bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Creep Deformation and Rupture Behavior of DS GTD-111 Using the Kachanov–Rabotnov Constitutive Model
Authors: Stewart Calvin M. , Gordon Ali P. , Hogan Erik A. , Saxena Ashok
Published: March 2011

Creep deformation and rupture experiments are conducted on samples of the Ni-base superalloy directionally solidified GTD-111 tested at temperatures between 649°C and 982°C and two orientations (longitudinally and transversely oriented). The secondary creep constants are analytically determined from creep deformation experiments. The classical Kachanov–Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. The simulated annealing optimization routine is utilized in conjunction with the FEA implementation to determine the creep damage constants. A comparison of FEA and creep deformation data demonstrates high accuracy. Using regression analysis, the creep constants are characterized for temperature dependence. A rupture prediction model derived from creep damage evolution is compared with rupture experiments.
Thermal Fly-Height Control Slider Instability and Dynamics at Touchdown: Explanations Using Nonlinear Systems Theory
Authors: Canchi Sripathi Vangipuram , Bogy David B.
Published: March 2011

Thermal fly-height control sliders are widely used in current hard disk drives to control and maintain subnanometer level clearance between the read-write head and the disk. The peculiar dynamics observed during touchdown/contact tests for certain slider designs is investigated through experiments and analytical modeling. Nonlinear systems theory is used to highlight slider instabilities arising from an unfavorable coupling of system vibration modes through an internal resonance condition, as well as the favorable suppression of instabilities through a jump condition. Excitation frequencies that may lead to large amplitude slider vibrations and the dominant frequencies at which slider response occurs are also predicted from theory. Using parameters representative of the slider used in experiments, the theoretically predicted frequencies are shown to be in excellent agreement with experimental results. This analytical study highlights some important air bearing surface design considerations that can help prevent slider instability as well as help mitigate unwanted slider vibrations, thereby ensuring the reliability of the head-disk interface at extremely low head-disk clearances.
Tensile and Fracture Characterization of PETI-5 and IM7/PETI-5 Graphite/Epoxy Composites Under Quasi-Static and Dynamic Loading Conditions
Authors: Lee Dongyeon , Tippur Hareesh V. , Jensen Brian J. , Bogert Philip B.
Published: March 2011

Tensile and fracture responses of the phenylethynyl terminated imide oligomer (PETI-5) are studied. Since this polymer is a candidate aerospace structural adhesive as well as a matrix material in composite systems, neat as well as fiber reinforced forms of PETI-5 are studied under static and dynamic loading conditions. A split-Hopkinson tension bar apparatus is used for performing tensile tests on dogbone specimens. The dynamic fracture tests are carried out using a drop tower in conjunction with 2D image correlation method and high-speed digital photography on edge cracked specimens in three-point bend configuration. A toughened neat epoxy system, Hexcel 3900, is also studied to provide a baseline comparison for neat PETI-5 system. The tensile stress-strain responses show PETI-5 to have excellent mechanical characteristics under quasi-static and dynamic loading conditions when compared with 3900. Fracture behavior of PETI-5 under quasi-static and impact loading conditions also shows superiority relative to 3900. The dynamic fracture behavior of a PETI-5 based graphite fiber reinforced composite, IM7/PETI-5, is also studied and the results are comparatively evaluated relative to the ones corresponding to a more common aerospace composite system, T800/3900-2 graphite/epoxy. Once again, the IM7/PETI-5 system shows excellent fracture performance in terms of dynamic crack initiation and growth behaviors.
Fatigue Behavior and Damage Assessment of Stainless Steel/Aluminum Composites
Authors: Eskizeybek Volkan , Avci Ahmet , Akdemir Ahmet , Şahin Ömer Sinan
Published: March 2011

Fatigue crack growth and related damage mechanisms were investigated experimentally in a stainless steel/aluminum laminated composite with middle through thickness crack, and two different fracture mechanics approaches applied to the composite to reveal their differences under fatigue loading. The laminated composite material, which has a unidirectional continuous AISI 304 stainless steel as fibers and Al 1060 as matrix, was produced by using diffusion bonding. Fatigue tests were conducted in accordance with ASTM E 647. The relationships between fatigue crack growth rate (da/dN), stress intensity factor (ΔK), and strain energy release rate (ΔG) were determined; and damage behavior was discussed. Both linear elastic fracture mechanics (LEFM) and compliance method were used, and the results were compared with each other. It is found that as the crack propagates, the LEFM overestimates the ΔG values. Interlaminar and fiber/matrix interface damage were evaluated by fractographic examination.
Mechanism of VFB/VTH shift in Dysprosium incorporated HfO2 gate dielectric n-Type Metal-Oxide-Semiconductor devices
Authors: Lee Tackhwi , Choi Kisik , Ando Takashi , Park Dae-Gyu , Gribelyuk Michael A. , Kwon Unoh , Banerjee Sanjay K.
Published: March 2011

