bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Atomic Force Microscopy on Studying Micro- and Nano-Structures of Starch
Authors: Liu Peng , Chen Ling , Corrigan Penny A , Yu Long , Liu Zhongdong
Published: February 2009

This paper reviews the application of atomic force microscopy (AFM) to the study of starch structures, including both macrostructure of starch granules and the nanostructure of molecular chains. It introduces the different techniques of sample preparation and discusses what AFM could observe. The paper summarises the present situation of the application of AFM in the study of starch structures and guides the direction for further research.
Protective Effect of Perindopril on Diabetic Retinopathy Is Associated With Decreased Vascular Endothelial Growth Factor–to–Pigment Epithelium–Derived Factor Ratio
Authors: Zheng Zhi , Chen Haibing , Ke Genjie , Fan Ying , Zou Haidong , Sun Xiaodong , Gu Qing , Xu Xun , Ho Patrick C.P.
Published: February 2009

OBJECTIVE

This study aimed to verify whether the decreased vascular endothelial growth factor (VEGF)–to–pigment epithelium–derived factor (PEDF) ratio can serve as an indicator for the protective effect of angiotensin-converting enzyme inhibitors (ACEIs) on diabetic retinopathy (DR) and to investigate the role of mitochondrial reactive oxygen species (ROS) in the downregulated VEGF-to-PEDF ratio.

RESEARCH DESIGN AND METHODS

Diabetic rats and control animals were randomly assigned to receive perindopril or vehicle for 24 weeks, and bovine retinal capillary endothelial cells (BRECs) were incubated with normal or high glucose with or without perindopril. VEGF, PEDF, PPARγ, and uncoupling protein-2 (UCP-2) in the rat retinas or BREC extracts were examined by Western blotting and real-time RT-PCR. The levels of VEGF and PEDF in cell culture media were examined by ELISA. Mitochondrial membrane potential (Δψm) and ROS production were assayed using JC-1 or CM-H2DCFDA.

RESULTS

The VEGF-to-PEDF ratio was increased in the retina of diabetic rats; perindopril lowered the increased VEGF-to-PEDF ratio in diabetic rats and ameliorated the retinal damage. In BRECs, perindopril lowered the hyperglycemia-induced elevation of VEGF-to-PEDF ratio by reducing mitochondrial ROS. We found the decreased ROS production was a result of perindopril-induced upregulation of PPARγ and UCP-2 expression and the subsequent decrease of Δψm.

CONCLUSIONS

It is concluded that the protective effect of ACEI on DR is associated with a decreased VEGF-to-PEDF ratio, which involves the mitochondria-ROS pathway through PPARγ-mediated changes of UCP-2. This study paves a way for future application of ACEI in treatment of DR.
Functional Targets of the Monogenic Diabetes Transcription Factors HNF-1α and HNF-4α Are Highly Conserved Between Mice and Humans
Authors: Boj Sylvia F. , Servitja Joan Marc , Martin David , Rios Martin , Talianidis Iannis , Guigo Roderic , Ferrer Jorge
Published: February 2009

OBJECTIVE

The evolutionary conservation of transcriptional mechanisms has been widely exploited to understand human biology and disease. Recent findings, however, unexpectedly showed that the transcriptional regulators hepatocyte nuclear factor (HNF)-1α and -4α rarely bind to the same genes in mice and humans, leading to the proposal that tissue-specific transcriptional regulation has undergone extensive divergence in the two species. Such observations have major implications for the use of mouse models to understand HNF-1α– and HNF-4α–deficient diabetes. However, the significance of studies that assess binding without considering regulatory function is poorly understood.

RESEARCH DESIGN AND METHODS

We compared previously reported mouse and human HNF-1α and HNF-4α binding studies with independent binding experiments. We also integrated binding studies with mouse and human loss-of-function gene expression datasets.

RESULTS

First, we confirmed the existence of species-specific HNF-1α and -4α binding, yet observed incomplete detection of binding in the different datasets, causing an underestimation of binding conservation. Second, only a minor fraction of HNF-1α– and HNF-4α–bound genes were downregulated in the absence of these regulators. This subset of functional targets did not show evidence for evolutionary divergence of binding or binding sequence motifs. Finally, we observed differences between conserved and species-specific binding properties. For example, conserved binding was more frequently located near transcriptional start sites and was more likely to involve multiple binding events in the same gene.

CONCLUSIONS

Despite evolutionary changes in binding, essential direct transcriptional functions of HNF-1α and -4α are largely conserved between mice and humans.
High Glucose Suppresses Epidermal Growth Factor Receptor/Phosphatidylinositol 3-Kinase/Akt Signaling Pathway and Attenuates Corneal Epithelial Wound Healing
Authors: Xu Ke-Ping , Li Yanfeng , Ljubimov Alexander V. , Yu Fu-Shin X.
Published: February 2009

OBJECTIVE

Patients with diabetes are at an increased risk for developing corneal complications and delayed wound healing. This study investigated the effects of high glucose on epidermal growth factor receptor (EGFR) signaling and on epithelial wound healing in the cornea.

