bluuebunny/crossref_metadata_2025 huggingface dataset:
Expanding network communities from representative examples
Authors: Mehler Andrew , Skiena Steven
Published: April 2009

We present an approach to leverage a small subset of a coherent community within a social network into a much larger, more representative sample. Our problem becomes identifying a small conductance subgraph containing many (but not necessarily all) members of the given seed set. Starting with an initial seed set representing a sample of a community, we seek to discover as much of the full community as possible.

We present a general method for network community expansion, demonstrating that our methods work well in expanding communities in real world networks starting from small given seed groups (20 to 400 members). Our approach is marked by incremental expansion from the seeds with retrospective analysis to determine the ultimate boundaries of our community. We demonstrate how to increase the robustness of the general approach through bootstrapping multiple random partitions of the input set into seed and evaluation groups.

We go beyond statistical comparisons against gold standards to careful subjective evaluations of our expanded communities. This process explains the causes of most disagreement between our expanded communities and our gold-standards—arguing that our expansion methods provide more reliable communities than can be extracted from reference sources/gazetteers such as Wikipedia.
Introducing...acmqueue
Authors: Maurer James
Published: April 2009

You may already know that Queue’s new Web site, acmqueue, was launched at the beginning of March. If not, you owe it to yourself to get acquainted with it, as the new site offers readers a wider choice of delivery options and an expanded range of fresh content. Among the new offerings is Planet Queue, where Queue authors blog about the contemporary relevance of classic engineering work detailed in important articles contained in the ACM Digital Library.
Fighting Physics: A Tough Battle
Authors: Smith Jonathan M.
Published: April 2009

Over the past several years, SaaS (software as a service) has become an attractive option for companies looking to save money and simplify their computing infrastructures. SaaS is an interesting group of techniques for moving computing from the desktop to the cloud; however, as it grows in popularity, engineers should be aware of some of the fundamental limitations they face when developing these kinds of distributed applications - in particular, the finite speed of light.
Network Front-end Processors, Yet Again
Authors: O'Dell Mike
Published: April 2009

The history of the NFE (network front-end) processor, currently best known as a TOE (TCP offload engine), extends all the way back to the Arpanet IMP (interface message processor) and possibly before. The notion is beguilingly simple: partition the work of executing communications protocols from the work of executing the "applications" that require the services of those protocols. That way, the applications and the network machinery can achieve maximum performance and efficiency, possibly taking advantage of special hardware performance assistance. While this looks utterly compelling on the whiteboard, architectural and implementation realities intrude, often with considerable force.
All-Optical Computing and All-Optical Networks are Dead
Authors: Beeler Charles , Partridge Craig
Published: April 2009

We’re a venture capitalist and a communications researcher, and we come bearing bad news: optical computers and all-optical networks aren’t going to happen anytime soon. All those well-intentioned stories about computers operating at the speed of light, computers that would free us from Internet delays and relieve us from the tyranny of slow and hot electronic devices were, alas, overoptimistic. We won’t be computing or routing at the speed of light anytime soon. (In truth, we probably should have told you this about two years ago, but we only recently met, compared notes, and realized our experiences were consistent.)
The GreatSPN tool
Authors: Baarir Soheib , Beccuti Marco , Cerotti Davide , De Pierro Massimiliano , Donatelli Susanna , Franceschinis Giuliana
Published: April 2009

GreatSPN is a tool that supports the design and the qualitative and quantitative analysis of Generalized Stochastic Petri Nets (GSPN) and of Stochastic Well-Formed Nets (SWN). The very first version of GreatSPN saw the light in the late eighties of last century: since then two main releases where developed and widely distributed to the research community: GreatSPN1.7 [13], and GreatSPN2.0 [8]. This paper reviews the main functionalities of GreatSPN2.0 and presents some recently added features that significantly enhance the efficacy of the tool.
Performance and dependability modeling with Möbius
Authors: Gaonkar Shravan , Keefe Ken , Lamprecht Ruth , Rozier Eric , Kemper Peter , Sanders William H.
Published: April 2009

Möbius is a multi-paradigm multi-solution framework to describe and analyze stochastic models of discrete-event dynamic systems. Möbius is widely used in academia and industry for the performance and dependability assessment of technical systems. It comes with a design of experiments as well as automated support for distributing a series of simulation experiments over a network to support the exploration of design spaces for real-world applications. In addition to that, the Möbius simulator interfaces with Traviando, a separate trace analyzer and visualizer that helps to investigate the details of a complex model for validation, verification, and debugging purposes. In this paper, we outline the development of a multi-formalism model of a Lustre-like file system, the analysis of its detailed simulated behavior, and the results obtained from a simulation study.
OPEDo
Authors: Arns Markus , Buchholz Peter , Müller Dennis
Published: April 2009

OPEDo is a software tool for the optimization of discrete event systems according to performance or dependability measures. The tool can be seen as an add on to various tools for performance and dependability analysis. The goal of OPEDo is to provide a wide variety of optimization algorithms for complex black box functions as they are required for the model based optimization of discrete event systems using analytically tractable models or simulation models. The paper introduces the software architecture of the tool, gives a brief sketch of the integrated optimization algorithms and presents several examples.
PIPE2
Authors: Dingle Nicholas J. , Knottenbelt William J. , Suto Tamas
Published: April 2009

