bluuebunny/crossref_metadata_2025 huggingface dataset:
Preliminary Results of a Vortex Method for Stand-Alone Vertical Axis Marine Current Turbine
Authors: Li Ye , Calisal Sander M.
Published: May 2009

Tidal power technology has been dwarfed once to take hold in the late 1970’s, because the early generations were expensive at small scale and some applications (such as barrages) had negative environmental impacts. In a similar working manner as a wind turbine, a tidal current turbine has been recognized as a promising ocean energy conversion device in the past two decades. However, the industrialization process is still slow. One of the important reasons is lack of comprehensive turbine hydrodynamics analysis which can not only predict turbine power but also assess impacts on the surrounding areas. Although a lot can be learned from the marine propeller or the wind turbine studies, a systematic hydrodynamics analysis on a vertical axis tidal current turbine has not been reported yet. In this paper, we employed vortex method to calculate the performance of stand-alone vertical axis tidal turbine in term of power efficiency, torque and forces. This method focuses on power prediction, hydrodynamics analysis and design, which can provide information for turbines distribution planning in a turbine farm and other related studies, which are presented in Li and Calisal (2007), a companion paper in the conference. In this method, discrete vortex method is the core for numerical calculation. Free vortex wake structure, nascent vortex and vortex decay mechanism are discussed in detail. Good agreements in turbine efficiency comparison are obtained with both the newly-designed tidal turbine test in a towing tank and early wind turbine test.
A Procedure for Predicting Energy From a Tidal Turbine Farm
Authors: Li Ye , Calisal Sander M.
Published: May 2009

A tidal current turbine is a device for harnessing energy from tidal current. A group of tidal current turbines, distributed schematically at a site, is called a tidal turbine farm. A tidal turbine farm has to be located in a confined channel or a straight where consistent high-velocity tidal current flow is available for the cost-effectiveness concern. This narrow geographical condition poses challenges for turbine farm planners to distribute turbines strategically. Turbines’ distribution in a farm affects power generation efficiency and the resultant tidal unit power cost. In this paper, we propose a procedure for predicting energy generation from a tidal turbine farm by investigating the optimal distribution of turbines at a given site. The objective of optimizing the turbines distribution is to maximize the power output efficiency. To fulfill this, we conducted a systematic analysis on power generation from a tidal turbine farm to identify the key factors affecting the optimal tidal turbines distribution with an emphasis on the turbines’ hydrodynamics analysis and briefed the turbine working principle. As a companion paper to Li and Calisal (2007) which discusses the principle of a stand alone turbine, turbine configuration and interactions (i.e. angle of attack, turbine relative distance and turbine size) are extended here. The main assumption of this discussion is that vortex shedding impact is the dominant factor causing the turbine efficiency loss. Considering the turbine design principle, a simplified relationship between turbines distribution and turbine farm efficiency is formulated. Then, numerical simulation results are presented for a given site in British Columbia together with extended general solution.
A Standardized Approach for Reliability-Based Design and Assessment of Pipelines
Authors: Nessim Maher , Zhou Wenxing , Zhou Joe , Rothwell Brian
Published: May 2009

A new Annex on reliability-based design and assessment of onshore natural gas pipelines has been adopted for inclusion in the 2007 edition of the Canadian Standard Association’s pipeline standard (CSA-Z662). The same Annex is also being reviewed for inclusion in the next edition of the ASME gas pipeline code (ASME B31.8). The Annex defines a set of specific reliability targets as a function of pipeline diameter, pressure and population density; prescribes the process of demonstrating compliance with these targets; specifies the key requirements of a valid reliability calculation; and gives guidance on specific analysis methods, limit state functions and input parameter distributions. It is one of the few full reliability-based standards in the industry and is the first to mandate specific reliability targets. This paper describes the reliability-based approach adopted, the risk-based methodology used in defining the reliability targets and the key elements of the codified approach. It discusses current applications of the methodology as well as existing and potential plans developing similar codes for liquid and offshore pipelines.
Multi-Hull Configuration Design: A Framework for Powering Minimization
Authors: Yeung Ronald W. , Wan Hui
Published: May 2009

The powering issue of a high-speed marine vehicle with multi-hulls is addressed, since there is an often need to quickly evaluate the effects of several configuration parameters in the early stage of ship design. For component hulls with given geometry, the parameters considered include the relative locations of individual hulls and the relative volumetric ratios. Within the realm of linearized theory, an interference resistance expression for hull-to-hull interaction is first reviewed, and then a new formula for hull-and-pressure distribution interference is derived. Each of these analytical expressions is expressed in terms of the Fourier signatures or Kochin functions of the interacting components, with the separation, stagger, and speed as explicit parameters. Based on this framework, examples are given for assessing the performance of a di-hull as opposed to a tetra-hull system. Also examined is the wave resistance generated by a Surface-Effect Ship (SES) in comparison with that by a baseline catamaran, subject to the constraint of constant total displacement.
Measurement and Analysis of Ocean Wave Fields in Four Dimensions
Authors: MacHutchon Keith R. , Liu Paul C.
Published: May 2009

