bluuebunny/crossref_metadata_2025 huggingface dataset:
An Approximate Method of Estimating the Yield of a Strip Under Tension Cut by Serrated Surfaces on Opposite Faces
Authors: Shi Jingyu , McElwain D. L. S. , Domanti S. A.
Published: April 2003

In view of the well-known disparity between predictions from temper rolling models and measured values from rolling mills, there is a need to obtain a better understanding of the effect of roll asperities on the yielding characteristics of the rolled strip. This paper models a roll with asperities as a rigid body with a regular serrated surface and the rolling process as an indentation, and uses the plane strain model and slip-line theory to determine the critical pressure that is required to yield the strip throughout the thickness beneath the tips of the asperities. The strip is also under lateral tension at both ends. The emphasis of the paper is the effect of the lateral tension and the thickness of the strip on the critical pressure. For the case when the indenting surface has sharp teeth, the critical pressure can be found in close form. For the case when the indenting surface has blunt teeth, a robust approximate scheme for estimation of the critical values that does not require extensive computation is given and this scheme can be used in an on-line control process. It is found that when the tooth angle is smaller than a critical angle, the sharper the tooth, the lower the average critical pressure needed to make the strip yield. When the tooth angle is larger than the critical angle, then the blunter the tooth, the lower the pressure that is needed. The effect of the asperities is to reduce the critical pressure and it is found that this effect is more pronounced for thin strips than for thick strips. The lateral tension reduces the critical pressure further. These findings give some implications for the rolling of metal sheets.
Determination of Interface Fracture Toughness in Thermal Barrier Coating System by Blister Tests
Authors: Zhou Y. C. , Hashida T. , Jian C. Y.
Published: April 2003

The theoretical model for the blister test method was used to analyze the interface fracture toughness of zirconia coating deposited on an SUS304 stainless steel substrate by a plasma-spraying method. The elastic parameters of the debonded coating were determined by testing the oil pressure q and maximum deflection w(0). SEM observation, compliance method and ultrasonic detection were used to determine the radius of the debonded coating. The three methods gave the same results for the debonded coating radius. Micro-observations showed that the interfacial crack propagates by the growth of voids or microcracks ahead of the main crack and coalescence with the main crack. The energy release rate G0 with phase angle ψ=0 for type A coating and type B coating was, respectively, 14.54∼25.88J/m2 and 11.88∼16.21J/m2. The corresponding interface fracture toughness for type A TBC coating and for type B TBC coating is, respectively, 0.77∼1.02MPas˙m1/2 and 0.52∼0.61MPas˙m1/2. The stable phase angle was approximately −31.5° and −30.2° for coating A and coating B, respectively.
A Biomechanical Evaluation of Whiplash Using a Multi-Body Dynamic Model
Authors: Garcia Tanya , Ravani Bahram
Published: April 2003

This paper presents a biomechanical evaluation of whiplash injury potential during the initial extension motion of the head in a rear-end collision. A four-segment dynamic model is developed in the sagittal plane for the analysis. The model response is validated using the existing experimental data and is shown to simulate the “S-shape” kinematics of the cervical spine and the resulting dynamics observed in human and cadaver experiments. The model is then used to evaluate the effects of parameters such as collision severity, head/headrest separation, and the initial head orientation in the sagittal plane on the “S-shape” kinematics of the cervical spine and the resulting neck loads. It is shown, for example, that the cervical spine forms an “S-shape” for a range of change in speeds and that at lower and higher speeds changes the spine does not form the “S-shape.” Furthermore, it is shown that the “S-shape” formation also depends on the head to headrest separation distance.
The Use of Sequential MR Image Sets for Determining Tibiofemoral Motion: Reliability of Coordinate Systems and Accuracy of Motion Tracking Algorithm
Authors: Lerner Amy L. , Tamez-Pena Jose G. , Houck Jeff R. , Yao Jiang , Harmon Heather L. , Salo Arthur D. , Totterman Saara M. S.
Published: April 2003

The use of magnetic resonance imaging has been proposed by many investigators for establishment of joint reference systems and kinematic tracking of musculoskeletal joints. In this study, the intraobserver and interobserver reliability of a strategy to establish anatomic reference systems using manually selected fiducial points were quantified for seven sets of MR images of the human knee joint. The standard error of the measurement of the intraobserver and interobserver errors were less than 2.6°, and 1.2 mm for relative tibiofemoral orientation and displacement, respectively. An automated motion tracking algorithm was also validated with a controlled motion experiment in a cadaveric knee joint. The controlled displacements and rotations prescribed in our motion tracking validation were highly correlated to those predicted (Pearson’s correlation=0.99, RMS errors=0.39 mm, 0.38°). Finally, the system for anatomic reference system definition and motion tracking was demonstrated with a set of MR images of in vivo passive flexion in the human knee.
Modeling the Human Body/Seat System in a Vibration Environment
Authors: Rosen Jacob , Arcan Mircea
Published: April 2003

