bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimal placement of dampers for passive response control
Authors: Singh Mahendra P. , Moreschi Luis M. 
Published: January 2005

AbstractThe effectiveness of viscous and viscoelastic dampers for seismic response reduction of structures is quite well known in the earthquake engineering community. This paper deals with the optimal utilization of these dampers in a structure to achieve a desired performance under earthquake‐induced ground excitations. Frequency‐dependent and ‐independent viscous dampers and viscoelastic dampers have been considered as the devices of choice. To determine the optimal size and location of these dampers in the structure, a genetic algorithm is used. The desired performance is defined in terms of several different forms of performance functions. The use of the genetic approach is not limited to any particular form of performance function as long as it can be calculated numerically. For illustration, numerical examples for different building structures are presented showing the distribution and size of different dampers required to achieve a desired level of reduction in the response or a performance index. Copyright © 2002 John Wiley & Sons, Ltd.
Simulations of non‐stationary frequency content and its importance to seismic assessment of structures
Authors: Wang Junjie , Fan Lichu , Qian Shie , Zhou Jing 
Published: January 2005

AbstractTo verify the importance of the non‐stationary frequency characteristic of seismic ground motion, a joint time–frequency analysis technique of time signals, called chirplet‐based signal approximation, is developed to extract the non‐stationary frequency information from the recorded data. The chirplet‐based signal approximation is clear in concept, similar to Fourier Transform in mathematical expressions but with different base functions. Case studies show that the chirplet‐based signal approximation can represent the joint time–frequency variation of seismic ground motion quite well. Both the random models of uniform modulating process and evolutionary process are employed to generate artificial seismic waves. The joint time–frequency modulating function in the random model of evolutionary process is determined by chirplet‐based signal approximation. Finally, non‐linear response analysis of a SODF system and a frame structure is performed based on the generated artificial seismic waves. The results show that the non‐stationary frequency characteristic of seismic ground motion can significantly change the non‐linear response characteristics of structures, particularly when a structure goes into collapse phase under seismic action. It is concluded that non‐stationary frequency characteristic of seismic ground motion should be considered for the assessment of seismic capacity of structures. Copyright © 2002 John Wiley & Sons, Ltd.
Probabilistic approach for modal identification using non‐stationary noisy response measurements only
Authors: Yuen Ka‐Veng , Beck James L. , Katafygiotis Lambros S. 
Published: January 2005

AbstractThis paper addresses the problem of identification of the modal parameters for a structural system using measured non‐stationary response time histories only. A Bayesian time‐domain approach is presented which is based on an approximation of the probability distribution of the response to a non‐stationary stochastic excitation. It allows one to obtain not only the most probable values of the updated modal parameters and stochastic excitation parameters but also their associated uncertainties using only one set of response data. It is found that the updated probability distribution can be well approximated by a Gaussian distribution centred at the most probable values of the parameters. Examples using simulated data are presented to illustrate the proposed method. Copyright © 2002 John Wiley & Sons, Ltd.
Dynamic analysis method of a combined energy dissipation system and its experimental verification
Authors: Lu Xilin , Zhou Qiang 
Published: January 2005

AbstractA combined energy dissipation system is developed in this paper. In this system lead rubber dampers and their parallel connection with oil dampers are used in the braces of a structural frame. A dynamic analysis method of the system, including the modelling of the lead rubber damper and the oil damper, is proposed. In the analysis method, the restoring force characterestics of the lead rubber damper is simulated by the Bouc–Wen hysteretic model, and the behaviour of the oil damper is simulated by a velocity and displacement‐related model in which the contributions of the oil damper to the damping force and stiffness of the system are considered. A series of shaking table tests of a three‐storey steel frame with the combined energy dissipation system are carried out to evaluate the performance of the system and to verify the analysis method. The test and analysis show that the performance of the combined energy dissipation system is quite satisfactory and there is a good agreement between the analysis and test results, which indicates that the analysis method proposed in this paper is valid and suitable for the dynamic analysis of the combined energy dissipation system. Copyright © 2002 John Wiley & Sons, Ltd.
Bankfull discharge in mountain streams: theory and practice
Authors: Radecki‐Pawlik Artur 
Published: January 2005

