bluuebunny/crossref_metadata_2025 huggingface dataset:
Essential Role of Lymph Nodes in Contact Hypersensitivity Revealed in Lymphotoxin-α–Deficient Mice
Authors: Rennert Paul D. , Hochman Paula S. , Flavell Richard A. , Chaplin David D. , Jayaraman Sundararajan , Browning Jeffrey L. , Fu Yang-Xin
Published: July 2002

Lymph nodes (LNs) are important sentinal organs, populated by circulating lymphocytes and antigen-bearing cells exiting the tissue beds. Although cellular and humoral immune responses are induced in LNs by antigenic challenge, it is not known if LNs are essential for acquired immunity. We examined immune responses in mice that lack LNs due to genetic deletion of lymphotoxin ligands or in utero blockade of membrane lymphotoxin. We report that LNs are absolutely required for generating contact hypersensitivity, a T cell–dependent cellular immune response induced by epicutaneous hapten. We show that the homing of epidermal Langerhans cells in response to hapten application is specifically directed to LNs, providing a cellular basis for this unique LN function. In contrast, the spleen cannot mediate contact hypersensitivity because antigen-bearing epidermal Langerhans cells do not access splenic white pulp. Finally, we formally demonstrate that LNs provide a unique environment essential for generating this acquired immune response by reversing the LN defect in lymphotoxin-α−/− mice, thereby restoring the capacity for contact hypersensitivity.
Sodium and Calcium Inward Currents in Freshly Dissociated Smooth Myocytes of Rat Uterus
Authors: Yoshino M. , Wang S.Y. , Kao C.Y.
Published: July 2002

Freshly dissociated myocytes from nonpregnant, pregnant, and postpartum rat uteri have been studied with the tight-seal patch-clamp method. The inward current contains both INa and ICa that are vastly different from those in tissue-cultured material. INa is abolished by Na+-free medium and by 1 μM tetrodotoxin. It first appears at ∼−40 mV, reaches maximum at 0 mV, and reverses at 84 mV. It activates with a voltage-dependent τ of 0.2 ms at 20 mV, and inactivates as a single exponential with a τ of 0.4 ms. Na+ conductance is half activated at −21.5 mV, and half inactivated at −59 mV. INa reactivates with a τ of 20 ms. ICa is abolished by Ca2+-free medium, Co2+ (5 mM), or nisoldipine (2 μM), and enhanced in 30 mM Ca2+, Ba2+, or BAY-K 8644. It first appears at ∼−30 mV and reaches maximum at +10 mV. It activates with a voltage-dependent τ of 1.5 ms at 20 mV, and inactivates in two exponential phases, with τ's of 33 and 133 ms. Ca2+ conductance is half activated at −7.4 mV, and half inactivated at −34 mV. ICa reactivates with τ's of 27 and 374 ms. INa and ICa are seen in myocytes from nonpregnant estrus uteri and throughout pregnancy, exhibiting complex changes. The ratio of densities of peak INa/ICa changes from 0.5 in the nonpregnant state to 1.6 at term. The enhanced role of INa, with faster kinetics, allows more frequent repetitive spike discharges to facilitate simultaneous excitation of the parturient uterus. In postpartum, both currents decrease markedly, with INa vanishing from most myocytes. Estrogen-enhanced genomic influences may account for the emergence of INa, and increased densities of INa and ICa as pregnancy progresses. Other influences may regulate varied channel expression at different stages of pregnancy.
Position of singularities and fundamental group of the complement of a union of lines
Authors: Fan Kwai-Man
Published: July 2002

In this paper we give two examples of complex line arrangements in

C

P

2

CP^{2}

with 7 lines, that both have 3 triple points and 12 double points, and their complements have nonisomorphic global fundamental groups. These two line arrangements are, in some sense, a much simpler example of a pair of plane algebraic curves that have the same local topology but have complements with different global topology—compare with the example given by Zariski, or the recent example given by Artal-Bartolo.
The location of the zeros of the higher order derivatives of a polynomial
Authors: Pawlowski Piotr
Published: July 2002

Let

p
(
z
)

p(z)

be a complex polynomial of degree

n
n

having

k
k

zeros in a disk

D
D

. We deal with the problem of finding the smallest concentric disk containing

k
−
l

k-l

zeros of

p

(
l
)

(
z
)

p^{(l)}(z)

. We obtain some estimates on the radius of this disk in general as well as in the special case, where

k
k

zeros in

D
D

are isolated from the other zeros of

p
(
z
)

p(z)

. We indicate an application to the root-finding algorithms.
Hyperbolic automorphisms and Anosov diffeomorphisms on nilmanifolds
Authors: Dekimpe Karel
Published: July 2002

We translate the problem of finding Anosov diffeomorphisms on a nilmanifold which is covered by a free nilpotent Lie group into a problem of constructing matrices in

G
L

(
n
,

Z

)

\mathrm {GL}(n,\mathbb {Z})

whose eigenvalues satisfy certain conditions. Afterwards, we show how this translation can then be solved in some specific situations. The paper starts with a section on polynomial permutations of

Q

K

\mathbb {Q}^K

, a subject which is of interest on its own.
On the maximal Bochner-Riesz conjecture in the plane for 𝑝<2
Authors: Tao Terence
Published: July 2002

