bluuebunny/crossref_metadata_2025 huggingface dataset:
Frost heave and pipeline upheaval buckling
Authors: Palmer Andrew C , Williams Peter J
Published: October 2003

Frost heave of soils varies greatly with the type of soil and the moisture and thermal conditions of the ground. Consequently, the initially level trench-bottom profile of a pipeline can become uneven. Upheaval buckling is a well-known phenomenon in buried pipelines: it can lead to large upward movements of a pipeline and is caused by the interaction between the longitudinal compressive force present during operation and overbend irregularities in the profile. This paper examines the possibility that frost heave and upheaval buckling can interact adversely and threaten the security of Arctic pipelines.Key words: Arctic, buckling, frost heave, permafrost, pipelines.
Improvement of the load-carrying capacity of offshore skirted foundations by electrokinetics
Authors: Micic S , Shang J Q , Lo K Y
Published: October 2003

Originating from the problem facing offshore foundation engineering, the present study is focused on using electrokinetics to enhance the load-carrying capacity of skirted foundations embedded in soft marine deposits. An experimental study was carried out in a model tank having dimensions of 150 cm × 75 cm × 70 cm. The experiments were conducted on the Welland River sediment mixed with a high salinity solution that simulates the composition of seawater. A steel cylinder of 320 mm in diameter was embedded in the sediment to represent a skirted foundation. Electrodes were installed around the steel cylinder, and a voltage of 5.2 V was applied over 28 days with polarity reversal. The load-carrying capacity of the steel cylinder and the undrained shear strength of the adjacent soil were measured after the electrokinetic treatment. The effect of electrokinetics is evaluated by comparing a series of test results performed on the untreated and treated soil. The load-carrying capacity of the steel cylinder and the undrained shear strength of the adjacent soil increased up to three times after treatment. The study also shows that electrokinetics can regain and further enhance the load carrying capacity of the embedded skirted foundation model after failure. With further development, the technology has the potential to be applied in offshore engineering practice to increase the load-carrying capacity of skirted foundations installed in soft clayey sediments.Key words: electrokinetics, skirted foundations, soft marine clay, load-carrying capacity, soil improvement.
Calibration of thermal conductivity sensors with consideration of hysteresis
Authors: Feng Man , Fredlund Delwyn G
Published: October 2003

A thermal conductivity sensor monitors soil suction by measuring the changes in thermal conductivity of the porous tip. The thermal conductivity of the porous tip is a direct function of its water content. It has long been recognized that the suction versus water content relationship of a porous material exhibits hysteresis of various magnitudes between wetting and drying processes. The sensor output may correspond to various suction values of the sensor porous tip, depending on the wetting or drying state of the porous tip. The current calibration procedure, however, represents only one of the drying processes of the sensor porous tip. A laboratory testing program was carried out to better understand the hysteretic properties of the sensor output voltage versus the suction and to further improve the calibration procedure. The output of the sensor was monitored as the sensor porous tip was subjected to various drying and wetting processes. The test results indicate an error of 30%70% for suctions higher than 100 kPa if the hysteretic effects of the porous tip are not considered in data interpretation. Based on the laboratory testing results, a revised calibration procedure was proposed that takes into consideration the capillary hysteretic effects.Key words: thermal conductivity sensor, calibration, matric suction, capillary hysteresis.
Influence of mineralogy on swelling and consolidation of soils in eastern Saudi Arabia
Authors: Azam Shahid
Published: October 2003

The mineral calcium sulphate transforms from anhydrite through bassanite to gypsum and then can convert back to bassanite and anhydrite. This transformation of calcium sulphate causes volume change that adds to the potential hazards with indigenous soils containing expansive clay minerals. Heave and settlement are the most important geotechnical problems associated with many argillaceous soils in eastern Saudi Arabia. Mineralogical evolution and engineering behaviour of such soils are governed by local geology and severe climatic and environmental conditions prevalent in the region. Based on laboratory investigations, this paper discusses the influence of mineralogy on swelling and consolidation of expansive clay, calcium sulphate forms, and their mixtures. Mineralogy is investigated using geotechnical index properties and thermal and X-ray diffraction analyses. Swelling and consolidation characteristics are directly determined and are studied in conjunction with microstructural assessment. Results indicate that under the hot and humid climate prevalent in eastern Saudi Arabia, form changes in calcium sulphate can take place in the time frame of engineering importance. The volume-change behaviour of local expansive clay depends on the form and amount of calcium sulphate present in the soil.Key words: calcium sulphate, expansive clay, swelling, consolidation.
Pullout resistance of single and double nails in a model sandbox
Authors: Hong Yung-Shan , Wu Cho-Sen , Yang Shang-Heng
Published: October 2003

Pullout tests on single and double soil nails were conducted in a model sandbox. The test parameters included variations in the surface roughness, the ratio of nail length to nail diameter, the overburden pressure, and the distance between two nails. The characteristic of a single asperity, the asperity number per unit length, and the ratio of the thread depth to the soil particle size were used to define the surface roughness factor. The test results showed that the apparent friction coefficients at the soilnail interface were dependent upon the surface roughness of the nail. Group efficiency was used to evaluate the effectiveness of a nail when installed within a group. The test results showed that the group efficiency of a double-nail system was dependent upon the surface roughness factor and has a linear relationship with the nail distance until 100% efficiency is reached. The minimum required distance for 100% efficiency also varied with the surface roughness factor.Key words: apparent friction coefficient, group efficiency, pullout test, surface roughness factor.
Infiltration characteristics of two instrumented residual soil slopes
Authors: Tsaparas Illias , Rahardjo Harianto , Toll David G , Leong Eng-Choon
Published: October 2003

