bluuebunny/crossref_metadata_2025 huggingface dataset:
KCNE4 is an inhibitory subunit to the KCNQ1 channel
Authors: Grunnet Morten , Jespersen Thomas , Rasmussen Hanne Borger , Ljungstrøm Trine , Jorgensen Nanna K. , Olesen Søren‐Peter , Klaerke Dan A.
Published: July 2002

KCNE4 is a membrane protein belonging to a family of single transmembrane domain proteins known to have dramatic effect on the gating of certain potassium channels. However, no functional role of KCNE4 has been suggested so far. In the present paper we demonstrate that KCNE4 is an inhibitory subunit to KCNQ1 channels. Co‐expression of KCNQ1 and KCNE4 in Xenopus oocytes completely inhibited the KCNQ1 current. This was reproduced in mammalian CHO‐K1 cells. Experiments with delayed expression of mRNA coding for KCNE4 in KCNQ1‐expressing oocytes suggested that KCNE4 exerts its effect on KCNQ1 channels already expressed in the plasma membrane. This notion was supported by immunocytochemical studies and Western blotting, showing no significant difference in plasma membrane expression of KCNQ1 channels in the presence or absence of KCNE4. The impact of KCNE4 on KCNQ1 was specific since no effect of KCNE4 could be detected if co‐expressed with KCNQ2‐5 channels or hERG1 channels. RT‐PCR studies revealed high KCNE4 expression in embryos and adult uterus, where significant expression of KCNQ1 channels has also been demonstrated.
Molecular identification of Kvα subunits that contribute to the oxygen‐sensitive K+ current of chemoreceptor cells of the rabbit carotid body
Authors: Sanchez Diego , López‐López Jose R. , Pérez‐García M. Teresa , Sanz‐Alfayate Gloria , Obeso Ana , Ganfornina Maria D. , Gonzalez Constancio
Published: July 2002

Rabbit carotid body (CB) chemoreceptor cells possess a fast‐inactivating K+ current that is specifically inhibited by hypoxia. We have studied the expression of Kvα subunits, which might be responsible for this current. RT‐PCR experiments identified the expression of Kv1.4, Kv3.4, Kv4.1 and Kv4.3 mRNAs in the rabbit CB. There was no expression of Kv3.3 or Kv4.2 transcripts. Immunocytochemistry with antibodies to tyrosine hydroxylase (anti‐TH) and to specific Kv subunits revealed the expression of Kv3.4 and Kv4.3 in chemoreceptor cells, while Kv1.4 was only found in nerve fibres. Kv4.1 mRNA was also found in chemoreceptor cells following in situ hybridization combined with anti‐TH antibody labelling. Kv4.1 and Kv4.3 appeared to be present in all chemoreceptor cells, but Kv3.4 was only expressed in a population of them. Electrophysiological experiments applying specific toxins or antibodies demonstrated that both Kv3.4 and Kv4.3 participate in the oxygen‐sensitive K+ current of chemoreceptor cells. However, toxin application experiments confirmed a larger contribution of members of the Kv4 subfamily. [Ca2+]i measurements under hypoxic conditions and immunocytochemistry experiments in dispersed CB cells demonstrated the expression of Kv3.4 and Kv4.3 in oxygen‐sensitive cells; the presence of Kv3.4 in the chemoreceptor cell membrane was not required for the response to low PO2. In summary, three Kv subunits (Kv3.4, Kv4.1 and Kv4.3) may be involved in the fast‐inactivating outward K+ current of rabbit CB chemoreceptor cells. The homogeneous distribution of the Kv4 subunits in chemoreceptor cells, along with their electrophysiological properties, suggest that Kv4.1, Kv4.3, or their heteromultimers, are the molecular correlate of the oxygen‐sensitive K+ channel.
Intermittent ATP release from nerve terminals elicits focal smooth muscle Ca2+ transients in mouse vas deferens
Authors: Brain Keith L. , Jackson V. Margaret , Trout Stephen J. , Cunnane Thomas C.
Published: July 2002

A confocal Ca2+ imaging technique has been used to detect ATP release from individual sympathetic varicosities on the same nerve terminal branch. Varicose nerve terminals and smooth muscle cells in mouse vas deferens were loaded with the Ca2+ indicator Oregon Green 488 BAPTA‐1. Field (nerve) stimulation evoked discrete, focal increases in [Ca2+] in smooth muscle cells adjacent to identified varicosities. These focal increases in [Ca2+] have been termed ‘neuroeffector Ca2+ transients’ (NCTs). NCTs were abolished by α,β‐methylene ATP (1 μM), but not by nifedipine (1 μM) or prazosin (100 nm), suggesting that NCTs are generated by Ca2+ influx through P2X receptors without a detectable contribution from L‐type Ca2+ channels or α1‐adrenoceptor‐mediated pathways. Action potential‐evoked ATP release was highly intermittent (mean probability 0.019 ± 0.002; range 0.001‐0.10) at 1 Hz stimulation, even though there was no failure of action potential propagation in the nerve terminals. Twenty‐eight per cent of varicosities failed to release transmitter following more than 500 stimuli. Spontaneous ATP release was very infrequent (0.0014 Hz). No Ca2+ transient attributable to noradrenaline release was detected even in response to 5 Hz stimulation. There was evidence of local noradrenaline release as the α2‐adrenoceptor antagonist yohimbine increased the probability of occurrence of NCTs by 55 ± 21 % during trains of stimuli at 1 Hz. Frequency‐dependent facilitation preferentially occurred at low probability release sites. The monitoring of NCTs now allows transmitter release to be detected simultaneously from each functional varicosity on an identified nerve terminal branch on an impulse‐to‐impulse basis.
Ceramic Turbine Engine Demonstration Project: A Summary Report
Authors: Schenk B.
Published: July 2002

