bluuebunny/crossref_metadata_2025 huggingface dataset:
Discovery of the previously unrecorded family Copromorphidae Meyrick (Lepidoptera) in Japan, with description of a new species and autapomorphies for the family
Authors: NASU Yoshitsugu , SAITO Tosihisa , KOMAI Furumi
Published: March 2004

Copromorpha kijimuna sp. nov., which is closely related to C. pleurophanes Meyrick (Copromorphidae), is described from the Ryukyus, Japan, with illustrations of the adult stage, including its genitalia, and of the immature stage. The larva bores into the fruit of Ficus virgata (Moraceae). Descriptions of the immature stages of the genus are given for the first time. The lectotype of C. pleurophanes, including its genitalia, is illustrated. Both the family and the genus are newly added to the Japanese moth fauna. Autapomorphies for the Copromorphidae are proposed on the basis of larval and pupal characters.
Social wasps of the subfamily Vespinae (Hymenoptera, Vespidae) of the Kyrghyz Republic
Authors: DUBATOLOV Vladimir V. , MILKO Dmitry A.
Published: March 2004

Based on newly collected and museum material, the distribution of species of the Vespinae in the Kyrghyz Republic is discussed. Vespula austriaca is recorded for the first time from Kyrghyzstan. Dolichovespula norwegica is first reported in the Pamir‐Alai Mountains, providing the southernmost record for the species.
Effect of metanotal secretion ingestion on oviposition in a tree cricket, Truljalia hibinonis (Orthoptera: Gryllidae)
Authors: ONO Tomohiro , ANDO Chie , KONDO Yuki
Published: March 2004

The female Truljalia hibinonis ingests metanotal secretions of the male during copulation. The effect of ingestion on oviposition behavior was compared between three female groups: females that copulated once with an intact male (a male that had not been manipulated; M group); females that copulated once with a male from which most of the metanotal secretion had been removed (NO group); and females that copulated once with an intact male followed by being artificially supplied with metanotal secretion three times (MS group). There were no obvious differences in female fecundity across the three groups. However, within the MS group, intake of an optimal amount of metanotal secretion increased the number of eggs laid. This effect appeared quickly after ingestion and was most effective on the first bout (eggs laid during the first few days after copulation) after ingestion of the metanotal secretion. In contrast, the number of eggs laid had a negative correlation with the amount of metanotal secretion ingested when the amount exceeded the optimal in this experimental arrangement.
Private Benefits of Control: An International Comparison
Authors: Dyck Alexander , Zingales Luigi
Published: March 2004

We estimate private benefits of control in 39 countries using 393 controlling blocks sales. On average the value of control is 14 percent, but in some countries can be as low as −4 percent, in others as high a +65 percent. As predicted by theory, higher private benefits of control are associated with less developed capital markets, more concentrated ownership, and more privately negotiated privatizations. We also analyze what institutions are most important in curbing private benefits. We find evidence for both legal and extra‐legal mechanisms. In a multivariate analysis, however, media pressure and tax enforcement seem to be the dominating factors.
The Information Content of Share Repurchase Programs
Authors: Grullon Gustavo , Michaely Roni
Published: March 2004

Contrary to the implications of many payout theories, we find that announcements of open‐market share repurchase programs are not followed by an increase in operating performance. However, we find that repurchasing firms experience a significant reduction in systematic risk and cost of capital relative to non‐repurchasing firms. Further, consistent with the free cash‐flow hypothesis, we find that the market reaction to share repurchase announcements is more positive among those firms that are more likely to overinvest. Finally, we find evidence to indicate that investors underreact to repurchase announcements because they initially underestimate the decline in cost of capital.
Liquidity Externalities and Adverse Selection: Evidence from Trading after Hours
Authors: Barclay Michael J. , Hendershott Terrence
Published: March 2004

This paper examines liquidity externalities by analyzing trading costs after hours. There is less than 1/20 as many trades per unit time after hours as during the trading day. The reduced trading activity results in substantially higher trading costs: quoted and effective spreads are three to four times larger than during the trading day. The higher spreads reflect greater adverse selection and order persistence, but not higher dealer profits. Because liquidity provision remains competitive after hours, the greater adverse selection and higher trading costs provide a direct measure of the magnitude of the liquidity externalities generated during the trading day.
Does Net Buying Pressure Affect the Shape of Implied Volatility Functions?
Authors: Bollen Nicolas P. B. , Whaley Robert E.
Published: March 2004

This paper examines the relation between net buying pressure and the shape of the implied volatility function (IVF) for index and individual stock options. We find that changes in implied volatility are directly related to net buying pressure from public order flow. We also find that changes in implied volatility of S&P 500 options are most strongly affected by buying pressure for index puts, while changes in implied volatility of stock options are dominated by call option demand. Simulated delta‐neutral option‐writing trading strategies generate abnormal returns that match the deviations of the IVFs above realized historical return volatilities.
Second Births and the Second Shift: A Research Note on Gender Equity and Fertility
Authors: Torr Berna Miller , Short Susan E.
Published: March 2004

