Science.gov

Sample records for mechanism underlying evaluative

  1. Implicit Misattribution as a Mechanism Underlying Evaluative Conditioning

    PubMed Central

    Jones, Christopher R.; Fazio, Russell H.; Olson, Michael A.

    2009-01-01

    Evaluative conditioning (EC) refers to the formation or change of an attitude towards an object following that object’s pairing with positively or negatively valenced stimuli. We provide evidence that EC can occur through an implicit misattribution mechanism in which an evaluative response evoked by a valenced stimulus is incorrectly and implicitly attributed to another stimulus, forming or changing an attitude towards this other stimulus. Five studies measured or manipulated variables related to the potential for the misattribution of an evaluation, or “source confusability.” Greater EC was observed when participants’ eye gaze shifted frequently between a valenced and neutral stimulus (Studies 1 & 2), when the two stimuli appeared in close spatial proximity (Study 3), and when the neutral stimulus was made more perceptually salient than the valenced stimulus due to its larger size (Study 4). In other words, conditions conducive to source confusability increased EC. Study 5 provided evidence for multiple mechanisms of EC by comparing the effects of mildly evocative valenced stimuli (those evoking responses that might more easily be misattributed to another object) to more strongly evocative stimuli. PMID:19379028

  2. Evaluation of the behavior of ceramic powders under mechanical vibration and its effect on the mechanics of auto-granulation

    NASA Astrophysics Data System (ADS)

    Ku, Nicholas

    In ceramic powder processing, the correlations between the constituent particles and the product structure-property outcomes are well established. However, the influence of static powder properties on the dynamic bulk powder behavior in such advance powder processes remains elusive. A multi-scale evaluation is necessary to understand the full effects of the particle ensemble on the bulk powder behavior, ranging from the particle micro-scale to the bulk powder macro-scale. Fine powders, with particle size of 10 ?m or less, often exhibit cohesive behavior. Cohesion in powders can cause poor flowability, affect agglomerate formation, as well as induce powder caking, all of which can be detrimental to the processing of the powders and/or final product structure-property outcomes. For this reason, it is critical to correlate the causal properties of the powders to this detrimental behavior. In this study, the bulk behavior of ceramic powders is observed under a simple powder process: harmonic, mechanical vibration. Four powder samples, two titania and two alumina powders, were studied. The main difference between the two powder variants of each material is particle size. The two alumina (Al2O3) powder samples had a primary particle size at 50% less than, or d50 of, 0.5 and 2.3 microm and the titania (TiO2) powder samples had a d 50 particle size of 0.1 and 1 microm. Due to mechanical vibration, the titania powder variant with a primary particle size of 0.1 microm exhibited a clustering behavior known as auto-granulation. Auto-granulation is the growth of particle clusters within a dry, fine powder bed without the addition of any binder or liquid to the system. The amplitude and frequency of the mechanical vibration was varied to view the effect on the equilibrium granule size and density. Furthermore, imaging of cross-sections of the granules was conducted to provide insight into to the internal microstructure and measure the packing fraction of the constituent

  3. Evaluation of Possible Proximate Mechanisms Underlying the Kinship Theory of Intragenomic Conflict in Social Insects.

    PubMed

    Galbraith, David A; Yi, Soojin V; Grozinger, Christina M

    2016-12-01

    Kinship theory provides a universal framework in which to understand the evolution of altruism, but there are many molecular and genetic mechanisms that can generate altruistic behaviors. Interestingly, kinship theory specifically predicts intragenomic conflict between maternally-derived alleles (matrigenes) and paternally-derived alleles (patrigenes) over the generation of altruistic behavior in cases where the interests of the matrigenes and patrigenes are not aligned. Under these conditions, individual differences in selfish versus altruistic behavior are predicted to arise from differential expression of the matrigenes and patrigenes (parent-specific gene expression or PSGE) that regulate selfish versus altruistic behaviors. As one of the leading theories to describe PSGE and genomic imprinting, kinship theory has been used to generate predictions to describe the reproductive division of labor in social insect colonies, which represents an excellent model system to test the hypotheses of kinship theory and examine the underlying mechanisms driving it. Recent studies have confirmed the predicted differences in the influence of matrigenes and patrigenes on reproductive division of labor in social insects, and demonstrated that these differences are associated with differences in PSGE of key genes involved in regulating reproductive physiology, providing further support for kinship theory. However, the mechanisms mediating PSGE in social insects, and how PSGE leads to differences in selfish versus altruistic behavior, remain to be determined. Here, we review the available supporting evidence for three possible epigenetic mechanisms (DNA methylation, piRNAs, and histone modification) that may generate PSGE in social insects, and discuss how these may lead to variation in social behavior.

  4. Evaluation of Mechanical Properties and Structural Changes of Ceramic Filter Materials for Hot Gas Cleaning under Simulated Process Conditions

    SciTech Connect

    Westerheide, R.; von der Wehd, C.; Adler, J.; Rehak, P.

    2002-09-19

    The objective of this study is to evaluate changes in structure and mechanical properties of ceramic filter materials under simulated corrosive process conditions. Due to an analysis of the mechanisms of degradation firstly an optimization of materials shall be enabled and secondly a material selection for specific applications shall be relieved. This publication describes the investigations made on many ceramic support materials based on oxides and carbides. Both commercially available and newly developed support materials have been evaluated for specific applications in hot gas cleaning.

  5. Evaluating the use of captive insurance as a financial assurance mechanism under RCRA

    SciTech Connect

    Finney, J.R.; Chan, E.K.; Clark, E.M.; Evans, M.L.; Johnson, M.F.

    1994-12-31

    This paper evaluates the use of insurance coverage underwritten by captive insurance companies to provide financial assurance for closure and post-closure care for facilities regulated under the Resource Conservation and Recovery Act of 1976 (RCRA). Regulations under RCRA subtitle C and subtitle D require that owners and operators of both hazardous waste treatment, storage, and disposal facilities (TSDF) and municipal solid waste landfills (MSWLF) demonstrate financial assurance for closure and post-closure care of such facilities. Those requirements help ensure that funds are available to cover the costs of closure and post-closure care, should the owner or operator be unable or unwilling to pay those costs. This paper provides a detailed analysis of how owners and operators use captive insurance companies to demonstrate financial assurance for closure and post-closure care under RCRA. The analysis explores, from a regulator`s point of view, the potential limitations of accepting captive insurance coverage as financial assurance for obligations for closure and post-closure care. The paper also provides: (1) an overview of captive insurance arrangements; (2) specific requirements for insurance for closure and post-closure care under RCRA; (3) state insurance regulations pertaining to the operations of captive insurance companies; and (4) recommendations that EPA and state agencies might consider to improve the current regulations and to ensure that funds will be available to pay for future environmental obligations.

  6. Change of plans: an evaluation of the effectiveness and underlying mechanisms of successful talent transfer.

    PubMed

    Collins, Rosie; Collins, Dave; MacNamara, Aine; Jones, Martin Ian

    2014-01-01

    Talent transfer (TT) is a recently formalised process used to identify and develop talented athletes by selecting individuals who have already succeeded in one sport and transferring them to another. Despite the increasing popularity of TT amongst national organisations and sport governing body professionals, however, there is little empirical evidence as to its efficacy or how it may be most efficiently employed. Accordingly, this investigation was designed to gain a deeper understanding of the effectiveness and underlying mechanisms of TT, achieved through a two-part study. Stage 1 provided a quantitative analysis of the incidence and distribution or, in this respect, epidemiology of TT, finding the most popular transfer to be sprinting to bobsleigh, with an average transfer age of 19 years. Stage 2 scrutinised the TT process and explored the specific cases revealed in stage 1 by examining the perceptions of four sport science support specialists who had worked in TT settings, finding several emergent themes which, they felt, could explain the TT processes. The most prominent theme was the psychosocial mechanism of TT, an aspect currently missing from TT initiatives, suggesting that current TT systems are poorly structured and should redress their approach to develop a more integrated scheme that encompasses all potential mechanisms of transfer.

  7. Fabrication of Open-Cell Al Foams and Evaluation of their Mechanical Response under Tension

    NASA Astrophysics Data System (ADS)

    Michailidis, N.; Stergioudi, F.; Omar, H.; Tsipas, D. N.

    2010-01-01

    In the present paper a novel procedure for describing the solid geometry of open cell foams is introduced, facilitating the establishment of a corresponding FEM model for simulating the material behaviour in micro-tension. Open-cell Al-foams were fabricated using the polymer impregnating method. A serial sectioning image-based process is described to capture, reproduce and visualize the exact three-dimensional (3D) microstructure of the examined foam. The generated 3D geometry of the Al-foam, derived from the synthesis of digital cross sectional images of the foam, was appropriately adjusted to build a FE model simulating the deformation conditions of the Al-foam under micro-tension loads. The obtained results enabled the visualisation of the stress fields in the Al-foam, allowing for a full investigation of its mechanical behaviour.

  8. Evaluation of Damage and Fracture Mechanisms of Different Characteristic Honeycomb Structures Under Thermomechanical Loading

    NASA Astrophysics Data System (ADS)

    Settet, A. T.; Nour, A.; Zahloul, H.; Naceur, H.

    2014-11-01

    A model able to predict the delamination mechanisms of composite honeycomb structures under thermal loading is presented. The use of a simulation software for some applications may not be sufficient to obtain the results expected; hence, the interest in developing modular calculation codes which would allow one to determine the rigidity matrix of a honeycomb panel, the deformation of its members, the field of shear strains, strains, and stresses in the panel plane on varying the physical parameters and checking the strength of each layer and of the entire panel. In order to test the reliability of the program developed, the results obtained are compared with those given in the literature. A specific model of Young's modulus under thermal loads is proposed, which takes into consideration the heat flux function, the thermal conductivity, the convection heat-transfer coefficients of the surrounding area inside and outside the panel, the exchange area in contact with air, the thickness of the honeycomb core, the upper and lower skins, and the adhesive layer. To verify the fracture strength of each panel, the Tsai-Wu criterion is used.

  9. An evaluation of the underlying mechanisms of bloodstain pattern analysis error.

    PubMed

    Behrooz, Nima; Hulse-Smith, Lee; Chandra, Sanjeev

    2011-09-01

    An experiment was designed to explore the underlying mechanisms of blood disintegration and its subsequent effect on area of origin (AO) calculations. Blood spatter patterns were created through the controlled application of pressurized air (20-80 kPa) for 0.1 msec onto suspended blood droplets (2.7-3.2 mm diameter). The resulting disintegration process was captured using high-speed photography. Straight-line triangulation resulted in a 50% height overestimation, whereas using the lowest calculated height for each spatter pattern reduced this error to 8%. Incorporation of projectile motion resulted in a 28% height underestimation. The AO xy-coordinate was found to be very accurate with a maximum offset of only 4 mm, while AO size calculations were found to be two- to fivefold greater than expected. Subsequently, reverse triangulation analysis revealed the rotational offset for 26% of stains could not be attributed to measurement error, suggesting that some portion of error is inherent in the disintegration process.

  10. Nondestructive evaluation of the mechanical behavior of cement-based nanocomposites under bending

    NASA Astrophysics Data System (ADS)

    Tragazikis, I. K.; Dalla, P. T.; Exarchos, D. A.; Dassios, K.; Matikas, T. E.

    2015-03-01

    The present paper describes the acoustic emission (AE) behavior and the mechanical properties of Portlant cement-based mortars due to the addition of multi wall carbon nanotubes (MWCNTs). This research aims in investigating the crack growth behavior of modified cement mortar with MWCNTs that act as nanoreinforcement during an unaxial compression test using acoustic emission technique. MWCNTs were used in various concentrations inside the matrix. Density, sound's speed, modulus, bending strength, compression strength were studied for five different concentrations. The adding and the increase of MWCNTs concentrations upper to 0.2 % by weight of cement not improving the mechanical properties of cement-based mortar but increase the acoustic emission activity.

  11. Experimental evaluation of mechanical and electrical properties of RBC suspensions under flow. Role of RBC aggregating agent.

    PubMed

    Antonova, N; Riha, P; Ivanov, I

    2010-01-01

    Mechanical and electrical properties of red blood cells (RBC) suspensions in dextran 70 (Dx70), dextran 150 (Dx150), dextran 500 (Dx500) and polyethileneglycol (PEG) 35,000 with different concentrations were evaluated through apparent viscosity and conductivity measurements under steady and unsteady flow conditions. RBCs suspensions of the washed RBS in PBS (control) and Dx70, Dx150, Dx500 and PEG in PBS with different concentrations, adjusted to the same hematocrit of 40% were used for the experiments. Conductivity time and shear rate dependences in parallel with the rheological properties of the samples were studied under transient flow regimes at different local structure of the uniform Couette flow. Their relationships on dextrans and PEG concentrations were evaluated too. Low shear viscosity increased and conductivity decreased of RBC suspensions, compared to non-aggregating suspensions, depending on dextrans and PEG concentrations. A time course of blood conductivity recorded under different flow conditions provides experimental description of RBC aggregation-disaggregation processes and other cell-cell interactions. The results show that the blood conductivity is strongly dependent on the considered blood factors and is influenced by flow, shear rates and concentration of dextran and PEG solutions.

  12. Evaluation of models of the mechanisms underlying intron loss and gain in Aspergillus fungi.

    PubMed

    Zhang, Lei-Ying; Yang, Yu-Fei; Niu, Deng-Ke

    2010-12-01

    Although intron loss and gain have been widely observed, their mechanisms are still to be determined. In four Aspergillus genomes, we found 204 cases of intron loss and 84 cases of intron gain. Using this data, we tested common hypotheses of intron loss or gain. Statistical analysis showed that adjacent introns tend to be lost simultaneously and small introns were preferentially lost, supporting the model of mRNA-mediated intron loss. The lost introns reside in internal regions of genes, which is inconsistent with the traditional version of the model (partial length cDNAs are reverse transcribed from 3' ends of mRNAs), but consistent with an alternate version (partial length cDNAs are produced by self-primed reverse transcription). The latter version was not supported by examination of the abundance of T-rich segments in mRNAs. Preferential loss of internal introns might be explained by highly efficient recombination at internal regions of genes. Among the 84 cases of intron gain, we found a significantly higher frequency of short direct repeats near exon-intron boundary than in conserved introns, supporting the double-strand break repair model. We also found possible source sequences for two cases of intron gain, one by gene conversion and one by insertion of a mitochondrial sequence during double-strand break repair. Source sequences for most gained introns could not be identified and the possible reasons were discussed. In the four Aspergillus genomes studied, we did not find evidence of frequent parallel intron gains.

  13. The mechanisms underlying overgeneral autobiographical memory: An evaluative review of evidence for the CaR-FA-X model

    PubMed Central

    Sumner, Jennifer A.

    2011-01-01

    Overgeneral autobiographical memory (OGM) has been found to be an important cognitive phenomenon with respect to depression and trauma-related psychopathology (e.g., posttraumatic stress disorder), and researchers have been interested in better understanding the factors that contribute to this proposed vulnerability factor. The most prominent model of mechanisms underlying OGM to date is Williams et al.’s (2007) CaR-FA-X model. This model proposes that three processes influence OGM: capture and rumination, functional avoidance, and impaired executive control. The author reviews the current state of support for the CaR-FA-X model by evaluating 38 studies that have examined OGM and one or more mechanisms of the model. Collectively, these studies reveal robust support for associations between OGM and both rumination and impaired executive control. OGM also appears to be a cognitive avoidance strategy, and there is evidence that avoiding the retrieval of specific memories reduces distress after an aversive event, at least in the short term. Important issues that have been left unresolved are highlighted, including the nature of the capture phenomenon, the role of trauma in functional avoidance, and the developmental nature of functional avoidance. Recommendations for future research that will enhance understanding of the factors that contribute to OGM are suggested. PMID:22142837

  14. The mechanisms underlying overgeneral autobiographical memory: an evaluative review of evidence for the CaR-FA-X model.

    PubMed

    Sumner, Jennifer A

    2012-02-01

    Overgeneral autobiographical memory (OGM) has been found to be an important cognitive phenomenon with respect to depression and trauma-related psychopathology (e.g., posttraumatic stress disorder), and researchers have been interested in better understanding the factors that contribute to this proposed vulnerability factor. The most prominent model of mechanisms underlying OGM to date is Williams et al.'s (2007) CaR-FA-X model. This model proposes that three processes influence OGM: capture and rumination, functional avoidance, and impaired executive control. The author reviews the current state of support for the CaR-FA-X model by evaluating 38 studies that have examined OGM and one or more mechanisms of the model. Collectively, these studies reveal robust support for associations between OGM and both rumination and impaired executive control. OGM also appears to be a cognitive avoidance strategy, and there is evidence that avoiding the retrieval of specific memories reduces distress after an aversive event, at least in the short term. Important issues that have been left unresolved are highlighted, including the nature of the capture phenomenon, the role of trauma in functional avoidance, and the developmental nature of functional avoidance. Recommendations for future research that will enhance understanding of the factors that contribute to OGM are suggested.

  15. EVALUATION OF AN IMPROVED CONVECTION TRIGGERING MECHANISM IN THE NCAR COMMUNITY ATMOSPHERE MODEL CAM2 UNDER CAPT FRAMEWORK

    SciTech Connect

    Xie, S; Boyle, J S; Cederwall, R T; Potter, G L; Zhang, M

    2003-10-15

    The problem that convection over land is overactive during warm-season daytime in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model CAM2 and its previous version (CCM3) has been found both in its single-column model (SCM) simulations (Xie and Zhang 2000; Ghan et al. 2000; Xie et al. 2002) and in its full general circulation model (GCM) short-range weather forecasts (Phillips et al. 2003) and climate simulations (Dai and Trenberth 2003). These studies showed that this problem is closely related to the convection triggering mechanism used in its deep convection scheme (Zhang and McFarlane 1995), which assumes that convection is triggered whenever there is positive convective available potential energy (CAPE). The positive CAPE triggering mechanism initiates model convection too often during the day because of the strong diurnal variations in the surface isolation and the induced CAPE diurnal change over land in the warm season. To reduce the problem, Xie and Zhang (2000) introduced a dynamic constraint, i.e., a dynamic CAPE generation rate (DCAPE) determined by the large-scale advective tendencies of temperature and moisture, to control the onset of deep convection. They showed that positive DCAPE is closely associated with convection in observations and the dynamic constraint could largely reduce the effect of the strong diurnal variations in the surface fluxes on the initiation of convection. Using the SCM version of CCM3, which has the same deep convection scheme as CAM2, Xie and Zhang (2000) showed that considerable improvements can be obtained in the model simulation of precipitation and other thermodynamic fields when the dynamic constraint was applied to the model triggering function. However, the performance of the improved convection triggering mechanism in the full GCM has not been tested. In this study, we will test the improved convection trigger mechanism in CAM2 under the U.S. Department of Energy's Climate Change Prediction

  16. Snapping mechanical metamaterials under tension.

    PubMed

    Rafsanjani, Ahmad; Akbarzadeh, Abdolhamid; Pasini, Damiano

    2015-10-21

    A snapping mechanical metamaterial is designed, which exhibits a sequential snap-through behavior under tension. The tensile response of this mechanical metamaterial can be altered by tuning the architecture of the snapping segments to achieve a range of nonlinear mechanical responses, including monotonic, S-shaped, plateau, and non-monotonic snap-through behavior.

  17. A predictive mechanical model for evaluating vertebral fracture probability in lumbar spine under different osteoporotic drug therapies.

    PubMed

    López, E; Ibarz, E; Herrera, A; Puértolas, S; Gabarre, S; Más, Y; Mateo, J; Gil-Albarova, J; Gracia, L

    2016-07-01

    Osteoporotic vertebral fractures represent a major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture from bone mineral density (BMD) measurements. A previously developed model, based on the Damage and Fracture Mechanics, was applied for the evaluation of the mechanical magnitudes involved in the fracture process from clinical BMD measurements. BMD evolution in untreated patients and in patients with seven different treatments was analyzed from clinical studies in order to compare the variation in the risk of fracture. The predictive model was applied in a finite element simulation of the whole lumbar spine, obtaining detailed maps of damage and fracture probability, identifying high-risk local zones at vertebral body. For every vertebra, strontium ranelate exhibits the highest decrease, whereas minimum decrease is achieved with oral ibandronate. All the treatments manifest similar trends for every vertebra. Conversely, for the natural BMD evolution, as bone stiffness decreases, the mechanical damage and fracture probability show a significant increase (as it occurs in the natural history of BMD). Vertebral walls and external areas of vertebral end plates are the zones at greatest risk, in coincidence with the typical locations of osteoporotic fractures, characterized by a vertebral crushing due to the collapse of vertebral walls. This methodology could be applied for an individual patient, in order to obtain the trends corresponding to different treatments, in identifying at-risk individuals in early stages of osteoporosis and might be helpful for treatment decisions.

  18. A pilot study evaluating non-contact low-frequency ultrasound and underlying molecular mechanism on diabetic foot ulcers.

    PubMed

    Yao, Min; Hasturk, Hatice; Kantarci, Alpdogan; Gu, Guosheng; Garcia-Lavin, Silvia; Fabbi, Matteo; Park, Nanjin; Hayashi, Hisae; Attala, Khaled; French, Michael A; Driver, Vickie R

    2014-12-01

    Non-contact low-frequency ultrasound (NCLF-US) devices have been increasingly used for the treatment of chronic non-healing wounds. The appropriate dose for NCLF-US is still in debate. The aims of this pilot study were to evaluate the relationship between dose and duration of treatment for subjects with non-healing diabetic foot ulcers (DFUs) and to explore the correlation between wound healing and change of cytokine/proteinase/growth factor profile. This was a prospective randomised clinical study designed to evaluate subjects with non-healing DFUs for 5 weeks receiving standard of care and/or NCLF-US treatment. Subjects were randomly assigned to one of the three groups: application of NCLF-US thrice per week (Group 1), NCLF-US once per week (Group 2) and the control (Group 3) that received no NCLF-US. All subjects received standard wound care plus offloading for a total of 4 weeks. Percent area reduction (PAR) of each wound compared with baseline was evaluated weekly. Profiles of cytokines/proteinase/growth factors in wound fluid and biopsied tissue were quantified to explore the correlation between wound healing and cytokines/growth factor expression. Twelve DFU patients, 2 (16·7%) type 1 and 10 (83·3%) type 2 diabetics, with an average age of 58 ± 10 years and a total of 12 foot ulcers were enrolled. Average ulcer duration was 36·44 ± 24·78 weeks and the average ABI was 0·91 ± 0·06. Group 1 showed significant wound area reduction at weeks 3, 4 and 5 compared with baseline, with the greatest PAR, 86% (P < 0·05); Groups 2 and 3 showed 25% PAR and 39% PAR, respectively, but there were no statistically significant differences between Groups 2 and 3 over time. Biochemical and histological analyses indicated a trend towards reduction of pro-inflammatory cytokines (IL-6, IL-8, IL-1β, TNF-α and GM-CSF), matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor (VEGF) and macrophages in response to NCLF-US consistent with wound reduction, when

  19. Evaluation of underlying mechanisms in the link between childhood ADHD symptoms and risk for early initiation of substance use.

    PubMed

    Vitulano, Michael L; Fite, Paula J; Hopko, Derek R; Lochman, John; Wells, Karen; Asif, Irfan

    2014-09-01

    Although there has been support for attention-deficit/hyperactivity disorder (ADHD) as a risk for early substance use, this link is not fully established or understood. Furthermore, the potential mechanisms explaining these associations are unclear. The current study examined peer rejection, school bonding, and internalizing problems as potential mediators of the association between childhood ADHD symptoms and risk for early initiation of substance use. The sample included a control group of 126 students with problematic aggression (79% African American, 66% male) from an intervention study following children from fourth to ninth grade. Results suggested that ADHD symptoms follow a path to early initiation of tobacco use through the combined effects of peer rejection and internalizing problems as well as through internalizing problems alone. ADHD symptoms were also associated with the cubic slope of marijuana use initiation, such that increased ADHD symptoms were associated with a strong cubic trend (e.g., a more rapid acceleration of risk for initiation). ADHD symptoms were not associated with risk for early initiation of alcohol use. Identification of important vulnerability factors in children with ADHD symptoms highlight the need for primary prevention and psychological interventions that target these factors and decrease the likelihood of early tobacco and marijuana use initiation.

  20. A 3-D Finite Element Model of Anterior Vaginal Wall Support to Evaluate Mechanisms Underlying Cystocele Formation

    PubMed Central

    Chen, Luyun; Ashton-Miller, James A.; DeLancey, John O.L.

    2009-01-01

    Objectives To develop a 3D computer model of the anterior vaginal wall and its supports, validate that model, and then use it to determine the combinations of muscle and connective tissue impairments that result in cystocele formation, as observed on dynamic magnetic resonance imaging (MRI). Methods A subject-specific 3D model of the anterior vaginal wall and its supports was developed based on MRI geometry from a healthy nulliparous woman. It included simplified representations of the anterior vaginal wall, levator muscle, cardinal and uterosacral ligaments, arcus tendineus fascia pelvis and levator ani, paravaginal attachments, and the posterior compartment. This model was then imported into ABAQUS™ and tissue properties were assigned from the literature. An iterative process was used to refine anatomical assumptions until convergence was obtained between model behavior under increases of abdominal pressure up to 168 cmH2O and deformations observed on dynamic MRI. Results Cystocele size was sensitive to abdominal pressure and impairment of connective tissue and muscle. Larger cystocele formed in the presence of impairments in muscular and apical connective tissue support compared to either support element alone. Apical impairment resulted in a larger cystocele than paravaginal impairment. Levator ani muscle impairment caused a larger urogenital hiatus size, longer length of the distal vagina exposed to a pressure differential, larger apical descent and resulted in a larger cystocele size. Conclusions Development of a cystocele requires a levator muscle impairment, an increase in abdominal pressure, and apical and paravaginal support defects. PMID:19481208

  1. A novel anatomical short glass fiber reinforced post in an endodontically treated premolar mechanical resistance evaluation using acoustic emission under fatigue testing.

    PubMed

    Wang, Hsuan-Wen; Chang, Yen-Hsiang; Lin, Chun-Li

    2017-01-01

    This study evaluates the fracture resistance in an endodontically treated tooth using circular fiber-reinforced composite (FRC) and innovated anatomical short glass fiber reinforced (SGFR) posts under fatigue testing, monitored using the acoustic emission (AE) technique. An anatomical SGFR fiber post with an oval shape and slot/notch design was manufactured using an injection-molding machine. Crown/core maxillary second premolar restorations were executed using the anatomical SGFR and commercial cylindrical fiber posts under fatigue test to understand the mechanical resistances. The load versus AE signals in the fracture and fatigue tests were recorded to evaluate the restored tooth failure resistance. The static fracture resistance results showed that teeth restored using the anatomical SGFR post presented higher resistance than teeth restored using the commercial FRC post. The fatigue test endurance limitation (1.2×10(6) cycles) was 207.1N for the anatomical SGFR fiber post, higher than the 185.3N found with the commercial FRC post. The average accumulated number of AE signals and corresponding micro cracks for the anatomical SGFR fiber post (153.0 hits and 2.44 cracks) were significantly lower than those for the commercial FRC post (194.7 hits and 4.78 cracks) under 40% of the static maximum resistance fatigue test load (pass 1.2×10(6) cycles). This study concluded that the anatomical SGFR fiber post with surface slot/notch design made using precise injection molding presented superior static fracture resistance and fatigue endurance limitation than those for the commercial FRC post in an endodontically treated premolar.

  2. Mechanical resistance evaluation of a novel anatomical short glass fiber reinforced post in artificial endodontically treated premolar under rotational/lateral fracture fatigue testing.

    PubMed

    Wang, Hsuan-Wen; Chang, Yen-Hsiang; Lin, Chun-Li

    2016-01-01

    This study develops a novel anatomical short glass fiber reinforced (anatomical SGFR) post and evaluates the mechanical performance in artificial endodontically treated premolars. An anatomical SGFR fiber post with an oval shape and slot/notch designs was manufactured using an injection-molding machine. The three-point bending test and crown/core restorations using the anatomical SGFR and commercial cylindrical fiber posts under fatigue test were executed to understand the mechanical resistances. The results showed that static and dynamic rotational resistance were found significantly higher in the anatomical SGFR fiber post than in the commercial post. The endurance limitations at 1.2×10(6) cycles were 66.81 and 64.77 N for the anatomical SGFR and commercial fiber posts, respectively. The anatomical SGFR fiber post presented acceptable value of flexural strength and modulus, better fit adaption in the root canal resist torque more efficiency but was not a key issue in the lateral fracture resistance in an endodontically treated premolar.

  3. Experimental evaluation of mechanical and electrical properties of RBC suspensions in Dextran and PEG under flow II. Role of RBC deformability and morphology.

    PubMed

    Antonova, N; Riha, P; Ivanov, I; Gluhcheva, Y

    2011-01-01

    Mechanical and electrical properties of the normal RBCs suspensions and of hardened after treatment with glutaraldehyde (0.01-2.5%) RBCs in isotonic physiological solution and Dextran 70,000 (Dextran 70) and Polyethylene glycol 35,000 (PEG) and adjusted to hematocrit of 40%, were evaluated. Apparent viscosity and conductivity were measured under steady and transient flow regimes at low shear rates and at different local structure of the flow at 37 °C. A time course of conductivity was recorded in parallel with the rheological properties of the RBC suspensions and conductivity and apparent viscosity dependences on shear rates were studied and compared at different concentrations of Dextran 70, PEG and glutaraldehyde. Low shear viscosity decreased after RBCs treatment with glutaraldehyde and at 0.5-2.5% it is constant. Echinocytes are observed at low Dextran 70 and PEG concentrations while spherocytes are found mainly in smears treated with higher concentrations. The results show that the apparent viscosity and conductivity of RBCs suspensions in Dextran 70 and PEG are strongly influenced by flow, shear rates, concentration, cell deformability and morphology and the method is sensitive to study the mechanical and electrical properties of RBC suspension and to provide experimental description of RBCs and other cell-to-cell interactions.

  4. Molecular Mechanisms Underlying Pituitary Pathogenesis.

    PubMed

    Sapochnik, Melanie; Nieto, Leandro Eduardo; Fuertes, Mariana; Arzt, Eduardo

    2016-04-01

    During the last years, progress has been made on the identification of mechanisms involved in anterior pituitary cell transformation and tumorigenesis. Oncogene activation, tumor suppressor gene inactivation, epigenetic changes, and microRNAs deregulation contribute to the initiation of pituitary tumors. Despite the high prevalence of pituitary adenomas, they are mostly benign, indicating that intrinsic mechanisms may regulate pituitary cell expansion. Senescence is characterized by an irreversible cell cycle arrest and represents an important protective mechanism against malignancy. Pituitary tumor transforming gene (PTTG) is an oncogene involved in early stages of pituitary tumor development, and also triggers a senescence response by activating DNA-damage signaling pathway. Cytokines, as well as many other factors, play an important role in pituitary physiology, affecting not only cell proliferation but also hormone secretion. Special interest is focused on interleukin-6 (IL-6) because its dual function of stimulating pituitary tumor cell growth but inhibiting normal pituitary cells proliferation. It has been demonstrated that IL-6 has a key role in promoting and maintenance of the senescence program in tumors. Senescence, triggered by PTTG activation and mediated by IL-6, may be a mechanism for explaining the benign nature of pituitary tumors.

  5. Mechanisms Underlying Inflammation in Neurodegeneration

    PubMed Central

    Glass, Christopher K.; Saijo, Kaoru; Winner, Beate; Marchetto, Maria Carolina; Gage, Fred H.

    2010-01-01

    Inflammation is associated with many neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. In this Review, we discuss inducers, sensors, transducers, and effectors of neuroinflammation that contribute to neuronal dysfunction and death. Although inducers of inflammation may be generated in a disease-specific manner, there is evidence for a remarkable convergence in the mechanisms responsible for the sensing, transduction, and amplification of inflammatory processes that result in the production of neurotoxic mediators. A major unanswered question is whether pharmacological inhibition of inflammation pathways will be able to safely reverse or slow the course of disease. PMID:20303880

  6. Metacognitive mechanisms underlying lucid dreaming.

    PubMed

    Filevich, Elisa; Dresler, Martin; Brick, Timothy R; Kühn, Simone

    2015-01-21

    Lucid dreaming is a state of awareness that one is dreaming, without leaving the sleep state. Dream reports show that self-reflection and volitional control are more pronounced in lucid compared with nonlucid dreams. Mostly on these grounds, lucid dreaming has been associated with metacognition. However, the link to lucid dreaming at the neural level has not yet been explored. We sought for relationships between the neural correlates of lucid dreaming and thought monitoring. Human participants completed a questionnaire assessing lucid dreaming ability, and underwent structural and functional MRI. We split participants based on their reported dream lucidity. Participants in the high-lucidity group showed greater gray matter volume in the frontopolar cortex (BA9/10) compared with those in the low-lucidity group. Further, differences in brain structure were mirrored by differences in brain function. The BA9/10 regions identified through structural analyses showed increases in blood oxygen level-dependent signal during thought monitoring in both groups, and more strongly in the high-lucidity group. Our results reveal shared neural systems between lucid dreaming and metacognitive function, in particular in the domain of thought monitoring. This finding contributes to our understanding of the mechanisms enabling higher-order consciousness in dreams.

  7. Multimodal nociceptive mechanisms underlying chronic pelvic pain

    PubMed Central

    HELLMAN, Kevin M.; PATANWALA, Insiyyah Y.; POZOLO, Kristen E.; TU, Frank F.

    2015-01-01

    Objective To evaluate candidate mechanisms underlying the pelvic floor dysfunction in women with chronic pelvic pain and/or painful bladder syndrome/interstitial cystitis. Notably, prior studies have not consistently controlled for potential confounding by psychological or anatomical factors. Study Design As part of a larger study on pelvic floor pain dysfunction and bladder pain sensitivity, we compared a measure of mechanical pain sensitivity, pressure pain thresholds, between women with pelvic pain and pain-free controls. We also assessed a novel pain measure using degree and duration of post-exam pain aftersensation, and conducted structural and functional assessments of the pelvic floor to account for any potential confounding. Phenotypic specificity of pelvic floor measures was assessed with receiver-operator characteristic curves adjusted for prevalence. Results A total of 23 women with chronic pelvic pain, 23 painful bladder syndrome, and 42 pain-free controls completed the study. Women with chronic pelvic pain or painful bladder syndrome exhibited enhanced pain sensitivity with lower pressure pain thresholds (1.18 [interquartile range: 0.87–1.41] kg/cm2) than pain-free participants (1.48 [1.11–1.76] kg/cm2; p<0.001) and prolonged pain aftersensation (3.5 [0–9] vs 0 [0–1] minutes; p< 0.001). Although genital hiatus (p<0.01) was wider in women with chronic pelvic pain there were no consistently observed group differences in pelvic floor anatomy, muscle tone or strength. The combination of pressure pain thresholds and aftersensation duration correlated with severity of pelvic floor tenderness (R2 =41–51, p’s< 0.01). Even after adjustment for prevalence, the combined metrics discriminated pain-free controls from women with chronic pelvic pain or painful bladder syndrome (area under the curve=0.87). Conclusion Both experimental assessment of pelvic floor pain thresholds and measurement of sustained pain are independently associated with pelvic pain

  8. Mechanical Properties and Real-Time Damage Evaluations of Environmental Barrier Coated SiC/SiC CMCs Subjected to Tensile Loading Under Thermal Gradients

    NASA Technical Reports Server (NTRS)

    Appleby, Matthew; Zhu, Dongming; Morscher, Gregory

    2015-01-01

    SiC/SiC ceramic matrix composites (CMCs) require new state-of-the art environmental barrier coatings (EBCs) to withstand increased temperature requirements and high velocity combustion corrosive combustion gasses. The present work compares the response of coated and uncoated SiC/SiC CMC substrates subjected to simulated engine environments followed by high temperature mechanical testing to asses retained properties and damage mechanisms. Our focus is to explore the capabilities of electrical resistance (ER) measurements as an NDE technique for testing of retained properties under combined high heat-flux and mechanical loading conditions. Furthermore, Acoustic Emission (AE) measurements and Digital Image Correlation (DIC) were performed to determine material damage onset and accumulation.

  9. Fracture mechanics evaluation of progressive fatigue damage in a circular-hole-notched GRP composite under combined tension/torsion loading

    NASA Astrophysics Data System (ADS)

    Takemura, Kenichi; Fujii, Toru

    Progressive failure from a circular hole in glass-fiber-reinforced plastics (GRP) under combined tension/torsion cyclic loading has been investigated. Thin-walled tubular specimens were used. The composition of the specimens was the same as in previous work. As pseudo-crack growth was observed under fatigue loading leading to the final failure, fracture mechanics methods were applied to characterize the fatigue failure process. The energy release rate was used as a parameter for progressive failure. Fatigue life under combined cyclic loading was estimated on the basis of the relationship between pseudo-crack-growth rate and energy release rate. The prediced S/N lines agree with the experimental results in all except a few cases.

  10. Peeling mechanism of tomato under infrared heating

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Critical behaviors of peeling tomatoes using infrared heat are thermally induced peel loosening and subsequent cracking. However, the mechanism of peel loosening and cracking due to infrared heating remains unclear. This study aimed at investigating the mechanism of peeling tomatoes under infrared h...

  11. Urethral closure mechanisms under sneeze-induced stress condition in rats: a new animal model for evaluation of stress urinary incontinence.

    PubMed

    Kamo, Izumi; Torimoto, Kazumasa; Chancellor, Michael B; de Groat, William C; Yoshimura, Naoki

    2003-08-01

    The urethral closure mechanism under a stress condition induced by sneezing was investigated in urethane-anesthetized female rats. During sneezing, while the responses measured by microtip transducer catheters in the proximal and middle parts of the urethra increased, the response in the proximal urethra was almost negligible when the bladder response was subtracted from the urethral response or when the abdomen was opened. In contrast, the response in the middle urethra during sneezing was still observed after subtracting the bladder response or after opening the abdomen. These responses in the middle urethra during sneezing were significantly reduced approximately 80% by bilateral transection of the pudendal nerves and the nerves to the iliococcygeous and pubococcygeous muscles but not by transection of the visceral branches of the pelvic nerves and hypogastric nerves. The sneeze leak point pressure was also measured to investigate the role of active urethral closure mechanisms in maintaining total urethral resistance against sneeze-induced urinary incontinence. In sham-operated rats, no urinary leakage was observed during sneeze, which produced an increase of intravesical pressure up to 37 +/- 2.2 cmH2O. However, in nerve-transected rats urinary leakage was observed when the intravesical pressure during sneezing exceeded 16.3 +/- 2.1 cmH2O. These results indicate that during sneezing, pressure increases elicited by reflex contractions of external urethral sphincter and pelvic floor muscles occur in the middle portion of the urethra. These reflexes in addition to passive transmission of increased abdominal pressure significantly contribute to urinary continence mechanisms under a sneeze-induced stress condition.

  12. Mechanical buckling of artery under pulsatile pressure.

    PubMed

    Liu, Qin; Han, Hai-Chao

    2012-04-30

    Tortuosity that often occurs in carotid and other arteries has been shown to be associated with high blood pressure, atherosclerosis, and other diseases. However the mechanisms of tortuosity development are not clear. Our previous studies have suggested that arteries buckling could be a possible mechanism for the initiation of tortuous shape but artery buckling under pulsatile flow condition has not been fully studied. The objectives of this study were to determine the artery critical buckling pressure under pulsatile pressure both experimentally and theoretically, and to elucidate the relationship of critical pressures under pulsatile flow, steady flow, and static pressure. We first tested the buckling pressures of porcine carotid arteries under these loading conditions, and then proposed a nonlinear elastic artery model to examine the buckling pressures under pulsatile pressure conditions. Experimental results showed that under pulsatile pressure arteries buckled when the peak pressures were approximately equal to the critical buckling pressures under static pressure. This was also confirmed by model simulations at low pulse frequencies. Our results provide an effective tool to predict artery buckling pressure under pulsatile pressure.

  13. DNA under Force: Mechanics, Electrostatics, and Hydration

    PubMed Central

    Li, Jingqiang; Wijeratne, Sithara S.; Qiu, Xiangyun; Kiang, Ching-Hwa

    2015-01-01

    Quantifying the basic intra- and inter-molecular forces of DNA has helped us to better understand and further predict the behavior of DNA. Single molecule technique elucidates the mechanics of DNA under applied external forces, sometimes under extreme forces. On the other hand, ensemble studies of DNA molecular force allow us to extend our understanding of DNA molecules under other forces such as electrostatic and hydration forces. Using a variety of techniques, we can have a comprehensive understanding of DNA molecular forces, which is crucial in unraveling the complex DNA functions in living cells as well as in designing a system that utilizes the unique properties of DNA in nanotechnology.

  14. Woven TPS Mechanical Property Evaluation

    NASA Technical Reports Server (NTRS)

    Gonzales, Gregory Lewis; Kao, David Jan-Woei; Stackpoole, Margaret M.

    2013-01-01

    Woven Thermal Protection Systems (WTPS) is a relatively new program funded by the Office of the Chief Technologist (OCT). The WTPS approach to producing TPS architectures uses precisely engineered 3-D weaving techniques that allow tailoring material characteristics needed to meet specific mission requirements. A series of mechanical tests were performed to evaluate performance of different weave types, and get a better understanding of failure modes expected in these three-dimensional architectures. These properties will aid in material down selection and guide selection of the appropriate WTPS for a potential mission.

  15. Enhanced self-administration of the CB1 receptor agonist WIN55,212-2 in olfactory bulbectomized rats: evaluation of possible serotonergic and dopaminergic underlying mechanisms

    PubMed Central

    Amchova, Petra; Kucerova, Jana; Giugliano, Valentina; Babinska, Zuzana; Zanda, Mary T.; Scherma, Maria; Dusek, Ladislav; Fadda, Paola; Micale, Vincenzo; Sulcova, Alexandra; Fratta, Walter; Fattore, Liana

    2013-01-01

    Depression has been associated with drug consumption, including heavy or problematic cannabis use. According to an animal model of depression and substance use disorder comorbidity, we combined the olfactory bulbectomy (OBX) model of depression with intravenous drug self-administration procedure to verify whether depressive-like rats displayed altered voluntary intake of the CB1 receptor agonist WIN55,212-2 (WIN, 12.5 μg/kg/infusion). To this aim, olfactory-bulbectomized (OBX) and sham-operated (SHAM) Lister Hooded rats were allowed to self-administer WIN by lever-pressing under a continuous [fixed ratio 1 (FR-1)] schedule of reinforcement in 2 h daily sessions. Data showed that both OBX and SHAM rats developed stable WIN intake; yet, responses in OBX were constantly higher than in SHAM rats soon after the first week of training. In addition, OBX rats took significantly longer to extinguish the drug-seeking behavior after vehicle substitution. Acute pre-treatment with serotonin 5HT1B receptor agonist, CGS-12066B (2.5–10 mg/kg), did not significantly modify WIN intake in OBX and SHAM Lister Hooded rats. Furthermore, acute pre-treatment with CGS-12066B (10 and 15 mg/kg) did not alter responses in parallel groups of OBX and SHAM Sprague Dawley rats self-administering methamphetamine under higher (FR-2) reinforcement schedule with nose-poking as operandum. Finally, dopamine levels in the nucleus accumbens (NAc) of OBX rats did not increase in response to a WIN challenge, as in SHAM rats, indicating a dopaminergic dysfunction in bulbectomized rats. Altogether, our findings suggest that a depressive-like state may alter cannabinoid CB1 receptor agonist-induced brain reward function and that a dopaminergic rather than a 5-HT1B mechanism is likely to underlie enhanced WIN self-administration in OBX rats. PMID:24688470

  16. Mechanisms underlying the hepatotoxic effects of ecstasy.

    PubMed

    Carvalho, Márcia; Pontes, Helena; Remião, Fernando; Bastos, Maria L; Carvalho, Félix

    2010-08-01

    3,4-Methylenedioxymethamphetamine (MDMA or ecstasy) is a worldwide illegally used amphetamine-derived designer drug known to be hepatotoxic to humans. Jaundice, hepatomegaly, centrilobular necrosis, hepatitis and fibrosis represent some of the adverse effects caused by MDMA in the liver. Although there is irrefutable evidence of MDMA-induced hepatocellular damage, the mechanisms responsible for that toxicity remain to be thoroughly clarified. One well thought-of mechanism imply MDMA metabolism in the liver into reactive metabolites as responsible for the MDMA-elicited hepatotoxicity. However, other factors, including MDMA-induced hyperthermia, the increase in neurotransmitters efflux, the oxidation of biogenic amines, polydrug abuse pattern, and environmental features accompanying illicit MDMA use, may increase the risk for liver complications. Liver damage patterns of MDMA in animals and humans and current research on the mechanisms underlying the hepatotoxic effects of MDMA will be highlighted in this review.

  17. Surface Damage Mechanism of Monocrystalline Si Under Mechanical Loading

    NASA Astrophysics Data System (ADS)

    Zhao, Qingliang; Zhang, Quanli; To, Suet; Guo, Bing

    2017-03-01

    Single-point diamond scratching and nanoindentation on monocrystalline silicon wafer were performed to investigate the surface damage mechanism of Si under the contact loading. The results showed that three typical stages of material removal appeared during dynamic scratching, and a chemical reaction of Si with the diamond indenter and oxygen occurred under the high temperature. In addition, the Raman spectra of the various points in the scratching groove indicated that the Si-I to β-Sn structure (Si-II) and the following β-Sn structure (Si-II) to amorphous Si transformation appeared under the rapid loading/unloading condition of the diamond grit, and the volume change induced by the phase transformation resulted in a critical depth (ductile-brittle transition) of cut (˜60 nm ± 15 nm) much lower than the theoretical calculated results (˜387 nm). Moreover, it also led to abnormal load-displacement curves in the nanoindentation tests, resulting in the appearance of elbow and pop-out effects (˜270 nm at 20 s, 50 mN), which were highly dependent on the loading/unloading conditions. In summary, phase transformation of Si promoted surface deformation and fracture under both static and dynamic mechanical loading.

  18. Mechanical stability of iron under hydrostatic stresses

    NASA Astrophysics Data System (ADS)

    Mishra, K. L.; Thakur, O. P.; Thakur, K. P.

    1991-09-01

    A comprehensive investigation of the mechanics of iron subjected to arbitrary fluid pressure has been carried out. Apart from the classical elastic moduli ( k, μ, and μ') and conventional elastic moduli (Green and stretch moduli) computations are carried out for a family of generalised moduli of which the conventional moduli are just specific members. With the generalised moduli the mechanical stability of iron is investigated through Born criteria. It is found that classical stability, Green stability and stretch stability are all represented uniquely by the present generalised scheme. The definition of effective classical moduli under stresses enabled the amalgamation of the Born criteria of lattice stability into the single classical criteria of lattice stability of cubic crystal under hydrostatic loading environment. Computations are also carried out to investigate the coordinate and stress dependence of Young's modulus of elasticity, Poisson's ratio, mean velocity of elastic wave, and Debye temperature. Surprisingly, it is found that all these properties of solids play an important role in representing the mechanical stability of the solid. The path of uniaxial loading of iron is also investigated along with its internal energy variation on this path. This indicated the existance of stress-free fcc phase of iron on the path of uniaxial deformation at cell length a=3.6444 Å giving enthalpy of transformation (bcc→fcc) of 1.1 kJ/mol in good agreement with experimental results.

  19. MECHANICS OF CRACK BRIDGING UNDER DYNAMIC LOADS

    SciTech Connect

    N. SRIDHAR; ET AL

    2001-02-01

    A bridging law for fiber reinforced composites under dynamic crack propagation conditions has been derived. Inertial effects in the mechanism of fiber pullout during dynamic propagation of a bridged crack are critically examined for the first time. By reposing simple shear lag models of pullout as problems of dynamic wave propagation, the effect of the frictional coupling between the fibers and the matrix is accounted for in a fairly straightforward way. The solutions yield the time-dependent relationship between the crack opening displacement and the bridging traction. Engineering criteria and the role of material and geometrical parameters for significant inertial effects are identified.

  20. Cellular and molecular mechanisms underlying muscular dystrophy

    PubMed Central

    2013-01-01

    The muscular dystrophies are a group of heterogeneous genetic diseases characterized by progressive degeneration and weakness of skeletal muscle. Since the discovery of the first muscular dystrophy gene encoding dystrophin, a large number of genes have been identified that are involved in various muscle-wasting and neuromuscular disorders. Human genetic studies complemented by animal model systems have substantially contributed to our understanding of the molecular pathomechanisms underlying muscle degeneration. Moreover, these studies have revealed distinct molecular and cellular mechanisms that link genetic mutations to diverse muscle wasting phenotypes. PMID:23671309

  1. Modelling RNA folding under mechanical tension

    PubMed Central

    VIEREGG, JEFFREY R.; TINOCO, IGNACIO

    2006-01-01

    We investigate the thermodynamics and kinetics of RNA unfolding and refolding under mechanical tension. The hierarchical nature of RNA structure and the existence of thermodynamic parameters for base pair formation based on nearest-neighbour interactions allows modelling of sequence-dependent folding dynamics for any secondary structure. We calculate experimental observables such as the transition force for unfolding, the end-to-end distribution function and its variance, as well as kinetic information, for a representative RNA sequence and for a sequence containing two homopolymer segments: A.U and G.C. PMID:16969426

  2. Theory Underlying a National Teacher Evaluation Program

    ERIC Educational Resources Information Center

    Taut, Sandy; Santelices, Veronica; Araya, Carolina; Manzi, Jorge

    2010-01-01

    The paper describes a study conducted to explicate the multiple theories underlying Chile's national teacher evaluation program. These theories will serve as the basis for evaluating the intended consequences of this evaluation system, while not losing sight of emerging unintended consequences. We first analyzed legal and policy documents and then…

  3. Neural mechanisms underlying selective attention to threat.

    PubMed

    Bishop, Sonia J

    2008-01-01

    Biased competition models of selective attention suggest that attentional competition is influenced both by bottom-up sensory mechanisms sensitive to stimulus salience and top-down control mechanisms that support the processing of task-relevant stimuli. This provides a framework for investigating the neural mechanisms underlying selective attention to threat. Both subcortical regions implicated in threat detection--specifically the amygdala--and prefrontal cortical regions implicated in top-down attentional control are activated in response to task-irrelevant threat stimuli. A number of questions including the automaticity of the amygdala response to threat distractors, the modulation by anxiety of the amygdala and prefrontal response to these stimuli, and the impact of genetic and environmental factors upon this circuitry are addressed. The empirical literature is considered in the context of theoretical accounts of the neural substrate of selective attention and conscious awareness. It is suggested that the neural activity provoked by a given visual stimulus is influenced by factors impacting upon the strength of the bottom-up trace (e.g., presentation time, backward masking), stimulus salience (including threat relatedness), competition with other visual stimuli for perceptual processing resources, and the augmentation of the stimulus trace by allocation of top-down attentional resources. Individual differences in trait and state anxiety, and in genetic makeup, are thought to modulate the influence of stimulus valence and top-down attention through their impact upon amygdala and prefrontal function.

  4. Deformation Mechanisms of Gum Metals Under Nanoindentation

    NASA Astrophysics Data System (ADS)

    Sankaran, Rohini Priya

    defect structures to applied loading, we perform ex-situ nanoindentation. Nanoindentation is a convenient method as the plastic deformation is localized and probes a nominally defect free volume of the material. We subsequently characterize the defect structures in these alloys with both conventional TEM and advanced techniques such as HAADF HRSTEM and nanoprobe diffraction. These advanced techniques allow for a more thorough understanding of the observed deformation features. The main findings from this investigation are as follows. As expected we observe that a non-equilibrium phase, o, is present in the leaner beta-stabilized alloy, ST Ref-1. We do not find any direct evidence of secondary phases in STGM, and we find the beta phase in CWGM, along with lath microstructure with subgrain structure consisting of dislocation cell networks. Upon nanoindentation, we find twinning accompanied by beta nucleation on the twin boundary in ST Ref-1 samples. This result is consistent with previous findings and is reasonable considering the alloy is unstable with respect to beta transformation. We find deformation nanotwinning in cold worked gum metals under nanoindentation, which is initially surprising. We argue that when viewed as a nanocrystalline material, such a deformation mechanism is consistent with previous work, and furthermore, a deformation nanotwinned structure does not preclude an ideal shear mechanism from operating in the alloy. Lastly, we observe continuous lattice rotations in STGM under nanoindentation via nanoprobe diffraction. With this technique, for the first time we can demonstrate that the lattice rotations are truly continuous at the nanoscale. We can quantify this lattice rotation, and find that even though the rotation is large, it may be mediated by a reasonable geometrically necessary dislocation density, and note that similar rotations are typically observed in other materials under nanoindentation. HRSTEM and conventional TEM data confirm the

  5. Innate immunesenescence: underlying mechanisms and clinical relevance.

    PubMed

    Hazeldine, Jon; Lord, Janet M

    2015-04-01

    A well-established feature of physiological ageing is altered immune function, a phenomenon termed immunesenescence. Thought to be responsible in part for the increased incidence and severity of infection reported by older adults, as well as the age-related decline in vaccine efficacy and autoimmunity, immunesenescence affects both the innate and adaptive arms of the immune system. Whilst much is known regarding the impact of age on adaptive immunity, innate immunity has received far less attention from immune gerontologists. However, over the last decade it has become increasingly apparent that this non-specific arm of the immune response undergoes considerable functional and phenotypical alterations with age. Here, we provide a detailed overview of innate immunesenescence and its underlying molecular mechanisms, and highlight those studies whose results indicate that changes in innate immunity with age have a significant impact upon the health and well-being of older adults.

  6. Mechanical buckling of veins under internal pressure.

    PubMed

    Martinez, Ricky; Fierro, Cesar A; Shireman, Paula K; Han, Hai-Chao

    2010-04-01

    Venous tortuosity is associated with multiple disease states and is often thought to be a consequence of venous hypertension and chronic venous disease. However, the underlying mechanisms of vein tortuosity are unclear. We hypothesized that increased pressure causes vein buckling that leads to a tortuous appearance. The specific aim of this study was to determine the critical buckling pressure of veins. We determined the buckling pressure of porcine jugular veins and measured the mechanical properties of these veins. Our results showed that the veins buckle when the transmural pressure exceeds a critical pressure that is strongly related to the axial stretch ratio in the veins. The critical pressures of the eight veins tested were 14.2 +/- 5.4 and 26.4 +/- 9.0 mmHg at axial stretch ratio 1.5 and 1.7, respectively. In conclusion, veins buckle into a tortuous shape at high lumen pressures or reduced axial stretch ratios. Our results are useful in understanding the development of venous tortuosity associated with varicose veins, venous valvular insufficiency, diabetic retinopathy, and vein grafts.

  7. Mechanisms Underlying Early Medieval Droughts in Mesoamerica

    NASA Astrophysics Data System (ADS)

    Bhattacharya, T.; Chiang, J. C. H.

    2015-12-01

    Multidecadal drought during the early Medieval Climate Anomaly (MCA, 800-1200 CE) in Mesoamerica has been implicated in the demise of many pre-Columbian societies, including the Maya. The mechanisms behind these droughts, however, are poorly understood. Researchers most often interpret these records as tracking the mean position of the ITCZ, with a southward shifted ITCZ resulting in Mesoamerican drought. This is puzzling, however, because our dynamical understanding of the ITCZ and its role in interhemispheric heat transport would suggest a more northward shifted ITCZ during the MCA. Here, we evaluate two hypotheses to reconcile existing proxies and dynamics. First, we assess whether evidence for dry conditions during the MCA is robust across multiple Mesoamerican proxy records, focusing on the influence of radiometric dating uncertainty on estimates of drought timing. Second, we use control simulations of CCSM4 and HadCM3, as well as a broader synthesis of oceanic and terrestrial proxies, to explore the mechanisms responsible for long-term drought in Mesoamerica. Ultimately, we suggest that a temporary slowdown of the AMOC, either internally or externally forced, combined with local and regional land surface feedbacks can explain these droughts in Mesoamerica.

  8. Emotional responses to music: the need to consider underlying mechanisms.

    PubMed

    Juslin, Patrik N; Västfjäll, Daniel

    2008-10-01

    Research indicates that people value music primarily because of the emotions it evokes. Yet, the notion of musical emotions remains controversial, and researchers have so far been unable to offer a satisfactory account of such emotions. We argue that the study of musical emotions has suffered from a neglect of underlying mechanisms. Specifically, researchers have studied musical emotions without regard to how they were evoked, or have assumed that the emotions must be based on the "default" mechanism for emotion induction, a cognitive appraisal. Here, we present a novel theoretical framework featuring six additional mechanisms through which music listening may induce emotions: (1) brain stem reflexes, (2) evaluative conditioning, (3) emotional contagion, (4) visual imagery, (5) episodic memory, and (6) musical expectancy. We propose that these mechanisms differ regarding such characteristics as their information focus, ontogenetic development, key brain regions, cultural impact, induction speed, degree of volitional influence, modularity, and dependence on musical structure. By synthesizing theory and findings from different domains, we are able to provide the first set of hypotheses that can help researchers to distinguish among the mechanisms. We show that failure to control for the underlying mechanism may lead to inconsistent or non-interpretable findings. Thus, we argue that the new framework may guide future research and help to resolve previous disagreements in the field. We conclude that music evokes emotions through mechanisms that are not unique to music, and that the study of musical emotions could benefit the emotion field as a whole by providing novel paradigms for emotion induction.

  9. Molecular mechanics of silk nanostructures under varied mechanical loading.

    PubMed

    Bratzel, Graham; Buehler, Markus J

    2012-06-01

    Spider dragline silk is a self-assembling tunable protein composite fiber that rivals many engineering fibers in tensile strength, extensibility, and toughness, making it one of the most versatile biocompatible materials and most inviting for synthetic mimicry. While experimental studies have shown that the peptide sequence and molecular structure of silk have a direct influence on the stiffness, toughness, and failure strength of silk, few molecular-level analyses of the nanostructure of silk assemblies, in particular, under variations of genetic sequences have been reported. In this study, atomistic-level structures of wildtype as well as modified MaSp1 protein from the Nephila clavipes spider dragline silk sequences, obtained using an in silico approach based on replica exchange molecular dynamics and explicit water molecular dynamics, are subjected to simulated nanomechanical testing using different force-control loading conditions including stretch, pull-out, and peel. The authors have explored the effects of the poly-alanine length of the N. clavipes MaSp1 peptide sequence and identify differences in nanomechanical loading conditions on the behavior of a unit cell of 15 strands with 840-990 total residues used to represent a cross-linking β-sheet crystal node in the network within a fibril of the dragline silk thread. The specific loading condition used, representing concepts derived from the protein network connectivity at larger scales, have a significant effect on the mechanical behavior. Our analysis incorporates stretching, pull-out, and peel testing to connect biochemical features to mechanical behavior. The method used in this study could find broad applications in de novo design of silk-like tunable materials for an array of applications.

  10. Molecular Mechanisms Underlying Peritoneal EMT and Fibrosis

    PubMed Central

    Strippoli, Raffaele; Moreno-Vicente, Roberto; Battistelli, Cecilia; Cicchini, Carla; Noce, Valeria; Amicone, Laura; Marchetti, Alessandra; del Pozo, Miguel Angel; Tripodi, Marco

    2016-01-01

    Peritoneal dialysis is a form of renal replacement alternative to the hemodialysis. During this treatment, the peritoneal membrane acts as a permeable barrier for exchange of solutes and water. Continual exposure to dialysis solutions, as well as episodes of peritonitis and hemoperitoneum, can cause acute/chronic inflammation and injury to the peritoneal membrane, which undergoes progressive fibrosis, angiogenesis, and vasculopathy, eventually leading to discontinuation of the peritoneal dialysis. Among the different events controlling this pathological process, epithelial to mesenchymal transition of mesothelial cells plays a main role in the induction of fibrosis and in subsequent functional deterioration of the peritoneal membrane. Here, the main extracellular inducers and cellular players are described. Moreover, signaling pathways acting during this process are elucidated, with emphasis on signals delivered by TGF-β family members and by Toll-like/IL-1β receptors. The understanding of molecular mechanisms underlying fibrosis of the peritoneal membrane has both a basic and a translational relevance, since it may be useful for setup of therapies aimed at counteracting the deterioration as well as restoring the homeostasis of the peritoneal membrane. PMID:26941801

  11. Human Cooperation and Its Underlying Mechanisms.

    PubMed

    Strang, Sabrina; Park, Soyoung Q

    2017-01-01

    Cooperation is a uniquely human behavior and can be observed across cultures. In order to maintain cooperative behavior in society, people are willing to punish deviant behavior on their own expenses and even without any personal benefits. Cooperation has been object of research in several disciplines. Psychologists, economists, sociologists, biologists, and anthropologists have suggested several motives possibly underlying cooperative behavior. In recent years, there has been substantial progress in understanding neural mechanisms enforcing cooperation. Psychological as well as economic theories were tested for their plausibility using neuroscientific methods. For example, paradigms from behavioral economics were adapted to be tested in the magnetic resonance imaging (MRI) scanner. Also, related brain functions were modulated by using transmagnetic brain stimulation (TMS). While cooperative behavior has often been associated with positive emotions, noncooperative behavior was found to be linked to negative emotions. On a neural level, the temporoparietal junction (TPJ), the striatum, and other reward-related brain areas have been shown to be activated by cooperation, whereas noncooperation has mainly been associated with activity in the insula.

  12. Directional motion of liquid under mechanical vibrations

    NASA Astrophysics Data System (ADS)

    Costalonga, Maxime; Brunet, Philippe; Peerhossaini, Hassan

    2014-11-01

    When a liquid is submitted to mechanical vibrations, steady flows or motion can be generated by non-linear effects. One example is the steady acoustic streaming one can observe when an acoustic wave propagates in a fluid. At the scale of a droplet, steady motion of the whole amount of liquid can arise from zero-mean periodic forcing. As It has been observed by Brunet et al. (PRL 2007), a drop can climb an inclined surface when submitted to vertical vibrations above a threshold in acceleration. Later, Noblin et al. (PRL 2009) showed the velocity and the direction of motion of a sessile drop submitted to both horizontal and vertical vibrations can be tuned by the phase shift between these two excitations. Here we present an experimental study of the mean motion of a sessile drop under slanted vibrations, focusing on the effects of drop properties, as well as the inclination angle of the axis of vibrations. It is shown that the volume and viscosity strongly affect the drop mean velocity, and can even change the direction of its motion. In the case of a low viscous drop, gravity can become significant and be modulated by the inclination of the axis of vibrations. Contact line dynamic during the drop oscillations is also investigated.

  13. Vascular Adventitia Calcification and Its Underlying Mechanism

    PubMed Central

    Li, Na; Cheng, Wenli; Huang, Tiequn; Yuan, Jie; Wang, Xi; Song, Meiyue

    2015-01-01

    Previous research on vascular calcification has mainly focused on the vascular intima and media. However, we show here that vascular calcification may also occur in the adventitia. The purpose of this work is to help elucidate the pathogenic mechanisms underlying vascular calcification. The calcified lesions were examined by Von Kossa staining in ApoE−/− mice which were fed high fat diets (HFD) for 48 weeks and human subjects aged 60 years and older that had died of coronary heart disease, heart failure or acute renal failure. Explant cultured fibroblasts and smooth muscle cells (SMCs)were obtained from rat adventitia and media, respectively. After calcification induction, cells were collected for Alizarin Red S staining. Calcified lesions were observed in the aorta adventitia and coronary artery adventitia of ApoE-/-mice, as well as in the aorta adventitia of human subjects examined. Explant culture of fibroblasts, the primary cell type comprising the adventitia, was successfully induced for calcification after incubation with TGF-β1 (20 ng/ml) + mineralization media for 4 days, and the phenotype conversion vascular adventitia fibroblasts into myofibroblasts was identified. Culture of SMCs, which comprise only a small percentage of all cells in the adventitia, in calcifying medium for 14 days resulted in significant calcification.Vascular calcification can occur in the adventitia. Adventitia calcification may arise from the fibroblasts which were transformed into myofibroblasts or smooth muscle cells. PMID:26148272

  14. An underlying geometrical manifold for Hamiltonian mechanics

    NASA Astrophysics Data System (ADS)

    Horwitz, L. P.; Yahalom, A.; Levitan, J.; Lewkowicz, M.

    2017-02-01

    We show that there exists an underlying manifold with a conformal metric and compatible connection form, and a metric type Hamiltonian (which we call the geometrical picture), that can be put into correspondence with the usual Hamilton-Lagrange mechanics. The requirement of dynamical equivalence of the two types of Hamiltonians, that the momenta generated by the two pictures be equal for all times, is sufficient to determine an expansion of the conformal factor, defined on the geometrical coordinate representation, in its domain of analyticity with coefficients to all orders determined by functions of the potential of the Hamiltonian-Lagrange picture, defined on the Hamilton-Lagrange coordinate representation, and its derivatives. Conversely, if the conformal function is known, the potential of a Hamilton-Lagrange picture can be determined in a similar way. We show that arbitrary local variations of the orbits in the Hamilton-Lagrange picture can be generated by variations along geodesics in the geometrical picture and establish a correspondence which provides a basis for understanding how the instability in the geometrical picture is manifested in the instability of the the original Hamiltonian motion.

  15. Stress evaluations under rolling/sliding contacts

    NASA Technical Reports Server (NTRS)

    Kannel, J. W.; Tevaarwerk, J. L.

    1981-01-01

    The state of stress beneath traction drive type of contacts were analyzed. Computing stresses and stress reversals on various planes for points beneath the surface were examined. The effect of tangential and axial friction under gross slip conditions is evaluated with the models. Evaluations were performed on an RC (rolling contact) tester configuration and it is indicated that the classical fatigue stresses are not altered by friction forces typical of lubricated contact. Higher values of friction can result in surface shear reversal that exceeds the stresses at the depth of maximum shear reversal under rolling contact.

  16. Giant panda׳s tooth enamel: Structure, mechanical behavior and toughening mechanisms under indentation.

    PubMed

    Weng, Z Y; Liu, Z Q; Ritchie, R O; Jiao, D; Li, D S; Wu, H L; Deng, L H; Zhang, Z F

    2016-12-01

    The giant panda׳s teeth possess remarkable load-bearing capacity and damage resistance for masticating bamboos. In this study, the hierarchical structure and mechanical behavior of the giant panda׳s tooth enamel were investigated under indentation. The effects of loading orientation and location on mechanical properties of the enamel were clarified and the evolution of damage in the enamel under increasing load evaluated. The nature of the damage, both at and beneath the indentation surfaces, and the underlying toughening mechanisms were explored. Indentation cracks invariably were seen to propagate along the internal interfaces, specifically the sheaths between enamel rods, and multiple extrinsic toughening mechanisms, e.g., crack deflection/twisting and uncracked-ligament bridging, were active to shield the tips of cracks from the applied stress. The giant panda׳s tooth enamel is analogous to human enamel in its mechanical properties, yet it has superior hardness and Young׳s modulus but inferior toughness as compared to the bamboo that pandas primarily feed on, highlighting the critical roles of the integration of underlying tissues in the entire tooth and the highly hydrated state of bamboo foods. Our objective is that this study can aid the understanding of the structure-mechanical property relations in the tooth enamel of mammals and further provide some insight on the food habits of the giant pandas.

  17. Evaluation of postural mechanisms under dynamic conditions

    NASA Technical Reports Server (NTRS)

    Anderson, D. J.

    1978-01-01

    A stimulus delivery and data acquisition system for assessment of human posture was developed based on a digital computer and a translating platform. The movement of the platform acts to displace the subject's base of support while the computer tracks the corrections which are made by the subject to maintain balance. Various stimuli are used ranging from fast transients to sine waves.

  18. On Logical Error Underlying Classical Mechanics

    NASA Astrophysics Data System (ADS)

    Kalanov, Temur Z.

    2012-03-01

    The logical analysis of the general accepted description of mechanical motion of material point M in classical mechanics is proposed. The key idea of the analysis is as follows. Let point M be moved in the positive direction of the axis O 1ptx. Motion is characterized by a change of coordinate x,( t ) -- continuous function of time t(because motion is a change in general). If δ,->;0;δ,;=;0, then δ,;->;0δ,;=;0, i.e., according to practice and formal logic, value of coordinate does not change and, hence, motion does not exist. But, contrary to practice and formal logic, differential calculus and classical mechanics contain the assertion that velocity δ,;->;0;δ,δ,;exists without motion. Then velocity δ,;->;0;δ,δ,;is not real (i.e. not physical) quantity, but fictitious quantity. Therefore, use of non-physical (unreal) quantity (i.e. the first and second derivatives of function) in classical mechanics is a logic error.

  19. The Mechanism Underlying Inhibition of Saccadic Return

    ERIC Educational Resources Information Center

    Ludwig, Casimir J. H.; Farrell, Simon; Ellis, Lucy A.; Gilchrist, Iain D.

    2009-01-01

    Human observers take longer to re-direct gaze to a previously fixated location. Although there has been some exploration of the characteristics of inhibition of saccadic return (ISR), the exact mechanisms by which ISR operates are currently unknown. In the framework of accumulation models of response times, in which evidence is integrated over…

  20. Investigation of Mechanisms Underlying Odor Recognition.

    DTIC Science & Technology

    1984-02-01

    olfactory epithelium of the rat using a procedure similar to that used in .amphibian forms (e.g., Kubie & Moulton, 1979). The detailed description of most...distinct differences in responsiveness of the underlying receptor sheet depending upon the region stimulated (e.g., Kauer & Moulton, 1979; Kubie M...patterns of olfactory bulb neurons using odor stimulation of small nasal areas in the salamander. J. Physiol. (London), 1974, 243, 717-737. Kubie , J.S

  1. Mechanical stability of trees under dynamic loads.

    PubMed

    James, Kenneth R; Haritos, Nicholas; Ades, Peter K

    2006-10-01

    Tree stability in windstorms and tree failure are important issues in urban areas where there can be risks of damage to people and property and in forests where wind damage causes economic loss. Current methods of managing trees, including pruning and assessment of mechanical strength, are mainly based on visual assessment or the experience of people such as trained arborists. Only limited data are available to assess tree strength and stability in winds, and most recent methods have used a static approach to estimate loads. Recent research on the measurement of dynamic wind loads and the effect on tree stability is giving a better understanding of how different trees cope with winds. Dynamic loads have been measured on trees with different canopy shapes and branch structures including a palm (Washingtonia robusta), a slender Italian cypress (Cupressus sempervirens) and trees with many branches and broad canopies including hoop pine (Araucaria cunninghamii) and two species of eucalypt (Eucalyptus grandis, E. teretecornus). Results indicate that sway is not a harmonic, but is very complex due to the dynamic interaction of branches. A new dynamic model of a tree is described, incorporating the dynamic structural properties of the trunk and branches. The branch mass contributes a dynamic damping, termed mass damping, which acts to reduce dangerous harmonic sway motion of the trunk and so minimizes loads and increases the mechanical stability of the tree. The results from 12 months of monitoring sway motion and wind loading forces are presented and discussed.

