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At least 307 records · Page 17Linked to original sources
PubMed1991

Finding the impedance of the organ of Corti.

Measurements of the nonlinear response of the basilar membrane to a pure tone are shown to have a simple form for moderate membrane velocities: V(x,f;Vu)/Vu approximately [V(x,f)/Vu]v(x,f), f less than or equal to fc(x), where the response V is the velocity of the membrane at measurement position x, Vu is the umbo velocity, f is the frequency of the stimulus, and fc(x) is the local characteristic frequency. The frequency dependence of the functions v(x,f) and V(x,f) is determined from the data, and v(x,f) and ln V(x,f) are shown to be analytic functions in the lower half of the complex frequency plane, with Re [v(x,f)] a monotonically increasing function of f at fixed x. The linear limit of basilar membrane motion is characterized by a transfer function T(x,f) = (V/V1)v/(1-v), estimated by extrapolating V(x,f;Vu)/Vu to a small membrane velocity V1.T(x,f) and ln T(x,f) are shown to be analytic functions in the lower half of the complex frequency plane. The inverse of the amplitude of the transfer function, which has both a deep dip at f approximately fc(x) and a broad shoulder at lower frequencies, bears a striking resemblance to the neural threshold tuning curve. The functional form of T(x,f) is used to deduce the equation governing the motion of a section of the organ of Corti. Each section acts like a negatively damped harmonic oscillator stabilized at time t by a feedback force proportional to the velocity at the previous time t-tau. The time delay tau is proportional to the oscillator period [tau approximately 1.75/fc(x)]. Like a laser, the organ of Corti pumps energy into harmonic traveling waves. Unlike the laser, the direction of energy flow abruptly reverses as the traveling wave approaches the point of maximum membrane velocity [fc(x) approximately f]. All accumulated wave energy is then pumped back into a small section of the organ of Corti where transduction presumably occurs. Outer hair cells are conjectured to be active elements contributing to the negative damping and feedback of the cochlear amplifier.

Animals↗
PubMed2006

Fatal respiratory depression after multiple intravenous morphine injections.

A 26-year-old female was treated with morphine within the first 2 hours after knee surgery, in an attempt to titrate analgesia. The patient received a total of four intravenous injections of morphine 35 mg in total. Soon after the last injection the patient had adequate pain relief, was in a good clinical state and had adequate blood oxygenation. However, 40 minutes later, the patient had a deep respiratory depression followed by a fatal cardiac arrest. Solving the case in a medico-legal context was possible by applying results of clinical pharmacokinetic research on opioid analgesics, most importantly morphine, to this particular clinical case. This knowledge made it possible to estimate the probable concentrations of morphine at the site of its effect, the brain, during the time of the fatal event, and to show that these concentrations could have produced respiratory depression. We mainly attribute the fatal intoxication of morphine to the lag period needed for the transfer of morphine across the blood-brain barrier. Because of its slow transfer between plasma and the effect site, the CNS effects of morphine are delayed from its plasma concentrations to a clinically relevant degree. Successive injections at short intervals of relatively high amounts of morphine increase the clinical relevance of this delay. The present report demonstrates an important application of clinical pharmacokinetics for explaining clinical observations at a scientific level and transferring theoretical knowledge from clinical pharmacokinetics into daily clinical practice as a basis for rational opioid selection.

Adult↗
PubMed2006

The complete mitochondrial genome of the black coral Chrysopathes formosa (Cnidaria:Anthozoa:Antipatharia) supports classification of antipatharians within the subclass Hexacorallia.

Black corals comprise a globally distributed shallow- and deep-water taxon whose phylogenetic position within the Anthozoa has been debated. We sequenced the complete mitochondrial genome of the antipatharian Chrysopathes formosa to further evaluate its phylogenetic relationships. The circular mitochondrial genome (18,398 bp) consists of 13 energy pathway protein-coding genes and two ribosomal RNAs, but only two transfer RNA genes (trnM and trnW), as well as a group I intron within the nad5 gene that contains the only copies of nad1 and nad3. No novel genes were found in the antipatharian mitochondrial genome. Gene order and genome content are most similar to those of the sea anemone Metridium senile (subclass Hexacorallia), with differences being the relative location of three contiguous genes (cox2-nad4-nad6) and absence (from the antipatharian) of a group I intron within the cox1 gene. Phylogenetic analyses of multiple protein-coding genes support classifying the Antipatharia within the subclass Hexacorallia and not the subclass Ceriantipatharia; however, the sister-taxon relationships of black corals within Hexacorallia remain inconclusive.

