bluuebunny/crossref_metadata_2025 huggingface dataset:
On subglottal formant analysis
Authors: Cranen Bert , Boves Louis
Published: October 2005

When subglottal pressure signals which are recorded during normal speech production are spectrally analyzed, the frequency of the first spectral maximum appears to deviate appreciably from the first resonance frequency which has been reported in the literature and which stems from measurements of the acoustic impedance of the subglottal system. It is postulated that this is caused by the spectrum of the excitation function. This hypothesis is corroborated by a modeling study. Using an extended version of the well-known two-mass model of the vocal folds that can account for a glottal leak, it is shown that under realistic physiological assumptions glottal flow waveforms are generated whose spectral properties cause a downward shift of the location of the first spectral maximum in the subglottal pressure signals. The order of magnitude of this effect is investigated for different glottal settings and with a subglottal system that is modeled according to the impedance measurements reported in the literature. The outcomes of this modeling study show that the location of the first spectral maximum of the subglottal pressure may deviate appreciably from the natural frequency of the subglottal system. As a consequence, however, the comfortable assumption that in normal speech the glottal excitation function is constant and zero during the ‘‘closed glottis interval’’ has to be called into question.
Determination of natural frequencies of a thick spinning annular disk using a numerical Rayleigh–Ritz’s trial function
Authors: Sinha Sunil K.
Published: October 2005

Consideration is given in this paper to the problem of a thick, spinning, annular disk constrained at its inner radius. Mindlin’s transverse shear deformation and rotary inertia terms are included in the eigenvalue formulation. In the modified Rayleigh–Ritz method used here, the ‘‘admissible’’ or ‘‘trial functions’’ are developed numerically by an iterative scheme so that all the forced, as well as natural, boundary conditions are fully satisfied. The natural frequencies for different mode shapes of the disk have been computed and are presented in a nondimensional form as a function of rotating speed.
Measuring helmet sound attenuation characteristics using an acoustic manikin
Authors: Ivey Elizabeth S. , Nerbonne G. Patrick , Tolhurst Gilbert C.
Published: October 2005

The sound attenuation characteristics of two military helmets were measured using an acoustic manikin as the test apparatus. The manikin results are compared to the results of attenuation measurements made on human subjects wearing identical helmets. The testing room and instrumentation were the same for both the manikin and human subjects. Procedures in ANSI S3.19-1974 were used in the real-ear attentuation at threshold (REAT) part of this study. The results are encouraging as they suggest that the manikin may be used in place of a panel of human subjects to evaluate the hearing protection characteristics of military head gear.
Generalized nearfield acoustical holography for cylindrical geometry: Theory and experiment
Authors: Williams Earl G. , Dardy Henry D. , Washburn Karl B.
Published: October 2005

From the measurement of the acoustic pressure on a cylindrical, two-dimensional contour located close to the surface of an underwater, vibrating cylinder, the complete three-dimensional sound field can be reproduced (reconstructed) with the aid of a computer. This reconstruction technique, called GENAH (generalized nearfield acoustical holography), is unlike conventional holography because it provides a super resolution image of the sound-pressure field from the surface of the cylinder to the farfield. At the same time, GENAH reconstructs, from this two-dimensional measurement, the vector velocity and the vector intensity fields (energy flow) in the nearfield of the source, and identifies modes of surface vibration of the cylinder. Experimental results are provided and the accuracy of GENAH is demonstrated by comparison with the two-hydrophone technique.
On Riccati equations describing impedance relations for forward and backward excitation in the one-dimensional cochlea model
Authors: Kaernbach Christian , König Peter , Schillen Thomas
Published: October 2005

Recent experimental observations of otoacoustic emissions suggest the existence of spontaneous emitters of sound on the basilar membrane. These tend to send off waves not only in the normal direction of propagation. It is therefore significant to study the environmental conditions such an emitter finds inside the cochlea. The impedance relations seen by these emitters are described by the Riccati equation for an inhomogeneous transmission line. The results reported in this paper differ considerably for forward and backward excitation. This reflects the quite different behavior of the cochlea pertaining to waves traveling forward and backward. Because of reflections, backward waves cannot be treated with the Liouville–Green approximation.
Perception of front vowels: The role of harmonics in the first formant region
Authors: Assmann Peter F. , Nearey Terrance M.
Published: October 2005

Vowel matching and identification experiments were carried out to investigate the perceptual contribution of harmonics in the first formant region of synthetic front vowels. In the first experiment, listeners selected the best phonetic match from an F1 continuum, for reference stimuli in which a band of two to five adjacent harmonics of equal intensity replaced the F1 peak; F1 values of best matches were near the frequency of the highest frequency harmonic in the band. Attenuation of the highest harmonic in the band resulted in lower F1 matches. Attenuation of the lowest harmonic had no significant effects, except in the case of a 2-harmonic band, where higher F1 matches were selected. A second experiment investigated the shifts in matched F1 resulting from an intensity increment to either one of a pair of harmonics in the F1 region. These shifts were relatively invariant over different harmonic frequencies and proportional to the fundamental frequency. A third experiment used a vowel identification task to determine phoneme boundaries on an F1 continuum. These boundaries were not substantially altered when the stimuli comprised only the two most prominent harmonics in the F1 region, or these plus either the higher or lower frequency subset of the remaining F1 harmonics. The results are consistent with an estimation procedure for the F1 peak which assigns greatest weight to the two most prominent harmonics in the first formant region.
Piano string excitation II: General solution for a hard narrow hammer
Authors: Hall Donald E.
Published: October 2005

