bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular Uptake of Chloroquine Is Dependent on Binding to Ferriprotoporphyrin IX and Is Independent of NHE Activity in Plasmodium falciparum
Authors: Bray Patrick G. , Janneh Omar , Raynes Kaylene J. , Mungthin Mathirut , Ginsburg Hagai , Ward Stephen A.
Published: July 2002

Here we provide definitive evidence that chloroquine (CQ) uptake in Plasmodium falciparum is determined by binding to ferriprotoporphyrin IX (FPIX). Specific proteinase inhibitors that block the degradation of hemoglobin and stop the generation of FPIX also inhibit CQ uptake. Food vacuole enzymes can generate cell-free binding, using human hemoglobin as a substrate. This binding accounts for CQ uptake into intact cells and is subject to identical inhibitor specificity. Inhibition of CQ uptake by amiloride derivatives occurs because of inhibition of CQ–FPIX binding rather than inhibition of the Na+/H+ exchanger (NHE). Inhibition of parasite NHE using a sodium-free medium does not inhibit CQ uptake nor does it alter the ability of amilorides to inhibit uptake. CQ resistance is characterized by a reduced affinity of CQ–FPIX binding that is reversible by verapamil. Diverse compounds that are known to disrupt lysosomal pH can mimic the verapamil effect. These effects are seen in sodium-free medium and are not due to stimulation of the NHE. We propose that these compounds increase CQ accumulation and overcome CQ resistance by increasing the pH of lysosomes and endosomes, thereby causing an increased affinity of binding of CQ to FPIX.
Roles of the Tumor Suppressor p53 and the Cyclin-dependent Kinase Inhibitor p21WAF1/CIP1 in Receptor-mediated Apoptosis of WEHI 231 B Lymphoma Cells
Authors: Wu Min , Bellas Robert E. , Shen Jian , Sonenshein Gail E.
Published: July 2002

Treatment of WEHI 231 immature B lymphoma cells with an antibody against their surface immunoglobulin M (anti-IgM) induces apoptosis and has been studied extensively as a model of self-induced B cell tolerance. Since the tumor suppressor protein p53 has been implicated in apoptosis in a large number of cell types and has been found to be mutated in a variety of B cell tumors, here we sought to determine whether p53 and the p53 target gene cyclin-dependent kinase inhibitor p21WAF1/CIP1 were involved in anti-IgM–induced cell death. Anti-IgM treatment of WEHI 231 cells increased expression of p53 and p21 protein levels. Ectopic expression of wild-type p53 in WEHI 231 cells induced both p21 expression and apoptosis. Ectopic expression of p21 similarly induced apoptosis. Rescue of WEHI 231 cells from apoptosis by costimulation with CD40 ligand ablated the increase in p21 expression. Lastly, a significant decrease in anti-IgM–mediated apoptosis was seen upon downregulation of endogenous p53 activity by expression of a dominant-negative p53 protein or upon microinjection of an antisense p21 expression vector or antibody. Taken together, the above data demonstrate important roles for p53 and p21 proteins in receptor-mediated apoptosis of WEHI 231 B cells.
Time Course and Ca2+ Dependence of Sensitivity Modulation in Cyclic Gmp-Gated Currents of Intact Cone Photoreceptors
Authors: Rebrik Tatiana I. , Kotelnikova Ekaterina A. , Korenbrot Juan I.
Published: July 2002

We determined the Ca2+ dependence and time course of the modulation of ligand sensitivity in cGMP-gated currents of intact cone photoreceptors. In electro-permeabilized single cones isolated from striped bass, we measured outer segment current amplitude as a function of cGMP or 8Br-cGMP concentrations in the presence of various Ca2+ levels. The dependence of current amplitude on nucleotide concentration is well described by the Hill function with values of K1/2, the ligand concentration that half-saturates current, that, in turn, depend on Ca2+. K1/2 increases as Ca2+ rises, and this dependence is well described by a modified Michaelis-Menten function, indicating that modulation arises from the interaction of Ca2+ with a single site without apparent cooperativity. CaKm, the Michaelis-Menten constant for Ca2+ concentration is 857 ± 68 nM for cGMP and 863 ± 51 for 8Br-cGMP. In single cones under whole-cell voltage clamp, we simultaneously measured changes in membrane current and outer segment free Ca2+ caused by sudden Ca2+ sequestration attained by uncaging diazo-2. In the presence of constant 8Br-cGMP, 15 μΜ, Ca2+ concentration decrease was complete within 50 ms and membrane conductance was enhanced 2.33 ± 0.95-fold with a mean time to peak of 1.25 ± 0.23 s. We developed a model that assumes channel modulation is a pseudo–first-order process kinetically limited by free Ca2+. Based on the experimentally measured changes in Ca2+ concentration, model simulations match experimental data well by assigning the pseudo-first-order time constant a mean value of 0.40 ± 0.14 s. Thus, Ca2+-dependent ligand modulation occurs over the concentration range of the normal, dark-adapted cone. Its time course suggests that its functional effects are important in the recovery of the cone photoresponse to a flash of light and during the response to steps of light, when cones adapt.
On beta expansions for Pisot numbers
Authors: Boyd David
Published: July 2002