We give a new estimate on the maximal Bochner-Riesz operator in the plane, for

p
>
2

p>2

; as a corollary we obtain an almost everywhere convergence result for certain Bochner-Riesz means. This work was inspired by discussions with Michael Christ and Chris Sogge.
Constructing nonresidues in finite fields and the extended Riemann hypothesis
Authors: Buchmann Johannes , Shoup Victor
Published: July 2002

We present a new deterministic algorithm for the problem of constructing

k
k

th power nonresidues in finite fields

F

p
n

\mathbf {F}_{p^n}

, where

p
p

is prime and

k
k

is a prime divisor of

p
n

−
1

p^n-1

. We prove under the assumption of the Extended Riemann Hypothesis (ERH), that for fixed

n
n

and

p
→
∞

p \rightarrow \infty

, our algorithm runs in polynomial time. Unlike other deterministic algorithms for this problem, this polynomial-time bound holds even if

k
k

is exponentially large. More generally, assuming the ERH, in time

(
n
log
⁡
p

)

O
(
n
)

(n \log p)^{O(n)}

we can construct a set of elements that generates the multiplicative group

F

p
n

∗

\mathbf {F}_{p^n}^*

. An extended abstract of this paper appeared in Proc. 23rd Ann. ACM Symp. on Theory of Computing, 1991.
Decomposing 40 billion integers by four tetrahedral numbers
Authors: Chou Chung-Chiang , Deng Yuefan
Published: July 2002

Based upon a computer search performed on a massively parallel supercomputer, we found that any integer

n
n

less than

40
40

billion (

40
40

B) but greater than

343
,
867

343,867

can be written as a sum of four or fewer tetrahedral numbers. This result has established a new upper bound for a conjecture compared to an older one,

1
1

B, obtained a year earlier. It also gives more accurate asymptotic forms for partitioning. All this improvement is a direct result of algorithmic advances in efficient memory and cpu utilizations. The heuristic complexity of the new algorithm is

O
(
n
)

O(n)

compared with that of the old,

O
(

n

5

/

3

log
⁡
n
)

O(n^{5/3}\log n)

.
Convergence of non-stationary parallel multisplitting methods for hermitian positive definite matrices
Authors: Castel M. , Migallón Violeta , Penadés José
Published: July 2002

Non-stationary multisplitting algorithms for the solution of linear systems are studied. Convergence of these algorithms is analyzed when the coefficient matrix of the linear system is hermitian positive definite. Asynchronous versions of these algorithms are considered and their convergence investigated.
Solitons on pseudo-Riemannian manifolds: stability and motion
Authors: Stuart David
Published: July 2002

This is an announcement of results concerning a class of solitary wave solutions to semilinear wave equations. The solitary waves studied are solutions of the form

ϕ
(
t
,
x
)
=

e

i
ω
t

f
ω

(
x
)

\phi (t,x)=e^{i\omega t}f_\omega (x)

to semilinear wave equations such as

◻

ϕ
+

m
2

ϕ
=
β
(

|

ϕ

|

)
ϕ

\Box \phi +m^2\phi =\beta (|\phi |)\phi

on

R

1
+
n

\mathbb {R}^{1+n}

and are called nontopological solitons. The first preprint provides a new modulational approach to proving the stability of nontopological solitons. This technique, which makes strong use of the inherent symplectic structure, provides explicit information on the time evolution of the various parameters of the soliton. In the second preprint a pseudo-Riemannian structure

g
_

\underline {g}

is introduced onto

R

1
+
n

\mathbb {R}^{1+n}

and the corresponding wave equation is studied. It is shown that under the rescaling

g
_

→

ϵ

−
2

g
_

\underline {g}\to \epsilon ^{-2} \underline {g}

, with

ϵ
→
0

\epsilon \to 0

, it is possible to construct solutions representing nontopological solitons concentrated along a time-like geodesic.
State-sum invariants of knotted curves and surfaces from quandle cohomology
Authors: Carter J. , Jelsovsky Daniel , Kamada Seiichi , Langford Laurel , Saito Masahico
Published: July 2002

State-sum invariants for classical knots and knotted surfaces in

4
4

-space are developed via the cohomology theory of quandles. Cohomology groups of quandles are computed to evaluate the invariants. Some twist spun torus knots are shown to be noninvertible using the invariants.
Weighting hidden Markov models for maximum discrimination.
Authors: Karchin R , Hughey R
Published: July 2002

MOTIVATION: Hidden Markov models can efficiently and automatically build statistical representations of related sequences. Unfortunately, training sets are frequently biased toward one subgroup of sequences, leading to an insufficiently general model. This work evaluates sequence weighting methods based on the maximum-discrimination idea. RESULTS: One good method scales sequence weights by an exponential that ranges between 0.1 for the best scoring sequence and 1.0 for the worst. Experiments with a curated data set show that while training with one or two sequences performed worse than single-sequence Probabilistic Smith-Waterman, training with five or ten sequences reduced errors by 20% and 51%, respectively. This new version of the SAM HMM suite outperforms HMMer (17% reduction over PSW for 10 training sequences), Meta-MEME (28% reduction), and unweighted SAM (31% reduction). AVAILABILITY: A WWW server, as well as information on obtaining the Sequence Alignment and Modeling (SAM) software suite and additional data from this work, can be found at http://www.cse.ucse. edu/research/compbio/sam.html
Development of the receptor database (RDB): application to the endocrine disruptor problem.
Authors: Nakata K , Takai T , Kaminuma T
Published: July 2002

