bluuebunny/crossref_metadata_2025 huggingface dataset:
Targeting of HIV-1 Antigens for Rapid Intracellular Degradation Enhances Cytotoxic T Lymphocyte (CTL) Recognition and the Induction of De Novo CTL Responses In Vivo After Immunization
Authors: Tobery Timothy W. , Siliciano Robert F.
Published: July 2002

CD8+ cytotoxic T lymphocytes (CTLs) have the ability to recognize and eliminate virally infected cells before new virions are produced within that cell. Therefore, a rapid and vigorous CD8+ CTL response, induced by vaccination, can, in principle, prevent disseminated infection in vaccinated individuals who are exposed to the relevant virus. There has thus been interest in novel vaccine strategies that will enhance the induction of CD8+ CTLs. In this study, we have tested the hypothesis that targeting an antigen to undergo more efficient processing by the class I processing pathway will elicit a more vigorous CD8+ CTL response against that antigen. Targeting a type I transmembrane protein, the HIV-1 envelope (env) protein, for expression in the cytoplasm, rather than allowing its normal co-translational translocation into the endoplasmic reticulum, sensitized target cells expressing this mutant more rapidly for lysis by an env-specific CTL clone. Additionally, a greatly enhanced de novo env-specific CTL response was induced in vivo after immunization of mice with recombinant vaccinia vectors expressing the cytoplasmic env mutant. Similarly, targeting a cytoplasmic protein, HIV-1 nef, to undergo rapid cytoplasmic degradation induced a greatly enhanced de novo nef-specific CD8+ CTL response in vivo after immunization of mice with either recombinant vaccinia vectors or DNA expression plasmids expressing the degradation targeted nef mutant. The targeting of viral antigens for rapid cytoplasmic degradation represents a novel and highly effective vaccine strategy for the induction of enhanced de novo CTL responses in vivo.
Differential Effects of B Cell Receptor and B Cell Receptor–FcγRIIB1 Engagement on Docking of Csk to GTPase-activating Protein (GAP)-associated p62
Authors: Vuica Milena , Desiderio Stephen , Schneck Jonathan P.
Published: July 2002

The stimulatory and inhibitory pathways initiated by engagement of stimulatory receptors such as the B cell receptor for antigen (BCR) and inhibitory receptors such as Fcγ receptors of the IIB1 type (FcγRIIB1) intersect in ways that are poorly understood at the molecular level. Because the tyrosine kinase Csk is a potential negative regulator of lymphocyte activation, we examined the effects of BCR and FcγRIIB1 engagement on the binding of Csk to phosphotyrosine-containing proteins. Stimulation of a B lymphoma cell line, A20, with intact anti-IgG antibody induced a direct, SH2-mediated association between Csk and a 62-kD phosphotyrosine-containing protein that was identified as RasGTPase-activating protein–associated p62 (GAP-A.p62). In contrast, stimulation of A20 cells with anti-IgG F(ab′)2 resulted in little increase in the association of Csk with GAP-A.p62. The effect of FcγRIIB1 engagement on this association was abolished by blockade of FcγRIIB1 with the monoclonal antibody 2.4G2. Furthermore, the increased association between Csk and GAP-A.p62 seen upon stimulation with intact anti-Ig was abrogated in the FcγRIIB1-deficient cell line IIA1.6 and recovered when FcγRIIB1 expression was restored by transfection. The differential effects of BCR and BCR-FcγRIIB1–mediated signaling on the phosphorylation of GAP-A.p62 and its association with Csk suggest that docking of Csk to GAP-A.p62 may function in the negative regulation of antigen receptor–mediated signals in B cells.
T Helper Cell Type 2 Cytokine–Mediated Comitogenic Responses and Ccr3 Expression during Differentiation of Human Mast Cells in Vitro
Authors: Ochi Hiroshi , Hirani W. Mona , Yuan Qian , Friend Daniel S. , Austen K. Frank , Boyce Joshua A.
Published: July 2002

