bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the refractive indices of AlN, GaN, and AlxGa1−xN grown on (111)Si substrates
Authors: Antoine-Vincent N. , Natali F. , Mihailovic M. , Vasson A. , Leymarie J. , Disseix P. , Byrne D. , Semond F. , Massies J.
Published: April 2003

The refractive indices of several AlxGa1−xN alloys deposited on silicon are determined by ellipsometry and reflectivity experiments at room temperature. The AlGaN layers are grown on (111)Si substrate by molecular-beam epitaxy on top of an AlN/GaN/AlN buffer in order to reduce the strain of the alloy. The Al composition is deduced from energy dispersive x-ray spectroscopy and photoluminescence experiments. The refractive index n and the extinction coefficient k are determined in the 300–600 nm range. For the transparent region of AlxGa1−xN, the refractive index is given in form of a Sellmeier law.
Dynamic mechanisms in photoluminescence of gallium-doped ZnSe grown by molecular-beam epitaxy
Authors: Wang S. Z. , Yoon S. F.
Published: April 2003

Reported are the temperature-dependent photoluminescence (PL) results of molecular-beam epitaxy-grown gallium-doped zinc selenide (ZnSe:Ga) sample with the sample temperature varied from 10 to 300 K. The physical origins of a twin PL structure peaked at 2.794 and 2.733 eV, respectively, that overwhelm the whole PL spectrum are discussed, and the dynamic processes behind these temperature-dependent PL results are also investigated.
Photoluminescence emission and Raman scattering polarization in birefringent organic microcavities in the strong coupling regime
Authors: Krizhanovskii D. N. , Butté R. , Connolly L. G. , Tartakovskii A. I. , Lidzey D. G. , Skolnick M. S. , Walker S.
Published: April 2003

We have investigated the polarization properties of photoluminescence and Raman scattering in strongly coupled organic microcavities containing cyanine dye J aggregates. The birefringence of radially aligned J aggregates results in a large energy splitting of polariton modes when the electric field of the incoming laser light is perpendicular or parallel to the alignment direction. This splitting allows the degree of polarization of doubly resonant Raman processes involving the vibrational modes of J aggregates to be controlled, where the ingoing and outgoing channels are in resonance with the lower polariton branch. As well as providing insight into the properties of polaritons in organic microcavities, these experiments are a sensitive probe of alignment effects arising during the spin-coating deposition process.
Effect of electric field, solvent, and concentration on the electroluminescence spectra and performance of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] based light emitting diodes
Authors: Sinha S. , Monkman A. P.
Published: April 2003

The electroluminescence (EL) spectra and performance of polymer light emitting diodes based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] are found to depend significantly on the applied electric field as well as the solvent and concentration used in the fabrication of the polymer layer. Drastic changes in the EL spectra with the electric field are observed in devices in which the polymer layer is spin cast from chlorobenzene (CB) at high concentration. At low electric field, the broad reddish-orange emission from these devices originates mostly from aggregate species formed by interchain interactions. However, at high electric field, a narrow yellow emission is observed, which originates from both aggregate species (minor part) as well as single-chain species (major part) arising out of intrachain interactions. The individual emission intensities of the two species are estimated at different electric fields and are found to behave in a different manner with the change in electric field. The fractional contribution of the aggregate species in the overall EL spectra changes from 98% to 17% as the electric field is increased from low to a high value. Either changing the solvent from CB to tetrahydrofuran (THF) or decreasing the concentration (in any particular solvent) reduces the possibility of the formation of aggregate species. At any particular concentration, the turn-on field is found to be always higher in CB-cast films than THF-cast ones. This fact is explained by the presence of deeply trapped holes at low electric field. Devices made from CB are found to give better performance regarding external quantum efficiency, power efficiency, etc., than those made from THF, irrespective of the concentration. Again, devices made from any particular solvent are found to perform better at low concentration than at high concentration. Enhanced carrier mobility accounts for the improved performance of the devices made from CB than those made from THF. On the other hand, device performance becomes poor at high concentration (in any particular solvent) due to the formation of aggregate species. The optimum performance is obtained from the devices in which the polymer layer is spin cast from CB at low concentration.
Quantifiable combinatorial materials science approach applied to perpendicular magnetic recording media
Authors: Svedberg Erik B. , van de Veerdonk Rene J. M. , Howard Kent J. , Madsen Lynnette D.
Published: April 2003

Deposition of films with controlled gradients across the wafer in terms of both composition and thickness were used together with statistical experimental design methodologies to explore large parameter spaces relevant to the optimization of perpendicular magnetic recording media. With this approach, thickness and composition of the media and the interdependencies of these variables were efficiently investigated and correlated to the coercivity of the material and the squareness of the hysteresis loops. To determine dependencies and codependencies between additives to CoCr alloys on the magnetic properties, this method was used to study magnetic layers of CoCrPt, CoCrPtTa, CoCrPtTi, and CoCrTiTa. The best models associated with each alloy had the same terms for the three magnetic parameters measured (Hc, S, and θk,perp). Additions to the CoCr alloy introduced dependencies on the Cr and cross-term dependencies with Cr (i.e., CrTa, CrPt, or CrTi). In some cases, thickness became an important parameter and for the CoCrPtTa case, the Pt concentration directly influenced the magnetic properties. These findings, obtained in a concise manner with fully descriptive empirical models, agree with the bulk of published literature. In this study, the variables are tightly controlled and variables such as temperature and residual gas concentrations are identical for all data points used within each alloy system generating an accurate transfer function. Once the transfer function between the input and output parameters is established, the sensitivity or stability to changes in the different factors can easily be investigated.
Reactions of gold cluster cations Aun+ (n=1–12) with H2S and H2
Authors: Sugawara Ko-ichi , Sobott Frank , Vakhtin Andrei B.
Published: April 2003

