Beamformer performance with acoustic vector sensors in air

For some time, compact acoustic vector sensors (AVSs) capable of sensing particle velocity in three orthogonal directions have been used in underwater acoustic sensing applications. Potential advantages of using AVSs in air include substantial noise reduction with a very small aperture and few channels. For this study, a four-microphone array approximating a small (1 cm3) AVS in air was constructed using three gradient microphones and one omnidirectional microphone. This study evaluates the signal extraction performance of one nonadaptive and four adaptive beamforming algorithms. Test signals, consisting of two to five speech sources, were processed with each algorithm, and the signal extraction performance was quantified by calculating the signal-to-noise ratio (SNR) of the output. For a three-microphone array, robust and nonrobust versions of a frequency-domain minimum-variance (FMV) distortionless-response beamformer produced SNR improvements of 11 to 14 dB, and a generalized sidelobe canceller (GSC) produced improvements of 5.5 to 8.5 dB. In comparison, a two-microphone omnidirectional array with a spacing of 15 cm yielded slightly lower SNR improvements for similar multi-interferer speech signals.     

Monaural speech segregation using synthetic speech signals

When listening to natural speech, listeners are fairly adept at using cues such as pitch, vocal tract length, prosody, and level differences to extract a target speech signal from an interfering speech masker. However, little is known about the cues that listeners might use to segregate synthetic speech signals that retain the intelligibility characteristics of speech but lack many of the features that listeners normally use to segregate competing talkers. In this experiment, intelligibility was measured in a diotic listening task that required the segregation of two simultaneously presented synthetic sentences. Three types of synthetic signals were created: (1) sine-wave speech (SWS); (2) modulated noise-band speech (MNB); and (3) modulated sine-band speech (MSB). The listeners performed worse for all three types of synthetic signals than they did with natural speech signals, particularly at low signal-to-noise ratio (SNR) values. Of the three synthetic signals, the results indicate that SWS signals preserve more of the voice characteristics used for speech segregation than MNB and MSB signals. These findings have implications for cochlear implant users, who rely on signals very similar to MNB speech and thus are likely to have difficulty understanding speech in cocktail-party listening environments.     

Influence of confinement on the fragility of antiplasticized and pure polymer films

We investigate by molecular dynamics simulation how thin film confinement modifies the fragility of a model glass-forming liquid characterized previously in the bulk. Film confinement is found to reduce the relative fragility of the polymer fluid, leading to effects similar to simulations of the addition of an antiplasticizer additive. A reduction of fragility is not observed for the antiplasticized polymer film. These effects are interpreted in terms of variation in the string (cooperatively moving segments) concentration with film confinement and the addition of antiplasticizing additives.     

Multimodal imaging of the sonic organ of Porichthys notatus, the singing midshipman fish

The sonic midshipman fish, Porichthys notatus, is a bottom-dwelling species whose swim bladder has evolved into a highly specialized, sound-producing organ. The males of this species exist in two distinct morphs with different physical characteristics and sexual strategies. The Type I males have a much larger sound organ and are capable of generating a loud approximately 100 Hz tone continuously for over an hour to attract females. This sound is produced by sonic muscle and represents one of the most superfast and super-enduring striated muscles found in nature. Each fiber contains a hollow, tubular contractile apparatus composed of radially arranged myofibrils with extremely broad Z-bands that are supported by a desmin-rich cytoskeleton. We have used micro computed tomography (CT) imaging and magnetic resonance (MR) imaging to visualize the location of the sonic organ in an intact male fish. We have also obtained high-resolution MR images of the excised swim bladders from both male types. The images of the Type I sonic organ are strikingly detailed and high-contrast, revealing both the internal organization of the bladder and the crisscrossing muscle fibers and their mode of attachment to the underlying bladder. The high-contrast variation in these images is due to different T(2) values for fiber bundles and the spaces between the bundles. Direct MR imaging of intact Type I sonic organ in Type I midshipman fish is a powerful approach to understanding the contraction of this superfast muscle and the oscillation of its bladder to produce mating calls, and how placement of the sonic organ in the body of the fish sheds light on its prodigious ability to produce and transmit its loud mating call.     

