bluuebunny/crossref_metadata_2025 huggingface dataset:
A peptide model of insulin folding intermediate with one disulfide
Authors: Yan Han , Guo Zhan‐Yun , Gong Xiao‐Wen , Xi Dan , Feng You‐Min
Published: March 2003

Insulin folds into a unique three‐dimensional structure stabilized by three disulfide bonds. Our previous work suggested that during in vitro refolding of a recombinant single‐chain insulin (PIP) there exists a critical folding intermediate containing the single disulfide A20–B19. However, the intermediate cannot be trapped during refolding because once this disulfide is formed, the remaining folding process is very quick. To circumvent this difficulty, a model peptide ([A20‐B19]PIP) containing the single disulfide A20–B19 was prepared by protein engineering. The model peptide can be secreted from transformed yeast cells, but its secretion yield decreases 2–3 magnitudes compared with that of the wild‐type PIP. The physicochemical property analysis suggested that the model peptide adopts a partially folded conformation. In vitro, the fully reduced model peptide can quickly and efficiently form the disulfide A20–B19, which suggested that formation of the disulfide A20–B19 is kinetically preferred. In redox buffer, the model peptide is reduced gradually as the reduction potential is increased, while the disulfides of the wild‐type PIP are reduced in a cooperative manner. By analysis of the model peptide, it is possible to deduce the properties of the critical folding intermediate with the single disulfide A20–B19.
Comparison of family 12 glycoside hydrolases and recruited substitutions important for thermal stability
Authors: Sandgren Mats , Gualfetti Peter J. , Shaw Andrew , Gross Laurie S. , Saldajeno Mae , Day Anthony G. , Jones T. Alwyn , Mitchinson Colin
Published: March 2003

As part of a program to discover improved glycoside hydrolase family 12 (GH 12) endoglucanases, we have studied the biochemical diversity of several GH 12 homologs. The H. schweinitzii Cel12A enzyme differs from the T. reesei Cel12A enzyme by only 14 amino acids (93% sequence identity), but is much less thermally stable. The bacterial Cel12A enzyme from S. sp. 11AG8 shares only 28% sequence identity to the T. reesei enzyme, and is much more thermally stable. Each of the 14 sequence differences from H. schweinitzii Cel12A were introduced in T. reesei Cel12A to determine the effect of these amino acid substitutions on enzyme stability. Several of the T. reesei Cel12A variants were found to have increased stability, and the differences in apparent midpoint of thermal denaturation (Tm) ranged from a 2.5°C increase to a 4.0°C decrease. The least stable recruitment from H. schweinitzii Cel12A was A35S. Consequently, the A35V substitution was recruited from the more stable S. sp. 11AG8 Cel12A and this T. reesei Cel12A variant was found to have a Tm 7.7°C higher than wild type. Thus, the buried residue at position 35 was shown to be of critical importance for thermal stability in this structural family. There was a ninefold range in the specific activities of the Cel12 homologs on o‐NPC. The most and least stable T. reesei Cel12A variants, A35V and A35S, respectively, were fully active. Because of their thermal tolerance, S. sp. 11AG8 Cel12A and T. reesei Cel12A variant A35V showed a continual increase in activity over the temperature range of 25°C to 60°C, whereas the less stable enzymes T. reesei Cel12A wild type and the destabilized A35S variant, and H. schweinitzii Cel12A showed a decrease in activity at the highest temperatures. The crystal structures of the H. schweinitzii, S. sp. 11AG8, and T. reesei A35V Cel12A enzymes have been determined and compared with the wild‐type T. reesei Cel12A enzyme. All of the structures have similar Cα traces, but provide detailed insight into the nature of the stability differences. These results are an example of the power of homolog recruitment as a method for identifying residues important for stability.
Amphiphilic biopolymers (amphibiopols) as new surfactants for membrane protein solubilization
Authors: Duval‐Terrié Caroline , Cosette Pascal , Molle Gérard , Muller Guy , Dé Emmanuelle
Published: March 2003

The aim of this study was to develop new surfactants for membrane protein solubilization, from a natural, biodegradable polymer: the polysaccharide pullulan. A set of amphiphilic pullulans (HMCMPs), differing in hydrophobic modification ratio, charge ratio, and the nature of the hydrophobic chains introduced, were synthesized and tested in solubilization experiments with outer membranes of Pseudomonas fluorescens. The membrane proteins were precipitated, and then resolubilized with various HMCMPs. The decyl alkyl chain (C10) was the hydrophobic graft that gave the highest level of solubilization. Decyl alkyl chain‐bearing HMCMPs were also able to extract integral membrane proteins from their lipid environment. The best results were obtained with an amphiphilic pullulan bearing 18% decyl groups (18C10). Circular dichroism spectroscopy and membrane reconstitution experiments were used to test the structural and functional integrity of 18C10‐solubilized proteins (OmpF from Escherichia coli and bacteriorhodopsin from Halobacterium halobium). Whatever their structure type (α or β), 18C10 did not alter either the structure or the function of the proteins analyzed. Thus, HMCMPs appear to constitute a promising new class of polymeric surfactants for membrane protein studies.
Structural and kinetic characterization of the simplified SH3 domain FP1
Authors: Yi Qian , Rajagopal Ponni , Klevit Rachel E. , Baker David
Published: March 2003

