bluuebunny/crossref_metadata_2025 huggingface dataset:
Transcranial cerebellar direct current stimulation and transcutaneous spinal cord direct current stimulation as innovative tools for neuroscientists
Authors: Priori Alberto , Ciocca Matteo , Parazzini Marta , Vergari Maurizio , Ferrucci Roberta
Published: June 2014

Two neuromodulatory techniques based on applying direct current (DC) non‐invasively through the skin, transcranial cerebellar direct current stimulation (tDCS) and transcutaneous spinal DCS, can induce prolonged functional changes consistent with a direct influence on the human cerebellum and spinal cord. In this article we review the major experimental works on cerebellar tDCS and on spinal tDCS, and their preliminary clinical applications. Cerebellar tDCS modulates cerebellar motor cortical inhibition, gait adaptation, motor behaviour, and cognition (learning, language, memory, attention). Spinal tDCS influences the ascending and descending spinal pathways, and spinal reflex excitability. In the anaesthetised mouse, DC stimulation applied under the skin along the entire spinal cord may affect GABAergic and glutamatergic systems. Preliminary clinical studies in patients with cerebellar disorders, and in animals and patients with spinal cord injuries, have reported beneficial effects. Overall the available data show that cerebellar tDCS and spinal tDCS are two novel approaches for inducing prolonged functional changes and neuroplasticity in the human cerebellum and spinal cord, and both are new tools for experimental and clinical neuroscientists.
Diabetic kidney disease: from physiology to therapeutics
Authors: Mora‐Fernández Carmen , Domínguez‐Pimentel Virginia , de Fuentes Mercedes Muros , Górriz José L. , Martínez‐Castelao Alberto , Navarro‐González Juan F.
Published: June 2014

Diabetic kidney disease (DKD) defines the functional, structural and clinical abnormalities of the kidneys that are caused by diabetes. This complication has become the single most frequent cause of end‐stage renal disease. The pathophysiology of DKD comprises the interaction of both genetic and environmental determinants that trigger a complex network of pathophysiological events, which leads to the damage of the glomerular filtration barrier, a highly specialized structure formed by the fenestrated endothelium, the glomerular basement membrane and the epithelial podocytes, that permits a highly selective ultrafiltration of the blood plasma. DKD evolves gradually over years through five progressive stages. Briefly they are: reversible glomerular hyperfiltration, normal glomerular filtration and normoalbuminuria, normal glomerular filtration and microalbuminuria, macroalbuminuria, and renal failure. Approximately 20–40% of diabetic patients develop microalbuminuria within 10–15 years of the diagnosis of diabetes, and about 80–90% of those with microalbuminuria progress to more advanced stages. Thus, after 15–20 years, macroalbuminuria occurs approximately in 20–40% of patients, and around half of them will present renal insufficiency within 5 years. The screening and early diagnosis of DKD is based on the measurement of urinary albumin excretion and the detection of microalbuminuria, the first clinical sign of DKD. The management of DKD is based on the general recommendations in the treatment of patients with diabetes, including optimal glycaemic and blood pressure control, adequate lipid management and abolishing smoking, in addition to the lowering of albuminuria.
Less is more: minimal expression of myoendothelial gap junctions optimizes cell–cell communication in virtual arterioles
Authors: Hald Bjørn Olav , Jacobsen Jens Christian Brings , Sandow Shaun L. , Holstein‐Rathlou Niels‐Henrik , Welsh Donald G.
Published: June 2014

Key points

Electrical signalling in blood vessels is important in acute and long‐term flow regulation.

As myoendothelial gap junctions (MEGJs) provide electrical contacts between endothelial cells and smooth muscle cells (SMCs), a high MEGJ expression is thought to be important for intercellular communication despite observations of heterogeneous MEGJ expression.

Using a computational approach, we find that a minimal but sufficient number of heterogeneously distributed MEGJs optimize electrical cell–cell communication.

Tailoring SMC–SMC coupling to the MEGJ distribution and permeability ensures a smooth electrical response while retaining the ability to display local responses.

As heterogeneous MEGJ distributions allow for different conduction profiles along the SMC and endothelial cell layers, it is possible to observe an apparently non‐decaying conduction profile in the SMC layer of a vessel with passive electrical properties.

These findings expand our understanding of how heterogeneity in MEGJ distribution affects local and global flow.

Dysfunctional electrical signalling within the arteriolar wall is a major cause of cardiovascular disease. The endothelial cell layer constitutes the primary electrical pathway, co‐ordinating contraction of the overlying smooth muscle cell (SMC) layer. As myoendothelial gap junctions (MEGJs) provide direct contact between the cell layers, proper vasomotor responses are thought to depend on a high, uniform MEGJ density. However, MEGJs are observed to be expressed heterogeneously within and among vascular beds. This discrepancy is addressed in the present study. As no direct measures of MEGJ conductance exist, we employed a computational modelling approach to vary the number, conductance and distribution of MEGJs. Our simulations demonstrate that a minimal number of randomly distributed MEGJs augment arteriolar cell–cell communication by increasing conduction efficiency and ensuring appropriate membrane potential responses in SMCs. We show that electrical coupling between SMCs must be tailored to the particular MEGJ distribution. Finally, observation of non‐decaying mechanical conduction in arterioles without regeneration has been a long‐standing controversy in the microvascular field. As heterogeneous MEGJ distributions provide for different conduction profiles along the cell layers, we demonstrate that a non‐decaying conduction profile is possible in the SMC layer of a vessel with passive electrical properties. These intriguing findings redefine the concept of efficient electrical communication in the microcirculation, illustrating how heterogeneous properties, ubiquitous in biological systems, may have a profound impact on system behaviour and how acute local and global flow control is explained from the biophysical foundations.
Nutrient‐induced changes in the phenotype and function of the enteric nervous system
Authors: Neunlist Michel , Schemann Michael
Published: June 2014