In a set of propositions on fertility transition, Peter McDonald recently proposed that the decline from replacement‐level fertility to low fertility is associated with a combination of high levels of gender equity in individual‐oriented institutions, such as education and market employment, and low levels of gender equity in the family and family‐oriented institutions. Similarly, the “second shift,” or the share of domestic work performed by formally employed women, forms a critical piece of current cross‐national explanations for low fertility. Building on this scholarship, the authors explore whether there is empirical evidence at the individual level for a relationship between gender equity at home, as indicated by the division of housework among working couples with one child, and the transition to a second birth. Results, based on a sample of US couples, indicate a U‐shaped relationship between gender equity and fertility. Both the most modern and the most traditional housework arrangements are positively associated with fertility. This empirical test elaborates the family‐fertility relationship and underscores the need to incorporate family context, including gender equity, into explanations for fertility change.
Removal of dry etch damage in p-type GaN by wet etching of sacrificial oxide layer
Authors: Lee Ji-Myon , Lee Kug-Seung , Park Seong-Ju
Published: March 2004

We describe etch-induced damage in p-type GaN caused by an inductively coupled Cl2/Ar/O2 plasma and a method for its removal by means of wet etching. When p-GaN was etched by a Cl2/Ar/O2 plasma, an oxide layer was formed on the p-GaN surface by the oxygen in the plasma. The electrical properties of the etched p-GaN films deteriorated, as a result of the oxide on the surface, as well as etch-induced damage. However, a HF postwet etching of the dry-etched samples effectively removed the sacrificial oxide layer on the surface that contained the etch-induced defects and damage, resulting in improved characteristics in surface morphology and photoluminescence in the etched p-type GaN.
Influence of polymer phase separation on roughness of resist features
Authors: Yasin Shazia , Hasko D. G. , Khalid M. N. , Weaver D. J. , Ahmed H.
Published: March 2004

The dependence of roughness of poly(methylmethacrylate) resist features on developer composition and development time, using methyl isobutyl ketone:propanol (MIBK:IPA) developer with and without ultrasonic assistance, is investigated using atomic force microscopy. It is found that the roughness decreases with increasing proportion of MIBK in the developer and that for a weak developer (1:4 MIBK:IPA at 25 °C), the roughness increases with development time. Ultrasonically assisted development is also found to reduce the roughness when using a weak developer, but has no significant effect with a strong developer (1:1 MIBK:IPA), or when using 3:7 water:IPA. We propose that the origin of the roughness is due to phase separation during development in weak solvents and for long development times.
Critical cluster size of InAs quantum dots formed by Stranski–Krastanow mode
Authors: Shiramine Ken-ichi , Itoh Tomohiko , Muto Shunichi
Published: March 2004

The number of In atoms in a critical cluster, i*, in Stranski–Krastanow (S–K) mode of InAs islands was determined to be 1–10. The i* was determined using an activation energy EA of 2.0 eV determined from an Arrhenius plot of the saturated density of InAs islands formed on a GaAs (001) surface by S–K mode of molecular beam epitaxy [K. Shiramine et al., J. Cryst. Growth 242, 332 (2002)], and an activation energy of 1.6 eV for migration (surface diffusion) of In adatoms, inferred from other references. The common value ∼2.0 eV of EA in S–K mode was ascribed to the small i*.
Approach curve method for large anode–cathode distances
Authors: Mammana V. P. , Monteiro O. R. , Fonseca L. R. C.
Published: March 2004

An important technique used to characterize field emission is the measurement of the emitted current against electric field (I×E). In this work we discuss a procedure for obtaining I×E data based on multiple approach curves. We show that the simulated features obtained for an idealized uniform surface matches available experimental data for small anode–cathode distances, while for large distances the simulation predicts a departure from the linear regime. We also discuss the shape of the approach curves for large anode–cathode distances for a cathode made of carbon nanotubes.
Post-growth process relaxation properties of strained Cd0.92Zn0.08Te/Cd0.83Zn0.17Te quantum well heterostructures grown by molecular beam epitaxy
Authors: Jacob A. P. , Myrberg T. , Nur O. , Willander M. , Kyutt R. N.
Published: March 2004

The post-growth structural stability regarding relaxation and defect propagation in Cd0.83Zn0.17Te/Cd0.92Zn0.08Te/Cd0.83Zn0.17Te quantum well (QW) heterostructures grown on [001] oriented Cd0.88Zn0.12Te substrates at 300 °C by molecular beam epitaxy is investigated. The investigated heterostructures were subjected to post-growth thermal treatment in an ambient atmosphere in a temperature range between 280 and 550 °C for 3 h each. We have used high-resolution x-ray diffraction as the main characterization tool. High-resolution rocking curves as well as the powerful two-dimensional reciprocal space mapping were employed in both symmetrical as well as asymmetrical reflections. The results indicate that at a post-growth temperature cycle of 350 °C for 3 h slight modification of the Cd0.83Zn0.17Te/Cd0.92Zn0.08Te barrier/QW heterointerface smoothness is affected. This indicates the onset of migration of Zn atoms at this post-growth temperature time cycle. At 450 °C, this effect is more pronounced and seen as the complete disappearance of thickness fringes. For higher post-growth thermal treatment at 550 °C for 3 h, a high relaxation level accompanied by Zn content reduction is observed. A reduction of the Zn content down to 0.11 fractional value in the thick Cd0.83Zn0.17Te barrier is attributed to Zn out diffusion and/or Zn precipitation.
Ultrahigh resolution secondary ion mass spectrometry profiling with oblique O2+ beams below 200 eV
Authors: Jiang Z. X. , Lerma J. , Sieloff D. , Lee J. J. , Backer S. , Bagchi S. , Conner J.
Published: March 2004