The simplified SH3 domain sequence, FP1, obtained in phage display selection experiments has an amino acid composition that is 95% Ile, Lys, Glu, Ala, Gly. Here we use NMR to investigate the tertiary structure of FP1. We find that the overall topology of FP1 resembles that of the src SH3 domain, the hydrogen‐deuterium exchange and chemical shift perturbation profiles are similar to those of naturally occurring SH3 domains, and the 15N relaxation rates are in the range of naturally occurring small proteins. Guided by the structure, we further simplify the FP1 sequence and compare the effects on folding kinetics of point mutations in FP1 and the wild‐type src SH3 domain. The results suggest that the folding transition state of FP1 is similar to but somewhat less polarized than that of the wild‐type src SH3 domain.
A Dynamic Model of a Contacting Mechanical Seal for Down-Hole Tools
Authors: Xiong Shunhe , Salant Richard F.
Published: March 2003

A dynamic model of a contacting mechanical seal for down-hole tools, operating in the mixed lubrication regime, has been constructed. Two dynamic cases are examined: the behavior of the seal after it is subjected to a non-equilibrium initial condition and the behavior of the seal as it tracks axial runout of the rotating face. In both cases the seal experiences much larger leakage and inflow (incursion) rates than under steady-state conditions, although in the former case the duration of the increased rates is very short.
Evolution of Surface Pits on Stainless Steel Strip in Cold Rolling and Strip Drawing
Authors: Le H. R. , Sutcliffe M. P. F.
Published: March 2003

Theoretical models are presented for describing the evolution of pits in the inlet and work zone during cold rolling and strip drawing of shot-blast stainless steel under ‘mixed’ lubrication. Results shows that the rough shot-blast surface is flattened rapidly in a short inlet zone, thereby entrapping the lubricant in surface pits. The subsequent evolution of these surface pits in the work zone can be explained by micro-plasto-hydrodynamic-lubrication (MPHL) models described previously. A development of these models is presented which takes into account the effects of the oil film entrained in the inlet, an oil film penetrating from adjacent pits and the finite depth of the pits. The role of an inlet oil film and penetrating MPHL oil film is to limit the potential reduction of pit size. Lubrication regime maps are constructed which describe the evolution of the surface pits for a range of pit geometries. Results explain the experimental observation that some pits survive even after a multi-pass schedule. Predictions of the pit area show good agreement with measurements on samples obtained in strip drawing or rolled under industrial conditions.
Theory Versus Experiment for the Rotordynamic Characteristics of a High Pressure Honeycomb Annular Gas Seal at Eccentric Positions
Authors: Weatherwax Mark , Childs Dara W.
Published: March 2003

Test results for leakage and rotordynamic coefficients are presented for a honeycomb-stator/smooth-rotor annular seal for eccentricity ratios out to 0.5 using air as the test fluid. Tests were conducted at supply pressures up to 70 bars and running speeds up to 20200 rpm. The seal has a diameter of 115 mm, a cell width of 0.79 mm, and a cell depth of 3.10 mm. Tests were conducted for the back-pressure ratios of 0.35, and 0.5. Comparisons are made to predictions from an analysis due to San Andres. The test results show a minimal sensitivity of either leakage or rotordynamic coefficients to changes in the eccentricity ratio. The predictions generally agree well with measurements.
Formation Mechanism of Steady Multi-Dimples in Thermal EHL Point Contacts
Authors: Kaneta M. , Yang P.
Published: March 2003

With optical interferometry technique, an interesting multi-dimple phenomenon has been discovered under pure-sliding conditions in the point contact between a glass disk and a 3-inch diameter steel ball. At low sliding speeds, two or three stable dimples can be generated in the contact, but at higher sliding speeds, such multi-dimples become unstable. At even higher sliding speeds, however, dimples become stable again, but two dimples become single dimple, or three become two. Numerical solutions of the steady-state thermal elastohydrodynamic lubrication (EHL) theory based on the Newtonian flow model can simulate the stable multi-dimples very well. By changing the slide-roll conditions from pure-rolling to pure-sliding, the theoretical analysis shows clearly that the stable multi-dimples are produced by the thermal effect through the familiar EHL pressure spike.
Modeling of a Bubbling AFBC with Volatiles Release
Authors: Selc¸uk Nevin , Degirmenci Engin , Gogebakan Yusuf
Published: March 2003

A comprehensive model for continuous combustion of lignite with wide size distribution burning in its own ash in an atmospheric bubbling fluidized bed combustor (ABFBC) has been presented and used to correlate the data from a 0.3 MW ABFBC test rig. The model consists of submodels for hydrodynamics, volatiles release and combustion, char combustion, particle size distribution, entrainment and elutriation and is based on conservation equations for energy and chemical species. The volatiles release model is based on a particle movement model for estimation of portion of volatiles released in bed and a devolatilization kinetics model described by the distributed activation energy model for determination of time-resolved devolatilization profile of lignite particles. Uniform in-bed volatiles release is assumed. The overall model was applied to a 0.3 MW ABFBC test rig fired with lignite with VCM/FC ratio of 2.16. The fuel was fed 0.22 m above the distributor plate and the expanded bed height was 1 m. Predictions of the model were compared with measured concentration and temperature profiles and good agreement was obtained. Bed/freeboard combustion split predicted by the model was found to be 80/20 as opposed to the value 84/16 determined from measured species profiles.
Effects of Air Bearing Stiffness on a Hard Disk Drive Subject to Shock and Vibration
Authors: Jayson Eric M. , Murphy J. , Smith P. W. , Talke Frank E.
Published: March 2003