Mast cells (MCs) arise in situ from circulating stem cell factor (SCF)-dependent committed progenitors (PrMCs) and accumulate at sites of allergic mucosal inflammation. We hypothesized that human (h)PrMCs and their mature counterparts might share overlapping patterns of chemokine and cytokine receptor utilization with eosinophils, basophils, and T helper type 2 (Th2) lymphocytes for their homing and allergy-associated hyperplasia. We have characterized committed hPrMCs and fully mature hMCs derived in vitro from cord blood for their functional responses to chemokine and cytokine agonists germane to allergic inflammation and for their maturation-related expression of the corresponding receptors. After 4 wk of culture in the presence of recombinant stem cell factor (SCF), interleukin (IL)-6, and IL-10, the cells were characterized as hPrMCs based upon their uniform surface expression of c-kit and CD13, low-level expression of Fc∈RIα, absence of CD14 and CD16 expression, and immunoreactivity for MC chymase in >80%, and about half were immunoreactive for tryptase and metachromatic with toluidine blue. By week 9, the cells had matured into hMCs, identified by higher levels of c-kit, continued expression of CD13 and low-level Fc∈RIα, uniform toluidine blue metachromasia, and uniform immunoreactivity for both tryptase and chymase. The 4-wk-old hPrMCs expressed four chemokine receptors (CXCR2, CCR3, CXCR4, and CCR5). Each receptor mediated transient rapid calcium fluxes in response to its respective ligand. Both recombinant human eotaxin and stromal cell–derived factor 1α elicited chemotaxis of hPrMCs. Only CCR3 was retained on the mature 9-wk-old hMCs from among these chemokine receptors, and hMCs responded to eotaxin with a sustained calcium flux but without chemotaxis. The Th2 cytokines IL-3, IL-5, IL-6, IL-9, and granulocyte/macrophage colony-stimulating factor each augmented the SCF-dependent proliferation of hPrMCs and hMCs. In contrast, the prototypical Th1 cytokine, interferon γ, suppressed SCF-driven proliferation of both hPrMCs and hMCs. Thus, throughout their development in vitro, hMCs obey SCF-dependent, cytokine-driven mitogenic responses that reflect a Th2-type polarization characteristic of allergy and asthma. Furthermore, committed hPrMCs have a unique profile of chemokine receptor expression from among reported hematopoietic cells, including CCR3, which is shared with the other cells central to allergic inflammation (eosinophils, basophils, and Th2 lymphocytes).
Tumor Necrosis Factor α Is a Critical Component of Interleukin 13–Mediated Protective T Helper Cell Type 2 Responses during Helminth Infection
Authors: Artis David , Humphreys Neil E. , Bancroft Allison J. , Rothwell Nancy J. , Potten Christopher S. , Grencis Richard K.
Published: July 2002

In vivo manipulation of cytokine and/or cytokine receptor expression has previously shown that resistance to infection with the caecum-dwelling helminth Trichuris muris is dependent on interleukin (IL)-4 and IL-13 while susceptibility is associated with a T helper cell type 1 (Th1) cytokine response. Using gene-targeted mice deficient in tumor necrosis factor (TNF) receptor signaling and anti–TNF-α monoclonal antibody treatment, we have extended these studies to reveal a critical role for TNF-α in regulation of Th2 cytokine–mediated host protection. In vivo blockade of TNF-α in normally resistant mice, although not altering IL-4, IL-5, or IL-13 production in the draining lymph node, significantly delayed worm expulsion for the duration of treatment. IL-13–mediated worm expulsion in IL-4 knockout (KO) mice was also shown to be TNF-α dependent, and could be enhanced by administration of recombinant TNF-α. Furthermore, TNF receptor KO mice failed to expel T. muris, producing high levels of parasite-specific immunoglobulin G2a and the generation of a predominantly Th1 response, suggesting that the absence of TNF function from the onset of infection dramatically alters the phenotype of the response. These results provide the first demonstration of the role of TNF-α in regulating Th2 cytokine–mediated responses at mucosal sites, and have implications for the design of rational therapies against helminth infection and allergy.
The Reduced Expression of 6ckine in the plt Mouse Results from the Deletion of One of Two 6ckine Genes
Authors: Vassileva Galya , Soto Hortensia , Zlotnik Albert , Nakano Hideki , Kakiuchi Terutaka , Hedrick Joseph A. , Lira Sergio A.
Published: July 2002

6Ckine is an unusual chemokine capable of attracting naive T lymphocytes in vitro. It has been recently reported that lack of 6Ckine expression in lymphoid organs is a prominent characteristic of mice homozygous for the paucity of lymph node T cell (plt) mutation. These mice show reduced numbers of T cells in lymph nodes, Peyer's patches, and the white pulp of the spleen. The genetic reason for the lack of 6Ckine expression in the plt mouse, however, has remained unknown. Here we demonstrate that mouse 6Ckine is encoded by two genes, one of which is expressed in lymphoid organs and is deleted in plt mice. A second 6Ckine gene is intact and expressed in the plt mouse.
Differential Roles of CD36 and αvβ5 Integrin in Photoreceptor Phagocytosis by the Retinal Pigment Epithelium
Authors: Finnemann Silvia C. , Silverstein Roy L.
Published: July 2002

Retinal pigment epithelial (RPE) cells employ αvβ5 integrin and CD36 receptors to phagocytose photoreceptor outer segment fragments (OS). We explored special properties of RPE phagocytosis to identify the contribution of CD36 to RPE phagocytosis measuring effects of CD36 antibodies on OS binding and internalization kinetics. Early, CD36 antibodies had no effect on OS binding or internalization. Both control and CD36 antibody treated RPE initiated internalization approximately 2 hours after OS challenge. Later, bivalent CD36 IgG accelerated OS engulfment while monovalent Fab fragments inhibited engulfment. Cross-linking Fab fragments restored the accelerating activity of intact IgG. Strikingly, antibodies were effective even if added to OS already bound by RPE. αvβ5 blocking antibody reduced OS binding equally well in the presence of CD36 antibodies but CD36 antibodies accelerated internalization of remaining bound OS. Furthermore, CD36 ligation at either apical or basal RPE surface partially substituted for soluble factors that are required for internalization but not for binding of OS at the RPE apical surface. Our results demonstrate that CD36 ligation is necessary and sufficient to activate the OS internalization mechanism of RPE. They suggest that CD36 acts as a signaling molecule in postbinding steps of RPE phagocytosis independently of the OS binding receptor αvβ5 integrin.
Structural Basis of Cytochrome c Presentation by IEk
Authors: Fremont Daved H. , Dai Shaodong , Chiang Herbert , Crawford Frances , Marrack Philippa , Kappler John
Published: July 2002

