bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of a Five-Bar Mechanism of Variable Topology Type With Transmission Angle Control
Authors: Balli Shrinivas S. , Chand Satish
Published: March 2004

A method to synthesize a planar five-bar mechanism of variable topology type with transmission angle control is suggested. The method is useful to reduce the solution space and thus the number of trials and the time required for synthesis. Synthesis of mechanism for function, motion and path generation for two finitely separated positions is considered. The portion of the five-bar linkage in each phase is assumed to be a crank type four-bar mechanism.
Optimal Mechanism Design for Path Generation and Motions With Reduced Harmonic Content
Authors: Yuan Zhongfan , Gilmartin M. J. , Douglas S. S.
Published: March 2004

The optimal design of linkage mechanisms for path generation and motions with reduced harmonic content is investigated in this paper. The designs are carried out using a two-objective optimizer based on fuzzy theory. The four-bar mechanism is first optimally designed to follow a specified coupler path with the harmonic content of the output link motion being simultaneously minimized to reduce its oscillating frequency bandwidth. For more complicated paths, a five-bar hybrid mechanism driven by a constant speed motor and a servo motor is also optimally designed. The harmonics in the servo motion are also reduced in the design to improve the dynamic characteristics for the servo motor.
Estimation of Object Kinematics From Point Data
Authors: Vithani Anand R. , Gupta Krishna C.
Published: March 2004

One of the fundamental problems arising in kinematics is that of determining object position, velocity and acceleration from given point position, velocity and acceleration data. This type of problem is frequently encountered in robotics, biomechanics, real-time control of space structures, automatic guided vehicles, etc. Complications arise when redundant data are used and when the data have errors. Chutakanonta and Gupta proposed two simple and elegant methods for the estimation of object position from the given point position data. The present work is an extension of these methods for estimating the object velocity and acceleration states from the given point position, velocity and acceleration data. The method proposed herein uses Singular Value Decomposition (SVD) to effectively estimate the object velocity and acceleration states. Such matrix decompositions can be performed by using readily available matrix-oriented software like MATLAB and can be successfully used to simplify the solution of the over-determined system of equations encountered in these types of problems. Several hypothetical examples and examples that simulate practical situations are presented to determine the effectiveness, robustness and applicability of the proposed method. The method is found to be very effective in estimating the object velocity and acceleration states in the presence of imprecise and redundant data as well as for nearly co-planar point data.
Compliant Floating-Opposing-Arm (FOA) Centrifugal Clutch
Authors: Crane Nathan B. , Howell Larry L. , Weight Brent L. , Magleby Spencer P.
Published: March 2004

This paper introduces the floating-opposing-arm (FOA) centrifugal clutch, presents a mathematical model for its analysis, and demonstrates the validity of a model to predict clutch performance with experimental data. The novelty of the clutch includes an arrangement of aggressive and non-aggressive contact surfaces in connected pairs to achieve a high torque carrying capability while maintaining starting smoothness and stability. As a compliant mechanism, it has fewer parts than traditional centrifugal clutches, and has the potential for significant cost reductions in manufacturing and assembly. Analysis of the FOA clutch is made difficult by the combination of dynamics and elastic deformation required for its operation. A model, based on the pseudo-rigid-body model, simplifies the engagement speed and torque capacity analyses. The model is validated by testing individual clutches and by demonstrating clutch designs in typical applications.
Transmission Error in Synchronous Belt Drives With Idler (Influence of Thickness Error of Belt Back Face Under No Load Conditions)
Authors: Makita Kenichi , Kagotani Masanori , Ueda Hiroyuki , Koyama Tomio
Published: March 2004

Synchronous belt drives are commonly used in conjunction with an idler on the back face of the belt. However, thickness errors between the belt pitch line and back face of the belt, if present, will result in a change in belt tension on the span, and are considered to affect transmission error. In the present study, the transmission error in a synchronous belt drive with an idler under no load was investigated both theoretically and experimentally using a belt of known thickness error. The computed transmission error agrees well with the experimental data thereby verifying the applicability of the analysis method. In addition, a transmission error was mainly generated by the change in length of the belt pitch line due to the thickness error of the belt. It is shown that the transmission error due to the belt thickness error can be removed by using an automatic tensioner.
A Finite Element Formulation for the Determination of Unknown Boundary Conditions for Three-Dimensional Steady Thermoelastic Problems
Authors: Dennis Brian H. , Dulikravich George S. , Yoshimura Shinobu
Published: March 2004

A three-dimensional finite element method (FEM) formulation for the prediction of unknown boundary conditions in linear steady thermoelastic continuum problems is presented. The present FEM formulation is capable of determining displacements, surface stresses, temperatures, and heat fluxes on the boundaries where such quantities are unknown or inaccessible, provided such quantities are sufficiently over-specified on other boundaries. The method can also handle multiple material domains and multiply connected domains with ease. A regularized form of the method is also presented. The regularization is necessary for solving problems where the over-specified boundary data contain errors. Several regularization approaches are shown. The inverse FEM method described is an extension of a method previously developed by the leading authors for two-dimensional steady thermoelastic inverse problems and three-dimensional thermal inverse problems. The method is demonstrated for several three-dimensional test cases involving simple geometries although it is applicable to arbitrary three-dimensional configurations. Several different solution techniques for sparse rectangular systems are briefly discussed.
Exploring the Effectiveness of Various Patterns in an Extended Pattern Search Layout Algorithm
Authors: Yin Su , Cagan Jonathan
Published: March 2004

