bluuebunny/crossref_metadata_2025 huggingface dataset:
A Mediator Role For Metallothionein in Tumor Necrosis Factor–induced Lethal Shock
Authors: Waelput Wim , Broekaert Daniël , Vandekerckhove Joël , Brouckaert Peter , Tavernier Jan , Libert Claude
Published: July 2002

Tumor necrosis factor (TNF) is a proinflammatory cytokine, which is centrally involved in several inflammatory disorders. Administration of TNF leads to a potentially lethal systemic inflammatory response syndrome (SIRS). We observed that (a) mice lacking functional genes for metallothionein 1 and 2 (MT-null) were protected compared with wild-type controls (P = 0.0078), and (b) mice overexpressing MT-1 (MT-TG) were more sensitized for the lethal effect of TNF than control mice (P = 0.0003), indicating a mediating role for MT in TNF induced SIRS. As MT is involved in the body zinc homeostasis, we tested whether zinc-deprivation or -supplementation alters the response to TNF. Although zinc-depletion strongly sensitized (P = 0.036), and pretreatment with zinc sulfate (ZnSO4) conferred protection against the deleterious effects of TNF (P < 0.0002), it was also found that the protection provided by zinc is independent of MT. Our observation that hsp70 is strongly induced in jejunum after ZnSO4 treatment, suggests a contribution of hsp70 in the protection against TNF. In addition, ZnSO4 cotreatment allowed complete regression of inoculated tumors with TNF and interferon γ, leading to a significantly better survival (P = 0.0045).
Evidence for a Role of Mast Cells in the Evolution to Congestive Heart Failure
Authors: Hara Masatake , Ono Koh , Hwang Myung-Woo , Iwasaki Atsushi , Okada Masaharu , Nakatani Kazuki , Sasayama Shigetake , Matsumori Akira
Published: July 2002

Mast cells are believed to be involved in the pathophysiology of heart failure, but their precise role in the process is unknown. This study examined the role of mast cells in the progression of heart failure, using mast cell-deficient (WBB6F1-W/Wv) mice and their congenic controls (wild-type [WT] mice). Systolic pressure overload was produced by banding of the abdominal aorta, and cardiac function was monitored over 15 wk. At 4 wk after aortic constriction, cardiac hypertrophy with preserved left ventricular performance (compensated hypertrophy) was observed in both W/Wv and WT mice. Thereafter, left ventricular performance gradually decreased in WT mice, and pulmonary congestion became apparent at 15 wk (decompensated hypertrophy). In contrast, decompensation of cardiac function did not occur in W/Wv mice; left ventricular performance was preserved throughout, and pulmonary congestion was not observed. Perivascular fibrosis and upregulation of mast cell chymase were all less apparent in W/Wv mice. Treatment with tranilast, a mast cell–stabilizing agent, also prevented the evolution from compensated hypertrophy to heart failure. These observations suggest that mast cells play a critical role in the progression of heart failure. Stabilization of mast cells may represent a new approach in the management of heart failure.
Autoreactive B Cells in the Marginal Zone that Express Dual Receptors
Authors: Li Yijin , Li Hui , Weigert Martin
Published: July 2002

Allotype and isotype exclusion is a property of most lymphocytes. The reason for this property is not known but it guarantees a high concentration of a single receptor, and threshold numbers of receptors may be required for efficient positive and negative selection. Receptor editing compromises exclusion by sustaining recombination even after a functional receptor is formed. Consequently, B cells expressing multiple receptors arise. We have studied such B cells in which one of the two receptors is anti-self, and find that these partially autoreactive B cells accumulate in the marginal zone. The restriction of these cells in this location may help to prevent them from undergoing diversification and developing into fully autoreactive B cells.
Dissection of Mitochondrial Ca2+ Uptake and Release Fluxes in Situ after Depolarization-Evoked [Ca2+]i Elevations in Sympathetic Neurons
Authors: Colegrove Stephen L. , Albrecht Meredith A. , Friel David D.
Published: July 2002

We studied how mitochondrial Ca2+ transport influences [Ca2+]i dynamics in sympathetic neurons. Cells were treated with thapsigargin to inhibit Ca2+ accumulation by SERCA pumps and depolarized to elevate [Ca2+]i; the recovery that followed repolarization was then examined. The total Ca2+ flux responsible for the [Ca2+]i recovery was separated into mitochondrial and nonmitochondrial components based on sensitivity to the proton ionophore FCCP, a selective inhibitor of mitochondrial Ca2+ transport in these cells. The nonmitochondrial flux, representing net Ca2+ extrusion across the plasma membrane, has a simple dependence on [Ca2+]i, while the net mitochondrial flux (Jmito) is biphasic, indicative of Ca2+ accumulation during the initial phase of recovery when [Ca2+]i is high, and net Ca2+ release during later phases of recovery. During each phase, mitochondrial Ca2+ transport has distinct effects on recovery kinetics. Jmito was separated into components representing mitochondrial Ca2+ uptake and release based on sensitivity to the specific mitochondrial Na+/Ca2+ exchange inhibitor, CGP 37157 (CGP). The CGP-resistant (uptake) component of Jmito increases steeply with [Ca2+]i, as expected for transport by the mitochondrial uniporter. The CGP-sensitive (release) component is inhibited by lowering the intracellular Na+ concentration and depends on both intra- and extramitochondrial Ca2+ concentration, as expected for the Na+/Ca2+ exchanger. Above ∼400 nM [Ca2+]i, net mitochondrial Ca2+ transport is dominated by uptake and is largely insensitive to CGP. When [Ca2+]i is ∼200–300 nM, the net mitochondrial flux is small but represents the sum of much larger uptake and release fluxes that largely cancel. Thus, mitochondrial Ca2+ transport occurs in situ at much lower concentrations than previously thought, and may provide a mechanism for quantitative control of ATP production after brief or low frequency stimuli that raise [Ca2+]i to levels below ∼500 nM.
An equivalent definition of functions of the first Baire class
Authors: Lee Peng-Yee , Tang Wee-Kee , Zhao Dongsheng
Published: July 2002

