The Experts below are selected from a list of 177 Experts worldwide ranked by ideXlab platform
Nicholas J Severs - One of the best experts on this subject based on the ideXlab platform.
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connexin45 a major connexin of the rabbit sinoatrial node is co expressed with connexin43 in a Restricted Zone at the nodal crista terminalis border
Journal of Histochemistry and Cytochemistry, 1999Co-Authors: Steven R Coppen, Itsuo Kodama, Mark R Boyett, Halina Dobrzynski, Yoshiko Takagishi, Haruo Honjo, Hungi Yeh, Nicholas J SeversAbstract:The pacemaker of the heart, the sinoatrial (SA) node, is characterized by unique electrical coupling properties. To investigate the contribution of gap junction organization and composition to these properties, the spatial pattern of expression of three gap junctional proteins, connexin45 (Cx45), connexin40 (Cx40), and connexin43 (Cx43), was investigated by immunocytochemistry combined with confocal microscopy. The SA nodal regions of rabbits were dissected and rapidly frozen. Serial cryosections were double labeled for Cx45 and Cx43 and for Cx40 and Cx43, using pairs of antibody probes raised in different species. Dual-channel scanning confocal microscopy was applied to allow simultaneous visualization of the different connexins. Cx45 and Cx40, but not Cx43, were expressed in the central SA node. The major part of the SA nodal-crista terminalis border revealed a sharply demarcated boundary between Cx43-expressing myocytes of the crista terminalis and Cx45/Cx40-expressing myocytes of the node. On the endocardial side, however, a transitional Zone between the crista terminalis and the periphery of the node was detected in which Cx43 and Cx45 expression merged. These distinct patterns of connexin compartmentation and merger identified suggest a morphological basis for minimization of contact between the tissues, thereby restricting the hyperpolarizing influence of the atrial muscle on the SA node while maintaining a communication route for directed exit of the impulse into the crista terminalis.
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connexin45 a major connexin of the rabbit sinoatrial node is co expressed with connexin43 in a Restricted Zone at the nodal crista terminalis border
Journal of Histochemistry and Cytochemistry, 1999Co-Authors: Steven R Coppen, Itsuo Kodama, Mark R Boyett, Halina Dobrzynski, Yoshiko Takagishi, Haruo Honjo, Nicholas J SeversAbstract:The pacemaker of the heart, the sinoatrial (SA) node, is characterized by unique electrical coupling properties. To investigate the contribution of gap junction organization and composition to thes...
Steven R Coppen - One of the best experts on this subject based on the ideXlab platform.
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connexin45 a major connexin of the rabbit sinoatrial node is co expressed with connexin43 in a Restricted Zone at the nodal crista terminalis border
Journal of Histochemistry and Cytochemistry, 1999Co-Authors: Steven R Coppen, Itsuo Kodama, Mark R Boyett, Halina Dobrzynski, Yoshiko Takagishi, Haruo Honjo, Hungi Yeh, Nicholas J SeversAbstract:The pacemaker of the heart, the sinoatrial (SA) node, is characterized by unique electrical coupling properties. To investigate the contribution of gap junction organization and composition to these properties, the spatial pattern of expression of three gap junctional proteins, connexin45 (Cx45), connexin40 (Cx40), and connexin43 (Cx43), was investigated by immunocytochemistry combined with confocal microscopy. The SA nodal regions of rabbits were dissected and rapidly frozen. Serial cryosections were double labeled for Cx45 and Cx43 and for Cx40 and Cx43, using pairs of antibody probes raised in different species. Dual-channel scanning confocal microscopy was applied to allow simultaneous visualization of the different connexins. Cx45 and Cx40, but not Cx43, were expressed in the central SA node. The major part of the SA nodal-crista terminalis border revealed a sharply demarcated boundary between Cx43-expressing myocytes of the crista terminalis and Cx45/Cx40-expressing myocytes of the node. On the endocardial side, however, a transitional Zone between the crista terminalis and the periphery of the node was detected in which Cx43 and Cx45 expression merged. These distinct patterns of connexin compartmentation and merger identified suggest a morphological basis for minimization of contact between the tissues, thereby restricting the hyperpolarizing influence of the atrial muscle on the SA node while maintaining a communication route for directed exit of the impulse into the crista terminalis.
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connexin45 a major connexin of the rabbit sinoatrial node is co expressed with connexin43 in a Restricted Zone at the nodal crista terminalis border
Journal of Histochemistry and Cytochemistry, 1999Co-Authors: Steven R Coppen, Itsuo Kodama, Mark R Boyett, Halina Dobrzynski, Yoshiko Takagishi, Haruo Honjo, Nicholas J SeversAbstract:The pacemaker of the heart, the sinoatrial (SA) node, is characterized by unique electrical coupling properties. To investigate the contribution of gap junction organization and composition to thes...