Animals↗
PubMed1984

An unexpected major groove binding of netropsin and distamycin A to tRNA(phe).

Crystalline complexes of yeast tRNA(phe) and the oligopeptide antibiotics netropsin and distamycin A were prepared by diffusing drugs into crystals of tRNA. X-ray structure analyses of these complexes reveal a single common binding site for both drugs which is located in the major or deep groove of the tRNA T-stem. The netropsin-tRNA complex is stabilized by specific hydrogen bonds between the amide groups of the drug and the tRNA bases G51 O(6), U52 O(4) and G53 N(7) on one strand, and is further stabilized by electrostatic interactions between the positively charges guanidino side chain of the drug and the tRNA phosphate P53 on the same strand and the positively charged amidino propyl side chain and the phosphates P61, P62 and P63 on the opposite strand of the double helix. These results are in contrast to the implicated minor groove binding of these drugs to non-guanine sequences in DNA. The binding to the GUG sequence in tRNA implies that major groove binding to certain DNA sequences is possible.

Binding Sites↗
PubMed2005

Reference biospheres for post-closure performance assessment: inter-comparison of SHETRAN simulations and BIOMASS results.

Example Reference Biosphere 2B (ERB2B) is a hypothetical river catchment, described in the IAEA-sponsored BIOMASS study on biosphere aspects of post-closure radiological safety assessments for repositories for solid radioactive wastes. In ERB2B, a radioactively contaminated aquifer interacts with the soils and sediments of the river catchment. A 'semi-distributed', lumped-parameter model (SDLP) was set up for the site as part of the BIOMASS study. In the model, empirically derived transfer functions are used to reduce the complexity of real hydrological transport systems to readily calculable mass-balance accounting routines. In this work, a physically based, spatially distributed modelling system SHETRAN was set up for the site and comparison made with the existing SDLP model. The work has shown that, using standard soil properties in SHETRAN, the soil rapidly saturates and much of the hydrologically effective rainfall (precipitation less evapotranspiration) is lost as saturation-excess surface runoff. This is contrary to the assumptions in the SDLP model. The difficulty arose from the original formulation of catchment characteristics in BIOMASS. Specifically, there was a large water volume entering the soils from precipitation together with an upward flux of groundwater across the lower boundary of a substantial part of the catchment. This water had to be lost from the catchment in some way and the thinness of the soil zone precluded dominance of subsurface, lateral flow over surface runoff. Increasing the saturated conductivity from 1 to 20 m d(-1) reduced the surface flows to similar values to those assumed in the SDLP model (this could also have been achieved by increasing the soil depth). Even with the high saturated conductivity there were still major differences between the two representations. In the woodland on the upper slopes of the valley, the SHETRAN simulation was slightly wetter than the SDLP model, whereas in the shrubland and marshland near the river it was drier than the SDLP model. In the SDLP model, subsurface lateral flows are ignored if there is surface flow, and deep subsurface flows are ignored if there are shallow subsurface flows. In the SDLP model, there is a major assumed change in flow regime between summer and winter. This is not the case in the SHETRAN simulation. Overall, this work illustrates the problems of using 'semi-distributed', lumped-parameter models without prior calibration against a physically based model and the potential for implying unexpected and possibly implausible hydrological characteristics through the specification of flows without considering whether they could occur for realistic soil depths and properties. As there is a need for application of such SDLP models, particularly when undertaking probabilistic calculations, it is suggested that, in future, explicit hydrological modelling should be undertaken first, so that a physically realistic representation can be produced as a basis for assessment studies of the migration of radionuclides or other contaminants.

Fresh Water↗
PubMed1999

The structure of the exo-beta-(1,3)-glucanase from Candida albicans in native and bound forms: relationship between a pocket and groove in family 5 glycosyl hydrolases.

