bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced Gas Turbine Technology: ABB/BCC Historical Firsts
Authors: Eckardt D. , Rufli P.
Published: July 2002

During more than 100 years engineers of the Swiss development center of A.-G. BBC Brown, Boveri & Cie., from 1988 onwards ABB Asea Brown Boveri Ltd., in 1999 ABB ALSTOM POWER Ltd., and now ALSTOM Power Ltd. in Baden, Switzerland, have significantly contributed to the achievement of today’s advanced gas turbine concept. Numerous “firsts” are highlighted in this paper—ranging from the first realization of the industrial, heavy-duty gas turbine in the 1930s to today’s high-technology gas turbine (GT) products, combining excellent performance, extraordinary low environmental impact with commercial attractiveness for global power generation. Interesting connections could be unveiled for the early parallel development of industrial and areo gas turbines.
Forced Convection Heat Transfer Enhancement Using a Self-Oscillating Impinging Planar Jet
Authors: Camci Cengiz , Herr Frank
Published: July 2002

Impinging jets are widely used in the local enhancement of heat removed from internal passages of gas turbine blades. Arrays of stationary jets are usually impinged on surfaces of internal cooling passages. The current practice is to benefit from the high heat transfer coefficients existing in the vicinity of the jet impingement region on a target wall. The present study shows that a self-oscillating impinging-jet configuration is extremely beneficial in enhancing the heat removal performance of a conventional (stationary) impinging jet. In addition to a highly elevated stagnation line Nusselt number, the area coverage of the impingement zone is significantly enhanced because of the inherent sweeping motion of the oscillating coolant jet. When an oscillating jet (Re=14,000) is impinged on a plate normal to the jet axis (x/d=24 hole to plate distance), a typical enhancement of Nu number on the stagnation line is about 70 percent. The present paper explains detailed fluid dynamics structure of the self-oscillating jet by using a triple decomposition technique on a crossed hot wire signal. The current heat transfer enhancement levels achieved suggest that it may be possible to implement the present self-oscillating-impinging-jet concept in future gas turbine cooling systems, on rotating disks, glass tempering/quenching, electronic equipment cooling, aircraft de-icing, combustors and heat exchangers.
Onset of Nucleate Boiling and Active Nucleation Site Density During Subcooled Flow Boiling
Authors: Basu Nilanjana , Warrier Gopinath R. , Dhir Vijay K.
Published: July 2002

The partitioning of the heat flux supplied at the wall is one of the key issues that needs to be resolved if one is to model subcooled flow boiling accurately. The first step in studying wall heat flux partitioning is to account for the various heat transfer mechanisms involved and to know the location at which the onset of nucleate boiling (ONB) occurs. Active nucleation site density data is required to account for the energy carried away by the bubbles departing from the wall. Subcooled flow boiling experiments were conducted using a flat plate copper surface and a nine-rod (zircalloy-4) bundle. The location of ONB during the experiments was determined from visual observations as well as from the thermocouple output. From the data obtained it is found that the heat flux and wall superheat required for inception are dependent on flow rate, liquid subcooling, and contact angle. The existing correlations for ONB underpredict the wall superheat at ONB in most cases. A correlation for predicting the wall superheat and wall heat flux at ONB has been developed from the data obtained in this study and that reported in the literature. Experimental data are within ±30 percent of that predicted from the correlation. Active nucleation site density was determined by manually counting the individual sites in pictures obtained using a CCD camera. Correlations for nucleation site density, which are independent of flow rate and liquid subcooling, but dependent on contact angle have been developed for two ranges of wall superheat—one below 15°C and another above 15°C.
A Reflective Fiber Optic Sensor for Surface Roughness In-Process Measurement
Authors: Liu Jiancheng , Yamazaki Kazuo , Zhou Yi , Matsumiya Sadayuki
Published: July 2002

The paper deals with the development of a fiber optic sensor for surface roughness measurement. A new method for the calculation of reflection light intensity is proposed. By numerically counting the amount of reflection light rays from a measured surface, the relationship between the reflection light intensity and the surface roughness can be found. The simulation method is useful in understanding the effects of the sensor probe structure and the component parameters on the performance of the sensor such that an optimum sensor design can be obtained. A fiber optic sensor probe for surface roughness measurement was designed and fabricated using the results obtained by simulation. Experimental results show that the prototype sensor probe has high resolution and sensitivity for ground and milled surfaces with the roughness value (Ra) of 0.1μm∼3.2μm. The experimental results also show that the simulation method is accurate, and hence useful in designing fiber optic sensors. The simulation procedure and feasibility of the simulation method as well as the experimental results obtained from the prototype sensor probe are presented in this paper.
A Local Theory of Elastoplastic Deformation of Two-Phase Metal Matrix Random Structure Composites
Authors: Buryachenko V. A. , Rammerstorfer F. G. , Plankensteiner A. F.
Published: July 2002

A two-phase material is considered, which consists of a homogeneous elastoplastic matrix containing a homogeneous statistically uniform random set of ellipsoidal inclusions with the same form, orientation, and mechanical properties. The multiparticle effective field method (used in this paper) in the original form assumes constant plastic strains in the matrix. This assumption is replaced by the following micromechanical model: Each inclusion consists of an elastic core and a thin coating. The mechanical properties of both the matrix and the coating are the same but with different plastic strains. Homogeneous plastic strains are assumed inside the matrix and in each of separate subdomains of the coating. A general theory of plasticity is developed for arbitrary loading based on incremental elastoplastic analysis. The consideration of inhomogeneity of plastic strains in the coating enables to obtain some principally new effects of elastoplastic deformation.
Modeling the HSK Toolholder-Spindle Interface
Authors: Hanna Ihab M. , Agapiou John S. , Stephenson David A.
Published: July 2002

