bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled Synthesis and Characterization of CuO Nanostructures through a Facile Hydrothermal Route in the Presence of Sodium Citrate
Authors: Xiao Hong‐Mei , Fu Shao‐Yun , Zhu Lu‐Ping , Li Yuan‐Qing , Yang Guo
Published: March 2007

The controlled synthesis of one‐dimensional, two dimensional, and three‐dimensional CuO nanostructures has been achieved by a hydrothermal process in the presence of sodium citrate (SC) by simply controlling the reaction conditions. When the molar ratio of sodium citrate to CuSO4·5H2O (represented by SC/Cu2+) is below 1.0, 1D CuO nanorods with 30–40 nm diameters and 100–200 nm lengths are formed. In the absence of citrate, 2D flakelike CuO nanostructures with 150–200 nm widths and 300–400 nm lengths are obtained. When the SC/Cu2+ ratio is more than 1.0, 3D branchlike CuO nanostructures with lengths of hundreds of nanometers and diameters of 20–100 nm are attained. On the basis of the morphology and X‐ray diffraction patterns of the samples, a possible growth mechanism for the CuO nanostructures is proposed. Moreover, it is shown that the optical bandgap energy (Eg) of resulting CuO nanostructures can be tuned through morphological control of the CuO nanostructures. Ultraviolet absorption measurements reveal that the estimated bandgap energy of the 1D rodlike, 2D flakelike, and 3D branchlike CuO nanostructures is 2.36, 1.60, and 1.40 eV, respectively.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Oral Bioaccessibility and Leaching: Tests for Soil Risk Assessment
Authors: Hansen J. B. , Oomen A. G. , Edelgaard I. , Grøn C.
Published: March 2007

A set of test methods for estimating the risk for human health (oral bioaccessibility tests) and groundwater (leaching tests) was applied to contaminated soils from three sites with different sources of contamination. The bioaccessible soil concentrations of the contaminants cadmium, lead, nickel, benzo(a)pyrene and dibenz(a,h)anthracene were considerably lower than the total concentrations. The leached concentrations of the polycyclic aromatic hydrocarbons, cadmium and nickel were below the EU drinking water and Danish groundwater criteria, whereas the leached lead concentrations were below the drinking water criteria but above the groundwater criteria. Based upon the test results, a risk assessment of the soils with respect to human health (oral exposure) and groundwater was established that reflected a reduced availability and mobility of PAH and heavy metals in the soils.
Characterization of Growth and Metabolism of Commercial Strains of Propionic Acid Bacteria by Pressure Measurement
Authors: Benjelloun H. , Rabe Ravelona M. , Lebeault J.‐M.
Published: March 2007

Dairy propionibacteria are essential starters for Emmental cheese manufacture. The behavior of three commercial strains of Propionibacterium freudenreichii subsp. shermanii (P.f. 1, P.f. 2 and P.f 3) were studied in a liquid medium under air and N2 atmosphere using an on‐line pressure measurement technique. Growth kinetics and metabolite production were characterized under conditions usually reported as “optimal conditions” (pH 6.5, NaCl 0 %, temperature 30 °C) and also evaluated under “stressful conditions” (pH 5.2, NaCl 2 %, temperature 20 °C) simulating the cheese ripening conditions. In both cases, the effects of oxygen on growth were strain‐dependent. Under “stressful conditions”, two of the three strains were inhibited by oxygen under conditions of air atmosphere, while all three strains grew under conditions of N2 atmosphere. In the latter case, the duration of the lag phase and the maximum rate of pressure variation were significantly different, however, no significant differences were found between the strains with regard to the total fermentation time. Under “optimal conditions” metabolite production was strain‐dependent. In an air atmosphere, all strains produced more acetate and CO2 and less propionate than in a nitrogen atmosphere.
Effect of Pollution Load and Oxygen Availability on Thermophilic Aerobic Continuous Biodegradation of Potato Processing Wastewater
Authors: Lasik M. , Nowak J.
Published: March 2007

The possibility of enhancing the effectiveness of the biodegradation process of potato wastewater was evaluated. The effect of wastewater pollution load, dilution rate and oxygen supplementation during the thermophilic aerobic continuous utilization process on biodegradation of the main organic pollutants was investigated. Aeration performed using a stirred tank reactor (1.5 vvm, 300 rpm, 55 °C) proved to be not sufficient to provide aerobic conditions. During the continuous process, the amount of oxygen introduced into the wastewater was totally utilized by the microflora. The accumulation and decomposition of the fermentative metabolism products of the Bacillus mixed culture during oxygen limitation and supplementation were analyzed. Under microaerobic conditions (DOT < 1 %), a biosynthesis of acetic acid was observed up to a concentration of 6.5 g/dm3. After chemostat conditions were achieved, the level of acetic acid stabilized at 2.2 g/dm3. The addition of oxygen for aeration allowed a total decomposition of organic acids like acetic and lactic acid (the by‐products were synthesized from partially oxidized substrates) as well as an increase in COD reduction of the wastewater (from 66 % to 79 %). The periodic fortification of aeration with pure oxygen is proposed for critical situations during the continuous wastewater biodegradation when an unexpected inflow of highly polluted wastewater occurs in the system.
Modal analysis of non‐classically damped linear systems
Authors: Veletsos Anestis S. , Ventura Carlos E.
Published: March 2007