Automated synthesis of product layout has the potential of substantially reducing design cycle time while allowing for quick check of interference, clearance, scale and fit prior to the building of physical prototypes. The search for optimal positions and orientations of parts in the layout typically requires a huge number of iterations. An extended pattern search layout algorithm based on coordinate search was introduced in an earlier paper and shown quite effective over the previous state-of-the-art. Coordinate search is a simple and straightforward way of implementing the extended pattern search method in the layout problem. However, it is not taking advantage of the wide variety of heuristics admissible in pattern search methods for identifying promising search directions. By introducing various search patterns and exploring their effectiveness in the layout problem, the question of whether complex tactics can do better than the basic coordinate pattern search is addressed. This paper presents four different heuristics for generating pattern directions in the extended pattern search layout algorithm: the conjugate direction method, the modified gradient method, the rank ordering method, and the simplex method. These heuristics are utilized to identify promising search directions and update the set of pattern directions used in the algorithm over iterations. The performance of the different heuristics is compared to that of the basic coordinate extended pattern search layout approach.
Optimal Motion Generation for Groups of Robots: A Geometric Approach
Authors: Belta Calin , Kumar Vijay
Published: March 2004

In this paper we generate optimal smooth trajectories for a set of fully-actuated mobile robots. Given two end configurations, by tuning one parameter, the user can choose an interpolating trajectory from a continuum of curves varying from that corresponding to maintaining a rigid formation to motion of the robots toward each other. The idea behind our method is to change the original constant kinetic energy metric in the configuration space and can be summarized into three steps. First, the energy of the motion as a rigid structure is decoupled from the energy of motion along directions that violate the rigid constraints. Second, the metric is “shaped” by assigning different weights to each term. Third, geodesic flow is constructed for the modified metric. The optimal motions generated on the manifolds of rigid body displacements in 3-D space SE3 or in plane SE2 and the uniform rectilinear motion of each robot corresponding to a totally uncorrelated approach are particular cases of our general treatment.
Analysis of Multiplicity Phenomena in Longitudinal Fins Under Multi-Boiling Conditions
Authors: Krikkis Rizos N. , Sotirchos Stratis V. , Razelos Panagiotis
Published: March 2004

A numerical bifurcation analysis is carried out in order to determine the solution structure of longitudinal fins subject to multi-boiling heat transfer mode. The thermal analysis can no longer be performed independently of the working fluid since the heat transfer coefficient is temperature dependent and includes the nucleate, the transition and the film boiling regimes where the boiling curve is obtained experimentally for a specific fluid. The heat transfer process is modeled using one-dimensional heat conduction with or without heat transfer from the fin tip. Furthermore, five fin profiles are considered: the constant thickness, the trapezoidal, the triangular, the convex parabolic and the parabolic. The multiplicity structure is obtained in order to determine the different types of bifurcation diagrams, which describe the dependence of a state variable of the system (for instance the fin temperature or the heat dissipation) on a design (Conduction-Convection Parameter) or operation parameter (base Temperature Difference). Specifically the effects of the base Temperature Difference, of the Conduction-Convection Parameter and of the Biot number are analyzed and presented in several diagrams since it is important to know the behavioral features of the heat rejection mechanism such as the number of the possible steady states and the influence of a change in one or more operating variables to these states.
Radiative Heating of Semi-Transparent Diesel Fuel Droplets
Authors: Sazhin S. S. , Abdelghaffar W. A. , Sazhina E. M. , Mikhalovsky S. V. , Meikle S. T. , Bai C.
Published: March 2004

Absorption spectra of four types of diesel fuel are studied experimentally in the range between 0.2 μm and 6 μm. The ageing process of fuels is simulated by prolonged boiling. The average absorption efficiency factor of droplets is assumed to be proportional to ardb, where rd is the droplet radius, and a and b are polynomial functions of external gas temperature. Explicit expressions for a and b are derived for diesel fuel droplets in various realistic droplet radii and external gas temperature ranges for all four types of fuel.
The Effect of Support Grid Features on Local, Single-Phase Heat Transfer Measurements in Rod Bundles
Authors: Holloway Mary V. , McClusky Heather L. , Beasley Donald E. , Conner Michael E.
Published: March 2004

Locally averaged heat transfer measurements in a rod bundle downstream of support grids with and without flow-enhancing features are investigated for Reynolds numbers of 28,000 and 42,000. Support grids with disk blockage flow-enhancing features and support grids with split-vane pair flow enhancing features are examined. Grid pressure loss coefficients and feature loss coefficients are determined based on pressure drop measurements for each support grid design. Results indicate the greatest heat transfer enhancement downstream of the support grid designs with disk blockages. In addition, the local heat transfer measurements downstream of the split-vane pair grid designs indicate a region of decreased heat transfer below that of the hydrodynamically fully developed value. This decreased region of heat transfer is more pronounced for the lower Reynolds number case. A correlation for the local Nusselt numbers downstream of the standard support grid designs is developed based on the blockage of the support grid. In addition, a correlation for the local Nusselt numbers downstream of support grids with flow-enhancing features is developed based on the blockage ratio of the grid straps and the normalized feature loss coefficients of the support grid designs. The correlations demonstrate the tradeoff between initial heat transfer enhancement downstream of the support grid and the pressure drop created by the support grid.
Single-Side Heated Monoblock, High Heat Flux Removal Using Water Subcooled Turbulent Flow Boiling
Authors: Boyd Ronald D. , Cofie Penrose , Zhang Hongtao , Ekhlassi Ali
Published: March 2004