Amy L Epps - One of the best experts on this subject based on the ideXlab platform.
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impact of gradation relative to superpave Restricted Zone on hot mix asphalt performance
Transportation Research Record, 2001Co-Authors: Adam J. T. Hand, Amy L EppsAbstract:Significant controversy has revolved around the Superpave gradation specifications, in particular the Restricted Zone, since the completion of the Strategic Highway Research Program (SHRP). Historically, dense-graded mixtures that encroach on the Restricted Zone had provided good performance prior to SHRP. However, current Superpave guidelines recommend that gradations passing through the Restricted Zone not be used. A synopsis of recent research related specifically to the impact of the Superpave Restricted Zone on performance of hot-mix asphalt (HMA) is provided. The evolution and purpose of the Superpave Restricted Zone are presented, along with findings of both recently completed and ongoing research. Studies involving laboratory and full-scale accelerated performance tests of mixtures with gradations plotting above (ARZ), through (TRZ), and below the Restricted Zone were considered. The research reviewed clearly suggests that good performance can be achieved with fine-graded (ARZ and TRZ) mixtures and that no relationship exists between the Superpave Restricted Zone and HMA rutting or fatigue performance. It is suggested on the basis of this research that the Restricted Zone recommendation be eliminated from the Superpave volumetric mixture design specifications.
L A Cooley - One of the best experts on this subject based on the ideXlab platform.
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effect of superpave defined Restricted Zone on hot mix asphalt performance
Transportation Research Record, 2004Co-Authors: Jingna Zhang, L A Cooley, Graham C Hurley, Frazier ParkerAbstract:The effect of the Superpaver defined Restricted Zone on hot-mix asphalt rutting performance was evaluated. One gradation that violated the Restricted Zone (TRZ) and two gradations that did not violate the Restricted Zone (BRZ and ARZ) were evaluated. Evaluated mixes represented a range of maximum aggregate sizes (MASs), design traffic levels, and aggregate types. Three laboratory tests—asphalt pavement analyzer, rotary-loaded wheel tester, and Marshall test—were used to evaluate the rutting performance. From the analysis, it was found that mixes with gradations violating the Restricted Zone performed similarly to or better than the mixes with gradations passing outside the Restricted Zone with respect to laboratory rutting tests. This conclusion was drawn from the results of experiments with 12.5-, 19.0-, and 25.0-mm MAS gradations at Ndesign (design number of gyrations) values of 100, 75, and 50 gyrations. This conclusion is confirmed and supported by the recently completed NCHRP Project 9-14: The Restri...
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significance of Restricted Zone in superpave aggregate gradation specification
Transportation research circular, 2002Co-Authors: L A Cooley, Adam J. T. Hand, Jianping Zhang, P S Kandhal, Epps A MartinAbstract:Asphalt technologists recognized it for many years prior to Superpave (Registered trademark) -- a characteristic hump in a mix gradation within the intermediate sieve sizes which could cause a hot-mix asphalt (HMA) mix to be prone to tenderness and rut susceptibility. The Strategic Highway Research Program (SHRP) gave it a name -- the Restricted Zone -- and included it in Superpave as a recommended guideline. Some transportation agencies interpreted it as a requirement. However, based on experiences with mixes violating the Restricted Zone, many asphalt technologists did not agree with its inclusion in Superpave. The authors of this Circular present the historical basis of the Restricted Zone in HMA mixes and summarize the published research conducted on the Restricted Zone to determine its significance within the Superpave gradation specification. The Transportation Research Board Committee on General Issues in Asphalt Technology (A2D05) finds that this information should be of interest to materials and pavement engineers and others responsible for designing HMA pavements.