Based on a model that formation of (near) full oxide slows down or eliminates development of surface topography in Si, we explored conditions under which an oblique O2+ beam at a few hundred electron Volts does not stimulate significant surface roughening in Si in ultrahigh vacuum. It was found that bombardment of Si by an 158 eV/45° O2+ beam achieved (near) full oxidation at the initial stage of sputtering erosion of Si and eliminated rapid onset of roughening as often observed for sub-keV oblique O2+ beams. Thanks to the minimal surface roughening and atomic mixing in Si with the 158 eV/45° O2+ beam, secondary ion mass spectrometry profiling with this beam provided an unprecedented high depth resolution in characterizing SiGe deltas in Si.
Image placement issues for ITO-based step and flash imprint lithography templates
Authors: Nordquist K. J. , Ainley E. S. , Mancini D. P. , Dauksher W. J. , Gehoski K. A. , Baker J. , Resnick D. J. , Masnyj Z. , Mangat P. J. S.
Published: March 2004

Step and flash imprint lithography (SFIL) is an attractive, low-cost method for printing sub-100 nm geometries. The imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Since SFIL is a 1× lithography technology, the template will require precise image placement in order to meet overlay specifications for multiple level device fabrication. In order to simplify the template fabrication process and facilitate post fabrication scanning-electron-microscope-based inspection, an integrated charge dissipation layer, such as indium tin oxide (ITO), is desired that is transparent to the SFIL exposure wavelength. The use of low-stress dielectric films such as SiON for the image relief layer minimizes the pattern distortions (<9 nm, mean+3σ) that occur after the pattern transfer process. Although ITO uniformity was also significantly improved by switching the ITO deposition process to an MRC sputter deposition system, image placement results were adversely affected.
Effect of thin-film imaging on line edge roughness transfer to underlayers during etch processes
Authors: Goldfarb Dario L. , Mahorowala Arpan P. , Gallatin Gregg M. , Petrillo Karen E. , Temple Karen , Angelopoulos Marie , Rasgon Stacy , Sawin Herbert H. , Allen Scott D. , Lawson Margaret C. , Kwong Ranee W.
Published: March 2004

For the patterning of sub-100 nm features, a clear understanding of the origin and control of line edge roughness (LER) is extremely desirable, from a fundamental as well as a manufacturing perspective. With the migration to thin photoresists coupled with bottom antireflective coating (ARC)-hardmask underlayers, LER analysis of the developed resist structures is perhaps an inaccurate representation of the substrate roughness after the etch process, since those underlayers can play a significant role in increasing/decreasing linewidth variations during the image transfer process and hence can impact the device performance. In this article, atomic force microscopy is used to investigate the contribution of the imaging resist sidewall topography to the sidewall roughness of the final etched feature in thin photoresists, ARC, and hardmasks. Resist systems suitable for 248 and 193 nm lithography as well as fluorine-containing resists were processed using N2-H2 or fluorocarbon plasma etch. It is shown that the interaction of different etch chemistries with existing sidewall profiles can result in loss of the original morphological information and creation of new spatial frequency domains that act as physical templates for subsequent image transfer processes. Excessive roughness transfer into the hardmask layer due to insufficient resist thickness or inadequate etch resistance originates from striation propagation from the resist layer into the hardmask layer. In the case of fluorine-containing materials, a decreased etch resistance and reduced initial film thickness values give rise to critical underlayer roughening during plasma etch. Based on the results shown, it is predicted that advanced resist systems for 157 nm lithography and beyond will require the use of ARC layers with built-in hardmask properties in those particular cases in which patterning of deep trenches is needed, in order to maintain LER values within acceptable levels.
Ion bombardment energy control for selective fluorocarbon plasma etching of organosilicate glass
Authors: Silapunt R. , Wendt A. E. , Kirmse K. , Losey L. P.
Published: March 2004

The role of ion bombardment in plasma etch selectivity of organosilicate glass to etch stop layers of silicon carbide and silicon nitride has been investigated in a C4F8/N2/Ar plasma using a method that produces a narrow ion energy distribution (IED) at the substrate surface. The effects of the narrow IED are compared with those of the broad, bimodal IED produced by the conventional sinusoidal bias voltage wave form (at 13.56 MHz). A comparison of etch rate versus average ion bombardment energy shows a higher ion energy threshold for etching, a larger gap between the thresholds for the two materials, and high selectivity over a wider range of bias voltage with the narrow IED. A physical explanation of the observed phenomena is proposed.
Compositional shift in AlxGa1−xN beneath annealed metal contacts
Authors: Hull B. A. , Mohney S. E. , Chowdhury U. , Dupuis R. D.
Published: March 2004

