bluuebunny/crossref_metadata_2025 huggingface dataset:
The "allosteric three-site model" of elongation cannot be confirmed in a well-defined ribosome system from Escherichia coli.
Authors: Semenkov Y P , Rodnina M V , Wintermeyer W
Published: July 2002

For the functional role of the ribosomal tRNA exit (E) site, two different models have been proposed. It has been suggested that transient E-site binding of the tRNA leaving the peptidyl (P) site promotes elongation factor G (EF-G)-dependent translocation by lowering the energetic barrier of tRNA release [Lill, R., Robertson, J. M. & Wintermeyer, W. (1989) EMBO J. 8, 3933-3938]. The alternative "allosteric three-site model" [Nierhaus, K.H. (1990) Biochemistry 29, 4997-5008] features stable, codon-dependent tRNA binding to the E site and postulates a coupling between E and aminoacyl (A) sites that regulates the tRNA binding affinity of the two sites in an anticooperative manner. Extending our testing of the two conflicting models, we have performed translocation experiments with fully active ribosomes programmed with heteropolymeric mRNA. The results confirm that the deacylated tRNA released from the P site is bound to the E site in a kinetically labile fashion, and that the affinity of binding, i.e., the occupancy of the E site, is increased by Mg2+ or polyamines. At conditions of high E-site occupancy in the posttranslocation complex, filling the A site with aminoacyl-tRNA had no influence on the E site, i.e., there was no detectable anticooperative coupling between the two sites, provided that second-round translocation was avoided by removing EF-G. On the basis of these results, which are entirely consistent with our previous results, we consider the allosteric three-site model of elongation untenable. Rather, as proposed earlier, the E site-bound state of the leaving tRNA is a transient intermediate and, as such, is a mechanistic feature of the classic two-state model of the elongating ribosome.
Mammalian phospholipase D: phosphatidylethanolamine as an essential component.
Authors: Nakamura S , Kiyohara Y , Jinnai H , Hitomi T , Ogino C , Yoshida K , Nishizuka Y
Published: July 2002

Bovine kidney phospholipase D (PLD) was assayed by measuring the formation of phosphatidylethanol from added radioactive phosphatidylcholine (PtdCho) in the presence of ethanol, guanosine 5'-[gamma-thio]triphosphate, ammonium sulfate, and cytosol factor that contained small GTP-binding regulatory proteins. The PLD enzyme associated with particulate fractions was solubilized by deoxycholate and partially purified by chromatography on a heparin-Sepharose column. This PLD preferentially used PtdCho as substrate. After purification, the enzyme per se showed little or practically no activity but required an additional factor for the enzymatic reaction. This factor was extracted with chloroform/methanol directly from particulate fractions of various tissues, including kidney, liver, and brain, and identified as phosphatidylethanolamine (PtdEtn), although this phospholipid did not serve as a good substrate. Plasmalogen-rich PtdEtn, dioleoyl-PtdEtn, and L-alpha-palmitoyl-beta-linoleoyl-PtdEtn were effective, but dipalmitoyl-PtdEtn was inert. Sphingomyelin was 30% as active as PtdEtn. The results suggest that mammalian PLD reacts nearly selectively with PtdCho in the form of mixed micelles or membranes with other phospholipids, especially PtdEtn.
In vitro
and
in vivo
characterization of novel mRNA motifs that bind special elongation factor SelB
Authors: Klug Stefanie J. , Hüttenhofer Alexander , Kromayer Matthias , Famulok Michael
Published: July 2002

The special elongation factor SelB of
Escherichia coli
promotes selenocysteine incorporation into formate dehydrogenases. This is thought to be achieved through simultaneous binding to selenocysteyl-tRNA
Sec
and, in the case of formate dehydrogenase H, to an
fdhF
mRNA hairpin structure 3′ adjacent to the UGA selenocysteine codon. By
in vitro
selection, novel RNA sequences (“aptamers”), which can interact tightly and specifically with SelB, were isolated from an RNA library. The library was comprised of mutagenized variants of the wild-type
fdhF
mRNA hairpin. One-half of the selected sequences contained the apical stem–loop of the
fdhF
mRNA hairpin highly conserved. Some of the aptamers showed deviations in the primary sequence within this region of the wild-type
fdhF
hairpin motif while still binding with high affinity to SelB. Binding studies performed with truncated versions of SelB revealed that aptamers binding to different sites on the protein have been selected. To dissect SelB binding to the
fdhF
hairpin from the overall biological function of this complex, four selected aptamers were analyzed
in vivo
for UGA readthrough in a
lacZ
fusion construct. Among these, one promoted UGA readthrough
in vivo
. Three of the aptamers, however, were drastically reduced or unable to replace the
fdhF
mRNA hairpin
in vivo
, despite the similar secondary structure and binding affinities of these RNAs compared with the wild-type motif. This finding implies functions of the
fdhF
hairpin that go beyond the mere tethering of selenocysteyl-tRNA
Sec
to the UGA codon.
CooB plays a chaperone-like role for the proteins involved in formation of CS1 pili of enterotoxigenic
Escherichia coli
Authors: Voegele Karl , Sakellaris Harry , Scott June R.
Published: July 2002