The vibration environment is a common man-made artificial surrounding with which humans have a limited tolerance to cope due to their body dynamics. This research studied the dynamic characteristics of a seated human body/seat system in a vibration environment. The main result is a multi degrees of freedom lumped parameter model that synthesizes two basic dynamics: (i) global human dynamics, the apparent mass phenomenon, including a systematic set of the model parameters for simulating various conditions like body posture, backrest, footrest, muscle tension, and vibration directions, and (ii) the local human dynamics, represented by the human pelvis/vibrating seat contact, using a cushioning interface. The model and its selected parameters successfully described the main effects of the apparent mass phenomenon compared to experimental data documented in the literature. The model provided an analytical tool for human body dynamics research. It also enabled a primary tool for seat and cushioning design. The model was further used to develop design guidelines for a composite cushion using the principle of quasi-uniform body/seat contact force distribution. In terms of evenly distributing the contact forces, the best result for the different materials and cushion geometries simulated in the current study was achieved using a two layer shaped geometry cushion built from three materials. Combining the geometry and the mechanical characteristics of a structure under large deformation into a lumped parameter model enables successful analysis of the human/seat interface system and provides practical results for body protection in dynamic environment.
A Spatial Mechanism With Higher Pairs for Modelling the Human Knee Joint
Authors: Di Gregorio Raffaele , Parenti-Castelli Vincenzo
Published: April 2003

By generalizing a previous model proposed in the literature, a new spatial kinematic model of the knee joint passive motion is presented. The model is based on an equivalent spatial parallel mechanism which relies upon the assumption that fibers within the anterior cruciate ligament (ACL), the medial collateral ligament (MCL) and the posterior cruciate ligament (PCL) can be considered as isometric during the knee flexion in passive motion (virtually unloaded motion). The articular surfaces of femoral and tibial condyles are modelled as 3-D surfaces of general shapes. In particular, the paper presents the closure equations of the new mechanism both for surfaces represented by means of scalar equations that have the Cartesian coordinates of the points of the surface as variables and for surfaces represented in parametric form. An example of simulation is presented in the case both femoral condyles are modelled as ellipsoidal surfaces and tibial condyles as spherical surfaces. The results of the simulation are compared to those of the previous models and to measurements. The comparison confirms the expectation that a better approximation of the tibiofemoral condyle surfaces leads to a more accurate model of the knee passive motion.
In-Vivo Measurement of Dynamic Joint Motion Using High Speed Biplane Radiography and CT: Application to Canine ACL Deficiency
Authors: Tashman Scott , Anderst William
Published: April 2003

Dynamic assessment of three-dimensional (3D) skeletal kinematics is essential for understanding normal joint function as well as the effects of injury or disease. This paper presents a novel technique for measuring in-vivo skeletal kinematics that combines data collected from high-speed biplane radiography and static computed tomography (CT). The goals of the present study were to demonstrate that highly precise measurements can be obtained during dynamic movement studies employing high frame-rate biplane video-radiography, to develop a method for expressing joint kinematics in an anatomically relevant coordinate system and to demonstrate the application of this technique by calculating canine tibio-femoral kinematics during dynamic motion. The method consists of four components: the generation and acquisition of high frame rate biplane radiographs, identification and 3D tracking of implanted bone markers, CT-based coordinate system determination, and kinematic analysis routines for determining joint motion in anatomically based coordinates. Results from dynamic tracking of markers inserted in a phantom object showed the system bias was insignificant (−0.02 mm). The average precision in tracking implanted markers in-vivo was 0.064 mm for the distance between markers and 0.31° for the angles between markers. Across-trial standard deviations for tibio-femoral translations were similar for all three motion directions, averaging 0.14 mm (range 0.08 to 0.20 mm). Variability in tibio-femoral rotations was more dependent on rotation axis, with across-trial standard deviations averaging 1.71° for flexion/extension, 0.90° for internal/external rotation, and 0.40° for varus/valgus rotation. Advantages of this technique over traditional motion analysis methods include the elimination of skin motion artifacts, improved tracking precision and the ability to present results in a consistent anatomical reference frame.
Constitutive Modeling of Porcine Coronary Arteries Using Designed Experiments
Authors: Dixon Stacey A. , Heikes Russell G. , Vito Raymond P.
Published: April 2003

The development of new coronary artery constitutive models is of critical importance in the design and analysis of coronary replacement grafts. In this study, a two-parameter logarithmic complementary energy function, with normalized measured force and internal pressure as the independent variables and strains as the dependent variables, was developed for healthy porcine coronary arteries. Data was collected according to an experimental design with measured force ranging from 9.8 to 201 mN and internal pressure ranging from 0.1 to 16.1 kPa (1 to 121 mmHg). Comparisons of the estimated constitutive parameters showed statistically significant differences between the left anterior descending [LAD] and right coronary artery [RCA], but no differences between the LAD and left circumflex [LCX] or between the LCX and RCA. Point-by-point strain comparisons confirm the findings of the model parameter study and isolate the difference to the axial strain response. Average axial strains for the LAD, LCX, and RCA are 0.026±0.009,0.015±0.005, and 0.011±0.009, respectively, at all physiologic loads, suggesting that the axial strains in the LAD are significantly higher than in the other regions.
Morphology and Stress-Strain Properties Along the Small Intestine in the Rat
Authors: Dou Yanling , Zhao Jingbo , Gregersen Hans
Published: April 2003