Plasma-facing components for fusion reactors and other high heat flux heat sinks are subjected to a peripherally nonuniform heat flux. The monoblock test section under study is a single-side heated square cross-section heat sink with a circular coolant channel bored through the center. The heated length of the test section is 180 mm. The inside diameter and outside square sides are 10 mm and 30 mm, respectively. It was subjected to a constant heat flux on one side of the outside surfaces, and the remaining portion was not heated. The exit water subcooling varied from 55 to 101°C, the exit pressure was maintained at 0.207 MPa, and the mass velocity was 0.59Mg/m2s. The results consist of three-dimensional wall temperature distributions and a display of two-dimensional quasi-boiling curves. These results are among the first full set of three-dimensional wall temperature measurements for a single-side heated monoblock flow channel which contains the effects of conjugate heat transfer for turbulent, subcooled flow boiling. In the single-phase region, good predictability resulted when the thermal hydraulic diameter was used.
Transient Hydrodynamic Phenomena and Conjugate Heat Transfer During Cooling of Water in an Underground Thermal Storage Tank
Authors: Papanicolaou E. , Belessiotis V.
Published: March 2004

The flow and heat transfer phenomena inside an underground thermal storage tank, initially filled with hot water at an almost uniform temperature and then left to interact with the cold surroundings, are studied numerically. The purpose of the study is to gain insight into how these phenomena affect the heat losses to the surroundings, before a new charging process takes place. A two-dimensional numerical model to solve for the transient flow and thermal fields within the tank coupled with the heat transport through the tank walls and within the ground are employed. Natural convection is found to dominate at the early transients when a strong recirculation develops, with a Rayleigh number characteristic of turbulent flow. A low-Re k−ε turbulence model is used for the computation. As time proceeds and the temperature differences between water and surroundings decrease, the recirculation decays and the heat transfer is dominated by thermal diffusion. The ground properties are varied, mainly in order to account for different moisture contents in the ground. Comparisons are made under realistic conditions with preliminary experimental results showing satisfactory agreement.
Prediction of Nusselt Number and Flow Rate of Buoyancy Driven Flow Between Vertical Parallel Plates
Authors: Olsson Carl-Olof
Published: March 2004

Literature on buoyancy driven flow in vertical channels have been reviewed in order to investigate formulas for Nusselt number and flow rate, which can be used in fast calculations of temperature rise in electrical apparatuses. The Rayleigh number range spans from fully developed duct flow to isolated plate boundary layer flow, and both uniform heat flux and uniform wall temperature boundary conditions are considered. Several heat transfer formulas are compared, and, for uniform temperature, an improved formula is presented that indicates the existence of an optimum plate separation. Flow rate formulas are proposed based on asymptotic estimates and adaptation to data available in the literature. Based on the flow rate formulas, the influence on flow rate of Rayleigh number and plate separation is discussed.
Numerical Computation of Hydrodynamically and Thermally Developing Liquid Flow in Microchannels With Electrokinetics Effects
Authors: Chen X. Y. , Toh K. C. , Yang C. , Chai J. C.
Published: March 2004

Developing fluid flow and heat transfer with temperature dependent properties in microchannels with electrokinetic effects is investigated numerically. The electrokinetic effect on liquid flow in a parallel slit is modeled by the general Nernst-Planck equation describing anion and cation distributions, the Poisson equation determining the electrical potential profile, the continuity equation, and the modified Navier-Stokes equation governing the velocity field. A Finite-Volume Method is utilized to solve the proposed model.
Dimensional analysis, falling bodies, and the fine art of not solving differential equations
Authors: Bohren Craig F.
Published: March 2004

Dimensional analysis is a simple, physically transparent and intuitive method for obtaining approximate solutions to physics problems, especially in mechanics. It may—indeed sometimes should—precede or even supplant mathematical analysis. And yet dimensional analysis usually is given short shrift in physics textbooks, presented mostly as a diagnostic tool for finding errors in solutions rather than in finding solutions in the first place. Dimensional analysis is especially well suited to estimating the magnitude of errors associated with the inevitable simplifying assumptions in physics problems. For example, dimensional arguments quickly yield estimates for the errors in the simple expression 2h/g for the descent time of a body dropped from a height h on a spherical, rotating planet with an atmosphere as a consequence of ignoring the variation of the acceleration due to gravity g with height, rotation, relativity, and atmospheric drag.
Symmetries and conservation laws: Consequences of Noether’s theorem
Authors: Hanc Jozef , Tuleja Slavomir , Hancova Martina
Published: March 2004

We derive conservation laws from symmetry operations using the principle of least action. These derivations, which are examples of Noether’s theorem, require only elementary calculus and are suitable for introductory physics. We extend these arguments to the transformation of coordinates due to uniform motion to show that a symmetry argument applies more elegantly to the Lorentz transformation than to the Galilean transformation.
The use of models in problems of energy conservation
Authors: Legge K. A. , Petrolito J.
Published: March 2004