Ocean wave data comprises either instrumentally measured data or model-derived data, and the former type of data is preferred in the offshore industry. Instrumental data can be considered to be comprised of both directly measured sea surface displacement data and derived data, from the acceleration of buoys. It has been found that significant differences can occur between sea surface displacements, which are recorded in steep waves by fixed probes or lasers (Eulerian), or by free-floating buoys (Lagrangian). This has given rise to the situation where wave buoy data should not be used to estimate wave profiles in steep waves. Short crested and heaped waves, in moderate to high sea states, can also cause a problem when recording wave data at a fixed point, when it comes to determining the representivity of the results across a wave field. Recorded wave data is used as the basis for the development as well as the verification of all wave models and, given the above uncertainties, the authors propose a new wave measurement method, using the recently developed Automated Trinocular Stereo Imaging System (ATSIS), for the recording of three-dimensional surface wave displacements with respect to time. The ATSIS is a novel system, which measures the temporal evolution of three-dimensional wave characteristics for analysis. An oblique configuration for the system effectively increases spatial coverage, allowing observations of wave phenomena over a broad range of temporal and spatial scales. The details in the paper provide a solution of quantifying the behaviour of irregular, non-linear, and directionally spread (short crested waves), and provides an efficient method for developing better design criteria in the future.
Nonlinear Peak to Trough Distributions in Sea States With Double-Peaked Spectra
Authors: Arena Felice , Guedes Soares C.
Published: May 2009

The peaks to trough distributions of nonlinear high sea waves in bi-modal sea states are investigated. The statistical distribution of wave height is firstly investigated by considering the Boccotti’s distribution, where the parameters of the distribution are calculated for some bimodal spectra of sea states recorded in the Atlantic Ocean. The nonlinear crest and trough distributions are then obtained particularizing for two peaked spectra the second-order Fedele & Arena distribution, which depends upon two parameters. The results have been finally validated by means of Monte Carlo simulations of nonlinear random waves with bimodal spectra.
Tensegrity Structures in the Design of Flexible Structures for Offshore Aquaculture
Authors: Jensen O̸sten , Wroldsen Anders Sunde , Lader Pa˚l Furset , Fredheim Arne , Heide Mats , Johansen Vegar
Published: May 2009

Aquaculture is the fastest growing food producing sector in the world. Considerable interest exists in developing open ocean aquaculture in response to a shortage of suitable, sheltered inshore locations. The harsh weather conditions experienced offshore lead to a focus on new structure concepts, remote monitoring and a higher degree of automation in order to keep the cost of structures and operations within an economically viable range. This paper proposes tensegrity structures in the design of flexible structures for offshore aquaculture. The finite element analysis program ABAQUS™ has been used to investigate stiffness properties and performance of tensegrity structures when subjected to various forced deformations and hydrodynamic load conditions. The suggested concept, the tensegrity beam, shows promising stiffness properties in tension, compression and bending, which are relevant for development of open ocean aquaculture construction for high energy environments. When designing a tensegrity beam, both pre-stress and spring stiffness should be considered to ensure the desired structural properties. A large strength to mass ratio and promising properties with respect to control of geometry, stiffness and vibration could make tensegrity an enabling technology for future developments.
Wave Energy Hyperbaric Device for Electricity Production
Authors: Estefen Segen F. , da Costa Paulo Roberto , Ricarte Eliab , Pinheiro Marcelo M.
Published: May 2009

Wave energy is a renewable and non-polluting source and its use is being studied in different countries. The paper presents an overview on the harnessing of energy from waves and the activities associated with setting up a plant for extracting energy from waves in Port of Pecem, on the coast of Ceara State, Brazil. The technology employed is based on storing water under pressure in a hyperbaric chamber, from which a controlled jet of water drives a standard turbine. The wave resource at the proposed location is presented in terms of statistics data obtained from previous monitoring. The device components are described and small scale model tested under regular waves representatives of the installation region. Based on the experimental results values of prescribed pressures are identified in order to optimize the power generation.
Numerical Simulation of Two-Phase Sloshing Flow in LNG Tank Using Finite-Analytic Level-Set Method
Authors: Yu Kai , Chen Hamn-Ching , Kim Jang Whan , Lee Young-Bum
Published: May 2009

Impact pressure due to sloshing is of great concern for the ship owners, designers and builders of the LNG carriers regarding the safety of LNG containment system and hull structure. Sloshing of LNG in a partially filled tank has been an active area of research with numerous experimental and numerical investigations over the past decade. In order to accurately predict the sloshing impact load, it is necessary to develop advanced numerical simulation tools which can provide accurate resolution of local flow phenomena including wave breaking, jet formation, gas entrapping and liquid-gas interactions. In the present study, a new numerical method is developed for the simulation of violent sloshing flow inside a three-dimensional LNG tank considering wave breaking and liquid-gas interaction. The sloshing flow inside a membrane-type LNG tank is simulated numerically using the Finite-Analytic Navier-Stokes (FANS) method. The governing equations for two-phase air and water flows are formulated in curvilinear coordinate system and discretized using the finite-analytic method on a non-staggered grid. Simulations were performed for LNG tank in transverse and longitudinal motions including horizontal, vertical, and rotational motions. The predicted impact pressures were compared with the corresponding experimental data. The validation results clearly illustrate the capability of the present two-phase FANS method for accurate prediction of impact pressure in sloshing LNG tank including violent free surface motion, three-dimensional instability and air trapping effects.
Thermo-Mechanical Considerations for Flexible Joint Applications in Deepwater Production Risers
Authors: Hogan Mike , Pottorff Todd , Mekha Basim
Published: May 2009