This paper presents the analysis of a 12 month long field study of the infiltration characteristics of two residual soil slopes in Singapore. The field measurements consist of rainfall data, runoff data of natural and simulated rainfall events, and pore-water pressure changes during infiltration at several depths and at several locations on the two slopes. The analysis of the field measurements identifies the total rainfall and the initial pore-water pressures within the two slopes as the controlling parameters for the changes in the pore-water pressures within the slopes during infiltration.Key words: infiltration, rainfall, runoff, pore-water pressure, field measurements.
Experimental compression of loose sands: relevance to porosity reduction during burial in sedimentary basins
Authors: Chuhan Fawad A , Kjeldstad Arild , Bjørlykke Knut , Høeg Kaare
Published: October 2003

This study examines the one-dimensional stressstrain behaviour of sand at effective stresses as high as 50 MPa. Experiments were performed on 22 sands (approx. 150 tests) with different grain size, uniformity coefficient, angularity, density, grain mineralogy, and clay content. The results show that minor grain corner crushing starts at stresses of 28 MPa. The point of maximum curvature (yield point) in the porosity (n) versus logarithm of vertical effective stress (σ'v) curve defines the initiation of marked particle crushing. The stress at the yield point varies between 3 and 31 MPa depending on sand characteristics. A low yield stress is indicative of high porosity loss in the interval of intermediate stress (525 MPa). The yield stress is low when the grain size is large, grains are angular, grain strength is low, and uniformity coefficient is low. The lowest yield stress value occurs in the coarser carbonate sand, and the highest in the chert-rich sands. The sands rich in clays are highly compressible up to 25 MPa. At stresses higher than ~10 MPa, the coarser biogenic carbonate sands maintain higher porosities than the other sands. This can be explained by the fact that coarser biogenic carbonate sands have low yield stresses due to high angularity and low grain strength and initially there is local grain crushing at grain contacts. This increases the area of the grain contacts, so the coarser carbonate sands become less compressible at higher stresses. Within the high stress range (2550 MPa) the porosity loss differences related to grain size, grain shape, grain mineralogy, and sand uniformity coefficient are significantly reduced. Hence the greater compressibility of lithic and carbonate sands becomes less evident in the high-stress interval as the grain size increases.Key words: sand, grain crushing, grain size, high stress, compression.
A new working stress method for prediction of reinforcement loads in geosynthetic walls
Authors: Allen T M , Bathurst Richard J , Holtz Robert D , Walters D , Lee Wei F
Published: October 2003

Proper estimation of soil reinforcement loads and strains is key to accurate internal stability design of reinforced soil structures. Current design methodologies use limit equilibrium concepts to estimate reinforcement loads for internal stability design of geosynthetic and steel reinforced soil walls. For geosynthetic walls, however, it appears that these methods are excessively conservative based on the performance of geosynthetic walls to date. This paper presents a new method, called the K-stiffness method, that is shown to give more accurate estimates of reinforcement loads, thereby reducing reinforcement quantities and improving the economy of geosynthetic walls. The paper is focused on the new method as it applies to geosynthetic walls constructed with granular (noncohesive, relatively low silt content) backfill soils. A database of 11 full-scale geosynthetic walls was used to develop the new design methodology based on working stress principles. The method considers the stiffness of the various wall components and their influence on reinforcement loads. Results of simple statistical analyses show that the current American Association of State Highway and Transportation Officials (AASHTO) Simplified Method results in an average ratio of measured to predicted loads (bias) of 0.45, with a coefficient of variation (COV) of 91%, whereas the proposed method results in an average bias of 0.99 and a COV of 36%. A principle objective of the method is to design the wall reinforcement so that the soil within the wall backfill is prevented from reaching a state of failure, consistent with the notion of working stress conditions. This concept represents a new approach for internal stability design of geosynthetic-reinforced soil walls because prevention of soil failure as a limit state is considered in addition to the current practice of preventing reinforcement rupture.Key words: geosynthetics, reinforcement, walls, loads, strains, design, K-stiffness method.
Logarithmic Factors, Critical Temperature, and Zero Temperature Flipping in the 4D Kinetic Ising Model
Authors: Stauffer Dietrich , Adler Joan
Published: October 2003

We determine the critical temperature in the four-dimensional nearest-neighbor Ising model as J/kB Tc=0.149694±0.000002 from kinetic Monte Carlo simulations of up to 5764 spins. Here we assume the critical magnetization to decay with time as (t/ log t)-1/2. However, possible logarithmic additions to this leading scaling behavior could change the estimate beyond these error bars. A reanalyzis of old series expansions for the susceptibility and fourth moment gives 0.149696±0.000004.
Elastic Behavior of YMnO3 and ErMnO3 Manganites
Authors: Sekhar M. Chandra , Padmavathi K. , Park J. G. , Venugopal Reddy P.
Published: October 2003