Given a number

β
>
1

\beta > 1

, the beta-transformation

T
=

T

β

T =T_{\beta }

is defined for

x
∈
[
0
,
1
]

x \in [0,1]

by

T
x
:=
β
x

Tx := \beta x

(mod 1). The number

β
\beta

is said to be a beta-number if the orbit

{

T

n

(
1
)
}

\{T^{n}(1)\}

is finite, hence eventually periodic. In this case

β
\beta

is the root of a monic polynomial

R
(
x
)

R(x)

with integer coefficients called the characteristic polynomial of

β
\beta

. If

P
(
x
)

P(x)

is the minimal polynomial of

β
\beta

, then

R
(
x
)
=
P
(
x
)
Q
(
x
)

R(x) = P(x)Q(x)

for some polynomial

Q
(
x
)

Q(x)

. It is the factor

Q
(
x
)

Q(x)

which concerns us here in case

β
\beta

is a Pisot number. It is known that all Pisot numbers are beta-numbers, and it has often been asked whether

Q
(
x
)

Q(x)

must be cyclotomic in this case, particularly if

1
>
β
>
2

1 > \beta > 2

. We answer this question in the negative by an examination of the regular Pisot numbers associated with the smallest 8 limit points of the Pisot numbers, by an exhaustive enumeration of the irregular Pisot numbers in

[
1
,
1.9324
]
∪
[
1.9333
,
1.96
]

[1,1.9324]\cup [1.9333,1.96]

(an infinite set), by a search up to degree

50
50

in

[
1.9
,
2
]

[1.9,2]

, to degree

60
60

in

[
1.96
,
2
]

[1.96,2]

, and to degree

20
20

in

[
2
,
2.2
]

[2,2.2]

. We find the smallest counterexample, the counterexample of smallest degree, examples where

Q
(
x
)

Q(x)

is nonreciprocal, and examples where

Q
(
x
)

Q(x)

is reciprocal but noncyclotomic. We produce infinite sequences of these two types which converge to

2
2

from above, and infinite sequences of

β
\beta

with

Q
(
x
)

Q(x)

nonreciprocal which converge to

2
2

from below and to the

6
6

th smallest limit point of the Pisot numbers from both sides. We conjecture that these are the only limit points of such numbers in

[
1
,
2
]

[1,2]

. The Pisot numbers for which

Q
(
x
)

Q(x)

is cyclotomic are related to an interesting closed set of numbers

F

\mathcal {F}

introduced by Flatto, Lagarias and Poonen in connection with the zeta function of

T
T

. Our examples show that the set

S
S

of Pisot numbers is not a subset of

F

\mathcal {F}

.
Segmentation of yeast DNA using hidden Markov models
Authors: Peshkin Leonid , S.Gelfand Mikhail
Published: July 2002

Motivation: Compositionally homogeneous segments of genomic DNA often correspond to meaningful biological units. Simple sliding window analysis is usually insufficient for compositional segmentation of natural sequences. Hidden Markov models (HMM) with a small number of states are a natural language for description of compositional properties of chromosome-size DNA sequences.

Results: The algorithms were applied to yeast Saccharomyces cerevisiae chromosomes (YC) I, III, IV, VI and IX. The optimal number of HMM states is found to be four. The optimal four-state HMMs for all chromosomes are very similar, as well as the reconstructed segmentations. In most cases the models with k + 1 states are obtained by ‘splitting’ one of the states in the model with k states, and the corresponding increase of the level of detail in segmentation. The high AT states usually correspond to intergenic regions. We also explore the model’s likelihood landscape and analyze the dynamics of the optimization process, thus addressing the problem of reliability of the obtained optima and efficiency of the algorithms.

Availability: The system is available on request from the first author.

Contact: ldp@cs.brown.edu
On the complexity measures of genetic sequences
Authors: D.Gusev Vladimir , A.Nemytikova Lubov , A.Chuzhanova Nadia
Published: July 2002

Motivation: It is well known that the regulatory regions of genomes are highly repetitive. They are rich in direct, symmetric and complemented repeats, and there is no doubt about the functional significance of these repeats. Among known measures of complexity, the Ziv–Lempel complexity measure reflects most adequately repeats occurring in the text. But this measure does not take into account isomorphic repeats. By isomorphic repeats we mean fragments that are identical (or symmetric) modulo some permutation of the alphabet letters.

Results: In this paper, two complexity measures of symbolic sequences are proposed that generalize the Ziv–Lempel complexity measure by taking into account any isomorphic repeats in the text (rather than just direct repeats as in Ziv–Lempel). The first of them, the complexity vector, is designed for small alphabets such as the alphabet of nucleotides. The second is based on a search for the longest isomorphic fragment in the history of sequence synthesis and can be used for alphabets of arbitrary cardinality. These measures have been used for recognition of structural regularities in DNA sequences. Some interesting structures related to the regulatory region of the human growth hormone are reported.

Availability: Available on request from the authors.

