bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensing and Control of Double-Sided Arc Welding Process
Authors: Zhang Y. M. , Zhang S. B. , Jiang M.
Published: July 2002

The welding industry is driven to improve productivity without sacrificing quality. For thick material welding, the current practice is to use backing or multiple passes. The laser welding process, capable of achieving deep narrow penetration, can significantly improve welding productivity for such applications by reducing the number of passes. However, its competitiveness in comparison with traditional arc welding is weakened by its high cost, strict fit-up requirement, and difficulty in welding large structures. In this work, a different method, referred to as double-sided arc welding (DSAW) is developed to improve the arc concentration for arc welding. A sensing and control system is developed to achieve deep narrow penetration under variations in welding conditions. Experiments verified that the pulsed keyhole DSAW system developed is capable of achieving deep narrow penetration on a 1/2 inch thick square butt joint in a single pass.
Surface Steps: From Atomistics to Continuum
Authors: Kukta R. , Peralta A. , Kouris D.
Published: July 2002

The elastic interaction between surface steps biases growth and can have a dominant influence on growth modes of thin films. A new continuum solution is presented that takes into account the actual geometry of the steps. It is shown that even in the absence of external stress, the interaction energy contains a logarithmic dependence not previously reported in the literature. This additional term is of the same order of magnitude as the ones contained in the solution of Marchenko and Parshin that has been generally used during the past twenty years. Opposite and similar steps are investigated and closed-form expressions for the relevant elastic fields and interaction energies are derived. Results compare favorably with the ones obtained from embedded atom method (EAM) simulations and a recent elastic lattice model.
Interpretations of Indentation Size Effects
Authors: Gerberich W. W. , Tymiak N. I. , Grunlan J. C. , Horstemeyer M. F. , Baskes M. I.
Published: July 2002

For very shallow indentations in W, Al, Au, and Fe-3wt%Si single crystals, hardness decreased with increasing depth irrespective of increasing or decreasing strain gradients. As such, strain gradient theory appears insufficient to explain the indentation size effect (ISE) at depths less than several hundred nanometers. Present research links the ISE to a ratio between the energy of newly created surface and plastic strain energy dissipation. Also, the contact surface to plastic volume ratio was nearly constant for a range of shallow depths. Based on the above, an analytical model of hardness versus depth provides a satisfactory fit to the experimental data and correlates well with embedded atom simulations.
Heat Transfer in Rotating Rectangular Cooling Channels AR=4 With Angled Ribs
Authors: Griffith Todd S. , Al-Hadhrami Luai , Han Je-Chin
Published: July 2002

An investigation into determining the effect of rotation on heat transfer in a rib-roughened rectangular channel with aspect ratio of 4:1 is detailed in this paper. A broad range of flow parameters have been selected including Reynolds number (Re=5000–40000), rotation number (Ro=0.04–0.3) and coolant to wall density ratio at the inlet Δρ/ρi=0.122. The rib turbulators, attached to the leading and trailing surface, are oriented at an angle α=45deg to the direction of flow. The effect of channel orientations of β=90 deg and 135 deg with respect to the plane of rotation is also investigated. Results show that the narrow rectangular passage exhibits a much higher heat transfer enhancement for the ribbed surface than the square and 2:1 duct previously investigated. Also, duct orientation significantly affects the leading and side surfaces, yet does not have much affect on the trailing surfaces for both smooth and ribbed surfaces. Furthermore, spanwise heat transfer distributions exist across the leading and trailing surfaces and are accentuated by the use of angled ribs. The smooth and ribbed case trailing surfaces and smooth case side surfaces exhibited a strong dependence on rotation number.
An Inverse Method for Simultaneous Estimation of the Center and Surface Thermal Behavior of a Heated Cylinder Normal to a Turbulent Air Stream
Authors: Lin Jiin-Hong , Chen Cha’o-Kuang , Yang Yue-Tzu
Published: July 2002

A two-dimensional inverse analysis utilizes a different perspective to simultaneously estimate the center and surface thermal behavior of a heated cylinder normal to a turbulent air stream. A finite-difference method is used to discretize the governing equations and then a linear inverse model is constructed to identify the unknown boundary conditions. The present approach is to rearrange the matrix forms of the governing differential equations and estimate the unknown boundary conditions of the heated cylinder. Then, the linear least-squares-error method is adopted to find the solutions. The results show that only a few measuring points inside the cylinder are needed to estimate the unknown quantities of the thermal boundary behavior, even when measurement errors are considered. In contrast to the traditional approach, the advantages of this method are that no prior information is needed on the functional form of the unknown quantities, no initial guesses are required, no iterations in the calculating process are necessary, and the inverse problem can be solved in a linear domain. Furthermore, the existence and uniqueness of the solutions can easily be identified.
Coupling of Buoyant Convections in Boron Oxide and a Molten Semiconductor in a Vertical Magnetic Field
Authors: Farrell Martin V. , Ma Nancy
Published: July 2002