As an important preliminary exercise for understanding excitation of real piano strings, the general solution for a point mass hammer hitting a perfectly flexible string is developed. The extensive literature on this problem is critically reviewed, and the previously known analytic theory presented in such a way as to emphasize its physical meaning. Use of a microcomputer to overcome the difficulties of multiple contacts between string and hammer is described, and representative results obtained by this method are presented. While this approach constitutes a general solution of the problem in principle, it is most practical for moderate values of the ratio of hammer mass to string mass. For extremely heavy hammers, it is argued that there is no good way to predict any details of the string energy spectrum without allowing for additional physical processes such as damping.
Geometrical strong discontinuity formulas for computational wave motions
Authors: Ziv M.
Published: October 2005

Geometrical, strong discontinuity formulas are obtained here in order to accommodate multidimensional wave characteristic equations which are the interior differential equations on wave surfaces. As they stand, the multidimensional wave characteristic equations are integrable only in a weak material motion where discontinuities across waves are allowed in first partial derivatives of continuous dependent variables. This paper deals with the extension of these equations in order to make them also compatible with strong material motion where the dependent variables are themselves discontinuous across the wave surfaces. In particular, the discontinuity formulas are obtained for the characteristics computational scheme on Huygen’s wavelets. For this purpose, strong discontinuity formulas are derived which do not depend on the motion of a surface. The derivation is guided by the intrinsic properties of the wave characteristic equations and is based on concepts of differential geometry in conjunction with Hadamard’s basic proposition of a jump across a surface of discontinuity. The known concepts of differential geometry needed for the analysis are obtained directly from the propagation derivative of the two-point parallel propagator tensor by a unified approach in non-Riemannian geometry.
Phase gradient method of measuring the acoustic impedance of materials
Authors: Legouis T. , Nicolas J.
Published: October 2005

A free-field method using a point source has been developed to measure the normal specific impedance of porous materials. The phase gradient is measured as a function of distance along the normal to the materials passing through the point source. The phase gradient is obtained from a two-microphone probe. The phase and amplitude of the complex reflection coefficient are used as constants adjusted for the best fit to experimental results using a standard optimization technique. Results are obtained on layers of fiberglass and polyurethane foam in the frequency range between 250 and 400 Hz. Good agreement is found when the measured results are compared to the predictions of Delany and Bazley [Appl. Acoust. 3, 105–116 (1970)]. The method has the advantages of requiring a minimum of instrumentation and is particularly adapted to measurements at low frequencies.
Theoretical description of a focused Gaussian ultrasonic beam in a nonlinear medium
Authors: Du Gonghuan , Breazeale M. A.
Published: October 2005

The focusing of an ultrasonic beam is described by beginning with a nondimensional form of the nonlinear wave equation. The method of successive approximations is used to arrive at analytical expressions for the fundamental and the second harmonic of an initially sinusoidal wave with a Gaussian amplitude distribution. The results show that both the fundamental and the second harmonic retain the Gaussian distribution even through the focus. Plots are given of the fundamental and second harmonic Gaussian coefficients, their radial amplitude distributions, their beamwidths, and their pressure amplitudes as a function of distance from a focusing transducer. Acoustic power in the second harmonic as a function of propagation distance in a lossless medium also is evaluated.
A simple model of a vapor bubble
Authors: Vokurka Karel
Published: October 2005

A simple yet reasonably accurate vapor bubble model based on switching between an empty bubble and a gas bubble is introduced. The switching bubble wall velocity is determined by adjusting the theoretical model to experimental data. A comparison with gas bubble models is given.
Underwater noise due to rain, hail, and snow
Authors: Scrimger Joseph A. , Evans Donald J. , McBean Gordon A. , Farmer David M. , Kerman Bryan R.
Published: October 2005

The spectra of underwater noise generated by rain, hail, and snow have been measured in a lake at a depth of 35 m, for a variety of atmospheric conditions. Rain noise spectra, for light winds (<1.2 m s−1), have a sharp peak at 13.5 kHz with a steep falloff (∼60 dB/oct) on the low-frequency side and a more gradual falloff (9 dB/oct) on the high-frequency side. A quasi-flat spectral regime exists in the frequency interval 2–10 kHz. Wind, for speeds increasing above 1.2 m s−1, progressively rounds the peak. The spectral level at 15 kHz (i.e., near the peak) shows a linear dependence on the log of the rain rate with wind speed as a parameter. Correlation of the rain noise spectra with raindrop-size distributions suggests that low frequencies are generated by the larger drops, although this aspect of the problem needs further work. Hail noise spectra have rounded maxima appearing between 2 and 5 kHz with an approximately 10-dB falloff on each side. The spectrum of underwater sound generated by gently falling snow shows a linear increase in level, averaging 5 dB/oct, when plotted against the log of frequency.
Measurement and modeling of downslope acoustic propagation loss over a continental slope
Authors: Dosso S. E. , Chapman N. R.
Published: October 2005