MOTIVATION: To represent various aspects of receptors effectively, we developed the receptor database (RDB), using an object-oriented database management system ACEDB and the Internet/WWW technology. RESULTS: RDB was constructed so that the system collects data items such as attributes of proteins from distributed data sources of the Internet, and so that it provides various viewing tools effectively, depending on different types of receptor data. Such sources include standard international biological databases such as the up-to-date database of PIR, Swiss Prot, PDB, GenBank and GDB. Application to the endocrine disruptor problem is presented. AVAILABILITY: RDB is available through the Internet at http://impact.nihs.go.jp/RDB.html.
MPBLAST : improved BLAST performance with multiplexed

queries
Authors: Korf Ian , Gish Warren
Published: July 2002

Summary: We have developed a program, MPBLAST, that increases the throughput of batch BLASTN searches by multiplexing (concatenating) query sequences and thereby reducing the number of actual database searches performed. Throughput was observed to increase in reciprocal proportion to the component sequence length. For sequencing read-sized queries of 500 bp, an order of magnitude speed-up was seen.

Availability: Free (see http://blast.wustl.edu)

Contact: {ikorf, gish}@watson.wustl.edu
Tobacco mosiac virus particle structure and the initiation of disassembly
Authors: Stubbs Gerald
Published: July 2002

The structure of an intact tobacco mosaic virus (TMV) particle was determined at 2.9 Å resolution using fibre diffraction methods. All residues of the coat protein and the three nucleotides of RNA that are bound to each protein subunit were visible in the electron density map. Examination of the structures of TMV, cucumber green mottle mosaic virus and ribgrass mosaic virus, and site–directed mutagenesis experiments in which carboxylate groups were changed to the corresponding amides, showed that initial stages of disassembly are driven by complex electrostatic interactions involving at least seven carboxylate side–chains and a phosphate group. The locations of these interactions can drift during evolution, allowing the viruses to evade plant defensive responses that depend on recognition of the viral coat protein surface.
Nuclear magnetic resonance characterization of peptide models of collagen–folding diseases
Authors: Buevich Alexei , Baum Jean
Published: July 2002

Misfolding of the triple helix has been shown to play a critical role in collagen diseases. The substitution of a single Gly by another amino acid breaks the characteristic repeating (Gly–X–Y)nsequence pattern and results in connective tissue disease such as osteogenesis imperfecta. Nuclear magnetic resonance (NMR) studies of normal and mutated collagen triple–helical peptides offer an opportunity to characterize folding and conformational alterations at the substitution site, as well as at positions upstream and downstream of a Gly mutation. The NMR studies suggest that the local sequences surrounding the substitution site, and the renucleation sequences N–terminal to and adjacent to the substitution site, may be critical in defining the clinical phenotype of osteogenesis imperfecta. These studies may pave the way to understanding the mechanism by which a single Gly substitution in collagen can lead to pathological conditions.
Linker-Mediated Recombinational Subcloning of Large DNA Fragments Using Yeast
Authors: Raymond Christopher K. , Sims Elizabeth H. , Olson Maynard V.
Published: July 2002

The homologous recombination pathway in yeast is an ideal tool for the sequence-specific assembly of plasmids. Complementary 80-nucleotide oligonucleotides that overlap a vector and a target fragment were found to serve as efficient recombination linkers for fragment subcloning. Using electroporation, single-stranded 80-mers were adequate for routine plasmid construction. A cycloheximide-based counterselection was introduced to increase the specificity of cloning by homologous recombination relative to nonspecific vector background. Reconstruction experiments suggest this counterselection increased cloning specificity by 100-fold. Cycloheximide counterselection was used in conjunction with 80-bp linkers to subclone targeted regions from bacterial artificial chromosomes. This technology may find broad application in the final stages of completing the Human Genome Sequencing Project and in applications of BAC clones to the functional analysis of complex genomes.
Generation of ligand‐receptor alliances by “SEA” module‐mediated cleavage of membrane‐associated mucin proteins
Authors: Wreschner Daniel H. , McGuckin Michael A. , Williams Stefanie J. , Baruch Amos , Yoeli Merav , Ziv Ravit , Okun Liron , Zaretsky Joseph , Smorodinsky Nechama , Keydar Iafa , Neophytou Pavlos , Stacey Martin , Lin His‐Hsien , Gordon Siamon
Published: July 2002

A mechanism is described whereby one and the same gene can encode both a receptor protein as well as its specific ligand. Generation of this receptor–ligand partnership is effected by proteolytic cleavage within a specific module located in a membrane resident protein. It is postulated here that the “SEA” module, found in a number of heavily O‐linked glycosylated membrane‐associated proteins, serves as a site for proteolytic cleavage. The subunits generated by proteolytic cleavage of the SEA module reassociate, and can subsequently elicit a signaling cascade. We hypothesize that all membrane resident proteins containing such a “SEA” module will undergo cleavage, thereby generating a receptor–ligand alliance. This requires that the protein subunits resulting from the proteolytic cleavage reassociate with each other in a highly specific fashion. The same SEA module that serves as the site for proteolytic cleavage, probably also contains the binding sites for reassociation of the resultant two subunits. More than one type of module can function as a site for proteolytic cleavage; this can occur not only in one‐pass membrane proteins but also in 7‐transmembrane proteins and other membrane‐associated proteins. The proposal presented here is likely to have significant practical consequences. It could well lead to the rational design and identification of molecules that, by binding to one of the cleaved partners, will act either as agonists or antagonists, alter signal transduction and, hence, cellular behavior.
Correcting organ motion artifacts in x‐ray CT medical imaging systems by adaptive processing. I. Theory
Authors: Dhanantwari A. C. , Stergiopoulos S. , Iakovidis I.
Published: July 2002

