bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Occurrence of Mathieu Instabilities of Vertical Cylinders
Authors: Neves Marcelo A. S. , Sphaier Sergio H. , Mattoso Bruno M. , Rodri´guez Claudio A. , Santos Alberto L. , Vileti Vinicius L. , Torres Fernando G. S.
Published: July 2009

Large offshore platforms with vertical circular cylindrical hull shapes have been designed and employed in recent times. Classical spar platforms and mono-column concepts are just two examples of designs with such simple configuration, supposed to perform limited motion responses in waves. Reports on investigations on the occurrence of parametric resonance of spar platforms have been published recently in which the relevance of Mathieu amplifications have been assessed making use of different mathematical models. However, some uncertainties still remain on the influence of crucial design parameters as, for instance, metacentric height, draft/diameter ratio, associated damping and mooring system. In an attempt to clarify some of these aspects, in this paper the dynamic stability of a vertical cylinder in regular waves is investigated theoretically and experimentally. A coupled non-linear mathematical model is employed to model and simulate the coupled heave, roll and pitch motions. Theoretical aspects related to the development of resonant motions are discussed. In addition to the numerical and theoretical investigations, an extensive series of experiments with a model of a typical mono-column have been recently conducted at LabOceano. The findings of these investigations are compared and summarized.
Coupled Analysis of DP-Tugboat and Onshore Pre-Assembled SCR (Steel Catenary Riser) Transportation System
Authors: Rampazzo Fabiano P. , Tsukamoto Marcio M. , Quadrante Luis A. , Nishimoto Kazuo , de Siqueira Marcos Q. , Franciss Ricardo , Pereira Felipe Rateiro
Published: July 2009

This paper presents the study of the dynamic behavior of an onshore pre-assembled 8" SCR (Steel Catenary Riser) being transported to the installation place by two tugboats with DP system. The system is composed by two tugboats similar to a Normand Neptun (LOA 80m and displacement of 4200t), one in front of the riser (Lead) and the other at the back of the riser (Trail) controlled by DP system to keep the trajectory for installation location. During the transportation, the system passes through 3 different configurations: Offbottom, BuoyCatenary and Catenary. Offbottom configuration is composed by many buoys (effective buoyancy of 30kN) and chains distributed along the riser to guarantee the relative distance between the riser and the seabed, independently of seabed irregularities. When the sea gets deeper, the riser assume the BuoyCatenary configuration, where the riser forms a catenary with buoys; when it achieves a water depth up to 500 meters, all the system buoy+chain are removed and the riser assume the form of a free catenary until it arrives at the installation place. Two approaches was used to evaluate transport analysis of a onshore pre-assembled SCR. In the first approach (uncoupled analysis), the transportation was simulated using the Anflex software to calculate the dynamic response of the line composed by beam elements, imposing, at the top of the riser, the tugboat motion obtained from spectral analysis. In the second approach (coupled analysis), the transport was simulated using the TPN software to calculate the dynamic motion of the tugboats considering the dynamic positioning system and the Anflex software to calculate the dynamic response of the lines. The main propose of this paper is show the necessity of do coupled analysis for the SCR transport. This study are focus in a parametric analysis of the tugboat viscous damping influence, that were performed (1, 5 and 10% of the critic damping), as well as the damping generated by the riser in the tugboat motion, the relative motion influence in risers tensions and the tugboat’s bollard pull.
A Comparison Between Modal Push-Over and Nonlinear Dynamic Response of Jacket Type Offshore Platforms Subjected to Strong Ground Motions
Authors: Roshandel Tavana M. A. , Asgarian B.
Published: July 2009

Nonlinear dynamic analysis for offshore structures has been a major challenge in marine structures and earthquake engineering. Nonlinear Dynamic Analysis of the structures subjected to strong ground motions is the most reliable prediction method. This method is very complex and expensive. An alternative procedure that has found to be much applicable in recent years is the nonlinear static analysis called push-over analysis method. Many attempts have been made to improve the predictive capabilities of the push-over analysis, particularly by employing adaptive load patterns and accounting for higher modes of vibration effects through modal push-over. In this paper, modal push-over analysis (MPA) of jacket type offshore platforms considering soil-pile-structure interaction subjected to strong ground motion has been studied and the results have been compared with “exact” nonlinear response history analysis (NLRHA). A jacket type offshore platform includes of piles, jacket and deck with different behaviors during strong ground motion. In this paper, three-dimensional model of jacket and pile has been considered using a combination of finite element method (FEM) and beam on nonlinear winkler foundation (BNWF) approach in an integrated model. Both jacket and pile elements have been modeled using fiber sections. The model has been developed using Open System for Earthquake Engineering Simulation (OpenSEES) software. In this paper, nonlinear seismic analysis of a new designed jacket type offshore platform located in Persian Gulf subjected to different levels of earthquake has been performed and the results have been compared with MPA ones. It can be concluded that the error percentage in MPA procedure is negligible when more modes of vibration are participated in the evaluation of the structure behavior.
Numerical and Experimental Investigation on the Dynamics of Catenary Risers and the Riser-Induced-Damping Phenomenon
Authors: Chatjigeorgiou Ioannis K. , Damy Gilbert , LeBoulluec Marc
Published: July 2009

