Objective and Subjective Evaluation of the Use of Directional Sound Sources in Auralizations

Omni-directional sources are often used in room acoustic computer simulations, as opposed to directional sources, since measured directivity data are quite limited and difficult to obtain. The purpose of this study is to investigate the objective and subjective significance of adding more complex directivity to the sources used in computer simulations and auralizations. A simple hall was used as the modelled space in the software program ODEON. Three source positions on stage and three receiver audience positions were chosen. Impulse responses (IRs) were calculated for the nine source/receiver combinations, using (a) an omni-directional source, (b) a highly directional source beaming in a sixteenth-tant of a sphere, and (c) three realistic sources: piano, singing voice and violin. The directivity data for the three realistic sources, obtained from the Physikalisch-Technischen Bundesanstalt website, were available in octave bands from 1 kHz – 4 kHz for the piano and violin, and from 125 Hz – 4 kHz for the singing voice. The objective measures evaluated were Sound Pressure Level (SPL), Reverberation Time (T60) and Clarity Index (C80). In general, there is at least 5% difference in T60 data between the omni-directional source and the realistic directional ones. Differences in SPL and C80 are more irregular across frequency bands and appear to be more apparent for sources with higher directivity index. For select source/receiver combinations, the IRs resulting from each source directivity have been convolved with anechoic musical recordings of piano, singing and violin to produce auralizations. Subjective testing revealed a noticeable difference between the omni-directional and the sixteenth-tant sources, but not with the realistic sources

Objective and Subjective Evaluation of the Use of Directional Sound Sources in Auralizations

Omni-directional sources are often used in room acoustic computer simulations, as opposed to directional sources, since measured directivity data are quite limited and difficult to obtain. The purpose of this study is to investigate the objective and subjective significance of adding more complex directivity to the sources used in computer simulations and auralizations. A simple hall was used as the modelled space in the software program ODEON. Three source positions on stage and three receiver audience positions were chosen. Impulse responses (IRs) were calculated for the nine source/receiver combinations, using (a) an omni-directional source, (b) a highly directional source beaming in a sixteenth-tant of a sphere, and (c) three realistic sources: piano, singing voice and violin. The directivity data for the three realistic sources, obtained from the Physikalisch-Technischen Bundesanstalt website, were available in octave bands from 1 kHz – 4 kHz for the piano and violin, and from 125 Hz – 4 kHz for the singing voice. The objective measures evaluated were Sound Pressure Level (SPL), Reverberation Time (T60) and Clarity Index (C80). In general, there is at least 5% difference in T60 data between the omni-directional source and the realistic directional ones. Differences in SPL and C80 are more irregular across frequency bands and appear to be more apparent for sources with higher directivity index. For select source/receiver combinations, the IRs resulting from each source directivity have been convolved with anechoic musical recordings of piano, singing and violin to produce auralizations. Subjective testing revealed a noticeable difference between the omni-directional and the sixteenth-tant sources, but not with the realistic sources

Room acoustics computer modelling: Study of the effect of source directivity on auralizations

Auralizations are very useful in the design of performing arts spaces, where auralization is the process of rendering audible the sound field in a space, in such a way as to simulate the binaural listening experience at a given position in the modeled space. One of the fundamental modeling inputs to create auralizations is the source directivity. Standard methods involve inputting the measured source directivity, calculating the impulse response and convolving it with a single channel anechoic recording. An initial study was conducted using this method and the results showed significant differences in reverberation time and clarity index when using a directional versus omni-directional source. Further research was conducted focusing on an alternative method of modeling source directivity that involves multi-channel anechoic recordings to create auralizations. Subjective tests were conducted comparing auralizations made with one, four and thirteen channels, with three different instrument types and subjects rated differences in realism. An analysis of variance (ANOVA) was carried out to determine the effect of the number of channels and instrument on realism. The primary result from this study was that subjects rated the auralizations made with an increasing number of channels as sounding more realistic, indicating that when more accurate source directivity information is used a more realistic auralization is possible

Swimming in circles: Motion of bacteria near solid boundaries

Near a solid boundary, E. coli swims in clockwise circular motion. We provide a hydrodynamic model for this behavior. We show that circular trajectories are natural consequences of force-free and torque-free swimming, and the hydrodynamic interactions with the boundary, which also leads to a hydrodynamic trapping of the cells close to the surface. We compare the results of the model with experimental data and obtain reasonable agreement. In particular, we show that the radius of curvature of the trajectory increases with the length of the bacterium body.Comment: Also available at http://people.deas.harvard.edu/~lauga

Enhanced diffusion due to active swimmers at a solid surface

We consider two systems of active swimmers moving close to a solid surface, one being a living population of wild-type \textit{E. coli} and the other being an assembly of self-propelled Au-Pt rods. In both situations, we have identified two different types of motion at the surface and evaluated the fraction of the population that displayed ballistic trajectories (active swimmers) with respect to those showing random-like behavior. We studied the effect of this complex swimming activity on the diffusivity of passive tracers also present at the surface. We found that the tracer diffusivity is enhanced with respect to standard Brownian motion and increases linearly with the activity of the fluid, defined as the product of the fraction of active swimmers and their mean velocity. This result can be understood in terms of series of elementary encounters between the active swimmers and the tracers.Comment: 4 pages, 2 figures in color, Physical Review Letters (in production