Contact: gusev@math.nsc.ru; nadia.chuzhanova@cs.cf.ac.uk
GPI‐anchored proteins: now you see ’em, now you don’t
Authors: BÜTIKOFER PETER , MALHERBE TATIANA , BOSCHUNG MONIKA , RODITI ISABEL
Published: July 2002

Many cell surface proteins are attached to membranes via covalent glycosylphosphatidylinositol (GPI) anchors that are posttranslationally linked to the carboxy‐terminus of the protein. Removal of the GPI lipid moieties by enzymes such as GPI‐specific phospholipases or by chemical treatments generates a soluble form of the protein that no longer associates with lipid bilayers. We have found that the removal of lipid moieties from the anchor can also have a second, unexpected effect on the antigenicity of a variety of GPI‐anchored surface molecules, suggesting that they undergo major conformational changes. Several antibodies raised against GPI‐anchored proteins from protozoa and mammalian cells were no longer capable of binding the corresponding antigens once the lipid moieties had been removed. Conversely, antibodies raised against soluble (delipidated) forms reacted poorly with intact GPI‐anchored proteins, but showed enhanced binding after treatment with phospholipases. In the light of these findings, we have reevaluated a number of publications on GPI‐anchored proteins. Many of the results are best explained by lipid‐dependent changes in antigenicity, indicating this might be a widespread phenomenon. Since many pathogen surface proteins are GPI‐anchored, researchers should be aware that the presence or absence of the GPI lipid moieties may have a major impact on the host immune response to infection or vaccination.—Bütikofer, P., Malherbe, T., Boschung, M., Roditi, I. GPI‐anchored proteins: now you see 'em, now you don't. FASEB J. 15, 545–548 (2001)
An acoustic/thermal model for self-heating in PMN sonar projectors
Authors: Shankar Natarajan , Hom Craig L.
Published: July 2002

Dielectric hysteresis and a strong material temperature dependence uniquely couple the acoustic output and temperature of a sonar projector driven by electrostrictive Pb(Mg1/3, Nb2/3)O3 (PMN). Both the source level and the source of self-heating, i.e., dielectric hysteresis, dramatically decrease as the PMN driver heats. The final temperature delineates outstanding PMN transducers from mediocre PMN transducers, so accurate acoustic performance prediction requires accurate transducer temperature prediction. This study examined this self-heating phenomenon by combining an electro-acoustics model for a PMN flextensional transducer with a thermal finite element model. The sonar model calculated the source level and heat generation rate for the PMN driver as a function of temperature. This computed source level varied 12 dB over a 75 °C temperature range solely due to the temperature dependent ceramic. The heat transfer model used the computed heat rate to predict the transducer’s transient thermal response. The results clearly demonstrate that the transducer reached a steady-state equilibrium temperature, where the heat generated by the PMN driver balanced the heat dissipated. While the transducer model predicted a significant temperature rise, the corresponding acoustic output still surpassed the output of an equivalent Pb(Zr, Ti)O3 (PZT) transducer by 8 dB. Good agreement with experiments made on a PMN flextensional transducer validated the model.
Investigating perceptual features of electrode stimulation via a multidimensional scaling paradigm
Authors: Collins Leslie M. , Throckmorton Chandra S.
Published: July 2002

To achieve the most effective speech processing for individuals with cochlear implants, it is important to understand the perceptual features associated with the stimulation parameters. In general, when electrodes are stimulated in order from apex to base, the pitch of the perceived sound changes in an orderly fashion from low to high. Some deviations from this assumed order have been documented. Also, pitch is the dominant perceptual attribute of a sound when the stimuli associated with different electrodes have been accurately loudness balanced. In this study, the results of a multidimensional scaling (MDS) paradigm were compared to the results of a pitch-ranking procedure for six subjects implanted with multichannel cochlear prostheses. Results indicate that there may be multiple percepts that change with electrode location. Not surprisingly, the dominant percept is strongly correlated with pitch. The results also indicate that the structure of the second percept is consistent across subjects, although not interpretable using the data measured in this study. Furthermore, results indicate that MDS data can be used to pinpoint indiscriminable electrodes more accurately than pitch data. The results of this study may have importance for the design of the next generation of speech processors.
Transverse curvature of the acoustic slowness surface in crystal symmetry planes and associated phonon focusing cusps
Authors: Shuvalov A. L. , Every A. G.
Published: July 2002

Conditions are derived for the existence of focusing cusps in ballistic phonon intensity patterns for propagation directions in crystal symmetry planes. Line caustics are known to be associated with lines of vanishing Gaussian curvature (parabolic lines) on the acoustic slowness surface, while cusps are associated specifically with points where the direction of vanishing principal curvature is parallel to the parabolic line. A parabolic line meets a crystal symmetry plane σ at a right angle, and so it is the vanishing of the slowness-surface curvature transverse to σ that conditions the existence of a cusp. A relation for the transverse curvature is derived and analyzed. It is shown that in an arbitrary symmetry plane σ there may be up to four pairs of inversion-equivalent cuspidal points for SH (out-of-plane polarized) waves, and up to eight pairs of cuspidal points associated with the in-plane polarized (usually quasi-transverse) waves. In tetragonal crystals, the symmetry planes containing the four-fold axis can have at most two pairs of cusps for the SH waves and up to six pairs of cusps for the in-plane waves. In cubic crystals, the face symmetry planes σ cannot have cuspidal points for SH waves, as is known, while four pairs of cusps for in-plane waves exist in σ if and only if the outer-most slowness sheet has a concave region embracing the four-fold axis. The points of vanishing transverse curvature on the slowness surface in symmetry planes of tetragonal and cubic media are identified by concise relations, facilitating their explicit analysis.
Wideband reflectance tympanometry in chinchillas and humans
Authors: Margolis Robert H. , Paul Saurav , Saly George L. , Schachern Patricia A. , Keefe Douglas H.
Published: July 2002