This paper presents an overview of Platform-Independent Petri Net Editor 2 (PIPE2 ), an open-source tool that supports the design and analysis of Generalised Stochastic Petri Net (GSPN) models. PIPE2 's extensible design enables developers to add functionality via pluggable analysis modules. It also acts as a front-end for a parallel and distributed performance evaluation environment. With PIPE2, users are able to design and evaluate performance queries expressed in the Performance Tree formalism.
PRISM
Authors: Kwiatkowska Marta , Norman Gethin , Parker David
Published: April 2009

Probabilistic model checking is a formal verification technique for the modelling and analysis of stochastic systems. It has proved to be useful for studying a wide range of quantitative properties of models taken from many diffierent application domains. This includes, for example, performance and reliability properties of computer and communication systems. In this paper, we give an overview of the probabilistic model checking tool PRISM, focusing in particular on its support for continuous-time Markov chains and Markov reward models, and how these can be used to analyse performability properties.
QPME
Authors: Kounev Samuel , Dutz Christofer
Published: April 2009

Queueing Petri nets are a powerful formalism that can be exploited for modeling distributed systems and analyzing their performance and scalability. By combining the modeling power and expressiveness of queueing networks and stochastic Petri nets, queueing Petri nets provide a number of advantages. In this paper, we present QPME (Queueing Petri net Modeling Environment) - a tool that supports the modeling and analysis of systems using queueing Petri nets. QPME provides an Eclipse-based editor for designing queueing Petri net models and a powerful simulation engine for analyzing the models. After presenting the tool, we discuss the ongoing work on the QPME project and the planned future enhancements of the tool.
Advanced features in SMART
Authors: Ciardo Gianfranco , Miner Andrew S. , Wan Min
Published: April 2009

We describe some of the advanced features of the software tool SmArT, the Stochastic Model checking Analyzer for Reliability and Timing. Initially conceived as a software package for numerical solution and discrete-event simulation of stochastic models, SmArT now also provides powerful modelchecking capabilities, thanks to its extensive use of various forms of decision diagrams, which in turn also greatly increase the efficiency of its stochastic analysis algorithms. These aspects make it an excellent choice when tackling systems with extremely large state spaces.
The TANGRAMII integrated modeling environment for computer systems and networks
Authors: de Souza e Silva Edmundo , Figueiredo Daniel R. , Leão Rosa M.M.
Published: April 2009

The TANGRAM-II tool has been developed aiming at supporting the performance analyst throughout the entire modeling process, from model construction and model solution to experimentation. The tool has a powerful user interface that can be tailored to specific problem domain, it includes a rich set of analytic solution techniques, distinct options for obtaining the measures of interest, a hybrid fluid and event driven simulator, visualization features to follow the model's evolution with time, traffic generators and active measurement techniques to assist the user in performing computer networking experimentation. These and additional characteristics make TANGRAM-II a unique tool for research and education.
The Experimental Approach to Development Economics
Authors: Banerjee Abhijit V. , Duflo Esther
Published: April 2009

Randomized experiments have become a popular tool in development economics research and have been the subject of a number of criticisms. This paper reviews the recent literature and discusses the strengths and limitations of this approach in theory and in practice. We argue that the main virtue of randomized experiments is that, owing to the close collaboration between researchers and implementers, they allow the estimation of parameters that would not otherwise be possible to evaluate. We discuss the concerns that have been raised regarding experiments and generally conclude that, although real, they are often not specific to experiments. We conclude by discussing the relationship between theory and experiments.
A Functional Single-Nucleotide Polymorphism in the
TRPC6
Gene Promoter Associated With Idiopathic Pulmonary Arterial Hypertension
Authors: Yu Ying , Keller Steve H. , Remillard Carmelle V. , Safrina Olga , Nicholson Ann , Zhang Shenyuan L. , Jiang Weihua , Vangala Nivruthi , Landsberg Judd W. , Wang Jian-Ying , Thistlethwaite Patricia A. , Channick Richard N. , Robbins Ivan M. , Loyd James E. , Ghofrani Hossein A. , Grimminger Friedrich , Schermuly Ralph T. , Cahalan Michael D. , Rubin Lewis J. , Yuan Jason X.-J.
Published: April 2009

Background—

Excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) plays an important role in the development of idiopathic pulmonary arterial hypertension (IPAH), whereas a rise in cytosolic Ca
2+
concentration triggers PASMC contraction and stimulates PASMC proliferation. Recently, we demonstrated that upregulation of the TRPC6 channel contributes to proliferation of PASMCs isolated from IPAH patients. This study sought to identify single-nucleotide polymorphisms (SNPs) in the
TRPC6
gene promoter that are associated with IPAH and have functional significance in regulating TRPC6 activity in PASMCs.

Methods and Results—

Genomic DNA was isolated from blood samples of 237 normal subjects and 268 IPAH patients. Three biallelic SNPs, −361 (A/T), −254(C/G), and −218 (C/T), were identified in the 2000-bp sequence upstream of the transcriptional start site of TRPC6. Although the allele frequencies of the −361 and −218 SNPs were not different between the groups, the allele frequency of the −254(C→G) SNP in IPAH patients (12%) was significantly higher than in normal subjects (6%;
P
<0.01). Genotype data showed that the percentage of −254G/G homozygotes in IPAH patients was 2.85 times that of normal subjects. Moreover, the −254(C→G) SNP creates a binding sequence for nuclear factor-κB. Functional analyses revealed that the −254(C→G) SNP enhanced nuclear factor-κB-mediated promoter activity and stimulated TRPC6 expression in PASMCs. Inhibition of nuclear factor-κB activity attenuated TRPC6 expression and decreased agonist-activated Ca
2+
influx in PASMCs of IPAH patients harboring the −254G allele.