This paper treats the buoyant convection in a layer of boron oxide, called a liquid encapsulant, which lies above a layer of a molten compound semiconductor (melt) between cold and hot vertical walls in a rectangular container with a steady vertical magnetic field B. The magnetic field provides an electromagnetic (EM) damping of the molten semiconductor which is an excellent electrical conductor but has no direct effect on the motion of the liquid encapsulant. The temperature gradient drives counter clockwise circulations in both the melt and encapsulant. These circulations alone would lead to positive and negative values of the horizontal velocity in the encapsulant and melt, respectively, near the interface. The competition between the two buoyant convections determines the direction of the horizontal velocity of the interface. For B=5 T, there is significant EM damping of the melt motion and the encapsulant drives a positive interfacial velocity and a small clockwise circulation in the melt. For a much weaker field B=0.1 T, the maximum velocity in the melt is hundreds of times larger than that of the encapsulant, thus causing nearly all the encapsulant to circulate in the clockwise direction.
Hidden Markov Model-based Tool Wear Monitoring in Turning
Authors: Wang Litao , Mehrabi Mostafa G. , Kannatey-Asibu, Elijah
Published: July 2002

This paper presents a new modeling framework for tool wear monitoring in machining processes using hidden Markov models (HMMs). Feature vectors are extracted from vibration signals measured during turning. A codebook is designed and used for vector quantization to convert the feature vectors into a symbol sequence for the hidden Markov model. A series of experiments are conducted to evaluate the effectiveness of the approach for different lengths of training data and observation sequence. Experimental results show that successful tool state detection rates as high as 97% can be achieved by using this approach.
Bubble Dynamic Parameters and Pool Boiling Heat Transfer on Plasma Coated Tubes in Saturated R-134a and R-600a
Authors: Hsieh Shou-Shing , Ke Chung-Guang
Published: July 2002

An optical method for measuring the bubble dynamic data subject to an isolated bubble model is presented at low heat flux q⩽1kW/m2; while the operating heat fluxes are up to 30 kW/m2. By simultaneous measurements of departure diameters, velocities, frequencies and nucleation site densities, the heat transfer contribution of an individual active site is evaluated. A single phase heat transfer correlation was used to model the present heat transfer data. The test specimens consisted of tubes with porous copper (Cu) and molybdenum (Mo) plasma coated surfaces. The porosity (ε), the thickness of the porous layer (δ), and the mean pore diameter (η) of the tested tubes are the following: 0.055⩽ε⩽0.057,100⩽δ⩽300μm, and 3⩽η⩽4μm. The tests were carried out using R-134a and R-600a as working fluid at a saturation temperature of 18°C and with low and moderate heat fluxes (⩽1 kW/m2) for boiling visualization and related measurements (⩽30 kW/m2).
Enhanced Convection or Quasi-Conduction States Measured in a Super-Conducting Magnet for Air in a Vertical Cylindrical Enclosure Heated From Below and Cooled From Above in a Gravity Field
Authors: Maki Syou , Tagawa Toshio , Ozoe Hiroyuki
Published: July 2002

Magnetizing force was applied for natural convection of air in a shallow cylindrical enclosure heated from below and cooled from above. The cylinder measured 45 mm in diameter and 14.8 mm in height. The convection enclosure was located 66 mm above or below the coil center in the bore of a super-conducting magnet. The average Nusselt numbers were enhanced about twice at the location +66 mm above the coil center under 3.40 Tesla and decreased to Nu=1.12∼1.28 at the location −66 mm below the coil center for the Rayleigh number from 3520 to 6980. These two locations were selected as the most effective positions for application of the magnetizing force in this super-conducting magnet. A model equation for magnetizing force was derived and numerically computed for Pr=0.7 and Ra=2100 and 7000. One turn coil was presumed as a model of thousand turns real superconductor. The magnetic strength is represented by a new parameter γ and varied from 2345 to 9124. By adjusting the location of the enclosure in the bore of the super-conducting magnet, the average Nusselt number of 1.14 at Ra=2100 varied from 1.8 to 1.0001 depending on the magnetic strength, and that of 2.02 at Ra=7000 varied from 2.6 to 1.0003. These data are plotted versus magnetic Rayleigh number Ram=Raγ∂Bz2/∂Z+1R=0,Z=0.5 at the center of the enclosure and agreed well with Silveston’s data for a classical nonmagnetic field.
Structure and Dynamics of Laminar Jet Micro-Slot Diffusion Flames
Authors: Baker John , Calvert Mark E. , Murphy David W.
Published: July 2002

Results of an experimental investigation into the behavior of laminar jet diffusion flames, produced using micro-slot burner ports, are presented. Under certain conditions, the cross-sectional shape of micro-slot flames is qualitatively similar to the cross-sectional shape of circular burner port flames produced in an environment where molecular diffusion is the primary transport mechanism. An order of magnitude analysis reveals that, over the range of experimental conditions examined, the behavior of the experimentally observed micro-slot flames is not necessarily diffusion-controlled. A comparison of the experimental data with an accepted theoretical model shows that current theoretical models do not accurately predict the experimentally observed flame heights. A theoretical expression for purely diffusion-controlled micro-slot flame height is developed and compared with experimental micro-slot flame data. The region where this theoretical expression is valid is identified through an examination of the diffusion to buoyancy parameter. A qualitative discussion of micro-slot flame structure is also presented.
Calibration stability of hot cathode ionization gauges: A discussion of the importance of electron path length and gauge constant
Authors: Peacock R. N.
Published: July 2002