Honeywell Engines, Systems & Services has successfully addressed critical concerns that are slowing commercialization of structural ceramics in gas turbines. The U.S. Department of Energy (DoE) sponsored Ceramic Turbine Engine Demonstration Project (CTEDP) had the mission of advancing ceramic gas turbine component technology toward commercialization. The thrust of the program was to “bridge the gap” between ceramics in the laboratory and near-term commercial heat engine applications. Most of this mission has been achieved. The 331-200[CT] auxiliary power unit (APU) test bed featured ceramic first-stage nozzles and blades. Fabrication of ceramic components provided manufacturing process demonstration scale-up to the minimum levels needed for commercial viability. Through this program, design methods refinement and the development of new design methods unique to ceramic turbine components have been supported and validated in rig and development engine testing. Over 6800 hours of on-site endurance tests demonstrated component reliability. Additional field testing in APUs onboard commercial aircraft and stationary industrial engines has been initiated and will continue beyond completion of this program.
Development and Evaluation of a High-Resolution Turbine Pyrometer System
Authors: Eggert Torsten , Schenk Bjoern , Pucher Helmut
Published: July 2002

Optical pyrometers provide many advantages over intrusive measuring techniques in determining the spatial and time varying temperature distribution of fast rotating components in gas turbines. This paper describes the development and evaluation of a versatile high-resolution pyrometer system and its application to radial turbine rotor temperature mapping as has been done in a R&D project at the Technical University Berlin under funding from Siemens Power Generation (KWU). The development goal was a pyrometer system with a temporal resolution of 1 μs, a minimum field of view of 1 mm, and a measurement range from 600 to 1500°C. A prototype of the pyrometer system has been built and tested at the small gas turbine test facility of the Technical University Berlin. The system yielded excellent results with respect to measurement uncertainty, resolution, and reliability. Finally, measurement results obtained with the new system on a radial turbine rotor and on a heavy duty industrial gas turbine are compared with measurements conducted with a commercially available turbine pyrometer system.
Rig and Engine Testing of Melt Infiltrated Ceramic Composites for Combustor and Shroud Applications
Authors: Corman G. S. , Dean A. J. , Brabetz S. , Brun M. K. , Luthra K. L. , Tognarelli L. , Pecchioli M.
Published: July 2002

General Electric has developed SiC fiber-reinforced SiC-Si matrix composites produced by silicon melt infiltration for use in gas turbine engine applications. High temperature, high-pressure combustion rig testing, and engine testing has been performed on combustor liners and turbine shrouds made from such MI composites. Frame 5 sized combustor liners were rig tested under lean head end diffusion flame conditions for 150 hours, including 20 thermal trip cycles, with no observed damage to the ceramic liners. Similarly, 46-cm diameter, single-piece turbine shroud rings were fabricated and tested in a GE-2 gas turbine engine. The fabrication and testing of both components are described.
Internal Combustion Engine Noise Analysis With Time-Frequency Distribution
Authors: Zheng G. T. , Leung A. Y. T.
Published: July 2002

An analysis procedure, using the time-frequency distribution, has been developed for the analysis of internal combustion engine noise signals. It provides an approach making use of advantages of both the linear time-frequency distribution and the bilinear time-frequency distribution but avoiding their disadvantages. In order to identify requirements on the time-frequency analysis and also correlate a time-frequency analysis result with noise sources, the composition of the noise signal is discussed first. With this discussion, a mathematical model has been suggested for the noise signal. An example of identifying noise sources and detecting the abnormal condition of an injector with the noise signal time-frequency distribution for a diesel engine is also provided.
Analysis of the Combustion Process in a EURO III Heavy-Duty Direct Injection Diesel Engine
Authors: Desantes J. M. , Pastor J. V. , Arre`gle J. , Molina S. A.
Published: July 2002

To fulfill the commitments of future pollutant regulations, current development of direct injection (DI) Diesel engines requires to improve knowledge on the injection/combustion process and the effect of the injection parameters and engine operation conditions upon the spray and flame characteristics and how they affect engine performance and pollutant emissions. In order to improve comprehension of the phenomena inherent to Diesel combustion, a deep experimental study has been performed in a single-cylinder engine with the main characteristics of a six-cylinder engine passing the EURO III legislation. Some representative points of the 13-mode engine test cycle have been considered modifying the nominal values of injection pressure, injection load, intake pressure, engine speed, and injection timing. The study combines performance and emissions experimental measurements together with heat release law (HRL) analysis and high-speed visualization. Controlling parameters for BSFC, NOx, and soot emissions are identified in the last part of the paper.
Stress Distribution in Porous Ceramic Bodies During Binder Burnout
Authors: Feng Z. C. , He B. , Lombardo S. J.
Published: July 2002