A critical, textbook‐like review of the generalized modal superposition method of evaluating the dynamic response of nonclassically damped linear systems is presented, which it is hoped will increase the attractiveness of the method to structural engineers and its application in structural engineering practice and research. Special attention is given to identifying the physical significance of the various elements of the solution and to simplifying its implementation. It is shown that the displacements of a non‐classically damped n‐degree‐of‐freedom system may be expressed as a linear combination of the displacements and velocities of n similarly excited single‐degree‐of‐freedom systems, and that once the natural frequencies of vibration of the system have been determined, its response to an arbitrary excitation may be computed with only minimal computational effort beyond that required for the analysis of a classically damped system of the same size. The concepts involved are illustrated by a series of examples, and comprehensive numerical data for a three‐degree‐of‐freedom system are presented which elucidate the effects of several important parameters. The exact solutions for the system are also compared over a wide range of conditions with those computed approximately considering the system to be classically damped, and the interrelationship of two sets of solutions is discussed.
Equivalent stationary motion and average response spectra
Authors: Lin Jeen‐Shang , Tyan Jaung‐Yann
Published: March 2007

This study not only attempts to justify an equivalent stationary motion model, but also endeavours to illustrate its potentials as an attractive analysis tool. Using 38 ground accelerations recorded on rock sites as data base, this study first demonstrates that the equivalent stationary motions do give average response spectra compatible with real records. This study also shows that through the equivalent stationary model, a set of motions may be defined by specifying the joint distributions of the model parameters. Finally, by converting a relationship between earthquake magnitude and liquefaction potentials of ground motions, this study has derived normalized magnitude‐dependent response spectra for rock sites.
Seismic inelastic design spectra
Authors: Mostaghel N. , Hernried A. G.
Published: March 2007

To alleviate some of the shortcomings associated with the statistically based inelastic spectral shapes, a rigorous method for the construction of inelastic design spectra is proposed. The method is based on several bounds which are derived from the differential equation of motion for a single degree of freedom system. Comparisons of the proposed spectral bounds with the actual elastoplastic response spectra and with the 84 per cent Newmark elastoplastic design spectra reveal that the proposed method yields a more economical, reliable and simple design aid. To demonstrate the quality of the proposed bounds, comparisons of the bounding spectra with their corresponding constant ductility elastoplastic response spectra for a number of records have been presented.
Dynamic stiffness of rigid rectangular foundations on the half‐space
Authors: Triantafyllidis Th.
Published: March 2007

The dynamic soil–structure interaction of a rigid rectangular foundation with the subsoil represents a mixed‐boundary value problem. This problem is formulated in terms of a system of coupled Fredholm integral equations of the first kind. The subsoil is modelled by a homogeneous, linear‐elastic and isotropic half‐space which is perfectly bonded to the rigid, rectangular foundation. An approximate solution for the resultant loads between the foundation and the half‐space due to a unit forced displacement or rotation is obtained using the Bubnov–Galerkin method. Using this method the displacement boundary value conditions are exactly satisfied and the contact stress distributions between the foundation and the half‐space are approximated by series expansions of Chebyshev polynomials. This method provides a simple means of studying the soil‐structure interaction of rectangular foundations with different inertia properties.
Stability of elastic frames subjected to earthquake excitations
Authors: Ahmadi Goodarz , Abdel‐Rahman Samir
Published: March 2007

Dynamic stability of elastic multistorey frame structures subjected to vertical earthquake ground accelerations is studied. Different stationary, non‐stationary, white and non‐white random models for earthquake strong motion are considered. The concepts of mean‐square and almost‐sure stability are reviewed and the corresponding stability theorems are presented. Several general criteria regarding the dynamic stability of the equilibrium state of multistorey frames subjected to random excitations are developed. A few examples concerning the stability of single and multi‐degree‐of‐freedom structures under earthquake excitations are presented. The stability of motion of frames under combined horizontal–vertical acceleration is also briefly discussed.
Transient waves in a rod subjected to impulsive end loading
Authors: Thambiratnam David P
Published: March 2007

Herein the propagation of transient waves in a rod due to impulsive end loading is investigated using the method of wavefront expansion. The Mindlin–Herrmann equations which include the Poisson effect are used to model the rod. Since this rod theory is restricted to lower values of Poisson's ratio (< 0.283), the present work also has the same restriction. The impulsive end loading on the rod can be prescribed in the form of stress, strain, velocity or acceleration boundary conditions. The analysis is based on the concept of a wave as a carrier of discontinuities in the field variables and their derivatives. These discontinuities are determined from a set of recurrence relations which are in turn generated by the use of time harmonic asymptotic series solutions to the equations of motion. Transients due to both velocity and strain (or stress) boundary conditions are treated. Numerical examples are presented to illustrate the method of solution. The results indicate the distortion of the transient waves due to the dispersive nature of the governing equations. Transients due to other boundary conditions at the rod end can be treated by using the results presented in the paper.
Inferred displacements, velocities and rotations of a long rigid foundation located at el centro differential array site during the 1979 imperial valley, california, earthquake
Authors: Niazi Mansour
Published: March 2007