The authors discuss temperature-dependent dysprosium (Dy) diffusion and the diffusion-driven Dy-silicate formation process in Dy incorporated HfO2. The Dy-induced dipoles are closely related to the Dy-silicate formation at the high-k/SiO2 interfaces since the VFB shift in Dy2O3 is caused by the dipole and coincides with the Dy-silicate formation. Dipole formation is a thermally activated process, and more dipoles are formed at a higher temperature with a given Dy content. The Dy-silicate related bonding structure at the interface is associated with the strength of the Dy dipole moment and becomes dominant in controlling the VFB/VTH shift during the high temperature annealing in the Dy–Hf–O/SiO2 gate oxide system. Dy-induced dipole reduces the degradation of the electron mobility.
Metamorphic growth of III-V semiconductor bicrystals
Authors: Richardson C. J. K. , He L. , Kanakaraju S.
Published: March 2011

The authors report on the structural properties of III-V semiconductor films that are not lattice matched to the GaAs substrates on which they are grown. Using molecular beam epitaxy, a uniform two-dimensional edge dislocation network is formed that abruptly relaxes the misfit strain at the film/substrate interface. The nucleation and initial growth of a GaSb film on GaAs are analyzed using reflection high-energy electron diffraction to show growth that becomes two dimensional in approximately five monolayers. Comparisons of the experimental reciprocal space map peak shapes and theoretical shapes show that some of these films are approaching the theoretical limit where all of the strain is completely relaxed at the interface.
QUANTUM COMPLEXITY IN GRAPHENE
Authors: BASKARAN G.
Published: March 2011

Carbon has a unique position among elements in the periodic table. It produces an allotrope, graphene, a mechanically robust two dimensional semimetal. The multifarious properties that graphene exhibits has few parallels among elemental metals. From simplicity, namely carbon atoms connected by pure sp2 bonds, a wealth of novel quantum properties emerge. In classical complex systems such as a spin glass or a finance market, several competing agents or elements are responsible for unanticipated and difficult to predict emergent properties. The complex (sic) structure of quantum mechanics is responsbile for an unanticipated set of emergent properties in graphene. We call this quantum complexity. In fact, most quantum systems, phenomena and modern quantum field theory could be viewed as examples of quantum complexity. After giving a brief introduction to the quantum complexity we focus on our own work, which indicates the breadth in the type of quantum phenomena that graphene could support. We review our theoretical suggestions of, (i) spin-1 collective mode in netural graphene, (ii) relativistic type of phenomena in crossed electric and magnetic fields, (iii) room temperature superconductivity in doped graphene and (iv) composite Fermi sea in neutral graphene in uniform magnetic field and (v) two-channel Kondo effect. Except for the relativistic type of phenomena, the rest depend in a fundamental way on a weak electron correlation that exists in the broad two-dimensional band of graphene.
THEORY OF THERMAL CONDUCTIVITY OF HIGH TEMPERATURE SUPERCONDUCTORS: A NEW APPROACH
Authors: ASHOKAN VINOD , INDU B. D.
Published: March 2011

An ab initio formulation of relaxation times of various contributing processes have been observed with newer understanding in terms of electron and phonon line widths. This is dealt with the help of double time temperature-dependent Green's function via a non-perturbative approach using a crystal Hamiltonian which comprises of the effects of electrons, phonons, impurities, anharmonicities and interactions thereof. The frequency line widths is observed as an extremely sensitive quantity in the transport phenomena of high temperature superconductors (HTS) as a collection of a large number of scattering processes, namely: boundary scattering, impurity scattering, multi-phonon scattering, interference scattering, electron–phonon processes and resonance scattering. The behavior of electrons and phonons is then investigated to describe the thermal conductivity of a variety of HTS samples specially in the vicinity of transition temperature to successfully explain the spectacular dip region of thermal conductivity curve which was lacking in explanation earlier with a sound physical justification.
SOLITON SOLUTIONS FOR SEVENTH-ORDER KAWAHARA EQUATION WITH TIME-DEPENDENT COEFFICIENTS
Authors: WAZWAZ ABDUL-MAJID
Published: March 2011

In this work, a generalized seventh-order Kawahara equation characterized by time-dependent coefficients will be examined. The solitary wave ansatz will be used to obtain soliton solutions for this equation. The necessary conditions for the existence of the soliton solutions will also be derived.
MACROSCOPIC AHARONOV–BOHM EFFECT AT L-BAND MICROWAVE FREQUENCIES
Authors: ZIMMERMAN ROBERT K.
Published: March 2011

Experimental tests using a TM 01 mode circular waveguide verify the Aharonov–Bohm effect at L-band frequencies. Additional tests on a free-space range verify longitudinal vector potential wave propagation across 1.5 meters out to a range of 25 meters and beyond. We verify the Lorenz gauge as the only physically correct gauge for these propagating vector potential A waves.
PERTURBATION OF THE CHAOTIC 1D MIXED WAVE SYSTEM CAUSES THE UNBOUNDED GROWTH OF THE SNAPSHOTS OF THE GRADIENT
Authors: HU CHUNG-CHE
Published: March 2011

Consider the one-dimensional mixed wave equation on a unit interval, where the left-end boundary condition is linear, pumping energy into the system, while the right-end boundary condition is self-regulating of the van der Pol type with a cubic nonlinearity. First, we show a certain parameter range of the chaotic vibration of the system. Furthermore, if the right-end van der Pol boundary contains an extra linear displacement feedback term, then we show that under some suitable conditions, the system is still chaotic in the sense of unbounded growth of the snapshots of the gradient.
THE PERSISTENCE OF SNAP-BACK REPELLER UNDER SMALL C1 PERTURBATIONS IN BANACH SPACES
Authors: CHEN YUANLONG , HUANG YU , LI LIANGLIANG
Published: March 2011

