bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization of Na+/H+ and Cl−/Hco 3− Exchangers in Migrating Renal Epithelial Cells
Authors: Klein Magnus , Seeger Ponke , Schuricht Barbara , Alper Seth L. , Schwab Albrecht
Published: July 2002

Cell migration is crucial for processes such as immune defense, wound healing, or the formation of tumor metastases. Typically, migrating cells are polarized within the plane of movement with lamellipodium and cell body representing the front and rear of the cell, respectively. Here, we address the question of whether this polarization also extends to the distribution of ion transporters such as Na+/H+ exchanger (NHE) and anion exchanger in the plasma membrane of migrating cells. Both transporters are required for locomotion of renal epithelial (Madin-Darby canine kidney, MDCK-F) cells and human melanoma cells since their blockade reduces the rate of migration in a dose-dependent manner. Inhibition of migration of MDCK-F cells by NHE blockers is accompanied by a decrease of pHi. However, when cells are acidified with weak organic acids, migration of MDCK-F cells is normal despite an even more pronounced decrease of pHi. Under these conditions, NHE activity is increased so that cells are swelling due to the accumulation of organic anions and Na+. When exclusively applied to the lamellipodium, blockers of NHE or anion exchange inhibit migration of MDCK-F cells as effectively as when applied to the entire cell surface. When they are directed to the cell body, migration is not affected. These data are confirmed immunocytochemically in that the anion exchanger AE2 is concentrated at the front of MDCK-F cells. Our findings show that NHE and anion exchanger are distributed in a polarized way in migrating cells. They are consistent with important contributions of both transporters to protrusion of the lamellipodium via solute uptake and consequent volume increase at the front of migrating cells.
Anion Permeation in Ca2+-Activated Cl− Channels
Authors: Qu Zhiqiang , Hartzell H. Criss
Published: July 2002

Ca2+-activated Cl channels (ClCaCs) are an important class of anion channels that are opened by increases in cytosolic [Ca2+]. Here, we examine the mechanisms of anion permeation through ClCaCs from Xenopus oocytes in excised inside-out and outside-out patches. ClCaCs exhibited moderate selectivity for Cl over Na: PNa/PCl = 0.1. The apparent affinity of ClCaCs for Cl was low: Kd = 73 mM. The channel had an estimated pore diameter >0.6 nm. The relative permeabilities measured under bi-ionic conditions by changes in Erev were as follows: C(CN)3 > SCN > N(CN)2 > ClO4 > I > N3 > Br > Cl > formate > HCO3 > acetate = F > gluconate. The conductance sequence was as follows: N3 > Br > Cl > N(CN)2 > I > SCN > COOH > ClO4 > acetate > HCO3 = C(CN)3 > gluconate. Permeant anions block in a voltage-dependent manner with the following affinities: C(CN)3 > SCN = ClO4 > N(CN)2 > I > N3 > Br > HCO3 > Cl > gluconate > formate > acetate. Although these data suggest that anionic selectivity is determined by ionic hydration energy, other factors contribute, because the energy barrier for permeation is exponentially related to anion hydration energy. ClCaCs exhibit weak anomalous mole fraction behavior, implying that the channel may be a multi-ion pore, but that ions interact weakly in the pore. The affinity of the channel for Ca2+ depended on the permeant anion at low [Ca2+] (100–500 nM). Apparently, occupancy of the pore by a permeant anion increased the affinity of the channel for Ca2+. The current was strongly dependent on pH. Increasing pH on the cytoplasmic side decreased the inward current, whereas increasing pH on the external side decreased the outward current. In both cases, the apparent pKa was voltage-dependent with apparent pKa at 0 mV = ∼9.2. The channel may be blocked by OH− ions, or protons may titrate a site in the pore necessary for ion permeation. These data demonstrate that the permeation properties of ClCaCs are different from those of CFTR or ClC-1, and provide insights into the nature of the ClCaC pore.
A continuous space-time finite element method for the wave equation
Authors: French Donald , Peterson Todd
Published: July 2002

We consider a finite element method for the nonhomogeneous second-order wave equation, which is formulated in terms of continuous approximation functions in both space and time, thereby giving a unified treatment of the spatial and temporal discretizations. Our analysis uses primarily energy arguments, which are quite common for spatial discretizations but not for time.

We present a priori nodal (in time) superconvergence error estimates without any special time step restrictions. Our method is based on tensor-product spaces for the full discretization.
A posteriori error estimate for the mixed finite element method
Authors: Carstensen Carsten
Published: July 2002

A computable error bound for mixed finite element methods is established in the model case of the Poisson–problem to control the error in the H(div,

Ω
\Omega

)

×

L
2

(
Ω
)

\times L^2(\Omega )

–norm. The reliable and efficient a posteriori error estimate applies, e.g., to Raviart–Thomas, Brezzi-Douglas-Marini, and Brezzi-Douglas-Fortin-Marini elements.
On factor refinement in number fields
Authors: Buchmann Johannes , Eisenbrand Friedrich
Published: July 2002

Let

O

\mathcal O

be an order of an algebraic number field. It was shown by Ge that given a factorization of an

