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Sample records for frequency-dependent stress fiber

  1. Frequency dependence of power and its implications for contractile function of muscle fibers from the digital flexors of horses

    PubMed Central

    Butcher, Michael T.; Bertram, John E.A.; Syme, Douglas A.; Hermanson, John W.; Chase, P. Bryant

    2014-01-01

    Abstract The digital flexors of horses must produce high force to support the body weight during running, and a need for these muscles to generate power is likely limited during locomotion over level ground. Measurements of power output from horse muscle fibers close to physiological temperatures, and when cyclic strain is imposed, will help to better understand the in vivo performance of the muscles as power absorbers and generators. Skinned fibers from the deep (DDF) and superficial (SDF) digital flexors, and the soleus (SOL) underwent sinusoidal oscillations in length over a range of frequencies (0.5–16 Hz) and strain amplitudes (0.01–0.06) under maximum activation (pCa 5) at 30°C. Results were analyzed using both workloop and Nyquist plot analyses to determine the ability of the fibers to absorb or generate power and the frequency dependence of those abilities. Power absorption was dominant at most cycling frequencies and strain amplitudes in fibers from all three muscles. However, small amounts of power were generated (0.002–0.05 Wkg−1) at 0.01 strain by all three muscles at relatively slow cycling frequencies: DDF (4–7 Hz), SDF (4–5 Hz) and SOL (0.5–1 Hz). Nyquist analysis, reflecting the influence of cross‐bridge kinetics on power generation, corroborated these results. The similar capacity for power generation by DDF and SDF versus lower for SOL, and the faster frequency at which this power was realized in DDF and SDF fibers, are largely explained by the fast myosin heavy chain isoform content in each muscle. Contractile function of DDF and SDF as power absorbers and generators, respectively, during locomotion may therefore be more dependent on their fiber architectural arrangement than on the physiological properties of their muscle fibers. PMID:25293602

  2. Fiber networks amplify active stress

    NASA Astrophysics Data System (ADS)

    Lenz, Martin; Ronceray, Pierre; Broedersz, Chase

    Large-scale force generation is essential for biological functions such as cell motility, embryonic development, and muscle contraction. In these processes, forces generated at the molecular level by motor proteins are transmitted by disordered fiber networks, resulting in large-scale active stresses. While fiber networks are well characterized macroscopically, this stress generation by microscopic active units is not well understood. I will present a comprehensive theoretical study of force transmission in these networks. I will show that the linear, small-force response of the networks is remarkably simple, as the macroscopic active stress depends only on the geometry of the force-exerting unit. In contrast, as non-linear buckling occurs around these units, local active forces are rectified towards isotropic contraction and strongly amplified. This stress amplification is reinforced by the networks' disordered nature, but saturates for high densities of active units. I will show that our predictions are quantitatively consistent with experiments on reconstituted tissues and actomyosin networks, and that they shed light on the role of the network microstructure in shaping active stresses in cells and tissue.

  3. Considerable different frequency dependence of dynamic tensile modulus between self-heating (Joule heat) and external heating for polymer--nickel-coated carbon fiber composites.

    PubMed

    Zhang, Rong; Bin, Yuezhen; Dong, Enyuan; Matsuo, Masaru

    2014-06-26

    Dynamic tensile moduli of polyethylene--nickel-coated carbon fiber (NiCF) composites with 10 and 4 vol % NiCF contents under electrical field were measured by a homemade instrument in the frequency range of 100--0.01 Hz. The drastic descent of the storage modulus of the composite with 10 vol % was verified in lower frequency range with elevating surface temperature (T(s)) by self-heating (Joule heat). The composite was cut when T(s) was beyond 108 °C. On the other hand, the measurement of the composite with 4 vol % beyond 88 °C was impossible, since T(s) did not elevate because of the disruption of current networks. Incidentally, the dynamic tensile moduli by external heating could be measured up to 130 and 115 °C for 10 and 4 vol %, respectively, but the two composites could be elongated beyond the above temperatures. Such different properties were analyzed in terms of crystal dispersions, electrical treeing, and thermal fluctuation-induced tunneling effect. PMID:24893179

  4. Considerable different frequency dependence of dynamic tensile modulus between self-heating (Joule heat) and external heating for polymer--nickel-coated carbon fiber composites.

    PubMed

    Zhang, Rong; Bin, Yuezhen; Dong, Enyuan; Matsuo, Masaru

    2014-06-26

    Dynamic tensile moduli of polyethylene--nickel-coated carbon fiber (NiCF) composites with 10 and 4 vol % NiCF contents under electrical field were measured by a homemade instrument in the frequency range of 100--0.01 Hz. The drastic descent of the storage modulus of the composite with 10 vol % was verified in lower frequency range with elevating surface temperature (T(s)) by self-heating (Joule heat). The composite was cut when T(s) was beyond 108 °C. On the other hand, the measurement of the composite with 4 vol % beyond 88 °C was impossible, since T(s) did not elevate because of the disruption of current networks. Incidentally, the dynamic tensile moduli by external heating could be measured up to 130 and 115 °C for 10 and 4 vol %, respectively, but the two composites could be elongated beyond the above temperatures. Such different properties were analyzed in terms of crystal dispersions, electrical treeing, and thermal fluctuation-induced tunneling effect.

  5. Axial residual stresses in boron fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1978-01-01

    The axial residual stress distribution as a function of radius was determined from the fiber surface to the core including the average residual stress in the core. Such measurements on boron on tungsten (B/W) fibers show that the residual stresses for 102, 142, 203, and 366 micron diameter fibers were similar, being compressive at the surface and changing monotonically to a region of tensile within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile stress of about 860 mn/sq.m and then decreases to a compressive stress near the tungsten boride core. Data were presented for 203 micron diameter B/W fibers that show annealing above 900 C reduces the residual stresses. A comparison between 102 micron diameter B/W and boron on carbon (b/C) shows that the residual stresses were similar in the outer regions of the fibers, but that large differences near and in the core were observed. The effects of these residual stresses on the fracture of boron fibers were discussed.

  6. Triboluminescent Fiber-Optic Sensors Measure Stresses

    NASA Technical Reports Server (NTRS)

    Rogowski, Robert S.

    1994-01-01

    Triboluminescence exploited in fiber-optic sensor system for measuring changes in pressures, strains, vibrations, and acoustic emissions, in structural members. Sensors embedded in members for in situ monitoring of condition of structure. System passive in sense no source of radiation required to interrogate optical fiber. Technique has potential for wide range of applications in which detection and measurement of structural stress required.

  7. Longitudinal residual stresses in boron fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1976-01-01

    A technique is proposed for measuring the longitudinal residual stress distribution in commercial CVD (Chemical Vapor Deposition) boron on tungsten fibers of 102, 142, and 203 microns in diameter. The experimental apparatus is so designed that continuous measurements are made of the length changes of a boron fiber specimen as the surface of the fiber is removed by electropolishing. The effects of surface removal on core residual stress and core-initiated fracture are discussed. The three sizes of boron fibers investigated show similar residual stress distributions, i.e., compressive at the surface, tensile near the core, and for the 102-micron fiber compressive again in the core. It is shown that an increase in UTS is due to the increase in the compressive stress at the core produced by fiber contraction during surface removal. An expression is derived for calculating the longitudinal residual stress at a given radius for an as-received fiber of a certain radius from measurements of the axial strain produced by removal of the surface by electropolishing.

  8. Longitudinal residual stresses in boron fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1976-01-01

    A method of measuring the longitudinal residual stress distribution in boron fibers is presented. The residual stresses in commercial CVD boron on tungsten fibers of 102, 142, and 203 microns (4, 5.6, and 8 mil) diameters were determined. Results for the three sizes show a compressive stress at the surface 800 to -1400 MN/sq m 120 to -200 ksi), changing monotonically to a region of tensile stress within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile 600 to 1000 MN/sq m(90 to 150 ksi) and then decreases to compressive near the tungsten boride core. The core itself is under a compressive stress of approximately -1300 MN/sq m (-190 ksi). The effects of surface removal on core residual stress and core-initiated fracture are discussed.

  9. Stress effects in twisted highly birefringent fibers

    NASA Astrophysics Data System (ADS)

    Wolinski, Tomasz R.

    1994-03-01

    Hydrostatic pressure and uniaxial longitudinal strain effects in twisted highly birefringent optical fibers have been investigated from the point of the Marcuse mode-coupling theory. The problem is analyzed in terms of local normal modes of the ideal fiber and in the limit of weak twist, where large linear birefringence dominates over twist effect, and therefore twist coupling between local modes is not effective. The authors present the results of birefringence measurements in highly birefringent bow-tie fibers influenced simultaneously by hydrostatic pressure up to 100 MPa and twisting the result for highly birefringent elliptical-core fibers influenced by uniaxial longitudinal strain up to 4000 (mu) (epsilon) and twisting effect. The birefringence measurement method is based on twist-induced effects and has been successfully applied in a stress environment. The experiment was conducted with a specially designed stress generating device that makes it possible to simultaneously generate various mechanical perturbations such as hydrostatic and radial pressure, axial strain and twist, allowing study of their influence on mode propagation in optical fibers. A comparison with theoretical results as well as with pervious experimental data on stress influence on the beat length parameter in highly birefringent fibers is also provided.

  10. Behaviour of a few mode fiber modal pattern under stress

    NASA Technical Reports Server (NTRS)

    Egalon, Claudio O.; Rogowski, Robert S.

    1991-01-01

    A numerical model was developed to calculate the interference pattern at the end of a multimode weakly guiding optical fiber under stress. Whenever an optical fiber is under stress, the modal phase in the interference term of the intensity formula changes. Plots of the simulated output of a stressed fiber are presented. For multimode fibers, very complicated patterns result. Under stress, lobes in the pattern are generated, displaced and power is exchanged among them.

  11. Intermittency and transient chaos from simple frequency-dependent selection.

    PubMed

    Gavrilets, S; Hastings, A

    1995-08-22

    Frequency-dependent selection is an important determinant of the evolution of gametophytic self-incompatibility systems in plants, aposematic (warning) and cryptic coloration, systems of mimicry, competitive interactions among members of a population, mating preferences, predator-prey and host-parasite interactions, aggression and other behavioural traits. Past theoretical studies of frequency-dependent selection have shown it to be a plausible mechanism for the maintenance of genetic variability in natural populations. Here, through an analysis of a simple deterministic model for frequency-dependent selection, we demonstrate that complex dynamic behaviour is possible under a broad range of parameter values. In particular we show that the model exhibits not only cycles and chaos but also, for a more restricted set of parameters, transient chaos and intermittency: alterations between an apparently deterministic behaviour and apparently chaotic fluctuations. This behaviour, which has not been stressed within the population genetics literature, provides an explanation for erratic dynamics of gene frequencies.

  12. Monitoring Fiber Stress During Curing of Single Fiber Glass- and Graphite-Epoxy Composites

    NASA Technical Reports Server (NTRS)

    Madhukar, Madhu S.; Kosuri, Ranga P.; Bowles, Kenneth J.

    1994-01-01

    The difference in thermal expansion characteristics of epoxy matrices and graphite fibers can produce significant residual stresses in the fibers during curing of composite materials. Tests on single fiber glass-epoxy and graphite-epoxy composite specimens were conducted in which the glass and graphite fibers were preloaded in tension, and the epoxy matrix was cast around the fibers. The fiber tension was monitored while the matrix was placed around the fiber and subjected to the temperature-time curing cycle. Two mechanisms responsible for producing stress in embedded fibers were identified as matrix thermal expansion and contraction and matrix cure shrinkage. A simple analysis based on the change in fiber tension during the curing cycle was conducted to estimate the produced stresses. Experimental results on single fiber glass- and graphite-epoxy composites show that the fiber was subjected to significant tensile stresses when the temperature was raised from the first to the second dwell period. When initial fiber pretension is about 60 percent of the fiber failure load, these curing-induced stresses can cause tensile fracture of the embedded fiber.

  13. An analysis of fiber-matrix interface failure stresses for a range of ply stress states

    NASA Technical Reports Server (NTRS)

    Crews, J. H.; Naik, R. A.; Lubowinski, S. J.

    1993-01-01

    A graphite/bismaleimide laminate was prepared without the usual fiber treatment and was tested over a wide range of stress states to measure its ply cracking strength. These tests were conducted using off-axis flexure specimens and produced fiber-matrix interface failure data over a correspondingly wide range of interface stress states. The absence of fiber treatment, weakened the fiber-matrix interfaces and allowed these tests to be conducted at load levels that did not yield the matrix. An elastic micromechanics computer code was used to calculate the fiber-matrix interface stresses at failure. Two different fiber-array models (square and diamond) were used in these calculations to analyze the effects of fiber arrangement as well as stress state on the critical interface stresses at failure. This study showed that both fiber-array models were needed to analyze interface stresses over the range of stress states. A linear equation provided a close fit to these critical stress combinations and, thereby, provided a fiber-matrix interface failure criterion. These results suggest that prediction procedures for laminate ply cracking can be based on micromechanics stress analyses and appropriate fiber-matrix interface failure criteria. However, typical structural laminates may require elastoplastic stress analysis procedures that account for matrix yielding, especially for shear-dominated ply stress states.

  14. A Multimodular Tensegrity Model of an Actin Stress Fiber

    PubMed Central

    Luo, Yaozhi; Xu, Xian; Lele, Tanmay; Kumar, Sanjay; Ingber, Donald E.

    2008-01-01

    Stress fibers are contractile bundles in the cytoskeleton that stabilize cell structure by exerting traction forces on extracellular matrix. Individual stress fibers are molecular bundles composed of parallel actin and myosin filaments linked by various actin-binding proteins, which are organized end-on-end in a sarcomere-like pattern within an elongated three-dimensional network. While measurements of single stress fibers in living cells show that they behave like tensed viscoelastic fibers, precisely how this mechanical behavior arises from this complex supramolecular arrangement of protein components remains unclear. Here we show that computationally modeling a stress fiber as a multi-modular tensegrity network can predict several key behaviors of stress fibers measured in living cells, including viscoelastic retraction, fiber splaying after severing, non-uniform contraction, and elliptical strain of a puncture wound within the fiber. The tensegrity model also can explain how they simultaneously experience passive tension and generate active contraction forces; in contrast, a tensed cable net model predicts some, but not all, of these properties. Thus, tensegrity models may provide a useful link between molecular and cellular scale mechanical behaviors, and represent a new handle on multi-scale modeling of living materials. PMID:18632107

  15. Dynamics of Mechanical Signal Transmission through Prestressed Stress Fibers

    PubMed Central

    Hwang, Yongyun; Barakat, Abdul I.

    2012-01-01

    Transmission of mechanical stimuli through the actin cytoskeleton has been proposed as a mechanism for rapid long-distance mechanotransduction in cells; however, a quantitative understanding of the dynamics of this transmission and the physical factors governing it remains lacking. Two key features of the actin cytoskeleton are its viscoelastic nature and the presence of prestress due to actomyosin motor activity. We develop a model of mechanical signal transmission through prestressed viscoelastic actin stress fibers that directly connect the cell surface to the nucleus. The analysis considers both temporally stationary and oscillatory mechanical signals and accounts for cytosolic drag on the stress fibers. To elucidate the physical parameters that govern mechanical signal transmission, we initially focus on the highly simplified case of a single stress fiber. The results demonstrate that the dynamics of mechanical signal transmission depend on whether the applied force leads to transverse or axial motion of the stress fiber. For transverse motion, mechanical signal transmission is dominated by prestress while fiber elasticity has a negligible effect. Conversely, signal transmission for axial motion is mediated uniquely by elasticity due to the absence of a prestress restoring force. Mechanical signal transmission is significantly delayed by stress fiber material viscosity, while cytosolic damping becomes important only for longer stress fibers. Only transverse motion yields the rapid and long-distance mechanical signal transmission dynamics observed experimentally. For simple networks of stress fibers, mechanical signals are transmitted rapidly to the nucleus when the fibers are oriented largely orthogonal to the applied force, whereas the presence of fibers parallel to the applied force slows down mechanical signal transmission significantly. The present results suggest that cytoskeletal prestress mediates rapid mechanical signal transmission and allows

  16. Frequency-dependent viscoelasticity measurement by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Yang, Nan; Wong, Kenneth Kar Ho; de Bruyn, John R.; Hutter, Jeffrey L.

    2009-02-01

    We demonstrate a new technique for investigating viscoelastic properties of soft materials using the atomic force microscope. A small oscillatory voltage is added to the deflection signal of the atomic force microscope causing a vertical oscillatory sample motion. Monitoring the amplitude and phase of this motion allows determination of the viscous and elastic moduli of the sample as a function of frequency during contact imaging. This technique is applied to suspended poly(vinyl alcohol) nanofibers and poly(vinyl alcohol) hydrogels, giving results similar to those measured using traditional static methods. However, the moduli of both the fibers and the hydrogels show a significant frequency dependence. The Young's modulus of the fibers increases with frequency, while for the viscoelastic hydrogels, the storage modulus dominates the mechanical response at low frequency whereas the loss modulus dominates at high frequency.

  17. Kinship as a frequency dependent strategy

    PubMed Central

    Ji, Ting; Zheng, Xiu-Deng; He, Qiao-Qiao; Wu, Jia-Jia; Tao, Yi

    2016-01-01

    Humans divide themselves up into separate cultures, which is a unique and ubiquitous characteristic of our species. Kinship norms are one of the defining features of such societies. Here we show how norms of marital residence can evolve as a frequency-dependent strategy, using real-world cases from southwestern China and an evolutionary game model. The process of kinship change has occurred in the past and is also occurring now in southwestern China. Our data and models show how transitions between residence types can occur both as response to changing costs and benefits of co-residence with kin, and also due to the initial frequency of the strategies adopted by others in the population: patrilocal societies can become matrilocal, and neolocal societies can become duolocal. This illustrates how frequency-dependent selection plays a role both in the maintenance of group-level cultural diversity and in cultural extinction. PMID:26998333

  18. Frequency-dependent selection by predators.

    PubMed

    Allen, J A

    1988-07-01

    Sometimes predators tend to concentrate on common varieties of prey and overlook rare ones. Within prey species, this could result in the fitness of each variety being inversely related to its frequency in the population. Such frequency-dependent or 'apostatic' selection by predators hunting by sight could maintain polymorphism for colour pattern, and much of the supporting evidence for this idea has come from work on birds and artificial prey. These and other studies have shown that the strength of the observed selection is affected by prey density, palatability, coloration and conspicuousness. When the prey density is very high, selection becomes 'anti-apostatic': predators preferentially remove rare prey. There is still much to be learned about frequency-dependent selection by predators on artificial prey: work on natural polymorphic prey has hardly begun. PMID:2905488

  19. Kinship as a frequency dependent strategy.

    PubMed

    Ji, Ting; Zheng, Xiu-Deng; He, Qiao-Qiao; Wu, Jia-Jia; Mace, Ruth; Tao, Yi

    2016-02-01

    Humans divide themselves up into separate cultures, which is a unique and ubiquitous characteristic of our species. Kinship norms are one of the defining features of such societies. Here we show how norms of marital residence can evolve as a frequency-dependent strategy, using real-world cases from southwestern China and an evolutionary game model. The process of kinship change has occurred in the past and is also occurring now in southwestern China. Our data and models show how transitions between residence types can occur both as response to changing costs and benefits of co-residence with kin, and also due to the initial frequency of the strategies adopted by others in the population: patrilocal societies can become matrilocal, and neolocal societies can become duolocal. This illustrates how frequency-dependent selection plays a role both in the maintenance of group-level cultural diversity and in cultural extinction. PMID:26998333

  20. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1994-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading about 800 C, these fibers display creep related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of a mechanism-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the Bend Stress Relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model, but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model tensile creep predictions based on the BSR test results with the literature data show good agreement, supporting both the predictive capability of the model and the use of the BSR text as a simple method for parameter determination for other fibers.

  1. Time temperature-stress dependence of boron fiber deformation

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1976-01-01

    Flexural stress relaxation (FSR) and flexural internal friction (FIF) techniques were employed to measure the time-dependent deformation of boron fibers from -190 to 800 C. The principal specimens were 203 micrometers diameter fibers commercially produced by chemical vapor deposition (CVD) on a 13 micrometer tungsten substrate. The observation of complete creep strain recovery with time and temperature indicated that CVD boron fibers deform flexurally as anelastic solids with no plastic component.

  2. Stress concentration in notched anisotropically fiber-reinforced plates

    NASA Astrophysics Data System (ADS)

    Hufenbach, W.; Kroll, L.

    1992-06-01

    As notches represent the most relevant sites of failure in a construction, a calculation of the stress distribution around holes is essential for the design of fiber-reinforced materials. Especially in the case of anisotropic materials the maximal stress concentration factor on the cutout is considerably higher than in conventional isotropic materials. In fiber-reinforced materials the stress distribution around holes is strongly dependent on the degree of anisotropy as well as on the notch geometry and load parameters. The plain stress field around a notch of known geometry will be calculated by means of the method of conformal mapping and complex stress functions, based on the mathematical model of an infinite anisotropic plate with various shapes of the aperture. For some standard types of notches and load cases, the stress concentration factor as a function of various construction parameters will be studied for fiber-reinforced materials used in lightweight construction.

  3. Factors Controlling Stress Rupture of Fiber-Reinforced Ceramic Composites

    NASA Technical Reports Server (NTRS)

    DiCarlo, J. A.; Yun, H. M.

    1999-01-01

    The successful application of fiber-reinforced ceramic matrix composites (CMC) depends strongly on maximizing material rupture life over a wide range of temperatures and applied stresses. The objective of this paper is to examine the various intrinsic and extrinsic factors that control the high-temperature stress rupture of CMC for stresses below and above those required for cracking of the 0 C plies (Regions I and II, respectively). Using creep-rupture results for a variety of ceramic fibers and rupture data for CMC reinforced by these fibers, it is shown that in those cases where the matrix carries little structural load, CMC rupture conditions can be predicted very well from the fiber behavior measured under the appropriate test environment. As such, one can then examine the intrinsic characteristics of the fibers in order to develop design guidelines for selecting fibers and fiber microstructures in order to maximize CMC rupture life. For those cases where the fiber interfacial coatings are unstable in the test environment, CMC lives are generally worse than those predicted by fiber behavior alone. For those cases where the matrix can support structural load, CMC life can even be greater provided matrix creep behavior is properly controlled. Thus the achievement of long CMC rupture life requires understanding and optimizing the behavior of all constituents in the proper manner.

  4. Efficient computational simulation of actin stress fiber remodeling.

    PubMed

    Ristori, T; Obbink-Huizer, C; Oomens, C W J; Baaijens, F P T; Loerakker, S

    2016-09-01

    Understanding collagen and stress fiber remodeling is essential for the development of engineered tissues with good functionality. These processes are complex, highly interrelated, and occur over different time scales. As a result, excessive computational costs are required to computationally predict the final organization of these fibers in response to dynamic mechanical conditions. In this study, an analytical approximation of a stress fiber remodeling evolution law was derived. A comparison of the developed technique with the direct numerical integration of the evolution law showed relatively small differences in results, and the proposed method is one to two orders of magnitude faster.

  5. Efficient computational simulation of actin stress fiber remodeling.

    PubMed

    Ristori, T; Obbink-Huizer, C; Oomens, C W J; Baaijens, F P T; Loerakker, S

    2016-09-01

    Understanding collagen and stress fiber remodeling is essential for the development of engineered tissues with good functionality. These processes are complex, highly interrelated, and occur over different time scales. As a result, excessive computational costs are required to computationally predict the final organization of these fibers in response to dynamic mechanical conditions. In this study, an analytical approximation of a stress fiber remodeling evolution law was derived. A comparison of the developed technique with the direct numerical integration of the evolution law showed relatively small differences in results, and the proposed method is one to two orders of magnitude faster. PMID:26823159

  6. Core stress distribution of phase shifting multimode polymer optical fiber

    SciTech Connect

    Furukawa, Rei Matsuura, Motoharu; Nagata, Morio; Mishima, Kenji; Inoue, Azusa; Tagaya, Akihiro; Koike, Yasuhiro

    2013-11-18

    Poly-(methyl methacrylate-co-benzyl methacrylate) polarization-maintaining optical fibers are known for their high response to normal stress. In this report, responses to higher stress levels up to 0.45 MPa were investigated. The stress amplitude and direction in the fiber cross section were calculated and analyzed with a coincident mode-field obtained from the near-field pattern. The stress amplitude varies significantly in the horizontal direction and is considered to create multiple phases, explaining the measurement results. To investigate possible permanent deformation, the core yield point profile was analyzed. Although it largely exceeds the average applied stress, the calculated stress distribution indicates that the core could partially experience stress that exceeds the yield point.

  7. Time-temperature-stress dependence of boron fiber deformation

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1976-01-01

    The time-dependent deformation of boron fibers over the temperature range from -190 to 800 C is studied by flexural stress relaxation and flexural internal friction techniques on 203-micron diam specimen fibers commercially produced by chemical vapor deposition (CVD) on a 13-micron tungsten substrate. It is shown that up to at least 800 C all nonelastic behavior observed during axial deformation of CVD boron fibers can be explained solely by anelastic mechanisms and that although creep strains are small, boron fiber anelasticity can produce significant mechanical effects which would otherwise be neglected under the elastic approximation. Relations are obtained to demonstrate the considerable effects of anelasticity on such fiber/composite properties as modulus, creep, creep recovery, stress relaxation, and damping capacity. For an elastic-core/anelastic-sheath model, boron fibers on tungsten substrates are shown to have predictable fracture stresses for time-temperature conditions ranging from impact to long-time stress rupture. Possible techniques for altering these stresses are discussed.

  8. Anomalous frequency dependent diamagnetism in metal silicide

    NASA Astrophysics Data System (ADS)

    Dahal, Ashutosh; Gunasekera, Jagat; Harriger, Leland; Singh, David J.; Singh, Deepak K.; Leland Harriger Collaboration

    Discovery of superconductivity in PbO-type FeSe has generated a lot of interest. Among the samples we synthesize with similar structure, NiSi has showed anomalous but very interesting results. Nickel silicides are important electronic materials that have been used as contacts for field effect transistors, as interconnects and in nanoelectronic devices. The magnetic properties of NiSi are not well known, however. In this presentation, we report a highly unusual magnetic phenomenon in NiSi. The ac susceptibility measurements on NiSi reveal strong frequency dependence of static and dynamic susceptibilities that are primarily diamagnetic at room temperature. The static susceptibility is found to exhibit a strong frequency dependence of the diamagnetic response below 100K, while dynamic susceptibility showed peak type feature at 10KHz frequency around 50K. Detailed neutron scattering measurements on high quality powder sample of NiSi on SPINS cold spectrometer further revealed an inelastic peak around 1.5meV, even though no magnetic order is detected. The inelastic peak dissipates above 100K, which is where the static susceptibility starts to diverge with frequency. Research is supported by U.S. Department of Energy, Office of Basic Energy Sciences under Grant No. DE-SC0014461.

  9. Frequency dependent thermal expansion in binary viscoelasticcomposites

    SciTech Connect

    Berryman, James G.

    2007-12-01

    The effective thermal expansion coefficient beta* of abinary viscoelastic composite is shown to be frequency dependent even ifthe thermal expansion coefficients beta A and beta B of both constituentsare themselves frequency independent. Exact calculations for binaryviscoelastic systems show that beta* is related to constituent valuesbeta A, beta B, volume fractions, and bulk moduli KA, KB, as well as tothe overall bulk modulus K* of the composite system. Then, beta* isdetermined for isotropic systems by first bounding (or measuring) K* andtherefore beta*. For anisotropic systems with hexagonal symmetry, theprincipal values of the thermal expansion beta*perp and beta*para can bedetermined exactly when the constituents form a layered system. In allthe examples studied, it is shown explicitly that the eigenvectors of thethermoviscoelastic system possess non-negative dissipation -- despite thecomplicated analytical behavior of the frequency dependent thermalexpansivities themselves. Methods presented have a variety ofapplications from fluid-fluid mixtures to fluid-solid suspensions, andfrom fluid-saturated porous media to viscoelastic solid-solidcomposites.

  10. Determining the frequency dependence of elastic properties of fractured rocks

    NASA Astrophysics Data System (ADS)

    Ahrens, Benedikt; Renner, Jörg

    2016-04-01

    In the brittle crust, rocks often contain joints or faults on various length scales that have a profound effect on fluid flow and heat transport, as well as on the elastic properties of rocks. Improving the understanding of the effect of fractures and the role of stress state and heterogeneity along the fractures on elastic properties of rocks is potentially important for the characterization of deep geothermal reservoirs. Seismic surveys, typically covering a frequency range of about 1 to 1000 Hz, are a valuable tool to investigate fractured rocks but the extraction of fracture properties remains difficult. The elementary frequency-dependent interaction between fractured rock matrix and viscous pore fluids and the resulting effects on wave propagation require well-founded dispersion analyses of heterogeneous rocks. In this laboratory study, we investigate the stress dependence of the effective elastic properties of fractured reservoir rocks over a broad frequency range. To assess the effect of faults on the effective elastic properties, we performed cyclic axial loading tests on intact and fractured samples of Solnhofen limestone and Padang granodiorite. The samples contained an idealized fault, which was created by stacking two sample discs on top of each other that experienced various surface treatments to vary their roughness. The dynamic loading tests were conducted with frequencies up to 10 Hz and amplitudes reaching 10% of the statically applied stress. Simultaneously, P- and S-wave measurements were performed in the ultrasonic frequency range (above 100 kHz) with a total of 16 sensors, whose positioning above and below the samples guarantees a wide range of transmission and reflection angles. Preliminary results of static and dynamic elastic properties of intact Padang granodiorite show a pronounced increase in Young's moduli and Poisson's ratio with increasing axial stress. Stress relaxation is accompanied by a decrease of the modulus and the Poisson

  11. Optimal matrix rigidity for stress fiber polarization in stem cells

    PubMed Central

    Rehfeldt, F.; Brown, A. E. X.; Discher, D. E.; Safran, S. A.

    2010-01-01

    The shape and differentiation of human mesenchymal stem cells is especially sensitive to the rigidity of their environment; the physical mechanisms involved are unknown. A theoretical model and experiments demonstrate here that the polarization/alignment of stress-fibers within stem cells is a non-monotonic function of matrix rigidity. We treat the cell as an active elastic inclusion in a surrounding matrix whose polarizability, unlike dead matter, depends on the feedback of cellular forces that develop in response to matrix stresses. The theory correctly predicts the monotonic increase of the cellular forces with the matrix rigidity and the alignment of stress-fibers parallel to the long axis of cells. We show that the anisotropy of this alignment depends non-monotonically on matrix rigidity and demonstrate it experimentally by quantifying the orientational distribution of stress-fibers in stem cells. These findings offer a first physical insight for the dependence of stem cell differentiation on tissue elasticity. PMID:20563235

  12. Frequency-dependent numerical dynamics in mosquitofish.

    PubMed Central

    Horth, Lisa; Travis, Joseph

    2002-01-01

    Altering the genetic composition of a population can alter several aspects of its numerical dynamics. Whether natural populations routinely contain the genetic variation capable of affecting the stability of those dynamics is less clear. Here we report a study of experimental populations of mosquitofish (Gambusia holbrooki), designed to examine this issue. The experiment examined the numerical effects of varying the initial relative frequency of a rare male genotype. A higher relative frequency of the rare, melanic genotype produced higher mortality rates in melanic males, higher mortality rates in females, higher juvenile abundance, and fewer fluctuations in the numbers of females across time. This work demonstrates that a natural population can harbour genetic variants in a single gender that are capable of inducing qualitative differences in the numerical dynamics of the opposite gender, through the effects of negative frequency-dependent selection. PMID:12427317

  13. Frequency dependent squeezed light at audio frequencies

    NASA Astrophysics Data System (ADS)

    Miller, John

    2015-04-01

    Following successful implementation in the previous generation of instruments, squeezed states of light represent a proven technology for the reduction of quantum noise in ground-based interferometric gravitational-wave detectors. As a result of lower noise and increased circulating power, the current generation of detectors places one further demand on this technique - that the orientation of the squeezed ellipse be rotated as function of frequency. This extension allows previously negligible quantum radiation pressure noise to be mitigated in addition to quantum shot noise. I will present the results of an experiment which performs the appropriate rotation by reflecting the squeezed state from a detuned high-finesse optical cavity, demonstrating frequency dependent squeezing at audio frequencies for the first time and paving the way for broadband quantum noise reduction in Advanced LIGO. Further, I will indicate how a realistic implementation of this approach will impact Advanced LIGO both alone and in combination with other potential upgrades.

  14. Effects of Frequency-Dependent Membrane Capacitance on Neural Excitability

    PubMed Central

    Grill, Warren M.

    2015-01-01

    Objective Models of excitable cells consider the membrane specific capacitance as a ubiquitous and constant parameter. However, experimental measurements show that the membrane capacitance declines with increasing frequency, i.e., exhibits dispersion. We quantified the effects of frequency-dependent membrane capacitance, c(f), on the excitability of cells and nerve fibers across the frequency range from dc to hundreds of kilohertz. Approach We implemented a model of c(f) using linear circuit elements, and incorporated it into several models of neurons with different channel kinetics: the Hodgkin-Huxley (HH) model of an unmyelinated axon, the McIntyre-Richardson-Grill (MRG) of a mammalian myelinated axon, and a model of a cortical neuron from prefrontal cortex. We calculated thresholds for excitation and kHz frequency conduction block, the conduction velocity, recovery cycle, strength-distance relationship and firing rate. Main results The impact of c(f) on activation thresholds depended on the stimulation waveform and channel kinetics. We observed no effect using rectangular pulse stimulation, and a reduction for frequencies of 10 kHz and above using sinusoidal signals only for the MRG model. c(f) had minimal impact on the recovery cycle and the strength-distance relationship, whereas the conduction velocity increased by up to 7.9% and 1.7% for myelinated and unmyelinated fibers, respectively. Block thresholds declined moderately when incorporating c(f), the effect was greater at higher frequencies, and the maximum reduction was 11.5%. Finally, c(f) marginally altered the firing pattern of a model of a prefrontal cortex cell, reducing the median interspike interval by less than 2%. Significance This is the first comprehensive analysis of the effects of dispersive capacitance on neural excitability, and as the interest on stimulation with kHz signals gains more attention, it defines the regions over which frequency-dependent membrane capacitance, c(f), should be

  15. Actomyosin stress fiber mechanosensing in 2D and 3D

    PubMed Central

    Lee, Stacey; Kumar, Sanjay

    2016-01-01

    Mechanotransduction is the process through which cells survey the mechanical properties of their environment, convert these mechanical inputs into biochemical signals, and modulate their phenotype in response. These mechanical inputs, which may be encoded in the form of extracellular matrix stiffness, dimensionality, and adhesion, all strongly influence cell morphology, migration, and fate decisions. One mechanism through which cells on planar or pseudo-planar matrices exert tensile forces and interrogate microenvironmental mechanics is through stress fibers, which are bundles composed of actin filaments and, in most cases, non-muscle myosin II filaments. Stress fibers form a continuous structural network that is mechanically coupled to the extracellular matrix through focal adhesions. Furthermore, myosin-driven contractility plays a central role in the ability of stress fibers to sense matrix mechanics and generate tension. Here, we review the distinct roles that non-muscle myosin II plays in driving mechanosensing and focus specifically on motility. In a closely related discussion, we also describe stress fiber classification schemes and the differing roles of various myosin isoforms in each category. Finally, we briefly highlight recent studies exploring mechanosensing in three-dimensional environments, in which matrix content, structure, and mechanics are often tightly interrelated. Stress fibers and the myosin motors therein represent an intriguing and functionally important biological system in which mechanics, biochemistry, and architecture all converge. PMID:27635242

  16. Actomyosin stress fiber mechanosensing in 2D and 3D.

    PubMed

    Lee, Stacey; Kumar, Sanjay

    2016-01-01

    Mechanotransduction is the process through which cells survey the mechanical properties of their environment, convert these mechanical inputs into biochemical signals, and modulate their phenotype in response. These mechanical inputs, which may be encoded in the form of extracellular matrix stiffness, dimensionality, and adhesion, all strongly influence cell morphology, migration, and fate decisions. One mechanism through which cells on planar or pseudo-planar matrices exert tensile forces and interrogate microenvironmental mechanics is through stress fibers, which are bundles composed of actin filaments and, in most cases, non-muscle myosin II filaments. Stress fibers form a continuous structural network that is mechanically coupled to the extracellular matrix through focal adhesions. Furthermore, myosin-driven contractility plays a central role in the ability of stress fibers to sense matrix mechanics and generate tension. Here, we review the distinct roles that non-muscle myosin II plays in driving mechanosensing and focus specifically on motility. In a closely related discussion, we also describe stress fiber classification schemes and the differing roles of various myosin isoforms in each category. Finally, we briefly highlight recent studies exploring mechanosensing in three-dimensional environments, in which matrix content, structure, and mechanics are often tightly interrelated. Stress fibers and the myosin motors therein represent an intriguing and functionally important biological system in which mechanics, biochemistry, and architecture all converge. PMID:27635242

  17. Actomyosin stress fiber mechanosensing in 2D and 3D

    PubMed Central

    Lee, Stacey; Kumar, Sanjay

    2016-01-01

    Mechanotransduction is the process through which cells survey the mechanical properties of their environment, convert these mechanical inputs into biochemical signals, and modulate their phenotype in response. These mechanical inputs, which may be encoded in the form of extracellular matrix stiffness, dimensionality, and adhesion, all strongly influence cell morphology, migration, and fate decisions. One mechanism through which cells on planar or pseudo-planar matrices exert tensile forces and interrogate microenvironmental mechanics is through stress fibers, which are bundles composed of actin filaments and, in most cases, non-muscle myosin II filaments. Stress fibers form a continuous structural network that is mechanically coupled to the extracellular matrix through focal adhesions. Furthermore, myosin-driven contractility plays a central role in the ability of stress fibers to sense matrix mechanics and generate tension. Here, we review the distinct roles that non-muscle myosin II plays in driving mechanosensing and focus specifically on motility. In a closely related discussion, we also describe stress fiber classification schemes and the differing roles of various myosin isoforms in each category. Finally, we briefly highlight recent studies exploring mechanosensing in three-dimensional environments, in which matrix content, structure, and mechanics are often tightly interrelated. Stress fibers and the myosin motors therein represent an intriguing and functionally important biological system in which mechanics, biochemistry, and architecture all converge.

  18. High temperature battery cell comprising stress free hollow fiber bundle

    SciTech Connect

    Anand, J. N.; Revak, T. T.; Rossini, F. J.

    1985-04-16

    Thermal stressing of hollow fibers constituting the electrolyte-separator in a high temperature battery cell, and of certain other elements thereof, is avoided by suspending the assembly comprising the anolyte tank, the tube-sheet, the hollow fibers and a cathodic current collector-distributor within the casing and employing a limp connection between the collector-distributor and the cathode terminal of the cell.

  19. The influence of motion and stress on optical fibers

    NASA Astrophysics Data System (ADS)

    Murphy, Jeremy D.; Hill, Gary J.; MacQueen, Phillip J.; Taylor, Trey; Soukup, Ian; Moreira, Walter; Cornell, Mark E.; Good, John; Anderson, Seth; Fuller, Lindsay; Lee, Hanshin; Kelz, Andreas; Rafal, Marc; Rafferty, Tom; Tuttle, Sarah; Vattiat, Brian

    2012-09-01

    We report on extensive testing carried out on the optical fibers for the VIRUS instrument. The primary result of this work explores how 10+ years of simulated wear on a VIRUS fiber bundle affects both transmission and focal ratio degradation (FRD) of the optical fibers. During the accelerated lifetime tests we continuously monitored the fibers for signs of FRD. We find that transient FRD events were common during the portions of the tests when motion was at telescope slew rates, but dropped to negligible levels during rates of motion typical for science observation. Tests of fiber transmission and FRD conducted both before and after the lifetime tests reveal that while transmission values do not change over the 10+ years of simulated wear, a clear increase in FRD is seen in all 18 fibers tested. This increase in FRD is likely due to microfractures that develop over time from repeated flexure of the fiber bundle, and stands in contrast to the transient FRD events that stem from localized stress and subsequent modal diffusion of light within the fibers. There was no measurable wavelength dependence on the increase in FRD over 350 nm to 600 nm. We also report on bend radius tests conducted on individual fibers and find the 266 μm VIRUS fibers to be immune to bending-induced FRD at bend radii of R 10 cm. Below this bend radius FRD increases slightly with decreasing radius. Lastly, we give details of a degradation seen in the fiber bundle currently deployed on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory. The degradation is shown to be caused by a localized shear in a select number of optical fibers that leads to an explosive form of FRD. In a few fibers, the overall transmission loss through the instrument can exceed 80%. These results are important for the VIRUS instrument, and for both current and proposed instruments that make use of optical fibers, particularly when the fibers are in continual motion during an observation, or experience

  20. Failure mechanics of fiber composite notched charpy specimens. [stress analysis

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.

    1976-01-01

    A finite element stress analysis was performed to determine the stress variation in the vicinity of the notch and far field of fiber composites Charpy specimens (ASTM Standard). NASTRAN was used for the finite element analysis assuming linear behavior and equivalent static load. The unidirectional composites investigated ranged from Thornel 75 Epoxy to S-Glass/Epoxy with the fiber direction parallel to the long dimension of the specimen. The results indicate a biaxial stress state exists in (1) the notch vicinity which is dominated by transverse tensile and interlaminar shear and (2) near the load application point which is dominated by transverse compression and interlaminar shear. The results also lead to the postulation of hypotheses for the predominant failure modes, the fracture initiation, and the fracture process. Finally, the results indicate that the notched Charpy test specimen is not suitable for assessing the impact resistance of nonmetallic fiber composites directly.

  1. Stress-rupture behavior of small diameter polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; Goldsby, Jon C.; Dicarlo, James A.

    1993-01-01

    Continuous length polycrystalline alumina fibers are candidates as reinforcement in high temperature composite materials. Interest therefore exists in characterizing the thermomechanical behavior of these materials, obtaining possible insights into underlying mechanisms, and understanding fiber performance under long term use. Results are reported on the time-temperature dependent strength behavior of Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Below 1000 C and 100 hours, Nextel 610 with the smaller grain size had a greater fast fracture and rupture strength than Fiber FP. The time exponents for stress-rupture of these fibers were found to decrease from approximately 13 at 900 C to below 3 near 1050 C, suggesting a transition from slow crack growth to creep rupture as the controlling fracture mechanism. For both fiber types, an effective activation energy of 690 kJ/mol was measured for rupture. This allowed stress-rupture predictions to be made for extended times at use temperatures below 1000 C.

  2. Characterization of Optical Fiber Strength Under Applied Tensile Stress and Bending Stress

    SciTech Connect

    P.E. Klingsporn

    2011-08-01

    Various types of tensile testing and bend radius tests were conducted on silica core/silica cladding optical fiber of different diameters with different protective buffer coatings, fabricated by different fiber manufacturers. The tensile tests were conducted to determine not only the average fiber strengths at failure, but also the distribution in fracture strengths, as well as the influence of buffer coating on fracture strength. The times-to-failure of fiber subjected to constant applied bending stresses of various magnitudes were measured to provide a database from which failure times of 20 years or more, and the corresponding minimum bend radius, could be extrapolated in a statistically meaningful way. The overall study was done to provide an understanding of optical fiber strength in tensile loading and in applied bending stress as related to applications of optical fiber in various potential coizfgurations for weapons and enhanced surveillance campaigns.

  3. Mechanotransduction of Ultrasound is Frequency Dependent Below the Cavitation Threshold

    PubMed Central

    Louw, Tobias M.; Budhiraja, Gaurav; Viljoen, Hendrik J.; Subramanian, Anuradha

    2013-01-01

    This study provides evidence that low-intensity ultrasound directly affects nuclear processes, and the magnitude of the effect varies with frequency. In particular, we show that the transcriptional induction of first load-inducible genes, which is independent of new protein synthesis, is frequency dependent. Bovine chondrocytes were exposed to low-intensity below the cavitational threshold) ultrasound at 2,5 and 8 MHz. Ultrasound elevated the expression of early response genes c-Fos, c-Jun and c-Myc, maximized at 5 MHz. The phosphorylated ERK inhibitor PD98059 abrogated any increase in c-series gene expression, suggesting that signaling occurs via the MAPPK/ERK pathway. However, phosphorylated ERK levels did not change with ultrasound frequency, indicating that processes downstream of ERK phosphorylation (such as nuclear transport and chromatin reorganization) respond to ultrasound with frequency dependence. A quantitative, biphasic mathematical model based on Biot theory predicted that cytoplasmic and nuclear stress is maximized at 5.2 ± 0.8 MHz for a chondrocyte, confirming experimental measurements. PMID:23562015

  4. AC Magnetic Field Frequency Dependence of Magnetoacoustic Emission

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Wincheski, B.; Fulton, J. P.; DeNale, R.

    1992-01-01

    Our recent study has proved a strong correlation between the low-frequency AC applied magnetic field amplitude dependence of the asymmetry of the magnetoacoustic emission (MAE) burst and the strength of the domain wall-defect interaction in iron-base ferromagnets. For the present study the AC magnetic field frequency dependence of the asymmetry has been investigated in the range of 1 to 200 Hz. When represented by the third moment of the rectified acoustic emission pulses, the asymmetry becomes a bell-shaped function of frequency with its center located around 25 Hz. This experiment has been performed with low carbon, high yield stress steel specimens of three different levels of domain wall-defect interaction strength. The results show that the increase in the interaction strength causes a vertical down shift of the asymmetry in the entire frequency range investigated.

  5. The influence of the fiber drawing process on intrinsic stress and the resulting birefringence optimization of PM fibers

    NASA Astrophysics Data System (ADS)

    Just, Florian; Spittel, Ron; Bierlich, Jörg; Grimm, Stephan; Jäger, Matthias; Bartelt, Hartmut

    2015-04-01

    The propagation properties of optical fibers can be significantly influenced by intrinsic stress. These effects are often undesired but in some cases essential for certain applications, e.g. in polarization maintaining (PM) fibers. In this paper, we present systematic studies on the influence of the fiber drawing process on the generated stress and demonstrate an approach to significantly increase the stress induced birefringence of PM-fibers. It is shown that the thermal stress caused by the material composition is superimposed with the mechanical stress caused by the fiber fabrication process. This intrinsic stress has a strong effect on the optical and mechanical properties of the glass and thus influences the fiber stability and modal behavior. By applying a thermal annealing step, the mechanical stress due to the fiber drawing process can be canceled. It is shown that this annealing step compensates the stress reducing influence of the drawing process on the birefringence of PM-fibers with panda structure. The comparison of the intrinsic stress states after fabrication with the state after the additional high temperature annealing step clearly shows that it is possible to improve the overall birefringence of panda fibers using appropriate preparation steps.

  6. Stress transfer of a Kevlar 49 fiber pullout test studied by micro-Raman spectroscopy.

    PubMed

    Lei, Zhenkun; Wang, Quan; Qiu, Wei

    2013-06-01

    The interfacial stress transfer behavior of a Kevlar 49 aramid fiber-epoxy matrix was studied with fiber pullout tests, the fibers of which were stretched by a homemade microloading device. Raman spectra on the embedded fiber were recorded by micro-Raman spectroscopy, under different strain levels. Then, the fiber axial stress was obtained by the relationship between the stress and Raman shift of the aramid fiber. Experimental results revealed that the fiber axial stress increased significantly with the load. The shear stress concentration occurred at the fiber entry to the epoxy resin. Thus, interfacial friction stages exist in the debonded fiber segment, and the interfacial friction shear stress is constant within one stage. The experimental results are consistent with the theoretical model predictions.

  7. Lamination residual stresses in fiber composites

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.; Liber, T.

    1975-01-01

    An experimental investigation was conducted to determine the magnitude of lamination residual stresses in angle-ply composites and to evaluate their effects on composite structural integrity. The materials investigated were boron/epoxy, boron/polyimide, graphite/low modulus epoxy, graphite/high modulus epoxy, graphite/polyimide and s-glass/epoxy. These materials were fully characterized. Static properties of laminates were also determined. Experimental techniques using embedded strain gages were developed and used to measure residual strains during curing. The extent of relaxation of lamination residual stresses was investigated. It was concluded that the degree of such relaxation is low. The behavior of angle-ply laminates subjected to thermal cycling, tensile load cycling, and combined thermal cycling with tensile load was investigated. In most cases these cycling programs did not have any measurable influence on residual strength and stiffness of the laminates. In the tensile load cycling tests, the graphite/polyimide shows the highest endurance with 10 million cycle runouts at loads up to 90 percent of the static strength.

  8. Increased molecular mobility in humid silk fibers under tensile stress

    NASA Astrophysics Data System (ADS)

    Seydel, Tilo; Knoll, Wiebke; Greving, Imke; Dicko, Cedric; Koza, Michael M.; Krasnov, Igor; Müller, Martin

    2011-01-01

    Silk fibers are semicrystalline nanocomposite protein fibers with an extraordinary mechanical toughness that changes with humidity. Diffusive or overdamped motion on a molecular level is absent in dry silkworm silk, but present in humid silk at ambient temperature. This microscopic diffusion distinctly depends on the externally applied macroscopic tensile force. Quasielastic and inelastic neutron-scattering data as a function of humidity and of tensile strain on humid silk fibers support the model that both the adsorbed water and parts of the amorphous polymers participate in diffusive motion and are affected by the tensile force. It is notable that the quasielastic linewidth of humid silk at 100% relative humidity increases significantly with the applied force. The effect of the tensile force is discussed in terms of an increasing alignment of the polymer chains in the amorphous fraction with increasing tensile stress which changes the geometrical restrictions of the diffusive motions.

  9. Comparison of methods for predicting fiber stresses in a cracked Kevlar/epoxy monolayer

    SciTech Connect

    Reedy, E.D. Jr.

    1984-01-01

    Shear-lag and 3-D finite element predictions for the fiber stresses in a cracked Kevlar 49/epoxy monolayer are compared. Results are given for a 5-fiber wide monolayer containing a single broken fiber. Both methods of analysis are found to predict nearly the same fiber stress distribution along the crack-tip fiber when the monolayer is fully elastic. Results for highly loaded monolayers with extensive matrix yielding are not in quite as good agreement, but even then the predicted stress distributions are within 5%. These calculations show that a shear-lag analysis is accurate even though the Kevlar 49 fiber is highly anisotropic.

  10. Stress transfer problems for a fully embedded fiber with a bonded interface and bonded ends

    SciTech Connect

    Hsueh, Chun-Hway

    1996-06-01

    Stress transfer between fibers and matrix in fiber-reinforced composite was analyzed extensively using a shear lag model. Ends of the embedded fiber are generally assumed to debond from the matrix and stress transfer occurs only at the interface along the fiber length. The debonded ends are stress-free and the boundary condition at debonded ends in solving the stress transfer problem is trivial. When the fiber ends are bonded to the matrix, stress transfer also occurs at bonded ends, and the sress at bonded endsis finite. However, this finite stress is not a predetermined value, and the boundary condition at bonded ends becomes ambiguous. To resolve this ambiguity, a technique of adding imaginary fibers in the shear lag model is developed. Stress trnafer problems are analyzed when the composite is subjected to residual stresses or load. Comparison with experimental result is also made.

  11. Cyclic stretch-induced stress fiber dynamics - Dependence on strain rate, Rho-kinase and MLCK

    SciTech Connect

    Lee, Chin-Fu; Haase, Candice; Deguchi, Shinji; Kaunas, Roland

    2010-10-22

    Research highlights: {yields} Cyclic stretch induces stress fiber disassembly, reassembly and fusion perpendicular to the direction of stretch. {yields} Stress fiber disassembly and reorientation were not induced at low stretch frequency. {yields} Stretch caused actin fiber formation parallel to stretch in distinct locations in cells treated with Rho-kinase and MLCK inhibitors. -- Abstract: Stress fiber realignment is an important adaptive response to cyclic stretch for nonmuscle cells, but the mechanism by which such reorganization occurs is not known. By analyzing stress fiber dynamics using live cell microscopy, we revealed that stress fiber reorientation perpendicular to the direction of cyclic uniaxial stretching at 1 Hz did not involve disassembly of the stress fiber distal ends located at focal adhesion sites. Instead, these distal ends were often used to assemble new stress fibers oriented progressively further away from the direction of stretch. Stress fiber disassembly and reorientation were not induced when the frequency of stretch was decreased to 0.01 Hz, however. Treatment with the Rho-kinase inhibitor (Y27632) reduced stress fibers to thin fibers located in the cell periphery which bundled together to form thick fibers oriented parallel to the direction of stretching at 1 Hz. In contrast, these thin fibers remained diffuse in cells subjected to stretch at 0.01 Hz. Cyclic stretch at 1 Hz also induced actin fiber formation parallel to the direction of stretch in cells treated with the myosin light chain kinase (MLCK) inhibitor ML-7, but these fibers were located centrally rather than peripherally. These results shed new light on the mechanism by which stress fibers reorient in response to cyclic stretch in different regions of the actin cytoskeleton.

  12. Residual stresses in boron/tungsten and boron/carbon fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1977-01-01

    Longitudinal residual stress distribution is determined for 102-micron diam B/W and B/C fibers. The 102-micron diam B/W fibers are deposited on a 12.7-micron diam tungsten wire resistively heated in a BCl3-H2 reactor. The 102-micron diam B/C fibers are made by deposition of boron on a pyrolytic graphite-coated carbon fiber. The longitudinal residual stress distribution is calculated from measurements of the change in length of the fiber produced by removal of the surface through electropolishing. It is found that for both types of fibers, the residual stress vary from a compressive stress at the surface to a tensile stress in the boron near the core. Closer to the core and in the core, significant differences in the residual stresses are observed for the B/W and B/C fibers.

  13. Residual stresses in continuous graphite fiber Al metal matrix composites

    NASA Technical Reports Server (NTRS)

    Park, Hun Sub; Zong, Gui Sheng; Marcus, Harris L.

    1988-01-01

    The residual stresses in graphite fiber reinforced aluminum (Gr/Al) composites with various thermal histories are measured using X-ray diffraction (XRD) methods. The XRD stress analysis is based on the determination of lattice strains by precise measurements of the interplanar spacings in different directions of the sample. The sample is a plate consisting of two-ply P 100 Gr/Al 6061 precursor wires and Al 6061 overlayers. Prior to XRD measurement, the 6061 overlayers are electrochemically removed. In order to calibrate the relationship between stress magnitude and lattice spacing shift, samples of Al 6061 are loaded at varying stress levels in a three-point bend fixture, while the stresses are simultaneously determined by XRD and surface-attached strain gages. The stresses determined by XRD closely match those determined by the strain gages. Using these calibrations, the longitudinal residual stresses of P 100 Gr/Al 6061 composites are measured for various heat treatments, and the results are presented.

  14. Developing Fiber Specific Promoter-Reporter Transgenic Lines to Study the Effect of Abiotic Stresses on Fiber Development in Cotton

    PubMed Central

    Chen, Junping; Burke, John J.

    2015-01-01

    Cotton is one of the most important cash crops in US agricultural industry. Environmental stresses, such as drought, high temperature and combination of both, not only reduce the overall growth of cotton plants, but also greatly decrease cotton lint yield and fiber quality. The impact of environmental stresses on fiber development is poorly understood due to technical difficulties associated with the study of developing fiber tissues and lack of genetic materials to study fiber development. To address this important question and provide the need for scientific community, we have generated transgenic cotton lines harboring cotton fiber specific promoter (CFSP)-reporter constructs from six cotton fiber specific genes (Expansin, E6, Rac13, CelA1, LTP, and Fb late), representing genes that are expressed at different stages of fiber development. Individual CFSP::GUS or CFSP::GFP construct was introduced into Coker 312 via Agrobacterium mediated transformation. Transgenic cotton lines were evaluated phenotypically and screened for the presence of selectable marker, reporter gene expression, and insertion numbers. Quantitative analysis showed that the patterns of GUS reporter gene activity during fiber development in transgenic cotton lines were similar to those of the native genes. Greenhouse drought and heat stress study showed a correlation between the decrease in promoter activities and decrease in fiber length, increase in micronaire and changes in other fiber quality traits in transgenic lines grown under stressed condition. These newly developed materials provide new molecular tools for studying the effects of abiotic stresses on fiber development and may be used in study of cotton fiber development genes and eventually in the genetic manipulation of fiber quality. PMID:26030401

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

    PubMed

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

    1999-01-01

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

  16. Noninvasive detection of plant nutrient stress using fiber optic spectrophotometry

    NASA Astrophysics Data System (ADS)

    Chen, Jun-Wei; Asundi, Anand K.; Liew, Oi Wah; Boey, William S. L.

    2001-05-01

    In a previous paper, we described the use of fiber optic spectrophotometry as a non-destructive and sensitive method to detect early symptoms of plant nutrient deficiency. We report further developments of our work on Brassica chinensis var parachinensis (Bailey) showing reproducibility of our data collected at a different seasonal period. Plants at the mid-log growth phase were subjected to nutrient stress by transferring them to nitrate- and calcium- deficient nutrient solution in a standing aerated hydroponic system. After tracking changes in leaf reflectance by FOSpectr for nine days, the plants were returned to complete nutrient solution and their recovery was monitored for a further nine days. The responses of nutrient stressed plants were compared with those grown under complete nutrient solution over the 18-day trial period. We also compared the sensitivity of FOSpectr detection against plant growth measurements vis-a-vis average leaf number and leaf width and show that the former method gave an indication of nutrient stress much earlier than the latter. In addition, this work indicated that while normal and nutrient-stressed plants could not be distinguished within the first 7 days by tracking plant growth indicators, stressed plants did show a clear decline in average leaf number and leaf width in later stages of growth even after the plants were returned to complete nutrient solution. The results further reinforce the need for early detection of nutrient stress, as late remedial action could not reverse the loss in plant growth in later stages of plant development.