Digitally recorded acceleration time histories of the 1979 Imperial Valley earthquake by the five elements of the El Centro Differential Array are used to estimate the induced torsional and rocking vibrations of long structures in the near field of strong earthquakes. The underlying assumptions in these estimates are high rigidity of the foundation relative to the surrounding soil and its negligible mass. Based on these analyses, the peak rotation amplitude of an 18 m long foundation within 5 km of the fault is approximately 1 × 10−3 rad, or nearly 0·06 degrees, and decreases rapidly for larger foundation dimensions for either the rocking or torsional mode. The strongest impulses of rotations coincide with arrival of the S phase. This paper examines the sensitivity of the resulting peak displacement and particle velocity amplitudes to the foundation dimension. It is inferred that the base averaging effects of displacement and velocity fields at frequencies contributing to peak values (f < 1 Hz) are negligibly small. Rocking and torsional amplitudes for the specific site and geometry considered here show a tendency to reduce with the increase of foundation dimensions.
Random vibration of hysteretic systems under bi‐directional ground motions
Authors: Park Y. J. , Wen Y. K. , Ang A. H‐S.
Published: March 2007

A random vibration method is developed for the response analysis of hysteretic structural systems under stochastic two‐dimensional earthquake excitations. The biaxial hysteretic restoring force is modelled by coupled non‐linear differential equations; the response statistics are obtained using the equivalent linearization technique. The validity of the proposed model is appraised using available biaxial loading tests of reinforced concrete columns. A parametric study was performed to examine the significance of the effects of biaxial interaction under earthquake excitations. A practical method to evaluate the extreme response statistics is also presented.
Simplified analysis of dynamic response of rigid foundations with arbitrary geometries
Authors: Chow Y. K.
Published: March 2007

A simple, efficient numerical procedure is presented for the analysis of the steady‐state dynamic response of rigid foundations of arbitrary shape on a homogeneous, isotropic elastic half‐space. The contact area of the foundation and soil medium is discretized into square subregions. The influence of the rigid square subregion is approximated by that of an equivalent rigid circular base with the same contact area. This approximation is a better representation of a rigid square subregion than a uniformly stressed subregion used in earlier approaches. Simple expressions are used to determine the influence of the subregion on itself and on the rest of the subregions, without the expense of numerical integration procedures. The present method is demonstrated to converge rapidly. The accuracy of this method is examined by comparison with available published theoretical and experimental results.
An index for measuring the effects of topography on seismic ground motion intensity
Authors: Sánchez‐sesma Francisco J. , Faccioli Ezio , Fregonese Roberto
Published: March 2007

An index is proposed for the quantitative evaluation of topographical effects, as may be required in seismic microzoning and structural design applications. This topographical effects index (TEI) is defined as the relative Arias intensity for a given position.

As an example, the TEI is calculated for a semicircular canyon excited by an earthquake signal that consists of plane elastic SH waves and is characterized by a theoretical spectrum of accelerations. The analytical solution by Trifunac15 provides the transfer functions for this problem. The behaviour and spacial distribution of the calculated TEI values are illustrated for different incidence angles and spectral parameters.

The proposed index appears useful for generating quantitative criteria which, after proper confirmation by instrumental recordings, could be considered in earthquake code provisions.
Dynamic modelling of axisymmetric foundations
Authors: Chen Cheng‐Hsing , Penzien Joseph
Published: March 2007

A boundary impedance matrix to characterize a homogeneous half‐space with a cylindrical cavity is formulated by the global Ritz method. This method, which is basically the same as the indirect boundary element method, uses a very limited number of distributed sources to generate Ritz vector sets representing the far‐field impedances. The resulting impedance matrix is fully‐coupled, complex‐valued, frequency‐dependent and can be combined with any compatible finite element near field for carrying out soil–structure interaction analyses. The numerical results obtained by this method for surface supported and embedded foundations are very close to corresponding published results obtained by different procedures. Combining the boundary impedance matrix with a finite element near field provides an hybrid model which is effective and efficient in carrying out dynamic soil–structure interaction analyses.
Modal analysis for random vibration of hysteretic frames
Authors: Baber T. T.
Published: March 2007

An algorithm is presented for the direct stiffness formulation of hysteretic frames which is suitable for random vibration analysis under zero mean or non‐zero mean random excitation. A modal transformation is used to reduce the number of active degrees of freedom. First and second order response statistics are presented for two example frames using stochastic equivalent linearization and Monte Carlo simulation. The modal transformation stabilizes the stationary response calculation algorithm by eliminating superfluous higher modes. The iterations for transient response calculations under non‐zero mean excitations are destabilized by elimination of too many modes. The modal transformation allows reasonable response estimates to be obtained with significant reductions in computing time. The expected lower modes dominate the response, but inclusion of several higher modes is necessary to provide reasonable response estimates.
A model for system identification of degrading structures
Authors: Iwan Wilfred D. , Cifuentes Arturo O.
Published: March 2007

