bluuebunny/crossref_metadata_2025 huggingface dataset:
Pension Reform in the EU Accession Countries: Challenges, Achievements and Pitfalls
Authors: Fultz Elaine
Published: March 2004

Like the current member States of the European Union (EU), the 13 accession countries have diverse pension systems that vary in the adequacy of benefits, the degree of solidarity, and the roles of government, workers, employers, and pension funds in scheme management. Since the mid‐1990s, nearly all have increased their pensionable age and adopted new systems for voluntary supplemental pension savings. Five have scaled down their social insurance schemes in favour of new systems of commercially managed individual savings accounts. The article discusses these reforms and their match with key elements of the countries' political and economic environments, financial markets and regulatory experience. It highlights alternative approaches to pension protection for retired workers in conditions of ageing populations.
Combining Welfare‐to‐Work Measures with Tax credits: A New Hybrid Approach to Social Security in the United Kingdom
Authors: Adler Michael
Published: March 2004

The changes described in this article reflect a shift in social security away from social insurance and towards a mixture of social assistance, occupational or private insurance and tax credits. It suggests that what is new and distinctive about UK social security policy is the way in which a new strategy has been forged by linking the New Deal, which provides job opportunities for people who are not in employment but can often only offer them low‐paid jobs, with tax credit schemes, which provide in‐work benefits and are designed to ensure that, if necessary, people accept poorly paid employment.
From skin microrelief to wrinkles. An area ripe for investigation
Authors: Piérard Gérald E , Uhoda Isabelle , Piérard‐Franchimont Claudine
Published: March 2004

Skin microrelief alters progressively with age. Wrinkles do not result from these changes but are superimposed upon them. Wrinkles result from structural changes in the epidermis, dermis and hypodermis. Four types of wrinkles can be recognized.

Type 1 wrinkles are atrophic.

Type 2 wrinkles are elastotic.

Type 3 wrinkles are expressional.

Type 4 wrinkles are gravitational.

Each type of wrinkle is characterized by distinct microanatomical changes and each type of wrinkle develops in specific skin regions. Each is likely to respond differently to treatment. Skin microrelief and skin folds can be identified on histological examination. By contrast, only minimal dermal changes are found beneath permanent or reducible wrinkles compared with immediately adjacent skin. A series of objective and non‐invasive methods is available to quantify the severity of wrinkling.
Comparison of hand‐to‐hand bioimpedance and anthropometry equations versus dual‐energy X‐ray absorptiometry for the assessment of body fat percentage in 17–18‐year‐old conscripts
Authors: Lintsi Mart , Kaarma Helje , Kull Ingrid
Published: March 2004

In the present study, hand‐to‐hand bioelectrical impedance analysis (BIA), skinfold (SKF) thickness and height–weight (body mass index, BMI)‐based equations and dual‐energy X‐ray absorptiometry (DEXA), as a criterion method, were compared with each other in the assessment of body fat percentage (BF%) in 17–18‐year‐old Estonian conscripts (n = 32). The Omron®BF body fat monitor estimated that BF% was lower than that of the criterion method DEXA. The difference between DEXA and Omron®BF 300 (III) was higher (1·1 ± 3·0%; P = 0·04) and that between DEXA and Omron®BF 306 lower (0·2 ± 3·0%; P>0·05). Omron®BF 300 (I) and (II) (series 8) had intermediate difference (0·9 ± 3·0 and 0·9 ± 3·0; P>0·05) when compared with DEXA. Three anthropometric equations estimated a higher BF% than cthat of DEXA. The Durnin & Womersley SKF equation BF% (1·0 ± 2·4; P = 0·03) was higher than that of the DEXA. Deurenberg et al. and Gallagher et al. BMI‐based equations overestimation yielded 0·9 ± 3·7 and 0·6 ± 3·8 BF% (P>0·05). From the anthropometric equations, only the Deurenberg et al. SKF equation slightly underestimated 0·5 ± 3·4 BF% (P>0·05). DEXA‐assessed BF% had highest correlation with SKF equations (r = 0·93), less so with BIA (r = 0·88–0·89) and lowest with BMI equation‐assessed BF% (r = 0·81–0·84). All values were significant at P<0·001. We can conclude that the Omron®BF 306 body fat monitor and the anthropometric Deurenberg et al. SKF equation yielded results close to the DEXA BF%.
Cosmosycanus, a new genus of harpactorine assassin bug established for Agriosphodrus perelegans (Heteroptera: Reduviidae)
Authors: ISHIKAWA Tadashi , TOMOKUNI Masaaki
Published: March 2004

A new monotypic genus Cosmosycanus is established for Agriosphodrus perelegans Breddin, 1903. This genus is separable from Agriosphodrus Stål, 1867 by the head being much longer than the pronotum, and the posterior pronotal lobe lacking a median depression. The new genus is also distinguished from Sycanus Amyot and Serville, 1843 by the smooth posterior pronotal lobe and the unspined and non‐tuberculate scutellum. The type species, Cosmosycanus perelegans, comb. nov. is redescribed and considered the senior synonym of Sycanus elongatulus Distant, 1919.
Chalcididae (Hymenoptera) from rice stores in Thailand, with description of two new species
Authors: KONISHI Kazuhiko , NARENDRAN Thekke C. , IMAMURA Taro , VISARATHANONTH Porntip
Published: March 2004