A finite element model of a hard disk drive (HDD) is developed to investigate the transient response of an operational HDD subject to shock and vibration. The air bearing stiffness of the head disk interface is determined from a finite element solution of the Reynolds equation and approximated with linear springs. The structural response is analyzed for several types of sliders with a wide range of air bearing stiffness. Results show the response of the head-disk interface subject to shock and the modes excited by vertical and lateral vibrations of the HDD.
Two-Dimensional Anisotropic Contact Behavior of Unidirectional Continuous FRP Composites
Authors: Ning, Xinguo , Lovell, and Michael R. , Slaughter William S.
Published: March 2003

Using an explicit expression for the Barnett-Lothe tensors, an analytical method is introduced for determining the contact characteristics of anisotropic composite materials. The influence of arbitrary fiber orientations on the contact pressure distribution for unidirectional continuous fiber-reinforced polymer (FRP) composites is investigated. To demonstrate the proposed analytical method, the frictional sliding contact between a unidirectional FRP composites and a rigid parabolic cylinder is analyzed. Based on the theoretical results for different fiber orientation angles, the relationships between the contact characteristics of fiber-reinforced plastics and their tribological performance are analyzed and discussed.
Flow Visualization and Forces From a Squeeze Film Damper Operating With Natural Air Entrainment
Authors: Andre´s Luis San , Diaz Sergio E.
Published: March 2003

Measurements of dynamic film pressures and high-speed photographs of the flow field in an open-ended Squeeze Film Damper (SFD) operating with natural free air entrainment are presented for increasing whirl frequencies (8.33–50 Hz), and a range of feed pressures to 250 kPa (37 psig). The flow conditions range from lubricant starvation (air ingestion) to a fully flooded discharge operation. The test dynamic pressures and video recordings show that air entrainment leads to large and irregular gas fingering and striation patterns. This is a natural phenomenon in SFDs operating with low levels of external pressurization (reduced lubricant through flow rates). Air ingestion and entrapment becomes more prevalent as the whirl frequency raises, and increasing the feed pressure aids little to ameliorate the loss in dynamic forced performance. As a result of the severity of air entrainment, experimentally estimated damping forces decrease steadily as the whirl frequency (operating speed) increases.
Intrinsic Strain Modeling and Residual Stress Analysis for Thin-Film Processing of Layered Structures
Authors: Ghasemi Nejhad Mehrdad N. , Pan Chiling , Feng Hongwei
Published: March 2003

Residual stresses develop due to intrinsic and extrinsic strains that form during the processing. Extrinsic strains can be determined using coefficient of thermal expansion, material properties, and processing conditions. An “Equivalent Reference Temperature (ERT)” technique is described and used to model and evaluate the intrinsic strains. piezoelectric microelectromechanical systems (P-MEMS) are considered in this work. Laminate theory with three-dimensional state of stress and strain is used to evaluate residual stresses using the ERT model. In finite element analysis (FEA), the residual stresses and strains of multi-layer P-MEMS structures deposited layer-by-layer during processing, are simulated using the “element birth-and-death” approach. The evaluated residual stresses for a simplified geometry using ANSYS three-dimensional FEA and analytical analysis employing three-dimensional laminate theory are presented along with their corresponding experimental results. A user-friendly software based on the 3-D laminate theory is developed and installed on the Internet. The “equivalent reference temperature” as well as residual stresses and strains can be determined using this software. The level of residual stresses and strains of P-MEMS depend upon various factors such as geometrical design, material selection, and process conditions.
Extending the Fatigue Life of Solder Grid Array (SGA) Electronic Packages
Authors: Larson Michael C. , Verges Melody A.
Published: March 2003

A fracture mechanics approach is used to investigate how the fatigue life of a solder grid array (SGA) may be increased or decreased by the application of an axial force to individual solder interconnects, such as may be induced by use of an underfill, by warping of a printed wiring board, or by some other mechanical constraint. The predominant loading on the SGA is assumed to be the shear resulting from a difference in thermal expansion between the package and the printed wiring board in the presence of cyclic temperature variations. A fatigue crack growth model, akin to the Paris law, is proposed for the cycles to failure of an individual cracked interconnect which undergoes a cyclic mode-II shear loading in conjunction with either a constant crack opening force (mode-I) or a constant crack closing force. For typical SGA packages in use today, the model predicts that forces on the order of only one newton can significantly impede or accelerate the propagation of a fatigue crack.
Moisture Absorption Analysis of Interfacial Fracture Test Specimens Composed of No-Flow Underfill Materials
Authors: Ferguson Timothy , Qu Jianmin
Published: March 2003