AbstractThe results are presented of an investigation of bankfull discharge in two Polish Carpathian streams: Skawica and Krzyworzeka. Existing definitions of river bankfull were reviewed and applied in tests carried out on selected cross‐sections of the streams. The Woodyer method was given special attention, with a correspondingly detailed survey of plants characterizing river benches. Riley's bench index method and the methods of Williams, Wolman, Schumm and Brown, and Woloszyn were tested. The report concludes that bankfull discharge value for a mountain stream should not be reported as a single number, but rather as a range of discharges within which one could expect the bankfull value to lie. Copyright © 2002 John Wiley & Sons, Ltd.
Rates of development of tafoni in the Moenkopi and Kaibab formations in Meteor Crater and on the Colorado Plateau, northeastern Arizona
Authors: Norwick Stephen A. , Dexter Leland R. 
Published: January 2005

AbstractTafoni are pits formed by non‐uniform weathering in otherwise uniform rock. Two equations have been proposed for the rate of development of tafoni, both based on 2000‐year‐old outcrops from the coast of Japan. We have taken tafoni measurements from the Meteor Crater, Arizona, and vicinity that extend the equations back at least 50 000 years. As reported in earlier studies, we found pit depth to be the best tafone parameter to measure. The size of the pit decreases significantly with increasing inclination of the rock surface; however, the size of the pit can vary greatly for other reasons. In some cases the measurements are statistically significantly different between two stations taken from contiguous areas of similar inclination and aspect in an apparently homogeneous bed. It is clear, however, that over tens of thousands of years tafoni enlarge significantly. Our data are generally log‐normal and all are markedly heteroscedastic. The 1991 equation proposed by Matsukura and Matsuoka does not fit our data. The 1996 equation proposed by Sunamura provides a better fit. We propose a sigmoidal equation D = b1 + e(b2+(b3/t)) where D is the depth, t is the age, and b1, b2 and b3 vary with lithology. This new equation fits our data far better than the earlier published equations. Copyright © 2002 John Wiley & Sons, Ltd.
Insights into river bank erosion processes derived from analysis of negative erosion‐pin recordings: observations from three recent UK studies
Authors: Couper Pauline , Stott Tim , Maddock Ian 
Published: January 2005

AbstractRecent studies of river bank erosion in three catchments in the UK have been characterized by the persistent occurrence of negative erosion‐pin results. The cause of these negative recordings is considered with reference to field data from the Afon Trannon, Nant Tanllwyth and River Arrow, and to a laboratory study of freeze–thaw and desiccation processes. It seems that there is potential for, and in some cases evidence of, a number of different circumstances that generate negative results, but none of these alone is sufficient to explain all incidents. Factors considered include: deposition of sediment during high flows; soil fall from the upper parts of the bank on to lower erosion pins; loosening of the soil surface and expansion/contraction of the soil mass with fluctuations in temperature and moisture content; movement of the erosion‐pin within the bank and human interference. Each has its own implications for the use of erosion pins.Further issues arise when including negative data in subsequent data analysis, and it is demonstrated that attempts to correlate erosion rates with hydro‐meteorological data in order to ascertain causes of erosion will be influenced by the way in which negative data are handled. It is thus suggested that any study of river bank erosion using erosion pins should state whether or not negative data were obtained, and if so, how they were included in data analysis. Failure to include this information could lead to comparison of mean erosion rates that reflect bank processes very differently.The studies presented here offer a clear example of the value of ‘anomalous’ field data: results which do not appear to fit expected patterns can reveal as much about the processes in operation as those that do. Copyright © 2002 John Wiley & Sons, Ltd.
Unifying analysis of ergodic MIMO capacity in correlated Rayleigh fading environments
Authors: Kießling Mario 
Published: January 2005

