bluuebunny/crossref_metadata_2025 huggingface dataset:
Recursive Identification of Thermal Convection
Authors: Park H. M. , Lee W. J.
Published: March 2003

A method is developed for the recursive identification of thermal convection system governed by the Boussinesq equation using an extended Kalman filter. A computationally feasible Kalman filter is constructed by reducing the Boussinesq equation to a small number of ordinary differential equations by means of the Karhunen-Loe`ve Galerkin procedure which is a type of Galerkin method employing the empirical eigenfunctions of the Karhunen-Loe`ve decomposition. Employing the Kalman filter constructed by using the reduced order model, the thermal convection induced by a spatially varying heat flux at the bottom is identified recursively by using either the Boussinesq equation or the reduced order model itself. The recursive identification technique developed in the present work is found to yield accurate results for thermal convection even with approximate covariance equation and noisy measurements. It is also shown that a reasonably accurate and computationally feasible method of recursive identification can be constructed even with a relatively inaccurate reduced order model.
Asymptotic Parameter Estimation via Implicit Averaging on a Nonlinear Extended System
Authors: Chatterjee Anindya , Cusumano Joseph P.
Published: March 2003

We present an observer for parameter estimation in nonlinear oscillating systems (periodic, quasiperiodic or chaotic). The observer requires measurements of generalized displacements. It estimates generalized velocities on a fast time scale and unknown parameters on a slow time scale, with time scale separation specified by a small parameter ε. Parameter estimates converge asymptotically like e−εt where t is time, provided the data is such that a certain averaged coefficient matrix is positive definite. The method is robust: small model errors and noise cause small estimation errors. The effects of zero mean, high frequency noise can be reduced by faster sampling. Several numerical examples show the effectiveness of the method.
Robust Perfect Tracking Control With Discrete Sliding Mode Controller
Authors: Wang Jian , Van Brussel Hendrik , Swevers Jan
Published: March 2003

The closed-loop transfer function of a plant controlled with a classical feedback controller, depends on the dynamics of the plant. Since most feedforward tracking controllers are designed based on this closed-loop transfer function, they are not robust against plant model uncertainties. Sliding-mode controllers have the property that when the system is on the switching line, the closed-loop behavior is independent of the plant dynamics. As a result, it can be expected that a feedforward control design based on this closed-loop behavior is robust against plant model uncertainties. This paper studies this feedforward robustness issue in detail and verifies the results on an experimental test setup: a stage driven by a linear motor. An integrated procedure is proposed in designing the closed-loop discrete-time sliding mode controller using the reaching law method.
Discrete-Delay-Independent and Discrete-Delay-Dependent Criteria for a Class of Neutral Systems
Authors: Lien Chang-Hua , Chen Jenq-Der
Published: March 2003

In this paper, the asymptotic stability for a class of neutral systems with discrete and distributed multiple time delays is considered. Discrete-delay-independent and discrete-delay-dependent criteria are proposed to guarantee stability for such systems. The resulting stability criteria are written in the form of spectral radius and linear matrix inequality (LMI). Some numerical examples are given to illustrate that our obtained results are less conservative.
Nonlinear Analysis of Train Derailment in Severe Braking
Authors: Durali Mohammad , Shadmehri Baabak
Published: March 2003

A nonlinear comprehensive model has been developed in this paper to study the train derailment and hunting in severe braking conditions. The train consists of cars each having 40 dof, connected to each other by couplers and buffers. The car model is nonlinear and three-dimensional and includes nonlinear springs and dampers of primary and secondary suspensions, dry friction between different parts such as car body and side bearers, center-plate parts, wheelset bearings and bogie frames, and also clearances and mechanical stops. Nonlinearities of wheel and rail profiles, pressure build-up delay in brake circuit, and nonlinearities of connecting parts have also been included in the model. A complete set of equations has been derived for the train. The equations are solved numerically for different car weight configurations when severe brake is applied. Derailment coefficient is determined for several train make-ups and tendency of the wheels towards derailment is investigated. Optimum configuration of cars in a light-heavy set, and critical derailment velocity can be determined to minimize the tendency of train derailment. The results are in excellent agreement with the field experience.
Load Haul Dump Vehicle Kinematics and Control
Authors: Ridley Peter , Corke Peter
Published: March 2003

This paper examines the kinematics and control of a Load Haul Dump Vehicle used in underground mining operations. The aim of the work is to develop an autonomous guidance strategy. A linear, state-space, mathematical model of the vehicle is derived purely from geometric consideration of the vehicle and its desired path. Autonomous regulation of the vehicle is shown to be theoretically feasible using state variable feedback of displacement, heading, and curvature error. A relationship between stability and vehicle speed is derived. This expression forms the basis of an adaptive tuning strategy, which optimizes the vehicle’s dynamic response.
Linear Robust Control of Identified Nonlinear Inverse Compensated SI Engine
Authors: Petridis A. P. , Shenton A. T.
Published: March 2003

