bluuebunny/crossref_metadata_2025 huggingface dataset:
Infant Skull and Suture Properties: Measurements and Implications for Mechanisms of Pediatric Brain Injury
Authors: Margulies Susan S. , Thibault Kirk L.
Published: July 2002

The mechanical properties of the adult human skull are well documented, but little information is available for the infant skull. To determine the age-dependent changes in skull properties, we tested human and porcine infant cranial bone in three-point bending. The measurement of elastic modulus in the human and porcine infant cranial bone agrees with and extends previous published data [McPherson, G. K., and Kriewall, T. J. (1980), J. Biomech., 13, pp. 9–16] for human infant cranial bone. After confirming that the porcine and human cranial bone properties were comparable, additional tensile and three-point bending studies were conducted on porcine cranial bone and suture. Comparisons of the porcine infant data with previously published adult human data demonstrate that the elastic modulus, ultimate stress, and energy absorbed to failure increase, and the ultimate strain decreases with age for cranial bone. Likewise, we conclude that the elastic modulus, ultimate stress, and energy absorbed to failure increase with age for sutures. We constructed two finite element models of an idealized one-month old infant head, one with pediatric and the other adult skull properties, and subjected them to impact loading to investigate the contribution of the cranial bone properties on the intracranial tissue deformation pattern. The computational simulations demonstrate that the comparatively compliant skull and membranous suture properties of the infant brain case are associated with large cranial shape changes, and a more diffuse pattern of brain distortion than when the skull takes on adult properties. These studies are a fundamental initial step in predicting the unique mechanical response of the pediatric skull to traumatic loads associated with head injury and, thus, for defining head injury thresholds for children. [S0148-0731(00)00904-3]
Discussion: “Response Bounds for Linear Damped Systems” (Hu, B. and Eberhard, P., 1999, ASME J. Appl. Mech., 66, pp. 997–1003)
Authors: Shahruz S. M.
Published: July 2002

[S0021-8936(00)03703-X]
Energy Pumping in Nonlinear Mechanical Oscillators: Part I—Dynamics of the Underlying Hamiltonian Systems
Authors: Gendelman O. , Manevitch L. I. , Vakakis A. F. , M’Closkey R.
Published: July 2002

The systems considered in this work are composed of weakly coupled, linear and essentially nonlinear (nonlinearizable) components. In Part I of this work we present numerical evidence of energy pumping in coupled nonlinear mechanical oscillators, i.e., of one-way (irreversible) “channeling” of externally imparted energy from the linear to the nonlinear part of the system, provided that the energy is above a critical level. Clearly, no such phenomenon is possible in the linear system. To obtain a better understanding of the energy pumping phenomenon we first analyze the dynamics of the underlying Hamiltonian system (corresponding to zero damping). First we reduce the equations of motion on an isoenergetic manifold of the dynamical flow, and then compute subharmonic orbits by employing nonsmooth transformation of coordinates which lead to nonlinear boundary value problems. It is conjectured that a 1:1 stable subharmonic orbit of the underlying Hamiltonian system is mainly responsible for the energy pumping phenomenon. This orbit cannot be excited at sufficiently low energies. In Part II of this work the energy pumping phenomenon is further analyzed, and it is shown that it is caused by transient resonance capture on a 1:1 resonance manifold of the system.
Pyrometric Temperature Measurements in Solar Furnaces
Authors: Tschudi Hans Rudolf , Morian Gerd
Published: July 2002

Surface temperatures are key parameters in many applications of concentrated solar radiation. Pyrometric temperature determination is, however, hampered by reflected solar radiation. Two approaches to solve this problem were experimentally tested on a solar reactor at the Paul Scherrer Institute (PSI): the flash assisted multi-wavelength pyrometry (FAMP) developed at PSI and a solar-blind pyrometer developed by the IMPAC Electronic GmbH in Frankfurt, Germany, in collaboration with PSI. Performance, advantages, and disadvantages of the two pyrometers are reported and discussed.
Drillstring Stability Based on Variable Material Specific Force and Using a Sharp Three-Insert Polycrystalline Diamond Compact (PDC) Coring Bit
Authors: Elsayed M. A. , Washington L. F.
Published: July 2002

Previous research in stability of drillstrings was based on the assumption of constant material specific force, i.e., a bit force that is proportional to the area of cut. Moreover, earlier work used a simplified bit model that consisted of planar radial blades. In this paper, correlation between the material specific force and area of cut is obtained for Sierra White granite and Berea sandstone from test data developed at Sandia National Laboratories in Albuquerque, NM. These correlations, together with an improved bit model in which cylindrical cutters are arrayed in an overlapping pattern over a flat surface, are used to obtain the stability equations. Laboratory testing shows good correlation between measured bit vibrations and relative instability as predicted by the stability equations. These results are useful in predicting the appropriate operating conditions for stable drilling and serve as a basis for future development of more accurate models of PDC bits.
Exact Solution for Simply Supported and Multilayered Magneto-Electro-Elastic Plates
Authors: Pan E.
Published: July 2002