AbstractWe present a novel mathematical approach that for the first time allows for calculating the moment generating function (MGF) of mutual information of Rayleigh fading MIMO channels with arbitrary fading correlation at transmitter and receiver. Specifically, we make use of certain hypergeometric functions of matrix argument, which are frequently used in multivariate statistics. This allows for a concise general expression for the MGF and we specialise the general result to scenarios with one‐side correlated and uncorrelated channels. Using the MGF, we derive exact formulas of the ergodic capacity, thus unifying the capacity analysis of correlated Rayleigh fading MIMO channels. It turns out that the ergodic capacity in all cases can be expressed in terms of a sum of determinants with elements that are a combination of polynomials, exponentials and the exponential integral E1 solely. The analysis is verified by Monte–Carlo simulations and shows a perfect match. Copyright © 2005 AEIT.
A study of impact of inband signalling and realistic channel knowledge for an example dynamic OFDM–FDMA system
Authors: Gross James , Valentin Stefan , Karl Holger , Wolisz Adam 
Published: January 2005

AbstractDynamically assigning sub‐carriers oforthogonalfrequencydivisionmultiplexing (OFDM) systems to multiple different terminals in a cell has been shown to be beneficial in terms of different transmission metrics. The success of such a scheme, however depends on the ability of the access point to inform terminals of their newest sub‐carrier assignments as well as on the accuracy of the channel state information used to generate new assignments. It is not clear whether the overhead required to implement these two functions consumes all of the potential performance increase possible by dynamically assigning sub‐carriers. In this paper, a specific MAC structure is selected enabling the operation of a dynamic OFDM system, incorporating a signalling scheme for dynamically assigned sub‐carriers. Based on this structure, we study the overhead required for a dynamic sub‐carrier scheme; a static variant that serves as a comparison case. We investigate the performance difference of these two schemes for various scenarios where at first signalling and then realistic channel knowledge is added to the system model. Average throughput and goodput per terminal serve as figures of merit; the number of terminals in the cell, the transmission power per sub‐carrier, the delay spread and the movement speed of the terminals are varied. We find that a realistic overhead model decreases the performance of both static and dynamic schemes such that the overall ratio favours in all cases except for higher speeds the dynamic rather than the static scheme especially in realistic system environments. Copyright © 2005 AEIT.
Downlink WCDMA receivers based on combined chip and symbol level equalisation
Authors: Baştuğ Ahmet , Slock Dirk T. M. 
Published: January 2005

AbstractIn this paper, we consider iterative receiver techniques for the downlink in WCDMA systems (UMTS FDD mode). We start from the linear minimum mean square error (MMSE) receiver (at symbol level), which is time varying and hence too complex to implement. By applying polynomial expansion (PE) to the LMMSE receiver, an iterative solution is obtained in which the complexity per iteration becomes comparable to twice that of the Rake receiver. Our one contribution is to replace the channel matched filter by a channel equaliser within this PE to accelerate the convergence of the iterations. We also investigate various scenarios for the introduction of non‐linearities in the PE scheme that are particularly applicable to the multicode case of the high speed downlink packet access (HSDPA) mode since it is well known that non‐linearities in the PE scheme lead, in fact, to the parallel interference canceler (PIC). Copyright © 2005 AEIT.
Flow‐level performance analysis of some opportunistic scheduling algorithms
Authors: Bonald T. 
Published: January 2005

AbstractWhile fading effects have long been combatted in 2G wireless networks, primarily devoted to voice calls, they are now seen as an opportunity to increase the capacity of 3G networks that incorporate data traffic. The packet delay tolerance of data applications, such as file transfers and Web browsing for instance, allows the system flexibility in scheduling a user's packets. So‐called opportunistic scheduling, which ensures transmission occurs when radio conditions are most favourable, is the key component of currently developed systems like cdma2000 IS‐856 and UMTS HSDPA. We compare the performance of some scheduling schemes using a flow‐level approach where the random evolution of the number of ongoing flows is explicitly taken into account. Copyright © 2005 AEIT.
A finite‐source queuing model for the IEEE 802.11 DCF
Authors: Winands E. M. M. , Denteneer T. J. J. , Resing J. A. C. , Rietman R. 
Published: January 2005