Five species of Chalcididae (Hymenoptera) were collected from rice stores in Thailand.Proconura minusaNarendran was dominant and is thought to be an important parasitoid ofSitotroga cerealella(Olivier). Many individuals ofProconura caryobori(Hanna) were collected, and the host in rice stores of this species wasCorcyra cephalonica(Stainton).Antrocephalus mitys(Walker) is known to parasitizeC. cephalonica, but few individuals were collected; therefore, it is thought not to be important in Thailand.Notaspidiella clavataNarendran and Konishi sp. nov. andNotaspidium thailandicumNarendran and Konishi sp. nov. are described.
Banks versus Venture Capital: Project Evaluation, Screening, and Expropriation
Authors: Ueda Masako
Published: March 2004

Why do some start‐up firms raise funds from banks and others from venture capitalists? To address this question, I study a model in which the venture capitalist can evaluate the entrepreneur's project more accurately than the bank but can also threaten to steal it from the entrepreneur. Consistent with evidence regarding venture capital finance, the model implies that the characteristics of a firm financing through venture capitalists are relatively little collateral, high growth, high risk, and high profitability. The model also suggests that tighter protection of intellectual property rights encourages entrepreneurs to finance through venture capitalists.
Default Risk in Equity Returns
Authors: Vassalou Maria , Xing Yuhang
Published: March 2004

This is the first study that uses Merton's (1974) option pricing model to compute default measures for individual firms and assess the effect of default risk on equity returns. The size effect is a default effect, and this is also largely true for the book‐to‐market (BM) effect. Both exist only in segments of the market with high default risk. Default risk is systematic risk. The Fama–French (FF) factors SMB and HML contain some default‐related information, but this is not the main reason that the FF model can explain the cross section of equity returns.
International Evidence on Institutional Trading Behavior and Price Impact
Authors: Chiyachantana Chiraphol N. , Jain Pankaj K. , Jiang Christine , Wood Robert A.
Published: March 2004

This study characterizes institutional trading in international stocks from 37 countries during 1997 to 1998 and 2001. We find that the underlying market condition is a major determinant of the price impact and, more importantly, of the asymmetry between price impacts of institutional buy and sell orders. In bullish markets, institutional purchases have a bigger price impact than sells; however, in the bearish markets, sells have a higher price impact. This differs from previous findings on price impact asymmetry. Our study further suggests that price impact varies depending on order characteristics, firm‐specific factors, and cross‐country differences.
Trading Activity and Price Volatility in the Municipal Bond Market
Authors: Downing Chris , Zhang Frank
Published: March 2004

Utilizing a comprehensive database of transactions in municipal bonds, we investigate the volume–volatility relation in the municipal bond market. We find a positive relation between the number of transactions and a bond's price volatility. In contrast to previous studies, we find a negative relation between average deal size and price volatility. These results are found to be robust throughout the sample. Our results are inconsistent with current theoretical models of the volume–volatility relation. These inconsistencies may arise because current models fail to account for the effects of overall market liquidity on the costs of large transactions.
Toward a National Market System for U.S. Exchange–listed Equity Options
Authors: Battalio Robert , Hatch Brian , Jennings Robert
Published: March 2004

In its response to the 1975 Congressional mandate to implement a national market system for financial securities, the Securities and Exchange Commission (SEC) initially exempted the option market. Recent dramatic changes in the structure of the option market prompted the SEC to revisit this issue. We examine a sample of actively traded, multiply listed equity options to ask whether this market's characteristics appear consistent with the goals of producing economically efficient transactions and facilitating “best execution.” We find marked changes between June 2000, when quotes are often ignored, and January 2002, when the market more closely resembles a national market.
When Does Religion Influence Fertility?
Authors: McQuillan Kevin
Published: March 2004

Religious affiliation as a determinant of demographic behavior is receiving renewed attention in demography. Interest in the role of cultural factors in affecting fertility and a specific concern with the role of Islam in many developing countries have helped re‐invigorate research on the role of religion. This article reviews theoretical and empirical work on that relationship, with special attention to a number of cases in which religion has been identified as an important determinant of fertility patterns. The article concludes that religion plays an influential role when three conditions are satisfied: first, the religion articulates behavioral norms with a bearing on fertility behavior; second, the religion holds the means to communicate these values and promote compliance; and, third, religion forms a central component of the social identity of its followers.
Recovery of dry-etch-induced surface damage on Mg-doped GaN by NH3 ambient thermal annealing
Authors: Moon Yong-Tae , Kim Dong-Joon , Park Jin-Sub , Oh Jeong-Tak , Lee Ji-Myon , Park Seong-Ju
Published: March 2004

We report that NH3 ambient thermal annealing is a promising method for recovering the dry- etch-induced damage on Mg-doped GaN surfaces. The surface electrical properties of dry-etched Mg-doped GaN can be fully recovered by thermal annealing using NH3 as an ambient gas at temperatures above 900 °C. The complete recovery of sheet hole concentration in dry-etched Mg-doped GaN can be attributed to a reduction in excess nitrogen vacancies in the damaged surface region by reactive nitrogen atoms supplied during NH3 ambient thermal annealing.
Utilizing maximum likelihood deblurring algorithm to recover high frequency components of scanning electron microscopy images
Authors: Williamson Mike , Neureuther Andrew
Published: March 2004