The HSK toolholder-spindle connection was developed to overcome shortcomings of the 7/24 steep-taper interface, especially at higher speeds. However, the HSK system was standardized quickly, without detailed evaluation based on operational experience. Several issues concerning the reliability, maintainability, and safety of the interface have been raised within the international engineering community. This study was undertaken to analytically investigate factors which influence the performance and limitations of the HSK toolholder system. Finite Element Models were created to analyze the effects of varying toolholder and spindle taper geometry, axial spindle taper length, drawbar/clamping load, spindle speed, applied bending load, and applied torsional load on HSK toolholders. Outputs considered include taper-to-taper contact pressures, taper-to-taper clearances, minimum drawbar forces, interface stiffnesses, and stresses in the toolholder. Static deflections at the end of the holder predicted by the models agreed well with measured values. The results showed that the interface stiffness and load-carrying capability are significantly affected by taper mismatch and dimensional variations, and that stresses in the toolholder near the drive slots can be quite high, leading to potential fatigue issues for smaller toolholders subjected to frequent clamping-unclamping cycles (e.g., in high volume applications). The results can be used to specify minimum toolholder material properties for critical applications, as well as drawbar design and spindle/toolholder gaging guidelines to increase system reliability and maintainability.
Maintaining reproducible plasma reactor wall conditions: SF6 plasma cleaning of films deposited on chamber walls during Cl2/O2 plasma etching of Si
Authors: Ullal Saurabh J. , Singh Harmeet , Daugherty John , Vahedi Vahid , Aydil Eray S.
Published: July 2002

Silicon oxychloride films deposited on plasma etching reactor walls during the Cl2/O2 plasma etching of Si must be removed to return the reactor to a reproducible state prior to etching the next wafer. Using multiple surface and plasma diagnostics, we have investigated the removal of this silicon oxychloride film using an SF6 plasma. In particular, a diagnostic technique based on the principles of multiple total internal reflection Fourier transform infrared spectroscopy was used to monitor the films that formed on the reactor walls. The silicon oxychloride film etching proceeds by incorporation of F, which also abstracts and replaces the Cl atoms in the film. If the SF6 plasma is not maintained for a sufficiently long period to remove all the deposits, the F incorporated into the film leaches out into the gas phase during the subsequent etch processes. This residual F can have undesirable effects on the etching performance and the wafer-to-wafer reproducibility. The removal of the silicon oxychloride film from the reactor walls is inherently nonuniform and the end of the cleaning can be detected most easily by monitoring reactor averaged F and SiF emissions.
Influence of deposition temperature on the structure and internal stress of TiN films deposited by filtered cathodic vacuum arc
Authors: Cheng Y. H. , Tay B. K , Lau S. P.
Published: July 2002

TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. Atomic force microscopy and x-ray diffraction (XRD) were used to study the surface morphology and crystal structure of TiN films. Substrate bending methods were used to measure the internal stress. The influence of deposition temperature on the surface morphology, crystal structure, and internal stress were systematically studied. The surface roughness, grain size and the intensity of the XRD peak increase linearly with increasing deposition temperature. The crystallographic orientation develops from (111) preferred orientation to (200) preferred orientation as the deposition temperature is increased. The increase of deposition temperature from 50 to 450 °C results in a linear decrease of internal stress from 9.88 to 4.30 GPa. The enhancement of the mobility of atoms in the films and the variation of crystallographic orientation with increasing deposition temperature contribute to the decrease of internal stress in the films.
Characterization of TiAlN thin film annealed under O2 by in situ time of flight direct recoil spectroscopy/mass spectroscopy of recoiled ions and ex situ x-ray photoelectron spectroscopy
Authors: Tempez A. , Bensaoula A. , Schultz A.
Published: July 2002

The oxidation of an amorphous TiAlN coating has been studied by in situ direct recoil spectroscopy (DRS) and mass spectroscopy of recoiled ions (MSRI) and ex situ x-ray photoelectron spectroscopy (XPS). DRS and MSRI monitored the changes in surface composition as the sample was heated to 460 °C under an O218 pressure of 10−6 Torr. Angular resolved XPS data were acquired for thickness-dependence information. The initial surface was partially oxidized from air exposure. Both DRS and XPS showed the Al-rich near surface and the presence of N in the subsurface. As shown by DRS and MSRI, oxidation at elevated temperatures yielded surface nitrogen loss and Ti enrichment. XPS confirmed the preferential formation of TiO2 on the surface. This study also provides a comparison between the direct recoil (neutrals and ions) and the ionic recoil signals. In our conditions, the negative ionic fraction of all elements except H tracks their true surface content variations given by DRS. The results were compared with early work performed on identical samples. In this case the TiAlN film was oxidized with an O2 pressure in the mTorr range and the surface changes are followed in situ by positive MSRI and XPS. This experiment also indicates that Al and N are buried under TiO2 but from 600 °C.
Microstructure and mechanical properties of nanocomposite amorphous carbon films
Authors: Zhang P. , Tay B. K. , Sun C. Q. , Lau S. P.
Published: July 2002