X‐ray CT scanners provide images of transverse cross sections of the human body from a large number of projections. During the data acquisition process, which usually takes about 1 s, motion effects such as respiration, cardiac motion, and patient restlessness produce artifacts that appear as blurring, doubling, and distortion in the reconstructed images, and may lead to inaccurate diagnosis. To address this problem several processing techniques have been proposed that require a priori knowledge of the motion characteristics. This paper proposes a method, which makes no assumptions about the properties of the motion, to eliminate the motion artifacts. The approach in this paper uses a spatial overlap correlator scheme to accurately track organ motion in computed tomography imaging systems. Then, it is shown that as optimum processing scheme to remove organ motion effects is to apply adaptive interference cancellation (AIC) methods, which treat the output of the spatial overlap correlator as noise interference at the input of the AIC process. Furthermore, an AIC method does not require any kind of periodicity of the motion effects. Synthetic data tests demonstrate the validity of this approach and show that hardware modifications are essential for its implementation in x‐ray CT medical imaging systems.
Discretizing large traceable vessels and using DE‐MRI perfusion maps yields numerical temperature contours that match the MR noninvasive measurements
Authors: Craciunescu Oana I. , Raaymakers Bas W. , Kotte Alexis N. T. J. , Das Shiva K. , Samulski Thaddeus V. , Lagendijk Jan J. W.
Published: July 2002

The success of hyperthermia treatments is dependent on thermal dose distribution. However, the three‐dimensional temperature distribution remains largely unknown. Without this knowledge, the relationship between thermal dose and outcome is noisy, and therapy cannot be optimized. Accurate computations of thermal distribution can contribute to an optimized therapy. The hyperthermia modeling group in the Department of Radiotherapy, University Medical Center Utrecht devised a Discrete Vasculature [Kotte et al., Phys. Med. Biol. 41, 865–884 (1996)] model that accounts for the presence of vessel trees in the computational domain. The vessel tree geometry is tracked using magnetic resonance (MR) angiograms to a minimum diameter between 0.6 and 1 mm. However, smaller vessels (0.2–0.6 mm) are known to account for significant heat transfer. The hyperthermia group at Duke University Medical Center has proposed using perfusion maps derived from dynamic‐enhanced magnetic resonance imaging to account for the tissue perfusion heterogeneity [Craciunescu et al., Int. J. Hyperthermia 17, 221–239 (2001)]. In addition, techniques for noninvasive temperature measurements have been devised to measure temperatures in vivo [Samulski et al., Int. J. Hypertherminal, 819–829 (1992)]. In this work, a patient with high‐grade sarcoma has been retrospectively modeled to determine the temperature distribution achieved during a hyperthermia treatment. Available for this model were MR depicted geometry, angiograms, perfusion maps, as necessary for accurate thermal modeling, as well as MR thermometry data for validation purposes. The vasculature assembly through modifiable potential program [Van Leeuwen et al., IEEE Trans. Biomed. Eng. 45, 596–604 (1998)] was used in order to incorporate the traceable large vessels. Temperature simulations were made using different approaches to describe perfusion. The simulated cases were the bioheat equation with constant perfusion rates per tissue type, perfusion maps alone, tracked vessel tree and perfusion maps, and generated vessel tree. The results were compared with MR thermometry data for a single patient data set, concluding that a combination between large traceable vessels and perfusion map yields the best results for this particular patient. The technique has to be repeated on several patients, first with the same type of malignancy, and after that, on patients having malignancies at other different sites.
Human lead metabolism: Chronic exposure, bone lead, and physiological models
Authors: Fleming David E. B.
Published: July 2002

Exposure to lead is associated with a variety of detrimental health effects. After ingestion or inhalation, lead may be taken up from the bloodstream and retained by bone tissue. X‐ray fluorescence was used to make in vivo measurements of bone lead concentration at the tibia and calcaneus for 367 active and 14 retired lead smelter workers. Blood lead levels following a labor disruption were used in conjunction with bone lead readings to examine the endogenous release of lead from bone. Relations between bone lead and a cumulative blood lead index differed depending on time of hiring. This suggests that the transfer of lead from blood to bone has changed over time, possibly as a result of varying exposure conditions. A common polymorphism in the δ‐aminolevulinate dehydratase (ALAD) enzyme may influence the distribution of lead in humans. Blood lead levels were higher for smelter workers expressing the more rare allele. Bone lead concentrations, however, were not significantly different. This implies that a smaller proportion of lead in blood is distributed to tissue for individuals expressing the allele. The O'Flaherty physiological model of lead metabolism was modified slightly and tested with input from the personal exposure histories of smelter workers. The model results were consistent with observation in terms of endogenous exposure to lead and accumulation of lead in cortical bone. Modeling the calcaneus as a trabecular bone site did not reproduce observed trends. Variations in lead metabolism between different trabecular sites may therefore be significant. The model does not incorporate a genetic component, and its output did not reflect observed differences in this respect. This result provides further support for the influence of the ALAD polymorphism on lead metabolism. Experimental trials with a digital spectrometer revealed superior energy resolution and count throughput relative to the conventional x‐ray fluorescence system. The associated reduction in the uncertainty of lead measurement has the potential to benefit future surveys and modeling efforts.
Inelastic collision and the Hertz theory of impact
Authors: Gugan D.
Published: July 2002