  17. Effect of stress on ultrasonic pulses in fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Hemann, J. H.; Baaklini, G. Y.

    1986-01-01

    An acoustical-ultrasonic technique was used to demonstrate relationships existing between changes in attenuation of stress waves and tensile stress on an eight ply 0 degree graphite-epoxy fiber reinforced composite. All tests were conducted in the linear range of the material for which no mechanical or macroscopic damage was evident. Changes in attenuation were measured as a function of tensile stress in the frequency domain and in the time domain. Stress wave propagation in these specimens was dispersive, i.e., the wave speed depends on frequency. Wave speeds varied from 267,400 cm/sec to 680,000 cm/sec as the frequency of the signal was varied from 150 kHz to 1.9 MHz which strongly suggests that flexural/lamb wave modes of propagation exist. The magnitude of the attenuation changes depended strongly on tensile stress. It was further observed that the wave speeds increased slightly for all tested frequencies as the stress was increased.

  18. Modeling of stress/strain behavior of fiber-reinforced ceramic matrix composites including stress redistribution

    NASA Technical Reports Server (NTRS)

    Mital, Subodh K.; Murthy, Pappu L. N.; Chamis, Christos C.

    1994-01-01

    A computational simulation procedure is presented for nonlinear analyses which incorporates microstress redistribution due to progressive fracture in ceramic matrix composites. This procedure facilitates an accurate simulation of the stress-strain behavior of ceramic matrix composites up to failure. The nonlinearity in the material behavior is accounted for at the constituent (fiber/matrix/interphase) level. This computational procedure is a part of recent upgrades to CEMCAN (Ceramic Matrix Composite Analyzer) computer code. The fiber substructuring technique in CEMCAN is used to monitor the damage initiation and progression as the load increases. The room-temperature tensile stress-strain curves for SiC fiber reinforced reaction-bonded silicon nitride (RBSN) matrix unidirectional and angle-ply laminates are simulated and compared with experimentally observed stress-strain behavior. Comparison between the predicted stress/strain behavior and experimental stress/strain curves is good. Collectively the results demonstrate that CEMCAN computer code provides the user with an effective computational tool to simulate the behavior of ceramic matrix composites.

  19. Effects of fiber ellipticity and orientation on dynamic stress concentrations in porous fiber-reinforced composites

    NASA Astrophysics Data System (ADS)

    Hasheminejad, Seyyed M.; Sanaei, Roozbeh

    2007-11-01

    Interaction of time harmonic fast longitudinal and shear incident plane waves with an elliptical fiber embedded in a porous elastic matrix is studied. The novel features of Biot dynamic theory of poroelasticity along with the classical method of eigen-function expansion and the pertinent boundary conditions are employed to develop a closed form series solution involving Mathieu and modified Mathieu functions of complex arguments. The complications arising due to the non-orthogonality of angular Mathieu functions corresponding to distinct wave numbers in addition to the problems associated with appearance of additional angular dependent terms in the boundary conditions are all avoided by expansion of the angular Mathieu functions in terms of transcendental functions and subsequent integration, leading to a linear set of independent equations in terms of the unknown scattering coefficients. A MATHEMATICA code is developed for computing the Mathieu functions in terms of complex Fourier coefficients which are themselves calculated by numerically solving appropriate sets of eigen-systems. The analytical results are illustrated with numerical examples in which an elastic fiber of elliptic cross section is insonified by a plane fast compressional or shear wave at normal incidence. The effects of fiber cross sectional ellipticity, angle of incidence (fiber two-dimensional orientation), and incident wave polarization (P, SV, SH) on dynamic stress concentrations are studied in a relatively wide frequency range. Limiting cases are considered and fair agreements with well-known solutions are established.

  20. Discrete diffusion Monte Carlo for frequency-dependent radiative transfer

    SciTech Connect

    Densmore, Jeffrey D; Kelly, Thompson G; Urbatish, Todd J

    2010-11-17

    Discrete Diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Implicit Monte Carlo radiative-transfer simulations. In this paper, we develop an extension of DDMC for frequency-dependent radiative transfer. We base our new DDMC method on a frequency-integrated diffusion equation for frequencies below a specified threshold. Above this threshold we employ standard Monte Carlo. With a frequency-dependent test problem, we confirm the increased efficiency of our new DDMC technique.

  1. Frequency-dependent FDTD methods using Z transforms

    NASA Technical Reports Server (NTRS)

    Sullivan, Dennis M.

    1992-01-01

    While the frequency-dependent finite-difference time-domain, or (FD)2TD, method can correctly calculate EM propagation through media whose dielectric properties are frequency-dependent, more elaborate applications lead to greater (FD)2TD complexity. Z-transform theory is presently used to develop the mathematical bases of the (FD)2TD method, simultaneously obtaining a clearer formulation and allowing researchers to draw on the existing literature of systems analysis and signal-processing.

  2. Frequency-Dependent Selection Predicts Patterns of Radiations and Biodiversity

    PubMed Central

    Melián, Carlos J.; Alonso, David; Vázquez, Diego P.; Regetz, James; Allesina, Stefano

    2010-01-01

    Most empirical studies support a decline in speciation rates through time, although evidence for constant speciation rates also exists. Declining rates have been explained by invoking pre-existing niches, whereas constant rates have been attributed to non-adaptive processes such as sexual selection and mutation. Trends in speciation rate and the processes underlying it remain unclear, representing a critical information gap in understanding patterns of global diversity. Here we show that the temporal trend in the speciation rate can also be explained by frequency-dependent selection. We construct a frequency-dependent and DNA sequence-based model of speciation. We compare our model to empirical diversity patterns observed for cichlid fish and Darwin's finches, two classic systems for which speciation rates and richness data exist. Negative frequency-dependent selection predicts well both the declining speciation rate found in cichlid fish and explains their species richness. For groups like the Darwin's finches, in which speciation rates are constant and diversity is lower, speciation rate is better explained by a model without frequency-dependent selection. Our analysis shows that differences in diversity may be driven by incipient species abundance with frequency-dependent selection. Our results demonstrate that genetic-distance-based speciation and frequency-dependent selection are sufficient to explain the high diversity observed in natural systems and, importantly, predict decay through time in speciation rate in the absence of pre-existing niches. PMID:20865126

  3. Characterization of the stress and refractive-index distributions in optical fibers and fiber-based devices

    NASA Astrophysics Data System (ADS)

    Hutsel, Michael R.

    2011-07-01

    Optical fiber technology continues to advance rapidly as a result of the increasing demands on communication systems and the expanding use of fiber-based sensing. New optical fiber types and fiber-based communications components are required to permit higher data rates, an increased number of channels, and more flexible installation requirements. Fiber-based sensors are continually being developed for a broad range of sensing applications, including environmental, medical, structural, industrial, and military. As optical fibers and fiber-based devices continue to advance, the need to understand their fundamental physical properties increases. The residual-stress distribution (RSD) and the refractive-index distribution (RID) play fundamental roles in the operation and performance of optical fibers. Custom RIDs are used to tailor the transmission properties of fibers used for long-distance transmission and to enable fiber-based devices such as long-period fiber gratings (LPFGs). The introduction and modification of RSDs enable specialty fibers, such as polarization-maintaining fiber, and contribute to the operation of fiber-based devices. Furthermore, the RSD and the RID are inherently linked through the photoelastic effect. Therefore, both the RSD and the RID need to be characterized because these fundamental properties are coupled and affect the fabrication, operation, and performance of fibers and fiber-based devices. To characterize effectively the physical properties of optical fibers, the RSD and the RID must be measured without perturbing or destroying the optical fiber. Furthermore, the techniques used must not be limited in detecting small variations and asymmetries in all directions through the fiber. Finally, the RSD and the RID must be characterized concurrently without moving the fiber to enable the analysis of the relationship between the RSD and the RID. Although many techniques exist for characterizing the residual stress and the refractive index in

  4. Distributed transverse stress measurement along an optic fiber using polarimetric OFDR.

    PubMed

    Wei, Changjiang; Chen, Hongxin; Chen, Xiaojun; Chen, David; Li, Zhihong; Yao, X Steve

    2016-06-15

    We report a novel polarimetric optical frequency domain reflectometer (P-OFDR) that can simultaneously measure both space-resolved transverse stresses and light back-reflections along an optic fiber with sub-mm spatial resolution. By inducing transversal stresses and optical back-reflections at multiple points along a length of optic fiber, we demonstrate that our system can unambiguously distinguish the stresses from the back-reflections of a fiber with a fiber length longer than 800 m, a spatial resolution of 0.5 mm, a maximum stress level of up to 200 kpsi (1379 Mpa), a minimum stress of about 10 kpsi (69 Mpa), and a stress measurement uncertainty of 10%. We show that our P-OFDR can clearly identify the locations and magnitudes of the stresses inside a fiber coil induced during a fiber winding process. The P-OFDR can be used for fiber health monitoring for critical fiber links, fiber gyro coil characterization, and other distributed fiber sensing applications.

  5. Characterization of the stress and refractive-index distributions in optical fibers and fiber-based devices

    NASA Astrophysics Data System (ADS)

    Hutsel, Michael R.

    2011-07-01

    Optical fiber technology continues to advance rapidly as a result of the increasing demands on communication systems and the expanding use of fiber-based sensing. New optical fiber types and fiber-based communications components are required to permit higher data rates, an increased number of channels, and more flexible installation requirements. Fiber-based sensors are continually being developed for a broad range of sensing applications, including environmental, medical, structural, industrial, and military. As optical fibers and fiber-based devices continue to advance, the need to understand their fundamental physical properties increases. The residual-stress distribution (RSD) and the refractive-index distribution (RID) play fundamental roles in the operation and performance of optical fibers. Custom RIDs are used to tailor the transmission properties of fibers used for long-distance transmission and to enable fiber-based devices such as long-period fiber gratings (LPFGs). The introduction and modification of RSDs enable specialty fibers, such as polarization-maintaining fiber, and contribute to the operation of fiber-based devices. Furthermore, the RSD and the RID are inherently linked through the photoelastic effect. Therefore, both the RSD and the RID need to be characterized because these fundamental properties are coupled and affect the fabrication, operation, and performance of fibers and fiber-based devices. To characterize effectively the physical properties of optical fibers, the RSD and the RID must be measured without perturbing or destroying the optical fiber. Furthermore, the techniques used must not be limited in detecting small variations and asymmetries in all directions through the fiber. Finally, the RSD and the RID must be characterized concurrently without moving the fiber to enable the analysis of the relationship between the RSD and the RID. Although many techniques exist for characterizing the residual stress and the refractive index in

  6. Frequency dependence of the acoustic field generated from a spherical cavity transducer with open ends

    SciTech Connect

    Li, Faqi; Zeng, Deping; He, Min; Wang, Zhibiao E-mail: wangzhibiao@haifu.com.cn; Song, Dan; Lei, Guangrong; Lin, Zhou; Zhang, Dong E-mail: wangzhibiao@haifu.com.cn; Wu, Junru

    2015-12-15

    Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.

  7. Thermal dependence of stress-induced birefringence in single mode optical fibers

    NASA Technical Reports Server (NTRS)

    Berthold, J. W., III; Thompson, L. B.

    1984-01-01

    Measurements of the change in stress-induced birefringence with temperature in single mode optical fibers are reported. The fibers examined include those with low residual stress birefringence that have circular and elliptical cores. A section of each fiber was placed under constant load with weights and heated inside a furnace. Polarized light was coupled into and out of the fiber ends outside the furnace. Two mutually perpendicular polarization components were analyzed and detected at the fiber output end. Changes in the detected signal levels were monitored as a function of the temperature of the single mode fiber stressed under constant load. Discussion of results and applications to localized stress measurements at high temperatures are presented.

  8. Dependence of cyclic stretch-induced stress fiber reorientation on stretch waveform.

    PubMed

    Tondon, Abhishek; Hsu, Hui-Ju; Kaunas, Roland

    2012-03-15

    Cyclic uniaxial stretching of adherent nonmuscle cells induces the gradual reorientation of their actin stress fibers perpendicular to the stretch direction to an extent dependent on stretch frequency. By subjecting cells to various temporal waveforms of cyclic stretch, we revealed that stress fibers are much more sensitive to strain rate than strain frequency. By applying asymmetric waveforms, stress fibers were clearly much more responsive to the rate of lengthening than the rate of shortening during the stretch cycle. These observations were interpreted using a theoretical model of networks of stress fibers with sarcomeric structure. The model predicts that stretch waveforms with fast lengthening rates generate greater average stress fiber tension than that generated by fast shortening. This integrated approach of experiment and theory provides new insight into the mechanisms by which cells respond to matrix stretching to maintain tensional homeostasis.

  9. The effects of uneven fiber spacing on thermal residual stresses in a unidirectional SCS-6/Ti-15-3 laminate

    NASA Technical Reports Server (NTRS)

    Bigelow, Catherine A.

    1992-01-01

    High residual stresses develop in SCS-6/Ti-15-3 composites during cooldown from the fabrication temperature; these residual stresses can effect the mechanical and physical properties of the composite. Discrete fiber-matrix finite element models were used to study the residual stresses due to the temperature change during the fabrication process, including the effects of uneven fiber spacing, the free surface, and increased fiber volume fractions. To accurately model the effects of the free surface, it is only necessary to model one fiber through the thickness. Below the first ply, the analysis predicts stress distributions that are identical to the infinite array predictions. For uneven fiber space less than 0.042 mm in an interior ply, the maximum hoop stress was predicted to occur between fibers within a ply and to increase as the fiber spacing decreased. The maximum hoop stress correlated well with the observed radial cracking between fibers. For the case of touching fibers, the analysis predicted tensile radial stresses at the fiber-matrix debonding during the fabrication cooldown. Identical trends were predicted for uneven fiber spacing in surface plies with slightly greater values of maximum stresses. The analysis predicted matrix yielding to occur upon cooldown when the edge-to-edge fiber spacing was less than or equal to 0.022 mm. The stress distributions preidcted for increasing fiber volume fractions were similar to those predicted for decreasing the fiber spacing for two adjacent fibers within a ply.

  10. The effects of uneven fiber spacing on thermal residual stresses in a unidirectional SCS-6Ti-15-3 laminate

    NASA Technical Reports Server (NTRS)

    Bigelow, C. A.

    1992-01-01

    High residual stresses develop in SCS-6/Ti-15-3 composites during cooldown from the fabrication temperature; these residual stresses can effect the mechanical and physical properties of the composite. Discrete fiber-matrix finite element models were used to study the residual stresses due to the temperature change during the fabrication process, including the effects of uneven fiber spacing, the free surface, and increased fiber volume fractions. To accurately model the effects of the free surface, it is only necessary to model one fiber through the thickness. Below the first ply, the analysis predicts stress distributions that are identical to the infinite array predictions. For uneven fiber space less then 0.042 mm in an interior ply, the maximum hoop stress was predicted to occur between fibers within a ply and to increase as the fiber spacing decreased. The maximum hoop stress correlated well with the observed radial cracking between fibers. For the case of touching fibers, the analysis predicted tensile radial stresses at the fiber-matrix debonding during the fabrication cooldown. Identical trends were predicted for uneven fiber spacing in surface plies with slightly greater values of maximum stresses. The analysis predicted matrix yielding to occur upon cooldown when the edge-to-edge fiber spacing was less than or equal to 0.022 mm. The stress distributions predicted for increasing fiber volume fractions were similar to those predicted for decreasing the fiber spacing for two adjacent fibers within a ply.

  11. Frequency dependent elastic impedance inversion for interstratified dispersive elastic parameters

    NASA Astrophysics Data System (ADS)

    Zong, Zhaoyun; Yin, Xingyao; Wu, Guochen

    2016-08-01

    The elastic impedance equation is extended to frequency dependent elastic impedance equation by taking partial derivative to frequency. With this equation as the forward solver, a practical frequency dependent elastic impedance inversion approach is presented to implement the estimation of the interstratified dispersive elastic parameters which makes full use of the frequency information of elastic impedances. Three main steps are included in this approach. Firstly, the elastic Bayesian inversion is implemented for the estimation of elastic impedances from different incident angle. Secondly, with those estimated elastic impedances, their variations are used to estimate P-wave velocity and S-wave velocity. Finally, with the prior elastic impedance and P-wave and S-wave velocity information, the frequency dependent elastic variation with incident angle inversion is presented for the estimation of the interstratified elastic parameters. With this approach, the interstratified elastic parameters rather than the interface information can be estimated, making easier the interpretation of frequency dependent seismic attributes. The model examples illustrate the feasibility and stability of the proposed method in P-wave velocity dispersion and S-wave velocity dispersion estimation. The field data example validates the possibility and efficiency in hydrocarbon indication of the estimated P-wave velocity dispersion and S-wave velocity dispersion.

  12. A comparative study of the stress-rupture lifetimes of high-strength carbon fibers

    NASA Astrophysics Data System (ADS)

    Grimes-Ledesma, Lorie

    Stress-rupture life is the time a composite can survive under load at an assigned risk level. The stress-rupture lifetimes of high-strength PAN-based carbon fibers are important to the development and use of lightweight composite structures such as composite overwrapped pressure vessels (COPVs). To quantify appropriate stress-rupture risk levels based on available models, quantification of single fiber variability and lifetime is necessary to understand the variability observed in larger composite structures. In the present work, three PAN-based carbon fibers commonly used in COPV technology were examined, Hexcel IM9, Toray T700, and Toray T1000. The diameter of each fiber type was quantified by measuring samples in the scanning electron microscope and failure loads were determined by performing tensile tests on single fibers. Weibull statistics were used to describe the results. Fractography was performed on IM9 and T1000 fibers after tensile failure. The fracture surfaces are consistent with crack growth from a volume or surface defect. Stress-rupture testing was completed at two stress levels at each fiber type, 97% and 93% of the mean fiber strength for each of the fiber types. The results indicate that differences in stress-rupture life performance exist between the three fiber types. Differences in stress ratio of between 5 and 10% were observed, which may translate to significant difference in stress-rupture life behavior for larger composite structures. The results indicate that a relationship may exist between strength and stress-rupture life. However, if this relationship exists, it is not a simple one, and the relationship is likely complicated by manufacturing.

  13. Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop.

    PubMed

    Kim, Hyunjin; Sampath, Umesh; Song, Minho

    2015-07-29

    Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems.

  14. Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop

    PubMed Central

    Kim, Hyunjin; Sampath, Umesh; Song, Minho

    2015-01-01

    Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems. PMID:26230700

  15. Nondestructive evaluation of residual stress in short-fiber reinforced plastics by x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Tanaka, Keisuke; Tokoro, Syouhei; Akiniwa, Yoshiaki; Egami, Noboru

    2014-06-01

    The X-ray diffraction method is used to measure the residual stress in injection-molded plates of short-fiber reinforced plastics (SFRP) made of crystalline thermoplastics, polyphenylene sulphide (PPS), reinforced by carbon fibers with 30 mass%. Based on the orientation of carbon fibers, injection molded plates can be modeled as three-layered lamella where the core layer is sandwiched by skin layers. The stress in the matrix in the skin layer was measured using Cr-Kα radiation with the sin2Ψ method. Since the X-ray penetration depth is shallow, the state of stresses measured by X-rays in FRP can be assumed to be plane stress. The X-ray measurement of stress in carbon fibers was not possible because of high texture. A new method was proposed to evaluate the macrostress in SFRP from the measurement of the matrix stress. According to micromechanics analysis of SFRP, the matrix stresses in the fiber direction, σ1m, and perpendicular to the fiber direction, σ2m, and shear stress τ12m can be expressed as the functions of the applied (macro-) stresses, σ1A, σ2A , τ12A as follows: σ1m = α11σ1A +α12σ2A, σ2m = α21σ1A + α22σ2A, τ12m = α66τ12A, where α11 ,α12, α21, α22, α66 are stress-partitioning coefficients. Using skin-layer strips cut parallel, perpendicular and 45° to the molding direction, the stress in the matrix was measured under the uniaxial applied stress and the stress-partitioning coefficients of the above equations were determined. Once these relations are established, the macrostress in SFRP can be determined from the measurements of the matrix stresses by X-rays.

  16. Frequency-dependent effective hydraulic conductivity of strongly heterogeneous media.

    PubMed

    Caspari, E; Gurevich, B; Müller, T M

    2013-10-01

    The determination of the transport properties of heterogeneous porous rocks, such as an effective hydraulic conductivity, arises in a range of geoscience problems, from groundwater flow analysis to hydrocarbon reservoir modeling. In the presence of formation-scale heterogeneities, nonstationary flows, induced by pumping tests or propagating elastic waves, entail localized pressure diffusion processes with a characteristic frequency depending on the pressure diffusivity and size of the heterogeneity. Then, on a macroscale, a homogeneous equivalent medium exists, which has a frequency-dependent effective conductivity. The frequency dependence of the conductivity can be analyzed with Biot's equations of poroelasticity. In the quasistatic frequency regime of this framework, the slow compressional wave is a proxy for pressure diffusion processes. This slow compressional wave is associated with the out-of-phase motion of the fluid and solid phase, thereby creating a relative fluid-solid displacement vector field. Decoupling of the poroelasticity equations gives a diffusion equation for the fluid-solid displacement field valid in a poroelastic medium with spatial fluctuations in hydraulic conductivity. Then, an effective conductivity is found by a Green's function approach followed by a strong-contrast perturbation theory suggested earlier in the context of random dielectrics. This theory leads to closed-form expressions for the frequency-dependent effective conductivity as a function of the one- and two-point probability functions of the conductivity fluctuations. In one dimension, these expressions are consistent with exact solutions in both low- and high-frequency limits for arbitrary conductivity contrast. In 3D, the low-frequency limit depends on the details of the microstructure. However, the derived approximation for the effective conductivity is consistent with the Hashin-Shtrikman bounds.

  17. Frequency-dependent force fields for QMMM calculations.

    PubMed

    Harczuk, Ignat; Vahtras, Olav; Ågren, Hans

    2015-03-28

    We outline the construction of frequency-dependent polarizable force fields. The force fields are derived from analytic response theory for different frequencies using a generalization of the LoProp algorithm giving a decomposition of a molecular dynamical polarizability to localized atomic dynamical polarizabilities. These force fields can enter in a variety of applications - we focus on two such applications in this work: firstly, they can be incorporated in a physical, straightforward, way for current existing methods that use polarizable embeddings, and we can show, for the first time, the effect of the frequency dispersion within the classical environment of a quantum mechanics-molecular mechanics (QMMM) method. Our methodology is here evaluated for some test cases comprising water clusters and organic residues. Secondly, together with a modified Silberstein-Applequist procedure for interacting inducible point-dipoles, these frequency-dependent polarizable force fields can be used for a classical determination of frequency-dependent cluster polarizabilities. We evaluate this methodology by comparing with the corresponding results obtained from quantum mechanics or QMMM where the absolute mean [small alpha, Greek, macron] is determined with respect to the size of the QM and MM parts of the total system.

  18. Frequency dependent Lg attenuation in south-central Alaska

    USGS Publications Warehouse

    McNamara, D.E.

    2000-01-01

    The characteristics of seismic energy attenuation are determined using high frequency Lg waves from 27 crustal earthquakes, in south-central Alaska. Lg time-domain amplitudes are measured in five pass-bands and inverted to determine a frequency-dependent quality factor, Q(f), model for south-central Alaska. The inversion in this study yields the frequency-dependent quality factor, in the form of a power law: Q(f) = Q0fη = 220(±30) f0.66(±0.09) (0.75≤f≤12Hz). The results from this study are remarkably consistent with frequency dependent quality factor estimates, using local S-wave coda, in south-central Alaska. The consistency between S-coda Q(f) and Lg Q(f) enables constraints to be placed on the mechanism of crustal attenuation in south-central Alaska. For the range of frequencies considered in this study both scattering and intrinsic attenuation mechanisms likely play an equal role.

  19. Frequency-Dependent Attenuation of Blasting Vibration Waves

    NASA Astrophysics Data System (ADS)

    Zhou, Junru; Lu, Wenbo; Yan, Peng; Chen, Ming; Wang, Gaohui

    2016-10-01

    The dominant frequency, in addition to the peak particle velocity, is a critical factor for assessing adverse effects of the blasting vibration on surrounding structures; however, it has not been fully considered in blasting design. Therefore, the dominant frequency-dependent attenuation mechanism of blast-induced vibration is investigated in the present research. Starting with blasting vibration induced by a spherical charge propagating in an infinite viscoelastic medium, a modified expression of the vibration amplitude spectrum was derived to reveal the frequency dependency of attenuation. Then, ground vibration induced by more complex and more commonly used cylindrical charge that propagates in a semi-infinite viscoelastic medium was analyzed by numerical simulation. Results demonstrate that the absorptive property of the medium results in the frequency attenuation versus distance, whereas a rapid drop or fluctuation occurs during the attenuation of ground vibration. Fluctuation usually appears at moderate to far field, and the dominant frequency generally decreases to half the original value when rapid drop occurs. The decay rate discrepancy between different frequency components and the multimodal structure of vibration spectrum lead to the unsmooth frequency-dependent attenuation. The above research is verified by two field experiments. Furthermore, according to frequency-based vibration standards, frequency drop and fluctuation should be considered when evaluating blast safety. An optimized piecewise assessment is proposed for more accurate evaluation: With the frequency drop point as the breakpoint, the assessment is divided into two independent sections along the propagating path.

  20. Frequency-dependent force fields for QMMM calculations.

    PubMed

    Harczuk, Ignat; Vahtras, Olav; Ågren, Hans

    2015-03-28

    We outline the construction of frequency-dependent polarizable force fields. The force fields are derived from analytic response theory for different frequencies using a generalization of the LoProp algorithm giving a decomposition of a molecular dynamical polarizability to localized atomic dynamical polarizabilities. These force fields can enter in a variety of applications - we focus on two such applications in this work: firstly, they can be incorporated in a physical, straightforward, way for current existing methods that use polarizable embeddings, and we can show, for the first time, the effect of the frequency dispersion within the classical environment of a quantum mechanics-molecular mechanics (QMMM) method. Our methodology is here evaluated for some test cases comprising water clusters and organic residues. Secondly, together with a modified Silberstein-Applequist procedure for interacting inducible point-dipoles, these frequency-dependent polarizable force fields can be used for a classical determination of frequency-dependent cluster polarizabilities. We evaluate this methodology by comparing with the corresponding results obtained from quantum mechanics or QMMM where the absolute mean [small alpha, Greek, macron] is determined with respect to the size of the QM and MM parts of the total system. PMID:25714984

  1. Residual stresses in boron/tungsten and boron/carbon fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1977-01-01

    By measuring the change in fracture stress of 203 micrometer diameter fibers of boron on tungsten (B/W) as a function of fiber diameter as reduced by chemical etching, it is shown that the flaws which limit B/W fiber strength are located at the surface and in the tungsten boride core. After etching to a diameter of 188 micrometers m virtually all fiber fractures were caused by core flaws, the average strength being 4.50 GN/sq m. If both the surface and core flaws are removed, the fracture strength, limited by flaws in the boron itself, is approximately 6.89 GN/sq m. This was measured on B/W fibers which were split longitudinally and had their cores removed by chemical etching. The longitudinal residual stress distribution was determined for 102 micrometer diameter B/W and B/C fibers.

  2. Arc-discharge effects on residual stress and refractive index in single-mode optical fibers.

    PubMed

    Wang, Pengfei; Jenkins, Micah H; Gaylord, Thomas K

    2016-03-20

    Arc-discharge effects on the residual stress and refractive index in single-mode optical fibers are investigated using a previously developed three-dimensional concurrent stress-index measurement method. Using commercial optical fibers and a commercial fusion splicer, the residual stress and refractive index perturbations caused by weak electrical arc discharges in single-mode fibers were measured. Refractive index changes greater than 10-4 and longitudinal perturbation lengths of less than 500 μm were shown to be possible. The subsequent prospects for arc-induced long-period fiber gratings are analyzed, and a typical transmission resonance is predicted to have a depth of 56 dB and a bandwidth of 0.08 nm at a wavelength of 1585 nm. The results of this investigation will be useful in modeling device performance and optimization of arc-induced long-period fiber grating fabrication.

  3. Frequency-dependent Lg Q within the continental United States

    USGS Publications Warehouse

    Erickson, D.; McNamara, D.E.; Benz, H.M.

    2004-01-01

    Frequency-dependent crustal attenuation (1/Q) is determined for seven distinct physiographic/tectonic regions of the continental United States using high-quality Lg waveforms recorded on broadband stations in the frequency band 0.5 to 16 Hz. Lg attenuation is determined from time-domain amplitude measurements in one-octave frequency bands centered on the frequencies 0.75, 1.0, 3.0, 6.0, and 12.0 Hz. Modeling errors are determined using a delete-j jackknife resampling technique. The frequency-dependent quality factor is modeled in the form of Q = Q0 fη. Regions were initially selected based on tectonic provinces but were eventually limited and adjusted to maximize ray path coverage in each area. Earthquake data was recorded on several different networks and constrained to events occurring within the crust (<40 km depth) and at least mb 3.5 in size. A singular value decomposition inversion technique was applied to the data to simultaneously solve for source and receiver terms along with Q for each region at specific frequencies. The lowest crustal Q was observed in northern and southern California where Q is described by the functions Q = 152(±37)f0.72(±0.16) and Q = 105(±26)f0.67(±0.16), respectively. The Basin and Range Province, Pacific Northwest, and Rocky Mountain states also display lower Q and a strong frequency dependence characterized by the functions Q = 200(±40)f0.68(±0.12), Q = 152(±49)f0.76(±0.18), and Q = 166(±37)f0.61(±0.14), respectively. In contrast, in the central and northeast United States Q functions are Q = 640(±225)f0.344(±0.22) and Q = 650(±143)f0.36(±0.14), respectively, show a high crustal Q and a weaker frequency dependence. These results improve upon previous Lg modeling by subdividing the United States into smaller, distinct tectonic regions and using significantly more data that provide improved constraints on frequency-dependent attenuation and errors. A detailed attenuation map of the continental United States can

  4. Augmented stress fiber arrays after cytopharmacologic disassembly of microtubules

    SciTech Connect

    Godman, G.C.; Tannenbaum, J.; Brett, J.B.

    1986-03-01

    Disruption of microtubules (mt) of bovine aortic endothelial (BAE) cells, and normal and transformed fibroblasts, by exposure to 2.5 ..mu..M colchicine; 12 ..mu..M vinblastine; or 1 ..mu..M nocodazole, for 5 or 20 hrs results in aggregation of vimentin-intermediate filament (IF) and the development of markedly augmented stress fiber (SF) arrays. After disassembly of mt, confluent BAE, with circumferential marginal microfilament bands and few central SF, develop dense ribbon-like SF arrays, and spontaneously transformed fibroblasts (tHmf-e), which before treatment are apolar or epithelioid and have few or no SF, acquire extensive organized SF arrays. The axially oriented SF span the entire cell length and terminate in vinculin-containing adhesion plaques, polarizing these cells. The visible increase in SF associated actin is not accompanied by an increase either in actin synthesis (determined from electropherograms after pulse labeling with (/sup 35/S)methionine), or content (DNAse I assay for total cell actin). The reorganization of actin into SF and the development of vinculin adhesion plaques is independent of protein synthesis and occurs in the presence of cycloheximide (10 ..mu..g/ml). These results suggest a role for mt and IF in the regulation of the organizational state of the actin-based cytoskeleton.

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

    PubMed Central

    2013-01-01

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

  6. High temperature battery cell comprising stress-free hollow fiber bundle

    SciTech Connect

    Anand, J.N.; Revak, T.T.; Rossini, F.J.

    1982-06-01

    Thermal stressing of hollow fibers constituting the electrolyteseparator in a high temperature battery cell, and of certain other elements thereof, is avoided by suspending the assembly comprising the anolyte tank, the tubesheet, the hollow fibers and a cathodic current collector-distributing means, within the casing and employing a limp connection between the latter means and the cathode terminal of the cell.

  7. Optical fiber sensors and their application in monitoring stress build-up in dental resin cements

    NASA Astrophysics Data System (ADS)

    Ottevaere, H.; Tabak, M.; Fernandez Fernandez, A.; Berghmans, F.; Thienpont, H.

    2005-09-01

    The field of optical fiber sensing is highly diverse and this diversity is perceived as a great advantage over more conventional sensors in that an optical sensor can be tailored to measure any of a myriad of physical parameters. In this paper we present a niche application for optical fiber sensors in the domain of biophotonics, namely the monitoring of stress build-up during the curing process of dental resin cements. We discuss the origin of this stress build-up and the problems it can cause when treating patients. Optical fiber sensors aim at excelling in two kind of applications: firstly to perform quality control on batch produced dental cements and measure their total material shrinkage, secondly to monitor the hardening of the cement during in-vivo measurements resulting in the dynamic measurement of the shrinkage and to control the stress in a facing based restoration. We therefore investigated two types of optical fiber sensors as alternatives to conventional measurement techniques; namely polarimetric optical fiber sensors and fiber Bragg gratings written in polarization maintaining fibers. After discussing the results obtained with both optical fiber sensors, we will conclude with a critical assessment of the suitability of the two proposed sensing configurations for multi-parameter stress monitoring.

  8. Developing fiber specific promoter-reporter transgenic lines to study the effect of abiotic stresses on fiber development in cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cotton is one of the most important cash crops in US agricultural industry. Environmental stresses, such as drought, high temperature and combination of both, not only reduce the overall growth of cotton plants, but also greatly decrease cotton lint yield and fiber quality. The impact of environment...

  9. Frequency-dependent Lg-wave attenuation in northern Morocco

    NASA Astrophysics Data System (ADS)

    Noriega, Raquel; Ugalde, Arantza; Villaseñor, Antonio; Harnafi, Mimoun

    2015-11-01

    Frequency-dependent attenuation (Q- 1) in the crust of northern Morocco is estimated from Lg-wave spectral amplitude measurements every quarter octave in the frequency band 0.8 to 8 Hz. This study takes advantage of the improved broadband data coverage in the region provided by the deployment of the IberArray seismic network. Earthquake data consist of 71 crustal events with magnitudes 4 ≤ mb ≤ 5.5 recorded on 110 permanent and temporary seismic stations between January 2008 and December 2013 with hypocentral distances between 100 and 900 km. 1274 high-quality Lg waveforms provide dense path coverage of northern Morocco, crossing a region with a complex structure and heterogeneous tectonic setting as a result of continuous interactions between the African and Eurasian plates. We use two different methods: the coda normalization (CN) analysis, that allows removal of the source and site effects from the Lg spectra, and the spectral amplitude decay (SAD) method, that simultaneously inverts for source, site, and path attenuation terms. The CN and SAD methods return similar results, indicating that the Lg Q models are robust to differences in the methodologies. Larger errors and no significant frequency dependence are observed for frequencies lower than 1.5 Hz. For distances up to 400 km and the frequency band 1.5 ≤ ƒ (Hz) ≤ 4.5, the model functions Q(f) = (529- 22+ 23)(f/1.5)0.23 ± 0.06 and Q(f) = (457- 7+ 7)(f/1.5)0.44 ± 0.02 are obtained using the CN and SAD methods, respectively. A change in the frequency dependence is observed above 4.5 Hz for both methods which may be related to the influence of the Sn energy on the Lg window. The frequency-dependent Q- 1 estimates represent an average attenuation beneath a broad region including the Rif and Tell mountains, the Moroccan and Algerian mesetas, the Atlas Mountains and the Sahara Platform structural domains, and correlate well with areas of moderate seismicity where intermediate Q values have been obtained.

  10. Microscale Modelling of the Frequency Dependent Resistivity of Porous Media

    NASA Astrophysics Data System (ADS)

    Volkmann, J.; Klitzsch, N.; Mohnke, O.; Blaschek, R.

    2009-04-01

    In geophysics frequency dependent complex resistivity measurements are called Spectral Induced Polarization (SIP). In other fields this method is known as Impedance Spectroscopy. In the last two decades many empirical relations were proposed which relate the frequency dependent electrical properties of water saturated rocks to structural properties such as pore radius, and inner surface area, or to hydraulic conductivity. Unfortunately, these relations are not universal; they apply only for specific rock types and water compositions. In order to quantify the influence of inner rock structure (as well as of electrochemical water and rock properties) on the frequency dependent electrical properties we model the charge transport processes at the pore space using Comsol Multiphysics. In the frequency domain the effect of Induced Polarization (IP) is characterised by a phase shift between a measured electric current and an alternating voltage applied to the ground. A possible origin of this behaviour particularly for non-conducting rock minerals can be seen in the membrane polarization model as proposed by Marshall and Madden (1959). This model describes a system of electrolyte filled pores. Different mobilities of cations and anions in the small pores cause a membrane effect and thus an electrical polarization. We aim to find a more realistic way of modelling the membrane polarization effect than using the simple Marshall and Madden model. The electric double layer, the origin of the Induced Polarization effect, is caused by surface charges located at the electrolyte rock interface. Thus, the EDL as a boundary effect is accounted for by reduced counterion mobilities at the inner surface area. The governing equations and boundary conditions for a system of larger and smaller pores with applied voltage are expressed in frequency domain using a time harmonic approach, the electric current is determined to obtain information about amplitude and phase of the complex

  11. Divergences in the vacuum energy for frequency-dependent interactions

    NASA Astrophysics Data System (ADS)

    Vassilevich, D. V.

    2009-03-01

    We propose a method for determining ultraviolet divergences in the vacuum energy for systems whose spectrum of perturbations is defined through a nonlinear spectrum problem, i.e., when the fluctuation operator itself depends on the frequency. The method is applied to the plasma shell model, which describes some properties of the interaction of electromagnetic field with fullerenes. We formulate a scalar model, which simplifies the matrix structure, but keeps the frequency dependence of the plasma shell, and calculate the ultraviolet divergences in the case when the plasma sheet is slightly curved. The divergent terms are expressed in terms of surface integrals of corresponding invariants.

  12. In-situ Frequency Dependent Dielectric Sensing of Cure

    NASA Technical Reports Server (NTRS)

    Kranbuehl, David E.

    1996-01-01

    With the expanding use of polymeric materials as composite matrices, adhesives, coatings and films, the need to develop low cost, automated fabrication processes to produce consistently high quality parts is critical. Essential to the development of reliable, automated, intelligent processing is the ability to continuously monitor the changing state of the polymeric resin in-situ in the fabrication tool. This final report discusses work done on developing dielectric sensing to monitor polymeric material cure and which provides a fundamental understanding of the underlying science for the use of frequency dependent dielectri sensors to monitor the cure process.

  13. Frequency-Dependent Selection in a Periodic Environment

    PubMed Central

    Forster, Robert; Wilke, Claus O.

    2007-01-01

    We examine the action of natural selection in a periodically changing environment where two competing strains are specialists respectively for each environmental state. When the relative fitness of the strains is subject to a very general class of frequency-dependent selection, we show that coexistence rather than extinction is the likely outcome. This coexistence may be a stable periodic equilibrium, stable limit cycles of varying lengths, or be deterministically chaotic. Our model is applicable to the population dynamics commonly found in many types of viruses. PMID:17940581

  14. Stress-Transfer Micromechanics For Fiber Length with a Photocure Vinyl Ester Composite

    PubMed Central

    Petersen, Richard C.; Lemons, Jack E.; McCracken, Michael S.

    2014-01-01

    The objective was to test how increasing fiber length above the critical length would influence mechanical properties and fracture crack propagation. Micromechanics considering fiber/matrix stress-transfer was used to evaluate the results in addition to a shear debonding volume percent correction term necessary for the final analysis. Fiber lengths of 0.5, 1.0, 2.0, 3.0, and 6.0 mm with 9 μm diameters were added into a photocure vinyl ester particulate-filled composite at a uniform 28.2 vol%. Mechanical flexural testing was performed using four-point fully articulated fixtures for samples measuring 2 × 2 × 50 mm3 across a 40 mm span. Fiber length correlated with improved mechanical properties for flexural strength, modulus, yield strength, strain, work of fracture, and strain energy release, p < 0.001. In addition, sample fracture depth significantly decreased with increasing fiber lengths, p < 0.00001. All mechanical properties correlated significantly as predictors for fracture failure, p < 0.000001, and as estimators for each other, p < 0.0001. The stress-transfer micromechanics for fiber length were improved upon for strength by including a simple correction factor to account for loss of fiber volume percent related to cracks deflecting around debonded fiber ends. In turn, the elastic property of modulus was shown to exhibit a tendency to follow stress-transfer micromechanics. PMID:25382894

  15. Effects of EB irradiation on stress-strain curves for carbon fiber reinforced composite materials

    NASA Astrophysics Data System (ADS)

    Kobayashi, H.; Yamada, K.; Mizutani, A.; Uchida, N.; Tanaka, K.; Nishi, Yoshitake

    2004-02-01

    In order to evaluate influence of electron beam (EB) irradiation on elasticity and stress- strain curve of composite materials reinforced by carbon fiber (CF), carbon fiber reinforced polymer (CFRP) and carbon fiber reinforced graphite (C/C) were treated by EB irradiation of 0.3 MGy. Since the EB strengthening was mainly dominated by the ductility enhancements of carbon fiber and matrix of epoxy resin, EB irradiation enlarged fracture stress and enhanced fracture strain of CFRP. Furthermore, EB irradiation slightly enhanced bending elasticity of CFRP and largely enhanced the initial spring constant related to elasticity of C/C coil. Although the elasticity enhancement of carbon fibers did not largely contribute that of CFRP, that of treated graphite matrix in C/C mainly caused the C/C coil elasticity enhancement by EB irradiation. Such a new treatment is a dream-worthy technology for structural materials to be applied in the fields of future engineering.

  16. Removal of interference from fetal MEG by frequency dependent subtraction

    PubMed Central

    Vrba, J.; McCubbin, J.; Govindan, R.B.; Vairavan, S.; Murphy, P.; Preissl, H.; Lowery, C.L.; Eswaran, H.

    2011-01-01

    Fetal magnetoencephalography (fMEG) recordings are contaminated by maternal and fetal magnetocardiography (MCG) signals and by other biological and environmental interference. Currently, all methods for the attenuation of these signals are based on a time-domain approach. We have developed and tested a frequency dependent procedure for removal of MCG and other interference from the fMEG recordings. The method uses a set of reference channels and performs subtraction of interference in the frequency domain (SUBTR). The interference-free frequency domain signals are converted back to the time domain. We compare the performance of the frequency dependent approach with our present approach for MCG attenuation based on orthogonal projection (OP). SUBTR has an advantage over OP and similar template approaches because it removes not only the MCG but also other small amplitude biological interference, avoids the difficulties with inaccurate determination of the OP operator, provides more consistent and stable fMEG results, does not cause signal redistribution, and if references are selected judiciously, it does not reduce fMEG signal amplitude. SUBTR was found to perform well in simulations and on real fMEG recordings, and has a potential to improve the detection of fetal brain signals. The SUBTR removes interference without the need for a model of the individual interference sources. The method may be of interest for any sensor array noise reduction application where signal-free reference channels are available. PMID:21930216

  17. Direct measurements of the frequency-dependent dielectrophoresis force.

    PubMed

    Wei, Ming-Tzo; Junio, Joseph; Ou-Yang, H Daniel

    2009-01-01

    Dielectrophoresis (DEP), the phenomenon of directed motion of electrically polarizable particles in a nonuniform electric field, is promising for applications in biochemical separation and filtration. For colloidal particles in suspension, the relaxation of the ionic species in the shear layer gives rise to a frequency-dependent, bidirectional DEP force in the radio frequency range. However, quantification methods of the DEP force on individual particles with the pico-Newton resolution required for the development of theories and design of device applications are lacking. We report the use of optical tweezers as a force sensor and a lock-in phase-sensitive technique for analysis of the particle motion in an amplitude modulated DEP force. The coherent detection and sensing scheme yielded not only unprecedented sensitivity for DEP force measurements, but also provided a selectivity that clearly distinguishes the pure DEP force from all the other forces in the system, including electrophoresis, electro-osmosis, heat-induced convection, and Brownian forces, all of which can hamper accurate measurements through other existing methods. Using optical tweezers-based force transducers already developed in our laboratory, we have results that quantify the frequency-dependent DEP force and the crossover frequency of individual particles with this new experimental method. PMID:19693384

  18. Reversible frequency-dependent switches in male mate choice.

    PubMed

    van Gossum, H; Stoks, R; De Bruyn, L

    2001-01-01

    Current sexual-selection theories predict that mating should occur preferentially with the highest-quality partner, and assume that for distinguishing among potential mates the choosy sex applies an internal representation of the characteristics of the desired mate, i.e. a template. Binary choice experiments were performed to test male mate choice between two different female colour morphs in the damselfly Ischnura elegans. Choice experiments were conducted before and after an habituation period, during which males were exposed to only one female colour morph. Given the choice between the two female morphs, males did exhibit a choice for the most recently experienced female morph. This is the first evidence for a reversible switch in mate choice in a frequency-dependent way. In contrast with previous studies on mate choice, template formation in male I. elegans seems not to be based on quality. Switching mate choice in a frequency-dependent manner, choosing the most common morph, probably allows males to minimize their search efforts and to maximize fitness. PMID:12123302

  19. Spatial frequency dependence of target signature for infrared performance modeling

    NASA Astrophysics Data System (ADS)

    Du Bosq, Todd; Olson, Jeffrey

    2011-05-01

    The standard model used to describe the performance of infrared imagers is the U.S. Army imaging system target acquisition model, based on the targeting task performance metric. The model is characterized by the resolution and sensitivity of the sensor as well as the contrast and task difficulty of the target set. The contrast of the target is defined as a spatial average contrast. The model treats the contrast of the target set as spatially white, or constant, over the bandlimit of the sensor. Previous experiments have shown that this assumption is valid under normal conditions and typical target sets. However, outside of these conditions, the treatment of target signature can become the limiting factor affecting model performance accuracy. This paper examines target signature more carefully. The spatial frequency dependence of the standard U.S. Army RDECOM CERDEC Night Vision 12 and 8 tracked vehicle target sets is described. The results of human perception experiments are modeled and evaluated using both frequency dependent and independent target signature definitions. Finally the function of task difficulty and its relationship to a target set is discussed.

  20. Nucleation and Crystallization as Induced by Bending Stress in Lithium Silicate Glass Fibers

    NASA Technical Reports Server (NTRS)

    Reis, Signo T.; Kim, Cheol W.; Brow, Richard K.; Ray, Chandra S.

    2003-01-01

    Glass Fibers of Li2O.2SiO2 (LS2) and Li2O.1.6SiO2 (LS1.6) compositions were heated near, but below, the glass transition temperature for different times while subjected to a constant bending stress of about 1.2 GPa. The nucleation density and the crystallization tendency estimated by differential thermal analysis (DTA) of a glass sample in the vicinity of the maximum of the bending stress increased relative to that of stress-free glass fibers. LS2 glass fibers were found more resistant to nucleation and crystallization than the Ls1.6 glass fibers. These results are discussed in regards to shear thinning effects on glass stability.

  1. Collagen fibers reduce stresses and stabilize motion of aortic valve leaflets during systole.

    PubMed

    De Hart, J; Peters, G W M; Schreurs, P J G; Baaijens, F P T

    2004-03-01

    The effect of collagen fibers on the mechanics and hemodynamics of a trileaflet aortic valve contained in a rigid aortic root is investigated in a numerical analysis of the systolic phase. Collagen fibers are known to reduce stresses in the leaflets during diastole, but their role during systole has not been investigated in detail yet. It is demonstrated that also during systole these fibers substantially reduce stresses in the leaflets and provide smoother opening and closing. Compared to isotropic leaflets, collagen reinforcement reduces the fluttering motion of the leaflets. Due to the exponential stress-strain behavior of collagen, the fibers have little influence on the initial phase of the valve opening, which occurs at low strains, and therefore have little impact on the transvalvular pressure drop. PMID:14757449

  2. Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

    2004-01-01

    The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

  3. A numerical algorithm for stress integration of a fiber-fiber kinetics model with Coulomb friction for connective tissue

    NASA Astrophysics Data System (ADS)

    Kojic, M.; Mijailovic, S.; Zdravkovic, N.

    Complex behaviour of connective tissue can be modeled by a fiber-fiber kinetics material model introduced in Mijailovic (1991), Mijailovic et al. (1993). The model is based on the hypothesis of sliding of elastic fibers with Coulomb and viscous friction. The main characteristics of the model were verified experimentally in Mijailovic (1991), and a numerical procedure for one-dimensional tension was developed considering sliding as a contact problem between bodies. In this paper we propose a new and general numerical procedure for calculation of the stress-strain law of the fiber-fiber kinetics model in case of Coulomb friction. Instead of using a contact algorithm (Mijailovic 1991), which is numerically inefficient and never enough reliable, here the history of sliding along the sliding length is traced numerically through a number of segments along the fiber. The algorithm is simple, efficient and reliable and provides solutions for arbitrary cyclic loading, including tension, shear, and tension and shear simultaneously, giving hysteresis loops typical for soft tissue response. The model is built in the finite element technique, providing the possibility of its application to general and real problems. Solved examples illustrate the main characteristics of the model and of the developed numerical method, as well as its applicability to practical problems. Accuracy of some results, for the simple case of uniaxial loading, is verified by comparison with analytical solutions.

  4. Stress-induced birefringence and fabrication of in-fiber polarization devices by controlled femtosecond laser irradiations.

    PubMed

    Yuan, Lei; Cheng, Baokai; Huang, Jie; Liu, Jie; Wang, Hanzheng; Lan, Xinwei; Xiao, Hai

    2016-01-25

    Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core along the fiber axis using a femtosecond laser. The stress-induced birefringence was estimated to be 2.4 × 10(-4) at the wavelength of 1550 nm. By adding the desired numbers of stressed rods, an in-fiber quarter waveplate was fabricated with a insertion loss of 0.19 dB. The stress-induced birefringence was further explored to fabricate in-fiber polarizers based on the polarization-dependent long-period fiber grating (LPFG) structure. A polarization extinction ratio of more than 20 dB was observed at the resonant wavelength of 1523.9 nm. The in-fiber polarization devices may be useful in optical communications and fiber optic sensing applications. PMID:26832490

  5. Residual stresses in silicon carbide-zircon composites from thermal expansion measurements and fiber pushout tests

    SciTech Connect

    Reddy, S.K.; Kumar, S.; Singh, R.N. . Dept. of Materials Science and Engineering)

    1994-12-01

    Coefficients of thermal expansion (CTE) in the axial direction of two types of SiC fibers, monolithic zircon, monolithic SiC, and several SiC[sub f]-zircon composites were measured in the temperature range of 50 to 1,380 C. The measured CTE values of composites were compared with values predicted by the rule-of-mixtures approach, and a small difference in measured and calculated values was ascribed to the nature of interfacial bonding and assumptions implicit in the rule-of-mixture approach. Fiber pushout tests were performed on these composites and the residual stresses were extracted from the analysis of the load-displacement plots in terms of the shear-lag and progressive debonding models. The radial and axial residual stresses arising from the mismatch in CTE were calculated and compared with values obtained from the fiber pushout tests. The fiber pushout tests in general produced lower values of the residual stresses, but the residual stresses obtained using shear-lag analysis were in good agreement with the calculated values based on the CTE mismatch in composites with lower values of the interfacial shear stress. The influence of anisotropic fiber expansion in the radial and axial directions on the radial and axial residual stresses in composites were also examined.

  6. High extensibility of stress fibers revealed by in vitro micromanipulation with fluorescence imaging

    SciTech Connect

    Matsui, Tsubasa S.; Sato, Masaaki; Deguchi, Shinji

    2013-05-10

    Highlights: •We isolate contractile stress fibers from vascular smooth muscle cells. •We measure the extensibility of individual stress fibers. •We present the first direct evidence that individual stress fibers are highly extensible. •We quantitatively determine the local strain along the length of stress fibers. •The high extensibility we found is beyond that explained by a conventional model. -- Abstract: Stress fibers (SFs), subcellular bundles of actin and myosin filaments, are physically connected at their ends to cell adhesions. The intracellular force transmitted via SFs plays an essential role in cell adhesion regulation and downstream signaling. However, biophysical properties intrinsic to individual SFs remain poorly understood partly because SFs are surrounded by other cytoplasmic components that restrict the deformation of the embedded materials. To characterize their inherent properties independent of other structural components, we isolated SFs from vascular smooth muscle cells and mechanically stretched them by in vitro manipulation while visualizing strain with fluorescent quantum dots attached along their length. SFs were elongated along their entire length, with the length being approximately 4-fold of the stress-free length. This surprisingly high extensibility was beyond that explained by the tandem connection of actin filaments and myosin II bipolar filaments present in SFs, thus suggesting the involvement of other structural components in their passive biophysical properties.

  7. Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

    NASA Technical Reports Server (NTRS)

    Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

    1995-01-01

    Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

  8. Research on the fiber Bragg grating sensor for the shock stress measurement

    PubMed Central

    Deng, Xiangyang; Chen, Guanghua; Peng, Qixian; Li, Zeren; Meng, Jianhua; Liu, Jun

    2011-01-01

    A fiber Bragg grating (FBG) sensor with an unbalanced Mach-Zehnder fiber interferometer for the shock stress measurement is proposed and demonstrated. An analysis relationship between the shock stress and the central reflection wavelength shift of the FBG is firstly derived. In this sensor, the optical path difference of the unbalanced Mach-Zehnder fiber interferometer is ∼3.1 mm and the length of the FBG is 2 mm. An arctangent function reduction method, which can avoid sine function's insensitive zone where the shock stress measurement has a reduced accuracy, is presented. A shock stress measurement of water driven by one stage gun (up to 1.4 GPa), with good theoretical accuracy (∼10%), is launched. PMID:22047282

  9. Micromechanics analysis of space simulated thermal deformations and stresses in continuous fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Bowles, David E.

    1990-01-01

    Space simulated thermally induced deformations and stresses in continuous fiber reinforced composites were investigated with a micromechanics analysis. The investigation focused on two primary areas. First, available explicit expressions for predicting the effective coefficients of thermal expansion (CTEs) for a composite were compared with each other, and with a finite element (FE) analysis, developed specifically for this study. Analytical comparisons were made for a wide range of fiber/matrix systems, and predicted values were compared with experimental data. The second area of investigation focused on the determination of thermally induced stress fields in the individual constituents. Stresses predicted from the FE analysis were compared to those predicted from a closed-form solution to the composite cylinder (CC) model, for two carbon fiber/epoxy composites. A global-local formulation, combining laminated plate theory and FE analysis, was used to determine the stresses in multidirectional laminates. Thermally induced damage initiation predictions were also made.

  10. Dissecting Regional Variations in Stress Fiber Mechanics in Living Cells with Laser Nanosurgery

    SciTech Connect

    Tanner, Kandice; Boudreau, Aaron; Bissell, Mina J; Kumar, Sanjay

    2010-03-02

    The ability of a cell to distribute contractile stresses across the extracellular matrix in a spatially heterogeneous fashion underlies many cellular behaviors, including motility and tissue assembly. Here we investigate the biophysical basis of this phenomenon by using femtosecond laser nanosurgery to measure the viscoelastic recoil and cell-shape contributions of contractile stress fibers (SFs) located in specific compartments of living cells. Upon photodisruption and recoil, myosin light chain kinase-dependent SFs located along the cell periphery display much lower effective elasticities and higher plateau retraction distances than Rho-associated kinase-dependent SFs located in the cell center, with severing of peripheral fibers uniquely triggering a dramatic contraction of the entire cell within minutes of fiber irradiation. Image correlation spectroscopy reveals that when one population of SFs is pharmacologically dissipated, actin density flows toward the other population. Furthermore, dissipation of peripheral fibers reduces the elasticity and increases the plateau retraction distance of central fibers, and severing central fibers under these conditions triggers cellular contraction. Together, these findings show that SFs regulated by different myosin activators exhibit different mechanical properties and cell shape contributions. They also suggest that some fibers can absorb components and assume mechanical roles of other fibers to stabilize cell shape.

  11. A frequency dependent preconditioned wavelet method for atmospheric tomography

    NASA Astrophysics Data System (ADS)

    Yudytskiy, Mykhaylo; Helin, Tapio; Ramlau, Ronny

    2013-12-01

    Atmospheric tomography, i.e. the reconstruction of the turbulence in the atmosphere, is a main task for the adaptive optics systems of the next generation telescopes. For extremely large telescopes, such as the European Extremely Large Telescope, this problem becomes overly complex and an efficient algorithm is needed to reduce numerical costs. Recently, a conjugate gradient method based on wavelet parametrization of turbulence layers was introduced [5]. An iterative algorithm can only be numerically efficient when the number of iterations required for a sufficient reconstruction is low. A way to achieve this is to design an efficient preconditioner. In this paper we propose a new frequency-dependent preconditioner for the wavelet method. In the context of a multi conjugate adaptive optics (MCAO) system simulated on the official end-to-end simulation tool OCTOPUS of the European Southern Observatory we demonstrate robustness and speed of the preconditioned algorithm. We show that three iterations are sufficient for a good reconstruction.

  12. Frequency-dependent complex modulus of the uterus: preliminary results

    NASA Astrophysics Data System (ADS)

    Kiss, Miklos Z.; Hobson, Maritza A.; Varghese, Tomy; Harter, Josephine; Kliewer, Mark A.; Hartenbach, Ellen M.; Zagzebski, James A.