The enteric nervous system (ENS) integrates numerous sensory signals in order to control and maintain normal gut functions. Nutrients are one of the prominent factors which determine the chemical milieu in the lumen and, after absorption, also within the gut wall. This review summarizes current knowledge on the impact of key nutrients on ENS functions and phenotype, covering their acute and long‐term effects. Enteric neurones contain the molecular machinery to respond specifically to nutrients. These transporters and receptors are not expressed exclusively in the ENS but are also present in other cells such as enteroendocrine cells (EECs) and extrinsic sensory nerves, signalling satiety or hunger. Glucose, amino acids and fatty acids all activate enteric neurones, as suggested by enhanced c‐Fos expression or spike discharge. These excitatory effects are the result of a direct neuronal activation but also involve the activation of EECs which, upon activation by luminal nutrients, release mediators such as ghrelin, cholecystokinin or serotonin. The presence or absence of nutrients in the intestinal lumen induces long‐term changes in neurotransmitter expression, excitability, neuronal survival and ultimately impact upon gut motility, secretion or intestinal permeability. Together with EECs and vagal nerves, the ENS must be recognized as an important player initiating concerted responses to nutrients. It remains to be studied how, for instance, nutrient‐induced changes in the ENS may influence additional gut functions such as intestinal barrier repair, intestinal epithelial stem cell proliferation/differentiation and also the signalling of extrinsic nerves to brain regions which control food intake.
Cardiorenal syndrome: acute kidney injury secondary to cardiovascular disease and role of protein‐bound uraemic toxins
Authors: Lekawanvijit Suree , Krum Henry
Published: June 2014

Cardiovascular disease (CVD) and kidney disease are closely interrelated. Disease of one organ can induce dysfunction of the other, ultimately leading to failure of both. Clinical awareness of synergistic adverse clinical outcomes in patients with coexisting CVD and kidney disease or ‘cardiorenal syndrome (CRS)’ has existed. Renal dysfunction, even mild, is a strong independent predictor for poor prognosis in CVD patients. Developing therapeutic interventions targeting acute kidney injury (AKI) has been limited due mainly to lack of effective tools to accurately detect AKI in a timely manner. Neutrophil gelatinase‐associated lipocalin and kidney injury molecule‐1 have been recently demonstrated to be potential candidate biomarkers in patients undergoing cardiac surgery. However, further validation of AKI biomarkers is needed in other CVD settings, especially acute decompensated heart failure and acute myocardial infarction where AKI commonly occurs. The other concern with regard to understanding the pathogenesis of renal complications in CVD is that mechanistically oriented studies have been relatively rare. Pre‐clininal studies have shown that activation of renal inflammation–fibrosis processes, probably triggered by haemodynamic derangement, underlies CVD‐associated renal dysfunction. On the other hand, it is postulated that there still are missing links in the heart–kidney connection in CRS patients who have significant renal dysfunction. At present, non‐dialysable protein‐bound uraemic toxins (PBUTs) appear to be the main focus in this regard. Evidence of the causal role of PBUTs in CRS has been increasingly demonstrated, mainly focusing on indoxyl sulfate (IS) and p‐cresyl sulfate (pCS). Both IS and pCS are derived from colonic microbiotic metabolism of dietary amino acids, and hence the colon has become a target of treatment in addition to efforts to improve dialysis techniques for better removal of PBUTs. Novel therapy targeting the site of toxin production has led to new prospects in early intervention for predialysis patients with chronic kidney disease.
Developmental changes in Ca2+ channel subtypes regulating endocytosis at the calyx of Held
Authors: Midorikawa Mitsuharu , Okamoto Yuji , Sakaba Takeshi
Published: June 2014

Key points

We examined the roles of each Ca2+ channel subtype in the time course of endocytosis at the calyx of Held terminal by a capacitance measurement technique.

At the calyx of Held terminal, endocytosis is mediated by two kinetically distinct components, a fast mode and a slow mode of endocytosis, in animals at postnatal days 8–11.

R‐Type Ca2+ channels are more tightly coupled to the slow mode of endocytosis than P/Q‐ and N‐type, demonstrating the differential contribution from different Ca2+ channels to endocytosis.

The fast mode of endocytosis, which was observed only following strong stimulation, was mainly mediated by P/Q‐type Ca2+ channels.