Catenary risers can be equally efficient as catenary moorings in producing damping which is subsequently offered to the floating structure. Mooring-induced-damping has been investigated adequately in the recent past. The same however is not valid as far as the contribution of risers is concerned. It should be acknowledged that the main source of damping, i.e. the drag forces, is higher in risers than in moorings as the external diameter of the former is larger and the drag coefficients, at least assuming a Morison’s formula, are comparable. Therefore, the investigation of the so called riser-induced-damping phenomenon is an interesting issue. The present work is a contribution to this direction. This is performed both numerically and experimentally. For estimating damping the method proposed by Brown and Mavrakos (1999) is followed. Thus, damping due to risers is represented by the equivalent linearized coefficient the calculation of which lies on the knowledge of the energy dissipated per cycle that is calculated with the aid of the horizontal force applied at the top of the structure.
An Analysis of Noise Characteristics of Drill Bits
Authors: Gradl Christian , Eustes Alfred W. , Thonhauser Gerhard
Published: July 2009

There have been papers that analyze the relationship between bit design and a bit’s vibrational characteristics. These papers typically are based on the analysis of three-axis near-bit down-hole vibration sensors. In this paper, the authors take a simpler approach. Using a standard microphone literally pointed at the bit, they record the noise of the bit/rock interaction while drilling and analyze the resulting noise for these but vibrational characteristics. The data were gathered at the Colorado School of Mines in Golden, Colorado. The noise of a PDC core, roller cone, and diamond core bits were recorded under various weight and rotary speeds using a microphone and a vertically mounted uniaxial geophone (used for confirming the data recorded on the microphones). Using a Fast Fourier Transform, the frequency spectra were extracted from the recorded data and analyzed. The data was normalized for rotational speed. The results of the frequency analysis of the roller cone, the PDC, and the natural diamond bits are presented in this paper. The major differences in the three bit frequency characteristics could be detected and furthermore, for drag bits, the frequency characteristics could be related to the bit’s design. The frequency spectra of the roller cone bit can best be described with a general high amplitude level that is relatively evenly distributed over the whole frequency spectrum. The drag bit data showed a strong relationship between the number and arrangement of cutting elements and frequency peaks on a plot of amplitude vs. cycles per revolution. Frequency peaks were observed at multiples of the number of cutting elements. In general this relationship was strongly visible on the PDC bit data but not as strongly visible on the diamond bit data. The conclusion is that bit characteristics can be determined using only the noise of a bit. Potential applications of this research include detecting and diagnosing bit problems (e.g. broken teeth, bit balling) in real time using simple microphone based acoustic data.
Frequency-Domain Calculations of Moored Vessel Motion Including Low Frequency Effect
Authors: Le Cunff C. , Ryu Sam , Heurtier Jean-Michel , Duggal Arun S.
Published: July 2009

Frequency-domain analysis can be used to evaluate the motions of the FPSO with its mooring and riser. The main assumption of the frequency-domain analysis is that the coupling is essentially linear. Calculations are performed taking into account first order wave loads on the floating structure. Added mass and radiation damping terms are frequency dependent, and can be easily considered in this formulation. The major non-linearity comes from the drag force both on lines and the floating structure. Linearization of the non-linear drag force acting on the lines is applied. The calculations can be extended to derive the low frequency motion of the floating structure. Second order low frequency quadratic transfer function is computed with a diffraction/radiation method. Given a wave spectrum, the second order force spectrum can then be derived. At the same time frequency-domain analysis is used to derive the low frequency motion and wave frequency motion of the floating system. As an example case, an FPSO is employed. Comparison is performed with time domain simulation to show the robustness of the frequency-domain analysis. Some calculations are also performed with either low frequency terms only or wave frequency terms only in order to check the effect of modeling low and wave frequency terms, separately. In the case study it is found that the low frequency motion is reduced by the wave frequency motion while the wave frequency motion is not affected by the low frequency motion.
Risers Clashing Induced by the Wake Interference
Authors: Fernandes Antonio C. , Rocha Stefania D. , Coelho Fabio M. , Jacob Breno P. , Queiroz Joseane V. , Capanema Bruna , Merino Jorge A.
Published: July 2009

The offshore petroleum industry has great technological challenges as new field discoveries are made in increasing water depths. Risers of systems having little space between its elements, subjected to current reach static deflections that depend on the wakes formed by the each riser. Depending on the relative position, each riser will be submitted to a stronger or weaker effect from each neighbor. This work presents results from experiments with flexible jumpers submitted to current. The clashing between the lines caused by the wake interference is the focus of the work. The work presents results in terms of minimum distance between the jumpers comparing experimental results to a numerical code that applies automatically the Huse’s formula for the drag coefficients. It also discusses the validity of this theory. As expected, during the tests the jumpers presented Vortex Induced Vibration (VIV), VIV under Interference (VIV-UI) and friction after contact. The results can be extrapolated to real cases and shows the possibility of clashing on closely spaced systems, putting in evidence other phenomena related to it.
Fluctuating Wind Induced Response of Double Hinged Articulated Loading Platform
Authors: Zaheer Mohd Moonis , Islam Nazrul
Published: July 2009