A technique based on Horowitz’s nonlinear quantitative feedback theory is presented, in which the size of the uncertainty is reduced by cancellation of the plant nonlinearity through nonlinear inverse compensation. Linear identification of the open loop nonlinear inverse compensated plant is used to obtain an unstructured uncertainty representation, however, rather than computing QFT templates based on parametric uncertainty. An increase in achievable robust performance with any linear robust performance control design technique may then be obtained. The method is experimentally validated by application to a SISO automotive SI engine idle speed control problem using an electric dynamometer.
Reducing the Impact of False Alarms in Induction Motor Fault Diagnosis
Authors: Kim Kyusung , Parlos Alexander G.
Published: March 2003

Early detection and diagnosis of incipient faults is desirable for on-line condition assessment, product quality assurance, and improved operational efficiency of induction motors. At the same time, reducing the probability of false alarms increases the confidence of equipment owners in this new technology. In this paper, a model-based fault diagnosis system recently proposed by the authors for induction motors is experimentally compared for fault detection and false alarm performance with a more traditional signal-based motor fault estimator. In addition to the nameplate information required for the initial set-up, the proposed model-based fault diagnosis system uses measured motor terminal currents and voltages, and motor speed. The motor model embedded in the diagnosis system is empirically obtained using dynamic recurrent neural networks, and the resulting residuals are processed using wavelet packet decomposition. The effectiveness of the model-based diagnosis system in detecting the most widely encountered motor electrical and mechanical faults, while minimizing the impact of false alarms resulting from power supply and load variations, is demonstrated through extensive testing with staged motor faults. The model-based fault diagnosis system is scalable to motors of different power ratings and it has been successfully tested with fault data from 2.2kW,373kW, and 597kW induction motors.
A dipole in a dielectric: Intriguing results and shape dependence of the distant electric field
Authors: Amaral R. L. P. G. , Lemos N. A.
Published: March 2003

The field of a point electric dipole in an infinite dielectric is obtained by placing the dipole at the center of a spherical cavity of radius R inside the dielectric and then letting R→0. The result disagrees with the elementary answer found in textbooks. The mathematical and physical reasons for the disagreement are discussed. The discrepancy is confirmed by the same limiting procedure applied to a uniformly polarized sphere embedded in the dielectric. We next solve the same problem for a polarized spheroid immersed in an infinite dielectric and find that the asymptotic potential shows an unexpected shape dependence, even after taking the limit of an arbitrarily small spheroid. By considering both oblate and prolate spheroids and taking appropriate limits, we recover either the elementary textbook answer or the previous result found for the polarized sphere.
Simple derivation of Newtonian mechanics from the principle of least action
Authors: Hanc Jozef , Tuleja Slavomir , Hancova Martina
Published: March 2003

We present a method for introducing students to the classical principle of least action, using a novel approach based on the ordinary calculus of one variable. We define the classical action for a path and draw the connection between it and Newton’s laws for a free particle and for a particle in a conservative potential. The use of software to help students visualize the principle of least action and analyze rectilinear motion is discussed. We also briefly discuss the origin of the principle of least action in Feynman’s sum over paths formulation of quantum mechanics.
Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects
Authors: Davis Tamara M. , Lineweaver Charles H. , Webb John K.
Published: March 2003

We use the dynamics of a galaxy, set up initially at a constant proper distance from an observer, to derive and illustrate two counter-intuitive general relativistic results. Although the galaxy does gradually join the expansion of the universe (Hubble flow), it does not necessarily recede from us. In particular, in the currently favored cosmological model, which includes a cosmological constant, the galaxy recedes from the observer as it joins the Hubble flow, but in the previously favored cold dark matter model, the galaxy approaches, passes through the observer, and joins the Hubble flow on the opposite side of the sky. We show that this behavior is consistent with the general relativistic idea that space is expanding and is determined by the acceleration of the expansion of the universe—not a force or drag associated with the expansion itself. We also show that objects at a constant proper distance will have a nonzero redshift; receding galaxies can be blueshifted and approaching galaxies can be redshifted.
Josephson junctions in a magnetic field: Insights from coupled pendula
Authors: Altshuler E. , Garcı́a R.
Published: March 2003

Josephson effects are macroscopic quantum phenomena that can be understood at the undergraduate level with the help of mechanical analogs. Although Josephson junctions in zero magnetic field can be modeled by pendulum analogs, a simple mechanical model of Josephson junctions in nonzero fields has been elusive. We demonstrate how the magnetic field dependence of the maximum Josephson current can be visualized by the analogs of a set of interconnected pendula attached to pulleys.
Physics of the cardiovascular system: An intrinsic control mechanism of the human heart
Authors: Uehara Mituo , Sakane Kumiko K.
Published: March 2003

Differential equations for the cardiovascular system are derived by applying the continuity equation of fluid mechanics to the rate of blood flow and variation of blood volume in different parts of the system. The equations are used to explain the Frank–Starling mechanism, which plays an important role in the maintenance of the stability of the distribution of blood in the system. This treatment can be easily understood by undergraduate physics students with no previous knowledge of human physiology.
Resource Letter: SM-1: The standard model and beyond
Authors: Rosner Jonathan L.
Published: March 2003