A model has been developed for describing the stresses that arise during binder burnout in three-dimensional porous bodies. The pressure gradient that arises from the decomposition of binder in the pore space is treated as an equivalent body force. For input into the mechanics model, the pressure distribution is obtained from the analytical solution for three-dimensional porous bodies with anisotropic permeability. The normal and shear stresses are then calculated from finite element analysis for bodies of parallelepiped geometry. In general, the normal stresses occur at the center of the body and are an order of magnitude larger than the shear stresses. Both the normal and shear stresses depend on the body size, the body geometry, and on the permeability.
Kinematic Characterization of Chip Lateral-Curl—The Third Pattern of Chip Curl in Machining
Authors: Fang Ning
Published: July 2002

Two patterns of chip curl, namely up- and side-curl, have been widely recognized in machining operations. This paper presents the third pattern of chip curl that is called lateral-curl. The rotating axis of chip lateral-curl is perpendicular to the rotating axes of up- and side-curl. The essential differences are illustrated between the chip lateral-curl concept and the “chip-twisting” concept presented in other related studies. Based on an analytical vector analysis, a new kinematic characterization is presented for the natural (or born) lateral-curl of the chip that is associated with flat-faced tool machining. It is demonstrated that chip forms (or shapes) can be determined by four governing variables: the chip up-, lateral-, and side-curl radii and the chip side-flow angle. A method to indirectly measure the chip lateral-curl radius is presented. The effect of chip lateral-curl on chip forms is investigated through cutting tests, theoretical analysis, and computer simulations.
Confined Capillary Stresses During the Initial Growth of Thin Films on Amorphous Substrates
Authors: Gill S. P. A. , Gao H. , Ramaswamy V. , Nix W. D.
Published: July 2002

Changes in substrate curvature indicating the existence of compressive stress in isolated crystallites are commonly observed during the initial stages of thin film deposition of metals on glass or ceramic substrates. Following the suggestion of Abermann et al. (R. Abermann et al., 1978, Thin Solid Films, 52, p. 215), we attribute the origin of this compressive stress to the action of capillary forces during film growth. As new atomic layers are deposited, the capillary forces acting on atoms near the surface are stored as transformation strains in the bulk of the crystallites. To test this concept, we propose three models for evaluating the capillary strains and their induced compressive stresses in a crystalline. A finite element analysis is performed to show that the model predictions agree well with experimental data.
Modeling the Thermostructural Capability of Continuous Fiber-Reinforced Ceramic Composites
Authors: DiCarlo J. A. , Yun H. M.
Published: July 2002

There exists today considerable interest in developing continuous fiber-reinforced ceramic matrix composites (CMC) that can operate as hot-section components in advanced gas turbine engines. The objective of this paper is to present simple analytical and empirical models for predicting the effects of time and temperature on CMC tensile rupture under various composite and engine conditions. These models are based on the average rupture behavior measured in air for oxide and SiC-based fibers of current technical interest. For example, assuming a cracked matrix and Larson-Miller rupture curves for single fibers, it is shown that model predictions agree quite well with high-temperature stress-rupture data for SiC/SiC CMC. Rupture models, yet to be validated, are also presented for three other relevant conditions: (a) SiC fibers become oxidatively bonded to each other in a cracked CMC, (b) applied CMC stresses are low enough to avoid matrix cracking, and (c) Si-based CMC are subjected to surface recession in high-temperature combustion gases. The practical implications of the modeling results are discussed, particularly in regard to the optimum fibers and matrices for CMC engine applications and the thermostructural capability of SiC/SiC CMC in comparison to nickel-based superalloys, monolithic ceramics, and oxide/oxide CMC.
Optimal Placement of Fixture Clamps: Maintaining Form Closure and Independent Regions of Form Closure
Authors: Marin Rodrigo A. , Ferreira Placid M.
Published: July 2002

This paper addresses the problem of computing frictionless optimal clamping schemes with form closure on three-dimensional parts with planar and cylindrical faces. Given a work part with a pre-defined 3-2-1 locator scheme, a set of polygonal convex regions on the clamping faces are defined as the admissible positions of the clamps. The work part-fixture contact is assumed to be of the point-surface type. Using extended screw theory, we present a linear algebraic method that computes the sub-regions of the clamping faces such that clamps located within them are guaranteed to achieve form closure. These are termed dependent regions of form closure, since the clamps must be placed according to a precise relationship. We develop methods to compute these regions on work parts with planar and cylindrical faces. This result is incorporated into a new linear programming formulation to compute frictionless optimal clamping schemes. Clamping schemes with form closure are robust when uncertainty in knowledge of the external loads acting on the work part is present. Next, we extend the method to compute maximal independent regions of form closure. These are sub-regions of the dependent regions of form closure where the clamps can be placed completely independent of each other while maintaining form closure. When the clamps are placed within the independent regions of form closure, the clamping scheme is made robust against errors in their positions.
Kinetostatic Analysis and Design Optimization of the Tricept Machine Tool Family
Authors: Zhang Dan , Gosselin Cle´ment M.
Published: July 2002

Selecting a mechanism for a machine tool that will best suit the needs of a forecast set of rigidities can be a difficult and costly exercise. This problem can now be addressed using a kinetostatic modeling method. In this paper, a kinetostatic model for the Tricept machine tool family is established based on lumped flexibilities. This model can be used to analyze the effect of link flexibility on the machine tool’s global stiffness and the platform positioning precision. The Tricept machine tool is a new type of parallel mechanism with prismatic actuators whose degree of freedom is dependent on a passive constraining leg connecting the base and the platform. The geometric model and the mechanical design of the Tricept machine tool is first recalled. Then, a lumped kinetostatic model is proposed in order to account for joint and link compliances. It is shown that the link flexibility has a significant effect on the machine tool’s precision and that it is necessary to take the link flexibility into account. Additionally, the inverse kinematics and velocity equations are given for both rigid-link and flexible-link mechanisms. Finally, the optimization of the stiffness is addressed using a genetic algorithm.
Experimental Demonstration of Precision Control of a Deployable Optics Structure
Authors: Erwin R. Scott , Schrader Karl , Moser Ruth L. , Griffin Steven F.
Published: July 2002