Wind and wave loadings have a predominant role in the design of articulated loading platforms (ALP) for its successful service and survival. Such platforms are very sensitive to the dynamic effects of wind, waves and currents. The compliant nature of these platforms with environmental loads introduces geometric nonlinearity due to large displacements, which becomes an important consideration in the analysis of these structures. In this study, dynamic behaviour of the tower under different wind spectra along with varying platform sizes is carried out. The exposed portion of the platform is subjected to the action of mean and turbulent wind, while the submerged portion is acted upon by random wave forces. The fluctuating component of the wind velocity is modeled using Emil Simiu’s wind spectrum while the sea state is characterized by Pierson-Moskowitz spectrum. Both correlated and uncorrelated wind and waves are considered in the analysis. Random wind and waves are simulated by Monte Carlo simulation technique. The drag force, either due to wind or wave is obtained by transforming the latticed portion of the platform into its equivalent drag diameters. For comparative studies of the ALP, responses under different wind spectra suggested by Kareem, Davenport and API-RP2A are employed. Furthermore, the analysis of the same structure under wind alone with buoyancy as a restoring force is also investigated to establish the severity among the events. The nonlinear dynamic equation of motion is derived by Lagrangian approach. The analysis includes the nonlinearities due to non linear drag force, fluctuating buoyancy, variable added mass and instantaneous tower orientation. The equation of motion is solved in time domain for incorporating the nonlinearities involved in the system by using Newmark-β integration scheme. The response study in terms of time histories of deck displacement, hinge rotation and hinge shear are presented. Also, their power spectral density functions (PSDFs) are plotted to highlight the wind induced dynamic response of the platform. Response time histories are further analyzed by statistical process under various parametric combinations. The outcome of the analyses establishes that the contribution of wind force in the platform responses is mainly governed by the size of the wind generated waves.
An Experimental Investigation of Roll Motions of an FPSO
Authors: Esperanc¸a Paulo T. T. , Sales Joel S. , Liapis Stergios , Matsuura Joa˜o Paulo J. , Schott Wes
Published: July 2009

FPSO roll motions can be major contributor to riser fatigue. This is especially true in regions where wind, waves and currents are non-collinear. Roll motions as high as 23 degrees have been reported in the Campos Basin. The most common roll mitigation strategy consists of adding bilge keels to the FPSO. Motivation for this work came from a need to develop a better understanding of roll motions as a function of bilge keel width. In addition to roll motions, the hydrodynamic forces on the bilge keels were measured. A series of tests were conducted at the LabOceano offshore basin. This new facility has a length of 4 0 m, a width of 30 m, a depth of 15 m and is equipped with a multi-flap wave generator on one side. A ship-shaped FPSO design with sponsons for a deepwater offshore development in Brazil was tested. It has a length of 316 m, a breadth of 57.2 m and a draft of 28.3 m. A 1:70 scale model was constructed. A horizontal soft mooring system consisting of four lines with springs was used. Regular waves of different amplitudes as well as random waves were generated in the basin. Two different loading conditions, ballast (draft = 6.7 m) and loaded (draft = 21.7 m), as well as three wave headings, beam seas (90°), and quartering seas (22.5°, 45°) were considered. Tests were undertaken for four bilge keel configurations, corresponding to a case without bilge keels, as well as bilge keels of 3 different widths (1 m, 2 m and 3 m). In all cases, the bilge keels had a length of 200 m. An optical system was used to measure ship motions in all six degrees of freedom. The hydrodynamic loads on the bilge keels were measured using strain gages.
Vessel Adapted for Multiple Installation and Salvage
Authors: Cholley Jean-Marc , Tcherniguin Nicolas , Thomas Pierre Armand
Published: July 2009

For offshore developments, the installation of production decks onto floaters (e.g. spars for deep water developments) or fixed platforms using a heavy lift derrick barge is now well established, though, for high payloads, this requires multiple lifts and hence extensive offshore hook-up. As demand for lift vessels increases, their availability to match a specific project’s schedule cannot be guaranteed. Consequently, an alternative deck installation vessel design has been developed for not only installing decks onto floaters, but also onto high air gap (circa 20 m) fixed platforms. This paper will present this new design. The new vessel design consists of a linked catamaran shaped vessel with dimensions that permit it to go around the floater hull or jacket so that the deck can be lowered and stabbed. The procedure for lowering is based on motorized “legs” to achieve a rapid weight transfer in severe sea-states and also permits the deck to be raised up once at site to achieve a high air gap installation on a fixed substructure. This new vessel design greatly extends the geographical range for deck installation using the float-over method and offers a cost effective alternative to relying on crane vessels for installation. Additionally, the vessel can perform a range of other tasks, particularly relating to decommissioning of facilities, or offshore wind-farm turbine installation.
A Robust Asymptotically Based Modeling Approach for Two-Phase Flow in Porous Media
Authors: Awad M. M. , Butt S. D.
Published: July 2009