Conclusions—

These results suggest that the −254(C→G) SNP may predispose individuals to an increased risk of IPAH by linking abnormal TRPC6 transcription to nuclear factor-κB, an inflammatory transcription factor.
One-Year Clinical Outcomes, Midterm Survival, and Predictors of Mortality After Carotid Stenting in Elderly Patients
Authors: Chiam Paul T.L. , Roubin Gary S. , Panagopoulos Georgia , Iyer Sriram S. , Green Richard M. , Brennan Christina , Vitek Jiri J.
Published: April 2009

Background—

It has been demonstrated recently that carotid stenting can be performed safely in patients ≥80 years of age. However, it is uncertain whether these patients will derive benefit because longevity after revascularization is an important consideration. This study was conducted to determine survival and predictors of mortality of selected elderly patients after stenting.

Methods and Results—

One hundred forty-two consecutive elderly patients who were non–high risk for stenting underwent 153 procedures. Patients had either symptomatic stenosis ≥50% or asymptomatic stenosis ≥70%. Demographics and in-hospital outcomes were entered into a database; subsequent outcomes and mortality data were obtained retrospectively. Mean±SD age was 83.3±3.1 years. Symptomatic patients accounted for 28%. Overall survival at 3 years was 76% (85% at 2 years). At 1 year, 1 fatal stroke had occurred, with 97% of survivors (n=114) free of neurological events (neurological status was undetermined in the remaining 3%). Predictors of mortality were remote (≥6 months) transient ischemic attack or cerebrovascular accident, smoking history, and creatinine clearance (hemoglobin level showed a strong trend toward achieving significance); for the asymptomatic subgroup, predictors of mortality were smoking history, previous carotid endarterectomy, hemoglobin level, and increasing age. In particular, symptom status and sex were not independent predictors of mortality.

Conclusions—

This study demonstrates that in selected elderly patients, a high proportion (85%) survived 2 years and >75% survived 3 years after stenting. Carotid stenting may be considered a revascularization option in such patients. Better selection of patients using the predictors of mortality may help to reduce unwarranted procedures and to optimize survival likelihood.
Conventional Dendritic Cells at the Crossroads Between Immunity and Cholesterol Homeostasis in Atherosclerosis
Authors: Gautier Emmanuel L. , Huby Thierry , Saint-Charles Flora , Ouzilleau Betty , Pirault John , Deswaerte Virginie , Ginhoux Florent , Miller Elizabeth R. , Witztum Joseph L. , Chapman M. John , Lesnik Philippe
Published: April 2009

Background—

Immunoinflammatory mechanisms are implicated in the atherogenic process. The polarization of the immune response and the nature of the immune cells involved, however, are major determinants of the net effect, which may be either proatherogenic or antiatherogenic. Dendritic cells (DCs) are central to the regulation of immunity, the polarization of the immune response, and the induction of tolerance to antigens. The potential role of DCs in atherosclerosis, however, remains to be defined.

Methods and Results—

We created a mouse model in which the lifespan and immunogenicity of conventional DCs are enhanced by specific overexpression of the antiapoptotic gene
hBcl-2
under the control of the CD11c promoter. When studied in either low-density lipoprotein receptor–deficient or apolipoprotein E–deficient backgrounds,
DC-hBcl2
mice exhibited an expanded DC population associated with enhanced T-cell activation, a T-helper 1 and T-helper 17 cytokine expression profile, and elevated production of T-helper 1–driven IgG2c autoantibodies directed against oxidation-specific epitopes. This proatherogenic signature, however, was not associated with acceleration of atherosclerotic plaque progression, because expansion of the DC population was unexpectedly associated with an atheroprotective decrease in plasma cholesterol levels. Conversely, depletion of DCs in hyperlipidemic CD11c–diphtheria toxin receptor/apolipoprotein E–deficient transgenic mice resulted in enhanced cholesterolemia, thereby arguing for a close relationship between the DC population and plasma cholesterol levels.

Conclusions—

Considered together, the present data reveal that conventional DCs are central to the atherosclerotic process, because they are directly implicated in both cholesterol homeostasis and the immune response.
MicroRNA-320 Is Involved in the Regulation of Cardiac Ischemia/Reperfusion Injury by Targeting Heat-Shock Protein 20
Authors: Ren Xiao-Ping , Wu Jinghai , Wang Xiaohong , Sartor Maureen A. , Qian Jiang , Jones Keith , Nicolaou Persoulla , Pritchard Tracy J. , Fan Guo-Chang
Published: April 2009

Background—

Recent studies have identified critical roles for microRNAs (miRNAs) in a variety of cellular processes, including regulation of cardiomyocyte death. However, the signature of miRNA expression and possible roles of miRNA in the ischemic heart have been less well studied.