Exact solutions are derived for three-dimensional, anisotropic, linearly magneto-electro-elastic, simply-supported, and multilayered rectangular plates under static loadings. While the homogeneous solutions are obtained in terms of a new and simple formalism that resemble the Stroh formalism, solutions for multilayered plates are expressed in terms of the propagator matrix. The present solutions include all the previous solutions, such as piezoelectric, piezomagnetic, purely elastic solutions, as special cases, and can therefore serve as benchmarks to check various thick plate theories and numerical methods used for the modeling of layered composite structures. Typical numerical examples are presented and discussed for layered piezoelectric/piezomagnetic plates under surface and internal loads.
Effects of Pressure Relief Valve Behavior on 2-Phase Energy Storage in a Pressure Vessel Exposed to Fire
Authors: Pierorazio A. J. , Birk A. M.
Published: July 2002

Recent studies have shown that the hazards associated with loss of containment and BLEVEs (boiling liquid expanding vapor explosions) are strongly tied to the energy stored in the liquid phase of a pressure vessel. This stored energy is affected by heat transfer with the surroundings (e.g., fire exposure) and pressure relief valve (PRV) action. Since it would be desirable to minimize this stored energy to reduce hazards, a study was initiated by Transport Canada and Queen’s University to quantify the effect of various PRV parameters on the thermal energy storage of a pressure vessel. A fully automated state-of-the-art test facility has been constructed to perform 2-phase blowdown tests using steam and water. This paper describes the Queen’s University/Transport Canada PRV Test Program and the test procedures and facilities used. It goes on to show some preliminary results from 2-phase testing currently underway to determine the optimal PRV operating characteristics from a hazard mitigation standpoint. The results of this study may be useful for standards-writing bodies to set experimentally determined optimal behavior criteria for PRVs and acceptable tolerances for deviation from this.
Multiresolution Curve Editing With Linear Constraints
Authors: Elber Gershon
Published: July 2002

The use of multiresolution control toward the editing of freeform curves and surfaces has already been recognized as a valuable modeling tool [1–3]. Similarly, in contemporary computer aided geometric design, the use of constraints to precisely prescribe freeform shape is considered an essential capability [4,5]. This paper presents a scheme that combines multiresolution control with linear constraints into one framework, allowing one to perform multiresolution manipulation of nonuniform B-spline curves, while specifying and satisfying various linear constraints on the curves. Positional, tangential, and orthogonality constraints are all linear and can be easily incorporated into a multiresolution freeform curve editing environment, as will be shown. Moreover, we also show that the symmetry as well as the area constraints can be reformulated as linear constraints and similarly incorporated. The presented framework is extendible and we also portray this same framework in the context of freeform surfaces.
On the Beneficial Effects of Anti-Squat in Rear Suspension Design of a Drag Racing Motorcycle
Authors: Wiers Paul C. , Dhingra Anoop K.
Published: July 2002

In the drag racing environment, maximizing tractive effort is essential to competitive performance. Anti-squat is a transient vehicle suspension parameter which can dramatically affect tractive effort available at the motorcycle drive tire. This paper addresses the design of a four-link rear suspension for a drag racing motorcycle to provide anti-squat, which increases rear tire traction, thereby improving vehicle acceleration performance. Utilizing PC based CAD, finite element analysis and dynamic system analysis software, a motorcycle rear suspension system was designed, built and tested under actual racing conditions. Parametric studies using dynamic theoretical models were conducted for both unsuspended and four-link equipped versions of the same vehicle. Based on the results, it is shown that the four-link suspension, when applied to a drag racing motorcycle, does provide opportunity for improving tractive effort at the beginning of a race which will improve overall drag racing performance.
On the Elastic Properties of PVD Coatings in Relation to Their
Microstructure
Authors: Sevostianov I. , Kachanov M. , Ruud J.
Published: July 2002

Physical vapor deposited (PVD) coatings have low effective stiffness Eeff (as compared to the bulk material) in directions parallel to the substrate. It increases with an increasing residual compressive stress. A simple micromechanical model, based on the contact problem, is constructed that explains the observed behavior. Quantitative characterization of microstructure relevant for Eeff is developed.
Modeling of Pig Assisted Production Methods
Authors: Yeung Hoi C. , Lima Paulo C. R.
Published: July 2002

More and more transient gas-liquid operations in pipes have been successfully applied in the oil and gas industry. Pigging operation in two-phase pipelines to remove liquid accumulation or for cleaning purpose is an important transient operation. Another important operation is the injection of gas to transport the accumulated liquid in the pipeline to process facilities. Analysis of such transient two-phase flow in a pipeline is necessary not only for designing the liquid and gas handling facilities, but also for establishing safe operating procedures. In pipeline-riser systems, such operations cause even more severe change in flow conditions. A two-fluid model has been developed to determine the transient behavior of fluids during these operations. A one-dimensional set of equations for bubble/mist, annular and stratified flows has been derived. Slug flows were modeled as a combination of the foregoing. Semi-implicit finite difference schemes were used to solve the initial and boundary value problem for each phase of the pigging process: gas/pig injection, gas shut-in, slug production, and gas flow out of the system. An extensive experimental program was carried out to acquire two-phase transient flow and pigging data on a 69-m-long, 9.9-m-high, 50-mm-dia pipeline-riser system. A computer based data acquisition system was used to obtain rapidly changing and detailed information of the flow behavior during tests. The model compared well with the experimental data for characteristics such as inlet pressure, hold-up, and pig velocity. Liquid production efficiencies for different operations were compared.
Effect on Natural Convection of the Distance Between an Inclined
Discretely Heated Plate and a Parallel Shroud Below
Authors: Manca Oronzio , Nardini Sergio , Naso Vincenzo
Published: July 2002