Interfacial reactions between Ni, Pd, or Au contacts and AlxGa1−xN with compositions x=0.15 and 0.47 were studied in this investigation. X-ray photoelectron spectroscopy and scanning transmission electron microscopy coupled with energy dispersive spectroscopy showed that reaction between these metals and AlxGa1−xN results in a pronounced shift in the AlxGa1−xN beneath the contact to an Al-enriched composition. This Al enrichment results from the preferential outdiffusion of Ga into the metal films, and this reaction is consistent with thermodynamic driving forces in these systems. Possible consequences of the observed compositional shift on the electrical properties of contacts to AlxGa1−xN are also discussed.
Temperature characteristics due to stress-induced migration
Authors: Aoyagi Minoru
Published: March 2004

The stress-induced migration phenomenon causes voids and disconnections in metal interconnections in semiconductor devices during high-temperature storage. This phenomenon is one of the problems related to the reliability of metal interconnections. The following discrepancies with respect to high-temperature storage are found among results reported by researchers concerning the temperature dependence of the interconnection lifetime: maximum failure rate appears at a certain temperature; failure rate increases with temperature; and failure rate is independent of temperature. The reasons for these discrepancies have not been clarified as yet. The purpose of this work is to theoretically clarify the temperature characteristic of stress-induced migration. First, we present the theoretical model for the vacancy behavior due to stress-induced migration. Next, the theoretical model is applied to void formation and disconnection to confirm its validity. Finally, the results of the theoretical analysis are compared with the experimental results of high-temperature storage. We find that the temperature characteristics of void formation change depending on the void interval, and those of disconnection change depending on the void interval and the void radius. The presented model can qualitatively explain that the discrepancies among various researchers’ findings concern the temperature dependence of the interconnection lifetime.
Electron induced nanodeposition of tungsten using field emission scanning and transmission electron microscopes
Authors: Shimojo M. , Mitsuishi K. , Tameike A. , Furuya K.
Published: March 2004

Electron beam induced chemical vapor deposition (EBI-CVD) is one of the promising methods for nanofabrication. EBI-CVD has generally been carried out in conventional scanning electron microscopes and the minimum size of the deposits was in the range between 20 and 300 nm. In this study, a field emission gun scanning electron microscope (FE-SEM) and a field emission gun transmission electron microscope (FE-TEM) with gas introduction systems were employed for deposition using a W(CO)6 precursor in order to reduce the size of deposits. Dots, 15–20 nm in diameter, were produced using the FE-SEM. The dots consist mainly of tungsten with small amounts of carbon and oxygen. By using the FE-TEM, the diameter of the dots can be reduced to 3.5 nm. The relationship between probe size and dot diameter is discussed. Rods, the diameter of which was 8 nm, were also fabricated by scanning the beam position in the FE-TEM. Deposits produced by FE-TEM are smaller than those by conventional electron microscopes.
Semiconducting and ferromagnetic properties of Ti1−xCoxO2 thin films grown by liquid-delivery metalorganic chemical vapor deposition
Authors: Seong Nak-Jin , Yoon Soon-Gil
Published: March 2004

We have used liquid-delivery metalorganic chemical vapor deposition to grow polycrystalline Ti1−xCoxO2 anatase films with various Co concentrations onto SiO2/Si(100), and have measured the elemental distribution, magnetic properties, and chemical bonding states of the resulting films. The ionic states of Co in ferromagnetic Ti1−xCoxO2 films have the +2 formal oxidation states. Co-rich clusters on the Ti1−xCoxO2 film surface were formed above the limit of solubility of approximately x=0.05. Co-rich clusters formed in Ti1−xCoxO2 films decreased the value of Hc (coercive field) and increased the value of Ms (saturation magnetic field). The Ms and Hc of Ti0.97Co0.03O2 thin films were approximately 20 emu/cm2 and 250 Oe, respectively. The Curie temperature (Tc) of Ti0.97Co0.03O2 thin films is estimated to be higher than 300 K.
Effects of hydrogen plasma treatment on electrical properties of p-AlGaN
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Baik K. H. , Pearton S. J. , Luo B. , Ren F. , Zavada J. M.
Published: March 2004

Effects of hydrogen plasma treatment at 250 °C on electrical properties and deep level spectra of the p-AlGaN films with the Al mole fraction of x=0.15 are reported. It is shown that the concentration of Mg acceptors is strongly (about an order of magnitude) decreased after such a treatment, most likely due to hydrogen passivation of acceptors. It is also shown that there are in fact two closely spaced in energy shallow acceptors and that the ones dominant in the virgin and Mg-related samples are more effectively passivated than the others. Hydrogen plasma treatment also leads to suppression of deep nonradiative recombination centers as evidenced by the increase in the microcathodoluminescence intensity.
Fabrication of nanoelectrodes based on controlled placement of carbon nanotubes using alternating-current electric field
Authors: Chen Zhi , Hu Wenchong , Guo Jun , Saito Kozo
Published: March 2004

