects suffering from severe to profound MHL

Clinical Presentation, Processes and Outcomes of Care for Patients with Pneumococcal Pneumonia

OBJECTIVE: To describe the presentation, resolution of symptoms, processes of care, and outcomes of pneumococcal pneumonia, and to compare features of the bacteremic and nonbacteremic forms of this illness. DESIGN: A prospective cohort study. SETTING: Five medical institutions in 3 geographic locations. PARTICIPANTS: Inpatients and outpatients with community-acquired pneumonia (CAP). MEASUREMENTS: Sociodemographic characteristics, respiratory and nonrespiratory symptoms, and physical examination findings were obtained from interviews or chart review. Severity of illness was assessed using a validated prediction rule for short-term mortality in CAP. Pneumococcal pneumonia was categorized as bacteremic; nonbacteremic, pure etiology; or nonbacteremic, mixed etiology. MAIN RESULTS: One hundred fifty-eight (6.9%) of 2,287 patients (944 outpatients, 1,343 inpatients) with CAP had pneumococcal pneumonia. Sixty-five (41%) of the 158 with pneumococcal pneumonia were bacteremic; 74 (47%) were nonbacteremic with S. pneumoniae as sole pathogen; and 19 (12%) were nonbacteremic with S. pneumoniae as one of multiple pathogens. The pneumococcal bacteremia rate for outpatients was 2.6% and for inpatients it was 6.6%. Cough, dyspnea, and pleuritic pain were common respiratory symptoms. Hemopytsis occurred in 16% to 22% of the patients. A large number of nonrespiratory symptoms were noted. Bacteremic patients were less likely than nonbacteremic patients to have sputum production and myalgias (60% vs 82% and 33% vs 57%, respectively; P <.01 for both), more likely to have elevated blood urea nitrogen and serum creatinine levels, and more likely to receive pencillin therapy. Half of bacteremic patients were in the low risk category for short-term mortality (groups I to III), similar to the nonbacteremic patients. None of the 32 bacteremic patients in risk groups I to III died, while 7 of 23 (30%) in risk group V died. Intensive care unit admissions and pneumonia-related mortality were similar between bacteremic and nonbacteremic groups, although 46% of the bacteremic group had respiratory failure compared with 32% and 37% for the other groups. The nonbacteremic pure etiology patients returned to household activities faster than bacteremic patients. Symptoms frequently persisted at 30 days: cough (50%); dyspnea (53%); sputum production (48%); pleuritic pain (13%); and fatigue (63%). CONCLUSIONS: There were few differences in the presentation of bacteremic and nonbacteremic pneumococcal pneumonia. About half of bacteremic pneumococcal pneumonia patients were at low risk for mortality. Symptom resolution frequently was slow