Nanocomposite amorphous carbon films such as a-C:Al, a-C:Ti, and a-C:Si have been prepared using a filtered cathodic vacuum arc technique. The films were characterized using x-ray photoelectron spectroscopy (XPS), atomic force microscopy, surface profilometry, a nanoindenter, and Raman spectrometry. It was found that metal contents in the films deviate from the target depending on the constituent element, which is attributed to the effect of dynamic balance deposition. XPS results revealed the presence of a carbide phase in a-C:Ti and a-C:Si but not in a-C:Al nanocomposite carbon films. Incorporating metal into amorphous carbon films significantly reduces the compressive stress but maintains the relative high hardness and Young’s modulus.
Thickness-dependent microstructural and electrochromic properties of sputter-deposited Ni oxide films
Authors: Ahn Kwang-Soon , Nah Yoon-Chae , Sung Yung-Eun
Published: July 2002

Thickness-dependent microstructural and electrochromic properties of sputter-deposited Ni oxide films were investigated as a function of growth time using x-ray diffraction, in situ transmittance measurements, and x-ray photoelectron spectroscopy. By increasing the thickness of the Ni oxide, the transmittance or optical differences during coloring/bleaching process were increased. However, thick Ni oxides showed a lower maximum bleached transmittance and coloration efficiency and a larger response time. Crystallinity developed with growth time, mainly due to the plasma heating effect. The evolution of crystallinity with the growth time resulted in the electrochromic inactive Ni oxide components even after several tens of potential cyclings, leading to a decreased maximum bleached transmittance and lower coloration efficiency.
Study on modification of hydrogen trap site in nickel and stainless steel using atom probe
Authors: Yoshimura Toshihiko , Ishikawa Yuichi
Published: July 2002

Nickel and aged stainless steel that was composed of nanometer-scale Cr-rich and Fe-rich regions were chosen as model systems for the modification of hydrogen-trap sites. Nickel and stainless steel were annealed and oxidized to modify the types and numbers of hydrogen-trap sites. Deuterium was used in this experiment to enhance the detectability of hydrogen isotope detected in the atom probe analysis. Strongly bound deuterium trap sites are observed and have a higher density than the solubility in lattice. The amount of deuterium trapped in nickel decreases after annealing. This is a result of the modification of trap sites by annealing. Deuterium trapped in the oxide layer and in the oxide–nickel interface of nickel was observed at a sufficient resolution to determine the extent of trapping on an atomic scale, and thus to gather quantitative data on the modification of trap sites by oxidation. The deuterium atoms are trapped into the Cr-rich region on the ferritic phase of duplex stainless steel. The deuterium atoms trapped are associated with nickel atoms and oxygen atoms.
Nanocomposite tribological coatings with “chameleon” surface adaptation
Authors: Voevodin A. A. , Fitz T. A. , Hu J. J. , Zabinski J. S.
Published: July 2002

Nanocomposite tribological coatings were designed to respond to changing environmental conditions by self-adjustment of their surface properties to maintain good tribological performance in any environment. These smart coatings have been dubbed “chameleon” because, analogous to a chameleon changing its skin color to avoid predators, the coating changes its “skin” chemistry and structure to avoid wear. The concept was originally developed using WC, diamondlike carbon, and WS2 material combination for adaptation to a humid/dry environment cycling. In order to address temperature variation, nanocomposite coatings made of yttria-stabilized zirconia (YSZ) in a gold matrix were developed with encapsulated nanosized reservoirs of MoS2 and diamondlike carbon (DLC). Coatings were produced using a combination of laser ablation and magnetron sputtering. They were characterized by x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, x-ray energy dispersive spectroscopy, and micro-Raman spectroscopy. Results were correlated with mechanical and tribological characterization. Coating hardness was evaluated using nanoindentation, while coating adhesion and toughness were estimated using scratch and Vickers indentation tests. Friction and wear endurance measurements of YSZ/Au/MoS2/DLC coatings against steel and Si3N4 balls were performed at room temperature in controlled humidity air, dry nitrogen, and vacuum environments, as well as at 500 °C in air. Depending on the environment, coating friction surface changed its chemistry and structure between (i) graphitic carbon for sliding in humid air [coating friction coefficients (c.o.f. 0.10–0.15)], (ii) hexagonal MoS2 for sliding in dry N2 and vacuum (c.o.f. 0.02–0.05), and (iii) metallic Au for sliding in air at 500 °C (c.o.f. 0.10–0.20). The unique coating skin adaptation realized with YSZ/Au/MoS2/DLC and WC/DLC/WS composites proves a universal applicability of the chameleon design concept.
GaAs surface cleaning by low energy hydrogen ion beam treatment
Authors: Razek N. , Otte K. , Chassé T. , Hirsch D. , Schindler A. , Frost F. , Rauschenbach B.
Published: July 2002

A technology of semiconductor surface cleaning has been applied to GaAs surfaces for the preparation of contamination free surfaces. This technique combines a low energy hydrogen ion beam (ion energy <500 eV) with an increased substrate temperature (150 °C). The long term change of the GaAs (001) surface composition under the influence of this process was investigated with in situ x-ray photoelectron spectroscopy and atomic force microscopy. A removal of surface oxides and carbon as well as of surface contaminations due to the hydrogen ion beam treatment could be observed. At an elevated substrate temperature of 150 °C, the hydrogen ion beam produces a contamination-free surface without changes in surface composition (stoichiometry) or surface roughness, whereas room temperature hydrogen exposure results in an As-depleted surface composition. This technique could be used for wafer direct bonding of III–V semiconductors and other processes which require highly efficient quality cleaning procedures.
CdZnTe detector in diagnostic x‐ray spectroscopy
Authors: Miyajima Satoshi , Imagawa Kotaro , Matsumoto Masao
Published: July 2002

