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Sample records for aaa wall stress

  1. Distribution of Wall Stress in Abdominal Aortic Aneurysm (AAA)

    NASA Astrophysics Data System (ADS)

    Lasheras, Juan

    2005-11-01

    Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. Therefore, knowledge of the AAA wall stress distribution could be useful in assessing its risk of rupture. In our research, a finite element analysis was used to determine the wall stresses both in idealized models and in a real clinical model in which the aorta was considered isotropic with nonlinear material properties and was loaded with a given pressure. In the idealized models, both maximum diameter and asymmetry were found to have substantial influence on the distribution of the wall stress. The thrombus inside the AAA was also found to help protecting the walls from high stresses. Using CT scans of the AAA, the actual geometry of the aneurysm was reconstructed and we found that wall tension increases on the flatter surface (typically corresponds to the posterior surface) and at the inflection points of the bulge. In addition to the static analysis, we also performed simulations of the effect of unsteady pressure wave propagation inside the aneurysm.

  2. Effects of the Transient Blood Flow-Wall Interaction on the Wall Stress Distribution in Abdominal Aortic Aneurysm (AAA)

    NASA Astrophysics Data System (ADS)

    Tang, Rubing; Geindreau, Christian; Lasheras, Juan

    2006-11-01

    Our static finite element analysis (FEA) of both idealized and real clinical models has shown that the maximum diameter and asymmetry have substantial influence on the AAA wall stress distribution. The thrombus inside the AAA was also found to reduce the magnitude of the wall stresses. To achieve a better understanding of the wall stress distribution in real AAAs, a dynamic FEA was also performed. We considered models, both symmetric and non-symmetric, in which the aorta is assumed isotropic with nonlinear material properties. For the limiting case of rigid walls, the evolution of the flow pattern and the wall shear stresses due to fluid flow at different stages of cardiac cycle predicted by our simulations are compared with experimental results obtained in in-vitro models. A good agreement is found between both results. Finally, we have extended the analysis to the physiologically correct case of deformable walls and characterized the transient effects on the wall stresses.

  3. Changes in the wall shear stresses (WSS) during the enlargement of Abdominal Aortic Aneurysms (AAA)

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Sparks, Steven R.; Chomaz, Jean-Marc; Lasheras, Juan C.

    2004-11-01

    The changes in the evolution of the spatial and temporal distribution of the WSS and gradients of WSS at different stages of the enlargement of AAAs are important to understand the etiology and progression of this vascular disease, since they affect the wall structural integrity, primarily via the changes induced on the shape, functions and metabolism of the endothelial cells. PIV measurements were performed in aneurysm models, while changing systematically their geometric parameters. We show that, even at very early stages of the disease (dilatation > 30%), the flow separates from the wall and the formation of a large vortex ring followed by internal shear layers leads to the generation of WSS that drastically differ from the healthy vessel. Inside the AAA, the mean WSS decreases to zero and the magnitude of the WSS can be as low as 26% of the value in a healthy vessel. Two regions with distinct patterns of WSS were identified. The region of flow detachment, with oscillatory WSS of very low mean, and the region of flow reattachment, located distally, where large, negative WSS and sustained gradients of WSS are produced as a result of the impact of the vortex ring on the wall.

  4. Effects of the changes in the wall shear stresses (WSS) acting on endothelial cells (EC) during the enlargement of Abdominal Aortic Aneurysms (AAA)

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie

    2005-03-01

    The changes in the spatial and temporal distribution of the WSS and gradients of WSS during the enlargement of AAAs are important to understand the etiology and progression of this vascular disease, since they affect the wall structural integrity, primarily via the changes induced on the shape, functions and metabolism of the endothelial cells. PIV measurements were performed in aneurysm models, while changing systematically their size and geometry. Two regions with distinct patterns of WSS were identified. The region of flow detachment extends over the proximal half and is characterized by oscillatory WSS of very low mean. The region of flow reattachment, located distally, is dominated by large, negative WSS and sustained gradients of WSS that result from the impact of the vortex ring on the wall. Cultured EC were subjected to these two types of stimuli in vitro. The permeability of the endothelium was found to be largely increased in the flow detachment region. Endothelium cell-cell adhesion, proliferation and apoptosis were also affected by the high gradients of WSS.

  5. Modelling of residually stressed materials with application to AAA.

    PubMed

    Ahamed, T; Dorfmann, L; Ogden, R W

    2016-08-01

    Residual stresses are generated in living tissues by processes of growth and adaptation and they significantly influence the mechanical behaviour of the tissues. Thus, to effectively model the elastic response of the tissues relative to a residually stressed configuration the residual stresses need to be incorporated into the constitutive equations. The purposes of this paper are (a) to summarise a general elastic constitutive formulation that includes residual stress, (b) to specify the tensors needed for the three-dimensional implementation of the theory in a nonlinear finite element code, and (c) to use the theory and its implementation to evaluate the wall stress distribution in an abdominal aortic aneurysm (AAA) using patient specific geometry and material model parameters. The considered material is anisotropic with two preferred directions indicating the orientation of the collagen fibres in the aortic tissue. The method described in this paper is general and can be used, by specifying appropriate energy functions, to investigate other residually stressed biological systems. PMID:26874252

  6. Cell-Activation by Shear Stresses in Abdominal Aortic Aneurysms (AAA)

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Sparks, Steven; Chomaz, Jean-Marc; Lasheras, Juan C.

    2003-11-01

    Increasing experimental evidence indicates that low and oscillatory shear stresses promote proliferative, thrombotic, adhesive and inflammatory-mediated degenerative conditions throughout the wall of the aorta. These degenerative conditions have been shown to be involved in the pathogenesis of AAAs, a permanent, localized dilatation of the abdominal aorta. The purpose of this study is to measure both the magnitude and the duration of the shear stresses acting on both the arterial walls and on the blood cells inside AAAs, and to characterize their changes as the AAA enlarges. We conducted a parametric in-vitro study of the pulsatile blood flow in elastic models of AAAs while systematically varying the blood flow parameters, and the geometry of the aneurysm's bulging. The instantaneous flow characteristic inside the AAA was measured using DPIV at a sampling rate of 15 Hertz. A "cell-activation parameter" defined as the integral of the product of the magnitude of the shear stress and the time during which the stress acts was computed along each of the blood cell pathlines. The Lagrangian tracking of the blood cells shows that a large majority of them are subjected first to very high level of shear-induced "cell-activation" while later on they are entrained in regions of stasis where their residence time can increase up to several cardiac cycles. This cell-activation followed by the entrainment in low shear regions creates the optimal cell-adhesive and inflammatory-mediated degenerative conditions that are postulated to play an important role in the etiology and progressive enlargement of AAAs.

  7. Development and Analysis of Synthetic Composite Materials Emulating Patient AAA Wall Material Properties

    NASA Astrophysics Data System (ADS)

    Margossian, Christa M.

    Abdominal Aortic Aneurysm (AAA) rupture accounts for 14,000 deaths a year in the United States. Since the number of ruptures has not decreased significantly in recent years despite improvements in imaging and surgical procedures, there is a need for an accurate, noninvasive technique capable of establishing rupture risk for specific patients and discriminating lesions at high risk. In this project, synthetic composite materials replicating patient-specific wall stiffness and strength were developed and their material properties evaluated. Composites utilizing various fibers were developed to give a range of stiffness from 1825.75 kPa up through 8187.64 kPa with one base material, Sylgard 170. A range of strength from 631.12 kPa to 1083 kPa with the same base material was also found. By evaluating various base materials and various reinforcing fibers, a catalogue of stiffnesses and strengths was started to allow for adaptation to specific patient properties. Three specific patient properties were well-matched with two composites fabricated: silk thread-reinforced Sylgard 170 and silk thread-reinforced Dragon Skin 20. The composites showed similar stiffnesses to the specific patients while reaching target stresses at particular strains. Not all patients were matched with composites as of yet, but recommendations for future matches are able to be determined. These composites will allow for the future evaluation of flow-induced wall stresses in models replicating patient material properties and geometries.

  8. Impact of calcifications on patient-specific wall stress analysis of abdominal aortic aneurysms.

    PubMed

    Maier, A; Gee, M W; Reeps, C; Eckstein, H-H; Wall, W A

    2010-10-01

    As a degenerative and inflammatory desease of elderly patients, about 80% of abdominal aortic aneurysms (AAA) show considerable wall calcification. Effect of calcifications on computational wall stress analyses of AAAs has been rarely treated in literature so far. Calcifications are heterogeneously distributed, non-fibrous, stiff plaques which are most commonly found near the luminal surface in between the intima and the media layer of the vessel wall. In this study, we therefore investigate the influence of calcifications as separate AAA constituents on finite element simulation results. Thus, three AAAs are reconstructed with regard to intraluminal thrombus (ILT), calcifications and vessel wall. Each patient-specific AAA is simulated twice, once including all three AAA constituents and once neglecting calcifications as it is still common in literature. Parameters for constitutive modeling of calcifications are thereby taken from experiments performed by the authors, showing that calcifications exhibit an almost linear stress-strain behavior with a Young's modulus E ≥ 40 MPa. Simulation results show that calcifications exhibit significant load-bearing effects and reduce stress in adjacent vessel wall. Average stress within the vessel wall is reduced by 9.7 to 59.2%. For two out of three AAAs, peak wall stress decreases when taking calcifications into consideration (8.9 and 28.9%). For one AAA, simulated peak wall stress increases by 5.5% due to stress peaks near calcification borders. However, such stress singularities due to sudden stiffness jumps are physiologically doubtful. It can further be observed that large calcifications are mostly situated in concavely shaped regions of the AAA wall. We deduce that AAA shape is influenced by existent calcifications, thus crucial errors occur if they are neglected in computational wall stress analyses. A general increase in rupture risk for calcified AAAs is doubted.

  9. Impact of calcifications on patient-specific wall stress analysis of abdominal aortic aneurysms.

    PubMed

    Maier, A; Gee, M W; Reeps, C; Eckstein, H-H; Wall, W A

    2010-10-01

    As a degenerative and inflammatory desease of elderly patients, about 80% of abdominal aortic aneurysms (AAA) show considerable wall calcification. Effect of calcifications on computational wall stress analyses of AAAs has been rarely treated in literature so far. Calcifications are heterogeneously distributed, non-fibrous, stiff plaques which are most commonly found near the luminal surface in between the intima and the media layer of the vessel wall. In this study, we therefore investigate the influence of calcifications as separate AAA constituents on finite element simulation results. Thus, three AAAs are reconstructed with regard to intraluminal thrombus (ILT), calcifications and vessel wall. Each patient-specific AAA is simulated twice, once including all three AAA constituents and once neglecting calcifications as it is still common in literature. Parameters for constitutive modeling of calcifications are thereby taken from experiments performed by the authors, showing that calcifications exhibit an almost linear stress-strain behavior with a Young's modulus E ≥ 40 MPa. Simulation results show that calcifications exhibit significant load-bearing effects and reduce stress in adjacent vessel wall. Average stress within the vessel wall is reduced by 9.7 to 59.2%. For two out of three AAAs, peak wall stress decreases when taking calcifications into consideration (8.9 and 28.9%). For one AAA, simulated peak wall stress increases by 5.5% due to stress peaks near calcification borders. However, such stress singularities due to sudden stiffness jumps are physiologically doubtful. It can further be observed that large calcifications are mostly situated in concavely shaped regions of the AAA wall. We deduce that AAA shape is influenced by existent calcifications, thus crucial errors occur if they are neglected in computational wall stress analyses. A general increase in rupture risk for calcified AAAs is doubted. PMID:20143120

  10. Patient-specific models of wall stress in abdominal aortic aneurysm: a comparison between MR and CT

    NASA Astrophysics Data System (ADS)

    de Putter, Sander; Breeuwer, Marcel; van de Vosse, Frans N.; Kose, Ursula; Gerritsen, Frans A.

    2006-03-01

    Finite element method based patient-specific wall stress in abdominal aortic aneurysm (AAA) may provide a more accurate rupture risk predictor than the currently used maximum transverse diameter. In this study, we have investigated the sensitivity of the wall stress in AAA with respect to geometrical variations. We have acquired MR and CT images for four patients with AAA. Three individual users have delineated the AAA vessel wall contours on the image slices. These contours were used to generate synthetic feature images for a deformable model based segmentation method. We investigated the reproducibility and the influence of the user variability on the wall stress. For sufficiently smooth models of the AAA wall, the peak wall stress is reproducible for three out of the four AAA geometries. The 0.99 percentiles of the wall stress show excellent reproducibility for all four AAAs. The variations induced by user variability are larger than the errors caused by the segmentation variability. The influence of the user variability appears to be similar for MR and CT. We conclude that the peak wall stress in AAA is sensitive to small geometrical variations. To increase reproducibility it appears to be best not to allow too much geometrical detail in the simulations. This could be achieved either by using a sufficiently smooth geometry representation or by using a more robust statistical parameter derived from the wall stress distribution.

  11. 2D FSI determination of mechanical stresses on aneurismal walls.

    PubMed

    Veshkina, Natalia; Zbicinski, Ireneusz; Stefańczyk, Ludomir

    2014-01-01

    In this study, a fluid-structure interaction analysis based on the application of patient-specific mechanical parameters of the aneurismal walls was carried out to predict the rupture side during an abdominal aortic aneurysm (AAA). Realistic geometry of the aneurysm was reconstructed from CT data acquired from the patient, and patient-specific flow conditions were applied as boundary conditions. A newly developed non-invasive methodology for determining the mechanical parameters of the patient-specific aortic wall was employed to simulate realistic aortic wall behaviors. Analysis of the results included time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and von Mises stress (VMS). Results of the TAWSS, OSI, and VMS were compared to identify the most probable region of the AAA's rupture. High OSI, which identified the region of wall degradation, coincided with the location of maximum VMS, meaning that the anterior part of the aneurismal wall was a potential region of rupture. PMID:25226953

  12. A simulation framework for estimating wall stress distribution of abdominal aortic aneurysm.

    PubMed

    Qin, Jing; Zhang, Jing; Chui, Chee-Kong; Huang, Wei-Min; Yang, Tao; Pang, Wai-Man; Sudhakar, Venkatesh; Chang, Stephen

    2011-01-01

    Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. In endovascular aneurysm repair, a stent-graft in a catheter is released at the aneurysm site to form a new blood vessel and protect the weakened AAA wall from the pulsatile pressure and, hence, possible rupture. In this paper, we propose a framework to estimate the wall stress distribution of non-stented/stented AAA based on fluid-structure interaction, which is utilized in a surgical simulation system (IRAS). The 3D geometric model of AAA is reconstructed from computed tomography angiographic (CTA) images. Based on our experiments, a combined logarithm and polynomial strain energy equation is applied to model the elastic properties of arterial wall. The blood flow is modeled as laminar, incompressible, and non-Newtonian flow by applying Navier-Stokes equation. The obtained pressure of blood flow is applied as load on the AAA meshes with and without stent-graft and the wall stress distribution is calculated by fluid-structure interaction (FSI) solver equipped in ANSYS. Experiments demonstrate that our analytical results are consistent with clinical observations. PMID:22254456

  13. Improving the Efficiency of Abdominal Aortic Aneurysm Wall Stress Computations

    PubMed Central

    Zelaya, Jaime E.; Goenezen, Sevan; Dargon, Phong T.; Azarbal, Amir-Farzin; Rugonyi, Sandra

    2014-01-01

    An abdominal aortic aneurysm is a pathological dilation of the abdominal aorta, which carries a high mortality rate if ruptured. The most commonly used surrogate marker of rupture risk is the maximal transverse diameter of the aneurysm. More recent studies suggest that wall stress from models of patient-specific aneurysm geometries extracted, for instance, from computed tomography images may be a more accurate predictor of rupture risk and an important factor in AAA size progression. However, quantification of wall stress is typically computationally intensive and time-consuming, mainly due to the nonlinear mechanical behavior of the abdominal aortic aneurysm walls. These difficulties have limited the potential of computational models in clinical practice. To facilitate computation of wall stresses, we propose to use a linear approach that ensures equilibrium of wall stresses in the aneurysms. This proposed linear model approach is easy to implement and eliminates the burden of nonlinear computations. To assess the accuracy of our proposed approach to compute wall stresses, results from idealized and patient-specific model simulations were compared to those obtained using conventional approaches and to those of a hypothetical, reference abdominal aortic aneurysm model. For the reference model, wall mechanical properties and the initial unloaded and unstressed configuration were assumed to be known, and the resulting wall stresses were used as reference for comparison. Our proposed linear approach accurately approximates wall stresses for varying model geometries and wall material properties. Our findings suggest that the proposed linear approach could be used as an effective, efficient, easy-to-use clinical tool to estimate patient-specific wall stresses. PMID:25007052

  14. Reduction of aneurysm pressure and wall stress after endovascular repair of abdominal aortic aneurysm in a canine model.

    PubMed

    Marston, W A; Criado, E; Baird, C A; Keagy, B A

    1996-03-01

    A canine model was designed to evaluate the changes in abdominal aortic aneurysm (AAA) pressure and wall stress after endovascular repair. Eight canines underwent laparotomy and creation of an AAA. The aneurysm was then excluded with a transluminally placed endovascular graft (TPEG) inserted through the right femoral artery and deployed across the AAA to exclude the infrarenal aortic branches from aortic perfusion. Blood pressure and flow data were recorded for 6 hours. The AAA blood pressure decreased from 135 +/- 9.3 mm Hg before exclusion to 45 +/- 17.6 mm Hg at 10 minutes after exclusion (p < 0.001). At 6 hours, AAA blood pressure had declined further to 26 +/- 12.5 mm Hg. Blood flow in the excluded iliac artery decreased from a baseline of 242 +/- 58 ml/min to 41 +/- 29 ml/min 10 minutes after TPEG placement (p < 0.001). At 6 hours, flow was reduced to 12 +/- 3.5 ml/min (p < 0.05 compared with that at 10 minutes). Aortic wall stress was significantly reduced by TPEG placement but was only slightly lower than baseline aortic wall stress before AAA creation. The lumbar arteries were patent with retrograde flow in all cases and were found to be the major contributors to postexclusion aneurysm pressure. Endovascular AAA exclusion results in an immediate decrease in blood pressure and wall stress within the excluded aneurysm, but the aneurysm remains perfused by retrograde flow through the lumbar arteries, which resulted in near-baseline levels of aneurysm wall stress in this canine model. Embolization of patient lumbar vessels at prosthesis placement may further reduce the risk of late rupture. PMID:8733869

  15. Characterizations and Correlations of Wall Shear Stress in Aneurysmal Flow.

    PubMed

    Arzani, Amirhossein; Shadden, Shawn C

    2016-01-01

    Wall shear stress (WSS) is one of the most studied hemodynamic parameters, used in correlating blood flow to various diseases. The pulsatile nature of blood flow, along with the complex geometries of diseased arteries, produces complicated temporal and spatial WSS patterns. Moreover, WSS is a vector, which further complicates its quantification and interpretation. The goal of this study is to investigate WSS magnitude, angle, and vector changes in space and time in complex blood flow. Abdominal aortic aneurysm (AAA) was chosen as a setting to explore WSS quantification. Patient-specific computational fluid dynamics (CFD) simulations were performed in six AAAs. New WSS parameters are introduced, and the pointwise correlation among these, and more traditional WSS parameters, was explored. WSS magnitude had positive correlation with spatial/temporal gradients of WSS magnitude. This motivated the definition of relative WSS gradients. WSS vectorial gradients were highly correlated with magnitude gradients. A mix WSS spatial gradient and a mix WSS temporal gradient are proposed to equally account for variations in the WSS angle and magnitude in single measures. The important role that WSS plays in regulating near wall transport, and the high correlation among some of the WSS parameters motivates further attention in revisiting the traditional approaches used in WSS characterizations. PMID:26592536

  16. Experimental and computational studies on the flow fields in aortic aneurysms associated with deployment of AAA stent-grafts

    NASA Astrophysics Data System (ADS)

    Zhang, Xiwen; Yao, Zhaohui; Zhang, Yan; Xu, Shangdong

    2007-10-01

    Pulsatile flow fields in rigid abdominal aortic aneurysm (AAA) models were investigated numerically, and the simulation results are found in good agreement with particle image velocimetry (PIV) measurements. There are one or more vortexes in the AAA bulge, and a fairly high wall shear stress exists at the distal end, and thus the AAA is in danger of rupture. Medical treatment consists of inserting a vascular stent-graft in the AAA, which would decrease the blood impact to the inner walls and reduce wall shear stress so that the rupture could be prevented. A new computational model, based on porous medium model, was developed and results are documented. Therapeutic effect of the stent-graft was verified numerically with the new model.

  17. Evolution of the wall shear stresses during the progressive enlargement of symmetric abdominal aortic aneurysms

    NASA Astrophysics Data System (ADS)

    Salsac, A.-V.; Sparks, S. R.; Chomaz, J.-M.; Lasheras, J. C.

    2006-08-01

    The changes in the evolution of the spatial and temporal distribution of the wall shear stresses (WSS) and gradients of wall shear stresses (GWSS) at different stages of the enlargement of an abdominal aortic aneurysm (AAA) are important in understanding the aetiology and progression of this vascular disease since they affect the wall structural integrity, primarily via the changes induced on the shape, functions and metabolism of the endothelial cells. Particle image velocimetry (PIV) measurements were performed in in vitro aneurysm models, while changing their geometric parameters systematically. It has been shown that, even at the very early stages of the disease, i.e. increase in the diameter ≤ 50%, the flow separates from the wall and a large vortex ring, usually followed by internal shear layers, is created. These lead to the generation of WSS that drastically differ in mean and fluctuating components from the healthy vessel. Inside the AAA, the mean WSS becomes negative along most of the aneurysmal wall and the magnitude of the WSS can be as low as 26% of the value in a healthy abdominal aorta.

  18. Cell wall remodeling under abiotic stress

    PubMed Central

    Tenhaken, Raimund

    2015-01-01

    Plants exposed to abiotic stress respond to unfavorable conditions on multiple levels. One challenge under drought stress is to reduce shoot growth while maintaining root growth, a process requiring differential cell wall synthesis and remodeling. Key players in this process are the formation of reactive oxygen species (ROS) and peroxidases, which initially cross-link phenolic compounds and glycoproteins of the cell walls causing stiffening. The function of ROS shifts after having converted all the peroxidase substrates in the cell wall. If ROS-levels remain high during prolonged stress, OH°-radicals are formed which lead to polymer cleavage. In concert with xyloglucan modifying enzymes and expansins, the resulting cell wall loosening allows further growth of stressed organs. PMID:25709610

  19. Abdominal Aortic Aneurysm (AAA)

    MedlinePlus

    ... Resources Professions Site Index A-Z Abdominal Aortic Aneurysm (AAA) Abdominal aortic aneurysm (AAA) occurs when atherosclerosis ... aortic aneurysm treated? What is an abdominal aortic aneurysm? The aorta, the largest artery in the body, ...

  20. Image-based biomechanical modeling of aortic wall stress and vessel deformation: response to pulsatile arterial pressure simulations

    NASA Astrophysics Data System (ADS)

    Hazer, Dilana; Bauer, Miriam; Unterhinninghofen, Roland; Dillmann, Rüdiger; Richter, Götz-M.

    2008-03-01

    Image-based modeling of cardiovascular biomechanics may be very helpful for patients with aortic aneurysms to predict the risk of rupture and evaluate the necessity of a surgical intervention. In order to generate a reliable support it is necessary to develop exact patient-specific models that simulate biomechanical parameters and provide individual structural analysis of the state of fatigue and characterize this to the potential of rupture of the aortic wall. The patient-specific geometry used here originates from a CT scan of an Abdominal Aortic Aneurysm (AAA). The computations are based on the Finite Element Method (FEM) and simulate the wall stress distribution and the vessel deformation. The wall transient boundary conditions are based on real time-dependent pressure simulations obtained from a previous computational fluid dynamics study. The physiological wall material properties consider a nonlinear hyperelastic constitutive model, based on realistic ex-vivo analysis of the aneurismal arterial tissue. The results showed complex deformation and stress distribution on the AAA wall. The maximum stresses occurred at the systole and are found around the aneurismal bulge in regions close to inflection points. Biomechanical modeling based on medical images and coupled with patient-specific hemodynamics allows analysing and quantifying the effects of dilatation of the arterial wall due to the pulsatile aortic pressure. It provides a physical and realistic insight into the wall mechanics and enables predictive simulations of AAA growth and assessment of rupture. Further development integrating endovascular models would help evaluating non-invasively individual treatment strategies for optimal placement and improved device design.

  1. Hydroide Storage Vessel wall stress measurements

    SciTech Connect

    Clark, E.A.; Pechersky, M.J.

    1997-07-31

    Holographic Interferometry and strain gauge measurements were used to determine whether a prototype Hydride Storage Vessel (HSV) swelled while it was loaded in eleven stages with hydrogen. Bed swelling is inferred from deformation of the surface of the HSV. No swelling was detected, even after saturating the hydride material inside the HSV. The large chunky morphology of the titanium is likely responsible for the lack of wall stress. This morphology also implies that decay helium that remains in the titanium hydride (that is, helium that is not released as gas to the free volume) should not cause significant wall stresses when the HSV is used for long-term tritium storage. Holographic interferometry proved to be an extremely sensitive technique to measure swelling, having a detection limit of about 3 microns surface displacement.

  2. Stent implantation influence wall shear stress evolution

    NASA Astrophysics Data System (ADS)

    Bernad, S. I.; Totorean, A. F.; Bosioc, A. I.; Petre, I.; Bernad, E. S.

    2016-06-01

    Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. The impact of flow alterations around struts vary as the strut geometrical parameters change. Our results provide data regarding the hemodynamic parameters for the blood flow in both stenosed and stented coronary artery under physiological conditions, namely wall shear stress and pressure drop.

  3. A Near-Wall Reynolds-Stress Closure Without Wall Normals

    NASA Technical Reports Server (NTRS)

    Yuan, S. P.; So, R. M. C.

    1997-01-01

    Turbulent wall-bounded complex flows are commonly encountered in engineering practice and are of considerable interest in a variety of industrial applications. The presence of a wall significantly affects turbulence characteristics. In addition to the wall effects, turbulent wall-bounded flows become more complicated by the presence of additional body forces (e.g. centrifugal force and Coriolis force) and complex geometry. Most near-wall Reynolds stress models are developed from a high-Reynolds-number model which assumes turbulence is homogenous (or quasi-homogenous). Near-wall modifications are proposed to include wall effects in near-wall regions. In this process, wall normals are introduced. Good predictions could be obtained by Reynolds stress models with wall normals. However, ambiguity arises when the models are applied in flows with multiple walls. Many models have been proposed to model turbulent flows. Among them, Reynolds stress models, in which turbulent stresses are obtained by solving the Reynolds stress transport equations, have been proved to be the most successful ones. To apply the Reynolds stress models to wall-bounded flows, near-wall corrections accounting for the wall effects are needed, and the resulting models are called near-wall Reynolds stress models. In most of the existing near-wall models, the near-wall corrections invoke wall normals. These wall-dependent near-wall models are difficult to implement for turbulent flows with complex geometry and may give inaccurate predictions due to the ambiguity of wall normals at corners connecting multiple walls. The objective of this study is to develop a more general and flexible near-wall Reynolds stress model without using any wall-dependent variable for wall-bounded turbulent flows. With the aid of near-wall asymptotic analysis and results of direct numerical simulation, a new near-wall Reynolds stress model (NNWRS) is formulated based on Speziale et al.'s high-Reynolds-stress model with wall

  4. Fluid Characteristics in Abdominal Aortic Aneurysms (AAAs) and Its Correlation to Thrombus Formation

    NASA Astrophysics Data System (ADS)

    Tang, Rubing; Bar-Yoseph, Pinhas Z.; Lasheras, Juan

    2008-11-01

    It has been observed that most large Abdominal Aortic Aneurysms (AAAs) develop an intraluminal thrombus as they progressively enlarge. Previous studies have suggested that the build up of the thrombus may be associated with the altered hemodynamic patterns that arise inside the AAA. We have performed a parametrical computational study of the flow patterns inside enlarging AAA to investigate the possible mechanism controlling the thrombus formation. Pulsatile blood flows were simulated in idealized models of fusiform aneurysms with different dilatation ratios and the effects of shear-activated platelet accumulation and platelet/wall interaction were evaluated based on the calculated flow fields. The platelet activation level (PAL) was determined by computing the integral over time of flow shear stresses exerted over the platelets as they are transported throughout the aneurysm. Our results have shown that the values of PAL in AAAs are in fact smaller than the maximum value obtained in a healthy abdominal aorta. However, we show that the transportation of blood cells towards the wall and the formation of stagnation points on the aneurysm's wall play more significant roles in thrombus formation than PAL.

  5. AAAS: Politics. . . and Science

    ERIC Educational Resources Information Center

    Science News, 1978

    1978-01-01

    Reviews topics discussed during the American Association for the Advancement of Science (AAAS) meeting held in Washington, D.C. Topics included: the equal rights amendment, laetrile, nuclear radiation hazards, sociobiology, and various science topics. (SL)

  6. Science Education at AAAS

    ERIC Educational Resources Information Center

    Livermore, Arthur H.

    1975-01-01

    Describes several programs of the American Association for the Advancement of Science (AAAS) Office of Science Education (OSE), including short courses offered in the natural and social sciences, mathematics, and engineering to college teachers. Discusses several OSE publications. (MLH)

  7. Transcripts and MicroRNAs Responding to Salt Stress in Musa acuminata Colla (AAA Group) cv. Berangan Roots

    PubMed Central

    Lee, Wan Sin; Gudimella, Ranganath; Wong, Gwo Rong; Tammi, Martti Tapani; Khalid, Norzulaani; Harikrishna, Jennifer Ann

    2015-01-01

    Physiological responses to stress are controlled by expression of a large number of genes, many of which are regulated by microRNAs. Since most banana cultivars are salt-sensitive, improved understanding of genetic regulation of salt induced stress responses in banana can support future crop management and improvement in the face of increasing soil salinity related to irrigation and climate change. In this study we focused on determining miRNA and their targets that respond to NaCl exposure and used transcriptome sequencing of RNA and small RNA from control and NaCl-treated banana roots to assemble a cultivar-specific reference transcriptome and identify orthologous and Musa-specific miRNA responding to salinity. We observed that, banana roots responded to salinity stress with changes in expression for a large number of genes (9.5% of 31,390 expressed unigenes) and reduction in levels of many miRNA, including several novel miRNA and banana-specific miRNA-target pairs. Banana roots expressed a unique set of orthologous and Musa-specific miRNAs of which 59 respond to salt stress in a dose-dependent manner. Gene expression patterns of miRNA compared with those of their predicted mRNA targets indicated that a majority of the differentially expressed miRNAs were down-regulated in response to increased salinity, allowing increased expression of targets involved in diverse biological processes including stress signaling, stress defence, transport, cellular homeostasis, metabolism and other stress-related functions. This study may contribute to the understanding of gene regulation and abiotic stress response of roots and the high-throughput sequencing data sets generated may serve as important resources related to salt tolerance traits for functional genomic studies and genetic improvement in banana. PMID:25993649

  8. Transcripts and MicroRNAs Responding to Salt Stress in Musa acuminata Colla (AAA Group) cv. Berangan Roots.

    PubMed

    Lee, Wan Sin; Gudimella, Ranganath; Wong, Gwo Rong; Tammi, Martti Tapani; Khalid, Norzulaani; Harikrishna, Jennifer Ann

    2015-01-01

    Physiological responses to stress are controlled by expression of a large number of genes, many of which are regulated by microRNAs. Since most banana cultivars are salt-sensitive, improved understanding of genetic regulation of salt induced stress responses in banana can support future crop management and improvement in the face of increasing soil salinity related to irrigation and climate change. In this study we focused on determining miRNA and their targets that respond to NaCl exposure and used transcriptome sequencing of RNA and small RNA from control and NaCl-treated banana roots to assemble a cultivar-specific reference transcriptome and identify orthologous and Musa-specific miRNA responding to salinity. We observed that, banana roots responded to salinity stress with changes in expression for a large number of genes (9.5% of 31,390 expressed unigenes) and reduction in levels of many miRNA, including several novel miRNA and banana-specific miRNA-target pairs. Banana roots expressed a unique set of orthologous and Musa-specific miRNAs of which 59 respond to salt stress in a dose-dependent manner. Gene expression patterns of miRNA compared with those of their predicted mRNA targets indicated that a majority of the differentially expressed miRNAs were down-regulated in response to increased salinity, allowing increased expression of targets involved in diverse biological processes including stress signaling, stress defence, transport, cellular homeostasis, metabolism and other stress-related functions. This study may contribute to the understanding of gene regulation and abiotic stress response of roots and the high-throughput sequencing data sets generated may serve as important resources related to salt tolerance traits for functional genomic studies and genetic improvement in banana.

  9. Transcripts and MicroRNAs Responding to Salt Stress in Musa acuminata Colla (AAA Group) cv. Berangan Roots.

    PubMed

    Lee, Wan Sin; Gudimella, Ranganath; Wong, Gwo Rong; Tammi, Martti Tapani; Khalid, Norzulaani; Harikrishna, Jennifer Ann

    2015-01-01

    Physiological responses to stress are controlled by expression of a large number of genes, many of which are regulated by microRNAs. Since most banana cultivars are salt-sensitive, improved understanding of genetic regulation of salt induced stress responses in banana can support future crop management and improvement in the face of increasing soil salinity related to irrigation and climate change. In this study we focused on determining miRNA and their targets that respond to NaCl exposure and used transcriptome sequencing of RNA and small RNA from control and NaCl-treated banana roots to assemble a cultivar-specific reference transcriptome and identify orthologous and Musa-specific miRNA responding to salinity. We observed that, banana roots responded to salinity stress with changes in expression for a large number of genes (9.5% of 31,390 expressed unigenes) and reduction in levels of many miRNA, including several novel miRNA and banana-specific miRNA-target pairs. Banana roots expressed a unique set of orthologous and Musa-specific miRNAs of which 59 respond to salt stress in a dose-dependent manner. Gene expression patterns of miRNA compared with those of their predicted mRNA targets indicated that a majority of the differentially expressed miRNAs were down-regulated in response to increased salinity, allowing increased expression of targets involved in diverse biological processes including stress signaling, stress defence, transport, cellular homeostasis, metabolism and other stress-related functions. This study may contribute to the understanding of gene regulation and abiotic stress response of roots and the high-throughput sequencing data sets generated may serve as important resources related to salt tolerance traits for functional genomic studies and genetic improvement in banana. PMID:25993649

  10. Effects of the flexibility of the arterial wall on the wall shear stresses and wall tension in Abdominal Aortic Aneurysms.

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Fernandez, Miguel; Chomaz, Jean-Marc

    2005-11-01

    As an abdominal aortic aneurysm develops, large changes occur in the composition and structure of the arterial wall, which result in its stiffening. So far, most studies, whether experimental or numerical, have been conducted assuming the walls to be rigid. A numerical simulation of the fluid structure interactions is performed in different models of aneurysms in order to analyze the effects that the wall compliance might have on the flow topology. Both symmetric and non-symmetric models of aneurysms are considered, all idealistic in shape. The wall mechanical properties are varied in order to simulate the progressive stiffening of the walls. The spatial and temporal distributions of wall tension are calculated for the different values of the wall elasticity and compared to the results for the rigid walls. In the case of rigid walls, the calculation of the wall shear stresses and pressure compare very well with experimental results.

  11. A Near-Wall Reynolds-Stress Closure without Wall Normals

    NASA Technical Reports Server (NTRS)

    Yuan, S. P.; So, R. M. C.

    1997-01-01

    With the aid of near-wall asymptotic analysis and results of direct numerical simulation, a new near-wall Reynolds stress model (NNWRS) is formulated based on the SSG high-Reynolds-stress model with wall-independent near-wall corrections. Only one damping function is used for flows with a wide range of Reynolds numbers to ensure that the near-wall modifications diminish away from the walls. The model is able to reproduce complicated flow phenomena induced by complex geometry, such as flow recirculation, reattachment and boundary-layer redevelopment in backward-facing step flow and secondary flow in three-dimensional square duct flow. In simple flows, including fully developed channel/pipe flow, Couette flow and boundary-layer flow, the wall effects are dominant, and the NNWRS model predicts less degree of turbulent anisotropy in the near-wall region compared with a wall-dependent near-wall Reynolds Stress model (NWRS) developed by So and colleagues. The comparison of the predictions given by the two models rectifies the misconception that the overshooting of skin friction coefficient in backward-facing step flow prevalent in those near-wall, models with wall normal is caused by he use of wall normal.

  12. Cell Wall Metabolism in Response to Abiotic Stress.

    PubMed

    Le Gall, Hyacinthe; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine

    2015-01-01

    This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions. PMID:27135320

  13. Cell Wall Metabolism in Response to Abiotic Stress

    PubMed Central

    Gall, Hyacinthe Le; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine

    2015-01-01

    This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions. PMID:27135320

  14. Cell Wall Metabolism in Response to Abiotic Stress.

    PubMed

    Le Gall, Hyacinthe; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine

    2015-02-16

    This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.

  15. AAA Foundation for Traffic Safety

    MedlinePlus

    ... Survey: Teens should be wired less while driving, AAA Arizona says ... - ABC15 Arizona Graduated Licensing Laws - Insurance ... of Top Deadly Mistakes Made by Teen Drivers -- AAA More... Spotlight American Driving Survey This survey provides ...

  16. Wall shear stress estimates in coronary artery constrictions

    NASA Technical Reports Server (NTRS)

    Back, L. H.; Crawford, D. W.

    1992-01-01

    Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.

  17. Aortic wall shear stress in Marfan syndrome.

    PubMed

    Geiger, Julia; Arnold, Raoul; Herzer, Lena; Hirtler, Daniel; Stankovic, Zoran; Russe, Max; Langer, Mathias; Markl, Michael

    2013-10-01

    The aim of this study was to quantify changes in thoracic aortic wall shear stress (WSS) in asymptomatic patients with Marfan syndrome (MFS) compared with healthy controls. WSS in the thoracic aorta was quantified based on time-resolved 3D phase contrast MRI with three-directional velocity encoding (4D flow MRI, temporal resolution ∼44 ms, spatial resolution ∼2.5 mm) in 24 patients with confirmed MFS (age = 18 ± 12 years) and in 12 older healthy volunteers (age = 25 ± 3 years). Diameters of the thoracic aorta normalized to body surface area were similar for both groups. Peak systolic velocity, absolute WSS, time-averaged WSS, circumferential WSS, peak systolic WSS, and WSS eccentricity were calculated in eight analysis planes distributed along the thoracic aorta. Plane-wise comparison revealed significant differences between MFS patients and volunteers in the proximal ascending aorta for peak systolic velocities (1.11 ± 0.23 m/s vs. 1.34 ± 0.18 m/s, P = 0.004) and circumferential WSS (0.14 ± 0.03 N/m(2) vs. 0.11 ± 0.02 N/m(2), P = 0.007). WSS eccentricity was altered in most of the ascending aorta and proximal arch (P = 0.009-0.020). MFS patients demonstrated segmental differences in peak systolic WSS with a significantly higher WSS at the inner curvature in the proximal ascending aorta and at the anterior part in the more distal ascending aorta (P < 0.01). These findings indicate differences in WSS associated with MFS despite similar aortic dimensions compared to controls.

  18. Passive wireless wall shear stress sensors

    NASA Astrophysics Data System (ADS)

    Sells, Jeremy

    The design and realization of the first ever passive wireless wall shear stress sensors are presented. The sensors are capable of directly measuring shear forces, 4 mPa to 4 Pa, created at the solid-fluid boundary of a flow. To capture the spatially small structures of a turbulent flow, a micromachined, variable-capacitor floating element sensor is designed. Passive wireless capability is achieved with the addition of an inductive coil and interrogating antenna. These sensors will enable characterization of complex flow phenomena. The primary benefit of the system is that the sensors operate without the need of a direct electrical connection. This simplifies installation of the sensors and enables their placement in locations where the rest of the system either will not fit or cannot survive. By using a passive wireless technique, a power source is not required, extending the life of the sensor and simplifying fabrication. The system makes use of frequency separation, allowing one interrogating antenna to query multiple sensors configured as an array simultaneously. Two generations of the wireless sensor are presented. The design, fabrication, packaging, and characterization of two first-generation sensors have dynamic ranges of 37 and 52 dB. Following this work, specific design improvements were identified and integrated into a second-generation sensor design, resulting in an improvement to 62 dB dynamic range and an order of magnitude reduction in parasitic capacitance and humidity sensitivity. Ideas for a third generation are presented, but realization of this design is left for future work.

  19. Wall ablation, gas dynamics, and the history of wall stresses in ICF target chambers

    SciTech Connect

    Orth, C.D. )

    1989-09-30

    We calculate the history of wall stresses for spherical aluminum LMF-type ICF target chambers 10 cm thick with 1400-MJ pellets using a simple computer program called CHAMBER that incorporates the physics of first-wall ablation and chamber gas dynamics, including dissociation, ionization, and gas reverberations. By considering the time dependence of the wall stresses, we calculate peak stresses that are higher or lower than previous estimates based on the dynamic formula {sigma}{sub dyn} {approx}Pr/{Delta}R, depending on the radius of the chamber. Here P is the interior pressure, R is the chamber radius, and {Delta}R is the wall thickness. In particular, the previous estimates are too small for chambers with radii R > 4 m or R < 0.5 m, because the ablation impulse dominates the stress for R > 4 m, and the post-ablation pressure impulse dominates for R < 0.5 cm. CHAMER also shows that considerably more wall mass can be ablated after the x-ray-vaporized mass fills the chamber if the thermalized vapor radiates more energy to the wall than the wall can conduct away by heat condition, as in small chambers. Venting of a chamber can reduce the wall stress only to that caused by the ablation impulse, and only for vents with radii comparable to the radius of the chamber. 1 ref., 2 figs.

  20. Local influence of calcifications on the wall mechanics of abdominal aortic aneurysm

    NASA Astrophysics Data System (ADS)

    de Putter, Sander; van de Vosse, Frans N.; Breeuwer, Marcel; Gerritsen, Frans A.

    2006-03-01

    Finite element wall stress simulations on patient-specific models of abdominal aortic aneurysm (AAA) may provide a better rupture risk predictor than the currently used maximum transverse diameter. Calcifications in the wall of AAA lead to a higher maximum wall stress and thus may lead to an elevated rupture risk. The reported material properties for calcifications and the material properties actually used for simulations show great variation. Previous studies have focused on simplified modelling of the calcification shapes within a realistic aneurysm shape. In this study we use an accurate representation of the calcification geometry and a simplified model for the AAA. The objective of this approach is to investigate the influence of the calcification geometry, the material properties and the modelling approach for the computed peak wall stress. For four realistic calcification shapes from standard clinical CT images of AAA, we performed simulations with three distinct modelling approaches, at five distinct elasticity settings. The results show how peak wall stress is sensitive to the material properties of the calcifications. For relatively elastic calcifications, the results from the different modelling approaches agree. Also, for relatively elastic calcifications the computed wall stress in the tissue surrounding the calcifications shows to be insensitive to the exact calcification geometry. For stiffer calcifications the different modelling approaches and the different geometries lead to significantly different results. We conclude that an important challenge for future research is accurately estimating the material properties and the rupture potential of the AAA wall including calcifications.

  1. Geometrical factors influencing the hemodynamic behavior of the AAA stent grafts: essentials for the clinician.

    PubMed

    Georgakarakos, Efstratios; Argyriou, Christos; Schoretsanitis, Nikolaos; Ioannou, Chris V; Kontopodis, Nikolaos; Morgan, Robert; Tsetis, Dimitrios

    2014-12-01

    Endovascular aneurysm repair (EVAR) is considered to be the treatment of choice for abdominal aortic aneurysms (AAA). Despite the initial technical success, EVAR is amenable to early and late complications, among which the migration of the endograft (EG) with subsequent proximal endoleak (Type Ia) leads to repressurization of the AAA sac, exposure to excessive wall stress, and, hence, to potential rupture. This article discusses the influence that certain geometrical factors, such as neck angulation, iliac bifurcation, EG curvature, neck-to-iliac diameter, and length ratios, as well as iliac limbs configuration can exert on the hemodynamic behavior of the EGs. The information provided could help both clinicians and EG manufacturers towards further development and improvement of EG designs and better operational planning. PMID:24938906

  2. On determining wall shear stress in spatially developing two-dimensional wall-bounded flows

    NASA Astrophysics Data System (ADS)

    Mehdi, Faraz; Johansson, T. Gunnar; White, Christopher M.; Naughton, Jonathan W.

    2014-01-01

    A full momentum integral-based method for determining wall shear stress is presented. The method is mathematically exact and has the advantage of having no explicit streamwise gradient terms. It is applicable for flows that change rapidly in the streamwise direction and, in particular, to flows with ill-defined outer boundary conditions or when the measurement grid does not extend over the whole boundary layer thickness. The method is applied to two different experimental plane turbulent wall jet data sets for which independent estimates of wall shear stress were known, and the different results compare favorably. Complications owing to experimental limitations and measurement error in determining wall shear stress from the proposed method are presented, and mitigating strategies are described.

  3. Changes in wall shear stresses in abdominal aortic aneurysms with increasing wall stiffness

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Fernandez, Miguel

    2006-11-01

    During the growth of abdominal aortic aneurysms, local changes occur in the composition and structure of the diseased wall, resulting in its stiffening. A numerical simulation of the fluid structure interactions is performed in idealized models of aneurysms using a finite element method. A full coupling of the equations governing the pulsatile blood flow and the deformation of the compliant wall is undertaken. The effect of the progressive stiffening of the wall is analyzed at various stages in the growth of the aneurysm. Increasing the wall stiffness alters the distribution of wall shear stresses and leads to an increase in their magnitude. The wall compliance is shown to have a more pronounced effect on non-axisymmetric aneurysms, which sustain large displacements. The overall movement of the aneurysm models increases the three-dimensionality of the flow.

  4. Wall shear stress manifolds and near wall flow topology in aneurysms

    NASA Astrophysics Data System (ADS)

    Arzani, Amirhossein; Gambaruto, Alberto M.; Chen, Guoning; Shadden, Shawn C.

    2015-11-01

    Transport of atherogenic and thrombogenic chemicals near the vessel wall highly influences atherosclerosis and thrombosis. The high Schmidt number of these species leads to a thin concentration boundary layer near the wall. The wall shear stress (WSS) vector field can be scaled to obtain the near wall velocity in this region, thus providing first order approximation to near wall transport. In this study, the complex blood flow in patient-specific abdominal aortic aneurysms was considered. Lagrangian tracking of surface-bound tracers representing near wall species was employed to identify Lagrangian coherent structures (LCS) for the WSS surface vector field. The WSS LCS matched the stable and unstable manifolds of saddle type fixed points of the time-average WSS vector field, due to the quasi-steady nature of these near wall transport processes. A WSS exposure time measure is introduced to quantify the concentration of near wall species. The effect of diffusion and normal flow on these structures is investigated. The WSS LCS highly influence the concentration of near wall species, and provide a template for near-wall transport.

  5. A review of near-wall Reynolds-stress

    NASA Technical Reports Server (NTRS)

    So, R. M. C.; Lai, Y. G.; Zhang, H. S.; Hwang, B. C.

    1991-01-01

    The advances made in second-order near-wall turbulence closures are summarized. All closures examined are based on some form of high Reynolds number models for the Reynolds stress and the turbulent kinetic energy dissipation rate equations. Consequently, most near-wall closures proposed to data attempt to modify the high Reynolds number models for the dissipation rate equation so that the resultant models are applicable all the way to the wall. The near-wall closures are examined for their asymptotic behavior so that they can be compared with the proper near-wall behavior of the exact equations. A comparison of the closure's performance in the calculation of a low Reynolds number plane channel flow is carried out. In addition, the closures are evaluated for their ability to predict the turbulence statistics and the limiting behavior of the structure parameters compared to direct simulation data.

  6. Xylem Wall Collapse in Water-Stressed Pine Needles

    PubMed Central

    Cochard, Hervé; Froux, Fabienne; Mayr, Stefan; Coutand, Catherine

    2004-01-01

    Wall reinforcement in xylem conduits is thought to prevent wall implosion by negative pressures, but direct observations of xylem geometry during water stress are still largely lacking. In this study, we have analyzed the changes in xylem geometry during water stress in needles of four pine species (Pinus spp.). Dehydrated needles were frozen with liquid nitrogen, and xylem cross sections were observed, still frozen, with a cryo-scanning electron microscope and an epifluorescent microscope. Decrease in xylem pressure during drought provoked a progressive collapse of tracheids below a specific threshold pressure (Pcollapse) that correlates with the onset of cavitation in the stems. Pcollapse was more negative for species with smaller tracheid diameter and thicker walls, suggesting a tradeoff between xylem efficiency, xylem vulnerability to collapse, and the cost of wall stiffening. Upon severe dehydration, tracheid walls were completely collapsed, but lumens still appeared filled with sap. When dehydration proceeded further, tracheids embolized and walls relaxed. Wall collapse in dehydrated needles was rapidly reversed upon rehydration. We discuss the implications of this novel hydraulic trait on the xylem function and on the understanding of pine water relations. PMID:14657404

  7. Pressure and wall shear stress in blood hammer - Analytical theory.

    PubMed

    Mei, Chiang C; Jing, Haixiao

    2016-10-01

    We describe an analytical theory of blood hammer in a long and stiffened artery due to sudden blockage. Based on the model of a viscous fluid in laminar flow, we derive explicit expressions of oscillatory pressure and wall shear stress. To examine the effects on local plaque formation we also allow the blood vessel radius to be slightly nonuniform. Without resorting to discrete computation, the asymptotic method of multiple scales is utilized to deal with the sharp contrast of time scales. The effects of plaque and blocking time on blood pressure and wall shear stress are studied. The theory is validated by comparison with existing water hammer experiments. PMID:27474207

  8. Pressure and wall shear stress in blood hammer - Analytical theory.

    PubMed

    Mei, Chiang C; Jing, Haixiao

    2016-10-01

    We describe an analytical theory of blood hammer in a long and stiffened artery due to sudden blockage. Based on the model of a viscous fluid in laminar flow, we derive explicit expressions of oscillatory pressure and wall shear stress. To examine the effects on local plaque formation we also allow the blood vessel radius to be slightly nonuniform. Without resorting to discrete computation, the asymptotic method of multiple scales is utilized to deal with the sharp contrast of time scales. The effects of plaque and blocking time on blood pressure and wall shear stress are studied. The theory is validated by comparison with existing water hammer experiments.

  9. Optimization of multiplane μPIV for wall shear stress and wall topography characterization

    NASA Astrophysics Data System (ADS)

    Rossi, Massimiliano; Lindken, Ralph; Westerweel, Jerry

    2010-02-01

    Multiplane μPIV can be utilized to determine the wall shear stress and wall topology from the measured flow over a structured surface. A theoretical model was developed to predict the measurement error for the surface topography and shear stress, based on a theoretical analysis of the precision in PIV measurements. The main parameters that affect the accuracy of the measurement are identified. The effect of different parameter settings is studied by means of Monte Carlo simulations, and the results are compared with an experimental test case. The results are used to determine the recommended parameter settings for this measurement approach.

  10. Differential expression of TRAIL and its receptors relative to calcification in AAA

    SciTech Connect

    Liu, Xun . E-mail: mpscrs@bath.ac.uk; Winrow, Vivienne R.; Horrocks, Michael; Stevens, Cliff R.

    2007-06-22

    Abdominal aortic aneurysm (AAA) is commonly associated with atherosclerosis. Human AAA tissue displays cells undergoing all stages of apoptosis. Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumour cells but not in normal cells. It has death receptors and decoy receptors. An inhibitor of TRAIL, osteoprotegerin (OPG), is involved in osteogenesis and vascular calcification. We investigated TRAIL and its receptors in AAA compared within normal aorta (NA). Both qualitative and quantitative analyses of calcification in AAA walls were determined using Von Kossa staining and pre-operation computer tomography (CT) scans. There was a significant difference in calcification level at different locations in the AAA wall (p < 0.05). Apoptosis was confirmed in AAA by TUNEL assay. A significant difference in TRAIL and its receptor expression was observed between normal aortae and AAA (p < 0.05). Significant differences were also observed between tissues displaying different extents of calcification for TRAIL mRNA (p < 0.05) by RT-PCR examination and OPG protein (p < 0.01) by protein blotting examination. We propose that this pattern of expression of TRAIL and its receptors may contribute to AAA formation and calcification in the AAA wall.

  11. Vascular wall stress during intravascular optical coherence tomography imaging

    NASA Astrophysics Data System (ADS)

    Sun, Cuiru; Yang, Victor

    2015-03-01

    Biomechanical properties of arterial wall is crucial for understanding the changes in the cardiovascular system. Catheters are used during intravascular optical coherence tomography (IVOCT) imaging. The presence of a catheter alters the flow field, pressure distribution and frictional resistance to flow in an artery. In this paper, we first study the transmural stress distribution of the catheterized vessel. COMSOL (COMSOL 4.4) was used to simulate the blood flow induced deformation in a catheterized vessel. Blood is modeled as an incompressible Newtonian fluid. Stress distribution from an three-layer vascular model with an eccentric catheter are simulated, which provides a general idea about the distribution of the displacement and the stress. Optical coherence elastography techniques were then applied to porcine carotid artery samples to look at the deformation status of the vascular wall during saline or water injection. Preliminary simulation results show nonuniform stress distribution in the circumferential direction of the eccentrically catheterized vascular model. Three strain rate methods were tested for intravascular OCE application. The tissue Doppler method has the potential to be further developed to image the vascular wall biomechnical properties in vivo. Although results in this study are not validated quantitatively, the experiments and methods may be valuable for intravascular OCE studies, which may provide important information for cardiovascular disease prevention, diagnosis and treatment.

  12. Wall shear stress measurements using a new transducer

    NASA Technical Reports Server (NTRS)

    Vakili, A. D.; Wu, J. M.; Lawing, P. L.

    1986-01-01

    A new instrument has been developed for direct measurement of wall shear stress. This instrument is simple and symmetric in design with small moving mass and no internal friction. Features employed in the design of this instrument eliminate most of the difficulties associated with the traditional floating element balances. Vibration problems associated with the floating element skin friction balances have been found to be minimized by the design features and optional damping provided. The unique design of this instrument eliminates or reduces the errors associated with conventional floating-element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Measurement made in three different tunnels show good agreement with theory and data obtained by the floating element devices.

  13. Dynamic response of wall shear stress on the stenosed artery.

    PubMed

    Sen, S; Chakravarty, S

    2009-10-01

    The present study deals with an appropriate mathematical model of an artery in the presence of constriction in which the generated wall shear stress due to blood flow is analysed. The geometry of the stenosed arterial segment in the diseased state, causing malfunction of the cardiovascular system, is formed mathematically. The flowing blood contained in the stenosed artery is treated as non-Newtonian and the flow is considered to be two-dimensional. The motion of the arterial wall and its effect on local fluid mechanics is not ruled out from the present pursuit. The flow analysis applies the time-dependent, two-dimensional incompressible nonlinear Navier-Stokes equations for non-Newtonian fluids. The flow-field can be obtained primarily following the radial coordinate transformation, using the appropriate boundary conditions and finally adopting a suitable finite difference scheme numerically. The influences of flow unsteadiness, the arterial wall distensibility and the presence of stenosis on the flow-field and the wall shear stresses are quantified in order to indicate the susceptibility to atherosclerotic lesions and thereby to validate the applicability of the present theoretical model. PMID:19294542

  14. Wall stress and deformation analysis in a numerical model of pulse wave propagation.

    PubMed

    He, Fan; Hua, Lu; Gao, Lijian

    2015-01-01

    To simulate pulse wave propagation, we set up a wave propagation model using blood-wall interaction in previous work. In this paper, our purpose is to investigate wall stress and deformation of the wave propagation model. The finite element method is employed for solving the governing equations of blood and wall. Our results suggest that there are two peaks in the circumferential stress and strain distributions of the normal model. The stress and strain values change with the varieties of different factors, such as wall thickness and vessel diameter. The results indicate that different parameters of fluid and tube wall have remarked impact on wall stress and deformation. PMID:26406044

  15. Wall stress and deformation analysis in a numerical model of pulse wave propagation.

    PubMed

    He, Fan; Hua, Lu; Gao, Lijian

    2015-01-01

    To simulate pulse wave propagation, we set up a wave propagation model using blood-wall interaction in previous work. In this paper, our purpose is to investigate wall stress and deformation of the wave propagation model. The finite element method is employed for solving the governing equations of blood and wall. Our results suggest that there are two peaks in the circumferential stress and strain distributions of the normal model. The stress and strain values change with the varieties of different factors, such as wall thickness and vessel diameter. The results indicate that different parameters of fluid and tube wall have remarked impact on wall stress and deformation.

  16. Reynolds stress closure modeling in wall-bounded flows

    NASA Technical Reports Server (NTRS)

    Durbin, Paul A.

    1993-01-01

    This report describes two projects. Firstly, a Reynolds stress closure for near-wall turbulence is described. It was motivated by the simpler k-epsilon-(v-bar(exp 2)) model described in last year's annual research brief. Direct Numerical Simulation of three-dimensional channel flow shows a curious decrease of the turbulent kinetic energy. The second topic of this report is a model which reproduces this effect. That model is described and used to discuss the relevance of the three dimensional channel flow simulation to swept wing boundary layers.

  17. Stress analysis for wall structure in mobile hot cell design

    NASA Astrophysics Data System (ADS)

    Bahrin, Muhammad Hannan; Rahman, Anwar Abdul; Hamzah, Mohd Arif; Mamat, Mohd Rizal; Azman, Azraf; Hasan, Hasni

    2016-01-01

    Malaysian Nuclear Agency is developing a Mobile Hot Cell (MHC) in order to handle and manage Spent High Activity Radioactive Sources (SHARS) such as teletherapy heads and irradiators. At present, there are only two units of MHC in the world, in South Africa and China. Malaysian Mobile Hot cell is developed by Malaysian Nuclear Agency with the assistance of IAEA expert, based on the design of South Africa and China, but with improved features. Stress analysis has been performed on the design in order to fulfil the safety requirement in operation of MHC. This paper discusses the loading analysis effect from the sand to the MHC wall structure.

  18. Mathematical Modeling of Intravascular Blood Coagulation under Wall Shear Stress.

    PubMed

    Rukhlenko, Oleksii S; Dudchenko, Olga A; Zlobina, Ksenia E; Guria, Georgy Th

    2015-01-01

    Increased shear stress such as observed at local stenosis may cause drastic changes in the permeability of the vessel wall to procoagulants and thus initiate intravascular blood coagulation. In this paper we suggest a mathematical model to investigate how shear stress-induced permeability influences the thrombogenic potential of atherosclerotic plaques. Numerical analysis of the model reveals the existence of two hydrodynamic thresholds for activation of blood coagulation in the system and unveils typical scenarios of thrombus formation. The dependence of blood coagulation development on the intensity of blood flow, as well as on geometrical parameters of atherosclerotic plaque is described. Relevant parametric diagrams are drawn. The results suggest a previously unrecognized role of relatively small plaques (resulting in less than 50% of the lumen area reduction) in atherothrombosis and have important implications for the existing stenting guidelines.

  19. Mathematical Modeling of Intravascular Blood Coagulation under Wall Shear Stress

    PubMed Central

    Rukhlenko, Oleksii S.; Dudchenko, Olga A.; Zlobina, Ksenia E.; Guria, Georgy Th.

    2015-01-01

    Increased shear stress such as observed at local stenosis may cause drastic changes in the permeability of the vessel wall to procoagulants and thus initiate intravascular blood coagulation. In this paper we suggest a mathematical model to investigate how shear stress-induced permeability influences the thrombogenic potential of atherosclerotic plaques. Numerical analysis of the model reveals the existence of two hydrodynamic thresholds for activation of blood coagulation in the system and unveils typical scenarios of thrombus formation. The dependence of blood coagulation development on the intensity of blood flow, as well as on geometrical parameters of atherosclerotic plaque is described. Relevant parametric diagrams are drawn. The results suggest a previously unrecognized role of relatively small plaques (resulting in less than 50% of the lumen area reduction) in atherothrombosis and have important implications for the existing stenting guidelines. PMID:26222505

  20. Space-time characteristics of wall-pressure and wall shear-stress fluctuations in wall-modeled large eddy simulation

    NASA Astrophysics Data System (ADS)

    Park, George Ilhwan; Moin, Parviz

    2016-06-01

    We report the space-time characteristics of the wall-pressure fluctuations and wall shear-stress fluctuations from wall-modeled large eddy simulation (WMLES) of a turbulent channel flow at Reτ=2000 . Two standard zonal wall models (equilibrium stress model and nonequilibrium model based on unsteady RANS) are employed, and it is shown that they yield similar results in predicting these quantities. The wall-pressure and wall shear-stress fields from WMLES are analyzed in terms of their r.m.s. fluctuations, spectra, two-point correlations, and convection velocities. It is demonstrated that the resolution requirement for predicting the wall-pressure fluctuations is more stringent than that for predicting the velocity. At least δ /Δ x >20 and δ /Δ z >30 are required to marginally resolve the integral length scales of the pressure-producing eddies near the wall. Otherwise, the pressure field is potentially aliased. Spurious high wave number modes dominate in the streamwise direction, and they contaminate the pressure spectra leading to significant overprediction of the second-order pressure statistics. When these conditions are met, the pressure statistics and spectra at low wave number or low frequency agree well with the DNS and experimental data. On the contrary, the wall shear-stress fluctuations, modeled entirely through the RANS-based wall models, are largely underpredicted and relatively insensitive to the grid resolution. The short-time, small-scale near-wall eddies, which are neither resolved nor modeled adequately in the wall models, seem to be important for accurate prediction of the wall shear-stress fluctuations.

  1. Wall shear stress indicators in abnormal aortic geometries

    NASA Astrophysics Data System (ADS)

    Prahl Wittberg, Lisa; van Wyk, Stevin; Fuchs, Laszlo; Gutmark, Ephraim; Gutmark-Little, Iris

    2015-11-01

    Cardiovascular disease, such as atherosclerosis, occurs at specific locations in the arterial tree. Characterizing flow and forces at these locations is crucial to understanding the genesis of disease. Measures such as time average wall shear stress, oscillatory shear index, relative residence time and temporal wall shear stress gradients have been shown to identify plaque prone regions. The present paper examines these indices in three aortic geometries obtained from patients whose aortas are deformed due to a genetic pathology and compared to one normal geometry. This patient group is known to be prone to aortic dissection and our study aims to identify early indicators that will enable timely intervention. Data obtained from cardiac magnetic resonance imaging is used to reconstruct the aortic arch. The local unsteady flow characteristics are calculated, fully resolving the flow field throughout the entire cardiac cycle. The Quemada model is applied to account for the non-Newtonian properties of blood, an empirical model valid for different red blood cell loading. The impact of the deformed aortic geometries is analyzed to identify flow patterns that could lead to arterial disease at certain locations.

  2. The Lon AAA+ protease.

    PubMed

    Gur, Eyal

    2013-01-01

    As the first ATP-dependent protease to be identified, Lon holds a special place in the history of cellular biology. In fact, the concept of ATP-dependent protein degradation was established through the findings that led to the discovery of Lon. Therefore, this chapter begins with a historical perspective, describing the milestones that led to the discovery of Lon and ATP-dependent proteolysis, starting from the early findings in the 1960s until the demonstration of Lon's ATP-dependent proteolytic activity in vitro, in 1981. Most of our knowledge on Lon derives from studies of the Escherichia coli Lon ortholog, and, therefore, most of this chapter relates to this particular enzyme. Nonetheless, Lon is not only found in most bacterial species, it is also found in Archaea and in the mitochondrion and chloroplast of eukaryotic cells. Therefore many of the conclusions gained from studies on the E. coli enzyme are relevant to Lon proteases in other organisms. Lon, more than any other bacterial or organellar protease, is associated with the degradation of misfolded proteins and protein quality control. In addition, Lon also degrades many regulatory proteins that are natively folded, thus it also plays a prominent role in regulation of physiological processes. Throughout the years, many Lon substrates have been identified, confirming its role in the regulation of diverse cellular processes, including cell division, DNA replication, differentiation, and adaptation to stress conditions. Some examples of these functions are described and discussed here, as is the role of Lon in the degradation of misfolded proteins and in protein quality control. Finally, this chapter deals with the exquisite sensitivity of protein degradation inside a cell. How can a protease distinguish so many substrates from cellular proteins that should not be degraded? Can the specificity of a protease be regulated according to the physiological needs of a cell? This chapter thus broadly discusses the

  3. Wall Morphology, Blood Flow and Wall Shear Stress: MR Findings in Patients with Peripheral Artery Disease

    PubMed Central

    Galizia, Mauricio S.; Barker, Alex; Liao, Yihua; Collins, Jeremy; Carr, James; McDermott, Mary; Markl, Michael

    2014-01-01

    Objectives: To investigate the influence of atherosclerotic plaques on femoral haemodynamics assessed by 2D phase contrast (PC) MRI with three-directional velocity encoding. Methods: During one year, patients with peripheral artery disease and an ankle brachial index <1.00 were enrolled. After IRB approval and written informed consent, 44 patients (age=70±12 years) underwent common femoral artery MRI. Patients with contraindications for MRI were excluded. Sequences included 2D time-of-flight, proton-density, T1-, and T2-weighted MRI. ECG-gated 2D PC-MRI with 3D velocity encoding was acquired. A radiologist classified images in five categories. Blood flow, velocity, and WSS along the vessel circumference were quantified from the PC-MRI data. Results: The acquired images were of good quality for interpretation. There were no image quality problems related to poor ECG-gating or slice positioning. Velocities, oscillatory shear stress, and total flow were similar between patients with normal arteries and wall thickening/plaque. Patients with plaques demonstrated regionally increased peak systolic WSS and enhanced WSS eccentricity. Conclusions: Combined multi-contrast morphological imaging of the peripheral arterial wall with PC-MRI with 3 directional velocity encoding is a feasible technique. Further study is needed to determine whether flow is an appropriate marker for altered endothelial cell function, vascular remodelling, and plaque progression. PMID:24326757

  4. Inhibition of early AAA formation by aortic intraluminal pentagalloyl glucose (PGG) infusion in a novel porcine AAA model

    PubMed Central

    Kloster, Brian O.; Lund, Lars; Lindholt, Jes S.

    2016-01-01

    Background The vast majority of abdominal aortic aneurysms found in screening programs are small, and as no effective treatment exits, many will expand until surgery is indicated. Therefore, it remains intriguing to develop a safe and low cost treatment of these small aneurysms, that is able to prevent or delay their expansion. In this study, we investigated whether intraluminal delivered pentagalloyl glucose (PGG) can impair the early AAA development in a porcine model. Methods The infrarenal aorta was exposed in thirty pigs. Twenty underwent an elastase based AAA inducing procedure and ten of these received an additional intraluminal PGG infusion. The final 10 were sham operated and served as controls. Results All pigs who only had an elastase infusion developed macroscopically expanding AAAs. In pigs treated with an additional PGG infusion the growth rate of the AP-diameter rapidly returned to physiological values as seen in the control group. In the elastase group, histology revealed more or less complete resolution of the elastic lamellae in the media while they were more abundant, coherent and structurally organized in the PGG group. The control group displayed normal physiological growth and histology. Conclusion In our model, intraluminal delivered PGG is able to penetrate the aortic wall from the inside and impair the early AAA development by stabilizing the elastic lamellae and preserving their integrity. The principle holds a high clinical potential if it can be translated to human conditions, since it, if so, potentially could represent a new drug for stabilizing small abdominal aneurysms. PMID:27144001

  5. Estimation of wall properties and wall strength of aortic aneurysms using modern imaging techniques. One more step towards a patient-specific assessment of aneurysm rupture risk.

    PubMed

    Kontopodis, Nikolaos; Georgakarakos, Efstratios; Metaxa, Eleni; Pagonidis, Konstantinos; Papaharilaou, Yannis; Ioannou, Christos V

    2013-08-01

    Abdominal aortic aneurysmal disease is a major health problem with rupture representing its main complication accompanied by great mortality. Elective repair is currently performed with mortality rates <3%, based upon size or expansion rate, with a recommended threshold of 5.5 cm maximum diameter or >1cm/year enlargement. It is well established that even small AAAs without indication for surgical repair can experience rupture with catastrophic outcomes whereas larger aneurysms often remain intact for a long period. It is recognized, therefore, that the currently used, maximum diameter criterion can not accurately predict AAAs evolution. There is increasing interest in the role of patient-specific biomechanical profiling of AAA development and rupture. Biomechanically, rupture of a vessel occurs when intravascular forces exceed vessel wall structural endurance. Peak Wall Stress (PWS) has been previously shown to better identify AAAs prone to rupture than maximum diameter, but currently stress analysis takes into account several assumptions that influence results to a large extent and limit their use. Moreover stress represents only one of two determinants of rupture risk according to the biomechanical perspective. Wall strength and mechanical properties on the other hand cannot be assessed in vivo but only ex vivo through mechanical studies with mean values of these parameters taken into account for rupture risk estimations. New possibilities in the field of aortic imaging offer promising tools for the validation and advancement of stress analysis and the in vivo evaluation of AAAs' wall properties and wall strength. Documentation of aortic wall motion during cardiac cycle is now feasible through ECG-gated multi-detector CT imaging offering new possibilities towards an individualized method for rupture risk and expansion-rate predictions based on data acquired in vivo. PMID:23714223

  6. Relation between wall shear stress and carotid artery wall thickening MRI versus CFD.

    PubMed

    Cibis, Merih; Potters, Wouter V; Selwaness, Mariana; Gijsen, Frank J; Franco, Oscar H; Arias Lorza, Andres M; de Bruijne, Marleen; Hofman, Albert; van der Lugt, Aad; Nederveen, Aart J; Wentzel, Jolanda J

    2016-03-21

    Wall shear stress (WSS), a parameter associated with endothelial function, is calculated by computational fluid dynamics (CFD) or phase-contrast (PC) MRI measurements. Although CFD is common in WSS (WSSCFD) calculations, PC-MRI-based WSS (WSSMRI) is more favorable in population studies; since it is straightforward and less time consuming. However, it is not clear if WSSMRI and WSSCFD show similar associations with vascular pathology. Our aim was to test the associations between wall thickness (WT) of the carotid arteries and WSSMRI and WSSCFD. The subjects (n=14) with an asymptomatic carotid plaque who underwent MRI scans two times within 4 years of time were selected from the Rotterdam Study. We compared WSSCFD and WSSMRI at baseline and follow-up. Baseline WSSMRI and WSSCFD values were divided into 3 categories representing low, medium and high WSS tertiles. WT of each tertile was compared by a one-way ANOVA test. The WSSMRI and WSSCFD were 0.50±0.13Pa and 0.73±0.25Pa at baseline. Although WSSMRI was underestimated, a significant regression was found between WSSMRI and WSSCFD (r(2)=0.71). No significant difference was found between baseline and follow-up WSS by CFD and MRI-based calculations. The WT at baseline was 1.36±0.16mm and did not change over time. The WT was 1.55±0.21mm in low, 1.33±0.20mm in medium and 1.21±0.21mm in the high WSSMRI tertiles. Similarly, the WT was 1.49±0.21mm in low, 1.33±0.20mm in medium and 1.26±0.21mm in high WSSCFD tertiles. We found that WSSMRI and WSSCFD were inversely related with WT. WSSMRI and WSSCFD patterns were similar although MRI-based calculations underestimated WSS.

  7. KRE5 Suppression Induces Cell Wall Stress and Alternative ER Stress Response Required for Maintaining Cell Wall Integrity in Candida glabrata.

    PubMed

    Tanaka, Yutaka; Sasaki, Masato; Ito, Fumie; Aoyama, Toshio; Sato-Okamoto, Michiyo; Takahashi-Nakaguchi, Azusa; Chibana, Hiroji; Shibata, Nobuyuki

    2016-01-01

    The maintenance of cell wall integrity in fungi is required for normal cell growth, division, hyphae formation, and antifungal tolerance. We observed that endoplasmic reticulum stress regulated cell wall integrity in Candida glabrata, which possesses uniquely evolved mechanisms for unfolded protein response mechanisms. Tetracycline-mediated suppression of KRE5, which encodes a predicted UDP-glucose:glycoprotein glucosyltransferase localized in the endoplasmic reticulum, significantly increased cell wall chitin content and decreased cell wall β-1,6-glucan content. KRE5 repression induced endoplasmic reticulum stress-related gene expression and MAP kinase pathway activation, including Slt2p and Hog1p phosphorylation, through the cell wall integrity signaling pathway. Moreover, the calcineurin pathway negatively regulated cell wall integrity, but not the reduction of β-1,6-glucan content. These results indicate that KRE5 is required for maintaining both endoplasmic reticulum homeostasis and cell wall integrity, and that the calcineurin pathway acts as a regulator of chitin-glucan balance in the cell wall and as an alternative mediator of endoplasmic reticulum stress in C. glabrata. PMID:27548283

  8. KRE5 Suppression Induces Cell Wall Stress and Alternative ER Stress Response Required for Maintaining Cell Wall Integrity in Candida glabrata

    PubMed Central

    Sasaki, Masato; Ito, Fumie; Aoyama, Toshio; Sato-Okamoto, Michiyo; Takahashi-Nakaguchi, Azusa; Chibana, Hiroji; Shibata, Nobuyuki

    2016-01-01

    The maintenance of cell wall integrity in fungi is required for normal cell growth, division, hyphae formation, and antifungal tolerance. We observed that endoplasmic reticulum stress regulated cell wall integrity in Candida glabrata, which possesses uniquely evolved mechanisms for unfolded protein response mechanisms. Tetracycline-mediated suppression of KRE5, which encodes a predicted UDP-glucose:glycoprotein glucosyltransferase localized in the endoplasmic reticulum, significantly increased cell wall chitin content and decreased cell wall β-1,6-glucan content. KRE5 repression induced endoplasmic reticulum stress-related gene expression and MAP kinase pathway activation, including Slt2p and Hog1p phosphorylation, through the cell wall integrity signaling pathway. Moreover, the calcineurin pathway negatively regulated cell wall integrity, but not the reduction of β-1,6-glucan content. These results indicate that KRE5 is required for maintaining both endoplasmic reticulum homeostasis and cell wall integrity, and that the calcineurin pathway acts as a regulator of chitin-glucan balance in the cell wall and as an alternative mediator of endoplasmic reticulum stress in C. glabrata. PMID:27548283

  9. Thin-walled butt welded stress intensification factors and stress indices

    SciTech Connect

    Glickstein, A.B.

    1995-11-01

    The baseline for the butt weld stress intensification factor (SIF or i-factors) of 1.0 for nominal pipe wall thickness equal to or greater than 0.237 inch is largely based on the Markl`s fatigue tests performed during the late forties and early fifties. An attempt to address piping products with nominal wall thicknesses less than 0.237 inch has resulted in the ASME Section 3 Code increasing the SIF to a maximum value of 1.9 in lieu of 1.0 for a girth butt weld. A corresponding increase in the C-stress index for Class 1 girth butt welds has also been incorporated into the ASME Section 3 Code for Class 1 components. Based on an evaluation of data obtained from the fatigue testing of eleven thin-walled Alloy 625 girth butt welds (t = 0.103 inches), it has been shown that an i-factor of 1.0 is adequate for thicknesses less than 0.237.

  10. Solutions of the Maxwell viscoelastic equations for displacement and stress distributions within the arterial wall.

    PubMed

    Hodis, S; Zamir, M

    2008-08-01

    Mechanical events within the thickness of the vessel wall caused by pulsatile blood flow are considered, with focus on axial dynamics of the wall, driven by the oscillatory drag force exerted by the fluid on the endothelial layer of the wall. It is shown that the focus on the axial direction makes it possible to derive simplified equations of motion which, combined with a viscoelastic model of the wall material, makes it possible in turn to obtain solutions in closed form for the displacement and stress of material elements within the wall. The viscoelastic model allows a study of the dynamics of the wall with different ratios of viscosity to elasticity of the wall material, to mimic changes in the properties of the arterial wall caused by disease or aging. It is found that when the wall is highly viscous the displacements and stresses caused by the flow are confined to a thin layer close to the inner boundary of the wall, while as the wall material becomes less viscous and more rigid the displacements and stresses spread deeper into the thickness of the wall to affect most of its elements.

  11. Microflow-induced shear stress on biomaterial wall by ultrasound-induced encapsulated microbubble oscillation

    NASA Astrophysics Data System (ADS)

    Hu, Ji-Wen; Qian, Sheng-You; Sun, Jia-Na; Lü, Yun-Bin; Hu, Ping

    2015-09-01

    A model of an ultrasound-driven encapsulated microbubble (EMB) oscillation near biomaterial wall is presented and used for describing the microflow-induced shear stress on the wall by means of a numerical method. The characteristic of the model lies in the explicit treatment of different types of wall for the EMB responses. The simulation results show that the radius-time change trends obtained by our model are consistent with the existing models and experimental results. In addition, the effect of the elastic wall on the acoustic EMB response is stronger than that of the rigid wall, and the shear stress on the elastic wall is larger than that of the rigid wall. The closer the EMB to the wall, the greater the shear stress on the wall. The substantial shear stress on the wall surface occurs inside a circular zone with a radius about two-thirds of the bubble radius. This paper may be of interest in the study of potential damage mechanisms to the microvessel for drug and gene delivery due to sonoporation. Projects supported by the National Natural Science Foundation of China (Grant Nos. 11174077 and 11474090), the Natural Science Foundation of Hunan Province, China (Grant No. 13JJ3076), the Science Research Program of Education Department of Hunan Province, China (Grant No. 14A127), and the Doctoral Fund of University of South China (Grant No. 2011XQD46).

