bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymptotic expansions for wavenumbers in orthotropic fluid-filled circular cylindrical shells for intermediate fluid loading
Authors: S. Vijay Prakash , Sonti Venkata R.
Published: June 2014

Coupled wavenumbers in infinite fluid-filled isotropic and orthotropic cylindrical shells are considered. Using the Donnell-Mushtari (DM) theory for thin shells, compact and elegant asymptotic expansions for the wavenumbers are found at an intermediate fluid loading for both the coupled rigid-duct modes (“fluid-originated”) and the coupled structural wavenumbers (“structure-originated modes”) over the entire frequency range where DM theory is valid. The coupled rigid-duct expansions are found to be valid for O(1) orthotropy and for all circumferential orders, whereas the coupled structural wavenumber expansions are valid for small orthotropy and for low circumferential orders. These two above results are then used to derive the expansions for a set of multiple complex roots that display a locking behavior at this intermediate fluid-loading. The expansions are matched with the numerical solutions of the coupled dispersion relation and the match is found to be good over most of the frequency range.
Aircraft noise and speech intelligibility in an outdoor living space
Authors: Alvarsson Jesper J. , Nordström Henrik , Lundén Peter , Nilsson Mats E.
Published: June 2014

Studies of effects on speech intelligibility from aircraft noise in outdoor places are currently lacking. To explore these effects, first-order ambisonic recordings of aircraft noise were reproduced outdoors in a pergola. The average background level was 47 dB LAeq. Lists of phonetically balanced words (LASmax,word = 54 dB) were reproduced simultaneously with aircraft passage noise (LASmax,noise = 72–84 dB). Twenty individually tested listeners wrote down each presented word while seated in the pergola. The main results were (i) aircraft noise negatively affects speech intelligibility at sound pressure levels that exceed those of the speech sound (signal-to-noise ratio, S/N < 0), and (ii) the simple A-weighted S/N ratio was nearly as good an indicator of speech intelligibility as were two more advanced models, the Speech Intelligibility Index and Glasberg and Moore's [J. Audio Eng. Soc. 53, 906–918 (2005)] partial loudness model. This suggests that any of these indicators is applicable for predicting effects of aircraft noise on speech intelligibility outdoors.
Auditory acclimatization and hearing aids: Late auditory evoked potentials and speech recognition following unilateral and bilateral amplification
Authors: Dawes Piers , Munro Kevin J. , Kalluri Sridhar , Edwards Brent
Published: June 2014

The aim of this study was to investigate changes in central auditory processing following unilateral and bilateral hearing aid fitting using a combination of physiological and behavioral measures: late auditory event-related potentials (ERPs) and speech recognition in noise, respectively. The hypothesis was that for fitted ears, the ERP amplitude would increase over time following hearing aid fitting in parallel with improvement in aided speech recognition. The N1 and P2 ERPs were recorded to 500 and 3000 Hz tones presented at 65, 75, and 85 dB sound pressure level to either the left or right ear. New unilateral and new bilateral hearing aid users were tested at the time of first fitting and after 12 weeks hearing aid use. A control group of long-term hearing aid users was tested over the same time frame. No significant changes in the ERP were observed for any group. There was a statistically significant 2% improvement in aided speech recognition over time for all groups, although this was consistent with a general test–retest effect. This study does not support the existence of an acclimatization effect observable in late ERPs following 12 weeks' hearing aid use.
Shear wave attenuation and micro-fluidics in water-saturated sand and glass beads
Authors: Chotiros Nicholas P. , Isakson Marcia J.
Published: June 2014

An improvement in the modeling of shear wave attenuation and speed in water-saturated sand and glass beads is introduced. Some dry and water-saturated materials are known to follow a constant-Q model in which the attenuation, expressed as Q−1, is independent of frequency. The associated loss mechanism is thought to lie within the solid frame. A second loss mechanism in fluid-saturated porous materials is the viscous loss due to relative motion between pore fluid and solid frame predicted by the Biot–Stoll model. It contains a relaxation process that makes the Q−1 change with frequency, reaching a peak at a characteristic frequency. Examination of the published measurements above 1 kHz, particularly those of Brunson (Ph.D. thesis, Oregon State University, Corvalis, 1983), shows another peak, which is explained in terms of a relaxation process associated with the squirt flow process at the grain-grain contact. In the process of deriving a model for this phenomenon, it is necessary to consider the micro-fluidic effects associated with the flow within a thin film of water confined in the gap at the grain-grain contact and the resulting increase in the effective viscosity of water. The result is an extended Biot model that is applicable over a broad band of frequencies.
Observations regarding coarse sediment classification based on multi-beam echo-sounder's backscatter strength and depth residuals in Dutch rivers
Authors: Eleftherakis Dimitrios , Snellen Mirjam , Amiri-Simkooei AliReza , Simons Dick G. , Siemes Kerstin
Published: June 2014

