bluuebunny/crossref_metadata_2025 huggingface dataset:
Onset of Degenerate Hopf Bifurcation of a Vibro-Impact Oscillator
Authors: Wen GuiLin , Xie JianHua , Xu Daolin
Published: September 2004

An analytical method of the degenerate Hopf bifurcation is proposed for vibro-impact systems. The phenomenon of the bifurcation and its complicated dynamics are observed. This type of bifurcation originates multi-coexisting solutions dependent of the initial state of the system.
Interaction Between Dislocations in a Couple Stress Medium
Authors: Shankar M. Ravi , Chandrasekar Srinivasan , Farris Thomas N.
Published: September 2004

Taylor’s theory of crystal plasticity is reformulated for dislocations in a couple stress medium. The divergence between Taylor’s approach and an approach that includes the effects of couple stresses on dislocation interactions is demonstrated. It is shown that dislocations separated by a distance that is comparable to a characteristic material length scale, have mutual interaction somewhat weaker than that predicted by classical elasticity.
Modeling of Air Venting in Pressure Die Casting Process
Authors: Nouri-Borujerdi A. , Goldak J. A.
Published: September 2004

In this study an analytical model has been developed to describe air pressure and residual air mass variations in pressure die casting for atmospheric venting. During injection of molten metal into a die cavity, air is evacuated from the cavity through vents. In this study, the influences of air velocity and friction factor due to temperature dependent viscosity and vent roughness change have been investigated. The results of the model show that there is a critical area ratio over which a quasi steady state is reached, therefore, the air pressure in the cavity remains constant. In addition, for each area ratio there is a critical/minimum time ratio below which outlet Mach number is not large enough to create choked flow. In this case, the rate of outflow air mass is not maximum. Finally, the results of the model addresses that the friction factor depends on hydraulic diameter of the vent and assuming a constant value for it is not valid.
Three-Dimensional Vibration Analysis of Thick, Complete Conical Shells
Authors: Kang Jae-Hoon , Leissa Arthur W.
Published: September 2004

A three-dimensional (3D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, complete (not truncated) conical shells of revolution. Unlike conventional shell theories, which are mathematically two-dimensional (2D), the present method is based upon the 3D dynamic equations of elasticity. Displacement components ur,uz, and uθ in the radial, axial, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the r and z-directions. Potential (strain) and kinetic energies of the conical shells are formulated, the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated for the first five frequencies of the conical shells. Novel numerical results are presented for thick, complete conical shells of revolution based upon the 3D theory. Comparisons are also made between the frequencies from the present 3D Ritz method and a 2D thin shell theory.
Recognition of Multi Axis Milling Features: Part I-Topological and Geometric Characteristics
Authors: Sridharan Nandakumar , Shah Jami J.
Published: September 2004

Most of the work in machining feature recognition has been limited to 2-1/2 and 3 axis milling features. The major impediment to recognition of complex features has been the difficulty in generalizing the characteristics of their shape. This two-part paper describes general purpose methods for recognizing both simple and complex features; the latter may have freeform surfaces and may require 4 or 5 axis machining. Part I of this paper attempts to describe features in terms of geometric and topological characteristics. Part II of the paper uses the characterization and classification developed in Part I for designing feature recognition algorithms. Part I proposes five basic categories and several sub-classifications of features derived both from machining considerations and computational methods for NC toolpath generation. Rather than using topologically rigid features, such as slots and steps, etc., machining features are classified as “Cut-Thru,” “Cut-Around” and “Cut-on” and further classified into sub-categories. Each feature class is described by a list of properties. Apart from the obvious use in feature recognition, this feature classification and characterization may have potential use in developing future data exchange standards for complex features.
A nonmusical paradigm for identifying absolute pitch possessors
Authors: Ross David A. , Olson Ingrid R. , Marks Lawrence E. , Gore John C.
Published: September 2004

The ability to identify and reproduce sounds of specific frequencies is remarkable and uncommon. The etiology and defining characteristics of this skill, absolute pitch (AP), have been very controversial. One theory suggests that AP requires a specific type of early musical training and that the ability to encode and remember tones depends on these learned musical associations. An alternate theory argues that AP may be strongly dependent on hereditary factors and relatively independent of musical experience. To date, it has been difficult to test these hypotheses because all previous paradigms for identifying AP have required subjects to employ knowledge of musical nomenclature. As such, these tests are insensitive to the possibility of discovering AP in either nonmusicians or musicians of non-Western training. Based on previous literature in pitch memory, a paradigm is presented that is intended to distinguish between AP possessors and nonpossessors independent of the subjects’ musical experience. The efficacy of this method is then tested with 20 classically defined AP possessors and 22 nonpossessors. Data from these groups strongly support the validity of the paradigm. The use of a nonmusical paradigm to identify AP may facilitate research into many aspects of this phenomenon.
Masked auditory thresholds in sciaenid fishes: A comparative study
Authors: Ramcharitar John , Popper Arthur N.
Published: September 2004