A simple semi-theoretical method for calculating two-phase frictional pressure gradient in porous media using asymptotic analysis is presented. Two-phase frictional pressure gradient is expressed in terms of the asymptotic single-phase frictional pressure gradients for liquid and gas flowing alone. In the present model, the two-phase frictional pressure gradient for x ≅ 0 is nearly identical to single-phase liquid frictional pressure gradient. Also, the two-phase frictional pressure gradient for x ≅ 1 is nearly identical to single-phase gas frictional pressure gradient. The proposed model can be transformed into either a two-phase frictional multiplier for liquid flowing alone (φl2) or two-phase frictional multiplier for gas flowing alone (φg2) as a function of the Lockhart-Martinelli parameter, X. The advantage of the new model is that it has only one fitting parameter (p) while the other existing correlations such as Larkins et al. correlation, Sato et al. correlation, and Goto and Gaspillo correlation have three constants. Therefore, calibration of the new model to experimental data is greatly simplified. The new model is able to model the existing multi parameters correlations by fitting the single parameter p. Specifically, p = 1/3.25 for Midoux et al. correlation, p = 1/3.25 for Rao et al. correlation, p = 1/3.5 for Tosun correlation, p = 1/3.25 for Larkins et al. correlation, p = 1/3.75 for Sato et al. correlation, and p = 1/3.5 for Goto and Gaspillo correlation.
Hydrodynamic Analysis of Multi-Body Floating Piers
Authors: Tajali Zahra , Shafieefar Mehdi , Akhyani Mahmood
Published: July 2009

Hydrodynamic analysis of a floating multi-body pier interacting with incident waves is carried out in the present research and results of wave-induced motions and structural responses are described. The objective is to develop a procedure which can be used to analyze the motions of such a floating structure consisting of a number of rigid pontoons linked together. Also, optimization of pontoons geometry for a desired length of the pier is examined. In this regard, different alternative arrangements of pontoons with different numbers and dimensions are studied and dynamic responses of these alternatives are investigated. Analysis of the multi-body floating structure is carried out in the frequency domain. The wave-induced forces and the responses are computed by three-dimensional diffraction method. To examine the effect of using different pontoons on pier hydrodynamic response, motion-amplitude transfer functions (RAO) and connector forces for a wide range of wave frequency and heading angle are computed. Results include the absolute and relative responses of the individual pontoons and prediction of pier motions for a wide variety of pontoon geometries in different wave frequencies and heading angles. Also results include effects of pontoons dimension on the response of structure and present heave, roll and pitch motions for floating pier structural system.
Mating of the Topsides Onto the Lower Hull: P52 Semi-Submersible
Authors: Emery David , Ferron Loic , Naudin Jean Claude , Thomas Pierre Armand , Weber Philippe
Published: July 2009

Since the early 80’s, Technip has developed a special technology, called the UNIDECK® concept, for the float over installation of topsides. This method has been used for platform installations in benign areas such as the Persian Gulf or Far East Asia and in particular, in difficult sea conditions such as the long period swells occurring in West Africa. Based on its extensive experiences for topsides’ float over installation over more than twenty years, Technip has recently adapted this proven technology to semi-submersible units for their assembly by a mating operation of the topsides onto the lower hull. This paper gives an overview of the technical aspects involved in a mating operation of two floating units through a description of the operation performed for Petrobras’ P52 semi-submersible in June 2006.
Computing Large Amplitude Motions of a Floating Offshore Structure in the Time Domain
Authors: Qiu Wei , Peng Hongxuan
Published: July 2009

Based on the panel-free method, large-amplitude motions of floating offshore structures have been computed by solving the body-exact problem in the time domain using the exact geometry. The body boundary condition is imposed on the instantaneous wetted surface exactly at each time step. The free surface boundary is assumed linear so that the time-domain Green function can be applied. The instantaneous wetted surface is obtained by trimming the entire NURBS surfaces of a floating structure. At each time step, Gaussian points are automatically distributed on the instantaneous wetted surface. The velocity potentials and velocities are computed accurately on the body surface by solving the desingularized integral equations. Nonlinear Froude-Krylov forces are computed on the instantaneous wetted surface under the incident wave profile. Validation studies have been carried out for a Floating Production Storage and Offloading (FPSO) vessel. Computed results were compared with experimental results and solutions by the panel method.
Dynamic Analysis and Design of LNG Tanks Considering Fluid Structure Interactions
Authors: Xiong Y. P. , Xing J. T.
Published: July 2009