CS1 pili serve as the prototype of a class of filamentous appendages found on the surface of strains of enterotoxigenic
Escherichia coli
. The four genes needed to synthesize functional CS1 pili in
E. coli
K12 are:
cooA
, which encodes the major pilin protein;
cooD
, which encodes a minor pilin protein found at the tip of the structure;
cooC
, which encodes a protein found in the outer membrane of piliated bacteria; and
cooB
. We show here that CooB, which is required for pilus assembly but is not part of the final structure, stabilizes CooA, CooC, and CooD. We previously reported that CooB is complexed with CooA in the periplasm and show here that CooB also is found complexed with CooD in the periplasm. CooB is associated with the membrane fraction only in the presence of CooC, suggesting that these two proteins also interact. This suggests that although it has no homology to known chaperone proteins, CooB serves a chaperone-like role for assembly of CS1.
Direct mapping of an agonist-binding domain within the parathyroid hormone/parathyroid hormone-related protein receptor by photoaffinity crosslinking
Authors: Zhou Alice T. , Bessalle Roberto , Bisello Alessandro , Nakamoto Chizu , Rosenblatt Michael , Suva Larry J. , Chorev Michael
Published: July 2002

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are calciotropic hormones interacting with a shared seven-transmembrane domain G protein-coupled receptor, which is located predominantly in bone and kidney. To map the interface of the bimolecular interaction between hormone and receptor, we designed and radioiodinated a bioactive, photoreactive PTH agonist,
125
I-[Nle
8,18
,Lys
13
(ɛ-
p
-(3-I-Bz)Bz),
l
-2-Nal
23
,Arg
26,27
,Tyr
34
]bPTH-(1–34)NH
2
(
125
I-all-R-K13). This ligand contains a photoreactive benzophenone moiety attached to the side chain of Lys
13
. All other lysyl residues are substituted by argynyls. The analog photocrosslinks specifically to the recombinant hPTH/PTHrP receptor stably transfected into human embryonic kidney cells (HEK-293/C-21 cells, ≈400,000 receptors per cell), generating a diffuse ≈87-kDa band on SDS/PAGE autoradiography. To identify the “contact domain” within the hPTH/PTHrP receptor involved in binding of
125
I-all-R-K13, the radiolabeled band containing the ligand–receptor conjugate was subjected to chemical and enzymatic cleavage. Two independent pathways of sequential digestion were used: Route A, lysyl endopeptidase C, then endo-N-glycosidase F, followed by cyanogen bromide; Route B, cyanogen bromide followed by endo-
N
-glycosydase F. The identified domain is in contact with position 13 in
125
I-all-R-K13 and corresponds to amino acids 173–189 of the hPTH/PTHrP receptor, located at the C-terminal region of the N-terminal extracellular domain.
Heteroduplex joint formation in
Escherichia coli
recombination is initiated by pairing of a 3′-ending strand
Authors: Friedman-Ohana Rachel , Cohen Amikam
Published: July 2002

The formation of heteroduplex joints in
Escherichia coli
recombination is initiated by invasion of double-stranded DNA by a single-stranded homologue. To determine the polarity of the invasive strand, linear molecules with direct terminal repeats were released by
in vivo
restriction of infecting chimeric phage DNA and heteroduplex products of intramolecular recombination were analyzed. With this substrate, the invasive strand is expected to be incorporated into the circular crossover product and the complementary strand is expected to be incorporated into the reciprocal linear product. Strands of both polarities were incorporated into heteroduplex structures, but only strands ending 3′ at the break were incorporated into circular products. This result indicates that invasion of the 3′-ending strand initiates the heteroduplex joint formation and that the complementary 5′-ending strand is incorporated into heteroduplex structures in the process of reciprocal strand exchange. The polarity of the invasive strand was not affected by
recD, recJ
, or
xonA
mutations. However,
xonA
and
recJ
mutations increased the proportion of heteroduplexes containing 5′-ending strands. This observation suggests that RecJ exonuclease and exonuclease I may enhance recombination by degrading the displaced strands during branch migration and thereby causing strand exchange to be unidirectional.
An N-terminal fragment of the gene 4 helicase/primase of bacteriophage T7 retains primase activity in the absence of helicase activity
Authors: Frick David N. , Baradaran Khandan , Richardson Charles C.
Published: July 2002