Applying an image deblurring technique used in image processing fields, scanning electron microscopy (SEM) images were enhanced by recovering the high frequency components of the image, thereby reducing image blur. The accuracy of the deblurring method was tested by examining isolated trenches, dense lines:trenches, and unpatterned photoresist. The images were artificially blurred, then deblurred. They were also rotated and compared. Any periodic structures on the image must have a pitch larger than the expected image blur. When that qualification is satisfied, a statistical confidence level far greater than 99% demonstrated that the method does indeed deblur properly and as desired. To some degree, the deblurring technique can be used to determine stage drift, aperture misalignment, astigmation, or other problems with the SEM that affect image blur.
Magnetic field and temperature dependence of an atomic force microscope-defined quantum point contact
Authors: Mori G. , Lazzarino M. , Ercolani D. , Biasiol G. , Sorba L.
Published: March 2004

We report on the transport properties of a quantum point contact defined by local anodic oxidation using an atomic force microscope on an AlGaAs/GaAs two-dimensional electron gas. Quantization of the conductance G in units of 2e2/h has been observed for temperatures ranging from 1.4 to 30 K. The evolution of the conductance plateaus has been studied as a function of the perpendicular magnetic field. The observed behavior agrees well with the one predicted and experimentally found on surface gated quantum point contacts.
Transformer coupled plasma etching of 3C-SiC films using fluorinated chemistry for microelectromechanical systems applications
Authors: Gao Di , Wijesundara Muthu B. J. , Carraro Carlo , Howe Roger T. , Maboudian Roya
Published: March 2004

Polycrystalline 3C-SiC films are etched by oxygen-mixed sulfur hexafluoride transformer coupled plasmas for microelectromechanical systems (MEMS) applications. Silicon dioxide is employed as etching masks, which avoids the micromasking phenomena and chamber contamination commonly involved when using metals as masks. The etch rate, selectivity, and profile are characterized as functions of O2 percentage in the etching gas. Etch rates of SiC remain almost unchanged at about 3600 Å/min up to 50% O2, but decrease significantly when more than 50% O2 is used. Etch selectivity of SiC over SiO2 reaches maximum of 2.6 when using 50% O2. The chemical composition and the topography of the etched SiC films are also examined. By integrating the etching process with conventional surface micromachining technology, functional SiC-based MEMS resonators are fabricated.
Band-gap expansion, core-level shift, and dielectric suppression of porous silicon passivated by plasma fluorination
Authors: Pan L. K. , Ee Y. K. , Sun C. Q. , Yu G. Q. , Zhang Q. Y. , Tay B. K.
Published: March 2004

The effect of plasma fluorination on the band gap, 2p core-level energy, and the dielectric behavior of porous silicon (PS) prepared under constant conditions has been examined using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, photoluminescence, and reflection. It has been found that with increasing extent of fluorination, the band gap expands, and the 2p level and the dielectric constant drop down substantially compared with those of the as-grown PS, being quite similar to the effect of particle size reduction. These findings could be interpreted as the fluorination-induced crystal field enhancement and the valence charge repopulation of silicon. The surface fluorination may provide an effective method for tuning the optical and dielectric properties of nanometric silicon.
Investigation of ash damage to ultralow-k inorganic materials
Authors: Yonekura Kazumasa , Sakamori Shigenori , Goto Kinya , Matsuura Masazumi , Fujiwara Nobuo , Yoneda Masahiro
Published: March 2004

The degradation of porous methyl silsesquioxane (MSQ) films (k=2.2) by plasma irradiation has been investigated using several kinds of gas chemistries, which are used for photoresist strip. The porous MSQ is easily degraded by O2 plasma ash process and the dielectric constant increases largely, even by using the condition that minimizes the damage to nonporous SiOCH films. As the results of several kinds of plasma irradiation, it is clarified that N2 plasma minimizes the degradation of porous MSQ. O2 and H2 plasmas extract methyl (CH3) groups from the porous MSQ films and degrade even the deep part from the film surface. On the other hand, N2 plasma changes the quality of only the film surface and suppresses the degradation of the inside of the film. Furthermore, the small amount of H2 addition to N2 plasma is effective in the increase of the ash rate and the removal of the deposition on the sidewall without the remarkable increase of the dielectric constant. Finally, the optimized N2/H2 ash process minimizes the damaged layer thickness of the sidewall with single damascene structures.
Atomic layer diffusion and electronic structure at In0.53Ga0.47As/InP interfaces
Authors: Smith P. E. , Goss S. H. , Bradley S. T. , Hudait M. K. , Lin Y. , Ringel S. A. , Brillson L. J.
Published: March 2004