The stress-strain relationship is determined by the inherent mechanical properties of the intestinal wall, the geometric configurations, the loading conditions and the zero-stress state of the segment. The purpose of this project was to provide morphometric and biomechanical data for rat duodenum, jejunum and ileum. The circumferential strains were referenced to the zero-stress state. Large morphometric variations were found along the small intestine with an increase in the outer circumferential length and luminal area and a decrease in wall thickness in distal direction. The serosal residual strain was tensile and decreased in distal direction P<0.05. The mucosal residual strain was compressive and the absolute value decreased in distal direction P<0.001. The stress-strain experiments showed that the duodenum was stiffest. All segments were stiffest in longitudinal direction P<0.05. In conclusion, axial variation in morphometric and biomechanical properties was found in the small intestine. The zero-stress state must be considered in future biomechanical studies in the gastrointestinal tract.
Toward An MRI-Based Method to Measure Non-Uniform Cartilage Deformation: An MRI-Cyclic Loading Apparatus System and Steady-State Cyclic Displacement of Articular Cartilage Under Compressive Loading
Authors: Neu C. P. , Hull M. L.
Published: April 2003

Recent magnetic resonance imaging (MRI) techniques have shown potential for measuring non-uniform deformations throughout the volume (i.e. three-dimensional (3D) deformations) in small orthopedic tissues such as articular cartilage. However, to analyze cartilage deformation using MRI techniques, a system is required which can construct images from multiple acquisitions of MRI signals from the cartilage in both the undeformed and deformed states. The objectives of the work reported in this article were to 1) design an apparatus that could apply highly repeatable cyclic compressive loads of 400 N and operate in the bore of an MRI scanner, 2) demonstrate that the apparatus and MRI scanner can be successfully integrated to observe 3D deformations in a phantom material, 3) use the apparatus to determine the load cycle necessary to achieve a steady-state deformation response in normal bovine articular cartilage samples using a flat-surfaced and nonporous indentor in unconfined compression. Composed of electronic and pneumatic components, the apparatus regulated pressure to a double-acting pneumatic cylinder so that (1) load-controlled compression cycles were applied to cartilage samples immersed in a saline bath, (2) loading and recovery periods within a cycle varied in time duration, and (3) load magnitude varied so that the stress applied to cartilage samples was within typical physiological ranges. In addition the apparatus allowed gating for MR image acquisition, and operation within the bore of an MRI scanner without creating image artifacts. The apparatus demonstrated high repeatability in load application with a standard deviation of 1.8% of the mean 400 N load applied. When the apparatus was integrated with an MRI scanner programmed with appropriate pulse sequences, images of a phantom material in both the undeformed and deformed states were constructed by assembling data acquired through multiple signal acquisitions. Additionally, the number of cycles to reach a steady-state response in normal bovine articular cartilage was 49 for a total cycle duration of 5 seconds, but decreased to 33 and 27 for increasing total cycle durations of 10 and 15 seconds, respectively. Once the steady-state response was achieved, 95% of all displacements were within ±7.42μm of the mean displacement, indicating that the displacement response to the cyclic loads was highly repeatable. With this performance, the MRI-loading apparatus system meets the requirements to create images of articular cartilage from which 3D deformation can be determined.
Strain-rate Dependent Stiffness of Articular Cartilage in Unconfined Compression
Authors: Li L. P. , Buschmann M. D. , Shirazi-Adl A.
Published: April 2003

The stiffness of articular cartilage is a nonlinear function of the strain amplitude and strain rate as well as the loading history, as a consequence of the flow of interstitial water and the stiffening of the collagen fibril network. This paper presents a full investigation of the interplay between the fluid kinetics and fibril stiffening of unconfined cartilage disks by analyzing over 200 cases with diverse material properties. The lower and upper elastic limits of the stress (under a given strain) are uniquely established by the instantaneous and equilibrium stiffness (obtained numerically for finite deformations and analytically for small deformations). These limits could be used to determine safe loading protocols in order that the stress in each solid constituent remains within its own elastic limit. For a given compressive strain applied at a low rate, the loading is close to the lower limit and is mostly borne directly by the solid constituents (with little contribution from the fluid). In contrast, however in case of faster compression, the extra loading is predominantly transported to the fibrillar matrix via rising fluid pressure with little increase of stress in the nonfibrillar matrix. The fibrillar matrix absorbs the loading increment by self-stiffening: the quicker the loading the faster the fibril stiffening until the upper elastic loading limit is reached. This self-protective mechanism prevents cartilage from damage since the fibrils are strong in tension. The present work demonstrates the ability of the fibril reinforced poroelastic models to describe the strain rate dependent behavior of articular cartilage in unconfined compression using a mechanism of fibril stiffening mainly induced by the fluid flow.
A Growth Mixture Theory for Cartilage With Application to Growth-Related Experiments on Cartilage Explants
Authors: Klisch Stephen M. , Chen Silvia S. , Sah Robert L. , Hoger Anne
Published: April 2003