  2. Mechanical Evaluation of Polymer Composite Hip Protectors

    PubMed Central

    Melo, Jose Daniel Diniz; Barbosa, Ayrles S. Gonçalves; Guerra, Ricardo Oliveira

    2010-01-01

    Hip fractures often result in serious health implications, particularly in the geriatric population, and have been related to long-term morbidity and death. In most cases, these fractures are caused by impact loads in the area of the greater trochanter, which are produced in a fall. This work is aimed at developing hip protectors using composite materials and evaluating their effectiveness in preventing hip fractures under high impact energy (120 J). The hip protectors were developed with an inner layer of energy absorbing soft material and an outer rigid shell of fiberglass-reinforced polymer composite. According to the experimental results, all tested configurations proved to be effective at reducing the impact load to below the average fracture threshold of proximal femur. Furthermore, an addition of Ethylene Vinyl Acetate (EVA) to the impacted area of the composite shell proved to be beneficial to increase impact strength of the hip protectors. Thus, composite hip protectors proved to be a viable alternative for a mechanically efficient and cost-effective solution to prevent hip fractures. PMID:20871841

  3. The peripheral and central mechanisms underlying itch

    PubMed Central

    Lee, Jae Seung; Han, Jasmin Sanghyun; Lee, Kyeongho; Bang, Juwon; Lee, Hyosang

    2016-01-01

    Itch is one of the most distressing sensations that substantially impair quality of life. It is a cardinal symptom of many skin diseases and is also caused by a variety of systemic disorders. Unfortunately, currently available itch medications are ineffective in many chronic itch conditions, and they often cause undesirable side effects. To develop novel therapeutic strategies, it is essential to identify primary afferent neurons that selectively respond to itch mediators as well as the central nervous system components that process the sensation of itch and initiate behavioral responses. This review summarizes recent progress in the study of itch, focusing on itch-selective receptors, signaling molecules, neuronal pathways from the primary sensory neurons to the brain, and potential decoding mechanisms based on which itch is distinguished from pain. [BMB Reports 2016; 49(9): 474-487] PMID:27418284

  4. Environmental genotoxicity: Probing the underlying mechanisms

    SciTech Connect

    Shugart, L.; Theodorakis, C.

    1993-12-31

    Environmental pollution is a complex issue because of the diversity of anthropogenic agents, both chemical and physical, that have been detected and catalogued. The consequences to biota from exposure to genotoxic agents present an additional problem because of the potential for these agents to produce adverse change at the cellular and organismal levels. Past studies in genetic toxicology at the Oak Ridge National Laboratory have focused on structural damage to the DNA of environmental species that may occur after exposure to genotoxic agents and the use of this information to document exposure and to monitor remediation. In an effort to predict effects at the population, community and ecosystem levels, current studies in genetic ecotoxicology are attempting to characterize the biological mechanisms at the gene level that regulate and limit the response of an individual organism to genotoxic factors in their environment.

  5. Imitation in Newborn Infants: Exploring the Range of Gestures Imitated and the Underlying Mechanisms.

    ERIC Educational Resources Information Center

    Meltzoff, Andrew N.; Moore, M. Keith

    1989-01-01

    Evaluated psychological mechanisms underlying imitation of facial actions in 40 newborn infants. Results showed imitation of head movement and a tongue-protrusion gesture. Subjects imitated from memory after displays had stopped. (RJC)

  6. Mechanisms underlying the auditory continuity illusion

    NASA Astrophysics Data System (ADS)

    Pressnitzer, Daniel; Tardieu, Julien; Ragot, Richard; Baillet, Sylvain

    2004-05-01

    This study investigates the auditory continuity illusion, combining psychophysics and magnetoencephalography. Stimuli consisted of amplitude-modulated (AM) noise interrupted by bursts of louder, unmodulated noise. Subjective judgments confirmed that the AM was perceived as continuous, a case of illusory continuity. Psychophysical measurements showed that the illusory modulation had little effect on the detection of a physical modulation, i.e., the illusory modulation produced no modulation masking. Duration discrimination thresholds for the AM noise segments, however, were elevated by the illusion. A whole-head magnetoencephalographic system was used to record brain activity when listeners attended passively to the stimuli. The AM noise produced a modulated magnetic activity, the auditory steady-state response. The illusory modulation did not produce such a response, instead, a possible neural correlate of the illusion was found in transient evoked responses. When the AM was interrupted by silence, oscillatory activity in the gamma-band range as well as slow evoked potentials were observed at each AM onset. In the case of the illusion, these neural responses were largely reduced. Both sets of results are inconsistent with a restoration of the modulation in the case of illusory continuity. Rather, they point to a role for onset-detection mechanisms in auditory scene analysis.

  7. Molecular mechanisms underlying chemical liver injury

    PubMed Central

    Gu, Xinsheng; Manautou, Jose E.

    2013-01-01

    The liver is necessary for survival. Its strategic localisation, blood flow and prominent role in the metabolism of xenobiotics render this organ particularly susceptible to injury by chemicals to which we are ubiquitously exposed. The pathogenesis of most chemical-induced liver injuries is initiated by the metabolic conversion of chemicals into reactive intermediate species, such as electrophilic compounds or free radicals, which can potentially alter the structure and function of cellular macromolecules. Many reactive intermediate species can produce oxidative stress, which can be equally detrimental to the cell. When protective defences are overwhelmed by excess toxicant insult, the effects of reactive intermediate species lead to deregulation of cell signalling pathways and dysfunction of biomolecules, leading to failure of target organelles and eventual cell death. A myriad of genetic factors determine the susceptibility of specific individuals to chemical-induced liver injury. Environmental factors, lifestyle choices and pre-existing pathological conditions also have roles in the pathogenesis of chemical liver injury. Research aimed at elucidating the molecular mechanism of the pathogenesis of chemical-induced liver diseases is fundamental for preventing or devising new modalities of treatment for liver injury by chemicals. PMID:22306029

  8. The basics and underlying mechanisms of mucoadhesion.

    PubMed

    Smart, John D

    2005-11-03

    Mucoadhesion is where two surfaces, one of which is a mucous membrane, adhere to each other. This has been of interest in the pharmaceutical sciences in order to enhance localised drug delivery, or to deliver 'difficult' molecules (proteins and oligonucleotides) into the systemic circulation. Mucoadhesive materials are hydrophilic macromolecules containing numerous hydrogen bond forming groups, the carbomers and chitosans being two well-known examples. The mechanism by which mucoadhesion takes place has been said to have two stages, the contact (wetting) stage followed by the consolidation stage (the establishment of the adhesive interactions). The relative importance of each stage will depend on the individual application. For example, adsorption is a key stage if the dosage form cannot be applied directly to the mucosa of interest, while consolidation is important if the formulation is exposed to significant dislodging stresses. Adhesive joint failure will inevitably occur as a result of overhydration of a dosage form, or as a result of epithelia or mucus turnover. New mucoadhesive materials with optimal adhesive properties are now being developed, and these should enhance the potential applications of this technology.

  9. Chlorpromazine and ethanol intoxication: an underlying mechanism.

    PubMed

    Messiha, F S

    1985-01-01

    The in vitro effect of chlorpromazine on hepatic alcohol dehydrogenase (L-ADH) was studied as a function of sex and species. The presence of chlorpromazine, 50 muMol, in reaction mixture noncompetitively inhibited rat L-ADH in a dose dependent fashion in the concentration range between 5 X 10(-5) Mol and 10(-4) Mol. This drug concentration also inhibited L-ADH of albino mice of both sexes, but chlorpromazine-produced a decrease in Km which was greater in the female than in the male mouse. Likewise, chlorpromazine, 50 muMol, noncompetitively inhibited mouse L-ADH of C57BL/6J, a mouse strain with ethanol preference, but without a concomitant change in the apparent Km. The KI50 determination indicates 3.5 fold lower concentration requirement of the drug in the C57BL mouse strain compared to that of the albino rat liver preparation. The results suggest that the inhibitory action of the drug on L-ADH and the genetic factor involved may influence the legal limit of serum ethanol concentration during alcohol intoxication in subjects under psychotropic medications. A medical forensic implication is suggested.

  10. Mechanisms underlying selecting objects for action

    PubMed Central

    Wulff, Melanie; Laverick, Rosanna; Humphreys, Glyn W.; Wing, Alan M.; Rotshtein, Pia

    2015-01-01

    We assessed the factors which affect the selection of objects for action, focusing on the role of action knowledge and its modulation by distracters. Fourteen neuropsychological patients and 10 healthy aged-matched controls selected pairs of objects commonly used together among distracters in two contexts: with real objects and with pictures of the same objects presented sequentially on a computer screen. Across both tasks, semantically related distracters led to slower responses and more errors than unrelated distracters and the object actively used for action was selected prior to the object that would be passively held during the action. We identified a sub-group of patients (N = 6) whose accuracy was 2SDs below the controls performances in the real object task. Interestingly, these impaired patients were more affected by the presence of unrelated distracters during both tasks than intact patients and healthy controls. Note that the impaired patients had lesions to left parietal, right anterior temporal and bilateral pre-motor regions. We conclude that: (1) motor procedures guide object selection for action, (2) semantic knowledge affects action-based selection, (3) impaired action decision making is associated with the inability to ignore distracting information and (4) lesions to either the dorsal or ventral visual stream can lead to deficits in making action decisions. Overall, the data indicate that impairments in everyday tasks can be evaluated using a simulated computer task. The implications for rehabilitation are discussed. PMID:25954177

  11. Neurochemical mechanisms underlying responses to psychostimulants

    SciTech Connect

    Volkow, N.D.; Fowler, J.S.; Hitzemann, R.; Wang, G.J. |

    1994-11-01

    This study employed positron emission tomography (PET) to investigate biochemical and metabolic characteristics of the brain of individuals which could put them at risk for drug addiction. It takes advantage of the normal variability between individuals in response to psychoactive drugs to investigate relation between mental state, brain neurochemistry and metabolism and the behavioral response to drugs. We discuss its use to assess if there is an association between mental state and dompaminergic reactivity in response to the psychostimulant drug methylphenidate (MP). Changes in synaptic dopamine induced by MP were evaluated with PET and [11C]raclopride, a D{sub 2} receptor radioligand that is sensitive to endogenous dopamine. Methylpphenidate significantly decreased striatal [11C]raclopride binding. The study showed a correlation between the magnitude of the dopamine-induced changes by methylphenidate, and the mental state of the subjects. Subjects reporting high levels of anxiety and restlessness at baseline had larger changes in MP-induced dopamine changes than those that did not. Further investigations on the relation between an individual`s response to a drug and his/her mental state and personality as well as his neurochemical brain composition may enable to understand better differences in drug addiction vulnerability.

  12. [Molecular mechanisms underlying thermosensation in mammals].

    PubMed

    Sokabe, Takaaki; Tominaga, Makoto

    2009-07-01

    Sensing environmental temperature is one of the most important fundamental functions of the living things on the earth. Recently, it has been revealed that several members of the TRP ion channel super family are activated by temperature changes. A number of reports clearly demonstrate that thermal activation of these thermosensitive TRP channels contributes to various temperature-dependent responses in vivo, such as thermosensation, thermotaxis, and the regulation of cellular/tissue functions at physiological body temperature. Nine TRP channels have been reported to respond to a physiological range of temperatures in mammals. TRPV1 and TRPV2 expressed in nociceptive neurons are activated by heat (> 43 degrees C and > 52 degrees C, respectively), and TRPV1-null mice show defects in sensing noxious heat. TRPV3 and TRPV4 are predominantly expressed in skin keratinocytes rather than in sensory neurons, and the gene knock-out of each channel causes abnormal thermotaxis in vivo. TRPM8, which senses cold temperatures (< 27 degrees C), is expressed in nociceptive and non-nociceptive neurons and its loss impairs cold sensitivity. TRPA1 is expressed in nociceptive neurons and acts as a sensor for various harmful stimuli, whereas its responsiveness to noxious cold stimuli is controversial even after the analysis of mice lacking the channel. Other thermoTRPs, TRPM2, TRPM4, and TRPM5 are not expressed in sensory neurons, and are reportedly involved in several functions at physiological body temperatures including insulin secretion, taste sensation, and immune response. In this review, I summarize the molecular mechanisms of thermosensation in mammals by focusing on thermosensitive TRP channels.

  13. Static strength and failure mechanism of CFRP under biaxial loadings

    NASA Astrophysics Data System (ADS)

    Lee, C. S.; Hwang, W.; Park, H. C.; Han, K. S.

    1998-01-01

    Tests of cross-ply composite tubes were performed under combined axial and torsional loading up to failure. Strength properties and failure mechanisms were evaluated with reference to the biaxiality ratio of the loading. The scattering of the biaxial strength data was analyzed using the Weibull distribution. The axial contraction of carbon fiber-reinforced plastic (CFRP) tubes under biaxial loading was investigated theoretically and experimentally. Artificial neural networks were introduced to predict the failure strength using the algorithm of the error back-propagation. The prediction was also made by the Tsai-Wu theory using the experimental data and by the combined optimized tensor-polynomial theory. A comparison shows that the artificial neural network has the smallest root-mean square (RMS) error of the three prediction methods. The prediction of the axial contraction of the tubes correlates well with the results of a linear variable differential transformer (LVDT) of the testing machine. From the phenomenological analysis of the failure and the fractographic observations of the fracture surface, three types of failure modes and microscopic failure were investigated, depending on the biaxiality ratio, and the corresponding failure mechanisms are suggested.

  14. Theory underlying a national teacher evaluation program.

    PubMed

    Taut, Sandy; Santelices, Verónica; Araya, Carolina; Manzi, Jorge

    2010-11-01

    The paper describes a study conducted to explicate the multiple theories underlying Chile's national teacher evaluation program. These theories will serve as the basis for evaluating the intended consequences of this evaluation system, while not losing sight of emerging unintended consequences. We first analyzed legal and policy documents and then interviewed fourteen representatives of the four stakeholder groups involved in the program's design and implementation, in order to gain insight into their respective conceptions of the program's functioning and intended effects. The results show that, as to be expected and despite the long and difficult negotiation process that preceded implementation of this program, multiple political stakeholders still view the program's intended effects differently. However, there was substantial overlap regarding a number of intended effects, such as building the capacity of, and triggering change in, teachers with shortcomings, and informing the selection of new teachers and facilitating the exit of unsatisfactory teachers from the system. It was difficult to get interviewees to talk about how exactly these intended effects are supposed to be achieved. The paper draws conclusions regarding theory elaboration process involving multiple stakeholders in a highly political context.

  15. Mechanisms underlying 18F-fluorodeoxyglucose accumulation in colorectal cancer

    PubMed Central

    Kawada, Kenji; Iwamoto, Masayoshi; Sakai, Yoshiharu

    2016-01-01

    Positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) is a diagnostic tool to evaluate metabolic activity by measuring accumulation of FDG, an analogue of glucose, and has been widely used for detecting small tumors, monitoring treatment response and predicting patients’ prognosis in a variety of cancers. However, the molecular mechanism of FDG accumulation into tumors remains to be investigated. It is well-known that most cancers are metabolically active with elevated glucose metabolism, a phenomenon known as the Warburg effect. The underlying mechanisms for elevated glucose metabolism in cancer tissues are complex. Recent reports have indicated the potential of FDG-PET/CT scans in predicting mutational status (e.g., KRAS gene mutation) of colorectal cancer (CRC), which suggests that FDG-PET/CT scans may play a key role in determining therapeutic strategies by non-invasively predicting treatment response to anti-epidermal growth factor receptor (EGFR) therapy. In this review, we summarize the current findings investigating the molecular mechanism of 18F-FDG accumulation in CRC. PMID:27928469

  16. Eye movements reveal mechanisms underlying attentional biases towards threat.

    PubMed

    Sagliano, Laura; D'Olimpio, Francesca; Taglialatela Scafati, Ilaria; Trojano, Luigi

    2016-11-01

    Mechanisms underlying attentional biases towards threat (ABTs), such as attentional avoidance and difficulty of disengagement, are still unclear. To address this issue, we recorded participants' eye movements during a dot detection task in which threatening or neutral stimuli served as peripheral cues. We evaluated response times (RTs) in trials where participants looked at the central fixation cross (not at the cues), as they were required, and number and duration of (unwanted) fixations towards threatening or neutral cues; in all analyses trait anxiety was treated as a covariate. Difficulty in attentional disengagement (longer RTs) was found when peripheral threatening stimuli were presented for 100 ms. Moreover, we observed significantly shorter (unwanted) fixations on threatening than on neutral peripheral stimuli, compatible with an avoidance bias, for longer presentation times. These findings demonstrate that, independent of trait anxiety levels, disengagement bias occurs without eye movements, whereas eye movements are implied in threat avoidance.

  17. Mechanisms underlying allergy vaccination with recombinant hypoallergenic allergen derivatives

    PubMed Central

    Linhart, Birgit; Valenta, Rudolf

    2015-01-01

    Hundred years ago therapeutic vaccination with allergen-containing extracts has been introduced as a clinically effective, disease-modifying, allergen-specific and long-lasting form of therapy for allergy, a hypersensitivity disease affecting more than 25% of the population. Today, the structures of most of the disease-causing allergens have been elucidated and recombinant hypoallergenic allergen derivatives with reduced allergenic activity have been engineered to reduce side effects during allergen-specific immunotherapy (SIT). These recombinant hypoallergens have been characterized in vitro, in experimental animal models and in clinical trials in allergic patients. This review provides a summary of the molecular, immunological and preclinical evaluation criteria applied for this new generation of allergy vaccines. Furthermore, we summarize the mechanisms underlying SIT with recombinant hypoallergens which are thought to be responsible for their therapeutic effect. PMID:22100888

  18. Molecular Mechanisms Regulating Muscle Fiber Composition Under Microgravity

    NASA Technical Reports Server (NTRS)

    Rosenthal, Nadia A.

    1999-01-01

    The overall goal of this project is to reveal the molecular mechanisms underlying the selective and debilitating atrophy of specific skeletal muscle fiber types that accompanies sustained conditions of microgravity. Since little is currently known about the regulation of fiber-specific gene expression programs in mammalian muscle, elucidation of the basic mechanisms of fiber diversification is a necessary prerequisite to the generation of therapeutic strategies for attenuation of muscle atrophy on earth or in space. Vertebrate skeletal muscle development involves the fusion of undifferentiated mononucleated myoblasts to form multinucleated myofibers, with a concomitant activation of muscle-specific genes encoding proteins that form the force-generating contractile apparatus. The regulatory circuitry controlling skeletal muscle gene expression has been well studied in a number of vertebrate animal systems. The goal of this project has been to achieve a similar level of understanding of the mechanisms underlying the further specification of muscles into different fiber types, and the role played by innervation and physical activity in the maintenance and adaptation of different fiber phenotypes into adulthood. Our recent research on the genetic basis of fiber specificity has focused on the emergence of mature fiber types and have implicated a group of transcriptional regulatory proteins, known as E proteins, in the control of fiber specificity. The restriction of E proteins to selected muscle fiber types is an attractive hypothetical mechanism for the generation of muscle fiber-specific patterns of gene expression. To date our results support a model wherein different E proteins are selectively expressed in muscle cells to determine fiber-restricted gene expression. These studies are a first step to define the molecular mechanisms responsible for the shifts in fiber type under conditions of microgravity, and to determine the potential importance of E proteins as

  19. Quality of protection evaluation of security mechanisms.

    PubMed

    Ksiezopolski, Bogdan; Zurek, Tomasz; Mokkas, Michail

    2014-01-01

    Recent research indicates that during the design of teleinformatic system the tradeoff between the systems performance and the system protection should be made. The traditional approach assumes that the best way is to apply the strongest possible security measures. Unfortunately, the overestimation of security measures can lead to the unreasonable increase of system load. This is especially important in multimedia systems where the performance has critical character. In many cases determination of the required level of protection and adjustment of some security measures to these requirements increase system efficiency. Such an approach is achieved by means of the quality of protection models where the security measures are evaluated according to their influence on the system security. In the paper, we propose a model for QoP evaluation of security mechanisms. Owing to this model, one can quantify the influence of particular security mechanisms on ensuring security attributes. The methodology of our model preparation is described and based on it the case study analysis is presented. We support our method by the tool where the models can be defined and QoP evaluation can be performed. Finally, we have modelled TLS cryptographic protocol and presented the QoP security mechanisms evaluation for the selected versions of this protocol.

  20. Quality of Protection Evaluation of Security Mechanisms

    PubMed Central

    Ksiezopolski, Bogdan; Zurek, Tomasz; Mokkas, Michail

    2014-01-01

    Recent research indicates that during the design of teleinformatic system the tradeoff between the systems performance and the system protection should be made. The traditional approach assumes that the best way is to apply the strongest possible security measures. Unfortunately, the overestimation of security measures can lead to the unreasonable increase of system load. This is especially important in multimedia systems where the performance has critical character. In many cases determination of the required level of protection and adjustment of some security measures to these requirements increase system efficiency. Such an approach is achieved by means of the quality of protection models where the security measures are evaluated according to their influence on the system security. In the paper, we propose a model for QoP evaluation of security mechanisms. Owing to this model, one can quantify the influence of particular security mechanisms on ensuring security attributes. The methodology of our model preparation is described and based on it the case study analysis is presented. We support our method by the tool where the models can be defined and QoP evaluation can be performed. Finally, we have modelled TLS cryptographic protocol and presented the QoP security mechanisms evaluation for the selected versions of this protocol. PMID:25136683

  1. The Pathophysiological Mechanism Underlying Brugada Syndrome. Depolarization versus Repolarization

    PubMed Central

    Wilde, Arthur A.M.; Postema, Pieter G.; Di Diego, José M.; Viskin, Sami; Morita, Hiroshi; Fish, Jeffrey M.; Antzelevitch, Charles

    2010-01-01

    This Point/Counterpoint presents a scholarly debate of the mechanisms underlying the electrocardiographic and arrhythmic manifestations of Brugada syndrome (BrS), exploring in detail the available evidence in support of the repolarization vs. depolarization hypothesis. PMID:20659475

  2. Neurocomputational mechanisms underlying subjective valuation of effort costs

    PubMed Central

    Giehl, Kathrin; Sillence, Annie

    2017-01-01

    In everyday life, we have to decide whether it is worth exerting effort to obtain rewards. Effort can be experienced in different domains, with some tasks requiring significant cognitive demand and others being more physically effortful. The motivation to exert effort for reward is highly subjective and varies considerably across the different domains of behaviour. However, very little is known about the computational or neural basis of how different effort costs are subjectively weighed against rewards. Is there a common, domain-general system of brain areas that evaluates all costs and benefits? Here, we used computational modelling and functional magnetic resonance imaging (fMRI) to examine the mechanisms underlying value processing in both the cognitive and physical domains. Participants were trained on two novel tasks that parametrically varied either cognitive or physical effort. During fMRI, participants indicated their preferences between a fixed low-effort/low-reward option and a variable higher-effort/higher-reward offer for each effort domain. Critically, reward devaluation by both cognitive and physical effort was subserved by a common network of areas, including the dorsomedial and dorsolateral prefrontal cortex, the intraparietal sulcus, and the anterior insula. Activity within these domain-general areas also covaried negatively with reward and positively with effort, suggesting an integration of these parameters within these areas. Additionally, the amygdala appeared to play a unique, domain-specific role in processing the value of rewards associated with cognitive effort. These results are the first to reveal the neurocomputational mechanisms underlying subjective cost–benefit valuation across different domains of effort and provide insight into the multidimensional nature of motivation. PMID:28234892

  3. Neurocomputational mechanisms underlying subjective valuation of effort costs.

    PubMed

    Chong, Trevor T-J; Apps, Matthew; Giehl, Kathrin; Sillence, Annie; Grima, Laura L; Husain, Masud

    2017-02-01

    In everyday life, we have to decide whether it is worth exerting effort to obtain rewards. Effort can be experienced in different domains, with some tasks requiring significant cognitive demand and others being more physically effortful. The motivation to exert effort for reward is highly subjective and varies considerably across the different domains of behaviour. However, very little is known about the computational or neural basis of how different effort costs are subjectively weighed against rewards. Is there a common, domain-general system of brain areas that evaluates all costs and benefits? Here, we used computational modelling and functional magnetic resonance imaging (fMRI) to examine the mechanisms underlying value processing in both the cognitive and physical domains. Participants were trained on two novel tasks that parametrically varied either cognitive or physical effort. During fMRI, participants indicated their preferences between a fixed low-effort/low-reward option and a variable higher-effort/higher-reward offer for each effort domain. Critically, reward devaluation by both cognitive and physical effort was subserved by a common network of areas, including the dorsomedial and dorsolateral prefrontal cortex, the intraparietal sulcus, and the anterior insula. Activity within these domain-general areas also covaried negatively with reward and positively with effort, suggesting an integration of these parameters within these areas. Additionally, the amygdala appeared to play a unique, domain-specific role in processing the value of rewards associated with cognitive effort. These results are the first to reveal the neurocomputational mechanisms underlying subjective cost-benefit valuation across different domains of effort and provide insight into the multidimensional nature of motivation.

  4. The Challenge of Characterizing Operations in the Mechanisms Underlying Behavior

    ERIC Educational Resources Information Center

    Bechtel, William

    2005-01-01

    Neuroscience and cognitive science seek to explain behavioral regularities in terms of underlying mechanisms. An important element of a mechanistic explanation is a characterization of the operations of the parts of the mechanism. The challenge in characterizing such operations is illustrated by an example from the history of physiological…

  5. Modelling approaches for evaluating multiscale tendon mechanics

    PubMed Central

    Fang, Fei; Lake, Spencer P.

    2016-01-01

    Tendon exhibits anisotropic, inhomogeneous and viscoelastic mechanical properties that are determined by its complicated hierarchical structure and varying amounts/organization of different tissue constituents. Although extensive research has been conducted to use modelling approaches to interpret tendon structure–function relationships in combination with experimental data, many issues remain unclear (i.e. the role of minor components such as decorin, aggrecan and elastin), and the integration of mechanical analysis across different length scales has not been well applied to explore stress or strain transfer from macro- to microscale. This review outlines mathematical and computational models that have been used to understand tendon mechanics at different scales of the hierarchical organization. Model representations at the molecular, fibril and tissue levels are discussed, including formulations that follow phenomenological and microstructural approaches (which include evaluations of crimp, helical structure and the interaction between collagen fibrils and proteoglycans). Multiscale modelling approaches incorporating tendon features are suggested to be an advantageous methodology to understand further the physiological mechanical response of tendon and corresponding adaptation of properties owing to unique in vivo loading environments. PMID:26855747

  6. Inelastic deformation mechanisms in a transverse MMC lamina under compression

    NASA Technical Reports Server (NTRS)

    Newaz, Golam M.; Majumdar, Bhaskar S.

    1992-01-01

    An investigation was undertaken to study the inelastic deformation mechanisms in (90)(sub 8) Ti 15-3/SCS-6 lamina subjected to pure compression. Both mechanical behavior and microstructural evaluation were undertaken at room temperature, 538 and 650 C. Results indicate that mechanical response and deformation characteristics are significantly different in monotonic tension and compression. The inelastic deformation mechanisms in compression are controlled by radial fiber fracture, matrix plasticity and fiber-matrix debonding. The radial fiber fracture is a new damage mode observed for metal-matrix composites (MMC).

  7. Micromechanical evaluation of bone microstructures under load

    NASA Astrophysics Data System (ADS)

    Mueller, Ralph; Boesch, Tobias; Jarak, Drazen; Stauber, Martin; Nazarian, Ara; Tantillo, Michelle; Boyd, Steven

    2002-01-01

    Many bones within the axial and appendicular skeleton are subjected to repetitive, cyclic loading during the course of ordinary daily activities. If this repetitive loading is of sufficient magnitude or duration, fatigue failure of the bone tissue may result. In clinical orthopedics, trabecular fatigue fractures are observed as compressive stress fractures in the proximal femur, vertebrae, calcaneus and tibia, and are often preceded by buckling and bending of microstructural elements. However, the relative importance of bone density and architecture in the aetiology of these fractures is poorly understood. The aim of the study was to investigate failure mechanisms of 3D trabecular bone using micro-computed tomography (mCT). Because of its nondestructive nature, mCT represents an ideal approach for performing not only static measurements of bone architecture but also dynamic measurements of failure initiation and propagation as well as damage accumulation. For the purpose of the study, a novel micro-compression device was devised to measure loaded trabecular bone specimens directly in a micro-tomographic system. A 3D snapshot of the structure under load was taken for each load step in the mCT providing 34 mm nominal resolution. An integrated mini-button load cell in the compression device combined with the displacement computed directly from the mCT scout view was used to record the load-displacement curve. From the series of 3D images, failure of the trabecular architecture could be observed, and in a rod-like type of architecture it could be described by an initial buckling and bending of structural elements followed by a collapse of the overloaded trabeculae. A computational method was developed to quantify individual trabecular strains during failure. The four main steps of the algorithm were (i) sequential image alignment, (ii) identification of landmarks (trabecular nodes), (iii) determine nodal connectivity, and (iv) to compute the nodal displacements and

  8. Molecular Mechanisms Regulating Muscle Fiber Composition Under Microgravity

    NASA Technical Reports Server (NTRS)

    Rosenthal, Nadia A.

    1999-01-01

    The overall goal of this project is to reveal the molecular mechanisms underlying the selective and debilitating atrophy of specific skeletal muscle fiber types that accompanies sustained conditions of microgravity. Since little is currently known about the regulation of fiber-specific gene expression programs in mammalian muscle, elucidation of the basic mechanisms of fiber diversification is a necessary prerequisite to the generation of therapeutic strategies for attenuation of muscle atrophy on earth or in space. Vertebrate skeletal muscle development involves the fusion of undifferentiated mononucleated myoblasts to form multinucleated myofibers, with a concomitant activation of muscle-specific genes encoding proteins that form the force-generating contractile apparatus. The regulatory circuitry controlling skeletal muscle gene expression has been well studied in a number of vertebrate animal systems. The goal of this project has been to achieve a similar level of understanding of the mechanisms underlying the further specification of muscles into different fiber types, and the role played by innervation and physical activity in the maintenance and adaptation of different fiber phenotypes into adulthood. Our recent research on the genetic basis of fiber specificity has focused on the emergence of mature fiber types and have implicated a group of transcriptional regulatory proteins, known as E proteins, in the control of fiber specificity. The restriction of E proteins to selected muscle fiber types is an attractive hypothetical mechanism for the generation of muscle fiber-specific patterns of gene expression. To date our results support a model wherein different E proteins are selectively expressed in muscle cells to determine fiber-restricted gene expression. These studies are a first step to define the molecular mechanisms responsible for the shifts in fiber type under conditions of microgravity, and to determine the potential importance of E proteins as

  9. Study of mechanical behavior of AFM silicon tips under mechanical load

    NASA Astrophysics Data System (ADS)

    Kopycinska-Mueller, M.; Gluch, J.; Köhler, B.

    2016-11-01

    In this paper we address critical issues concerning calibration of AFM based methods used for nanoscale mechanical characterization of materials. It has been shown that calibration approaches based on macroscopic models for contact mechanics may yield excellent results in terms of the indentation modulus of the sample, but fail to provide a comprehensive and actual information concerning the tip-sample contact radius or the mechanical properties of the tip. Explanations for the severely reduced indentation modulus of the tip included the inadequacies of the models used for calculations of the tip-sample contact stiffness, discrepancies in the actual and ideal shape of the tip, presence of the amorphous silicon phase within the silicon tip, as well as negligence of the actual size of the stress field created in the tip during elastic interactions. To clarify these issues, we investigated the influence of the mechanical load applied to four AFM silicon tips on their crystalline state by exposing them to systematically increasing loads, evaluating the character of the tip-sample interactions via the load-unload stiffness curves, and assessing the state of the tips from HR-TEM images. The results presented in this paper were obtained in a series of relatively simple and basic atomic force acoustic microscopy (AFAM) experiments. The novel combination of TEM imaging of the AFM tips with the analysis of the load-unload stiffness curves gave us a detailed insight into their mechanical behavior under load conditions. We were able to identify the limits for the elastic interactions, as well as the hallmarks for phase transformation and dislocation formation and movement. The comparison of the physical dimensions of the AFM tips, geometry parameters determined from the values of the contact stiffness, and the information on the crystalline state of the tips allowed us a better understanding of the nanoscale contact.

  10. Molecular mechanisms underlying phosphate sensing, signaling, and adaptation in plants.

    PubMed

    Zhang, Zhaoliang; Liao, Hong; Lucas, William J

    2014-03-01

    As an essential plant macronutrient, the low availability of phosphorus (P) in most soils imposes serious limitation on crop production. Plants have evolved complex responsive and adaptive mechanisms for acquisition, remobilization and recycling of phosphate (Pi) to maintain P homeostasis. Spatio-temporal molecular, physiological, and biochemical Pi deficiency responses developed by plants are the consequence of local and systemic sensing and signaling pathways. Pi deficiency is sensed locally by the root system where hormones serve as important signaling components in terms of developmental reprogramming, leading to changes in root system architecture. Root-to-shoot and shoot-to-root signals, delivered through the xylem and phloem, respectively, involving Pi itself, hormones, miRNAs, mRNAs, and sucrose, serve to coordinate Pi deficiency responses at the whole-plant level. A combination of chromatin remodeling, transcriptional and posttranslational events contribute to globally regulating a wide range of Pi deficiency responses. In this review, recent advances are evaluated in terms of progress toward developing a comprehensive understanding of the molecular events underlying control over P homeostasis. Application of this knowledge, in terms of developing crop plants having enhanced attributes for P use efficiency, is discussed from the perspective of agricultural sustainability in the face of diminishing global P supplies.

  11. Regulatory mechanisms underlying the differential growth of dendrites and axons.

    PubMed

    Wang, Xin; Sterne, Gabriella R; Ye, Bing

    2014-08-01

    A typical neuron is comprised of an information input compartment, or the dendrites, and an output compartment, known as the axon. These two compartments are the structural basis for functional neural circuits. However, little is known about how dendritic and axonal growth are differentially regulated. Recent studies have uncovered two distinct types of regulatory mechanisms that differentiate dendritic and axonal growth: dedicated mechanisms and bimodal mechanisms. Dedicated mechanisms regulate either dendritespecific or axon-specific growth; in contrast, bimodal mechanisms direct dendritic and axonal development in opposite manners. Here, we review the dedicated and bimodal regulators identified by recent Drosophila and mammalian studies. The knowledge of these underlying molecular mechanisms not only expands our understanding about how neural circuits are wired, but also provides insights that will aid in the rational design of therapies for neurological diseases.

  12. On the mechanical properties of tooth enamel under spherical indentation.

    PubMed

    Chai, Herzl

    2014-11-01

    The mechanical properties of tooth enamel generally exhibit large variations, which reflect its structural and material complexity. Some key properties were evaluated under localized contact, simulating actual functioning conditions. Prominent cusps of extracted human molar teeth were polished down ~0.7 mm below the cusp tip and indented by tungsten carbide balls. The internal damage was assessed after unloading from longitudinal or transverse sections. The ultimate tensile stress (UTS) was determined using a novel bilayer specimen. The damage is characterized by penny-like radial cracks driven by hoop stresses and cylindrical cracks driven along protein-rich interrod materials by shear stresses. Shallow cone cracks typical of homogeneous materials which may cause rapid tooth wear under repeat contact are thus avoided. The mean stress vs. indentation strain curve is highly nonlinear, attributable to plastic shearing of protein between and within enamel rods. This curve is also affected by damage, especially radial cracks, the onset of which depends on ball radius. Several material properties were extracted from the tests, including shear strain at the onset of ring cracks γ(F) (=0.14), UTS (=119 MPa), toughness K(C) (=0.94 MPa m(1/2)), a crack propagation law and a constitutive response determined by trial and error with the aid of a finite-element analysis. These quantities, which are only slightly sensitive to anatomical location within the enamel region tested, facilitate a quantitative assessment of crown failure. Causes for variations in published UTS and K(C) values are discussed.

  13. Systematic evaluation of skeletal mechanical function

    PubMed Central

    Smith, Lauren; Bigelow, Erin M.R.; Jepsen, Karl J.

    2013-01-01

    Many genetic and environmental perturbations lead to measurable changes in bone morphology, matrix composition, and matrix organization. The skeletal system is highly adaptive, such that genetic and environmental perturbations affecting one trait are often accompanied by compensatory changes in other traits. This adaptation should be considered when attempting to draw meaningful conclusions about the role of a gene, for example. The challenge is to figure out which alterations can be attributed to the perturbation and which result from adaptive changes associated with establishing mechanical function. The goal of this chapter is to describe straight-forward biomechanical methods that can be used to determine whether a genetic or environmental perturbation affected bone strength. We introduce a systematic method for evaluating how bone strength was altered in the context of morphology and tissue-level mechanical properties, which are determined in large part from matrix composition, matrix organization, and porosity. We present this work as a first step toward screening mice for a phenotypic effect and for establishing the associated biomechanical mechanism by which function was altered. The outcome of these analyses generally provides insight into the next set of experiments required to further connect the cellular perturbation with the functional changes. The protocols were written to enable researchers without a background in engineering to conduct the assays or to enable researchers to better understand the outcomes of similar assays conducted by colleagues knowledgeable in engineering. PMID:24634803

  14. Molecular mechanisms underlying the fetal programming of adult disease.

    PubMed

    Vo, Thin; Hardy, Daniel B

    2012-08-01

    Adverse events in utero can be critical in determining quality of life and overall health. It is estimated that up to 50 % of metabolic syndrome diseases can be linked to an adverse fetal environment. However, the mechanisms linking impaired fetal development to these adult diseases remain elusive. This review uncovers some of the molecular mechanisms underlying how normal physiology may be impaired in fetal and postnatal life due to maternal insults in pregnancy. By understanding the mechanisms, which include epigenetic, transcriptional, endoplasmic reticulum (ER) stress, and reactive oxygen species (ROS), we also highlight how intervention in fetal and neonatal life may be able to prevent these diseases long-term.

  15. Cell-Nonautonomous Mechanisms Underlying Cellular and Organismal Aging.

    PubMed

    Medkour, Younes; Svistkova, Veronika; Titorenko, Vladimir I

    2016-01-01

    Cell-autonomous mechanisms underlying cellular and organismal aging in evolutionarily distant eukaryotes have been established; these mechanisms regulate longevity-defining processes within a single eukaryotic cell. Recent findings have provided valuable insight into cell-nonautonomous mechanisms modulating cellular and organismal aging in eukaryotes across phyla; these mechanisms involve a transmission of various longevity factors between different cells, tissues, and organisms. Herein, we review such cell-nonautonomous mechanisms of aging in eukaryotes. We discuss the following: (1) how low molecular weight transmissible longevity factors modulate aging and define longevity of cells in yeast populations cultured in liquid media or on solid surfaces, (2) how communications between proteostasis stress networks operating in neurons and nonneuronal somatic tissues define longevity of the nematode Caenorhabditis elegans by modulating the rates of aging in different tissues, and (3) how different bacterial species colonizing the gut lumen of C. elegans define nematode longevity by modulating the rate of organismal aging.

  16. Neural Circuitry and Plasticity Mechanisms Underlying Delay Eyeblink Conditioning

    ERIC Educational Resources Information Center

    Freeman, John H.; Steinmetz, Adam B.

    2011-01-01

    Pavlovian eyeblink conditioning has been used extensively as a model system for examining the neural mechanisms underlying associative learning. Delay eyeblink conditioning depends on the intermediate cerebellum ipsilateral to the conditioned eye. Evidence favors a two-site plasticity model within the cerebellum with long-term depression of…

  17. Mechanisms underlying transcranial direct current stimulation in rehabilitation.

    PubMed

    Roche, N; Geiger, M; Bussel, B

    2015-09-01

    For a few years, the non-invasive modulation of motor cortex has become the centre of much attention because of its possible clinical impact. Among the different mechanism allowing to modify motor-cortex excitability, transcranial direct current stimulation (tDCS), with its efficacy and ease of use, plays a major role. The aim of this review is to improve the understanding of the underlying mechanisms of the tDCS effect in the field of rehabilitation. The mechanisms underlying tDCS effects when applied over the motor cortex differ depending on the polarity used. Moreover, the mechanisms underlying these effects differ during stimulation (per-stimulation) and after the end of it (after-effects). This review highlights the known mechanisms involved in tDCS effects on brain excitability and illustrates that most remain not well understood and debated. Further studies are necessary to elucidate the mode of action of tDCS and determine the best paradigm of stimulation depending on the goals.

  18. Damage mechanisms in PBT-GF30 under thermo-mechanical cyclic loading

    SciTech Connect

    Schaaf, A. De Monte, M. Hoffmann, C.; Vormwald, M.; Quaresimin, M.

    2014-05-15

    The scope of this paper is the investigation of damage mechanisms at microscopic scale on a short glass fiber reinforced polybutylene terephthalate (PBT-GF30) under thermo-mechanical cyclic loading. In addition the principal mechanisms are verified through micro mechanical FE models. In order to investigate the fatigue behavior of the material both isothermal strain controlled fatigue (ISCF) tests at three different temperatures and thermo-mechanical fatigue (TMF) tests were conducted on plain and notched specimens, manufactured by injection molding. The goal of the work is to determine the damage mechanisms occurring under TMF conditions and to compare them with the mechanisms occurring under ISCF. For this reason fracture surfaces of TMF and ISCF samples loaded at different temperature levels were analyzed using scanning electron microscopy. Furthermore, specimens that failed under TMF were examined on microsections revealing insight into both crack initiation and crack propagation. The findings of this investigation give valuable information about the main damage mechanisms of PBT-GF30 under TMF loading and serve as basis for the development of a TMF life estimation methodology.

  19. Airtight metallic sealing at room temperature under small mechanical pressure

    NASA Astrophysics Data System (ADS)

    Stagon, Stephen P.; Huang, Hanchen

    2013-10-01

    Metallic seals can be resistant to air leakage, resistant to degradation under heat, and capable of carrying mechanical loads. Various technologies - such as organic solar cells and organic light emitting diodes - need, at least benefit from, such metallic seals. However, these technologies involve polymeric materials and can tolerate neither the high-temperature nor the high-pressure processes of conventional metallic sealing. Recent progress in nanorod growth opens the door to metallic sealing for these technologies. Here, we report a process of metallic sealing using small well-separated Ag nanorods; the process is at room temperature, under a small mechanical pressure of 9.0 MPa, and also in ambient. The metallic seals have an air leak rate of 1.1 × 10-3 cm3atm/m2/day, and a mechanical shear strength higher than 8.9 MPa. This leak rate meets the requirements of organic solar cells and organic light emitting diodes.

  20. Cognitive mechanisms underlying instructed choice exploration of small city maps.

    PubMed

    Sakellaridi, Sofia; Christova, Peka; Christopoulos, Vassilios N; Vialard, Alice; Peponis, John; Georgopoulos, Apostolos P

    2015-01-01

    We investigated the cognitive mechanisms underlying the exploration and decision-making in realistic and novel environments. Twelve human subjects were shown small circular U.S. city maps with two locations highlighted on the circumference, as possible choices for a post office ("targets"). At the beginning of a trial, subjects fixated a spot at the center of the map and ultimately chose one of the two locations. A space syntax analysis of the map paths (from the center to each target) revealed that the chosen location was associated with the less convoluted path, as if subjects navigated mentally the paths in an "ant's way," i.e., by staying within street boundaries, and ultimately choosing the target that could be reached from the center in the shortest way, and the fewest turns and intersections. The subjects' strategy for map exploration and decision making was investigated by monitoring eye position during the task. This revealed a restricted exploration of the map delimited by the location of the two alternative options and the center of the map. Specifically, subjects explored the areas around the two target options by repeatedly looking at them before deciding which one to choose, presumably implementing an evaluation and decision-making process. The ultimate selection of a specific target was significantly associated with the time spent exploring the area around that target. Finally, an analysis of the sequence of eye fixations revealed that subjects tended to look systematically toward the target ultimately chosen even from the beginning of the trial. This finding indicates an early cognitive selection bias for the ensuing decision process.

  1. [Neuronal mechanisms underlying pain-induced negative emotions].

    PubMed

    Minami, Masabumi

    2012-11-01

    Pain consists of sensory-discriminative and negative emotional components. Although the neuronal basis of the sensory component of pain has been studied extensively, the neuronal mechanisms underlying the negative emotional component are not well understood. Recently, behavioral studies using a conditioned place paradigm have successfully elucidated the neuronal circuits and mechanisms underlying the negative emotional component of pain. Excitotoxic lesions of the anterior cingulate cortex (ACC), central amygdaloid nucleus, basolateral amygdaloid nucleus (BLA), or bed nucleus of the stria terminalis (BNST) suppress intraplantar formalin-induced aversive responses. Glutamatergic transmission within the ACC and BLA via N-methyl-D-asparate (NMDA) receptors has been shown to play a critical role in these aversive responses. In the BNST, especially its ventral part, noradrenergic transmission via β-adrenergic receptors has been shown to be important for pain-induced aversion. Because persistent pain is frequently associated with psychological and emotional dysfunctions, studies on the neuronal circuits and molecular mechanisms involved in the negative emotional component of pain may have considerable clinical importance in the treatment of chronic pain. Here, I have reviewed behavioral studies investigating the neuronal mechanisms underlying the negative emotional component of pain and have introduced our data showing the pivotal role of amygdala and BNST in pain-induced aversion.

  2. Investigation of defect nucleation in titanium under mechanical loading

    SciTech Connect

    Zolnikov, Konstantin P. Kryzhevich, Dmitrij S.; Korchuganov, Aleksandr V.; Psakhie, Sergey G.

    2014-11-14

    The paper undertakes a study of plastic deformation in a titanium crystallite under mechanical loading (uniaxial tension and indentation) in terms of atomic mechanisms of its generation and development. The molecular dynamics method with many-body interatomic potentials is employed. It is shown that there is a threshold strain, at which a crystal reveals the generation of local structural transformations associated with changes in atomic configurations of the first and second coordination spheres. The onset of plastic deformation in a crystallite is accompanied by a stepwise decrease in potential energy. The effect of free surfaces and grain boundaries on the generation of local structural transformations in a titanium crystallite is investigated.

  3. Experimental Analysis of the Mechanism of Hearing under Water

    PubMed Central

    Chordekar, Shai; Kishon-Rabin, Liat; Kriksunov, Leonid; Adelman, Cahtia; Sohmer, Haim

    2015-01-01

    The mechanism of human hearing under water is debated. Some suggest it is by air conduction (AC), others by bone conduction (BC), and others by a combination of AC and BC. A clinical bone vibrator applied to soft tissue sites on the head, neck, and thorax also elicits hearing by a mechanism called soft tissue conduction (STC) or nonosseous BC. The present study was designed to test whether underwater hearing at low intensities is by AC or by osseous BC based on bone vibrations or by nonosseous BC (STC). Thresholds of normal hearing participants to bone vibrator stimulation with their forehead in air were recorded and again when forehead and bone vibrator were under water. A vibrometer detected vibrations of a dry human skull in all similar conditions (in air and under water) but not when water was the intermediary between the sound source and the skull forehead. Therefore, the intensities required to induce vibrations of the dry skull in water were significantly higher than the underwater hearing thresholds of the participants, under conditions when hearing by AC and osseous BC is not likely. The results support the hypothesis that hearing under water at low sound intensities may be attributed to nonosseous BC (STC). PMID:26770975

  4. Evaluation of mechanical tractor pedal extensions.

    PubMed

    Kelso, S A; Stangherlin, A M; Mann, D D

    2008-10-01

    Many farmers with disabilities choose to modify their work environments to accommodate their personal abilities; however, modified tractors may present greater risk to the operator as they are often one-of-a-kind designs that have not been subjected to rigorous safety testing. The objective of this research was to evaluate mechanical tractor pedal , extensions from a safety perspective. This objective was achieved by identifying potential hazards associated with the introduction of a pedal extension into the cab environment so that both existing and novel designs could be compared using a common methodology. Based on review of the published literature, 19 potential hazards associated with the introduction of a pedal extension into the cab of a tractor were identified. A hazard self-assessment worksheet (HSAW), created based on the 19 hazards, was validated through a pilot study. The overall inter-rater reliability and concurrent criterion validity proved to be acceptable. With the use of the HSAW six pedal extensions (three existing designs and three novel designs) were evaluated by 14 experts. Statistical analysis of the results did not identify a "best" design; however, several important trends were observed. Four of the six designs tended to block access to the exit path. The two designs that did not block access to the exit path might be considered to be the best designs for the tractors used in this study, but other designs likely would have been acceptable if they had been custom-fit for these tractors. The results of this research suggest that custom fabrication of pedal extensions for each specific tractor will likely yield the safest work environment for those who choose to use this assistive technology.

  5. Prediction of glycosaminoglycan synthesis in intervertebral disc under mechanical loading.

    PubMed

    Gao, Xin; Zhu, Qiaoqiao; Gu, Weiyong

    2016-09-06

    The loss of glycosaminoglycan (GAG) content is a major biochemical change during intervertebral disc (IVD) degeneration. Abnormal mechanical loading is one of the major factors causing disc degeneration. In this study, a multiscale mathematical model was developed to quantify the effect of mechanical loading on GAG synthesis. This model was based on a recently developed cell volume dependent GAG synthesis theory that predicts the variation of GAG synthesis rate of a cell under the influence of mechanical stimuli, and the biphasic theory that describes the deformation of IVD under mechanical loading. The GAG synthesis (at the cell level) was coupled with the mechanical loading (at the tissue level) via a cell-matrix unit approach which established a relationship between the variation of cell dilatation and the local tissue dilatation. This multiscale mathematical model was used to predict the effect of static load (creep load) on GAG synthesis in bovine tail discs. The predicted results are in the range of experimental results. This model was also used to investigate the effect of static (0.2MPa) and diurnal loads (0.1/0.3MPa and 0.15/0.25MPa in 12/12 hours shift with an average of 0.2MPa over a cycle) on GAG synthesis. It was found that static load and diurnal loads have different effects on GAG synthesis in a diurnal cycle, and the diurnal load effects depend on the amplitude of the load. The model is important to understand the effect of mechanical loading at the tissue level on GAG synthesis at the cellular level, as well as to optimize the mechanical loading in growing engineered tissue.

  6. Damage Evolution On Mechanical Parts Under Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Lestriez, P.; Bogard, F.; Shan, J. L.; Guo, Y. Q.

    2007-05-01

    This paper presents a fatigue damage model, based on the continuum damage mechanics and general thermodynamic theory, proposed by Lemaitre and Chaboche, for rolling bearings under very numerous loading cycles. A flow surface of fatigue using the Sines criterion is adopted. The coupling between the hardening plasticity and damage effects is considered in the constitutive equations. An explicit algorithm of weak coupling leads to a calculation very fast. This fatigue damage model is implemented into Abaqus/Explicit using a Vumat user's subroutine. Moreover, the damage variable in function of time is transformed into a function of number of cycles. An algorithm of cycle jump, with a criterion for choosing the number increment of cycles, is proposed, which allows to largely reduce the CPU time. The present damage simulation allows to determine the lifetime of mechanical parts under cyclic loading.

  7. An NMDA Receptor-Dependent Mechanism Underlies Inhibitory Synapse Development.

    PubMed

    Gu, Xinglong; Zhou, Liang; Lu, Wei

    2016-01-26

    In the mammalian brain, GABAergic synaptic transmission provides inhibitory balance to glutamatergic excitatory drive and controls neuronal output. The molecular mechanisms underlying the development of GABAergic synapses remain largely unclear. Here, we report that NMDA-type ionotropic glutamate receptors (NMDARs) in individual immature neurons are the upstream signaling molecules essential for GABAergic synapse development, which requires signaling via Calmodulin binding motif in the C0 domain of the NMDAR GluN1 subunit. Interestingly, in neurons lacking NMDARs, whereas GABAergic synaptic transmission is strongly reduced, the tonic inhibition mediated by extrasynaptic GABAA receptors is increased, suggesting a compensatory mechanism for the lack of synaptic inhibition. These results demonstrate a crucial role for NMDARs in specifying the development of inhibitory synapses, and suggest an important mechanism for controlling the establishment of the balance between synaptic excitation and inhibition in the developing brain.

  8. Dislocation mechanism of deuterium retention in tungsten under plasma implantation.

    PubMed

    Dubinko, V I; Grigorev, P; Bakaev, A; Terentyev, D; van Oost, G; Gao, F; Van Neck, D; Zhurkin, E E

    2014-10-01

    We have developed a new theoretical model for deuterium (D) retention in tungsten-based alloys on the basis of its being trapped at dislocations and transported to the surface via the dislocation network with parameters determined by ab initio calculations. The model is used to explain experimentally observed trends of D retention under sub-threshold implantation, which does not produce stable lattice defects to act as traps for D in conventional models. Saturation of D retention with implantation dose and effects due to alloying of tungsten with, e.g. tantalum, are evaluated, and comparison of the model predictions with experimental observations under high-flux plasma implantation conditions is presented.

  9. Directionally solidified composite systems under evaluation

    NASA Technical Reports Server (NTRS)

    Ashbrook, R. L.

    1974-01-01

    The directionally solidified eutectic in-situ composites being evaluated for use as turbine materials range from ductile-ductile systems, where both matrix and reinforcement are ductile, to brittle-brittle systems, where both phases are brittle. The alloys most likely to be used in gas turbine engines in the near term are the lamellar ductile-semi ductile alloys gamma prime-delta, Ni3Al-Ni3Nb and gamma/gamma prime-delta Ni,Cr,Cb,Al/Ni3Al-Ni3Nb and the fibrous ductile-brittle alloys M-MC CoTaC or NiTaC and M-M7C3(Co,Cr,Al)-(Cr,Co)7C3. The results of tests are given which indicate that gamma prime strengthened NiTaC alloys and a (Co,Cr,Al)7C3 have greater tensile strength than the strongest superalloys at temperatures up to about 600 C. The gamma prime-delta and gamma/gamma prime-delta alloys in the Ni,Al,Nb(Cr) systems have greater tensile strength than the superalloys at temperatures greater than 800 C. At low stresses fibrous carbide reinforced eutectic alloys have longer lives at high temperatures than the strongest superalloys. Lamellar delta, Ni3Nb reinforced eutectic alloys have longer lives at high temperatures than the strongest superalloys at all stresses. The experience currently being gained in designing with the brittle ceramics SiC and Si3N4 may eventually be applied to ceramic matrix eutectic in-situ composites. However, the refractory metal fiber reinforced brittle-ductile systems may find acceptance as turbine materials before the ceramic-ceramic brittle-brittle systems.

  10. Stellar performance: mechanisms underlying Milky Way orientation in dung beetles.

    PubMed

    Foster, James J; El Jundi, Basil; Smolka, Jochen; Khaldy, Lana; Nilsson, Dan-Eric; Byrne, Marcus J; Dacke, Marie

    2017-04-05

    Nocturnal dung beetles (Scarabaeus satyrus) are currently the only animals that have been demonstrated to use the Milky Way for reliable orientation. In this study, we tested the capacity of S. satyrus to orient under a range of artificial celestial cues, and compared the properties of these cues with images of the Milky Way simulated for a beetle's visual system. We find that the mechanism that permits accurate stellar orientation under the Milky Way is based on an intensity comparison between different regions of the Milky Way. We determined the beetles' contrast sensitivity for this task in behavioural experiments in the laboratory, and found that the resulting threshold of 13% is sufficient to detect the contrast between the southern and northern arms of the Milky Way under natural conditions. This mechanism should be effective under extremely dim conditions and on nights when the Milky Way forms a near symmetrical band that crosses the zenith. These findings are discussed in the context of studies of stellar orientation in migratory birds and itinerant seals.This article is part of the themed issue 'Vision in dim light'.

  11. Peripheral Receptor Mechanisms Underlying Orofacial Muscle Pain and Hyperalgesia

    NASA Astrophysics Data System (ADS)

    Saloman, Jami L.

    Musculoskeletal pain conditions, particularly those associated with temporomandibular joint and muscle disorders (TMD) are severely debilitating and affect approximately 12% of the population. Identifying peripheral nociceptive mechanisms underlying mechanical hyperalgesia, a prominent feature of persistent muscle pain, could contribute to the development of new treatment strategies for the management of TMD and other muscle pain conditions. This study provides evidence of functional interactions between ligand-gated channels, P2X3 and TRPV1/TRPA1, in trigeminal sensory neurons, and proposes that these interactions underlie the development of mechanical hyperalgesia. In the masseter muscle, direct P2X3 activation, via the selective agonist αβmeATP, induced a dose- and time-dependent hyperalgesia. Importantly, the αβmeATP-induced hyperalgesia was prevented by pretreatment of the muscle with a TRPV1 antagonist, AMG9810, or the TRPA1 antagonist, AP18. P2X3 was co-expressed with both TRPV1 and TRPA1 in masseter muscle afferents confirming the possibility for intracellular interactions. Moreover, in a subpopulation of P2X3 /TRPV1 positive neurons, capsaicin-induced Ca2+ transients were significantly potentiated following P2X3 activation. Inhibition of Ca2+-dependent kinases, PKC and CaMKII, prevented P2X3-mechanical hyperalgesia whereas blockade of Ca2+-independent PKA did not. Finally, activation of P2X3 induced phosphorylation of serine, but not threonine, residues in TRPV1 in trigeminal sensory neurons. Significant phosphorylation was observed at 15 minutes, the time point at which behavioral hyperalgesia was prominent. Similar data were obtained regarding another nonselective cation channel, the NMDA receptor (NMDAR). Our data propose P2X3 and NMDARs interact with TRPV1 in a facilitatory manner, which could contribute to the peripheral sensitization underlying masseter hyperalgesia. This study offers novel mechanisms by which individual pro-nociceptive ligand

  12. Shoestring Evaluation: Designing Impact Evaluations under Budget, Time and Data Constraints

    ERIC Educational Resources Information Center

    Bamberger, Michael; Rugh, Jim; Church, Mary; Fort, Lucia

    2004-01-01

    The paper discusses two common scenarios in which evaluators must conduct impact evaluations when working under budget, time, or data constraints. Under the first scenario the evaluator is not called in until the project is already well advanced, and there is a tight deadline for completing the evaluation, frequently combined with a limited budget…

  13. Empirical extraction of mechanisms underlying real world network generation

    NASA Astrophysics Data System (ADS)

    Itzhack, Royi; Muchnik, Lev; Erez, Tom; Tsaban, Lea; Goldenberg, Jacob; Solomon, Sorin; Louzoun, Yoram

    2010-11-01

    The generation mechanisms of real world networks have been described using multiple models. The mathematical features of these models are usually extrapolated from statistical properties of a snapshot of these networks. We here propose an alternative method based on direct measurement of a sequence of consecutive snapshots to uncover the dynamics underlying real world generation. We assume that the probability of adding a node or an edge depends only on local features surrounding the newly added node/edge, and directly measure the contribution of these features to the node/edge addition probability. These measurements are performed using newly defined N-node local structures. Each N-node local structure represents the configuration of edges surrounding a newly added edge. The N-node local structure measurements reproduce for some networks the now classical addition of edges between high degree node mechanisms. It also provides quantitative estimates of more complex mechanisms driving other networks’ evolution, such as the effect of common first and second neighbors. This new methodology reveals the relative importance of different generation mechanisms. We show, for example, that the main mechanism driving hyperlink addition between two websites is the existence of a third website linking to both the source and the target of the new hyperlink.

  14. Mechanical Solder Characterisation Under High Strain Rate Conditions

    NASA Astrophysics Data System (ADS)

    Meier, Karsten; Roellig, Mike; Wiese, Steffen; Wolter, Klaus-Juergen

    2010-11-01

    Using a setup for high strain rate tensile experiments the mechanical behavior of two lead-free tin based solders is investigated. The first alloy is SnAg1.3Cu0.5Ni. The second alloy has a higher silver content but no addition of Ni. Solder joints are the main electrical, thermal and mechanical interconnection technology on the first and second interconnection level. With the recent rise of 3D packaging technologies many novel interconnection ideas are proposed with innovative or visionary nature. Copper pillar, stud bump, intermetallic (SLID) and even spring like joints are presented in a number of projects. However, soldering will remain one of the important interconnect technologies. Knowing the mechanical properties of solder joints is important for any reliability assessment, especially when it comes to vibration and mechanical shock associated with mobile applications. Taking the ongoing miniaturization and linked changes in solder joint microstructure and mechanical behavior into account the need for experimental work on that issue is not satisfied. The tests are accomplished utilizing miniature bulk specimens to match the microstructure of real solder joints as close as possible. The dogbone shaped bulk specimens have a crucial diameter of 1 mm, which is close to BGA solder joints. Experiments were done in the strain rate range from 20 s-1 to 600 s-1. Solder strengthening has been observed with increased strain rate for both SAC solder alloys. The yield stress increases by about 100% in the investigated strain rate range. The yield level differs strongly. A high speed camera system was used to assist the evaluation process of the stress and strain data. Besides the stress and strain data extracted from the experiment the ultimate fracture strain is determined and the fracture surfaces are evaluated using SEM technique considering rate dependency.

  15. Clinical value of DNA fragmentation evaluation tests under ART treatments.

    PubMed

    Tavukçuoğlu, Ilkay Şafak; Al-Azawi, Tahani; Khaki, Amir Afshin; Khaki, Arash; Khalil, Ahmed; Al-Hasani, Safaa

    2012-01-01

    Male reproductive health has been under scrutiny recently. Many studies in the literature have concluded that semen quality is declining and that the incidence of testicular cancers is increasing. The reason for this change has been attributed to damage in sperm chromatin. During in vivo reproduction, the natural selection process ensures that only a spermatozoon with normal genomic material can fertilize an oocyte. However, the assisted reproduction technique (ART) is our selection process, leading to the possibility that abnormal spermatozoa could be used to fertilize an oocyte. We could avoid this by quantifying the amount and type of genomic damage in sperm using well-accepted laboratory methods. The sperm deoxyribonucleic acid (DNA) integrity is important for success of natural or assisted fertilization as well as normal development of the embryo, fetus and child. Intra cytoplasmic sperm injection (ICSI) is bypassing natural sperm selection mechanisms, which increases the risk of transmitting damaged DNA. The significance of required investigations and multiple techniques is that they could evaluate DNA defects in human spermatozoa. The ability of these techniques to accurately estimate sperm DNA damage depends on many technical and biological aspects. The aim of this review is to evaluate the most commonly used methods.

  16. Deciphering the mechanism underlying late-onset Alzheimer disease.

    PubMed

    Krstic, Dimitrije; Knuesel, Irene

    2013-01-01

    Despite tremendous investments in understanding the complex molecular mechanisms underlying Alzheimer disease (AD), recent clinical trials have failed to show efficacy. A potential problem underlying these failures is the assumption that the molecular mechanism mediating the genetically determined form of the disease is identical to the one resulting in late-onset AD. Here, we integrate experimental evidence outside the 'spotlight' of the genetic drivers of amyloid-β (Aβ) generation published during the past two decades, and present a mechanistic explanation for the pathophysiological changes that characterize late-onset AD. We propose that chronic inflammatory conditions cause dysregulation of mechanisms to clear misfolded or damaged neuronal proteins that accumulate with age, and concomitantly lead to tau-associated impairments of axonal integrity and transport. Such changes have several neuropathological consequences: focal accumulation of mitochondria, resulting in metabolic impairments; induction of axonal swelling and leakage, followed by destabilization of synaptic contacts; deposition of amyloid precursor protein in swollen neurites, and generation of aggregation-prone peptides; further tau hyperphosphorylation, ultimately resulting in neurofibrillary tangle formation and neuronal death. The proposed sequence of events provides a link between Aβ and tau-related neuropathology, and underscores the concept that degenerating neurites represent a cause rather than a consequence of Aβ accumulation in late-onset AD.

  17. Peptide formation mechanism on montmorillonite under thermal conditions.

    PubMed

    Fuchida, Shigeshi; Masuda, Harue; Shinoda, Keiji

    2014-02-01

    The oligomerization of amino acids is an essential process in the chemical evolution of proteins, which are precursors to life on Earth. Although some researchers have observed peptide formation on clay mineral surfaces, the mechanism of peptide bond formation on the clay mineral surface has not been clarified. In this study, the thermal behavior of glycine (Gly) adsorbed on montmorillonite was observed during heating experiments conducted at 150 °C for 336 h under dry, wet, and dry-wet conditions to clarify the mechanism. Approximately 13.9 % of the Gly monomers became peptides on montmorillonite under dry conditions, with diketopiperazine (cyclic dimer) being the main product. On the other hand, peptides were not synthesized in the absence of montmorillonite. Results of IR analysis showed that the Gly monomer was mainly adsorbed via hydrogen bonding between the positively charged amino groups and negatively charged surface sites (i.e., Lewis base sites) on the montmorillonite surface, indicating that the Lewis base site acts as a catalyst for peptide formation. In contrast, peptides were not detected on montmorillonite heated under wet conditions, since excess water shifted the equilibrium towards hydrolysis of the peptides. The presence of water is likely to control thermodynamic peptide production, and clay minerals, especially those with electrophilic defect sites, seem to act as a kinetic catalyst for the peptide formation reaction.

  18. The mechanisms of cachexia underlying muscle dysfunction in COPD.

    PubMed

    Remels, A H V; Gosker, H R; Langen, R C J; Schols, A M W J

    2013-05-01

    Pulmonary cachexia is a prevalent, debilitating, and well-recognized feature of COPD associated with increased mortality and loss of peripheral and respiratory muscle function. The exact cause and underlying mechanisms of cachexia in COPD are still poorly understood. Increasing evidence, however, shows that pathological changes in intracellular mechanisms of muscle mass maintenance (i.e., protein turnover and myonuclear turnover) are likely involved. Potential factors triggering alterations in these mechanisms in COPD include oxidative stress, myostatin, and inflammation. In addition to muscle wasting, peripheral muscle in COPD is characterized by a fiber-type shift toward a more type II, glycolytic phenotype and an impaired oxidative capacity (collectively referred to as an impaired oxidative phenotype). Atrophied diaphragm muscle in COPD, however, displays an enhanced oxidative phenotype. Interestingly, intrinsic abnormalities in (lower limb) peripheral muscle seem more pronounced in either cachectic patients or weight loss-susceptible emphysema patients, suggesting that muscle wasting and intrinsic changes in peripheral muscle's oxidative phenotype are somehow intertwined. In this manuscript, we will review alterations in mechanisms of muscle mass maintenance in COPD and discuss the involvement of oxidative stress, inflammation, and myostatin as potential triggers of cachexia. Moreover, we postulate that an impaired muscle oxidative phenotype in COPD can accelerate the process of cachexia, as it renders muscle in COPD less energy efficient, thereby contributing to an energy deficit and weight loss when not dietary compensated. Furthermore, loss of peripheral muscle oxidative phenotype may increase the muscle's susceptibility to inflammation- and oxidative stress-induced muscle damage and wasting.

  19. Mechanisms underlying astringency: introduction to an oral tribology approach

    NASA Astrophysics Data System (ADS)

    Upadhyay, Rutuja; Brossard, Natalia; Chen, Jianshe

    2016-03-01

    Astringency is one of the predominant factors in the sensory experience of many foods and beverages ranging from wine to nuts. The scientific community is discussing mechanisms that explain this complex phenomenon, since there are no conclusive results which correlate well with sensory astringency. Therefore, the mechanisms and perceptual characteristics of astringency warrant further discussion and investigation. This paper gives a brief introduction of the fundamentals of oral tribology forming a basis of the astringency mechanism. It discusses the current state of the literature on mechanisms underlying astringency describing the existing astringency models. The review discusses the crucial role of saliva and its physiology which contributes significantly in astringency perception in the mouth. It also provides an overview of research concerned with the physiological and psychophysical factors that mediate the perception of this sensation, establishing the ground for future research. Thus, the overall aim of the review is to establish the critical roles of oral friction (thin-film lubrication) in the sensation of astringency and possibly of some other specific sensory features.

  20. The mechanism underlying fast germination of tomato cultivar LA2711.

    PubMed

    Yang, Rongchao; Chu, Zhuannan; Zhang, Haijun; Li, Ying; Wang, Jinfang; Li, Dianbo; Weeda, Sarah; Ren, Shuxin; Ouyang, Bo; Guo, Yang-Dong

    2015-09-01

    Seed germination is important for early plant morphogenesis as well as abiotic stress tolerance, and is mainly controlled by the phytohormones abscisic acid (ABA) and gibberellic acid (GA). Our previous studies identified a salt-tolerant tomato cultivar, LA2711, which is also a fast-germinating genotype, compared to its salt-sensitive counterpart, ZS-5. In an effort to further clarify the mechanism underlying this phenomenon, we compared the dynamic levels of ABA and GA4, the transcript abundance of genes involved in their biosynthesis and catabolism as well as signal transduction between the two cultivars. In addition, we tested seed germination sensitivity to ABA and GAs. Our results revealed that insensitivity of seed germination to exogenous ABA and low ABA content in seeds are the physiological mechanisms conferring faster germination rates of LA2711 seeds. SlCYP707A2, which encodes an ABA catabolic enzyme, may play a decisive role in the fast germination rate of LA2711, as it showed a significantly higher level of expression in LA2711 than ZS-5 at most time points tested during germination. The current results will enable us to gain insight into the mechanism(s) regarding seed germination of tomato and the role of fast germination in stress tolerance.

  1. Mechanisms Underlying T Cell Immunosenescence: Aging and Cytomegalovirus Infection

    PubMed Central

    Tu, Wenjuan; Rao, Sudha

    2016-01-01

    The ability of the human immune system to protect against infectious disease declines with age and efficacy of vaccination reduces significantly in the elderly. Aging of the immune system, also termed as immunosenescence, involves many changes in human T cell immunity that is characterized by a loss in naïve T cell population and an increase in highly differentiated CD28- memory T cell subset. There is extensive data showing that latent persistent human cytomegalovirus (HCMV) infection is also associated with age-related immune dysfunction in the T cells, which might enhance immunosenescence. Understanding the molecular mechanisms underlying age-related and HCMV-related immunosenescence is critical for the development of effective age-targeted vaccines and immunotherapies. In this review, we will address the role of both aging and HCMV infection that contribute to the T cell senescence and discuss the potential molecular mechanisms in aged T cells. PMID:28082969

  2. Biochemical mechanisms of signaling: perspectives in plants under arsenic stress.

    PubMed

    Islam, Ejazul; Khan, Muhammad Tahir; Irem, Samra

    2015-04-01

    Plants are the ultimate food source for humans, either directly or indirectly. Being sessile in nature, they are exposed to various biotic and abiotic stresses because of changing climate that adversely effects their growth and development. Contamination of heavy metals is one of the major abiotic stresses because of anthropogenic as well as natural factors which lead to increased toxicity and accumulation in plants. Arsenic is a naturally occurring metalloid toxin present in the earth crust. Due to its presence in terrestrial and aquatic environments, it effects the growth of plants. Plants can tolerate arsenic using several mechanisms like phytochelation, vacuole sequestration and activation of antioxidant defense systems. Several signaling mechanisms have evolved in plants that involve the use of proteins, calcium ions, hormones, reactive oxygen species and nitric oxide as signaling molecules to cope with arsenic toxicity. These mechanisms facilitate plants to survive under metal stress by activating their defense systems. The pathways by which these stress signals are perceived and responded is an unexplored area of research and there are lots of gaps still to be filled. A good understanding of these signaling pathways can help in raising the plants which can perform better in arsenic contaminated soil and water. In order to increase the survival of plants in contaminated areas there is a strong need to identify suitable gene targets that can be modified according to needs of the stakeholders using various biotechnological techniques. This review focuses on the signaling mechanisms of plants grown under arsenic stress and will give an insight of the different sensory systems in plants. Furthermore, it provides the knowledge about several pathways that can be exploited to develop plant cultivars which are resistant to arsenic stress or can reduce its uptake to minimize the risk of arsenic toxicity through food chain thus ensuring food security.