Methods and Results—

We performed miRNA arrays to detect the expression pattern of miRNAs in murine hearts subjected to ischemia/reperfusion (I/R) in vivo and ex vivo. Surprisingly, we found that only miR-320 expression was significantly decreased in the hearts on I/R in vivo and ex vivo. This was further confirmed by TaqMan real-time polymerase chain reaction. Gain-of-function and loss-of-function approaches were employed in cultured adult rat cardiomyocytes to investigate the functional roles of miR-320. Overexpression of miR-320 enhanced cardiomyocyte death and apoptosis, whereas knockdown was cytoprotective, on simulated I/R. Furthermore, transgenic mice with cardiac-specific overexpression of miR-320 revealed an increased extent of apoptosis and infarction size in the hearts on I/R in vivo and ex vivo relative to the wild-type controls. Conversely, in vivo treatment with antagomir-320 reduced infarction size relative to the administration of mutant antagomir-320 and saline controls. Using TargetScan software and proteomic analysis, we identified heat-shock protein 20 (Hsp20), a known cardioprotective protein, as an important candidate target for miR-320. This was validated experimentally by utilizing a luciferase/GFP reporter activity assay and examining the expression of Hsp20 on miR-320 overexpression and knockdown in cardiomyocytes.

Conclusions—

Our data demonstrate that miR-320 is involved in the regulation of I/R-induced cardiac injury and dysfunction via antithetical regulation of Hsp20. Thus, miR-320 may constitute a new therapeutic target for ischemic heart diseases.
Genetic Deficit of SK3 and IK1 Channels Disrupts the Endothelium-Derived Hyperpolarizing Factor Vasodilator Pathway and Causes Hypertension
Authors: Brähler Sebastian , Kaistha Anuradha , Schmidt Volker J. , Wölfle Stephanie E. , Busch Christoph , Kaistha Brajesh P. , Kacik Michael , Hasenau Anna-Lena , Grgic Ivica , Si Han , Bond Chris T. , Adelman John P. , Wulff Heike , de Wit Cor , Hoyer Joachim , Köhler Ralf
Published: April 2009

Background—

It has been proposed that activation of endothelial SK3 (K
Ca
2.3) and IK1 (K
Ca
3.1) K
+
channels plays a role in the arteriolar dilation attributed to an endothelium-derived hyperpolarizing factor (EDHF). However, our understanding of the precise function of SK3 and IK1 in the EDHF dilator response and in blood pressure control remains incomplete. To clarify the roles of SK3 and IK1 channels in the EDHF dilator response and their contribution to blood pressure control in vivo, we generated mice deficient for both channels.

Methods and Results—

Expression and function of endothelial SK3 and IK1 in IK1
−/−
/SK3
T/T
mice was characterized by patch-clamp, membrane potential measurements, pressure myography, and intravital microscopy. Blood pressure was measured in conscious mice by telemetry. Combined IK1/SK3 deficiency in IK1
−/−
/SK3
T/T
(+doxycycline) mice abolished endothelial K
Ca
currents and impaired acetylcholine-induced smooth muscle hyperpolarization and EDHF-mediated dilation in conduit arteries and in resistance arterioles in vivo. IK1 deficiency had a severe impact on acetylcholine-induced EDHF-mediated vasodilation, whereas SK3 deficiency impaired NO-mediated dilation to acetylcholine and to shear stress stimulation. As a consequence, SK3/IK1-deficient mice exhibited an elevated arterial blood pressure, which was most prominent during physical activity. Overexpression of SK3 in IK1
−/−
/SK3
T/T
mice partially restored EDHF- and nitric oxide-mediated vasodilation and lowered elevated blood pressure. The IK1-opener SKA-31 enhanced EDHF-mediated vasodilation and lowered blood pressure in SK3-deficient IK1
+/+
/SK3
T/T
(+doxycycline) mice to normotensive levels.

Conclusions—

Our study demonstrates that endothelial SK3 and IK1 channels have distinct stimulus-dependent functions, are major players in the EDHF pathway, and significantly contribute to arterial blood pressure regulation. Endothelial K
Ca
channels may represent novel therapeutic targets for the treatment of hypertension.
D1-Like Receptors Regulate NADPH Oxidase Activity and Subunit Expression in Lipid Raft Microdomains of Renal Proximal Tubule Cells
Authors: Li Hewang , Han Weixing , Villar Van Anthony M. , Keever Lindsay B. , Lu Quansheng , Hopfer Ulrich , Quinn Mark T. , Felder Robin A. , Jose Pedro A. , Yu Peiying
Published: April 2009

NADPH oxidase (Nox)–dependent reactive oxygen species production is implicated in the pathogenesis of cardiovascular diseases, including hypertension. We tested the hypothesis that oxidase subunits are differentially regulated in renal proximal tubules from normotensive and spontaneously hypertensive rats. Basal Nox2 and Nox4, but not Rac1, in immortalized renal proximal tubule cells and brush border membranes were greater in hypertensive than in normotensive rats. However, more Rac1 was expressed in lipid rafts in cells from hypertensive rats than in cells from normotensive rats; the converse was observed with Nox4, whereas Nox2 expression was similar. The D1-like receptor agonist fenoldopam decreased Nox2 and Rac1 protein in lipid rafts to a greater extent in hypertensive than in normotensive rats. Basal oxidase activity was 3-fold higher in hypertensive than in normotensive rats but was inhibited to a greater extent by fenoldopam in normotensive (58±3.3%) than in hypertensive rats (31±5.2%;P<0.05; n=6 per group). Fenoldopam decreased the amount of Nox2 that coimmunoprecipitated with p67phoxin cells from normotensive rats. D1-like receptors may decrease oxidase activity by disrupting the distribution and assembly of oxidase subunits in cell membrane microdomains. The cholesterol-depleting reagent methyl–β-cyclodextrin decreased oxidase activity and cholesterol content to a greater extent in hypertensive than in normotensive rats. The greater basal levels of Nox2 and Nox4 in cell membranes and Nox2 and Rac1 in lipid rafts in hypertensive rats than in normotensive rats may explain the increased basal oxidase activity in hypertensive rats.
Prenatal Cocaine Exposure Differentially Causes Vascular Dysfunction in Adult Offspring
Authors: Xiao DaLiao , Huang Xiaohui , Xu Zhice , Yang Shumei , Zhang Lubo
Published: April 2009