    2006-08-01

    The frequency-dependent complex moduli of human uterine tissue have been characterized. Quantification of the modulus is required for developing uterine ultrasound elastography as a viable imaging modality for diagnosing and monitoring causes for abnormal uterine bleeding and enlargement, as well assessing the integrity of uterine and cervical tissue. The complex modulus was measured in samples from hysterectomies of 24 patients ranging in age from 31 to 79 years. Measurements were done under small compressions of either 1 or 2%, at low pre-compression values (either 1 or 2%), and over a frequency range of 0.1-100 Hz. Modulus values of cervical tissue monotonically increased from approximately 30-90 kPa over the frequency range. Normal uterine tissue possessed modulus values over the same range, while leiomyomas, or uterine fibroids, exhibited values ranging from approximately 60-220 kPa.

  13. Improving Planck calibration by including frequency-dependent relativistic corrections

    SciTech Connect

    Quartin, Miguel; Notari, Alessio E-mail: notari@ffn.ub.es

    2015-09-01

    The Planck satellite detectors are calibrated in the 2015 release using the 'orbital dipole', which is the time-dependent dipole generated by the Doppler effect due to the motion of the satellite around the Sun. Such an effect has also relativistic time-dependent corrections of relative magnitude 10{sup −3}, due to coupling with the 'solar dipole' (the motion of the Sun compared to the CMB rest frame), which are included in the data calibration by the Planck collaboration. We point out that such corrections are subject to a frequency-dependent multiplicative factor. This factor differs from unity especially at the highest frequencies, relevant for the HFI instrument. Since currently Planck calibration errors are dominated by systematics, to the point that polarization data is currently unreliable at large scales, such a correction can in principle be highly relevant for future data releases.

  14. Frequency-dependent viability in mutant strains of Drosophila melanogaster.

    PubMed

    Curtsinger, J W; Sheen, F M

    1991-01-01

    We investigated the effects of genotypic frequencies on egg-to-adult viabilities in pairwise combinations of four strains of Drosophila melanogaster. The experiments involved mixture of a total of 42,000 eggs in varying proportions under controlled densities and observation of surviving adults. Viabilities were found to depend on frequencies in several genotypic combinations. In the most extreme case, the absolute viability of cn;bw females increased monotonically from 54% when common to 70% when rare. The results illustrate several statistical and methodological problems that might explain why some experiments have failed to detect frequency-dependent viabilities. These problems include heterogeneity between replications, sex differences in susceptibility to competition, and strong dependence of the experimental outcome on the choice of competitor genotypes. PMID:1901577

  15. Frequency-dependent ultrasound-induced transformation in E. coli.

    PubMed

    Deeks, Jeremy; Windmill, James; Agbeze-Onuma, Maduka; Kalin, Robert M; Argondizza, Peter; Knapp, Charles W

    2014-12-01

    Ultrasound-enhanced gene transfer (UEGT) is continuing to gain interest across many disciplines; however, very few studies investigate UEGT efficiency across a range of frequencies. Using a variable frequency generator, UEGT was tested in E. coli at six ultrasonic frequencies. Results indicate frequency can significantly influence UEGT efficiency positively and negatively. A frequency of 61 kHz improved UEGT efficiency by ~70 % higher, but 99 kHz impeded UEGT to an extent worse than no ultrasound exposure. The other four frequencies (26, 133, 174, and 190 kHz) enhanced transformation compared to no ultrasound, but efficiencies did not vary. The influence of frequency on UEGT efficiency was observed across a range of operating frequencies. It is plausible that frequency-dependent dynamics of mechanical and chemical energies released during cavitational-bubble collapse (CBC) are responsible for observed UEGT efficiencies.

  16. Frequency-dependent graded reflectivity mirror: characterization and laser implementation.

    PubMed

    Keselbrener, M; Ruschin, S

    1999-10-20

    We present a theoretical and experimental investigation of a new family of variable reflectivity mirrors, based on frustrated total internal reflection and interference effects. These mirrors are sensitive to frequency in the sense that their transverse reflectivity distribution changes significantly as a function of the frequency of light. The mirror reported here shows total power reflectivity changes of 50% within 8.0 GHz. The mirror was tested as the output coupler of an unstable resonator in a Nd:YAG laser working in the free-running regime. This configuration was compared with the standard stable multimode resonator configuration. The beam divergence was reduced by more than 1 order of magnitude and the output power was reduced by only 10%. The laser resonator mode competition that is due to the frequency-dependent mirror reflectivity distribution is discussed. PMID:18324158

  17. Improving Planck calibration by including frequency-dependent relativistic corrections

    NASA Astrophysics Data System (ADS)

    Quartin, Miguel; Notari, Alessio

    2015-09-01

    The Planck satellite detectors are calibrated in the 2015 release using the "orbital dipole", which is the time-dependent dipole generated by the Doppler effect due to the motion of the satellite around the Sun. Such an effect has also relativistic time-dependent corrections of relative magnitude 10-3, due to coupling with the "solar dipole" (the motion of the Sun compared to the CMB rest frame), which are included in the data calibration by the Planck collaboration. We point out that such corrections are subject to a frequency-dependent multiplicative factor. This factor differs from unity especially at the highest frequencies, relevant for the HFI instrument. Since currently Planck calibration errors are dominated by systematics, to the point that polarization data is currently unreliable at large scales, such a correction can in principle be highly relevant for future data releases.

  18. Frequency-dependence stabilizes competitive interactions among four annual plants.

    PubMed

    Harpole, W Stanley; Suding, Katharine N

    2007-12-01

    It is the combination of large fitness differences and strong stabilizing mechanisms that often constitute niche-based explanations for species abundance patterns. Despite the importance of this assumption to much of community ecology, empirical evidence is surprisingly limited. Empirical tests are critical because many abundance patterns are also consistent with neutral-based alternatives (that assume no fitness differences or stabilization). We quantified interactions of four annual grassland species in two-species mixtures at varying frequencies. We found evidence of strong negative frequency-dependent stabilization, where scaled population growth rates increased with decreasing frequency for all four species. There was also a consistent competitive hierarchy among these species indicative of strong fitness differences that, in most cases, suggested potential competitive exclusion despite the observed strong stabilization.

  19. FREQUENCY DEPENDENCE OF PULSE WIDTH FOR 150 RADIO NORMAL PULSARS

    SciTech Connect

    Chen, J. L.; Wang, H. G.

    2014-11-01

    The frequency dependence of the pulse width is studied for 150 normal pulsars, mostly selected from the European Pulsar Network, for which the 10% multifrequency pulse widths can be well fit with the Thorsett relationship W {sub 10} = Aν{sup μ} + W {sub 10,} {sub min}. The relative fraction of pulse width change between 0.4 GHz and 4.85 GHz, η = (W {sub 4.85} – W {sub 0.4})/W {sub 0.4}, is calculated in terms of the best-fit relationship for each pulsar. It is found that 81 pulsars (54%) have η < –10% (group A), showing considerable profile narrowing at high frequencies, 40 pulsars (27%) have –10% ≤η ≤ 10% (group B), meaning a marginal change in pulse width, and 29 pulsars (19%) have η > 10% (group C), showing a remarkable profile broadening at high frequencies. The fractions of the group-A and group-C pulsars suggest that the profile narrowing phenomenon at high frequencies is more common than the profile broadening phenomenon, but a large fraction of the group-B and group-C pulsars (a total of 46%) is also revealed. The group-C pulsars, together with a portion of group-B pulsars with slight pulse broadening, can hardly be explained using the conventional radius-to-frequency mapping, which only applies to the profile narrowing phenomenon. Based on a recent version of the fan beam model, a type of broadband emission model, we propose that the diverse frequency dependence of pulse width is a consequence of different types of distribution of emission spectra across the emission region. The geometrical effect predicting a link between the emission beam shrinkage and spectrum steepening is tested but disfavored.

  20. Myosin II phosphorylation and the dynamics of stress fibers in serum-deprived and stimulated fibroblasts.

    PubMed Central

    Giuliano, K A; Kolega, J; DeBiasio, R L; Taylor, D L

    1992-01-01

    The actin-based cytomatrix generates stress fibers containing a host of proteins including actin and myosin II and whose dynamics are easily observable in living cells. We developed a dual-radioisotope-based assay of myosin II phosphorylation and applied it to serum-deprived fibroblasts treated with agents that modified the dynamic distribution of stress fibers and/or altered the phosphorylation state of myosin II. Serum-stimulation induced an immediate and sustained increase in the level of myosin II heavy chain (MHC) and 20-kDa light chain (LC20) phosphorylation over the same time course that it caused stress fiber contraction. Cytochalasin D, shown to cause stress fiber fragmentation and contraction, had little effect on myosin II phosphorylation. Okadaic acid, a protein phosphatase inhibitor, induced a delayed but massive cell shortening preceded by a large increase in MHC and LC20 phosphorylation. Staurosporine, a kinase inhibitor known to effect dissolution but not contraction of stress fibers, immediately caused an increase in MHC and LC20 phosphorylation followed within minutes by the dephosphorylation of LC20 to a level below that of untreated cells. We therefore propose that the contractility of the actin-based cytomatrix is regulated by both modulating the activity of molecular motors such as myosin II and by altering the gel structure in such a manner as to either resist or yield to the tension applied by the motors. Images PMID:1421576

  1. A Fiber Optic Sensor Sensitive To Normal Pressure And Shear Stress

    NASA Astrophysics Data System (ADS)

    Cuomo, Frank W.; Kidwell, Robert S.; Hu, Andong

    1986-11-01

    A fiber optic lever sensing technique that can be used to measure normal pressure as well as shear stresses is discussed. This method uses three unequal fibers combining small size and good sensitivity. Static measurements appear to confirm the theoretical models predicted by geometrical optics and dynamic tests performed at frequencies up to 10 kHz indicate a flat response within this frequency range. These sensors are intended for use in a low speed wind tunnel environment.

  2. Thermal Stress-Induced Depolarization Loss in Conventional and Panda-Shaped Photonic Crystal Fiber Lasers

    NASA Astrophysics Data System (ADS)

    Mousavi, Seyedeh Laleh; Sabaeian, Mohammad

    2016-07-01

    We report on the modeling of the depolarization loss in the conventional and panda-shaped photonic crystal fiber lasers (PCFLs) due to the self-heating of the fiber, which we call it thermal stress-induced depolarization loss (TSIDL). We first calculated the temperature distribution over the fiber cross sections and then calculated the thermal stresses/strains as a function of heat load per meter. Thermal stress-induced birefringence (TSIB), which is defined as |n x - n y |, in the core and cladding regions was calculated. Finally, TSIDL was calculated for the conventional and panda-shaped PCFLs as a function of fiber length and, respectively, saturated values of 22 and 25 % were obtained which were independent of heat load per meter. For panda-shaped PCFLs, prior to being saturated, an oscillating and damping behavior against the fiber length was seen where in some lengths reached 35 %. The results are close to an experimental value of 30 % reported for a pulsed PCFL (Limpert et al., Opt Express 12:1313-1319, 2004) where the authors reported a degree of polarization of 70 % (i.e., a depolarization of 30 %). The most important result of this work is a saturation behavior of TSIDL at long-enough lengths of the fiber laser which is independent of heat load per meter. To our knowledge, this the first report of TSIBL for PCFLs.

  3. Thermal Stress-Induced Depolarization Loss in Conventional and Panda-Shaped Photonic Crystal Fiber Lasers

    NASA Astrophysics Data System (ADS)

    Mousavi, Seyedeh Laleh; Sabaeian, Mohammad

    2016-10-01

    We report on the modeling of the depolarization loss in the conventional and panda-shaped photonic crystal fiber lasers (PCFLs) due to the self-heating of the fiber, which we call it thermal stress-induced depolarization loss (TSIDL). We first calculated the temperature distribution over the fiber cross sections and then calculated the thermal stresses/strains as a function of heat load per meter. Thermal stress-induced birefringence (TSIB), which is defined as | n x - n y |, in the core and cladding regions was calculated. Finally, TSIDL was calculated for the conventional and panda-shaped PCFLs as a function of fiber length and, respectively, saturated values of 22 and 25 % were obtained which were independent of heat load per meter. For panda-shaped PCFLs, prior to being saturated, an oscillating and damping behavior against the fiber length was seen where in some lengths reached 35 %. The results are close to an experimental value of 30 % reported for a pulsed PCFL (Limpert et al., Opt Express 12:1313-1319, 2004) where the authors reported a degree of polarization of 70 % (i.e., a depolarization of 30 %). The most important result of this work is a saturation behavior of TSIDL at long-enough lengths of the fiber laser which is independent of heat load per meter. To our knowledge, this the first report of TSIBL for PCFLs.

  4. Microscale Modelling of the Frequency Dependent Resistivity of Porous Media

    NASA Astrophysics Data System (ADS)

    Volkmann, J.; Klitzsch, N.; Mohnke, O.; Clauser, C.

    2009-12-01

    In geophysics frequency dependent complex resistivity measurements are called Spectral Induced Polarization (SIP). In other fields this method is known as Impedance Spectroscopy. In the last two decades many empirical relations were proposed which relate the frequency dependent electrical properties of water saturated rocks to structural properties such as pore radius and inner surface area, or to hydraulic conductivity. Unfortunately, these relations are not universal; they apply only for specific rock types and water compositions. In order to quantify the influence of inner rock structure (as well as of electrochemical water and rock properties) on the frequency dependent electrical properties we model the charge transport processes at the pore space using Comsol Multiphysics. In the frequency domain the effect of Induced Polarization (IP) is characterised by a phase shift between a measured electric current and an alternating voltage applied to the ground. A possible origin of this behaviour particularly for nonconducting rock minerals can be seen in the membrane polarization model as proposed by Marshall and Madden. This model describes a system of electrolyte filled pores. Different mobilities of cations and anions in the small pores cause a membrane effect and thus an electrical polarization. We aim to find a more realistic way of modelling the membrane polarization effect than using the simple Marshall and Madden model. The electric double layer, the origin of the Induced Polarization effect, is caused by surface charges located at the electrolyte rock interface. Thus, the EDL as a boundary effect is accounted for by reduced ion mobilities at the inner surface area. The governing equations and boundary conditions for a system of larger and smaller pores with applied voltage are expressed in frequency domain using a time harmonic approach, the electric current is determined to obtain information about amplitude and phase of the complex resistivity. The

  5. Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality

    PubMed Central

    Davis, R. F.; Earl, H. J.; Timper, P.

    2014-01-01

    Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive. PMID:24987162

  6. Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality.

    PubMed

    Davis, R F; Earl, H J; Timper, P

    2014-06-01

    Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive. PMID:24987162

  7. Tensile creep and stress-rupture behavior of polymer derived SiC fibers

    SciTech Connect

    Yun, H.M.; Goldsby, J.C.; Dicarlo, J.A.

    1994-08-01

    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400 C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1 percent creep strengths than as-produced as well as-coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  8. Tensile creep and stress-rupture behavior of polymer derived SiC fibers

    SciTech Connect

    Yun, H.M.; Goldsby, J.C.; DiCarlo, J.A.

    1994-12-31

    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400{degrees}C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1% creep strengths than as-produced as well as coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  9. Time and frequency dependent rheology of reactive silica gels.

    PubMed

    Wang, Miao; Winter, H Henning; Auernhammer, Günter K

    2014-01-01

    In a mixture of sodium silicate and low concentrated sulfuric acid, nano-sized silica particles grow and may aggregate to a system spanning gel network. We studied the influence of the finite solubility of silica at high pH on the mechanical properties of the gel with classical and piezo-rheometers. Direct preparation of the gel sample in the rheometer cell avoided any pre-shear of the gel structure during the filling of the rheometer. The storage modulus of the gel grew logarithmically with time with two distinct growth laws. The system passes the gel point very quickly but still shows relaxation at low frequency, typically below 6 rad/s. We attribute this as a sign of structural rearrangements due to the finite solubility of silica at high pH. The reaction equilibrium between bond formation and dissolution maintains a relatively large bond dissolution rate, which leads to a finite life time of the bonds and behavior similar to physical gels. This interpretation is also compatible with the logarithmic time dependence of the storage modulus. The frequency dependence was more pronounced for lower water concentrations, higher temperatures and shorter reaction times. With two relaxation models (the modified Cole-Cole model and the empirical Baumgaertel-Schausberger-Winter model) we deduced characteristic times from the experimental data. Both models approximately described the data and resulted in similar relaxation times.

  10. The frequency dependence of scattering imprints on pulsar observations

    NASA Astrophysics Data System (ADS)

    Geyer, M.; Karastergiou, A.

    2016-11-01

    Observations of pulsars across the radio spectrum are revealing a dependence of the characteristic scattering time (τ) on frequency, which is more complex than the simple power law with a theoretically predicted power-law index. In this paper, we investigate these effects using simulated pulsar data at frequencies below 300 MHz. We investigate different scattering mechanisms, namely isotropic and anisotropic scattering, by thin screens along the line of sight, and the particular frequency-dependent impact on pulsar profiles and scattering time-scales of each. We also consider how the screen shape, location and offset along the line of sight lead to specific observable effects. We evaluate how well forward fitting techniques perform in determining τ. We investigate the systematic errors in τ associated with the use of an incorrect fitting method and with the determination of an off-pulse baseline. Our simulations provide examples of average pulse profiles at various frequencies. Using these, we compute spectra of τ and mean flux for different scattering setups. We identify setups that lead to deviations from the simple theoretical picture. This work provides a framework for interpretation of upcoming low-frequency data, both in terms of modelling the interstellar medium and understanding intrinsic emission properties of pulsars.

  11. Inverse characterisation of frequency-dependent properties of adhesives

    NASA Astrophysics Data System (ADS)

    Rouleau, Lucie; Deü, Jean-François; Legay, Antoine

    2016-09-01

    Traditional damping treatments are usually applied to the vibrating structure by means of adhesive layers. Environmental parameters, such as frequencies of excitation, may influence the behaviour of the bonding layer and modify the damping efficiency of the treatment. Therefore it is desired to take into account the viscoelastic behaviour of the adhesive layer in the finite element model. The goal of this work is to present a procedure to characterise and model the adhesive layer. To that purpose, an experimental-numerical method for inverse characterisation of the frequency dependent properties of the adhesive layer is applied. The proposed inverse approach is based on a four-parameter fractional derivative model whose parameters are identified by minimising the difference between the simulated and the measured dynamic response of a multi-layered structure assembled by bonding. In the finite element model used for the optimisation, the adhesive layer is modelled by interface finite elements. The influence of the adhesive layer on the efficiency of a damping treatment is evidenced by performing dynamic testing on a sandwich structure with a viscoelastic core, assembled by bonding. The proposed approach is applied to the characterisation of a pressure-sensitive adhesive.

  12. Comment on ``Frequency-dependent dispersion in porous media''

    NASA Astrophysics Data System (ADS)

    Davit, Yohan; Quintard, Michel

    2012-07-01

    In a recent paper, Valdès-Parada and Alvarez-Ramirez [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.84.031201 84, 031201 (2011)] used the technique of volume averaging to derive a “frequency-dependent” dispersion tensor, Dγ*, the goal of which is to describe solute transport in porous media undergoing periodic processes. We describe two issues related to this dispersion tensor. First, we demonstrate that the definition of Dγ* is erroneous and derive a corrected version, Dγ*c. With this modification, the approach of Valdès-Parada and Alvarez-Ramirez becomes strictly equivalent to the one devised by Moyne [Adv. Water Res.10.1016/S0309-1708(96)00023-1 20, 63 (1997)]. Second, we show that the term “frequency-dependent dispersion” is misleading because Dγ* and Dγ*c do not depend on the process operating frequency, χ. The study carried out by Valdès-Parada and Alvarez-Ramirez represents a spectral analysis of the relaxation of Dγ* towards its steady-state, independent of any periodic operation or excitation.

  13. Frequency-dependent energy harvesting via magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Sayyaadi, Hassan; Askari Farsangi, Mohammad Amin

    2015-11-01

    This paper is focused on presenting an accurate framework to describe frequency-dependent energy harvesting via magnetic shape memory alloys (MSMAs). Modeling strategy incorporates the phenomenological constitutive model developed formerly together with the magnetic diffusion equation. A hyperbolic hardening function is employed to define reorientation-induced strain hardening in the material, and the diffusion equation is used to add dynamic effects to the model. The MSMA prismatic specimen is surrounded by a pickup coil, and the induced voltage during martensite-variant reorientation is investigated with the help of Faraday’s law of magnetic field induction. It has been shown that, in order to harvest the maximum RMS voltage in the MSMA-based energy harvester, an optimum value of bias magnetic field exists, which is the corresponding magnetic field for the start of pseudoelasticity behavior. In addition, to achieve a more compact energy harvester with higher energy density, a specimen with a lower aspect ratio can be chosen. As the main novelty of the paper, it is found that the dynamic effects play a major role in determining the harvested voltage and power, especially for high excitation frequency or specimen thickness.

  14. Frequency-dependent selection at rough expanding fronts

    NASA Astrophysics Data System (ADS)

    Kuhr, Jan-Timm; Stark, Holger

    2015-10-01

    Microbial colonies are experimental model systems for studying the colonization of new territory by biological species through range expansion. We study a generalization of the two-species Eden model, which incorporates local frequency-dependent selection, in order to analyze how social interactions between two species influence surface roughness of growing microbial colonies. The model includes several classical scenarios from game theory. We then concentrate on an expanding public goods game, where either cooperators or defectors take over the front depending on the system parameters. We analyze in detail the critical behavior of the nonequilibrium phase transition between global cooperation and defection and thereby identify a new universality class of phase transitions dealing with absorbing states. At the transition, the number of boundaries separating sectors decays with a novel power law in time and their superdiffusive motion crosses over from Eden scaling to a nearly ballistic regime. In parallel, the width of the front initially obeys Eden roughening and, at later times, passes over to selective roughening.

  15. Advanced Reservoir Imaging Using Frequency-Dependent Seismic Attributes

    SciTech Connect

    Fred Hilterman; Tad Patzek; Gennady Goloshubin; Dmitriy Silin; Charlotte Sullivan; Valeri Korneev

    2007-12-31

    Our report concerning advanced imaging and interpretation technology includes the development of theory, the implementation of laboratory experiments and the verification of results using field data. We investigated a reflectivity model for porous fluid-saturated reservoirs and demonstrated that the frequency-dependent component of the reflection coefficient is asymptotically proportional to the reservoir fluid mobility. We also analyzed seismic data using different azimuths and offsets over physical models of fractures filled with air and water. By comparing our physical model synthetics to numerical data we have identified several diagnostic indicators for quantifying the fractures. Finally, we developed reflectivity transforms for predicting pore fluid and lithology using rock-property statistics from 500 reservoirs in both the shelf and deep-water Gulf of Mexico. With these transforms and seismic AVO gathers across the prospect and its down-dip water-equivalent reservoir, fluid saturation can be estimated without a calibration well that ties the seismic. Our research provides the important additional mechanisms to recognize, delineate, and validate new hydrocarbon reserves and assist in the development of producing fields.

  16. Fiber

    MedlinePlus

    ... it can help with weight control. Fiber aids digestion and helps prevent constipation . It is sometimes used ... fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in ...

  17. Yeh-Stratton Criterion for Stress Concentrations on Fiber-Reinforced Composite Materials

    NASA Technical Reports Server (NTRS)

    Yeh, Hsien-Yang; Richards, W. Lance

    1996-01-01

    This study investigated the Yeh-Stratton Failure Criterion with the stress concentrations on fiber-reinforced composites materials under tensile stresses. The Yeh-Stratton Failure Criterion was developed from the initial yielding of materials based on macromechanics. To investigate this criterion, the influence of the materials anisotropic properties and far field loading on the composite materials with central hole and normal crack were studied. Special emphasis was placed on defining the crack tip stress fields and their applications. The study of Yeh-Stratton criterion for damage zone stress fields on fiber-reinforced composites under tensile loading was compared with several fracture criteria; Tsai-Wu Theory, Hoffman Theory, Fischer Theory, and Cowin Theory. Theoretical predictions from these criteria are examined using experimental results.

  18. Microsurgery-aided in-situ force probing reveals extensibility and viscoelastic properties of individual stress fibers

    PubMed Central

    Labouesse, Céline; Gabella, Chiara; Meister, Jean-Jacques; Vianay, Benoît; Verkhovsky, Alexander B.

    2016-01-01

    Actin-myosin filament bundles (stress fibers) are critical for tension generation and cell shape, but their mechanical properties are difficult to access. Here we propose a novel approach to probe individual peripheral stress fibers in living cells through a microsurgically generated opening in the cytoplasm. By applying large deformations with a soft cantilever we were able to fully characterize the mechanical response of the fibers and evaluate their tension, extensibility, elastic and viscous properties. PMID:27025817

  19. Neural correlates of stimulus spatial frequency-dependent contrast detection

    PubMed Central

    Meng, Jianjun; Liu, Ruilong; Wang, Ke; Hua, Tianmiao; Lu, Zhong-Lin; Xi, Minmin

    2016-01-01

    Psychophysical studies on human and non-human vertebrate species have shown that visual contrast sensitivity function (CSF) peaks at a certain stimulus spatial frequency and declines in both lower and higher spatial frequencies. The underlying neural substrate and mechanisms remain in debate. Here, we investigated the role of primary visual cortex (V1: area 17) in spatial frequency-dependent contrast detection in cats. Perceptual CSFs of three cats were measured using a two-alternative forced choice task. The responses of V1 neurons to their optimal visual stimuli in a range of luminance contrast levels (from 0 to 1.0) were recorded subsequently using in vivo extracellular single-unit recording techniques. The contrast sensitivity of each neuron was determined. The neuronal CSF for each cat was constructed from the mean contrast sensitivity of neurons with different preferred stimulus spatial frequencies. Results (1) The perceptual and neuronal CSFs of each of the three cats exhibited a similar shape with peak amplitude near 0.4 c/deg. (2) The neuronal CSF of each cat was highly correlated with its perceptual CSF. (3) V1 neurons with different preferred stimulus spatial frequencies had different contrast gains. Conclusion (1) Contrast detection of visual stimuli with different spatial frequencies may likely involve population coding of V1 neurons with different preferred stimulus spatial frequencies. (2) Difference in contrast-gain may underlie the observed contrast sensitivity variation of V1 neurons with different preferred stimulus spatial frequencies, possibly from either evolution or postnatal visual experiences. PMID:23314692

  20. A geographic cline induced by negative frequency-dependent selection

    PubMed Central

    2011-01-01

    Background Establishment of geographic morph frequency clines is difficult to explain in organisms with limited gene flow. Balancing selection, such as negative frequency-dependent selection (NFDS), is instead suggested to establish a morph frequency cline on a geographic scale at least theoretically. Here we tested whether a large-scale smooth cline in morph frequency is established by NFDS in the female-dimorphic damselfly, Ischnura senegalensis, where andromorphs and gynomorphs are maintained by NFDS. Results We found a large-scale latitudinal cline in the morph frequency: andromorph frequency ranged from 0.05 (South) to 0.79 (North). Based on the empirical data on the numbers of eggs, the number of ovariole, abdomen length and latitude, the potential fitness of andromorphs was estimated to be lower than that of gynomorphs in the south, and higher in the north, suggesting the gene-by-environment interaction. From the morph-specific latitudinal cline in potential fitness, the frequency of andromorphs was expected to shift from 0 to 1 without NFDS, because a morph with higher potential fitness wins completely and the two morphs will switch at some point. In contrast, NFDS led to the coexistence of two morphs with different potential fitness in a certain geographic range along latitude due to rare morph advantage, and resulted in a smooth geographic cline of morph frequency. Conclusion Our results provide suggestive evidence that the combination of NFDS and gene-by-environment interaction, i.e., multi-selection pressure on color morphs, can explain the geographic cline in morph frequency in the current system. PMID:21917171

  1. Interplay between Solo and keratin filaments is crucial for mechanical force-induced stress fiber reinforcement.

    PubMed

    Fujiwara, Sachiko; Ohashi, Kazumasa; Mashiko, Toshiya; Kondo, Hiroshi; Mizuno, Kensaku

    2016-03-15

    Mechanical force-induced cytoskeletal reorganization is essential for cell and tissue remodeling and homeostasis; however, the underlying cellular mechanisms remain elusive. Solo (ARHGEF40) is a RhoA-targeting guanine nucleotide exchange factor (GEF) involved in cyclical stretch-induced human endothelial cell reorientation and convergent extension cell movement in zebrafish gastrula. In this study, we show that Solo binds to keratin-8/keratin-18 (K8/K18) intermediate filaments through multiple sites. Solo overexpression promotes the formation of thick actin stress fibers and keratin bundles, whereas knockdown of Solo, expression of a GEF-inactive mutant of Solo, or inhibition of ROCK suppresses stress fiber formation and leads to disorganized keratin networks, indicating that the Solo-RhoA-ROCK pathway serves to precisely organize keratin networks, as well as to promote stress fibers. Of importance, knockdown of Solo or K18 or overexpression of GEF-inactive or deletion mutants of Solo suppresses tensile force-induced stress fiber reinforcement. Furthermore, knockdown of Solo or K18 suppresses tensile force-induced RhoA activation. These results strongly suggest that the interplay between Solo and K8/K18 filaments plays a crucial role in tensile force-induced RhoA activation and consequent actin cytoskeletal reinforcement.

  2. Interplay between Solo and keratin filaments is crucial for mechanical force–induced stress fiber reinforcement

    PubMed Central

    Fujiwara, Sachiko; Ohashi, Kazumasa; Mashiko, Toshiya; Kondo, Hiroshi; Mizuno, Kensaku

    2016-01-01

    Mechanical force–induced cytoskeletal reorganization is essential for cell and tissue remodeling and homeostasis; however, the underlying cellular mechanisms remain elusive. Solo (ARHGEF40) is a RhoA-targeting guanine nucleotide exchange factor (GEF) involved in cyclical stretch–induced human endothelial cell reorientation and convergent extension cell movement in zebrafish gastrula. In this study, we show that Solo binds to keratin-8/keratin-18 (K8/K18) intermediate filaments through multiple sites. Solo overexpression promotes the formation of thick actin stress fibers and keratin bundles, whereas knockdown of Solo, expression of a GEF-inactive mutant of Solo, or inhibition of ROCK suppresses stress fiber formation and leads to disorganized keratin networks, indicating that the Solo-RhoA-ROCK pathway serves to precisely organize keratin networks, as well as to promote stress fibers. Of importance, knockdown of Solo or K18 or overexpression of GEF-inactive or deletion mutants of Solo suppresses tensile force–induced stress fiber reinforcement. Furthermore, knockdown of Solo or K18 suppresses tensile force-induced RhoA activation. These results strongly suggest that the interplay between Solo and K8/K18 filaments plays a crucial role in tensile force–induced RhoA activation and consequent actin cytoskeletal reinforcement. PMID:26823019

  3. A model for cell density effect on stress fiber alignment and collective directional migration

    NASA Astrophysics Data System (ADS)

    Abeddoust, Mohammad; Shamloo, Amir

    2015-12-01

    In this study, numerical simulation of collective cell migration is presented in order to mimic the group migration of endothelial cells subjected to the concentration gradients of a biochemical factor. The developed 2D model incorporates basic elements of the cell, including both the cell membrane and the cell cytoskeleton, based on a viscoelastic cell mechanic model. Various cell processes—including cell random walk, cell-cell interactions, cell chemotaxis, and cellular cytoskeleton rearrangements—are considered and analyzed in our developed model. After validating the model by using available experimental data, the model is used to investigate various important parameters during collective cell chemotaxis, such as cell density, cytoskeleton organization, stress fiber reorientations, and intracellular forces. The results suggest that increasing the cell density causes the cell-cell interactions to affect the orientation of stress fibers throughout the cytoskeleton and makes the stress fibers more aligned in the direction of the imposed concentration gradient. This improved alignment of the stress fibers correlates with the intensification of the intracellular forces transferred in the gradient direction; this improves the cell group migration. Comparison of the obtained results with available experimental observations of collective chemotaxis of endothelial cells shows an interesting agreement.

  4. A model for cell density effect on stress fiber alignment and collective directional migration.

    PubMed

    Abeddoust, Mohammad; Shamloo, Amir

    2015-12-01

    In this study, numerical simulation of collective cell migration is presented in order to mimic the group migration of endothelial cells subjected to the concentration gradients of a biochemical factor. The developed 2D model incorporates basic elements of the cell, including both the cell membrane and the cell cytoskeleton, based on a viscoelastic cell mechanic model. Various cell processes--including cell random walk, cell-cell interactions, cell chemotaxis, and cellular cytoskeleton rearrangements--are considered and analyzed in our developed model. After validating the model by using available experimental data, the model is used to investigate various important parameters during collective cell chemotaxis, such as cell density, cytoskeleton organization, stress fiber reorientations, and intracellular forces. The results suggest that increasing the cell density causes the cell-cell interactions to affect the orientation of stress fibers throughout the cytoskeleton and makes the stress fibers more aligned in the direction of the imposed concentration gradient. This improved alignment of the stress fibers correlates with the intensification of the intracellular forces transferred in the gradient direction; this improves the cell group migration. Comparison of the obtained results with available experimental observations of collective chemotaxis of endothelial cells shows an interesting agreement. PMID:26717999

  5. Fibers in the extracellular matrix enable long-range stress transmission between cells.

    PubMed

    Ma, Xiaoyue; Schickel, Maureen E; Stevenson, Mark D; Sarang-Sieminski, Alisha L; Gooch, Keith J; Ghadiali, Samir N; Hart, Richard T

    2013-04-01

    Cells can sense, signal, and organize via mechanical forces. The ability of cells to mechanically sense and respond to the presence of other cells over relatively long distances (e.g., ∼100 μm, or ∼10 cell-diameters) across extracellular matrix (ECM) has been attributed to the strain-hardening behavior of the ECM. In this study, we explore an alternative hypothesis: the fibrous nature of the ECM makes long-range stress transmission possible and provides an important mechanism for long-range cell-cell mechanical signaling. To test this hypothesis, confocal reflectance microscopy was used to develop image-based finite-element models of stress transmission within fibroblast-seeded collagen gels. Models that account for the gel's fibrous nature were compared with homogenous linear-elastic and strain-hardening models to investigate the mechanisms of stress propagation. Experimentally, cells were observed to compact the collagen gel and align collagen fibers between neighboring cells within 24 h. Finite-element analysis revealed that stresses generated by a centripetally contracting cell boundary are concentrated in the relatively stiff ECM fibers and are propagated farther in a fibrous matrix as compared to homogeneous linear elastic or strain-hardening materials. These results support the hypothesis that ECM fibers, especially aligned ones, play an important role in long-range stress transmission. PMID:23561517

  6. Fracture strength and stress distributions of pulpless premolars restored with fiber posts.

    PubMed

    Furuya, Yu; Huang, Shih-Hao; Takeda, Yuko; Fok, Alex; Hayashi, Mikako

    2014-01-01

    This study examined the effect of glass fiber posts on increasing the fracture resistance of endodontically treated teeth. Extracted upper premolars with two canals in a root were divided into three groups according to the number of posts they were restored with: none, one, or two. All teeth were endodontically treated, crown-sectioned, and restored with a composite core and a metallic crown. A static oblique load was applied to the restored tooth until fracture, and the fracture pattern was recorded. Stress distributions were examined by finite element analysis (FEA). Teeth with glass fiber post(s) showed significantly higher fracture loads compared with those without posts. In the premolars without posts, von Mises and maximum principal stresses were found on the root surface alone; in premolars restored with posts, stresses were distributed on both root and post surfaces. Risk of root dentin fracture was significantly lowest in teeth restored with two posts. PMID:25483385

  7. Effect of Initial Stress on a Fiber-Reinforced Anisotropic Thermoelastic Thick Plate

    NASA Astrophysics Data System (ADS)

    Abbas, Ibrahim A.; Abd-alla, Abo-el-nour N.

    2011-05-01

    The two-dimensional problem of generalized thermoelasticity for a fiber-reinforced anisotropic thick plate under initial stress is studied in the context of the Lord and Shulman theory. The upper surface of the plate is thermally insulated with prescribed surface loading while the lower surface of the plate rests on a rigid foundation and temperature. The problem is solved numerically using a finite element method. Numerical results for the temperature distribution, and the displacement and stress components are given and illustrated graphically. It is found from the graphs that the initial stress significantly influences the variations of field quantities. The results obtained in this paper may offer a theoretical basis and meaningful suggestions for the design of various fiber-reinforced anisotropic thermoelastic elements under loading to meet special engineering requirements.

  8. Experimental and theoretical investigation of stress wave attenuation in fiber reinforced composites.

    NASA Technical Reports Server (NTRS)

    Yang, J. C. S.; Tsui, C. Y.

    1972-01-01

    The propagation of an initialrcidrical pressure pulse through a linear elastic fiber reinforced composite medium is analysed, both experimentally and analytically. In the experiment, tests were performed on plates with single and multiple circular inclusions embedded in a matrix of lower characteristic impedance. Sharp compression pulses were generated at an edge of the plate. Strain gages were mounted on various positions of the plate to determine the attenuation of the transient stress in the fiber reinforced composite. The qualitative analytical treatment is based on the methods of propagating stress discontinuities. Computer programs were written to numerically determine the changes in the shape of the leading wave front and the stresses immediately behind it. Experimental results for the attenuation of stress wave on steel-aluminum and steel-brass fiber-matrix composites compared very well with the computed analytical results when the applied pressure is generated by small explosive charges. The results did not compare well when the applied pressure is generated by projectile impact.

  9. Intermediate Temperature Stress Rupture of Woven SiC Fiber, BN Interphase, SiC Matrix Composites in Air

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Levine, Stanley (Technical Monitor)

    2000-01-01

    Tensile stress-rupture experiments were performed on woven Hi-Nicalon reinforced SiC matrix composites with BN interphases in air. Modal acoustic emission (AE) was used to monitor the damage accumulation in the composites during the tests and microstructural analysis was performed to determine the amount of matrix cracking that occurred for each sample. Fiber fractograph), was also performed for individual fiber failures at the specimen fracture surface to determine the strengths at which fibers failed. The rupture strengths were significantly worse than what would have been expected front the inherent degradation of the fibers themselves when subjected to similar rupture conditions. At higher applied stresses the rate of rupture "?as larger than at lower applied stresses. It was observed that the change in rupture rate corresponded to the onset of through-thickness cracking in the composites themselves. The primary cause of the sen,ere degradation was the ease with which fibers would bond to one another at their closest separation distances, less than 100 nanometers, when exposed to the environment. The near fiber-to-fiber contact in the woven tows enabled premature fiber failure over large areas of matrix cracks due to the stress-concentrations created b), fibers bonded to one another after one or a few fibers fail. i.e. the loss of global load sharing. An@, improvement in fiber-to-fiber separation of this composite system should result in improved stress- rupture properties. A model was den,eloped in order to predict the rupture life-time for these composites based on the probabilistic nature of indin,idual fiber failure at temperature. the matrix cracking state during the rupture test, and the rate of oxidation into a matrix crack. Also incorporated into the model were estimates of the stress-concentration that would occur between the outer rim of fibers in a load-bearing bundle and the unbridged region of a matrix crack after Xia et al. For the lower stresses

  10. Failure of a fiber composite lamina under three-dimensional stresses

    SciTech Connect

    DeTeresa, S J

    1999-08-31

    The efficient use of thick-section fiber composites requires a proven three-dimensional failure model. Numerous failure criteria have been proposed, but the lack of critical experimental results makes it difficult to assess the accuracy of these models. It is shown that the various predictions for failure of a lamina due to the simple state of uniaxial stress plus superposed hydrostatic pressure are disparate. These differences are sufficient to allow evaluation of failure criteria using data that has the normal scatter found for composite materials. A high-pressure test system for fiber composites is described and results for the effects of pressure on the transverse and longitudinal compression strengths of a carbon fiber/epoxy lamina are discussed. Results are compared with a few representative failure models.

  11. Optical fiber fatigue behavior over very extended periods at low stress levels in the field and in laboratory tests

    NASA Astrophysics Data System (ADS)

    Stockton, David J.; Mayhew, Andi J.

    1999-12-01

    The reliability of optical fiber exposed to relatively high static strains (> 2%) has been extensively modelled and investigated by experiment. Fatigue `knees' have been demonstrated predicting the premature fracture of fiber particularly where elevated temperatures and relatively large volumes of water have been used to soak the samples. The cause has been attributed to simultaneous stress- assisted and stress-free corrosion of the fiber surface. In this paper we show that, a t more moderate strains (1 to 2%) and using a limited volume of water, there is evidence of a strength recovery caused either by a healing process or the observance of some form of lower strain threshold. The expected strength reduction of the fiber, from contemporary models is contrasted to that observed. The unusually high strength retention shown by the test fiber in water is shown to have important implications for optical cable design and for the bending of fiber within joint housings.

  12. Multiscale stress and damage initiation analyses of graphite fiber/polyimide composites

    NASA Astrophysics Data System (ADS)

    Rupnowski, Przemyslaw

    This work focuses on multi-scale stress and damage initiation analyses of unidirectional and woven graphite/polyimide composites subjected to mechanical, thermal and aging loads. The macro, meso and micro scales representing respectively a specimen, woven fabric and fiber/matrix levels were investigated using both analytical and numerical methods. The Eshelby/Mori-Tanaka and finite element models based on the concept of a unit-cell were utilized to model visco-elastic and elasto-plastic effects in the unidirectional and woven systems both at room and elevated temperatures. To determine the properties of graphite fibers the analyses were performed from macro to micro scale, whereas in order to predict the composites response a reversed micro to macro approach was employed. Both mechanical and resonance testing results were used as input macro data for the fiber properties analysis. It was shown that using the proposed technique the elastic and thermal properties of T650, M40J and M60J graphite fibers can be determined from the macro data for the unidirectional and woven composites. Next, based on the fiber and neat resin data, the effective macro behavior of the T650/PMR-15 unidirectional and woven composites was predicted as a function of temperature. The predictions were subsequently compared with the available experimental results. The computations of the meso and micro stresses in the woven systems were conducted and the most critical combination of in-plane mechanical loads was determined. The analyses also revealed the difference between the micro stress states in the composite subjected to the Iosipescu and +/-45° shear tests. Finally, the long term relaxation modulus for PMR-15 resin was measured and simulation of aging at 315° in nitrogen was performed for the woven 8HS T650/PMR-15 composite.

  13. Bidirectional Interplay between Vimentin Intermediate Filaments and Contractile Actin Stress Fibers.

    PubMed

    Jiu, Yaming; Lehtimäki, Jaakko; Tojkander, Sari; Cheng, Fang; Jäälinoja, Harri; Liu, Xiaonan; Varjosalo, Markku; Eriksson, John E; Lappalainen, Pekka

    2015-06-16

    The actin cytoskeleton and cytoplasmic intermediate filaments contribute to cell migration and morphogenesis, but the interplay between these two central cytoskeletal elements has remained elusive. Here, we find that specific actin stress fiber structures, transverse arcs, interact with vimentin intermediate filaments and promote their retrograde flow. Consequently, myosin-II-containing arcs are important for perinuclear localization of the vimentin network in cells. The vimentin network reciprocally restricts retrograde movement of arcs and hence controls the width of flat lamellum at the leading edge of the cell. Depletion of plectin recapitulates the vimentin organization phenotype of arc-deficient cells without affecting the integrity of vimentin filaments or stress fibers, demonstrating that this cytoskeletal cross-linker is required for productive interactions between vimentin and arcs. Collectively, our results reveal that plectin-mediated interplay between contractile actomyosin arcs and vimentin intermediate filaments controls the localization and dynamics of these two cytoskeletal systems and is consequently important for cell morphogenesis.

  14. Residual internal stress optimization for EPON 828/DEA thermoset resin using fiber Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Rohr, Garth D.; Rasberry, Roger D.; Kaczmarowski, Amy K.; Stavig, Mark E.; Gibson, Cory S.; Udd, Eric; Roach, Allen R.; Nation, Brendan

    2015-05-01

    Internal residual stresses and overall mechanical properties of thermoset resins are largely dictated by the curing process. It is well understood that fiber Bragg grating (FBG) sensors can be used to evaluate temperature and cure induced strain while embedded during curing. Herein, is an extension of this work whereby we use FBGs as a probe for minimizing the internal residual stress of an unfilled and filled Epon 828/DEA resin. Variables affecting stress including cure cycle, mold (release), and adhesion promoting additives will be discussed and stress measurements from a strain gauge pop-off test will be used as comparison. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  15. Calculation of Stress Intensity Factors for Interfacial Cracks in Fiber Metal Laminates

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2009-01-01

    Stress intensity factors for interfacial cracks in Fiber Metal Laminates (FML) are computed by using the displacement ratio method recently developed by Sun and Qian (1997, Int. J. Solids. Struct. 34, 2595-2609). Various FML configurations with single and multiple delaminations subjected to different loading conditions are investigated. The displacement ratio method requires the total energy release rate, bimaterial parameters, and relative crack surface displacements as input. Details of generating the energy release rates, defining bimaterial parameters with anisotropic elasticity, and selecting proper crack surface locations for obtaining relative crack surface displacements are discussed in the paper. Even though the individual energy release rates are nonconvergent, mesh-size-independent stress intensity factors can be obtained. This study also finds that the selection of reference length can affect the magnitudes and the mode mixity angles of the stress intensity factors; thus, it is important to report the reference length used with the calculated stress intensity factors.

  16. Stress generated by customized glass fiber posts and other types by photoelastic analysis.

    PubMed

    Bosso, Kátia; Gonini Júnior, Alcides; Guiraldo, Ricardo Danil; Berger, Sandrine Bittencourt; Lopes, Murilo Baena

    2015-01-01

    Endodontic posts are necessary to provide adequate retention and support when no sufficient remaining structure is available to retain the core. There are different materials and techniques to construct post-and-core, but there is no consensus about which one promotes better stress distribution on the remaining tooth structure. This study aimed to quantify and evaluate the distribution of stress in the root produced by customized glass fiber posts compared to different endodontic posts. Twenty-five simulated roots from photoelastic resin were made and divided into 5 groups: CPC, cast post-and-core; SP, screw post; CF, carbon fiber post; GF, glass fiber post; and CGF, customized glass fiber post. After cementing CPC and SP posts with zinc phosphate cement, and CF, GF and CGF posts with resin cement, resin cores were made for groups 2-5. Specimens were evaluated with vertical or 45° oblique loading. To analyze the fringes, the root was divided into 6 parts: palatal cervical, palatal middle, palatal apical, vestibular cervical, vestibular middle, and vestibular apical. The formed fringes were photographed and quantified. Data were recorded and subjected to two-way ANOVA and Tukey's test (5%). SP (1.95±0.60) showed higher stress (p<0.05) compared to the others (CPC-0.52±0.74; CF-0.50±0.75, GF-0.23±0.48 and CGF-0.45±0.83). All posts showed high stress in apical third (CPC-1.40±0.65; SP-2.30±0.44, CF-1.80±0.45, GF-1.20±0.45, CGF-1.70±1.03) Low stress was found in cervical third (CPC-0.20±0.45; CF-0.00±0.00, GF-0.00±0.00, CGF-0.00±0.00), except by SP (1.90±0.65), which showed statistical difference (p<0.05). Customized post showed high stress concentration at the root and conventional glass fiber posts showed more favorable biomechanical behavior.

  17. Impact damage characterization in cross-plied carbon fiber/thermoplastic composites using thermoelastic stress analysis

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Uenoya, T.; Miyamoto, H.

    2012-04-01

    Carbon fiber (CF)-plastic composites are expected from the view point of light weighting vehicle structures. The CF/thermoset plastic laminates have low damage resistance to out-of-plane impact as a problem to be solved, because they behave as a low strength inter-laminar as compared with high-strength in fiber direction. Accordingly it is strongly desired to develop CF-composite materials based thermoplastics that have higher toughness than thermoset, for vehicle use. The present paper describes investigation of impact damages through thermoelastic stress analysis (TSA). Lowvelocity impact test using drop weight was conducted on stitched non-crimp-fabric CF/NY6 composite specimens. Stress distribution of the specimens under impact loading was monitored by a lock-in thermography system from the opposite side of the impact direction. The instrumentation system, which had a focal plane array detector, provided a succession of thermoelastic stress information as a sequence of TSA images at a high rate. The measured stress distribution agreed well with a theoretical. And also, selecting a contour feature of the stress distribution determined with a suitable level conformed approximately to the internal damage image that was processed from the TSA images obtained before and after impact.

  18. Development of In-Fiber Reflective Bragg Gratings as Shear Stress Monitors in Aerodynamic Facilities

    NASA Technical Reports Server (NTRS)

    Parmar, Devendra S.; Sprinkle, Danny R.; Singh, Jag J.

    1998-01-01

    Bragg gratings centered at nominal wavelengths of 1290 nm and 1300 run were inscribed in a 9/125 microns germano-silicate optical fiber, using continuous wave frequency doubled Ar+ laser radiation at 244 nm. Such gratings have been used extensively as temperature and strain monitors in smart structures. They have, however, never been used for measuring aerodynamic shear stresses. As a test of their sensitivity as shear stress monitors, a Bragg fiber attached to a metal plate was subjected to laminar flows in a glass pipe. An easily measurable large flow-induced wavelength shift (Delta Lambda(sub B)) was observed in the Bragg reflected wavelength. Thereafter, the grating was calibrated by making one time, simultaneous measurements of Delta Lambda(sub B) and the coefficient of skin friction (C(sub f)) with a skin friction balance, as a function of flow rates in a subsonic wind tunnel. Onset of fan-induced transition in the tunnel flow provided a unique flow rate for correlating Delta Lambda(sub B) and (C(sub f) values needed for computing effective modulus of rigidity (N(sub eff)) of the fiber attached to the metal plate. This value Of N(sub eff) is expected to remain constant throughout the elastic stress range expected during the Bragg grating aerodynamic tests. It has been used for calculating the value of Cf at various tunnel speeds, on the basis of measured values of Bragg wavelength shifts at those speeds.

  19. A Critique of a Phenomenological Fiber Breakage Model for Stress Rupture of Composite Materials

    NASA Technical Reports Server (NTRS)

    Reeder, James R.

    2010-01-01

    Stress rupture is not a critical failure mode for most composite structures, but there are a few applications where it can be critical. One application where stress rupture can be a critical design issue is in Composite Overwrapped Pressure Vessels (COPV's), where the composite material is highly and uniformly loaded for long periods of time and where very high reliability is required. COPV's are normally required to be proof loaded before being put into service to insure strength, but it is feared that the proof load may cause damage that reduces the stress rupture reliability. Recently, a fiber breakage model was proposed specifically to estimate a reduced reliability due to proof loading. The fiber breakage model attempts to model physics believed to occur at the microscopic scale, but validation of the model has not occurred. In this paper, the fiber breakage model is re-derived while highlighting assumptions that were made during the derivation. Some of the assumptions are examined to assess their effect on the final predicted reliability.

  20. Stress-temperature-lifetime response of nicalon fiber-reinforced SiC composites in air

    SciTech Connect

    Lin, Hua-Tay; Becher, P.F.

    1996-02-01

    Time-to-failure tests were conducted in four-point flexure and in air as a function of stress levels and temperatures to study the lifetime response of various Nicalon fiber-reinforced SiC (designated as Nic/SiC) composites with a graphitic interfacial coating. The results indicated that all of the Nic/SiC composites exhibit a similar stress-dependent failure at applied stress greater than a threshold value. In this case, the lifetimes of the composites increased with decrease in both stress level and test temperature. The lifetime of the composites appeared to be relatively insensitive to the thickness of graphitic interface layer and was enhanced somewhat by the addition of oxidation inhibitors. Electron microscopy and oxidation studies indicated that the life of the Nic/SiC composites was governed by the oxidation of the graphitic interfaces and the on of glass(es) in composites due to the oxidation of the fiber and matrix, inhibitor phases.

  1. Modeling for Fatigue Hysteresis Loops of Carbon Fiber-Reinforced Ceramic-Matrix Composites under Multiple Loading Stress Levels

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    In this paper, the fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) under multiple loading stress levels considering interface wear has been investigated using micromechanical approach. Under fatigue loading, the fiber/matrix interface shear stress decreases with the increase of cycle number due to interface wear. Upon increasing of fatigue peak stress, the interface debonded length would propagate along the fiber/matrix interface. The difference of interface shear stress existed in the new and original debonded region would affect the interface debonding and interface frictional slipping between the fiber and the matrix. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading and subsequent reloading, the interface slip lengths, i.e., the interface debonded length, interface counter-slip length and interface new-slip length, are determined by fracture mechanics approach. The fatigue hysteresis loops models under multiple loading stress levels have been developed. The effects of single/multiple loading stress levels and different loading sequences on fatigue hysteresis loops have been investigated. The fatigue hysteresis loops of unidirectional C/SiC composite under multiple loading stress levels have been predicted.

  2. Three-dimensional finite element analysis of stress distribution in composite resin cores with fiber posts of varying diameters.

    PubMed

    Okamoto, Kazuhiko; Ino, Teruno; Iwase, Naoki; Shimizu, Eitaroh; Suzuki, Megumi; Satoh, Goh; Ohkawa, Shuji; Fujisawa, Masanori

    2008-01-01

    Using three-dimensional finite element analysis (3D-FEA), stress distributions in the remaining radicular tooth structure were investigated under the condition of varying diameters of fiber post for fiber post-reinforced composite resin cores (fiber post and core) in maxillary central incisors. Four 3D-FEA models were constructed: (1) fiber post (ø1.2, ø1.4, and ø1.6 mm) and composite resin core; and (2) gold-cast post and core. Maximum stresses in the tooth structure for fiber post and core were higher than that for gold-cast post and core. In the former models, stresses in the tooth structure as well as in the composite resin were slightly reduced with increase in fiber post diameter. These results thus suggested that to reduce stress in the remaining radicular tooth with a large coronal defect, it is recommended to accompany a composite resin core with a fiber post of a large diameter. PMID:18309611

  3. Prediction of the Elastic-Plastic Stress/Strain Response for Injection-Molded Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba N.; Kunc, Vlastimil; Phelps, Jay H; TuckerIII, Charles L.; Bapanapalli, Satish K

    2009-01-01

    This paper proposes a model to predict the elastic-plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elastic-plastic behavior obeying the Ramberg-Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using an anisotropic rotary diffusion model recently developed for LFTs. An incremental procedure using Eshelby's equivalent inclusion method and the Mori-Tanaka assumption is proposed to compute the overall stress increment resulting from an overall strain increment for an aligned-fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the latter is then obtained from the solution for the aligned-fiber composite by averaging over all fiber orientations. Failure during incremental loading is predicted using the Van Hattum-Bernado model. The model is validated against the experimental stress-strain results obtained for long-glass-fiber/polypropylene specimens.

  4. Prediction of the Elastic-Plastic Stress/Strain Response for Injection-Molded Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba Nghiep; Bapanapalli, Satish K.; Kunc, Vlastimil; Phelps, Jay; Tucker III, Charles L.

    2009-01-26

    This paper proposes a model to predict the elastic-plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elastic-plastic behavior obeying the Ramberg-Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using the anisotropic rotary diffusion model recently developed by Phelps and Tucker for LFTs. An incremental procedure using the Eshelby’s equivalent inclusion method and the Mori-Tanaka model is proposed to compute the overall stress increment resulting from an overall strain increment for an aligned fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the later is then obtained from the solution for the aligned fiber composite that is averaged over all possible fiber orientations using the orientation averaging method. Failure during incremental loading is predicted using the Van Hattum-Bernado model. The elastic-plastic and strength prediction model for LFTs was validated against the experimental stress-strain results obtained for long glass fiber/polypropylene specimens.

  5. Determination of local debonding stress and investigation of its effect on mechanical properties of glass short fiber reinforced polycarbonate composites

    NASA Astrophysics Data System (ADS)

    Zhao, Wenjie; Kim, Hyung-ick; Suhr, Jonghwan

    2012-04-01

    Thermoplastic polymers are often reinforced by adding short fibers to improve mechanical properties including Young's modulus and tensile strength of the polymers. In many engineering applications, energy absorbing characteristics in such particulate polymers is known to be a very important property to be considered in composite designs, and meanwhile debonding at the interface between fiber and matrix in the composites may affect the energy absorption properties. Here, the focus of this study is to employ a semi-empirical approach to determine the debonding stress and investigate the effect of the debonding stress on energy absorbing properties of short glass fiber reinforced polycarbonate composites. Glass short fiber reinforced polycarbonate composites are fabricated via a solution mixing technique. Tensile testing and acoustic emission measurement are simultaneously performed for the polycarbonate composites. The test results including toughness are compared for the composites over neat polycarbonate. Also the local debonding stress in the vicinity of each glass fiber in composites is estimated by combining modeling and experiments. A finite element model is developed to determine local debonding stress at the interface between the fiber and matrix. The local debonding stress appears to considerably affect the toughness of the composites.

  6. Frequency dependence and intensity fluctuations due to shallow water internal waves.

    PubMed

    Badiey, Mohsen; Katsnelson, Boris G; Lynch, James F; Pereselkov, Serguey

    2007-08-01

    A theory and experimental results for sound propagation through an anisotropic shallow water environment are presented to examine the frequency dependence of the scintillation index in the presence of internal waves. The theory of horizontal rays and vertical modes is used to establish the azimutal and frequency behavior of the sound intensity fluctuations, specifically for shallow water broadband acoustic signals propagating through internal waves. This theory is then used to examine the frequency dependent, anisotropic acoustic field measured during the SWARM'95 experiment. The frequency dependent modal scintillation index is described for the frequency range of 30-200 Hz on the New Jersey continental shelf.