Flexible joint technology is a common means of limiting motion-induced moments between coupled steel risers and production vessels. Production conditions in modern deepwater developments can include both high and low temperature conditions. The stiffness behavior of the elastomeric materials used in flexible joints is a function of temperature. For this reason, the engineering approach to this interface must account for flowline operating temperatures in order to ensure the mechanical integrity of the riser system. The analysis technique used to predict fatigue of the coupled structures should employ an accurate model of the stiffness behavior at the temperatures associated with various production cases. Examples of fatigue-critical applications in low and high temperature applications are presented, as well as design alternatives for reducing the influence of flowline temperature on flexible joint stiffness. One recent example was the design of the flexible joints for Independence Hub gas production steel catenary risers for which the gas arrival temperature was below freezing.
Very Large Floating Structures
Authors: Suzuki H. , Riggs H. R. , Fujikubo M. , Shugar T. A. , Seto H. , Yasuzawa Y. , Bhattacharya B. , Hudson D. A. , Shin H.
Published: May 2009

Very Large Floating Structure (VLFS) is a unique concept of ocean structures primary because of their unprecedented length, displacement cost and associated hydroelastic response. International Ship and Offshore Structures Congress (ISSC) had paid attention to the emerging novel technology and launched Special Task Committee to investigate the state of the art in the technology. This paper summarizes the activities of the committee. A brief overview of VLFS is given first for readers new to the subject. History, application and uniqueness with regard to engineering implication are presented. The Mobile Offshore Base (MOB) and Mega-Float, which are typical VLFS projects that have been investigated in detail and are aimed to be realized in the near future, are introduced. Uniqueness of VLFS, such as differences in behavior of VLFS from conventional ships and offshore structures, are described. The engineering challenges associated with behavior, design procedure, environment, and the structural analysis of VLFS are introduced. A comparative study of hydroelastic analysis tools that were independently developed for MOB and Mega-Float is made in terms of accuracy of global behavior. The effect of structural modeling on the accuracy of stress analysis is also discussed. VLFS entails innovative design methods and procedure. Development of design criteria and design procedures are described and application of reliability-based approaches are documented and discussed.
Fatigue and Fracture of Ship and Offshore Structures: Summary of the Fatigue and Fracture Committee Report to the International Ship and Offshore Structures Congress (ISSC) 2006
Authors: Wa¨stberg Stig
Published: May 2009

The paper summarizes the main conclusions and recommendations from the report of Committee III.2 Fatigue and Fracture to the International Ship and Offshore Structures Congress (ISSC) 2006. The report reviewed more than 200 recent publications on the subject and summarized the main findings and trends, mainly within the areas of; Current Design Practice, Practical Use and Implementation of Fatigue Results, Fabrication, Inspection and Fitness for Service, Application of Non-Traditional Materials and Fabrication and Design Alternatives. The report also made recommendations for future work. For the whole report it is referred to the ISSC 2006 proceedings.
Why Great Britain’s success in Beijing could have been anticipated and why it should continue beyond 2012
Authors: Nevill A M , Balmer N J , Winter E M
Published: May 2009

Background:

Home advantage in the summer Olympic Games is well known. What is not so well known is that countries that host the Olympic Games perform better in the games before and after the games in which they were hosts.

Objective:

To model/quantify the significance associated with these “hosting” effects and to explain the likely causes of Great Britain’s improved medals haul in Beijing, while examining implications for London 2012 and beyond.

Results:

Using all hosting cities/countries since World War II and analysing the number of medals awarded to competitors as a binomial proportion (p) response variable within a logit model, we identified a significant increase in the probability/odds of a country obtaining a medal in the Olympic Games before, during and after hosting the Olympics.

Conclusions:

Funding appears to be an important factor when explaining these findings. Almost all countries that have been awarded the games after World War II would appear to have invested heavily in sport before being awarded the games. A second factor in Great Britain’s success is the legacy of hosting the Commonwealth Games in 2002 (a post-hosting games effect) that undoubtedly provided an infrastructure that benefited, in particular, cycling. Whether the International Olympics Committee either consciously or subconsciously take these factors into account is unclear when awarding the games to a city. What is clear is that based on these findings, Great Britain’s prospects of maintaining the Olympic success achieved in Beijing is likely to continue to London 2012 and beyond.
A SCALING LAW FOR THE COSMOLOGICAL CONSTANT FROM A STOCHASTIC MODEL FOR COSMIC STRUCTURES
Authors: CAPOZZIELLO SALVATORE , FUNKHOUSER SCOTT
Published: May 2009

A set of scaling laws, based on the stochastic motions of the granular components of astronomical systems, is applied to a cosmological model with a positive cosmological constant. It follows that the mass of the dominant particle in the observable universe must be proportional to the sixth root of the cosmological constant and of order near the nucleon mass, which is consistent with the Zel'dovich scaling law. The approach is a natural way to solve the "cosmic coincidence" problem. On the other hand, the observed value of the cosmological constant emerges as the result of a scaling law induced by the stochastic mechanism which gives rise to the gravitationally bound systems.
REFLECTION AND DIPS IN ELASTIC SCATTERING
Authors: TROSHIN S. M. , TYURIN N. E.
Published: May 2009