  3. Physical mechanisms underlying the strain-rate-dependent mechanical behavior of kangaroo shoulder cartilage

    NASA Astrophysics Data System (ADS)

    Thibbotuwawa, Namal; Oloyede, Adekunle; Li, Tong; Singh, Sanjleena; Senadeera, Wijitha; Gu, YuanTong

    2015-09-01

    Due to anatomical and biomechanical similarities to human shoulder, kangaroo was chosen as a model to study shoulder cartilage. Comprehensive enzymatic degradation and indentation tests were applied on kangaroo shoulder cartilage to study mechanisms underlying its strain-rate-dependent mechanical behavior. We report that superficial collagen plays a more significant role than proteoglycans in facilitating strain-rate-dependent behavior of the kangaroo shoulder cartilage. By comparing the mechanical properties of degraded and normal cartilages, it was noted that proteoglycan and collagen degradation significantly compromised strain-rate-dependent mechanical behavior of the cartilage. Superficial collagen contributed equally to the tissue behavior at all strain-rates. This is different to the studies reported on knee cartilage and confirms the importance of superficial collagen on shoulder cartilage mechanical behavior. A porohyperelastic numerical model also indicated that collagen disruption would lead to faster damage of the shoulder cartilage than when proteoglycans are depleted.

  4. Principles of cellular-molecular mechanisms underlying neuron functions.

    PubMed

    Ratushnyak, Alexander S; Zapara, Tatiana A

    2009-12-01

    In the present work, it was experimentally shown that a neuron in vitro was capable of responding in a manner similar to habituation, Pavlov's reflex and avoidance of the reinforcements. The locality of plastic property modifications and molecular morphology, as well as the connection between functional activity and cytoskeleton have been revealed. A hypothesis is formulated that the neuron is a molecular system which may exercise the control, forecast, recognition, and classification. The basic principles of the molecular mechanisms of the responses underlying integrative activity, learning and memory at the neuronal level are discussed.

  5. [Underlying mechanisms of the heavy metal tolerance of mycorrhizal fungi].

    PubMed

    Chen, Bao-Dong; Sun, Yu-Qing; Zhang, Xin; Wu, Song-Lin

    2015-03-01

    Mycorrhizal fungi are ubiquitous in natural ecosystems and can form symbiotic associations with the majority of terrestrial plants. They can be detected even in heavy metal-contaminated soils, while some fungal strains show strong heavy metal tolerance and could potentially be used in bioremediation of contaminated soils. We reviewed current research progresses in the underlying mechanisms of heavy metal tolerance of mycorrhizal fungi, with focuses on habitat selection, physiological adaptation and functional genes. Future research perspectives were proposed to promote the basic research and development of mycorrhizal technology for remediation of heavy metal-contaminated soils.

  6. Continuous damage parameter calculation under thermo-mechanical random loading.

    PubMed

    Nagode, Marko

    2014-01-01

    The paper presents a method on how the mean stress effect on fatigue damage can be taken into account under an arbitrary low cycle thermo-mechanical loading. From known stress, elastoplastic strain and temperature histories the cycle amplitudes and cycle mean values are extracted and the damage parameter is computed. In contrast to the existing methods the proposed method enables continuous damage parameter computation without the need of waiting for the cycles to close. The limitations of the standardized damage parameters are thus surpassed. The damage parameters derived initially for closed and isothermal cycles assuming that the elastoplastic stress-strain response follows the Masing and memory rules can now be used to take the mean stress effect into account under an arbitrary low cycle thermo-mechanical loading. The method includes:•stress and elastoplastic strain history transformation into the corresponding amplitude and mean values;•stress and elastoplastic strain amplitude and mean value transformation into the damage parameter amplitude history;•damage parameter amplitude history transformation into the damage parameter history.

  7. Continuous damage parameter calculation under thermo-mechanical random loading

    PubMed Central

    Nagode, Marko

    2014-01-01

    The paper presents a method on how the mean stress effect on fatigue damage can be taken into account under an arbitrary low cycle thermo-mechanical loading. From known stress, elastoplastic strain and temperature histories the cycle amplitudes and cycle mean values are extracted and the damage parameter is computed. In contrast to the existing methods the proposed method enables continuous damage parameter computation without the need of waiting for the cycles to close. The limitations of the standardized damage parameters are thus surpassed. The damage parameters derived initially for closed and isothermal cycles assuming that the elastoplastic stress–strain response follows the Masing and memory rules can now be used to take the mean stress effect into account under an arbitrary low cycle thermo-mechanical loading. The method includes:•stress and elastoplastic strain history transformation into the corresponding amplitude and mean values;•stress and elastoplastic strain amplitude and mean value transformation into the damage parameter amplitude history;•damage parameter amplitude history transformation into the damage parameter history. PMID:26150939

  8. Mechanisms underlying skin disorders induced by EGFR inhibitors

    PubMed Central

    Holcmann, Martin; Sibilia, Maria

    2015-01-01

    The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is frequently mutated or overexpressed in a large number of tumors such as carcinomas or glioblastoma. Inhibitors of EGFR activation have been successfully established for the therapy of some cancers and are more and more frequently being used as first or later line therapies. Although the side effects induced by inhibitors of EGFR are less severe than those observed with classic cytotoxic chemotherapy and can usually be handled by out-patient care, they may still be a cause for dose reduction or discontinuation of treatment that can reduce the effectiveness of antitumor therapy. The mechanisms underlying these cutaneous side effects are only partly understood. Important questions, such as the reasons for the correlation between the intensity of the side effects and the efficiency of treatment with EGFR inhibitors, remain to be answered. Optimized adjuvant strategies to accompany anti-EGFR therapy need to be found for optimal therapeutic application and improved quality of life of patients. Here, we summarize current literature on the molecular and cellular mechanisms underlying the cutaneous side effects induced by EGFR inhibitors and provide evidence that keratinocytes are probably the optimal targets for adjuvant therapy aimed at alleviating skin toxicities. PMID:27308503

  9. Shared neural mechanisms underlying social warmth and physical warmth.

    PubMed

    Inagaki, Tristen K; Eisenberger, Naomi I

    2013-11-01

    Many of people's closest bonds grow out of socially warm exchanges and the warm feelings associated with being socially connected. Indeed, the neurobiological mechanisms underlying thermoregulation may be shared by those that regulate social warmth, the experience of feeling connected to other people. To test this possibility, we placed participants in a functional MRI scanner and asked them to (a) read socially warm and neutral messages from friends and family and (b) hold warm and neutral-temperature objects (a warm pack and a ball, respectively). Findings showed an overlap between physical and social warmth: Participants felt warmer after reading the positive (compared with neutral) messages and more connected after holding the warm pack (compared with the ball). In addition, neural activity during social warmth overlapped with neural activity during physical warmth in the ventral striatum and middle insula, but neural activity did not overlap during another pleasant task (soft touch). Together, these results suggest that a common neural mechanism underlies physical and social warmth.

  10. Response mechanism of post-earthquake slopes under heavy rainfall

    NASA Astrophysics Data System (ADS)

    Qiu, Hong-zhi; Kong, Ji-ming; Wang, Ren-chao; Cui, Yun; Huang, Sen-wang

    2017-01-01

    This paper uses the catastrophic landslide that occurred in Zhongxing Town, Dujiangyan City, as an example to study the formation mechanism of landslides induced by heavy rainfall in the post-Wenchuan earthquake area. The deformation characteristics of a slope under seismic loading were investigated via a shaking table test. The results show that a large number of cracks formed in the slope due to the tensile and shear forces of the vibrations, and most of the cracks had angles of approximately 45° with respect to the horizontal. A series of flume tests were performed to show how the duration and intensity of rainfall influence the responses of the shaken and non-shaken slopes. Wetting fronts were recorded under different rainfall intensities, and the depth of rainfall infiltration was greater in the shaken slope than in the non-shaken slope because the former experienced a greater extreme rainfall intensity under the same early rainfall and rainfall duration conditions. At the beginning of the rainfall infiltration experiment, the pore water pressure in the slope was negative, and settling occurred at the top of the slope. With increasing rainfall, the pore water pressure changed from negative to positive, and cracks were observed on the back surface of the slope and the shear outlet of the landslide on the front of the slope. The shaken slope was more susceptible to crack formation than the non-shaken slope under the same rainfall conditions. A comparison of the responses of the shaken and non-shaken slopes under heavy rainfall revealed that cracks formed by earthquakes provided channels for infiltration. Soil particles in the cracks of slopes were washed away, and the pore water pressure increased rapidly, especially the transient pore water pressure in the slope caused by short-term concentrated rainfall which decreased rock strength and slope stability.

  11. Effects of manual hyperinflation in preterm newborns under mechanical ventilation

    PubMed Central

    Viana, Camila Chaves; Nicolau, Carla Marques; Juliani, Regina Celia Turola Passos; de Carvalho, Werther Brunow; Krebs, Vera Lucia Jornada

    2016-01-01

    Objective To assess the effects of manual hyperinflation, performed with a manual resuscitator with and without the positive end-expiratory pressure valve, on the respiratory function of preterm newborns under mechanical ventilation. Methods Cross-sectional study of hemodynamically stable preterm newborns with gestational age of less than 32 weeks, under mechanical ventilation and dependent on it at 28 days of life. Manual hyperinflation was applied randomly, alternating the use or not of the positive end-expiratory pressure valve, followed by tracheal aspiration for ending the maneuver. For nominal data, the two-tailed Wilcoxon test was applied at the 5% significance level and 80% power. Results Twenty-eight preterm newborns, with an average birth weight of 1,005.71 ± 372.16g, an average gestational age of 28.90 ± 1.79 weeks, an average corrected age of 33.26 ± 1.78 weeks, and an average mechanical ventilation time of 29.5 (15 - 53) days, were studied. Increases in inspiratory and expiratory volumes occurred between time-points A5 (before the maneuver) and C1 (immediately after tracheal aspiration) in both the maneuver with the valve (p = 0.001 and p = 0.009) and without the valve (p = 0.026 and p = 0.001), respectively. There was also an increase in expiratory resistance between time-points A5 and C1 (p = 0.044). Conclusion Lung volumes increased when performing the maneuver with and without the valve, with a significant difference in the first minute after aspiration. There was a significant difference in expiratory resistance between the time-points A5 (before the maneuver) and C1 (immediately after tracheal aspiration) in the first minute after aspiration within each maneuver. PMID:27737427

  12. Piezoelectric compliant mechanism energy harvesters under large base excitations

    NASA Astrophysics Data System (ADS)

    Ma, Xiaokun; Trolier-McKinstry, Susan; Rahn, Christopher D.

    2016-09-01

    A piezoelectric compliant mechanism (PCM) energy harvester is designed, modeled, and analyzed that consists of a polyvinylidene diflouoride, PVDF unimorph clamped at its base and attached to a compliant mechanism at its tip. The compliant hinge stiffness is carefully tuned to approach a low frequency first mode with an efficient (nearly quadratic) shape that provides a uniform strain distribution. A nonlinear model of the PCM energy harvester under large base excitation is derived to determine the maximum power that can be generated by the device. Experiments with a fabricated PCM energy harvester prototype show that the compliant mechanism introduces a stiffening effect and a much wider bandwidth than a benchmark proof mass cantilever design. The PCM bridge structure self-limits the displacement and maximum strain at large excitations compared with the proof mass cantilever, improving the device robustness. The PCM outperforms the cantilever in both average power and power-strain sensitivity at high accelerations due to the PCM axial stretching effect and its more uniform strain distribution.

  13. Autophagy as a Possible Underlying Mechanism of Nanomaterial Toxicity

    PubMed Central

    Cohignac, Vanessa; Landry, Marion Julie; Boczkowski, Jorge; Lanone, Sophie

    2014-01-01

    The rapid development of nanotechnologies is raising safety concerns because of the potential effects of engineered nanomaterials on human health, particularly at the respiratory level. Since the last decades, many in vivo studies have been interested in the pulmonary effects of different classes of nanomaterials. It has been shown that some of them can induce toxic effects, essentially depending on their physico-chemical characteristics, but other studies did not identify such effects. Inflammation and oxidative stress are currently the two main mechanisms described to explain the observed toxicity. However, the exact underlying mechanism(s) still remain(s) unknown and autophagy could represent an interesting candidate. Autophagy is a physiological process in which cytoplasmic components are digested via a lysosomal pathway. It has been shown that autophagy is involved in the pathogenesis and the progression of human diseases, and is able to modulate the oxidative stress and pro-inflammatory responses. A growing amount of literature suggests that a link between nanomaterial toxicity and autophagy impairment could exist. In this review, we will first summarize what is known about the respiratory effects of nanomaterials and we will then discuss the possible involvement of autophagy in this toxicity. This review should help understand why autophagy impairment could be taken as a promising candidate to fully understand nanomaterials toxicity.

  14. Stainless Steel Microstructure and Mechanical Properties Evaluation

    SciTech Connect

    Switzner, Nathan T

    2010-06-01

    A nitrogen strengthened 21-6-9 stainless steel plate was spinformed into hemispherical test shapes. A battery of laboratory tests was used to characterize the hemispheres. The laboratory tests show that near the pole (axis) of a spinformed hemisphere the yield strength is the lowest because this area endures the least “cold-work” strengthening, i.e., the least deformation. The characterization indicated that stress-relief annealing spinformed stainless steel hemispheres does not degrade mechanical properties. Stress-relief annealing reduces residual stresses while maintaining relatively high mechanical properties. Full annealing completely eliminates residual stresses, but reduces yield strength by about 30%.

  15. The mechanisms underlying fructose-induced hypertension: a review

    PubMed Central

    Klein, Alice Victoria; Kiat, Hosen

    2015-01-01

    We are currently in the midst of an epidemic of metabolic disorders, which may, in part, be explained by excess fructose intake. This theory is supported by epidemiological observations as well as experimental studies in animals and humans. Rising consumption of fructose has been matched with growing rates of hypertension, leading to concern from public health experts. At this stage, the mechanisms underlying fructose-induced hypertension have not been fully characterized and the bulk of our knowledge is derived from animal models. Animal studies have shown that high-fructose diets up-regulate sodium and chloride transporters, resulting in a state of salt overload that increases blood pressure. Excess fructose has also been found to activate vasoconstrictors, inactivate vasodilators, and over-stimulate the sympathetic nervous system. Further work is required to determine the relevance of these findings to humans and to establish the level at which dietary fructose increases the risk of developing hypertension PMID:25715094

  16. Mechanisms Underlying Development of Visual Maps and Receptive Fields

    PubMed Central

    Huberman, Andrew D.; Feller, Marla B.; Chapman, Barbara

    2008-01-01

    Patterns of synaptic connections in the visual system are remarkably precise. These connections dictate the receptive field properties of individual visual neurons and ultimately determine the quality of visual perception. Spontaneous neural activity is necessary for the development of various receptive field properties and visual feature maps. In recent years, attention has shifted to understanding the mechanisms by which spontaneous activity in the developing retina, lateral geniculate nucleus, and visual cortex instruct the axonal and dendritic refinements that give rise to orderly connections in the visual system. Axon guidance cues and a growing list of other molecules, including immune system factors, have also recently been implicated in visual circuit wiring. A major goal now is to determine how these molecules cooperate with spontaneous and visually evoked activity to give rise to the circuits underlying precise receptive field tuning and orderly visual maps. PMID:18558864

  17. Neural mechanisms underlying nicotine addiction: acute positive reinforcement and withdrawal.

    PubMed

    Watkins, S S; Koob, G F; Markou, A

    2000-02-01

    The neurobiology of nicotine addiction is reviewed within the context of neurobiological and behavioral theories postulated for other drugs of abuse. The roles of various neurotransmitter systems, including acetylcholine, dopamine, serotonin, glutamate, gamma-aminobutyric acid, and opioid peptides in acute nicotine reinforcement and withdrawal from chronic administration are examined followed by a discussion of potential neuroadaptations within these neurochemical systems that may lead to the development of nicotine dependence. The link between nicotine administration, depression and schizophrenia are also discussed. Finally, a theoretical model of the neurobiological mechanisms underlying acute nicotine withdrawal and protracted abstinence involves alterations within dopaminergic, serotonergic, and stress systems that are hypothesized to contribute to the negative affective state associated with nicotine abstinence.

  18. Possible Mechanisms Underlying the Therapeutic Effects of Transcranial Magnetic Stimulation

    PubMed Central

    Chervyakov, Alexander V.; Chernyavsky, Andrey Yu.; Sinitsyn, Dmitry O.; Piradov, Michael A.

    2015-01-01

    Transcranial magnetic stimulation (TMS) is an effective method used to diagnose and treat many neurological disorders. Although repetitive TMS (rTMS) has been used to treat a variety of serious pathological conditions including stroke, depression, Parkinson’s disease, epilepsy, pain, and migraines, the pathophysiological mechanisms underlying the effects of long-term TMS remain unclear. In the present review, the effects of rTMS on neurotransmitters and synaptic plasticity are described, including the classic interpretations of TMS effects on synaptic plasticity via long-term potentiation and long-term depression. We also discuss the effects of rTMS on the genetic apparatus of neurons, glial cells, and the prevention of neuronal death. The neurotrophic effects of rTMS on dendritic growth and sprouting and neurotrophic factors are described, including change in brain-derived neurotrophic factor concentration under the influence of rTMS. Also, non-classical effects of TMS related to biophysical effects of magnetic fields are described, including the quantum effects, the magnetic spin effects, genetic magnetoreception, the macromolecular effects of TMS, and the electromagnetic theory of consciousness. Finally, we discuss possible interpretations of TMS effects according to dynamical systems theory. Evidence suggests that a rTMS-induced magnetic field should be considered a separate physical factor that can be impactful at the subatomic level and that rTMS is capable of significantly altering the reactivity of molecules (radicals). It is thought that these factors underlie the therapeutic benefits of therapy with TMS. Future research on these mechanisms will be instrumental to the development of more powerful and reliable TMS treatment protocols. PMID:26136672

  19. Does Motor Simulation Theory Explain the Cognitive Mechanisms Underlying Motor Imagery? A Critical Review

    PubMed Central

    O’Shea, Helen; Moran, Aidan

    2017-01-01

    Motor simulation theory (MST; Jeannerod, 2001) purports to explain how various action-related cognitive states relate to actual motor execution. Specifically, it proposes that motor imagery (MI; imagining an action without executing the movements involved) shares certain mental representations and mechanisms with action execution, and hence, activates similar neural pathways to those elicited during the latter process. Furthermore, MST postulates that MI works by rehearsing neural motor systems off-line via a hypothetical simulation process. In this paper, we review evidence cited in support of MST and evaluate its efficacy in understanding the cognitive mechanisms underlying MI. In doing so, we delineate the precise postulates of simulation theory and clarify relevant terminology. Based on our cognitive-level analysis, we argue firstly that the psychological mechanisms underlying MI are poorly understood and require additional conceptual and empirical analysis. In addition, we identify a number of potentially fruitful lines of inquiry for future investigators of MST and MI. PMID:28261079

  20. Does Motor Simulation Theory Explain the Cognitive Mechanisms Underlying Motor Imagery? A Critical Review.

    PubMed

    O'Shea, Helen; Moran, Aidan

    2017-01-01

    Motor simulation theory (MST; Jeannerod, 2001) purports to explain how various action-related cognitive states relate to actual motor execution. Specifically, it proposes that motor imagery (MI; imagining an action without executing the movements involved) shares certain mental representations and mechanisms with action execution, and hence, activates similar neural pathways to those elicited during the latter process. Furthermore, MST postulates that MI works by rehearsing neural motor systems off-line via a hypothetical simulation process. In this paper, we review evidence cited in support of MST and evaluate its efficacy in understanding the cognitive mechanisms underlying MI. In doing so, we delineate the precise postulates of simulation theory and clarify relevant terminology. Based on our cognitive-level analysis, we argue firstly that the psychological mechanisms underlying MI are poorly understood and require additional conceptual and empirical analysis. In addition, we identify a number of potentially fruitful lines of inquiry for future investigators of MST and MI.

  1. Quantitative Ultrasonic Evaluation of Mechanical Properties of Engineering Materials

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1978-01-01

    Progress in the application of ultrasonic techniques to nondestructive measurement of mechanical strength of engineering materials is reviewed. A dormant concept in nondestructive evaluation (NDE) is invoked. The availability of ultrasonic methods that can be applied to actual parts to assess their potential susceptibility to failure under design conditions is discussed. It was shown that ultrasonic methods yield measurements of elastic moduli, microstructure, hardness, fracture toughness, tensile strength, yield strength, and shear strength for a wide range of materials (including many types of metals, ceramics, and fiber composites). It was also indicated that although most of these methods were shown feasible in laboratory studies, more work is needed before they can be used on actual parts in processing, assembly, inspection, and maintenance lines.

  2. Mechanisms underlying the social enhancement of vocal learning in songbirds

    PubMed Central

    Chen, Yining; Matheson, Laura E.; Sakata, Jon T.

    2016-01-01

    Social processes profoundly influence speech and language acquisition. Despite the importance of social influences, little is known about how social interactions modulate vocal learning. Like humans, songbirds learn their vocalizations during development, and they provide an excellent opportunity to reveal mechanisms of social influences on vocal learning. Using yoked experimental designs, we demonstrate that social interactions with adult tutors for as little as 1 d significantly enhanced vocal learning. Social influences on attention to song seemed central to the social enhancement of learning because socially tutored birds were more attentive to the tutor’s songs than passively tutored birds, and because variation in attentiveness and in the social modulation of attention significantly predicted variation in vocal learning. Attention to song was influenced by both the nature and amount of tutor song: Pupils paid more attention to songs that tutors directed at them and to tutors that produced fewer songs. Tutors altered their song structure when directing songs at pupils in a manner that resembled how humans alter their vocalizations when speaking to infants, that was distinct from how tutors changed their songs when singing to females, and that could influence attention and learning. Furthermore, social interactions that rapidly enhanced learning increased the activity of noradrenergic and dopaminergic midbrain neurons. These data highlight striking parallels between humans and songbirds in the social modulation of vocal learning and suggest that social influences on attention and midbrain circuitry could represent shared mechanisms underlying the social modulation of vocal learning. PMID:27247385

  3. The Challenge of Characterizing Operations in the Mechanisms Underlying Behavior

    PubMed Central

    Bechtel, William

    2005-01-01

    Neuroscience and cognitive science seek to explain behavioral regularities in terms of underlying mechanisms. An important element of a mechanistic explanation is a characterization of the operations of the parts of the mechanism. The challenge in characterizing such operations is illustrated by an example from the history of physiological chemistry in which some investigators tried to characterize the internal operations in the same terms as the overall physiological system while others appealed to elemental chemistry. In order for biochemistry to become successful, researchers had to identify a new level of operations involving operations over molecular groups. Existing attempts at mechanistic explanation of behavior are in a situation comparable to earlier approaches to physiological chemistry, drawing their inspiration either from overall psychology activities or from low-level neural processes. Successful mechanistic explanations of behavior require the discovery of the appropriate component operations. Such discovery is a daunting challenge but one on which success will be beneficial to both behavioral scientists and cognitive and neuroscientists. PMID:16596967

  4. Network-Based Analysis for Uncovering Mechanisms Underlying Alzheimer's Disease.

    PubMed

    Kikuchi, Masataka; Ogishima, Soichi; Mizuno, Satoshi; Miyashita, Akinori; Kuwano, Ryozo; Nakaya, Jun; Tanaka, Hiroshi

    2016-01-01

    Alzheimer's disease (AD) is known to be a multifactorial neurodegenerative disorder, and is one of the main causes of dementia in the elderly. Many studies have demonstrated molecules involved in the pathogenesis of AD, however its underlying mechanisms remain obscure. It may be simplistic to try to explain the disease based on the role of a few genes only. Accumulating new, huge amount of information from e.g. genome, proteome and interactome datasets and new knowledge, we are now able to clarify and characterize diseases essentially as a result of dysfunction of molecular networks. Recent studies have indicated that relevant genes affected in human diseases concentrate in a part of the network, often called as "disease module." In the case of AD, some disease-associated pathways seem different, but some of them are clearly disease-related and coherent. This suggests the existence of a common pathway that negatively drives from healthy state to disease state (i.e., the disease module(s)). Additionally, such disease modules should dynamically change through AD progression. Thus, network-level approaches are indispensable to address unknown mechanisms of AD. In this chapter, we introduce network strategies using gene co-expression and protein interaction networks.

  5. Mechanism underlying renal failure caused by pathogenic Candida albicans infection.

    PubMed

    Jae-Chen, Shin; Young-Joo, Jeon; Seon-Min, Park; Kang Seok, Seo; Jung-Hyun, Shim; Jung-Il, Chae

    2015-03-01

    Candida albicans (C. albicans) is an opportunistic fungal pathogen that commonly causes nosocomial infections. Systemic candidiasis is encountered with increasing frequency in immunocompromised hosts, leading to renal failure that results in severe morbidity and mortality. The present study investigated the mechanisms underlying kidney susceptibility following infection with several C. albicans strains, such as B311 and SC5314. Fungal growth of the highly virulent SC5314 strain was 10(3)-fold higher compared to the nonpathogenic B311 strain in the kidneys. An intravenous challenge of SC5314 in mice, elevated blood urea nitrogen (BUN) and creatine levels, which resulted in mortality at 8 or 35 days after infection in a dose- and time-dependent manner, whereas all the B311-infected mice had BUN and creatinine levels in the normal range and survived. Whether virulent C. albicans may escape clearance by activating signaling pathways that lead to the production of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β, was investigated. B311 infections significantly elevated TNF-α and IL-1β mRNA expression in the kidneys, whereas the expression in SC5314-infected mice remained unchanged. Furthermore, B311 infection significantly elevated the plasma levels of TNF-α and IL-1β. These results indicated that the less virulent strains of C. albicans induced pro-inflammatory cytokines in mice. These results determined that an impairment of the protective mechanisms occurred in the kidneys with virulent C. albicans infection.

  6. Continuing to illuminate the mechanisms underlying UV-mediated melanomagenesis.

    PubMed

    Dellinger, Ryan W; Liu-Smith, Feng; Meyskens, Frank L

    2014-09-05

    The incidence of melanoma is one of the fastest growing of all tumor types in the United States and the number of cases worldwide has doubled in the past 30 years. Melanoma, which arises from melanocytes, is an extremely aggressive tumor that invades the vascular and lymphatic systems to establish tumors elsewhere in the body. Melanoma is a particularly resilient cancer and systemic therapy approaches have achieved minimal success against metastatic melanoma resulting in only a few FDA-approved treatments with limited benefit. Leading treatments offer minimal efficacy with response rates generally under 15% in the long term with no clear effect on melanoma-related mortality. Even the recent success of the specific BRAF mutant inhibitor vemurafenib has been tempered somewhat since acquired resistance is rapidly observed. Thus, understanding the mechanism(s) of melanoma carcinogenesis is paramount to combating this deadly disease. Not only for the treatment of melanoma but, ultimately, for prevention. In this report, we will summarize our work to date regarding the characterization of ultraviolet radiation (UVR)-mediated melanomagenesis and highlight several promising avenues of ongoing research.

  7. Molecular mechanisms underlying nutrient detection by incretin-secreting cells

    PubMed Central

    Reimann, Frank

    2010-01-01

    The hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are secreted postprandially from intestinal K- and L-cells, respectively. As incretins, these hormones stimulate insulin secretion from the pancreatic β-cell, and have independently been implicated in the control of food intake and lipid metabolism. Whilst the enteroendocrine cells producing GIP and GLP-1 are therefore attractive targets for the treatment of diabetes and obesity, our understanding of their physiology is fairly limited. The mechanisms employed to sense the arrival of carbohydrate, fat and protein in the gut lumen have been investigated using organ perfusion techniques, primary epithelial cultures and cell line models. The recent development of mice with fluorescently labeled GIP or GLP-1-expressing cells is now enabling the use of single cell techniques to investigate stimulus-secretion coupling mechanisms. This review will focus on the current knowledge of the molecular machinery underlying nutrient sensing within K- and L-cells. PMID:20204054

  8. Simulation of Electrical Transport in Rocks under Mechanical Action

    NASA Astrophysics Data System (ADS)

    Salgueiro da Silva, M. A.; Seixas, T. M.

    2015-12-01

    Rock's electrical properties can be changed by mechanical action, especially when deformation is accompanied by micro-fracturing processes. Knowing how electrical charge is generated in inelastically deformed rocks, the nature and properties of the generated charge carriers, and their spatial distribution and propagation is crucial to gain insight into the origin of seismo-electromagnetic signals. In this work, we describe briefly a model for the numerical simulation of electrical transport in rocks under mechanical action, assuming that high and low mobility charge carriers of opposite signs can be simultaneously generated by micro-fracturing processes and recombine, diffuse and drift across the sample rock. The electrical behavior can then be described using an adaptation of the formalism applied to semiconductors. We provide simulation results on a one-dimensional lattice using finite-difference discretization. Our results show that a large mobility contrast among charge carriers allows charge separation inside the deformation region, which leads to the formation of charged layers of alternate signs. Inside these layers, rapid electric field variations are observed which can lead to the emission of electromagnetic radiation. With proper positioning of current electrodes inside the deformation region, it is possible to collect electrical current even without any applied voltage. We discuss our results in the light of available experimental results on the generation of electrical and electromagnetic signals in deformed rocks.

  9. Mechanisms underlying the social enhancement of vocal learning in songbirds.

    PubMed

    Chen, Yining; Matheson, Laura E; Sakata, Jon T

    2016-06-14

    Social processes profoundly influence speech and language acquisition. Despite the importance of social influences, little is known about how social interactions modulate vocal learning. Like humans, songbirds learn their vocalizations during development, and they provide an excellent opportunity to reveal mechanisms of social influences on vocal learning. Using yoked experimental designs, we demonstrate that social interactions with adult tutors for as little as 1 d significantly enhanced vocal learning. Social influences on attention to song seemed central to the social enhancement of learning because socially tutored birds were more attentive to the tutor's songs than passively tutored birds, and because variation in attentiveness and in the social modulation of attention significantly predicted variation in vocal learning. Attention to song was influenced by both the nature and amount of tutor song: Pupils paid more attention to songs that tutors directed at them and to tutors that produced fewer songs. Tutors altered their song structure when directing songs at pupils in a manner that resembled how humans alter their vocalizations when speaking to infants, that was distinct from how tutors changed their songs when singing to females, and that could influence attention and learning. Furthermore, social interactions that rapidly enhanced learning increased the activity of noradrenergic and dopaminergic midbrain neurons. These data highlight striking parallels between humans and songbirds in the social modulation of vocal learning and suggest that social influences on attention and midbrain circuitry could represent shared mechanisms underlying the social modulation of vocal learning.

  10. Dopaminergic mechanisms underlying catalepsy, fear and anxiety: do they interact?

    PubMed

    Colombo, Ana Caroline; de Oliveira, Amanda Ribeiro; Reimer, Adriano Edgar; Brandão, Marcus Lira

    2013-11-15

    Haloperidol is a dopamine D2 receptor antagonist that induces catalepsy when systemically administered to rodents. The haloperidol-induced catalepsy is a state of akinesia and rigidity very similar to that seen in Parkinson's disease. There exists great interest in knowing whether or not some degree of emotionality underlies catalepsy. If so, what kind of emotional distress would permeate such motor disturbance? This study is an attempt to shed some light on this issue through an analysis of ultrasound vocalizations (USVs) of 22 kHz, open-field test, and contextual conditioned fear in rats with some degree of catalepsy induced by haloperidol. Systemic administration of haloperidol caused catalepsy and decreased exploratory activity in the open-field. There was no difference in the emission of USVs between groups during the catalepsy or the exploratory behavior in the open-field test. In the contextual conditioned fear, when administered before training session, haloperidol did not change the emission of USVs or the freezing response. When administered before testing session, haloperidol enhanced the freezing response and decreased the emission of USVs on the test day. These findings suggest that the involvement of dopaminergic mechanisms in threatening situations depends on the nature of the aversive stimulus. Activation of D2 receptors occurs in the setting up of adaptive responses to conditioned fear stimuli so that these mechanisms seem to be important for the emission of 22 kHz USVs during the testing phase of the contextual conditioned fear, but not during the training session or the open-field test (unconditioned fear stimuli). Catalepsy, on the other hand, is the result of the blockage of D2 receptors in neural circuits associated to motor behavior that appears to be dissociated from those directly linked to dopamine-mediated neural mechanisms associated to fear.

  11. Different neurophysiological mechanisms underlying word and rule extraction from speech.

    PubMed

    De Diego Balaguer, Ruth; Toro, Juan Manuel; Rodriguez-Fornells, Antoni; Bachoud-Lévi, Anne-Catherine

    2007-11-14

    The initial process of identifying words from spoken language and the detection of more subtle regularities underlying their structure are mandatory processes for language acquisition. Little is known about the cognitive mechanisms that allow us to extract these two types of information and their specific time-course of acquisition following initial contact with a new language. We report time-related electrophysiological changes that occurred while participants learned an artificial language. These changes strongly correlated with the discovery of the structural rules embedded in the words. These changes were clearly different from those related to word learning and occurred during the first minutes of exposition. There is a functional distinction in the nature of the electrophysiological signals during acquisition: an increase in negativity (N400) in the central electrodes is related to word-learning and development of a frontal positivity (P2) is related to rule-learning. In addition, the results of an online implicit and a post-learning test indicate that, once the rules of the language have been acquired, new words following the rule are processed as words of the language. By contrast, new words violating the rule induce syntax-related electrophysiological responses when inserted online in the stream (an early frontal negativity followed by a late posterior positivity) and clear lexical effects when presented in isolation (N400 modulation). The present study provides direct evidence suggesting that the mechanisms to extract words and structural dependencies from continuous speech are functionally segregated. When these mechanisms are engaged, the electrophysiological marker associated with rule-learning appears very quickly, during the earliest phases of exposition to a new language.

  12. Genetic, Molecular and Cellular Mechanisms Underlying the J Wave Syndromes

    PubMed Central

    Antzelevitch, Charles

    2012-01-01

    An early repolarization (ER) pattern in the ECG, distinguished by J-point elevation, slurring of the terminal part of the QRS and ST-segment elevation has long been recognized and considered to be a benign electrocardiographic manifestation. Experimental studies conducted over a decade ago suggested that some cases of ER may be associated with malignant arrhythmias. Validation of this hypothesis was provided by recent studies demonstrating that an ER pattern in the inferior or inferolateral leads is associated with increased risk for life-threatening arrhythmias, termed ER syndrome (ERS). Because accentuated J waves characterize both Brugada syndrome (BS) and ERS, these syndromes have been grouped under the term “J wave syndromes”. ERS and BS share similar ECG characteristics, clinical outcomes and risk factors, as well as a common arrhythmic platform related to amplification of Ito-mediated J waves. Although BS and ERS differ with respect to the magnitude and lead location of abnormal J wave manifestation, they can be considered to represent a continuous spectrum of phenotypic expression. Although most subjects exhibiting an ER pattern are at minimal to no risk, mounting evidence suggests that careful attention should be paid to subjects with “high risk” ER. The challenge ahead is to be able to identify those at risk for sudden cardiac death. Here I review the clinical and genetic aspects as well as the cellular and molecular mechanisms underlying the J wave syndromes. PMID:22498570

  13. Subchondral bone microarchitecture and failure mechanism under compression: A finite element study.

    PubMed

    Malekipour, Fatemeh; Oetomo, Denny; Lee, Peter Vee-Sin

    2017-02-21

    Subchondral bone (SCB) microdamage is commonly observed in traumatic joint injuries and has been strongly associated with post-traumatic osteoarthritis (PTOA). Knowledge of the three-dimensional stress and strain distribution within the SCB tissue helps to understand the mechanism of SCB failure, and may lead to an improved understanding of mechanisms of PTOA initiation, prevention and treatment. In this study, we used high-resolution micro-computed tomography (µCT)-based finite element (FE) modelling of cartilage-bone to evaluate the failure mechanism and the locations of SCB tissue at high-risk of initial failure under compression. The µCT images of five cartilage-bone specimens with an average SCB thickness of 1.23±0.20mm were used to develop five µCT-based FE models. The FE models were analysed under axial compressions of approximately 30MPa applied to the cartilage surface while the bone edges were constrained. Strain and stress-based failure criteria were then applied to evaluate the failure mechanism of the SCB tissue under excessive compression through articular cartilage. µCT-based FE models predicted two locations in the SCB at high-risk of initial failure: (1) the interface of the calcified-uncalcified cartilage due to excessive tension, and (2) the trabecular bone beneath the subchondral plate due to excessive compression. µCT-based FE models of cartilage-bone enabled us to quantify the distribution of the applied compression which was transferred through the articular cartilage to its underlying SCB, and to investigate the mechanism and the mode of SCB tissue failure. Ultimately, the results will help to understand the mechanism of injury formation in relation to PTOA.

  14. Algorithmic Mechanisms for Reliable Crowdsourcing Computation under Collusion

    PubMed Central

    Fernández Anta, Antonio; Georgiou, Chryssis; Mosteiro, Miguel A.; Pareja, Daniel

    2015-01-01

    We consider a computing system where a master processor assigns a task for execution to worker processors that may collude. We model the workers’ decision of whether to comply (compute the task) or not (return a bogus result to save the computation cost) as a game among workers. That is, we assume that workers are rational in a game-theoretic sense. We identify analytically the parameter conditions for a unique Nash Equilibrium where the master obtains the correct result. We also evaluate experimentally mixed equilibria aiming to attain better reliability-profit trade-offs. For a wide range of parameter values that may be used in practice, our simulations show that, in fact, both master and workers are better off using a pure equilibrium where no worker cheats, even under collusion, and even for colluding behaviors that involve deviating from the game. PMID:25793524

  15. Algorithmic mechanisms for reliable crowdsourcing computation under collusion.

    PubMed

    Fernández Anta, Antonio; Georgiou, Chryssis; Mosteiro, Miguel A; Pareja, Daniel

    2015-01-01

    We consider a computing system where a master processor assigns a task for execution to worker processors that may collude. We model the workers' decision of whether to comply (compute the task) or not (return a bogus result to save the computation cost) as a game among workers. That is, we assume that workers are rational in a game-theoretic sense. We identify analytically the parameter conditions for a unique Nash Equilibrium where the master obtains the correct result. We also evaluate experimentally mixed equilibria aiming to attain better reliability-profit trade-offs. For a wide range of parameter values that may be used in practice, our simulations show that, in fact, both master and workers are better off using a pure equilibrium where no worker cheats, even under collusion, and even for colluding behaviors that involve deviating from the game.

  16. Microcracking in composite laminates under thermal and mechanical loading. Thesis

    NASA Technical Reports Server (NTRS)

    Maddocks, Jason R.

    1995-01-01

    Composites used in space structures are exposed to both extremes in temperature and applied mechanical loads. Cracks in the matrix form, changing the laminate thermoelastic properties. The goal of the present investigation is to develop a predictive methodology to quantify microcracking in general composite laminates under both thermal and mechanical loading. This objective is successfully met through a combination of analytical modeling and experimental investigation. In the analysis, the stress and displacement distributions in the vicinity of a crack are determined using a shear lag model. These are incorporated into an energy based cracking criterion to determine the favorability of crack formation. A progressive damage algorithm allows the inclusion of material softening effects and temperature-dependent material properties. The analysis is implemented by a computer code which gives predicted crack density and degraded laminate properties as functions of any thermomechanical load history. Extensive experimentation provides verification of the analysis. AS4/3501-6 graphite/epoxy laminates are manufactured with three different layups to investigate ply thickness and orientation effects. Thermal specimens are cooled to progressively lower temperatures down to -184 C. After conditioning the specimens to each temperature, cracks are counted on their edges using optical microscopy and in their interiors by sanding to incremental depths. Tensile coupons are loaded monotonically to progressively higher loads until failure. Cracks are counted on the coupon edges after each loading. A data fit to all available results provides input parameters for the analysis and shows them to be material properties, independent of geometry and loading. Correlation between experiment and analysis is generally very good under both thermal and mechanical loading, showing the methodology to be a powerful, unified tool. Delayed crack initiation observed in a few cases is attributed to a

  17. Mechanical Modeling of a WIPP Drum Under Pressure

    SciTech Connect

    Smith, Jeffrey A.

    2014-11-25

    Mechanical modeling was undertaken to support the Waste Isolation Pilot Plant (WIPP) technical assessment team (TAT) investigating the February 14th 2014 event where there was a radiological release at the WIPP. The initial goal of the modeling was to examine if a mechanical model could inform the team about the event. The intention was to have a model that could test scenarios with respect to the rate of pressurization. It was expected that the deformation and failure (inability of the drum to contain any pressure) would vary according to the pressurization rate. As the work progressed there was also interest in using the mechanical analysis of the drum to investigate what would happen if a drum pressurized when it was located under a standard waste package. Specifically, would the deformation be detectable from camera views within the room. A finite element model of a WIPP 55-gallon drum was developed that used all hex elements. Analyses were conducted using the explicit transient dynamics module of Sierra/SM to explore potential pressurization scenarios of the drum. Theses analysis show similar deformation patterns to documented pressurization tests of drums in the literature. The calculated failure pressures from previous tests documented in the literature vary from as little as 16 psi to 320 psi. In addition, previous testing documented in the literature shows drums bulging but not failing at pressures ranging from 69 to 138 psi. The analyses performed for this study found the drums failing at pressures ranging from 35 psi to 75 psi. When the drums are pressurized quickly (in 0.01 seconds) there is significant deformation to the lid. At lower pressurization rates the deformation of the lid is considerably less, yet the lids will still open from the pressure. The analyses demonstrate the influence of pressurization rate on deformation and opening pressure of the drums. Analyses conducted with a substantial mass on top of the closed drum demonstrate that the

  18. Clinical phenotype network: the underlying mechanism for personalized diagnosis and treatment of traditional Chinese medicine.

    PubMed

    Zhou, Xuezhong; Li, Yubing; Peng, Yonghong; Hu, Jingqing; Zhang, Runshun; He, Liyun; Wang, Yinghui; Jiang, Lijie; Yan, Shiyan; Li, Peng; Xie, Qi; Liu, Baoyan

    2014-09-01

    Traditional Chinese medicine (TCM) investigates the clinical diagnosis and treatment regularities in a typical schema of personalized medicine, which means that individualized patients with same diseases would obtain distinct diagnosis and optimal treatment from different TCM physicians. This principle has been recognized and adhered by TCM clinical practitioners for thousands of years. However, the underlying mechanisms of TCM personalized medicine are not fully investigated so far and remained unknown. This paper discusses framework of TCM personalized medicine in classic literatures and in real-world clinical settings, and investigates the underlying mechanisms of TCM personalized medicine from the perspectives of network medicine. Based on 246 well-designed outpatient records on insomnia, by evaluating the personal biases of manifestation observation and preferences of herb prescriptions, we noted significant similarities between each herb prescriptions and symptom similarities between each encounters. To investigate the underlying mechanisms of TCM personalized medicine, we constructed a clinical phenotype network (CPN), in which the clinical phenotype entities like symptoms and diagnoses are presented as nodes and the correlation between these entities as links. This CPN is used to investigate the promiscuous boundary of syndromes and the co-occurrence of symptoms. The small-world topological characteristics are noted in the CPN with high clustering structures, which provide insight on the rationality of TCM personalized diagnosis and treatment. The investigation on this network would help us to gain understanding on the underlying mechanism of TCM personalized medicine and would propose a new perspective for the refinement of the TCM individualized clinical skills.

  19. Mechanical analysis on individualized finite element of temporal-mandibular joint under overlarge jaw opening status

    PubMed Central

    Sun, Mingxu; Yang, Jianjun; Zhou, Ruizhi; Li, Ningyi; Xia, Junnan; Gu, Fang

    2015-01-01

    Background: Analyze the stress status of temporal-mandibular joint (TMJ) of a healthy volunteer under the overlarge jaw opening status through the finite element method, with the purpose of clarifying the loading features of each structure in the joint area, and achieving further understanding of the pathogenesis of the temporomandibular disorders (TMD). Methods: Collect the CBCT and MRI data of a volunteer respectively under the maximum jaw opening, establish the finite element model (FEM) of TMJ under the maximum jaw opening status through a series of software, image segmentation, rectification, meshing, material evaluation and other related processing, simulate the mechanical environment of this joint area under this status, and analyze the stress status of the articular disc, condyle cartilage, and condyle process. Results: Based on CT and MRI image data, build 3D model and FEM of TMJ, fully simulate the mechanical environment under the large jaw opening status, and calculate the stress value of the articular disc, condyle process and condylar cartilage. Conclusions: This research result reminds us that the normal people’s articular disc are easy to generate stress concentration under large jaw opening, but its stress is far less than the one under the tight biting status. Perhaps the TMJ symptom induced under the large jaw opening status is mainly caused by the displacement of the articular disc. Under the large jaw opening status, the condylar cartilage plays a vital role in dispersing the stress. This method can be applied for carrying out individualized mechanical analysis on the patients with TMD. PMID:26309558

  20. Mechanisms Underlying Stage-1 TRPL Channel Translocation in Drosophila Photoreceptors

    PubMed Central

    Lieu, Minh-Ha; Vallejos, Maximiliano J.; Michael, Emily; Tsunoda, Susan

    2012-01-01

    Background TRP channels function as key mediators of sensory transduction and other cellular signaling pathways. In Drosophila, TRP and TRPL are the light-activated channels in photoreceptors. While TRP is statically localized in the signaling compartment of the cell (the rhabdomere), TRPL localization is regulated by light. TRPL channels translocate out of the rhabdomere in two distinct stages, returning to the rhabdomere with dark-incubation. Translocation of TRPL channels regulates their availability, and thereby the gain of the signal. Little, however, is known about the mechanisms underlying this trafficking of TRPL channels. Methodology/Principal Findings We first examine the involvement of de novo protein synthesis in TRPL translocation. We feed flies cycloheximide, verify inhibition of protein synthesis, and test for TRPL translocation in photoreceptors. We find that protein synthesis is not involved in either stage of TRPL translocation out of the rhabdomere, but that re-localization to the rhabdomere from stage-1, but not stage-2, depends on protein synthesis. We also characterize an ex vivo eye preparation that is amenable to biochemical and genetic manipulation. We use this preparation to examine mechanisms of stage-1 TRPL translocation. We find that stage-1 translocation is: induced with ATP depletion, unaltered with perturbation of the actin cytoskeleton or inhibition of endocytosis, and slowed with increased membrane sterol content. Conclusions/Significance Our results indicate that translocation of TRPL out of the rhabdomere is likely due to protein transport, and not degradation/re-synthesis. Re-localization from each stage to the rhabdomere likely involves different strategies. Since TRPL channels can translocate to stage-1 in the absence of ATP, with no major requirement of the cytoskeleton, we suggest that stage-1 translocation involves simple diffusion through the apical membrane, which may be regulated by release of a light-dependent anchor in

  1. Video analysis of concussion injury mechanism in under-18 rugby

    PubMed Central

    Hendricks, Sharief; O'Connor, Sam; Lambert, Michael; Brown, James C; Burger, Nicholas; Mc Fie, Sarah; Readhead, Clint; Viljoen, Wayne

    2016-01-01

    Background Understanding the mechanism of injury is necessary for the development of effective injury prevention strategies. Video analysis of injuries provides valuable information on the playing situation and athlete-movement patterns, which can be used to formulate these strategies. Therefore, we conducted a video analysis of the mechanism of concussion injury in junior-level rugby union and compared it with a representative and matched non-injury sample. Methods Injury reports for 18 concussion events were collected from the 2011 to 2013 under-18 Craven Week tournaments. Also, video footage was recorded for all 3 years. On the basis of the injury events, a representative ‘control’ sample of matched non-injury events in the same players was identified. The video footage, which had been recorded at each tournament, was then retrospectively analysed and coded. 10 injury events (5 tackle, 4 ruck, 1 aerial collision) and 83 non-injury events were analysed. Results All concussions were a result of contact with an opponent and 60% of players were unaware of the impending contact. For the measurement of head position on contact, 43% had a ‘down’ position, 29% the ‘up and forward’ and 29% the ‘away’ position (n=7). The speed of the injured tackler was observed as ‘slow’ in 60% of injurious tackles (n=5). In 3 of the 4 rucks in which injury occurred (75%), the concussed player was acting defensively either in the capacity of ‘support’ (n=2) or as the ‘jackal’ (n=1). Conclusions Training interventions aimed at improving peripheral vision, strengthening of the cervical muscles, targeted conditioning programmes to reduce the effects of fatigue, and emphasising safe and effective playing techniques have the potential to reduce the risk of sustaining a concussion injury. PMID:27900149

  2. Investigation of Nucleate Boiling Mechanisms Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Dhir, V. K.; Qiu, D. M.; Ramanujapu, N.; Hasan, M. M.

    1999-01-01

    The present work is aimed at the experimental studies and numerical modeling of the bubble growth mechanisms of a single bubble attached to a heating surface and of a bubble sliding along an inclined heated plate. Single artificial cavity of 10 microns in diameter was made on the polished Silicon wafer which was electrically heated at the back side in order to control the surface nucleation superheat. Experiments with a sliding bubble were conducted at different inclination angles of the downward facing heated surface for the purpose of studying the effect of magnitude of components of gravity acting parallel to and normal to the heat transfer surface. Information on the bubble shape and size, the bubble induced liquid velocities as well as the surface temperature were obtained using the high speed imaging and hydrogen bubble techniques. Analytical/numerical models were developed to describe the heat transfer through the micro-macro layer underneath and around a bubble formed at a nucleation site. In the micro layer model the capillary and disjoining pressures were included. Evolution of the bubble-liquid interface along with induced liquid motion was modeled. As a follow-up to the studies at normal gravity, experiments are being conducted in the KC-135 aircraft to understand the bubble growth/detachment under low gravity conditions. Experiments have been defined to be performed under long duration of microgravity conditions in the space shuttle. The experiment in the space shuttle will provide bubble growth and detachment data at microgravity and will lead to validation of the nucleate boiling heat transfer model developed from the preceding studies conducted at normal and low gravity (KC-135) conditions.

  3. Investigation of Mechanisms Associated with Nucleate Boiling Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Dhir, Vijay K.

    1996-01-01

    The focus of the present work is to experimentally study and to analytically/numerically model the mechanisms of growth of bubbles attached to, and sliding along, a heated surface. To control the location of the active cavities, the number, the spacing, and the nucleation superheat, artificial cavities will be formed on silicon wafers. In order to study the effect of magnitude of components of gravitational acceleration acting parallel to, and normal to the surface, experiments will be conducted on surfaces inclined at different angles including a downward facing surface. Information on the temperature field around bubbles, bubble shape and size, and bubble induced liquid velocities will be obtained through the use of holography, video/high speed photography and hydrogen bubble techniques, respectively. Analytical/numerical models will be developed to describe the heat transfer including that through the micro-macro layer underneath and around a bubble. In the micro layer model capillary and disjoining pressures will be included. Evolution of the interface along with induced liquid motion will be modelled. Subsequent to the world at normal gravity, experiments will be conducted in the KC-135 or the Lear jet especially to learn about bubble growth/detachment under low gravity conditions. Finally, an experiment will be defined to be conducted under long duration of microgravity conditions in the space shuttle. The experiment in the space shuttle will provide microgravity data on bubble growth and detachment and will lead to a validation of the nucleate boiling heat transfer model developed from the preceding studies performed at normal and low gravity (KC-135 or Lear jet) conditions.

  4. Contact mechanics of the human finger pad under compressive loads.

    PubMed

    Dzidek, Brygida M; Adams, Michael J; Andrews, James W; Zhang, Zhibing; Johnson, Simon A

    2017-02-01

    The coefficient of friction of most solid objects is independent of the applied normal force because of surface roughness. This behaviour is observed for a finger pad except at long contact times (greater than 10 s) against smooth impermeable surfaces such as glass when the coefficient increases with decreasing normal force by about a factor of five for the load range investigated here. This is clearly an advantage for some precision manipulation and grip tasks. Such normal force dependence is characteristic of smooth curved elastic bodies. It has been argued that the occlusion of moisture in the form of sweat plasticises the surface topographical features and their increased compliance allows flattening under an applied normal force, so that the surfaces of the fingerprint ridges are effectively smooth. While the normal force dependence of the friction is consistent with the theory of elastic frictional contacts, the gross deformation behaviour is not and, for commonly reported values of the Young's modulus of stratum corneum, the deformation of the ridges should be negligible compared with the gross deformation of the finger pad even when fully occluded. This paper describes the development of a contact mechanics model that resolves these inconsistencies and is validated against experimental data.

  5. [Underlying Mechanisms and Management of Refractory Gastroesophageal Reflux Disease].

    PubMed

    Lee, Kwang Jae

    2015-08-01

    The prevalence of gastroesophageal reflux disease (GERD) in South Korea has increased over the past 10 years. Patients with erosive reflux disease (ERD) shows better response to proton pump inhibitors (PPIs) than those with non-erosive reflux disease (NERD). NERD is a heterogeneous condition, showing pathological gastroesophageal reflux or esophageal hypersensitivity to reflux contents. NERD patients with pathological gastroesophageal reflux or hypersensitivity to acid may respond to PPIs. However, many patients with esophageal hypersensitivity to nonacid or functional heartburn do not respond to PPIs. Therefore, careful history and investigations are required when managing patients with refractory GERD who show poor response to conventional dose PPIs. Combined pH-impedance studies and a PPI diagnostic trial are recommended to reveal underlying mechanisms of refractory symptoms. For those with ongoing reflux-related symptoms, split dose administration, change to long-acting PPIs or PPIs less influenced by CYP2C19 genotypes, increasing dose of PPIs, and the addition of alginate preparations, prokinetics, selective serotonin reuptake inhibitors, or tricyclic antidepressants can be considered. Pain modulators, selective serotonin reuptake inhibitors, or tricyclic antidepressants are more likely to be effective for those with reflux-unrelated symptoms. Surgery or endoscopic per oral fundoplication may be effective in selected patients.

  6. Mechanisms underlying the antihypertensive effects of garlic bioactives.

    PubMed

    Shouk, Reem; Abdou, Aya; Shetty, Kalidas; Sarkar, Dipayan; Eid, Ali H

    2014-02-01

    Cardiovascular disease remains the leading cause of death worldwide with hypertension being a major contributing factor to cardiovascular disease-associated mortality. On a population level, non-pharmacological approaches, such as alternative/complementary medicine, including phytochemicals, have the potential to ameliorate cardiovascular risk factors, including high blood pressure. Several epidemiological studies suggest an antihypertensive effect of garlic (Allium sativum) and of many its bioactive components. The aim of this review is to present an in-depth discussion regarding the molecular, biochemical and cellular rationale underlying the antihypertensive properties of garlic and its bioactive constituents with a primary focus on S-allyl cysteine and allicin. Key studies, largely from PubMed, were selected and screened to develop a comprehensive understanding of the specific role of garlic and its bioactive constituents in the management of hypertension. We also reviewed recent advances focusing on the role of garlic bioactives, S-allyl cysteine and allicin, in modulating various parameters implicated in the pathogenesis of hypertension. These parameters include oxidative stress, nitric oxide bioavailability, hydrogen sulfide production, angiotensin converting enzyme activity, expression of nuclear factor-κB and the proliferation of vascular smooth muscle cells. This review suggests that garlic and garlic derived bioactives have significant medicinal properties with the potential for ameliorating hypertension and associated morbidity; however, further clinical and epidemiological studies are required to determine completely the specific physiological and biochemical mechanisms involved in disease prevention and management.

  7. Mechanical degradation of fuel cell membranes under fatigue fracture tests

    NASA Astrophysics Data System (ADS)

    Khorasany, Ramin M. H.; Sadeghi Alavijeh, Alireza; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

    2015-01-01

    The effects of cyclic stresses on the fatigue and mechanical stability of perfluorosulfonic acid (PFSA) membranes are experimentally investigated under standard fuel cell conditions. The experiments are conducted ex-situ by subjecting membrane specimens to cyclic uniaxial tension at controlled temperature and relative humidity. The fatigue lifetime is measured in terms of the number of cycles until ultimate fracture. The results indicate that the membrane fatigue lifetime is a strong function of the applied stress, temperature, and relative humidity. The fatigue life increases exponentially with reduced stresses in all cases. The effect of temperature is found to be more significant than that of humidity, with reduced fatigue life at high temperatures. The maximum membrane strain at fracture is determined to decrease exponentially with increasing membrane lifetime. At a given fatigue life, a membrane exposed to fuel cell conditions is shown to accommodate more plastic strain before fracture than one exposed to room conditions. Overall, the proposed ex-situ membrane fatigue experiment can be utilized to benchmark the fatigue lifetime of new materials in a fraction of the time and cost associated with conventional in-situ accelerated stress testing methods.

  8. Cellular mechanisms underlying spatiotemporal features of cholinergic retinal waves

    PubMed Central

    Ford, Kevin J.; Félix, Aude L.; Feller, Marla B.

    2012-01-01

    Prior to vision, a transient network of recurrently connected cholinergic interneurons, called starburst amacrine cells (SACs), generates spontaneous retinal waves. Despite an absence of robust inhibition, cholinergic retinal waves initiate infrequently and propagate within finite boundaries. Here we combine a variety of electrophysiological and imaging techniques and computational modeling to elucidate the mechanisms underlying these spatial and temporal properties of waves in developing mouse retina. Waves initiate via rare spontaneous depolarizations of SACs. Waves propagate through recurrent cholinergic connections between SACs and volume release of ACh as demonstrated using paired recordings and a cell-based ACh optical sensor. Perforated patch recordings and two-photon calcium imaging reveal that individual SACs have slow afterhyperpolarizations that induce SACs to have variable depolarizations during sequential waves. Using a computational model in which the properties of SACs are based on these physiological measurements, we reproduce the slow frequency, speed, and finite size of recorded waves. This study represents a detailed description of the circuit that mediates cholinergic retinal waves and indicates that variability of the interneurons that generate this network activity may be critical for the robustness of waves across different species and stages of development. PMID:22262883

  9. Dissociable mechanisms underlying individual differences in visual working memory capacity.

    PubMed

    Gulbinaite, Rasa; Johnson, Addie; de Jong, Ritske; Morey, Candice C; van Rijn, Hedderik

    2014-10-01

    Individuals scoring relatively high on measures of working memory tend to be more proficient at controlling attention to minimize the effect of distracting information. It is currently unknown whether such superior attention control abilities are mediated by stronger suppression of irrelevant information, enhancement of relevant information, or both. Here we used steady-state visual evoked potentials (SSVEPs) with the Eriksen flanker task to track simultaneously the attention to relevant and irrelevant information by tagging target and distractors with different frequencies. This design allowed us to dissociate attentional biasing of perceptual processing (via SSVEPs) and stimulus processing in the frontal cognitive control network (via time-frequency analyses of EEG data). We show that while preparing for the upcoming stimulus, high- and low-WMC individuals use different strategies: High-WMC individuals show attentional suppression of the irrelevant stimuli, whereas low-WMC individuals demonstrate attentional enhancement of the relevant stimuli. Moreover, behavioral performance was predicted by trial-to-trial fluctuations in strength of distractor-suppression for high-WMC participants. We found no evidence for WMC-related differences in cognitive control network functioning, as measured by midfrontal theta-band power. Taken together, these findings suggest that early suppression of irrelevant information is a key underlying neural mechanism by which superior attention control abilities are implemented.

  10. Neural mechanisms underlying respiratory rhythm generation in the lamprey.

    PubMed

    Bongianni, Fulvia; Mutolo, Donatella; Cinelli, Elenia; Pantaleo, Tito

    2016-04-01

    The isolated brainstem of the adult lamprey spontaneously generates respiratory activity. The paratrigeminal respiratory group (pTRG), the proposed respiratory central pattern generator, has been anatomically and functionally characterized. It is sensitive to opioids, neurokinins and acetylcholine. Excitatory amino acids, but not GABA and glycine, play a crucial role in the respiratory rhythmogenesis. These results are corroborated by immunohistochemical data. While only GABA exerts an important modulatory control on the pTRG, both GABA and glycine markedly influence the respiratory frequency via neurons projecting from the vagal motoneuron region to the pTRG. Noticeably, the removal of GABAergic transmission within the pTRG causes the resumption of rhythmic activity during apnea induced by blockade of glutamatergic transmission. The same result is obtained by microinjections of substance P or nicotine into the pTRG during apnea. The results prompted us to present some considerations on the phylogenesis of respiratory pattern generation. They may also encourage comparative studies on the basic mechanisms underlying respiratory rhythmogenesis of vertebrates.

  11. Spread of Epidemic on Complex Networks Under Voluntary Vaccination Mechanism

    NASA Astrophysics Data System (ADS)

    Xue, Shengjun; Ruan, Feng; Yin, Chuanyang; Zhang, Haifeng; Wang, Binghong

    Under the assumption that the decision of vaccination is a voluntary behavior, in this paper, we use two forms of risk functions to characterize how susceptible individuals estimate the perceived risk of infection. One is uniform case, where each susceptible individual estimates the perceived risk of infection only based on the density of infection at each time step, so the risk function is only a function of the density of infection; another is preferential case, where each susceptible individual estimates the perceived risk of infection not only based on the density of infection but only related to its own activities/immediate neighbors (in network terminology, the activity or the number of immediate neighbors is the degree of node), so the risk function is a function of the density of infection and the degree of individuals. By investigating two different ways of estimating the risk of infection for susceptible individuals on complex network, we find that, for the preferential case, the spread of epidemic can be effectively controlled; yet, for the uniform case, voluntary vaccination mechanism is almost invalid in controlling the spread of epidemic on networks. Furthermore, given the temporality of some vaccines, the waves of epidemic for two cases are also different. Therefore, our work insight that the way of estimating the perceived risk of infection determines the decision on vaccination options, and then determines the success or failure of control strategy.

  12. A redox mechanism underlying nucleolar stress sensing by nucleophosmin

    PubMed Central

    Yang, Kai; Wang, Ming; Zhao, Yuzheng; Sun, Xuxu; Yang, Yi; Li, Xie; Zhou, Aiwu; Chu, Huilin; Zhou, Hu; Xu, Jianrong; Wu, Mian; Yang, Jie; Yi, Jing

    2016-01-01

    The nucleolus has been recently described as a stress sensor. The nucleoplasmic translocation of nucleolar protein nucleophosmin (NPM1) is a hallmark of nucleolar stress; however, the causes of this translocation and its connection to p53 activation are unclear. Using single live-cell imaging and the redox biosensors, we demonstrate that nucleolar oxidation is a general response to various cellular stresses. During nucleolar oxidation, NPM1 undergoes S-glutathionylation on cysteine 275, which triggers the dissociation of NPM1 from nucleolar nucleic acids. The C275S mutant NPM1, unable to be glutathionylated, remains in the nucleolus under nucleolar stress. Compared with wild-type NPM1 that can disrupt the p53–HDM2 interaction, the C275S mutant greatly compromises the activation of p53, highlighting that nucleoplasmic translocation of NPM1 is a prerequisite for stress-induced activation of p53. This study elucidates a redox mechanism for the nucleolar stress sensing and may help the development of therapeutic strategies. PMID:27886181

  13. Mechanisms underlying heterologous skin scaffold-mediated tissue remodeling

    PubMed Central

    Mimura, Kallyne K. O.; Moraes, Andréia R.; Miranda, Aline C.; Greco, Rebecca; Ansari, Tahera; Sibbons, Paul; Greco, Karin V.; Oliani, Sonia M.

    2016-01-01

    Biocompatibility of two newly developed porcine skin scaffolds was assessed after 3, 14, 21 and 90 days of implantation in rats. Both scaffolds showed absence of cells, preservation of ECM and mechanical properties comparable to non-decellularised skin before implantation. Host cell infiltration was much prominent on both scaffolds when compared to Permacol (surgical control). At day 3, the grafts were surrounded by polymorphonuclear cells, which were replaced by a notable number of IL-6-positive cells at day 14. Simultaneously, the number of pro-inflammatory M1-macrophage was enhanced. Interestingly, a predominant pro-remodeling M2 response, with newly formed vessels, myofibroblasts activation and a shift on the type of collagen expression was sequentially delayed (around 21 days). The gene expression of some trophic factors involved in tissue remodeling was congruent with the cellular events. Our findings suggested that the responsiveness of macrophages after non-crosslinked skin scaffolds implantation seemed to intimately affect various cell responses and molecular events; and this range of mutually reinforcing actions was predictive of a positive tissue remodeling that was essential for the long-standing success of the implants. Furthermore, our study indicates that non-crosslinked biologic scaffold implantation is biocompatible to the host tissue and somehow underlying molecular events involved in tissue repair. PMID:27725772

  14. Global mechanical behavior of Sutong Bridge under static loads

    NASA Astrophysics Data System (ADS)

    Li, Y. B.; Zhang, Q. W.

    2010-04-01

    The global mechanical behaviors of Sutong Bridge, China, the longest cable-stayed bridge in the world, are presented by using measurements from field static load tests compared with numerical analysis in this paper. A total of 37 loading cases with 64 test trucks, each being 300kN in weight, were conducted on 10 key sections to investigate the bridge behavior. The level of loading is about 50-88% of the code-specified serviceability load. A three-dimensional finite-element model is developed and calibrated to match the experiment data. The results show that, under the load test conditions, the incremental deflections, stresses as well as cable force of the structure are linearly proportional to the incremental loads. Moreover, the transverse shear lag effects of the steel box girder are significant and the longitudinal stress distributions in the slabs and diaphragms of the box girder are non-uniform. A good agreement is achieved between the experimental tests and the numerical simulations based on the nonlinear theories of long span bridges.

  15. CFRP Mechanical Anchorage for Externally Strengthened RC Beams under Flexure

    NASA Astrophysics Data System (ADS)

    Ali, Alnadher; Abdalla, Jamal; Hawileh, Rami; Galal, Khaled

    De-bonding of carbon fiber reinforced polymers (CFRP) sheets and plates from the concrete substrate is one of the major reasons behind premature failures of beams that are externally strengthened with such CFRP materials. To delay or prevent de-bonding and therefore enhancing the load carrying capacity of strengthened beams, several anchorage systems were developed and used. This paper investigates the use of CFRP mechanical anchorage of CFRP sheets and plates used to externally strengthen reinforced concrete beams under flexure. The pin-and-fan shape CFRP anchor, which is custom-made from typical rolled fiber sheets and bundles of loose fiber is used. Several reinforced concrete beams were casted and tested in standard four-point bending scheme to study the effectiveness of this anchorage system. The beams were externally strengthened in flexure with bonded CFRP sheets and plates and then fastened to the soffit of the beams' using various patterns of CFRP anchors. It is observed that the CFRP plates begins to separate from the beams as soon as de-bonding occurs in specimens without CFRP anchors, while in beams with CFRP anchors de-bonding was delayed leading to increase in the load carrying capacity over the un-anchored strengthened beams.

  16. A Method to Evaluate Groundwater flow system under the Seabed

    NASA Astrophysics Data System (ADS)

    Kohara, N.; Marui, A.

    2011-12-01

    A rapid increase of population in the world causes growth of water demands, and this may result worldwide water shortage in future. Especially, in the coastal area, water resource development becomes important because the half of the world population is concentrated in this area. Recently, countermeasures to mitigate climate change are discussed. Coastal area is one of the promising places for disposal of high-level nuclear waste or carbon dioxide capture and storage. Lots of development will be conducted in the coastal areas, however there are a lot of uncertainties remaining to understand the hydrogeological environment in there. It has been said that salt water / fresh water interface is formed in the place where meteoric fresh groundwater and salt groundwater from the ocean meet, and there is a large amount of groundwater discharge on the seafloor of the end of this interface so far. Recently, there is a lot of research about this submarine groundwater discharge because of the protection of the coastal ecosystem. In addition, there is a report that fresh water under the seabed was discovered on the continental shelf away from a present coastline by tens of kilometers in many parts of the world, because recently offshore drilling technology has been improving. Classical theory about formulation of salt water / fresh water interface could not explain completely, and consideration of longterm geochemical process (e.g., sea level fluctuations) is needed to understand this mechanism. Fresh (or brackish) groundwater under the seabed have been found on the investigation related to a seabed resources exploration in the field of coal mining, oceanic engineering works such as submarine tunnels, the atomic research, and the collection investigations of the basic data in the earth science field. A lot of fresh water under the seabed is confirmed on the offshore side from a present coastline as for these cases, and it is suggested that the end position of the salt water

  17. Recent experimental developments concerning the mechanisms underlying dust emission

    NASA Astrophysics Data System (ADS)

    McKenna Neuman, C. L.; Sanderson, R. S.; O'Brien, P.

    2012-12-01

    Field based studies have been invaluable in elucidating the great variability and complexity in natural surfaces that emit dust. Spanning hours to days, and meters to kilometers, measurements of the regional and global characteristics of dust emission and transport are contributing to a clearer understanding of these phenomena. This work has been complimented by the development of increasingly more sophisticated atmospheric dispersion models. Only very recently, however, has much attention been paid to the physics of dust emission from the bed surface that necessarily require precise, high frequency measurements over fractions of millimeters under carefully manipulated conditions. This paper provides an overview of recent advances in our understanding of the mechanisms of dust emission, as derived from experiments carried out in the Trent boundary layer wind tunnel by a variety of workers. Energy transfer to the bed surface through the impacts of saltating particles has long been recognized as crucial for the ejection of silt and clay sized particles from surfaces where interparticle bonding is significant. Using Particle Tracking Velocimetry (PTV) and laser Doppler anemometry (LDA), we are now able to measure the energy transfer to the surface and the consequent deformation/rupture for both loose and consolidated beds of silt. The coefficient of restitution is found to decrease with particle impact speed, although some compaction may also occur with plowing and displacement of loose bed material (Gordon and McKenna Neuman, 2009). Further consideration is given to wind pumping as an alternate mechanism for dust entrainment from surfaces that are armored; that is, where insufficient sand supply is available to the support the development of a saltation cloud. LDA and pressure tap measurements confirm that turbulent structures measured in the atmospheric boundary layer are able to penetrate into the pores of gravel sized material, and specifically, the smelter waste

  18. Evaluating Admission Criteria Effects for Under-Represented Groups

    ERIC Educational Resources Information Center

    Childs, Ruth A.; Ferguson, Amanda K.; Herbert, Monique B.; Broad, Kathryn; Zhang, Jingshun

    2016-01-01

    The effects that admission criteria may have for under-represented groups are an important concern for programs seeking to improve access to post-secondary education. Using data from a large preservice teacher education program in the Canadian province of Ontario, we demonstrate two approaches to evaluating the effects of admission criteria. The…

  19. Explant culture of mouse embryonic whole lung, isolated epithelium, or mesenchyme under chemically defined conditions as a system to evaluate the molecular mechanism of branching morphogenesis and cellular differentiation.

    PubMed

    Del Moral, Pierre-Marie; Warburton, David

    2010-01-01

    Lung primordial specification as well as branching morphogenesis, and the formation of various pulmonary cell lineages, requires a specific interaction of the lung endoderm with its surrounding mesenchyme and mesothelium. Lung mesenchyme has been shown to be the source of inductive signals for lung branching morphogenesis. Epithelial-mesenchymal-mesothelial interactions are also critical to embryonic lung morphogenesis. Early embryonic lung organ culture is a very useful system to study epithelial-mesenchymal interactions. Both epithelial and mesenchymal morphogenesis proceed under specific conditions that can be readily manipulated in this system (in the absence of maternal influence and blood flow). More importantly this technique can be readily done in a serumless, chemically defined culture media. Gain and loss of function can be achieved using expressed proteins, recombinant viral vectors, and/or analysis of transgenic mouse strains, antisense RNA, as well as RNA interference gene knockdown. Additionally, to further study epithelial-mesenchymal interactions, the relative roles of epithelium versus mesenchyme signaling can also be determined using tissue recombination (e.g., epithelial and mesenchymal separation) and microbead studies.