The COOH-terminal peptides of pigeon and moth cytochrome c, bound to mouse IEk, are two of the most thoroughly studied T cell antigens. We have solved the crystal structures of the moth peptide and a weak agonist–antagonist variant of the pigeon peptide bound to IEk. The moth peptide and all other peptides whose structures have been solved bound to IEk, have a lysine filling the p9 pocket of IEk. However, the pigeon peptide has an alanine at p9 shifting the lysine to p10. Rather than kinking to place the lysine in the anchor pocket, the pigeon peptide takes the extended course through the binding groove, which is characteristic of all other peptides bound to major histocompatibility complex (MHC) class II. Thus, unlike MHC class I, in which peptides often kink to place optimally anchoring side chains, MHC class II imposes an extended peptide conformation even at the cost of a highly conserved anchor residue. The substitution of Ser for Thr at p8 in the variant pigeon peptide induces no detectable surface change other than the loss of the side chain methyl group, despite the dramatic change in recognition by T cells. Finally, these structures can be used to interpret the many published mutational studies of these ligands and the T cell receptors that recognize them.
Block of the Kir2.1 Channel Pore by Alkylamine Analogues of Endogenous Polyamines
Authors: Pearson W.L. , Nichols C.G.
Published: July 2002

Inward rectification induced by mono- and diaminoalkane application to inside-out membrane patches was studied in Kir2.1 (IRK1) channels expressed in Xenopus oocytes. Both monoamines and diamines block Kir2.1 channels, with potency increasing as the alkyl chain length increases (from 2 to 12 methylene groups), indicating a strong hydrophobic interaction with the blocking site. For diamines, but not monoamines, increasing the alkyl chain also increases the steepness of the voltage dependence, at any concentration, from a limiting minimal value of ∼1.5 (n = 2 methylene groups) to ∼4 (n = 10 methylene groups). These observations lead us to hypothesize that monoamines and diamines block inward rectifier K+ channels by entering deeply into a long, narrow pore, displacing K+ ions to the outside of the membrane, with this displacement of K+ ions contributing to “extra” charge movement. All monoamines are proposed to lie with the “head” amine at a fixed position in the pore, determined by electrostatic interaction, so that zδ is independent of monoamine alkyl chain length. The head amine of diamines is proposed to lie progressively further into the pore as alkyl chain length increases, thus displacing more K+ ions to the outside, resulting in charge movement (zδ) increasing with the increase in alkyl chain length.
Movement of Voltage Sensor S4 in Domain 4 Is Tightly Coupled to Sodium Channel Fast Inactivation and Gating Charge Immobilization
Authors: Kühn Frank J.P. , Greeff Nikolaus G.
Published: July 2002

The highly charged transmembrane segments in each of the four homologous domains (S4D1–S4D4) represent the principal voltage sensors for sodium channel gating. Hitherto, the existence of a functional specialization of the four voltage sensors with regard to the control of the different gating modes, i.e., activation, deactivation, and inactivation, is problematic, most likely due to a functional coupling between the different domains. However, recent experimental data indicate that the voltage sensor in domain 4 (S4D4) plays a unique role in sodium channel fast inactivation. The correlation of fast inactivation and the movement of the S4D4 voltage sensor in rat brain IIA sodium channels was examined by site-directed mutagenesis of the central arginine residues to histidine and by analysis of both ionic and gating currents using a high expression system in Xenopus oocytes and an optimized two-electrode voltage clamp. Mutation R1635H shifts the steady state inactivation to more hyperpolarizing potentials and drastically increases the recovery time constant, thereby indicating a stabilized inactivated state. In contrast, R1638H shifts the steady state inactivation to more depolarizing potentials and strongly increases the inactivation time constant, thereby suggesting a preferred open state occupancy. The double mutant R1635/1638H shows intermediate effects on inactivation. In contrast, the activation kinetics are not significantly influenced by any of the mutations. Gating current immobilization is markedly decreased in R1635H and R1635/1638H but only moderately in R1638H. The time courses of recovery from inactivation and immobilization correlate well in wild-type and mutant channels, suggesting an intimate coupling of these two processes that is maintained in the mutations. These results demonstrate that S4D4 is one of the immobilized voltage sensors during the manifestation of the inactivated state. Moreover, the presented data strongly suggest that S4D4 is involved in the control of fast inactivation.
A sampling theorem on homogeneous manifolds
Authors: Pesenson Isaac
Published: July 2002

We consider a generalization of entire functions of spherical exponential type and Lagrangian splines on manifolds. An analog of the Paley-Wiener theorem is given. We also show that every spectral entire function on a manifold is uniquely determined by its values on some discrete sets of points.