In animals at postnatal days 14–17, when fast endocytosis becomes less prominent, slow endocytosis was regulated by Ca2+ influx through P/Q‐type Ca2+ channels, indicating developmental changes in the functional coupling between Ca2+ channel subtypes and endocytosis.

At the mammalian central synapse, Ca2+ influx through Ca2+ channels triggers neurotransmitter release by exocytosis of synaptic vesicles, which fuse with the presynaptic membrane and are subsequently retrieved by endocytosis. At the calyx of Held terminal, P/Q‐type Ca2+ channels mainly mediate exocytosis, while N‐ and R‐type channels have a minor role in young terminals (postnatal days 8–11). The role of each Ca2+ channel subtype in endocytosis remains to be elucidated; therefore, we examined the role of each type of Ca2+ channel in endocytosis, by using whole‐cell patch‐clamp recordings in conjunction with capacitance measurement techniques. We found that at the young calyx terminal, when R‐type Ca2+ channels were blocked, the slow mode of endocytosis was further slowed, while blocking of either P/Q‐ or N‐type Ca2+ channels had no major effect. In more mature terminals (postnatal days 14–17), the slow mode of endocytosis was mainly triggered by P/Q‐type Ca2+ channels, suggesting developmental changes in the regulation of the slow mode of endocytosis by different Ca2+ channel subtypes. In contrast, a fast mode of endocytosis was observed after strong stimulation in young terminals that was mediated mainly by P/Q‐type, but not R‐ or N‐type Ca2+ channels. These results suggest that different types of Ca2+ channels regulate the two different modes of endocytosis. The results may also suggest that exo‐ and endocytosis are regulated independently at different sites in young animals but are more tightly coupled in older animals, allowing more efficient synaptic vesicle cycling adapted for fast signalling.
Depression biased non‐Hebbian spike‐timing‐dependent synaptic plasticity in the rat subiculum
Authors: Pandey Anurag , Sikdar Sujit Kumar
Published: June 2014

Key points

Spike‐timing‐dependent plasticity (STDP) is the induction of synaptic plasticity by coincident activity of pre‐ and postsynaptic neurons.

In most of the excitatory synapses, an EPSP immediately followed by a back‐propagating action potential (bAP) enhances the synaptic efficacy, whereas the reverse weakens it.

Contrary to the above observation, we demonstrate that, at the proximal excitatory synapses on the subicular pyramidal neurons, an EPSP immediately followed by a burst of bAPs weakens the synaptic strength, whereas the reverse strengthens the synapse in both bursting and regular firing neurons.

This reverse STDP rule may have strong implications in synaptic integration and information outflow from the hippocampus.

Interestingly, the mechanisms associated with synaptic depression using the same induction protocol were different in the two neuronal subtypes, being postsynaptic in the bursting neurons requiring NMDA receptor activity, but presynaptic in the regular firing neurons involving L‐type calcium channels.

The subiculum is a structure that forms a bridge between the hippocampus and the entorhinal cortex (EC), and plays a major role in the memory consolidation process. Here, we demonstrate spike‐timing‐dependent plasticity (STDP) at the proximal excitatory inputs on the subicular pyramidal neurons of juvenile rat. Causal (positive) pairing of a single EPSP with a single back‐propagating action potential (bAP) after a time interval of 10 ms (+10 ms) failed to induce plasticity. However, increasing the number of bAPs in a burst to three, at two different frequencies of 50 Hz (bAP burst) and 150 Hz, induced long‐term depression (LTD) after a time interval of +10 ms in both the regular‐firing (RF), and the weak burst firing (WBF) neurons. The LTD amplitude decreased with increasing time interval between the EPSP and the bAP burst. Reversing the order of the pairing of the EPSP and the bAP burst induced LTP at a time interval of −10 ms. This finding is in contrast with reports at other synapses, wherein pre‐ before postsynaptic (causal) pairing induced LTP and vice versa. Our results reaffirm the earlier observations that the relative timing of the pre‐ and postsynaptic activities can lead to multiple types of plasticity profiles. The induction of timing‐dependent LTD (t‐LTD) was dependent on postsynaptic calcium change via NMDA receptors in the WBF neurons, while it was independent of postsynaptic calcium change, but required active L‐type calcium channels in the RF neurons. Thus the mechanism of synaptic plasticity may vary within a hippocampal subfield depending on the postsynaptic neuron involved. This study also reports a novel mechanism of LTD induction, where L‐type calcium channels are involved in a presynaptically induced synaptic plasticity. The findings may have strong implications in the memory consolidation process owing to the central role of the subiculum and LTD in this process.
The multifaceted subunit interfaces of ionotropic glutamate receptors
Authors: Green Tim , Nayeem Naushaba
Published: June 2014

The past fifteen years has seen a revolution in our understanding of ionotropic glutamate receptor (iGluR) structure, starting with the first view of the ligand binding domain (LBD) published in 1998, and in many ways culminating in the publication of the full‐length structure of GluA2 in 2009. These reports have revealed not only the central role played by subunit interfaces in iGluR function, but also myriad binding sites within interfaces for endogenous and exogenous factors. Changes in the conformation of inter‐subunit interfaces are central to transmission of ligand gating into pore opening (itself a rearrangement of interfaces), and subsequent closure through desensitization. With the exception of the agonist binding site, which is located entirely within individual subunits, almost all modulatory factors affecting iGluRs appear to bind to sites in subunit interfaces. This review seeks to summarize what we currently understand about the diverse roles interfaces play in iGluR function, and to highlight questions for future research.
The Effect of Small Intestine Heterogeneity on Irreversible Electroporation Treatment Planning
Authors: Phillips Mary
Published: June 2014