The reactions of gold cluster cations Aun+ (n=1–12) with H2S and H2 have been studied using Fourier-transform ion-cyclotron resonance (FT–ICR) mass spectrometry. The cluster cations were produced by laser ablation of a gold rod in He atmosphere, and their reactions were observed at room temperature and low total pressures of 10−7–10−5 Torr. Initial products of the reactions with H2S were mainly AuSH+ for n=2, AunS+ for n=4–8 and 10, and AunSH2+ for n=9, 11, and 12. No reactions of Au+ and Au3+ with H2S were observed. Even n cluster cations were more reactive than adjacent odd n clusters. The particularly low reactivity at n=1, 3, 9, and 11 is consistent with the low ionization potential of Aun and the weak binding energy of Aun+–Au. Further sulfuration reactions of AunS+ proceeded to give AunSm+ and finally stopped at AunSm+xH2+ when H2 release did not occur. The maximum number of sulfur atoms m+x increased with the cluster size up to n=8, while the sulfuration reaction stopped at early stages for n⩾9. In another series of experiments, no reaction of Aun+ (n=1–12) with H2 gas pulses introduced into the FT–ICR cell was observed. To investigate the stability of gold hydride clusters, laser ablation of gold in a H2/He mixture was performed. The hydride cluster cations AunHm+ were produced for n=1–7, while bare Aun+ clusters were the main products for n⩾8. There is a distinct border between n=7 and 8, as the structure of Aun+ changes from planar for n⩽7 to three-dimensional for n⩾8, suggesting the stability of hydride cluster cations with planar gold frameworks.
Ferroelectric state analysis in grain boundary of Na0.85Li0.15NbO3 ceramic
Authors: Nobre M. A. L. , Lanfredi S.
Published: April 2003

The electric and dielectric properties of the grain boundary of Na0.85Li0.15NbO3 lead-free ferroelectric-semiconductor perovskite were investigated. The impedance spectroscopy was carried out as a function of a thermal cycle. The sodium lithium niobate was synthesized by a chemical route based on the evaporation method. Dense ceramic, relative density of 97%, was prepared at 1423 K for 2 h in air atmosphere. ac measurements were carried out in the frequency range of 5 Hz–13 MHz and from 673 to 1023 K. Theoretical adjust of the impedance data was performed to deriving the electric parameters of the grain boundary. The electric conductivity follows the Arrhenius law, with activation energy values equal to 1.55 and 1.54 eV for heating and cooling cycle, respectively. The nonferroelectric state of the grain boundary and its correlation with symmetry are discussed in the temperature domain.
Effect of a nucleating agent on lamellar growth in melt-crystallizing polyethylene oxide
Authors: Aliotta F. , Di Marco G. , Ober R. , Pieruccini M.
Published: April 2003

The effects of a (non co-crystallizing) nucleating agent on secondary nucleation rate and final lamellar thickness in isothermally melt-crystallizing polyethylene oxide are considered. Small angle x-ray scattering reveals that lamellae formed in nucleated samples are thinner than in the pure samples crystallized at the same undercoolings. These results are in quantitative agreement with growth rate data obtained by calorimetry, and are interpreted as the effect of a local decrease of the basal surface tension, determined mainly by the nucleant molecules diffused out of the regions being about to crystallize. Quantitative agreement with a simple lattice model allows for some interpretation of the mechanism.
Field emission of large-area and graphitized carbon nanotube array on anodic aluminum oxide template
Authors: Gao Han , Mu Cheng , Wang Fan , Xu Dongsheng , Wu Kai , Xie Youchang , Liu Shuang , Wang Enge , Xu Jun , Yu Dapeng
Published: April 2003

Large-area, graphitized, and patterned carbon nanotube (CNT) arrays were prepared via cracking of ethylene on an open-ended anodized aluminum oxide (AAO) template that also served as a catalyst. With ion-milling and gold coating techniques, ohmic contact between the CNTs and electrode for field emission measurements was greatly improved. In both tip-plane and plane-plane field emitting experiments, the CNTs/AAO displayed a low turn-on field of ∼2.8 V/μm, a high maximum emitting current density of ∼24 mA/cm2, and a fairly good emitting stability.
Measurement of elastic modulus of nanotubes by resonant contact atomic force microscopy
Authors: Cuenot Stéphane , Frétigny Christian , Demoustier-Champagne Sophie , Nysten Bernard
Published: April 2003