The main result of the paper is a formula for reconstruction of spectral entire functions from their values on discrete sets using Lagrangian splines.
Convergence of relaxation schemes for hyperbolic conservation laws with stiff source terms
Authors: Chalabi A.
Published: July 2002

We focus in this study on the convergence of a class of relaxation numerical schemes for hyperbolic scalar conservation laws including stiff source terms. Following Jin and Xin, we use as approximation of the scalar conservation law, a semi-linear hyperbolic system with a second stiff source term. This allows us to avoid the use of a Riemann solver in the construction of the numerical schemes. The convergence of the approximate solution toward a weak solution is established in the cases of first and second order accurate MUSCL relaxed methods.
Differential expression of genes coding for ribosomal proteins
in different human tissues
Authors: Bortoluzzi S. , d’Alessi F. , Romualdi C. , Danieli G. A.
Published: July 2002

Motivation: To perform a computational and statistical study on a large set of gene expression data pertaining six adult human tissues (brain, liver, skeletal muscle, ovary, retina and uterus) for analyzing the expression of ribosomal protein genes.

Results: Unexpectedly, in each of the considered tissues large variations in the expression of ribosomal protein genes were observed. Moreover, when comparing the expression levels of 89 ribosomal protein genes in six different tissues, 13 genes appeared differentially expressed among tissues.

Avalilability: The expression data of the ribosomal protein genes together with supplementary material (complete transcriptional profiles of the considered human tissues) are freely available at the site GETProfiles (http://telethon.bio.unipd.it/GETProfiles/).

Contact: danieli@bio.unipd.it

* To whom all correspondence should be addressed.
GRR: graphical representation of relationship errors
Authors: Abecasis Gonçalo
   R. , Cherny Stacey S. , Cookson W. O. C. , Cardon Lon R.
Published: July 2002

Summary: A graphical tool for verifying assumed relationships between individuals in genetic studies is described. GRR can detect many common errors using genotypes from many markers.

Availability: GRR is available at http://bioinformatics.well.ox.ac.uk/GRR.

Contact: goncalo@well.ox.ac.uk; lon@well.ox.ac.uk
Distortionary Taxation and Optimal Public Spending on Productive Activities
Authors: Feehan James P. , Matsumoto Mutsumi
Published: July 2002

Using a general‐equilibrium model with endogenous factor supplies, this article investigates the provision of factor‐augmenting public inputs. Such inputs are intermediate goods that affect production functions in a collective manner and give rise to increasing returns. Unlike with collective consumption goods, deviation from the first‐best condition for a public input is inappropriate if taxes are set optimally. When taxes are not optimal, a second‐best rule must include a feedback effect on revenue as well as the deadweight cost of taxes. Implications for benefit‐cost analysis and for interpretation of estimates of the social returns to public capital are explored.
The EXT1/EXT2 tumor suppressors: catalytic activities and role in heparan sulfate biosynthesis
Authors: Senay Claire , Lind Thomas , Muguruma Kumi , Tone Yuko , Kitagawa Hiroshi , Sugahara Kazuyuki , Lidholt Kerstin , Lindahl Ulf , Kusche‐Gullberg Marion
Published: July 2002

The D‐glucuronyltransferase and N‐acetyl‐D‐glucosaminyltransferase reactions in heparan sulfate biosynthesis have been associated with two genes, EXT1 and EXT2, which are also implicated in the inherited bone disorder, multiple exostoses. Since the cell systems used to express recombinant EXT proteins synthesize endogenous heparan sulfate, and the EXT proteins tend to associate, it has not been possible to define the functional roles of the individual protein species. We therefore expressed EXT1 and EXT2 in yeast, which does not synthesize heparan sulfate. The recombinant EXT1 and EXT2 were both found to catalyze both glycosyltransferase reactions in vitro. Coexpression of the two proteins, but not mixing of separately expressed recombinant EXT1 and EXT2, yields hetero‐oligomeric complexes in yeast and mammalian cells, with augmented glycosyltransferase activities. This stimulation does not depend on the membrane‐bound state of the proteins.
Manly Boys and Enterprising Dreamers: Business Ideology and the Construction of the Boy Consumer, 1910–1930
Authors: Jacobson Lisa
Published: July 2002

Early twentieth-century advertising discourses on the archetypal boy consumer promoted a masculinized ideal of consumption that broke decisively from the stereotype of the emotion-driven female shopper. Boys were lauded as rational, informed buyers who prized technological innovation and influenced parents and peers. While touting boys' ample consumer appetites, promoters of the boy consumer also depicted boys' interest in advertised goods as worthy of entrepreneurial-minded self-improvers. The ideal of the boy consumer thus harmonized the potentially hedonistic ethos of consumerism with older ideals of productivity and industriousness. New ideologies of manhood that valorized enthusiasm, loyalty, and salesmanship confirmed the boy consumer's manly vitality.
Field nonuniformity correction for quantitative analysis of digitized mammograms
Authors: Pawluczyk Olga , Yaffe Martin J.
Published: July 2002