In this paper, we present a growth mixture model for cartilage. The main features of this model are illustrated in a simple equilibrium boundary-value problem that is chosen to illustrate how a mechanical theory of cartilage growth may be applied to growth-related experiments on cartilage explants. The cartilage growth mixture model describes the independent growth of the proteoglycan and collagen constituents due to volumetric mass deposition, which leads to the remodeling of the composition and the mechanical properties of the solid matrix. The model developed here also describes how the material constants of the collagen constituent depend on a scalar parameter that may change over time (e.g., crosslink density); this leads to a remodeling of the structural and mechanical properties of the collagen constituent. The equilibrium boundary-value problem that describes the changes observed in cartilage explants harvested at different stages of a growth or a degenerative process is formulated. This boundary-value problem is solved using existing experimental data for developing bovine cartilage explants harvested at three developmental stages. The solution of the boundary-value problem in conjunction with existing experimental data suggest the types of experimental studies that need to be conducted in the future to determine model parameters and to further refine the model.
Implementation of a Viscoplastic Model for a Plasma Sprayed Ceramic Thermal Barrier Coating
Authors: Xie Wangang , Walker Kevin P. , Jordan Eric H. , Gell Maurice
Published: April 2003

This paper describes the implementation and modification of a previously proposed unified viscoplastic constitutive model to simulate the behavior of a Yttria Stabilized Zirconia plasma sprayed thermal barrier coating. The model was recast for use in finite strain situations and modified to have a more physically acceptable non-associated flow rule. Temperature dependent material constants were found for a specific material using a novel approach based on Genetic Algorithms.
New Estimation Method of Fatigue Properties of Aluminum Alloys
Authors: Park Jun-Hyub , Song Ji-Ho
Published: April 2003

A new method on estimating fatigue properties from simple tensile data was proposed for aluminum alloys. The method is based on experimental strain-life curves. An optimization technique was used to get the best fatigue properties. The four-point correlation method, the universal slopes method, Mitchell’s method, the modified universal slopes method, the uniform material law by Ba¨umel and Seeger, the modified four-point correlation method by Ong and a new method proposed in this work were evaluated in a quantitative manner. Mitchell’s method, the uniform materials law and the new method give good life predictions for aluminum alloys. In particular, the new method provided the best results.
Listening to the coefficient of restitution and the gravitational acceleration of a bouncing ball
Authors: Aguiar C. E. , Laudares F.
Published: April 2003

We show that a well known method for measuring the coefficient of restitution of a bouncing ball can also be used to obtain the gravitational acceleration.
Automation of the Franck–Hertz experiment and the Tel-X-Ometer x-ray machine using LABVIEW
Authors: Fedak W. , Bord D. , Smith C. , Gawrych D. , Lindeman K.
Published: April 2003

We describe the use of LABVIEW to automate data collection and instrument control for the Franck–Hertz experiment and for the popular Tel-X-Ometer x-ray machine. Such automation permits the rapid collection and reduction of large amounts of data, thus facilitating exploration of the basic physics of these experiments. The use of industry-standard software packages, such as ORIGIN and MATHEMATICA, provides students with valuable exposure to professional tools for the display and analysis of data.
Resource Letter: LBMOM-1: Laser-based modern optical microscopy
Authors: Imhof Joseph M. , Vanden Bout David A.
Published: April 2003

This Resource Letter provides a guide to the literature exploring widely used laser-based modern optical microscopic techniques. Journal articles and books are cited for the following topics: confocal, near-field, nonlinear, total internal reflection, photon tunneling, and coherent microscopies. Review articles, books, and websites are included to support references to primary literature sources.
Dimensional analysis of models and data sets
Authors: Price James F.
Published: April 2003

Dimensional analysis is a widely applicable and sometimes very powerful technique that is demonstrated here in a study of the simple, viscous pendulum. The first and crucial step of dimensional analysis is to define a suitably idealized representation of a phenomenon by listing the relevant variables, called the physical model. The second step is to learn the consequences of the physical model and the general principle that complete equations are independent of the choice of units. The calculation that follows yields a basis set of nondimensional variables. The final step is to interpret the nondimensional basis set in the light of observations or existing theory, and if necessary to modify the basis set to maximize its utility. One strategy is to nondimensionalize the dependent variable by a scaling estimate. The remaining nondimensional variables can then be formed in ways that define aspect ratios or that correspond to the ratio of terms in a governing equation.
The universal Lagrangian for one particle in a potential
Authors: Evans James
Published: April 2003

In a system consisting of a single particle in a potential, the classical action ∫L dt is the number of phase waves that pass through the moving particle, as the particle moves from its initial to its final position. Thus the Lagrangian can be cast into the form L=p(vg−vp), where vg and vp are the group and phase velocities and p is the momentum.
The Braess paradox in mechanical, traffic, and other networks
Authors: Penchina Claude M. , Penchina Leora J
Published: April 2003

We examine a network of strings and springs that exhibit counter-intuitive behavior. When a support string is cut, the load rises instead of falling. Our experimental and theoretical results lead to some general qualitative conditions for the existence of this paradoxical behavior, including effects of nonideal and nonlinear components. A simple procedure is given for doing a classroom demonstration of this behavior. This behavior is analogous to the well-known Braess paradox in traffic networks and also has (not well known) analogs in electrical, hydraulic, and thermal networks. Some new insights into the traffic paradox are gained from a study of the mechanical paradox.
Physics of quiet and suffocative breathing
Authors: Menon V. J. , Agrawal D. C.
Published: April 2003