A group of fungal exo-beta-(1,3)-glucanases, including that from the human pathogen Candida albicans (Exg), belong to glycosyl hydrolase family 5 that also includes many bacterial cellulases (endo-beta-1, 4-glucanases). Family members, despite wide sequence variations, share a common mechanism and are characterised by possessing eight invariant residues making up the active site. These include two glutamate residues acting as nucleophile and acid/base, respectively. Exg is an abundant secreted enzyme possessing both hydrolase and transferase activity consistent with a role in cell wall glucan metabolism and possibly morphogenesis. The structures of Exg in both free and inhibited forms have been determined to 1.9 A resolution. A distorted (beta/alpha)8 barrel structure accommodates an active site which is located within a deep pocket, formed when extended loop regions close off a cellulase-like groove. Structural analysis of a covalently bound mechanism-based inhibitor (2-fluoroglucosylpyranoside) and of a transition-state analogue (castanospermine) has identified the binding interactions at the -1 glucose binding site. In particular the carboxylate of Glu27 serves a dominant hydrogen-bonding role. Access by a 1,3-glucan chain to the pocket in Exg can be understood in terms of a change in conformation of the terminal glucose residue from chair to twisted boat. The geometry of the pocket is not, however, well suited for cleavage of 1,4-glycosidic linkages. A second glucose site was identified at the entrance to the pocket, sandwiched between two antiparallel phenylalanine side-chains. This aromatic entrance-way must not only direct substrate into the pocket but also may act as a clamp for an acceptor molecule participating in the transfer reaction.

Amino Acid Sequence↗
PubMed2006

Positron follow-up in liquid water: I. A new Monte Carlo track-structure code.

When biological matter is irradiated by charged particles, a wide variety of interactions occur, which lead to a deep modification of the cellular environment. To understand the fine structure of the microscopic distribution of energy deposits, Monte Carlo event-by-event simulations are particularly suitable. However, the development of these track-structure codes needs accurate interaction cross sections for all the electronic processes: ionization, excitation, positronium formation and even elastic scattering. Under these conditions, we have recently developed a Monte Carlo code for positrons in water, the latter being commonly used to simulate the biological medium. All the processes are studied in detail via theoretical differential and total cross-section calculations performed by using partial wave methods. Comparisons with existing theoretical and experimental data in terms of stopping powers, mean energy transfers and ranges show very good agreements. Moreover, thanks to the theoretical description of positronium formation, we have access, for the first time, to the complete kinematics of the electron capture process. Then, the present Monte Carlo code is able to describe the detailed positronium history, which will provide useful information for medical imaging (like positron emission tomography) where improvements are needed to define with the best accuracy the tumoural volumes.

Algorithms↗
PubMed2000

Gamma knife radiosurgery as a primary treatment for prolactinomas.

OBJECT: The purpose of this study was to estimate the efficacy of gamma knife radiosurgery (GKS) in controlling tumor growth and endocrinopathy associated with prolactinomas. METHODS: Between 1993 and 1997, 164 of 469 patients with pituitary adenomas treated by GKS harbored prolactinomas. The dose to the tumor margin ranged from 9 to 35 Gy (mean 31.2 Gy), and the visual pathways were exposed to a dose of less than 10 Gy. The mean tumor diameter was 13.4 mm. The mean follow-up time for 128 cases was 33.2 months (range 6-72 months). Tumor control was observed in all but two patients who underwent surgery 18 and 36 months, respectively, after GKS. Clinical cure was achieved in 67 cases. Clinical improvement was noted with a decrease in the hyperprolactinemia after GKS. Nonetheless, in 31 (29%) of 108 patients who were followed for more than 2 years no improvement in serum prolactin levels was demonstrated, although this could be normalized by bromocriptine administration after treatment. Nine infertile women became pregnant 2 to 13 months after GKS and all gave birth to normal children. There was no visual deterioration related to GKS. Five women experienced premature menopause. In these patients there was subtotal disappearance of the tumor and an empty sella developed. CONCLUSIONS: Gamma knife radiosurgery as a primary treatment for prolactinomas can be safe and effective both for controlling tumor growth and for normalization of prolactin hypersecretion. A higher margin dose (> or = 30 Gy) seemed to be associated with a better clinical outcome. Gamma knife radiosurgery may make prolactinomas more sensitive to the bromocriptine.

Humans↗
PubMed1999

Shielding from solar particle event exposures in deep space.