This paper presents a physically motivated model for the gross dynamic behaviour of degrading hysteretic structures subjected to damaging earthquake motions. The model is intended to provide a vehicle for gaining insight into the nature of the non‐linear response of such structures and to be used in system identification studies. A concept is presented for identifying the model parameters based on examination of the gross restoring force characteristic of a real structure. The model is applied to data from two damaged structures: the Bank of California building in the 1971 San Fernando earthquake and the Imperial County Services building in the 1979 Imperial County earthquake.
Structural response to non‐stationary non‐white stochastic ground motions
Authors: Langley R. S.
Published: March 2007

A numerical procedure is presented for calculating the survival probability of a linear multidegree of freedom structure subjected to non‐stationary non‐white ground motions using the concept of qualified envelope crossings. The moment equations governing the covariances of the structural response and its Hillbert transform are derived, and efficient techniques for calculating various convolution integrals which appear in these equations are discussed. Numerical integration of the moment equations yields the statistics of the response and the response envelope, from which the survival probability can be estimated. Excellent agreement is found with published analytical results for the response variances of a three storey building, and it is shown that the method can readily deal with cases for which there is no analytical solution.
Vertical vibration of ring foundations
Authors: Veletsos Anestis S. , Tang Yu
Published: March 2007

A comprehensive analysis is made of the harmonic response of vertically excited, massless, rigid ring foundations supported at the surface of an homogeneous elastic halfspace. The parameters considered include the thickness to radius ratio for the ring, the frequency of the exciting force and of the resulting steady‐state response, and Poisson's ratio for the supporting medium. The response quantities examined include the stiffness and damping coefficients of the system in an equivalent spring–dashpot representation of the supporting medium, the displacements of the foundation and of points on the ground surface away from the foundation, and the normal pressure at the foundation–medium interface. The results in each case are compared with those obtained for a solid disk having the same radius as the outer radius of the ring, and a simple approximate model is used to interpret the results and to provide insight into the action of the system. The reported data are computed by a method of analysis that takes due account of the mixed boundary conditions at the surface of the halfspace, and are believed to be of high accuracy.
Dynamic stability of liquid‐filled cylindrical shells under vertical excitation, Part II: Theoretical results
Authors: Chiba M. , Tani J.
Published: March 2007

Theoretical analyses are presented for the dynamic stability of a clamped‐free cylindrical shell partially filled with liquid, under vertical excitation. In the analyses, the dynamic version of the Donnell equations and the velocity potential theory were used for the motions of the shell and the liquid, respectively. The problem was solved by using the modified Galerkin method so as to satisfy the boundary conditions. The equations of motion coupling the shell and the liquid were derived from a type of coupled Mathieu's equation. It is found that the parametric principal resonance could occur, as well as the parametric combination resonance of the sum type, involving two natural vibrations with the same circumferential wave number but with different axial mode number. The latter type of parametric resonance apparently has not been previously studied. The instability regions where parametric resonance occurs were determined by using Hsu's method.17 To compare with the experimental results which had been stated in a companion paper,15 detailed numerical calculations were carried out for the two test cylinders partially filled with water. Excellent agreement between theory and experiment was demonstrated for the instability regions.
Impedance functions for foundations embedded in a layered medium: An integral equation approach
Authors: Apsel R. J. , Luco J. E.
Published: March 2007

An integral equation technique to calculate the dynamic response of foundations embedded in a layered viscoelastic half‐space when subjected to external forces and moments is presented. The technique is based on representing the radiated field as resulting from a set of sources distributed over a surface internal to the actual boundary of the foundation and by imposing the boundary conditions in an integral sense. The resulting non‐singular integral equation with symmetric kernel is solved by discretization and reduction to a system of linear algebraic equations. The technique is validated by comparison with previous results for cylindrical foundations with different embedment ratios.
Finite element analysis of the seismic response of anchored and unanchored liquid storage tanks
Authors: Barton D. C. , Parker J. V.
Published: March 2007

The seismic response of liquid‐filled cylindrical storage tanks has been investigated using finite element techniques implemented in the general purpose structural analysis computer code ANSYS. Both added mass concepts and displacement‐based fluid finite elements were employed to allow for the effects of the liquid. Simplified response spectrum modal analyses of a tank making use of the axisymmetric harmonic displacement patterns of the principal modes of deformation were found to give accurate predictions of the tank behaviour with a rigidly anchored base. Time history analyses of three‐dimensional finite element models of unanchored and flexibly anchored tanks, with gap conditions between the tank base and the supporting floor to allow lift‐off of the base, indicated that stresses in the tank and resultant loads on the floor can be much greater than for a rigidly restrained tank. These results demonstrate the importance of carefully considering the restraint conditions when performing seismic design calculations on storage tanks.
Dynamic interaction between adjacent foundations
Authors: Lin H.‐T. , Roesset J. M. , Tassoulas J. L.
Published: March 2007