  12. Combined Visualization of Wall Thickness and Wall Shear Stress for the Evaluation of Aneurysms.

    PubMed

    Glaßer, Sylvia; Lawonn, Kai; Hoffmann, Thomas; Skalej, Martin; Preim, Bernhard

    2014-12-01

    For an individual rupture risk assessment of aneurysms, the aneurysm's wall morphology and hemodynamics provide valuable information. Hemodynamic information is usually extracted via computational fluid dynamic (CFD) simulation on a previously extracted 3D aneurysm surface mesh or directly measured with 4D phase-contrast magnetic resonance imaging. In contrast, a noninvasive imaging technique that depicts the aneurysm wall in vivo is still not available. Our approach comprises an experiment, where intravascular ultrasound (IVUS) is employed to probe a dissected saccular aneurysm phantom, which we modeled from a porcine kidney artery. Then, we extracted a 3D surface mesh to gain the vessel wall thickness and hemodynamic information from a CFD simulation. Building on this, we developed a framework that depicts the inner and outer aneurysm wall with dedicated information about local thickness via distance ribbons. For both walls, a shading is adapted such that the inner wall as well as its distance to the outer wall is always perceivable. The exploration of the wall is further improved by combining it with hemodynamic information from the CFD simulation. Hence, the visual analysis comprises a brushing and linking concept for individual highlighting of pathologic areas. Also, a surface clustering is integrated to provide an automatic division of different aneurysm parts combined with a risk score depending on wall thickness and hemodynamic information. In general, our approach can be employed for vessel visualization purposes where an inner and outer wall has to be adequately represented. PMID:26356964

  13. Accuracy and grid convergence of wall shear stress measured by lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Kang, Xiuying; Dun, Zhiya

    2014-04-01

    Based on a two-dimensional Poiseuille and Wormersley flow, accuracy and grid convergence of velocity, shear stress and wall shear stress (WSS) measurements were investigated using the single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann models under various open and wall boundary conditions. The results showed that grid convergence of shear stress and WSS are not consistent with that of velocity when flow channels are not aligned to the grids, and strongly rely on the used wall boundary conditions. And the MRT model is slightly superior to the SRT when simulating the complicated border flow. Moreover the WSS should be approximately calculated on the fluid nodes closest to walls under the curved boundary (CB) condition but not for the bounce-back (BB) boundary scheme. As applications, distributions of WSS in a wavy-walled channel and distensible carotid artery were simulated which would much more depend on local roughness of vessel intima than channel diameters.

  14. Effect of Wall Shear Stress on Corrosion Inhibitor Film Performance

    NASA Astrophysics Data System (ADS)

    Canto Maya, Christian M.

    In oil and gas production, internal corrosion of pipelines causes the highest incidence of recurring failures. Ensuring the integrity of ageing pipeline infrastructure is an increasingly important requirement. One of the most widely applied methods to reduce internal corrosion rates is the continuous injection of chemicals in very small quantities, called corrosion inhibitors. These chemical substances form thin films at the pipeline internal surface that reduce the magnitude of the cathodic and/or anodic reactions. However, the efficacy of such corrosion inhibitor films can be reduced by different factors such as multiphase flow, due to enhanced shear stress and mass transfer effects, loss of inhibitor due to adsorption on other interfaces such as solid particles, bubbles and droplets entrained by the bulk phase, and due to chemical interaction with other incompatible substances present in the stream. The first part of the present project investigated the electrochemical behavior of two organic corrosion inhibitors (a TOFA/DETA imidazolinium, and an alkylbenzyl dimethyl ammonium chloride), with and without an inorganic salt (sodium thiosulfate), and the resulting enhancement. The second part of the work explored the performance of corrosion inhibitor under multiphase (gas/liquid, solid/liquid) flow. The effect of gas/liquid multiphase flow was investigated using small and large scale apparatus. The small scale tests were conducted using a glass cell and a submersed jet impingement attachment with three different hydrodynamic patterns (water jet, CO 2 bubbles impact, and water vapor cavitation). The large scale experiments were conducted applying different flow loops (hilly terrain and standing slug systems). Measurements of weight loss, linear polarization resistance (LPR), and adsorption mass (using an electrochemical quartz crystal microbalance, EQCM) were used to quantify the effect of wall shear stress on the performance and integrity of corrosion inhibitor

  15. Experimental investigation of the wall shear stress in a circular impinging jet

    NASA Astrophysics Data System (ADS)

    El Hassan, M.; Assoum, H. H.; Martinuzzi, R.; Sobolik, V.; Abed-Meraim, K.; Sakout, A.

    2013-07-01

    The influence of the large-scale vortical structures on the wall shear stress in a circular impinging jet is investigated experimentally for a Reynolds number of 1260. Time-resolved particle image velocimetry and polarographic measurements are performed simultaneously. It is found that the instantaneous wall shear stress is strongly dependent on the vortex dynamics, particularly for different parts of the transverse vortex. The influence of the vortex ring, the secondary and tertiary vortices on the ejection/sweep process near the wall is the main mechanism involved in the wall shear stress variation. In the region of the boundary layer separation, the wall shear stress amplitude increases just upstream of the separation and dramatically decreases in the recirculation zone downstream from the separation. The interaction between primary and secondary structures and their pairing process with the tertiary structure affects the sweep/ejection process near the wall and subsequently the wall shear stress variation. A comparison between the Finite Time Lyapunov Exponent (FTLE) method and the phase average technique is performed. It is shown that both methods describe the flow dynamics in the impinging region of the vortex ring. However, the FTLE method is more suitable for describing the unsteady separation of the boundary layer.

  16. Large scale structures in a turbulent boundary layer and their imprint on wall shear stress

    NASA Astrophysics Data System (ADS)

    Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

    2015-11-01

    Experiments were performed on a turbulent boundary layer developing on a flat plate model under zero pressure gradient flow. A MEMS differential capacitive shear stress sensor with a 1 mm × 1 mm floating element was used to capture the fluctuating wall shear stress simultaneously with streamwise velocity measurements from a hot-wire anemometer traversed in the wall normal direction. Near the wall, the peak in the cross correlation corresponds to an organized motion inclined 45° from the wall. In the outer region, the peak diminishes in value, but is still significant at a distance greater than half the boundary layer thickness, and corresponds to a structure inclined 14° from the wall. High coherence between the two signals was found for the low-frequency content, reinforcing the belief that large scale structures have a vital impact on wall shear stress. Thus, estimation of the wall shear stress from the low-frequency velocity signal will be performed, and is expected to be statistically significant in the outer boundary layer. Additionally, conditionally averaged mean velocity profiles will be presented to assess the effects of high and low shear stress. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

  17. Equations for estimating muscle fiber stress in the left ventricular wall.

    PubMed

    Rabben, S I; Irgens, F; Angelsen, B

    1999-01-01

    Left ventricular muscle fiber stress is an important parameter in cardiac energetics. Hence, we developed equations for estimating regional fiber stresses in rotationally symmetric chambers, and equatorial and apical fiber stresses in prolate spheroidal chambers. The myocardium was modeled as a soft incompressible material embedding muscle fibers that support forces only in their longitudinal direction. A thin layer of muscle fibers then contributes with a pressure increment determined by the fiber stress and curvature. The fiber curvature depends on the orientation of the fibers, which varies continuously across the wall. However, by assuming rotational symmetry about the long axis of the ventricle and including a longitudinal force balance, we obtained equations where fiber stress is completely determined by the principal curvatures of the middle wall surface, wall thickness, and cavity pressure. The equations were validated against idealized prolate spheroidal chambers, whose wall thicknesses are such that the fiber stress is uniform from the equator to the apex. Because the apex is free to rotate, the resultant moment about the long axis of the LV must be zero. By using this constraint together with our fiber-stress equations, we were able to estimate a muscle fiber orientation distribution across the wall that was in qualitative agreement with published measurements.

  18. Wall shear stress and near-wall convective transport: Comparisons with vascular remodelling in a peripheral graft anastomosis

    NASA Astrophysics Data System (ADS)

    Gambaruto, A. M.; Doorly, D. J.; Yamaguchi, T.

    2010-08-01

    Fluid dynamic properties of blood flow are implicated in cardiovascular diseases. The interaction between the blood flow and the wall occurs through the direct transmission of forces, and through the dominating influence of the flow on convective transport processes. Controlled, in vitro testing in simple geometric configurations has provided much data on the cellular-level responses of the vascular walls to flow, but a complete, mechanistic explanation of the pathogenic process is lacking. In the interim, mapping the association between local haemodynamics and the vascular response is important to improve understanding of the disease process and may be of use for prognosis. Moreover, establishing the haemodynamic environment in the regions of disease provides data on flow conditions to guide investigations of cellular-level responses. This work describes techniques to facilitate comparison between the temporal alteration in the geometry of the vascular conduit, as determined by in vivo imaging, with local flow parameters. Procedures to reconstruct virtual models from images by means of a partition-of-unity implicit function formulation, and to align virtual models of follow-up scans to a common coordinate system, are outlined. A simple Taylor series expansion of the Lagrangian dynamics of the near-wall flow is shown to provide both a physical meaning to the directional components of the flow, as well as demonstrating the relation between near-wall convection in the wall normal direction and spatial gradients of the wall shear stress. A series of post-operative follow-up MRI scans of two patient cases with bypass grafts in the peripheral vasculature are presented. These are used to assess how local haemodynamic parameters relate to vascular remodelling at the location of the distal end-to-side anastomosis, i.e. where the graft rejoins the host artery. Results indicate that regions of both low wall shear stress and convective transport towards the wall tend to be

  19. Freezing stresses and hydration of isolated cell walls.

    PubMed

    Yoon, Yonghyeon; Pope, Jim; Wolfe, Joe

    2003-06-01

    The hydration of the cell walls of the giant alga Chara australis was measured as a function of temperature using quantitative deuterium nuclear magnetic resonance (NMR) of samples hydrated with D2O. At temperatures 23-5K below freezing, the hydration ratio (the ratio of mass of unfrozen water in microscopic phases in the cell wall to the dry mass) increases slowly with increasing temperature from about 0.2 to 0.4. It then rises rapidly with temperature in the few Kelvin below the freezing temperature. The linewidth of the NMR signal varies approximately linearly with the reciprocal of the hydration ratio, and with the freezing point depression or water potential. These empirical relations may be useful in estimating cell wall water contents in heterogeneous samples.

  20. Pulmonary endarterectomy normalizes interventricular dyssynchrony and right ventricular systolic wall stress

    PubMed Central

    2012-01-01

    Background Interventricular mechanical dyssynchrony is a characteristic of pulmonary hypertension. We studied the role of right ventricular (RV) wall stress in the recovery of interventricular dyssynchrony, after pulmonary endarterectomy (PEA) in chronic thromboembolic pulmonary hypertension (CTEPH). Methods In 13 consecutive patients with CTEPH, before and 6 months after pulmonary endarterectomy, cardiovascular magnetic resonance myocardial tagging was applied. For the left ventricular (LV) and RV free walls, the time to peak (Tpeak) of circumferential shortening (strain) was calculated. Pulmonary Artery Pressure (PAP) was measured by right heart catheterization within 48 hours of PEA. Then the RV free wall systolic wall stress was calculated by the Laplace law. Results After PEA, the left to right free wall delay (L-R delay) in Tpeak strain decreased from 97 ± 49 ms to -4 ± 51 ms (P < 0.001), which was not different from normal reference values of -35 ± 10 ms (P = 0.18). The RV wall stress decreased significantly from 15.2 ± 6.4 kPa to 5.7 ± 3.4 kPa (P < 0.001), which was not different from normal reference values of 5.3 ± 1.39 kPa (P = 0.78). The reduction of L-R delay in Tpeak was more strongly associated with the reduction in RV wall stress (r = 0.69,P = 0.007) than with the reduction in systolic PAP (r = 0.53, P = 0.07). The reduction of L-R delay in Tpeak was not associated with estimates of the reduction in RV radius (r = 0.37,P = 0.21) or increase in RV systolic wall thickness (r = 0.19,P = 0.53). Conclusion After PEA for CTEPH, the RV and LV peak strains are resynchronized. The reduction in systolic RV wall stress plays a key role in this resynchronization. PMID:22240072

  1. Finite element formulation and analysis for an arterial wall with residual and active stresses.

    PubMed

    Kida, Naoki; Adachi, Taiji

    2015-08-01

    In this study, for predicting arterial function and pathogenesis from a mechanical viewpoint, we develop a continuum mechanical model of an arterial wall that embodies residual and active stresses following a traditional anisotropic passive constitutive law. The residual and active stresses are incorporated into finite element methods based on a two-field variational principle described in the Lagrangian form. The linearisation of nonlinear weak-form equations derived from this variational principle is then described for developing an original finite element algorithm. Numerical simulations reveal the following: (i) residual stresses lead to a reduction in stress gradient regardless of the magnitude of external load; (ii) active stresses help homogenise stress distribution under physiological external load, but this homogeneity collapses under pathological external load; (iii) when residual and active stresses act together, the effect of the residual stresses is relatively obscured by that of the active stresses. We conclude that residual stresses have minor but persistent mechanical effects on the arterial wall under both physiological and pathological external loads; active stresses play an important role in the physiological functions and pathogenesis of arteries, and the mechanical effect of residual stresses is dependent on the presence/absence of active stresses.

  2. Determining the influence of calcification on the failure properties of abdominal aortic aneurysm (AAA) tissue.

    PubMed

    O'Leary, Siobhan A; Mulvihill, John J; Barrett, Hilary E; Kavanagh, Eamon G; Walsh, Michael T; McGloughlin, Tim M; Doyle, Barry J

    2015-02-01

    Varying degrees of calcification are present in most abdominal aortic aneurysms (AAAs). However, their impact on AAA failure properties and AAA rupture risk is unclear. The aim of this work is evaluate and compare the failure properties of partially calcified and predominantly fibrous AAA tissue and investigate the potential reasons for failure. Uniaxial mechanical testing was performed on AAA samples harvested from 31 patients undergoing open surgical repair. Individual tensile samples were divided into two groups: fibrous (n=31) and partially calcified (n=38). The presence of calcification was confirmed by fourier transform infrared spectroscopy (FTIR). A total of 69 mechanical tests were performed and the failure stretch (λf), failure stress (σf) and failure tension (Tf) were recorded for each test. Following mechanical testing, the failure sites of a subset of both tissue types were examined using scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) to investigate the potential reasons for failure. It has been shown that the failure properties of partially calcified tissue are significantly reduced compared to fibrous tissue and SEM and EDS results suggest that the junction between a calcification deposit and the fibrous matrix is highly susceptible to failure. This study implicates the presence of calcification as a key player in AAA rupture risk and provides further motivation for the development of non-invasive methods of measuring calcification.

  3. Determining the influence of calcification on the failure properties of abdominal aortic aneurysm (AAA) tissue.

    PubMed

    O'Leary, Siobhan A; Mulvihill, John J; Barrett, Hilary E; Kavanagh, Eamon G; Walsh, Michael T; McGloughlin, Tim M; Doyle, Barry J

    2015-02-01

    Varying degrees of calcification are present in most abdominal aortic aneurysms (AAAs). However, their impact on AAA failure properties and AAA rupture risk is unclear. The aim of this work is evaluate and compare the failure properties of partially calcified and predominantly fibrous AAA tissue and investigate the potential reasons for failure. Uniaxial mechanical testing was performed on AAA samples harvested from 31 patients undergoing open surgical repair. Individual tensile samples were divided into two groups: fibrous (n=31) and partially calcified (n=38). The presence of calcification was confirmed by fourier transform infrared spectroscopy (FTIR). A total of 69 mechanical tests were performed and the failure stretch (λf), failure stress (σf) and failure tension (Tf) were recorded for each test. Following mechanical testing, the failure sites of a subset of both tissue types were examined using scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) to investigate the potential reasons for failure. It has been shown that the failure properties of partially calcified tissue are significantly reduced compared to fibrous tissue and SEM and EDS results suggest that the junction between a calcification deposit and the fibrous matrix is highly susceptible to failure. This study implicates the presence of calcification as a key player in AAA rupture risk and provides further motivation for the development of non-invasive methods of measuring calcification. PMID:25482218

  4. An in-plane cantilever for wall shear stress measurement

    NASA Astrophysics Data System (ADS)

    Allen, N. J.; Sims-Williams, D. B.; Wood, D.

    2012-07-01

    A sensor capable of measuring small shear stresses in wind tunnel applications is presented. The sensor utilizes an in-plane cantilever concept for shear stress measurement, designed to minimize intrusiveness into the airflow and allow easy incorporation into wind tunnel test models. The sensor operates independently of input voltage, and can measure <1 Pa shear stresses with a sensitivity of 8.6 (mV V-1) Pa. Altering the geometry of the sensor has a direct effect on the sensitivity and so can be used to adapt the sensor for different applications.

  5. Genetic analysis of abdominal aortic aneurysms (AAA)

    SciTech Connect

    St. Jean, P.L.; Hart, B.K.; Zhang, X.C.

    1994-09-01

    The association between AAA and gender, smoking (SM), hypertension (HTN) and inguinal herniation (IH) was examined in 141 AAA probands and 139 of their 1st degree relatives with aortic exam (36 affected, 103 unaffected). There was no significant difference between age at diagnosis of affecteds and age at exam of unaffecteds. Of 181 males, 142 had AAA; of 99 females, 35 had AAA. Using log-linear modeling AAA was significantly associated at the 5% level with gender, SM and HTN but not IH. The association of AAA with SM and HTN held when males and females were analyzed separately. HTN was -1.5 times more common in both affected males and females, while SM was 1.5 and 2 times more common in affected males and females, respectively. Tests of association and linkage analyses were performed with relevant candidate genes: 3 COL3A1 polymorphisms (C/T, ALA/THR, AvaII), 2 ELN polymorphisms (SER/GLY, (CA)n), FBN1(TAAA)n, 2 APOB polymorphisms (Xbal,Ins/Del), CLB4B (CA)n, PI and markers D1S243 (CA)n, HPR (CA)n and MFD23(CA)n. The loci were genotyped in > 100 AAA probands and > 95 normal controls. No statistically significant evidence of association at the 5% level was obtained for any of the loci using chi-square test of association. 28 families with 2 or more affecteds were analyzed using the affected pedigree member method (APM) and lod-score analyses. There was no evidence for linkage with any loci using APM. Lod-score analysis under an autosomal recessive model resulted in excluding linkage (lod score < -2) of all loci to AAA at {theta}=0.0. Under an autosomal dominant model, linkage was excluded at {theta}=0.0 to ELN, APOB, CLG4B, D1S243, HPR and MFD23. The various genes previously proposed in AAA pathogenesis are neither associated nor casually related in our study population.

  6. Pathophysiology of AAA: heredity vs environment.

    PubMed

    Björck, Martin; Wanhainen, Anders

    2013-01-01

    Abdominal aortic aneurysm (AAA) has a complex pathophysiology, in which both environmental and genetic factors play important roles, the most important being smoking. The recently reported falling prevalence rates of AAA in northern Europe and Australia/New Zeeland are largely explained by healthier smoking habits. Dietary factors and obesity, in particular abdominal obesity, are also of importance. A family history of AAA among first-degree relatives is present in approximately 13% of incident cases. The probability that a monozygotic twin of a person with an AAA has the disease is 24%, 71 times higher than that for a monozygotic twin of a person without AAA. Approximately 1000 SNPs in 100 candidate genes have been studied, and three genome-wide association studies were published, identifying different diverse weak associations. An example of interaction between environmental and genetic factors is the effect of cholesterol, where genetic and dietary factors affect levels of both HDL and LDL. True epigenetic studies have not yet been published.

  7. Analysis of Stress Responsive Genes Induced by Single-Walled Carbon Nanotubes in BJ Foreskin Cells

    PubMed Central

    Sarkar, Shubhashish; Sharma, Chidananda; Yog, Rajeshwari; Periakaruppan, Adaikkappan; Jejelowo, Olufisayo; Thomas, Renard; Barrera, Enrique V.; Rice-Ficht, Allison C.; Wilson, Bobby L.; Ramesh, Govindarajan T.

    2009-01-01

    Nanotechnology is finding its use as a potential technology in consumer products, defense, electronics, and medical applications by exploiting the properties of nanomaterials. Single-walled carbon nanotubes are novel forms of these nanomaterials with potential for large applications. However, the toxicity studies on this material are not explored in detail and therefore limiting its use. It has been earlier reported that single-walled carbon nanotubes induces oxidative stress and also dictates activation of specific signaling pathway in keratinocytes. The present study explores the effect of single-walled carbon nanotubes on stress genes in human BJ Foreskin cells. The results show induction of oxidative stress in BJ Foreskin cells by single-walled carbon nanotubes and increase in stress responsive genes. The genes included inducible genes like HMOX1, HMOX2, and Cyp1B1. In addition we validated increase for four genes by SWCNT, namely ATM, CCNC, DNAJB4, and GADD45A by RT-PCR. Moreover results of the altered stress related genes have been discussed and that partially explains some of the toxic responses induced by single-walled carbon nanotubes. PMID:17450800

  8. Effects of Wall Shear Stress on Unsteady MHD Conjugate Flow in a Porous Medium with Ramped Wall Temperature

    PubMed Central

    Khan, Arshad; Khan, Ilyas; Ali, Farhad; ulhaq, Sami; Shafie, Sharidan

    2014-01-01

    This study investigates the effects of an arbitrary wall shear stress on unsteady magnetohydrodynamic (MHD) flow of a Newtonian fluid with conjugate effects of heat and mass transfer. The fluid is considered in a porous medium over a vertical plate with ramped temperature. The influence of thermal radiation in the energy equations is also considered. The coupled partial differential equations governing the flow are solved by using the Laplace transform technique. Exact solutions for velocity and temperature in case of both ramped and constant wall temperature as well as for concentration are obtained. It is found that velocity solutions are more general and can produce a huge number of exact solutions correlative to various fluid motions. Graphical results are provided for various embedded flow parameters and discussed in details. PMID:24621775

  9. Debonding Stress Concentrations in a Pressurized Lobed Sandwich-Walled Generic Cryogenic Tank

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    2004-01-01

    A finite-element stress analysis has been conducted on a lobed composite sandwich tank subjected to internal pressure and cryogenic cooling. The lobed geometry consists of two obtuse circular walls joined together with a common flat wall. Under internal pressure and cryogenic cooling, this type of lobed tank wall will experience open-mode (a process in which the honeycomb is stretched in the depth direction) and shear stress concentrations at the junctures where curved wall changes into flat wall (known as a curve-flat juncture). Open-mode and shear stress concentrations occur in the honeycomb core at the curve-flat junctures and could cause debonding failure. The levels of contributions from internal pressure and temperature loading to the open-mode and shear debonding failure are compared. The lobed fuel tank with honeycomb sandwich walls has been found to be a structurally unsound geometry because of very low debonding failure strengths. The debonding failure problem could be eliminated if the honeycomb core at the curve-flat juncture is replaced with a solid core.

  10. Direct measurement of cell wall stress stiffening and turgor pressure in live bacterial cells.

    PubMed

    Deng, Yi; Sun, Mingzhai; Shaevitz, Joshua W

    2011-10-01

    We study intact and bulging Escherichia coli cells using atomic force microscopy to separate the contributions of the cell wall and turgor pressure to the overall cell stiffness. We find strong evidence of power-law stress stiffening in the E. coli cell wall, with an exponent of 1.22±0.12, such that the wall is significantly stiffer in intact cells (E=23±8  MPa and 49±20  MPa in the axial and circumferential directions) than in unpressurized sacculi. These measurements also indicate that the turgor pressure in living cells E. coli is 29±3  kPa.

  11. Direct Measurement of Cell Wall Stress Stiffening and Turgor Pressure in Live Bacterial Cells

    NASA Astrophysics Data System (ADS)

    Deng, Yi; Sun, Mingzhai; Shaevitz, Joshua W.

    2011-10-01

    We study intact and bulging Escherichia coli cells using atomic force microscopy to separate the contributions of the cell wall and turgor pressure to the overall cell stiffness. We find strong evidence of power-law stress stiffening in the E. coli cell wall, with an exponent of 1.22±0.12, such that the wall is significantly stiffer in intact cells (E=23±8MPa and 49±20MPa in the axial and circumferential directions) than in unpressurized sacculi. These measurements also indicate that the turgor pressure in living cells E. coli is 29±3kPa.

  12. A computational model to predict aortic wall stresses in patients with systolic arterial hypertension.

    PubMed

    Giannakoulas, George; Giannoglou, George; Soulis, Johannes; Farmakis, Thomas; Papadopoulou, Stella; Parcharidis, George; Louridas, George

    2005-01-01

    Computational cardiovascular mechanics has allowed scientists to create complex 3D models for the simulation of cardiovascular problems. Mechanical stress plays a crucial role in the function of the cardiovascular system; stress analysis is a useful tool for the understanding of vascular pathophysiology. By using the spiral CT imaging and computational structural analysis, we present a noninvasive method of wall stress analysis in the normal aorta. The aortic segment was extended from the origin of the inferior mesenteric artery to the aortic bifurcation. The length of this segment was 12 cm, while the maximum transverse diameter was 2.075+/-0.129 cm. A 3D aortic model was constructed based on the CT scan images. The aorta was assumed to have a uniform wall thickness of 1.5mm. The generated unstructured grid, which was used for the structural analysis, consisted of 14,440 hexahedral elements. The wall material was assumed to be hyperelastic, homogeneous, isotropic and nearly incompressible (Poisson ratio=0.45). According to experimental studies, the Young modulus of aortic wall was set equal to 4.66 MPa. The shear stress induced by the blood flow was neglected. A finite-element static structural analysis was performed. Three different cases were examined applying constant intraluminal systolic blood pressures of 120, 180 and 240 mmHg, respectively. The von Mises stress distribution and the displacements of the aortic wall were calculated. Peak wall stress for the normal load case of 120 mmHg was 22.5 N/cm2, while the max displacement was 0.44 mm. The case with the intraluminal pressure of 180 mmHg resulted into peak wall stress of 32 N/cm2 with max displacement 0.59 mm, while for 240 mmHg was 40.6N/cm2, max displacement 0.72 mm. The rise in blood pressure caused all stresses to increase. The pattern of stress distribution and the orientation of the stress were similar for all test cases. A quantitative evaluation of the aortic wall stresses under systolic

  13. A computational model to predict aortic wall stresses in patients with systolic arterial hypertension.

    PubMed

    Giannakoulas, George; Giannoglou, George; Soulis, Johannes; Farmakis, Thomas; Papadopoulou, Stella; Parcharidis, George; Louridas, George

    2005-01-01

    Computational cardiovascular mechanics has allowed scientists to create complex 3D models for the simulation of cardiovascular problems. Mechanical stress plays a crucial role in the function of the cardiovascular system; stress analysis is a useful tool for the understanding of vascular pathophysiology. By using the spiral CT imaging and computational structural analysis, we present a noninvasive method of wall stress analysis in the normal aorta. The aortic segment was extended from the origin of the inferior mesenteric artery to the aortic bifurcation. The length of this segment was 12 cm, while the maximum transverse diameter was 2.075+/-0.129 cm. A 3D aortic model was constructed based on the CT scan images. The aorta was assumed to have a uniform wall thickness of 1.5mm. The generated unstructured grid, which was used for the structural analysis, consisted of 14,440 hexahedral elements. The wall material was assumed to be hyperelastic, homogeneous, isotropic and nearly incompressible (Poisson ratio=0.45). According to experimental studies, the Young modulus of aortic wall was set equal to 4.66 MPa. The shear stress induced by the blood flow was neglected. A finite-element static structural analysis was performed. Three different cases were examined applying constant intraluminal systolic blood pressures of 120, 180 and 240 mmHg, respectively. The von Mises stress distribution and the displacements of the aortic wall were calculated. Peak wall stress for the normal load case of 120 mmHg was 22.5 N/cm2, while the max displacement was 0.44 mm. The case with the intraluminal pressure of 180 mmHg resulted into peak wall stress of 32 N/cm2 with max displacement 0.59 mm, while for 240 mmHg was 40.6N/cm2, max displacement 0.72 mm. The rise in blood pressure caused all stresses to increase. The pattern of stress distribution and the orientation of the stress were similar for all test cases. A quantitative evaluation of the aortic wall stresses under systolic

  14. Sequence analysis of the AAA protein family.

    PubMed Central

    Beyer, A.

    1997-01-01

    The AAA protein family, a recently recognized group of Walker-type ATPases, has been subjected to an extensive sequence analysis. Multiple sequence alignments revealed the existence of a region of sequence similarity, the so-called AAA cassette. The borders of this cassette were localized and within it, three boxes of a high degree of conservation were identified. Two of these boxes could be assigned to substantial parts of the ATP binding site (namely, to Walker motifs A and B); the third may be a portion of the catalytic center. Phylogenetic trees were calculated to obtain insights into the evolutionary history of the family. Subfamilies with varying degrees of intra-relatedness could be discriminated; these relationships are also supported by analysis of sequences outside the canonical AAA boxes: within the cassette are regions that are strongly conserved within each subfamily, whereas little or even no similarity between different subfamilies can be observed. These regions are well suited to define fingerprints for subfamilies. A secondary structure prediction utilizing all available sequence information was performed and the result was fitted to the general 3D structure of a Walker A/GTPase. The agreement was unexpectedly high and strongly supports the conclusion that the AAA family belongs to the Walker superfamily of A/GTPases. PMID:9336829

  15. In vivo porcine left atrial wall stress: Computational model.

    PubMed

    Di Martino, Elena S; Bellini, Chiara; Schwartzman, David S

    2011-10-13

    Most computational models of the heart have so far concentrated on the study of the left ventricle, mainly using simplified geometries. The same approach cannot be adopted to model the left atrium, whose irregular shape does not allow morphological simplifications. In addition, the deformation of the left atrium during the cardiac cycle strongly depends on the interaction with its surrounding structures. We present a procedure to generate a comprehensive computational model of the left atrium, including physiological loads (blood pressure), boundary conditions (pericardium, pulmonary veins and mitral valve annulus movement) and mechanical properties based on planar biaxial experiments. The model was able to accurately reproduce the in vivo dynamics of the left atrium during the passive portion of the cardiac cycle. A shift in time between the peak pressure and the maximum displacement of the mitral valve annulus allows the appendage to inflate and bend towards the ventricle before the pulling effect associated with the ventricle contraction takes place. The ventricular systole creates room for further expansion of the appendage, which gets in close contact with the pericardium. The temporal evolution of the volume in the atrial cavity as predicted by the finite element simulation matches the volume changes obtained from CT scans. The stress field computed at each time point shows remarkable spatial heterogeneity. In particular, high stress concentration occurs along the appendage rim and in the region surrounding the pulmonary veins. PMID:21907340

  16. Relationships between growth, morphology and wall stress in the stalk of Acetabularia acetabulum.

    PubMed

    von Dassow, M; Odell, G M; Mandoli, D F

    2001-08-01

    With carbon particles we analyzed patterns of growth in Acetabularia acetabulum (Lam.) P.C. Silva, a giant unicell famous for classic development studies. We focused on the stalk apex, which generates the stalk, whorls of hairs, and whorls of gametophores. To gain visual and physical accessibility, we amputated the youngest whorls of hair and the original apex and performed experiments on the apex that regenerated. Video analysis indicated that most growth occurred near the tip of the new apex. Less growth occured throughout the cut-interwhorl. We also analyzed cell wall thickness along stalks cleared of cytoplasm. Correlating growth data to wall morphology suggests growth near the apex may be proportional to stress on the cell wall. We propose that turgor-pressure wall stress modulates local apical cell wall growth rates. A supplementary model, relating cell wall curvature and growth rate in the cut-interwhorl, characterizes how the stalk's final dimensions and nearly cylindrical shap may arise. See http://faculty.washington.edu/mandoli/vondassow for supplementary data, analysis, and mathematical appendices. We believe this is the first quantiative description of apex morphogenesis of A. acetabulum.

  17. Measurement of turbulent wall shear-stress using micro-pillars

    NASA Astrophysics Data System (ADS)

    Gnanamanickam, E. P.; Nottebrock, B.; Große, S.; Sullivan, J. P.; Schröder, W.

    2013-12-01

    In experimental fluid mechanics, measuring spatially and temporally resolved wall shear-stress (WSS) has proved a challenging problem. The micro-pillar shear-stress sensor (MPS3) has been developed with the goal of filling this gap in measurement techniques. The MPS3 comprises an array of flexible micro-pillars flush mounted on the wall of a wall-bounded flow field. The deflection of these micro-pillars in the presence of a shear field is a direct measure of the WSS. This paper presents the MPS3 development work carried out by RWTH Aachen University and Purdue University. The sensor concept, static and dynamic characterization and data reduction issues are discussed. Also presented are demonstrative experiments where the MPS3 was used to measure the WSS in both water and air. The salient features of the measurement technique, sensor development issues, current capabilities and areas for improvement are highlighted.

  18. Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not

    NASA Technical Reports Server (NTRS)

    Gao, Q.; Fang, A.; Pierson, D. L.; Mishra, S. K.; Demain, A. L.

    2001-01-01

    Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

  19. Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not.

    PubMed

    Gao, Q; Fang, A; Pierson, D L; Mishra, S K; Demain, A L

    2001-08-01

    Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

  20. The Plant Cell Wall: A Complex and Dynamic Structure As Revealed by the Responses of Genes under Stress Conditions.

    PubMed

    Houston, Kelly; Tucker, Matthew R; Chowdhury, Jamil; Shirley, Neil; Little, Alan

    2016-01-01

    The plant cell wall has a diversity of functions. It provides a structural framework to support plant growth and acts as the first line of defense when the plant encounters pathogens. The cell wall must also retain some flexibility, such that when subjected to developmental, biotic, or abiotic stimuli it can be rapidly remodeled in response. Genes encoding enzymes capable of synthesizing or hydrolyzing components of the plant cell wall show differential expression when subjected to different stresses, suggesting they may facilitate stress tolerance through changes in cell wall composition. In this review we summarize recent genetic and transcriptomic data from the literature supporting a role for specific cell wall-related genes in stress responses, in both dicot and monocot systems. These studies highlight that the molecular signatures of cell wall modification are often complex and dynamic, with multiple genes appearing to respond to a given stimulus. Despite this, comparisons between publically available datasets indicate that in many instances cell wall-related genes respond similarly to different pathogens and abiotic stresses, even across the monocot-dicot boundary. We propose that the emerging picture of cell wall remodeling during stress is one that utilizes a common toolkit of cell wall-related genes, multiple modifications to cell wall structure, and a defined set of stress-responsive transcription factors that regulate them. PMID:27559336

  1. The Plant Cell Wall: A Complex and Dynamic Structure As Revealed by the Responses of Genes under Stress Conditions

    PubMed Central

    Houston, Kelly; Tucker, Matthew R.; Chowdhury, Jamil; Shirley, Neil; Little, Alan

    2016-01-01

    The plant cell wall has a diversity of functions. It provides a structural framework to support plant growth and acts as the first line of defense when the plant encounters pathogens. The cell wall must also retain some flexibility, such that when subjected to developmental, biotic, or abiotic stimuli it can be rapidly remodeled in response. Genes encoding enzymes capable of synthesizing or hydrolyzing components of the plant cell wall show differential expression when subjected to different stresses, suggesting they may facilitate stress tolerance through changes in cell wall composition. In this review we summarize recent genetic and transcriptomic data from the literature supporting a role for specific cell wall-related genes in stress responses, in both dicot and monocot systems. These studies highlight that the molecular signatures of cell wall modification are often complex and dynamic, with multiple genes appearing to respond to a given stimulus. Despite this, comparisons between publically available datasets indicate that in many instances cell wall-related genes respond similarly to different pathogens and abiotic stresses, even across the monocot-dicot boundary. We propose that the emerging picture of cell wall remodeling during stress is one that utilizes a common toolkit of cell wall-related genes, multiple modifications to cell wall structure, and a defined set of stress-responsive transcription factors that regulate them. PMID:27559336

  2. 26 CFR 1.1368-2 - Accumulated adjustments account (AAA).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 11 2010-04-01 2010-04-01 true Accumulated adjustments account (AAA). 1.1368-2... adjustments account (AAA). (a) Accumulated adjustments account—(1) In general. The accumulated adjustments account is an account of the S corporation and is not apportioned among shareholders. The AAA is...

  3. Stress-induced phase transition in ferroelectric domain walls of BaTiO3.

    PubMed

    Stepkova, V; Marton, P; Hlinka, J

    2012-05-30

    The seminal paper by Zhirnov (1958 Zh. Eksp. Teor. Fiz. 35 1175-80) explained why the structure of domain walls in ferroelectrics and ferromagnets is drastically different. Here we show that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO(3) can be switched between the Ising-like state (typical for ferroelectrics) and a Bloch-like state (unusual for ferroelectric walls but typical for magnetic ones). Phase-field simulations using a Ginzburg-Landau-Devonshire model suggest that this symmetry-breaking transition can be induced by a compressive epitaxial stress. The strain-tunable chiral properties of these domain walls promise a range of novel phenomena in epitaxial ferroelectric thin films.

  4. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 2: Wall shear stress

    NASA Technical Reports Server (NTRS)

    Liou, M. S.; Adamson, T. C., Jr.

    1979-01-01

    An analysis is presented of the flow in the two inner layers, the Reynolds stress sublayer and the wall layer. Included is the calculation of the shear stress at the wall in the interaction region. The limit processes considered are those used for an inviscid flow.

  5. Estimation of aneurysm wall stresses created by treatment with a shape memory polymer foam device

    PubMed Central

    Hwang, Wonjun; Volk, Brent L.; Akberali, Farida; Singhal, Pooja; Criscione, John C.

    2012-01-01

    In this study, compliant latex thin-walled aneurysm models are fabricated to investigate the effects of expansion of shape memory polymer foam. A simplified cylindrical model is selected for the in-vitro aneurysm, which is a simplification of a real, saccular aneurysm. The studies are performed by crimping shape memory polymer foams, originally 6 and 8 mm in diameter, and monitoring the resulting deformation when deployed into 4-mm-diameter thin-walled latex tubes. The deformations of the latex tubes are used as inputs to physical, analytical, and computational models to estimate the circumferential stresses. Using the results of the stress analysis in the latex aneurysm model, a computational model of the human aneurysm is developed by changing the geometry and material properties. The model is then used to predict the stresses that would develop in a human aneurysm. The experimental, simulation, and analytical results suggest that shape memory polymer foams have potential of being a safe treatment for intracranial saccular aneurysms. In particular, this work suggests oversized shape memory foams may be used to better fill the entire aneurysm cavity while generating stresses below the aneurysm wall breaking stresses. PMID:21901546

  6. The role of plant cell wall proteins in response to salt stress.

    PubMed

    Zagorchev, Lyuben; Kamenova, Plamena; Odjakova, Mariela

    2014-01-01

    Contemporary agriculture is facing new challenges with the increasing population and demand for food on Earth and the decrease in crop productivity due to abiotic stresses such as water deficit, high salinity, and extreme fluctuations of temperatures. The knowledge of plant stress responses, though widely extended in recent years, is still unable to provide efficient strategies for improvement of agriculture. The focus of study has been shifted to the plant cell wall as a dynamic and crucial component of the plant cell that could immediately respond to changes in the environment. The investigation of plant cell wall proteins, especially in commercially important monocot crops revealed the high involvement of this compartment in plants stress responses, but there is still much more to be comprehended. The aim of this review is to summarize the available data on this issue and to point out the future areas of interest that should be studied in detail. PMID:24574917

  7. The Role of Plant Cell Wall Proteins in Response to Salt Stress

    PubMed Central

    2014-01-01

    Contemporary agriculture is facing new challenges with the increasing population and demand for food on Earth and the decrease in crop productivity due to abiotic stresses such as water deficit, high salinity, and extreme fluctuations of temperatures. The knowledge of plant stress responses, though widely extended in recent years, is still unable to provide efficient strategies for improvement of agriculture. The focus of study has been shifted to the plant cell wall as a dynamic and crucial component of the plant cell that could immediately respond to changes in the environment. The investigation of plant cell wall proteins, especially in commercially important monocot crops revealed the high involvement of this compartment in plants stress responses, but there is still much more to be comprehended. The aim of this review is to summarize the available data on this issue and to point out the future areas of interest that should be studied in detail. PMID:24574917

  8. AAA-DDD triple hydrogen bond complexes.

    PubMed

    Blight, Barry A; Camara-Campos, Amaya; Djurdjevic, Smilja; Kaller, Martin; Leigh, David A; McMillan, Fiona M; McNab, Hamish; Slawin, Alexandra M Z

    2009-10-01

    Experiment and theory both suggest that the AAA-DDD pattern of hydrogen bond acceptors (A) and donors (D) is the arrangement of three contiguous hydrogen bonding centers that results in the strongest association between two species. Murray and Zimmerman prepared the first example of such a system (complex 3*2) and determined the lower limit of its association constant (K(a)) in CDCl(3) to be 10(5) M(-1) by (1)H NMR spectroscopy (Murray, T. J. and Zimmerman, S. C. J. Am. Chem. Soc. 1992, 114, 4010-4011). The first cationic AAA-DDD pair (3*4(+)) was described by Bell and Anslyn (Bell, D. A. and Anslyn, E. A. Tetrahedron 1995, 51, 7161-7172), with a K(a) > 5 x 10(5) M(-1) in CH(2)Cl(2) as determined by UV-vis spectroscopy. We were recently able to quantify the strength of a neutral AAA-DDD arrangement using a more chemically stable AAA-DDD system, 6*2, which has an association constant of 2 x 10(7) M(-1) in CH(2)Cl(2) (Djurdjevic, S., Leigh, D. A., McNab, H., Parsons, S., Teobaldi, G. and Zerbetto, F. J. Am. Chem. Soc. 2007, 129, 476-477). Here we report on further AA(A) and DDD partners, together with the first precise measurement of the association constant of a cationic AAA-DDD species. Complex 6*10(+)[B(3,5-(CF(3))(2)C(6)H(3))(4)(-)] has a K(a) = 3 x 10(10) M(-1) at RT in CH(2)Cl(2), by far the most strongly bound triple hydrogen bonded system measured to date. The X-ray crystal structure of 6*10(+) with a BPh(4)(-) counteranion shows a planar array of three short (NH...N distances 1.95-2.15 A), parallel (but staggered rather than strictly linear; N-H...N angles 165.4-168.8 degrees), primary hydrogen bonds. These are apparently reinforced, as theory predicts, by close electrostatic interactions (NH-*-N distances 2.78-3.29 A) between each proton and the acceptor atoms of the adjacent primary hydrogen bonds.

  9. Cell Wall Amine Oxidases: New Players in Root Xylem Differentiation under Stress Conditions.

    PubMed

    Ghuge, Sandip A; Tisi, Alessandra; Carucci, Andrea; Rodrigues-Pousada, Renato A; Franchi, Stefano; Tavladoraki, Paraskevi; Angelini, Riccardo; Cona, Alessandra

    2015-01-01

    Polyamines (PAs) are aliphatic polycations present in all living organisms. A growing body of evidence reveals their involvement as regulators in a variety of physiological and pathological events. They are oxidatively deaminated by amine oxidases (AOs), including copper amine oxidases (CuAOs) and flavin adenine dinucleotide (FAD)-dependent polyamine oxidases (PAOs). The biologically-active hydrogen peroxide (H₂O₂) is a shared compound in all of the AO-catalyzed reactions, and it has been reported to play important roles in PA-mediated developmental and stress-induced processes. In particular, the AO-driven H₂O₂ biosynthesis in the cell wall is well known to be involved in plant wound healing and pathogen attack responses by both triggering peroxidase-mediated wall-stiffening events and signaling modulation of defense gene expression. Extensive investigation by a variety of methodological approaches revealed high levels of expression of cell wall-localized AOs in root xylem tissues and vascular parenchyma of different plant species. Here, the recent progresses in understanding the role of cell wall-localized AOs as mediators of root xylem differentiation during development and/or under stress conditions are reviewed. A number of experimental pieces of evidence supports the involvement of apoplastic H₂O₂ derived from PA oxidation in xylem tissue maturation under stress-simulated conditions. PMID:27135338

  10. Effect of shape and size of lung and chest wall on stresses in the lung

    NASA Technical Reports Server (NTRS)

    Vawter, D. L.; Matthews, F. L.; West, J. B.

    1975-01-01

    To understand better the effect of shape and size of lung and chest wall on the distribution of stresses, strains, and surface pressures, we analyzed a theoretical model using the technique of finite elements. First we investigated the effects of changing the chest wall shape during expansion, and second we studied lungs of a variety of inherent shapes and sizes. We found that, in general, the distributions of alveolar size, mechanical stresses, and surface pressures in the lungs were dominated by the weight of the lung and that changing the shape of the lung or chest wall had relatively little effect. Only at high states of expansion where the lung was very stiff did changing the shape of the chest wall cause substantial changes. Altering the inherent shape of the lung generally had little effect but the topographical differences in stresses and surface pressures were approximately proportional to lung height. The results are generally consistent with those found in the dog by Hoppin et al (1969).

  11. Bioinjection Treatment: Effects of Post-Injection Residual Stress on Left Ventricular Wall Stress

    PubMed Central

    Lee, Lik Chuan; Wall, Samuel T.; Genet, Martin; Hinson, Andy; Guccione, Julius M.

    2014-01-01

    Injection of biomaterials into diseased myocardium has been associated with decreased myofiber stress, restored left ventricular (LV) geometry and improved LV function. However, its exact mechanism(s) of action remained unclear. In this work, we present the first patient-specific computational model of biomaterial injection that accounts for the possibility of residual strain and stress introduced by this treatment. We show that the presence of residual stress can create more heterogeneous regional myofiber stress and strain fields. Our simulation results show that the treatment generates low stress and stretch areas between injection sites, and high stress and stretch areas between the injections and both the endocardium and epicardium. Globally, these local changes are translated into an increase in average myofiber stress and its standard deviation (from 6.9 ± 4.6 to 11.2 ± 48.8 kPa and 30 ± 15 to 35.1 ± 50.9 kPa at end-diastole and end-systole, respectively). We also show that the myofiber stress field is sensitive to the void-to-injection size ratio – for a constant void size, the myofiber stress field became less heterogeneous with decreasing injection volume. These results suggest that the residual stress and strain possibly generated by biomaterial injection treatment can have large effects on the regional myocardial stress and strain fields, which may be important in the remodeling process. PMID:25065728

  12. Stabilization procedures for near-wall full Reynolds stress closures in complex 3-D CFD simulations

    SciTech Connect

    Kunz, R.F.; Siebert, B.W.

    1996-06-01

    Near-wall full Reynolds stress models (FRSMs) were implemented in an implicit, incompressible full Navier-Stokes algorithm. The method was applied to flow in a 3-D duct with significant curvature induced secondary motions as well as 2-D and 3-D turbine cascade flows. FRSM computation of such flows, provides several numerical challenges germane to the very highly clustered near-wall meshes required, and to the incorporation of FRSMs themselves. Several stabilization procedures have been deployed within the scheme, which enable convergent solutions to large scale flow simulations of engineering interest. This paper summarizes the numerical strategies employed. it is shown that near-wall FRSM convergence rates commensurate with those of two-equation models are obtained.

  13. Stress-mediated magnetoelectric control of ferromagnetic domain wall position in multiferroic heterostructures

    NASA Astrophysics Data System (ADS)

    Mathurin, Théo; Giordano, Stefano; Dusch, Yannick; Tiercelin, Nicolas; Pernod, Philippe; Preobrazhensky, Vladimir

    2016-02-01

    The motion of a ferromagnetic domain wall in nanodevices is usually induced by means of external magnetic fields or polarized currents. Here, we demonstrate the possibility to reversibly control the position of a Néel domain wall in a ferromagnetic nanostripe through a uniform mechanical stress. The latter is generated by an electro-active substrate combined with the nanostripe in a multiferroic heterostructure. We develop a model describing the magnetization distribution in the ferromagnetic material, properly taking into account the magnetoelectric coupling. Through its numerical implementation, we obtain the relationship between the electric field applied to the piezoelectric substrate and the position of the magnetic domain wall in the nanostripe. As an example, we analyze a structure composed of a PMN-PT substrate and a TbCo2/FeCo composite nanostripe.

  14. Carotid wall stress calculated with continuous intima-media thickness assessment using B-mode ultrasound

    NASA Astrophysics Data System (ADS)

    Pascaner, A. F.; Craiem, D.; Casciaro, M. E.; Danielo, R.; Graf, S.; Guevara, E.

    2016-04-01

    Cardiovascular risk is normally assessed using clinical risk factors but it can be refined using non-invasive infra-clinical markers. Intima-Media Thickness (IMT) is recognized as an early indicator of cardiovascular disease. Carotid Wall Stress (CWS) can be calculated using arterial pressure and carotid size (diameter and IMT). Generally, IMT is measured during diastole when it reaches its maximum value. However, it changes during the cardiac cycle and a time-dependant waveform can be obtained using B-mode ultrasound images. In this work we calculated CWS considering three different approaches for IMT assessment: (i) constant IMT (standard diastolic value), (ii) estimated IMT from diameter waveform (assuming a constant cross-sectional wall area) and (iii) continuously measured IMT. Our results showed that maximum wall stress depends on the IMT estimation method. Systolic CWS progressively increased using the three approaches (p<0.024). We conclude that maximum CWS is highly dependent on wall thickness and accurate IMT measures during systole should be encouraged.

  15. Impact of Wall Shear Stress and Pressure Variation on the Stability of Atherosclerotic Plaque

    NASA Astrophysics Data System (ADS)

    Taviani, V.; Li, Z. Y.; Sutcliffe, M.; Gillard, J.

    Rupture of vulnerable atheromatous plaque in the carotid and coronary arteries often leads to stroke and heart attack respectively. The mechanism of blood flow and plaque rupture in stenotic arteries is still not fully understood. A three dimensional rigid wall model was solved under steady and unsteady conditions assuming a time-varying inlet velocity profile to investigate the relative importance of axial forces and pressure drops in arteries with asymmetric stenosis. Flow-structure interactions were investigated for the same geometry and the results were compared with those retrieved with the corresponding one dimensional models. The Navier-Stokes equations were used as the governing equations for the fluid. The tube wall was assumed linearly elastic, homogeneous isotropic. The analysis showed that wall shear stress is small (less than 3.5%) with respect to pressure drop throughout the cycle even for severe stenosis. On the contrary, the three dimensional behavior of velocity, pressure and wall shear stress is in general very different from that predicted by one dimensional models. This suggests that the primary source of mistakes in one dimensional studies comes from neglecting the three dimensional geometry of the plaque. Neglecting axial forces only involves minor errors.

  16. Plasmolysis and cell wall deposition in wheat root hairs under osmotic stress.

    PubMed

    Volgger, Michael; Lang, Ingeborg; Ovecka, Miroslav; Lichtscheidl, Irene

    2010-07-01

    We analysed cell wall formation in rapidly growing root hairs of Triticum aestivum under reduced turgor pressure by application of iso- and hypertonic mannitol solutions. Our experimental series revealed an osmotic value of wheat root hairs of 150 mOsm. In higher concentrations (200-650 mOsm), exocytosis of wall material and its deposition, as well as callose synthesis, still occurred, but the elongation of root hairs was stopped. Even after strong plasmolysis when the protoplast retreated from the cell wall, deposits of wall components were observed. Labelling with DiOC(6)(3) and FM1-43 revealed numerous Hechtian strands that spanned the plasmolytic space. Interestingly, the Hechtian strands also led towards the very tip of the root hair suggesting strong anchoring sites that are readily incorporated into the new cell wall. Long-term treatments of over 24 h in mannitol solutions (150-450 mOsm) resulted in reduced growth and concentration-dependent shortening of root hairs. However, the formation of new root hairs does occur in all concentrations used. This reflects the extraordinary potential of wheat root cells to adapt to environmental stress situations.

  17. Plasmolysis and cell wall deposition in wheat root hairs under osmotic stress.

    PubMed

    Volgger, Michael; Lang, Ingeborg; Ovecka, Miroslav; Lichtscheidl, Irene

    2010-07-01

    We analysed cell wall formation in rapidly growing root hairs of Triticum aestivum under reduced turgor pressure by application of iso- and hypertonic mannitol solutions. Our experimental series revealed an osmotic value of wheat root hairs of 150 mOsm. In higher concentrations (200-650 mOsm), exocytosis of wall material and its deposition, as well as callose synthesis, still occurred, but the elongation of root hairs was stopped. Even after strong plasmolysis when the protoplast retreated from the cell wall, deposits of wall components were observed. Labelling with DiOC(6)(3) and FM1-43 revealed numerous Hechtian strands that spanned the plasmolytic space. Interestingly, the Hechtian strands also led towards the very tip of the root hair suggesting strong anchoring sites that are readily incorporated into the new cell wall. Long-term treatments of over 24 h in mannitol solutions (150-450 mOsm) resulted in reduced growth and concentration-dependent shortening of root hairs. However, the formation of new root hairs does occur in all concentrations used. This reflects the extraordinary potential of wheat root cells to adapt to environmental stress situations. PMID:19533299

  18. A model of crosslink kinetics in the expanding plant cell wall: yield stress and enzyme action

    PubMed Central

    Dyson, R.J.; Band, L.R.; Jensen, O.E.

    2012-01-01

    The plant primary cell wall is a composite material containing stiff cellulose microfibrils that are embedded within a pectin matrix and crosslinked through a network of hemicellulose polymers. This microstructure endows the wall with nonlinear anisotropic mechanical properties and allows enzymatic regulation of expansive cell growth. We present a mathematical model of hemicellulose crosslink dynamics in an expanding cell wall incorporating strain-enhanced breakage and enzyme-mediated crosslink kinetics. The model predicts the characteristic yielding behaviour in the relationship between stress and strain-rate seen experimentally, and suggests how the effective yield and extensibility of the wall depend on microstructural parameters and on the action of enzymes of the XTH and expansin families. The model suggests that the yielding behaviour encapsulated in the classical Lockhart equation can be explained by the strongly nonlinear dependence of crosslink breakage rate on crosslink elongation. The model also demonstrates how enzymes that target crosslink binding can be effective in softening the wall in its pre-yield state, whereas its post-yield extensibility is determined primarily by the pectin matrix. PMID:22584249

  19. Analysis of fluid flow and wall shear stress patterns inside partially filled agitated culture well plates.

    PubMed

    Salek, M Mehdi; Sattari, Pooria; Martinuzzi, Robert J

    2012-03-01

    The appearance of highly resistant bacterial biofilms in both community and hospitals environments is a major challenge in modern clinical medicine. The biofilm structural morphology, believed to be an important factor affecting the behavioral properties of these "super bugs", is strongly influenced by the local hydrodynamics over the microcolonies. Despite the common use of agitated well plates in the biology community, they have been used rather blindly without knowing the flow characteristics and influence of the rotational speed and fluid volume in these containers. The main purpose of this study is to characterize the flow in these high-throughput devices to link local hydrodynamics to observed behavior in cell cultures. In this work, the flow and wall shear stress distribution in six-well culture plates under planar orbital translation is simulated using Computational Fluid Dynamics (CFD). Free surface, flow pattern and wall shear stress for two shaker speeds (100 and 200 rpm) and two volumes of fluid (2 and 4 mL) were investigated. Measurements with a non-intrusive optical shear stress sensor and High Frame-rate Particle Imaging Velocimetry (HFPIV) are used to validate CFD predictions. An analytical model to predict the free surface shape is proposed. Results show a complex three-dimensional flow pattern, varying in both time and space. The distribution of wall shear stress in these culture plates has been related to the topology of flow. This understanding helps explain observed endothelial cell orientation and bacterial biofilm distributions observed in culture dishes. The results suggest that the mean surface stress field is insufficient to capture the underlying dynamics mitigating biological processes. PMID:22042624

  20. Analysis of fluid flow and wall shear stress patterns inside partially filled agitated culture well plates.

    PubMed

    Salek, M Mehdi; Sattari, Pooria; Martinuzzi, Robert J

    2012-03-01

    The appearance of highly resistant bacterial biofilms in both community and hospitals environments is a major challenge in modern clinical medicine. The biofilm structural morphology, believed to be an important factor affecting the behavioral properties of these "super bugs", is strongly influenced by the local hydrodynamics over the microcolonies. Despite the common use of agitated well plates in the biology community, they have been used rather blindly without knowing the flow characteristics and influence of the rotational speed and fluid volume in these containers. The main purpose of this study is to characterize the flow in these high-throughput devices to link local hydrodynamics to observed behavior in cell cultures. In this work, the flow and wall shear stress distribution in six-well culture plates under planar orbital translation is simulated using Computational Fluid Dynamics (CFD). Free surface, flow pattern and wall shear stress for two shaker speeds (100 and 200 rpm) and two volumes of fluid (2 and 4 mL) were investigated. Measurements with a non-intrusive optical shear stress sensor and High Frame-rate Particle Imaging Velocimetry (HFPIV) are used to validate CFD predictions. An analytical model to predict the free surface shape is proposed. Results show a complex three-dimensional flow pattern, varying in both time and space. The distribution of wall shear stress in these culture plates has been related to the topology of flow. This understanding helps explain observed endothelial cell orientation and bacterial biofilm distributions observed in culture dishes. The results suggest that the mean surface stress field is insufficient to capture the underlying dynamics mitigating biological processes.

  1. Laser bending of pre-stressed thin-walled nickel micro-tubes

    NASA Astrophysics Data System (ADS)

    Che Jamil, M. S.; Imam Fauzi, E. R.; Juinn, C. S.; Sheikh, M. A.

    2015-10-01

    Laser forming is an innovative technique of producing bending, spatial forming and alignment of both metallic and non-metallic parts by introducing thermal stresses into a work piece with a laser beam. It involves a complex interaction of process parameters to mechanical and thermal characteristics of materials. This paper presents a comprehensive experimental and numerical study of laser bending process of thin-walled micro-tubes. The effect of input parameters, namely laser power, pulse length and pre-stress constraint, on the process and the final product characteristics are investigated. Results of the analysis show that the bending angle of the tube increases considerably when a constraint is imposed at the tube's free end during the heating period. The introduction of compressive pre-stresses (from mechanical bending) in the irradiated region increases the final deformation which varies almost linearly with the amount of pre-stress. Due to high thermal conductivity and thin-walled structure of the tube, the heat dissipates quickly from the irradiated region to its surrounding material. Therefore, a combination of short pulse duration and high power is preferable to generate a higher thermal gradient and induce plastic strain. Design of experiment and regression analysis are implemented to develop an empirical model based on simulation results. Sensitivity analysis is also performed to determine the influence of independent variables on output response. It is evident that initial displacement and pulse length have a stronger positive effect on the output response as compared to laser power.

  2. Oscillatory motion based measurement method and sensor for measuring wall shear stress due to fluid flow

    DOEpatents

    Armstrong, William D.; Naughton, Jonathan; Lindberg, William R.

    2008-09-02

    A shear stress sensor for measuring fluid wall shear stress on a test surface is provided. The wall shear stress sensor is comprised of an active sensing surface and a sensor body. An elastic mechanism mounted between the active sensing surface and the sensor body allows movement between the active sensing surface and the sensor body. A driving mechanism forces the shear stress sensor to oscillate. A measuring mechanism measures displacement of the active sensing surface relative to the sensor body. The sensor may be operated under periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor measurably changes the amplitude or phase of the motion of the active sensing surface, or changes the force and power required from a control system in order to maintain constant motion. The device may be operated under non-periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor change the transient motion of the active sensor surface or change the force and power required from a control system to maintain a specified transient motion of the active sensor surface.

  3. Growth promoting effects of prebiotic yeast cell wall products in starter broilers under an immune stress and Clostridium perfringens challenge

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study was designed to investigate the growth promoting effects of supplementing different sources and concentrations of prebiotic yeast cell wall (YCW) products containing mannanoligosaccharides in starter broilers under an immune stress and Clostridium perfringens challenge. Through a series ...

  4. Measurement of wall shear stress in chick embryonic heart using optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Ma, Zhenhe; Dou, Shidan; Zhao, Yuqian; Wang, Yi; Suo, Yanyan; Wang, Fengwen

    2015-03-01

    The cardiac development is a complicated process affected by genetic and environmental factors. Wall shear stress (WSS) is one of the components which have been proved to influence the morphogenesis during early stages of cardiac development. To study the mechanism, WSS measurement is a step with significant importance. WSS is caused by blood flow imposed on the inner surface of the heart wall and it can be determined by calculating velocity gradients of blood flow in a direction perpendicular to the wall. However, the WSS of the early stage embryonic heart is difficult to measure since the embryonic heart is tiny and beating fast. Optical coherence tomography (OCT) is a non-invasive imaging modality with high spatial and temporal resolution, which is uniquely suitable for the study of early stage embryonic heart development. In this paper, we introduce a method to measure the WSS of early stage chick embryonic heart based on high speed spectral domain optical coherence tomography (SDOCT). 4D (x,y,z,t) scan was performed on the outflow tract (OFT) of HH18 (~3 days of incubation) chick embryonic heart. After phase synchronization, OFT boundary segmentation, and OFT center line calculation, Doppler angle of the blood flow in the OFT can be achieved (This method has been described in previous publications). Combining with the Doppler OCT results, we calculate absolute blood flow velocity distribution in the OFT. The boundary of the OFT was segmented at each cross-sectional structural image, then geometrical center of the OFT can be calculated. Thus, the gradients of blood flow in radial direction can be calculated. This velocity gradient near the wall is termed wall shear rate and the WSS value is proportional to the wall shear rate. Based on this method, the WSS at different heart beating phase are compare. The result demonstrates that OCT is capable of early stage chicken embryonic heart WSS study.

  5. Wall shear stress characterization of a 3D bluff-body separated flow

    NASA Astrophysics Data System (ADS)

    Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi

    2013-10-01

    Efficient flow control strategies aimed at reducing the aerodynamic drag of road vehicles require a detailed knowledge of the reference flow. In this work, the flow around the rear slanted window of a generic car model was experimentally studied through wall shear stress measurements using an electrochemical method. The mean and fluctuating wall shear stress within the wall impact regions of the recirculation bubble and the main longitudinal vortex structures which develop above the rear window are presented. Correlations allow a more detailed characterization of the recirculation phenomenon within the separation bubble. In the model symmetry plane the recirculation structure compares well with simpler 2D configurations; specific lengths, flapping motion and shedding of large-scale vortices are observed, these similarities diminish when leaving the middle plane due to the strong three-dimensionality of the flow. A specific attention is paid to the convection processes occurring within the recirculation: a downstream convection velocity is observed, in accordance with 2D recirculations from the literature, and an upstream convection is highlighted along the entire bubble length which has not been underlined in some previous canonical configurations.

  6. Quantitative Assessment of Wall Shear Stress in an Aortic Coarctation - Impact of Virtual Interventions

    NASA Astrophysics Data System (ADS)

    Karlsson, Matts; Andersson, Magnus; Lantz, Jonas

    2014-11-01

    Turbulent and wall impinging blood flow causes abnormal shear forces onto the lumen and may play an important role in the pathogenesis of numerous cardiovascular diseases. In the present study, wall shear stress (WSS) and related flow parameters were studied in a pre-treated aortic coarctation (CoA) as well as after several virtual interventions using computational fluid dynamics (CFD). Patient-specific geometry and flow conditions were derived from magnetic resonance imaging (MRI) data. Finite element analysis was performed to acquire six different dilated CoAs. The unsteady pulsatile flow was resolved by large eddy simulation (LES) including non-Newtonian blood rheology. Pre-intervention, the presence of jet flow wall impingement caused an elevated WSS zone, with a distal region of low and oscillatory WSS. After intervention, cases with a more favorable centralized jet showed reduced high WSS values at the opposed wall. Despite significant turbulence reduction post-treatment, enhanced regions of low and oscillatory WSS were observed for all cases. This numerical method has demonstrated the morphological impact on WSS distribution in an CoA. With the predictability and validation capabilities of a combined CFD/MRI approach, a step towards patient-specific intervention planning is taken.

  7. Wall Shear Stress Characteristics for the Progression of the Disease, Atherosclerosis

    NASA Astrophysics Data System (ADS)

    Goswami, P.; Mandal, D. K.; Manna, N. K.; Chakrabarti, S.

    2014-12-01

    Wall shear stress (WSS) characteristics of a stenosed artery which are the important physiological parameters for the progression of the arterial diseases atherosclerosis, are studied and compared for different Reynolds numbers and different Womersley numbers. Numerical simulations of physiological pulsatile flow through a model stenotic artery are performed by finite volume method. From this study, it is revealed that the chance of formation of atherosclerosis increases with increase in Reynolds number and decreases with increase in Womersley number. The phenomenon of mass transportation across arterial wall is more in case of increase in Womersley number rather than Reynolds number. The chance of formation of atheromatous plaque will be high with higher Reynolds number and Womersley number. In the low WSS region, high magnitude of Womersley number indicates high chance of progression of the disease atherosclerosis. High magnitude of Womersley number with low Reynolds number is more dangerous for the progression of the disease in the low WSS region.

  8. Viscoelastic Poiseuille flows with total normal stress dependent, nonlinear Navier slip at the wall

    NASA Astrophysics Data System (ADS)

    Housiadas, Kostas D.

    2013-04-01

    The effect of slip at the wall in steady, isothermal, incompressible Poiseuille flows in channel/slits and circular tubes of viscoelastic fluids is investigated analytically. The nonlinear Navier law at the wall, for the dependence on the shear stress, along with an exponential dependence of the slip coefficient on the total normal stress is assumed. The viscoelasticity of the fluid is taken into account by employing the Oldroyd-B constitutive model. The flow problems are solved using a regular perturbation scheme in terms of the dimensionless exponential decay parameter of the slip coefficient, ɛ. The sequence of partial differential equations resulting from the perturbation procedure is solved analytically up to third order. As a consequence of the nonlinearity of the slip model, a two-dimensional, continuously developing, flow field arises. Spectral analysis on the solution shows that the velocity and pressure profiles are fully resolved even for high values of ɛ, which indicates that the perturbation series up to third order approximates the full solution very well. The effects of the dimensionless slip coefficient, isotropic pressure, and deviatoric part of the total normal stress in the slip model, as well as the other parameters and dimensionless numbers in the flow are presented and discussed. Average quantities, in the cross section of the channel/slit or tube, with emphasis given on the pressure drop and the skin friction factor, are also offered.

  9. Effects of dynamic shear and transmural pressure on wall shear stress sensitivity in collecting lymphatic vessels.

    PubMed

    Kornuta, Jeffrey A; Nepiyushchikh, Zhanna; Gasheva, Olga Y; Mukherjee, Anish; Zawieja, David C; Dixon, J Brandon

    2015-11-01

    Given the known mechanosensitivity of the lymphatic vasculature, we sought to investigate the effects of dynamic wall shear stress (WSS) on collecting lymphatic vessels while controlling for transmural pressure. Using a previously developed ex vivo lymphatic perfusion system (ELPS) capable of independently controlling both transaxial pressure gradient and average transmural pressure on an isolated lymphatic vessel, we imposed a multitude of flow conditions on rat thoracic ducts, while controlling for transmural pressure and measuring diameter changes. By gradually increasing the imposed flow through a vessel, we determined the WSS at which the vessel first shows sign of contraction inhibition, defining this point as the shear stress sensitivity of the vessel. The shear stress threshold that triggered a contractile response was significantly greater at a transmural pressure of 5 cmH2O (0.97 dyne/cm(2)) than at 3 cmH2O (0.64 dyne/cm(2)). While contraction frequency was reduced when a steady WSS was applied, this inhibition was reversed when the applied WSS oscillated, even though the mean wall shear stresses between the conditions were not significantly different. When the applied oscillatory WSS was large enough, flow itself synchronized the lymphatic contractions to the exact frequency of the applied waveform. Both transmural pressure and the rate of change of WSS have significant impacts on the contractile response of lymphatic vessels to flow. Specifically, time-varying shear stress can alter the inhibition of phasic contraction frequency and even coordinate contractions, providing evidence that dynamic shear could play an important role in the contractile function of collecting lymphatic vessels.

  10. Cell wall pectic arabinans influence the mechanical properties of Arabidopsis thaliana inflorescence stems and their response to mechanical stress.

    PubMed

    Verhertbruggen, Yves; Marcus, Susan E; Chen, Jianshe; Knox, J Paul

    2013-08-01

    Little is known of the dynamics of plant cell wall matrix polysaccharides in response to the impact of mechanical stress on plant organs. The capacity of the imposition of a mechanical stress (periodic brushing) to reduce the height of the inflorescence stem of Arabidopsis thaliana seedlings has been used to study the role of pectic arabinans in the mechanical properties and stress responsiveness of a plant organ. The arabinan-deficient-1 (arad1) mutation that affects arabinan structures in epidermal cell walls of inflorescence stems is demonstrated to reduce the impact on inflorescence stem heights caused by mechanical stress. The arabinan-deficient-2 (arad2) mutation, that does not have detectable impact on arabinan structures, is also shown to reduce the impact on stem heights caused by mechanical stress. The LM13 linear arabinan epitope is specifically detected in epidermal cell walls of the younger, flexible regions of inflorescence stems and increases in abundance at the base of inflorescence stems in response to an imposed mechanical stress. The strain (percentage deformation) of stem epidermal cells in the double mutant arad1 × arad2 is lower in unbrushed plants than in wild-type plants, but rises to wild-type levels in response to brushing. The study demonstrates the complexity of arabinan structures within plant cell walls and also that their contribution to cell wall mechanical properties is a factor influencing responsiveness to mechanical stress.

  11. Elevated ejection-phase myocardial wall stress in children with chronic kidney disease.

    PubMed

    Gu, Haotian; Sinha, Manish D; Li, Ye; Simpson, John; Chowienczyk, Phil J

    2015-10-01

    Myocardial wall stress (MWS) is thought to be the mechanical stimulus to ventricular hypertrophy. The objective of this study was to examine whether MWS is elevated in children with chronic kidney disease (CKD) who are at high risk of developing adverse cardiovascular events related to left ventricular (LV) hypertrophy. MWS, a function of left ventricular pressure, myocardial wall volume, and cavity volume, was obtained using carotid tonometry to estimate ventricular pressure and 2-dimensional transthoracic echocardiographic wall-tracking to obtain LV cavity and wall volumes. Ninety-two children (50 boys) aged 11.2±3.2 (mean±SD) years, including healthy controls (n=16), and those with CKD disease divided into 3 groups according to estimated glomerular filtration rate (mL/min per 1.73 m2) >90 (CKD 1, n=26), 60 to 90(CKD 2, n=23), and <60 (CKD≥3, n=27) were studied. There was no significant difference in age, height, weight, central or peripheral blood pressure, LV mass, or mass index in the 4 study groups. By contrast, peak, mean, and end-systolic MWS were higher in children with CKD and increased across stages of CKD (peak MWS, 338.8±18.5 and 397.5±14.3 s/cm2 in controls and CKD≥3, respectively; P=0.01). Higher systolic MWS was explained by a form of LV dysfunction whereby dynamic values of the ratio of wall volume/cavity size during systole were lower in children with CKD than in those without (P=0.001). Children with CKD exhibit blood pressure–independent LV dysfunction which results in increased systolic MWS and which may predispose to LV hypertrophy in later life. PMID:26324503

  12. Discovery of Novel Cell Wall-Active Compounds Using PywaC, a Sensitive Reporter of Cell Wall Stress, in the Model Gram-Positive Bacterium Bacillus subtilis

    PubMed Central

    Czarny, T. L.; Perri, A. L.; French, S.

    2014-01-01

    The emergence of antibiotic resistance in recent years has radically reduced the clinical efficacy of many antibacterial treatments and now poses a significant threat to public health. One of the earliest studied well-validated targets for antimicrobial discovery is the bacterial cell wall. The essential nature of this pathway, its conservation among bacterial pathogens, and its absence in human biology have made cell wall synthesis an attractive pathway for new antibiotic drug discovery. Herein, we describe a highly sensitive screening methodology for identifying chemical agents that perturb cell wall synthesis, using the model of the Gram-positive bacterium Bacillus subtilis. We report on a cell-based pilot screen of 26,000 small molecules to look for cell wall-active chemicals in real time using an autonomous luminescence gene cluster driven by the promoter of ywaC, which encodes a guanosine tetra(penta)phosphate synthetase that is expressed under cell wall stress. The promoter-reporter system was generally much more sensitive than growth inhibition testing and responded almost exclusively to cell wall-active antibiotics. Follow-up testing of the compounds from the pilot screen with secondary assays to verify the mechanism of action led to the discovery of 9 novel cell wall-active compounds. PMID:24687489

  13. Quantifying blood flow and wall shear stresses in the outflow tract of chick embryonic hearts

    PubMed Central

    Liu, Aiping; Nickerson, Andrew; Troyer, Aaron; Yin, Xin; Cary, Robert; Thornburg, Kent; Wang, Ruikang; Rugonyi, Sandra

    2011-01-01

    Wall shear stresses (WSS) exerted by blood flow on cardiac tissues modulate growth and development of the heart. To study the role of hemodynamic conditions on cardiac morphogenesis, here, we present a methodology that combines imaging and finite element modeling to quantify the in vivo blood flow dynamics and WSS in the cardiac outflow tract (OFT) of early chicken embryos (day 3 out of 21-day incubation period). We found a distinct blood flow field and heterogeneous distribution of WSS in the chicken embryonic heart OFT, which have physiological implications for OFT morphogenesis. PMID:21572557

  14. Transcriptional reporters for genes activated by cell wall stress through a non-catalytic mechanism involving Mpk1 and SBF

    PubMed Central

    Kim, Ki-Young; Levin, David E.

    2011-01-01

    The Mpk1 MAP kinase of the Cell Wall Integrity (CWI) signaling pathway induces transcription of the FKS2 gene in response to cell wall stress through a non-catalytic mechanism that involves stable association of Mpk1 with the Swi4 transcription factor. This dimeric complex binds to a Swi4 recognition site in the FKS2 promoter. The Swi6 transcription factor is also required to bind this ternary complex for transcription initiation to ensue. In this context, the Mlp1 pseudokinase serves a redundant function with Mpk1. We have identified three additional genes, CHA1, YLR042c, and YKR013w that are induced by cell wall stress through the same mechanism. We report on the behavior of several promoter-lacZ reporter plasmids designed to detect cell wall stress transcription through this pathway. PMID:20641022

  15. Effects of verapamil, carbenoxolone and N-acetylcysteine on gastric wall mucus and ulceration in stressed rats.

    PubMed

    Koo, M W; Ogle, C W; Cho, C H

    1986-01-01

    The effects of verapamil on gastric wall mucus and ulceration were studied in rats which were restrained and exposed to 4 degrees C (stress). Stress for 2 h significantly depleted stomach wall mucus and produced marked gastric glandular ulcers. Verapamil pretreatment (2, 4, 8 or 16 mg/kg), injected intraperitoneally 30 min before experimentation, significantly prevented stress-induced mucus depletion and gastric ulceration; however, it did not itself influence stomach wall mucus levels in nonstressed animals. Intragastric administration of carbenoxolone (100 or 200 mg/kg), also given 30 min before stress, exhibited similar actions as verapamil. A 15% solution of N-acetylcysteine (10 ml/kg), given orally, strongly decreased the mucus content in both nonstress and stress conditions; it induced ulcers in nonstressed rats, and worsened stress ulceration. These effects were not reversed by verapamil pretreatment. The influence of multiple-dose pretreatment with verapamil or carbenoxolone on mucus content and ulceration in the gastric glandular mucosa during stress is also discussed. It is concluded that gastric wall mucus depletion is likely to play an important role in stress ulcer formation; the antiulcer action of verapamil could partly be due to the preservation of mucus.

  16. Residual stress analysis in forming process of filament wound thick-walled CFRP pipes

    SciTech Connect

    Kondo, Toshimi; Sekine, Hideki; Nakano, Kunio

    1995-11-01

    Residual stress analysis for the cracking phenomenon of filament would thick-walled CFRP pipes, which frequently occurs in the forming process of curing and thermal cycling through the course of the wet filament winding, was made from both the experimental and theoretical points of view. A simple analytical model to study the cracking in the CFRP pipes was proposed. The pipes are multilayered and reinforced in the axial and circumferential directions alternatively by carbon fibers. Taking account of the anisotropy of mechanical and thermal properties including the shrinkage strain, which depend considerably on the temperature, the residual stresses in the CFRP pipes were elucidated in the forming process, particularly, in cooling of the cure process.

  17. Stress distribution in and equivalent width of flanges of wide, thin-wall steel beams

    NASA Technical Reports Server (NTRS)

    Winter, George

    1940-01-01

    The use of different forms of wide-flange, thin-wall steel beams is becoming increasingly widespread. Part of the information necessary for a national design of such members is the knowledge of the stress distribution in and the equivalent width of the flanges of such beams. This problem is analyzed in this paper on the basis of the theory of plane stress. As a result, tables and curves are given from which the equivalent width of any given beam can be read directly for use in practical design. An investigation is given of the limitations of this analysis due to the fact that extremely wide and thin flanges tend to curve out of their plane toward the neutral axis. A summary of test data confirms very satisfactorily the analytical results.

  18. Integrated Control of Axonemal Dynein AAA+ Motors

    PubMed Central

    King, Stephen M.