In this paper, we consider the persistence of snap-back repellers under small C1 perturbations in Banach spaces. Let X be a Banach space and f be a C1-map from X into itself. We show that if f has a snap-back repeller, then any small C1 perturbations of f has a snap-back repeller and exhibits chaos in the sense of Devaney. The obtained results further extend the existing relevant results in finite-dimensional Euclidean spaces. As applications, we will discuss the chaotic behavior of two nonlocal population models.
OBSERVER-BASED SYNCHRONIZATION FOR A CLASS OF FRACTIONAL CHAOTIC SYSTEMS VIA A SCALAR SIGNAL: RESULTS INVOLVING THE EXACT SOLUTION OF THE ERROR DYNAMICS
Authors: CAFAGNA DONATO , GRASSI GIUSEPPE
Published: March 2011

This paper deals with chaos synchronization for a class of fractional-order systems characterized by one nonlinearity. In particular, an observer-based approach is illustrated, which presents two remarkable features: (i) it provides an exact analytical solution of the fractional error dynamics, written in terms of Mittag-Leffler function; (ii) it enables synchronization to be achieved using a scalar transmitted signal. Finally, a synchronization example based on fractional Chua's system is illustrated, with the aim to show the capabilities of the developed approach.
INVOLUTE, MINIMAL, OUTER AND INCREASINGLY TRAPPED SURFACES
Authors: HAYWARD SEAN A.
Published: March 2011

Eight different refinements of trapped surfaces are proposed, of three basic types, each intended as potential stability conditions. Minimal trapped surfaces are strictly minimal with respect to the dual expansion vector. Outer trapped surfaces have positivity of a certain curvature, related to surface gravity. Increasingly (future, respectively past) trapped surfaces generate surfaces which are more trapped in a (future, respectively past) causal variation, with three types: in any such causal variation; along the expansion vector; and in some such causal variation. This suggests a definition of doubly outer trapped surface involving two independent curvatures. This in turn suggests a definition of involute trapped surface. Adding a weaker condition, the eight conditions form an interwoven hierarchy, with four independent relations which assume the null energy condition, and another holding in a special case of symmetric curvature.
NEW HOLOGRAPHIC CHAPLYGIN GAS MODEL OF DARK ENERGY
Authors: MALEKJANI M. , KHODAM-MOHAMMADI A.
Published: March 2011

In this work, we investigate the holographic dark energy model with a new infrared cutoff (new HDE model), proposed by Granda and Oliveros. Using this new definition for the infrared cutoff, we establish the correspondence between the new HDE model and the standard Chaplygin gas (SCG), generalized Chaplygin gas (GCG) and modified Chaplygin gas (MCG) scalar field models in a nonflat universe. The potential and dynamics for these scalar field models, which describe the accelerated expansion of the universe, are reconstructed. According to the evolutionary behavior of the new HDE model, we derive the same form of dynamics and potential for the different SCG, GCG and MCG models. We also calculate the squared sound speed of the new HDE model as well as the SCG, GCG and MCG models, and investigate the new HDE Chaplygin gas models from the viewpoint of linear perturbation theory. In addition, all results in the nonflat universe are discussed in the limiting case of the flat universe, i.e. k = 0.
INTERACTING MODIFIED HOLOGRAPHIC DARK ENERGY IN A NONFLAT UNIVERSE
Authors: SETARE M. R. , BANIJAMALI A. , FAZLPOUR B.
Published: March 2011

In this paper, we extend the modified holographic dark energy proposed by Wei [H. Wei, Nucl. Phys. B819 (2009) 210] to the interacting case and in a nonflat universe. We first choose the IR cutoff to be the radius of the event horizon Rh measured on the sphere of the horizon and derive the equation of state for the holographic energy density in the nonflat universe. Then, by choosing the Jeans length as the IR cutoff, we obtain the necessary conditions for having a cosmologically consistent model.
LENGTH OF INFLATION AND NON-GAUSSIANITY
Authors: HIRAI SHIRO , TAKAMI TOMOYUKI
Published: March 2011

Certain inflation models are shown to have large non-Gaussianity in special cases. Namely, slow-roll inflation models with an effective higher derivative interaction, in which the length of inflation is finite and a scalar-matter-dominated period or power inflation is adopted as pre-inflation, are considered. Using Holman and Tolley's formula of the nonlinearity parameter in the flattened triangle configurations [Formula: see text], we calculate the value of [Formula: see text]. The value of [Formula: see text] is found to be largest [Formula: see text] when the inflation length is approximately 60 e-folds, and [Formula: see text] is found to depend strongly on the length of inflation and the cut-off scale.
AN EMPIRICAL MODEL OF PRODUCTION AND ATTENUATION OF FLUORESCENCE LIGHT IN ATMOSPHERE FOR SATELLITE-BASED ULTRA HIGH ENERGY COSMIC RAY EXPERIMENTS
Authors: STRAZZERI E. , CATALANO O. , SBARUFATTI B.
Published: March 2011