We discuss how the reflective scattering would affect elastic scattering in the region of small and moderate values of -t, in particular, we demonstrate that diffractive pattern in the angular distribution will be kept in a modified form.
THE PROTON SPIN PUZZLE: WHERE ARE WE TODAY?
Authors: BASS STEVEN D.
Published: May 2009

The proton spin puzzle has challenged our understanding of QCD for the last 20 years. New measurements of polarized glue, valence and sea quark polarization, including strange quark polarization, are available. What is new and exciting in the data, and what might this tell us about the structure of the proton? The proton spin puzzle seems to be telling us about the interplay of valence quarks with the complex vacuum structure of QCD.
ESTIMATIONS AND OPTIMAL DESIGNS FOR TWO-DIMENSIONAL HAAR-WAVELET REGRESSION MODELS
Authors: TIAN YONGGE
Published: May 2009

Estimations and optimal experimental designs for two-dimensional Haar-wavelet regression models are discussed. It is shown that the eigenvalues of the covariance matrix of the best linear unbiased estimator of the unknown parameters in a two-dimensional linear Haar-wavelet model can be represented in closed form. Some common discrete optimal designs for the model are constructed analytically from the eigenvalues. Some equivalences among these optimal designs are also given, and an example is demonstrated.
Platelet-activating factor induces the processing of nuclear factor-κB p105 into p50, which mediates acute bowel injury in mice
Authors: Liu Shirley X. L. , Tian Runlan , Baskind Heather , Hsueh Wei , De Plaen Isabelle G.
Published: May 2009

Platelet-activating factor (PAF), an endogenous proinflammatory phospholipid, when injected intravascularly to rats and mice, causes shock, acute bowel injury, and a rapid activation of NF-κB p50-p50 with upregulation of the chemokine CXCL2 in the intestine. In this study, we investigate the mechanism of NF-κB activation and the role of the NF-κB p50 subunit in PAF-induced shock and acute bowel injury. NF-κB p50-deficient mice and wild-type mice were anesthetized and tracheotomized, and their carotid artery was cannulated for blood pressure monitoring, blood sampling, and PAF administration. For determination of bowel injury, shock, and survival, PAF (2.2 μg/kg, intra-arterially, i.a.) was injected. Two hours later, animals were euthanized, and their small intestines were removed for histological examination. For biochemical studies, PAF (1.5 μg/kg i.a.) was administered and the small intestine removed after 15–60 min. We found that PAF induced an increase in p105 processing within 30 min, but there were no changes in the levels of the NF-κB inhibitory proteins IκBα and β. NF-κB p50-deficient mice were protected against PAF-induced mortality, shock, intestinal hypoperfusion, and injury compared with wild-type animals. We also found that p50-deficient mice had decreased gene expression of CXCL2 and TNF and a decrease in CXCL2 protein production compared with wild-type mice. Our study suggests that PAF increases the processing of NF-κB p105 into p50, with upregulation of proinflammatory cytokines, which leads to PAF-induced systemic inflammatory response and acute bowel injury.
Validation of a simple model for the morphology of the T wave in unipolar electrograms
Authors: Potse Mark , Vinet Alain , Opthof Tobias , Coronel Ruben
Published: May 2009

Local unipolar electrograms (UEGs) permit assessment of local activation and repolarization times at multiple sites simultaneously. However, UEG-based indexes of local repolarization are still debated, in particular for positive T waves. Previous experimental and computer modeling studies have not been able to terminate the debate. In this study we validate a simple theoretical model of the UEG and use it to explain how repolarization statistics in the UEG relate to those in the action potential. The model reconstructs the UEG by taking the difference between an inverted local action potential and a position-independent remote signal. In normal tissue, this extremely simple model predicts T-wave morphology with surprising accuracy while explaining in a readily understandable way why the instant of repolarization is always related to the steepest upstroke of the UEG, both in positive and negative T waves, and why positive T waves are related to early repolarizing sites, whereas negative T waves are related to late repolarizing sites.
Skeletal muscle contraction-induced vasodilator complement production is dependent on stimulus and contraction frequency
Authors: Dua Ashok K. , Dua Nickesh , Murrant Coral L.
Published: May 2009

To test the hypothesis that the vasodilator complement that produces arteriolar vasodilation during muscle contraction depends on both stimulus and contraction frequency, we stimulated four to five skeletal muscle fibers in the anesthetized hamster cremaster preparation in situ and measured the change in diameter of arterioles at a site of overlap with the stimulated muscle fibers. Diameter was measured before, during, and after 2 min of skeletal muscle contraction stimulated over a range of stimulus frequencies [4, 20, and 40 Hz; 15 contractions/min (cpm), 250 ms train duration] and a range of contraction frequencies (6, 15, and 60 cpm; 20 Hz stimulus frequency, 250 ms train duration). Muscle fibers were stimulated in the absence and presence of an inhibitor of adenosine receptors [10−6 M xanthine amine congener (XAC)], an ATP-dependent potassium (K+) channel inhibitor (10−5 M glibenclamide), an inhibitor of a source of K+ by inhibition of voltage-dependent K+ channels [3 × 10−4 M 3,4-diaminopyridine (DAP)], and an inhibitor of nitric oxide synthase [10−6 M NG-nitro-l-arginine methyl ester (l-NAME) + 10−7 S-nitroso- N-acetylpenicillamine (a nitric oxide donor)]. l-NAME inhibited the dilations at all stimulus frequencies and contraction frequencies except 60 cpm. XAC inhibited the dilations at all contraction frequencies and stimulus frequencies except 40 Hz. Glibenclamide inhibited all dilations at all stimulus and contraction frequencies, and DAP did not inhibit dilations at any stimulus frequencies while attenuating dilation at a contraction frequency of 60 cpm only. Our data show that the complement of dilators responsible for the vasodilations induced by skeletal muscle contraction differed depending on the stimulus and contraction frequency; therefore, both are important determinants of the dilators involved in the processes of arteriolar vasodilation associated with active hyperemia.
Apoptosis predominates in nonmyocytes in heart failure
Authors: Park Misun , Shen You-Tang , Gaussin Vinciane , Heyndrickx Guy R. , Bartunek Jozef , Resuello Ranillo R. G. , Natividad Filipinas F. , Kitsis Richard N. , Vatner Dorothy E. , Vatner Stephen F.
Published: May 2009