AbstractThe most mature medium access control protocol for wireless local area networks is the IEEE 802.11 standard. The primary access mode of this protocol is based on the mechanism of carrier sense multiple access with binary exponential backoff. We develop a finite‐source feedback queueing model for this access mode. In this model, we derive expressions for the throughput and the first moment of the delay and a set of equations to compute the Laplace Stieltjes Transform and higher moments of the delay. The accuracy of the model is verified by simulation. Copyright © 2005 AEIT.
Iterative PIC detection and channel estimation for DS‐CDMA communications in AWGN and satellite/HAPS channels
Authors: Morosi Simone , del Re Enrico , Fantacci Romano , Rufolo Paola 
Published: January 2005

AbstractThis paper presents a turbo multiuser detector for turbo‐coded DS‐code division multiple access (CDMA) systems, based on the utilisation of a parallel interference cancellator (PIC) and a bank of turbo decoders: in the proposed receiver the interference cancellation is performed after each constituent decoder of the turbo decoding scheme. Moreover, the soft outputs of the turbo decoders are used iteratively to improve the channel parameter estimation during the updating step, which is formally equivalent to one step of the expectation‐maximisation algorithm. By means of computer simulations, we will show that the proposed receiver achieves performance comparable with the one obtained by systems, which suppose perfect knowledge of the channel parameters for medium to high system loads, in AWGN channel. Finally, the proposed receiver is also applied in HAPS (high altitude platform station) and satellite channel, for different values of the elevation angle, affording remarkable performance. Copyright © 2005 AEIT.
Analysis of the essential oil of Nepeta fissa C.A. Mey from Iran
Authors: Sefidkon F. , Dabiri M. , Alamshahi A. 
Published: January 2005

AbstractWater‐distilled volatile oil from the aerial parts of Nepeta fissa C.A. Mey. was analysed by a combination of GC and GC–MS. Forty‐two components were identified, constituting approximately 99.3% of the oil. The main constituents of the essential oil were β‐caryophyllene (17.4%), caryophyllene oxide (12.3%), γ‐muurolene (7.9%), valencene (6.6%), β‐pinene (6.0%) and α‐pinene (5.8%). Copyright © 2002 John Wiley & Sons, Ltd.
Composition of the essential oils from three Laggera Spp. from Cameroon
Authors: Kuiate J.‐R. , Bessière J.‐M. , Amvam Zollo P.‐H. 
Published: January 2005

AbstractThe essential oils from the leaves of Laggera alata var. montana C. D. Adams, and Laggera gracilis (O. Hoffm. & Muschl.) C. D. Adams, and those from leaves, roots and stems of Laggera oloptera (DC.) C. D. Adams from the western highlands of Cameroon were analysed by GC and GC–MS. The essential oils of L. alata var. montana and L. gracilis were found to be rich in dimethoxy‐p‐cymene (34% and 33%, respectively). The other most abundant components in these oils were 7‐epi‐γ‐ eudesmol (21%), juniper camphor (7%) for L. alata var. montana and γ‐eudesmol (10%), β‐caryophyllene (7%) for L. gracilis. The essential oils from leaves of L. oloptera were found to be poor in dimethoxy‐p‐cymene (0.1–0.3%) but afforded β‐caryophyllene (15–20%), germacrene‐D (10–17%) and sabinene (2–28%) while the volatile extract from roots and stems were rich in dimethoxy‐p‐cymene (67% and 36%, respectively) and β‐caryophyllene (6% and 16%, respectively). The essential oil from the stems also contained a high proportion of γ‐eudesmol (20%). Copyright © 2002 John Wiley & Sons, Ltd.
Identification of regions of fastest mixing in a system of point vortices
Authors: Ramachandran Prabhu , Rajan S. C. 
Published: January 2005

AbstractThis paper describes a numerical method for efficiently identifying the regions of fastest mixing of a passive dye in a flow due to a system of point vortices. Results obtained from computations are presented for systems of three and four point vortices, both in the unbounded domain and inside a circular cylinder. The flow is two‐dimensional and the fluid is incompressible. The regions where mixing is possible are found by studying the largest Lagrangian Lyapunov exponent distribution with respect to various initial positions of tracer particles. The regions of fastest mixing are then identified from the Lyapunov exponent distribution at small times. The results of the method are verified by quantifying the mixing by using a traditional box counting technique. The technique is then applied to several different initial configurations of vortices and some interesting results are obtained. Some numerical findings about the nature of the exponents computed are also discussed. Copyright © 2002 John Wiley Sons, Ltd.
Application of local grid refinement to vortex motion due to a solitary wave passing over a submerged body
Authors: Tang Chii‐Jau , Chang Jyh‐Hwa 
Published: January 2005