Wideband reflectance tympanometry was performed on twelve chinchillas ears. The complex input impedance of the middle ear, multifrequency admittance tympanograms, reflectance patterns (reflectance versus frequency), and reflectance tympanograms (reflectance versus ear-canal air pressure) were analyzed and compared to human data. The complex impedance of the chinchilla ear has a lower stiffness reactance at low frequencies, a higher mass reactance at high frequencies, and a lower resistance compared to the human. Multifrequency admittance tympanograms from chinchillas follow the same sequence of patterns as humans for low frequencies (<2 kHz). At higher frequencies tympanograms from both species are poorly organized and do not follow a consistent sequence of patterns. Reflectance patterns of chinchillas and humans are different. However, both species show high reflectance at low frequencies, regions of lower reflectance in mid-frequencies (2–6 kHz), and high reflectance at high frequencies (>8 kHz). Reflectance tympanograms for the two species show a single, centrally located minimum at low frequencies (<2 kHz) and are substantially different at higher frequencies. Results are shown for two animals that underwent eustachian tube obstruction. Reflectance patterns obtained with different ear-canal air pressures are substantially different. Reflectance results at any single ear-canal pressure (including ambient pressure) do not completely characterize the effects of middle-ear pathology.
The variation across time of sensitivity to interaural disparities: Behavioral measurements and quantitative analyses
Authors: Akeroyd Michael A. , Bernstein Leslie R.
Published: July 2002

Zurek (1980) measured listeners’ sensitivities to interaural disparities conveyed by a 5-ms “probe” segment embedded within a 50-ms burst of otherwise diotic broadband noise [P. M. Zurek, J. Acoust. Soc. Am. 67, 952–964 (1980)]. He found that thresholds for interaural time delay (ITD) and interaural intensitive difference (IID) were markedly elevated when the onset of the probe segment occurred between 1 and 5 ms after the onset of the burst. Zurek postulated that this occurred because the leading portion of the noise briefly inhibited sensitivity to subsequent binaural information. If such inhibition were the primary factor responsible for the elevation in thresholds, then the omission of the portion of the noise trailing the probe segment would be expected to have little, if any, influence on performance. In order to test this hypothesis, listeners’ sensitivities to ITD and IID were measured using a paradigm similar to that employed by Zurek. The results revealed that the omission of either the leading or the trailing portions of the diotic noise led to substantial reductions in threshold ITDs and IIDs. The data were successfully accounted for by a model based upon a combination of a temporal window with an equivalent rectangular duration of approximately 10 ms and a weighting function representing a brief loss of binaural sensitivity just after the onset of a sound.
Performance of a low-frequency, multi-resonant broadband Tonpilz transducer
Authors: Rajapan Dhilsha
Published: July 2002

The underwater performance of a high-power multi-resonant Tonpilz transducer with a nearly flat frequency response and a power handling capability of 2 kW (peak) is reported here. A maximum transmitting voltage response (TVR) value of 156 dB re: 1 μPa/V at 1 m has been achieved at 3 kHz with a specially designed matching coil. A maximum receiving sensitivity (RS) of −164 dB re: 1 V/μPa at 3 kHz has been measured without using a matching coil. The horizontal half-power beam width of the transducer at 4 kHz is 101 degrees with a directivity index of 4 dB. This transmitter can be used for oceanographic applications such as subbottom profiling as well as long-range underwater communication.
Viscous effects on the interaction force between two small gas bubbles in a weak acoustic field
Authors: Doinikov Alexander A.
Published: July 2002

The relative motion of two gas bubbles in an acoustic field is investigated by calculating the time-averaged interaction force known as the secondary Bjerknes force. The surrounding medium is assumed to be an incompressible viscous liquid and the separation distance between the bubbles much larger than their radii. A refined formula for the interaction force is derived, which allows for translational oscillations of the bubbles, the vorticity of the linear scattered field, and acoustic streaming. The boundary condition of slippage on the gas–liquid interface is assumed. It is shown that viscous effects can cause small bubbles, driven well below resonance, to repel each other within a relatively wide parameter range. This result discloses a significant boundedness of the classical Bjerknes theory according to which bubbles of this sort are capable of mutual attraction alone.
Vibration measurement of the tympanic membrane of guinea pig temporal bones using time-averaged speckle pattern interferometry
Authors: Wada Hiroshi , Ando Masayoshi , Takeuchi Masataka , Sugawara Hironori , Koike Takuji , Kobayashi Toshimitsu , Hozawa Koji , Gemma Takashi , Nara Makoto
Published: July 2002

“Time-averaged holography” and “holographic interferometry” enable recording of the complete vibration pattern of a surface within several seconds. The results appear in the form of fringes. Vibration amplitudes smaller than 100 nm are not readily measurable by these techniques, because such small amplitudes produce variations in gray level, but not fringes. In practice, to obtain clear fringes in these measurements, stimulus sound pressures higher than 100 dB SPL must be used. The phase of motion is also not obtainable from such fringe techniques. In this study, a sinusoidal phase modulation technique is described, which allows detection of both small amplitudes of motion and their phase from time-averaged speckle pattern interferometry. In this technique, the laser injection current is modulated and digital image processing is used to analyze the measured patterns. When the sound-pressure level of stimuli is between 70 and 85 dB SPL, this system is applied to measure the vibratory response of the tympanic membrane (TM) of guinea pig temporal bones at frequencies up to 4 kHz where complicated vibration modes are observed. The effect of the bulla on TM displacements is also quantified. Results indicate that this system is capable of measuring the nanometer displacements of the TM, produced by stimuli of 70 dB SPL.
Optimal undercuts for the tuning of percussive beams
Authors: Petrolito J. , Legge K. A.
Published: July 2002