  7. The mechanics of delamination in fiber-reinforced composite materials. I - Stress singularities and solution structure

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    The fundamental mechanics of delamination in fiber composite laminates is studied. Mathematical formulation of the problem is based on laminate anisotropic elasticity theory and interlaminar fracture mechanics concepts. Stress singularities and complete solution structures associated with general composite delaminations are determined. For a fully open delamination with traction-free surfaces, oscillatory stress singularities always appear, leading to physically inadmissible field solutions. A refined model is introduced by considering a partially closed delamination with crack surfaces in finite-length contact. Stress singularities associated with a partially closed delamination having frictional crack-surface contact are determined, and are found to be different from the inverse square-root one of the frictionless-contact case. In the case of a delamination with very small area of crack closure, a simplified model having a square-root stress singularity is employed by taking the limit of the partially closed delamination. The possible presence of logarithmic-type stress singularity is examined; no logarithmic singularity of any kind is found in the composite delamination problem. Numerical examples of dominant stress singularities are shown for delaminations having crack-tip closure with different frictional coefficients between general (1) and (2) graphite-epoxy composites. Previously announced in STAR as N84-13221

  8. The effect of stress on ultrasonic pulses in fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Hemann, J. H.; Baaklini, G. Y.

    1983-01-01

    An acoustical-ultrasonic technique was used to demonstrate relationships existing between changes in attenuation of stress waves and tensile stress for an eight ply 0 degree graphite-epoxy fiber reinforced composite. All tests were conducted in the linear range of the material for which no mechanical or macroscopic damage was evident. Changes in attenuation were measured as a function of tensile stress in the frequency domain and in the time domain. Stress wave propagation in these specimens was dispersive, i.e., the wave speed depends on frequency. Wave speeds varied from 267 400 cm/sec to 680 000 cm/sec as the frequency of the signal was varied from 150 kHz to 1.9 MHz which strongly suggests that flexural/lamb wave modes of propagation exist. The magnitude of the attenuation changes depended strongly on tensile stress. It was further observed that the wave speeds increased slightly for all tested frequencies as the stress was increased.

  9. A fiber optics sensor for strain and stress management in superconducting accelerator magnets

    SciTech Connect

    van Oort, J.M.; ten Kate, H.H.J.

    1993-09-20

    A novel cryogenic interferometric fiber optics sensor for the measurement of strain and stress in the coil windings of superconducting accelerator magnets is described. The sensor can operate with two different readout sources, monochromatic laser light and white light respectively. The sensor head is built up as an extrinsic Fabry-Perot interferometer formed with two cleaved fiber surfaces, and can be mounted in several configurations. When read with laser light, the sensor is an extremely sensitive relative strain or temperature detector. When read with white light the absolute strain and pressure can be measured. Results are presented of tests in several configurations at 77 K and 4.2 K, both for the relative and absolute readout method. Finally, the possible use for quench localization using the temperature sensitivity is described.

  10. A fiber optics sensor for strain and stress measurements in superconducting accelerator magnets

    SciTech Connect

    Oort, J.M. van ); Kate, H.H.J. ten . Applied Superconductivity Centre)

    1994-07-01

    A novel cryogenic interferometric fiber optics sensor for the measurement of strain and stress in the coil windings of superconducting accelerator magnets is described. The sensor can operate with two different readout sources, monochromatic laser light and white light respectively. The sensor head is built up as an extrinsic Fabry-Perot interferometer formed with two cleaved fiber surfaces, and can be mounted in several configurations. When read with laser light, the sensor is an extremely sensitive relative strain or temperature detector. When read with white light the absolute strain and pressure can be measured. Results are presented of tests in several configurations at 77 K and 4.2 K, both for the relative and absolute readout method. Finally, the possible use for quench localization using the temperature sensitivity is described.

  11. The study of the thermal annealing of the Bragg gratings induced in the hydrogenated birefringent optical fiber with an elliptical stress cladding

    NASA Astrophysics Data System (ADS)

    Munko, A. S.; Varzhel', S. V.; Arkhipov, S. V.; Gribaev, A. I.; Konnov, K. A.; Belikin, M. N.

    2016-08-01

    In this work the comparative results on the dynamics of fiber Bragg gratings inscription in both the conventional and the subjected to hydrogenation birefringent optical fiber with elliptical stress cladding as well as in the same type of lightguide with the increased GeO2 concentration are presented. Also the research on the thermal impact on the fiber Bragg gratings written in the birefringent fiber with elliptical stress cladding has been carried out. The dependences of the fiber Bragg reflectance coefficient on the time of the thermal impact, obtained by annealing of the refractive index gratings, induced in the optical fibers with increased photorefractivity, are shown.

  12. Fiber

    MedlinePlus

    ... broccoli, spinach, and artichokes legumes (split peas, soy, lentils, etc.) almonds Look for the fiber content of ... salsa, taco sauce, and cheese for dinner. Add lentils or whole-grain barley to your favorite soups. ...

  13. Seismic dynamic monitoring in CO2 flooding based on characterization of frequency-dependent velocity factor

    NASA Astrophysics Data System (ADS)

    Zhang, Jun-Hua; Li, Jun; Xiao, Wen; Tan, Ming-You; Zhang, Yun-Ying; Cui, Shi-Ling; Qu, Zhi-Peng

    2016-06-01

    The phase velocity of seismic waves varies with the propagation frequency, and thus frequency-dependent phenomena appear when CO2 gas is injected into a reservoir. By dynamically considering these phenomena with reservoir conditions it is thus feasible to extract the frequency-dependent velocity factor with the aim of monitoring changes in the reservoir both before and after CO2 injection. In the paper, we derive a quantitative expression for the frequency-dependent factor based on the Robinson seismic convolution model. In addition, an inversion equation with a frequency-dependent velocity factor is constructed, and a procedure is implemented using the following four processing steps: decomposition of the spectrum by generalized S transform, wavelet extraction of cross-well seismic traces, spectrum equalization processing, and an extraction method for frequency-dependent velocity factor based on the damped least-square algorithm. An attenuation layered model is then established based on changes in the Q value of the viscoelastic medium, and spectra of migration profiles from forward modeling are obtained and analyzed. Frequency-dependent factors are extracted and compared, and the effectiveness of the method is then verified using a synthetic data. The frequency-dependent velocity factor is finally applied to target processing and oil displacement monitoring based on real seismic data obtained before and after CO2 injection in the G89 well block within Shengli oilfield. Profiles and slices of the frequency-dependent factor determine its ability to indicate differences in CO2 flooding, and the predicting results are highly consistent with those of practical investigations within the well block.

  14. Investigation on Stress-Rupture Behavior of a Chopped-Glass-Fiber Composite for Automotive Durability Design Criteria

    SciTech Connect

    Ren, W

    2001-08-24

    Practical and inexpensive testing methods were developed to investigate stress-rupture properties of a polymeric composite with chopped glass fiber reinforcement for automotive applications. The material was tested in representative automotive environments to generate experimental data. The results indicate that environments have substantial effects on the stress-rupture behavior. The data were analyzed and developed into stress-rupture design criteria to address one of the durability aspects of the material for automotive structural applications.

  15. Dynamic stress analysis of smooth and notched fiber composite flexural specimens

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1984-01-01

    A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.

  16. Dynamic stress analysis of smooth and notched fiber composite flexural specimens

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1986-01-01

    A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.

  17. Method for Forming Fiber Reinforced Composite Bodies with Graded Composition and Stress Zones

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay (Inventor); Levine, Stanley R. (Inventor); Smialek, James A. (Inventor)

    1999-01-01

    A near-net, complex shaped ceramic fiber reinforced silicon carbide based composite bodies with graded compositions and stress zones is disclosed. To provide the composite a fiber preform is first fabricated and an interphase is applied by chemical vapor infiltration, sol-gel or polymer processes. This first body is further infiltrated with a polymer mixture containing carbon, and/or silicon carbide, and additional oxide, carbide, or nitride phases forming a second body. One side of the second body is spray coated or infiltrated with slurries containing high thermal expansion and oxidation resistant. crack sealant phases and the other side of this second body is coated with low expansion phase materials to form a third body. This third body consisting of porous carbonaceous matrix surrounding the previously applied interphase materials, is then infiltrated with molten silicon or molten silicon-refractory metal alloys to form a fourth body. The resulting fourth body comprises dense composites consisting of fibers with the desired interphase which are surrounded by silicon carbide and other second phases materials at the outer and inner surfaces comprising material of silicon, germanium, refractory metal suicides, borides, carbides, oxides, and combinations thereof The resulting composite fourth body has different compositional patterns from one side to the other.

  18. Strain measurement during stress rupture of composite over-wrapped pressure vessel with fiber Bragg gratings sensors

    NASA Astrophysics Data System (ADS)

    Banks, Curtis E.; Grant, Joseph; Russell, Sam; Arnett, Shawn

    2008-03-01

    Fiber optic Bragg gratings were used to measure strain fields during Stress Rupture (SSM) test of Kevlar Composite Over-Wrapped Pressure Vessels (COPVs). The sensors were embedded under the over-wrapped attached to the liner released from the Kevlar and attached to the Kevlar released from the liner. Additional sensors (foil gages and fiber bragg gratings) were surface mounted on the COPV liner.

  19. Strain Measurement during Stress Rupture of Composite Over-Wrapped Pressure Vessel with Fiber Bragg Gratings Sensors

    NASA Technical Reports Server (NTRS)

    Banks, Curtis E.; Grant, Joseph; Russell, Sam; Arnett, Shawn

    2008-01-01

    Fiber optic Bragg gratings were used to measure strain fields during Stress Rupture (SSM) test of Kevlar Composite Over-Wrapped Pressure Vessels (COPV). The sensors were embedded under the over-wrapped attached to the liner released from the Kevlar and attached to the Kevlar released from the liner. Additional sensors (foil gages and fiber bragg gratings) were surface mounted on the COPY liner.

  20. Time-Dependent Stress Rupture Strength Degradation of Hi-Nicalon Fiber-Reinforced Silicon Carbide Composites at Intermediate Temperatures

    NASA Technical Reports Server (NTRS)

    Sullivan, Roy M.

    2016-01-01

    The stress rupture strength of silicon carbide fiber-reinforced silicon carbide composites with a boron nitride fiber coating decreases with time within the intermediate temperature range of 700 to 950 degree Celsius. Various theories have been proposed to explain the cause of the time-dependent stress rupture strength. The objective of this paper is to investigate the relative significance of the various theories for the time-dependent strength of silicon carbide fiber-reinforced silicon carbide composites. This is achieved through the development of a numerically based progressive failure analysis routine and through the application of the routine to simulate the composite stress rupture tests. The progressive failure routine is a time-marching routine with an iterative loop between a probability of fiber survival equation and a force equilibrium equation within each time step. Failure of the composite is assumed to initiate near a matrix crack and the progression of fiber failures occurs by global load sharing. The probability of survival equation is derived from consideration of the strength of ceramic fibers with randomly occurring and slow growing flaws as well as the mechanical interaction between the fibers and matrix near a matrix crack. The force equilibrium equation follows from the global load sharing presumption. The results of progressive failure analyses of the composite tests suggest that the relationship between time and stress-rupture strength is attributed almost entirely to the slow flaw growth within the fibers. Although other mechanisms may be present, they appear to have only a minor influence on the observed time-dependent behavior.

  1. Characterization of Palladin, a Novel Protein Localized to Stress Fibers and Cell Adhesions

    PubMed Central

    Parast, Mana M.; Otey, Carol A.

    2000-01-01

    Here, we describe the identification of a novel phosphoprotein named palladin, which colocalizes with α-actinin in the stress fibers, focal adhesions, cell–cell junctions, and embryonic Z-lines. Palladin is expressed as a 90–92-kD doublet in fibroblasts and coimmunoprecipitates in a complex with α-actinin in fibroblast lysates. A cDNA encoding palladin was isolated by screening a mouse embryo library with mAbs. Palladin has a proline-rich region in the NH2-terminal half of the molecule and three tandem Ig C2 domains in the COOH-terminal half. In Northern and Western blots of chick and mouse tissues, multiple isoforms of palladin were detected. Palladin expression is ubiquitous in embryonic tissues, and is downregulated in certain adult tissues in the mouse. To probe the function of palladin in cultured cells, the Rcho-1 trophoblast model was used. Palladin expression was observed to increase in Rcho-1 cells when they began to assemble stress fibers. Antisense constructs were used to attenuate expression of palladin in Rcho-1 cells and fibroblasts, and disruption of the cytoskeleton was observed in both cell types. At longer times after antisense treatment, fibroblasts became fully rounded. These results suggest that palladin is required for the normal organization of the actin cytoskeleton and focal adhesions. PMID:10931874

  2. ADF and Cofilin1 Control Actin Stress Fibers, Nuclear Integrity, and Cell Survival

    PubMed Central

    Kanellos, Georgios; Zhou, Jing; Patel, Hitesh; Ridgway, Rachel A.; Huels, David; Gurniak, Christine B.; Sandilands, Emma; Carragher, Neil O.; Sansom, Owen J.; Witke, Walter; Brunton, Valerie G.; Frame, Margaret C.

    2015-01-01

    Summary Genetic co-depletion of the actin-severing proteins ADF and CFL1 triggers catastrophic loss of adult homeostasis in multiple tissues. There is impaired cell-cell adhesion in skin keratinocytes with dysregulation of E-cadherin, hyperproliferation of differentiated cells, and ultimately apoptosis. Mechanistically, the primary consequence of depleting both ADF and CFL1 is uncontrolled accumulation of contractile actin stress fibers associated with enlarged focal adhesions at the plasma membrane, as well as reduced rates of membrane protrusions. This generates increased intracellular acto-myosin tension that promotes nuclear deformation and physical disruption of the nuclear lamina via the LINC complex that normally connects regulated actin filaments to the nuclear envelope. We therefore describe a pathway involving the actin-severing proteins ADF and CFL1 in regulating the dynamic turnover of contractile actin stress fibers, and this is vital to prevent the nucleus from being damaged by actin contractility, in turn preserving cell survival and tissue homeostasis. PMID:26655907

  3. A versatile micro-mechanical tester for actin stress fibers isolated from cells.

    PubMed

    Matsui, Tsubasa S; Deguchi, Shinji; Sakamoto, Naoya; Ohashi, Toshiro; Sato, Masaaki

    2009-01-01

    Conventional atomic force microscopy is one of the major techniques to evaluate mechanical properties of cells and subcellular components. The use of a cantilever probe for sample manipulation within the vertical plane often makes absolute positioning of the probe, subject to thermal drift, difficult. In addition, the vertical test is unable to observe changes in the sample structure responsible for mechanical behavior detected by the probe. In the present study, an alternative mechanical tester was developed that incorporated a pair of micro-needles to manipulate a sample in a project plane, allowing acquisition of the accurate probe position and entire sample image. Using a vision-based feedback control, a micro-needle driven by a piezo actuator is moved to give user-defined displacements or forces to sample. To show its usefulness and versatility, three types of viscoelastic measurements on actin stress fibers isolated from smooth muscle cells were demonstrated: strain rate-controlled tensile tests, relaxation tests and creep tests. Fluorescence imaging of the stress fibers using Qdots over the course of the measurements, obtained through multiple image detectors, was also carried out. The technique described here is useful for examining the quantitative relationship between mechanical behavior and related structural changes of biomaterials. PMID:19940356

  4. Lateral communication between stress fiber sarcomeres facilitates a local remodeling response.

    PubMed

    Chapin, Laura M; Blankman, Elizabeth; Smith, Mark A; Shiu, Yan-Ting; Beckerle, Mary C

    2012-11-21

    Actin stress fibers (SFs) are load-bearing and mechanosensitive structures. To our knowledge, the mechanisms that enable SFs to sense and respond to strain have not been fully defined. Acute local strain events can involve a twofold extension of a single SF sarcomere, but how these dramatic local events affect the overall SF architecture is not believed to be understood. Here we have investigated how SF architecture adjusts to episodes of local strain that occur in the cell center. Using fluorescently tagged zyxin to track the borders of sarcomeres, we characterize the dynamics of resting sarcomeres and strain-site sarcomeres. We find that sarcomeres flanking a strain site undergo rapid shortening that directly compensates for the strain-site extension, illustrating lateral communication of mechanical information along the length of a stress fiber. When a strain-site sarcomere extends asymmetrically, its adjacent sarcomeres exhibit a parallel asymmetric shortening response, illustrating that flanking sarcomeres respond to strain magnitude. After extension, strain-site sarcomeres become locations of new sarcomere addition, highlighting mechanical strain as a trigger of sarcomere addition and revealing a, to our knowledge, novel type of SF remodeling. Our findings provide evidence to suggest SF sarcomeres act as strain sensors and are interconnected to support communication of mechanical information.

  5. WAXS studies of heat - mechanically modified amorphous PET fibers. Role of the tensile stress

    NASA Astrophysics Data System (ADS)

    Velev, V.; Popov, A.; Kyurkchiev, P.; Veleva, L.; Pencheva, M.

    2014-12-01

    The present work is devoted to the investigation of the structure developments in as- spun amorphous poly (ethylene terephthalate) (PET) filaments occurred as a result of heat mechanically modification. The degree of crystallinity of the untreated samples was 1,7 %. The thermal deformation experiments were carried out under isothermal conditions. PET yarn was annealed during 10 min at constant temperature of 80°C after which the sample is subjected to a well-defined constant tensile stress for 120 s at the same temperature. The mechanical load is gravitationally in the range from 0 MPa to 30 MPa and with increment step of 3 MPa. Using of wide angle X-ray scattering (WAXS) were investigated the structural rearrangements in the studied samples caused by the fibers treatments. Dependences between the strain force values and the running in the specimen's structure development are established. And in particular, it was found that a small increase of the tensile stress from 3 MPa to 6 MPa leads to a massive increase in the fibers degree of crystallinity with more than 33%.

  6. Carbon fiber based composites stress analysis. Experimental and computer comparative studies

    NASA Astrophysics Data System (ADS)

    Sobek, M.; Baier, A.; Buchacz, A.; Grabowski, Ł.; Majzner, M.

    2015-11-01

    Composite materials used nowadays for the production of composites are the result of advanced research. This allows assuming that they are among the most elaborate tech products of our century. That fact is evidenced by the widespread use of them in the most demanding industries like aerospace and space industry. But the heterogeneous materials and their advantages have been known to mankind in ancient times and they have been used by nature for millions of years. Among the fibers used in the industry most commonly used are nylon, polyester, polypropylene, boron, metal, glass, carbon and aramid. Thanks to their physical properties last three fiber types deserve special attention. High strength to weight ratio allow the use of many industrial solutions. Composites based on carbon and glass fibers are widely used in the automotive. Aramid fibers ideal for the fashion industry where the fabric made from the fibers used to produce the protective clothing. In the paper presented issues of stress analysis of composite materials have been presented. The components of composite materials and principles of composition have been discussed. Particular attention was paid to the epoxy resins and the fabrics made from carbon fibers. The article also includes basic information about strain measurements performed on with a resistance strain gauge method. For the purpose of the laboratory tests a series of carbon - epoxy composite samples were made. For this purpose plain carbon textile was used with a weight of 200 g/mm2 and epoxy resin LG730. During laboratory strain tests described in the paper Tenmex's delta type strain gauge rosettes were used. They were arranged in specific locations on the surface of the samples. Data acquisition preceded using HBM measurement equipment, which included measuring amplifier and measuring head. Data acquisition was performed using the Easy Catman. In order to verify the results of laboratory tests numerical studies were carried out in a

  7. Modeling of the cooling rate effect on the residual stress formation in the cantala fiber/recycled HDPE composites

    NASA Astrophysics Data System (ADS)

    Probotinanto, Yosafat C.; Raharjo, Wijang W.; Budiana, Eko P.

    2016-03-01

    Residual stress has great influence on the mechanical properties of polymer composites. Therefore, its formation during the manufacturing process needs to be investigated. The aim of this study is to investigate the influences of cooling rate on the residual stress distribution of the cantala/rHDPE composite by simulation. The simulation was done by using a SOLID227 element type of ANSYS. The cooling rates that used in this study are 0.5°C/minute, 1°C/minute, and 60°C/minute. The values of the residual stress correspond to the increasing of the cooling rate are 1171.31 kPa, 1171.42 kPa, 1172.36 kPa. In the radial direction, the residual stress was tensile inside the fibers, while in the longitudinal direction, the tensile residual stress occurred in the matrix zones and compressive in the fiber zones.

  8. HIPPOCAMPAL MOSSY FIBER LEU-ENKEPHALIN IMMUNOREACTIVITY IN FEMALE RATS IS SIGNIFICANTLY ALTERED FOLLOWING BOTH ACUTE AND CHRONIC STRESS

    PubMed Central

    Pierce, Joseph P.; Kelter, David T.; McEwen, Bruce S.; Waters, Elizabeth M.; Milner, Teresa A.

    2013-01-01

    Research indicates that responses to stress are sexually dimorphic, particularly in regard to learning and memory processes: while males display impaired cognitive performance and hippocampal CA3 pyramidal cell dendritic remodeling following chronic stress, females exhibit enhanced performance and no remodeling. Leu-enkephalin, an endogenous opioid peptide found in the hippocampal mossy fiber pathway, plays a critical role in mediating synaptic plasticity at the mossy fiber-CA3 pyramidal cell synapse. Estrogen is known to influence the expression of leu-enkephalin in the mossy fibers of females, with leu-enkephalin levels being highest at proestrus and estrus, when estrogen levels are elevated. Since stress is also known to alter the expression of leu-enkephalin in various brain regions, this study was designed to determine whether acute or chronic stress had an effect on mossy fiber leu-enkephalin levels in females or males, through the application of correlated quantitative light and electron microscopic immunocytochemistry. Both acute and chronic stress eliminated the estrogen-dependence of leu-enkephalin levels across the estrous cycle in females, but had no effect on male levels. However, following acute stress leu-enkephalin levels in females were consistently lowered to values comparable to the lowest control values, while following chronic stress they were consistently elevated to values comparable to the highest control values. Ultrastructural changes in leu-enkephalin labeled dense core vesicles paralleled light microscopic observations, with acute stress inducing a decrease in leu-enkephalin labeled dense core vesicles, and chronic stress inducing an increase in leu-enkephalin labeled dense-core vesicles in females. These findings suggest that alterations in leu-enkephalin levels following stress could play an important role in the sex-specific responses that females display in learning processes, including those important in addiction. PMID:24275289

  9. Effect of fabric structure and polymer matrix on flexural strength, interlaminar shear stress, and energy dissipation of glass fiber-reinforced polymer composites

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We report the effect of glass fiber structure and the epoxy polymer system on the flexural strength, interlaminar shear stress (ILSS), and energy absorption properties of glass fiber-reinforced polymer (GFRP) composites. Four different GFRP composites were fabricated from two glass fiber textiles of...

  10. Thermal stress modification in regenerated fiber Bragg grating via manipulation of glass transition temperature based on CO₂-laser annealing.

    PubMed

    Lai, Man-Hong; Lim, Kok-Sing; Gunawardena, Dinusha S; Yang, Hang-Zhou; Chong, Wu-Yi; Ahmad, Harith

    2015-03-01

    In this work, we have demonstrated thermal stress relaxation in regenerated fiber Bragg gratings (RFBGs) by using direct CO₂-laser annealing technique. After the isothermal annealing and slow cooling process, the Bragg wavelength of the RFBG has been red-shifted. This modification is reversible by re-annealing and rapid cooling. It is repeatable with different cooling process in the subsequent annealing treatments. This phenomenon can be attributed to the thermal stress modification in the fiber core by means of manipulation of glass transition temperature with different cooling rates. This finding in this investigation is important for accurate temperature measurement of RFBG in dynamic environment. PMID:25723423

  11. Effects of Thermal Treatment on Tensile Creep and Stress-Rupture Behavior of Hi-Nicalon SiC Fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.; Dicarlo, J. A.

    1995-01-01

    Tensile creep and stress-rupture studies were conducted on Hi-Nicalon SiC fibers at 1200 and 1400 C in argon and air. Examined were as-received fibers as well as fibers annealed from 1400 to 1800 C for 1 hour in argon before testing. The creep and rupture results for these annealed fibers were compared to those of the as-received fibers to determine the effects of annealing temperature, test temperature, and test environment. Argon anneals up to 1500 C degrade room temperature strength of Hi-Nicalon fibers, but improve fiber creep resistance in argon or air by as much as 100% with no significant degradation in rupture strength. Argon anneals above 1500 C continue to improve fiber creep resistance when tested in argon, but significantly degrade creep resistance and rupture strength when tested in air. Decrease in creep resistance in air is greater at 1200 C than at 1400 C. Mechanisms are suggested for the observed behavior.

  12. Stabilizing soliton-based multichannel transmission with frequency dependent linear gain-loss

    NASA Astrophysics Data System (ADS)

    Chakraborty, Debananda; Peleg, Avner; Nguyen, Quan M.

    2016-07-01

    We report several major theoretical steps towards realizing stable long-distance multichannel soliton transmission in Kerr nonlinear waveguide loops. We find that transmission destabilization in a single waveguide is caused by resonant formation of radiative sidebands and investigate the possibility to increase transmission stability by optimization with respect to the Kerr nonlinearity coefficient γ. Moreover, we develop a general method for transmission stabilization, based on frequency dependent linear gain-loss in Kerr nonlinear waveguide couplers, and implement it in two-channel and three-channel transmission. We show that the introduction of frequency dependent loss leads to significant enhancement of transmission stability even for non-optimal γ values via decay of radiative sidebands, which takes place as a dynamic phase transition. For waveguide couplers with frequency dependent linear gain-loss, we observe stable oscillations of soliton amplitudes due to decay and regeneration of the radiative sidebands.

  13. A kinetic model for the frequency dependence of cholinergic modulation at hippocampal GABAergic synapses.

    PubMed

    Stone, Emily; Haario, Heikki; Lawrence, J Josh

    2014-12-01

    In this paper we use a simple model of presynaptic neuromodulation of GABA signaling to decipher paired whole-cell recordings of frequency dependent cholinergic neuromodulation at CA1 parvalbumin-containing basket cell (PV BC)-pyramidal cell synapses. Variance-mean analysis is employed to normalize the data, which is then used to estimate parameters in the mathematical model. Various parameterizations and hidden parameter dependencies are investigated using Markov Chain Monte Carlo (MCMC) parameter estimation techniques. This analysis reveals that frequency dependence of cholinergic modulation requires both calcium-dependent recovery from depression and mAChR-induced inhibition of presynaptic calcium entry. A reduction in calcium entry into the presynaptic terminal in the kinetic model accounted for the frequency-dependent effects of mAChR activation. PMID:25445738

  14. On the modal decoupling of linear mechanical systems with frequency-dependent viscoelastic behavior

    NASA Astrophysics Data System (ADS)

    Mastroddi, Franco; Calore, Paolo

    2016-03-01

    Linear Multi-Degree of Freedom (MDOF) mechanical systems having frequency-dependent viscoelastic behaviors are often studied and modelled in frequency or Laplace domains. Indeed, once this modelling process is carried out, it is not generally possible to reduce the obtained MDOF damped mechanical system to a set of uncoupled damped modal oscillators apart from some special cases. In this paper a general procedure has been proposed to transform a coupled linear mechanical system having frequency-dependent viscoelastic characteristics to a set of independent damped modal oscillators. The procedure is based on a linear co-ordinate transformation procedure using matrices in real field only. The approach is exact and based on the solution of one associated eigenproblem for the case of linearly viscous damping. In the general case of frequency-dependent viscoelastic materials, the approach includes an iterative procedure solving local eigenproblems.Some numerical results are reported to show the capabilities of the proposed approach.

  15. A kinetic model for the frequency dependence of cholinergic modulation at hippocampal GABAergic synapses.

    PubMed

    Stone, Emily; Haario, Heikki; Lawrence, J Josh

    2014-12-01

    In this paper we use a simple model of presynaptic neuromodulation of GABA signaling to decipher paired whole-cell recordings of frequency dependent cholinergic neuromodulation at CA1 parvalbumin-containing basket cell (PV BC)-pyramidal cell synapses. Variance-mean analysis is employed to normalize the data, which is then used to estimate parameters in the mathematical model. Various parameterizations and hidden parameter dependencies are investigated using Markov Chain Monte Carlo (MCMC) parameter estimation techniques. This analysis reveals that frequency dependence of cholinergic modulation requires both calcium-dependent recovery from depression and mAChR-induced inhibition of presynaptic calcium entry. A reduction in calcium entry into the presynaptic terminal in the kinetic model accounted for the frequency-dependent effects of mAChR activation.

  16. Dynamical gap generation in graphene with frequency-dependent renormalization effects

    NASA Astrophysics Data System (ADS)

    Carrington, M. E.; Fischer, C. S.; von Smekal, L.; Thoma, M. H.

    2016-09-01

    We study the frequency dependencies in the renormalization of the fermion Green's function for the π -band electrons in graphene and their influence on the dynamical gap generation at sufficiently strong interaction. Adopting the effective QED-like description for the low-energy excitations within the Dirac-cone region, we self-consistently solve the fermion Dyson-Schwinger equation in various approximations for the photon propagator and the vertex function with special emphasis on frequency-dependent Lindhard screening and retardation effects.

  17. Portable polarimetric fiber stress sensor system for visco-elastic and biomimetic material analysis

    NASA Astrophysics Data System (ADS)

    Harrison, Mark C.; Armani, Andrea M.

    2015-05-01

    Non-destructive materials characterization methods have significantly changed our fundamental understanding of material behavior and have enabled predictive models to be developed. However, the majority of these efforts have focused on crystalline and metallic materials, and transitioning to biomaterials, such as tissue samples, is non-trivial, as there are strict sample handling requirements and environmental controls which prevent the use of conventional equipment. Additionally, the samples are smaller and more complex in composition. Therefore, more advanced sample analysis methods capable of operating in these environments are needed. In the present work, we demonstrate an all-fiber-based material analysis system based on optical polarimetry. Unlike previous polarimetric systems which relied on free-space components, our method combines an in-line polarizer, polarization-maintaining fiber, and a polarimeter to measure the arbitrary polarization state of the output, eliminating all free-space elements. Additionally, we develop a more generalized theoretical analysis which allows more information about the polarization state to be obtained via the polarimeter. We experimentally verify our system using a series of elastomer samples made from polydimethylsiloxane (PDMS), a commonly used biomimetic material. By adjusting the base:curing agent ratio of the PDMS, we controllably tune the Young's modulus of the samples to span over an order of magnitude. The measured results are in good agreement with those obtained using a conventional load-frame system. Our fiber-based polarimetric stress sensor shows promise for use as a simple research tool that is portable and suitable for a wide variety of applications.

  18. Mathematical modeling of the dynamic mechanical behavior of neighboring sarcomeres in actin stress fibers

    PubMed Central

    Chapin, L.M.; Edgar, L.T.; Blankman, E.; Beckerle, M.C.; Shiu, Y T

    2014-01-01

    Actin stress fibers (SFs) in live cells consist of series of dynamic individual sarcomeric units. Within a group of consecutive SF sarcomeres, individual sarcomeres can spontaneously shorten or lengthen without changing the overall length of this group, but the underlying mechanism is unclear. We used a computational model to test our hypothesis that this dynamic behavior is inherent to the heterogeneous mechanical properties of the sarcomeres and the cytoplasmic viscosity. Each sarcomere was modeled as a discrete element consisting of an elastic spring, a viscous dashpot and an active contractile unit all connected in parallel, and experiences forces as a result of actin filament elastic stiffness, myosin II contractility, internal viscoelasticity, or cytoplasmic drag. When all four types of forces are considered, the simulated dynamic behavior closely resembles the experimental observations, which include a low-frequency fluctuation in individual sarcomere length and compensatory lengthening and shortening of adjacent sarcomeres. Our results suggest that heterogeneous stiffness and viscoelasticity of actin fibers, heterogeneous myosin II contractility, and the cytoplasmic drag are sufficient to cause spontaneous fluctuations in SF sarcomere length. Our results shed new light to the dynamic behavior of SF and help design experiments to further our understanding of SF dynamics. PMID:25110525

  19. Image Analysis for the Quantitative Comparison of Stress Fibers and Focal Adhesions

    PubMed Central

    Elosegui-Artola, Alberto; Jorge-Peñas, Alvaro; Moreno-Arotzena, Oihana; Oregi, Amaia; Lasa, Marta; García-Aznar, José Manuel; De Juan-Pardo, Elena M.; Aldabe, Rafael

    2014-01-01

    Actin stress fibers (SFs) detect and transmit forces to the extracellular matrix through focal adhesions (FAs), and molecules in this pathway determine cellular behavior. Here, we designed two different computational tools to quantify actin SFs and the distribution of actin cytoskeletal proteins within a normalized cellular morphology. Moreover, a systematic cell response comparison between the control cells and those with impaired actin cytoskeleton polymerization was performed to demonstrate the reliability of the tools. Indeed, a variety of proteins that were present within the string beginning at the focal adhesions (vinculin) up to the actin SFs contraction (non-muscle myosin II (NMMII)) were analyzed. Finally, the software used allows for the quantification of the SFs based on the relative positions of FAs. Therefore, it provides a better insight into the cell mechanics and broadens the knowledge of the nature of SFs. PMID:25269086

  20. Geldanamycin anisimycins activate Rho and stimulate Rho- and ROCK-dependent actin stress fiber formation.

    PubMed

    Amiri, Anahita; Noei, Farahnaz; Feroz, Tahir; Lee, Jonathan M

    2007-09-01

    Heat shock protein 90 (Hsp90) is a member of the heat shock family of molecular chaperones that regulate protein conformation and activity. Hsp90 regulates multiple cell signaling pathways by controlling the abundance and activity of several important protein kinases and cell cycle-related proteins. In this report, we show that inhibition of Hsp90 by geldanamycin or its derivative, 17-allylamino-17-desmethoxygeldamycin, leads to activation of the Rho GTPase and a dramatic increase in actin stress fiber formation in human tumor cell lines. Inactivation of Rho prevents geldanamycin-induced actin reorganization. Hsp90 inactivation does not alter the appearance of filopodia or lamellipodia and tubulin architecture is not visibly perturbed. Our observations suggest that Hsp90 has an important and specific role in regulating Rho activity and Rho-dependent actin cytoskeleton remodeling.

  1. Implementation of thermal residual stresses in the analysis of fiber bridged matrix crack growth in titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Bakuckas, John G., Jr.; Johnson, W. Steven

    1994-01-01

    In this research, thermal residual stresses were incorporated in an analysis of fiber-bridged matrix cracks in unidirectional and cross-ply titanium matrix composites (TMC) containing center holes or center notches. Two TMC were investigated, namely, SCS-6/Timelal-21S laminates. Experimentally, matrix crack initiation and growth were monitored during tension-tension fatigue tests conducted at room temperature and at an elevated temperature of 200 C. Analytically, thermal residual stresses were included in a fiber bridging (FB) model. The local R-ratio and stress-intensity factor in the matrix due to thermal and mechanical loadings were calculated and used to evaluate the matrix crack growth behavior in the two materials studied. The frictional shear stress term, tau, assumed in this model was used as a curve-fitting parameter to matrix crack growth data. The scatter band in the values of tau used to fit the matrix crack growth data was significantly reduced when thermal residual stresses were included in the fiber bridging analysis. For a given material system, lay-up and temperature, a single value of tau was sufficient to analyze the crack growth data. It was revealed in this study that thermal residual stresses are an important factor overlooked in the original FB models.

  2. Fiber-based polarimetric stress sensor for measuring the Young's modulus of biomaterials

    NASA Astrophysics Data System (ADS)

    Harrison, Mark C.; Armani, Andrea M.

    2015-03-01

    Polarimetric optical fiber-based stress and pressure sensors have proven to be a robust tool for measuring and detecting changes in the Young's modulus (E) of materials in response to external stimuli, including the real-time monitoring of the structural integrity of bridges and buildings. These sensors typically work by using a pair of polarizers before and after the sensing region of the fiber, and often require precise alignment to achieve high sensitivity. The ability to perform similar measurements in natural and in engineered biomaterials could provide significant insights and enable research advancement and preventative healthcare. However, in order for this approach to be successful, it is necessary to reduce the complexity of the system by removing free-space components and the need for alignment. As the first step in this path, we have developed a new route for performing these measurements. By generalizing and expanding established theoretical analyses for these types of sensors, we have developed a predictive theoretical model. Additionally, by replacing the conventional free space components and polarization filters with a polarimeter, we have constructed a sensor system with higher sensitivity and which is semi-portable. In initial experiments, a series of polydimethylsiloxane (PDMS) samples with several base:curing agent ratios ranging from 5:1 up to 30:1 were prepared to simulate tissues with different stiffnesses. By simultaneously producing stress-strain curves using a load frame and monitoring the polarization change of light traveling through the samples, we verified the accuracy of our theoretical model.

  3. Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549.

    PubMed

    Rapisarda, Venerando; Loreto, Carla; Ledda, Caterina; Musumeci, Giuseppe; Bracci, Massimo; Santarelli, Lory; Renis, Marcella; Ferrante, Margherita; Cardile, Venera

    2015-04-01

    Man-made vitreous fibers have been widely used as insulation material as asbestos substitutes; however their morphology and composition raises concerns. In 1988 the International Agency for Research on Cancer classified fiberglass, rock wool, slag wool, and ceramic fibers as Group 2B, i.e. possibly carcinogenic to humans. In 2002 it reassigned fiberglass, rock and slag wool, and continuous glass filaments to Group 3, not classifiable as carcinogenic to humans. The aim of this study was to verify the cytotoxic and genotoxic effects and oxidative stress production induced by in vitro exposure of human alveolar epithelial cells A549 to glass fibers with a predominant diameter <3 μm (97%) and length >5 μm (93%). A549 cells were incubated with 5, 50, or 100 μg/ml (2.1, 21, and 42 μg/cm(2), respectively) of glass fibers for 72 h. Cytotoxicity and DNA damage were tested by the MTT and the Comet assay, respectively. Oxidative stress was determined by measuring inducible nitric oxide synthase (iNOS) expression by Western blotting, production of nitric oxide (NO) with Griess reagent, and concentration of reactive oxygen species by fluorescent quantitative analysis with 2',7'-dichlorofluorescein-diacetate (DCFH-DA). The results showed that glass fiber exposure significantly reduced cell viability and increased DNA damage and oxidative stress production in a concentration-dependent manner, demonstrating that glass fibers exert cytotoxic and genotoxic effects related to increased oxidative stress on the human alveolar cell line A549.

  4. Modeling of process-induced residual stresses and resin flow behavior in resin transfer molded composites with woven fiber mats

    NASA Astrophysics Data System (ADS)

    Golestanian, Hossein

    This research focuses on modeling Resin Transfer Molding process for manufacture of composite parts with woven fiber mats. Models are developed to determine cure dependent stiffness matrices for composites manufactured with two types of woven fiber mats. Five-harness carbon and eight-harness fiberglass mats with EPON 826 resin composites are considered. The models presented here take into account important material/process parameters with emphasis on; (1) The effects of cure-dependent resin mechanical properties, (2) Fiber undulation due to the weave of the fiber fill and warp bundles, and (3) Resin interaction with the fiber bundles at a microscopic scale. Cure-dependent mechanical properties were then used in numerical models to determine residual stresses and deformation in the composite parts. The complete cure cycle was modeled in these analyses. Also the cool down stage after the composite cure was analyzed. The effect of 5% resin shrinkage on residual stresses and deformations was also investigated. In the second part of the study, Finite Element models were developed to simulate mold filling in RTM processes. Resin flow in the fiber mats was modeled as flow through porous media. Physical models were also developed to investigate resin flow behavior into molds of rectangular and irregular shapes. Silicone fluids of 50 and 100 centistoke viscosities as well as EPON 826 epoxy resin were used in the mold filling experiments. The reinforcements consisted of several layers of woven fiberglass and carbon fiber mats. The effects of injection pressure, fluid viscosity, type of reinforcement, and mold geometry on mold filling times were investigated. Fiber mat permeabilities were determined experimentally for both types of reinforcements. Comparison of experimental and numerical resin front positions indicated the importance of edge effects in resin flow behavior in small cavities. The resin front positions agreed well for the rectangular mold geometry.

  5. The vestibular implant: frequency-dependency of the electrically evoked vestibulo-ocular reflex in humans.

    PubMed

    van de Berg, Raymond; Guinand, Nils; Nguyen, T A Khoa; Ranieri, Maurizio; Cavuscens, Samuel; Guyot, Jean-Philippe; Stokroos, Robert; Kingma, Herman; Perez-Fornos, Angelica

    2014-01-01

    The vestibulo-ocular reflex (VOR) shows frequency-dependent behavior. This study investigated whether the characteristics of the electrically evoked VOR (eVOR) elicited by a vestibular implant, showed the same frequency-dependency. Twelve vestibular electrodes implanted in seven patients with bilateral vestibular hypofunction (BVH) were tested. Stimuli consisted of amplitude-modulated electrical stimulation with a sinusoidal profile at frequencies of 0.5, 1, and 2 Hz. The main characteristics of the eVOR were evaluated and compared to the "natural" VOR characteristics measured in a group of age-matched healthy volunteers who were subjected to horizontal whole body rotations with equivalent sinusoidal velocity profiles at the same frequencies. A strong and significant effect of frequency was observed in the total peak eye velocity of the eVOR. This effect was similar to that observed in the "natural" VOR. Other characteristics of the (e)VOR (angle, habituation-index, and asymmetry) showed no significant frequency-dependent effect. In conclusion, this study demonstrates that, at least at the specific (limited) frequency range tested, responses elicited by a vestibular implant closely mimic the frequency-dependency of the "normal" vestibular system.

  6. Interactions between frequency-dependent and vertical transmission in host-parasite systems.

    PubMed Central

    Altizer, S M; Augustine, D J

    1997-01-01

    We investigate host-pathogen dynamics and conditions for coexistence in two models incorporating frequency-dependent horizontal transmission in conjunction with vertical transmission. The first model combines frequency-dependent and uniparental vertical transmission, while the second addresses parasites transmitted vertically via both parents. For the first model, we ask how the addition of vertical transmission changes the coexistence criteria for parasites transmitted by a frequency-dependent horizontal route, and show that vertical transmission significantly broadens the conditions for parasite invasion. Host-parasite coexistence is further affected by the form of density-dependent host regulation. Numerical analyses demonstrate that within a host population, a parasite strain with horizontal frequency-dependent transmission can be driven to extinction by a parasite strain that is additionally transmitted vertically for a wide range of parameters. Although models of asexual host populations predict that vertical transmission alone cannot maintain a parasite over time, analysis of our second model shows that vertical transmission via both male and female parents can maintain a parasite at a stable equilibrium. These results correspond with the frequent co-occurrence of vertical with sexual transmission in nature and suggest that these transmission modes can lead to host-pathogen coexistence for a wide range of systems involving hosts with high reproductive rates. PMID:9265188

  7. FREQUENCY-DEPENDENT CHANGES IN GAP JUNCTION FUNCTION IN PRIMARY HEPATOCYTES

    EPA Science Inventory

    FREQUENCY-DEPENDENT CHANGES IN GAP JUNCTION FUNCTION IN PRIMARY HEPATOCYTES. X. Wang1 *, D.E. Housel *, J. Page2, C.F. Blackmanl. 1 National Health and Environmental Effects Research Laboratory, USEPA, Research Triangle Park, North Carolina 27711 USA, 2Oakland, California USA
    ...

  8. Modeling and quantifying frequency-dependent fitness in microbial populations with cross-feeding interactions.

    PubMed

    Ribeck, Noah; Lenski, Richard E

    2015-05-01

    Coexistence of two or more populations by frequency-dependent selection is common in nature, and it often arises even in well-mixed experiments with microbes. If ecology is to be incorporated into models of population genetics, then it is important to represent accurately the functional form of frequency-dependent interactions. However, measuring this functional form is problematic for traditional fitness assays, which assume a constant fitness difference between competitors over the course of an assay. Here, we present a theoretical framework for measuring the functional form of frequency-dependent fitness by accounting for changes in abundance and relative fitness during a competition assay. Using two examples of ecological coexistence that arose in a long-term evolution experiment with Escherichia coli, we illustrate accurate quantification of the functional form of frequency-dependent relative fitness. Using a Monod-type model of growth dynamics, we show that two ecotypes in a typical cross-feeding interaction-such as when one bacterial population uses a byproduct generated by another-yields relative fitness that is linear with relative frequency.

  9. Colour polymorphism torn apart by opposing positive frequency-dependent selection, yet maintained in space.

    PubMed

    Gordon, Swanne P; Kokko, Hanna; Rojas, Bibiana; Nokelainen, Ossi; Mappes, Johanna

    2015-11-01

    Polymorphic warning signals in aposematic species are enigmatic because predator learning and discrimination should select for the most common coloration, resulting in positive frequency-dependent survival selection. Here, we investigated whether differential mating success could create sufficiently strong negative frequency-dependent selection for rare morphs to explain polymorphic (white and yellow) warning coloration in male wood tiger moths (Parasemia plantaginis). We conducted an experiment in semi-natural conditions where we estimated mating success for both white and yellow male moths under three different morph frequencies. Contrary to expectations, mating success was positively frequency-dependent: white morph males had high relative fitness when common, likewise yellow morph males had high relative fitness when instead they were common. We hence built a model parameterized with our data to examine whether polymorphism can be maintained despite two sources of positive frequency dependence. The model includes known spatial variation in the survival advantage enjoyed by the yellow morph and assumes that relative mating success follows our experimentally derived values. It predicts that polymorphism is possible under migration for up to approximately 20% exchange of individuals between subpopulations in each generation. Our results suggest that differential mating success combined with spatial variation in predator communities may operate as a selection mosaic that prevents complete fixation of either morph.

  10. Thermal stress and Ca-independent contractile activation in mammalian skeletal muscle fibers at high temperatures.

    PubMed Central

    Ranatunga, K W

    1994-01-01

    Temperature dependence of the isometric tension was examined in chemically skinned, glycerinated, rabbit Psoas, muscle fibers immersed in relaxing solution (pH approximately 7.1 at 20 degrees C, pCa approximately 8, ionic strength 200 mM); the average rate of heating/cooling was 0.5-1 degree C/s. The resting tension increased reversibly with temperature (5-42 degrees C); the tension increase was slight in warming to approximately 25 degrees C (a linear thermal contraction, -alpha, of approximately 0.1%/degree C) but became more pronounced above approximately 30 degrees C (similar behavior was seen in intact rat muscle fibers). The extra tension rise at the high temperatures was depressed in acidic pH and in the presence of 10 mM inorganic phosphate; it was absent in rigor fibers in which the tension decreased with heating (a linear thermal expansion, alpha, of approximately 4 x 10(-5)/degree C). Below approximately 20 degrees C, the tension response after a approximately 1% length increase (complete < 0.5 ms) consisted of a fast decay (approximately 150.s-1 at 20 degrees C) and a slow decay (approximately 10.s-1) of tension. The rate of fast decay increased with temperature (Q10 approximately 2.4); at 35-40 degrees C, it was approximately 800.s-1, and it was followed by a delayed tension rise (stretch-activation) at 30-40.s-1. The linear rise of passive tension in warming to approximately 25 degrees C may be due to increase of thermal stress in titin (connectin)-myosin composite filament, whereas the extra tension above approximately 30 degrees C may arise from cycling cross-bridges; based on previous findings from regulated actomyosin in solution (Fuchs, 1975), it is suggested that heating reversibly inactivates the troponin-tropomyosin control mechanism and leads to Ca-independent thin filament activation at high temperatures. Additionally, we propose that the heating-induced increase of endo-sarcomeric stress within titin-myosin composite filament makes the

  11. Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Pujar, Vijay

    2004-01-01

    Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

  12. Phase-Shifted Based Numerical Method for Modeling Frequency-Dependent Effects on Seismic Reflections

    NASA Astrophysics Data System (ADS)

    Chen, Xuehua; Qi, Yingkai; He, Xilei; He, Zhenhua; Chen, Hui

    2016-08-01

    The significant velocity dispersion and attenuation has often been observed when seismic waves propagate in fluid-saturated porous rocks. Both the magnitude and variation features of the velocity dispersion and attenuation are frequency-dependent and related closely to the physical properties of the fluid-saturated porous rocks. To explore the effects of frequency-dependent dispersion and attenuation on the seismic responses, in this work, we present a numerical method for seismic data modeling based on the diffusive and viscous wave equation (DVWE), which introduces the poroelastic theory and takes into account diffusive and viscous attenuation in diffusive-viscous-theory. We derive a phase-shift wave extrapolation algorithm in frequencywavenumber domain for implementing the DVWE-based simulation method that can handle the simultaneous lateral variations in velocity, diffusive coefficient and viscosity. Then, we design a distributary channels model in which a hydrocarbon-saturated sand reservoir is embedded in one of the channels. Next, we calculated the synthetic seismic data to analytically and comparatively illustrate the seismic frequency-dependent behaviors related to the hydrocarbon-saturated reservoir, by employing DVWE-based and conventional acoustic wave equation (AWE) based method, respectively. The results of the synthetic seismic data delineate the intrinsic energy loss, phase delay, lower instantaneous dominant frequency and narrower bandwidth due to the frequency-dependent dispersion and attenuation when seismic wave travels through the hydrocarbon-saturated reservoir. The numerical modeling method is expected to contribute to improve the understanding of the features and mechanism of the seismic frequency-dependent effects resulted from the hydrocarbon-saturated porous rocks.

  13. Performance analysis of fiber optic concrete stress sensors in polarimetric and white-light interferometric configurations applicable to nuclear facilities

    NASA Astrophysics Data System (ADS)

    Bock, Wojtek J.; Urbanczyk, Waclaw; Voet, Marc R. H.

    1994-12-01

    In this paper we discuss two particular topologies of fiber-optic sensors developed recently at the Laboratory of Optoelectronics at UQAH, based on pressure induced birefringence effects occurring in HB fibers, and both in temperature-compensating configurations. We present a thorough analysis of the performance of our first industrial prototype of fiber-optic stress cell developed around the concept of polarimetric pressure sensor. This prototype is based on all- fiber configuration and uses a Corning highly birefringent fiber for sensing, for temperature compensation and for transmission of light signal; a 3M polarizing fiber is also employed as a distributed polarizer. The leading input and output HB fibers are connectorized to the semiconductor laser diode and to the portable electronic detection unit. Metrological data presented in this paper show an overall accuracy of the system better than 1% of full scale in the pressure range up to 21 MPa, including stability, repeatability and temperature drift in the range of about 35 degree(s)C. Both pressure hysteresis effects and sensitivity of the leading fibers to external perturbations are negligible, and the excellent power budget of the sensor allows for remote operation up to several kilometers. The paper presents also a novel configuration of the white-light interferometric pressure sensor based entirely on HB fibers and employing electronic scanning to improve mechanical stability of the receiving interferometer, where the white-light interference pattern registered by the CCD detector is transversally shifted with pressure. We present metrological evaluation of the laboratory prototype of this sensor for the pressures up to 40 MPa for the temperatures from 10 to 35 deg. C. We also evaluate the application of coherence multiplexing for networking this type of sensors.

  14. Effects of mechanical properties of adhesive resin cements on stress distribution in fiber-reinforced composite adhesive fixed partial dentures.

    PubMed

    Yokoyama, Daiichiro; Shinya, Akikazu; Gomi, Harunori; Vallittu, Pekka K; Shinya, Akiyoshi

    2012-01-01

    Using finite element analysis (FEA), this study investigated the effects of the mechanical properties of adhesive resin cements on stress distributions in fiber-reinforced resin composite (FRC) adhesive fixed partial dentures (AFPDs). Two adhesive resin cements were compared: Super-Bond C&B and Panavia Fluoro Cement. The AFPD consisted of a pontic to replace a maxillary right lateral incisor and retainers on a maxillary central incisor and canine. FRC framework was made of isotropic, continuous, unidirectional E-glass fibers. Maximum principal stresses were calculated using finite element method (FEM). Test results revealed that differences in the mechanical properties of adhesive resin cements led to different stress distributions at the cement interfaces between AFPD and abutment teeth. Clinical implication of these findings suggested that the safety and longevity of an AFPD depended on choosing an adhesive resin cement with the appropriate mechanical properties. PMID:22447051

  15. Shear-lag analysis of fiber push-out (indentation) tests for estimating interfacial friction stress in ceramic-matrix composites

    SciTech Connect

    Shetty, D.K.

    1988-02-01

    A shear-lag analysis is presented for estimating sliding friction stress at fiber-matrix interfaces in ceramic-matrix composites using the single-fiber push-out test. The analysis includes an approximate correction for the increased interfacial compression and, therefore, the interfacial friction stress arising from the transverse (Poisson) expansion of the fibers subjected to the compressive load. An exponential decrease of the interfacial shear stress along the fiber length is predicted. This result is similar to the results of a finite-element analysis reported in the literature. The analysis also provides a basis for the experimental determination of a coefficient of interfacial friction (..mu..) and a residual interfacial compression (sigma/sub O/). It is shown that the sliding friction stress (tau/sub f/=..mu..sigma/sub O/) can be overestimated if the transverse expansion of the fibers is not taken into account.

  16. Hydrothermal and mechanical stresses degrade fiber-matrix interfacial bond strength in dental fiber-reinforced composites.

    PubMed

    Bouillaguet, Serge; Schütt, Andrea; Alander, Pasi; Schwaller, Patrick; Buerki, Gerhard; Michler, Johann; Cattani-Lorente, Maria; Vallittu, Pekka K; Krejci, Ivo

    2006-01-01

    Fiber-reinforced composites (FRCs) show great promise as long-term restorative materials in dentistry and medicine. Recent evidence indicates that these materials degrade in vivo, but the mechanisms are unclear. The objective of this study was to investigate mechanisms of deterioration of glass fiber-polymer matrix bond strengths in dental fiber-reinforced composites during hydrothermal and mechanical aging. Conventional three-point bending tests on dental FRCs were used to assess flexural strengths and moduli. Micro push-out tests were used to measure glass fiber-polymer matrix bond strengths, and nanoindentation tests were used to determine the modulus of elasticity of fiber and polymer matrix phases separately. Bar-shaped specimens of FRCs (EverStick, StickTech, and Vectris Pontic, Ivoclar-Vivadent) were either stored at room temperature, in water (37 and 100 degrees C) or subjected to ageing (10(6) cycles, load: 49 N), then tested by three-point bending. Thin slices were prepared for micro push-out and nanoindentation tests. The ultimate flexural strengths of both FRCs were significantly reduced after aging (p < 0.05). Both water storage and mechanical loading reduced the interfacial bond strengths of glass fibers to polymer matrices. Nanoindentation tests revealed a slight reduction in the elastic modulus of the EverStick and Vectris Pontic polymer matrix after water storage. Mechanical properties of FRC materials degrade primarily by a loss of interfacial bond strength between the glass and resin phases. This degradation is detectable by micro push-out and nanoindentation methods.

  17. An asymptotic preserving unified gas kinetic scheme for frequency-dependent radiative transfer equations

    NASA Astrophysics Data System (ADS)

    Sun, Wenjun; Jiang, Song; Xu, Kun; Li, Shu

    2015-12-01

    This paper presents an extension of previous work (Sun et al., 2015 [22]) of the unified gas kinetic scheme (UGKS) for the gray radiative transfer equations to the frequency-dependent (multi-group) radiative transfer system. Different from the gray radiative transfer equations, where the optical opacity is only a function of local material temperature, the simulation of frequency-dependent radiative transfer is associated with additional difficulties from the frequency-dependent opacity. For the multiple frequency radiation, the opacity depends on both the spatial location and the frequency. For example, the opacity is typically a decreasing function of frequency. At the same spatial region the transport physics can be optically thick for the low frequency photons, and optically thin for high frequency ones. Therefore, the optical thickness is not a simple function of space location. In this paper, the UGKS for frequency-dependent radiative system is developed. The UGKS is a finite volume method and the transport physics is modeled according to the ratio of the cell size to the photon's frequency-dependent mean free path. When the cell size is much larger than the photon's mean free path, a diffusion solution for such a frequency radiation will be obtained. On the other hand, when the cell size is much smaller than the photon's mean free path, a free transport mechanism will be recovered. In the regime between the above two limits, with the variation of the ratio between the local cell size and photon's mean free path, the UGKS provides a smooth transition in the physical and frequency space to capture the corresponding transport physics accurately. The seemingly straightforward extension of the UGKS from the gray to multiple frequency radiation system is due to its intrinsic consistent multiple scale transport modeling, but it still involves lots of work to properly discretize the multiple groups in order to design an asymptotic preserving (AP) scheme in all

  18. Free radical activity of industrial fibers: role of iron in oxidative stress and activation of transcription factors.

    PubMed Central

    Gilmour, P S; Brown, D M; Beswick, P H; MacNee, W; Rahman, I; Donaldson, K

    1997-01-01

    We studied asbestos, vitreous fiber (MMVF10), and refractory ceramic fiber (RCF1) from the Thermal Insulation Manufacturers' Association fiber repository regarding the following: free radical damage to plasmid DNA, iron release, ability to deplete glutathione (GSH), and activate redox-sensitive transcription factors in macrophages. Asbestos had much more free radical activity than any of the man-made vitreous fibers. More Fe3+ was released than Fe2+ and more of both was released at pH 4.5 than at pH 7.2. Release of iron from the different fibers was generally not a good correlate of ability to cause free radical injury to the plasmid DNA. All fiber types caused some degree of oxidative stress, as revealed by depletion of intracellular GSH. Amosite asbestos upregulated nuclear binding of activator protein 1 transcription factor to a greater level than MMVF10 and RCF1; long-fiber amosite was the only fiber to enhance activation of the transcription factor nuclear factor kappa B (NF kappa B). The use of cysteine methyl ester and buthionine sulfoximine to modulate GSH suggested that GSH homeostasis was important in leading to activation of transcription factors. We conclude that the intrinsic free radical activity is the major determinant of transcription factor activation and therefore gene expression in alveolar macrophages. Although this was not related to iron release or ability to deplete macrophage GSH at 4 hr, GSH does play a role in activation of NF kappa B. Images Figure 1. Figure 5. A Figure 5. B Figure 6. A Figure 6. B PMID:9400744

  19. The Evolution of Interfacial Sliding Stresses During Cyclic Push-in Testing of C- and BN-Coated Hi-Nicalon Fiber-Reinforced CMCs

    NASA Technical Reports Server (NTRS)

    Eldridge, J. I.; Bansal, N. P.; Bhatt, R. T.