The process of breathing is analyzed theoretically by setting up and solving the hydrodynamic equation of motion for air flow, obtaining an expression for the work due to the pressure-drop, viscosity and drag, deriving relations for the effective length and cross section of the respiratory track, and deriving an expression for the surface energy generated in the lungs.
Three methods for calculating the Feynman propagator
Authors: Barone F. A. , Boschi-Filho H. , Farina C.
Published: April 2003

We present three methods for calculating the Feynman propagator for the nonrelativistic harmonic oscillator. The first method was employed by Schwinger a half a century ago, but has rarely been used in nonrelativistic problems since. Also discussed is an algebraic method and a path integral method so that the reader can compare the advantages and disadvantages of each method.
The strip grating as a circular polarizer
Authors: Brand G. F.
Published: April 2003

A conducting strip grating can convert a linearly polarized plane wave into one that is circularly polarized. The conversion of a normally incident wave is most efficient when the grating period is 0.874 times the wavelength, the width of the strips is half the grating period and the angle between the direction of polarization and the strips is 45°. This result is confirmed by a microwave experiment at 35 GHz.
Gravitational assist in celestial mechanics—a tutorial
Authors: Van Allen James A.
Published: April 2003

In planning certain types of trajectories of spacecraft within the solar system, engineers rely on a technique called gravitational assist, or gravity assist. This technique underlies the feasibility of effecting a net change in both the speed and direction of motion of a spacecraft by passage through the gravitational field of a planet or a planetary satellite. The resulting increase, or decrease, in the kinetic energy of the spacecraft appears to contradict the casual expectation that in such an encounter the kinetic energy of the spacecraft after the encounter would be the same as that before the encounter. This paper describes the December 1973 encounter of the Pioneer 10 spacecraft with the planet Jupiter as a real-life example of gravitational assist. It then discusses the physical principles involved in understanding the dynamics of the encounter and concludes with remarks on the important role of gravitational assist in space exploration with artificial spacecraft and in understanding the motion of comets within the solar system.
Derivatives of the Dirac delta function by explicit construction of sequences
Authors: Boykin Timothy B.
Published: April 2003

Explicit sequences that approach the Dirac delta function and its derivatives are often helpful in presenting generalized functions. We present a method by which a finite difference formula may be easily converted into a sequence that approaches a derivative of the Dirac delta function in one dimension. In three dimensions, we employ a sequence for the Dirac delta function based on a uniformly charged sphere of infinitesimal radius and infinite charge density and show that the charge density of an electric dipole is (in the sense of a generalized function) equal to −(∂/∂z)δ3(r). We use this result to derive Gauss’ law in a dielectric medium directly from the charge densities, without using the potentials.
A successful applied physics program at the University of Puerto Rico at Humacao
Authors: Muller Rafael J. , Guerra-Vela Claudio
Published: April 2003

We describe the innovative ideas that have been incorporated into the applied physics program at the Humacao Campus of the University of Puerto Rico since 1981. The program was designed as a professional (terminal) one with mechanisms to guide students who wish to pursue graduate studies. Dwindling student registration in the program led to an aggressive recruitment/retention plan in the early 1990s. We describe our highly successful efforts and their results, including an increase in the number of majors, an increase of 25% in female students, and a graduation rate of 12.5 students/year for the past six years.
A Coalescence of Scientific Cultures
Authors: Berger Shelley L.
Published: April 2003

Chromatin and Gene Regulation
Molecular Mechanisms in Epigenetics.
By Bryan M. Turner
. Blackwell Science, Oxford, 2001. 296 pp. Paper, $54.95, £27.50. ISBN 0-865-42743-7.

Weaving together perspectives from the fields of gene regulation and chromatin, Turner offers a concise discussion of the relations between the packing and organization of DNA within the cell nucleus and the regulation and expression of genes.
Fluid Core Size of Mars from Detection of the Solar Tide
Authors: Yoder C. F. , Konopliv A. S. , Yuan D. N. , Standish E. M. , Folkner W. M.
Published: April 2003

The solar tidal deformation of Mars, measured by its
k
2
potential Love number, has been obtained from an analysis of Mars Global Surveyor radio tracking. The observed
k
2
of 0.153 ± 0.017 is large enough to rule out a solid iron core and so indicates that at least the outer part of the core is liquid. The inferred core radius is between 1520 and 1840 kilometers and is independent of many interior properties, although partial melt of the mantle is one factor that could reduce core size. Ice-cap mass changes can be deduced from the seasonal variations in air pressure and the odd gravity harmonic
J
3
, given knowledge of cap mass distribution with latitude. The south cap seasonal mass change is about 30 to 40% larger than that of the north cap.
Enhanced Upper Tropical Tropospheric COS: Impact on the Stratospheric Aerosol Layer
Authors: Notholt J. , Kuang Z. , Rinsland C. P. , Toon G. C. , Rex M. , Jones N. , Albrecht T. , Deckelmann H. , Krieg J. , Weinzierl C. , Bingemer H. , Weller R. , Schrems O.
Published: April 2003