A resonant contact atomic force microscopy technique is used to quantitatively measure the elastic modulus of polymer nanotubes. An oscillating electric field is applied between the sample holder and the microscope head to excite the oscillation of the cantilever in contact with nanotubes. The nanotubes are suspended over the pores of a membrane. The measured resonance frequency of this system, a cantilever with the tip in contact with a nanotube, is shifted to higher values with respect to the resonance frequency of the free cantilever. It is experimentally demonstrated that the system can simply be modeled by a cantilever with the tip in contact with two springs. The measurement of the frequency shift thus enables the direct determination of the spring stiffness, i.e., the nanotube stiffness. The method also enables the determination of the boundary conditions of the nanotube on the membrane. The tensile elastic modulus is then simply determined using the classical theory of beam deflection. The obtained results fairly agree to previously measured values using nanoscopic three points bending tests. It is demonstrated that resonant contact atomic force microscopy allows us to quantitatively measure the mechanical properties of nanomaterials.
Photoluminescence transitions in semiconductor superlattices. Theoretical calculations for InGaN blue laser device
Authors: Kunold A. , Pereyra P.
Published: April 2003

The optical response of an AlGaN/GaN/(InxGa1−xN)n/GaN/AlGaN heterostructure is obtained from precise, and comparatively simple, transition probability calculations. A comprehensive approach to evaluate these quantities from rigorous expressions of the heterostructure's energy eigenvalues and eigenfunctions is given. Taking full account of the longitudinal quantum wells and the lateral quantum dot confinement, quite precise intraband energy levels and wave functions have been obtained. Photoluminescence results for sectionally constant band-edge profile differ from the experimental measurements by approximately 45 meV. We show that the band-edge modulation arising from charge polarization, is responsible for this difference.
Structural phase transitions in ZrO2 films induced by ion bombardment—Argon irradiation versus implantation
Authors: Müller Th. , Kästle G. , Boyen H.-G. , Eisenmenger J. , Ziemann P. , Holgado J. P. , Gonzalez-Elipe A. R.
Published: April 2003

ZrO 2 films prepared at ambient temperature (RT) by ion beam induced chemical vapor deposition onto Si substrates and subsequently annealed at 1300 K in order to obtain their equilibrium monoclinic structure, were bombarded at RT with Ar+ ions of either 90/100 or 350 keV. For the lower energies, the ions are implanted into the sample with their concentration profile approximately at the film center, while for the higher energy the corresponding average projected range of the ions is significantly larger than the film thickness. Thus, in this case, the ions penetrate the ZrO2 sample thereby producing radiation damage, and are implanted deep into the substrate. For ZrO2 films containing no Argon in the as-prepared state, both types of ion bombardments resulted in a structural phase transition from the monoclinic into the tetragonal/cubic phase indicating that the incorporation of argon is not necessary to accomplish this transformation for the energy range used in this experiment.
Two color InAs/InGaAs dots-in-a-well detector with background-limited performance at 91 K
Authors: Krishna S. , Raghavan S. , von Winckel G. , Rotella P. , Stintz A. , Morath C. P. , Le D. , Kennerly S. W.
Published: April 2003

Normal incidence long wave infrared (λc∼9 μm) InAs/In0.15Ga0.85As dots-in-a-well detectors with background limited performance at 91 K, under f#1.7 300 K background irradiance, are reported. Two distinct peaks (λp1∼4.2 μm and λp2∼7.6 μm) are observed in the spectral response, which could possibly be due to a bound-to-continuum transition and a bound-to-bound transition, respectively. The operating wavelength of the detector can be varied by changing the width of the quantum well surrounding the quantum dots. Using calibrated blackbody measurements, the peak responsivity of the detector is measured to be 0.73 A/W (Vb=−1.7 V at T=60 K).
Low-density open-cell foams in the NiTi system
Authors: Grummon David S. , Shaw John A. , Gremillet Antoine
Published: April 2003

It is shown that open-cell metallic foams having very low density, and that display martensite transformations required for shape memory and superelastic behavior, can be fabricated using a powder-metallurgy technique. Results are presented on experiments in which a polymeric precursor foam was coated with an equiatomic NiTi powder slurry and subsequently sintered to yield foams with relative densities as low as 0.039. Although contaminated with interstitial impurities, they displayed unambiguous calorimetric signature of the B2→B19′ transformation. The results are of considerable significance to potential applications requiring ultralightweight structures with the unusual dissipative and strain-recovery properties of NiTi shape-memory materials.
Multiples of Six: The Six Companies and West Coast Industrialization, 1930–1945
Authors: Tassava Christopher James
Published: April 2003

In this article I explore the protean organizational forms used by the Kaiser and Bechtel construction companies between 1930 and 1950. Kaiser and Bechtel prospered during the Depression and World War II because, as members of the Six Companies consortium of construction firms, they refused to adopt a “best practice” model of corporate organization drawn from the diversified manufacturing and distribution sectors. Instead, Kaiser and Bechtel used a variety of organizational forms to win numerous government contracts for public works and defense production, transforming themselves from small regional firms into substantial national and global corporations. I contribute to modern academic debate over the historical forms of business enterprise and the conjunction of state consumption and private production.
National Determinants of Family Firm Development? Family Firms in Britain, Spain, and Italy in the Nineteenth and Twentieth Centuries
Authors: Colli Andrea , Pérez Paloma Fernández , Rose Mary B.
Published: April 2003