An equivalent definition of functions of the first Baire class in terms of

ε
−
δ

\varepsilon -\delta

is given.
Estimation of spectral gap for elliptic operators
Authors: Chen Mu-Fa , Wang Feng-Yu
Published: July 2002

A variational formula for the lower bound of the spectral gap of an elliptic operator is presented in the paper for the first time. The main known results are either recovered or improved. A large number of new examples with sharp estimate are illustrated. Moreover, as an application of the march coupling, the Poincaré inequality with respect to the absolute distribution of the process is also studied.
An atlas of regular thin geometries for small groups
Authors: Leemans Dimitri
Published: July 2002

For some small groups, we give, up to isomorphism, an exhaustive list of all residually connected thin geometries on which these groups act regularly. We then show the utility of such an atlas by proving several results about smallest groups acting on a given diagram. The results have been obtained using a series of Magma programs.
The closure diagrams for nilpotent orbits of the real forms EVI and EVII of 𝐄₇
Authors: Đoković Dragomir
Published: July 2002

Let

O

1

\mathcal {O}_1

and

O

2

\mathcal {O}_2

be adjoint nilpotent orbits in a real semisimple Lie algebra. Write

O

1

≥

O

2

\mathcal {O}_1\geq \mathcal {O}_2

if

O

2

\mathcal {O}_2

is contained in the closure of

O

1

.

\mathcal {O}_1.

This defines a partial order on the set of such orbits, known as the closure ordering. We determine this order for the two noncompact nonsplit real forms of the simple complex Lie algebra

E
7

.

E_7.
The Multiprotein Exocyst Complex Is Essential for Cell Separation inSchizosaccharomyces pombe
Authors: Wang Hongyan , Tang Xie , Liu Jianhua , Trautmann Susanne , Balasundaram David , McCollum Dannel , Balasubramanian Mohan K.
Published: July 2002

Schizosaccharomyces pombe cells divide by medial fission through the use of an actomyosin-based contractile ring. A mulitlayered division septum is assembled in concert with ring constriction. Finally, cleavage of the inner layer of the division septum results in the liberation of daughter cells. Although numerous studies have focused on actomyosin ring and division septum assembly, little information is available on the mechanism of cell separation. Here we describe a mutant, sec8-1, that is defective in cell separation but not in other aspects of cytokinesis.sec8-1 mutants accumulate ∼100-nm vesicles and have reduced secretion of acid phosphatase, suggesting that they are defective in exocytosis. Sec8p is a component of the exocyst complex. Using biochemical methods, we show that Sec8p physically interacts with other members of the exocyst complex, including Sec6p, Sec10p, and Exo70p. These exocyst proteins localize to regions of active exocytosis—at the growing ends of interphase cells and in the medial region of cells undergoing cytokinesis—in an F-actin–dependent and exocytosis-independent manner. Analysis of a number of mutations in various exocyst components has established that these components are essential for cell viability. Interestingly, all exocyst mutants analyzed appear to be able to elongate and to assemble division septa but are defective for cell separation. We therefore propose that the fission yeast exocyst is involved in targeting of enzymes responsible for septum cleavage. We further propose that cell elongation and division septum assembly can continue with minimal levels of exocyst function.
Bargaining Experiments With Deadlines and Random Delays
Authors: Sterbenz Frederic P. , Phillips Owen R.
Published: July 2002

In many bargaining environments there are random delays in the transmission of proposals. Two computerized bargaining experiments are designed to study behavior with this condition. A clock starts counting down from three minutes when the first offer is sent. In one experiment the clock is not stopped once the bargaining begins; in the other it is paused during the time an agent thinks about a counteroffer. All proposals are randomly delayed. Results are compared to a control design with no such delays. Delays create a first mover advantage, and agreements are more uniformly spread across a bargaining period.
In-vitro activity of levofloxacin, ofloxacin and d -ofloxacin against coryneform bacteria and Listeria monocytogenes
Authors: Martínez-Martínez L. , Pascual A. , Suárez A. I. , Perea E. J.
Published: July 2002