Following a general description and analysis of the fundamental criteria for the dynamic design concerning dynamic stiffness, strength and environment issues, it is considered that the natural characteristics of the dynamic system and the dynamic responses of the system subject to various dynamic loads are two key critical issues in the dynamic design. Therefore, for the dynamic design of a LNG tank filled with liquid and operated on seaway, it is necessary to accurately predict its natural characteristics and dynamic response considering fluid structure interactions. To address these two key issues in the dynamic design stage, the developed computer software based on a mixed displacement–pressure finite element model to complete fluid-structure interaction analysis is introduced. An integrated internal liquid-tank-external water interaction system investigated by numerical simulations is summarised to consider the two issues involving the dynamic design of LNG tanks. The five studied cases include: i) 50% filled LNG liquid in a fixed rigid tank, ii) elastic tank only, iii) 50% filled LNG liquid-elastic tank interaction, iv) empty elastic tank-external sea water interaction and v) internally 50% filled LNG liquid-elastic tank-external sea water interaction. The calculated results are compared to reveal the coupling effects on the dynamic design of LNG tanks. To further demonstrate the effects of the natural characteristics affected by different interactions on the dynamic responses involving the dynamic strength, stiffness and vibration environment problems considered in dynamic design, the numerical simulations of the studied systems subject to regular sea wave excitations and earthquake excitations are carried out. The dynamic displacements for stiffness analysis, the dynamic stress for strength analysis and vibration level for dynamic environment analysis are presented and discussed. Guidelines provided in this paper maybe useful for dynamic designs of LNG tank operating in complex marine environments.
Global Performance and Sloshing Analysis of a New Deep-Draft Semi-Submersible LNG FPSO
Authors: Kim Jang W. , O’Sullivan Jim , Steen Atle , Halkyard John
Published: July 2009

A new concept of LNG FPSO based on a deep-draft semi-submersible hull is introduced. With the deep draft, small water plane area, low center of gravity and large radius of gyration, the new LNG FPSO offers very low motions. This low-motion LNG FPSO platform provides more options and flexibilities in the selection of LNG liquefaction units, LNG containment systems, construction sites, installation methods, mooring systems (i.e. no requirements for weather-vaning), riser system and less down time compared with a conventional FPSO hull. Global performance and sloshing analyses for the new LNG FPSO hull and the conventional FPSO hull are performed to compare their operating performance for West Africa and the Northwest Australia environments.
Second-Order Low-Frequency Wave Forces on a SPM Offloading Tanker in Shallow Water
Authors: Ma S. , Shi S. , Kim M. H.
Published: July 2009

This paper studies the influence of three different calculation methods of the second-order low-frequency (LF) wave forces on the tanker responses and hawser/mooring tensions in relatively shallow water region. The vessel-mooring-riser coupled dynamic analysis computer program HARP is used to simulate the coupled dynamic responses of offloading tanker moored to a SPM (Single Point Mooring). Because the SPM is supposed to be deployed in shallow water and the slowly varying drift motions of the tanker are to dominate the motion responses in typical operational conditions, the accurate calculation of LF wave-force quadratic transfer functions (QTFs) becomes important especially for mooring and hawser tensions. Like common practice, the so-called Newman’s approximation and another approximation method without including complicated free-surface integrals are first used to calculate the LF QTFs on the offloading tanker and they are compared with the complete QTF results. Further comparison is performed by calculating the resulting LF wave-force spectra and response time series by using the three different methods. The impact of the three different approaches on vessel surge motions and hawser/mooring line tensions is also addressed.
Voice gender perception by cochlear implantees
Authors: Kovačić Damir , Balaban Evan
Published: July 2009

Gender identification of human voices was studied in a juvenile population of cochlear implant (CI) users exposed to naturalistic speech stimuli from 20 male and 20 female speakers using two different voice gender perception tasks. Stimulus output patterns were recorded from each individual CI for each stimulus, and features related to voice fundamental frequency and spectral envelope were extracted from these electrical output signals to evaluate the relationship between implant output and behavioral performance. In spite of the fact that temporal and place cues of similar quality were produced by all CI devices, only about half of the subjects were able to label male and female voices correctly. Participants showed evidence of using available temporal cues, but showed no evidence of using place cues. The implants produced a consistent and novel cue to voice gender that participants did not appear to utilize. A subgroup of participants could discriminate male and female voices when two contrasting voices were presented in succession, but were unable to identify gender when voices were singly presented. It is suggested that the nature of long-term auditory categorical memories needs to be studied in more detail in these individuals.
Response to noise from modern wind farms in The Netherlands
Authors: Pedersen Eja , van den Berg Frits , Bakker Roel , Bouma Jelte
Published: July 2009

The increasing number and size of wind farms call for more data on human response to wind turbine noise, so that a generalized dose-response relationship can be modeled and possible adverse health effects avoided. This paper reports the results of a 2007 field study in The Netherlands with 725 respondents. A dose-response relationship between calculated A-weighted sound pressure levels and reported perception and annoyance was found. Wind turbine noise was more annoying than transportation noise or industrial noise at comparable levels, possibly due to specific sound properties such as a “swishing” quality, temporal variability, and lack of nighttime abatement. High turbine visibility enhances negative response, and having wind turbines visible from the dwelling significantly increased the risk of annoyance. Annoyance was strongly correlated with a negative attitude toward the visual impact of wind turbines on the landscape. The study further demonstrates that people who benefit economically from wind turbines have a significantly decreased risk of annoyance, despite exposure to similar sound levels. Response to wind turbine noise was similar to that found in Sweden so the dose-response relationship should be generalizable.
Sound absorption of porous metals at high sound pressure levels
Authors: Wang Xiaolin , Peng Feng , Chang Baojun
Published: July 2009