The physical composition and intensities of solar particle event exposures of sensitive astronaut tissues are examined under conditions approximating an astronaut in deep space. Response functions for conversion of particle fluence into dose and dose equivalent averaged over organ tissues are used to establish significant fluence levels and the expected dose and dose rates of the most important events from past observations. The BRYNTRN transport code is used to evaluate the local environment experienced by sensitive tissues and used to evaluate bioresponse models developed for use in tactical nuclear warfare. The present results will help to clarify the biophysical aspects of such exposure in the assessment of RBE and dose rate effects and their impact on design of protection systems for the astronauts. The use of polymers as shielding material in place of an equal mass of aluminum would provide a large safety factor without increasing the vehicle mass. This safety factor is sufficient to provide adequate protection if a factor of two larger event than has ever been observed in fact occurs during the mission.

Bone Marrow↗
PubMed1996

Load redistribution after desmotomy of the accessory ligament of the deep digital flexor tendon in adult horses.

An analysis of joint moments was used to study the biomechanical implications, load redistribution and kinematic pattern following desmotomy of the accessory ligament of the deep digital flexor tendon (AL) in adult horses. Recordings of 6 sound horses were made before and 10 days after desmotomy of the AL of the right forelimb at the walk and the trot. Kinematic recordings of the right forelimb and the left distal forelimb were made using the CODA-3 system. Kinetic recordings of the ground reaction forces in both forelimbs were made using a Kistler force plate simultaneously with the kinematic recordings. Radiographic localisation of the CODA-3 markers in both distal limbs allowed an analysis of coffin and fetlock joint moments, moment arms and forces in the digital flexor tendons. No transfer of load from the operated to the contralateral limb was found. In the operated limb the total joint moment of the coffin joint decreased substantially due to a reduced moment arm of the vertical ground reaction force component during the entire stance phase, while the fetlock joint moment decreased only slightly. To compensate for the loss of AL function, the superficial digital flexor tendon (SDFT) took a higher load during midstance, while at the end of the stance phase, the deep digital flexor tendon (DDFT) carried a higher load with a marked load peak just before heel off. While the compensation was adequate during midstance (no changes in maximal hyperextension of the fetlock joint), a prolonged hyperextension of the fetlock joint together with a rapid flexion at the start of the swing phase indicated that the DDFT was unable to compensate completely for the loss of AL function. It was concluded that the changes in total joint moments and increases in loading of the SDFT and DDFT allow locomotion without serious overloading of the compensating tendons following AL desmotomy.

Analysis of Variance↗
PubMed1999

An approach to long-range electron transfer mechanisms in metalloproteins: in situ scanning tunneling microscopy with submolecular resolution.

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.

Adsorption↗
PubMed2005

Hydraulic redistribution in three Amazonian trees.

About half of the Amazon rainforest is subject to seasonal droughts of 3 months or more. Despite this drought, several studies have shown that these forests, under a strongly seasonal climate, do not exhibit significant water stress during the dry season. In addition to deep soil water uptake, another contributing explanation for the absence of plant water stress during drought is the process of hydraulic redistribution; the nocturnal transfer of water by roots from moist to dry regions of the soil profile. Here, we present data on patterns of soil moisture and sap flow in roots of three dimorphic-rooted species in the Tapajós Forest, Amazônia, which demonstrate both upward (hydraulic lift) and downward hydraulic redistribution. We measured sap flow in lateral and tap roots of our three study species over a 2-year period using the heat ratio method, a sap-flow technique that allows bi-directional measurement of water flow. On certain nights during the dry season, reverse or acropetal flow (i.e.,in the direction of the soil) in the lateral roots and positive or basipetal sap flow (toward the plant) in the tap roots of Coussarea racemosa (caferana), Manilkara huberi (maçaranduba) and Protium robustum (breu) were observed, a pattern consistent with upward hydraulic redistribution (hydraulic lift). With the onset of heavy rains, this pattern reversed, with continuous night-time acropetal sap flow in the tap root and basipetal sap flow in lateral roots, indicating water movement from wet top soil to dry deeper soils (downward hydraulic redistribution). Both patterns were present in trees within a rainfall exclusion plot (Seca Floresta) and to a more limited extent in the control plot. Although hydraulic redistribution has traditionally been associated with arid or strongly seasonal environments, our findings now suggest that it is important in ameliorating water stress and improving rain infiltration in Amazonian rainforests. This has broad implications for understanding and modeling ecosystem process and forest function in this important biome.

Brazil↗
PubMed1991

Fluorescence energy transfer distance measurements using site-directed single cysteine mutants. The membrane insertion of colicin A.