Western Atlantic sciaenids comprise a taxonomically diverse teleost family with significant variations in the relationship between the swim bladder and the otic capsule. In this study, the auditory brainstem response (ABR) was used to test the hypothesis that fishes with different peripheral auditory structures (black drum, Pogonias chromis and Atlantic croaker, Micropogonias undulatus) show differences in frequency selectivity. In a black drum the swim bladder is relatively distant from the otic capsule while the swim bladder in Atlantic croaker possesses anteriorly-directed diverticulas that terminate relatively near the otic capsule. Signals were pure tones in the frequency range, 100 Hz to 1.5 kHz, and thresholds were determined both with and without the presence of simultaneous white noise at two intensity levels (124 dB and 136 dB, re: 1 μPa). At the 124 dB level of white noise background, both the black drum and Atlantic croaker showed similar changes in auditory sensitivity. However, in the presence of the 136 dB white noise masker, black drum showed significantly greater shifts in auditory thresholds between 300 and 600 Hz. The results indicate that the two species differ in frequency selectivity since the Atlantic croaker was less susceptible to auditory threshold shifts, particularly at the higher level of masking. This difference may be linked to peripheral auditory mechanisms.
On Webster’s horn equation and some generalizations
Authors: Martin P. A.
Published: September 2004

Sound waves along a rigid axisymmetric tube with a variable cross-section are considered. The governing Helmholtz equation is solved using power-series expansions in a stretched radial coordinate, leading to a hierarchy of one-dimensional ordinary differential equations in the longitudinal direction. The lowest approximation for axisymmetric motion turns out to be Webster’s horn equation. Fourth-order differential equations are obtained at the next level of approximation. Comparisons with existing asymptotic theories for waves in slender tubes are made.
Otoacoustic emissions without somatic motility: Can stereocilia mechanics drive the mammalian cochlea?
Authors: Liberman M. C. , Zuo Jian , Guinan J. J.
Published: September 2004

Distortion product otoacoustic emissions (DPOAEs) evoked by low-level tones are a sensitive indicator of outer hair cell (OHC) function. High-level DPOAEs are less vulnerable to cochlear insult, and their dependence on the OHC function is more controversial. Here, the mechanism underlying high-level DPOAE generation is addressed using a mutant mouse line lacking prestin, the molecular motor driving OHC somatic motility, required for cochlear amplification. With prestin deletion, attenuated DPOAEs were measurable at high sound levels. DPOAE thresholds were shifted by ∼50 dB, matching the loss of cochlear amplifier gain measured in compound action potentials. In contrast, at high sound levels, distortion products in the cochlear microphonic (CM) of mutants were not decreased re wildtypes (expressed re CM at the primaries). Distortion products in both CM and otoacoustic emissions disappeared rapidly after death. The results show that OHC somatic motility is not necessary for the production of DPOAEs at high SPLs. They also suggest that the small, physiologically vulnerable DPOAE that remains without prestin-based motility is due directly to the mechanical nonlinearity associated with stereociliary transduction, and that this stereocilia mechanical nonlinearity is robustly coupled to the motion of the cochlear partition to the extent that it can drive the middle ear.
Open cycle traveling wave thermoacoustics: Energy fluxes and thermodynamics
Authors: Weiland Nathan T. , Zinn Ben T.
Published: September 2004

In an open cycle traveling wave thermoacoustic engine, hot gas steadily flows into the hot side of the regenerator, replacing the hot heat exchanger as the primary energy source for the engine. In such an engine, interactions between the acoustic, convective, conductive and thermoacoustic energy fluxes facilitate conversion of the input thermal energy into acoustic energy. This study describes the energy flux interactions throughout the engine, thus clarifying the important role of the mean temperature difference that exists between the mean flow of hot gas and the hot-side regenerator interface in the open cycle engine. Furthermore, this study derives an optimal regenerator interface temperature that maximizes the acoustic power output of the engine for a given thermal energy input. The acoustic power output and thermal efficiency of the open cycle engine are compared to those in a closed cycle engine in which a crossflow heat exchanger is used to supply the required heat input. By accounting for the effectiveness of the heat exchanger, it is shown that the open cycle has the potential to achieve higher efficiencies than the closed cycle in converting the thermal energy in a stream of gas into acoustic energy.
Modeling the growth rate of distortion product otoacoustic emissions by active nonlinear oscillators
Authors: Sisto Renata , Moleti Arturo
Published: September 2004

In this work, growth-rate curves of the 2 f1-f2 distortion product otoacoustic emission (DPOAE) are analyzed in a population of 30 noise exposed subjects, including both normal-hearing and hearing impaired subjects. A particular embedded limit-cycle oscillator equation is used to model the cochlear resonant response at the cochlear places of the primary and secondary tone frequencies (f2 and 2 f1-f2). The parameters of the oscillator equation can be directly interpreted in terms of effectiveness of the cochlear feedback mechanisms associated with the active filter amplification. A two-sources paradigm is included in the model, in agreement with experimental evidence and with the assumptions of more detailed full cochlear models based on the transmission line formalism. According to this paradigm, DPOAEs are nonlinearly generated at the cochlear place that is resonant at frequency f2, and coherently reflected at the 2 f1-f2 place. The analysis shows that the model, which had been previously used to describe the relaxation dynamics of transient evoked otoacoustic emissions (TEOAEs), also correctly predicts the observed growth rate of the DPOAE response as a function of the primary tones amplitude. A significant difference is observed between normal and impaired ears. The comparison between the growth rate curves at different frequencies provides information about the dependence of cochlear tuning on frequency.
Sound level distribution and scatter in proportionate spaces
Authors: Chiles Stephen , Barron Mike
Published: September 2004