O

\mathcal O

-ideal

a

\mathfrak {a}

into a product of

O

\mathcal O

-ideals it is possible to compute in polynomial time an overorder

O

′

\mathcal O’

of

O

\mathcal O

and a gcd-free refinement of the input factorization; i.e., a factorization of

a

O

′

\mathfrak {a}\mathcal O’

into a power product of

O

′

\mathcal O’

-ideals such that the bases of that power product are all invertible and pairwise coprime and the extensions of the factors of the input factorization are products of the bases of the output factorization. In this paper we prove that the order

O

′

\mathcal O’

is the smallest overorder of

O

\mathcal O

in which such a gcd-free refinement of the input factorization exists. We also introduce a partial ordering on the gcd-free factorizations and prove that the factorization which is computed by Ge’s algorithm is the smallest gcd-free refinement of the input factorization with respect to this partial ordering.
Relative Bogomolov’s inequality and the cone of positive divisors on the moduli space of stable curves
Authors: Moriwaki Atsushi
Published: July 2002

Let

f
:
X
→
Y

f : X \to Y

be a surjective and projective morphism of smooth quasi-projective varieties over an algebraically closed field of characteristic zero with

dim
⁡
f
=
1

\dim f = 1

. Let

E
E

be a vector bundle of rank

r
r

on

X
X

. In this paper, we would like to show that if

X
y

X_y

is smooth and

E
y

E_y

is semistable for some

y
∈
Y

y \in Y

, then

f
∗

(
2
r

c
2

(
E
)
−
(
r
−
1
)

c
1

(
E

)
2

)

f_*\left ( 2rc_2(E) - (r-1)c_1(E)^2 \right )

is weakly positive at

y
y

. We apply this result to obtain the following description of the cone of weakly positive

Q

\mathbb {Q}

-Cartier divisors on the moduli space of stable curves. Let

M

¯

g

\overline {\mathcal {M}}_g

(resp.

M

g

\mathcal {M}_g

) be the moduli space of stable (resp. smooth) curves of genus

g
≥
2

g \geq 2

. Let

λ
\lambda

be the Hodge class, and let the

δ
i

\delta _i

’s (

i
=
0
,
…
,
[
g

/

2
]

i = 0, \ldots , [g/2]

) be the boundary classes. Then, a

Q

\mathbb {Q}

-Cartier divisor

x
λ
+

∑

i
=
0

[
g

/

2
]

y
i

δ
i

x \lambda + \sum _{i=0}^{[g/2]} y_i \delta _i

on

M

¯

g

\overline {\mathcal {M}}_g

is weakly positive over

M

g

\mathcal {M}_g

if and only if

x
≥
0

x \geq 0

,

g
x
+
(
8
g
+
4
)

y
0

≥
0

g x + (8g + 4) y_0 \geq 0

, and

i
(
g
−
i
)
x
+
(
2
g
+
1
)

y
i

≥
0

i(g-i) x + (2g+1) y_i \geq 0

for all

1
≤
i
≤
[
g

/

2
]

1 \leq i \leq [g/2]

.
Drinfel’d doubles and Ehresmann doubles for Lie algebroids and Lie bialgebroids
Authors: Mackenzie K.
Published: July 2002

We show that the Manin triple characterization of Lie bialgebras in terms of the Drinfel’d double may be extended to arbitrary Poisson manifolds and indeed Lie bialgebroids by using double cotangent bundles, rather than the direct sum structures (Courant algebroids) utilized for similar purposes by Liu, Weinstein and Xu. This is achieved in terms of an abstract notion of double Lie algebroid (where “double” is now used in the Ehresmann sense) which unifies many iterated constructions in differential geometry.
Bases in equivariant 𝐾-theory
Authors: Lusztig G.
Published: July 2002

In this paper we construct a canonical basis for the equivariant

K
K

-theory of the flag manifold of a semisimple simply connected

C

\mathbf {C}

-algebraic group with respect to the action of a maximal torus times

C

∗

\mathbf {C}^{*}

. We relate this basis to the canonical basis of the “periodic module” for the affine Hecke algebra. The construction admits a (conjectural) generalization to the case where the flag manifold is replaced by the zero set of a nilpotent vector field.
Koszul duality for parabolic and singular category 𝒪
Authors: Backelin Erik
Published: July 2002

This paper deals with a generalization of the “Koszul duality theorem” for the Bernstein-Gelfand-Gelfand category

O

\mathcal O

over a complex semi-simple Lie-algebra, established by Beilinson, Ginzburg and Soergel in Koszul duality patterns in representation theory, J. Amer. Math. Soc. 9 (1996), 473–527. In that paper it was proved that any “block” in

O

\mathcal O

, determined by an integral, but possibly singular weight, is Koszul (i.e. equivalent to the category of finitely generated modules over some Koszul ring) and, moreover, that the “Koszul dual” of such a block is isomorphic to a “parabolic subcategory” of the trivial block in

O

\mathcal O

. We extend these results to prove that a parabolic subcategory of an integral and (possibly) singular block in

O

\mathcal O

is Koszul and we also calculate the Koszul dual of such a category.
Locating probable genes using Fourier transform approach
Authors: Issac Biju , Singh Harpreet , Kaur Harpreet , Raghava G. P. S.
Published: July 2002

Summary: FTG is a web server for analyzing nucleotide sequences to predict the genes using Fourier transform techniques. This server implements the existing Fourier transform algorithms for gene prediction and allows the rapid visualization of analysis by output in GIF format.