We provide here a complement to recent work on family business, which has demonstrated the need to go beyond the generic definition of the family firm to place personal capitalism in an appropriate institutional, historical, and cultural framework. By focusing on the nineteenth‐ and twentieth‐century experiences in Britain, Spain, and Italy, we challenge the notion that in the nineteenth and twentieth centuries there was anything so simple as a Mediterranean model for family business. Rather, we demonstrate the need to consider family businesses in national and regional contexts if we are to understand their various capabilities and characteristics. We use similarities and differences in the experiences and responses of families and firms in the three countries to support this claim.
Tensions within an Industrial Research Laboratory: The Philips Laboratory's X-Ray Department between the Wars
Authors: Boersma Kees
Published: April 2003

Tensions arose in the X-ray department of the Philips research laboratory during the interwar period, caused by the interplay among technological development, organizational culture, and individual behavior. This article traces the efforts of Philips researchers to find a balance between their professional goals and status and the company's strategy. The X-ray research, overseen by Gilles Holst, the laboratory's director, and Albert Bouwers, the group leader for the X-ray department, was a financial failure despite technological successes. Nevertheless, Bouwers was able to continue his X-ray research, having gained the support of company owner Anton Philips. The narrative of the X-ray department allows us to explore not only the personal tensions between Holst and Bouwers, but also the interaction between individual goals and company strategy in an industrial research laboratory.
Jardine Matheson & Company: The Role of External Organization in a Nineteenth-Century Trading Firm
Authors: Connell Carol Matheson
Published: April 2003

Jardine Matheson & Company, a Hong Kong conglomerate founded in 1832, has survived political upheaval and global and regional economic crises, transforming itself several times. From their beginnings in the commission business, William Jardine and James Matheson developed a reputation for sound financial management that furthered their trading relationships and supported their firm's expansion from agency house to managing agent to investment house between 1832 and 1885. Fundamental to Jardine Matheson's success was the strategic decision to eschew speculation and to concentrate on building a pattern of relationships within and outside the business that would foster the flow of information, the knowledge with which to interpret it, the ability to influence others, and a reputation for probity that would attract and retain trading partners.
A biocultural model of aging
Authors: Martinez Mario E.
Published: April 2003

Addresses how the life sciences have concentrated on the pathology of aging while ignoring the biocultural aspects of health in the process of growing older. Argues that growing older is a dynamic cognitive, biological and cultural coauthoring of health rather than a hopeless unfolding of progressive pathology. Proposes that this fragmented concept of aging precludes operationalizing and understanding the cultural markers that affect longevity. These cultural milestones, or biocultural portals include middle age markers, retirement markers, perceived wisdom, sexuality, status in the community, transcendental beliefs, sense of empowerment vs helplessness and any other biocultural phase in human development. Suggests that the biocultural portals define and trigger the phase transitions of life as well as influence how they are accommodated. For example, the markers for middle age established by a culture, strongly influence the cognitive and biological expectations for the second half of life.
Statistical validation of simulation models of observable systems
Authors: Vasermanis Edgars K. , Nechval Konstantin N. , Nechval Nicholas A.
Published: April 2003

In this paper, for validating computer simulation models of real, observable systems, an uniformly most powerful invariant (UMPI) test is developed from the generalized maximum likelihood ratio (GMLR). This test can be considered as a result of a new approach to solving the Behrens‐Fisher problem when covariance matrices of two multivariate normal populations (compared with respect to their means) are different and unknown. The test is based on invariant statistic whose distribution, under the null hypothesis, does not depend on the unknown (nuisance) parameters. The sample size and threshold of the UMPI test are determined from minimization of the weighted sum of the model builder's risk and the model user's risk. The proposed test could result in the saving of sample items, if the items of the sample are observed sequentially. In this paper, we present the exact form of the proposed curtailed procedure and examine the expected sample size savings under the null hypothesis. The sample size savings can be bounded by a constant, which is independent of the sample size. Tables are given for the expected sample size savings and maximum sample size saving under the null hypothesis for a range of significance levels (α), dimensions (p) and sample sizes (n). The curtailed test considered in this paper represents improvement over the noncurtailed or standard fixed sample tests.
Towards a cybernetics of value, presence, and anticipation
Authors: Wood John
Published: April 2003

The paper asks whether we can popularise a cybernetics of human presence. It suggests that, despite its implicit critique of mechanistic thinking, cybernetics inherited its mindset from classical science, and therefore played a part in the evolution of technologically induced forms of alienation. Cybernetics also upholds a strongly western model of “self” that, given the technological power implicit in established cybernetic principles, reinforces instrumentalist, solipsistic, and cynical modes of reasoning in the economically “advanced” nations. These effects, in turn, continue to precipitate ecological damage. In discussing more recent developments, the paper notes the possibilities for modes of cybernetics that could become operative at the site of our self‐world interface. At this level, it argues, our human ontology becomes more synonymous with our senses. This can also be shown by reminding ourselves of the crucial role of our “creative presence”, in which a greater acknowledgement of anticipatory reasoning might inform an actative, flow‐based grammar of cybernetics. It concludes that clocks need to be radically re‐designed within terms that are in accord with (at least) second‐order cybernetics.
Pansystems mathematics: an analysis of panweighted field‐network
Authors: Wu Xiaolong , Guo Dinghe , Pan Jinghong , Wu Xuemou
Published: April 2003