This paper is a study about sound absorption properties of porous metals at high sound pressure levels. A method of deriving the nonlinear static flow resistance for highly porous fibrous metals is proposed by solving Oseen’s equation to take account of the inertia effect, validated by experiments of airflow measurement. In order to predict nonlinear sound absorbing performance of a finite thickness porous metal layer, a numerical method is employed, verified by sound absorption measurement in an impedance tube. Accordingly, the effects of the nonlinear coefficient on the porous metal sound absorption are investigated.
Regulation of Fimbrial Expression
Authors: Blomfield Ian , van der Woude Marjan
Published: July 2009

Fimbria-mediated interaction with the host elicits both innate and adaptive immune responses, and thus their expression may not always be beneficial in vivo. Furthermore, the metabolic drain of producing fimbriae is significant. It is not surprising, therefore, to find that fimbrial production in
Escherichia coli
and
Salmonella enterica
is under extensive environmental regulation. In many instances, fimbrial expression is regulated by phase variation, in which individual cells are capable of switching between fimbriate and afimbriate states to produce a mixed population. Mechanisms of phase variation vary considerably between different fimbriae and involve both genetic and epigenetic processes. Notwithstanding this, fimbrial expression is also sometimes controlled at the posttranscriptional level. In this chapter, we review key features of the regulation of fimbrial gene expression in
E. coli
and
Salmonella
. The occurrence and distribution of fimbrial operons vary significantly among
E. coli
pathovars and even among the many
Salmonella
serovars. Therefore, general principles are presented on the basis of detailed discussion of paradigms that have been extensively studied, including Pap, type 1 fimbriae, and curli. The roles of operon specific regulators like FimB or CsgD and of global regulatory proteins like Lrp, CpxR, and the histone-like proteins H-NS and IHF are reviewed as are the roles of sRNAs and of signalling nucleotide cyclic-di-GMP. Individual examples are discussed in detail to illustrate how the regulatory factors cooperate to allow tight control of expression of single operons. Molecular networks that allow coordinated expression between multiple fimbrial operons and with flagella in a single isolate are also presented. This chapter illustrates how adhesin expression is controlled, and the model systems also illustrate general regulatory principles germane to our overall understanding of bacterial gene regulation.
Respiration of Nitrate and Nitrite
Authors: Cole Jeffrey A. , Richardson David J.
Published: July 2009

Nitrate reduction to ammonia via nitrite occurs widely as an anabolic process through which bacteria, archaea, and plants can assimilate nitrate into cellular biomass.
Escherichia coli
and related enteric bacteria can couple the eight-electron reduction of nitrate to ammonium to growth by coupling the nitrate and nitrite reductases involved to energy-conserving respiratory electron transport systems. In global terms, the respiratory reduction of nitrate to ammonium dominates nitrate and nitrite reduction in many electron-rich environments such as anoxic marine sediments and sulfide-rich thermal vents, the human gastrointestinal tract, and the bodies of warm-blooded animals. This review reviews the regulation and enzymology of this process in
E. coli
and, where relevant detail is available, also in
Salmonella
and draws comparisons with and implications for the process in other bacteria where it is pertinent to do so. Fatty acids may be present in high levels in many of the natural environments of
E. coli
and
Salmonella
in which oxygen is limited but nitrate is available to support respiration. In
E. coli
, nitrate reduction in the periplasm involves the products of two seven-gene operons,
napFDAGHBC
, encoding the periplasmic nitrate reductase, and
nrfABCDEFG
, encoding the periplasmic nitrite reductase. No bacterium has yet been shown to couple a periplasmic nitrate reductase solely to the cytoplasmic nitrite reductase NirB. The cytoplasmic pathway for nitrate reduction to ammonia is restricted almost exclusively to a few groups of facultative anaerobic bacteria that encounter high concentrations of environmental nitrate.
Modulation of Chemical Composition and Other Parameters of the Cell at Different Exponential Growth Rates
Authors: Bremer Hans , Dennis Patrick P.
Published: July 2009

This review begins by briefly presenting the history of research on the chemical composition and other parameters of cells of E. coli and S. enterica at different exponential growth rates. Studies have allowed us to determine the in vivo strength of promoters and have allowed us to distinguish between factor-dependent transcriptional control of the promoter and changes in promoter activity due to changes in the concentration of free functional RNA polymerase associated with different growth conditions. The total, or bulk, amounts of RNA and protein are linked to the growth rate, because most bacterial RNA is ribosomal RNA (rRNA). Since ribosomes are required for protein synthesis, their number and their rate of function determine the rate of protein synthesis and cytoplasmic mass accumulation. Many mRNAs made in the presence of amino acids have strong ribosome binding sites whose presence reduces the expression of all other active genes. This implies that there can be profound differences in the spectrum of gene activities in cultures grown in different media that produce the same growth rate. Five classes of growth-related parameters that are generally useful in describing or establishing the macromolecular composition of bacterial cultures are described in detail in this review. A number of equations have been reported that describe the macromolecular composition of an average cell in an exponential culture as a function of the culture doubling time and five additional parameters: the C- and D-periods, protein per origin (PO), ribosome activity, and peptide chain elongation rate.
COHOMOLOGICALLY HYPERBOLIC ENDOMORPHISMS OF COMPLEX MANIFOLDS
Authors: ZHANG DE-QI
Published: July 2009