This contribution investigates the behavior of two important riverbed sediment classifiers, derived from multi-beam echo-sounder (MBES)—operating at 300 kHz—data, in very coarse sediment environments. These are the backscatter strength and the depth residuals. Four MBES data sets collected at different parts of rivers in the Netherlands are employed. From previous research the backscatter strength was found to increase for increasing mean grain sizes. Depth residuals, however, are often found to have lower values for coarser sediments. Investigation of the four data sets indicates that these statements are valid only for moderately coarse sediment such as sand. For very coarse sediments (e.g., coarse gravel) the backscatter strength is found to decrease and the depth residuals increase for increasing mean grain sizes. This is observed when the sediment mean grain size becomes significantly larger than the acoustic wavelength of the MBES (5 mm). Knowledge regarding this behavior is of high importance when using backscatter strength and depth residuals for sediment classification purposes as the reverse in behavior can induce ambiguity in the classification.
Effect of fracture compliance on wave propagation within a fluid-filled fracture
Authors: Nakagawa Seiji , Korneev Valeri A.
Published: June 2014

Open and partially closed fractures can trap seismic waves. Waves propagating primarily within fluid in a fracture are sometimes called Krauklis waves, which are strongly dispersive at low frequencies. The behavior of Krauklis waves has previously been examined for an open, fluid-filled channel (fracture), but the impact of finite fracture compliance resulting from contacting asperities and porous fillings in the fracture (e.g., debris, proppants) has not been fully investigated. In this paper, a dispersion equation is derived for Krauklis wave propagation in a fracture with finite fracture compliance, using a modified linear-slip-interface model (seismic displacement-discontinuity model). The resulting equation is formally identical to the dispersion equation for the symmetric fracture interface wave, another type of guided wave along a fracture. The low-frequency solutions of the newly derived dispersion equations are in good agreement with the exact solutions available for an open fracture. The primary effect of finite fracture compliance on Krauklis wave propagation is to increase wave velocity and attenuation at low frequencies. These effects can be used to monitor changes in the mechanical properties of a fracture.
On compressibility assumptions in aeroacoustic integrals: A numerical study with subsonic mixing layers
Authors: Margnat Florent , Gloerfelt Xavier
Published: June 2014

Two assumptions commonly made in predictions based on Lighthill's formalism are investigated: A constant density in the quadrupole expression and the evaluation of the source quantity from incompressible simulations. Numerical predictions of the acoustic field are conducted in the case of a subsonic spatially evolving two-dimensional mixing layer at Re = 400. Published results of the direct noise computation (DNC) of the flow are used as reference and input for hybrid approaches before the assumptions on density are progressively introduced. Divergence free velocity fields are obtained from an incompressible simulation of the same flow case, exhibiting the same hydrodynamic field as the DNC. For the tested values of the Mach number, hybrid predictions reproduce correctly the reference acoustic field, validating both assumptions in the source region. However, in the observer region, the inclusion of flow effects in the Lighthill source term is not preserved, which is illustrated through a comparison with the Kirchhoff wave-extrapolation formalism, and with the use of a convected Green function in the integration process.
The perception of apparent auditory source width in hearing-impaired adults
Authors: Whitmer William M. , Seeber Bernhard U. , Akeroyd Michael A.
Published: June 2014

In a previous study [Whitmer, Seeber and Akeroyd, J. Acoust. Soc. Am. 132, 369–379 (2012)], it was demonstrated that older hearing-impaired (HI) listeners produced visual sketches of headphone-presented noises that were insensitive to changes in interaural coherence. The current study further explores this insensitivity by comparing (a) binaural temporal fine-structure (TFS) resolution and (b) sound localization precision to (c) auditory source width judgments. Thirty-five participants aged 26–81 years with normal to moderately impaired hearing (a) discriminated interaurally phase-shifted tones from diotic tones presented over headphones, (b) located 500-ms speech-spectrum filtered click trains presented over loudspeakers between ±30° in quiet, and (c) sketched the perceived width of low-pass, high-pass, and speech-spectrum noise stimuli presented over loudspeakers from 0° and simultaneously from ±45° at attenuations of 0–20 dB to generate partially coherent stimuli. The results showed a decreasing sensitivity to width with age and impairment which was related to binaural TFS threshold: the worse one's threshold—which was correlated with age—the less the perceived width increased with decreasing interaural coherence. These results suggest that senescent changes to the auditory system do not necessarily lead to perceptions of broader, more diffuse sound images based on interaural coherence.
Real-time separation of non-stationary sound fields with pressure and particle acceleration measurements
Authors: Bi Chuan-Xing , Geng Lin , Zhang Xiao-Zheng
Published: June 2014

To extract the desired non-stationary sound field generated by a target source in the presence of disturbing sources, a real-time sound field separation method with pressure and particle acceleration measurements is proposed. In this method, the pressure and particle acceleration signals at a time instant are first measured on one measurement plane, where the particle acceleration is obtained by the finite difference approximation with the aid of an auxiliary measurement plane; then, the desired pressure signal generated by the target source at the same time instant can be extracted in a timely manner, by a simple superposition of the measured pressure and the convolution between the measured particle acceleration and the derived impulse response function. Thereby, the proposed method possesses a significant feature of real-time separation of non-stationary sound fields, which provides the potential to in situ analyze the radiation characteristics of a non-stationary source. The proposed method was examined through numerical simulation and experiment. Results demonstrated that the proposed method can not only extract the desired time-evolving pressure signal generated by the target source at any space point, but can also obtain the desired spatial distribution of the pressure field generated by the target source at any time instant.
Characterization of underwater sounds produced by hydraulic and mechanical dredging operations
Authors: Reine Kevin J. , Clarke Douglas , Dickerson Charles
Published: June 2014