Primase and helicase activities of bacteriophage T7 are present in a single polypeptide coded by gene 4. Because the amino terminal region of the gene 4 protein contributes to primase activity, we constructed a truncated gene 4 encoding the N-terminal 271-aa residues. The truncated protein, purified from cells overexpressing the protein, is a dimer in solution; the full-length protein is a hexamer. Although the fragment is devoid of dTTPase and helicase activities, it catalyzes template-directed synthesis of di-, tri-, and tetranucleotides. The rates for tetraribonucleotide synthesis and for dinucleotide extension on a 20-nucleotide template are similar for the full-length and truncated proteins. However, the activity of the primase fragment is unaffected by dTTP whereas the primase activity of the full-length protein is stimulated >14-fold. The primase fragment is defective in the interaction with T7 DNA polymerase in that primer synthesis cannot be coupled to DNA synthesis.
Proton exit from the heme–copper oxidase of
Escherichia coli
Authors: Puustinen Anne , Wikström Mårten
Published: July 2002

Pathways of proton entry have been identified in the proton-translocating heme–copper oxidases, but the proton exit pathway is unknown. Here we report experiments with cytochrome
bo
3
in
Escherichia coli
cells that may identify the beginning of the exit pathway. Systematic mutations of arginines 438 and 439 (R481 and R482 in the
E. coli
enzyme), numbering as in cytochrome
aa
3
from bovine heart mitochondria, which interact with the ring D propionates of the two heme groups, reveal that the D propionate of the oxygen-binding heme is involved in proton pumping; its anionic form must be stabilized in order for proton translocation to occur. This may locate the beginning of the pathway by which pumped protons exit from the enzyme structure.
Characterization of bone quality using computer‐extracted radiographic features
Authors: Jiang Chunsheng , Giger Maryellen L. , Chinander Michael R. , Martell John M. , Kwak Sandy , Favus Murray J.
Published: July 2002

Both bone mineral density (BMD) and trabecular structure are important determinates of bone mechanical properties. However, neither BMD or trabecular structural features can completely explain the variations in bone mechanical properties. In this study, we combine BMD and bone structural features to characterize bone mechanical behavior. Radiographs were obtained from 34 femoral neck specimens excised during total hip arthroplasties. Each neck radiograph was digitized and a region of interest (ROI) was selected from the medial side of the femoral neck. Textural features, the global Minkoswski dimension and trabecular orientation, were extracted from each ROI image using Minkowski dimension analysis. The BMD of each specimen was measured using dual‐energy x‐ray absorptiometry (DXA) and subsequently normalized by bone size as measured from a standard pelvis radiograph. Mechanical testing was performed on the trabecular bone cubes machined from each femoral neck to yield bone mechanical properties. Multiple regression was performed to select the best features to predict bone mechanical properties. The results suggest that, using multiple predictors including normalized BMD structural features, and patient age, the coefficients of determination improved over the use of BMD alone. For bone strength, the was improved from 0.24 using conventional BMD to 0.48 using a four‐predictor model. Similar results were obtained in the prediction of Young's modulus, i.e., the was improved from 0.25 to 0.55 in going from the model using conventional BMD to a four‐predictor model. This study demonstrates the contributions of normalized BMD, structural features, and age to bone mechanical properties, and suggests a potential method for the noninvasive evaluation of bone mechanical properties.
Regularization method for scatter‐glare correction in fluoroscopic images
Authors: Close Robert A. , Shah Kokila C. , Whiting James S.
Published: July 2002

Fluoroscopic images are degraded by scattering of x rays from within the patient and by veiling glare in the image intensifier. Both of these degradations are well described by a response function applied to either the scatter‐free or primary intensity. The response function is variable, with dependence on such factors as patient thickness and imaging geometry. We describe an automated regularization technique for obtaining response function parameters with a minimal loss of signal. This method requires a high‐transmission structured reference object to be interposed between the x‐ray source and the subject. We estimate the parameters by minimizing residual correlations between the reference object and the computed subject density after a scatter‐glare correction. We use simulated images to evaluate our method for both ideal and clinically realistic conditions. We find that the residual root‐mean‐square (rms) error ideally decreases with an increasing number of independent pixels (N) as In simulated angiograms mean normalized rms errors were reduced from 40% to 11% in noise‐free images, and from 41% to 17% in noisy images, with a similar improvement in densitometric vessel cross‐section measurements. These results demonstrate the validity of the method for simulated images and characterize its expected performance on clinical images.
An experiment for measuring the low temperature vapor line of water
Authors: Velasco S. , Faro J. , Román F. L.
Published: July 2002

A simple and low cost, but accurate, method to measure the vapor pressure curve of water below the normal boiling temperature is described. The apparatus uses the expansion power of hot air and steam. The vapor pressure is calculated by applying the ideal gas law, some elementary hydrostatics, and taking into account the water expansivity.
Response to “Lorentz transformation of a system carrying ‘Hidden Momentum,’ ” by E. Comay [Am. J. Phys. 68, 1007 (2000)]
Authors: Hnizdo V.
Published: July 2002

We respond to Comay’s criticism of the use of covariant definitions of the electromagnetic and mechanical energy–momenta in an analysis of the role of hidden momentum in the total energy–momentum four vector of a macroscopic body.
A Hamiltonian decomposition technique for improving the convergence of perturbation series
Authors: Mavromatis Harry A.
Published: July 2002