We show that if a compact Kähler manifold X admits a cohomologically hyperbolic surjective endomorphism then its Kodaira dimension is non-positive. This gives an affirmative answer to a conjecture of Guedj in the holomorphic case. The main part of the paper is to determine the geometric structure and the fundamental groups (up to finite index) for those X of dimension 3.
ON THE DEFORMATION SPACE OF CLIFFORD–KLEIN FORMS OF SOME EXPONENTIAL HOMOGENEOUS SPACES
Authors: BAKLOUTI ALI , KÉDIM IMED
Published: July 2009

Let H be a closed connected subgroup of a connected, simply connected exponential solvable Lie group G. We consider the deformation space [Formula: see text] of a discontinuous subgroup Γ of G for the homogeneous space G/H. When H contains [G, G], we exhibit a description of the space [Formula: see text] which appears to involve GLk(ℝ) as a direct product factor, where k designates the rank of Γ. The moduli space [Formula: see text] is also described. Consequently, we prove in such a setup that the local rigidity property fails to hold globally on [Formula: see text] and that every element of the parameters space is topologically stable.
INVARIANTS OF KNOTS DERIVED FROM EQUIVARIANT LINKING MATRICES OF THEIR SURGERY PRESENTATIONS
Authors: OHTSUKI TOMOTADA
Published: July 2009

The quantum U(1) invariant of a closed 3-manifold M is defined from the linking matrix of a framed link of a surgery presentation of M. As an equivariant version of it, we formulate an invariant of a knot K from the equivariant linking matrix of a lift of a framed link of a surgery presentation of K. We show that this invariant is determined by the Blanchfield pairing of K, or equivalently, determined by the S-equivalent class of a Seifert matrix of K, and that the "product" of this invariant and its complex conjugation is presented by the Alexander module of K. We present some values of this invariant of some classes of knots concretely.
EVA: Does Size Matter?
Authors: Hamilton Janet , Rahman Shafiqur , Lee Alice C.
Published: July 2009

Value-added performance measures, such as economic value added (EVA), are promoted as a means to better align managerial incentives and improve firm performance. This paper empirically examines whether EVA adopters outperform a peer group of non-adopters over a long term horizon. It also explores the determinants associated with differences in relative market performance of these two groups. We find mixed results consistent with previous studies. In examining risk adjusted market returns, we find that the full sample significantly underperforms the market. However, during the period of the study, EVA adopters exhibit less negative performance than non-adopters. Moreover, over the entire study period, adopter performance improves in a positive direction, while non-adopters experience a performance decline. Adopting firms also exhibit higher earnings growth and higher returns. In perspective, these results suggest there is some benefit to EVA adoption, relative to a peer group, as adopters outperform their peer group. In a comparison of peer matched groups, firm size and growth opportunities are found to have a significant impact on performance for three size-based groups.
Multi-operator media retargeting
Authors: Rubinstein Michael , Shamir Ariel , Avidan Shai
Published: July 2009

Content aware resizing gained popularity lately and users can now choose from a battery of methods to retarget their media. However, no single retargeting operator performs well on all images and all target sizes. In a user study we conducted, we found that users prefer to combine seam carving with cropping and scaling to produce results they are satisfied with. This inspires us to propose an algorithm that combines different operators in an optimal manner. We define a
resizing space
as a conceptual multi-dimensional space combining several resizing operators, and show how a path in this space defines a sequence of operations to retarget media. We define a new image similarity measure, which we term Bi-Directional Warping (BDW), and use it with a dynamic programming algorithm to find an optimal path in the resizing space. In addition, we show a simple and intuitive user interface allowing users to explore the resizing space of various image sizes interactively. Using key-frames and interpolation we also extend our technique to retarget video, providing the flexibility to use the best combination of operators at different times in the sequence.
Mixed-integer quadrangulation
Authors: Bommes David , Zimmer Henrik , Kobbelt Leif
Published: July 2009

We present a novel method for quadrangulating a given triangle mesh. After constructing an as smooth as possible symmetric cross field satisfying a sparse set of directional constraints (to capture the geometric structure of the surface), the mesh is cut open in order to enable a low distortion unfolding. Then a seamless globally smooth parametrization is computed whose iso-parameter lines follow the cross field directions. In contrast to previous methods, sparsely distributed directional constraints are sufficient to automatically determine the appropriate number, type and position of singularities in the quadrangulation. Both steps of the algorithm (cross field and parametrization) can be formulated as a mixed-integer problem which we solve very efficiently by an adaptive greedy solver. We show several complex examples where high quality quad meshes are generated in a fully automatic manner.
Methodologies for data quality assessment and improvement
Authors: Batini Carlo , Cappiello Cinzia , Francalanci Chiara , Maurino Andrea
Published: July 2009