    2012-01-01

    Axonemal dyneins are AAA+ enzymes that convert ATP hydrolysis to mechanical work. This leads to the sliding of doublet microtubules with respect to each other and ultimately the generation of ciliary/flagellar beating. However, in order for useful work to be generated, the action of individual dynein motors must be precisely controlled. In addition, cells modulate the motility of these organelles through a variety of second messenger systems and these signals too must be integrated by the dynein motors to yield an appropriate output. This review describes the current status of efforts to understand dynein control mechanisms and their connectivity focusing mainly on studies of the outer dynein arm from axonemes of the unicellular biflagellate green alga Chlamydomonas. PMID:22406539

  19. The Interaction between Fluid Wall Shear Stress and Solid Circumferential Strain Affects Endothelial Gene Expression.

    PubMed

    Amaya, Ronny; Pierides, Alexis; Tarbell, John M

    2015-01-01

    Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS) and circumferential stress (CS) that can be characterized by the temporal phase angle between WSS and CS (stress phase angle - SPA). Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180°) such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0°) are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 °) and synchronous hemodynamics (SPA=0 °). This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS) exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2) and CS (4 ± 4%) over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NFκB and other NFκB target genes. The up regulation of NFκB p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NFκB p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 °) can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease.

  20. Cell wall yield properties of growing tissue: evaluation by in vivo stress relaxation. [Pisum sativus L

    SciTech Connect

    Cosgrove, D.J.

    1985-06-01

    Growing pea stem tissue, when isolated from an external supply of water, undergoes stress relaxation because of continued loosening of the cell wall. A theoretical analysis is presented to show that such stress relaxation should result in an exponential decrease in turgor pressure down to the yield threshold (Y), with a rate constant given by phi epsilon where phi is the metabolically maintained irreversible extensibility of the cell wall and epsilon is the volumetric elastic modulus of the cell. Stress relaxation was measured in pea (Pisum sativus L.) stem segments using the pressure microprobe technique. From the rate of stress relaxation, phi of segments pretreated with water was calculated to be 0.08 per megapascal per hour while that of auxin-pretreated tissue was 0.24 per megapascal per hour. These values agreed closely with estimates of phi made by a steady-state technique. The yield threshold (0.29 megapascal) was not affected by auxin. A theoretical analysis is also presented to show that the tissue hydraulic conductance may be estimated from the T/sub 1/2/ of tissue swelling. Experimentally, pea stems had a swelling T/sub 1/2/ of 2.0 minutes, corresponding to a relative hydraulic conductance of about 2.0 per megapascal per hour. This value is at least 8 times larger than phi. From these data and from computer modeling, it appears that the radial gradient in water potential which sustains water uptake in growing pea segments is small (0.04 megapascal). This means that hydraulic conductance does not substantially restrict growth. The results also demonstrate that the stimulation of growth by auxin can be entirely accounted for by the change in phi.

  1. The Interaction between Fluid Wall Shear Stress and Solid Circumferential Strain Affects Endothelial Gene Expression

    PubMed Central

    Amaya, Ronny; Pierides, Alexis; Tarbell, John M.

    2015-01-01

    Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS) and circumferential stress (CS) that can be characterized by the temporal phase angle between WSS and CS (stress phase angle – SPA). Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180°) such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0°) are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 °) and synchronous hemodynamics (SPA=0 °). This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS) exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2) and CS (4 ± 4 %) over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NFκB and other NFκB target genes. The up regulation of NFκB p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NFκB p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 °) can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease. PMID:26147292

  2. Numerical design and optimization of hydraulic resistance and wall shear stress inside pressure-driven microfluidic networks.

    PubMed

    Damiri, Hazem Salim; Bardaweel, Hamzeh Khalid

    2015-11-01

    Microfluidic networks represent the milestone of microfluidic devices. Recent advancements in microfluidic technologies mandate complex designs where both hydraulic resistance and pressure drop across the microfluidic network are minimized, while wall shear stress is precisely mapped throughout the network. In this work, a combination of theoretical and modeling techniques is used to construct a microfluidic network that operates under minimum hydraulic resistance and minimum pressure drop while constraining wall shear stress throughout the network. The results show that in order to minimize the hydraulic resistance and pressure drop throughout the network while maintaining constant wall shear stress throughout the network, geometric and shape conditions related to the compactness and aspect ratio of the parent and daughter branches must be followed. Also, results suggest that while a "local" minimum hydraulic resistance can be achieved for a geometry with an arbitrary aspect ratio, a "global" minimum hydraulic resistance occurs only when the aspect ratio of that geometry is set to unity. Thus, it is concluded that square and equilateral triangular cross-sectional area microfluidic networks have the least resistance compared to all rectangular and isosceles triangular cross-sectional microfluidic networks, respectively. Precise control over wall shear stress through the bifurcations of the microfluidic network is demonstrated in this work. Three multi-generation microfluidic network designs are considered. In these three designs, wall shear stress in the microfluidic network is successfully kept constant, increased in the daughter-branch direction, or decreased in the daughter-branch direction, respectively. For the multi-generation microfluidic network with constant wall shear stress, the design guidelines presented in this work result in identical profiles of wall shear stresses not only within a single generation but also through all the generations of the

  3. Numerical design and optimization of hydraulic resistance and wall shear stress inside pressure-driven microfluidic networks.

    PubMed

    Damiri, Hazem Salim; Bardaweel, Hamzeh Khalid

    2015-11-01

    Microfluidic networks represent the milestone of microfluidic devices. Recent advancements in microfluidic technologies mandate complex designs where both hydraulic resistance and pressure drop across the microfluidic network are minimized, while wall shear stress is precisely mapped throughout the network. In this work, a combination of theoretical and modeling techniques is used to construct a microfluidic network that operates under minimum hydraulic resistance and minimum pressure drop while constraining wall shear stress throughout the network. The results show that in order to minimize the hydraulic resistance and pressure drop throughout the network while maintaining constant wall shear stress throughout the network, geometric and shape conditions related to the compactness and aspect ratio of the parent and daughter branches must be followed. Also, results suggest that while a "local" minimum hydraulic resistance can be achieved for a geometry with an arbitrary aspect ratio, a "global" minimum hydraulic resistance occurs only when the aspect ratio of that geometry is set to unity. Thus, it is concluded that square and equilateral triangular cross-sectional area microfluidic networks have the least resistance compared to all rectangular and isosceles triangular cross-sectional microfluidic networks, respectively. Precise control over wall shear stress through the bifurcations of the microfluidic network is demonstrated in this work. Three multi-generation microfluidic network designs are considered. In these three designs, wall shear stress in the microfluidic network is successfully kept constant, increased in the daughter-branch direction, or decreased in the daughter-branch direction, respectively. For the multi-generation microfluidic network with constant wall shear stress, the design guidelines presented in this work result in identical profiles of wall shear stresses not only within a single generation but also through all the generations of the

  4. AAAS Communicating Science Program: Reflections on Evaluation

    NASA Astrophysics Data System (ADS)

    Braha, J.

    2015-12-01

    The AAAS Center for Public Engagement (Center) with science builds capacity for scientists to engage public audiences by fostering collaboration among natural or physical scientists, communication researchers, and public engagement practitioners. The recently launched Leshner Leadership Institute empowers cohorts of mid-career scientists to lead public engagement by supporting their networks of scientists, researchers, and practitioners. The Center works closely with social scientists whose research addresses science communication and public engagement with science to ensure that the Communicating Science training program builds on empirical evidence to inform best practices. Researchers ( Besley, Dudo, & Storkdieck 2015) have helped Center staff and an external evaluator develop pan instrument that measures progress towards goals that are suggested by the researcher, including internal efficacy (increasing scientists' communication skills and confidence in their ability to engage with the public) and external efficacy (scientists' confidence in engagement methods). Evaluation results from one year of the Communicating Science program suggest that the model of training yields positive results that support scientists in the area that should lead to greater engagement. This talk will explore the model for training, which provides a context for strategic communication, as well as the practical factors, such as time, access to public engagement practitioners, and technical skill, that seems to contribute to increased willingness to engage with public audiences. The evaluation program results suggest willingness by training participants to engage directly or to take preliminary steps towards engagement. In the evaluation results, 38% of trained scientists reported time as a barrier to engagement; 35% reported concern that engagement would distract from their work as a barrier. AAAS works to improve practitioner-researcher-scientist networks to overcome such barriers.

  5. Quantification of disturbed wall shear stress patterns in complex cardiovascular flows

    NASA Astrophysics Data System (ADS)

    Arzani, Amirhossein; Shadden, Shawn C.

    2014-11-01

    Wall shear stress (WSS) affects the cardiovascular system in numerous ways, and is thought to play an important role in the pathology of many cardiovascular diseases. The (endothelial) cells lining the inner wall of blood vessels, and perhaps the cells inside the vessel wall, can actively sense WSS and respond both chemically and mechanically. The complexity of WSS in cardiovascular flows extends both spatially and temporally. Furthermore, WSS has magnitude and direction. These facets make simple quantification of WSS in cardiovascular applications difficult. In this study we propose a framework to quantify measures such as WSS angle gradient, WSS magnitude gradient, WSS angle time derivative and WSS magnitude time derivative. We will explain the relation of these parameters to the tensorial WSS gradient and WSS vector time derivative, and propose a new methodology to unify these concepts into a single measure. The correlation between these metrics and more common WSS metrics used in the literature will be demonstrated. For demonstration, these methods will be used for the quantification of complex blood flow inside abdominal aortic aneurysms.

  6. Stress-induced self-rolled metal/insulator bifilm microtube with micromesh walls

    NASA Astrophysics Data System (ADS)

    Lee, Kook-Nyung; Seo, Yeong-Tai; Lee, Min-Ho; Jung, Suk-Won; Kim, Yong-Kweon; Kim, Jung-Mu; Kyeong Seong, Woo

    2013-01-01

    A metal/insulator microtube with micromesh walls was constructed using stress-assisted self-rolling technology. The mesh-sidewall Pt/Ti/SiO2 microtube was self-formed by a tensile-stressed metal Pt/Ti film deposited onto a pre-patterned SiO2 micromesh layer. The microtube measured about 25 µm in diameter and was longer than 7 mm. The sidewall of the microtube was a square mesh, 5-20 µm long, and was electrically connected to electrical pads for electrical conductance measurement. The electrical resistance of the rolled-up microtube was measured to be 250-350 Ω when the microtube resistor's length was around 540 µm. The real-time measurement of the conductance change of the microtube with a Pt resistor could monitor the temperature change generated by heat injection. The microtube with micromesh walls is expected to be an interesting structure that has promising potential for use in electronics, chemical and biological applications.

  7. Numerical study of wall shear stress-based descriptors in the human left coronary artery.

    PubMed

    Pinto, S I S; Campos, J B L M

    2016-10-01

    The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion. PMID:26883291

  8. Numerical study of wall shear stress-based descriptors in the human left coronary artery.

    PubMed

    Pinto, S I S; Campos, J B L M

    2016-10-01

    The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion.

  9. A multi-layer description of Reynolds stresses in canonical wall bounded flows

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Hussain, Fazle; She, Zhen-Su

    2015-11-01

    A complete description of the Reynolds stress tensor is obtained for all three canonical wall turbulence (channel, pipe and turbulent boundary layer - TBL). The result builds on a multi-layer description of length (order) functions and their ratios, including viscous sublayer, buffer layer, meso-layer for the near wall (inner) region, and bulk flow or a central core (absent in TBL) for the outer region. It is shown that the streamwise mean kinetic-energy profile is quantified with high accuracy over the entire flow domain. The model contains only three Re-dependent parameters for Reynolds number (Re) covering nearly three decades. Furthermore, the inner peak location is predicted to be invariant at y+ = 15, while its magnitude shows notable Re and geometry effects, predicted to be .9.2 for high Re's pipe flows. A mechanism is proposed for the emergence of outer peak in pipes, whose magnitude is predicted to scale as .Reτ0. 05 beyond a critical Reτ about 104(). The recently reported logarithmic dependence in the bulk is recovered, but with an alternative explanation. The result is successfully extended to TBL flows by a fractional total stress and an absence of core. Equally accurate descriptions of vertical and spanwise kinetic-energy are also presented for the three flows. The result has been used to modify turbulent engineering models (i.e. k- ω model) with significant improvement.

  10. The effect of wall depletion and hydrodynamic interactions on stress-gradient-induced polymer migration.

    PubMed

    Rezvantalab, Hossein; Zhu, Guorui; Larson, Ronald G

    2016-07-21

    We generalize our recent continuum theory for the stress-gradient-induced migration of polymers [Zhu et al., J. Rheol., 2016, 60, 327-343] by incorporating the effect of solid boundaries on concentration variations. For a model flow in a channel with periodic slip wall velocity, which can in principle be produced by an electric field in the presence of a sinusoidal wall charge, we obtain theoretical results for the steady-state distribution of dilute solutions of polymer dumbbells using a systematic perturbation analysis in Weissenberg number Wi. We find that the presence of a thin wall depletion zone changes the lowest order solution from second to first in Wi and drastically affects the concentration field far from the depletion layer, due both to a coupling of the second derivative of the velocity field to the concentration gradient, and to convection of the polymer-depleted fluid in this layer into the bulk of the fluid. Additional effects induced by wall hydrodynamic interaction (HI) are assessed by incorporating polymer flux from the wall-HI migration theory of Ma and Graham into our continuum theory. We establish the range of validity of our theory by comparing the theoretical results with Brownian dynamics (BD) simulations: excellent agreement is achieved for relatively small molecules, while the theory breaks down when the Gradient number Gd is greater than 0.5, where Gd is the ratio of polymer coil size to the length scale over which the velocity gradient changes. The BD simulations are also extended to the case of long Hookean chains with numbers of springs per chain ranging from 1 to 32, where it is found that for fixed Gd and Wi, the results are nearly identical, showing that all important phenomena are captured by a simple dumbbell model, thus supporting the continuum theory which was derived for the case of dumbbells. In addition, the Stochastic Rotation Dynamics (SRD) method is employed to evaluate the role of HI on the migration pattern, producing

  11. The effect of wall depletion and hydrodynamic interactions on stress-gradient-induced polymer migration.

    PubMed

    Rezvantalab, Hossein; Zhu, Guorui; Larson, Ronald G

    2016-07-21

    We generalize our recent continuum theory for the stress-gradient-induced migration of polymers [Zhu et al., J. Rheol., 2016, 60, 327-343] by incorporating the effect of solid boundaries on concentration variations. For a model flow in a channel with periodic slip wall velocity, which can in principle be produced by an electric field in the presence of a sinusoidal wall charge, we obtain theoretical results for the steady-state distribution of dilute solutions of polymer dumbbells using a systematic perturbation analysis in Weissenberg number Wi. We find that the presence of a thin wall depletion zone changes the lowest order solution from second to first in Wi and drastically affects the concentration field far from the depletion layer, due both to a coupling of the second derivative of the velocity field to the concentration gradient, and to convection of the polymer-depleted fluid in this layer into the bulk of the fluid. Additional effects induced by wall hydrodynamic interaction (HI) are assessed by incorporating polymer flux from the wall-HI migration theory of Ma and Graham into our continuum theory. We establish the range of validity of our theory by comparing the theoretical results with Brownian dynamics (BD) simulations: excellent agreement is achieved for relatively small molecules, while the theory breaks down when the Gradient number Gd is greater than 0.5, where Gd is the ratio of polymer coil size to the length scale over which the velocity gradient changes. The BD simulations are also extended to the case of long Hookean chains with numbers of springs per chain ranging from 1 to 32, where it is found that for fixed Gd and Wi, the results are nearly identical, showing that all important phenomena are captured by a simple dumbbell model, thus supporting the continuum theory which was derived for the case of dumbbells. In addition, the Stochastic Rotation Dynamics (SRD) method is employed to evaluate the role of HI on the migration pattern, producing

  12. Our Paths Might Cross: the Role of the Fungal Cell Wall Integrity Pathway in Stress Response and Cross Talk with Other Stress Response Pathways▿

    PubMed Central

    Fuchs, Beth Burgwyn; Mylonakis, Eleftherios

    2009-01-01

    Fungi occupy diverse environments and are subjected to many extreme conditions. Among the stressful conditions faced by fungi are pH changes, osmotic changes, thermal changes, oxide radicals, nutrient deprivation, and exposure to chemicals. These adversities can be found either in the environment or in animal and human hosts. The cell wall integrity (CWI) pathway provides a means to fortify and repair damages to the cell wall in order to withstand stressful environments. The CWI pathway in comprised of cell wall stress sensors that lead to activation of a mitogen-activated protein kinase (MAPK) cascade. Signaling through the MAPK cascade leads to expression of transcription factors that facilitate biosynthesis of cell wall components and actin organization. Given the relatively limited number of components of the CWI pathway and the very diverse stimuli, there must be a means of expanding the pathway. To manage the diverse stress conditions, the CWI pathway cross talks with other pathways or proteins, and these cross talk events enhance the signaling capabilities of the CWI pathway. Lateral influences that facilitate maintaining the cell wall under stress conditions are TOR signaling, calcineurin signaling, the high-osmolarity glycerol pathway, the cyclic AMP-protein kinase A pathway, and additional proteins. In this article, we highlight several of the cross talk events that have been described for Saccharomyces cerevisiae and several other fungi. PMID:19717745

  13. Increased Inlet Blood Flow Velocity Predicts Low Wall Shear Stress in the Cephalic Arch of Patients with Brachiocephalic Fistula Access

    PubMed Central

    Boghosian, Michael; Cassel, Kevin; Watson, Sydeaka; Funaki, Brian; Doshi, Taral; Mahmoudzadeh Akherat, S. M. Javid; Hines, Jane; Coe, Fredric

    2016-01-01

    Background An autogenous arteriovenous fistula is the optimal vascular access for hemodialysis. In the case of brachiocephalic fistula, cephalic arch stenosis commonly develops leading to access failure. We have hypothesized that a contribution to fistula failure is low wall shear stress resulting from post-fistula creation hemodynamic changes that occur in the cephalic arch. Methods Twenty-two subjects with advanced renal failure had brachiocephalic fistulae placed. The following procedures were performed at mapping (pre-operative) and at fistula maturation (8–32 weeks post-operative): venogram, Doppler to measure venous blood flow velocity, and whole blood viscosity. Geometric and computational modeling was performed to determine wall shear stress and other geometric parameters. The relationship between hemodynamic parameters and clinical findings was examined using univariate analysis and linear regression. Results The percent low wall shear stress was linearly related to the increase in blood flow velocity (p < 0.01). This relationship was more significant in non-diabetic patients (p < 0.01) than diabetic patients. The change in global measures of arch curvature and asymmetry also evolve with time to maturation (p < 0.05). Conclusions The curvature and hemodynamic changes during fistula maturation increase the percentage of low wall shear stress regions within the cephalic arch. Low wall shear stress may contribute to subsequent neointimal hyperplasia and resultant cephalic arch stenosis. If this hypothesis remains tenable with further studies, ways of protecting the arch through control of blood flow velocity may need to be developed. PMID:27074019

  14. Effect of cell wall integrity stress and RlmA transcription factor on asexual development and autolysis in Aspergillus nidulans.

    PubMed

    Kovács, Zsuzsanna; Szarka, Máté; Kovács, Szilvia; Boczonádi, Imre; Emri, Tamás; Abe, Keietsu; Pócsi, István; Pusztahelyi, Tünde

    2013-05-01

    The cell wall integrity (CWI) signaling pathway is responsible for cell wall remodeling and reinforcement upon cell wall stress, which is proposed to be universal in fungal cultures. In Aspergillus nidulans, both the deletion of rlmA encoding the RlmA transcription factor in CWI signaling and low concentrations of the cell wall polymer intercalating agent Congo Red caused significant physiological changes. The gene deletion mutant ΔrlmA strain showed decreased CWI and oxidative stress resistances, which indicated the connection between the CWI pathway and the oxidative stress response system. The Congo Red stress resulted in alterations in the cell wall polymer composition in submerged cultures due to the induction of the biosynthesis of the alkali soluble fraction as well as the hydrolysis of cell wall biopolymers. Both RlmA and RlmA-independent factors induced by Congo Red stress regulated the expression of glucanase (ANID_00245, engA) and chitinase (chiB, chiA) genes, which promoted the autolysis of the cultures and also modulated the pellet sizes. CWI stress and rlmA deletion affected the expression of brlA encoding the early conidiophore development regulator transcription factor BrlA and, as a consequence, the formation of conidiophores was significantly changed in submerged cultures. Interestingly, the number of conidiospores increased in surface cultures of the ΔrlmA strain. The in silico analysis of genes putatively regulated by RlmA and the CWI transcription factors AnSwi4/AnSwi6 in the SBF complex revealed only a few jointly regulated genes, including ugmA and srrA coding for UgmA UDP-galactopyranose mutase and SrrA stress response regulator, respectively. PMID:23485399

  15. Plaque components affect wall stress in stented human carotid artery: A numerical study

    NASA Astrophysics Data System (ADS)

    Fan, Zhen-Min; Liu, Xiao; Du, Cheng-Fei; Sun, An-Qiang; Zhang, Nan; Fan, Zhan-Ming; Fan, Yu-Bo; Deng, Xiao-Yan

    2016-09-01

    Carotid artery stenting presents challenges of in-stent restenosis and late thrombosis, which are caused primarily by alterations in the mechanical environment of the artery after stent implantation. The present study constructed patient-specific carotid arterial bifurcation models with lipid pools and calcified components based on magnetic resonance imaging. We numerically analyzed the effects of multicomponent plaques on the distributions of von Mises stresses (VMSs) in the patient-specific models after stenting. The results showed that when a stent was deployed, the large soft lipid pool in atherosclerotic plaques cushioned the host artery and reduced the stress within the arterial wall; however, this resulted in a sharp increase of VMS in the fibrous cap. When compared with the lipid pool, the presence of the calcified components led to slightly increased stresses on the luminal surface. However, when a calcification was located close to the luminal surface of the host artery and the stenosis, the local VMS was elevated. Overall, compared with calcified components, large lipid pools severely damaged the host artery after stenting. Furthermore, damage due to the calcified component may depend on location.

  16. Stress corrosion cracking of candidate structural materials under simulated first-wall/aqueous coolant environments

    SciTech Connect

    Fox, M.R.; Hull, A.B.; Kassner, T.F.

    1990-10-01

    Stress corrosion cracking (SCC) susceptibility of Types 316NG, 316, and 304 stainless steels (SS) was investigated in slow-strain-rate tests (SSRTs) in oxygenated water that simulates important parameters anticipated in first-wall/blanket systems. The water chemistry was based on a computer code which yielded the nominal concentrations of radiolytic species produced in an aqueous environment under ITER-type conditions. Actual SSRTs were performed in a less benign, more oxidizing reference environment at temperatures from 52 to 150{degree}C. Predominantly ductile fracture was observed in Type 316NG and nonsensitized Types 316 SS and 304 SS SSRT specimens strained to failure in a reference ITER water chemistry. The failure behavior of Type 304 SS specimens heat-treated to yield sensitization values of 2, 3, or 20 Coulomb (C)/cm{sup 2} by the electrochemical potentiokinetic reactivation (EPR) technique, demonstrated that the degree of sensitization had a dramatic effect on intergranular stress corrosion cracking (IGSCC) susceptibility. Ranking for resistance to SCC in simulated ITER water by electron microscopy and SSRT parameters, i.e., failure time, ultimate strength, total elongation and stress ratio is 304 SS (EPR = 20 <2 C/cm{sup 2}) < 316NG SS. 11 refs., 6 figs., 7 tabs.

  17. A mathematical model for estimating the axial stress of the common carotid artery wall from ultrasound images.

    PubMed

    Soleimani, Effat; Mokhtari-Dizaji, Manijhe; Saberi, Hajir; Sharif-Kashani, Shervin

    2016-08-01

    Clarifying the complex interaction between mechanical and biological processes in healthy and diseased conditions requires constitutive models for arterial walls. In this study, a mathematical model for the displacement of the carotid artery wall in the longitudinal direction is defined providing a satisfactory representation of the axial stress applied to the arterial wall. The proposed model was applied to the carotid artery wall motion estimated from ultrasound image sequences of 10 healthy adults, and the axial stress waveform exerted on the artery wall was extracted. Consecutive ultrasonic images (30 frames per second) of the common carotid artery of 10 healthy subjects (age 44 ± 4 year) were recorded and transferred to a personal computer. Longitudinal displacement and acceleration were extracted from ultrasonic image processing using a block-matching algorithm. Furthermore, images were examined using a maximum gradient algorithm and time rate changes of the internal diameter and intima-media thickness were extracted. Finally, axial stress was estimated using an appropriate constitutive equation for thin-walled tubes. Performance of the proposed model was evaluated using goodness of fit between approximated and measured longitudinal displacement statistics. Values of goodness-of-fit statistics indicated high quality of fit for all investigated subjects with the mean adjusted R-square (0.86 ± 0.08) and root mean squared error (0.08 ± 0.04 mm). According to the results of the present study, maximum and minimum axial stresses exerted on the arterial wall are 1.7 ± 0.6 and -1.5 ± 0.5 kPa, respectively. These results reveal the potential of this technique to provide a new method to assess arterial stress from ultrasound images, overcoming the limitations of the finite element and other simulation techniques.

  18. Echocardiographic Evaluation of Left Ventricular Function, Mass and Wall Stress in Children with Isolated Ventricular Septal Defect

    PubMed Central

    Waggoner, Alan D.; Nouri, Soraya; Schaffer, Michael S.; Chen, Su-Chiung

    1985-01-01

    M-Mode echocardiography was performed in 22 normal children and 22 children with ventricular septal defects. Left ventricular and left atrial chamber dimensions and wall thicknesses were measured in all patients. Utilizing these data, indices of left ventricular function were derived: shortening fraction, velocity of fiber shortening, peak diastolic fiber lengthening, end-systolic wall stress, radius thickness ratio, and ventricular mass. The results showed that ventricular septal defect was associated with enlarged left ventricular and atrial dimensions and increased shortening fraction, but that velocity of shortening and early diastolic lengthening remained normal. Left ventricular mass was increased, thus maintaining normal wall stress and radius/thickness ratio. Cardiac failure complicating ventricular septal defect was associated with enlarged left ventricular and atrial dimensions (indexed for weight). Ventricular mass, wall stress and function, however, were similar in subjects with ventricular septal defect, with or without cardiac failure. Since left ventricular mass was adequate to maintain wall stress and function in subjects with heart failure, other factors were presumably responsible for heart failure complicating ventricular septal defect. PMID:15227026

  19. Wall shear stress in the development of in-stent restenosis revisited. A critical review of clinical data on shear stress after intracoronary stent implantation.

    PubMed

    Jenei, Csaba; Balogh, Emília; Szabó, Gábor Tamás; Dézsi, Csaba András; Kőszegi, Zsolt

    2016-01-01

    The average wall shear stress (WSS) is in 1 Pa range in coronary arteries, while the stretching effect of an implanted coronary stent can generate up to 3 × 105 times higher circumferential stress in the vessel wall. It is widely accepted that WSS plays a critical role in the development of restenosis after coronary stent implantation, but relevant clinical endpoint studies are lack-ing. Fluid dynamics modeling suggests an association between WSS and intimal hyperplasia, however, such an association is not established when the compensating healing process becomes an overshoot phenomenon. This review summarizes available clinical results and concepts of potential clinical importance. PMID:27439365

  20. Dynamic blood flow and wall shear stress in pulmonary hypertensive disease.

    PubMed

    Postles, Arthur; Clark, Alys R; Tawhai, Merryn H

    2014-01-01

    This study provides new model of pulsatile flow in the pulmonary circulation in health and pulmonary hypertensive disease. Structural vascular remodeling typical of pulmonary hypertensive disease was implemented in the model by progressively altering the mechanical properties of the arterial geometry and progressively increasing the inlet pulse pressure (PP). The transmission of PP throughout the tree was shown to increase in advanced stages of disease, creating the potential for a `vicious-cycle' of damage to vasculature. Wall shear stress (WSS) was shown to be highest in the terminal arteries of the model and increased significantly with disease. A further trend observed in WSS results was that high WSS values began to `climb' the arterial tree towards the proximal vessels as disease progressed. This suggests a link between WSS and distal remodeling in pulmonary hypertensive disease, which initiates in the small muscular arteries and arterioles and spreads into larger arteries as the disease progresses. PMID:25571282

  1. Wall shear stress variations and unsteadiness of pulsatile blood-like flows in 90-degree bifurcations.

    PubMed

    van Wyk, Stevin; Prahl Wittberg, Lisa; Fuchs, Laszlo

    2013-09-01

    Complex and slow interaction of different mechanical and biochemical processes in hemodynamics is believed to govern atherogenesis. Over the last decades studies have shown that fluid mechanical factors such as the Wall Shear Stress (WSS) and WSS gradients can play an important role in the pathological changes of the endothelium. This study provides further indications that the effects of fluid mechanical aspects are correlated with the diseased regions of the larger arteries. Unsteady high temporal WSS gradients (TWSSG), a function of the shear-thinning property of the non-Newtonian viscosity, move with the separation bubble. Red Blood Cell (RBC) dilution due to the secondary flows determines the magnitudes of the WSS and TWSSG. The results indicate that the focal nature of the TWSSG may have implications on the response of the endothelium.

  2. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. II - Wall shear stress

    NASA Technical Reports Server (NTRS)

    Liou, M. S.; Adamson, T. C., Jr.

    1980-01-01

    Asymptotic methods are used to calculate the shear stress at the wall for the interaction between a normal shock wave and a turbulent boundary layer on a flat plate. A mixing length model is used for the eddy viscosity. The shock wave is taken to be strong enough that the sonic line is deep in the boundary layer and the upstream influence is thus very small. It is shown that unlike the result found for laminar flow an asymptotic criterion for separation is not found; however, conditions for incipient separation are computed numerically using the derived solution for the shear stress at the wall. Results are compared with available experimental measurements.

  3. Main pulmonary arterial wall shear stress correlates with invasive hemodynamics and stiffness in pulmonary hypertension

    PubMed Central

    Kheyfets, Vitaly O.; Schroeder, Joyce D.; Dunning, Jamie; Shandas, Robin; Buckner, J. Kern; Browning, James; Hertzberg, Jean; Hunter, Kendall S.; Fenster, Brett E.

    2016-01-01

    Abstract Pulmonary hypertension (PH) is associated with proximal pulmonary arterial remodeling characterized by increased vessel diameter, wall thickening, and stiffness. In vivo assessment of wall shear stress (WSS) may provide insights into the relationships between pulmonary hemodynamics and vascular remodeling. We investigated the relationship between main pulmonary artery (MPA) WSS and pulmonary hemodynamics as well as markers of stiffness. As part of a prospective study, 17 PH patients and 5 controls underwent same-day four-dimensional flow cardiac magnetic resonance imaging (4-D CMR) and right heart catheterization. Streamwise velocity profiles were generated in the cross-sectional MPA in 45° increments from velocity vector fields determined by 4-D CMR. WSS was calculated as the product of hematocrit-dependent viscosity and shear rate generated from the spatial gradient of the velocity profiles. In-plane average MPA WSS was significantly decreased in the PH cohort compared with that in controls (0.18 ± 0.07 vs. 0.32 ± 0.08 N/m2; P = 0.01). In-plane MPA WSS showed strong inverse correlations with multiple hemodynamic indices, including pulmonary resistance (ρ = −0.74, P < 0.001), mean pulmonary pressure (ρ = −0.64, P = 0.006), and elastance (ρ = −0.70, P < 0.001). In addition, MPA WSS had significant associations with markers of stiffness, including capacitance (ρ = 0.67, P < 0.001), distensibility (ρ = 0.52, P = 0.013), and elastic modulus (ρ = −0.54, P = 0.01). In conclusion, MPA WSS is decreased in PH and is significantly associated with invasive hemodynamic indices and markers of stiffness. 4-D CMR–based assessment of WSS may represent a novel methodology to study blood-vessel wall interactions in PH. PMID:27076906

  4. Wall Shear Stress-Based Model for Adhesive Dynamics of Red Blood Cells in Malaria

    PubMed Central

    Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George Em

    2011-01-01

    Red blood cells (RBCs) infected by the Plasmodium falciparum (Pf-RBCs) parasite lose their membrane deformability and they also exhibit enhanced cytoadherence to vascular endothelium and other healthy and infected RBCs. The combined effect may lead to severe disruptions of normal blood circulation due to capillary occlusions. Here we extend the adhesion model to investigate the adhesive dynamics of Pf-RBCs as a function of wall shear stress (WSS) and other parameters using a three-dimensional, multiscale RBC model. Several types of adhesive behavior are identified, including firm adhesion, flipping dynamics, and slow slipping along the wall. In particular, the flipping dynamics of Pf-RBCs observed in experiments appears to be due to the increased stiffness of infected cells and the presence of the solid parasite inside the RBC, which may cause an irregular adhesion behavior. Specifically, a transition from crawling dynamics to flipping behavior occurs at a Young's modulus approximately three times larger than that of healthy RBCs. The simulated dynamics of Pf-RBCs is in excellent quantitative agreement with available microfluidic experiments if the force exerted on the receptors and ligands by an existing bond is modeled as a nonlinear function of WSS. PMID:21539775

  5. Relaxed incremental variational approach for the modeling of damage-induced stress hysteresis in arterial walls.

    PubMed

    Schmidt, Thomas; Balzani, Daniel

    2016-05-01

    In this paper, a three-dimensional relaxed incremental variational damage model is proposed, which enables the description of complex softening hysteresis as observed in supra-physiologically loaded arterial tissues, and which thereby avoids a loss of convexity of the underlying formulation. The proposed model extends the relaxed formulation of Balzani and Ortiz [2012. Relaxed incremental variational formulation for damage at large strains with application to fiber-reinforced materials and materials with truss-like microstructures. Int. J. Numer. Methods Eng. 92, 551-570], such that the typical stress-hysteresis observed in arterial tissues under cyclic loading can be described. This is mainly achieved by constructing a modified one-dimensional model accounting for cyclic loading in the individual fiber direction and numerically homogenizing the response taking into account a fiber orientation distribution function. A new solution strategy for the identification of the convexified stress potential is proposed based on an evolutionary algorithm which leads to an improved robustness compared to solely Newton-based optimization schemes. In order to enable an efficient adjustment of the new model to experimentally observed softening hysteresis, an adjustment scheme using a surrogate model is proposed. Therewith, the relaxed formulation is adjusted to experimental data in the supra-physiological domain of the media and adventitia of a human carotid artery. The performance of the model is then demonstrated in a finite element example of an overstretched artery. Although here three-dimensional thick-walled atherosclerotic arteries are considered, it is emphasized that the formulation can also directly be applied to thin-walled simulations of arteries using shell elements or other fiber-reinforced biomembranes.

  6. Fundamental Characteristics of AAA+ Protein Family Structure and Function

    PubMed Central

    2016-01-01

    Many complex cellular events depend on multiprotein complexes known as molecular machines to efficiently couple the energy derived from adenosine triphosphate hydrolysis to the generation of mechanical force. Members of the AAA+ ATPase superfamily (ATPases Associated with various cellular Activities) are critical components of many molecular machines. AAA+ proteins are defined by conserved modules that precisely position the active site elements of two adjacent subunits to catalyze ATP hydrolysis. In many cases, AAA+ proteins form a ring structure that translocates a polymeric substrate through the central channel using specialized loops that project into the central channel. We discuss the major features of AAA+ protein structure and function with an emphasis on pivotal aspects elucidated with archaeal proteins. PMID:27703410

  7. An estimation of mechanical stress on alveolar walls during repetitive alveolar reopening and closure.

    PubMed

    Chen, Zheng-Long; Song, Yuan-Lin; Hu, Zhao-Yan; Zhang, Su; Chen, Ya-Zhu

    2015-08-01

    Alveolar overdistension and mechanical stresses generated by repetitive opening and closing of small airways and alveoli have been widely recognized as two primary mechanistic factors that may contribute to the development of ventilator-induced lung injury. A long-duration exposure of alveolar epithelial cells to even small, shear stresses could lead to the changes in cytoskeleton and the production of inflammatory mediators. In this paper, we have made an attempt to estimate in situ the magnitudes of mechanical stresses exerted on the alveolar walls during repetitive alveolar reopening by using a tape-peeling model of McEwan and Taylor (35). To this end, we first speculate the possible ranges of capillary number (Ca) ≡ μU/γ (a dimensionless combination of surface tension γ, fluid viscosity μ, and alveolar opening velocity U) during in vivo alveolar opening. Subsequent calculations show that increasing respiratory rate or inflation rate serves to increase the values of mechanical stresses. For a normal lung, the predicted maximum shear stresses are <15 dyn/cm(2) at all respiratory rates, whereas for a lung with elevated surface tension or viscosity, the maximum shear stress will notably increase, even at a slow respiratory rate. Similarly, the increased pressure gradients in the case of elevated surface or viscosity may lead to a pressure drop >300 dyn/cm(2) across a cell, possibly inducing epithelial hydraulic cracks. In addition, we have conceived of a geometrical model of alveolar opening to make a prediction of the positive end-expiratory pressure (PEEP) required to splint open a collapsed alveolus, which as shown by our results, covers a wide range of pressures, from several centimeters to dozens of centimeters of water, strongly depending on the underlying pulmonary conditions. The establishment of adequate regional ventilation-to-perfusion ratios may prevent recruited alveoli from reabsorption atelectasis and accordingly, reduce the required levels of

  8. Wall scaling laws for turbulent BL before and after the Reynolds shear stress maxima

    NASA Astrophysics Data System (ADS)

    Afzal, Noor; Seena, Abu; Afzal, Bushra; Noor Afzal Collaboration; Abu Seena Team; Bushra Afzal Team

    2015-11-01

    The turbulent shear flow has a critical point due to maximas of Reynolds stress tensor has significant role. Three layers with length scales (inner ν /uτ , meso √{ νδ /uτ }, outer δ) have been analyzed. Below this crucial point the mesolayer inner limit matches with with outer limit of wall layer. Above this crucial point the outer limit of mesolayer matches with inner limit of outer layer. The log law velocity and Reynolds in two overlap regions, above and below the critical point, have been presented. The Reynolds shear stress maxima τmax /τw occurs at a point where ratio of mesolayer to outer lengths is of order Rτ-1 / 2 (= √{ ν / δuτ }), and at this point DNS and experimental data predict Um /Ue = 2 / 3 (where Um = mesolayer velocity and Ue = velocity at boundary edge). The turbulent burst time period also scale with mesolayer time. The shape factor in a TBL shows linear behavior with non-dimensional mesolayer length scale. In special case Um /Ue = 1 / 2 , is due to Izakson and Millikan. The above predictions are supported by experimental and DNS data.

  9. Proteomic analysis of cell wall in four pathogenic species of Candida exposed to oxidative stress.

    PubMed

    Ramírez-Quijas, Mayra Denisse; López-Romero, Everardo; Cuéllar-Cruz, Mayra

    2015-10-01

    In order for Candida species to adhere and colonize human host cells they must express cell wall proteins (CWP) and adapt to reactive oxygen species (ROS) generated by phagocytic cells of the human host during the respiratory burst. However, how these pathogens change the expression of CWP in response to oxidative stress (OSR) is not known. Here, fifteen moonlight-like CWP were identified that expressed differentially in four species of Candida after they were exposed to H2O2 or menadione (O2(-)). These proteins included: (i) glycolytic enzymes, such as glyceraldehyde-3-phosphate dehydrogenase (Gapdh), fructose-bisphosphate aldolase (Fba1), phosphoglycerate mutase (Gpm1), phosphoglycerate kinase (Pgk), pyruvate kinase (Pk) and enolase (Eno1); (ii) the heat shock proteins Ssb1 and Ssa2; (iii) OSR proteins such as peroxyredoxin (Tsa1), the stress protein Ddr48 (Ddr48) and glutathione reductase (Glr1); (iv) other metabolic enzymes such as ketol-acid reductoisomerase (Ilv5) and pyruvate decarboxylase (Pdc1); and (v) other proteins such as elongation factor 1-beta (Efb1) and the 14-3-3 protein homolog. RT-PCR revealed that transcription of the genes coding for some of the identified CWP are differentially regulated. To our knowledge this is the first report showing that moonlight-like CWP are the first line of defense of Candida against ROS, and that they are differentially regulated in each of these pathogens.

  10. Subunit dynamics and nucleotide-dependent asymmetry of an AAA(+) transcription complex.

    PubMed

    Zhang, Nan; Gordiyenko, Yuliya; Joly, Nicolas; Lawton, Edward; Robinson, Carol V; Buck, Martin

    2014-01-01

    Bacterial enhancer binding proteins (bEBPs) are transcription activators that belong to the AAA(+) protein family. They form higher-order self-assemblies to regulate transcription initiation at stress response and pathogenic promoters. The precise mechanism by which these ATPases utilize ATP binding and hydrolysis energy to remodel their substrates remains unclear. Here we employed mass spectrometry of intact complexes to investigate subunit dynamics and nucleotide occupancy of the AAA(+) domain of one well-studied bEBP in complex with its substrate, the σ(54) subunit of RNA polymerase. Our results demonstrate that the free AAA(+) domain undergoes significant changes in oligomeric states and nucleotide occupancy upon σ(54) binding. Such changes likely correlate with one transition state of ATP and are associated with an open spiral ring formation that is vital for asymmetric subunit function and interface communication. We confirmed that the asymmetric subunit functionality persists for open promoter complex formation using single-chain forms of bEBP lacking the full complement of intact ATP hydrolysis sites. Outcomes reconcile low- and high-resolution structures and yield a partial sequential ATP hydrolysis model for bEBPs. PMID:24055699

  11. Inhibitors of the AAA+ Chaperone p97

    PubMed Central

    Chapman, Eli; Maksim, Nick; de la Cruz, Fabian; La Clair, James J.

    2015-01-01

    It is remarkable that a pathway as ubiquitous as protein quality control can be targeted to treat cancer. Bortezomib, an inhibitor of the proteasome, was first approved by the US Food and Drug Administration (FDA) more than 10 years ago to treat refractory myeloma and later extended to lymphoma. Its use has increased the survival rate of myeloma patients by as much as three years. This success was followed with the recent accelerated approval of the natural product derived proteasome inhibitor carfilzomib (Kyprolis®), which is used to treat patients with bortezomib-resistant multiple myeloma. The success of these two drugs has validated protein quality control as a viable target to fight select cancers, but begs the question why are proteasome inhibitors limited to lymphoma and myeloma? More recently, these limitations have encouraged the search for additional targets within the protein quality control system that might offer heightened cancer cell specificity, enhanced clinical utility, a lower rate of resistance, reduced toxicity, and mitigated side effects. One promising target is p97, an ATPase associated with various cellular activities (AAA+) chaperone. p97 figures prominently in protein quality control as well as serving a variety of other cellular functions associated with cancer. More than a decade ago, it was determined that up-regulation of p97 in many forms of cancer correlates with a poor clinical outcome. Since these initial discoveries, a mechanistic explanation for this observation has been partially illuminated, but details are lacking. Understandably, given this clinical correlation, myriad roles within the cell, and its importance in protein quality control, p97 has emerged as a potential therapeutic target. This review provides an overview of efforts towards the discovery of small molecule inhibitors of p97, offering a synopsis of efforts that parallel the excellent reviews that currently exist on p97 structure, function, and physiology. PMID

  12. A case of recurrent earthquake stress cardiomyopathy with a differing wall motion abnormality.

    PubMed

    Bridgman, Paul G; Chan, Christina W; Elliott, John M

    2012-02-01

    We present the case of a Caucasian woman who survived two major earthquakes, presenting on each occasion with stress cardiomyopathy, but with a different pattern of regional wall motion abnormality on the second occasion. The first Christchurch earthquake struck on September 4, 2010. At 7.1 on the Richter scale, it was larger than the major Haiti quake, but miraculously there were no direct fatalities. In the week following, eight women meeting modified Mayo criteria for stress cardiomyopathy presented to Christchurch Hospital. The second Christchurch earthquake was on February 22, 2011. It measured 6.4 on the Richter scale and caused 180 direct fatalities. In the week following this earthquake, 24 women were admitted with stress cardiomyopathy. One patient presented after both earthquakes. This 76-year-old woman first presented on September 4 with 10 hours of chest pain. Electrocardiogram showed inferolateral deep T-wave inversion and QT prolongation. TnI peaked at 0.81 μg/L. Coronary angiography demonstrated diffuse atheroma with a moderate mid LAD lesion that was stented at the time. Echocardiography showed a classic takotsubo pattern. Her follow-up echocardiogram on September 28 was normal and she was completely well at that point. However, during the second earthquake of February 22, she again developed chest pain and shortness of breath. TnI peaked at 1.3 μg/L. Echocardiogram showed a midwall variant takotsubo with apical sparing. She was discharged from hospital on the 25th, planning to leave Christchurch for a new home in another city, but returned for follow-up echocardiogram on July 27. This was normal.

  13. Analysis of Cell Wall-Related Genes in Organs of Medicago sativa L. under Different Abiotic Stresses

    PubMed Central

    Behr, Marc; Legay, Sylvain; Hausman, Jean-Francois; Guerriero, Gea

    2015-01-01

    Abiotic constraints are a source of concern in agriculture, because they can have a strong impact on plant growth and development, thereby affecting crop yield. The response of plants to abiotic constraints varies depending on the type of stress, on the species and on the organs. Although many studies have addressed different aspects of the plant response to abiotic stresses, only a handful has focused on the role of the cell wall. A targeted approach has been used here to study the expression of cell wall-related genes in different organs of alfalfa plants subjected for four days to three different abiotic stress treatments, namely salt, cold and heat stress. Genes involved in different steps of cell wall formation (cellulose biosynthesis, monolignol biosynthesis and polymerization) have been analyzed in different organs of Medicago sativa L. Prior to this analysis, an in silico classification of dirigent/dirigent-like proteins and class III peroxidases has been performed in Medicago truncatula and M. sativa. The final goal of this study is to infer and compare the expression patterns of cell wall-related genes in response to different abiotic stressors in the organs of an important legume crop. PMID:26193255

  14. New Insights into Regulation of Proteome and Polysaccharide in Cell Wall of Elsholtzia splendens in Response to Copper Stress

    PubMed Central

    Liu, Tingting; Shen, Chaofeng; Wang, Yi; Huang, Canke; Shi, Jiyan

    2014-01-01

    Background and Aims Copper (Cu) is an essential micronutrient for plants. However, excess amounts of Cu are toxic and result in a wide range of harmful effects on the physiological and biochemical processes of plants. Cell wall has a crucial role in plant defense response to toxic metals. To date, the process of cell wall response to Cu and the detoxification mechanism have not been well documented at the proteomic level. Methods An recently developed 6-plex Tandem Mass Tag was used for relative and absolute quantitation methods to achieve a comprehensive understanding of Cu tolerance/detoxification molecular mechanisms in the cell wall. LC–MS/MS approach was performed to analyze the Cu-responsive cell wall proteins and polysaccharides. Key Results The majority of the 22 up-regulated proteins were involved in the antioxidant defense pathway, cell wall polysaccharide remodeling, and cell metabolism process. Changes in polysaccharide amount, composition, and distribution could offer more binding sites for Cu ions. The 33 down-regulated proteins were involved in the signal pathway, energy, and protein synthesis. Conclusions Based on the abundant changes in proteins and polysaccharides, and their putative functions, a possible protein interaction network can provide new insights into Cu stress response in root cell wall. Cu can facilitate further functional research on target proteins associated with metal response in the cell wall. PMID:25340800

  15. Valve-Related Hemodynamics Mediate Human Bicuspid Aortopathy: Insights from Wall Shear Stress Mapping

    PubMed Central

    Guzzardi, David G.; Barker, Alex J.; van Ooij, Pim; Malaisrie, S. Chris; Puthumana, Jyothy J.; Belke, Darrell D.; Mewhort, Holly E.M.; Svystonyuk, Daniyil A.; Kang, Sean; Verma, Subodh; Collins, Jeremy; Carr, James; Bonow, Robert O.; Markl, Michael; Thomas, James D.; McCarthy, Patrick M.; Fedak, Paul W.M.

    2015-01-01

    BACKGROUND Suspected genetic causes for extracellular matrix (ECM) dysregulation in the ascending aorta in patients with bicuspid aortic valves (BAV) has influenced strategies and thresholds for surgical resection of BAV aortopathy. Using 4-dimensional (4D) flow cardiac magnetic resonance imaging (CMR), we have documented increased regional wall shear stress (WSS) in the ascending aorta of BAV patients. OBJECTIVES We assessed the relationship between WSS and regional aortic tissue remodeling in BAV patients to determine the influence of regional WSS on the expression of ECM dysregulation. METHODS BAV patients (n = 20) undergoing ascending aortic resection underwent preoperative 4D flow CMR to regionally map WSS. Paired aortic wall samples (i.e., within-patient samples obtained from regions of elevated and normal WSS) were collected and compared for medial elastin degeneration by histology and ECM regulation by protein expression. RESULTS Regions of increased WSS showed greater medial elastin degradation compared to adjacent areas with normal WSS: decreased total elastin (p = 0.01) with thinner fibers (p = 0.00007) that were farther apart (p = 0.001). Multiplex protein analyses of ECM regulatory molecules revealed an increase in transforming growth factor β-1 (p = 0.04), matrix metalloproteinase (MMP)-1 (p = 0.03), MMP-2 (p = 0.06), MMP-3 (p = 0.02), and tissue inhibitor of metalloproteinase-1 (p = 0.04) in elevated WSS regions, indicating ECM dysregulation in regions of high WSS. CONCLUSIONS Regions of increased WSS correspond with ECM dysregulation and elastic fiber degeneration in the ascending aorta of BAV patients, implicating valve-related hemodynamics as a contributing factor in the development of aortopathy. Further study to validate the use of 4D flow CMR as a noninvasive biomarker of disease progression and its ability to individualize resection strategies is warranted. PMID:26293758

  16. Plaque development, vessel curvature, and wall shear stress in coronary arteries assessed by X-ray angiography and intravascular ultrasound

    PubMed Central

    Wahle, Andreas; Lopez, John J.; Olszewski, Mark E.; Vigmostad, Sarah C.; Chandran, Krishnan B.; Rossen, James D.; Sonka, Milan

    2008-01-01

    The relationships among vascular geometry, hemodynamics, and plaque development in the coronary arteries are complex and not yet well understood. This paper reports a methodology for the quantitative analysis of in vivo coronary morphology and hemodynamics, with particular emphasis placed on the critical issues of image segmentation and the automated classification of disease severity. We were motivated by the observation that plaque more often developed at the inner curvature of a vessel, presumably due to the relatively lower wall shear stress at these locations. The presented studies are based on our validated methodology for the three-dimensional fusion of intravascular ultrasound (IVUS) and X-ray angiography, introducing a novel approach for IVUS segmentation that incorporates a robust, knowledge-based cost function and a fully optimal, three-dimensional segmentation algorithm. Our first study shows that circumferential plaque distribution depends on local vessel curvature in the majority of vessels. The second study analyzes the correlation between plaque distribution and wall shear stress in a set of 48 in vivo vessel segments. The results were conclusive for both studies, with a stronger correlation of circumferential plaque thickness with local curvature than with wall shear stress. The inverse relationship between local wall shear stress and plaque thickness was significantly more pronounced (p < 0.025) in vessel cross sections exhibiting compensatory enlargement (positive remodeling) without luminal narrowing than when the full spectrum of disease severity was considered. The inverse relationship was no longer observed in vessels where less than 35% of vessel cross sections remained without luminal narrowing. The findings of this study confirm, in vivo, the hypothesis that relatively lower wall shear stress is associated with early plaque development. PMID:16644262

  17. Adipocyte in vascular wall can induce the rupture of abdominal aortic aneurysm

    PubMed Central

    Kugo, Hirona; Zaima, Nobuhiro; Tanaka, Hiroki; Mouri, Youhei; Yanagimoto, Kenichi; Hayamizu, Kohsuke; Hashimoto, Keisuke; Sasaki, Takeshi; Sano, Masaki; Yata, Tatsuro; Urano, Tetsumei; Setou, Mitsutoshi; Unno, Naoki; Moriyama, Tatsuya

    2016-01-01

    Abdominal aortic aneurysm (AAA) is a vascular disease involving the gradual dilation of the abdominal aorta. It has been reported that development of AAA is associated with inflammation of the vascular wall; however, the mechanism of AAA rupture is not fully understood. In this study, we investigated the mechanism underlying AAA rupture using a hypoperfusion-induced animal model. We found that the administration of triolein increased the AAA rupture rate in the animal model and that the number of adipocytes was increased in ruptured vascular walls compared to non-ruptured walls. In the ruptured group, macrophage infiltration and the protein levels of matrix metalloproteinases 2 and 9 were increased in the areas around adipocytes, while collagen-positive areas were decreased in the areas with adipocytes compared to those without adipocytes. The administration of fish oil, which suppresses adipocyte hypertrophy, decreased the number and size of adipocytes, as well as decreased the risk of AAA rupture ratio by 0.23 compared to the triolein administered group. In human AAA samples, the amount of triglyceride in the adventitia was correlated with the diameter of the AAA. These results suggest that AAA rupture is related to the abnormal appearance of adipocytes in the vascular wall. PMID:27499372

  18. Adipocyte in vascular wall can induce the rupture of abdominal aortic aneurysm.

    PubMed

    Kugo, Hirona; Zaima, Nobuhiro; Tanaka, Hiroki; Mouri, Youhei; Yanagimoto, Kenichi; Hayamizu, Kohsuke; Hashimoto, Keisuke; Sasaki, Takeshi; Sano, Masaki; Yata, Tatsuro; Urano, Tetsumei; Setou, Mitsutoshi; Unno, Naoki; Moriyama, Tatsuya

    2016-01-01

    Abdominal aortic aneurysm (AAA) is a vascular disease involving the gradual dilation of the abdominal aorta. It has been reported that development of AAA is associated with inflammation of the vascular wall; however, the mechanism of AAA rupture is not fully understood. In this study, we investigated the mechanism underlying AAA rupture using a hypoperfusion-induced animal model. We found that the administration of triolein increased the AAA rupture rate in the animal model and that the number of adipocytes was increased in ruptured vascular walls compared to non-ruptured walls. In the ruptured group, macrophage infiltration and the protein levels of matrix metalloproteinases 2 and 9 were increased in the areas around adipocytes, while collagen-positive areas were decreased in the areas with adipocytes compared to those without adipocytes. The administration of fish oil, which suppresses adipocyte hypertrophy, decreased the number and size of adipocytes, as well as decreased the risk of AAA rupture ratio by 0.23 compared to the triolein administered group. In human AAA samples, the amount of triglyceride in the adventitia was correlated with the diameter of the AAA. These results suggest that AAA rupture is related to the abnormal appearance of adipocytes in the vascular wall. PMID:27499372

  19. Application of the new Section XI, A-3000 method for stress intensity factor calculation to thick-walled pressure vessels

    SciTech Connect

    Kendall, D.P.

    1996-12-01

    The ASME Boiler and Pressure Vessel Code, Section XI, Appendix A, Article A-3000 has been recently revised to include a more accurate method for calculating stress intensity factors. It is based on fitting the distribution of the stress normal to the plane of the crack in the uncracked body, over the depth of the crack, with a cubic equation. The coefficients of this equation are used with correction factors given in the code to calculate the stress intensity factors at the deepest point of the crack and near the free surface. Correction factors are given for a range of values of relative crack depth and crack shape. In a pressurized thick-walled cylinder the stresses of interest are the tangential stresses due to internal pressure as given by the Lame Equations, plus the effect of the pressure in the crack. This paper shows that the Lame stresses, as a function of distance from the inner surface, can be accurately fitted with a simple set of cubic equations over the full wall thickness for a wide range of diameter ratios. The coefficients of these equations, combined with the correction factors, are used to calculate stress intensity factors for a range of diameter ratios and at both the deepest point of the crack and near the free surface. The results are compared with stress intensity factors calculated using the linearized stress method proposed by Kendall and Perez. The effect of the plastic zone correction given in the new method is reported. The stress intensity factors due to autofrettage residual stresses calculated by the new method are also reported.

  20. Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model.

    PubMed

    Raben, Jaime S; Hariharan, Prasanna; Robinson, Ronald; Malinauskas, Richard; Vlachos, Pavlos P

    2016-03-01

    We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000. Images included a twofold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were computed using radial basis functions. In addition, in-field spatially resolved pressure distributions, Reynolds stresses, and energy dissipation rates were computed from PIV measurements. Velocity measurement uncertainty was estimated directly from the PIV correlation plane, and uncertainty analysis for wall shear stress at each measurement location was performed using a Monte Carlo model. Local velocity uncertainty varied greatly and depended largely on local conditions such as particle seeding, velocity gradients, and particle displacements. Uncertainty in low velocity regions in the sudden expansion section of the nozzle was greatly reduced by over an order of magnitude when dynamic range enhancement was applied. Wall shear stress uncertainty was dominated by uncertainty contributions from velocity estimations, which were shown to account for 90-99% of the total uncertainty. This study provides advancements in the PIV processing methodologies over

  1. Moonlight-like proteins of the cell wall protect sessile cells of Candida from oxidative stress.

    PubMed

    Serrano-Fujarte, Isela; López-Romero, Everardo; Cuéllar-Cruz, Mayra

    2016-01-01

    Biofilms of Candida species are associated with high morbidity and hospital mortality. Candida forms biofilms by adhering to human host epithelium through cell wall proteins (CWP) and simultaneously neutralizing the reactive oxygen species (ROS) produced during the respiratory burst by phagocytic cells. The purpose of this paper is to identify the CWP of Candida albicans, Candida glabrata, Candida krusei and Candida parapsilosis expressed after exposure to different concentrations of H2O2 using a proteomic approach. CWP obtained from sessile cells, both treated and untreated with the oxidizing agent, were resolved by one and two-dimensional (2D-PAGE) gels and identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Some of these proteins were identified and found to correspond to moonlighting CWP such as: (i) glycolytic enzymes, (ii) heat shock, (iii) OSR proteins, (iv) general metabolic enzymes and (v) highly conserved proteins, which are up- or down-regulated in the presence or absence of ROS. We also found that the expression of these CWP is different for each Candida species. Moreover, RT-PCR assays allowed us to demonstrate that transcription of the gene coding for Eno1, one of the moonlight-like CWP identified in response to the oxidant agent, is differentially regulated. To our knowledge this is the first demonstration that, in response to oxidative stress, each species of Candida, differentially regulates the expression of moonlighting CWP, which may protect the organism from the ROS generated during phagocytosis. Presumptively, these proteins allow the pathogen to adhere and form a biofilm, and eventually cause invasive candidiasis in the human host. We propose that, in addition to the antioxidant mechanisms present in Candida, the moonlighting CWP also confer protection to these pathogens from oxidative stress.

  2. Cell Wall Invertase Promotes Fruit Set under Heat Stress by Suppressing ROS-Independent Cell Death.

    PubMed

    Liu, Yong-Hua; Offler, Christina E; Ruan, Yong-Ling

    2016-09-01

    Reduced cell wall invertase (CWIN) activity has been shown to be associated with poor seed and fruit set under abiotic stress. Here, we examined whether genetically increasing native CWIN activity would sustain fruit set under long-term moderate heat stress (LMHS), an important factor limiting crop production, by using transgenic tomato (Solanum lycopersicum) with its CWIN inhibitor gene silenced and focusing on ovaries and fruits at 2 d before and after pollination, respectively. We found that the increase of CWIN activity suppressed LMHS-induced programmed cell death in fruits. Surprisingly, measurement of the contents of H2O2 and malondialdehyde and the activities of a cohort of antioxidant enzymes revealed that the CWIN-mediated inhibition on programmed cell death is exerted in a reactive oxygen species-independent manner. Elevation of CWIN activity sustained Suc import into fruits and increased activities of hexokinase and fructokinase in the ovaries in response to LMHS Compared to the wild type, the CWIN-elevated transgenic plants exhibited higher transcript levels of heat shock protein genes Hsp90 and Hsp100 in ovaries and HspII17.6 in fruits under LMHS, which corresponded to a lower transcript level of a negative auxin responsive factor IAA9 but a higher expression of the auxin biosynthesis gene ToFZY6 in fruits at 2 d after pollination. Collectively, the data indicate that CWIN enhances fruit set under LMHS through suppression of programmed cell death in a reactive oxygen species-independent manner that could involve enhanced Suc import and catabolism, HSP expression, and auxin response and biosynthesis. PMID:27462084

  3. Holographic microscopy and microfluidics platform for measuring wall stress and 3D flow over surfaces textured by micro-pillars

    PubMed Central

    Bocanegra Evans, Humberto; Gorumlu, Serdar; Aksak, Burak; Castillo, Luciano; Sheng, Jian

    2016-01-01

    Understanding how fluid flow interacts with micro-textured surfaces is crucial for a broad range of key biological processes and engineering applications including particle dispersion, pathogenic infections, and drag manipulation by surface topology. We use high-speed digital holographic microscopy (DHM) in combination with a correlation based de-noising algorithm to overcome the optical interference generated by surface roughness and to capture a large number of 3D particle trajectories in a microfluidic channel with one surface patterned with micropillars. It allows us to obtain a 3D ensembled velocity field with an uncertainty of 0.06% and 2D wall shear stress distribution at the resolution of ~65 μPa. Contrary to laminar flow in most microfluidics, we find that the flow is three-dimensional and complex for the textured microchannel. While the micropillars affect the velocity flow field locally, their presence is felt globally in terms of wall shear stresses at the channel walls. These findings imply that micro-scale mixing and wall stress sensing/manipulation can be achieved through hydro-dynamically smooth but topologically rough micropillars. PMID:27353632

  4. Holographic microscopy and microfluidics platform for measuring wall stress and 3D flow over surfaces textured by micro-pillars

    NASA Astrophysics Data System (ADS)

    Bocanegra Evans, Humberto; Gorumlu, Serdar; Aksak, Burak; Castillo, Luciano; Sheng, Jian

    2016-06-01

    Understanding how fluid flow interacts with micro-textured surfaces is crucial for a broad range of key biological processes and engineering applications including particle dispersion, pathogenic infections, and drag manipulation by surface topology. We use high-speed digital holographic microscopy (DHM) in combination with a correlation based de-noising algorithm to overcome the optical interference generated by surface roughness and to capture a large number of 3D particle trajectories in a microfluidic channel with one surface patterned with micropillars. It allows us to obtain a 3D ensembled velocity field with an uncertainty of 0.06% and 2D wall shear stress distribution at the resolution of ~65 μPa. Contrary to laminar flow in most microfluidics, we find that the flow is three-dimensional and complex for the textured microchannel. While the micropillars affect the velocity flow field locally, their presence is felt globally in terms of wall shear stresses at the channel walls. These findings imply that micro-scale mixing and wall stress sensing/manipulation can be achieved through hydro-dynamically smooth but topologically rough micropillars.

  5. Wall-to-wall stress induced in (6,5) semiconducting nanotubes by encapsulation in metallic outer tubes of different diameters: a resonance Raman study of individual C60-derived double-wall carbon nanotubes.

    PubMed

    Villalpando-Paez, Federico; Muramatsu, Hiroyuki; Kim, Yoong Ahm; Farhat, Hootan; Endo, Morinobu; Terrones, Mauricio; Dresselhaus, Mildred S

    2010-03-01

    We measure resonant Raman scattering from 11 individual C(60)-derived double-wall carbon nanotubes all having inner semiconducting (6,5) tubes and various outer metallic tubes. The Raman spectra show the radial breathing modes (RBM) of the inner and the outer tubes to be simultaneously in resonance with the same laser energy. We observe that an increase in the RBM frequency of the inner tubes is related to an increase in the RBM frequency of the outer tubes. The Raman spectra also contain a sharp G(-) feature that increases in frequency as the nominal diameter of the outer metallic tubes decreases. Finally, the one-phonon second-order D-band mode shows a two-way frequency splitting that decreases with decreasing nominal wall-to-wall distance. We suggest that the stress which increases with decreasing nominal wall-to-wall distance is responsible for the hardening that is observed in the frequencies of the RBM, D and G(-) modes of the inner (6,5) semiconducting tubes.

  6. Noninvasive determination of spatial distribution and temporal gradient of wall shear stress at common carotid artery.

    PubMed

    Sui, Binbin; Gao, Peiyi; Lin, Yan; Qin, Haiqiang; Liu, Long; Liu, Guangrui

    2008-10-20

    Wall shear stress (WSS) has been proved to play a critical role in formation and development of atherosclerotic plaques. Our objective was to quantify local WSS in vivo in normal subjects, and to analyze spatial distribution patterns and determine the temporal gradient of WSS. Seventy-eight CCAs of 42 healthy volunteers at common carotid arteries (CCAs) were studied. Cine phase-contrast MR sequence was used to acquire the flow velocity information. Three-dimensional paraboloid modeling was applied to fit the velocity profiles and WSS values were calculated. Mean WSS value for CCAs was 0.783+/-0.209, with the range of WSS value from -0.541 to 3.464 N/m(2). The 95% confidence interval for mean WSS value in CCA was (0.736-0.830) N/m(2). Different WSS spatial distribution patterns were classified into three types according to the location of low WSS values during a cardiac cycle. Mean value of maximum temporal gradient of WSS was 14.12+/-5.46, with the range from 5.87 to 33.23 N/m(2)s(-1). Skewed velocity profiles were displayed in most CCAs, indicating the flow patterns in CCA were more complicated than commonly assumed. Obvious inter-subject variation were found in magnitude, spatial distribution and the temporal gradient of WSS in CCAs, and the blood flow patterns as well.

  7. Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms

    PubMed Central

    Goubergrits, L.; Schaller, J.; Kertzscher, U.; van den Bruck, N.; Poethkow, K.; Petz, Ch.; Hege, H.-Ch.; Spuler, A.

    2012-01-01

    Haemodynamics and morphology play an important role in the genesis, growth and rupture of cerebral aneurysms. The goal of this study was to generate and analyse statistical wall shear stress (WSS) distributions and shapes in middle cerebral artery (MCA) saccular aneurysms. Unsteady flow was simulated in seven ruptured and 15 unruptured MCA aneurysms. In order to compare these results, all geometries must be brought in a uniform coordinate system. For this, aneurysms with corresponding WSS data were transformed into a uniform spherical shape; then, all geometries were uniformly aligned in three-dimensional space. Subsequently, we compared statistical WSS maps and surfaces of ruptured and unruptured aneurysms. No significant (p > 0.05) differences exist between ruptured and unruptured aneurysms regarding radius and mean WSS. In unruptured aneurysms, statistical WSS map relates regions with high (greater than 3 Pa) WSS to the neck region. In ruptured aneurysms, additional areas with high WSS contiguous to regions of low (less than 1 Pa) WSS are found in the dome region. In ruptured aneurysms, we found significantly lower WSS. The averaged aneurysm surface of unruptured aneurysms is round shaped, whereas the averaged surface of ruptured cases is multi-lobular. Our results confirm the hypothesis of low WSS and irregular shape as the essential rupture risk parameters. PMID:21957117

  8. Characterization of abnormal wall shear stress using 4D flow MRI in human bicuspid aortopathy

    PubMed Central

    van Ooij, Pim; Potters, Wouter V.; Collins, Jeremy; Carr, Maria; Carr, James; Malaisrie, S. Chris; Fedak, Paul W.M.; McCarthy, Patrick M.; Markl, Michael; Barker, Alex J.

    2014-01-01

    There exists considerable controversy surrounding the timing and extent of aortic resection for patients with BAV disease. Since abnormal wall shear stress (WSS) is potentially associated with tissue remodeling in BAV-related aortopathy, we propose a methodology that creates patient-specific ‘heat maps’ of abnormal WSS, based on 4D flow MRI. The heat maps were created by detecting outlier measurements from a volumetric 3D map of ensemble-averaged WSS in healthy controls. 4D flow MRI was performed in 13 BAV patients, referred for aortic resection and 10 age-matched controls. Systolic WSS was calculated from this data, and an ensemble-average and standard deviation (SD) WSS map of the controls was created. Regions of the individual WSS maps of the BAV patients that showed a higher WSS than the mean+1.96SD of the ensemble-average control WSS map were highlighted. Elevated WSS was found on the greater ascending aorta (35% ± 15 of the surface area), which correlated significantly with peak systolic velocity (R2=0.5, P=0.01) and showed good agreement with the resected aortic regions. This novel approach to characterize regional aortic WSS may allow clinicians to gain unique insights regarding the heterogeneous expression of aortopathy and may be leveraged to guide patient-specific resection strategies for aorta repair. PMID:25118671

  9. INCREASED PULMONARY PRESSURES AND MYOCARDIAL WALL STRESS IN CHILDREN WITH SEVERE MALARIA*

    PubMed Central

    Janka, Jacqueline J.; Koita, Ousmane A.; Traoré, Broulaye; Traoré, Josépha M.; Mzayek, Fawaz; Sachdev, Vandana; Wang, Xunde; Sanogo, Kassoum; Sangaré, Lansana; Mendelsohn, Laurel; Masur, Henry; Kato, Gregory J.; Gladwin, Mark T.; Krogstad, Donald J.

    2011-01-01

    Background Chronic intravascular hemolysis leads to nitric oxide (NO) depletion and pulmonary hypertension in sickle cell disease. To test whether this pathophysiology occurs in malaria, we examined 53 children admitted to hospital with severe malaria (excluding cerebral malaria) and 31 age-matched controls in Mali. Methods Severity of hemolysis was assessed from plasma free hemoglobin (Hb) and arginase-1 levels. NO metabolism was assessed by whole blood nitrite levels and plasma NO consumption. Effects on the cardiovascular system and endothelial function were assessed by using echocardiography to measure peak tricuspid regurgitant jet velocity (TRV) and from plasma levels of N-terminal prohormone brain natriuretic peptide (NT-proBNP) and soluble vascular cell adhesion molecule-1 (sVCAM-1). Results Children with severe malaria had higher plasma Hb and arginase-1 levels, reduced whole blood nitrite levels and increased NO consumption relative to controls. They also had increased pulmonary arterial pressures (p < 0.05) with elevated levels of NT-proBNP and sVCAM-1 (p < 0.001). Conclusions Children with severe malaria have increased pulmonary pressures and myocardial wall stress. These complications are consistent with NO depletion from intravascular hemolysis, and indicate that the pathophysiologic cascade from intravascular hemolysis to NO depletion and its cardiopulmonary effects is activated in children with severe malaria. PMID:20662718

  10. Characterization of abnormal wall shear stress using 4D flow MRI in human bicuspid aortopathy.

    PubMed

    van Ooij, Pim; Potters, Wouter V; Collins, Jeremy; Carr, Maria; Carr, James; Malaisrie, S Chris; Fedak, Paul W M; McCarthy, Patrick M; Markl, Michael; Barker, Alex J

    2015-06-01

    There exists considerable controversy surrounding the timing and extent of aortic resection for patients with BAV disease. Since abnormal wall shear stress (WSS) is potentially associated with tissue remodeling in BAV-related aortopathy, we propose a methodology that creates patient-specific 'heat maps' of abnormal WSS, based on 4D flow MRI. The heat maps were created by detecting outlier measurements from a volumetric 3D map of ensemble-averaged WSS in healthy controls. 4D flow MRI was performed in 13 BAV patients, referred for aortic resection and 10 age-matched controls. Systolic WSS was calculated from this data, and an ensemble-average and standard deviation (SD) WSS map of the controls was created. Regions of the individual WSS maps of the BAV patients that showed a higher WSS than the mean + 1.96SD of the ensemble-average control WSS map were highlighted. Elevated WSS was found on the greater ascending aorta (35% ± 15 of the surface area), which correlated significantly with peak systolic velocity (R (2) = 0.5, p = 0.01) and showed good agreement with the resected aortic regions. This novel approach to characterize regional aortic WSS may allow clinicians to gain unique insights regarding the heterogeneous expression of aortopathy and may be leveraged to guide patient-specific resection strategies for aorta repair. PMID:25118671

  11. Flow visualization and wall shear stress of a flapping model hummingbird wing

    NASA Astrophysics Data System (ADS)

    Swanton, Erik W. M.; Vanier, Blake A.; Mohseni, Kamran

    2010-09-01

    The unsteady low Reynolds number aerodynamics of flapping flight was investigated experimentally through flow visualization by suspended particle imagery and wall shear stress measurement from micro-array hot-film anemometry. In conjunction, a mechanism was developed to create a flapping motion with three degrees of freedom and adjustable flapping frequency. The flapping kinematics and wing shape were selected for dynamic similarity to a hummingbird during hovering flight. Flow visualization was used to validate the anemometry observations of leading edge vortex (LEV) characteristics and to investigate the necessity of spanwise flow in LEV stability. The shear sensors determined LEV characteristics throughout the translation section of the stroke period for various wing speeds. It was observed that a minimum frequency between 2 and 3.5 Hz is required for the formation and stabilization of a LEV. The vortex strength peaked around 30% of the flapping cycle (corresponding to just past the translation midpoint), which agrees with results from previous studies conducted by others. The shear sensors also indicated a mild growth in LEV size during translation sections of the wing’s motion. This growth magnitude was nearly constant through a range of operating frequencies.

  12. Redox Signaling in an In Vivo Murine Model of Low Magnitude Oscillatory Wall Shear Stress

    PubMed Central

    Willett, Nick J.; Kundu, Kousik; Knight, Sarah F.; Dikalov, Sergey; Murthy, Niren

    2011-01-01

    Abstract Wall Shear Stress (WSS) has been identified as an important factor in the pathogenesis of atherosclerosis. We utilized a novel murine aortic coarctation model to acutely create a region of low magnitude oscillatory WSS in vivo. We employed this model to test the hypothesis that acute changes in WSS in vivo induce upregulation of inflammatory proteins, mediated by reactive oxygen species (ROS). Superoxide generation and VCAM-1 expression both increased in regions of low magnitude oscillatory WSS. WSS-dependent superoxide formation was attenuated by tempol treatment, but was unchanged in p47 phox knockout (ko) mice. However, in both the p47 phox ko mice and the tempol-treated mice, low magnitude oscillatory WSS produced an increase in VCAM-1 expression comparable to control mice. Additionally, this same VCAM-1 expression was observed in ebselen-treated mice and catalase overexpressing mice. These results suggest that although the redox state is important to the overall pathogenesis of atherosclerosis, the initial WSS-dependent inflammatory response leading to lesion localization is not dependent on ROS. Antioxid. Redox Signal. 15, 1369–1378. PMID:20712414

  13. Association of Early Atherosclerosis with Vascular Wall Shear Stress in Hypercholesterolemic Zebrafish

    PubMed Central

    Lee, Sang Joon; Choi, Woorak; Seo, Eunseok; Yeom, Eunseop

    2015-01-01

    Although atherosclerosis is a multifactorial disease, the role of hemodynamic information has become more important. Low and oscillating wall shear stress (WSS) that changes its direction is associated with the early stage of atherosclerosis. Several in vitro and in vivo models were proposed to reveal the relation between the WSS and the early atherosclerosis. However, these models possess technical limitations in mimicking real physiological conditions and monitoring the developmental course of the early atherosclerosis. In this study, a hypercholesterolaemic zebrafish model is proposed as a novel experimental model to resolve these limitations. Zebrafish larvae are optically transparent, which enables temporal observation of pathological variations under in vivo condition. WSS in blood vessels of 15 days post-fertilisation zebrafish was measured using a micro particle image velocimetry (PIV) technique, and spatial distribution of lipid deposition inside the model was quantitatively investigated after feeding high cholesterol diet for 10 days. Lipids were mainly deposited in blood vessel of low WSS. The oscillating WSS was not induced by the blood flows in zebrafish models. The present hypercholesterolaemic zebrafish would be used as a potentially useful model for in vivo study about the effects of low WSS in the early atherosclerosis. PMID:26561854

  14. Role of AAA(+)-proteins in peroxisome biogenesis and function.

    PubMed

    Grimm, Immanuel; Erdmann, Ralf; Girzalsky, Wolfgang

    2016-05-01

    Mutations in the PEX1 gene, which encodes a protein required for peroxisome biogenesis, are the most common cause of the Zellweger spectrum diseases. The recognition that Pex1p shares a conserved ATP-binding domain with p97 and NSF led to the discovery of the extended family of AAA+-type ATPases. So far, four AAA+-type ATPases are related to peroxisome function. Pex6p functions together with Pex1p in peroxisome biogenesis, ATAD1/Msp1p plays a role in membrane protein targeting and a member of the Lon-family of proteases is associated with peroxisomal quality control. This review summarizes the current knowledge on the AAA+-proteins involved in peroxisome biogenesis and function.

  15. Evaluation of aneurysm-associated wall shear stress related to morphological variations of circle of Willis using a microfluidic device.

    PubMed

    Nam, Seong-Won; Choi, Samjin; Cheong, Youjin; Kim, Yeon-Hee; Park, Hun-Kuk

    2015-01-21

    Although microfluidic systems have been important tools in analytical chemistry, life sciences, and medical research, their application was rather limited for drug-screening and biosensors. Here, we described a microfluidic device consisting of a multilayer micro-channel system that represented the hemodynamic cerebral vascular system. We analyzed wall shear stresses related to aneurysm formation in the circle of Willis (CoW) and their morphological variations using this system. This device was controlled by pneumatic valves, which occluded various major arteries by closing the associated channels. The hemodynamic analysis indicated that higher degrees of shear stress occurred in an anterior communicating artery (ACoA), particularly in the hypoplastic region of the posterior communicating artery (PCoA) and the P1 segment. Furthermore, occlusion of a common carotid artery (CCA) or a middle cerebral artery (MCA) increased the shear stress, whereas occlusion of a vertebral artery (VA) decreased the shear stress. These results indicate that the morphological variation of the CoW may affect aneurysm formation resulting from increased wall shear stress. Therefore, the technique described in this paper provides a novel method to investigate the hemodynamics of complex cerebral vascular systems not accessible from previous clinical studies. PMID:25497378

  16. Wall stress in media layer of stented three-layered aortic aneurysm at different intraluminal thrombus locations with pulsatile heart cycle.