Sound recordings were made of two dredging operations at hydrophone depths of 3 and 9.1 m at distances up to 1.2 km from the source in shallow waters (<15 m) of New York Harbor. Sound sources included rock fracturing by a hydraulic cutterhead dredge and six distinct sources associated with a mechanical backhoe dredging operation during rock excavation. To place sound emitted from these dredges in perspective with other anthropogenic sounds, recordings were also made of several deep-draft commercial vessels. Results are presented as sound pressure levels (SPLs) in one-third octave versus range across the 20 Hz to 20 kHz frequency band. To address concerns for protection of fishery resource occupying the harbor, SPL were examined at frequency bands of 50–1000 Hz and 100–400 Hz, the ranges where the majority of fishes without hearing specializations detect sound and the range of greatest sensitivity, respectively. Source levels (dB re 1 μPa-1 m rms) were back calculated using fitted regression (15LogR). The strongest sound sources (180–188.9 dB) were emitted by commercial shipping. Rock fracturing produced a source level of 175 dB, whereas six distinct sources associated with rock excavation had source levels ranging from 164.2 to 179.4 dB re 1 μPa-1 m (rms).
Reflection and transmission coefficients of a single layer in poroelastic media
Authors: Martinez Corredor Robiel , Santos Juan E. , Gauzellino Patricia M. , Carcione José M.
Published: June 2014

Wave propagation in poroelastic media is a subject that finds applications in many fields of research, from geophysics of the solid Earth to material science. In geophysics, seismic methods are based on the reflection and transmission of waves at interfaces or layers. It is a relevant canonical problem, which has not been solved in explicit form, i.e., the wave response of a single layer, involving three dissimilar media, where the properties of the media are described by Biot's theory. The displacement fields are recast in terms of potentials and the boundary conditions at the two interfaces impose continuity of the solid and fluid displacements, normal and shear stresses, and fluid pressure. The existence of critical angles is discussed. The results are verified by taking proper limits—zero and 100% porosity—by comparison to the canonical solutions corresponding to single-phase solid (elastic) media and fluid media, respectively, and the case where the layer thickness is zero, representing an interface separating two poroelastic half-spaces. As examples, it was calculated the reflection and transmission coefficients for plane wave incident at a highly permeable and compliant fluid-saturated porous layer, and the case where the media are saturated with the same fluid.
A comparative study of interaural time delay estimation methods
Authors: Katz Brian F. G. , Noisternig Markus
Published: June 2014

The Interaural Time Delay (ITD) is an important binaural cue for sound source localization. Calculations of ITD values are obtained either from measured time domain Head-Related Impulse Responses (HRIRs) or from their frequency transform Head-Related Transfer Functions (HRTFs). Numerous methods exist in current literature, based on a variety of definitions and assumptions of the nature of the ITD as an acoustic cue. This work presents a thorough comparative study of the degree of variability between some of the most common methods for calculating the ITD from measured data. Thirty-two different calculations or variations are compared for positions on the horizontal plane for the HRTF measured on both a KEMAR mannequin and a rigid sphere. Specifically, the spatial variations of the methods are investigated. Included is a discussion of the primary potential causes of these differences, such as the existence of multiple peaks in the HRIR of the contra-lateral ear for azimuths near the inter-aural axis due to multipath propagation and head/pinnae shadowing.
Analysis of feedback control of piezoelectric transducers
Authors: Randall Robert C. , Brown David A.
Published: June 2014

Velocity control feedback may be required for implementation in large underwater acoustic arrays to mitigate the effects of strong acoustic field coupling when specific beam pattern performance over a variety of operating conditions is desired. This paper presents an analysis of velocity control with piezoelectric loads using motional current monitoring [as an extension to Aronov, J. Acoust. Soc. Am. 119(6), 3822–3830 (2006) and Bachand, Brown, and Aronov, J. Acoust. Soc. Am. 124(4), 2568 (2008)], with particular interest in automated wideband acoustic beamforming. The analysis is applicable to other forms of motional feedback control such as accelerometer or displacement signal feedback. Topics presented include the control loop's effectiveness, stability criteria, and the array equations governing the acoustical outputs. The conditions that can cause negative radiation impedance are also presented, concluding that in any velocity control system with acoustic interactions, the likelihood of a transmit channel absorbing more energy than it is transmitting increases with the feedback loop gain. This fundamental limitation must be considered before developing any practical acoustic velocity control system with strong inter-element acoustic field coupling.
Drawing melodies: Evaluation of chironomic singing synthesis
Authors: d'Alessandro Christophe , Feugère Lionel , Le Beux Sylvain , Perrotin Olivier , Rilliard Albert
Published: June 2014

