Simulated room impulse responses have been proven to be both useful and indispensable for comprehensive testing of acoustic signal processing algorithms while controlling parameters such as the ...reverberation time, room dimensions, and source-array distance. In this work, a method is proposed for simulating the room impulse responses between a sound source and the microphones positioned on a spherical array. The method takes into account specular reflections of the source by employing the well-known image method, and scattering from the rigid sphere by employing spherical harmonic decomposition. Pseudocode for the proposed method is provided, taking into account various optimizations to reduce the computational complexity. The magnitude and phase errors that result from the finite order spherical harmonic decomposition are analyzed and general guidelines for the order selection are provided. Three examples are presented: an analysis of a diffuse reverberant sound field, a study of binaural cues in the presence of reverberation, and an illustration of the algorithm's use as a mouth simulator.
Inference of Room Geometry From Acoustic Impulse Responses Antonacci, F.; Filos, J.; Thomas, M. R. P. ...
IEEE transactions on audio, speech and language processing/IEEE transactions on audio, speech, and language processing,
12/2012, Volume:
20, Issue:
10
Journal Article
Peer reviewed
Open access
Acoustic scene reconstruction is a process that aims to infer characteristics of the environment from acoustic measurements. We investigate the problem of locating planar reflectors in rooms, such as ...walls and furniture, from signals obtained using distributed microphones. Specifically, localization of multiple two- dimensional (2-D) reflectors is achieved by estimation of the time of arrival (TOA) of reflected signals by analysis of acoustic impulse responses (AIRs). The estimated TOAs are converted into elliptical constraints about the location of the line reflector, which is then localized by combining multiple constraints. When multiple walls are present in the acoustic scene, an ambiguity problem arises, which we show can be addressed using the Hough transform. Additionally, the Hough transform significantly improves the robustness of the estimation for noisy measurements. The proposed approach is evaluated using simulated rooms under a variety of different controlled conditions where the floor and ceiling are perfectly absorbing. Results using AIRs measured in a real environment are also given. Additionally, results showing the robustness to additive noise in the TOA information are presented, with particular reference to the improvement achieved through the use of the Hough transform.
Nutrient Imbalances in Agricultural Development Vitousek, P.M; Naylor, R; Crews, T ...
Science (American Association for the Advancement of Science),
06/2009, Volume:
324, Issue:
5934
Journal Article
Peer reviewed
Nutrient additions to intensive agricultural systems range from inadequate to excessive--and both extremes have substantial human and environmental costs.
Abstract Although there is level I evidence supporting the role of carotid endarterectomy (CEA) in patients with asymptomatic disease, opinion remains polarised regarding what constitutes optimal ...management, especially as carotid artery stenting (CAS) has emerged as a less invasive alternative. Reasons for this lack of consensus amongst surgeons, interventionists, neurologists and stroke physicians include our continued inability to identify ‘high risk for stroke' patients in whom to target costly therapies. For example, recent data from the USA suggest that up to $21 billion is being spent each year on ultimately ‘unnecessary' interventions. Second, is growing evidence that improvements in what now constitutes modern ‘best medical therapy' has significantly reduced the risk of stroke compared to that observed in ACAS and ACST. If true, this will compromise risk:benefit analyses used in national and international guidelines. At a time when evidence suggests that up to 94% of interventions may not benefit the patient, the authors urge that at least one of the randomised trials comparing CEA with CAS in asymptomatic patients includes an adequately powered third limb for BMT. Timely investment now could optimise patient care and resource utilisation for all of us in the future.
Identification of the relative importance of within- and between-host variability in infectiousness and the impact of these heterogeneities on the transmission dynamics of infectious agents can ...enable efficient targeting of control measures. Cattle, a major reservoir host for the zoonotic pathogen Escherichia coli O157, are known to exhibit a high degree of heterogeneity in bacterial shedding densities. By relating bacterial count to infectiousness and fitting dynamic epidemiological models to prevalence data from a cross-sectional survey of cattle farms in Scotland, we identify a robust pattern: approximately equal to 80% of the transmission arises from the 20% most infectious individuals. We examine potential control options under a range of assumptions about within- and between-host variability in infection dynamics. Our results show that the within-herd basic reproduction ratio, R0, could be reduced to <1 with targeted measures aimed at preventing infection in the 5% of individuals with the highest overall infectiousness. Alternatively, interventions such as vaccination or the use of probiotics that aim to reduce bacterial carriage could produce dramatic reductions in R0 by preventing carriage at concentrations corresponding to the top few percent of the observed range of counts. We conclude that a greater understanding of the cause of the heterogeneity in bacterial carriage could lead to highly efficient control measures to reduce the prevalence of E. coli O157.
Despite their efficacy in the treatment of chronic inflammation, the prolonged application of therapeutic glucocorticoids (GCs) is limited by significant systemic side effects including ...glucocorticoid-induced osteoporosis (GIOP). 11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) is a bi-directional enzyme that primarily activates GCs in vivo, regulating tissue-specific exposure to active GC. We aimed to determine the contribution of 11β-HSD1 to GIOP.