    PubMed

    Rahmani, Shahrokh; Alagheband, Mohammad; Karimi, Alireza; Alizadeh, Mansour; Navidbakhsh, Mahdi

    2015-05-01

    At the point when the aorta ruptures suddenly, as opposed to as the after-effect of injury, it is for the most part in aortic aneurysm. Aortic aneurysm rupture happens when the wall stress surpasses the strength of the vascular tissue. Intraluminal thrombus (ILT) may have advantages as it can absorb tension and decrease aortic aneurysm wall stress. This study aims to investigate the presence and growth effects of ILT on the wall stress in a stented aneurysm in one heart cycle. A virtual stented aneurysm model with ILT was made to study the flow and wall dynamics using fluid-structure interaction (FSI) analysis. Wall stresses at the center line of media layer of aorta thickness were calculated by two-dimensional axisymmetric finite element analysis. Calculations were executed as thrombus elastic modulus increased from 0.1 to 2 MPa and calculations were repeated as thrombus depth was increased in 10% increment until thrombus filled the whole aneurysm cavity. The von Mises stresses were compared in three sections, namely proximal, aneurysm and distal sections in the abdominal aorta. The wall stress showed its maximum value during a peak flow and pressure and gradually decreased as the pressure and velocity of blood reduced in all three aforementioned sections. As the intraluminal thrombus depth increased from 10% to 100%, the wall stress in distal, proximal and centre of aneurysm during one heart cycle was decreased. Furthermore, increasing the elastic modulus of thrombus from 10% to 100% triggered a reduction in wall stress in proximal, centre of intraluminal thrombus and distal regions during one heart cycle. The achievements of this study may have implications not only for understanding the wall stress in ILT, but also for providing more detailed information about aortic aneurysm with intraluminal thrombus and can help surgeons to do their best.

  17. In vitro blood flow model with physiological wall shear stress for hemocompatibility testing-An example of coronary stent testing.

    PubMed

    Engels, Gerwin Erik; Blok, Sjoerd Leendert Johannes; van Oeveren, Willem

    2016-01-01

    Hemocompatibility of blood contacting medical devices has to be evaluated before their intended application. To assess hemocompatibility, blood flow models are often used and can either consist of in vivo animal models or in vitro blood flow models. Given the disadvantages of animal models, in vitro blood flow models are an attractive alternative. The in vitro blood flow models available nowadays mostly focus on generating continuous flow instead of generating a pulsatile flow with certain wall shear stress, which has shown to be more relevant in maintaining hemostasis. To address this issue, the authors introduce a blood flow model that is able to generate a pulsatile flow and wall shear stress resembling the physiological situation, which the authors have coined the "Haemobile." The authors have validated the model by performing Doppler flow measurements to calculate velocity profiles and (wall) shear stress profiles. As an example, the authors evaluated the thrombogenicity of two drug eluting stents, one that was already on the market and one that was still under development. After identifying proper conditions resembling the wall shear stress in coronary arteries, the authors compared the stents with each other and often used reference materials. These experiments resulted in high contrast between hemocompatible and incompatible materials, showing the exceptional testing capabilities of the Haemobile. In conclusion, the authors have developed an in vitro blood flow model which is capable of mimicking physiological conditions of blood flow as close as possible. The model is convenient in use and is able to clearly discriminate between hemocompatible and incompatible materials, making it suitable for evaluating the hemocompatible properties of medical devices. PMID:27435456

  18. The impact of scaled boundary conditions on wall shear stress computations in atherosclerotic human coronary bifurcations.

    PubMed

    Schrauwen, Jelle T C; Schwarz, Janina C V; Wentzel, Jolanda J; van der Steen, Antonius F W; Siebes, Maria; Gijsen, Frank J H

    2016-05-15

    The aim of this study was to determine if reliable patient-specific wall shear stress (WSS) can be computed when diameter-based scaling laws are used to impose the boundary conditions for computational fluid dynamics. This study focused on mildly diseased human coronary bifurcations since they are predilection sites for atherosclerosis. Eight patients scheduled for percutaneous coronary intervention were imaged with angiography. The velocity proximal and distal of a bifurcation was acquired with intravascular Doppler measurements. These measurements were used for inflow and outflow boundary conditions for the first set of WSS computations. For the second set of computations, absolute inflow and outflow ratios were derived from geometry-based scaling laws based on angiography data. Normalized WSS maps per segment were obtained by dividing the absolute WSS by the mean WSS value. Absolute and normalized WSS maps from the measured-approach and the scaled-approach were compared. A reasonable agreement was found between the measured and scaled inflows, with a median difference of 0.08 ml/s [-0.01; 0.20]. The measured and the scaled outflow ratios showed a good agreement: 1.5 percentage points [-19.0; 4.5]. Absolute WSS maps were sensitive to the inflow and outflow variations, and relatively large differences between the two approaches were observed. For normalized WSS maps, the results for the two approaches were equivalent. This study showed that normalized WSS can be obtained from angiography data alone by applying diameter-based scaling laws to define the boundary conditions. Caution should be taken when absolute WSS is assessed from computations using scaled boundary conditions. PMID:26945083

  19. The impact of scaled boundary conditions on wall shear stress computations in atherosclerotic human coronary bifurcations.

    PubMed

    Schrauwen, Jelle T C; Schwarz, Janina C V; Wentzel, Jolanda J; van der Steen, Antonius F W; Siebes, Maria; Gijsen, Frank J H

    2016-05-15

    The aim of this study was to determine if reliable patient-specific wall shear stress (WSS) can be computed when diameter-based scaling laws are used to impose the boundary conditions for computational fluid dynamics. This study focused on mildly diseased human coronary bifurcations since they are predilection sites for atherosclerosis. Eight patients scheduled for percutaneous coronary intervention were imaged with angiography. The velocity proximal and distal of a bifurcation was acquired with intravascular Doppler measurements. These measurements were used for inflow and outflow boundary conditions for the first set of WSS computations. For the second set of computations, absolute inflow and outflow ratios were derived from geometry-based scaling laws based on angiography data. Normalized WSS maps per segment were obtained by dividing the absolute WSS by the mean WSS value. Absolute and normalized WSS maps from the measured-approach and the scaled-approach were compared. A reasonable agreement was found between the measured and scaled inflows, with a median difference of 0.08 ml/s [-0.01; 0.20]. The measured and the scaled outflow ratios showed a good agreement: 1.5 percentage points [-19.0; 4.5]. Absolute WSS maps were sensitive to the inflow and outflow variations, and relatively large differences between the two approaches were observed. For normalized WSS maps, the results for the two approaches were equivalent. This study showed that normalized WSS can be obtained from angiography data alone by applying diameter-based scaling laws to define the boundary conditions. Caution should be taken when absolute WSS is assessed from computations using scaled boundary conditions.

  20. The influence of boundary conditions on wall shear stress distribution in patients specific coronary trees.

    PubMed

    van der Giessen, Alina G; Groen, Harald C; Doriot, Pierre-André; de Feyter, Pim J; van der Steen, Antonius F W; van de Vosse, Frans N; Wentzel, Jolanda J; Gijsen, Frank J H

    2011-04-01

    Patient specific geometrical data on human coronary arteries can be reliably obtained multislice computer tomography (MSCT) imaging. MSCT cannot provide hemodynamic variables, and the outflow through the side branches must be estimated. The impact of two different models to determine flow through the side branches on the wall shear stress (WSS) distribution in patient specific geometries is evaluated. Murray's law predicts that the flow ratio through the side branches scales with the ratio of the diameter of the side branches to the third power. The empirical model is based on flow measurements performed by Doriot et al. (2000) in angiographically normal coronary arteries. The fit based on these measurements showed that the flow ratio through the side branches can best be described with a power of 2.27. The experimental data imply that Murray's law underestimates the flow through the side branches. We applied the two models to study the WSS distribution in 6 coronary artery trees. Under steady flow conditions, the average WSS between the side branches differed significantly for the two models: the average WSS was 8% higher for Murray's law and the relative difference ranged from -5% to +27%. These differences scale with the difference in flow rate. Near the bifurcations, the differences in WSS were more pronounced: the size of the low WSS regions was significantly larger when applying the empirical model (13%), ranging from -12% to +68%. Predicting outflow based on Murray's law underestimates the flow through the side branches. Especially near side branches, the regions where atherosclerotic plaques preferentially develop, the differences are significant and application of Murray's law underestimates the size of the low WSS region.

  1. Single-Walled Carbon Nanotubes Induces Oxidative Stress in Rat Lung Epithelial Cells

    PubMed Central

    Sharma, Chidananda S.; Sarkar, Shubhashish; Periyakaruppan, Adaikkappan; Barr, Johnny; Wise, Kimberly; Thomas, Renard; Wilson, Bobby L.

    2009-01-01

    Single-walled carbon nanotubes (SWCNT) show unique properties find applications in micro devices; electronics to biological systems specially drug delivery and gene therapy. However the manufacture and extensive use of nanotubes raises concern about its safe use and human health. Very few studies have been carried out on toxicity of carbon nanotubes in experimental animals and humans, thus resulted in limiting their use. The extensive toxicological studies using in vitro and in vivo models are necessary and are required to establish safe manufacturing guidelines and also the use of SWCNT. These studies also help the chemists to prepare derivative of SWCNT with less or no toxicity. The present study was undertaken to determine the toxicity exhibited by SWCNT in rat lung epithelial cells as a model system. Lung epithelial cells (LE cells) were cultured with or without SWCNT and reactive oxygen species (ROS) produced were measured by change in fluorescence using dichloro fluorescein (DCF). The results show increased ROS on exposure to SWCNT in a dose and time dependent manner. The decrease in glutathione content suggested the depletion and loss of protective mechanism against ROS in SWCNT treated cells. Use of rotenone, the inhibitor of mitochondrial function have no effect on ROS levels suggested that mitochondria is not involved in SWCNT induced ROS production. Studies carried out on the effect of SWCNT on superoxide dismutase (SOD-1 and SOD-2) levels in LE cells, indicates that these enzyme levels decreased by 24 hours. The increased ROS induced by SWCNT on LE cells decreased by treating the cells with 1 mM of glutathione, N-Acetyl Cysteine, and Vitamin C. These results further prove that SWCNT induces oxidative stress in LE cells and shows loss of antioxidants. PMID:17663266

  2. Bicuspid aortic valves are associated with increased wall and turbulence shear stress levels compared to trileaflet aortic valves.

    PubMed

    Saikrishnan, Neelakantan; Mirabella, Lucia; Yoganathan, Ajit P

    2015-06-01

    Congenital bicuspid aortic valves (BAVs) are associated with accelerated disease progression, such as leaflet calcification and ascending aorta dilatation. Although common underlying genetic factors have been implicated in accelerated disease in BAV patients, several studies have suggested that altered hemodynamics also play a role in this disease process. The present study compares turbulence and wall shear stress (WSS) measurements between various BAV and trileaflet aortic valve (TAV) models to provide information for mechanobiological models of BAV disease. BAV and TAV models were constructed from excised porcine aortic valves to simulate parametric variations in BAV stenosis, hemodynamics and geometry. Particle image velocimetry experiments were conducted at physiological pressure conditions to characterize velocity fields in the ascending aorta. The velocity fields were post-processed to calculate turbulence, viscous and wall shear stresses in the ascending aorta. Stenosed BAV models showed the presence of eccentric systolic jets, causing increased WSS. Lower cardiac output resulted in a narrower jet, lower turbulence and lower viscous shear stress (VSS). The specific severe stenosis BAV model studied here showed reduced WSS due to reduction in non-fused leaflet mobility. Dilation of the aorta did not affect any turbulence or VSS, but reduced the WSS. In comparison with BAVs, TAVs have similar VSS values, but much smaller WSS and turbulence levels. These increased turbulence  and WSS levels in BAVs may play a key role in amplifying the biological responses of the ascending aorta wall and valvular leaflets, and support the hemodynamic underpinnings of BAV disease processes.

  3. Development of a wall-shear-stress sensor and measurements in mini-channels with partial blockages

    NASA Astrophysics Data System (ADS)

    Afara, Samer; Medvescek, James; Mydlarski, Laurent; Baliga, Bantwal R.; MacDonald, Mark

    2014-05-01

    The design, construction, operation and validation of a wall-shear-stress sensor, and measurements obtained using this sensor in air flows downstream of partial blockages in a mini-channel are presented. The sensor consisted of a hot wire mounted over a small rectangular slot and operated using a constant-temperature anemometer. It was used to investigate flows similar to those within the mini-channels inside notebook computers. The overall goal of the present work was to develop a sensor suitable for measurements of the wall-shear stress in such flows, which can be used to validate corresponding numerical simulations, as the latter are known to be often surprisingly inaccurate. To this end, measurements of the wall-shear stress, and the corresponding statistical moments and power spectral densities, were obtained at different distances downstream of the partial blockage, with blockage ratios of 39.7, 59.2, and 76.3 %. The Reynolds number (based on average velocity and hydraulic diameter) ranged from 100 to 900. The results confirmed the presence of unsteadiness, separation, reattachment, and laminar-turbulent transition in the ostensibly laminar flow of air in mini-channels with partial blockages. The present results demonstrate why accurate numerical predictions of cooling air flows in laptop and notebook computers remain a challenging task.

  4. Analysis of wall shear stress around a competitive swimmer using 3D Navier-Stokes equations in CFD.

    PubMed

    Popa, C V; Zaidi, H; Arfaoui, A; Polidori, G; Taiar, R; Fohanno, S

    2011-01-01

    This paper deals with the flow dynamics around a competitive swimmer during underwater glide phases occurring at the start and at every turn. The influence of the head position, namely lifted up, aligned and lowered, on the wall shear stress and the static pressure distributions is analyzed. The problem is considered as 3D and in steady hydrodynamic state. Three velocities (1.4 m/s, 2.2 m/s and 3.1 m/s) that correspond to inter-regional, national and international swimming levels are studied. The flow around the swimmer is assumed turbulent. The Reynolds-averaged Navier-Stokes (RANS) equations are solved with the standard k-ω turbulent model by using the CFD (computational fluid dynamics) numerical method based on a volume control approach. Numerical simulations are carried out with the ANSYS FLUENT® CFD code. The results show that the wall shear stress increases with the velocity and consequently the drag force opposing the movement of the swimmer increases as well. Also, high wall shear stresses are observed in the areas where the body shape, globally rigid in form, presents complex surface geometries such as the head, shoulders, buttocks, heel and chest.

  5. Ex-congressman Rush Holt to lead AAAS

    NASA Astrophysics Data System (ADS)

    Banks, Michael

    2015-01-01

    The particle physicist Rush Holt, who served in the US Congress for 15 years, has been named as the next chief executive of the American Association for the Advancement of Science (AAAS) - the non-profit US society that promotes public engagement with science and technology.

  6. The Adult Asperger Assessment (AAA): A Diagnostic Method

    ERIC Educational Resources Information Center

    Baron-Cohen, Simon; Wheelwright, Sally; Robinson, Janine; Woodbury-Smith, Marc

    2005-01-01

    At the present time there are a large number of adults who have "suspected" Asperger syndrome (AS). In this paper we describe a new instrument, the Adult Asperger Assessment (AAA), developed in our clinic for adults with AS. The need for a new instrument relevant to the diagnosis of AS in adulthood arises because existing instruments are designed…

  7. Influence of thick-walled cylinders length on the residual stresses generated during the single-cycle mandrelling

    NASA Astrophysics Data System (ADS)

    Skvortsov, V. F.; Boznak, A. O.; Kim, A. B.; Arlyapov, A. Yu

    2015-09-01

    The paper presents methodology and results of experimental study by Sachs method the effect of length of mandrelled thick-walled cylinders made of steel grade 50 (0.5% C) with 5 mm diameter hole, outer diameter of 15 and 25 mm on residual stresses. Based on the review of studies, it was noted that this effect may be both due to uneven process of mandrelling along the cylinder length and due to zero axial residual stresses on its faces. It was found that the length of cylinders has the strongest influence on axial residual stresses. With allowances between 0.9 and 7.1% and length reduction from 40 to 10 mm, the largest absolute value of axial residual stresses decreases from 210 to 50 MPa. It was noted that when the outer diameter of cylinders is 15 mm their length significantly influence on both hoop and radial residual stresses. With the above-mentioned decrease in cylinders length, absolute values of hoop and radial residual stresses in the region adjacent to the hole, depending on the mandrelling allowance, increase (from -135 to -205 MPa and from -45 to 55 MPa respectively, when allowance is 7.1%), decrease (from -315 to -235 MPa and from -135 to -95 MPa respectively, when allowance is 0.9%) and remain almost unchanged (when allowance is 3.4%). Impact of length on these stresses is weak when the outer diameter of cylinders is 25 mm.

  8. THE AAA3 DOMAIN OF CYTOPLASMIC DYNEIN ACTS AS A SWITCH TO FACILITATE MICROTUBULE RELEASE

    PubMed Central

    Dewitt, Mark A.; Cypranowska, Caroline A.; Cleary, Frank B.; Belyy, Vladislav; Yildiz, Ahmet

    2014-01-01

    Cytoplasmic dynein is an AAA+ motor responsible for intracellular cargo transport and force generation along microtubules (MTs). Unlike kinesin and myosin, dynein contains multiple ATPase subunits, with AAA1 serving as the primary catalytic site. ATPase activity at AAA3 is also essential for robust motility, but its role in dynein’s mechanochemical cycle remains unclear. Here, we introduced transient pauses in Saccharomyces cerevisiae dynein motility by using a slowly hydrolyzing ATP analog. Analysis of pausing behavior revealed that AAA3 hydrolyzes nucleotide an order of magnitude slower than AAA1 and the two sites do not coordinate. ATPase mutations to AAA3 abolish the ability of dynein to modulate MT release. Nucleotide hydrolysis at AAA3 lifts this “MT gate” to fast motility. These results suggest that AAA3 acts as a switch that repurposes cytoplasmic dynein for fast cargo transport and MT anchoring tasks in cells. PMID:25486306

  9. Free convection in parallelogram-shaped enclosures with isothermal active walls: viscous shear stress in active systems

    NASA Astrophysics Data System (ADS)

    Baïri, A.; Zarco-Pernia, E.; García de María, J.-M.; Laraqi, N.

    2012-10-01

    Thermocouples are often used for thermoregulation of active thermal systems. When the junctions of these sensors are under a natural convection flow, it is necessary to take into account the viscous stress that can affect the measurement of temperature and therefore the regulation set points. The main objective of this work is to study the viscous shear stress taking place close to the active hot wall in closed air-filled cavities of parallelogrammic shape. The influence of shear stress is examined for different inclination angles of the cavity and large Rayleigh numbers which are usual in thermal applications. The local stress distributions are presented for the steady state for all the geometric configurations considered. The Nusselt number at the hot wall as well as the temperature and stream function distributions in the cavities are also included. The findings obtained from the numerical simulation using the finite volume method are validated by thermal measurements on an experimental cavity. This study confirms the need to properly choose the location of thermocouples in the reference cell used for controlling the active system.

  10. The Cell Wall Protein Ecm33 of Candida albicans is Involved in Chronological Life Span, Morphogenesis, Cell Wall Regeneration, Stress Tolerance, and Host-Cell Interaction.

    PubMed

    Gil-Bona, Ana; Reales-Calderon, Jose A; Parra-Giraldo, Claudia M; Martinez-Lopez, Raquel; Monteoliva, Lucia; Gil, Concha

    2016-01-01

    Ecm33 is a glycosylphosphatidylinositol-anchored protein in the human pathogen Candida albicans. This protein is known to be involved in fungal cell wall integrity (CWI) and is also critical for normal virulence in the mouse model of hematogenously disseminated candidiasis, but its function remains unknown. In this work, several phenotypic analyses of the C. albicans ecm33/ecm33 mutant (RML2U) were performed. We observed that RML2U displays the inability of protoplast to regenerate the cell wall, activation of the CWI pathway, hypersensitivity to temperature, osmotic and oxidative stresses and a shortened chronological lifespan. During the exponential and stationary culture phases, nuclear and actin staining revealed the possible arrest of the cell cycle in RML2U cells. Interestingly, a "veil growth," never previously described in C. albicans, was serendipitously observed under static stationary cells. The cells that formed this structure were also observed in cornmeal liquid cultures. These cells are giant, round cells, without DNA, and contain large vacuoles, similar to autophagic cells observed in other fungi. Furthermore, RML2U was phagocytozed more than the wild-type strain by macrophages at earlier time points, but the damage caused to the mouse cells was less than with the wild-type strain. Additionally, the percentage of RML2U apoptotic cells after interaction with macrophages was fewer than in the wild-type strain.

  11. The Cell Wall Protein Ecm33 of Candida albicans is Involved in Chronological Life Span, Morphogenesis, Cell Wall Regeneration, Stress Tolerance, and Host–Cell Interaction

    PubMed Central

    Gil-Bona, Ana; Reales-Calderon, Jose A.; Parra-Giraldo, Claudia M.; Martinez-Lopez, Raquel; Monteoliva, Lucia; Gil, Concha

    2016-01-01

    Ecm33 is a glycosylphosphatidylinositol-anchored protein in the human pathogen Candida albicans. This protein is known to be involved in fungal cell wall integrity (CWI) and is also critical for normal virulence in the mouse model of hematogenously disseminated candidiasis, but its function remains unknown. In this work, several phenotypic analyses of the C. albicans ecm33/ecm33 mutant (RML2U) were performed. We observed that RML2U displays the inability of protoplast to regenerate the cell wall, activation of the CWI pathway, hypersensitivity to temperature, osmotic and oxidative stresses and a shortened chronological lifespan. During the exponential and stationary culture phases, nuclear and actin staining revealed the possible arrest of the cell cycle in RML2U cells. Interestingly, a “veil growth,” never previously described in C. albicans, was serendipitously observed under static stationary cells. The cells that formed this structure were also observed in cornmeal liquid cultures. These cells are giant, round cells, without DNA, and contain large vacuoles, similar to autophagic cells observed in other fungi. Furthermore, RML2U was phagocytozed more than the wild-type strain by macrophages at earlier time points, but the damage caused to the mouse cells was less than with the wild-type strain. Additionally, the percentage of RML2U apoptotic cells after interaction with macrophages was fewer than in the wild-type strain. PMID:26870022

  12. Molecularly Defined Nanostructures Based on a Novel AAA-DDD Triple Hydrogen-Bonding Motif.

    PubMed

    Papmeyer, Marcus; Vuilleumier, Clément A; Pavan, Giovanni M; Zhurov, Konstantin O; Severin, Kay

    2016-01-26

    A facile and flexible method for the synthesis of a new AAA-DDD triple hydrogen-bonding motif is described. Polytopic supramolecular building blocks with precisely oriented AAA and DDD groups are thus accessible in few steps. These building blocks were used for the assembly of large macrocycles featuring four AAA-DDD interactions and a macrobicyclic complex with a total of six AAA-DDD interactions.

  13. Use of PIV to highlight possible errors in hot-wire Reynolds stress data over a 2D rough wall

    NASA Astrophysics Data System (ADS)

    Djenidi, Lyazid; Antonia, Robert A.; Amielh, Muriel; Anselmet, Fabien

    2014-10-01

    Particle image velocimetry (PIV) measurements are carried out in a turbulent boundary layer over a 2D rough surface consisting of transverse square bars. The aim of this work is to investigate a possible cause for the near-wall X-wire measurement errors observed on similar rough surfaces. The PIV measurements do not show the anomalous near-wall deficit of Reynolds stresses as measured with X-wires over the same surface. An extensive flow visualization analysis of the PIV data for a spacing between the roughness elements of p = 7 k ( k is the roughness element height) shows the occurrence of large-scale inward (sweeps) and outward (ejections) motions with a period of about 10.6 δ/ U 0 ( δ and U 0 are the boundary layer thickness and the free-stream velocity). While these motions dominate the near-wall region and contribute almost equally to the Reynolds shear stress -‹ uv›, the mean outward deviation from the mean flow direction is stronger than the inward deviation. Also, when the roughness spacing is reduced to p = 3 k, the outward deviation reduces significantly more than the inward deviation. The results support the argument that the outward motions, which can have an instantaneous deviation angle of more than 50° in the case p = 7 k, make the X-wire probe inefficient for detecting the ejection events (associated with the outward motions), particularly if the apex angle of the X-wire is not optimized for capturing the strong flow ejections with large deviations. The results explain in part the disparate information on the effect of the roughness on the Reynolds stresses in the outer region of the turbulent boundary layer over rough walls.

  14. Measurement of wall shear stress in a pulsatile pipe flow system using micro-pillar shear sensor (MPS3)

    NASA Astrophysics Data System (ADS)

    Raghav, Vrishank; Garcia, Christine; Gnanamanickam, Ebenezer; Yoganathan, Ajit; GT-Embry-Riddle Collaboration

    2014-11-01

    The measurement of unsteady wall shear stress (WSS) in a pulsatile flow system is quite a challenge in experimental fluid mechanics. Recent developments in micro fabrication techniques have resulted in a novel measurement technique called the micro-pillar shear stress sensor (MPS3). It is a micro-pillar mounted on the surface of interest, which deflects an amount proportional to the shear stress it experiences. This technique has been widely used, validated and applied to measure turbulent WSS in several flow configurations. In this work, the MPS3 technique is used to measure WSS for a pulsatile fully developed pipe flow. The main objective here is to validate this technique for pulsatile pipe flow applications. For this purpose the WSS measurements obtained are compared with those obtained from analytical womersley solutions of the pulsatile flow system in the laminar flow regime. Statistical metrics will be used to better understand the measured WSS through the time period of the pulsatile flow.

  15. In vivo creep and stress relaxation experiments to determine the wall extensibility and yield threshold for the sporangiophores of phycomyces

    PubMed Central

    Ortega, Joseph K. E.; Zehr, Edwin G.; Keanini, Russell G.

    1989-01-01

    The pressure probe was used to conduct in vivo creep and in vivo stress relaxation experiments on the sporangiophores of Phycomyces blakesleeanus. The in vivo creep and in vivo stress relaxation methods are compared with respect to their utility for determining the irreversible wall extensibility and the yield threshold. The results of the in vivo stress relaxation experiments demonstrate that the growth usually does not cease when the external water supply is removed, and the turgor pressure does not decay for hours afterwards. A successful stress relaxation experiment requires that the cell enlargement rate (growth rate) be zero during the turgor pressure decay. In a few experiments, the growth rate was zero during the turgor pressure decay. However, in general only the yield threshold could be determined. In vivo creep experiments proved to be easier to conduct and more useful in determining values for both the irreversible wall extensibility and the yield threshold. The results of the in vivo creep experiments demonstrate that small steps-up in turgor pressure, generally <0.02 MPa, elicit increases in growth rate as predicted by the growth equations and the augmented growth equations. The irreversible wall extensibility and the yield threshold were determined from these results. The results also demonstrate that steps-up in turgor pressure larger than 0.02 MPa, produce a different response; a decrease in growth rate. The decreased growth rate behavior is related to the magnitude of the step-up, and in general, larger steps-up in turgor pressure produce larger decreases in growth rate and longer periods of decreased growth rate. Qualitatively, this growth behavior is very similar to the “stretch response” previously reported by Dennison and Roth (1967). PMID:19431745

  16. Experimental and numerical study of fatigue crack propagation in a thick-walled cylinder under cyclic hoop stress

    NASA Astrophysics Data System (ADS)

    Salam, I.; Malik, M. A.; Abid, M.; Farooque, M.

    2014-06-01

    In present work, after finding the anisotropy resulting in dissimilar properties in different orientations of a thick-walled cylinder, experimental and numerical study was performed to reveal the fatigue crack growth behavior of the cylinder under cyclic hoop stress. Fatigue crack growth experiments were conducted on middle tension M(T) samples prepared in an orientation to simulate the hoop stress on the cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The fatigue crack growth data was compiled and applied to simulate and predict the crack growth process using two dimensional parametric finite element technique. The fatigue crack propagation was simulated, based on linear elastic fracture mechanics and stress intensity factor determination. Both the experimental and numerical results of crack growth data, at stress levels of 10 to 40 per cent of the yield stress of the material, were found in close agreement. The disparity observed was concluded in the range of statistical scatter in the experimental data. The crack growth rate and the fatigue life of the samples obtained from the experiments and the simulation were also in good agreement at all the stress levels analyzed.

  17. Computational solution of the velocity and wall shear stress distribution inside a left carotid artery under pulsatile flow conditions

    NASA Astrophysics Data System (ADS)

    Arslan, Nurullah; Turmuş, Hakan

    2014-08-01

    Stroke is still one of the leading causes for death after heart diseases and cancer in all over the world. Strokes happen because an artery that carries blood uphill from the heart to the head is clogged. Most of the time, as with heart attacks, the problem is atherosclerosis, hardening of the arteries, calcified buildup of fatty deposits on the vessel wall. In this study, the fluid dynamic simulations were done in a left carotid bifurcation under the pulsatile flow conditions computationally. Pulsatile flow waveform is given in the paper. In vivo geometry and boundary conditions were obtained from a patient who has stenosis located at external carotid artery (ECA) and internal carotid artery (ICA) of his common carotid artery (CCA). The location of critical flow fields such as low wall shear stress (WSS), stagnation regions and separation regions were detected near the highly stenosed region and at branching region.

  18. Instrumented thick-walled tube method for measuring thermal pressure in fluids and isotropic stresses in thermosetting resins

    NASA Astrophysics Data System (ADS)

    Merzlyakov, Mikhail; Simon, Sindee L.; McKenna, Gregory B.

    2005-06-01

    We have developed a method for measuring the thermal pressure coefficient and cure-induced and thermally induced stresses based on an instrumented thick-walled tube vessel. The device has been demonstrated at pressures up to 330 MPa and temperatures to 300 °C. The method uses a sealed stainless steel thick-walled tube to impose three-dimensional isotropic constraints. The tube is instrumented with strain gauges in hoop and in axial directions and can be used in open or closed configurations. By making measurements of the isotropic stresses as a function of temperature, the method allows determination of the thermal pressure coefficient in both the glassy and rubbery (or liquid) states. The method also can be used to measure isotropic stress development in thermosetting resins during cure and subsequent thermal cycling. Experimental results are presented for sucrose benzoate, di-2-ethylhexylsebacate, and an epoxy resin. The current report shows that the method provides reliable estimates for the thermal pressure coefficient. The thermal pressure coefficient is determined with resolution on the order of 10kPa/K. Among advantages of the method is that the tubes are reusable, even when measurements are made for cure response of thermosetting resins.

  19. Passive control of wall shear stress and mass transfer generated by submerged lobed impinging jet

    NASA Astrophysics Data System (ADS)

    Sodjavi, Kodjovi; Montagné, Brice; Meslem, Amina; Byrne, Paul; Serres, Laurent; Sobolik, Vaclav

    2016-05-01

    Particle image velocimetry was used to investigate the flow field in an impinging lobed daisy hemispherical nozzle jet in comparison to its counterpart round jet, at a Reynolds number of 5620 based on the exit velocity and the equivalent diameter D e of the nozzle. The limitations of the PIV technique in the vicinity of the target wall due to the laser scattering were addressed by using the electrodiffusion (ED) technique to determine the wall shear rate distribution. The distribution of the mass transfer coefficient is also obtained using the ED technique. The target wall is placed at a distance H = 2 D e from the plane tangent to the nozzle, at the center of the orifice. The entrainment of ambient fluid in the free jet region, which is larger in the lobed jet compared to the round jet, feeds in turn the wall jet region. The maximum wall shear rate was found significantly higher in the daisy jet, with an excess of 93 % compared to the reference round jet. The maximum mass transfer is 35 % higher in the former compared to the latter. Therefore, the hemispherical daisy nozzle is an excellent candidate in passive strategies to enhance local skin-friction and the subsequent local mass transfer at a constant exit Reynolds number.

  20. Reduction in left ventricular wall stress and improvement in function in failing hearts using Algisyl-LVR.

    PubMed

    Lee, Lik Chuan; Zhihong, Zhang; Hinson, Andrew; Guccione, Julius M

    2013-01-01

    Injection of Algisyl-LVR, a treatment under clinical development, is intended to treat patients with dilated cardiomyopathy. This treatment was recently used for the first time in patients who had symptomatic heart failure. In all patients, cardiac function of the left ventricle (LV) improved significantly, as manifested by consistent reduction of the LV volume and wall stress. Here we describe this novel treatment procedure and the methods used to quantify its effects on LV wall stress and function. Algisyl-LVR is a biopolymer gel consisting of Na(+)-Alginate and Ca(2+)-Alginate. The treatment procedure was carried out by mixing these two components and then combining them into one syringe for intramyocardial injections. This mixture was injected at 10 to 19 locations mid-way between the base and apex of the LV free wall in patients. Magnetic resonance imaging (MRI), together with mathematical modeling, was used to quantify the effects of this treatment in patients before treatment and at various time points during recovery. The epicardial and endocardial surfaces were first digitized from the MR images to reconstruct the LV geometry at end-systole and at end-diastole. Left ventricular cavity volumes were then measured from these reconstructed surfaces. Mathematical models of the LV were created from these MRI-reconstructed surfaces to calculate regional myofiber stress. Each LV model was constructed so that 1) it deforms according to a previously validated stress-strain relationship of the myocardium, and 2) the predicted LV cavity volume from these models matches the corresponding MRI-measured volume at end-diastole and end-systole. Diastolic filling was simulated by loading the LV endocardial surface with a prescribed end-diastolic pressure. Systolic contraction was simulated by concurrently loading the endocardial surface with a prescribed end-systolic pressure and adding active contraction in the myofiber direction. Regional myofiber stress at end

  1. Reduction in Left Ventricular Wall Stress and Improvement in Function in Failing Hearts using Algisyl-LVR

    PubMed Central

    Lee, Lik Chuan; Zhihong, Zhang; Hinson, Andrew; Guccione, Julius M.

    2013-01-01

    Injection of Algisyl-LVR, a treatment under clinical development, is intended to treat patients with dilated cardiomyopathy. This treatment was recently used for the first time in patients who had symptomatic heart failure. In all patients, cardiac function of the left ventricle (LV) improved significantly, as manifested by consistent reduction of the LV volume and wall stress. Here we describe this novel treatment procedure and the methods used to quantify its effects on LV wall stress and function. Algisyl-LVR is a biopolymer gel consisting of Na+-Alginate and Ca2+-Alginate. The treatment procedure was carried out by mixing these two components and then combining them into one syringe for intramyocardial injections. This mixture was injected at 10 to 19 locations mid-way between the base and apex of the LV free wall in patients. Magnetic resonance imaging (MRI), together with mathematical modeling, was used to quantify the effects of this treatment in patients before treatment and at various time points during recovery. The epicardial and endocardial surfaces were first digitized from the MR images to reconstruct the LV geometry at end-systole and at end-diastole. Left ventricular cavity volumes were then measured from these reconstructed surfaces. Mathematical models of the LV were created from these MRI-reconstructed surfaces to calculate regional myofiber stress. Each LV model was constructed so that 1) it deforms according to a previously validated stress-strain relationship of the myocardium, and 2) the predicted LV cavity volume from these models matches the corresponding MRI-measured volume at end-diastole and end-systole. Diastolic filling was simulated by loading the LV endocardial surface with a prescribed end-diastolic pressure. Systolic contraction was simulated by concurrently loading the endocardial surface with a prescribed end-systolic pressure and adding active contraction in the myofiber direction. Regional myofiber stress at end-diastole and

  2. New UK in-situ stress orientation for northern England and controls on borehole wall deformation identified using borehole imaging

    NASA Astrophysics Data System (ADS)

    Kingdon, Andrew; Fellgett, Mark W.; Waters, Colin N.

    2016-04-01

    The nascent development of a UK shale gas industry has highlighted the inadequacies of previous in-situ stress mapping which is fundamental to the efficacy and safety of potential fracturing operations. The limited number of stress inversions from earthquake focal plane mechanisms and overcoring measurements of in-situ stress in prospective areas increases the need for an up-to-date stress map. Borehole breakout results from 36 wells with newly interpreted borehole imaging data are presented. Across northern England these demonstrate a consistent maximum horizontal stress orientation (SHmax) orientation of 150.9° and circular standard deviation of 13.1°. These form a new and quality assured evidence base for both industry and its regulators. Widespread use of high-resolution borehole imaging tools has facilitated investigation of micro-scale relationships between stress and lithology, facilitating identification of breakouts as short as 25 cm. This is significantly shorter than those identified by older dual-caliper logging (typically 1-10+ m). Higher wall coverage (90%+ using the highest resolution tools) and decreasing pixel size (down to 4mm vertically by 2° of circumference) also facilitates identification of otherwise undetectable sub-centimetre width Drilling Induced Tensile Fractures (DIFs). Examination of borehole imaging from wells in North Yorkshire within the Carboniferous Pennine Coal Measures Group has showed that even though the stress field is uniform, complex micro-stress relationships exist. Different stress field indicators (SFI) are significantly affected by geology with differing failure responses from adjacent lithologies, highlighted by borehole imaging on sub-metre scales. Core-log-borehole imaging integration over intervals where both breakouts and DIFs have been identified allows accurate depth matching and thus allows a synthesis of failure for differing lithology and micro-structures under common in-situ conditions. Understanding these

  3. Evaluation on double-wall-tube residual stress distribution of sodium-heated steam generator by neutron diffraction and numerical analysis

    SciTech Connect

    Kisohara, N.; Suzuki, H.; Akita, K.; Kasahara, N.

    2012-07-01

    A double-wall-tube is nominated for the steam generator heat transfer tube of future sodium fast reactors (SFRs) in Japan, to decrease the possibility of sodium/water reaction. The double-wall-tube consists of an inner tube and an outer tube, and they are mechanically contacted to keep the heat transfer of the interface between the inner and outer tubes by their residual stress. During long term SG operation, the contact stress at the interface gradually falls down due to stress relaxation. This phenomenon might increase the thermal resistance of the interface and degrade the tube heat transfer performance. The contact stress relaxation can be predicted by numerical analysis, and the analysis requires the data of the initial residual stress distributions in the tubes. However, unclear initial residual stress distributions prevent precious relaxation evaluation. In order to resolve this issue, a neutron diffraction method was employed to reveal the tri-axial (radius, hoop and longitudinal) initial residual stress distributions in the double-wall-tube. Strain gauges also were used to evaluate the contact stress. The measurement results were analyzed using a JAEA's structural computer code to determine the initial residual stress distributions. Based on the stress distributions, the structural computer code has predicted the transition of the relaxation and the decrease of the contact stress. The radial and longitudinal temperature distributions in the tubes were input to the structural analysis model. Since the radial thermal expansion difference between the inner (colder) and outer (hotter) tube reduces the contact stress and the tube inside steam pressure contributes to increasing it, the analytical model also took these effects into consideration. It has been conduced that the inner and outer tubes are contacted with sufficient stresses during the plant life time, and that effective heat transfer degradation dose not occur in the double-wall-tube SG. (authors)

  4. Salinity stress inhibits bean leaf expansion by reducing turgor, not wall extensibility

    NASA Technical Reports Server (NTRS)

    Neumann, P. M.; Van Volkenburgh, E.; Cleland, R. E.

    1988-01-01

    Treatment of bean (Phaseolus vulgaris L.) seedlings with low levels of salinity (50 or 100 millimolar NaCl) decreased the rate of light-induced leaf cell expansion in the primary leaves over a 3 day period. This decrease could be due to a reduction in one or both of the primary cellular growth parameters: wall extensibility and cell turgor. Wall extensibility was assessed by the Instron technique. Salinity did not decrease extensibility and caused small increases relative to the controls after 72 hours. On the other hand, 50 millimolar NaCl caused a significant reduction in leaf bulk turgor at 24 hours; adaptive decreases in leaf osmotic potential (osmotic adjustment) were more than compensated by parallel decreases in xylem tension potential and the leaf apoplastic solute potential, resulting in a decreased leaf water potential. It is concluded that in bean seedlings, mild salinity initially affects leaf growth rate by a decrease in turgor rather than by a reduction in wall extensibility. Moreover, long-term salinization (10 days) resulted in an apparent mechanical adjustment, i.e. an increase in wall extensibility, which may help counteract reductions in turgor and maintain leaf growth rates.

  5. F-18 deoxyglucose and stress N-13 ammonia positron emission tomography in anterior wall healed myocardial infarction

    SciTech Connect

    Fudo, T.; Kambara, H.; Hashimoto, T.; Hayashi, M.; Nohara, R.; Tamaki, N.; Yonekura, Y.; Senda, M.; Konishi, J.; Kawai, C.

    1988-06-01

    To evaluate myocardial blood flow and glucose utilization, N-13 ammonia (NH3) and F-18 deoxyglucose positron emission tomography scanning was performed in 22 patients with previous anterior wall myocardial infarction, using a high-resolution, multi-slice, whole-body scanner. The N-13 ammonia study was performed at rest and after exercise. The F-18 deoxyglucose study was performed at rest after fasting greater than 5 hours. The N-13 ammonia study revealed a hypoperfused area in 19 of the 22 patients (86%), that corresponded to the infarcted regions as diagnosed by electrocardiography, coronary arteriography and left ventriculography (21 patients). The hypoperfused areas expanded after exercise in 16 of 22 patients (73%). F-18 deoxyglucose uptake was observed in these hypoperfused areas, especially in patients with hypokinetic wall motion on left ventriculography and in exercise-induced hypoperfused areas. However, positron emission tomography demonstrated diffuse uptake of F-18 deoxyglucose in 3 of 8 patients with dyskinetic wall motion. Thus, metabolically active myocardium in infarcted areas or periinfarct ischemia can be visualized with F-18 deoxyglucose and stress N-13 ammonia studies.

  6. Effect of Turbulence on the Temporal Variation of Hemodynamic Stresses in Aneurysm Model under Resting and Exercise Conditions

    NASA Astrophysics Data System (ADS)

    Khanafer, Khalil

    2005-11-01

    A numerical model is developed to analyze pulsatile turbulent flow in axisymmetric abdominal aortic aneurysm models (AAM) using realistic physiological resting and exercise waveforms. The transport equations are solved using the finite element formulation based on the Galerkin method of weighted residuals. The κ-ɛ model is used in this work to simulate turbulence characteristics of the convective flow by incorporating Boussinesq eddy-viscosity model. A number of interesting features of the flow field resulting from using realistic physiological waveforms are obtained for various pertinent parameters. Such parameters include Reynolds number, size of aneurysm, flexibility of aneurysm's wall, and the propagation of pressure and flow waves through AAM. The effect of non-Newtonian behavior of blood on hemodynamic stresses and compared with Newtonian behavior through AAM is investigated in the present study. The results of the present work illustrate that maximum turbulent shear stress occurs at the distal end of the AAA model. Furthermore, turbulence is found to have a significant effect on the pressure distribution along AAA wall for both physiological waveforms. This work paves the road for researchers in the area of AAA risk rupture to improve their understanding on the mechanics of aneurysm rupture enhanced by increased flow turbulence.

  7. Cell wall modifications in maize pulvini in response to gravitational stress.

    PubMed

    Zhang, Qisen; Pettolino, Filomena A; Dhugga, Kanwarpal S; Rafalski, J Antoni; Tingey, Scott; Taylor, Jillian; Shirley, Neil J; Hayes, Kevin; Beatty, Mary; Abrams, Suzanne R; Zaharia, L Irina; Burton, Rachel A; Bacic, Antony; Fincher, Geoffrey B

    2011-08-01

    Changes in cell wall polysaccharides, transcript abundance, metabolite profiles, and hormone concentrations were monitored in the upper and lower regions of maize (Zea mays) pulvini in response to gravistimulation, during which maize plants placed in a horizontal position returned to the vertical orientation. Heteroxylan levels increased in the lower regions of the pulvini, together with lignin, but xyloglucans and heteromannan contents decreased. The degree of substitution of heteroxylan with arabinofuranosyl residues decreased in the lower pulvini, which exhibited increased mechanical strength as the plants returned to the vertical position. Few or no changes in noncellulosic wall polysaccharides could be detected on the upper side of the pulvinus, and crystalline cellulose content remained essentially constant in both the upper and lower pulvinus. Microarray analyses showed that spatial and temporal changes in transcript profiles were consistent with the changes in wall composition that were observed in the lower regions of the pulvinus. In addition, the microarray analyses indicated that metabolic pathways leading to the biosynthesis of phytohormones were differentially activated in the upper and lower regions of the pulvinus in response to gravistimulation. Metabolite profiles and measured hormone concentrations were consistent with the microarray data, insofar as auxin, physiologically active gibberellic acid, and metabolites potentially involved in lignin biosynthesis increased in the elongating cells of the lower pulvinus. PMID:21697508

  8. Cell Wall Modifications in Maize Pulvini in Response to Gravitational Stress1[W][OA

    PubMed Central

    Zhang, Qisen; Pettolino, Filomena A.; Dhugga, Kanwarpal S.; Rafalski, J. Antoni; Tingey, Scott; Taylor, Jillian; Shirley, Neil J.; Hayes, Kevin; Beatty, Mary; Abrams, Suzanne R.; Zaharia, L. Irina; Burton, Rachel A.; Bacic, Antony; Fincher, Geoffrey B.

    2011-01-01

    Changes in cell wall polysaccharides, transcript abundance, metabolite profiles, and hormone concentrations were monitored in the upper and lower regions of maize (Zea mays) pulvini in response to gravistimulation, during which maize plants placed in a horizontal position returned to the vertical orientation. Heteroxylan levels increased in the lower regions of the pulvini, together with lignin, but xyloglucans and heteromannan contents decreased. The degree of substitution of heteroxylan with arabinofuranosyl residues decreased in the lower pulvini, which exhibited increased mechanical strength as the plants returned to the vertical position. Few or no changes in noncellulosic wall polysaccharides could be detected on the upper side of the pulvinus, and crystalline cellulose content remained essentially constant in both the upper and lower pulvinus. Microarray analyses showed that spatial and temporal changes in transcript profiles were consistent with the changes in wall composition that were observed in the lower regions of the pulvinus. In addition, the microarray analyses indicated that metabolic pathways leading to the biosynthesis of phytohormones were differentially activated in the upper and lower regions of the pulvinus in response to gravistimulation. Metabolite profiles and measured hormone concentrations were consistent with the microarray data, insofar as auxin, physiologically active gibberellic acid, and metabolites potentially involved in lignin biosynthesis increased in the elongating cells of the lower pulvinus. PMID:21697508

  9. Distinct quaternary structures of the AAA+ Lon protease control substrate degradation.

    PubMed

    Vieux, Ellen F; Wohlever, Matthew L; Chen, James Z; Sauer, Robert T; Baker, Tania A

    2013-05-28

    Lon is an ATPase associated with cellular activities (AAA+) protease that controls cell division in response to stress and also degrades misfolded and damaged proteins. Subunits of Lon are known to assemble into ring-shaped homohexamers that enclose an internal degradation chamber. Here, we demonstrate that hexamers of Escherichia coli Lon also interact to form a dodecamer at physiological protein concentrations. Electron microscopy of this dodecamer reveals a prolate structure with the protease chambers at the distal ends and a matrix of N domains forming an equatorial hexamer-hexamer interface, with portals of ∼45 Å providing access to the enzyme lumen. Compared with hexamers, Lon dodecamers are much less active in degrading large substrates but equally active in degrading small substrates. Our results support a unique gating mechanism that allows the repertoire of Lon substrates to be tuned by its assembly state.

  10. Mechanical analysis of the strains generated by water tension in plant stems. Part I: stress transmission from the water to the cell walls.

    PubMed

    Alméras, Tancrède; Gril, Joseph

    2007-11-01

    Plant tissues shrink and swell in response to changes in water pressure. These strains can be easily measured, e.g., at the surface of tree stems, to obtain indirect information about plant water status and other physiological parameters. We developed a mechanical model to clarify how water pressure is transmitted to cell walls and causes shrinkage of plant tissues, particularly in the case of thick-walled cells such as wood fibers. Our analysis shows that the stress inside the fiber cell walls is lower than the water tension. The difference is accounted for by a stress transmission factor that depends on two main effects. The first effect is the dilution of the stress through the cell wall, because water acts at the lumen border and is transmitted to the outer border of the cell, which has a larger circumference. The second effect is the partial conversion of radial stress into tangential stress. Both effects are quantified as functions of parameters of the cell wall structure and its mechanical properties.

  11. Explicit algebraic reynolds stress models for anisotropic wall-bounded flows

    NASA Astrophysics Data System (ADS)

    Menter, F. R.; Garbaruk, A. V.; Egorov, Y.

    2012-01-01

    In the present paper, two variants of Explicit Algebraic Reynolds Stress Model (EARSM) are presented and applied to a number of test cases. Both formulations start from the Wallin Johansson (WJ) EARSM stress-strain relationship. The goal of the first step was to combine the EARSM with the ω-equation-based Baseline (BSL) model, to avoid freestream sensitivities and ambiguities in comparison with the Shear Stress Transport (SST) model. This could be achieved by a slight change in the A1 constant. In addition, the standard eddy-viscosity formulation is used in the diffusion terms of the k- and the ω-equations. Secondly, a simplified version of the stress-strain relationship was developed. It is based on a linear form of the implicit algebraic model. It is not clear at the time if this formulation possess significant advantages against the WJ stress-strain model. For the current cases, both variants produced essentially identical results. Several test cases have been computed. The main interest in the simulations was on corner flow separation.

  12. Effect of type of load on stress analysis of thin-walled ducts

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Aggarwal, P. K.

    1992-01-01

    The standard procedure for qualifying the design of duct (pipe) systems in the Space Shuttle Main Engine (SSME) has been fairly well defined. However, since pipe elbows are quite common and important in the SSME duct systems, a clear understanding of the detailed stress profile of the components is necessary for accurate structural and life assessments. This study was initiated to predict the stress profile at/near the tangent point along the cross section of the duct under various types of loads. Also, this study was further extended to understand the stiffening effect on stresses due to pressure at the tangent point. The intention of this study was to identify the importance of selecting proper locations for mounting strain gauges and to utilize the obtained results to anchor dynamic models for accurate structural and life assessments of the SSME ducts under a dynamic environment. The finite element method was utilized in this study.

  13. Molecular and proteome analyses highlight the importance of the Cpx envelope stress system for acid stress and cell wall stability in Escherichia coli.

    PubMed

    Surmann, Kristin; Ćudić, Emina; Hammer, Elke; Hunke, Sabine

    2016-08-01

    Two-component systems (TCS) play a pivotal role for bacteria in stress regulation and adaptation. However, it is not well understood how these systems are modulated to meet bacterial demands. Especially, for those TCS using an accessory protein to integrate additional signals, no data concerning the role of the accessory proteins within the coordination of the response is available. The Cpx envelope stress two-component system, composed of the sensor kinase CpxA and the response regulator CpxR, is orchestrated by the periplasmic protein CpxP which detects misfolded envelope proteins and inhibits the Cpx system in unstressed cells. Using selected reaction monitoring, we observed that the amount of CpxA and CpxR, as well as their stoichiometry, are only marginally affected, but that a 10-fold excess of CpxP over CpxA is needed to switch off the Cpx system. Moreover, the relative quantification of the proteome identified not only acid stress response as a new indirect target of the Cpx system, but also suggests a general function of the Cpx system for cell wall stability.

  14. Molecular and proteome analyses highlight the importance of the Cpx envelope stress system for acid stress and cell wall stability in Escherichia coli.

    PubMed

    Surmann, Kristin; Ćudić, Emina; Hammer, Elke; Hunke, Sabine

    2016-08-01

    Two-component systems (TCS) play a pivotal role for bacteria in stress regulation and adaptation. However, it is not well understood how these systems are modulated to meet bacterial demands. Especially, for those TCS using an accessory protein to integrate additional signals, no data concerning the role of the accessory proteins within the coordination of the response is available. The Cpx envelope stress two-component system, composed of the sensor kinase CpxA and the response regulator CpxR, is orchestrated by the periplasmic protein CpxP which detects misfolded envelope proteins and inhibits the Cpx system in unstressed cells. Using selected reaction monitoring, we observed that the amount of CpxA and CpxR, as well as their stoichiometry, are only marginally affected, but that a 10-fold excess of CpxP over CpxA is needed to switch off the Cpx system. Moreover, the relative quantification of the proteome identified not only acid stress response as a new indirect target of the Cpx system, but also suggests a general function of the Cpx system for cell wall stability. PMID:27039284

  15. Accumulation of stress and inducer-dependent plant-cell-wall-degrading enzymes during asexual development in Aspergillus nidulans.

    PubMed Central

    Prade, R A; Ayoubi, P; Krishnan, S; Macwana, S; Russell, H

    2001-01-01

    Determination and interpretation of fungal gene expression profiles based on digital reconstruction of expressed sequenced tags (ESTs) are reported. A total of 51,524 DNA sequence files processed with PipeOnline resulted in 9775 single and 5660 contig unique ESTs, 31.2% of a typical fungal transcriptome. Half of the unique ESTs shared homology with genes in public databases, 35.8% of which are functionally defined and 64.2% are unclear or unknown. In Aspergillus nidulans 86% of transcripts associate with intermediate metabolism functions, mainly related to carbohydrate, amino acid, protein, and peptide biosynthesis. During asexual development, A. nidulans unexpectedly accumulates stress response and inducer-dependent transcripts in the absence of an inducer. Stress response genes in A. nidulans ESTs total 1039 transcripts, contrasting with 117 in Neurospora crassa, a 14.3-fold difference. A total of 5.6% of A. nidulans ESTs implicate inducer-dependent cell wall degradation or amino acid acquisition, 3.5-fold higher than in N. crassa. Accumulation of stress response and inducer-dependent transcripts suggests general derepression of cis-regulation during terminal asexual development. PMID:11238386

  16. Release of bacterial spores from inner walls of a stainless steel cup subjected to thermal stress

    NASA Technical Reports Server (NTRS)

    Wolochow, H.; Chatigny, M. A.; Herbert, J.

    1974-01-01

    In an earlier report thermal stresses, simulating those expected on a Mars Lander, dislodged approximately 0.01% of an aerosol deposited surface burden, as did a landing shock of 8-10 G deceleration. This work confirms earlier results and demonstrates that release rate is not dependent on surface burden.

  17. Exercise-Mediated Wall Shear Stress Increases Mitochondrial Biogenesis in Vascular Endothelium

    PubMed Central

    Kim, Boa; Lee, Hojun; Kawata, Keisuke; Park, Joon-Young

    2014-01-01

    Objective Enhancing structural and functional integrity of mitochondria is an emerging therapeutic option against endothelial dysfunction. In this study, we sought to investigate the effect of fluid shear stress on mitochondrial biogenesis and mitochondrial respiratory function in endothelial cells (ECs) using in vitro and in vivo complementary studies. Methods and Results Human aortic- or umbilical vein-derived ECs were exposed to laminar shear stress (20 dyne/cm2) for various durations using a cone-and-plate shear apparatus. We observed significant increases in the expression of key genes related to mitochondrial biogenesis and mitochondrial quality control as well as mtDNA content and mitochondrial mass under the shear stress conditions. Mitochondrial respiratory function was enhanced when cells were intermittently exposed to laminar shear stress for 72 hrs. Also, shear-exposed cells showed diminished glycolysis and decreased mitochondrial membrane potential (ΔΨm). Likewise, in in vivo experiments, mice that were subjected to a voluntary wheel running exercise for 5 weeks showed significantly higher mitochondrial content determined by en face staining in the conduit (greater and lesser curvature of the aortic arch and thoracic aorta) and muscle feed (femoral artery) arteries compared to the sedentary control mice. Interestingly, however, the mitochondrial biogenesis was not observed in the mesenteric artery. This region-specific adaptation is likely due to the differential blood flow redistribution during exercise in the different vessel beds. Conclusion Taken together, our findings suggest that exercise enhances mitochondrial biogenesis in vascular endothelium through a shear stress-dependent mechanism. Our findings may suggest a novel mitochondrial pathway by which a chronic exercise may be beneficial for vascular function. PMID:25375175

  18. Free and Cell Wall-Bound Polyamines under Long-Term Water Stress Applied at Different Growth Stages of ×Triticosecale Wittm

    PubMed Central

    Hura, Tomasz; Dziurka, Michał; Hura, Katarzyna; Ostrowska, Agnieszka; Dziurka, Kinga

    2015-01-01

    Background Long-stemmed and semi-dwarf cultivars of triticale were exposed to water stress at tillering, heading and anthesis stage. Quantitative determination of free and cell wall-bound polyamines, i.e. agmatine, cadaverine, putrescine, spermidine and spermine, was supplemented with an analysis of quantitative relationships between free and cell wall-bound polyamines. Results The content of free and cell wall-bound polyamines varied depending on the development stage, both under optimal and water stress conditions. Drought-induced increase in free agmatine content was observed at all developmental stages in long-stemmed cultivar. A depletion of spermidine and putrescine was also reported in this cultivar, and spermidine was less abundant in semi-dwarf cultivar exposed to drought stress at the three analyzed developmental stages. Changes in the content of the other free polyamines did not follow a steady pattern reflecting the developmental stages. On the contrary, the content of cell wall-bound polyamines gradually increased from tillering, through heading and until anthesis period. Conclusion Water stress seemed to induce a progressive decrease in the content of free polyamines and an accumulation of cell wall-bound polyamines. PMID:26247474

  19. Adapting the machine: adaptor proteins for Hsp100/Clp and AAA+ proteases.

    PubMed

    Kirstein, Janine; Molière, Noël; Dougan, David A; Turgay, Kürşad

    2009-08-01

    Members of the AAA+ protein superfamily contribute to many diverse aspects of protein homeostasis in prokaryotic cells. As a fundamental component of numerous proteolytic machines in bacteria, AAA+ proteins play a crucial part not only in general protein quality control but also in the regulation of developmental programmes, through the controlled turnover of key proteins such as transcription factors. To manage these many, varied tasks, Hsp100/Clp and AAA+ proteases use specific adaptor proteins to enhance or expand the substrate recognition abilities of their cognate protease. Here, we review our current knowledge of the modulation of bacterial AAA+ proteases by these cellular arbitrators.

  20. Mechanisms of Multi-walled Carbon Nanotubes-Induced Oxidative Stress and Genotoxicity in Mouse Fibroblast Cells.

    PubMed

    Alarifi, Saud; Ali, Daoud

    2015-01-01

    The extensive production and wide application of carbon nanotubes have made investigations of its toxic potentials necessary. In the present study, we explored the underlying mechanism through which multi-walled carbon nanotubes (MWCNTs) induce toxicity in mouse fibroblast cells (L929). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and neutral red uptake viability assays were used to examine mechanisms of cytotoxicity. Dose and time-dependent cytotoxicity was observed in L929 cells. The MWCNTs significantly increased the generation of reactive oxygen species, lipid peroxidation, superoxide dismutase, and decreased glutathione. It was observed that the MWCNTs induced caspase 3 activity. The highest DNA strand breakage was detected by comet assay at 300 µg/mL of MWCNTs. Thus, the data indicate that MWCNTs induced cytotoxicity and apoptosis in L929 cells via oxidative stress.

  1. Bicuspid Aortic Cusp Fusion Morphology Alters Aortic 3D Outflow Patterns, Wall Shear Stress and Expression of Aortopathy

    PubMed Central

    Mahadevia, Riti; Barker, Alex J; Schnell, Susanne; Entezari, Pegah; Kansal, Preeti; Fedak, Paul W.M.; Malaisrie, S Chris; McCarthy, Patrick; Collins, Jeremy; Carr, James; Markl, Michael

    2014-01-01

    Background: Aortic 3D blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy. Methods and Results: 4D flow MRI measured in vivo 3D blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4mm; n=15 RN-BAV, 39.6±7.2mm); aorta size controls with tricuspid aortic valves (n=30, 41.1±4.4mm); healthy volunteers (n=15, 24.9±3.0mm). Aortopathy type (0-3), systolic flow angle, flow displacement, and regional wall shear stress (WSS) were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional WSS (p<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV compared to aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV were associated with altered flow displacement in the proximal and mid AAo for type 1 (42-81% decrease versus type 2) and distal AAo for type 3 (33-39% increase versus type 2). Conclusions: The presence and type of BAV fusion was associated with changes in regional WSS distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiologic mechanism by which valve morphology phenotype can influence phenotypes of BAV aortopathy. PMID:24345403

  2. Biomechanical and morphometric properties of the arterial wall referenced to the zero-stress state in experimental diabetes.

    PubMed

    Zhao, J; Lu, X; Zhuang, F; Gregersen, H

    2000-01-01

    Morphometric and passive biomechanical properties were studied in isolated segments of the thoracic and abdominal aorta, left common carotid artery, left femoral artery and the left pulmonary artery in 20 non-diabetic and 28 streptozotocin (STZ)-induced diabetic rats. The diabetic and non-diabetic rats were divided into groups living 1, 4, 8, and 12 weeks after the induction of diabetes (n = 7 for each diabetic group) or sham injection (n = 5 for each group). The mechanical test was performed as a distension experiment where the proximal end of the arterial segment was connected via a tube to the container used for applying pressures to the segment and the distal end was left free. The vessel diameter and length were obtained from digitized images of the arterial segments at pre-selected pressures and at no-load and zero-stress states. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed from the length, diameter and pressure data and from the zero-stress state data. The zero-stress state was obtained by cutting vessel rings radially causing the rings to open up into a sector. Diabetes was associated with pronounced morphometric changes, e.g., wall thickness. With respect to the biomechanical data, the opening angle increased and reached a plateau in 4 weeks after which it decreased again (p < 0.05). The opening angle was smallest in the thoracic aorta and largest in the pulmonary artery. Furthermore, it was found that the circumferential stiffness of the arteries studied increased with the duration of diabetes. In the longitudinal direction significant differences were found 8 weeks after injection of STZ in all arteries except the pulmonary artery. In the 12 weeks group, the femoral artery was stiffest in the circumferential direction whereas the thoracic aorta was stiffest in the longitudinal direction. The accumulated serum glucose level correlated with the arterial wall thickness and elastic modulus (correlation

  3. Recovery of cell-free layer and wall shear stress profile symmetry downstream of an arteriolar bifurcation.

    PubMed

    Ye, Swe Soe; Ju, Meongkeun; Kim, Sangho

    2016-07-01

    Unequal RBC partitioning at arteriolar bifurcations contributes to dissimilar flow developments between daughter vessels in a bifurcation. Due to the importance of the cell-free layer (CFL) and the wall shear stress (WSS) to physiological processes such as vasoregulation and gas diffusion, we investigated the effects of a bifurcation disturbance on the development of the CFL width and WSS in bifurcation daughter branches. The analysis was performed on a two-dimensional (2-D) computational model of a transverse arteriole at three different flow rates corresponding to parent branch (PB) pseudoshear rates of 60, 170 and 470s(-1), while maintaining a 2-D hematocrit of about 55% in the PB. Flow symmetry was defined using the statistical similarity of the CFL and WSS distributions between the two walls of the vessel branch. In terms of the flow symmetry recovery, higher flow rates caused larger reductions in the flow symmetry indices in the MB and subsequently required longer vessel lengths for complete recovery. Lower tube hematocrits in the SB led to complete symmetry recovery for all flow rates despite the higher initial asymmetry in the SB than in the MB. Arteriolar bifurcations produce unavoidable local CFL asymmetry and the persistence of the asymmetry downstream may increase effective blood viscosity which is especially significant at higher physiological flow rates.

  4. Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

    NASA Astrophysics Data System (ADS)

    Long, J.; New, T. H.

    2016-07-01

    Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

  5. Extremal states of energy of a double-layered thick-walled tube - application to residually stressed arteries.

    PubMed

    Waffenschmidt, Tobias; Menzel, Andreas

    2014-01-01

    Various biological tissues are designed to optimally support external loads for complex geometries and mechanobiological structures. This results in complex microstructures of such materials. The design of, for instance, (healthy) arteries, which are in the focus of this work, is characterised by a residually stressed fibre-reinforced multi-layered composite with highly non-linear elastic response. The complex interaction of material properties with the geometry and residual stress effects enables the optimal support under different blood pressures, respectively blood flow, within the vessel. The fibres reinforcing the arterial wall, as well as residual stresses present in the vessel, strongly influence its overall behaviour and performance. Turn-over and remodelling processes of the collagenous fibres occurring in the respective layers - either resulting from natural growth phenomena or from artificially induced changes in loading condition such as stent deployment - support the optimisation of the multi-layered composite structure of arteries for the particular loading conditions present in the artery. Within this contribution, the overall energetic properties of an artery are discussed by means of the inflation, bending and extension of a double-layered cylindrical tube. Different states of residual stresses and different fibre orientations are considered so that, for instance, representative fibre angles that result in extremal states of the total potential energy can be identified. In view of turn-over and remodelling processes, these orientations are considered to constitute preferred directions of fibre alignment. In summary, the main goal of this work is to calculate optimal material, structural and loading parameters by concepts of energy-minimisation. Several numerical studies show that the obtained values - such as the fibre orientations, the residual axial stretch and the opening angle - are in good agreement with respective physiological parameters

  6. Extremal states of energy of a double-layered thick-walled tube - application to residually stressed arteries.

    PubMed

    Waffenschmidt, Tobias; Menzel, Andreas

    2014-01-01

    Various biological tissues are designed to optimally support external loads for complex geometries and mechanobiological structures. This results in complex microstructures of such materials. The design of, for instance, (healthy) arteries, which are in the focus of this work, is characterised by a residually stressed fibre-reinforced multi-layered composite with highly non-linear elastic response. The complex interaction of material properties with the geometry and residual stress effects enables the optimal support under different blood pressures, respectively blood flow, within the vessel. The fibres reinforcing the arterial wall, as well as residual stresses present in the vessel, strongly influence its overall behaviour and performance. Turn-over and remodelling processes of the collagenous fibres occurring in the respective layers - either resulting from natural growth phenomena or from artificially induced changes in loading condition such as stent deployment - support the optimisation of the multi-layered composite structure of arteries for the particular loading conditions present in the artery. Within this contribution, the overall energetic properties of an artery are discussed by means of the inflation, bending and extension of a double-layered cylindrical tube. Different states of residual stresses and different fibre orientations are considered so that, for instance, representative fibre angles that result in extremal states of the total potential energy can be identified. In view of turn-over and remodelling processes, these orientations are considered to constitute preferred directions of fibre alignment. In summary, the main goal of this work is to calculate optimal material, structural and loading parameters by concepts of energy-minimisation. Several numerical studies show that the obtained values - such as the fibre orientations, the residual axial stretch and the opening angle - are in good agreement with respective physiological parameters

  7. Methods and results for stress analyses on 14-ton, thin-wall depleted UF{sub 6} cylinders

    SciTech Connect

    Kirkpatrick, J.R.; Chung, C.K.; Frazier, J.L.; Kelley, D.K.

    1996-10-01

    Uranium enrichment operations at the three US gaseous diffusion plants produce depleted uranium hexafluoride (DUF{sub 6}) as a residential product. At the present time, the inventory of DUF{sub 6} in this country is more than half a million tons. The inventory of DUF{sub 6} is contained in metal storage cylinders, most of which are located at the gaseous diffusion plants. The principal objective of the project is to ensure the integrity of the cylinders to prevent causing an environmental hazard by releasing the contents of the cylinders into the atmosphere. Another objective is to maintain the cylinders in such a manner that the DUF{sub 6} may eventually be converted to a less hazardous material for final disposition. An important task in the DUF{sub 6} cylinders management project is determining how much corrosion of the walls can be tolerated before the cylinders are in danger of being damaged during routine handling and shipping operations. Another task is determining how to handle cylinders that have already been damaged in a manner that will minimize the chance that a breach will occur or that the size of an existing breach will be significantly increased. A number of finite element stress analysis (FESA) calculations have been done to analyze the stresses for three conditions: (1) while the cylinder is being lifted, (2) when a cylinder is resting on two cylinders under it in the customary two-tier stacking array, and (3) when a cylinder is resting on tis chocks on the ground. Various documents describe some of the results and discuss some of the methods whereby they have been obtained. The objective of the present report is to document as many of the FESA cases done at Oak Ridge for 14-ton thin-wall cylinders as possible, giving results and a description of the calculations in some detail.

  8. Residual stress effect on fatigue crack growth in thick wall cylinders

    SciTech Connect

    Kiciak, A.; Glinka, G.; Burns, D.J.

    1995-11-01

    Recently derived weight functions for a single, semi-elliptical, longitudinal crack in a thick wall cylinder with the diameter ratio D{sub 0}/D{sub i} = 2, have been used to analyze fatigue crack propagation in autofrettaged and non-autofrettaged, pressurized cylinders. Two levels of autofrettage, 30 and 60%, have been considered. The influences of the level of autofrettage, surface crack closure, and different sets of parameters of crack closure, and different sets of parameters of crack propagation relation have been investigated. The development of cracks has been compared to the experimental results. The results of analyses confirm beneficial influence of autofrettage. It has been shown that the discrepancies between the observed and calculated crack developments cannot be ascribed to the influence of surface crack closure. The comparison of the experiments and predictions unveils the need for an additional series of experiments.

  9. Algisyl-LVR™ with coronary artery bypass grafting reduces left ventricular wall stress and improves function in the failing human heart☆,☆☆

    PubMed Central

    Lee, Lik Chuan; Wall, Samuel T.; Klepach, Doron; Ge, Liang; Zhang, Zhihong; Lee, Randall J.; Hinson, Andy; Gorman, Joseph H.; Gorman, Robert C.; Guccione, Julius M.

    2013-01-01

    Background Left ventricular (LV) wall stress reduction is a cornerstone in treating heart failure. Large animal models and computer simulations indicate that adding non-contractile material to the damaged LV wall can potentially reduce myofiber stress. We sought to quantify the effects of a novel implantable hydrogel (Algisyl-LVR™) treatment in combination with coronary artery bypass grafting (i.e. Algisyl-LVR™+CABG) on both LV function and wall stress in heart failure patients. Methods and results Magnetic resonance images obtained before treatment (n=3), and at 3 months (n=3) and 6 months (n=2) afterwards were used to reconstruct the LV geometry. Cardiac function was quantified using end-diastolic volume (EDV), end-systolic volume (ESV), regional wall thickness, sphericity index and regional myofiber stress computed using validated mathematical modeling. The LV became more ellipsoidal after treatment, and both EDV and ESV decreased substantially 3 months after treatment in all patients; EDV decreased from 264±91 ml to 146±86 ml and ESV decreased from 184±85 ml to 86±76 ml. Ejection fraction increased from 32±8% to 47±18% during that period. Volumetric-averaged wall thickness increased in all patients, from 1.06±0.21 cm (baseline) to 1.3±0.26 cm (3 months). These changes were accompanied by about a 35% decrease in myofiber stress at end-of-diastole and at end-of-systole. Post-treatment myofiber stress became more uniform in the LV. Conclusions These results support the novel concept that Algisyl-LVR™+CABG treatment leads to decreased myofiber stress, restored LV geometry and improved function. PMID:23394895

  10. Xylem sap in cotton contains proteins that contribute to environmental stress response and cell wall development.

    PubMed

    Zhang, Zhiyong; Xin, Wanwan; Wang, Sufang; Zhang, Xin; Dai, Haifang; Sun, Runrun; Frazier, Taylor; Zhang, Baohong; Wang, Qinglian

    2015-01-01

    The xylem sap of a plant is primarily responsible for transporting molecules from the underground root system to the aboveground parts of the plant body. In order to understand the role that roots play in cotton growth and development, the components present in xylem sap must be elucidated. In this study, we used a shotgun HPLC-ESI-MS/MS proteomics approach to identify 455 peptides from the xylem sap of field-grown cotton plants at peak blooming stage. Of these peptides, 384 (84.4%) were found to be secreted proteins and 320 (70.3%) had special molecular functions. Based on Gene Ontology (GO) analysis, 348 peptides were annotated in terms of molecular function, biological process, and cellular localization, with 46.9 and 45.1% being related to catalytic activity and binding activity, respectively. Many xylem sap-containing proteins were predicted to be involved in different phases of xylem differentiation including cell wall metabolism, secondary cell wall development and patterning, and programmed cell death. The identification of starch and sucrose hydrolyzing enzymes implicated the interaction between roots and aboveground parts on the aspect of carbohydrate metabolism. Many of the proteins identified in this study are involved in defense mechanisms including pathogen-related proteins, such as peroxidases, chitinases, and germin-like proteins, proteases involved in disease resistance, and phytoalexin phenylpropanoid synthesis-related proteins. The majority of identified signaling proteins were fasciclin-like arabinogalactan proteins and kinases. The results of this study provide useful insight into the communication mechanisms between cotton roots and the rest of the cotton plant.

  11. Effects of Argentilactone on the Transcriptional Profile, Cell Wall and Oxidative Stress of Paracoccidioides spp.

    PubMed

    Araújo, Felipe Souto; Coelho, Luciene Melo; Silva, Lívia do Carmo; da Silva Neto, Benedito Rodrigues; Parente-Rocha, Juliana Alves; Bailão, Alexandre Melo; de Oliveira, Cecília Maria Alves; Fernandes, Gabriel da Rocha; Hernández, Orville; Ochoa, Juan Guillermo McEwen; Soares, Célia Maria de Almeida; Pereira, Maristela

    2016-01-01

    Paracoccidioides spp., a dimorphic pathogenic fungus, is the etiologic agent of paracoccidioidomycosis (PCM). PCM is an endemic disease that affects at least 10 million people in Latin America, causing severe public health problems. The drugs used against pathogenic fungi have various side effects and limited efficacy; therefore, there is an inevitable and urgent medical need for the development of new antifungal drugs. In the present study, we evaluated the transcriptional profile of Paracoccidioides lutzii exposed to argentilactone, a constituent of the essential oil of Hyptis ovalifolia. A total of 1,058 genes were identified, of which 208 were up-regulated and 850 were down-regulated. Cell rescue, defense and virulence, with a total of 26 genes, was a functional category with a large number of genes induced, including heat shock protein 90 (hsp90), cytochrome c peroxidase (ccp), the hemoglobin ligand RBT5 (rbt5) and superoxide dismutase (sod). Quantitative real-time PCR revealed an increase in the expression level of all of those genes. An enzymatic assay showed a significant increase in SOD activity. The reduced growth of Pbhsp90-aRNA, Pbccp-aRNA, Pbsod-aRNA and Pbrbt5-aRNA isolates in the presence of argentilactone indicates the importance of these genes in the response of Paracoccidioides spp. to argentilactone. The response of the P. lutzii cell wall to argentilactone treatment was also evaluated. The results showed that argentilactone caused a decrease in the levels of polymers in the cell wall. These results suggest that argentilactone is a potential candidate for antifungal therapy.

  12. Effects of Argentilactone on the Transcriptional Profile, Cell Wall and Oxidative Stress of Paracoccidioides spp.

    PubMed Central

    Araújo, Felipe Souto; Coelho, Luciene Melo; Silva, Lívia do Carmo; da Silva Neto, Benedito Rodrigues; Parente-Rocha, Juliana Alves; Bailão, Alexandre Melo; de Oliveira, Cecília Maria Alves; Fernandes, Gabriel da Rocha; Hernández, Orville; Ochoa, Juan Guillermo McEwen; Soares, Célia Maria de Almeida; Pereira, Maristela

    2016-01-01

    Paracoccidioides spp., a dimorphic pathogenic fungus, is the etiologic agent of paracoccidioidomycosis (PCM). PCM is an endemic disease that affects at least 10 million people in Latin America, causing severe public health problems. The drugs used against pathogenic fungi have various side effects and limited efficacy; therefore, there is an inevitable and urgent medical need for the development of new antifungal drugs. In the present study, we evaluated the transcriptional profile of Paracoccidioides lutzii exposed to argentilactone, a constituent of the essential oil of Hyptis ovalifolia. A total of 1,058 genes were identified, of which 208 were up-regulated and 850 were down-regulated. Cell rescue, defense and virulence, with a total of 26 genes, was a functional category with a large number of genes induced, including heat shock protein 90 (hsp90), cytochrome c peroxidase (ccp), the hemoglobin ligand RBT5 (rbt5) and superoxide dismutase (sod). Quantitative real-time PCR revealed an increase in the expression level of all of those genes. An enzymatic assay showed a significant increase in SOD activity. The reduced growth of Pbhsp90-aRNA, Pbccp-aRNA, Pbsod-aRNA and Pbrbt5-aRNA isolates in the presence of argentilactone indicates the importance of these genes in the response of Paracoccidioides spp. to argentilactone. The response of the P. lutzii cell wall to argentilactone treatment was also evaluated. The results showed that argentilactone caused a decrease in the levels of polymers in the cell wall. These results suggest that argentilactone is a potential candidate for antifungal therapy. PMID:26734764

  13. Engineering fluorescent protein substrates for the AAA+ Lon protease.

    PubMed

    Wohlever, Matthew L; Nager, Andrew R; Baker, Tania A; Sauer, Robert T

    2013-04-01

    AAA+ proteases, such as Escherichia coli Lon, recognize protein substrates by binding to specific peptide degrons and then unfold and translocate the protein into an internal degradation chamber for proteolysis. For some AAA+ proteases, attaching specific degrons to the N- or C-terminus of green fluorescent protein (GFP) generates useful substrates, whose unfolding and degradation can be monitored by loss of fluorescence, but Lon fails to degrade appropriately tagged GFP variants at a significant rate. Here, we demonstrate that Lon catalyzes robust unfolding and degradation of circularly permuted variants of GFP with a β20 degron appended to the N terminus or a sul20 degron appended to the C terminus. Lon degradation of non-permuted GFP-sul20 is very slow, in part because the enzyme cannot efficiently extract the degron-proximal C-terminal β-strand to initiate denaturation. The circularly permuted GFP substrates described here allow convenient high-throughput assays of the kinetics of Lon degradation in vitro and also permit assays of Lon proteolysis in vivo.