Nonthermal irreversible electroporation (NTIRE) is an ablation modality that utilizes microsecond electric fields to produce nanoscale defects in the cell membrane. This results in selective cell death while preserving all other molecules, including the extracellular matrix. Here, finite element analysis and experimental results are utilized to examine the effect of NTIRE on the small intestine due to concern over collateral damage to this organ during NTIRE treatment of abdominal cancers. During previous studies, the electrical treatment parameters were chosen based on a simplified homogeneous tissue model. The small intestine, however, has very distinct layers, and a more realistic model is needed to further develop this technology for precise clinical applications. This study uses a two-dimensional finite element solution of the Laplace and heat conduction equations to investigate how small intestine heterogeneities affect the electric field and temperature distribution. Experimental results obtained by applying NTIRE to the rat small intestine in vivo support the heterogeneous effect of NTIRE on the tissue. The numerical modeling indicates that the electroporation parameters chosen for this study avoid thermal damage to the tissue. This is supported by histology obtained from the in vivo study, which showed preservation of extracellular structures. The finite element model also indicates that the heterogeneous structure of the small intestine has a significant effect on the electric field and volume of cell ablation during electroporation and could have a large impact on the extent of treatment. The heterogeneous nature of the tissue should be accounted for in clinical treatment planning.
Elastic and Inelastic Responses of C(T) Specimens With Discontinuous Cracks
Authors: Kim Nak-Hyun , Kim Yun-Jae , Dean Dave W. , Davies Catrin M. , Nikbin Kamran , Mehmanparast Ali
Published: June 2014

This paper investigates elastic and elastic–plastic responses of a plane strain compact tension specimen containing a discontinuous crack using two-dimensional (2D) finite element analyses. Discontinuous cracking is represented by modeling two (main and sub) cracks with the distance between them systematically varied. The finite element predictions show that the presence of subcracks has minimal effect on the elastic compliance and potential difference but significantly influences the plastic limit loads and load line displacements (LLDs). The evaluation of the elastic and elastic–plastic behavior of the J-integrals evaluated using different contours for discontinuous cracks are also examined and explained.
Aeroengine Multivariable Nonlinear Tracking Control Based on Uncertainty and Disturbance Estimator
Authors: Xiao Lingfei
Published: June 2014

The multivariable robust tracking control problem for aeroengine is considered in this paper. On the basis of the aeroengine nonlinear affine uncertain dynamic model, and according to uncertainty and disturbance estimator (UDE) control approach, a novel aeroengine multivariable robust nonlinear tracking control method is presented in order to provide favorable tracking and disturbance rejection performance. After getting a generalization form of UDE-based aeroengine multivariable controller, a simplification form of control law is obtained when a specified form of low-pass filter is applied. Reference model of the aeroengine system should have satisfying dynamic, thus an optional reference model is provided. Simulation on a twin-shaft aeroengine with two inputs, verifies the effectiveness of the proposed method.
Discussion: “Entransy is Now Clear”
Authors: Awad M. M.
Published: June 2014

The purpose of this discussion is to place in perspective the concept of entransy, in view of the critiques published by Grazzini et al. (2013, “Entropy Versus Entransy,” J. Non-Equilib. Thermodyn., 38, pp. 259–271), Herwig (2014, “Do We Really Need ‘Entransy’? A Critical Assessment of a New Quantity in Heat Transfer Analysis,” ASME J. Heat Trans., 136(4), 045501), and Bejan 2014, ““Entransy,” and Its Lack of Content in Physics,” ASME J. Heat Trans., 136(5), 055501), and especially the response just published by Guo et al. (2014, “A Response to Do We Really Need ‘Entransy’?” ASME J. Heat Trans., 136(4), 046001). The conclusion is that entransy is improper and not needed, and that Guo et al.'s own response actually confirms this conclusion.
On the Self-Recovery Phenomenon for a Cylindrical Rigid Body Rotating in an Incompressible Viscous Fluid
Authors: Eui Chang Dong , Jeon Soo
Published: June 2014

The damping-induced self-recovery phenomenon is well understood for finite-dimensional mechanical systems. In this paper, we discover a self-recovery phenomenon in a composite system that consists of a cylindrical vessel and a surrounding fluid, where the vessel is equipped with an internal rotor and the fluid is incompressible and viscous. In the system dynamics, interactions between the vessel and the ambient fluid are fully taken into account. A combination of the Lyapunov method and the final-value theorem is applied for analysis of the dynamics. It is mathematically shown that after the spin of the rotor comes to a complete stop in finite time or exponentially as time tends to infinity, the vessel, which has deviated from its initial position due to the reaction to rotor spinning, converges back to its initial position as time tends to infinity, and so does every fluid particle. An experimental test is conducted to verify the occurrence of this phenomenon. The simultaneous self-recovery of the vessel and the fluid to the initial configuration is induced by the fluid viscosity as if the viscosity has a memory of the initial configuration. We envision that our discovery may be useful in designing and operating mechatronic systems interacting with fluids such as underwater vehicles.
Steady and Pulsating Turbulent Flows in Complex Pipe Geometries
Authors: Colonia Simone , Romano Giovanni P.
Published: June 2014