AbstractA numerical method based on the streamfunction–vorticity formulation is applied to simulate the two‐dimensional, transient, viscous flow with a free surface. This method successfully uses the locally refined grid in an inviscid–viscous model to explore the processes of vortex formation due to a solitary wave passing over a submerged bluff body. The two particular bodies considered here are a blunt rectangular block and a semicircular cylinder. Flow visualization to track dyelines is carried out in the laboratory in order to confirm the validity of the numerical results. Numerical results examined by different grid configurations ensure the locally refined grid to be useful in practical application. Flow phenomena, including the vortex motion and wave patterns during non‐linear wave–structure interaction, are also discussed. Copyright © 2002 John Wiley & Sons, Ltd.
A simple and efficient error analysis for multi‐step solution of the Navier–Stokes equations
Authors: Fithen R. M. 
Published: January 2005

AbstractA simple error analysis is used within the context of segregated finite element solution scheme to solve incompressible fluid flow. An error indicator is defined based on the difference between a numerical solution on an original mesh and an approximated solution on a related mesh. This error indicator is based on satisfying the steady‐state momentum equations. The advantages of this error indicator are, simplicity of implementation (post‐processing step), ability to show regions of high and/or low error, and as the indicator approaches zero the solution approaches convergence. Two examples are chosen for solution; first, the lid‐driven cavity problem, followed by the solution of flow over a backward facing step. The solutions are compared to previously published data for validation purposes. It is shown that this rather simple error estimate, when used as a re‐meshing guide, can be very effective in obtaining accurate numerical solutions. Copyright © 2002 John Wiley & Sons, Ltd.
Numerical solution of the flow of thin viscous sheets under gravity and the inverse windscreen sagging problem
Authors: Hunt Roland 
Published: January 2005

AbstractThe slumping of a thin sheet of very viscous liquid glass is used in the manufacture of windscreens in the automotive industry. The governing equations for an asymptotically thin sheet with variable viscosity are derived in which the vertical coordinate forms the centre‐line of the sheet. The time‐dependant equations have been solved numerically using the backward Euler method to give results in both two and three dimensions. The flow of an initially flat sheet falls freely under gravity until it becomes curved and the flow becomes very slow in the ‘slumped’ phase. Finally the sheet freefalls as the thickness becomes small at the boundaries. The inverse problem in which the viscosity profile is to be determined for a given shape can be solved as an embedding problem in which a search is made amongst the forward solutions. Possible shapes in the two‐dimensional problem are very restrictive and are shown to be related to the sheet thickness. In three dimensions the range of shapes is much greater. Copyright © 2002 John Wiley & Sons, Ltd.
Statistical analyses of freeway traffic flows
Authors: Tebaldi Claudia , West Mike , Karr Alan F. 
Published: January 2005

AbstractThis paper concerns the exploration of statistical models for the analysis of observational freeway flow data, and the development of empirical models to capture and predict short‐term changes in traffic flow characteristics on sequences of links in a partially detectorized freeway network. A first set of analyses explores regression models for minute‐by‐minute traffic flows, taking into account time of day, day of the week, and recent upstream detector‐based flows. Day‐ and link‐specific random effects are used in a hierarchical statistical modelling framework. A second set of analyses captures day‐specific idiosyncrasies in traffic patterns by including parameters that may vary throughout the day. Model fit and short‐term predictions of flows are thus improved significantly. A third set of analyses includes recent downstream flows as additional predictors. These further improvements, though marginal in most cases, can be quite radically useful in cases of very marked breakdown of freeway flows on some links. These three modelling stages are described and developed in analyses of observational flow data from a set of links on Interstate Highway 5 (I‐5) near Seattle. Copyright © 2002 John Wiley & Sons, Ltd.