The ion current, i+, in an ionization gauge is given by the equation i+=Ki−P where K is a gas dependent gauge constant, i− is the electron current, and P is the pressure. Values of K for nitrogen for gauges designed for use at ultrahigh vacuum and extreme high vacuum range from 10/Torr to 106/Torr. It is important to know whether calibration stability is sacrificed when K, and the electron path length are large. Using a simple model, the electron path length is estimated as a function of the probability, β, that an electron will make another pass through the ionizing region. An equation is obtained for K as a function of β. The fractional change in K, ΔK/K, is zero for those gauges where the electrons make a single pass, but is increasingly larger for higher sensitivity gauges with greater probabilities of multiple passes. As an example, assume that the probability of the next pass changes by 1%, then the change in sensitivity is 1.5% for a B-A with K=25/Torr, and 9% for a gauge with K=102/Torr.
Evolution of tungsten film deposition induced by focused ion beam
Authors: Langfischer H. , Basnar B. , Hutter H. , Bertagnolli E.
Published: July 2002

Direct write metallization is an important approach for circuit modification and prototyping. We investigate the evolution of the chemical vapor deposition of tungsten induced by a 50 keV focused Ga+ ion beam. Time resolved imaging in combination with atomic force microscopy reveals that chemical vapor deposition of tungsten by focused ion beam proceeds via two clearly distinguishable regimes of layer growth. Deposition starts with the nucleation of nanoscale tungsten deposits scattered over the substrate surface. Despite local impacts of the ion beam within the irradiated area of the substrate the localization of the nucleation spots is not correlated to the scan path of the ion beam. The nanoscale tungsten particles preserve their position and typical shape during further deposition. Only after merging of the particles into a contiguous tungsten layer, does the second regime of growth characterized by deposition of tungsten on a tungsten surface set in. In this regime the deposition process is determined by the total ion dose and the average current density the sample was subjected to. Deposition yields up to 3.5 atoms per incident gallium ion are achieved. The layer quality is determined by Auger electron analysis, which shows fractions of Ga, C, Si and O in the W layer. Depth profiling by secondary ion mass spectroscopy showed the depth profiles of these constituents and confirmed the existence of a 50–100 nm thick transition zone between the tungsten layer and the substrate. Electrical resistivity of metal layers of 250 μ Ω cm and current densities up to 3.5×106 A/cm2 are measured by means of van der Pauw test structures. In order to give a concise description of the experimental findings the data were interpreted utilizing an analytic model that mainly incorporates the precursor gas coverage, precursor gas transformation cross section and ion induced sputtering. The critical ion current density, where ion sputtering exceeds the deposition, was identified by the model. Because the model shows excellent agreement with the measurement it should be suitable for a further survey of focused ion beam process development.
Surface and microstructural characterization of laser beam welds in an aluminum alloy
Authors: Nascente P. A. P. , Bolfarini C. , Benassi C. L. , Alcȃntara N. G. , Santos J. F.
Published: July 2002

The weldability of aluminum alloys is one of the main requirements to be considered for their application in the automotive and aerospace industry. In this work, the weld joints of an AA7020 alloy obtained by laser process were characterized by scanning electron microscopy, energy-dispersive x-ray spectrometry, wavelength-dispersive x-ray spectrometry, and x-ray photoelectron spectroscopy. The laser process can be described as a high-speed solidification process. The solidification rate can be estimated from the correlation among several solidification rates and the corresponding dendritic/cellular spacings, and the value calculated for this rate was 3.0×103 K/s. The inclusions present in the base metal were identified as (Cr,Fe)4Si4Al13, which were not observed in the fused zone. The fused zone microstructure showed two distinct phases: an aluminum solid solution and fine precipitates of MgZn2. The transition from the base metal to the fused zone presented a narrow heat-affected zone. A strong depletion of Zn was observed, and this does not influence the hot tearing susceptibility since hot cracks were not observed in the weld zone.
Unique structure/properties of chemical vapor deposited parylene E
Authors: Senkevich Jay J. , Mitchell Christopher J. , Vijayaraghavan Aravind , Barnat Edward V. , McDonald John F. , Lu Toh-Ming
Published: July 2002

Parylene E, a low κ polymer thin film, with the approximate composition 69% diethylated and 25% monoethylated poly(p-xylylene), has been chemical vapor deposited via a cyclophane precursor at room temperature. It has a dielectric constant of 2.34±0.03 and dielectric loss of <0.005 at 10 kHz from MIMCAP structures. It is particularly unique compared to the other common parylene polymers. Namely, it is nearly optically isotropic and it is soluble in common laboratory solvents such as methylene chloride, chloroform, and toluene. It is shown to have an optical birefringence of −0.0112 at 634.1 nm and a correspondingly low degree of crystallization after a 150 °C postdeposition anneal. The low degree of crystallization results in a smooth film (10 Å rms surface roughness for a 2060 Å thin film) with no optical loss (in reflection mode), i.e., an extinction coefficient of zero. These properties for parylene E make it appropriate for use as an optical waveguide and for archival conservation or other applications where low optical loss or film removal might be necessary.
Phase behavior in the CdTe–CdS pseudobinary system
Authors: McCandless Brian E. , Hanket Gregory M. , Jensen D. Garth , Birkmire Robert W.
Published: July 2002