In this paper, we will introduce charm pansystems and provide mathematical models for panweighted field‐network. Various mathematical models of pansystems will be discussed. Some traditional mathematical concepts such as topology space and rough sets theory will be analyzed within this framework.
Drop‐in security for distributed and portable computing elements
Authors: Prevelakis Vassilis , Keromytis Angelos
Published: April 2003

Proposes the use of a special purpose drop‐in firewall/VPN gateway called Sieve, that can be inserted between the mobile workstation and the network to provide individualized security services for that particular station. Sieve is meant to be used like an external modem: the user only needs to plug it in. Its existence is transparent to the user, requiring no modification to the workstation configuration. To function in this role, Sieve has been designed to be compact, low‐cost, requiring little administration or maintenance. Discusses the features and advantages of the system and demonstrates how Sieve was used in various application areas (home, university environment, etc.).
An Analytical Model for Tailor Welded Blank Forming
Authors: Kinsey Brad L. , Cao Jian
Published: April 2003

Tailor Welded Blanks (TWBs) offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. In order to take advantage of these benefits, however, designers need to overcome the reduced formability of TWBs and be able to accurately predict unique characteristics related to TWB forming early in the design process. In this paper, an analytical model to predict the weld line movement and forming height for a uniform binder force, TWB forming application is presented. Comparison to numerical simulation results demonstrates the accuracy of this methodology. The analytical model provides designers a valuable tool to determine the location of steps on the die surface to accommodate the weld line movement and the potential forming height for a TWB forming with a uniform binder force. The methodology presented here has the potential to be extended to analyze a non-uniform binder force forming of TWBs.
Reliability-Based Structural Design of Ship-Type FPSO Units
Authors: Sun Hai-Hong , Soares C. Guedes
Published: April 2003

Design criteria based on LRFD format is proposed here for FPSO structural design. The design criteria of FPSO structures accounts for load effects and their probabilistic distributions, in which an “Environmental Severity Factor” is introduced for considering the site-specific conditions of hydrodynamic loading; and for limit states for three types of failure modes: primary, secondary and tertiary. The method presented in this paper can be applied to develop structural design criteria for new-built FPSO and converted FPSO from oil tankers.
Structural Reliability of Monopods Under Storm Overload
Authors: Ronalds B. F. , Anthony N. R. , Tuty S. , Fakas E.
Published: April 2003

The structural reliability of a generic caisson under storm overload is investigated using typical Australian North West Shelf (NWS) environmental data. The bending moment due to the hydrodynamic loading is shown to increase in proportion to the fourth power of the wave height in certain critical cases, rather than the more usual exponent of α≈2. Combined with the steep wave height return period curve on the NWS, this may lead to low structural reliability, as much as two orders of magnitude smaller than more typical structures in other locations. The wave height exponent α varies with water depth and environmental force type (e.g. shear or bending moment) and increases rapidly near water line. This nonproportional nature of the loading is not addressed in design codes of practice or in traditional pushover analysis.
Fixture Kinematic Analysis Based on the Full Contact Model of Rigid Bodies
Authors: Wang Michael Yu , Liu Tong , Pelinescu Diana M.
Published: April 2003

The conventional point-kinematic model of fixtures has only treated point geometry of the contacts between locators and workpiece. However, this model, which ignores the underlying surface properties of the locators-plus-workpiece system, is inherently incapable of capturing the effects of the geometric properties important to accurate positioning of the workpiece. In this paper, we present a fixture kinematic analysis based on the full kinematics of locator-workpiece contact. This model incorporates a “virtual” kinematic chain with meshing parameters of contact kinematics in a velocity formulation. Conditions of a deterministic fixture are derived. It is shown that the workpiece position and orientation are completely characterized by the kinematic properties of the locator contacts with the workpiece, including not only the arbitrary locator location errors but also the surface properties at nonprismatic locator-workpiece contacts. This is illustrated with numerical examples. The fixture kinematic analysis developed here has a strong implication for designing fixtures with high locating precision requirements.
Contact Force Prediction and Force Closure Analysis of a Fixtured Rigid Workpiece With Friction
Authors: Wang Michael Yu , Pelinescu Diana M.
Published: April 2003

Analysis and characterization of workpiece-fixture contact forces are important in fixture design since they define the fixture stability during clamping and strongly influence workpiece accuracy during manufacturing. This paper presents a method for predicting and analyzing the normal and frictional contact forces between workpiece-fixture contacts. The fixture and workpiece are considered to be rigid bodies, and the model solution is solved as a constrained quadratic optimization by applying the minimum norm principle. The model reveals some intricate properties of the passive contact forces, including the potential of a locator release and the history dependency during a sequence of clamping and/or external force loading. Further, a notion of passive force closure is considered to characterize the passive nature of the fixture forces. Geometric conditions for two types of passive force closure (concordant and discordant closures) are provided, showing a complication of released locator under clamping with a limited role in force closure. Model predictions are shown to be in good agreement with known results of an elastic-contact model prediction and experimental measurements. The passive force closure conditions are illustrated with examples. This presented method is conceptually simple and computationally efficient. It is particularly useful in the early stages of fixture design and process planning.
Mechanistic Model for Spade Drills for Wood Drilling Operations, Part 2: Analysis of Spade Bit Geometry and Performance
Authors: Zhao Hanxin , Ehmann Kornel F.
Published: April 2003