  14. Training Scientists to be Effective Communicators: AAAS Communicating Science Workshops

    NASA Astrophysics Data System (ADS)

    Cendes, L.; Lohwater, T.

    2012-12-01

    "Communicating Science: Tools for Scientists and Engineers" is a workshop program developed by AAAS to provide guidance and practice for scientists and engineers in communicating about science with public audiences. The program was launched at the 2008 AAAS Annual Meeting in Boston and has since provided 24 workshops for more than 1,500 scientist and engineer attendees at universities, science society meetings, and government agency labs around the United States. Each interactive workshop targets scientists and engineers specifically and has included content such as message development, defining audience, identifying opportunities for engaging the public, and practice with public presentations and cameras. The workshop format allows for collaborative learning through small-group discussion, resource sharing, and participation in critique of other participants' presentations. Continuous monitoring of the program includes on-site and online surveys and evaluation. On an assessment of workshops from 2008-2010, attendees reported that knowledge gained from the workshop helped in crafting messages about their scientific work for use in communicating with public audiences, and approximately 80 percent of respondents reported participation in communication with a public audience after attending the workshop. Through workshop content and feedback of participating scientists, this presentation will highlight some best practices and resources for scientists who want to take a proactive role in science communication.

  15. Unsteady wall shear stress analysis from image-based computational fluid dynamic aneurysm models under Newtonian and Casson rheological models.

    PubMed

    Castro, Marcelo A; Ahumada Olivares, María C; Putman, Christopher M; Cebral, Juan R

    2014-10-01

    The aim of this work was to determine whether or not Newtonian rheology assumption in image-based patient-specific computational fluid dynamics (CFD) cerebrovascular models harboring cerebral aneurysms may affect the hemodynamics characteristics, which have been previously associated with aneurysm progression and rupture. Ten patients with cerebral aneurysms with lobulations were considered. CFD models were reconstructed from 3DRA and 4DCTA images by means of region growing, deformable models, and an advancing front technique. Patient-specific FEM blood flow simulations were performed under Newtonian and Casson rheological models. Wall shear stress (WSS) maps were created and distributions were compared at the end diastole. Regions of lower WSS (lobulation) and higher WSS (neck) were identified. WSS changes in time were analyzed. Maximum, minimum and time-averaged values were calculated and statistically compared. WSS characterization remained unchanged. At high WSS regions, Casson rheology systematically produced higher WSS minimum, maximum and time-averaged values. However, those differences were not statistically significant. At low WSS regions, when averaging over all cases, the Casson model produced higher stresses, although in some cases the Newtonian model did. However, those differences were not significant either. There is no evidence that Newtonian model overestimates WSS. Differences are not statistically significant.

  16. Surface mapping for visualization of wall stresses during inhalation in a human nasal cavity.

    PubMed

    Inthavong, Kiao; Shang, Yidan; Tu, Jiyuan

    2014-01-01

    Airflow analysis can assist in better understanding the physiology however the human nasal cavity is an extremely complicated geometry that is difficult to visualize in 3D space, let alone in 2D space. In this paper, an anatomically accurate 3D surface of the nasal passages derived from CT data was unwrapped and transformed into a 2D space, into a UV-domain (where u and v are the coordinates) to allow a complete view of the entire wrapped surface. This visualization technique allows surface flow parameters to be analyzed with greater precision. A UV-unwrapping tool is developed and a strategy is presented to allow deeper analysis to be performed. This includes (i) the ability to present instant comparisons of geometry and flow variables between any number of different nasal cavity models through normalization of the 2D unwrapped surface; (ii) visualization of an entire surface in one view and; (iii) a planar surface that allows direct 1D and 2D analytical solutions of diffusion of inhaled vapors and particles through the nasal walls. This work lays a foundation for future investigations that correlates adverse and therapeutic health responses to local inhalation of gases and particles.

  17. Osmotic stress adaptation in Lactobacillus casei BL23 leads to structural changes in the cell wall polymer lipoteichoic acid.

    PubMed

    Palomino, Maria Mercedes; Allievi, Mariana C; Gründling, Angelika; Sanchez-Rivas, Carmen; Ruzal, Sandra M

    2013-11-01

    The probiotic Gram-positive bacterium Lactobacillus casei BL23 is naturally confronted with salt-stress habitats. It has been previously reported that growth in high-salt medium, containing 0.8 M NaCl, leads to modifications in the cell envelope of this bacterium. In this study, we report that L. casei BL23 has an increased ability to form biofilms and to bind cations in high-salt conditions. This behaviour correlated with modifications of surface properties involving teichoic acids, which are important cell wall components. We also showed that, in these high-salt conditions, L. casei BL23 produces less of the cell wall polymer lipoteichoic acid (LTA), and that this anionic polymer has a shorter mean chain length and a lower level of d-alanyl-substitution. Analysis of the transcript levels of the dltABCD operon, encoding the enzymes required for the incorporation of d-alanine into anionic polymers, showed a 16-fold reduction in mRNA levels, which is consistent with a decrease in d-alanine substitutions on LTA. Furthermore, a 13-fold reduction in the transcript levels was observed for the gene LCABL_09330 coding for a putative LTA synthase. To provide further experimental evidence that LCABL_09330 is a true LTA synthase (LtaS) in L. casei BL23, the enzymic domain was cloned and expressed in E. coli. The purified protein was able to hydrolyse the membrane lipid phosphatidylglycerol as expected for an LTA synthase enzyme, and hence LCABL_09330 was renamed LtaS. The purified enzyme showed Mn(2+)-ion dependent activity, and its activity was modulated by differences in NaCl concentration. The decrease in both ltaS transcript levels and enzyme activity observed in high-salt conditions might influence the length of the LTA backbone chain. A putative function of the modified LTA structure is discussed that is compatible with the growth under salt-stress conditions and with the overall envelope modifications taking place during this stress condition. PMID:24014660

  18. Three-dimensional macro-scale assessment of regional and temporal wall shear stress characteristics on aortic valve leaflets.

    PubMed

    Cao, K; Bukač, M; Sucosky, P

    2016-01-01

    The aortic valve (AV) achieves unidirectional blood flow between the left ventricle and the aorta. Although hemodynamic stresses have been shown to regulate valvular biology, the native wall shear stress (WSS) experienced by AV leaflets remains largely unknown. The objective of this study was to quantify computationally the macro-scale leaflet WSS environment using fluid-structure interaction modeling. An arbitrary Lagrangian-Eulerian approach was implemented to predict valvular flow and leaflet dynamics in a three-dimensional AV geometry subjected to physiologic transvalvular pressure. Local WSS characteristics were quantified in terms of temporal shear magnitude (TSM), oscillatory shear index (OSI) and temporal shear gradient (TSG). The dominant radial WSS predicted on the leaflets exhibited high amplitude and unidirectionality on the ventricularis (TSM>7.50 dyn/cm(2), OSI < 0.17, TSG>325.54 dyn/cm(2) s) but low amplitude and bidirectionality on the fibrosa (TSM < 2.73 dyn/cm(2), OSI>0.38, TSG < 191.17 dyn/cm(2) s). The radial WSS component computed in the leaflet base, belly and tip demonstrated strong regional variability (ventricularis TSM: 7.50-22.32 dyn/cm(2), fibrosa TSM: 1.26-2.73 dyn/cm(2)). While the circumferential WSS exhibited similar spatially dependent magnitude (ventricularis TSM: 1.41-3.40 dyn/cm(2), fibrosa TSM: 0.42-0.76 dyn/cm(2)) and side-specific amplitude (ventricularis TSG: 101.73-184.43 dyn/cm(2) s, fibrosa TSG: 41.92-54.10 dyn/cm(2) s), its temporal variations were consistently bidirectional (OSI>0.25). This study provides new insights into the role played by leaflet-blood flow interactions in valvular function and critical hemodynamic stress data for the assessment of the hemodynamic theory of AV disease.

  19. Analysis of Peristaltic Motion of a Nanofluid with Wall Shear Stress, Microrotation, and Thermal Radiation Effects.

    PubMed

    Dhanapal, C; Kamalakkannan, J; Prakash, J; Kothandapani, M

    2016-01-01

    This paper analyzes the peristaltic flow of an incompressible micropolar nanofluid in a tapered asymmetric channel in the presence of thermal radiation and heat sources parameters. The rotation of the nanoparticles is incorporated in the flow model. The equations governing the nanofluid flow are modeled and exact solutions are managed under long wavelength and flow Reynolds number and long wavelength approximations. Explicit expressions of axial velocity, stream function, microrotation, nanoparticle temperature, and concentration have been derived. The phenomena of shear stress and trapping have also been discussed. Finally, the influences of various parameters of interest on flow variables have been discussed numerically and explained graphically. Besides, the results obtained in this paper will be helpful to those who are working on the development of various realms like fluid mechanics, the rotation, Brownian motion, thermophoresis, coupling number, micropolar parameter, and the nondimensional geometry parameters. PMID:27688703

  20. Analysis of Peristaltic Motion of a Nanofluid with Wall Shear Stress, Microrotation, and Thermal Radiation Effects

    PubMed Central

    Dhanapal, C.; Kamalakkannan, J.; Prakash, J.

    2016-01-01

    This paper analyzes the peristaltic flow of an incompressible micropolar nanofluid in a tapered asymmetric channel in the presence of thermal radiation and heat sources parameters. The rotation of the nanoparticles is incorporated in the flow model. The equations governing the nanofluid flow are modeled and exact solutions are managed under long wavelength and flow Reynolds number and long wavelength approximations. Explicit expressions of axial velocity, stream function, microrotation, nanoparticle temperature, and concentration have been derived. The phenomena of shear stress and trapping have also been discussed. Finally, the influences of various parameters of interest on flow variables have been discussed numerically and explained graphically. Besides, the results obtained in this paper will be helpful to those who are working on the development of various realms like fluid mechanics, the rotation, Brownian motion, thermophoresis, coupling number, micropolar parameter, and the nondimensional geometry parameters. PMID:27688703

  1. Analysis of Peristaltic Motion of a Nanofluid with Wall Shear Stress, Microrotation, and Thermal Radiation Effects

    PubMed Central

    Dhanapal, C.; Kamalakkannan, J.; Prakash, J.

    2016-01-01

    This paper analyzes the peristaltic flow of an incompressible micropolar nanofluid in a tapered asymmetric channel in the presence of thermal radiation and heat sources parameters. The rotation of the nanoparticles is incorporated in the flow model. The equations governing the nanofluid flow are modeled and exact solutions are managed under long wavelength and flow Reynolds number and long wavelength approximations. Explicit expressions of axial velocity, stream function, microrotation, nanoparticle temperature, and concentration have been derived. The phenomena of shear stress and trapping have also been discussed. Finally, the influences of various parameters of interest on flow variables have been discussed numerically and explained graphically. Besides, the results obtained in this paper will be helpful to those who are working on the development of various realms like fluid mechanics, the rotation, Brownian motion, thermophoresis, coupling number, micropolar parameter, and the nondimensional geometry parameters.

  2. Properties of sizeable [n]cycloparaphenylenes as molecular models of single-wall carbon nanotubes elucidated by Raman spectroscopy: structural and electron-transfer responses under mechanical stress.

    PubMed

    Peña Alvarez, Miriam; Mayorga Burrezo, Paula; Kertesz, Miklos; Iwamoto, Takahiro; Yamago, Shigeru; Xia, Jianlong; Jasti, Ramesh; López Navarrete, Juan T; Taravillo, Mercedes; Baonza, Valentín G; Casado, Juan

    2014-07-01

    [n]Cycloparaphenylenes behave as molecular templates of "perfectly chemically defined" single-wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge-transfer salts, or complexes with fullerene, by one-electron concave-convex electron transfer. PMID:24838669

  3. Analysis of a Typical Chinese High School Biology Textbook Using the AAAS Textbook Standards

    ERIC Educational Resources Information Center

    Liang, Ye; Cobern, William W.

    2013-01-01

    The purpose of this study was to evaluate a typical Chinese high school biology textbook using the textbook standards of the American Association for the Advancement of Science (AAAS). The data were composed of three chapters selected from the textbook. Each chapter was analyzed and rated using the AAAS textbook standards. Pearson correlations…

  4. Alteration of the Physical and Chemical Structure of the Primary Cell Wall of Growth-Limited Plant Cells Adapted to Osmotic Stress 1

    PubMed Central

    Iraki, Naim M.; Bressan, Ray A.; Hasegawa, P. M.; Carpita, Nicholas C.

    1989-01-01

    Cells of tobacco (Nicotiana tabacum L.) adapted to grow in severe osmotic stress of 428 millimolar NaCl (−23 bar) or 30% polyethylene glycol 8000 (−28 bar) exhibit a drastically altered growth physiology that results in slower cell expansion and fully expanded cells with volumes only one-fifth to one-eighth those of unadapted cells. This reduced cell volume occurs despite maintenance of turgor pressures sometimes severalfold higher than those of unadapted cells. This report and others (NM Iraki et al [1989] Plant Physiol 90: 000-000 and 000-000) document physical and biochemical alterations of the cell walls which might explain how adapted cells decrease the ability of the wall to expand despite diversion of carbon used for osmotic adjustment away from synthesis of cell wall polysaccharides. Tensile strength measured by a gas decompression technique showed empirically that walls of NaCl-adapted cells are much weaker than those of unadapted cells. Correlated with this weakening was a substantial decrease in the proportion of crystalline cellulose in the primary cell wall. Even though the amount of insoluble protein associated with the wall was increased relative to other wall components, the amount of hydroxyproline in the insoluble protein of the wall was only about 10% that of unadapted cells. These results indicate that a cellulosic-extensin framework is a primary determinant of absolute wall tensile strength, but complete formation of this framework apparently is sacrificed to divert carbon to substances needed for osmotic adjustment. We propose that the absolute mass of this framework is not a principal determinant of the ability of the cell wall to extend. PMID:16667031

  5. Hemodynamic analysis in an idealized artery tree: differences in wall shear stress between Newtonian and non-Newtonian blood models.

    PubMed

    Weddell, Jared C; Kwack, JaeHyuk; Imoukhuede, P I; Masud, Arif

    2015-01-01

    Development of many conditions and disorders, such as atherosclerosis and stroke, are dependent upon hemodynamic forces. To accurately predict and prevent these conditions and disorders hemodynamic forces must be properly mapped. Here we compare a shear-rate dependent fluid (SDF) constitutive model, based on the works by Yasuda et al in 1981, against a Newtonian model of blood. We verify our stabilized finite element numerical method with the benchmark lid-driven cavity flow problem. Numerical simulations show that the Newtonian model gives similar velocity profiles in the 2-dimensional cavity given different height and width dimensions, given the same Reynolds number. Conversely, the SDF model gave dissimilar velocity profiles, differing from the Newtonian velocity profiles by up to 25% in velocity magnitudes. This difference can affect estimation in platelet distribution within blood vessels or magnetic nanoparticle delivery. Wall shear stress (WSS) is an important quantity involved in vascular remodeling through integrin and adhesion molecule mechanotransduction. The SDF model gave a 7.3-fold greater WSS than the Newtonian model at the top of the 3-dimensional cavity. The SDF model gave a 37.7-fold greater WSS than the Newtonian model at artery walls located immediately after bifurcations in the idealized femoral artery tree. The pressure drop across arteries reveals arterial sections highly resistive to flow which correlates with stenosis formation. Numerical simulations give the pressure drop across the idealized femoral artery tree with the SDF model which is approximately 2.3-fold higher than with the Newtonian model. In atherosclerotic lesion models, the SDF model gives over 1 Pa higher WSS than the Newtonian model, a difference correlated with over twice as many adherent monocytes to endothelial cells from the Newtonian model compared to the SDF model. PMID:25897758

  6. Time analysis of aneurysm wall shear stress for both Newtonian and Casson flows from image-based CFD models

    NASA Astrophysics Data System (ADS)

    Castro, Marcelo A.; Ahumada Olivares, María. C.; Putman, Christopher M.; Cebral, Juan R.

    2014-03-01

    The optimal management of unruptured aneurysms is controversial, and current decision making is mainly based on aneurysm size and location. Incidentally detected unruptured aneurysms less than 5mm in diameter should be treated conservatively. However, small unruptured aneurysms also bleed. Risk factors based on the hemodynamic forces exerted over the arterial wall have been investigated using image-based computational fluid dynamic (CFD) methodologies during the last decade. Accurate estimation of wall shear stress (WSS) is required to properly study associations between flow features and aneurysm processes. Previous works showed that Newtonian and non-Newtonian (Casson) models produce similar WSS distributions and characterization, with no significant differences. Other authors showed that the WSS distribution computed from time-averaged velocity fields is significantly higher for the Newtonian model where WSS is low. In this work we reconstructed ten patient-specific CFD models from angiography images to investigate the time evolution of WSS at selected locations such as aneurysm blebs (low WSS), and the parent artery close to the aneurysm neck (high WSS). When averaging all cases it is seen that the estimation of the time-averaged WSS, the peak WSS and the minimum WSS value before the systolic peak were all higher when the Casson rheology was considered. However, none of them showed statistically significant differences. At the afferent artery Casson rheology systematically predicted higher WSS values. On the other hand, at the selected blebs either Newtonian or Casson WSS estimations are higher in some phases of the cardiac cycle. Those observations differ among individual cases.

  7. Hemodynamic Analysis in an Idealized Artery Tree: Differences in Wall Shear Stress between Newtonian and Non-Newtonian Blood Models

    PubMed Central

    Weddell, Jared C.; Kwack, JaeHyuk; Imoukhuede, P. I.; Masud, Arif

    2015-01-01

    Development of many conditions and disorders, such as atherosclerosis and stroke, are dependent upon hemodynamic forces. To accurately predict and prevent these conditions and disorders hemodynamic forces must be properly mapped. Here we compare a shear-rate dependent fluid (SDF) constitutive model, based on the works by Yasuda et al in 1981, against a Newtonian model of blood. We verify our stabilized finite element numerical method with the benchmark lid-driven cavity flow problem. Numerical simulations show that the Newtonian model gives similar velocity profiles in the 2-dimensional cavity given different height and width dimensions, given the same Reynolds number. Conversely, the SDF model gave dissimilar velocity profiles, differing from the Newtonian velocity profiles by up to 25% in velocity magnitudes. This difference can affect estimation in platelet distribution within blood vessels or magnetic nanoparticle delivery. Wall shear stress (WSS) is an important quantity involved in vascular remodeling through integrin and adhesion molecule mechanotransduction. The SDF model gave a 7.3-fold greater WSS than the Newtonian model at the top of the 3-dimensional cavity. The SDF model gave a 37.7-fold greater WSS than the Newtonian model at artery walls located immediately after bifurcations in the idealized femoral artery tree. The pressure drop across arteries reveals arterial sections highly resistive to flow which correlates with stenosis formation. Numerical simulations give the pressure drop across the idealized femoral artery tree with the SDF model which is approximately 2.3-fold higher than with the Newtonian model. In atherosclerotic lesion models, the SDF model gives over 1 Pa higher WSS than the Newtonian model, a difference correlated with over twice as many adherent monocytes to endothelial cells from the Newtonian model compared to the SDF model. PMID:25897758

  8. Fine-Tuning of the Cpx Envelope Stress Response Is Required for Cell Wall Homeostasis in Escherichia coli

    PubMed Central

    Delhaye, Antoine; Collet, Jean-François

    2016-01-01

    ABSTRACT The envelope of Gram-negative bacteria is an essential compartment that constitutes a protective and permeability barrier between the cell and its environment. The envelope also hosts the cell wall, a mesh-like structure made of peptidoglycan (PG) that determines cell shape and provides osmotic protection. Since the PG must grow and divide in a cell-cycle-synchronized manner, its synthesis and remodeling are tightly regulated. Here, we discovered that PG homeostasis is intimately linked to the levels of activation of the Cpx system, an envelope stress response system traditionally viewed as being involved in protein quality control in the envelope. We first show that Cpx is activated when PG integrity is challenged and that this activation provides protection to cells exposed to antibiotics inhibiting PG synthesis. By rerouting the outer membrane lipoprotein NlpE, a known Cpx activator, to a different envelope subcompartment, we managed to manipulate Cpx activation levels. We found that Cpx overactivation leads to aberrant cellular morphologies, to an increased sensitivity to β-lactams, and to dramatic division and growth defects, consistent with a loss of PG homeostasis. Remarkably, these phenotypes were largely abrogated by the deletion of ldtD, a Cpx-induced gene involved in noncanonical PG cross-linkage, suggesting that this transpeptidase is an important link between PG homeostasis and the Cpx system. Altogether our data show that fine-tuning of an envelope quality control system constitutes an important layer of regulation of the highly organized cell wall structure. PMID:26908573

  9. Simulation of bifurcated stent grafts to treat abdominal aortic aneurysms (AAA)

    NASA Astrophysics Data System (ADS)

    Egger, J.; Großkopf, S.; Freisleben, B.

    2007-03-01

    In this paper a method is introduced, to visualize bifurcated stent grafts in CT-Data. The aim is to improve therapy planning for minimal invasive treatment of abdominal aortic aneurysms (AAA). Due to precise measurement of the abdominal aortic aneurysm and exact simulation of the bifurcated stent graft, physicians are supported in choosing a suitable stent prior to an intervention. The presented method can be used to measure the dimensions of the abdominal aortic aneurysm as well as simulate a bifurcated stent graft. Both of these procedures are based on a preceding segmentation and skeletonization of the aortic, right and left iliac. Using these centerlines (aortic, right and left iliac) a bifurcated initial stent is constructed. Through the implementation of an ACM method the initial stent is fit iteratively to the vessel walls - due to the influence of external forces (distance- as well as balloonforce). Following the fitting process, the crucial values for choosing a bifurcated stent graft are measured, e.g. aortic diameter, right and left common iliac diameter, minimum diameter of distal neck. The selected stent is then simulated to the CT-Data - starting with the initial stent. It hereby becomes apparent if the dimensions of the bifurcated stent graft are exact, i.e. the fitting to the arteries was done properly and no ostium was covered.

  10. Cell Wall Invertase Promotes Fruit Set under Heat Stress by Suppressing ROS-Independent Cell Death1[OPEN

    PubMed Central

    2016-01-01

    Reduced cell wall invertase (CWIN) activity has been shown to be associated with poor seed and fruit set under abiotic stress. Here, we examined whether genetically increasing native CWIN activity would sustain fruit set under long-term moderate heat stress (LMHS), an important factor limiting crop production, by using transgenic tomato (Solanum lycopersicum) with its CWIN inhibitor gene silenced and focusing on ovaries and fruits at 2 d before and after pollination, respectively. We found that the increase of CWIN activity suppressed LMHS-induced programmed cell death in fruits. Surprisingly, measurement of the contents of H2O2 and malondialdehyde and the activities of a cohort of antioxidant enzymes revealed that the CWIN-mediated inhibition on programmed cell death is exerted in a reactive oxygen species-independent manner. Elevation of CWIN activity sustained Suc import into fruits and increased activities of hexokinase and fructokinase in the ovaries in response to LMHS. Compared to the wild type, the CWIN-elevated transgenic plants exhibited higher transcript levels of heat shock protein genes Hsp90 and Hsp100 in ovaries and HspII17.6 in fruits under LMHS, which corresponded to a lower transcript level of a negative auxin responsive factor IAA9 but a higher expression of the auxin biosynthesis gene ToFZY6 in fruits at 2 d after pollination. Collectively, the data indicate that CWIN enhances fruit set under LMHS through suppression of programmed cell death in a reactive oxygen species-independent manner that could involve enhanced Suc import and catabolism, HSP expression, and auxin response and biosynthesis. PMID:27462084

  11. Acetylation of cell wall is required for structural integrity of the leaf surface and exerts a global impact on plant stress responses

    PubMed Central

    Nafisi, Majse; Stranne, Maria; Fimognari, Lorenzo; Atwell, Susanna; Martens, Helle J.; Pedas, Pai R.; Hansen, Sara F.; Nawrath, Christiane; Scheller, Henrik V.; Kliebenstein, Daniel J.; Sakuragi, Yumiko

    2015-01-01

    The epidermis on leaves protects plants from pathogen invasion and provides a waterproof barrier. It consists of a layer of cells that is surrounded by thick cell walls, which are partially impregnated by highly hydrophobic cuticular components. We show that the Arabidopsis T-DNA insertion mutants of REDUCED WALL ACETYLATION 2 (rwa2), previously identified as having reduced O-acetylation of both pectins and hemicelluloses, exhibit pleiotrophic phenotype on the leaf surface. The cuticle layer appeared diffused and was significantly thicker and underneath cell wall layer was interspersed with electron-dense deposits. A large number of trichomes were collapsed and surface permeability of the leaves was enhanced in rwa2 as compared to the wild type. A massive reprogramming of the transcriptome was observed in rwa2 as compared to the wild type, including a coordinated up-regulation of genes involved in responses to abiotic stress, particularly detoxification of reactive oxygen species and defense against microbial pathogens (e.g., lipid transfer proteins, peroxidases). In accordance, peroxidase activities were found to be elevated in rwa2 as compared to the wild type. These results indicate that cell wall acetylation is essential for maintaining the structural integrity of leaf epidermis, and that reduction of cell wall acetylation leads to global stress responses in Arabidopsis. PMID:26257757

  12. Acetylation of cell wall is required for structural integrity of the leaf surface and exerts a global impact on plant stress responses

    DOE PAGES

    Nafisi, Majse; Stranne, Maria; Fimognari, Lorenzo; Atwell, Susanna; Martens, Helle J.; Pedas, Pai R.; Hansen, Sara F.; Nawrath, Christiane; Scheller, Henrik V.; Kliebenstein, Daniel J.; et al

    2015-07-22

    Here we report that the epidermis on leaves protects plants from pathogen invasion and provides a waterproof barrier. It consists of a layer of cells that is surrounded by thick cell walls, which are partially impregnated by highly hydrophobic cuticular components. We show that the Arabidopsis T-DNA insertion mutants of REDUCED WALL ACETYLATION 2 (rwa2), previously identified as having reduced O-acetylation of both pectins and hemicelluloses, exhibit pleiotrophic phenotype on the leaf surface. The cuticle layer appeared diffused and was significantly thicker and underneath cell wall layer was interspersed with electron-dense deposits. A large number of trichomes were collapsed andmore » surface permeability of the leaves was enhanced in rwa2 as compared to the wild type. A massive reprogramming of the transcriptome was observed in rwa2 as compared to the wild type, including a coordinated up-regulation of genes involved in responses to abiotic stress, particularly detoxification of reactive oxygen species and defense against microbial pathogens (e.g., lipid transfer proteins, peroxidases). In accordance, peroxidase activities were found to be elevated in rwa2 as compared to the wild type. These results indicate that cell wall acetylation is essential for maintaining the structural integrity of leaf epidermis, and that reduction of cell wall acetylation leads to global stress responses in Arabidopsis.« less

  13. Acetylation of cell wall is required for structural integrity of the leaf surface and exerts a global impact on plant stress responses

    SciTech Connect

    Nafisi, Majse; Stranne, Maria; Fimognari, Lorenzo; Atwell, Susanna; Martens, Helle J.; Pedas, Pai R.; Hansen, Sara F.; Nawrath, Christiane; Scheller, Henrik V.; Kliebenstein, Daniel J.; Sakuragi, Yumiko

    2015-07-22

    Here we report that the epidermis on leaves protects plants from pathogen invasion and provides a waterproof barrier. It consists of a layer of cells that is surrounded by thick cell walls, which are partially impregnated by highly hydrophobic cuticular components. We show that the Arabidopsis T-DNA insertion mutants of REDUCED WALL ACETYLATION 2 (rwa2), previously identified as having reduced O-acetylation of both pectins and hemicelluloses, exhibit pleiotrophic phenotype on the leaf surface. The cuticle layer appeared diffused and was significantly thicker and underneath cell wall layer was interspersed with electron-dense deposits. A large number of trichomes were collapsed and surface permeability of the leaves was enhanced in rwa2 as compared to the wild type. A massive reprogramming of the transcriptome was observed in rwa2 as compared to the wild type, including a coordinated up-regulation of genes involved in responses to abiotic stress, particularly detoxification of reactive oxygen species and defense against microbial pathogens (e.g., lipid transfer proteins, peroxidases). In accordance, peroxidase activities were found to be elevated in rwa2 as compared to the wild type. These results indicate that cell wall acetylation is essential for maintaining the structural integrity of leaf epidermis, and that reduction of cell wall acetylation leads to global stress responses in Arabidopsis.

  14. Acetylation of cell wall is required for structural integrity of the leaf surface and exerts a global impact on plant stress responses.

    PubMed

    Nafisi, Majse; Stranne, Maria; Fimognari, Lorenzo; Atwell, Susanna; Martens, Helle J; Pedas, Pai R; Hansen, Sara F; Nawrath, Christiane; Scheller, Henrik V; Kliebenstein, Daniel J; Sakuragi, Yumiko

    2015-01-01

    The epidermis on leaves protects plants from pathogen invasion and provides a waterproof barrier. It consists of a layer of cells that is surrounded by thick cell walls, which are partially impregnated by highly hydrophobic cuticular components. We show that the Arabidopsis T-DNA insertion mutants of REDUCED WALL ACETYLATION 2 (rwa2), previously identified as having reduced O-acetylation of both pectins and hemicelluloses, exhibit pleiotrophic phenotype on the leaf surface. The cuticle layer appeared diffused and was significantly thicker and underneath cell wall layer was interspersed with electron-dense deposits. A large number of trichomes were collapsed and surface permeability of the leaves was enhanced in rwa2 as compared to the wild type. A massive reprogramming of the transcriptome was observed in rwa2 as compared to the wild type, including a coordinated up-regulation of genes involved in responses to abiotic stress, particularly detoxification of reactive oxygen species and defense against microbial pathogens (e.g., lipid transfer proteins, peroxidases). In accordance, peroxidase activities were found to be elevated in rwa2 as compared to the wild type. These results indicate that cell wall acetylation is essential for maintaining the structural integrity of leaf epidermis, and that reduction of cell wall acetylation leads to global stress responses in Arabidopsis. PMID:26257757

  15. A study of wall shear stress in 12 aneurysms with respect to different viscosity models and flow conditions.

    PubMed

    Evju, Øyvind; Valen-Sendstad, Kristian; Mardal, Kent-André

    2013-11-15

    Recent computational fluid dynamics (CFD) studies relate abnormal blood flow to rupture of cerebral aneurysms. However, it is still debated how to model blood flow with sufficient accuracy. Common assumptions made include Newtonian behaviour of blood, traction free outlet boundary conditions and inlet boundary conditions based on available literature. These assumptions are often required since the available patient specific data is usually restricted to the geometry of the aneurysm and the surrounding vasculature. However, the consequences of these assumptions have so far been inadequately addressed. This study investigates the effects of 4 different viscosity models, 2 different inflow conditions and 2 different outflow conditions in 12 middle cerebral artery aneurysms. The differences are quantified in terms of 3 different wall shear stress (WSS) metrics, involving maximal WSS, average WSS, and proportion of aneurysm sac area with low WSS. The results were compared with common geometrical metrics such as volume, aspect ratio, size ratio and parent vessel diameter and classifications in terms of sex and aneurysm type. The results demonstrate strong correlations between the different viscosity models and boundary conditions. The correlation between the different WSS metrics range from weak to medium. No strong correlations were found between the different WSS metrics and the geometrical metrics or classifications. PMID:24099744

  16. Ecotoxicity of single-wall carbon nanotubes to freshwater snail Lymnaea luteola L.: Impacts on oxidative stress and genotoxicity.

    PubMed

    Ali, Daoud; Ahmed, Mukhtar; Alarifi, Saud; Ali, Huma

    2015-01-01

    Mammalian studies have raised concerns about the toxicity of carbon nanotubes, but there is very limited data on ecogenotoxicity to aquatic organisms. The aim of this study was to determine eco-geno toxic effects of single walled carbon nanotubes (SWCNTs) in fresh water snail, Lymnea luteola (L. luteola). A static test system was used to expose L. luteola to a freshwater control, 0.05, 0.15, 0.30, 0.46 mg/L SWCNTs for up to 4 days. SWCNTs changed a significant reduction in glutathione, glutathione-S-transferase, and glutathione peroxidase with in hepatopancreas of L. luteola. Lipid peroxidation (LPO) and catalase showed dose- and time-dependent and statistically significant increase in hepatopancreas during SWCNTs exposure compared with control. However, a significant (p < 0.01) induction in DNA damage was observed by the comet assay in hepatopancreas cells treated with SWCNTs. These results demonstrate that SWCNTs are ecogenotoxic to freshwater snail L. luteola. The oxidative stress and comet assay can successfully be used as sensitive tools of aquatic pollution biomonitoring.

  17. Flow-induced vibration and instability of embedded double-walled carbon nanotubes based on a modified couple stress theory

    NASA Astrophysics Data System (ADS)

    Ke, Liao-Liang; Wang, Yue-Sheng

    2011-03-01

    Vibration and instability of fluid-conveying double-walled carbon nanotubes (DWNTs) are investigated in this paper based on the modified couple stress theory and the Timoshenko beam theory. The microstructure-dependent Timoshenko beam model, which contains a material length scale parameter and can take the size effect into account, is employed. The Poisson's ratio effect is also included in this model. The surrounding elastic medium is described as the Winkler model characterized by the spring. The higher-order governing equations and boundary conditions are derived by using Hamilton's principle. The differential quadrature (DQ) method is employed to discretize the governing equations, which are then solved to obtain the resonant frequencies of fluid-conveying DWNTs with different boundary conditions. A detailed parametric study is conducted to study the influences of length scale parameter, Poisson's ratio, spring constant, aspect ratio of the DWNTs, velocity of the fluid and end supports on the vibration and flow-induced instability of DWNTs. Results show that the imaginary component of the frequency and the critical flow velocity of the fluid-conveying DWNTs increase with increase in the length scale parameter.

  18. Effects of aortic root motion on wall stress in the Marfan aorta before and after personalised aortic root support (PEARS) surgery.

    PubMed

    Singh, S D; Xu, X Y; Pepper, J R; Izgi, C; Treasure, T; Mohiaddin, R H

    2016-07-01

    Aortic root motion was previously identified as a risk factor for aortic dissection due to increased longitudinal stresses in the ascending aorta. The aim of this study was to investigate the effects of aortic root motion on wall stress and strain in the ascending aorta and evaluate changes before and after implantation of personalised external aortic root support (PEARS). Finite element (FE) models of the aortic root and thoracic aorta were developed using patient-specific geometries reconstructed from pre- and post-PEARS cardiovascular magnetic resonance (CMR) images in three Marfan patients. The wall and PEARS materials were assumed to be isotropic, incompressible and linearly elastic. A static load on the inner wall corresponding to the patients' pulse pressure was applied. Cardiovascular MR cine images were used to quantify aortic root motion, which was imposed at the aortic root boundary of the FE model, with zero-displacement constraints at the distal ends of the aortic branches and descending aorta. Measurements of the systolic downward motion of the aortic root revealed a significant reduction in the axial displacement in all three patients post-PEARS compared with its pre-PEARS counterparts. Higher longitudinal stresses were observed in the ascending aorta when compared with models without the root motion. Implantation of PEARS reduced the longitudinal stresses in the ascending aorta by up to 52%. In contrast, the circumferential stresses at the interface between the supported and unsupported aorta were increase by up to 82%. However, all peak stresses were less than half the known yield stress for the dilated thoracic aorta. PMID:27255604

  19. Fall of blood ionized calcium on watching a provocative TV program and its prevention by active absorbable algal calcium (AAA Ca).

    PubMed

    Fujita, T; Ohgitani, S; Nomura, M

    1999-01-01

    In December 1997, more than 680 children developed convulsive seizures while watching a notorious audiovisually provocative TV program, "Pocket Monster." Emotional stimulation via hyperventilation may cause respiratory alkalosis, fall of blood ionized calcium (Ca), and sensitization of the nervous system to excessive emotional stress. A study was therefore undertaken to follow the changes of blood ionized Ca in eight healthy volunteers after watching the "Pocket Monster" and also a quiet program, "Classical Music," as a control for 20min from 4 P.M. Although neither marked hyperventilation nor convulsions developed in any of these adult volunteers, blood ionized Ca showed a significantly more pronounced fall during and after watching "Pocket Monster," and their plasma intact parathyroid hormone (iPTH) was significantly higher 120min after the beginning of "Pocket Monster" than the "Classical Music" program. Plasma total Ca, pH, and albumin were free of detectable changes. Ingestion of 600mg Ca as active absorbable algal Ca (AAA Ca) with high bioavailability completely prevented the fall of ionized Ca and suppressed iPTH. Plama osteocalcin was also significantly suppressed after ingestion of AAA Ca. It may be worthwhile to ingest AAA Ca before anticipated emotional stress such as watching a provocative TV program to prevent possible neuromuscular instability. PMID:10340641

  20. The quasi-static failure properties of the abdominal aortic aneurysm wall estimated by a mixed experimental-numerical approach.

    PubMed

    Forsell, Caroline; Swedenborg, Jesper; Roy, Joy; Gasser, T Christian

    2013-07-01

    Assessing the risk for abdominal aortic aneurysm (AAA) rupture is critical in the management of aneurysm patients and an individual assessment is possible with the biomechanical rupture risk assessment. Such an assessment could potentially be improved by a constitutive AAA wall model that accounts for irreversible damage-related deformations. Because of that the present study estimated the elastic and inelastic properties of the AAA wall through a mixed experimental-numerical approach. Specifically, finite element (FE) models of bone-shaped tensile specimens were used to merge data from failure testing of the AAA wall with their measured collagen orientation distribution. A histo-mechanical constitutive model for collagen fibers was employed, where plastic fibril sliding determined not only remaining deformations but also weakening of the fiber. The developed FE models were able to replicate the experimentally recorded load-displacement property of all 16 AAA wall specimens that were investigated in the study. Tensile testing in longitudinal direction of the AAA defined a Cauchy strength of 569(SD 411) kPa that was reached at a stretch of 1.436(SD 0.118). The stiffness and strength of specimens decreased with the wall thickness and were elevated (p = 0.018; p = 0.030) in patients with chronic obstructive pulmonary disease (COPD). Smoking affected the tissue parameters that were related to the irreversible deformation response, and no correlation with gender and age was found. The observed effects on the biomechanical properties of the AAA wall could have long-term consequences for the management of aneurysm patients, i.e., specifically they might influence future AAA rupture risk assessments. However, in order to design appropriate clinical validation studies our findings should firstly be verified in a larger patient cohort. PMID:23263935

  1. Localization and regulation of c-fos and c-jun protooncogene induction by systolic wall stress in normal and hypertrophied rat hearts.

    PubMed Central

    Schunkert, H; Jahn, L; Izumo, S; Apstein, C S; Lorell, B H

    1991-01-01

    The effect of changes in left ventricular (LV) systolic force generation on cardiac c-fos and c-jun protooncogene expression was studied by using isolated beating hearts from male Wistar rats. An isovolumic buffer-perfused heart preparation was utilized in which coronary flow and heart rate were held constant and increments in LV balloon volume were used to generate defined levels of LV systolic wall stress. Using Northern and slot-blot analyses, we found that LV tissue from control hearts that generated high levels of LV systolic wall stress expressed 3- to 4.4-fold higher c-fos and c-jun mRNA levels in comparison with tissue from the respective flaccid right ventricles, and in comparison with LV tissue from hearts that generated minimal LV systolic wall stress. To distinguish the role of passive LV diastolic wall stretch from active LV force generation, we found that distension of the LV balloon per se did not have a significant effect on protooncogene induction in hearts perfused with 2,3-butanedione monoxime, which prevents systolic cross-bridge cycling and force generation. In additional hearts studied at a constant LV balloon volume to generate an LV end-diastolic pressure of 10 mm Hg, c-fos mRNA levels were proportional to the magnitude of peak LV systolic wall stress (r = 0.823, P less than 0.05). In these protocols, Fos protein was localized by immunohistochemistry in myocyte nuclei with minimal staining in fibroblasts and vascular smooth muscle. When c-fos and c-jun mRNA expression was compared in hearts with chronic LV hypertrophy due to ascending aortic banding and age-matched control hearts that generated similar incremental levels of LV systolic wall stress, significantly lower levels of c-fos and c-jun mRNA were measured in the hypertrophied hearts. However, there was no difference in protooncogene mRNA expression in response to stimulation by the Ca2+ ionophore A23187. These data suggest that, in this isolated isovolumic beating heart preparation

  2. The MAP kinase MpkA controls cell wall integrity, oxidative stress response, gliotoxin production and iron adaptation in Aspergillus fumigatus

    PubMed Central

    Jain, Radhika; Valiante, Vito; Remme, Nicole; Docimo, Teresa; Heinekamp, Thorsten; Hertweck, Christian; Gershenzon, Jonathan; Haas, Hubertus; Brakhage, Axel A

    2011-01-01

    The saprophytic fungus Aspergillus fumigatus is the most important air-borne fungal pathogen. The cell wall of A. fumigatus has been studied intensively as a potential target for development of effective antifungal agents. A major role in maintaining cell wall integrity is played by the mitogen-activated protein kinase (MAPK) MpkA. To gain a comprehensive insight into this central signal transduction pathway, we performed a transcriptome analysis of the ΔmpkA mutant under standard and cell wall stress conditions. Besides genes involved in cell wall remodelling, protection against ROS and secondary metabolism such as gliotoxin, pyomelanin and pseurotin A, also genes involved in siderophore biosynthesis were regulated by MpkA. Consistently, northern and western blot analyses indicated that iron starvation triggers phosphorylation and thus activation of MpkA. Furthermore, localization studies indicated that MpkA accumulates in the nucleus under iron depletion. Hence, we report the first connection between a MAPK pathway and siderophore biosynthesis. The measurement of amino acid pools and of the pools of polyamines indicated that arginine was continuously converted into ornithine to fuel the siderophore pool in the ΔmpkA mutant strain. Based on our data, we propose that MpkA fine-tunes the balance between stress response and energy consuming cellular processes. PMID:21883519

  3. Computational Fluid Dynamic Simulations of Maternal Circulation: Wall Shear Stress in the Human Placenta and Its Biological Implications

    PubMed Central

    Lecarpentier, E.; Bhatt, M.; Bertin, G. I.; Deloison, B.; Salomon, L. J.; Deloron, P.; Fournier, T.; Barakat, A. I.; Tsatsaris, V.

    2016-01-01

    Introduction In the human placenta the maternal blood circulates in the intervillous space (IVS). The syncytiotrophoblast (STB) is in direct contact with maternal blood. The wall shear stress (WSS) exerted by the maternal blood flow on the STB has not been evaluated. Our objective was to determine the physiological WSS exerted on the surface of the STB during the third trimester of pregnancy. Material and Methods To gain insight into the shear stress levels that the STB is expected to experience in vivo, we have formulated three different computational models of varying levels of complexity that reflect different physical representations of the IVS. Computations of the flow fields in all models were performed using the CFD module of the finite element code COMSOL Multiphysics 4.4. The mean velocity of maternal blood in the IVS during the third trimester was measured in vivo with dynamic MRI (0.94±0.14 mm.s-1). To investigate if the in silico results are consistent with physiological observations, we studied the cytoadhesion of human parasitized (Plasmodium falciparum) erythrocytes to primary human STB cultures, in flow conditions with different WSS values. Results The WSS applied to the STB is highly heterogeneous in the IVS. The estimated average values are relatively low (0.5±0.2 to 2.3±1.1 dyn.cm-2). The increase of WSS from 0.15 to 5 dyn.cm-2 was associated with a significant decrease of infected erythrocyte cytoadhesion. No cytoadhesion of infected erythrocytes was observed above 5 dyn.cm-2 applied for one hour. Conclusion Our study provides for the first time a WSS estimation in the maternal placental circulation. In spite of high maternal blood flow rates, the average WSS applied at the surface of the chorionic villi is low (<5 dyn.cm-2). These results provide the basis for future physiologically-relevant in vitro studies of the biological effects of WSS on the STB. PMID:26815115

  4. Left Ventricular Wall Stress-Mass-Heart Rate Product and Cardiovascular Events in Treated Hypertensive Patients: LIFE Study.

    PubMed

    Devereux, Richard B; Bang, Casper N; Roman, Mary J; Palmieri, Vittorio; Boman, Kurt; Gerdts, Eva; Nieminen, Markku S; Papademetriou, Vasilios; Wachtell, Kristian; Hille, Darcy A; Dahlöf, Björn

    2015-11-01

    In the Losartan Intervention for End Point Reduction in Hypertension (LIFE) study, 4.8 years' losartan- versus atenolol-based antihypertensive treatment reduced left ventricular hypertrophy and cardiovascular end points, including cardiovascular death and stroke. However, there was no difference in myocardial infarction (MI), possibly related to greater reduction in myocardial oxygen demand by atenolol-based treatment. Myocardial oxygen demand was assessed indirectly by the left ventricular mass×wall stress×heart rate (triple product) in 905 LIFE participants. The triple product was included as time-varying covariate in Cox models assessing predictors of the LIFE primary composite end point (cardiovascular death, MI, or stroke), its individual components, and all-cause mortality. At baseline, the triple product in both treatment groups was, compared with normal adults, elevated in 70% of patients. During randomized treatment, the triple product was reduced more by atenolol, with prevalences of elevated triple product of 39% versus 51% on losartan (both P≤0.001). In Cox regression analyses adjusting for age, smoking, diabetes mellitus, and prior stroke, MI, and heart failure, 1 SD lower triple product was associated with 23% (95% confidence interval 13%-32%) fewer composite end points, 31% (18%-41%) less cardiovascular mortality, 30% (15%-41%) lower MI, and 22% (11%-33%) lower all-cause mortality (all P≤0.001), without association with stroke (P=0.34). Although losartan-based therapy reduced ventricular mass more, greater heart rate reduction with atenolol resulted in larger reduction of the triple product. Lower triple product during antihypertensive treatment was strongly, independently associated with lower rates of the LIFE primary composite end point, cardiovascular death, and MI, but not stroke.

  5. Long-Term Serial Follow-Up of Pulmonary Artery Size and Wall Shear Stress in Fontan Patients.

    PubMed

    Bossers, Sjoerd S M; Cibis, Merih; Kapusta, Livia; Potters, Wouter V; Snoeren, Miranda M; Wentzel, Jolanda J; Moelker, Adriaan; Helbing, Willem A

    2016-04-01

    Pulmonary arterial (PA) flow is abnormal after the Fontan operation and is marked by a lack of pulsatility. We assessed the effects of this abnormal flow on the size and function of the PA's in Fontan patients in long-term serial follow-up. Twenty-three Fontan patients with serial follow-up were included. Median age was 11.1 (9.5-16.0) years at baseline and 15.5 (12.5-22.7) years at follow-up. Median follow-up duration was 4.4 (4.0-5.8) years. Flow and size of the left pulmonary artery were determined using phase-contrast MRI. From this wall shear stress (WSS), distensibility and pulsatility were determined. A group of healthy peers was included for reference. Flow and pulsatility were significantly lower in patients than in controls (p < 0.001). Mean area was comparable in patients and controls, but distensibility was significantly higher in controls (p < 0.001). Mean and peak WSS were significantly lower in Fontan patients (p < 0.001). Between baseline and follow-up, there was a significant increase in normalized flow (15.1 (14.3-19.1) to 18.7 (14.0-22.6) ml/s/m(2), p = 0.023). Area, pulsatility, distensibility and WSS did not change, but there was a trend toward a lower mean WSS (p = 0.068). Multivariable regression analysis showed that flow, area and age were important predictors for WSS. WSS in Fontan patients is decreased compared to healthy controls and tends to decrease further with age. Pulsatility and distensibility are significantly lower compared to healthy controls. Pulmonary artery size, however, is not significantly different from healthy controls and long-term growth after Fontan operation is proportionate to body size.

  6. Link between deviations from Murray's Law and occurrence of low wall shear stress regions in the left coronary artery.

    PubMed

    Doutel, E; Pinto, S I S; Campos, J B L M; Miranda, J M

    2016-08-01

    Murray developed two laws for the geometry of bifurcations in the circulatory system. Based on the principle of energy minimization, Murray found restrictions for the relation between the diameters and also between the angles of the branches. It is known that bifurcations are prone to the development of atherosclerosis, in regions associated to low wall shear stresses (WSS) and high oscillatory shear index (OSI). These indicators (size of low WSS regions, size of high OSI regions and size of high helicity regions) were evaluated in this work. All of them were normalized by the size of the outflow branches. The relation between Murray's laws and the size of low WSS regions was analysed in detail. It was found that the main factor leading to large regions of low WSS is the so called expansion ratio, a relation between the cross section areas of the outflow branches and the cross section area of the main branch. Large regions of low WSS appear for high expansion ratios. Furthermore, the size of low WSS regions is independent of the ratio between the diameters of the outflow branches. Since the expansion ratio in bifurcations following Murray's law is kept in a small range (1 and 1.25), all of them have regions of low WSS with similar size. However, the expansion ratio is not small enough to completely prevent regions with low WSS values and, therefore, Murray's law does not lead to atherosclerosis minimization. A study on the effect of the angulation of the bifurcation suggests that the Murray's law for the angles does not minimize the size of low WSS regions.

  7. CODAS syndrome is associated with mutations of LONP1, encoding mitochondrial AAA+ Lon protease.

    PubMed

    Strauss, Kevin A; Jinks, Robert N; Puffenberger, Erik G; Venkatesh, Sundararajan; Singh, Kamalendra; Cheng, Iteen; Mikita, Natalie; Thilagavathi, Jayapalraja; Lee, Jae; Sarafianos, Stefan; Benkert, Abigail; Koehler, Alanna; Zhu, Anni; Trovillion, Victoria; McGlincy, Madeleine; Morlet, Thierry; Deardorff, Matthew; Innes, A Micheil; Prasad, Chitra; Chudley, Albert E; Lee, Irene Nga Wing; Suzuki, Carolyn K

    2015-01-01

    CODAS syndrome is a multi-system developmental disorder characterized by cerebral, ocular, dental, auricular, and skeletal anomalies. Using whole-exome and Sanger sequencing, we identified four LONP1 mutations inherited as homozygous or compound-heterozygous combinations among ten individuals with CODAS syndrome. The individuals come from three different ancestral backgrounds (Amish-Swiss from United States, n = 8; Mennonite-German from Canada, n = 1; mixed European from Canada, n = 1). LONP1 encodes Lon protease, a homohexameric enzyme that mediates protein quality control, respiratory-complex assembly, gene expression, and stress responses in mitochondria. All four pathogenic amino acid substitutions cluster within the AAA(+) domain at residues near the ATP-binding pocket. In biochemical assays, pathogenic Lon proteins show substrate-specific defects in ATP-dependent proteolysis. When expressed recombinantly in cells, all altered Lon proteins localize to mitochondria. The Old Order Amish Lon variant (LONP1 c.2161C>G[p.Arg721Gly]) homo-oligomerizes poorly in vitro. Lymphoblastoid cell lines generated from affected children have (1) swollen mitochondria with electron-dense inclusions and abnormal inner-membrane morphology; (2) aggregated MT-CO2, the mtDNA-encoded subunit II of cytochrome c oxidase; and (3) reduced spare respiratory capacity, leading to impaired mitochondrial proteostasis and function. CODAS syndrome is a distinct, autosomal-recessive, developmental disorder associated with dysfunction of the mitochondrial Lon protease.

  8. CODAS Syndrome Is Associated with Mutations of LONP1, Encoding Mitochondrial AAA+ Lon Protease

    PubMed Central

    Strauss, Kevin A.; Jinks, Robert N.; Puffenberger, Erik G.; Venkatesh, Sundararajan; Singh, Kamalendra; Cheng, Iteen; Mikita, Natalie; Thilagavathi, Jayapalraja; Lee, Jae; Sarafianos, Stefan; Benkert, Abigail; Koehler, Alanna; Zhu, Anni; Trovillion, Victoria; McGlincy, Madeleine; Morlet, Thierry; Deardorff, Matthew; Innes, A. Micheil; Prasad, Chitra; Chudley, Albert E.; Lee, Irene Nga Wing; Suzuki, Carolyn K.

    2015-01-01

    CODAS syndrome is a multi-system developmental disorder characterized by cerebral, ocular, dental, auricular, and skeletal anomalies. Using whole-exome and Sanger sequencing, we identified four LONP1 mutations inherited as homozygous or compound-heterozygous combinations among ten individuals with CODAS syndrome. The individuals come from three different ancestral backgrounds (Amish-Swiss from United States, n = 8; Mennonite-German from Canada, n = 1; mixed European from Canada, n = 1). LONP1 encodes Lon protease, a homohexameric enzyme that mediates protein quality control, respiratory-complex assembly, gene expression, and stress responses in mitochondria. All four pathogenic amino acid substitutions cluster within the AAA+ domain at residues near the ATP-binding pocket. In biochemical assays, pathogenic Lon proteins show substrate-specific defects in ATP-dependent proteolysis. When expressed recombinantly in cells, all altered Lon proteins localize to mitochondria. The Old Order Amish Lon variant (LONP1 c.2161C>G[p.Arg721Gly]) homo-oligomerizes poorly in vitro. Lymphoblastoid cell lines generated from affected children have (1) swollen mitochondria with electron-dense inclusions and abnormal inner-membrane morphology; (2) aggregated MT-CO2, the mtDNA-encoded subunit II of cytochrome c oxidase; and (3) reduced spare respiratory capacity, leading to impaired mitochondrial proteostasis and function. CODAS syndrome is a distinct, autosomal-recessive, developmental disorder associated with dysfunction of the mitochondrial Lon protease. PMID:25574826

  9. AAA: Road Debris a Mounting Danger on U.S. Highways

    MedlinePlus

    ... Highways Crashes involving objects that have fallen from vehicles up 40 percent since 2001 To use the ... the AAA Foundation for Traffic Safety. Crashes involving vehicle-related debris are up 40 percent since the ...

  10. Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant infer that fiber cell wall development is associated with stress responses

    PubMed Central

    2013-01-01

    Background Cotton fiber maturity is an important factor for determining the commercial value of cotton. How fiber cell wall development affects fiber maturity is not well understood. A comparison of fiber cross-sections showed that an immature fiber (im) mutant had lower fiber maturity than its near isogenic wild type, Texas marker-1 (TM-1). The availability of the im mutant and TM-1 provides a unique way to determine molecular mechanisms regulating cotton fiber maturity. Results Transcriptome analysis showed that the differentially expressed genes (DEGs) in the im mutant fibers grown under normal stress conditions were similar to those in wild type cotton fibers grown under severe stress conditions. The majority of these DEGs in the im mutant were related to stress responses and cellular respiration. Stress is known to reduce the activity of a classical respiration pathway responsible for energy production and reactive oxygen species (ROS) accumulation. Both energy productions and ROS levels in the im mutant fibers are expected to be reduced if the im mutant is associated with stress responses. In accord with the prediction, the transcriptome profiles of the im mutant showed the same alteration of transcriptional regulation that happened in energy deprived plants in which expressions of genes associated with cell growth processes were reduced whereas expressions of genes associated with recycling and transporting processes were elevated. We confirmed that ROS production in developing fibers from the im mutant was lower than that from the wild type. The lower production of ROS in the im mutant fibers might result from the elevated levels of alternative respiration induced by stress. Conclusion The low degree of fiber cell wall thickness of the im mutant fibers is associated with deregulation of the genes involved in stress responses and cellular respiration. The reduction of ROS levels and up-regulation of the genes involved in alternative respirations suggest that

  11. An AAA-DDD triply hydrogen-bonded complex easily accessible for supramolecular polymers.

    PubMed

    Han, Yi-Fei; Chen, Wen-Qiang; Wang, Hong-Bo; Yuan, Ying-Xue; Wu, Na-Na; Song, Xiang-Zhi; Yang, Lan

    2014-12-15

    For a complementary hydrogen-bonded complex, when every hydrogen-bond acceptor is on one side and every hydrogen-bond donor is on the other, all secondary interactions are attractive and the complex is highly stable. AAA-DDD (A=acceptor, D=donor) is considered to be the most stable among triply hydrogen-bonded sequences. The easily synthesized and further derivatized AAA-DDD system is very desirable for hydrogen-bonded functional materials. In this case, AAA and DDD, starting from 4-methoxybenzaldehyde, were synthesized with the Hantzsch pyridine synthesis and Friedländer annulation reaction. The association constant determined by fluorescence titration in chloroform at room temperature is 2.09×10(7)  M(-1) . The AAA and DDD components are not coplanar, but form a V shape in the solid state. Supramolecular polymers based on AAA-DDD triply hydrogen bonded have also been developed. This work may make AAA-DDD triply hydrogen-bonded sequences easily accessible for stimuli-responsive materials.

  12. Elements in nucleotide sensing and hydrolysis of the AAA+ disaggregation machine ClpB: a structure-based mechanistic dissection of a molecular motor

    SciTech Connect

    Zeymer, Cathleen Barends, Thomas R. M.; Werbeck, Nicolas D.; Schlichting, Ilme; Reinstein, Jochen

    2014-02-01

    High-resolution crystal structures together with mutational analysis and transient kinetics experiments were utilized to understand nucleotide sensing and the regulation of the ATPase cycle in an AAA+ molecular motor. ATPases of the AAA+ superfamily are large oligomeric molecular machines that remodel their substrates by converting the energy from ATP hydrolysis into mechanical force. This study focuses on the molecular chaperone ClpB, the bacterial homologue of Hsp104, which reactivates aggregated proteins under cellular stress conditions. Based on high-resolution crystal structures in different nucleotide states, mutational analysis and nucleotide-binding kinetics experiments, the ATPase cycle of the C-terminal nucleotide-binding domain (NBD2), one of the motor subunits of this AAA+ disaggregation machine, is dissected mechanistically. The results provide insights into nucleotide sensing, explaining how the conserved sensor 2 motif contributes to the discrimination between ADP and ATP binding. Furthermore, the role of a conserved active-site arginine (Arg621), which controls binding of the essential Mg{sup 2+} ion, is described. Finally, a hypothesis is presented as to how the ATPase activity is regulated by a conformational switch that involves the essential Walker A lysine. In the proposed model, an unusual side-chain conformation of this highly conserved residue stabilizes a catalytically inactive state, thereby avoiding unnecessary ATP hydrolysis.

  13. Impact of wall shear stress and ligand avidity on binding of anti-CD146-coated nanoparticles to murine tumor endothelium under flow.

    PubMed

    Thomann, Stefan; Baek, Sunhwa; Ryschich, Eduard

    2015-11-24

    The endothelial phenotype of tumor blood vessels differs from the liver and forms an important base for endothelium-specific targeting by antibody-coated nanoparticles. Although differences of shear stress and ligand avidity can modulate the nanoparticle binding to endothelium, these mechanisms are still poorly studied. This study analyzed the binding of antibody-coated nanoparticles to tumor and liver endothelium under controlled flow conditions and verified this binding in tumor models in vivo. Binding of anti-CD146-coated nanoparticles, but not of antibody was significantly reduced under increased wall shear stress and the degree of nanoparticle binding correlated with the avidity of the coating. The intravascular wall shear stress favors nanoparticle binding at the site of higher avidity of endothelial epitope which additionally promotes the selectivity to tumor endothelium. After intravenous application in vivo, pegylated self-coated nanoparticles showed specific binding to tumor endothelium, whereas the nanoparticle binding to the liver endothelium was very low. This study provides a rationale that selective binding of mAb-coated nanoparticles to tumor endothelium is achieved by two factors: higher expression of endothelial epitope and higher nanoparticle shearing from liver endothelium. The combination of endothelial marker targeting and the use of shear stress-controlled nanoparticle capture can be used for selective intratumoral drug delivery.

  14. Development of a near-wall Reynolds-stress closure based on the SSG model for the pressure strain

    NASA Technical Reports Server (NTRS)

    So, R. M. C.; Aksoy, H.; Sommer, T. P.; Yuan, S. P.

    1994-01-01

    In this research, a near-wall second-order closure based on the Speziable et al.(1991) or SSG model for the pressure-strain term is proposed. Unlike the LRR model, the SSG model is quasi-nonlinear and yields better results when applied to calculate rotating homogeneous turbulent flows. An asymptotic analysis near the wall is applied to both the exact and modeled, equations so that appropriate near-wall corrections to the SSG model and the modeled dissipation-rate equation can be derived to satisfy the physical wall boundary conditions as well as the asymptotic near-wall behavior of the exact equations. Two additional model constants are introduced and they are determined by calibrating against one set of near-wall channel flow data. Once determined, their values are found to remain constant irrespective of the type of flow examined. The resultant model is used to calculate simple turbulent flows, near separating turbulent flows, complex turbulent flows and compressible turbulent flows with a freestream Mach number as high as 10. In all the flow cases investigated, the calculated results are in good agreement with data. This new near-wall model is less ad hoc, physically and mathematically more sound and eliminates the empiricism introduced by Zhang. Therefore, it is quite general, as demonstrated by the good agreement achieved with measurements covering a wide range of Reynolds numbers and Mach numbers.

  15. A proteomic study of Corynebacterium glutamicum AAA+ protease FtsH

    PubMed Central

    Lüdke, Alja; Krämer, Reinhard; Burkovski, Andreas; Schluesener, Daniela; Poetsch, Ansgar

    2007-01-01

    Background The influence of the membrane-bound AAA+ protease FtsH on membrane and cytoplasmic proteins of Corynebacterium glutamicum was investigated in this study. For the analysis of the membrane fraction, anion exchange chromatography was combined with SDS-PAGE, while the cytoplasmic protein fraction was studied by conventional two-dimensional gel electrophoresis. Results In contrast to the situation in other bacteria, deletion of C. glutamicum ftsH has no significant effect on growth in standard minimal medium or response to heat or osmotic stress. On the proteome level, deletion of the ftsH gene resulted in a strong increase of ten cytoplasmic and membrane proteins, namely biotin carboxylase/biotin carboxyl carrier protein (accBC), glyceraldehyde-3-phosphate dehydrogenase (gap), homocysteine methyltransferase (metE), malate synthase (aceB), isocitrate lyase (aceA), a conserved hypothetical protein (NCgl1985), succinate dehydrogenase A (sdhA), succinate dehydrogenase B (sdhB), succinate dehydrogenase CD (sdhCD), and glutamate binding protein (gluB), while 38 cytoplasmic and membrane-associated proteins showed a decreased abundance. The decreasing amount of succinate dehydrogenase A (sdhA) in the cytoplasmic fraction of the ftsH mutant compared to the wild type and its increasing abundance in the membrane fraction indicates that FtsH might be involved in the cleavage of a membrane anchor of this membrane-associated protein and by this changes its localization. Conclusion The data obtained hint to an involvement of C. glutamicum FtsH protease mainly in regulation of energy and carbon metabolism, while the protease is not involved in stress response, as found in other bacteria. PMID:17254330

  16. Targeting the AAA ATPase p97 as an approach to treat cancer through disruption of protein homeostasis

    PubMed Central

    Anderson, Daniel J.; Le Moigne, Ronan; Djakovic, Stevan; Kumar, Brajesh; Rice, Julie; Wong, Steve; Wang, Jinhai; Yao, Bing; Valle, Eduardo; von Soly, Szerenke Kiss; Madriaga, Antonett; Soriano, Ferdie; Menon, Mary-Kamala; Wu, Zhi Yong; Kampmann, Martin; Chen, Yuwen; Weissman, Jonathan S.; Aftab, Blake T.; Yakes, F. Michael; Shawver, Laura; Zhou, Han-Jie; Wustrow, David; Rolfe, Mark

    2016-01-01

    Summary p97 is a AAA-ATPase with multiple cellular functions, one of which is critical regulation of protein homeostasis pathways. We describe the characterization of CB-5083, a potent, selective and orally bioavailable inhibitor of p97. Treatment of tumor cells with CB-5083 leads to accumulation of poly-ubiquitinated proteins, retention of endoplasmic reticulum associated degradation (ERAD) substrates and generation of irresolvable proteotoxic stress leading to activation of the apoptotic arm of the unfolded protein response (UPR). In xenograft models, CB-5083 causes modulation of key p97-related pathways, induces apoptosis and has antitumor activity in a broad range of both hematological and solid tumor models. Molecular determinants of CB-5083 activity include expression of genes in the ERAD pathway providing a potential strategy for patient selection. PMID:26555175

  17. Verification of IMRT dose calculations using AAA and PBC algorithms in dose buildup regions.

    PubMed

    Oinam, Arun S; Singh, Lakhwant

    2010-08-26

    The purpose of this comparative study was to test the accuracy of anisotropic analytical algorithm (AAA) and pencil beam convolution (PBC) algorithms of Eclipse treatment planning system (TPS) for dose calculations in the low- and high-dose buildup regions. AAA and PBC algorithms were used to create two intensity-modulated radiotherapy (IMRT) plans of the same optimal fluence generated from a clinically simulated oropharynx case in an in-house fabricated head and neck phantom. The TPS computed buildup doses were compared with the corresponding measured doses in the phantom using thermoluminescence dosimeters (TLD 100). Analysis of dose distribution calculated using PBC and AAA shows an increase in gamma value in the dose buildup region indicating large dose deviation. For the surface areas of 1, 50 and 100 cm2, PBC overestimates doses as compared to AAA calculated value in the range of 1.34%-3.62% at 0.6 cm depth, 1.74%-2.96% at 0.4 cm depth, and 1.96%-4.06% at 0.2 cm depth, respectively. In high-dose buildup region, AAA calculated doses were lower by an average of -7.56% (SD = 4.73%), while PBC was overestimated by 3.75% (SD = 5.70%) as compared to TLD measured doses at 0.2 cm depth. However, at 0.4 and 0.6 cm depth, PBC overestimated TLD measured doses by 5.84% (SD = 4.38%) and 2.40% (SD = 4.63%), respectively, while AAA underestimated the TLD measured doses by -0.82% (SD = 4.24%) and -1.10% (SD = 4.14%) at the same respective depth. In low-dose buildup region, both AAA and PBC overestimated the TLD measured doses at all depths except -2.05% (SD = 10.21%) by AAA at 0.2 cm depth. The differences between AAA and PBC at all depths were statistically significant (p < 0.05) in high-dose buildup region, whereas it is not statistically significant in low-dose buildup region. In conclusion, AAA calculated the dose more accurately than PBC in clinically important high-dose buildup region at 0.4 cm and 0.6 cm depths. The use of an orfit cast increases the dose buildup

  18. The MAPKKKs Ste11 and Bck1 jointly transduce the high oxidative stress signal through the cell wall integrity MAP kinase pathway

    PubMed Central

    Jin, Chunyan; Kim, Stephen K.; Willis, Stephen D.; Cooper, Katrina F.

    2016-01-01

    Oxidative stress stimulates the Rho1 GTPase, which in turn induces the cell wall integrity (CWI) MAP kinase cascade. CWI activation promotes stress-responsive gene expression through activation of transcription factors (Rlm1, SBF) and nuclear release and subsequent destruction of the repressor cyclin C. This study reports that, in response to high hydrogen peroxide exposure, or in the presence of constitutively active Rho1, cyclin C still translocates to the cytoplasm and is degraded in cells lacking Bck1, the MAPKKK of the CWI pathway. However, in mutants defective for both Bck1 and Ste11, the MAPKKK from the high osmolarity, pseudohyphal and mating MAPK pathways, cyclin C nuclear to cytoplasmic relocalization and destruction is prevented. Further analysis revealed that cyclin C goes from a diffuse nuclear signal to a terminal nucleolar localization in this double mutant. Live cell imaging confirmed that cyclin C transiently passes through the nucleolus prior to cytoplasmic entry in wild-type cells. Taken together with previous studies, these results indicate that under low levels of oxidative stress, Bck1 activation is sufficient to induce cyclin C translocation and degradation. However, higher stress conditions also stimulate Ste11, which reinforces the stress signal to cyclin C and other transcription factors. This model would provide a mechanism by which different stress levels can be sensed and interpreted by the cell. PMID:27135035

  19. Quantification of wall shear stress using a finite-element method in multidimensional phase-contrast MR data of the thoracic aorta.

    PubMed

    Sotelo, Julio; Urbina, Jesús; Valverde, Israel; Tejos, Cristian; Irarrázaval, Pablo; Hurtado, Daniel E; Uribe, Sergio

    2015-07-16

    We present a computational method for calculating the distribution of wall shear stress (WSS) in the aorta based on a velocity field obtained from two-dimensional (2D) phase-contrast magnetic resonance imaging (PC-MRI) data and a finite-element method. The WSS vector was obtained from a global least-squares stress-projection method. The method was benchmarked against the Womersley model, and the robustness was assessed by changing resolution, noise, and positioning of the vessel wall. To showcase the applicability of the method, we report the axial, circumferential and magnitude of the WSS using in-vivo data from five volunteers. Our results showed that WSS values obtained with our method were in good agreement with those obtained from the Womersley model. The results for the WSS contour means showed a systematic but decreasing bias when the pixel size was reduced. The proposed method proved to be robust to changes in noise level, and an incorrect position of the vessel wall showed large errors when the pixel size was decreased. In volunteers, the results obtained were in good agreement with those found in the literature. In summary, we have proposed a novel image-based computational method for the estimation of WSS on vessel sections with arbitrary cross-section geometry that is robust in the presence of noise and boundary misplacements.

  20. Quantification of wall shear stress using a finite-element method in multidimensional phase-contrast MR data of the thoracic aorta.

    PubMed

    Sotelo, Julio; Urbina, Jesús; Valverde, Israel; Tejos, Cristian; Irarrázaval, Pablo; Hurtado, Daniel E; Uribe, Sergio

    2015-07-16

    We present a computational method for calculating the distribution of wall shear stress (WSS) in the aorta based on a velocity field obtained from two-dimensional (2D) phase-contrast magnetic resonance imaging (PC-MRI) data and a finite-element method. The WSS vector was obtained from a global least-squares stress-projection method. The method was benchmarked against the Womersley model, and the robustness was assessed by changing resolution, noise, and positioning of the vessel wall. To showcase the applicability of the method, we report the axial, circumferential and magnitude of the WSS using in-vivo data from five volunteers. Our results showed that WSS values obtained with our method were in good agreement with those obtained from the Womersley model. The results for the WSS contour means showed a systematic but decreasing bias when the pixel size was reduced. The proposed method proved to be robust to changes in noise level, and an incorrect position of the vessel wall showed large errors when the pixel size was decreased. In volunteers, the results obtained were in good agreement with those found in the literature. In summary, we have proposed a novel image-based computational method for the estimation of WSS on vessel sections with arbitrary cross-section geometry that is robust in the presence of noise and boundary misplacements. PMID:26050955

  1. Apyrase Suppression Raises Extracellular ATP Levels and Induces Gene Expression and Cell Wall Changes Characteristic of Stress Responses1[C][W][OPEN

    PubMed Central

    Lim, Min Hui; Wu, Jian; Yao, Jianchao; Gallardo, Ignacio F.; Dugger, Jason W.; Webb, Lauren J.; Huang, James; Salmi, Mari L.; Song, Jawon; Clark, Greg; Roux, Stanley J.

    2014-01-01

    Plant cells release ATP into their extracellular matrix as they grow, and extracellular ATP (eATP) can modulate the rate of cell growth in diverse tissues. Two closely related apyrases (APYs) in Arabidopsis (Arabidopsis thaliana), APY1 and APY2, function, in part, to control the concentration of eATP. The expression of APY1/APY2 can be inhibited by RNA interference, and this suppression leads to an increase in the concentration of eATP in the extracellular medium and severely reduces growth. To clarify how the suppression of APY1 and APY2 is linked to growth inhibition, the gene expression changes that occur in seedlings when apyrase expression is suppressed were assayed by microarray and quantitative real-time-PCR analyses. The most significant gene expression changes induced by APY suppression were in genes involved in biotic stress responses, which include those genes regulating wall composition and extensibility. These expression changes predicted specific chemical changes in the walls of mutant seedlings, and two of these changes, wall lignification and decreased methyl ester bonds, were verified by direct analyses. Taken together, the results are consistent with the hypothesis that APY1, APY2, and eATP play important roles in the signaling steps that link biotic stresses to plant defense responses and growth changes. PMID:24550243

  2. Requirement for pectin methyl esterase and preference for fragmented over native pectins for wall-associated kinase-activated, EDS1/PAD4-dependent stress response in Arabidopsis.

    PubMed

    Kohorn, Bruce D; Kohorn, Susan L; Saba, Nicholas J; Martinez, Victoriano Meco

    2014-07-01

    The wall-associated kinases (WAKs) have a cytoplasmic protein kinase domain that spans the plasma membrane and binds pectin in the extracellular matrix of plants. WAKs are required for cell expansion during Arabidopsis seedling development but are also an integral part of the response to pathogens and stress that present oligogalacturonides (OGs), which subsequently bind to WAKs and activate a MPK6 (mitogen-activated protein kinase)-dependent pathway. It was unclear how WAKs distinguish native pectin polymers and OGs to activate one or the other of these two pathways. A dominant allele of WAK2 constitutively activates the stress response, and we show here that the effect is dependent upon EDS1 and PAD4, transcriptional activators involved in the pathogen response. Moreover, the WAK2 dominant allele is suppressed by a null allele of a pectin methyl esterase (PME3) whose activity normally leads to cross-linking of pectins in the cell wall. Although OGs activate a transcriptional response in wild type, the response is enhanced in a pme3/pme3 null, consistent with a competition by OG and native polymers for activation of WAKs. This provides a plausible mechanism for WAKs to distinguish an expansion from a stress pathway.

  3. Saccharomyces cerevisiae Mid2p Is a Potential Cell Wall Stress Sensor and Upstream Activator of the PKC1-MPK1 Cell Integrity Pathway

    PubMed Central

    Ketela, Troy; Green, Robin; Bussey, Howard

    1999-01-01

    The MID2 gene of Saccharomyces cerevisiae encodes a protein with structural features indicative of a plasma membrane-associated cell wall sensor. MID2 was isolated as a multicopy activator of the Skn7p transcription factor. Deletion of MID2 causes resistance to calcofluor white, diminished production of stress-induced cell wall chitin under a variety of conditions, and changes in growth rate and viability in a number of different cell wall biosynthesis mutants. Overexpression of MID2 causes hyperaccumulation of chitin and increased sensitivity to calcofluor white. α-Factor hypersensitivity of mid2Δ mutants can be suppressed by overexpression of upstream elements of the cell integrity pathway, including PKC1, RHO1, WSC1, and WSC2. Mid2p and Wsc1p appear to have overlapping roles in maintaining cell integrity since mid2Δ wsc1Δ mutants are inviable on medium that does not contain osmotic support. A role for MID2 in the cell integrity pathway is further supported by the finding that MID2 is required for induction of Mpk1p tyrosine phosphorylation during exposure to α-factor, calcofluor white, or high temperature. Our data are consistent with a role for Mid2p in sensing cell wall stress and in activation of a response that includes both increased chitin synthesis and the Mpk1p mitogen-activated protein kinase cell integrity pathway. In addition, we have identified an open reading frame, MTL1, which encodes a protein with both structural and functional similarity to Mid2p. PMID:10348843

  4. Mutations in mmpL and in the cell wall stress stimulon contribute to resistance to oxadiazole antibiotics in methicillin-resistant Staphylococcus aureus.

    PubMed

    Xiao, Qiaobin; Vakulenko, Sergei; Chang, Mayland; Mobashery, Shahriar

    2014-10-01

    Staphylococcus aureus is a leading cause of hospital- and community-acquired infections, which exhibit broad resistance to various antibiotics. We recently disclosed the discovery of the oxadiazole class of antibiotics, which has in vitro and in vivo activities against methicillin-resistant S. aureus (MRSA). We report herein that MmpL, a putative member of the resistance, nodulation, and cell division (RND) family of proteins, contributes to oxadiazole resistance in the S. aureus strain COL. Through serial passages, we generated two S. aureus COL variants that showed diminished susceptibilities to an oxadiazole antibiotic. The MICs for the oxadiazole against one strain (designated S. aureus COL(I)) increased reproducibly 2-fold (to 4 μg/ml), while against the other strain (S. aureus COL(R)), they increased >4-fold (to >8 μg/ml, the limit of solubility). The COL(R) strain was derived from the COL(I) strain. Whole-genome sequencing revealed 31 mutations in S. aureus COL(R), of which 29 were shared with COL(I). Consistent with our previous finding that oxadiazole antibiotics inhibit cell wall biosynthesis, we found 13 mutations that occurred either in structural genes or in promoters of the genes of the cell wall stress stimulon. Two unique mutations in S. aureus COL(R) were substitutions in two genes that encode the putative thioredoxin (SACOL1794) and MmpL (SACOL2566). A role for mmpL in resistance to oxadiazoles was discerned from gene deletion and complementation experiments. To our knowledge, this is the first report that a cell wall-acting antibiotic selects for mutations in the cell wall stress stimulon and the first to implicate MmpL in resistance to antibiotics in S. aureus.