RESEARCH DESIGN AND METHODS

Effects of high glucose on wound healing and on EGFR signaling were investigated in cultured porcine corneas, human corneal epithelial cells, and human corneas using Western blotting and immunofluorescence. Effects of high glucose on reactive oxygen species (ROS) and glutathione levels and on EGFR pathways were assessed in porcine and primary human corneal epithelial cells, respectively. The effects of EGFR ligands and antioxidants on high glucose–delayed epithelial wound healing were assessed in cultured porcine corneas.

RESULTS

High glucose impaired ex vivo epithelial wound healing and disturbed cell responses and EGFR signaling to wounding. High glucose suppressed Akt phosphorylation in an ROS-sensitive manner and decreased intracellular glutathione in cultured porcine corneas. Exposure to high glucose for 24 h resulted in an increase in ROS-positive cells in primary human corneal epithelial cells. Whereas heparin-binding EGF-like growth factor and antioxidant N-acetylcysteine had beneficial effects on epithelial wound closure, their combination significantly accelerated high glucose–delayed wound healing to a level similar to that seen in control subjects. Finally, Akt signaling pathway was perturbed in the epithelia of human diabetic corneas, but not in the corneas of nondiabetic, age-matched donors.

CONCLUSIONS

High glucose, likely through ROS, impairs the EGFR–phosphatidylinositol 3-kinase/Akt pathway, resulting in delayed corneal epithelial wound healing. Antioxidants in combination with EGFR ligands may be promising potential therapeutics for diabetic keratopathy.
Munc18c Depletion Selectively Impairs the Sustained Phase of Insulin Release
Authors: Oh Eunjin , Thurmond Debbie C.
Published: February 2009

OBJECTIVE

The Sec1/Munc18 protein Munc18c has been implicated in Syntaxin 4–mediated exocytosis events, although its purpose in exocytosis has remained elusive. Given that Syntaxin 4 functions in the second phase of glucose-stimulated insulin secretion (GSIS), we hypothesized that Munc18c would also be required and sought insight into the possible mechanism(s) using the islet β-cell as a model system.

RESEARCH DESIGN AND METHODS

Perifusion analyses of isolated Munc18c- (−/+) or Munc18c-depleted (RNAi) mouse islets were used to assess biphasic secretion. Protein interaction studies used subcellular fractions and detergent lysates prepared from MIN6 β-cells to determine the mechanistic role of Munc18c in Syntaxin 4 activation and docking/fusion of vesicle-associated membrane protein (VAMP)2-containing insulin granules. Electron microscopy was used to gauge changes in granule localization.

RESULTS

Munc18c (−/+) islets secreted ∼60% less insulin selectively during second-phase GSIS; RNAi-mediated Munc18c depletion functionally recapitulated this in wild-type and Munc18c (−/+) islets in a gene dosage-dependent manner. Munc18c depletion ablated the glucose-stimulated VAMP2–Syntaxin 4 association as well as Syntaxin 4 activation, correlating with the deficit in insulin release. Remarkably, Munc18c depletion resulted in aberrant granule localization to the plasma membrane in response to glucose stimulation, consistent with its selective effect on the second phase of secretion.

CONCLUSIONS

Collectively, these studies demonstrate an essential positive role for Munc18c in second-phase GSIS and suggest novel roles for Munc18c in granule localization to the plasma membrane as well as in triggering Syntaxin 4 accessibility to VAMP2 at a step preceding vesicle docking/fusion.
Prenatal Stress or High-Fat Diet Increases Susceptibility to Diet-Induced Obesity in Rat Offspring
Authors: Tamashiro Kellie L.K. , Terrillion Chantelle E. , Hyun Jayson , Koenig James I. , Moran Timothy H.
Published: February 2009

OBJECTIVE

Perturbations to the prenatal environment have been associated with the development of adult chronic disease, findings that gave rise to the “Barker Hypothesis” or the “developmental origins of adult disease” concept. In this study, we used an animal model to determine the metabolic consequences of maternal prenatal stress and high-fat feeding on the developing offspring.

RESEARCH DESIGN AND METHODS

Pregnant female Sprague-Dawley rats were maintained on standard chow or 60% high-fat diet throughout gestation and lactation. Half of each group were exposed to a novel variable stress paradigm during the 3rd week of gestation, whereas control dams were left undisturbed. Body weight, body composition, glucose tolerance, and endocrine parameters were measured in offspring through early adulthood.

RESULTS

Male and female pups from dams that experienced prenatal stress and/or were on a high-fat diet weighed more beginning on postnatal day 7 compared with standard chow–control pups. Access to high-fat diet at weaning increased the body weight effect through early adulthood and was attributable to greater adiposity. Pups weaned onto standard chow diet showed no significant difference in glucose clearance or insulin secretion. However, pups weaned onto high-fat diet had impaired glucose tolerance if their dams were on a high-fat diet, experienced prenatal stress, or both.

CONCLUSIONS

Our data demonstrate that prenatal stress and/or high-fat diet during the intrauterine or postnatal environment affects offspring in a manner that increases their susceptibility to diet-induced obesity and leads to secondary adverse metabolic consequences.
MicroRNAs Induced During Adipogenesis that Accelerate Fat Cell Development Are Downregulated in Obesity
Authors: Xie Huangming , Lim Bing , Lodish Harvey F.
Published: February 2009

OBJECTIVE

We investigated the regulation and involvement of microRNAs (miRNAs) in fat cell development and obesity.