A simple, one-parameter Hamiltonian decomposition is discussed that modifies the convergence rate of perturbation expansions and converts diverging into converging series. Two upper bound expressions are used to monitor the resulting series. The x2 and x4 potentials are studied as illustrations of this technique.
Measurement of group velocity dispersion using white light interferometry: A teaching laboratory experiment
Authors: Cormack I. G. , Baumann F. , Reid D. T.
Published: July 2002

A teaching laboratory experiment is described which uses a basic Michelson interferometer arrangement to make fast and accurate measurements of the group velocity dispersion of an optical material using a method based on recording white-light fringes. We present a brief analysis of the theory behind the technique and describe two example measurements, one of the material dispersion of a KTP crystal and another of the reflectivity dispersion of a silver-coated mirror. Details are also given of our implementation of the data analysis using the MATLAB programming environment
Measures of spread for periodic distributions and the associated uncertainty relations
Authors: Forbes G. W. , Alonso M. A.
Published: July 2002

A physicist’s intuition in Fourier theory is generally established from the parallels between Fourier series and transforms. Remarkably, one element of this theory that is especially significant in physics, namely the uncertainty principle, is never treated for Fourier series. We resolve this by first showing that a natural measure of spread for a periodic distribution follows simply upon regarding the distribution as a mass density on a ring. Even though the centroid of this ring is expressed in terms of just a first moment, its distance from the geometric center gives a close analog of variance. We then derive direct analogs of the uncertainty principle for both the Fourier series of a continuous periodic function as well as the fast Fourier transform of discrete data. The results have similar applications to those of the standard uncertainty principle.
The charge distribution on a conductor for non-Coulombic potentials
Authors: Griffiths David J. , Uvanović Daniel Z.
Published: July 2002

We study the distribution of charge on a conductor for Yukawa (e−μr/r) and power-law (1/rn) potentials. In the Yukawa case some charge goes to the surface, while the remainder distributes uniformly over the volume. In the power-law case no such general result is available, but we obtain the distribution for spheres, cylinders, and slabs, on the range 1⩽n⩽3. In the Coulomb limit (n=1) the charge all goes to the surface; at the other extreme (n=3) it distributes uniformly over the volume.
The effect of electric fields in a classic introductory physics treatment of eddy current forces
Authors: Salzman P. J. , Burke John Robert , Lea Susan M.
Published: July 2002

A simple model of eddy currents in which current is computed solely from magnetic forces acting on electrons proves accessible to introductory students and gives a good qualitative account of eddy current forces. However, this model cannot be complete; it ignores the electric fields that drive current outside regions of significant magnetic field. In this paper we show how to extend the model to obtain a boundary value problem for current density. Solution of this problem in polar coordinates shows that the electric field significantly affects the quantitative results and presents an exercise suitable for upper division students. We apply elliptic cylindrical coordinates to generalize the result and offer an exercise useful for teaching graduate students how to use nonstandard coordinate systems.
An alternating voltage battery with two salt-water oscillators
Authors: Cervellati Rinaldo , Soldà Roberto
Published: July 2002

We built a simple alternating voltage battery that periodically reverses value and sign of its electromotive force (emf). This battery consists of two coupled concentration salt-water oscillators that are phase shifted by initially extracting some drops of salt solution from one of the two oscillators. Although the actual frequency (period: ∼30 s) and emf (∼±55 mV) is low, our battery is suitable to demonstrate a practical application of oscillating systems in the physical, chemical, or biological laboratory for undergraduates. Interpretation of the phenomenon is given.
An unusual approach to Kepler’s first law
Authors: Osler Thomas J.
Published: July 2002

Kepler’s first law of planetary motion states that the orbits of planets are elliptical, with the sun at one focus. We present an unusual verification of this law for use in classes in mechanics. It has the advantages of resembling the simple verification of circular orbits, and stressing the importance of Kepler’s equation.
Surface response of a conductor: static and dynamic, electric and magnetic
Authors: Schaich W. L.
Published: July 2002

The response of a flat metal surface to an external point charge or monopole moving parallel to it is analyzed for a variety of cases. The same basic formalism of matching partial wave expansions is used for each case with slight adaptations in order to emphasize the common physics as one determines the induced forces. The point disturbance is either stationary or moving at constant speed (and height) or suddenly appearing. The metal’s response is first treated via electrostatics and then generalized to electrodynamics. The influence of the metal’s thickness is studied in separate calculations wherein it ranges from semi-infinite down to much less than the penetration depth of the induced fields. The latter limit allows considerable analytic progress and an alternate description in terms of receding images.
An experimental apparatus for white light imaging by means of a spherical obstacle
Authors: Kolodziejczyk Andrzej , Jaroszewicz Zbigniew , Henao Rodrigo , Quintero Orlando
Published: July 2002