Measurements have been conducted in two scale models of proportionate spaces each containing measures to promote a diffuse sound field. Contrary to classical statistical theory, it was found that reflected sound levels decrease with the distance from the source. Measured levels follow behavior predicted by a revised theory previously proposed for concert halls. The scatter of the measured reflected sound levels is shown consistently to exceed values predicted by Lubman/Schroeder’s theory. However, it is demonstrated that this theory does accurately predict scatter of late sound levels when the early reflections are omitted. Investigation into the scatter of reverberation times shows that it is generally well predicted by Davy’s theory.
Localization ability with bimodal hearing aids and bilateral cochlear implants
Authors: Seeber Bernhard U. , Baumann Uwe , Fastl Hugo
Published: September 2004

After successful cochlear implantation in one ear, some patients continue to use a hearing aid at the contralateral ear. They report an improved reception of speech, especially in noise, as well as a better perception of music when the hearing aid and cochlear implant are used in this bimodal combination. Some individuals in this bimodal patient group also report the impression of an improved localization ability. Similar experiences are reported by the group of bilateral cochlear implantees. In this study, a survey of 11 bimodally and 4 bilaterally equipped cochlear implant users was carried out to assess localization ability. Individuals in the bimodal implant group were all provided with the same type of hearing aid in the opposite ear, and subjects in the bilateral implant group used cochlear implants of the same manufacturer on each ear. Subjects adjusted the spot of a computer-controlled laser-pointer to the perceived direction of sound incidence in the frontal horizontal plane by rotating a trackball. Two subjects of the bimodal group who had substantial residual hearing showed localization ability in the bimodal configuration, whereas using each single device only the subject with better residual hearing was able to discriminate the side of sound origin. Five other subjects with more pronounced hearing loss displayed an ability for side discrimination through the use of bimodal aids, while four of them were already able to discriminate the side with a single device. Of the bilateral cochlear implant group one subject showed localization accuracy close to that of normal hearing subjects. This subject was also able to discriminate the side of sound origin using the first implanted device alone. The other three bilaterally equipped subjects showed limited localization ability using both devices. Among them one subject demonstrated a side-discrimination ability using only the first implanted device.
Analysis of screw pitch effects on the performance of bolt-clamped Langevin-type transducers
Authors: Adachi Kazunari , Takahashi Toru , Hasegawa Hiroshi
Published: September 2004

Bolt-clamped Langevin-type transducers (BLTs) are common vibration sources in high-power ultrasonic applications such as ultrasonic plastic joining. In this paper, the authors propose a low-aspect-ratio BLT shape based on numerical solutions of a complex elastic contact problem concerning the bearing stress (prestress) imposed on the interfaces between the parts by clamping with the screw bolt. The prestress distribution at the interface has significant influence on the mechanical quality factor (Q) of the BLT. It is found that the screw pitch of the clamping bolt heavily affects the prestress distribution in the simulation using the finite element method. The newly developed BLTs with a high resonance frequency of approximately 80 kHz has a relatively wide radiating face and sufficient volume ratio of the piezoelectric elements that convert electrical energy into mechanical energy. The average of their measured Q values exceeds 1000 despite their high resonance frequency when they are driven at a voltage higher than 17 V rms.
A super-spectral finite element method for sound transmission in waveguides
Authors: Peplow Andrew , Finnveden Svante
Published: September 2004

A super-spectral finite element method is developed for the study of acoustical wave propagation in nonuniform waveguides. The formulation is based on a finite-element approach using a mixture of high order element shape functions and wave solutions. The numerical method provides solutions to acoustic duct or fluid waveguide environments which may be divided into rectangular sectors. Examples of its use for infinite acoustic waveguides include sound transmission through large ambient density variations and propagation over a geometric stair-step perturbation. Computation of a trapped mode waveform due to a point volume source within a uniform waveguide is also presented.
Frequency-dependent acoustic properties of a fluid/porous solid interface
Authors: Gubaidullin A. A. , Kuchugurina O. Y. , Smeulders D. M. J. , Wisse C. J.
Published: September 2004

We investigate numerically the frequency dependence of the velocities and damping coefficients of the various surface waves that exist on the interface between a fluid half-space and a half-space of a water-saturated porous Biot medium including viscous attenuation. We find that there is a f1 frequency dependence for pure radiation damping. For a sealed-pore surface configuration, the pseudo-Stoneley wave is radiating at high frequencies, but becomes purely viscosity-damped as frequency decreases. For the open-pore surface configuration, the pseudo-Rayleigh wave remains radiative over the entire frequency domain and is damped by a combination of radiation and viscous fluid–solid interaction. It is also found that the pseudo-Rayleigh wave may even become faster than the bulk shear mode, at low frequencies.
Acoustoelastic effects on guided waves in a fluid-filled pressurized borehole in a prestressed formation
Authors: Cao Zhengliang , Wang Kexie , Ma Zaitian
Published: September 2004