Measurements of propagation loss were obtained in an experiment to study downslope acoustic propagation over the continental slope off the Canadian west coast. The propagation was strongly influenced by the bathymetry and a downslope enhancement was observed at a receiver in the deep sound channel for shallow explosive charges deployed over the continental slope. The maximum enhancement was observed for sources near the edge of the continental shelf at a range of about 110 km, where conversion to low-loss water column propagation paths by bottom interaction occurred at a depth approximately equal to the sound channel axis. The propagation loss measured for these sources was as much as 15 dB less than that estimated for propagation over a flat ocean bottom, and was equivalent to levels recorded for sources at only 25–30 km. The data were interpreted by examining the structure of the signals received from the charges deployed over the slope, and by using ray theory to determine the propagation paths. The range dependence of the propagation loss was modeled using a wide-angle parabolic equation method with a realistic geoacoustic model of the environment which included sound speed, density, and attenuation profiles. The model results were in excellent agreement with the measured values over the entire frequency band of the measurements.
Comparative learning of pitch and loudness identification
Authors: Houtsma A. J. M. , Durlach N. I. , Horowitz D. M.
Published: October 2005

This study investigated possible similarities between the ability to identify pitches and the ability to identify loudnesses. Systematic training of musically naive subjects indicated that frequency identification performance improves at about the same rate as intensity identification performance. Examination of frequency and intensity identification behavior of musically trained subjects showed that their ability to code pitch information efficiently does not generalize to an ability to encode loudness information more efficiently than untrained subjects. Intensity identification training curves of musically trained and untrained subjects are similar, but final performance levels are below frequency identification performance levels exhibited by musically trained subjects, especially those with absolute pitch.
An aerodynamic study of Korean stop consonants: Measurements and modeling
Authors: Dart Sarah N.
Published: October 2005

Measurements were made of intraoral air pressure and oral flow of ten native speakers uttering word pairs contrasting Korean fortis and lenis voiceless stop consonants in initial position. The production of fortis stops was found to be characterized by a higher intraoral pressure before release, yet a lower oral flow after release, than corresponding lenis stops. Possible reasons for this difference were explored with the use of a computer implemented aerodynamic model, giving an output of air pressure and flow. Input parameters were adjusted in accordance with known or hypothesized variations in glottal area function, vocal tract wall tension, respiratory muscle force, and supraglottal cavity volume, as given in the literature. In addition to the previously known differences in glottal area, it is inferred from the results of the modeling experiment that fortis stops are produced with greater vocal tract wall tension than lenis stops. Speaker-specific production strategies such as larynx lowering and heightened subglottal pressure during fortis stops and differences noted between word pairs are also discussed.
A methodology for modeling vowel formant contours in CVC context
Authors: Broad David J. , Clermont Frantz
Published: October 2005

Models for the formant-frequency contours of vowels in CVC′ context are presented and illustrated with an American English database comprising isolated syllables with C, C′=/b,d,g/ and V=/i,i,q,æ,a,c,U,u,v,W/. Both established and reinterpreted regularities among context effects are cast in a series of successively elaborated mathematical models. The first model (model I), in common with all its successors, embodies the notion of the superposition of CV and VC′ transitions, according to which a formant trajectory FCVC′(n) is modeled as  fCV(n)+TV+gVC′(n), where n is duration-normalized time, TV is a vowel target, and  fCV(n) and gVC′(n) are initial- and final-consonant transition functions. The rms errors for F1, F2, and F3 (30, 89, and 111 Hz) against independent test data are near the minimum theoretical values (32, 69, and 100 Hz) predicted from interrepetition variation and its contribution to uncertainty in the model elements. Subsequently, the elements of the additive model are individually characterized by further incorporating per-consonant transition shape similarity (model II), target-locus scaling (model III), exponential transition shapes (model IVa), and exponential duration dependence (model IVb).

In model II, the CV and VC′ trajectories are respectively defined as L+k f*(n) and L′+k′g*(n), with contour shape functions  f* and g*, scale factors k and k′, and consonant loci L and L′. The loci are herein defined as baselines about which families of formant transitions are scaled. This model fits the data nearly as well as theory allows, except for F2 of C/i/C′ and C/ud/. Then, in model III, the scale factors k and k′ are represented by forms proportional to the target-locus distances T−L and T−L′. The vowel target T is then redefined to best fit these forms. The target-locus scaling hypothesis fares quite well except for F2 of CV sequences. In model IVa, the shape functions  f* and g* are fit to exponentials with asymptotes associated with the vowel targets. Target-locus scaling is a corollary of this vowel target definition. Finally, in model IVb, the exponential model is redefined on a recovered real-time scale. The resulting context effect follows Lindblom’s [J. Acoust. Soc. Am. 35, 1773–1781 (1963)] in decaying exponentially with vowel duration.
A release from masking by continuous, random, notched noise
Authors: Carlyon Robert P.
Published: October 2005