Several factors, including the heel effect, variation in distance from the x‐ray source to points in the image and path obliquity contribute to the signal nonuniformity of mammograms. To best use digitized mammograms for quantitative image analysis, these field non‐uniformities must be corrected. An empirically based correction method, which uses a bowl‐shaped calibration phantom, has been developed. Due to the annular spherical shape of the phantom, its attenuation is constant over the entire image. Remaining nonuniformities are due only to the heel and inverse square effects as well as the variable path through the beam filter, compression plate and image receptor. In logarithmic space, a normalized image of the phantom can be added to mammograms to correct for these effects. Then, an analytical correction for path obliquity in the breast can be applied to the images. It was found that the correction causes the errors associated with field nonuniformity to be reduced from 14% to 2% for a 4 cm block of material corresponding to a combination of 50% fibroglandular and 50% fatty breast tissue. A repeatability study has been conducted to show that in regions as far as 20 cm away from the chest wall, variations due to imaging conditions and phantom alignment contribute to <2% of overall corrected signal.
Registration of magnetic resonance spectroscopic imaging to computed tomography for radiotherapy treatment planning
Authors: Graves Edward E. , Pirzkall Andrea , Nelson Sarah J. , Larson David , Verhey Lynn
Published: July 2002

The incorporation of multiple imaging modalities into radiotherapy treatment planning offers the potential to improve identification of regions of pathology. This work outlines and evaluates a methodology for registration of magnetic resonance images (MRI) and spectroscopic images (MRSI) to computed tomography (CT) images, and visualization of the multimodality data on the treatment planning workstation. Volumetric magnetic resonance images were acquired during an examination prior to the initiation of radiotherapy. Registration between these images and the treatment planning computed tomography images was performed using an automated alignment routine, and was improved manually using an interactive registration tool. The parameters of the alignment were then used to transform the spectroscopic images into the same reference frame. The spectroscopy data were represented in terms of a statistical measure of abnormality, and embedded within the MRI data as overlaid contours. These images were sent via DICOM transfer to the treatment planning workstation. An analysis of the reproducibility of the MRSI contours for varying acquisition grid positions was also performed. The technique was applied to ten patients with malignant gliomas. In each case the quality of the final CT/MR registration was demonstrated by at least a 97% volume overlap. All data were reliably transmitted across the PACS network to the treatment planning workstation, and were able to be evaluated by a radiation oncologist prior to treatment planning. The median variation in contour location for a half‐voxel shift of the MRSI acquisition grid was found to be 1.4 mm. In this study, we demonstrate the feasibility of including functional magnetic resonance spectroscopic imaging information in the treatment planning process for radiation therapy. This technique has facilitated research into uses of MRSI in radiation therapy, and we are currently investigating methods of implementing our procedure into commercial treatment planning systems.
Teaching antenna radiation from a time-domain perspective
Authors: Smith Glenn S.
Published: July 2002

Radiation from a simple wire antenna, such as a dipole, is a topic discussed in many courses on electromagnetism. These discussions are almost always restricted to harmonic time dependence. A time-harmonic current distribution is assumed on the wire, and the time-harmonic radiated field is determined. The purpose of this paper is to show that simple wire antennas with a general excitation, e.g., a pulse in time, can be analyzed easily using approximations no worse than those used with time-harmonic excitation, viz. an assumed current distribution. Expressions are obtained for the electromagnetic field of the current that apply at any point in space (in the near zone as well as in the far zone). The analysis in the time domain provides physical understanding not readily available from the time-harmonic analysis. In addition, an interesting analogy can be drawn between the radiation from these antennas when excited by a short pulse of current and the radiation from a moving point charge.
Lower size limit of aquatic mammals
Authors: Ahlborn Boye K. , Blake Robert W.
Published: July 2002

Warm blooded aquatic mammals require a minimum diameter of about 15 cm in order to survive in cold oceans. This follows from the thermal balance and the diameter-to-length aspect ratio D/L≈1/4 of minimum drag, which is characteristic for fast swimming animals.
Playing Physics Jeopardy
Authors: Van Heuvelen Alan , Maloney David P.
Published: July 2002

This article presents a new format for physics problems that is similar to the game show Jeopardy in which contestants are given the answer to a question and asked to state the question. In Physics Jeopardy, the problem starts with a mathematical equation, a graph or a diagram that describes a physical process. The solver constructs other representations of the problem including a word or picture description of a problem and process that is consistent with the equation, graph, or diagram. The Jeopardy Problem solution becomes an effort to represent a physical process in a variety of ways—sketches, diagrams, graphs, and equations—more like the method used by experienced physicists when analyzing problems.
Resource Letter EIRLD-1: Effects of ionizing radiation at low doses
Authors: Wilson Richard
Published: July 2002

This Resource Letter provides a guide to the literature on the effects of ionizing radiation on people at low doses. Journal articles, books, and web pages are provided for the following: data at high dose levels, effects of moderate to high doses (leukemia, solid cancer, lung cancer, childhood cancer and noncancer outcomes), effects of dose rate, relationship to background, supra linearity and homesis, and policy implications.
Analysis of doubly excited symmetric ladder networks
Authors: Bapeswara Rao V. V.
Published: July 2002

A simple procedure to determine the effective resistance between the center and a vertex of an n-sided polygon made of resistors is presented.
Psychophysical suppression effects for tonal and speech signals
Authors: Dubno Judy R. , Ahlstrom Jayne B.
Published: July 2002