We have used secondary ion mass spectrometry and cathodoluminescence spectroscopy to determine the effects that growth and postgrowth conditions have on interdiffusion and near band edge emissions in In0.53Ga0.47As/InP heterojunctions grown by molecular beam epitaxy. This lattice-matched interface represents a model system for the study of atomic movements and electronic changes with controlled anion overlap during growth. Structures subjected to anneals ranging from 440 to 495 °C provide a quantitative measure of concentration-driven cross diffusion of group-III and group-V atoms. By measuring anneal-induced broadening at the InGaAs-on-InP interface we have determined an activation energy for As diffusion into InP of ∼2.44±0.40 eV. An interface layer with Ga–P bonds indicates Ga competes favorably versus As for bonding in the preannealed InP near-surface region. In addition, we present evidence that interface chemical effects manifest themselves electronically as variations of the InGaAs band gap energy.
Fabrication of very fine copper lines on silicon substrates patterned with poly(methylmethacrylate) via selective chemical vapor deposition
Authors: Davazoglou D. , Raptis I. , Gleizes A. , Vasilopoulou M.
Published: March 2004

This Brief Report follows a previous paper [Davazoglou et al., J. Vac. Sci. Technol. B 19, 759 (2001)] in which the selective chemical vapor deposition (SCVD) of Cu on W-covered Si substrates patterned with AZ 5214™ photoresist was demonstrated. Cu was then deposited by decomposition at temperatures between 110 and 140 °C from 1, 5 cyclooctadiene Cu (I) hexafluoracetylacetonate (COD-Cu-hfac) vapors. It was also shown that features with characteristic dimensions down to 0.5 μm are achievable with conventional optical lithography and SCVD of Cu. Moreover, it was shown that the process was reproducible and robust because sometimes Cu SCVD took place several weeks after tungsten deposition and AZ5214™ patterning. Following this work, we targeted a further decrease of the characteristic dimensions of the obtained features by SCVD from COD-Cu-hfac decomposition. We used, for the patterning, electron-beam lithography instead of optical lithography, and a well-known electron-beam resist.
Formation processes of fine structures induced by high electric fields
Authors: Dou Juying , Shang Weijia , Chen Zhongwei
Published: March 2004

The buildup processes of a [100]-oriented tungsten surface in two steps have been studied by field-electron microscopy (FEM). An initial thermal field treatment is necessary to obtain an ideal tip profile around the [100] orientation. Based on this pretreated tip, some fine and unusual emission patterns result. Three types of buildup processes that cannot be obtained by conventional methods are observed. The experiment shows that the application of FEM can go one step further for the thermal-field case based on conventional methods.
Fabrication of hyperboloid-drum structure for electrically pumped laser of sub-micrometer to nanometer diameter active areas
Authors: Kim Jun-Youn , An Sung-Jae , Kim Jungyeon , Lee Jawoong , Kang Bongkoo , Kwon O’Dae
Published: March 2004

This article proposes a method of fabricating a hyperboloid-drum structure, which can be applied to develop an electrically pumped laser with an active-layer diameter as small as 100 nm, while maintaining a wide contact area for easy electrical connection. The structure is fabricated using conventional photolithography and the chemically assisted ion-beam etching (CAIBE) process with an Ar:Cl2:BCl3=5:2:3 gas mixture. The process conditions for CAIBE and the size of etch mask are adjusted to obtain the required structure with a height of ∼8 μm, an active layer diameter of 0.1–2.0 μm, and a contact diameter larger than 4 μm. It is demonstrated that a laser device with an active layer diameter as small as 600 nm and a contact layer diameter of ∼5 μm can also be fabricated with the proposed method.
Size-dependent resonant tunneling and storing of electrons in a nanocrystalline silicon floating-gate double-barrier structure
Authors: Wu Liangcai , Dai Min , Huang Xinfan , Li Wei , Chen Kunji
Published: March 2004

We use frequency-dependent capacitance spectroscopy to study electron tunneling and storing in nanocrystalline silicon (nc-Si) floating-gate double-barrier structure (SiO2/nc-Si/SiO2) fabricated in situ by plasma oxidation and layer-by-layer deposition in a plasma-enhanced chemical vapor deposition system. Distinct size- and frequency-dependent capacitance peaks due to Coulomb blockade charging and quantum-confinement effects have been observed by capacitance spectroscopy in a large ensemble of nc-Si dots at room temperature for the first time in a SiO2/nc-Si/SiO2 system. This finding demonstrates that the Coulomb blockade for electrons in nc-Si dots is larger than the size fluctuation effects on the quantum confinement for our nc-Si floating-gate double-barrier structure.
Acid–base reactions in a positive tone chemically amplified photoresist and their effect on imaging
Authors: Houle F. A. , Hinsberg W. D. , Sanchez M. I.
Published: March 2004

The inclusion of base in chemically amplified resist formulations is known to improve imaging, yet the mechanism by which this occurs, and the effect of different chemical types of base is poorly understood. Previously we showed that tetrabutylammonium hydroxide, an ionic base, added to p-tert-butyloxycarbonyloxystyrene (PTBOCST)-t-butyl iodonium perfluorobutane sulfonate (TBI-PFBS) positive tone chemically amplified resist affects local acid concentrations in exposed photoresist through a proportional neutralization mechanism. We have now extended these studies to include a neutral base, 7-diethylamino-4-methylcoumarin, and show that it operates by a qualitatively different process, competitive neutralization. Using the rate coefficients obtained for both bases, we investigate the impact of the details of the neutralization kinetics on image formation in PTBOCST/TBI-PFBS resist as a function of pitch, dose, base concentration, and temperature. The results show that base dynamically reduces local acid concentrations in competition with acid-catalyzed deprotection, and does not significantly block acid diffusion as a primary process. Thus, the selection of base can be expected to play an important and complex role in the evolution of the acid and deprotected resist images during postexposure bake.
Enhanced hole injection in organic electroluminescent device with an additional oxygen-rich indium–tin–oxide sublayer
Authors: Choi M. W. , Cho K. , Sung C. , Yang J. , Yi Y. , Noh M. , Choi J. C. , Jeong K.
Published: March 2004