RESEARCH DESIGN AND METHODS

Using miRNA microarrays, we profiled the expression of >370 miRNAs during adipogenesis of preadipocyte 3T3-L1 cells and adipocytes from leptin deficient ob/ob and diet-induced obese mice. Changes in key miRNAs were validated by RT-PCR. We further assessed the contribution of the chronic inflammatory environment in obese adipose tissue to the dysregulated miRNA expression by tumor necrosis factor (TNF)-α treatment of adipocytes. We functionally characterized two adipocyte-enriched miRNAs, miR-103 and miR-143, by a gain-of-function approach.

RESULTS

Similar miRNAs were differentially regulated during in vitro and in vivo adipogenesis. Importantly, miRNAs that were induced during adipogenesis were downregulated in adipocytes from both types of obese mice and vice versa. These changes are likely associated with the chronic inflammatory environment, since they were mimicked by TNF-α treatment of differentiated adipocytes. Ectopic expression of miR-103 or miR-143 in preadipocytes accelerated adipogenesis, as measured both by the upregulation of many adipogenesis markers and by an increase in triglyceride accumulation at an early stage of adipogenesis.

CONCLUSIONS

Our results provide the first experimental evidence for miR-103 function in adipose biology. The remarkable inverse regulatory pattern for many miRNAs during adipogenesis and obesity has important implications for understanding adipose tissue dysfunction in obese mice and humans and the link between chronic inflammation and obesity with insulin resistance.
Breast-Feeding Modifies the Association of PPARγ2 Polymorphism Pro12Ala With Growth in Early Life
Authors: Mook-Kanamori Dennis O. , Steegers Eric A.P. , Uitterlinden Andre G. , Moll Henriëtte A. , van Duijn Cornelia M. , Hofman Albert , Jaddoe Vincent W.V.
Published: February 2009

OBJECTIVE

We examined whether the PPARγ2 Ala12 allele influences growth in early life and whether this association is modified by breast-feeding.

RESEARCH DESIGN AND METHODS

This study was embedded in the Generation R Study, a prospective cohort study from early fetal life onward. PPARγ2 was genotyped in DNA obtained from cord blood samples in 3,432 children. Information about breast-feeding was available from questionnaires. Weight, head circumference, and femur length were repeatedly measured in second and third trimesters of pregnancy, at birth, and at the ages of 1.5, 6, 11, 14, and 18 months.

RESULTS

Genotype frequency distribution was 77.6% (Pro12Pro), 20.7% (Pro12Ala), and 1.7% (Ala12Ala). Growth rates in weight from second trimester of pregnancy to 18 months were higher for Pro12Ala and Ala12Ala than for Pro12Pro carriers (differences 1.11 g/week [95% CI 0.47–1.74] and 2.65 g/week [0.45–4.87], respectively). We found an interaction between genotype and breast-feeding duration (P value for interaction <0.0001). In infants who were breast-fed for ≥4 months, PPARγ2 Pro12Ala was not associated with growth rate. When breast-feeding duration was <2 months or 2–4 months, growth rate was higher in Ala12Ala than Pro12Pro carriers (differences 9.80 g/week [3.97–15.63] and 6.32 g/week [−1.04 to 13.68], respectively).

CONCLUSIONS

The PPARγ2 Ala12 allele is associated with an increased growth rate in early life. This effect may be influenced by breast-feeding duration. Further studies should replicate these findings, identify the underlying mechanisms, and assess whether these effects persist into later life.
Weight Loss May Reverse Blunted Sympathetic Neural Responsiveness to Glucose Ingestion in Obese Subjects With Metabolic Syndrome
Authors: Straznicky Nora E. , Lambert Gavin W. , McGrane Mariee T. , Masuo Kazuko , Dawood Tye , Nestel Paul J. , Eikelis Nina , Schlaich Markus P. , Esler Murray D. , Socratous Florentia , Chopra Reena , Lambert Elisabeth A.
Published: February 2009

OBJECTIVE

The purpose of this study was to examine the effects of weight loss on sympathetic nervous system responsiveness to glucose ingestion in obese subjects with metabolic syndrome, in whom such responses are reportedly blunted.

RESEARCH DESIGN AND METHODS

Thirty four subjects, 19 insulin resistant and 15 insulin sensitive and aged 55 ± 1 years (mean ± SE) with BMI 31.6 ± 0.6 kg/m2, who fulfilled the Adult Treatment Panel III criteria for metabolic syndrome participated. Simultaneous measurements of whole-body norepinephrine spillover rate, calf blood flow, and intra-arterial blood pressure were made at times 0, 30, 60, 90, and 120 min postglucose (75 g). The experiment was repeated after a 3-month hypocaloric diet with or without an exercise program.