We discuss the use of a spherical obstacle as an imaging device for white light illumination. A brief description of the phenomenon is given and then a simple, compact experimental apparatus is described in detail. The experimental results underline the importance of the spatial incoherence of light used in the imaging arrangement. The superiority of incoherent over coherent illumination is demonstrated and some interesting features of imaging by a spherical obstacle are discussed.
Simple Internet data collection for physics laboratories
Authors: Forinash Kyle , Wisman Raymond
Published: July 2002

We present a surprisingly simple yet flexible method for remote data collection over the Internet. The method requires minimal development effort, has considerable hardware and software independence, and is essentially free. The basic approach is to convert a scientific measurement instrument into an Internet device to give remote computers access to the instrument. The method is compatible with most programming languages and software applications that have Internet access. It can be used with many serial port measurement instruments and allows different computers, operating systems, and instruments to be intermixed when collecting data. We give three examples of how the method has been used to enhance the undergraduate physics laboratory experience.
Visualizing the phonon wave function
Authors: Johnson Scott C. , Gutierrez Thomas D.
Published: July 2002

A phonon often is described as “a quantum of lattice vibration,” but this description can be difficult to reconcile with the wave functions explored in a typical undergraduate quantum mechanics class. A phonon wave function is similar to the harmonic oscillator wave functions studied in introductory quantum mechanics, except that it is many-dimensional. We suggest a way to visualize the probability density for this very high-dimensional wave function. The resulting pictures are especially clear and intuitive for a coherent state, which is both a good approximation to a sound wave and a discrete analog to laser light. These pictures can also provide a qualitative introduction to quantum field theory.
Teaching statistics in the physics curriculum: Unifying and clarifying role of subjective probability
Authors: D’Agostini Giulio
Published: July 2002

Subjective probability is based on the intuitive idea that probability quantifies the degree of belief that an event will occur. A probability theory based on this idea represents the most general framework for handling uncertainty. A brief introduction to subjective probability and Bayesian inference is given, with comments on typical misconceptions which tend to discredit it and with comparisons to other approaches.
Diffraction by disordered gratings and the Debye–Waller effect
Authors: Licinio P. , Lerotic M. , Dantas M. S. S.
Published: July 2002

We analyze the effect of disorder in a slit array upon the resulting laser diffraction pattern. This problem is analogous to the Debye–Waller effect, which applies to x-ray scattering by crystals, where disorder is due to uncorrelated thermal vibrations. We have made quantitative measurements using equipment available at our undergraduate laboratory. The measurements were analyzed with the aid of phasor diagrams.
A spin network primer
Authors: Major Seth A.
Published: July 2002

Spin networks, essentially labeled graphs, are “good quantum numbers” for the quantum theory of geometry. These structures encompass a diverse range of techniques which may be used in the quantum mechanics of finite dimensional systems, gauge theory, and knot theory. Though accessible to undergraduates, spin network techniques are buried in more complicated formulations. In this paper a diagrammatic method, simple but rich, is introduced through an association of 2×2 matrices with diagrams. This spin network diagrammatic method offers new perspectives on the quantum mechanics of angular momentum, group theory, knot theory, and even quantum geometry. Examples in each of these areas are discussed.
Relationship of the commutation rules to classical-like representations of quantum angular momenta addition
Authors: Morales Alejandro , Amaya-Tapia Alejandro
Published: July 2002

We perform an analysis of a graphical representation for the addition of two angular momenta, focusing our attention on the angle δ between the xy components of two angular momenta. Then we propose a new complete set of commuting observables, which differ from the usual sets that are connected by the Clebsch–Gordan coefficients. This set shows that the angle δ can be a well-defined variable in quantum mechanics. An empirical analysis of the graphical representations of the angular momenta relations, which may include the angle δ, followed by quantum mechanical considerations, leads to the vanishing of certain quantum angular momentum commutators for specific states. Therefore, although the commutators are not null in general, the quantum addition of angular momenta may be represented using classical-like diagrams.
Dispersion in acoustic waveguides—A teaching laboratory experiment
Authors: Meykens K. , Van Rompaey B. , Janssen H.
Published: July 2002

A laboratory experiment for undergraduate students in mathematics and physics is introduced. The experiment concentrates on dispersion in acoustic waveguides. The dispersion relation is measured for different propagation modes and its effect on the transmission of signals is examined, looking at it from several points of view, with the main focus on Fourier aspects. The distortion caused by single mode dispersion is explained in terms of the convolution relation between the input signals and the impulse response of the waveguides.
Path integrals and propagators for quadratic Lagrangians in three dimensions
Authors: Poon Kai-Man , Muñoz Gerardo
Published: July 2002

Functional methods are employed to derive the propagator for a three-dimensional system described by a Lagrangian at most quadratic in the velocity and position variables. Two physically relevant examples are presented to illustrate the concrete application of the general formula.
Scattering amplitudes and bound state energies for one-dimensional, weak potentials
Authors: Patil S. H.
Published: July 2002