The manganite oxides, YMnO 3 and ErMnO 3 having hexagonal structures were prepared by the solid state reaction method. After characterizing these materials by studying their various physical properties such as lattice parameters, X-ray density, bulk density etc., ultrasonic velocity measurements were carried out over a temperature range 80–300 K to investigate their elastic behavior. As the materials are porous, the measured elastic moduli were corrected to zero porosity. Using the room temperature elastic moduli, Debye temperature values of both the manganites have also been obtained. Surprisingly it has been found that the Young's moduli of both the materials increase continuously with decreasing temperature. A qualitative explanation for the observed behavior is offered.
A Study on Anisotropy in Ultrathin Epitaxial Fe Films in the Few-Monolayer Region
Authors: Zhai Y. , Shi L. , Zhang W. , Xu Y. X. , Lu M. , Zhai H. R. , Tang W. X. , Xu Y. B. , Bland J. A. C.
Published: October 2003

The magnetic properties and magnetic anisotropy of epitaxial ultrathin Fe films (4.1–12.7 ML) grown on GaAs (100) are studied using ex situ magnetooptical Kerr (MOKE) loop measurement and Ferromagnetic Resonance (FMR). They give consistent results. The behavior of out-of-plane and in-plane magnetic anisotropy is evaluated from the FMR data. A strong second order out-of-plane anisotropy and an in-plane uniaxial anisotropy are observed to decrease with thickness. A moderate fourth order out-of-plane anisotropy and a four-fold in-plane anisotropy appear for thicker films and increase with thickness. Their origins are discussed.
Magnetic Relaxation and Flux Creep in Superconducting YBCO Thin Films
Authors: Demirel Ali Ihsan
Published: October 2003

In this work, the temperature dependence of the magnetic relaxation in samples of YBa 2 Cu 3 O 7 (YBCO) thin films of two different qualities grown on MgO by metal organic chemical deposition technique (MOCVD) is measured in the range of 4.2–80 K using an initial applied magnetic field of 0.1 T. The relaxation data are analyzed in terms of a single effective activation energy and then more correctly of a distribution of activation energies. The single activation energies extracted are in broad agreement with published results.
Photorefractive Effect of Fe:KLN Crystal
Authors: Xu Wusheng , Zhen Xihe , Xu Zhaopeng , Xu Yuheng
Published: October 2003

We have grown KLN and Fe:KLN crystals using the TSSG method. The crystal lattice constants are measured by the X-ray diffraction technique and the crystal optical absorption edges are characterized by an ultraviolet-visible absorption spectrum measurement. The results show that the absorption edge of the Fe:KLN crystal shifts to the longer wavelengths compared with that of the KLN crystal. The exponential gain coefficient and erasure time are examined by two-beam coupling experiment. The results indicate that the exponential gain coefficient of Fe:KLN crystal is twice as large as that of the KLN crystal, and the photoconductivity of the Fe:KLN is three orders of magnitude higher than that of KLN. The enhancement of photorefractive properties of Fe:KLN crystal is also discussed.
Structural, Electrical and Magnetic Properties of Pb2Mg1-xCoxWO6 Solid Solutions
Authors: Ardelean I. , Barbur I. , Timar V. , Borodi Gh.
Published: October 2003

X-ray diffraction, electrical and magnetic measurements performed on Pb 2 Mg 1-x Co x WO 6 solid solutions with 0≤x≤1 are reported. By cobalt substitution for magnesium the diffraction patterns indicate the transition from orthorhombic structure characteristics for Pb 2 MgWO 6 to the cubic structure specific for Pb 2 CoWO 6. The Curie temperature decreases with cobalt content from 38°C to 32°C. The magnetic data indicate that the cobalt ions are in a bivalent state and, for x>0.1, experience negative magnetic interactions.
Charge Ordering under a Magnetic Field in the Extended Hubbard Model
Authors: Le Duc Anh , Hoang Anh Tuan , Nguyen Toan Thang
Published: October 2003

We study the charge ordering behavior under magnetic field H in the extended Hubbard model within the coherent potential approximation. At quarter filling, for small H we find that the relative variation of critical temperature is quadratic with the coefficient α smaller than the one for conventional spin-Peierls systems. For intermediate fields, a melting of the charge ordering on decreasing temperature under fixed H at various band filling is found.
Electron-Phonon Interaction in a Multi-Shell Spherical Nanoheterosystem
Authors: Zhang Li , Xie Hong-Jing , Chen Chuan-Yu
Published: October 2003

Under the dielectric continuum approximation, the confined longitudinal-optical (LO) phonon and interface-optical (IO) phonon modes of a multi-shell spherical nanoheterosystem are discussed. To describe the vibrations of the LO phonons, a proper eigenfunction for LO phonon modes in the core region is adopted and a legitimate eigenfunction for LO modes in the shell region is constructed. To deal with the IO phonon modes, determinant methods are employed, and the determinant deciding the frequencies of IO phonon modes are obtained. The quantized LO and IO phonons fields as well as their corresponding electron-phonon interaction Hamiltonians are also derived.
Exact Solutions for Hydrogenic Impurity States in Quantum Dots
Authors: Xie Qiongtao , Hai Wenhua , Chong Guishu
Published: October 2003