  5. Analysis of thermal residual stress in a thick-walled ring of Duralcan-base Al-SiC functionally graded material

    SciTech Connect

    Fukui, Yasuyoshi; Watanabe, Yoshimi

    1996-12-01

    A ring-cutting test and an elastic theory were applied to evaluate the macroscopic residual stress in a thick-walled ring made of Al-SiC functionally graded material (FGM). The FGM ring specimens, with outer diameter 90 mm, radial thickness approximately 8.4 to 10 mm, and width 30 mm, were fabricated by the centrifugal casting method from an ingot of Duralcan F3D.20S of Al-20 vol pct SiC master composite. Because of a difference in centrifugal forces of SiC particles and of molten aluminum alloy, the rings had a graded composition of SiC particles in the radial direction. The volume fractions of SiC particles in each ring specimen varied in the range of 0 to 43 vol pct from the inner to the outer surface of the ring, depending on the applied mold spin speed. A ring diametral compression test was performed to validate an analytical formula based on the curved beam theory that can account for the graded properties of the material. Excellent agreement between the theory that can account for the graded properties of the material. Excellent agreement between the theory and the experiment was found. The residual stress was found to be generated by a cooling of {Delta}T = 140 K, which was from half the melting point corresponding stress-free condition to the ambient temperature. The hoop residual stresses in the FGM ring varied in the range of {minus}50 to +35 MPa and from tension at the inner surface to compression at the outer space because of the graded composition. With an increase in wall thickness and/or composition gradation, the residual stresses were found to increase.

  6. Structural insights into the Escherichia coli lysine decarboxylases and molecular determinants of interaction with the AAA+ ATPase RavA

    PubMed Central

    Kandiah, Eaazhisai; Carriel, Diego; Perard, Julien; Malet, Hélène; Bacia, Maria; Liu, Kaiyin; Chan, Sze W. S.; Houry, Walid A.; Ollagnier de Choudens, Sandrine; Elsen, Sylvie; Gutsche, Irina

    2016-01-01

    The inducible lysine decarboxylase LdcI is an important enterobacterial acid stress response enzyme whereas LdcC is its close paralogue thought to play mainly a metabolic role. A unique macromolecular cage formed by two decamers of the Escherichia coli LdcI and five hexamers of the AAA+ ATPase RavA was shown to counteract acid stress under starvation. Previously, we proposed a pseudoatomic model of the LdcI-RavA cage based on its cryo-electron microscopy map and crystal structures of an inactive LdcI decamer and a RavA monomer. We now present cryo-electron microscopy 3D reconstructions of the E. coli LdcI and LdcC, and an improved map of the LdcI bound to the LARA domain of RavA, at pH optimal for their enzymatic activity. Comparison with each other and with available structures uncovers differences between LdcI and LdcC explaining why only the acid stress response enzyme is capable of binding RavA. We identify interdomain movements associated with the pH-dependent enzyme activation and with the RavA binding. Multiple sequence alignment coupled to a phylogenetic analysis reveals that certain enterobacteria exert evolutionary pressure on the lysine decarboxylase towards the cage-like assembly with RavA, implying that this complex may have an important function under particular stress conditions. PMID:27080013

  7. Cytoplasmic dynein regulates its attachment to microtubules via nucleotide state-switched mechanosensing at multiple AAA domains.

    PubMed

    Nicholas, Matthew P; Berger, Florian; Rao, Lu; Brenner, Sibylle; Cho, Carol; Gennerich, Arne

    2015-05-19

    Cytoplasmic dynein is a homodimeric microtubule (MT) motor protein responsible for most MT minus-end-directed motility. Dynein contains four AAA+ ATPases (AAA: ATPase associated with various cellular activities) per motor domain (AAA1-4). The main site of ATP hydrolysis, AAA1, is the only site considered by most dynein motility models. However, it remains unclear how ATPase activity and MT binding are coordinated within and between dynein's motor domains. Using optical tweezers, we characterize the MT-binding strength of recombinant dynein monomers as a function of mechanical tension and nucleotide state. Dynein responds anisotropically to tension, binding tighter to MTs when pulled toward the MT plus end. We provide evidence that this behavior results from an asymmetrical bond that acts as a slip bond under forward tension and a slip-ideal bond under backward tension. ATP weakens MT binding and reduces bond strength anisotropy, and unexpectedly, so does ADP. Using nucleotide binding and hydrolysis mutants, we show that, although ATP exerts its effects via binding AAA1, ADP effects are mediated by AAA3. Finally, we demonstrate "gating" of AAA1 function by AAA3. When tension is absent or applied via dynein's C terminus, ATP binding to AAA1 induces MT release only if AAA3 is in the posthydrolysis state. However, when tension is applied to the linker, ATP binding to AAA3 is sufficient to "open" the gate. These results elucidate the mechanisms of dynein-MT interactions, identify regulatory roles for AAA3, and help define the interplay between mechanical tension and nucleotide state in regulating dynein motility.

  8. The Effect of Varied Support Models of BJUT-IIVAD on Coronary Arterial blood flow and wall shear stress: A Primary CFD Study.

    PubMed

    Zhang, Qi; Gao, Bin; Gu, Kaiyun; Chang, Yu; Xu, Jinchao; Deuflhard, Peter

    2014-09-17

    BJUT-II VAD is a novel left ventricular assist devices. Because of the special connection between the pump and native heart, the hemodynamic effects of BJTU-II VAD on coronary artery are still unclear. Hence, numerical simulations have conducted to clarify changes in hemodynamic effects of different support modes. A patient specific left coronary arterial geometric model is reconstructed based on the CT data. And 3 support modes, "constant speed mode", "co-pulse modes" and "counter pulse mode" are used in this study. The wall shear stress (WSS), wall shear stress gradient (WSSG), cycle averaged wall shear stress (avWSS), oscillatory shear index (OSI) and the flow pattern are calculated to evaluate the hemodynamic states of coronary artery. The computational results demonstrate that the hemodynamic states of coronary artery are directly affected by the support modes. The co-pulse modes could achieve the highest blood perfusion (constant speed: 153ml/min vs. co-pulse: 775ml/min vs. counter pulse: 140ml/min) and the highest avWSS (constant speed: 18.1Pa vs. co-pulse: 42.6Pa vs. counter pulse: 22.6Pa). In addition, the WSS and WSSG at the time of peak blood velocity under the constant speed mode are both lower than those under other two support modes. In contrast, the counter pulse mode generates the highest OSI value (constant speed: 0.365 vs. co-pulse: 0.379 vs. counter pulse: 0.426). In brief, BJUT-II VAD under co-pulse mode may have benefits for improving coronary perfusion and preventing the development of atherosclerosis, however, the constant speed mode may have benefit for preventing the development of plaque vulnerability. PMID:25232766

  9. Identification of AAAS gene mutation in Allgrove syndrome: A report of three cases

    PubMed Central

    LI, WENJING; GONG, CHUNXIU; QI, ZHAN; WU, DI; CAO, BINGYAN

    2015-01-01

    Allgrove syndrome (AS) is an autosomal recessive congenital disease, caused by mutations in the AAAS gene, and is characterized by the triad of Addison's disease, achalasia and alacrima. The present study describes three newly diagnosed cases of AS, in which genetic analysis of the AAAS gene was used to identify AAAS gene mutations, to enhance the understanding of the pathogenesis and clinical manifestations of AS in the Chinese population. Two of the cases exhibited homozygous mutations of c.771delG (p.Arg258GlyfsX33) in exon 8 and one case exhibited a homozygous mutation of c.1366C>T (p.Q456X) in exon 15. A review of the current literature suggests that the AAAS c.771delG mutation has only been reported in the Chinese population. Genetic analysis of the AAAS gene in Chinese AS patients at a young age may facilitate an earlier diagnosis and the timely initiation of the appropriate treatment, ultimately improving the patient outcome. PMID:26622478

  10. Water Stress and Foliar Boron Application Altered Cell Wall Boron and Seed Nutrition in Near-Isogenic Cotton Lines Expressing Fuzzy and Fuzzless Seed Phenotypes

    PubMed Central

    2015-01-01

    Our previous research, conducted under well-watered conditions without fertilizer application, showed that fuzziness cottonseed trait resulted in cottonseed nutrition differences between fuzzy (F) and fuzzless (N) cottonseed. Under water stress conditions, B mobility is further limited, inhibiting B movement within the plant, affecting seed nutrition (quality). Therefore, we hypothesized that both foliar B and water stress can affect B mobility, altering cottonseed protein, oil, and mineral nutrition. The objective of the current research was to evaluate the effects of the fuzziness seed trait on boron (B) and seed nutrition under water stress and foliar B application using near-isogenic cotton lines (NILs) grown in a repeated greenhouse experiment. Plants were grown under-well watered conditions (The soil water potential was kept between -15 to -20 kPa, considered field capacity) and water stress conditions (soil water potential between -100 and -150 kPa, stressed conditions). Foliar B was applied at a rate of 1.8 kg B ha-1 as H3BO3. Under well-watered conditions without B the concentrations of seed oil in N lines were higher than in F lines, and seed K and N levels were lower in N lines than in F lines. Concentrations of K, N, and B in leaves were higher in N lines than in F lines, opposing the trend in seeds. Water-stress resulted in higher seed protein concentrations, and the contribution of cell wall (structural) B to the total B exceeded 90%, supporting the structural role of B in plants. Foliar B application under well-watered conditions resulted in higher seed protein, oil, C, N, and B in only some lines. This research showed that cottonseed nutrition differences can occur due to seed fuzziness trait, and water stress and foliar B application can alter cottonseed nutrition. PMID:26098564

  11. Water Stress and Foliar Boron Application Altered Cell Wall Boron and Seed Nutrition in Near-Isogenic Cotton Lines Expressing Fuzzy and Fuzzless Seed Phenotypes.

    PubMed

    Bellaloui, Nacer; Turley, Rickie B; Stetina, Salliana R

    2015-01-01

    Our previous research, conducted under well-watered conditions without fertilizer application, showed that fuzziness cottonseed trait resulted in cottonseed nutrition differences between fuzzy (F) and fuzzless (N) cottonseed. Under water stress conditions, B mobility is further limited, inhibiting B movement within the plant, affecting seed nutrition (quality). Therefore, we hypothesized that both foliar B and water stress can affect B mobility, altering cottonseed protein, oil, and mineral nutrition. The objective of the current research was to evaluate the effects of the fuzziness seed trait on boron (B) and seed nutrition under water stress and foliar B application using near-isogenic cotton lines (NILs) grown in a repeated greenhouse experiment. Plants were grown under-well watered conditions (The soil water potential was kept between -15 to -20 kPa, considered field capacity) and water stress conditions (soil water potential between -100 and -150 kPa, stressed conditions). Foliar B was applied at a rate of 1.8 kg B ha(-1) as H3BO3. Under well-watered conditions without B the concentrations of seed oil in N lines were higher than in F lines, and seed K and N levels were lower in N lines than in F lines. Concentrations of K, N, and B in leaves were higher in N lines than in F lines, opposing the trend in seeds. Water-stress resulted in higher seed protein concentrations, and the contribution of cell wall (structural) B to the total B exceeded 90%, supporting the structural role of B in plants. Foliar B application under well-watered conditions resulted in higher seed protein, oil, C, N, and B in only some lines. This research showed that cottonseed nutrition differences can occur due to seed fuzziness trait, and water stress and foliar B application can alter cottonseed nutrition.

  12. Water Stress and Foliar Boron Application Altered Cell Wall Boron and Seed Nutrition in Near-Isogenic Cotton Lines Expressing Fuzzy and Fuzzless Seed Phenotypes.

    PubMed

    Bellaloui, Nacer; Turley, Rickie B; Stetina, Salliana R

    2015-01-01

    Our previous research, conducted under well-watered conditions without fertilizer application, showed that fuzziness cottonseed trait resulted in cottonseed nutrition differences between fuzzy (F) and fuzzless (N) cottonseed. Under water stress conditions, B mobility is further limited, inhibiting B movement within the plant, affecting seed nutrition (quality). Therefore, we hypothesized that both foliar B and water stress can affect B mobility, altering cottonseed protein, oil, and mineral nutrition. The objective of the current research was to evaluate the effects of the fuzziness seed trait on boron (B) and seed nutrition under water stress and foliar B application using near-isogenic cotton lines (NILs) grown in a repeated greenhouse experiment. Plants were grown under-well watered conditions (The soil water potential was kept between -15 to -20 kPa, considered field capacity) and water stress conditions (soil water potential between -100 and -150 kPa, stressed conditions). Foliar B was applied at a rate of 1.8 kg B ha(-1) as H3BO3. Under well-watered conditions without B the concentrations of seed oil in N lines were higher than in F lines, and seed K and N levels were lower in N lines than in F lines. Concentrations of K, N, and B in leaves were higher in N lines than in F lines, opposing the trend in seeds. Water-stress resulted in higher seed protein concentrations, and the contribution of cell wall (structural) B to the total B exceeded 90%, supporting the structural role of B in plants. Foliar B application under well-watered conditions resulted in higher seed protein, oil, C, N, and B in only some lines. This research showed that cottonseed nutrition differences can occur due to seed fuzziness trait, and water stress and foliar B application can alter cottonseed nutrition. PMID:26098564

  13. A mixture of peptides and sugars derived from plant cell walls increases plant defense responses to stress and attenuates ageing-associated molecular changes in cultured skin cells.

    PubMed

    Apone, Fabio; Tito, Annalisa; Carola, Antonietta; Arciello, Stefania; Tortora, Assunta; Filippini, Lucio; Monoli, Irene; Cucchiara, Mirna; Gibertoni, Simone; Chrispeels, Maarten J; Colucci, Gabriella

    2010-02-15

    Small peptides and aminoacid derivatives have been extensively studied for their effect of inducing plant defense responses, and thus increasing plant tolerance to a wide range of abiotic stresses. Similarly to plants, these compounds can activate different signaling pathways in mammalian skin cells as well, leading to the up-regulation of anti-aging specific genes. This suggests the existence of analogous defense response mechanisms, well conserved both in plants and animal cells. In this article, we describe the preparation of a new mixture of peptides and sugars derived from the chemical and enzymatic digestion of plant cell wall glycoproteins. We investigate the multiple roles of this product as potential "biostimulator" to protect plants from abiotic stresses, and also as potential cosmeceutical. In particular, the molecular effects of the peptide/sugar mixture of inducing plant defense responsive genes and protecting cultured skin cells from oxidative burst damages were deeply evaluated.

  14. MOLECULAR PHENOTYPING OF LIGNIN-MODIFIED TOBACCO REVEALS ASSOCIATED CHANGES IN CELL WALL METABOLISM, PRIMARY METABOLISM, STRESS METABOLISM AND PHOTORESPIRATION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Lignin is an important component of secondary thickened cell walls. Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) are two key enzymes catalyzing the penultimate and last step in the biosynthesis of the monolignols. Down-regulation of CCR in tobacco has been shown to reduce l...

  15. Dynein motors: How AAA+ ring opening and closing coordinates microtubule binding and linker movement.

    PubMed

    Schmidt, Helgo

    2015-05-01

    Dyneins are a family of motor proteins that move along the microtubule. Motility is generated in the motor domain, which consists of a ring of six AAA+ (ATPases associated with diverse cellular activities) domains, the linker and the microtubule-binding domain (MTBD). The cyclic ATP-hydrolysis in the AAA+ ring causes the remodelling of the linker, which creates the necessary force for movement. The production of force has to be synchronized with cycles of microtubule detachment and rebinding to efficiently create movement along the microtubule. The analysis of four dynein motor domain crystal structures in the essay presented here provides evidence that this crucial coordination is carried out by open/closed AAA+ ring conformations.

  16. Effects of PHENYLALANINE AMMONIA LYASE (PAL) knockdown on cell wall composition, biomass digestibility, and biotic and abiotic stress responses in Brachypodium

    PubMed Central

    Cass, Cynthia L.; Peraldi, Antoine; Dowd, Patrick F.; Mottiar, Yaseen; Santoro, Nicholas; Karlen, Steven D.; Bukhman, Yury V.; Foster, Cliff E.; Thrower, Nick; Bruno, Laura C.; Moskvin, Oleg V.; Johnson, Eric T.; Willhoit, Megan E.; Phutane, Megha; Ralph, John; Mansfield, Shawn D.; Nicholson, Paul; Sedbrook, John C.

    2015-01-01

    The phenylpropanoid pathway in plants synthesizes a variety of structural and defence compounds, and is an important target in efforts to reduce cell wall lignin for improved biomass conversion to biofuels. Little is known concerning the trade-offs in grasses when perturbing the function of the first gene family in the pathway, PHENYLALANINE AMMONIA LYASE (PAL). Therefore, PAL isoforms in the model grass Brachypodium distachyon were targeted, by RNA interference (RNAi), and large reductions (up to 85%) in stem tissue transcript abundance for two of the eight putative BdPAL genes were identified. The cell walls of stems of BdPAL-knockdown plants had reductions of 43% in lignin and 57% in cell wall-bound ferulate, and a nearly 2-fold increase in the amounts of polysaccharide-derived carbohydrates released by thermochemical and hydrolytic enzymic partial digestion. PAL-knockdown plants exhibited delayed development and reduced root growth, along with increased susceptibilities to the fungal pathogens Fusarium culmorum and Magnaporthe oryzae. Surprisingly, these plants generally had wild-type (WT) resistances to caterpillar herbivory, drought, and ultraviolet light. RNA sequencing analyses revealed that the expression of genes associated with stress responses including ethylene biosynthesis and signalling were significantly altered in PAL knocked-down plants under non-challenging conditions. These data reveal that, although an attenuation of the phenylpropanoid pathway increases carbohydrate availability for biofuel, it can adversely affect plant growth and disease resistance to fungal pathogens. The data identify notable differences between the stress responses of these monocot pal mutants versus Arabidopsis (a dicot) pal mutants and provide insights into the challenges that may arise when deploying phenylpropanoid pathway-altered bioenergy crops. PMID:26093023

  17. Effects of PHENYLALANINE AMMONIA LYASE (PAL) knockdown on cell wall composition, biomass digestibility, and biotic and abiotic stress responses in Brachypodium.

    PubMed

    Cass, Cynthia L; Peraldi, Antoine; Dowd, Patrick F; Mottiar, Yaseen; Santoro, Nicholas; Karlen, Steven D; Bukhman, Yury V; Foster, Cliff E; Thrower, Nick; Bruno, Laura C; Moskvin, Oleg V; Johnson, Eric T; Willhoit, Megan E; Phutane, Megha; Ralph, John; Mansfield, Shawn D; Nicholson, Paul; Sedbrook, John C

    2015-07-01

    The phenylpropanoid pathway in plants synthesizes a variety of structural and defence compounds, and is an important target in efforts to reduce cell wall lignin for improved biomass conversion to biofuels. Little is known concerning the trade-offs in grasses when perturbing the function of the first gene family in the pathway, PHENYLALANINE AMMONIA LYASE (PAL). Therefore, PAL isoforms in the model grass Brachypodium distachyon were targeted, by RNA interference (RNAi), and large reductions (up to 85%) in stem tissue transcript abundance for two of the eight putative BdPAL genes were identified. The cell walls of stems of BdPAL-knockdown plants had reductions of 43% in lignin and 57% in cell wall-bound ferulate, and a nearly 2-fold increase in the amounts of polysaccharide-derived carbohydrates released by thermochemical and hydrolytic enzymic partial digestion. PAL-knockdown plants exhibited delayed development and reduced root growth, along with increased susceptibilities to the fungal pathogens Fusarium culmorum and Magnaporthe oryzae. Surprisingly, these plants generally had wild-type (WT) resistances to caterpillar herbivory, drought, and ultraviolet light. RNA sequencing analyses revealed that the expression of genes associated with stress responses including ethylene biosynthesis and signalling were significantly altered in PAL knocked-down plants under non-challenging conditions. These data reveal that, although an attenuation of the phenylpropanoid pathway increases carbohydrate availability for biofuel, it can adversely affect plant growth and disease resistance to fungal pathogens. The data identify notable differences between the stress responses of these monocot pal mutants versus Arabidopsis (a dicot) pal mutants and provide insights into the challenges that may arise when deploying phenylpropanoid pathway-altered bioenergy crops. PMID:26093023

  18. Intraventricular Flow Velocity Vector Visualization Based on the Continuity Equation and Measurements of Vorticity and Wall Shear Stress

    NASA Astrophysics Data System (ADS)

    Itatani, Keiichi; Okada, Takashi; Uejima, Tokuhisa; Tanaka, Tomohiko; Ono, Minoru; Miyaji, Kagami; Takenaka, Katsu

    2013-07-01

    We have developed a system to estimate velocity vector fields inside the cardiac ventricle by echocardiography and to evaluate several flow dynamical parameters to assess the pathophysiology of cardiovascular diseases. A two-dimensional continuity equation was applied to color Doppler data using speckle tracking data as boundary conditions, and the velocity component perpendicular to the echo beam line was obtained. We determined the optimal smoothing method of the color Doppler data, and the 8-pixel standard deviation of the Gaussian filter provided vorticity without nonphysiological stripe shape noise. We also determined the weight function at the bilateral boundaries given by the speckle tracking data of the ventricle or vascular wall motion, and the weight function linear to the distance from the boundary provided accurate flow velocities not only inside the vortex flow but also around near-wall regions on the basis of the results of the validation of a digital phantom of a pipe flow model.

  19. Effects of foliar boron application on seed composition, cell wall boron, and seed δ15N and δ13C isotopes in water-stressed soybean plants

    PubMed Central

    Bellaloui, Nacer; Hu, Yanbo; Mengistu, Alemu; Kassem, My A.; Abel, Craig A.

    2013-01-01

    Limited information is available on the effects of foliar boron (B) application on soybean seed composition. The objective of this research was to investigate the effects of foliar B on seed composition (protein, oil, fatty acids, and sugars). Our hypothesis was that since B is involved in nitrogen and carbon metabolism, it may impact seed composition. A repeated greenhouse experiment was conducted where half of the soybean plants was exposed to water stress (WS) and the other half was well-watered. Foliar boron (FB) in the form of boric acid was applied twice at a rate of 1.1 kg ha−1. The first application was during flowering stage, and the second application was during seed-fill stage. Treatments were water stressed plants with no FB (WS–B); water stressed plants with FB (WS+B); watered plants without FB (W–B), and watered plants with FB (W+B). The treatment W–B was used as a control. Comparing with WS–B plants, B concentration was the highest in leaves and seed of W+B plants (84% increase in leaves and 73% in seed). Seeds of W+B plants had higher protein (11% increase), oleic acid (27% increase), sucrose (up to 40% increase), glucose, and fructose comparing with W–B. However, seed stachyose concentrations increased by 43% in WS–B plants seed compared with W–B plants. Cell wall (structural) B concentration in leaves was higher in all plants under water stress, especially in WS–B plants where the percentage of cell wall B reached up to 90%. Water stress changed seed δ15N and δ13C values in both B applied and non-B applied plants, indicating possible effects on nitrogen and carbon metabolism. This research demonstrated that FB increased B accumulation in leaves and seed, and altered seed composition of well-watered and water stressed plants, indicating a possible involvement of B in seed protein, and oleic and linolenic fatty acids. Further research is needed to explain mechanisms of B involvement in seed protein and fatty acids. PMID:23888163

  20. Semiautomatic vessel wall detection and quantification of wall thickness in computed tomography images of human abdominal aortic aneurysms

    SciTech Connect

    Shum, Judy; DiMartino, Elena S.; Goldhammer, Adam; Goldman, Daniel H.; Acker, Leah C.; Patel, Gopal; Ng, Julie H.; Martufi, Giampaolo; Finol, Ender A.

    2010-02-15

    Purpose: Quantitative measurements of wall thickness in human abdominal aortic aneurysms (AAAs) may lead to more accurate methods for the evaluation of their biomechanical environment. Methods: The authors describe an algorithm for estimating wall thickness in AAAs based on intensity histograms and neural networks involving segmentation of contrast enhanced abdominal computed tomography images. The algorithm was applied to ten ruptured and ten unruptured AAA image data sets. Two vascular surgeons manually segmented the lumen, inner wall, and outer wall of each data set and a reference standard was defined as the average of their segmentations. Reproducibility was determined by comparing the reference standard to lumen contours generated automatically by the algorithm and a commercially available software package. Repeatability was assessed by comparing the lumen, outer wall, and inner wall contours, as well as wall thickness, made by the two surgeons using the algorithm. Results: There was high correspondence between automatic and manual measurements for the lumen area (r=0.978 and r=0.996 for ruptured and unruptured aneurysms, respectively) and between vascular surgeons (r=0.987 and r=0.992 for ruptured and unruptured aneurysms, respectively). The authors' automatic algorithm showed better results when compared to the reference with an average lumen error of 3.69%, which is less than half the error between the commercially available application Simpleware and the reference (7.53%). Wall thickness measurements also showed good agreement between vascular surgeons with average coefficients of variation of 10.59% (ruptured aneurysms) and 13.02% (unruptured aneurysms). Ruptured aneurysms exhibit significantly thicker walls (1.78{+-}0.39 mm) than unruptured ones (1.48{+-}0.22 mm), p=0.044. Conclusions: While further refinement is needed to fully automate the outer wall segmentation algorithm, these preliminary results demonstrate the method's adequate reproducibility

  1. Hyperpulsatile pressure, systemic inflammation and cardiac stress are associated with cardiac wall remodeling in an African male cohort: the SABPA study.

    PubMed

    van Vuren, Esmé Jansen; Malan, Leoné; von Känel, Roland; Cockeran, Marike; Malan, Nicolaas T

    2016-09-01

    Inflammation may contribute to an increase in cardiac wall stress through pathways related to cardiac remodeling. Cardiac remodeling is characterized by myocyte hypertrophy, myocyte death and modifications of the extracellular matrix. We sought to explore associations among cardiac remodeling, inflammation and myocardial cell injury in a bi-ethnic cohort of South African men and women. We included 165 men (76 African and 89 Caucasian) and 174 women (80 African and 94 Caucasian) between 20 and 65 years of age. Inflammatory markers used were C-reactive protein (CRP), interleukin-6 and tumor necrosis factor-alpha (TNF-α), whereas troponin T (Trop T) and the N-terminal of pro B-type natriuretic peptide (NT-proBNP) were used as cardiac markers. The frequency of ischemic events (ST segment depression) and left ventricular strain (left ventricular hypertrophy: LVH) were monitored by a 24-h recording of ambulatory blood pressure (BP), ECG and 12-lead standard ECG. Hypertension diagnosed with ambulatory monitoring was more frequent in Africans (53.85 vs. 24.59%; P<0.001), as was the number of ischemic events (6±15 (1; 5) vs. 3±6 (0; 3)). Inflammatory markers (CRP, IL-6 and TNF-α) and the degree of LVH were all significantly higher in Africans (P<0.05). BP was associated (P<0.05) with Trop T in men across ethnic groups. In African men, cardiac stress (NT-proBNP) was associated with TNF-alpha (P<0.001), Trop T (P<0.001) and pulse pressure (P=0.048; adjusted R(2)=0.45). The susceptibility for cardiac wall remodeling appears to increase with hyperpulsatile pressure, low-grade systemic inflammation and ventricular stress, and may lead to the development of future cardiovascular events in African men. PMID:27169396

  2. Norwalk Community College AA-AS Degree Review Committee Curriculum Report, August 21, 1989.

    ERIC Educational Resources Information Center

    Pennino, Eileen M.; Luster, Gwen Tolliver

    In an attempt to revitalize and reform its curriculum, the Associate of Arts-Associate of Science (AA-AS) Degree Review Committee (DRC) of Connecticut's Norwalk Community College issued a curriculum report proposing a 21 credit, limited distributive core for the AS degree (which accounts for 80% of the college's degree recipients). This proposal…

  3. Professional Ethics Activities in the Scientific and Engineering Societies. AAAS Professional Ethics Project.

    ERIC Educational Resources Information Center

    Chalk, Rosemary; And Others

    Presented is an overview of the depth and range of the ethics activities undertaken by societies affiliated with the American Association for the Advancement of Science (AAAS). Included in this report are: (1) reviews of previous surveys of organizations which had adopted codes of ethics; (2) descriptions of the methodology and findings of the…

  4. Effects of doping and bias voltage on the screening in AAA-stacked trilayer graphene

    NASA Astrophysics Data System (ADS)

    Mohammadi, Yawar; Moradian, Rostam; Shirzadi Tabar, Farzad

    2014-09-01

    We calculate the static polarization of AAA-stacked trilayer graphene (TLG) and study its screening properties within the random phase approximation (RPA) in all undoped, doped and biased regimes. We find that the static polarization of undoped AAA-stacked TLG is a combination of the doped and undoped single-layer graphene static polarization. This leads to an enhancement of the dielectric background constant along a Thomas-Fermi screening with the Thomas-Fermi wave vector which is independent of carrier concentrations and a 1/r3 power law decay for the long-distance behavior of the screened Coulomb potential. We show that effects of a bias voltage can be taken into account by a renormalization of the interlayer hopping energy to a new bias-voltage-dependent value, indicating screening properties of AAA-stacked TLG can be tuned electrically. We also find that screening properties of doped AAA-stacked TLG, when μ exceeds √{2}γ, are similar to that of doped SLG only depending on doping. While for μ<√{2}γ, its screening properties are combination of SLG and AA-stacked bilayer graphene screening properties and they are determined by doping and the interlayer hopping energy.

  5. Structure of Lmaj006129AAA, a hypothetical protein from Leishmania major

    SciTech Connect

    Arakaki, Tracy; Le Trong, Isolde; Phizicky, Eric; Quartley, Erin; DeTitta, George; Luft, Joseph; Lauricella, Angela; Anderson, Lori; Kalyuzhniy, Oleksandr; Worthey, Elizabeth; Myler, Peter J.; Kim, David; Baker, David; Hol, Wim G. J.; Merritt, Ethan A.

    2006-03-01

    The crystal structure of a conserved hypothetical protein from L. major, Pfam sequence family PF04543, structural genomics target ID Lmaj006129AAA, has been determined at a resolution of 1.6 Å. The gene product of structural genomics target Lmaj006129 from Leishmania major codes for a 164-residue protein of unknown function. When SeMet expression of the full-length gene product failed, several truncation variants were created with the aid of Ginzu, a domain-prediction method. 11 truncations were selected for expression, purification and crystallization based upon secondary-structure elements and disorder. The structure of one of these variants, Lmaj006129AAH, was solved by multiple-wavelength anomalous diffraction (MAD) using ELVES, an automatic protein crystal structure-determination system. This model was then successfully used as a molecular-replacement probe for the parent full-length target, Lmaj006129AAA. The final structure of Lmaj006129AAA was refined to an R value of 0.185 (R{sub free} = 0.229) at 1.60 Å resolution. Structure and sequence comparisons based on Lmaj006129AAA suggest that proteins belonging to Pfam sequence families PF04543 and PF01878 may share a common ligand-binding motif.

  6. The two faces of hydrogen-bond strength on triple AAA-DDD arrays.

    PubMed

    Lopez, Alfredo Henrique Duarte; Caramori, Giovanni Finoto; Coimbra, Daniel Fernando; Parreira, Renato Luis Tame; da Silva, Éder Henrique

    2013-12-01

    Systems that are connected through multiple hydrogen bonds are the cornerstone of molecular recognition processes in biology, and they are increasingly being employed in supramolecular chemistry, specifically in molecular self-assembly processes. For this reason, the effects of different substituents (NO2, CN, F, Cl, Br, OCH3 and NH2) on the electronic structure, and consequently on the magnitude of hydrogen bonds in triple AAA-DDD arrays (A=acceptor, D=donor) were evaluated in the light of topological [electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM)], energetic [Su-Li energy-decomposition analysis (EDA) and natural bond orbital analysis (NBO)], and geometrical analysis. The results based on local H-bond descriptors (geometries, QTAIM, ELF, and NBO) indicate that substitutions with electron-withdrawing groups on the AAA module tend to strengthen, whereas electron-donating substituents tend to weaken the covalent character of the AAA-DDD intermolecular H-bonds, and also indicate that the magnitude of the effect is dependent on the position of substitution. In contrast, Su-Li EDA results show an opposite behavior when compared to local H-bond descriptors, indicating that electron-donating substituents tend to increase the magnitude of H-bonds in AAA-DDD arrays, and thus suggesting that the use of local H-bond descriptors describes the nature of H bonds only partially, not providing enough insight about the strength of such H bonds.

  7. Anonymous Communication Policies for the Internet: Results and Recommendations of the AAAS Conference.

    ERIC Educational Resources Information Center

    Teich, Al; Frankel, Mark S.; Kling, Rob; Lee, Yaching

    1999-01-01

    Reports the results of a conference on the Internet and anonymous communication organized by the American Association for the Advancement of Science (AAAS). Discusses how anonymous communications can be shaped by the law, education, and public awareness, and highlights the importance of involving all affected interests in policy development.…

  8. The mouse fidgetin gene defines a new role for AAA family proteins in mammalian development.

    PubMed

    Cox, G A; Mahaffey, C L; Nystuen, A; Letts, V A; Frankel, W N

    2000-10-01

    The mouse mutation fidget arose spontaneously in a heterogeneous albino stock. This mutant mouse is characterized by a side-to-side head-shaking and circling behaviour, due to reduced or absent semicircular canals. Fidget mice also have small eyes, associated with cell-cycle delay and insufficient growth of the retinal neural epithelium, and lower penetrance skeletal abnormalities, including pelvic girdle dysgenesis, skull bone fusions and polydactyly. By positional cloning, we found the gene mutated in fidget mice, fidgetin (Fign), which encodes a new member of the 'meiotic' or subfamily-7 (SF7; ref. 7) group of ATPases associated with diverse cellular activities (AAA proteins). We also discovered two closely related mammalian genes. AAA proteins are molecular chaperones that facilitate a variety of functions, including membrane fusion, proteolysis, peroxisome biogenesis, endosome sorting and meiotic spindle formation, but functions for the SF7 AAA proteins are largely unknown. Fidgetin is the first mutant AAA protein found in a mammalian developmental mutant, thus defining a new role for these proteins in embryonic development.

  9. National dosimetric audit network finds discrepancies in AAA lung inhomogeneity corrections.

    PubMed

    Dunn, Leon; Lehmann, Joerg; Lye, Jessica; Kenny, John; Kron, Tomas; Alves, Andrew; Cole, Andrew; Zifodya, Jackson; Williams, Ivan

    2015-07-01

    This work presents the Australian Clinical Dosimetry Service's (ACDS) findings of an investigation of systematic discrepancies between treatment planning system (TPS) calculated and measured audit doses. Specifically, a comparison between the Anisotropic Analytic Algorithm (AAA) and other common dose-calculation algorithms in regions downstream (≥2cm) from low-density material in anthropomorphic and slab phantom geometries is presented. Two measurement setups involving rectilinear slab-phantoms (ACDS Level II audit) and anthropomorphic geometries (ACDS Level III audit) were used in conjunction with ion chamber (planar 2D array and Farmer-type) measurements. Measured doses were compared to calculated doses for a variety of cases, with and without the presence of inhomogeneities and beam-modifiers in 71 audits. Results demonstrate a systematic AAA underdose with an average discrepancy of 2.9 ± 1.2% when the AAA algorithm is implemented in regions distal from lung-tissue interfaces, when lateral beams are used with anthropomorphic phantoms. This systemic discrepancy was found for all Level III audits of facilities using the AAA algorithm. This discrepancy is not seen when identical measurements are compared for other common dose-calculation algorithms (average discrepancy -0.4 ± 1.7%), including the Acuros XB algorithm also available with the Eclipse TPS. For slab phantom geometries (Level II audits), with similar measurement points downstream from inhomogeneities this discrepancy is also not seen. PMID:25921329

  10. Transcriptome Profiling of the Green Alga Spirogyra pratensis (Charophyta) Suggests an Ancestral Role for Ethylene in Cell Wall Metabolism, Photosynthesis, and Abiotic Stress Responses1[OPEN

    PubMed Central

    2016-01-01

    It is well known that ethylene regulates a diverse set of developmental and stress-related processes in angiosperms, yet its roles in early-diverging embryophytes and algae are poorly understood. Recently, it was shown that ethylene functions as a hormone in the charophyte green alga Spirogyra pratensis. Since land plants evolved from charophytes, this implies conservation of ethylene as a hormone in green plants for at least 450 million years. However, the physiological role of ethylene in charophyte algae has remained unknown. To gain insight into ethylene responses in Spirogyra, we used mRNA sequencing to measure changes in gene expression over time in Spirogyra filaments in response to an ethylene treatment. Our analyses show that at the transcriptional level, ethylene predominantly regulates three processes in Spirogyra: (1) modification of the cell wall matrix by expansins and xyloglucan endotransglucosylases/hydrolases, (2) down-regulation of chlorophyll biosynthesis and photosynthesis, and (3) activation of abiotic stress responses. We confirmed that the photosynthetic capacity and chlorophyll content were reduced by an ethylene treatment and that several abiotic stress conditions could stimulate cell elongation in an ethylene-dependent manner. We also found that the Spirogyra transcriptome harbors only 10 ethylene-responsive transcription factor (ERF) homologs, several of which are regulated by ethylene. These results provide an initial understanding of the hormonal responses induced by ethylene in Spirogyra and help to reconstruct the role of ethylene in ancestral charophytes prior to the origin of land plants. PMID:27489312

  11. Transcriptome Profiling of the Green Alga Spirogyra pratensis (Charophyta) Suggests an Ancestral Role for Ethylene in Cell Wall Metabolism, Photosynthesis, and Abiotic Stress Responses.

    PubMed

    Van de Poel, Bram; Cooper, Endymion D; Van Der Straeten, Dominique; Chang, Caren; Delwiche, Charles F

    2016-09-01

    It is well known that ethylene regulates a diverse set of developmental and stress-related processes in angiosperms, yet its roles in early-diverging embryophytes and algae are poorly understood. Recently, it was shown that ethylene functions as a hormone in the charophyte green alga Spirogyra pratensis Since land plants evolved from charophytes, this implies conservation of ethylene as a hormone in green plants for at least 450 million years. However, the physiological role of ethylene in charophyte algae has remained unknown. To gain insight into ethylene responses in Spirogyra, we used mRNA sequencing to measure changes in gene expression over time in Spirogyra filaments in response to an ethylene treatment. Our analyses show that at the transcriptional level, ethylene predominantly regulates three processes in Spirogyra: (1) modification of the cell wall matrix by expansins and xyloglucan endotransglucosylases/hydrolases, (2) down-regulation of chlorophyll biosynthesis and photosynthesis, and (3) activation of abiotic stress responses. We confirmed that the photosynthetic capacity and chlorophyll content were reduced by an ethylene treatment and that several abiotic stress conditions could stimulate cell elongation in an ethylene-dependent manner. We also found that the Spirogyra transcriptome harbors only 10 ethylene-responsive transcription factor (ERF) homologs, several of which are regulated by ethylene. These results provide an initial understanding of the hormonal responses induced by ethylene in Spirogyra and help to reconstruct the role of ethylene in ancestral charophytes prior to the origin of land plants.

  12. Transcriptome Profiling of the Green Alga Spirogyra pratensis (Charophyta) Suggests an Ancestral Role for Ethylene in Cell Wall Metabolism, Photosynthesis, and Abiotic Stress Responses.

    PubMed

    Van de Poel, Bram; Cooper, Endymion D; Van Der Straeten, Dominique; Chang, Caren; Delwiche, Charles F

    2016-09-01

    It is well known that ethylene regulates a diverse set of developmental and stress-related processes in angiosperms, yet its roles in early-diverging embryophytes and algae are poorly understood. Recently, it was shown that ethylene functions as a hormone in the charophyte green alga Spirogyra pratensis Since land plants evolved from charophytes, this implies conservation of ethylene as a hormone in green plants for at least 450 million years. However, the physiological role of ethylene in charophyte algae has remained unknown. To gain insight into ethylene responses in Spirogyra, we used mRNA sequencing to measure changes in gene expression over time in Spirogyra filaments in response to an ethylene treatment. Our analyses show that at the transcriptional level, ethylene predominantly regulates three processes in Spirogyra: (1) modification of the cell wall matrix by expansins and xyloglucan endotransglucosylases/hydrolases, (2) down-regulation of chlorophyll biosynthesis and photosynthesis, and (3) activation of abiotic stress responses. We confirmed that the photosynthetic capacity and chlorophyll content were reduced by an ethylene treatment and that several abiotic stress conditions could stimulate cell elongation in an ethylene-dependent manner. We also found that the Spirogyra transcriptome harbors only 10 ethylene-responsive transcription factor (ERF) homologs, several of which are regulated by ethylene. These results provide an initial understanding of the hormonal responses induced by ethylene in Spirogyra and help to reconstruct the role of ethylene in ancestral charophytes prior to the origin of land plants. PMID:27489312

  13. The Effect of Internal Pressure on the Buckling Stress of Thin-Walled Circular Cylinders Under Torsion

    NASA Technical Reports Server (NTRS)

    Crate, Harold; Batdorf, S B; Baab, George W

    1944-01-01

    The results of a series of tests to determine the effect of internal pressure on the buckling load of a thin cylinder under an applied torque indicated that internal pressure raises the shear buckling stress. The experimental results were analyzed with the aid of previously developed theory and a simple interaction formula was derived. (author)

  14. Asymmetric processing of a substrate protein in sequential allosteric cycles of AAA+ nanomachines

    NASA Astrophysics Data System (ADS)

    Kravats, Andrea N.; Tonddast-Navaei, Sam; Bucher, Ryan J.; Stan, George

    2013-09-01

    Essential protein quality control includes mechanisms of substrate protein (SP) unfolding and translocation performed by powerful ring-shaped AAA+ (ATPases associated with various cellular activities) nanomachines. These SP remodeling actions are effected by mechanical forces imparted by AAA+ loops that protrude into the central channel. Sequential intra-ring allosteric motions, which underlie repetitive SP-loop interactions, have been proposed to comprise clockwise (CW), counterclockwise (CCW), or random (R) conformational transitions of individual AAA+ subunits. To probe the effect of these allosteric mechanisms on unfoldase and translocase functions, we perform Langevin dynamics simulations of a coarse-grained model of an all-alpha SP processed by the single-ring ClpY ATPase or by the double-ring p97 ATPase. We find that, in all three allosteric mechanisms, the SP undergoes conformational transitions along a common set of pathways, which reveals that the active work provided by the ClpY machine involves single loop-SP interactions. Nevertheless, the rates and yields of SP unfolding and translocation are controlled by mechanism-dependent loop-SP binding events, as illustrated by faster timescales of SP processing in CW allostery compared with CCW and R allostery. The distinct efficacy of allosteric mechanisms is due to the asymmetric collaboration of adjacent subunits, which involves CW-biased structural motions of AAA+ loops and results in CW-compatible torque applied onto the SP. Additional simulations of mutant ClpY rings, which render a subset of subunits catalytically-defective or reduce their SP binding affinity, reveal that subunit-based conformational transitions play the major role in SP remodeling. Based on these results we predict that the minimally functional AAA+ ring includes three active subunits, only two of which are adjacent.

  15. Asymmetric processing of a substrate protein in sequential allosteric cycles of AAA+ nanomachines.

    PubMed

    Kravats, Andrea N; Tonddast-Navaei, Sam; Bucher, Ryan J; Stan, George

    2013-09-28

    Essential protein quality control includes mechanisms of substrate protein (SP) unfolding and translocation performed by powerful ring-shaped AAA+ (ATPases associated with various cellular activities) nanomachines. These SP remodeling actions are effected by mechanical forces imparted by AAA+ loops that protrude into the central channel. Sequential intra-ring allosteric motions, which underlie repetitive SP-loop interactions, have been proposed to comprise clockwise (CW), counterclockwise (CCW), or random (R) conformational transitions of individual AAA+ subunits. To probe the effect of these allosteric mechanisms on unfoldase and translocase functions, we perform Langevin dynamics simulations of a coarse-grained model of an all-alpha SP processed by the single-ring ClpY ATPase or by the double-ring p97 ATPase. We find that, in all three allosteric mechanisms, the SP undergoes conformational transitions along a common set of pathways, which reveals that the active work provided by the ClpY machine involves single loop-SP interactions. Nevertheless, the rates and yields of SP unfolding and translocation are controlled by mechanism-dependent loop-SP binding events, as illustrated by faster timescales of SP processing in CW allostery compared with CCW and R allostery. The distinct efficacy of allosteric mechanisms is due to the asymmetric collaboration of adjacent subunits, which involves CW-biased structural motions of AAA+ loops and results in CW-compatible torque applied onto the SP. Additional simulations of mutant ClpY rings, which render a subset of subunits catalytically-defective or reduce their SP binding affinity, reveal that subunit-based conformational transitions play the major role in SP remodeling. Based on these results we predict that the minimally functional AAA+ ring includes three active subunits, only two of which are adjacent.

  16. Shear-stress-induced structural arrangement of water molecules in nanoscale Couette flow with slipping at wall boundary

    SciTech Connect

    Lin, Jau-Wen

    2014-08-07

    This study investigated the structuring of water molecules in a nanoscale Couette flow with the upper plate subjected to lateral forces with various magnitudes and water slipping against a metal wall. It was found that when the upper plate is subjected to a force, the water body deforms into a parallelepiped. Water molecules in the channel are then gradually arranged into lattice positions, creating a layered structure. The structural arrangement of water molecules is caused by the water molecules accommodating themselves to the increase in energy under the application of a lateral force on the moving plate. The ordering arrangement of water molecules increases the rotational degree of freedom, allowing the molecules to increase their Coulomb potential energy through polar rotation that accounts for the energy input through the upper plate. With a force continuously applied to the upper plate, the water molecules in contact with the upper plate move forward until slip between the water and upper plate occurs. The relation between the structural arrangement of water molecules, slip at the wall, and the shear force is studied. The relation between the slip and the locking/unlocking of water molecules to metal atoms is also studied.

  17. Contrasting strategies used by lichen microalgae to cope with desiccation-rehydration stress revealed by metabolite profiling and cell wall analysis.

    PubMed

    Centeno, Danilo C; Hell, Aline F; Braga, Marcia R; Del Campo, Eva M; Casano, Leonardo M

    2016-05-01

    Most lichens in general, and their phycobionts in particular, are desiccation tolerant, but their mechanisms of desiccation tolerance (DT) remain obscure. The physiological responses and cell wall features of two putatively contrasting lichen-forming microalgae, Trebouxia sp. TR9 (TR9), isolated from Ramalina farinacea (adapted to frequent desiccation-rehydration cycles), and Coccomyxa solorina-saccatae (Csol), obtained from Solorina saccata (growing in usually humid limestone crevices, subjected to seasonal dry periods) was characterized. Microalgal cultures were desiccated under 25%-30% RH and then rehydrated. Under these conditions, RWC and ψw decreased faster and simultaneously during dehydration in Csol, whereas TR9 maintained its ψw until 70% RWC. The metabolic profile indicated that polyols played a key role in DT of both microalgae. However, TR9 constitutively accumulated higher amounts of polyols, whereas Csol induced the polyol synthesis under desiccation-rehydration. Csol also accumulated ascorbic acid, while TR9 synthesized protective raffinose-family oligosaccharides (RFOs) and increased its content of phenolics. Additionally, TR9 exhibited thicker and qualitatively different cell wall and extracellular polymeric layer compared with Csol, indicating higher water retention capability. The findings were consistent with the notion that lichen microalgae would have evolved distinct strategies to cope with desiccation-rehydration stress in correspondence with the water regime of their respective habitats. PMID:26914009

  18. FvBck1, a component of cell wall integrity MAP kinase pathway, is required for virulence and oxidative stress response in sugarcane Pokkah Boeng pathogen

    PubMed Central

    Zhang, Chengkang; Wang, Jianqiang; Tao, Hong; Dang, Xie; Wang, Yang; Chen, Miaoping; Zhai, Zhenzhen; Yu, Wenying; Xu, Liping; Shim, Won-Bo; Lu, Guodong; Wang, Zonghua

    2015-01-01

    Fusarium verticillioides (formerly F. moniliforme) is suggested as one of the causal agents of Pokkah Boeng, a serious disease of sugarcane worldwide. Currently, detailed molecular and physiological mechanism of pathogenesis is unknown. In this study, we focused on cell wall integrity MAPK pathway as one of the potential signaling mechanisms associated with Pokkah Boeng pathogenesis. We identified FvBCK1 gene that encodes a MAP kinase kinase kinase homolog and determined that it is not only required for growth, micro- and macro-conidia production, and cell wall integrity but also for response to osmotic and oxidative stresses. The deletion of FvBCK1 caused a significant reduction in virulence and FB1 production, a possibly carcinogenic mycotoxin produced by the fungus. Moreover, we found the expression levels of three genes, which are known to be involved in superoxide scavenging, were down regulated in the mutant. We hypothesized that the loss of superoxide scavenging capacity was one of the reasons for reduced virulence, but overexpression of catalase or peroxidase gene failed to restore the virulence defect in the deletion mutant. When we introduced Magnaporthe oryzae MCK1 into the FvBck1 deletion mutant, while certain phenotypes were restored, the complemented strain failed to gain full virulence. In summary, FvBck1 plays a diverse role in F. verticillioides, and detailed investigation of downstream signaling pathways will lead to a better understanding of how this MAPK pathway regulates Pokkah Boeng on sugarcane. PMID:26500635

  19. Release of Bacterial Spores from the Inner Walls of a Stainless Steel Cup Subjected to Thermal Stresses and Mechanical Shock

    NASA Technical Reports Server (NTRS)

    Wolochow, H.; Chatigny, M.; Hebert, J.

    1973-01-01

    The release and fallout of particulates from surfaces afforded thermal or impact stress is of concern for control of contamination of Mars from planetary landing vehicles. A metal vessel contaminated by aerosols of spores was used as a model system and the fallout of spores as affected by various mechanisms was examined. Thermal stresses simulating those expected on the Mars lander dislodged approximately .01% of the aerosol deposited surface burden as did a landing shock of 8 to 10G deceleration. Spores imprinted by finger or swab contact yielded similar results. In all cases where repeated cycling of temperature, motion, or shock were employed the majority of fallout occurred in the first cycle. Particles released from the surface were predominantly in the size range 1 to 5 microns.

  20. Side-wall gas 'creep' and 'thermal stress convection' in microgravity experiments on film growth by vapor transport

    NASA Technical Reports Server (NTRS)

    Rosner, Daniel E.

    1989-01-01

    While 'no-slip' boundary conditions and the Navier-Stokes equations of continuum fluid mechanics have served the vapor transport community well until now, it is pointed out that transport conditions within highly nonisothermal ampoules are such that the nonisothermal side walls 'drive' the dominant convective flow, and the familiar Stokes-Fourier-Fick laws governing the molecular fluxes of momentum, energy, and (species) mass in the 'continuum' field equations will often prove to be inadequate, even at Knudsen numbers as small as 0.001. The implications of these interesting gas kinetic phenomena under microgravity conditions, and even under 'earth-bound' experimental conditions, are outlined here, along with a tractable approach to their systematic treatment.

  1. Cell wall integrity

    PubMed Central

    Pogorelko, Gennady; Lionetti, Vincenzo; Bellincampi, Daniela; Zabotina, Olga

    2013-01-01

    The plant cell wall, a dynamic network of polysaccharides and glycoproteins of significant compositional and structural complexity, functions in plant growth, development and stress responses. In recent years, the existence of plant cell wall integrity (CWI) maintenance mechanisms has been demonstrated, but little is known about the signaling pathways involved, or their components. Examination of key mutants has shed light on the relationships between cell wall remodeling and plant cell responses, indicating a central role for the regulatory network that monitors and controls cell wall performance and integrity. In this review, we present a short overview of cell wall composition and discuss post-synthetic cell wall modification as a valuable approach for studying CWI perception and signaling pathways. PMID:23857352

  2. A Generalized Wall Function

    NASA Technical Reports Server (NTRS)

    Shih, Tsan-Hsing; Povinelli, Louis A.; Liu, Nan-Suey; Potapczuk, Mark G.; Lumley, J. L.

    1999-01-01

    The asymptotic solutions, described by Tennekes and Lumley (1972), for surface flows in a channel, pipe or boundary layer at large Reynolds numbers are revisited. These solutions can be extended to more complex flows such as the flows with various pressure gradients, zero wall stress and rough surfaces, etc. In computational fluid dynamics (CFD), these solutions can be used as the boundary conditions to bridge the near-wall region of turbulent flows so that there is no need to have the fine grids near the wall unless the near-wall flow structures are required to resolve. These solutions are referred to as the wall functions. Furthermore, a generalized and unified law of the wall which is valid for whole surface layer (including viscous sublayer, buffer layer and inertial sublayer) is analytically constructed. The generalized law of the wall shows that the effect of both adverse and favorable pressure gradients on the surface flow is very significant. Such as unified wall function will be useful not only in deriving analytic expressions for surface flow properties but also bringing a great convenience for CFD methods to place accurate boundary conditions at any location away from the wall. The extended wall functions introduced in this paper can be used for complex flows with acceleration, deceleration, separation, recirculation and rough surfaces.

  3. Carboxylated multi-walled carbon nanotubes aggravated biochemical and subcellular damages in leaves of broad bean (Vicia faba L.) seedlings under combined stress of lead and cadmium.

    PubMed

    Wang, Chengrun; Liu, Haitao; Chen, Jinyun; Tian, Yuan; Shi, Jian; Li, Dongdong; Guo, Chen; Ma, Qingping

    2014-06-15

    Increasing industrialization of multi-walled carbon nanotubes (MWCNTs) would inevitably lead to their release into the environment and combination with heavy metals. However, studies concerning the combined effects of MWCNTs and heavy metals on agricultural crops are limited. Herein, effects and mechanisms of carboxylated MWCNTs (MWCNTs-COOH) (2.5, 5 and 10mg/L) and their combination with 20 μM Pb and 5 μM Cd (shortened as Pb+Cd) on Vicia faba L. seedlings were investigated. The results showed that the MWCNTs-COOH disturbed the imbalance of nutrient elements, and caused oxidative stress and damages in the leaves. Additionally, the combination of MWCNTs-COOH with Pb+Cd resulted in enrichment of Pb and Cd, and deterioration of oxidative damages compared with the treatments of MWCNTs-COOH or Pb+Cd alone in the leaves. As the results, the concentrations of MWCNTs-COOH not only caused oxidative stress, but also exacerbated the biochemical and subcellular damages due to the treatment of Pb+Cd in the leaves. It also suggests that persistent release of MWCNTs-COOH into the environment may cause phytotoxicity and aggravate ecological risks due to combination of heavy metals.

  4. Single-Walled Carbon Nanotubes Induce Fibrogenic Effect by Disturbing Mitochondrial Oxidative Stress and Activating NF-κB Signaling

    PubMed Central

    He, Xiaoqing; Young, Shih-Houng; Fernback, Joseph E; Ma, Qiang

    2015-01-01

    Single-walled carbon nanotubes (SWCNTs) are newly discovered material of crystalline carbon that forms single-carbon layer cylinders with nanometer diameters and varying lengths. Although SWCNTs are potentially suitable for a range of novel applications, their extremely small size, fiber-like shape, large surface area, and unique surface chemistry raise potential hazard to humans, including lung toxicity and fibrosis. The molecular mechanisms by which SWCNTs cause lung damage remain elusive. Here we show that SWCNTs dose and time-dependently caused toxicity in cultured human bronchial epithelial (BEAS-2B), alveolar epithelial (A549), and lung fibroblast (WI38) cells. At molecular levels, SWCNTs induced significant mitochondrial depolarization and ROS production at subtoxic doses. SWCNTs stimulated the secretion of proinflammatory cytokines and chemokines TNFα, IL-1β, IL-6, IL-10 and MCP1 from macrophages (Raw 264.7), which was attributed to the activation of the canonical signaling pathway of NF-κB by SWCNT. Finally, SWCNTs stimulated profibrogenic growth factors TGFβ1 production and fibroblast-to-myofibroblast-transformation. These results indicate that SWCNTs has a potential to induce human lung damage and fibrosis by damaging mitochondria, generating ROS, and stimulating production of proinflammatory and profibrogenic cytokines and growth factors. PMID:26702365

  5. In vivo monitoring of oxidative burst on aloe under salinity stress using hemoglobin and single-walled carbon nanotubes modified carbon fiber ultramicroelectrode.

    PubMed

    Ren, Qiong-Qiong; Yuan, Xiao-Jun; Huang, Xiao-Rong; Wen, Wei; Zhao, Yuan-Di; Chen, Wei

    2013-12-15

    Single-walled carbon nanotubes (SWCNTs) and hemoglobin (Hb) modified carbon fiber ultramicroelectrode (CFUME) were employed to construct a direct electron transfer based in vivo H2O2 sensor. At the low working potential of -0.1 V, Hb/SWCNTs/CFUME showed a dynamic range up to 0.405 mM with a low detection limit of 4 μM (S/N=3) and a high sensitivity of 1.07 log(A) log(M)(-1) cm(-2). The apparent Michaelis-Menten constant (Km, app) was estimated to be as low as 1.35 mM. Due to the extremely small dimension and low working potential, Hb/SWCNTs/CFUME could give directly amperometric in vivo monitoring of H2O2 in aloe leaves with salt stress for 19.5h without the requirement of complex data processing and extra surface coatings to avoid interferences. The sharp increase of H2O2 level in aloe leaves with salt stress was clearly observed using Hb/SWCNTs/CFUME from 12.5 h, while in the aloe without salt stress, H2O2 level remained stable in the whole measurement. For further confirming the in vivo response of Hb/SWCNTs/CFUME, catalase (CAT) was injected into the spot adjacent to the sensor and caused rapid current decrease, which suggests the scavenging of H2O2. These results indicate that Hb/SWCNTs/CFUME can be a powerful tool for in vivo investigation of ROS.

  6. SFM-FDTD analysis of triangular-lattice AAA structure: Parametric study of the TEM mode

    NASA Astrophysics Data System (ADS)

    Hamidi, M.; Chemrouk, C.; Belkhir, A.; Kebci, Z.; Ndao, A.; Lamrous, O.; Baida, F. I.

    2014-05-01

    This theoretical work reports a parametric study of enhanced transmission through annular aperture array (AAA) structure arranged in a triangular lattice. The effect of the incidence angle in addition to the inner and outer radii values on the evolution of the transmission spectra is carried out. To this end, a 3D Finite-Difference Time-Domain code based on the Split Field Method (SFM) is used to calculate the spectral response of the structure for any angle of incidence. In order to work through an orthogonal unit cell which presents the advantage to reduce time and space of computation, special periodic boundary conditions are implemented. This study provides a new modeling of AAA structures useful for producing tunable ultra-compact devices.

  7. Substituent effects in double-helical hydrogen-bonded AAA-DDD complexes.

    PubMed

    Wang, Hong-Bo; Mudraboyina, Bhanu P; Wisner, James A

    2012-01-27

    Two series of DDD and AAA hydrogen-bond arrays were synthesized that form triply-hydrogen-bonded double-helical complexes when combined in CDCl(3) solution. Derivatization of the DDD arrays with electron-withdrawing groups increases the complex association constants by up to a factor of 30 in those arrays examined. Derivatization of the AAA arrays with electron donating substituents reveals a similar magnitude effect on the complex stabilities. The effect of substitution on both types of arrays are modeled quite satisfactorily (R(2) > 0.96 in all cases) as free energy relationships with respect to the sums of their Hammett substituent constants. In all, the complex stabilities can be manipulated over more than three orders of magnitude (>20 kJ mol(-1)) using this type of modification.

  8. Dosimetric comparison of Acuros XB, AAA, and XVMC in stereotactic body radiotherapy for lung cancer

    SciTech Connect

    Tsuruta, Yusuke; Nakata, Manabu; Higashimura, Kyoji; Nakamura, Mitsuhiro Matsuo, Yukinori; Monzen, Hajime; Mizowaki, Takashi; Hiraoka, Masahiro

    2014-08-15

    Purpose: To compare the dosimetric performance of Acuros XB (AXB), anisotropic analytical algorithm (AAA), and x-ray voxel Monte Carlo (XVMC) in heterogeneous phantoms and lung stereotactic body radiotherapy (SBRT) plans. Methods: Water- and lung-equivalent phantoms were combined to evaluate the percentage depth dose and dose profile. The radiation treatment machine Novalis (BrainLab AG, Feldkirchen, Germany) with an x-ray beam energy of 6 MV was used to calculate the doses in the composite phantom at a source-to-surface distance of 100 cm with a gantry angle of 0°. Subsequently, the clinical lung SBRT plans for the 26 consecutive patients were transferred from the iPlan (ver. 4.1; BrainLab AG) to the Eclipse treatment planning systems (ver. 11.0.3; Varian Medical Systems, Palo Alto, CA). The doses were then recalculated with AXB and AAA while maintaining the XVMC-calculated monitor units and beam arrangement. Then the dose-volumetric data obtained using the three different radiation dose calculation algorithms were compared. Results: The results from AXB and XVMC agreed with measurements within ±3.0% for the lung-equivalent phantom with a 6 × 6 cm{sup 2} field size, whereas AAA values were higher than measurements in the heterogeneous zone and near the boundary, with the greatest difference being 4.1%. AXB and XVMC agreed well with measurements in terms of the profile shape at the boundary of the heterogeneous zone. For the lung SBRT plans, AXB yielded lower values than XVMC in terms of the maximum doses of ITV and PTV; however, the differences were within ±3.0%. In addition to the dose-volumetric data, the dose distribution analysis showed that AXB yielded dose distribution calculations that were closer to those with XVMC than did AAA. Means ± standard deviation of the computation time was 221.6 ± 53.1 s (range, 124–358 s), 66.1 ± 16.0 s (range, 42–94 s), and 6.7 ± 1.1 s (range, 5–9 s) for XVMC, AXB, and AAA, respectively. Conclusions: In the

  9. The Drug Diazaborine Blocks Ribosome Biogenesis by Inhibiting the AAA-ATPase Drg1*

    PubMed Central

    Loibl, Mathias; Klein, Isabella; Prattes, Michael; Schmidt, Claudia; Kappel, Lisa; Zisser, Gertrude; Gungl, Anna; Krieger, Elmar; Pertschy, Brigitte; Bergler, Helmut

    2014-01-01

    The drug diazaborine is the only known inhibitor of ribosome biogenesis and specifically blocks large subunit formation in eukaryotic cells. However, the target of this drug and the mechanism of inhibition were unknown. Here we identify the AAA-ATPase Drg1 as a target of diazaborine. Inhibitor binding into the second AAA domain of Drg1 requires ATP loading and results in inhibition of ATP hydrolysis in this site. As a consequence the physiological activity of Drg1, i.e. the release of Rlp24 from pre-60S particles, is blocked, and further progression of cytoplasmic preribosome maturation is prevented. Our results identify the first target of an inhibitor of ribosome biogenesis and provide the mechanism of inhibition of a key step in large ribosomal subunit formation. PMID:24371142

  10. Indications for and outcome of open AAA repair in the endovascular era.

    PubMed

    Wieker, Carola M; Spazier, Max; Böckler, Dittmar

    2016-04-01

    The benefits, safety and efficacy of endovascular aortic aneurysm repair (EVAR) is well documented and intensively reported in multiple randomized trials and meta-analysis. Therefore, EVAR became the first choice of abdominal aortic aneurysms (AAA) treatment in almost 70-100% of patients. Consecutively, open repair (OR) is performed less frequently in morphologically preselected patients. Anatomical condition remains the most important factor for indication for OR. Especially unfavorable intrarenal landing zone based on difficult neck anatomy like very short neck or excessive neck angulation is still the most predictive factor. Furthermore, patients presenting additional iliac aneurysms, aortoiliac occlusive disease or variations of renal arteries are recommended for OR. Randomized trials like EVAR 1, DREAM and OVER from the year 2004/2005 and 2009 showed lower 30-day mortality rates in EVAR compared to OR. However, the late mortality rates after two years became equal in both treatment options. Furthermore, reinterventions after EVAR occur more frequently than after OR. Analysis from our own data showed a higher 30-day mortality in the patients who underwent OR in the endovascular era (15% vs. 2.5%), however the number of emergency open AAA repair because of ruptured aneurysms was much higher in the endovascular era (32.5% vs. 5%). In conclusion, treatment of AAA has changed in the past decade. Nevertheless OR of AAA still remains as a safe and durable method in experienced surgeons, even in the endovascular era. High volume centres are needed to offer the best patients' treatment providing the best postoperative outcome. Therefore OR must remain a part of fellowship training in the future. To decide the best treatment option many facts like patients' fitness and preference or finally the anatomic suitability for endovascular repair have to be considered. PMID:26822580

  11. Structures of the double-ring AAA ATPase Pex1-Pex6 involved in peroxisome biogenesis.

    PubMed

    Tan, Dongyan; Blok, Neil B; Rapoport, Tom A; Walz, Thomas

    2016-03-01

    The Pex1 and Pex6 proteins are members of the AAA family of ATPases and are involved in peroxisome biogenesis. Recently, cryo-electron microscopy structures of the Pex1-Pex6 complex in different nucleotide states have been determined. This Structural Snapshot describes the structural features of the complex and their implications for its function, as well as questions that still await answers.

  12. Roles of the N domain of the AAA+ Lon protease in substrate recognition, allosteric regulation and chaperone activity.

    PubMed

    Wohlever, Matthew L; Baker, Tania A; Sauer, Robert T

    2014-01-01

    Degron binding regulates the activities of the AAA+ Lon protease in addition to targeting proteins for degradation. The sul20 degron from the cell-division inhibitor SulA is shown here to bind to the N domain of Escherichia coli Lon, and the recognition site is identified by cross-linking and scanning for mutations that prevent sul20-peptide binding. These N-domain mutations limit the rates of proteolysis of model sul20-tagged substrates and ATP hydrolysis by an allosteric mechanism. Lon inactivation of SulA in vivo requires binding to the N domain and robust ATP hydrolysis but does not require degradation or translocation into the proteolytic chamber. Lon-mediated relief of proteotoxic stress and protein aggregation in vivo can also occur without degradation but is not dependent on robust ATP hydrolysis. In combination, these results demonstrate that Lon can function as a protease or a chaperone and reveal that some of its ATP-dependent biological activities do not require translocation.

  13. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 1: Pressure distribution. Part 2: Wall shear stress. Part 3: Simplified formulas for the prediction of surface pressures and skin friction

    NASA Technical Reports Server (NTRS)

    Adamson, T. C., Jr.; Liou, M. S.; Messiter, A. F.

    1980-01-01

    An asymptotic description is derived for the interaction between a shock wave and a turbulent boundary layer in transonic flow, for a particular limiting case. The dimensionless difference between the external flow velocity and critical sound speed is taken to be much smaller than one, but large in comparison with the dimensionless friction velocity. The basic results are derived for a flat plate, and corrections for longitudinal wall curvature and for flow in a circular pipe are also shown. Solutions are given for the wall pressure distribution and the shape of the shock wave. Solutions for the wall shear stress are obtained, and a criterion for incipient separation is derived. Simplified solutions for both the wall pressure and skin friction distributions in the interaction region are given. These results are presented in a form suitable for use in computer programs.

  14. Characterization of ATPase activity of the AAA ARC from Bifidobacterium longum subsp. infantis.

    PubMed

    Guzmán-Rodríguez, Mabel; de la Rosa, Ana Paulina Barba; Santos, Leticia

    2015-01-01

    Bifidobacteria are considered to be probiotics that exist in the large intestine and are helpful to maintain human health. Oral administration of bifidobacteria may be effective in improving the intestinal flora and environment, stimulating the immune response and possibly preventing cancer. However, for consistent and positive results, further well-controlled studies are urgently needed to describe the basic mechanisms of this microorganism. Analysis of the proteasome-lacking Bifidobacterium longum genome reveals that it possesses a gene, IPR003593 AAA ATPase core, which codes a 56 kDa protein containing one AAA ATPase domain. Phylogenetic classification made by CLANS, positioned this sequence into the ARC divergent branch of the AAA ATPase family of proteins. N-terminal analysis of the sequence indicates this protein is closely related to other ATPases such as the Rhodococcus erythropolis ARC, Archaeoglobus fulgidus PAN, Mycobacterium tuberculosis Mpa and the human proteasomal Rpt1 subunit. This gene was cloned, the full-length recombinant protein was overexpressed in Escherichia coli, purified as a high-molecular size complex and named Bl-ARC. Enzymatic characterization showed that Bl-ARC ATPase is active, Mg(+2)-dependent and sensitive to N-ethylmaleimide. Gene organization positions bl-arc in a region flanked by a cluster of genes that includes pup, dop and pafA genes. These findings point to a possible function as a chaperone in the degradation pathway via pupylation.

  15. An atypical AAA+ ATPase assembly controls efficient transposition through DNA remodeling and transposase recruitment

    PubMed Central

    Arias-Palomo, Ernesto; Berger, James M.

    2015-01-01

    Transposons are ubiquitous genetic elements that drive genome rearrangements, evolution, and the spread of infectious disease and drug-resistance. Many transposons, such as Mu, Tn7 and IS21, require regulatory AAA+ ATPases for function. We use x-ray crystallography and cryo-electron microscopy to show that the ATPase subunit of IS21, IstB, assembles into a clamshell-shaped decamer that sandwiches DNA between two helical pentamers of ATP-associated AAA+ domains, sharply bending the duplex into a 180° U-turn. Biochemical studies corroborate key features of the structure, and further show that the IS21 transposase, IstA, recognizes the IstB•DNA complex and promotes its disassembly by stimulating ATP hydrolysis. Collectively, these studies reveal a distinct manner of higher-order assembly and client engagement by a AAA+ ATPase and suggest a mechanistic model where IstB binding and subsequent DNA bending primes a selected insertion site for efficient transposition. PMID:26276634

  16. Structural basis for DNA-mediated allosteric regulation facilitated by the AAA+ module of Lon protease.

    PubMed

    Lee, Alan Yueh-Luen; Chen, Yu-Da; Chang, Yu-Yung; Lin, Yu-Ching; Chang, Chi-Fon; Huang, Shing-Jong; Wu, Shih-Hsiung; Hsu, Chun-Hua

    2014-02-01

    Lon belongs to a unique group of AAA+ proteases that bind DNA. However, the DNA-mediated regulation of Lon remains elusive. Here, the crystal structure of the α subdomain of the Lon protease from Brevibacillus thermoruber (Bt-Lon) is presented, together with biochemical data, and the DNA-binding mode is delineated, showing that Arg518, Arg557 and Arg566 play a crucial role in DNA binding. Electrostatic interactions contributed by arginine residues in the AAA+ module are suggested to be important to DNA binding and allosteric regulation of enzymatic activities. Intriguingly, Arg557, which directly binds DNA in the α subdomain, has a dual role in the negative regulation of ATPase stimulation by DNA and in the domain-domain communication in allosteric regulation of Bt-Lon by substrate. In conclusion, structural and biochemical evidence is provided to show that electrostatic interaction in the AAA+ module is important for DNA binding by Lon and allosteric regulation of its enzymatic activities by DNA and substrate.

  17. Functional characterization of fidgetin, an AAA-family protein mutated in fidget mice

    SciTech Connect

    Yang Yan; Mahaffey, Connie L.; Berube, Nathalie; Nystuen, Arne; Frankel, Wayne N. . E-mail: wnf@jax.org

    2005-03-10

    The mouse fidget mutation is an autosomal recessive mutation that renders reduced or absent semicircular canals, microphthalmia, and various skeletal abnormalities to affected mice. We previously identified the defective gene which encodes fidgetin, a new member of the ATPases associated with diverse cellular activities (AAA proteins). Here, we report on the subcellular localization of fidgetin as well as that of two closely related proteins, fidgetin-like 1 and fidgetin-like 2. Epitope-tagging and immunostaining revealed that both fidgetin and fidgetin-like 2 were predominantly localized to the nucleus, whereas fidgetin-like 1 was both nuclear and cytoplasmic. Furthermore, deletion studies identified a putative bipartite nuclear localization signal in the middle portion of the fidgetin protein. Since AAA proteins are known to form functional hetero- or homo-hexamers, we used reciprocal immunoprecipitation to examine the potential interaction among these proteins. We found that fidgetin interacted with itself and this specific interaction was abolished when either the N- or C-terminus of the protein was truncated. Taken together, our results suggest that fidgetin is a nuclear AAA-family protein with the potential to form homo-oligomers, thus representing the first step towards the elucidation of fidgetin's cellular function and the disease mechanism in fidget mutant mice.

  18. Molecular snapshots of the Pex1/6 AAA+ complex in action

    PubMed Central

    Ciniawsky, Susanne; Grimm, Immanuel; Saffian, Delia; Girzalsky, Wolfgang; Erdmann, Ralf; Wendler, Petra

    2015-01-01

    The peroxisomal proteins Pex1 and Pex6 form a heterohexameric type II AAA+ ATPase complex, which fuels essential protein transport across peroxisomal membranes. Mutations in either ATPase in humans can lead to severe peroxisomal disorders and early death. We present an extensive structural and biochemical analysis of the yeast Pex1/6 complex. The heterohexamer forms a trimer of Pex1/6 dimers with a triangular geometry that is atypical for AAA+ complexes. While the C-terminal nucleotide-binding domains (D2) of Pex6 constitute the main ATPase activity of the complex, both D2 harbour essential substrate-binding motifs. ATP hydrolysis results in a pumping motion of the complex, suggesting that Pex1/6 function involves substrate translocation through its central channel. Mutation of the Walker B motif in one D2 domain leads to ATP hydrolysis in the neighbouring domain, giving structural insights into inter-domain communication of these unique heterohexameric AAA+ assemblies. PMID:26066397

  19. Functional characterization of fidgetin, an AAA-family protein mutated in fidget mice.

    PubMed

    Yang, Yan; Mahaffey, Connie L; Bérubé, Nathalie; Nystuen, Arne; Frankel, Wayne N

    2005-03-10

    The mouse fidget mutation is an autosomal recessive mutation that renders reduced or absent semicircular canals, microphthalmia, and various skeletal abnormalities to affected mice. We previously identified the defective gene which encodes fidgetin, a new member of the ATPases associated with diverse cellular activities (AAA proteins). Here, we report on the subcellular localization of fidgetin as well as that of two closely related proteins, fidgetin-like 1 and fidgetin-like 2. Epitope-tagging and immunostaining revealed that both fidgetin and fidgetin-like 2 were predominantly localized to the nucleus, whereas fidgetin-like 1 was both nuclear and cytoplasmic. Furthermore, deletion studies identified a putative bipartite nuclear localization signal in the middle portion of the fidgetin protein. Since AAA proteins are known to form functional hetero- or homo-hexamers, we used reciprocal immunoprecipitation to examine the potential interaction among these proteins. We found that fidgetin interacted with itself and this specific interaction was abolished when either the N- or C-terminus of the protein was truncated. Taken together, our results suggest that fidgetin is a nuclear AAA-family protein with the potential to form homo-oligomers, thus representing the first step towards the elucidation of fidgetin's cellular function and the disease mechanism in fidget mutant mice.

  20. [Calculation of the peak systolic wall stress at the equator of the left ventricle by coupled M mode echo and pressure recordings].

    PubMed

    Drobinski, G; Fechner, J; Eugène, M; Evans, J I; Béjean-Lebuisson, A; Leighton, R F; Grosgogeat, Y

    1983-11-01

    The peak systolic wall stress at the equator of the left ventricle (sigma max) is the maximum load that the myocardial fibres bear during contraction. It is an index of the adaptation of the left ventricle to cardiac disease, and, when elevated, it indicates cardiac decompensation. sigma max was calculated by coupled M mode echo-LV pressure recordings in 51 cases: 11 patients without LV disease, 14 patients with aortic stenosis (AS), 14 patients with aortic incompetence (AI), 7 patients with severe mitral incompetence (MI) and 5 patients with cardiomyopathy with dilatation (CMP). sigma max was calculated from Mirsky's formula, the length of the long axis being deduced from the short axis and the diastolic:systolic ratio of these two axes from ventriculography. The normal value of sigma max by this method is 220 dynes 10(3)/cm2 +/- 30 with an upper limit of normal of 280 dynes 10(3)/cm2. sigma max was normal in patients with AS and AI, and increased in the cases of MI and CMP, in positive correlation with LV volume (r = 0,47) and the shape of the LV (long:short axis ratio). No correlations were found between sigma max and maximum LV pressure. The relatively low values of sigma max compared to the results obtained from coupled echo-angio recordings are partly due to the thick walled LV model and, to a large extent, to the lower values of short axis when measured by echo compared to angiography.(ABSTRACT TRUNCATED AT 250 WORDS)

  1. Large-scale proteomic analysis of the grapevine leaf apoplastic fluid reveals mainly stress-related proteins and cell wall modifying enzymes

    PubMed Central

    2013-01-01

    Background The extracellular space or apoplast forms a path through the whole plant and acts as an interface with the environment. The apoplast is composed of plant cell wall and space within which apoplastic fluid provides a means of delivering molecules and facilitates intercellular communications. However, the apoplastic fluid extraction from in planta systems remains challenging and this is particularly true for grapevine (Vitis vinifera L.), a worldwide-cultivated fruit plant. Large-scale proteomic analysis reveals the protein content of the grapevine leaf apoplastic fluid and the free interactive proteome map considerably facilitates the study of the grapevine proteome. Results To obtain a snapshot of the grapevine apoplastic fluid proteome, a vacuum-infiltration-centrifugation method was optimized to collect the apoplastic fluid from non-challenged grapevine leaves. Soluble apoplastic protein patterns were then compared to whole leaf soluble protein profiles by 2D-PAGE analyses. Subsequent MALDI-TOF/TOF mass spectrometry of tryptically digested protein spots was used to identify proteins. This large-scale proteomic analysis established a well-defined proteomic map of whole leaf and leaf apoplastic soluble proteins, with 223 and 177 analyzed spots, respectively. All data arising from proteomic, MS and MS/MS analyses were deposited in the public database world-2DPAGE. Prediction tools revealed a high proportion of (i) classical secreted proteins but also of non-classical secreted proteins namely Leaderless Secreted Proteins (LSPs) in the apoplastic protein content and (ii) proteins potentially involved in stress reactions and/or in cell wall metabolism. Conclusions This approach provides free online interactive reference maps annotating a large number of soluble proteins of the whole leaf and the apoplastic fluid of grapevine leaf. To our knowledge, this is the first detailed proteome study of grapevine apoplastic fluid providing a comprehensive overview of

  2. Thin film strain transducer. [in-flight measurement of stress or strain in walls of high altitude balloons

    NASA Technical Reports Server (NTRS)

    Rand, J. L.