This experiment assessed the benefits of suppression and the impact of reduced or absent suppression on speech recognition in noise. Psychophysical suppression was measured in forward masking using tonal maskers and suppressors and band limited noise maskers and suppressors. Subjects were 10 younger and 10 older adults with normal hearing, and 10 older adults with cochlear hearing loss. For younger subjects with normal hearing, suppression measured with noise maskers increased with masker level and was larger at 2.0 kHz than at 0.8 kHz. Less suppression was observed for older than younger subjects with normal hearing. There was little evidence of suppression for older subjects with cochlear hearing loss. Suppression measured with noise maskers and suppressors was larger in magnitude and more prevalent than suppression measured with tonal maskers and suppressors. The benefit of suppression to speech recognition in noise was assessed by obtaining scores for filtered consonant-vowel syllables as a function of the bandwidth of a forward masker. Speech-recognition scores in forward maskers should be higher than those in simultaneous maskers given that forward maskers are less effective than simultaneous maskers. If suppression also mitigated the effects of the forward masker and resulted in an improved signal-to-noise ratio, scores should decrease less in forward masking as forward-masker bandwidth increased, and differences between scores in forward and simultaneous maskers should increase, as was observed for younger subjects with normal hearing. Less or no benefit of suppression to speech recognition in noise was observed for older subjects with normal hearing or hearing loss. In general, as suppression measured with tonal signals increased, the combined benefit of forward masking and suppression to speech recognition in noise also increased.
DPOAE suppression tuning: Cochlear immaturity in premature neonates or auditory aging in normal-hearing adults?
Authors: Abdala Carolina
Published: July 2002

Previous work has shown that distortion product otoacoustic emission (DPOAE) suppression tuning curves (STCs) recorded from premature neonates are narrower than adult STCs at both low and high frequencies. This has been interpreted to indicate an immaturity in cochlear function prior to term birth. However, an alternative explanation for this finding is that adult DPOAE STCs are broadened and reflect cochlear hair cell loss in normal-hearing adults due to aging, and natural exposure to noise and ototoxins. This alternative hypothesis can be tested by studying suppression tuning in normal-hearing school-aged children. If normal-hearing children, who have not aged significantly or been exposed to noise/ototoxins, have DPOAE suppression tuning similar to adults, the auditory aging hypothesis can be ruled out. However, if children have tuning similar to premature neonates and dissimilar from adults, it implicates aging or other factors intrinsic to the adult cochlea. DPOAE STCs were recorded at 1500, 3000, and 6000 Hz using optimal parameters in normal-hearing children and adults. DPOAE STCs collected previously from premature neonates were used for age comparisons. In general, results indicate that tuning curves from children are comparable to adult STCs and significantly different from neonatal STCS at 1500 and 6000 Hz. Only the growth of suppression was not adultlike in children and only at 6000 Hz. These findings do not strongly support the auditory aging hypothesis as a primary explanation for previously observed neonatal–adult differences in DPOAE suppression tuning. It suggests that these age differences are most likely due to immaturities in the neonatal cochlea. However, nonadultlike suppression growth observed in children at 6000 Hz warrants further attention and may be indicative of subtle alternations in the adult cochlea at high frequencies.
On the selection of loads in the multiload method for measuring the acoustic source parameters of duct systems
Authors: Jang Seung-Ho , Ih Jeong-Guon
Published: July 2002

The in-duct source can be characterized by two acoustical parameters such as the source strength and the source impedance, which permit the prediction of radiated sound pressure or insertion loss of the whole duct system. One-port acoustic characteristics of an in-duct source can be measured by the multiload method using an overdetermined set of open pipes or side-branch pipes with different lengths as applied loads. The input data, viz. load pressure and load impedance, are usually contaminated by measurement error in the actual measurements, which result in errors in the calculated source parameters. In this paper, the effects of the errors in the input data on the results have been studied numerically, varying the number of loads and their impedances in order to determine what combination of the loads will yield the best result. It is noted that, frequently, only a set of open pipes is used when applying the multiload method to the internal combustion engine sources. A set of pipe lengths, which cause the calculated results to be least sensitive to the input data error, can be found when using open pipe loads. The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties of fluid machines.
Radiation force on a spherical object in the field of a focused cylindrical transducer
Authors: Chen Xucai , Apfel Robert E.
Published: July 2002

An exact solution of the radiation force on a spherical object, when positioned on the acoustic axis of a cylindrical transducer, is provided. The solution is valid for any type of sphere of any size. The radiation force function allows the calibration of high-frequency focused ultrasound fields from radiation force measurements and expands the utility of the elastic sphere radiometer developed by Dunn et al. [Acustica 38, 58–61 (1977)]. Numeral results reveal an oscillatory behavior of the radiation force function for small spheres near the transducer surface and this behavior may present an opportunity for particle sorting based on the mechanical properties of the particle and other types of manipulation.
Interpretation of distortion product otoacoustic emission measurements. I. Two stimulus tones
Authors: Mills David M.
Published: July 2002