  20. Optimization of astilbin extraction from the rhizome of Smilax glabra, and evaluation of its anti-inflammatory effect and probable underlying mechanism in lipopolysaccharide-induced RAW264.7 macrophages.

    PubMed

    Lu, Chuan-Li; Zhu, Yan-Fang; Hu, Meng-Mei; Wang, Dong-Mei; Xu, Xiao-Jie; Lu, Chuan-Jian; Zhu, Wei

    2015-01-06

    Astilbin, a dihydroflavonol derivative found in many food and medicine plants, exhibited multiple pharmacological functions. In the present study, the ethanol extraction of astilbin from the rhizome of smilax glabra Roxb was optimized by response surface methodology (RSM) using Box-Behnken design. Results indicated that the obtained experimental data was well fitted to a second-order polynomial equation by using multiple regression analysis, and the optimal extraction conditions were identified as an extraction time of 40 min, ethanol concentration of 60%, temperature of 73.63 °C, and liquid-solid ratio of 29.89 mL/g for the highest predicted yield of astilbin (15.05 mg/g), which was confirmed through validation experiments. In addition, the anti-inflammatory efficiency of astilbin was evaluated in lipopolysaccharide (LPS)-induced RAW 264.7 cells. Results showed that astilbin, at non-cytotoxicity concentrations, significantly suppressed the production of nitric oxide (NO) and tumor necrosis factor-α (TNF-α), as well as the mRNA expression of inducible nitric oxide synthase (iNOS) and TNF-α in LPS-induced RAW 264.7 cells, but did not affect interleukin-6 (IL-6) release or its mRNA expression. These effects may be related to its up-regulation of the phosphorylation of p65, extracellular signal-regulated kinases 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK).

  1. Sex differences in the mechanisms underlying long QT syndrome.

    PubMed

    Salama, Guy; Bett, Glenna C L

    2014-09-01

    Sexual dimorphism is a well-established phenomenon, but its degree varies tremendously among species. Since the early days of Einthoven's development of the three-lead galvanometer ECG, we have known there are marked differences in QT intervals of men and women. It required over a century to appreciate the profound implications of sex-based electrophysiological differences in QT interval on the panoply of sex differences with respect to arrhythmia risk, drug sensitivity, and treatment modalities. Little is known about the fundamental mechanism responsible for sex differences in electrical substrate of the human heart, in large part due to the lack of tissue availability. Animal models are an important research tool, but species differences in the sexual dimorphism of the QT interval, the ionic currents underlying the cardiac repolarization, and effects of sex steroids make it difficult to interpolate animal to human sex differences. In addition, in some species, different strains of the same animal model yield conflicting data. Each model has its strengths, such as ease of genetic manipulation in mice or size in dogs. However, many animals do not reproduce the sexual dimorphism of QT seen in humans. To match sex linked prolongation of QT interval and arrhythmogenic phenotype, the current data suggest that the rabbit may be best suited to provide insight into sex differences in humans. In the future, emerging technologies such as induced pluripotent stem cell derived cardiac myocyte systems may offer the opportunity to study sex differences in a controlled hormonal situation in the context of a sex specific human model system.

  2. Mechanisms underlying obesity resistance associated with high spontaneous physical activity

    PubMed Central

    Teske, Jennifer A.; Billington, Charles J.; Kotz, Catherine M.

    2013-01-01

    Obesity resistance due to elevated orexin signaling is accompanied by high levels of spontaneous physical activity (SPA). The behavioral and neural mechanisms underlying this observation have not been fully worked out. We determined the contribution of hypothalamic orexin receptors (OXR) to SPA stimulated by orexin A (OXA), whether OXA-stimulated SPA was secondary to arousal and whether voluntary wheel running led to compensations in 24-h SPA. We further tested whether orexin action on dopamine one receptors (DA1R) in the substantia nigra (SN) plays an important role in generation of SPA. To test this, SPA response was determined in lean and obese rats with cannulae targeted towards the rostral lateral hypothalamus (rLH) or SN. Sleep/wake states were also measured in rats with rLH cannula and EEG/EMG radiotelemetry transmitters. SPA in lean rats was more sensitive to antagonism of the orexin 1 receptor (OX1R) and in the early response to the orexin 2 agonist. OXA increased arousal equally in lean and obese rodents, which is discordant from the greater SPA response in lean rats. Obesity resistant rats ran more and wheel running was directly related to 24-h SPA levels. The OX1R antagonist, SB-334867-A, and the DA1R antagonist, SCH3390, in SN more effectively reduced SPA stimulated by OXA in OR rats. These data suggest OXA-stimulated SPA is not secondary to enhanced arousal, propensity for SPA parallels inclination to run and that orexin action on dopaminergic neurons in SN may participate in mediation of SPA and running wheel activity. PMID:24161277

  3. Unraveling the Molecular Mechanisms Underlying the Nasopharyngeal Bacterial Community Structure

    PubMed Central

    de Steenhuijsen Piters, Wouter A. A.

    2016-01-01

    ABSTRACT The upper respiratory tract is colonized by a diverse array of commensal bacteria that harbor potential pathogens, such as Streptococcus pneumoniae. As long as the local microbial ecosystem—also called “microbiome”—is in balance, these potentially pathogenic bacterial residents cause no harm to the host. However, similar to macrobiological ecosystems, when the bacterial community structure gets perturbed, potential pathogens can overtake the niche and cause mild to severe infections. Recent studies using next-generation sequencing show that S. pneumoniae, as well as other potential pathogens, might be kept at bay by certain commensal bacteria, including Corynebacterium and Dolosigranulum spp. Bomar and colleagues are the first to explore a specific biological mechanism contributing to the antagonistic interaction between Corynebacterium accolens and S. pneumoniae in vitro [L. Bomar, S. D. Brugger, B. H. Yost, S. S. Davies, K. P. Lemon, mBio 7(1):e01725-15, 2016, doi:10.1128/mBio.01725-15]. The authors comprehensively show that C. accolens is capable of hydrolyzing host triacylglycerols into free fatty acids, which display antipneumococcal properties, suggesting that these bacteria might contribute to the containment of pneumococcus. This work exemplifies how molecular epidemiological findings can lay the foundation for mechanistic studies to elucidate the host-microbe and microbial interspecies interactions underlying the bacterial community structure. Next, translation of these results to an in vivo setting seems necessary to unveil the magnitude and importance of the observed effect in its natural, polymicrobial setting. PMID:26838716

  4. Unpacking Black Boxes: Mechanisms and Theory Building in Evaluation

    ERIC Educational Resources Information Center

    Astbury, Brad; Leeuw, Frans L.

    2010-01-01

    There is growing interest in the concept of "mechanism" across many areas of the social sciences. In the field of program and policy evaluation, a number of scholars have also emphasized the importance of causal mechanisms for explaining how and why programs work. However, there appears to be some ambiguity about the meaning and uses of…

  5. Plant-insect interactions under bacterial influence: ecological implications and underlying mechanisms.

    PubMed

    Sugio, Akiko; Dubreuil, Géraldine; Giron, David; Simon, Jean-Christophe

    2015-02-01

    Plants and insects have been co-existing for more than 400 million years, leading to intimate and complex relationships. Throughout their own evolutionary history, plants and insects have also established intricate and very diverse relationships with microbial associates. Studies in recent years have revealed plant- or insect-associated microbes to be instrumental in plant-insect interactions, with important implications for plant defences and plant utilization by insects. Microbial communities associated with plants are rich in diversity, and their structure greatly differs between below- and above-ground levels. Microbial communities associated with insect herbivores generally present a lower diversity and can reside in different body parts of their hosts including bacteriocytes, haemolymph, gut, and salivary glands. Acquisition of microbial communities by vertical or horizontal transmission and possible genetic exchanges through lateral transfer could strongly impact on the host insect or plant fitness by conferring adaptations to new habitats. Recent developments in sequencing technologies and molecular tools have dramatically enhanced opportunities to characterize the microbial diversity associated with plants and insects and have unveiled some of the mechanisms by which symbionts modulate plant-insect interactions. Here, we focus on the diversity and ecological consequences of bacterial communities associated with plants and herbivorous insects. We also highlight the known mechanisms by which these microbes interfere with plant-insect interactions. Revealing such mechanisms in model systems under controlled environments but also in more natural ecological settings will help us to understand the evolution of complex multitrophic interactions in which plants, herbivorous insects, and micro-organisms are inserted.

  6. Identifying serotonergic mechanisms underlying the corticolimbic response to threat in humans

    PubMed Central

    Fisher, Patrick M.; Hariri, Ahmad R.

    2013-01-01

    A corticolimbic circuit including the amygdala and medial prefrontal cortex (mPFC) plays an important role in regulating sensitivity to threat, which is heightened in mood and anxiety disorders. Serotonin is a potent neuromodulator of this circuit; however, specific serotonergic mechanisms mediating these effects are not fully understood. Recent studies have evaluated molecular mechanisms mediating the effects of serotonin signalling on corticolimbic circuit function using a multi-modal neuroimaging strategy incorporating positron emission tomography and blood oxygen level-dependent functional magnetic resonance imaging. This multi-modal neuroimaging strategy can be integrated with additional techniques including imaging genetics and pharmacological challenge paradigms to more clearly understand how serotonin signalling modulates neural pathways underlying sensitivity to threat. Integrating these methodological approaches offers novel opportunities to identify mechanisms through which serotonin signalling contributes to differences in brain function and behaviour, which in turn can illuminate factors that confer risk for illness and inform the development of more effective treatment strategies. PMID:23440464

  7. A Model for Evaluating Vocational Automobile Mechanics Programs.

    ERIC Educational Resources Information Center

    Daugherty, Ronald D.; Suzuki, Warren N.

    The purpose of this manual is to suggest adaptable procedures and materials that can be used by Alaska vocational educators to evaluate their automotive mechanic programs systematically. Section 1 is an introduction to the manual and to the evaluation process. The remaining six sections represent major tasks or activities that should be…

  8. Under Pressure: Mechanical Stress Management in the Nucleus

    PubMed Central

    Belaadi, Néjma; Aureille, Julien; Guilluy, Christophe

    2016-01-01

    Cells are constantly adjusting to the mechanical properties of their surroundings, operating a complex mechanochemical feedback, which hinges on mechanotransduction mechanisms. Whereas adhesion structures have been shown to play a central role in mechanotransduction, it now emerges that the nucleus may act as a mechanosensitive structure. Here, we review recent advances demonstrating that mechanical stress emanating from the cytoskeleton can activate pathways in the nucleus which eventually impact both its structure and the transcriptional machinery. PMID:27314389

  9. MECHANICAL STRENGTH RESPONSES OF POLED LEAD ZIRCONATE TITANATE UNDER EXTREME ELECTRIC FIELD AND VARIOUS TEMPERATURE CONDITIONS

    SciTech Connect

    Wang, Hong; Matsunaga, Tadashi; Zhang, Kewei; Lin, Hua-Tay; Wereszczak, Andrew A

    2016-01-01

    PZT (lead zirconate titanate), particularly PZT-5A, is used in a variety of critical actuation and sensing systems because of its high Curie temperature and large piezoelectric coefficients. However, PZT is susceptible to mechanical failure. The evaluation of the mechanical strength of the material under the target working conditions is very important. This study presents part of the recent experimental developments in mechanical testing and evaluation of PZT materials at Oak Ridge National Laboratory. Ball-on-ring and four-point bending testing setups were used, with modifications made to account for testing requirements from high-level electric field and elevated temperature. The poled PZT-5A or equivalent material was tested under various specimen and testing conditions. The parameters of the distribution of strengths (characteristic strength and Weibull modulus) are discussed in relation to the testing conditions. Fractographic results based on scanning electron microscopy are also presented and discussed. The related data can serve as input for the design of piezoceramic devices, not only those used in energy systems like fuel injectors in heavy-duty diesel engines, but also those used in structural health monitoring, energy harvesting, and other critical systems in aerospace and civil engineering.

  10. Molecular mechanisms underlying sex change in hermaphroditic groupers.

    PubMed

    Zhou, Li; Gui, Jian-Fang

    2010-06-01

    , the SOX3-positive primordial germ cells develop toward spermatogonia. Therefore, we suggest that SOX3, as a transcription factor, might have more important roles in oogenesis than in spermatogenesis. Based on the findings, a hypothetic molecular mechanism underlying sex change is proposed in the hermaphroditic groupers, and some candidate genes related to the grouper sex change are also suggested for further research.

  11. Parasitic rotation evaluation and avoidance of 3-UPU parallel mechanism

    NASA Astrophysics Data System (ADS)

    Qu, Haibo; Fang, Yuefa; Guo, Sheng

    2012-06-01

    Based on the prototype of 3-UPU (universal-prismatic-universal joint) parallel mechanism proposed by Tsai [1], the parasitic rotation evaluation is performed and calculated the bound of instability of SNU (Seoul National University) 3-UPU parallel mechanism. Through analysis of the terminal constraint system of the 3-UPU parallel mechanism, the equation about the parasitic rotation and limited clearance is presented. Then the norm of possible parasitic rotation is employed to evaluate the mechanism stability with limited clearance. The higher this number the worst is the pose, the lower it is the best it is. And the contour atlas of parasitic rotation is obtained, which can be used for further analysis and design. With the practice experiment result of SUN 3-UPU parallel mechanism, we find it's bound of instability, which indicates there will appear the parasitic rotation when the number exceeds the bound. Finally, the method for avoidance of possible parasitic motions is presented by adding redundantly actuated limbs.

  12. Phenomenological and mechanics aspects of nondestructive evaluation and characterization by sound and ultrasound of material and fracture properties

    NASA Technical Reports Server (NTRS)

    Fu, L. S. W.

    1982-01-01

    Developments in fracture mechanics and elastic wave theory enhance the understanding of many physical phenomena in a mathematical context. Available literature in the material, and fracture characterization by NDT, and the related mathematical methods in mechanics that provide fundamental underlying principles for its interpretation and evaluation are reviewed. Information on the energy release mechanism of defects and the interaction of microstructures within the material is basic in the formulation of the mechanics problems that supply guidance for nondestructive evaluation (NDE).

  13. Molecular Mechanics: The Method and Its Underlying Philosophy.

    ERIC Educational Resources Information Center

    Boyd, Donald B.; Lipkowitz, Kenny B.

    1982-01-01

    Molecular mechanics is a nonquantum mechanical method for solving problems concerning molecular geometries and energy. Methodology based on: the principle of combining potential energy functions of all structural features of a particular molecule into a total force field; derivation of basic equations; and use of available computer programs is…

  14. Epigenetic mechanisms underlying learning and the inheritance of learned behaviors

    PubMed Central

    Klengel, Torsten; Ressler, Kerry J

    2014-01-01

    Gene expression and regulation is an important sculptor of the behavior of organisms. Epigenetic mechanisms regulate gene expression not by altering the genetic alphabet but rather by the addition of chemical modifications to proteins associated with the alphabet or of methyl marks to the alphabet itself. Being dynamic, epigenetic mechanisms of gene regulation serve as an important bridge between environmental stimuli and genotype. In this review, we outline epigenetic mechanisms by which gene expression is regulated in animals and humans. Using fear learning as a framework, we then delineate how such mechanisms underlie learning and stress responsiveness. Finally, we discuss how epigenetic mechanisms might inform us about the transgenerational inheritance of behavioral traits that are being increasingly reported. PMID:25544352

  15. Student Performance and Attitudes under Formative Evaluation by Teacher, Self and Peer Evaluators

    ERIC Educational Resources Information Center

    Ozogul, Gamze; Sullivan, Howard

    2009-01-01

    This study investigated the effects of teacher, self and peer evaluation on preservice teachers' performance, knowledge and attitudes. Earlier research by the same authors revealed that students made significant improvements in their lesson plans under all three of these conditions, but the teacher-evaluation improved significantly more than the…

  16. Concurrent material-fabrication optimization of metal-matrix laminates under thermo-mechanical loading

    NASA Technical Reports Server (NTRS)

    Saravanos, D. A.; Morel, M. R.; Chamis, C. C.

    1991-01-01

    A methodology is developed to tailor fabrication and material parameters of metal-matrix laminates for maximum loading capacity under thermomechanical loads. The stresses during the thermomechanical response are minimized subject to failure constrains and bounds on the laminate properties. The thermomechanical response of the laminate is simulated using nonlinear composite mechanics. Evaluations of the method on a graphite/copper symmetric cross-ply laminate were performed. The cross-ply laminate required different optimum fabrication procedures than a unidirectional composite. Also, the consideration of the thermomechanical cycle had a significant effect on the predicted optimal process.

  17. Mechanical stability of particle-stabilized droplets under micropipette aspiration

    NASA Astrophysics Data System (ADS)

    Samudrala, Niveditha; Nam, Jin; Sarfati, Raphaël; Style, Robert W.; Dufresne, Eric R.

    2017-01-01

    We investigate the mechanical behavior of particle-stabilized droplets using micropipette aspiration. We observe that droplets stabilized with amphiphilic dumbbell-shaped particles exhibit a two-stage response to increasing suction pressure. Droplets first drip, then wrinkle and buckle like an elastic shell. While particles have a dramatic impact on the mechanism of failure, the mechanical strength of the droplets is only modestly increased. On the other hand, droplets coated with the molecular surfactant sodium dodecyl sulfate are even weaker than bare droplets. In all cases, the magnitude of the critical pressure for the onset of instabilities is set by the fluid surface tension.

  18. Behavior of cracked cylinders under combined thermal and mechanical loading

    SciTech Connect

    Ignaccolo, S.

    1996-12-01

    Nuclear pressure vessels and pipings can be submitted in their life to severe mechanical and thermal loadings. Engineering methods easy to apply, but sufficiently accurate, are needed to assess the flaws. In the field of non-linear fracture mechanics a lot of work has been achieved for structures submitted to mechanical loadings. But for thermal loadings, and particularly for thermal gradients, only few contributions are available. The authors propose, here, to present the main results of a complete set of finite element computations, conducted in France by CEA, EDF and FRAMATOME, on cracked cylinders submitted to combined mechanical and thermal loads. The interaction between these two types of loads is analyzed in the cases of austenitic and ferritic structures. Moreover, these results are compared to the predictions obtained by simplified engineering methods (R6 procedure, J{sub SA16}, and J{sub EDF} approaches). Their domain of validity is also discussed.

  19. A model for hierarchical patterns under mechanical stresses

    NASA Astrophysics Data System (ADS)

    Corson, F.; Henry, H.; Adda-Bedia, M.

    2010-01-01

    We present a model for mechanically-induced pattern formation in growing biological tissues and discuss its application to the development of leaf venation networks. Drawing an analogy with phase transitions in solids, we use a phase field method to describe the transition between two states of the tissue, e.g. the differentiation of leaf veins, and consider a layered system where mechanical stresses are generated by differential growth. We present analytical and numerical results for one-dimensional systems, showing that a combination of growth and irreversibility gives rise to hierarchical patterns. Two-dimensional simulations suggest that such a mechanism could account for the hierarchical, reticulate structure of leaf venation networks, yet point to the need for a more detailed treatment of the coupling between growth and mechanical stresses.

  20. Drosophila models reveal novel insights into mechanisms underlying neurodegeneration

    PubMed Central

    Mohan, Ryan D; Workman, Jerry L; Abmayr, Susan M

    2014-01-01

    The SAGA chromatin modifying complex functions as a transcriptional coactivator for a large number of genes, and SAGA dysfunction has been linked to carcinogenesis and neurodegenerative disease. The protein complex is comprised of approximately 20 subunits, arranged in a modular fashion, and includes 2 enzymatic subunits: the Gcn5 acetyltransferase and the Non-stop deubiquitinase. As we learn more about SAGA, it becomes evident that this complex functions through sophisticated mechanisms that support very precise regulation of gene expression. Here we describe recent findings in which a Drosophila loss-of-function model revealed novel mechanisms for regulation of SAGA-mediated histone H2B deubiquitination. This model also yielded novel and surprising insights into mechanisms that underlie progressive neurodegenerative disease. Lastly, we comment on the utility of Drosophila as a model for neurodegenerative disease through which crucial and conserved mechanisms may be revealed. PMID:25483136

  1. Programmable tactile pattern presentations operational under MRI to investigate neural mechanisms of tactile shape discrimination.

    PubMed

    Yang, Jiajia; Wu, Jinglong; He, Jiping

    2011-09-30

    We have developed a novel tactile presentation system for assessing and training cognitive function on tactile senses. The device is operational in magnetic resonance imaging (MRI) environment and capable of investigating the underlying neural mechanisms of tactile pattern discrimination. The primary components of the system include a finger movement control unit (FCU), a disk for multiple tactile pattern delivery (DPD), and a force-sensing unit (FSU). An ultrasonic motor rotates the DPD to deliver different tactile patterns for cognitive sensitivity test. We evaluated the operational reliability and the performance of the system in a MRI environment. The results showed that the system performance was not affected by the magnetic field, nor did the system operation interfere with the magnetic field either. The results from the two functional MRI experiments also indicated that the brain activation can be reliably detected with the present system. Furthermore, a tactile pattern discrimination experiment was conducted using the system to investigate cognitive characteristics of shape discrimination under active and passive touch conditions. We found that the mean accuracy of discrimination under active touch was significantly higher than that under passive touch. The high accuracy and magnetic field compatibility of the device suggest that the device provides a powerful means of investigating the neural mechanisms of perception and cognitive function for touch discrimination.

  2. Mechanical properties of a lap joint under uniform clamping pressure

    NASA Technical Reports Server (NTRS)

    Diller, S. V.; Metherell, A. F.

    1969-01-01

    Equations were derived for the load deflection relations, the energy dissipation per cycle, and the instantaneous rate of dissipation for a lap joint idealized as two overlapping plates clamped together under a uniform clamping pressure.

  3. Numerical investigation of pulmonary drug delivery under mechanical ventilation conditions

    NASA Astrophysics Data System (ADS)

    Banerjee, Arindam; van Rhein, Timothy

    2012-11-01

    The effects of mechanical ventilation waveform on fluid flow and particle deposition were studied in a computer model of the human airways. The frequency with which aerosolized drugs are delivered to mechanically ventilated patients demonstrates the importance of understanding the effects of ventilation parameters. This study focuses specifically on the effects of mechanical ventilation waveforms using a computer model of the airways of patient undergoing mechanical ventilation treatment from the endotracheal tube to generation G7. Waveforms were modeled as those commonly used by commercial mechanical ventilators. Turbulence was modeled with LES. User defined particle force models were used to model the drag force with the Cunningham correction factor, the Saffman lift force, and Brownian motion force. The endotracheal tube (ETT) was found to be an important geometric feature, causing a fluid jet towards the right main bronchus, increased turbulence, and a recirculation zone in the right main bronchus. In addition to the enhanced deposition seen at the carinas of the airway bifurcations, enhanced deposition was also seen in the right main bronchus due to impaction and turbulent dispersion resulting from the fluid structures created by the ETT. Authors acknowledge financial support through University of Missouri Research Board Award.

  4. MSFC Skylab structures and mechanical systems mission evaluation

    NASA Technical Reports Server (NTRS)

    1974-01-01

    A performance analysis for structural and mechanical major hardware systems and components is presented. Development background testing, modifications, and requirement adjustments are included. Functional narratives are provided for comparison purposes as are predicted design performance criterion. Each item is evaluated on an individual basis: that is, (1) history (requirements, design, manufacture, and test); (2) in-orbit performance (description and analysis); and (3) conclusions and recommendations regarding future space hardware application. Overall, the structural and mechanical performance of the Skylab hardware was outstanding.

  5. Cognitive interventions for addiction medicine: Understanding the underlying neurobiological mechanisms.

    PubMed

    Zilverstand, Anna; Parvaz, Muhammad A; Moeller, Scott J; Goldstein, Rita Z

    2016-01-01

    Neuroimaging provides a tool for investigating the neurobiological mechanisms of cognitive interventions in addiction. The aim of this review was to describe the brain circuits that are recruited during cognitive interventions, examining differences between various treatment modalities while highlighting core mechanisms, in drug addicted individuals. Based on a systematic Medline search we reviewed neuroimaging studies on cognitive behavioral therapy, cognitive inhibition of craving, motivational interventions, emotion regulation, mindfulness, and neurofeedback training in addiction. Across intervention modalities, common results included the normalization of aberrant activity in the brain's reward circuitry, and the recruitment and strengthening of the brain's inhibitory control network. Results suggest that different cognitive interventions act, at least partly, through recruitment of a common inhibitory control network as a core mechanism. This implies potential transfer effects between training modalities. Overall, results confirm that chronically hypoactive prefrontal regions implicated in cognitive control in addiction can be normalized through cognitive means.

  6. Cognitive interventions for addiction medicine: Understanding the underlying neurobiological mechanisms

    PubMed Central

    Zilverstand, Anna; Parvaz, Muhammad A.; Moeller, Scott J.; Goldstein, Rita Z.

    2016-01-01

    Neuroimaging provides a tool for investigating the neurobiological mechanisms of cognitive interventions in addiction. The aim of this review was to describe the brain circuits that are recruited during cognitive interventions, examining differences between various treatment modalities while highlighting core mechanisms, in drug addicted individuals. Based on a systematic Medline search we reviewed neuroimaging studies on cognitive behavioral therapy, cognitive inhibition of craving, motivational interventions, emotion regulation, mindfulness, and neurofeedback training in addiction. Across intervention modalities, common results included the normalization of aberrant activity in the brain’s reward circuitry, and the recruitment and strengthening of the brain’s inhibitory control network. Results suggest that different cognitive interventions act, at least partly, through recruitment of a common inhibitory control network as a core mechanism. This implies potential transfer effects between training modalities. Overall, results confirm that chronically hypoactive prefrontal regions implicated in cognitive control in addiction can be normalized through cognitive means. PMID:26822363

  7. Common mechanism underlies repeated evolution of extreme pollution tolerance.

    PubMed

    Whitehead, Andrew; Pilcher, Whitney; Champlin, Denise; Nacci, Diane

    2012-02-07

    Human alterations to the environment can exert strong evolutionary pressures, yet contemporary adaptation to human-mediated stressors is rarely documented in wildlife populations. A common-garden experimental design was coupled with comparative transcriptomics to discover evolved mechanisms enabling three populations of killifish resident in urban estuaries to survive normally lethal pollution exposure during development, and to test whether mechanisms are unique or common across populations. We show that killifish populations from these polluted sites have independently converged on a common adaptive mechanism, despite variation in contaminant profiles among sites. These populations are united by a similarly profound desensitization of aryl-hydrocarbon receptor-mediated transcriptional activation, which is associated with extreme tolerance to the lethal effects of toxic dioxin-like pollutants. The rapid, repeated, heritable and convergent nature of evolved tolerance suggests that ancestral killifish populations harboured genotypes that enabled adaptation to twentieth-century industrial pollutants.

  8. Common mechanism underlies repeated evolution of extreme pollution tolerance

    PubMed Central

    Whitehead, Andrew; Pilcher, Whitney; Champlin, Denise; Nacci, Diane

    2012-01-01

    Human alterations to the environment can exert strong evolutionary pressures, yet contemporary adaptation to human-mediated stressors is rarely documented in wildlife populations. A common-garden experimental design was coupled with comparative transcriptomics to discover evolved mechanisms enabling three populations of killifish resident in urban estuaries to survive normally lethal pollution exposure during development, and to test whether mechanisms are unique or common across populations. We show that killifish populations from these polluted sites have independently converged on a common adaptive mechanism, despite variation in contaminant profiles among sites. These populations are united by a similarly profound desensitization of aryl-hydrocarbon receptor-mediated transcriptional activation, which is associated with extreme tolerance to the lethal effects of toxic dioxin-like pollutants. The rapid, repeated, heritable and convergent nature of evolved tolerance suggests that ancestral killifish populations harboured genotypes that enabled adaptation to twentieth-century industrial pollutants. PMID:21733895

  9. Underlying molecular and cellular mechanisms in childhood irritable bowel syndrome.

    PubMed

    Chumpitazi, Bruno P; Shulman, Robert J

    2016-12-01

    Irritable bowel syndrome (IBS) affects a large number of children throughout the world. The symptom expression of IBS is heterogeneous, and several factors which may be interrelated within the IBS biopsychosocial model play a role. These factors include visceral hyperalgesia, intestinal permeability, gut microbiota, psychosocial distress, gut inflammation, bile acids, food intolerance, colonic bacterial fermentation, and genetics. The molecular and cellular mechanisms of these factors are being actively investigated. In this mini-review, we present updates of these mechanisms and, where possible, relate the findings to childhood IBS. Mechanistic elucidation may lead to the identification of biomarkers as well as personalized childhood IBS therapies.

  10. Numerical test concerning bone mass apposition under electrical and mechanical stimulus

    PubMed Central

    2012-01-01

    This article proposes a model of bone remodeling that encompasses mechanical and electrical stimuli. The remodeling formulation proposed by Weinans and collaborators was used as the basis of this research, with a literature review allowing a constitutive model evaluating the permittivity of bone tissue to be developed. This allowed the mass distribution that depends on mechanical and electrical stimuli to be obtained. The remaining constants were established through numerical experimentation. The results demonstrate that mass distribution is altered under electrical stimulation, generally resulting in a greater deposition of mass. In addition, the frequency of application of an electric field can affect the distribution of mass; at a lower frequency there is more mass in the domain. These numerical experiments open up discussion concerning the importance of the electric field in the remodeling process and propose the quantification of their effects. PMID:22578031

  11. High temperature behavior of nanostructured Al powders obtained by mechanical alloying under NH3 flow

    NASA Astrophysics Data System (ADS)

    Caballero, E. S.; Cintas, J.; Cuevas, F. G.; Montes, J. M.; Herrera-García, M.

    2015-03-01

    Aluminium powder was mechanically alloyed under ammonia gas flow for different times (1-5 h) in order to produce a second-phase reinforcement, mainly by aluminium nitride (AlN). After milling, powders were consolidated by cold uniaxial pressing and vacuum sintering. A small amount of copper powder was added to the Al milled powder to improve its sintering behavior. Hardness and indirect tensile test were carried out at room and high temperature to evaluate the mechanical properties evolution. Results showed an remarkable hardness increase with the second phases content, even at high temperature (up to 229 HB at 400 °C). However, the high content of second phases of ceramic nature decreases the ductility, resulting in low values of tensile strength (lower than 160 MPa).

  12. Numerical test concerning bone mass apposition under electrical and mechanical stimulus.

    PubMed

    Garzón-Alvarado, Diego A; Ramírez-Martínez, Angélica M; Cardozo de Martínez, Carmen Alicia

    2012-05-11

    This article proposes a model of bone remodeling that encompasses mechanical and electrical stimuli. The remodeling formulation proposed by Weinans and collaborators was used as the basis of this research, with a literature review allowing a constitutive model evaluating the permittivity of bone tissue to be developed. This allowed the mass distribution that depends on mechanical and electrical stimuli to be obtained. The remaining constants were established through numerical experimentation. The results demonstrate that mass distribution is altered under electrical stimulation, generally resulting in a greater deposition of mass. In addition, the frequency of application of an electric field can affect the distribution of mass; at a lower frequency there is more mass in the domain. These numerical experiments open up discussion concerning the importance of the electric field in the remodeling process and propose the quantification of their effects.

  13. Mechanical Behaviour of Bolted Joints Under Impact Rates of Loading

    DTIC Science & Technology

    2012-01-01

    bolt. This pressure distribution has led to the conclusion that the compressive pressure drops dramatically after 1.5 bolt radii [ Budynas & Nisbett...Joints. New York: Marcel Dekker, Inc. Budynas , & Nisbett. (2006). Shigley’s Mechanical Engineering Design, Eigth Edition. United States: Mcgraw-Hill

  14. Photodegradation of naproxen in water under simulated solar radiation: mechanism, kinetics, and toxicity variation.

    PubMed

    Ma, Dujuan; Liu, Guoguang; Lv, Wenying; Yao, Kun; Zhang, Xiangdan; Xiao, Huahua

    2014-01-01

    The main objective of this study was to investigate the degradation mechanism, the reaction kinetics, and the evolution of toxicity of naproxen in waters under simulated solar radiation. These criteria were investigated by conducting quenching experiments with reactive oxygen species (ROS), oxygen concentration experiments, and toxicity evaluations with Vibrio fischeri bacteria. The results indicated that the degradation of naproxen proceeds via pseudo first-order kinetics in all cases and that photodegradation included degradation by direct photolysis and by self-sensitization via ROS; the contribution rates of self-sensitized photodegradation were 1.4%, 65.8%, and 31.7% via ·OH, (1)O₂ and O₂(•-), respectively. Furthermore, the oxygen concentration experiments indicated that dissolved oxygen inhibited the direct photodegradation of naproxen, and the higher the oxygen content, the more pronounced the inhibitory effect. The toxicity evaluation illustrated that some of the intermediate products formed were more toxic than naproxen.

  15. Underlying mechanisms of transient luminous events: a review

    NASA Astrophysics Data System (ADS)

    Surkov, V. V.; Hayakawa, M.

    2012-08-01

    Transient luminous events (TLEs) occasionally observed above a strong thunderstorm system have been the subject of a great deal of research during recent years. The main goal of this review is to introduce readers to recent theories of electrodynamics processes associated with TLEs. We examine the simplest versions of these theories in order to make their physics as transparent as possible. The study is begun with the conventional mechanism for air breakdown at stratospheric and mesospheric altitudes. An electron impact ionization and dissociative attachment to neutrals are discussed. A streamer size and mobility of electrons as a function of altitude in the atmosphere are estimated on the basis of similarity law. An alternative mechanism of air breakdown, runaway electron mechanism, is discussed. In this section we focus on a runaway breakdown field, characteristic length to increase avalanche of runaway electrons and on the role played by fast seed electrons in generation of the runaway breakdown. An effect of thunderclouds charge distribution on initiation of blue jets and gigantic jets is examined. A model in which the blue jet is treated as upward-propagating positive leader with a streamer zone/corona on the top is discussed. Sprite models based on streamer-like mechanism of air breakdown in the presence of atmospheric conductivity are reviewed. To analyze conditions for sprite generation, thunderstorm electric field arising just after positive cloud-to-ground stroke is compared with the thresholds for propagation of positively/negatively charged streamers and with runway breakdown. Our own estimate of tendril's length at the bottom of sprite is obtained to demonstrate that the runaway breakdown can trigger the streamer formation. In conclusion we discuss physical mechanisms of VLF (very low frequency) and ELF (extremely low frequency) phenomena associated with sprites.

  16. Early Damage Mechanisms in Nuclear Grade Graphite under Irradiation

    SciTech Connect

    Eapen, Dr. Jacob; Krishna, Dr Ram; Burchell, Timothy D; Murty, Prof K.L.

    2014-01-01

    Using Raman and X-ray photoelectron spectroscopy,we delineate the bond and defect structures in nuclear block graphite (NBG-18) under neutron and ion irradiation. The strengthening of the defect (D) peak in the Raman spectra under irradiation is attributed to an increase in the topological, sp2-hybridized defects. Using transmission electron microscopy, we provide evidence for prismatic dislocations as well as a number of basal dislocations dissociating into Shockley partials. The non-vanishing D peak in the Raman spectra, together with a generous number of dislocations, even at low irradiation doses, indicates a dislocation-mediated amorphization process in graphite.

  17. Latrepirdine: molecular mechanisms underlying potential therapeutic roles in Alzheimer's and other neurodegenerative diseases

    PubMed Central

    Bharadwaj, P R; Bates, K A; Porter, T; Teimouri, E; Perry, G; Steele, J W; Gandy, S; Groth, D; Martins, R N; Verdile, Giuseppe

    2013-01-01

    Latrepirdine (DimebonTM) was originally marketed as a non-selective antihistamine in Russia. It was repurposed as an effective treatment for patients suffering from Alzheimer's disease (AD) and Huntington's disease (HD) following preliminary reports showing its neuroprotective functions and ability to enhance cognition in AD and HD models. However, latrepirdine failed to show efficacy in phase III trials in AD and HD patients following encouraging phase II trials. The failure of latrepirdine in the clinical trials has highlighted the importance of understanding the precise mechanism underlying its cognitive benefits in neurodegenerative diseases before clinical evaluation. Latrepirdine has shown to affect a number of cellular functions including multireceptor activity, mitochondrial function, calcium influx and intracellular catabolic pathways; however, it is unclear how these properties contribute to its clinical benefits. Here, we review the studies investigating latrepirdine in cellular and animal models to provide a complete evaluation of its mechanisms of action in the central nervous system. In addition, we review recent studies that demonstrate neuroprotective functions for latrepirdine-related class of molecules including the β-carbolines and aminopropyl carbazoles in AD, Parkinson's disease and amyotrophic lateral sclerosis models. Assessment of their neuroprotective effects and underlying biological functions presents obvious value for developing structural analogues of latrepirdine for dementia treatment. PMID:24301650

  18. Mechanisms underlying social inequality in post-menopausal breast cancer.

    PubMed

    Hvidtfeldt, Ulla Arthur

    2014-10-01

    This thesis is based on studies conducted in the period 2010-2014 at Department of Public Health, University of Copenhagen and at Department of Epidemiology and Population Health, Albert Einstein College of Medicine, New York. The results are presented in three scientific papers and a synopsis. The main objective of the thesis was to determine mechanisms underlying social inequality (defined by educational level) in postmenopausal breast cancer (BC) by addressing mediating effects through hormone therapy (HT) use, BMI, lifestyle and reproductive factors. The results of previous studies suggest that the higher risk of postmenopausal BC among women of high socioeconomic position (SEP) may be explained by reproductive factors and health behaviors. Women of higher SEP generally have fewer children and give birth at older ages than women of low SEP, and these factors have been found to affect the risk of BC - probably through altered hormone levels. Adverse effects on BC risk have also been documented for modifiable health behaviors that may affect hormone levels, such as alcohol consumption, high BMI, physical inactivity, and HT use. Alcohol consumption and HT use are likewise more common among women of higher SEP. The analyses were based on the Social Inequality in Cancer (SIC) cohort and a subsample of the Women's Health Initiative Observational Study (WHI-OS). The SIC cohort was derived by pooling 6 individual studies from the Copenhagen area including 33,562 women (1,733 BC cases) aged 50-70 years at baseline. The subsample of WHI-OS consisted of two case-cohort studies with measurements of endogenous estradiol (N = 1,601) and insulin (N = 791). Assessment of mediation often relies on comparing multiplicative models with and without the potential mediator. Such approaches provide potentially biased results, because they do not account for mediator-outcome confounding, exposure-dependent mediator-outcome confounding, exposure-mediator interaction and interactions

  19. Cognitive Mechanism Underlying the Relationship between Rapid Automatized Naming and Reading: A Longitudinal Study on Bilingual Children

    ERIC Educational Resources Information Center

    Yeung, Susanna S.

    2016-01-01

    Rapid automatized naming has been demonstrated as an important correlate of various reading outcomes. However, the cognitive mechanism underlying the RAN-reading relationship is not well understood. The primary goal of this study is to evaluate three major theoretical accounts for the RAN--reading relationship: phonological processing account,…

  20. Mechanism Underlying the Spatial Pattern Formation of Dominant Tree Species in a Natural Secondary Forest

    PubMed Central

    Jia, Guodong; Yu, Xinxiao; Fan, Dengxing; Jia, Jianbo

    2016-01-01

    Studying the spatial pattern of plant species may provide significant insights into processes and mechanisms that maintain stand stability. To better understand the dynamics of naturally regenerated secondary forests, univariate and bivariate Ripley’s L(r) functions were employed to evaluate intra-/interspecific relationships of four dominant tree species (Populus davidiana, Betula platyphylla, Larix gmelinii and Acer mono) and to distinguish the underlying mechanism of spatial distribution. The results showed that the distribution of soil, water and nutrients was not fragmented but presented clear gradients. An overall aggregated distribution existed at most distances. No correlation was found between the spatial pattern of soil conditions and that of trees. Both positive and negative intra- and interspecific relationships were found between different DBH classes at various distances. Large trees did not show systematic inhibition of the saplings. By contrast, the inhibition intensified as the height differences increased between the compared pairs. Except for Larix, universal inhibition of saplings by upper layer trees occurred among other species, and this reflected the vertical competition for light. Therefore, we believe that competition for light rather than soil nutrients underlies the mechanism driving the formation of stand spatial pattern in the rocky mountainous areas examined. PMID:27028757

  1. Peer influence: neural mechanisms underlying in-group conformity.

    PubMed

    Stallen, Mirre; Smidts, Ale; Sanfey, Alan G

    2013-01-01

    People often conform to the behavior of others with whom they identify. However, it is unclear what fundamental mechanisms underlie this type of conformity. Here, we investigate the processes mediating in-group conformity by using functional magnetic resonance imaging (fMRI). Participants completed a perceptual decision-making task while undergoing fMRI, during which they were exposed to the judgments of both in-group and out-group members. Our data suggest that conformity to the in-group is mediated by both positive affect as well as the cognitive capacity of perspective taking. Examining the processes that drive in-group conformity by utilizing a basic decision-making paradigm combined with neuroimaging methods provides important insights into the potential mechanisms of conformity. These results may provide an integral step in developing more effective campaigns using group conformity as a tool for behavioral change.

  2. Grained composite materials prepared by combustion synthesis under mechanical pressure

    DOEpatents

    Dunmead, Stephen D.; Holt, Joseph B.; Kingman, Donald D.; Munir, Zuhair A.

    1990-01-01

    Dense, finely grained composite materials comprising one or more ceramic phase or phase and one or more metallic and/or intermetallic phase or phases are produced by combustion synthesis. Spherical ceramic grains are homogeneously dispersed within the matrix. Methods are provided, which include the step of applying mechanical pressure during or immediately after ignition, by which the microstructures in the resulting composites can be controllably selected.

  3. Evaluating the Atrial Myopathy Underlying Atrial Fibrillation: Identifying the Arrhythmogenic and Thrombogenic Substrate

    PubMed Central

    Goldberger, Jeffrey J.; Arora, Rishi; Green, David; Greenland, Philip; Lee, Daniel C.; Lloyd-Jones, Donald M.; Markl, Michael; Ng, Jason; Shah, Sanjiv J.

    2015-01-01

    Atrial disease or myopathy forms the substrate for atrial fibrillation (AF) and underlies the potential for atrial thrombus formation and subsequent stroke. Current diagnostic approaches in patients with AF focus on identifying clinical predictors with evaluation of left atrial size by echocardiography serving as the sole measure specifically evaluating the atrium. Although the atrial substrate underlying AF is likely developing for years prior to the onset of AF, there is no current evaluation to identify the pre-clinical atrial myopathy. Atrial fibrosis is one component of the atrial substrate that has garnered recent attention based on newer MRI techniques that have been applied to visualize atrial fibrosis in humans with prognostic implications regarding success of treatment. Advanced ECG signal processing, echocardiographic techniques, and MRI imaging of fibrosis and flow provide up-to-date approaches to evaluate the atrial myopathy underlying AF. While thromboembolic risk is currently defined by clinical scores, their predictive value is mediocre. Evaluation of stasis via imaging and biomarkers associated with thrombogenesis may provide enhanced approaches to assess risk for stroke in patients with AF. Better delineation of the atrial myopathy that serves as the substrate for AF and thromboembolic complications might improve treatment outcomes. Furthermore, better delineation of the pathophysiologic mechanisms underlying the development of the atrial substrate for AF, particularly in its earlier stages, could help identify blood and imaging biomarkers that could be useful to assess risk for developing new onset AF and suggest specific pathways that could be targeted for prevention. PMID:26216085

  4. Strain-driven criticality underlies nonlinear mechanics of fibrous networks

    NASA Astrophysics Data System (ADS)

    Sharma, A.; Licup, A. J.; Rens, R.; Vahabi, M.; Jansen, K. A.; Koenderink, G. H.; MacKintosh, F. C.

    2016-10-01

    Networks with only central force interactions are floppy when their average connectivity is below an isostatic threshold. Although such networks are mechanically unstable, they can become rigid when strained. It was recently shown that the transition from floppy to rigid states as a function of simple shear strain is continuous, with hallmark signatures of criticality [Sharma et al., Nature Phys. 12, 584 (2016), 10.1038/nphys3628]. The nonlinear mechanical response of collagen networks was shown to be quantitatively described within the framework of such mechanical critical phenomenon. Here, we provide a more quantitative characterization of critical behavior in subisostatic networks. Using finite-size scaling we demonstrate the divergence of strain fluctuations in the network at well-defined critical strain. We show that the characteristic strain corresponding to the onset of strain stiffening is distinct from but related to this critical strain in a way that depends on critical exponents. We confirm this prediction experimentally for collagen networks. Moreover, we find that the apparent critical exponents are largely independent of the spatial dimensionality. With subisostaticity as the only required condition, strain-driven criticality is expected to be a general feature of biologically relevant fibrous networks.

  5. Theoretical considerations underlying Na(+) uptake mechanisms in freshwater fishes.

    PubMed

    Parks, Scott K; Tresguerres, Martin; Goss, Greg G

    2008-11-01

    Ion and acid-base regulating mechanisms have been studied at the fish gill for almost a century. Original models proposed for Na(+) and Cl(-) uptake, and their linkage with H(+) and HCO(3)(-) secretion have changed substantially with the development of more sophisticated physiological techniques. At the freshwater fish gill, two dominant mechanisms for Na(+) uptake from dilute environments have persisted in the literature. The use of an apical Na(+)/H(+) exchanger driven by a basolateral Na(+)/K(+)-ATPase versus an apical Na(+) channel electrogenically coupled to an apical H(+)-ATPase have been the source of debate for a number of years. Advances in molecular biology have greatly enhanced our understanding of the basic ion transport mechanisms at the fish gill. However, it is imperative to ensure that thermodynamic principles are followed in the development of new models for gill ion transport. This review will focus on the recent molecular advances for Na(+) uptake in freshwater fish. Emphasis will be placed on thermodynamic constraints that prevent electroneutral apical NHE function in most freshwater environments. By combining recent advances in molecular and functional physiology of fish gills with thermodynamic considerations of ion transport, our knowledge in the field should continue to grow in a logical manner.

  6. Investigations of Mechanisms Associated with Nucleate Boiling Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Dhir, Vijay K.; Hasan, M.; Chao, David (Technical Monitor)

    2003-01-01

    In this work a building block type of approach is used so that a basic understanding of the processes that contribute to nucleate boiling heat fluxes under microgravity conditions can be developed. This understanding will lead to development of a mechanistic model for nucleate boiling heat transfer which could eventually be used as a design tool in space applications. Task Description Task 1: Fabrication of the Experimental Setup. Under this task, the test section and liquid holding and viewing chambers will be fabricated. Artificial cylinder cavities will be formed on silicon wafers. A single cavity and two or four cavities, with a prescribed spacing and size, will be formed. The desired nucleation wall superheat will be used to determine the size of the mouth of the cavities. Task 2: Experiments. The basic experiments for flow and temperature field around single and multiple (2 or 4 separated or merged bubbles growing on downward facing or inclined surfaces) will be carried out under normal gravity conditions. The experiments will be conducted at one atmosphere pressure, but liquid subcooling will be varied from 0 to 30C. Water and PF-5050 will be used as test liquids. Task 3: Analytical/Numerical Models. In this task, transient temperature and flow field in vapor and liquid will be determined during growth of a single bubble. Analysis will include the evolution of the vapor-liquid interface and development of microlayer underneath the bubbles. For merged bubbles, detailed calculations of flow and temperature field will be carried out for transient shapes of vapor stems supporting a large bubble and the corresponding evaporation rate. Flow and temperature field for a bubble sliding along a heated wall will also be determined. Microgravity conditions will be simulated and a framework of a numerical tool for prediction of nucleate boiling heat fluxes under microgravity conditions will be developed. Task 4: Experiments in a KC-135. To understand bubble growth and

  7. Mechanical response of unidirectional boron/aluminum under combined loading

    NASA Technical Reports Server (NTRS)

    Becker, Wolfgang; Pindera, Marek-Jerzy; Herakovich, Carl T.

    1987-01-01

    Three test methods were employed to characterize the response of unidirectional Boron/Aluminum metal matrix composite material under monotonic and cyclic loading conditions, namely, losipescu shear, off-axis tension and compression. The characterization of the elastic and plastic response includes the elastic material properties, yielding and subsequent hardening of the unidirectional composite under different stress ratios in the material principal coordinate system. Yield loci generated for different stress ratios are compared for the three different test methods, taking into account residual stresses and specimen geometry. Subsequently, the yield locus for in-plane shear is compared with the prediction of an analytical, micromechanical model. The influence of the scatter in the experimental data on the predicted yield surface is also analyzed. Lastly, the experimental material strengths in tension and compression are correlated with the maximum stress and the Tsai-Wu failure criterion.

  8. Atomic mechanism of flow in simple liquids under shear

    SciTech Connect

    Iwashita, T.; Egami, Takeshi

    2012-01-01

    Atomic correlations in a simple liquid in steady-state flow under shear stress are studied by molecular dynamics simulation. The local atomic level strain is determined through the anisotropic pair-density function. The atomic level strain has a limited spatial extension whose range is dependent on the strain rate and extrapolates to zero at the critical strain rate. A failure event is identified with altering the local topology of atomic connectivity by exchanging bonds among neighboring atoms.

  9. Millimeter Wave Nondestructive Evaluation of Corrosion Under Paint in Steel Structures

    SciTech Connect

    Kharkovsky, S.; Zoughi, R.

    2006-03-06

    Millimeter wave nondestructive evaluation techniques have shown great potential for detection of corrosion under paint in steel structures. They may also provide for detection of other anomalies associated with the corrosion process such as precursor pitting. This paper presents the results of an extensive investigation spanning a frequency range of 30-100 GHz and using magnitude- and phase-sensitive reflectometers. Using 2D automated scanning mechanisms, raster images of two corrosion patches are produced showing the spatial resolution capabilities of these systems as well as their potential for evaluating localized corrosion severity.

  10. Fracture mechanics evaluation for at typical PWR primary coolant pipe

    SciTech Connect

    Tanaka, T.; Shimizu, S.; Ogata, Y.

    1997-04-01

    For the primary coolant piping of PWRs in Japan, cast duplex stainless steel which is excellent in terms of strength, corrosion resistance, and weldability has conventionally been used. The cast duplex stainless steel contains the ferrite phase in the austenite matrix and thermal aging after long term service is known to change its material characteristics. It is considered appropriate to apply the methodology of elastic plastic fracture mechanics for an evaluation of the integrity of the primary coolant piping after thermal aging. Therefore we evaluated the integrity of the primary coolant piping for an initial PWR plant in Japan by means of elastic plastic fracture mechanics. The evaluation results show that the crack will not grow into an unstable fracture and the integrity of the piping will be secured, even when such through wall crack length is assumed to equal the fatigue crack growth length for a service period of up to 60 years.

  11. Chemical and Mechanical Alteration of Fractured Caprock Under Reactive Flow

    NASA Astrophysics Data System (ADS)

    Elkhoury, J. E.; Ameli, P.; Detwiler, R. L.

    2013-12-01

    Permeability evolution of fractures depends on chemical and mechanical processes. Stress perturbations lead to mechanical deformation and fracture propagation that can increase formation permeability. Chemical disequilibrium between fluids and resident minerals leads to dissolution and precipitation that further alter fracture porosity and permeability. The ability to predict whether these coupled chemical and mechanical processes will enhance or diminish fracture permeability remains elusive. Here, we present results from reactive-transport experiments in fractured anhydrite cores, with significant alteration of the rock matrix, where only the flow rate differed. For high flow rate, the transformation of anhydrite to gypsum occurred uniformly within the fracture leading to compaction and a two-order-of-magnitude decrease in permeability. For low flow rate, rock-fluid reactions proceeded to near equilibrium within the fracture with preferential flow paths persisting over the 6-month duration of the experiment and a negligible change in permeability. Anticipating such permeability evolution is critical for successful geologic CO2 sequestration and waste injection. Additionally, reactive alteration of the porous matrix bounding fractures will influence the strength of earthquake fault zones. Comparison of the aperture field before (a) and after (b) the reactive flow-through experiment at low flow rate. a) Aperture field from optical profilometry measurements of the fracture surfaces. b) Inferred aperture from x-ray computed tomography scans. Color scale I (blue) denotes mainly unaltered regions of the fracture and/or aperture < 200 μm. Color scale II (green/yellow) denotes reacted regions of the fracture surfaces and the matrix adjacent to the fracture. Persistent flow paths are clearly observed in panel (b) (color scale III corresponds to aperture > 200 μm) leading to negligible change in permeability after a 6-month run.

  12. Molecular and Electrophysiological Mechanisms Underlying Cardiac Arrhythmogenesis in Diabetes Mellitus

    PubMed Central

    Tse, Vivian; Yeo, Jie Ming

    2016-01-01

    Diabetes is a common endocrine disorder with an ever increasing prevalence globally, placing significant burdens on our healthcare systems. It is associated with significant cardiovascular morbidities. One of the mechanisms by which it causes death is increasing the risk of cardiac arrhythmias. The aim of this article is to review the cardiac (ion channel abnormalities, electrophysiological and structural remodelling) and extracardiac factors (neural pathway remodelling) responsible for cardiac arrhythmogenesis in diabetes. It is concluded by an outline of molecular targets for future antiarrhythmic therapy for the diabetic population. PMID:27642609

  13. Cellular mechanisms underlying growth asymmetry during stem gravitropism

    NASA Technical Reports Server (NTRS)

    Cosgrove, D. J.

    1997-01-01

    Plant stems respond to gravitropic stimulation with a rapid, local and reversible change in cell growth rate (elongation), generally on both the upper and lower sides of the stem. The cellular and biochemical mechanisms for this differential growth are reviewed. Considerable evidence implicates an asymmetry in wall pH in the growth response. The strengths and weaknesses of the wall "loosening enzyme" concept are reviewed and the possibility of expansin involvement in the bending response of stems is considered. Also discussed is the possibility that wall stiffening processes, e.g. phenolic coupling driven by oxidative bursts or altered orientation of newly deposited cellulose, might mediate the growth responses during gravitropism.

  14. Electronic, mechanical and dielectric properties of silicane under tensile strain

    NASA Astrophysics Data System (ADS)

    Jamdagni, Pooja; Kumar, Ashok; Sharma, Munish; Thakur, Anil; Ahluwalia, P. K.

    2015-05-01

    The electronic, mechanical and dielectric properties of fully hydrogenated silicene i.e. silicane in stable configuration are studied by means of density functional theory based calculations. The band gap of silicane monolayer can be flexibly reduced to zero when subjected to bi-axial tensile strain, leading to semi-conducting to metallic transition, whereas the static dielectric constant for in-plane polarization increases monotonically with increasing strain. Also the EEL function show the red shift in resonance peak with tensile strain. Our results offer useful insight for the application of silicane monolayer in nano-optical and electronics devices.

  15. Electronic, mechanical and dielectric properties of silicane under tensile strain

    SciTech Connect

    Jamdagni, Pooja Sharma, Munish; Ahluwalia, P. K.; Kumar, Ashok; Thakur, Anil

    2015-05-15

    The electronic, mechanical and dielectric properties of fully hydrogenated silicene i.e. silicane in stable configuration are studied by means of density functional theory based calculations. The band gap of silicane monolayer can be flexibly reduced to zero when subjected to bi-axial tensile strain, leading to semi-conducting to metallic transition, whereas the static dielectric constant for in-plane polarization increases monotonically with increasing strain. Also the EEL function show the red shift in resonance peak with tensile strain. Our results offer useful insight for the application of silicane monolayer in nano-optical and electronics devices.

  16. Self-DNA inhibitory effects: Underlying mechanisms and ecological implications

    PubMed Central

    Cartenì, Fabrizio; Bonanomi, Giuliano; Giannino, Francesco; Incerti, Guido; Vincenot, Christian Ernest; Chiusano, Maria Luisa; Mazzoleni, Stefano

    2016-01-01

    ABSTRACT DNA is usually known as the molecule that carries the instructions necessary for cell functioning and genetic inheritance. A recent discovery reported a new functional role for extracellular DNA. After fragmentation, either by natural or artificial decomposition, small DNA molecules (between ∼50 and ∼2000 bp) exert a species specific inhibitory effect on individuals of the same species. Evidence shows that such effect occurs for a wide range of organisms, suggesting a general biological process. In this paper we explore the possible molecular mechanisms behind those findings and discuss the ecological implications, specifically those related to plant species coexistence. PMID:26950417

  17. Enhancement of wind stress evaluation method under storm conditions

    NASA Astrophysics Data System (ADS)

    Chen, Yingjian; Yu, Xiping

    2016-12-01

    Wind stress is an important driving force for many meteorological and oceanographical processes. However, most of the existing methods for evaluation of the wind stress, including various bulk formulas in terms of the wind speed at a given height and formulas relating the roughness height of the sea surface with wind conditions, predict an ever-increasing tendency of the wind stress coefficient as the wind speed increases, which is inconsistent with the field observations under storm conditions. The wave boundary layer model, which is based on the momentum and energy conservation, has the advantage to take into account the physical details of the air-sea interaction process, but is still invalid under storm conditions without a modification. By including the energy dissipation due to the presence of sea spray, which is speculated to be an important aspect of the air-sea interaction under storm conditions, the wave boundary layer model is improved in this study. The improved model is employed to estimate the wind stress caused by an idealized tropical cyclone motion. The computational results show that the wind stress coefficient reaches its maximal value at a wind speed of about 40 m/s and decreases as the wind speed further increases. This is in fairly good agreement with the field data.

  18. Reliability Evaluation for Clustered WSNs under Malware Propagation.

    PubMed

    Shen, Shigen; Huang, Longjun; Liu, Jianhua; Champion, Adam C; Yu, Shui; Cao, Qiying

    2016-06-10

    We consider a clustered wireless sensor network (WSN) under epidemic-malware propagation conditions and solve the problem of how to evaluate its reliability so as to ensure efficient, continuous, and dependable transmission of sensed data from sensor nodes to the sink. Facing the contradiction between malware intention and continuous-time Markov chain (CTMC) randomness, we introduce a strategic game that can predict malware infection in order to model a successful infection as a CTMC state transition. Next, we devise a novel measure to compute the Mean Time to Failure (MTTF) of a sensor node, which represents the reliability of a sensor node continuously performing tasks such as sensing, transmitting, and fusing data. Since clustered WSNs can be regarded as parallel-serial-parallel systems, the reliability of a clustered WSN can be evaluated via classical reliability theory. Numerical results show the influence of parameters such as the true positive rate and the false positive rate on a sensor node's MTTF. Furthermore, we validate the method of reliability evaluation for a clustered WSN according to the number of sensor nodes in a cluster, the number of clusters in a route, and the number of routes in the WSN.

  19. Reliability Evaluation for Clustered WSNs under Malware Propagation

    PubMed Central

    Shen, Shigen; Huang, Longjun; Liu, Jianhua; Champion, Adam C.; Yu, Shui; Cao, Qiying

    2016-01-01

    We consider a clustered wireless sensor network (WSN) under epidemic-malware propagation conditions and solve the problem of how to evaluate its reliability so as to ensure efficient, continuous, and dependable transmission of sensed data from sensor nodes to the sink. Facing the contradiction between malware intention and continuous-time Markov chain (CTMC) randomness, we introduce a strategic game that can predict malware infection in order to model a successful infection as a CTMC state transition. Next, we devise a novel measure to compute the Mean Time to Failure (MTTF) of a sensor node, which represents the reliability of a sensor node continuously performing tasks such as sensing, transmitting, and fusing data. Since clustered WSNs can be regarded as parallel-serial-parallel systems, the reliability of a clustered WSN can be evaluated via classical reliability theory. Numerical results show the influence of parameters such as the true positive rate and the false positive rate on a sensor node’s MTTF. Furthermore, we validate the method of reliability evaluation for a clustered WSN according to the number of sensor nodes in a cluster, the number of clusters in a route, and the number of routes in the WSN. PMID:27294934

  20. Peripheral Afferent Mechanisms Underlying Acupuncture Inhibition of Cocaine Behavioral Effects in Rats

    PubMed Central

    Lee, Bong Hyo; Bae, Jong Han; Kim, Kwang Joong; Steffensen, Scott C.; Leem, Joong Woo; Yang, Chae Ha; Kim, Hee Young

    2013-01-01

    Administration of cocaine increases locomotor activity by enhancing dopamine transmission. To explore the peripheral mechanisms underlying acupuncture treatment for drug addiction, we developed a novel mechanical acupuncture instrument (MAI) for objective mechanical stimulation. The aim of this study was to evaluate whether acupuncture inhibition of cocaine-induced locomotor activity is mediated through specific peripheral nerves, the afferents from superficial or deep tissues, or specific groups of nerve fibers. Mechanical stimulation of acupuncture point HT7 with MAI suppressed cocaine-induced locomotor activity in a stimulus time-dependent manner, which was blocked by severing the ulnar nerve or by local anesthesia. Suppression of cocaine-induced locomotor activity was elicited after HT7 stimulation at frequencies of either 50 (for Meissner corpuscles) or 200 (for Pacinian corpuscles) Hz and was not affected by block of C/Aδ-fibers in the ulnar nerve with resiniferatoxin, nor generated by direct stimulation of C/Aδ-fiber afferents with capsaicin. These findings suggest that HT7 inhibition of cocaine-induced locomotor activity is mediated by A-fiber activation of ulnar nerve that originates in superficial and deep tissue. PMID:24260531

  1. Mechanisms Underlying Carotenoid Absorption in Oxygenic Photosynthetic Proteins*

    PubMed Central

    Mendes-Pinto, Maria M.; Galzerano, Denise; Telfer, Alison; Pascal, Andrew A.; Robert, Bruno; Ilioaia, Cristian

    2013-01-01

    The electronic properties of carotenoid molecules underlie their multiple functions throughout biology, and tuning of these properties by their in vivo locus is of vital importance in a number of cases. This is exemplified by photosynthetic carotenoids, which perform both light-harvesting and photoprotective roles essential to the photosynthetic process. However, despite a large number of scientific studies performed in this field, the mechanism(s) used to modulate the electronic properties of carotenoids remain elusive. We have chosen two specific cases, the two β-carotene molecules in photosystem II reaction centers and the two luteins in the major photosystem II light-harvesting complex, to investigate how such a tuning of their electronic structure may occur. Indeed, in each case, identical molecular species in the same protein are seen to exhibit different electronic properties (most notably, shifted absorption peaks). We assess which molecular parameters are responsible for this in vivo tuning process and attempt to assign it to specific molecular events imposed by their binding pockets. PMID:23720734

  2. Mechanisms underlying carotenoid absorption in oxygenic photosynthetic proteins.

    PubMed

    Mendes-Pinto, Maria M; Galzerano, Denise; Telfer, Alison; Pascal, Andrew A; Robert, Bruno; Ilioaia, Cristian

    2013-06-28

    The electronic properties of carotenoid molecules underlie their multiple functions throughout biology, and tuning of these properties by their in vivo locus is of vital importance in a number of cases. This is exemplified by photosynthetic carotenoids, which perform both light-harvesting and photoprotective roles essential to the photosynthetic process. However, despite a large number of scientific studies performed in this field, the mechanism(s) used to modulate the electronic properties of carotenoids remain elusive. We have chosen two specific cases, the two β-carotene molecules in photosystem II reaction centers and the two luteins in the major photosystem II light-harvesting complex, to investigate how such a tuning of their electronic structure may occur. Indeed, in each case, identical molecular species in the same protein are seen to exhibit different electronic properties (most notably, shifted absorption peaks). We assess which molecular parameters are responsible for this in vivo tuning process and attempt to assign it to specific molecular events imposed by their binding pockets.

  3. Molecular mechanisms underlying the exceptional adaptations of batoid fins

    PubMed Central

    Nakamura, Tetsuya; Klomp, Jeff; Pieretti, Joyce; Schneider, Igor; Gehrke, Andrew R.; Shubin, Neil H.

    2015-01-01

    Extreme novelties in the shape and size of paired fins are exemplified by extinct and extant cartilaginous and bony fishes. Pectoral fins of skates and rays, such as the little skate (Batoid, Leucoraja erinacea), show a strikingly unique morphology where the pectoral fin extends anteriorly to ultimately fuse with the head. This results in a morphology that essentially surrounds the body and is associated with the evolution of novel swimming mechanisms in the group. In an approach that extends from RNA sequencing to in situ hybridization to functional assays, we show that anterior and posterior portions of the pectoral fin have different genetic underpinnings: canonical genes of appendage development control posterior fin development via an apical ectodermal ridge (AER), whereas an alternative Homeobox (Hox)–Fibroblast growth factor (Fgf)–Wingless type MMTV integration site family (Wnt) genetic module in the anterior region creates an AER-like structure that drives anterior fin expansion. Finally, we show that GLI family zinc finger 3 (Gli3), which is an anterior repressor of tetrapod digits, is expressed in the posterior half of the pectoral fin of skate, shark, and zebrafish but in the anterior side of the pelvic fin. Taken together, these data point to both highly derived and deeply ancestral patterns of gene expression in skate pectoral fins, shedding light on the molecular mechanisms behind the evolution of novel fin morphologies. PMID:26644578

  4. Understanding ultrasound induced sonoporation: definitions and underlying mechanisms.

    PubMed

    Lentacker, I; De Cock, I; Deckers, R; De Smedt, S C; Moonen, C T W

    2014-06-01

    In the past two decades, research has underlined the potential of ultrasound and microbubbles to enhance drug delivery. However, there is less consensus on the biophysical and biological mechanisms leading to this enhanced delivery. Sonoporation, i.e. the formation of temporary pores in the cell membrane, as well as enhanced endocytosis is reported. Because of the variety of ultrasound settings used and corresponding microbubble behavior, a clear overview is missing. Therefore, in this review, the mechanisms contributing to sonoporation are categorized according to three ultrasound settings: i) low intensity ultrasound leading to stable cavitation of microbubbles, ii) high intensity ultrasound leading to inertial cavitation with microbubble collapse, and iii) ultrasound application in the absence of microbubbles. Using low intensity ultrasound, the endocytotic uptake of several drugs could be stimulated, while short but intense ultrasound pulses can be applied to induce pore formation and the direct cytoplasmic uptake of drugs. Ultrasound intensities may be adapted to create pore sizes correlating with drug size. Small molecules are able to diffuse passively through small pores created by low intensity ultrasound treatment. However, delivery of larger drugs such as nanoparticles and gene complexes, will require higher ultrasound intensities in order to allow direct cytoplasmic entry.

  5. Silk Fibroin-Sophorolipid Gelation: Deciphering the Underlying Mechanism.

    PubMed

    Dubey, Parul; Kumar, Sugam; Aswal, Vinod K; Ravindranathan, Sapna; Rajamohanan, Pattuparambil R; Prabhune, Asmita; Nisal, Anuya

    2016-10-10

    Silk fibroin (SF) protein, produced by silkworm Bombyx mori, is a promising biomaterial, while sophorolipid (SL) is an amphiphilic functional biosurfactant synthesized by nonpathogenic yeast Candida bombicola. SL is a mixture of two forms, acidic (ASL) and lactonic (LSL), which when added to SF results in accelerated gelation of silk fibroin. LSL is known to have multiple biological functionalities and hence hydrogels of these green molecules have promising applications in the biomedical sector. In this work, SANS, NMR, and rheology are employed to examine the assembling properties of individual and mixed SLs and their interactions with SF to understand the mechanism that leads to rapid gelation. SANS and NMR studies show that ASL assembles to form charged micelles, while LSL forms micellar assemblies and aggregates of a mass fractal nature. ASL and LSL together form larger mixed micelles, all of which interact differently with SF. It is shown that preferential binding of LSL to SF causes rapid unfolding of the SF chain leading to the formation of intermolecular beta sheets, which trigger fast gelation. Based on the observations, a mechanism for gelation of SF in the presence of different sophorolipids is proposed.

  6. Gastric sensitivity and reflexes: basic mechanisms underlying clinical problems.

    PubMed

    Azpiroz, Fernando; Feinle-Bisset, Christine; Grundy, David; Tack, Jan

    2014-02-01

    Both reflex and sensory mechanisms control the function of the stomach, and disturbances in these mechanisms may explain the pathophysiology of disorders of gastric function. The objective of this report is to perform a literature-based critical analysis of new, relevant or conflicting information on gastric sensitivity and reflexes, with particular emphasis on the comprehensive integration of basic and clinical research data. The stomach exerts both phasic and tonic muscular (contractile and relaxatory) activity. Gastric tone determines the capacity of the stomach and mediates both gastric accommodation to a meal as well as gastric emptying, by partial relaxation or progressive recontraction, respectively. Perception and reflex afferent pathways from the stomach are activated independently by specific stimuli, suggesting that the terminal nerve endings operate as specialized receptors. Particularly, perception appears to be related to stimulation of tension receptors, while the existence of volume receptors in the stomach is uncertain. Reliable techniques have been developed to measure gastric perception and reflexes both in experimental and clinical conditions, and have facilitated the identification of abnormal responses in patients with gastric disorders. Gastroparesis is characterised by impaired gastric tone and contractility, whereas patients with functional dyspepsia have impaired accommodation, associated with antral distention and increased gastric sensitivity. An integrated view of fragmented knowledge allows the design of pathophysiological models in an attempt to explain disorders of gastric function, and may facilitate the development of mechanistically orientated treatments.

  7. Sequential mechanisms underlying concentration invariance in biological olfaction

    PubMed Central

    Cleland, Thomas A.; Chen, Szu-Yu T.; Hozer, Katarzyna W.; Ukatu, Hope N.; Wong, Kevin J.; Zheng, Fangfei

    2011-01-01

    Concentration invariance—the capacity to recognize a given odorant (analyte) across a range of concentrations—is an unusually difficult problem in the olfactory modality. Nevertheless, humans and other animals are able to recognize known odors across substantial concentration ranges, and this concentration invariance is a highly desirable property for artificial systems as well. Several properties of olfactory systems have been proposed to contribute to concentration invariance, but none of these alone can plausibly achieve full concentration invariance. We here propose that the mammalian olfactory system uses at least six computational mechanisms in series to reduce the concentration-dependent variance in odor representations to a level at which different concentrations of odors evoke reasonably similar representations, while preserving variance arising from differences in odor quality. We suggest that the residual variance then is treated like any other source of stimulus variance, and categorized appropriately into “odors” via perceptual learning. We further show that naïve mice respond to different concentrations of an odorant just as if they were differences in quality, suggesting that, prior to odor categorization, the learning-independent compensatory mechanisms are limited in their capacity to achieve concentration invariance. PMID:22287949

  8. Mechanisms underlying vertebrate limb regeneration: lessons from the salamander.

    PubMed

    Brockes, Jeremy P; Gates, Phillip B

    2014-06-01

    Limb regeneration in adult salamanders proceeds by formation of a mound of progenitor cells called the limb blastema. It provides several pointers for regenerative medicine. These include the role of differentiated cells in the origin of the blastema, the role of regenerating axons of peripheral nerves and the importance of cell specification in conferring morphogenetic autonomy on the blastema. One aspect of regeneration that has received less attention is the ability to undergo multiple episodes without detectable change in the outcome, and with minimal effect of aging. We suggest that, although such pointers are valuable, it is important to understand why salamanders are the only adult tetrapod vertebrates able to regenerate their limbs. Although this remains a controversial issue, the existence of salamander-specific genes that play a significant role in the mechanism of regeneration provides evidence for the importance of local evolution, rather than a purely ancestral mechanism. The three-finger protein called Prod1 is discussed in the present article as an exemplar of this approach.