An experimental study on air natural convection on an inclined discretely heated plate with a parallel shroud below was carried out. Three heated strips were located in different positions on the upper wall. The distance between the walls, b, was changed in the range 7.0–40.0 mm and two values of the heat flux dissipated by the heaters were taken into account. Several inclination angles between the vertical and the horizontal were tested. The wall temperature distribution as a function of the channel spacing and the inclination angle, the source heat flux, the number and the arrangement of the heat sources are presented. The analysis shows that, for angles not greater than 85 deg, increasing the distance between walls does not reduce the wall temperatures, whereas at greater tilting angles (>85 deg) there is an opposite tendency. This is confirmed by flow visualization at angles equal to 85 deg and 90 deg and b=20.0 and 32.3 mm. Dimensionless maximum wall temperatures are correlated to the process parameters in the ranges 1.2s˙104⩽Ral cos θ⩽8.6s˙105; 0 deg⩽θ⩽88 deg; 0.48⩽l/b⩽1.6 and 10⩽L/b⩽32.6 with 1.0⩽d/l⩽3.0; the agreement with experimental data is good. The spacing which yields the best thermal performance of the channel is given. Local Nusselt numbers are evaluated and correlated to the local Rayleigh numbers and the tilting angles in the ranges 20⩽Rax′⩽8.0s˙105 and 0 deg⩽θ⩽88 deg. The exponent of monomial correlations between local Nusselt and Rayleigh numbers are in the 0.23–0.26 range. Comparisons with data from the literature, in terms of Nusselt number, exhibited minor discrepancies, mainly because of some difference in test conditions and of heat conduction in the channel walls.
Similarity Solution for Marangoni Convection Over a Flat Surface
Authors: Christopher David M. , Wang Buxuan
Published: July 2002

A similarity solution is presented for Marangoni flow over a flat surface for both the velocity and temperature profiles assuming developing boundary layer flow along the surface with various imposed temperature profiles. Marangoni flow results from variations of the surface tension along a liquid-vapor interface and is especially noticeable in microgravity. Solutions are presented for the surface velocity, the total flow rate and the heat transfer for various temperature profiles and various Prandtl numbers.
Mechanical Analysis of Electronic Packaging Systems
Authors: McKeown, Stephen A. , Rafanelli, A. J.
Published: July 2002

[S1043-7398(00)01301-3]
Mechanical Property Scatter in CFCCs
Authors: Steen M. , Filiou C.
Published: July 2002

The tensile response of continuous fibre reinforced ceramic matrix composites (CFCCs) is not expected to show the large variation in strength properties commonly observed for monolithic ceramics. Results of recent investigations on a number of two-dimensional reinforced CFCCs have nevertheless revealed a considerable scatter in the initial elastic modulus, in the first matrix cracking stress and in the failure stress. One school of thought considers that the observed variability is caused by experimental factors. Elaborate testing programmes have been set up to clarify the origins of this scatter by investigation of the effects of control mode, loading rate, specimen shape, etc. Another school explains the scatter by the presence of (axial) residual stresses in the fibres and in the matrix. Although plausible, this hypothesis is difficult to verify because experimental determination of the residual stress state in CFCCs is not straightforward. In addition, with the available methods it is impractical to determine the residual stresses in every test specimen. This approach is indeed required for establishing the relationship between the magnitude of the residual stresses and the experimentally observed scatter. At IAM a method has been developed and validated which allows to quantify the axial residual stress state in individual CFCC specimens by subjecting them to intermittent unloading-reloading cycles. The method as well as the derived relationship between residual stress state and scatter in mechanical response will be presented. [S0742-4795(00)01101-7]
On the Prediction of Axisymmetric Rotating Flows by a One-Equation Turbulence Model
Authors: Vasiliev V. I.
Published: July 2002

A one-equation model previously tested for parabolic flows and 2-D separated flows was implemented for rotating flows. Flows in rotor-stator disk systems, and in sealed cavities between contrarotating and corotating disks, were calculated and compared with known experimental and numerical data. For buoyancy-driven flow in a rotating cavity, an analytic solution for the turbulent regime was obtained. [S0098-2202(00)01302-X]
Heat Transfer and Friction Characteristics of Internal Helical-Rib
Roughness
Authors: Webb R. L. , Narayanamurthy R. , Thors P.
Published: July 2002