Stewardship Prompts to Improve Antibiotic Selection for Urinary Tract Infection

ImportanceUrinary tract infection (UTI) is the second most common infection leading to hospitalization and is often associated with gram-negative multidrug-resistant organisms (MDROs). Clinicians overuse extended-spectrum antibiotics although most patients are at low risk for MDRO infection. Safe strategies to limit overuse of empiric antibiotics are needed.ObjectiveTo evaluate whether computerized provider order entry (CPOE) prompts providing patient- and pathogen-specific MDRO risk estimates could reduce use of empiric extended-spectrum antibiotics for treatment of UTI.Design, setting, and participantsCluster-randomized trial in 59 US community hospitals comparing the effect of a CPOE stewardship bundle (education, feedback, and real-time and risk-based CPOE prompts; 29 hospitals) vs routine stewardship (n = 30 hospitals) on antibiotic selection during the first 3 hospital days (empiric period) in noncritically ill adults (≥18 years) hospitalized with UTI with an 18-month baseline (April 1, 2017-September 30, 2018) and 15-month intervention period (April 1, 2019-June 30, 2020).InterventionsCPOE prompts recommending empiric standard-spectrum antibiotics in patients ordered to receive extended-spectrum antibiotics who have low estimated absolute risk (<10%) of MDRO UTI, coupled with feedback and education.Main outcomes and measuresThe primary outcome was empiric (first 3 days of hospitalization) extended-spectrum antibiotic days of therapy. Secondary outcomes included empiric vancomycin and antipseudomonal days of therapy. Safety outcomes included days to intensive care unit (ICU) transfer and hospital length of stay. Outcomes were assessed using generalized linear mixed-effect models to assess differences between the baseline and intervention periods.ResultsAmong 127 403 adult patients (71 991 baseline and 55 412 intervention period) admitted with UTI in 59 hospitals, the mean (SD) age was 69.4 (17.9) years, 30.5% were male, and the median Elixhauser Comorbidity Index count was 4 (IQR, 2-5). Compared with routine stewardship, the group using CPOE prompts had a 17.4% (95% CI, 11.2%-23.2%) reduction in empiric extended-spectrum days of therapy (rate ratio, 0.83 [95% CI, 0.77-0.89]; P < .001). The safety outcomes of mean days to ICU transfer (6.6 vs 7.0 days) and hospital length of stay (6.3 vs 6.5 days) did not differ significantly between the routine and intervention groups, respectively.Conclusions and relevanceCompared with routine stewardship, CPOE prompts providing real-time recommendations for standard-spectrum antibiotics for patients with low MDRO risk coupled with feedback and education significantly reduced empiric extended-spectrum antibiotic use among noncritically ill adults admitted with UTI without changing hospital length of stay or days to ICU transfers.Trial registrationClinicalTrials.gov Identifier: NCT03697096

Stewardship Prompts to Improve Antibiotic Selection for Pneumonia

ImportancePneumonia is the most common infection requiring hospitalization and is a major reason for overuse of extended-spectrum antibiotics. Despite low risk of multidrug-resistant organism (MDRO) infection, clinical uncertainty often drives initial antibiotic selection. Strategies to limit empiric antibiotic overuse for patients with pneumonia are needed.ObjectiveTo evaluate whether computerized provider order entry (CPOE) prompts providing patient- and pathogen-specific MDRO infection risk estimates could reduce empiric extended-spectrum antibiotics for non-critically ill patients admitted with pneumonia.Design, setting, and participantsCluster-randomized trial in 59 US community hospitals comparing the effect of a CPOE stewardship bundle (education, feedback, and real-time MDRO risk-based CPOE prompts; n = 29 hospitals) vs routine stewardship (n = 30 hospitals) on antibiotic selection during the first 3 hospital days (empiric period) in non-critically ill adults (≥18 years) hospitalized with pneumonia. There was an 18-month baseline period from April 1, 2017, to September 30, 2018, and a 15-month intervention period from April 1, 2019, to June 30, 2020.InterventionCPOE prompts recommending standard-spectrum antibiotics in patients ordered to receive extended-spectrum antibiotics during the empiric period who have low estimated absolute risk (<10%) of MDRO pneumonia, coupled with feedback and education.Main outcomes and measuresThe primary outcome was empiric (first 3 days of hospitalization) extended-spectrum antibiotic days of therapy. Secondary outcomes included empiric vancomycin and antipseudomonal days of therapy and safety outcomes included days to intensive care unit (ICU) transfer and hospital length of stay. Outcomes compared differences between baseline and intervention periods across strategies.ResultsAmong 59 hospitals with 96 451 (51 671 in the baseline period and 44 780 in the intervention period) adult patients admitted with pneumonia, the mean (SD) age of patients was 68.1 (17.0) years, 48.1% were men, and the median (IQR) Elixhauser comorbidity count was 4 (2-6). Compared with routine stewardship, the group using CPOE prompts had a 28.4% reduction in empiric extended-spectrum days of therapy (rate ratio, 0.72 [95% CI, 0.66-0.78]; P < .001). Safety outcomes of mean days to ICU transfer (6.5 vs 7.1 days) and hospital length of stay (6.8 vs 7.1 days) did not differ significantly between the routine and CPOE intervention groups.Conclusions and relevanceEmpiric extended-spectrum antibiotic use was significantly lower among adults admitted with pneumonia to non-ICU settings in hospitals using education, feedback, and CPOE prompts recommending standard-spectrum antibiotics for patients at low risk of MDRO infection, compared with routine stewardship practices. Hospital length of stay and days to ICU transfer were unchanged.Trial registrationClinicalTrials.gov Identifier: NCT03697070