Recent discussions regarding the misconceptions students develop about work and conservation of energy has focused attention on introductory mechanics and the use of the “center-of-mass” or particle model. This discussion has led to suggestions that the model is insufficient for introductory mechanics and that more complex models should be used. We suggest that it is not the model that requires re-working, but rather an appreciation of the use and limitations of models in general. We include some examples illustrating the misapplication of the particle model to systems with internal energy.
The driven pendulum at arbitrary drive angles
Authors: VanDalen Gordon J.
Published: March 2004

We discuss the equation of motion of the driven pendulum and generalize it to arbitrary driving angle. The pendulum will oscillate about a stable angle other than straight down if the drive amplitude and frequency are large enough for a given drive angle. The emphasis is on the parameters associated with a simply made demonstration apparatus.
Deriving Lagrange’s equations using elementary calculus
Authors: Hanc Jozef , Taylor Edwin F. , Tuleja Slavomir
Published: March 2004

We derive Lagrange’s equations of motion from the principle of least action using elementary calculus rather than the calculus of variations. We also demonstrate the conditions under which energy and momentum are constants of the motion.
Theory and examples of intrinsically nonlinear oscillators
Authors: Mohazzabi Pirooz
Published: March 2004

Contrary to the general claim that small oscillations in any system can be approximately treated in terms of simple harmonic motion, it is shown that in principle there are infinitely many oscillating systems for which this approximation is not valid. The theory of intrinsically nonlinear oscillators is discussed and examples are given in several areas including elasticity, electrodynamics, and gravitation.
Sea gulls, butterflies, and grasshoppers: A brief history of the butterfly effect in nonlinear dynamics
Authors: Hilborn Robert C.
Published: March 2004

The butterfly effect has become a popular metaphor for sensitive dependence on initial conditions—the hallmark of chaotic behavior. I describe how, where, and when this term was conceived in the 1970s. Surprisingly, the butterfly metaphor was predated by more than 70 years by the grasshopper effect.
Real-time finite difference bifurcation diagrams from analog electronic circuits
Authors: Hellen Edward H.
Published: March 2004

Bifurcation diagrams are a convenient way of displaying the variety of behaviors exhibited by nonlinear systems. One of the simplest nonlinear systems is a finite difference equation with a quadratic return map. This system exhibits a range of behaviors: stability, periodic oscillations, and chaos. We present simple inexpensive electronic circuits that perform analog computations of bifurcation diagrams for finite difference equations with quadratic return maps. These bifurcation diagrams, including one for the logistic equation, are easily displayed on an oscilloscope and agree well with analytical and computational predictions.
Investigating student understanding in intermediate mechanics: Identifying the need for a tutorial approach to instruction
Authors: Ambrose Bradley S.
Published: March 2004

The conceptual understanding and reasoning skills of advanced undergraduates as they make the transition from a traditional sequence in introductory calculus-based physics to their first course in upper-level mechanics are probed. The results thus far are consistent with findings from other investigations in upper-division courses, which indicate that persistent difficulties with fundamental concepts can hinder meaningful learning of advanced topics. To address this problem, the tutorial approach developed at the University of Washington has been adapted and incorporated into the intermediate mechanics course at Grand Valley State University. This modification has produced promising results.
Student use of vectors in introductory mechanics
Authors: Flores Sergio , Kanim Stephen E. , Kautz Christian H.
Published: March 2004

Most students’ initial exposure to physics is in the context of kinematics and dynamics. An understanding of how these topics relate to each other requires the ability to reason about vectors that represent forces and kinematic quantities. We present data that suggest that after traditional instruction in mechanics many students lack this ability. Modifications to instruction can significantly improve student performance on questions about vector addition and subtraction and increase the likelihood that students employ vectors in their attempt to solve mechanics problems. However, an increased emphasis on these topics has so far been only moderately successful in promoting the level of proficiency required to understand the connection between force and acceleration as vector quantities. We describe some of the procedural and reasoning difficulties we have observed in students’ use of vectors.
A unit on oscillations, determinism and chaos for introductory physics students
Authors: Laws Priscilla W.
Published: March 2004

This article describes a unit on oscillations, determinism and chaos developed for calculus-based introductory physics students as part of the laboratory-centered Workshop Physics curriculum. Students begin by observing the motion of a simple pendulum with a paper clip bob with and without magnets in its vicinity. This observation provides an introduction to the contrasting concepts of Laplacian determinism and chaos. The rest of the unit involves a step-by-step study of a pendulum system that becomes increasingly complex until it is driven into chaotic motion. The time series graphs and phase plots of various configurations of the pendulum are created using a computer data acquisition system with a rotary motion sensor. These experimental results are compared to iterative spreadsheet models developed by students based on the nature of the torques the system experiences. The suitability of the unit for introductory physics students in traditional laboratory settings is discussed.
Intersubject Synchronization of Cortical Activity During Natural Vision
Authors: Hasson Uri , Nir Yuval , Levy Ifat , Fuhrmann Galit , Malach Rafael
Published: March 2004