This Resource Letter provides a guide to literature on the standard model of elementary particles and possible extensions. In the successful theory of quarks and leptons and their interactions, important questions remain, such as the mechanism of electroweak symmetry breaking, the origin of quark and lepton masses, the source of the baryon asymmetry of the Universe, and the makeup of its matter and energy density. References are cited for quarks and leptons, gauge theories, color and chromodynamics, weak interactions, electroweak unification, CP violation, dynamics of heavy quarks, Higgs bosons, precision electroweak measurements, supersymmetry, dynamical electroweak symmetry breaking, composite quarks and leptons, grand unification and extended gauge groups, string theories, large extra dimensions, neutrino masses, cosmic microwave background radiation, dark matter, dark energy, accelerator facilities, and non-accelerator experiments.
Evolution of Virulence in a Plant Host-Pathogen Metapopulation
Authors: Thrall Peter H. , Burdon Jeremy J.
Published: March 2003

In a wild plant–pathogen system, host resistance and pathogen virulence varied markedly among local populations. Broadly virulent pathogens occurred more frequently in highly resistant host populations, whereas avirulent pathogens dominated susceptible populations. Experimental inoculations indicated a negative trade-off between spore production and virulence. The nonrandom spatial distribution of pathogens, maintained through time despite high pathogen mobility, implies that selection favors virulent strains of
Melampsora lini
in resistant
Linum marginale
populations and avirulent strains in susceptible populations. These results are consistent with gene-for-gene models of host-pathogen coevolution that require trade-offs to prevent pathogen virulence increasing until host resistance becomes selectively neutral.
Taming Winfree Turbulence of Scroll Waves in Excitable Media
Authors: Alonso Sergio , Sagués Francesc , Mikhailov Alexander S.
Published: March 2003

Winfree turbulence of scroll waves is a special kind of spatiotemporal chaos that exists exclusively in three-dimensional excitable media and is currently considered one of the principal mechanisms of cardiac fibrillation. A chaotic wave pattern develops through the negative-tension instability of vortex filaments, which tend to spontaneously stretch, bend, loop, and produce an expanding tangle that fills up the volume. We demonstrate that such turbulence can readily be controlled by weak nonresonant modulation of the medium excitability. Depending on the forcing frequency, either suppression or induction of turbulence can be achieved.
Asymmetric Inheritance of Oxidatively Damaged Proteins During Cytokinesis
Authors: Aguilaniu Hugo , Gustafsson Lena , Rigoulet Michel , Nyström Thomas
Published: March 2003

Carbonylated proteins were visualized in single cells of the budding yeast
Saccharomyces cerevisiae
, revealing that they accumulate with replicative age. Furthermore, carbonylated proteins were not inherited by daughter cells during cytokinesis. Mother cells of a yeast strain lacking the
sir2
gene, a life-span determinant, failed to retain oxidatively damaged proteins during cytokinesis. These findings suggest that a genetically determined, Sir2p-dependent asymmetric inheritance of oxidatively damaged proteins may contribute to free-radical defense and the fitness of newborn cells.
Climate and the Collapse of Maya Civilization
Authors: Haug Gerald H. , Günther Detlef , Peterson Larry C. , Sigman Daniel M. , Hughen Konrad A. , Aeschlimann Beat
Published: March 2003

In the anoxic Cariaco Basin of the southern Caribbean, the bulk titanium content of undisturbed sediment reflects variations in riverine input and the hydrological cycle over northern tropical South America. A seasonally resolved record of titanium shows that the collapse of Maya civilization in the Terminal Classic Period occurred during an extended regional dry period, punctuated by more intense multiyear droughts centered at approximately 810, 860, and 910 A.D. These new data suggest that a century-scale decline in rainfall put a general strain on resources in the region, which was then exacerbated by abrupt drought events, contributing to the social stresses that led to the Maya demise.
Modulating Sphingolipid Biosynthetic Pathway Rescues Photoreceptor Degeneration
Authors: Acharya Usha , Patel Shetal , Koundakjian Edmund , Nagashima Kunio , Han Xianlin , Acharya Jairaj K.
Published: March 2003

Mutations in proteins of the
Drosophila
phototransduction cascade, a prototypic guanine nucleotide–binding protein–coupled receptor signaling system, lead to retinal degeneration and have been used as models to understand human degenerative disorders. Here, modulating the sphingolipid biosynthetic pathway rescued retinal degeneration in
Drosophila
mutants. Targeted expression of
Drosophila
neutral ceramidase rescued retinal degeneration in arrestin and phospholipase C mutants. Decreasing flux through the de novo sphingolipid biosynthetic pathway also suppressed degeneration in these mutants. Both genetic backgrounds modulated the endocytic machinery because they suppressed defects in a dynamin mutant. Suppression of degeneration in arrestin mutant flies expressing ceramidase correlated with a decrease in ceramide levels. Thus, enzymes of sphingolipid metabolism may be suitable targets in the therapeutic management of retinal degeneration.
Epitaxial BiFeO
3
Multiferroic Thin Film Heterostructures
Authors: Wang J. , Neaton J. B. , Zheng H. , Nagarajan V. , Ogale S. B. , Liu B. , Viehland D. , Vaithyanathan V. , Schlom D. G. , Waghmare U. V. , Spaldin N. A. , Rabe K. M. , Wuttig M. , Ramesh R.
Published: March 2003

Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO
3
, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.
Grain Boundary Scars and Spherical Crystallography
Authors: Bausch A. R. , Bowick M. J. , Cacciuto A. , Dinsmore A. D. , Hsu M. F. , Nelson D. R. , Nikolaides M. G. , Travesset A. , Weitz D. A.
Published: March 2003

We describe experimental investigations of the structure of two-dimensional spherical crystals. The crystals, formed by beads self-assembled on water droplets in oil, serve as model systems for exploring very general theories about the minimum-energy configurations of particles with arbitrary repulsive interactions on curved surfaces. Above a critical system size we find that crystals develop distinctive high-angle grain boundaries, or scars, not found in planar crystals. The number of excess defects in a scar is shown to grow linearly with the dimensionless system size. The observed slope is expected to be universal, independent of the microscopic potential.
Millennial Status Report As Debate Wanes
Authors: Livezey Bradley C.
Published: March 2003

Mesozoic Birds
Above the Heads of Dinosaurs. Luis M. Chiappe and Lawrence M. Witmer, Eds. University of California Press, Berkeley, 2002. 532 pp. $95, £66. ISBN 0-520-20094-2.

Covering a wide variety of aspects of the nature and evolution of birds during the Mesozoic, the contributors discuss topics including the origin, phylogeny, functional transformations, and morphological diversity of the clade through its first 85 million years.
The Impact of Nanoscience on Heterogeneous Catalysis
Authors: Bell Alexis T.
Published: March 2003

Most catalysts consist of nanometer-sized particles dispersed on a high-surface-area support. Advances in characterization methods have led to a molecular-level understanding of the relationships between nanoparticle properties and catalytic performance. Together with novel approaches to nanoparticle synthesis, this knowledge is contributing to the design and development of new catalysts.
Macroporous Hydrogels Based on 2-Hydroxyethyl Methacrylate. Part 1. Copolymers of 2-Hydroxyethyl Methacrylate with Methacrylic Acid
Authors: Přádný Martin , Lesný Petr , Fiala Jindřich , Vacík Jiří , Šlouf Miroslav , Michálek Jiří , Syková Eva
Published: March 2003

A series of macroporous crosslinked copolymers of 2-hydroxyethyl methacrylate (HEMA) with methacrylic acid (MA) was prepared in the presence of fractionated particles of sodium chloride. The hydrogels were characterized by the number of pores in unit volume, the pore size, the water content in pores and diffusion parameters. The structure of the hydrogels was followed by confocal and scanning electron microscopy.
Development of a folded thrust stack: Humber Arm Allochthon, Bay of Islands, Newfoundland Appalachians
Authors: Waldron John WF , Henry Amber D , Bradley James C , Palmer Sarah E
Published: March 2003

In the Humber Arm area of the western Newfoundland Appalachians, four distinct stratigraphic successions derived from the Laurentian continental margin are exposed. Each succession is believed to be characteristic of a separate thrust sheet. The platform sheet represents the ancient Laurentian shelf and its foreland basin cover; the Watsons Brook sheet is characterized by a succession including shelf-margin carbonates overlying foreland basin clastics; the Corner Brook sheet comprises continental slope and rise clastic and carbonate sedimentary rocks of the Humber Arm Supergroup; and the Woods Island sheet includes clastics of the Blow Me Down Brook formation that overlie mafic volcanics. Sheets are subdivided by thrusts into tectonic slices. Disrupted units and mélange, with scaly S1 foliation, are found along the boundaries of some slices. Thrust sheets and related structures have been deformed by F2 folds with axial planar S2 cleavage. S1 scaly foliations are transposed into parallelism with S2. There is a transition in the style of F2 folds across the area, from upright and subhorizontal in the west to overturned folds with west-dipping axial planes and steeply raking or reclined fold hinges in the east. Strongly curved fold hinges may reflect later shearing along the S2 surfaces, producing sheath-like fold geometries. Shear zones close to the east edge of the outcrop of the Watsons Brook sheet display kinematic indicators indicating both D2 reverse-sense and D3 normal-sense dip-slip shears. Subsequent events produced L4 and L5 crenulation lineations on the S2 surfaces. At minimum, several tens of kilometres of shortening affected the part of the margin preserved in the Humber Arm area; true shortening and transport amounts may have been much larger.
Reappraisal of the Beekmantown Group sedimentology and stratigraphy, Montréal area, southwestern Quebec: implications for understanding the depositional evolution of the Lower-Middle Ordovician Laurentian passive margin of eastern Canada
Authors: Hersi O Salad , Lavoie D , Nowlan G S
Published: March 2003