This paper presents the development, design, and implementation of a precision control system for a large, sparse-aperture space-deployable telescope testbed. Aspects of the testbed and laboratory environment relevant to nanometer-level control and performance objectives are provided. There are four main objectives of the control system: 1) reduction of natural resonances of the supporting structure, 2) rejection of tonal disturbances, 3) tip, tilt, and piston set-point tracking for optical surfaces, and 4) reduction in settling time of optical surfaces after an impulsive slew-type disturbance. The development of a three-input, three-output, high-bandwidth structural control system for the testbed is presented, and experimental data demonstrating that all objectives were attained is provided. The paper concludes with a discussion of the results and a description of research issues remaining to be addressed.
Development of the Cylindrical Wire Electrical Discharge Machining Process, Part 2: Surface Integrity and Roundness
Authors: Qu Jun , Shih Albert J. , Scattergood Ronald O.
Published: July 2002

This study investigates the surface integrity and roundness of parts created by the cylindrical wire EDM process. A mathematical model for the arithmetic average surface roughness on the ideal surface of a cylindrical wire EDM workpiece is first derived. Effects of wire feed rate and part rotational speed on the surface finish and roundness for brass and carbide work-materials at high material removal rates are investigated. The pulse on-time and wire feed rate are varied to explore the best possible surface finish and roundness achievable by the cylindrical wire EDM process. This study has demonstrated that, for carbide parts, an arithmetic average surface roughness and roundness as low as 0.68 and 1.7 μm, respectively, can be achieved. Surfaces of the cylindrical EDM parts were examined using Scanning Electron Microscopy (SEM) to identify the macro-ridges and craters on the surface. Cross-sections of the EDM parts are examined using the SEM to quantify the sub-surface recast layers and heat-affected zones under various process parameters. This study has demonstrated that the cylindrical wire EDM process parameters can be adjusted to achieve either high material removal rate or good surface integrity and roundness.
Investigation and reduction of spurious peaks caused by electron-stimulated desorption and outgassing by means of a grid heating method in a hot-cathode quadrupole residual gas analyzer
Authors: Watanabe Fumio
Published: July 2002

In the year 2001, two issues remain for extreme high vacuum (XHV) pressure measurements with hot-cathode ionization gauges: measurement limits caused by electron-stimulated desorption (ESD) and outgassing. The limit caused by ESD is significantly clarified and at least partially solved by means of a grid heating method in a residual gas analyzer. After system bakeout and at 10−9 Pa, when the surface of a platinum alloy grid remains contaminated with F and Cl atoms and CO molecules, the mass spectrum is dominated by spurious peaks (which set the measurement limit for a total pressure gauge) caused by ESD species of F, Cl, and O, with a yield of 10−11 (species/electron, with neutral/ion ≅0.3) and by CO molecule ESD, with a yield of 10−11 (species/electron, with CO neutral/O ion ≅18). In this condition, a spurious H peak caused by hydrogen ESD is still low. However, once the grid surface is thoroughly cleaned at over 900 °C by ohmic heating or electron bombardment, the major ESD species observed for both neutrals and ions dramatically changes to mainly a spurious H peak with a yield of 10−11 (species/electron, with neutral/ion ≅2). When the operational grid temperature is then increased to 500 °C, the spurious H peak is decreased by over 3 orders of magnitude and the spectrum becomes mainly H2 molecules, reflecting the true pressure of the system; i.e., the relative error for the pressure is reduced to 8% from 614%. The lower limit caused by outgassing in these instruments is due to the grid bulk content of hydrogen. Finding a lower-hydrogen solubility material for the grid may become the last work required for lower-limit XHV gauge development. In order to decrease the limits caused by ESD and outgassing in a hot-cathode gauge, employing ion energy filters and cold-cathode field emitters is unnecessary.
Critical issues in the heteroepitaxial growth of alkaline-earth oxides on silicon
Authors: Lettieri J. , Haeni J. H. , Schlom D. G.
Published: July 2002

The critical aspects of the epitaxial growth of alkaline-earth oxides on silicon are described in detail. The step by step transition from the silicon to the alkaline-earth oxide as shown through reflection high energy electron diffraction is presented, with emphasis placed on the favorable interface stability, oxidation, structural, and strain considerations for each stage of the growth via molecular beam epitaxy.
Thin film transistors with anodic gate dielectrics and chemical bath deposited active layers
Authors: Gan Feng Yuan , Shih Ishiang
Published: July 2002