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investigation of the Restricted Zone in the superpave aggregate gradation specification with discussion
Asphalt Paving Technology 2002Association of Asphalt Paving Technologists (AAPT), 2002Co-Authors: P S Kandhal, L A CooleyAbstract:The recommended aggregate specification for Superpave hot mix asphalt (HMA) mixtures includes a Restricted Zone which lies along the maximum density gradation between the intermediate size (either 4.75 or 2.36 mm, depending on the nominal maximum size of the aggregate) and the 300 micron size. The Restricted Zone forms a band through which gradations were recommended not to pass. The Restricted Zone requirement was adopted in Superpave to help reduce the incidence of tender or rut-prone HMA mixes. According to many asphalt paving technologists, compliance with the Restricted Zone criteria may not be desirable or necessary to produce paving mixes that give good performance. Some highway agencies and suppliers can provide examples of aggregate gradations that pass through the Restricted Zone, but produce paving mixes that have historically performed well. This research project was undertaken to evaluate the effect of the Superpave Restricted Zone on permanent deformation of dense-graded HMA mixtures. Its primary objective was to determine under what conditions, if any, compliance with the Restricted Zone requirement is necessary when the HMA meets all the other Superpave requirements such as fine aggregate angularity and volumetric mix criteria for the specific project. The following factors were evaluated: two coarse aggregates, ten fine aggregates, two nominal maximum aggregate size mixes (9.5 and 19.0 mm), five aggregate gradations, and three compactive efforts (Ndesign = 75, 100, and 125). Of the five gradations used, three violate the Restricted Zone and two fall outside of the Restricted Zone (control). Permanent deformation characteristics of mixes meeting Superpave volumetric requirements were evaluated by two different types of tests: empirical and fundamental. For the empirical test, the Asphalt Pavement Analyzer was used. The Superpave shear tester and a repeated load confined creep test were utilized as fundamental tests. Test results from the three mechanical tests were analyzed statistically to evaluate the effect of the five gradations on permanent deformation of the HMA mixtures. Based upon the analysis of data, mixes having gradations passing through the Restricted Zone did not necessarily have lower rut resistance compared to mixes having gradations outside the Restricted Zone. It was recommended to delete the Restricted Zone as a guideline or requirement in Superpave mix design.
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the Restricted Zone in the superpave aggregate gradation specification
NCHRP Report, 2001Co-Authors: P S Kandhal, L A CooleyAbstract:This report presents the findings of a research project to determine whether the Restricted Zone requirement is necessary for aggregate gradations designed in accordance with American Association of State Highway and Transportation Officials (AASHTO) MP2 and PP28 if mix volumetric and fine aggregate angularity criteria are met. Its main finding is that, based on an evaluation of the performance properties of hot mix asphalt, the Restricted Zone requirement is redundant in these circumstances. The report will be of particular interest to materials engineers in state highway agencies, as well as to materials suppliers and paving contractor personnel responsible for the specification and production of hot mix asphalt.
Adam J. T. Hand - One of the best experts on this subject based on the ideXlab platform.
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significance of Restricted Zone in superpave aggregate gradation specification
Transportation research circular, 2002Co-Authors: L A Cooley, Adam J. T. Hand, Jianping Zhang, P S Kandhal, Epps A MartinAbstract:Asphalt technologists recognized it for many years prior to Superpave (Registered trademark) -- a characteristic hump in a mix gradation within the intermediate sieve sizes which could cause a hot-mix asphalt (HMA) mix to be prone to tenderness and rut susceptibility. The Strategic Highway Research Program (SHRP) gave it a name -- the Restricted Zone -- and included it in Superpave as a recommended guideline. Some transportation agencies interpreted it as a requirement. However, based on experiences with mixes violating the Restricted Zone, many asphalt technologists did not agree with its inclusion in Superpave. The authors of this Circular present the historical basis of the Restricted Zone in HMA mixes and summarize the published research conducted on the Restricted Zone to determine its significance within the Superpave gradation specification. The Transportation Research Board Committee on General Issues in Asphalt Technology (A2D05) finds that this information should be of interest to materials and pavement engineers and others responsible for designing HMA pavements.
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impact of gradation relative to superpave Restricted Zone on hot mix asphalt performance
Transportation Research Record, 2001Co-Authors: Adam J. T. Hand, Amy L EppsAbstract:Significant controversy has revolved around the Superpave gradation specifications, in particular the Restricted Zone, since the completion of the Strategic Highway Research Program (SHRP). Historically, dense-graded mixtures that encroach on the Restricted Zone had provided good performance prior to SHRP. However, current Superpave guidelines recommend that gradations passing through the Restricted Zone not be used. A synopsis of recent research related specifically to the impact of the Superpave Restricted Zone on performance of hot-mix asphalt (HMA) is provided. The evolution and purpose of the Superpave Restricted Zone are presented, along with findings of both recently completed and ongoing research. Studies involving laboratory and full-scale accelerated performance tests of mixtures with gradations plotting above (ARZ), through (TRZ), and below the Restricted Zone were considered. The research reviewed clearly suggests that good performance can be achieved with fine-graded (ARZ and TRZ) mixtures and that no relationship exists between the Superpave Restricted Zone and HMA rutting or fatigue performance. It is suggested on the basis of this research that the Restricted Zone recommendation be eliminated from the Superpave volumetric mixture design specifications.