In a previous study, we found that moisture preconditioning strongly influenced the interfacial fracture toughness of the underfill/solder mask interface, decreasing the interfacial adhesion by approximately one-half for both classifications of underfill/solder mask interfaces after 725 h of exposure at 85°C/85%RH. To better understand the rate and mechanisms for moisture transport through the interfacial fracture test specimens, a diffusion analysis was implemented based on traditional, analytical solutions of Fick’s second law of diffusion. Test specimens were constructed to experimentally determine the diffusion coefficient for each underfill. Since both underfill encapsulants proved to exhibit non-Fickian behavior at 85°C/85%RH, the application of the analytical Fickian solution for the test specimens was limited to the associated JEDEC criteria of 168 hours for 85°C/85%RH. A finite element analysis was performed to illustrate the moisture concentration in the interfacial fracture test specimens for initial times of exposure to the humid environment. The results of this study demonstrate that the presence of amine functional groups considerably retard moisture penetration through underfill encapsulants.
Quantum-theoretic Shapes of Constituents of Systems in Various States
Authors: Gyftopoulos Elias P. , von Spakovsky Michael R.
Published: March 2003

In previous publications, it has been shown that entropy is a measure of the quantum-theoretic shape of the constituents of a system. In this paper, we present examples of quantum-theoretic shapes of some systems each consisting of one unit of a single constituent, in either a stable (thermodynamic) equilibrium state or in states that are not stable equilibrium. The systems that we consider are a structureless particle confined in either a linear box or a square box, and a harmonic oscillator. In general, we find that the shape of each constituent is “smooth”—without ripples—for each thermodynamic equilibrium state, and oscillatory or rippled for states that are either nonequilibrium or unstable equilibrium.
Stresses and Fracture at the Chip/Underfill Interface in Flip-Chip Assemblies
Authors: Park Ji Eun , Jasiuk Iwona , Zubelewicz Alek
Published: March 2003

We study stresses and fracture due to temperature change in a flip-chip assembly at the chip/underfill interface for various thermo-mechanical properties of underfill and the device’s geometry. We conduct our calculations numerically using a finite element method, and employ the J-integral approach and calculate the stress intensity factors for fracture analysis. We assume that all materials are linear elastic and isotropic, and properties are temperature independent. We use several simplified models of flip-chip devices, while neglecting C4 solder interconnects. We represent the devices as either bi-material strips or as three different types of a three-layer model.
An Experimental Assessment of Numerical Predictive Accuracy for Electronic Component Heat Transfer in Forced Convection—Part I: Experimental Methods and Numerical Modeling
Authors: Rodgers Peter J. , Eveloy Vale´rie C. , Davies Mark R. D.
Published: March 2003

Numerical predictive accuracy is assessed for component-printed circuit board (PCB) heat transfer in forced convection using a computational fluid dynamics (CFD) software for the thermal analysis of electronic equipment. This is achieved by comparing numerical predictions with experimental benchmark data for three different components, mounted individually on single-component PCBs, and collectively on a multi-component PCB. Benchmark criteria are based on measured steady-state component junction temperature and component-PCB surface temperature profiles. The benchmark strategy applied permits the impact of both aerodynamic conditions and component thermal interaction on predictive accuracy to be quantified. In the accompanying Part II of this paper, the experimental measurements are reported and numerical predictive accuracy is assessed.
An Efficient Solution for Wire Sweep Analysis in IC Packaging
Authors: Su Jerry , Hwang Sheng-Jye , Su Francis , Chen Shou-Kang
Published: March 2003

Various methodologies of wire sweep analysis have been introduced to get better prediction and matching the experimental measurements by many researchers. As more and more high pin-count packages (such as BGA, QFP) are used today, efficiency has become an important requirement besides accuracy for software used to predict wire sweep in IC packaging. This study introduces a newly developed wire sweep analysis solution (InPack), not only to meet the need of accuracy, but also enhance the efficiency for actual applications. It combines global flow analysis (C-MOLD) and structure analysis (ANSYS) to become a solution for general wire sweep analysis.
Numerical Study of the Pressure Pattern in a Two-Dimensional Hybrid Journal Bearing Recess, Laminar, and Turbulent Flow Results
Authors: Helene Mathieu , Arghir Mihai , Frene Jean
Published: March 2003

The present work is a parametric study of the pressure pattern in a two-dimensional recess of a hybrid journal bearing (HJB). It is known that theoretical models of HJB are largely dependent on the recess pressure pattern especially for severe working conditions (high rotation speeds, shallow pockets, etc.). The difficulty is that the recess flow is dominated by the interaction of viscous and inertia forces and cannot be analyzed using a thin film model. The present analysis is based on the numerical resolution of the two-dimensional Navier-Stokes equations where only one recess is modeled (with the film lands and the supply region), the fluid being regarded as incompressible and isothermal. Both the laminar and the turbulent flow regimes are considered. The study is governed by two parameters, one related to the HJB operating conditions and the other related to the recess geometric characteristics. The first parameter is the ratio of the runner versus the supply Reynolds number, Rer/Res∈{0,1/4,1/2,1,4,8}. The supply Reynolds number is fixed at 100 for the laminar regime and at 5000 for the turbulent one. The second parameter is the ratio of the recess depth versus the film thickness. Six values of this ratio are considered, ranging from 4 (shallow recess) to 152 (deep recess). Detailed pressure patterns on the runner wall are presented in a systematic manner giving a clear insight of the flow effects intervening in the recess and of their mutual interaction. Some effects are explained by analyzing the recirculation zones inside the recess. It is also shown that for certain parameters turbulent flows have qualitatively similar effects as laminar ones but they can also have specific trends. In order to sustain this remark, the pressure variation at the recess downstream end is analyzed in the paper. Finally, the present results and specially the turbulent ones are intended to contribute to the understanding of viscous and inertia effects interactions in a recess flow and to represent a database in view of HJB theoretical modeling.
Measurement and Prediction of Tape Cupping Under Mechanical and Hygrothermal Loads and Its Influence on Debris Generation in Linear Tape Drives
Authors: Scott William W. , Bhushan Bharat
Published: March 2003