Polycrystalline thin films deposited by coevaporation of CdTe and CdS form metastable single-phase CdTe–CdS alloys. Subsequent heating in a kinetic-enhancing ambient segregates CdTe1−xSx and CdS1−yTey phases from the original alloy phase. The equilibrium miscibility gap between the resulting CdTe1−xSx and CdS1−yTey alloy phases is determined for CdTe1−xSx films with initial x ∼ 0.4 treated from 360 to 700 °C. At 625 °C, the equilibrium compositions correspond to published results for mixed crystals. Below 625 °C the miscibility gap widens asymmetrically due to different mixing free energies for S in CdTe and Te in CdS. The solubility thermodynamics are modeled with an excess mixing free energy to account for nonideal mixing behavior.
Low frictional coating by cosputtering in combination with excimer laser irradiation for aerospace applications
Authors: Goto Masahiro , Kasahara Akira , Tosa Masahiro , Hobley Jonathan , Kishimoto Maki , Yoshihara Kazuhiro , Fukumura Hiroshi
Published: July 2002

Low frictional coatings made of copper, boron nitride, and oxygen on a stainless steel substrate were synthesized by magnetron cosputter deposition combined with excimer laser irradiation. The frictional force of the coating films was observed by a system developed for measuring vacuum friction. The coating properties were also observed by a conventional contact angle measuring system, a scanning Auger electron spectrometer, and a Vickers hardness measuring system. The surface layer of the coating films was oxidized by the excimer laser irradiation. Surface energy and film hardness were also modified by the laser irradiation. Frictional coefficients as low as 0.075 were achieved after irradiating the films under ultrahigh vacuum conditions. Since these coating films have already been oxidized and irradiated with high energy UV light they will be applicable for aerospace coatings.
Monolithic multiple wavelength ridge waveguide laser array fabricated by Nd:YAG laser-induced quantum well intermixing
Authors: Dubowski J. J. , Feng Y. , Poole P. J. , Buchanan M. , Poirier S. , Genest J. , Aimez V.
Published: July 2002

Maskless selective area cw Nd:YAG laser annealing of GaInAsP/InP quantum well (QW) structures has been investigated as a possible route towards the fabrication of monolithically integrated photonic circuits. Laser irradiation of a 5 QW laser structure, originally designed for lasers emitting at 1.52 μm, yielded material having a continuously changing band gap ranging from 1.52 to 1.4 μm over the distance of about 3 mm. Bars with arrays of ridge waveguide lasers, having cavity lengths from 300 to 600 μm, were fabricated from the processed material. An individual bar, 2–3 mm long, comprised lasers operating typically between 1.4 and 1.52 μm. The lasers showed stable threshold current density and high quantum efficiency at all operating wavelengths. The results indicate that the applied approach has the potential to realize the cost-effective fabrication of advanced photonic devices and photonic integrated circuits.
Physical properties of nitrogen-doped diamond-like amorphous carbon films deposited by supermagnetron plasma chemical vapor deposition
Authors: Kinoshita Haruhisa , Otaka Naoki
Published: July 2002

Diamond-like amorphous carbon films doped with nitrogen (DAC:N) were deposited on Si and glass wafers intermittently using i-C4H10/N2 repetitive supermagnetron plasma chemical vapor deposition. Deposition duration, which is equal to a plasma heating time of wafer, was selected to be 40 or 60 s, and several layers were deposited repetitively to form one thick film. DAC:N films were deposited at a lower-electrode temperature of 100 °C as a function of upper- and lower-electrode rf powers (200 W/200 W–1 kW/1 kW) and N2 concentration (0%–80%). With an increase in N2 concentration and rf power, the resistivity and the optical band gap decreased monotonously. With increase of the deposition duration from 40 to 60 s, resistivity decreased to 0.03Ω cm and optical band gap decreased to 0.02 eV (substantially equal to 0 eV within the range of experimental error), at an N2 concentration of 80% and rf power of 1 kW(/1 kW).
Relative biological effectiveness enhancement of a brachytherapy seed with characteristic x rays from its constitutive materials
Authors: Taschereau Richard , Roy René , Pouliot Jean
Published: July 2002

The isotopes used for permanent prostate implants, and provide about equivalent tumor control. The purpose of this study is to investigate how characteristic x rays may be used to raise the relative biological effectiveness (RBE) of an iodine seed at short distances to increase the differential effect between tumor and healthy tissue. Within the theoretical framework of microdosimetry, the GEANT4 Monte Carlo simulation toolkit has been used to calculate the RBE of experimental seed designs in which shell and core dimensions and composition were varied independently. A new seed model was also simulated based on the best results obtained. The RBE could be enhanced by increasing the shell thickness and for the range considered, optimum results were obtained by using gradually lower atomic number elements. For a practical 50–60 μm shell, molybdenum is the material of choice. The core diameter has little influence on RBE, but maximum effectiveness is obtained with yttrium or zirconium. These results were put together to design a Mo‐shell and Y‐core seed for which the RBE enhancement was at least 5–7 % (close to the source), which is higher than palladium. This enhanced RBE combined with the longer half‐life of iodine could mean comparable tumor control and better protection to organs at risk than with current seeds. The RBE dependence on distance is an interesting feature that could benefit other applications such as ocular melanoma or coronary brachytherapy where a highly localized dose distribution is desired.
Computerized lesion detection on breast ultrasound
Authors: Drukker Karen , Giger Maryellen L. , Horsch Karla , Kupinski Matthew A. , Vyborny Carl J. , Mendelson Ellen B.
Published: July 2002