In this part of the paper the analytical models for the prediction of the force system, established in Part 1, in conjunction with a complete geometric model of the spade bit, will be used in a systematic simulation analysis of the spade drill’s performance. The aim of this analysis is to identify the most desirable geometric characteristics of the different topological features of the spade bit that would result in desirable performance measures expressed in terms of reduced torque and thrust force. The obtained results are intended to guide the development of more efficient tools of this type.
Extracellular Adherence Protein from
Staphylococcus aureus
Enhances Internalization into Eukaryotic Cells
Authors: Haggar Axana , Hussain Muzaffar , Lönnies Helena , Herrmann Mathias , Norrby-Teglund Anna , Flock Jan-Ingmar
Published: April 2003

In this study we have shown that Eap (extracellular adherence protein) plays a role in the internalization process of
Staphylococcus aureus
into eukaryotic cells. Eap is a protein that is mostly extracellularly and to a lesser extent is bound to the bacterial surface as a result of rebinding. Eap is able to bind to several plasma proteins, such as fibronectin, fibrinogen, and prothrombin. It has the capacity to form oligomers and is able to agglutinate
S. aureus.
A mutant strain, Newman mAH12 (
eap
:: Ery
r
), with a deficient
eap
gene was used in the present study. We have demonstrated that (i) strain Newman mAH12 could adhere to and become internalized to a higher extent by eukaryotic cells than the isogenic mutant, (ii) strain Newman mAH12 complemented with the
eap
gene displayed restoration of the internalization level, (iii) externally added Eap enhanced the internalization of laboratory and clinical
S. aureus
strains as well as of
S. carnosus
(a coagulase-negative species devoid of proteins important for internalization), and (iv) antibodies against Eap were able to block the internalization process in strain Newman mAH12 and clinical isolates. Eap, with its broad binding capacity and its surface localization, thus seems to contribute to the internalization of
S. aureus
into eukaryotic cells. We therefore propose a novel internalization pathway for
S. aureus
in which Eap plays an enhancing role.
Trojan Horse Effect: Phagocyte-Mediated
Streptococcus iniae
Infection of Fish
Authors: Zlotkin Amir , Chilmonczyk Stefan , Eyngor Marina , Hurvitz Avshalom , Ghittino Claudio , Eldar Avi
Published: April 2003

The salmonid macrophage-like cell line RTS-11 and purified trout pronephros phagocytes were used to analyze in vitro entry and survival of two
Streptococcus iniae
serotypes. Efficient invasion by
S. iniae
occurred in both cells, but only the type II strain persisted in pronephros phagocytes for at least 48 h. Ex vivo models of opsonin-dependent phagocytosis by pronephros phagocytes demonstrated increased phagocytosis efficacy. Analysis of phagocytes collected from diseased fish demonstrated that ∼70% of the bacteria contained in the blood during the septic phase of the disease were located within phagocytes, suggesting an in vivo intracellular lifestyle. In addition to the augmented levels of bacteremia and enhanced survival within phagocytes,
S. iniae
type II induces considerable apoptosis of phagocytes. These variabilities in intramacrophage lifestyle might explain differences in the outcomes of infections caused by different serotypes. The generalized septic disease associated with serotype II strains is linked not only to the ability to enter and multiply within macrophages but also to the ability to cause considerable death of macrophages via apoptotic processes, leading to a highly virulent infection. We assume that the phenomenon of survival within phagocytes coupled to their apoptosis plays a crucial role in
S. iniae
infection. In addition, it may provide the pathogen an efficient mechanism of translocation into the central nervous system.
Brucella abortusRB51 Induces Protection in Mice Orally Infected with the Virulent StrainB. abortus2308
Authors: Pasquali Paolo , Rosanna Adone , Pistoia Claudia , Petrucci Paola , Ciuchini Franco
Published: April 2003

Brucellae are gram-negative, facultative intracellular bacteria which are one of the most common causes of abortion in animals. In addition, they are the source of a severe zoonosis. In this trial, we evaluated the effect of oral inoculation ofBrucella abortusRB51 in mice against a challenge infection withB. abortus2308. First, we showed that a gastric acid neutralization prior to the oral inoculation contributed to a more homogeneous and consistent infection with both vaccine strainB. abortusRB51 and virulent strainB. abortus2308. Successively, we assessed the clearance and the immune response following an oral infection withB. abortusRB51. Oral inoculation gave a mild infection which was cleared 42 days after infection, and it induced a delayed humoral and cell-mediated immune response. Finally, we immunized mice by oral inoculation withB. abortusRB51, and we challenged them with the virulent strainB. abortus2308 by an oral or intraperitoneal route 42 days after vaccination. Oral inoculation ofB. abortusRB51 was able to give protection to mice infected with the virulent strainB. abortus2308 by the oral route but not to mice infected intraperitoneally. Our results indicate that oral inoculation of mice withB. abortusRB51 is able to give a protective immunity against an oral infection with virulent strains, and this protection seems to rely on an immune response at the mucosal level.
Oral Immunization with a Recombinant Malaria Protein Induces Conformational Antibodies and Protects Mice against Lethal Malaria
Authors: Wang Lina , Kedzierski Lukasz , Wesselingh Steven L. , Coppel Ross L.
Published: April 2003