A method to utilize CdZnTe (CZT) detectors in diagnostic x‐ray spectroscopy is described in this article. Spectral distortion due to transmission of primary x rays, the escape of cadmium‐ and tellurium‐K fluorescent x rays, and tailing was severe in measured x‐ray spectra. Therefore, correction for the distortion was performed with the stripping method using response functions. The response functions were calculated with the Monte Carlo method. The Hecht equation was employed to approximate the effects of carrier trapping in the calculations. The parameters in the Hecht equation, the mean‐free path (λ) of electrons and holes, were determined such that the tailing in calculated response functions fit that in measured γ‐ray spectra. Corrected x‐ray spectra agreed well with the reference spectra measured with an HPGe detector. The results indicate that CZT detectors are suitable for diagnostic x‐ray spectroscopy with appropriate corrections.
Dose broadening due to target position variability during fractionated breath‐held radiation therapy
Authors: O'Dell W. G. , Schell M. C. , Reynolds D. , Okunieff P.
Published: July 2002

Recent advances in Stereotactic Radiosurgery/Conformal Radiotherapy have made it possible to deliver surgically precise radiation therapy to small lesions while preserving the surrounding tissue. However, because of physiologic motion, the application of conformal radiotherapy to extra‐cranial tumors is, at present, geared toward slowing the progression of disease rather than obtaining a cure. At the University of Rochester, we are investigating the use of patient breath‐holding to reduce respiratory‐derived motion in fractional radiotherapy. The primary targeting problem then becomes the small variation in tumor location over repeated breath‐holds. This paper describes the effects of residual target position uncertainty on the dose distribution observed by small extra‐cranial tumors and their neighboring tissues during fractional radiation treatment using breath holding. We employ two computational methods to study these effects: numerical analysis via Monte Carlo simulation and analytical computation using three‐dimensional convolution. These methods are demonstrated on a 2‐arc, 10‐fraction treatment plan used to treat a representative lung tumor in a human subject. In the same human subject, the variability in position of a representative lung tumor was measured over repeated end‐expiration breath‐holds using volumetric imaging. For the 7×7×10 mm margin used to treat this 12 mm diameter tumor and the measured target position variability, we demonstrated that the entire tumor volume was irradiated to at least 48 Gy—well above the tumoricidal threshold. The advantages, in terms of minimizing the volume of surrounding lung tissue that is radiated to high dose during treatment, of using end‐expiration breath holding compared with end‐inspiration breath‐holding are demonstrated using representative tumor size and position variability parameters. It is hoped that these results will ultimately lead to improved, if not curative, treatment for small (5–20 mm diameter) lung, liver, and other extra‐cranial lesions.
An in‐phantom dosimetry system using pin silicon photodiode radiation sensors for measuring organ doses in x‐ray CT and other diagnostic radiology
Authors: Aoyama Takahiko , Koyama Shuji , Kawaura Chiyo
Published: July 2002

A dosimetry system using commercially available pin silicon photodiodes as the sensor is evaluated for in‐phantom dose measurements in x‐ray CT and other diagnostic radiology. System sensitivity measured as a function of the effective energy of x rays was between 0.37 and 0.49 V/mGy at an effective energy range between 23.5 and 72 keV. The minimum detectable organ dose with 25% uncertainty was estimated to be 0.02 mGy. The excellent output linearity was found over a dose range from 0.03 to more than 10 mGy with flat dose rate response of system sensitivity up to 35 mGy s−1, though the sensitivity indicated some energy dependence across the diagnostic energy range with a maximum of about 10%/10 keV. Since angular dependence of the sensitivity of the photodiode sensor was found to be small enough it would induce negligible dose error. Dose profile measurement along the axis of a thoracic phantom undergoing CT chest examination indicated the reliability of dose values over a range of two orders of magnitude from less than 0.2 to 12 mGy. The present dosimetry system having advantages of high sensitivity with immediate readout of dose values, low cost, and easy construction would widely be used as an alternative to TLD dosimeters for organ and skin dose measurements in CT and other diagnostic radiology.
Use of a Mariotte bottle for the experimental study of the transition from laminar to turbulent flow
Authors: Maroto J. A. , de Dios J. , de las Nieves F. J.
Published: July 2002

A Mariotte bottle is a device that provides a constant effusion velocity for liquids. We discuss a Mariotte bottle that has been designed to study the flow regime and the transition from laminar to turbulent flow. Several straight, smooth, circular glass tubes with different lengths and sections were inserted into the lower part of the bottle so that the rate of flow could be measured in very different experimental conditions by using a precision balance. Reynolds numbers in the interval 1014⩽R⩽6098 were obtained, showing that the flow regime is laminar for R⩽3000. There is a transition in the flow regime for R in the interval 3000–4000 and a turbulent flow regime for higher R. Because the device is very simple and the results obtained are very clear and exemplary, we recommend using this device as a laboratory experiment for physics or engineering students who require a knowledge of fluid mechanics.
Asymptotic behavior of the probability density in one dimension
Authors: Damborenea J. A. , Egusquiza I. L. , Muga J. G.
Published: July 2002