Wild type (WT) and 11β-HSD1 knockout (KO) mice were treated with corticosterone (100 μg/ml, 0.66% ethanol) or vehicle (0.66% ethanol) in drinking water over 4 weeks (six animals per group). Bone parameters were assessed by micro-CT, sub-micron absorption tomography and serum markers of bone metabolism. Osteoblast and osteoclast gene expression was assessed by quantitative RT-PCR.
Wild type mice receiving corticosterone developed marked trabecular bone loss with reduced bone volume to tissue volume (BV/TV), trabecular thickness (Tb.Th) and trabecular number (Tb.N). Histomorphometric analysis revealed a dramatic reduction in osteoblast numbers. This was matched by a significant reduction in the serum marker of osteoblast bone formation P1NP and gene expression of the osteoblast markers Alp and Bglap. In contrast, 11β-HSD1 KO mice receiving corticosterone demonstrated almost complete protection from trabecular bone loss, with partial protection from the decrease in osteoblast numbers and markers of bone formation relative to WT counterparts receiving corticosterone.
This study demonstrates that 11β-HSD1 plays a critical role in GIOP, mediating GC suppression of anabolic bone formation and reduced bone volume secondary to a decrease in osteoblast numbers. This raises the intriguing possibility that therapeutic inhibitors of 11β-HSD1 may be effective in preventing GIOP in patients receiving therapeutic steroids.
A Speech Distortion and Interference Rejection Constraint Beamformer Habets, E. A. P.; Benesty, J.; Naylor, P. A.
IEEE transactions on audio, speech and language processing/IEEE transactions on audio, speech, and language processing,
03/2012, Volume:
20, Issue:
3
Journal Article
Peer reviewed
Open access
Signals captured by a set of microphones in a speech communication system are mixtures of desired and undesired signals and ambient noise. Existing beamformers can be divided into those that preserve ...or distort the desired signal. Beamformers that preserve the desired signal are, for example, the linearly constrained minimum variance (LCMV) beamformer that is supposed, ideally, to reject the undesired signal and reduce the ambient noise power, and the minimum variance distortionless response (MVDR) beamformer that reduces the interference-plus-noise power. The multichannel Wiener filter, on the other hand, reduces the interference-plus-noise power without preserving the desired signal. In this paper, a speech distortion and interference rejection constraint (SDIRC) beamformer is derived that minimizes the ambient noise power subject to specific constraints that allow a tradeoff between speech distortion and interference-plus-noise reduction on the one hand, and undesired signal and ambient noise reductions on the other hand. Closed-form expressions for the performance measures of the SDIRC beamformer are derived and the relations to the aforementioned beamformers are derived. The performance evaluation demonstrates the tradeoffs that can be made using the SDIRC beamformer.
Documented cases of convergent molecular evolution due to selection are fairly unusual, and examples to date have involved only a few amino acid positions. However, because convergence mimics shared ...ancestry and is not accommodated by current phylogenetic methods, it can strongly mislead phylogenetic inference when it does occur. Here, we present a case of extensive convergent molecular evolution between snake and agamid lizard mitochondrial genomes that overcomes an otherwise strong phylogenetic signal. Evidence from morphology, nuclear genes, and most sites in the mitochondrial genome support one phylogenetic tree, but a subset of mostly amino acid-altering substitutions (primarily at the first and second codon positions) across multiple mitochondrial genes strongly supports a radically different phylogeny. The relevant sites generally evolved slowly but converged between ancient lineages of snakes and agamids. We estimate that ≈44 of 113 predicted convergent changes distributed across all 13 mitochondrial protein-coding genes are expected to have arisen from nonneutral causes—a remarkably large number. Combined with strong previous evidence for adaptive evolution in snake mitochondrial proteins, it is likely that much of this convergent evolution was driven by adaptation. These results indicate that nonneutral convergent molecular evolution in mitochondria can occur at a scale and intensity far beyond what has been documented previously, and they highlight the vulnerability of standard phylogenetic methods to the presence of nonneutral convergent sequence evolution.
Distributed acoustic tracking estimates the trajectories of source positions using an acoustic sensor network. As it is often difficult to estimate the source-sensor range from individual nodes, the ...source positions have to be inferred from the direction-of-arrival (DoA) estimates. Due to reverberation and noise, the sound field becomes increasingly diffuse with increasing source-sensor distance, leading to a decreased Direction of Arrival (DoA)-estimation accuracy. To distinguish between accurate and uncertain DoA estimates, this letter proposes to incorporate the coherent-to-diffuse ratio as a measure of DoA reliability for single-source tracking. It is shown that the source positions, therefore, can be probabilistically triangulated by exploiting the spatial diversity of all nodes.
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