In this paper, measurements of velocity and stress fields in rigid pipes are performed by means of planar particle image velocimetry (PIV). The attention is focused onto the effect of Reynolds number and of continuous or pulsating flows by investigating pipe geometries ranging from the straight pipe to the reduced section and bifurcated ones. The obtained results show that, in the tested range, the effect of Reynolds number is limited for straight and reduced section pipes, while significant for the bifurcated one. Independently of Reynolds number, different geometries and forcing (continuous or pulsed) produce strong variations in intensity and spatial distribution of velocity and stress fields. Considering the latter, the contribution of viscous and turbulent stresses are measured separately and compared. Indeed turbulent stresses are always larger than the viscous ones, but the relative intensity is highly variable as also the spatial distribution of maxima and minima. Specifically, in the pulsating flows, this distribution is phase-dependent reflecting the oscillations of regions of flow separation which form especially in reduced section and bifurcated pipes. These results are useful for all engineering applications in which turbulent pipe flows are involved.
Selective Raman modes and strong photoluminescence of gallium selenide flakes on sp2 carbon
Authors: Rodriguez Raul D. , Müller Susanne , Sheremet Evgeniya , Zahn Dietrich R. T. , Villabona Alexander , Lopez-Rivera Santos A. , Tonndorf Philipp , de Vasconcellos Steffen Michaelis , Bratschitsch Rudolf
Published: June 2014

Two-dimensional materials awakened a strong interest in the scientific and technological communities due to their exceptional properties that can be tuned by the material thickness and chemistry. In order to correlate optical properties with crystallographic structure and morphology, in this work, the authors aim at studying GaSe nanoflakes deposited on highly ordered pyrolytic graphite by means of atomic force microscopy, Raman, and photoluminescence (PL) spectroscopies. The authors found that the basal plane of the flakes can be attributed to the ε-phase expected for bulk samples grown by the Bridgman method. However, a strong difference in the Raman spectra was systematically found at the edge of our GaSe flakes. Forbidden Raman modes located around 250 cm−1 were selectively observed at specific locations. These modes could not be directly attributed to the ε-phase observed in the basal plane or in the bulk. The atomic force microscopy investigations show that high topographical features characterize the regions with the highest photoluminescence and the forbidden Raman modes. This change in crystal orientation at selective locations of the flake could activate the E′(LO) Raman mode at 255 cm−1. The enhancement of the PL emission around 620 nm is also linked to the change in crystal orientation due to an increase in the probability of electronic transitions. These results show the rich physics of GaSe flakes in contrast to what is known from its bulk counterpart with possible applications in photovoltaics and photodetectors for nanoflakes with engineered geometries.
Modelling of multiscale nonlinear interaction of elastic waves with three-dimensional cracks
Authors: Ciampa Francesco , Barbieri Ettore , Meo Michele
Published: June 2014

This paper presents a nonlinear elastic material model able to simulate the nonlinear effects generated by the interaction of acoustic/ultrasonic waves with damage precursors and micro-cracks in a variety of materials. Such a constitutive model is implemented in an in-house finite element code and exhibits a multiscale nature where the macroscopic behavior of damaged structures can be represented through a contribution of a number of mesoscopic elements, which are composed by a statistical collection of microscopic units. By means of the semi-analytical Landau formulation and Preisach-Mayergoyz space representation, this multiscale model allows the description of the structural response under continuous harmonic excitation of micro-damaged materials showing both anharmonic and dissipative hysteretic effects. In this manner, nonlinear effects observed experimentally, such as the generation of both even and odd harmonics, can be reproduced. In addition, by using Kelvin eigentensors and eigenelastic constants, the wave propagation problem in both isotropic and orthotropic solids was extended to the three-dimensional Cartesian space. The developed model has been verified for a number of different geometrical and material configurations. Particularly, the influence of a small region with classical and non-classical elasticity and the variations of the input amplitudes on the harmonics generation were analyzed.
Linear elastic properties derivation from microstructures representative of transport parameters
Authors: Hoang Minh Tan , Bonnet Guy , Tuan Luu Hoang , Perrot Camille
Published: June 2014

It is shown that three-dimensional periodic unit cells (3D PUC) representative of transport parameters involved in the description of long wavelength acoustic wave propagation and dissipation through real foam samples may also be used as a standpoint to estimate their macroscopic linear elastic properties. Application of the model yields quantitative agreement between numerical homogenization results, available literature data, and experiments. Key contributions of this work include recognizing the importance of membranes and properties of the base material for the physics of elasticity. The results of this paper demonstrate that a 3D PUC may be used to understand and predict not only the sound absorbing properties of porous materials but also their transmission loss, which is critical for sound insulation problems.
Characteristics of group velocities of backward waves in a hollow cylinder
Authors: Cui Hanyin , Lin Weijun , Zhang Hailan , Wang Xiuming , Trevelyan Jon
Published: June 2014