According to the hydrogenic-effective-mass theory and assumed finite barrier height for a confining potential, the analytical solutions and quantum energy-level structure for a hydrogenic impurity located at the center of a spherical quantum dot (SQD) are obtained. The calculated results reveal that because of the spatial confinement of the quantum dots, the energy, quantum numbers and radius of the SQD must satisfy a certain relation which arises from the boundary conditions. Given a barrier height or energy, the relation allows for the existence of bound states only for some discrete values of the radius of the SQD. On the other hand, for a fixed radius the energies of the bound states are discrete.
Vassiliev-type Invariants of a Theta-curve
Authors: Kanenobu Taizo
Published: October 2003

We consider Vassiliev-type invariants for an knotted theta-curve in a 3-sphere in the sense of Stanford. We give a basis for the space of the Vassiliev-type invariants of orders 2 and 3 in terms of those of the associated 3-component link of a theta-curve.
Relativistic Mean-Field Approximation with Density-Dependent Screening Meson Masses in Nuclear Matter
Authors: Sun Bao-Xi , Lu Xiao-Fu , Shen Peng-Nian , Zhao En-Guang
Published: October 2003

The Debye screening masses of the σ, ω and neutral ρ mesons and the photon are calculated in the relativistic mean-field approximation. As the density of the nucleon increases, all the screening masses of mesons increase. A different result with Brown–Rho scaling is shown, which implies a reduction in the mass of all the mesons in the nuclear matter, except the pion. Replacing the masses of the mesons with their corresponding screening masses in the Walecka-1 model, five saturation properties of the nuclear matter are fixed reasonably, and then a density-dependent relativistic mean-field model is proposed without introducing the nonlinear self-coupling terms of mesons.
A Six-Quark Dressed-Bag Description of np→dγ Radiative Capture
Authors: Kaskulov M. M. , Grabmayr P. , Kukulin V. I.
Published: October 2003

The radiative capture process np→dγ is considered within the framework of a recently developed six-quark dressed-bag model for the nucleon-nucleon interaction. The calculations presented here include both the nucleon current and the meson-exchange current contributions. The latter uses short-range hadronic form factors for the pion exchange currents consistent with the soft cut-off parameter ΛπNN from the NN-potential. Contributions of the pion exchange current and Δ-isobar current to the total cross-section still cannot explain the discrepancy between the theoretical and experimental cross-sections. Possibilities for new types of meson exchange currents associated with chiral fields inside multi-quark dressed-bag states in nuclei are discussed.
The Klein–Gordon Equation with a Coulomb Potential in D Dimensions
Authors: Dong Shi-Hai , Gu Xiao-Yan , Ma Zhong-Qi , Yu Jiang
Published: October 2003

The solutions of the Klein–Gordon equation with a Coulomb potential in D dimensions are obtained exactly, and the energy levels E(n,l,D) are analytically presented. The dependence of the energy difference ΔE(n,l,D) for D and D-1 on the dimension D is demonstrated as three different kinds of rules. The dependence of the energy E(n,l,D) on the dimension D is also analyzed. It is shown that the energy E(n,l,D) (l≠0) is almost independent of the quantum number l, while E(n,0,D) first decreases and then increases as the dimension D increases. There is no bound state of the S-wave for D=2.
Tangential Velocity Corrections to a Second-Order Coulomb-Modified Eikonal Model for Heavy-Ion Elastic Scattering
Authors: Kim Yong Joo , Cha Moon Hoe
Published: October 2003

We present the tangential velocity corrections to the second-order Coulomb-modified eikonal model at the distance of closest approach. It has been applied to elastic angular distributions of the 16 O +16 O system at E lab =350 and 480 MeV. The calculated results with tangential velocity show better agreements with the experimental data compared to those with asymptotic velocity. The Fraunhöfer oscillations observed in the elastic angular distributions can be explained by the strong interference between the near- and the far-side amplitudes. Airy structures can be shown by reducing the effective imaginary potential strength. It is found that the Airy minimum is more visible as the effective imaginary potential strength is reduced. Deep real potentials associated with rather weak imaginary ones are found to be essential to describe the refractive 16 O +16 O elastic scatterings at E lab =350 and 480 MeV.
Is the Non-Observation of Neutrinoless Double Beta Decay a Question of Sensitivity?
Authors: Tsan Ung Chan
Published: October 2003

Hypothetical neutrinoless double beta decay is possible only if the neutrino is a truly neutral particle and if it is massive. A truly neutral particle (e.g. a particle identical with its antiparticle) should have all its algebraic intrinsic properties equal to zero, in particular, its lepton number should be 0. Now, since the neutrino is a lepton, its lepton number should be 1. This contradiction would lead one to conclude that neutrinoless double beta decay cannot take place in nature. This conclusion is, up to now, in agreement with persistent failures to find evidence for this long sought key hypothetical decay despite huge efforts dedicated to this aim.
Physics Potential of the e-RHIC Based FEL-Nucleus Collider
Authors: Koru H. , Özcan A. , Sultansoy S. , Yavaş Ö
Published: October 2003