We demonstrate that the probability density of a quantum state moving freely in one dimension may decay faster than t−1. The t−2 and t−3 dependencies are illustrated with analytically solvable examples. Decays faster than t−1 allow the existence of dwell times and delay times.
Teaching the photon gas in introductory physics
Authors: Leff Harvey S.
Published: July 2002

The ideal gas is often the only thermodynamic system for which equations of state are studied in introductory physics. The photon gas can be a rich supplement to the ideal gas, and a vehicle for introducing 20th century physics concepts.
The easiest way to the Heaviside ellipsoid
Authors: Dmitriyev Valery P.
Published: July 2002

The equation for the electromagnetic field of a point charge moving with constant velocity is derived from Maxwell’s equations using the symmetry properties of the system. In contrast to conventional treatments, the derivation does not use retarded integrals or relativistic transformations.
Measures of auditory-visual integration for speech understanding: A theoretical perspective (L)
Authors: Grant Ken W.
Published: July 2002

Recent studies of auditory-visual integration have reached diametrically opposed conclusions as to whether individuals differ in their ability to integrate auditory and visual speech cues. A study by Massaro and Cohen [J. Acoust. Soc. Am. 108(2), 784–789 (2000)] reported that individuals are essentially equivalent in their ability to integrate auditory and visual speech information, whereas a study by Grant and Seitz [J. Acoust. Soc. Am. 104(4), 2438–2450 (1998)] reported substantial variability across subjects in auditory-visual integration for both sentences and nonsense syllables. This letter discusses issues related to the measurement of auditory-visual integration and modeling efforts employed to separate information extraction from information processing.
Depth-dependent acoustic features of diving sperm whales (Physeter macrocephalus) in the Gulf of Mexico
Authors: Thode Aaron , Mellinger David K. , Stienessen Sarah , Martinez Anthony , Mullin Keith
Published: July 2002

Three-dimensional dive trajectories of three sperm whales in the Gulf of Mexico have been obtained by measuring the relative arrival times and bearings of the animals’ acoustic multipath reflections, using two elements of a towed hydrophone array deployed at an unknown depth and orientation. Within the first 6–12 min of the start of a dive, the intervals between successive “clicks” of all three whales corresponded closely with the two-way travel time of an acoustic pulse traveling vertically between the animals’ position and the ocean bottom. The click spectra contained multiple peaks, including a faint band of energy originally centered near 10 kHz. As the animals descended over 500 m in depth, the center frequency of this band shifted to nearly 15 kHz, but subsequently remained near this value during the rest of the dive. This frequency shift is consistent with that expected from energy scattering from an ensemble of incompressible small-scale air-filled resonators, with diameters on the order of 4 mm. One possible candidate for such an ensemble is proposed to reside in the collapsed frontal sac of the animal. A comparison of the received levels for the bottom and direct multipath arrivals indicates that the whales’ acoustic directivity must range between 10–30 dB in the 5–20-kHz region.
Features of stimulation affecting tonal-speech perception: Implications for cochlear prostheses
Authors: Xu Li , Tsai Yuhjung , Pfingst Bryan E.
Published: July 2002

Tone languages differ from English in that the pitch pattern of a single-syllable word conveys lexical meaning. In the present study, dependence of tonal-speech perception on features of the stimulation was examined using an acoustic simulation of a CIS-type speech-processing strategy for cochlear prostheses. Contributions of spectral features of the speech signals were assessed by varying the number of filter bands, while contributions of temporal envelope features were assessed by varying the low-pass cutoff frequency used for extracting the amplitude envelopes. Ten normal-hearing native Mandarin Chinese speakers were tested. When the low-pass cutoff frequency was fixed at 512 Hz, consonant, vowel, and sentence recognition improved as a function of the number of channels and reached plateau at 4 to 6 channels. Subjective judgments of sound quality continued to improve as the number of channels increased to 12, the highest number tested. Tone recognition, i.e., recognition of the four Mandarin tone patterns, depended on both the number of channels and the low-pass cutoff frequency. The trade-off between the temporal and spectral cues for tone recognition indicates that temporal cues can compensate for diminished spectral cues for tone recognition and vice versa. An additional tone recognition experiment using syllables of equal duration showed a marked decrease in performance, indicating that duration cues contribute to tone recognition. A third experiment showed that recognition of processed FM patterns that mimic Mandarin tone patterns was poor when temporal envelope and duration cues were removed.
Floquet wave homogenization of periodic anisotropic media
Authors: Wang L. , Rokhlin S. I.
Published: July 2002

A dynamic homogenization method based on Floquet wave theory is developed. The theory is based on the equivalency within the homogenization domain of Floquet waves in a periodic anisotropic medium and plane waves in a dispersive homogeneous anisotropic medium. A simple procedure has been developed to estimate analytically critical angles and the upper frequency bound of this homogenization domain. Using this method, the frequency dependent effective elastic constants are obtained and examples for [0/90] and [0/45/90/−45] composites are given. By comparison with an exact theory, it is shown that the time domain signal propagation in a periodic laminate is well described by the Floquet wave homogenization theory in the homogenization domain. It is also shown that in the static limit the results are identical to those calculated by static homogenization theory (the generalized method of cells). The potential applications of the method are discussed.
Deriving a cochlear transducer function from low-frequency modulation of distortion product otoacoustic emissions
Authors: Bian Lin , Chertoff Mark E. , Miller Emily
Published: July 2002