Thresholds for 10-ms sinusoids simultaneously masked by bursts of bandpass noise centered on the signal frequency were measured for a wide range of signal frequencies and noise levels. Thresholds were defined as the signal power relative to the masker power at the output of an auditory filter centered on the signal frequency. It was found that the presentation of a continuous random noise, with a spectral notch centered on the signal frequency, produced a reduction in signal thresholds of up to 11 dB. A notched noise spectrum level of 0–5 dB above that of the masker proved most effective in producing a masking release, as measured by a reduction in masked threshold. A release from masking of up to 7 dB could be obtained with a continuous bandpass noise. The most effective spectrum level of this noise was 5 dB below that of the masker. The effect of the continuous notched noise was to reduce signal-to-masker ratios at threshold to about 0 dB, regardless of the threshold in the absence of continuous noise. Thus the greatest release from masking occurred when ‘‘unreleased’’ thresholds were highest. The release from masking is almost complete within 320 ms of notched noise onset, and persists for about 160 ms after notched noise offset, regardless of notched noise level. The phenomenon is similar in many ways to the ‘‘overshoot’’ effect reported by Zwicker [J. Acoust. Soc. Am. 37, 653–663 (1965)]. It is argued that both effects can be largely attributed to peripheral short-term adaptation, a mechanism which is also believed to be involved in forward masking.
Acoustic waves in alternating fluid/solid layers
Authors: Plona T. J. , Winkler K. W. , Schoenberg M.
Published: October 2005

This article describes the results of ultrasonic experiments made to investigate several features of wave propagation in parallel fluid/solid layer systems and compares the results to theory. Immersion experiments were made at frequencies from 0.2–2 MHz on systems composed of water/Plexiglas and water/aluminum parallel layers. The one wave normal to the layering, and the two waves that can propagate parallel to the layering were both observed. Key experimental results demonstrating anisotropy, wavenumber and frequency stop bands, and phase velocity dispersion are shown that are in agreement with theory. The exact analytical theory based on first principles and the corresponding model experiments have implications leading to a better understanding of Biot’s theory of long wavelength propagation in a fluid saturated porous elastic medium.
Temporal resolution in sensorineural hearing-impaired listeners
Authors: Nelson David A. , Freyman Richard L.
Published: October 2005

Temporal masking curves were obtained from 12 normal-hearing and 16 hearing-impaired listeners using 200-ms, 1000-Hz pure-tone maskers and 20-ms, 1000-Hz fixed-level probe tones. For the delay times used here (>40 ms), temporal masking curves obtained from both groups can be well described by an exponential function with a single level-independent time constant for each listener. Normal-hearing listeners demonstrated time constants that ranged between 37 and 67 ms, with a mean of 50 ms. Most hearing-impaired listeners, with significant hearing loss at the probe frequency, demonstrated longer time constants (range 58–114 ms) than those obtained from normal-hearing listeners. Time constants were found to grow exponentially with hearing loss according to the function τ=52e0.011(HL), when the slope of the growth of masking is unity. The longest individual time constant was larger than normal by a factor of 2.3 for a hearing loss of 52 dB. The steep slopes of the growth of masking functions typically observed at long delay times in hearing-impaired listeners’ data appear to be a direct result of longer time constants. When iterative fitting procedures included a slope parameter, the slopes of the growth of masking from normal-hearing listeners varied around unity, while those from hearing-impaired listeners tended to be less (flatter) than normal. Predictions from the results of these fixed-probe-level experiments are consistent with the results of previous fixed-masker-level experiments, and they indicate that deficiencies in the ability to detect sequential stimuli should be considerable in hearing-impaired listeners, partially because of extended time constants, but mostly because forward masking involves a recovery process that depends upon the sensory response evoked by the masking stimulus. Large sensitivity losses reduce the sensory response to high SPL maskers so that the recovery process is slower, much like the recovery process for low-level stimuli in normal-hearing listeners.
Matching impedance of a nonuniform transmission line: Application to cochlear modeling
Authors: Viergever M. A. , de Boer E.
Published: October 2005

A generalization of the concept of characteristic impedance to nonuniform transmission lines leads to an impedance having a local character. This matching impedance depends on the solution of the transmission line equations, and cannot generally be obtained in analytical form. However, when the propagation properties of the line vary only slowly (as is the case in cochlear macromechanics), a convenient analytical approximation of the matching impedance can be derived by means of the Liouville–Green method.
The Radiative Signature of Upper Tropospheric Moistening
Authors: Soden Brian J. , Jackson Darren L. , Ramaswamy V. , Schwarzkopf M. D. , Huang Xianglei
Published: October 2005

Climate models predict that the concentration of water vapor in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. Such moistening plays a key role in amplifying the rate at which the climate warms in response to anthropogenic activities, but has been difficult to detect because of deficiencies in conventional observing systems. We use satellite measurements to highlight a distinct radiative signature of upper tropospheric moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming.
Ordered Liquid Aluminum at the Interface with Sapphire
Authors: Oh S. H. , Kauffmann Y. , Scheu C. , Kaplan W. D. , Rühle M.
Published: October 2005