To what extent do all brains work alike during natural conditions? We explored this question by letting five subjects freely view half an hour of a popular movie while undergoing functional brain imaging. Applying an unbiased analysis in which spatiotemporal activity patterns in one brain were used to “model” activity in another brain, we found a striking level of voxel-by-voxel synchronization between individuals, not only in primary and secondary visual and auditory areas but also in association cortices. The results reveal a surprising tendency of individual brains to “tick collectively” during natural vision. The intersubject synchronization consisted of a widespread cortical activation pattern correlated with emotionally arousing scenes and regionally selective components. The characteristics of these activations were revealed with the use of an open-ended “reverse-correlation” approach, which inverts the conventional analysis by letting the brain signals themselves “pick up” the optimal stimuli for each specialized cortical area.
Mobile Elements: Drivers of Genome Evolution
Authors: Kazazian Haig H.
Published: March 2004

Mobile elements within genomes have driven genome evolution in diverse ways. Particularly in plants and mammals, retrotransposons have accumulated to constitute a large fraction of the genome and have shaped both genes and the entire genome. Although the host can often control their numbers, massive expansions of retrotransposons have been tolerated during evolution. Now mobile elements are becoming useful tools for learning more about genome evolution and gene function.
Columnar Architecture Sculpted by GABA Circuits in Developing Cat Visual Cortex
Authors: Hensch Takao K. , Stryker Michael P.
Published: March 2004

The mammalian visual cortex is organized into columns. Here, we examine cortical influences upon developing visual afferents in the cat by altering intrinsic γ-aminobutyric acid (GABA)–mediated inhibition with benzodiazepines. Local enhancement by agonist (diazepam) infusion did not perturb visual responsiveness, but did widen column spacing. An inverse agonist (DMCM) produced the opposite effect. Thus, intracortical inhibitory circuits shape the geometry of incoming thalamic arbors, suggesting that cortical columnar architecture depends on neuronal activity.
Specific GABA
A
Circuits for Visual Cortical Plasticity
Authors: Fagiolini Michela , Fritschy Jean-Marc , Löw Karin , Möhler Hanns , Rudolph Uwe , Hensch Takao K.
Published: March 2004

Weak inhibition within visual cortex early in life prevents experience-dependent plasticity. Loss of responsiveness to an eye deprived of vision can be initiated prematurely by enhancing γ-aminobutyric acid (GABA)–mediated transmission with benzodiazepines. Here, we use a mouse “knockin” mutation to α subunits that renders individual GABA type A (GABA
A
) receptors insensitive to diazepam to show that a particular inhibitory network controls expression of the critical period. Only α1-containing circuits were found to drive cortical plasticity, whereas α2-enriched connections separately regulated neuronal firing. This dissociation carries implications for models of brain development and the safe design of benzodiazepines for use in infants.
Induction of Protective IgA by Intestinal Dendritic Cells Carrying Commensal Bacteria
Authors: Macpherson Andrew J. , Uhr Therese
Published: March 2004

The enormous number of commensal bacteria in the lower intestine of vertebrates share abundant molecular patterns used for innate immune recognition of pathogenic bacteria. We show that, even though commensals are rapidly killed by macrophages, intestinal dendritic cells (DCs) can retain small numbers of live commensals for several days. This allows DCs to selectively induce IgA, which helps protect against mucosal penetration by commensals. The commensal-loaded DCs are restricted to the mucosal immune compartment by the mesenteric lymph nodes, which ensures that immune responses to commensal bacteria are induced locally, without potentially damaging systemic immune responses.
Identification of Polymers as Major Components of Atmospheric Organic Aerosols
Authors: Kalberer M. , Paulsen D. , Sax M. , Steinbacher M. , Dommen J. , Prevot A. S. H. , Fisseha R. , Weingartner E. , Frankevich V. , Zenobi R. , Baltensperger U.
Published: March 2004

Results from photooxidation of aromatic compounds in a reaction chamber show that a substantial fraction of the organic aerosol mass is composed of polymers. This polymerization results from reactions of carbonyls and their hydrates. After aging for more than 20 hours, about 50% of the particle mass consists of polymers with a molecular mass up to 1000 daltons. This results in a lower volatility of this secondary organic aerosol and a higher aerosol yield than a model using vapor pressures of individual organic species would predict.
Force-Clamp Spectroscopy Monitors the Folding Trajectory of a Single Protein
Authors: Fernandez Julio M. , Li Hongbin
Published: March 2004

We used force-clamp atomic force micoscopy to measure the end-to-end length of the small protein ubiquitin during its folding reaction at the single-molecule level. Ubiquitin was first unfolded and extended at a high force, then the stretching force was quenched and protein folding was observed. The folding trajectories were continuous and marked by several distinct stages. The time taken to fold was dependent on the contour length of the unfolded protein and the stretching force applied during folding. The folding collapse was marked by large fluctuations in the end-to-end length of the protein, but these fluctuations vanished upon the final folding contraction. These direct observations of the complete folding trajectory of a protein provide a benchmarkto determine the physical basis of the folding reaction.
X-ray Diffraction Study of the Ultrathin Al
2
O
3
Layer on NiAl(110)
Authors: Stierle A. , Renner F. , Streitel R. , Dosch H. , Drube W. , Cowie B. C.
Published: March 2004

Ultrathin Al
2
O
3
layers on alloys are used as templates for model catalysts, tunneling barriers in electronic devices, or corrosion-resistant layers. The complex atomic structure of well-ordered alumina overlayers on NiAl(110) was solved by surface x-ray diffraction. The oxide layer is composed of a double layer of strongly distorted hexagonal oxygen ions that hosts aluminum ions on both octahedral and tetrahedral sites with equal probability. The alumina overlayer exhibits a domain structure that can be related to characteristic growth defects and is generated during the growth of a hexagonally ordered overlayer (Al
2
O
3
) on a body-centered cubic (110) substrate (NiAl).
Looking for Life in Far Distant Places
Authors: Nittler Larry R.
Published: March 2004

Lonely Planets
The Natural Philosophy of Alien Life. by David Grinspoon. Ecco (HarperCollins), New York, 2003. 460 pp. $25.95, C$39.95. ISBN 0-06-018540-6.