Detailed lithostratigraphic mapping of the Beekmantown Group of southwestern Quebec has refined the field application of the previously proposed tripartite division of the group (i.e., Theresa, Beauharnois, and Carillon formations). The group is a peritidal-dominated succession that accumulated on the epicontinental Laurentian passive margin. Biostratigraphic data based on conodonts from this group indicate an Early to early Middle Ordovician age and are partially time-correlative with the Wallace Creek to Naylor Ledge strata of the Philipsburg Group, southern Quebec. This conodont biostratigraphy sheds new light on the temporal evolution and depositional framework of the Beekmantown platform. The platform evolved as a distally steepened ramp during deposition of the Theresa Formation and the Ogdensburg Member of the Beauharnois Formation (early to middle Ibexian). Correlative strata of the Philipsburg Group include the Wallace Creek and Morgan Corner formations, which represent outer platform sediments. The coarse-grained sandstone of the Theresa Formation accumulated in the innermost platform, whereas coarse-grained carbonates of the Ogdensburg Member indicate open-marine, subtidal to intertidal carbonate sand shoals. By late Ibexian, the platform developed a pronounced margin where thrombolites flourished under high-energy conditions. These are represented by the thrombolite-rich Hasting Creek and Naylor Ledge formations of the Philipsburg Group. Consequently, a broad lagoon formed on the lee side of the platform margin, where low-energy conditions prevailed and accumulation of burrow-mottled dolostones of the Huntingdon Member of the upper Beauharnois Formation took place. The lagoon became more restricted during the latest stages of the basin fill (Whiterockian), and high intertidal to supratidal sediments of the Carillon Formation were deposited.
Stratigraphic framework for the CambrianOrdovician rift and passive margin successions from southern Quebec to western Newfoundland
Authors: Lavoie Denis , Burden Elliott , Lebel Daniel
Published: March 2003

The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the riftdrift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in earlymiddle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (TremadocianArenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession.
Neodymium isotope geochemistry of felsic volcanic and intrusive rocks from the YukonTanana Terrane in the Finlayson Lake Region, Yukon, Canada
Authors: Piercey Stephen J , Mortensen James K , Creaser Robert A
Published: March 2003

DevonianMississippian felsic rocks from the Finlayson Lake region have variable geochemical and Nd isotopic characteristics that provide insights into the tectonic and metallogenic evolution of the YukonTanana terrane (YTT), and the northern Cordillera. Late Devonian (~365360 Ma) calc-alkaline and tholeiitic arc felsic rocks in the mafic-dominated Fire Lake unit yield εNd350 = 4.8 and +0.1, respectively, and have 1.491.94 Ga depleted mantle model ages (TDM). DevonianMississippian (~360356 Ma) felsic volcanic (Kudz Ze Kayah unit, Wolverine succession) and intrusive rocks (Grass Lakes suite) associated with volcanogenic massive sulphide (VMS) deposits have εNd350 = 7.8 to 9.5 with TDM = 1.592.25 Ga. A granitoid sample from the Early Mississippian (~350345 Ma) Simpson Range plutonic suite has εNd350 = 12.9 and TDM = 2.01 Ga, similar to previously reported values for this suite. The VMS-associated Grass Lakes suite of granitoids has higher high field strength element (HFSE) and rare-earth element (REE) contents, and higher Zr/Sc, Zr/TiO2, Nb/La, and Zr/La values relative to the Simpson Range plutonic suite; these geochemical features are similar to coeval VMS-associated felsic volcanic rocks in the Kudz Ze Kayah unit. The identification of similar HFSEREE-enriched felsic volcanic and subvolcanic intrusive rocks may aid in delineating prospective regions for VMS mineralization in the YTT and other continental-margin arc to back-arc environments. The geochemical and Nd isotopic data for these YTT felsic rocks suggest that they reflect episodic mid-Paleozoic arc (Fire Lake unit; Simpson Range plutonic suite) and back-arc magmatism (Kudz Ze Kudz unit; Wolverine succession) built upon a transitional basement with variable, but significant, influence from evolved (Proterozoic) crustal materials.
Conodont biostratigraphy of the Lower to Middle Devonian Deserters Formation (new), Road River Group, northeastern British Columbia
Authors: Pyle Leanne J , Orchard Michael J , Barnes Christopher R , Landry Michelle L
Published: March 2003

A new Lower to Middle Devonian basinal unit of the Road River Group, herein formally named the Deserters Formation, contains argillaceous, crinoidal limestone and black shale deposited in a linear sub-basin of the Ospika Embayment, southern Kechika Trough. The abrupt lateral facies changes in the region, facies thickness, and occurrence of volcanics indicate a period of extensional tectonism. A total of 53 (45 kg each) samples from the Deserters Formation yielded 7766 conodont elements assigned to 14 genera representing 33 species. The formation ranges from the Lochkovian (eleanorae Zone, or lower part of the delta Zone of the Cordilleran Region) to Eifelian (australis Zone). The temporal constraints established by conodont biostratigraphy allow correlation to the Grizzly Bear Formation, a regionally restricted Lower to Middle Devonian unit in the Selwyn Basin to the north.
Greenschist-facies metamorphism of the Burgess Shale and its implications for models of fossil formation and preservation
Authors: Powell Wayne
Published: March 2003