Understanding the nature of solid-liquid interfaces is important for many processes of technological interest, such as solidification, liquid-phase epitaxial growth, wetting, liquid-phase joining, crystal growth, and lubrication. Recent studies have reported on indirect evidence of density fluctuations at solid-liquid interfaces on the basis of x-ray scattering methods that have been complemented by atomistic simulations. We provide evidence for ordering of liquid atoms adjacent to an interface with a crystal, based on real-time high-temperature observations of alumina-aluminum solid-liquid interfaces at the atomic-length scale. In addition, crystal growth of alumina into liquid aluminum, facilitated by interfacial transport of oxygen from the microscope column, was observed in situ with the use of high-resolution transmission electron microscopy.
Analysis of
Paramecium tetraurelia A-51
Surface Antigen Gene Mutants Reveals Positive-Feedback Mechanisms for Maintenance of Expression and Temperature-Induced Activation
Authors: Matsuda Atsushi , Forney James D.
Published: October 2005

In
Paramecium tetraurelia
, variable surface antigen loci show mutually exclusive expression which is controlled primarily at the transcriptional level. Clonally stable expression of a single antigen has attracted models involving self-regulation by their gene products. However, direct demonstration of self-feedback at the molecular level has been complicated due to the inability to separate the functional gene from its product as well as copy number effects associated with injected extrachromosomal DNA in the polygenomic somatic nucleus. In this study, we exploited several germ line termination and frameshift mutations in the
A-51
surface antigen gene to analyze variable surface antigen expression. These mutant alleles have the same copy number as the wild-type allele and therefore eliminate possible copy number effects. The mutant alleles were not transcribed at 27°C, consistent with positive-feedback models for gene expression. However, further analysis showed that high temperatures (34°C) induced transcription of the mutant
A
genes even in the presence of a different antigen on the cell surface. Thus, transcription was temperature dependent. Unlike wild-type cells, transcription of the mutant
A
genes at high temperatures was not maintained after temperature shift back to 27°C in homozygous mutant cells. Importantly, transcription of the mutant allele was maintained at 27°C in heterozygous cells with one copy of the wild-type allele. These results indicate that expression of the wild-type gene is required to stabilize its own transcriptional state at 27°C.
Rho4 GTPase Is Involved in Secretion of Glucanases during Fission Yeast Cytokinesis
Authors: Santos Beatriz , Martín-Cuadrado Ana Belén , Vázquez de Aldana Carlos R. , del Rey Francisco , Pérez Pilar
Published: October 2005

Rho GTPases are regulators of signaling pathways that control actin organization and cell polarity processes in all eukaryotic cells. In
Schizosaccharomyces pombe
, Rho4p is involved in the regulation of septum degradation during cytokinesis. Here we show that Rho4p participates in the secretion of the glucanases Eng1p and Agn1p, which are responsible for the septum degradation. First,
eng1
+
or
agn1
+
overexpression suppressed the
rho4Δ
multiseptation phenotype, and simultaneous overproduction of Rho4p and Eng1p or of Rho4p and Agn1p caused a dramatic lysis. Second, Rho4p was not necessary for Eng1p-mediated glucanase activity as measured in cell extracts; however,
rho4Δ
cells have a lower level of (1,3)-β-
d
-glucanase activity in the culture medium. Additionally, Eng1- or Agn1-green fluorescent protein did not properly localize to the septum in
rho4Δ
cells grown at 37°C. There was a decreased amount of these enzymes in the cell wall and in the culture medium of
rho4Δ
cells at 37°C. These results provide evidence that Rho4p is involved in the regulation of Eng1p and Agn1p secretion during cytokinesis.
Nuclear Accumulation of the GATA Factor AreA in Response to Complete Nitrogen Starvation by Regulation of Nuclear Export
Authors: Todd Richard B. , Fraser James A. , Wong Koon Ho , Davis Meryl A. , Hynes Michael J.
Published: October 2005

Both the availability and the quality of nutrients affect cellular functions by controlling gene activity. AreA, a member of the GATA family of transcription factors, globally activates expression of genes involved in nitrogen source utilization in
Aspergillus nidulans.
The quality of the nitrogen source determines the level and activation capacity of AreA through controls at the level of
areA
mRNA stability and by interaction of AreA with the corepressor NmrA. The availability of potential nitrogen sources also affects the activation capacity of AreA. We show that the complete absence of a nitrogen source results in an enhanced level of AreA-dependent gene expression and that this response is independent of mechanisms regulating AreA activity in response to nitrogen source quality. During nitrogen starvation AreA accumulates in the nucleus, but the presence of a potential nitrogen source or carbon starvation prevents this accumulation. Furthermore, accumulated AreA is rapidly lost from the nuclei of nitrogen-starved cells when a nitrogen source is supplied or when a carbon source is absent, and this accompanies arrest of the AreA-dependent nitrogen starvation response on regulated gene expression. By the generation of a leptomycin B-sensitive mutant, we have been able to show that nuclear exit occurs via the CrmA exportin. We conclude that sensing mechanisms discriminate between starvation and the presence of potential nutrients that can signal to the AreA transcription factor. Nitrogen source availability, but not quality, affects nuclear accumulation by regulating nuclear exit of AreA, providing a rapid response to changes in the supply of nutrients.
Novel Regulatory Function for the CCAAT-Binding Factor in
Candida albicans
Authors: Johnson Duncan C. , Cano Kristin E. , Kroger Erika C. , McNabb David S.
Published: October 2005