The objective of this study was to evaluate the in-vitro activity of levofloxacin, ofloxacin and d -ofloxacin compared with ciprofloxacin, norfloxacin and sparfloxacin against coryneform bacteria and Listeria monocytogenes isolated from clinical samples. The following organisms (and number of strains) were studied: Corynebacterium jeikeium (20), Corynebacterium urealyticum (20), Corynebacterium minutissimum (20), Corynebacterium striatum (20), Corynebacterium amycolatum (30), Brevibacterium spp. (15) and Listeria monocytogenes (15). Antimicrobial activity was determined by microdilution using cation-adjusted Mueller–Hinton broth supplemented with 0.5% Tween 80 when testing C. jeikeium or C. urealyticum. Fluoroquinolones were used in the range 0.015–16 mg/L. Plates were incubated in air at 35°C for 18–20 h (24 h when testing C. jeikeium or C. urealyticum ). The following MIC 50 values were obtained for all 140 organisms tested: levofloxacin, 1 mg/L; ofloxacin, 2 mg/L; d -ofloxacin, >16 mg/L; ciprofloxacin, 1 mg/L; norfloxacin, 16 mg/L; sparfloxacin, 1 mg/L. MIC 90 values were >16 mg/L for all test antibiotics with the exception of levofloxacin, which had an MIC 90 value of 16 mg/L. At a concentration of 2 mg/L, levofloxacin inhibited all L. monocytogenes strains and 35–93% of the remaining species. MIC 90 values of ofloxacin were one dilution step higher than those of levofloxacin against C. minutissimum,C. striatum,Brevibacterium spp. and L. monocytogenes. Levofloxacin showed similar ( C. jeikeium,C. urealyticum,C. amycolatum and Brevibacterium spp.) or greater ( C. minutissimum and C. striatum ) activity than ciprofloxacin and sparfloxacin, and higher than d -ofloxacin or norfloxacin against all species studied. In conclusion, levofloxacin was the most active of the six fluoroquinolones evaluated against coryneform bacteria isolated from clinical samples and could therefore be a promising treatment option in this setting.
Sensory receptors in monotremes
Authors: Proske U. , Gregory J. E. , Iggo A.
Published: July 2002

This is a summary of the current knowledge of sensory receptors in skin of the bill of the platypus,Ornithorhynchus anatinus, and the snout of the echidna,Tachyglossus aculeatus. Brief mention is also made of the third living member of the monotremes, the long–nosed echidna,Zaglossus bruijnii. The monotremes are the only group of mammals known to have evolved electroreception. The structures in the skin responsible for the electric sense have been identified as sensory mucous glands with an expanded epidermal portion that is innervated by large–diameter nerve fibres. Afferent recordings have shown that in both platypuses and echidnas the receptors are excited by cathodal (negative) pulses and inhibited by anodal (positive) pulses. Estimates give a total of 40 000 mucous sensory glands in the upper and lower bill of the platypus, whereas there are only about 100 in the tip of the echidna snout. Recordings of electroreceptor–evoked activity from the brain of the platypus have shown that the largest area dedicated to somatosensory input from the bill, S1, shows alternating rows of mechanosensory and bimodal neurons. The bimodal neurons respond to both electrosensory and mechanical inputs. In skin of the platypus bill and echidna snout, apart from the electroreceptors, there are structures called push rods, which consist of a column of compacted cells that is able to move relatively independently of adjacent regions of skin. At the base of the column are Merkel cell complexes, known to be type I slowly adapting mechanoreceptors, and lamellated corpuscles, probably vibration receptors. It has been speculated that the platypus uses its electric sense to detect the electromyographic activity from moving prey in the water and for obstacle avoidance. Mechanoreceptors signal contact with the prey. For the echidna, a role for the electrosensory system has not yet been established during normal foraging behaviour, although it has been shown that it is able to detect the presence of weak electric fields in water. Perhaps the electric sense is used to detect moving prey in moist soil.
The sensory world of the platypus
Authors: Pettigrew J. D. , Manger P. R. , Fine S. L. B.
Published: July 2002

Vision, audition and somatic sensation in the platypus are reviewed. Recent work on the eye and retinal ganglion cell layer of the platypus is presented that provides an estimate of visual acuity and suggests that platypus ancestors may have used vision, as well as the bill organ, for underwater predation. The combined electroreceptor and mechanoreceptor array in the bill is considered in detail, with special reference to the elaborate cortical structure, where inputs from these two sensory arrays are integrated in a manner that is astonishingly similar to the stripe–like ocular dominance array in primate visual cortex, that integrates input from the two eyes. A new hypothesis, along with supporting data, is presented for this combined mechanoreceptive–electroreceptive complex in platypus cortex. Bill mechanoreceptors are shown to be capable of detecting mechanical waves travelling through the water from moving prey. These mechanical waves arrive after the electrical activity from the same prey, as a function of distance. Bimodal cortical neurones, sensitive to combined mechanical and electrical stimulation, with a delay, can thus signal directly the absolute distance of the prey. Combined with the directional information provided by signal processing of the thousands of receptors on the bill surface, the stripe–like cortical array enables the platypus to use two different sensory systems in its bill to achieve a complete, three–dimensional ‘fix’ on its underwater prey.
Some related aspects of platypus electroreception: temporal integration behaviour, electroreceptive thresholds and directionality of the bill acting as an antenna
Authors: Fjällbrant Tore T. , Manger Paul R. , Pettigrew John D.
Published: July 2002