The Maximum Flow Network Interdiction Problem: Valid inequalities, integrality gaps, and approximability

We present two classes of polynomially separable valid inequalities for the Maximum Flow Network Interdiction Problem. We prove that the integrality gap of the standard integer program is not bounded by a constant, even when strengthened by our valid inequalities. Finally, we provide an approximation-factor-preserving reduction from a simpler interdiction problem.     

Online sum-paintability: The slow-coloring game

The slow-coloring game is played by Lister and Painter on a graph $G$. On each round, Lister marks a nonempty subset $M$ of the uncolored vertices, scoring $\left|M\right|$ points. Painter then gives a color to a subset of $M$ that is independent in $G$. The game ends when all vertices are colored. Painter and Lister want to minimize and maximize the total score, respectively. The best score that each player can guarantee is the sum-color cost of $G$, written $\stackrel{?}{s}\left(G\right)$. The game is an online variant of online sum list coloring.We prove $\frac{\left|V\left(G\right)\right|}{2\alpha \left(G\right)}+\frac{1}{2}\le \frac{\stackrel{?}{s}\left(G\right)}{\left|V\left(G\right)\right|}\le max\left\{\frac{\left|V\left(H\right)\right|}{\alpha \left(H\right)}:H?G\right\}$, where $\alpha \left(G\right)$ is the independence number, and we study when equality holds in the bounds. We compute $\stackrel{?}{s}\left(G\right)$ for graphs with $\alpha \left(G\right)=2$. Among $n$-vertex trees, we prove that $\stackrel{?}{s}$ is minimized by the star and maximized by the path. We also study $\stackrel{?}{s}\left(K_{r,s}\right)$.     

Balloons,cut‐edges,matchings, and total domination in regular graphs of odd degree

A balloon in a graph G is a maximal 2‐edge‐connected subgraph incident to exactly one cut‐edge of G. Let b(G) be the number of balloons, let c(G) be the number of cut‐edges, and let α′(G) be the maximum size of a matching. Let ${\mathcal{F}}_{{{n}},{{r}}}A balloon in a graph G is a maximal 2‐edge‐connected subgraph incident to exactly one cut‐edge of G. Let b(G) be the number of balloons, let c(G) be the number of cut‐edges, and let α′(G) be the maximum size of a matching. Let ${\mathcal{F}}_{{{n}},{{r}}}$ be the family of connected (2r+1)‐regular graphs with n vertices, and let ${{b}}={{max}}\{{{b}}({{G}}): {{G}}\in {\mathcal{F}}_{{{n}},{{r}}}\}$. For ${{G}}\in{\mathcal{F}}_{{{n}},{{r}}}$, we prove the sharp inequalities c(G)?[r(n?2)?2]/(2r²+2r?1)?1 and α′(G)?n/2?rb/(2r+1). Using b?[(2r?1)n+2]/(4r²+4r?2), we obtain a simple proof of the bound proved by Henning and Yeo. For each of these bounds and each r, the approach using balloons allows us to determine the infinite family where equality holds. For the total domination number γ_t(G) of a cubic graph, we prove γ_t(G)?n/2?b(G)/2 (except that γ_t(G) may be n/2?1 when b(G)=3 and the balloons cover all but one vertex). With α′(G)?n/2?b(G)/3 for cubic graphs, this improves the known inequality γ_t(G)?α′(G). © 2009 Wiley Periodicals, Inc. J Graph Theory 64: 116–131, 2010     

Proteasome-inhibitory and cytotoxic constituents of Garcinia lateriflora: absolute configuration of caged xanthones

A new biflavonoid (1), a new xanthone enantiomer (2), five new caged xanthones (3-7), and several known compounds were isolated from the stem bark of Garcinia lateriflora, collected in Indonesia. The structures of the new compounds were determined by analysis of spectroscopic data, and the absolute configuration of the caged xanthones was shown for the first time at carbons 5, 7, 8, 8a, 10a, and 27, by analysis of COSY and NOESY NMR and ECD spectra. The biflavonoids exhibited proteasome-inhibitory activity, and the known compound, morelloflavone (8) was found to have the greatest potency (IC₅₀=1.3 μM). The caged xanthones were cytotoxic toward HT-29 cells, with the known compound, morellic acid (10) being the most active (ED₅₀=0.36 μM). However, when tested in an in vivo hollow fiber assay, it was inactive at the highest dose tested (20 mg/kg).