It is emphasized that one-dimensional, weak potentials have some special properties. They sustain a bound state provided the potential is attractive, and the transmission coefficient for them vanishes in the low energy limit. It is pointed out that a perturbation series for the inverse of the scattering amplitude provides a convenient expression for the analysis of these properties.
A conference experience for undergraduates
Authors: Collins L. A. , Magee N. H. , Bryant H. C. , Zeilik M.
Published: July 2002

Programs launched by many universities and the federal government expose many undergraduate students in the physical sciences to research early in their careers. However, in their research experiences, undergraduates are not usually introduced to the modes by which scientific knowledge, which they may have helped gather, is communicated and evaluated by working scientists. Nor is it always made clear where the research frontiers really lie. To this end, we guided a selected group of undergraduates through a national scientific conference, followed by a week of tutorials and discussions to help them better understand what had transpired. The program complemented the basic undergraduate research endeavors by emphasizing the importance of disseminating results both to other scientists and to society in general. Tutors and discussion leaders in the second week were experts in their fields and included some of the invited speakers from the main meeting. A considerable improvement in the understanding of the issues and prospects for a career in physics was discernible among the students after their two-week experience.
A simple numerical model to simulate a gas in a constant gravitational field
Authors: Pantellini Filippo G. E.
Published: July 2002

The equilibrium pressure of a perfect gas in a constant gravitational field decreases exponentially with height. This result, known as the barometric formula, can be observed in a one-dimensional numerical simulation where the gas molecules are represented by colliding massive points.
A simple demonstration of the Alford–Gold effect using a diode laser and optical fibers
Authors: Basano Lorenzo , Ottonello Pasquale
Published: July 2002

We present an apparatus for demonstrating the Alford–Gold effect (in the more complete case of a continuous optical source) which uses only cheap commercial components such as a diode laser, a coil of optical fibers, and a photodiode. The effect is introduced on the basis of intuitive arguments; the experimental results are compared with the theoretical predictions that were first obtained by Givens and by Mandel. The demonstration turns out to be, both for graduates and undergraduates, an instructive exercise in modern coherence theory.
Air-wood coupling and the Swiss-cheese violin
Authors: Weinreich Gabriel , Holmes Colin , Mellody Maureen
Published: July 2002

Some problems with the conventional formalism for describing the coupling of fluid vibrations to those of an enclosing shell are examined. An alternative (“dynamic”) basis for expanding the normal modes, in which the “pure shell modes” include incompressible motion of the fluid, is proposed. This new approach is applied to Hutchins’s “Swiss-cheese violin,” the behavior of whose air modes for the case of a rigid shell have been calculated by Shaw. Measurements are presented of various response functions of this instrument as a function of both frequency and the number of open rib holes. These results show the predicted “mode veering” behavior, and can be easily matched to theory with the assumption of plausible parameters.
Data processing options and response scoring for OAE-based newborn hearing screening
Authors: Tognola Gabriella , Grandori Ferdinando , Ravazzani Paolo
Published: July 2002

Scoring of click-evoked otoacoustic emissions (CEOAEs) is typically achieved by the evaluation of the reproducibility of the whole emission and/or within narrow bands. Screening outcomes are influenced not only by the specific combination of the subdivision scheme (i.e., the number, position, and bandwidth of the narrow bands) and the threshold used to determine pass and refer, but also by the accuracy with which the reproducibility is estimated. This study was designed to examine what factors affect the accuracy of the reproducibility estimate and how the accuracy of the reproducibility estimate together with the choice of the subdivision scheme/thresholds affect CEOAE scoring. Simulations with real CEOAEs corrupted with synthesized noise indicated that the reproducibility estimate is influenced by time-windowing and band-pass filtering: the longer the time-window or the broader the bandwidth of the filter, the more accurate the estimate. Quantitative figures on numerical scoring were given in terms of the referral rate and were derived from CEOAEs recorded in a clinical environment from more than 3400 newborns. The narrow bands were extracted according to 12 different subdivision schemes covering the 1.5–4-kHz range. The referral rate was found to depend on the subdivision scheme being used: (i) the worst results were obtained considering four narrow bands at 1.6–2.4–3.2–4 kHz; (ii) the best results were obtained considering two narrow bands at 2.25 and 3.75 kHz; (iii) bandwidths greater than 1 kHz resulted in the lowest referral rates. Also, scoring based on the extraction of four narrow bands produced the most unstable results, i.e., a small change in the threshold might cause even a great change in the referral rate.
Manipulating the “straightness” and “curvature” of patterns of interaural cross correlation affects listeners’ sensitivity to changes in interaural delay
Authors: Trahiotis Constantine , Bernstein Leslie R. , Akeroyd Michael A.
Published: July 2002