The main parameters of the FEL–RHIC collider are estimated. The physics search potential of this machine is illustrated using excitations of the 232 Th nucleus as an example. It is shown that, due to the tunability and monochromacity of the FEL beam and high statistics, the proposed collider will play an important role in the field of "traditional" nuclear physics. In addition, spin and parity of nucleus excitations can be easily identified at FEL-nucleus colliders.
Hadronic Molecular Contribution to Cryptoexotic Meson Amplitude
Authors: Gerasyuta S. M. , Kochkin V. I.
Published: October 2003

The solutions of four-quark equations using the method of extracting leading singularities of the amplitudes are obtained. The calculations of cryptoexotic meson amplitudes provide the estimates of four-quark amplitude, glueball amplitude and hadronic molecule amplitudes. We find that the main contributions to the cryptoexotic meson amplitude are given by the four-quark state and the glueball.
Multiple Production of Mesons in Au+Au and Pb+Pb Collisions
Authors: Guptaroy P. , De Bhaskar , Bhattacharyya S. , Bhattacharyya D. P.
Published: October 2003

The study presented here pertains to the model-based analyses for production of some important charged secondaries in lead-lead and gold-gold collisions at AGS, SPS and RHIC energies. We examine the role of a particular version of the Sequential Chain Model (SCM) in interpreting the data on the production of only the secondary mesons of the most abundant variety in relativistic nucleus-nucleus collisions. The initial results derived for basic pp collisions have been transformed into the corresponding cases for nucleus-nucleus collisions through the appropriate physical-mathematical formalisms. The agreement between the model of choice and the measured data for the most important varieties of mesons in the two above-stated nuclear collisions could so far be rated to be barely modest. This is presumably due to our neglect of the effects of rescattering and cascading, while we choose to obtain only the first-order results in the initial attempt.
Nuclear Spin Responses for Neutrinos in Astroparticle Physics
Authors: Ejiri H.
Published: October 2003

Nuclear spin responses are of vital importance for studies of neutrinos, weakly interacting particles and of weak interactions in nuclei. The physics objectives are concerned with lepton nuclear physics within and beyond the standard theory. Here nuclei, which consist of elementary particles in good quantum (eigen) states, are used as excellent micro-laboratories for studying fundamental particles and interactions. Subjects discussed include neutrinos(ν) and weak interactions, weakly interacting massive particles as candidates for dark matters (DM), and other related problems. Experimental studies of them are made by investigating ultra rare nuclear processes at low background underground laboratories. Nuclear responses relevant to electroweak processes, neutrinos, and weakly interacting massive particles are discussed. Nuclear spin isospin responses associated with axial charged weak currents are investigated by using charge-exchange spin flip nuclear reactions at the RCNP ring cyclotron laboratory.
Some Properties of Coupled RPA Equations with Separable Interactions
Authors: Sakamoto Hideo
Published: October 2003

We investigate some properties of coupled eigenvalue equations in the random phase approximation for fundamental modes of motion in a nuclear many-body system undergoing several separable two-body interactions. Based on the Sturm's method, a new algorithm is proposed for solving such coupled secular equations and for testing the stability condition of the Hartree-Fock ground state. A transition strength in general is expressed in a compact form and, in a restricted case, a continuous strength function is constructed by averaging with a Lorentzian distribution function.
Interacting Boson-Fermion Description of Odd-Odd Nuclei
Authors: Maino Giuseppe
Published: October 2003

I present an algebraic model and the relevant computing code for the analysis of low-energy spectra and electromagnetic properties of nuclei with an odd number of neutrons and/or protons within the framework of the Interacting Boson–Fermion Model (IBFM), taking explicitly into account the isospin degree of freedom. Some results for odd–mass and doubly–odd nuclei in the shape-transitional region around A ≈ 100 will be shown and compared with the experimental data.
Backward Stochastic PDE and Imperfect Hedging
Authors: Mania M. , Tevzadze R.
Published: October 2003

We consider a problem of minimization of a hedging error, measured by a positive convex random function, in an incomplete financial market model, where the dynamics of asset prices is given by an Rd-valued continuous semimartingale. Under some regularity assumptions we derive a backward stochastic PDE for the value function of the problem and show that the strategy is optimal if and only if the corresponding wealth process satisfies a certain forward-SDE. As an example the case of mean-variance hedging is considered.
Multiple Optimal Solutions in the Portfolio Selection Model with Short-Selling
Authors: Schianchi A. , Bongini L. , Esposti M. D. , Giardinà C.
Published: October 2003

In this paper an extension of the Lintner model [1] is considered: the problem of portfolio optimization is studied when short-selling is allowed through the mechanism of margin requirements. This induces a non-linear constraint on the wealth. When interest on deposited margin is present, Lintner ingeniously solved the problem by recovering the unique optimal solution of the linear model (no margin requirements). In this paper an alternative and more realistic approach is explored: the nonlinear constraint is maintained but no interest is perceived on the money deposited against short-selling. This leads to a fully non-linear problem which admits multiple and unstable solutions very different among themselves but corresponding to similar risk levels. Our analysis is built on a seminal idea by Galluccio, Bouchaud and Potters [3], who have re-stated the problem of finding solutions of the portfolio optimization problem in futures markets in terms of a spin glass problem. In order to get the best portfolio (i.e. the one lying on the efficiency frontier), we have to implement a two-step procedure. A worked example with real data is presented.
Inventory Effects on Daily Returns in Financial Markets
Authors: Krause Andreas
Published: October 2003