    1998-01-01

    Interfacial debond cracks and fiber/matrix sliding stresses in ceramic matrix composites (CMCs) can evolve under cyclic fatigue conditions as well as with changes in the environment, strongly affecting the crack growth behavior, and therefore, the useful service lifetime of the composite. In this study, room temperature cyclic fiber push-in testing was applied to monitor the evolution of frictional sliding stresses and fiber sliding distances with continued cycling in both C- and BN-coated Hi-Nicalon SiC fiber-reinforced CMCs. A SiC matrix composite reinforced with C-coated Hi-Nical on fibers as well as barium strontium aluminosilicate (BSAS) matrix composites reinforced with BN-coated (four different deposition processes compared) Hi-Nicalon fibers were examined. For failure at a C interface, test results indicated progressive increases in fiber sliding distances during cycling in room air but not in nitrogen. These results suggest the presence of moisture will promote crack growth when interfacial failure occurs at a C interface. While short-term testing environmental effects were not apparent for failure at the BN interfaces, long-term exposure of partially debonded BN-coated fibers to humid air resulted in large increases in fiber sliding distances and decreases in interfacial sliding stresses for all the BN coatings, presumably due to moisture attack. A wide variation was observed in debond and frictional sliding stresses among the different BN coatings.

  20. Negative frequency-dependent preferences and variation in male facial hair.

    PubMed

    Janif, Zinnia J; Brooks, Robert C; Dixson, Barnaby J

    2014-01-01

    Negative frequency-dependent sexual selection maintains striking polymorphisms in secondary sexual traits in several animal species. Here, we test whether frequency of beardedness modulates perceived attractiveness of men's facial hair, a secondary sexual trait subject to considerable cultural variation. We first showed participants a suite of faces, within which we manipulated the frequency of beard thicknesses and then measured preferences for four standard levels of beardedness. Women and men judged heavy stubble and full beards more attractive when presented in treatments where beards were rare than when they were common, with intermediate preferences when intermediate frequencies of beardedness were presented. Likewise, clean-shaven faces were least attractive when clean-shaven faces were most common and more attractive when rare. This pattern in preferences is consistent with negative frequency-dependent selection.

  1. Audio-Band Frequency-Dependent Squeezing for Gravitational-Wave Detectors.

    PubMed

    Oelker, Eric; Isogai, Tomoki; Miller, John; Tse, Maggie; Barsotti, Lisa; Mavalvala, Nergis; Evans, Matthew

    2016-01-29

    Quantum vacuum fluctuations impose strict limits on precision displacement measurements, those of interferometric gravitational-wave detectors among them. Introducing squeezed states into an interferometer's readout port can improve the sensitivity of the instrument, leading to richer astrophysical observations. However, optomechanical interactions dictate that the vacuum's squeezed quadrature must rotate by 90° around 50 Hz. Here we use a 2-m-long, high-finesse optical resonator to produce frequency-dependent rotation around 1.2 kHz. This demonstration of audio-band frequency-dependent squeezing uses technology and methods that are scalable to the required rotation frequency and validates previously developed theoretical models, heralding application of the technique in future gravitational-wave detectors. PMID:26871318

  2. Time-domain representation of frequency-dependent foundation impedance functions

    USGS Publications Warehouse

    Safak, E.

    2006-01-01

    Foundation impedance functions provide a simple means to account for soil-structure interaction (SSI) when studying seismic response of structures. Impedance functions represent the dynamic stiffness of the soil media surrounding the foundation. The fact that impedance functions are frequency dependent makes it difficult to incorporate SSI in standard time-history analysis software. This paper introduces a simple method to convert frequency-dependent impedance functions into time-domain filters. The method is based on the least-squares approximation of impedance functions by ratios of two complex polynomials. Such ratios are equivalent, in the time-domain, to discrete-time recursive filters, which are simple finite-difference equations giving the relationship between foundation forces and displacements. These filters can easily be incorporated into standard time-history analysis programs. Three examples are presented to show the applications of the method.

  3. Audio-Band Frequency-Dependent Squeezing for Gravitational-Wave Detectors

    NASA Astrophysics Data System (ADS)

    Oelker, Eric; Isogai, Tomoki; Miller, John; Tse, Maggie; Barsotti, Lisa; Mavalvala, Nergis; Evans, Matthew

    2016-01-01

    Quantum vacuum fluctuations impose strict limits on precision displacement measurements, those of interferometric gravitational-wave detectors among them. Introducing squeezed states into an interferometer's readout port can improve the sensitivity of the instrument, leading to richer astrophysical observations. However, optomechanical interactions dictate that the vacuum's squeezed quadrature must rotate by 90° around 50 Hz. Here we use a 2-m-long, high-finesse optical resonator to produce frequency-dependent rotation around 1.2 kHz. This demonstration of audio-band frequency-dependent squeezing uses technology and methods that are scalable to the required rotation frequency and validates previously developed theoretical models, heralding application of the technique in future gravitational-wave detectors.

  4. Influence of Gaussian white noise on the frequency-dependent linear polarizability of doped quantum dot

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Ghosh, Manas

    2014-06-01

    We investigate the profiles of diagonal components of frequency-dependent linear (αxx and αyy) optical response of repulsive impurity doped quantum dots. The dopant impurity potential chosen assumes Gaussian form. The study principally puts emphasis on investigating the role of noise on the polarizability components. In view of this we have exploited Gaussian white noise containing additive and multiplicative characteristics (in Stratonovich sense). The frequency-dependent polarizabilities are studied by exposing the doped dot to a periodically oscillating external electric field of given intensity. The oscillation frequency, confinement potentials, dopant location, and above all, the noise characteristics tune the linear polarizability components in a subtle manner. Whereas the additive noise fails to have any impact on the polarizabilities, the multiplicative noise influences them delicately and gives rise to additional interesting features.

  5. Effect of Frequency-Dependent Attenuation on Predicted Histotripsy Waveforms in Tissue-Mimicking Phantoms.

    PubMed

    Bader, Kenneth B; Crowe, Michael J; Raymond, Jason L; Holland, Christy K

    2016-07-01

    Tissue-mimicking phantoms are employed for the assessment of shocked histotripsy pulses in vitro. These broadband shock waves are critical for tissue ablation and are influenced by the frequency-dependent attenuation of the medium. The density, sound speed and attenuation spectra (2-25 MHz) were measured for phantoms that mimic key histotripsy targets. The influence of non-linear propagation relative to the attenuation was described in terms of Gol'dberg number. An expression was derived to estimate the bandwidth of shocked histotripsy pulses for power law-dependent attenuation. The expression is independent of the fundamental frequency of the histotripsy pulse for linear frequency-dependent attenuation. PMID:27108036

  6. Demonstrating frequency-dependent transmission of sarcoptic mange in red foxes

    PubMed Central

    Devenish-Nelson, Eleanor S.; Richards, Shane A.; Harris, Stephen; Soulsbury, Carl; Stephens, Philip A.

    2014-01-01

    Understanding the relationship between disease transmission and host density is essential for predicting disease spread and control. Using long-term data on sarcoptic mange in a red fox Vulpes vulpes population, we tested long-held assumptions of density- and frequency-dependent direct disease transmission. We also assessed the role of indirect transmission. Contrary to assumptions typical of epidemiological models, mange dynamics are better explained by frequency-dependent disease transmission than by density-dependent transmission in this canid. We found no support for indirect transmission. We present the first estimates of R0 and age-specific transmission coefficients for mange in foxes. These parameters are important for managing this poorly understood but highly contagious and economically damaging disease. PMID:25296930

  7. Influence of damping on the frequency-dependent polarizabilities of doped quantum dot

    NASA Astrophysics Data System (ADS)

    Pal, Suvajit; Ghosh, Manas

    2014-09-01

    We investigate the profiles of diagonal components of frequency-dependent linear (αxx and αyy), and first nonlinear (βxxx and βyyy) optical response of repulsive impurity doped quantum dots. The dopant impurity potential chosen assumes Gaussian form. The study principally focuses on investigating the role of damping on the polarizability components. In view of this the dopant is considered to be propagating under damped condition which is otherwise linear inherently. The frequency-dependent polarizabilities are then analyzed by placing the doped dot to a periodically oscillating external electric field of given intensity. The damping strength, in conjunction with external oscillation frequency and confinement potentials, fabricate the polarizability components in a fascinating manner which is adorned with emergence of maximization, minimization, and saturation. The discrimination in the values of the polarizability components in x and y-directions has also been addressed in the present context.

  8. Frequency dependence of thermal noise in gram-scale cantilever flexures

    NASA Astrophysics Data System (ADS)

    Nguyen, Thanh T.-H.; Mow-Lowry, Conor M.; Slagmolen, Bram J. J.; Miller, John; Mullavey, Adam J.; Goßler, Stefan; Altin, Paul A.; Shaddock, Daniel A.; McClelland, David E.

    2015-12-01

    We present measurements of the frequency dependence of thermal noise in aluminum and niobium flexures. Our measurements cover the audio-frequency band from 10 Hz to 10 kHz, which is of particular relevance to ground-based interferometric gravitational wave detectors, and span up to an order of magnitude above and below the fundamental flexure resonances. Results from two flexures are well explained by a simple model in which both structural and thermoelastic loss play a role. The ability of such a model to explain this interplay is important for investigations of quantum-radiation-pressure noise and the standard quantum limit. Furthermore, measurements on a third flexure provide evidence that surface damage can affect the frequency dependence of thermal noise in addition to reducing the quality factor, a result which will aid the understanding of how aging effects impact on thermal noise behavior.

  9. Investigating the frequency-dependent amplification of a tapered amplifier in atom interferometers.

    PubMed

    Zhan, Su; Duan, Xiao-Chun; Zhou, Min-Kang; Yao, Hui-Bin; Xu, Wen-Jie; Hu, Zhong-Kun

    2015-01-01

    We present the investigation on the frequency-dependent amplification (FDA) of a tapered amplifier (TA) and the corresponding influence on Raman-type atom interferometers. In our interferometer, the output of two phase-locked diode lasers is injected into a TA to generate Raman beams. The frequency of one laser is chirped during the interfering process, which induces a variance of the Raman lasers power as a result of the FDA of the TA. The corresponding power ratio variation of the Raman lasers is measured by beat note method, which shows a linear dependence with a slope of -0.087(4)/GHz when the laser frequency changes over 2 GHz at 780 nm. The corresponding error related to AC Stark effect due to this frequency-dependent variation is estimated for our atom interferometer. The investigation presented here may provide hints for other experiments involving TAs. PMID:25531600

  10. Demonstrating frequency-dependent transmission of sarcoptic mange in red foxes.

    PubMed

    Devenish-Nelson, Eleanor S; Richards, Shane A; Harris, Stephen; Soulsbury, Carl; Stephens, Philip A

    2014-10-01

    Understanding the relationship between disease transmission and host density is essential for predicting disease spread and control. Using long-term data on sarcoptic mange in a red fox Vulpes vulpes population, we tested long-held assumptions of density- and frequency-dependent direct disease transmission. We also assessed the role of indirect transmission. Contrary to assumptions typical of epidemiological models, mange dynamics are better explained by frequency-dependent disease transmission than by density-dependent transmission in this canid. We found no support for indirect transmission. We present the first estimates of R0 and age-specific transmission coefficients for mange in foxes. These parameters are important for managing this poorly understood but highly contagious and economically damaging disease. PMID:25296930

  11. Frequency Dependence of Single-Event Upset in Highly Advanced PowerPC Microprocessors

    NASA Technical Reports Server (NTRS)

    Irom, Farokh; Farmanesh, Farhad; White, Mark; Kouba, Coy K.

    2006-01-01

    Single-event upset effects from heavy ions were measured for Motorola silicon-on-insulator (SOI) microprocessor with 90 nm feature sizes at three frequencies of 500, 1066 and 1600 MHz. Frequency dependence of single-event upsets is discussed. The results of our studies suggest the single-event upset in registers and D-Cache tend to increase with frequency. This might have important implications for the overall single-event upset trend as technology moves toward higher frequencies.

  12. Wavevector- and frequency-dependent dielectric constant of the Stockmayer fluid

    NASA Astrophysics Data System (ADS)

    Omelyan, Igor P.

    A self-consistent computer adapted theory to calculate the wavevector- and frequency-dependent dielectric constant of polar fluids with permanent dipoles is proposed. The dielectric tensor of the Stockmayer fluid is evaluated in a wide region of wavevectors and frequencies using molecular dynamics simulations. Wavevector-dependent relaxation time and longitudinal dipolaron frequency are calculated. Application of a generalized two-variable theory is discussed.

  13. Frequency dependence and viral diversity imply chaos in an HIV model

    NASA Astrophysics Data System (ADS)

    Iwami, Shingo; Nakaoka, Shinji; Takeuchi, Yasuhiro

    2006-11-01

    In this paper, we consider the effect of viral diversity on the human immune system with frequency dependent rate of proliferation of CTLs (cytotoxic T-lymphocytes) and rate of elimination of infected cells by CTLs. We show that the interior equilibrium of our model can become unstable without viral diversity and we observe stable periodic orbits. Furthermore, our mathematical models suggest that viral diversity produces strange attractors.

  14. The impact of random frequency-dependent mutations on the average population fitness

    PubMed Central

    2012-01-01

    Background In addition to selection, the process of evolution is accompanied by stochastic effects, such as changing environmental conditions, genetic drift and mutations. Commonly it is believed that without genetic drift, advantageous mutations quickly fixate in a halpoid population due to strong selection and lead to a continuous increase of the average fitness. This conclusion is based on the assumption of constant fitness. However, for frequency dependent fitness, where the fitness of an individual depends on the interactions with other individuals in the population, this does not hold. Results We propose a mathematical model that allows to understand the consequences of random frequency dependent mutations on the dynamics of an infinite large population. The frequencies of different types change according to the replicator equations and the fitness of a mutant is random and frequency dependent. To capture the interactions of different types, we employ a payoff matrix of variable size and thus are able to accommodate an arbitrary number of mutations. We assume that at most one mutant type arises at a time. The payoff entries to describe the mutant type are random variables obeying a probability distribution which is related to the fitness of the parent type. Conclusions We show that a random mutant can decrease the average fitness under frequency dependent selection, based on analytical results for two types and simulations for n types. Interestingly, in the case of at most two types the probabilities to increase or decrease the average fitness are independent of the concrete probability density function. Instead, they only depend on the probability that the payoff entries of the mutant are larger than the payoff entries of the parent type. PMID:22935138

  15. Optimal SNR exposure time for speckle imaging: experimental results with frequency-dependent detector noise

    NASA Astrophysics Data System (ADS)

    Tyler, David W.; Suzuki, Andrew H.; von Bokern, Mark A.; Keating, Donna D.; Roggemann, Michael C.

    1994-06-01

    We review recent arguments for using increased spectral bandwidth and exposure times to optimize the signal-to-noise ratio of speckle imaging estimators and discuss the tradeoff between camera exposure time and the number of data frames collected when observing time is fixed. We compare experimental results with a previously-derived expression for optimal exposure time and find reasonable agreement after accounting for frequency-dependent camera noise.

  16. Positively Frequency-Dependent Interference Competition Maintains Diversity and Pervades a Natural Population of Cooperative Microbes.

    PubMed

    Rendueles, Olaya; Amherd, Michaela; Velicer, Gregory J

    2015-06-29

    Positively frequency-dependent selection is predicted from theory to promote diversity in patchily structured populations and communities, but empirical support for this prediction has been lacking. Here, we investigate frequency-dependent selection among isolates from a local natural population of the highly social bacterium Myxococcus xanthus. Upon starvation, closely related cells of M. xanthus cooperate to construct multicellular fruiting bodies, yet recently diverged genotypes co-residing in a local soil population often antagonize one another during fruiting-body development in mixed groups. In the experiments reported here, both fitness per se and strong forms of interference competition exhibit pervasive and strong positive frequency dependence (PFD) among many isolates from a centimeter-scale soil population of M. xanthus. All strains that compete poorly at intermediate frequency are shown to be competitively dominant at high frequency in most genotype pairings during both growth and development, and strongly so. Interference competition is often lethal and appears to be contact dependent rather than mediated by diffusible compounds. Finally, we experimentally demonstrate that positively frequency-dependent selection maintains diversity when genotype frequencies vary patchily in structured populations. These results suggest that PFD contributes to the high levels of local diversity found among M. xanthus social groups in natural soil populations by reinforcing social barriers to cross-territory invasion and thereby also promotes high within-group relatedness. More broadly, our results suggest that potential roles of PFD in maintaining patchily distributed diversity should be investigated more extensively in other species. PMID:26051889

  17. Real-time seismic intensity prediction using frequency-dependent site amplification factors

    NASA Astrophysics Data System (ADS)

    Ogiso, Masashi; Aoki, Shigeki; Hoshiba, Mitsuyuki

    2016-05-01

    A promising approach for the next generation of earthquake early warning system is based on predicting ground motion directly from observed ground motion, without any information of hypocenter. In this study, we predicted seismic intensity at the target stations from the observed ground motion at adjacent stations, employing two different methods of correction for site amplification factors. The first method was frequency-dependent correction prediction, in which we used a digital causal filter to correct the site amplification for the observed waveform in the time domain. The second method was scalar correction, in which we used average differences in seismic intensity between two stations for the site amplification correction. Results from thousands of station pairs that covered almost all of Japan showed that seismic intensity prediction with frequency-dependent correction prediction was more accurate than prediction with scalar correction. Frequency-dependent correction for site amplification in the time domain may lead to more accurate prediction of ground motion in real time.

  18. Frequency dependence of electron spin-lattice relaxation for semiquinones in alcohol solutions

    NASA Astrophysics Data System (ADS)

    Elajaili, Hanan B.; Biller, Joshua R.; Eaton, Sandra S.; Eaton, Gareth R.

    2014-10-01

    The spin-lattice relaxation rates at 293 K for three anionic semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, and 2,3,5,6-tetramethoxy-1,4-benzosemiquinone) were studied at up to 8 frequencies between 250 MHz and 34 GHz in ethanol or methanol solution containing high concentrations of OH-. The relaxation rates are about a factor of 2 faster at lower frequencies than at 9 or 34 GHz. However, in perdeuterated alcohols the relaxation rates exhibit little frequency dependence, which demonstrates that the dominant frequency-dependent contribution to relaxation is modulation of dipolar interactions with solvent nuclei. The relaxation rates were modeled as the sum of two frequency-independent contributions (spin rotation and a local mode) and two frequency-dependent contributions (modulation of dipolar interaction with solvent nuclei and a much smaller contribution from modulation of g anisotropy). The correlation time for modulation of the interaction with solvent nuclei is longer than the tumbling correlation time of the semiquinone and is consistent with hydrogen bonding of the alcohol to the oxygen atoms of the semiquinones.

  19. Non-channel mechanosensors working at focal adhesion-stress fiber complex.

    PubMed

    Hirata, Hiroaki; Tatsumi, Hitoshi; Hayakawa, Kimihide; Sokabe, Masahiro

    2015-01-01

    Mechanosensitive ion channels (MSCs) have long been the only established molecular class of cell mechanosensors; however, in the last decade, a variety of non-channel type mechanosensor molecules have been identified. Many of them are focal adhesion-associated proteins that include integrin, talin, and actin. Mechanosensors must be non-soluble molecules firmly interacting with relatively rigid cellular structures such as membranes (in terms of lateral stiffness), cytoskeletons, and adhesion structures. The partner of MSCs is the membrane in which MSC proteins efficiently transduce changes in the membrane tension into conformational changes that lead to channel opening. By contrast, the integrin, talin, and actin filament form a linear complex of which both ends are typically anchored to the extracellular matrices via integrins. Upon cell deformation by forces, this structure turns out to be a portion that efficiently transduces the generated stress into conformational changes of composite molecules, leading to the activation of integrin (catch bond with extracellular matrices) and talin (unfolding to induce vinculin bindings). Importantly, this structure also serves as an "active" mechanosensor to detect substrate rigidity by pulling the substrate with contraction of actin stress fibers (SFs), which may induce talin unfolding and an activation of MSCs in the vicinity of integrins. A recent study demonstrates that the actin filament acts as a mechanosensor with unique characteristics; the filament behaves as a negative tension sensor in which increased torsional fluctuations by tension decrease accelerate ADF/cofilin binding, leading to filament disruption. Here, we review the latest progress in the study of those non-channel mechanosensors and discuss their activation mechanisms and physiological roles. PMID:24965068

  20. High temperature fiber optic microphone having a pressure-sensing reflective membrane under tensile stress

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J. (Inventor); Cuomo, Frank W. (Inventor); Robbins, William E. (Inventor); Hopson, Purnell, Jr. (Inventor)

    1992-01-01

    A fiber optic microphone is provided for measuring fluctuating pressures. An optical fiber probe having at least one transmitting fiber for transmitting light to a pressure-sensing membrane and at least one receiving fiber for receiving light reflected from a stretched membrane is provided. The pressure-sensing membrane may be stretched for high frequency response. Further, a reflecting surface of the pressure-sensing membrane may have dimensions which substantially correspond to dimensions of a cross section of the optical fiber probe. Further, the fiber optic microphone can be made of materials for use in high temperature environments, for example greater than 1000 F. A fiber optic probe is also provided with a backplate for damping membrane motion. The backplate further provides a means for on-line calibration of the microphone.

  1. Differential Contributions of Nonmuscle Myosin II Isoforms and Functional Domains to Stress Fiber Mechanics.

    PubMed

    Chang, Ching-Wei; Kumar, Sanjay

    2015-09-04

    While is widely acknowledged that nonmuscle myosin II (NMMII) enables stress fibers (SFs) to generate traction forces against the extracellular matrix, little is known about how specific NMMII isoforms and functional domains contribute to SF mechanics. Here we combine biophotonic and genetic approaches to address these open questions. First, we suppress the NMMII isoforms MIIA and MIIB and apply femtosecond laser nanosurgery to ablate and investigate the viscoelastic retraction of individual SFs. SF retraction dynamics associated with MIIA and MIIB suppression qualitatively phenocopy our earlier measurements in the setting of Rho kinase (ROCK) and myosin light chain kinase (MLCK) inhibition, respectively. Furthermore, fluorescence imaging and photobleaching recovery reveal that MIIA and MIIB are enriched in and more stably localize to ROCK- and MLCK-controlled central and peripheral SFs, respectively. Additional domain-mapping studies surprisingly reveal that deletion of the head domain speeds SF retraction, which we ascribe to reduced drag from actomyosin crosslinking and frictional losses. We propose a model in which ROCK/MIIA and MLCK/MIIB functionally regulate common pools of SFs, with MIIA crosslinking and motor functions jointly contributing to SF retraction dynamics and cellular traction forces.

  2. Cell shape, spreading symmetry and the polarization of stress-fibers in cells

    PubMed Central

    Zemel, A.; Rehfeldt, F.; Brown, A. E. X.; Discher, D. E.; Safran, S. A.

    2010-01-01

    The active regulation of cellular forces during cell adhesion plays an important role in the determination of cell size, shape and internal structure. While on flat, homogeneous and isotropic substrates some cells spread isotropically, others spread anisotropically and assume elongated structures. In addition, in their native environment as well as in vitro experiments, the cell shape and spreading asymmetry can be modulated by the local distribution of adhesive molecules and topography of the environment. We present a simple elastic model, and experiments on stem cells to explain the variation of cell size with the matrix rigidity. In addition, we predict the experimental consequences of two mechanisms of acto-myosin polarization and focus here on the effect of the cell spreading asymmetry on the regulation of the stress-fiber alignment in the cytoskeleton. We show that when cell spreading is sufficiently asymmetric the alignment of acto-myosin forces in the cell increases monotonically with the matrix rigidity; however, in general this alignment is non-monotonic as shown previously. These results highlight the importance of the symmetry characteristics of cell spreading in the regulation of cytoskeleton structure and suggest a mechanism by which different cell types may acquire different morphologies and internal structures in different mechanical environments. PMID:20458358

  3. Cell shape, spreading symmetry, and the polarization of stress-fibers in cells

    NASA Astrophysics Data System (ADS)

    Zemel, A.; Rehfeldt, F.; Brown, A. E. X.; Discher, D. E.; Safran, S. A.

    2010-05-01

    The active regulation of cellular forces during cell adhesion plays an important role in the determination of cell size, shape, and internal structure. While on flat, homogeneous and isotropic substrates some cells spread isotropically, others spread anisotropically and assume elongated structures. In addition, in their native environment as well as in vitro experiments, the cell shape and spreading asymmetry can be modulated by the local distribution of adhesive molecules and topography of the environment. We present a simple elastic model and experiments on stem cells to explain the variation of cell size with the matrix rigidity. In addition, we predict the experimental consequences of two mechanisms of acto-myosin polarization and focus here on the effect of the cell spreading asymmetry on the regulation of the stress-fiber alignment in the cytoskeleton. We show that when cell spreading is sufficiently asymmetric the alignment of acto-myosin forces in the cell increases monotonically with the matrix rigidity; however, in general this alignment is non-monotonic, as shown previously. These results highlight the importance of the symmetry characteristics of cell spreading in the regulation of cytoskeleton structure and suggest a mechanism by which different cell types may acquire different morphologies and internal structures in different mechanical environments.

  4. Effect of temperature on fiber/matrix interface sliding stress in SCS-6/Timetal{reg_sign}21S

    SciTech Connect

    Hutson, A.; John, R.; Jira, J.

    1999-02-05

    Many potential applications exist for components manufactured using Titanium Matrix Composites (TMC) because of the high specific strength and stiffness the material exhibits at elevated temperature. Several methods have been employed to determine or deduce the fiber/matrix interfacial shear stress, {tau}. Fiber push-out and pull-out techniques have been used to measure {tau}, but efforts to apply these values to accurate fatigue crack growth prediction have failed. Other methods include determination of {tau} as a fitting parameter based on correlation with parameters measured during fatigue crack growth tests. A common approach is to calibrate {tau} using the crack length versus cycles data (a-N) from a fully bridged crack growth test at a given applied stress. Subsequently, this value of {tau} has been shown to have predictive capabilities for crack opening displacements (COD), slip lengths, and a-N at other stress levels and volume fractions. Application of fiber bridging models to components under service loading conditions requires {tau} as a function of temperature over a wide range of crack lengths. Hence, this paper discusses the determination of {tau} as a function of temperature from COD measured in situ during crack growth along long fully-bridged cracks in SCS-6/TIMETAL{reg_sign}21S. Two commonly used shear lag models were evaluated during this study.

  5. Actin stress fiber disruption and tropomysin isoform switching in normal thyroid epithelial cells stimulated by thyrotropin and phorbol esters

    SciTech Connect

    Roger, P.P.; Rickaert, F.; Lamy, F.; Authelet, M.; Dumont, J.E. )

    1989-05-01

    Thyrotropin (TSH), through cyclic AMP, promotes both proliferation and differentiation expression in dog thyroid epithelial cells in primary culture, whereas the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) also stimulates proliferation but antagonizes differentiating effects of TSH. In this study, within 20 min both factors triggered the disruption of actin-containing stress fibers. This process preceded distinct morphological changes: cytoplasmic retraction and arborization in response to TSH and cyclic AMP, cell shape distortion, and increased motility in response to TPA and diacylglycerol. TSH and TPA also induced a marked decrease in the synthesis of three high M{sub r} tropomyosin isoforms, which were not present in dog thyroid tissue but appeared in culture during cell spreading and stress fiber formation. The tropomyosin isoform switching observed here closely resembled similar processes in various cells transformed by oncogenic viruses. However, it did not correlate with differentiation or mitogenic activation. Contrasting with current hypothesis on this process in transformed cells, tropomyosin isoform switching in normal thyroid cells was preceded and thus might be caused by early disruption of stress fibers.

  6. Raman Study of Uncoated and P-bn/sic-coated Hi-nicalon Reinforced Celsian Matrix Composites. Part 2; Residual Stress in the Fibers

    NASA Technical Reports Server (NTRS)

    Gouadec, Gwenael; Colomban, Philippe; Bansal, Narottam P.

    2000-01-01

    Band shifts on Raman spectra were used to assess, at a microscopic scale, the residual strain existing in Hi-Nicalon fibers reinforcing celsian matrix composites. Uncoated as well as p-BN/SiC- and p-B(Si)N/SiC-coated Hi-Nicalon fibers were used as the reinforcements. We unambiguously conclude that the fibers are in a state of compressive residual stress. Quantitative determination of the residual stress was made possible by taking into account the heating induced by laser probing and by using a reference line, of fixed wavenumber. We found fiber compressive residual stress values between 110 and 960 MPa depending on the fiber/matrix coating in the composite. A stress relaxation-like phenomenon was observed at the surface of p-BN/SiC-coated Hi-Nicalon fibers whereas the uncoated or p-B(Si)N/SiC-coated Hi-Nicalon fibers did not show any stress relaxation in the Celsian matrix composites.

  7. Feeding and lying behavior of heat-stressed early lactation cows fed low fiber diets containing roughage and nonforage fiber sources.

    PubMed

    Kanjanapruthipong, J; Junlapho, W; Karnjanasirm, K

    2015-02-01

    In addition to reduced nutrient intake, an environmental thermal load may directly affect milk yield in heat-stressed dairy cows. Feeding and lying behaviors of early lactation cows fed low fiber diets containing neutral detergent fiber (NDF) from roughage and nonforage fiber sources (NFFS) were investigated under summer conditions in Thailand. Immediately after calving, 30 multiparous cows (87.5% Holstein × 12.5% Sahiwal) were randomly allocated to dietary treatments for 63 d in a completely randomized design. The dietary treatments contained 25% of dry matter (DM) as dietary NDF. The control diet consisted of 13.9% roughage NDF from rice straw (RS). Two additional treatments were created by replacing 3.9% of DM with NDF from either soy hulls (SH) or cassava (Manihot esculenta Grantz) residues (CR), so that the roughage NDF content was reduced to 10%. During the experimental period, the minimum and maximum temperature-humidity indices (THI) were 86.4±2.5 and 91.5±2.7 during the day and 74.2±2.1 and 81.0±2.5 during the night, respectively, indicating conditions appropriate for induction of extreme heat stress. The duration of feeding and lying bouts decreased linearly with increasing THI. The DM intake during the day was greater for cows fed diets containing SH and CR than for those fed the diet containing NDF from RS. The number of meals during the day and night was lower, whereas meal size and meal length during the day and night were greater for cows fed diets containing SH and CR. Cows fed diets containing SH and CR lay down less frequently and longer during the day. These results suggest that under the severe heat stress during the day, early lactation cows fed the diet containing NFFS increased DM intake by increasing meal length and meal size rather than by increasing meal frequency and they spent more time lying. Cows fed diets containing NDF from SH and CR produced more 4% fat-corrected milk, lost less body weight, and had lower rectal temperatures

  8. Feeding and lying behavior of heat-stressed early lactation cows fed low fiber diets containing roughage and nonforage fiber sources.

    PubMed

    Kanjanapruthipong, J; Junlapho, W; Karnjanasirm, K

    2015-02-01

    In addition to reduced nutrient intake, an environmental thermal load may directly affect milk yield in heat-stressed dairy cows. Feeding and lying behaviors of early lactation cows fed low fiber diets containing neutral detergent fiber (NDF) from roughage and nonforage fiber sources (NFFS) were investigated under summer conditions in Thailand. Immediately after calving, 30 multiparous cows (87.5% Holstein × 12.5% Sahiwal) were randomly allocated to dietary treatments for 63 d in a completely randomized design. The dietary treatments contained 25% of dry matter (DM) as dietary NDF. The control diet consisted of 13.9% roughage NDF from rice straw (RS). Two additional treatments were created by replacing 3.9% of DM with NDF from either soy hulls (SH) or cassava (Manihot esculenta Grantz) residues (CR), so that the roughage NDF content was reduced to 10%. During the experimental period, the minimum and maximum temperature-humidity indices (THI) were 86.4±2.5 and 91.5±2.7 during the day and 74.2±2.1 and 81.0±2.5 during the night, respectively, indicating conditions appropriate for induction of extreme heat stress. The duration of feeding and lying bouts decreased linearly with increasing THI. The DM intake during the day was greater for cows fed diets containing SH and CR than for those fed the diet containing NDF from RS. The number of meals during the day and night was lower, whereas meal size and meal length during the day and night were greater for cows fed diets containing SH and CR. Cows fed diets containing SH and CR lay down less frequently and longer during the day. These results suggest that under the severe heat stress during the day, early lactation cows fed the diet containing NFFS increased DM intake by increasing meal length and meal size rather than by increasing meal frequency and they spent more time lying. Cows fed diets containing NDF from SH and CR produced more 4% fat-corrected milk, lost less body weight, and had lower rectal temperatures

  9. Sensitivity of seismic measurements to frequency-dependent attenuation and upper mantle structure: An initial approach

    NASA Astrophysics Data System (ADS)

    Bellis, C.; Holtzman, B.

    2014-07-01

    This study addresses the sensitivity of seismic attenuation measurements to dissipative mechanisms and structure in the Earth's upper mantle. The Andrade anelastic model fits experimental attenuation data with a mild power law frequency dependence and can be scaled from laboratory to Earth conditions. We incorporate this anelastic model into 400km 1-D thermal profiles of the upper mantle. These continuous-spectrum models are approximated by multiple relaxation mechanisms that are implemented within a finite-difference scheme to perform wave propagation simulations in 1-D domains. In two sets of numerical experiments, we evaluate the measurable signature of the intrinsic attenuation structure. The two sets are defined by thermal profiles with added step functions of temperature, varying in (i) amplitude and depth or (ii) amplitude and sharpness. The corresponding synthetic data are processed using both the conventional t* approach, i.e., a linear regression of the displacement frequency spectrum, and an alternative nonlinear fit to identify the integrated value of attenuation and its frequency dependence. The measured sensitivity patterns are analyzed to assess the effects of the anelastic model and its spatial distribution on seismic data (in the absence of scattering effects). We have two straightforward results: (1) the frequency dependence power law is recoverable from the measurements; (2) t* is sensitive to both the depth and the amplitude of the step, and it is insensitive to the sharpness of the step, in the 0.25 to 2 Hz band. There is much potential for gaining information about the upper mantle thermodynamic state from careful interpretation of attenuation.

  10. Spatial mosaic formation through frequency-dependent selection in Müllerian mimicry complexes.

    PubMed

    Sherratt, Thomas N

    2006-05-21

    Although contemporary models of Müllerian mimicry have considered the movement of interfacial boundaries between two distinct mimetic forms, and even the possibility of polymorphisms in two patch systems, no model has considered how multiple forms of Müllerian mimics might evolve and be maintained over large geographical areas. A spatially explicit individual-based model for the evolution of Müllerian mimicry is presented, in which two unpalatable species are distributed over discrete cells within a regular lattice. Populations in each cell are capable of genetic drift and experience localized dispersal as well as frequency-dependent selection by predators. When each unpalatable prey species was introduced into a random cell and allowed to spread, then mimicry evolved throughout the system in the form of a spatial mosaic of phenotypes, separated by narrow "hybrid zones". The primary mechanism generating phenotypic diversity was the occasional establishment of new mutant forms in unoccupied cells and their subsequent maintenance (and spread) through frequency-dependent selection. The mean number of discrete clusters of the same morph that formed in the lattice was higher the higher the intensity of predation, and higher the lower the dispersal rate of unpalatable prey. Under certain conditions the hybrid zones moved, in a direction dependent on the curvature of their interfacial boundaries. However, the mimetic mosaics were highly stable when the intensity of predation was high and the rate of prey dispersal was low. Overall, this model highlights how a stable mosaic of different mimetic forms can evolve from a range of starting conditions through a combination of chance effects and localized frequency-dependent selection.

  11. Frequency dependence of optical third-harmonic generation from doped graphene

    NASA Astrophysics Data System (ADS)

    Margulis, Vl. A.; Muryumin, E. E.; Gaiduk, E. A.

    2016-01-01

    In connection with the controversial question about the frequency dependence of the optical third-harmonic generation (THG) from doped graphene, which has recently been discussed in the literature, we develop an analytical theory for the THG susceptibility of doped graphene by using the original Genkin-Mednis nonlinear-conductivity-theory formalism including mixed intra- and interband terms. The theory is free of any nonphysical divergences at zero frequency, and it predicts the main resonant peak in the THG spectrum to be located at the photon energy ħω equal to two thirds of the Fermi energy EF of charge carriers in doped graphene.

  12. Monitoring processing properties of high performance thermoplastics using frequency dependent electromagnetic sensing

    NASA Technical Reports Server (NTRS)

    Kranbuehl, D. E.; Delos, S. E.; Hoff, M. S.; Weller, L. W.; Haverty, P. D.

    1987-01-01

    An in situ NDE dielectric impedance measurement method has been developed for ascertaining the cure processing properties of high temperature advanced thermoplastic and thermosetting resins, using continuous frequency-dependent measurements and analyses of complex permittivity over 9 orders of magnitude and 6 decades of frequency at temperatures up to 400 C. Both ionic and Debye-like dipolar relaxation processes are monitored. Attention is given to LARC-TPI, PEEK, and poly(arylene ether) resins' viscosity, glass transition temperature, recrystallization, and residual solvent content and evolution properties.

  13. Conceptual design of an apparatus for measuring frequency-dependent streaming potential of porous media

    NASA Astrophysics Data System (ADS)

    Tardif, Eric; Walker, Emilie; Glover, Paul; Ruel, Jean

    2010-05-01

    Electro-kinetic phenomena link fluid flow and electrical flow in porous and fractured media such that a hydraulic flow will generate an electrical current and vice versa. Such a link is likely to be extremely useful, especially in the development of the theory of the electro-seismic method. However, surprisingly little experimental determination, numerical modeling and theoretical development have taken place, and what exists is for steady state flow. There have been only a few attempts at making experimental determinations of the frequency-dependent streaming potential coupling coefficient because of their difficulty, and only one rare measurement made on rocks. Here we have considered six different approaches to making laboratory determinations of the frequency-dependent streaming potential coupling coefficient. In each case, we have quantified the practical difficulties involved in each method. We conclude that the electro-magnetic drive and the piezo-electric are the only approaches that are practicable with current technology. We have also constructed a simplified trial apparatus using the electro-magnetic drive to test the conceptual design with samples in the form of sands and beads. Tests with this apparatus on Ottawa sandstone and glass bead packs have shown that high quality measurements of the frequency-dependent streaming potential coupling coefficient can be made, and we are currently extending its frequency range. Tests have indicated that it is important to ascertain whether the measured frequency-dependent streaming potential coupling coefficient is independent of the volume of fluid passing through the sample per cycle. We have used our experience with the trial apparatus to design a new apparatus for a 1 cm diameter sample, and with the help of an engineering approach we have determined the range of possible sample permeabilities for samples between 0.5 and 2 cm in length. The new cell will have a maximum confining pressure of compressed nitrogen

  14. Frequency-dependent traveltime tomography for near-surface seismic refraction data

    NASA Astrophysics Data System (ADS)

    Zelt, Colin A.; Chen, Jianxiong

    2016-10-01

    Traveltime tomography is the main method by which the Earth's seismic velocity is determined on all scales, from the near-surface (<100 m) to the core. Usually traveltime tomography uses ray theory, an infinite-frequency approximation of wave propagation. A theory developed in global seismology to account for the finite-frequency nature of seismic data, known as finite-frequency traveltime tomography (FFTT), can theoretically provide a more accurate estimation of velocity. But the FFTT theory is generally not applicable to near-surface data because there is no reference velocity model known in advance that is capable of yielding synthetic waveforms that are close enough to the recorded seismograms to yield a reliable delay time. Also, there is usually no reference model for which the unknown velocity model represents a small (linear) perturbation from the reference model. This paper presents a frequency dependent form of non-linear traveltime tomography specifically designed for near-surface seismic data in which a starting model, iterative approach with recalculated travel paths at each iteration, and the calculation of a frequency-dependent total traveltime, as opposed to a delay time, are used. Frequency-dependent traveltime tomography (FDTT) involves two modifications to conventional traveltime tomography: (1) the calculation of frequency-dependent traveltimes using wavelength-dependent velocity smoothing (WDVS) and (2) the corresponding sensitivity kernels that arise from using WDVS. Results show that the former modification is essential to achieve significant benefits from FDTT, whereas the latter is optional in that similar results can be achieved using infinite-frequency kernels. The long seismic wavelengths relative to the total path lengths and the size of subsurface heterogeneities of typical near-surface data means the improvements over ray theory tomography are significant. The benefits of FDTT are demonstrated using conventional minimum

  15. Frequency-dependent dielectric response model for polyimide-poly(vinilydenefluoride) multilayered dielectrics

    NASA Astrophysics Data System (ADS)

    Di Lillo, Luigi; Bergamini, Andrea; Albino Carnelli, Dario; Ermanni, Paolo

    2012-07-01

    A physical model for the frequency-dependent dielectric response of multilayered structures is reported. Two frequency regimes defined by the relative permittivities and volume resistivities of the layers have been analytically identified and experimentally investigated on a structure consisting of polyimide and poly(vinilydenefluoride) layers. The relative permittivity follows an effective medium model at high frequency while showing a dependence on the volume resistivity at low frequency. In this regime, relative permittivities exceeding those expected from effective medium model are recorded. These findings provide insights into inhomogeneous dielectrics behavior for the development of high energy density dielectric films.

  16. Determination of ferroelectric contributions to electromechanical response by frequency dependent piezoresponse force microscopy

    PubMed Central

    Seol, Daehee; Park, Seongjae; Varenyk, Olexandr V.; Lee, Shinbuhm; Lee, Ho Nyung; Morozovska, Anna N.; Kim, Yunseok

    2016-01-01

    Hysteresis loop analysis via piezoresponse force microscopy (PFM) is typically performed to probe the existence of ferroelectricity at the nanoscale. However, such an approach is rather complex in accurately determining the pure contribution of ferroelectricity to the PFM. Here, we suggest a facile method to discriminate the ferroelectric effect from the electromechanical (EM) response through the use of frequency dependent ac amplitude sweep with combination of hysteresis loops in PFM. Our combined study through experimental and theoretical approaches verifies that this method can be used as a new tool to differentiate the ferroelectric effect from the other factors that contribute to the EM response. PMID:27466086

  17. Acoustic analysis of the frequency-dependent coupling between the frog's ears.

    PubMed

    Shofner, William P

    2015-09-01

    The ears of anurans are coupled through the Eustachian tubes and mouth cavity. The degree of coupling varies with frequency showing a bandpass characteristic, but the characteristics differ between empirically measured data based on auditory nerve responses and tympanic membrane vibration. In the present study, the coupling was modeled acoustically as a tube connected with a side branch. This tube corresponds to the Eustachian tubes, whereas the side branch corresponds to the mouth cavity and nares. The analysis accounts for the frequency dependency shown by the empirical data and reconciles the differences observed between the coupling as measured by tympanic membrane vibration and auditory nerve responses.

  18. Spatially resolved frequency-dependent elasticity measured with pulsed force microscopy and nanoindentation.

    PubMed

    Sweers, Kim K M; van der Werf, Kees O; Bennink, Martin L; Subramaniam, Vinod

    2012-03-21

    Recently several atomic force microscopy (AFM)-based surface property mapping techniques like pulsed force microscopy (PFM), harmonic force microscopy or Peakforce QNM® have been introduced to measure the nano- and micro-mechanical properties of materials. These modes all work at different operating frequencies. However, complex materials are known to display viscoelastic behavior, a combination of solid and fluid-like responses, depending on the frequency at which the sample is probed. In this report, we show that the frequency-dependent mechanical behavior of complex materials, such as polymer blends that are frequently used as calibration samples, is clearly measurable with AFM. Although this frequency-dependent mechanical behavior is an established observation, we demonstrate that the new high frequency mapping techniques enable AFM-based rheology with nanoscale spatial resolution over a much broader frequency range compared to previous AFM-based studies. We further highlight that it is essential to account for the frequency-dependent variation in mechanical properties when using these thin polymer samples as calibration materials for elasticity measurements by high-frequency surface property mapping techniques. These results have significant implications for the accurate interpretation of the nanomechanical properties of polymers or complex biological samples. The calibration sample is composed of a blend of soft and hard polymers, consisting of low-density polyethylene (LDPE) islands in a polystyrene (PS) surrounding, with a stiffness of 0.2 GPa and 2 GPa respectively. The spring constant of the AFM cantilever was selected to match the stiffness of LDPE. From 260 Hz to 1100 Hz the sample was imaged with the PFM method. At low frequencies (0.5-35 Hz), single-point nanoindentation was performed. In addition to the material's stiffness, the relative heights of the LDPE islands (with respect to the PS) were determined as a function of the frequency. At the lower

  19. Frequency-dependent traveltime tomography for near-surface seismic refraction data

    NASA Astrophysics Data System (ADS)

    Zelt, Colin A.; Chen, Jianxiong

    2016-07-01

    Traveltime tomography is the main method by which the Earth's seismic velocity is determined on all scales, from the near-surface (< 100 m) to the core. Usually traveltime tomography uses ray theory, an infinite-frequency approximation of wave propagation. A theory developed in global seismology to account for the finite-frequency nature of seismic data, known as finite-frequency traveltime tomography (FFTT), can theoretically provide a more accurate estimation of velocity. But the FFTT theory is generally not applicable to near-surface data because there is no reference velocity model known in advance that is capable of yielding synthetic waveforms that are close enough to the recorded seismograms to yield a reliable delay time. Also, there is usually no reference model for which the unknown velocity model represents a small (linear) perturbation from the reference model. This paper presents a frequency dependent form of nonlinear traveltime tomography specifically designed for near-surface seismic data in which a starting model, iterative approach with recalculated travel paths at each iteration, and the calculation of a frequency-dependent total traveltime, as opposed to a delay time, are used. Frequency-dependent traveltime tomography (FDTT) involves two modifications to conventional traveltime tomography: (1) the calculation of frequency-dependent traveltimes using wavelength-dependent velocity smoothing (WDVS), and (2) the corresponding sensitivity kernels that arise from using WDVS. Results show that the former modification is essential to achieve significant benefits from FDTT, whereas the latter is optional in that similar results can be achieved using infinite-frequency kernels. The long seismic wavelengths relative to the total path lengths and the size of subsurface heterogeneities of typical near-surface data means the improvements over ray theory tomography are significant. The benefits of FDTT are demonstrated using conventional minimum

  20. Determination of ferroelectric contributions to electromechanical response by frequency dependent piezoresponse force microscopy

    DOE PAGES

    Seol, Daehee; Park, Seongjae; Varenyk, Olexandr V.; Lee, Shinbuhm; Lee, Ho Nyung; Morozovska, Anna N.; Kim, Yunseok

    2016-07-28

    Hysteresis loop analysis via piezoresponse force microscopy (PFM) is typically performed to probe the existence of ferroelectricity at the nanoscale. But, such an approach is rather complex in accurately determining the pure contribution of ferroelectricity to the PFM. We suggest a facile method to discriminate the ferroelectric effect from the electromechanical (EM) response through the use of frequency dependent ac amplitude sweep with combination of hysteresis loops in PFM. This combined study through experimental and theoretical approaches verifies that this method can be used as a new tool to differentiate the ferroelectric effect from the other factors that contribute tomore » the EM response.« less

  1. Frequency-dependent polarization-angle-phase-shift in the microwave-induced magnetoresistance oscillations

    SciTech Connect

    Liu, Han-Chun; Ye, Tianyu; Mani, R. G.; Wegscheider, W.

    2015-02-14

    Linear polarization angle, θ, dependent measurements of the microwave radiation-induced oscillatory magnetoresistance, R{sub xx}, in high mobility GaAs/AlGaAs 2D electron devices have shown a θ dependence in the oscillatory amplitude along with magnetic field, frequency, and extrema-dependent phase shifts, θ{sub 0}. Here, we suggest a microwave frequency dependence of θ{sub 0}(f) using an analysis that averages over other smaller contributions, when those contributions are smaller than estimates of the experimental uncertainty.

  2. Monitoring cure of composite resins using frequency dependent electromagnetic sensing techniques

    NASA Technical Reports Server (NTRS)

    Kranbuehl, D. E.; Hoff, M. S.; Loos, A. C.; Freeman, W. T., Jr.; Eichinger, D. A.

    1988-01-01

    A nondestructive in situ measurement technique has been developed for monitoring and measuring the cure processing properties of composite resins. Frequency dependent electromagnetic sensors (FDEMS) were used to directly measure resin viscosity during cure. The effects of the cure cycle and resin aging on the viscosity during cure were investigated using the sensor. Viscosity measurements obtained using the sensor are compared with the viscosities calculated by the Loos-Springer cure process model. Good overall agreement was obtained except for the aged resin samples.

  3. Frequency dependence of the electrical conductivity in Ag/PAN nanocomposites

    NASA Astrophysics Data System (ADS)

    Kudryashov, M. A.; Mashin, A. I.; Logunov, A. A.; Chidichimo, G.; De Filpo, G.

    2012-07-01

    The frequency dispersion of the electrical conductivity of silver/polyacrylonitrile nanocomposite films is studied at various temperatures and AgNO3 contents in an initial mixture. The frequency dependences of the nanocomposites in the range 103-106 Hz are found to be well described by power law f 0.8. A charge transfer mechanism responsible for the conductivity of the nanocomposites is proposed. Silver clusters Ag{4/2+} and Ag{8/2+} are assumed to be present in the polymer.

  4. Homodyne and heterodyne optical interferometry for frequency dependent piezoelectric displacement measurement

    NASA Astrophysics Data System (ADS)

    Delahoussaye, Keith; Guo, Ruyan; Bhalla, Amar

    2014-09-01

    The electromechanical coupling in piezoelectric materials has been widely studied however a unified view of this interaction as function of frequencies using different measurement techniques has not previously been available. This study examines and compares multiple optical based homodyne and heterodyne interferometry techniques for displacement measurement over a wide range of frequencies and including a comparison made by using a commercial Laser Doppler Vibrometer. Ferroelectric lead titanate PbTiO3 with high ferroelectric strain is studied in this work. Frequency dependence of the electromechanical displacement is obtained using multiple techniques and the emphasis is given to near resonant frequency interrogations.

  5. Evaluation of frequency dependent non-linear optical property using long-range correction method

    NASA Astrophysics Data System (ADS)

    Yokoi, Yukina; Ishimaru, Hiroki; Kamiya, Muneaki; Sekino, Hideo

    2015-02-01

    We for the first time performed a systematic evaluation of dynamic second hyperpolarizabilities corresponding to all the third-order Nonlinear Optical (NLO) processes using Time Dependent Density Functional Theory (TDDFT) with exchange functional corrected for long-range interaction. We develop a program system which quantitatively evaluate the frequency dependent non-linear optical property of molecules, and apply to the polyene molecules of different lengths. The dispersion curves obtained for each NLO processes have divergence at the frequency corresponding to the one predicted by Sum Over State (SOS) interpretation of the property.

  6. Ixaru's extended frequency dependent quadrature rules for slater integrals: Parallel computation issues

    NASA Astrophysics Data System (ADS)

    Scott, N. S.; Scott, M. P.; Jézéquel, F.

    2012-09-01

    We describe recent progress of an ongoing research programme aimed at producing computational science software that can exploit high performance architectures in the atomic physics application domain. We examine the computational bottleneck of matrix construction in a suite of two-dimensional R-matrix propagation programs, 2DRMP, that are aimed at creating virtual electron collision experiments on HPC architectures. We build on Ixaru's extended frequency dependent quadrature rules (EFDQR) for Slater integrals and examine the challenge of constructing Hamiltonian matrices in parallel across an m-processor compute node in a block cyclic distribution for subsequent diagonalization by ScaLAPACK.

  7. ENDOPLASMIC RETICULUM STRESS INDUCES MYOSTATIN PRECURSOR PROTEIN AND NF-κB IN CULTURED HUMAN MUSCLE FIBERS: RELEVANCE TO INCLUSION-BODY MYOSITIS.

    PubMed Central

    Nogalska, Anna; Wojcik, Slawomir; Engel, W. King; McFerrin, Janis; Askanas, Valerie

    2007-01-01

    Sporadic-inclusion body myositis (s-IBM) is the most common progressive muscle disease of older persons. It leads to pronounced muscle fiber atrophy and weakness, and there is no successful treatment. We have previously shown that myostatin precursor protein (MstnPP) and myostatin (Mstn) dimer are increased in biopsied s-IBM muscle fibers, and proposed that MstnPP/Mstn increase may contribute to muscle fiber atrophy and weakness in s-IBM patients. Mstn is known to be a negative regulator of muscle-fiber mass. It is synthesized as MstnPP, which undergoes posttranslational processing in the muscle fiber to produce mature, active Mstn. To explore possible mechanisms involved in Mstn abnormalities in s-IBM, in the present study we utilized primary cultures of normal human muscle fibers and experimentally modified the intracellular micro-environment to induce endoplasmic-reticulum (ER)-stress, thereby mimicking an important aspect of the s-IBM muscle fiber milieu. ER-stress was induced by treating well-differentiated cultured muscle fibers with either tunicamycin or thapsigargin, both well-established ER-stress inducers. Our results indicate for the first time that the ER-stress significantly increased MstnPP mRNA and protein. The results also suggest that in our system ER-stress activates NF-κB, and we suggest that MstnPP increase occurred through the ER-stress-activated NF-κB. We therefore propose a novel mechanism leading to the Mstn increase in s-IBM. Accordingly, interfering with pathways inducing ER-stress, NF-κB activation, or its action on the MstnPP gene promoter might prevent Mstn increase and provide a new therapeutic approach for s-IBM and, possibly, for muscle atrophy in other neuromuscular diseases. PMID:17261282

  8. Fiber Bragg Grating Sensor to Monitor Stress Kinetics in Drying Process of Commercial Latex Paints

    PubMed Central

    de Lourenço, Ivo; Possetti, Gustavo R. C.; Muller, Marcia; Fabris, José L.

    2010-01-01

    In this paper, we report a study about the application of packaged fiber Bragg gratings used as strain sensors to monitor the stress kinetics during the drying process of commercial latex paints. Three stages of drying with distinct mechanical deformation and temporal behaviors were identified for the samples, with mechanical deformation from 15 μm to 21 μm in the longitudinal film dimension on time intervals from 370 to 600 minutes. Drying time tests based on human sense technique described by the Brazilian Technical Standards NBR 9558 were also done. The results obtained shows that human sense technique has a limited perception of the drying process and that the optical measurement system proposed can be used to characterize correctly the dry-through stage of paint. The influence of solvent (water) addition in the drying process was also investigated. The paint was diluted with four parts paint and one part water (80% paint), and one part paint and one part water (50% paint). It was observed that the increase of the water ratio mixed into the paint decreases both the mechanical deformation magnitude and the paint dry-through time. Contraction of 5.2 μm and 10.4 μm were measured for concentrations of 50% and 80% of paint in the mixture, respectively. For both diluted paints the dry-through time was approximately 170 minutes less than undiluted paint. The optical technique proposed in this work can contribute to the development of new standards to specify the drying time of paint coatings. PMID:22399906

  9. Vinculin tension distributions of individual stress fibers within cell–matrix adhesions

    PubMed Central

    Chang, Ching-Wei; Kumar, Sanjay

    2013-01-01

    Summary Actomyosin stress fibers (SFs) enable cells to exert traction on planar extracellular matrices (ECMs) by tensing focal adhesions (FAs) at the cell–ECM interface. Although it is widely appreciated that the spatial and temporal distribution of these tensile forces play key roles in polarity, motility, fate choice, and other defining cell behaviors, virtually nothing is known about how an individual SF quantitatively contributes to tensile loads borne by specific molecules within associated FAs. We address this key open question by using femtosecond laser ablation to sever single SFs in cells while tracking tension across vinculin using a molecular optical sensor. We show that disruption of a single SF reduces tension across vinculin in FAs located throughout the cell, with enriched vinculin tension reduction in FAs oriented parallel to the targeted SF. Remarkably, however, some subpopulations of FAs exhibit enhanced vinculin tension upon SF irradiation and undergo dramatic, unexpected transitions between tension-enhanced and tension-reduced states. These changes depend strongly on the location of the severed SF, consistent with our earlier finding that different SF pools are regulated by distinct myosin activators. We critically discuss the extent to which these measurements can be interpreted in terms of whole-FA tension and traction and propose a model that relates SF tension to adhesive loads and cell shape stability. These studies represent the most direct and high-resolution intracellular measurements of SF contributions to tension on specific FA proteins to date and offer a new paradigm for investigating regulation of adhesive complexes by cytoskeletal force. PMID:23687380

  10. Influences of temperature, oxidative stress, and phosphorylation on binding of heat shock proteins in skeletal muscle fibers.