This paper focuses on how the electric field from the prey of the platypus is detected with respect to the questions of threshold determination and how the platypus might localize its prey. A new behaviour in response to electrical stimuli below the thresholds previously reported is presented. The platypus shows a voluntary exploratory behaviour that results from a temporal integration of a number of consecutive stimulus pulses. A theoretical analysis is given, which includes the threshold dependence on the number of receptors and temporal integration of consecutive stimuli pulses, the close relationships between electrical field decay across the bill, electroreceptive thresholds and directionality of the platypus bill acting as an antenna. It is shown that a lobe shape, similar to that which has been measured, can be obtained by combining responses in a specific way from receptors sensing the electric field decay across the bill. Two possible methods for such combinations are discussed and analysed with respect to measurements and observed behaviour of the platypus. A number of factors are described which need to be considered when electroreceptive thresholds are to be determined. It is shown that some information about the distance to the source is theoretically available from the pattern of field decay across the platypus's bill. The paper includes a comparative analysis of radar target tracking and platypus prey localization.
Studies of antibiotic resistance within the patient, hospitals and the community using simple mathematical models
Authors: Austin D. J. , Anderson R. M.
Published: July 2002

The emergence of antibiotic resistance in a wide variety of important pathogens of humans presents a worldwide threat to public health. This paper describes recent work on the use of mathematical models of the emergence and spread of resistance bacteria, on scales ranging from within the patient, in hospitals and within communities of people. Model development starts within the treated patient, and pharmacokinetic and pharmacodynamic principles are melded within a framework that mirrors the interaction between bacterial population growth, drug treatment and the immunological responses targeted at the pathogen. The model helps identify areas in which more precise information is needed, particularly in the context of how drugs influence pathogen birth and death rates (pharmacodynamics). The next area addressed is the spread of multiply drug–resistant bacteria in hospital settings. Models of the transmission dynamics of the pathogen provide a framework for assessing the relative merits of different forms of intervention, and provide criteria for control or eradication. The model is applied to the spread of Vancomycin–resistant enterococci in an intensive care setting. This model framework is generalized to consider the spread of resistant organisms between hospitals. The model framework allows for heterogeneity in hospital size and highlights the importance of large hospitals in the maintenance of resistant organisms within a defined country. The spread of methicillin resistantStaphylococcus aureus(MRSA) in England and Wales provides a template for model construction and analysis. The final section addresses the emergence and spread of resistant organisms in communities of people and the dependence on the intensity of selection as measured by the volume or rate of drug use. Model output is fitted to data for Finland and Iceland and conclusions drawn concerning the key factors determining the rate of spread and decay once drug pressure is relaxed.
Coordinate–independent mapping of structural and functional data by objective relational transformation (ORT)
Authors: Stephan Klaas E. , Zilles Karl , Kötter Rolf
Published: July 2002

Neuroscience has produced an enormous amount of structural and functional data. Powerful database systems are required to make these data accessible for computational approaches such as higher–order analyses and simulations. Available databases for key data such as anatomical and functional connectivity between cortical areas, however, are still hampered by methodological problems. These problems arise predominantly from the parcellation problem, the use of incongruent parcellation schemes by different authors.We here present a coordinate–independent mathematical method to overcome this problem: objective relational transformation (ORT). Based on new classifications for brain data and on methods from theoretical computer science, ORT represents a formally defined, transparent transformation method for reproducible, coordinate–independent mapping of brain data to freely chosen parcellation schemes. We describe the methodology of ORTand discuss its strengths and limitations. Using two practical examples, we show that ORT in conjunction with connectivity databases like CoCoMac (http://www.cocomac.org) is an important tool for analyses of cortical organization and structure–function relationships.
Clinical effectiveness and cost effectiveness of zanamivir (Relenza): translating the evidence into clinical practice, a National Institute for Clinical Excellence view
Authors: Barnett David
Published: July 2002

The UK National Institute for Clinical Excellence (NICE) is charged with the duty of providing informed guidance on clinical practice (clinical effectiveness and cost effectiveness) to patients and health professionals. The Appraisal Committee through its process of review of evidence advises NICE on the clinical effectiveness and cost effectiveness of new and existing technologies and their appropriate use within the National Health Service in England and Wales. The appraisal process takes into account both published and unpublished evidence as well as input from professional and patient and carer groups when coming to its decisions. The appraisal of a new technology often has to bridge the gap between the evidence required for licensing purposes and that needed to provide pragmatic advice to practising clinicians. The appraisal of zanamivir (Relenza) is an excellent working example of this difficult and important process.
Emi1 regulates the anaphase-promoting complex by a different mechanism than Mad2 proteins
Authors: Reimann Julie D.R. , Gardner Bryan E. , Margottin-Goguet Florence , Jackson Peter K.
Published: July 2002

The anaphase-promoting complex/cyclosome (APC) ubiquitin ligase is activated by Cdc20 and Cdh1 and inhibited by Mad2 and the spindle assembly checkpoint complex, Mad2B, and the early mitotic inhibitor Emi1. Mad2 inhibits APCCdc20, whereas Mad2B preferentially inhibits APCCdh1. We have examined the mechanism of APC inhibition by Emi1 and find that unlike Mad2 proteins, Emi1 binds and inhibits both APCCdh1 and APCCdc20. Also unlike Mad2, Emi1 stabilizes cyclin A in the embryo and requires zinc for its APC inhibitory activity. We find that Emi1 binds the substrate-binding region of Cdc20 and prevents substrate binding to the APC, illustrating a novel mechanism of APC inhibition.
PPARγ knockdown by engineered transcription factors: exogenous PPARγ2 but not PPARγ1 reactivates adipogenesis
Authors: Ren Delin , Collingwood Trevor N. , Rebar Edward J. , Wolffe Alan P. , Camp Heidi S.
Published: July 2002