RESULTS

Body weight decreased by 8.1 ± 0.9 and 8.4 ± 1.1 kg and resting norepinephrine spillover by 94 ± 31 and 166 ± 58 ng/min (all P ≤ 0.01) in insulin-resistant and insulin-sensitive subjects, respectively. Weight loss was accompanied by a marked increase in sympathetic responsiveness after glucose but only in insulin-resistant subjects. In this subgroup, comparative increases in norepinephrine spillover rates at baseline and after weight loss averaged −3 ± 25 versus 73 ± 24 ng/min at 30 min (P = 0.039), 36 ± 21 versus 115 ± 28 ng/min at 60 min (P = 0.045), 9 ± 21 versus 179 ± 50 ng/min at 90 min (P < 0.001), and 40 ± 48 versus 106 ± 39 ng/min at 120 min (P = 0.24).

CONCLUSIONS

Weight loss reverses blunted sympathetic responsiveness to glucose ingestion in insulin-resistant subjects with metabolic syndrome, which is relevant to postprandial energy utilization and body weight homeostasis.
Conflicts, Commitments, and Cliques in the University: Moral Seduction as a Threat to Trustee Independence
Authors: Bastedo Michael N.
Published: February 2009

The ability of trustees to make independent judgments in the best interests of the university is a fundamental characteristic of an effective governing board. Trustee independence is increasingly threatened, however, as the university becomes more deeply embedded in government, industry, networks, and the professions. This topic is investigated through analysis of qualitative interviews, focus group observations, and informant-produced documents from 59 public university presidents. It is argued that threats to trustee independence are produced primarily through a process of moral seduction that allows trustees to engage in self-interested decision making while maintaining an ethical self-concept. The article then provides a conceptual model to frame our understanding of how important social actors seek to capture and co-opt boards of trustees to serve external interests and describes how the institutional mechanism of moral seduction creates important policy considerations.
Testing and Improving Voters’ Political Knowledge
Authors: Stewart Kennedy , MacIver Patricia , Young Stewart
Published: February 2009

This article presents data from Canada's first comprehensive Election-Day Exit Poll, which surveyed 664 voters as they exited polling booths during the 2005 Vancouver civic election. Researchers asked voters to take two tests to estimate their political knowledge levels. The results reveal that voters’ knowledge regarding political actors can be most effectively enhanced by increasing information dissemination and reducing candidates’ voter-contact costs, perhaps best accomplished through electoral reform and more directly distributing relevant information to voters. Increasing voters’ political system knowledge is more difficult but also less critical as respondents’ test scores in this area are already very high. Suggested policy measures might help improve political knowledge, and hence voting participation rates, among non-voters.
The Grants are Falling! The Grants are Falling! How Municipal Governments Changed Taxes in Response to Provincial Support in New Brunswick, 1983–2003
Authors: Brett Craig , Tardif Christina
Published: February 2009

The real value of grants to New Brunswick municipal councils from the provincial government fell dramatically from 1983 to 2003. At the same time, municipal property tax rates increased, especially among municipalities with comparatively low tax rates in 1983. This study uses an econometric model of the joint determination of local property tax rates and local property tax bases to examine the hypothesis that municipal responses to falling grants were constrained by tax competition. After controlling for observable characteristics, there is little evidence of spatial interaction among jurisdictions, suggesting that tax competition was not a major factor in municipal decisions. The grant cuts themselves appear to be a far more important determinant of changes in property tax rates. There is also some evidence that the tax base is sensitive to a municipality's own tax rates. However, the elasticity of the tax base with respect to the tax rate is small enough that there remains scope for municipalities to increase tax revenue by increasing their tax rates.
The “Taxing” Issue of Interprovincial and Cross-Border Migration
Authors: Collins Kirk A.
Published: February 2009

This paper examines interprovincial and cross-border migration incentives brought about by the Canadian and US tax systems for first-time university graduates in 2006. To illustrate the differences in the systems, effective tax rates (ETRs) on human capital are calculated. Results show that Canadian students face greater tax-side incentives to migrate after graduation, when compared to their US counterparts, and provincial tax structures can have a significant impact on interprovincial migration incentives. The results support policy initiatives aimed at reducing taxation of returns to education as a way of reducing brain drain.
New Behavioral Model for Microscopic Freeway Traffic-Flow Simulation
Authors: Harding Jochen
Published: February 2009

A new behavioral model for microscopic freeway traffic-flow simulation is presented. As a key feature, the model is subdivided into small modules, each dealing with one distinct problem or intention of the current driving task. The modules operate independently of each other. Each module provides a situation-based vote for the longitudinal and the lateral movement of the vehicle. Subsequently, the individual votes are combined by applying a procedure that can be described as a virtual fuzzification. The model also incorporates the chronological sequence of the individual votes; decisions depend not only on the current evaluation of a driving task but also on the trend of prior evaluations. Thus, it emulates actual driver behavior. The behavioral model was implemented into the simulation software BABSIM and field tested. It is shown that the model is valid for various applications ranging from rather simple freeway sections over a lane reduction up to complex multilane on ramps and off ramps. Thus, the new approach is a valuable contribution to freeway traffic-flow modeling and simulation. It provides more accurate results and a more flexible use of the simulation software. At the same time, the straightforward and concise structure of the model simplifies its maintenance and ensures the expandability of the concept. All this promotes further use of traffic-flow simulation and leads the way for promising future developments.
Use of Microsimulation to Model Day-to-Day Variability of Intersection Performance
Authors: Abdy Zeeshan R. , Hellinga Bruce R.
Published: February 2009