Candida albicans
is an opportunistic human pathogen that can sense environmental changes and respond by altering its cell morphology and physiology. A number of environmental factors have been shown to influence this dimorphic transition, including pH, starvation, serum, and amino acids. In this report, we investigate the function of the
C. albicans
CCAAT-binding factor. In
Saccharomyces cerevisiae
, this heterooligomeric transcriptional activator stimulates the expression of genes that encode proteins involved in respiration. To examine the function of this transcription factor in
C. albicans
, we cloned
CaHAP5
and generated a
hap5Δ/hap5Δ
mutant of
C. albicans
. Using mobility shift studies, we identified four separate complexes from
C. albicans
cell extracts whose DNA-binding activities were abolished in the
hap5Δ/hap5Δ
mutant, suggesting that they represented sequence-specific CCAAT-binding complexes. We found that the
C. albicans hap5Δ
homozygote was defective in hyphal development under a variety of conditions, and the mutant displayed a carbon source-dependent “hyperfilamentation” phenotype under certain growth conditions. In addition, the mRNA levels for two enzymes involved in respiration, encoded by
COX5
and
CYC1
, were overexpressed in the
hap5Δ/hap5Δ
mutant when grown in medium containing amino acids as the sole carbon and nitrogen source. Thus, the
C. albicans
CCAAT-binding factor appeared to function as a repressor of genes encoding mitochondrial electron transport components, in contrast to its activator function in
S. cerevisiae
. These data provide the first evidence that the CCAAT-binding factor can act as a transcriptional repressor and raise new and interesting questions about how carbon metabolism is regulated in this opportunistic human pathogen.
Global Role of the Protein Kinase Gcn2 in the Human Pathogen
Candida albicans
Authors: Tournu Hélène , Tripathi Gyanendra , Bertram Gwyneth , Macaskill Susan , Mavor Abigail , Walker Louise , Odds Frank C. , Gow Neil A. R. , Brown Alistair J. P.
Published: October 2005

The pathogen
Candida albicans
responds to amino acid starvation by activating pseudohyphal development and the expression of amino acid biosynthetic genes (GCN response). In
Saccharomyces cerevisiae
, the GCN response is dependent on Gcn2, which regulates the translation of the transcription factor Gcn4. Therefore, we examined the role of Gcn2 in
C. albicans
by using molecular, cellular, and genomic approaches. We show that
C. albicans GCN2
encodes an eIF2α kinase, like its
S. cerevisiae
homologue. However,
GCN4
appears to be regulated mainly at the transcriptional level in
C. albicans
. Furthermore, the inactivation of
C. albicans
Gcn2 only partially attenuates growth under amino acid starvation conditions and resistance to the histidine analogue 3-aminotriazole. Our comparison of the Gcn4 and Gcn2 regulons by transcript profiling reinforces the view that Gcn2 contributes to, but is not essential for, the activation of general amino acid control in
C. albicans
.
Microtubules in
Candida albicans
Hyphae Drive Nuclear Dynamics and Connect Cell Cycle Progression to Morphogenesis
Authors: Finley Kenneth R. , Berman Judith
Published: October 2005

Candida albicans
is an opportunistic fungal pathogen whose virulence is related to its ability to switch between yeast, pseudohyphal, and true-hyphal morphologies. To ask how long-distance nuclear migration occurs in
C. albicans
hyphae, we identified the fundamental properties of nuclear movements and microtubule dynamics using time-lapse microscopy. In hyphae, nuclei migrate to, and divide across, the presumptive site of septation, which forms 10 to 15 μm distal to the basal cell. The mother nucleus returns to the basal cell, while the daughter nucleus reiterates the process. We used time-lapse microscopy to identify the mechanisms by which
C. albicans
nuclei move over long distances and are coordinated with hyphal morphology. We followed nuclear migration and spindle dynamics, as well as the time and position of septum specification, defined it as the presumptum, and established a chronology of nuclear, spindle, and morphological events. Analysis of microtubule dynamics revealed that premitotic forward nuclear migration is due to the repetitive sliding of astral microtubules along the cell cortex but that postmitotic forward and reverse nuclear migrations are due primarily to spindle elongation. Free microtubules exhibit cell cycle regulation; they are present during interphase and disappear at the time of spindle assembly. Finally, a growth defect in strains expressing Tub2-green fluorescent protein revealed a connection between hyphal elongation and the nuclear cell cycle that is coordinated by hyphal length and/or volume.
Chlamydospore Formation during Hyphal Growth in
Cryptococcus neoformans
Authors: Lin Xiaorong , Heitman Joseph
Published: October 2005