The paper investigates the use of optimization techniques for the design of percussive beams. Profiles were generated to satisfy predetermined overtone tunings and specified optimization criteria. It is shown that there is no unique solution to the problem, and that the generated profiles need not be the same as traditionally used profiles. The vibration of the beams was modeled using a thick beam theory to take into account the possible effects of shear deformation on the natural frequencies. A number of beams were manufactured with the generated profiles, and their frequency characteristics were obtained experimentally. The experimental results confirm the validity of the numerically generated profiles.
Cochlear models and minimum phase
Authors: de Boer Egbert
Published: July 2002

In this paper the extent to which the response of a linear cochlear model has the “minimum-phase” property is discussed, along with the topic of what it should mean when experiments confirm or deny the validity of minimum-phase in the response of the actual cochlea. This paper shows that short-wave, long-wave and three-dimensional cochlear models of the “classical” type, in which the operation of the cochlear partition is described by a local function (namely, a driving-point impedance) that produces a cochlear map (from frequency to place), have a response that is minimum-phase, or very close to minimum-phase. Conversely, when the response is found to be non-minimum-phase, the best-fitting model cannot be a classical one.
Solitary waves and solitons in acoustics
Authors: Sugimoto Nobumasa
Published: July 2002

This study reports on the propagation of acoustic solitary waves and solitons in ordinary air. In theory, it can be predicted by using a long and rigid tube with an array of Helmholtz resonators (or more generally, compact and closed side branches) connected to it with equal axial spacing. In the framework of nonlinear acoustics, the theory exploits three assumptions: (1) a plane wave over the tube, (2) continuum approximation for the array, and (3) negligibly small dissipation. It can be shown that solitary waves are compressive, that their speed is subsonic but faster than a threshold value determined by the array, and that the solitary waves tend to solitons of Korteweg–de Vries type asymptotically as the speed approaches the threshold. Thus it may be possible to implement a ‘‘soliton tube.’’ As the speed approaches the linear speed of sound, the height of the solitary waves becomes greater, approaching the limiting value. Discussions are given on amplification of solitary waves and also on solitary waves in a tube with a double array of resonators.
Measurement of grain bulk modulus using sound speed measurements through liquid/grain suspensions
Authors: Briggs Kevin , Richardson Michael , Williams Kevin , Thorsos Eric
Published: July 2002

Under certain conditions, Woods equation can be used to predict the speed of sound in liquid/solid grain suspensions when the bulk moduli and densities of the grains and the liquid are known. Alternatively, if the sound speed is measured through a suspension where the bulk modulus of the liquid and the densities of the fluid and grains are known, it is possible to estimate the grain bulk modulus. An experiment was carried out as an initial test of the resolution of measuring grain bulk modulus via this method. Bulk modulus measurements were made of polystyrene beads suspended in water, and of glass beads and sand grains suspended in a high-density liquid. The polystyrene and glass beads had known bulk moduli (4.2e9 and 6.3e10 Nt/m2, respectively) and acted as controls. The polystyrene (glass) bead radii were such that the mean ka was 0.42 (0.25), where k is the acoustic wave number in the liquid and a is the bead radius. Corrections to Woods equation are considered as ka approaches 1. The sand grain modulus results are discussed in the context of porous media sediment models. Planned experimental improvements will be discussed. [Work supported by ONR.]
Modeling nonlinearity in electrostrictive sonar transducers
Authors: Hom Craig L. , Shankar Natarajan
Published: July 2002

Electrostrictive driver materials with large strain capability hold great promise for the advancement of sonar projector technology. However, the nonlinear induced strain of these materials can create acoustic distortion in transducers through higher-order harmonics. Electrostrictors also possess complicated prestress and temperature dependencies, and an elastic modulus that depends strongly on electric field. This investigation examined these issues with a nonlinear, frequency domain model for a flextensional transducer powered by an electrostrictive stacked actuator. A simple, linear lumped-parameter model of a flextensional shell and its surrounding acoustic medium were combined with a nonlinear model of the electrostrictive driver. This model accounted for the material’s nonlinear dependencies and behavior. Predictions of the device’s acoustic/electric response during operation compared favorably with experiments performed on a single element flextensional transducer. The model’s results showed that proper adjustment of the power supply’s parameters minimizes the level of distortion without completely sacrificing the transducer’s improved source level.
Influence of speech stimuli intensity on the activation of auditory cortex investigated with functional magnetic resonance imaging
Authors: Mohr Cécile M. , King Wayne M. , Freeman Alan J. , Briggs Richard W. , Leonard Christiana M.
Published: July 2002

Understanding the impact of variations in the acoustic signal is critical for the development of auditory and language fMRI as an experimental tool. We describe the dependence of the BOLD signal and speech intelligibility on the intensity of auditory stimuli. Eighteen subjects were imaged on a 1.5-T MRI scanner. Speech stimuli were English monosyllabic words played at five intensity levels. Intrasubject reproducibility was measured on one subject by presenting the stimulus five times at the same intensity level. Intelligibility was measured during data acquisition as subjects signaled when hearing two targets. Each functional trial consisted of four cycles (30 s off–30 s on). Five oblique slices covering primary and association auditory areas were imaged. Activated voxels were identified by cross-correlation analysis and their percent signal change (ΔS) was measured. Intersubject differences in activation extent, asymmetry, and dependence on intensity were striking. Volume of activation was significantly greater in the left than in the right hemisphere. Intrasubject reproducibility for ΔS was higher than for volume of activation. ΔS and intelligibility showed a similar dependence on intensity suggesting that not only intensity but also intelligibility affect the fMRI signal.
Effects of aspirin on psychophysical measures of frequency selectivity, two-tone suppression, and growth of masking
Authors: Hicks Michelle L. , Bacon Sid P.
Published: July 2002