    1981-01-01

    Previous attempts to develop an appropriate sensor for measuring the stress or strain of high altitude balloons during flight are reviewed as well as the various conditions that must be met by such a device. The design, development and calibration of a transducer which promises to satisfy the necessary design constraints are described. The thin film strain transducer has a low effective modulus so as not to interfere with the strain that would naturally occur in the balloon. In addition, the transducer has a high sensitivity to longitudinal strain (7.216 mV/V/unit strain) which is constant for all temperature from room temperature to -80 C and all strains from 5 percent compression to 10 percent tensile strain. At the same time, the sensor is relatively insensitive (0.27 percent) to transverse forces. The device has a standard 350 ohm impedance which is compatible with available bridge balance, amplification and telemetry instrumentation now available for balloon flight. Recommendations are included for improved coatings to provide passive thermal control as well as model, tethered and full scale flight testing.

  3. Structural Insights into the Unusually Strong ATPase Activity of the AAA Domain of the Caenorhabditis elegans Fidgetin-like 1 (FIGL-1) Protein*

    PubMed Central

    Peng, Wentao; Lin, Zhijie; Li, Weirong; Lu, Jing; Shen, Yuequan; Wang, Chunguang

    2013-01-01

    The FIGL-1 (fidgetin like-1) protein is a homolog of fidgetin, a protein whose mutation leads to multiple developmental defects. The FIGL-1 protein contains an AAA (ATPase associated with various activities) domain and belongs to the AAA superfamily. However, the biological functions and developmental implications of this protein remain unknown. Here, we show that the AAA domain of the Caenorhabditis elegans FIGL-1 protein (CeFIGL-1-AAA), in clear contrast to homologous AAA domains, has an unusually high ATPase activity and forms a hexamer in solution. By determining the crystal structure of CeFIGL-1-AAA, we found that the loop linking helices α9 and α10 folds into the short helix α9a, which has an acidic surface and interacts with a positively charged surface of the neighboring subunit. Disruption of this charge interaction by mutagenesis diminishes both the ATPase activity and oligomerization capacity of the protein. Interestingly, the acidic residues in helix α9a of CeFIGL-1-AAA are not conserved in other homologous AAA domains that have relatively low ATPase activities. These results demonstrate that the sequence of CeFIGL-1-AAA has adapted to establish an intersubunit charge interaction, which contributes to its strong oligomerization and ATPase activity. These unique properties of CeFIGL-1-AAA distinguish it from other homologous proteins, suggesting that CeFIGL-1 may have a distinct biological function. PMID:23979136

  4. Determination of uptake, accumulation, and stress effects in corn (Zea mays L.) grown in single-wall carbon nanotube contaminated soil.

    PubMed

    Cano, Amanda M; Kohl, Kristina; Deleon, Sabrina; Payton, Paxton; Irin, Fahmida; Saed, Mohammad; Shah, Smit Alkesh; Green, Micah J; Cañas-Carrell, Jaclyn E

    2016-06-01

    Single-wall carbon nanotubes (SWNTs) are projected to increase in usage across many industries. Two studies were conducted using Zea L. (corn) seeds exposed to SWNT spiked soil for 40 d. In Study 1, corn was exposed to various SWNT concentrations (0, 10, and 100 mg/kg) with different functionalities (non-functionalized, OH-functionalized, or surfactant stabilized). A microwave induced heating method was used to determine SWNTs accumulated mostly in roots (0-24 μg/g), with minimal accumulation in stems and leaves (2-10 μg/g) with a limit of detection at 0.1 μg/g. Uptake was not functional group dependent. In Study 2, corn was exposed to 10 mg/kg SWNTs (non-functionalized or COOH-functionalized) under optimally grown or water deficit conditions. Plant physiological stress was determined by the measurement of photosynthetic rate throughout Study 2. No significant differences were seen between control and SWNT treatments. Considering the amount of SWNTs accumulated in corn roots, further studies are needed to address the potential for SWNTs to enter root crop species (i.e., carrots), which could present a significant pathway for human dietary exposure. PMID:26966810

  5. Determination of uptake, accumulation, and stress effects in corn (Zea mays L.) grown in single-wall carbon nanotube contaminated soil.

    PubMed

    Cano, Amanda M; Kohl, Kristina; Deleon, Sabrina; Payton, Paxton; Irin, Fahmida; Saed, Mohammad; Shah, Smit Alkesh; Green, Micah J; Cañas-Carrell, Jaclyn E

    2016-06-01

    Single-wall carbon nanotubes (SWNTs) are projected to increase in usage across many industries. Two studies were conducted using Zea L. (corn) seeds exposed to SWNT spiked soil for 40 d. In Study 1, corn was exposed to various SWNT concentrations (0, 10, and 100 mg/kg) with different functionalities (non-functionalized, OH-functionalized, or surfactant stabilized). A microwave induced heating method was used to determine SWNTs accumulated mostly in roots (0-24 μg/g), with minimal accumulation in stems and leaves (2-10 μg/g) with a limit of detection at 0.1 μg/g. Uptake was not functional group dependent. In Study 2, corn was exposed to 10 mg/kg SWNTs (non-functionalized or COOH-functionalized) under optimally grown or water deficit conditions. Plant physiological stress was determined by the measurement of photosynthetic rate throughout Study 2. No significant differences were seen between control and SWNT treatments. Considering the amount of SWNTs accumulated in corn roots, further studies are needed to address the potential for SWNTs to enter root crop species (i.e., carrots), which could present a significant pathway for human dietary exposure.

  6. Numerical analysis of non-Newtonian blood flow and wall shear stress in realistic single, double and triple aorto-coronary bypasses.

    PubMed

    Vimmr, J; Jonášová, A; Bublík, O

    2013-10-01

    Considering the fact that hemodynamics plays an important role in the patency and overall performance of implanted bypass grafts, this work presents a numerical investigation of pulsatile non-Newtonian blood flow in three different patient-specific aorto-coronary bypasses. The three bypass models are distinguished from each other by the number of distal side-to-side and end-to-side anastomoses and denoted as single, double and triple bypasses. The mathematical model in the form of time-dependent nonlinear system of incompressible Navier-Stokes equations is coupled with the Carreau-Yasuda model describing the shear-thinning property of human blood and numerically solved using the principle of the SIMPLE algorithm and cell-centred finite volume method formulated for hybrid unstructured tetrahedral grids. The numerical results computed for non-Newtonian and Newtonian blood flow in the three aorto-coronary bypasses are compared and analysed with emphasis placed on the distribution of cycle-averaged wall shear stress and oscillatory shear index. As shown in this study, the non-Newtonian blood flow in all of the considered bypass models does not significantly differ from the Newtonian one. Our observations further suggest that, especially in the case of sequential grafts, the resulting flow field and shear stimulation are strongly influenced by the diameter of the vessels involved in the bypassing. PMID:23733715

  7. 4D Flow Assessment of Pulmonary Artery Flow and Wall Shear Stress in Adult Pulmonary Arterial Hypertension: Results from Two Institutions

    PubMed Central

    Barker, Alex J; Roldán-Alzate, Alejandro; Entezari, Pegah; Shah, Sanjiv J.; Chesler, Naomi C; Wieben, Oliver; Markl, Michael; François, Christopher J

    2014-01-01

    Purpose To compare pulmonary artery flow using Cartesian and radially sampled four-dimensional flow sensitive (4D flow) magnetic resonance imaging at two institutions. Methods 19 healthy and 17 pulmonary arterial hypertension (PAH) subjects underwent a Cartesian 4D flow acquisition (institution 1) or a three-dimensional radial acquisition (institution 2). The diameter, peak systolic velocity (Vmax), peak flow (Qmax), stroke volume (SV), and wall shear stress (WSS) were computed in two-dimensional analysis planes at the main, right, and left pulmonary artery. Inter-observer variability, inter-institutional differences, flow continuity, and the hemodynamic measurements in healthy and PAH subjects were assessed. Results Vmax, Qmax, SV, and WSS at all locations were significantly lower (p<0.05) in PAH compared to healthy subjects. The limits of agreement were 0.16 m/s, 2.4 L/min, 10 mL, and 0.31 N/m2 for Vmax, Qmax, SV, and WSS, respectively. Differences between Qmax, and SV using Cartesian and radial sequences were not significant. Plane placement and acquisition exhibited isolated, site-based differences between Vmax and WSS. Conclusions 4D flow MRI was used to detect differences in pulmonary artery hemodynamics for PAH subjects. Flow and WSS in healthy and PAH subject cohorts were similar between Cartesian- and radial-based 4D flow MRI acquisitions with minimal inter-observer variability. PMID:24974951

  8. A Methodology to Detect Abnormal Relative Wall Shear Stress on the Full Surface of the Thoracic Aorta Using 4D Flow MRI

    PubMed Central

    van Ooij, Pim; Potters, Wouter V.; Nederveen, Aart J.; Allen, Bradley D.; Collins, Jeremy; Carr, James; Malaisrie, S. Chris; Markl, Michael; Barker, Alex J.

    2014-01-01

    Purpose To compute cohort-averaged wall shear stress (WSS) maps in the thoracic aorta of patients with aortic dilatation or valvular stenosis and to detect abnormal regional WSS. Methods Systolic WSS vectors, estimated from 4D flow MRI data, were calculated along the thoracic aorta lumen in 10 controls, 10 patients with dilated aortas and 10 patients with aortic valve stenosis. 3D segmentations of each aorta were co-registered by group and used to create a cohort-specific aortic geometry. The WSS vectors of each subject were interpolated onto the corresponding cohort-specific geometry to create cohort-averaged WSS maps. A Wilcoxon rank sum test was used to generate aortic P-value maps (P<0.05) representing regional relative WSS differences between groups. Results Cohort-averaged systolic WSS maps and P-value maps were successfully created for all cohorts and comparisons. The dilation cohort showed significantly lower WSS on 7% of the ascending aorta surface, whereas the stenosis cohort showed significantly higher WSS aorta on 34% the ascending aorta surface. Conclusions The findings of this study demonstrated the feasibility of generating cohort-averaged WSS maps for the visualization and identification of regionally altered WSS in the presence of disease, as compared to healthy controls. PMID:24753241

  9. Experimental study of laminar blood flow through an artery treated by a stent implantation: characterisation of intra-stent wall shear stress.

    PubMed

    Benard, Nicolas; Coisne, Damien; Donal, Erwan; Perrault, Robert

    2003-07-01

    The stimulation of endothelial cells by arterial wall shear stress (WSS) plays a central role in restenosis. The fluid-structure interaction between stent wire and blood flow alters the WSS, particularly between stent struts. We have designed an in vitro model of struts of an intra-vascular prosthesis to study blood flow through a 'stented' section. The experimental artery consisted of a transparent square section test vein, which reproduced the strut design (100x magnifying power). A programmable pump was used to maintain a steady blood flow. Particle image velocimetry method was used to measure the flow between and over the stent branches, and to quantify WSS. Several prosthesis patterns that were representative of the total stent strut geometry were studied in a greater detail. We obtained WSS values of between -1.5 and 1.5Pa in a weak SS area which provided a source of endothelial stimulation propitious to restenosis. We also compared two similar patterns located in two different flow areas (one at the entry of the stent and one further downstream). We only detected a slight difference between the weakest SS levels at these two sites. As the endothelial proliferation is greatly influenced by the SS, knowledge of the SS modification induced by the stent implantation could be of importance for intra-vascular prostheses design optimisation and thus can help to reduce the restenosis incidence rate. PMID:12757808

  10. Great Walls.

    ERIC Educational Resources Information Center

    Blackburn, Steve; Moore, Tim

    1996-01-01

    Explains why installing a well-designed indoor climbing wall can draw new users to an athletic facility. Climbing-wall design elements and gear are discussed and a checklist for working with contractors is provided.(GR)

  11. Stress

    MedlinePlus

    ... hurt or killed. Examples include a major accident, war, assault, or a natural disaster. This type of ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  12. NASA Astrophysics E/PO Impact: NASA SOFIA AAA Program Evaluation Results

    NASA Astrophysics Data System (ADS)

    Harman, Pamela; Backman, Dana E.; Clark, Coral; Inverness Research Sofia Aaa Evaluation Team, Wested Sofia Aaa Evaluation Team

    2015-01-01

    SOFIA is an airborne observatory, studying the universe at infrared wavelengths, capable of making observations that are impossible for even the largest and highest ground-based telescopes. SOFIA also inspires the development of new scientific instrumentation and fosters the education of young scientists and engineers.SOFIA is an 80% - 20% partnership of NASA and the German Aerospace Center (DLR), consisting of an extensively modified Boeing 747SP aircraft carrying a reflecting telescope with an effective diameter of 2.5 meters (100 inches). The SOFIA aircraft is based at NASA Armstrong Flight Research Center, Building 703, in Palmdale, California. The Science Program and Outreach Offices are located at NASA Ames Research center. SOFIA is a program in NASA's Science Mission Directorate, Astrophysics Division.Data will be collected to study many different kinds of astronomical objects and phenomena, including star cycles, solar system formation, identification of complex molecules in space, our solar system, galactic dust, nebulae and ecosystems.Airborne Astronomy Ambassador (AAA) Program:The SOFIA Education and Communications program exploits the unique attributes of airborne astronomy to contribute to national goals for the reform of science, technology, engineering, and math (STEM) education, and to elevate public scientific and technical literacy.The AAA effort is a professional development program aspiring to improve teaching, inspire students, and inform the community. To date, 55 educators from 21 states; Cycles 0, 1 and 2; have completed their astronomy professional development and their SOFIA science flight experience. Evaluation has confirmed the program's positive impact on the teacher participants, on their students, and in their communities. The inspirational experience has positively impacted their practice and career trajectory. AAAs have incorporated content knowledge and specific components of their experience into their curricula, and have given

  13. Morphological State as a Predictor for Reintervention and Mortality After EVAR for AAA

    SciTech Connect

    Ohrlander, Tomas; Dencker, Magnus; Acosta, Stefan

    2012-10-15

    Purpose: This study was designed to assess aorto-iliac morphological characteristics in relation to reintervention and all-cause long-term mortality in patients undergoing standard EVAR for infrarenal AAA. Methods: Patients treated with EVAR (Zenith{sup Registered-Sign} Stentgrafts, Cook) between May 1998 and February 2006 were prospectively enrolled in a computerized database where comorbidities and preoperative aneurysm morphology were entered. Reinterventions and mortality were checked until December 1, 2010. Median follow-up time was 68 months. Results: A total of 304 patients were included, of which 86% were men. Median age was 74 years. The reintervention rate was 23.4% (71/304). A greater diameter of the common iliac artery (p = 0.037; hazard ratio (HR) 1.037 [1.002-1.073]) was an independent factor for an increased number of reinterventions. The 30-day mortality rate was 3.0% (9/304). Aneurysm-related deaths due to AAA occurred in 4.9% (15/304). Five patients died due to a concomitant ruptured thoracic aortic aneurysm. The mortality until end of follow-up was 54.3% (165/304). The proportion of deaths caused by vascular diseases was 61.6%. The severity of angulation of the iliac arteries (p = 0.014; HR 1.018 [95% confidence interval (CI) 1.004-1.033]) and anemia (p = 0.044; HR 2.79 [95% CI 1.029-7.556]) remained as independent factors associated with all-cause long-term mortality. The crude reintervention-free survival rate at 1, 3, and 5 years was 84.5%, 64.8%, and 51.6%, respectively. Conclusions: The initial aorto-iliac morphological state in patients scheduled for standard EVAR for AAA seems to be strongly related to the need for reinterventions and long-term mortality.

  14. SU-E-P-16: A Feasibility Study of Using Eclipse AAA for SRS Treatement

    SciTech Connect

    Lim, S; LoSasso, T

    2015-06-15

    Purpose: To commission Varian Eclipse AAA for SRS treatment and compare the accuracy with Brainlab iPlan system for clinical cases measured with radiochromic film. Methods: A 6MV AAA clinical model for a Varian TrueBeam STx is used as baseline. The focal spot and field size of the baseline model(BASE) are (1.75,0.75) and 40×40cm{sup 2} respectively. Maximum field sizes, output factors(S{sub t}), FWHM focal spot and secondary source sizes are systematically adjusted to obtain an optimized model(OPT) by comparing the calculated PDD’s, profiles, and output factors with measurements taken with a stereotactic diode(SD) and, cc01 and cc04 ion chambers in Blue Phantom. In-phantom dose distributions of clinical SRS fields are calculated using the OPT and the clinical Brainlab iPlan pencil-beam. Within the 90% isodose-line(ROI), the average dose difference between the calculations and radiochromic film measurements are assessed. Results: The maximum field, focal spot and secondary source sizes for the OPT are 15×15cm{sup 2}, (0,0), and 32.3mm respectively. The OPT St input at 1.0 and 2.0cm fields are increased by 4.5% and 1.5% from BASE. The calculated output of the BASE and OPT underestimate by 16.1%–3.2% respectively at 0.5×0.5cm{sup 2} field and 3.1%−0.02% respectively at 1.0×1.0cm{sup 2} field. The depth doses at 10cm are within 3.5% and 0.4% of measurements for 0.5×0.5 and 1.0×1.0cm{sup 2}. The ROI dose of OPT and iPlan are within 1.6% and 0.6% of film measurements for 3.0cm clinical fields. For 1.0cm fields, the ROI dose of OPT underestimate 0.0–2.0% and iPlan overestimates 1.7–2.9% relative to measurements. Conclusion: The small field dose calculation of Eclipse AAA algorithm can be significantly improved by carefully adjusting the input parameters. The larger deviation of the OPT for 0.5×0.5cm{sup 2} field from measurements can be attributed to the lowest 1.0cm field size input limit of AAA. The OPT compares reasonably well with the iPlan pencil

  15. [Morphological and functional parameters of the left ventricle (mass, wall thickness and end-systolic stress) in school children with different levels of blood pressure, at rest and during maximal exercise].

    PubMed

    Muñoz, S; Soltero, I; Onorato, E; Pietri, C; Zambrano, F

    1990-01-01

    Echocardiographically determined left ventricular mass, diastolic septal and posterior wall thickness and end-systolic wall stress, as well as electrocardiographic indexes of left ventricular enlargement (Sokolow-Lyon index and Romhilt-Estes score) and of left atrial enlargement (P terminal index) were correlated with resting and exercise systolic and diastolic blood pressures, and with several parameters of body size (weight, height, body surface area, Quetelet index), in 130 school children (61 boys, 69 girls) 6 to 15 years of age. Parameters of body size had a positive correlation both with systolic and diastolic blood pressures and with parameters of left ventricular size. Thus, the latter were adjusted for body surface area, for correlation with blood pressure. Left ventricular mass and diastolic septal and posterior wall thickness had a very poor correlation with resting and exercise diastolic blood pressures. Left ventricular mass and diastolic posterior wall thickness had a significantly higher correlation with peak exercise systolic blood pressure than with resting systolic blood pressure. End-systolic wall stress had a positive correlation with resting diastolic and systolic blood pressures. Electrocardiographic parameters of left ventricular and left atrial enlargement had a very poor correlation with resting and exercise blood pressure. Our findings suggest that early in life left ventricular mass and wall thickness are more closely related to maximal systolic blood pressure during physical exercise than to blood pressure in basal conditions. The electrocardiogram is an insensitive method to detect early modifications of left ventricular size in relation to different levels of blood pressure. The echocardiogram is the method of choice for this purpose.

  16. A higher plant mitochondrial homologue of the yeast m-AAA protease. Molecular cloning, localization, and putative function.

    PubMed

    Kolodziejczak, Marta; Kolaczkowska, Anna; Szczesny, Bartosz; Urantowka, Adam; Knorpp, Carina; Kieleczawa, Jan; Janska, Hanna

    2002-11-15

    Mitochondrial AAA metalloproteases play a fundamental role in mitochondrial biogenesis and function. They have been identified in yeast and animals but not yet in plants. This work describes the isolation and sequence analysis of the full-length cDNA from the pea (Pisum sativum) with significant homology to the yeast matrix AAA (m-AAA) protease. The product of this clone was imported into isolated pea mitochondria where it was processed to its mature form (PsFtsH). We have shown that the central region of PsFtsH containing the chaperone domain is exposed to the matrix space. Furthermore, we have demonstrated that the pea protease can complement respiration deficiency in the yta10 and/or yta12 null yeast mutants, indicating that the plant protein can compensate for the loss of at least some of the important m-AAA functions in yeast. Based on biochemical experiments using isolated pea mitochondria, we propose that PsFtsH-like m-AAA is involved in the accumulation of the subunit 9 of the ATP synthase in the mitochondrial membrane.

  17. V-ATPase-dependent luminal acidification is required for endocytic recycling of a yeast cell wall stress sensor, Wsc1p

    SciTech Connect

    Ueno, Kazuma; Saito, Mayu; Nagashima, Makiko; Kojima, Ai; Nishinoaki, Show; Toshima, Junko Y.; Toshima, Jiro

    2014-01-10

    Highlights: •A targeted genome screen identified 5 gene groups affecting Wsc1p recycling. •V-ATPase-dependent luminal acidification is required for Wsc1p recycling. •Activity of V-ATPase might be required for cargo recognition by the retromer complex. -- Abstract: Wsc1p is a major cell wall sensor protein localized at the polarized cell surface. The localization of Wsc1p is maintained by endocytosis and recycling from endosomes back to the cell surface, but changes to the vacuole when cells are subjected to heat stress. Exploiting this unique property of Wsc1p, we screened for yeast single-gene deletion mutants exhibiting defects in Wsc1p trafficking. By expressing 3GFP-tagged Wsc1p in mutants with deleted genes whose function is related to intracellular trafficking, we identified 5 gene groups affecting Wsc1p trafficking, impaired respectively in endocytic internalization, multivesicular body sorting, the GARP complex, endosomal maturation/vacuolar fusion, and V-ATPase. Interestingly, deletion of the VPH1 gene, encoding the V{sub o} subunit of vacuolar-type H{sup +}-ATPase (V-ATPase), led to mis-localization of Wsc1p from the plasma membrane to the vacuole. In addition, disruption of other V-ATPase subunits (vma mutants) also caused defects of Wsc1p trafficking and vacuolar acidification similar to those seen in the vph1Δ mutant. Moreover, we found that deletion of the VPS26 gene, encoding a subunit of the retromer complex, also caused a defect in Wsc1p recycling and mis-localization of Wsc1p to the vacuole. These findings clarified the previously unidentified Wsc1p recycling pathway and requirement of V-ATPase-dependent luminal acidification for Wsc1p recycling.

  18. Vitamin E deficiency enhances pulmonary inflammatory response and oxidative stress induced by single-walled carbon nanotubes in C57BL/6 mice

    SciTech Connect

    Shvedova, Anna A.; Arepalli, Sivaram; Castranova, Vincent; Tyurina, Yulia Y.; Oury, Tim D.; Kagan, Valerian E. . E-mail: kagan@pitt.edu

    2007-06-15

    Exposure of mice to single-walled carbon nanotubes (SWCNTs) induces an unusually robust pulmonary inflammatory response with an early onset of fibrosis, which is accompanied by oxidative stress and antioxidant depletion. The role of specific components of the antioxidant protective system, specifically vitamin E, the major lipid-soluble antioxidant, in the SWCNT-induced reactions has not been characterized. We used C57BL/6 mice, maintained on vitamin E-sufficient or vitamin E-deficient diets, to explore and compare the pulmonary inflammatory reactions to aspired SWCNTs. The vitamin E-deficient diet caused a 90-fold depletion of {alpha}-tocopherol in the lung tissue and resulted in a significant decline of other antioxidants (GSH, ascorbate) as well as accumulation of lipid peroxidation products. A greater decrease of pulmonary antioxidants was detected in SWCNT-treated vitamin E-deficient mice as compared to controls. Lowered levels of antioxidants in vitamin E-deficient mice were associated with a higher sensitivity to SWCNT-induced acute inflammation (total number of inflammatory cells, number of polymorphonuclear leukocytes, released LDH, total protein content and levels of pro-inflammatory cytokines, TNF-{alpha} and IL-6) and enhanced profibrotic responses (elevation of TGF-{beta} and collagen deposition). Exposure to SWCNTs markedly shifted the ratio of cleaved to full-length extracellular superoxide dismutase (EC-SOD). Given that pulmonary levels of vitamin E can be manipulated through diet, its effects on SWCNT-induced inflammation may be of practical importance in optimizing protective strategies.

  19. Influence of the Accuracy of Angiography-Based Reconstructions on Velocity and Wall Shear Stress Computations in Coronary Bifurcations: A Phantom Study

    PubMed Central

    Schrauwen, Jelle T. C.; Karanasos, Antonios; van Ditzhuijzen, Nienke S.; Aben, Jean-Paul; van der Steen, Antonius F. W.

    2015-01-01

    Introduction Wall shear stress (WSS) plays a key role in the onset and progression of atherosclerosis in human coronary arteries. Especially sites with low and oscillating WSS near bifurcations have a higher propensity to develop atherosclerosis. WSS computations in coronary bifurcations can be performed in angiography-based 3D reconstructions. It is essential to evaluate how reconstruction errors influence WSS computations in mildly-diseased coronary bifurcations. In mildly-diseased lesions WSS could potentially provide more insight in plaque progression. Materials Methods Four Plexiglas phantom models of coronary bifurcations were imaged with bi-plane angiography. The lumens were segmented by two clinically experienced readers. Based on the segmentations 3D models were generated. This resulted in three models per phantom: one gold-standard from the phantom model itself, and one from each reader. Steady-state and transient simulations were performed with computational fluid dynamics to compute the WSS. A similarity index and a noninferiority test were used to compare the WSS in the phantoms and their reconstructions. The margin for this test was based on the resolution constraints of angiography. Results The reconstruction errors were similar to previously reported data; in seven out of eight reconstructions less than 0.10 mm. WSS in the regions proximal and far distal of the stenosis showed a good agreement. However, the low WSS areas directly distal of the stenosis showed some disagreement between the phantoms and the readers. This was due to small deviations in the reconstruction of the stenosis that caused differences in the resulting jet, and consequently the size and location of the low WSS area. Discussion This study showed that WSS can accurately be computed within angiography-based 3D reconstructions of coronary arteries with early stage atherosclerosis. Qualitatively, there was a good agreement between the phantoms and the readers. Quantitatively, the

  20. TRIP13 is a protein-remodeling AAA+ ATPase that catalyzes MAD2 conformation switching

    PubMed Central

    Ye, Qiaozhen; Rosenberg, Scott C; Moeller, Arne; Speir, Jeffrey A; Su, Tiffany Y; Corbett, Kevin D

    2015-01-01

    The AAA+ family ATPase TRIP13 is a key regulator of meiotic recombination and the spindle assembly checkpoint, acting on signaling proteins of the conserved HORMA domain family. Here we present the structure of the Caenorhabditis elegans TRIP13 ortholog PCH-2, revealing a new family of AAA+ ATPase protein remodelers. PCH-2 possesses a substrate-recognition domain related to those of the protein remodelers NSF and p97, while its overall hexameric architecture and likely structural mechanism bear close similarities to the bacterial protein unfoldase ClpX. We find that TRIP13, aided by the adapter protein p31(comet), converts the HORMA-family spindle checkpoint protein MAD2 from a signaling-active ‘closed’ conformer to an inactive ‘open’ conformer. We propose that TRIP13 and p31(comet) collaborate to inactivate the spindle assembly checkpoint through MAD2 conformational conversion and disassembly of mitotic checkpoint complexes. A parallel HORMA protein disassembly activity likely underlies TRIP13's critical regulatory functions in meiotic chromosome structure and recombination. DOI: http://dx.doi.org/10.7554/eLife.07367.001 PMID:25918846

  1. Going the distance: validation of Acuros and AAA at an extended SSD of 400 cm.

    PubMed

    Lamichhane, Narottam; Patel, Vivek N; Studenski, Matthew T

    2016-01-01

    Accurate dose calculation and treatment delivery is essential for total body irradiation (TBI). In an effort to verify the accuracy of TBI dose calculation at our institution, we evaluated both the Varian Eclipse AAA and Acuros algorithms to predict dose distributions at an extended source-to-surface distance (SSD) of 400 cm. Measurements were compared to calculated values for a 6 MV beam in physical and virtual phantoms at 400 cm SSD using open beams for both 5 × 5 and 40 × 40cm2 field sizes. Inline and crossline profiles were acquired at equivalent depths of 5 cm, 10 cm, and 20 cm. Depth-dose curves were acquired using EBT2 film and an ion chamber for both field sizes. Finally, a RANDO phantom was used to simulate an actual TBI treatment. At this extended SSD, care must be taken using the planning system as there is good relative agreement between measured and calculated profiles for both algorithms, but there are deviations in terms of the absolute dose. Acuros has better agreement than AAA in the penumbra region. PMID:27074473

  2. Structural Characterization of the ATPase Reaction Cycle of Endosomal AAA Protein Vps4

    SciTech Connect

    Xiao, Junyu; Xia, Hengchuan; Yoshino-Koh, Kae; Zhou, Jiahai; Xu, Zhaohui

    2008-12-12

    The multivesicular body (MVB) pathway functions in multiple cellular processes including cell surface receptor down-regulation and viral budding from host cells. An important step in the MVB pathway is the correct sorting of cargo molecules, which requires the assembly and disassembly of endosomal sorting complexes required for transport (ESCRTs) on the endosomal membrane. Disassembly of the ESCRTs is catalyzed by ATPase associated with various cellular activities (AAA) protein Vps4. Vps4 contains a single AAA domain and undergoes ATP-dependent quaternary structural change to disassemble the ESCRTs. Structural and biochemical analyses of the Vps4 ATPase reaction cycle are reported here. Crystal structures of Saccharomyces cerevisiae Vps4 in both the nucleotide-free form and the ADP-bound form provide the first structural view illustrating how nucleotide binding might induce conformational changes within Vps4 that lead to oligomerization and binding to its substrate ESCRT-III subunits. In contrast to previous models, characterization of the Vps4 structure now supports a model where the ground state of Vps4 in the ATPase reaction cycle is predominantly a monomer and the activated state is a dodecamer. Comparison with a previously reported human VPS4B structure suggests that Vps4 functions in the MVB pathway via a highly conserved mechanism supported by similar protein-protein interactions during its ATPase reaction cycle.

  3. An atomic model AAA-ATPase/20S core particle sub-complex of the 26S proteasome

    PubMed Central

    Förster, Friedrich; Lasker, Keren; Beck, Florian; Nickell, Stephan; Sali, Andrej; Baumeister, Wolfgang

    2009-01-01

    The 26S proteasome is the most downstream element of the ubiquitin-proteasome pathway of protein degradation. It is composed of the 20S core particle (CP) and the 19S regulatory particle (RP). The RP consists of 6 AAA-ATPases and at least 13 non-ATPase subunits. Based on a cryo-EM map of the 26S proteasome, structures of homologs, and physical protein-protein interactions we derive an atomic model of the AAA-ATPase-CP sub-complex. The ATPase order in our model (Rpt1/Rpt2/Rpt6/Rpt3/Rpt4/Rpt5) is in excellent agreement with the recently identified base-precursor complexes formed during the assembly of the RP. Furthermore, the atomic CP-AAA-ATPase model suggests that the assembly chaperone Nas6 facilitates CP-RP association by enhancing the shape complementarity between Rpt3 and its binding CP alpha subunits partners. PMID:19653995

  4. An atomic model AAA-ATPase/20S core particle sub-complex of the 26S proteasome.

    PubMed

    Förster, Friedrich; Lasker, Keren; Beck, Florian; Nickell, Stephan; Sali, Andrej; Baumeister, Wolfgang

    2009-10-16

    The 26S proteasome is the most downstream element of the ubiquitin-proteasome pathway of protein degradation. It is composed of the 20S core particle (CP) and the 19S regulatory particle (RP). The RP consists of 6 AAA-ATPases and at least 13 non-ATPase subunits. Based on a cryo-EM map of the 26S proteasome, structures of homologs, and physical protein-protein interactions we derive an atomic model of the AAA-ATPase-CP sub-complex. The ATPase order in our model (Rpt1/Rpt2/Rpt6/Rpt3/Rpt4/Rpt5) is in excellent agreement with the recently identified base-precursor complexes formed during the assembly of the RP. Furthermore, the atomic CP-AAA-ATPase model suggests that the assembly chaperone Nas6 facilitates CP-RP association by enhancing the shape complementarity between Rpt3 and its binding CP alpha subunits partners.

  5. The ATPase of the phi29 DNA packaging motor is a member of the hexameric AAA+ superfamily.

    PubMed

    Schwartz, Chad; De Donatis, Gian Marco; Fang, Huaming; Guo, Peixuan

    2013-08-15

    The AAA+ superfamily of proteins is a class of motor ATPases performing a wide range of functions that typically exist as hexamers. The ATPase of phi29 DNA packaging motor has long been a subject of debate in terms of stoichiometry and mechanism of action. Here, we confirmed the stoichiometry of phi29 motor ATPase to be a hexamer and provide data suggesting that the phi29 motor ATPase is a member of the classical hexameric AAA+ superfamily. Native PAGE, EMSA, capillary electrophoresis, ATP titration, and binomial distribution assay show that the ATPase is a hexamer. Mutations in the known Walker motifs of the ATPase validated our previous assumptions that the protein exists as another member of this AAA+ superfamily. Our data also supports the finding that the phi29 DNA packaging motor uses a revolution mechanism without rotation or coiling (Schwartz et al., this issue).

  6. Moyamoya disease-associated protein mysterin/RNF213 is a novel AAA+ ATPase, which dynamically changes its oligomeric state

    NASA Astrophysics Data System (ADS)

    Morito, Daisuke; Nishikawa, Kouki; Hoseki, Jun; Kitamura, Akira; Kotani, Yuri; Kiso, Kazumi; Kinjo, Masataka; Fujiyoshi, Yoshinori; Nagata, Kazuhiro

    2014-03-01

    Moyamoya disease is an idiopathic human cerebrovascular disorder that is characterized by progressive stenosis and abnormal collateral vessels. We recently identified mysterin/RNF213 as its first susceptibility gene, which encodes a 591-kDa protein containing enzymatically active P-loop ATPase and ubiquitin ligase domains and is involved in proper vascular development in zebrafish. Here we demonstrate that mysterin further contains two tandem AAA+ ATPase modules and forms huge ring-shaped oligomeric complex. AAA+ ATPases are known to generally mediate various biophysical and mechanical processes with the characteristic ring-shaped structure. Fluorescence correlation spectroscopy and biochemical evaluation suggested that mysterin dynamically changes its oligomeric forms through ATP/ADP binding and hydrolysis cycles. Thus, the moyamoya disease-associated gene product is a unique protein that functions as ubiquitin ligase and AAA+ ATPase, which possibly contributes to vascular development through mechanical processes in the cell.

  7. An atomic model AAA-ATPase/20S core particle sub-complex of the 26S proteasome

    SciTech Connect

    Foerster, Friedrich; Lasker, Keren; Beck, Florian; Nickell, Stephan; Sali, Andrej; Baumeister, Wolfgang

    2009-10-16

    The 26S proteasome is the most downstream element of the ubiquitin-proteasome pathway of protein degradation. It is composed of the 20S core particle (CP) and the 19S regulatory particle (RP). The RP consists of 6 AAA-ATPases and at least 13 non-ATPase subunits. Based on a cryo-EM map of the 26S proteasome, structures of homologs, and physical protein-protein interactions we derive an atomic model of the AAA-ATPase-CP sub-complex. The ATPase order in our model (Rpt1/Rpt2/Rpt6/Rpt3/Rpt4/Rpt5) is in excellent agreement with the recently identified base-precursor complexes formed during the assembly of the RP. Furthermore, the atomic CP-AAA-ATPase model suggests that the assembly chaperone Nas6 facilitates CP-RP association by enhancing the shape complementarity between Rpt3 and its binding CP alpha subunits partners.

  8. Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant reveal that fiber cell wall development is associated with sensitivity to stress.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background: Cotton fiber maturity refers the degree of fiber cell wall development and is an important factor for determining commercial value of cotton. The molecular mechanism regulating the fiber cell wall development has not been well characterized. Microscopic image analysis of the cross-sect...

  9. SecAAA trimer is fully functional as SecAA dimer in the membrane: Existence of higher oligomers?

    PubMed Central

    Wang, Hongyun; Ma, Yamin; Hsieh, Ying-Hsin; Yang, Hsiuchin; Li, Minyong; Wang, Binghe; Tai, Phang C.

    2014-01-01

    SecA is an essential ATPase in bacterial Sec-dependent protein translocation pathway, and equilibrates between monomers and dimers in solution. The question of whether SecA functions as monomers or dimers in membranes during the protein translocation is controversial. We previously constructed a tail-to-head SecAA tandem dimer, and showed it is fully functional by complementation in vivo and protein translocation in vitro, indicating that SecA can function at least as a dimer in the membrane without dissociating into monomers. In this study, we further constructed genetically a tail-to-head SecAAA trimer, which is functional in complementing a temperature-sensitive secA mutant. The purified SecAAA trimer per protomer is fully active as SecAA tandem dimers in ATPase activity, in protein translocation in vitro and in ion channel activities in the oocytes. With these functional tail-to-head trimer SecAAA and tandem SecAA, we examined their surface topology in the presence of liposomes using AFM. As expected, the soluble SecAAA without lipids are larger than SecAA. However, the ring/pore structures of SecAAA trimers were, surprisingly, almost identical to the SecA 2-monomers and SecAA dimers, raising the intriguing possibility that the SecA may exist and function as hexamer ring-structures in membranes. Cross-linking with formaldehyde showed that SecA, SecAA and SecAAA could form larger oligomers, including the hexamers. The molecular modeling simulation shows that both tail-to-head and tail-to-tail hexamers in the membranes are possible. PMID:24704204

  10. Walker-A threonine couples nucleotide occupancy with the chaperone activity of the AAA+ ATPase ClpB

    PubMed Central

    Nagy, Maria; Wu, Hui-Chuan; Liu, Zhonghua; Kedzierska-Mieszkowska, Sabina; Zolkiewski, Michal

    2009-01-01

    Hexameric AAA+ ATPases induce conformational changes in a variety of macromolecules. AAA+ structures contain the nucleotide-binding P-loop with the Walker A sequence motif: GxxGxGK(T/S). A subfamily of AAA+ sequences contains Asn in the Walker A motif instead of Thr or Ser. This noncanonical subfamily includes torsinA, an ER protein linked to human dystonia and DnaC, a bacterial helicase loader. Role of the noncanonical Walker A motif in the functionality of AAA+ ATPases has not been explored yet. To determine functional effects of introduction of Asn into the Walker A sequence, we replaced the Walker-A Thr with Asn in ClpB, a bacterial AAA+ chaperone which reactivates aggregated proteins. We found that the T-to-N mutation in Walker A partially inhibited the ATPase activity of ClpB, but did not affect the ClpB capability to associate into hexamers. Interestingly, the noncanonical Walker A sequence in ClpB induced preferential binding of ADP vs. ATP and uncoupled the linkage between the ATP-bound conformation and the high-affinity binding to protein aggregates. As a consequence, ClpB with the noncanonical Walker A sequence showed a low chaperone activity in vitro and in vivo. Our results demonstrate a novel role of the Walker-A Thr in sensing the nucleotide's γ-phosphate and in maintaining an allosteric linkage between the P-loop and the aggregate binding site of ClpB. We postulate that AAA+ ATPases with the noncanonical Walker A might utilize distinct mechanisms to couple the ATPase cycle with their substrate-remodeling activity. PMID:19177562

  11. Wonderful Walls

    ERIC Educational Resources Information Center

    Greenman, Jim

    2006-01-01

    In this article, the author emphasizes the importance of "working" walls in children's programs. Children's programs need "working" walls (and ceilings and floors) which can be put to use for communication, display, storage, and activity space. The furnishings also work, or don't work, for the program in another sense: in aggregate, they serve as…

  12. Corrections to the thin wall approximation in general relativity

    NASA Technical Reports Server (NTRS)

    Garfinkle, David; Gregory, Ruth

    1989-01-01

    The question is considered whether the thin wall formalism of Israel applies to the gravitating domain walls of a lambda phi(exp 4) theory. The coupled Einstein-scalar equations that describe the thick gravitating wall are expanded in powers of the thickness of the wall. The solutions of the zeroth order equations reproduce the results of the usual Israel thin wall approximation for domain walls. The solutions of the first order equations provide corrections to the expressions for the stress-energy of the wall and to the Israel thin wall equations. The modified thin wall equations are then used to treat the motion of spherical and planar domain walls.

  13. The Effect of Spatial and Temporal Resolution of Cine Phase Contrast MRI on Wall Shear Stress and Oscillatory Shear Index Assessment

    PubMed Central

    Gijsen, Frank J.; Marquering, Henk; van Ooij, Pim; vanBavel, Ed; Wentzel, Jolanda J.; Nederveen, Aart J.

    2016-01-01

    Introduction Wall shear stress (WSS) and oscillatory shear index (OSI) are associated with atherosclerotic disease. Both parameters are derived from blood velocities, which can be measured with phase-contrast MRI (PC-MRI). Limitations in spatiotemporal resolution of PC-MRI are known to affect these measurements. Our aim was to investigate the effect of spatiotemporal resolution using a carotid artery phantom. Methods A carotid artery phantom was connected to a flow set-up supplying pulsatile flow. MRI measurement planes were placed at the common carotid artery (CCA) and internal carotid artery (ICA). Two-dimensional PC-MRI measurements were performed with thirty different spatiotemporal resolution settings. The MRI flow measurement was validated with ultrasound probe measurements. Mean flow, peak flow, flow waveform, WSS and OSI were compared for these spatiotemporal resolutions using regression analysis. The slopes of the regression lines were reported in %/mm and %/100ms. The distribution of low and high WSS and OSI was compared between different spatiotemporal resolutions. Results The mean PC-MRI CCA flow (2.5±0.2mL/s) agreed with the ultrasound probe measurements (2.7±0.02mL/s). Mean flow (mL/s) depended only on spatial resolution (CCA:-13%/mm, ICA:-49%/mm). Peak flow (mL/s) depended on both spatial (CCA:-13%/mm, ICA:-17%/mm) and temporal resolution (CCA:-19%/100ms, ICA:-24%/100ms). Mean WSS (Pa) was in inverse relationship only with spatial resolution (CCA:-19%/mm, ICA:-33%/mm). OSI was dependent on spatial resolution for CCA (-26%/mm) and temporal resolution for ICA (-16%/100ms). The regions of low and high WSS and OSI matched for most of the spatiotemporal resolutions (CCA:30/30, ICA:28/30 cases for WSS; CCA:23/30, ICA:29/30 cases for OSI). Conclusion We show that both mean flow and mean WSS are independent of temporal resolution. Peak flow and OSI are dependent on both spatial and temporal resolution. However, the magnitude of mean and peak flow, WSS and

  14. Flow and wall shear stress in end-to-side and side-to-side anastomosis of venous coronary artery bypass grafts

    PubMed Central

    Frauenfelder, Thomas; Boutsianis, Evangelos; Schertler, Thomas; Husmann, Lars; Leschka, Sebastian; Poulikakos, Dimos; Marincek, Borut; Alkadhi, Hatem

    2007-01-01

    Purpose Coronary artery bypass graft (CABG) surgery represents the standard treatment of advanced coronary artery disease. Two major types of anastomosis exist to connect the graft to the coronary artery, i.e., by using an end-to-side or a side-to-side anastomosis. There is still controversy because of the differences in the patency rates of the two types of anastomosis. The purpose of this paper is to non-invasively quantify hemodynamic parameters, such as mass flow and wall shear stress (WSS), in end-to-side and side-to-side anastomoses of patients with CABG using computational fluid dynamics (CFD). Methods One patient with saphenous CABG and end-to-side anastomosis and one patient with saphenous CABG and side-to-side anastomosis underwent 16-detector row computed tomography (CT). Geometric models of coronary arteries and bypasses were reconstructed for CFD analysis. Blood flow was considered pulsatile, laminar, incompressible and Newtonian. Peri-anastomotic mass flow and WSS were quantified and flow patterns visualized. Results CFD analysis based on in-vivo CT coronary angiography data was feasible in both patients. For both types of CABG, flow patterns were characterized by a retrograde flow into the native coronary artery. WSS variations were found in both anastomoses types, with highest WSS values at the heel and lowest WSS values at the floor of the end-to-side anastomosis. In contrast, the highest WSS values of the side-to-side anastomosis configuration were found in stenotic vessel segments and not in the close vicinity of the anastomosis. Flow stagnation zones were found in end-to-side but not in side-to-side anastomosis, the latter also demonstrating a smoother stream division throughout the cardiac cycle. Conclusion CFD analysis of venous CABG based on in-vivo CT datasets in patients was feasible producing qualitative and quantitative information on mass flow and WSS. Differences were found between the two types of anastomosis warranting further

  15. Lytic Water Dynamics Reveal Evolutionarily Conserved Mechanisms of ATP Hydrolysis by TIP49 AAA+ ATPases

    PubMed Central

    Afanasyeva, Arina; Hirtreiter, Angela; Schreiber, Anne; Grohmann, Dina; Pobegalov, Georgii; McKay, Adam R.; Tsaneva, Irina; Petukhov, Michael; Käs, Emmanuel; Grigoriev, Mikhail; Werner, Finn

    2014-01-01

    Summary Eukaryotic TIP49a (Pontin) and TIP49b (Reptin) AAA+ ATPases play essential roles in key cellular processes. How their weak ATPase activity contributes to their important functions remains largely unknown and difficult to analyze because of the divergent properties of TIP49a and TIP49b proteins and of their homo- and hetero-oligomeric assemblies. To circumvent these complexities, we have analyzed the single ancient TIP49 ortholog found in the archaeon Methanopyrus kandleri (mkTIP49). All-atom homology modeling and molecular dynamics simulations validated by biochemical assays reveal highly conserved organizational principles and identify key residues for ATP hydrolysis. An unanticipated crosstalk between Walker B and Sensor I motifs impacts the dynamics of water molecules and highlights a critical role of trans-acting aspartates in the lytic water activation step that is essential for the associative mechanism of ATP hydrolysis. PMID:24613487

  16. The AAA-ATPase NVL2 is a telomerase component essential for holoenzyme assembly

    SciTech Connect

    Her, Joonyoung; Chung, In Kwon

    2012-01-20

    Highlights: Black-Right-Pointing-Pointer Identification of the AAA-ATPase NVL2 as a novel hTERT-interacting protein. Black-Right-Pointing-Pointer NVL2 associates with catalytically active telomerase via an interaction with hTERT. Black-Right-Pointing-Pointer NVL2 is a telomerase component essential for holoenzyme assembly. Black-Right-Pointing-Pointer ATP-binding activity of NVL2 is required for hTERT binding and telomerase assembly. -- Abstract: Continued cell proliferation requires telomerase to maintain functional telomeres that are essential for chromosome integrity. Although the core enzyme includes a telomerase reverse transcriptase (TERT) and a telomerase RNA component (TERC), a number of auxiliary proteins have been identified to regulate telomerase assembly, localization, and enzymatic activity. Here we describe the characterization of the AAA-ATPase NVL2 as a novel hTERT-interacting protein. NVL2 interacts and co-localizes with hTERT in the nucleolus. NLV2 is also found in association with catalytically competent telomerase in cell lysates through an interaction with hTERT. Depletion of endogenous NVL2 by small interfering RNA led to a decrease in hTERT without affecting the steady-state levels of hTERT mRNA, thereby reducing telomerase activity, suggesting that NVL2 is an essential component of the telomerase holoenzyme. We also found that ATP-binding activity of NVL2 is required for hTERT binding as well as telomerase assembly. Our findings suggest that NVL2, in addition to its role in ribosome biosynthesis, is essential for telomerase biogenesis and provides an alternative approach for inhibiting telomerase activity in cancer.

  17. Endosomal transport function in yeast requires a novel AAA-type ATPase, Vps4p.

    PubMed Central

    Babst, M; Sato, T K; Banta, L M; Emr, S D

    1997-01-01

    In a late-Golgi compartment of the yeast Saccharomyces cerevisiae, vacuolar proteins such as carboxypeptidase Y (CPY) are actively sorted away from the secretory pathway and transported to the vacuole via a pre-vacuolar, endosome-like intermediate. The vacuolar protein sorting (vps) mutant vps4 accumulates vacuolar, endocytic and late-Golgi markers in an aberrant multilamellar pre-vacuolar compartment. The VPS4 gene has been cloned and found to encode a 48 kDa protein which belongs to the protein family of AAA-type ATPases. The Vps4 protein was purified and shown to exhibit an N-ethylmaleimide-sensitive ATPase activity. A single amino acid change within the AAA motif of Vps4p yielded a protein that lacked ATPase activity and did not complement the protein sorting or morphological defects of the vps4 delta1 mutant. Indeed, when expressed at normal levels in wild-type cells, the mutant vps4 gene acted as a dominant-negative allele. The phenotypic characterization of a temperature-sensitive vps4 allele showed that the immediate consequence of loss of Vps4p function is a defect in vacuolar protein delivery. In this mutant, precursor CPY was not secreted but instead accumulated in an intracellular compartment, presumably the pre-vacuolar endosome. Electron microscopy revealed that upon temperature shift, exaggerated stacks of curved cisternal membranes (aberrant endosome) also accumulated in the vps4ts mutant. Based on these and other observations, we propose that Vps4p function is required for efficient transport out of the pre-vacuolar endosome. PMID:9155008

  18. Student-Athlete Perceptions of a Summer Pre-Enrollment Experience at an NCAA Division I-AAA Institution

    ERIC Educational Resources Information Center

    Dalgety, Michael Franklin

    2012-01-01

    The purpose of this exploratory qualitative study was to examine student-athlete perceptions of the role of summer pre-enrollment in their adjustment and transition to college. The study focused on student-athletes who received athletically-related financial aid at a National Collegiate Athletic Association (NCAA) Division I-AAA institution. The…

  19. Pareto front analysis of 6 and 15 MV dynamic IMRT for lung cancer using pencil beam, AAA and Monte Carlo

    NASA Astrophysics Data System (ADS)

    Ottosson, R. O.; Karlsson, A.; Behrens, C. F.

    2010-08-01

    The pencil beam dose calculation method is frequently used in modern radiation therapy treatment planning regardless of the fact that it is documented inaccurately for cases involving large density variations. The inaccuracies are larger for higher beam energies. As a result, low energy beams are conventionally used for lung treatments. The aim of this study was to analyze the advantages and disadvantages of dynamic IMRT treatment planning for high and low photon energy in order to assess if deviating from the conventional low energy approach could be favorable in some cases. Furthermore, the influence of motion on the dose distribution was investigated. Four non-small cell lung cancer cases were selected for this study. Inverse planning was conducted using Varian Eclipse. A total number of 31 dynamic IMRT plans, distributed amongst the four cases, were created ranging from PTV conformity weighted to normal tissue sparing weighted. All optimized treatment plans were calculated using three different calculation algorithms (PBC, AAA and MC). In order to study the influence of motion, two virtual lung phantoms were created. The idea was to mimic two different situations: one where the GTV is located centrally in the PTV and another where the GTV was close to the edge of the PTV. PBC is in poor agreement with MC and AAA for all cases and treatment plans. AAA overestimates the dose, compared to MC. This effect is more pronounced for 15 than 6 MV. AAA and MC both predict similar perturbations in dose distributions when moving the GTV to the edge of the PTV. PBC, however, predicts results contradicting those of AAA and MC. This study shows that PB-based dose calculation algorithms are clinically insufficient for patient geometries involving large density inhomogeneities. AAA is in much better agreement with MC, but even a small overestimation of the dose level by the algorithm might lead to a large part of the PTV being underdosed. It is advisable to use low energy as a

  20. Pareto front analysis of 6 and 15 MV dynamic IMRT for lung cancer using pencil beam, AAA and Monte Carlo.

    PubMed

    Ottosson, R O; Karlsson, A; Behrens, C F

    2010-08-21

    The pencil beam dose calculation method is frequently used in modern radiation therapy treatment planning regardless of the fact that it is documented inaccurately for cases involving large density variations. The inaccuracies are larger for higher beam energies. As a result, low energy beams are conventionally used for lung treatments. The aim of this study was to analyze the advantages and disadvantages of dynamic IMRT treatment planning for high and low photon energy in order to assess if deviating from the conventional low energy approach could be favorable in some cases. Furthermore, the influence of motion on the dose distribution was investigated. Four non-small cell lung cancer cases were selected for this study. Inverse planning was conducted using Varian Eclipse. A total number of 31 dynamic IMRT plans, distributed amongst the four cases, were created ranging from PTV conformity weighted to normal tissue sparing weighted. All optimized treatment plans were calculated using three different calculation algorithms (PBC, AAA and MC). In order to study the influence of motion, two virtual lung phantoms were created. The idea was to mimic two different situations: one where the GTV is located centrally in the PTV and another where the GTV was close to the edge of the PTV. PBC is in poor agreement with MC and AAA for all cases and treatment plans. AAA overestimates the dose, compared to MC. This effect is more pronounced for 15 than 6 MV. AAA and MC both predict similar perturbations in dose distributions when moving the GTV to the edge of the PTV. PBC, however, predicts results contradicting those of AAA and MC. This study shows that PB-based dose calculation algorithms are clinically insufficient for patient geometries involving large density inhomogeneities. AAA is in much better agreement with MC, but even a small overestimation of the dose level by the algorithm might lead to a large part of the PTV being underdosed. It is advisable to use low energy as a

  1. Wall Turbulence.

    ERIC Educational Resources Information Center

    Hanratty, Thomas J.

    1980-01-01

    This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)

  2. Genome-wide data (ChIP-seq) enabled identification of cell wall-related and aquaporin genes as targets of tomato ASR1, a drought stress-responsive transcription factor

    PubMed Central

    2014-01-01

    Background Identifying the target genes of transcription factors is important for unraveling regulatory networks in all types of organisms. Our interest was precisely to uncover the spectrum of loci regulated by a widespread plant transcription factor involved in physiological adaptation to drought, a type of stress that plants have encountered since the colonization of land habitats 400 MYA. The regulator under study, named ASR1, is exclusive to the plant kingdom (albeit absent in Arabidopsis) and known to alleviate the stress caused by restricted water availability. As its target genes are still unknown despite the original cloning of Asr1 cDNA 20 years ago, we examined the tomato genome for specific loci interacting in vivo with this conspicuous protein. Results We performed ChIP followed by high throughput DNA sequencing (ChIP-seq) on leaves from stressed tomato plants, using a high-quality anti-ASR1 antibody. In this way, we unraveled a novel repertoire of target genes, some of which are clearly involved in the response to drought stress. Many of the ASR1-enriched genomic loci we found encode enzymes involved in cell wall synthesis and remodeling as well as channels implicated in water and solute flux, such as aquaporins. In addition, we were able to determine a robust consensus ASR1-binding DNA motif. Conclusions The finding of cell wall synthesis and aquaporin genes as targets of ASR1 is consistent with their suggested role in the physiological adaptation of plants to water loss. The results gain insight into the environmental stress-sensing pathways leading to plant tolerance of drought. PMID:24423251

  3. How do plant cell walls extend?

    NASA Technical Reports Server (NTRS)

    Cosgrove, D. J.

    1993-01-01

    This article briefly summarizes recent work that identifies the biophysical and biochemical processes that give rise to the extension of plant cell walls. I begin with the biophysical notion of stress relaxation of the wall and follow with recent studies of wall enzymes thought to catalyze wall extension and relaxation. Readers should refer to detailed reviews for more comprehensive discussion of earlier literature (Taiz, 1984; Carpita and Gibeaut, 1993; Cosgrove, 1993).

  4. Catalysts of plant cell wall loosening

    PubMed Central

    Cosgrove, Daniel J.

    2016-01-01

    The growing cell wall in plants has conflicting requirements to be strong enough to withstand the high tensile forces generated by cell turgor pressure while selectively yielding to those forces to induce wall stress relaxation, leading to water uptake and polymer movements underlying cell wall expansion. In this article, I review emerging concepts of plant primary cell wall structure, the nature of wall extensibility and the action of expansins, family-9 and -12 endoglucanases, family-16 xyloglucan endotransglycosylase/hydrolase (XTH), and pectin methylesterases, and offer a critical assessment of their wall-loosening activity PMID:26918182

  5. Wall relaxation and the driving forces for cell expansive growth

    NASA Technical Reports Server (NTRS)

    Cosgrove, D. J.

    1987-01-01

    When water uptake by growing cells is prevented, the turgor pressure and the tensile stress in the cell wall are reduced by continued wall loosening. This process, termed in vivo stress relaxation, provides a new way to study the dynamics of wall loosening and to measure the wall yield threshold and the physiological wall extensibility. Stress relaxation experiments indicate that wall stress supplies the mechanical driving force for wall yielding. Cell expansion also requires water absorption. The driving force for water uptake during growth is created by wall relaxation, which lowers the water potential of the expanding cells. New techniques for measuring this driving force show that it is smaller than believed previously; in elongating stems it is only 0.3 to 0.5 bar. This means that the hydraulic resistance of the water transport pathway is small and that rate of cell expansion is controlled primarily by wall loosening and yielding.

  6. Relative importance of aneurysm diameter and body size for predicting AAA rupture in men and women

    PubMed Central

    Lo, Ruby C.; Lu, Bing; Fokkema, Margriet T.M.; Conrad, Mark; Patel, Virendra I.; Fillinger, Mark; Matyal, Robina; Schermerhorn, Marc L.

    2014-01-01

    Objectives Women have been shown to have up to a four-fold higher risk of abdominal aortic aneurysm (AAA) rupture at any given aneurysm diameter compared to men, leading to recommendations to offer repair to women at lower diameter thresholds. Although this higher risk of rupture may simply reflect greater relative aortic dilatation in women who have smaller aortas to begin with, this has never been quantified. Our objective was therefore to quantify the relationship between rupture and aneurysm diameter relative to body size and to determine whether a differential association between aneurysm diameter, body size, and rupture risk exists for men and women. Methods We performed a retrospective review of all patients in the Vascular Study Group of New England (VSGNE) database who underwent endovascular or open AAA repair. Using each patient’s height and weight, body mass index (BMI) and body surface area (BSA) were calculated. Next, indices of each measure of body size (height, weight, BMI, BSA) relative to aneurysm diameter were calculated for each patient. To generate these indices, we divided aneurysm diameter (in cm) by the measure of body size [e.g. aortic size index (ASI) = aneurysm diameter (cm) / BSA (m2)]. Along with other relevant clinical variables, we used these indices to construct different age-adjusted and multivariable-adjusted logistic regression models to determine predictors of ruptured repair vs. elective repair. Models for men and women were developed separately and different models were compared using the area under the curve (AUC). Results We identified 4045 patients who underwent AAA repair (78% male, 53% EVAR). Women had significantly smaller diameter aneurysms, lower BSA, and higher BSA indices than men (Table 1). For men, the variable that increased the odds of rupture the most was aneurysm diameter (AUC = 0.82). Men exhibited an increased rupture risk with increasing aneurysm diameter (<5.5cm: OR 1.0; 5.5–6.4cm: OR 0.9, 95% CI 0.5–1

  7. AAAS Mass Media Science and Engineering Fellowship Program: Building Communication Skills in Young Scientists

    NASA Astrophysics Data System (ADS)

    Pasco, S.

    2006-12-01

    The AAAS Mass Media Science &Engineering Fellowship program has succeeded in training scientists to become more effective communicators for more than 30 years. The program places advanced science, engineering and mathematics students at media sites to work as science reporters for ten weeks each summer. AAAS places between 15 to 20 students a year at newspapers, magazines and radio stations. Our goal is to create better science communicators who understand their role in fostering the public's understanding of science. Fellows leave the program with a greater awareness of how to communicate complex issues by making the connection as to why people should be interested in certain developments, and more specifically, how they will impact their communities. 2004 AGU Fellow Rei Ueyama put her lessons learned to good use during her Fellowship at the Sacramento Bee. "In a regional paper like The Bee, a (story) also had to have a local touch. I needed to show why people in Sacramento (or California) should bother to read the story. One example is the story I wrote about seeding the ocean with iron particles to fight global warming. Since ocean fertilization is a global issue, I had to clearly specify the reason why The Bee and not The New York Times was running the story. The local angle I chose was to point out that the core group of scientists involved in this study was from Monterey Bay, Calif." Many alumni tell us the program has been an integral force in shaping the course of their career. Similarly, sites often report that having a scientist on staff is an invaluable resource that allows them to cover additional science stories as well as report some technical stories in more depth. The American Geophysical Union has sponsored a Mass Media Fellow since 1997. Sponsorship allows affiliate program partners to establish connections with young professionals in their field. They are then also able to take advantage of the communication skills resident in their alumni base

  8. 'Stucco' Walls

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This projected mosaic image, taken by the microscopic imager, an instrument located on the Mars Exploration Rover Opportunity 's instrument deployment device, or 'arm,' shows the partial clotting or cement-like properties of the sand-sized grains within the trench wall. The area in this image measures approximately 3 centimeters (1.2 inches) wide and 5 centimeters (2 inches) tall.(This image also appears as an inset on a separate image from the rover's navigation camera, showing the location of this particular spot within the trench wall.)

  9. Prediction of Residual Stress Distributions in Welded Sections of P92 Pipes with Small Diameter and Thick Wall based on 3D Finite Element Simulation

    NASA Astrophysics Data System (ADS)

    Wang, Xiaowei; Gong, Jianming; Zhao, Yanping; Wang, Yanfei

    2015-05-01

    This study used ABAQUS finite element (FE) software to investigate the residual stress distributions of P92 welded pipes in both the as-weld and post weld heat treated (PWHT) condition. Sequential coupling quasi-static thermo-mechanical in conjunction with moving double ellipsoidal heat source and an element add/remove technique to simulate deposition of new weld material, are combined in the 3D FE analysis. To validate the simulation results, the residual stresses in axial direction at the surface of pipe were measured by X-ray diffraction technique and compared with the results of FE analysis. Detailed characteristic distributions of the residual stresses are discussed. Results show that the FE model can predict the residual stress distributions satisfactorily. Highest residual stresses on the outer surface are found in the last weld bead to be deposited. And the highest tensile residual stress for the full welded section take place in heat affected zone (HAZ) near the middle thickness. Larger residual sstress can be found around the welding start point along the pipe circumference. Comparison of heat treated specimen and untreated specimen illustrates that PWHT has a strong effect on the residual stress field.

  10. Computation of Turbulent Heat Transfer on the Walls of a 180 Degree Turn Channel With a Low Reynolds Number Reynolds Stress Model

    NASA Technical Reports Server (NTRS)

    Ameri, A. A.; Rigby, D. L.; Steinthorsson, E.; Gaugler, Raymond (Technical Monitor)

    2002-01-01

    The Low Reynolds number version of the Stress-omega model and the two equation k-omega model of Wilcox were used for the calculation of turbulent heat transfer in a 180 degree turn simulating an internal coolant passage. The Stress-omega model was chosen for its robustness. The turbulent thermal fluxes were calculated by modifying and using the Generalized Gradient Diffusion Hypothesis. The results showed that using this Reynolds Stress model allowed better prediction of heat transfer compared to the k-omega two equation model. This improvement however required a finer grid and commensurately more CPU time.

  11. Wall Covering

    NASA Technical Reports Server (NTRS)

    1978-01-01

    The attractive wall covering shown below is one of 132 styles in the Mirror Magic II line offered by The General Tire & Rubber Company, Akron, Ohio. The material is metallized plastic fabric, a spinoff from space programs. Wall coverings are one of many consumer applications of aluminized plastic film technology developed for NASA by a firm later bought by King-Seeley Thermos Company, Winchester, Massachusetts, which now produces the material. The original NASA use was in the Echo 1 passive communications satellite, a "space baloon" made of aluminized mylar; the high reflectivity of the metallized coating enabled relay of communications signals from one Earth station to another by "bouncing" them off the satellite. The reflectivity feature also made the material an extremely efficient insulator and it was subsequently widely used in the Apollo program for such purposes as temperature control of spacecraft components and insulation of tanks for fuels that must be maintained at very low temperatures. I Used as a wall covering, the aluminized material offers extra insulation, reflects light and I resists cracking. In addition to General Tire, King-Seeley also supplies wall covering material to Columbus Coated Fabrics Division of Borden, Incorporated, Columbus, Ohio, among others.

  12. Wall Art

    ERIC Educational Resources Information Center

    McGinley, Connie Q.

    2004-01-01

    The author of this article, an art teacher at Monarch High School in Louisville, Colorado, describes how her experience teaching in a new school presented an exciting visual challenge for an art teacher--monotonous brick walls just waiting for decoration. This school experienced only minimal instances of graffiti, but as an art teacher, she did…

  13. Critical clamp loader processing by an essential AAA+ protease in Caulobacter crescentus.

    PubMed

    Vass, Robert H; Chien, Peter

    2013-11-01

    Chromosome replication relies on sliding clamps that are loaded by energy-dependent complexes. In Escherichia coli, the ATP-binding clamp loader subunit DnaX exists as both long (τ) and short (γ) forms generated through programmed translational frameshifting, but the need for both forms is unclear. Here, we show that in Caulobacter crescentus, DnaX isoforms are unexpectedly generated through partial proteolysis by the AAA+ protease casein lytic proteinase (Clp) XP. We find that the normally processive ClpXP protease partially degrades DnaX to produce stable fragments upon encountering a glycine-rich region adjacent to a structured domain. Increasing the sequence complexity of this region prevents partial proteolysis and generates a τ-only form of DnaX in vivo that is unable to support viability on its own. Growth is restored when γ is provided in trans, but these strains are more sensitive to DNA damage compared with strains that can generate γ through proteolysis. Our work reveals an unexpected mode of partial processing by the ClpXP protease to generate DnaX isoforms, demonstrates that both τ and γ forms of DnaX are required for Caulobacter viability, and identifies a role for clamp loader diversity in responding to DNA damage. The conservation of distinct DnaX isoforms throughout bacteria despite fundamentally different mechanisms for producing them suggests there may be a conserved need for alternate clamp loader complexes during DNA damaging conditions.

  14. Abo1, a conserved bromodomain AAA-ATPase, maintains global nucleosome occupancy and organisation.

    PubMed

    Gal, Csenge; Murton, Heather E; Subramanian, Lakxmi; Whale, Alex J; Moore, Karen M; Paszkiewicz, Konrad; Codlin, Sandra; Bähler, Jürg; Creamer, Kevin M; Partridge, Janet F; Allshire, Robin C; Kent, Nicholas A; Whitehall, Simon K

    2016-01-01

    Maintenance of the correct level and organisation of nucleosomes is crucial for genome function. Here, we uncover a role for a conserved bromodomain AAA-ATPase, Abo1, in the maintenance of nucleosome architecture in fission yeast. Cells lacking abo1(+) experience both a reduction and mis-positioning of nucleosomes at transcribed sequences in addition to increased intragenic transcription, phenotypes that are hallmarks of defective chromatin re-establishment behind RNA polymerase II. Abo1 is recruited to gene sequences and associates with histone H3 and the histone chaperone FACT. Furthermore, the distribution of Abo1 on chromatin is disturbed by impaired FACT function. The role of Abo1 extends to some promoters and also to silent heterochromatin. Abo1 is recruited to pericentromeric heterochromatin independently of the HP1 ortholog, Swi6, where it enforces proper nucleosome occupancy. Consequently, loss of Abo1 alleviates silencing and causes elevated chromosome mis-segregation. We suggest that Abo1 provides a histone chaperone function that maintains nucleosome architecture genome-wide.

  15. AAA-ATPase FIDGETIN-LIKE 1 and Helicase FANCM Antagonize Meiotic Crossovers by Distinct Mechanisms

    PubMed Central

    Girard, Chloe; Chelysheva, Liudmila; Choinard, Sandrine; Froger, Nicole; Macaisne, Nicolas; Lehmemdi, Afef; Mazel, Julien; Crismani, Wayne; Mercier, Raphael

    2015-01-01

    Meiotic crossovers (COs) generate genetic diversity and are critical for the correct completion of meiosis in most species. Their occurrence is tightly constrained but the mechanisms underlying this limitation remain poorly understood. Here we identified the conserved AAA-ATPase FIDGETIN-LIKE-1 (FIGL1) as a negative regulator of meiotic CO formation. We show that Arabidopsis FIGL1 limits CO formation genome-wide, that FIGL1 controls dynamics of the two conserved recombinases DMC1 and RAD51 and that FIGL1 hinders the interaction between homologous chromosomes, suggesting that FIGL1 counteracts DMC1/RAD51-mediated inter-homologue strand invasion to limit CO formation. Further, depleting both FIGL1 and the previously identified anti-CO helicase FANCM synergistically increases crossover frequency. Additionally, we showed that the effect of mutating FANCM on recombination is much lower in F1 hybrids contrasting from the phenotype of inbred lines, while figl1 mutation equally increases crossovers in both contexts. This shows that the modes of action of FIGL1 and FANCM are differently affected by genomic contexts. We propose that FIGL1 and FANCM represent two successive barriers to CO formation, one limiting strand invasion, the other disassembling D-loops to promote SDSA, which when both lifted, leads to a large increase of crossovers, without impairing meiotic progression. PMID:26161528

  16. Critical clamp loader processing by an essential AAA+ protease in Caulobacter crescentus

    PubMed Central

    Vass, Robert H.; Chien, Peter

    2013-01-01

    Chromosome replication relies on sliding clamps that are loaded by energy-dependent complexes. In Escherichia coli, the ATP-binding clamp loader subunit DnaX exists as both long (τ) and short (γ) forms generated through programmed translational frameshifting, but the need for both forms is unclear. Here, we show that in Caulobacter crescentus, DnaX isoforms are unexpectedly generated through partial proteolysis by the AAA+ protease casein lytic proteinase (Clp) XP. We find that the normally processive ClpXP protease partially degrades DnaX to produce stable fragments upon encountering a glycine-rich region adjacent to a structured domain. Increasing the sequence complexity of this region prevents partial proteolysis and generates a τ-only form of DnaX in vivo that is unable to support viability on its own. Growth is restored when γ is provided in trans, but these strains are more sensitive to DNA damage compared with strains that can generate γ through proteolysis. Our work reveals an unexpected mode of partial processing by the ClpXP protease to generate DnaX isoforms, demonstrates that both τ and γ forms of DnaX are required for Caulobacter viability, and identifies a role for clamp loader diversity in responding to DNA damage. The conservation of distinct DnaX isoforms throughout bacteria despite fundamentally different mechanisms for producing them suggests there may be a conserved need for alternate clamp loader complexes during DNA damaging conditions. PMID:24145408

  17. Maintenance of mitochondrial genome distribution by mitochondrial AAA+ protein ClpX.

    PubMed

    Kasashima, Katsumi; Sumitani, Megumi; Endo, Hitoshi

    2012-11-01

    The segregation of mitochondrial DNA (mtDNA) is important for the maintenance and transmission of the genome between generations. Recently, we clarified that human mitochondrial transcription factor A (TFAM) is required for equal distribution and symmetric segregation of mtDNA in cultured cells; however, the molecular mechanism involved is largely unknown. ClpX is an ATPase associated with various cellular activities (AAA+) proteins that localize to the mitochondrial matrix and is suggested to associate with mtDNA. In this study, we found that RNAi-mediated knockdown of ClpX in HeLa cells resulted in enlarged mtDNA nucleoids, which is very similar to that observed in TFAM-knockdown cells in several properties. The expression of TFAM protein was not significantly reduced in ClpX-knockdown cells. However, the enlarged mtDNA nucleoids caused by ClpX-knockdown were suppressed by overexpression of recombinant TFAM and the phenotype was not observed in knockdown with ClpP, a protease subunit of ClpXP. Endogenous ClpX and TFAM exist in close vicinity, and ClpX enhanced DNA-binding activity of TFAM in vitro. These results suggest that human ClpX, a novel mtDNA regulator, maintains mtDNA nucleoid distribution through TFAM function as a chaperone rather than as a protease and its involvement in mtDNA segregation. PMID:22841477

  18. ATP-binding sites in brain p97/VCP (valosin-containing protein), a multifunctional AAA ATPase.

    PubMed Central

    Zalk, Ran; Shoshan-Barmatz, Varda

    2003-01-01

    VCP (valosin-containing protein) or p97 is a member of the AAA family (ATPases associated with a variety of cellular activities family), a diverse group of proteins sharing a key conserved AAA module containing duplicate putative ATP-binding sites. Although the functions of the AAA family are related to their putative ATP-binding sites, the binding of ATP to these sites has not yet been demonstrated. In the present study, the ATP-binding site(s) of brain VCP was characterized using the photoreactive ATP analogue, BzATP [3'- O -(4-benzoylbenzoyl)ATP]. Photo-activation of Bz-[alpha-(32)P]ATP resulted in its covalent binding to a 97-kDa purified soluble or membrane-associated protein, identified by amino acid sequencing as VCP. Bz-[alpha-(32)P]ATP covalently bound to the purified homo-hexameric VCP with an apparent high affinity (74-111 nM). A molar stoichiometry of 2.23+/-0.14 BzATP bound per homo-hexameric VCP (n =6) was determined using different methods for analysis of radiolabelling and protein determination. Nucleotides inhibited the binding of Bz-[alpha-(32)P]ATP to VCP with the following efficiency: BzATP>ATP>ADP>>adenosine 5'-[beta,gamma-imido]triphosphate>or=adenosine 5'-[beta,gamma-methylene]triphosphate, whereas AMP, GTP and CTP were ineffective. VCP was observed to possess very low ATPase activity, with nucleotide specificity similar to that for BzATP binding. Conformational changes induced by an alternating site mechanism for ATP binding are suggested as a molecular mechanism for coupling ATP binding to the diverse activities of the AAA family. PMID:12747802

  19. Patient-specific finite element modeling of the Cardiokinetix Parachute(®) device: effects on left ventricular wall stress and function.

    PubMed

    Lee, Lik Chuan; Ge, Liang; Zhang, Zhihong; Pease, Matthew; Nikolic, Serjan D; Mishra, Rakesh; Ratcliffe, Mark B; Guccione, Julius M

    2014-06-01

    The Parachute(®) (Cardiokinetix, Inc., Menlo Park, California) is a catheter-based device intended to reverse left ventricular (LV) remodeling after antero-apical myocardial infarction. When deployed, the device partitions the LV into upper and lower chambers. To simulate its mechanical effects, we created a finite element LV model based on computed tomography (CT) images from a patient before and 6 months after Parachute(®) implantation. Acute mechanical effects were determined by in silico device implantation (VIRTUAL-Parachute). Chronic effects of the device were determined by adjusting the diastolic and systolic material parameters to better match the 6-month post-implantation CT data and LV pressure data at end-diastole (ED) (POST-OP). Regional myofiber stress and pump function were calculated in each case. The principal finding is that VIRTUAL-Parachute was associated with a 61.2 % reduction in the lower chamber myofiber stress at ED. The POST-OP model was associated with a decrease in LV diastolic stiffness and a larger reduction in myofiber stress at the upper (27.1%) and lower chamber (78.4%) at ED. Myofiber stress at end-systole and stroke volume was little changed in the POST-OP case. These results suggest that the primary mechanism of Parachute(®) is a reduction in ED myofiber stress, which may reverse eccentric post-infarct LV hypertrophy.

  20. Involvement of Abscisic Acid in the Coordinated Regulation of a Stress-Inducible Hexose Transporter (VvHT5) and a Cell Wall Invertase in Grapevine in Response to Biotrophic Fungal Infection[W

    PubMed Central

    Hayes, Matthew A.; Feechan, Angela; Dry, Ian B.

    2010-01-01

    Biotrophic fungal and oomycete pathogens alter carbohydrate metabolism in infected host tissues. Symptoms such as elevated soluble carbohydrate concentrations and increased invertase activity suggest that a pathogen-induced carbohydrate sink is established. To identify pathogen-induced regulators of carbohydrate sink strength, quantitative real-time polymerase chain reaction was used to measure transcript levels of invertase and hexose transporter genes in biotrophic pathogen-infected grapevine (Vitis vinifera) leaves. The hexose transporter VvHT5 was highly induced in coordination with the cell wall invertase gene VvcwINV by powdery and downy mildew infection. However, similar responses were also observed in response to wounding, suggesting that this is a generalized response to stress. Analysis of the VvHT5 promoter region indicated the presence of multiple abscisic acid (ABA) response elements, suggesting a role for ABA in the transition from source to sink under stress conditions. ABA treatment of grape leaves was found to reproduce the same gene-specific transcriptional changes as observed under biotic and abiotic stress conditions. Furthermore, the key regulatory ABA biosynthetic gene, VvNCED1, was activated under these same stress conditions. VvHT5 promoter::β-glucuronidase-directed expression in transgenic Arabidopsis (Arabidopsis thaliana) was activated by infection with powdery mildew and by ABA treatment, and the expression was closely associated with vascular tissue adjacent to infected regions. Unlike VvHT1 and VvHT3, which appear to be predominantly involved in hexose transport in developing leaves and berries, VvHT5 appears to have a specific role in enhancing sink strength under stress conditions, and this is controlled through ABA. Our data suggest a central role for ABA in the regulation of VvcwINV and VvHT5 expression during the transition from source to sink in response to infection by biotrophic pathogens. PMID:20348211

  1. Expression of SOD and APX genes positively regulates secondary cell wall biosynthesis and promotes plant growth and yield in Arabidopsis under salt stress.