Thin film transistors (TFTs) with an anodic dielectric layer and chemical bath deposited active layer have been fabricated on glass substrates. The effects of anodization conditions on the quality of the anodic dielectric were investigated by measuring the breakdown electric field and leakage current density of the metal–insulator–metal capacitors fabricated. Using the anodic gate dielectric, preliminary thin film transistors with CdS and CdSe films formed by a chemical bath deposition method were fabricated and evaluated. Results of electrical measurements carried out on the CdSe-TFTs with Al2O3 and Ta2O5 gate dielectrics showed field effect mobilities of 3.4 and 0.67 cm2/V s and threshold voltages of 3.2 and 8.2 V, respectively. Field effect mobilities of 0.2 and 2 cm2/V s and threshold voltages of 4.3 and 5.2 V were observed for CdS-TFTs, again with Al2O3 and Ta2O5 gate dielectrics. The mobilities obtained from the present TFTs fabricated on glass substrates are smaller than that on similar TFTs fabricated on thermally grown gate oxides on Si substrates in our previous work.
Rhodium and Rhodium Oxide Thin Films Characterized by XPS
Authors: Abe Yoshio , Kato Kiyohiko , Kawamura Midori , Sasaki Katsutaka
Published: July 2002

RhO2 belongs to the family of conducting platinum group metal oxides, which have attracted attention as new capacitor electrode materials for dynamic random access memories (DRAMs) and nonvolatile ferroelectric random access memories (FeRAMs). Rh, Rh2O3, and RhO2 thin films were prepared by sputtering and their XPS spectra were collected with a monochromatic Al Kα x-ray source. This report includes XPS spectra of Rh 3d and O 1s core regions for these films.
Application of imaging‐derived parameters to dosimetry of intravascular brachytherapy sources: Perturbation effects of residual plaque burden
Authors: Sehgal Varun , Li Zuofeng , Palta Jatinder R. , Smith Karen M. , Bolch W. E.
Published: July 2002

The dosimetric effect of geometric and material heterogeneities on intravascular brachytherapy dose delivery has been studied recently. Residual plaque within the coronary vessel appears to have an impact on the uniform delivery of radiation dose to the arterial tissue. In this study, we have examined the effect of residual plaque burden and post‐PCI (percutaneous coronary intervention) plaque configuration on the dose to the arterial wall from clinical intravascular brachytherapy β‐emitting sources containing and Monte Carlo simulations using the MCNP4B code were performed for these catheter‐based sources with residual plaque burden ranging between 25% and 50%. The residual plaque burden values were derived from post‐PCI data provided in several recent clinical studies. Dose calculations were performed for three different values of plaque density (1.45 g cm−3, 2.20 g cm−3, and 3.1 g cm−3) and three different plaque morphologies for the same residual plaque burden. The dose perturbation factor (DPF), defined as the ratio of dose at 2 mm radial distance for a given case to the dose at the same radial distance in homogeneous water medium, was determined for each of the three different plaque densities. The range of DPF values was 0.81–1.01, 0.62–0.99, and 0.41–0.97 for different plaque densities for the source. Corresponding DPF values for the source were 0.90–1.01, 0.84–1.01, and 0.62–1.01. The results indicate the need for accurate assessment of post‐PCI clinical measurements such as minimal lumen diameter and residual plaque burden and incorporation of these values into dose calculations.
Teaching antenna reception and scattering from a time-domain perspective
Authors: Smith Glenn S.
Published: July 2002

The reception and scattering of an incident plane wave by simple wire receiving antennas are analyzed. The approach is the same as used in an earlier paper where the radiation from similar transmitting antennas was considered. First, analytic expressions are obtained for the current and field of a basic traveling-wave receiving element. Then, a more complicated receiving antenna is viewed as a combination of basic traveling-wave elements, and the current and scattered electromagnetic field of the antenna are obtained by superimposing the currents and fields of these elements. The emphasis throughout is on the use of the time domain, viz., pulsed excitation, to establish physical understanding of the process of radiation/reception, unlike conventional treatments that use time-harmonic excitation. Two examples are discussed in detail: reception by a loaded dipole antenna and scattering by a straight wire. The relationship between the transmission and reception for the dipole, i.e., reciprocity, and the phenomenon of resonant scattering for the wire are also examined.
An experiment to determine the skin depth and Fermi velocity in metals
Authors: Singh N. P. , Gupta S. C. , Sood B. R.
Published: July 2002

A simple experimental method for measuring the anomalous skin depth and Fermi velocity in metals is presented. The skin depth is evaluated by measuring the resistance at 77 K of a thick metal wire specimen at frequencies of 100 Hz and 0.1 MHz. The Fermi velocity is obtained by using the theoretical expression that relates the anomalous skin depth to the Fermi velocity.
Time-resolved tracking of a sound scatterer in a complex flow: Nonstationary signal analysis and applications
Authors: Mordant Nicolas , Pinton Jean-François , Michel Olivier
Published: July 2002

It is known that ultrasound techniques yield nonintrusive measurements of hydrodynamic flows. For example, the study of the echoes produced by a large number of particles insonified by pulsed wavetrains has led to a now-standard velocimetry device. In this paper, a new technique for the measurement of the velocity of individual solid particles moving in fluid flows is proposed. It relies on the ability to resolve in time the Doppler shift of the sound scattered by the continuously insonified particle. For this signal-processing problem two classes of approaches can be used: time-frequency analysis and parametric high-resolution methods. In the first class the spectrogram and reassigned spectrogram is considered, and applied to detect the motion of a small bead settling in a fluid at rest. In nonstationary flows, methods in the second class are more robust. An approximated maximum likelihood (AML) technique has been adapted, coupled with a generalized Kalman filter. This method allows for the estimation of rapidly varying frequencies; the parametric nature of the algorithm also provides an estimate of the variance of the identified frequency parameters.
Design of optimal configuration for generating A0 Lamb mode in a composite plate using piezoceramic transducers
Authors: Grondel Sébastien , Paget Christophe , Delebarre Christophe , Assaad Jamal , Levin Klas
Published: July 2002