A fabrication process for nanoelectrodes with a nanogap of ∼35 nm is presented. This process is based on controlled placement of carbon nanotubes on metal electrodes using an alternating-current (ac) electric field. One bundle of single-walled nanotubes (SWNT) was placed successfully between two electrodes using an ac electric field. Electrical measurement of the SWNT bundle through the two metal contacts shows nonlinear current-voltage characteristics, similar to those of the two back-to-back Schottky diodes. The nanoelectrodes were fabricated using a single bundle of SWNTs as a shadow mask. The SWNT bundle was suspended on the metal electrodes on top of the photoresist supporter using the ac electric-field alignment. After evaporation of Al and liftoff, nanoelectrodes with a gap of ∼35 nm were successfully obtained. A simple model is proposed which suggests that gaps ranging from 10 to 50 nm can be fabricated through adjustment of the distance from the source to the substrate.
Quantification of Optison bubble size and lifetime during sonication dominant role of secondary cavitation bubbles causing acoustic bioeffects
Authors: Kamaev Pavel P. , Hutcheson Joshua D. , Wilson Michelle L. , Prausnitz Mark R.
Published: March 2004

Acoustic cavitation has been shown to deliver molecules into viable cells, which is of interest for drug and gene delivery applications. To address mechanisms of these acoustic bioeffects, this work measured the lifetime of albumin-stabilized cavitation bubbles (Optison) and correlated it with desirable (intracellular uptake of molecules) and undesirable (loss of cell viability) bioeffects. Optison was exposed to 500 kHz ultrasound (acoustic pressures of 0.6–3.0 MPa and energy exposures of 0.2–200 J/cm2) either with or without the presence of DU145 prostate cancer cells (106 cells/ml) bathed in calcein, a cell-impermeant tracer molecule. Bubble lifetime was determined using a Coulter counter and flow cytometer, while bioeffects were evaluated by flow cytometry. The lifetime of Optison cavitation nuclei was found to decrease and bioeffects (molecular uptake and loss of cell viability) were found to increase with increasing acoustic energy exposure. These bioeffects correlated well with the disappearance of bubbles, suggesting that contrast agent destruction either directly or indirectly affected cells, probably involving unstabilized cavitation nuclei created upon the destruction of Optison. Because Optison solutions presonicated to destroy all detectable bubbles also caused significant bioeffects, the indirect mechanism involving secondary cavitation bubbles is more likely.
Partial sound field decomposition in multireference near-field acoustical holography by using optimally located virtual references
Authors: Kim Yong-Joe , Bolton J. Stuart , Kwon Hyu-Sang
Published: March 2004

It has been shown previously that the multiple reference and field signals recorded during a scanning acoustical holography measurement can be used to decompose the sound field radiated by a composite sound source into mutually incoherent partial fields. To obtain physically meaningful partial fields, i.e., fields closely related to particular component sources, the reference microphones should be positioned as close as possible to the component physical sources that together comprise the complete source. However, it is not always possible either to identify the optimal reference microphone locations prior to performing a holographic measurement, or to place reference microphones at those optimal locations, even if known, owing to physical constraints. Here, post-processing procedures are described that make it possible both to identify the optimal reference microphone locations and to place virtual references at those locations after performing a holographic measurement. The optimal reference microphone locations are defined to be those at which the MUSIC power is maximized in a three-dimensional space reconstructed by holographic projection. The acoustic pressure signals at the locations thus identified can then be used as optimal “virtual” reference signals. It is shown through an experiment and numerical simulation that the optimal virtual reference signals can be successfully used to identify physically meaningful partial sound fields, particularly when used in conjunction with partial coherence decomposition procedures.
Pressure and velocity fields produced by an underwater explosion
Authors: Hunter Kendall S. , Geers Thomas L.
Published: March 2004

An integrated model for a moderately deep underwater explosion bubble has recently been developed. For the initial shock-wave phase, the model employs an empirical pressure-profile expression for the far field to determine bubble radius as a function of time. For the subsequent oscillation phase, the model accounts for first-order wave effects in both the external liquid and the internal gas. In the present paper, a radiation model consistent with the integrated bubble model is formulated and evaluated. The distant pressure and velocity fields produced during the shock-wave phase derive from the empirical pressure-profile expression. Those produced during the oscillation phase derive from a matched-asymptotic-expansion solution for a translating acoustic source/dipole. Response histories and snapshots for far-field pressure and velocity are computed. Comparisons with existing experimental data exhibit good correlation.
Echo-to-reverberation enhancement using a time reversal mirror
Authors: Kim S. , Kuperman W. A. , Hodgkiss W. S. , Song H. C. , Edelmann G. , Akal T.
Published: March 2004

Reverberation from rough ocean boundaries often degrades the performance of active sonar systems in the ocean. The focusing capability of the time-reversal method provides a new approach to this problem. A time-reversal mirror (TRM) focuses acoustic energy on a target enhancing the target echo while shadowing the boundaries below and above the focus in a waveguide, thereby reducing reverberation. The resulting echo-to-reverberation enhancement has been demonstrated experimentally using a time-reversal mirror in the 3–4 kHz band in shallow water.
Acoustic identification of a single transmission at 3115 km from a bottom-mounted source at Kauai
Authors: Spiesberger John L.
Published: March 2004