It is known that modes in axially uniform waveguides exhibit backward-propagation characteristics for which group and phase velocities have opposite signs. For elastic plates, group velocities of backward Lamb waves depend only on Poisson's ratio. This paper explores ways to achieve a large group velocity of a backward mode in hollow cylinders by changing the outer to inner radius ratio, in order that such a mode with strong backward-propagation characteristics may be used in acoustic logging tools. Dispersion spectra of guided waves in hollow cylinders of varying radii are numerically simulated to explore the existence of backward modes and to choose the clearly visible backward modes with high group velocities. Analyses of group velocity characteristics show that only a small number of low order backward modes are suitable for practical use, and the radius ratio to reach the highest group velocity corresponds to the accidental degeneracy of neighboring pure transverse and compressional modes at the wavenumber k = 0. It is also shown that large group velocities of backward waves are achievable in hollow cylinders made of commonly encountered materials, which may bring cost benefits when using acoustic devices which take advantage of backward-propagation effects.
Experimental vibroacoustic testing of plane panels using synthesized random pressure fields
Authors: Robin Olivier , Berry Alain , Moreau Stéphane
Published: June 2014

The experimental reproduction of random pressure fields on a plane panel and corresponding induced vibrations is studied. An open-loop reproduction strategy is proposed that uses the synthetic array concept, for which a small array element is moved to create a large array by post-processing. Three possible approaches are suggested to define the complex amplitudes to be imposed to the reproduction sources distributed on a virtual plane facing the panel to be tested. Using a single acoustic monopole, a scanning laser vibrometer and a baffled simply supported aluminum panel, experimental vibroacoustic indicators such as the Transmission Loss for Diffuse Acoustic Field, high-speed subsonic and supersonic Turbulent Boundary Layer excitations are obtained. Comparisons with simulation results obtained using a commercial software show that the Transmission Loss estimation is possible under both excitations. Moreover and as a complement to frequency domain indicators, the vibroacoustic behavior of the panel can be studied in the wave number domain.
Assessing the effects of temporal coherence on auditory stream formation through comodulation masking release
Authors: Krogholt Christiansen Simon , Oxenham Andrew J.
Published: June 2014

Recent studies of auditory streaming have suggested that repeated synchronous onsets and offsets over time, referred to as “temporal coherence,” provide a strong grouping cue between acoustic components, even when they are spectrally remote. This study uses a measure of auditory stream formation, based on comodulation masking release (CMR), to assess the conditions under which a loss of temporal coherence across frequency can lead to auditory stream segregation. The measure relies on the assumption that the CMR, produced by flanking bands remote from the masker and target frequency, only occurs if the masking and flanking bands form part of the same perceptual stream. The masking and flanking bands consisted of sequences of narrowband noise bursts, and the temporal coherence between the masking and flanking bursts was manipulated in two ways: (a) By introducing a fixed temporal offset between the flanking and masking bands that varied from zero to 60 ms and (b) by presenting the flanking and masking bursts at different temporal rates, so that the asynchronies varied from burst to burst. The results showed reduced CMR in all conditions where the flanking and masking bands were temporally incoherent, in line with expectations of the temporal coherence hypothesis.
Statistical inference of seabed sound-speed structure in the Gulf of Oman Basin
Authors: Sagers Jason D. , Knobles David P.
Published: June 2014

Addressed is the statistical inference of the sound-speed depth profile of a thick soft seabed from broadband sound propagation data recorded in the Gulf of Oman Basin in 1977. The acoustic data are in the form of time series signals recorded on a sparse vertical line array and generated by explosive sources deployed along a 280 km track. The acoustic data offer a unique opportunity to study a deep-water bottom-limited thickly sedimented environment because of the large number of time series measurements, very low seabed attenuation, and auxiliary measurements. A maximum entropy method is employed to obtain a conditional posterior probability distribution (PPD) for the sound-speed ratio and the near-surface sound-speed gradient. The multiple data samples allow for a determination of the average error constraint value required to uniquely specify the PPD for each data sample. Two complicating features of the statistical inference study are addressed: (1) the need to develop an error function that can both utilize the measured multipath arrival structure and mitigate the effects of data errors and (2) the effect of small bathymetric slopes on the structure of the bottom interacting arrivals.
The role of auditory spectro-temporal modulation filtering and the decision metric for speech intelligibility prediction
Authors: Chabot-Leclerc Alexandre , Jørgensen Søren , Dau Torsten
Published: June 2014