The area, A, and the duration of contact, T, have been measured as a function of impact speed, U, for balls striking a flat surface. The balls lost about 40% of their kinetic energy over the range of speeds studied, but, surprisingly, the results for A(U) and T(U) appear to be consistent with Hertz’s elastic theory of impact. Possible reasons are discussed for this unexpected behavior.
Acoustic quality factor and energy losses in cylindrical pipes
Authors: Moloney Michael J. , Hatten Daniel L.
Published: July 2002

The quality factor Q of a damped oscillator equals 2π times the ratio of stored energy to the energy dissipated per cycle. This makes Q a sensitive probe of energy losses. Using modest equipment, we measured the acoustical Q for a set of cylindrical pipes having the same resonant frequency, but different diameters D. The graph of Q vs D could be well fitted with two parameters, one of which corresponds to energy loss via radiation from the ends of the pipe, and the other to thermal and viscous losses very close to the pipe wall. The wall loss parameter was quite constant no matter where the pipes were located, but the radiative loss parameter varied significantly with location inside a room, suggesting that room reflections affected the sound radiated from the pipe. This study offers valuable insights at no great expense, and could be the basis of an upper-division undergraduate laboratory experiment.
Do cathedral glasses flow?—Additional remarks
Authors: Zanotto Edgar D. , Gupta Prabhat K.
Published: July 2002

We present a revised estimate of the relaxation time at room temperature for a window glass based on extrapolated isostructural viscosity data. This estimate, while several orders of magnitude less than the previous estimate of Zanotto [Am. J. Phys. 66 (5), 392–395 (1998)], supports his conclusion that window glass cannot flow at room temperature in human time scales.
A simplified algorithm for the second-order sound fields
Authors: Ding Desheng
Published: July 2002

An analytical description for the second-order field of the sum-, difference-frequency and second harmonic components is derived. This treatment is based on the fact that an arbitrary axially symmetric beam can be expressed as the linear superposition of a set of Gaussian beams [J. J. Wen and M. A. Breazeale, J. Acoust. Soc. Am. 83, 1752–1756 (1988)], so that the three-dimensional integral for the second-order components is typically expressed as a combination of a set of interaction terms of the Gaussian beams. Correspondingly, the evaluation of the field distribution is reduced to the summation of exponential integral functions. From some examples, the present approach provides the results for the second-order field, which are in good agreement with those obtained directly by numerical integration.
Pitch strength and pitch dominance of iterated rippled noises in hearing-impaired listeners
Authors: Leek Marjorie R. , Summers Van
Published: July 2002

Reports using a variety of psychophysical tasks indicate that pitch perception by hearing-impaired listeners may be abnormal, contributing to difficulties in understanding speech and enjoying music. Pitches of complex sounds may be weaker and more indistinct in the presence of cochlear damage, especially when frequency regions are affected that form the strongest basis for pitch perception in normal-hearing listeners. In this study, the strength of the complex pitch generated by iterated rippled noise was assessed in normal-hearing and hearing-impaired listeners. Pitch strength was measured for broadband noises with spectral ripples generated by iteratively delaying a copy of a given noise and adding it back into the original. Octave-band-pass versions of these noises also were evaluated to assess frequency dominance regions for rippled-noise pitch. Hearing-impaired listeners demonstrated consistently weaker pitches in response to the rippled noises relative to pitch strength in normal-hearing listeners. However, in most cases, the frequency regions of pitch dominance, i.e., strongest pitch, were similar to those observed in normal-hearing listeners. Except where there exists a substantial sensitivity loss, contributions from normal pitch dominance regions associated with the strongest pitches may not be directly related to impaired spectral processing. It is suggested that the reduced strength of rippled-noise pitch in listeners with hearing loss results from impaired frequency resolution and possibly an associated deficit in temporal processing.
Scattering from an elastic shell and a rough fluid–elastic interface: Theory
Authors: Bishop Garner C. , Smith Judy
Published: July 2002

A null-field T-matrix formalism is developed for scattering a pressure wave from a stationary elastic shell immersed in a homogeneous and isotropic fluid half-space and in proximity to a rough fluid–elastic interface. Helmholtz–Kirchhoff integral representations of the various scattered pressure and displacement fields are constructed. The surface fields are required to satisfy the elastic tensor boundary conditions and the scattered fields are required to satisfy the extended boundary condition. Spherical basis functions are used to construct a free-field T-matrix for the elastic shell and rectangular vector basis functions are used to construct a representation of the free-field T- matrix for the rough fluid–elastic interface. The free-field T-matrices are introduced into the Helmholtz–Kirchhoff and the null-field equations for the shell-interface system and a general system of equations for the spectral amplitudes of the various fields is obtained. The general system of equations is specialized to scattering from periodic surface roughness and an exact solution for the scattered pressure field in the fluid is obtained. Then the general system of equations is specialized to scattering from small-amplitude arbitrary roughness profiles and a perturbative solution is obtained. It is shown that the formalism contains multiple scattering effects on the rough surface and between the rough surface and the shell.
Dynamic shear modulus of vocal-fold tissues and phonosurgical biomaterials
Authors: Chan Roger W. , Titze Ingo R.
Published: July 2002