In the context of detection of Ultra High Energy Cosmic Ray (UHECR) showers from space the details of fluorescence light production and transmission in the atmosphere are given. An analytical model of the fluorescence yield, in dependence on nitrogen molecular parameters and the atmospheric conditions, is presented. Seasonal and geographical variations of the total fluorescence photon yield between 300 nm and 400 nm in air excited by 0.85 MeV electrons are shown as a function of the altitude, using different atmospheric models. In the frame of a satellite-based UHECR experiment the fluorescence yield has been corrected by the overall atmospheric transmission which takes into account, in the simplest approximation, the wavelength-dependent scattering and absorption of the fluorescence light from air molecules, from stratospheric ozone, and from aerosol. The effect of the atmospheric attenuation on the fluorescence yield is shown as a function of the altitude of the emission point of light.
ANALYTIC APPROACH TO PERTURBED EINSTEIN RING WITH ELLIPTICAL NFW LENS MODEL
Authors: HABARA YUTA , YAMAMOTO KAZUHIRO
Published: March 2011

We investigate the validity of the approximate method to describe a strong gravitational lensing which was extended by Alard on the basis of a perturbative approach to an Einstein ring. Adopting an elliptical Navarro–Frenk–White (NFW) lens model, we demonstrate how the approximate method works, focusing on the shape of the image, the magnification, caustics, and the critical line. Simplicity of the approximate method enables us to investigate the lensing phenomena in an analytic way. We derive simple approximate formulas which characterize a lens system near the Einstein ring.
PHOTON ROCKETS MOVING ARBITRARILY IN ANY DIMENSION
Authors: PODOLSKÝ JIŘÍ
Published: March 2011

A family of explicit exact solutions of Einstein's equations in four and higher dimensions is studied which describes the gravitational field of an object accelerating due to an anisotropic emission of photons. It is possible to prescribe an arbitrary motion, so that the acceleration of such photon rocket need not be uniform — both its magnitude and direction may vary with time. Except at the location of the rocket the space–times have no curvature singularities, and topological defects like cosmic strings are also absent. Any value of a cosmological constant is allowed. We investigate some particular examples of motion, namely a straight flight and a circular trajectory, and we derive the corresponding radiation patterns and the mass loss of the rockets. We also demonstrate the absence of "gravitational aberration" in such space–times. This interesting member of the higher-dimensional Robinson–Trautman class of pure radiation space–times of algebraic Type D generalizes the class of Kinnersley's solutions that has long been known in four-dimensional general relativity.
SELF-GRAVITATING SPHERES OF ANISOTROPIC FLUID IN GEODESIC FLOW
Authors: IVANOV B. V.
Published: March 2011

The fluid models mentioned in the title are classified. All characteristics of the fluid are expressed through a master potential, satisfying an ordinary second-order differential equation. Different constraints are imposed on this core of relations, to find new solutions and to derive the classical results for perfect fluids and dust as particular cases. Many uncharged and charged anisotropic solutions, all conformally flat, and some uniform density solutions are found. A number of solutions with linear equation among the two pressures are derived, including the case of vanishing tangential pressure.
AN EXAMINATION OF UNIVERSITY STUDENT ENTREPRENEURIAL INTENTIONS BY TYPE OF VENTURE
Authors: CAREY THOMAS A. , FLANAGAN DAVID J. , PALMER TIMOTHY B.
Published: March 2011

Learning what initially drives university students to be open to the thought of starting their own businesses has been of great interest to entrepreneurship researchers/educators. Past literature looks at a variety of important motivators that impact student intentions toward entrepreneurship but has tended to view entrepreneurial intentions as a homogeneous construct. This study uses Ajzen's theory of planned behavior to examine university students' intentions to start various types of ventures (small lifestyle, small high income and high growth). Results indicate that intentions to start small high income and high growth ventures share many commonalities and are significantly driven by behavioral beliefs and perceived behavioral control. Intentions to start small lifestyle ventures, on the other hand, are found to be independent from intentions to start either small, high income or high growth ventures and are not as well explained by the theory of planned behavior. Implications and ideas for future research and entrepreneurship education are discussed.
ISLAMIC ENTREPRENEURSHIP: A CASE STUDY OF SAUDI ARABIA
Authors: KAYED RASEM N. , HASSAN M. KABIR
Published: March 2011

As this paper examines the relationship between Islamic values and entrepreneurial activity, it seeks to establish whether these values can be more effectively tapped into to raise the profile of Islamic form of entrepreneurship. A written, self-administered questionnaire among a random sample of Saudi entrepreneurs in the city of Riyadh was employed to generate descriptive data to assess the views and attitudes of Saudi entrepreneurs toward both conventional and Islamic forms of entrepreneurship. We find that Saudi entrepreneurs perceive themselves to be committed Muslims who consider entrepreneurship a religious and economic duty intended to generate halal (lawful) income to meet their financial obligations and to contribute to the falah (well-being) of the Muslim ummah (nation) in this life and hereafter. The findings also negate the prevalent conventional assumption that Islam is intrinsically anti-modernization and anti-development, and that the religiously-based Saudi culture would hinder the emergence and the development of a vibrant entrepreneurship culture in Saudi Arabia.
CHANGE MANAGEMENT THROUGH ENTREPRENEURSHIP IN PUBLIC SECTOR ENTERPRISES
Authors: KEARNEY CLAUDINE , HISRICH ROBERT D. , ROCHE FRANK W.
Published: March 2011