Carbonyl sulfide (COS) is considered to be a major source of the stratospheric sulfate aerosol during periods of volcanic quiescence. We measured COS at the tropical tropopause and find mixing ratios to be 20 to 50% larger than are assumed in models. The enhanced COS levels are correlated with high concentrations of biomass-burning pollutants like carbon monoxide (CO) and hydrogen cyanide (HCN). The analysis of backward trajectories and global maps of fire statistics suggest that biomass-burning emissions transported upward by deep convection are the source of the enhanced COS in the upper tropical troposphere.
Polyubiquitination of p53 by a Ubiquitin Ligase Activity of p300
Authors: Grossman Steven R. , Deato Maria E. , Brignone Chrystelle , Chan Ho Man , Kung Andrew L. , Tagami Hideaki , Nakatani Yoshihiro , Livingston David M.
Published: April 2003

Rapid turnover of the tumor suppressor protein p53 requires the MDM2 ubiquitin ligase, and both interact with p300–CREB-binding protein transcriptional coactivator proteins. p53 is stabilized by the binding of p300 to the oncoprotein E1A, suggesting that p300 regulates p53 degradation. Purified p300 exhibited intrinsic ubiquitin ligase activity that was inhibited by E1A. In vitro, p300 with MDM2 catalyzed p53 polyubiquitination, whereas MDM2 catalyzed p53 monoubiquitination. E1A expression caused a decrease in polyubiquitinated but not monoubiquitinated p53 in cells. Thus, generation of the polyubiquitinated forms of p53 that are targeted for proteasome degradation requires the intrinsic ubiquitin ligase activities of MDM2 and p300.
Role of the
Arabidopsis
Glucose Sensor HXK1 in Nutrient, Light, and Hormonal Signaling
Authors: Moore Brandon , Zhou Li , Rolland Filip , Hall Qi , Cheng Wan-Hsing , Liu Yan-Xia , Hwang Ildoo , Jones Tamara , Sheen Jen
Published: April 2003

Glucose modulates many vital processes in photosynthetic plants. Analyses of
Arabidopsis glucose insensitive2
(
gin2
) mutants define the physiological functions of a specific hexokinase (HXK1) in the plant glucose-signaling network. HXK1 coordinates intrinsic signals with extrinsic light intensity. HXK1 mutants lacking catalytic activity still support various signaling functions in gene expression, cell proliferation, root and inflorescence growth, and leaf expansion and senescence, thus demonstrating the uncoupling of glucose signaling from glucose metabolism. The
gin2
mutants are also insensitive to auxin and hypersensitive to cytokinin. Plants use HXK as a glucose sensor to interrelate nutrient, light, and hormone signaling networks for controlling growth and development in response to the changing environment.
Chromosomal Speciation and Molecular Divergence--Accelerated Evolution in Rearranged Chromosomes
Authors: Navarro Arcadi , Barton Nick H.
Published: April 2003

Humans and their closest evolutionary relatives, the chimpanzees, differ in ∼1.24% of their genomic DNA sequences. The fraction of these changes accumulated during the speciation processes that have separated the two lineages may be of special relevance in understanding the basis of their differences. We analyzed human and chimpanzee sequence data to search for the patterns of divergence and polymorphism predicted by a theoretical model of speciation. According to the model, positively selected changes should accumulate in chromosomes that present fixed structural differences, such as inversions, between the two species. Protein evolution was more than 2.2 times faster in chromosomes that had undergone structural rearrangements compared with colinear chromosomes. Also, nucleotide variability is slightly lower in rearranged chromosomes. These patterns of divergence and polymorphism may be, at least in part, the molecular footprint of speciation events in the human and chimpanzee lineages.
Origin of the Superflock of Cichlid Fishes from Lake Victoria, East Africa
Authors: Verheyen Erik , Salzburger Walter , Snoeks Jos , Meyer Axel
Published: April 2003

Lake Victoria harbors a unique species-rich flock of more than 500 endemic haplochromine cichlid fishes. The origin, age, and mechanism of diversification of this extraordinary radiation are still debated. Geological evidence suggests that the lake dried out completely about 14,700 years ago. On the basis of phylogenetic analyses of almost 300 DNA sequences of the mitochondrial control region of East African cichlids, we find that the Lake Victoria cichlid flock is derived from the geologically older Lake Kivu. We suggest that the two seeding lineages may have already been lake-adapted when they colonized Lake Victoria. A haplotype analysis further shows that the most recent desiccation of Lake Victoria did not lead to a complete extinction of its endemic cichlid fauna and that the major lineage diversification took place about 100,000 years ago.
Charge-Induced Reversible Strain in a Metal
Authors: Weissmüller J. , Viswanath R. N. , Kramer D. , Zimmer P. , Würschum R. , Gleiter H.
Published: April 2003

Dimension changes on the order of 0.1% or above in response to an applied voltage have been reported for many types of materials, including ceramics, polymers, and carbon nanostructures, but not, so far, for metals. We show that reversible strain amplitudes comparable to those of commercial piezoceramics can be induced in metals by introducing a continuous network of nanometer-sized pores with a high surface area and by controlling the surface electronic charge density through an applied potential relative to an electrolyte impregnating the pores.
Near-Perfect Elastoplasticity in Pure Nanocrystalline Copper
Authors: Champion Yannick , Langlois Cyril , Guérin-Mailly Sandrine , Langlois Patrick , Bonnentien Jean-Louis , Hÿtch Martin J.
Published: April 2003