In this paper, a new method is introduced to derive a cochlear transducer function from measuring distortion product otoacoustic emissions (DPOAEs). It is shown that the cubic difference tone (CDT, 2 f1–f2) is produced from the odd-order terms of a power series that approximates a nonlinear function characterizing cochlear transduction. Exploring the underlying mathematical formulation, it is found that the CDT is proportional to the third derivative of the transduction function when the primary levels are sufficiently small. DPOAEs were measured from nine gerbils in response to two-tone signals biased by a low-frequency tone with different amplitudes. The CDT magnitude was obtained at the peak regions of the bias tone. The results of the experiment demonstrated that the shape of the CDT magnitudes as a function of bias levels was similar to the absolute value of the third derivative of a sigmoidal function. A second-order Boltzmann function was derived from curve fitting the CDT data with an equation that represents the third derivative of the Boltzmann function. Both the CDT-bias function and the derived nonlinear transducer function showed effects of primary levels. The results of the study indicate that the low-frequency modulated DPOAEs can be used to estimate the cochlear transducer function.
An Essential Role of N-Terminal Arginylation in Cardiovascular Development
Authors: Kwon Yong Tae , Kashina Anna S. , Davydov Ilia V. , Hu Rong-Gui , An Jee Young , Seo Jai Wha , Du Fangyong , Varshavsky Alexander
Published: July 2002

The enzymatic conjugation of arginine to the N-termini of proteins is a part of the ubiquitin-dependent N-end rule pathway of protein degradation. In mammals, three N-terminal residues—aspartate, glutamate, and cysteine—are substrates for arginylation. The mouse
ATE1
gene encodes a family of Arg-tRNA-protein transferases (R-transferases) that mediate N-terminal arginylation. We constructed ATE1-lacking mouse strains and found that
ATE1
−/−
embryos die with defects in heart development and in angiogenic remodeling of the early vascular plexus. Through biochemical analyses, we show that N-terminal cysteine, in contrast to N-terminal aspartate and glutamate, is oxidized before its arginylation by R-transferase, suggesting that the arginylation branch of the N-end rule pathway functions as an oxygen sensor.
Alternatively Spliced TCR mRNA Induced by Disruption of Reading Frame
Authors: Wang Jun , Hamilton John I. , Carter Mark S. , Li Shulin , Wilkinson Miles F.
Published: July 2002

Nonsense codons that prematurely terminate translation generate potentially deleterious truncated proteins. Here, we show that the T cell receptor–β (TCRβ) gene, which acquires in-frame nonsense codons at high frequency during normal lymphocyte development, gives rise to an alternatively spliced transcript [alternative messenger RNA (alt-mRNA)] that skips the offending mutations that generate such nonsense codons. This alt-mRNA is up-regulated by a transfer RNA–dependent scanning mechanism that responds specifically to mutations that disrupt the reading frame. The finding that translation signals regulate the levels of alternatively spliced mRNAs generated in the nucleus may alter the current view of how gene expression is controlled in eukaryotic cells.
The Mass Disruption of Oort Cloud Comets
Authors: Levison Harold F. , Morbidelli Alessandro , Dones Luke , Jedicke Robert , Wiegert Paul A. , Bottke William F.
Published: July 2002

We have calculated the number of dormant, nearly isotropic Oort cloud comets in the solar system by (i) combining orbital distribution models with statistical models of dormant comet discoveries by well-defined surveys and (ii) comparing the model results to observations of a population of dormant comets. Dynamical models that assume that comets are not destroyed predict that we should have discovered ∼100 times more dormant nearly isotropic comets than are actually seen. Thus, as comets evolve inward from the Oort cloud, the majority of them must physically disrupt.
Place Cells and Place Recognition Maintained by Direct Entorhinal-Hippocampal Circuitry
Authors: Brun Vegard H. , Otnæss Mona K. , Molden Sturla , Steffenach Hill-Aina , Witter Menno P. , Moser May-Britt , Moser Edvard I.
Published: July 2002

Place cells in hippocampal area CA1 may receive positional information from the intrahippocampal associative network in area CA3 or directly from the entorhinal cortex. To determine whether direct entorhinal connections support spatial firing and spatial memory, we removed all input from areas CA3 to CA1, thus isolating the CA1 area. Pyramidal cells in the isolated CA1 area developed sharp and stable place fields. Rats with an isolated CA1 area showed normal acquisition of an associative hippocampal-dependent spatial recognition task. Spatial recall was impaired. These results suggest that the hippocampus contains two functionally separable memory circuits: The direct entorhinal-CA1 system is sufficient for recollection-based recognition memory, but recall depends on intact CA3-CA1 connectivity.
Role for Stearoyl-CoA Desaturase-1 in Leptin-Mediated Weight Loss
Authors: Cohen Paul , Miyazaki Makoto , Socci Nicholas D. , Hagge-Greenberg Aaron , Liedtke Wolfgang , Soukas Alexander A. , Sharma Ratnendra , Hudgins Lisa C. , Ntambi James M. , Friedman Jeffrey M.
Published: July 2002