The results of a parametric study on the dynamic interaction between adjacent foundations are presented. Addressed in this study are the effects of distance, direction of alignment, embedment and structural inertia. Several conclusions are drawn regarding the significance of each of these factors.
Marginal cost based seismic decision: A probabilistic approach
Authors: Parisi Maria A.
Published: March 2007

Among various methodologies for seismic risk mitigation, the use of the marginal cost of saving a life as decision variable, proposed in the literature, does not require to assign a cost to human life. Also, optimization of resources over a territory can be profitably performed in terms of such a variable. Parameters of different type (seismic, structural, financial) enter into the analytical definition of the marginal cost of saving a life. These parameters are subject to intrinsic variability and uncertainty that are bound to affect the decision variable. This aspect was not originally taken into account systematically. The influence of the uncertainty in the various basic parameters on the decision variable is studied here. A procedure is suggested to develop constant probability of exceedance contours of the decision variable versus the design coefficient to be selected. The suggested procedure is exemplified for two regions of different seismicity.
Cumulative experimental errors in pseudodynamic tests
Authors: Shing Pui‐Shum B. , Mahin Stephen A.
Published: March 2007

In pseudodynamic tests, experimental feedback errors are accumulated in the step‐by‐step integration procedure. In this paper, the growth of cumulative experimental errors is examined. Approximate cumulative error bounds are derived for linear single‐ and multi‐degree‐of‐freedom systems, based on realistic models of random and systematic feedback errors. These studies show that the rate of cumulative error growth with respect to the integration time step increases rapidly with the natural frequency of the specimen and the integration time interval used. Hence, the higher modes of a multi‐degree‐of‐freedom system are more sensitive to experimental errors than the lower ones. Furthermore, it is shown that some systematic errors are extremely undesirable. Rational criteria for assessing the reliability of pseudodynamic test results are presented.
Eigenproperties of non‐classically damped primary structure and equipment systems by a perturbation approach
Authors: Suarez L. E. , Singh M. P.
Published: March 2007

Closed‐form expressions are obtained to calculate the approximate complex eigenvalues and eigenvectors of a system composed of a non‐classically damped primary structure and a single degree of freedom oscillator. The expressions are obtained through a systematic second order perturbation analysis of a transformed eigenvalue problem of the combined system. The possibility of tuning between the structure and equipment is considered. The dynamic properties of the combined system are derived in terms of the complex eigenvalues and eigenvectors of the supporting structure and the frequency, mass and damping ratio of the equipment. Examples demonstrating the accuracy of the expressions for the eigenvalues and eigenvectors are presented. These eigenproperties are used for generation of floor response spectra for non‐classically damped structures to incorporate the dynamic interaction effects between the structure and equipment.
Diabetes mellitus and risk of breast cancer: A meta‐analysis
Authors: Larsson Susanna C. , Mantzoros Christos S. , Wolk Alicja
Published: March 2007

Diabetes mellitus has been associated with an increased risk of several types of cancers, but its relationship with breast cancer remains unclear. We conducted a meta‐analysis of case–control and cohort studies to assess the evidence regarding the association between diabetes and risk of breast cancer. Studies were identified by searching MEDLINE (1966–February 2007) and the references of retrieved articles. We identified 20 studies (5 case–control and 15 cohort studies) that reported relative risk (RR) estimates (odds ratio, rate ratio/hazard ratio, or standardized incidence ratio) with 95% confidence intervals (CIs) for the relation between diabetes (largely Type II diabetes) and breast cancer incidence. Summary RRs were calculated using a random‐effects model. Analysis of all 20 studies showed that women with (versus without) diabetes had a statistically significant 20% increased risk of breast cancer (RR, 1.20; 95% CI, 1.12–1.28). The summary estimates were similar for case–control studies (RR, 1.18; 95% CI, 1.05–1.32) and cohort studies (RR, 1.20; 95% CI, 1.11–1.30). Meta‐analysis of 5 cohort studies on diabetes and mortality from breast cancer yielded a summary RR of 1.24 (95% CI, 0.95–1.62) for women with (versus without) diabetes. Findings from this meta‐analysis indicate that diabetes is associated with an increased risk of breast cancer. © 2007 Wiley‐Liss, Inc.
Central bank intervention with limited arbitrage
Authors: Neely Christopher J. , Weller Paul A.
Published: March 2007

Shleifer and Vishny (SV) pointed out some of the practical and theoretical problems associated with assuming that rational risk‐arbitrage would quickly drive asset prices back to long‐run equilibrium. In particular, they showed that the possibility that asset price disequilibrium would worsen, before being corrected, tends to limit rational speculators. Uniquely, SV showed that ‘performance‐based asset management’ would tend to reduce risk‐arbitrage when it is needed most, when asset prices are furthest from equilibrium. We analyse a generalized SV model for central bank intervention. We show that increasing availability of arbitrage capital has a pronounced effect on the dynamic intervention strategy of the central bank. Intervention is reduced during periods of moderate misalignment and amplified at times of extreme misalignment. This pattern is consistent with empirical observation. Copyright © 2007 John Wiley & Sons, Ltd.
The diffusion process of sodium hyaluronate (Na‐Ha) and Na‐Ha‐n‐alkyl derivatives films swelling
Authors: Mráček Aleš , Benešová Karolína , Minařík Antonín , Urban Pavel , Lapčík Lubomír
Published: March 2007