Quantifying intersection performance is often a key aspect of transportation engineering studies. These studies commonly use microsimulation tools to evaluate intersection performance for vehicle delay by averaging results from several simulation runs (each with a different pseudorandom number seed) for a set of traffic and control conditions. Previous research has showed that this approach may lead to a bias in the estimation of both the mean and the standard deviation of field delay. This paper examines the issue of explicitly modeling the day-to-day variability in intersection delay by using microsimulation modeling. The results show that the prevalent method of using multiple runs, each with the same traffic demands but with different pseudorandom number seeds, does not adequately capture the day-to-day variability observed in the field. Consequently, two alternative methods for modeling day-to-day variability of intersection performance are presented and examined.
Evaluation of Corridor Traffic Management and Planning Strategies that use Microsimulation
Authors: Liu Henry X. , Jabari Saif Eddin
Published: February 2009

The California SR-41 corridor simulation project is presented as a case study of how to utilize microscopic traffic simulation for planning purposes. Two of the most important components of preparing simulation models for planning purposes are emphasized: origin-destination (O-D) matrix calibration and peak spreading for long-term testing (e.g., 20-year horizons) to overcome unrealistic network gridlock. With streamlining of the O-D calibration process, it is shown that the proposed model reproduces count and travel-time information collected from the field. Incorporating peak spreading as a result of congestion for long-term scenarios is also shown to yield performance improvements in the models and overcome network gridlock issues common to such applications.
From Existing Accident-Free Car-Following Models to Colliding Vehicles
Authors: Hamdar Samer H. , Mahmassani Hani S.
Published: February 2009

The study explores the specifications of microscopic traffic models that could capture congestion dynamics and model accident-prone behaviors on a highway section in greater realism than existing models currently used in practice (commercial software). A comparative assessment of several major acceleration models is conducted, especially for congestion formation and incident modeling. On the basis of this assessment, alternative specifications for car-following and lane-changing models are developed and implemented in a microscopic simulation framework. The models are calibrated and compared for resulting vehicle trajectories and macroscopic flow-density relationships. Experiments are conducted with the models under different degrees of relaxation of the safety constraints typically applied in conjunction with simulation codes used in practice. The ability of the proposed specifications to capture traffic behavior in extreme situations is examined. The results suggest that these specifications offer an improved basis for microscopic traffic simulation for situations that do not require an accident-free environment. As such, the same basic behavior model structure could accommodate both extreme situations (evacuation scenarios, oversaturated networks) as well as normal daily traffic conditions.
Empirical Measurement of Freeway Oscillation Characteristics
Authors: Zielke Benjamin A. , Bertini Robert L. , Treiber Martin
Published: February 2009

A country-specific analysis of freeway traffic oscillations was conducted. Loop detector data from sites in the United States, Germany, and the United Kingdom were analyzed. With the use of a method applied in previous work, traffic oscillations were identified in all three countries. Calculation of the cross-correlation coefficient revealed that they traveled upstream at speeds of about 19 to 20 km/h at the U.S. site, 16 km/h at the German site, and 14 km/h on the U.K. freeway. Similar magnitudes were found in the literature verifying the hypothesis that they propagated faster in the United States than in Germany. Furthermore, an oscillation frequency was identified by calculation of the data's autocorrelation. However, since the oscillation frequency was likely to be site specific, conclusions regarding general differences between the frequencies measured in different countries cannot yet be made. For the sites analyzed, it was found that oscillations appeared every 8 to 12 min on the M4 (U.K. site), every 10 to 30 min on the A9 (German site), and every 3 to 6 min on OR-217 (U.S. site). Although the magnitudes of the latter two countries were supported by the literature, further empirical research on several different sites should be pursued to draw final conclusions.
On-Ramp Metering Based on Three-Phase Traffic Theory Downstream Off-Ramp and Upstream On-Ramp Bottlenecks
Authors: Kerner Boris S.
Published: February 2009

An ANCONA method is suggested for control of congestion at an off-ramp bottleneck through the use of feedback on-ramp metering at an upstream on-ramp bottleneck. The method is based on a recent ANCONA method for feedback on-ramp metering at an isolated on-ramp bottleneck, which allows congestion to set in at the bottleneck. With the use of the Kerner-Klenov traffic flow model in the context of three-phase traffic theory, simulations of ANCONA for a section of highway with downstream off-ramp and upstream on-ramp bottlenecks are made. It was found that if a wide moving jam occurs spontaneously within synchronized flow, then through the use of ANCONA, emergence of a wide moving jam can be prevented. As a result, a congested pattern at the off-ramp bottleneck, which consists of synchronized flow of higher speed (about or higher than 60 km/h) only, is spatially limited, that is, congestion does not propagate continuously upstream.
Estimating Acceleration and Lane-Changing Dynamics from Next Generation Simulation Trajectory Data
Authors: Thiemann Christian , Treiber Martin , Kesting Arne
Published: February 2009