Knowledge of the mechanical properties of vocal fold tissues is necessary for the constitutive modeling of vocal-fold mechanics. Assuming transverse isotropy in a linear, elastic continuum model of vocal-fold tissues, five material constants are needed to solve the constitutive equation [D. A. Berry and I. R. Titze, J. Acoust. Soc. Am. 100, 3345–3354 (1996)]. Among these constants, Poisson’s ratios can be estimated by assuming tissue incompressibility, while the shear moduli and Young’s moduli are related to one another. A parallel-plate rotational rheometer was used to examine the dynamic shear behavior of human vocal fold tissues and three commonly used phonosurgical biomaterials (bovine collagen suspension, absorbable gelatin suspension, and human subcutaneous fat). In oscillation at 0.1–10 Hz and at 37 °C, the magnitude of dynamic shear modulus of vocal fold mucosa was on the order of 100 Pa, close to that of fat. The shear modulus magnitudes of collagen and gelatin were an order of magnitude higher. These results suggest that the use of fat for vocal-fold augmentation surgery is more conducive to phonation, because of its similarity to the vocal-fold mucosa in shear stiffness. [Work supported by NIH.]
Nonlinear tomographic inversion by using Wentzel–Kramers–Brillouin modal condition
Authors: Shang E. C. , Wang Y. Y. , Voronovich A. G.
Published: July 2002

In the horizontal refraction tomography (HRT) scheme [A. G. Voronovich and E. C. Shang, J. Acoust. Soc. Am. 98, 2708–2716 (1995)], the 3-D tomographic inversion is performed in two stages: (1) retrieving the modal wave numbers km(x,y) in the horizontal plane, and (2) reconstructing the vertical sound-speed profile (SSP) at each node of the horizontal plane based on a set of retrieved modal wave numbers km(x,y). Usually, a nonlinear approach must be considered for the 1-D vertical inversion of the second stage. In this paper, a nonlinear inversion method based on the WKB modal condition is proposed. Using the WKB modal condition has the following advantages: (a) it is efficient because the data km(x,y) can be matched directly to the SSP without a model-based replica calculation; (b) it works even when just a few modes are available; and (c) the error of the inversion can be estimated analytically. Some results of the simulation to verify the concept are presented.
Acoustic and physiologic characteristics of inspiratory phonation
Authors: Orlikoff Robert F. , Baken R. J. , Kraus Dennis H.
Published: July 2002

Voice produced on inhaled air is a form of phonation that has received relatively little attention despite its apparent usefulness in the assessment of vocal function. This preliminary investigation was designed to describe the general characteristics of vocalization driven by an ingressive phonatory airflow. Vocal fundamental frequency (F0), electroglottographic (EGG), and airflow measures were examined in 16 normal men and women, who alternated between inspiratory and expiratory voice. Mean F0 routinely increased during inspiratory voice segments, shifting on average 5.1 semitones above the subjects’ comfortable expiratory voice frequency. EGG data showed inspiratory voice to be associated with a more symmetrical pattern of vocal fold contact characterized by a prolonged interval of increasing contact. Both short-term F0 variability (jitter) and EGG amplitude perturbation were significantly higher during inspiratory voice. Stroboscopic examination of four of the subjects showed caudal displacement of the larynx and lengthened vocal folds associated with inspiratory phonation. The absolute airflow rate was significantly greater for inspiratory phonation, on average 48.5% higher than during normal expiratory voice. It was also found that both inspiratory pulse and falsetto vibratory patterns could be produced by at least some of the subjects, indicating some control over the mode and frequency of vocal fold vibration when driven by an ingressive airflow.
An experimental-numerical technique for evaluating the bulk and shear dynamic moduli of viscoelastic materials
Authors: Willis R. Lance , Stone T. Shane , Berthelot Yves H. , Madigosky Walter M.
Published: July 2002

An experimental/numerical technique has been implemented to determine simultaneously the bulk and shear dynamic moduli (and loss factor) of viscoelastic materials of arbitrary shape under low-frequency (0.5–2.5 kHz) harmonic excitation. The method consists of measuring the dynamic response of the sample at several points on the surface with a set of five independent laser interferometers, and matching the response with the predictions from a finite element code in which the two complex elastic moduli are the adjustable parameters. Results are presented for measurements made in air, under standard pressure and temperature conditions, and compared with predictions based on Kerner’s model.
Acoustic radiation force on a bubble: Viscous and thermal effects
Authors: Doinikov Alexander A.
Published: July 2002

The acoustic radiation forces on a gas bubble in a plane standing wave and a plane traveling wave are calculated, taking account of viscous and thermal effects. The dissipative effects are introduced into calculations in a natural way, by applying the viscous heat-conducting equations of fluid motion to both the surrounding liquid and the gas inside the bubble. The limits of low and high energy dissipation are examined.
Auditory filter nonlinearity at 2 kHz in normal hearing listeners
Authors: Rosen Stuart , Baker Richard J. , Darling Angela
Published: July 2002