To determine functional differences between the two splice variants of PPARγ (γ1 and γ2), we sought to selectively repress γ2 expression by targeting engineered zinc finger repressor proteins (ZFPs) to the γ2-specific promoter, P2. In 3T3-L1 cells, expression of ZFP55 resulted in >50% reduction in γ2 expression but had no effect on γ1, whereas adipogenesis was similarly reduced by 50%. However, ZFP54 virtually abolished both γ2 and γ1 expression, and completely blocked adipogenesis. Overexpression of exogenous γ2 in the ZFP54-expressing cells completely restored adipogenesis, whereas overexpression of γ1 had no effect. This finding clearly identifies a unique role for the PPARγ2 isoform.
Involvement of the cohesin protein, Smc1, in Atm-dependent and independent responses to DNA damage
Authors: Kim Seong-Tae , Xu Bo , Kastan Michael B.
Published: July 2002

Structural maintenance of chromosomes (SMC) proteins play important roles in sister chromatid cohesion, chromosome condensation, sex-chromosome dosage compensation, and DNA recombination and repair. Protein complexes containing heterodimers of the Smc1 and Smc3 proteins have been implicated specifically in both sister chromatid cohesion and DNA recombination. Here, we show that the protein kinase, Atm, which belongs to a family of phosphatidylinositol 3-kinases that regulate cell cycle checkpoints and DNA recombination and repair, phosphorylates Smc1 protein after ionizing irradiation. Atm phosphorylates Smc1 on serines 957 and 966 in vitro and in vivo, and expression of an Smc1 protein mutated at these phosphorylation sites abrogates the ionizing irradiation-induced S phase cell cycle checkpoint. Optimal phosphorylation of these sites in Smc1 after ionizing irradiation also requires the presence of the Atm substrates Nbs1 and Brca1. These same sites in Smc1 are phosphorylated after treatment with UV irradiation or hydroxyurea in an Atm-independent manner, thus demonstrating that another kinase must be involved in responses to these cellular stresses. Yeast containing hypomorphic mutations in SMC1 and human cells overexpressing Smc1 mutated at both of these phosphorylation sites exhibit decreased survival following ionizing irradiation. These results demonstrate that Smc1 participates in cellular responses to DNA damage and link Smc1 to the Atm signal transduction pathway.
SMC1 is a downstream effector in the ATM/NBS1 branch of the human S-phase checkpoint
Authors: Yazdi Parvin T. , Wang Yi , Zhao Song , Patel Nimitt , Lee Eva Y.-H.P. , Qin Jun
Published: July 2002

Structural maintenance of chromosomes (SMC) proteins (SMC1, SMC3) are evolutionarily conserved chromosomal proteins that are components of the cohesin complex, necessary for sister chromatid cohesion. These proteins may also function in DNA repair. Here we report that SMC1 is a component of the DNA damage response network that functions as an effector in the ATM/NBS1-dependent S-phase checkpoint pathway. SMC1 associates with BRCA1 and is phosphorylated in response to IR in an ATM- and NBS1-dependent manner. Using mass spectrometry, we established that ATM phosphorylates S957 and S966 of SMC1 in vivo. Phosphorylation of S957 and/or S966 of SMC1 is required for activation of the S-phase checkpoint in response to IR. We also discovered that the phosphorylation of NBS1 by ATM is required for the phosphorylation of SMC1, establishing the role of NBS1 as an adaptor in the ATM/NBS1/SMC1 pathway. The ATM/CHK2/CDC25A pathway is also involved in the S-phase checkpoint activation, but this pathway is intact in NBS cells. Our results indicate that the ATM/NBS1/SMC1 pathway is a separate branch of the S-phase checkpoint pathway, distinct from the ATM/CHK2/CDC25A branch. Therefore, this work establishes the ATM/NBS1/SMC1 branch, and provides a molecular basis for the S-phase checkpoint defect in NBS cells.
Resource Letter: PER-1: Physics Education Research
Authors: McDermott Lillian C. , Redish Edward F.
Published: July 2002

The purpose of this Resource Letter is to provide an overview of research on the learning and teaching of physics. The references have been selected to meet the needs of two groups of physicists engaged in physics education. The first is the growing number whose field of scholarly inquiry is (or might become) physics education research. The second is the much larger community of physics instructors whose primary interest is in using the results from research as a guide for improving instruction.
An experimental study of the impedance of perforated plates with grazing flow
Authors: Dickey N. S. , Selamet A. , Ciray M. S.
Published: July 2002