  9. Constitutive response of Rene 80 under thermal mechanical loads

    NASA Technical Reports Server (NTRS)

    Kim, K. S.; Cook, T. S.; Mcknight, R. L.

    1988-01-01

    The applicability of a classical constitutive model for stress-strain analysis of a nickel base superalloy, Rene' 80, in the gas turbine thermomechanical fatigue (TMF) environment is examined. A variety of tests were conducted to generate basic material data and to investigate the material response under cyclic thermomechanical loading. Isothermal stress-strain data were acquired at a variety of strain rates over the TMF temperature range. Creep curves were examined at 2 temperature ranges, 871 to 982 C and 760 to 871 C. The results provide optimism on the ability of the classical constitutive model for high temperature applications.

  10. Preliminary Evaluation of Greases for Space Mechanisms Using a Vacuum Spiral Orbit Tribometer

    NASA Technical Reports Server (NTRS)

    Marchetti, Mario; Jones, William R., Jr.; Street, Kenneth W.; Pepper, Stephen V.; Jansen, Mark J.

    2001-01-01

    Most currently used greases for space applications are based on perfluoropolyalkylethers (PFPE) and multiply alkylated cyclopentane (MAC) oils. Evaluation of the greases includes outgassing properties, rheological behavior, and particularly the ability to create EHL films under conditions as close as possible to an actual application. A spiral orbit tribometer (SOT) has been developed to conduct accelerated tests under realistic conditions. The SOT was employed to evaluate two greases used in space mechanisms: a PFPE oil with polytetrafluoroethylene (PTFE) thickener, and a multiply alkylated cyclopentane oil with n-octadecylterephthalamate soap. The results from the greases are in agreement with results previously obtained with the base oils.

  11. Mechanisms Underlying Mammalian Hybrid Sterility in Two Feline Interspecies Models

    PubMed Central

    Davis, Brian W.; Seabury, Christopher M.; Brashear, Wesley A.; Li, Gang; Roelke-Parker, Melody; Murphy, William J.

    2015-01-01

    The phenomenon of male sterility in interspecies hybrids has been observed for over a century, however, few genes influencing this recurrent phenotype have been identified. Genetic investigations have been primarily limited to a small number of model organisms, thus limiting our understanding of the underlying molecular basis of this well-documented “rule of speciation.” We utilized two interspecies hybrid cat breeds in a genome-wide association study employing the Illumina 63 K single-nucleotide polymorphism array. Collectively, we identified eight autosomal genes/gene regions underlying associations with hybrid male sterility (HMS) involved in the function of the blood-testis barrier, gamete structural development, and transcriptional regulation. We also identified several candidate hybrid sterility regions on the X chromosome, with most residing in close proximity to complex duplicated regions. Differential gene expression analyses revealed significant chromosome-wide upregulation of X chromosome transcripts in testes of sterile hybrids, which were enriched for genes involved in chromatin regulation of gene expression. Our expression results parallel those reported in Mus hybrids, supporting the “Large X-Effect” in mammalian HMS and the potential epigenetic basis for this phenomenon. These results support the value of the interspecies feline model as a powerful tool for comparison to rodent models of HMS, demonstrating unique aspects and potential commonalities that underpin mammalian reproductive isolation. PMID:26006188

  12. Mechanisms Underlying Mammalian Hybrid Sterility in Two Feline Interspecies Models.

    PubMed

    Davis, Brian W; Seabury, Christopher M; Brashear, Wesley A; Li, Gang; Roelke-Parker, Melody; Murphy, William J

    2015-10-01

    The phenomenon of male sterility in interspecies hybrids has been observed for over a century, however, few genes influencing this recurrent phenotype have been identified. Genetic investigations have been primarily limited to a small number of model organisms, thus limiting our understanding of the underlying molecular basis of this well-documented "rule of speciation." We utilized two interspecies hybrid cat breeds in a genome-wide association study employing the Illumina 63 K single-nucleotide polymorphism array. Collectively, we identified eight autosomal genes/gene regions underlying associations with hybrid male sterility (HMS) involved in the function of the blood-testis barrier, gamete structural development, and transcriptional regulation. We also identified several candidate hybrid sterility regions on the X chromosome, with most residing in close proximity to complex duplicated regions. Differential gene expression analyses revealed significant chromosome-wide upregulation of X chromosome transcripts in testes of sterile hybrids, which were enriched for genes involved in chromatin regulation of gene expression. Our expression results parallel those reported in Mus hybrids, supporting the "Large X-Effect" in mammalian HMS and the potential epigenetic basis for this phenomenon. These results support the value of the interspecies feline model as a powerful tool for comparison to rodent models of HMS, demonstrating unique aspects and potential commonalities that underpin mammalian reproductive isolation.

  13. Mechanical Alterations Associated with Repeated Treadmill Sprinting under Heat Stress

    PubMed Central

    Brocherie, Franck; Morin, Jean-Benoit; Racinais, Sébastien; Millet, Grégoire P.; Périard, Julien D.

    2017-01-01

    Purpose Examine the mechanical alterations associated with repeated treadmill sprinting performed in HOT (38°C) and CON (25°C) conditions. Methods Eleven recreationally active males performed a 30-min warm-up followed by three sets of five 5-s sprints with 25-s recovery and 3-min between sets in each environment. Constant-velocity running for 1-min at 10 and 20 km.h-1 was also performed prior to and following sprinting. Results Mean skin (37.2±0.7 vs. 32.7±0.8°C; P<0.001) and core (38.9±0.2 vs. 38.8±0.3°C; P<0.05) temperatures, together with thermal comfort (P<0.001) were higher following repeated sprinting in HOT vs. CON. Step frequency and vertical stiffness were lower (-2.6±1.6% and -5.5±5.5%; both P<0.001) and contact time (+3.2±2.4%; P<0.01) higher in HOT for the mean of sets 1–3 compared to CON. Running distance per sprint decreased from set 1 to 3 (-7.0±6.4%; P<0.001), with a tendency for shorter distance covered in HOT vs. CON (-2.7±3.4%; P = 0.06). Mean vertical (-2.6±5.5%; P<0.01), horizontal (-9.1±4.4%; P<0.001) and resultant ground reaction forces (-3.0±2.8%; P<0.01) along with vertical stiffness (-12.9±2.3%; P<0.001) and leg stiffness (-8.4±2.7%; P<0.01) decreased from set 1 to 3, independently of conditions. Propulsive power decreased from set 1 to 3 (-16.9±2.4%; P<0.001), with lower propulsive power values in set 2 (-6.6%; P<0.05) in HOT vs. CON. No changes in constant-velocity running patterns occurred between conditions, or from pre-to-post repeated-sprint exercise. Conclusions Thermal strain alters step frequency and vertical stiffness during repeated sprinting; however without exacerbating mechanical alterations. The absence of changes in constant-velocity running patterns suggests a strong link between fatigue-induced velocity decrements during sprinting and mechanical alterations. PMID:28146582

  14. Circuit Mechanisms Underlying Motor Memory Formation in the Cerebellum

    PubMed Central

    Lee, Ka Hung; Mathews, Paul J.; Reeves, Alexander M.B.; Choe, Katrina Y.; Jami, Shekib A.; Serrano, Raul E.; Otis, Thomas S.

    2015-01-01

    SUMMARY The cerebellum stores associative motor memories essential for properly timed movement; however, the mechanisms by which these memories form and are acted upon remain unclear. To determine how cerebellar activity relates to movement and motor learning, we used optogenetics to manipulate spontaneously firing Purkinje neurons (PNs) in mouse simplex lobe. Using high-speed videography and motion tracking, we found that altering PN activity produced rapid forelimb movement. PN inhibition drove movements time-locked to stimulus onset, whereas PN excitation drove delayed movements time-locked to stimulus offset. Pairing either PN inhibition or excitation with sensory stimuli triggered the formation of robust, associative motor memories; however, PN excitation led to learned movements whose timing more closely matched training intervals. These findings implicate inhibition of PNs as a teaching signal, consistent with a model whereby learning leads first to reductions in PN firing that subsequently instruct circuit changes in the cerebellar nucleus. PMID:25843404

  15. Mechanisms underlying the antimotion sickness effects of psychostimulants

    NASA Technical Reports Server (NTRS)

    Kohl, Randall L.; Lewis, Michael R.

    1987-01-01

    Data related to the mechanism responsible for the antimotion sickness effects of psychostimulants such as amphetamine are examined. From the analysis of current literature and new evidence, the following three hypotheses are suggested: (1) selective enhancement of dopaminergic, but not noradrenergic, transmission is sufficient to account for amphetamine-induced resistance and, perhaps, for natural resistance to motion sickness; (2) the site of this enhanced dopaminergic transmission is probably within the basal ganglia; and (3) the neuropharmacology of the basal ganglia, but not of the brain-stem vestibular areas, can account for the therapeutic synergism of scopolamine and amphetamine. The therapeutic action of psychostimulants may be dissociable from some of their side effects, particularly cardiovascular effects related to peripheral norepinephrine release.

  16. Mechanisms underlying spontaneous patterned activity in developing neural circuits

    PubMed Central

    Blankenship, Aaron G.; Feller, Marla B.

    2010-01-01

    Patterned, spontaneous activity occurs in many developing neural circuits, including the retina, the cochlea, the spinal cord, the cerebellum and the hippocampus, where it provides signals that are important for the development of neurons and their connections. Despite differences in adult architecture and output across these various circuits, the patterns of spontaneous network activity and the mechanisms that generate it are remarkably similar and can include a depolarizing action of GABA, transient synaptic connections, extrasynaptic transmission, gap junction coupling and the presence of pacemaker-like neurons. Interestingly, spontaneous activity is robust; if one element of a circuit is disrupted another will generate similar activity. This research suggests that developing neural circuits exhibit transient and tunable features that maintain a source of correlated activity during critical stages of development. PMID:19953103

  17. Functional methods underlying classical mechanics, relativity and quantum theory

    NASA Astrophysics Data System (ADS)

    Kryukov, A.

    2013-04-01

    The paper investigates the physical content of a recently proposed mathematical framework that unifies the standard formalisms of classical mechanics, relativity and quantum theory. In the framework states of a classical particle are identified with Dirac delta functions. The classical space is "made" of these functions and becomes a submanifold in a Hilbert space of states of the particle. The resulting embedding of the classical space into the space of states is highly non-trivial and accounts for numerous deep relations between classical and quantum physics and relativity. One of the most striking results is the proof that the normal probability distribution of position of a macroscopic particle (equivalently, position of the corresponding delta state within the classical space submanifold) yields the Born rule for transitions between arbitrary quantum states.

  18. Autonomous mechanism of internal choice estimate underlies decision inertia.

    PubMed

    Akaishi, Rei; Umeda, Kazumasa; Nagase, Asako; Sakai, Katsuyuki

    2014-01-08

    Our choice is influenced by choices we made in the past, but the mechanism responsible for the choice bias remains elusive. Here we show that the history-dependent choice bias can be explained by an autonomous learning rule whereby an estimate of the likelihood of a choice to be made is updated in each trial by comparing between the actual and expected choices. We found that in perceptual decision making without performance feedback, a decision on an ambiguous stimulus is repeated on the subsequent trial more often than a decision on a salient stimulus. This inertia of decision was not accounted for by biases in motor response, sensory processing, or attention. The posterior cingulate cortex and frontal eye field represent choice prediction error and choice estimate in the learning algorithm, respectively. Interactions between the two regions during the intertrial interval are associated with decision inertia on a subsequent trial.

  19. Ecological mechanisms underlying arthropod species diversity in grasslands.

    PubMed

    Joern, Anthony; Laws, Angela N

    2013-01-01

    Arthropods are an important component of grassland systems, contributing significantly to biodiversity and ecosystem structure and function. Climate, fire, and grazing by large herbivores are important drivers in grasslands worldwide. Arthropod responses to these drivers are highly variable and clear patterns are difficult to find, but responses are largely indirect with respect to changes in resources, species interactions, habitat structure, and habitat heterogeneity resulting from interactions among fire, grazing, and climate. Here, we review these ecological mechanisms influencing grassland arthropod diversity. We summarize hypotheses describing species diversity at local and regional scales and then discuss specific factors that may affect arthropod diversity in grassland systems. These factors include direct and indirect effects of grazing, fire, and climate, species interactions, above- and belowground interactions, and landscape-level effects.

  20. Mechanical characterization of stomach tissue under uniaxial tensile action.

    PubMed

    Jia, Z G; Li, W; Zhou, Z R

    2015-02-26

    In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15-20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue.

  1. Multiple mechanisms underlying troglitazone-induced mitochondrial permeability transition

    SciTech Connect

    Okuda, Takuya; Norioka, Misaki; Shitara, Yoshihisa; Horie, Toshiharu

    2010-11-01

    Troglitazone, a thiazolidinedione class antidiabetic drug, was withdrawn from the market because of its severe idiosyncratic hepatotoxicity. It causes a mitochondrial permeability transition (MPT), which may in part contribute to its hepatotoxicity. In the present study, the mechanism of troglitazone mitochondrial toxicity was investigated in isolated rat liver mitochondria. Mitochondrial swelling induced by 10 {mu}M troglitazone was attenuated by bromoenol lactone (BEL), an inhibitor of Ca{sup 2+}-independent phospholipase A{sub 2} (iPLA{sub 2}). In contrast, that induced by 50 {mu}M troglitazone was exacerbated by BEL. This exacerbation was diminished by addition of 2 mM glutathione, an antioxidant. Oxygen consumption by state 3 respiration in isolated mitochondria was also decreased by troglitazone, but it was not affected by BEL. Mitochondrial swelling induced by 10 {mu}M troglitazone was completely attenuated in the absence of Ca{sup 2+} while that induced by 50 {mu}M troglitazone was not affected. Addition of 1 {mu}M cyclosporin A (CsA), an inhibitor of MPT pores, completely attenuated swelling induced by 10 {mu}M troglitazone while it only partly diminished that induced by 50 {mu}M troglitazone. Thus, the MPT induced by 10 and 50 {mu}M troglitazone are regulated by different mechanism; the MPT induced by 10 {mu}M troglitazone is regulated by the activation of iPLA{sub 2} and caused by the opening of CsA-regulating MPT pores followed by accumulation of Ca{sup 2+} in mitochondria, while that induced by 50 {mu}M troglitazone is partly regulated by reactive oxygen species and mainly caused by the opening of CsA-insensitive MPT pores.

  2. Synaptic mechanisms underlying cholinergic control of thalamic reticular nucleus neurons

    PubMed Central

    Beierlein, Michael

    2014-01-01

    Neuronal networks of the thalamus are the target of extensive cholinergic projections from the basal forebrain and the brainstem. Activation of these afferents can regulate neuronal excitability, transmitter release, and firing patterns in thalamic networks, thereby altering the flow of sensory information during distinct behavioural states. However, cholinergic regulation in the thalamus has been primarily examined by using receptor agonist and antagonist, which has precluded a detailed understanding of the spatiotemporal dynamics that govern cholinergic signalling under physiological conditions. This review summarizes recent studies on cholinergic synaptic transmission in the thalamic reticular nucleus (TRN), a brain structure intimately involved in the control of sensory processing and the generation of rhythmic activity in the thalamocortical system. This work has shown that acetylcholine (ACh) released from individual axons can rapidly and reliably activate both pre- and postsynaptic cholinergic receptors, thereby controlling TRN neuronal activity with high spatiotemporal precision. PMID:24973413

  3. A Neural Mechanism of Preference Shifting Under Zero Price Condition

    PubMed Central

    Votinov, Mikhail; Aso, Toshihiko; Fukuyama, Hidenao; Mima, Tatsuya

    2016-01-01

    In everyday life, free products have a strong appeal to us, even if we do not need them. Behavioral studies demonstrated that people have a tendency to switch their preference from preferred more expensive products to less preferable, cheaper alternatives, when the cheaper option becomes free. However, the neural representation of this behavioral anomaly called “Zero price” is still unclear. Using fMRI, we studied subjects while they performed binary preference choice task for items with different prices. We found that zero-related change of preference was associated with activation of the choice network, which includes inferior parietal lobule (IPL), posterior cingulate cortex and medial prefrontal cortex. Moreover, the amount of activation in medial prefrontal cortex was positively correlated with the subjective happiness score of getting free products. Our findings suggest that the Zero-price effect is driven by affective evaluations during decision-making. PMID:27148024

  4. The Behavioral and Neural Mechanisms Underlying the Tracking of Expertise

    PubMed Central

    Boorman, Erie D.; O’Doherty, John P.; Adolphs, Ralph; Rangel, Antonio

    2013-01-01

    Summary Evaluating the abilities of others is fundamental for successful economic and social behavior. We investigated the computational and neurobiological basis of ability tracking by designing an fMRI task that required participants to use and update estimates of both people and algorithms’ expertise through observation of their predictions. Behaviorally, we find a model-based algorithm characterized subject predictions better than several alternative models. Notably, when the agent’s prediction was concordant rather than discordant with the subject’s own likely prediction, participants credited people more than algorithms for correct predictions and penalized them less for incorrect predictions. Neurally, many components of the mentalizing network—medial prefrontal cortex, anterior cingulate gyrus, temporoparietal junction, and precuneus—represented or updated expertise beliefs about both people and algorithms. Moreover, activity in lateral orbitofrontal and medial prefrontal cortex reflected behavioral differences in learning about people and algorithms. These findings provide basic insights into the neural basis of social learning. PMID:24360551

  5. The effects of divided attention on encoding processes under incidental and intentional learning instructions: underlying mechanisms?

    PubMed

    Naveh-Benjamin, Moshe; Guez, Jonathan; Hara, Yoko; Brubaker, Matthew S; Lowenschuss-Erlich, Iris

    2014-01-01

    Divided attention (DA) at encoding has been shown to significantly disrupt later memory for the studied information. However, what type of processing gets disrupted during DA remains unresolved. In this study, we assessed the degree to which strategic effortful processes are affected under DA by comparing the effects of DA at encoding under intentional and pure incidental learning instructions. In three experiments, participants studied list of words or word pairs under either full or divided attention. Results of three experiments, which used different methodologies, converged to show that the effects of DA at encoding reduce memory performance to the same degree under incidental and intentional learning. Secondary task performance indicated that encoding under intentional learning instructions was more effortful than under incidental learning instructions. In addition, the results indicated enhanced attention to the initial appearance of the words under both types of learning instructions. Results are interpreted to imply that other processes, rather than only strategic effortful ones, might be affected by DA at encoding.

  6. Evaluation of Chest Injury Mechanisms in Nearside Oblique Frontal Impacts

    PubMed Central

    Iraeus, Johan; Lindquist, Mats; Wistrand, Sofie; Sibgård, Elin; Pipkorn, Bengt

    2013-01-01

    Despite the use of seat belts and modern safety systems, many automobile occupants are still seriously injured or killed in car crashes. Common configurations in these crashes are oblique and small overlap frontal impacts that often lead to chest injuries. To evaluate the injury mechanism in these oblique impacts, an investigation was carried out using mathematical human body model simulations. A model of a simplified vehicle interior was developed and validated by means of mechanical sled tests with the Hybrid III dummy. The interior model was then combined with the human body model THUMS and validated by means of mechanical PMHS sled tests. Occupant kinematics as well as rib fracture patterns were predicted with reasonable accuracy. The final model was updated to conform to modern cars and a simulation matrix was run. In this matrix the boundary conditions, ΔV and PDOF, were varied and rib fracture risk as a function of the boundary conditions was evaluated using a statistical framework. In oblique frontal impacts, two injury producing mechanisms were found; (i) diagonal belt load and (ii) side structure impact. The second injury mechanism was found for PDOFs of 25°–35°, depending on ΔV. This means that for larger PDOFs, less ΔV is needed to cause a serious chest injury. PMID:24406957

  7. Evaluation of chest injury mechanisms in nearside oblique frontal impacts.

    PubMed

    Iraeus, Johan; Lindquist, Mats; Wistrand, Sofie; Sibgård, Elin; Pipkorn, Bengt

    2013-01-01

    Despite the use of seat belts and modern safety systems, many automobile occupants are still seriously injured or killed in car crashes. Common configurations in these crashes are oblique and small overlap frontal impacts that often lead to chest injuries.To evaluate the injury mechanism in these oblique impacts, an investigation was carried out using mathematical human body model simulations. A model of a simplified vehicle interior was developed and validated by means of mechanical sled tests with the Hybrid III dummy. The interior model was then combined with the human body model THUMS and validated by means of mechanical PMHS sled tests. Occupant kinematics as well as rib fracture patterns were predicted with reasonable accuracy.The final model was updated to conform to modern cars and a simulation matrix was run. In this matrix the boundary conditions, ΔV and PDOF, were varied and rib fracture risk as a function of the boundary conditions was evaluated using a statistical framework.In oblique frontal impacts, two injury producing mechanisms were found; (i) diagonal belt load and (ii) side structure impact. The second injury mechanism was found for PDOFs of 25°-35°, depending on ΔV. This means that for larger PDOFs, less ΔV is needed to cause a serious chest injury.

  8. Underlying brain mechanisms that regulate sleep-wakefulness cycles.

    PubMed

    Gvilia, Irma

    2010-01-01

    Daily cycles of wakefulness and sleep are regulated by coordinated interactions between wakefulness- and sleep-regulating neural circuitry. Wakefulness is associated with neuronal activity in cholinergic neurons in the brainstem and basal forebrain, monoaminergic neurons in the brainstem and posterior hypothalamus, and hypocretin (orexin) neurons in the lateral hypothalamus that act in a coordinated manner to stimulate cortical activation on the one hand and behavioral arousal on the other hand. Each of these neuronal groups subserves distinct aspects of wakefulness-related functions of the brain. Normal transitions from wakefulness to sleep involve sleep-related inhibition and/or disfacilitation of the multiple arousal systems. The cell groups that shut off the network of arousal systems, at sleep onset, occur with high density in the ventral lateral preoptic area (VLPO) and the median preoptic nucleus (MnPN) of the hypothalamus. Preoptic neurons are activated during sleep and exhibit sleep-wake state-dependent discharge patterns that are reciprocal of that observed in several arousal systems. Neurons in the VLPO contain the inhibitory neuromodulator, galanin, and the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). The majority of MnPN sleep-active neurons synthesize GABA. VLPO and MnPN neurons are sources of projections to arousal-regulatory systems in the posterior and lateral hypothalamus and the rostral brainstem. Mechanisms of sleep induction by these nuclei are hypothesized to involve GABA-mediated inhibition of multiple arousal systems. Normal cycling between discrete behavioral states is mediated by the combined influence of a sleep need that increases with continued wakefulness and an intrinsic circadian oscillation. This chapter will review anatomical and functional properties of populations of sleep-/wake-regulating neurons, focusing on recent findings supporting functional significance of the VLPO and MnPN in the regulation of sleep

  9. Evaluation of DOVID security under first-line inspection

    NASA Astrophysics Data System (ADS)

    Andrade, Ana A.; Rebordao, Jose M.

    2002-04-01

    The relative value of optical security features submitted to 1st line inspection - performed by the layman - depends on how easily they are memorized, recognized and identified. The relative security value of different Diffractive Optically Variable Image Devices (DOVID), under this type of inspection, depends on the same criteria taking specific forms for such kind of dense and dynamical visual elements. For DOVID, the relevant security components include image complexity, resemblance to other images, easiness of inspection, interconnection to product characteristics, and others. In this paper we review and analyze such kind of properties and how they can be used to implement a quantitative measure of the 1st line security value of DOVID, encompassing a number of constrains and specifications derived from human ergonomic factors. These insights are integrated in a broader context of an evaluation model of the security value of DOVID, elaborated through Multicriteria Decision Analysis methodologies, already assessed for 2nd line inspection.

  10. Common neural mechanisms underlying reversal learning by reward and punishment.

    PubMed

    Xue, Gui; Xue, Feng; Droutman, Vita; Lu, Zhong-Lin; Bechara, Antoine; Read, Stephen

    2013-01-01

    Impairments in flexible goal-directed decisions, often examined by reversal learning, are associated with behavioral abnormalities characterized by impulsiveness and disinhibition. Although the lateral orbital frontal cortex (OFC) has been consistently implicated in reversal learning, it is still unclear whether this region is involved in negative feedback processing, behavioral control, or both, and whether reward and punishment might have different effects on lateral OFC involvement. Using a relatively large sample (N = 47), and a categorical learning task with either monetary reward or moderate electric shock as feedback, we found overlapping activations in the right lateral OFC (and adjacent insula) for reward and punishment reversal learning when comparing correct reversal trials with correct acquisition trials, whereas we found overlapping activations in the right dorsolateral prefrontal cortex (DLPFC) when negative feedback signaled contingency change. The right lateral OFC and DLPFC also showed greater sensitivity to punishment than did their left homologues, indicating an asymmetry in how punishment is processed. We propose that the right lateral OFC and anterior insula are important for transforming affective feedback to behavioral adjustment, whereas the right DLPFC is involved in higher level attention control. These results provide insight into the neural mechanisms of reversal learning and behavioral flexibility, which can be leveraged to understand risky behaviors among vulnerable populations.

  11. Linking Pesticide Exposure with Pediatric Leukemia: Potential Underlying Mechanisms.

    PubMed

    Hernández, Antonio F; Menéndez, Pablo

    2016-03-29

    Leukemia is the most common cancer in children, representing 30% of all childhood cancers. The disease arises from recurrent genetic insults that block differentiation of hematopoietic stem and/or progenitor cells (HSPCs) and drives uncontrolled proliferation and survival of the differentiation-blocked clone. Pediatric leukemia is phenotypically and genetically heterogeneous with an obscure etiology. The interaction between genetic factors and environmental agents represents a potential etiological driver. Although information is limited, the principal toxic mechanisms of potential leukemogenic agents (e.g., etoposide, benzene metabolites, bioflavonoids and some pesticides) include topoisomerase II inhibition and/or excessive generation of free radicals, which may induce DNA single- and double-strand breaks (DNA-DSBs) in early HSPCs. Chromosomal rearrangements (duplications, deletions and translocations) may occur if these lesions are not properly repaired. The initiating hit usually occurs in utero and commonly leads to the expression of oncogenic fusion proteins. Subsequent cooperating hits define the disease latency and occur after birth and may be of a genetic, epigenetic or immune nature (i.e., delayed infection-mediated immune deregulation). Here, we review the available experimental and epidemiological evidence linking pesticide exposure to infant and childhood leukemia and provide a mechanistic basis to support the association, focusing on early initiating molecular events.

  12. [Study on novel mechanism underlying analgesia targeting TRPV1].

    PubMed

    Maeda, Takehiko; Ozaki, Masanobu

    2014-01-01

    Transient receptor potential protein (TRP) channels are distributed in pain pathways including primary afferent neurons and function as transduction of various noxious stimuli to innocuous stimuli. TRP channels are considered as molecular basis of chronic pain. Targeting TRPs may lead to novel class of analgesics, and so drug-discovery efforts are focused on TRP agonists and its antagonists. Few products have, however, been placed on the market, because most of candidates have adverse effects. A lesion or disease of the somatosensory nervous system causes neuropathic pain, a type of chronic pain. Neuropathic pain is intolerable and obstinate and therefore, debilitates the affected patients. A great deal of effort has been made to develop medicine targeting molecules involved in neuropathic pain, whereby the promising therapeutically targeted molecules have been identified. Neuroinflammation, based on pathological alteration in crosstalk between nervous system and immune system, has been a focus of attention as pathological mechanism involved in development of neuropathic pain. Recently, we used an animal model for neuropathic pain to find the possibility that neuropathic pain was exacerbated by adipokines derived from perineural adipocytes distributed in injured peripheral neurons. A working hypothesis is therefore proposed that the perineural adipocytes interacts with the immune cells, which also have TRPV1, in injured peripheral nerve, followed by a paracrine loop involving proinflammatory cytokines, chemokines and adipokines derived from them which aggravates and prolongs pain. Here, we overview the developmental status in TRPV1-targetting analgesics and illustrate our recent findings in terms of neuroinflammation.

  13. Neural mechanisms underlying social conformity in an ultimatum game.

    PubMed

    Wei, Zhenyu; Zhao, Zhiying; Zheng, Yong

    2013-01-01

    When individuals' actions are incongruent with those of the group they belong to, they may change their initial behavior in order to conform to the group norm. This phenomenon is known as "social conformity." In the present study, we used event-related functional magnetic resonance imaging (fMRI) to investigate brain activity in response to group opinion during an ultimatum game. Results showed that participants changed their choices when these choices conflicted with the normative opinion of the group they were members of, especially in conditions of unfair treatment. The fMRI data revealed that a conflict with group norms activated the brain regions involved in norm violations and behavioral adjustment. Furthermore, in the reject-unfair condition, we observed that a conflict with group norms activated the medial frontal gyrus. These findings contribute to recent research examining neural mechanisms involved in detecting violations of social norms, and provide information regarding the neural representation of conformity behavior in an economic game.

  14. The neural sociometer: brain mechanisms underlying state self-esteem.

    PubMed

    Eisenberger, Naomi I; Inagaki, Tristen K; Muscatell, Keely A; Byrne Haltom, Kate E; Leary, Mark R

    2011-11-01

    On the basis of the importance of social connection for survival, humans may have evolved a "sociometer"-a mechanism that translates perceptions of rejection or acceptance into state self-esteem. Here, we explored the neural underpinnings of the sociometer by examining whether neural regions responsive to rejection or acceptance were associated with state self-esteem. Participants underwent fMRI while viewing feedback words ("interesting," "boring") ostensibly chosen by another individual (confederate) to describe the participant's previously recorded interview. Participants rated their state self-esteem in response to each feedback word. Results demonstrated that greater activity in rejection-related neural regions (dorsal ACC, anterior insula) and mentalizing regions was associated with lower-state self-esteem. Additionally, participants whose self-esteem decreased from prescan to postscan versus those whose self-esteem did not showed greater medial prefrontal cortical activity, previously associated with self-referential processing, in response to negative feedback. Together, the results inform our understanding of the origin and nature of our feelings about ourselves.

  15. Dissociable early attentional control mechanisms underlying cognitive and affective conflicts

    PubMed Central

    Chen, Taolin; Kendrick, Keith M.; Feng, Chunliang; Sun, Shiyue; Yang, Xun; Wang, Xiaogang; Luo, Wenbo; Yang, Suyong; Huang, Xiaoqi; Valdés-Sosa, Pedro A.; Gong, Qiyong; Fan, Jin; Luo, Yue-Jia

    2016-01-01

    It has been well documented that cognitive conflict is sensitive to the relative proportion of congruent and incongruent trials. However, few studies have examined whether affective conflict processing is modulated as a function of proportion congruency (PC). To address this question we recorded event-related potentials (ERP) while subjects performed both cognitive and affective face-word Stroop tasks. By varying the proportion of congruent and incongruent trials in each block, we examined the extent to which PC impacts both cognitive and affective conflict control at different temporal stages. Results showed that in the cognitive task an anteriorly localized early N2 component occurred predominantly in the low proportion congruency context, whereas in the affective task it was found to occur in the high proportion congruency one. The N2 effects across the two tasks were localized to the dorsolateral prefrontal cortex, where responses were increased in the cognitive task but decreased in the affective one. Furthermore, high proportions of congruent items produced both larger amplitude of a posteriorly localized sustained potential component and a larger behavioral Stroop effect in cognitive and affective tasks. Our findings suggest that cognitive and affective conflicts engage early dissociable attentional control mechanisms and a later common conflict response system. PMID:27892513

  16. Mechanisms underlying the formation of induced pluripotent stem cells.

    PubMed

    González, Federico; Huangfu, Danwei

    2016-01-01

    Human pluripotent stem cells (hPSCs) offer unique opportunities for studying human biology, modeling diseases, and therapeutic applications. The simplest approach so far to generate human PSC lines is through reprogramming of somatic cells from an individual by defined factors, referred to simply as reprogramming. Reprogramming circumvents the ethical controversies associated with human embryonic stem cells (hESCs) and nuclear transfer hESCs (nt-hESCs), and the resulting induced pluripotent stem cells (hiPSCs) retain the same basic genetic makeup as the somatic cell used for reprogramming. Since the first report of iPSCs by Takahashi and Yamanaka (Cell 2006, 126:663-676), the molecular mechanisms of reprogramming have been extensively investigated. A better mechanistic understanding of reprogramming is fundamental not only to iPSC biology and improving the quality of iPSCs for therapeutic use, but also to our understanding of the molecular basis of cell identity, pluripotency, and plasticity. Here, we summarize the genetic, epigenetic, and cellular events during reprogramming, and the roles of various factors identified thus far in the reprogramming process. WIREs Dev Biol 2016, 5:39-65. doi: 10.1002/wdev.206 For further resources related to this article, please visit the WIREs website.

  17. Focal-contact clusterization of osteoblasts under mechanical stresses

    NASA Astrophysics Data System (ADS)

    Guignandon, A.; Akhouayri, O.; Laroche, N.; Alexandre, C.; Vico, L.

    We compared quantitatively vinculin-related adhesion parameters in osteoblastic cells submitted to opposite mechanical stress (i.e. low deformation and frequency strain regimens (strained condition) and microgravity exposure (relaxed condition). In both ROS 17/2.8 and rat primary osteoblastic cells, 1% cyclic deformations at 0.05 Hz during a daily 10 min episode over 7 days stimulated cell growth whereas relaxed ROS proliferated similarly to static culture (BC). We studied short term (up to 24 hrs) adaptation of focal contact re-organization in these two conditions. Strain induced a biphasic response comprising new focal contacts formation followed by their clusterization in both ROS and primary osteoblasts. Microgravity exposure induced a reduction in focal contact number and clusterization in ROS cells. To relate the proliferation (strain) or the survival (relaxed) status of ROS cells with focal contact organization, we inhibited ERKs proliferative-dependent pathway. Inhibition of proliferation by PD98059 was overcome although not fully restored by strain and strain-induced clusterization of vinculin positive contact still occurs in presence of PD98059 whereas the increase in focal contact number is abolished. In conclusion, we showed that focal contacts are mechanoeffectors and we suggested that their morphological organization might serve as a discriminant functional parameter between survival and proliferation status in ROS 17/2.8 osteoblastic cells.

  18. Mechanisms Underlying Desynchronization of Cholinergic-Evoked Thalamic Network Activity

    PubMed Central

    Pita-Almenar, Juan Diego; Yu, Dinghui; Lu, Hui-Chen

    2014-01-01

    Synchronous neuronal activity in the thalamocortical system is critical for a number of behaviorally relevant computations, but hypersynchrony can limit information coding and lead to epileptiform responses. In the somatosensory thalamus, afferent inputs are transformed by networks of reciprocally connected thalamocortical neurons in the ventrobasal nucleus (VB) and GABAergic neurons in the thalamic reticular nucleus (TRN). These networks can generate oscillatory activity, and studies in vivo and in vitro have suggested that thalamic oscillations are often accompanied by synchronous neuronal activity, in part mediated by widespread divergence and convergence of both reticulothalamic and thalamoreticular pathways, as well as by electrical synapses interconnecting TRN neurons. However, the functional organization of thalamic circuits and its role in shaping input-evoked activity patterns remain poorly understood. Here we show that optogenetic activation of cholinergic synaptic afferents evokes near-synchronous firing in mouse TRN neurons that is rapidly desynchronized in thalamic networks. We identify several mechanisms responsible for desynchronization: (1) shared inhibitory inputs in local VB neurons leading to asynchronous and imprecise rebound bursting; (2) TRN-mediated lateral inhibition that further desynchronizes firing in the VB; and (3) powerful yet sparse thalamoreticular connectivity that mediates re-excitation of the TRN but preserves asynchronous firing. Our findings reveal how distinct local circuit features interact to desynchronize thalamic network activity. PMID:25339757

  19. Pathophysiological mechanisms underlying phenotypic differences in pulmonary radioresponse

    PubMed Central

    Jackson, Isabel L.; Zhang, Yuji; Bentzen, Søren M.; Hu, Jingping; Zhang, Angel; Vujaskovic, Zeljko

    2016-01-01

    Differences in the pathogenesis of radiation-induced lung injury among murine strains offer a unique opportunity to elucidate the molecular mechanisms driving the divergence in tissue response from repair and recovery to organ failure. Here, we utilized two well-characterized murine models of radiation pneumonitis/fibrosis to compare and contrast differential gene expression in lungs 24 hours after exposure to a single dose of whole thorax lung irradiation sufficient to cause minor to major morbidity/mortality. Expression of 805 genes was altered as a general response to radiation; 42 genes were identified whose expression corresponded to the threshold for lethality. Three genes were discovered whose expression was altered within the lethal, but not the sublethal, dose range. Time-course analysis of the protein product of the most promising gene, resistin-like molecule alpha, demonstrated a significant difference in expression between radiosensitive versus radiotolerant strains, suggesting a unique role for this protein in acute lung injury. PMID:27845360

  20. Linking Pesticide Exposure with Pediatric Leukemia: Potential Underlying Mechanisms

    PubMed Central

    Hernández, Antonio F.; Menéndez, Pablo

    2016-01-01

    Leukemia is the most common cancer in children, representing 30% of all childhood cancers. The disease arises from recurrent genetic insults that block differentiation of hematopoietic stem and/or progenitor cells (HSPCs) and drives uncontrolled proliferation and survival of the differentiation-blocked clone. Pediatric leukemia is phenotypically and genetically heterogeneous with an obscure etiology. The interaction between genetic factors and environmental agents represents a potential etiological driver. Although information is limited, the principal toxic mechanisms of potential leukemogenic agents (e.g., etoposide, benzene metabolites, bioflavonoids and some pesticides) include topoisomerase II inhibition and/or excessive generation of free radicals, which may induce DNA single- and double-strand breaks (DNA-DSBs) in early HSPCs. Chromosomal rearrangements (duplications, deletions and translocations) may occur if these lesions are not properly repaired. The initiating hit usually occurs in utero and commonly leads to the expression of oncogenic fusion proteins. Subsequent cooperating hits define the disease latency and occur after birth and may be of a genetic, epigenetic or immune nature (i.e., delayed infection-mediated immune deregulation). Here, we review the available experimental and epidemiological evidence linking pesticide exposure to infant and childhood leukemia and provide a mechanistic basis to support the association, focusing on early initiating molecular events. PMID:27043530

  1. Mechanisms Underlying Acute Protection from Cardiac Ischemia-Reperfusion Injury

    PubMed Central

    Murphy, Elizabeth; Steenbergen, Charles

    2009-01-01

    Mitochondria play an important role in cell death and cardioprotection. During ischemia, when ATP is progressively deleted, ion pumps cannot function resulting in a rise in calcium (Ca2+), which further accelerates ATP depletion. The rise in Ca2+ during ischemia and reperfusion leads to mitochondrial Ca2+ accumulation, particularly during reperfusion when oxygen is reintroduced. Reintroduction of oxygen allows generation of ATP; however damage to electron transport chain results in increased mitochondrial generation of reactive oxygen species (ROS). Mitochondrial Ca2+ overload, and increased ROS can result in opening of the mitochondrial permeability transition pore, which further compromises cellular energetics. The resultant low ATP and altered ion homeostasis result in rupture of the plasma membrane and cell death. Mitochondria have long been proposed as central players in cell death, since the mitochondria are central to synthesis of both ATP and ROS and since mitochondrial and cytosolic Ca2+ overload are key components of cell death. Many cardioprotective mechanisms converge on the mitochondria to reduce cell death. Reducing Ca2+ overload and reducing ROS have both been reported to reduce ischemic injury. Preconditioning activates a number of signaling pathways that reduce Ca2+ overload and reduce activation of the mitochondrial permeability transition pore. The mitochondrial targets of cardioprotective signals will be discussed in detail. PMID:18391174

  2. Signaling mechanisms underlying the insulin-sensitizing effects of adiponectin.

    PubMed

    Cheng, Kenneth K Y; Lam, Karen S L; Wang, Baile; Xu, Aimin

    2014-01-01

    Adiponectin is an insulin-sensitizing adipokine with protective effects against a cluster of obesity-related metabolic and cardiovascular disorders. The adipokine exerts its insulin-sensitizing effects by alleviation of obesity-induced ectopic lipid accumulation, lipotoxicity and chronic inflammation, as well as by direct cross-talk with insulin signaling cascades. Adiponectin and insulin signaling pathways converge at the adaptor protein APPL1. On the one hand, APPL1 interacts with adiponectin receptors and mediates both metabolic and vascular actions of adiponectin through activation of AMP-activated protein kinase and p38 MAP kinase. On the other hand, APPL1 potentiates both the actions and secretion of insulin by fine-tuning the Akt activity in multiple insulin target tissues. In obese animals, reduced APPL1 expression contributes to both insulin resistance and defective insulin secretion. This review summarizes recent advances on the molecular mechanisms by which adiponectin sensitizes insulin actions, and discusses the roles of APPL1 in regulating both adiponectin and insulin signaling cascades.

  3. Assessing mechanical vulnerability in water distribution networks under multiple failures

    NASA Astrophysics Data System (ADS)

    Berardi, Luigi; Ugarelli, Rita; Røstum, Jon; Giustolisi, Orazio

    2014-03-01

    Understanding mechanical vulnerability of water distribution networks (WDN) is of direct relevance for water utilities since it entails two different purposes. On the one hand, it might support the identification of severe failure scenarios due to external causes (e.g., natural or intentional events) which result into the most critical consequences on WDN supply capacity. On the other hand, it aims at figure out the WDN portions which are more prone to be affected by asset disruptions. The complexity of such analysis stems from the number of possible scenarios with single and multiple simultaneous shutdowns of asset elements leading to modifications of network topology and insufficient water supply to customers. In this work, the search for the most disruptive combinations of multiple asset failure events is formulated and solved as a multiobjective optimization problem. The higher vulnerability failure scenarios are detected as those causing the lower supplied demand due to the lower number of simultaneous failures. The automatic detection of WDN topology, subsequent to the detachments of failed elements, is combined with pressure-driven analysis. The methodology is demonstrated on a real water distribution network. Results show that, besides the failures causing the detachment of reservoirs, tanks, or pumps, there are other different topological modifications which may cause severe WDN service disruptions. Such information is of direct relevance to support planning asset enhancement works and improve the preparedness to extreme events.

  4. Dissociable early attentional control mechanisms underlying cognitive and affective conflicts.

    PubMed

    Chen, Taolin; Kendrick, Keith M; Feng, Chunliang; Sun, Shiyue; Yang, Xun; Wang, Xiaogang; Luo, Wenbo; Yang, Suyong; Huang, Xiaoqi; Valdés-Sosa, Pedro A; Gong, Qiyong; Fan, Jin; Luo, Yue-Jia

    2016-11-28

    It has been well documented that cognitive conflict is sensitive to the relative proportion of congruent and incongruent trials. However, few studies have examined whether affective conflict processing is modulated as a function of proportion congruency (PC). To address this question we recorded event-related potentials (ERP) while subjects performed both cognitive and affective face-word Stroop tasks. By varying the proportion of congruent and incongruent trials in each block, we examined the extent to which PC impacts both cognitive and affective conflict control at different temporal stages. Results showed that in the cognitive task an anteriorly localized early N2 component occurred predominantly in the low proportion congruency context, whereas in the affective task it was found to occur in the high proportion congruency one. The N2 effects across the two tasks were localized to the dorsolateral prefrontal cortex, where responses were increased in the cognitive task but decreased in the affective one. Furthermore, high proportions of congruent items produced both larger amplitude of a posteriorly localized sustained potential component and a larger behavioral Stroop effect in cognitive and affective tasks. Our findings suggest that cognitive and affective conflicts engage early dissociable attentional control mechanisms and a later common conflict response system.

  5. Molecular mechanism for cavitation in water under tension.

    PubMed

    Menzl, Georg; Gonzalez, Miguel A; Geiger, Philipp; Caupin, Frédéric; Abascal, José L F; Valeriani, Chantal; Dellago, Christoph

    2016-11-29

    Despite its relevance in biology and engineering, the molecular mechanism driving cavitation in water remains unknown. Using computer simulations, we investigate the structure and dynamics of vapor bubbles emerging from metastable water at negative pressures. We find that in the early stages of cavitation, bubbles are irregularly shaped and become more spherical as they grow. Nevertheless, the free energy of bubble formation can be perfectly reproduced in the framework of classical nucleation theory (CNT) if the curvature dependence of the surface tension is taken into account. Comparison of the observed bubble dynamics to the predictions of the macroscopic Rayleigh-Plesset (RP) equation, augmented with thermal fluctuations, demonstrates that the growth of nanoscale bubbles is governed by viscous forces. Combining the dynamical prefactor determined from the RP equation with CNT based on the Kramers formalism yields an analytical expression for the cavitation rate that reproduces the simulation results very well over a wide range of pressures. Furthermore, our theoretical predictions are in excellent agreement with cavitation rates obtained from inclusion experiments. This suggests that homogeneous nucleation is observed in inclusions, whereas only heterogeneous nucleation on impurities or defects occurs in other experiments.

  6. Risk factors for pancreatic cancer: underlying mechanisms and potential targets

    PubMed Central

    Kolodecik, Thomas; Shugrue, Christine; Ashat, Munish; Thrower, Edwin C.

    2014-01-01

    Purpose of the review: Pancreatic cancer is extremely aggressive, forming highly chemo-resistant tumors, and has one of the worst prognoses. The evolution of this cancer is multi-factorial. Repeated acute pancreatic injury and inflammation are important contributing factors in the development of pancreatic cancer. This article attempts to understand the common pathways linking pancreatitis to pancreatic cancer. Recent findings: Intracellular activation of both pancreatic enzymes and the transcription factor NF-κB are important mechanisms that induce acute pancreatitis (AP). Recurrent pancreatic injury due to genetic susceptibility, environmental factors such as smoking, alcohol intake, and conditions such as obesity lead to increases in oxidative stress, impaired autophagy and constitutive activation of inflammatory pathways. These processes can stimulate pancreatic stellate cells, thereby increasing fibrosis and encouraging chronic disease development. Activation of oncogenic Kras mutations through inflammation, coupled with altered levels of tumor suppressor proteins (p53 and p16) can ultimately lead to development of pancreatic cancer. Summary: Although our understanding of pancreatitis and pancreatic cancer has tremendously increased over many years, much remains to be elucidated in terms of common pathways linking these conditions. PMID:24474939

  7. Comparative analysis reveals the underlying mechanism of vertebrate seasonal reproduction.

    PubMed

    Ikegami, Keisuke; Yoshimura, Takashi

    2016-02-01

    Animals utilize photoperiodic changes as a calendar to regulate seasonal reproduction. Birds have highly sophisticated photoperiodic mechanisms and functional genomics analysis in quail uncovered the signal transduction pathway regulating avian seasonal reproduction. Birds detect light with deep brain photoreceptors. Long day (LD) stimulus induces secretion of thyroid-stimulating hormone (TSH) from the pars tuberalis (PT) of the pituitary gland. PT-derived TSH locally activates thyroid hormone (TH) in the hypothalamus, which induces gonadotropin-releasing hormone (GnRH) and hence gonadotropin secretion. However, during winter, low temperatures increase serum TH for adaptive thermogenesis, which accelerates germ cell apoptosis by activating the genes involved in metamorphosis. Therefore, TH has a dual role in the regulation of seasonal reproduction. Studies using TSH receptor knockout mice confirmed the involvement of PT-derived TSH in mammalian seasonal reproduction. In addition, studies in mice revealed that the tissue-specific glycosylation of TSH diversifies its function in the circulation to avoid crosstalk. In contrast to birds and mammals, one of the molecular machineries necessary for the seasonal reproduction of fish are localized in the saccus vasculosus from the photoreceptor to the neuroendocrine output. Thus, comparative analysis is a powerful tool to uncover the universality and diversity of fundamental properties in various organisms.

  8. Consensus Paper: Pathological Mechanisms Underlying Neurodegeneration in Spinocerebellar Ataxias

    PubMed Central

    Matilla-Dueñas, A.; Ashizawa, T.; Brice, A.; Magri, S.; McFarland, K. N.; Pandolfo, M.; Pulst, S. M.; Riess, O.; Rubinsztein, D. C.; Schmidt, J.; Schmidt, T.; Scoles, D. R.; Stevanin, G.; Taroni, F.; Underwood, B. R.; Sánchez, I.

    2014-01-01

    Intensive scientific research devoted in the recent years to understand the molecular mechanisms or neurodegeneration in spinocerebellar ataxias (SCAs) are identifying new pathways and targets providing new insights and a better understanding of the molecular pathogenesis in these diseases. In this consensus manuscript, the authors discuss their current views on the identified molecular processes causing or modulating the neurodegenerative phenotype in spinocerebellar ataxias with the common opinion of translating the new knowledge acquired into candidate targets for therapy. The following topics are discussed: transcription dysregulation, protein aggregation, autophagy, ion channels, the role of mitochondria, RNA toxicity, modulators of neurodegeneration and current therapeutic approaches. Overall point of consensus includes the common vision of neurodegeneration in SCAs as a multifactorial, progressive and reversible process, at least in early stages. Specific points of consensus include the role of the dysregulation of protein folding, transcription, bioenergetics, calcium handling and eventual cell death with apoptotic features of neurons during SCA disease progression. Unresolved questions include how the dysregulation of these pathways triggers the onset of symptoms and mediates disease progression since this understanding may allow effective treatments of SCAs within the window of reversibility to prevent early neuronal damage. Common opinions also include the need for clinical detection of early neuronal dysfunction, for more basic research to decipher the early neurodegenerative process in SCAs in order to give rise to new concepts for treatment strategies and for the translation of the results to preclinical studies and, thereafter, in clinical practice. PMID:24307138

  9. Raynaud's Phenomenon: A Brief Review of the Underlying Mechanisms.

    PubMed

    Fardoun, Manal M; Nassif, Joseph; Issa, Khodr; Baydoun, Elias; Eid, Ali H

    2016-01-01

    Raynaud's phenomenon (RP) is characterized by exaggerated cold-induced vasoconstriction. This augmented vasoconstriction occurs by virtue of a reflex response to cooling via the sympathetic nervous system as well as by local activation of α2C adrenoceptors (α2C-AR). In a cold-initiated, mitochondrion-mediated mechanism involving reactive oxygen species and the Rho/ROCK pathway, cytoskeletal rearrangement in vascular smooth muscle cells orchestrates the translocation of α2C-AR to the cell membrane, where this receptor readily interacts with its ligand. Different parameters are involved in this spatial and functional rescue of α2C-AR. Of notable relevance is the female hormone, 17β-estradiol, or estrogen. This is consistent with the high prevalence of RP in premenopausal women compared to age-matched males. In addition to dissecting the role of these various players, the contribution of pollution as well as genetic background to the onset and prevalence of RP are also discussed. Different therapeutic approaches employed as treatment modalities for this disease are also highlighted and analyzed. The lack of an appropriate animal model for RP mandates that more efforts be undertaken in order to better understand and eventually treat this disease. Although several lines of treatment are utilized, it is important to note that precaution is often effective in reducing severity or frequency of RP attacks.

  10. Miniaturization and Evaluation of Laser Communication System for Satellite by 2-Axis Steering Mirror Mechanism

    NASA Astrophysics Data System (ADS)

    Aoyanagi, Yoshihide; Kato, Toshiki; Yasunaka, Toshihiko; Uematsu, Tsutomu; Satori, Shin

    A laser communication system has an advantage of realizing the high speed transmission under the conditions of small size and low electrical power. The laser communication system requires a high accuracy of pointing control because of the directional characteristics of laser beam. Due to the attitude control accuracy of micro-satellites, the pointing device carried in micro-satellite is required to have mitigated pointing accuracy, wide range pointing, small size, mass and low electrical power. We have developed a new pointing device characterized by two-axis pointing control mechanism. Breadboard model of pointing control mechanism consists of steering mirror, angular sensor and electrical unit. The steering mirror mechanism is accomplished using rod-end-bearings. The pointing accuracy and the performance of tracking system of the laser communication device were evaluated in simulator of between satellite and ground station. This paper describes development of the breadboard model of pointing control mechanism and the performance evaluation.

  11. Neural mechanism underlying autobiographical memory modulated by remoteness and emotion

    NASA Astrophysics Data System (ADS)

    Ge, Ruiyang; Fu, Yan; Wang, DaHua; Yao, Li; Long, Zhiying

    2012-03-01

    Autobiographical memory is the ability to recollect past events from one's own life. Both emotional tone and memory remoteness can influence autobiographical memory retrieval along the time axis of one's life. Although numerous studies have been performed to investigate brain regions involved in retrieving processes of autobiographical memory, the effect of emotional tone and memory age on autobiographical memory retrieval remains to be clarified. Moreover, whether the involvement of hippocampus in consolidation of autobiographical events is time dependent or independent has been controversial. In this study, we investigated the effect of memory remoteness (factor1: recent and remote) and emotional valence (factor2: positive and negative) on neural correlates underlying autobiographical memory by using functional magnetic resonance imaging (fMRI) technique. Although all four conditions activated some common regions known as "core" regions in autobiographical memory retrieval, there are some other regions showing significantly different activation for recent versus remote and positive versus negative memories. In particular, we found that bilateral hippocampal regions were activated in the four conditions regardless of memory remoteness and emotional valence. Thus, our study confirmed some findings of previous studies and provided further evidence to support the multi-trace theory which believes that the role of hippocampus involved in autobiographical memory retrieval is time-independent and permanent in memory consolidation.

  12. Molecular mechanisms underlying a cellular analogue of operant reward learning

    PubMed Central

    Lorenzetti, Fred D.; Baxter, Douglas A.; Byrne, John H.

    2008-01-01

    SUMMARY Operant conditioning is a ubiquitous but mechanistically poorly understood form of associative learning in which an animal learns the consequences of its behavior. Using a single-cell analogue of operant conditioning in neuron B51 of Aplysia, we examined second-messenger pathways engaged by activity and reward and how they may provide a biochemical association underlying operant learning. Conditioning was blocked by Rp-cAMP, a peptide inhibitor of PKA, a PKC inhibitor and by expressing a dominant negative isoform of Ca2+-dependent PKC (apl-I). Thus, both PKA and PKC were necessary for operant conditioning. Injection of cAMP into B51 mimicked the effects of operant conditioning. Activation of PKC also mimicked conditioning, but was dependent on both cAMP and PKA, suggesting that PKC acted at some point upstream of PKA activation. Our results demonstrate how these molecules can interact to mediate operant conditioning in an individual neuron important for the expression of the conditioned behavior. PMID:18786364

  13. Mechanical Model for Dynamic Behavior of Concrete Under Impact Loading

    NASA Astrophysics Data System (ADS)

    Sun, Yuanxiang

    Concrete is a geo-material which is used substantively in the civil building and military safeguard. One coupled model of damage and plasticity to describe the complex behavior of concrete subjected to impact loading is proposed in this research work. The concrete is assumed as homogeneous continuum with pre-existing micro-cracks and micro-voids. Damage to concrete is caused due to micro-crack nucleation, growth and coalescence, and defined as the probability of fracture at a given crack density. It induces a decrease of strength and stiffness of concrete. Compaction of concrete is physically a collapse of the material voids. It produces the plastic strain in the concrete and, at the same time, an increase of the bulk modulus. In terms of crack growth model, micro-cracks are activated, and begin to propagate gradually. When crack density reaches a critical value, concrete takes place the smashing destroy. The model parameters for mortar are determined using plate impact experiment with uni-axial strain state. Comparison with the test results shows that the proposed model can give consistent prediction of the impact behavior of concrete. The proposed model may be used to design and analysis of concrete structures under impact and shock loading. This work is supported by State Key Laboratory of Explosion science and Technology, Beijing Institute of Technology (YBKT14-02).

  14. Price Analysis of Railway Freight Transport under Marketing Mechanism

    NASA Astrophysics Data System (ADS)

    Shi, Ying; Fang, Xiaoping; Chen, Zhiya

    Regarding the problems in the reform of the railway tariff system and the pricing of the transport, by means of assaying the influence of the price elasticity on the artifice used for price, this article proposed multiple regressive model which analyzed price elasticity quantitatively. This model conclude multi-factors which influences on the price elasticity, such as the averagely railway freight charge, the averagely freight haulage of proximate supersede transportation mode, the GDP per capita in the point of origin, and a series of dummy variable which can reflect the features of some productive and consume demesne. It can calculate the price elasticity of different classes in different domains, and predict the freight traffic volume on different rate levels. It can calculate confidence-level, and evaluate the relevance of each parameter to get rid of irrelevant or little relevant variables. It supplied a good theoretical basis for directing the pricing of transport enterprises in market economic conditions, which is suitable for railway freight, passenger traffic and other transportation manner as well. SPSS (Statistical Package for the Social Science) software was used to calculate and analysis the example. This article realized the calculation by HYFX system(Ministry of Railways fund).

  15. Enhancement of sleep slow waves: underlying mechanisms and practical consequences

    PubMed Central

    Bellesi, Michele; Riedner, Brady A.; Garcia-Molina, Gary N.; Cirelli, Chiara; Tononi, Giulio

    2014-01-01

    Even modest sleep restriction, especially the loss of sleep slow wave activity (SWA), is invariably associated with slower electroencephalogram (EEG) activity during wake, the occurrence of local sleep in an otherwise awake brain, and impaired performance due to cognitive and memory deficits. Recent studies not only confirm the beneficial role of sleep in memory consolidation, but also point to a specific role for sleep slow waves. Thus, the implementation of methods to enhance sleep slow waves without unwanted arousals or lightening of sleep could have significant practical implications. Here we first review the evidence that it is possible to enhance sleep slow waves in humans using transcranial direct-current stimulation (tDCS) and transcranial magnetic stimulation. Since these methods are currently impractical and their safety is questionable, especially for chronic long-term exposure, we then discuss novel data suggesting that it is possible to enhance slow waves using sensory stimuli. We consider the physiology of the K-complex (KC), a peripheral evoked slow wave, and show that, among different sensory modalities, acoustic stimulation is the most effective in increasing the magnitude of slow waves, likely through the activation of non-lemniscal ascending pathways to the thalamo-cortical system. In addition, we discuss how intensity and frequency of the acoustic stimuli, as well as exact timing and pattern of stimulation, affect sleep enhancement. Finally, we discuss automated algorithms that read the EEG and, in real-time, adjust the stimulation parameters in a closed-loop manner to obtain an increase in sleep slow waves and avoid undesirable arousals. In conclusion, while discussing the mechanisms that underlie the generation of sleep slow waves, we review the converging evidence showing that acoustic stimulation is safe and represents an ideal tool for slow wave sleep (SWS) enhancement. PMID:25389394

  16. Molecular mechanisms underlying the breakdown of gametophytic self-incompatibility.

    PubMed

    Stone, J L

    2002-03-01

    The breakdown of self-incompatibility has occurred repeatedly throughout the evolution of flowering plants and has profound impacts on the genetic structure of populations. Recent advances in understanding of the molecular basis of self-incompatibility have provided insights into the mechanisms of its loss in natural populations, especially in the tomato family, the Solanaceae. In the Solanaceae, the gene that controls self-incompatibility in the style codes for a ribonuclease that causes the degradation of RNA in pollen tubes bearing an allele at the S-locus that matches either of the two alleles held by the maternal plant. The pollen component of the S-locus has yet to be identified. Loss of self-incompatibility can be attributed to three types of causes: duplication of the S-locus, mutations that cause loss of S-RNase activity, and mutations that do not cause loss of S-RNase activity. Duplication of the S-locus has been well studied in radiation-induced mutants but may be a relatively rare cause of the breakdown of self-incompatibility in nature. Point mutations within the S-locus that disrupt the production of S-RNase have been documented in natural populations. There are also a number of mutants in which S-RNase production is unimpaired, yet self-incompatibility is disrupted. The identity and function of these mutations is not well understood. Careful work on a handful of model organisms will enable population biologists to better understand the breakdown of self-incompatibility in nature.

  17. Enhancement of sleep slow waves: underlying mechanisms and practical consequences.

    PubMed

    Bellesi, Michele; Riedner, Brady A; Garcia-Molina, Gary N; Cirelli, Chiara; Tononi, Giulio

    2014-01-01

    Even modest sleep restriction, especially the loss of sleep slow wave activity (SWA), is invariably associated with slower electroencephalogram (EEG) activity during wake, the occurrence of local sleep in an otherwise awake brain, and impaired performance due to cognitive and memory deficits. Recent studies not only confirm the beneficial role of sleep in memory consolidation, but also point to a specific role for sleep slow waves. Thus, the implementation of methods to enhance sleep slow waves without unwanted arousals or lightening of sleep could have significant practical implications. Here we first review the evidence that it is possible to enhance sleep slow waves in humans using transcranial direct-current stimulation (tDCS) and transcranial magnetic stimulation. Since these methods are currently impractical and their safety is questionable, especially for chronic long-term exposure, we then discuss novel data suggesting that it is possible to enhance slow waves using sensory stimuli. We consider the physiology of the K-complex (KC), a peripheral evoked slow wave, and show that, among different sensory modalities, acoustic stimulation is the most effective in increasing the magnitude of slow waves, likely through the activation of non-lemniscal ascending pathways to the thalamo-cortical system. In addition, we discuss how intensity and frequency of the acoustic stimuli, as well as exact timing and pattern of stimulation, affect sleep enhancement. Finally, we discuss automated algorithms that read the EEG and, in real-time, adjust the stimulation parameters in a closed-loop manner to obtain an increase in sleep slow waves and avoid undesirable arousals. In conclusion, while discussing the mechanisms that underlie the generation of sleep slow waves, we review the converging evidence showing that acoustic stimulation is safe and represents an ideal tool for slow wave sleep (SWS) enhancement.

  18. Molecular Mechanisms Underlying Origin and Diversification of the Angiosperm Flower

    PubMed Central

    Theissen, Guenter; Melzer, Rainer

    2007-01-01

    Background Understanding the mode and mechanisms of the evolution of the angiosperm flower is a long-standing and central problem of evolutionary biology and botany. It has essentially remained unsolved, however. In contrast, considerable progress has recently been made in our understanding of the genetic basis of flower development in some extant model species. The knowledge that accumulated this way has been pulled together in two major hypotheses, termed the ‘ABC model’ and the ‘floral quartet model’. These models explain how the identity of the different types of floral organs is specified during flower development by homeotic selector genes encoding transcription factors. Scope We intend to explain how the ‘ABC model’ and the ‘floral quartet model’ are now guiding investigations that help to understand the origin and diversification of the angiosperm flower. Conclusions Investigation of orthologues of class B and class C floral homeotic genes in gymnosperms suggest that bisexuality was one of the first innovations during the origin of the flower. The transition from dimer to tetramer formation of floral homeotic proteins after establishment of class E proteins may have increased cooperativity of DNA binding of the transcription factors controlling reproductive growth. That way, we hypothesize, better ‘developmental switches’ originated that facilitated the early evolution of the flower. Expression studies of ABC genes in basally diverging angiosperm lineages, monocots and basal eudicots suggest that the ‘classical’ ABC system known from core eudicots originated from a more fuzzy system with fading borders of gene expression and gradual transitions in organ identity, by sharpening of ABC gene expression domains and organ borders. Shifting boundaries of ABC gene expression may have contributed to the diversification of the angiosperm flower many times independently, as may have changes in interactions between ABC genes and their target

  19. Mechanism underlying prolongevity induced by bifidobacteria in Caenorhabditis elegans.

    PubMed

    Komura, Tomomi; Ikeda, Takanori; Yasui, Chikako; Saeki, Shigeru; Nishikawa, Yoshikazu

    2013-02-01

    Lactobacilli and bifidobacteria are probiotic bacteria that modify host defense systems and have the ability to extend the lifespan of the nematode Caenorhabditis elegans. Here, we attempted to elucidate the mechanism by which bifidobacteria prolong the lifespan of C. elegans. When the nematode was fed Bifidobacterium infantis (BI) mixed at various ratios with the standard food bacterium Escherichia coli strain OP50 (OP), the mean lifespan of worms was extended in a dose-dependent manner. Worms fed BI displayed higher locomotion and produced more offspring than control worms. The growth curves of nematodes were similar regardless of the amount of BI mixed with OP, suggesting that BI did not induce prolongevity effects through caloric restriction. Notably, feeding worms the cell wall fraction of BI alone was sufficient to promote prolongevity. The accumulation of protein carbonyls and lipofuscin, a biochemical marker of aging, was also lower in worms fed BI; however, the worms displayed similar susceptibility to heat, hydrogen peroxide, and paraquat, an inducer of free radicals, as the control worms. As a result of BI feeding, loss-of-function mutants of daf-16, jnk-1, aak-2, tol-1, and tir-1 exhibited a longer lifespan than OP-fed control worms, but BI failed to extend the lifespan of pmk-1, skn-1, and vhp-1 mutants. As skn-1 induces phase 2 detoxification enzymes, our findings suggest that cell wall components of bifidobacteria increase the average lifespan of C. elegans via activation of skn-1, regulated by the p38 MAPK pathway, but not by general activation of the host defense system via DAF-16.

  20. Quantitative ultrasonic evaluation of mechanical properties of engineering materials

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1978-01-01

    Current progress in the application of ultrasonic techniques to nondestructive measurement of mechanical strength properties of engineering materials is reviewed. Even where conventional NDE techniques have shown that a part is free of overt defects, advanced NDE techniques should be available to confirm the material properties assumed in the part's design. There are many instances where metallic, composite, or ceramic parts may be free of critical defects while still being susceptible to failure under design loads due to inadequate or degraded mechanical strength. This must be considered in any failure prevention scheme that relies on fracture analysis. This review will discuss the availability of ultrasonic methods that can be applied to actual parts to assess their potential susceptibility to failure under design conditions.

  1. Mechanical evaluation of two canine iliac fracture fixation systems.

    PubMed

    Vangundy, T E; Hulse, D A; Nelson, J K; Boothe, H W

    1988-01-01

    Twenty-three canine pelves were tested bilaterally to determine the stiffness and strength of intact ilium and stabilized oblique iliac osteotomies that simulated a common clinical fracture. Fixation systems tested were three 4.0 mm cancellous screws inserted ventral to dorsal across the osteotomy site and one laterally placed five hole 3.5 mm dynamic compression plate. Specimens were mechanically tested to failure under torsional, axial, or axial plus bending loads. Lag screw fixation was stiffer and stronger than plate fixation in all testing modes. The differences were statistically significant (p less than .05) in the torsional and axial plus bending loading modes. Fatigue testing was performed on implanted specimens with low-level cyclic loading under axial plus bending loading conditions. Physiologic loading conditions failed to produce mechanical failure of either fixation system after 100,000 cycles.

  2. An insight into the gastrointestinal component of fibromyalgia: clinical manifestations and potential underlying mechanisms.

    PubMed

    Slim, Mahmoud; Calandre, Elena Pita; Rico-Villademoros, Fernando

    2015-03-01

    Fibromyalgia syndrome is characterized by chronic generalized pain accompanied by a broad symptomatologic spectrum. Besides chronic fatigue, sleep disturbances, headaches and cognitive dysfunction that are extensively described in the literature, a considerable proportion of patients with fibromyalgia experience gastrointestinal symptoms that are commonly overlooked in the studies that are not specifically dedicated to evaluate these manifestations. Nevertheless, various attempts were undertaken to explore the gastrointestinal dimension of fibromyalgia. Several studies have demonstrated an elevated comorbidity of irritable bowel syndrome (IBS) among patients with fibromyalgia. Other studies have investigated the frequency of presentation of gastrointestinal symptoms in fibromyalgia in a nonspecific approach describing several gastrointestinal complaints frequently reported by these patients such as abdominal pain, dyspepsia and bowel changes, among others. Several underlying mechanisms that require further investigation could serve as potential explanatory hypotheses for the appearance of such manifestations. These include sensitivity to dietary constituents such as gluten, lactose or FODMAPs or alterations in the brain-gut axis as a result of small intestinal bacterial overgrowth or subclinical enteric infections such as giardiasis. The gastrointestinal component of fibromyalgia constitutes a relevant element of the multidisciplinary pathophysiologic mechanisms underlying fibromyalgia that need to be unveiled, as this would contribute to the adequate designation of relevant treatment alternatives corresponding to these manifestations.

  3. Prolonged secretion of cortisol as a possible mechanism underlying stress and depressive behaviour

    PubMed Central

    Qin, Dong-dong; Rizak, Joshua; Feng, Xiao-li; Yang, Shang-chuan; Lü, Long-bao; Pan, Lei; Yin, Yong; Hu, Xin-tian

    2016-01-01

    Stress is associated with the onset of depressive episodes, and cortisol hypersecretion is considered a biological risk factor of depression. However, the possible mechanisms underlying stress, cortisol and depressive behaviours are inconsistent in the literature. This study examined the interrelationships among stress, cortisol and observed depressive behaviours in female rhesus macaques for the first time and explored the possible mechanism underlying stress and depressive behaviour. Female monkeys were video-recorded, and the frequencies of life events and the duration of huddling were analysed to measure stress and depressive behaviour. Hair samples were used to measure chronic cortisol levels, and the interactions between stress and cortisol in the development of depressive behaviour were further evaluated. Significant correlations were found between stress and depressive behaviour measures and between cortisol levels and depressive behaviour. Stress was positively correlated with cortisol levels, and these two factors interacted with each other to predict the monkeys’ depressive behaviours. This finding extends the current understanding of stress/cortisol interactions in depression, especially pertaining to females. PMID:27443987

  4. Mechanisms underlying the sparing of masticatory versus limb muscle function in an experimental critical illness model.

    PubMed

    Aare, Sudhakar; Ochala, Julien; Norman, Holly S; Radell, Peter; Eriksson, Lars I; Göransson, Hanna; Chen, Yi-Wen; Hoffman, Eric P; Larsson, Lars

    2011-12-16

    Acute quadriplegic myopathy (AQM) is a common debilitating acquired disorder in critically ill intensive care unit (ICU) patients that is characterized by tetraplegia/generalized weakness of limb and trunk muscles. Masticatory muscles, on the other hand, are typically spared or less affected, yet the mechanisms underlying this striking muscle-specific difference remain unknown. This study aims to evaluate physiological parameters and the gene expression profiles of masticatory and limb muscles exposed to factors suggested to trigger AQM, such as mechanical ventilation, immobilization, neuromuscular blocking agents, corticosteroids (CS), and sepsis for 5 days by using a unique porcine model mimicking the ICU conditions. Single muscle fiber cross-sectional area and force-generating capacity, i.e., maximum force normalized to fiber cross-sectional area (specific force), revealed maintained masseter single muscle fiber cross-sectional area and specific-force after 5 days' exposure to all triggering factors. This is in sharp contrast to observations in limb and trunk muscles, showing a dramatic decline in specific force in response to 5 days' exposure to the triggering factors. Significant differences in gene expression were observed between craniofacial and limb muscles, indicating a highly complex and muscle-specific response involving transcription and growth factors, heat shock proteins, matrix metalloproteinase inhibitor, oxidative stress responsive elements, and sarcomeric proteins underlying the relative sparing of cranial vs. spinal nerve innervated muscles during exposure to the ICU intervention.

  5. Deep volcanic tremor and magma ascent mechanism under Kilauea, Hawaii

    SciTech Connect

    Aki, K.; Koyanagi, R.