Cantor Digitalis, a real-time formant synthesizer controlled by a graphic tablet and a stylus, is used for assessment of melodic precision and accuracy in singing synthesis. Melodic accuracy and precision are measured in three experiments for groups of 20 and 28 subjects. The task of the subjects is to sing musical intervals and short melodies, at various tempi, using chironomy (hand-controlled singing), mute chironomy (without audio feedback), and their own voices. The results show the high accuracy and precision obtained by all the subjects for chironomic control of singing synthesis. Some subjects performed significantly better in chironomic singing compared to natural singing, although other subjects showed comparable proficiency. For the chironomic condition, mean note accuracy is less than 12 cents and mean interval accuracy is less than 25 cents for all the subjects. Comparing chironomy and mute chironomy shows that the skills used for writing and drawing are used for chironomic singing, but that the audio feedback helps in interval accuracy. Analysis of blind chironomy (without visual reference) indicates that a visual feedback helps greatly in both note and interval accuracy and precision. This study demonstrates the capabilities of chironomy as a precise and accurate mean for controlling singing synthesis.
Nonuniform temporal weighting of interaural time differences in 500 Hz tones
Authors: Stecker G. Christopher , Bibee Jacqueline M.
Published: June 2014

The discrimination and lateralization of interaural time differences (ITD) in rapidly modulated high-frequency sounds is dominated by cues present in the initial portion of the sound (i.e., at sound onset). The importance of initial ITD at low frequencies is, however, less clear. Here, ITD discrimination thresholds were measured in 500 Hz pure tones with diotic envelopes and static or dynamic fine-structure ITD. Static-ITD thresholds improved as tone duration increased from 40 to 640 ms but by an amount less than expected from uniform temporal weighting of binaural information. Dynamic conditions eliminated ITD from either the beginning or end of the sound by presenting slightly different frequencies to the two ears. While overall thresholds were lower when ITD was available at sound onset than when it was not, listeners differed appreciably in that regard. The results demonstrate that weighting of ITD is not temporally uniform. Instead, for many listeners, ITD discrimination at 500 Hz appears dominated by ITD cues present in the initial part of the sound. To a variable degree, other listeners rely more equally on ITD cues occurring near sound onsets and offsets, although no listeners appear to utilize such cues uniformly throughout the sound's duration.
Determination of the in-plane components of motion in a Lamb wave from single-axis laser vibrometry
Authors: Rajic Nik , Rosalie Cedric , Norman Patrick , Davis Claire
Published: June 2014

A method is proposed for determining in-plane components of motion in a Lamb wave from laser vibrometer measurements of surface motion out of plane. The approach relies on a frequency domain transformation that assumes knowledge only of the plate thickness and the bulk wave speeds. An outline of the relevant theory is followed by several validation case studies that generally affirm a useful level of accuracy and robust performance across a relatively wide frequency-thickness product range. In a comparison to the two-angle vibrometry approach, the proposed method is shown to be simpler to implement and to yield estimates with a consistently higher signal to noise ratio. The approach is then used to furnish estimates of the in-plane strains in Lamb waves propagating in an aluminum plate at frequencies below the first cut-off. These estimates are compared to strain measurements obtained from an adhesively bonded fiber Bragg grating. The agreement is shown to be excellent overall with an average discrepancy of less than 6%; however, systematic errors of twice that amount were recorded in the low-frequency-thickness product regime. These low-frequency discrepancies are not consistent with known sources of experimental error and cannot be explained by shear-lag theory.
Comparison of the transmission properties of self-similar, periodic, and random multilayers at normal incidence
Authors: Ponge Marie-Fraise , Jacob Xavier , Gibiat Vincent
Published: June 2014

The effect of self-similarity on acoustic and elastic wave propagation at normal incidence is investigated using Classical Cantor and Fibonacci multilayered structures. They are made of two sorts of orthotropic plies having differently oriented orthotropic axes with respect to the propagation direction. The properties of their transmission coefficient are presented using a unidirectional numerical model based on a transfer matrix formalism. It was found that stack self-similarity influences the acoustic transmission properties. Transmission coefficients of self-similar stacks present a self-similar shape and behavior. A self-similar process, applied to layer orientation allows multilayered stacks to be created. A thickness-equivalent model was developed to compare these structures with standard self-similar multilayers which are finally compared to periodic and random stacks. The transmission coefficient of a deterministic self-similar Fibonacci structure is similar to that of an averaged transmission coefficient of random stacks.
Lattice Boltzmann investigation of acoustic damping mechanism and performance of an in-duct circular orifice
Authors: Ji Chenzhen , Zhao Dan
Published: June 2014