This paper provides heat transfer and friction data for single-phase flow in seven 15.54-mm inside diameter tubes having internal helical-rib roughness. The range of geometric parameters were number of rib starts (18 to 45), helix angle (25 to 45 deg), and rib height (0.33 to 0.55 mm). These geometries provide data on a new class of internal enhancement that is typical of commercially rough tubes presently used. The tested geometries provide enhancement by flow separation at the ribs, and by a significant surface area increase. The data were taken with water having 5.08⩽Pr⩽6.29. Two different correlations were employed to predict the Stanton number and friction factor as a function of geometric variables and Reynolds number. The average deviation of the multiple regression heat transfer and correlations were 2.9 percent and 3.8 percent, respectively. Heat transfer and friction correlations based on the heat-momentum transfer analogy for rough surfaces yielded standard deviations of 1.4 percent and 5.4 percent, respectively. The correlations were shown to reasonably predict the heat transfer and friction for commercially used helical-rib roughened tubes. [S0022-1481(00)03001-2]
An Experimental Investigation of Natural Convection in a Cubic
Inclined Enclosure With Multiple Isolated Plates
Authors: Wang Q. W. , Tao W. Q. , Lin Z. , Chow T. T.
Published: July 2002

Natural convection in a cubic inclined enclosure with three isolated plates was investigated experimentally. The influences of the plates’ spacing, the inclination angles of the enclosure, and the Rayleigh number on the heat transfer of the plate group were obtained. It was found that under a fixed Rayleigh number, there is a plate spacing at which the heat transfer rate of the three plates is approximately the same for the horizontal plate group. Under the range of Rayleigh numbers considered, the heat transfer rate of the plate group is less than that of the natural convection of the plate group in infinite space. The heat transfer rate of the plates increases with the plate inclined angle tilting from θ=90 deg to θ=0 deg, with the most steep increase occurring in the range of θ=90 deg to 45 deg. A global correlation of the heat transfer results for all the inclination between 0 deg and 60 deg can be obtained as Nul,m=0.5360Ralcos θ0.25 with a spread of ±8.9 percent. [S0022-1481(00)00501-6]
Challenges in Requalification and Rehabilitation of Offshore
Platforms—On the Experience and Developments of a Norwegian Operator
Authors: Gudmestad Ove T.
Published: July 2002

This paper reviews some of the major challenges in requalification and rehabilitation of offshore platforms. Main emphasis is put on requalification needs, acceptance criteria, and methods. This review is also applied to the decommissioning phase of older platforms. Finally, some important requalification projects are reviewed with emphasis on rehabilitation needs. [S0892-7219(00)00501-X]
Mexico Engineering Experiences and Developments
Authors: Ramos Rafael , Pe´rez Faustino , Ortega Ramirez Roberto
Published: July 2002

This paper presents an overall view of the research and developments achieved during the generation of local risk-based criteria for design and assessment of platforms in Bay of Campeche. The results from two studies on meteorological and oceanographic characterization and wave height attenuation due to soft bottom interaction are first presented and discussed. Then, the results from a study on wave loading on decks is presented followed by a discussion on earthquake characterization. Two more studies on the biases and uncertainties involved in the evaluation of the capacities of tubular joints and pile foundations are next presented. Finally, a brief discussion on fatigue life of tubular joints is presented. In each section, the final uncertainty values considered to set the safety requirements are shown. [S0892-7219(00)00301-0]
Influence of apparatus geometry and deposition conditions on the structure and topography of thick sputtered coatings
Authors: Thornton John A.
Published: July 2002

Two cylindrically symmetric and complementary sputtering geometries, the post and hollow cathodes, were used to deposit thick (∼25-μ) coatings of various metals (Mo, Cr, Ti, Fe, Cu, and Al-alloy) onto glass and metallic substrates at deposition rates of 1000–2000 Å/min under various conditions of substrate temperature, argon pressure, and plasma bombardment. Coating surface topographies and fracture cross sections were examined by scanning electron microscopy. Polished cross sections were examined metallographically. Crystallographic orientations were determined by x-ray diffraction. Microstructures were generally consistent with the three-zone model proposed by Movchan and Demchishin [Fiz. Metal. Metalloved. 28, 653 (1969)]. Three differences were noted: (1) at low argon pressures a broad zone 1–zone 2 transition zone consisting of densely packed fibrous grains was identified; (2) zone 2 columnar grains tended to be faceted at elevated temperatures, although facets were often replaced by smooth flat surfaces at higher temperatures; (3) zone 3 equiaxed grains were generally not observed at the deposition conditions investigated. Hollow cathode deposition accentuated those features of coating growth that relate to intergrain shading.
Gas-phase production of carbon single-walled nanotubes from carbon monoxide via the HiPco process: A parametric study
Authors: Bronikowski Michael J. , Willis Peter A. , Colbert Daniel T. , Smith K. A. , Smalley Richard E.
Published: July 2002

We have demonstrated large-scale production (10 g/day) of high-purity carbon single-walled nanotubes (SWNTs) using a gas-phase chemical-vapor-deposition process we call the HiPco process. SWNTs grow in high-pressure (30–50 atm), high-temperature (900–1100 °C) flowing CO on catalytic clusters of iron. The clusters are formed in situ: Fe is added to the gas flow in the form of Fe(CO)5. Upon heating, the Fe(CO)5 decomposes and the iron atoms condense into clusters. These clusters serve as catalytic particles upon which SWNT nucleate and grow (in the gas phase) via CO disproportionation: CO+CO⇒CO2+C(SWNT). SWNT material of up to 97 mol % purity has been produced at rates of up to 450 mg/h. The HiPco process has been studied and optimized with respect to a number of process parameters including temperature, pressure, and catalyst concentration. The behavior of the SWNT yield with respect to various parameters sheds light on the processes that currently limit SWNT production, and suggests ways that the production rate can be increased still further.
Plasma-assisted chemical vapor deposition of titanium nitride in a capacitively coupled radio-frequency discharge
Authors: Laimer J. , Störi H. , Rödhammer P.
Published: July 2002