Corporate entrepreneurship has been of interest to academics, business leaders and government officials over the past four decades, particularly in terms of enhancing organizational performance. Although the understanding of corporate entrepreneurship continues to develop, the research usually focuses on private sector business activity. The research to date has not provided a consensus on the nature of public sector corporate entrepreneurship. Even though in recent years the topic has appeared in the public administration literature with increasing frequency, public sector corporate entrepreneurship remains poorly defined and its interpretation fragmented. In this study, public sector corporate entrepreneurship is investigated by developing and testing an integrative model using data obtained from 134 public sector state and semi-state enterprises in Ireland. The results indicate public sector organizations can manage change through entrepreneurship when they adapt to a munificent environment and when the decision-making style and control system is aligned. Public sector organizations focusing on corporate entrepreneurship (renewal) are at least marginally positively associated with organizational performance (growth and development) a primary policy goal particularly in the current economic climate. The article concludes by discussing the implications for theory, practice and future research areas.
DIRECT AND INDIRECT EFFECTS OF INDIVIDUAL AND ENVIRONMENTAL FACTORS ON MOTIVATION FOR SELF-EMPLOYMENT
Authors: WANG LEI , PRIETO LEONEL , HINRICHS KIM T.
Published: March 2011

The objective of this paper is to study the direct and mediating effects on the motivation to become self-employed of a set of two individual factors (entrepreneurial self-efficacy and risk-taking) and five environmental factors (family self-employment background, social networks, social norms, legal system support and governmental support). Based on 535 cases from the United States, results show that legal system support, social networks, social norms, entrepreneurial self-efficacy and risk-taking had a strong impact on motivation for self-employment. Family self-employment history only had a direct effect and social networks and social norms only had an indirect effect on motivation for self-employment. Our study contributes to the literature by studying motivation for self-employment, at the "middle level" of complexity by providing a summary evaluation of a model involving 17 relationships among eight constructs. In so doing, we have also given substantial attention to context. Our results suggest the need to take into account individual and environmental factors systemically and contextually. Limitations and future research are discussed.
ENTREPRENEURSHIP AND THE INFORMAL ECONOMY: AN OVERVIEW
Authors: WILLIAMS COLIN C. , NADIN SARA
Published: March 2011

In recent decades, the field of entrepreneurship studies has become increasingly interested in the relationship between entrepreneurship and the informal economy. This paper reviews this burgeoning sub-field of entrepreneurship studies that recognizes how entrepreneurs do not always conduct their business affairs wholly by the rulebook. Evaluating this rapidly growing body of literature, it reviews the findings regarding the preponderance of entrepreneurs to engage in the informal economy, the nature of such informal entrepreneurship, the characteristics of informal entrepreneurs and the motives underpinning participation in such endeavor, along with the competing theories that have sought to explain engagement in this type of entrepreneurship. The tentative finding is that there are marked socio-spatial variations in the prevalence and nature of informal entrepreneurship, the characteristics of informal entrepreneurs and their rationales. The implication is not only that different theorizations of informal entrepreneurship apply more in some populations than others, but also that some populations usually seen as lacking in entrepreneurial spirit are perhaps more enterprising and entrepreneurial than currently recognized. Consequently, legitimizing this hidden enterprise culture could be an important means of promoting enterprise and economic development in such populations. The paper concludes by highlighting future avenues for research on this subject.
SIMPLE EXAMPLES OF DISTINCT LIOUVILLE TYPE SYMPLECTIC STRUCTURES
Authors: SEIDEL PAUL
Published: March 2011

We provide simple examples of open manifolds which support inequivalent symplectic structures that are Liouville (exact, and with an infinite end modeled on the convex part of a symplectization).
SPECTRAL FLOW, INDEX AND THE SIGNATURE OPERATOR
Authors: AZZALI SARA , WAHL CHARLOTTE
Published: March 2011

We relate the spectral flow to the index for paths of selfadjoint Breuer–Fredholm operators affiliated to a semifinite von Neumann algebra, generalizing results of Robbin–Salamon and Pushnitski. Then we prove the vanishing of the von Neumann spectral flow for the tangential signature operator of a foliated manifold when the metric is varied. We conclude that the tangential signature of a foliated manifold with boundary does not depend on the metric. In the Appendix we reconsider integral formulas for the spectral flow of paths of bounded operators.
INVARIANT EXPECTATIONS AND VANISHING OF BOUNDED COHOMOLOGY FOR EXACT GROUPS
Authors: DOUGLAS RONALD G. , NOWAK PIOTR W.
Published: March 2011

We study exactness of groups and establish a characterization of exact groups in terms of the existence of a continuous linear operator, called an invariant expectation, whose properties make it a weak counterpart of an invariant mean on a group. We apply this operator to show that exactness of a finitely generated group G implies the vanishing of the bounded cohomology of G with coefficients in a new class of modules, which are defined using the Hopf algebra structure of ℓ1(G).
ON GROMOV'S WAIST OF THE SPHERE THEOREM
Authors: MEMARIAN YASHAR
Published: March 2011

The goal of this paper is to give a detailed and complete proof of M. Gromov's waist of the sphere theorem.
Tectonic evolution of the northern Ural Orogen
Authors: Otto S. C. , Bailey R. J.
Published: March 2011