Three psychophysical measures of nonlinearity were evaluated before and during a course of aspirin ingestion to investigate the role of outer hair cells (OHCs) in these measures, as aspirin is thought to alter the functioning of OHCs. Six normal-hearing individuals received a moderate dose (3.9 g/day) of aspirin for four days, producing essentially flat, temporary hearing losses that ranged from 5–20 dB. The losses were about 2 dB greater for a 300-ms signal than for a 15-ms signal, indicating reduced temporal integration with aspirin. On the final three days of aspirin use, three experiments were completed; each was designed to measure one aspect of nonlinear behavior: (1) the effects of level on frequency selectivity in simultaneous masking using notched-noise maskers, (2) two-tone suppression using forward maskers at the signal frequency (fs) and suppressor tones above fs, and (3) growth-of-masking functions in forward masking using a masking tone below fs. Signal frequencies of 750 and 3000 Hz were used to evaluate the effects of aspirin at relatively low- and high-frequency regions of the cochlea. In experiment 1, aspirin broadened the auditory filters and reduced the effect of level on frequency selectivity. In experiment 2, aspirin reduced or eliminated two-tone suppression. And, in experiment 3, aspirin reduced the slopes of the growth-of-masking functions. Thus, the aspirin was effective in reducing nonlinearity in all three experiments, suggesting that these measures reflect the same (or a similar) active, nonlinear mechanism, namely the compressive nonlinearity provided by the OHCs. In all experiments, aspirin tended to have larger detrimental effects on the nonlinear measures at 3000 Hz than at 750 Hz, which can be explained in terms of greater involvement of nonlinear processing at higher frequencies. Finally, these effects of aspirin were found to be similar to those observed in preliminary measurements in two subjects with mild, permanent hearing loss.
Perception of coarticulatory nasalization by speakers of English and Thai: Evidence for partial compensation
Authors: Beddor Patrice Speeter , Krakow Rena Arens
Published: July 2002

The conditions under which listeners do and do not compensate for coarticulatory vowel nasalization were examined through a series of experiments of listeners’ perception of naturally produced American English oral and nasal vowels spliced into three contexts: oral (C_C), nasal (N_N), and isolation. Two perceptual paradigms, a rating task in which listeners judged the relative nasality of stimulus pairs and a 4IAX discrimination task in which listeners judged vowel similarity, were used with two listener groups, native English speakers and native Thai speakers. Thai and English speakers were chosen because their languages differ in the temporal extent of anticipatory vowel nasalization. Listeners’ responses were highly context dependent. For both perceptual paradigms and both language groups, listeners were less accurate at judging vowels in nasal than in non-nasal (oral or isolation) contexts; nasal vowels in nasal contexts were the most difficult to judge. Response patterns were generally consistent with the hypothesis that, given an appropriate and detectable nasal consonant context, listeners compensate for contextual vowel nasalization and attribute the acoustic effects of the nasal context to their coarticulatory source. However, the results also indicated that listeners do not hear nasal vowels in nasal contexts as oral; listeners retained some sensitivity to vowel nasalization in all contexts, indicating partial compensation for coarticulatory vowel nasalization. Moreover, there were small but systematic differences between the native Thai- and native English-speaking groups. These differences are as expected if perceptual compensation is partial and the extent of compensation is linked to patterns of coarticulatory nasalization in the listeners’ native language.
Basilar-membrane nonlinearity estimated by pulsation threshold
Authors: Plack Christopher J. , Oxenham Andrew J.
Published: July 2002

The pulsation threshold technique was used to estimate the basilar-membrane (BM) response to a tone at characteristic frequency (CF). A pure-tone signal was alternated with a pure-tone masker. The frequency of the masker was 0.6 times that of the signal. For signal levels from around 20 dB above absolute threshold to 85 dB SPL, the masker level was varied to find the level at which a transition occurred between the signal being perceived as “pulsed” or “continuous” (the pulsation threshold). The transition is assumed to occur when the masker excitation is somewhat greater than the signal excitation at the place on the BM tuned to the signal. If it is assumed further that the response at this place to the lower-frequency masker is linear, then the shape of the masking function provides an estimate of the BM response to the signal. Signal frequencies of 0.25, 0.5, 1, 2, 4, and 8 kHz were tested. The mean slopes of the masking functions for signal levels between 50 and 80 dB SPL were 0.76, 0.50, 0.34, 0.32, 0.35, and 0.41, respectively. The results suggest that compression on the BM increases between CFs of 0.25 and 1 kHz and is roughly constant for frequencies of 1 kHz and above. Despite requiring a subjective criterion, the pulsation threshold measurements had a reasonably low variability. However, the estimated compression was less than in an earlier study using forward masking. The smaller amount of compression observed here may be due to the effects of off-frequency listening.
Modeling the temporal behavior of distortion product otoacoustic emissions
Authors: Tubis Arnold , Talmadge Carrick L. , Tong Christopher
Published: July 2002