In this work, three-dimensional numerical simulations of acoustically excited flow through a millimeter-size circular orifice are conducted to assess its noise damping performance, with particular emphasis on applying the lattice Boltzmann method (LBM) as an alternative computational aeroacoustics tool. The model is intended to solve the discrete lattice Boltzmann equation (LBE) by using the pseudo-particle based technique. The LBE controls the particles associated with collision and propagation over a discrete lattice mesh. Flow variables such as pressure, density, momentum, and internal energy are determined by performing a local integration of the particle distribution at each time step. This is different from the conventional numerical investigation attempting to solve Navier-Stokes (NS) equations by using high order finite-difference or finite-volume methods. Compared with the conventional NS solvers, one of the main advantages of LBM may be a reduced computational cost. Unlike frequency domain simulations, the present investigation is conducted in time domain, and the orifice damping behavior is quantified over a broad frequency range at a time by forcing an oscillating flow with multiple tones. Comparing the numerical results with those obtained from the theoretical models, large eddy simulation, and experimental measurements, good agreement is observed.
Using Gaussian mixture models to detect and classify dolphin whistles and pulses
Authors: Peso Parada Pablo , Cardenal-López Antonio
Published: June 2014

In recent years, a number of automatic detection systems for free-ranging cetaceans have been proposed that aim to detect not just surfaced, but also submerged, individuals. These systems are typically based on pattern-recognition techniques applied to underwater acoustic recordings. Using a Gaussian mixture model, a classification system was developed that detects sounds in recordings and classifies them as one of four types: background noise, whistles, pulses, and combined whistles and pulses. The classifier was tested using a database of underwater recordings made off the Spanish coast during 2011. Using cepstral-coefficient-based parameterization, a sound detection rate of 87.5% was achieved for a 23.6% classification error rate. To improve these results, two parameters computed using the multiple signal classification algorithm and an unpredictability measure were included in the classifier. These parameters, which helped to classify the segments containing whistles, increased the detection rate to 90.3% and reduced the classification error rate to 18.1%. Finally, the potential of the multiple signal classification algorithm and unpredictability measure for estimating whistle contours and classifying cetacean species was also explored, with promising results.
Mechanisms of Antiviral Action of Plant Antimicrobials against Murine Norovirus
Authors: Gilling Damian H. , Kitajima Masaaki , Torrey Jason R. , Bright Kelly R.
Published: June 2014

Numerous plant compounds have antibacterial or antiviral properties; however, limited research has been conducted with nonenveloped viruses. The efficacies of allspice oil, lemongrass oil, and citral were evaluated against the nonenveloped murine norovirus (MNV), a human norovirus surrogate. The antiviral mechanisms of action were also examined using an RNase I protection assay, a host cell binding assay, and transmission electron microscopy. All three antimicrobials produced significant reductions (
P
≤ 0.05) in viral infectivity within 6 h of exposure (0.90 log
10
to 1.88 log
10
). After 24 h, the reductions were 2.74, 3.00, and 3.41 log
10
for lemongrass oil, citral, and allspice oil, respectively. The antiviral effect of allspice oil was both time and concentration dependent; the effects of lemongrass oil and citral were time dependent. Based on the RNase I assay, allspice oil appeared to act directly upon the viral capsid and RNA. The capsids enlarged from ≤35 nm to up to 75 nm following treatment. MNV adsorption to host cells was not significantly affected. Alternatively, the capsid remained intact following exposure to lemongrass oil and citral, which appeared to coat the capsid, causing nonspecific and nonproductive binding to host cells that did not lead to successful infection. Such contrasting effects between allspice oil and both lemongrass oil and citral suggest that though different plant compounds may yield similar reductions in virus infectivity, the mechanisms of inactivation may be highly varied and specific to the antimicrobial. This study demonstrates the antiviral properties of allspice oil, lemongrass oil, and citral against MNV and thus indicates their potential as natural food and surface sanitizers to control noroviruses.
Genomic Heterogeneity and Ecological Speciation within One Subspecies of Bacillus subtilis
Authors: Kopac Sarah , Wang Zhang , Wiedenbeck Jane , Sherry Jessica , Wu Martin , Cohan Frederick M.
Published: June 2014

Closely related bacterial genomes usually differ in gene content, suggesting that nearly every strain in nature may be ecologically unique. We have tested this hypothesis by sequencing the genomes of extremely close relatives within a recognized taxon and analyzing the genomes for evidence of ecological distinctness. We compared the genomes of four Death Valley isolates plus the laboratory strain W23, all previously classified asBacillus subtilissubsp.spizizeniiand hypothesized through multilocus analysis to be members of the same ecotype (an ecologically homogeneous population), named putative ecotype 15 (PE15). These strains showed a history of positive selection on amino acid sequences in 38 genes. Each of the strains was under a different regimen of positive selection, suggesting that each strain is ecologically unique and represents a distinct ecological speciation event. The rate of speciation appears to be much faster than can be resolved with multilocus sequencing. Each PE15 strain contained unique genes known to confer a function for bacteria. Remarkably, no unique gene conferred a metabolic system or subsystem function that was not already present in all the PE15 strains sampled. Thus, the origin of ecotypes within this clade shows no evidence of qualitative divergence in the set of resources utilized. Ecotype formation within this clade is consistent with the nanoniche model of bacterial speciation, in which ecotypes use the same set of resources but in different proportions, and genetic cohesion extends beyond a single ecotype to the set of ecotypes utilizing the same resources.
Carriage of Staphylococcus aureus by Free-Living Wild Animals in Spain
Authors: Porrero M. Concepción , Mentaberre Gregorio , Sánchez Sergio , Fernández-Llario Pedro , Casas-Díaz Encarna , Mateos Ana , Vidal Dolors , Lavín Santiago , Fernández-Garayzábal José-Francisco , Domínguez Lucas
Published: June 2014