To reduce the hole-injection barrier, an additional indium–tin–oxide (ITO) sublayer with high oxygen concentration is introduced between the ITO anode layer and hole-transporting layer. A thin ITO layer with a high oxygen concentration is prepared by increasing oxygen partial pressure during deposition of the last few tens Å of ITO layer via rf magnetron sputtering. The workfunction and chemical composition of the resulting film are determined by using ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. UPS results indicate the increment of the workfunction by 0.19 eV. The measured luminescence–voltage and current–voltage characteristics of the final organic electroluminescent devices with an oxygen-rich ITO sublayer demonstrate enhanced characteristics. Our result suggests that the film resistivity, as well as the workfunction of the ITO layer, should be optimized for the best device performance.
Thermodynamic considerations in the stability of binary oxides for alternative gate dielectrics in complementary metal–oxide–semiconductors
Authors: Stemmer Susanne
Published: March 2004

A number of binary oxides have been predicted to be thermodynamically stable in contact with Si and are candidates to replace SiO2 in complementary metal–oxide–semiconductors. However, reactions leading to the formation of interfacial silicide, silicate, or SiO2 layers have been reported when these oxides are exposed to high temperatures during device processing. Different pathways have been proposed in the literature to explain these reactions. In this article, a thermodynamic analysis of the proposed reactions is performed. The analysis includes gaseous species, because typical gate dielectrics are ultrathin layers and diffusivities for species from the surrounding atmosphere, such as oxygen, may be high. Furthermore, nonstoichiometry of the high-k oxide, as may be resulting from nonequilibrium deposition processes or reducing atmospheres during processing is also considered. Studies are proposed to distinguish between possible reaction mechanisms. Finally guidelines for stable interfaces are presented.
Improvement of Rayleigh criterion with duty ratio characterization for subwavelength lithography
Authors: Chua Gek Soon , Tay Cho Jui , Quan Chenggen , Lin Qunying
Published: March 2004

In this article, we have systematically investigated the dependencies of k1 on illumination conditions such as coherence setting and opening angle in off-axis illumination scheme. As result, conventional Rayleigh’s equations are not sufficient to address the effect of the numerical aperature and coherence on the depth of focus. Therefore, a metric called the coherency factor (σc) is proposed as a complementary metric of the low k1 lithography. Coherency factor (σc) is defined as the ratio of areas of captured first order and zero order light. The theory is based on simple geometrical analysis of the diffraction orders in the pupil plane. Areas of different diffraction orders captured by the pupil are evaluated as a function of wavelength, numerical aperture, and pitch. As corresponding to experimental results, a higher σc value concurs with a larger depth of focus. Extracting from Fraunhofer diffraction equation for a single slit and incorporating coherency factor σc, we have modified and extend the use of Rayleigh’s equations for 90 nm processes and below. Results show that the extension of Rayleigh’s equations is capable to optimize the depth of focus and map out the forbidden pitch locations for any design rules and illumination conditions. More importantly, it can complement the concept of objective lens pupil filling to provide the theoretical ground for illumination design in order to suppress the forbidden pitch phenomenon.
Mechanism of etching and surface relief development of PMMA under low-energy ion bombardment
Authors: Koval Y.
Published: March 2004

The structure of the subsurface layer of polymethylmethacrylate (PMMA) formed by bombardment with low-energy ions of Ar is reported. It was found that the subsurface region contains a graphitized, cross-linked, and low-molecular weight layers. We argue that ion etching of PMMA is mostly determined by the properties of the top graphitized layer and the processes leading to the formation of this layer. Also, it was found that ion etching causes various defects and typical features to appear on the surface of PMMA: bubbles, waves, and a net with a cell of nanometer size. The stratification of PMMA was demonstrated to play an important role for the development of the surface topology.
Time-reversal processing for an acoustic communications experiment in a highly reverberant environment
Authors: Candy James V. , Meyer Alan W. , Poggio Andrew J. , Guidry Brian L.
Published: March 2004

Time-reversal (T/R) communications is a new application area motivated by the recent advances in T/R theory. Although perceived by many in signal processing as simply an application of matched-filter theory, a T/R receiver offers an interesting solution to the communications problem for a reverberant channel. In this paper, the performance of various realizations of the T/R receiver for an acoustic communications experiment in air is described along with its associated processing. The experiment is developed to evaluate the performance of point-to-point T/R receivers designed to extract a transmitted information sequence propagating in a highly reverberant environment. It is demonstrated that T/R receivers are capable of extracting the transmitted coded sequence from noisy microphone sensor measurements with zero-symbol error. The processing required to validate these experimental results is discussed. These results are also compared with those produced by an equivalent linear equalizer or inverse filter, which provides the optimal solution when it incorporates all of the reverberations.
Fractional Laplacian time-space models for linear and nonlinear lossy media exhibiting arbitrary frequency power-law dependency
Authors: Chen W. , Holm S.
Published: March 2004