In this paper we investigate the properties of daily returns arising from inventory effects. We therefore use the well established framework of inventory-based models from market microstructure theory. It is shown using simulation studies that from this model daily returns exhibit excess volatility, negative first-order autocovariances and the volatility has a positive first-order autocovariance, which is consistent with a GARCH-process. An empirical investigation shows that a substantial part of the properties of daily returns in stock market data can be explained by inventory effects.
Independent Component Analysis and Immunization: An Exploratory Study
Authors: Bellini Fabio , Salinelli Ernesto
Published: October 2003

In this work we apply Independent Component Analysis (ICA) to the identification of the factors driving spot rates curve movements. A comparison between the standard Principal Components Analysis (PCA) approach and ICA is carried out both from a theoretical point of view, critically analyzing the negentropy based approach to ICA, and from an empirical point of view, where the performance of immunization strategies based on PCA and ICA are tested.
Optimal Strategies for Prudent Investors
Authors: Baviera Roberto , Pasquini Michele , Serva Maurizio , Vulpiani Angelo
Published: October 2003

We consider a stochastic model of investment on an asset in a stock market for a prudent investor. she decides to buy permanent goods with a fraction α of the maximum amount of money owned in her life in order that her economic level never decreases. The optimal strategy is obtained by maximizing the exponential growth rate for a fixed α. We derive analytical expressions for the typical exponential growth rate of the capital and its fluctuations by solving an one-dimensional random walk with drift.
A Simple Model for Option Pricing with Jumping Stochastic Volatility
Authors: Herzel Stefano
Published: October 2003

This paper proposes a simple modification of the Black–Scholes model by assuming that the volatility of the stock may jump at a random time τ from a value σa to a value σb. It shows that, if the market price of volatility risk is unknown, but constant, all contingent claims can be valued from the actual price C0, of some arbitrarily chosen "basis" option. Closed form solutions for the prices of European options as well as explicit formulas for vega and delta hedging are given. All such solutions only depend on σa, σb and C0. The prices generated by the model produce a "smile"-shaped curve of the implied volatility.
Pricing Multi-Asset Options with an External Barrier
Authors: Kwok Yue-Kuen , Wu Lixin , Yu Hong
Published: October 2003

An external barrier of an option contract is a stochastic variable which determines whether the option is knocked in or out when the value of the variable is above or below some predetermined level, but itself is not the price of an asset which underlies the option. In this paper, we present analytic formulation for the valuation of European options on one or multiple assets with single external barrier, where the barrier level can be exponential. As the domain of the problem becomes semi-infinite due to the presence of the external barrier, we employ the method of images to find the Green function of the governing differential equation. An efficient and accurate fractional step finite difference scheme is proposed for the numerical valuation of these barrier options.
Interval estimates of functionals in time‐delay systems with uncertainty
Authors: Zaika Yury V.
Published: October 2003

We consider a linear dynamical system with delay and uncertainty in initial
data and movement and measurement equations. We present an
algorithm of estimating an interval of possible values of
functionals on solutions. We construct suboptimal weight
functions in integral observation operators to
minimize a sure estimation.
A generalization of Mulholland′s inequality
Authors: Bicheng Yang , Debnath Lokenath
Published: October 2003

By introducing three parameters r, s, and λ, we give a
generalization of Mulholland′s inequality with a best constant
factor involving the β function. As its applications, we
also consider its equivalent form and some particular results.
Heegaard splittings and Morse‐Smale flows
Authors: Gautschi Ralf , Robbin Joel W. , Salamon Dietmar A.
Published: October 2003

We describe three theorems which summarize what survives in
three dimensions of Smale′s proof of the higher‐dimensional
Poincaré conjecture. The proofs require Smale′s cancellation
lemma and a lemma asserting the existence of a 2‐gon. Such
2‐gons are the analogues in dimension two of Whitney disks in
higher dimensions. They are also embedded lunes; an (immersed)
lune is an index‐one connecting orbit in the Lagrangian Floer
homology determined by two embedded loops in a 2‐manifold.
Regulation of Superoxide Anion Production by NADPH Oxidase in Monocytes/Macrophages
Authors: Cathcart Martha K.
Published: October 2003

Monocyte extravasation into the vessel wall has been shown to be a critical step in the development of atherosclerosis. Upon activation, monocytes produce a burst of superoxide anion due to activation of the NADPH oxidase enzyme complex. Monocyte-derived superoxide anion contributes to oxidant stress in inflammatory sites, is required for monocyte-mediated LDL oxidation, and alters basic cell functions such as adhesion and proliferation. We hypothesize that monocyte-derived superoxide anion production contributes to atherosclerotic lesion formation. In this brief review, we summarize our current understanding of the signal transduction pathways regulating NADPH oxidase activation and related superoxide anion production in activated human monocytes. Novel pathways are identified that may serve as future targets for therapeutic intervention in this pathogenic process. The contributions of superoxide anion and NADPH oxidase to atherogenesis are discussed. Future experiments are needed to clarify the exact role of NADPH oxidase-derived superoxide anion in atherogenesis, particularly that derived from monocytes.
Coronary Vessel Development
Authors: Wada Aya M. , Willet Spencer G. , Bader David
Published: October 2003