Metamorphosed silty mudstones of the Burgess Shale and Stephen Shale formations record a poly metamorphic history. An early greenschist-facies event associated with burial by Paleozoic strata produced a nearly ubiquitous bedding-parallel cleavage (S1). Tectonic exhumation during the formation of the southern Canadian Rocky Mountains produced a domainal subgreenschist-facies retrograde overprint in which a high-angle crenulation cleavage (S2) was developed. Whereas all rocks have experienced these two events, the degree of deformation and fossil pre servation varies with position relative to the Cathedral Escarpment. This paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis. Fossil-bearing strata are composed of a typical greenschist assemblage of muscovitechloritequartzalbite, are devoid of clays, and contain an average of 0.28% organic carbon. This typical metamudstone assemblage is consistent with the typical whole-rock composition of these rocks which tends to be richer in K and Al and poorer in Fe relative to the Post-Archean Average Shale. These mineralogicalcompositional characteristics suggest that the premetamorphic clay assemblage was likely illitesmectitekaolinite, with no evidence of highly reactive species such as nontronite or Na-montmorillonite. This is contrary to the required conditions for taphonomic models involving organic preservation due to clay-related suppression of decomposition-related reactions. Metamorphism of the Burgess Shale has also re duced the total organic carbon content to <20% of initial values. This must be considered in any models that involve interpretation of organic carbon in diagenetic processes (e.g., fossil formation and determination of paleoredox conditions).
K-Ar dating constraints on the tectonothermal evolution of the external Humber zone, southern Quebec Appalachians
Authors: Glasmacher Ulrich A , Tremblay Alain , Clauer Norbert
Published: March 2003

In the external Humber zone, the emplacement episodes of allochthonous nappes and related low-grade metamorphism are mainly based on paleontological ages from the St. Lawrence Lowlands. In fact, Late Ordovician flysches are affected by thrusting, and it is not clear if the nappe imbrication is the result of the Taconian or the Acadian deformation. Along the Chaudière River transect, fourteen shales and phyllites of Cambrian to Ordovician age were sampled for determination of the KAr values of their < 2 µm-size fractions. To interpret the KAr data, mineral composition and clay mineral crystallinity of the < 2 µm-size fractions and maturation of the organic matter were determined. In addition, the intensity of deformation was characterized by describing the rock texture at macroscopic and microscopic scale. The combined approach used in this study emphasized that nearly all KAr dates are mixed or partly reset values. However, it can be stated that in the Quebec Promontory nappe and part of the Chaudière nappe, a Cretaceous thermal overprint might have occurred on the basis of a low KAr value at 256 Ma. Furthermore, the KAr dates of 491467 Ma obtained in the Chaudière nappe to the southeast, most probably represent mixed values of detrital material affected by diagenetic or tectonic processes. It might also be stated that the base of the Sainte-Hénédine nappe appears to be characterized by southeast-dipping thrust sheets with KAr dates of 439418 Ma, which may represent either a late-stage emplacement of the nappe or a yet unrecognized structural effect of hinterland-directed deformation that characterizes the internal Humber zone. In the southeastern part of the Sainte-Hénédine nappe, the thermal grade increases to epizonal conditions and the KAr dates that, in this case, could be of meaningful geological significance increase to 455445 Ma. Such ages are consistent with Ordovician 40Ar/39Ar metamorphic ages attributed to the Taconian orogeny in the internal Humber zone.
The Prospect Rock thrust: western limit of the Taconian accretionary prism in the northern Green Mountain anticlinorium, Vermont
Authors: Thompson Peter J , Thompson Thelma B
Published: March 2003

This paper presents evidence for an early Taconian, west-directed fault in northern Vermont, the Prospect Rock thrust, which represents the trace of the contact between the Taconian oceanic accretionary prism (Dunnage Zone) and less allochthonous, continental margin rocks (Humber Zone). Mapping at 1 : 24 000 over the last decade has led to reassessment of units within the Camels Hump Group, resulting in newly defined lithotectonic packages: the Green Mountain slice and the Prospect Rock slice. Rocks in these slices may be of similar age, but those in the Green Mountain slice were originally deposited as more proximal sediments and remained on the Humber side of the sub duction zone, whereas those in the Prospect Rock slice were transferred by underplating to the accretionary prism. Both slices contain ultramafics. Motion on the Prospect Rock thrust (D1) preceded Taconian garnet-grade metamorphism and subsequent east-directed back-folding. However, D1 structures were diachronous across the orogen. Late Taconian (D2) structures record a change from east-verging back-folds in northern Vermont and southern Quebec to west-verging folds farther south. The Prospect Rock thrust does not correspond exactly to Cameron's line nor to the Baie Verte  Brompton line as originally defined. However, our understanding of the geometry of the Prospect Rock thrust demonstrates that the Dunnage Zone extends farther west than previously recognized and may also explain features farther to the east.
The CambrianOrdovician successions along the ancient continental margin of Laurentia  recent advances
Authors: Lavoie Denis , Malo Michel , Tremblay Alain
Published: March 2003