The increasing death toll from malaria, due to the decreasing effectiveness of current prophylactic and therapeutic regimens, has sparked a search for alternative methods of control, such as vaccines. Although several single proteins have shown some promise as subunit vaccines against sexual blood stages in experimental systems, it is clear that multicomponent vaccines are required. Many logistic difficulties make such an approach prohibitively expensive. In an effort to try to overcome some of these issues, we examined the possibility of oral immunization as a route for inducing host protective immunity. We report here that oral feeding of a malaria protein induced serum antibody levels similar to those induced by intraperitoneal immunization with Freund's adjuvant. Further, responses to conformational epitopes were induced. In the rodent challenge system, significant levels of protection to lethal challenge with malaria were induced in mice. The protective efficacy was highly correlated with antibody levels, which depended on the antigen dosage and required cholera toxin subunit B as an oral adjuvant. These findings offer new approaches to the development of a malaria vaccine and provide justification for the investigation of transgenic plants as a means of vaccine delivery.
Potential of Lipid Core Peptide Technology as a Novel Self-Adjuvanting Vaccine Delivery System for Multiple Different Synthetic Peptide Immunogens
Authors: Olive Colleen , Batzloff Michael , Horváth Aniko , Clair Timothy , Yarwood Penny , Toth Istvan , Good Michael F.
Published: April 2003

This study demonstrates the effectiveness of a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens by use of lipid core peptide (LCP) technology. An LCP formulation incorporating two different protective epitopes of the surface antiphagocytic M protein of group A streptococci (GAS)—the causative agents of rheumatic fever and subsequent rheumatic heart disease—was tested in a murine parenteral immunization and GAS challenge model. Mice were immunized with the LCP-GAS formulation, which contains an M protein amino-terminal type-specific peptide sequence (8830) in combination with a conserved non-host-cross-reactive carboxy-terminal C-region peptide sequence (J8) of the M protein. Our data demonstrated immunogenicity of the LCP-8830-J8 formulation in B10.BR mice when coadministered in complete Freund's adjuvant and in the absence of a conventional adjuvant. In both cases, immunization led to induction of high-titer GAS peptide-specific serum immunoglobulin G antibody responses and induction of highly opsonic antibodies that did not cross-react with human heart tissue proteins. Moreover, mice were completely protected from GAS infection when immunized with LCP-8830-J8 in the presence or absence of a conventional adjuvant. Mice were not protected, however, following immunization with an LCP formulation containing a control peptide from aSchistosomasp. These data support the potential of LCP technology in the development of novel self-adjuvanting multi-antigen component vaccines and point to the potential application of this system in the development of human vaccines against infectious diseases.
LipL21 Is a Novel Surface-Exposed Lipoprotein of Pathogenic
Leptospira
Species
Authors: Cullen Paul A. , Haake David A. , Bulach Dieter M. , Zuerner Richard L. , Adler Ben
Published: April 2003

Leptospira
is the etiologic agent of leptospirosis, a bacterial zoonosis distributed worldwide. Leptospiral lipopolysaccharide is a protective immunogen, but the extensive serological diversity of leptospires has inspired a search for conserved outer membrane proteins (OMPs) that may stimulate heterologous immunity. Previously, a global analysis of leptospiral OMPs (P. A. Cullen, S. J. Cordwell, D. M. Bulach, D. A. Haake, and B. Adler, Infect. Immun.
70:
2311-2318, 2002) identified pL21, a novel 21-kDa protein that is the second most abundant constituent of the
Leptospira interrogans
serovar Lai outer membrane proteome. In this study, we identified the gene encoding pL21 and found it to encode a putative lipoprotein; accordingly, the protein was renamed LipL21. Southern hybridization analysis revealed the presence of
lipL21
in all of the pathogenic species but in none of the saprophytic species examined. Alignment of the LipL21 sequence from six strains of
Leptospira
revealed 96 to 100% identity. When specific polyclonal antisera to recombinant LipL21 were used, LipL21 was isolated together with other known leptospiral OMPs by both Triton X-114 extraction and sucrose density gradient membrane fractionation. All nine strains of pathogenic leptospires investigated by Western blotting, whether culture attenuated or virulent, were found to express LipL21. In contrast, the expression of LipL21 or an antigenically related protein could not be detected in nonpathogenic
L. biflexa
. Infected hamster sera and two of eight human leptospirosis sera tested were found to react with recombinant LipL21. Native LipL21 was found to incorporate tritiated palmitic acid, consistent with the prediction of a lipoprotein signal peptidase cleavage site. Biotinylation of the leptospiral surface resulted in selective labeling of LipL21 and the previously known OMPs LipL32 and LipL41. These findings show that LipL21 is a surface-exposed, abundant outer membrane lipoprotein that is expressed during infection and conserved among pathogenic
Leptospira
species.
Modulation of Intestinal Muscle Contraction by Interleukin-9 (IL-9) or IL-9 Neutralization: Correlation with Worm Expulsion in Murine Nematode Infections
Authors: Khan W. I. , Richard M. , Akiho H. , Blennerhasset P. A. , Humphreys N. E. , Grencis R. K. , Van Snick J. , Collins S. M.
Published: April 2003