The purpose of this study was to test the hypothesis that stimuli characterized by “straight” trajectories of their patterns of cross correlation foster greater sensitivity to changes in interaural temporal disparities (ITDs) than do stimuli characterized by more “curved” trajectories of their patterns of cross correlation. To do so, sensitivity to changes in ITD was measured, as a function of duration, using a set of “reference” stimuli that yielded differing relative amounts of straightness within their patterns of cross correlation while keeping the dominant trajectory at or near midline. The relative amounts of straightness were manipulated by employing specific combinations of bandwidth, ITD, and interaural phase disparity (IPD) of Gaussian noises centered at 500 Hz. The results were consistent with expectations in that the patterning of the threshold ITDs revealed increasingly poorer sensitivity as greater and greater curvature was imposed on the dominant, “midline,” trajectory. The variations in threshold ITD across the stimulus conditions can be accounted for quite well quantitatively by assuming either that the listeners based their judgments on changes in the position of the most central peak of the cross-correlation function or that they based their judgments on changes in the centroid of a second-level cross-correlation function. In a second experiment, binaural detection was measured using a subset of the reference stimuli as maskers. As expected, sensitivity was poorest with the maskers characterized by the greatest curvature, which were also those having the lowest interaural correlation.
On the effectiveness of whole spectral shape for vowel perception
Authors: Ito Masashi , Tsuchida Jun , Yano Masafumi
Published: July 2002

The formant hypothesis of vowel perception, where the lowest two or three formant frequencies are essential cues for vowel quality perception, is widely accepted. There has, however, been some controversy suggesting that formant frequencies are not sufficient and that the whole spectral shape is necessary for perception. Three psychophysical experiments were performed to study this question. In the first experiment, the first or second formant peak of stimuli was suppressed as much as possible while still maintaining the original spectral shape. The responses to these stimuli were not radically different from the ones for the unsuppressed control. In the second experiment, F2-suppressed stimuli, whose amplitude ratios of high- to low-frequency components were systemically changed, were used. The results indicate that the ratio changes can affect perceived vowel quality, especially its place of articulation. In the third experiment, the full-formant stimuli, whose amplitude ratios were changed from the original and whose F2’s were kept constant, were used. The results suggest that the amplitude ratio is equal to or more effective than F2 as a cue for place of articulation. We conclude that formant frequencies are not exclusive cues and that the whole spectral shape can be crucial for vowel perception.
Acoustic flowmeter for the measurement of the mean flow velocity in pipes
Authors: Cheung Wan-Sup , Kwon Hyu-Sang , Park Kyung-Am , Paik Jong-Seung
Published: July 2002

This paper proposes a new technique for measuring the gas flow velocity averaged along the finite length of a pipe as well as over its cross-sectional area. Unlike the conventional gas flowmeters, the proposed technique exploits the one-dimensional plane waves that propagate uniformly across the pipe cross-sectional area. When a fluid flows along the pipe, the plane waves are superposed with the flow field such that the positive-going and negative-going plane wave components undergo the change of their wave numbers. Such wave number variation due to the mean flow velocity has provided a major motivation for developing a new way of measuring the mean flow velocity in the pipe, which is referred to as the acoustic flowmeter. To examine the feasibility of the developed flow velocity measurement method, including its theoretical backgrounds, experimental setups are illustrated in this paper. Detailed experimental data for the flow velocity range of 2–27 m/s reveal the linearity of the proposed acoustic flowmeter and its salient environmental robustness for the different acoustic pressure patterns in the pipe and, furthermore, for different velocity profiles over the pipe cross-section area.
On representing signals using only timing information
Authors: Kumaresan Ramdas , Wang Yadong
Published: July 2002

It is well known that only a special class of bandpass signals, called real-zero (RZ) signals can be uniquely represented (up to a scale factor) by their zero crossings, i.e., the time instants at which the signals change their sign. However, it is possible to invertibly map arbitrary bandpass signals into RZ signals, thereby, implicitly represent the bandpass signal using the mapped RZ signal’s zero crossings. This mapping is known as real-zero conversion (RZC). In this paper a class of novel signal-adaptive RZC algorithms is proposed. Specifically, algorithms that are analogs of well-known adaptive filtering methods to convert an arbitrary bandpass signal into other signals, whose zero crossings contain sufficient information to represent the bandpass signal’s phase and envelope are presented. Since the proposed zero crossings are not those of the original signal, but only indirectly related to it, they are called hidden or covert zero crossings (CoZeCs). The CoZeCs-based representations are developed first for analytic signals, and then extended to real-valued signals. Finally, the proposed algorithms are used to represent synthetic signals and speech signals processed through an analysis filter bank, and it is shown that they can be reconstructed given the CoZeCs. This signal representation has potential in many speech applications.
Broadband measurements of the attenuation coefficient and backscatter coefficient for suspensions: A potential calibration tool
Authors: Hall Christopher S. , Marsh Jon N. , Hughes Michael S. , Mobley Joel , Wallace Kirk D. , Miller James G. , Brandenburger Gary H.
Published: July 2002