Sounds received in the Gulf of Alaska at 3115 km from the ATOC/NPAL source at Kauai (75 Hz, 0.027-s resolution, bottom-mounted) are compared with acoustic and oceanographic models. Unlike data collected at stationary SOSUS arrays, these data come from a towed horizontal array at 372-m depth of military origin. A plausible identification of the acoustic reception is made despite the fact that only one transmission is collected and sound interacts with the bottom near the source. The similarity between the modeled and measured impulse response here may be useful for understanding the signals between this same source and the NPAL array near southern California. The plausible identification of sound from the horizontal array here appears to point toward the feasibility of using other military platforms of opportunity besides SOSUS to study acoustic propagation and possibly map climatic changes in temperature by means of tomography.
Air-coupled ultrasonic sensing of grass-covered vibrating surfaces; qualitative comparisons with laser Doppler vibrometry
Authors: Petculescu Andi G. , Sabatier James M.
Published: March 2004

The paper addresses several sensitive issues concerning the use of air-coupled ultrasound to probe small vibrations of surfaces covered with low-lying vegetation such as grass. The operation of the ultrasonic sensor is compared to that of a laser Doppler vibrometer, in various contexts. It is shown that ambient air motion affects either system, albeit differently. As air speed increases, the acoustic sensor detects a progressively richer turbulent spectrum, which reduces its sensitivity. In turn, optical sensors are prone to tremendous signal losses when probing moving vegetation, due to randomly varying speckle patterns. The work was supported by the Office of Naval Research.
Infinite-impulse-response models of the head-related transfer function
Authors: Kulkarni Abhijit , Colburn H. Steven
Published: March 2004

Head-related transfer functions (HRTFs) measured from human subjects were approximated using infinite-impulse-response (IIR) filter models. Models were restricted to rational transfer functions (plus simple delays) so that specific models are characterized by the locations of poles and zeros in the complex plane. The all-pole case (with no nontrivial zeros) is treated first using the theory of linear prediction. Then the general pole-zero model is derived using a weighted-least-squares (WLS) formulation of the modified least-squares problem proposed by Kalman (1958). Both estimation algorithms are based on solutions of sets of linear equations and result in efficient computational schemes to find low-order model HRTFs. The validity of each of these two low-order models was assessed in psychophysical experiments. Specifically, a four-interval, two-alternative, forced-choice paradigm was used to test the discriminability of virtual stimuli constructed from empirical and model HRTFs for corresponding locations. For these experiments, the stimuli were 80 ms, noise tokens generated from a wideband noise generator. Results show that sounds synthesized through model HRTFs were indistinguishable from sounds synthesized from original HRTF measurements for the majority of positions tested. The advantages of the techniques described here are the computational efficiencies achieved for low-order IIR models. Properties of the all-pole and pole-zero estimators are discussed in the context of low-order HRTF representations, and implications for basic and applied contexts are considered.
Simulations of cochlear implant hearing using filtered harmonic complexes: Implications for concurrent sound segregation
Authors: Deeks John M. , Carlyon Robert P.
Published: March 2004

Two experiments used simulations of cochlear implant hearing to investigate the use of temporal codes in speech segregation. Sentences were filtered into six bands, and their envelopes used to modulate filtered alternating-phase harmonic complexes with rates of 80 or 140 pps. Experiment 1 showed that identification of single sentences was better for the higher rate. In experiment 2, maskers (time-reversed concatenated sentences) were scaled by −9 dB relative to a target sentence, which was added with an offset of 1.2 s. When the target and masker were each processed on all six channels, and then summed, processing the masker on a different rate to the target improved performance only when the target rate was 140 pps. When the target sentence was processed on the odd-numbered channels and the masker on the even-numbered channels, or vice versa, performance was worse overall, but showed similar effects of pulse rate. The results, combined with recent psychophysical evidence, suggest that differences in pulse rate are unlikely to prove useful for concurrent sound segregation.
The influence of duration and level on human sound localization
Authors: Vliegen Joyce , Van Opstal A. John
Published: March 2004

The localization of sounds in the vertical plane (elevation) deteriorates for short-duration wideband sounds at moderate to high intensities. The effect is described by a systematic decrease of the elevation gain (slope of stimulus–response relation) at short sound durations. Two hypotheses have been proposed to explain this finding. Either the sound localization system integrates over a time window that is too short to accurately extract the spectral localization cues (neural integration hypothesis), or the effect results from cochlear saturation at high intensities (adaptation hypothesis). While the neural integration model predicts that elevation gain is independent of sound level, the adaptation hypothesis holds that low elevation gains for short-duration sounds are only obtained at high intensities. Here, these predictions are tested over a larger range of stimulus parameters than has been done so far. Subjects responded with rapid head movements to noise bursts in the two-dimensional frontal space. Stimulus durations ranged from 3 to 100 ms; sound levels from 26 to 73 dB SPL. Results show that the elevation gain decreases for short noise bursts at all sound levels, a finding that supports the integration model. On the other hand, the short-duration gain also decreases at high sound levels, which is in line with the adaptation hypothesis. The finding that elevation gain was a nonmonotonic function of sound level for all sound durations, however, is predicted by neither model. It is concluded that both mechanisms underlie the elevation gain effect and a conceptual model is proposed to reconcile these findings.
Propagating and evanescent elastic waves in cylindrical waveguides of arbitrary cross section
Authors: Damljanović Vesna , Weaver Richard L.
Published: March 2004