The interpretation of common but poorly understood observed characteristics of distortion product emissions is assisted by the development of a simple model. This model essentially includes only saturation of the cochlear amplifier, with emissions arising naturally from the same nonlinear processes which cause the saturation. The model provides useful physical explanations of emission behavior, particularly considered as a function of the stimulus intensities of the two primaries, i.e., behavior with fixed stimulus frequencies. It is assumed that emission generation consists of two main components which are always present in the total emission, but which most often have approximately opposite, i.e., canceling, phases. One component arises in a small region centered about the peak of the emission generation function, while the other arises from the region basal to this peak. At low stimulus levels with normal cochlear amplifier operation, the peak of the emission generation function is sharp, so the emission from the peak region dominates the total emission. This “peak” emission has typically been characterized as the “active” emission. At high stimulus levels where saturation is important, or at all levels when the gain of the cochlear amplifier is reduced, the summed “basal” component dominates the total emission. The characteristics of this basal emission are similar to, and continuous with, the characteristics of the truly “passive” emission, i.e., the emission observed when the cochlear amplifier gain is identically zero. Under circumstances when the emissions from the peak and basal components are approximately equal, there is seen a sharp “notch” characteristic of phase cancellation. The simple model produces emission distributions as a function of independent variation of the two stimulus amplitudes which are in good agreement with observation. It is shown that the furosemide assay provides a good estimate of cochlear amplifier gain when a correction factor of about 10 dB is added. However, when using two stimulus tones, neither absolute emission amplitudes, or emission input–output functions, or the furosemide assay can adequately distinguish between cases of moderate versus poor cochlear amplifier dysfunction when the cochlear amplifier gains are in the range from about half normal to zero.
Detection of increments and decrements in sinusoids as a function of frequency, increment, and decrement duration and pedestal duration
Authors: Moore Brian C. J. , Peters Robert W.
Published: July 2002

Thresholds for the detection of increments and decrements in level of 70 dB SPL sinusoidal signals were measured as a function signal duration (10, 20, or 200 ms), pedestal duration before the signal (10 ms, 200 ms, or pedestal on continuously) and frequency (250, 1000, or 4000 Hz). The sinusoids were presented in a low-pass filtered background noise with an overall level of 68–69 dB SPL which had two purposes: (1) to mask spectral splatter; (2) to induce an adaptation effect, which caused the continuous 4000-Hz pedestal (but not the other two pedestals) to decay to inaudibility (adaptation). We were particularly interested in determining whether the difference in noise-induced adaptation across frequency would influence the pattern of results. Seven normal-hearing subjects were used. Thresholds improved with increasing frequency and with increasing duration for both increments and decrements. However, the effect of increment/decrement duration decreased with increasing frequency; at 4000 Hz thresholds were almost the same for increment durations of 10 and 20 ms. The energy of the increments at threshold increased markedly with increasing increment duration (especially from 20 to 200 ms), suggesting a dominant role for the onsets of the increments as opposed to ongoing differences in level. Increasing the pedestal duration before the increment from 10 to 200 ms slightly improved thresholds for increment and decrement durations of 10 and 20 ms. Increment thresholds were similar for the gated and continuous pedestals at all frequencies, even though the 4000-Hz continuous pedestal decayed to inaudibility. However, thresholds for 200-ms increments were somewhat lower for continuous than for gated pedestals, and supplementary experiments found a larger gated-continuous difference for pedestals presented in quiet. Making the pedestal continuous adversely affected performance for the 10- and 20-ms decrements, but not for the 200-ms decrement. We suggest that the results for decrement detection may be affected by neural long-term adaptation, although they are not clearly related to loudness adaptation.
Auditory suppression and frequency selectivity in older and younger adults
Authors: Sommers Mitchell S. , Gehr Sara E.
Published: July 2002

Age differences in auditory suppression were examined by comparing auditory-filter shapes obtained with simultaneous and forward masking at 2 kHz in young and elderly normal-hearing listeners. To compensate for the decay of forward masking, growth of masking functions were used to transform thresholds obtained with a notched-noise masker to the level of a continuous noise band that would give the same threshold values. Although both age groups exhibited smaller equivalent rectangular bandwidths (ERBs) when the filters derived from transformed thresholds were obtained with forward masking, the change from simultaneous to nonsimultaneous masking was significantly greater for young adults. Measures of the low- (Pl) and high- (Pu) frequency sides of the filters for young listeners indicated that the slopes of both sides increased following a change from simultaneous to forward masking but that the high-frequency side exhibited significantly greater sharpening. Filter slopes (both upper and lower) for older adults, in contrast, did not differ between the two masking procedures. The findings from the study are discussed as reflecting possible age differences in auditory suppression. However, it is also noted that conclusions regarding differences between filter shapes derived with simultaneous and forward masking are limited to filter parameters determined with transformed (as described above) thresholds.
Complementarity and synergy in bimodal speech: Auditory, visual, and audio-visual identification of French oral vowels in noise
Authors: Robert-Ribes Jordi , Schwartz Jean-Luc , Lallouache Tahar , Escudier Pierre
Published: July 2002