    PubMed

    Larkins, Noni T; Murphy, Robyn M; Lamb, Graham D

    2012-09-15

    Heat shock proteins (HSPs) help maintain cellular function in stressful situations, but the processes controlling their interactions with target proteins are not well defined. This study examined the binding of HSP72, HSP25, and αB-crystallin in skeletal muscle fibers following various stresses. Rat soleus (SOL) and extensor digitorum longus (EDL) muscles were subjected in vitro to heat stress or strongly fatiguing stimulation. Superficial fibers were "skinned" by microdissection and HSP diffusibility assessed from the extent of washout following 10- to 30 min exposure to a physiological intracellular solution. In fibers from nonstressed (control) SOL muscle, >80% of each HSP is readily diffusible. However, after heating a muscle to 40°C for 30 min ∼95% of HSP25 and αB-crystallin becomes tightly bound at nonmembranous myofibrillar sites, whereas HSP72 bound at membranous sites only after heat treatment to ≥44°C. The ratio of reduced to oxidized cytoplasmic glutathione (GSH:GSSG) decreased approximately two- and fourfold after heating muscles to 40° and 45°C, respectively. The reducing agent dithiothreitol reversed HSP72 binding in heated muscles but had no effect on the other HSPs. Intense in vitro stimulation of SOL muscles, sufficient to elicit substantial oxidation-related loss of maximum force and approximately fourfold decrease in the GSH:GSSG ratio, had no effect on diffusibility of any of the HSPs. When skinned fibers from heat-treated muscles were bathed with additional exogenous HSP72, total binding increased approximately two- and 10-fold, respectively, in SOL and EDL fibers, possibly reflective of the relative sarco(endo)plasmic reticulum Ca(2+)-ATPase pump densities in the two fiber types. Phosphorylation at Ser59 on αB-crystallin and Ser85 on HSP25 increased with heat treatment but did not appear to determine HSP binding. The findings highlight major differences in the processes controlling binding of HSP72 and the two small HSPs. Binding

  11. Negative frequency-dependent interactions can underlie phenotypic heterogeneity in a clonal microbial population.

    PubMed

    Healey, David; Axelrod, Kevin; Gore, Jeff

    2016-01-01

    Genetically identical cells in microbial populations often exhibit a remarkable degree of phenotypic heterogeneity even in homogenous environments. Such heterogeneity is commonly thought to represent a bet-hedging strategy against environmental uncertainty. However, evolutionary game theory predicts that phenotypic heterogeneity may also be a response to negative frequency-dependent interactions that favor rare phenotypes over common ones. Here we provide experimental evidence for this alternative explanation in the context of the well-studied yeast GAL network. In an environment containing the two sugars glucose and galactose, the yeast GAL network displays stochastic bimodal activation. We show that in this mixed sugar environment, GAL-ON and GAL-OFF phenotypes can each invade the opposite phenotype when rare and that there exists a resulting stable mix of phenotypes. Consistent with theoretical predictions, the resulting stable mix of phenotypes is not necessarily optimal for population growth. We find that the wild-type mixed strategist GAL network can invade populations of both pure strategists while remaining uninvasible by either. Lastly, using laboratory evolution we show that this mixed resource environment can directly drive the de novo evolution of clonal phenotypic heterogeneity from a pure strategist population. Taken together, our results provide experimental evidence that negative frequency-dependent interactions can underlie the phenotypic heterogeneity found in clonal microbial populations. PMID:27487817

  12. Importance of frequency-dependent grain boundary scattering in nanocrystalline silicon and silicon-germanium thermoelectrics

    NASA Astrophysics Data System (ADS)

    Hua, Chengyun; Minnich, Austin J.

    2014-12-01

    Nanocrystalline silicon and silicon-germanium alloys are promising thermoelectric (TE) materials that have achieved substantially improved figure of merits compared to their bulk counterparts. This enhancement is typically attributed to a reduction in lattice thermal conductivity by phonon scattering at grain boundaries. However, further improvements are difficult to achieve because grain boundary scattering is poorly understood, with recent experimental observations suggesting that the phonon transmissivity may depend on phonon frequency rather than being constant as in the commonly used gray model. Here, we examine the impact of frequency-dependent grain boundary scattering in nanocrystalline silicon and silicon-germanium alloys in a realistic 3D geometry using frequency-dependent variance-reduced Monte Carlo simulations. We find that the grain boundary may not be as effective as predicted by the gray model in scattering certain phonons, with a substantial amount of heat being carried by low frequency phonons with mean free paths longer than the grain size. Our result will help guide the design of more efficient TEs.

  13. Theoretical modelling of frequency dependent elastic loss in composite piezoelectric transducers.

    PubMed

    Orr, Leigh-Ann; Mulholland, Anthony J; O'Leary, Richard L; Parr, Agnes; Pethrick, Richard A; Hayward, Gordon

    2007-12-01

    The large number of degrees of freedom in the design of piezoelectric transducers requires a theoretical model that is computationally efficient so that a large number of iterations can be performed in the design optimisation. The materials used are often lossy, and indeed loss can be used to enhance the operational characteristics of these designs. Motivated by these needs, this paper extends the one-dimensional linear systems model to incorporate frequency dependent elastic loss. The reception sensitivity, electrical impedance and electromechanical coupling coefficient of a 1-3 composite transducer, with frequency dependent loss in the polymer filler, are investigated. By plotting these operating characteristics as a function of the volume fraction of piezoelectric ceramic an optimum design is obtained. A device with a non-standard, high shear attenuation polymer is also simulated and this leads to an increase in the electromechanical coupling coefficient. A comparison with finite element simulations is then performed. This shows that the two methods are in reasonable agreement in their electrical impedance profiles in all the cases considered. The plots are almost identical away from the main resonant peak where the frequency location of the peaks are comparable but there is in some cases a 20% discrepancy in the magnitude of the peak value and in its bandwidth. The finite element model also shows that the use of a high shear attenuation polymer filler damps out the unwanted, low frequency modes whilst maintaining a reasonable impedance magnitude.

  14. Estimate error of frequency-dependent Q introduced by linear regression and its nonlinear implementation

    NASA Astrophysics Data System (ADS)

    Li, Guofa; Huang, Wei; Zheng, Hao; Zhang, Baoqing

    2016-02-01

    The spectral ratio method (SRM) is widely used to estimate quality factor Q via the linear regression of seismic attenuation under the assumption of a constant Q. However, the estimate error will be introduced when this assumption is violated. For the frequency-dependent Q described by a power-law function, we derived the analytical expression of estimate error as a function of the power-law exponent γ and the ratio of the bandwidth to the central frequency σ . Based on the theoretical analysis, we found that the estimate errors are mainly dominated by the exponent γ , and less affected by the ratio σ . This phenomenon implies that the accuracy of the Q estimate can hardly be improved by adjusting the width and range of the frequency band. Hence, we proposed a two-parameter regression method to estimate the frequency-dependent Q from the nonlinear seismic attenuation. The proposed method was tested using the direct waves acquired by a near-surface cross-hole survey, and its reliability was evaluated in comparison with the result of SRM.

  15. Frequency dependence of the onset voltage of electroconvection in the nematic liquid crystal N4

    NASA Astrophysics Data System (ADS)

    Xu, Xiaochao; Bowers, Steve; Bajaj, Kapil; Ahlers, Guenter

    2003-03-01

    Onset voltages Vc of electroconvection in a nematic liquid crystal (NLC) cell were measured as a function of the drive frequency ω/ 2 π. The cell (from E.H.C Co, Ltd Japan) had a nominal spacing of 25 μm and planar alignment. It was filled with the NLC Merck phase IV (N4). The NLC was doped with 0.1% by weight of tetra butylammonium bromide(TBAB) and the conductivity was near 1.0 × 10-6 (Ω m)-1 at 30^oC. At low frequencies (15 to 80Hz) the onset voltage dropped as the frequency increased. This is contrary to the usual interpretation of the standard model which yields Vc (1+ω^2 τ^2)/[ξ^2-(1+ω^2 τ^2)] (ξ is related to NLC material properities), with the charge relaxation time τ=ɛ/ ( 4π σ) assumed to be independent of ω. Measurements at higher frequencies agreed reasonably with the standard model prediction. Further measurements using an AC bridge revealed that the dielectric constant ɛ is strongly frequency dependent at low frequencies, whereas the conductivity σ was roughly constant. Taking into account the frequency dependence of ɛ (and thus of τ), the onset-voltage measurements agreed fairly well with the standard-model prediction.

  16. Models of Frequency-Dependent Selection with Mutation from Parental Alleles

    PubMed Central

    Trotter, Meredith V.; Spencer, Hamish G.

    2013-01-01

    Frequency-dependent selection (FDS) remains a common heuristic explanation for the maintenance of genetic variation in natural populations. The pairwise-interaction model (PIM) is a well-studied general model of frequency-dependent selection, which assumes that a genotype’s fitness is a function of within-population intergenotypic interactions. Previous theoretical work indicated that this type of model is able to sustain large numbers of alleles at a single locus when it incorporates recurrent mutation. These studies, however, have ignored the impact of the distribution of fitness effects of new mutations on the dynamics and end results of polymorphism construction. We suggest that a natural way to model mutation would be to assume mutant fitness is related to the fitness of the parental allele, i.e., the existing allele from which the mutant arose. Here we examine the numbers and distributions of fitnesses and alleles produced by construction under the PIM with mutation from parental alleles and the impacts on such measures due to different methods of generating mutant fitnesses. We find that, in comparison with previous results, generating mutants from existing alleles lowers the average number of alleles likely to be observed in a system subject to FDS, but produces polymorphisms that are highly stable and have realistic allele-frequency distributions. PMID:23852384

  17. Frequency-dependent damping in propagating slow magneto-acoustic waves

    SciTech Connect

    Prasad, S. Krishna; Banerjee, D.; Van Doorsselaere, T.

    2014-07-10

    Propagating slow magneto-acoustic waves are often observed in polar plumes and active region fan loops. The observed periodicities of these waves range from a few minutes to a few tens of minutes and their amplitudes were found to decay rapidly as they travel along the supporting structure. Previously, thermal conduction, compressive viscosity, radiation, density stratification, and area divergence were identified to be some of the causes for change in the slow wave amplitude. Our recent studies indicate that the observed damping in these waves is frequency-dependent. We used imaging data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly to study this dependence in detail and for the first time via observations we attempted to deduce a quantitative relation between the damping length and frequency of these oscillations. We developed a new analysis method to obtain this relation. The observed frequency dependence does not seem to agree with the current linear wave theory and it was found that the waves observed in the polar regions show a different dependence from those observed in the on-disk loop structures despite the similarity in their properties.

  18. On the frequency dependence and spatial coherence of PKP precursor amplitudes

    NASA Astrophysics Data System (ADS)

    Mancinelli, Nicholas; Shearer, Peter; Thomas, Christine

    2016-03-01

    Studies now agree that small-scale (˜10 km) weak (˜0.1%) velocity perturbations throughout the lowermost mantle generate the globally averaged amplitudes of 1 Hz precursors to the core phase, . The possible frequency dependence and spatial coherence of this scattered phase, however, has been given less attention. Using a large global data set of ˜150,000 PKP precursor recordings, we characterize the frequency dependence of PKP precursors at central frequencies ranging from 0.5 to 4 Hz. At greater frequencies, we observe more scattered energy (relative to the reference phase PKPdf), particularly at shorter ranges. We model this observation by invoking heterogeneity at length scales from 2 to 30 km. Amplitudes at 0.5 Hz, in particular, suggest the presence of more heterogeneity at scales >8 km than present in previously published models. Using a regional bootstrap approach, we identify large (>20°), spatially coherent regions of anomalously strong scattering beneath the West Pacific, Central/North America, and—to a lesser extent—East Africa. Finally, as proof of concept, we use array processing techniques to locate the origin of scattered energy observed in Southern California by the Anza and Southern California Seismic Networks. The energy appears to come primarily from out-of-plane scattering on the receiver side. We suggest that such improvised arrays can increase global coverage and may reveal whether a majority of precursor energy comes from localized heterogeneity in the lowermost mantle.

  19. Frequency-dependent attenuation of the Hispaniola Island region of the Caribbean Sea

    USGS Publications Warehouse

    McNamara, D.; Meremonte, M.; Maharrey, J.Z.; Mildore, S-L.; Altidore, J.R.; Anglade, D.; Hough, S.E.; Given, D.; Benz, H.; Gee, L.; Frankel, A.

    2012-01-01

    We determine frequency-dependent attenuation 1/Q(f) for the Hispaniola region using direct S and Lg waves over five distinct passbands from 0.5 to 16 Hz. Data consist of 832 high-quality vertical and horizontal component waveforms recorded on short-period and broadband seismometers from the devastating 12 January 2010 M 7.0 Haiti earthquake and the rich sequence of aftershocks. For the distance range 250–700 km, we estimate an average frequency-dependent Q(f)=224(±27)f0.64(±0.073) using horizontal components of motion and note that Q(f) estimated with Lg at regional distances is very consistent across vertical and horizontal components. We also determine a Q(f)=142(±21)f0.71(±0.11) for direct S waves at local distances, ≤100 km. The strong attenuation observed on both vertical and horizontal components of motion is consistent with expectations for a tectonically active region.

  20. Dynamics of structural systems with various frequency-dependent damping models

    NASA Astrophysics Data System (ADS)

    Li, Li; Hu, Yujin; Deng, Weiming; Lü, Lei; Ding, Zhe

    2015-03-01

    The aim of this paper is to present the dynamic analyses of the system involving various damping models. The assumed frequency-dependent damping forces depend on the past history of motion via convolution integrals over some damping kernel functions. By choosing suitable damping kernel functions of frequency-dependent damping model, it may be derived from the familiar viscoelastic materials. A brief review of literature on the choice of available damping models is presented. Both the mode superposition method and Fourier transform method are developed for calculating the dynamic response of the structural systems with various damping models. It is shown that in the case of non-deficient systems with various damping models, the modal analysis with repeated eigenvalues are very similar to the traditional modal analysis used in undamped or viscously damped systems. Also, based on the pseudo-force approach, we transform the original equations of motion with nonzero initial conditions into an equivalent one with zero initial conditions and therefore present a Fourier transform method for the dynamics of structural systems with various damping models. Finally, some case studies are used to show the application and effectiveness of the derived formulas.

  1. Evolution of identity signals: frequency-dependent benefits of distinctive phenotypes used for individual recognition.

    PubMed

    Sheehan, Michael J; Tibbetts, Elizabeth A

    2009-12-01

    Identifying broad-scale evolutionary processes that maintain phenotypic polymorphisms has been a major goal of modern evolutionary biology. There are numerous mechanisms, such as negative frequency-dependent selection, that may maintain polymorphisms, although it is unknown which mechanisms are prominent in nature. Traits used for individual recognition are strikingly variable and have evolved independently in numerous lineages, providing an excellent model to investigate which factors maintain ecologically relevant phenotypic polymorphisms. Theoretical models suggest that individuals may benefit by advertising their identities with distinctive, recognizable phenotypes. Here, we test the benefits of advertising one's identity with a distinctive phenotype. We manipulated the appearance of Polistes fuscatus paper wasp groups so that three individuals had the same appearance and one individual had a unique, easily recognizable appearance. We found that individuals with distinctive appearances received less aggression than individuals with nondistinctive appearances. Therefore, individuals benefit by advertising their identity with a unique phenotype. Our results provide a potential mechanism through which negative frequency-dependent selection may maintain the polymorphic identity signals in P. fuscatus. Given that recognition is important for many social interactions, selection for distinctive identity signals may be an underappreciated and widespread mechanism underlying the evolution of phenotypic polymorphisms in social taxa. PMID:19744121

  2. Experimental methods for the characterization of the frequency-dependent viscoelastic properties of soft materials

    PubMed Central

    Kazemirad, Siavash; K. Heris, Hossein; Mongeau, Luc

    2013-01-01

    A characterization method based on Rayleigh wave propagation was developed for the quantification of the frequency-dependent viscoelastic properties of soft materials at high frequencies; i.e., up to 4 kHz. Planar harmonic surface waves were produced on the surface of silicone rubber samples. The phase and amplitude of the propagating waves were measured at different locations along the propagation direction, which allowed the calculation of the complex Rayleigh wavenumbers at each excitation frequency using a transfer function method. An inverse wave propagation problem was then solved to obtain the complex shear/elastic moduli from the measured wavenumbers. In a separate, related investigation, dynamic indentation tests using atomic force microscopy (AFM) were performed at frequencies up to 300 Hz. No systematic verification study is available for the AFM-based method, which can be used when the dimensions of the test samples are too small for other existing testing methods. The results obtained from the Rayleigh wave propagation and AFM-based indentation methods were compared with those from a well-established method, which involves the generation of standing longitudinal compression waves in rod-shaped test specimens. The results were cross validated and qualitatively confirmed theoretical expectations presented in the literature for the frequency-dependence of polymers. PMID:23654420

  3. Frequency-dependent selection with dominance: a window onto the behavior of the mean fitness.

    PubMed Central

    Asmussen, Marjorie A; Cartwright, Reed A; Spencer, Hamish G

    2004-01-01

    Selection in which fitnesses vary with the changing genetic composition of the population may facilitate the maintenance of genetic diversity in a wide range of organisms. Here, a detailed theoretical investigation is made of a frequency-dependent selection model, in which fitnesses are based on pairwise interactions between the two phenotypes at a diploid, diallelic, autosomal locus with complete dominance. The allele frequency dynamics are fully delimited analytically, along with all possible shapes of the mean fitness function in terms of where it increases or decreases as a function of the current allele frequency in the population. These results in turn allow possibly the first complete characterization of the dynamical behavior by the mean fitness through time under frequency-dependent selection. Here the mean fitness (i) monotonically increases, (ii) monotonically decreases, (iii) initially increases and then decreases, or (iv) initially decreases and then increases as equilibrium is approached. We analytically derive the exact initial and fitness conditions that produce each dynamic and how often each arises. Computer simulations with random initial conditions and fitnesses reveal that the potential decline in mean fitness is not negligible; on average a net decrease occurs 20% of the time and reduces the mean fitness by >17%. PMID:15166172

  4. Tissue characterization by imaging the local frequency dependent relative backscatter coefficient

    NASA Astrophysics Data System (ADS)

    Jenderka, Klaus V.; Gaertner, Tilio; Cobet, Ulrich; Zacharias, Mario; Heynemann, Hans

    2000-04-01

    Conventional B-scan systems only use the amplitude information of the backscattered signals for imaging. By imaging the local frequency dependent relative backscatter coefficient it is possible to improve the image contrast and to reduce system effects. Based on spectral analysis of rf echo signals, a procedure was developed to correct for system specific effects and to determine the relative backscatter coefficient. A new image with improved contrast results from grayscale or color coding of the frequency components of the relative backscatter coefficient. The method was applied to in vivo measurements of human prostate and transplanted kidney. For cancerous prostate tissue the relative backscatter coefficient is about 8 dB lower than for normal tissue regions. The results of the investigations on kidneys show no correlation to the current function of the organ. Certainly the different course of the frequency dependence of the relative backscatter coefficient of renal cortex and calices regions allows a contrast improvement. The method provides a system independent imaging procedure with improved image contrast for tissues with different scattering behavior and slightly reduced spatial resolution. Imaging the relative backscatter coefficient will not substitute the conventional B-mode image, but it is a useful tool providing additional information about the tissue state.

  5. The mechanics of delamination in fiber-reinforced composite materials. Part 1: Stress singularities and solution structure

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    The fundamental mechanics of delamination in fiber composite laminates is studied. Mathematical formulation of the problem is based on laminate anisotropic elasticity theory and interlaminar fracture mechanics concepts. Stress singularities and complete solution structures associated with general composite delaminations are determined. For a fully open delamination with traction-free surfaces, oscillatory stress singularities always appear, leading to physically inadmissible field solutions. A refined model is introduced by considering a partially closed delamination with crack surfaces in finite-length contact. Stress singularities associated with a partially closed delamination having frictional crack-surface contact are determined, and are found to be diferent from the inverse square-root one of the frictionless-contact case. In the case of a delamination with very small area of crack closure, a simplified model having a square-root stress singularity is employed by taking the limit of the partially closed delamination. The possible presence of logarithmic-type stress singularity is examined; no logarithmic singularity of any kind is found in the composite delamination problem. Numerical examples of dominant stress singularities are shown for delaminations having crack-tip closure with different frictional coefficients between general (1) and (2) graphite-epoxy composites.

  6. Hygrothermomechanical fracture stress criteria for fiber composites with sense-parity

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Ginty, C. A.

    1983-01-01

    Hygrothermomechanical fracture stress criteria are developed and evaluated for unidirectional composites (plies) with sense-parity. These criteria explicity quantify the individual contributions of applied, hygral and thermal stresses as well as couplings among these stresses. The criteria are for maximum stress, maximum strain, internal friction, work-to-fracture and combined-stress fracture. Predicted results obtained indicate that first ply failure will occur at stress levels lower than those predicted using criteria currently available in the literature. Also, the contribution of the various stress couplings (predictable only by fracture criteria with sense-parity) is significant to first ply failure and attendant fracture modes.

  7. Frequency dependent attenuation characteristics of coda waves in the Northwestern Himalayan (India) region

    NASA Astrophysics Data System (ADS)

    Kumar, Sushil; Singh, Priyamvada; Singh, Pitam; Biswal, Shubhasmita; Parija, Mahesh Prasad

    2016-03-01

    Digital seismogram data of 82 earthquakes from the Northwestern Himalayan (India) region recorded at different stations during 2004-2006 were analyzed to study the seismic coda wave attenuation characteristics in this region. We used 132 seismic observations from local earthquakes with a hypocentral distance <240 km and a magnitude range of 1.2-4.9 to study the coda QC using the single isotropic scattering model. These earthquakes were recorded at 20 temporary seismic stations installed in the Northwestern Himalayas (India) by the Wadia institute of Himalayan Geology, Dehradun. The QC values were estimated at 10 central frequencies: 1.5, 3, 5, 7, 9, 12, 16, 20, 24, and 28 Hz using starting lapse-times of 10, 20, 30, 40, 50, and 60 s and coda window-lengths of 10, 20, 30, 40, and 50 s. The QC fits the frequency dependent power-law, QC =Q0fn . For a 10 s lapse time with a 10-s coda window length QC = 47.42f1.012 and for a 50 s lapse time with a 50 s coda window length, QC = 204.1f0.934 . Q0 (QC at 1 Hz) varied from ∼47 for a 10 s lapse time and a 10 s window length, to ∼204 for a 50 s lapse time and a 50 s window length. An average frequency dependent power law fit for the study region may be given as QC = 116.716f0.9943 . The exponent of the frequency dependence law n ranged from 1.08 to 0.9, which correlates well with values obtained in other seismically and tectonically active and heterogeneous regions of the world. In our study region, QC increases both with respect to lapse time and frequency, i.e., the attenuation decreases as the quality factor is inversely proportional to attenuation. The low QC values or high attenuation at lower frequencies and high QC values or low attenuation at higher frequencies suggest that the heterogeneity decreases with increasing depth in our study region.

  8. Frequency dependence 3.0: an attempt at codifying the evolutionary ecology perspective.

    PubMed

    Metz, Johan A J; Geritz, Stefan A H

    2016-03-01

    The fitness concept and perforce the definition of frequency independent fitnesses from population genetics is closely tied to discrete time population models with non-overlapping generations. Evolutionary ecologists generally focus on trait evolution through repeated mutant substitutions in populations with complicated life histories. This goes with using the per capita invasion speed of mutants as their fitness. In this paper we develop a concept of frequency independence that attempts to capture the practical use of the term by ecologists, which although inspired by population genetics rarely fits its strict definition. We propose to call the invasion fitnesses of an eco-evolutionary model frequency independent when the phenotypes can be ranked by competitive strength, measured by who can invade whom. This is equivalent to the absence of weak priority effects, protected dimorphisms and rock-scissor-paper configurations. Our concept differs from that of Heino et al. (TREE 13:367-370, 1998) in that it is based only on the signs of the invasion fitnesses, whereas Heino et al. based their definitions on the structure of the feedback environment, summarising the effect of all direct and indirect interactions between individuals on fitness. As it turns out, according to our new definition an eco-evolutionary model has frequency independent fitnesses if and only if the effect of the feedback environment on the fitness signs can be summarised by a single scalar with monotonic effect. This may be compared with Heino et al.'s concept of trivial frequency dependence defined by the environmental feedback influencing fitness, and not just its sign, in a scalar manner, without any monotonicity restriction. As it turns out, absence of the latter restriction leaves room for rock-scissor-paper configurations. Since in 'realistic' (as opposed to toy) models frequency independence is exceedingly rare, we also define a concept of weak frequency dependence, which can be interpreted

  9. Frequency-dependent Effects of Rupture for the 2004 Parkfield, California, Mainshock at UPSAR

    NASA Astrophysics Data System (ADS)

    Fletcher, J. B.

    2014-12-01

    We processed the accelerograms for the Sept. 28, 2004 Parkfield mainshock (M6) from the Parkfield Dense Seismograph Array (UPSAR) using beam forming techniques to determine coherence and slowness of incoming arrivals and we found that the frequency-dependent effects of rupture propagation of can be seen in the acceleration records in at least two ways. The first is the effect of directivity. During the 4-6s interval after nucleation, UPSAR lies in the forward azimuth of the rupture front and coherence and amplitudes are relatively high. In this interval, the records are rich in frequencies as high as 40 Hz. As the rupture front progresses, UPSAR becomes perpendicular to the location of the rupture front on the fault and then passes into the back azimuth. During this 5-7s interval, the coherence drops off, amplitudes are typically smaller and the traces are depleted in high frequencies compared to when UPSAR was in the forward azimuth. We model the rupture process of the Parkfield mainshock using realistic distributions of slip and show that they also have significant changes in frequency as the rupture passes from the forward to the back azimuth. The second effect is the frequency dependence of the rupture front. That is observations at UPSAR were used to address the question of whether low frequency energy emerges from the same parts of the fault as high frequency energy. Acceleration records of the Parkfield mainshock from UPSAR were filtered in 5 different narrow frequency bands (0.25-0.5 Hz, 0.5-1 Hz, 1-2 Hz, 2-4 Hz, and 4-8 Hz) and beam forming was repeated. Above 1 Hz the estimates of back azimuth and apparent velocity are about the same and are independent of frequency. Below 1 Hz, however, the estimates appear to be significantly different with a change of about of 0.34 km/s in apparent velocity and 22 degrees in back azimuth at 2s after the S wave arrival, for example, between the middle and lowest band. From previous work on mapping values of apparent

  10. Frequency dependence 3.0: an attempt at codifying the evolutionary ecology perspective.

    PubMed

    Metz, Johan A J; Geritz, Stefan A H

    2016-03-01

    The fitness concept and perforce the definition of frequency independent fitnesses from population genetics is closely tied to discrete time population models with non-overlapping generations. Evolutionary ecologists generally focus on trait evolution through repeated mutant substitutions in populations with complicated life histories. This goes with using the per capita invasion speed of mutants as their fitness. In this paper we develop a concept of frequency independence that attempts to capture the practical use of the term by ecologists, which although inspired by population genetics rarely fits its strict definition. We propose to call the invasion fitnesses of an eco-evolutionary model frequency independent when the phenotypes can be ranked by competitive strength, measured by who can invade whom. This is equivalent to the absence of weak priority effects, protected dimorphisms and rock-scissor-paper configurations. Our concept differs from that of Heino et al. (TREE 13:367-370, 1998) in that it is based only on the signs of the invasion fitnesses, whereas Heino et al. based their definitions on the structure of the feedback environment, summarising the effect of all direct and indirect interactions between individuals on fitness. As it turns out, according to our new definition an eco-evolutionary model has frequency independent fitnesses if and only if the effect of the feedback environment on the fitness signs can be summarised by a single scalar with monotonic effect. This may be compared with Heino et al.'s concept of trivial frequency dependence defined by the environmental feedback influencing fitness, and not just its sign, in a scalar manner, without any monotonicity restriction. As it turns out, absence of the latter restriction leaves room for rock-scissor-paper configurations. Since in 'realistic' (as opposed to toy) models frequency independence is exceedingly rare, we also define a concept of weak frequency dependence, which can be interpreted

  11. TECHNICAL NOTE: Active control for stress intensity of crack-tips under mixed mode by shape memory TiNi fiber epoxy composites

    NASA Astrophysics Data System (ADS)

    Shimamoto, A.; Zhao, H.; Azakami, T.

    2007-06-01

    The paper presented the effectiveness of a shape memory alloy hybrid composite. It was designed to actively suppress stress intensity in the vicinity of a crack-tip. A shape memory alloy (SMA) TiNi fiber reinforced epoxy composite was fabricated based on the proposed design concept and its material and mechanical properties were investigated by photoelastic examinations. The stress intensity factors, KI and KII, at a crack-tip decreased temperatures greater than Af under mixed mode. The phenomenon was caused by the recovery force of the TiNi fiber. The relationship of the stress intensity factors with the prestrain in the SMA fiber as well as with the ambient temperature in an isothermal furnace was clarified. On this basis, the active control for stress intensity by a shape memory composite was discussed.

  12. Recurrent connections form a phase-locking neuronal tuner for frequency-dependent selective communication

    PubMed Central

    Shin, Dongkwan; Cho, Kwang-Hyun

    2013-01-01

    The brain requires task-dependent interregional coherence of information flow in the anatomically connected neural network. However, it is still unclear how a neuronal group can flexibly select its communication target. In this study, we revealed a hidden routing mechanism on the basis of recurrent connections. Our simulation results based on the spike response model show that recurrent connections between excitatory and inhibitory neurons modulate the resonant frequency of a local neuronal group, and that this modulation enables a neuronal group to receive selective information by filtering a preferred frequency component. We also found that the recurrent connection facilitates the successful routing of any necessary information flow between neuronal groups through frequency-dependent resonance of synchronized oscillations. Taken together, these results suggest that recurrent connections act as a phase-locking neuronal tuner which determines the resonant frequency of a local group and thereby controls the preferential routing of incoming signals. PMID:23981983

  13. Layer- and frequency-dependent second harmonic generation in reflection from GaSe atomic crystals

    NASA Astrophysics Data System (ADS)

    Tang, Yanhao; Mandal, Krishna C.; McGuire, John A.; Lai, Chih Wei

    2016-09-01

    We report optical second-harmonic generation (SHG) in reflection from GaSe crystals of 1 to more than 100 layers using a fundamental picosecond pulsed pump at 1.58 eV and a supercontinuum white light pulsed laser with energies ranging from 0.85 to 1.4 eV. The measured reflected SHG signal is maximal in samples of ˜20 layers, decreasing in thicker samples as a result of interference. The thickness- and frequency-dependence of the SHG response of samples thicker than ˜7 layers can be reproduced by a second-order optical susceptibility that is the same as in bulk samples. For samples ≲7 layers, the second-order optical susceptibility is reduced compared to that in thicker samples, which is attributed to the expected band-gap increase in mono- and few-layer GaSe.

  14. Full frequency-dependent phase-domain modelling of transmission lines and corona phenomena

    NASA Astrophysics Data System (ADS)

    Castellanos, Fernando

    This thesis presents two main developments in the modelling of power transmission lines for the simulation of electric networks. The first one is wide bandwidth circuit corona model and the second a phase-domain multiphase full frequency-dependent line model. The latter can be easily used in connection with the former. Both models have been developed for implementation in time domain simulation computer programs, such as the ElectroMagnetic Transients Program (EMTP). Corona in overhead transmission lines is a highly nonlinear and non deterministic phenomenon. Circuit models have been developed in the past to represent its behaviour, but the response of these models is usually limited to a narrow band of frequencies. The corona model presented in this thesis overcomes this problem by: (1) matching closely the topology of the circuit to the topology of the physical system, and (2) duplicating the high-order dynamic response of the phenomenon with a high-order transient circuit response. The resulting model is valid for a wide range of frequencies and is able to represent waveshapes from switching to lightning surges. A unique set of model parameters can be obtained directly from test-cage measurements, and the same set can be used directly for an arbitrary overhead line configuration. The model uses only standard EMTP circuit elements and requires no iterations. Simulations of corona charge-voltage (q-v) curves and of travelling surges were performed and compared to existing field test measurements. The proposed new transmission line model (z-line) can be used for the representation of multicircuit transmission lines in time-domain transient solutions. The model includes a full representation of the frequency-dependent line parameters and is formulated directly in phase coordinates. The solution in phase coordinates, as opposed to modal coordinates, avoids the problems associated with the representation of the frequency-dependent transformation matrices that relate

  15. Frequency dependent plasma characteristics in a capacitively coupled 300 mm wafer plasma processing chamber.

    SciTech Connect

    Hebner, Gregory Albert; Holland, J.P.; Paterson, A.M.; Barnat, Edward V.; Miller, Paul Albert

    2006-01-01

    Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative optical emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K.

  16. Negative frequency-dependent selection is intensified at higher population densities in protist populations

    PubMed Central

    Minter, Ewan J. A.; Watts, Phillip C.; Lowe, Chris D.; Brockhurst, Michael A.

    2015-01-01

    Natural populations of free-living protists often exhibit high-levels of intraspecific diversity, yet this is puzzling as classic evolutionary theory predicts dominance by genotypes with high fitness, particularly in large populations where selection is efficient. Here, we test whether negative frequency-dependent selection (NFDS) plays a role in the maintenance of diversity in the marine flagellate Oxyrrhis marina using competition experiments between multiple pairs of strains. We observed strain-specific responses to frequency and density, but an overall signature of NFDS that was intensified at higher population densities. Because our strains were not selected a priori on the basis of particular traits expected to exhibit NFDS, these data represent a relatively unbiased estimate of the role for NFDS in maintaining diversity in protist populations. These findings could help to explain how bloom-forming plankton, which periodically achieve exceptionally high population densities, maintain substantial intraspecific diversity. PMID:26063750

  17. Features of the duration frequency dependence for type III solar radio bursts

    NASA Astrophysics Data System (ADS)

    Tsybko, Y. G.

    1989-11-01

    Averaged data on type III solar radio bursts at fixed frequencies in the 12.5-25 MHz range and beyond are examined, showing that there are two branches of the burst duration dependence on frequency. This splitting is used to distinguish between bursts occurring at the fundamental and the second harmonics of the plasma frequency. Type IIIb radiation is characterized by a diagram of the mean duration vs frequency of the stria bursts at the fundamental harmonic. Type III bursts at meter and decameter wavelengths are compared, showing a change in the behavior of the duration frequency dependence. It is suggested that this change may be associated with the initial acceleration and the subsequent expansion of the source along its path in the lower and intermediate corona.

  18. Frequency dependence of viscous and viscoelastic dissipation in coated micro-cantilevers from noise measurement.

    PubMed

    Paolino, P; Bellon, L

    2009-10-01

    We measure the mechanical thermal noise of soft silicon atomic force microscope cantilevers. Using an interferometric setup, we obtain a resolution down to 10(-14) m Hz(-1/2) on a wide spectral range (3-10(5) Hz). The low frequency behavior depends dramatically on the presence of a reflective coating: almost flat spectra for uncoated cantilevers versus a 1/f like trend for coated ones. The addition of a viscoelastic term in models of the mechanical system can account for this observation. Use of Kramers-Kronig relations validate this approach with a complete determination of the response of the cantilever: a power law with a small coefficient is found for the frequency dependence of viscoelasticity due to the coating, whereas the viscous damping due to the surrounding atmosphere is accurately described by the Sader model. PMID:19738311

  19. Negative frequency-dependent selection is intensified at higher population densities in protist populations.

    PubMed

    Minter, Ewan J A; Watts, Phillip C; Lowe, Chris D; Brockhurst, Michael A

    2015-06-01

    Natural populations of free-living protists often exhibit high-levels of intraspecific diversity, yet this is puzzling as classic evolutionary theory predicts dominance by genotypes with high fitness, particularly in large populations where selection is efficient. Here, we test whether negative frequency-dependent selection (NFDS) plays a role in the maintenance of diversity in the marine flagellate Oxyrrhis marina using competition experiments between multiple pairs of strains. We observed strain-specific responses to frequency and density, but an overall signature of NFDS that was intensified at higher population densities. Because our strains were not selected a priori on the basis of particular traits expected to exhibit NFDS, these data represent a relatively unbiased estimate of the role for NFDS in maintaining diversity in protist populations. These findings could help to explain how bloom-forming plankton, which periodically achieve exceptionally high population densities, maintain substantial intraspecific diversity.

  20. Modeling soil magnetic susceptibility and frequency-dependent susceptibility to aid landmine clearance.

    NASA Astrophysics Data System (ADS)

    Hannam, Jacqueline A.; Dearing, John A.

    2006-05-01

    Information on the electromagnetic properties of soils and their effects on metal detectors is increasingly necessary for effective demining due to limited detector efficacy in highly magnetic soils and the difficulty of detecting minimummetal mines. Magnetic measurements of soils, such as magnetic susceptibility and frequency dependent susceptibility can aid the detection of problem soils, but are not part of standard soil analyses. Consequently, little information about soil magnetism exists within the soil, environmental science and environmental geophysics communities. Lack of empirical data may be compensated through the estimation of soil magnetic characteristics by predictive modeling approaches. Initial modeling of soil types in Bosnia and Herzegovina (BiH) was attempted by expert and analogue approaches, using only coarse scale soil type information, which resulted in the production of national soil maps for low field and frequency-dependent susceptibility. Validation of the maps was achieved by comparison of empirical magnetic data from soil samples in the National Bosnian soil archive in Sarajevo. Discrepancies between the model and empirical data are explained in part by the differences in soil parent material within each soil type, which controls the amount of Fe released into the soil system available for in situ conversion to magnetic Fe oxides. The integration of soil information (type and parent material), expert knowledge and empirical data refines the predictive modeling of soil magnetic characteristics in temperate-Mediterranean environments such as BiH. Further spatial separation of soil types in the landscape can be achieved by digital terrain modeling. Preliminary fine-scale, landscape-soil modeling indicates improved spatial resolution of soil types compared with the original coarsely-mapped soil units, and the potential to synthesize local scale soil magnetic maps.

  1. The Frequency-Dependent Neuronal Length Constant in Transcranial Magnetic Stimulation

    PubMed Central

    Ilmoniemi, Risto J.; Mäki, Hanna; Saari, Jukka; Salvador, Ricardo; Miranda, Pedro C.

    2016-01-01

    Background: The behavior of the dendritic or axonal membrane voltage due to transcranial magnetic stimulation (TMS) is often modeled with the one-dimensional cable equation. For the cable equation, a length constant λ0 is defined; λ0 describes the axial decay of the membrane voltage in the case of constant applied electric field. In TMS, however, the induced electric field waveform is typically a segment of a sinusoidal wave, with characteristic frequencies of the order of several kHz. Objective: To show that the high frequency content of the stimulation pulse causes deviations in the spatial profile of the membrane voltage as compared to the steady state. Methods: We derive the cable equation in complex form utilizing the complex frequency-dependent representation of the membrane conductivity. In addition, we define an effective length constant λeff, which governs the spatial decay of the membrane voltage. We model the behavior of a dendrite in an applied electric field oscillating at 3.9 kHz with the complex cable equation and by solving the traditional cable equation numerically. Results: The effective length constant decreases as a function of frequency. For a model dendrite or axon, for which λ0 = 1.5 mm, the effective length constant at 3.9 kHz is decreased by a factor 10 to 0.13 mm. Conclusion: The frequency dependency of the neuronal length constant has to be taken into account when predicting the spatial behavior of the membrane voltage as a response to TMS. PMID:27555808

  2. Frequency-dependent signal processing in apical dendrites of hippocampal CA1 pyramidal cells.

    PubMed

    Watanabe, H; Tsubokawa, H; Tsukada, M; Aihara, T

    2014-10-10

    Depending on an animal's behavioral state, hippocampal CA1 pyramidal cells receive distinct patterns of excitatory and inhibitory synaptic inputs. The time-dependent changes in the frequencies of these inputs and the nonuniform distribution of voltage-gated channels lead to dynamic fluctuations in membrane conductance. In this study, using a whole-cell patch-clamp method, we attempted to record and analyze the frequency dependencies of membrane responsiveness in Wistar rat hippocampal CA1 pyramidal cells following noise current injection directly into dendrites and somata under pharmacological blockade of all synaptic inputs. To estimate the frequency-dependent properties of membrane potential, membrane impedance was determined from the voltage response divided by the input current in the frequency domain. The cell membrane of most neurons showed low-pass filtering properties in all regions. In particular, the properties were strongly expressed in the somata or proximal dendrites. Moreover, the data revealed nonuniform distribution of dendritic impedance, which was high in the intermediate segment of the apical dendritic shaft (∼220-260μm from the soma). The low-pass filtering properties in the apical dendrites were more enhanced by membrane depolarization than those in the somata. Coherence spectral analysis revealed high coherence between the input signal and the output voltage response in the theta-gamma frequency range, and large lags emerged in the distal dendrites in the gamma frequency range. Our results suggest that apical dendrites of hippocampal CA1 pyramidal cells integrate synaptic inputs according to the frequency components of the input signal along the dendritic segments receiving the inputs.

  3. Frequency-dependent traveltime tomography using fat rays: application to near-surface seismic imaging

    NASA Astrophysics Data System (ADS)

    Jordi, Claudio; Schmelzbach, Cedric; Greenhalgh, Stewart

    2016-08-01

    Frequency-dependent traveltime tomography does not rely on the high frequency assumption made in classical ray-based tomography. By incorporating the effects of velocity structures in the first Fresnel volume around the central ray, it offers a more realistic and accurate representation of the actual physics of seismic wave propagation and thus, enhanced imaging of near-surface structures is expected. The objective of this work was to apply frequency-dependent first arrival traveltime tomography to surface seismic data that were acquired for exploration scale and near-surface seismic imaging. We adapted a fat ray tomography algorithm from global-earth seismology that calculates the Fresnel volumes based on source and receiver (adjoint source) traveltime fields. The fat ray tomography algorithm was tested on synthetic model data that mimics the dimensions of two field data sets. The field data sets are presented as two case studies where fat ray tomography was applied for near-surface seismic imaging. The data set of the first case study was recorded for high-resolution near-surface imaging of a Quaternary valley (profile length < 1 km); the second data set was acquired for hydrocarbon search (profile length > 10 km). All results of fat ray tomography are compared against the results of classical ray-based tomography. We show that fat ray tomography can provide enhanced tomograms and that it is possible to recover more information on the subsurface when compared to ray tomography. However, model assessment based on the column sum of the Jacobian matrix revealed that especially the deep parts of the structure in the fat ray tomograms might not be adequately covered by fat rays. Furthermore, the performance of the fat ray tomography depends on the chosen input frequency in relation to the scale of the seismic survey. Synthetic data testing revealed that the best results were obtained when the frequency was chosen to correspond to an approximate wavelength

  4. Hubbard interactions in iron-based pnictides and chalcogenides: Slater parametrization, screening channels, and frequency dependence

    NASA Astrophysics Data System (ADS)

    van Roekeghem, Ambroise; Vaugier, Loïg; Jiang, Hong; Biermann, Silke

    2016-09-01

    We calculate the strength of the frequency-dependent on-site electronic interactions in the iron pnictides LaFeAsO, BaFe2As2 , BaRu2As2 , and LiFeAs and the chalcogenide FeSe from first principles within the constrained random phase approximation. We discuss the accuracy of an atomiclike parametrization of the two-index density-density interaction matrices based on the calculation of an optimal set of three independent Slater integrals, assuming that the angular part of the Fe d localized orbitals can be described within spherical harmonics as for isolated Fe atoms. We show that its quality depends on the ligand-metal bonding character rather than on the dimensionality of the lattice: it is excellent for ionic-like Fe-Se (FeSe) chalcogenides and a more severe approximation for more covalent Fe-As (LaFeAsO, BaFe2As2 ) pnictides. We furthermore analyze the relative importance of different screening channels, with similar conclusions for the different pnictides but a somewhat different picture for the benchmark oxide SrVO3: the ligand channel does not appear to be dominant in the pnictides, while oxygen screening is the most important process in the oxide. Finally, we analyze the frequency dependence of the interaction. In contrast to simple oxides, in iron pnictides its functional form cannot be simply modeled by a single plasmon, and the actual density of modes enters the construction of an effective Hamiltonian determining the low-energy properties.

  5. Is it possible to infer the frequency-dependent seismic attenuation of fractured materials from high-strain creep tests?

    NASA Astrophysics Data System (ADS)

    mallet, celine; quintal, beatriz; caspari, eva; holliger, klaus

    2016-04-01

    The seismic and hydraulic characterization of fractured rocks is an important objective for reservoir development in general and the production of geothermal energy in particular. The attenuation of seismic waves in saturated fractured media is governed by local displacements of the fluid relative to the solid induced by the compressions and extensions associated with the passing wavefield. This phenomenon is generally referred to as wave-induced fluid flow (WIFF). Recent evidence suggests that this energy dissipation mechanism is sensitive to the interconnectivity of the fractures, which offers the perspective of linking seismic observations to the hydraulic properties of fractured rocks. Here, we consider the results of laboratory experiments, which are referred to as creep tests. Such tests consist of applying a constant stress to a water-saturated thermally cracked glass sample and recording the resulting strain response as a function of time. The primary advantages of the considered material are (i) that the fracture network is well documented and (ii) that the homogeneous and non-porous glass matrix limits WIFF to the fracture network. Due to the high stress levels as well as other technical issues, creep tests are not commonly used for laboratory-based measurements of energy dissipation. Therefore, an objective of this study is to explore whether and to what extent such data can be interpreted in terms of the seismic attenuation characteristics of the probed samples, as this might open access to a vast reservoir of corresponding data, notably for cracked materials. Transforming the observed time-dependent stress-strain relation into the Fourier domain, allows us to infer the corresponding frequency-dependent attenuation characteristics, which we then seek to interpret through numerical simulations based on Biot's quasi-static poroelastic equations. The 2D geometry of the fracture network considered in these simulations is derived from a scanning electron

  6. Frequency dependence of Q sub Lg and its relation to crustal anelasticity in the Basin and Range province

    SciTech Connect

    Mitchell, B.J. )

    1991-04-01

    The high observed frequency dependence of Q for 1-hz Lg waves (f{sup 0.4 - 0.6}) in the Basin and Range province can be explained by a frequency-independent layered model of intrinsic Q for shear waves (Q{sub mu}) which has very low values in the upper crust and rapidly increasing values at greater depths. By contrast, earlier work in the eastern United States indicated Q{sub mu} values in the upper crust which are high and which vary with frequency. The Q{mu} model which best explains reported values of Q{sub Lg} and its frequency dependence in the Basin-and-Range consists of an 8-km thick low-Q layer (60 or less) overlying Q values as high as 1,000 or more at mid-crustal depths. This Q{sub mu} distribution is best explained by an upper crust which contains fluids in interconnected cracks overlying a lower crust where higher lithostatic pressure has closed those cracks. These results indicate that whereas the frequency dependence of Q{mu} is an intrinsic property of crustal material, the frequency dependence of Q{sub Lg} arises from both the intrinsic frequency dependence of crustal material and its layered structure. A notation is suggested which distinguishes between the frequency dependence of Q{sub Lg} and Q{sub mu}.

  7. Three-dimensional finite element analysis of stress distribution in a tooth restored with metal and fiber posts of varying diameters: An in-vitro study

    PubMed Central

    Kumar, Pradeep; Rao, R. Nageswar

    2015-01-01

    Objective: To compare stress distribution in a tooth restored with metal and fiber posts of varying diameters (1.2 and 1.4 mm) by means of three-dimensional finite element analysis (3D-FEA). Materials and Methods: Four 3D-FEA models were constructed: (1) fiber post (1.2 and 1.4 mm) and (2) metal post (1.2 and 1.4 mm). The material properties were assigned and a force of 100 N was applied at 45° angle to the longitudinal axis of the tooth onto the palatal surface incisal to the cingulum. Analysis was run and stress distribution pattern was studied. Results: Maximum stresses in the radicular tooth structure for fiber post were higher than that for metal post. In the former models, stresses in the tooth structure were slightly reduced with increase in fiber post diameter. Conclusions: To reduce stress in the remaining radicular tooth structure, it is better to use a fiber post of a large diameter. PMID:25829685

  8. Stress distribution of endodontically treated teeth with titanium alloy post and carbon fiber post with different alveolar bone height: A three-dimensional finite element analysis

    PubMed Central

    Singh, S. Vijay; Bhat, Manohar; Gupta, Saurabh; Sharma, Deepak; Satija, Harsha; Sharma, Sumeet

    2015-01-01

    Objective: A three-dimensional (3D) finite element analysis (FEA) on the stress distribution of endodontically treated teeth with titanium alloy post and carbon fiber post with different alveolar bone height. Materials and Methods: The 3D model was fabricated using software to represent an endodontically treated mandibular second premolar with post and restored with a full ceramic crown restoration, which was then analyzed using FEA using FEA ANSYS Workbench V13.0 (ANSYS Inc., Canonsburg, Pennsylvania, U.S.A) software. Results: The FEA showed the maximum stresses of 137.43 Mpa in dentin with alveolar bone height of 4 mm when the titanium post was used, 138.48 Mpa when carbon fiber post was used as compared to 105.91 Mpa in the model with alveolar bone height of 2 mm from the cement enamel junction (CEJ) when the titanium post was used and 107.37 Mpa when the carbon fiber post was used. Conclusions: Stress was observed more in alveolar bone height level of 4 mm from CEJ than 2 mm from CEJ. Stresses in the dentin were almost similar when the carbon fiber post was compared to titanium post. However, stresses in the post and the cement were much higher when titanium post was used as compared to carbon fiber post. PMID:26430375

  9. Mild heat stress enhances differentiation and proliferation of Japanese quail myoblasts and enhances slow muscle fiber characteristics.

    PubMed

    Choi, Y M; Chen, P R; Shin, S; Zhang, J; Hwang, S; Lee, K

    2016-08-01

    The objective of this study was to investigate the effect of mild heat stress on muscle fiber hyperplastic and hypertrophic growth in quail primary myogenic cells to better understand the mechanisms leading to increased skeletal muscle development in avian embryos incubated at a higher temperature. Compared to control cultures maintained at 37°C, incubation at 39°C enhanced myotube length (P < 0.01) and diameter (P < 0.001) at 3 days after differentiation (D3). This enlargement of the myotubes incubated at 39°C can be explained by differences in the fusion index (56.7 vs. 46.2%, P < 0.05) and nuclei number per myotube (18.1 vs. 10.8, P < 0.001) compared to the control cells at D3. Additionally, a higher density of myotubes at D3 in cultures exposed to a higher temperature were related to higher levels of Pax-7 (P < 0.05) compared to the control cells incubated continuously at 37°C. These results indicated a higher proliferative capacity in cells exposed to mild heat stress compared to the control cells. On the other hand, mild heat stress enhanced protein levels of slow myosin heavy chain isoform (P < 0.01) and cytochrome c oxidase subunit IV (P < 0.01) compared to the control cells at D3. These discrepancies in protein expression indicated maintenance of slow muscle fiber type characteristics in myotubes incubated at 39°C. Our results suggest that mild heat stress plays a significant role in myogenic mechanisms related to muscle mass and development.

  10. On intrinsic stress fiber contractile forces in semilunar heart valve interstitial cells using a continuum mixture model.

    PubMed

    Sakamoto, Yusuke; Buchanan, Rachel M; Sacks, Michael S

    2016-02-01

    Heart valve interstitial cells (VICs) play a critical role in the maintenance and pathophysiology of heart valve tissues. Normally quiescent in the adult, VICs can become activated in periods of growth and disease. When activated, VICs exhibit increased levels of cytokines and extracellular matrix (ECM) synthesis, and upregulated expression and strong contraction of α-smooth muscle actin (α-SMA) fibers. However, it remains unknown how expression and contraction of the α-SMA fibers, which vary among different VIC types, contribute to the overall VIC mechanical responses, including the nucleus and cytoskeleton contributions. In the present study, we developed a novel solid-mixture model for VIC biomechanical behavior that incorporated 1) the underlying cytoskeletal network, 2) the oriented α-SMA stress fibers with passive elastic and active contractile responses, 3) a finite deformable elastic nucleus. We implemented the model in a full 3D finite element simulation of a VIC based on known geometry. Moreover, we examined the respective mechanical responses of aortic and pulmonary VICs (AVICs and PVICs, respectively), which are known to have different levels of α-SMA expression levels and contractile behaviors. To calibrate the model, we simulated the combined mechanical responses of VICs in both micropipette aspiration (MA) and atomic force microscopy (AFM) experiments. These two states were chosen as the VICs were under significantly different mechanical loading conditions and activation states, with the α-SMA fibers inactivated in the MA studies while fully activated in the AFM studies. We also used the AFM to study the mechanical property of the nucleus. Our model predicted that the substantial differences found in stiffening of the AVIC compared to the PVICs was due to a 9 to 16 times stronger intrinsic AVIC α-SMA stress fiber contractile force. Model validation was done by simulating a traction force microscopy experiment to estimate the forces the VICs

  11. Numerical analysis of stress distribution in embedded highly birefringent PANDA fibers

    NASA Astrophysics Data System (ADS)

    Lesiak, Piotr; Woliński, Tomasz

    2015-09-01

    The paper presents numerical analysis compared with experimental data of influence of polymerization shrinkage on highly birefringent (HB) PANDA optical fibers embedded in a composite material. Since polymerization is a chemical process consisting in combining single molecules in a macromolecular compound [1], principal directions of the polymerization shrinkage depend on a number of the composite layers associated with this process. In this paper a detailed analysis of the piezo-optic effects occurring in HB optical fibers before and after the lamination process answers the question to what extent a degree of the material degradation can be properly estimated.

  12. Impaired Autophagy in Sporadic Inclusion-Body Myositis and in Endoplasmic Reticulum Stress-Provoked Cultured Human Muscle Fibers

    PubMed Central

    Nogalska, Anna; D'Agostino, Carla; Terracciano, Chiara; Engel, W. King; Askanas, Valerie

    2010-01-01

    The hallmark pathologies of sporadic inclusion-body myositis (s-IBM) muscle fibers are autophagic vacuoles and accumulation of ubiquitin-positive multiprotein aggregates that contain amyloid-β or phosphorylated tau in a β-pleated sheet amyloid configuration. Endoplasmic reticulum stress (ERS) and 26S proteasome inhibition, also associated with s-IBM, putatively aggrandize the accumulation of misfolded proteins. However, autophagosomal-lysosomal pathway formation and function, indicated by autophagosome maturation, have not been previously analyzed in this system. Here we studied the autophagosomal-lysosomal pathway using 14 s-IBM and 30 disease control and normal control muscle biopsy samples and our cultured human muscle fibers in a microenvironment modified to resemble aspects of s-IBM pathology. We report for the first time that in s-IBM, lysosomal enzyme activities of cathepsin D and B were decreased 60% (P < 0.01) and 40% (P < 0.05), respectively. We also detected two indicators of increased autophagosome maturation, the presence of LC3-II and decreased mammalian target of rapamycin-mediated phosphorylation of p70S6 kinase. Moreover, in cultured human muscle fibers, ERS induction significantly decreased activities of cathepsins D and B, increased levels of LC3-II, decreased phosphorylation of p70S6 kinase, and decreased expression of VMA21, a chaperone for assembly of lysosomal V-ATPase. We conclude that in s-IBM muscle, decreased lysosomal proteolytic activity might enhance accumulation of misfolded proteins, despite increased maturation of autophagosomes, and that ERS is a possible cause of s-IBM-impaired lysosomal function. Thus, unblocking protein degradation in s-IBM muscle fibers may be a desirable therapeutic strategy. PMID:20616343

  13. Fracture Mechanisms For SiC Fibers And SiC/SiC Composites Under Stress-Rupture Conditions at High Temperatures

    NASA Technical Reports Server (NTRS)

    DiCarlo, James A.; Yun, Hee Mann; Hurst, Janet B.; Viterna, L. (Technical Monitor)

    2002-01-01

    The successful application of SiC/SiC ceramic matrix composites as high-temperature structural materials depends strongly on maximizing the fracture or rupture life of the load-bearing fiber and matrix constituents. Using high-temperature data measured under stress-rupture test conditions, this study examines in a mechanistic manner the effects of various intrinsic and extrinsic factors on the creep and fracture behavior of a variety of SiC fiber types. It is shown that although some fiber types fracture during a large primary creep stage, the fiber creep rate just prior to fracture plays a key role in determining fiber rupture time (Monkman-Grant theory). If it is assumed that SiC matrices rupture in a similar manner as fibers with the same microstructures, one can develop simple mechanistic models to analyze and optimize the stress-rupture behavior of SiC/SiC composites for applied stresses that are initially below matrix cracking.

  14. Frequency dependence of long-period tidal factors determined from gravity and space geodetic data

    NASA Astrophysics Data System (ADS)

    Kim, T.; Nilsson, T.; Doi, K.; Aoyama, Y.