Magnetic tapes, which may be modeled as three-ply laminates, exhibit transverse curvature, or cupping, as manufactured and when mechanical and hygrothermal loads are applied. Among other things, this cupping affects debris generation since it influences the contact between the flawed tape edge and head, the point where much of the debris generation occurs. This influence on debris generation is demonstrated experimentally in this study. Much more debris accumulates near the tape edge-head contact than at other contact locations. No difference in debris generation was found for two tapes with slightly different residual cupping (which is controlled during manufacturing). The target residual cupping is usually negative, which means that the tape bows out towards the tape so that the edges are farther away from the head than the center of contact is, so as to reduce contact pressure with the tape edges. However, cupping generally changes upon application of a tension and generally reduces the importance of residual cupping, which accounts for the failure to find a difference in debris generation for tapes with slightly different residual cupping. A finite element method model that uses laminate shell elements and accounts for in-plane stress stiffening, thus making it suitable for thin laminate modeling, was created. This modeling demonstrates that application of tensile and normal (used to simulate head contact) loads leads to cupping movement in the positive direction, which indicates a more severe edge contact, for an increase in front coat Young’s modulus and/or an increase in front coat thickness. The same trends hold for an increase in back coat Young’s modulus and/or an increase in back coat thickness. Modeling also demonstrates that cupping moves in the positive direction for an increase in the substrate’s Young’s modulus in the transverse direction for MP and ME tapes. An analytical model demonstrates that increases in temperature and front coat thermal expansion coefficient leads to cupping movement in the negative direction. The same trends hold for changes in relative humidity.
The Measurement of Viscosity of Liquids Under Tension
Authors: Kottke Peter A. , Bair Scott S. , Winer Ward O.
Published: March 2003

The rheological significance of a state of hydrostatic tension was investigated. A method for measuring the limiting low shear viscosity of liquids under tension was developed. The ability of nine liquids to withstand tension was verified, and the magnitudes of tension achievable through different methods were compared. The use of viscosity data from liquids under tension to more accurately determine the initial pressure viscosity coefficient was investigated. The continuity of the pressure viscosity coefficient across absolute zero pressure was verified.
An Elliptical Microcontact Model Considering Elastic, Elastoplastic, and Plastic Deformation
Authors: Jeng Yeau-Ren , Wang Pei-Ying
Published: March 2003

This study developed an elastic-plastic microcontact model that considers the elliptical contact of surface asperities. In the elastoplastic regime, the relations of the mean contact pressure and contact area of asperity to its contact interference are modeled considering the continuity and smoothness of variables across different modes of deformation. Results obtained from this model are compared with other existing models such as that calculated by the GW, CEB, Zhao and Horng models. The elliptic contact model and circular contact model can deviate considerably in regard to the separation and real area of contact.
Mechanical Properties of Nanocomposite TiN/Si3N4 Films Synthesized by Ion Beam Assisted Deposition (IBAD)
Authors: Zhang Chenhui , Luo Jianbin , Li Wenzhi , Chen Darong
Published: March 2003

Nanocomposite coatings of TiN/Si3N4 have been prepared by ion beam assisted deposition (IBAD): simultaneous sputtering of Ti and Si targets and film bombardment by N2+ ions at 1000 eV. The Si/Ti ratio in the film varies from 0 to 0.9. The coatings are composed of amorphous Si3N4 and TiN nanocrystals with grain size of several nanometers. Such nanocomposites exhibit improved mechanical properties in comparison with TiN or Si3N4 deposited under the same conditions. The nanoindentation hardness of TiN/Si3N4 film at the Si/Ti ratio of 0.3 reaches a maximum of 42 GPa, compared with 22 GPa for TiN and 18 GPa for Si3N4. The wear resistance of AISI 52100 steel coated with these nanocomposite coatings is increased about three times.
Counter-Current and Co-Current Gas Kicks in “Horizontal” Wells: Non-Newtonian Rheology Effects
Authors: Baca H. , Nikitopoulos D. E. , Smith J. R. , Bourgoyne A. T.
Published: March 2003