Auditory filters broaden with increasing level. Using a recently developed method of fitting filter shapes to notched-noise masking data that explicitly models the nonlinear changes in filter shape across level, results at 2 kHz from 9 listeners over a wide range of levels and notch widths are reported. Families of roex(p,w,t) filter shapes lead to models which account well for the observed data. The primary effect of level is a broadening in the tails of the filter as level increases. In all cases, models with filter parameters depending on probe level fit the data much better than masker-dependent models. Thus auditory filter shapes appear to be controlled by their output, not by their input. Notched-noise tests, if performed at a single level, should use a fixed probe level. Filter shapes derived in this way, and normalized to have equal tail gain, are highly reminiscent of measurements made directly on the basilar membrane, including the degree of compression evidenced in the input–output function.
The role of the envelope in processing iterated rippled noise
Authors: Yost William A. , Patterson Roy , Sheft Stanley
Published: July 2002

Iterated rippled noise (IRN) is generated by a cascade of delay and add (the gain after the delay is 1.0) or delay and subtract (the gain is −1.0) operations. The delay and add/subtract operations impart a spectral ripple and a temporal regularity to the noise. The waveform fine structure is different in these two conditions, but the envelope can be extremely similar. Four experiments were used to determine conditions in which the processing of IRN stimuli might be mediated by the waveform fine structure or by the envelope. In experiments 1 and 3 listeners discriminated among three stimuli in a single-interval task: IRN stimuli generated with the delay and add operations (g=1.0), IRN stimuli generated using the delay and subtract operations (g=−1.0), and a flat-spectrum noise stimulus. In experiment 2 the listeners were presented two IRN stimuli that differed in delay (4 vs 6 ms) and a flat-spectrum noise stimulus that was not an IRN stimulus. In experiments 1 and 2 both the envelope and waveform fine structure contained the spectral ripple and temporal regularity. In experiment 3 only the envelope had this spectral and temporal structure. In all experiments discrimination was determined as a function of high-pass filtering the stimuli, and listeners could discriminate between the two IRN stimuli up to frequency regions as high as 4000–6000 Hz. Listeners could discriminate the IRN stimuli from the flat-spectrum noise stimulus at even higher frequencies (as high as 8000 Hz), but these discriminations did not appear to depend on the pitch of the IRN stimuli. A control experiment (fourth experiment) suggests that IRN discriminations in high-frequency regions are probably not due entirely to low-frequency nonlinear distortion products. The results of the paper imply that pitch processing of IRN stimuli is based on the waveform fine structure.
The effect of abdominal wall morphology on ultrasonic pulse distortion. Part II. Simulations
Authors: Mast T. Douglas , Hinkelman Laura M. , Orr Michael J. , Waag Robert C.
Published: July 2002

Wavefront propagation through the abdominal wall was simulated using a finite-difference time-domain implementation of the linearized wave propagation equations for a lossless, inhomogeneous, two-dimensional fluid as well as a simplified straight-ray model for a two-dimensional absorbing medium. Scanned images of six human abdominal wall cross sections provided the data for the propagation media in the simulations. The images were mapped into regions of fat, muscle, and connective tissue, each of which was assigned uniform sound speed, density, and absorption values. Propagation was simulated through each whole specimen as well as through each fat layer and muscle layer individually. Wavefronts computed by the finite-difference method contained arrival time, energy level, and wave shape distortion similar to that in measurements. Straight-ray simulations produced arrival time fluctuations similar to measurements but produced much smaller energy level fluctuations. These simulations confirm that both fat and muscle produce significant wavefront distortion and that distortion produced by fat sections differs from that produced by muscle sections. Spatial correlation of distortion with tissue composition suggests that most major arrival time fluctuations are caused by propagation through large-scale inhomogeneities such as fatty regions within muscle layers, while most amplitude and waveform variations are the result of scattering from smaller inhomogeneities such as septa within the subcutaneous fat. Additional finite-difference simulations performed using uniform-layer models of the abdominal wall indicate that wavefront distortion is primarily caused by tissue structures and inhomogeneities rather than by refraction at layer interfaces or by variations in layer thicknesses.
Psychophysical measures of auditory nonlinearities as a function of frequency in individuals with normal hearing
Authors: Hicks Michelle L. , Bacon Sid P.
Published: July 2002

In order to gain a better understanding of how auditory nonlinear phenomena vary as a function of location along the cochlea, several psychophysical measures of nonlinearity were examined as a function of signal frequency. Six normal-hearing individuals completed three experiments, each designed to measure one aspect of nonlinear behavior: (1) the effects of level on frequency selectivity in simultaneous masking, measured using notched-noise maskers at spectrum levels of 30 and 50 dB, (2) two-tone suppression, measured using forward maskers at the signal frequency (fs) and suppressor tones above fs, and (3) growth of masking, measured using forward maskers below fs at a signal/masker frequency ratio of 1.44. Four signal frequencies (375, 750, 1500, and 3000 Hz) were tested to sample the nonlinear behavior at different locations along the basilar membrane, in order to test the hypothesis that the apical (low-frequency) region of the cochlea behaves more linearly than the basal (high-frequency) region. In general, all three measures revealed a progressive increase in nonlinear behavior as signal frequency increased, with little or no nonlinearity at the lowest frequency, consistent with the hypothesis.
Acoustic radiation from an elastic baffled rectangular plate covered by a decoupling coating and immersed in a heavy acoustic fluid
Authors: Foin Olivier , Berry Alain , Szabo Jeffrey
Published: July 2002