The efficacy of audio-visual interactions in speech perception comes from two kinds of factors. First, at the information level, there is some “complementarity” of audition and vision: It seems that some speech features, mainly concerned with manner of articulation, are best transmitted by the audio channel, while some other features, mostly describing place of articulation, are best transmitted by the video channel. Second, at the information processing level, there is some “synergy” between audition and vision: The audio-visual global identification scores in a number of different tasks involving acoustic noise are generally greater than both the auditory-alone and the visual-alone scores. However, these two properties have been generally demonstrated until now in rather global terms. In the present work, audio-visual interactions at the feature level are studied for French oral vowels which contrast three series, namely front unrounded, front rounded, and back rounded vowels. A set of experiments on the auditory, visual, and audio-visual identification of vowels embedded in various amounts of noise demonstrate that complementarity and synergy in bimodal speech appear to hold for a bundle of individual phonetic features describing place contrasts in oral vowels. At the information level (complementarity), in the audio channel the height feature is the most robust, backness the second most robust one, and rounding the least, while in the video channel rounding is better than height, and backness is almost invisible. At the information processing (synergy) level, transmitted information scores show that all individual features are better transmitted with the ear and the eye together than with each sensor individually.
Theory of acoustic streaming generated by ultrasonic Lamb waves
Authors: Zhu Zhemin , Zhao Xiaoliang , Du Gonghuan , Wu Junru
Published: July 2002

A theory on acoustic streaming generated by Lamb waves propagating in a thin composite membrane was developed. Using this theory, the mass-transport velocity in water, which is loaded on a 4-μm-thick membrane, due to Lamb waves at 4.7 MHz was calculated. The results are in good agreement with the experimental values measured by Moroney et al. [Appl. Phys. Lett. 59, 774 (1991)].
Criterion for the minimum source distance at which plane-wave beamforming can be applied
Authors: Ryan James G.
Published: July 2002

An expression is derived which can be used to determine the extent of the near field for a given microphone array size and operating wavelength. This expression is based on the distortion of the near-field array response, and approximates the distance at which the magnitude response error due to plane-wave beamforming is 1 dB.
The complementary operators method applied to acoustic finite-difference time-domain simulations
Authors: Schneider John B. , Ramahi Omar M.
Published: July 2002

The complementary operators method (COM) has recently been introduced as a mesh-truncation technique for open-domain radiation problems in electromagnetics. The COM entails the construction of two solutions that employ absorbing boundary conditions (ABCs) with complementary behavior, i.e., the reflection coefficients associated with the two ABCs are exactly opposite each other. The average of these solutions then yields a new solution in which the errors caused by artificial reflections from the termination of grid are nearly eliminated. In this work, COM is introduced for the finite-difference time-domain (FDTD) solution of acoustics problems. The development of COM is presented in terms of Higdon’s absorbing boundary operators, but generalization to non-Higdon operators is straightforward. The effectiveness of COM in comparison to other absorbing boundary conditions is demonstrated with numerical experiments in two and three dimensions.
The insertion loss of screens under the influence of wind
Authors: Rasmussen Karsten B. , Arranz Marta Galindo
Published: July 2002

Point source propagation over a screen located on a finite impedance surface representative of grass-covered ground is investigated under upwind and downwind conditions. The theoretical part of the investigation involves extended use of parabolic equation methods (PE) allowing for the changes in the vertical wind speed profile when the wind field passes the screen. The influence of turbulence is also implemented. The experimental part of the investigation relies on a scale model technique based upon a 1:25 scaling ratio and a triggered spark source. The main results relate to the size of the insertion loss of a screen under windy conditions and to the acoustic importance of the redirection of the flow before and after the screen.
Acoustics of fluid-filled boreholes with pipe: Guided propagation and radiation
Authors: Rama Rao V. N. , Vandiver J. K.
Published: July 2002

The study of the guided propagation and radiation from radially layered boreholes has applications in monitoring exploratory drilling. Axisymmetric propagation through pipes immersed inside fluid-filled bores in infinite elastic spaces was modeled using full 3-D elastodynamic equations. Three propagating modes are present for frequencies below 1 kHz. These are the lowest order modes and are characterized through their dispersion, attenuation, modeshapes, and particle motions. Mode I is confined mainly to the cross section of the pipe, while modes II and III are present in the fluid layers. Modes I and II are weakly dispersive, while mode III is strongly dispersive. Mode III is the equivalent of the Stoneley mode present in fluid-filled bores without pipe and is most influenced by the properties of the surrounding elastic space. Mode III has a cutoff frequency, below which it radiates, when the shear speed of the surrounding elastic space is sufficiently low.
The secondary field of a parametric source following interaction with sea surface
Authors: Wang Lian Sheng , Smith Brian V. , Coates Rodney
Published: July 2002

The effects of a flat sea surface on the secondary wave field for a nonsaturation limited parametric source with a piston-type transmit transducer have been assessed both theoretically and experimentally. When the virtual array of the parametric source interacts with the sea surface, the amplitude of the secondary signal is reduced. In addition to the normal interference between the direct and surface reflection paths, there is also one extra mechanism which causes the reduction of the secondary signal level. This is the destructive summation of the secondary field generated before and after intersection with the water surface. A numerical model and the Westervelt model are used to predict the secondary field which is a function of grazing angle. Experiments in an in-door laboratory tank have been carried out to measure the primary and secondary fields of a parametric array under these circumstances. It is shown that the surface reflection affects the beam pattern of the secondary field and the induced reduction in the signal level depends on the characteristics of the parametric source and the geometry of the problem. The level of reduction caused by the effects of the surface interaction approaches a constant at large grazing angles.