We investigated the use of a radial gradient index (RGI) filtering technique to automatically detect lesions on breast ultrasound. After initial RGI filtering, a sensitivity of 87% at 0.76 false‐positive detections per image was obtained on a database of 400 patients (757 images). Next, lesion candidates were segmented from the background by maximizing an average radial gradient (ARD) index for regions grown from the detected points. At an overlap of 0.4 with a radiologist lesion outline, 75% of the lesions were correctly detected. Subsequently, round robin analysis was used to assess the quality of the classification of lesion candidates into actual lesions and false‐positives by a Bayesian neural network. The round robin analysis yielded an value of 0.84, and an overall performance by case of 94% sensitivity at 0.48 false‐positives per image. Use of computerized analysis of breast sonograms may ultimately facilitate the use of sonography in breast cancer screening programs.
Determination and use of radiobiological response parameters in radiation therapy optimization (in English)
Authors: Mavroidis Panayiotis
Published: July 2002

In the present thesis, a treatment optimization procedure is used that considers the shape and the structure of the target tissues and healthy organs at risk, their relative position and their dose‐response relations for the individual patient. Mathematical models largely based on the Poisson statistics and the linear‐quadratic model of cell kill, have been used to quantify the radiobiological response of normal human tissues and tumors to radiation therapy. The radiobiological parameters γ, s, and of the Poisson and relative seriality models have been estimated for certain normal tissues and targets. The determination of these dose‐response relations was based on clinical materials where the treatment information and follow‐up records of the individual patients were available. The clinical use of the derived dose‐response relations is demonstrated through a biological evaluation procedure, which is applied to certain clinical cases. This procedure uses the biological models and dose‐response data of the involved organs and optimizes the dose level of the treatment technique under study. The clinical value of biologically based treatment planning is compared with alternative physical criteria and with the judgment of personnel. It is demonstrated that the radiobiological objective functions allow a much higher conformity and a more clinically relevant scoring of the treatment outcome. In these cases the reliability of the patient setup becomes critical for the effectiveness of the treatment. It is realized that accurate information concerning the response of different organs to fractionated intensity modulated radiation therapy is the key to true optimization of the delivered dose distribution.
On the experimental values of the water surface tension used in some textbooks
Authors: Pellicer J. , García-Morales V. , Guanter L. , Hernández M. J. , Dolz M.
Published: July 2002

A thermodynamic study of one component liquid–vapor planar interfaces and the temperature dependence of some relevant thermodynamic quantities is presented. A critical review of data for the surface tension of water found in some textbooks is given. More accurate measurements show a qualitative change in the temperature dependence of the surface tension, from the almost linear dependence of the old data to nonlinear behavior and the occurrence of an inflection point in the more accurate, more recent data.
Relating speech intelligibility to useful-to-detrimental sound ratios (L)
Authors: Bradley J. S. , Bistafa S. R.
Published: July 2002

This letter corrects typographical errors in two previously published regression equations relating measured speech intelligibility scores and useful-to-detrimental sound ratios. The implications of one of these corrections on a more recent paper are shown to be small. A new and more generally applicable relationship is presented that was derived from a larger data set. This new relationship is presented as a better means of estimating expected speech intelligibility from useful-to-detrimental sound ratios in a wide range of rooms.
The attention filter for tones in noise has the same shape and effective bandwidth in the elderly as it has in young listeners
Authors: Ison James R. , Virag Tracy M. , Allen Paul D. , Hammond Geoffrey R.
Published: July 2002

Listeners asked to detect tones masked by noise hear frequent signals but miss infrequent probes, suggesting that they attend to spectral regions where they expect the signals to occur. The narrow detection pattern centered on the frequent target approximates that obtained in notched noise, indicating that attention is focused on the auditory filter. We measured attention bands in young and elderly listeners (n=5, 4; 20–25 and 62–82 years of age) for targets (800 or 1200 Hz) and infrequent probe signals (target ±25–100 Hz) masked in wideband noise. We anticipated that their width would increase with age, as has been reported for auditory filters. A yes–no single-interval procedure provided detection probabilities and detection response speeds. Both measures showed near-linear declines with decreasing signal level, and graded decay functions as probe frequency deviated from the target frequency. Probes deviating from the target by 25 to 50 Hz were equivalent to a 2-dB reduction in signal level for both measures. The equivalent rectangular bandwidth (ERB) for detection approximated 11% of the signal frequency for each age group. Confidence intervals (95%) showed that the elderly ERB could be at most only about 20% larger than that of younger listeners.
Parametric dependencies for photoacoustic leak localization
Authors: Yönak Serdar H. , Dowling David R.
Published: July 2002