The ion-channel-forming C-terminal fragment of colicin A binds to negatively charged lipid vesicles and provides an example of insertion of a soluble protein into a lipid bilayer. The soluble structure is known from X-ray crystallography and consists of a ten-helix bundle containing a hydrophobic helical hairpin. In this work fluorescence spectroscopy was used to study the membrane-bound structure. An extrinsic probe, N'-(iodoacetyl)-N'-(5-sulfol-naphthyl)ethylenediamine (IAEDANS) was attached to mutant proteins each of which bears a unique cysteine residue. Three mutants K39C (helix 2), T127C (between helices 6 and 7) and S16Crpt (helix 1, which bears a decapeptide repeat before the mutation) gave useful derivatives. In the soluble protein they showed emission wavelengths decreasing in the order K39C greater than T127C greater than S16Crpt and although all showed blue shifts on addition of dimyristoylphosphatidylglycerol (DMPG) this order was maintained in the membrane-bound state. These shifts were not indicative of deep membrane insertion. Polarization of IAEDANS revealed differences in mobility between mutants. The three tryptophan residues were used as a compound donor to IAEDANS in resonance energy transfer distance determinations. The values obtained for the soluble form were 1.2 A to 3.2 A longer than in the crystal structure. On addition of lipids the indicated distances increased: S16Crpt-I(AEDANS) 6.45 A (22%), K39C-I 5.45 A (18%) and T127C-I 2.4 A (14%). N-bromosuccinimide (NBS) completely abolishes the tryptophan emission from the thermolytic fragment. When lipids were added to a mixture containing ten NBS-treated channel-forming fragments to one IAEDANS labelled fragment the indicated distances increased rather more: S16Crpt-I 9.7 A (38%), K39C-I 8.1 A (36%) and T127C-I 2.5 A (16%). This showed that intermolecular transfer reduces the distance estimated in samples containing only labelled protein. The ensemble of results shows that the amphipathic helices of the C-terminal fragment open out on the surface of the lipid bilayer during the initial phase of membrane insertion.

Colicins↗
PubMed2026

Mul-PheG2P: decoupled learning and prediction-space fusion enables robust and interpretable multi-phenotype genomic prediction.

Genomic prediction of multiple phenotypes is crucial in modern plant breeding; however, existing methods struggle with negative transfer and lack interpretability, particularly across high-dimensional small-sample data and diverse species. To address this, we propose Mul-PheG2P, a novel paradigm based on decoupled learning and predictive space fusion. It employs a two-stage design: first training phenotype-specific encoders using genetic data, then decoupling phenotype-specific learning from cross-phenotype aggregation via an interpretable prediction layer. Mul-PheG2P outperforms existing methods across diverse crop datasets, including maize (Zea mays), wheat (Triticum aestivum), and tomato (Solanum lycopersicum). It provides a multi-scale interpretability chain: at the macro level, it quantifies phenotypic contributions via attention-based weighting; at the micro level, Integrated Gradients reveal the genetic basis of predictions. Notably, the model successfully identified the CCT (CONSTANS, CO-like, and TOC) motif regulating photoperiodism and the SQUAMOSA (SQUAMOSA promoter binding protein) promoter for inflorescence development, confirming its ability to capture functional biological mechanisms. These results highlight the high performance and interpretability of Mul-PheG2P, showcasing its value for low-cost, large-scale screening to advance precision breeding.

Phenotype↗
PubMed1999

Gene therapy and dermatology: more than just skin deep.

BACKGROUND: Recent advances in the molecular characterization of dermatologic disease have substantively augmented the understanding of the pathogenetic processes underlying disorders of the skin. This new knowledge coupled with progress in gene delivery technologies has paved the way for introducing cutaneous gene therapy into the dermatologic therapeutic armamentorium. OBJECTIVE: This review article includes an overview of the current strategies for delivery of gene therapy with an emphasis on the potential role of cutaneous gene delivery in the treatment of skin and systemic diseases. CONCLUSIONS: Accessibility for gene delivery, clinical evaluation, and topical modulation of gene expression render the skin a very attractive tissue for therapeutic gene delivery. However, there are several key hurdles to be overcome before cutaneous gene therapy becomes a viable clinical option. These include difficulties in inducing sustained expression of the desired gene in vivo, the challenge of targeting genes to long-lived stem cells, and the difficulty in achieving specific and uniform transfer to different compartments of the skin. However, these problems are not insurmountable and will likely be resolved in conjunction with ongoing advances in delineating gene expression profiles and other molecular properties of the skin, strategies for stem cell isolation, and improved approaches to regulating gene delivery and expression. These advances should create the framework for translating the enormous potential of cutaneous gene therapy into the clinical arena and, thereby, substantively improving the management of both cutaneous and systemic disease.