Cryptococcus neoformans
, a basidiomycetous fungal pathogen, infects hosts through inhalation and can cause fatal meningoencephalitis in individuals if untreated. This fungus undergoes a dimorphic transition from yeast to filamentous growth during mating and monokaryotic fruiting, which leads to the production of hyphae and airborne infectious basidiospores. Here we characterized a novel morphological feature associated with the filamentous stages of the life cycle of
C. neoformans
which resembles resting or survival structures known as chlamydospores in other fungi. The
C. neoformans
chlamydospore-like structure is rich in glycogen, suggesting that it might have a role as an energy store. However, characterization of mutants with decreased or increased levels of glycogen production showed that glycogen levels have little effect on filamentous growth, sporulation, or chlamydospore formation. These results suggest that the formation of chlamydospores is independent of glycogen accumulation level. We also show that chlamydospore formation does not require successful sporulation and that the presence of chlamydospores is not sufficient for sporulation. Although the biological functions of chlamydospores remain to be established for this pathogenic fungus, their formation appears to be an integral part of the filamentation process, suggesting that they could be necessary to support sexual sporulation under adverse conditions and thereby facilitate the production of infectious basidiospores or long-term survival propagules in harsh environments.
THE HEUN–SCHRÖDINGER RADIAL EQUATION FOR DH-ATOMS
Authors: TARASOV V. F.
Published: October 2005

This article deals with the connection between Schrödinger's multidimensional equation for DH-atoms (D≥1) and the confluent Heun equation with two auxiliary parameters ν and τ, where |1-ν| = o(1) and τ∈ℚ+, which influence the spectrum of eigenvalues, the Coulomb potential and the radial function. The case τ = ν = 1 and D = 3 corresponds to the "standard" form of Schrödinger's equation for a 3H-atom. With the help of parameter ν, e.g., some "quantum corrections" may be considered. The cases 0<τ<1 and τ>1, but â = (n-l-1)τ≥0 is an integer, change the "geometry" of the electron cloud in the atom, i.e. the so-called "exotic" 3H-like atoms arise, where Kummer's function 1F1(-â; c; z) has â zeros and the discrete spectrum depends only on Z/(νn) but not on l and τ. Diagrams of the radial functions [Formula: see text] as n≤3 are given.
COHERENCE IN TRANSPORT IN A SPECIAL CLASS OF INHOMOGENEOUS RATCHET
Authors: KRISHNAN RAISHMA , DAN DEBASIS , JAYANNAVAR A. M.
Published: October 2005

We study the noise induced transport of an overdamped Brownian particle in frictional ratchet systems in the presence of a special class of external multiplicative Gaussian white noise fluctuations. The analytical expressions for current and diffusion coefficient are derived and the reliability or coherence of transport are discussed by means of their ratio. We show that these frictional ratchets exhibit larger coherence as compared to the flashing and rocking ratchets.
THEORETICAL CHARACTERIZATION OF QUANTUM BALLISTIC CONDUCTION THROUGH MULTIWALLED CARBON NANOTUBES
Authors: GRADO-CAFFARO M. A. , GRADO-CAFFARO M.
Published: October 2005

We study, by utilizing analytic techniques, electrical conduction in multiwalled carbon nanotubes. In fact, by using the well-known concept of Fermi velocity and the Drude theory, a mathematical relationship for conductance is derived so that this conductance is found to be quantized. In addition, our results are compared with experimental data.
ORGANIZATIONAL STRATEGY, INDIVIDUAL PERSONALITY AND INNOVATION BEHAVIOR
Authors: ÅMO BJØRN WILLY , KOLVEREID LARS
Published: October 2005

Two competing models of innovation behavior in organizations are tested. The first model is derived from the corporate entrepreneurship literature, suggesting that the extent to which the organization has a deliberate entrepreneurship strategy determine employees' involvement in innovation and change (Kanter, 1984). The competing model is derived from the intrapreneurship literature, primarily Pinchot (1985) and Pinchot and Pellman (1999), where the emphasis is on the employee's individual personality measured by items derived from Pinchot's (1985) test: "Are you an intrapreneur?" Both models are compared to a base model that contains relevant control variables. Finally, a fourth model, which combines all variables are compared to the other three. The models are tested using a sample of 634 business graduates employed in a diverse set of occupations and organizations. The results indicate that both the strategy and personality models outperform the base model. Moreover, the model that combines the personality of the individual and the strategy of the organization performs even better than the each of the two models separately.
THE ECONOMIC DYNAMICS AS FEATURE OF AN AREA: THE CASE OF ENTREPRENEURSHIP OF SFAX?
Authors: ZGHAL RIADH
Published: October 2005