Unintended gas or liquid leaks from manufactured components or manufacturing systems may be detrimental to consumers, manufacturers, and the environment. Thus, leak testing is important for quality, safety, and environmental reasons. This paper describes parametric dependencies for photoacoustic leak localization. The technique is based on the interaction of 10.6-micrometer radiation from a carbon dioxide (CO2) laser and a photoactive tracer gas, sulfur hexafluoride (SF6). For the current investigations, acoustic signals are generated by scanning a laser beam at high speed through gas plumes formed above calibrated leaks. These signals are remotely measured with a four-microphone linear array and analyzed using Bartlett and minimum-variance-distortionless (MVD) matched-field processing (MFP) techniques to determine leak location. This paper extends prior work in photoacoustic leak testing through (i) use of more signal frequencies; (ii) parametric study of four different laser scan rates; and (iii) examination of mismatch between the actual acoustic environment and the propagation model used in the MFP; and (iv) presentation of leak localization results on a curved surface. For a 12-watt CO2 laser exciting the small SF6 gas plume produced by a one-cm3-per-day leak with microphones placed 0.41 m from the leak location, root-mean-square localization uncertainties as small as ±0.5 mm on a line scan of 0.46 m can be achieved when the largest possible number of signal frequencies fall in a measurement bandwidth of approximately 70 kHz.
Evaluation of a noise reduction system for the assessment of click-evoked otoacoustic emissions
Authors: Müller Pascal , Kompis Martin
Published: July 2002

A recently proposed noise reduction system intended to facilitate the assessment of click-evoked otoacoustic emission (CEOAE) in noisy environments [Comput. Biol. Med. 30, 341 (2000)] is evaluated using 13 normally hearing ears and 9 ears with a sensorineural hearing loss. The noise reduction system is based on an adaptive noise canceller design using an additional noise-only reference microphone and intended to reduce externally generated noise. The system is tested in quiet and at different levels of white noise. The three main design parameters of the noise reduction system (adaptation time constant, length of the adaptive filter, and position of the noise reference microphone) are varied systematically in different experiments. With the noise reduction system active, CEOAE can be assessed correctly at noise levels which are 5 to 9 dB higher than without the noise reduction system. For the range of adaptation time constants considered (65.6 to 656 ms), no statistically significant effect on the amount of noise reduction is observed. Noise reduction is highest when the reference microphone is positioned close to the ear probe. Using this reference microphone position and adaptive filters of 6.56 ms in length, average noise reductions of 7.17 to 8.50 dB are achieved.
The performance of matched-field track-before-detect methods using shallow-water Pacific data
Authors: Tantum Stacy L. , Nolte Loren W. , Krolik Jeffrey L. , Harmanci Kerem
Published: July 2002

Matched-field track-before-detect processing, which extends the concept of matched-field processing to include modeling of the source dynamics, has recently emerged as a promising approach for maintaining the track of a moving source. In this paper, optimal Bayesian and minimum variance beamforming track-before-detect algorithms which incorporate a priori knowledge of the source dynamics in addition to the underlying uncertainties in the ocean environment are presented. A Markov model is utilized for the source motion as a means of capturing the stochastic nature of the source dynamics without assuming uniform motion. In addition, the relationship between optimal Bayesian track-before-detect processing and minimum variance track-before-detect beamforming is examined, revealing how an optimal tracking philosophy may be used to guide the modification of existing beamforming techniques to incorporate track-before-detect capabilities. Further, the benefits of implementing an optimal approach over conventional methods are illustrated through application of these methods to shallow-water Pacific data collected as part of the SWellEX-1 experiment. The results show that incorporating Markovian dynamics for the source motion provides marked improvement in the ability to maintain target track without the use of a uniform velocity hypothesis.
Strongly Correlated Superconductivity
Authors: Capone M. , Fabrizio M. , Castellani C. , Tosatti E.
Published: July 2002

High-temperature superconductivity in doped Mott insulators such as the cuprates contradicts the conventional wisdom that electron repulsion is detrimental to superconductivity. Because doped fullerene conductors are also strongly correlated, the recent discovery of high-critical-temperature, presumably
s
-wave, superconductivity in C
60
field effect devices is even more puzzling. We examine a dynamical mean-field solution of a model for electron-doped fullerenes that shows how strong correlations can indeed enhance superconductivity close to the Mott transition. We argue that the mechanism responsible for this enhancement could be common to a wider class of strongly correlated models, including those for cuprate superconductors.
A Large Paleolake Basin at the Head of Ma'adim Vallis, Mars
Authors: Irwin Rossman P. , Maxwell Ted A. , Howard Alan D. , Craddock Robert A. , Leverington David W.
Published: July 2002

At 8 to 15 kilometers wide, Ma'adim Vallis is one of the largest valleys in the martian highlands. Although a groundwater source was previously suggested, the channel originates at a spillway in the divide of a ∼3,000,000-square-kilometer closed drainage basin. The interior morphology of this source basin, including likely shoreline features following topographic contours, suggests that Ma'adim Vallis was created through catastrophic overflow of a ∼1,100,000-square-kilometer highland lake. The size, constant levels, and interior morphology of three regional paleolake basins require a warmer paleoclimate and a long-term, recharged, stable highland water table more than ∼3.5 billion years ago.
Rooting the Eukaryote Tree by Using a Derived Gene Fusion
Authors: Stechmann Alexandra , Cavalier-Smith Thomas
Published: July 2002