Availability: The server is available at http://www.imtech.res.in/raghava/ftg/

Contact: raghava@imtech.res.in

Supplementary information: http://www.imtech.res.in/raghava/ftg/help/supl.html

* To whom correspondence should be addressed.
Separation of nearly identical repeats in shotgun assemblies
using defined nucleotide positions, DNPs
Authors: Tammi Martti T. , Arner Erik , Britton Tom , Andersson Björn
Published: July 2002

An increasingly important problem in genome sequencing is the failure of the commonly used shotgun assembly programs to correctly assemble repetitive sequences. The assembly of non-repetitive regions or regions containing repeats considerably shorter than the average read length is in practice easy to solve, while longer repeats have been a difficult problem. We here present a statistical method to separate arbitrarily long, almost identical repeats, which makes it possible to correctly assemble complex repetitive sequence regions. The differencesbetween repeat units may be as low as 1% and the sequencing error may be up to ten times higher. The method is based on the realization that a comparison of only a part of all overlapping sequences at a time in a data set does not generate enough information for a conclusive analysis. Our method uses optimal multi-alignments consisting of all the overlaps of each read. This makes it possible to determine defined nucleotide positions, DNPs, which constitute the differences between the repeat units. Differences between repeats are distinguished from sequencing errors using statistical methods, where the probabilities of obtaining certain combinations of candidate DNPs are calculated using the information from the multi-alignments. The use of DNPs and combinations of DNPs will allow for optimal and rapid assemblies of repeated regions. This method can solve repeats that differ in only two positions in a read length, which is the theoretical limit for repeat separation. We predict that this method will be highly useful in shotgun sequencing in the future.

Contact: bjorn.andersson@genpat.uu.se

* To whom correspondence should be addressed.
Advanced pairwise structure alignments of proteins and analysis
of conformational changes
Authors: Ochagavia Maria Elena , Richelle Jean , Wodak Shoshana J.
Published: July 2002

Motivation: Comparing the 3D structures of two proteins or analyzing the structural changes undergone by a protein upon ligand binding or when it crystallizes under different conditions, can be both tricky and tedious, especially when the two proteins are distantly related, or when the structural changes are complex. Readily accessible tools for performing these tasks automatically and reliably should therefore be welcome.

Results: We describe a web interface to several automatic procedures for performing pairwise structure superposition in a flexible manner, for detailed analyses of conformational changes and for displaying the results in a pictorial fashion.

Availability: This interface can be accessed at the Brussels and Cuba Web sites, respectively: http://www.ucmb.ulb.ac.be/SCMBB/Tools.htmland http://bio.cigb.edu.cu.

Contact: shosh@ucmb.ulb.ac.be

* To whom correspondence should be addressed.
Seasonal plankton dynamics in a Mediterranean hypersaline coastal lagoon: the Mar Menor
Authors: Gilabert Javier
Published: July 2002

The seasonal distribution of plankton in a Mediterranean hypersaline coastal lagoon has been studied through a dataset, comprising the taxonomic composition and the size–abundance distribution of both phyto- and zooplankton, measured by image analysis techniques during a one-year time series of weekly samplings. The studied organisms ranged from small nanoplanktonic heterotrophic flagellates (2 μm diameter) to fish larvae (>2 μm). The phytoplankton annual succession was characterized by a winter period dominated by Rhodomonas spp. and Cryptomonas spp. with Cyclotella spp. as the main diatom represented, a spring phase where diatoms (mainly Cyclotella) were the dominant group with some monospecific blooms of other diatoms (mainly of Chaetoceros sp.), a summer phase characterized by diatoms with blooms of Niztschia closterium, and a post-summer phase where dinoflagellates increased with peaks of Ceratium furca. High densities of the microbial food web elements, flagellates and ciliates, indicate the importance of the microbial loop in the ecosystem. Meroplankton contributed widely to the seasonal character of the zooplankton distribution. Copepods, represented by Oithona nana, Centropages ponticus and Acartia spp. (mainly latisetosa), remained relatively constant throughout the year, exhibiting a lower density in the warmer water period (July–September). At the end of the sampling period, a massive proliferation of copepods (>1000 ind l –1), mainly due to O. nana, took place. The autotrophs to heterotrophs biovolume ratio (A:H) remained lower than 1 throughout the year except when, occasionally, large phytoplankton cells bloomed. Persistent very low values of A:H suggest that additional sources of energy, such as the microbial loop or detrital pathways, would be needed to sustain the high heterotrophic biovolume found in the lagoon.
Contractile response to low peroxide concentrations: myofibrillar calcium sensitivity as a likely target for redox‐modulation of skeletal muscle function
Authors: Andrade Francisco H. , Reid Michael B. , Westerblad Håkan
Published: July 2002