The economic dynamics of a geographical area as an "industrial district" or as an "innovative milieu" has been analyzed by numerous theories and approaches. Therefore, the complexity of the phenomenon needs more than one theory or approach to grasp all its aspects. Nevertheless, one needs to identify the core characteristics that provide the economic dynamics of a given territory. For this purpose we will adopt a synthetic analysis method to identify the main characteristics of an industrial cluster, and then elaborate a comprehensive concept that elucidates the whole phenomenon. The theoretical findings will be applied to the case of Sfax -the second biggest city of Tunisia- which presents exceptional economic dynamics. The research focusing on the economic activities of Sfax was led by authors from various disciplines, providing data needed for this paper.
HOLOMORPHIC FOLIATIONS AND CHARACTERISTIC NUMBERS
Authors: SOARES MARCIO G.
Published: October 2005

We relate the characteristic numbers of the normal sheaf of a k-dimensional holomorphic foliation [Formula: see text] of a compact complex manifold Mn, to the characteristic numbers of the normal sheaf of a one-dimensional holomorphic foliation associated to [Formula: see text]. In case M is a complex projective space, we also obtain bounds for the degrees of the components of codimension k - 1 of the singular set of [Formula: see text].
DIRECTED EMBEDDINGS OF CLOSED MANIFOLDS
Authors: SPRING DAVID
Published: October 2005

Gromov's theorem on directed embeddings of open manifolds is generalized to the case of closed manifolds, where the embeddings are directed with respect to a given codimension ≥ 1 foliation on the manifold. Applications include directed embeddings with prescribed codimension 1 cusp singularities.
ANISOTROPIC EXPANSION OF THE PLANT CELL WALL
Authors: Baskin Tobias I.
Published: October 2005

Plants shape their organs with a precision demanded by optimal function; organ shaping requires control over cell wall expansion anisotropy. Focusing on multicellular organs, I survey the occurrence of expansion anisotropy and discuss its causes and proposed controls. Expansion anisotropy of a unit area of cell wall is characterized by the direction and degree of anisotropy. The direction of maximal expansion rate is usually regulated by the direction of net alignment among cellulose microfibrils, which overcomes the prevailing stress anisotropy. In some stems, the directionality of expansion of epidermal cells is controlled by that of the inner tissue. The degree of anisotropy can vary widely as a function of position and of treatment. The degree of anisotropy is probably controlled by factors in addition to the direction of microfibril alignment. I hypothesize that rates of expansion in maximal and minimal directions are regulated by distinct molecular mechanisms that regulate interactions between matrix and microfibrils.
RNA TRANSPORT AND LOCAL CONTROL OF TRANSLATION
Authors: Kindler Stefan , Wang Huidong , Richter Dietmar , Tiedge Henri
Published: October 2005

In eukaryotes, the entwined pathways of RNA transport and local translational regulation are key determinants in the spatio-temporal articulation of gene expression. One of the main advantages of this mechanism over transcriptional control in the nucleus lies in the fact that it endows local sites with independent decision-making authority, a consideration that is of particular relevance in cells with complex cellular architecture such as neurons. Localized RNAs typically contain codes, expressed within cis-acting elements, that specify subcellular targeting. Such codes are recognized by trans-acting factors, adaptors that mediate translocation along cytoskeletal elements by molecular motors. Most transported mRNAs are assumed translationally dormant while en route. In some cell types, especially in neurons, it is considered crucial that translation remains repressed after arrival at the destination site (e.g., a postsynaptic microdomain) until an appropriate activation signal is received. Several candidate mechanisms have been suggested to participate in the local implementation of translational repression and activation, and such mechanisms may target translation at the level of initiation and/or elongation. Recent data indicate that untranslated RNAs may play important roles in the local control of translation.
Postnatal developmental consequences of altered insulin sensitivity in female sheep treated prenatally with testosterone
Authors: Recabarren Sergio E. , Padmanabhan Vasantha , Codner Ethel , Lobos Alejandro , Durán Claudio , Vidal Mónica , Foster Douglas L. , Sir-Petermann Teresa
Published: October 2005

Prenatally testosterone (T)-treated female sheep exhibit ovarian and endocrinological features that resemble those of women with polycystic ovarian syndrome (PCOS), which include luteinizing hormone excess, polyfollicular ovaries, functional hyperandrogenism, and anovulation. In this study, we determined the developmental impact of prenatal T treatment on insulin sensitivity indexes (ISI), a variable that is affected in a majority of PCOS women. Pregnant ewes were treated with 60 mg testosterone propionate intramuscularly in cottonseed oil two times a week or vehicle [control (C)] from days 30 to 90 of gestation. T-females weighed less than C-females or males ( P < 0.05) at birth and at 5 wk of age. T-females had an increased anogenital ratio. An intravenous glucose tolerance test followed by an insulin tolerance test conducted after an overnight fast at 5, 20, and 30 wk of age ( n = 7–8/group) revealed that ISI were higher at 5 than 30 wk of age in C-females, reflective of a developing insulin resistance associated with puberty. T-females had higher basal insulin levels, higher fasting insulin-to-glucose ratio, and higher incremental area under the insulin curve to the glucose challenge. The ISI of T-females was similar to that of males. No differences in ISI were evident between groups at 20 and 30 wk of age. Mean basal plasma glucose concentrations and glucose disappearance and uptake did not differ between groups at any age. Our findings suggest that prenatal T treatment leads to offspring with reduced birth weight and impaired insulin sensitivity in early postnatal life.