Frequency-dependent attenuation typically obeys an empirical power law with an exponent ranging from 0 to 2. The standard time-domain partial differential equation models can describe merely two extreme cases of frequency-independent and frequency-squared dependent attenuations. The otherwise nonzero and nonsquare frequency dependency occurring in many cases of practical interest is thus often called the anomalous attenuation. In this study, a linear integro-differential equation wave model was developed for the anomalous attenuation by using the space-fractional Laplacian operation, and the strategy is then extended to the nonlinear Burgers equation. A new definition of the fractional Laplacian is also introduced which naturally includes the boundary conditions and has inherent regularization to ease the hypersingularity in the conventional fractional Laplacian. Under the Szabo’s smallness approximation, where attenuation is assumed to be much smaller than the wave number, the linear model is found consistent with arbitrary frequency power-law dependency.
Invarient patterns in articulatory movements
Authors: Bonaventura Patrizia
Published: March 2004

The purpose of the reported study is to discover an effective method of characterizing movement patterns of the crucial articulator as the function of an abstract syllable magnitude and the adjacent boundary, and at the same time to investigate effects of prosodic control on utterance organization. In particular, the speed of movement when a flesh point on the tongue blade or the lower lip crosses a selected position relative to the occlusion plane is examined. The time of such crossing provides an effective measure of syllable timing and syllable duration according to previous work. In the present work, using a very limited vocabulary with only a few consonants and one vowel as the key speech materials, effects of contrastive emphasis on demisyllabic movement patterns were studied. The theoretical framework for this analysis is the C/D model of speech production in relation to the concept of an invariant part of selected articulatory movements. The results show evidence in favor of the existence of “iceberg” patterns, but a linear dependence of slope on the total excursion of the demisyllabic movement, instead of the approximate constancy of the threshold crossing speed as suggested in the original proposal of the iceberg, has been found. Accordingly, a revision of the original concept of iceberg, seems necessary. This refinement is consistent with the C/D model assumption on “prominence control” that the syllable magnitude determines the movement amplitude, accompanying directly related syllable duration change. In this assumption, the movement of a consonantal component should also be proportional to syllable magnitude. The results suggests, however, systematic outliers deviating from the linear dependence of movement speed on excursion. This deviation may be caused by the effect of the immediately following boundary, often referred to as phrase-final elongation.

Thesis advisor: Osamu Fujimura

Copies of this thesis written in English can be obtained from
Mechanisms determining the salience of coloration in echoed sound: Influence of interaural time and level differences
Authors: Krumbholz Katrin , Maresh Kate , Tomlinson Jennifer , Patterson Roy D. , Seither-Preisler Annemarie , Lütkenhöner Bernd
Published: March 2004

This study investigates whether the salience of the pitch associated with a single reflection of a broadband sound, such as noise, is determined by the monaural information mediated by the stimuli at the two ears, or by the relative locations of the primary sound and the reflection. Pitch strength was measured as a function of the reflection delay and the lateral displacement between the primary sound and the reflection. Thereby, lateral displacement was produced by means of interaural time differences (ITDs) in experiment 1 and interaural level differences (ILDs) in experiment 3. The results from both experiments are in accordance with the assumption that the strength of the pitch associated with a reflection is based on a central average of the internal representations of the stimuli at the two ears. This notion was corroborated by experiment 2, which showed that the results from experiment 1 could be mimicked by simply adding the stimuli from the two ears and presenting the merged stimulus identically to both ears.
Sequential streaming and effective level differences due to phase-spectrum manipulations
Authors: Stainsby Thomas H. , Moore Brian C. J. , Medland Peter J. , Glasberg Brian R.
Published: March 2004

Roberts et al. [J. Acoust. Soc. Am. 112, 2074–2085 (2002)] demonstrated that sequential stream segregation occurs with stimuli that differ only in phase spectrum. We investigated if this was partly due to differences in effective excitation level. Stimuli were harmonic complexes with a 100 Hz fundamental, 1250–2500 Hz passband, and cosine, alternating, or random component phase. In experiment 1, the complex tones were used as forward maskers of 20-ms probe tones at 1000, 1250, 1650, 2050, 2500, and 3000 Hz. While there was no significant difference in the masking produced by the cosine- and alternating-phase stimuli, the random-phase stimulus produced significantly greater masking, equivalent to a difference in overall effective excitation level of 12.6 dB. Experiments 2 and 3 used the asynchrony detection and subjective streaming tasks of Roberts et al. Successive stimuli had identical phase, but differed in level by 0, 1, 3, 5, 10, or 15 dB. Stream segregation increased once the level difference reached 5 dB. While some of the stream segregation observed by Roberts et al. may have been due to a difference in effective excitation level, this does not account for the stream segregation between cosine- and alternating-phase stimuli.
Auditory target detection in reverberation
Authors: Zurek Patrick M. , Freyman Richard L. , Balakrishnan Uma
Published: March 2004