The literature provides a wide range of techniques to assess and improve the quality of data. Due to the diversity and complexity of these techniques, research has recently focused on defining methodologies that help the selection, customization, and application of data quality assessment and improvement techniques. The goal of this article is to provide a systematic and comparative description of such methodologies. Methodologies are compared along several dimensions, including the methodological phases and steps, the strategies and techniques, the data quality dimensions, the types of data, and, finally, the types of information systems addressed by each methodology. The article concludes with a summary description of each methodology.
Self-organizing fault-tolerant topology control in large-scale three-dimensional wireless networks
Authors: Wang Yu , Cao Lijuan , Dahlberg Teresa A. , Li Fan , Shi Xinghua
Published: July 2009

Topology control protocol aims to efficiently adjust the network topology of wireless networks in a self-adaptive fashion to improve the performance and scalability of networks. This is especially essential to large-scale multihop wireless networks (e.g., wireless sensor networks). Fault-tolerant topology control has been studied recently. In order to achieve both sparseness (i.e., the number of links is linear with the number of nodes) and fault tolerance (i.e., can survive certain level of node/link failures), different geometric topologies were proposed and used as the underlying network topologies for wireless networks. However, most of the existing topology control algorithms can only be applied to two-dimensional (2D) networks where all nodes are distributed in a 2D plane. In practice, wireless networks may be deployed in three-dimensional (3D) space, such as under water wireless sensor networks in ocean or mobile ad hoc networks among space shuttles in space. This article seeks to investigate self-organizing fault-tolerant topology control protocols for large-scale 3D wireless networks. Our new protocols not only guarantee
k
-connectivity of the network, but also ensure the bounded node degree and constant power stretch factor even under
k
−1 node failures. All of our proposed protocols are localized algorithms, which only use one-hop neighbor information and constant messages with small time complexity. Thus, it is easy to update the topology efficiently and self-adaptively for large-scale dynamic networks. Our simulation confirms our theoretical proofs for all proposed 3D topologies.
The calcium-sensing receptor (CaSR) defends against hypercalcemia independently of its regulation of parathyroid hormone secretion
Authors: Kantham Lakshmi , Quinn Steven J. , Egbuna Ogo I. , Baxi Khanjan , Butters Robert , Pang Jian L. , Pollak Martin R. , Goltzman David , Brown Edward M.
Published: July 2009

The calcium-sensing receptor (CaSR) controls parathyroid hormone (PTH) secretion, which, in turn, via direct and indirect actions on kidney, bone, and intestine, maintains a normal extracellular ionized calcium concentration (Ca2+o). There is less understanding of the CaSR's homeostatic importance outside of the parathyroid gland. We have employed single and double knockout mouse models, namely mice lacking PTH alone (CaSR+/+ PTH−/−, referred to as C+P−), lacking both CaSR and PTH (CaSR−/− PTH−/−, C−P−) or wild-type (CaSR+/+ PTH+/+, C+P+) mice to study CaSR-specific functions without confounding CaSR-mediated changes in PTH. The mice received three hypercalcemic challenges: an oral Ca2+ load, injection or constant infusion of PTH via osmotic pump, or a phosphate-deficient diet. C−P− mice show increased susceptibility to developing hypercalcemia with all three challenges compared with the other two genotypes, whereas C+P− mice defend against hypercalcemia similarly to C+P+ mice. Reduced renal Ca2+ clearance contributes to the intolerance of the C−P− mice to Ca2+ loads, as they excrete less Ca2+ at any given Ca2+o than the other two genotypes, confirming the CaSR's direct role in regulating renal Ca2+ handling. In addition, C+P+ and C+P−, but not C−P−, mice showed increases in serum calcitonin (CT) levels during hypercalcemia. The level of 1,25(OH)2D3 in C−P− mice, in contrast, was similar to those in C+P− and C+P+ mice during an oral Ca2+ load, indicating that increased 1,25(OH)2D3 production cannot account for the oral Ca2+-induced hypercalcemia in the C−P− mice. Thus, CaSR-stimulated PTH release serves as a “floor” to defend against hypocalcemia. In contrast, high-Ca2+o-induced inhibition of PTH is not required for a robust defense against hypercalcemia, at least in mice, whereas high-Ca2+o-stimulated, CaSR-mediated CT secretion and renal Ca2+ excretion, and perhaps other factors, serve as a “ceiling” to limit hypercalcemia resulting from various types of hypercalcemic challenges.
MicroRNAs as New Players for Diagnosis, Prognosis, and Therapeutic Targets in Breast Cancer
Authors: Ng Enders K. O. , Wong Chris L. P. , Ma Edmond S. K. , Kwong Ava
Published: July 2009

MicroRNAs are small nonprotein-coding RNAs that regulate the expressions of a wide variety of genes by sequence-specific base pairing on the UTR of mRNA targets resulting in mRNA degradation or inhibition of translation. Aberrant expressions of miRNAs have been linked to tumor development, metastasis, diagnosis, prognosis, and therapy response in human breast cancer. Some miRNAs have been considered to have potential clinical applications as a tool for breast cancer prognosis and therapy. Here we describe and discuss lines of evidence supporting the important relationship between miRNAs and breast cancer, and its therapeutic strategies.