Results from experiments conducted in downward liquid-gas flows in inclined, eccentric annular pipes, with water-air and water-polymer-air mixtures as the working fluids, are presented. The gas was injected near the middle of the test-section length. This flow is directly relevant to what is found in down-grade portions of “horizontal” wells. Flow maps, in terms of liquid and gas superficial velocities, indicating the transitions between counter-current and co-current gas flows have been determined experimentally for four dip angles. The counter-current gas flow observed was always in the slug regime while the co-current one appeared as stratified. Counter-current flow fraction and void fraction measurements were carried out at various liquid superficial velocities and gas-injection rates and correlated to visual observations through a full-scale transparent test section. Results indicate that increase of the liquid yield point favors the development of counter current flow which is shown to occur at representative liquid superficial velocities and gas injection rates. Thus, counter-current flow can be easily generated at small downward dip angles, within the practical range of liquid superficial velocity for drilling operations, especially at low gas-injection rates.
ZrO2 Sol-Gel Thin Films by XPS
Authors: Armelao Lidia , Tondello Eugenio , Bigliani Laura , Bottaro Gregorio
Published: March 2003

ZrO2 thin films were prepared by dip-coating on silica glass via sol-gel processing. Ethanolic sols of zirconium butoxide were used as precursors. The ZrO2 films were prepared under controlled atmosphere and resulted transparent, homogeneous, crack-free, and well adherent to the substrates under heating up to 900 °C. The composition of the films was investigated by x-ray photoelectron spectroscopy. In particular, the principal core levels were analyzed for the sample annealed for 1 h at 900 °C. The microstructure of the films was studied by glancing incidence x-ray diffraction as a function of the annealing temperature. The coatings were amorphous up to 400 °C and crystalline ZrO2 with tetragonal structure was observed at 600 °C. Nanostructured layers with an average crystallite dimension of 15 nm were obtained up to 900 °C.
Stoichiometric and Ar-ion Sputtered Uranium Dioxide (111) Single Crystal by XPS
Authors: Chong Shen V. , Barteau Mark A. , Idriss Hicham
Published: March 2003

XPS was performed on UHV O2 annealed and Ar-ion sputtered UO2(111) single crystal surfaces. Ar-ion sputtering for 1 h decreased the XPS O 1s/U 4f corrected total peak areas ratio from 2.11 to 1.19. A shoulder at ∼377.4 eV attributed to Ux atoms (x close to zero) is also observed. Annealing the UO2(111) at 873 K for at least 1 h in the presence of 1E−4 Pa of molecular oxygen was required for restoring the oxygen defects created by Ar-ion bombardment.
How Russian physics teachers are prepared
Authors: Etkina Eugenia
Published: April 2003

This paper describes the system of secondary physics education and the system of preparation of physics teachers in Russia.
Measurement of the fractal dimension of a cauliflower
Authors: Zanoni Michele
Published: April 2003

This paper deals with the wonderful fractal structure of a kind of cauliflower (Brassica oleracea botrytis cimosa). The fractal dimension of the vegetable is empirically detected by measurement.
Revisiting Black’s experiments on the latent heats of water
Authors: Güémez J. , Fiolhais C. , Fiolhais M.
Published: April 2003

Historical experiments may help students to better understand some physical phenomena. We reproduced Black’s original experiments on the latent heats of water (fusion and vaporization). To obtain both latent heats with reasonable accuracy we needed concepts, which were not used by Black, such as the water equivalent of a calorimeter and Newton’s law of cooling. The melting experiment is adequate to obtain an accurate value for the latent heat with a small uncertainty, but the same is not true for the vaporization experiment.
Polarization of Reflected Light
Authors: Ouseph P. J.
Published: April 2003

Students in both calculus-based and noncalculus-based courses are introduced to the topic of polarization of reflected light.1 In these courses, variation of the level of polarization with angle of incidence and the Brewster angle are often discussed. The apparatus discussed here can demonstrate variation of polarization of reflected light as a function of angle of incidence including maximum polarization at the Brewster angle.
A Compact Disk Transmission Spectroscope
Authors: Knauer Tim
Published: April 2003

A student spectroscope with resolution of < 3 nm can be constructed from essentially free materials. Construction details and a brief analysis are demonstrated.
What’s the use of high-school physics texts?
Authors:   Physics Textbook Review Committee
Published: April 2003

Do students read physics texts? How do teachers use physics texts? How can students be persuaded to read the text? Should physics teachers encourage the reading of texts? These questions are addressed, and recommendations are given for choosing a text for your high school physics class.
Do they stay fixed?
Authors: Francis Gregory E. , Adams Jeffrey P. , Noonan Elizabeth J.
Published: April 2003

We report the results of a longitudinal study of three nonmajor introductory classes that achieved relatively high FCI gains (g=1.5) using an inquiry-based tutorial approach. Original FCI gains persisted as many as four years following instruction.
Reality and theory in a collision
Authors: Derby Norman , Fuller Robert
Published: April 2003

A well-known, slow-motion film of a head-on collision between real billiard balls was analyzed by digitizing a video version of the film and then employing modern video analysis software designed for introductory physics courses. This method is compared to the method designed for student use with the original film. The data are compared to the predictions of simple theory and to computer simulations produced by software often encountered in introductory physics courses.
Book Report
Authors: Swartz Clifford E.
Published: April 2003

A major share of this month’s issue of The Physics Teacher is devoted to a review of high school physics texts. This review was commissioned and supported by The David and Lucile Packard Foundation as part of their continued interest in science education.
Templating Organic Semiconductors via Self-Assembly of Polymer Colloids
Authors: Mezzenga Raffaele , Ruokolainen Janne , Fredrickson Glenn H. , Kramer Edward J. , Moses Daniel , Heeger Alan J. , Ikkala Olli
Published: March 2003