Ductile metals and alloys undergo plastic yielding at room temperature, during which they exhibit work-hardening and the generation of surface instabilities that lead to necking and failure. We show that pure nanocrystalline copper behaves differently, displaying near-perfect elastoplastic behavior characterized by Newtonian flow and the absence of both work-hardening and neck formation. We observed this behavior in tensile tests on fully dense large-scale bulk nanocrystalline samples. The experimental results further our understanding of the unique mechanical properties of nanocrystalline materials and also provide a basis for commercial technologies for the plastic (and superplastic) formation of such materials.
Intimate Interactions
Authors: Schmid-Hempel Paul
Published: April 2003

Immunology and Evolution of Infectious Disease
.
By Steven A. Frank
. Princeton University Press, Princeton, NJ, 2002. 360 pp. $75, £52. ISBN 0-691-09594-9. Paper, $24.95, £17.95. ISBN 0-691-09595-7.

Frank weaves immunology, population ecology, and evolutionary biology together to provide multidisciplinary perspectives on infection dynamics and antigenic variation.
Early Origin and Recent Expansion of
Plasmodium falciparum
Authors: Joy Deirdre A. , Feng Xiaorong , Mu Jianbing , Furuya Tetsuya , Chotivanich Kesinee , Krettli Antoniana U. , Ho May , Wang Alex , White Nicholas J. , Suh Edward , Beerli Peter , Su Xin-zhuan
Published: April 2003

The emergence of virulent
Plasmodium falciparum
in Africa within the past 6000 years as a result of a cascade of changes in human behavior and mosquito transmission has recently been hypothesized. Here, we provide genetic evidence for a sudden increase in the African malaria parasite population about 10,000 years ago, followed by migration to other regions on the basis of variation in 100 worldwide mitochondrial DNA sequences. However, both the world and some regional populations appear to be older (50,000 to 100,000 years old), suggesting an earlier wave of migration out of Africa, perhaps during the Pleistocene migration of human beings.
A Fossil Record of Galaxy Encounters
Authors: Elbaz David , Cesarsky Catherine J.
Published: April 2003

The cosmic infrared background (CIRB) is a record of a large fraction of the emission of light by stars and galaxies over time. The bulk of this emission has been resolved by the Infrared Space Observatory camera. The dominant contributors are bright starburst galaxies with redshift
z
∼ 0.8; that is, in the same redshift range as the active galactic nuclei responsible for the bulk of the x-ray background. At the longest wavelengths, sources of redshift
z
≥ 2 tend to dominate the CIRB. It appears that the majority of present-day stars have been formed in dusty starbursts triggered by galaxy-galaxy interactions and the buildup of large-scale structures.
LRP: Role in Vascular Wall Integrity and Protection from Atherosclerosis
Authors: Boucher Philippe , Gotthardt Michael , Li Wei-Ping , Anderson Richard G. W. , Herz Joachim
Published: April 2003

Vascular smooth muscle cell (SMC) proliferation and migration are important events in the development of atherosclerosis. The low-density lipoprotein receptor–related protein (LRP1) mediates suppression of SMC migration induced by platelet-derived growth factor (PDGF). Here we show that LRP1 forms a complex with the PDGF receptor (PDGFR). Inactivation of LRP1 in vascular SMCs of mice causes PDGFR overexpression and abnormal activation of PDGFR signaling, resulting in disruption of the elastic layer, SMC proliferation, aneurysm formation, and marked susceptibility to cholesterol-induced atherosclerosis. The development of these abnormalities was reduced by treatment with Gleevec, an inhibitor of PDGF signaling. Thus, LRP1 has a pivotal role in protecting vascular wall integrity and preventing atherosclerosis by controlling PDGFR activation.
Band Structure and Fermi Surface of Electron-Doped C
60
Monolayers
Authors: Yang W. L. , Brouet V. , Zhou X. J. , Choi Hyoung J. , Louie Steven G. , Cohen Marvin L. , Kellar S. A. , Bogdanov P. V. , Lanzara A. , Goldoni A. , Parmigiani F. , Hussain Z. , Shen Z.-X.
Published: April 2003

C
60
fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C
60
monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.
Requirement for CD4 T Cell Help in Generating Functional CD8 T Cell Memory
Authors: Shedlock Devon J. , Shen Hao
Published: April 2003

Although primary CD8 responses to acute infections are independent of CD4 help, it is unknown whether a similar situation applies to secondary responses. We show that depletion of CD4 cells during the recall response has minimal effect, whereas depletion during the priming phase leads to reduced responses by memory CD8 cells to reinfection. Memory CD8 cells generated in CD4
+/+
mice responded normally when transferred into CD4
−/−
hosts, whereas memory CD8 cells generated in CD4
−/−
mice mounted defective recall responses in CD4
+/+
adoptive hosts. These results demonstrate a previously undescribed role for CD4 help in the development of functional CD8 memory.
14
C Dates from Tel Rehov: Iron-Age Chronology, Pharaohs, and Hebrew Kings
Authors: Bruins Hendrik J. , van der Plicht Johannes , Mazar Amihai
Published: April 2003