Animals↗
PubMed2004

Folding behavior of model proteins with weak energetic frustration.

The native structure of fast-folding proteins, albeit a deep local free-energy minimum, may involve a relatively small energetic penalty due to nonoptimal, though favorable, contacts between amino acid residues. The weak energetic frustration that such contacts represent varies among different proteins and may account for folding behavior not seen in unfrustrated models. Minimalist model proteins with heterogeneous contacts--as represented by lattice heteropolymers consisting of three types of monomers--also give rise to weak energetic frustration in their corresponding native structures, and the present study of their equilibrium and nonequilibrium properties reveals some of the breadth in their behavior. In order to capture this range within a detailed study of only a few proteins, four candidate protein structures (with their cognate sequences) have been selected according to a figure of merit called the winding index--a characteristic of the number of turns the protein winds about an axis. The temperature-dependent heat capacities reveal a high-temperature collapse transition, and an infrequently observed low-temperature rearrangement transition that arises because of the presence of weak energetic frustration. Simulation results motivate the definition of a new measure of folding affinity as a sequence-dependent free energy--a function of both a reduced stability gap and high accessibility to non-native structures--that correlates strongly with folding rates.

Amino Acid Sequence↗
PubMed2005

Characterization and calculation of a cytochrome c-cytochrome b5 complex using NMR data.

To identify the binding site for bovine cytochrome b(5) (cyt b(5)) on horse cytochrome c (cyt c), cross-saturation transfer NMR experiments were performed with (2)H- and (15)N-enriched cyt c and unlabeled cyt b(5). In addition, chemical shift changes of the cyt c backbone amide and side chain methyl resonances were monitored as a function of cyt b(5) concentration. The chemical shift changes indicate that the complex is in fast exchange, and are consistent with a 1:1 stoichiometry. A K(a) of (4 +/- 3) x 10(5) M(-)(1) was obtained with a lower limit of 855 s(-)(1) for the dissociation rate of the complex. Mapping of the chemical shift variations and intensity changes upon cross-saturation NMR experiments in the complex reveals a single, contiguous interaction interface on cyt c. Using NMR data as constraints, a protein docking program was used to calculate two low-energy model complex clusters. Independent calculations of the effect of the cyt b(5) heme ring current-induced magnetic dipole on cyt c were used to discriminate between the different models. The interaction surface of horse cyt c in the current experimentally constrained model of the cyt c-cyt b(5) complex is similar but not identical to the interface predicted in yeast cyt c by Brownian dynamics and docking calculations. The occurrence of different amino acids at the protein-protein interface and the dissimilar assumptions employed in the calculations can largely account for the nonidentical interfaces.

Animals↗
PubMed2003

Acoustic backscattering by Hawaiian lutjanid snappers. II. Broadband temporal and spectral structure.

The characteristics of acoustic echoes from six species of deep-dwelling (up to 400 m) Hawaiian Lujanid snappers were determined by backscatter measurements at the surface. A broadband linear frequency-modulated signal and a short dolphinlike sonar signal were used as the incident signals. The fish were anesthetized and attached to a monofilament net that was attached to a rotor so echoes could be collected along the roll, tilt, and lateral axes of each fish. The temporal highlight structure of broadband echoes was determined by calculating the envelope of the cross-correlation function between the incident signal and the echoes. The echo waveforms were complex with many highlights and varied with the orientation of the fish. In the tilt plane, the strongest echoes occurred when the incident signal was perpendicular to the long axis of the swimbladder. The number of highlights was the fewest at this orientation. The number of echo highlights and the length of echoes increased as the fish was tilted from this orientation. The highlight structure of the echoes resulted in the transfer function being rippled, with local maxima and minima that changed with fish size and species. The echo structures in both the time and frequency domains were generally consistent within species and were easily distinguishable between species.

Acoustics↗