    1981-08-10

    Deep harmonic tremor originating at depths around 40 km under Kilauea was studied using records accumulated since 1962 at the Hawaii Volcano Observatory of the U. S. Geological Survey. The deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island-wide network of seismometers. The period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode. The tremor appeared to be primarily composed of P waves. We interpret the observation period and amplitude in terms of the stationary crack model of Aki et al. (1977) and find that the seismic moment rates for deep tremors are considerably larger than those for shallow-tremors suggesting mor vigorous transport for the former. We propose a kinematic source model which may be more appropriate for deep tremor. According to this model, a measurable quantity called 'reduced displacement' is directly proportional to the rate of magma flow. A systematic search for deep tremor episodes was made for the period from 1962 through 1979, and the amplitude, period, and duration of the tremor were tabulated. We then constructed a cumulative reduced-displacement plot over the 18-year period. The result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface. The total magma flow estimated from the reduced displacement is however, one order of magnitude smaller than that estimated by Swanson (1972). It may be that most channels transport magma aseismically, and only those with strong barriers generate tremor.

  6. An electrophysiological insight into visual attention mechanisms underlying schizotypy.

    PubMed

    Fuggetta, Giorgio; Bennett, Matthew A; Duke, Philip A

    2015-07-01

    A theoretical framework has been put forward to understand attention deficits in schizophrenia (Luck SJ & Gold JM. Biological Psychiatry. 2008; 64:34-39). We adopted this framework to evaluate any deficits in attentional processes in schizotypy. Sixteen low schizotypal (LoS) and 16 high schizotypal (HiS) individuals performed a novel paradigm combining a match-to-sample task, with inhibition of return (using spatially uninformative cues) and memory-guided efficient visual-search within one trial sequence. Behavioural measures and event-related potentials (ERPs) were recorded. Behaviourally, HiS individuals exhibited a spatial cueing effect while LoS individuals showed the more typical inhibition of return effect. These results suggest HiS individuals have a relative deficit in rule selection - the endogenous control process involved in disengaging attention from the uninformative location cue. ERP results showed that the late-phase of N2pc evoked by the target stimulus had greater peak latency and amplitude in HiS individuals. This suggests a relative deficit in the implementation of selection - the process of focusing attention onto target features that enhances relevant/suppresses irrelevant inputs. This is a different conclusion than when the same theoretical framework has been applied to schizophrenia, which argues little or no deficit in implementation of selection amongst patients. Also, HiS individuals exhibited earlier onset and greater amplitude of the mismatch-triggered negativity component. In summary, our results indicate deficits of both control and implementation of selection in HiS individuals.

  7. Revealing the mechanisms underlying embolic stroke using computational modelling.

    PubMed

    Chung, Emma M L; Hague, James P; Evans, David H

    2007-12-07

    Computational forecasting of arterial blockages in a virtual patient has the potential to provide the next generation of advanced clinical monitoring aids for stroke prevention. As a first step towards a physiologically realistic virtual patient, we have created a computer model investigating the effects of emboli (particles or gas bubbles) as they become lodged in the brain. Our model provides a framework for predicting the severity of microvascular obstruction by simulating fundamental interactions between emboli and the fractal geometry of the arterial tree through which they travel. The model vasculature consisted of a bifurcating fractal tree comprising over a million branches ranging between 1 mm and 12 microm in diameter. Motion of emboli through the tree was investigated using a Monte Carlo simulation to evaluate the effects of the embolus size, clearance time and embolization rate on the number and persistence of blocked arterioles. Our simulations reveal with striking clarity that the relationship between embolus properties and vascular obstruction is nonlinear. We observe a rapid change between free-flowing and severely blocked arteries at specific combinations of the embolus size and embolization rate. The model predicts distinct patterns of cerebral injury for solid and gaseous emboli which are consistent with clinical observations. Solid emboli are predicted to be responsible for focal persistent injuries, while fast-clearing gas emboli produce diffuse transient blockages similar to global hypoperfusion. The impact of solid emboli was found to be dramatically reduced by embolus fragmentation. Computer simulations of embolization provide a novel means of investigating the role of emboli in producing neurological injury and assessing effective strategies for stroke prevention.

  8. Mechanical and morphological evaluation of osteochondral implants in dogs.

    PubMed

    Bavaresco, Vanessa P; Garrido, Luiz; Batista, Nilza A; Malmonge, Sônia M; Belangero, William D

    2008-04-01

    The mechanical behavior of osteochondral defects was evaluated in this study with the intention of developing alternative procedures. Cylindrical pins (5.00 mm in diameter and in height) made of pHEMA hydrogel covered ultra-high molecular weight polyethylene (UHMWPE) or beta-tricalcium phosphate (beta-TCP) matrix were used. Ostoechondral defects were caused in the knees of adult dogs and the evaluation was carried out after a 9-month follow-up period. The mechanical behavior of the implants was evaluated by means of an indentation creep test that showed that the UHMWPE matrix maintained its viscoelastic behavior even after follow-up time, while the beta-TCP matrix osteochondral implants presented significant alterations. It is believed that the beta-TCP osteochondral implants were unable to withstand the load applied, causing an increase of complacency when compared to the UHMWPE osteochondral implants. Based on micro and macroscopic analysis, no significant wear was observed in either of the osteochondral implants when compared to the controls. However, morphological alterations, with fragmentation indices in the patella, were observed either due to friction with the hydrogel in the first postoperative months or due to forming of a dense conjunctive tissue. This wear mechanism caused on the counterface of the implant (patella) was observed, notwithstanding the osteochondral implant studied.

  9. Defect induced plasticity and failure mechanism of boron nitride nanotubes under tension

    SciTech Connect

    Anoop Krishnan, N. M. Ghosh, Debraj

    2014-07-28

    The effects of Stone-Wales (SW) and vacancy defects on the failure behavior of boron nitride nanotubes (BNNTs) under tension are investigated using molecular dynamics simulations. The Tersoff-Brenner potential is used to model the atomic interaction and the temperature is maintained close to 300 K. The effect of a SW defect is studied by determining the failure strength and failure mechanism of nanotubes with different radii. In the case of a vacancy defect, the effect of an N-vacancy and a B-vacancy is studied separately. Nanotubes with different chiralities but similar diameter is considered first to evaluate the chirality dependence. The variation of failure strength with the radius is then studied by considering nanotubes of different diameters but same chirality. It is observed that the armchair BNNTs are extremely sensitive to defects, whereas the zigzag configurations are the least sensitive. In the case of pristine BNNTs, both armchair and zigzag nanotubes undergo brittle failure, whereas in the case of defective BNNTs, only the zigzag ones undergo brittle failure. An interesting defect induced plastic behavior is observed in defective armchair BNNTs. For this nanotube, the presence of a defect triggers mechanical relaxation by bond breaking along the closest zigzag helical path, with the defect as the nucleus. This mechanism results in a plastic failure.

  10. Photoelasticity and DIC as optical techniques for monitoring masonry specimens under mechanical loads

    NASA Astrophysics Data System (ADS)

    Colla, C.; Gabrielli, E.

    2017-01-01

    To evaluate the complex behaviour of masonry structures under mechanical loads, numerical models are developed and continuously implemented at diverse scales, whilst, from an experimental viewpoint, laboratory standard mechanical tests are usually carried out by instrumenting the specimens via traditional measuring devices. Extracted values collected in the few points where the tools were installed are assumed to represent the behaviour of the whole specimen but this may be quite optimistic or approximate. Optical monitoring techniques may help in overcoming some of these limitations by providing full-field visualization of mechanical parameters. Photoelasticity and the more recent DIC, employed to monitor masonry columns during compression tests are here presented and a lab case study is compared listing procedures, data acquisitions, advantages and limitations. It is shown that the information recorded by traditional measuring tools must be considered limited to the specific instrumented points. Instead, DIC in particular among the optical techniques, is proving both a very precise global and local picture of the masonry performance, opening new horizons towards a deeper knowledge of this complex construction material. The applicability of an innovative DIC procedure to cultural heritage constructions is also discussed.

  11. Multi-targeted mechanisms underlying the endothelial protective effects of the diabetic-safe sweetener erythritol.

    PubMed

    Boesten, Daniëlle M P H J; Berger, Alvin; de Cock, Peter; Dong, Hua; Hammock, Bruce D; den Hartog, Gertjan J M; Bast, Aalt

    2013-01-01

    Diabetes is characterized by hyperglycemia and development of vascular pathology. Endothelial cell dysfunction is a starting point for pathogenesis of vascular complications in diabetes. We previously showed the polyol erythritol to be a hydroxyl radical scavenger preventing endothelial cell dysfunction onset in diabetic rats. To unravel mechanisms, other than scavenging of radicals, by which erythritol mediates this protective effect, we evaluated effects of erythritol in endothelial cells exposed to normal (7 mM) and high glucose (30 mM) or diabetic stressors (e.g. SIN-1) using targeted and transcriptomic approaches. This study demonstrates that erythritol (i.e. under non-diabetic conditions) has minimal effects on endothelial cells. However, under hyperglycemic conditions erythritol protected endothelial cells against cell death induced by diabetic stressors (i.e. high glucose and peroxynitrite). Also a number of harmful effects caused by high glucose, e.g. increased nitric oxide release, are reversed. Additionally, total transcriptome analysis indicated that biological processes which are differentially regulated due to high glucose are corrected by erythritol. We conclude that erythritol protects endothelial cells during high glucose conditions via effects on multiple targets. Overall, these data indicate a therapeutically important endothelial protective effect of erythritol under hyperglycemic conditions.

  12. Mechanical characterization of IM7/8551-7 carbon/epoxy under biaxial stress: (Final report)

    SciTech Connect

    Colvin, G.E. Jr.; Swanson, S.R.

    1987-11-13

    This is the final report on an investigation to evaluate the mechanical response of Hercules IM7/8551-7 carbon/epoxy, which is a high strength, high elongation fiber and a high toughness resin system used in a prepreg form. The material characterization involved testing both laminate and lamina forms under a wide range of biaxial stress states. Tubular specimens were employed that have been designed to eliminate undesirable end effects, permitting uniform stress states to be achieved. Quasi-isotropic (90/+-45/0)/sub ns/laminates and (90)/sub 16T/ lamina specimens were loaded under combinations of internal pressure, axial load, and torsion. Both stiffness and strength data were obtained under these multiaxial stress conditions. The measured laminate stiffnesses correlated well using classical laminated plate theory, and that laminate failure occurred in the two separate modes of matrix cracking and fiber failure. Like the previously examined carbon/epoxy systems, laminate failure could be predicted by using a fiber failure criterion to identify the critical plies and critical load levels. It was found that either maximum fiber stress or fiber direction strain could be used as a failure criterion on a ply level. 16 refs., 10 figs., 3 tabs.

  13. Coupled mechanical-electrical-thermal modeling for short-circuit prediction in a lithium-ion cell under mechanical abuse

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Santhanagopalan, Shriram; Sprague, Michael A.; Pesaran, Ahmad A.

    2015-09-01

    In order to better understand the behavior of lithium-ion batteries under mechanical abuse, a coupled modeling methodology encompassing the mechanical, electrical and thermal response is presented for predicting short-circuit under external crush. The combined mechanical-electrical-thermal response is simulated in a commercial finite element software LS-DYNA® using a representative-sandwich finite-element model, where electrical-thermal modeling is conducted after an instantaneous mechanical crush. The model includes an explicit representation of each individual component such as the active material, current collector, separator, etc., and predicts their mechanical deformation under quasi-static indentation. Model predictions show good agreement with experiments: the fracture of the battery structure under an indentation test is accurately predicted. The electrical-thermal simulation predicts the current density and temperature distribution in a reasonable manner. Whereas previously reported models consider the mechanical response exclusively, we use the electrical contact between active materials following the failure of the separator as a criterion for short-circuit. These results are used to build a lumped representative sandwich model that is computationally efficient and captures behavior at the cell level without resolving the individual layers.

  14. Neural mechanisms underlying the integration of situational information into attribution outcomes.

    PubMed

    Brosch, Tobias; Schiller, Daniela; Mojdehbakhsh, Rachel; Uleman, James S; Phelps, Elizabeth A

    2013-08-01

    When forming impressions and trying to figure out why other people behave the way they do, we should take into account not only dispositional factors (i.e., personality traits) but also situational constraints as potential causes for a behavior. However, in their attributions, people often ignore the importance of situational factors. To investigate the neural mechanisms underlying the integration of situational information into attributions, we decomposed the attribution process by separately presenting information about behaviors and about the situational circumstances in which they occur. After reading the information, participants judged whether dispositional or situational causes explained the behavior (attribution), and how much they liked the person described in the scenario (affective evaluation). The dorsolateral prefrontal cortex showed increased blood oxygenation-level-dependent activation during the encoding of situational information when the resulting attribution was situational, relative to when the attribution was dispositional, potentially reflecting a controlled process that integrates situational information into attributions. Interestingly, attributions were strongly linked to subsequent affective evaluations, with the dorsomedial prefrontal cortex emerging as potential substrate of the integration of attributions and affective evaluations. Our findings demonstrate how top-down control processes regulate impression formation when situational information is taken into account to understand others.

  15. Evaluation of the compressive mechanical properties of endoluminal metal stents.

    PubMed

    Schrader, S C; Beyar, R

    1998-06-01

    The mechanical properties of metal stents are important parameters in the consideration of stent design, matched to resist arterial recoil and vascular spasm. The purpose of this study was to develop a system for a standardized quantitative evaluation of the mechanical characteristics of various coronary stents. Several types of stents were compressed by external hydrostatic pressure. The stent diameter was assessed by placing a pair of small ultrasonic sono-crystals on the stent. From pressure-strain diagrams the ultimate strength and radial stiffness for each stent were determined. For all stents, except the MICRO-II and the Wiktor stent, the diameter decreased homogeneously until an ultimate compressive strength was exceeded, causing an abrupt collapse. Expanded to 3 mm, the mechanical behavior of the beStent, the Crown and the Palmaz-Schatz stent (PS153-series) were comparable. The spiral articulated Palmaz-Schatz stent showed twice the strength (1.26 atm) of the PS-153 (0.65 atm). The NIR stent yielded a maximum strength of 1.05 atm. The MICRO-II and the Wiktor stent did not collapse abruptly but rather showed a continuous decline of diameter with increasing external pressure. The Cardiocoil stent behaved in a fully elastic manner and showed the largest radial stiffness. Difference in mechanical properties between stents were documented using a new device specifically developed for that purpose. These mechanical stent parameters may have important clinical implications.

  16. Fracture mechanics analyses of ceramic/veneer interface under mixed-mode loading.

    PubMed

    Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

    2014-11-01

    Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive

  17. Ultrasonic evaluation of the physical and mechanical properties of granites.

    PubMed

    Vasconcelos, G; Lourenço, P B; Alves, C A S; Pamplona, J

    2008-09-01

    Masonry is the oldest building material that survived until today, being used all over the world and being present in the most impressive historical structures as an evidence of spirit of enterprise of ancient cultures. Conservation, rehabilitation and strengthening of the built heritage and protection of human lives are clear demands of modern societies. In this process, the use of nondestructive methods has become much common in the diagnosis of structural integrity of masonry elements. With respect to the evaluation of the stone condition, the ultrasonic pulse velocity is a simple and economical tool. Thus, the central issue of the present paper concerns the evaluation of the suitability of the ultrasonic pulse velocity method for describing the mechanical and physical properties of granites (range size between 0.1-4.0 mm and 0.3-16.5 mm) and for the assessment of its weathering state. The mechanical properties encompass the compressive and tensile strength and modulus of elasticity, and the physical properties include the density and porosity. For this purpose, measurements of the longitudinal ultrasonic pulse velocity with distinct natural frequency of the transducers were carried out on specimens with different size and shape. A discussion of the factors that induce variations on the ultrasonic velocity is also provided. Additionally, statistical correlations between ultrasonic pulse velocity and mechanical and physical properties of granites are presented and discussed. The major output of the work is the confirmation that ultrasonic pulse velocity can be effectively used as a simple and economical nondestructive method for a preliminary prediction of mechanical and physical properties, as well as a tool for the assessment of the weathering changes of granites that occur during the serviceable life. This is of much interest due to the usual difficulties in removing specimens for mechanical characterization.

  18. Evaluating environmental justice under the National Environmental Policy Act

    SciTech Connect

    Bass, R.

    1998-01-01

    Environmental justice refers to the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws. To avoid inequities in future federal activities, President Clinton issued Executive Order (EO) 12898, which requires federal agencies to consider environmental justice in carrying out their missions. Guidance issued by the Executive Office of the President requires every federal agency to consider environmental justice in conducting impact evaluations under the National Environmental Policy Act (NEPA). Thus, an environmental justice analysis is a highly focused form of social impact assessment that must be conducted within the framework of NEPA. The specific purpose of such an analysis is to determine whether a proposed federal activity would impact low-income and minority populations to a greater extent than it would impact a community`s general population. This article explains the development and implementation of EO 12898 and explores what federal agencies are doing to incorporate environmental justice into their NEPA procedures. It also includes recommendations for other authorities to consider when incorporating environmental justice into their environmental impact assessments.

  19. Evaluation of confinement effects in zeolites under Henry's adsorption regime

    NASA Astrophysics Data System (ADS)

    Pera-Titus, Marc; Llorens, Joan

    2010-06-01

    This paper provides a detailed thermodynamic analysis of gas/vapour adsorption in zeolites at low pressures. At these conditions, we show first that Henry's isotherm can be conveniently rewritten using the thermodynamic isotherm model developed in a previous study [J. Llorens, M. Pera-Titus, Description of gas adsorption on microporous materials: evaluation of energy heterogeneity, J. Colloid Interface Sci. 331, 2009, 302-311], linking the integral free energy of adsorption relative to saturation, Ψ/ RT, expressed as a Kiselev integral, with the variable Z = 1/-ln( Π), being Π the relative pressure. Relevant information about sorbate confinement effects in zeolites can be inferred using strong sorbates under Henry's adsorption regime using the thermodynamic formulation provided here. The confining level of zeolites can be characterized by a parameter ( m1), whose value depends on the zeolite framework, but remains essentially unchanged with the sorbate probe molecule and temperature. We illustrate the application of these concepts using a collection of MFI and MTW-type zeolites as model systems.

  20. Wear mechanism evaluation and measurement in fuel-lubricated components

    NASA Astrophysics Data System (ADS)

    Lacey, Paul I.

    1994-09-01

    Previous studies have demonstrated that the durability of some fuel injection systems on compression-ignition engines will be adversely affected by fuels of sufficiently low lubricity. However, no widely accepted lubricity measure is available; indeed, the wear mechanisms present have not been conclusively defined. The results of the present study indicate that oxidative corrosion is the predominant mechanism with very highly processed fuels, resulting in catastrophic wear and rapid failure. A laboratory test procedure directed toward the oxidative wear mechanism was evaluated and a number of modifications suggested. Two closely related laboratory wear test procedures that rely on the transition from mild boundary lubricated wear to adhesive scuffing were also developed. The resulting procedures allow the fuels to be either ranked using a continuous scale or separated using a simple pass/fail criteria. All the procedures are sensitive to the addition of trace quantities of lubricity additives and show directional correlation with refinery severity, as measured by sulfur and aromatic content. As a result, the tests produced excellent correlation with full-scale equipment tests performed at a number of locations, as well as the criteria necessary for oxidative corrosion. However, the scuffing load tests show greatly increased separation between good and unacceptable fluids compared to the oxidative corrosion tests. Evaluation of commercially available fuels indicates that fuel lubricity is decreasing and that very poor lubricity fuels are occasionally observed.

  1. Evaluation of Mechanical Tomato Harvesting Using Wireless Sensors

    PubMed Central

    Arazuri, Silvia; Arana, Ignacio; Jaren, Carmen

    2010-01-01

    The harvesting of processing tomatoes is fully mechanised and it is well known that during harvest, fruits are subjected to mechanical stress causing physical injuries, including skin punctures, pulp and cell rupture. Some wireless sensors have been used for research during recent years with the main purpose of reducing the quality loss of tomato fruits by diminishing the number and intensity of impacts. In this study the IRD (impact recorder device) sensor was used to evaluate several tomato harvesters. The specific objectives were to evaluate the impacts during mechanical harvest using a wireless sensor, to determine the critical points at which damage occurs, and to assess the damage levels. Samples were taken to determine the influence of mechanical harvest on texture, or on other quality characteristics including percentage of damages. From the obtained data it has been possible to identify the critical points where the damages were produced for each one of the five harvester models examined. The highest risk of damage was in zone 1 of the combine—from the cutting system to the colour selector—because the impacts were of higher intensity and hit less absorbing surfaces than in zone 2—from colour selector to discharge. The shaker and exit from the shaker are two of the harvester elements that registered the highest intensity impacts. By adjusting, in a specific way each harvester model, using the results from this research, it has been possible to reduce the tomato damage percentage from 20 to 29% to less than 10%. PMID:22163516

  2. Evaluation of resolution of flexure parallel mechanisms for ultraprecision manipulation

    SciTech Connect

    Pham, H.-H.; Chen, I-M.

    2004-09-01

    A method for evaluating the resolution of ultraprecision manipulation systems based on the flexure parallel mechanism (FPM) is presented. The resolution of the open-loop system is theoretically determined by the resolution transmission from the actuated joints to the end-effector and the resolution of actuators. The method studies the definition of the resolution indicators that includes the global resolution transmission scale and the uniformity of resolution over the entire workspace of the flexure mechanism. The computational algorithm for the defined resolution indicators is established based on the sampling method. For illustration, the evaluation method is employed to gauge the resolution performance of a two-degree-of-freedom and a three-degree-of-freedom (3-DOF) planar FPM. To demonstrate its application for optimal design, we use this method for the development of a 3-DOF spatial translational FPM. An experiment is carried out to determine the resolution and the repeatability of the developed FPM and verify the proposed evaluation method. The result shows that the method is suitable for the design of FPM for any desired resolution.

  3. Optimally oriented grooves on dental implants improve bone quality around implants under repetitive mechanical loading.

    PubMed

    Kuroshima, Shinichiro; Nakano, Takayoshi; Ishimoto, Takuya; Sasaki, Muneteru; Inoue, Maaya; Yasutake, Munenori; Sawase, Takashi

    2017-01-15

    The aim was to investigate the effect of groove designs on bone quality under controlled-repetitive load conditions for optimizing dental implant design. Anodized Ti-6Al-4V alloy implants with -60° and +60° grooves around the neck were placed in the proximal tibial metaphysis of rabbits. The application of a repetitive mechanical load was initiated via the implants (50N, 3Hz, 1800 cycles, 2days/week) at 12weeks after surgery for 8weeks. Bone quality, defined as osteocyte density and degree of biological apatite (BAp) c-axis/collagen fibers, was then evaluated. Groove designs did not affect bone quality without mechanical loading; however, repetitive mechanical loading significantly increased bone-to-implant contact, bone mass, and bone mineral density (BMD). In +60° grooves, the BAp c-axis/collagen fibers preferentially aligned along the groove direction with mechanical loading. Moreover, osteocyte density was significantly higher both inside and in the adjacent region of the +60° grooves, but not -60° grooves. These results suggest that the +60° grooves successfully transmitted the load to the bone tissues surrounding implants through the grooves. An optimally oriented groove structure on the implant surface was shown to be a promising way for achieving bone tissue with appropriate bone quality. This is the first report to propose the optimal design of grooves on the necks of dental implants for improving bone quality parameters as well as BMD. The findings suggest that not only BMD, but also bone quality, could be a useful clinical parameter in implant dentistry.

  4. Evaluating Arctic warming mechanisms in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Franzke, Christian L. E.; Lee, Sukyoung; Feldstein, Steven B.

    2016-07-01

    Arctic warming is one of the most striking signals of global warming. The Arctic is one of the fastest warming regions on Earth and constitutes, thus, a good test bed to evaluate the ability of climate models to reproduce the physics and dynamics involved in Arctic warming. Different physical and dynamical mechanisms have been proposed to explain Arctic amplification. These mechanisms include the surface albedo feedback and poleward sensible and latent heat transport processes. During the winter season when Arctic amplification is most pronounced, the first mechanism relies on an enhancement in upward surface heat flux, while the second mechanism does not. In these mechanisms, it has been proposed that downward infrared radiation (IR) plays a role to a varying degree. Here, we show that the current generation of CMIP5 climate models all reproduce Arctic warming and there are high pattern correlations—typically greater than 0.9—between the surface air temperature (SAT) trend and the downward IR trend. However, we find that there are two groups of CMIP5 models: one with small pattern correlations between the Arctic SAT trend and the surface vertical heat flux trend (Group 1), and the other with large correlations (Group 2) between the same two variables. The Group 1 models exhibit higher pattern correlations between Arctic SAT and 500 hPa geopotential height trends, than do the Group 2 models. These findings suggest that Arctic warming in Group 1 models is more closely related to changes in the large-scale atmospheric circulation, whereas in Group 2, the albedo feedback effect plays a more important role. Interestingly, while Group 1 models have a warm or weak bias in their Arctic SAT, Group 2 models show large cold biases. This stark difference in model bias leads us to hypothesize that for a given model, the dominant Arctic warming mechanism and trend may be dependent on the bias of the model mean state.

  5. Experimental evaluation of stent retrievers’ mechanical properties and effectiveness

    PubMed Central

    Machi, Paolo; Jourdan, Franck; Ambard, Dominique; Reynaud, Cedric; Lobotesis, Kyriakos; Sanchez, Mathieu; Bonafé, Alain; Costalat, Vincent

    2017-01-01

    Background Five randomized controlled trials recently appeared in the literature demonstrating that early mechanical thrombectomy in patients with acute ischemic stroke is significantly related to an improved outcome. Stent retrievers are accepted as the most effective devices for intracranial thrombectomy. Objective To analyze the mechanical properties of stent retrievers, their behavior during retrieval, and interaction with different clots and to identify device features that might correlate with the effectiveness of thrombus removal. Materials and methods All stent retrievers available in France up to June 2015 were evaluated by mechanical and functional tests aimed at investigating the variation of their radial force and their behavior during retrieval. Devices were also tested during in vitro thrombectomies using white and red experimental thrombi produced with human blood. Functional tests and in vitro thrombectomies were conducted using a rigid 3D printed vascular model. Results Mechanical tests showed a variation in radial force during retrieval for each stent. A constant radial force during retrieval was related to continuous cohesion over the vessel wall and a higher rate of clot removal efficacy. All stent retrievers failed when interacting with white large thrombi (diameter ≥6 mm). Conclusions None of the tested devices were effective in removing white clots of large diameter (≥6 mm). Constant radial force during retrieval allows constant cohesion to the vessel wall and pressure over the clot; such features allow for a higher rate of clot removal. PMID:27016318

  6. Left Atrial Reverse Remodeling: Mechanisms, Evaluation, and Clinical Significance.

    PubMed

    Thomas, Liza; Abhayaratna, Walter P

    2017-01-01

    The left atrium is considered a biomarker for adverse cardiovascular outcomes, particularly in patients with left ventricular diastolic dysfunction and atrial fibrillation in whom left atrial (LA) enlargement is of prognostic importance. LA enlargement with a consequent decrease in LA function represents maladaptive structural and functional "remodeling" that in turn promotes electrical remodeling and a milieu conducive for incident atrial fibrillation. Medical and nonmedical interventions may arrest this pathophysiologic process to the extent that subsequent reverse remodeling results in a reduction in LA size and improvement in LA function. This review examines cellular and basic mechanisms involved in LA remodeling, evaluates the noninvasive techniques that can assess these changes, and examines potential mechanisms that may initiate reverse remodeling.

  7. Alveolar recruiting maneuver in dogs under general anesthesia: effects on alveolar ventilation, gas exchange, and respiratory mechanics.

    PubMed

    Staffieri, F; De Monte, V; De Marzo, C; Scrascia, F; Crovace, A

    2010-06-01

    The aim of this study was to evaluate the effects of a recruiting maneuver (RM) on lung aeration, gas exchange, and respiratory mechanics during general anesthesia in mechanically ventilated dogs. A thoracic computed tomography (CT) scan, an arterial blood sample, and measurement of respiratory mechanics were performed 10 min before (baseline) and both 5 and 30 min after a vital capacity RM in 10 dogs under general anesthesia. The RM was performed by inflating the lung at 40 cm H(2)O for 20 s. Lung aeration was estimated by analyzing the radiographic attenuation of the CT images. Lung aeration and gas exchange improved significantly 5 min after the RM compared to baseline and returned to values similar to baseline by 30 min. Static lung compliance was not significantly affected by the RM. An RM induces a temporary improvement in lung function in healthy dogs under general anesthesia.

  8. Damage evaluation in graphene underlying atomic layer deposition dielectrics

    PubMed Central

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A.

    2015-01-01

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors. PMID:26311131

  9. Damage evaluation in graphene underlying atomic layer deposition dielectrics.

    PubMed

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A

    2015-08-27

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  10. Damage evaluation in graphene underlying atomic layer deposition dielectrics

    NASA Astrophysics Data System (ADS)

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A.

    2015-08-01

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  11. Galangin suppresses human osteosarcoma cells: An exploration of its underlying mechanism.

    PubMed

    Yang, Zhifan; Li, Xiucheng; Han, Weiqi; Lu, Xuanyuan; Jin, Songtao; Yang, Wanlei; Li, Jianlei; He, Wei; Qian, Yu

    2017-01-01

    Osteosarcoma is the most common malignant bone tumor that frequently affects adolescents. Osteosarcoma cells tend to proliferate and invade other tissues such as those of the lungs. Currently, neoadjuvant chemotherapy is the primary strategy to prevent tumor progression. However, its adverse effects result in poor long-term outcomes. Previous research has shown that galangin exhibits antitumor properties on several types of cancer cells; however its effect on osteosarcoma cells is yet unknown. The aims of this study were to evaluate the effects of galangin on the proliferation, apoptosis, migration, and invasion of osteosarcoma cells and to explore the underlying mechanisms. We found that the proliferation of MG63 and U20S osteosarcoma cells decreased significantly, while the apoptosis of MG63 cells accelerated significantly after exposure to galangin. In addition, the migration and invasion of MG63 cells were significantly inhibited by galangin. Moreover, phosphoinositide 3-kinase (PI3K) and Aktp-Thr308 expression levels were found to be significantly lower in galangin-treated MG63 cells than in the control cells, and the protein expression levels of their downstream regulators cyclin D1 and matrix metalloproteinase 2/9 were also downregulated in galangin-treated groups, while those of p27Kip1, caspase-3, and caspase-8 were upregulated. These findings suggest that galangin suppresses osteosarcoma cells by inhibiting their proliferation and invasion and accelerating their apoptosis, and the mechanism may be associated with the inhibition of PI3K and its downstream signaling pathway.

  12. The neuronal mechanisms underlying improvement of impulsivity in ADHD by theta/beta neurofeedback

    PubMed Central

    Bluschke, Annet; Broschwitz, Felicia; Kohl, Simon; Roessner, Veit; Beste, Christian

    2016-01-01

    Neurofeedback is increasingly recognized as an intervention to treat core symptoms of attention deficit hyperactivity disorder (ADHD). Despite the large number of studies having been carried out to evaluate its effectiveness, it is widely elusive what neuronal mechanisms related to the core symptoms of ADHD are modulated by neurofeedback. 19 children with ADHD undergoing 8 weeks of theta/beta neurofeedback and 17 waiting list controls performed a Go/Nogo task in a pre-post design. We used neurophysiological measures combining high-density EEG recording with source localization analyses using sLORETA. Compared to the waiting list ADHD control group, impulsive behaviour measured was reduced after neurofeedback treatment. The effects of neurofeedback were very specific for situations requiring inhibitory control over responses. The neurophysiological data shows that processes of perceptual gating, attentional selection and resource allocation processes were not affected by neurofeedback. Rather, neurofeedback effects seem to be based on the modulation of response inhibition processes in medial frontal cortices. The study shows that specific neuronal mechanisms underlying impulsivity are modulated by theta/beta neurofeedback in ADHD. The applied neurofeedback protocol could be particularly suitable to address inhibitory control. The study validates assumed functional neuroanatomical target regions of an established neurofeedback protocol on a neurophysiological level. PMID:27514985

  13. Investigation of Heat Transfer Mechanisms under Shutdown Plant Conditions with TRACEv4.160

    SciTech Connect

    Jasiulevicius, A.; Zerkak, O.; Macian-Juan, R.

    2006-07-01

    This paper presents the results of simulations of the PKL experiment F1.2 with the TRACE code (version v4.160). The PKL experiment F1.2 was performed in a closed primary system, stepwise reducing the primary coolant mass inventory at a constant pressure in order to evaluate the heat transfer mechanisms and transport of borated water from the steam generator inlet to outlet sides as a function of the primary coolant mass inventory. A complete TRACE input model of the primary system and the four secondary loops of the PKL facility was developed for this purpose. The aim of the TRACEv4.160 calculations presented in this paper was to assess the code predictions of the heat transfer mechanisms occurring during the different phases of the experiment: single-phase natural circulation, two-phase natural circulation and reflux condensation in the steam generator U-tubes. In addition, TRACEv4.160 calculated de-boration rates during the reflux-condensation phase in various parts of the primary system were compared with the results of the experiment in order to assess the capabilities of the code to predict the formation of low-boron concentration coolant slugs in the primary system during plant transients under similar conditions. (authors)

  14. Factors Underlying the Public's Credibility Perceptions in Educational Evaluations

    ERIC Educational Resources Information Center

    Jacobson, Miriam R.

    2016-01-01

    Understanding how evaluation audiences perceive credibility can help evaluators design evaluations and reports that support appropriate use. While researchers have studied credibility assessment among various educational stakeholders, little research has been conducted with the broader public. This study explored potential factors affecting the…

  15. Effect of Positive End-Expiratory Pressure on Central Venous Pressure in Patients under Mechanical Ventilation

    PubMed Central

    Shojaee, Majid; Sabzghabaei, Anita; Alimohammadi, Hossein; Derakhshanfar, Hojjat; Amini, Afshin; Esmailzadeh, Bahareh

    2017-01-01

    Introduction: Finding the probable governing pattern of PEEP and CVP changes is an area of interest for in-charge physicians and researchers. Therefore, the present study was designed with the aim of evaluating the relationship between the mentioned pressures. Methods: In this quasi-experimental study, patients under mechanical ventilation were evaluated with the aim of assessing the effect of PEEP change on CVP. Non-trauma patients, over 18 years of age, who were under mechanical ventilation and had stable hemodynamics, with inserted CV line were entered. After gathering demographic data, patients underwent 0, 5, and 10 cmH2O PEEPs and the respective CVPs of the mentioned points were recorded. The relationship of CVP and PEEP in different cut points were measured using SPSS 21.0 statistical software. Results: 60 patients with the mean age of 73.95 ± 11.58 years were evaluated (68.3% male). The most frequent cause of ICU admission was sepsis with 45.0%. 5 cmH2O increase in PEEP led to 2.47 ± 1.53 mean difference in CVP level. If the PEEP baseline is 0 at the time of 5 cmH2O increase, it leads to a higher raise in CVP compared to when the baseline is 5 cmH2O (2.47 ± 1.53 vs. 1.57 ± 1.07; p = 0.039). The relationship between CVP and 5 cmH2O (p = 0.279), and 10 cmH2O (p = 0.292) PEEP changes were not dependent on the baseline level of CVP. Conclusion: The findings of this study revealed the direct relationship between PEEP and CVP. Approximately, a 5 cmH2O increase in PEEP will be associated with about 2.5 cmH2O raise in CVP. When applying a 5 cmH2O PEEP increase, if the baseline PEEP is 0, it leads to a significantly higher raise in CVP compared to when it is 5 cmH2O (2.5 vs. 1.6). It seems that sex, history of cardiac failure, baseline CVP level, and hypertension do not have a significant effect in this regard. PMID:28286808

  16. Mechanical and ultrastructural evaluation of quartz post-endodontic reconstructions.

    PubMed

    Majori, M; Bedini, R; Altamura, C; Filippini, P; Caiazza, S

    2004-01-01

    Aesthetics is a very important element in dentistry, but requires the support of good mechanical performance. Quartz fiber used in post-endodontic reconstruction is an aesthetic material, although there is little research concerning its mechanical properties. This study evaluated the retentive property of post-endodontic reconstruction, composed of a quartz fiber post. Different thermal stresses were applied in vitro to post-endodontic reconstructions, in order to simulate oral thermal action on post-system dental structure linkage. We chose 30 human extracted teeth, endodontically treated and restored, and then divided them into three groups of 10 teeth. A different treatment was applied to each group before mechanical testing: in the 1st group no treatment was done (controls); in the 2nd group teeth were subjected, in a climatic chamber, to 10 thermo-cycles between 4 degrees C and 58 degrees C; in the 3rd group teeth were stored in a saline solution at 37 degrees C for 48 hr. The teeth then underwent tensile shear stress tests at break point using a computerized electronic dynamometer. After mechanical testing, two teeth from each group were longitudinally half-sectioned, sputter-coated in gold and observed by scanning electron microscopy (SEM). The extracted quartz fiber post of each tooth also underwent SEM observation. Mechanical test results demonstrated that thermal cyclic variations could affect bond stability between dental structures and posts in quartz fiber reconstructions, whereas their bond strength seemed unaffected by humidity increases. Quartz fiber post SEM observation demonstrated a homogeneous structure and a regular fiber disposition. Dental root canal morphology SEM images always showed a different thickness in the cement layer. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 156-61).

  17. Numerical simulation of effective mechanical properties of stochastic composites with consideration for structural evolution under intensive dynamic loading

    SciTech Connect

    Karakulov, Valerii V.; Smolin, Igor Yu. E-mail: skrp@ftf.tsu.ru; Skripnyak, Vladimir A. E-mail: skrp@ftf.tsu.ru

    2014-11-14

    Mechanical behavior of stochastic metal-ceramic composites with the aluminum matrix under high-rate deformation at shock-wave loading is numerically simulated with consideration for structural evolution. Effective values of mechanical parameters of metal-ceramic composites AlB{sub 4}C, AlSiC, and AlAl{sub 2}O{sub 3} are evaluated depending on different concentration of ceramic inclusions.

  18. Adaptive response of bacteria: Multiple hurdles, cross-tolerance and tools to illustrate underlying mechanisms

    NASA Astrophysics Data System (ADS)

    Paramythiotis, Spyridon; Skandamis, Panagiotis N.

    2015-01-01

    A basic principle in the bacterial resistance against lethal stresses is that exposure of microbial cells to a sublethal hurdle (e.g., pH 5.0, 3% NaCl, or 48°C) may induce resistance to lethal level of the same or different stress. The latter is called "cross-tolerance" and the bacteria experiencing such situations are termed "stress-hardened". The majority of scientific reports on the adaptive responses of bacteria to stresses have recently addressed the need to elucidate the underlying mechanisms controlling bacterial stress response. This in turn, will assist in the efficient application of the multiple hurdle approach, e.g., by selecting specific sanitizers, combining stress treatments or antimicrobials, especially in mild processing, against specific cellular targets, eliminating the possibility of the development of stress adapted cells. Common scientific approaches for studying the link between phenotype (e.g., inactivation, survival, or growth) and physiology is the assessment of global transcriptional changes (up- or down-regulation) or those of certain genes, as well as of proteins involved in certain metabolic pathways, occurring during exposure to stress. This may also be performed in parallel to comparative evaluation of the phenotypic response of wild and mutant strains. The post-genomics research on foodborne pathogens has extended our knowledge beyond their phenotypic behavior and may offer mechanistic insights in the following: (i) the top-down approach (induction), which is the search of the underlying mechanisms (low level) responsible for a specific phenotype based on "-omic" studies; and (ii) the bottom-up approach (deduction), which starts from intracellular level and forms a mechanistic (functional) basis for the cellular response. All these may eventually enable the development of mechanistic microbial models and efficient strategies for controlling survival and growth of pathogens in foods.

  19. Exploring the host transcriptome for mechanisms underlying protective immunity and resistance to nematode infections in ruminants.

    PubMed

    Li, Robert W; Choudhary, Ratan K; Capuco, Anthony V; Urban, Joseph F

    2012-11-23

    Nematode infections in ruminants are a major impediment to the profitable production of meat and dairy products, especially for small farms. Gastrointestinal parasitism not only negatively impacts weight gain and milk yield, but is also a major cause of mortality in small ruminants. The current parasite control strategy involves heavy use of anthelmintics that has resulted in the emergence of drug-resistant parasite strains. This, in addition to increasing consumer demand for animal products that are free of drug residues has stimulated development of alternative strategies, including selective breeding of parasite resistant ruminants. The development of protective immunity and manifestations of resistance to nematode infections relies upon the precise expression of the host genome that is often confounded by mechanisms simultaneously required to control multiple nematode species as well as ecto- and protozoan parasites, and microbial and viral pathogens. Understanding the molecular mechanisms underlying these processes represents a key step toward development of effective new parasite control strategies. Recent progress in characterizing the transcriptome of both hosts and parasites, utilizing high-throughput microarrays and RNA-seq technology, has led to the recognition of unique interactions and the identification of genes and biological pathways involved in the response to parasitism. Innovative use of the knowledge gained by these technologies should provide a basis for enhancing innate immunity while limiting the polarization of acquired immunity can negatively affect optimal responses to co-infection. Strategies for parasite control that use diet and vaccine/adjuvant combination could be evaluated by monitoring the host transcriptome for induction of appropriate mechanisms for imparting parasite resistance. Knowledge of different mechanisms of host immunity and the critical regulation of parasite development, physiology, and virulence can also selectively

  20. Mechanisms Underlying Lexical Access in Native and Second Language Processing of Gender and Number Agreement

    ERIC Educational Resources Information Center

    Romanova, Natalia

    2013-01-01

    Despite considerable evidence suggesting that second language (L2) learners experience difficulties when processing morphosyntactic aspects of L2 in online tasks, the mechanisms underlying these difficulties remain unknown. The aim of this dissertation is to explore possible causes for the difficulties by comparing attentional mechanisms engaged…

  1. Mechanical Behavior of Liquid Route Processed SiCf/Ti Composites Under Longitudinal and Transverse Loadings

    NASA Astrophysics Data System (ADS)

    Valle, Roger; Daux, Jean-Claude

    2017-02-01

    Due to the high melting point and strong chemical reactivity of titanium alloys, titanium matrix composites (TMCs) are usually processed through solid-state routes such as the foil-fiber-foil technique. An alternative method consists in the deposition of the matrix on the fibers. However, techniques such as physical vapor deposition lead to a very low deposition rate, contrary to liquid route processing using a levitating liquid alloy sphere held in a cold crucible. In order to investigate the effects of the resulting thermal shock on carbon-coated SiC fibers, and select an appropriate fiber, fibers are subjected to a pure thermal shock using a laser bench facility. These fibers are then tensile tested to failure in order to evaluate the resulting fiber strength degradation and, thus, the maximum acceptable temperature. Mechanical characterization of the liquid route processed TMC is then investigated through longitudinal and transverse tensile and creep tests at temperatures representative of aeronautical applications. The specimens, unbroken after long-duration creep tests, are then subjected to tensile loading to failure: conditions representative of service, i.e., short-time overspeeding of a gas turbine. Finally, interpretation of the mechanical tests through micrographical and microfractographical examinations is focused on the identification of the deformation and failure mechanisms specific to the liquid route processed composite, e.g., nucleation, under either longitudinal or transverse loadings, of internal cracks in the α-phase of the titanium-based matrix, explained through a physical model involving a high shear stress and normal stress combination, leading to cleavage.

  2. The effects of different size gold nanoparticles on mechanical properties of vascular smooth muscle cells under mechanical stretching

    NASA Astrophysics Data System (ADS)

    Kieu, Tri Minh

    Nanotechnology is an emerging and promising frontier for medicine and biomedical research due to its potential for applications such as drug delivery, imaging enhancement, and cancer treatment. While these materials may possess significant possibilities, the effects of these particles in the body and how the particles affect the cells is not fully understood. In this study, vascular smooth muscle cells (VSMCs) will be exposed to 5 and 20 nm diameter citrate AuNPs under mechanical conditions. The cytotoxicity properties of these particles will be investigated using LDH and MTT assays. Atomic force microscopy will be used to study how the size of the nanoparticles affect the mechanical properties of the VSMCs. Immunofluorescence staining for alpha actin will also be performed to enhance understanding of the phenotypic shift. The LDH and MTT cytotoxicity assay results demonstrated that neither 5 nor 20 nm diameter nanoparticles are cytotoxic to the cells. However, the mechanical properties and cell morphology of the VSMCs was altered. Under static conditions, both AuNP treatments decreased the mechanical properties of the cells. The size of the nanoparticles had a softening effect on elastic modulus of the cell and sign of a synthetic phenotype was observed. The VSMCs subjected to mechanical stretching exhibited higher elastic modulus compared to the static experimental groups. Again, both AuNPs treatments decreased the mechanical properties of the cells and signs of more synthetic phenotype was seen. However, the size of the nanoparticles did not have any influence on cell's elastic modulus unlike the static treated cells. The mechanical testing condition provided a better look at how these particles would affect the cells in vivo. While the nanoparticles are not cytotoxic to the VSMCs, they are altering the mechanical properties and phenotype of the cell.

  3. Changes in Evaluation Practice and Policy under Compensatory Education.

    ERIC Educational Resources Information Center

    Hansen, Joe B.

    Major changes have occurred in compensatory education evaluation practices and policies since the introduction of the Title I Evaluation and Reporting System (TIERS) and the Technical Assistance Centers (TAC) in 1976. This paper has three purposes: (1) to discuss these changes at the state and local levels; (2) to illustrate these changes with…

  4. Towards incorporating epigenetic mechanisms into carcinogen identification and evaluation

    PubMed Central

    Herceg, Zdenko

    2013-01-01

    Remarkable progress in the field of epigenetics has turned academic, medical and public attention to the potential applications of these new advances in medicine and various fields of biomedical research. The result is a broader appreciation of epigenetic phenomena in the a etiology of common human diseases, most notably cancer. These advances also represent an exciting opportunity to incorporate epigenetics and epigenomics into carcinogen identification and safety assessment. Current epigenetic studies, including major international sequencing projects, are expected to generate information for establishing the ‘normal’ epigenome of tissues and cell types as well as the physiological variability of the epigenome against which carcinogen exposure can be assessed. Recently, epigenetic events have emerged as key mechanisms in cancer development, and while our search of the Monograph Volume 100 revealed that epigenetics have played a modest role in evaluating human carcinogens by the International Agency for Research on Cancer (IARC) Monographs so far, epigenetic data might play a pivotal role in the future. Here, we review (i) the current status of incorporation of epigenetics in carcinogen evaluation in the IARC Monographs Programme, (ii) potential modes of action for epigenetic carcinogens, (iii) current in vivo and in vitro technologies to detect epigenetic carcinogens, (iv) genomic regions and epigenetic modifications and their biological consequences and (v) critical technological and biological issues in assessment of epigenetic carcinogens. We also discuss the issues related to opportunities and challenges in the application of epigenetic testing in carcinogen identification and evaluation. Although the application of epigenetic assays in carcinogen evaluation is still in its infancy, important data are being generated and valuable scientific resources are being established that should catalyse future applications of epigenetic testing. PMID:23749751

  5. Towards incorporating epigenetic mechanisms into carcinogen identification and evaluation.

    PubMed

    Herceg, Zdenko; Lambert, Marie-Pierre; van Veldhoven, Karin; Demetriou, Christiana; Vineis, Paolo; Smith, Martyn T; Straif, Kurt; Wild, Christopher P

    2013-09-01

    Remarkable progress in the field of epigenetics has turned academic, medical and public attention to the potential applications of these new advances in medicine and various fields of biomedical research. The result is a broader appreciation of epigenetic phenomena in the a etiology of common human diseases, most notably cancer. These advances also represent an exciting opportunity to incorporate epigenetics and epigenomics into carcinogen identification and safety assessment. Current epigenetic studies, including major international sequencing projects, are expected to generate information for establishing the 'normal' epigenome of tissues and cell types as well as the physiological variability of the epigenome against which carcinogen exposure can be assessed. Recently, epigenetic events have emerged as key mechanisms in cancer development, and while our search of the Monograph Volume 100 revealed that epigenetics have played a modest role in evaluating human carcinogens by the International Agency for Research on Cancer (IARC) Monographs so far, epigenetic data might play a pivotal role in the future. Here, we review (i) the current status of incorporation of epigenetics in carcinogen evaluation in the IARC Monographs Programme, (ii) potential modes of action for epigenetic carcinogens, (iii) current in vivo and in vitro technologies to detect epigenetic carcinogens, (iv) genomic regions and epigenetic modifications and their biological consequences and (v) critical technological and biological issues in assessment of epigenetic carcinogens. We also discuss the issues related to opportunities and challenges in the application of epigenetic testing in carcinogen identification and evaluation. Although the application of epigenetic assays in carcinogen evaluation is still in its infancy, important data are being generated and valuable scientific resources are being established that should catalyse future applications of epigenetic testing.

  6. 3,4-Methylenedioxypyrovalerone (MDPV): in vitro mechanisms of hepatotoxicity under normothermic and hyperthermic conditions.

    PubMed

    Valente, Maria João; Araújo, Ana Margarida; Silva, Renata; Bastos, Maria de Lourdes; Carvalho, Félix; Guedes de Pinho, Paula; Carvalho, Márcia

    2016-08-01

    Synthetic cathinones have emerged in recreational drug markets as legal alternatives for classical amphetamines. Though currently banned in several countries, 3,4-methylenedioxypyrovalerone (MDPV) is one of the most commonly abused cathinone derivatives worldwide. We have recently reported the potential of MDPV to induce hepatocellular damage, but the underlying mechanisms responsible for such toxicity remain to be elucidated. Similar to amphetamines, a prominent toxic effect of acute intoxications by MDPV is hyperthermia. Therefore, the present in vitro study aimed to provide insights into cellular mechanisms involved in MDPV-induced hepatotoxicity and also evaluate the contribution of hyperthermia to the observed toxic effects. Primary cultures of rat hepatocytes were exposed to 0.2-1.6 mM MDPV for 48 h, at 37 or 40.5 °C, simulating the rise in body temperature that follows MDPV intake. Cell viability was measured through the MTT reduction and LDH leakage assays. Oxidative stress endpoints and cell death pathways were evaluated, namely the production of reactive oxygen and nitrogen species (ROS and RNS), intracellular levels of reduced (GSH) and oxidized (GSSG) glutathione, adenosine triphosphate (ATP) and free calcium (Ca(2+)), as well as the activities of caspases 3, 8 and 9, and nuclear morphological changes with Hoechst 33342/PI double staining. At 37 °C, MDPV induced a concentration-dependent loss of cell viability that was accompanied by GSH depletion, as one of the first signs of toxicity, observed already at low concentrations of MDPV, with negligible changes on GSSG levels, followed by accumulation of ROS and RNS, depletion of ATP contents and increases in intracellular Ca(2+) concentrations. Additionally, activation of caspases 3, 8, and 9 and apoptotic nuclear morphological changes were found in primary rat hepatocytes exposed to MDPV, indicating that this cathinone derivative activates both intrinsic and extrinsic apoptotic death pathways. The

  7. Evaluation of the mechanical and architectural properties of glenoid bone.

    PubMed

    Mimar, Raghad; Limb, David; Hall, Richard M

    2008-01-01

    Successful glenoid fixation in shoulder arthroplasty is partly dependent on the properties of the underlying bone. Therefore, mapping of the glenoid surface and locating the bone with the highest quality, in terms of mechanical properties and morphology, is a key requirement in ensuring effective fixation. To this end, an investigation was undertaken to study the relationship between indentation behavior and the quality of the glenoid bone. Nineteen embalmed glenoids were obtained from human cadavers (mean age at death, 82 years). Each specimen was tested using a cylindrical indentor at 11 predetermined points to investigate load-displacement behavior. Microcomputed tomography analysis was performed to ascertain the bone volume (BV)/total volume (TV) fraction of the trabecular bone and the subchondral thickness. Statistical analysis showed that both strength and modulus varied with indentation position. Significant relationships were found between either strength or modulus and BV/TV or subchondral thickness, although the explained variance was relatively low.

  8. Selective Automated Perimetry Under Photopic, Mesopic, and Scotopic Conditions: Detection Mechanisms and Testing Strategies

    PubMed Central

    Simunovic, Matthew P.; Moore, Anthony T.; MacLaren, Robert E.

    2016-01-01

    Purpose Automated scotopic, mesopic, and photopic perimetry are likely to be important paradigms in the assessment of emerging treatments of retinal diseases, yet our knowledge of the photoreceptor mechanisms detecting targets under these conditions remains largely dependent on simian data. We therefore aimed to establish the photoreceptor/postreceptoral mechanisms detecting perimetric targets in humans under photopic, mesopic, and scotopic conditions and to make recommendations for suitable clinical testing strategies for selective perimetry. Methods Perimetric sensitivities within 30° of fixation were determined for eight wavelengths (410, 440, 480, 520, 560, 600, 640, and 680 nm) under scotopic, mesopic (1.3 cd.m−2) and photopic (10 cd.m−2) conditions. Data were fitted with vector combinations of rod, S-cone, nonopponent M+L-cone mechanism, and opponent M- versus L-cone mechanism templates. Results Scotopicperimetric sensitivity was determined by rods peripherally and by a combination of rods and cones at, and immediately around, fixation. Mesopic perimetric sensitivity was mediated by M+L-cones and S-cones centrally and by M+L-cones and rods more peripherally. Photopic perimetric sensitivity was determined by an opponent M- versus L-cone, a nonopponent M+L-cone, and an S-cone mechanism centrally and by a combination of an S-cone and an M+L-cone mechanism peripherally. Conclusions Under scotopic conditions, a 480-nm stimulus provides adequate isolation (≥28 dB) of the rod mechanism. Several mechanisms contribute to mesopic sensitivity: this redundancy in detection may cause both insensitivity to broadband white targets and ambiguity in determining which mechanism is being probed with short-wavelength stimuli. M- and L-cone–derived mechanisms are well isolated at 10 cd.m−2: these may be selectively probed by a stimulus at 640 nm (≥ 20 dB isolation). Translation Relevance In human observers, multiple mechanisms contribute to the detection of Goldmann

  9. The research on mechanical effect etching Si in pulsed laser micromaching under water

    NASA Astrophysics Data System (ADS)

    Yuhong, Long; Liangcai, Xiong; Tielin, Shi

    2011-02-01

    To explore further the influencing of mechanical effects on laser machining in the liquid, in the process of great-energy and short-pulsed laser irradiating matter in the liquid, the experiments of 248 nm laser etching n-Si under water were carried out. The removal mechanism of brittle material etched by mechanical effects, which is induced during high-energy and short-pulsed laser machining in the liquid, was discussed. In the paper, the approximate mechanics model of indentation fracture was used to analyze the mechanical effects for removing brittle materials of silicon when laser machining in the liquid. Based on this, a theoretical model of material removal rate was proposed; the experiment of laser machining under water was adopted to validate the model. The experimental results indicate that the removal rate of brittle material caused by shock forces is relatively great.

  10. Terahertz NDE for Under Paint Corrosion Detection and Evaluation

    NASA Technical Reports Server (NTRS)

    Anastasi, Robert F.; Madaras, Eric I.

    2005-01-01

    Corrosion under paint is not visible until it has caused paint to blister, crack, or chip. If corrosion is allowed to continue then structural problems may develop. Identifying corrosion before it becomes visible would minimize repairs and costs and potential structural problems. Terahertz NDE imaging under paint for corrosion is being examined as a method to inspect for corrosion by examining the terahertz response to paint thickness and to surface roughness.

  11. Researches of mechanical behaviour of the bone micro volumes and porous ceramics under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Kolmakova, T. V.; Buyakova, S. P.; Kulkov, S. N.

    2017-02-01

    The research results of the mechanics are presented and the effective mechanical characteristics under uniaxial compression of the simulative micro volume of the compact bone are defined subject to the direction of the collagen-mineral fibers, porosity and mineral content. The experimental and computer studies of the mechanics are performed and the effective mechanical characteristics of the porous zirconium oxide ceramics are defined. The recommendations are developed on the selection of the ceramic samples designed to replace the fragment of the compact bone of a definite structure and mineral content.

  12. Deformation and failure mechanisms of graphite/epoxy composites under static loading

    NASA Technical Reports Server (NTRS)

    Clements, L. L.

    1981-01-01

    The mechanisms of deformation and failure of graphite epoxy composites under static loading were clarified. The influence of moisture and temperature upon these mechanisms were also investigated. Because the longitudinal tensile properties are the most critical to the performance of the composite, these properties were investigated in detail. Both ultimate and elastic mechanical properties were investigated, but the study of mechanisms emphasized those leading to failure of the composite. The graphite epoxy composite selected for study was the system being used in several NASA sponsored flight test programs.

  13. Research of mechanics of the compact bone microvolume and porous ceramics under uniaxial compression

    SciTech Connect

    Kolmakova, T. V. Buyakova, S. P. Kul’kov, S. N.

    2015-11-17

    The research results of the mechanics are presented and the effective mechanical characteristics under uniaxial compression of the simulative microvolume of the compact bone are defined subject to the direction of the collagen-mineral fibers, porosity and mineral content. The experimental studies of the mechanics are performed and the effective mechanical characteristics of the produced porous zirconium oxide ceramics are defined. The recommendations are developed on the selection of the ceramic samples designed to replace the fragment of the compact bone of a definite structure and mineral content.

  14. A path-independent integral for fracture of solids under combined electrochemical and mechanical loadings

    NASA Astrophysics Data System (ADS)

    Haftbaradaran, Hamed; Qu, Jianmin

    2014-11-01

    In this study, we first demonstrate that the J-integral in classical linear elasticity becomes path-dependent when the solid is subjected to combined electrical, chemical and mechanical loadings. We then construct an electro-chemo-mechanical J-integral that is path-independent under such combined multiple driving forces. Further, we show that this electro-chemo-mechanical J-integral represents the rate at which the grand potential releases per unit crack growth. As an example, the path-independent nature of the electro-chemo-mechanical J-integral is demonstrated by solving the problem of a thin elastic film delaminated from a thick elastic substrate.

  15. Using stable isotopes and functional wood anatomy to identify underlying mechanisms of drought tolerance in different provenances of lodgepole pine

    NASA Astrophysics Data System (ADS)

    Isaac-Renton, Miriam; Montwé, David; Hamann, Andreas; Spiecker, Heinrich; Cherubini, Paolo; Treydte, Kerstin

    2016-04-01

    Choosing drought-tolerant seed sources for reforestation may help adapt forests to climate change. By combining dendroecological growth analysis with a long-term provenance trial, we assessed growth and drought tolerance of different populations of a wide-ranging conifer, lodgepole pine (Pinus contorta). This experimental design simulated a climate warming scenario through southward seed transfer, and an exceptional drought also occurred in 2002. We felled over 500 trees, representing 23 seed sources, which were grown for 32 years at three warm, dry sites in southern British Columbia, Canada. Northern populations showed poor growth and drought tolerance. These seed sources therefore appear to be especially at risk under climate change. Before recommending assisted migration of southern seeds towards the north, however, it is important to understand the physiological mechanisms underlying these responses. We combine functional wood anatomy with a dual-isotope approach to evaluate these mechanisms to drought response.

  16. Mechanical properties of gold twinned nanocubes under different triaxial tensile rates

    NASA Astrophysics Data System (ADS)

    Yang, Zailin; Zhang, Guowei; Luo, Gang; Sun, Xiaoqing; Zhao, Jianwei

    2016-08-01

    The gold twinned nanocubes under different triaxial tensile rates are explored by molecular dynamics simulation. Hydrostatic stress and Mises stress are defined in order to understand triaxial stresses. Twin boundaries prevent dislocations between twin boundaries from developing and dislocation angles are inconspicuous, which causes little difference between triaxial stresses. The mechanical properties of the nanocubes under low and high tensile rates are different. The curves of nanocubes under high tensile rates are more abrupt than those under low tensile rates. When the tensile rate is extremely big, the loadings are out of the nanocubes and there are not deformation and fracture in the internal nanocubes.

  17. Mechanisms Underlying Food-Drug Interactions: Inhibition of Intestinal Metabolism and Transport

    PubMed Central

    Won, Christina S.; Oberlies, Nicholas H.; Paine, Mary F.

    2012-01-01

    Food-drug interaction studies are critical to evaluate appropriate dosing, timing, and formulation of new drug candidates. These interactions often reflect prandial-associated changes in the extent and/or rate of systemic drug exposure. Physiologic and physicochemical mechanisms underlying food effects on drug disposition are well-characterized. However, biochemical mechanisms involving drug metabolizing enzymes and transport proteins remain underexplored. Several plant-derived beverages have been shown to modulate enzymes and transporters in the intestine, leading to altered pharmacokinetic (PK) and potentially negative pharmacodynamic (PD) outcomes. Commonly consumed fruit juices, teas, and alcoholic drinks contain phytochemicals that inhibit intestinal cytochrome P450 and phase II conjugation enzymes, as well as uptake and efflux transport proteins. Whereas myriad phytochemicals have been shown to inhibit these processes in vitro, translation to the clinic has been deemed insignificant or undetermined. An overlooked prerequisite for elucidating food effects on drug PK is thorough knowledge of causative bioactive ingredients. Substantial variability in bioactive ingredient composition and activity of a given dietary substance poses a challenge in conducting robust food-drug interaction studies. This confounding factor can be addressed by identifying and characterizing specific components, which could be used as marker compounds to improve clinical trial design and quantitatively predict food effects. Interpretation and integration of data from in vitro, in vivo, and in silico studies require collaborative expertise from multiple disciplines, from botany to clinical pharmacology (i.e., plant to patient). Development of more systematic methods and guidelines is needed to address the general lack of information on examining drug-dietary substance interactions prospectively. PMID:22884524

  18. The fundamental hemodynamic mechanism underlying gastric "stress ulceration" in cardiogenic shock.

    PubMed Central

    Bailey, R W; Bulkley, G B; Hamilton, S R; Morris, J B; Haglund, U H; Meilahn, J E

    1987-01-01

    Acute hemorrhagic ulceration of the gastric mucosa is seen frequently in patients with hypovolemic or cardiogenic shock. Although such lesions clearly are related to regional gastric ischemia, little attention has been directed at the underlying mechanism(s) mediating the ischemia itself. To this end, anesthetized pigs were subjected to sustained cardiogenic shock (mild hemorrhage and pericardial tamponade) such that cardiac output was reduced to 38 +/- 1% of the baseline level for 4 hours, followed by release of the tamponade, reinfusion of the shed blood, and resuscitation for 2 hours. During the period of shock, there was profound regional gastric ischemia, resulting from severe and disproportionate gastric vasoconstriction. "Blinded" gross and microscopic evaluation of the stomachs removed after the experiment revealed severe mucosal ischemic necrosis, hemorrhage, and ulceration, whereas sham-operated pigs showed no lesions. The characteristics of this model therefore mimic the essential features of the gastric "stress ulceration" syndrome. Prior confirmed total alpha-adrenergic blockade with phenoxybenzamine failed to alter these features significantly. In contrast, prior ablation of the renin-angiotensin axis, whether by angiotensin-converting enzyme inhibition with teprotide or by bilateral nephrectomy, significantly and substantially ameliorated the ischemia, vasospasm, and mucosal injury. In this model of cardiogenic shock, acute gastric mucosal "stress ulceration" is caused by a disproportionately severe regional gastric ischemia resulting from selective splanchnic vasospasm that is unaffected by sympathetic blockade but abolished by prior ablation of the renin-angiotensin axis. Like nonocclusive small bowel ischemia, ischemic colitis, and the "shock liver" syndrome, gastric "stress ulceration" is yet another component of the multiple splanchnic organ failure syndrome that appears to be mediated primarily by the remarkable sensitivity of the splanchnic

  19. Mechanisms underlying food-drug interactions: inhibition of intestinal metabolism and transport.

    PubMed

    Won, Christina S; Oberlies, Nicholas H; Paine, Mary F

    2012-11-01

    Food-drug interaction studies are critical to evaluate appropriate dosing, timing, and formulation of new drug candidates. These interactions often reflect prandial-associated changes in the extent and/or rate of systemic drug exposure. Physiologic and physicochemical mechanisms underlying food effects on drug disposition are well-characterized. However, biochemical mechanisms involving drug metabolizing enzymes and transport proteins remain underexplored. Several plant-derived beverages have been shown to modulate enzymes and transporters in the intestine, leading to altered pharmacokinetic (PK) and potentially negative pharmacodynamic (PD) outcomes. Commonly consumed fruit juices, teas, and alcoholic drinks contain phytochemicals that inhibit intestinal cytochrome P450 and phase II conjugation enzymes, as well as uptake and efflux transport proteins. Whereas myriad phytochemicals have been shown to inhibit these processes in vitro, translation to the clinic has been deemed insignificant or undetermined. An overlooked prerequisite for elucidating food effects on drug PK is thorough knowledge of causative bioactive ingredients. Substantial variability in bioactive ingredient composition and activity of a given dietary substance poses a challenge in conducting robust food-drug interaction studies. This confounding factor can be addressed by identifying and characterizing specific components, which could be used as marker compounds to improve clinical trial design and quantitatively predict food effects. Interpretation and integration of data from in vitro, in vivo, and in silico studies require collaborative expertise from multiple disciplines, from botany to clinical pharmacology (i.e., plant to patient). Development of more systematic methods and guidelines is needed to address the general lack of information on examining drug-dietary substance interactions prospectively.

  20. 2-Phenyl-APB-144-Induced Retinal Pigment Epithelium Degeneration and Its Underlying Mechanisms

    PubMed Central

    Kurashima, Hiroaki; Nakamura, Daisuke; Komatsu, Tomoko; Yasuda, Yuki; Habashita-Obata, Sayo; Ichikawa, Sanae; Katsuta, Osamu; Iwawaki, Takao; Kohno, Kenji

    2015-01-01

    Abstract Purpose: To investigate the efficacy of 2-phenyl-APB-144 (APB)-induced retinopathy in a rat model and its underlying mechanisms, with a particular focus on retinal pigment epithelium (RPE) degeneration. Methods: Electroretinograms (ERGs) were evaluated in APB-administered rats. In ARPE-19 cells, cathepsin, and autophagy marker LC3 were analyzed by western blotting or immunohistochemistry. Organelle pH alterations were detected by Acridine Orange Staining. Endoplasmic reticulum stress-dependent or -independent cell death signaling was analyzed by reporter gene assays of activating transcription factor 4 (ATF4), immunoglobulin heavy-chain binding protein (BiP), inositol-requiring enzyme 1α (IRE1α), quantitative reverse transcription-polymerase chain reaction of CHOP mRNA, and the effects of pharmacological eukaryotic initiation factor 2α (eIF2α) dephosphorylation inhibitor, Salubrinal. The pharmacological effects of Salubrinal were examined by fluorophotometry, electrophysiology, and histopathology. Results: APB-induced ERG amplitude reduction and fluorescein permeability enhancement into the vitreous body of rats were determined. In ARPE-19 cells, APB-induced organelle pH alterations, imbalances of procathepsin and cathepsin expression, the time-dependent accumulation of LC3-II, and the translational activation of ATF4 were determined. Salubrinal protected against APB-induced cell death and inhibited ATF4 downstream factor CHOP mRNA induction. In APB-induced rat retinopathy, systemic Salubrinal alleviated the enhanced fluorescein permeability into the vitreous body from the RPE, the reductions in ERG amplitudes, and RPE degeneration. Conclusions: Organelle pH alterations and autophagy impairments are involved in APB-induced RPE cell death. Inhibition of eIF2α dephosphorylation protected the RPE in vivo and in vitro. These findings suggested that APB-induced retinopathy is a valuable animal model for exploring the mechanism of RPE-driven retinopathy

  1. The Mechanism Underlying the Antibacterial Activity of Shikonin against Methicillin-Resistant Staphylococcus aureus

    PubMed Central

    Lee, Young-Seob; Lee, Dae-Young; Kim, Yeon Bok; Lee, Sang-Won; Cha, Seon-Woo; Park, Hong-Woo; Kim, Geum-Soog; Kwon, Dong-Yeul; Lee, Min-Ho; Han, Sin-Hee

    2015-01-01

    Shikonin (SKN), a highly liposoluble naphthoquinone pigment isolated from the roots of Lithospermum erythrorhizon, is known to exert antibacterial, wound-healing, anti-inflammatory, antithrombotic, and antitumor effects. The aim of this study was to examine SKN antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The SKN was analyzed in combination with membrane-permeabilizing agents Tris and Triton X-100, ATPase inhibitors sodium azide and N,N′-dicyclohexylcarbodiimide, and S. aureus-derived peptidoglycan; the effects on MRSA viability were evaluated by the broth microdilution method, time-kill test, and transmission electron microscopy. Addition of membrane-permeabilizing agents or ATPase inhibitors together with a low dose of SKN potentiated SKN anti-MRSA activity, as evidenced by the reduction of MRSA cell density by 75% compared to that observed when SKN was used alone; in contrast, addition of peptidoglycan blocked the antibacterial activity of SKN. The results indicate that the anti-MRSA effect of SKN is associated with its affinity to peptidoglycan, the permeability of the cytoplasmic membrane, and the activity of ATP-binding cassette (ABC) transporters. This study revealed the potential of SKN as an effective natural antibiotic and of its possible use to substantially reduce the use of existing antibiotic may also be important for understanding the mechanism underlying the antibacterial activity of natural compounds. PMID:26265924

  2. Mechanism Underlying Linezolid-induced Thrombocytopenia in a Chronic Kidney Failure Mouse Model

    PubMed Central

    Nishijo, Nao; Tsuji, Yasuhiro; Matsunaga, Kazuhisa; Kutsukake, Masahiko; Okazaki, Fumiyasu; Fukumori, Shiro; Kasai, Hidefumi; Hiraki, Yoichi; Sakamaki, Ippei; Yamamoto, Yoshihiro; Karube, Yoshiharu; To, Hideto

    2017-01-01

    Objective: To investigate the relationship between renal function and linezolid (LZD)-induced thrombocytopenia and elucidate the underlying mechanism using a chronic renal disease (CRD) mouse model. Materials and Methods: CRD was induced in 5-week-old male Institute of Cancer Research (ICR) mice by 5/6 nephrectomy. After this procedure, LZD (25 and 100 mg/kg) was administered intraperitoneally once every day for 28 days. Platelet counts, white blood cell (WBC) counts, and hematocrit (HCT) levels were measured every 7 days. 2-14C-thymidine (0.185 MBq) was administrated intravenously to LZD-administered mice to evaluate the thymidine uptake ability of bone marrow. Results: Platelet counts were significantly lower in the LZD-administered CRD group than in the LZD-nonadministered groups at 14, 21, and 28 days (P < 0.05); however, these changes were not observed in LZD-administered mice with normal renal function, regardless of the duration of LZD administration. No significant changes were observed in WBC counts or HCT levels in any LZD-administered CRD mouse. Moreover, radioactive levels in bone marrow were not significantly different in each group. Conclusions: These results indicate that LZD-induced decreases in platelet counts were enhanced by renal impairment in vivo, suggesting that LZD-induced thrombocytopenia is not caused by nonimmune-mediated bone marrow suppression.