Speech intelligibility models typically consist of a preprocessing part that transforms stimuli into some internal (auditory) representation and a decision metric that relates the internal representation to speech intelligibility. The present study analyzed the role of modulation filtering in the preprocessing of different speech intelligibility models by comparing predictions from models that either assume a spectro-temporal (i.e., two-dimensional) or a temporal-only (i.e., one-dimensional) modulation filterbank. Furthermore, the role of the decision metric for speech intelligibility was investigated by comparing predictions from models based on the signal-to-noise envelope power ratio, SNRenv, and the modulation transfer function, MTF. The models were evaluated in conditions of noisy speech (1) subjected to reverberation, (2) distorted by phase jitter, or (3) processed by noise reduction via spectral subtraction. The results suggested that a decision metric based on the SNRenv may provide a more general basis for predicting speech intelligibility than a metric based on the MTF. Moreover, the one-dimensional modulation filtering process was found to be sufficient to account for the data when combined with a measure of across (audio) frequency variability at the output of the auditory preprocessing. A complex spectro-temporal modulation filterbank might therefore not be required for speech intelligibility prediction.
Development of speech glimpsing in synchronously and asynchronously modulated noise
Authors: Hall Joseph W. , Buss Emily , Grose John H.
Published: June 2014

This study investigated development of the ability to integrate glimpses of speech in modulated noise. Noise was modulated synchronously across frequency or asynchronously such that when noise below 1300 Hz was “off,” noise above 1300 Hz was “on,” and vice versa. Asynchronous masking was used to examine the ability of listeners to integrate speech glimpses separated across time and frequency. The study used the Word Intelligibility by Picture Identification (WIPI) test and included adults, older children (age 8–10 yr) and younger children (5–7 yr). Results showed poorer masking release for the children than the adults for synchronous modulation but not for asynchronous modulation. It is possible that children can integrate cues relatively well when all intervals provide at least partial speech information (asynchronous modulation) but less well when some intervals provide little or no information (synchronous modulation). Control conditions indicated that children appeared to derive less benefit than adults from speech cues below 1300 Hz. This frequency effect was supported by supplementary conditions where the noise was unmodulated and the speech was low- or high-pass filtered. Possible sources of the developmental frequency effect include differences in frequency weighting, effective speech bandwidth, and the signal-to-noise ratio in the unmodulated noise condition.
Time-of-flight modeling of transversal ultrasonic scan of wood
Authors: Yaitskova Natalia , van de Kuilen Jan Willem
Published: June 2014

Time-of-flight is a time for an ultrasonic pulse to cross a sample. It contains valuable information about the mechanical properties of a material. For the ultrasonic pulse propagating in wood perpendicular to the grain the relation between the time-of-flight and the elastic constants is rather complex due to the strong anisotropicity of wood. With the help of some assumptions this relation can be established from the elastic theory. The analytical calculation results in a function which represents a change of time-of-flight when the direction of propagation shifts from the radial to the tangential direction while scanning a board crosswise. The function takes into account the location of the pith and the geometry of the growth rings. The measurement performed on a sample of European spruce confirms the theoretical prediction.
Acoustic pulse propagation in an urban environment using a three-dimensional numerical simulation
Authors: Mehra Ravish , Raghuvanshi Nikunj , Chandak Anish , Albert Donald G. , Keith Wilson D. , Manocha Dinesh
Published: June 2014

Acoustic pulse propagation in outdoor urban environments is a physically complex phenomenon due to the predominance of reflection, diffraction, and scattering. This is especially true in non-line-of-sight cases, where edge diffraction and high-order scattering are major components of acoustic energy transport. Past work by Albert and Liu [J. Acoust. Soc. Am. 127, 1335–1346 (2010)] has shown that many of these effects can be captured using a two-dimensional finite-difference time-domain method, which was compared to the measured data recorded in an army training village. In this paper, a full three-dimensional analysis of acoustic pulse propagation is presented. This analysis is enabled by the adaptive rectangular decomposition method by Raghuvanshi, Narain and Lin [IEEE Trans. Visual. Comput. Graphics 15, 789–801 (2009)], which models sound propagation in the same scene in three dimensions. The simulation is run at a much higher usable bandwidth (nearly 450 Hz) and took only a few minutes on a desktop computer. It is shown that a three-dimensional solution provides better agreement with measured data than two-dimensional modeling, especially in cases where propagation over rooftops is important. In general, the predicted acoustic responses match well with measured results for the source/sensor locations.
Acoustic correlates of vowel intelligibility in clear and conversational speech for young normal-hearing and elderly hearing-impaired listeners
Authors: Hargus Ferguson Sarah , Quené Hugo
Published: June 2014

The present investigation carried out acoustic analyses of vowels in clear and conversational speech produced by 41 talkers. Mixed-effects models were then deployed to examine relationships among acoustic and perceptual data for these vowels. Acoustic data include vowel duration, steady-state formant frequencies, and two measures of dynamic formant movement. Perceptual data consist of vowel intelligibility in noise for young normal-hearing and elderly hearing-impaired listeners, as reported by Ferguson in 2004 and 2012 [J. Acoust. Soc. Am. 116, 2365–2373 (2004); J. Speech Lang. Hear. Res. 55, 779–790 (2012)], respectively. Significant clear speech effects were observed for all acoustic metrics, although not all measures changed for all vowels and considerable talker variability was observed. Mixed-effects analyses revealed that the contribution of duration and steady-state formant information to vowel intelligibility differed for the two listener groups. This outcome is consistent with earlier research suggesting that hearing loss, and possibly aging, alters the way acoustic cues are used for identifying vowels.
Modeling the receptivity of an air jet to transverse acoustic disturbance with application to musical instruments
Authors: Blanc F. , François V. , Fabre B. , de la Cuadra P. , Lagrée P.-Y.
Published: June 2014