The closure of the Uralian Ocean occurred in Early Permian-Early Triassic time. In the northern Ural fold belt, overthrusting to the west produced a major foreland basin to the west of the mountain chain. In contrast, in the northern extension of the Ural Orogen, the Taymyr fold belt, thrusting was directed to the SE. It is proposed that Novaya Zemlya, at the interface of these two zones, acted as a thin-skinned allochthonous nappe emplaced by gravity tectonics into a basin produced by rapid Permo-Triassic rifting in the eastern Barents Sea.
Late-orogenic extensional tectonics at the NW margin of the Caledonides in Scotland
Authors: Potts G. J. , Hunter R. H. , Harris A. L. , Fraser F. M.
Published: March 2011

A major ductile extensional structure throwing down several kilometres to the ESE probably marks the southern portion of the NW Caledonian orogenic margin in Scotland. This structure, the Sound of Iona Fault, is probably related to the intensely mylonitized zones that cut the Lewisian and adjacent Iona Group (?Torridonian) metasedimentary cover on Iona. The fault-related mylonites predated the 414±3 Ma Ross of Mull Granite and are inferred to have postdated the
c.
425 Ma Moine Thrust. It is concluded that the Sound of Iona Fault is one of the many late Caledonian faults in Scotland, but is exposed at a deeper structural level than normal. Its position at the orogenic margin of the Caledonides is similar to that of the Loch Gruinart Fault on Islay, hinting that (a) major steep fault(s) may be a significant feature of the largely concealed Caledonian margin south of Skye
Neodymium isotopic constraints on the protolith ages of rocks involved in Pan-African tectonism in the Mozambique Belt of Tanzania
Authors: Maboko M. A. H.
Published: March 2011

Nd isotopic data from samples collected across the Tanzanian sector of the Mozambique belt indicate that the bulk of the belt consists of early Proterozoic crust which was tectonothermally reworked during Pan-African time. The only evidence for younger crust is preserved in granulite complexes that are surrounded by older amphibolite-facies gneisses. The uniformity of crustal formation ages of the gneisses across most of the belt indicates that models explaining the Mozambique belt as a tectonic collage of terranes with different pre-Pan-African crustal histories are invalid.
Mass mortalities on an Irish Silurian seafloor
Authors: Harper D. A. T. , Scrutton C. T. , Williams D. M.
Published: March 2011

Recurrent deep-water benthic communities, dominated by diverse tabulate corals, colonized soft substrates during the late Llandovery transgression in western Ireland. A number of autochthonous shelly assemblages dominated by brachiopods, corals and crinoids occur in the upper parts of the Kilbride Formation; the highest and most distal levels are dominated by
in situ
tabulate corals that are mantled by a thin layer of volcanic ash. Most of the coral colonies could cope with limited sedimentation: growth ceased after the volcaniclastic surge. This catastrophic mode of preservation permits an accurate analysis of an early stage of community development in deep-water benthos on a soft Llandovery seabed, periodically swept by volcaniclastic debris. The Kilbride faunas have implications for the palaeoenvironments and taphonomy of deep-water marine faunas associated with areas of active volcanism.
The Iceland plume and its influence on the evolution of the NE Atlantic
Authors: White R. S. , Morton A. C.
Published: March 2011

The papers printed below were contributed by scientists who attended the second Arthur Holmes European Research Meeting held in Reykjavik, Iceland in early July 1994. The igneous rocks produced by mantle plumes and at seafloor spreading-centres provide a powerful probe for investigating the state of the mantle beneath the lithosphere. Iceland is a particularly good window into the convecting mantle because the North Atlantic spreading-centre crosses directly above the mantle plume: the plate divergence allows decompression melting to occur to depths as shallow as 15 km below the surface. In other mantle plumes, such as Hawaii, the thick lithospheric lid above the plume prevents the convecting mantle rising shallower than the base of the lithosphere which lies at a depth of many tens of kilometres. A further feature of the NE Atlantic is that decompression melting beneath the spreading centres adjacent to Iceland samples the asthenospheric mantle consistently at all distances from the mantle plume: this allows the spatial and temporal extent and variability of the plume to be investigated.

The Arthur Holmes meeting was held early July 1994 in Reykjavik, Iceland, fittingly enough at a location almost on top of the European-North American plate boundary, and directly above the Iceland plume. The presentations covered six main themes: melt generation; the relative importance of plume, depleted mid-ocean ridge basalt and other magma sources; breakup processes and effects on marginal basins; the timing and expression of volcanic and tectonic events; and geochemical and geophysical manifestations of the plume through space
Dynamic support by the Iceland Plume and its effect on the subsidence of the northern Atlantic margins
Authors: Clift Peter D. , Turner Jonathan ,   The ODP Leg 152 Scientific Party
Published: March 2011