The goal of this investigation was to determine the distribution of myocardial apoptosis in myocytes and nonmyocytes in primates and patients with heart failure (HF). Almost all clinical cardiologists and cardiovascular investigators believe that myocyte apoptosis is considered to be a cardinal sign of HF and a major factor in its pathogenesis. However, with the knowledge that 75% of the number of cells in the heart are nonmyocytes, it is important to determine whether the apoptosis in HF is occurring in myocytes or in nonmyocytes. We studied both a nonhuman primate model of chronic HF, induced by rapid pacing 2–6 mo after myocardial infarction (MI), and biopsies from patients with ischemic cardiomyopathy. Dual labeling with a cardiac muscle marker was used to discriminate apoptosis in myocytes versus nonmyocytes. Left ventricular ejection fraction decreased following MI (from 78% to 60%) and further with HF (35%, P < 0.05). As expected, total apoptosis was increased in the myocardium following recovery from MI (0.62 cells/mm2) and increased further with the development of HF (1.91 cells/mm2). Surprisingly, the majority of apoptotic cells in MI and MI + HF, and in both the adjacent and remote areas, were nonmyocytes. This was also observed in myocardial biopsies from patients with ischemic cardiomyopathy. We found that macrophages contributed the largest fraction of apoptotic nonmyocytes (41% vs. 18% neutrophils, 16% fibroblast, and 25% endothelial and other cells). Although HF in the failing human and monkey heart is characterized by significant apoptosis, in contrast to current concepts, the apoptosis in nonmyocytes was eight- to ninefold greater than in myocytes.
Hyperbaric oxygen pretreatment according to the gas micronuclei denucleation hypothesis reduces neurologic deficit in decompression sickness in rats
Authors: Katsenelson K. , Arieli R. , Arieli Y. , Abramovich A. , Feinsod M. , Tal D.
Published: May 2009

During sudden or too rapid decompression, gas is released within supersaturated tissues in the form of bubbles, the cause of decompression sickness. It is widely accepted that these bubbles originate in the tissue from preexisting gas micronuclei. Pretreatment with hyperbaric oxygen (HBO) has been hypothesized to shrink the gas micronuclei, thus reducing the number of emerging bubbles. The effectiveness of a new HBO pretreatment protocol on neurologic outcome was studied in rats. This protocol was found to carry the least danger of oxygen toxicity. Somatosensory evoked potentials (SSEPs) were chosen to serve as a measure of neurologic damage. SSEPs in rats given HBO pretreatment before a dive were compared with SSEPs from rats not given HBO pretreatment and SSEPs from non-dived rats. The incidence of abnormal SSEPs in the animals subjected to decompression without pretreatment (1,013 kPa for 32 min followed by decompression) was 78%. In the pretreatment group (HBO at 304 kPa for 20 min followed by exposure to 1,013 kPa for 33 min and decompression) this was significantly reduced to 44%. These results call for further study of the pretreatment protocol in higher animals.
Molecular Imaging of Macrophage Cell Death for the Assessment of Plaque Vulnerability
Authors: Laufer Eduard M. , Winkens Mark H.M. , Narula Jagat , Hofstra Leonard
Published: May 2009

The ability to identify atherosclerotic plaques that are prone to rupture, also called vulnerable plaques, may provide a major step forward in the recognition of patients that have a high risk of developing acute myocardial infarction. Current clinical risk profiling algorithms, such as the Framingham and Procam risk scores, have reasonable predictive value in the assessment of the 10 year risk. These clinical risk profiling scores typically classify patients into low risk (10-year risk, less than 5%), intermediate risk (5% to 20% risk), and high risk (greater than 20%). The challenge to imagers is to identify the risk that is beyond 2% yearly risk. Molecular imaging may help identify plaque inflammation and apoptosis of inflammatory cells, which are obligatory components of the plaque instability. These processes offer specific biological targets that can potentially be exploited to obtain biological information on atherosclerosis development in the individual patient.
Angiopoietin-2 Confers Atheroprotection in apoE
−/−
Mice by Inhibiting LDL Oxidation via Nitric Oxide
Authors: Ahmed Asif , Fujisawa Takeshi , Niu Xi-Lin , Ahmad Shakil , Al-Ani Bahjat , Chudasama Kunal , Abbas Allyah , Potluri Rahul , Bhandari Vineet , Findley Clarence M. , Lam Gregory K.W. , Huang Jianhua , Hewett Peter W. , Cudmore Melissa , Kontos Christopher D.
Published: May 2009