A simple analytical model for the interaction between a plane jet issued from a flue and a transverse acoustic disturbance is developed in this paper. The model is inspired by direct flow simulation results confronted to experimental data. The interaction is expected to take place in the vicinity of the separation points of the jet. The influence of the detailed geometry of the channel end on the jet receptivity is discussed, and more specifically the chamfer geometries found in flute-like musical instruments. The simplified model explains quite well the difference between the jet response of a flue with square edges compared to a chamfered flue exit. The effect of rounded, lip-like flue exit is not well captured by the model.
Measuring static viscous permeability of porous absorbing materials
Authors: Sadouki M. , Fellah Z. E. A. , Berbiche A. , Fellah M. , Mitri F. G. , Ogam E. , Depollier C.
Published: June 2014

Conventional acoustical methods for measuring the permeability or flow resistivity of a porous material require a priori estimation of the porosity. In this work, an acoustical method is presented in which a simplified expression (independent of both the frequency and porosity) for the transmitted waves at the Darcy's regime (low frequency range) is derived, and used for the inverse determination of both the viscous static permeability (or flow resistivity) and the thickness of air-saturated porous materials. The inverse problem is solved based on the least-square numerical method using experimental transmitted waves in time domain. Tests are performed using industrial plastic foams. Experimental and numerical validation results of this method are presented, which show the advantage of measuring the viscous permeability and thickness of a porous slab, without the required prior knowledge of the porosity, but by simply using the transmitted waves.
The effects of environmental variability and spatial sampling on the three-dimensional inversion problem
Authors: Bender Christopher M. , Ballard Megan S. , Wilson Preston S.
Published: June 2014

The overall goal of this work is to quantify the effects of environmental variability and spatial sampling on the accuracy and uncertainty of estimates of the three-dimensional ocean sound-speed field. In this work, ocean sound speed estimates are obtained with acoustic data measured by a sparse autonomous observing system using a perturbative inversion scheme [Rajan, Lynch, and Frisk, J. Acoust. Soc. Am. 82, 998–1017 (1987)]. The vertical and horizontal resolution of the solution depends on the bandwidth of acoustic data and on the quantity of sources and receivers, respectively. Thus, for a simple, range-independent ocean sound speed profile, a single source–receiver pair is sufficient to estimate the water-column sound-speed field. On the other hand, an environment with significant variability may not be fully characterized by a large number of sources and receivers, resulting in uncertainty in the solution. This work explores the interrelated effects of environmental variability and spatial sampling on the accuracy and uncertainty of the inversion solution though a set of case studies. Synthetic data representative of the ocean variability on the New Jersey shelf are used.
Shallow-water sparsity-cognizant source-location mapping
Authors: Forero Pedro A. , Baxley Paul A.
Published: June 2014

Using passive sonar for underwater acoustic source localization in a shallow-water environment is challenging due to the complexities of underwater acoustic propagation. Matched-field processing (MFP) exploits both measured and model-predicted acoustic pressures to localize acoustic sources. However, the ambiguity surface obtained through MFP contains artifacts that limit its ability to reveal the location of the acoustic sources. This work introduces a robust scheme for shallow-water source localization that exploits the inherent sparse structure of the localization problem and the use of a model characterizing the acoustic propagation environment. To this end, the underwater acoustic source-localization problem is cast as a sparsity-inducing stochastic optimization problem that is robust to model mismatch. The resulting source-location map (SLM) yields reduced ambiguities and improved resolution, even at low signal-to-noise ratios, when compared to those obtained via classical MFP approaches. An iterative solver based on block-coordinate descent is developed whose computational complexity per iteration is linear with respect to the number of locations considered for the SLM. Numerical tests illustrate the performance of the algorithm.
The effect of language experience on perceptual normalization of Mandarin tones and non-speech pitch contours
Authors: Luo Xin , Ashmore Krista B.
Published: June 2014

Context-dependent pitch perception helps listeners recognize tones produced by speakers with different fundamental frequencies (f0s). The role of language experience in tone normalization remains unclear. In this cross-language study of tone normalization, native Mandarin and English listeners were asked to recognize Mandarin Tone 1 (high-flat) and Tone 2 (mid-rising) with a preceding Mandarin sentence. To further test whether context-dependent pitch perception is speech-specific or domain-general, both language groups were asked to identify non-speech flat and rising pitch contours with a preceding non-speech flat pitch contour. Results showed that both Mandarin and English listeners made more rising responses with non-speech than with speech stimuli, due to differences in spectral complexity and listening task between the two stimulus types. English listeners made more rising responses than Mandarin listeners with both speech and non-speech stimuli. Contrastive context effects (more rising responses in the high-f0 context than in the low-f0 context) were found with both speech and non-speech stimuli for Mandarin listeners, but not for English listeners. English listeners' lack of tone experience may have caused more rising responses and limited use of context f0 cues. These results suggest that context-dependent pitch perception in tone normalization is domain-general, but influenced by long-term language experience.