Endogenous peroxides and related reactive oxygen species may influence various steps in the contractile process. Single mouse skeletal muscle fibers were used to study the effects of hydrogen peroxide (H2O2) andt‐butyl hydroperoxide (f‐BOOH) on force and myoplasmic Ca2+concentration ([Ca2+]i). Both peroxides (10−1to 10−5M) decreased tetanic [Ca2+]iand increased force during submaximal tetani. Catalase (1 kU/ml) blocked the effect of H2O2, but not oft‐BOOH. The decrease in tetanic [Ca2+]iwas constant, while the effect on force was biphasic: A transitory increase was followed by a steady decline to the initial level. Myofibrillar Ca2+sensitivity remained increased during incubation with either peroxide. Only the highest peroxide concentration (10 μM) increased resting [Ca2+]iand slowed the return of [Ca2+]ito its resting level after a contraction, evidence of impaired sarcoplasmic reticulum Ca2+re‐uptake. The peroxides increased maximal force production and the rate of force redevelopment, and decreased maximum shortening velocity. N‐ethylmaleimide (25 μM, thiol‐alkylating agent) prevented the response to 1 μM H2O2. These results show that myofibrillar Ca2+sensitivity and cross‐bridge kinetics are influenced by H2O2 andt‐BOOH concentrations that approach those found physiologically, and these findings indicate a role for endogenous oxidants in the regulation of skeletal muscle function.
Genetic control and dynamics of the cellular immune response to the human T–cell leukaemia virus, HTLV–I
Authors: Bangham Charles R. M. , Hall Sarah E. , Jeffery Katie J. M. , Vine Alison M. , Witkover Aviva , Nowak Martin A. , Wodarz Dominik , Usuku Koichiro , Osame Mitsuhiro
Published: July 2002

About 1% of people infected with the human T–cell leukaemia virus, type 1 (HTLV–I) develop a disabling chronic inflammatory disease of the central nervous system known as HTLV–I–associated myelopathy/tropical spastic paraparesis (HAM/TSP). Patients with HAM/TSP have a vigorous immune response to HTLV–I, and it has been widely suggested that this immune response, particularly the HTLV–I–specific cytotoxic T–lymphocyte (CTL) response, causes the tissue damage that is seen in HAM/TSP. In this paper we summarize recent evidence that a strong CTL response to HTLV–I does in fact protect against HAM/TSP by reducing the proviral load of HTLV–I. We conclude that HTLV–I is persistently replicating at a high level, despite the relative constancy of its genome sequence. These results imply that antiretroviral drugs could reduce the risk of HAM/TSP by reducing the viral load, and that an effective anti–HTLV–I vaccine should elicit a strong CTL response to the virus. The dynamic nature of the infection also has implications for the epidemiology and the evolution of HTLV–I.
The role of extreme events in the impacts of selective tropical forestry on erosion during harvesting and recovery phases at Danum Valley, Sabah
Authors: Douglas I. , Bidin K. , Balamurugan G. , Chappell N. A. , Walsh R. P. D. , Greer T. , Sinun W.
Published: July 2002

Ten years’ hydrological investigations at Danum have provided strong evidence of the effects of extremes of drought, as in the April 1992 El Niño southern oscillation (ENSO) event, and flood, as in January 1996. The 1.5 km2undisturbed forest control catchment experienced a complete drying out of the stream for the whole 1.5 km of defined channel above the gauging station in 1992, but concentrated surface flow along every declivity from within a few metres of the catchment divide after the exceptional rains of 19 January 1996. Under these natural conditions, erosion is episodic. Sediment is discharged in pulses caused by storm events, collapse of debris dams and occasional landslips. Disturbance by logging accentuates this irregular regime. In the first few months following disturbance, a wave of sediment is moved by each storm, but over subsequent years, rare events scour sediment from bare areas, gullies and channel deposits. The spatial distribution of sediment sources changes with time after logging, as bare areas on slopes are revegetated and small gullies are filled with debris. Extreme storm events, as in January 1996, cause logging roads to collapse, with landslides leading to surges of sediment into channels, reactivating the pulsed sediment delivery by every storm that happened immediately after logging. These effects are not dampened out with increasing catchment scale. Even the 721 km2Sungai Segama has a sediment yield regime dominated by extreme events, the sediment yield in that single day on 19 January 1996 exceeding the annual sediment load in several previous years. In a large disturbed catchment, such road failures and logging–activity–induced mass movements increase the mud and silt in floodwaters affecting settlements downstream. Management systems require long–term sediment reduction strategies. This implies careful road design and good water movement regulation and erosion control throughout the logging process.
FHY1: a phytochrome A-specific signal transducer
Authors: Desnos Thierry , Puente Pilar , Whitelam Garry C. , Harberd Nicholas P.
Published: July 2002

Phytochromes are plant photoreceptors that regulate plant growth and development with respect to the light environment. Following the initial light-perception event, the phytochromes initiate a signal-transduction process that eventually results in alterations in cellular behavior, including gene expression. Here we describe the molecular cloning and functional characterization of Arabidopsis FHY1. FHY1 encodes a product (FHY1) that specifically transduces signals downstream of the far-red (FR) light-responsive phytochrome A (PHYA) photoreceptor. We show that FHY1 is a novel light-regulated protein that accumulates in dark (D)-grown but not in FR-grown hypocotyl cells. In addition, FHY1 transcript levels are regulated by light, and by the product of FHY3, another gene implicated in FR signaling. These observations indicate that FHY1 function is both FR-signal transducing and FR-signal regulated, suggesting a negative feedback regulation of FHY1 function. Seedlings homozygous for loss-of-function fhy1 alleles are partially blind to FR, whereas seedlings overexpressing FHY1exhibit increased responses to FR, but not to white (WL) or red (R) light. The increased FR-responses conferred by overexpression ofFHY1 are abolished in a PHYA-deficient mutant background, showing that FHY1 requires a signal from PHYA for function, and cannot modulate growth independently of PHYA.
A convolution model to convert transmission dose images to exit dose distributions
Authors: Boellaard R. , van Herk M. , Mijnheer B. J.
Published: July 2002