The presence of methicillin-susceptible
Staphylococcus aureus
(MSSA) was analyzed in different free-living wild animals to assess the genetic diversity and predominant genotypes on each animal species. Samples were taken from the skin and/or nares, and isolates were characterized by
spa
typing, multilocus sequence typing (MLST) and antimicrobial susceptibility testing. The proportion of MSSA carriers were 5.00, 22.93, 19.78, and 17.67% in Eurasian griffon vulture, Iberian ibex, red deer, and wild boar, respectively (
P
= 0.057). A higher proportion of isolates (
P
= 0.000) were recovered from nasal samples (78.51%) than skin samples (21.49%), but the 9.26% of red deer and 18.25% of wild boar would have been undetected if only nasal samples had been tested. Sixty-three different
spa
types were identified, including 25 new
spa
types. The most common were t528 (43.59%) in Iberian ibex, t548 and t11212 (15.79% and 14.04%) in red deer, and t3750 (36.11%) in wild boar. By MLST, 27 STs were detected, of which 12 had not been described previously. The most frequent were ST581 for Iberian ibex (48.72%), ST425 for red deer (29.82%), and ST2328 for wild boar (42.36%). Isolates from Eurasian griffon vulture belong to ST133. Host specificity has been observed for the most frequent
spa
types and STs (
P
= 0.000). The highest resistance percentage was found against benzylpenicillin (average, 22.2%), although most of the
S. aureus
isolates were susceptible to all antimicrobial tested. Basically, MSSA isolates were different from those MRSA isolates previously detected in the same animal species.
Applied Usage of Yeast Spores as Chitosan Beads
Authors: Zhang Haini , Tachikawa Hiroyuki , Gao Xiao-Dong , Nakanishi Hideki
Published: June 2014

In this study, we present a nonhazardous biological method of producing chitosan beads using the budding yeastSaccharomyces cerevisiae. Yeast cells cultured under conditions of nutritional starvation cease vegetative growth and instead form spores. The spore wall has a multilaminar structure with the chitosan layer as the second outermost layer. Thus, removal of the outermost dityrosine layer by disruption of theDIT1gene, which is required for dityrosine synthesis, leads to exposure of the chitosan layer at the spore surface. In this way, spores can be made to resemble chitosan beads. Chitosan has adsorptive features and can be used to remove heavy metals and negatively charged molecules from solution. Consistent with this practical application, we find that spores are capable of adsorbing heavy metals such as Cu2+, Cr3+, and Cd2+, and removal of the dityrosine layer further improves the adsorption. Removal of the chitosan layer decreases the adsorption, indicating that chitosan works as an adsorbent in the spores. Besides heavy metals, spores can also adsorb a negatively charged cholesterol derivative, taurocholic acid. Furthermore, chitosan is amenable to chemical modifications, and, consistent with this property,dit1Δspores can serve as a carrier for immobilization of enzymes. Given that yeast spores are a natural product, our results demonstrate that they, and especiallydit1Δmutants, can be used as chitosan beads and used for multiple purposes.
Lactulose and Lactobacillus plantarum, a Potential Complementary Synbiotic To Control Postweaning Colibacillosis in Piglets
Authors: Guerra-Ordaz A. A. , González-Ortiz G. , La Ragione R. M. , Woodward M. J. , Collins J. W. , Pérez J. F. , Martín-Orúe S. M.
Published: June 2014

The potential of a prebiotic oligosaccharide lactulose, a probiotic strain of
Lactobacillus plantarum
, or their synbiotic combination to control postweaning colibacillosis in pigs was evaluated using an enterotoxigenic
Escherichia coli
(ETEC) K88 oral challenge. Seventy-two weanlings were fed four diets: a control diet (CTR), that diet supplemented with
L. plantarum
(2 × 10
10
CFU · day
−1
) (LPN), that diet supplemented with 10 g · kg
−1
lactulose (LAC), or a combination of the two treatments (SYN). After 7 days, the pigs were orally challenged. Six pigs per treatment were euthanized on days 6 and 10 postchallenge (PC). Inclusion of lactulose improved the average daily gain (ADG) (
P
< 0.05) and increased lactobacilli (
P
< 0.05) and the percentage of butyric acid (
P
< 0.02) in the colon. An increase in the ileum villous height (
P
< 0.05) and a reduction of the pig major acute-phase protein (Pig-MAP) in serum (
P
< 0.01) were observed also. The inclusion of the probiotic increased numbers of
L. plantarum
bacteria in the ileum and colon (
P
< 0.05) and in the total lactobacilli in the colon and showed a trend to reduce diarrhea (
P
= 0.09). The concentrations of ammonia in ileal and colonic digesta were decreased (
P
< 0.05), and the villous height (
P
< 0.01) and number of ileal goblet cells (
P
< 0.05) increased, at day 10 PC. A decrease in plasmatic tumor necrosis factor alpha (TNF-α) (
P
< 0.01) was also seen. The positive effects of the two additives were combined in the SYN treatment, resulting in a complementary synbiotic with potential to be used to control postweaning colibacillosis.
Thermal and Nonthermal Effects of Discontinuous Microwave Exposure (2.45 Gigahertz) on the Cell Membrane of Escherichia coli
Authors: Rougier Carole , Prorot Audrey , Chazal Philippe , Leveque Philippe , Leprat Patrick
Published: June 2014