Grinspoon offers an accessible discussion of how findings from astronomy, planetary science, and biology are shaping our considerations of the possibility and nature of extraterrestrial life.
Glass Formation at the Limit of Insufficient Network Formers
Authors: Kohara S. , Suzuya K. , Takeuchi K. , Loong C.-K. , Grimsditch M. , Weber J. K. R. , Tangeman J. A. , Key T. S.
Published: March 2004

Inorganic glasses normally exhibit a network of interconnected, covalent-bonded, structural elements that has no long-range order. In silicate glasses, the network formers are based on SiO
4
tetrahedra interconnected through oxygen atoms at the corners. Conventional wisdom implies that alkaline and alkaline-earth orthosilicate materials cannot be vitrified, because they do not contain sufficient network-forming SiO
2
to establish the needed interconnectivity. We studied a bulk magnesium orthosilicate glass obtained by containerless melting and cooling. We found that the role of network former was largely taken on by corner and edge sharing of highly distorted, ionic Mg-O species that adopt 4-, 5-, and 6-coordination with oxygen. The results suggest that similar glassy phases may be found in the containerless environment of interstellar space.
Antibody Response of Healthy Adults to Recombinant Thrombospondin-Related Adhesive Protein of
Cryptosporidium
1 after Experimental Exposure to
Cryptosporidium
Oocysts
Authors: Okhuysen Pablo C. , Rogers G. Aaron , Crisanti Andrea , Spano Furio , Huang David B. , Chappell Cynthia L. , Tzipori Saul
Published: March 2004

Thrombospondin-related adhesive protein of
Cryptosporidium
1 (TRAP-C1) belongs to a group of proteins that are also found in
Toxoplasma gondii
,
Eimeria tenella
, and
Plasmodium
species. TRAP-related proteins are needed for gliding motility, host-cell attachment, and invasion. The objective of this study was to characterize the antibody response to recombinant TRAP-C1 (rTRAP-C1) in healthy volunteers exposed to
C. parvum
and their association with clinical illness. A total of 31 healthy adult volunteers participated. Seven volunteers received the
C. parvum
TAMU isolate (inocula, 10 to 300 oocysts), and 24 volunteers received the
C. parvum
UCP isolate (500 to 10
5
oocysts). The total antibody (immunoglobulin M [IgM], IgG, and IgA) response to rTRAP C-1 was measured by enzyme-linked immunosorbent assays prior to and after exposure to
Cryptosporidium parvum
(days 0 to 45). Results of this study showed that individuals who were uninfected demonstrated higher reactivity at baseline compared to those who became infected. After challenge, increases in antibody reactivity were seen on days 30 and 45 compared to the results seen on days 0 to 5. The increases in antibody reactivity were statistically significant in subjects with diarrhea and with or without detectable oocysts compared to the results seen with those who were uninfected and asymptomatic. These findings suggest that increases in antibody reactivity to rTRAP-C1 occur after recent exposure to
C. parvum
.
Depressed Type 1 Cytokine Synthesis by Superantigen-Activated CD4
+
T Cells of Women with Human Papillomavirus-Related High-Grade Squamous Intraepithelial Lesions
Authors: Lee Bang-Ning , Follen Michele , Shen De-Yu , Malpica Anais , Adler-Storthz Karen , Shearer William T. , Reuben James M.
Published: March 2004

Carcinoma of the cervix is causally related to infection with the human papillomavirus (HPV), and T cells play a pivotal role in the immune response of the host to rid itself of HPV infection. Therefore, we assessed the T-cell function of women with HPV-related cervical neoplasia against a superantigen,
Staphylococcus
enterotoxin B (SEB). Each woman provided a cervical brush specimen for HPV DNA testing and Papanicolaou (Pap) smears for the staging of cervical lesions. They also provided a blood specimen for determination of the ability of CD4
+
T and CD8
+
T cells to synthesize Th1 (interleukin-2 [IL-2], gamma interferon [IFN-γ], and tumor necrosis factor alpha [TNF-α]) and Th2 (IL-10) cytokines in response to activation with SEB. Compared with control subjects with self-attested negative Pap smears, women with high-grade squamous intraepithelial lesions (HSIL) had significantly lower percentages of activated CD4
+
T cells that produced IL-2 (
P =
0.045), IFN-γ (
P =
0.040), and TNF-α (
P =
0.015) and a significantly lower percentage of activated CD8
+
T cells that produced IL-2 (
P
< 0.01). These data indicate that women with HPV-related cervical HSIL show a decrease in Th1 cytokine production by activated CD4
+
T cells and suggested that compromised T-helper functions may negatively impact the function of cytotoxic CD8
+
T cells.
Development of a Nucleoprotein-Based Enzyme-Linked Immunosorbent Assay Using a Synthetic Peptide Antigen for Detection of Avian Metapneumovirus Antibodies in Turkey Sera
Authors: Alvarez Rene , Njenga M. Kariuki , Scott Melissa , Seal Bruce S.
Published: March 2004