The vibroacoustic behavior of an elastic, simply supported rectangular plate covered by a locally reacting decoupling layer supporting thickness deformation is presented. The model simulates the vibration and acoustic response of the system immersed in water and subjected to a point force disturbance. A simplified version of the theory is derived in the limiting case of a large decoupling (low mechanical impedance of the layer/high frequency). An appropriate vibratory indicator, representative of the acoustic attenuation provided by the decoupling treatment, and independent of the structure dimensions, is also investigated from the perspective of small-scale laboratory characterization
Effects on sleep disturbance of changes in aircraft noise near three airports
Authors: Fidell Sanford , Pearsons Karl , Tabachnick Barbara G. , Howe Richard
Published: July 2002

Field measurements were conducted of potential sleep disturbance associated with changes in nighttime aircraft noise exposure near three airports. One study was conducted near Stapleton International Airport (DEN) and Denver International Airport (DIA) in anticipation of the closure of the former and opening of the latter. Sleep behavior was monitored in 57 homes located near runway ends at the two airports. A second study was conducted in the vicinity of DeKalb-Peachtree Airport (PDK), a large general aviation airport that expected increased nighttime flight operations due to the Olympic Games in July and August of 1996. Similar methods of measuring nighttime noise levels and sleep disturbance in the two studies were maintained over the course of 2717 and 686 subject-nights of observations, respectively. No major differences in noise-induced sleep disturbance were observed as a function of changes in nighttime aircraft noise exposure.
A triaxial rheometer for soft compressible solids
Authors: Alkhagen Mårten , Toll Staffan
Published: July 2002

The novel instrument measures the response to compression and shear of a class of materials we call soft compressible solids, examples of which are textile solids and foams. The sample is fixed between two parallel plates, and deformation is controlled by an x,y,z displacement on one plate while the stress is measured on the other. A key component is the triaxial stress transducer, which eliminates edge effects by only measuring the stress on an interior region of the plate. The edge effects and associated measurement errors are analyzed by simple isotropic elasticity theory, and compared to measurements done on chloroprene rubber foam.
Viscosity Measurements near a Million Seconds−1
Authors: Porter Roger S. , Johnson Julian F.
Published: July 2002

Viscosity measurements are reported for a variety of systems as a function of shear using a thin film, double-thermostatted, concentric cylinder viscometer. The basic instrument design and the cylinders which are of unusually narrow clearance and fine machining permit accurate and precise viscosity measurements to be made at homogeneous shear rates up to two million sec.−1 Measurements are reported on a molecular weight series of pure normal paraffin hydrocarbons from n-C8H18 to n-C32H66. Viscosities measured at the highest shear agree within a precision of 2% and better with known low shear hydrocarbon viscosities. This result indicates an absence of both heating effects and molecular degradation and reveals Newtonian flow over the entire 103 shear rate range of the instrument. Similar tests were also performed on several pure cyclic compounds in a test for conformational shifts between rotational isomers which possibly could be induced by a high shear field. The improved high shear concentric cylinder viscometer was also used to double the shear rate range for the established viscosity of standard API Oil 104, which is the most widely studied and the most non-Newtonian of current non-Newtonian viscosity standards.
Viscoelastic Behavior of a Filled Elastomer in the Linear and Nonlinear Range
Authors: Lenoe E. M. , Heller R. A. , Freudenthal A. M.
Published: July 2002

Rheological behavior of a filled elastomer consisting of a polyurethane rubber and granular potassium chloride was investigated with both long- and short-term loading producing conditions of torsion, uniaxial tension, and compression. The volumetric response and the thermo-rheological behavior of the elastomer was also studied. To represent the observed behavior for moderate stresses and strains a linear viscoelastic model was developed. The results of torsion relaxation tests performed on the inert solid propellant are presented for three strain levels over the temperature range −60 to +200°F. The torsion relaxation moduls (at 5 sec for 4.31% initial shear strain) was changed by 2 orders of magnitude for a temperature variation of −60 to +200°F. Prolonged exposure to high temperatures and humidity degraded the rubber-to-filler bond so that the predominant relaxation response was that of a polyurethane rubber foam.
Time-Dependent Concentrated Surface Load Moving with Diminishing Velocity on a Viscoelastic Half Space
Authors: Cakmak A. S. , Yau W. W. F.
Published: July 2002

The vertical and horizontal displacements are obtained for a time-dependent moving load on a viscoelastic half space. The load is assumed to increase exponentially with time and its velocity to decrease exponentially with time. The problem is solved as a quasistatic problem since the velocity of the load is small compared to stress wave velocities in the half space. The half space is characterized in shear by the four-parameter model and is assumed to be elastic in its volumetric behavior. The elastic viscoelastic analogy is used in the solution of the problem.
The Dynamic Response of Periodically Deformed Non-Newtonian Fluid Films
Authors: Wachmann C. , Dougherty D. E. , Pan C. H. T.
Published: July 2002

The periodic squeeze motion of a thin fluid film formed between two parallel planes is considered. The fluid is assumed to exhibit shear dependence and relaxation properties. Analysis shows that a time-average super- or subambient pressure is generated which depends on the ratio of the periods of the compression and expansion strokes. Fluid consistency, shear rate exponent, plate geometry, and stroke affect the magnitude of the pressure values. The relaxation constant of the fluid enters only into the transient and the periodic parts of the squeeze film response. These effects are not obtained for Newtonian fluids or if the compression and expansion periods are equal.