Epidemiological studies have shown a clear association of adverse intrauterine environment and an increased risk of cardiovascular diseases and hypertension in adult life. The present study tested the hypothesis that prenatal cocaine exposure causes reprogramming of vascular reactivity, leading to an increased risk of hypertension in adult offspring. Pregnant rats received cocaine (30 mg kg−1day−1) or saline from days 15 to 21 of gestational age, and experiments were conducted in 3-month-old offspring. Cocaine had no effect on the baseline blood pressure but significantly increased norepinephrine-stimulated blood pressure and decreased the baroreflex sensitivity in male but not female offspring. The cocaine treatment significantly increased norepinephrine-induced contractions in pressurized resistance–sized mesenteric arteries but not in aortas, which was primarily because of a loss of endothelial NO synthase–mediated inhibition and an enhanced Ca2+sensitivity in mesenteric arteries. In addition, the cocaine treatment significantly attenuated the endothelium-dependent relaxation in mesenteric arteries in male but not female offspring. Endothelial NO synthase protein levels in aortas but not mesenteric arteries were significantly increased in the cocaine-treated animals. However, cocaine significantly decreased phosphorylation levels of endothelial NO synthase in both aortas and mesenteric arteries. The results suggest that prenatal cocaine exposure programs vascular contractility via changes in endothelial NO synthase–regulated Ca2+sensitivity of myofilaments in the sex- and tissue-dependent manners in resistance arteries leading to an increased risk of hypertension in male offspring.
Does Wave Reflection Dominate Age-Related Change in Aortic Blood Pressure Across the Human Life Span?
Authors: Namasivayam Mayooran , McDonnell Barry J. , McEniery Carmel M. , O'Rourke Michael F.
Published: April 2009

Aortic systolic and pulse pressure rise with age because of aortic stiffening. Two factors are responsible: a larger incident wave because of increased aortic characteristic impedance and premature return of wave reflection from peripheral sites. This study aimed to determine the relative contribution of each factor before and after age 60 years. Aortic pressure waveforms were generated for 3682 healthy subjects using a generalized transfer function applied to radial pressure waveforms recorded by applanation tonometry. Linear regression and product of coefficient mediation analysis were performed in the cross-sectional cohort to determine the yearly contribution of the incident and reflected waves (waves measured as first systolic peak and augmented pressure, respectively) to aortic systolic and pulse pressure elevation with age. This was done separately for subjects ≤60 and >60 years of age, with both sexes initially pooled and subsequently separated. Analyses were repeated with correction for height, weight, heart rate, and mean arterial pressure. Before age 60 years, the reflected wave was a greater (
P
<0.05) contributor to age-related aortic systolic and pulse pressure elevations, with no significant contribution of the incident wave in this age group in sex-pooled analysis. After age 60 years, both incident and reflected waves were significant (
P
<0.05) and comparable contributors (
P
difference >0.05) to age-related aortic systolic and pulse pressure elevations. This general pattern was observed in both sexes and persisted after correction for confounders. Wave reflection is important across the life span, whereas aortic characteristic impedance contributes significantly only beyond age 60 years.
Retrograde Flow and Shear Rate Acutely Impair Endothelial Function in Humans
Authors: Thijssen Dick H.J. , Dawson Ellen A. , Tinken Toni M. , Cable N. Timothy , Green Daniel J.
Published: April 2009

Changes in arterial shear stress induce functional and structural vasculature adaptations. Recent studies indicate that substantial retrograde flow and shear can occur through human conduit arteries. In animals, retrograde shear is associated with atherogenic effects. The aim of this study was to examine the impact of incremental levels of retrograde shear on endothelial function in vivo. On 3 separate days, we examined bilateral brachial artery flow-mediated dilation, an index of NO-mediated endothelial function, in healthy men (24±3 years) before and after a 30-minute intervention consisting of cuff inflation to 25, 50, or 75 mm Hg. Cuff inflations resulted in “dose”-dependent increases in retrograde shear rate, compared with the noncuffed arm, within subjects (
P
<0.001). Flow-mediated dilation in the cuffed arm did not change in response to the 25-mm Hg stimulus but decreased significantly after both the 50- and 75-mm Hg interventions (
P
<0.05). The decrease in flow-mediated dilation after the 75-mm Hg intervention was significantly larger than that observed after a 50-mm Hg intervention (
P
=0.03). In the noncuffed arm, no changes in shear rate or flow-mediated dilation were observed. These results demonstrate that an increase in retrograde shear rate induces a dose-dependent attenuation of endothelial function in humans. This finding contributes to our understanding regarding the possible detrimental effects of retrograde shear rate in vivo.
Atorvastatin Prevents Endothelial Dysfunction in Mesenteric Arteries From Spontaneously Hypertensive Rats
Authors: Virdis Agostino , Colucci Rocchina , Versari Daniele , Ghisu Narcisa , Fornai Matteo , Antonioli Luca , Duranti Emiliano , Daghini Elena , Giannarelli Chiara , Blandizzi Corrado , Taddei Stefano , Del Tacca Mario
Published: April 2009