A transect of drill sites across the East Greenland margin made by ODP Leg 152 provides important new data on the subsidence history of this margin, complementing earlier ODP and DSDP drill sites on the conjugate Hatton Bank, as well as the Vøring Plateau. Fluvial sediments recovered from under the basalts of the dipping reflector series indicate uplift and subaerial exposure of the margin prior to basalt eruption. The basaltic basement at Site 918, located oceanward of the continent-ocean transition, shows anomalously slow subsidence during the first 15–20 Ma after continental break-up, compared to normal ocean crust. Similar anomalous subsidence characterizes the early subsidence at DSDP Sites 552–554 on the Hatton Bank. Here however the anomaly is of lower magnitude and of shorter duration. At the Vøring Plateau dynamic support is apparent on the landward side of the continent—ocean transition but offshore the evidence for strong, long duration support is lacking. We interpret the subsidence results to reflect dynamic support of the North Atlantic rifted margins by the Iceland plume, with the greater support at the East Greenland sites reflecting their position closer to the plume centre during the initial post-rift period than those on the Hatton Bank or Vøring Plateau. The subsidence data are in accord with models of a large plume head of 1000 km radius but cannot resolve between models proposing arrival of a pre-existing plume into the area during the late Palaeocene, rather than the incubation of a new plume under the area at that time. The low degree of dynamic support seen at the Vøring Plateau and the marked difference between the support at the East Greenland drill sites versus those at Hatton Bank does not support the plume centre being at Kangerdlugssuaq at 55 Ma, but instead at a location further west, under the Greenland craton.
Late Cretaceous basalts from Rosemary Bank, Northern Rockall Trough
Authors: Morton Andrew C. , Hitchen Ken , Ritchie J. Derek , Hine Nicolette M. , Whitehouse Martin , Carter Sam G.
Published: March 2011

A borehole drilled on the top of Rosemary Bank (Rockall Trough, NE Atlantic), recovered 16.72m of basalts and volcaniclastic sediments beneath a 1.53m thick limestone with basalt clasts, biostratigraphically dated as late Maastrichtian. Magnetostratigraphic data, constrained by the biostratigraphy, indicate extrusion of Rosemary Bank basalts took place during magnetochron C31R (71–69 Ma), or possibly earlier. This provides definite proof of pre-Tertiary volcanism in the Rockall Trough, and indicates that the onset of activity in the North Atlantic Igneous Province took place at least 7 Ma earlier than the postulated arrival of the Icelandic plume at 62 Ma. Geochemical and isotopic data suggest there was an enriched component to the magmatic source. Present data cannot resolve whether the Rosemary Bank basalts are an early manifestation of the Icelandic plume, whether they were associated with a different plume, or whether they were derived from enriched upper mantle without a significant thermal anomaly.
Transient regional uplift in the Early Tertiary of the northern North Sea and the development of the Iceland Plume
Authors: Nadin P. A. , Kusznir N. J. , Toth J.
Published: March 2011

Forward and reverse 2D flexural modelling of syn-rift and post-rift stratigraphy, has been used to investigate departures from McKenzie post-rift subsidence for the Cretaceous-Tertiary following Late Jurassic rifting in the northern North Sea Basin. The analysis shows uplift in the Palaeocene of 375–525 m relative to calibrated McKenzie subsidence curves, followed by a rapid decrease in uplift in the Early Eocene of 160–310 m. Both Palaeocene uplift and Eocene subsidence increase northwards. The timing, distribution and magnitude of regional Palaeocene uplift is consistent with an origin relating to the development of a mantle plume between 65 and 55 Ma. Transient regional Palaeocene uplift in the northern North Sea Basin was produced by long wavelength dynamic uplift generated by the flow field of a mantle plume. Heating of the asthenosphere or lithosphere beneath the North Sea by hot plume material, or magmatic underplating are not believed to have contributed to Palaeocene uplift in the northern North Sea Basin. Rapid Early Eocene subsidence was generated by a decrease in dynamic uplift caused by a reduction in plume activity. The plume responsible for North Sea Palaeocene uplift may have been the early Iceland plume or a distinct British Tertiary Igneous Province plume related to the same mantle convection event.
Early Tertiary magmatism in NE Greenland
Authors: Upton B.G.J. , Emeleus C.H. , Rex D.C. , Thirlwall M.F.
Published: March 2011

Between 73° and 74°N in NE Greenland, a Lower Series of quartz tholeiite lavas is overlain by an Upper Series which varies from quartz tholeiitic to basanitic. The Lower Series basalts are attributed to large melt fractions produced east of the present outcrop where lithospheric thinning permitted the Iceland plume to ascend to shallow levels.

Relocation of eruption sites up to 150 km (?) further west, preceeded Upper Series activity. In this, small-degree melts, generated principally from garnet-lherzolite facies sources, were followed by products of more extensive, shallower melting which gave rise successively to the Upper Series lavas, a post-Upper Series basaltic dyke swarm and its associated caldera complex. Palaeomagnetic observations and
40
Ar/
39
Ar dating suggest that the Lower Series (and part of the Upper Series) erupted in C24r at 58–57 Ma. Rejuvenescent activity at
c.
32 Ma, marking the termination of volcanism, may relate to decompressive mantle melting associated with late regional uplift.
Widespread Palaeocene volcanism around the northern North Atlantic and Labrador Sea: evidence for a large, hot, early plume head
Authors: Chalmers J. A. , Larsen L. M. , Pedersen A. K.
Published: March 2011

Voluminous volcanism took place west of Greenland and northwest of the British Isles in the Palaeocene, 6–7 Ma before the start of sea-floor spreading in the northern North Atlantic. Very hot (picritic) magmas were produced simultaneously in such widely separated areas that they could not all have been above the central stem of the same mantle plume. A single, large plume head with temperatures of
c.
1500°C over a diameter of
c.
2000 km can explain the observations if surface volcanic activity took place only where the lithosphere was thin. The presence of picrites does not indicate proximity to the plume stem.
Generation of the Pb isotopic characteristics of the Iceland plume
Authors: Thirlwall M.F.
Published: March 2011