The aim of this study is to develop a model which computes exit dose values from transmission dose data obtained during patient treatment with an electronic portal imaging device (EPID). The proposed model convolves the primary dose distribution, derived from transmission dose distributions at large air gaps, with a scatter kernel to obtain the exit dose. The influence of inhomogeneities on the scatter contribution is taken into account by using a radiological path length model. To determine the parameters of the model, an extensive set of transmission dose measurements was performed behind various phantoms in an 8 MV beam using a liquid‐filled EPID. The influence on the transmission dose of field size, phantom thickness, air gap between phantom and detector, and source‐phantom distance was investigated. At air gaps larger than 50 cm the distribution of scattered dose is almost flat and its contribution to the total dose is relatively small, thus allowing an accurate separation of the primary and scattered dose by subtraction. Scattered dose distributions for air gaps smaller than 50 cm were obtained by subtracting the primary dose (corrected for divergence) from the measured total transmission dose. The resulting scattered dose distribution behind homogeneous phantoms has a Gaussian shaped profile, which becomes wider with increasing air gap. The relative contribution of scattered dose depends on the phantom thickness and is maximal for a thickness of about 10 cm. Using these results, the parameters of the convolution model (i.e., the shape of the scatter kernel) were determined. With the model the absolute exit dose is predicted with an accuracy of about 2% (1 s.d.) within the entire radiation field for homogeneous phantoms. Inhomogeneities are taken into account by calculating the radiological path length from the measured primary dose, i.e., without using CT data. By using the measured radiological path length the exit dose can be determined for inhomogeneous phantoms with an accuracy of 2.5%. It is concluded that, using our convolution model, EPID measurements at large air gaps can be used to estimate absolute exit doses in an 8 MV beam with an accuracy of 2.5%.
Generalizing the Heisenberg uncertainty relation
Authors: Chisolm Eric D.
Published: July 2002

The proof of the Heisenberg uncertainty relation is modified to produce two improvements: (a) The resulting inequality is stronger because it includes the covariance between the two observables, and (b) the proof lifts certain restrictions on the state to which the relation is applied, increasing its generality. The restrictions necessary for the standard inequality to apply are not widely known, and they are discussed in detail. The classical analog of the Heisenberg relation is also derived, and the two are compared. Finally, the modified relation is used to address the apparent paradox that eigenfunctions of the z component of angular momentum Lz do not satisfy the φ–Lz Heisenberg relation; the resolution is that the restrictions mentioned above make the usual inequality inapplicable to these states. The modified relation does apply, however, and it is shown to be consistent with explicit calculations.
A pedestrian introduction to Gamow vectors
Authors: de la Madrid R. , Gadella M.
Published: July 2002

The Gamow vector description of resonances is compared with the S matrix and the Green function descriptions using the example of the square barrier potential. By imposing different boundary conditions on the time independent Schrödinger equation, we obtain either eigenvectors corresponding to real eigenvalues and the physical spectrum or eigenvectors corresponding to complex eigenvalues (Gamow vectors) and the resonance spectrum. We show that the poles of the S matrix are the same as the poles of the Green function and are the complex eigenvalues of the Schrödinger equation subject to a purely outgoing boundary condition. The intrinsic time asymmetry of the purely outgoing boundary condition is discussed. Finally, we show that the probability of detecting the decay within a shell around the origin of the decaying state follows an exponential law if the Gamow vector (resonance) contribution to this probability is the only contribution that is taken into account.
A simpler derivation of Feigenbaum’s renormalization group equation for the period-doubling bifurcation sequence
Authors: Coppersmith S. N.
Published: July 2002

One interesting and important property of nonlinear dynamical systems is that they can exhibit universality—behavior that is quantitatively identical for a broad class of systems. The first and most famous example of universality in a dynamical system was identified by Feigenbaum [M. J. Feigenbaum, J. Stat. Phys. 19, 25–52 (1978), 21, 669–706 (1979)] in the period-doubling route to chaos. This note presents a new derivation of Feigenbaum’s renormalization group equation, used to understand this universality. The argument, designed for incorporation into an undergraduate dynamical systems course, is simpler than those in standard textbooks.
Spectral integral representations of volume scattering in sediments in layered waveguides
Authors: LePage Kevin D. , Schmidt Henrik
Published: July 2002

In situ measurements of scattering strength are often obtained by analyzing the early-time, high-angle reverberation from bottom and subbottom features. In order to provide insight into the mechanisms which cause bottom reverberation, and to their distinguishing characteristics, it is necessary to have a capability for modeling both the rough surface and the volume scattering mechanisms. For high-angle, early-time backscatter, the most appropriate approach is to use a spectral integral representation, which naturally includes the continuous spectrum important for this angular regime. A rough surface scattering theory developed earlier in this framework has provided important insights into wave scattering and penetration physics at the seafloor. Here a consistent representation for the subbottom scattering is developed and examples are provided which illustrate the observable differences between the two scattering mechanisms.
Effect of turgor pressure on outer hair cell motility
Authors: Adachi M. , Sugawara M. , Iwasa K. H.
Published: July 2002