Leptin elicits a metabolic response that cannot be explained by its anorectic effects alone. To examine the mechanism underlying leptin's metabolic actions, we used transcription profiling to identify leptin-regulated genes in
ob/ob
liver. Leptin was found to specifically repress RNA levels and enzymatic activity of hepatic stearoyl–CoA desaturase-1 (SCD-1), which catalyzes the biosynthesis of monounsaturated fatty acids. Mice lacking SCD-1 were lean and hypermetabolic.
ob/ob
mice with mutations in SCD-1 were significantly less obese than
ob/ob
controls and had markedly increased energy expenditure.
ob/ob
mice with mutations in SCD-1 had histologically normal livers with significantly reduced triglyceride storage and VLDL (very low density lipoprotein) production. These findings suggest that down-regulation of SCD-1 is an important component of leptin's metabolic actions.
Deciphering the Cross-Talk of Implantation: Advances and Challenges
Authors: Paria B. C. , Reese Jeff , Das Sanjoy K. , Dey S. K.
Published: July 2002

Implantation involves a series of steps leading to an effective reciprocal signaling between the blastocyst and the uterus. Except for a restricted period when ovarian hormones induce a uterine receptive phase, the uterus is an unfavorable environment for blastocyst implantation. Because species-specific variations in implantation strategies exist, these differences preclude the formulation of a unifying theme for the molecular basis of this event. However, an increased understanding of mammalian implantation has been gained through the use of the mouse model. This review summarizes recognized signaling cascades and new research in mammalian implantation, based primarily on available genetic and molecular evidence from implantation studies in the mouse. Although the identification of new molecules associated with implantation in various species provides valuable insight, important questions remain regarding the common molecular mechanisms that govern this process. Understanding the mechanisms of implantation promises to help alleviate infertility, enhance fetal health, and improve contraceptive design.

The success of any species depends on its reproductive efficiency. For sexual reproduction, an egg and sperm must overcome many obstacles to fuse and co-mingle their genetic material at fertilization. The zygote develops into a blastocyst with two cell lineages (the inner cell mass and the trophectoderm), migrates within the reproductive tract, and ultimately implants into a transiently permissive host tissue, the uterus. However, the molecular basis of the road map connecting the blastocyst with the endometrium across species is diverse (1) and not fully understood. Recent advances have identified numerous molecules involved in implantation (1–4), yet new discoveries have not yielded a unifying scheme for the mechanisms of implantation.
Integrin-Mediated Long-Term B Cell Retention in the Splenic Marginal Zone
Authors: Lu Theresa T. , Cyster Jason G.
Published: July 2002

The mechanisms that control localization of marginal zone (MZ) B cells are poorly understood. Here we show that MZ B cells express elevated levels of the integrins LFA-1 (αLβ2) and α4β1 and that they bind to the ligands ICAM-1 and VCAM-1. These ligands are expressed within the MZ in a lymphotoxin-dependent manner. Combined inhibition of LFA-1 and α4β1 causes a rapid and selective release of B cells from the MZ. Furthermore, lipopolysaccharide-triggered MZ B cell relocalization involves down-regulation of integrin-mediated adhesion. These studies identify key requirements for MZ B cell localization and establish a role for integrins in peripheral lymphoid tissue compartmentalization.
Pollen-Mediated Movement of Herbicide Resistance Between Commercial Canola Fields
Authors: Rieger Mary A. , Lamond Michael , Preston Christopher , Powles Stephen B. , Roush Richard T.
Published: July 2002

There is considerable public and scientific debate for and against genetically modified (GM) crops. One of the first GM crops,
Brassica napus
(oilseed rape or canola) is now widely grown in North America, with proposed commercial release into Australia and Europe. Among concerns of opponents to these crops are claims that pollen movement will cause unacceptable levels of gene flow from GM to non-GM crops or to related weedy species, resulting in genetic pollution of the environment. Therefore, quantifying pollen-mediated gene flow is vital for assessing the environmental impact of GM crops. This study quantifies at a landscape level the gene flow that occurs from herbicide-resistant canola crops to nearby crops not containing herbicide resistance genes.
Rapid Population Growth Saps Development
Authors: Sachs Jeffrey D.
Published: July 2002

Population Matters
Demographic Change, Economic Growth, and Poverty in the Developing World. Nancy Birdsall, Allen C. Kelley, and Steven W. Sinding, Eds. Oxford University Press, New York, 2001. 456 pp. $72, £45. ISBN 0-19-924407-3.

Relying heavily on data from the 1980s and 1990s, the contributors examine the effects of population changes on economic development.
Rapid Wastage of Alaska Glaciers and Their Contribution to Rising Sea Level
Authors: Arendt Anthony A. , Echelmeyer Keith A. , Harrison William D. , Lingle Craig S. , Valentine Virginia B.
Published: July 2002

We have used airborne laser altimetry to estimate volume changes of 67 glaciers in Alaska from the mid-1950s to the mid-1990s. The average rate of thickness change of these glaciers was –0.52 m/year. Extrapolation to all glaciers in Alaska yields an estimated total annual volume change of –52 ± 15 km
3
/year (water equivalent), equivalent to a rise in sea level (SLE) of 0.14 ± 0.04 mm/year. Repeat measurements of 28 glaciers from the mid-1990s to 2000–2001 suggest an increased average rate of thinning, –1.8 m/year. This leads to an extrapolated annual volume loss from Alaska glaciers equal to –96 ± 35 km
3
/year, or 0.27 ± 0.10 mm/year SLE, during the past decade. These recent losses are nearly double the estimated annual loss from the entire Greenland Ice Sheet during the same time period and are much higher than previously published loss estimates for Alaska glaciers. They form the largest glaciological contribution to rising sea level yet measured.
Sp1 and TAFII130 Transcriptional Activity Disrupted in Early Huntington's Disease
Authors: Dunah Anthone W. , Jeong Hyunkyung , Griffin April , Kim Yong-Man , Standaert David G. , Hersch Steven M. , Mouradian M. Maral , Young Anne B. , Tanese Naoko , Krainc Dimitri
Published: July 2002