Immune responses associated with intestinal nematode infections are characterized by the activation of T-helper 2 (Th2) cells. Previous studies demonstrated that during
Trichinella spiralis
infection, Th2 cells contribute to the development of intestinal muscle hypercontractility and to worm eviction from the gut, in part through signal transducer and activator of transcription factor 6 (Stat6). Interleukin-9 (IL-9), a Th2-cell-derived cytokine, has pleiotropic activities on various cells that are not mediated through Stat6. In this study, we investigated the role of IL-9 in the generation of enteric muscle hypercontractility in mice infected with the intestinal parasite
T. spiralis
and the cecal parasite
Trichuris muris
. Treatment of mice with IL-9 enhanced infection-induced jejunal muscle hypercontractility and accelerated worm expulsion in
T. spiralis
infection. These effects were associated with an up-regulation of IL-4 and IL-13 production from in vitro-stimulated spleen cells. In addition, increases in the level of intestinal goblet cells and in the level of mouse mucosal mast cell protease 1 (MMCP-1) in serum were observed in infected mice following IL-9 administration. However, the neutralization of IL-9 by anti-IL-9 vaccination or by anti-IL-9 antibody had no significant effect on worm expulsion or muscle contraction in
T. spiralis
-infected mice. In contrast, the neutralization of IL-9 significantly attenuated
T. muris
infection-induced colonic muscle hypercontractility and inhibited worm expulsion. The attenuated expulsion of the parasite by IL-9 neutralization was not accompanied by changes in goblet cell hyperplasia or the MMCP-1 level. These findings suggest that IL-9 contributes to intestinal muscle function and to host protective immunity and that its importance and contribution may differ depending on the type of nematode infection.
Immunosuppression in Hamsters with Progressive Visceral Leishmaniasis Is Associated with an Impairment of Protein Kinase C Activity in Their Lymphocytes That Can Be Partially Reversed by Okadaic Acid or Anti-Transforming Growth Factor β Antibody
Authors: Mookerjee Ananda , Sen Parimal C. , Ghose Asoke C.
Published: April 2003

Progressive visceral infection of golden hamsters byLeishmania donovaniamastigotes led to gradual impairment of the proliferative responses of their splenic or peripheral blood mononuclear cells (SPMC or PBMC, respectively) to in vitro stimulation with phorbol 12-myristate 13-acetate (PMA) and ionomycin (Io). Removal of macrophage-like adherent cells from SPMC or PBMC of infected animals (I-SPMC or I-PBMC) was earlier shown to restore almost completely their lymphoproliferative responses to PMA plus Io. The present study was directed to evaluate the status of protein kinase C (PKC), a molecule(s) known to play a key role in the lymphoproliferative process. Our results demonstrate that PKC activities (Ca2+, phosphatidyl serine, and diacyl glycerol dependent) in the cytosolic fraction of untreated nonadherent I-SPMC or I-PBMC as well as in the membrane fraction of PMA-treated cells were decreased significantly relative to those for normal controls. However, removal of adherent cells from I-SPMC or I-PBMC and subsequent overnight in vitro cultivation of nonadherent cells (lymphocytes) resulted in significant restoration of PKC activity in the cytosolic or membrane fraction of untreated or PMA-treated cells, respectively. Partial, though significant, restoration of PKC activity could also be achieved in the membrane fraction of PMA-treated cells following overnight in vitro treatment of I-SPMC or I-PBMC with the Ser/Thr phosphatase inhibitor okadaic acid (OA) or an anti-transforming growth factor β (anti-TGF-β) neutralizing antibody. These results correlated well with the ability of OA or the anti-TGF-β antibody to restore the lymphoproliferative response of I-SPMC or I-PBMC following stimulation with PMA plus Io. Interestingly enough, immunoblotting experiments failed to show any reduction in the level or translocation (following PMA treatment) of conventional PKC isoforms in the SPMC or PBMC of infected animals compared to those of normal controls. The results presented in this study suggest that the adherent cells generated in the SPMC or PBMC of infected animals exert a suppressive effect on the proliferative response of nonadherent cells (lymphocytes) which is likely to be mediated through the downregulation of the activation pathway involving PKC and its downstream molecules such as mitogen-activated protein kinases. Further, the observed suppression of PKC activity and subsequent lymphoproliferative responses can be attributed to alternations in the intracellular phosphorylation-dephosphorylation events. The relevance of these results is discussed in relation to the role of TGF-β, levels of which are known to be elevated in visceral leishmaniasis.