The Next Generation Simulation (NGSIM) trajectory data sets provide longitudinal and lateral positional information for all vehicles in certain spatiotemporal regions. Velocity and acceleration information cannot be extracted directly because the noise in the NGSIM positional information is greatly increased by the necessary numerical differentiations. A smoothing algorithm is proposed for positions, velocities, and accelerations that can also be applied near the boundaries. The smoothing time interval is estimated on the basis of velocity time series and the variance of the processed acceleration time series. The velocity information obtained in this way is then applied to calculate the density function of the two-dimensional distribution of velocity and inverse distance and the density of the distribution corresponding to the “microscopic” fundamental diagram. It is also used to calculate the distributions of time gaps and times to collision, conditioned to several ranges of velocities and velocity differences. By simulating virtual stationary detectors, it is shown that the probability for critical values of the times to collision is greatly underestimated when estimated from single-vehicle data of stationary detectors. Finally, the lane-changing process is investigated, and a quantitative criterion is formulated for the duration of lane changes that is based on the trajectory density in normalized coordinates. There is a noisy but significant velocity advantage in favor of the targeted lane that decreases immediately before the change due to anticipatory accelerations.
Macroscopic Modeling Framework Unifying Kinematic Wave Modeling and Three-Phase Traffic Theory
Authors: Hoogendoorn Serge P. , van Lint Hans , Knoop Victor L.
Published: February 2009

Modeling breakdown probabilities or phase-transition probabilities is an important issue when assessing and predicting the reliability of traffic flow operations. Looking at empirical spatiotemporal patterns, these probabilities clearly are a function not only of the local prevailing traffic conditions (density, speed) but also of time and space. For instance, the probability that a start-stop wave occurs generally increases when moving upstream away from the bottleneck location. A simple partial differential equation is presented that can be used to model the dynamics of breakdown probabilities, in conjunction with the well-known kinematic wave model. The main assumption is that the breakdown probability dynamics satisfy the way information propagates in a traffic flow, that is, they move along with the characteristics. The main result is that the main characteristics of the breakdown probabilities can be reproduced. This is illustrated through two examples: free flow to synchronized flow (F-S transition) and synchronized to jam (S-J transition). It is shown that the probability of an F-S transition increases away from the on ramp in the direction of the flow; the probability of an S-J transition increases as one moves upstream in the synchronized flow area.
Validity of Trajectory-Based Calibration Approach of Car-Following Models in Presence of Measurement Errors
Authors: Ossen Saskia , Hoogendoorn Serge P.
Published: February 2009

Interest in calibration of car-following models by using real-life microscopic trajectory data is increasing. However, more information is needed on the influence of methodological issues on calibration results as well as on the influence of practical issues related to the use of real-life data. In particular, the influence of measurement errors on parameter estimates has not yet been considered in detail. To gain insight into the influence of measurement errors on calibration results, synthetic data were created to which several types of measurement error are introduced. These data are input to a validated calibration procedure, after which it is studied how well the parameters used for creating the data can be identified from the erroneous data. The sensitivity of the objective function to small changes in the optimal parameters also is assessed. The calibrations are repeated by using different variables in the objective. The three main findings are that (a) measurement errors can yield a considerable bias in the estimation results, (b) parameters minimizing the objective function do not necessarily capture following dynamics best, and (c) measurement errors substantially reduce the sensitivity of the objective function and consequently reduce the reliability of estimation results. The extent to which these problems caused by measurement errors can be avoided by smoothing the data carefully before use is assessed and discussed.
The Less-Than-Perfect Driver
Authors: Xin Wuping , Hourdos John , Michalopoulos Panos , Davis Gary
Published: February 2009

Unlike traditional car-following models that preclude vehicle collisions, a proposed model aims to emulate less-than-perfect everyday driving while capturing both safe and unsafe driver behavior. Most important, a realistic perception-response process is incorporated into the model on the basis of developments from visual perception studies. Driver inattention is characterized by a driver-specific variable called the scanning interval. This variable, when coupled with the driver's visual perception-response process, results in variable reaction times that are dependent not only on each driver's individual characteristics but also on instantaneous traffic conditions such as speed and density. This allows closer emulation of real-life human driving and its interactions with surrounding vehicles. Both inter- and intradriver variations in reaction time are captured in a plausible and coherent manner; in earlier studies, reaction time either was presumed fixed or was of limited variability. Furthermore, parameters of this model have a direct physical and behavioral meaning; this implies that vehicle collisions, if any, can be analyzed for behavioral patterns rather than simply being treated as numerical artifacts. In all, 54 detailed and accurate vehicle trajectories extracted from 10 real-life crashes were used to test the model's capability of replicating freeway rear-end collisions. High-resolution crash-free trajectory data were used to validate the model against normal driving behavior. Test results indicate that the proposed model is able to replicate both normal and unsafe driving behavior that could lead to vehicle collisions. The feasibility of integrating the proposed model with existing microsimulators is discussed. The outcome of this work could facilitate studying crash mechanisms at a high-definition microscopic level and could enable safety-related system design improvements and evaluation through microsimulation software.
What Do Different Traffic Flow Models Mean for System-Optimal Dynamic Traffic Assignment in a Many-to-One Network?
Authors: Shen Wei , Zhang H. M.
Published: February 2009