Single-gene trees have failed to locate the root of the eukaryote tree because of systematic biases in sequence evolution. Structural genetic data should yield more reliable insights into deep phylogenetic relationships. We searched major protist groups for the presence or absence of a gene fusion in order to locate the root of the eukaryote tree. In striking contrast to previous molecular studies, we show that all eukaryote groups ancestrally with two cilia (bikonts) are evolutionarily derived. The root lies between bikonts and opisthokonts (animals, Fungi, Choanozoa). Amoebozoa either diverged even earlier or are sister of bikonts or (less likely) opisthokonts.
Probing and Controlling the Bonds of an Artificial Molecule
Authors: Holleitner Alexander W. , Blick Robert H. , Hüttel Andreas K. , Eberl Karl , Kotthaus Jörg P.
Published: July 2002

We demonstrate how molecular quantum states of coupled semiconductor quantum dots are coherently probed and manipulated in transport experiments. The applied method probes quantum states by the virtual cotunneling of two electrons and hence resolves the sequences of molecular states simultaneously. This result is achieved by weakly probing the quantum system through parallel contacts to its constituting quantum dots. The overlap of the dots' wave functions and, in turn, the splitting of molecular states are adjusted by the direct influence of coupling electrodes.
Sustained Loss of a Neoplastic Phenotype by Brief Inactivation of
MYC
Authors: Jain Meenakshi , Arvanitis Constadina , Chu Kenneth , Dewey William , Leonhardt Edith , Trinh Maxine , Sundberg Christopher D. , Bishop J. Michael , Felsher Dean W.
Published: July 2002

Pharmacological inactivation of oncogenes is being investigated as a possible therapeutic strategy for cancer. One potential drawback is that cessation of such therapy may allow reactivation of the oncogene and tumor regrowth. We used a conditional transgenic mouse model for
MYC
-induced tumorigenesis to demonstrate that brief inactivation of
MYC
results in the sustained regression of tumors and the differentiation of osteogenic sarcoma cells into mature osteocytes. Subsequent reactivation of
MYC
did not restore the cells' malignant properties but instead induced apoptosis. Thus, brief
MYC
inactivation appears to cause epigenetic changes in tumor cells that render them insensitive to
MYC
-induced tumorigenesis. These results raise the possibility that transient inactivation of
MYC
may be an effective therapy for certain cancers.
A Low Genomic Number of Recessive Lethals in Natural Populations of Bluefin Killifish and Zebrafish
Authors: McCune Amy R. , Fuller Rebecca C. , Aquilina Allisan A. , Dawley Robert M. , Fadool James M. , Houle David , Travis Joseph , Kondrashov Alexey S.
Published: July 2002

Despite the importance of selection against deleterious mutations in natural populations, reliable estimates of the genomic numbers of mutant alleles in wild populations are scarce. We found that, in wild-caught bluefin killifish
Lucania goodei
(Fundulidae) and wild-caught zebrafish
Danio rerio
(Cyprinidae), the average numbers of recessive lethal alleles per individual are 1.9 (95% confidence limits 1.3 to 2.6) and 1.4 (95% confidence limits 1.0 to 2.0), respectively. These results, together with data on several
Drosophila
species and on
Xenopus laevis
, show that phylogenetically distant animals with different genome sizes and numbers of genes carry similar numbers of lethal mutations.
Sex Matters in Meiosis
Authors: Hunt Patricia A. , Hassold Terry J.
Published: July 2002

In mammals, fertilization typically involves the ovulation of one or a few eggs at one end of the female reproductive tract and the entry of millions of sperm at the other. Given this disparity in numbers, it might be expected that the more precious commodity—eggs—would be subject to more stringent quality-control mechanisms. However, information from engineered mutations of meiotic genes suggests just the opposite. Specifically, the available mutants demonstrate striking sexual dimorphism in response to meiotic disruption; for example, faced with adversity, male meiosis grinds to a halt, whereas female meiosis soldiers on. This female “robustness” comes with a cost, however, because aneuploidy appears to be increased in the resultant oocytes.
Channelrhodopsin-1: A Light-Gated Proton Channel in Green Algae
Authors: Nagel Georg , Ollig Doris , Fuhrmann Markus , Kateriya Suneel , Musti Anna Maria , Bamberg Ernst , Hegemann Peter
Published: July 2002

Phototaxis and photophobic responses of green algae are mediated by rhodopsins with microbial-type chromophores. We report a complementary DNA sequence in the green alga
Chlamydomonas reinhardtii
that encodes a microbial opsin-related protein, which we term Channelopsin-1. The hydrophobic core region of the protein shows homology to the light-activated proton pump bacteriorhodopsin. Expression of Channelopsin-1, or only the hydrophobic core, in
Xenopus laevis
oocytes in the presence of all-
trans
retinal produces a light-gated conductance that shows characteristics of a channel selectively permeable for protons. We suggest that Channelrhodopsins are involved in phototaxis of green algae.
Multiple Roles of
Arabidopsis VRN1
in Vernalization and Flowering Time Control
Authors: Levy Yaron Y. , Mesnage Stéphane , Mylne Joshua S. , Gendall Anthony R. , Dean Caroline
Published: July 2002