This paper investigates acoustoelastic effects on guided waves in a fluid-filled pressurized borehole in a biaxial prestressed formation, and develops a simplified formula that explicitly expresses the dependence of velocity dispersions on the stresses, the third-order elastic constants, and the azimuthal angle of multipole source polarization. The simplified formula shows that only in the flexural wave is there a crossover of the dispersion curves, and this phenomenon does not appear in every other guided wave. In particular, as a transformed result from the simplified expression, the square difference of flexural wave velocity dispersions is only dependent on the difference of the biaxial stresses, and neither the square sum of the flexural dispersions nor the velocity dispersions of the other guided waves is dependent on it. Computational results show that the sensitivity coefficients for the flexural dispersions induced by the biaxial stresses at low frequency asymptotically approach the corresponding coefficients of shear-waves in the formation, like the asymptotic behavior of velocities.
Integration across frequency bands for consonant identification
Authors: Ronan Diane , Dix Ann K. , Shah Phalguni , Braida Louis D.
Published: September 2004

A comparison of the predictions of models of integration to data on the reception of consonants filtered into a variety of frequency bands is reported. New data on the consonant identification are presented. Three experiments were conducted testing the following bands: experiment I, 0–2100 Hz and 2100–4500 Hz; experiment II, 0–700 Hz combined with 700–1400, 1400–2100, 2100–2800, and 2800–4500 Hz; experiment III, all combinations of 700–1400, 1400–2100, 2100–2800, and 2800–4500 Hz. The predictions of four models, Fletcher’s [Speech and Hearing in Communication (Van Nostrand, New York, 1950)] independent errors model, Massaro’s fuzzy logical model of perception [Proc. Int. Congress of Phonetic Sciences, Stockholm, Vol. 3, pp. 106–113 (1987)], and Braida’s pre-labelling and post-labelling models of integration [Q. J. Exp. Psychol. A 43, 647–677 (1991)], were compared in terms of their ability to predict combined-band scores. At least two models were capable of predicting performance for each combined-band condition. For experiment I, all models were able to make satisfactory predictions. For experiment II, a variant of the pre-labelling model was able to make satisfactory predictions. For experiment III, no model was able to make satisfactory predictions, but the fuzzy logical model of perception and a variant of the pre-labelling model made relatively good predictions. Thus the ability of the models to predict performance depended more on whether the condition included the lowest frequency band than on the adjacency or frequency separation.
Exploiting independent filter bandwidth of human factor cepstral coefficients in automatic speech recognition
Authors: Skowronski Mark D. , Harris John G.
Published: September 2004

Mel frequency cepstral coefficients (MFCC) are the most widely used speech features in automatic speech recognition systems, primarily because the coefficients fit well with the assumptions used in hidden Markov models and because of the superior noise robustness of MFCC over alternative feature sets such as linear prediction-based coefficients. The authors have recently introduced human factor cepstral coefficients (HFCC), a modification of MFCC that uses the known relationship between center frequency and critical bandwidth from human psychoacoustics to decouple filter bandwidth from filter spacing. In this work, the authors introduce a variation of HFCC called HFCC-E in which filter bandwidth is linearly scaled in order to investigate the effects of wider filter bandwidth on noise robustness. Experimental results show an increase in signal-to-noise ratio of 7 dB over traditional MFCC algorithms when filter bandwidth increases in HFCC-E. An important attribute of both HFCC and HFCC-E is that the algorithms only differ from MFCC in the filter bank coefficients: increased noise robustness using wider filters is achieved with no additional computational cost.
Detection of random alterations to time-varying musical instrument spectra
Authors: Horner Andrew , Beauchamp James , So Richard
Published: September 2004

The time-varying spectra of eight musical instrument sounds were randomly altered by a time-invariant process to determine how detection of spectral alteration varies with degree of alteration, instrument, musical experience, and spectral variation. Sounds were resynthesized with centroids equalized to the original sounds, with frequencies harmonically flattened, and with average spectral error levels of 8%, 16%, 24%, 32%, and 48%. Listeners were asked to discriminate the randomly altered sounds from reference sounds resynthesized from the original data. For all eight instruments, discrimination was very good for the 32% and 48% error levels, moderate for the 16% and 24% error levels, and poor for the 8% error levels. When the error levels were 16%, 24%, and 32%, the scores of musically experienced listeners were found to be significantly better than the scores of listeners with no musical experience. Also, in this same error level range, discrimination was significantly affected by the instrument tested. For error levels of 16% and 24%, discrimination scores were significantly, but negatively correlated with measures of spectral incoherence and normalized centroid deviation on unaltered instrument spectra, suggesting that the presence of dynamic spectral variations tends to increase the difficulty of detecting spectral alterations. Correlation between discrimination and a measure of spectral irregularity was comparatively low.
Auditory discontinuities interact with categorization: Implications for speech perception
Authors: Holt Lori L. , Lotto Andrew J. , Diehl Randy L.
Published: September 2004