The aim of this study was to investigate the effects on the cell membranes of
Escherichia coli
of 2.45-GHz microwave (MW) treatment under various conditions with an average temperature of the cell suspension maintained at 37°C in order to examine the possible thermal versus nonthermal effects of short-duration MW exposure. To this purpose, microwave irradiation of bacteria was performed under carefully defined and controlled parameters, resulting in a discontinuous MW exposure in order to maintain the average temperature of the bacterial cell suspensions at 37°C.
Escherichia coli
cells were exposed to 200- to 2,000-W discontinuous microwave (DW) treatments for different periods of time. For each experiment, conventional heating (CH) in a water bath at 37°C was performed as a control. The effects of DW exposure on cell membranes was investigated using flow cytometry (FCM), after propidium iodide (PI) staining of cells, in addition to the assessment of intracellular protein release in bacterial suspensions. No effect was detected when bacteria were exposed to conventional heating or 200 W, whereas cell membrane integrity was slightly altered when cell suspensions were subjected to powers ranging from 400 to 2,000 W. Thermal characterization suggested that the temperature reached by the microwave-exposed samples for the contact time studied was not high enough to explain the measured modifications of cell membrane integrity. Because the results indicated that the cell response is power dependent, the hypothesis of a specific electromagnetic threshold effect, probably related to the temperature increase, can be advanced.
A Third Subunit in Ancestral Cytochrome
c
-Dependent Nitric Oxide Reductases
Authors: Bricio C. , Alvarez L. , San Martin M. , Schurig-Briccio L. A. , Gennis R. B. , Berenguer J.
Published: June 2014

Reduction of NO to N
2
O by denitrifiying bacteria is catalyzed either by a monomeric quinol-nitric oxide reductase (qNor) or by a heterodimeric cytochrome
c
-dependent nitric oxide reductase (cNor). In ancient thermophilic bacteria belonging to the
Thermales
and
Aquificales
phylogenetic groups, the cluster encoding the cNor includes a small third gene (
norH
), in addition to those encoding homologues to the subunits of a typical cNor (
norC
and
norB
). We show in
Thermus thermophilus
that the three genes are cotranscribed in a single mRNA from an inducible promoter. The isolation of individual
nor
mutants and the production
in vivo
of His-tagged NorH protein followed by immobilized-metal affinity chromatography (IMAC) allowed us to conclude that NorH constitutes a third subunit of the cNor from
T. thermophilus
, which is involved in denitrification
in vivo
, likely allowing more efficient electron transport to cNor.
Effect of the Surfactant Tween 80 on the Detachment and Dispersal of Salmonella enterica Serovar Thompson Single Cells and Aggregates from Cilantro Leaves as Revealed by Image Analysis
Authors: Brandl Maria T. , Huynh Steven
Published: June 2014

Salmonella enterica
has the ability to form biofilms and large aggregates on produce surfaces, including on cilantro leaves. Aggregates of
S. enterica
serovar Thompson that remained attached to cilantro leaves after rigorous washing and that were present free or bound to dislodged leaf tissue in the wash suspension were observed by confocal microscopy. Measurement of
S.
Thompson population sizes in the leaf washes by plate counts failed to show an effect of 0.05% Tween 80 on the removal of the pathogen from cilantro leaves 2 and 6 days after inoculation. On the contrary, digital image analysis of micrographs of single cells and aggregates of green fluorescent protein (GFP)-
S.
Thompson present in cilantro leaf washes revealed that single cells represented 13.7% of the cell assemblages in leaf washes containing Tween 80, versus 9.3% in those without the surfactant. Moreover, Tween 80 decreased the percentage of the total
S.
Thompson cell population located in aggregates equal to or larger than 64 cells from 9.8% to 4.4% (
P
< 0.05). Regression analysis of the frequency distribution of aggregate size in leaf washes with and without Tween 80 showed that the surfactant promoted the dispersal of cells from large aggregates into smaller ones and into single cells (
P
< 0.05). Our study underlines the importance of investigating bacterial behavior at the scale of single cells in order to uncover trends undetectable at the population level by bacterial plate counts. Such an approach may provide valuable information to devise strategies aimed at enhancing the efficacy of produce sanitization treatments.
A Novel Immunofluorescence Flow Cytometry Technique Detects the Expansion of Brown Tides Caused by Aureoumbra lagunensis to the Caribbean Sea
Authors: Koch F. , Kang Y. , Villareal T. A. , Anderson D. M. , Gobler C. J.
Published: June 2014