The Appalachian Forelands and Platform NATMAP project in eastern Canada is a multi-discipline and multi-organization research endeavour aimed at the understanding of the evolution and architecture of the ancient continental margin of Laurentia. The Canadian Journal of Earth Sciences special issue presents some recent research progress for our knowledge of the CambrianOrdovician segment of that ancient margin.
THE FURTHER STUDY OF THE SPHEROIDAL BEAM EQUATION FOR FOCUSED FINITE-AMPLITUDE SOUND BEAMS
Authors: XIA RONGMIN , SHOU WENDE , CHENG GUOPING , ZHANG MEIDUN
Published: March 2003

The spheroidal beam equation (SBE)1 is a parabolic equation, which fits for focused, high-frequency beams from a large circular aperture. Partition of the acoustic field is one of the very important aspects of the SBE. But the criterion of division has not been given. In this paper, the criterion and corresponding numerical simulation are introduced. At the same time, the comparison of the SBE solution with Lucas's parabolic equation is fulfilled.
AN ANISOTROPIC COLE–COLE MODEL OF SEISMIC ATTENUATION
Authors: HANYGA ANDRZEJ
Published: March 2003

A simple model of seismic wave attenuation combining anisotropy with anelastic effects is constructed. The anelastic response is based on the Cole–Cole relaxation function. Time-stepping finite-difference and ray-asymptotic methods of numerical solution are discussed.
Ligands for L-Selectin: Homing, Inflammation, and Beyond
Authors: Rosen Steven D.
Published: March 2003

Understanding the molecular basis of lymphocyte homing to lymphoid organs was originally a problem of concern only to immunologists. With the discovery of l-selectin and its ligands, interested scientists have expanded to include glycobiologists, immunopathologists, cancer biologists, and developmental biologists. Going beyond its first discovered role in homing to lymph nodes, the l-selectin system is implicated in such diverse processes as inflammatory leukocyte trafficking in both acute and chronic settings, hematogenous metastasis of carcinoma cells, effector mechanisms for inflammatory demyelination of axons, and implantation of the early mammalian embryo. This review focuses on the ligands for l-selectin that are found on vascular endothelium, leukocytes, carcinoma cells, and at various extravascular sites. The discovery of selectins and their ligands has validated the long-predicted hypothesis that carbohydrate-directed cell adhesion is relevant in eukaryotic systems. Emphasis will be given to the carbohydrate and sulfation modifications of the ligands, which enable recognition by l-selectin.

The rapid “homing” of labeled cells into the lymph nodes presumably had its basis in the special affinity of small lymphocytes for the endothelium of the postcapillary venules.     Gowans & Knight ( 1 )
Lack of the CD8+ cell anti-HIV factor in CD8+ cell granules
Authors: Mackewicz Carl E. , Wang Baikun , Metkar Sunil , Richey Matthew , Froelich Christopher J. , Levy Jay A.
Published: March 2003

In HIV infection, CD8+ cells show cytotoxic and noncytotoxic anti-HIV activity. The latter function is mediated, at least in part, by a secreted antiviral protein, the CD8+ cell antiviral factor (CAF). Because antiviral effector molecules, such as perforin and granzymes, reside in the exocytic granules of CD8+ T cells, we examined the possibility that granules contain CAF-like activity. CD8+ cells from HIV-infected individuals showing strong CAF-mediated antiviral activity were induced to release their granule constituents into culture media. Within 1 hour of stimulation, high levels of granzyme B (a primary granule constituent) were found in the culture fluids of previously activated CD8+ cells. The same culture fluids contained no or very low amounts of CAF activity, as measured with HIV-infected CD4+ cells. Maximal levels of CAF activity were not observed until 5 or 7 days after stimulation, consistent with typical CAF production kinetics. In addition, extracts of granules purified from antiviral CD8+ cells did not show any CAF activity, whereas the cytoplasmic fraction of these cells showed substantial levels of antiviral activity. These findings suggest that CAF does not reside at appreciable levels in the exocytic granules of antiviral CD8+ T cells. (Blood. 2003;102: 180-183)
Sorting of soluble TNF-receptor for granule storage in hematopoietic cells as a principle for targeting of selected proteins to inflamed sites
Authors: Gao Ying , Rosén Hanna , Johnsson Ellinor , Calafat Jero , Tapper Hans , Olsson Inge
Published: March 2003