  3. Mechanisms underlying the production of false memories for famous people's names in aging and Alzheimer's disease.

    PubMed

    Plancher, Gaën; Guyard, Anne; Nicolas, Serge; Piolino, Pascale

    2009-10-01

    It is well known that the occurrence of false memories increases with aging, but the results remain inconsistent concerning Alzheimer's disease (AD). Moreover, the mechanisms underlying the production of false memories are still unclear. Using an experimental episodic memory test with material based on the names of famous people in a procedure derived from the DRM paradigm [Roediger, H. L., III, & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory & Cognition, 21, 803-814], we examined correct and false recall and recognition in 30 young adults, 40 healthy older adults, and 30 patients with AD. Moreover, we evaluated the relationships between false memory performance, correct episodic memory performance, and a set of neuropsychological assessments evaluating the semantic memory and executive functions. The results clearly indicated that correct recall and recognition performance decreased with the subjects' age, but it decreased even more with AD. In addition, semantically related false recalls and false recognitions increased with age but not with dementia. On the contrary, non-semantically related false recalls and false recognitions increased with AD. Finally, the regression analyses showed that executive functions mediated related false memories and episodic memory mediated related and unrelated false memories in aging. Moreover, executive functions predicted related and unrelated false memories in AD, and episodic and semantic memory predicted semantically related and unrelated false memories in AD. In conclusion, the results obtained are consistent with the current constructive models of memory suggesting that false memory creation depends on different cognitive functions and, consequently, that the impairments of these functions influence the production of false memories.

  4. Interactive buckling of an inflated envelope under mechanical and thermal loads

    NASA Astrophysics Data System (ADS)

    Wang, C. G.; Liu, M. X.; Tan, H. F.

    2017-02-01

    This paper elucidates the interactive buckling behaviors of an inflated envelope under coupled mechanical and thermal loads, especially the longitudinal wrinkling bifurcation and hoop ovalization buckling. The longitudinal bending buckling process of the inflated envelope can be divided into three continuous stages, which are global buckling, interactive global-local buckling, and kink. A variety of hoop ovalization buckling modes are observed under coupled mechanical-thermal load. Unlike the mechanical case, thermal load leads to a hoop negative ovalization buckling. In addition, it can accelerate the longitudinal coupled bifurcation and resist the hoop coupled ovalization buckling. Moreover, the bending resistance of the inflated envelope will be improved when the length of the structure is increased, resulting in the difficulty of it to become wrinkled. These results provide a new insight into the buckling behaviors of an inflated envelope under coupled external loads, and give a reference for the design of the inflated envelope.

  5. How diagnostic tests help to disentangle the mechanisms underlying neuropathic pain symptoms in painful neuropathies.

    PubMed

    Truini, Andrea; Cruccu, Giorgio

    2016-02-01

    Neuropathic pain, ie, pain arising directly from a lesion or disease affecting the somatosensory afferent pathway, manifests with various symptoms, the commonest being ongoing burning pain, electrical shock-like sensations, and dynamic mechanical allodynia. Reliable insights into the mechanisms underlying neuropathic pain symptoms come from diagnostic tests documenting and quantifying somatosensory afferent pathway damage in patients with painful neuropathies. Neurophysiological investigation and skin biopsy studies suggest that ongoing burning pain primarily reflects spontaneous activity in nociceptive-fiber pathways. Electrical shock-like sensations presumably arise from high-frequency ectopic bursts generated in demyelinated, nonnociceptive, Aβ fibers. Although the mechanisms underlying dynamic mechanical allodynia remain debatable, normally innocuous stimuli might cause pain by activating spared and sensitized nociceptive afferents. Extending the mechanistic approach to neuropathic pain symptoms might advance targeted therapy for the individual patient and improve testing for new drugs.

  6. Quantum versus classical foundation of statistical mechanics under experimentally realistic conditions.

    PubMed

    Reimann, Peter; Evstigneev, Mykhaylo

    2013-11-01

    Focusing on isolated macroscopic systems, described in terms of either a quantum mechanical or a classical model, our two key questions are how far does an initial ensemble (usually far from equilibrium and largely unknown in detail) evolve towards a stationary long-time behavior (equilibration) and how far is this steady state in agreement with the microcanonical ensemble as predicted by statistical mechanics (thermalization). A recently developed quantum mechanical treatment of the problem is briefly summarized, putting particular emphasis on the realistic modeling of experimental measurements and nonequilibrium initial conditions. Within this framework, equilibration can be proven under very weak assumptions about those measurements and initial conditions, while thermalization still requires quite strong additional hypotheses. An analogous approach within the framework of classical mechanics is developed and compared with the quantum case. In particular, the assumptions to guarantee classical equilibration are now rather strong, while thermalization then follows under relatively weak additional conditions.

  7. Mechanisms underlying cellular responses of cells from haemopoietic tissue to low

    SciTech Connect

    Kadhim, Munira A

    2012-08-22

    The above studies will provide fundamental mechanistic information relating genetic predisposition to important low dose phenomena, and will aid in the development of Department of Energy policy, as well as radiation risk policy for the public and the workplace. We believe the proposed studies accurately reflect the goals of the DOE low dose program. To accurately define the risks associated with human exposure to relevant environmental doses of low LET ionizing radiation, it is necessary to completely understand the biological effects at very low doses (i.e. less than 0.1 Gy), including the lowest possible dose, that of a single electron track traversal. At such low doses, a range of studies have shown responses in biological systems which are not related to the direct interaction of radiation tracks with DNA. The role of these "non-targeted responses in critical tissues is poorly understood and little is known regarding the underlying mechanisms. Although critical for dosimetry and risk assessment, the role of individual genetic susceptibility in radiation risk is not satisfactorily defined at present. The aim of the proposed grant is to critically evaluate non-targeted effects of ionizing radiation with a focus on the induction of genomic instability (GI) in key stem cell populations from haemopoietic tissue. Using stem cells from two mouse strains (CBA/CaH and C57BL/6J) known to differ in their susceptibility to radiation effects, we plan to carefully dissect the role of genetic predisposition in these models on genomic instability. We will specifically focus on the effects of low doses of low LET radiation, down to the dose of 10mGy (0.01Gy) X-rays. Using conventional X-ray and we will be able to assess the role of genetic variation under various conditions at a range of doses down to the very low dose of 0.01Gy. Irradiations will be carried out using facilities in routine operation for such studies. Mechanistic studies of instability in different cell

  8. Evaluation of a post-processing approach for multiscale analysis of biphasic mechanics of chondrocytes.

    PubMed

    Sibole, Scott C; Maas, Steve; Halloran, Jason P; Weiss, Jeffrey A; Erdemir, Ahmet

    2013-10-01

    Understanding the mechanical behaviour of chondrocytes as a result of cartilage tissue mechanics has significant implications for both evaluation of mechanobiological function and to elaborate on damage mechanisms. A common procedure for prediction of chondrocyte mechanics (and of cell mechanics in general) relies on a computational post-processing approach where tissue-level deformations drive cell-level models. Potential loss of information in this numerical coupling approach may cause erroneous cellular-scale results, particularly during multiphysics analysis of cartilage. The goal of this study was to evaluate the capacity of first- and second-order data passing to predict chondrocyte mechanics by analysing cartilage deformations obtained for varying complexity of loading scenarios. A tissue-scale model with a sub-region incorporating representation of chondron size and distribution served as control. The post-processing approach first required solution of a homogeneous tissue-level model, results of which were used to drive a separate cell-level model (same characteristics as the sub-region of control model). The first-order data passing appeared to be adequate for simplified loading of the cartilage and for a subset of cell deformation metrics, for example, change in aspect ratio. The second-order data passing scheme was more accurate, particularly when asymmetric permeability of the tissue boundaries was considered. Yet, the method exhibited limitations for predictions of instantaneous metrics related to the fluid phase, for example, mass exchange rate. Nonetheless, employing higher order data exchange schemes may be necessary to understand the biphasic mechanics of cells under lifelike tissue loading states for the whole time history of the simulation.

  9. Ultrasonic evaluations of Achilles tendon mechanical properties poststroke

    PubMed Central

    Zhao, Heng; Ren, Yupeng; Wu, Yi-Ning; Liu, Shu Q.; Zhang, Li-Qun

    2009-01-01

    Spasticity, contracture, and muscle weakness are commonly observed poststroke in muscles crossing the ankle. However, it is not clear how biomechanical properties of the Achilles tendon change poststroke, which may affect functions of the impaired muscles directly. Biomechanical properties of the Achilles tendon, including the length and cross-sectional area, in the impaired and unimpaired sides of 10 hemiparetic stroke survivors were evaluated using ultrasonography. Elongation of the Achilles tendon during controlled isometric ramp-and-hold and ramping up then down contractions was determined using a block-matching method. Biomechanical changes in stiffness, Young's modulus, and hysteresis of the Achilles tendon poststroke were investigated by comparing the impaired and unimpaired sides of the 10 patients. The impaired side showed increased tendon length (6%; P = 0.04), decreased stiffness (43%; P < 0.001), decreased Young's modulus (38%; P = 0.005), and increased mechanical hysteresis (1.9 times higher; P < 0.001) compared with the unimpaired side, suggesting Achilles tendon adaptations to muscle spasticity, contracture, and/or disuse poststroke. In vivo quantitative characterizations of the tendon biomechanical properties may help us better understand changes of the calf muscle-tendon unit as a whole and facilitate development of more effective treatments. PMID:19118156

  10. Evaluation of force generation mechanisms in natural, passive hydraulic actuators

    PubMed Central

    Le Duigou, A.; Castro, M.

    2016-01-01

    Pine cones are well known natural actuators that can move their scales upon humidity gradient. The mechanism manifests itself through a displacement easily observable by the naked eye, but coupled with stress generation. In ancient Egypt, wooden wedges were used to break soft blocks of stone by the generated swelling stress. The purpose of the present study is to evaluate the ability of pine cone scales to generate forces while being wetted. In our experiments, a blocking force of around 3N is measured depending on the position on the pine cone where the scales are extracted. A fairly good agreement is obtained when theoretical results based on bimetallic strip systems are compared with experimental data, even if overestimation is observed arising from the input data considered for dry tissues. Inspired by a simplified pine cone microstructure, a biocomposite analogue is manufactured and tested. Although an adequate blocking force can be generated, it has a lower value compared to natural pine cones which benefit from optimized swelling tissue content and interfacial bond strength between them. This study provides new insights to understand the generation of force by pine cones as well as to develop novel biocomposite functionalities. PMID:26726792

  11. Evaluation of force generation mechanisms in natural, passive hydraulic actuators

    NASA Astrophysics Data System (ADS)

    Le Duigou, A.; Castro, M.

    2016-01-01

    Pine cones are well known natural actuators that can move their scales upon humidity gradient. The mechanism manifests itself through a displacement easily observable by the naked eye, but coupled with stress generation. In ancient Egypt, wooden wedges were used to break soft blocks of stone by the generated swelling stress. The purpose of the present study is to evaluate the ability of pine cone scales to generate forces while being wetted. In our experiments, a blocking force of around 3N is measured depending on the position on the pine cone where the scales are extracted. A fairly good agreement is obtained when theoretical results based on bimetallic strip systems are compared with experimental data, even if overestimation is observed arising from the input data considered for dry tissues. Inspired by a simplified pine cone microstructure, a biocomposite analogue is manufactured and tested. Although an adequate blocking force can be generated, it has a lower value compared to natural pine cones which benefit from optimized swelling tissue content and interfacial bond strength between them. This study provides new insights to understand the generation of force by pine cones as well as to develop novel biocomposite functionalities.

  12. Non-destructive evaluation of mechanical properties of magnetic materials

    SciTech Connect

    Kankolenski, K.P.; Hua, S.Z.; Yang, D.X.; Hicho, G.E.; Swartzendruber, L.J.; Zang, Z.; Chopra, H.D.

    2000-07-01

    A magnetic-based non-destructive evaluation (NDE) method, which employs Barkhausen effect and measurement of the hysteresis loops, is used to correlate the magnetic and mechanical properties of ultra low carbon (ULC) steel. In particular, the NDE method was used to detect small deviations from linearity that occur in the stress-strain curve well below the 0.2% offset strain, and which generally defines the yield point in materials. Results show that three parameters: jumpsum and jumpsum rate (derived from the Barkhausen spectrum), and the relative permeability (derived from the B-H loops) varies sensitively with small permanent strains, and can be related to the plastic deformation in ULC steels. Investigation of micromagnetic structure revealed that plastic deformation leaves a residual stress state in the samples; the associated magneto-elastic energy makes the favorable easy axis of magnetization in a given grain to be the one that lies closest to the tensile axis. The consequence of this realignment of domains is that wall motion becomes intergranular in nature (as opposed to intragranular in unstrained samples). As a result, the more complex grain boundaries instead of dislocations, become the dominant pinning sites for domain walls. These observations provide a microscopic interpretation of the observed changes in the measured magnetic properties.

  13. Evaluation of hydro-mechanical pulsation for rocket injector research

    NASA Astrophysics Data System (ADS)

    Wilson, Matthew B.

    The Propulsion Research Center at the University of Alabama in Huntsville has designed and built a hydro-mechanical pulsator to simulate the pressure fluctuations created by high frequency combustion instability. The pressure response characteristics were evaluated in an atmospheric test rig using filtered de-ionized water as the working fluid. The outlet of the pulsator was connected to a swirl injector post to provide downstream flow resistance. Previous low pressure and mass flow experimental data revealed a complex relationship between the control parameters and the pulsation response. For each test, the average mass flow rates of the waste water, water lost through the seals, and injector mass flow rates are measured. A dynamic pressure transducer at the pulsator exit measures and records the pressure waveform. Pulsation magnitude, reliability, repeatability, pulsation effects, and detailed variable control are examined. The data shows the pulsator is capable of generating 30% pulsation at 1575 Hz input. The repeatability of the pulsator is questionable because the standard deviations exceeded 40% of the average. The detailed data obtained during this research provides is sufficient to develop a pulsator tuning procedure for future applications.

  14. Experimental evaluation of starch utilization mechanism by activated sludge.

    PubMed

    Karahan, Ozlem; Martins, António; Orhon, Derin; van Loosdrecht, Mark C M

    2006-04-05

    The study aimed to explore the conversion processes of hydrolysable substrates by activated sludge. Experimental data were collected from a sequencing batch reactor (SBR) and from batch tests using activated sludge acclimated to native potato starch (NPS). Parallel batch tests were run with NPS (particulate), soluble starch (SolS), maltose, and glucose for comparative evaluation. The fate of organic carbon in the reactor was followed directly by measuring substrate, poly-glucose, and oxygen uptake rate. Results indicated that adsorption was the dominant mechanism for starch removal with subsequent enzymatic hydrolysis inside the flocs. The role of bulk liquid enzyme activity was minimal. Starch was observed to hydrolyze to maltose rather than glucose. The behavior of NPS and SolS was quite similar to maltose in terms of poly-glucose formation and oxygen uptake. Since the simplest hydrolysis product was maltose, the biomass was not acclimated to glucose and thus, glucose exhibited a significantly different removal and storage pattern. The study also showed that differentiation of readily biodegradable and slowly biodegradable COD should better be based on the kinetics of their utilization rather than simple physical characterization.

  15. Ultrasonic evaluations of Achilles tendon mechanical properties poststroke.

    PubMed

    Zhao, Heng; Ren, Yupeng; Wu, Yi-Ning; Liu, Shu Q; Zhang, Li-Qun

    2009-03-01

    Spasticity, contracture, and muscle weakness are commonly observed poststroke in muscles crossing the ankle. However, it is not clear how biomechanical properties of the Achilles tendon change poststroke, which may affect functions of the impaired muscles directly. Biomechanical properties of the Achilles tendon, including the length and cross-sectional area, in the impaired and unimpaired sides of 10 hemiparetic stroke survivors were evaluated using ultrasonography. Elongation of the Achilles tendon during controlled isometric ramp-and-hold and ramping up then down contractions was determined using a block-matching method. Biomechanical changes in stiffness, Young's modulus, and hysteresis of the Achilles tendon poststroke were investigated by comparing the impaired and unimpaired sides of the 10 patients. The impaired side showed increased tendon length (6%; P = 0.04), decreased stiffness (43%; P < 0.001), decreased Young's modulus (38%; P = 0.005), and increased mechanical hysteresis (1.9 times higher; P < 0.001) compared with the unimpaired side, suggesting Achilles tendon adaptations to muscle spasticity, contracture, and/or disuse poststroke. In vivo quantitative characterizations of the tendon biomechanical properties may help us better understand changes of the calf muscle-tendon unit as a whole and facilitate development of more effective treatments.

  16. Evaluation of Geothermal Heat Pump Systems under Various Conditions

    NASA Astrophysics Data System (ADS)

    Lee, S.; Bae, G.; Lee, K.

    2006-12-01

    Experimental and numerical test were accomplished to evaluate the relations between the geothermal system and the hydrogeological condition. Sand tank experiment was designed. Combinations of different gradients and temperature gradients were applied for testing the real-time monitoring performance. Numerical modeling results were compared with the experimental data. Water injection-system imitating open- and closed-loop geothermal heat pumps were applied to estimate the change of the distribution of ambient groundwater temperature. The experimental results of different settings were used to estimate the effects of shallow depth geothermal energy utilization on the groundwater system.

  17. Evaluation of engine coolants under flow boiling conditions

    SciTech Connect

    McAssey, E.V. Jr.; Stinson, C.; Gollin, M.

    1995-12-31

    An experimental program has been conducted to evaluate the heat transfer performance of two engine coolant mixtures, propylene-glycol/water and ethylene-glycol/water. In each mixture, the concentration was 50-50 by volume. Performance in this situation is defined as the ability to maintain a lower surface temperature for a given flux. The heat transfer regimes considered covered the range from single phase forced convection through saturated flow boiling. Results show that both coolants perform satisfactorily. However, in single phase convection, ethylene-glycol/water is slightly more effective. Conversely, for sub-cooled nucleate boiling and saturated boiling, propylene-glycol/water results in slightly lower metal temperatures.

  18. Direct Associations or Internal Transformations? Exploring the Mechanisms Underlying Sequential Learning Behavior

    PubMed Central

    Gureckis, Todd M.; Love, Bradley C.

    2009-01-01

    We evaluate two broad classes of cognitive mechanisms that might support the learning of sequential patterns. According to the first, learning is based on the gradual accumulation of direct associations between events based on simple conditioning principles. The other view describes learning as the process of inducing the transformational structure that defines the material. Each of these learning mechanisms predict differences in the rate of acquisition for differently organized sequences. Across a set of empirical studies, we compare the predictions of each class of model with the behavior of human subjects. We find that learning mechanisms based on transformations of an internal state, such as recurrent network architectures (e.g., Elman, 1990), have difficulty accounting for the pattern of human results relative to a simpler (but more limited) learning mechanism based on learning direct associations. Our results suggest new constraints on the cognitive mechanisms supporting sequential learning behavior. PMID:20396653

  19. Endoplasmic reticulum stress regulates rat mandibular cartilage thinning under compressive mechanical stress.

    PubMed

    Li, Huang; Zhang, Xiang-Yu; Wu, Tuo-Jiang; Cheng, Wei; Liu, Xin; Jiang, Ting-Ting; Wen, Juan; Li, Jie; Ma, Qiao-Ling; Hua, Zi-Chun

    2013-06-21

    Compressive mechanical stress-induced cartilage thinning has been characterized as a key step in the progression of temporomandibular joint diseases, such as osteoarthritis. However, the regulatory mechanisms underlying this loss have not been thoroughly studied. Here, we used an established animal model for loading compressive mechanical stress to induce cartilage thinning in vivo. The mechanically stressed mandibular chondrocytes were then isolated to screen potential candidates using a proteomics approach. A total of 28 proteins were identified that were directly or indirectly associated with endoplasmic reticulum stress, including protein disulfide-isomerase, calreticulin, translationally controlled tumor protein, and peptidyl-prolyl cis/trans-isomerase protein. The altered expression of these candidates was validated at both the mRNA and protein levels. The induction of endoplasmic reticulum stress by mechanical stress loading was confirmed by the activation of endoplasmic reticulum stress markers, the elevation of the cytoplasmic Ca(2+) level, and the expansion of endoplasmic reticulum membranes. More importantly, the use of a selective inhibitor to block endoplasmic reticulum stress in vivo reduced the apoptosis observed at the early stages of mechanical stress loading and inhibited the proliferation observed at the later stages of mechanical stress loading. Accordingly, the use of the inhibitor significantly restored cartilage thinning. Taken together, these results demonstrated that endoplasmic reticulum stress is significantly activated in mechanical stress-induced mandibular cartilage thinning and, more importantly, that endoplasmic reticulum stress inhibition alleviates this loss, suggesting a novel pharmaceutical strategy for the treatment of mechanical stress-induced temporomandibular joint diseases.

  20. [Environmental efficiency evaluation under carbon emission constraint in Western China].

    PubMed

    Rong, Jian-bo; Yan, Li-jiao; Huang, Shao-rong; Zhang, Ge

    2015-06-01

    This research used the SBM model based on undesirable outputs to measure the static environmental efficiency of Western China under carbon emission constraint from 2000 to 2012. The researchers also utilized the Malmquist index to further analyze the change tendency of environmental efficiency. Additionally, Tobit regression analysis was used to study the factors relevant to environmental efficiency. Practical solutions to improve environmental quality in Western China were put forward. The study showed that in Western China, environmental efficiency with carbon emission constraint was significantly lower than that without carbon emission constraint, and the difference could be described as an inverse U-shaped curve which increased at first and then decreased. Guang-xi and Inner Mongolia, the two provinces met the effective environmental efficiency levels all the time under carbon emission constraint. However, the five provinces of Guizhou, Gansu, Qinghai, Ningxia and Xinjiang did not. Furthermore, Ningxia had the lowest level of environmental efficiency, with a score between 0.281-0.386. Although the environmental efficiency of most provinces was currently at an ineffective level, the environmental efficiency quality was gradually improving at an average speed of 6.6%. Excessive CO2 emission and a large amount of energy consumption were the primary factors causing environmental inefficiency in Western China, and energy intensity had the most negative impact on the environmental efficiency. The increase of import and export trade reduced the environmental efficiency significantly in Western China, while the increase of foreign direct investment had a positive effect on its environmental efficiency.

  1. Neural networks underlying implicit and explicit moral evaluations in psychopathy

    PubMed Central

    Yoder, K J; Harenski, C; Kiehl, K A; Decety, J

    2015-01-01

    Psychopathy, characterized by symptoms of emotional detachment, reduced guilt and empathy and a callous disregard for the rights and welfare of others, is a strong risk factor for immoral behavior. Psychopathy is also marked by abnormal attention with downstream consequences on emotional processing. To examine the influence of task demands on moral evaluation in psychopathy, functional magnetic resonance imaging was used to measure neural response and functional connectivity in 88 incarcerated male subjects (28 with Psychopathy Checklist Revised (PCL-R) scores ⩾30) while they viewed dynamic visual stimuli depicting interpersonal harm and interpersonal assistance in two contexts, implicit and explicit. During the implicit task, high psychopathy was associated with reduced activity in the dorsolateral prefrontal cortex and caudate when viewing harmful compared with helpful social interactions. Functional connectivity seeded in the right amygdala and right temporoparietal junction revealed decreased coupling with the anterior cingulate cortex (ACC), anterior insula, striatum and ventromedial prefrontal cortex. In the explicit task, higher trait psychopathy predicted reduced signal change in ACC and amygdala, accompanied by decreased functional connectivity to temporal pole, insula and striatum, but increased connectivity with dorsal ACC. Psychopathy did not influence behavioral performance in either task, despite differences in neural activity and functional connectivity. These findings provide the first direct evidence that hemodynamic activity and neural coupling within the salience network are disrupted in psychopathy, and that the effects of psychopathy on moral evaluation are influenced by attentional demands. PMID:26305476

  2. Neural networks underlying implicit and explicit moral evaluations in psychopathy.

    PubMed

    Yoder, K J; Harenski, C; Kiehl, K A; Decety, J

    2015-08-25

    Psychopathy, characterized by symptoms of emotional detachment, reduced guilt and empathy and a callous disregard for the rights and welfare of others, is a strong risk factor for immoral behavior. Psychopathy is also marked by abnormal attention with downstream consequences on emotional processing. To examine the influence of task demands on moral evaluation in psychopathy, functional magnetic resonance imaging was used to measure neural response and functional connectivity in 88 incarcerated male subjects (28 with Psychopathy Checklist Revised (PCL-R) scores ⩾ 30) while they viewed dynamic visual stimuli depicting interpersonal harm and interpersonal assistance in two contexts, implicit and explicit. During the implicit task, high psychopathy was associated with reduced activity in the dorsolateral prefrontal cortex and caudate when viewing harmful compared with helpful social interactions. Functional connectivity seeded in the right amygdala and right temporoparietal junction revealed decreased coupling with the anterior cingulate cortex (ACC), anterior insula, striatum and ventromedial prefrontal cortex. In the explicit task, higher trait psychopathy predicted reduced signal change in ACC and amygdala, accompanied by decreased functional connectivity to temporal pole, insula and striatum, but increased connectivity with dorsal ACC. Psychopathy did not influence behavioral performance in either task, despite differences in neural activity and functional connectivity. These findings provide the first direct evidence that hemodynamic activity and neural coupling within the salience network are disrupted in psychopathy, and that the effects of psychopathy on moral evaluation are influenced by attentional demands.

  3. Improvement and evaluation of thermal, electrical, sealing and mechanical contacts, and their interface materials

    NASA Astrophysics Data System (ADS)

    Luo, Xiangcheng

    Material contacts, including thermal, electrical, seating (fluid sealing and electromagnetic sealing) and mechanical (pressure) contacts, together with their interface materials, were, evaluated, and in some cases, improved beyond the state of the art. The evaluation involved the use of thermal, electrical and mechanical methods. For thermal contacts, this work evaluated and improved the heat transfer efficiency between two contacting components by developing various thermal interface pastes. Sodium silicate based thermal pastes (with boron nitride particles as the thermally conductive filler) as well as polyethylene glycol (PEG) based thermal pastes were developed and evaluated. The optimum volume fractions of BN in sodium silicate based pastes and PEG based pastes were 16% and 18% respectively. The contribution of Li+ ions to the thermal contact conductance in the PEG-based paste was confirmed. For electrical contacts, the relationship between the mechanical reliability and electrical reliability of solder/copper and silver-epoxy/copper joints was addressed. Mechanical pull-out testing was conducted on solder/copper and silver-epoxy/copper joints, while the contact electrical resistivity was measured. Cleansing of the copper surface was more effective for the reliability of silver-epoxy/copper joint than that of solder/copper joint. For sealing contacts, this work evaluated flexible graphite as an electromagnetic shielding gasket material. Flexible graphite was found to be at least comparable to conductive filled silicone (the state of the art) in terms of the shielding effectiveness. The conformability of flexible graphite with its mating metal surface under repeated compression was characterized by monitoring the contact electrical resistance, as the conformability is important to both electromagnetic scaling and fluid waling using flexible graphite. For mechanical contacts, this work focused on the correlation of the interface structure (such as elastic

  4. Structural and Mechanical Properties of Intermediate Filaments under Extreme Conditions and Disease

    NASA Astrophysics Data System (ADS)

    Qin, Zhao

    Intermediate filaments are one of the three major components of the cytoskeleton in eukaryotic cells. It was discovered during the recent decades that intermediate filament proteins play key roles to reinforce cells subjected to large-deformation as well as participate in signal transduction. However, it is still poorly understood how the nanoscopic structure, as well as the biochemical properties of these protein molecules contribute to their biomechanical functions. In this research we investigate the material function of intermediate filaments under various extreme mechanical conditions as well as disease states. We use a full atomistic model and study its response to mechanical stresses. Learning from the mechanical response obtained from atomistic simulations, we build mesoscopic models following the finer-trains-coarser principles. By using this multiple-scale model, we present a detailed analysis of the mechanical properties and associated deformation mechanisms of intermediate filament network. We reveal the mechanism of a transition from alpha-helices to beta-sheets with subsequent intermolecular sliding under mechanical force, which has been inferred previously from experimental results. This nanoscale mechanism results in a characteristic nonlinear force-extension curve, which leads to a delocalization of mechanical energy and prevents catastrophic fracture. This explains how intermediate filament can withstand extreme mechanical deformation of > 1 00% strain despite the presence of structural defects. We combine computational and experimental techniques to investigate the molecular mechanism of Hutchinson-Gilford progeria syndrome, a premature aging disease. We find that the mutated lamin tail .domain is more compact and stable than the normal one. This altered structure and stability may enhance the association of intermediate filaments with the nuclear membrane, providing a molecular mechanism of the disease. We study the nuclear membrane association

  5. Conception on the cell mechanisms of bone tissue loss under spase flight conditions

    NASA Astrophysics Data System (ADS)

    Rodionova, Natalia; Oganov, Victor; Kabitskaya, Olga

    Basing on the analysis of available literature and the results of our own electron microscopic and radioautographic researches the data are presented about the morpho-functional peculiarities and succession of cellular interactions in adaptive remodeling of bone structures under normal conditions and after exposure of animals (rats, monkeys, mice) to microgravity (SLS-2, Bion-11, BionM-1). The probable cellular mechanisms of the development of osteopenia and osteoporosis are considered. Our conception on remodeling proposes the following sequence in the development of cellular interactions after decrease of the mechanical loading: a primary response of osteocytes (mechanosensory cells) to the mechanical stimulus; osteocytic remodeling (osteolysis); transmission of the mechanical signals through a system of canals and processes to functionally active osteoblasts and surface osteocytes as well as to the bone-marrow stromal cells and to those lying on bone surfaces. As a response to the mechanical stimulus (microgravity) the system of stromal cell-preosteoblast-osteoblast shows a delay in proliferation, differentiation and specific functioning of the osteogenetic cells, some of the osteoblasts undergo apoptosis. Then the osteoclastic reaction occurs (attraction of monocytes and formation of osteoclasts and bone matrix resorption in the loci of apoptosis of osteoblasts and osteocytes). The macrophagal reaction is followed by osteoblastogenesis, which appears to be a rehabilitating process. However, during prolonged absence of mechanical stimuli (microgravity, long-time immobilization) the adaptive activization of osteoblastogenesis doesn’t occur (as it is the case during the physiological remodeling of bone tissue) or it occurs to a smaller degree. The loading deficit leads to an adaptive differentiation of stromal cells to fibroblastic cells and adipocytes in these remodeling loci. These cell reactions are considered as adaptive-compensatory, but they don’t result

  6. Speckle shearing pattern interferometry to assess mechanical strain in the human mandible jaw bone under physiological stress

    NASA Astrophysics Data System (ADS)

    Moreno, V.; Vázquez-Vázquez, C.; Gallas, M.; Crespo, J.

    2011-05-01

    Electronic Speckle Pattern Interferometry (ESPI) has been used in experiments to measure displacement on the surface of bones undergoing external forces. However in order to asses directly the derivative of the displacements a related technique, Shearography, is used. This technique has been applied in biomechanical experiments although limited to small pieces of bone to determine their elastic properties. In this work we propose the use of Shearing Speckle Interferometry to evaluate the mechanical behaviour of the human mandible under compressive stress, simulating masticatory forces or impacts, in order to analyze the strain distribution on mandibular bone.

  7. The Mediated MIMIC Model for Understanding the Underlying Mechanism of DIF

    ERIC Educational Resources Information Center

    Cheng, Ying; Shao, Can; Lathrop, Quinn N.

    2016-01-01

    Due to its flexibility, the multiple-indicator, multiple-causes (MIMIC) model has become an increasingly popular method for the detection of differential item functioning (DIF). In this article, we propose the mediated MIMIC model method to uncover the underlying mechanism of DIF. This method extends the usual MIMIC model by including one variable…

  8. A Framework for Studying Mechanisms Underlying Terminal Decline in Well-Being

    ERIC Educational Resources Information Center

    Gerstorf, Denis; Ram, Nilam

    2015-01-01

    Multiple facets of well-being are known to show steep end-of-life deteriorations. However, the underlying mechanisms and pathways are vague. Capitalizing on an earlier review of the existing empirical literature on terminal decline, we present a conceptual/methodological framework that can be used as a tool to structure future inquiry aimed at…

  9. Swallowing rehabilitation of dysphagic tracheostomized patients under mechanical ventilation in intensive care units: a feasibility study

    PubMed Central

    Rodrigues, Katia Alonso; Machado, Flávia Ribeiro; Chiari, Brasília Maria; Rosseti, Heloísa Baccaro; Lorenzon, Paula; Gonçalves, Maria Inês Rebelo

    2015-01-01

    Objective The aim of the present study was to assess the feasibility of the early implementation of a swallowing rehabilitation program in tracheostomized patients under mechanical ventilation with dysphagia. Methods This prospective study was conducted in the intensive care units of a university hospital. We included hemodynamically stable patients under mechanical ventilation for at least 48 hours following 48 hours of tracheostomy and with an appropriate level of consciousness. The exclusion criteria were previous surgery in the oral cavity, pharynx, larynx and/or esophagus, the presence of degenerative diseases or a past history of oropharyngeal dysphagia. All patients were submitted to a swallowing rehabilitation program. An oropharyngeal structural score, a swallowing functional score and an otorhinolaryngological structural and functional score were determined before and after swallowing therapy. Results We included 14 patients. The mean duration of the rehabilitation program was 12.4 ± 9.4 days, with 5.0 ± 5.2 days under mechanical ventilation. Eleven patients could receive oral feeding while still in the intensive care unit after 4 (2 - 13) days of therapy. All scores significantly improved after therapy. Conclusion In this small group of patients, we demonstrated that the early implementation of a swallowing rehabilitation program is feasible even in patients under mechanical ventilation. PMID:25909315

  10. Deformation Microstructures and Creep Mechanisms in Advanced ZR-Based Cladding Under Biazal Loading

    SciTech Connect

    K. Linga Murty

    2008-08-11

    Investigate creep behavior of Zr-based cladding tubes with attention to basic creep mechanisms and transitions in them at low stresses and/or temperatures and study the dislocation microstructures of deformed samples for correlation with the underlying micromechanism of creep

  11. Underlying Mechanisms in the Relationship between Africentric Worldview and Depressive Symptoms

    ERIC Educational Resources Information Center

    Neblett, Enrique W., Jr.; Hammond, Wizdom Powell; Seaton, Eleanor K.; Townsend, Tiffany G.

    2010-01-01

    This study examines underlying mechanisms in the relationship between an Africentric worldview and depressive symptoms. Participants were 112 African American young adults. An Africentric worldview buffered the association between perceived stress and depressive symptoms. The relationship between an Africentric worldview and depressive symptoms…

  12. The corrosion and corrosion mechanical properties evaluation for the LBB concept in VVERs

    SciTech Connect

    Ruscak, M.; Chvatal, P.; Karnik, D.

    1997-04-01

    One of the conditions required for Leak Before Break application is the verification that the influence of corrosion environment on the material of the component can be neglected. Both the general corrosion and/or the initiation and, growth of corrosion-mechanical cracks must not cause the degradation. The primary piping in the VVER nuclear power plant is made from austenitic steels (VVER 440) and low alloy steels protected with the austenitic cladding (VVER 1000). Inspection of the base metal and heterogeneous weldments from the VVER 440 showed that the crack growth rates are below 10 m/s if a low oxygen level is kept in the primary environment. No intergranular cracking was observed in low and high oxygen water after any type of testing, with constant or periodic loading. In the framework of the LBB assessment of the VVER 1000, the corrosion and corrosion mechanical properties were also evaluated. The corrosion and corrosion mechanical testing was oriented predominantly to three types of tests: stress corrosion cracking tests corrosion fatigue tests evaluation of the resistance against corrosion damage. In this paper, the methods used for these tests are described and the materials are compared from the point of view of response on static and periodic mechanical stress on the low alloyed steel 10GN2WA and weld metal exposed in the primary circuit environment. The slow strain rate tests and static loading of both C-rings and CT specimens were performed in order to assess the stress corrosion cracking characteristics. Cyclic loading of CT specimens was done to evaluate the kinetics of the crack growth under periodical loading. Results are shown to illustrate the approaches used. The data obtained were evaluated also from the point of view of comparison of the influence of different structure on the stress corrosion cracking appearance. The results obtained for the base metal and weld metal of the piping are presented here.

  13. Evaluating the Impact of Dwell Time on Solder Interconnect Durability Under Bending Loads

    NASA Astrophysics Data System (ADS)

    Menon, Sandeep; Osterman, Michael; Pecht, Michael

    2015-11-01

    With the increasing portability and miniaturization of modern-day electronics, the mechanical robustness of these systems has become more of a concern. Existing standards for conducting mechanical durability tests of electronic assemblies include bend, shock/drop, vibration, and torsion. Although these standards provide insights into both cyclic fatigue and overstress damage incurred in solder interconnects (widely regarded as the primary mode of failure in electronic assemblies), they fail to address the impact of time- dependent (creep) behavior due to sustained mechanical loads on solder interconnect durability. It has been seen in previous studies that solder durability under thermal cycling loads is inversely proportional to the dwell time or hold time at either temperature extreme of the imposed temperature cycle. Fatigue life models, which include dwell time, have been developed for solder interconnects subject to temperature cycling. However, the fatigue life models that have been developed in the literature for solder interconnects under mechanical loads fail to address the influence of the duration of loading. In this study, solder interconnect test vehicles were subjected to cyclic mechanical bending with various dwell times in order to understand the impact of the duration of mechanical loads on solder interconnect durability. The solder interconnects examined in this study were formed with 2512 resistor packages using various solder compositions [tin-lead (Sn-Pb) and 96.5Sn-3Ag-0.5Cu (SAC305)]. To evaluate the impact of dwell time, the boards were tested with 0 s, 60 s, and 300 s of dwell time at both extremes of the loading profile. It was observed that an increase in the dwell time of the loading profile resulted in a decrease in the characteristic life of the solder interconnects. The decrease in fatigue life was attributed to increased creep damage as identified using finite-element simulations. An energy partitioning approach was then used to

  14. Characteristic evaluation of CFRP composites under falling weight impact loading

    NASA Astrophysics Data System (ADS)

    Im, K. H.; Park, N. S.; Hsu, D. K.; Kim, S. K.; Park, J. W.; Yang, I. Y.

    2002-05-01

    This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of carbon-fiber reinforced plastics (CFRP) laminate plates based on considerations of stress wave propagation theory, which were converted to measurements of load and displacement verses time. The delamination area of impacted specimens for the different ply orientations was measured with an ultrasonic C-scanner to determine the correlation between impact energy and delamination area. The energy absorbed by a quasi-isotropic specimen having four interfaces was higher than that of orthotropic laminates with two interfaces. The more interfaces, the greater the energy absorbed. The absorbed energy of a hybrid specimen containing a CFRP layer was higher than that of normal specimens. Also, a falling weight impact tester was built to evaluate the characteristics and impact strength of CFRPs.

  15. An Evaluation Method for the Bursting Characteristics of Coal Under the Effect of Loading Rate

    NASA Astrophysics Data System (ADS)

    Haitao, Li; Hongwei, Zhou; Yaodong, Jiang; Hongwei, Wang

    2016-08-01

    Changes in loading rate can affect the strength performance and bursting characteristics of coal. Coal samples from the same source were subject to mechanical tests for multi-loading rates. These tests were carried out to determine changes in evaluation indicators for the law of bursting liability due to increases in the loading rate. The results show that indicators, including the uniaxial compressive strength and the bursting energy index, first increased and then decreased with the increase in loading rate. The value of the loading rate, which corresponds to the strength turning point, is named the "critical loading rate". The results of evaluating the bursting liability of coal (from the same source) show all the possibilities. The critical loading rate corresponds to the highest bursting liability. The "loading rate sensitivity" is proposed to describe the comprehensive response of the bursting characteristics to the loading rate. This index, combined with the scale conversion method, makes the field application of laboratory experimentation possible. This method for evaluating the bursting liability of coal under the effect of loading rate was systematically established and shows good applicability.

  16. Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients

    NASA Technical Reports Server (NTRS)

    Zju, Dongming; Ghosn, Louis J.; Miller, Robert A.

    2008-01-01

    Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.

  17. Identification of the mechanism underlying a human chimera by SNP array analysis.

    PubMed

    Shin, So Youn; Yoo, Han-Wook; Lee, Beom Hee; Kim, Kun Suk; Seo, Eul-Ju

    2012-09-01

    Human chimerism resulting from the fusion of two different zygotes is a rare phenomenon. Two mechanisms of chimerism have been hypothesized: dispermic fertilization of an oocyte and its second polar body and dispermic fertilization of two identical gametes from parthenogenetic activation, and these can be identified and discriminated using DNA polymorphism. In the present study we describe a patient with chimerism presenting as a true hermaphrodite and applied single nucleotide polymorphism array analysis to demonstrate dispermic fertilization of two identical gametes from parthenogenetic activation as the underlying mechanism at the whole chromosome level. We suggest that application of genotyping array analysis to the diagnostic process in patients with disorders of sex development will help identify more human chimera patients and increase our understanding of the underlying mechanisms.

  18. Progressive damage analysis of carbon/epoxy laminates under couple laser and mechanical loading

    NASA Astrophysics Data System (ADS)

    Liu, Wanlei; Chang, Xinlong; Zhang, Xiaojun; Zhang, Youhong

    A multiscale model based bridge theory is proposed for the progressive damage analysis of carbon/epoxy laminates under couple laser and mechanical loading. The ablation model is adopted to calculate ablation temperature changing and ablation surface degradation. The polynomial strengthening model of matrix is used to improve bridging model for reducing parameter input. Stiffness degradation methods of bridging model are also improved in order to analyze the stress redistribution more accurately when the damage occurs. Thermal-mechanical analyses of the composite plate are performed using the ABAQUS/Explicit program with the developed model implemented in the VUMAT. The simulation results show that this model can be used to proclaim the mesoscale damage mechanism of composite laminates under coupled loading.

  19. Intercomparison of chemical mechanisms for air quality policy formulation and assessment under North American conditions.

    PubMed

    Derwent, Richard

    2017-02-22

    The intercomparison of seven chemical mechanisms for their suitability for air quality policy formulation and assessment is described. Box modelling techniques were employed using 44 sets of background environmental conditions covering North America to constrain the chemical development of the longer-lived species. The selected mechanisms were modified to enable an unbiased assessment of the adequacy of the parameterisations of photochemical ozone production from VOC oxidation in the presence of NOx. Photochemical ozone production rates responded differently to 30% NOx and VOC reductions with the different mechanisms, despite the striking similarities between the base case ozone production rates. The 30% reductions in NOx and VOCs also produced changes in OH. The responses in OH to 30% reductions in NOx and VOCs appeared to be more sensitive to mechanism choice, compared with the responses in the photochemical ozone production rates. Whereas 30% NOx reductions generally led to decreases in OH, 30% reductions in VOCs led to increases in OH, irrespective of mechanism choice and background environmental conditions. The different mechanisms therefore gave different OH responses to NOx and VOC reductions and so would give different responses in terms of changes in the fate and behaviour of air toxics, acidification and eutrophication and fine particle formation compared with others, in response to ozone control strategies. Policy-makers need to understand that there are likely to be inherent differences in the responses to ozone control strategies between different mechanisms, depending on background environmental conditions and the extents of NOx and VOC reductions under consideration. IMPLICATIONS The purpose of this paper is to compare predicted ozone responses to NOx and VOC reductions with seven chemical mechanisms under North American conditions. The good agreement found between the tested mechanisms should provide some support for their application in the air

  20. Dual mechanisms regulate ecosystem stability under decade-long warming and hay harvest.

    PubMed

    Shi, Zheng; Xu, Xia; Souza, Lara; Wilcox, Kevin; Jiang, Lifen; Liang, Junyi; Xia, Jianyang; García-Palacios, Pablo; Luo, Yiqi

    2016-06-15

    Past global change studies have identified changes in species diversity as a major mechanism regulating temporal stability of production, measured as the ratio of the mean to the standard deviation of community biomass. However, the dominant plant functional group can also strongly determine the temporal stability. Here, in a grassland ecosystem subject to 15 years of experimental warming and hay harvest, we reveal that warming increases while hay harvest decreases temporal stability. This corresponds with the biomass of the dominant C4 functional group being higher under warming and lower under hay harvest. As a secondary mechanism, biodiversity also explains part of the variation in temporal stability of production. Structural equation modelling further shows that warming and hay harvest regulate temporal stability through influencing both temporal mean and variation of production. Our findings demonstrate the joint roles that dominant plant functional group and biodiversity play in regulating the temporal stability of an ecosystem under global change.

  1. Dual mechanisms regulate ecosystem stability under decade-long warming and hay harvest

    PubMed Central

    Shi, Zheng; Xu, Xia; Souza, Lara; Wilcox, Kevin; Jiang, Lifen; Liang, Junyi; Xia, Jianyang; García-Palacios, Pablo; Luo, Yiqi

    2016-01-01

    Past global change studies have identified changes in species diversity as a major mechanism regulating temporal stability of production, measured as the ratio of the mean to the standard deviation of community biomass. However, the dominant plant functional group can also strongly determine the temporal stability. Here, in a grassland ecosystem subject to 15 years of experimental warming and hay harvest, we reveal that warming increases while hay harvest decreases temporal stability. This corresponds with the biomass of the dominant C4 functional group being higher under warming and lower under hay harvest. As a secondary mechanism, biodiversity also explains part of the variation in temporal stability of production. Structural equation modelling further shows that warming and hay harvest regulate temporal stability through influencing both temporal mean and variation of production. Our findings demonstrate the joint roles that dominant plant functional group and biodiversity play in regulating the temporal stability of an ecosystem under global change. PMID:27302085

  2. Evaluating data worth for ground-water management under uncertainty

    USGS Publications Warehouse

    Wagner, B.J.

    1999-01-01

    A decision framework is presented for assessing the value of ground-water sampling within the context of ground-water management under uncertainty. The framework couples two optimization models-a chance-constrained ground-water management model and an integer-programing sampling network design model-to identify optimal pumping and sampling strategies. The methodology consists of four steps: (1) The optimal ground-water management strategy for the present level of model uncertainty is determined using the chance-constrained management model; (2) for a specified data collection budget, the monitoring network design model identifies, prior to data collection, the sampling strategy that will minimize model uncertainty; (3) the optimal ground-water management strategy is recalculated on the basis of the projected model uncertainty after sampling; and (4) the worth of the monitoring strategy is assessed by comparing the value of the sample information-i.e., the projected reduction in management costs-with the cost of data collection. Steps 2-4 are repeated for a series of data collection budgets, producing a suite of management/monitoring alternatives, from which the best alternative can be selected. A hypothetical example demonstrates the methodology's ability to identify the ground-water sampling strategy with greatest net economic benefit for ground-water management.A decision framework is presented for assessing the value of ground-water sampling within the context of ground-water management under uncertainty. The framework couples two optimization models - a chance-constrained ground-water management model and an integer-programming sampling network design model - to identify optimal pumping and sampling strategies. The methodology consists of four steps: (1) The optimal ground-water management strategy for the present level of model uncertainty is determined using the chance-constrained management model; (2) for a specified data collection budget, the monitoring

  3. Brain-computer interfacing under distraction: an evaluation study

    NASA Astrophysics Data System (ADS)

    Brandl, Stephanie; Frølich, Laura; Höhne, Johannes; Müller, Klaus-Robert; Samek, Wojciech

    2016-10-01

    Objective. While motor-imagery based brain-computer interfaces (BCIs) have been studied over many years by now, most of these studies have taken place in controlled lab settings. Bringing BCI technology into everyday life is still one of the main challenges in this field of research. Approach. This paper systematically investigates BCI performance under 6 types of distractions that mimic out-of-lab environments. Main results. We report results of 16 participants and show that the performance of the standard common spatial patterns (CSP) + regularized linear discriminant analysis classification pipeline drops significantly in this ‘simulated’ out-of-lab setting. We then investigate three methods for improving the performance: (1) artifact removal, (2) ensemble classification, and (3) a 2-step classification approach. While artifact removal does not enhance the BCI performance significantly, both ensemble classification and the 2-step classification combined with CSP significantly improve the performance compared to the standard procedure. Significance. Systematically analyzing out-of-lab scenarios is crucial when bringing BCI into everyday life. Algorithms must be adapted to overcome nonstationary environments in order to tackle real-world challenges.

  4. Mechanism underlying the changes in plasma potassium concentration during infusion of isosmotic nonelectrolyte solution.

    PubMed

    Hirose, M; Hashimoto, S; Nose, H; Morimoto, T; Itoh, T; Natsuyama, T; Tanaka, Y

    1992-08-01

    Generally, during infusion of an isosmotic nonelectrolyte solution that permeates the cell membrane, plasma K+ concentration ([K+]pl) either does not change or it increases slightly. The mechanism underlying this [K+]pl change has not been clarified. We continuously monitored the [K+]pl and plasma Na+ concentration ([Na+]pl) for 10 min during isosmotic mannitol infusion of 1.6 ml/100 g body weight in rats with intact kidney function (intact mannitol group). In addition, in nephrectomized rats, we compared the [K+]pl change during infusion with isosmotic mannitol (which permeates the cell membrane; mannitol nephrectomized group) with that during infusion with isosmotic sucrose (which does not permeate the cell membrane; sucrose nephrectomized group) to evaluate the effect of cell volume regulation. In the intact mannitol group, [Na+]pl decreased with dilution, and [K+]pl remained relatively constant. In the sucrose nephrectomized group, [K+]pl decreased by the same percentage as [Na+]pl and gradually increased to greater than the control level. In the mannitol nephrectomized group, however, [K+]pl increased immediately after the beginning of the infusion and reached the same level as that in the sucrose nephrectomized group. To confirm that the difference in [K+]pl between the mannitol and sucrose nephrectomized groups was dependent on cell volume regulation, we investigated the changes in mean corpuscular volume of red blood cells, using a Coulter counter. This value remained constant during isosmotic sucrose infusion but increased during isosmotic mannitol infusion, returning to the original volume after the infusion. We kept [HCO3-] and pH constant throughout the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

  5. Innovative Payment Mechanisms in Maryland Hospitals: An Empirical Analysis of Readmissions under Total Patient Revenue

    PubMed Central

    Mortensen, Karoline; Perman, Chad; Chen, Jie

    2014-01-01

    Background The state of Maryland implemented innovative budgeting of outpatient and inpatient services in eight rural hospitals under the Total Patient Revenue (TPR) system in July, 2010. Methods This paper uses data on Maryland discharges from the 2009-2011 Healthcare Cost and Utilization Project (HCUP) State Inpatient Databases (SID). Individual inpatient discharges from eight treatment hospitals and three rural control hospitals (n=374,353) are analyzed. To get robust estimates and control for trends in the state, we also compare treatment hospitals to all hospitals in Maryland that report readmissions (n=1,997,164). Linear probability models using the difference-in-differences approach with hospital fixed effects are estimated to determine the effect of the innovative payment mechanisms on hospital readmissions, controlling for patient demographics and characteristics. Results Difference-in-differences estimates show that after implementation of TPR in the treatment hospitals, there were no statistically significant changes in the predicted probability of readmissions. Conclusions Early evidence from the TPR program shows that readmissions were not affected in the 18 months after implementation. Implications : As the health care system innovates, it is important to evaluate the success of these innovations. One of the goals of TPR was to lower readmission rates, however these rates did not show consistent downward trends after implementation. Our results suggest that payment innovations that provide financial incentives to ensure patients receive care in the most appropriate setting while maintaining quality of care may not have immediate effects on commonly used measures of hospital quality, particularly for rural hospitals that may lack coordinated care delivery infrastructure. PMID:25264518

  6. The making of abnormal spermatozoa: cellular and molecular mechanisms underlying pathological spermiogenesis.

    PubMed

    Chemes, Hector E; Rawe, Vanesa Y

    2010-09-01

    Fertilization in mammals occurs via a series of well-defined events in the secluded environment of the female reproductive tract. The mode of selection of the fertilizing spermatozoon nevertheless remains unknown. As has become evident during in vitro fertilization by sperm microinjection into the oocyte, abnormal spermatozoa can successfully fertilize oocytes. Under these extreme conditions, post-fertilization events, early embryonic development and implantation are significantly compromised indicating that the contribution of spermatozoa extends beyond sperm penetration. Microscopic identification of normal spermatozoa is a well-standardized procedure but insights into the mechanisms that lead to aberrant sperm differentiation and into the subcellular nature of sperm abnormalities have only recently begun to be obtained. The spermatozoon is the result of a complex development in which spermatid organelles give rise to various structural components with characteristic functions. Similar to other differentiated cells, the spermatozoon has a specific pathology that is most clearly identified by ultrastructural evaluation coupled with immunocytochemistry and molecular techniques. This multidisciplinary approach allows the precise characterization of sperm abnormalities, including structural, molecular and functional aspects. We summarize here studies of the physiopathology of spermiogenesis in two abnormal sperm phenotypes of infertile men: dysplasia of the fibrous sheath and acephalic spermatozoa/abnormal head-tail attachment. The characterization of the abnormalities of the tail cytoskeleton and centrioles has uncovered aspects of the subcellular basis of pathological spermiogenesis, has suggested experimental approaches to explore the nature of these anomalies and has opened the way for genetic studies that will ultimately lead to the design of the therapeutic tools of the future.

  7. Retrospective Evaluation of Dental Treatment under General Anaesthesia

    PubMed Central

    Özkan, Ahmet Selim; Erdoğan, Mehmet Ali; Şanlı, Mukadder; Kaçmaz, Osman; Durmuş, Mahmut; Çolak, Cemil

    2015-01-01

    Objective Most dental procedures can be performed with local anaesthesia, however noncompliant paediatric patients, patients with mental retardation or psychiatric disorders, severe anxiety, severe craniofacial anomalies and orofacial trauma may need general anaesthesia. In these patients accompanying central nervous system diseases and airway problems increase the risk of complications. Anaesthesia records of 467 cases of dental surgery performed under general anaesthesia between 2011–2014 is reported with information from the recent literature. Methods In the study, 467 cases of dental procedures performed under general anaesthesia were taken from the İnönü University of Medicine, Dentistry Disabled Treatment Centre, after approval of the İnönü University Faculty of Medicine Ethics Committee. Demographic data, ASA classification, Mallampati (MP) score, duration of surgery, type of intubation and difficulties, comorbid diseases, premedication application, endocarditis prophylaxis, recovery time, analgesia and reasons for general anaesthesia were recorded as mean±standard deviation (SD) or as a number. Results The mean age of the patients was 16.78±12 years and the female/male ratio was 277/190 (59.3%/40.7%). Of the 467 patients, 219 (46.9%) were classified as ASA I, 234 (50.1%) as ASA II and 14 (3%) as ASA III. Furthermore, 182 (38.9%) patients with mental retardation, 33 (7.1%) with cerebral palsy and 28 (6%) with autism were identified. The mean operative time was 114.53±35.4 min, and the average recovery time 40.4±6 was min. Of the endotracheal intubations 277 (59.3%) were oral, 82 (17.6%) were nasal, and 108 (23.1%) were nasal with the help of fibreoptics. Difficult intubation was observed in 20 (4.3%) patients. The MP score was 1 in 397 (85%) patients, 2 in 50 (10.7%) patients, 3 in 18 (3.9%) patients and 4 in 2 (0.4%) patients. General anaesthesia was applied because of cooperation difficulties in 213 (45.6%), mental retardation in 182 (38

  8. Evaluation of thermal perception in schoolyards under Mediterranean climate conditions

    NASA Astrophysics Data System (ADS)

    Antoniadis, D.; Katsoulas, N.; Papanastasiou, D.; Christidou, V.; Kittas, C.

    2016-03-01

    The aim of this paper was to study qualitatively and quantitatively the thermal perception and corresponding heat stress conditions that prevail in two schoolyards in a coastal city in central Greece. For this purpose, meteorological parameters (i.e., wind speed, temperature, relative humidity, solar radiation) were recorded at 70 and 55 measuring points in the schoolyards, from 14:00 to 15:30 local time, during May and June of 2011. The measuring points were distributed so as to get measurements at points (a) directly exposed to the sun, (b) under the shadow of trees and building structures, and (c) near building structures. Cluster analysis was applied to group observations and revealed places that are microclimatically homogeneous. Thermal perception and heat stress conditions were assessed by means of the physiologically equivalent temperature (PET, °C), and the results are presented in relevant charts. The impact of material's albedo, radiation's reflection by structures and obstacles, and different tree species on thermal perception and heat stress conditions was also assessed. The analysis showed that trees triggered a reduction of incident solar radiation that ranged between 79 and 94 % depending on tree's species, crown dimension, tree height, and leaf area. PET values were mainly affected by solar radiation and wind speed. Trees caused a reduction of up to 37 % in PET values, while a 1-m s-1 increase in wind speed triggered a reduction of 3.7-5.0 °C in PET value. The effective shading area in the two schoolyards was small, being 27.5 and 11 %. The results of this study could be exploited by urban planning managers when designing or improving the outdoor environment of a school complex.

  9. Novel Model of Tendon Regeneration Reveals Distinct Cell Mechanisms Underlying Regenerative and Fibrotic Tendon Healing

    PubMed Central

    Howell, Kristen; Chien, Chun; Bell, Rebecca; Laudier, Damien; Tufa, Sara F.; Keene, Douglas R.; Andarawis-Puri, Nelly; Huang, Alice H.

    2017-01-01

    To date, the cell and molecular mechanisms regulating tendon healing are poorly understood. Here, we establish a novel model of tendon regeneration using neonatal mice and show that neonates heal via formation of a ‘neo-tendon’ that differentiates along the tendon specific lineage with functional restoration of gait and mechanical properties. In contrast, adults heal via fibrovascular scar, aberrant differentiation toward cartilage and bone, with persistently impaired function. Lineage tracing identified intrinsic recruitment of Scx-lineage cells as a key cellular mechanism of neonatal healing that is absent in adults. Instead, adult Scx-lineage tenocytes are not recruited into the defect but transdifferentiate into ectopic cartilage; in the absence of tenogenic cells, extrinsic αSMA-expressing cells persist to form a permanent scar. Collectively, these results establish an exciting model of tendon regeneration and uncover a novel cellular mechanism underlying regenerative vs non-regenerative tendon healing. PMID:28332620

  10. Effects of Delaying Transplanting on Agronomic Traits and Grain Yield of Rice under Mechanical Transplantation Pattern

    PubMed Central

    Liu, Qihua; Wu, Xiu; Ma, Jiaqing; Chen, Bocong; Xin, Caiyun

    2015-01-01

    A delay in the mechanical transplantation (MT) of rice seedlings frequently occurs in Huanghuai wheat-rice rotation cropping districts of China, due to the late harvest of wheat, the poor weather conditions and the insufficiency of transplanters, missing the optimum transplanting time and causing seedlings to age. To identify how delaying transplanting rice affects the agronomic characteristics including the growth duration, photosynthetic productivity and dry matter remobilization efficiency and the grain yield under mechanical transplanting pattern, an experiment with a split-plot design was conducted over two consecutive years. The main plot includes two types of cultivation: mechanical transplanting and artificial transplanting (AT). The subplot comprises four japonica rice cultivars. The results indicate that the rice jointing, booting, heading and maturity stages were postponed under MT when using AT as a control. The tiller occurrence number, dry matter weight per tiller, accumulative dry matter for the population, leaf area index, crop growth rate, photosynthetic potential, and dry matter remobilization efficiency of the leaf under MT significantly decreased compared to those under AT. In contrast, the reduction rate of the leaf area during the heading-maturity stage was markedly enhanced under MT. The numbers of effective panicles and filled grains per panicle and the grain yield significantly decreased under MT. A significant correlation was observed between the dry matter production, remobilization and distribution characteristics and the grain yield. We infer that, as with rice from old seedlings, the decrease in the tiller occurrence, the photosynthetic productivity and the assimilate remobilization efficiency may be important agronomic traits that are responsible for the reduced grain yield under MT. PMID:25875607

  11. Significant enhancement of photoreactivity of graphitic carbon nitride catalysts under acidic conditions and the underlying H(+)-mediated mechanism.

    PubMed

    Zhang, Xue-Song; Tian, Ke; Hu, Jian-Yang; Jiang, Hong

    2015-12-01

    Graphitic carbon nitride (g-C3N4) is an emerging photocatalyst for organic pollutants degradation owing to its excellent stability and metal-free property. In this study, the photocatalytic activity of acidified g-C3N4 (ag-C3N4) was systematically investigated using rhodamine B (rhB) as a model organic pollutant. The results showed the photoreactivity of ag-C3N4 is significantly enhanced with the decrease of pH values. The apparent rate constant (kapp) of rhB degradation over ag-C3N4 is 11.59×10(-3)min(-1) at pH7.0 and it increases to 103.50×10(-3)min(-1) at pH3.0 under visible light. A series of analyses demonstrate that the photodegradation mechanism is a combination of a H(+)-promoted generation of OH and elevation of the redox potential of conduct band of C3N4. The change of surface properties of C3N4 caused by pH variation also affects the degradation of some zwitterionic compounds by changing the adsorption orientation of pollutants. The revealed mechanism of visible light-C3N4-rhB system is meaningful to broaden the usage of C3N4 to the photodegradation of other organic pollutants.

  12. Mechanical properties of chiral and achiral silicon carbide nanotubes under oxygen chemisorption.

    PubMed

    Ansari, R; Mirnezhad, M; Hosseinzadeh, M

    2015-03-01

    In this paper, the mechanical properties of fully oxygenated silicon carbide nanotubes (O2-SiCNTs) are explored using a molecular mechanics model joined with the density functional theory (DFT). The closed-form analytical expressions suggested in this study can easily be adapted for nanotubes with different chiralities. The force constants of molecular mechanics model proposed herein are derived through DFT within a generalized gradient approximation. Moreover, the mechanical properties of fully oxygenated silicon carbide (O2-SiC) sheet are evaluated for the case that the oxygen atoms are adsorbed on one side of the SiC sheet. According to the results obtained for the bending stiffness of O2-SiC sheet, one can conclude that the O2-SiC sheet has isotropic characteristics.

  13. Preferential skeletal muscle myosin loss in response to mechanical silencing in a novel rat intensive care unit model: underlying mechanisms

    PubMed Central

    Ochala, Julien; Gustafson, Ann-Marie; Diez, Monica Llano; Renaud, Guillaume; Li, Meishan; Aare, Sudhakar; Qaisar, Rizwan; Banduseela, Varuna C; Hedström, Yvette; Tang, Xiaorui; Dworkin, Barry; Ford, G Charles; Nair, K Sreekumaran; Perera, Sue; Gautel, Mathias; Larsson, Lars

    2011-01-01

    Abstract The muscle wasting and impaired muscle function in critically ill intensive care unit (ICU) patients delay recovery from the primary disease, and have debilitating consequences that can persist for years after hospital discharge. It is likely that, in addition to pernicious effects of the primary disease, the basic life support procedures of long-term ICU treatment contribute directly to the progressive impairment of muscle function. This study aims at improving our understanding of the mechanisms underlying muscle wasting in ICU patients by using a unique experimental rat ICU model where animals are mechanically ventilated, sedated and pharmacologically paralysed for duration varying between 6 h and 14 days. Results show that the ICU intervention induces a phenotype resembling the severe muscle wasting and paralysis associated with the acute quadriplegic myopathy (AQM) observed in ICU patients, i.e. a preferential loss of myosin, transcriptional down-regulation of myosin synthesis, muscle atrophy and a dramatic decrease in muscle fibre force generation capacity. Detailed analyses of protein degradation pathways show that the ubiquitin proteasome pathway is highly involved in this process. A sequential change in localisation of muscle-specific RING finger proteins 1/2 (MuRF1/2) observed during the experimental period is suggested to play an instrumental role in both transcriptional regulation and protein degradation. We propose that, for those critically ill patients who develop AQM, complete mechanical silencing, due to pharmacological paralysis or sedation, is a critical factor underlying the preferential loss of the molecular motor protein myosin that leads to impaired muscle function or persisting paralysis. PMID:21320889

  14. Mechanisms underlying cellular responses of cells from haemopoietic tissue to low dose/low LET radiation

    SciTech Connect

    Munira A Kadhim

    2010-03-05

    To accurately define the risks associated with human exposure to relevant environmental doses of low LET ionizing radiation, it is necessary to completely understand the biological effects at very low doses (i.e., less than 0.1 Gy), including the lowest possible dose, that of a single electron track traversal. At such low doses, a range of studies have shown responses in biological systems which are not related to the direct interaction of radiation tracks with DNA. The role of these “non-targeted” responses in critical tissues is poorly understood and little is known regarding the underlying mechanisms. Although critical for dosimetry and risk assessment, the role of individual genetic susceptibility in radiation risk is not satisfactorily defined at present. The aim of the proposed grant is to critically evaluate radiation-induced genomic instability and bystander responses in key stem cell populations from haemopoietic tissue. Using stem cells from two mouse strains (CBA/H and C57BL/6J) known to differ in their susceptibility to radiation effects, we plan to carefully dissect the role of genetic predisposition on two non-targeted radiation responses in these models; the bystander effect and genomic instability, which we believe are closely related. We will specifically focus on the effects of low doses of low LET radiation, down to doses approaching a single electron traversal. Using conventional X-ray and γ-ray sources, novel dish separation and targeted irradiation approaches, we will be able to assess the role of genetic variation under various bystander conditions at doses down to a few electron tracks. Irradiations will be carried out using facilities in routine operation for bystander targeted studies. Mechanistic studies of instability and the bystander response in different cell lineages will focus initially on the role of cytokines which have been shown to be involved in bystander signaling and the initiation of instability. These studies also aim

  15. Bactericidal Mechanisms of Ag2O/TNBs under both Dark and Light Conditions

    NASA Astrophysics Data System (ADS)

    Jin, Yinjia; Dai, Zhaoyi; Liu, Fei; Kim, Hyunjung; Tong, Meiping; Hou, Yanglong

    2013-04-01

    Ag2O deposited titanium dioxides nanobelts (Ag2O/TNBs) were fabricated and used to investigate the toxic effects on aquatic microorganisms. The disinfection activities of Ag2O/TNBs on two representative bacterial strains: Gram-negative E. coli and Gram-positive B. subtilis, were examined under both dark and light conditions. Ag2O/TNBs exhibited stronger bactericidal activities than TNBs under both dark and light conditions. For both cell types, disinfection effects of Ag2O/TNBs were greater under light conditions relative to those under dark conditions. The bactericidal mechanisms of Ag2O/TNBs under both dark and light conditions were explored. Under dark conditions, neither Ag+ ions released from Ag2O/TNBs nor TNBs contributed to the bactericidal activities of Ag2O/TNBs. Under light conditions, both the released Ag+ions and TNBs yet were found to have contributions to the bactericidal effects of Ag2O/TNBs. Active species (H2O2, ?O2-, ande-) generated by Ag2O/TNBs played important roles in the disinfection processes under both dark and light conditions. Without the presence of active species, the direct contact of Ag2O/TNBs with bacterial cells had no bactericidal effect.

  16. Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains

    NASA Astrophysics Data System (ADS)

    Hu, Ting; Han, Yang; Dong, Jinming

    2014-11-01

    The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson’s ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isotropic tensile strains compared with that under uniaxial strain. 4) Under the isotropic compressive strain, the bilayer phosphorene exhibits a transition from a direct-gap semiconductor to a metal. In contrast, the monolayer phosphorene initially has the direct-indirect transition and then transitions to a metal. However, under isotropic tensile strain, both the bilayer and monolayer phosphorene show the direct-indirect transition and, finally, the transition to a metal. Our numerical results may open new potential applications of phosphorene in nanoelectronics and nanomechanical devices by external isotropic strain or uniaxial strain along different directions.

  17. Fatigue Response of a PZT Multilayer Actuator under High-Field Electric Cycling with Mechanical Preload

    SciTech Connect

    Wang, Hong; Wereszczak, Andrew A; Lin, Hua-Tay

    2009-01-01

    An electric fatigue test system has been developed for piezoelectric actuator with a mechanical loading capability. Fatigue responses of a lead zirconate titanate (PZT) multilayer actuator (MLA) with a plate-through electrode configuration have been studied under an electric field (1.7 times that of a coercive field of PZT material) and a concurrent mechanical preload (30.0 MPa). A total of 1.0x10^9 cycles were carried out. Variations in charge density and mechanical strain under a high electric field and constant mechanical loads were observed during the fatigue test. The dc and the first harmonic (at 10 Hz) dielectric and piezoelectric coefficients were subsequently characterized by using FFT (Fast Fourier Transformation). It has been observed that both the dielectric and the piezoelectric coefficients underwent a monotonic decrease prior to 2.86x10^8 cycles under the relevant preload, and then fluctuated to a certain extent. Both the dielectric loss tangent and the piezoelectric loss tangent also exhibited the fluctuations after a certain amount of drop but at different levels relative to the pre-fatigue. And finally, the results were discussed with respect to domain wall mobility, microcracking, and other pre-existing anomalies.

  18. 75 FR 68395 - Agency Self-Evaluation Under Section 504 of the Rehabilitation Act of 1973

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-05

    ... ADMINISTRATION Agency Self-Evaluation Under Section 504 of the Rehabilitation Act of 1973 AGENCY: Social Security Administration. ACTION: Notice and request for comments. SUMMARY: We are initiating a self-evaluation of our... a self-evaluation. We are particularly interested in ideas and suggestions from persons...

  19. Mechanical behavior of an individual adherent MLO-Y4 osteocyte under shear flow.

    PubMed

    Qiu, Jun; Li, Fang-Fang

    2017-02-01

    Mechanical properties of a single cell and its mechanical response under stimulation play an important role in regulating interactions between cell and extracellular matrix and affecting mechanotransduction. Osteocytes exhibit solid-like viscoelastic behavior in response to the interstitial fluid shear resulting from tissue matrix deformation. This study intends to quantitatively describe the mechanical behavior of osteocytes combining in vitro experiment and fluid-structure interaction (FSI) finite element (FE) model. The cell is configured in the FSI FE model using the observed data from quasi-3D images. Instead of simply assigning the cellular viscoelastic parameters by statistical data, the mechanical parameters are determined by an iterative algorithm comparing the experimental and the computational results from the FE model. The viscoelastic parameters of osteocytes are obtained as: the equilibrium elasticity modulus [Formula: see text], instantaneous elasticity modulus [Formula: see text], viscosity coefficient [Formula: see text]. A novel index to quantify the cell adhesion is also put forward. In addition, an interesting competition phenomenon is revealed on the cell surface concerning stress and strain, i.e., the place with high stress has low strain and that with low stress has high strain. The proposed method provides a novel technique to study the mechanical behavior of individual adherent cell in vitro. It is believed that this quantitative technique not only determines cell mechanical behavior but also helps elucidate the mechanism of mechanotransduction in various types of cells.

  20. Evaluation of Mechanical Losses in Piezoelectric Plates using Genetic algorithm

    NASA Astrophysics Data System (ADS)

    Arnold, F. J.; Gonçalves, M. S.; Massaro, F. R.; Martins, P. S.

    Numerical methods are used for the characterization of piezoelectric ceramics. A procedure based on genetic algorithm is applied to find the physical coefficients and mechanical losses. The coefficients are estimated from a minimum scoring of cost function. Electric impedances are calculated from Mason's model including mechanical losses constant and dependent on frequency as a linear function. The results show that the electric impedance percentage error in the investigated interval of frequencies decreases when mechanical losses depending on frequency are inserted in the model. A more accurate characterization of the piezoelectric ceramics mechanical losses should be considered as frequency dependent.