During the past 3 decades, brown tides caused by the pelagophytes
Aureococcus anophagefferens
and
Aureoumbra lagunensis
have caused ecological and economic damage to coastal ecosystems across the globe. While blooms of
A. lagunensis
had previously been confined to Texas, in 2012, an expansive brown tide occurred on Florida's East Coast, causing widespread disruption within the Indian River and Mosquito Lagoons and generating renewed interest in this organism. A major impediment to detailed investigations of
A. lagunensis
in an ecosystem setting has been the absence of a rapid and reliable method for cell quantification. The combination of their small size (3 to 5 μm) and nondescript extracellular features makes identification and enumeration of these cells with conventional methods a challenge. Here we report the development of an immunological-based flow cytometry method that uses a fluorescently labeled antibody developed against
A. lagunensis
. This method is species specific, sensitive (detection limit of 1.5 × 10
3
cells ml
−1
), precise (1% relative standard deviation of replicated samples), and accurate (108% ± 8% recovery of spiked samples) over a wide range of cell concentrations. Furthermore, this method effectively quantifies
A. lagunensis
in both glutaraldehyde- and formalin-preserved samples, yields a high throughput of samples (∼35 samples h
−1
), and is cost-effective, making it an ideal tool for managers and scientists. This method successfully documented the recurrence of a brown tide bloom in Florida in 2013. Bloom densities were highest in June (>2.0 × 10
6
cells ml
−1
) and spanned >60 km from the Ponce de Leon inlet in the northern Mosquito Lagoon south to Titusville in the Indian River Lagoon. Low levels of
A. lagunensis
cells were found >250 km south of this region. This method also quickly and accurately identified
A. lagunensis
as the causative agent of a 2013 brown tide bloom in Guantanamo Bay, Cuba, and thus should prove useful for both quantifying the dynamics of ongoing blooms of
A. lagunensis
as well as documenting new outbreaks of this harmful alga.
Antifouling Coatings Influence both Abundance and Community Structure of Colonizing Biofilms: a Case Study in the Northwestern Mediterranean Sea
Authors: Camps Mercedes , Barani Aude , Gregori Gérald , Bouchez Agnès , Le Berre Brigitte , Bressy Christine , Blache Yves , Briand Jean-François
Published: June 2014

When immersed in seawater, substrates are rapidly colonized by both micro- and macroorganisms. This process is responsible for important economic and ecological prejudices, particularly when related to ship hulls or aquaculture nets. Commercial antifouling coatings are supposed to reduce biofouling, i.e., micro- and macrofoulers. In this study, biofilms that primarily settled on seven different coatings (polyvinyl chloride [PVC], a fouling release coating [FRC], and five self-polishing copolymer coatings [SPC], including four commercial ones) were quantitatively studied, after 1 month of immersion in summer in the Toulon Bay (Northwestern Mediterranean Sea, France), by using flow cytometry (FCM), microscopy, and denaturing gradient gel electrophoresis. FCM was used after a pretreatment to separate cells from the biofilm matrix, in order to determine densities of heterotrophic bacteria, picocyanobacteria, and pico- and nanoeukaryotes on these coatings. Among diatoms, the only microphytobenthic class identified by microscopy,Licmophora,Navicula, andNitzschiawere determined to be the dominant taxa. Overall, biocide-free coatings showed higher densities than all other coatings, except for one biocidal coating, whatever the group of microorganisms. Heterotrophic bacteria always showed the highest densities, and diatoms showed the lowest, but the relative abundances of these groups varied depending on the coating. In particular, the copper-free SPC failed to prevent diatom settlement, whereas the pyrithione-free SPC exhibited high picocyanobacterial density. These results highlight the interest in FCM for antifouling coating assessment as well as specific selection among microbial communities by antifouling coatings.
Vertebrate Decomposition Is Accelerated by Soil Microbes
Authors: Lauber Christian L. , Metcalf Jessica L. , Keepers Kyle , Ackermann Gail , Carter David O. , Knight Rob
Published: June 2014

Carrion decomposition is an ecologically important natural phenomenon influenced by a complex set of factors, including temperature, moisture, and the activity of microorganisms, invertebrates, and scavengers. The role of soil microbes as decomposers in this process is essential but not well understood and represents a knowledge gap in carrion ecology. To better define the role and sources of microbes in carrion decomposition, lab-reared mice were decomposed on either (i) soil with an intact microbial community or (ii) soil that was sterilized. We characterized the microbial community (16S rRNA gene for bacteria and archaea, and the 18S rRNA gene for fungi and microbial eukaryotes) for three body sites along with the underlying soil (i.e., gravesoils) at time intervals coinciding with visible changes in carrion morphology. Our results indicate that mice placed on soil with intact microbial communities reach advanced stages of decomposition 2 to 3 times faster than those placed on sterile soil. Microbial communities associated with skin and gravesoils of carrion in stages of active and advanced decay were significantly different between soil types (sterile versus untreated), suggesting that substrates on which carrion decompose may partially determine the microbial decomposer community. However, the source of the decomposer community (soil- versus carcass-associated microbes) was not clear in our data set, suggesting that greater sequencing depth needs to be employed to identify the origin of the decomposer communities in carrion decomposition. Overall, our data show that soil microbial communities have a significant impact on the rate at which carrion decomposes and have important implications for understanding carrion ecology.