Avian metapneumoviruses (aMPV) cause an upper respiratory tract disease with low mortality but high morbidity, primarily in commercial turkeys, that can be exacerbated by secondary infections. There are three types of aMPV, of which type C is found only in the United States. The aMPV nucleoprotein (N) amino acid sequences of serotypes A, B, and C were aligned for comparative analysis. On the basis of the predicted antigenicity of consensus sequences, five aMPV-specific N peptides were synthesized for development of a peptide antigen enzyme-linked immunosorbent assay (aMPV N peptide-based ELISA) to detect aMPV-specific antibodies among turkeys. Sera from naturally and experimentally infected turkeys were used to demonstrate the presence of antibodies reactive to the chemically synthesized aMPV N peptides. Subsequently, aMPV N peptide 1, which had the sequence 10-DLSYKHAILKESQYTIKRDV-29, with variations at only three amino acids among aMPV serotypes, was evaluated as a universal aMPV ELISA antigen. Data obtained with the peptide-based ELISA correlated positively with total aMPV viral antigen-based ELISAs, and the peptide ELISA provided higher optical density readings. The results indicated that aMPV N peptide 1 can be used as a universal ELISA antigen to detect antibodies for all aMPV serotypes.
Rectal Nitric Oxide Gas and Stool Cytokine Levels during the Course of Infectious Gastroenteritis
Authors: Enocksson Anders , Lundberg Jon , Weitzberg Eddie , Norrby-Teglund Anna , Svenungsson Bo
Published: March 2004

Nitric oxide (NO) is known to be an important inflammatory mediator with a potential role in gastrointestinal diseases. We prospectively studied the luminal NO levels in 51 patients with infectious gastroenteritis, 35 patients with nonenteric bacterial infections, and 11 healthy control subjects. The levels of proinflammatory cytokines were simultaneously measured in the stools of patients with gastroenteritis. Rectal gas was sampled with balloon catheters made of silicone and was analyzed for NO levels by chemiluminescence. The median rectal NO level was 2,450 ppb in the acute phase of gastroenteritis and gradually decreased to 225 ppb after 3 to 8 weeks, whereas the median NO values were 150 ppb in patients with nonenteric bacterial infections and 100 ppb in healthy control subjects. Patients with
Salmonella
,
Shigella
, and
Campylobacter
infections generally had more severe symptoms and a higher median NO level (17,250 ppb) than patients with
Clostridium difficile
-associated diarrhea (median NO value, 275 ppb). Interleukin-1β levels were elevated in 82% of the patients at disease onset and decreased during the convalescent phase. In contrast, gamma interferon was detected in only 16% of the patients and was predominantly collected in stool samples collected during the subacute and convalescent stages. Our data point to the possibility of using this easy, minimally invasive method for luminal NO measurement as a diagnostic tool, among others, to evaluate the degree of intestinal inflammation in patients with infectious gastroenteritis.
Comparison of Benchtop Microplate Beta Counters with the Traditional Gamma Counting Method for Measurement of Chromium-51 Release in Cytotoxic Assays
Authors: Wallace Dora , Hildesheim Allan , Pinto Ligia A.
Published: March 2004

The most traditional method used to measure the lytic activity of cytotoxic T lymphocytes or natural killer (NK) cells is the chromium release assay (CRA). No study has been reported that systematically compares the traditional gamma counting method with various benchtop microplate scintillation formats to measure chromium release. Here we investigated the utilization of microplate beta counters in comparison with the traditional gamma counting method to quantitate antigen-specific cytolysis, lymphokine-activated killer (LAK) activity, and NK activity in the CRA. Supernatants from standard CRA (
n
= 7) were directly transferred to a 96-well microplate containing either a solid scintillant (Lumaplate) or a liquid scintillant (flexible beta plate). Samples were quantified by using two benchtop microplate beta counters, Wallac Microbeta Trilux (Lumalux and Trilux methods, respectively) and Packard TopCount instruments (TopCount method). These results were then compared with data from an identical assay run in parallel using the traditional gamma counting method (LKB). The lytic activity for influenza virus-stimulated effectors measured in the benchtop microplate beta counters using Lumalux and Trilux methods exhibited excellent correlations with the one measured in the traditional LKB (
r
= 0.967 and 0.968, respectively). The TopCount method demonstrated a similar correlation (
r
= 0.966). Similar findings were observed for LAK and NK activity. The 96-well microplate format, specifically the dry-scintillant Lumaplates, offers several advantages over the traditional gamma counting format. Most notable are the reductions in sample volume needed and in the total sample preparation and counting time. Furthermore, this system reduces the amount of dry and mixed radioactive waste generated while using the same instrument for gamma- and beta-emitting isotopes.
Role of C-Terminal Cysteine Residues ofAspergillus fumigatusAllergen Asp f 4 in Immunoglobulin E Binding
Authors: Ramachandran Harikrishnan , Banerjee Banani , Greenberger Paul A. , Kelly Kevin J. , Fink Jordan N. , Kurup Viswanath P.
Published: March 2004