Development of the coronary vascular system is an interesting model in developmental biology with major implications for the clinical setting. Although coronary vessel development is a form of vasculogenesis followed by angiogenesis, this system uses several unique developmental processes not observed in the formation of other blood vessels. This review summarizes the literature that describes the development of the coronary system, highlighting the unique aspects of coronary vessel development. It should be noted that many of the basic mechanisms that govern vasculogenesis in other systems have not been analyzed in coronary vessel development. In addition, we present recent advances in the field that uncover the basic mechanisms regulating the generation of these blood vessels and identify areas in need of additional studies.
Tissue Angiotensin-Converting-Enzyme (ACE) Deficiency Leads to a Reduction in Oxidative Stress and in Atherosclerosis
Authors: Hayek Tony , Pavlotzky Elsa , Hamoud Shadi , Coleman Raymond , Keidar Shlomo , Aviram Michael , Kaplan Marielle
Published: October 2003

Background—

Angiotensin II, produced by angiotensin-converting-enzyme (ACE), enhances oxidative stress and atherogenesis. In this study, we analyzed whether tissue ACE deficiency in ACE-knockout mice type-2 would affect their oxidative status. Moreover, by crossbreeding the ACE-knockout mice with atherosclerotic apolipoprotein E (apo E)–deficient (E
0
) mice, we questioned whether tissue ACE deficiency affects atherogenesis.

Methods and Results—

ACE-deficient mice type-2 (ACE
+/−
) exhibited reduced serum lipid peroxidation compared with ACE
+/+
mice. Peritoneal macrophages from ACE
+/−
mice demonstrated lower oxidative status, as exhibited by decreases of 47%, 33% 56%, and 51%, in their lipid peroxides, superoxide release, dichlorofluorescein fluorescence, and LDL oxidation, respectively, compared with ACE
+/+
mice. ACE
+/−
mice crossbred with E
0
mice, resulting in atherosclerotic mice heterozygous for ACE (ACE
+/−
/E
0
mice), exhibited reduced lipid peroxidation, increased paraoxonase activity, and lower macrophage LDL oxidation compared with E
0
and ACE
+/+
/E
0
mice. ACE
+/−
/E
0
mice also exhibited reduced NADPH-induced aortic superoxide ion production by 52% and a reduction of 43% in their atherosclerotic lesion size compared with E
0
mice. Finally, 2 animals genotyped as homozygous-knockout for both
ACE
and
APOE
genes (ACE
−
/
−
/E
0
), exhibited a striking reduction of 86% in their atherosclerotic lesion area compared with E
0
mice.

Conclusions—

Reduction of tissue ACE with the ACE-knockout mouse type-2 model inhibited oxidative stress and atherogenesis.
Thrombin and Phenotypic Modulation of the Endothelium
Authors: Minami Takashi , Sugiyama Akira , Wu Sheng-Qian , Abid Ruhul , Kodama Tatsuhiko , Aird William C.
Published: October 2003

Thrombin signaling in the endothelium is linked to multiple phenotypic changes, including alterations in permeability, vasomotor tone, and leukocyte trafficking. The thrombin signal is transduced, at least in part, at the level of gene transcription. In this review, we focus on the role of thrombin signaling and transcriptional networks in mediating downstream gene expression and endothelial phenotype. In addition, we report the results of DNA microarrays in control and thrombin-treated endothelial cells. We conclude that (1) thrombin induces the upregulation and downregulation of multiple genes in the endothelium, (2) thrombin-mediated gene expression involves a multitude of transcription factors, and (3) future breakthroughs in the field will depend on a better understanding of the spatial and temporal dynamics of these transcriptional networks.
Anoïkis in the Cardiovascular System
Authors: Michel Jean-Baptiste
Published: October 2003