The temporal behavior of the 2f1−f2 distortion product otoacoustic emission is theoretically investigated for the case in which the lower frequency (f1) primary tone is on continuously, and the higher frequency (f2) one is pulsed on and off [e.g., Talmadge et al., J. Acoust. Soc. Am. 105, 275–292 (1999)]. On physical grounds, this behavior is expected to be characterized by various group delays associated with the propagation of (1) the f2 cochlear primary wave between the cochlear base and the primary distortion product generation region around x̂2 (the f2 tonotopic place), and (2) the 2f1−f2 cochlear distortion product (DP) waves between the cochlear base, the primary generation region of the distortion product, and the region around the 2f1−f2 tonotopic place where the generated apical moving DP wave is reflected toward the cochlear base [e.g., Talmadge et al., J. Acoust. Soc. Am. 104, 1517–1543 (1998)]. An approximate analytic expression is obtained for this behavior from the analysis of the Fourier integral representation of the auditory peripheral response to the primary stimuli. This expression also approximately describes the transient build-up of the components of different latencies in terms of the damping properties of the cochlear partition. It is shown that considerable caution must be applied in attempting to relate phase derivatives of the distortion product otoacoustic emissions for steady state stimuli and the physical time delays which are associated with the temporal behavior of a distortion product emission in the case of a pulsed primary.
Time patterns of sperm whale codas recorded in the Mediterranean Sea 1985–1996
Authors: Pavan G. , Hayward T. J. , Borsani J. F. , Priano M. , Manghi M. , Fossati C. , Gordon J.
Published: July 2002

A distinctive vocalization of the sperm whale, Physeter macrocephalus (=P. catodon), is the coda: a short click sequence with a distinctive stereotyped time pattern [Watkins and Schevill, J. Acoust. Soc. Am. 62, 1485–1490 ()]. Coda repertoires have been found to vary both geographically and with group affiliation [Weilgart and Whitehead, Behav. Ecol. Sociobiol. 40, 277–285 ()]. In this work, the click timings and repetition patterns of sperm whale codas recorded in the Mediterranean Sea are characterized statistically, and the context in which the codas occurred are also taken into consideration. A total of 138 codas were recorded in the central Mediterranean in the years 1985–1996 by several research groups using a number of different detection instruments, including stationary and towed hydrophones, sonobuoys and passive sonars. Nearly all (134) of the recorded codas share the same “3+1” (/// /) click pattern. Coda durations ranged from 456 to 1280 ms, with an average duration of 908 ms and a standard deviation of 176 ms. Most of the codas (a total of 117) belonged to 20 coda series. Each series was produced by an individual, in most cases by a mature male in a small group, and consisted of between 2 and 16 codas, emitted in one or more “bursts” of 1 to 13 codas spaced fairly regularly in time. The mean number of codas in a burst was 3.46, and the standard deviation was 2.65. The time interval ratios within a coda are parameterized by the coda duration and by the first two interclick intervals normalized by coda duration. These three parameters remained highly stable within each coda series, with coefficients of variation within the series averaging less than 5%. The interval ratios varied somewhat across the data sets, but were highly stable over 8 of the 11 data sets, which span 11 years and widely dispersed geographic locations. Somewhat different interval ratios were observed in the other three data sets; in one of these data sets, the variant codas were produced by a young whale. Two sets of presumed sperm whale codas recorded in 1996 had 5- and 6-click patterns; the observation of these new patterns suggests that sperm whale codas in the Mediterranean may have more variations than previously believed.
Categorization of rheological scaling models for particle gels applied to casein gels
Authors: Mellema M. , van Opheusden J. H. J. , van Vliet T.
Published: July 2002

Rennet-induced casein gels made from skim milk were studied rheologically. A scaling model or framework for describing the rheological behavior of gels is discussed and used for classification of the structure of casein gels. There are two main parameters in the model that describe the number of deformable links in a strand and the bendability of the links. In the model at least five types of gel structure can be distinguished. Application of the model to experimental data on rennet-induced casein gels at pH of 6.0–6.6 and 25 °C shows that they contain straight strands with a large number of deformable links. Analysis of the experimental data of the storage modulus, maximum linear strain and yield stress as a function of the volume fraction results in the same information about the gel structure.
Travel Time Reliability
Authors: Karr Alan F.
Published: May 2022

Travel time reliability connotes variability in travel times on roadway segments and routes, often measured by extreme percentiles of distributions derived from multiple data sources. Variability results from changes in demand (e.g., rush hours and special events) or supply (e.g., weather, work zones, and traffic signals). Estimates of travel time reliability support informed departure decisions and route selection by drivers as well as interventions and design choices by system operators.
Design Method of the Conformal Lattice Structures
Authors: Liu Yabo , Qu Zhipeng , Li Yongfeng
Published: May 2022

Lattice structures have superior mechanical properties, however the structures in practical engineering cannot be directly filled with periodic lattice structures because of their special‐shaped surface profile, which also restricts its practical application. Herein this work, a mapping design method of conformal lattice structures is proposed considering the part's shape profiles with different characteristics. The main idea behind this method is inspired from isoparametric element in finite element method (FEM), an irregular domain can be meshed and solved with arbitrary quadratic element by mapping the element from a regular element. By introducing geometric transformation into the design of lattice structures, lattice unit cell in irregular volume can be achieved through mapping from the regular lattice unit cell, which will establish the conformal lattice structures rapidly. Then, the mechanical properties of regular and conformal lattice structures under three‐point bending are compared using FEM. Both the yield force and ultimate force of conformal lattice structures are increased by 45.83% and 15.03%, respectively. It is hoped that this work can make a contribution to the application of lattice structures in practical engineering with irregular geometric shape.
Controllable Design of Structural and Mechanical Behaviors of Al–Si Foams by Powder Metallurgy Foaming
Authors: Yang Xudong , Xie Mingrui , Li Weiting , Sha Junwei , Zhao Naiqin
Published: May 2022