    PubMed

    Shafi, Amrina; Chauhan, Rohit; Gill, Tejpal; Swarnkar, Mohit K; Sreenivasulu, Yelam; Kumar, Sanjay; Kumar, Neeraj; Shankar, Ravi; Ahuja, Paramvir Singh; Singh, Anil Kumar

    2015-04-01

    Abiotic stresses cause accumulation of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) in plants. Sophisticated mechanisms are required to maintain optimum level of H2O2 that acts as signalling molecule regulating adaptive response to salt stress. CuZn-superoxide dismutase (CuZn-SOD) and ascorbate peroxidase (APX) constitute first line of defence against oxidative stress. In the present study, PaSOD and RaAPX genes from Potentilla atrosanguinea and Rheum australe, respectively were overexpressed individually as well as in combination in Arabidopsis thaliana. Interestingly, PaSOD and dual transgenic lines exhibit enhanced lignin deposition in their vascular bundles with altered S:G ratio under salt stress. RNA-seq analysis revealed that expression of PaSOD gene in single and dual transgenics positively regulates expression of lignin biosynthesis genes and transcription factors (NACs, MYBs, C3Hs and WRKY), leading to enhanced and ectopic deposition of lignin in vascular tissues with larger xylem fibres and alters S:G ratio, as well. In addition, transgenic plants exhibit growth promotion, higher biomass production and increased yield under salt stress as compared to wild type plants. Our results suggest that in dual transgenics, ROS generated during salt stress gets converted into H2O2 by SOD and its optimum level was maintained by APX. This basal level of H2O2 acts as messenger for transcriptional activation of lignin biosynthesis in vascular tissue, which provides mechanical strength to plants. These findings reveal an important role of PaSOD and RaAPX in enhancing salt tolerance of transgenic Arabidopsis via increased accumulation of compatible solutes and by regulating lignin biosynthesis.

  2. AAA+ proteases and their role in distinct stages along the Vibrio cholerae lifecycle.

    PubMed

    Pressler, Katharina; Vorkapic, Dina; Lichtenegger, Sabine; Malli, Gerald; Barilich, Benjamin P; Cakar, Fatih; Zingl, Franz G; Reidl, Joachim; Schild, Stefan

    2016-09-01

    The facultative human pathogen Vibrio cholerae has to adapt to different environmental conditions along its lifecycle by means of transcriptional, translational and post-translational regulation. This study provides a first comprehensive analysis regarding the contribution of the cytoplasmic AAA+ proteases Lon, ClpP and HslV to distinct features of V. cholerae behaviour, including biofilm formation, motility, cholera toxin expression and colonization fitness in the mouse model. While absence of HslV did not yield to any altered phenotype compared to wildtype, absence of Lon or ClpP resulted in significantly reduced colonization in vivo. In addition, a Δlon deletion mutant showed altered biofilm formation and increased motility, which could be correlated with higher expression of V. cholerae flagella gene class IV. Concordantly, we could show by immunoblot analysis, that Lon is the main protease responsible for proteolytic control of FliA, which is required for class IV flagella gene transcription, but also downregulates virulence gene expression. FliA becomes highly sensitive to proteolytic degradation in absence of its anti-sigma factor FlgM, a scenario reported to occur during mucosal penetration due to FlgM secretion through the broken flagellum. Our results confirm that the high stability of FliA in the absence of Lon results in less cholera toxin and toxin corgulated pilus production under virulence gene inducing conditions and in the presence of a damaged flagellum. Thus, the data presented herein provide a molecular explanation on how V. cholerae can achieve full expression of virulence genes during early stages of colonization, despite FliA getting liberated from the anti-sigma factor FlgM. PMID:27345492

  3. Crystal structure of a novel archaeal AAA+ ATPase SSO1545 from Sulfolobus solfataricus

    SciTech Connect

    Xu, Qingping; Rife, Christopher L.; Carlton, Dennis; Miller, Mitchell D.; Krishna, S. Sri; Elsliger, Marc-André; Abdubek, Polat; Astakhova, Tamara; Chiu, Hsiu-Ju; Clayton, Thomas; Duan, Lian; Feuerhelm, Julie; Grzechnik, Slawomir K.; Hale, Joanna; Han, Gye Won; Jaroszewski, Lukasz; Jin, Kevin K.; Klock, Heath E.; Knuth, Mark W.; Kumar, Abhinav; McMullan, Daniel; Morse, Andrew T.; Nigoghossian, Edward; Okach, Linda; Oommachen, Silvya; Paulsen, Jessica; Reyes, Ron; van den Bedem, Henry; Hodgson, Keith O.; Wooley, John; Deacon, Ashley M.; Godzik, Adam; Lesley, Scott A.; Wilson, Ian A.

    2009-08-28

    Signal transduction ATPases with numerous domains (STAND), a large class of P-loop NTPases, belong to AAA+ ATPases. They include AP(apoptotic)-ATPases (e.g., animal apoptosis regulators CED4/Apaf-1, plant disease resistance proteins, and bacterial AfsR-like transcription regulators), NACHT NTPases (e.g. CARD4, NAIP, Het-E-1, TLP1), and several other less well-characterized families. STAND differ from other P-loop NTPases by their unique sequence motifs, which include an hhGRExE (h, hydrophobic; x, any residue) motif at the N-terminal region, a GxP/GxxP motif at the C-terminal region of the NTPase domain, in addition to a C-terminal helical domain and additional domains such as WD40, TPR, LRR or catalytic modules. Despite significant biological interests, structural coverage of STAND proteins is very limited and only two other structures are currently known: the cell death regulators Apaf-1 and CED-4. Here, we report the crystal structure of SSO1545 from Sulfolobus solfataricus, which was determined using the semi-automated, high-throughput pipeline of the Joint Center for Structural Genomics (JCSG; http://www.jcsg.org), as part of the National Institute of General Medical Sciences' Protein Structure Initiative (PSI). SSO1545 (NP-342973.1), a representative of the archaeal STANDs, is a member of Pfam PF01637 and encodes a protein of 356 residues with calculated molecular weight and isoelectric point of 41.7 kD and 8.2, respectively.

  4. Candida albicans cell shaving uncovers new proteins involved in cell wall integrity, yeast to hypha transition, stress response and host-pathogen interaction

    PubMed Central

    Hernáez, María Luisa; Reales-Calderon, Jose Antonio; Solis, Norma V.; Filler, Scott G.; Monteoliva, Lucia; Gil, Concha

    2015-01-01

    The ability to switch from yeast to hyphal growth is essential for virulence in Candida albicans. The cell surface is the initial point of contact between the fungus and the host. In this work, a free-gel proteomic strategy based on tryptic digestion of live yeast and hyphae cells and protein identification using LC-MS/MS methodology was used to identify cell surface proteins. Using this strategy, a total of 943 proteins were identified, of which 438 were in yeast and 928 were in hyphae. Of these proteins, 79 were closely related to the organization and biogenesis of the cell wall, including 28 GPI-anchored proteins, such as Hyr1 and Sod5 which were detected exclusively in hyphae, and Als2 and Sap10which were detected only in yeast. A group of 17 proteins of unknown function were subsequently studied by analysis of the corresponding deletion mutants. We found that four new proteins, Pst3, Tos1, Orf19.3060 and Orf19.5352 are involved in cell wall integrity and in C. albicans’ engulfment by macrophages. Moreover, the putative NADH-ubiquinone-related proteins, Ali1, Mci4, Orf19.287 and Orf19.7590, are also involved in osmotic and oxidative resistance, yeast to hypha transition and the ability to damage and invade oral epithelial cells. PMID:26087349

  5. SMAD3 deficiency promotes vessel wall remodeling, collagen fiber reorganization and leukocyte infiltration in an inflammatory abdominal aortic aneurysm mouse model

    PubMed Central

    Dai, Xiaohua; Shen, Jianbin; Priyanka Annam, Neeraja; Jiang, Hong; Levi, Edi; Schworer, Charles M.; Tromp, Gerard; Arora, Anandita; Higgins, Mary; Wang, Xiao-Fan; Yang, Maozhou; Li, Hui J.; Zhang, Kezhong; Kuivaniemi, Helena; Li, Li

    2015-01-01

    TGF-β signaling plays critical roles in the pathogenesis of aneurysms; however, it is still unclear whether its role is protective or destructive. In this study, we investigate the role of SMAD3 in the pathogenesis of calcium chloride (CaCl2)-induced abdominal aortic aneurysms (AAA) in Smad3−/−, Smad3+/− and Smad3+/+ mice. We find that loss of SMAD3 drastically increases wall thickening of the abdominal aorta. Histological analyses show significant vessel wall remodeling with elastic fiber fragmentation. Remarkably, under polarized light, collagen fibers in the hyperplastic adventitia of Smad3−/− mice show extensive reorganization accompanied by loosely packed thin and radial collagen fibers. The expressions of matrix metalloproteinases including MMP2, MMP9, and MMP12 and infiltration of macrophage/T cells are drastically enhanced in the vascular wall of Smad3−/− mice. We also observe marked increase of NF-κB and ERK1/2 signaling as well as the expression of nuclear Smad2, Smad4 and TGF-β1 in the vessel wall of Smad3−/− mice. In addition, we find that SMAD3 expression is reduced in the dedifferentiated medial smooth muscle-like cells of human AAA patients. These findings provide direct in vivo evidence to support the essential roles of SMAD3 in protecting vessel wall integrity and suppressing inflammation in the pathogenesis of AAAs. PMID:25985281

  6. Prevalence of previously undiagnosed abdominal aortic aneurysms in the area of Como: the ComoCuore "looking for AAA" ultrasonography screening.

    PubMed

    Corrado, Giovanni; Durante, Alessandro; Genchi, Vincenzo; Trabattoni, Loris; Beretta, Sandro; Rovelli, Enza; Foglia-Manzillo, Giovanni; Ferrari, Giovanni

    2016-08-01

    The prognosis for abdominal aortic aneurysm (AAA) rupture is poor. Long-term follow-up of population-based randomized trials has demonstrated that ultrasound (US) screening for abdominal aortic aneurysms (AAAs) measuring 3 cm or greater decreases AAA-related mortality rates and is cost-effective. We though to prospectively perform during a 26-month period a limited US examination of the infrarenal aorta in volunteers of both gender aged 60-85 years without history of AAA living in the area of Como, Italy. From September 2010 to November 2013 ComoCuore, a no-profit nongovernmental association, enrolled 1555 people (aged 68.8 ± 6.8 years; 48.6 % males). Clinical data and a US imaging of the aorta were collected for each participant. AAA was found in 22 volunteers (1.4 %) mainly males (2.5 % in males vs. 0.4 % in females p = 0.005). Overall, the prevalence of cardiovascular risk factors was higher in patients with vs. without AAA (mean 2.9 ± 3.0 vs. 1.4 ± 1.0 respectively, p < 0.0001). Independent predictors of AAA on multivariate analysis were age (OR 1.14, 1.06-1.22; p < 0.0001), male gender (OR 8.23, 1.79-37.91; p = 0.007), and both current (OR 4.98, 1.57-15.79; p = 0.007) and previous smoking (OR 2.76, 1.12-8.94; p = 0.03). Our study confirms the feasibility of one time US screening for AAA in a large cohort of asymptomatic people. Independent predictors of AAA were male sex, older age and a history of smoking. Accordingly to recent data the prevalence of AAA seems to be declining, maybe due to a reduction of smoking in Italy. PMID:27215751

  7. Prevalence of previously undiagnosed abdominal aortic aneurysms in the area of Como: the ComoCuore "looking for AAA" ultrasonography screening.

    PubMed

    Corrado, Giovanni; Durante, Alessandro; Genchi, Vincenzo; Trabattoni, Loris; Beretta, Sandro; Rovelli, Enza; Foglia-Manzillo, Giovanni; Ferrari, Giovanni

    2016-08-01

    The prognosis for abdominal aortic aneurysm (AAA) rupture is poor. Long-term follow-up of population-based randomized trials has demonstrated that ultrasound (US) screening for abdominal aortic aneurysms (AAAs) measuring 3 cm or greater decreases AAA-related mortality rates and is cost-effective. We though to prospectively perform during a 26-month period a limited US examination of the infrarenal aorta in volunteers of both gender aged 60-85 years without history of AAA living in the area of Como, Italy. From September 2010 to November 2013 ComoCuore, a no-profit nongovernmental association, enrolled 1555 people (aged 68.8 ± 6.8 years; 48.6 % males). Clinical data and a US imaging of the aorta were collected for each participant. AAA was found in 22 volunteers (1.4 %) mainly males (2.5 % in males vs. 0.4 % in females p = 0.005). Overall, the prevalence of cardiovascular risk factors was higher in patients with vs. without AAA (mean 2.9 ± 3.0 vs. 1.4 ± 1.0 respectively, p < 0.0001). Independent predictors of AAA on multivariate analysis were age (OR 1.14, 1.06-1.22; p < 0.0001), male gender (OR 8.23, 1.79-37.91; p = 0.007), and both current (OR 4.98, 1.57-15.79; p = 0.007) and previous smoking (OR 2.76, 1.12-8.94; p = 0.03). Our study confirms the feasibility of one time US screening for AAA in a large cohort of asymptomatic people. Independent predictors of AAA were male sex, older age and a history of smoking. Accordingly to recent data the prevalence of AAA seems to be declining, maybe due to a reduction of smoking in Italy.

  8. Regional wall motion abnormality in apical ballooning syndrome (Takotsubo/stress cardiomyopathy): importance of biplane left ventriculography for differentiating from spontaneously aborted anterior myocardial infarction.

    PubMed

    Patel, Sandeep M; Lennon, Ryan J; Prasad, Abhiram

    2012-04-01

    Understanding the precise distribution of the regional wall motion abnormality (RWMA) in apical ballooning syndrome (ABS) is important because the cardiomyopathy can mimic an acute anterior ST-elevation myocardial infarction (STEMI). The aim of the study was to quantify the severity and distribution of RWMA in ABS, compare it to anterior STEMI, and correlate with clinical features. RWMA (normal = 1, hypokinetic = 2, akinetic = 3) was quantified from the biplane left ventriculogram using a nine-segment model in 95 ABS and 17 anterior STEMI patients at the time of their presentation. Regional wall motion score index (RWMSI) was higher in ABS [2.1 (1.9, 2.1)] compared to anterior STEMI [2.0 (1.8, 2.0)], P = 0.024]. The region that most clearly differentiated ABS from anterior STEMI was the posterolateral segment (sensitivity 81% and specificity 100%) which was hypocontractile in 81% of ABS, but none of the STEMI patients (P < 0.001). RWMSI in ABS had a modest positive correlation with the troponin T levels (r = 0.23, P = 0.029). Patients with ABS with ST-segment elevation had the highest RWMSI [2.1(2.0, 2.2)], while those with non specific changes had the lowest [1.9 (1.8, 2.1)] (P = 0.007). In conclusion, patients with ABS have greater and more diffuse RWMA compared to anterior STEMI. The presence of systolic dysfunction in the posterolateral segment in the left anterior oblique projection of the left ventriculogram most accurately distinguishes ABS from an anterior STEMI highlighting the utility of biplane angiography for this purpose. The severity of RWMA correlates with the extent of troponin release and ECG abnormality.

  9. Cooling wall

    SciTech Connect

    Nosenko, V.I.

    1995-07-01

    Protecting the shells of blast furnaces is being resolved by installing cast iron cooling plates. The cooling plates become non-operational in three to five years. The problem is that defects occur in manufacturing the cooling plates. With increased volume and intensity of work placed on blast furnaces, heat on the cast iron cooling plates reduces their reliability that limits the interim repair period of blast furnaces. Scientists and engineers from the Ukraine studied this problem for several years, developing a new method of cooling the blast furnace shaft called the cooling wall. Traditional cast iron plates were replaced by a screen of steel tubes, with the area between the tubes filled with fireproof concrete. Before placing the newly developed furnace shaft into operation, considerable work was completed such as theoretical calculations, design, research of temperature fields and tension. Continual testing over many years confirms the value of this research in operating blast furnaces. The cooling wall works with water cooling as well as vapor cooling and is operating in 14 blast furnaces in the Ukraine and two in Russia, and has operated for as long as 14 years.

  10. Biomechanical rupture risk assessment of abdominal aortic aneurysms based on a novel probabilistic rupture risk index.

    PubMed

    Polzer, Stanislav; Gasser, T Christian

    2015-12-01

    A rupture risk assessment is critical to the clinical treatment of abdominal aortic aneurysm (AAA) patients. The biomechanical AAA rupture risk assessment quantitatively integrates many known AAA rupture risk factors but the variability of risk predictions due to model input uncertainties remains a challenging limitation. This study derives a probabilistic rupture risk index (PRRI). Specifically, the uncertainties in AAA wall thickness and wall strength were considered, and wall stress was predicted with a state-of-the-art deterministic biomechanical model. The discriminative power of PRRI was tested in a diameter-matched cohort of ruptured (n = 7) and intact (n = 7) AAAs and compared to alternative risk assessment methods. Computed PRRI at 1.5 mean arterial pressure was significantly (p = 0.041) higher in ruptured AAAs (20.21(s.d. 14.15%)) than in intact AAAs (3.71(s.d. 5.77)%). PRRI showed a high sensitivity and specificity (discriminative power of 0.837) to discriminate between ruptured and intact AAA cases. The underlying statistical representation of stochastic data of wall thickness, wall strength and peak wall stress had only negligible effects on PRRI computations. Uncertainties in AAA wall stress predictions, the wide range of reported wall strength and the stochastic nature of failure motivate a probabilistic rupture risk assessment. Advanced AAA biomechanical modelling paired with a probabilistic rupture index definition as known from engineering risk assessment seems to be superior to a purely deterministic approach. PMID:26631334

  11. Self rating of health is associated with stressful life events, social support and residency in East and West Berlin shortly after the fall of the wall

    PubMed Central

    Hillen, T.; Schaub, R.; Hiestermann, A.; Kirschner, W.; Robra, B.

    2000-01-01

    STUDY OBJECTIVE—To compare the health status and factors influencing the health of populations that had previously lived under different political systems.
DESIGN—Cross sectional health and social survey using postal interviews. The relation between self reported health and psychosocial factors (stressful life events, social support, education, health promoting life style and health endangering behaviour) was investigated. To determine East-West differences a logistic regression model including interaction terms was fitted.
SETTING—East and West Berlin shortly after reunification 1991.
PARTICIPANTS—Representative sample of 4430 Berlin residents aged 18 years and over (response rate 63%).
RESULTS—Of all respondents, 15.4% rated their health as unsatisfactory. Residents of East Berlin rated their health more frequently as unsatisfactory than residents of West Berlin (Orage adjusted= 1.29, 95%CI 1.08, 1.52), these differences occurred predominantly in the over 60 years age group. Logistic regression showed significant independent effects of stressful life events, social support, education, and health promoting life style on self rated health. The effects of education and health promoting life style were observed to be more pronounced in the western part of Berlin. Old age and female sex showed a stronger association with unsatisfactory health status in the eastern part of Berlin.
CONCLUSIONS—For subjects aged over 60 years there was evidence that living in the former East Berlin had an adverse effect on health compared with West Berlin. The impact of education and a health promoting lifestyle on self rated health seemed to be weaker in a former socialist society compared with that of a Western democracy. This study supports an "additive model" rather than a "buffering model" in explaining the effects of psychosocial factors on health.


Keywords: self rated health; health inequalities; stress; social support PMID:10890868

  12. Near-wall similarity in a pressure-driven three-dimensional turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Pierce, F. J.; Mcallister, J. E.

    1980-01-01

    Mean velocity, measured wall pressure and wall shear stress fields were made in a three dimensional pressure-driven turbulent boundary layer created by a cylinder with trailing edge placed normal to a flat plate floor. The direct force wall shear stress measurements were made with floating element direct force sensing shear meter that responded to both the magnitude and direction of the local wall shear stress. The ability of 10 near wall similarity models to describe the near wall velocity field for the measured flow under a wide range of skewing conditions and a variety of pressure gradient and wall shear vector orientations was used.

  13. The AAA+ proteins Pontin and Reptin enter adult age: from understanding their basic biology to the identification of selective inhibitors.

    PubMed

    Matias, Pedro M; Baek, Sung Hee; Bandeiras, Tiago M; Dutta, Anindya; Houry, Walid A; Llorca, Oscar; Rosenbaum, Jean

    2015-01-01

    Pontin and Reptin are related partner proteins belonging to the AAA+ (ATPases Associated with various cellular Activities) family. They are implicated in multiple and seemingly unrelated processes encompassing the regulation of gene transcription, the remodeling of chromatin, DNA damage sensing and repair, and the assembly of protein and ribonucleoprotein complexes, among others. The 2nd International Workshop on Pontin and Reptin took place at the Instituto de Tecnologia Química e Biológica António Xavier in Oeiras, Portugal on October 10-12, 2014, and reported significant new advances on the mechanisms of action of these two AAA+ ATPases. The major points under discussion were related to the mechanisms through which these proteins regulate gene transcription, their roles as co-chaperones, and their involvement in pathophysiology, especially in cancer and ciliary biology and disease. Finally, they may become anticancer drug targets since small chemical inhibitors were shown to produce anti-tumor effects in animal models.

  14. The AAA+ ATPase ATAD3A Controls Mitochondrial Dynamics at the Interface of the Inner and Outer Membranes ▿

    PubMed Central

    Gilquin, Benoît; Taillebourg, Emmanuel; Cherradi, Nadia; Hubstenberger, Arnaud; Gay, Olivia; Merle, Nicolas; Assard, Nicole; Fauvarque, Marie-Odile; Tomohiro, Shiho; Kuge, Osamu; Baudier, Jacques

    2010-01-01

    Dynamic interactions between components of the outer (OM) and inner (IM) membranes control a number of critical mitochondrial functions such as channeling of metabolites and coordinated fission and fusion. We identify here the mitochondrial AAA+ ATPase protein ATAD3A specific to multicellular eukaryotes as a participant in these interactions. The N-terminal domain interacts with the OM. A central transmembrane segment (TMS) anchors the protein in the IM and positions the C-terminal AAA+ ATPase domain in the matrix. Invalidation studies in Drosophila and in a human steroidogenic cell line showed that ATAD3A is required for normal cell growth and cholesterol channeling at contact sites. Using dominant-negative mutants, including a defective ATP-binding mutant and a truncated 50-amino-acid N-terminus mutant, we showed that ATAD3A regulates dynamic interactions between the mitochondrial OM and IM sensed by the cell fission machinery. The capacity of ATAD3A to impact essential mitochondrial functions and organization suggests that it possesses unique properties in regulating mitochondrial dynamics and cellular functions in multicellular organisms. PMID:20154147

  15. Unfolding the mechanism of the AAA+ unfoldase VAT by a combined cryo-EM, solution NMR study.

    PubMed

    Huang, Rui; Ripstein, Zev A; Augustyniak, Rafal; Lazniewski, Michal; Ginalski, Krzysztof; Kay, Lewis E; Rubinstein, John L

    2016-07-19

    The AAA+ (ATPases associated with a variety of cellular activities) enzymes play critical roles in a variety of homeostatic processes in all kingdoms of life. Valosin-containing protein-like ATPase of Thermoplasma acidophilum (VAT), the archaeal homolog of the ubiquitous AAA+ protein Cdc48/p97, functions in concert with the 20S proteasome by unfolding substrates and passing them on for degradation. Here, we present electron cryomicroscopy (cryo-EM) maps showing that VAT undergoes large conformational rearrangements during its ATP hydrolysis cycle that differ dramatically from the conformational states observed for Cdc48/p97. We validate key features of the model with biochemical and solution methyl-transverse relaxation optimized spectroscopY (TROSY) NMR experiments and suggest a mechanism for coupling the energy of nucleotide hydrolysis to substrate unfolding. These findings illustrate the unique complementarity between cryo-EM and solution NMR for studies of molecular machines, showing that the structural properties of VAT, as well as the population distributions of conformers, are similar in the frozen specimens used for cryo-EM and in the solution phase where NMR spectra are recorded.

  16. FtsH11 Proteases play a critical role in high temperature stress tolerance in plants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    FtsHs (Filamentous temperature sensitive H), ATP-dependent zinc metalloproteases of the AAA-superfamily, play essential roles in the turn over of thylakoid proteins damaged by high light stress during photosynthesis. Here, we show that FtsH11, one of the 12 FtsH members in Arabidopsis, plays critic...

  17. Large-eddy simulations with wall models

    NASA Technical Reports Server (NTRS)

    Cabot, W.

    1995-01-01

    The near-wall viscous and buffer regions of wall-bounded flows generally require a large expenditure of computational resources to be resolved adequately, even in large-eddy simulation (LES). Often as much as 50% of the grid points in a computational domain are devoted to these regions. The dense grids that this implies also generally require small time steps for numerical stability and/or accuracy. It is commonly assumed that the inner wall layers are near equilibrium, so that the standard logarithmic law can be applied as the boundary condition for the wall stress well away from the wall, for example, in the logarithmic region, obviating the need to expend large amounts of grid points and computational time in this region. This approach is commonly employed in LES of planetary boundary layers, and it has also been used for some simple engineering flows. In order to calculate accurately a wall-bounded flow with coarse wall resolution, one requires the wall stress as a boundary condition. The goal of this work is to determine the extent to which equilibrium and boundary layer assumptions are valid in the near-wall regions, to develop models for the inner layer based on such assumptions, and to test these modeling ideas in some relatively simple flows with different pressure gradients, such as channel flow and flow over a backward-facing step. Ultimately, models that perform adequately in these situations will be applied to more complex flow configurations, such as an airfoil.

  18. Advanced glycation end products (AGEs) on the surface of diabetic erythrocytes bind to the vessel wall via a specific receptor inducing oxidant stress in the vasculature: a link between surface-associated AGEs and diabetic complications.

    PubMed Central

    Wautier, J L; Wautier, M P; Schmidt, A M; Anderson, G M; Hori, O; Zoukourian, C; Capron, L; Chappey, O; Yan, S D; Brett, J

    1994-01-01

    Vascular complications are an important cause of morbidity and mortality in patients with diabetes. The extent of vascular complications has been linked statistically to enhanced adherence of diabetic erythrocytes to endothelial cells (ECs) and to the accumulation of a class of glycated proteins termed advanced glycation end products (AGEs). We hypothesized that formation of AGEs on the surface of diabetic erythrocytes could mediate their interaction with ECs leading to binding and induction of vascular dysfunction. Enhanced binding of diabetic erythrocytes to ECs was blocked by preincubation of erythrocytes with anti-AGE IgG or preincubation of ECs with antibodies to the receptor for AGE (RAGE). Immunoblotting of cultured human ECs and immunostaining of normal/diabetic human tissue confirmed the presence of RAGE in the vessel wall. Binding of diabetic erythrocytes to endothelium generated an oxidant stress, as measured by production of thiobarbituric acid-reactive substances (TBARS) and activation of the transcription factor NF-kappa B, both of which were blocked by probucol or anti-RAGE IgG. Erythrocytes from diabetic rats infused into normal rats had an accelerated, early phase of clearance that was prevented, in part, by antibody to RAGE. Liver tissue from rats infused with diabetic erythrocytes showed elevated levels of TBARS, which was prevented by pretreatment with anti-RAGE IgG or probucol. Thus, erythrocyte surface AGEs can function as ligands that interact with RAGE on endothelium. The extensive contact of diabetic erythrocytes bearing surface-associated AGEs with vessel wall RAGE could be important in the development of vascular complications. Images PMID:8052654

  19. Profiling of the toxicity mechanisms of coated and uncoated silver nanoparticles to yeast Saccharomyces cerevisiae BY4741 using a set of its 9 single-gene deletion mutants defective in oxidative stress response, cell wall or membrane integrity and endocytosis.

    PubMed

    Käosaar, Sandra; Kahru, Anne; Mantecca, Paride; Kasemets, Kaja

    2016-09-01

    The widespread use of nanosilver in various antibacterial, antifungal, and antiviral products warrants the studies of the toxicity pathways of nanosilver-enabled materials toward microbes and viruses. We profiled the toxicity mechanisms of uncoated, casein-coated, and polyvinylpyrrolidone-coated silver nanoparticles (AgNPs) using Saccharomyces cerevisiae wild-type (wt) and its 9 single-gene deletion mutants defective in oxidative stress (OS) defense, cell wall/membrane integrity, and endocytosis. The 48-h growth inhibition assay in organic-rich growth medium and 24-h cell viability assay in deionized (DI) water were applied whereas AgNO3, H2O2, and SDS served as positive controls. Both coated AgNPs (primary size 8-12nm) were significantly more toxic than the uncoated (~85nm) AgNPs. All studied AgNPs were ~30 times more toxic if exposed to yeast cells in DI water than in the rich growth medium: the IC50 based on nominal concentration of AgNPs in the growth inhibition test ranged from 77 to 576mg Ag/L and in the cell viability test from 2.7 to 18.7mg Ag/L, respectively. Confocal microscopy showed that wt but not endocytosis mutant (end3Δ) internalized AgNPs. Comparison of toxicity patterns of wt and mutant strains defective in OS defense and membrane integrity revealed that the toxicity of the studied AgNPs to S. cerevisiae was not caused by the OS or cell wall/membrane permeabilization. PMID:27260961

  20. Transcriptome analysis of Listeria monocytogenes exposed to biocide stress reveals a multi-system response involving cell wall synthesis, sugar uptake, and motility.

    PubMed

    Casey, Aidan; Fox, Edward M; Schmitz-Esser, Stephan; Coffey, Aidan; McAuliffe, Olivia; Jordan, Kieran

    2014-01-01

    Listeria monocytogenes is a virulent food-borne pathogen most often associated with the consumption of "ready-to-eat" foods. The organism is a common contaminant of food processing plants where it may persist for extended periods of time. A commonly used approach for the control of Listeria monocytogenes in the processing environment is the application of biocides such as quaternary ammonium compounds. In this study, the transcriptomic response of a persistent strain of L. monocytogenes (strain 6179) on exposure to a sub-lethal concentration of the quaternary ammonium compound benzethonium chloride (BZT) was assessed. Using RNA-Seq, gene expression levels were quantified by sequencing the transcriptome of L. monocytogenes 6179 in the presence (4 ppm) and absence of BZT, and mapping each data set to the sequenced genome of strain 6179. Hundreds of differentially expressed genes were identified, and subsequent analysis suggested that many biological processes such as peptidoglycan biosynthesis, bacterial chemotaxis and motility, and carbohydrate uptake, were involved in the response of L. monocyotogenes to the presence of BZT. The information generated in this study further contributes to our understanding of the response of bacteria to environmental stress. In addition, this study demonstrates the importance of using the bacterium's own genome as a reference when analysing RNA-Seq data.

  1. Transcriptome analysis of Listeria monocytogenes exposed to biocide stress reveals a multi-system response involving cell wall synthesis, sugar uptake, and motility

    PubMed Central

    Casey, Aidan; Fox, Edward M.; Schmitz-Esser, Stephan; Coffey, Aidan; McAuliffe, Olivia; Jordan, Kieran

    2014-01-01

    Listeria monocytogenes is a virulent food-borne pathogen most often associated with the consumption of “ready-to-eat” foods. The organism is a common contaminant of food processing plants where it may persist for extended periods of time. A commonly used approach for the control of Listeria monocytogenes in the processing environment is the application of biocides such as quaternary ammonium compounds. In this study, the transcriptomic response of a persistent strain of L. monocytogenes (strain 6179) on exposure to a sub-lethal concentration of the quaternary ammonium compound benzethonium chloride (BZT) was assessed. Using RNA-Seq, gene expression levels were quantified by sequencing the transcriptome of L. monocytogenes 6179 in the presence (4 ppm) and absence of BZT, and mapping each data set to the sequenced genome of strain 6179. Hundreds of differentially expressed genes were identified, and subsequent analysis suggested that many biological processes such as peptidoglycan biosynthesis, bacterial chemotaxis and motility, and carbohydrate uptake, were involved in the response of L. monocyotogenes to the presence of BZT. The information generated in this study further contributes to our understanding of the response of bacteria to environmental stress. In addition, this study demonstrates the importance of using the bacterium's own genome as a reference when analysing RNA-Seq data. PMID:24616718

  2. From AAA to Acuros XB-clinical implications of selecting either Acuros XB dose-to-water or dose-to-medium.

    PubMed

    Zifodya, Jackson M; Challens, Cameron H C; Hsieh, Wen-Long

    2016-06-01

    When implementing Acuros XB (AXB) as a substitute for anisotropic analytic algorithm (AAA) in the Eclipse Treatment Planning System, one is faced with a dilemma of reporting either dose to medium, AXB-Dm or dose to water, AXB-Dw. To assist with decision making on selecting either AXB-Dm or AXB-Dw for dose reporting, a retrospective study of treated patients for head & neck (H&N), prostate, breast and lung is presented. Ten patients, previously treated using AAA plans, were selected for each site and re-planned with AXB-Dm and AXB-Dw. Re-planning was done with fixed monitor units (MU) as well as non-fixed MUs. Dose volume histograms (DVH) of targets and organs at risk (OAR), were analyzed in conjunction with ICRU-83 recommended dose reporting metrics. Additionally, comparisons of plan homogeneity indices (HI) and MUs were done to further highlight the differences between the algorithms. Results showed that, on average AAA overestimated dose to the target volume and OARs by less than 2.0 %. Comparisons between AXB-Dw and AXB-Dm, for all sites, also showed overall dose differences to be small (<1.5 %). However, in non-water biological media, dose differences between AXB-Dw and AXB-Dm, as large as 4.6 % were observed. AXB-Dw also tended to have unexpectedly high 3D maximum dose values (>135 % of prescription dose) for target volumes with high density materials. Homogeneity indices showed that AAA planning and optimization templates would need to be adjusted only for the H&N and Lung sites. MU comparison showed insignificant differences between AXB-Dw relative to AAA and between AXB-Dw relative to AXB-Dm. However AXB-Dm MUs relative to AAA, showed an average difference of about 1.3 % signifying an underdosage by AAA. In conclusion, when dose is reported as AXB-Dw, the effect that high density structures in the PTV has on the dose distribution should be carefully considered. As the results show overall small dose differences between the algorithms, when

  3. From AAA to Acuros XB-clinical implications of selecting either Acuros XB dose-to-water or dose-to-medium.

    PubMed

    Zifodya, Jackson M; Challens, Cameron H C; Hsieh, Wen-Long

    2016-06-01

    When implementing Acuros XB (AXB) as a substitute for anisotropic analytic algorithm (AAA) in the Eclipse Treatment Planning System, one is faced with a dilemma of reporting either dose to medium, AXB-Dm or dose to water, AXB-Dw. To assist with decision making on selecting either AXB-Dm or AXB-Dw for dose reporting, a retrospective study of treated patients for head & neck (H&N), prostate, breast and lung is presented. Ten patients, previously treated using AAA plans, were selected for each site and re-planned with AXB-Dm and AXB-Dw. Re-planning was done with fixed monitor units (MU) as well as non-fixed MUs. Dose volume histograms (DVH) of targets and organs at risk (OAR), were analyzed in conjunction with ICRU-83 recommended dose reporting metrics. Additionally, comparisons of plan homogeneity indices (HI) and MUs were done to further highlight the differences between the algorithms. Results showed that, on average AAA overestimated dose to the target volume and OARs by less than 2.0 %. Comparisons between AXB-Dw and AXB-Dm, for all sites, also showed overall dose differences to be small (<1.5 %). However, in non-water biological media, dose differences between AXB-Dw and AXB-Dm, as large as 4.6 % were observed. AXB-Dw also tended to have unexpectedly high 3D maximum dose values (>135 % of prescription dose) for target volumes with high density materials. Homogeneity indices showed that AAA planning and optimization templates would need to be adjusted only for the H&N and Lung sites. MU comparison showed insignificant differences between AXB-Dw relative to AAA and between AXB-Dw relative to AXB-Dm. However AXB-Dm MUs relative to AAA, showed an average difference of about 1.3 % signifying an underdosage by AAA. In conclusion, when dose is reported as AXB-Dw, the effect that high density structures in the PTV has on the dose distribution should be carefully considered. As the results show overall small dose differences between the algorithms, when

  4. Cell wall-associated kinases and pectin perception.

    PubMed

    Kohorn, Bruce D

    2016-01-01

    The pectin matrix of the angiosperm cell wall is regulated in both synthesis and modification and greatly influences the direction and extent of cell growth. Pathogens, herbivory and mechanical stresses all influence this pectin matrix and consequently plant form and function. The cell wall-associated kinases (WAKs) bind to pectin and regulate cell expansion or stress responses depending upon the state of the pectin. This review explores the WAKs in the context of cell wall biology and signal transduction pathways.

  5. In-line inspection device to detect and size stress corrosion cracks utilizing low frequency eddy currents in combination with magnetic saturation of the pipe wall in natural gas pipelines

    SciTech Connect

    Hayford, D.T.; Davis, R.J.

    1992-12-21

    In two earlier research programs conducted for the NDT Supervisory Committee, Battelle developed low-frequency eddy current equipment for detecting and characterizing stress corrosion cracks from the outside of gas transmission pipelines without requiring the removal of the protective coating. In this program, Battelle examined the possibility of using this or similar equipment to detect stress corrosion cracks from the interior of the pipeline by magnetically saturating the pipeline to reduce the permeability of the pipeline material and thereby increase the penetration of eddy current fields into the pipeline. The study was divided into two parts, an analytical study to determine how well eddy currents could be used to detect cracks if the permeability of the pipeline material is reduced by using magnetic saturation and an experimental study to verify the results of the analytical study and to determine how much the permeability could be reduced using a large magnetizing field. The analytical study indicated that significant improvements could be made in the defect sensitivity of eddy current probes to external cracks even if the pipeline is not completely saturated; reducing the permeability to a value as high as 10 would be sufficient. However, the experimental study showed just how difficult it is to reduce the permeability of the pipeline to such a low value. The power required to reduce the permeability to 33 was about 5 kilowatts, which we believe is excessive for an internal inspection device; however, this power requirement may be reduced by a better design. With a transverse permeability of 33, we believe that defects which are 70 percent or more of the pipe wall in depth would be detectable with an eddy current device.

  6. SU-E-T-137: Dosimetric Validation for Pinnacle, Acuros, AAA, and Brainlab Algorithms with Induced Inhomogenieties

    SciTech Connect

    Lopez, P; Tambasco, M; LaFontaine, R; Burns, L

    2014-06-01

    Purpose: To compare the dosimetric accuracy of the Eclipse 11.0 Acuros XB and Anisotropic Analytical Algorithm (AAA), Pinnacle-3 9.2 Collapsed Cone Convolution, and the iPlan 4.1 Monte Carlo (MC) and Pencil Beam (PB) algorithms using measurement as the gold standard. Methods: Ion chamber and diode measurements were taken for 6, 10, and 18 MV beams in a phantom made up of slab densities corresponding to solid water, lung, and bone. The phantom was setup at source-to-surface distance of 100 cm, and the field sizes were 3.0 × 3.0, 5.0 × 5.0, and 10.0 × 10.0 cm2. Data from the planning systems were computed along the central axis of the beam. The measurements were taken using a pinpoint chamber and edge diode for interface regions. Results: The best agreement between data from the algorithms and our measurements occurs away from the slab interfaces. For the 6 MV beam, iPlan 4.1 MC software performs the best with 1.7% absolute average percent difference from measurement. For the 10 MV beam, iPlan 4.1 PB performs the best with 2.7% absolute average percent difference from measurement. For the 18 MV beam, Acuros performs the best with 2.0% absolute average percent difference from measurement. It is interesting to note that the steepest drop in dose occurred the at lung heterogeneity-solid water interface of the18 MV, 3.0 × 3.0 cm2 field size setup. In this situation, Acuros and AAA performed best with an average percent difference within −1.1% of measurement, followed by iPlan 4.1 MC, which was within 4.9%. Conclusion: This study shows that all of the algorithms perform reasonably well in computing dose in a heterogeneous slab phantom. Moreover, Acuros and AAA perform particularly well at the lung-solid water interfaces for higher energy beams and small field sizes.

  7. Dependence on injection temperature and on aquifer's petrophysical properties of the local stress applying on the pore wall of a crystallized pore in the context of CO2 storage in deep saline aquifers

    NASA Astrophysics Data System (ADS)

    Osselin, Florian; Fen-Chong, Teddy; Fabbri, Antonin; Lassin, Arnault; Pereira, Jean-Michel; Dangla, Patrick

    2013-11-01

    The development of CCS (carbon capture and storage) currently faces numerous problems and particularly the precipitation of salts induced by the drying of the porous medium during injection of carbon dioxide in deep saline aquifers. This precipitation has several consequences, and particularly the creation of a crystallization pressure which can have an important mechanical impact on the host rock. Literature on crystallization pressure is one century rich of experimental and theoretical works. However, applications have been performed in the field of civil engineering and building science only, and, despite they are of paramount importance in the context of CCS, studies about this phenomenon in deep reservoir conditions are currently lacking. In this paper, we retrieve the classic crystallization pressure equation within the framework of geochemistry and present its explicit form of dependence with temperature, pressure, and composition. Evaluation of the crystallization pressure has then been proceeded considering the injection conditions and a sketch of in-pore crystallization process. The evolution of the local stress transmitted to a crystallized pore wall is found to be strongly related to the petrophysical properties of the medium and to the injection temperature of the carbon dioxide under the assumption of constant salt concentration during the precipitation process. Values differ strongly with the considered mineral, depending particularly on the solubility, and can reach in some conditions 165 MPa, making crystallization pressure a major factor in the mechanical behavior of the aquifer.

  8. The Pex1/Pex6 complex is a heterohexameric AAA+ motor with alternating and highly coordinated subunits

    PubMed Central

    Gardner, Brooke M.; Chowdhury, Saikat; Lander, Gabriel C.; Martin, Andreas

    2015-01-01

    Pex1 and Pex6 are Type-2 AAA+ ATPases required for the de-novo biogenesis of peroxisomes. Mutations in Pex1 and Pex6 account for the majority of the most severe forms of peroxisome biogenesis disorders in humans. Here we show that the ATP-dependent complex of Pex1 and Pex6 from S. cerevisiae is a heterohexamer with alternating subunits. Within the Pex1/Pex6 complex, only the D2 ATPase ring hydrolyzes ATP, while nucleotide binding in the D1 ring promotes complex assembly. ATP hydrolysis by Pex1 is highly coordinated with that of Pex6. Furthermore, Pex15, the membrane anchor required for Pex1/Pex6 recruitment to peroxisomes inhibits the ATP-hydrolysis activity of Pex1/Pex6. PMID:25659908

  9. The talent endoluminal AAA stent-graft system. Report of the phase I USA trial, and summary of worldwide experience.

    PubMed

    Criado, F J; Fry, P D; Machan, L S; Twena, M; Patten, P

    1998-12-01

    In the United States, the Phase I Feasibility Study under IDE G970065 was approved by the Food and Drug Administration on 04/11/97. The approved protocol called for implantation of the bifurcated Talent spring stent-graft system on patients who are high-risk candidates for conventional surgery because of cardio-respiratory, medical, general, or local anatomical reasons which would likely complicate the technical execution of the operation or be accompanied by a high expected mortality rate. Patient enrollment was complete with 16 cases as of September 26, 1997. This was a multicenter experience involving five different sites. This is an ongoing study and patients, of course, will continue to be followed longitudinally. Phase II will likely be approved by the FDA for initiation in January or February of 1998. Standard-risk AAA patients will be entered into the study at this time; comparison with concurrent controls will be used for comparison with conventional surgery. PMID:9894193

  10. Structural Characterization of a Newly Identified Component of α-Carboxysomes: The AAA+ Domain Protein CsoCbbQ

    SciTech Connect

    Sutter, Markus; Roberts, Evan W.; Gonzalez, Raul C.; Bates, Cassandra; Dawoud, Salma; Landry, Kimberly; Cannon, Gordon C.; Heinhorst, Sabine; Kerfeld, Cheryl A.

    2015-11-05

    Carboxysomes are bacterial microcompartments that enhance carbon fixation by concentrating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and its substrate CO2 within a proteinaceous shell. They are found in all cyanobacteria, some purple photoautotrophs and many chemoautotrophic bacteria. Carboxysomes consist of a protein shell that encapsulates several hundred molecules of RuBisCO, and contain carbonic anhydrase and other accessory proteins. Genes coding for carboxysome shell components and the encapsulated proteins are typically found together in an operon. The α-carboxysome operon is embedded in a cluster of additional, conserved genes that are presumably related to its function. In many chemoautotrophs, products of the expanded carboxysome locus include CbbO and CbbQ, a member of the AAA+ domain superfamily. We bioinformatically identified subtypes of CbbQ proteins and show that their genes frequently co-occur with both Form IA and Form II RuBisCO. The α-carboxysome-associated ortholog, CsoCbbQ, from Halothiobacillus neapolitanus forms a hexamer in solution and hydrolyzes ATP. The crystal structure shows that CsoCbbQ is a hexamer of the typical AAA+ domain; the additional C-terminal domain, diagnostic of the CbbQ subfamily, structurally fills the inter-monomer gaps, resulting in a distinctly hexagonal shape. Finally, we show that CsoCbbQ interacts with CsoCbbO and is a component of the carboxysome shell, the first example of ATPase activity associated with a bacterial microcompartment.

  11. Structural Characterization of a Newly Identified Component of α-Carboxysomes: The AAA+ Domain Protein CsoCbbQ

    DOE PAGES

    Sutter, Markus; Roberts, Evan W.; Gonzalez, Raul C.; Bates, Cassandra; Dawoud, Salma; Landry, Kimberly; Cannon, Gordon C.; Heinhorst, Sabine; Kerfeld, Cheryl A.

    2015-11-05

    Carboxysomes are bacterial microcompartments that enhance carbon fixation by concentrating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and its substrate CO2 within a proteinaceous shell. They are found in all cyanobacteria, some purple photoautotrophs and many chemoautotrophic bacteria. Carboxysomes consist of a protein shell that encapsulates several hundred molecules of RuBisCO, and contain carbonic anhydrase and other accessory proteins. Genes coding for carboxysome shell components and the encapsulated proteins are typically found together in an operon. The α-carboxysome operon is embedded in a cluster of additional, conserved genes that are presumably related to its function. In many chemoautotrophs, products of the expanded carboxysome locusmore » include CbbO and CbbQ, a member of the AAA+ domain superfamily. We bioinformatically identified subtypes of CbbQ proteins and show that their genes frequently co-occur with both Form IA and Form II RuBisCO. The α-carboxysome-associated ortholog, CsoCbbQ, from Halothiobacillus neapolitanus forms a hexamer in solution and hydrolyzes ATP. The crystal structure shows that CsoCbbQ is a hexamer of the typical AAA+ domain; the additional C-terminal domain, diagnostic of the CbbQ subfamily, structurally fills the inter-monomer gaps, resulting in a distinctly hexagonal shape. Finally, we show that CsoCbbQ interacts with CsoCbbO and is a component of the carboxysome shell, the first example of ATPase activity associated with a bacterial microcompartment.« less

  12. Structural Characterization of a Newly Identified Component of α-Carboxysomes: The AAA+ Domain Protein CsoCbbQ

    PubMed Central

    Sutter, Markus; Roberts, Evan W.; Gonzalez, Raul C.; Bates, Cassandra; Dawoud, Salma; Landry, Kimberly; Cannon, Gordon C.; Heinhorst, Sabine; Kerfeld, Cheryl A.

    2015-01-01

    Carboxysomes are bacterial microcompartments that enhance carbon fixation by concentrating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and its substrate CO2 within a proteinaceous shell. They are found in all cyanobacteria, some purple photoautotrophs and many chemoautotrophic bacteria. Carboxysomes consist of a protein shell that encapsulates several hundred molecules of RuBisCO, and contain carbonic anhydrase and other accessory proteins. Genes coding for carboxysome shell components and the encapsulated proteins are typically found together in an operon. The α-carboxysome operon is embedded in a cluster of additional, conserved genes that are presumably related to its function. In many chemoautotrophs, products of the expanded carboxysome locus include CbbO and CbbQ, a member of the AAA+ domain superfamily. We bioinformatically identified subtypes of CbbQ proteins and show that their genes frequently co-occur with both Form IA and Form II RuBisCO. The α-carboxysome-associated ortholog, CsoCbbQ, from Halothiobacillus neapolitanus forms a hexamer in solution and hydrolyzes ATP. The crystal structure shows that CsoCbbQ is a hexamer of the typical AAA+ domain; the additional C-terminal domain, diagnostic of the CbbQ subfamily, structurally fills the inter-monomer gaps, resulting in a distinctly hexagonal shape. We show that CsoCbbQ interacts with CsoCbbO and is a component of the carboxysome shell, the first example of ATPase activity associated with a bacterial microcompartment. PMID:26538283

  13. In vitro propagation and assessment of the genetic fidelity of Musa acuminata (AAA) cv. Vaibalhla derived from immature male flowers.

    PubMed

    Hrahsel, Lalremsiami; Basu, Adreeja; Sahoo, Lingaraj; Thangjam, Robert

    2014-02-01

    An efficient in vitro propagation method has been developed for the first time for Musa acuminata (AAA) cv. Vaibalhla, an economically important banana cultivar of Mizoram, India. Immature male flowers were used as explants. Murashige and Skoog's (MS) medium supplemented with plant growth regulators (PGRs) were used for the regeneration process. Out of different PGR combinations, MS medium supplemented with 2 mg L(-1) 6-benzylaminopurine (BAP) + 0.5 mg L(-1) α-naphthalene acetic acid (NAA) was optimal for production of white bud-like structures (WBLS). On this medium, explants produced the highest number of buds per explant (4.30). The highest percentage (77.77) and number (3.51) of shoot formation from each explants was observed in MS medium supplemented with 2 mg L(-1) kinetin + 0.5 mg L(-1) NAA. While MS medium supplemented with a combination of 2 mg L(-1) BAP + 0.5 mg L(-1) NAA showed the maximum shoot length (14.44 cm). Rooting efficiency of the shoots was highest in the MS basal medium without any PGRs. The plantlets were hardened successfully in the greenhouse with 96% survival rate. Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were employed to assess the genetic stability of in vitro regenerated plantlets of M. acuminata (AAA) cv. Vaibalhla. Eight RAPD and 8 ISSR primers were successfully used for the analysis from the 40 RAPD and 30 ISSR primers screened initially. The amplified products were monomorphic across all the regenerated plants and were similar to the mother plant. The present standardised protocol will find application in mass production, conservation and genetic transformation studies of this commercially important banana.

  14. Wall surveyor project report

    SciTech Connect

    Mullenhoff, D.J.; Johnston, B.C.; Azevedo, S.G.

    1996-02-22

    A report is made on the demonstration of a first-generation Wall Surveyor that is capable of surveying the interior and thickness of a stone, brick, or cement wall. LLNL`s Micropower Impulse Radar is used, based on emitting and detecting very low amplitude and short microwave impulses (MIR rangefinder). Six test walls were used. While the demonstrator MIR Wall Surveyor is not fieldable yet, it has successfully scanned the test walls and produced real-time images identifying the walls. It is planned to optimize and package the evaluation wall surveyor into a hand held unit.

  15. Measuring in vitro extensibility of growing plant cell walls.

    PubMed

    Cosgrove, Daniel J

    2011-01-01

    This article summarizes the theory and practical aspects of measuring cell wall properties by four different extensometer techniques and how the results of these methods relate to the concept and ideal measurement of cell wall extensibility in the context of cell growth. These in vivo techniques are particularly useful for studies of the molecular basis of cell wall extension. Measurements of breaking strength, elastic compliance, and plastic compliance may be informative about changes in cell wall structure, whereas measurements of wall stress relaxation and creep are sensitive to both changes in wall structure and wall-loosening processes, such as those mediated by expansins and some lytic enzymes. A combination of methods is needed to obtain a broader view of cell wall behavior and properties connected with the concept of cell wall extensibility.

  16. Measuring in-vitro extensibility of growth plant cell walls

    SciTech Connect

    Cosgrove, Daniel

    2011-01-01

    This article summarizes the theory and practical aspects of measuring cell wall properties by four different extensometer techniques and how the results of these methods relate to the concept and ideal measurement of cell wall extensibility in the context of cell growth. These in vivo techniques are particularly useful for studies of the molecular basis of cell wall extension. Measurements of breaking strength, elastic compliance, and plastic compliance may be informative about changes in cell wall structure, whereas measurements of wall stress relaxation and creep are sensitive to both changes in wall structure and wall-loosening processes, such as those mediated by expansins and some lytic enzymes. A combination of methods is needed to obtain a broader view of cell wall behavior and properties connected with the concept of cell wall extensibility.

  17. If walls could talk

    NASA Technical Reports Server (NTRS)

    Braam, J.; McIntire, L. V. (Principal Investigator)

    1999-01-01

    The plant cell wall is very complex, both in structure and function. The wall components and the mechanical properties of the wall have been implicated in conveying information that is important for morphogenesis. Proteoglycans, fragments of polysaccharides and the structural integrity of the wall may relay signals that influence cellular differentiation and growth control. Furthering our knowledge of cell wall structure and function is likely to have a profound impact on our understanding of how plant cells communicate with the extracellular environment.

  18. Fluidized wall for protecting fusion chamber walls

    SciTech Connect

    Maniscalco, J.A.; Meier, W.R.

    1982-08-17

    Apparatus for protecting the inner wall of a fusion chamber from microexplosion debris, x-rays, neutrons, etc. Produced by deuterium-tritium (DT) targets imploded within the fusion chamber. The apparatus utilizes a fluidized wall similar to a waterfall comprising liquid lithium or solid pellets of lithiumceramic, the waterfall forming a blanket to prevent damage of the structural materials of the chamber.

  19. Children with ANSD fitted with hearing aids applying the AAA Pediatric Amplification Guideline: Current Practice and Outcomes

    PubMed Central

    Walker, Elizabeth A.; McCreery, Ryan W.; Spratford, Meredith; Roush, Patricia A.

    2015-01-01

    Background Up to 15% of children with permanent hearing loss have auditory neuropathy spectrum disorder (ANSD), which involves normal outer hair cell function and disordered afferent neural activity in the auditory nerve or brainstem. Given the varying presentations of ANSD in children, there is a need for more evidence-based research on appropriate clinical interventions for this population. Purpose This study compared the speech production, speech perception, and language outcomes of children with auditory neuropathy spectrum disorder (ANSD) who are hard of hearing and children with similar degrees of mild to moderately-severe sensorineural hearing loss (SNHL), all of whom were fitted with bilateral hearing aids based on the American Academy of Audiology (AAA) pediatric amplification guidelines. Research design Speech perception and communication outcomes data were gathered in a prospective accelerated longitudinal design, with entry into the study between six months and seven years of age. Three sites were involved in participant recruitment: Boys Town National Research Hospital, the University of North Carolina at Chapel Hill, and the University of Iowa. Study sample: The sample consisted of 12 children with ANSD and 22 children with SNHL. The groups were matched based on better-ear pure-tone average, better-ear aided speech intelligibility index, gender, maternal education level, and newborn hearing screening result (i.e., pass or refer). Data collection and analysis Children and their families participated in an initial baseline visit, followed by visits twice a year for children under age 2 years and once a year for children older than 2 years. Paired-sample t-tests were used to compare children with ANSD to children with SNHL. Results Paired t-tests indicated no significant differences between the ANSD and SNHL groups on language and articulation measures. Children with ANSD displayed functional speech perception skills in quiet. Although the number of

  20. Computational Growth and Remodeling of Abdominal Aortic Aneurysms Constrained by the Spine.

    PubMed

    Farsad, Mehdi; Zeinali-Davarani, Shahrokh; Choi, Jongeun; Baek, Seungik

    2015-09-01

    Abdominal aortic aneurysms (AAAs) evolve over time, and the vertebral column, which acts as an external barrier, affects their biomechanical properties. Mechanical interaction between AAAs and the spine is believed to alter the geometry, wall stress distribution, and blood flow, although the degree of this interaction may depend on AAAs specific configurations. In this study, we use a growth and remodeling (G&R) model, which is able to trace alterations of the geometry, thus allowing us to computationally investigate the effect of the spine for progression of the AAA. Medical image-based geometry of an aorta is constructed along with the spine surface, which is incorporated into the computational model as a cloud of points. The G&R simulation is initiated by local elastin degradation with different spatial distributions. The AAA-spine interaction is accounted for using a penalty method when the AAA surface meets the spine surface. The simulation results show that, while the radial growth of the AAA wall is prevented on the posterior side due to the spine acting as a constraint, the AAA expands faster on the anterior side, leading to higher curvature and asymmetry in the AAA configuration compared to the simulation excluding the spine. Accordingly, the AAA wall stress increases on the lateral, posterolateral, and the shoulder regions of the anterior side due to the AAA-spine contact. In addition, more collagen is deposited on the regions with a maximum diameter. We show that an image-based computational G&R model not only enhances the prediction of the geometry, wall stress, and strength distributions of AAAs but also provides a framework to account for the interactions between an enlarging AAA and the spine for a better rupture potential assessment and management of AAA patients.

  1. Regulation of Cell Wall Biogenesis in Saccharomyces cerevisiae: The Cell Wall Integrity Signaling Pathway

    PubMed Central

    Levin, David E.

    2011-01-01

    The yeast cell wall is a strong, but elastic, structure that is essential not only for the maintenance of cell shape and integrity, but also for progression through the cell cycle. During growth and morphogenesis, and in response to environmental challenges, the cell wall is remodeled in a highly regulated and polarized manner, a process that is principally under the control of the cell wall integrity (CWI) signaling pathway. This pathway transmits wall stress signals from the cell surface to the Rho1 GTPase, which mobilizes a physiologic response through a variety of effectors. Activation of CWI signaling regulates the production of various carbohydrate polymers of the cell wall, as well as their polarized delivery to the site of cell wall remodeling. This review article centers on CWI signaling in Saccharomyces cerevisiae through the cell cycle and in response to cell wall stress. The interface of this signaling pathway with other pathways that contribute to the maintenance of cell wall integrity is also discussed. PMID:22174182

  2. The Lamportian cell wall

    SciTech Connect

    Keiliszewski, M.; Lamport, D. )

    1991-05-01

    The Lamportian Warp-Weft hypothesis suggests a cellulose-extensin interpenetrating network where extensin mechanically couples the load-bearing cellulose microfibrils in a wall matrix that is best described as a microcomposite. This model is based on data gathered from the extensin-rich walls of tomato and sycamore cell suspension culture, wherein extensin precursors are insolubilized into the wall by undefined crosslinks. The authors recent work with cell walls isolated from intact tissue as well as walls from suspension cultured cells of the graminaceous monocots maize and rice, the non-graminaceous monocot asparagus, the primitive herbaceous dicot sugar beet, and the gymnosperm Douglas Fir indicate that although extensins are ubiquitous to all plant species examined, they are not the major structural protein component of most walls examined. Amino acid analyses of intact and HF-treated walls shows a major component neither an HRGP, nor directly comparable to the glycine-rich wall proteins such as those associated with seed coat walls or the 67 mole% glycine-rich proteins cloned from petunia and soybean. Clearly, structural wall protein alternatives to extensin exist and any cell wall model must take that into account. If we assume that extracellular matrices are a priori network structures, then new Hypless' structural proteins in the maize cell wall raise questions about the sort of network these proteins create: the kinds of crosslinks involved; how they are formed; and the roles played by the small amounts of HRGPs.

  3. Halogenation of microcapsule walls

    NASA Technical Reports Server (NTRS)

    Davis, T. R.; Schaab, C. K.; Scott, J. C.

    1972-01-01

    Procedure for halogenation of confining walls of both gelatin and gelatin-phenolic resin capsules is similar to that used for microencapsulation. Ten percent halogen content renders capsule wall nonburning; any higher content enhances flame-retardant properties of selected internal phase material. Halogenation decreases permeability of wall material to encapsulated materials.

  4. The Pch2 AAA+ ATPase promotes phosphorylation of the Hop1 meiotic checkpoint adaptor in response to synaptonemal complex defects.

    PubMed

    Herruzo, Esther; Ontoso, David; González-Arranz, Sara; Cavero, Santiago; Lechuga, Ana; San-Segundo, Pedro A

    2016-09-19

    Meiotic cells possess surveillance mechanisms that monitor critical events such as recombination and chromosome synapsis. Meiotic defects resulting from the absence of the synaptonemal complex component Zip1 activate a meiosis-specific checkpoint network resulting in delayed or arrested meiotic progression. Pch2 is an evolutionarily conserved AAA+ ATPase required for the checkpoint-induced meiotic block in the zip1 mutant, where Pch2 is only detectable at the ribosomal DNA array (nucleolus). We describe here that high levels of the Hop1 protein, a checkpoint adaptor that localizes to chromosome axes, suppress the checkpoint defect of a zip1 pch2 mutant restoring Mek1 activity and meiotic cell cycle delay. We demonstrate that the critical role of Pch2 in this synapsis checkpoint is to sustain Mec1-dependent phosphorylation of Hop1 at threonine 318. We also show that the ATPase activity of Pch2 is essential for its checkpoint function and that ATP binding to Pch2 is required for its localization. Previous work has shown that Pch2 negatively regulates Hop1 chromosome abundance during unchallenged meiosis. Based on our results, we propose that, under checkpoint-inducing conditions, Pch2 also possesses a positive action on Hop1 promoting its phosphorylation and its proper distribution on unsynapsed chromosome axes. PMID:27257060

  5. Thyroid Hormone Receptor Interacting Protein 13 (TRIP13) AAA-ATPase Is a Novel Mitotic Checkpoint-silencing Protein*

    PubMed Central

    Wang, Kexi; Sturt-Gillespie, Brianne; Hittle, James C.; Macdonald, Dawn; Chan, Gordon K.; Yen, Tim J.; Liu, Song-Tao

    2014-01-01

    The mitotic checkpoint (or spindle assembly checkpoint) is a fail-safe mechanism to prevent chromosome missegregation by delaying anaphase onset in the presence of defective kinetochore-microtubule attachment. The target of the checkpoint is the E3 ubiquitin ligase anaphase-promoting complex/cyclosome. Once all chromosomes are properly attached and bioriented at the metaphase plate, the checkpoint needs to be silenced. Previously, we and others have reported that TRIP13 AAA-ATPase binds to the mitotic checkpoint-silencing protein p31comet. Here we show that endogenous TRIP13 localizes to kinetochores. TRIP13 knockdown delays metaphase-to-anaphase transition. The delay is caused by prolonged presence of the effector for the checkpoint, the mitotic checkpoint complex, and its association and inhibition of the anaphase-promoting complex/cyclosome. These results suggest that TRIP13 is a novel mitotic checkpoint-silencing protein. The ATPase activity of TRIP13 is essential for its checkpoint function, and interference with TRIP13 abolished p31comet-mediated mitotic checkpoint silencing. TRIP13 overexpression is a hallmark of cancer cells showing chromosomal instability, particularly in certain breast cancers with poor prognosis. We suggest that premature mitotic checkpoint silencing triggered by TRIP13 overexpression may promote cancer development. PMID:25012665

  6. Disassembly of mitotic checkpoint complexes by the joint action of the AAA-ATPase TRIP13 and p31comet

    PubMed Central

    Eytan, Esther; Wang, Kexi; Miniowitz-Shemtov, Shirly; Sitry-Shevah, Danielle; Kaisari, Sharon; Yen, Tim J.; Liu, Song-Tao; Hershko, Avram

    2014-01-01

    The mitotic (or spindle assembly) checkpoint system delays anaphase until all chromosomes are correctly attached to the mitotic spindle. When the checkpoint is active, a Mitotic Checkpoint Complex (MCC) assembles and inhibits the ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C). MCC is composed of the checkpoint proteins Mad2, BubR1, and Bub3 associated with the APC/C activator Cdc20. When the checkpoint signal is turned off, MCC is disassembled and the checkpoint is inactivated. The mechanisms of the disassembly of MCC are not sufficiently understood. We have previously observed that ATP hydrolysis is required for the action of the Mad2-binding protein p31comet to disassemble MCC. We now show that HeLa cell extracts contain a factor that promotes ATP- and p31comet-dependent disassembly of a Cdc20–Mad2 subcomplex and identify it as Thyroid Receptor Interacting Protein 13 (TRIP13), an AAA-ATPase known to interact with p31comet. The joint action of TRIP13 and p31comet also promotes the release of Mad2 from MCC, participates in the complete disassembly of MCC and abrogates checkpoint inhibition of APC/C. We propose that TRIP13 plays centrally important roles in the sequence of events leading to MCC disassembly and checkpoint inactivation. PMID:25092294

  7. Multiple sequence signals direct recognition and degradation of protein substrates by the AAA+ protease HslUV.

    PubMed

    Sundar, Shankar; McGinness, Kathleen E; Baker, Tania A; Sauer, Robert T

    2010-10-29

    Proteolysis is important for protein quality control and for the proper regulation of many intracellular processes in prokaryotes and eukaryotes. Discerning substrates from other cellular proteins is a key aspect of proteolytic function. The Escherichia coli HslUV protease is a member of a major family of ATP-dependent AAA+ degradation machines. HslU hexamers recognize and unfold native protein substrates and then translocate the polypeptide into the degradation chamber of the HslV peptidase. Although a wealth of structural information is available for this system, relatively little is known about mechanisms of substrate recognition. Here, we demonstrate that mutations in the unstructured N-terminal and C-terminal sequences of two model substrates alter HslUV recognition and degradation kinetics, including changes in V(max). By introducing N- or C-terminal sequences that serve as recognition sites for specific peptide-binding proteins, we show that blocking either terminus of the substrate interferes with HslUV degradation, with synergistic effects when both termini are obstructed. These results support a model in which one terminus of the substrate is tethered to the protease and the other terminus is engaged by the translocation/unfolding machinery in the HslU pore. Thus, degradation appears to consist of discrete steps, which involve the interaction of different terminal sequence signals in the substrate with different receptor sites in the HslUV protease. PMID:20837023

  8. In-situ monitoring of blood glucose level for dialysis machine by AAA-battery-size ATR Fourier spectroscopy

    NASA Astrophysics Data System (ADS)

    Hosono, Satsuki; Sato, Shun; Ishida, Akane; Suzuki, Yo; Inohara, Daichi; Nogo, Kosuke; Abeygunawardhana, Pradeep K.; Suzuki, Satoru; Nishiyama, Akira; Wada, Kenji; Ishimaru, Ichiro

    2015-07-01

    For blood glucose level measurement of dialysis machines, we proposed AAA-battery-size ATR (Attenuated total reflection) Fourier spectroscopy in middle infrared light region. The proposed one-shot Fourier spectroscopic imaging is a near-common path and spatial phase-shift interferometer with high time resolution. Because numerous number of spectral data that is 60 (= camera frame rare e.g. 60[Hz]) multiplied by pixel number could be obtained in 1[sec.], statistical-averaging improvement realize high-accurate spectral measurement. We evaluated the quantitative accuracy of our proposed method for measuring glucose concentration in near-infrared light region with liquid cells. We confirmed that absorbance at 1600[nm] had high correlations with glucose concentrations (correlation coefficient: 0.92). But to measure whole-blood, complex light phenomenon caused from red blood cells, that is scattering and multiple reflection or so, deteriorate spectral data. Thus, we also proposed the ultrasound-assisted spectroscopic imaging that traps particles at standing-wave node. Thus, if ATR prism is oscillated mechanically, anti-node area is generated around evanescent light field on prism surface. By elimination complex light phenomenon of red blood cells, glucose concentration in whole-blood will be quantify with high accuracy. In this report, we successfully trapped red blood cells in normal saline solution with ultrasonic standing wave (frequency: 2[MHz]).

  9. The IbpA and IbpB small heat-shock proteins are substrates of the AAA+ Lon protease.

    PubMed

    Bissonnette, Sarah A; Rivera-Rivera, Izarys; Sauer, Robert T; Baker, Tania A

    2010-03-01

    Small heat-shock proteins (sHSPs) are a widely conserved family of molecular chaperones, all containing a conserved alpha-crystallin domain flanked by variable N- and C-terminal tails. We report that IbpA and IbpB, the sHSPs of Escherichia coli, are substrates for the AAA+ Lon protease. This ATP-fueled enzyme degraded purified IbpA substantially more slowly than purified IbpB, and we demonstrate that this disparity is a consequence of differences in maximal Lon degradation rates and not in substrate affinity. Interestingly, however, IbpB stimulated Lon degradation of IbpA both in vitro and in vivo. Furthermore, although the variable N- and C-terminal tails of the Ibps were dispensable for proteolytic recognition, these tails contain critical determinants that control the maximal rate of Lon degradation. Finally, we show that E. coli Lon degrades variants of human alpha-crystallin, indicating that Lon recognizes conserved determinants in the folded alpha-crystallin domain itself. These results suggest a novel mode for Lon substrate recognition and provide a highly suggestive link between the degradation and sHSP branches of the protein quality-control network.

  10. Random amplified polymorphic DNA (RAPD) detection of dwarf off-types in micropropagated Cavendish (Musa spp. AAA) bananas.

    PubMed

    Damasco, O P; Graham, G C; Henry, R J; Adkins, S W; Smiths, M K; Godwin, I D

    1996-11-01

    A RAPD marker specific to the dwarf off-type (hereafter known as dwarf) from micropropagation of Cavendish banana (Musa spp. AAA) cultivars New Guinea Cavendish and Williams was identified following an analysis of 57 normal (true-to-type) and 59 dwarf plants generated from several different micropropagation events. Sixty-six random decamer primers were used in the initial screen, of which 19 (28.8%) revealed polymorphisms between normal and dwarf plants. Primer OPJ-04 (5'-CCGAACACGG-3') was found to amplify an approx. 1.5 kb band which was consistently present in all normal but absent in all dwarf plants of both cultivars. Reliable detection of dwarf plants was achieved using this marker, providing the only available means ofin vitro detection of dwarfs. The use of this marker could facilitate early detection and elimination of dwarfs from batches of micropropagated bananas, and may be a useful tool in determining what factors in the tissue culture process lead to this off type production.Other micropropagation-induced RAPD polymorphisms were observed but were not associated with the dwarf trait. PMID:24178669

  11. The Pch2 AAA+ ATPase promotes phosphorylation of the Hop1 meiotic checkpoint adaptor in response to synaptonemal complex defects

    PubMed Central

    Herruzo, Esther; Ontoso, David; González-Arranz, Sara; Cavero, Santiago; Lechuga, Ana; San-Segundo, Pedro A.

    2016-01-01

    Meiotic cells possess surveillance mechanisms that monitor critical events such as recombination and chromosome synapsis. Meiotic defects resulting from the absence of the synaptonemal complex component Zip1 activate a meiosis-specific checkpoint network resulting in delayed or arrested meiotic progression. Pch2 is an evolutionarily conserved AAA+ ATPase required for the checkpoint-induced meiotic block in the zip1 mutant, where Pch2 is only detectable at the ribosomal DNA array (nucleolus). We describe here that high levels of the Hop1 protein, a checkpoint adaptor that localizes to chromosome axes, suppress the checkpoint defect of a zip1 pch2 mutant restoring Mek1 activity and meiotic cell cycle delay. We demonstrate that the critical role of Pch2 in this synapsis checkpoint is to sustain Mec1-dependent phosphorylation of Hop1 at threonine 318. We also show that the ATPase activity of Pch2 is essential for its checkpoint function and that ATP binding to Pch2 is required for its localization. Previous work has shown that Pch2 negatively regulates Hop1 chromosome abundance during unchallenged meiosis. Based on our results, we propose that, under checkpoint-inducing conditions, Pch2 also possesses a positive action on Hop1 promoting its phosphorylation and its proper distribution on unsynapsed chromosome axes. PMID:27257060

  12. Thyroid hormone receptor interacting protein 13 (TRIP13) AAA-ATPase is a novel mitotic checkpoint-silencing protein.

    PubMed

    Wang, Kexi; Sturt-Gillespie, Brianne; Hittle, James C; Macdonald, Dawn; Chan, Gordon K; Yen, Tim J; Liu, Song-Tao

    2014-08-22

    The mitotic checkpoint (or spindle assembly checkpoint) is a fail-safe mechanism to prevent chromosome missegregation by delaying anaphase onset in the presence of defective kinetochore-microtubule attachment. The target of the checkpoint is the E3 ubiquitin ligase anaphase-promoting complex/cyclosome. Once all chromosomes are properly attached and bioriented at the metaphase plate, the checkpoint needs to be silenced. Previously, we and others have reported that TRIP13 AAA-ATPase binds to the mitotic checkpoint-silencing protein p31(comet). Here we show that endogenous TRIP13 localizes to kinetochores. TRIP13 knockdown delays metaphase-to-anaphase transition. The delay is caused by prolonged presence of the effector for the checkpoint, the mitotic checkpoint complex, and its association and inhibition of the anaphase-promoting complex/cyclosome. These results suggest that TRIP13 is a novel mitotic checkpoint-silencing protein. The ATPase activity of TRIP13 is essential for its checkpoint function, and interference with TRIP13 abolished p31(comet)-mediated mitotic checkpoint silencing. TRIP13 overexpression is a hallmark of cancer cells showing chromosomal instability, particularly in certain breast cancers with poor prognosis. We suggest that premature mitotic checkpoint silencing triggered by TRIP13 overexpression may promote cancer development.

  13. Loss of the m-AAA protease subunit AFG₃L₂ causes mitochondrial transport defects and tau hyperphosphorylation.

    PubMed

    Kondadi, Arun Kumar; Wang, Shuaiyu; Montagner, Sara; Kladt, Nikolay; Korwitz, Anne; Martinelli, Paola; Herholz, David; Baker, Michael J; Schauss, Astrid C; Langer, Thomas; Rugarli, Elena I

    2014-05-01

    The m-AAA protease subunit AFG₃L₂ is involved in degradation and processing of substrates in the inner mitochondrial membrane. Mutations in AFG₃L₂ are associated with spinocerebellar ataxia SCA28 in humans and impair axonal development and neuronal survival in mice. The loss of AFG₃L₂ causes fragmentation of the mitochondrial network. However, the pathogenic mechanism of neurodegeneration in the absence of AFG₃L₂ is still unclear. Here, we show that depletion of AFG₃L₂ leads to a specific defect of anterograde transport of mitochondria in murine cortical neurons. We observe similar transport deficiencies upon loss of AFG₃L₂ in OMA1-deficient neurons, indicating that they are not caused by OMA1-mediated degradation of the dynamin-like GTPase OPA1 and inhibition of mitochondrial fusion. Treatment of neurons with antioxidants, such as N-acetylcysteine or vitamin E, or decreasing tau levels in axons restored mitochondrial transport in AFG₃L₂-depleted neurons. Consistently, tau hyperphosphorylation and activation of ERK kinases are detected in mouse neurons postnatally deleted for Afg3l2. We propose that reactive oxygen species signaling leads to cytoskeletal modifications that impair mitochondrial transport in neurons lacking AFG₃L₂.

  14. The Pch2 AAA+ ATPase promotes phosphorylation of the Hop1 meiotic checkpoint adaptor in response to synaptonemal complex defects.

    PubMed

    Herruzo, Esther; Ontoso, David; González-Arranz, Sara; Cavero, Santiago; Lechuga, Ana; San-Segundo, Pedro A

    2016-09-19

    Meiotic cells possess surveillance mechanisms that monitor critical events such as recombination and chromosome synapsis. Meiotic defects resulting from the absence of the synaptonemal complex component Zip1 activate a meiosis-specific checkpoint network resulting in delayed or arrested meiotic progression. Pch2 is an evolutionarily conserved AAA+ ATPase required for the checkpoint-induced meiotic block in the zip1 mutant, where Pch2 is only detectable at the ribosomal DNA array (nucleolus). We describe here that high levels of the Hop1 protein, a checkpoint adaptor that localizes to chromosome axes, suppress the checkpoint defect of a zip1 pch2 mutant restoring Mek1 activity and meiotic cell cycle delay. We demonstrate that the critical role of Pch2 in this synapsis checkpoint is to sustain Mec1-dependent phosphorylation of Hop1 at threonine 318. We also show that the ATPase activity of Pch2 is essential for its checkpoint function and that ATP binding to Pch2 is required for its localization. Previous work has shown that Pch2 negatively regulates Hop1 chromosome abundance during unchallenged meiosis. Based on our results, we propose that, under checkpoint-inducing conditions, Pch2 also possesses a positive action on Hop1 promoting its phosphorylation and its proper distribution on unsynapsed chromosome axes.

  15. High-speed atomic force microscopic observation of ATP-dependent rotation of the AAA+ chaperone p97.

    PubMed

    Noi, Kentaro; Yamamoto, Daisuke; Nishikori, Shingo; Arita-Morioka, Ken-ichi; Kato, Takayuki; Ando, Toshio; Ogura, Teru

    2013-11-01

    p97 (also called VCP and CDC-48) is an AAA+ chaperone, which consists of a substrate/cofactor-binding N domain and two ATPase domains (D1 and D2), and forms a homo-hexameric ring. p97 plays crucial roles in a variety of cellular processes such as the ubiquitin-proteasome pathway, the endoplasmic reticulum-associated protein degradation, autophagy, and modulation of protein aggregates. Mutations in human p97 homolog VCP are linked to neurodegenerative diseases. The key mechanism of p97 in these various functions has been proposed to be the disassembly of protein complexes. To understand the molecular mechanism of p97, we studied the conformational changes of hexameric CDC-48.1, a Caenorhabditis elegans p97 homolog, using high-speed atomic force microscopy. In the presence of ATP, the N-D1 ring repeatedly rotates ~23 ± 8° clockwise and resets relative to the D2 ring. Mutational analysis reveals that this rotation is induced by ATP binding to the D2 domain. PMID:24055316