A variety of macroscopic traffic flow models have been applied to formulate the link-based system optimal dynamic traffic assignment (SO-DTA) problem in a many-to-one network. It is expected that SO-DTA models based on various traffic flow models usually result in different optimal link traffic evolution patterns, but whether and how traffic flow models affect the minimal system cost and the corresponding optimal arrival pattern at the destination is unclear. Three traffic flow models–point-queue, spatial-queue, and cell-transmission–are examined, and their resulted minimal system cost in many-to-one networks is compared. It is proved that for three simple networks–a linear network with two sequential bottlenecks, a two-in-one-out merge network, and a one-in-two-out diverge network–the minimal system costs for the SO-DTA models based on these three traffic flow models are identical. Numerical experiments show that this property appears to be held for general many-to-one networks. The reason may be that all three traffic flow models propagate the uncongested flows at the same speed and release the congested flows always at the link capacity. In SO-DTA applications where only the minimal system cost or arrival pattern at the destination is of major interest, the findings can be utilized to substantially expedite the solution procedure.
Lane Selection Model for Urban Intersections
Authors: Choudhury Charisma F. , Ben-Akiva Moshe E.
Published: February 2009

A lane choice model for urban arterial intersections is presented. This model replaces the rule-based heuristics to assign vehicles in their subsequent lanes used in state-of-the-art microscopic traffic simulators. The lane choice at intersections is modeled as a two-step process: target lane choice and immediate lane selection based on the selected target lane. The target lane is one that the driver perceives as the best to be in, considering a wide range of factors and goals. These include path plan considerations and lane-specific attributes and can vary with the planning capability and aggressiveness of the driver. However, a maneuver to the target lane may not be possible immediately. The observed trajectories consist only of the immediate lane choices of the drivers. The choice of immediate lane is conditional on the target lane selection and affected by maneuverability considerations and aggressiveness of the driver. The parameters of the target lane and immediate lane choice models are jointly estimated with detailed vehicle trajectories. The heterogeneities of the driver population, for both planning capability and aggressiveness, are explicitly taken into account in the model formulation. The estimated model is compared with a single-level intersection lane choice model to demonstrate the improvements in the goodness of fit. The improvements are further strengthened by validation studies within the microscopic traffic simulator MITSIMLab, where the simulation results using the proposed model yield better matches with observed data compared to the rule-based models.
Desired Speed Distributions on Two-Lane Highways under various Conditions
Authors: Catbagan Jerome L. , Nakamura Hideki
Published: February 2009

On a two-lane highway with passing restrictions, user dissatisfaction usually is caused by the inability to drive at the desired speed because of a relatively slower lead vehicle. Although this condition clearly shows that vehicles in this state are following, current definitions of “following vehicle” are based mainly on headway alone. A “follower” can be more logically defined as a vehicle traveling below its desired speed because of the presence of a relatively slower lead vehicle. The problem arises because the desired speeds of different drivers vary significantly; the variation makes it difficult to assess whether a vehicle is constrained on the basis of directly accessible data alone. A study was done to develop desired speed distributions for various traffic, weather, and ambient conditions, which can be later used as input for simulation or to calculate a vehicle's following probability given its current speed. The collected data were classified according to different traffic, geometric, weather, and ambient conditions to form 64 data sets for analysis. The desired speed distributions were estimated by using the modified Kaplan-Meier approach and were found to be suitable for use as either simulation input or as a tool that can be used for follower identification. Differences between holiday and weekday travel speed preferences and effects of weather on driver speed choices were also found.
Hydromagnetic Three Dimensional Couette Flow and Heat Transfer
Authors: Das SS , Mohanty M , Panda JP , Sahoo SK
Published: February 2009

This paper is concerned with the theoretical analysis of three dimensional couette flow of a viscous incompressible electrically conducting fluid between two infinite horizontal parallel porous flat plates in presence of a transverse magnetic field. The stationary plate and the plate in uniform motion are, respectively, subjected to a transverse sinusoidal injection and uniform suction of the fluid. The governing equations of the flow field are solved by using series expansion method and the expressions for the velocity field, the temperature field, skin friction and heat flux in terms of Nusselt number are obtained. The effects of the flow parameters on the velocity, temperature, skin friction and heat flux have been studied and analyzed with the help of figures and tables. It is observed that the magnetic parameter (M) has a retarding effect on the main velocity (u) and an accelerating effect on the cross velocity (w1) of the flow field. The suction parameter (Re) has a retarding effect on the main velocity as well as on the temperature field. The Prandtl number (Pr) reduces the temperature of the flow field and increases the rate of heat transfer at the wall (Nu). The effect of suction parameter is to reduce the x-component of skin friction and to enhance the magnitude of z-component of the skin friction at the wall. This problem is very much significant in view of its several engineering, geophysical and industrial applications.Keywords: Hydromagnetic, couette flow, heat transfer, three dimensions doi:10.3329/jname.v5i1.1784 Journal of Naval Architecture and Marine Engineering Vol. 5, No.Â 1 (June, 2008) 1-10.
Numerical Solutions of Heat and Mass Transfer Effects of an Unsteady MHD Free Convective Flow past an Infinite Vertical Plate with Constant Suction
Authors: Ambethkar V
Published: February 2009