This work concerned a technique for a health monitoring system based on the generation and sensing of Lamb waves in composite structures by thin surface-bonded piezoceramic transducers. The objective was to develop transducers that are adapted for the damage detection in orthotropic composites. The key problem with the investigated Lamb waves was to select a mode to be sensitive to the damage. A hybrid modeling technique was therefore used to conceive transducers that were adapted to achieve such a feature. This modeling technique enabled studying the influence of the transducer characteristics on the Lamb waves propagating in orthotropic plates. It was demonstrated that a Lamb mode could be generated dominantly to other modes by using a multi-element transducer. The effectiveness of this technique was successfully verified experimentally on composite plates. It was shown that the dominant Lamb mode, obtained by use of dual-element transducers, was an appropriate mode for successfully detecting a damage in composites.
Existence of Mach cones and helical vortical structures around the underexpanded circular jet in the helical oscillation mode
Authors: Umeda Yoshikuni , Ishii Ryuji
Published: July 2002

Existence of Mach cone and helical vortical structure in the helical oscillation mode of an underexpanded circular jet was confirmed by using schlieren instantaneous photographs and drawing of the envelopes of the Mach cones by the superposition of spherical sound waves radiated from two moving sound sources about the jet axis at a supersonic speed. Existence of such structures was conjectured in our earlier paper [Umeda and Ishii, J. Acoust. Soc. Am. 110, 1845–1858 (2001)]. The envelopes of a Mach cone are observed as a V-shaped pattern composed of a pair of clear fine lines starting from a prominent point, which rotates about the jet axis. The helical vortical structure is observed as a bright pattern of the gathering of the tiny specks around the jet. It always appears to overlap on the envelopes of the moving Mach cones.
The optimal stack spacing for thermoacoustic refrigeration
Authors: Tijani M. E. H. , Zeegers J. C. H. , de Waele A. T. A. M.
Published: July 2002

The characteristic pore dimension in the stack is an important parameter in the design of thermoacoustic refrigerators. A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported. Parallel-plate stacks with a plate spacing varying between 0.15 and 0.7 mm are manufactured and measured. The performance measurements show that a plate spacing in the stack of 0.25 mm (2.5δk) is optimum for the cooling power. A spacing of 0.4 mm (4δk) leads to the lowest temperature. The optimum spacing for the performance is about 0.3 mm (3δk). It is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal (3δk) for thermoacoustic refrigeration.
Null-broadening in a waveguide
Authors: Kim J. S. , Hodgkiss W. S. , Kuperman W. A. , Song H. C.
Published: July 2002

Null-broadening, introduced in plane wave beamforming, is extended to an ocean waveguide in the context of matched field processing. The method is based on the minimum variance processor with white noise constraint and the distribution of fictitious sources using the theory of waveguide invariants. The proposed method is demonstrated in simulation as well as with data collected during the SWellEx-96 experiment. As another application, it is shown that the width of a null can be controlled in an adaptive time reversal mirror with a source-receive array.
Reversion of B Cell Commitment upon Loss of
Pax5
Expression
Authors: Mikkola Ingvild , Heavey Barry , Horcher Markus , Busslinger Meinrad
Published: July 2002

The transcription factor Pax5 is essential for initiating B cell lineage commitment, but its role in maintaining commitment is unknown. Using conditional
Pax5
inactivation in committed pro-B cells, we demonstrate that Pax5 is required not only to initiate its B lymphoid transcription program, but also to maintain it in early B cell development. As a consequence of
Pax5
inactivation, previously committed pro-B cells regained the capacity to differentiate into macrophages in vitro and to reconstitute T cell development in vivo in
RAG2
−/−
mice. Hence, Pax5 expression is continuously required to maintain B cell lineage commitment, because its loss converts committed pro-B cells into hematopoietic progenitors with multilineage potential.
Correction of ADA-SCID by Stem Cell Gene Therapy Combined with Nonmyeloablative Conditioning
Authors: Aiuti Alessandro , Slavin Shimon , Aker Memet , Ficara Francesca , Deola Sara , Mortellaro Alessandra , Morecki Shoshana , Andolfi Grazia , Tabucchi Antonella , Carlucci Filippo , Marinello Enrico , Cattaneo Federica , Vai Sergio , Servida Paolo , Miniero Roberto , Roncarolo Maria Grazia , Bordignon Claudio
Published: July 2002

Hematopoietic stem cell (HSC) gene therapy for adenosine deaminase (ADA)–deficient severe combined immunodeficiency (SCID) has shown limited clinical efficacy because of the small proportion of engrafted genetically corrected HSCs. We describe an improved protocol for gene transfer into HSCs associated with nonmyeloablative conditioning. This protocol was used in two patients for whom enzyme replacement therapy was not available, which allowed the effect of gene therapy alone to be evaluated. Sustained engraftment of engineered HSCs with differentiation into multiple lineages resulted in increased lymphocyte counts, improved immune functions (including antigen-specific responses), and lower toxic metabolites. Both patients are currently at home and clinically well, with normal growth and development. These results indicate the safety and efficacy of HSC gene therapy combined with nonmyeloablative conditioning for the treatment of SCID.
Diversity Considerations in HIV-1 Vaccine Selection
Authors: Gaschen Brian , Taylor Jesse , Yusim Karina , Foley Brian , Gao Feng , Lang Dorothy , Novitsky Vladimir , Haynes Barton , Hahn Beatrice H. , Bhattacharya Tanmoy , Korber Bette
Published: July 2002