    2013-12-01

    The effects of ocean tides, a fluid core and mantle inelasticity of the earth cause the frequency dependence on zonal tidal signals. In particular, because inelastic effects of the medium of the Earth become larger for lower frequencies (Wahr, 1985) and the long-periods tides have their maximum values at the poles, tidal observations and analysis of long-period at high latitudes is advantageous for studying the dissipative properties in the Earth (Iwano et al., 2005). From this view point, Sato et al. (1995) and Iwano et al. (2005) analyzed the data of the gravity observations using superconducting gravimeter (SG) at Syowa Station in Antarctica. However, they concluded that the residuals from theory is mainly due to the inaccurate ocean models for ocean tidal loading correction. Recently, new two ocean tide models (FES2012 and TPXO8-atlas) were developed, which provide long-period ocean tide information. Thus, we reanalyzed the gravity data of Syowa Station using these new ocean tide models for ocean loading correction, and evaluated the gravimetric factors (δ). The estimated gravimetric factors are 1.15822 (FES2012) and 1.15541 (TPXO8-atlas) for Mm and 1.15396 and 1.15405 for Mf. Meanwhile, the zonal response coefficient κ defined by Agnew and Farrell (1978) were also estimated using zonal tidal signals with periods from 5 to 35 days in dUT1 (UTC-UT1), a tidally induced variation of the rotation rate of the Earth. This coefficient show also the frequency dependent zonal response. In this study, the values of estimated κ for different tidal frequencies from dUT1 observed by VLBI were compared to theory and to the results of previous determinations of κ from observations of space geodetic techniques. We used VieVs (Vienna VLBI Software) program for the estimation of dUT1 and processed all 24 hours from 1984 to 2012 and also processed the IERS C04 dUT1 series. These time series of dUT1 data were subtracted by the UT1 variations from atmospheric, hydrologic, and

  15. Cav1.1 controls frequency-dependent events regulating adult skeletal muscle plasticity.

    PubMed

    Jorquera, Gonzalo; Altamirano, Francisco; Contreras-Ferrat, Ariel; Almarza, Gonzalo; Buvinic, Sonja; Jacquemond, Vincent; Jaimovich, Enrique; Casas, Mariana

    2013-03-01

    An important pending question in neuromuscular biology is how skeletal muscle cells decipher the stimulation pattern coming from motoneurons to define their phenotype as slow or fast twitch muscle fibers. We have previously shown that voltage-gated L-type calcium channel (Cav1.1) acts as a voltage sensor for activation of inositol (1,4,5)-trisphosphate [Ins(1,4,5)P₃]-dependent Ca(2+) signals that regulates gene expression. ATP released by muscle cells after electrical stimulation through pannexin-1 channels plays a key role in this process. We show now that stimulation frequency determines both ATP release and Ins(1,4,5)P₃ production in adult skeletal muscle and that Cav1.1 and pannexin-1 colocalize in the transverse tubules. Both ATP release and increased Ins(1,4,5)P₃ was seen in flexor digitorum brevis fibers stimulated with 270 pulses at 20 Hz, but not at 90 Hz. 20 Hz stimulation induced transcriptional changes related to fast-to-slow muscle fiber phenotype transition that required ATP release. Addition of 30 µM ATP to fibers induced the same transcriptional changes observed after 20 Hz stimulation. Myotubes lacking the Cav1.1-α1 subunit released almost no ATP after electrical stimulation, showing that Cav1.1 has a central role in this process. In adult muscle fibers, ATP release and the transcriptional changes produced by 20 Hz stimulation were blocked by both the Cav1.1 antagonist nifedipine (25 µM) and by the Cav1.1 agonist (-)S-BayK 8644 (10 µM). We propose a new role for Cav1.1, independent of its calcium channel activity, in the activation of signaling pathways allowing muscle fibers to decipher the frequency of electrical stimulation and to activate specific transcriptional programs that define their phenotype.

  16. Cav1.1 controls frequency-dependent events regulating adult skeletal muscle plasticity.

    PubMed

    Jorquera, Gonzalo; Altamirano, Francisco; Contreras-Ferrat, Ariel; Almarza, Gonzalo; Buvinic, Sonja; Jacquemond, Vincent; Jaimovich, Enrique; Casas, Mariana

    2013-03-01

    An important pending question in neuromuscular biology is how skeletal muscle cells decipher the stimulation pattern coming from motoneurons to define their phenotype as slow or fast twitch muscle fibers. We have previously shown that voltage-gated L-type calcium channel (Cav1.1) acts as a voltage sensor for activation of inositol (1,4,5)-trisphosphate [Ins(1,4,5)P₃]-dependent Ca(2+) signals that regulates gene expression. ATP released by muscle cells after electrical stimulation through pannexin-1 channels plays a key role in this process. We show now that stimulation frequency determines both ATP release and Ins(1,4,5)P₃ production in adult skeletal muscle and that Cav1.1 and pannexin-1 colocalize in the transverse tubules. Both ATP release and increased Ins(1,4,5)P₃ was seen in flexor digitorum brevis fibers stimulated with 270 pulses at 20 Hz, but not at 90 Hz. 20 Hz stimulation induced transcriptional changes related to fast-to-slow muscle fiber phenotype transition that required ATP release. Addition of 30 µM ATP to fibers induced the same transcriptional changes observed after 20 Hz stimulation. Myotubes lacking the Cav1.1-α1 subunit released almost no ATP after electrical stimulation, showing that Cav1.1 has a central role in this process. In adult muscle fibers, ATP release and the transcriptional changes produced by 20 Hz stimulation were blocked by both the Cav1.1 antagonist nifedipine (25 µM) and by the Cav1.1 agonist (-)S-BayK 8644 (10 µM). We propose a new role for Cav1.1, independent of its calcium channel activity, in the activation of signaling pathways allowing muscle fibers to decipher the frequency of electrical stimulation and to activate specific transcriptional programs that define their phenotype. PMID:23321639

  17. Hemispheric Asymmetry of Frequency-Dependent Suppression in the Ipsilateral Primary Motor Cortex During Finger Movement: A Functional Magnetic Resonance Imaging Study

    PubMed Central

    Hayashi, Masamichi J.; Saito, Daisuke N.; Aramaki, Yu; Asai, Tatsuya; Fujibayashi, Yasuhisa

    2008-01-01

    Electrophysiological studies have suggested that the activity of the primary motor cortex (M1) during ipsilateral hand movement reflects both the ipsilateral innervation and the transcallosal inhibitory control from its counterpart in the opposite hemisphere, and that their asymmetry might cause hand dominancy. To examine the asymmetry of the involvement of the ipsilateral motor cortex during a unimanual motor task under frequency stress, we conducted block-design functional magnetic resonance imaging with 22 normal right-handed subjects. The task involved visually cued unimanual opponent finger movement at various rates. The contralateral M1 showed symmetric frequency-dependent activation. The ipsilateral M1 showed task-related deactivation at low frequencies without laterality. As the frequency of the left-hand movement increased, the left M1 showed a gradual decrease in the deactivation. This data suggests a frequency-dependent increased involvement of the left M1 in ipsilateral hand control. By contrast, the right M1 showed more prominent deactivation as the frequency of the right-hand movement increased. This suggests that there is an increased transcallosal inhibition from the left M1 to the right M1, which overwhelms the right M1 activation during ipsilateral hand movement. These results demonstrate the dominance of the left M1 in both ipsilateral innervation and transcallosal inhibition in right-handed individuals. PMID:18413350

  18. Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant reveal that fiber cell wall development is associated with sensitivity to stress.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background: Cotton fiber maturity refers the degree of fiber cell wall development and is an important factor for determining commercial value of cotton. The molecular mechanism regulating the fiber cell wall development has not been well characterized. Microscopic image analysis of the cross-sect...

  19. Frequency-dependent performance and handedness in professional baseball players (Homo sapiens).

    PubMed

    Clotfelter, Ethan D

    2008-02-01

    I used data on handedness and pitching and hitting performance in annual cohorts of professional baseball players (1957-2005) to test the hypothesis that handedness among pitchers was subject to negative frequency-dependent selection. As predicted by this hypothesis, right-handed pitchers were more successful (i.e., opposing batters hit more poorly against them) when they were relatively rare in the population. Contrary to the predictions of this hypothesis, however, left-handed pitchers were more successful when they were relatively common. Both right- and left-handed batters performed better in years dominated by right-handed pitchers, despite the fact that right-handed batters perform relatively poorly against right-handed pitchers. I suggest that batters form cognitive representations based on pitcher handedness, and that these representations are strengthened by repeated exposure or priming. When the pitcher handedness polymorphism is more balanced (e.g., 67% right-handed, 33% left-handed), these cognitive representations are less effective, which leads to decreased batting averages and improved performance by all pitchers. Furthermore, these cognitive representations are likely to be more critical to the success of right-handed hitters, who have reduced visuomotor skills relative to left-handed hitters. PMID:18298283

  20. The protective effect of conditioning on noise-induced hearing loss is frequency-dependent.

    PubMed

    Pourbakht, Akram; Imani, Azadeh

    2012-01-01

    We compared the extent of temporary threshold shift (TTS) and hair cell loss following high level 4 kHz noise exposure with those preconditioned with moderate level 1 and 4 kHz octave band noise. Fifteen Male albino guinea pigs (300- 350 g in weight) were randomly allocated into three groups: those exposed to 4 kHz octave band noise at 102 dB SPL (group 1, n=5); those conditioned with 1 kHz octave band noise at 85 dB SPL, 6 hours per day for 5 days, then exposed to noise (group 2, n=5); those conditioned with 4 kHz octave band noise at 85 dB SPL, then exposed to noise (group 3, n=5). An hour and one week after noise exposure, threshold shifts were evaluated by auditory-evoked brainstem response (ABR) and then animals were euthanized for histological evaluation. We found that TTS and cochlear damage caused by noise exposure were significantly reduced by 1 kHz and 4 kHz conditioning (P<0.001). We also showed that 4 kHz protocol attenuates noise- induced TTS but no significant TTS reduction occurred by 1 kHz conditioning. Both protocol protected noise-induced cochlear damage. We concluded that lower tone conditioning could not protect against higher tone temporary noise-induced hearing loss, thus conditioning is a local acting and frequency-dependent phenomenon.

  1. Frequency-dependent fitness of hybrids between oilseed rape (Brassica napus) and weedy B. rapa (Brassicaceae).

    PubMed

    Hauser, Thure P; Damgaard, Christian; Jørgensen, Rikke B

    2003-04-01

    Fitness of interspecific hybrids is sometimes high relative to their parents, despite the conventional belief that they are mostly unfit. F(1) hybrids between oilseed rape (Brassica napus) and weedy B. rapa can be significantly more fit than their weedy parents under some conditions; however, under other conditions they are less fit. To understand the reasons, we measured the seed production of B. napus, B. rapa, and different generations of hybrid plants at three different densities and in mixtures of different frequencies (including pure stands). Brassica napus, B. rapa, and backcross plants (F(1) ♀ × B. rapa) produced many more seeds per plant in pure plots than in mixtures and more seeds in plots when each was present at high frequency. The opposite was true for F(1) plants that produced many more seeds than B. rapa in mixtures, but fewer in pure stands. Both vegetative and reproductive interactions may be responsible for these effects. Our results show that the fitness of both parents and hybrids is strongly frequency-dependent and that the likelihood of introgression of genes between the species thus may depend on the numbers and densities of parents and their various hybrid offspring in the population.

  2. Direction of information flow in large-scale resting-state networks is frequency-dependent.

    PubMed

    Hillebrand, Arjan; Tewarie, Prejaas; van Dellen, Edwin; Yu, Meichen; Carbo, Ellen W S; Douw, Linda; Gouw, Alida A; van Straaten, Elisabeth C W; Stam, Cornelis J

    2016-04-01

    Normal brain function requires interactions between spatially separated, and functionally specialized, macroscopic regions, yet the directionality of these interactions in large-scale functional networks is unknown. Magnetoencephalography was used to determine the directionality of these interactions, where directionality was inferred from time series of beamformer-reconstructed estimates of neuronal activation, using a recently proposed measure of phase transfer entropy. We observed well-organized posterior-to-anterior patterns of information flow in the higher-frequency bands (alpha1, alpha2, and beta band), dominated by regions in the visual cortex and posterior default mode network. Opposite patterns of anterior-to-posterior flow were found in the theta band, involving mainly regions in the frontal lobe that were sending information to a more distributed network. Many strong information senders in the theta band were also frequent receivers in the alpha2 band, and vice versa. Our results provide evidence that large-scale resting-state patterns of information flow in the human brain form frequency-dependent reentry loops that are dominated by flow from parieto-occipital cortex to integrative frontal areas in the higher-frequency bands, which is mirrored by a theta band anterior-to-posterior flow. PMID:27001844

  3. Direct Derivation of the Gravitational Red Shift (Einstein Shift) with the frequency dependent Gall metric

    NASA Astrophysics Data System (ADS)

    Gall, Clarence A.

    1999-05-01

    When an electromagnetic radiation (EMR) source is in uniform motion with respect to an observer, a spectral (Doppler) shift in frequency is seen (blue as it approaches, red as it recedes). Since special relativity is limited to coordinate systems in uniform relative motion, this theory should be subject to this condition. On the other hand, the gravitational red shift (Einstein; Relativity: The Special and the General Theory, Crown,(1961), p.129) claims that EMR frequency decreases as the gravitational field, where the source is located, increases. As a gravitational effect, one would expect its derivation from a solution of the general relativistic field equations (R_μσ=0). Up to now, it has only been possible to derive it indirectly, by comparing the gravitational field to a (centrifugal) field produced by coordinate systems in relative rotational motion as an approximation of special relativity. Since rotation implies acceleration, it does not meet the conditions of special relativity so this is unsatisfactory. This work shows that the problem lies in the Schwarzschild metric which is independent of EMR frequency. By contrast it is easy to deduce the gravitational red shift from the frequency dependent Gall metric (Gall in AIP Conference Proceedings 308, The Evolution of X-Ray Binaries,(1993), p. 87).

  4. Electromagnetic millimeter wave induced hypoalgesia: frequency dependence and involvement of endogenous opioids.

    PubMed

    Radzievsky, A A; Gordiienko, O V; Alekseev, S; Szabo, I; Cowan, A; Ziskin, M C

    2008-05-01

    Millimeter wave treatment (MMWT) is based on the systemic biological effects that develop following local skin exposure to low power electromagnetic waves in the millimeter range. In the present set of experiments, the hypoalgesic effect of this treatment was analyzed in mice. The murine nose area was exposed to MMW of "therapeutic" frequencies: 42.25, 53.57, and 61.22 GHz. MMWT-induced hypoalgesia was shown to be frequency dependent in two experimental models: (1) the cold water tail-flick test (chronic non-neuropathic pain), and (2) the wire surface test (chronic neuropathic pain following unilateral constriction injury to the sciatic nerve). Maximum hypoalgesic effect was obtained when the frequency was 61.22 GHz. Other exposure parameters were: incident power density = 13.3 mW/cm(2), duration of each exposure = 15 min. Involvement of delta and kappa endogenous opioids in the MMWT-induced hypoalgesia was demonstrated using selective blockers of delta- and kappa-opioid receptors and the direct ELISA measurement of endogenous opioids in CNS tissue. Possible mechanisms of the effect and the perspectives of the clinical application of MMWT are discussed.

  5. Frequency-dependent auditory space representation in the human planum temporale.

    PubMed

    Shrem, Talia; Deouell, Leon Y

    2014-01-01

    Functional magnetic resonance imaging (fMRI) findings suggest that a part of the planum temporale (PT) is involved in representing spatial properties of acoustic information. Here, we tested whether this representation of space is frequency-dependent or generalizes across spectral content, as required from high order sensory representations. Using sounds with two different spectral content and two spatial locations in individually tailored virtual acoustic environment, we compared three conditions in a sparse-fMRI experiment: Single Location, in which two sounds were both presented from one location; Fixed Mapping, in which there was one-to-one mapping between two sounds and two locations; and Mixed Mapping, in which the two sounds were equally likely to appear at either one of the two locations. We surmised that only neurons tuned to both location and frequency should be differentially adapted by the Mixed and Fixed mappings. Replicating our previous findings, we found adaptation to spatial location in the PT. Importantly, activation was higher for Mixed Mapping than for Fixed Mapping blocks, even though the two sounds and the two locations appeared equally in both conditions. These results show that spatially tuned neurons in the human PT are not invariant to the spectral content of sounds.

  6. Warning signals are under positive frequency-dependent selection in nature.

    PubMed

    Chouteau, Mathieu; Arias, Mónica; Joron, Mathieu

    2016-02-23

    Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication. However, whether and how positive FDS truly operates in nature remains unknown, which hampers our understanding of signal diversity. Here, we test for positive FDS operating on the warning color patterns of chemically defended butterflies forming multiple coexisting mimicry assemblages in the Amazon. Using malleable prey models placed in localities showing differences in the relative frequencies of warningly colored prey, we demonstrate that the efficiency of a warning signal increases steadily with its local frequency in the natural community, up to a threshold where protection stabilizes. The shape of this relationship is consistent with the direct effect of the local abundance of each warning signal on the corresponding avoidance knowledge of the local predator community. This relationship, which differs from purifying selection acting on each mimetic pattern, indicates that predator knowledge, integrated over the entire community, is saturated only for the most common warning signals. In contrast, among the well-established warning signals present in local prey assemblages, most are incompletely known to local predators and enjoy incomplete protection. This incomplete predator knowledge should generate strong benefits to life history traits that enhance warning efficiency by increasing the effective frequency of prey visible to predators. Strategies such as gregariousness or niche convergence between comimics may therefore readily evolve through their effects on predator knowledge and warning efficiency. PMID:26858416

  7. Direction of information flow in large-scale resting-state networks is frequency-dependent

    PubMed Central

    Hillebrand, Arjan; Tewarie, Prejaas; van Dellen, Edwin; Yu, Meichen; Carbo, Ellen W. S.; Douw, Linda; Gouw, Alida A.; van Straaten, Elisabeth C. W.; Stam, Cornelis J.

    2016-01-01

    Normal brain function requires interactions between spatially separated, and functionally specialized, macroscopic regions, yet the directionality of these interactions in large-scale functional networks is unknown. Magnetoencephalography was used to determine the directionality of these interactions, where directionality was inferred from time series of beamformer-reconstructed estimates of neuronal activation, using a recently proposed measure of phase transfer entropy. We observed well-organized posterior-to-anterior patterns of information flow in the higher-frequency bands (alpha1, alpha2, and beta band), dominated by regions in the visual cortex and posterior default mode network. Opposite patterns of anterior-to-posterior flow were found in the theta band, involving mainly regions in the frontal lobe that were sending information to a more distributed network. Many strong information senders in the theta band were also frequent receivers in the alpha2 band, and vice versa. Our results provide evidence that large-scale resting-state patterns of information flow in the human brain form frequency-dependent reentry loops that are dominated by flow from parieto-occipital cortex to integrative frontal areas in the higher-frequency bands, which is mirrored by a theta band anterior-to-posterior flow. PMID:27001844

  8. A General Model of Negative Frequency Dependent Selection Explains Global Patterns of Human ABO Polymorphism.

    PubMed

    Villanea, Fernando A; Safi, Kristin N; Busch, Jeremiah W

    2015-01-01

    The ABO locus in humans is characterized by elevated heterozygosity and very similar allele frequencies among populations scattered across the globe. Using knowledge of ABO protein function, we generated a simple model of asymmetric negative frequency dependent selection and genetic drift to explain the maintenance of ABO polymorphism and its loss in human populations. In our models, regardless of the strength of selection, models with large effective population sizes result in ABO allele frequencies that closely match those observed in most continental populations. Populations must be moderately small to fall out of equilibrium and lose either the A or B allele (N(e) ≤ 50) and much smaller (N(e) ≤ 25) for the complete loss of diversity, which nearly always involved the fixation of the O allele. A pattern of low heterozygosity at the ABO locus where loss of polymorphism occurs in our model is consistent with small populations, such as Native American populations. This study provides a general evolutionary model to explain the observed global patterns of polymorphism at the ABO locus and the pattern of allele loss in small populations. Moreover, these results inform the range of population sizes associated with the recent human colonization of the Americas. PMID:25946124

  9. Modeling ballistic effects in frequency-dependent transient thermal transport using diffusion equations

    NASA Astrophysics Data System (ADS)

    Maassen, Jesse; Lundstrom, Mark

    2016-03-01

    Understanding ballistic phonon transport effects in transient thermoreflectance experiments and explaining the observed deviations from classical theory remains a challenge. Diffusion equations are simple and computationally efficient but are widely believed to break down when the characteristic length scale is similar or less than the phonon mean-free-path. Building on our prior work, we demonstrate how well-known diffusion equations, namely, the hyperbolic heat equation and the Cattaneo equation, can be used to model ballistic phonon effects in frequency-dependent periodic steady-state thermal transport. Our analytical solutions are found to compare excellently to rigorous numerical results of the phonon Boltzmann transport equation. The correct physical boundary conditions can be different from those traditionally used and are paramount for accurately capturing ballistic effects. To illustrate the technique, we consider a simple model problem using two different, commonly used heating conditions. We demonstrate how this framework can easily handle detailed material properties, by considering the case of bulk silicon using a full phonon dispersion and mean-free-path distribution. This physically transparent approach provides clear insights into the nonequilibrium physics of quasi-ballistic phonon transport and its impact on thermal transport properties.

  10. Warning signals are under positive frequency-dependent selection in nature

    PubMed Central

    Chouteau, Mathieu; Arias, Mónica; Joron, Mathieu

    2016-01-01

    Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication. However, whether and how positive FDS truly operates in nature remains unknown, which hampers our understanding of signal diversity. Here, we test for positive FDS operating on the warning color patterns of chemically defended butterflies forming multiple coexisting mimicry assemblages in the Amazon. Using malleable prey models placed in localities showing differences in the relative frequencies of warningly colored prey, we demonstrate that the efficiency of a warning signal increases steadily with its local frequency in the natural community, up to a threshold where protection stabilizes. The shape of this relationship is consistent with the direct effect of the local abundance of each warning signal on the corresponding avoidance knowledge of the local predator community. This relationship, which differs from purifying selection acting on each mimetic pattern, indicates that predator knowledge, integrated over the entire community, is saturated only for the most common warning signals. In contrast, among the well-established warning signals present in local prey assemblages, most are incompletely known to local predators and enjoy incomplete protection. This incomplete predator knowledge should generate strong benefits to life history traits that enhance warning efficiency by increasing the effective frequency of prey visible to predators. Strategies such as gregariousness or niche convergence between comimics may therefore readily evolve through their effects on predator knowledge and warning efficiency. PMID:26858416

  11. A General Model of Negative Frequency Dependent Selection Explains Global Patterns of Human ABO Polymorphism.

    PubMed

    Villanea, Fernando A; Safi, Kristin N; Busch, Jeremiah W

    2015-01-01

    The ABO locus in humans is characterized by elevated heterozygosity and very similar allele frequencies among populations scattered across the globe. Using knowledge of ABO protein function, we generated a simple model of asymmetric negative frequency dependent selection and genetic drift to explain the maintenance of ABO polymorphism and its loss in human populations. In our models, regardless of the strength of selection, models with large effective population sizes result in ABO allele frequencies that closely match those observed in most continental populations. Populations must be moderately small to fall out of equilibrium and lose either the A or B allele (N(e) ≤ 50) and much smaller (N(e) ≤ 25) for the complete loss of diversity, which nearly always involved the fixation of the O allele. A pattern of low heterozygosity at the ABO locus where loss of polymorphism occurs in our model is consistent with small populations, such as Native American populations. This study provides a general evolutionary model to explain the observed global patterns of polymorphism at the ABO locus and the pattern of allele loss in small populations. Moreover, these results inform the range of population sizes associated with the recent human colonization of the Americas.

  12. FREQUENCY DEPENDENCE OF POLARIZATION OF ZEBRA PATTERN IN TYPE-IV SOLAR RADIO BURSTS

    SciTech Connect

    Kaneda, Kazutaka; Misawa, H.; Tsuchiya, F.; Obara, T.; Iwai, K.

    2015-08-01

    We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZPs. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50%–70% right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50–70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double-plasma-resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.

  13. Frequency-dependent photothermal measurement of transverse thermal diffusivity of organic semiconductors

    SciTech Connect

    Brill, J. W.; Shahi, Maryam; Yao, Y.; Payne, Marcia M.; Anthony, J. E.; Edberg, Jesper; Crispin, Xavier

    2015-12-21

    We have used a photothermal technique, in which chopped light heats the front surface of a small (∼1 mm{sup 2}) sample and the chopping frequency dependence of thermal radiation from the back surface is measured with a liquid-nitrogen-cooled infrared detector. In our system, the sample is placed directly in front of the detector within its dewar. Because the detector is also sensitive to some of the incident light, which leaks around or through the sample, measurements are made for the detector signal that is in quadrature with the chopped light. Results are presented for layered crystals of semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pn) and for papers of cellulose nanofibrils coated with semiconducting poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (NFC-PEDOT). For NFC-PEDOT, we have found that the transverse diffusivity, smaller than the in-plane value, varies inversely with thickness, suggesting that texturing of the papers varies with thickness. For TIPS-pn, we have found that the interlayer diffusivity is an order of magnitude larger than the in-plane value, consistent with previous estimates, suggesting that low-frequency optical phonons, presumably associated with librations in the TIPS side groups, carry most of the heat.

  14. The effect of frequency-dependent selection on resistance and tolerance to herbivory.

    PubMed

    Garrido, E; Llamas-Guzmán, L P; Fornoni, J

    2016-03-01

    Negative frequency-dependent selection (FDS), where rare genotypes are favoured by selection, is commonly invoked as a mechanism explaining the maintenance of genetic variation in plant defences. However, empirical tests of FDS in plant-herbivore interactions are lacking. We evaluated whether the oviposition preference of the specialist herbivore Lema daturaphila is a mechanism through which this herbivore can exert FDS on its host plant Datura stramonium. The frequency of contrasting resistance-tolerance strategies was manipulated within experimental plots, and the plants were exposed to a similar initial density of their natural herbivore. Herbivore oviposition preference and final density, as well as plant damage and seed production, were estimated. Overall, we found that the high-resistant-low-tolerant genotypes produced four times more seeds when common than when rare, whereas the high-tolerant-low-resistant genotypes achieved twice its fitness when rare than when common. This pattern was the result of differential oviposition preferences. In addition, when the high-resistant-low-tolerant genotypes were common, there was a three-fold decreased in herbivore final density which led to a decrease in damage level by 10%. Thus, in our experiment positive FDS seems to favour resistance over tolerance. We discuss how this result would change if the extent of herbivore local adaptation and damage modify the pattern of positive FDS acting on resistance and the optimal allocation to tolerance. PMID:26411698

  15. Plant-soil feedbacks promote negative frequency dependence in the coexistence of two aridland grasses.

    PubMed

    Chung, Y Anny; Rudgers, Jennifer A

    2016-07-27

    Understanding the mechanisms of species coexistence is key to predicting patterns of species diversity. Historically, the ecological paradigm has been that species coexist by partitioning resources: as a species increases in abundance, self-limitation kicks in, because species-specific resources decline. However, determining coexistence mechanisms has been a particular puzzle for sedentary organisms with high overlap in their resource requirements, such as plants. Recent evidence suggests that plant-associated microbes could generate the stabilizing self-limitation (negative frequency dependence) that is required for species coexistence. Here, we test the key assumption that plant-microbe feedbacks cause such self-limitation. We used competition experiments and modelling to evaluate how two common groups of soil microbes (rhizospheric microbes and biological soil crusts) influenced the self-limitation of two competing desert grass species. Negative feedbacks between the dominant plant competitor and its rhizospheric microbes magnified self-limitation, whereas beneficial interactions between both plant species and biological soil crusts partly counteracted this stabilizing effect. Plant-microbe interactions have received relatively little attention as drivers of vegetation dynamics in dry land ecosystems. Our results suggest that microbial mechanisms can contribute to patterns of plant coexistence in arid grasslands. PMID:27466448

  16. Frequency-dependent electrodeformation of giant phospholipid vesicles in AC electric field

    PubMed Central

    2010-01-01

    A model of vesicle electrodeformation is described which obtains a parametrized vesicle shape by minimizing the sum of the membrane bending energy and the energy due to the electric field. Both the vesicle membrane and the aqueous media inside and outside the vesicle are treated as leaky dielectrics, and the vesicle itself is modeled as a nearly spherical shape enclosed within a thin membrane. It is demonstrated (a) that the model achieves a good quantitative agreement with the experimentally determined prolate-to-oblate transition frequencies in the kilohertz range and (b) that the model can explain a phase diagram of shapes of giant phospholipid vesicles with respect to two parameters: the frequency of the applied alternating current electric field and the ratio of the electrical conductivities of the aqueous media inside and outside the vesicle, explored in a recent paper (S. Aranda et al., Biophys J 95:L19–L21, 2008). A possible use of the frequency-dependent shape transitions of phospholipid vesicles in conductometry of microliter samples is discussed. PMID:21886342

  17. Self-consistent modeling of terahertz waveguide and cavity with frequency-dependent conductivity

    SciTech Connect

    Huang, Y. J.; Chu, K. R.; Thumm, M.

    2015-01-15

    The surface resistance of metals, and hence the Ohmic dissipation per unit area, scales with the square root of the frequency of an incident electromagnetic wave. As is well recognized, this can lead to excessive wall losses at terahertz (THz) frequencies. On the other hand, high-frequency oscillatory motion of conduction electrons tends to mitigate the collisional damping. As a result, the classical theory predicts that metals behave more like a transparent medium at frequencies above the ultraviolet. Such a behavior difference is inherent in the AC conductivity, a frequency-dependent complex quantity commonly used to treat electromagnetics of metals at optical frequencies. The THz region falls in the gap between microwave and optical frequencies. However, metals are still commonly modeled by the DC conductivity in currently active vacuum electronics research aimed at the development of high-power THz sources (notably the gyrotron), although a small reduction of the DC conductivity due to surface roughness is sometimes included. In this study, we present a self-consistent modeling of the gyrotron interaction structures (a metallic waveguide or cavity) with the AC conductivity. The resulting waveguide attenuation constants and cavity quality factors are compared with those of the DC-conductivity model. The reduction in Ohmic losses under the AC-conductivity model is shown to be increasingly significant as the frequency reaches deeper into the THz region. Such effects are of considerable importance to THz gyrotrons for which the minimization of Ohmic losses constitutes a major design consideration.

  18. Frequency-dependent auditory space representation in the human planum temporale

    PubMed Central

    Shrem, Talia; Deouell, Leon Y.

    2014-01-01

    Functional magnetic resonance imaging (fMRI) findings suggest that a part of the planum temporale (PT) is involved in representing spatial properties of acoustic information. Here, we tested whether this representation of space is frequency-dependent or generalizes across spectral content, as required from high order sensory representations. Using sounds with two different spectral content and two spatial locations in individually tailored virtual acoustic environment, we compared three conditions in a sparse-fMRI experiment: Single Location, in which two sounds were both presented from one location; Fixed Mapping, in which there was one-to-one mapping between two sounds and two locations; and Mixed Mapping, in which the two sounds were equally likely to appear at either one of the two locations. We surmised that only neurons tuned to both location and frequency should be differentially adapted by the Mixed and Fixed mappings. Replicating our previous findings, we found adaptation to spatial location in the PT. Importantly, activation was higher for Mixed Mapping than for Fixed Mapping blocks, even though the two sounds and the two locations appeared equally in both conditions. These results show that spatially tuned neurons in the human PT are not invariant to the spectral content of sounds. PMID:25100973

  19. Frequency-Dependence of Mechanically Stimulated Osteoblastic Calcification in Tissue-Engineered Bone In Vitro.

    PubMed

    Tanaka, Shigeo M; Tachibana, Kohei

    2015-09-01

    The effect of mechanical stimulation on osteogenesis remains controversial, especially with respect to the loading frequency that maximizes osteogenesis. Mechanical stimulation at an optimized frequency may be beneficial for the bone tissue regeneration to promote osteoblastic calcification. The objective of this study was to investigate the frequency-dependent effect of mechanical loading on osteoblastic calcification in the tissue-engineered bones in vitro. Tissue-engineered bones were constructed by seeding rat osteoblasts into a type I collagen sponge scaffold at a cell density of 1600 or 24,000 cells/mm(3). Sinusoidal compressive deformation at the peak of 0.2% was applied to the tissue-engineered bones at 0.2, 2, 10, 20, 40, and 60 Hz for 3 min/day for 14 consecutive days. Optically-monitored calcium content started to increase on days 5-7 and reached the highest value at 2 Hz on day 14; however, no increase was observed at 0.2 Hz and in the control. Ash content measured after the mechanical stimulation also showed the highest at 2 Hz despite the differences in cell seeding density. It was concluded that mechanical stimulation at 2 Hz showed the highest promotional effect for osteogenesis in vitro among the frequencies selected in this study.

  20. Self-consistent modeling of terahertz waveguide and cavity with frequency-dependent conductivity

    NASA Astrophysics Data System (ADS)

    Huang, Y. J.; Chu, K. R.; Thumm, M.

    2015-01-01

    The surface resistance of metals, and hence the Ohmic dissipation per unit area, scales with the square root of the frequency of an incident electromagnetic wave. As is well recognized, this can lead to excessive wall losses at terahertz (THz) frequencies. On the other hand, high-frequency oscillatory motion of conduction electrons tends to mitigate the collisional damping. As a result, the classical theory predicts that metals behave more like a transparent medium at frequencies above the ultraviolet. Such a behavior difference is inherent in the AC conductivity, a frequency-dependent complex quantity commonly used to treat electromagnetics of metals at optical frequencies. The THz region falls in the gap between microwave and optical frequencies. However, metals are still commonly modeled by the DC conductivity in currently active vacuum electronics research aimed at the development of high-power THz sources (notably the gyrotron), although a small reduction of the DC conductivity due to surface roughness is sometimes included. In this study, we present a self-consistent modeling of the gyrotron interaction structures (a metallic waveguide or cavity) with the AC conductivity. The resulting waveguide attenuation constants and cavity quality factors are compared with those of the DC-conductivity model. The reduction in Ohmic losses under the AC-conductivity model is shown to be increasingly significant as the frequency reaches deeper into the THz region. Such effects are of considerable importance to THz gyrotrons for which the minimization of Ohmic losses constitutes a major design consideration.

  1. Frequency dependent steering with backward leaky waves via photonic crystal interface layer.

    PubMed

    Colak, Evrim; Caglayan, Humeyra; Cakmak, Atilla O; Villa, Alessandro D; Capolino, Filippo; Ozbay, Ekmel

    2009-06-01

    A Photonic Crystal (PC) with a surface defect layer (made of dimers) is studied in the microwave regime. The dispersion diagram is obtained with the Plane Wave Expansion Method. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Two facts are noted: First, a guided (bounded) wave is present, propagating along the surface of the dimer-layer. Second, above the light line, the fast traveling mode couple to the propagating spectra and as a result a directive (narrow beam) radiation with backward characteristics is observed and measured. In this leaky mode regime, symmetrical radiation patterns with respect to the normal to the PC surface are attained. Beam steering is observed and measured in a 70 degrees angular range when frequency ranges in the 11.88-13.69 GHz interval. Thus, a PC based surface wave structure that acts as a frequency dependent leaky wave antenna is presented. Angular radiation pattern measurements are in agreement with those obtained via numerical simulations that employ the Finite Difference Time Domain Method (FDTD). Finally, the backward radiation characteristics that in turn suggest the existence of a backward leaky mode in the dimer-layer are experimentally verified using a halved dimer-layer structure.

  2. Compressive sensing of frequency-dependent seismic radiation from subduction zone megathrust ruptures

    PubMed Central

    Yao, Huajian; Shearer, Peter M.; Gerstoft, Peter

    2013-01-01

    Megathrust earthquakes rupture a broad zone of the subducting plate interface in both along-strike and along-dip directions. The along-dip rupture characteristics of megathrust events, e.g., their slip and energy radiation distribution, reflect depth-varying frictional properties of the slab interface. Here, we report high-resolution frequency-dependent seismic radiation of the four largest megathrust earthquakes in the past 10 y using a compressive-sensing (sparse source recovery) technique, resolving generally low-frequency radiation closer to the trench at shallower depths and high-frequency radiation farther from the trench at greater depths. Together with coseismic slip models and early aftershock locations, our results suggest depth-varying frictional properties at the subducting plate interfaces. The shallower portion of the slab interface (above ∼15 km) is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip, deficient high-frequency radiation, and few early aftershocks. The slab interface at intermediate depths (∼15–35 km) is the main unstable seismogenic zone for the nucleation of megathrust quakes, typically with large coseismic slip, abundant early aftershocks, and intermediate- to high-frequency radiation. The deeper portion of the slab interface (∼35–45 km) is seismically unstable, however with small coseismic slip, dominant high-frequency radiation, and relatively fewer aftershocks.

  3. Shear wave anisotropy from aligned inclusions: ultrasonic frequency dependence of velocity and attenuation

    NASA Astrophysics Data System (ADS)

    de Figueiredo, J. J. S.; Schleicher, J.; Stewart, R. R.; Dayur, N.; Omoboya, B.; Wiley, R.; William, A.

    2013-04-01

    To understand their influence on elastic wave propagation, anisotropic cracked media have been widely investigated in many theoretical and experimental studies. In this work, we report on laboratory ultrasound measurements carried out to investigate the effect of source frequency on the elastic parameters (wave velocities and the Thomsen parameter γ) and shear wave attenuation) of fractured anisotropic media. Under controlled conditions, we prepared anisotropic model samples containing penny-shaped rubber inclusions in a solid epoxy resin matrix with crack densities ranging from 0 to 6.2 per cent. Two of the three cracked samples have 10 layers and one has 17 layers. The number of uniform rubber inclusions per layer ranges from 0 to 100. S-wave splitting measurements have shown that scattering effects are more prominent in samples where the seismic wavelength to crack aperture ratio ranges from 1.6 to 1.64 than in others where the ratio varied from 2.72 to 2.85. The sample with the largest cracks showed a magnitude of scattering attenuation three times higher compared with another sample that had small inclusions. Our S-wave ultrasound results demonstrate that elastic scattering, scattering and anelastic attenuation, velocity dispersion and crack size interfere directly in shear wave splitting in a source-frequency dependent manner, resulting in an increase of scattering attenuation and a reduction of shear wave anisotropy with increasing frequency.

  4. Frequency-dependent performance and handedness in professional baseball players (Homo sapiens).

    PubMed

    Clotfelter, Ethan D

    2008-02-01

    I used data on handedness and pitching and hitting performance in annual cohorts of professional baseball players (1957-2005) to test the hypothesis that handedness among pitchers was subject to negative frequency-dependent selection. As predicted by this hypothesis, right-handed pitchers were more successful (i.e., opposing batters hit more poorly against them) when they were relatively rare in the population. Contrary to the predictions of this hypothesis, however, left-handed pitchers were more successful when they were relatively common. Both right- and left-handed batters performed better in years dominated by right-handed pitchers, despite the fact that right-handed batters perform relatively poorly against right-handed pitchers. I suggest that batters form cognitive representations based on pitcher handedness, and that these representations are strengthened by repeated exposure or priming. When the pitcher handedness polymorphism is more balanced (e.g., 67% right-handed, 33% left-handed), these cognitive representations are less effective, which leads to decreased batting averages and improved performance by all pitchers. Furthermore, these cognitive representations are likely to be more critical to the success of right-handed hitters, who have reduced visuomotor skills relative to left-handed hitters.

  5. Frequency Dependent Alterations in Regional Homogeneity of Baseline Brain Activity in Schizophrenia

    PubMed Central

    Wang, Hsiao-Lan Sharon; Liu, Chih-Min; Liu, Chen-Chung; Hwang, Tzung-Jeng; Chien, Yi-Ling; Hwu, Hai-Gwo; Tseng, Wen-Yih Isaac

    2013-01-01

    Low frequency oscillations are essential in cognitive function impairment in schizophrenia. While functional connectivity can reveal the synchronization between distant brain regions, the regional abnormalities in task-independent baseline brain activity are less clear, especially in specific frequency bands. Here, we used a regional homogeneity (ReHo) method combined with resting-state functional magnetic resonance imaging to investigate low frequency spontaneous neural activity in the three different frequency bands (slow-5∶0.01–0.027 Hz; slow-4∶0.027–0.08 Hz; and typical band: 0.01–0.08 Hz) in 69 patients with schizophrenia and 62 healthy controls. Compared with controls, schizophrenia patients exhibited decreased ReHo in the precentral gyrus, middle occipital gyrus, and posterior insula, whereas increased ReHo in the medial prefrontal cortex and anterior insula. Significant differences in ReHo between the two bands were found in fusiform gyrus and superior frontal gyrus (slow-4> slow-5), and in basal ganglia, parahippocampus, and dorsal middle prefrontal gyrus (slow-5> slow-4). Importantly, we identified significant interaction between frequency bands and groups in the inferior occipital gyrus and caudate body. This study demonstrates that ReHo changes in schizophrenia are widespread and frequency dependent. PMID:23483911

  6. Frequency dependent capacitance and conductance properties of Schottky diode based on rubrene organic semiconductor

    NASA Astrophysics Data System (ADS)

    Barış, Behzad

    2013-10-01

    Al/rubrene/p-Si Schottky diode has been fabricated by forming a rubrene layer on p type Si by using the spin coating method. The frequency dependent capacitance-voltage (C-V-f) and conductance-voltage (G-V-f) characteristics of Al/rubrene/p-Si Schottky diyotes has been investigated in the frequency range of 5 kHz-500 kHz at room temperature. The C-V plots show a peak for each frequency. The capacitance of the device decreased with increasing frequency. The decrease in capacitance results from the presence of interface states. The plots of series resistance-voltage (Rs-V) gave a peak in the depletion region at all frequencies. The density of interface states (Nss) and relaxation time (τ) distribution profiles as a function of applied voltage bias have been determined from the C-V and G-V measurements. The values of the Nss and τ have been calculated in the ranges of 8.37×1011-4.85×1011 eV-1 cm-2 and 5.17×10-6-1.02×10-5 s, respectively.

  7. Finite element analysis of the dynamic behavior of a laminated windscreen with frequency dependent viscoelastic core.

    PubMed

    Bouayed, Kaïss; Hamdi, Mohamed-Ali

    2012-08-01

    This paper presents numerical and experimental validation of results obtained by a shell finite element, which has been developed for modeling of the dynamic behavior of sandwich multilayered structures with a viscoelastic core. The proposed shell finite element is very easy to implement in existing finite element solvers, since it uses only the displacements as degrees of freedom at external faces and at inter-layer interfaces. The displacement field is linearly interpolated in the thickness direction of each layer, and analytical integration is made in the thickness direction in order to avoid meshing of each sandwich layer by solid elements. Only the two dimensional mid-surface of reference is meshed, facilitating the mesh generation task. A simplified modal approach using a real modal basis is also proposed to efficiently calculate the dynamic response of the sandwich structure. The proposed method reduces the memory size and computing time and takes into account the frequency-dependence of the polymer core mechanical properties. Results obtained by the proposed element in conjunction with the simplified modal method have been numerically and experimentally validated by comparison to results obtained by commercial software codes (MSC/NASTRAN and ESI/RAYON-VTM), and to measurements done on automobile windscreens. PMID:22894198

  8. A General Model of Negative Frequency Dependent Selection Explains Global Patterns of Human ABO Polymorphism

    PubMed Central

    Villanea, Fernando A.; Safi, Kristin N.; Busch, Jeremiah W.

    2015-01-01

    The ABO locus in humans is characterized by elevated heterozygosity and very similar allele frequencies among populations scattered across the globe. Using knowledge of ABO protein function, we generated a simple model of asymmetric negative frequency dependent selection and genetic drift to explain the maintenance of ABO polymorphism and its loss in human populations. In our models, regardless of the strength of selection, models with large effective population sizes result in ABO allele frequencies that closely match those observed in most continental populations. Populations must be moderately small to fall out of equilibrium and lose either the A or B allele (Ne ≤ 50) and much smaller (Ne ≤ 25) for the complete loss of diversity, which nearly always involved the fixation of the O allele. A pattern of low heterozygosity at the ABO locus where loss of polymorphism occurs in our model is consistent with small populations, such as Native American populations. This study provides a general evolutionary model to explain the observed global patterns of polymorphism at the ABO locus and the pattern of allele loss in small populations. Moreover, these results inform the range of population sizes associated with the recent human colonization of the Americas. PMID:25946124

  9. Warning signals are under positive frequency-dependent selection in nature.

    PubMed

    Chouteau, Mathieu; Arias, Mónica; Joron, Mathieu

    2016-02-23

    Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication. However, whether and how positive FDS truly operates in nature remains unknown, which hampers our understanding of signal diversity. Here, we test for positive FDS operating on the warning color patterns of chemically defended butterflies forming multiple coexisting mimicry assemblages in the Amazon. Using malleable prey models placed in localities showing differences in the relative frequencies of warningly colored prey, we demonstrate that the efficiency of a warning signal increases steadily with its local frequency in the natural community, up to a threshold where protection stabilizes. The shape of this relationship is consistent with the direct effect of the local abundance of each warning signal on the corresponding avoidance knowledge of the local predator community. This relationship, which differs from purifying selection acting on each mimetic pattern, indicates that predator knowledge, integrated over the entire community, is saturated only for the most common warning signals. In contrast, among the well-established warning signals present in local prey assemblages, most are incompletely known to local predators and enjoy incomplete protection. This incomplete predator knowledge should generate strong benefits to life history traits that enhance warning efficiency by increasing the effective frequency of prey visible to predators. Strategies such as gregariousness or niche convergence between comimics may therefore readily evolve through their effects on predator knowledge and warning efficiency.

  10. AtRAV1 and AtRAV2 overexpression in cotton increases fiber length differentially under drought stress and delays flowering.

    PubMed

    Mittal, Amandeep; Jiang, Yingwen; Ritchie, Glen L; Burke, John J; Rock, Christopher D

    2015-12-01

    There is a longstanding problem of an inverse relationship between cotton fiber qualities versus high yields. To better understand drought stress signaling and adaptation in cotton (Gossypium hirsutum) fiber development, we expressed the Arabidopsis transcription factors RELATED_TO_ABA-INSENSITIVE3/VIVIPAROUS1/(RAV1) and AtRAV2, which encode APETALA2-Basic3 domain proteins shown to repress transcription of FLOWERING_LOCUS_T (FT) and to promote stomatal opening cell-autonomously. In three years of field trials, we show that AtRAV1 and AtRAV2-overexpressing cotton had ∼5% significantly longer fibers with only marginal decreases in yields under well-watered or drought stress conditions that resulted in 40-60% yield penalties and 3-7% fiber length penalties in control plants. The longer transgenic fibers from drought-stressed transgenics could be spun into yarn which was measurably stronger and more uniform than that from well-watered control fibers. The transgenic AtRAV1 and AtRAV2 lines flowered later and retained bolls at higher nodes, which correlated with repression of endogenous GhFT-Like (FTL) transcript accumulation. Elevated expression early in development of ovules was observed for GhRAV2L, GhMYB25-Like (MYB25L) involved in fiber initiation, and GhMYB2 and GhMYB25 involved in fiber elongation. Altered expression of RAVs controlling critical nodes in developmental and environmental signaling hierarchies has the potential for phenotypic modification of crops.

  11. AtRAV1 and AtRAV2 overexpression in cotton increases fiber length differentially under drought stress and delays flowering.

    PubMed

    Mittal, Amandeep; Jiang, Yingwen; Ritchie, Glen L; Burke, John J; Rock, Christopher D

    2015-12-01

    There is a longstanding problem of an inverse relationship between cotton fiber qualities versus high yields. To better understand drought stress signaling and adaptation in cotton (Gossypium hirsutum) fiber development, we expressed the Arabidopsis transcription factors RELATED_TO_ABA-INSENSITIVE3/VIVIPAROUS1/(RAV1) and AtRAV2, which encode APETALA2-Basic3 domain proteins shown to repress transcription of FLOWERING_LOCUS_T (FT) and to promote stomatal opening cell-autonomously. In three years of field trials, we show that AtRAV1 and AtRAV2-overexpressing cotton had ∼5% significantly longer fibers with only marginal decreases in yields under well-watered or drought stress conditions that resulted in 40-60% yield penalties and 3-7% fiber length penalties in control plants. The longer transgenic fibers from drought-stressed transgenics could be spun into yarn which was measurably stronger and more uniform than that from well-watered control fibers. The transgenic AtRAV1 and AtRAV2 lines flowered later and retained bolls at higher nodes, which correlated with repression of endogenous GhFT-Like (FTL) transcript accumulation. Elevated expression early in development of ovules was observed for GhRAV2L, GhMYB25-Like (MYB25L) involved in fiber initiation, and GhMYB2 and GhMYB25 involved in fiber elongation. Altered expression of RAVs controlling critical nodes in developmental and environmental signaling hierarchies has the potential for phenotypic modification of crops. PMID:26706061

  12. Electromagnetically induced transparency and lasing without inversion in three-level atoms imbedded in a frequency-dependent environment

    NASA Astrophysics Data System (ADS)

    Radeonychev, Y. V.; Erukhimova, M. A.; Kocharovskaya, O. A.; Vilaseca, R.

    2004-10-01

    The response of a three-level atomic system driven by a resonant coherent field acting on a transition near the photonic band-edge of a photonic band-gap material as well as the general case of a frequency-dependent reservoir is studied. The strong frequency dependence of the radiation mode spectral density on the scale of the driving field Rabi frequency is shown to lead to essential and controllable changes in the refractive index, as well as to effects of electromagnetically induced transparency and lasing without inversion. Such an effective dynamic control of the atomic response enables for applications in nonlinear optics and optical computing and communications.

  13. Development of a self-stressing NiTiNb shape memory alloy (SMA)/fiber reinforced polymer (FRP) patch

    NASA Astrophysics Data System (ADS)

    El-Tahan, M.; Dawood, M.; Song, G.

    2015-06-01

    The objective of this research is to develop a self-stressing patch using a combination of shape memory alloys (SMAs) and fiber reinforced polymer (FRP) composites. Prestressed carbon FRP patches are emerging as a promising alternative to traditional methods to repair cracked steel structures and civil infrastructure. However, prestressing these patches typically requires heavy and complex fixtures, which is impractical in many applications. This paper presents a new approach in which the prestressing force is applied by restraining the shape memory effect of NiTiNb SMA wires. The wires are subsequently embedded in an FRP overlay patch. This method overcomes the practical challenges associated with conventional prestressing. This paper presents the conceptual development of the self-stressing patch with the support of experimental observations. The bond between the SMA wires and the FRP is evaluated using pull-out tests. The paper concludes with an experimental study that evaluates the patch response during activation subsequent monotonic tensile loading. The results demonstrate that the self-stressing patch with NiTiNb SMA is capable of generating a significant prestressing force with minimal tool and labor requirements.

  14. Frequency-dependent effects of rupture for the 2004 Parkfield mainshock, results from UPSAR

    USGS Publications Warehouse

    Fletcher, Jon B.

    2014-01-01

    The frequency-dependent effects of rupture propagation of the Parkfield, California earthquake (Sept. 28, 2004, M6) to the northwest along the San Andreas fault can be seen in acceleration records at UPSAR (USGS Parkfield Seismic Array) in at least two ways. First, we can see the effects of directivity in the acceleration traces at UPSAR, which is about 11.5 km from the epicenter. Directivity or the seismic equivalent of a Doppler shift has been documented in many cases by comparing short duration, high-amplitude pulses (P or S) in the forward direction with longer duration body waves in the backward direction. In this case we detect a change from a relatively large amplitude, coherent, high-frequency signal at the start of rupture to a low-amplitude, low-coherent, low-frequency signal at about the time the rupture front transfers from the forward azimuth to the back azimuth at about 34-36 s (time is UTC and are the seconds after day 272 and 17 hours and 15 minutes. S arrival is just after 30s) for rays leaving the fault and propagating to UPSAR. The frequency change is obvious in the band about 5 to 30 Hz, which is significantly above the corner frequency of the earthquake (about 0.11Hz). From kinematic source models, the duration of faulting is about 9.2 s and the change in frequency is during faulting as the rupture extends to the northwest. Understanding the systematic change in frequency and amplitude of seismic waves in relation to the propagation of the rupture front is important for predicting strong ground motion. Second, we can filter the acceleration records from the array to determine if the low frequency energy emerges from the same part of the fault as the high frequency signal (e.g. has the same back azimuth and apparent velocity at UPSAR) an important clue to the dynamics of rupture. Analysis of sources of strong motion (characterized by relatively high frequencies) compared to kinematic slip models (relatively low frequency) for the

  15. Phase and Frequency-Dependent Effects of Transcranial Alternating Current Stimulation on Motor Cortical Excitability.

    PubMed

    Nakazono, Hisato; Ogata, Katsuya; Kuroda, Tsuyoshi; Tobimatsu, Shozo

    2016-01-01

    Transcranial alternating current stimulation (tACS) can entrain ongoing brain oscillations and modulate the motor system in a frequency-dependent manner. Recent animal studies have demonstrated that the phase of a sinusoidal current also has an important role in modulation of neuronal activity. However, the phase effects of tACS on the human motor system are largely unknown. Here, we systematically investigated the effects of tACS phase and frequency on the primary motor cortex (M1) by using motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS). First, we compared the phase effects (90°, 180°, 270° or 360°) of 10 and 20 Hz tACS on MEPs. The 20 Hz tACS significantly increased M1 excitability compared with the 10 Hz tACS at 90° phase only. Second, we studied the 90° phase effect on MEPs at different tACS frequencies (5, 10, 20 or 40 Hz). The 20 vs. 10 Hz difference was again observed, but the 90° phase in 5 and 40 Hz tACS did not influence M1 excitability. Third, the 90° phase effects of 10 and 20 Hz tACS were compared with sham stimulation. The 90° phase of 20 Hz tACS enhanced MEP amplitudes compared with sham stimulation, but there was no significant effect of 10 Hz tACS. Taken together, we assume that the differential 90° phase effects on 20 Hz and 10 Hz tACS can be attributed to the neural synchronization modulated by tACS. Our results further underline that phase and frequency are the important factors in the effects of tACS on M1 excitability.

  16. Phase and Frequency-Dependent Effects of Transcranial Alternating Current Stimulation on Motor Cortical Excitability.

    PubMed

    Nakazono, Hisato; Ogata, Katsuya; Kuroda, Tsuyoshi; Tobimatsu, Shozo

    2016-01-01

    Transcranial alternating current stimulation (tACS) can entrain ongoing brain oscillations and modulate the motor system in a frequency-dependent manner. Recent animal studies have demonstrated that the phase of a sinusoidal current also has an important role in modulation of neuronal activity. However, the phase effects of tACS on the human motor system are largely unknown. Here, we systematically investigated the effects of tACS phase and frequency on the primary motor cortex (M1) by using motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS). First, we compared the phase effects (90°, 180°, 270° or 360°) of 10 and 20 Hz tACS on MEPs. The 20 Hz tACS significantly increased M1 excitability compared with the 10 Hz tACS at 90° phase only. Second, we studied the 90° phase effect on MEPs at different tACS frequencies (5, 10, 20 or 40 Hz). The 20 vs. 10 Hz difference was again observed, but the 90° phase in 5 and 40 Hz tACS did not influence M1 excitability. Third, the 90° phase effects of 10 and 20 Hz tACS were compared with sham stimulation. The 90° phase of 20 Hz tACS enhanced MEP amplitudes compared with sham stimulation, but there was no significant effect of 10 Hz tACS. Taken together, we assume that the differential 90° phase effects on 20 Hz and 10 Hz tACS can be attributed to the neural synchronization modulated by tACS. Our results further underline that phase and frequency are the important factors in the effects of tACS on M1 excitability. PMID:27607431

  17. In vitro characterization of HCN channel kinetics and frequency dependence in myocytes predicts biological pacemaker functionality.

    PubMed

    Zhao, Xin; Bucchi, Annalisa; Oren, Ronit V; Kryukova, Yelena; Dun, Wen; Clancy, Colleen E; Robinson, Richard B

    2009-04-01

    The pacemaker current, mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, contributes to the initiation and regulation of cardiac rhythm. Previous experiments creating HCN-based biological pacemakers in vivo found that an engineered HCN2/HCN1 chimeric channel (HCN212) resulted in significantly faster rates than HCN2, interrupted by 1-5 s pauses. To elucidate the mechanisms underlying the differences in HCN212 and HCN2 in vivo functionality as biological pacemakers, we studied newborn rat ventricular myocytes over-expressing either HCN2 or HCN212 channels. The HCN2- and HCN212-over-expressing myocytes manifest similar voltage dependence, current density and sensitivity to saturating cAMP concentrations, but HCN212 has faster activation/deactivation kinetics. Compared with HCN2, myocytes expressing HCN212 exhibit a faster spontaneous rate and greater incidence of irregular rhythms (i.e. periods of rapid spontaneous rate followed by pauses). To explore these rhythm differences further, we imposed consecutive pacing and found that activation kinetics of the two channels are slower at faster pacing frequencies. As a result, time-dependent HCN current flowing during diastole decreases for both constructs during a train of stimuli at a rapid frequency, with the effect more pronounced for HCN2. In addition, the slower deactivation kinetics of HCN2 contributes to more pronounced instantaneous current at a slower frequency. As a result of the frequency dependence of both instantaneous and time-dependent current, HCN2 exhibits more robust negative feedback than HCN212, contributing to the maintenance of a stable pacing rhythm. These results illustrate the benefit of screening HCN constructs in spontaneously active myocyte cultures and may provide the basis for future optimization of HCN-based biological pacemakers. PMID:19171659

  18. Phase and Frequency-Dependent Effects of Transcranial Alternating Current Stimulation on Motor Cortical Excitability

    PubMed Central

    Kuroda, Tsuyoshi; Tobimatsu, Shozo

    2016-01-01

    Transcranial alternating current stimulation (tACS) can entrain ongoing brain oscillations and modulate the motor system in a frequency-dependent manner. Recent animal studies have demonstrated that the phase of a sinusoidal current also has an important role in modulation of neuronal activity. However, the phase effects of tACS on the human motor system are largely unknown. Here, we systematically investigated the effects of tACS phase and frequency on the primary motor cortex (M1) by using motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS). First, we compared the phase effects (90°, 180°, 270° or 360°) of 10 and 20 Hz tACS on MEPs. The 20 Hz tACS significantly increased M1 excitability compared with the 10 Hz tACS at 90° phase only. Second, we studied the 90° phase effect on MEPs at different tACS frequencies (5, 10, 20 or 40 Hz). The 20 vs. 10 Hz difference was again observed, but the 90° phase in 5 and 40 Hz tACS did not influence M1 excitability. Third, the 90° phase effects of 10 and 20 Hz tACS were compared with sham stimulation. The 90° phase of 20 Hz tACS enhanced MEP amplitudes compared with sham stimulation, but there was no significant effect of 10 Hz tACS. Taken together, we assume that the differential 90° phase effects on 20 Hz and 10 Hz tACS can be attributed to the neural synchronization modulated by tACS. Our results further underline that phase and frequency are the important factors in the effects of tACS on M1 excitability. PMID:27607431

  19. Temperature and frequency dependent conductivity of bismuth zinc vanadate semiconducting glassy system

    NASA Astrophysics Data System (ADS)

    Punia, R.; Kundu, R. S.; Dult, Meenakshi; Murugavel, S.; Kishore, N.