Hematopoietic cells have secretory lysosomes that degranulate at the inflammatory site upon stimulation. We asked whether one could target exogenous proteins with a therapeutic potential to secretory lysosomes in hematopoietic cells. For this purpose, we expressed a soluble tumor necrosis factor (TNF) receptor form (sTNFR1) in hematopoietic cell lines. In order to accomplish targeting to secretory lysosomes, both endoplasmic reticulum (ER) retention and constitutive secretion have to be prevented. ER export was facilitated by addition of a transmembrane (tm) sequence, and constitutive secretion was overcome by incorporating a cytosolic sorting signal (Y) from CD63. This signal directed the resulting sTNFR1-tm-Y to secretory lysosomes. Confirmation of these results was provided by biosynthetic radiolabeling, subcellular fractionation, immunofluorescence microscopy, and immunoelectron microscopy. The tm-Y fragment was cleaved by proteolysis, resulting in generation of the membrane-free sTNFR1 in secretory lysosomes. Our results suggest a potential for using the storage organelles of hematopoietic cells as vehicles for targeting sites of inflammation with therapeutically active agents.
Multiparity induces priming to male-specific minor histocompatibility antigen, HY, in mice and humans
Authors: James Edward , Chai Jian-Guo , Dewchand Hamlata , Macchiarulo Eugenio , Dazzi Francesco , Simpson Elizabeth
Published: March 2003

One of the factors that increases the risk of graft-versus-host disease following allogeneic stem cell transplantation is the use of multiparous females as donors. Since minor histocompatibility (H) antigens are the main targets of graft-versus-host and graft-versus-leukemia responses, we tested the hypothesis that multiparity could prime minor H antigen—specific T cells. We examined the peripheral lymphoid populations of multiparous mice and humans for evidence of priming of CD8+ T-cytotoxic lymphocytes against peptide epitopes of the male-specific minor H antigen, HY. In contrast to naive females, multiparous females have measurable levels of circulating HY-specific tetramer-positive T lymphocytes, which can be readily expanded in vitro. These findings have implications for the in vitro generation of T-cell clones as reagents for immunotherapy for tumors following stem cell transplantation. (Blood. 2003; 102:388-393)
Fanconi anemia protein complex: mapping protein interactions in the yeast 2- and 3-hybrid systems
Authors: Gordon Susan M. , Buchwald Manuel
Published: March 2003

Fanconi anemia (FA) is an autosomal recessive syndrome characterized by progressive bone marrow failure and cancer predisposition. Eight FA complementation groups have been identified. The FANCA, FANCC, FANCE, FANCF, and FANCG proteins form a nuclear complex required for the monoubiquination of the FANCD2 protein. To investigate the architecture of the FA protein complex, the yeast 2-hybrid system was used to map contact points of the FANCA/FANCG, FANCC/FANCE, and FANCF/FANCG interactions. FANCG was shown to interact with both the amino-terminus of FANCA and the carboxyl-terminal region of FANCF. A FANCG mutant truncated at the carboxyl-terminus retained the ability to interact with FANCA. The interaction between FANCG and FANCF was ablated by a Leu71Pro mutant of FANCG. A central region of FANCE was sufficient for FANCC binding. A Leu554Pro mutant of FANCC failed to interact with FANCE. To further examine complex assembly, the yeast 3-hybrid system was used to investigate the ability of FANCG to act as a molecular bridge in mediating interaction between other FA proteins. FANCG was able to mediate interaction between FANCA and FANCF, as well as between monomers of FANCA. Direct interaction between FANCE and FANCD2 was also demonstrated in the yeast 2-hybrid system. This interaction involving an amino-terminal region of FANCD2 may provide a link between the FA protein complex and its downstream targets. (Blood. 2003;102:136-141)
Human T lymphocytes transduced by lentiviral vectors in the absence of TCR activation maintain an intact immune competence
Authors: Cavalieri Simona , Cazzaniga Sabrina , Geuna Massimo , Magnani Zulma , Bordignon Claudio , Naldini Luigi , Bonini Chiara
Published: March 2003

Gene transfer into T lymphocytes is currently being tested for the treatment of lymphohematologic disorders. We previously showed that suicide gene transfer into donor lymphocytes infused to treat leukemic relapse after allogeneic hematopoietic stem cell transplantation allowed control of graft-versus-host disease. However, the T-cell receptor (TCR) activation and sustained proliferation required for retroviral vector transduction may impair the half-life and immune competence of transduced cells and reduce graft-versus-leukemia activity. Thus, we tested lentiviral vectors (LVs) and stimulation with cytokines involved in antigen-independent T-cell homeostasis, such as interleukin 7 (IL-7), IL-2, and IL-15. Late-generation LVs transduced efficiently nonproliferating T cells that had progressed from G0 to the G1 phase of the cell cycle on cytokine treatment. Importantly, IL-2 and IL-7, but not IL-15, stimulation preserved physiologic CD4/CD8 and naive-memory ratios in transduced cells with only minor induction of some activation markers. Functional analysis of immune response to cytomegalovirus (CMV) showed that, although CMV-specific T cells were preserved by all conditions of transduction, proliferation and specific killing of autologous cells presenting a CMV epitope were higher for IL-2 and IL-7 than for IL-15. Thus, LV transduction of IL-2 or IL-7 prestimulated cells overcomes the limitations of retroviral vectors and may significantly improve the efficacy of T-cell–based gene therapy.