The motor in the outer hair cell converts electrical energy directly into mechanical energy. There are two possible mechanisms for such a motor: one depends on changes in the membrane area (“area motor”) and the other on changes in the stiffness (“stiffness motor”). These two mechanisms, which are not mutually exclusive, give different predictions on turgor pressure dependence of the amplitude. It was found that an increased pressure shifts the voltage dependence but does not change the amplitude of length changes. This observation is incompatible with a pure stiffness motor model. It was also confirmed that length changes are closely related to charge movements by monitoring the membrane capacitance. It can be concluded that hair cell motility is primarily based on area changes, and not changes in the elastic moduli.
Leaky helical flexural wave scattering contributions from tilted cylindrical shells: Ray theory and wave-vector anisotropy
Authors: Blonigen Florian J. , Marston Philip L.
Published: July 2002

At sufficiently high frequencies, cylindrical shells support a wave whose properties are analogous to those of the lowest antisymmetric Lamb wave on plates. When the shell is in water and the frequency exceeds the coincidence frequency, the flexural wave is a leaky wave that can be a major contributor to the scattering by tilted shells [G. Kaduchak, C. M. Wassmuth, and C. M. Loeffler, J. Acoust. Soc. Am. 100, 64–71 (1996)]. While the meridional ray-scattering contributions for such leaky flexural waves were previously modeled, the helical contribution can also be significant. A ray theory for those contributions is compared with the exact partial wave series (PWS) solution for infinitely long empty shells. The agreement between the ray theory and the PWS is only possible when a weak anisotropy of the flexural wave parameters is included in the evaluation of the ray theory. The anisotropy is determined numerically from the roots of a denominator in the PWS because approximations for the anisotropy from thin-shell mechanics are not applicable significantly above the coincidence frequency.
A nonlinear material model of lead magnesium niobate (PMN)
Authors: Piquette Jean C. , Forsythe Stephen E.
Published: July 2002

A one-dimensional material model of lead magnesium niobate (PMN) is presented. The model includes saturation phenomenology, but excludes hysteresis and dispersion. (Constant temperature is assumed.) It is shown that the strain can be taken to respond as an exactly quadratic function in the electric displacement D throughout the saturation region and yet still deduce the full observed response of the material, including flattening of the curve, when the strain is expressed as a function of electric field E. The model developed here is shown to be compatible with experimental measurements previously acquired by other researchers.
Azimuthal and depth-dependent transmission loss caused by shelf internal waves
Authors: Orr Marshall H. , Oba Roger M.
Published: July 2002

The amplitude of an acoustic field propagating through a stratified continental shelf water column in the presence of internal wave packets is shown to be azimuthally and depth dependent when referenced to the propagation vector of the internal wave packet. Internal wave (IW) packets, which propagate across the continental shelf, are known to be regularly generated each tidal cycle at the shelf break edge in stratified water column conditions. They are dispersive in nature and change in physical structure as they propagate away from the generation site. Their wave directional spectrum is highly peaked. Consequently, the wave-number spectrum of the continental shelf sound velocity field is highly directional and will be shown to cause azimuthal dependency in the properties of the acoustic field as a function of range and bearing from the source. Preliminary results of numerical solutions to the parabolic equation approximation of the Helmholtz equation are presented to substantiate the above assertions, in particular for propagation through a uniform internal wave field of a fixed wave number and amplitude. [Work supported by the Office of Naval Research.]
Sensitivity calculations for structural acoustic EFEM predictions
Authors: Bitsie Fernando , Bernhard Robert
Published: July 2002

Recent research on the energy finite element method (EFEM) has focused on the development of structural–acoustic coupled capability. This formulation has been developed successfully in terms of radiation efficiency. The approach has been implemented into the finite element method and successfully verified against experimental results for an enclosure with one flexible wall. Calculation of the sensitivity of the response to various parameters of the model is reasonably straightforward in the EFEM formulation. This capability was used for system identification for the experimental verification problem and for understanding the dominant mechanisms which govern the structural acoustic response at high frequency for both acoustical and mechanical excitation of the enclosure problem. [See NOISE-CON Proceedings for full paper.]
Passive detection of transient signals in ambient shipping noise
Authors: Pflug Lisa A. , Ioup George E. , Ioup Juliette W.
Published: July 2002

A comparison between second- and fourth-order moment detectors for passive detection of low-frequency transient signals in both uncorrelated Gaussian and measured noise is presented. The measured noise, recorded in shallow water near the San Diego harbor, is dominated at low frequencies by ship-generated noise and is thus correlated in time and between sensors. The detectors do not assume noise or signal stationarity and use two channels of data to form the second-order moment, and two or four channels of data to form the fourth-order moment. Detection simulations with test transients of varying kurtosis reveal that in the Gaussian noise, the fourth-order moment detector with two channels of data performs best only for signals with high kurtosis. However, in the measured noise, the fourth-order moment detector performs best for most of the test signals if four channels of data are included. If knowledge of the signal passband is included in the processing and detection is restricted to be within the passband, the fourth-order moment detector with four channels of data generally performs best in both the Gaussian and measured noise. [This work was funded by the Office of Naval Research.]
Matched-field processing in a wedgelike ocean
Authors: Baxley Paul A.
Published: July 2002