A new type of plasma reactor for the plasma-assisted chemical vapor deposition (PACVD) of titanium nitride (TiN) was designed and built. The reactor uses a rf discharge operating at a pressure ∼1 mbar and at a frequency of 13.56 MHz. The dependence of various properties of the coating produced on the deposition parameters is studied in detail. Besides a determination of the thickness of the coating different analytical techniques such as Auger electron spectroscopy (AES), x-ray diffraction (XRD), and scanning electron microscopy (SEM) have been used to characterize the coating. In order to investigate mechanical properties of the deposit, Vickers hardness and critical load have been determined. TiN coatings of excellent quality have been deposited on all surfaces of objects of complex geometry. The quality of these coatings is equivalent to the quality obtained by classical CVD and physical vapor deposition (PVD) techniques. The deposition temperature of 500 °C permits the coating of hardened steel tools.
Copper adlayer formation on Au(111) from sulfuric acid electrolyte
Authors: Green Michael P. , Hanson Karrie J.
Published: July 2002

We have used in situ scanning tunneling microscopy to examine submonolayer Cu deposition from a sulfuric acid electrolyte on Au(111), sampling over large areas of the surface. We describe the growth of three distinct superlattice phases of Cu on the Au(111) surface before the onset of bulk deposition of Cu. In the earliest stages of deposition, during an electrochemical current peak, we observe the rapid growth of a low height phase, with an apparent height of 0.46±0.10 Å. During this time, a second, monolayer-height phase forms as small islands. We identify these phases as the (√3×√3)R30° and (1×1) Cu superlattices, respectively. A third phase appears at about 175 mV (versus Cu/Cu+2), and grows from nucleation points at the top edges of atomic steps and around the small (1×1) Cu islands. This phase, which we believe is a (5×5) Cu adlayer, slowly supplants the (√3×√3)R30° layer.
The search for novel, superhard materials
Authors: Vepřek Stan
Published: July 2002

The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of design for these materials are summarized and some unresolved questions outlined.
Passivation of GaAs(001) surfaces by incorporation of group VI atoms: A structural investigation
Authors: Chambers S. A. , Sundaram V. S.
Published: July 2002

We have investigated the relationship between interface chemistry, structure, and surface electronic states in the band gap of Se and Te-passivated GaAs(001). Metalorganic chemical vapor deposition was used to carry out the passivations. Chemical, structural, and electronic characterization of the surfaces was accomplished by means of x-ray photoelectron spectroscopy and diffraction, and low-energy electron diffraction. We find that the superior passivating capability of Se can be related to the structural quality of the interface created in the near-surface region. Se undergoes extensive, but diffusion-limited, anion exchange in the top five to seven anion layers. The majority of As atoms in the surface layer undergo anion exchange with Se, and the extent of anion exchange diminishes with increasing depth. Thus, a graded SexAs1−xGa/GaAs(001) heterojunction of high structural quality forms. In contrast, Te does not passivate GaAs(001), and this inability to passivate can also be related to interface structure. Te undergoes extensive anion exchange only in the surface layer; displacement of third-layer As atoms appears to be limited to ∼10 at. %. Furthermore, the interface is partially disordered and ∼1 monolayer-equivalent of unincorporated Te remains bound to the surface. The combined effect of these defects is to create a surface-state density sufficient to induce significant band bending.
Multielectron beam blanking aperture array system SYNAPSE-2000
Authors: Yasuda Hiroshi , Arai Soichiro , Kai Jun-ichi , Ooae Yoshihisa , Abe Tomohiko , Maruyama Shigeru , Kiuchi Takashi
Published: July 2002

A blanking aperture array (BAA) has 1024, 25-μm-square apertures and blanking electrodes on a 20-μm-thick Si membrane with a total aperture ratio of 1/6. These apertures are irradiated with an electron beam, and the electrons passing through the apertures are projected onto a wafer surface in a reduction ratio of about 1 to 200. A signal applied to each blanking electrode turns each beam on and off individually while raster-scanning the electron flux with a deflector; thereby the desired pattern on the wafer can be drawn. The SYNAPSE-2000 system uses 512 beams in the center of a BAA and exposes 18 8 in. wafers per hour using a single BAA column. Large convergence semiangle, refocusing, and multicolumns are effective measures to reduce Coulomb interaction and to accomplish higher throughput. This system provides a volume-production microelectronic device manufacturing method.
Radiation-induced reactions of chemically amplified x-ray and electron-beam resists based on deprotection of t-butoxycarbonyl groups
Authors: Kozawa T. , Nagahara S. , Yoshida Y. , Tagawa S. , Watanabe T. , Yamashita Y.
Published: July 2002