Among the several allergens cloned and expressed fromAspergillus fumigatus, Asp f 4 is a major one associated with allergic bronchopulmonary aspergillosis (ABPA). The structure-function relationship of allergens is important in understanding the immunopathogenesis, diagnosis, and treatment of allergic diseases. These include the epitopes, conformational or linear, deletion of the N or C terminus or both N and C termini, and glycosylation or nonglycosylation, all of which affect immune responses. Similarly, the role of cysteine residues present in allergens may yield useful information regarding the conformational structure of allergens and the immunoglobulin E (IgE) epitope interaction. Such information may help in developing new strategies towards immunotherapy. In order to define the role of cysteine in the interaction of the antibody with Asp f 4, we have constructed mutants by selectively deleting cysteine residues from the C-terminal region of the Asp f 4. Immunological evaluation of these engineered recombinant constructs was conducted by using sera from patients with ABPA,Aspergillusskin test-positive asthmatics, and healthy controls. The results demonstrate strong IgE binding with Asp f 4 and two truncated mutants, Asp f 41-234(amino acids [aa] 1 to 234) and Asp f 41-241(aa 1 to 241), while another mutant, Asp f 41-196(aa 1 to 196), showed reactivity with fewer patients. The result suggests that deletion of cysteines and the alteration of IgE epitopes at the C-terminal end resulted in conformational changes, which may have a potential role in the immunomodulation of the disease.
Potential Serological Use of a Recombinant Protein That Is a Replica of aMycobacterium tuberculosisProtein Found in the Urine of Infected Mice
Authors: Mukherjee Sandeep , Daifalla Nada , Zhang Yanni , Douglass John , Brooks Lisa , Vedvick Thomas , Houghton Raymond , Reed Steven G. , Campos-Neto Antonio
Published: March 2004

The recent availability of numerous well-characterizedMycobacterium tuberculosisrecombinant proteins has revived interest in the serological diagnosis of tuberculosis. Several promising results have been reported, particularly when more than one antigen is used in the test. However, thus far these antigens have not been used in routine diagnostic tests because they lack sufficient sensitivity. In addition, with the exception of one antigen, most recombinantM. tuberculosisproteins do not identify the majority of tuberculosis patients coinfected with human immunodeficiency virus (HIV). Here, we report a newerM. tuberculosisprotein that is a promising candidate for increasing the sensitivity of the serological tests, in particular for patients coinfected with HIV. The protein was found in the urine of mice during the early stages of infection withM. tuberculosis(10 to 14 days), thus suggesting that the antigen is abundantly released during the in vivo growth of the mycobacterium. Reverse genetics was used to produce the recombinant protein, which we named U1 (for urine protein 1). Using a conventional enzyme-linked immunosorbent assay (ELISA), antibody to U1 could be detected in 60% of patients with pulmonary tuberculosis with no signs of coinfection with HIV (n= 83). Conversely, anti-U1 antibody was detected in 87% of the sera from tuberculosis patients coinfected with HIV (n= 47). Out of 12 HIV-infected nontuberculosis patients' sera, 9 did not react with U1 and three sera gave borderline ELISA signals (signal/cutoff of ≤1.75). These results suggest that the high efficiency of U1 in identifying tuberculosis patients coinfected with HIV may be related to abundant release of this protein during the initial phase of the HIV coinfection. The immediate availability of the antigen at a time point in which the patient's immune system is still competent would lead to a secondary immune response to U1 that persists for months in the patient's serum.
Recombinant Protein-Based Enzyme-Linked Immunosorbent Assay and Immunochromatographic Tests for Detection of Immunoglobulin G Antibodies to Severe Acute Respiratory Syndrome (SARS) Coronavirus in SARS Patients
Authors: Guan Ming , Chen Hsiao Ying , Foo Shen Yun , Tan Yee-Joo , Goh Phuay-Yee , Wee Shock Hwa
Published: March 2004

An enzyme-linked immunosorbent assay (ELISA) and a rapid immunochromatographic test for detection of immunoglobulin G (IgG) antibodies in severe acute respiratory syndrome (SARS) patients were developed by utilizing the well-characterized recombinant proteins Gst-N and Gst-U274. The ELISA detected IgG antibodies to SARS-CoV in all 74 convalescent-phase samples from SARS patients while weakly cross-reacting to only 1 of the 210 control sera from healthy donors. This finding thus led to a kit sensitivity, specificity, and accuracy of 100, 99.5, and 99.6%, respectively. The test thus provided a positive predictive value (PPV) of 98.7% and a negative predictive value (NPV) of 100%. In addition, the ELISA gave a positive delta of 5.4 and a negative delta of 3.6, indicating an excellent differentiation between positives and negatives. The same recombinant proteins were also applied to a newly developed platform for the development of a 15-min rapid test. The resulting rapid test has an excellent agreement of 99.6%, with a kappa value of 1.00, with the ELISA. Again, this rapid test was able to detect 100% of the samples tested (
n
= 42) while maintaining a specificity of 99.0% (
n
= 210). The PPV and NPV for the rapid test thus reached 95.3 and 100%, respectively.