We study waves in elastic waveguides, with a view toward the nondestructive evaluation of slender structures by means of imposed vibrations. Envisioned applications demand an accurate understanding of both propagating and evanescent guided waves in waveguides of arbitrary cross section. Accordingly, we develop a theoretical framework in which energy principles and finite element discretization lead to a discrete set of solutions representing both wave types. We examine the solutions in great detail, with a particular emphasis on the accuracy of the finite element discretization. Results are compared with analytic solutions of the Pochhammer–Chree equations for the special case of a circular cross section, determining the combination of mesh parameters and frequency regimes for which the code yields accurate results. Convergence studies are conducted for the case of a more complex cross section, that of a typical railroad rail.
The Helmholtz equation least-squares method and Rayleigh hypothesis in near-field acoustical holography
Authors: Semenova Tatiana , Wu Sean F.
Published: March 2004

In this paper we present a numerical investigation of reconstructing time-harmonic acoustic pressure field in two dimensional space by using a series expansion—the so-called Helmholtz equation least-squares (HELS) method. Series expansion methods (or the Rayleigh methods) have been widely used in predicting the scattered acoustic pressure. With regularization, they can also be applied to reconstruction of acoustic pressure on the source surface from the measurements taken in the field, and HELS is the first such attempt for these problems. In this paper, we establish HELS in the framework of the Rayleigh methods and reveal its interrelationship with the Rayleigh hypothesis. In particular, to regularize a reconstruction problem, we use the method of quasisolutions, i.e., a Tikhonov regularization with an a posteriori choice of the regularization parameter. It is shown that without regularization HELS can still yield a satisfactory reconstruction of acoustic radiation from an arbitrary object when enough measurements are taken at sufficiently close range to the source. With regularization the number of measurements can be reduced and reconstruction accuracy be enhanced. It is concluded that HELS can be used to reconstruct acoustic radiation from a convex arbitrarily shaped vibrating object regardless of the validity of the Rayleigh hypothesis, although in practice the results will depend on the rate of convergence of the approximating sequence.
Acoustic and perceptual similarity of North German and American English vowels
Authors: Strange Winifred , Bohn Ocke-Schwen , Trent Sonja A. , Nishi Kanae
Published: March 2004

Current theories of cross-language speech perception claim that patterns of perceptual assimilation of non-native segments to native categories predict relative difficulties in learning to perceive (and produce) non-native phones. Cross-language spectral similarity of North German (NG) and American English (AE) vowels produced in isolated hVC(a) (di)syllables (study 1) and in hVC syllables embedded in a short sentence (study 2) was determined by discriminant analyses, to examine the extent to which acoustic similarity was predictive of perceptual similarity patterns. The perceptual assimilation of NG vowels to native AE vowel categories by AE listeners with no German language experience was then assessed directly. Both studies showed that acoustic similarity of AE and NG vowels did not always predict perceptual similarity, especially for “new” NG front rounded vowels and for “similar” NG front and back mid and mid-low vowels. Both acoustic and perceptual similarity of NG and AE vowels varied as a function of the prosodic context, although vowel duration differences did not affect perceptual assimilation patterns. When duration and spectral similarity were in conflict, AE listeners assimilated vowels on the basis of spectral similarity in both prosodic contexts.
Temporal effects in simultaneous masking with on- and off-frequency noise maskers: Effects of signal frequency and masker level
Authors: Bacon Sid P. , Savel Sophie
Published: March 2004

Temporal effects in simultaneous masking were measured as a function of masker level for an on-frequency broadband masker and an off-frequency narrow-band masker for signal frequencies of 750, 1730, and 4000 Hz. The on-frequency masker was 10 equivalent rectangular bandwidths (ERBs) wide and centered at the signal frequency; the off-frequency masker was 500 Hz wide and its lower frequency edge was 1.038 ERBs higher in frequency than the signal. The primary goal of the study was to determine whether previously observed differences regarding the effects of signal frequency and masker level on the temporal effect for these two different types of masker might be due to considerably different signal levels at threshold. Despite similar masked thresholds, the effects of signal frequency and masker level in the present study were different for the two masker types. The temporal effect was significant for the two highest frequencies and absent for the lowest frequency in the presence of the broadband masker, but was more or less independent of frequency for the narrow-band masker. The temporal effect increased but then decreased as a function of level for the broadband masker (at the two higher signal frequencies, where there was a temporal effect), but increased and reached an asymptote for the narrow-band masker. Despite the different effects of signal frequency and masker level, the temporal effects for both types of masker can be understood in terms of a basilar-membrane input–output function that becomes more linear during the course of masker stimulation.
Focusing at an arbitrary waveguide location using time reversal
Authors: Walker Shane C. , Roux Philippe , Kuperman W. A.
Published: March 2004