Behavioral experiments with infants, adults, and nonhuman animals converge with neurophysiological findings to suggest that there is a discontinuity in auditory processing of stimulus components differing in onset time by about 20 ms. This discontinuity has been implicated as a basis for boundaries between speech categories distinguished by voice onset time (VOT). Here, it is investigated how this discontinuity interacts with the learning of novel perceptual categories. Adult listeners were trained to categorize nonspeech stimuli that mimicked certain temporal properties of VOT stimuli. One group of listeners learned categories with a boundary coincident with the perceptual discontinuity. Another group learned categories defined such that the perceptual discontinuity fell within a category. Listeners in the latter group required significantly more experience to reach criterion categorization performance. Evidence of interactions between the perceptual discontinuity and the learned categories extended to generalization tests as well. It has been hypothesized that languages make use of perceptual discontinuities to promote distinctiveness among sounds within a language inventory. The present data suggest that discontinuities interact with category learning. As such, “learnability” may play a predictive role in selection of language sound inventories.
Neuro-computational processing of moving sonar echoes classifies and localizes foliage
Authors: Kuc Roman
Published: September 2004

Echoes from in situ tree trunks, similar to those observed by flying bats, are processed. A moving sonar converts echoes into spike sequences and applies neural-computational methods to classify objects and estimate passing range. Two classes of tree trunks act as retro-reflectors that generate strong echoes (SEs), identified by a locally dense spike pattern. Linear drive-by sonar trajectories cause SEs to follow hyperbolic curves specified by passing range. A glint is a collection of consecutive range readings matching expected values on a specific hyperbolic curve. Passing-range detectors compare successive SE data with expected values in a table and tally coincidences. Counters increment when coincidences occur and decrement when they do not. A glint terminates after tallying a sufficient number of coincidences and coincidence failure occurs in the maximum-count detector. Reflector roughness, deviations in sonar trajectory, and echo jitter necessitate a coincidence window to define matches. Short windows identify small glints over piecewise linear sonar trajectories, while long windows accommodate deviations in sonar speed and trajectory, and associate multiple glints observed with shorter windows. The minimum coincidence window size yielding glints classify smooth and rough retro-reflectors.
Flow separation in a computational oscillating vocal fold model
Authors: Alipour Fariborz , Scherer Ronald C.
Published: September 2004

A finite-volume computational model that solves the time-dependent glottal airflow within a forced-oscillation model of the glottis was employed to study glottal flow separation. Tracheal input velocity was independently controlled with a sinusoidally varying parabolic velocity profile. Control parameters included flow rate (Reynolds number), oscillation frequency and amplitude of the vocal folds, and the phase difference between the superior and inferior glottal margins. Results for static divergent glottal shapes suggest that velocity increase caused glottal separation to move downstream, but reduction in velocity increase and velocity decrease moved the separation upstream. At the fixed frequency, an increase of amplitude of the glottal walls moved the separation further downstream during glottal closing. Increase of Reynolds number caused the flow separation to move upstream in the glottis. The flow separation cross-sectional ratio ranged from approximately 1.1 to 1.9 (average of 1.47) for the divergent shapes. Results suggest that there may be a strong interaction of rate of change of airflow, inertia, and wall movement. Flow separation appeared to be “delayed” during the vibratory cycle, leading to movement of the separation point upstream of the glottal end only after a significant divergent angle was reached, and to persist upstream into the convergent phase of the cycle.
An integral equation approach to three-dimensional acoustic radiation and scattering problems
Authors: Yang S. A.
Published: September 2004

This paper provides numerical implementation and tests for a boundary integral equation method proposed recently by Krutitskii [IMA J. Appl. Math. 64, 259–269 (2000)] for evaluating three-dimensional acoustic radiation and scattering fields in the exterior Neumann problem for several obstacles. Auxiliary boundaries with certain prescribed boundary conditions are introduced inside the obstacles for the purpose of eliminating the fictitious characteristic frequencies. Applying the simple source formulation on all boundaries leads to a set of uniquely solvable integral equations with weakly singular kernels. To facilitate the numerical implementation, the modified integral equations are further transformed to ordinary ones that contain nonsingular kernels only. Test cases consist of the acoustic radiation and scattering by one sphere and a pair of equal spheres. Comparisons are made with analytical solutions and Schenck’s CHIEF method. Numerical results demonstrate the efficiency, robustness, and accuracy of the proposed method.
Simplifications for the calculation of surface wave pulses generated by laser-irradiation
Authors: Achenbach J. D.
Published: September 2004