The process of diffusion of sodium hyaluronate and its hydrophobically modified alkyl derivatives in water was studied by measuring the kinetics of solid polymer film swelling. The following fundamental thermodynamic parameters of the swelling process were calculated: the apparent diffusion coefficient of swelling by water Ds determined at three temperatures (25, 37, and 45°C), the activation enthalpy of diffusion connected with the swelling ΔHD,s and the activation enthalpy of the swelling process ΔHs. The thermodynamic activity of the solvent for the given sodium hyaluronate and its four alkyl derivatives has been expressed through the internal quantity RAδ,s, that is expansion work of polymer coil accomplished by the action of the internal pressure. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
The brain at work: A cerebral metabolic manifestation of central fatigue?
Authors: Dalsgaard Mads K. , Secher Niels H.
Published: March 2007

Central fatigue refers to circumstances in which strength appears to be limited by the ability of the central nervous system to recruit motoneurons. Central fatigue manifests when the effort to contract skeletal muscles is intense and, thus, is aggravated when exercise is performed under stress, whereas it becomes attenuated following training. Central fatigue has not been explained, but the cerebral metabolic response to intense exercise, as to other modalities of cerebral activation, is a reduction in its “metabolic ratio” (MR), i.e., the brain's uptake of oxygen relative to that of carbohydrate. At rest the MR is close to 6 but during intense whole‐body exercise it decreases to less than 3, with the uptake of lactate becoming as important as that of glucose. It remains debated what underlies this apparent inability of the brain to oxidize the carbohydrate taken up, but it may approach ∼10 mmol glucose equivalents. In the case of exercise, a concomitant uptake of ammonium for formation of amino acids may account for only ∼10% of this “extra” carbohydrate taken up. Also, accumulation of intermediates in metabolic pathways and compartmentalization of metabolism between astrocytes and neurons are avenues that have to be explored. Depletion of glycogen stores and subsequent supercompensation during periods of low neuronal activity may not only play a role but also link brain metabolism to its function. © 2007 Wiley‐Liss, Inc.
Preparation of lactose‐free milk by using salt‐fractionated almond (Amygdalus communis) β‐galactosidase
Authors: Haider Toshiba , Husain Qayyum
Published: March 2007

β‐galactosidase was isolated from almond (Amygdalus communis) extract by ammonium sulfate precipitation. Almond proteins precipitated by using ammonium sulfate and then dialysed exhibited 5.3‐fold purification of β‐galactosidase, and the yield of enzyme preparation was 96.5%. The partially purified β‐galactosidase exhibited pH and temperature optima at pH 5.5 and 50 °C, respectively. The enzyme was significantly stable against heat, pH, calcium and magnesium ions andD‐galactose. The almond β‐galactosidase preparation exhibited over 89% activity even after 2 months storage at 4 °C. Hydrolysis of lactose in milk and whey was performed in a stirred batch process by using this enzyme preparation. These observations indicated that the hydrolysis of lactose increased continuously with time. The enzyme could hydrolyse 94% of lactose in buffer solution and whey whereas 90% of lactose hydrolysis was achieved in milk. The main aim of the present study was to prepare lactose‐free milk, which must be free from contamination, and the process should be inexpensive. Copyright © 2007 Society of Chemical Industry
Gruppentheoretische aspekte der signalübertragung und der kardinalen interpolationssplines I
Authors: Schempp W. , Brosowski B.
Published: March 2007

As is well known the real Heisenberg nilpotent group A(R) constitutes the group‐theoretic embodiment of the Heisenberg canonical commutation relations (CCR) of classical quantum mechanics. In this connection, quantum mechanics stands for the quantum‐mechanical description, at a given instant of time, of a non‐relativistic microparticle moving in the one‐dimensional configuration space R and having the plane R2 as its (flat) phase space. In fact, the (nilpotent) Lie algebra n of Ã(R) reflects the Weyl equations which are global versions of the Heisenberg CCR. Unfortunately, the subject of Heisenberg nilpotent groups is outside quantum mechanics and all the more outside mathematical physics not as commonly known as it should be considering its wide range of applications in a variety of different fields. The present paper which has two parts aims to develop a central topic of nilpotent harmonic analysis, to wit, the microparticle model, the lattice model which will be realized on the Heisenberg compact nilmanifold, and the complex wave model (or Bargmann‐Fock‐Segal model) of the linear Schrödinger representation of Ã(R) in order to examine geometrically several applications which are governed by the real Heisenberg nilpotent group Ã(R). These applications are in Part I the classical Whittaker‐Shannon sampling theorem which is of basic importance in signal processing, to wit, for the transmission of digital signals as well as analog signals, and in Part II the Subbotin‐Schoenberg existence and uniqueness theorem of cardinal spline interpolation. Moreover, Part II indicates briefly some connections of the aforementioned models to the Wigner phase‐space quasiprobability density function of quantum statistical mechanics via the Schwartz kernels theory on unimodular Lie groups, an approach to the cross‐ and autoambiguity functions of radar synthesis, and to the Zak transform of solid state physics. The second part also points out some relations of harmonic analysis of the finite nilpotent group A(Z/NZ) to periodic spline interpolants admitting N equidistant knots on the one‐dimensional compact torus group T. These last examples should serve mainly as hints for some further lines of investigations in the field of applications of nilpotent harmonic analysis.
The sommerfeld half‐plane problem revisited III: Parallel plate media with mixed boundary conditions
Authors: Heins A. E. , Meister E.
Published: March 2007