Arabidopsis VRN
genes mediate vernalization, the process by which a long period of cold induces a mitotically stable state that leads to accelerated flowering during later development.
VRN1
encodes a protein that binds DNA in vitro in a non–sequence-specific manner and functions in stable repression of the major target of the vernalization pathway, the floral repressor
FLC
. Overexpression of
VRN1
reveals a vernalization-independent function for
VRN1
, mediated predominantly through the floral pathway integrator
FT
, and demonstrates that VRN1 requires vernalization-specific factors to target
FLC
.
Mediation of Poly(ADP-Ribose) Polymerase-1-Dependent Cell Death by Apoptosis-Inducing Factor
Authors: Yu Seong-Woon , Wang Hongmin , Poitras Marc F. , Coombs Carmen , Bowers William J. , Federoff Howard J. , Poirier Guy G. , Dawson Ted M. , Dawson Valina L.
Published: July 2002

Poly(ADP-ribose) polymerase-1 (PARP-1) protects the genome by functioning in the DNA damage surveillance network. PARP-1 is also a mediator of cell death after ischemia-reperfusion injury, glutamate excitotoxicity, and various inflammatory processes. We show that PARP-1 activation is required for translocation of apoptosis-inducing factor (AIF) from the mitochondria to the nucleus and that AIF is necessary for PARP-1–dependent cell death.
N
-methyl-
N
′-nitro-
N
-nitrosoguanidine, H
2
O
2
, and
N
-methyl-
d
-aspartate induce AIF translocation and cell death, which is prevented by PARP inhibitors or genetic knockout of PARP-1, but is caspase independent. Microinjection of an antibody to AIF protects against PARP-1–dependent cytotoxicity. These data support a model in which PARP-1 activation signals AIF release from mitochondria, resulting in a caspase-independent pathway of programmed cell death.
El Niño-Like Pattern in Ice Age Tropical Pacific Sea Surface Temperature
Authors: Koutavas Athanasios , Lynch-Stieglitz Jean , Marchitto Thomas M. , Sachs Julian P.
Published: July 2002

Sea surface temperatures (SSTs) in the cold tongue of the eastern equatorial Pacific exert powerful controls on global atmospheric circulation patterns. We examined climate variability in this region from the Last Glacial Maximum (LGM) to the present, using a SST record reconstructed from magnesium/calcium ratios in foraminifera from sea-floor sediments near the Galápagos Islands. Cold-tongue SST varied coherently with precession-induced changes in seasonality during the past 30,000 years. Observed LGM cooling of just 1.2°C implies a relaxation of tropical temperature gradients, weakened Hadley and Walker circulation, southward shift of the Intertropical Convergence Zone, and a persistent El Niño–like pattern in the tropical Pacific. This is contrasted with mid-Holocene cooling suggestive of a La Niña–like pattern with enhanced SST gradients and strengthened trade winds. Our results support a potent role for altered tropical Pacific SST gradients in global climate variations.
Generation and in Vitro Differentiation of a Spermatogonial Cell Line
Authors: Feng Li-Xin , Chen Yali , Dettin Luis , Pera Renee A. Reijo , Herr John C. , Goldberg Erwin , Dym Martin
Published: July 2002

Spermatogenesis is the process by which spermatogonial stem cells divide and differentiate to produce sperm. In vitro sperm production has been difficult to achieve because of the lack of a culture system to maintain viable spermatogonia for long periods of time. Here we report the in vitro generation of spermatocytes and spermatids from telomerase-immortalized mouse type A spermatogonial cells in the presence of stem cell factor. This differentiation can occur in the absence of supportive cells. The immortalized spermatogonial cell line may serve as a powerful tool in elucidating the molecular mechanisms of spermatogenesis. Furthermore, through genomic modification and transplantation techniques, this male germ cell line may be used to generate transgenic mice and to develop germ cell gene therapy.
The Food Pushers
Authors: Willett Walter
Published: July 2002

Food Politics
How the Food Industry Influences Nutrition and Health. Marion Nestle. University of California Press, Berkeley, 2002. 469 pp. $29.95, £19.95. ISBN 0-520-22465-5.

Nestle examines how U.S. food companies use political processes to counter regulations and dietary advice that may restrict their economically driven goal of convincing people to eat more of their products.
Novel Ciprofloxacin-Resistant, Nalidixic Acid-Susceptible Mutant of
Staphylococcus aureus
Authors: Piddock Laura J. V. , Jin Yu Fang , Webber Mark A. , Everett Martin J.
Published: July 2002

A ciprofloxacin-resistant, nalidixic acid-susceptible mutant of
Staphylococcus aureus
(F145) contained no mutations within
gyrA
,
gyrB
,
grlA
, and
grlB
or within
norA
or its promoter region. MICs and accumulation studies suggest the role of a novel multidrug efflux pump.
Neuroprotection and Reduced Proliferation of Microglia in Ribavirin-Treated Bornavirus-Infected Rats
Authors: Solbrig Marylou V. , Schlaberg Robert , Briese Thomas , Horscroft Nigel , Lipkin W. Ian
Published: July 2002

In a rat model of Borna disease, intracerebral ribavirin caused clinical improvement without changes in virus titer or nucleic acid. Levels of microglia and infiltrating CD4 and CD8 cells were decreased, despite increases in mRNAs encoding interleukin-1β (IL-1β), IL-10, and gamma interferon in the brain. Intracerebral ribavirin may reduce morbidity through effects on microglia cell proliferation.