Radiation-induced reactions in chemically amplified resists based on deprotection of t-butoxycarbonyl groups have been investigated by both time-resolved (the pulse radiolysis methods) and steady-state optical absorption spectroscopy. Upon exposure of a partially tBOC-protected novolak by electron and synchrotron radiation beams, the yields of the intermediates contributing to the acid generation (phenoxyl radical and proton adducts of base resin) decreased with increasing the protection ratio of hydroxyl groups. Therefore, the efficiency of the acid generation is closely related with the protection ratio. The relation of the acid generation mechanism with the protection ratio was discussed.
A Sperm Cytoskeletal Protein That Signals Oocyte Meiotic Maturation and Ovulation
Authors: Miller Michael A. , Nguyen Viet Q. , Lee Min-Ho , Kosinski Mary , Schedl Tim , Caprioli Richard M. , Greenstein David
Published: July 2002

Caenorhabditis elegans
oocytes, like those of most animals, arrest during meiotic prophase. Sperm promote the resumption of meiosis (maturation) and contraction of smooth muscle–like gonadal sheath cells, which are required for ovulation. We show that the major sperm cytoskeletal protein (MSP) is a bipartite signal for oocyte maturation and sheath contraction. MSP also functions in sperm locomotion, playing a role analogous to actin. Thus, during evolution, MSP has acquired extracellular signaling and intracellular cytoskeletal functions for reproduction. Proteins with MSP-like domains are found in plants, fungi, and other animals, suggesting that related signaling functions may exist in other phyla.
Photoinduction of Fast, Reversible Translational Motion in a Hydrogen-Bonded Molecular Shuttle
Authors: Brouwer Albert M. , Frochot Céline , Gatti Francesco G. , Leigh David A. , Mottier Loı̈c , Paolucci Francesco , Roffia Sergio , Wurpel George W. H.
Published: July 2002

A rotaxane is described in which a macrocycle moves reversibly between two hydrogen-bonding stations after a nanosecond laser pulse. Observation of transient changes in the optical absorption spectrum after photoexcitation allows direct quantitative monitoring of the submolecular translational process. The rate of shuttling was determined and the influence of the surrounding medium was studied: At room temperature in acetonitrile, the photoinduced movement of the macrocycle to the second station takes about 1 microsecond and, after charge recombination (about 100 microseconds), the macrocycle shuttles back to its original position. The process is reversible and cyclable and has properties characteristic of an energy-driven piston.
Nanobelts of Semiconducting Oxides
Authors: Pan Zheng Wei , Dai Zu Rong , Wang Zhong Lin
Published: July 2002

Ultralong beltlike (or ribbonlike) nanostructures (so-called nanobelts) were successfully synthesized for semiconducting oxides of zinc, tin, indium, cadmium, and gallium by simply evaporating the desired commercial metal oxide powders at high temperatures. The as-synthesized oxide nanobelts are pure, structurally uniform, and single crystalline, and most of them are free from defects and dislocations. They have a rectanglelike cross section with typical widths of 30 to 300 nanometers, width-to-thickness ratios of 5 to 10, and lengths of up to a few millimeters. The beltlike morphology appears to be a distinctive and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. The nanobelts could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and building functional devices along individual nanobelts.
Changes in Forest Biomass Carbon Storage in China Between 1949 and 1998
Authors: Fang Jingyun , Chen Anping , Peng Changhui , Zhao Shuqing , Ci Longjun
Published: July 2002

The location and mechanisms responsible for the carbon sink in northern mid-latitude lands are uncertain. Here, we used an improved estimation method of forest biomass and a 50-year national forest resource inventory in China to estimate changes in the storage of living biomass between 1949 and 1998. Our results suggest that Chinese forests released about 0.68 petagram of carbon between 1949 and 1980, for an annual emission rate of 0.022 petagram of carbon. Carbon storage increased significantly after the late 1970s from 4.38 to 4.75 petagram of carbon by 1998, for a mean accumulation rate of 0.021 petagram of carbon per year, mainly due to forest expansion and regrowth. Since the mid-1970s, planted forests (afforestation and reforestation) have sequestered 0.45 petagram of carbon, and their average carbon density increased from 15.3 to 31.1 megagrams per hectare, while natural forests have lost an additional 0.14 petagram of carbon, suggesting that carbon sequestration through forest management practices addressed in the Kyoto Protocol could help offset industrial carbon dioxide emissions.
Observation of a Train of Attosecond Pulses from High Harmonic Generation
Authors: Paul P. M. , Toma E. S. , Breger P. , Mullot G. , Augé F. , Balcou Ph. , Muller H. G. , Agostini P.
Published: July 2002

In principle, the temporal beating of superposed high harmonics obtained by focusing a femtosecond laser pulse in a gas jet can produce a train of very short intensity spikes, depending on the relative phases of the harmonics. We present a method to measure such phases through two-photon, two-color photoionization. We found that the harmonics are locked in phase and form a train of 250-attosecond pulses in the time domain. Harmonic generation may be a promising source for attosecond time-resolved measurements.
Cohesin Cleavage by Separase Required for Anaphase and Cytokinesis in Human Cells
Authors: Hauf Silke , Waizenegger Irene C. , Peters Jan-Michael
Published: July 2002