Globally, human immunodeficiency virus–type 1 (HIV-1) is extraordinarily variable, and this diversity poses a major obstacle to AIDS vaccine development. Currently, candidate vaccines are derived from isolates, with the hope that they will be sufficiently cross-reactive to protect against circulating viruses. This may be overly optimistic, however, given that HIV-1 envelope proteins can differ in more than 30% of their amino acids. To contend with the diversity, country-specific vaccines are being considered, but evolutionary relationships may be more useful than regional considerations. Consensus or ancestor sequences could be used in vaccine design to minimize the genetic differences between vaccine strains and contemporary isolates, effectively reducing the extent of diversity by half.
Systematic Identification of Pathways That Couple Cell Growth and Division in Yeast
Authors: Jorgensen Paul , Nishikawa Joy L. , Breitkreutz Bobby-Joe , Tyers Mike
Published: July 2002

Size homeostasis in budding yeast requires that cells grow to a critical size before commitment to division in the late prereplicative growth phase of the cell cycle, an event termed Start. We determined cell size distributions for the complete set of ∼6000Saccharomyces cerevisiaegene deletion strains and identified ∼500 abnormally small (whi) or large (lge) mutants. Genetic analysis revealed a complex network of newly found factors that govern critical cell size at Start, the most potent of which were Sfp1, Sch9, Cdh1, Prs3, and Whi5. Ribosome biogenesis is intimately linked to cell size through Sfp1, a transcription factor that controls the expression of at least 60 genes implicated in ribosome assembly. Cell growth and division appear to be coupled by multiple conserved mechanisms.
Knowledge and Social Norms
Authors: Goldman Alvin I.
Published: July 2002

The Fate of Knowledge
. Helen E. Longino. Princeton University Press, Princeton, NJ, 2002. 245 pp. $49.50, £35. ISBN 0-691-08875-6. Paper, $16.95, £11.95. ISBN 0-691-08876-4.

Arguing that social interactions help us "in securing firm, rationally based knowledge," Longino builds an account of scientific knowledge that weaves together social and cognitive strands.
Watching Vibrational Energy Transfer in Liquids with Atomic Spatial Resolution
Authors: Wang Zhaohui , Pakoulev Andrei , Dlott Dana D.
Published: July 2002

Ultrafast spectroscopy was used to study vibrational energy transfer between vibrational reporter groups on different parts of a molecule in a liquid. When OH stretching vibrations of different alcohols were excited by mid-infrared laser pulses, vibrational energy was observed to move through intervening CH
2
or CH groups, taking steps up and down in energy, ending up at terminal CH
3
groups. For each additional CH
2
group in the path between OH and CH
3
, the time for vibrational energy transfer increased by about 0.4 picosecond.
Mammals of the Sea in Science and Culture
Authors: Schusterman Ronald J.
Published: July 2002

Encyclopedia of Marine Mammals
. William F. Perrin, Bernd Würsig, and J. G. M. Thewissen, Eds. Academic Press, San Diego, 2002. 1452 pp. $139.95, £90. ISBN 0-12-551340-2.

Marine mammals-cetaceans, pinnipeds, sirens, sea otter, and polar bear-and their interactions with humans are covered in 283 entries, which range from "Abundance Estimation" to "White-Beaked Dolphin."
Germline Stem Cell Transplantation and Transgenesis
Authors: Brinster Ralph L.
Published: July 2002

The recently developed testis cell transplantation method provides a powerful approach to studying the biology of the male germline stem cell and its microenvironment, the stem cell niche. The technique also is being used to examine spermatogenic defects, correct male infertility, and generate transgenic animals.
Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow
Authors: Zwally H. Jay , Abdalati Waleed , Herring Tom , Larson Kristine , Saba Jack , Steffen Konrad
Published: July 2002

Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface. Interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting, with larger increases accompanying higher amounts of summer melting. The indicated coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming.
A New Skull of Early
Homo
from Dmanisi, Georgia
Authors: Vekua Abesalom , Lordkipanidze David , Rightmire G. Philip , Agusti Jordi , Ferring Reid , Maisuradze Givi , Mouskhelishvili Alexander , Nioradze Medea , de Leon Marcia Ponce , Tappen Martha , Tvalchrelidze Merab , Zollikofer Christoph
Published: July 2002

Another hominid skull has been recovered at Dmanisi (Republic of Georgia) from the same strata in which hominid remains have been reported previously. The Dmanisi site dated to ∼1.75 million years ago has now produced craniofacial portions of several hominid individuals, along with many well-preserved animal fossils and quantities of stone artifacts. Although there are certain anatomical differences among the Dmanisi specimens, the hominids do not clearly represent more than one taxon. We assign the new skull provisionally to
Homo erectus
(=
ergaster
). The Dmanisi specimens are the most primitive and small-brained fossils to be grouped with this species or any taxon linked unequivocally with genus
Homo
and also the ones most similar to the presumed
habilis
-like stem. We suggest that the ancestors of the Dmanisi population dispersed from Africa before the emergence of humans identified broadly with the
H. erectus
grade.
The Amyloid Hypothesis of Alzheimer's Disease: Progress and Problems on the Road to Therapeutics
Authors: Hardy John , Selkoe Dennis J.
Published: July 2002