We investigated the effect of atorvastatin on cyclooxygenase (COX) contribution to endothelial dysfunction in spontaneously hypertensive rat (SHR) mesenteric resistance arteries. Atorvastatin (10 mg/kg per day, oral gavage) or its vehicle was administered for 2 weeks to male SHR or Wistar-Kyoto rats. Endothelial function of mesenteric arteries was assessed by pressurized myograph. In Wistar-Kyoto rats, relaxation to acetylcholine was inhibited byNG-nitro-l-arginine methyl ester and unaffected by SC-560 (COX-1 inhibitor), DuP-697 (COX-2 inhibitor), or ascorbic acid. In SHRs, the response to acetylcholine was attenuated, less sensitive toNG-nitro-l-arginine methyl ester, unaffected by SC-560, and enhanced by DuP-697 or SQ-29548 (thromboxane-prostanoid receptor antagonist) to a similar extent. Endothelium-dependent relaxation was normalized by ascorbic acid or apocynin (NADPH oxidase inhibitor), which also restored the inhibition byNG-nitro-l-arginine methyl ester. In atorvastatin-treated SHRs, relaxation to acetylcholine was normalized, fully sensitive toNG-nitro-l-arginine methyl ester, and not affected by SC-560, DuP-697, SQ 29548, or antioxidants. Dihydroethidium assay showed an increased intravascular superoxide generation in SHRs, which was abrogated by atorvastatin. RT-PCR revealed a COX-2 induction in SHR arteries, which was downregulated by atorvastatin. The release of prostacyclin and 8-isoprostane was higher from SHR than Wistar-Kyoto mesenteric vessels. COX-2 inhibition and apocynin decreased 8-isoprostane without affecting prostacyclin levels. Atorvastatin increased phosphorylated extracellular signal-regulated kinase 1/2, pAkt, peNOS1177, and inducible NO synthase levels in SHR mesenteric vessels and decreased 8-isoprostane release. In conclusion, COX-2-derived 8-isoprostane contributes to endothelial dysfunction in SHR mesenteric arteries. Atorvastatin restores NO availability by increasing phosphorylated extracellular signal-regulated kinase 1/2, pAkt, peNOS1177, and inducible NO synthase levels and by abrogating vascular NADPH oxidase-driven superoxide production, which also results in a downregulation of COX-2-dependent 8-isoprostane generation.
Application of Virtual Environments to Assessment of Human Motor Learning During Reaching Movements
Authors: Nikooyan Ali Asadi , Zadpoor Amir Abbas
Published: April 2009

This paper studies learning of reaching movements in a dynamically variable virtual environment specially designed for this purpose. Learning of reaching movements in the physical world has been extensively studied by several researchers. In most of those studies, the subjects are asked to exercise reaching movements while being exposed to real force fields exerted through a robotic manipulandum. Those studies have contributed to our understanding of the mechanisms used by the human cognitive system to learn reaching movements in the physical world. The question that remains to be answered is how the learning mechanism in the physical world relates to its counterpart in the virtual world where the real force fields are replaced by virtual force fields. A limited number of studies have already addressed this question and have shown that there are, actually, quite a number of relationships between the learning mechanisms in these two different environments. In this study, we are focused on gaining a more in-depth understanding of these relationships. In our experiments, the subjects are asked to guide a virtual object to a desired target on a computer screen using a mouse. The movement of the virtual object is affected by a viscous virtual force field that is sensed by the examinees through their visual system. Three groups of examinees are used for the experiments. All the examinees are first trained in the null-field condition. Then, the viscous force field is introduced either suddenly (for the two first groups) or gradually (for the last group). While the first and third groups of the examinees used their dominant arm to guide the virtual object in the second step, the second group used their nondominant arm. Generalization of the learning from the dominant to the nondominant arm and vice versa was studied in the third phase of the experiments. Finally, the force field was removed and the examinees were asked to repeat the reaching task to study the so-called aftereffects phenomenon. The results of the experiments are compared with the studies performed in the physical world. It is shown that the trends of learning and generalization are similar to what is observed in the physical world for a sudden application of the virtual force field. However, the generalization behavior of the examinees is somewhat different from the physical world if the force field is gradually applied.
Comparative Evaluation of Display Technologies for Collaborative Design Review
Authors: Hou Ming , Hollands Justin G , Scipione Andrea , Magee Lochlan , Greenley Mike
Published: April 2009