Cell division depends on the separation of sister chromatids in anaphase. In yeast, sister separation is initiated by cleavage of cohesin by the protease separase. In vertebrates, most cohesin is removed from chromosome arms by a cleavage-independent mechanism. Only residual amounts of cohesin are cleaved at the onset of anaphase, coinciding with its disappearance from centromeres. We have identified two separase cleavage sites in the human cohesin subunit SCC1 and have conditionally expressed noncleavable SCC1 mutants in human cells. Our results indicate that cohesin cleavage by separase is essential for sister chromatid separation and for the completion of cytokinesis.
Ultrathin Single-Crystalline Silver Nanowire Arrays Formed in an Ambient Solution Phase
Authors: Hong Byung Hee , Bae Sung Chul , Lee Chi-Wan , Jeong Sukmin , Kim Kwang S.
Published: July 2002

We report the synthesis of single-crystalline silver nanowires of atomic dimensions. The ultrathin silver wires with 0.4 nanometer width grow up to micrometer-scale length inside the pores of self-assembled calix[4]hydroquinone nanotubes by electro-/photochemical redox reaction in an ambient aqueous phase. The present subnanowires are very stable under ambient air and aqueous environments, unlike previously reported metal wires of ∼1 nanometer diameter, which existed only transiently in ultrahigh vacuum. The wires exist as coherently oriented three-dimensional arrays of ultrahigh density and thus could be used as model systems for investigating one-dimensional phenomena and as nanoconnectors for designing nanoelectronic devices.
An fMRI Investigation of Emotional Engagement in Moral Judgment
Authors: Greene Joshua D. , Sommerville R. Brian , Nystrom Leigh E. , Darley John M. , Cohen Jonathan D.
Published: July 2002

The long-standing rationalist tradition in moral psychology emphasizes the role of reason in moral judgment. A more recent trend places increased emphasis on emotion. Although both reason and emotion are likely to play important roles in moral judgment, relatively little is known about their neural correlates, the nature of their interaction, and the factors that modulate their respective behavioral influences in the context of moral judgment. In two functional magnetic resonance imaging (fMRI) studies using moral dilemmas as probes, we apply the methods of cognitive neuroscience to the study of moral judgment. We argue that moral dilemmas vary systematically in the extent to which they engage emotional processing and that these variations in emotional engagement influence moral judgment. These results may shed light on some puzzling patterns in moral judgment observed by contemporary philosophers.
Crystal Structure of an Early Protein-RNA Assembly Complex of the Signal Recognition Particle
Authors: Wild Klemens , Sinning Irmgard , Cusack Stephen
Published: July 2002

The signal recognition particle (SRP) is a universally conserved ribonucleoprotein complex that mediates the cotranslational targeting of secretory and membrane proteins to cellular membranes. A crucial early step in SRP assembly in archaea and eukarya is the binding of protein SRP19 to specific sites on SRP RNA. Here we report the 1.8 angstrom resolution crystal structure of human SRP19 in complex with its primary binding site on helix 6 of SRP RNA, which consists of a stem-loop structure closed by an unusual GGAG tetraloop. Protein-RNA interactions are mediated by the specific recognition of a widened major groove and the tetraloop without any direct protein-base contacts and include a complex network of highly ordered water molecules. A model of the assembly of the SRP core comprising SRP19, SRP54, and SRP RNA based on crystallographic and biochemical data is proposed.
ARR1, a Transcription Factor for Genes Immediately Responsive to Cytokinins
Authors: Sakai Hiroe , Honma Takashi , Aoyama Takashi , Sato Shusei , Kato Tomohiko , Tabata Satoshi , Oka Atsuhiro
Published: July 2002

Cytokinins are a class of phytohormones involved in various physiological events of plants. The
Arabidopsis
sensor histidine kinase CRE1 was recently reported to be a cytokinin receptor. We used a steroid-inducible system to show that the transcription factor–type response regulator ARR1 directs transcriptional activation of the
ARR6
gene, which responds to cytokinins without de novo protein synthesis. This fact, together with characteristics of
ARR1
-overexpressing plants and
arr1
mutant plants, indicates that the phosphorelay to ARR1, probably from CRE1, constitutes an intracellular signal transduction occurring immediately after cytokinin perception.
Seismic Detection of Rigid Zones at the Top of the Core
Authors: Rost Sebastian , Revenaugh Justin
Published: July 2002

Data from earthquakes in the Tonga-Fiji region recorded at a seismic array in northern Australia show evidence for rigid zones at the top of the outer core. The
ScP
waveforms can be modeled by thin (0.12 to 0.18 kilometer) zones of molten iron mixed with solid material with a small, but positive,
S
-wave velocity (0.6 to 0.8 kilometer per second) that enables the propagation of
S
-waves in the outermost core. The zones may be topographic highs of the core-mantle boundary filled by light core sediments and might be important for variation of Earth's nutation and for convection of the outer core.
Chaotic Mixer for Microchannels
Authors: Stroock Abraham D. , Dertinger Stephan K. W. , Ajdari Armand , Mezić Igor , Stone Howard A. , Whitesides George M.
Published: July 2002