An experimental investigation of the linear impedance of perforated interfaces exposed to grazing fluid flow is presented, including a description of the branch-type setup used in the study. The experimental setup employs a movable microphone in the branch duct that improves the error characteristics of the system. The impedance parameters of three perforated samples have been measured including one circular, square-edged orifice and two production muffler louver geometries. The data are presented in terms of the equivalent length and resistance of the samples, with the friction velocity being used to characterize the grazing flow. At higher grazing flow velocities, the equivalent length of each sample decreased by an amount representative of the Rayleigh end correction for one side of an orifice. Resistance for the louvers appears to be somewhat less sensitive to grazing flow than the circular orifice, though all of the samples showed significant increases. While the experimental results for all three samples showed similar basic trends, distinct and substantial differences were observed between each perforate geometry.
A comparison of detection and discrimination of temporal asymmetry in amplitude modulation
Authors: Akeroyd Michael A. , Patterson Roy D.
Published: July 2002

Two compound experiments were performed to compare the detection of amplitude modulation with the discrimination of modulator shape when the modulators have strong temporal asymmetry. In experiment 1, an adaptive procedure was used to measure detection and discrimination as a function of modulation frequency from 4 to 400 Hz. In experiment 2, the method of constant stimuli was used to measure psychometric functions for detection and discrimination at one modulation frequency, 8 Hz. The asymmetric modulators were time-reversed pairs. Thus their envelope spectra are identical and models based on the envelope spectrum would predict no effect of asymmetry on detection or discrimination at any modulation depth. The detection results show, as predicted, that the direction of asymmetry does not affect the detectability of modulation in either experiment. In contrast, the discrimination results show that direction of asymmetry is readily discriminable for modulation frequencies less than about 50 Hz, indicating that envelope-spectrum models will require modification if they are to be extended to include discrimination of temporal asymmetry.
The use of large ultrasonic transducers to improve transmission coefficient measurements on viscoelastic anisotropic plates
Authors: Cawley Peter , Hosten Bernard
Published: July 2002

A study of the use of large transducers (80 mm×40 mm, 3.2 MHz center frequency) for the measurement of ultrasonic transmission coefficients is reported. Tests have been carried out on thick and thin glass plates and on a unidirectional carbon fiber composite plate. The material properties of the plates were obtained by comparing the transmission coefficient results at particular angles with the predictions of plane-wave theory for different material properties; the properties giving the best fit were then used to predict the transmission coefficients at other angles. The results of this preliminary study show that the use of large transducers makes it possible to obtain excellent agreement between measured transmission coefficients at all angles and those predicted using plane-wave theory. The large transducers give clearer definition of the transmission maxima than is obtained with smaller, conventional transducers, and also give good agreement with the predicted transmission coefficient amplitudes. This should improve the accuracy of inversion procedures for the determination of the real parts of the elastic constants from the frequencies of the transmission maxima, and the good amplitude agreement opens up the possibility of obtaining accurate estimates of the imaginary parts of the elastic constants.
Vibration and dynamic response control of cantilevers carrying externally mounted stores
Authors: Librescu L. , Na S. S.
Published: July 2002

The vibrational and dynamic response control of cantilevers carrying externally mounted stores is investigated. The cantilevered structure is modeled as a thin-walled beam of arbitrary cross section and incorporates a number of nonclassical effects such as transverse shear, secondary warping, anisotropy of constituent materials, and heterogeneity of the construction. The control is carried out via a dynamic bending moment applied at the tip of the structure. A feedback control law relating the boundary moment with one of the kinematical variables characterizing the response of the beam is implemented, and its results upon the closed-loop eigenfrequencies and dynamic response are highlighted. The obtained numerical results emphasize the efficiency of this control methodology to enhance, without weight penalties, vibrational and dynamic response behavior and inhibit and even suppress the occurrence of the resonance phenomenon.
“Central” auditory gap detection: A spatial case
Authors: Phillips D. P. , Hall S. E. , Harrington I. A. , Taylor T. L.
Published: July 2002

Normal listeners were tested for their temporal auditory gap detection thresholds using free-field presentation of white-noise stimuli delivered from the left (L) and right (R) poles of the interaural axis. The noise bursts serving as the leading and trailing markers for the silent period were presented in either the same (LL,RR) or different (LR,RL) auditory locations. The duration of the leading marker was a second independent variable. Gap thresholds for stimuli in which the markers had the same location were low, and usually were independent of the duration of the leading marker. Gap thresholds for the LR and RL conditions were longer. These gap thresholds were sensitive to the duration of the leading marker, and increased as the leading marker duration decreased. This finding is consistent with the hypothesis that a relative timing operation mediates gap detection when the markers activate different perceptual channels. The present data suggest that this timing process can operate on perceptual channels emerging from central nervous system processing.
Within-channel gap detection using dissimilar markers in cochlear implant listeners
Authors: Chatterjee Monita , Fu Qian-Jie , Shannon Robert V.
Published: July 2002

Temporal gap detection thresholds were measured between perceptually dissimilar electrical markers in cochlear implant listeners. Both markers were presented to the same electrode pair. The amplitude and pulse rate of the first marker were fixed, and gap thresholds were measured as a function of either the pulse rate or the amplitude of the second marker. In either case, U-shaped functions were obtained, with lowest gap thresholds occurring when the two markers were similar in both amplitude and pulse rate. Because the two markers were presented to the same electrode pair, the data cannot be accounted for on the basis of across-channel interactions. It is hypothesized that when different markers are used, the perceptual discontinuity from the first marker to the second is similar to the sensation of a brief gap, and dominates the gap detection process. Thus, gap threshold functions with electrically dissimilar markers serve more as indicators of perceptual distance between the markers and less as measures of temporal resolution.
Fundamental frequency synchronous spectral analysis for vowel classification
Authors: Dai Bingjun , Zahorian Stephen A.
Published: July 2002