The effectiveness of five display technologies for supporting a collaborative workspace design review was compared. Participants searched for design flaws in a model of the front dashboard of a vehicle including an in-vehicle navigation system. The display types were 2D CRT, 3D CRT, 3D via Curved plasma display, a large DataWall display, and a cave automatic virtual environment (CAVE). Detection accuracy, time, and usability measures were obtained. The results indicated that detection accuracy was higher for 3D CRT and Curved displays than the 2D display or more immersive DataWall and CAVE displays. Additionally, a speed-accuracy trade-off was observed such that detection time was longer for 3D CRT and Curved displays than for 2D, or the more immersive displays. Subjective measures revealed that participants' comfort and confidence level was lower with the 2D displays than the 3D displays. Lack of sufficient training time is likely to have affected detection accuracy with the more immersive 3D displays. Overall, the use of the 3D CAD model on a standard CRT or a Curved display was the most cost-effective for collaborative design review.
A Neuroscience Approach to Virtual Reality Experience Using Transcranial Doppler Monitoring
Authors: Alcañiz Mariano , Rey Beatriz , Tembl Jose , Parkhutik Vera
Published: April 2009

Virtual reality enables people to behave and feel as if they were present in a virtual environment and therefore is a useful tool in many fields. In order to study the usefulness of virtual environments, the concept of presence is examined. Up to now, the most common method to measure presence has been to use subjective measures based on validated questionnaires about user experience. However, more objective measurements, such as physiological measurements, are now being considered. In this study, transcranial Doppler (TCD) sonography is presented as a brain activity measurement technique that can be used to study presence in virtual environments. Thirty-two subjects navigated in a virtual environment in different immersive conditions while TCD was monitored. The results show that there are changes in blood flow velocity in the subjects during moments associated with different levels of presence.
Biophysical Evaluation of Land-Cover Products for Land–Climate Modeling
Authors: Ge Jianjun , Torbick Nathan , Qi Jiaguo
Published: April 2009

The need for accurate characterization of the land surface as boundary conditions in climate models has been recognized widely in the climate modeling community. A large number of land-cover datasets are currently used in climate models either to better represent surface conditions or to study the impacts of surface changes. Deciding upon land-cover datasets can be challenging because the datasets are made with different sensors, ranging methodologies, and varying classification objectives. A new statistical measure Q was developed to evaluate land-cover datasets in land–climate interaction research. This measure calculates biophysical precision of land-cover datasets using 1-km monthly Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) product. This method aggregates within-class biophysical consistency, calculated as LAI variation, across a study domain and over multiple years into a single statistic. A smaller mean Q value for a land-cover product indicates more precise biophysical characterization within the classes. As an illustration, four land-cover products were assessed in the East Africa region: Global Land Cover 2000 (GLC2000), MODIS land cover, Olson Global Ecosystems (OGE), and Land Ecosystem–Atmosphere Feedback (LEAF) model. The evaluation was conducted at three different spatial scales corresponding to 30 × 30, 50 × 50, and 100 × 100 km quadrates. The Q measure found that GLC2000 ranked higher compared to the other three land-cover products for every quadrate size. For the 30 × 30 km quadrate size GLC2000 was significantly better than LEAF, which is currently used in the Regional Atmospheric Modeling System. The statistic ranks MODIS land cover above OGE, which is above LEAF. As quadrate size increases, differences between Q decrease indicating greater uncertainty at coarser resolution. The utility of the measure is that it can be applied to any continuous parameter over any scale (space or time) to evaluate the biophysical precision of any land-cover dataset.
The Soil Moisture–Precipitation Feedback in Simulations with Explicit and Parameterized Convection
Authors: Hohenegger Cathy , Brockhaus Peter , Bretherton Christopher S. , Schär Christoph
Published: April 2009

Moist convection is a key aspect of the extratropical summer climate and strongly affects the delicate balance of processes that determines the surface climate in response to larger-scale forcings. Previous studies using parameterized convection have found that the feedback between soil moisture and precipitation is predominantly positive (more precipitation over wet soils) over Europe. Here this feedback is investigated for one full month (July 2006) over the Alpine region using two different model configurations. The first one employs regional climate simulations performed with the Consortium for Small-Scale Modeling Model in Climate Mode (CCLM) on a grid spacing of 25 km. The second one uses the same model but integrated on a cloud-resolving grid of 2.2 km, allowing an explicit treatment of convection. Each configuration comprises one control and two sensitivity experiments. The latter start from perturbed soil moisture initial conditions.

Comparison of the simulated soil moisture–precipitation feedback reveals significant differences between the two systems. The 25-km simulations sustain a strong positive feedback, while those at 2.2-km resolution are associated with a predominantly negative feedback. Thus the two systems yield not only different strengths of this key feedback but also different signs. This has important implications, with the cloud-resolving model exhibiting a shorter soil moisture memory and a smaller soil moisture–temperature feedback.

Analysis shows that the different feedback signs relate to the sensitivity of the simulated convective development to the presence of a stable layer sitting on top of the planetary boundary layer. In the 2.2-km integrations, dry initial soil moisture conditions yield more vigorous thermals (owing to stronger daytime heating), which can more easily break through the stable air barrier, thereby leading to deep convection and ultimately to a negative soil moisture–precipitation feedback loop. In the 25-km integrations, deep convection is much less sensitive to the stable layer because of the design of the employed convective parameterization. The authors also show that there are considerable differences in the simulated soil moisture–precipitation feedback between low-resolution modeling frameworks using different cloud convection schemes.
Interannual Variability of the Upper Ocean in the Southeast Pacific Stratus Cloud Region
Authors: Shinoda Toshiaki , Lin Jialin
Published: April 2009