Atherosclerosis is promoted by a combination of hypercholesterolemia and vascular inflammation. The function of Angiopoietin (Ang)-2, a key regulator of angiogenesis, in the maintenance of large vessels is unknown. A single systemic administration of Ang-2 adenovirus (AdAng-2) to apoE
−/−
mice fed a Western diet significantly reduced atherosclerotic lesion size (≈40%) and oxidized LDL and macrophage content of the plaques. These beneficial effects were abolished by the inhibition of nitric oxide synthase (NOS). In endothelial cells, endothelial NOS activation per se inhibited LDL oxidation and Ang-2 stimulated NO release in a Tie2-dependent manner to decrease LDL oxidation. These findings demonstrate a novel atheroprotective role for Ang-2 when endothelial cell function is compromised and suggest that growth factors, which stimulate NO release without inducing inflammation, could offer atheroprotection.
Accessory Subunit KChIP2 Modulates the Cardiac L-Type Calcium Current
Authors: Thomsen Morten B. , Wang Chaojian , Özgen Nazira , Wang Hong-Gang , Rosen Michael R. , Pitt Geoffrey S.
Published: May 2009

Complex modulation of voltage-gated Ca
2+
currents through the interplay among Ca
2+
channels and various Ca
2+
-binding proteins is increasingly being recognized. The K
+
channel interacting protein 2 (KChIP2), originally identified as an auxiliary subunit for K
V
4.2 and a component of the transient outward K
+
channel (
I
to
), is a Ca
2+
-binding protein whose regulatory functions do not appear restricted to K
V
4.2. Consequently, we hypothesized that KChIP2 is a direct regulator of the cardiac L-type Ca
2+
current (
I
Ca,L
). We found that
I
Ca,L
density from KChIP2
−/−
myocytes is reduced by 28% compared to
I
Ca,L
recorded from wild-type myocytes (
P
<0.05). This reduction in current density results from loss of a direct effect on the Ca
2+
channel current, as shown in a transfected cell line devoid of confounding cardiac ion currents.
I
Ca,L
regulation by KChIP2 was independent of Ca
2+
binding to KChIP2. Biochemical analysis suggested a direct interaction between KChIP2 and the Ca
V
1.2 α
1C
subunit N terminus. We found that KChIP2 binds to the N-terminal inhibitory module of α
1C
and augments
I
Ca,L
current density without increasing Ca
V
1.2 protein expression or trafficking to the plasma membrane. We propose a model in which KChIP2 impedes the N-terminal inhibitory module of Ca
V
1.2, resulting in increased
I
Ca,L
. In the context of recent reports that KChIP2 modulates multiple K
V
and Na
V
currents, these results suggest that KChIP2 is a multimodal regulator of cardiac ionic currents.
Hidden Dysfunctioning in Subacute Stroke
Authors: Jaillard Assia , Naegele Bernadette , Trabucco-Miguel Sandra , LeBas Jean François , Hommel Marc
Published: May 2009

Background and Purpose—

Determining cognitive dysfunctioning (CDF) after stroke is an important issue because it influences choices for management in terms of return to previous activities. Because previous research in subacute stroke has shown important variations in CDF rates, we aimed to describe the frequency and neuropsychological profile of CDF in subacute stroke outside dementia. We used a large battery of tests to screen any potentially hidden CDF.

Methods—

Patients with Mini-Mental State Examination scores ≥23 were prospectively and consecutively included 2 weeks after a first-ever ischemic brain infarct. Stroke features were based on MRI. Four domains were evaluated: instrumental and executive functions, episodic memory, and working memory (WM). Patients were scored using means and compared with education- and age-matched control subjects. Then we attributed Z-scores for each test and each domain. The most relevant cognitive tests characterizing CDF were determined using logistic regression.

Results—

Among 177 patients (mean age, 50.6 years), 91.5% failed in at least one cognitive domain. WM was the most impaired domain (87.6%) with executive functions (64.4%), episodic memory (64.4%), and instrumental functions (24.9%) being relatively preserved. CDF was associated with age, education, depression, neurological deficit, and leukoaraiosis in bivariate analysis. Using logistic regression, WM tests and age predicted CDF (Modified Paced Auditorial Serial Addition Test: OR=0.96 CI=0.93 to 0.98; Owen-spatial-WM: OR=1.07 CI=1.02 to 1.12; age: OR=0.96 CI=0.93 to 0.98).

Conclusion—

CDF appears to be almost constant, although underestimated, in subacute stroke. WM could reflect some hidden dysfunctioning, which may interfere with rehabilitation and return to work. Clinical routine may include WM tests in young patients with mild stroke.
Renal Dysfunction as an Independent Predictor of Outcome After Aneurysmal Subarachnoid Hemorrhage
Authors: Zacharia Brad E. , Ducruet Andrew F. , Hickman Zachary L. , Grobelny Bartosz T. , Fernandez Luis , Schmidt J. Michael , Narula Reshma , Ko Lauren N. , Cohen Margot E. , Mayer Stephan A. , Connolly E. Sander
Published: May 2009

Background and Purpose—

Acute kidney injury occurs in 1% to 25% of critically ill patients with small increases in creatinine adversely affecting outcome. We sought to determine the burden of acute kidney injury in patients with aneurysmal subarachnoid hemorrhage and whether this dysfunction affects outcome.