In this paper a simplified approach is presented to determine the ultrasonic surface wave motion generated by laser irradiation of a linearly elastic solid. It combines three novel ideas. The first is a way to directly determine the mechanical loading equivalent to laser irradiation by considering local thermoelastic effects in the area that is heated by the laser. The second idea is the use of a new formulation for surface waves which considers a surface wave as a carrier wave that satisfies Helmholtz’ equation in surface coordinates and that supports depth-dependent motions that are the same for any kind of carrier wave. The third idea is to directly determine the surface wave motion generated by the equivalent mechanical loading by applying the elastodynamic reciprocity relation for the generated surface wave motion and an appropriately selected “virtual” wave motion. The analysis based on the reciprocity relations is carried out for the time-harmonic case, but Fourier superposition is used to obtain the surface wave pulses corresponding to pulsed laser irradiation. The approach based on these ideas is taken through several steps for an isotropic and a transversely isotropic solid whose mechanical properties may depend on the distance from the surface. For a homogeneous isotropic solid the details have been worked out for the surface wave pulses generated by the laser irradiation of arbitrary time dependence at a point, an infinitely long line, and a line of finite length.
Material discrimination using bispectral signatures
Authors: Nyffenegger Paul A. , Hinich Melvin J. , Ritter Dillon , Hansen Stephen
Published: September 2004

One goal of investigative signal processing techniques is to discriminate between types of materials composing an object. This paper explores a method for material discrimination and characterization using bispectral signatures acquired from an object actively probed with acoustic pulses. The mathematical foundations of the bispectrum are presented, and the proposed technique is tested with an ultrasonic apparatus. Results indicate that at ultrasonic frequencies this technique provides signatures with the potential of discriminating between classes of materials such as plastic, aluminum, and rock.
Use of statistical energy analysis for the prediction of Sabine absorption coefficient of modally reactive panels
Authors: Sum K. S.
Published: September 2004

Statistical energy analysis (SEA) is used to establish a relationship between the Sabine absorption coefficient of a modally reactive panel and the coupling of the panel with the sound field in a room. The acoustic-structural coupling is described by the coupling loss factors between the panel and the room. The application of the consistency relationship in SEA, which is based on the reciprocity principle, is shown to enable the coupling loss factors to be determined by directly exciting either the panel or the room. Each way of driving the acoustic-structural coupled system produces different values of the coupling loss factors and thus, of the absorption coefficient. The nature of discrepancy between the results of both ways of exciting the system is explained by using distributions of energy among structural modes of the panel and acoustic modes of the sound field, as well as distributions of modal coupling-loss factor among acoustic-structural coupled pairs of the modes. This paper provides an insight into the effect of the use of the consistency relationship on the prediction of the Sabine absorption coefficient of modally reactive panels by SEA.
Estimation of seabed reflection loss properties from direct blast pulse shape (L)
Authors: Prior Mark K. , Harrison Chris H.
Published: September 2004

The decay rate of a smeared multipath arrival received many water depths from a broadband source has been shown to be closely related to bottom reflection loss properties [Smith, J. Acoust. Soc. Am. 50, 332–336 (1971)]; [Harrison, J. Acoust. Soc. Am. 114, 2744–2756 (2003)]. This suggests a simple way of measuring bottom properties with active sonars. The method is demonstrated with experimental data measured in a shallow water region of the Mediterranean Sea. Seabed properties are deduced directly by the method in the form of the rate of change of reflection loss with respect to angle close to grazing. Agreement is shown between the results of the method and the results of matched field inversions carried out in the same area. Good agreement is also shown between measurements and predictions of propagation loss made using seabed properties deduced via the method.
Notes on the Gaussian beam expansion
Authors: Ding Desheng , Zhang Yu
Published: September 2004

A powerful Gaussian-beam expansion technique [J. J. Wen and M. A. Breazeale, J. Acoust. Soc. Am. 83, 1752–1756 (1988)] is widely used in calculating the Fresnel field integral. A basic ideal of this treatment is to expand the source distribution function into the superposition of a series of Gaussian functions. The evaluation of the radiation field is then greatly simplified. As a supplement, this paper presents a simple approach to determine the expansion coefficients for the sound source. The results for the ultrasonic field radiated by piston transducers are typically given, in a fairly good agreement with those calculated by numerical integration and Breazeale’s. The limits of the present method are also discussed.
CO-Sensing Mechanisms
Authors: Roberts Gary P. , Youn Hwan , Kerby Robert L.
Published: September 2004

Carbon monoxide (CO) has long been known to have dramatic physiological effects on organisms ranging from bacteria to humans, but recently there have a number of suggestions that organisms might have specific sensors for CO. This article reviews the current evidence for a variety of proteins with demonstrated or potential CO-sensing ability. Particular emphasis is placed on the molecular description of CooA, a heme-containing CO sensor from
Rhodospirillum rubrum
, since its biological role as a CO sensor is clear and we have substantial insight into the basis of its sensing ability.
Microbial Type I Fatty Acid Synthases (FAS): Major Players in a Network of Cellular FAS Systems
Authors: Schweizer Eckhart , Hofmann Jörg
Published: September 2004