It is difficult to mix solutions in microchannels. Under typical operating conditions, flows in these channels are laminar—the spontaneous fluctuations of velocity that tend to homogenize fluids in turbulent flows are absent, and molecular diffusion across the channels is slow. We present a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number. Using this method, the length of the channel required for mixing grows only logarithmically with the Péclet number, and hydrodynamic dispersion along the channel is reduced relative to that in a simple, smooth channel. This method uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.
A Common Rule for the Scaling of Carnivore Density
Authors: Carbone Chris , Gittleman John L.
Published: July 2002

Population density in plants and animals is thought to scale with size as a result of mass-related energy requirements. Variation in resources, however, naturally limits population density and may alter expected scaling patterns. We develop and test a general model for variation within and between species in population density across the order Carnivora. We find that 10,000 kilograms of prey supports about 90 kilograms of a given species of carnivore, irrespective of body mass, and that the ratio of carnivore number to prey biomass scales to the reciprocal of carnivore mass. Using mass-specific equations of prey productivity, we show that carnivore number per unit prey productivity scales to carnivore mass near –0.75, and that the scaling rule can predict population density across more than three orders of magnitude. The relationship provides a basis for identifying declining carnivore species that require conservation measures.
Systemic RNAi in
C. elegans
Requires the Putative Transmembrane Protein SID-1
Authors: Winston William M. , Molodowitch Christina , Hunter Craig P.
Published: July 2002

Double-stranded RNA-mediated gene interference (RNAi) in
Caenorhabditis elegans
systemically inhibits gene expression throughout the organism. To investigate how gene-specific silencing information is transmitted between cells, we constructed a strain that permits visualization of systemic RNAi. We used this strain to identify systemic RNA interference–deficient (
sid
) loci required to spread gene-silencing information between tissues but not to initiate or maintain an RNAi response. One of these loci,
sid-1
, encodes a conserved protein with predicted transmembrane domains. SID-1 is expressed in cells sensitive to RNAi, is localized to the cell periphery, and is required cell-autonomously for systemic RNAi.
Genomic Instability in Mice Lacking Histone H2AX
Authors: Celeste Arkady , Petersen Simone , Romanienko Peter J. , Fernandez-Capetillo Oscar , Chen Hua Tang , Sedelnikova Olga A. , Reina-San-Martin Bernardo , Coppola Vincenzo , Meffre Eric , Difilippantonio Michael J. , Redon Christophe , Pilch Duane R. , Olaru Alexandru , Eckhaus Michael , Camerini-Otero R. Daniel , Tessarollo Lino , Livak Ferenc , Manova Katia , Bonner William M. , Nussenzweig Michel C. , Nussenzweig André
Published: July 2002

Higher order chromatin structure presents a barrier to the recognition and repair of DNA damage. Double-strand breaks (DSBs) induce histone H2AX phosphorylation, which is associated with the recruitment of repair factors to damaged DNA. To help clarify the physiological role of H2AX, we targeted H2AX in mice. Although H2AX is not essential for irradiation-induced cell-cycle checkpoints, H2AX
−/−
mice were radiation sensitive, growth retarded, and immune deficient, and mutant males were infertile. These pleiotropic phenotypes were associated with chromosomal instability, repair defects, and impaired recruitment of Nbs1, 53bp1, and Brca1, but not Rad51, to irradiation-induced foci. Thus, H2AX is critical for facilitating the assembly of specific DNA-repair complexes on damaged DNA.
A Mini-Surge on the Ryder Glacier, Greenland, Observed by Satellite Radar Interferometry
Authors: Joughin Ian , Tulaczyk Slawek , Fahnestock Mark , Kwok Ron
Published: July 2002

Satellite radar interferometry reveals that the speed of the Ryder Glacier increased roughly threefold and then returned to normal (100 to 500 meters/year) over a 7-week period near the end of the 1995 melt season. The accelerated flow represents a substantial, though short-lived, change in ice discharge. During the period of rapid motion, meltwater-filled supraglacial lakes may have drained, which could have increased basal water pressure and caused the mini-surge. There are too few velocity measurements on other large outlet glaciers to determine whether this type of event is a widespread phenomenon in Greenland, but because most other outlet glaciers are at lower latitudes, they should experience more extensive melting, making them more susceptible to meltwater-induced surges.
Identification of a Human Mitotic Checkpoint Gene:
hsMAD2
Authors: Li Yong , Benezra Robert
Published: July 2002

In
Saccharomyces cerevisiae
,
MAD2
is required for mitotic arrest if the spindle assembly is perturbed. The human homolog of
MAD2
was isolated and shown to be a necessary component of the mitotic checkpoint in HeLa cells by antibody electroporation experiments. Human, or
Homo sapiens
, MAD2 (hsMAD2) was localized at the kinetochore after chromosome condensation but was no longer observed at the kinetochore in metaphase, suggesting that MAD2 might monitor the completeness of the spindle-kinetochore attachment. Finally, T47D, a human breast tumor cell line that is sensitive to taxol and nocodazole, had reduced MAD2 expression and failed to arrest in mitosis after nocodazole treatment. Thus, defects in the mitotic checkpoint may contribute to the sensitivity of certain tumors to mitotic spindle inhibitors.