A plane wave is normally incident upon an infinite stack of equally spaced parallel plates which are semi‐infinite and not staggered. The plates satisfy the so‐called “Rawlins” boundary conditions. This problem is formulated as a pair of simultaneous integral equations of the Wiener‐Hopf type and solved by a method proposed by A. E. Heins in 1950.
Multiparameter acoustic imaging in the born approximation
Authors: Wilcox C. H.
Published: March 2007

Samples of biological tissue are modelled as inhomogeneous fluids with density ϱ(X) and sound speed c(x) at point x. The samples are contained in the sphere |x| ⩽ δ and it is assumed that ϱ(x)  ϱ0 = 1 and c(x)  c0 = 1 for |x| ⩾ δ, and |γn(x)| ≪ 1 and |∇γϱ(x)| ≫ 1 where γϱ(x) = ϱ(x) − 1 and γn(x) = c−2(x) − 1. The samples are insonified by plane pulses s(x · θ0 – t) where x = |θ0| = 1 and the scattered pulse is shown to have the form |x|−1 es(|x| – t, θ, θ0) in the far field, where x = |x| θ. The response es(τ, θ, θ0) is measurable. The goal of the work is to construct the sample parameters γn and γϱ from es(τ, θ, θ0) for suitable choiches of s, θ and θ0.

In the limiting case of constant density: γϱ(x)ϱ 0 it is shown that

magnified image

Where δ represents the Dirac δ and S2 is the unit sphere |θ| = 1. Analogous formulas, based on two sets of measurements, are derived for the case of variable c(x) and ϱ(x).
Interactions of fast and slow waves in hyperbolic systems with two time scales
Authors: Barker J. W. , Kreiss H.O.
Published: March 2007

We consider certain symmetric hyperbolic systems of nonlinear partial differential equations whose solutions vary on two time scales. The large part of the spatial operator is assumed to have constant coefficients, but a nonlinear term multiplying the time derivatives is allowed. We show that if the initial data are not prepared correctly for the suppression of the fast scale motion, but contain errors of amplitude O(ϵ), then the perturbation in the solution will also be of amplitude O(ϵ). Further, if the large part of the spatial operator is nonsingular, we show that the error introduced in the slow scale motion will be of amplitude O(ϵ2), even though fast scale waves of amplitude O(ϵ) will be present in the solution.
Local existence and uniqueness theorems for a free boundary problem
Authors: Wegmann R. , Brosowski B.
Published: March 2007

Free boundary problems are considered, where the tangential and normal components ut and un of an otherwise unknown plane harmonic vector field are prescribed along the unknown boundary curve as a function of the coordinates x, y and the tangent angle θ. The vector field is required to exist either in the interior region G+ or in the exterior G−. In each case the free boundary is characterized by a nonlinear integral equation. A linearised version of this equation is a one‐dimensional singular integral equation. Under rather general hypotheses which are easy to check, the properties of the linear equation are described by Noether's theorems. The regularity of the solution is studied and the effect of the nonlinear terms is estimated. A variant of the Nash‐Moser implicit‐function theorem can be applied. This yields local existence and uniqueness theorems for the free boundary problem in Hölder‐classes H2+μ. The boundary curve depends continuously on the defining data. Finally some examples are given, where the linearised equation can be completely discussed.
Existence for a characteristic boundary value problem for an equation of mixed type in three‐dimensional space
Authors: Müller‐Rettkowski A. H. , Gilbert P.P.
Published: March 2007

The equation of mixed type

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With k(x3) = sign x3|x3|m, m > 0, dϵC1(Ḡ), x = (x1, x2, x3), is considered in the threedimensional region G which is bounded by the surfaces: a piecewise smooth surface Γ0 lying in the half‐space x3 > 0 which intersects the plane x3 = 0 in the unit circle, and for x3 < 0 by the characteristic surfaces

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We prove existence of a generalized solution for the characteristic boundary value problem: Lu = fin G, uΓ0∪Γ1 = 0. The result is obtained by using a variant of the energy‐integral method.
Layer potentials and boundary value problems for the helmholtz equation in the complement of a thin obstacle
Authors: Durand M. , Meister E.
Published: March 2007