A method is described and tested for spectral analysis of vowels using window lengths that are integer multiples of the pitch period for voiced signals. For segments of vowels selected from steady-state vowels, the average fundamental frequency is first determined using ‘‘standard’’ autocorrelation methods. The acoustic signal is then analyzed again to determine fundamental frequency on a cycle-by-cycle basis. The signal is resampled at a higher rate so that each pitch period has the same number of samples. Spectral analysis is implemented such that harmonics of the fundamental coincide with FFT samples. Cepstral analysis is then performed on this spectrum with and without fundamental-frequency-dependent frequency shifting as a speaker normalization. This processing method was tested using a database of 150 speakers (50 children, 50 women, and 50 men) for ten monopthong vowels produced in isolation. As a control, spectral analysis was also performed on Hamming-windowed speech segments without regard to fundamental frequency. Neural network classification tests indicated only minor changes in classification rates with the fundamental-synchronous method versus the conventional method. The implication of this work is that spectral smearing due to window effects is a minor effect for vowel spectral analysis. [Funded by NSF, Grant No. NSF-BES-9411607.]
The effect of changes in hearing status on speech sound level and speech breathing: A study conducted with cochlear implant users and NF-2 patients
Authors: Lane Harlan , Perkell Joseph , Wozniak Jane , Manzella Joyce , Guiod Peter , Matthies Melanie , MacCollin Mia , Vick Jennell
Published: July 2002

According to a dual-process theory of the role of hearing in speech production, hearing helps maintain an internal model used by the speech control mechanism to achieve phonemic goals. It also monitors the acoustic environment and guides relatively rapid adjustments in postural parameters, such as those underlying average speech sound level and rate, in order to achieve suprasegmental goals that are a compromise between intelligibility and economy of effort. In order to obtain evidence bearing on this theory, acoustic and aerodynamic measures were collected from seven adventitiously deaf speakers who received cochlear implants, three speakers who had severe reduction in hearing following surgery for Neurofibromatosis-2, and one hard of hearing speaker. These speakers made recordings of the Rainbow Passage and an English vowel inventory before and after intervention. All but one of the postlingually deaf speakers who received prosthetic hearing reduced speech sound level, SPL. Three of these significantly increased a measure of inferred glottal aperture, H1–H2, and their session means for these two parameters were inversely correlated longitudinally. All but one of the speakers terminated respiratory limbs closer to functional residual capacity (FRC) once prosthetic hearing was supplied. Finally, the implant users’ average values of air expenditure moved toward normative values with prosthetic hearing. These results are attributed to the mediation of changes in respiratory and glottal posture aimed at reducing speech sound level and economizing effort.
Effects of a neoprene wetsuit hood on low-frequency underwater hearing thresholds
Authors: Sims John R. , Fothergill David M. , Curley Michael D.
Published: July 2002

In an effort to create guidelines for exposure to low-frequency underwater sound, it is necessary to obtain population data on the minimal detectable sound-pressure level at these frequencies. Underwater hearing thresholds were obtained from 15 male and 5 female recreational SCUBA divers with and without a 3-mm wetsuit hood. Dives were conducted at a 1-m depth in a large quiet anechoic pool. A J13 transducer was located 4 m directly below the subject. Thresholds were determined using two-interval forced-choice with a 0.71 probability of positive response at convergence. A 1-s pure tone was presented with a 20-ms rise and fall at 100, 200, 250, 300, 400, and 500 Hz. Results indicate there was no difference in thresholds between male and female divers. Without a wetsuit hood, mean thresholds decreased from 99 dB (s.d. 6 dB) re: 0.000001 Pa at 100 Hz to 85 dB (s.d. 10 dB) at 500 Hz. Thresholds were statistically similar at 100 to 300 Hz with and without the wetsuit hood, but were significantly increased at 400 and 500 Hz with the hood (p<0.001). In conclusion, a wetsuit hood attenuates frequencies at 400 Hz and above by approximately 10 dB. [Work supported by CNO, N-87.]
Does music performance allude to locomotion? A model of final ritardandi derived from measurements of stopping runners
Authors: Friberg Anders , Sundberg Johan
Published: July 2002