Silicon (Si) has a significant influence on the cellular structure and microstructure of the aluminum (Al) foams, which in turn will notably affect their mechanical responses. Herein, the Al–Si foams are fabricated via a novel powder metallurgy foaming approaches with multiple Si contents to investigate the role of Si concentrations on the structural and mechanical properties. The results show that the certain contents of Si can not only delay the expansion process, but also increase the maximum expansion rate to improve the cellular structure. Specifically, the AlSi7 foams process the optimal comprehensive compressive properties of yield stress (4.36 MPa), plateau stress (6.02 MPa), and energy absorption capacity (3.47 MJ m−3) with the relative density of 0.15. However, excessive Si can decrease the expansion rate and deteriorate the cellular structure. Moreover, the deformation mode of the Al foams during compressive process converts from plastic mode to brittle mode by the adding of Si. Generally, the AlSi7 foams possess an excellent trade‐off between toughness and brittleness and exhibit the optimal mechanical responses.
Organic Ion Template‐Guided Solution Growth of Ultrathin Bismuth Oxyselenide with Tunable Electronic Properties for Optoelectronic Applications
Authors: Dang Le‐Yang , Liu Mingqiang , Wang Gui‐Gen , Zhao Da‐Qiang , Han Jie‐Cai , Zhu Jia‐Qi , Liu Zheng
Published: May 2022

2D Bi2O2Se has recently attracted widespread research interest due to its high electron mobility and good air stability with tunable bandgap. However, the direct and controllable growth of large‐size, high‐quality ultrathin Bi2O2Se with tunable electronic properties remains a great challenge. Here, an organic ion template‐guided solution growth method, is developed using water as a solvent to efficiently obtain high‐quality 2D Bi2O2Se. Significantly, the thicknesses and morphologies of 2D Bi2OxSe with various oxygen deficiencies; are also achieved. Optical spectroscopic results indicate that oxygen defects can dramatically tune the electronic properties of Bi2O2Se, such as work function, band gap, and energy‐band positions. As a result, the optimized Bi2O2Se devices exhibit a high photoresponsivity of 842.91 A W−1, photo‐detectivity of 8.18 × 1012 Jones under 532 nm laser, and electron mobility of 334.7 cm2 V−1 s−1. This work proposes a new green solution method to synthesize large‐sized, high‐quality Bi2O2Se with tunable electronic structures that can be extended for various applications and provides a new possibility of transfer‐free large‐scale device manufacturing.
Sulfone‐Incorporated Multi‐Resonance TADF Emitter for High‐Performance Narrowband Blue OLEDs with EQE of 32%
Authors: Hua Tao , Miao Jingsheng , Xia Han , Huang Zhongyan , Cao Xiaosong , Li Nengquan , Yang Chuluo
Published: May 2022

The blue multi‐resonance thermally activated delayed fluorescence materials, simultaneously realizing narrow full‐width at half‐maximum, high external quantum efficiency (EQE), and low efficiency roll‐off, remains a formidable challenge. Herein, three novel emitters, namely PTZBN1, PTZBN2, and PTZBN3, are designed by gradual peripheral modification in boron/nitrogen (B/N) embedded polycyclic skeleton, which exhibit progressively hypsochromic‐shifted emission from 490 nm (PTZBN1) to 468 nm (PTZBN3) with photoluminescence quantum yields up to 98%. In particular, the incorporation of sulfone unit in the boron/nitrogen (B/N) embedded polycyclic skeleton provides a simple but effective tactic for narrowband blue emission. The organic light‐emitting diodes based on PTZBN2 achieve one of the‐state‐of‐the‐art EQEs of 34.8% with electroluminescence (EL) peak at 478 nm. Impressively, PTZBN3‐based device exhibits not only a high maximum EQE of 32.0% with EL peak at 468 nm, but also low efficiency roll‐off.
Integrated Memory Devices Based on 2D Materials
Authors: Xue Fei , Zhang Chenhui , Ma Yinchang , Wen Yan , He Xin , Yu Bin , Zhang Xixiang
Published: May 2022

With the advent of the Internet of Things and big data, massive data must be rapidly processed and stored within a short timeframe. This imposes stringent requirements on memory hardware implementation in terms of operation speed, energy consumption, and integration density. To fulfill these demands, 2D materials, which are excellent electronic building blocks, provide numerous possibilities for developing advanced memory device arrays with high performance, smart computing architectures, and desirable downscaling. Over the past few years, 2D‐material‐based memory‐device arrays with different working mechanisms, including defects, filaments, charges, ferroelectricity, and spins, have been increasingly developed. These arrays can be used to implement brain‐inspired computing or sensing with extraordinary performance, architectures, and functionalities. Here, recent research into integrated, state‐of‐the‐art memory devices made from 2D materials, as well as their implications for brain‐inspired computing are surveyed. The existing challenges at the array level are discussed, and the scope for future research is presented.