The present review focuses on microbial type I fatty acid synthases (FASs), demonstrating their structural and functional diversity. Depending on their origin and biochemical function, multifunctional type I FAS proteins form dimers or hexamers with characteristic organization of their catalytic domains. A single polypeptide may contain one or more sets of the eight FAS component functions. Alternatively, these functions may split up into two different and mutually complementing subunits. Targeted inactivation of the individual yeast FAS acylation sites allowed us to define their roles during the overall catalytic process. In particular, their pronounced negative cooperativity is presumed to coordinate the FAS initiation and chain elongation reactions. Expression of the unlinked genes, FAS1 and FAS2, is in part constitutive and in part subject to repression by the phospholipid precursors inositol and choline. The interplay of the involved regulatory proteins, Rap1, Reb1, Abf1, Ino2/Ino4, Opi1, Sin3 and TFIIB, has been elucidated in considerable detail. Balanced levels of subunits α and β are ensured by an autoregulatory effect of FAS1 on FAS2 expression and by posttranslational degradation of excess FAS subunits. The functional specificity of type I FAS multienzymes usually requires the presence of multiple FAS systems within the same cell.De novosynthesis of long-chain fatty acids, mitochondrial fatty acid synthesis, acylation of certain secondary metabolites and coenzymes, fatty acid elongation, and the vast diversity of mycobacterial lipids each result from specific FAS activities. The microcompartmentalization of FAS activities in type I multienzymes may thus allow for both the controlled and concerted action of multiple FAS systems within the same cell.
Determination of the Core of a Minimal Bacterial Gene Set
Authors: Gil Rosario , Silva Francisco J. , Peretó Juli , Moya Andrés
Published: September 2004

The availability of a large number of complete genome sequences raises the question of how many genes are essential for cellular life. Trying to reconstruct the core of the protein-coding gene set for a hypothetical minimal bacterial cell, we have performed a computational comparative analysis of eight bacterial genomes. Six of the analyzed genomes are very small due to a dramatic genome size reduction process, while the other two, corresponding to free-living relatives, are larger. The available data from several systematic experimental approaches to define all the essential genes in some completely sequenced bacterial genomes were also considered, and a reconstruction of a minimal metabolic machinery necessary to sustain life was carried out. The proposed minimal genome contains 206 protein-coding genes with all the genetic information necessary for self-maintenance and reproduction in the presence of a full complement of essential nutrients and in the absence of environmental stress. The main features of such a minimal gene set, as well as the metabolic functions that must be present in the hypothetical minimal cell, are discussed.
Phages and the Evolution of Bacterial Pathogens: from Genomic Rearrangements to Lysogenic Conversion
Authors: Brüssow Harald , Canchaya Carlos , Hardt Wolf-Dietrich
Published: September 2004

Comparative genomics demonstrated that the chromosomes from bacteria and their viruses (bacteriophages) are coevolving. This process is most evident for bacterial pathogens where the majority contain prophages or phage remnants integrated into the bacterial DNA. Many prophages from bacterial pathogens encode virulence factors. Two situations can be distinguished:Vibrio cholerae, Shiga toxin-producingEscherichia coli,Corynebacterium diphtheriae, andClostridium botulinumdepend on a specific prophage-encoded toxin for causing a specific disease, whereasStaphylococcus aureus,Streptococcus pyogenes, andSalmonella entericaserovar Typhimurium harbor a multitude of prophages and each phage-encoded virulence or fitness factor makes an incremental contribution to the fitness of the lysogen. These prophages behave like “swarms” of related prophages. Prophage diversification seems to be fueled by the frequent transfer of phage material by recombination with superinfecting phages, resident prophages, or occasional acquisition of other mobile DNA elements or bacterial chromosomal genes. Prophages also contribute to the diversification of the bacterial genome architecture. In many cases, they actually represent a large fraction of the strain-specific DNA sequences. In addition, they can serve as anchoring points for genome inversions. The current review presents the available genomics and biological data on prophages from bacterial pathogens in an evolutionary framework.
Pattern Formation in Uncatalyzed Bromate Oscillator with Pyrogallol
Authors: Adamčíková Ľubica , Bielik Róbert , Ševčík Peter
Published: September 2004

Stationary mosaic and trigger wave patterns may spontaneously develop in an unstirred thin film of solution containing bromate, pyrogallol and sulfuric acid (uncatalyzed bromate system). The propagation velocity of the waves was found to depend not only on the initial concentrations of H+ and BrO3- ions but also on the initial concentration of pyrogallol. For the explanation of the wave velocity dependence, a reaction scheme of the pyrogallol-BrO3- system has been proposed. The scheme is based on the well-known bromate chemistry combined with an organic radical control that takes into account the reactions of pyrogallol with BrO3-, HBrO2 and HOBr. Movement of the waves could be recorded also potentiometrically. The kinetics and mechanism of the reaction between pyrogallol and bromate in an H2SO4 medium were studied using a conventional polarographic method.
Palladium(II)-Catalyzed Oxidation of α-Hydroxy Acids with Sodium N-Chlorobenzenesulfonamide in Perchloric Acid Solution: A Kinetic and Mechanistic Study
Authors: Revathi Somanalli K. , Ananda Sannaiah , Mohana Kikkeri N. , Rangaswamy
Published: September 2004