Measurements and theoretical predictions of auditory target detection in simulated reverberant conditions are reported. The target signals were pulsed 13-octave bands of noise and the masker signal was a continuous wideband noise. Target and masker signals were passed through a software simulation of a reverberant room with a rigid sphere modeling a listener’s head. The location of the target was fixed while the location of the masker was varied in the simulated room. Degree of reverberation was controlled by varying the uniform acoustic absorption of the simulated room’s surfaces. The resulting target and masker signals were presented to the listeners over headphones in monaural-left, monaural-right, or binaural listening modes. Changes in detection performance in the monaural listening modes were largely predictable from the changes in target-to-masker ratio in the target band, but with a few dB of extra masking in reverberation. Binaural detection performance was generally well predicted by applying Durlach’s [in Foundations of Modern Auditory Theory (Academic, New York, 1972)] equalization-cancellation theory to the direct-plus-reverberant ear signals. Predictions in all cases were based on a statistical description of room acoustics and on acoustic diffraction by a sphere. The success of these detection models in the present well-controlled reverberant conditions suggests that they can be used to incorporate listening mode and source location as factors in speech-intelligibility predictions.
The role of temporal and dynamic signal components in the perception of syllable-final stop voicing by children and adults
Authors: Nittrouer Susan
Published: March 2004

Adults whose native languages permit syllable-final obstruents, and show a vocalic length distinction based on the voicing of those obstruents, consistently weight vocalic duration strongly in their perceptual decisions about the voicing of final stops, at least in laboratory studies using synthetic speech. Children, on the other hand, generally disregard such signal properties in their speech perception, favoring formant transitions instead. These age-related differences led to the prediction that children learning English as a native language would weight vocalic duration less than adults, but weight syllable-final transitions more in decisions of final-consonant voicing. This study tested that prediction. In the first experiment, adults and children (eight and six years olds) labeled synthetic and natural CVC words with voiced or voiceless stops in final C position. Predictions were strictly supported for synthetic stimuli only. With natural stimuli it appeared that adults and children alike weighted syllable-offset transitions strongly in their voicing decisions. The predicted age-related difference in the weighting of vocalic duration was seen for these natural stimuli almost exclusively when syllable-final transitions signaled a voiced final stop. A second experiment with adults and children (seven and five years old) replicated these results for natural stimuli with four new sets of natural stimuli. It was concluded that acoustic properties other than vocalic duration might play more important roles in voicing decisions for final stops than commonly asserted, sometimes even taking precedence over vocalic duration.
Inferred basilar-membrane response functions for listeners with mild to moderate sensorineural hearing loss
Authors: Plack Christopher J. , Drga Vit , Lopez-Poveda Enrique A.
Published: March 2004

Psychophysical estimates of cochlear function suggest that normal-hearing listeners exhibit a compressive basilar-membrane (BM) response. Listeners with moderate to severe sensorineural hearing loss may exhibit a linearized BM response along with reduced gain, suggesting the loss of an active cochlear mechanism. This study investigated how the BM response changes with increasing hearing loss by comparing psychophysical measures of BM compression and gain for normal-hearing listeners with those for listeners who have mild to moderate sensorineural hearing loss. Data were collected from 16 normal-hearing listeners and 12 ears from 9 hearing-impaired listeners. The forward masker level required to mask a fixed low-level, 4000-Hz signal was measured as a function of the masker–signal interval using a masker frequency of either 2200 or 4000 Hz. These plots are known as temporal masking curves (TMCs). BM response functions derived from the TMCs showed a systematic reduction in gain with degree of hearing loss. Contrary to current thinking, however, no clear relationship was found between maximum compression and absolute threshold.
Low-frequency whale and seismic airgun sounds recorded in the mid-Atlantic Ocean
Authors: Nieukirk Sharon L. , Stafford Kathleen M. , Mellinger David K. , Dziak Robert P. , Fox Christopher G.
Published: March 2004

Beginning in February 1999, an array of six autonomous hydrophones was moored near the Mid-Atlantic Ridge (35 °N–15 °N, 50 °W–33 °W). Two years of data were reviewed for whale vocalizations by visually examining spectrograms. Four distinct sounds were detected that are believed to be of biological origin: (1) a two-part low-frequency moan at roughly 18 Hz lasting 25 s which has previously been attributed to blue whales (Balaenoptera musculus); (2) series of short pulses approximately 18 s apart centered at 22 Hz, which are likely produced by fin whales (B. physalus); (3) series of short, pulsive sounds at 30 Hz and above and approximately 1 s apart that resemble sounds attributed to minke whales (B. acutorostrata); and (4) downswept, pulsive sounds above 30 Hz that are likely from baleen whales. Vocalizations were detected most often in the winter, and blue- and fin whale sounds were detected most often on the northern hydrophones. Sounds from seismic airguns were recorded frequently, particularly during summer, from locations over 3000 km from this array. Whales were detected by these hydrophones despite its location in a very remote part of the Atlantic Ocean that has traditionally been difficult to survey.
Speech recognition in noise for cochlear implant listeners: Benefits of residual acoustic hearing
Authors: Turner Christopher W. , Gantz Bruce J. , Vidal Corina , Behrens Amy , Henry Belinda A.
Published: March 2004