A route for producing semiconducting polymer blends is demonstrated in which a doped pi-conjugated polymer is forced into a three-dimensionally continuous minor phase by the self-assembly of colloidal particles and block copolymers. The resulting cellular morphology can be viewed as a high–internal phase polymeric emulsion. Compared with traditional blending procedures, this process reduces the percolation threshold for electrical conductivity by a factor of 10, increases the conductivity by several orders of magnitude, and simultaneously improves thermal stability. Following this route, new applications can be envisaged for semiconducting polymer blends that require only minimal concentrations of doped pi-conjugated polymer.
Swimming in Spacetime: Motion by Cyclic Changes in Body Shape
Authors: Wisdom Jack
Published: March 2003

Cyclic changes in the shape of a quasi-rigid body on a curved manifold can lead to net translation and/or rotation of the body. The amount of translation depends on the intrinsic curvature of the manifold. Presuming spacetime is a curved manifold as portrayed by general relativity, translation in space can be accomplished simply by cyclic changes in the shape of a body, without any external forces.
Wave-Induced Sediment Transport and Sandbar Migration
Authors: Hoefel Fernanda , Elgar Steve
Published: March 2003

Onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood. Here, a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach. In both the observations and the model, the location of the maximum acceleration-induced transport moves shoreward with the sandbar, resulting in feedback between waves and morphology that drives the bar shoreward until conditions change. A model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45-day period.
Two Nobel Prizes and a Hole-in-One
Authors: Cooper Leon
Published: March 2003

True Genius
The Life and Science of John Bardeen. Lillian Hoddeson and Vicki Daitch. Joseph Henry Press (National Academies Press), Washington, DC, 2002. 479 pp. $27.95, C$37.95. ISBN 0-309-08408-3.

Hoddeson and Daitch offer an account of the life and science of the researcher who won two Nobel Prizes in physics for his contributions to the invention of the transistor and the theory of superconductivity.
Sorting Sponges
Authors: Pawlik Joseph
Published: March 2003

Systema Porifera
A Guide to the Classification of Sponges. John N. A. Hooper and Rob W. M. Van Soest, Eds. Kluwer Academic/Plenum, New York, 2002. 2 vol., 1802 pp. $595, £398, €625. ISBN 0-306-47260-0.

The contributors synthesize and update information from the flurry of taxonomic research over the past fifty years, which have seen estimates of the diversity of sponges climb to some 15,000 extant species.
A Few-Polyhedra Mutant and Wild-Type Nucleopolyhedrovirus Remain as a Stable Polymorphism during Serial Coinfection in
Trichoplusia ni
Authors: Bull James C. , Godfray H. C. J. , O'Reilly David R.
Published: April 2003

Few-polyhedra (FP) mutants of nucleopolyhedroviruses (NPVs) are a well-known phenomenon during serial passage of virus in cell culture. Under these circumstances such mutants produce low yields of occlusion bodies (OBs) and poorly occlude virions, but they are selected for through advantageous rates of budded virus replication. Spontaneous insertion of transposable elements originating from host cell DNA into the viral
fp25
gene has been shown to be a common cause of the phenotype. A model of NPV population genetics predicts that mutants with these characteristics might persist within stable polymorphisms in viral populations during serial passage of virus in vivo. However, this hypothesis was previously untested, and FP mutants have not been recovered from field isolates of NPVs. We isolated and characterized an FP mutant that arose during routine passage of
Autographa californica
multinucleocapsid NPV (AcMNPV) in cell culture and identified a transposable element within the
fp25
gene. We tracked the fates of coinfecting wild-type and FP mutant AcMNPV strains through serial passage in fifth-instar
Trichoplusia ni
larvae. The levels of both strains remained stable during successive rounds of infection. We applied the data obtained to a model of NPV population genetics in order to derive the frequency distribution of the multiplicity of cell infection in infected insects and estimated that 4.3 baculovirus genomes per OB-producing cell would account for this equilibrium.
Identification, Timing, and Signal Specificity ofPseudomonas aeruginosaQuorum-Controlled Genes: a Transcriptome Analysis
Authors: Schuster Martin , Lostroh C. Phoebe , Ogi Tomoo , Greenberg E. P.
Published: March 2003

There are two interrelated acyl-homoserine lactone quorum-sensing-signaling systems inPseudomonas aeruginosa. These systems, the LasR-LasI system and the RhlR-RhlI system, are global regulators of gene expression. We performed a transcriptome analysis to identify quorum-sensing-controlled genes and to better understand quorum-sensing control ofP. aeruginosagene expression. We compared gene expression in a LasI-RhlI signal mutant grown with added signals to gene expression without added signals, and we compared a LasR-RhlR signal receptor mutant to its parent. In all, we identified 315 quorum-induced and 38 quorum-repressed genes, representing about 6% of theP. aeruginosagenome. The quorum-repressed genes were activated in the stationary phase in quorum-sensing mutants but were not activated in the parent strain. The analysis of quorum-induced genes suggests that the signal specificities are on a continuum and that the timing of gene expression is on a continuum (some genes are induced early in growth, most genes are induced at the transition from the logarithmic phase to the stationary phase, and some genes are induced during the stationary phase). In general, timing was not related to signal concentration. We suggest that the level of the signal receptor, LasR, is a critical trigger for quorum-activated gene expression. Acyl-homoserine lactone quorum sensing appears to be a system that allows ordered expression of hundreds of genes duringP. aeruginosagrowth in culture.
Microarray Analysis of
Pseudomonas aeruginosa
Quorum-Sensing Regulons: Effects of Growth Phase and Environment
Authors: Wagner Victoria E. , Bushnell Daniel , Passador Luciano , Brooks Andrew I. , Iglewski Barbara H.
Published: March 2003