The neglect of the three-dimensional nature of acoustic propagation in a wedgelike shallow-water ocean can cause significant localization errors in underwater acoustic array processors. This study examines in detail the effect of such neglect on the performance of matched-field processors in wedgelike environments, along with an analysis of the performance improvement gained by including known three-dimensional effects into the processor. Results were obtained via computer simulations of signals received on a vertical line array (VLA) from a source moving in the cross-slope direction relative to the ASA benchmark penetrable wedge. Typical effects observed when the three-dimensional nature of the propagation was ignored include an increase in the range error as the source moves away from the VLA (giving the impression of an accelerating source), distinct jumps to incorrect depths as modes are stripped, and loss of signals upon entering a horizontal shadow zone (all modes stripped). Incorporation of the known three-dimensional propagation into the processor not only eliminates the localization errors but provides azimuthal discrimination. Recent progress has also been made in the computer simulation and data analysis of a real wedge-shaped environment off San Clemente Island near San Diego. [Work supported by ONR/NRaD.]
Design and development of a marine acoustic accelerometer
Authors: Brown David , Buddhineni Rama
Published: July 2002

A push–pull fiber-optic acoustic accelerometer using Mach–Zehnder interferometry to detect surface strains in a centrally clamped, peripherally free disk will be described. The measured sensitivity is approximately 20 rad/g below the resonance of 10 kHz. A total of 36 m of optical fiber wound in a pancake spiral was used for each interferometer leg. The disk is housed in a cylindrical case that allows the device to be near neutrally buoyant in water, thus acting as an acoustic motion sensor. The interferometer was interrogated with a Nd:YAG laser at 1310 nm and a 3×3 fiber coupler. Considering a total disk mass of 19.6 gm, the fractional phase change per unit force is 4.0×10−6 N−1. Based on an electro-optic noise floor of 5 μrad/Hz1/2, the minimum detectable signal is 0.25×10−6g/Hz1/2. [Work supported by the University of Massachusetts, Dartmouth.]
Calibration. Primary—Secondary—Field
Authors: Schonthal Ernst
Published: July 2002

The primary calibration of acoustic and vibration transducers are well standardized and confirmed by a round-robin inter-laboratory test. Secondary calibration is also very common with traceability to primary calibration. Examples of setups for microphone and accelerometer secondary calibration are discussed regarding accuracy, frequency response testing, etc. Field check methods using reference sources and other methods like Phantom calibration are discussed regarding advantages and shortcomings.
Evaluation of instrument standards with virtual sound level meters
Authors: Wu Lixue , Wong George S. K.
Published: July 2002

It is not an easy task to evaluate instrument standards such as ANSI S1.4, IEC 651, IEC 804, and IEC 1672: Sound level meters, which is under development. Traditionally, proposed calibration procedures are tested with existing instruments from various manufacturers. Obtaining quantitative data to justify proposals on tolerances and to measure the combined effects of tolerances on the final instrument readings is extremely difficult. The above tasks can be done with relative ease with a computer emulation of virtual instruments. A sound level meter based on virtual instrumentation using the latest software technology, cost-effective data acquisition, control hardware, and a computer is presented. For manufacturers of acoustical instruments, a graphic designer interface also makes it possible to evaluate ‘‘user-defined’’ instrument systems with reduction in development time and costs.
The effects of microphone mismatch on the performance of a spherical acoustic vector-field sensor
Authors: Parkins John W. , Tichy Jiri , Sommerfeldt Scott D.
Published: July 2002

Elko previously established the performance improvement for intensity measurements of an acoustic sensor using two microphones embedded on the surface of a hard sphere to that of a sensor comprising two infinitely small microphones separated in space [G. Elko, Noise-Con 91, pp. 525–532]. Elko derived his results for perfectly matched microphones, with regard to phase and sensitivity, in a plane-wave field with a variable angle of incidence. The performance of a spherical sensor and a two-point sensor are compared here for the case of a one-dimensional standing wave field with an arbitrary reflection coefficient and incidence angle, when the measurement microphones have a phase and sensitivity mismatch. Results are generated using sensitivity and phase variations typically found in inexpensive electret microphones. The effect of bias errors in potential energy density, kinetic energy density, total energy density, and intensity are reported.
The ASHRAE Handbook on noise and vibration: A critical review
Authors: Peppin Richard J.
Published: July 2002