Kinetics of oxidation of glycolic acid (GA), lactic acid (LA) and 2-hydroxybutanoic acid (BA) with Chloramines B (CAB) catalyzed by Pd(II) in a HClO4 solution has been studied at 30 °C. The reaction rate shows first-order dependence each on [CAB], [hydroxy acid] and [Pd(II)] and a fractional-order dependence on [H+]. Additions of chloride ions, perchlorate ions and the reduction product of CAB, benzenesulfonamide (BSA), have no effect on the reaction rate. Variations of ionic strength and dielectric permittivity of the medium have no effect on the rate. Activation parameters have been evaluated. A mechanism consistent with kinetic data is proposed. A Taft linear free-energy relationship is observed for the reaction with ρ* = -3.593, indicating an increase in the rate with the presence of electron-donating substituents. An isokinetic relationship is observed with β = 376 K, indicating the effect of enthalpy factors on the rate.
Modified Tricyclic Analogues of Acyclovir. A Direct Alkynylation in the Fused Ring
Authors: Zeidler Joanna
Published: September 2004

Two types of new 7-alkynylated tricyclic analogues (3,9-dihydro-5H-imidazo[1,2-a]purin-9-ones) of acyclovir differing by the presence of N-5 substituent, a temporary 2-(4-nitrophenyl)ethyl or a permanent 3-hydroxypropyl were obtained by a Sonogashira coupling. 7-Alk-1-ynyl-5-(3-acetoxypropyl) compounds (19a-19d, 21a-21c) were efficiently prepared from 7-iodo, 7-iodo-6-methyl precursors 12 and 11, respectively, and deprotected while the products with unsubstituted N-5 were unstable (e.g. 17). Iodide 12 was generally less reactive than 11 and underwent a preferable reduction (48%) to deiodinated 8 when coupled with ethynyltrimethylsilane.
Rearrangement of Substituted 2,4,4,6-Tetraaryl-4H-thiopyrans to Triaryl-3aH-benzo[3,4]cyclopenta[1,2-b]thiophene
Authors: Kroulík Jiří , Čejka Jan , Sedmera Petr , Jegorov Alexandr , Kratochvíl Bohumil , Kuthan Josef
Published: September 2004

An intensive bromination of 2,6-diaryl-4,4-diphenyl-4H-thiopyrans can lead through 3,5-dibromo derivatives to unexpected 2,8-diaryl-3-bromo- and 2,8-diaryl-3,5-dibromo-3a-phenyl-3aH-benzo[3,4]cyclopenta[1,2-b]thiophene as demonstrated on examples where the respective aryl groups are phenyl or 4-fluorophenyl. On the other hand, analogous spiro- [fluorene-9,4'-thiopyran]s do not exhibit the rearrangement evidently due to a rigid conformation of the fluorene moiety. The reaction mechanism for the rearrangement is proposed.
Degradation Behavior of Poly(ethylene glycol) Diblock and Multiblock Polymers with Hydrolytically Degradable Ester Linkages
Authors: Braunová Alena , Pechar Michal , Ulbrich Karel
Published: September 2004

Diblock and multiblock polymers of poly(ethylene glycol) containing degradable ester bonds between the blocks were synthesized and characterized. Monofunctional poly(ethylene glycol) (PEG 2000) was modified by aliphatic dicarboxylic acids (malonic, succinic, glutaric, maleic) to obtain monocarboxylic polymers PEG-COOH containing ester bonds. Diblock polymers (4000) were prepared by polycondensation of a diamine (ethane-1,2-diamine, L-lysine) and the semitelechelic PEG-COOH. The relationship between the structure of the linkage connecting two PEG blocks and the rate of its hydrolytic degradation was studied at pH 5.5, 7.4 and 8.0. The rate of hydrolysis of all polymers was significant already under mild alkaline conditions (pH 7.4 and 8.0) and increased with increasing pH. The ester bonds of polymers with saturated dicarboxylic acid moieties were stable at pH 5.5. However, the presence of double bond in the acid moiety substantially decreased the stability of the polymer not only in alkaline but also in acid medium. The results of this model study can be utilized in the design of biodegradable high-molecular-weight drug carriers and polymers for preparation of "stealth" systems intended for therapeutic application.
New Minor Ecdysteroids from Silene viridiflora
Authors: Mamadalieva Nilufar Z. , Zibareva Larisa N. , Evrard-Todeschi Nathalie , Girault Jean-Pierre , Maria Annick , Ramazanov Nurmurod Sh. , Saatov Ziyadilla , Lafont René
Published: September 2004

Two new minor ecdysteroids, the 2,22- and 3,22-diacetates of 20,26-dihydroxyecdysone have been isolated from the aerial part of Silene viridiflora L. (Caryophyllaceae).
Fulminant liver failure: an indicator of silent myocardial rupture
Authors: Szawarski P , Sensky P R , Doshi M , Hudson I
Published: September 2004

A 56 year old man presented with an atypical chest infection. Remote inferoposterior myocardial infarction was noted on electrocardiography and transthoracic echocardiography. Hepatic failure developed with sudden gross elevation of liver aminotransferases and coagulopathy. No primary hepatic cause could be identified. Subsequent right heart failure led to transoesophageal echocardiography that revealed a large inoperable ventricular septal defect. Histopathological data showed ischaemic hepatitis and reinfarction of the inferoposterior myocardial wall. Acute cardiac events may be silent and precipitate misleading severe hepatic dysfunction.