A method for producing acoustic time reversal focusing at an arbitrary location is presented. In principle, producing a focus at any location in a waveguide is trivial once the point to point propagation matrix is known. In practice, the propagation matrix over a given range, G(zs,zr,R) between sources zs at r=0 and receivers zr at r=R, can be directly measured with a pair of vertical line arrays. Once known, repeated iterations of G(zs,zr,R) result in good approximations to the propagation matrices, G(zs,zr,mR), for ranges mR, where m=2,3,... is the number of iterations applied. By combining this iteration technique with frequency-dependent range shifting, it is possible to produce acoustic time reversal focusing at any range and depth.
G Protein-Coupled Receptor-Dependent Development of Human Frontal Cortex
Authors: Piao Xianhua , Hill R. Sean , Bodell Adria , Chang Bernard S. , Basel-Vanagaite Lina , Straussberg Rachel , Dobyns William B. , Qasrawi Bassam , Winter Robin M. , Innes A. Micheil , Voit Thomas , Ross M. Elizabeth , Michaud Jacques L. , Déscarie Jean-Claude , Barkovich A. James , Walsh Christopher A.
Published: March 2004

The mammalian cerebral cortex is characterized by complex patterns of anatomical and functional areas that differ markedly between species, but the molecular basis for this functional subdivision is largely unknown. Here, we show that mutations in
GPR56
, which encodes an orphan G protein–coupled receptor (GPCR) with a large extracellular domain, cause a human brain cortical malformation called bilateral frontoparietal polymicrogyria (BFPP). BFPP is characterized by disorganized cortical lamination that is most severe in frontal cortex. Our data suggest that GPCR signaling plays an essential role in regional development of human cerebral cortex.
Enjoy the Silence
Authors: van Rij Ronald P. , Andino Raul
Published: March 2004

RNAi
A Guide to Gene Silencing. Gregory J. Hannon, Ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 2003. 444 pp. $130, £95. ISBN 0-87969-641-9.

The contributors, who include many pioneers in the field, present the principles behind RNA interference and a series of protocols for the laboratory use of RNAi in a variety of plant and animal systems.
LE 2-RANG DU GROUPE DE CLASSES DE CERTAINS CORPS BIQUADRATIQUES ET APPLICATIONS
Authors: AZIZI ABDELMALEK , MOUHIB ALI
Published: March 2004

Let K be a real biquadratic field and let k be a quadratic field with odd class number contained in K. The aim of this article is to determine the rank of the 2-class group of K and we give applications to the structure of the 2-class group of some biquadratic fields and to the 2-class field tower of some real quadratic fields.

Résumé: Soient K un corps biquadratique réel et k un sous-corps quadratique de K dont le nombre de classes est impair. Dans ce papier on détermine le rang du 2-groupe de classes de K et on donne des applications à la structure du 2-groupe de classes de certains corps biquadratiques et aussi à la tour des 2-corps de classes de Hilbert de certains corps quadratiques réels.
PARALLEL NETWORK COMPUTING APPROACH FOR DEA-RAM MEASUREMENT
Authors: SUEYOSHI TOSHIYUKI , HWANG SHIUH-NAN
Published: March 2004

An efficiency measure, referred to as "Range-Adjusted Measure (RAM)," has been recently proposed as a new type of DEA (Data Envelopment Analysis) performance evaluator. To deal with large RAM problems, this study documents how the algorithm of RAM is designed in a parallel process. The parallel process is implemented on a Local Area Network (LAN) that connects multiple personal computers. A large simulation study examines the performance of the proposed RAM network computing approach.
Apoptosis and Dependence Receptors: A Molecular Basis for Cellular Addiction
Authors: BREDESEN DALE E. , MEHLEN PATRICK , RABIZADEH SHAHROOZ
Published: March 2004

Bredesen, Dale E., Patrick Mehlen, and Shahrooz Rabizadeh. Apoptosis and Dependence Receptors: A Molecular Basis for Cellular Addiction. Physiol Rev 84: 411–430, 2004; 10.1152/physrev.00027.2003.—Classical signal transduction is initiated by ligand-receptor interactions. We have described an alternative form of signal transduction that is initiated by the withdrawal of ligands from specific receptors referred to as dependence receptors. This process is widespread, featuring in developmental cell death, carcinogenesis (especially metastasis), neurodegeneration, and possibly subapoptotic events such as neurite retraction and somal atrophy. Initial mechanistic studies of dependence receptors suggest that these receptors form complexes that include specific caspases. Complex formation appears to be a function of ligand-receptor interaction, and dependence receptors appear to exist in at least two conformational states. Complex formation in the absence of ligand leads to caspase activation by a mechanism that in at least some cases is dependent on caspase cleavage of the receptor itself, releasing proapoptotic peptides. Thus these receptors may serve in caspase amplification, and in so doing create cellular states of dependence on their respective ligands.