Methods—

Between 1996 and 2008, 787 consecutive patients with aneurysmal subarachnoid hemorrhage were enrolled in our prospective database. Demographics, serum creatinine levels, and discharge modified Rankin scores were recorded, and changes in creatinine clearance were calculated. A multiple logistic regression was performed using known predictors for poor outcome after aneurysmal subarachnoid hemorrhage in addition to burden of contrast-enhanced imaging and change in creatinine clearance.

Results—

One hundred seventy-nine (23.1%) patients were at risk for renal failure during their hospitalization. In a multivariate model, those patients who developed risk for renal failure were twice as likely to have a poor 3-month outcome (OR, 2.01;
P
=0.021). Survival curves comparing those not at risk, those at risk (increasing severity classes Risk, Injury, and Failure, and the 2 outcome classes Loss and End-Stage Kidney Disease [RIFLE] R), and those with renal injury or failure (RIFLE I and F) demonstrated that risk of death increases significantly as one progresses through the RIFLE classes (log rank,
P
<0.0001).

Conclusions—

In a large, consecutive series of prospectively enrolled patients with aneurysmal subarachnoid hemorrhage, we demonstrate, using the newly defined RIFLE classification for risk of renal failure, that even seemingly insignificant decreases in creatinine clearance are associated with significantly worse 3-month outcomes. This study highlights the importance of close surveillance of renal function and stresses the value of renal hygiene in the aneurysmal subarachnoid hemorrhage population.
Sample Size Estimates for Clinical Trials of Vasospasm in Subarachnoid Hemorrhage
Authors: Kreiter Kurt T. , Mayer Stephan A. , Howard George , Knappertz Volker , Ilodigwe Don , Sloan Michael A. , Macdonald R. Loch
Published: May 2009

Background and Purpose—

Clinical trials for prevention of vasospasm after aneurysmal subarachnoid hemorrhage (SAH) seldom have improved overall outcome; one reason may be inadequate sample size. We used data from the tirilizad trials and the Columbia University subarachnoid hemorrhage outcomes project to estimate sample sizes for clinical trials for reduction of vasospasm after SAH, assuming trials must show effect on 90-day patient-centered outcome.

Methods—

Sample size calculations were based on different definitions of vasospasm, enrichment strategies, sensitivity of short- and long-term outcome instruments for reflecting vasospasm-related morbidity, different event rates of vasospasm, calculation of effect size of vasospasm on outcome instruments, and different treatment effect sizes. Sensitivity analysis was performed for variable event rates of vasospasm for a given treatment effect size. Sample size tables were constructed for different rates of vasospasm and outcome instruments for a given treatment effect size.

Results—

Vasospasm occurred in 12% to 30% of patients. Symptomatic deterioration and infarction from vasospasm exhibited the strongest relationship to mortality and morbidity after SAH. Enriching for vasospasm by selection of patients with thick SAH slightly decreased sample sizes. Assuming β=0.80, α=0.05 (2-tailed) and treatment effect size of 50%, total sample size exceeds 5000 patients to demonstrate efficacy on 3-month patient-centered outcome (modified Rankin Scale).

Conclusions—

Clinical trials targeting vasospasm and using traditional patient-centered outcome require very high sample sizes and will therefore be costly, time-consuming, and impractical. This will hinder development of new treatment strategies.
Pregnancy, Childrearing, and Risk of Stroke in Chinese Women
Authors: Zhang Xianglan , Shu Xiao-Ou , Gao Yu-Tang , Yang Gong , Li Honglan , Zheng Wei
Published: May 2009

Background and Purpose—

Although it has been suggested that high gravidity and parity increase the risk for coronary heart disease, their associations with stroke are unclear.

Methods—

We evaluated associations of gravidity and parity with incidence of stroke in the Shanghai Women’s Health Study (SWHS), a population-based cohort study of 74 942 Chinese women aged 40 to 70 years at enrollment (1996 to 2000). We also examined the association between number of children and stroke prevalence in both SWHS participants and their husbands. Stroke cases were ascertained through in-person interviews and linkage with vital statistics registries.

Results—

During a mean follow-up of 7.3 years, 2343 incident cases of stroke were identified. Women with more pregnancies or live births had a significantly increased risk for incident stroke. After adjustment for socioeconomic status and other potential confounders, women with ≥5 pregnancies had a hazard ratio for incident stroke of 1.45 (95% CI, 1.18 to 1.77) compared with those with only one pregnancy. At baseline recruitment, 859 and 1274 prevalent cases of stroke were reported among SWHS participants and their husbands, respectively. Stroke prevalence increased with increasing number of children in both women and men. Adjusted ORs of prevalent stroke for having ≥5 children versus having one child were 1.61 (95% CI, 1.16 to 2.23) in women and 1.45 (1.11 to 1.89) in men.

Conclusions—

High gravidity or parity may be related to increased risk of stroke in women. Chronic stress and adverse lifestyle factors related to childrearing may contribute importantly to the increased risk.
Brain Activity Changes Associated With Treadmill Training After Stroke
Authors: Enzinger Christian , Dawes Helen , Johansen-Berg Heidi , Wade Derick , Bogdanovic Marko , Collett Jonathan , Guy Claire , Kischka Udo , Ropele Stefan , Fazekas Franz , Matthews Paul M.
Published: May 2009

Background and Purpose—

The mechanisms underlying motor recovery after stroke are not fully understood. Several studies used functional MRI longitudinally to relate brain activity changes with performance gains of the upper limb after therapy, but research into training-induced recovery of lower limb function has been relatively neglected thus far.