  1. Molecular mechanisms underlying the emergence of bacterial pathogens: an ecological perspective.

    PubMed

    Bartoli, Claudia; Roux, Fabrice; Lamichhane, Jay Ram

    2016-02-01

    The rapid emergence of new bacterial diseases negatively affects both human health and agricultural productivity. Although the molecular mechanisms underlying these disease emergences are shared between human- and plant-pathogenic bacteria, not much effort has been made to date to understand disease emergences caused by plant-pathogenic bacteria. In particular, there is a paucity of information in the literature on the role of environmental habitats in which plant-pathogenic bacteria evolve and on the stress factors to which these microbes are unceasingly exposed. In this microreview, we focus on three molecular mechanisms underlying pathogenicity in bacteria, namely mutations, genomic rearrangements and the acquisition of new DNA sequences through horizontal gene transfer (HGT). We briefly discuss the role of these mechanisms in bacterial disease emergence and elucidate how the environment can influence the occurrence and regulation of these molecular mechanisms by directly impacting disease emergence. The understanding of such molecular evolutionary mechanisms and their environmental drivers will represent an important step towards predicting bacterial disease emergence and developing sustainable management strategies for crops.

  2. An analytical model of the mechanical properties of bulk coal under confined stress

    USGS Publications Warehouse

    Wang, G.X.; Wang, Z.T.; Rudolph, V.; Massarotto, P.; Finley, R.J.

    2007-01-01

    This paper presents the development of an analytical model which can be used to relate the structural parameters of coal to its mechanical properties such as elastic modulus and Poisson's ratio under a confined stress condition. This model is developed primarily to support process modeling of coalbed methane (CBM) or CO2-enhanced CBM (ECBM) recovery from coal seam. It applied an innovative approach by which stresses acting on and strains occurring in coal are successively combined in rectangular coordinates, leading to the aggregated mechanical constants. These mechanical properties represent important information for improving CBM/ECBM simulations and incorporating within these considerations of directional permeability. The model, consisting of constitutive equations which implement a mechanically consistent stress-strains correlation, can be used as a generalized tool to study the mechanical and fluid behaviors of coal composites. An example using the model to predict the stress-strain correlation of coal under triaxial confined stress by accounting for the elastic and brittle (non-elastic) deformations is discussed. The result shows a good agreement between the prediction and the experimental measurement. ?? 2007 Elsevier Ltd. All rights reserved.

  3. Consumption of Red/Processed Meat and Colorectal Carcinoma: Possible Mechanisms Underlying the Significant Association.

    PubMed

    Hammerling, Ulf; Bergman Laurila, Jonas; Grafström, Roland; Ilbäck, Nils-Gunnar

    2016-01-01

    Epidemiology and experimental studies provide an overwhelming support of the notion that diets high in red or processed meat accompany an elevated risk of developing pre-neoplastic colorectal adenoma and frank colorectal carcinoma (CRC). The underlying mechanisms are disputed; thus several hypotheses have been proposed. A large body of reports converges, however, on haem and nitrosyl haem as major contributors to the CRC development, presumably acting through various mechanisms. Apart from a potentially higher intestinal mutagenic load among consumers on a diet rich in red/processed meat, other mechanisms involving subtle interference with colorectal stem/progenitor cell survival or maturation are likewise at play. From an overarching perspective, suggested candidate mechanisms for red/processed meat-induced CRC appear as three partly overlapping tenets: (i) increased N-nitrosation/oxidative load leading to DNA adducts and lipid peroxidation in the intestinal epithelium, (ii) proliferative stimulation of the epithelium through haem or food-derived metabolites that either act directly or subsequent to conversion, and (iii) higher inflammatory response, which may trigger a wide cascade of pro-malignant processes. In this review, we summarize and discuss major findings of the area in the context of potentially pertinent mechanisms underlying the above-mentioned association between consumption of red/processed meat and increased risk of developing CRC.

  4. Uncovering the underlying physical mechanisms of biological systems via quantification of landscape and flux

    NASA Astrophysics Data System (ADS)

    Li, Xu; Xiakun, Chu; Zhiqiang, Yan; Xiliang, Zheng; Kun, Zhang; Feng, Zhang; Han, Yan; Wei, Wu; Jin, Wang

    2016-01-01

    In this review, we explore the physical mechanisms of biological processes such as protein folding and recognition, ligand binding, and systems biology, including cell cycle, stem cell, cancer, evolution, ecology, and neural networks. Our approach is based on the landscape and flux theory for nonequilibrium dynamical systems. This theory provides a unifying principle and foundation for investigating the underlying mechanisms and physical quantification of biological systems. Project supported by the Natural Science Foundation of China (Grant Nos. 21190040, 11174105, 91225114, 91430217, and 11305176) and Jilin Province Youth Foundation, China (Grant No. 20150520082JH).

  5. The underlying mechanism of action for various medicinal properties of Piper betle (betel).

    PubMed

    Haslan, H; Suhaimi, F H; Thent, Zar Chi; Das, S

    2015-01-01

    Piper betle (betel) plant belongs to the Piperaceae family. Piper. betle is widely known for its potent medicinal properties. Various active compounds are present in Piper. betle such as allylpyrocatechol, hydroxychavicol, piperbetol, ethylpiperbetol, piperol A, piperol B, chavibetol, and alkaloids which account for these beneficial medicinal properties. In the present narrative review, we looked into the various active compounds present in the Piper betle and attempted to understand their underlying mechanism of action. Proper understanding of the molecular biology involving the mechanism of action may help in better drug formulation and provide better therapeutic actions in the field of alternative and complementary medicine.

  6. The role of TRPA1 in muscle pain and mechanical hypersensitivity under inflammatory conditions in rats.

    PubMed

    Asgar, J; Zhang, Y; Saloman, J L; Wang, S; Chung, M-K; Ro, J Y

    2015-12-03

    Transient receptor potential cation channel, subfamily A, member 1 (TRPA1) is expressed in muscle afferents and direct activation of these receptors induces acute mechanical hypersensitivity. However, the functional role of TRPA1 under pathological muscle pain conditions and mechanisms by which TRPA1 mediate muscle pain and hyperalgesia are not clearly understood. Two rodent behavioral models validated to assess craniofacial muscle pain conditions were used to study ATP- and N-Methyl-D-aspartate (NMDA)-induced acute mechanical hypersensitivity and complete Freund's adjuvant (CFA)-induced persistent mechanical hypersensitivity. The rat grimace scale (RGS) was utilized to assess inflammation-induced spontaneous muscle pain. Behavioral pharmacology experiments were performed to assess the effects of AP18, a selective TRPA1 antagonist under these conditions. TRPA1 expression levels in trigeminal ganglia (TG) were examined before and after CFA treatment in the rat masseter muscle. Pre-treatment of the muscle with AP18 dose-dependently blocked the development of acute mechanical hypersensitivity induced by NMDA and α,β-methylene adenosine triphosphate (αβmeATP), a specific agonist for NMDA and P2X3 receptor, respectively. CFA-induced mechanical hypersensitivity and spontaneous muscle pain responses were significantly reversed by post-treatment of the muscle with AP18 when CFA effects were most prominent. CFA-induced myositis was accompanied by significant up-regulation of TRPA1 expression in TG. Our findings showed that TRPA1 in muscle afferents plays an important role in the development of acute mechanical hypersensitivity and in the maintenance of persistent muscle pain and hypersensitivity. Our data suggested that TRPA1 may serve as a downstream target of pro-nociceptive ion channels, such as P2X3 and NMDA receptors in masseter afferents, and that increased TRPA1 expression under inflammatory conditions may contribute to the maintenance of persistent muscle pain

  7. Oxidative Stress and Mitochondrial Activation as the Main Mechanisms Underlying Graphene Toxicity against Human Cancer Cells

    PubMed Central

    Jarosz, Anna; Skoda, Marta; Dudek, Ilona; Szukiewicz, Dariusz

    2016-01-01

    Due to the development of nanotechnology graphene and graphene-based nanomaterials have attracted the most attention owing to their unique physical, chemical, and mechanical properties. Graphene can be applied in many fields among which biomedical applications especially diagnostics, cancer therapy, and drug delivery have been arousing a lot of interest. Therefore it is essential to understand better the graphene-cell interactions, especially toxicity and underlying mechanisms for proper use and development. This review presents the recent knowledge concerning graphene cytotoxicity and influence on different cancer cell lines. PMID:26649139

  8. Evaluation of advanced materials through experimental mechanics and modelling

    NASA Technical Reports Server (NTRS)

    Yang, Yii-Ching

    1993-01-01

    Composite materials have been frequently used in aerospace vehicles. Very often defects are inherited during the manufacture and damages are inherited during the construction and services. It becomes critical to understand the mechanical behavior of such composite structure before it can be further used. One good example of these composite structures is the cylindrical bottle of solid rocket motor case with accidental impact damages. Since the replacement of this cylindrical bottle is expensive, it is valuable to know how the damages affects the material, and how it can be repaired. To reach this goal, the damage must be characterized and the stress/strain field must be carefully analyzed. First the damage area, due to impact, is surveyed and identified with a shearography technique which uses the principle of speckle shearing interferometry to measure displacement gradient. Within the damage area of a composite laminate, such as the bottle of solid rocket motor case, all layers are considered to be degraded. Once a lamina being degraded the stiffness as well as strength will be drastically decreased. It becomes a critical area of failure to the whole bottle. And hence the stress/strain field within and around a damage should be accurately evaluated for failure prediction. To investigate the stress/strain field around damages a Hybrid-Numerical method which combines experimental measurement and finite element analysis is used. It is known the stress or strain at the singular point can not be accurately measured by an experimental technique. Nevertheless, if the location is far away from the singular spot, the displacement can be found accurately. Since it reflects the true displacement field locally regardless of the boundary conditions, it is an excellent input data for a finite element analysis to replace the usually assumed boundary conditions. Therefore, the Hybrid-Numerical method is chosen to avoid the difficulty and to take advantage of both experimental

  9. Simulation of ionomer membrane fatigue under mechanical and hygrothermal loading conditions

    NASA Astrophysics Data System (ADS)

    Khorasany, Ramin M. H.; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

    2015-04-01

    Understanding the fatigue lifetime of common perfluorosulfonic acid (PFSA) ionomer membranes under fluctuating hygrothermal conditions is essential for the development of durable fuel cell technologies. For this purpose, a finite element based fatigue lifetime prediction model is developed based on an elastic-plastic constitutive model combined with a Smith-Watson-Topper (SWT) fatigue formulation. The model is validated against previously reported experimental results for a membrane under cyclic mechanical loadings. The validated model is then utilized to investigate the membrane fatigue lifetime in ex-situ applications under cyclic humidity and temperature conditions. The simulations suggest that the membrane fatigue lifetime is shorter under fluctuating humidity loadings than for temperature loadings. Additionally, the membrane fatigue lifetime is found to be more sensitive to the amplitude of the strain oscillations than to the mean strain under hygrothermal cycling. Most notably, the model predicts that simultaneous humidity and temperature cycling can exacerbate the fatigue process and reduce the fatigue lifetime by several orders of magnitude compared to isolated humidity or temperature cycling. The combination of measured mechanical fatigue data and the present numerical model provides a useful toolkit for analysis of membrane fatigue due to hygrothermal variations, which can be costly and time-consuming when addressed experimentally.

  10. Developing and Evaluating Animations for Teaching Quantum Mechanics Concepts

    ERIC Educational Resources Information Center

    Kohnle, Antje; Douglass, Margaret; Edwards, Tom J.; Gillies, Alastair D.; Hooley, Christopher A.; Sinclair, Bruce D.

    2010-01-01

    In this paper, we describe animations and animated visualizations for introductory and intermediate-level quantum mechanics instruction developed at the University of St Andrews. The animations aim to help students build mental representations of quantum mechanics concepts. They focus on known areas of student difficulty and misconceptions by…

  11. Mechanical response of cross-ply Si{sub 3}N{sub 4}/BN fibrous monoliths under uniaxial and biaxial loadings

    SciTech Connect

    Singh, D.; Cruse, T. A.; Hermanson, D. J.; Goretta, K. C.; Zok, F. W.; McNulty, J. C.

    2000-03-01

    Mechanical properties of hot-pressed Si{sub 3}N{sub 4}/BN fibrous monoliths (FMs) were evaluated under ambient conditions in four-point and biaxial flexure modes. Effects of cell orientation, 0{degree}/90{degree} and {+-}45{degree}, on elastic modulus and fracture strength of the FMs were investigated. Fracture surfaces were examined by scanning electron microscopy.

  12. Evaluation of the antineoplastic activity of gallic acid in oral squamous cell carcinoma under hypoxic conditions.

    PubMed

    Guimaraes, Talita A; Farias, Lucyana C; Fraga, Carlos A; Feltenberger, John D; Melo, Geraldo A; Coletta, Ricardo D; Souza Santos, Sergio H; de Paula, Alfredo M B; Guimaraes, Andre L

    2016-06-01

    The purpose of the current study was to develop and test a theoretical model that could explain the mechanism of action of gallic acid (GA) in the oral squamous cell carcinoma context for the first time. The theoretical model was developed using bioinformatics and interaction network analysis to evaluate the effect of GA on oral squamous cell carcinoma. In a second step to confirm theoretical results, migration, invasion, proliferation, and gene expression (Col1A1, E-cadherin, HIF-1α, and caspase-3) were performed under normoxic and hypoxic conditions. Our study indicated that treatment with GA resulted in the inhibition of cell proliferation, migration, and invasion in neoplastic cells. Observation of the molecular mechanism showed that GA upregulates E-cadherin expression and downregulates Col1A1 and HIF-1α expression, suggesting that GA might be a potential anticancer compound. In conclusion, the present study demonstrated that GA significantly reduces cell proliferation, invasion, and migration by increasing E-cadherin and repressing Col1A1.

  13. Mechanism of Small Current Generation under Impulse Voltage Applications in Vacuum

    NASA Astrophysics Data System (ADS)

    Aoki, Keita; Yasukawa, Hideaki; Kojima, Hiroki; Homma, Mitsutaka; Shioiri, Tetsu; Okubo, Hitoshi

    Small discharge not to accompany breakdown can occur under high electric field in vacuum, however the mechanism is not well clarified. We have found that the current of small discharge decreases with repeated voltage applications, and leads to electrode conditioning effect of raising withstand voltage. The inception of the current is delayed with the decrease of current, and the inception time and waveform change by gap length. On the other hand, under low vacuum condition, the current increases and reaches saturation with repeated voltage applications. From these discussions, we concluded that the generating process of small current depended on the adsorption and absorption gas of electrodes.

  14. Reliability-based optimization of maintenance scheduling of mechanical components under fatigue

    PubMed Central

    Beaurepaire, P.; Valdebenito, M.A.; Schuëller, G.I.; Jensen, H.A.

    2012-01-01

    This study presents the optimization of the maintenance scheduling of mechanical components under fatigue loading. The cracks of damaged structures may be detected during non-destructive inspection and subsequently repaired. Fatigue crack initiation and growth show inherent variability, and as well the outcome of inspection activities. The problem is addressed under the framework of reliability based optimization. The initiation and propagation of fatigue cracks are efficiently modeled using cohesive zone elements. The applicability of the method is demonstrated by a numerical example, which involves a plate with two holes subject to alternating stress. PMID:23564979

  15. Reliability-based optimization of maintenance scheduling of mechanical components under fatigue.

    PubMed

    Beaurepaire, P; Valdebenito, M A; Schuëller, G I; Jensen, H A

    2012-05-01

    This study presents the optimization of the maintenance scheduling of mechanical components under fatigue loading. The cracks of damaged structures may be detected during non-destructive inspection and subsequently repaired. Fatigue crack initiation and growth show inherent variability, and as well the outcome of inspection activities. The problem is addressed under the framework of reliability based optimization. The initiation and propagation of fatigue cracks are efficiently modeled using cohesive zone elements. The applicability of the method is demonstrated by a numerical example, which involves a plate with two holes subject to alternating stress.

  16. Simulation on the internal structure of three-dimensional proximal tibia under different mechanical environments

    PubMed Central

    2013-01-01

    Background Bone can adjust its morphological structure to adapt to the changes of mechanical environment, i.e. the bone structure change is related to mechanical loading. This implies that osteoarthritis may be closely associated with knee joint deformity. The purposes of this paper were to simulate the internal bone mineral density (BMD) change in three-dimensional (3D) proximal tibia under different mechanical environments, as well as to explore the relationship between mechanical environment and bone morphological abnormity. Methods The right proximal tibia was scanned with CT to reconstruct a 3D proximal tibia model in MIMICS, then it was imported to finite element software ANSYS to establish 3D finite element model. The internal structure of 3D proximal tibia of young normal people was simulated using quantitative bone remodeling theory in combination with finite element method, then based on the changing pattern of joint contact force on the tibial plateau in valgus knees, the mechanical loading was changed, and the simulated normal tibia structure was used as initial structure to simulate the internal structure of 3D proximal tibia for old people with 6° valgus deformity. Four regions of interest (ROIs) were selected in the proximal tibia to quantitatively analyze BMD and compare with the clinical measurements. Results The simulation results showed that the BMD distribution in 3D proximal tibia was consistent with clinical measurements in normal knees and that in valgus knees was consistent with the measurement of patients with osteoarthritis in clinics. Conclusions It is shown that the change of mechanical environment is the main cause for the change of subchondral bone structure, and being under abnormal mechanical environment for a long time may lead to osteoarthritis. Besides, the simulation method adopted in this paper can more accurately simulate the internal structure of 3D proximal tibia under different mechanical environments. It helps to better

  17. Mechanical Behavior of Tissue Simulants and Soft Tissues Under Extreme Loading Conditions

    NASA Astrophysics Data System (ADS)

    Kalcioglu, Zeynep Ilke

    Recent developments in computer-integrated surgery and in tissue-engineered constructs necessitate advances in experimental and analytical techniques in characterizing properties of mechanically compliant materials such as gels and soft tissues, particularly for small sample volumes. One goal of such developments is to quantitatively predict and mimic tissue deformation due to high rate impact events typical of industrial accidents and ballistic insults. This aim requires advances in mechanical characterization to establish tools and design principles for tissue simulant materials that can recapitulate the mechanical responses of hydrated soft tissues under dynamic contact-loading conditions. Given this motivation, this thesis studies the mechanical properties of compliant synthetic materials developed for tissue scaffold applications and of soft tissues, via modifying an established contact based technique for accurate, small scale characterization under fully hydrated conditions, and addresses some of the challenges in the implementation of this method. Two different engineered material systems composed of physically associating block copolymer gels, and chemically crosslinked networks including a solvent are presented as potential tissue simulants for ballistic applications, and compared directly to soft tissues from murine heart and liver. In addition to conventional quasistatic and dynamic bulk mechanical techniques that study macroscale elastic and viscoelastic properties, new methodologies are developed to study the small scale mechanical response of the aforementioned material systems to concentrated impact loading. The resistance to penetration and the energy dissipative constants are quantified in order to compare the deformation of soft tissues and mechanically optimized simulants, and to identify the underlying mechanisms by which the mechanical response of these tissue simulant candidates are modulated. Finally, given that soft tissues are biphasic in

  18. Mechanics and mechanisms of surface damage in Al-Si alloys under ultra-mild wear conditions

    NASA Astrophysics Data System (ADS)

    Chen, Ming

    Al-Si alloys intended for use in engine components must operate under ultra-mild wear (UMW) conditions to fit an acceptable amount of wear during a typical vehicle life. This study simulated surface damage in a UMW regime on five chemically etched Al-Si alloy surfaces using a pin-on-disc tribometer at low loads (0.5-2.0 N) under boundary lubricated conditions. The five alloys contained 11 to 25 wt.% Si and differed in matrix hardness, silicon particle morphology, and size. The mechanisms leading to the UMW damage and the role that the matrix hardness and microstructure play on said mechanisms were studied. Quantitative measurement methods based on statistical analysis of particle height changes and material loss from elevated aluminum using a profilometer technique were developed and used to assess UMW. The Greenwood and Tripp's numerical model was adapted to analyze the contact that occurred between Al-Si alloys with silicon particles protruding above the aluminum and steel balls. The estimation of the real contact pressure applied to the silicon particles was used to rationalize the damage mechanisms. The UMW mechanisms consisted of (i) abrasive wear on the top of the silicon particle surfaces; (ii) sinking-in of the silicon particles; (iii) piling-up of the aluminium around sunken-in particles and (vi) wear of the aluminium by the counterface, which eventually led to the initiation of UMW-II. Increasing the size or areal density of silicon particles with small aspect ratios delayed the onset of UMW-II by providing resistance against the silicon particles sinking-in and the aluminum piling-up. The UMW wear rates, however, began to decrease after long sliding cycles once an oil residue layer supported by hardened ultra-fine subsurface grains formed on the deformed aluminium matrix. The layer formation depended on the microstructure and applied load. Overall experimental observations suggested that Al-11% Si with small silicon particles exhibited optimal long

  19. [THE DIFFERENTIAL DIAGNOSTIC POSSIBILITIES IN EVALUATION OF IRON-DEFICIENT CONDITION UNDER ANEMIAS].

    PubMed

    Zubrikhina, G N; Blindar, V N; Matveeva, I I

    2016-03-01

    The article presents data concerning differential diagnostic possibilities of evaluation of genuine iron-deficient anemia and anemia of chronic diseases. The variety of mechanisms of development of anemia of chronic diseases is demonstrated, including effect of humoral inhibitors of erythropoiesis, disorder of iron metabolism at the expense of its redistribution into cells of macrophage system, suppression of erythropoiesis resulted in redistributed or functional iron deficiency. The data is presented concerning significance in diagnostic of anemia of chronic diseases of such factors as content of ferritin, dissolving receptors of transferrin and role of hepcidin protein in pathogenesis of anemia of chronic diseases. The analysis of scientific publications demonstrated that hepcidin is a negative regulator of iron metabolism. Under iron-deficient anemia its level in blood decreases that contribute to extensive absorption of iron in gastrointestinal tract. On the contrary, under anemia of chronic diseases its content drastically increases and results in blocking of iron transport everywhere, including internal epithelium, macrophages, placenta and other types of cells. The hyper-production of hepcidin during infection and inflammation is responsible for anemia of chronic diseases. The perspectives of development of pharmaceuticals decreasing level of hepcidin for treatment of anemia of chronic diseases is demonstrated.

  20. Electroluminescence and cathodoluminescence from polyethylene and polypropylene films: Spectra reconstruction from elementary components and underlying mechanisms

    SciTech Connect

    Qiao, B.; Teyssedre, G.; Laurent, C.

    2016-01-14

    The mechanisms of electroluminescence from large band gap polymers used as insulation in electric components are still under debate. It becomes important to unravel the underlying physics of the emission because of increasing thermo-electric stress and a possible relationship between electroluminescence and field withstand. We report herein on the cathodoluminescence spectra of polyethylene and polypropylene films as a way to uncover the nature of its contributions to electroluminescence emission. It is shown that spectra from the two materials are structured around four elementary components, each of them being associated with a specific process contributing to the overall emission with different weights depending on excitation conditions and on materials. The cathodoluminescence and electroluminescence spectra of each material are reconstructed from the four spectral components and their relative contribution are discussed. It is shown that electroluminescence from polyethylene and polypropylene has the same origin pointing towards generic mechanisms in both.

  1. Music and Memory in Alzheimer's Disease and The Potential Underlying Mechanisms.

    PubMed

    Peck, Katlyn J; Girard, Todd A; Russo, Frank A; Fiocco, Alexandra J

    2016-01-01

    With population aging and a projected exponential expansion of persons diagnosed with Alzheimer's disease (AD), the development of treatment and prevention programs has become a fervent area of research and discovery. A growing body of evidence suggests that music exposure can enhance memory and emotional function in persons with AD. However, there is a paucity of research that aims to identify specific underlying neural mechanisms associated with music's beneficial effects in this particular population. As such, this paper reviews existing anecdotal and empirical evidence related to the enhancing effects of music exposure on cognitive function and further provides a discussion on the potential underlying mechanisms that may explain music's beneficial effect. Specifically, this paper will outline the potential role of the dopaminergic system, the autonomic nervous system, and the default network in explaining how music may enhance memory function in persons with AD.

  2. Size and Geometry Effects on the Mechanical Properties of Carrara Marble Under Dynamic Loadings

    NASA Astrophysics Data System (ADS)

    Zou, Chunjiang; Wong, Louis Ngai Yuen

    2016-05-01

    The effects of specimen size and geometry on the dynamic mechanical properties of Carrara marble including compressive strength, failure strain and elastic modulus are investigated in this research. Four different groups of specimens of different sizes and cross-sectional geometries are loaded under a wide range of strain rates by the split Hopkinson pressure bar setup. The experimental results indicate that all these mechanical properties are significantly influenced by the specimen size and geometry to different extent, hence highlighting the importance of taking into account of the specimen size and geometry in dynamic tests on rock materials. In addition, the transmission coefficient and the determination of strain rate under dynamic tests are discussed in detail.

  3. Contact force and mechanical loss of multistage cable under tension and bending

    NASA Astrophysics Data System (ADS)

    Ru, Yanyun; Yong, Huadong; Zhou, Youhe

    2016-10-01

    A theoretical model for calculating the stress and strain states of cabling structures with different loadings has been developed in this paper. We solve the problem for the first- and second-stage cable with tensile or bending strain. The contact and friction forces between the strands are presented by two-dimensional contact model. Several theoretical models have been proposed to verify the results when the triplet subjected to the tensile strain, including contact force, contact stresses, and mechanical loss. It is found that loadings will affect the friction force and the mechanical loss of the triplet. The results show that the contact force and mechanical loss are dependent on the twist pitch. A shorter twist pitch can lead to higher contact force, while the trend of mechanical loss with twist pitch is complicated. The mechanical loss may be reduced by adjusting the twist pitch reasonably. The present model provides a simple analysis method to investigate the mechanical behaviors in multistage-structures under different loads.

  4. From Sound to Significance: Exploring the Mechanisms Underlying Emotional Reactions to Music.

    PubMed

    Juslin, Patrik N; Barradas, Gonçalo; Eerola, Tuomas

    2015-01-01

    A common approach to studying emotional reactions to music is to attempt to obtain direct links between musical surface features such as tempo and a listener's responses. However, such an analysis ultimately fails to explain why emotions are aroused in the listener. In this article we explore an alternative approach, which aims to account for musical emotions in terms of a set of psychological mechanisms that are activated by different types of information in a musical event. This approach was tested in 4 experiments that manipulated 4 mechanisms (brain stem reflex, contagion, episodic memory, musical expectancy) by selecting existing musical pieces that featured information relevant for each mechanism. The excerpts were played to 60 listeners, who were asked to rate their felt emotions on 15 scales. Skin conductance levels and facial expressions were measured, and listeners reported subjective impressions of relevance to specific mechanisms. Results indicated that the target mechanism conditions evoked emotions largely as predicted by a multimechanism framework and that mostly similar effects occurred across the experiments that included different pieces of music. We conclude that a satisfactory account of musical emotions requires consideration of how musical features and responses are mediated by a range of underlying mechanisms.

  5. Experimental research of mechanical behavior of porcine brain tissue under rotational shear stress.

    PubMed

    Li, Gang; Zhang, Jianhua; Wang, Kan; Wang, Mingyu; Gao, Changqing; Ma, Chao

    2016-04-01

    The objective of this paper is to investigate mechanical behavior of porcine brain tissue with a series of rotational shear stress control experiments. To this end, several experiments including stress sweep tests, frequency sweep tests and quasi-static creep tests were designed and conducted with a standard rheometer (HAAKE RheoStress6000). The effects of the loading stress rates to mechanical properties of brain tissue were also studied in stress sweep tests. The results of stress sweep tests performed on the same brain showed that brain tissue had an obvious regional inhomogeneity and the mechanical damage occurred at the rotational shear stress of 10-15Pa. The experimental data from three different loading stress rates demonstrated that the mechanical behavior of porcine brain tissue was loading stress rate dependent. With the decrease of loading stress rate, a stiffer mechanical characteristic of brain tissue was observed and the occurrence of mechanical damage can be delayed to a higher stress. From the results of frequency sweep tests we found that brain tissue had almost completely elastic properties at high frequency area. The nonlinear creep response under the rotational shear stress of 1, 3, 5, 7 and 9Pa was shown in results of creep tests. A new nonlinear viscoelastic solid model was proposed for creep tests and matched well with the test data. Considering the regional differences, loading stress rates and test conditions effects, loss tangent tan δ in porcine brain tissue showed a high uniformity of 0.25-0.45.

  6. The chemical and mechanical behaviors of polymer / reactive metal systems under high strain rates

    NASA Astrophysics Data System (ADS)

    Shen, Yubin

    As one category of energetic materials, impact-initiated reactive materials are able to release a high amount of stored chemical energy under high strain rate impact loading, and are used extensively in civil and military applications. In general, polymers are introduced as binder materials to trap the reactive metal powders inside, and also act as an oxidizing agent for the metal ingredient. Since critical attention has been paid on the metal / metal reaction, only a few types of polymer / reactive metal interactions have been studied in the literature. With the higher requirement of materials resistant to different thermal and mechanical environments, the understanding and characterization of polymer / reactive metal interactions are in great demand. In this study, PTFE (Polytetrafluoroethylene) 7A / Ti (Titanium) composites were studied under high strain rates by utilizing the Taylor impact and SHPB tests. Taylor impact tests with different impact velocities, sample dimensions and sample configurations were conducted on the composite, equipped with a high-speed camera for tracking transient images during the sudden process. SHPB and Instron tests were carried out to obtain the stress vs. strain curves of the composite under a wide range of strain rates, the result of which were also utilized for fitting the constitutive relations of the composite based on the modified Johnson-Cook strength model. Thermal analyses by DTA tests under different flow rates accompanied with XRD identification were conducted to study the reaction mechanism between PTFE 7A and Ti when only heat was provided. Numerical simulations on Taylor impact tests and microstructural deformations were also performed to validate the constitutive model built for the composite system, and to investigate the possible reaction mechanism between two components. The results obtained from the high strain rate tests, thermal analyses and numerical simulations were combined to provide a systematic study on

  7. Cavitation behavior observed in three monoleaflet mechanical heart valves under accelerated testing conditions.

    PubMed

    Lo, Chi-Wen; Liu, Jia-Shing; Li, Chi-Pei; Lu, Po-Chien; Hwang, Ned H

    2008-01-01

    Accelerated testing provides a substantial amount of data on mechanical heart valve durability in a short period of time, but such conditions may not accurately reflect in vivo performance. Cavitation, which occurs during mechanical heart valve closure when local flow field pressure decreases below vapor pressure, is thought to play a role in valve damage under accelerated conditions. The underlying flow dynamics and mechanisms behind cavitation bubble formation are poorly understood. Under physiologic conditions, random perivalvular cavitation is difficult to capture. We applied accelerated testing at a pulse rate of 600 bpm and transvalvular pressure of 120 mm Hg, with synchronized videographs and high-frequency pressure measurements, to study cavitation of the Medtronic Hall Standard (MHS), Medtronic Hall D-16 (MHD), and Omni Carbon (OC) valves. Results showed cavitation bubbles between 340 and 360 micros after leaflet/housing impact of the MHS, MHD, and OC valves, intensified by significant leaflet rebound. Squeeze flow, Venturi, and water hammer effects each contributed to cavitation, depending on valve design.

  8. Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression

    SciTech Connect

    Yuan, Fuping Wu, Xiaolei

    2014-12-15

    A series of large-scale molecular dynamics simulations were conducted to investigate the scaling laws and the related atomistic deformation mechanisms of Cu monocrystal samples containing randomly placed nanovoids under adiabatic uniaxial strain compression. At onset of yielding, plastic deformation is accommodated by dislocations emitted from void surfaces as shear loops. The collapse of voids are observed by continuous emissions of dislocations from void surfaces and their interactions with further plastic deformation. The simulation results also suggest that the effect modulus, the yield stress and the energy aborption density of samples under uniaxial strain are linearly proportional to the relative density ρ. Moreover, the yield stress, the average flow stress and the energy aborption density of samples with the same relative density show a strong dependence on the void diameter d, expressed by exponential relations with decay coefficients much higher than -1/2. The corresponding atomistic mechanisms for scaling laws of the relative density and the void diameter were also presented. The present results should provide insights for understanding deformation mechanisms of nanoporous metals under extreme conditions.

  9. Kinetic theory approach to modeling of cellular repair mechanisms under genome stress.

    PubMed

    Qi, Jinpeng; Ding, Yongsheng; Zhu, Ying; Wu, Yizhi

    2011-01-01

    Under acute perturbations from outer environment, a normal cell can trigger cellular self-defense mechanism in response to genome stress. To investigate the kinetics of cellular self-repair process at single cell level further, a model of DNA damage generating and repair is proposed under acute Ion Radiation (IR) by using mathematical framework of kinetic theory of active particles (KTAP). Firstly, we focus on illustrating the profile of Cellular Repair System (CRS) instituted by two sub-populations, each of which is made up of the active particles with different discrete states. Then, we implement the mathematical framework of cellular self-repair mechanism, and illustrate the dynamic processes of Double Strand Breaks (DSBs) and Repair Protein (RP) generating, DSB-protein complexes (DSBCs) synthesizing, and toxins accumulating. Finally, we roughly analyze the capability of cellular self-repair mechanism, cellular activity of transferring DNA damage, and genome stability, especially the different fates of a certain cell before and after the time thresholds of IR perturbations that a cell can tolerate maximally under different IR perturbation circumstances.

  10. Mechano-adaptive sensory mechanism of α-catenin under tension

    NASA Astrophysics Data System (ADS)

    Maki, Koichiro; Han, Sung-Woong; Hirano, Yoshinori; Yonemura, Shigenobu; Hakoshima, Toshio; Adachi, Taiji

    2016-04-01

    The contractile forces in individual cells drive the tissue processes, such as morphogenesis and wound healing, and maintain tissue integrity. In these processes, α-catenin molecule acts as a tension sensor at cadherin-based adherens junctions (AJs), accelerating the positive feedback of intercellular tension. Under tension, α-catenin is activated to recruit vinculin, which recruits actin filaments to AJs. In this study, we revealed how α-catenin retains its activated state while avoiding unfolding under tension. Using single-molecule force spectroscopy employing atomic force microscopy (AFM), we found that mechanically activated α-catenin fragment had higher mechanical stability than a non-activated fragment. The results of our experiments using mutated and segmented fragments showed that the key intramolecular interactions acted as a conformational switch. We also found that the conformation of α-catenin was reinforced by vinculin binding. We demonstrate that α-catenin adaptively changes its conformation under tension to a stable intermediate state, binds to vinculin, and finally settles into a more stable state reinforced by vinculin binding. Our data suggest that the plastic characteristics of α-catenin, revealed in response to both mechanical and biochemical cues, enable the functional-structural dynamics at the cellular and tissue levels.

  11. Investigation of mechanical properties of twin gold crystal nanowires under uniaxial load by molecular dynamics method

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-Wei; Yang, Zai-Lin; Luo, Gang

    2016-08-01

    Twin gold crystal nanowires, whose loading direction is parallel to the twin boundary orientation, are simulated. We calculate the nanowires under tensile or compressive loads, different length nanowires, and different twin boundary nanowires respectively. The Young modulus of nanowires under compressive load is about twice that under tensile load. The compressive properties of twin gold nanowires are superior to their tensile properties. For different length nanowires, there is a critical value of length with respect to the mechanical properties. When the length of nanowire is greater than the critical value, its mechanical properties are sensitive to length. The twin boundary spacing hardly affects the mechanical properties. Project supported by the National Science and Technology Pillar Program, China (Grant No. 2015BAK17B06), the Earthquake Industry Special Science Research Foundation Project, China (Grant No. 201508026-02), the Natural Science Foundation of Heilongjiang Province, China (Grant No. A201310), and the Scientific Research Starting Foundation for Post Doctorate of Heilongjiang Province, China (Grant No. LBHQ13040).

  12. Mechano-adaptive sensory mechanism of α-catenin under tension

    PubMed Central

    Maki, Koichiro; Han, Sung-Woong; Hirano, Yoshinori; Yonemura, Shigenobu; Hakoshima, Toshio; Adachi, Taiji

    2016-01-01

    The contractile forces in individual cells drive the tissue processes, such as morphogenesis and wound healing, and maintain tissue integrity. In these processes, α-catenin molecule acts as a tension sensor at cadherin-based adherens junctions (AJs), accelerating the positive feedback of intercellular tension. Under tension, α-catenin is activated to recruit vinculin, which recruits actin filaments to AJs. In this study, we revealed how α-catenin retains its activated state while avoiding unfolding under tension. Using single-molecule force spectroscopy employing atomic force microscopy (AFM), we found that mechanically activated α-catenin fragment had higher mechanical stability than a non-activated fragment. The results of our experiments using mutated and segmented fragments showed that the key intramolecular interactions acted as a conformational switch. We also found that the conformation of α-catenin was reinforced by vinculin binding. We demonstrate that α-catenin adaptively changes its conformation under tension to a stable intermediate state, binds to vinculin, and finally settles into a more stable state reinforced by vinculin binding. Our data suggest that the plastic characteristics of α-catenin, revealed in response to both mechanical and biochemical cues, enable the functional-structural dynamics at the cellular and tissue levels. PMID:27109499

  13. Nanoscopic dynamic mechanical analysis of resin-infiltrated dentine, under in vitro chewing and bruxism events.

    PubMed

    Toledano, Manuel; Osorio, Estrella; Cabello, Inmaculada; Aguilera, Fátima S; López-López, Modesto T; Toledano-Osorio, Manuel; Osorio, Raquel

    2016-02-01

    The aim of this study was to evaluate the induced changes in mechanical behavior and bonding capability of resin-infiltrated dentine interfaces, after application of mechanical stimuli. Dentine surfaces were subjected to partial demineralization through 37% phosphoric acid etching followed by the application of an etch-and-rinse dentine adhesive, Single Bond (3M/ESPE). Bonded interfaces were stored in simulated body fluid during 24h, and then tested or submitted to the mechanical loading challenge. Different loading waveforms were applied: No cycling (I), 24h cycled in sine (II) or square (III) waves, sustained loading held for 24h (IV) or sustained loading held for 72h (V). Microtensile bond strength (MTBS) was assessed for the different groups. Debonded dentine surfaces were studied by field emission scanning electron microscopy (FESEM). At the resin-dentine interface, both the hybrid layer (HL) and the bottom of the hybrid layer (BHL), and both peritubular and intertubular were evaluated using a nanoindenter in scanning mode. The load and displacement responses were used to perform the nano-Dynamic Mechanical analysis and to estimate the complex and storage modulus. Dye assisted Confocal Microscopy Evaluation was used to assess sealing ability. Load cycling increased the percentage of adhesive failures in all groups. Specimens load cycled in held 24h attained the highest complex and storage moduli at HL and BHL. The storage modulus was maximum in specimens load cycled in held 24h at peritubular dentine, and the lowest values were attained at intertubular dentine. The storage modulus increased in all mechanical tests, at peritubular dentine. An absence of micropermeability and nanoleakage after loading in sine and square waveforms were encountered. Porosity of the resin-dentine interface was observed when specimens were load cycled in held 72h. Areas of combined sealing and permeability were discovered at the interface of specimens load cycled in held 24h. Crack

  14. Neuronal mechanisms and circuits underlying repetitive behaviors in mouse models of autism spectrum disorder.

    PubMed

    Kim, Hyopil; Lim, Chae-Seok; Kaang, Bong-Kiun

    2016-01-20

    Autism spectrum disorder (ASD) refers to a broad spectrum of neurodevelopmental disorders characterized by three central behavioral symptoms: impaired social interaction, impaired social communication, and restricted and repetitive behaviors. However, the symptoms are heterogeneous among patients and a number of ASD mouse models have been generated containing mutations that mimic the mutations found in human patients with ASD. Each mouse model was found to display a unique set of repetitive behaviors. In this review, we summarize the repetitive behaviors of the ASD mouse models and variations found in their neural mechanisms including molecular and electrophysiological features. We also propose potential neuronal mechanisms underlying these repetitive behaviors, focusing on the role of the cortico-basal ganglia-thalamic circuits and brain regions associated with both social and repetitive behaviors. Further understanding of molecular and circuitry mechanisms of the repetitive behaviors associated with ASD is necessary to aid the development of effective treatments for these disorders.

  15. The cell-autonomous mechanisms underlying the activity of metformin as an anticancer drug.

    PubMed

    Sacco, Francesca; Calderone, Alberto; Castagnoli, Luisa; Cesareni, Gianni

    2016-12-06

    The biguanide drug metformin profoundly affects cell metabolism, causing an impairment of the cell energy balance and triggering a plethora of pleiotropic effects that vary depending on the cellular or environmental context. Interestingly, a decade ago, it was observed that metformin-treated diabetic patients have a significantly lower cancer risk. Although a variety of in vivo and in vitro observations emphasising the role of metformin as anticancer drug have been reported, the underlying mechanisms are still poorly understood. Here, we discuss our current understanding of the molecular mechanisms that are perturbed by metformin treatment and that might be relevant to understand its antitumour activities. We focus on the cell-autonomous mechanisms modulating growth and death of cancer cells.

  16. The cell-autonomous mechanisms underlying the activity of metformin as an anticancer drug

    PubMed Central

    Sacco, Francesca; Calderone, Alberto; Castagnoli, Luisa; Cesareni, Gianni

    2016-01-01

    The biguanide drug metformin profoundly affects cell metabolism, causing an impairment of the cell energy balance and triggering a plethora of pleiotropic effects that vary depending on the cellular or environmental context. Interestingly, a decade ago, it was observed that metformin-treated diabetic patients have a significantly lower cancer risk. Although a variety of in vivo and in vitro observations emphasising the role of metformin as anticancer drug have been reported, the underlying mechanisms are still poorly understood. Here, we discuss our current understanding of the molecular mechanisms that are perturbed by metformin treatment and that might be relevant to understand its antitumour activities. We focus on the cell-autonomous mechanisms modulating growth and death of cancer cells. PMID:27875520

  17. Potential neural mechanisms underlying the effectiveness of early intervention for children with autism spectrum disorder.

    PubMed

    Sullivan, Katherine; Stone, Wendy L; Dawson, Geraldine

    2014-11-01

    Although evidence supports the efficacy of early intervention for improving outcomes for children with autism spectrum disorder (ASD), the mechanisms underlying their effectiveness remain poorly understood. This paper reviews the research literature on the neural bases of the early core deficits in ASD and proposes three key features of early intervention related to the neural mechanisms that may contribute to its effectiveness in improving deficit areas. These features include (1) the early onset of intensive intervention which capitalizes on the experience-expectant plasticity of the immature brain, (2) the use of treatment strategies that address core deficits in social motivation through an emphasis on positive social engagement and arousal modulation, and (3) promotion of complex neural networks and connectivity through thematic, multi-sensory and multi-domain teaching approaches. Understanding the mechanisms of effective early intervention will enable us to identify common or foundational active ingredients for promoting optimal outcomes in children with ASD.

  18. The Molecular Mechanisms Underlying the Hijack of Host Proteins by the 1918 Spanish Influenza Virus.

    PubMed

    Shen, Qingliang; Zeng, Danyun; Zhao, Baoyu; Bhatt, Veer S; Li, Pingwei; Cho, Jae-Hyun

    2017-04-05

    The 1918 Spanish influenza A virus (IAV) caused one of the most serious pandemics in history. The nonstructural protein 1 (NS1) of the 1918 IAV hijacks the interaction between human CrkII and JNK1. Little is, however, known about its molecular mechanism. Here, we performed X-ray crystallography, NMR relaxation dispersion experiment, and fluorescence spectroscopy to determine the structural, kinetic, and thermodynamic mechanisms underlying the hijacking of CrkII by 1918 IAV NS1. We observed that the interaction between a proline-rich motif in NS1 and the N-terminal SH3 domain of CrkII displays strikingly rapid kinetics and exceptionally high affinity with 100-fold faster kon and 3300-fold lower Kd compared to those for the CrkII-JNK1 interaction. These results provide molecular insight into the mechanism by which 1918 IAV NS1 hijacks CrkII and disrupts its interactions with critical cellular signaling proteins.

  19. Insights into metabolic mechanisms underlying folate-responsive neural tube defects: a minireview.

    PubMed

    Beaudin, Anna E; Stover, Patrick J

    2009-04-01

    Neural tube defects (NTDs), including anencephaly and spina bifida, arise from the failure of neurulation during early embryonic development. Neural tube defects are common birth defects with a heterogenous and multifactorial etiology with interacting genetic and environmental risk factors. Although the mechanisms resulting in failure of neural tube closure are unknown, up to 70% of NTDs can be prevented by maternal folic acid supplementation. However, the metabolic mechanisms underlying the association between folic acid and NTD pathogenesis have not been identified. This review summarizes our current understanding of the mechanisms by which impairments in folate metabolism might ultimately lead to failure of neural tube closure, with an emphasis on untangling the relative contributions of nutritional deficiency and genetic risk factors to NTD pathogenesis.

  20. Determination of Temperature- Dependent Mechanical Properties of Carbon Composites Under Tensile and Flexural Loading

    NASA Astrophysics Data System (ADS)

    Chripunow, Andre; Kubisch, Aline; Ruder, Matthias; Forster, Andreas; Korber, Hannes

    2014-06-01

    The presented test setup utilises a custom-built furnace realising test temperatures of up to 500°C. In order to ensure always optimal test conditions the temperature cell can be exchanged depending on the mechanical tests and specimen sizes. Cells for tensile and flexural loadings had been developed. With the latter one it is possible to perform three-point-bending tests, interlaminar-shear-strength tests as well as tests to determine the interlaminar fracture toughness. In this work the effect of fibre orientation on the mechanical properties of CFRP prepreg material under tensile and flexural loads at elevated temperatures was studied. Especially the matrix dominated layups showed a rather early decay of the mechanical properties even at temperatures quite lower than Tg. An analytical model has been used to describe the temperature-dependent properties. The model shows good agreement concerning the strength whereas the proper prediction of the moduli was only possible for the matrix dominated layups.

  1. FInal Report: First Principles Modeling of Mechanisms Underlying Scintillator Non-Proportionality

    SciTech Connect

    Aberg, Daniel; Sadigh, Babak; Zhou, Fei

    2015-01-01

    This final report presents work carried out on the project “First Principles Modeling of Mechanisms Underlying Scintillator Non-Proportionality” at Lawrence Livermore National Laboratory during 2013-2015. The scope of the work was to further the physical understanding of the microscopic mechanisms behind scintillator nonproportionality that effectively limits the achievable detector resolution. Thereby, crucial quantitative data for these processes as input to large-scale simulation codes has been provided. In particular, this project was divided into three tasks: (i) Quantum mechanical rates of non-radiative quenching, (ii) The thermodynamics of point defects and dopants, and (iii) Formation and migration of self-trapped polarons. The progress and results of each of these subtasks are detailed.

  2. Experimental research on buckling of thin films in nano-scale under mechanical and thermal loading

    NASA Astrophysics Data System (ADS)

    Wang, S. B.; Jia, H. K.; Ren, X. C.; Li, L. A.

    2008-11-01

    In this paper, the mechanical and thermal properties of compressed thin film titanium films with 150nm thickness deposited on an organic glass substrate under mechanical and thermal loads were measured and characterized. In order to simulate the thin films in IT which subjected compound loads and to produce the buckle modes, the external uniaxial compression and thermal loading are subjected to the specimen by the symmetric loading device and the electrical resistance film in this experiment. The temperature of the thin film deposited on substrate was measured using thermoelectric couple. The range of temperature accords with the temperature range of the MEMS. It is found that the size and number of the delamination and buckling of the film are depended upon the pre-fixed mechanical loading. The transient conduction and thermal stability of the film and substrate was studied with finite element method.

  3. Potential neural mechanisms underlying the effectiveness of early intervention for children with autism spectrum disorder

    PubMed Central

    Sullivan, Katherine; Stone, Wendy L.; Dawson, Geraldine

    2014-01-01

    Although evidence supports the efficacy of early intervention for improving outcomes for children with autism spectrum disorder (ASD), the mechanisms underlying their effectiveness remain poorly understood. This paper reviews the research literature on the neural bases of the early core deficits in ASD and proposes three key features of early intervention related to the neural mechanisms that may contribute to its effectiveness in improving deficit areas. These features include (1) the early onset of intensive intervention which capitalizes on the experience-expectant plasticity of the immature brain, (2) the use of treatment strategies that address core deficits in social motivation through an emphasis on positive social engagement and arousal modulation, and (3) promotion of complex neural networks and connectivity through thematic, multi-sensory and multi-domain teaching approaches. Understanding the mechanisms of effective early intervention will enable us to identify common or foundational active ingredients for promoting optimal outcomes in children with ASD. PMID:25108609

  4. Experimental Study on the Thermal Damage Characteristics of Limestone and Underlying Mechanism

    NASA Astrophysics Data System (ADS)

    Zhang, Weiqiang; Sun, Qiang; Hao, Shuqing; Wang, Bo

    2016-08-01

    This work discusses an experimental investigation on the thermal damage characteristics of limestone and underlying mechanism. Cylindrical rock samples were heated to a specific temperature level of 25, 100, 200, 300, 400, 500, 600, 700, 800, and 900 °C. Then the thermal damage evolution equation was established based on the experimental results and the characteristics of thermal damage were analyzed. Last, possible mechanisms for the observed thermo-physical and mechanical response are discussed. The results show that with the increase of temperature in the tested range of temperature, the P-wave velocity, peak compressive strength and elastic modulus decrease, but the peak strain increases; the damage factors increase faster in 200-600 °C; the development of high-temperature-induced cracks conforms to the dislocation theory; the decomposition of magnesium carbonate and dolomite is the main reaction in the tested temperature range.

  5. Structural basis for the nonlinear mechanics of fibrin networks under compression

    PubMed Central

    Kim, Oleg V.; Litvinov, Rustem I.; Weisel, John W.; Alber, Mark S.

    2014-01-01

    Fibrin is a protein polymer that forms a 3D filamentous network, a major structural component of protective physiological blood clots as well as life threatening pathological thrombi. It plays an important role in wound healing, tissue regeneration and is widely employed in surgery as a sealant and in tissue engineering as a scaffold. The goal of this study was to establish correlations between structural changes and mechanical responses of fibrin networks exposed to compressive loads. Rheological measurements revealed nonlinear changes of fibrin network viscoelastic properties under dynamic compression, resulting in network softening followed by its dramatic hardening. Repeated compression/decompression enhanced fibrin clot stiffening. Combining fibrin network rheology with simultaneous confocal microscopy provided direct evidence of structural modulations underlying nonlinear viscoelasticity of compressed fibrin networks. Fibrin clot softening in response to compression strongly correlated with fiber buckling and bending, while hardening was associated with fibrin network densification. Our results suggest a complex interplay of entropic and enthalpic mechanisms accompanying structural changes and accounting for the nonlinear mechanical response in fibrin networks undergoing compressive deformations. These findings provide new insight into the fibrin clot structural mechanics and can be useful for designing fibrin-based biomaterials with modulated viscoelastic properties. PMID:24840618

  6. Psychogenic non-epileptic seizures: so-called psychiatric comorbidity and underlying defense mechanisms

    PubMed Central

    Beghi, Massimiliano; Negrini, Paola Beffa; Perin, Cecilia; Peroni, Federica; Magaudda, Adriana; Cerri, Cesare; Cornaggia, Cesare Maria

    2015-01-01

    In Diagnostic and Statistical Manual of Mental Disorders, fifth edition, psychogenic non-epileptic seizures (PNES) do not have a unique classification as they can be found within different categories: conversion, dissociative, and somatization disorders. The ICD-10, instead, considers PNES within dissociative disorders, merging the dissociative disorders and conversion disorders, although the underlying defense mechanisms are different. The literature data show that PNES are associated with cluster B (mainly borderline) personality disorders and/or to people with depressive or anxiety disorders. Defense mechanisms in patients with PNES with a prevalence of anxious/depressive symptoms are of “neurotic” type; their goal is to lead to a “split”, either vertical (dissociation) or horizontal (repression). The majority of patients with this type of PNES have alexithymia traits, meaning that they had difficulties in feeling or perceiving emotions. In subjects where PNES are associated with a borderline personality, in which the symbolic function is lost, the defense mechanisms are of a more archaic nature (denial). PNES with different underlying defense mechanisms have different prognoses (despite similar severity of PNES) and need usually a different treatment (pharmacological or psychological). Thus, it appears superfluous to talk about psychiatric comorbidity, since PNES are a different symptomatic expression of specific psychiatric disorders. PMID:26491330

  7. Structural basis for the nonlinear mechanics of fibrin networks under compression.

    PubMed

    Kim, Oleg V; Litvinov, Rustem I; Weisel, John W; Alber, Mark S

    2014-08-01

    Fibrin is a protein polymer that forms a 3D filamentous network, a major structural component of protective physiological blood clots as well as life threatening pathological thrombi. It plays an important role in wound healing, tissue regeneration and is widely employed in surgery as a sealant and in tissue engineering as a scaffold. The goal of this study was to establish correlations between structural changes and mechanical responses of fibrin networks exposed to compressive loads. Rheological measurements revealed nonlinear changes of fibrin network viscoelastic properties under dynamic compression, resulting in network softening followed by its dramatic hardening. Repeated compression/decompression enhanced fibrin clot stiffening. Combining fibrin network rheology with simultaneous confocal microscopy provided direct evidence of structural modulations underlying nonlinear viscoelasticity of compressed fibrin networks. Fibrin clot softening in response to compression strongly correlated with fiber buckling and bending, while hardening was associated with fibrin network densification. Our results suggest a complex interplay of entropic and enthalpic mechanisms accompanying structural changes and accounting for the nonlinear mechanical response in fibrin networks undergoing compressive deformations. These findings provide new insight into the fibrin clot structural mechanics and can be useful for designing fibrin-based biomaterials with modulated viscoelastic properties.

  8. Effect of different heating methods on deformation of metal plate under upsetting mechanism in laser forming

    NASA Astrophysics Data System (ADS)

    Shi, Yongjun; Liu, Yancong; Yi, Peng; Hu, Jun

    2012-03-01

    In a laser forming process, different forming mechanisms have different deformation behaviors. The aim of laser forming is to acquire plane strain under an upsetting mechanism, while a plate undergoes a small bending deformation. In some industrial applications, the bending strain should not occur. To achieve high-precision forming, the deformation behaviors of a metal plate when an upsetting mechanism plays a dominant role are studied in the paper. Several heating methods are proposed to reduce the plane strain difference along the thickness direction and little bending deformation resulting from a small temperature difference between the top and bottom surfaces of the plate. The results show that negligible bending deformation and a uniform plastic plane strain field can be obtained by simultaneously heating the top and bottom surfaces with the same process parameters. A conventional scanning method needs a larger spot diameter and slower scanning speed under the upsetting mechanism, but a smaller spot diameter and quicker scanning speed may be selected using the simultaneous heating method, which can greatly widen the potential scope of process parameters.

  9. Thermoset polymer performance under harsh environments to evaluate glass composite rebars for infrastructure applications

    SciTech Connect

    Altizer, S.D.; Vijay, P.V.; GangaRao, H.V.S.; Douglass, N.; Pauer, R.

    1996-11-01

    Corrosion of steel bars in concrete infrastructure facilities such as bridges, buildings, marine constructions and chemical plants is a serious problem. Various solutions have been tried in the past to counter the threat of corrosion in steel bars by using epoxy coatings, cathodic protection, increased concrete cover thickness and use of polymer concrete. None of the measures have provided a long term solution. The US Department of Transportation estimates the cost of repairing deteriorated infrastructure facilities to be billions of dollars. Glass fiber reinforced plastic (GFRP) bars have the potential to replace steel bars in concrete structures due to their superior mechanical and chemical properties such as non-corrosiveness, non-magnetic properties, high strength and light weight. Long term durability of GFRP under harsh environments needs to be completely understood before their field implementation. This paper describes the accelerated tests conducted on 13 mm and 19 mm (No. 4 and No. 6) E-glass fiber reinforced bars, manufactured with different durable resins, to evaluate the effect of environmental factors. Conditioning schemes consisted of exposing GFRP bars to ambient and freeze-thaw temperature cycles, chemical environments in the liquid form (pH{approximately}7--13) and sustained stress. GFRP bars used in this study were manufactured with five specially selected thermoset polymeric resins, and the conditioned bars were tested in tension to evaluate the changes in strength and stiffness with respect to unconditioned bars. Test results indicate that the GFRP bars with urethane modified bisphenol vinylester have excellent strength and stiffness properties as compared to bars with different resins under five conditioning schemes considered.

  10. Viscoelastic behaviour of hydrogel-based composites for tissue engineering under mechanical load.

    PubMed

    Kocen, Rok; Gasik, Michael; Gantar, Ana; Novak, Saša

    2017-03-06

    Along with biocompatibility, bioinductivity and appropriate biodegradation, mechanical properties are also of crucial importance for tissue engineering scaffolds. Hydrogels, such as gellan gum (GG), are usually soft materials, which may benefit from the incorporation of inorganic particles, e.g. bioactive glass, not only due to the acquired bioactivity, but also due to improved mechanical properties. They exhibit complex viscoelastic properties, which can be evaluated in various ways. In this work, to reliably evaluate the effect of the bioactive glass (BAG) addition on viscoelastic properties of the composite hydrogel, we employed and compared the three most commonly used techniques, analyzing their advantages and limitations: monotonic uniaxial unconfined compression, small amplitude oscillatory shear (SAOS) rheology and dynamic mechanical analysis (DMA). Creep and small amplitude dynamic strain-controlled tests in DMA are suggested as the best ways for the characterization of mechanical properties of hydrogel composites, whereas the SAOS rheology is more useful for studying the hydrogel's processing kinetics, as it does not induce volumetric changes even at very high strains. Overall, the results confirmed a beneficial effect of BAG (nano)particles on the elastic modulus of the GG-BAG composite hydrogel. The Young's modulus of 6.6 ± 0.8 kPa for the GG hydrogel increased by two orders of magnitude after the addition of 2 wt.% BAG particles (500-800 kPa).

  11. Individuality of breathing patterns in patients under noninvasive mechanical ventilation evidenced by chaotic global models

    NASA Astrophysics Data System (ADS)

    Letellier, Christophe; Rodrigues, Giovani G.; Muir, Jean-François; Aguirre, Luis A.

    2013-03-01

    Autonomous global models based on radial basis functions were obtained from data measured from patients under noninvasive mechanical ventilation. Some of these models, which are discussed in the paper, turn out to have chaotic or quasi-periodic solutions, thus providing a first piece of evidence that the underlying dynamics of the data used to estimate the global models are likely to be chaotic or, at least, have a chaotic component. It is explicitly shown that one of such global models produces attractors characterized by a Horseshoe map, two models produce toroidal chaos, and one model produces a quasi-periodic regime. These topologically inequivalent attractors evidence the individuality of breathing profiles observed in patient under noninvasive ventilation.

  12. Mechanical response of a fibre reinforced earthen material under static and impact loadings

    NASA Astrophysics Data System (ADS)

    Aymerich, Francesco; Fenu, Luigi; Francesconi, Luca; Meloni, Paola

    2015-09-01

    This study examines the improvements provided by the insertion of hemp fibres with different weight fractions and lengths in an earthen material. The structural response of the materials was investigated by means of static and impact bending tests carried out on notched samples. The main focus of the analyses was in the characterization of the structural properties of the materials in terms of fracture resistance, post-cracking performance and energy absorption capability. The results of the study show that hemp fibres improve significantly the mechanical and fracture properties of the earthen material under both static and dynamic bending. It was also found that the structural properties of unreinforced and reinforced earthen materials are highly sensitive to the stress-rate, with higher strength and fracture resistance under impact loading than under static loading.

  13. On-line updating Gaussian mixture model for aircraft wing spar damage evaluation under time-varying boundary condition

    NASA Astrophysics Data System (ADS)

    Qiu, Lei; Yuan, Shenfang; Chang, Fu-Kuo; Bao, Qiao; Mei, Hanfei

    2014-12-01

    Structural health monitoring technology for aerospace structures has gradually turned from fundamental research to practical implementations. However, real aerospace structures work under time-varying conditions that introduce uncertainties to signal features that are extracted from sensor signals, giving rise to difficulty in reliably evaluating the damage. This paper proposes an online updating Gaussian Mixture Model (GMM)-based damage evaluation method to improve damage evaluation reliability under time-varying conditions. In this method, Lamb-wave-signal variation indexes and principle component analysis (PCA) are adopted to obtain the signal features. A baseline GMM is constructed on the signal features acquired under time-varying conditions when the structure is in a healthy state. By adopting the online updating mechanism based on a moving feature sample set and inner probability structural reconstruction, the probability structures of the GMM can be updated over time with new monitoring signal features to track the damage progress online continuously under time-varying conditions. This method can be implemented without any physical model of damage or structure. A real aircraft wing spar, which is an important load-bearing structure of an aircraft, is adopted to validate the proposed method. The validation results show that the method is effective for edge crack growth monitoring of the wing spar bolts holes under the time-varying changes in the tightness degree of the bolts.

  14. Exploring mechanisms underlying sex-specific differences in mortality of Lake Michigan bloaters

    USGS Publications Warehouse

    Bunnell, D.B.; Madenjian, C.P.; Rogers, M.W.; Holuszko, J.D.; Begnoche, L.J.

    2012-01-01

    Sex-specific differences in mortality rates have been observed among freshwater and marine fish taxa, and underlying mechanisms can include sex-specific differences in (1) age at maturity, (2) growth rate, or (3) activity or behavior during the spawning period. We used a long-term (1973–2009) Lake Michigan data set to evaluate whether there were sex-specific differences in catch per unit effort, mortality, age at maturity, and length at age in bloaters Coregonus hoyi. Because bloater population biomass varied 200-fold during the years analyzed, we divided the data into three periods: (1) 1973–1982 (low biomass), (2) 1983–1997 (high biomass), and (3) 1998–2009 (low biomass). Mortality was higher for males than for females in periods 2 and 3; the average instantaneous total mortality rate (Z) over these two periods was 0.71 for males and 0.57 for females. Length at age was slightly greater (2–6%) for females than for males in different age-classes (3–6 years) during each period. Age at maturity was earlier for males than for females in periods 1 and 2, but the mean difference was only 0.2–0.4 years. To test the hypothesis that somatic lipids declined more in males than in females during spawning (perhaps due to increased activity or reduced feeding), we estimated sex-specific percent somatic lipids for fish sampled in 2005–2006 and 2007–2008. During 2005–2006, somatic lipids declined from prespawning to postspawning for males but were unchanged for females. During 2007–2008, however, somatic lipids were unchanged for males, whereas they increased for females. We found that sex-specific differences in Z occurred in the Lake Michigan bloater population, but our hypotheses that sex-specific differences in maturity and growth could explain this pattern were generally unsupported. Our hypothesis that somatic lipids in males declined during spawning at a faster rate than in females will require additional research to clarify its importance.

  15. Deformation and failure mechanisms of 18650 battery cells under axial compression

    NASA Astrophysics Data System (ADS)

    Zhu, Juner; Zhang, Xiaowei; Sahraei, Elham; Wierzbicki, Tomasz

    2016-12-01

    An important deformation mode during ground impacts of battery packs made of cylindrical battery cells is axial compression. This type of loading subjects the cell to a complex deformation pattern and failure mechanism. The design of endcaps plays an important role in such deformations. To explore the sequence of deformation and the underlying failure mechanisms, a combined experimental/numerical study was carried out. Tests were conducted on 18650 cells, and the deformation of each component was carefully investigated and documented. There are four different stages in the force-displacement curve, corresponding with deformation of various components in the endcap assembly. A short circuit happens at a displacement of 4 mm. To clarify these observations, a detailed Finite Element model was set up, covering the geometry and the mechanical property of almost all the components of the cell. Using the simulation results, the sequence of the axial compression was revealed, which was subsequently validated by Micro CT scans as well as analytical solutions. Based on the precise analysis of the mechanical behavior, the cause of the short circuit during axial loading was clarified. Two failure mechanisms in the separator at the top section of the cell explain the possible causes of short circuit.

  16. Simultaneous Measurement of [Ca2+]i and Membrane Potential under Mechanical or Biochemical Stimulation

    NASA Astrophysics Data System (ADS)

    Sano, Minoru; Imura, Katsuaki; Ushida, Takashi; Tateishi, Tetsuya

    In human umbilical endothelial cells (HUVEC), mechanical stress is known to induce transients of [Ca2+]i that lead to the regulation of vascular functions in vivo. The transmembraneous influx of Ca2+ is thought to be mediated by voltage-dependent ion channels or stretch-activated ion channels. In order to elucidate the correlation of [Ca2+]i and membrane potential under mechanical stress, the influences of mechanical or biochemical stimulation on endothelial cells stained with both fura-2 and DiBAC4(3) were studied in vitro, by constructing an imaging system that could capture four kinds of fluorescence images simultaneously at real-time. In the application of thrombin, [Ca2+]i transients were accompanied with preceding depolarization, while mechanical stress that were loaded on a single cell with a micropipette did not evoke dramatic changes of membrane potential. These results indicate that the signaling pathway initiated by mechanical stress could be independent of electrochemical activation, and different from that by biochemical stimulation in HUVEC.

  17. Comparative Evaluation of Tactile Sensation by Electrical and Mechanical Stimulation.

    PubMed

    Yem, Vibol; Kajimoto, Hiroyuki

    2017-01-01

    An electrotactile display is a tactile interface that provides tactile perception by passing electrical current through the surface of the skin. It is actively used instead of mechanical tactile displays for tactile feedback because of several advantages such as its small and thin size, light weight, and high responsiveness. However, the similarities and differences between these sensations is still not clear. This study directly compares the intensity sensation of electrotactile stimulation to that of mechanical stimulation, and investigates the characteristic sensation of anodic and cathodic stimulation. In the experiment, participants underwent a 30 pps electrotactile stimulus every one second to their middle finger, and were asked to match this intensity by adjusting the intensity of a mechanical tactile stimulus to an index finger. The results showed that anodic stimulation mainly produced vibration sensation, whereas cathodic sensation produced both vibration and pressure sensations. Relatively low pressure sensation was also observed for anodic stimulation but it remains low, regardless of the increasing of electrical intensity.

  18. USING COMPUTATIONAL PATIENTS TO EVALUATE ILLNESS MECHANISMS IN SCHIZOPHRENIA

    PubMed Central

    Hoffman, Ralph E.; Grasemann, Uli; Gueorguieva, Ralitza; Quinlan, Donald; Lane, Douglas; Miikkulainen, Risto

    2011-01-01

    Background Various malfunctions involving working memory, semantics, prediction error, and dopamine neuromodulation have been hypothesized to cause disorganized speech and delusions in schizophrenia. Computational models may provide insights into why some mechanisms are unlikely, suggest alternative mechanisms, and tie together explanations of seemingly disparate symptoms and experimental findings. Methods Eight corresponding illness mechanisms were simulated in DISCERN, an artificial neural network model of narrative understanding and recall. For this study, DISCERN learned sets of “autobiographical” and “impersonal” crime stories with associated emotion-coding. In addition, 20 healthy controls and 37 patients with schizophrenia or schizoaffective disorder matched for age, gender and parental education were studied using a delayed story-recall task. A goodness-of-fit analysis was performed to determine the mechanism best reproducing narrative breakdown profiles generated by healthy controls and patients with schizophrenia. Evidence of delusion-like narratives was sought in simulations best matching the narrative breakdown profile of patients. Results All mechanisms were equivalent in matching the narrative breakdown profile of healthy controls. However, exaggerated prediction-error signaling during consolidation of episodic memories, termed hyperlearning, was statistically superior to other mechanisms in matching the narrative breakdown profile of patients. These simulations also systematically confused “autobiographical” agents with “impersonal” crime story agents to model fixed, self-referential delusions. Conclusions Findings suggest that exaggerated prediction-error signaling in schizophrenia intermingles and corrupts narrative memories when incorporated into long-term storage, thereby disrupting narrative language and producing fixed delusional narratives. If further validated by clinical studies, these computational patients could provide a

  19. The effect of preparation under vacuum and microwave drying on the mechanical properties of porcelain ceramic foam via polymeric sponge method

    NASA Astrophysics Data System (ADS)

    Shahatha, S. H.; Mohammed, M. A.

    2016-04-01

    In this paper was demonstrated the effect of preparation condition under vacuum and microwave drying on the mechanical properties of porcelain ceramic foam. The study was based on five different polymeric foam templates with thickness ranging from 0.5 to 4 cm. The templates were impregnated in ceramic slurry with solid loading ranging from 35 to 55 wt. % under vacuum pressure 10-1 Torr and then sintered to 1250°C. Effects of polymeric foam template thickness and solid loading quantity were evaluated based on porosity, density and mechanical properties (compressive and flexural strengths) of the ceramic foam.

  20. Theoretical study of β-HMX decomposition mechanism of the solid phase under shock loadings

    NASA Astrophysics Data System (ADS)

    Ji, Guangfu; Ge, Nina; Chen, Xiangrong

    2015-06-01

    Study material properties under extreme conditions is a fundamental problem in the field of condensed matter physics. The decomposition mechanisms of energetic materials under the shock wave become a hot topic in recent years. In this paper, molecular dynamics simulations combined with multi-scale shock technology (MSST) are used to study the decomposition mechanism, shock sensitivity and electronic structure of β-HMX. First, the decomposition mechanism of β-HMX perfect crystal were studied at different shock speeds. We found that when the shock wave at a speed 8 km / s is loaded, the decomposition reaction start at N-NO2 bond breakage; when the shock wave at a speed of 10 km / s and 11 km / s is loaded, the the first decomposition reaction is CH bond breaking, and accompanied by the formation of five-membered ring and transfer of hydrogen ions. The simulation results also show that when the shock wave velocity is increased, the higher the pressure generated in the high-pressure N-NO2 bond cleavage was inhibited significantly. Secondly, the impact of its initial chemical reaction process along different crystal axis directions were studied, the results showed that along the a-axis and c-axis shock sensitivity is higher, and along the b-axis sensitivity is lower. We believe that the system of all sensitivity of direction is due to the rotation of the friction between the slip plane of crystals and molecules. Finally, we discussed the solid phase β-HMX electronic properties change under the shock wave loadings. We found that in the 11 km/s under the impact load, when the pressure reaches 130 GPa, zero bandgap is reached.

  1. Mechanisms of hydroxyl radical production from abiotic oxidation of pyrite under acidic conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Yuan, Songhu; Liao, Peng

    2016-01-01

    Hydroxyl radicals (radOH) produced from pyrite oxidation by O2 have been recognized, but mechanisms regarding the production under anoxic and oxic conditions are not well understood. In this study, the mechanisms of radOH production from pyrite oxidation under anoxic and oxic conditions were explored using benzoic acid (BA) as an radOH probe. Batch experiments were conducted at pH 2.6 to explore radOH production under anoxic and oxic conditions. The cumulative radOH concentrations produced under anoxic and oxic conditions increased linearly to 7.5 and 52.2 μM, respectively within 10 h at 10 g/L pyrite. Under anoxic conditions, radOH was produced from the oxidation of H2O on the sulfur-deficient sites on pyrite surface, showing an increased production with the increase of pyrite surface exposure due to oxidation. Under oxic conditions, the formation of radOH proceeds predominantly via the two-electron reduction of O2 on pyrite surface along with a minor contribution from the oxidation of H2O on surface sulfur-defects and the reactions of Fe2+/sulfur intermediates with O2. For both O2 reduction and H2O oxidation on the surface sulfur-defects, H2O2 was the predominant intermediate, which subsequently transformed to radOH through Fenton mechanism. The radOH produced had a significant impact on the transformation of contaminants in the environment. Anoxic pyrite suspensions oxidized 13.9% As(III) (C0 = 6.67 μM) and 17.6% sulfanilamide (C0 = 2.91 μM) within 10 h at pH 2.6 and 10 g/L pyrite, while oxic pyrite suspensions improved the oxidation perc