Bacterial communication via quorum sensing (QS) has been reported to be important in the production of virulence factors, antibiotic sensitivity, and biofilm development. Two QS systems, known as the
las
and
rhl
systems, have been identified previously in the opportunistic pathogen
Pseudomonas aeruginosa
. High-density oligonucleotide microarrays for the
P. aeruginosa
PAO1 genome were used to investigate global gene expression patterns modulated by QS regulons. In the initial experiments we focused on identifying
las
and/or
rhl
QS-regulated genes using a QS signal generation-deficient mutant (PAO-JP2) that was cultured with and without added exogenous autoinducers [
N
-(3-oxododecanoyl) homoserine lactone and
N
-butyryl homoserine lactone]. Conservatively, 616 genes showed statistically significant differential expression (
P
≤ 0.05) in response to the exogenous autoinducers and were classified as QS regulated. A total of 244 genes were identified as being QS regulated at the mid-logarithmic phase, and 450 genes were identified as being QS regulated at the early stationary phase. Most of the previously reported QS-promoted genes were confirmed, and a large number of additional QS-promoted genes were identified. Importantly, 222 genes were identified as being QS repressed. Environmental factors, such as medium composition and oxygen availability, eliminated detection of transcripts of many genes that were identified as being QS regulated.
OmcB, ac-Type Polyheme Cytochrome, Involved in Fe(III) Reduction inGeobacter sulfurreducens
Authors: Leang Ching , Coppi M. V. , Lovley D. R.
Published: March 2003

Microorganisms in the familyGeobacteraceaeare the predominant Fe(III)-reducing microorganisms in a variety of subsurface environments in which Fe(III) reduction is an important process, but little is known about the mechanisms for electron transport to Fe(III) in these organisms. TheGeobacter sulfurreducensgenome was found to contain a 10-kb chromosomal duplication consisting of two tandem three-gene clusters. The last genes of the two clusters, designatedomcBandomcC, encode putative outer membrane polyhemec-type cytochromes which are 79% identical. The role of theomcBandomcCgenes in Fe(III) reduction inG. sulfurreducenswas investigated. OmcB and OmcC were both expressed during growth with acetate as the electron donor and either fumarate or Fe(III) as the electron acceptor. OmcB was ca. twofold more abundant under both conditions. DisruptingomcBoromcCby gene replacement had no impact on growth with fumarate. However, the OmcB-deficient mutant was greatly impaired in its ability to reduce Fe(III) both in cell suspensions and under growth conditions. In contrast, the ability of the OmcC-deficient mutant to reduce Fe(III) was similar to that of the wild type. WhenomcBwas reintroduced into the OmcB-deficient mutant, the capacity for Fe(III) reduction was restored in proportion to the level of OmcB production. These results indicate that OmcB, but not OmcC, has a major role in electron transport to Fe(III) and suggest that electron transport to the outer membrane is an important feature in Fe(III) reduction in this organism.
Synthetic
lac
Operator Substitutions for Studying the Nitrate- and Nitrite-Responsive NarX-NarL and NarQ-NarP Two-Component Regulatory Systems of
Escherichia coli
K-12
Authors: Stewart Valley , Bledsoe Peggy J.
Published: March 2003

The NarX and NarQ sensor-histidine kinases control phosphorylation of the NarL and NarP response regulators in response to the respiratory oxidants nitrate and nitrite. Target operon transcription is activated by the Fnr protein in response to anaerobiosis, and it is further activated and/or repressed by the phospho-NarL and phospho-NarP proteins, which bind to heptamer DNA sequences. The location and arrangement of heptamers vary widely among different target operon control regions. We have constructed a series of monocopy
lac
operon control region constructs in which the primary operator O1-
lac
has been replaced by 7-2-7 heptamer pairs from the
nrfA
,
nirB
,
napF
, and
fdnG
operon control regions. These constructs provide tools for dissecting various aspects of ligand interactions with sensor-kinases, sensor interactions with response regulators, and phospho-response regulator interactions with DNA targets. Expression of the
lacZ
gene from these constructs was repressed to various degrees by nitrate and nitrite. In response to nitrate, the
nrfA
and
nirB
operon 7-2-7 heptamer pairs at operator O1 each mediated greater than 100-fold repression of
lacZ
gene expression, whereas the
napF
operon 7-2-7 heptamer pair mediated approximately tenfold repression. Introduction of
narL
,
narP
,
narX
, and
narQ
null alleles in various combinations allowed the in vivo interactions between different sensor-regulator pairs to be evaluated and compared.