Stratified radiocarbon dates provide an independent chronological link between archaeological layers and historical data. The invasion by Pharaoh Shoshenq I (Shishak) is a key historical synchronism,
∼
925 B.C.E., mentioned in both Egyptian inscriptions and the Hebrew Bible. The list of places raided by Shoshenq, mentioned at Karnak (Egypt), includes Rehov (Israel). The site yielded a consistent series of radiocarbon dates from the 12th to 9th century B.C.E. Our results (i) suggest a revised Iron-Age chronology; (ii) date an archaeological stratum to Shoshenq's campaign; (iii) indicate the similarity of “Solomonic” and “Omride” pottery; and (iv) provide correlation with Greece and Cyprus.
Dreams of an Antimetaphysical Physicist
Authors: Carson Cathryn
Published: April 2003

No Time To Be Brief
A Scientific Biography of Wolfgang Pauli.
By Charles P. Enz
. Oxford University Press, New York, 2002. 561 pp. $60, £35. ISBN 0-19-856479-1.

This biography combines an account of Pauli's life with analyses of his research and the development of his thinking. Enz, Pauli's last assistant, offers a close-up view that captures Pauli's sarcastic wit and his interest in dreams and their interpretation.
Defective CD8 T Cell Memory Following Acute Infection Without CD4 T Cell Help
Authors: Sun Joseph C. , Bevan Michael J.
Published: April 2003

The CD8
+
cytotoxic T cell response to pathogens is thought to be CD4
+
helper T cell independent because infectious agents provide their own inflammatory signals. Mice that lack CD4
+
T cells mount a primary CD8 response to
Listeria monocytogenes
equal to that of wild-type mice and rapidly clear the infection. However, protective memory to a challenge is gradually lost in the former animals. Memory CD8
+
T cells from normal mice can respond rapidly, but memory CD8
+
T cells that are generated without CD4 help are defective in their ability to respond to secondary encounters with antigen. The results highlight a previously undescribed role for CD4 help in promoting protective CD8 memory development.
From Knowing to Controlling: A Path from Genomics to Drugs Using Small Molecule Probes
Authors: Strausberg Robert L. , Schreiber Stuart L.
Published: April 2003

The National Cancer Institute Initiative in Chemical Genetics is designed to encourage the development of small molecular probes. The probes are useful for activating or inactivating protein functions, thereby providing resources that help discern the functions of gene products in normal and disease cells, as well as in tissues. This initiative includes “ChemBank,” a suite of informatics tools and databases aimed at promoting the development and use of chemical genetics by scientists worldwide. The information generated with such tools should provide a critical link from genomic discovery to drug development.
Developing a Platform for Genomic Medicine in Mexico
Authors: Jimenez-Sanchez Gerardo
Published: April 2003

Mexico is preparing to develop a genomic medicine program focused on national health problems. Modern Mexicans result from an admixture of more than 65 native Indian groups with Spaniards, leading to a unique genetic makeup and a characteristic set of disease susceptibilities. Since 1999, more than 100 experts from different fields have joined efforts with government, academia, and industry to identify priorities and goals for genomic medicine in Mexico. The plan includes establishment of an Institute of Genomic Medicine with strong intramural and extramural programs. This project is expected to ease the social and financial burden of health problems in Mexico.
The Human Genome Project: Lessons from Large-Scale Biology
Authors: Collins Francis S. , Morgan Michael , Patrinos Aristides
Published: April 2003

The Human Genome Project has been the first major foray of the biological and medical research communities into “big science.” In this Viewpoint, we present some of our experiences in organizing and managing such a complicated, publicly funded, international effort. We believe that many of the lessons we learned will be applicable to future large-scale projects in biology.
Realizing the Potential of the Genome Revolution: The Genomes to Life Program
Authors: Frazier Marvin E. , Johnson Gary M. , Thomassen David G. , Oliver Carl E. , Patrinos Aristides
Published: April 2003

The systems biology revolution is proceeding along multiple pathways as different science agencies and the private sector have adopted strategies suited to their particular needs and cultures. To meet this challenge, the U.S. Department of Energy has developed the Genomes to Life (GTL) program. A central focus of GTL is environmental microbial biology as a way to approach global environmental problems, and its key goal is to achieve, over the next 10 to 20 years, a basic understanding of thousands of microbes and microbial systems in their native environments. This focus demands that we address huge gaps in knowledge, technology, computing, data storage and manipulation, and systems-level integration.
Antimicrobial Growth Promoters Used in Animal Feed: Effects of Less Well Known Antibiotics on Gram-Positive Bacteria
Authors: Butaye Patrick , Devriese Luc A. , Haesebrouck Freddy
Published: April 2003

There are not many data available on antibiotics used solely in animals and almost exclusively for growth promotion. These products include bambermycin, avilamycin, efrotomycin, and the ionophore antibiotics (monensin, salinomycin, narasin, and lasalocid). Information is also scarce for bacitracin used only marginally in human and veterinary medicine and for streptogramin antibiotics. The mechanisms of action of and resistance mechanisms against these antibiotics are described. Special emphasis is given to the prevalence of resistance among gram-positive bacteria isolated from animals and humans. Since no susceptibility breakpoints are available for most of the antibiotics discussed, an alternative approach to the interpretation of MICs is presented. Also, some pharmacokinetic data and information on the influence of these products on the intestinal flora are presented.