This investigation explores the common assumption that music and motion are closely related by comparing the stopping of running and the termination of a piece of music. Video recordings were made of professional dancers’ stopping from running under different deceleration conditions, and instant values of body velocity, step frequency, and step length were estimated. In decelerations that were highly rated for aesthetic quality by a panel of choreographers, the mean body velocity could be approximated by a square-root function of time, which is equivalent to a cubic-root function of position. This implies a linear relationship between kinetic energy and time, i.e., a constant braking power. The mean body velocity showed a striking similarity with the mean tempo pattern of final ritardandi in music performances. The constant braking power was used as the basis for a model describing both the changes of tempo in final ritardandi and the changes of velocity in runners’ decelerations. The translation of physical motion to musical tempo was realized by assuming that velocity and musical tempo are equivalent. Two parameters were added to the model to account for the variation observed in individual ritardandi and in individual decelerations: (1) the parameter q controlling the curvature, q=3 corresponding to the runners’ deceleration, and (2) the parameter vend for the final velocity and tempo value, respectively. A listening experiment was carried out presenting music examples with final ritardandi according to the model with different q values or to an alternative function. Highest ratings were obtained for the model with q=2 and q=3. Out of three functions, the model produced the best fit to individual measured ritardandi as well as to individual decelerations. A function previously used for modeling phrase-related tempo variations (interonset duration as a quadratic function of score position) produced the lowest ratings and the poorest fits to individual ritardandi. The results thus seem to substantiate the commonly assumed analogies between motion and music.
Articulatory tradeoffs reduce acoustic variability during American English /r/ production
Authors: Guenther Frank H. , Espy-Wilson Carol Y. , Boyce Suzanne E. , Matthies Melanie L. , Zandipour Majid , Perkell Joseph S.
Published: July 2002

The American English phoneme /r/ has long been associated with large amounts of articulatory variability during production. This paper investigates the hypothesis that the articulatory variations used by a speaker to produce /r/ in different contexts exhibit systematic tradeoffs, or articulatory trading relations, that act to maintain a relatively stable acoustic signal despite the large variations in vocal tract shape. Acoustic and articulatory recordings were collected from seven speakers producing /r/ in five phonetic contexts. For every speaker, the different articulator configurations used to produce /r/ in the different phonetic contexts showed systematic tradeoffs, as evidenced by significant correlations between the positions of transducers mounted on the tongue. Analysis of acoustic and articulatory variabilities revealed that these tradeoffs act to reduce acoustic variability, thus allowing relatively large contextual variations in vocal tract shape for /r/ without seriously degrading the primary acoustic cue. Furthermore, some subjects appeared to use completely different articulatory gestures to produce /r/ in different phonetic contexts. When viewed in light of current models of speech movement control, these results appear to favor models that utilize an acoustic or auditory target for each phoneme over models that utilize a vocal tract shape target for each phoneme.
Psychometric functions for gap detection in a yes–no procedure
Authors: Florentine Mary , Buus Søren , Geng Wei
Published: July 2002

To examine models of temporal resolution and to investigate the decision processes underlying the detection of a brief pause in a bandpass noise, psychometric functions for gap detection were measured at octave frequencies from 0.25 to 8 kHz. Three normal listeners were tested using a constant-stimulus procedure with a cued Yes–No paradigm. The Minimum Detectable Gap (MDG) estimated from the midpoint of the psychometric functions decreased systematically with increasing frequency. The slopes of the psychometric functions generally increased as the test frequency increased up to 2 kHz, but remained constant at the higher frequencies. Two models were investigated: an energy-detector model and a loudness-detector model. Both consisted of auditory filtering, a nonlinearity, and short-term integration. In the energy-detector model, the nonlinearity was a square law. In the loudness-detector model, it was a compressive power law. Using the usual Gaussian approximations, the energy-detector model fails at low frequencies because the probability distributions of short-term energy differ from Gaussian distributions. The probability distributions of short-term loudness closely follow Gaussian distributions. The loudness-detector model predicts the frequency dependence of the MDG quite accurately, except at 0.25 kHz. It also predicts psychometric functions that resemble the data at low frequencies, but the predicted slopes increase much less with frequency than the measured slopes. This result may indicate that the onset response to the trailing marker of the gap provides an important cue for detection of gaps with durations exceeding the MDG.
The effect of temporal placement on gap detectability
Authors: Snell Karen B. , Hu Hue-Lu
Published: July 2002

The detectability of a masked sinusoid increases as its onset approaches the temporal center of a masker. This study was designed to determine whether a similar change in detectability would occur for a silent gap as it was parametrically displaced from the onset of a noise burst. Gap thresholds were obtained for 13 subjects who completed five replications of each condition in 3 to 13 days. Six subjects were inexperienced listeners who ranged in age from 18 to 25 years; seven subjects were highly experienced and ranged in age from 20 to 78 years. The gaps were placed in 150-ms, 6-kHz, low-passed noise bursts presented at an overall level of 75 dB SPL; the bursts were digitally shaped at onset and offset with 10-ms cosine-squared rise–fall envelopes. The gated noise bursts were presented in a continuous, unfiltered, white noise floor attenuated to an overall level of 45 dB SPL. Gap onsets were parametrically delayed from the onset of the noise burst (defined as the first nonzero point on the waveform envelope) by 10, 11, 13, 15, 20, 40, 60, 110, 120, and 130 ms. Results of ANOVAs indicated that the mean gap thresholds were longer when the gaps were proximal to signal onset or offset and shorter when the gaps approached the temporal center of the noise burst. Also, the thresholds of the younger, highly experienced subjects were significantly shorter than those of the younger, inexperienced subjects, especially at placements close to signal onset or offset. The effect of replication (short-term practice) was not significant nor was the interaction between gap placement and replication. Post hoc comparisons indicated that the effect of gap placement resulted from significant decreases in gap detectability when the gap was placed close to stimulus onset and offset.