Persistent stratus/stratocumulus cloud decks in the southeast Pacific near the coasts of Peru and northern Chile play an important role in regional and global climate variability. Interannual variability of the upper ocean under stratus cloud decks in the southeast Pacific is investigated using ocean general circulation model (OGCM) experiments. The model was first forced with daily surface fluxes based on the NCEP–NCAR reanalysis and satellite-derived surface shortwave and longwave radiation for the period of 1979–2004. Gridded surface heat flux estimates used in the model integration agree well with those based on Woods Hole Oceanographic Institution (WHOI) Improved Meteorology (IMET) buoy measurements at 20°S, 85°W. Also, the OGCM is able to reproduce well the observed interannual SST and sea surface height variations in this region. The results suggest that the interannual variation of the upper ocean north of 20°S is mostly associated with ENSO variability. Additional model experiments were conducted to examine the relative importance of ocean dynamics and surface heat fluxes in determining the interannual variation in SST. The results of these experiments indicate that upper-ocean dynamics play a dominant role in controlling the interannual variation of SST north of 20°S in the stratus cloud region. The upper-ocean heat budget analysis shows that meridional heat advection associated with ENSO events primarily controls the interannual SST variation in the stratus cloud region north of 20°S.
Estimating Oceanic Heat Content Change Using Isotherms
Authors: Palmer Matthew D. , Haines Keith
Published: April 2009

This paper presents a new analysis of ocean heat content changes over the last 50 yr using isotherms by calculating the mean temperature above the 14°C isotherm and the depth of the 14°C isotherm as separate variables. A new quantity called the “relative heat content” (“RHC”) is introduced, which represents the minimum local heat content change over time, relative to a fixed isotherm. It is shown how mean temperature and isotherm depth changes make separable and additive contributions to changes in RHC.

Maps of RHC change between 1970 and 2000 show similar spatial patterns to a traditional fixed-depth ocean heat content change to 220 m. However, the separate contributions to RHC suggest a more spatially uniform contribution from warming above the isotherm, while isotherm depth changes show wind-driven signals, of which some are identifiable as being related to the North Atlantic Oscillation. The time series show that the warming contribution to RHC dominates the global trend, while the depth contribution only dominates on the basin scale in the North Atlantic. The RHC shows minima associated with the major volcanic eruptions (particularly in the Indian Ocean), and these are entirely contributed by mean temperature changes rather than isotherm depth changes. The depth change contributions to RHC are strongly affected by the recently reported XBT fall-rate bias, whereas the mean temperature contributions are not. Therefore, only the isotherm depth change contributions to RHC will need to be reassessed as fall-rate-corrected data become available.
Structure and Evolution of Precipitation along a Cold Front in the Northeastern United States
Authors: Zhang Yan , Smith James A. , Ntelekos Alexandros A. , Baeck Mary Lynn , Krajewski Witold F. , Moshary Fred
Published: April 2009

Heavy precipitation in the northeastern United States is examined through observational and numerical modeling analyses for a weather system that produced extreme rainfall rates and urban flash flooding over the New York–New Jersey region on 4–5 October 2006. Hydrometeorological analyses combine observations from Weather Surveillance Radar-1988 Doppler (WSR-88D) weather radars, the National Lightning Detection Network, surface observing stations in the northeastern United States, a vertically pointing lidar system, and a Joss–Waldvogel disdrometer with simulations from the Weather Research and Forecasting Model (WRF). Rainfall analyses from the Hydro-Next Generation Weather Radar (NEXRAD) system, based on observations from WSR-88D radars in State College, Pennsylvania, and Fort Dix, New Jersey, and WRF model simulations show that heavy rainfall was organized into long-lived lines of convective precipitation, with associated regions of stratiform precipitation, that develop along a frontal zone.

Structure and evolution of convective storm elements that produced extreme rainfall rates over the New York–New Jersey urban corridor were influenced by the complex terrain of the central Appalachians, the diurnal cycle of convection, and the history of convective evolution in the frontal zone. Extreme rainfall rates and flash flooding were produced by a “leading line–trailing stratiform” system that was rapidly dissipating as it passed over the New York–New Jersey region. Radar, disdrometer, and lidar observations are used in combination with model analyses to examine the dynamical and cloud microphysical processes that control the spatial and temporal structure of heavy rainfall. The study illustrates key elements of the spatial and temporal distribution of rainfall that can be used to characterize flash flood hazards in the urban corridor of the northeastern United States.
Enhanced Diapycnal Mixing in the South China Sea
Authors: Tian Jiwei , Yang Qingxuan , Zhao Wei
Published: April 2009

Profiles of current velocity, temperature, and salinity were obtained in the Internal Wave and Mixing Experiment in the South China Sea (SCS), the Luzon Strait, and the North Pacific. The observations are examined for evidence of enhanced diapycnal mixing in the SCS, which reaches O(10−3 m2 s−1) in magnitude. Results from independent casts reveal that diapycnal diffusivity in the SCS and the Luzon Strait is elevated by two orders of magnitude over that of the smooth bathymetry in the North Pacific, which are typical of background values in an open ocean. The vertical distribution of diapycnal diffusivity is nonuniform in the SCS, exhibiting higher values at depths greater than about 1000 m. This result compares favorably with the direct microstructure measurements at four stations in the SCS. Velocity and density profiles are combined to estimate the internal tide energy flux generated in the Luzon Strait and directed into the SCS. The energy amounts to 10 GW, most of which is rationalized to be the potential energy source for enhanced mixing in the SCS.