Huntington's disease (HD) is an inherited neurodegenerative disease caused by expansion of a polyglutamine tract in the huntingtin protein. Transcriptional dysregulation has been implicated in HD pathogenesis. Here, we report that huntingtin interacts with the transcriptional activator Sp1 and coactivator TAFII130. Coexpression of Sp1 and TAFII130 in cultured striatal cells from wild-type and HD transgenic mice reverses the transcriptional inhibition of the dopamine D2 receptor gene caused by mutant huntingtin, as well as protects neurons from huntingtin-induced cellular toxicity. Furthermore, soluble mutant huntingtin inhibits Sp1 binding to DNA in postmortem brain tissues of both presymptomatic and affected HD patients. Understanding these early molecular events in HD may provide an opportunity to interfere with the effects of mutant huntingtin before the development of disease symptoms.
Tissue-Specific Regulation of Retinal and Pituitary Precursor Cell Proliferation
Authors: Li Xue , Perissi Valentina , Liu Forrest , Rose David W. , Rosenfeld Michael G.
Published: July 2002

Mammalian organogenesis requires the expansion of pluripotent precursor cells before the subsequent determination of specific cell types, but the tissue-specific molecular mechanisms that regulate the initial expansion of primordial cells remain poorly defined. We have genetically established that Six6 homeodomain factor, acting as a strong tissue-specific repressor, regulates early progenitor cell proliferation during mammalian retinogenesis and pituitary development. Six6, in association with Dach corepressors, regulates proliferation by directly repressing cyclin-dependent kinase inhibitors, including the
p27Kip1
promoter. These data reveal a molecular mechanism by which a tissue-specific transcriptional repressor-corepressor complex can provide an organ-specific strategy for physiological expansion of precursor populations.
Enhanced CpG Mutability and Tumorigenesis in MBD4-Deficient Mice
Authors: Millar Catherine B. , Guy Jacky , Sansom Owen J. , Selfridge Jim , MacDougall Eilidh , Hendrich Brian , Keightley Peter D. , Bishop Stefan M. , Clarke Alan R. , Bird Adrian
Published: July 2002

The mammalian protein MBD4 contains a methyl-CpG binding domain and can enzymatically remove thymine (T) or uracil (U) from a mismatched CpG site in vitro. These properties suggest that MBD4 might function in vivo to minimize the mutability of 5-methylcytosine by removing its deamination product from DNA. We tested this hypothesis by analyzing
Mbd4
−/−
mice and found that the frequency of of C → T transitions at CpG sites was increased by a factor of three. On a cancer-susceptible
Apc
Min/+
background,
Mbd4
−/−
mice showed accelerated tumor formation with CpG → TpG mutations in the
Apc
gene. Thus MBD4 suppresses CpG mutability and tumorigenesis in vivo.
Impaired B and T Cell Antigen Receptor Signaling in p110δ PI 3-Kinase Mutant Mice
Authors: Okkenhaug Klaus , Bilancio Antonio , Farjot Géraldine , Priddle Helen , Sancho Sara , Peskett Emma , Pearce Wayne , Meek Stephen E. , Salpekar Ashreena , Waterfield Michael D. , Smith Andrew J. H. , Vanhaesebroeck Bart
Published: July 2002

Class IA phosphoinositide 3-kinases (PI3Ks) are a family of p85/p110 heterodimeric lipid kinases that generate second messenger signals downstream of tyrosine kinases, thereby controlling cell metabolism, growth, proliferation, differentiation, motility, and survival. Mammals express three class IA catalytic subunits: p110α, p110β, and p110δ. It is unclear to what extent these p110 isoforms have overlapping or distinct biological roles. Mice expressing a catalytically inactive form of p110δ (p110δ
D910A
) were generated by gene targeting. Antigen receptor signaling in B and T cells was impaired and immune responses in vivo were attenuated in p110δ mutant mice. They also developed inflammatory bowel disease. These results reveal a selective role for p110δ in immunity.
Myeloperoxidase, a Leukocyte-Derived Vascular NO Oxidase
Authors: Eiserich Jason P. , Baldus Stephan , Brennan Marie-Luise , Ma Wenxin , Zhang Chunxiang , Tousson Albert , Castro Laura , Lusis Aldons J. , Nauseef William M. , White C. Roger , Freeman Bruce A.
Published: July 2002

Myeloperoxidase (MPO) is an abundant mammalian phagocyte hemoprotein thought to primarily mediate host defense reactions. Although its microbicidal functions are well established in vitro, humans deficient in MPO are not at unusual risk of infection. MPO was observed herein to modulate the vascular signaling and vasodilatory functions of nitric oxide (NO) during acute inflammation. After leukocyte degranulation, MPO localized in and around vascular endothelial cells in a rodent model of acute endotoxemia and impaired endothelium-dependent relaxant responses, to which MPO-deficient mice were resistant. Altered vascular responsiveness was due to catalytic consumption of NO by substrate radicals generated by MPO. Thus MPO can directly modulate vascular inflammatory responses by regulating NO bioavailability.