The objective of this work is to study heat and mass transfer in an unsteady MHD free convective flow past an infinite vertical plate with constant suction numerically.Â  Dimensionless governing equations of the problem have been solved by using finite difference technique. Numerical solutions for temperature, velocity, concentration have been obtained for suitable parameters like Grashoff number, mass Grashoff number, Prandtl number and Schmidt number. Rate of heat transfer and mass transfer are studied. The results obtained are discussed with the help of graphs and tables to observe effect of various parameters concerned in the problem under investigation. Stability and convergence of the finite difference scheme is established. Key words: MHD, unsteady, constant suction, finite difference technique, Heat and mass transfer. doi:10.3329/jname.v5i1.1785 Journal of Naval Architecture and Marine Engineering Vol. 5, No.Â 1 (June, 2008) 27-36
Separation Points of Magneto-hydrodynamic Boundary Layer Flow Along a Vertical Plate with Exponentially Decreasing Free Stream Velocity
Authors: Alim MA , Rahman MM , Karim MM
Published: February 2009

The points of separation of magneto-hydrodynamic mixed convection boundary layer flow along a vertical plate have been investigated. The free stream velocity is considered decreasing exponentially in the stream wise direction. The governing boundary layer equations are transformed into a non-dimensional form and the resulting nonlinear system of partial differential equations are reduced to local non-similar boundary layer equations, which are solved numerically by implicit finite difference method known as Keller box scheme. Here we have focused our attention to find the effects of suction, magnetic field and other relevant physical parameters on the position of boundary layer separation. The numerical results are expressed in terms of local shear stress showing the effects of suction, buoyancy, Prandlt number and magnetic field on the shear stress as well as on the points of separation. Keywords: Separation points, magneto-hydrodynamic, mixed convection, boundary layer, suction, finite difference method, Keller box scheme. Â  doi:10.3329/jname.v5i1.1868Journal of Naval Architecture and Marine Engineering Vol. 5, No.Â 1 (June, 2008) 11-18.Â
La producción informativa y documental del Estado: hacia un inventario de los recursos públicos
Authors: Ramos Simón Luis Fernando , Mendo Carmona Concepción , Arquero Avilés Rosario
Published: February 2009

Internet supone un nuevo escenario en la configuración de los mensajes que el Estado dirige a sus ciudadanos, así como en la generación de nuevas relaciones con los mismos. Desde ese enfoque, nos centraremos en cómo la producción de información del Estado debe ser organizada para que los ciudadanos reciban un conjunto de servicios informativos. Una adecuada creación y manejo de la información del sector público es crucial tanto por su valor en sí misma como por los activos económicos que representa. Además, en este contexto del acceso y la reutilización de la información pública se plantea la necesidad de contar con una terminología específica. Se establecen los principios de aplicación general que ha de regir el tratamiento de la información generada por el sector público y, en relación con el principio de inventario, se resumen los principales resultados obtenidos en el marco del Grupo de investigación sobre la identificación y descripción de los activos de información y documentación del sector público, en particular de la Administración General del Estado. El tema es de gran interés para los profesionales e investigadores en Biblioteconomía y Documentación, ya que esta perspectiva pone en valor los recursos de información documental y propicia un gran impulso a la creación de un mercado de servicios de información pública.
Análisis de la producción de la Universidad de Navarra en revistas de Ciencias Sociales y Humanidades empleando rankings de revistas españolas y la Web of Science
Authors: Torres-Salinas Daniel , Delgado López-Cózar Emilio , Jiménez-Contreras Evaristo
Published: February 2009

Se realiza un análisis bibliométrico de la producción en revistas de las facultades de Ciencias Sociales y Humanidades de la Universidad de Navarra durante el período 1999-2005. Se emplean junto al Journal Citation Reports diferentes rankings de revistas españolas: el Índice de Impacto de las Revistas Españolas de Ciencias Sociales (IN-RECS), Índice de Impacto de las Revistas Españolas de Ciencias Jurídicas (IN-REJS) y Revistas Españolas de Ciencias Sociales y Humanidades (RESH). El objetivo es estudiar la idoneidad de estos índices como herramienta bibliométrica a la hora de describir la producción en revistas españolas de una universidad. Respecto a los resultados la Universidad de Navarra publicó un total 7.281 documentos de los cuales 1908 eran trabajos en revistas, es decir, el 26 % de la producción. Del conjunto anterior solo el 39 % fueron en revistas científicas españolas, y 12 % de la Web of Science. La cobertura de los rankings varía según las facultades, IN-RECJ es óptimo para la Facultad de Derecho, IN-RECS para Comunicación y Economía y RESH para Filosofía y Letras. Se estudiaron asimismo los documentos presentes en revistas del primer cuartil. En IN-RECS el 43 % de los trabajos estaban en el primer cuartil, en RESH el 42 % y en JCR un 12 %. Se concluye que los rankings nacionales son útiles para complementar a la Web of Science y el JCR.