Methods—

We investigated functional reorganization after 4 weeks of treadmill training with partial body weight support in 18 chronic patients (mean age, 59.9±13.5 years) with mild to moderate paresis (Motricity Index affected leg: 77.7±10.5; range, 9 to 99) and gait impairment (Functional Ambulation Category: 4.4±0.6; range, 3 to 5) due to a single subcortical ischemic stroke using repeated 3.0-T functional MRI and an ankle-dorsiflexion paradigm.

Results—

Walking endurance improved after training (2-minute timed walking distance: 121.5±39.0 versus pre: 105.1±38.1 m;
P
=0.0001). For active movement of the paretic foot versus rest, greater walking endurance correlated with increased brain activity in the bilateral primary sensorimotor cortices, the cingulate motor areas, and the caudate nuclei bilaterally and in the thalamus of the affected hemisphere.

Conclusions—

Despite the strong subcortical contributions to gait control, rehabilitation-associated walking improvements are associated with cortical activation changes. This is similar to findings in upper limb rehabilitation with some differences in the involved cortical areas. We observed bihemispheric activation increases with greater recovery both in cortical and subcortical regions with movement of the paretic foot. However, although the dorsal premotor cortex appears to play an important role in recovery of hand movements, evidence for the involvement of this region in lower extremity recovery was not found.
Lipoprotein-Associated Phospholipase A
2
and C-Reactive Protein for Risk-Stratification of Patients With TIA
Authors: Cucchiara Brett L. , Messe Steve R. , Sansing Lauren , MacKenzie Larami , Taylor Robert A. , Pacelli James , Shah Qaisar , Kasner Scott E.
Published: May 2009

Background and Purpose—

Lipoprotein-associated phospholipase A
2
(Lp-PLA
2
) is a marker of unstable atherosclerotic plaque, and is predictive of both primary and secondary stroke in population-based studies.

Methods—

We conducted a prospective study of patients with acute TIA who presented to the ED. Clinical risk scoring using the ABCD
2
score was determined and Lp-PLA
2
mass (LpPLA
2
-M) and activity (LpPLA
2
-A) and high-sensitivity C-reactive protein (CRP) were measured. The primary outcome measure was a composite end point consisting of stroke or death within 90 days or identification of a high-risk stroke mechanism requiring specific early intervention (defined as ≥50% stenosis in a vessel referable to symptoms or a cardioembolic source warranting anticoagulation).

Results—

The composite outcome end point occurred in 41/167 (25%) patients. LpPLA
2
-M levels were higher in end point-positive compared to -negative patients (mean, 192±48 ng/mL versus 175±44 ng/mL,
P
=0.04). LpPLA
2
-A levels showed similar results (geometric mean, 132 nmol/min/mL, 95% CI 119 to 146 versus 114 nmol/min/mL, 95% CI 108 to 121,
P
=0.01). There was no relationship between CRP and outcome (
P
=0.82). Subgroup analysis showed that both LpPLA
2
-M (
P
=0.04) and LpPLA
2
-A (
P
=0.06) but not CRP (
P
=0.36) were elevated in patients with >50% stenosis. In multivariate analysis using cut-off points defined by the top quartile of each marker, predictors of outcome included LpPLA
2
-A (OR 3.75, 95% CI 1.58 to 8.86,
P
=0.003) and ABCD
2
score (OR 1.30 per point, 95% CI 0.97 to 1.75,
P
=0.08).

Conclusion—

Many patients with TIA have a high-risk mechanism (large vessel stenosis or cardioembolism) or will experience stroke/death within 90 days. In contrast to CRP, both Lp-PLA
2
mass and activity were associated with this composite end point, and LpPLA
2
-A appears to provide additional prognostic information beyond the ABCD
2
clinical risk score alone.
An Individual-Based Evolving Predator-Prey Ecosystem Simulation Using a Fuzzy Cognitive Map as the Behavior Model
Authors: Gras Robin , Devaurs Didier , Wozniak Adrianna , Aspinall Adam
Published: May 2009

We present an individual-based predator-prey model with, for the first time, each agent behavior being modeled by a fuzzy cognitive map (FCM), allowing the evolution of the agent behavior through the epochs of the simulation. The FCM enables the agent to evaluate its environment (e.g., distance to predator or prey, distance to potential breeding partner, distance to food, energy level) and its internal states (e.g., fear, hunger, curiosity), and to choose several possible actions such as evasion, eating, or breeding. The FCM of each individual is unique and is the result of the evolutionary process. The notion of species is also implemented in such a way that species emerge from the evolving population of agents. To our knowledge, our system is the only one that allows the modeling of links between behavior patterns and speciation. The simulation produces a lot of data, including number of individuals, level of energy by individual, choice of action, age of the individuals, and average FCM associated with each species. This study investigates patterns of macroevolutionary processes, such as the emergence of species in a simulated ecosystem, and proposes a general framework for the study of specific ecological problems such as invasive species and species diversity patterns. We present promising results showing coherent behaviors of the whole simulation with the emergence of strong correlation patterns also observed in existing ecosystems.