Our purpose is to show in a precise manner the mathematical approach of the problem of the acoustic diffraction by an infinitely thin screen. The classical equations of acoustics are transformed into integral equations. The sound field diffracted by the obstacle is described by a double layer potential, the density of which is equal to the step of the potential across the screen. To avoid the mathematical difficulties, the infinitely thin screen will be considered as the limit of a sequence of obstacles with finite thickness. On such obstacles, the operators can be defined, thanks to the theory of Pseudo‐differential operators and Pseudo‐Poisson kernels. Then a limiting process is used and gives existence and unicity of the desired solutions in Sobolev spaces.
Free boundary problem for a two‐layer inviscid incompressible fluid
Authors: Ton Bui An , Payne L.
Published: March 2007

The existence of a local (in time) classical solution of a free boundary problem for a two‐layer inviscid incompressible fluid is shown. The method of successive approximations and the novel approach to Lagrangian coordinates of Solonnikov are used.
An approximation method for a fokker‐planck‐vlasov equation
Authors: Hebeker F.‐K. , Neunzert H.
Published: March 2007

A simplified Fokker‐Planck equation of statistical plasma physics is mathematically investigated. For the Cauchy problem a constructive approximation method is introduced. This procedure yields a sequence (fn) of approximate densities, uniformly converging to the problem's global classical solution with linear convergence velocity.
Variational formulation of the roller contact problem
Authors: Bogomolny A. , Hsiao G. C.
Published: March 2007

We formulate the roller contact problem in terms of variational inequality with certain pseudodifferentional operator, and discuss a finite element technique for its numerical solution.
Bifurcation of periodic solutions for wave equations with scalar nonlinearities
Authors: Bazley N. W. , Weinacht R. J. , de Jager E.
Published: March 2007

We treat wave equations with “scalar nonlinearities” and demonstrate the connection between the bifurcation theory of an associated system of Hammerstein integral equations and the existence of periodic solutions of the nonlinear wave equation.
Bifurcation phenomena in a free boundary problem for a circulating flow with surface tension
Authors: Okamoto Hisashi , Fujita H.
Published: March 2007

A free boundary problem for a flow around a circle is analyzed. We find and mathematically prove that bifurcations from the trivial flow actually take place. Golubitsky‐Schaeffer theory, together with a formula concerning variations of domains, enables us to clarify the behaviors of the branches of nontrivial solutions.
Truncated random variables with application to random surfaces
Authors: Phillips M. J. , Roach G. F.
Published: March 2007

There has been considerable interest in obtaining discrete results for random surfaces. Standard results have been published in journals of physics or engineering which have emphasised the applications. This paper gives a detailed background of the mathematical methods needed so that the central connection, namely truncated random variables, between these standard results can be understood. Distributions of discrete peak measures are obtained from the distributions of discrete profile measures of a random Gaussian surface by applying results for the distributions of truncated random variables. This enable the moments to be obtained from known results for the truncated distributions.
Some applications of a galerkin‐collocation method for boundary integral equations of the first kind
Authors: Hsiao G. C. , Kopp P. , Wendland W. L.
Published: March 2007

Here we apply the boundary integral method to several plane interior and exterior boundary value problems from conformal mapping, elasticity and fluid dynamics. These are reduced to equivalent boundary integral equations on the boundary curve which are Fredholm integral equations of the first kind having kernels with logarithmic singularities and defining strongly elliptic pseudodifferential operators of order ‐ 1 which provide certain coercivity properties. The boundary integral equations are approximated by Galerkin's method usingB‐splines on the boundary curve in connection with an appropriate numerical quadrature, which yields a modified collocation scheme. We present a complete asymptotic error analysis for the fully discretized numerical equations which is based on superapproximation results for Galerkin's method, on consistency estimates and stability properties in connection with the illposedness of the first kind equations inL2. We also present computational results of several numerical experiments revealing accuracy, efficiency and an amazing asymptotical agreement of the numerical with the theoretical errors. The method is used for computations of conformal mappings, exterior Stokes flows and slow viscous flows past elliptic obstacles.
L2‐boundary integral equations for the robin problem
Authors: Angell T. S. , Kress R. , Roach G. F.
Published: March 2007

In this paper we study an integral equation method for the exterior Robin problem for the Helmholtz equation where the boundary condition is interpreted in the L2‐sense. In particular, we derive a composite integral equation from Green's theorem which is uniquely solvable for all wave numbers.
Applications of convex analysis and comparison functionals to extremum principles
Authors: Bailey Pat , Smith Peter , Roach G. F.
Published: March 2007

In many areas of applied mathematics, the govering equations can be expressed as dual equations which are elements in two vector spaces where a given functional defined on a cartesian product space has zero gradients. If this functional has a global saddle structure then the variational principle can be replaced by dual extremum principles of the Noble and Sewell type. The purpose of the present paper is to investigate how comparison functional which have convex, concave or saddle structure can be used to generate upper and lower bounding principles and critical sequences. The methods are illustrated by applications to the periodic solutions of a non‐linear differential equation and the Fredholm integral equation.