It has been more than 10 years since it was first proposed that the neurodegeneration in Alzheimer's disease (AD) may be caused by deposition of amyloid β-peptide (Aβ) in plaques in brain tissue. According to the amyloid hypothesis, accumulation of Aβ in the brain is the primary influence driving AD pathogenesis. The rest of the disease process, including formation of neurofibrillary tangles containing tau protein, is proposed to result from an imbalance between Aβ production and Aβ clearance.
More Bark Than Bites
Authors: Triunfol Marcia L.
Published: July 2002

The Fever Trail
In Search of the Cure for Malaria. Mark Honigsbaum. Farrar, Straus, and Giroux, New York, 2002. 341 pp. $25. ISBN 0-374-15469-4.

The Fever Trail
The Hunt for the Cure for Malaria. Macmillan, London, 2001. 363 pp. £18.99. ISBN 0-333-90185-1.

Honigsbaum anchors this history of the search to find a cure for malaria on the quinine) and efforts of the British to obtain the cinchona tree (the source of transport it to their colonies.
Regulation of Cerebral Cortical Size by Control of Cell Cycle Exit in Neural Precursors
Authors: Chenn Anjen , Walsh Christopher A.
Published: July 2002

Transgenic mice expressing a stabilized β-catenin in neural precursors develop enlarged brains with increased cerebral cortical surface area and folds resembling sulci and gyri of higher mammals. Brains from transgenic animals have enlarged lateral ventricles lined with neuroepithelial precursor cells, reflecting an expansion of the precursor population. Compared with wild-type precursors, a greater proportion of transgenic precursors reenter the cell cycle after mitosis. These results show that β-catenin can function in the decision of precursors to proliferate or differentiate during mammalian neuronal development and suggest that β-catenin can regulate cerebral cortical size by controlling the generation of neural precursor cells.
Multiplex PCR Strategy for Rapid Identification of Structural Types and Variants of the
mec
Element in Methicillin-Resistant
Staphylococcus aureus
Authors: Oliveira Duarte C. , Lencastre Hermínia de
Published: July 2002

Full characterization of methicillin-resistant
Staphylococcus aureus
(MRSA) requires definition of not only the bacterial genetic background but also the structure of the complex and heterologous
mec
element these bacteria carry, which is associated with drug resistance determinant
mecA
. We report the development, validation, and application of a multiplex PCR strategy that allows quick presumptive characterization of the
mec
element types based on the structural features that were shown to be typical of
mec
elements carried by several MRSA clones. The strategy was validated by using a representative collection of pandemic MRSA clones in which the full structure of the associated
mec
elements was previously determined by hybridization and PCR screenings and also by DNA sequencing. The method was tested together with multilocus sequence typing and other typing methods for the characterization of 18 isolates representative of the MRSA clones recovered during a hospital outbreak in Barcelona, Spain. The multiplex PCR was shown to be rapid, robust, and capable in a single assay of identifying five structural types of the
mec
element among these strains, three major and two minor variants, each one of which has been already been seen among MRSA characterized earlier. This technique should be a useful addition to the armamentarium of molecular typing tools for the characterization of MRSA clonal types and for the rapid tentative identification of structural variants of the
mec
element.
ATP-Dependent Removal of Nucleoside Reverse Transcriptase Inhibitors by Human Immunodeficiency Virus Type 1 Reverse Transcriptase
Authors: Naeger Lisa K. , Margot Nicolas A. , Miller Michael D.
Published: July 2002

Removal of nucleoside chain terminator inhibitors mediated by human immunodeficiency virus (HIV) reverse transcriptase (RT) using ATP as an acceptor molecule has been proposed as a novel mechanism of HIV resistance. Recombinant wild-type and mutant HIV type 1 (HIV-1) RT enzymes with thymidine analog resistance mutations D67N, K70R, and T215Y were analyzed for their ability to remove eight nucleoside reverse transcriptase inhibitors in the presence of physiological concentrations of ATP. The order for the rate of removal of the eight inhibitors by the mutant RT enzyme was zidovudine (AZT) > stavudine (d4T) ≫ zalcitabine (ddC) > abacavir > amdoxovir (DAPD) > lamivudine (3TC) > didanosine (ddI) > tenofovir. Thymidine analogs AZT and d4T were the most significantly removed by the mutant enzyme, suggesting that removal of these inhibitors by the ATP-dependent removal mechanism contributes to the AZT and d4T resistance observed in patients with HIV expressing thymidine analog resistance mutations. ATP-dependent removal of tenofovir was 22- to 35-fold less efficient than removal of d4T and AZT, respectively. The addition of ATP and the next complementary deoxynucleoside triphosphate caused a reduction of ATP-mediated removal of d4T, ddC, and DAPD, while AZT and abacavir removal was unaffected. The reduction of d4T, ddC, and DAPD removal in the presence of the deoxynucleoside triphosphate could explain the minor changes in susceptibility to these drugs observed in conventional in vitro phenotypic assays using cells that have higher deoxynucleoside triphosphate pools. The minimal removal of abacavir, ddC, DAPD, 3TC, ddI, and tenofovir is consistent with the minor changes in susceptibility to these drugs observed for HIV mutants with thymidine analog resistance mutations.