Anoïkis is defined as programmed cell death induced by the loss of cell/matrix interactions. Adhesion to structural glycoproteins of the extracellular matrix is necessary for survival of the differentiated adherent cells in the cardiovascular system, including endothelial cells, smooth muscle cells, fibroblasts, and cardiac myocytes. Adhesion is also a key factor for the differentiation of mesenchymal stem cells. In particular, fibronectin is considered a factor of survival and differentiation for many adherent cells. Adhesion generates cell tensional integrity (tensegrity) and repression of apoptotic signals, whereas detachment has the opposite effect. Anoïkis plays a physiological role by regulating cell homeostasis in tissues. However, anoïkis can also be involved in pathological processes, as illustrated by the resistance to anoïkis in cancer and its enhancement in degenerative tissue remodeling. Extracellular mediators of anoïkis include matrix retraction, leading to loss of tensegrity in fibroblasts, pharmacological disengagement of integrins by RGD-like peptides and fragments of fibronectin, and focal adhesion disassembly by fragments of thrombospondin, plasminogen activator-1, and high-molecular-weight kininogen. In addition to binding of the RGD peptide by integrins, the engagement of the heparin binding sites of adhesive glycoproteins with glycosaminoglycans on the cell surface is also involved in the prevention of cell detachment–induced apoptosis. Proteases able to degrade adhesive glycoproteins, such as fibronectin, induce anoïkis of vascular adherent cells. Active proteases can either be secreted directly by inflammatory cells, as elastase and cathepsin G by polymorphonuclear leukocytes, chymase and tryptase by mast cells, and granzymes by lymphocytes, or generated from circulating zymogens by activation in close contact with the cells. This is the case for the pericellular conversion of plasminogen to plasmin, which degrades fibronectin and induces anoïkis of smooth muscle cells. Involvement of proteases has also been proposed in the apoptotic response of cultured adherent cells to serum starvation. Anoïkis is probably involved in pathological remodeling of cardiovascular tissues, including cardiac myocyte detachment in heart failure, deendothelialization and plaque rupture in atherosclerosis, and smooth muscle cell disappearance in aneurysms and varicose veins. The absence of cell adhesion and growth resulting from cleavage of adhesive proteins also represents a major impediment to cellular healing, including the absence of cell recolonization of proteolytically injured tissue and the low efficacy of cell transplantation. However, the exact role of anoïkis in cardiovascular pathologies remains to be further defined.
Noninvasive Imaging of Transgene Expression by Use of Positron Emission Tomography in a Pig Model of Myocardial Gene Transfer
Authors: Bengel Frank M. , Anton Martina , Richter Thomas , Simoes Marcus V. , Haubner Roland , Henke Julia , Erhardt Wolf , Reder Sybille , Lehner Terry , Brandau Wolfgang , Boekstegers Peter , Nekolla Stephan G. , Gansbacher Bernd , Schwaiger Markus
Published: October 2003

Background—

Radionuclide imaging of reporter gene expression may be useful for noninvasive monitoring of clinical cardiac gene therapy. Experience until now, however, has been limited to small animals.

Methods and Results—

To evaluate feasibility in a clinically applicable setting, pigs were studied by conventional positron emission tomography (PET) 2 days after regional intramyocardial injection of control adenovirus or adenovirus carrying herpesviral thymidine kinase reporter gene (HSV1-tk). Myocardial blood flow was quantified by use of [
13
N]ammonia. Subsequently, kinetics of the reporter substrate [
124
I]-2′-fluoro-2′-deoxy-5-iodo-1-β-
d
-arabino-furanosyluracil (FIAU) were assessed over a period of 2 hours. Areas infected with adenovirus expressing HSV1-tk showed significantly elevated FIAU retention during the first 30 minutes after injection. At later times, washout was observed, and retention was not different from that in areas infected with control virus or remote myocardium. Early in vivo FIAU uptake correlated with ex vivo images, autoradiography, and immunohistochemistry for reporter gene product after euthanasia. After intramyocardial injection of both adenoviruses, myocardial blood flow was mildly elevated compared with that in remote areas, consistent with histological signs of regional inflammation.

Conclusions—

In vivo quantification of regional myocardial transgene expression is feasible with clinical PET methodology, the radioiodinated reporter probe FIAU, and the HSV1-tk reporter gene. Radioactivity efflux after specific initial uptake was not observed previously in tumor studies, suggesting that tissue-specific differences in nucleoside metabolism influence reporter probe kinetics. By coregistering reporter gene expression with additional biological parameters such as myocardial blood flow, PET allows for noninvasive characterization of the success of cardiac gene transfer along with its functional correlates.
Tumor Necrosis Factor-α Inhibits Insulin’s Stimulating Effect on Glucose Uptake and Endothelium-Dependent Vasodilation in Humans
Authors: Rask-Madsen Christian , Domínguez Helena , Ihlemann Nikolaj , Hermann Thomas , Køber Lars , Torp-Pedersen Christian
Published: October 2003

Background—

Inflammatory mechanisms could be involved in the pathogenesis of both insulin resistance and atherosclerosis. Therefore, we aimed at examining whether the proinflammatory cytokine tumor necrosis factor (TNF)-α inhibits insulin-stimulated glucose uptake and insulin-stimulated endothelial function in humans.

Methods and Results—

Healthy, lean male volunteers were studied. On each study day, 3 acetylcholine (ACh) or sodium nitroprusside (SNP) dose-response studies were performed by infusion into the brachial artery. Before and during the last 2 dose-response studies, insulin and/or TNF-α were coinfused. During infusion of insulin alone for 20 minutes, forearm glucose uptake increased by 220±44%. This increase was completely inhibited during coinfusion of TNF-α (started 10 min before insulin) with a more pronounced inhibition of glucose extraction than of blood flow. Furthermore, TNF-α inhibited the ACh forearm blood flow response (
P
<0.001), and this inhibition was larger during insulin infusion (
P
=0.01) but not further increased by
N
G
-monomethyl-
l
-arginine acetate (
P
=0.2). Insulin potentiated the SNP response less than the ACh response and the effect of TNF-α was smaller (
P
<0.001); TNF-α had no effect on the SNP response without insulin infusion. Thus, TNF-α inhibition of the combined response to insulin and ACh was likely mediated through inhibition of NO production.

Conclusion—

These results support the concept that TNF-α could play a role in the development of insulin resistance in humans, both in muscle and in vascular tissue.