Tissue characterization would be facilitated by improved methods of calibration with which to make absolute measurements of the backscatter and attenuation of tissue or contrast agents. In this paper, the use of polystyrene microspheres is examined as a potential broadband in vitro calibration tool by employing an experimental system designed to characterize ultrasonic contrast agents. The frequency-dependent attenuation coefficient and backscatter coefficient were measured for a series of microsphere size distributions with a broadband ultrasound system using a custom-built specimen chamber and a novel suspension mixing technique. The measurements were used in a broadband reduction method to yield the backscatter coefficient. The range of ka spanned in this study is from ka=0.5 to ka=12. The broadband nature of the pulses permitted simultaneous measurement of different regimes of scattering of the microspheres (specifically, the transition region from Rayleigh to short-wavelength asymptotic scattering). Experimental results were compared with corresponding theoretical predictions for the attenuation and backscatter of solid elastic spheres in liquid and yielded good quantitative agreement. Discussion of some possible applications of this technique to the fields of tissue characterization and contrast is presented.
Oscillation modes of supersonic multijets
Authors: Umeda Y. , Ishii R.
Published: July 2002

In this paper, oscillation modes of single jet, twin jet, and multijet with square configuration were investigated by using optical and acoustical observations. In the case of a single jet, axisymmetrical, helical, and lateral oscillation modes appeared with increasing pressure ratio of the jet. In the case of twin jets, two counter rotating helical oscillation modes and reversely lateral oscillation modes along a line through the center line of the two jets were observed for two different pressure ratios. In the case of multijets with square configuration, the quadrupolelike oscillation mode, four counter rotating helical oscillation modes, and a symmetrical oscillation mode were observed with increasing pressure ratio. The first and the last oscillation modes of the multijet with square configuration are unexpected based on observations for a single jet.
Transmission and reflection of transient elastodynamic waves at a linear slip interface
Authors: Verweij Martin D. , Chapman Christopher H.
Published: July 2002

A method is presented for the analysis of the transmitted and reflected transient elastodynamic wave field at a fracture that may be modeled as a linear slip interface. With this method, the space-time domain problem is first carried over to the transform domain by means of a temporal Laplace transformation and a two-dimensional, horizontal spatial Fourier transformation. Subsequently, for both the SH and the P/SV wave systems, expressions are determined for the transmitted and reflected wave fields at the interface. Afterward, a transformation back to the space-time domain is carried out. The method is capable of providing the exact transmitted and reflected waves (including the body wave, interface wave, and head wave contributions) that are caused by a spatially curved, incident wave field due to a point source. Moreover, it is especially designed to yield the time domain waveforms. Various exact numerical results are given. For the SH case, the directionally dependent filter behavior of the fracture is shown. For the P/SV case, first the reflection, transmission, and conversion of body waves is presented. The next set of results concerns the interface wave contribution and includes pictures of the particle movement on both sides of the fracture when either the transversal or the normal specific compliance of the fracture is equal to zero. Finally, the presence of head waves in case of SV→P and SV→SV reflection is shown.
Rational operators for filtering
Authors: Cederberg R. J. , Collins Michael D. , Schmidt Henrik , Siegmann William L.
Published: July 2002

The parabolic equation (PE) method has been applied to approximate the wave equation, construct radiation conditions, solve scattering problems, construct initial conditions, and derive energy flux conditions. A new application of the PE method, filters based on rational approximations of depth operators, is described and tested. The rational approximation is designed to act as the identity operator on the desired part of the spectrum of the depth separated wave equation and to annihilate other parts of the spectrum. This approach does not require explicit knowledge of the spectrum. The applications of the filter include directly solving eigenvalue problems, annihilating components of the wave-number spectrum, generating initial conditions at the source range, and eliminating Gibbs oscillations that arise in energy-conserving PE solutions.
Spectral weights in level discrimination by preschool children: Synthetic listening conditions
Authors: Willihnganz Melodie S. , Stellmack Mark A. , Lutfi Robert A. , Wightman Frederic L.
Published: July 2002

On most auditory discrimination and detection tasks young children perform more poorly than adults. The current experiment applies a technique which potentially can reveal the extent to which the adult–child performance difference results from suboptimal attentional strategies or simply greater internal noise in the children. In this experiment preschool children and adults were asked to discriminate between complex tones comprised of three random-amplitude sinusoidal components. A trial-by-trial correlational analysis [R. A. Lutfi, J. Acoust. Soc. Am. 97, 1333–1334 (1995)] provided an estimate of the weight listeners placed on the level information from individual spectral components in making the discrimination. The patterns of weights were interpreted as measures of “attentional strategy.” Both children and adults produced reliable patterns of weights. This is an especially important result since measuring a single weighting pattern requires large numbers of trials and hence multiple sessions with the children. While individual weighting patterns were reliable, weighting patterns differed both within and across groups. Moreover, neither the children nor the adults produced weighting patterns that would maximize percent correct in the task. A substantial proportion of the responses from both children and adults could be predicted from their weighting patterns even when performance was near chance. However, differences in overall performance between children and adults could not be accounted for by differences in their weighting functions.