The purpose of this study was to explore the potential advantages, both theoretical and applied, of preserving low-frequency acoustic hearing in cochlear implant patients. Several hypotheses are presented that predict that residual low-frequency acoustic hearing along with electric stimulation for high frequencies will provide an advantage over traditional long-electrode cochlear implants for the recognition of speech in competing backgrounds. A simulation experiment in normal-hearing subjects demonstrated a clear advantage for preserving low-frequency residual acoustic hearing for speech recognition in a background of other talkers, but not in steady noise. Three subjects with an implanted “short-electrode” cochlear implant and preserved low-frequency acoustic hearing were also tested on speech recognition in the same competing backgrounds and compared to a larger group of traditional cochlear implant users. Each of the three short-electrode subjects performed better than any of the traditional long-electrode implant subjects for speech recognition in a background of other talkers, but not in steady noise, in general agreement with the simulation studies. When compared to a subgroup of traditional implant users matched according to speech recognition ability in quiet, the short-electrode patients showed a 9-dB advantage in the multitalker background. These experiments provide strong preliminary support for retaining residual low-frequency acoustic hearing in cochlear implant patients. The results are consistent with the idea that better perception of voice pitch, which can aid in separating voices in a background of other talkers, was responsible for this advantage.
On the ability of a physiologically constrained area function model of the vocal tract to produce normal formant patterns under perturbed conditions
Authors: Story Brad H.
Published: March 2004

An area function model of the vocal tract is tested for its ability to produce typical vowel formant frequencies with a perturbation at the lips. The model, which consists of a neutral shape and two weighted orthogonal shaping patterns (modes), has previously been shown to produce a nearly one-to-one mapping between formant frequencies and the weighting coefficients of the modes [Story and Titze, J. Phonetics, 26, 223–260 (1998)]. In this study, a perturbation experiment was simulated by imposing a constant area “lip tube” on the model. The mapping between the mode coefficients and formant frequencies was then recomputed with the lip tube in place and showed that formant frequencies (F1 and F2) representative of the vowels [ʊ,o,u] could no longer be produced with the model. However, when the mode coefficients were allowed to exceed their typical bounding values, the mapping between them and the formant frequencies was expanded such that the vowels [ʊ,o,u] were compensated. The area functions generated by these exaggerated coefficients were shown to be similar to vocal-tract shapes reported for real speakers under similar perturbed conditions [Savariaux, Perrier, and Orliaguet, J. Acoust. Soc. Am., 98, 2428–2442 (1995)]. This suggests that the structure of this particular model captures some of the human ability to configure the vocal-tract shape under both ordinary and extraordinary conditions.
An analytic model for acoustic scattering from an impedance cylinder placed normal to an impedance plane
Authors: Swearingen Michelle E.
Published: March 2004

An analytic model, developed in cylindrical coordinates, is described for the scattering of a spherical wave off a semi-infinite reight cylinder placed normal to a ground surface. The motivation for the research is to have a model with which one can simulate scattering from a single tree and which can be used as a fundamental element in a model for estimating the attenuation in a forest comprised of multiple tree trunks. Comparisons are made to the plane wave case, the transparent cylinder case, and the rigid and soft ground cases as a method of theoretically verifying the model for the contemplated range of model parameters. Agreement is regarded as excellent for these benchmark cases. Model sensitivity to five parameters is also explored. An experiment was performed to study the scattering from a cylinder normal to a ground surface. The data from the experiment is analyzed with a transfer function method to yield frequency and impulse responses, and calculations based on the analytic model are compared to the experimental data.

Thesis advisor: David C. Swanson

Copies of this thesis written in English can be obtained from
Multilayer impedance coating for submerged objects—theory and applications
Authors: Hughes Ronald , Niemiec Jan , Uberall Herbert
Published: March 2004

We consider acoustic returns from water-immersed objects with partially absorptive single or multiple coating layers. For sufficiently high absorptivity, the effect of the layers, even when applied to a strongly reflective substructure, can be described by an effective impedance Z, acting at the outer surface of the top layer. Expressions for Z may be obtained following procedures for the corresponding case of electromagnetic scattering by Uberall. In acoustics, the surface impedance of a one-layer coating was obtained by Brekhovskikh and is presented here in a very concise form. For two-layer coatings, Z is obtained analytically by a procedure used by Glegg for sediment layers. Equations by Folds and Loggins or Brekhovskikh can be used for a multilayer case to obtain numerical solutions. With these procedures for obtaining surface impedances, applications have been developed for the study of acoustic reflections from coated submerged structures.
Oxygen Isotope Constraints on the Sulfur Cycle over the Past 10 Million Years
Authors: Turchyn Alexandra V. , Schrag Daniel P.
Published: March 2004

Oxygen isotopes in marine sulfate (δ
18
O
SO4
) measured in marine barite show variability over the past 10 million years, including a 5per mil decrease during the Plio-Pleistocene, with near-constant values during the Miocene that are slightly enriched over the modern ocean. A numerical model suggests that sea level fluctuations during Plio-Pleistocene glacial cycles affected the sulfur cycle by reducing the area of continental shelves and increasing the oxidative weathering of pyrite. The data also require that sulfate concentrations were 10 to 20% lower in the late Miocene than today.