Noise of heating, ventilating, and air conditioning (HVAC) systems could have been one of the most common single sources of noise in the developed countries, but it is not, partially because of well-known methods of HVAC noise control promulgated by professional organizations such as ASHRAE, and trade associations such as the Air Conditioning and Refrigeration Institute (ARI) and the Air Movement and Control Association (AMCA). Most people who live in air conditioned spaces are unaware of the work that went into making their environment quiet by many private consultants and by many corporate engineers and acousticians working for the major HVAC companies. It is true there are problem jobs, usually low-noise environments that do not meet expectations, but these jobs are constantly being worked on and the numbers are being reduced by people using the ASHRAE Handbook. But, unfortunately, the Noise and Vibration chapter is far from perfect. This paper reviews a standby in HVAC acoustics, the 1995 ASHRAE Handbook: HVAC Applications, I–P Edition, ‘‘Chapter 43 Sound and Vibration Control,’’ published by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. The review provides an evaluation based on the perspective of a member of the Technical Committee 2.6 on Sound and Vibration, from which the chapter originated. The paper points out just a few of the several areas in which the data and information contained need to be used with caution. [See NOISE-CON Proceedings for full paper.]
Environmental noises from different sources and overall annoyance ratings: An interdisciplinary evaluation concept
Authors: Schulte-Fortkamp Brigitte
Published: July 2002

In different studies of noise annoyance ratings, the overall annoyance of a multiple-noise-source situation is often rated to be less annoying than the most annoying single source. There have been various explanations for this phenomena, one of which is that people are not able to rate multiple-noise-source situations, because overall noise annoyance from more than one source presented a task too complicated to be achieved. Literature studies show the need for different methodical procedures and acoustical parameter sets to identify the particular effects of annoyance. In a socio- and psychoacoustical field and laboratory study on this issue, different combinations of synergetic environmental traffic noise are evaluated. Frames of reference for judging the annoyance of a single noise source are compared to the overall annoyance in a multisource environment. The meaning of social features like status, mode of living, courses of daily and weekly activity, strategies of noise perception and noise management, and degrees of the inhabitants’ capacity to deal with traffic and noise interference is analyzed. Further, psycho- and socioacoustic indicator models on the basis of these and future comparative case studies are discussed.
Using FUZZY logic to clean unattended blast noise monitor data
Authors: Schomer Paul D. , van Slooten Hans J.
Published: July 2002

Unattended noise monitors are a common tool used to manage the noise generated by large distributed sources such as airports and military installations. In most instances, the desire is to measure just the noise from the source under study or to separate out the noise from the source under study from other noises. In practice, this can be a difficult task. In the case of blast noise from military weapons (e.g., artillery, tanks, bombs), it is necessary to separate this particular noise from other low-frequency, short-duration sounds which can be generated by helicopters, quarries, and road construction, etc., or from wind-induced pseudonoise. The use of FUZZY logic to perform this separation and to designate those measured noise events that come from weapons fire at the military installation is described.
Time-domain modeling of damping in plates
Authors: Lambourg Christophe , Chaigne Antoine J.
Published: July 2002

A time-domain formulation of flexural vibrations in damped rectangular orthotropic plates has been developed, in order to investigate transient and nonlinear excitation of plates. The model includes three basic mechanisms of damping: thermoelasticity, viscoelasticity, and radiation. As a consequence, the four rigidity factors are modified by perturbation terms, each perturbation term corresponding to one specific damping mechanism. The thermoelastic term is derived from the coupling between the thermoelastic stress-strain relationships and the heat diffusion equation. The second perturbation term is obtained from the standard generalized partial differential equation formulation of viscoelasticity. The third term is obtained through a Padé approximant of the damping factor which governs the radiation of an infinite plate coupled with a light fluid. The flexural equations are solved numerically in the particular case of a sphere impacting the plate with the help of a finite difference scheme of second order in time and fourth order in space. A simulated sound pressure is then obtained by a simple discrete form of the Rayleigh integral. The simulated tones show the relative relevance of the three damping mechanisms, for four different materials: aluminium, glass, carbon fibers, and wood.
Impact of plates: Some questions on numerical precision and scaling
Authors: McMillan Alison J.
Published: July 2002

The deflection of an impacted plate may be treated as a time-dependent forced vibration at the impact point. The position of the impactor head can be determined from its initial velocity and deceleration on impact. The difference between the impactor position and the plate deflection is the relative approach of the contacting surfaces (Hertz’ law). This is a Volterra integral equation of the second kind which must be solved numerically. Two structures of different sizes but of the same shape will have proportional modal properties. For similar geometries, it can be shown that there are three basic variables; the fundamental frequency, the mass ratio of impactor and plate, and a contact parameter. It is of interest to determine the extent to which the distribution of the higher modes (or equivalently, the shape of the plate) governs the impact force and duration. For example, is it valid to approximate a circular plate by a rectangular one, or to use thin plate bending theory rather than thick? The benefit is the reduced precision required in the modal analysis: With a numerical modal analyzer such as finite-element method, reliable impact force levels may be determined with a low precision modal model.
Implementation of time-domain fuzzy structure representations
Authors: Barbone Paul E.
Published: July 2002

It is shown that complex dynamical vibratory subsystems can be represented in a numerical simulation by an equivalent boundary condition. This boundary condition is usually written in the form of a time convolution with a known kernel. It is shown that the kernel of this boundary condition can be replaced by a simple approximate kernel when the substructure has a high modal density (a ‘‘fuzzy’’ approximation). Depending on the properties of the kernel, the time convolution may be replaced by an equivalent condition that is local in time, but depends on high order time derivatives. The issues related to implementing the boundary condition in both convolution and differential form are discussed. In particular, the effects of the boundary condition on the stability and accuracy of numerical time integration are considered. [Work supported by ONR.]