Existing interpretations of the Pb isotopic compositions of recent basaltic lavas from Iceland and adjacent sectors of the Mid-Atlantic Ridge have regarded these as the products of mixing between a single Icelandic plume component and a depleted mantle component similar to that supplying mid-ocean ridge basalts (MORB) away from plume influences.
208
Pb-
207
Pb relationships are not consistent with these interpretations and suggest instead that few if any modern Icelandic lavas contain a MORB asthenosphere component. In particular, the low
207
Pb/
204
Pb of north Iceland picrites relative to MORB and the Northern Hemisphere Reference Line is very difficult to explain by mixing of currently proposed mantle components. The offset of the Icelandic data array to lower
207
Pb/
204
Pb than MORB on all Pb isotope diagrams might instead be viewed as the product of
206
Pb/
204
Pb and
208
Pb/
204
Pb increases, resulting from moderately high μ during the Phanerozoic, a HIMU character also indicated by K depletion in Iceland plume basalts. This mechanism can generate the Pb isotope compositions of most Icelandic basalts, but not those of Theistareykir picrites, the origin of which remains unclear.
The scale of source heterogeneity beneath the Eastern neovolcanic zone, Iceland
Authors: Furman T. , Frey F. , Park K.-H.
Published: March 2011

Geochemical characteristics of Icelandic basalts require mixing of several sources: depleted asthenosphere, a plume (presumably heterogeneous), and an enriched component (e.g. hydrothermally altered crust). We use lava compositions and Sr-Nd-Pb isotopic ratios from neighbouring coeval volcanic centres to define spatial variations in source components beneath the neovolcanic zones. Within the Eastern Volcanic Zone, basalt compositions vary systematically from tholeiitic near central Iceland (Veidivotn, Grimsvotn) to Fe-Ti tholeiites at Hekla and Katla, to alkaline in Vestmannaeyjar. Each volcanic centre has distinctive geochemical characteristics that require differences in source components and proportions on the scale of 10–20 km.
The heterogeneous Iceland plume: new insights from the alkaline basalts of the Snaefell volcanic centre
Authors: Hards V. L. , Kempton P. D. , Thompson R. N.
Published: March 2011

It has been accepted for some time that mixing between MORB-source mantle and the Iceland plume (geochemically relatively ‘reriched’ mantle) occurs along the Reykjanes Ridge. The composition of the basalts becomes progressively more enriched in lithophile elements towards Iceland. Within Iceland itself, there is significant variation in the composition of the mafic volcanic rocks. Although variations in degree of melting of a single source could have produced the elemental compositions of the Icelandic picritic, tholeiitic and alkalic basalts, their isotope systematics are not consistent with this model and require differences in source chemistry. Therefore, either MORB-source mantle has been mixed into the plume or the plume itself is heterogeneous. The clearest indications come from Pb isotopic data, which suggest that MORB-source mantle was
excluded
from the generation of Icelandic volcanic rocks.
Stress generation at ridge axes by plate divergence and magma rise
Authors: Jacoby W. R. , Higgs B.
Published: March 2011

A model is explored for the rifting process particularly at the divergent plate boundary in Iceland, based on direct observations of the Krafla rifting episode 1975–1984. Magma accumulates near the axial crust-mantle transition as the plates diverge from each other and compression on the boundary decreases. Two-dimensional finite-element modelling is applied to investigate how divergence and buoyant rise of magma interact in triggering rifting. Both processes are found to be important, but long intervals between rifting episodes require the time-average deviatoric stress to be compressible normal to the axis.
Ontong Java and Kerguelen Plateaux: Cretaceous Icelands?
Authors: Coffin M. F. , Gahagan L. M.
Published: March 2011

Together with Iceland, the two giant oceanic plateaux, Ontong Java in the western Pacific and Kerguelen/Broken Ridge in the Indian Ocean, are accumulations of mafic igneous rock which were not formed by ‘normal’ seafloor spreading. We compare published geochronological, crustal structure, and subsidence results with tectonic fabric highlighted in new satellite-derived free-air gravity data from the three igneous provinces, and conclude that existing evidence weighs lightly against the Ontong Java and Kerguelen plateaux originating at a seafloor spreading centre.
Modeling the Dynamic Behavior of Proton-Exchange Membrane Fuel Cells
Authors: Olapade Peter O. , Meyers Jeremy P. , Mukundan Rangachary , Davey John R. , Borup Rodney L.
Published: March 2011

A two-phase transient model has been developed which predicts the dynamic response of Proton-Exchange Membrane Fuel Cells (PEMFCs) to transients in operating power. The model uses experimentally measured Gas Diffusion Layer (GDL) capillary pressure to predict the fuel cell response to changing water production rates. Permanent hysteresis observed in experimentally measured capillary pressure of GDL is examined and found to have minimal effects on the modeling results. The model also provides explanations for the difference in time constants between membrane hydration and dehydration observed in the high frequency resistance (HFR) experiments. When there is liquid water at the cathode catalyst layer, the time it takes the water content in the membrane to reach steady state is closely tied to that of liquid water saturation in the cathode catalyst layer, as the vapor is already saturated. The water content in the membrane does not reach steady state as long as the liquid water flow in the cathode catalyst layer is not at steady state. The effects of membrane thickness on membrane hydration and dehydration time constants are investigated for Nafion 112, 115, and 117.