    2012-10-01

    The ac conductivity of bismuth zinc vanadate glasses with compositions 50V2O5. xBi2O3. (50-x) ZnO has been studied in the frequency range 10-1 Hz to 2 MHz and in temperature range 333.16 K to 533.16 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the compositions of bismuth zinc vanadate glass system. The dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of experimental data of ac conductivity with Jonscher's universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating center (Hf) and enthalpy of migration (Hm) have also been estimated. It has been observed that mobility of charge carriers and ac conductivity in case of zinc vanadate glass system increases with increase in Bi2O3 content. In order to determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed in the frame work of various theoretical models based on classical hopping over barriers and quantum mechanical tunneling. The ac conduction takes place via tunneling of overlapping large polarons in all the compositions of presently studied vanadate glasses. The fitting of experimental data of ac conductivity with overlapping large polarons tunneling model has also been done. The parameters; density of states at Fermi level (N(EF)), activation energy associated with charge transfer between the overlapping sites (WHO), inverse localization length (α) and polaron radius (rp) obtained from fitting of this model with experimental data are reasonable.

  20. Testing of Carbon Fiber Composite Overwrapped Pressure Vessel Stress-Rupture Lifetime

    NASA Technical Reports Server (NTRS)

    Grimes-Ledesma, Lorie; Phoenix, S. Leigh; Beeson, Harold; Yoder, Tommy; Greene, Nathaniel

    2006-01-01

    This paper contains summaries of testing procedures and analysis of stress rupture life testing for two stress rupture test programs, one for Kevlar COPVs performed at Lawrence Livermore National Laboratory, and the other a joint study between NASA JSC White Sands Test Facility and the Jet Propulsion Laboratory. These will be discussed in detail including test setup and issues encountered during testing. Lessons learned from testing in these two programs will be discussed.

  1. Fundamental x-ray interaction limits in diagnostic imaging detectors: frequency-dependent Swank noise.

    PubMed

    Hajdok, G; Battista, J J; Cunningham, I A

    2008-07-01

    A frequency-dependent x-ray Swank factor based on the "x-ray interaction" modulation transfer function and normalized noise power spectrum is determined from a Monte Carlo analysis. This factor was calculated in four converter materials: amorphous silicon (a-Si), amorphous selenium (a-Se), cesium iodide (CsI), and lead iodide (PbI2) for incident photon energies between 10 and 150 keV and various converter thicknesses. When scaled by the quantum efficiency, the x-ray Swank factor describes the best possible detective quantum efficiency (DQE) a detector can have. As such, this x-ray interaction DQE provides a target performance benchmark. It is expressed as a function of (Fourier-based) spatial frequency and takes into consideration signal and noise correlations introduced by reabsorption of Compton scatter and photoelectric characteristic emissions. It is shown that the x-ray Swank factor is largely insensitive to converter thickness for quantum efficiency values greater than 0.5. Thus, while most of the tabulated values correspond to thick converters with a quantum efficiency of 0.99, they are appropriate to use for many detectors in current use. A simple expression for the x-ray interaction DQE of digital detectors (including noise aliasing) is derived in terms of the quantum efficiency, x-ray Swank factor, detector element size, and fill factor. Good agreement is shown with DQE curves published by other investigators for each converter material, and the conditions required to achieve this ideal performance are discussed. For high-resolution imaging applications, the x-ray Swank factor indicates: (i) a-Si should only be used at low-energy (e.g., mammography); (ii) a-Se has the most promise for any application below 100 keV; and (iii) while quantum efficiency may be increased at energies just above the K edge in CsI and PbI2, this benefit is offset by a substantial drop in the x-ray Swank factor, particularly at high spatial frequencies.

  2. Planck intermediate results. XXII. Frequency dependence of thermal emission from Galactic dust in intensity and polarization

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Alves, M. I. R.; Aniano, G.; Armitage-Caplan, C.; Arnaud, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Burigana, C.; Cardoso, J.-F.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Donzelli, S.; Doré, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Galeotta, S.; Ganga, K.; Ghosh, T.; Giard, M.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Guillet, V.; Hansen, F. K.; Harrison, D. L.; Helou, G.; Hernández-Monteagudo, C.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Magalhães, A. M.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Noviello, F.; Novikov, D.; Novikov, I.; Oppermann, N.; Oxborrow, C. A.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Rachen, J. P.; Reach, W. T.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Salerno, E.; Sandri, M.; Savini, G.; Scott, D.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wandelt, B. D.; Zacchei, A.; Zonca, A.

    2015-04-01

    Planck has mapped the intensity and polarization of the sky at microwave frequencies with unprecedented sensitivity. We use these data to characterize the frequency dependence of dust emission. We make use of the Planck 353 GHz I, Q, and U Stokes maps as dust templates, and cross-correlate them with the Planck and WMAP data at 12 frequencies from 23 to 353 GHz, over circular patches with 10° radius. The cross-correlation analysis is performed for both intensity and polarization data in a consistent manner. The results are corrected for the chance correlation between the templates and the anisotropies of the cosmic microwave background. We use a mask that focuses our analysis on the diffuse interstellar medium at intermediate Galactic latitudes. We determine the spectral indices of dust emission in intensity and polarization between 100 and 353 GHz, for each sky patch. Both indices are found to be remarkably constant over the sky. The mean values, 1.59 ± 0.02 for polarization and 1.51 ± 0.01 for intensity, for a mean dust temperature of 19.6 K, are close, but significantly different (3.6σ). We determine the mean spectral energy distribution (SED) of the microwave emission, correlated with the 353 GHz dust templates, by averaging the results of the correlation over all sky patches. We find that the mean SED increases for decreasing frequencies at ν< 60 GHz for both intensity and polarization. The rise of the polarization SED towards low frequencies may be accounted for by a synchrotron component correlated with dust, with no need for any polarization of the anomalous microwave emission. We use a spectral model to separate the synchrotron and dust polarization and to characterize the spectral dependence of the dust polarization fraction. The polarization fraction (p) of the dust emission decreases by (21 ± 6)% from 353 to 70 GHz. We discuss this result within the context of existing dust models. The decrease in p could indicate differences in polarization

  3. Single all-optical platform for measurement of twist and transverse stress using polarization modulation in distinct dual-mode fiber placed in a Sagnac loop.

    PubMed

    Khan, Saba N; Chatterjee, Sudip K; Chaudhuri, Partha Roy

    2016-01-01

    We report here the experimental demonstration of measurement of both twist and transverse stress using polarization modulation in a single all-fiber circuit consisting of a single-mode fiber (SMF)/dual-mode fiber (DMF) in a Sagnac interferometer (SI) loop. The SMF-SI prototype setup is seen to be suitable for precise measurement of twist over a broad range of ±50° and transverse stress up to 5 N with a sensitivity as high as 2.85×10(6)  pW/° and 2.08×10(7)  pW/N, respectively. It is envisaged that nearly ideal operation for twist measurement can be achieved by appropriately selecting the operating domain (pretwisted Sagnac loop for practical realization of the device) and required magnitude of applied transverse stress (weight yielding maximum sensitivity). Unlike SMF-SI, a DMF assisted SI exhibits asymmetric transmittance yielding a peak shift (∼45°) in addition to falling/rising peak amplitude of effective power(∼20  μW). This key characteristic is further utilized for tunable measurement of torsion (unidirectional from -70° to 40°) while keeping the sensitivity fixed. This research problem is then analyzed on the avenue of theoretical consideration and using classical polarization optics; we have derived the Jones birefringence matrix that accurately describes the transmission behavior of the configured fiber circuit (SMF-SI and DMF-SI) for each of the three cases, namely, transverse stress, twist, and both twist and transverse stress. Series of experimental measurements for various conditions of induced birefringence (linear/circular) were performed at length, and the results were compared with those determined theoretically towards configuring a twist and stress measuring device. The study provides an understanding of the underlying physics of dual-mode interference in a Sagnac configuration experiencing linear and circular birefringence.

  4. Single all-optical platform for measurement of twist and transverse stress using polarization modulation in distinct dual-mode fiber placed in a Sagnac loop.

    PubMed

    Khan, Saba N; Chatterjee, Sudip K; Chaudhuri, Partha Roy

    2016-01-01

    We report here the experimental demonstration of measurement of both twist and transverse stress using polarization modulation in a single all-fiber circuit consisting of a single-mode fiber (SMF)/dual-mode fiber (DMF) in a Sagnac interferometer (SI) loop. The SMF-SI prototype setup is seen to be suitable for precise measurement of twist over a broad range of ±50° and transverse stress up to 5 N with a sensitivity as high as 2.85×10(6)  pW/° and 2.08×10(7)  pW/N, respectively. It is envisaged that nearly ideal operation for twist measurement can be achieved by appropriately selecting the operating domain (pretwisted Sagnac loop for practical realization of the device) and required magnitude of applied transverse stress (weight yielding maximum sensitivity). Unlike SMF-SI, a DMF assisted SI exhibits asymmetric transmittance yielding a peak shift (∼45°) in addition to falling/rising peak amplitude of effective power(∼20  μW). This key characteristic is further utilized for tunable measurement of torsion (unidirectional from -70° to 40°) while keeping the sensitivity fixed. This research problem is then analyzed on the avenue of theoretical consideration and using classical polarization optics; we have derived the Jones birefringence matrix that accurately describes the transmission behavior of the configured fiber circuit (SMF-SI and DMF-SI) for each of the three cases, namely, transverse stress, twist, and both twist and transverse stress. Series of experimental measurements for various conditions of induced birefringence (linear/circular) were performed at length, and the results were compared with those determined theoretically towards configuring a twist and stress measuring device. The study provides an understanding of the underlying physics of dual-mode interference in a Sagnac configuration experiencing linear and circular birefringence. PMID:26831594

  5. Quasi-interferometric scheme improved by fiber Bragg grating for detection of outer mechanical stress influence on distributed sensor being silica multimode optical fiber operating in a few-mode regime

    NASA Astrophysics Data System (ADS)

    Kafarova, Anastasia M.; Faskhutdinov, Lenar M.; Kuznetzov, Artem A.; Minaeva, Alina Y.; Sevruk, Nikita L.; Nureev, Ilnur I.; Vasilets, Alexander A.; Bourdine, Anton V.; Morozov, Oleg G.; Burdin, Vladimir A.

    2016-03-01

    This work presents results of experimental approbation of modified fiber optic stress sensor based on a few-mode effects occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is concerned with adding of quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm lengths improved by fiber Bragg grating (FBG) and special offset launching conditions providing laser-based excitation of higher-order modes. We tested FBGs written on graded-index MMFs 50/125 with Bragg wavelength 1550 nm connected to different parts of proposed scheme. Researches are focused on comparing analysis of both spectral and pulse responses under changing of selected mode mixing and power diffusion processes due to stress local and distributed action to sensor fiber depending on scheme configuration. Here we considered FBGs not only as particular wavelength reflector during spectral response measurement but also as local periodic microstructure defect strongly effecting few-mode signal components mixing process that provides pulse response variation. Some results of spectral and pulse response measurements produced for different scheme configuration and their comparison analysis are represented.

  6. Fiber Breakage Model for Carbon Composite Stress Rupture Phenomenon: Theoretical Development and Applications

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.; Phoenix, S. Leigh; Grimes-Ledesma, Lorie

    2010-01-01

    Stress rupture failure of Carbon Composite Overwrapped Pressure Vessels (COPVs) is of serious concern to Science Mission and Constellation programs since there are a number of COPVs on board space vehicles with stored gases under high pressure for long durations of time. It has become customary to establish the reliability of these vessels using the so called classic models. The classical models are based on Weibull statistics fitted to observed stress rupture data. These stochastic models cannot account for any additional damage due to the complex pressure-time histories characteristic of COPVs being supplied for NASA missions. In particular, it is suspected that the effects of proof test could significantly reduce the stress rupture lifetime of COPVs. The focus of this paper is to present an analytical appraisal of a model that incorporates damage due to proof test. The model examined in the current paper is based on physical mechanisms such as micromechanics based load sharing concepts coupled with creep rupture and Weibull statistics. For example, the classic model cannot accommodate for damage due to proof testing which every flight vessel undergoes. The paper compares current model to the classic model with a number of examples. In addition, several applications of the model to current ISS and Constellation program issues are also examined.

  7. Residual stress and debonding analysis using a fiber Bragg grating in a model composite specimen

    NASA Astrophysics Data System (ADS)

    Colpo, F.; Dunkel, G.; Humbert, L.; Botsis, J.

    2005-05-01

    Optical Fibre Bragg Grating (FBG) sensors are excellent non-destructive tools for internal strain characterization of composite materials and structures. They can be embedded at selected locations during material preparation to provide accurate in-situ measurements. In this study, long-gauge-FBGs are introduced in cylindrical specimens of epoxy. This configuration is particularly attractive because it simplifies the study of some relevant phenomena in micromechanics of composites, for instance residual stresses and fracture of the fibre-matrix interface. Because the matrix epoxy shrinks during the polymerisation process, the optical sensor undergoes substantial non-uniform strain along the fibre. The response of a FBG to a non-uniform strain distribution is investigated using a new Optical Low-Coherence Reflectometry (OLCR) technique developed at EPFL. This method provides a direct reconstruction of the optical period and the corresponding strain distribution along the grating without any a priori assumption about the strain field. Considering the non-uniform residual strain as a reference state, new Bragg wavelength distributions are obtained for two configurations. First, a new Bragg wavelength distribution is measured as a function of the depth of circular cracks machined in the radial direction. These measurements lead to the knowledge of (a) the zone of perturbation of the reinforcing fibre on the residual stresses and (b) the effect of the presence of the mechanically induced crack on the residual stress state in the specimen. A finite element modelling of the residual stress field based on an equivalent thermo-elastic approach is also proposed, showing a very good agreement with experimental data. Second, an interface crack (debonding) between the epoxy and the fibre is introduced by fatigue and monitored using a specifically designed video acquisition system. The induced variations in the FBG response are measured when the fibre is unloaded and then

  8. Stress and strain analysis of the bone-implant interface: a comparison of fiber-reinforced composite and titanium implants utilizing 3-dimensional finite element study.

    PubMed

    Shinya, Akikazu; Ballo, Ahmed M; Lassila, Lippo V J; Shinya, Akiyoshi; Närhi, Timo O; Vallittu, Pekka K

    2011-03-01

    This study analyzed stress and strain mediated by 2 different implant materials, titanium (Ti) and experimental fiber-reinforced composite (FRC), on the implant and on the bone tissue surrounding the implant. Three-dimensional finite element models constructed from a mandibular bone and an implant were subjected to a load of 50 N in vertical and horizontal directions. Postprocessing files allowed the calculation of stress and strain within the implant materials and stresses at the bone-to-implant interface (stress path). Maximum stress concentrations were located around the implant on the rim of the cortical bone in both implant materials; Ti and overall stresses decreased toward the Ti implant apex. In the FRC implant, a stress value of 0.6 to 2.0 MPa was detected not only on the screw threads but also on the implant surface between the threads. Clear differences were observed in the strain distribution between the materials. Based on the results, the vertical load stress range of the FRC implant was close to the stress level for optimal bone growth. Furthermore, the stress at the bone around the FRC implant was more evenly distributed than that with Ti implant.

  9. Temperature and frequency dependence of AC conductivity of new quaternary Se-Te-Bi-Pb chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Yadav, Preeti; Sharma, Ambika

    2016-05-01

    The aim of the present work is to study the temperature and frequency dependence of ac conductivity of new quaternary Se84-xTe15Bi1.0Pbx chalcogenide glasses. The Se84-xTe15Bi1.0Pbx (x = 2, 6) glassy alloys are prepared by using melt quenching technique. The temperature and frequency dependent behavior of ac conductivity σac(ω) has been carried out in the frequency range 42 Hz to 5 MHz and in the temperature range of 298-323 K below glass transition temperature. The behavior of ac conductivity is described in terms of the power law ωs. The obtained temperature dependence behavior of ac conductivity and frequency component (s) are explained by means of correlated barrier hopping model recommended by Elliot.

  10. Influence of Gaussian white noise on the frequency-dependent first nonlinear polarizability of doped quantum dot

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Ghosh, Manas

    2014-05-01

    We investigate the profiles of diagonal components of frequency-dependent first nonlinear (βxxx and βyyy) optical response of repulsive impurity doped quantum dots. We have assumed a Gaussian function to represent the dopant impurity potential. This study primarily addresses the role of noise on the polarizability components. We have invoked Gaussian white noise consisting of additive and multiplicative characteristics (in Stratonovich sense). The doped system has been subjected to an oscillating electric field of given intensity, and the frequency-dependent first nonlinear polarizabilities are computed. The noise characteristics are manifested in an interesting way in the nonlinear polarizability components. In case of additive noise, the noise strength remains practically ineffective in influencing the optical responses. The situation completely changes with the replacement of additive noise by its multiplicative analog. The replacement enhances the nonlinear optical response dramatically and also causes their maximization at some typical value of noise strength that depends on oscillation frequency.

  11. Influence of Gaussian white noise on the frequency-dependent first nonlinear polarizability of doped quantum dot

    SciTech Connect

    Ganguly, Jayanta; Ghosh, Manas

    2014-05-07

    We investigate the profiles of diagonal components of frequency-dependent first nonlinear (β{sub xxx} and β{sub yyy}) optical response of repulsive impurity doped quantum dots. We have assumed a Gaussian function to represent the dopant impurity potential. This study primarily addresses the role of noise on the polarizability components. We have invoked Gaussian white noise consisting of additive and multiplicative characteristics (in Stratonovich sense). The doped system has been subjected to an oscillating electric field of given intensity, and the frequency-dependent first nonlinear polarizabilities are computed. The noise characteristics are manifested in an interesting way in the nonlinear polarizability components. In case of additive noise, the noise strength remains practically ineffective in influencing the optical responses. The situation completely changes with the replacement of additive noise by its multiplicative analog. The replacement enhances the nonlinear optical response dramatically and also causes their maximization at some typical value of noise strength that depends on oscillation frequency.

  12. Modulation-frequency dependencies of the intensity and the phase delay of photoinduced absorption from conjugated polymers

    NASA Astrophysics Data System (ADS)

    Furukawa, Yukio

    2000-03-01

    The modulation-frequency dependencies of the intensity and the phase delay of photoinduced infrared absorption from poly(p-phenylene) have been observed and simulated numerically on the basis of a model based on second-order kinetics involving a neutralization recombination process between the positive and negative charge carriers (polarons) that are formed from a photogenerated polaron pair (interchain charge-transfer exciton). The rate constant of the bimolecular recombination has been obtained.

  13. Rupture and frequency-dependent seismic radiation of the 2012 Mw 8.6 Sumatra strike-slip earthquake

    NASA Astrophysics Data System (ADS)

    Yin, Jiuxun; Yao, Huajian

    2016-06-01

    On 2012 April 11, a great strike-slip earthquake (moment magnitude of Mw 8.6) occurred off the west coast of northern Sumatra area followed by an Mw 8.2 aftershock 2 hr later. Different geophysical data and methods have been used to investigate the mechanism, faulting, seismic radiation and slip propagation of this event, but frequency-dependent features of its rupture process have not been discussed much. In this study, we use a compressive sensing method based on sparsity inversion in the frequency domain to study the frequency-dependent seismic radiation and rupture process of this event. Our results indicate a very complex rupture process concerning at least three different rupture stages on multiple subfaults with nearly conjugate geometries. The main shock has triggered seismicity on a series of ridge-perpendicular or ridge-parallel conjugate strike-slip faults around the Nighty East Ridge. Obvious frequency-dependent rupture process has been presented and discussed. Combining results from slip inversion based on the finite-fault model, we observe that in the beginning stage of the rupture lower frequency radiation appears to originate from the areas with large slip, while the high-frequency radiation is located at the boundary of large-slip region or rupture front. Some radiation probably originates from the repeating slip on the main faults or triggered events on some nearby faults in the rupture area. The complex frequency-dependent seismic radiation patterns observed in this study provide important information for future investigation of rupture physics of this complex strike-slip event.

  14. Highlight fluid imaging via frequency-dependent anomalies of reservoir seismic response in both numerical simulation and real application

    NASA Astrophysics Data System (ADS)

    Chen, X.; He, Z.; Zhong, W.

    2012-12-01

    The numerous recent laboratory and field examples show frequency-dependent characteristics of seismic response and potential benefits of seismic low frequencies in hydrocarbon indication. Using analytic equations and Biot's theoretical model for predicting the attenuation and dispersion in poroelastic media, we have numerically investigated the frequency-dependent response of real-data-based models to indicate their properties such as dispersion, attenuation and spectral features. The characteristics of seismic reflection on fluid-bearing strata vary distinctly with frequency in seismic band. This provides inspired insight for frequency-dependent fluid indication. We present a methodology to highlight fluid images via both instantaneous spectral differences on multi-angle stacking gathers and fluid mobility measurement extracted from low-frequency spectra of stacked seismic data. This methodology and workflow are applied to a 3D marine seismic data volume from JX field in the Bohai Sea, China. The results show that the hydrocarbon anomalies measured by the methodology and workflow are well consistent with the real gas production of wells, and also demonstrate that low-frequency effects are especially important for delineation of the fluid signature.

  15. Bidirectional frequency-dependent effect of extremely low-frequency electromagnetic field on E. coli K-12.

    PubMed

    Martirosyan, Varsik; Baghdasaryan, Naira; Ayrapetyan, Sinerik

    2013-09-01

    In the present work, the frequency-dependent effects of extremely low-frequency electromagnetic field (ELF EMF) on Escherichia coli K-12 growth have been studied. The frequency-dependent effects of ELF EMF have shown that it can either stimulate or inhibit the growth of microbes. However, the mechanism by which the ELF EMF affects the bacterial cells is not clear yet. It was suggested that the aqua medium can serve as a target through which the biological effect of ELF EMF on microbes may be realized. To check this hypothesis, the frequency-dependent effects (2, 4, 6, 8, 10 Hz, B = 0.4 mT, 30 min) of ELF EMF on the bacterial growth were studied in both cases where the microbes were in the culture media during the exposure and where culture media was preliminarily exposed to the ELF EMF before the addition of bacteria. For investigating the cell proliferation, the radioactive [(3)H]-thymidine assay was carried out. It has been shown that EMF at 4 Hz exposure has pronounced stimulation while at 8 Hz it has inhibited cell proliferation.

  16. Similar patterns of frequency-dependent selection on animal personalities emerge in three species of social spiders.

    PubMed

    Lichtenstein, J L L; Pruitt, J N

    2015-06-01

    Frequency-dependent selection is thought to be a major contributor to the maintenance of phenotypic variation. We tested for frequency-dependent selection on contrasting behavioural strategies, termed here 'personalities', in three species of social spiders, each thought to represent an independent evolutionary origin of sociality. The evolution of sociality in the spider genus Anelosimus is consistently met with the emergence of two temporally stable discrete personality types: an 'aggressive' or 'docile' form. We assessed how the foraging success of each phenotype changes as a function of its representation within a colony. We did this by creating experimental colonies of various compositions (six aggressives, three aggressives and three dociles, one aggressive and five dociles, six dociles), maintaining them in a common garden for 3 weeks, and tracking the mass gained by individuals of either phenotype. We found that both the docile and aggressive phenotypes experienced their greatest mass gain in mixed colonies of mostly docile individuals. However, the performance of both phenotypes decreased as the frequency of the aggressive phenotype increased. Nearly identical patterns of phenotype-specific frequency dependence were recovered in all three species. Naturally occurring colonies of these spiders exhibit mixtures dominated by the docile phenotype, suggesting that these spiders may have evolved mechanisms to maintain the compositions that maximize the success of the colony without compromising the expected reproductive output of either phenotype.

  17. Algebraic processing technique for extracting frequency-dependent shear-wave splitting parameters in an anisotropic medium

    NASA Astrophysics Data System (ADS)

    Han, Kai-Feng; Zeng, Xin-Wu

    2011-06-01

    Based on the dual source cumulative rotation technique in the time-domain proposed by Zeng and MacBeth (1993), a new algebraic processing technique for extracting shear-wave splitting parameters from multi-component VSP data in frequency-dependent medium has been developed. By using this dual source cumulative rotation technique in the frequency-domain (DCTF), anisotropic parameters, including polarization direction of the shear-waves and timedelay between the fast and slow shear-waves, can be estimated for each frequency component in the frequency domain. It avoids the possible error which comes from using a narrow-band filter in the current commonly used method. By using synthetic seismograms, the feasibility and validity of the technique was tested and a comparison with the currently used method was also given. The results demonstrate that the shear-wave splitting parameters frequency dependence can be extracted directly from four-component seismic data using the DCTF. In the presence of larger scale fractures, substantial frequency dependence would be found in the seismic frequency range, which implies that dispersion would occur at seismic frequencies. Our study shows that shear-wave anisotropy decreases as frequency increases.

  18. Adaptation, Clonal Interference, and Frequency-Dependent Interactions in a Long-Term Evolution Experiment with Escherichia coli

    PubMed Central

    Maddamsetti, Rohan; Lenski, Richard E.; Barrick, Jeffrey E.

    2015-01-01

    Twelve replicate populations of Escherichia coli have been evolving in the laboratory for >25 years and 60,000 generations. We analyzed bacteria from whole-population samples frozen every 500 generations through 20,000 generations for one well-studied population, called Ara−1. By tracking 42 known mutations in these samples, we reconstructed the history of this population’s genotypic evolution over this period. The evolutionary dynamics of Ara−1 show strong evidence of selective sweeps as well as clonal interference between competing lineages bearing different beneficial mutations. In some cases, sets of several mutations approached fixation simultaneously, often conveying no information about their order of origination; we present several possible explanations for the existence of these mutational cohorts. Against a backdrop of rapid selective sweeps both earlier and later, two genetically diverged clades coexisted for >6000 generations before one went extinct. In that time, many additional mutations arose in the clade that eventually prevailed. We show that the clades evolved a frequency-dependent interaction, which prevented the immediate competitive exclusion of either clade, but which collapsed as beneficial mutations accumulated in the clade that prevailed. Clonal interference and frequency dependence can occur even in the simplest microbial populations. Furthermore, frequency dependence may generate dynamics that extend the period of coexistence that would otherwise be sustained by clonal interference alone. PMID:25911659

  19. Adaptation, Clonal Interference, and Frequency-Dependent Interactions in a Long-Term Evolution Experiment with Escherichia coli.

    PubMed

    Maddamsetti, Rohan; Lenski, Richard E; Barrick, Jeffrey E

    2015-06-01

    Twelve replicate populations of Escherichia coli have been evolving in the laboratory for >25 years and 60,000 generations. We analyzed bacteria from whole-population samples frozen every 500 generations through 20,000 generations for one well-studied population, called Ara-1. By tracking 42 known mutations in these samples, we reconstructed the history of this population's genotypic evolution over this period. The evolutionary dynamics of Ara-1 show strong evidence of selective sweeps as well as clonal interference between competing lineages bearing different beneficial mutations. In some cases, sets of several mutations approached fixation simultaneously, often conveying no information about their order of origination; we present several possible explanations for the existence of these mutational cohorts. Against a backdrop of rapid selective sweeps both earlier and later, two genetically diverged clades coexisted for >6000 generations before one went extinct. In that time, many additional mutations arose in the clade that eventually prevailed. We show that the clades evolved a frequency-dependent interaction, which prevented the immediate competitive exclusion of either clade, but which collapsed as beneficial mutations accumulated in the clade that prevailed. Clonal interference and frequency dependence can occur even in the simplest microbial populations. Furthermore, frequency dependence may generate dynamics that extend the period of coexistence that would otherwise be sustained by clonal interference alone.

  20. Frequency-dependent, cell type-divergent signaling in the hippocamposeptal projection.

    PubMed

    Mattis, Joanna; Brill, Julia; Evans, Suzanne; Lerner, Talia N; Davidson, Thomas J; Hyun, Minsuk; Ramakrishnan, Charu; Deisseroth, Karl; Huguenard, John R

    2014-08-27

    Hippocampal oscillations are critical for information processing, and are strongly influenced by inputs from the medial septum. Hippocamposeptal neurons provide direct inhibitory feedback from the hippocampus onto septal cells, and are therefore likely to also play an important role in the circuit; these neurons fire at either low or high frequency, reflecting hippocampal network activity during theta oscillations or ripple events, respectively. Here, we optogenetically target the long-range GABAergic projection from the hippocampus to the medial septum in rats, and thereby simulate hippocampal input onto downstream septal cells in an acute slice preparation. In response to optogenetic activation of hippocamposeptal fibers at theta and ripple frequencies, we elicit postsynaptic GABAergic responses in a subset (24%) of septal cells, most predominantly in fast-spiking cells. In addition, in another subset of septal cells (19%) corresponding primarily to cholinergic cells, we observe a slow hyperpolarization of the resting membrane potential and a decrease in input resistance, particularly in response to prolonged high-frequency (ripple range) stimulation. This slow response is partially sensitive to GIRK channel and D2 dopamine receptor block. Our results suggest that two independent populations of septal cells distinctly encode hippocampal feedback, enabling the septum to monitor ongoing patterns of activity in the hippocampus.

  1. Numerical analysis of residual stresses in preforms of stress applying part for PANDA-type polarization maintaining optical fibers in view of technological imperfections of the doped zone geometry

    NASA Astrophysics Data System (ADS)

    Trufanov, Aleksandr N.; Trufanov, Nikolay A.; Semenov, Nikita V.

    2016-09-01

    The experimental data analysis of the stress applying rod section geometry for the PANDA-type polarization maintaining optical fiber has been performed. The dependencies of the change in the radial dimensions of the preform and the doping boundary on the angular coordinate have been obtained. The original algorithm of experimental data statistic analysis, which enables determination of the specimens' characteristic form of section, has been described. The influence of actual doped zone geometry on the residual stress fields formed during the stress rod preform fabrication has been investigated. It has been established that the deviation of the boundary between pure silica and the doped zone from the circular shape results in dissymmetry and local concentrations of the residual stress fields along the section, which can cause preforms destruction at high degrees of doping. The observed geometry deviations of up to 10% lead to the increase of the maximum stress intensity value by over 20%.

  2. Temperature Dependence on the Strength and Stress Rupture Behavior of a Carbon-Fiber Reinforced Silicon Carbide (C/SiC) Composite

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Calomino, Anthony

    2002-01-01

    Tensile strengths and stress rupture lives of carbon-fiber reinforced silicon carbide (C/SiC) specimens were measured at 800 C and are compared to previously reported 1200 C data. All tests were conducted in an environmental chamber containing 1000 ppm of oxygen in argon. The average 800 C tensile strength of 610 MPa is 10% greater than at 1200 C. Average stress rupture lives at 800 C were 2.5 times longer than those obtained at 1200 C. The difference in the 800 and 1200 C lives is related to the oxidation rate of the reinforcing carbon fibers, which is the primary damage mode of C/SiC composites in oxygen-containing environments.

  3. Ephrin-Bs Drive Junctional Downregulation and Actin Stress Fiber Disassembly to Enable Wound Re-epithelialization.

    PubMed

    Nunan, Robert; Campbell, Jessica; Mori, Ryoichi; Pitulescu, Mara E; Jiang, Wen G; Harding, Keith G; Adams, Ralf H; Nobes, Catherine D; Martin, Paul

    2015-11-17

    For a skin wound to successfully heal, the cut epidermal-edge cells have to migrate forward at the interface between scab and healthy granulation tissue. Much is known about how lead-edge cells migrate, but very little is known about the mechanisms that enable active participation by cells further back. Here we show that ephrin-B1 and its receptor EphB2 are both upregulated in vivo, just for the duration of repair, in the first 70 or so rows of epidermal cells, and this signal leads to downregulation of the molecular components of adherens and tight (but not desmosomal) junctions, leading to loosening between neighbors and enabling shuffle room among epidermal cells. Additionally, this signaling leads to the shutdown of actomyosin stress fibers in these same epidermal cells, which may act to release tension within the wound monolayer. If this signaling axis is perturbed, then disrupted healing is a consequence in mouse and man. PMID:26549443

  4. Ephrin-Bs Drive Junctional Downregulation and Actin Stress Fiber Disassembly to Enable Wound Re-epithelialization

    PubMed Central

    Nunan, Robert; Campbell, Jessica; Mori, Ryoichi; Pitulescu, Mara E.; Jiang, Wen G.; Harding, Keith G.; Adams, Ralf H.; Nobes, Catherine D.; Martin, Paul

    2015-01-01

    Summary For a skin wound to successfully heal, the cut epidermal-edge cells have to migrate forward at the interface between scab and healthy granulation tissue. Much is known about how lead-edge cells migrate, but very little is known about the mechanisms that enable active participation by cells further back. Here we show that ephrin-B1 and its receptor EphB2 are both upregulated in vivo, just for the duration of repair, in the first 70 or so rows of epidermal cells, and this signal leads to downregulation of the molecular components of adherens and tight (but not desmosomal) junctions, leading to loosening between neighbors and enabling shuffle room among epidermal cells. Additionally, this signaling leads to the shutdown of actomyosin stress fibers in these same epidermal cells, which may act to release tension within the wound monolayer. If this signaling axis is perturbed, then disrupted healing is a consequence in mouse and man. PMID:26549443

  5. The Cdk5 activator P39 specifically links muskelin to myosin II and regulates stress fiber formation and actin organization in lens.

    PubMed

    Tripathi, Brajendra K; Lowy, Douglas R; Zelenka, Peggy S

    2015-01-01

    Cyclin dependent kinase 5 (Cdk5), a proline-directed serine/threonine kinase, requires p39 for its enzymatic activity, and is implicated in cytoskeletal organization and contraction in numerous cell types. The C-terminus of p39 binds muskelin, a multi-domain scaffolding protein known to affect cytoskeletal organization, but the mechanisms by which muskelin affects cytoskeletal organization remain unclear. The present study sought to determine whether p39 might serve as an adaptor protein that links muskelin to stress fibers and to investigate the possible biological relevance of such an interaction. Double immunoprecipitation showed that muskelin, p39, and myosin II are components of a single intracellular complex, and suppressing p39 abrogated the interaction between muskelin and the myosin subunits, demonstrating that p39 is required to link muskelin to myosin II. Muskelin is colocalized with myosin regulatory light chain (MRLC) and on stress fibers. The suppression of muskelin reduced Rho-GTP, MRLC phosphorylation, disrupted stress fiber organization, and promoted cell migration, all of which closely mimic the effect of Cdk5 inhibition. Moreover, suppressing muskelin and inhibiting Cdk5 together have no additional effect, indicating that muskelin plays an important role in Cdk5-dependent signaling. p39 is necessary and sufficient for Cdk5-dependent regulation of MRLC phosphorylation, as suppression of p39, but not p35, reduces MRLC phosphorylation. Together, these results demonstrate that p39 specifically links muskelin to myosin II and consequently, to stress fibers and reveal a novel role for muskelin in regulating myosin phosphorylation and cytoskeletal organization. PMID:25128817

  6. The Cdk5 activator P39 specifically links muskelin to myosin II and regulates stress fiber formation and actin organization in lens.

    PubMed

    Tripathi, Brajendra K; Lowy, Douglas R; Zelenka, Peggy S

    2015-01-01

    Cyclin dependent kinase 5 (Cdk5), a proline-directed serine/threonine kinase, requires p39 for its enzymatic activity, and is implicated in cytoskeletal organization and contraction in numerous cell types. The C-terminus of p39 binds muskelin, a multi-domain scaffolding protein known to affect cytoskeletal organization, but the mechanisms by which muskelin affects cytoskeletal organization remain unclear. The present study sought to determine whether p39 might serve as an adaptor protein that links muskelin to stress fibers and to investigate the possible biological relevance of such an interaction. Double immunoprecipitation showed that muskelin, p39, and myosin II are components of a single intracellular complex, and suppressing p39 abrogated the interaction between muskelin and the myosin subunits, demonstrating that p39 is required to link muskelin to myosin II. Muskelin is colocalized with myosin regulatory light chain (MRLC) and on stress fibers. The suppression of muskelin reduced Rho-GTP, MRLC phosphorylation, disrupted stress fiber organization, and promoted cell migration, all of which closely mimic the effect of Cdk5 inhibition. Moreover, suppressing muskelin and inhibiting Cdk5 together have no additional effect, indicating that muskelin plays an important role in Cdk5-dependent signaling. p39 is necessary and sufficient for Cdk5-dependent regulation of MRLC phosphorylation, as suppression of p39, but not p35, reduces MRLC phosphorylation. Together, these results demonstrate that p39 specifically links muskelin to myosin II and consequently, to stress fibers and reveal a novel role for muskelin in regulating myosin phosphorylation and cytoskeletal organization.

  7. Lysophosphatidic acid and microtubule-destabilizing agents stimulate fibronectin matrix assembly through Rho-dependent actin stress fiber formation and cell contraction.

    PubMed Central

    Zhang, Q; Magnusson, M K; Mosher, D F

    1997-01-01

    Fibronectin (FN) matrix assembly is a cell-dependent process mediated by cell surface-binding sites for the 70-kDa amino-terminal region of FN. We have shown recently that lysophosphatidic acid (LPA) is a stimulator of FN matrix assembly. Disruption of microtubules has been shown to mimic some of the intracellular effects of LPA including the formation of actin stress fibers and myosin light chain phosphorylation. We compared the effects of microtubule disruption and LPA on FN binding and actin cytoskeleton organization. The disruption of microtubules by nocodazole or vinblastine increased FN binding to adherent cells. The modulation of binding sites was rapid, dynamic, and reversible. Enhanced binding was due to increases in both the number and affinity of binding sites. These effects are similar to the effects of LPA on FN binding. Binding induced by nocodazole was inhibited by the microtubule-stabilizing agent Taxol but not by pretreatment with a concentration of phospholipase B that totally abolished the stimulatory effect of LPA. Fluorescence microscopy revealed a close correlation among actin stress fiber formation, cell contraction, and FN binding. Blockage of the small GTP binding protein Rho or actin-myosin interactions inhibited the effects of both nocodazole and LPA on FN binding. These observations demonstrate that Rho-dependent actin stress fiber formation and cell contraction induce increased FN binding and represent a rapid labile way that cells can modulate FN matrix assembly. Images PMID:9285815

  8. Capacitively-Coupled Resistivity measurements to determine frequency dependent electrical parameters in periglacial environment - theoretical considerations and first field tests.

    NASA Astrophysics Data System (ADS)

    Przyklenk, A.; Hördt, A.; Radić, T.

    2016-05-01

    Capacitively-Coupled Resistivity (CCR) is conventionally used to emulate DC resistivity measurements and may provide important information about the ice content of material in periglacial areas. The application of CCR theoretically enables the determination of both electrical parameters, i.e. the resistivity and the electrical permittivity, by analyzing magnitude and phase shift spectra. The electrical permittivity may dominate the impedance, especially in periglacial areas or regions of hydrogeological interest. However, previous theoretical work suggested that the phase shift may strongly depend on electrode height above ground, implying that electrode height must be known with great accuracy to determine electrical permittivity. Here, we demonstrate with laboratory test measurements, theoretical modelling and by analysing the Jacobian matrix of the inversion, that the sensitivity towards electrode height is drastically reduced if the electrical permittivity is frequency dependent in a way that is typical for ice. For the fist time, we used a novel broadband CCR device "Chameleon" for a field test located in one of the ridge galleries beneath the crest of Mount Zugspitze. A permanently ice covered bottom of a tunnel was examined. For the inversion of the measured spectra, the frequency dependance of the electrical parameters was parameterized in 3 different ways. A Debye Model for pure ices, a Cole-Cole Model for pure ices and a dual Cole-Cole Model including interfacial water additionally. The frequency-dependent resistivity and permittivity spectra obtained from the inversion, including low and high frequency limits, agree reasonably well with laboratory and field measurements reported in the literature.

  9. Frequency-dependent local field factors in dielectric liquids by a polarizable force field and molecular dynamics simulations

    SciTech Connect

    Davari, Nazanin; Haghdani, Shokouh; Åstrand, Per-Olof

    2015-12-31

    A force field model for calculating local field factors, i.e. the linear response of the local electric field for example at a nucleus in a molecule with respect to an applied electric field, is discussed. It is based on a combined charge-transfer and point-dipole interaction model for the polarizability, and thereby it includes two physically distinct terms for describing electronic polarization: changes in atomic charges arising from transfer of charge between the atoms and atomic induced dipole moments. A time dependence is included both for the atomic charges and the atomic dipole moments and if they are assumed to oscillate with the same frequency as the applied electric field, a model for frequency-dependent properties are obtained. Furthermore, if a life-time of excited states are included, a model for the complex frequency-dependent polariability is obtained including also information about excited states and the absorption spectrum. We thus present a model for the frequency-dependent local field factors through the first molecular excitation energy. It is combined with molecular dynamics simulations of liquids where a large set of configurations are sampled and for which local field factors are calculated. We are normally not interested in the average of the local field factor but rather in configurations where it is as high as possible. In electrical insulation, we would like to avoid high local field factors to reduce the risk for electrical breakdown, whereas for example in surface-enhanced Raman spectroscopy, high local field factors are desired to give dramatically increased intensities.

  10. Dynamics of electronic transitions and frequency dependence of negative capacitance in semiconductor diodes under high forward bias

    SciTech Connect

    Bansal, Kanika; Datta, Shouvik; Henini, Mohamed; Alshammari, Marzook S.

    2014-09-22

    We observed qualitatively dissimilar frequency dependence of negative capacitance under high charge injection in two sets of functionally different junction diodes: III-V based light emitting and Si-based non-light emitting diodes. Using an advanced approach based on bias activated differential capacitance, we developed a generalized understanding of negative capacitance phenomenon which can be extended to any diode based device structure. We explained the observations as the mutual competition of fast and slow electronic transition rates which are different in different devices. This study can be useful in understanding the interfacial effects in semiconductor heterostructures and may lead to superior device functionality.

  11. Frequency-dependent reduction of voltage-gated sodium current modulates retinal ganglion cell response rate to electrical stimulation

    NASA Astrophysics Data System (ADS)

    Tsai, David; Morley, John W.; Suaning, Gregg J.; Lovell, Nigel H.

    2011-10-01

    The ability to elicit visual percepts through electrical stimulation of the retina has prompted numerous investigations examining the feasibility of restoring sight to the blind with retinal implants. The therapeutic efficacy of these devices will be strongly influenced by their ability to elicit neural responses that approximate those of normal vision. Retinal ganglion cells (RGCs) can fire spikes at frequencies greater than 200 Hz when driven by light. However, several studies using isolated retinas have found a decline in RGC spiking response rate when these cells were stimulated at greater than 50 Hz. It is possible that the mechanism responsible for this decline also contributes to the frequency-dependent 'fading' of electrically evoked percepts recently reported in human patients. Using whole-cell patch clamp recordings of rabbit RGCs, we investigated the causes for the spiking response depression during direct subretinal stimulation of these cells at 50-200 Hz. The response depression was not caused by inhibition arising from the retinal network but, instead, by a stimulus-frequency-dependent decline of RGC voltage-gated sodium current. Under identical experimental conditions, however, RGCs were able to spike at high frequency when driven by light stimuli and intracellular depolarization. Based on these observations, we demonstrated a technique to prevent the spiking response depression.

  12. Frequency-dependent reduction of voltage-gated sodium current modulates retinal ganglion cell response rate to electrical stimulation.

    PubMed

    Tsai, David; Morley, John W; Suaning, Gregg J; Lovell, Nigel H

    2011-12-01

    The ability to elicit visual percepts through electrical stimulation of the retina has prompted numerous investigations examining the feasibility of restoring sight to the blind with retinal implants. The therapeutic efficacy of these devices will be strongly influenced by their ability to elicit neural responses that approximate those of normal vision. Retinal ganglion cells (RGCs) can fire spikes at frequencies greater than 200 Hz when driven by light. However, several studies using isolated retinas have found a decline in RGC spiking response rate when these cells were stimulated at greater than 50 Hz. It is possible that the mechanism responsible for this decline also contributes to the frequency-dependent 'fading' of electrically evoked percepts recently reported in human patients. Using whole-cell patch clamp recordings of rabbit RGCs, we investigated the causes for the spiking response depression during direct subretinal stimulation of these cells at 50-200 Hz. The response depression was not caused by inhibition arising from the retinal network but, instead, by a stimulus-frequency-dependent decline of RGC voltage-gated sodium current. Under identical experimental conditions, however, RGCs were able to spike at high frequency when driven by light stimuli and intracellular depolarization. Based on these observations, we demonstrated a technique to prevent the spiking response depression. PMID:22027396

  13. Increased BACE1 mRNA and noncoding BACE1-antisense transcript in sporadic inclusion body myositis muscle fibers – possibly caused by endoplasmic reticulum stress

    PubMed Central

    Nogalska, Anna; Engel, W. King; Askanas, Valerie

    2010-01-01

    Sporadic inclusion-body myositis (s-IBM) is the most common muscle disease of older persons. Its muscle-fiber phenotype shares several molecular similarities with Alzheimer-disease (AD) brain, including increased AβPP, accumulation of amyloid-β (Aβ), and increased BACE1 protein. Aβ42 is prominently increased in AD brain and within s-IBM fibers, and its oligomers are putatively toxic to both tissues -- accordingly, minimizing Aβ42 production can be a therapeutic objective in both tissues. The pathogenic development of s-IBM is unknown, including the mechanisms of BACE1 protein increase. BACE1 is an enzyme essential for production from AβPP of Aβ42 and Aβ40, which are proposed to be detrimental within s-IBM muscle fibers. Novel noncoding BACE1-antisense (BACE1-AS) was recently shown a)to be increased in AD brain, and b) to increase BACE1 mRNA and BACE1 protein. We studied BACE1-AS and BACE1 transcripts by real-time PCR a) in 10 s-IBM and 10 age-matched normal muscle biopsies; and b) in our established ER-Stress-Human-Muscle-Culture IBM Model, in which we previously demonstrated increased BACE1 protein. Our study demonstrated for the first time that a) in s-IBM biopsies BACE1-AS and BACE1 transcripts were significantly increased, suggesting that their increased expression can be responsible for the increase of BACE1 protein; and b) experimental induction of ER stress significantly increased both BACE1-AS and BACE1 transcripts, suggesting that ER stress can participate in their induction in s-IBM muscle. Accordingly, decreasing BACE1 through a targeted downregulation of its regulatory BACE1-AS, or reducing ER stress, might be therapeutic strategies in s-IBM, assuming that it would not impair any normal cellular functions of BACE1. PMID:20236612

  14. Formation of contractile networks and fibers in the medial cell cortex through myosin-II turnover, contraction, and stress-stabilization

    PubMed Central

    Nie, Wei; Wei, Ming-Tzo; Ou-Yang, Daniel H.; Jedlicka, Sabrina S.; Vavylonis, Dimitrios

    2015-01-01

    The morphology of adhered cells depends crucially on the formation of a contractile meshwork of parallel and cross-linked fibers along the contacting surface. The motor activity and minifilament assembly of non-muscle myosin-II is an important component of cortical cytoskeletal remodeling during mechanosensing. We used experiments and computational modeling to study cortical myosin-II dynamics in adhered cells. Confocal microscopy was used to image the medial cell cortex of HeLa cells stably expressing myosin regulatory light chain tagged with GFP (MRLC-GFP). The distribution of MRLC-GFP fibers and focal adhesions was classified into three types of network morphologies. Time-lapse movies show: myosin foci appearance and disappearance; aligning and contraction; stabilization upon alignment. Addition of blebbistatin, which perturbs myosin motor activity, leads to a reorganization of the cortical networks and to a reduction of contractile motions. We quantified the kinetics of contraction, disassembly and reassembly of myosin networks using spatio-temporal image correlation spectroscopy (STICS). Coarse-grained numerical simulations include bipolar minifilaments that contract and align through specified interactions as basic elements. After assuming that minifilament turnover decreases with increasing contractile stress, the simulations reproduce stress-dependent fiber formation in between focal adhesions above a threshold myosin concentration. The STICS correlation function in simulations matches the function measured in experiments. This study provides a framework to help interpret how different cortical myosin remodeling kinetics may contribute to different cell shape and rigidity depending on substrate stiffness. PMID:25641802

  15. Stress-Dependent Matrix Cracking in 2D Woven SiC-Fiber Reinforced Melt-Infiltrated SiC Matrix Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.

    2003-01-01

    The matrix cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the 2-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with SiC, slurry infiltrated with SiC particles followed by molten infiltration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the size of the tows. This resulted in composites with a fiber volume fraction in the loading direction that ranged from 0.12 to 0.20. Matrix cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of matrix cracks. It was found that the general matrix crack properties of this system could be fairly well characterized by assuming that no matrix cracks originated in the load-bearing fiber, interphase, chemical vapor infiltrated Sic tow-minicomposites, i.e., all matrix cracks originate in the 90 degree tow-minicomposites or the large unreinforced Sic-Si matrix regions. Also, it was determined that the larger tow size composites had a much narrower stress range for matrix cracking compared to the standard tow size composites.

  16. Coda Q and its Frequency Dependence in the Eastern Himalayan and Indo-Burman Plate Boundary Systems

    NASA Astrophysics Data System (ADS)

    Mitra, S.; Kumar, A.

    2015-12-01

    We use broadband waveform data for 305 local earthquakes from the Eastern Himalayan and Indo-Burman plate boundary systems, to model the seismic attenuation in NE India. We measure the decay in amplitude of coda waves at discreet frequencies (between 1 and 12Hz) to evaluate the quality factor (Qc) as a function of frequency. We combine these measurements to evaluate the frequency dependence of Qc of the form Qc(f)=Qof η, where Qo is the quality factor at 1Hz and η is the frequency dependence. Computed Qo values range from 80-360 and η ranges from 0.85-1.45. To study the lateral variation in Qo and η, we regionalise the Qc by combining all source-receiver measurements using a back-projection algorithm. For a single back scatter model, the coda waves sample an elliptical area with the epicenter and receiver at the two foci. We parameterize the region using square grids. The algorithm calculates the overlap in area and distributes Qc in the sampled grids using the average Qc as the boundary value. This is done in an iterative manner, by minimising the misfit between the observed and computed Qc within each grid. This process is repeated for all frequencies and η is computed for each grid by combining Qc for all frequencies. Our results reveal strong variation in Qo and η across NE India. The highest Qo are in the Bengal Basin (210-280) and the Indo-Burman subduction zone (300-360). The Shillong Plateau and Mikir Hills have intermediate Qo (~160) and the lowest Qo (~80) is observed in the Naga fold thrust belt. This variation in Qo demarcates the boundary between the continental crust beneath the Shillong Plateau and Mikir Hills and the transitional to oceanic crust beneath the Bengal Basin and Indo-Burman subduction zone. Thick pile of sedimentary strata in the Naga fold thrust belt results in the low Qo. Frequency dependence (η) of Qc across NE India is observed to be very high, with regions of high Qo being associated with relatively higher η.

  17. Interneuron Transcriptional Dysregulation Causes Frequency-Dependent Alterations in the Balance of Inhibition and Excitation in Hippocampus

    PubMed Central

    Bartley, Aundrea F.; Lucas, Elizabeth K.; Brady, Lillian J.; Li, Qin; Hablitz, John J.; Cowell, Rita M.

    2015-01-01

    Circuit dysfunction in complex brain disorders such as schizophrenia and autism is caused by imbalances between inhibitory and excitatory synaptic transmission (I/E). Short-term plasticity differentially alters responses from excitatory and inhibitory synapses, causing the I/E ratio to change as a function of frequency. However, little is known about I/E ratio dynamics in complex brain disorders. Transcriptional dysregulation in interneurons, particularly parvalbumin interneurons, is a consistent pathophysiological feature of schizophrenia. Peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α) is a transcriptional coactivator that in hippocampus is highly concentrated in inhibitory interneurons and regulates parvalbumin transcription. Here, we used PGC-1α−/− mice to investigate effects of interneuron transcriptional dysregulation on the dynamics of the I/E ratio at the synaptic and circuit level in hippocampus. We find that loss of PGC-1α increases the I/E ratio onto CA1 pyramidal cells in response to Schaffer collateral stimulation in slices from young adult mice. The underlying mechanism is enhanced basal inhibition, including increased inhibition from parvalbumin interneurons. This decreases the spread of activation in CA1 and dramatically limits pyramidal cell spiking, reducing hippocampal output. The I/E ratio and CA1 output are partially restored by paired-pulse stimulation at short intervals, indicating frequency-dependent effects. However, circuit dysfunction persists, indicated by alterations in kainate-induced gamma oscillations and impaired nest building. Together, these results show that transcriptional dysregulation in hippocampal interneurons causes frequency-dependent alterations in I/E ratio and circuit function, suggesting that PGC-1α deficiency in psychiatric and neurological disorders contributes to disease by causing functionally relevant alterations in I/E balance. SIGNIFICANCE STATEMENT Alteration in the inhibitory and

  18. Frequency-dependent hydrodynamic inductance and the determination of the thermal and quantum noise of a superfluid gyroscope

    SciTech Connect

    Chui, Talso; Penanen, Konstantin

    2005-04-01

    We reexamine mass flow in a superfluid gyroscope containing a superfluid Josephson weak link. We introduce a frequency-dependent hydrodynamic inductance to account for an oscillatory flow of the normal fluid component in the sensing loop. With this hydrodynamic inductance, we derive the thermal phase noise, and hence the thermal rotational noise of the gyroscope. We examine the thermodynamic stability of the system based on an analysis of the free energy. We derive a quantum phase noise, which is analogous to the zero-point motion of a simple harmonic oscillator. The configuration of the studied gyroscope is analogous to a conventional superconducting RF SQUID. We show that the gyroscope has very low intrinsic noise (1.9x10{sup -13} rad s{sup -1}/{radical}(Hz)), and it can potentially be applied to study general relativity, Earth science, and to improve global positioning systems (GPS)

  19. Determination of acoustic properties of thin polymer films utilizing the frequency dependence of the reflection coefficient of ultrasound

    NASA Astrophysics Data System (ADS)

    Tohmyoh, Hironori; Sakamoto, Yuhei

    2015-11-01

    This paper reports on a technique to measure the acoustic properties of a thin polymer film utilizing the frequency dependence of the reflection coefficient of ultrasound reflected back from a system comprising a reflection plate, the film, and a material that covers the film. The frequency components of the echo reflected from the back of the plate, where the film is attached, take their minimum values at the resonant frequency, and from these frequency characteristics, the acoustic impedance, sound velocity, and the density of the film can be determined. We applied this technique to characterize an ion exchange membrane, which has high water absorbability, and successfully determined the acoustic properties of the membrane without getting it wet.

  20. Towards strongly correlated photons in arrays of dissipative nonlinear cavities under a frequency-dependent incoherent pumping

    NASA Astrophysics Data System (ADS)

    Lebreuilly, José; Wouters, Michiel; Carusotto, Iacopo

    2016-10-01

    We report a theoretical study of a quantum optical model consisting of an array of strongly nonlinear cavities incoherently pumped by an ensemble of population-inverted two-level atoms. Projective methods are used to eliminate the atomic dynamics and write a generalized master equation for the photonic degrees of freedom only, where the frequency-dependence of gain introduces non-Markovian features. In the simplest single cavity configuration, this pumping scheme gives novel optical bistability effects and allows for the selective generation of Fock states with a well-defined photon number. For many cavities in a weakly non-Markovian limit, the non-equilibrium steady state recovers a Grand-Canonical statistical ensemble at a temperature determined by the effective atomic linewidth. For a two-cavity system in the strongly nonlinear regime, signatures of a Mott state with one photon per cavity are found.

  1. Compressive sensing of the Tohoku-Oki Mw 9.0 earthquake: Frequency-dependent rupture modes

    NASA Astrophysics Data System (ADS)

    Yao, Huajian; Gerstoft, Peter; Shearer, Peter M.; Mecklenbräuker, Christoph

    2011-10-01

    Compressive sensing (CS) is a technique for finding sparse signal representations to underdetermined linear measurement equations. We use CS to locate seismic sources during the rupture of the 2011 Tohoku-Oki Mw9.0 earthquake in Japan from teleseismic P waves recorded by an array of stations in the United States. The seismic sources are located by minimizing the ℓ2-norm of the difference between the observed and modeled waveforms penalized by the ℓ1-norm of the seismic source vector. The resulting minimization problem is convex and can be solved efficiently. Our results show clear frequency-dependent rupture modes with high-frequency energy radiation dominant in the down-dip region and low-frequency radiation in the updip region, which may be caused by differences in rupture behavior (more intermittent or continuous) at the slab interface due to heterogeneous frictional properties.

  2. Frequency-dependent study of solid 4He contained in a rigid double-torus torsional oscillator

    NASA Astrophysics Data System (ADS)

    Choi, Jaewon; Shin, Jaeho; Kim, Eunseong

    2015-10-01

    The rigid double-torus torsional oscillator (TO) is constructed to reduce any elastic effects inherent to complicated TO structures, allowing explicit probing for a genuine supersolid signature. We investigated the frequency- and temperature-dependent response of the rigid double-torus TO containing solid 4He with 0.6-ppb 3He and 300-ppb 3He . We did not find evidence to support the frequency-independent contribution proposed to be a property of supersolid helium. The frequency-dependent contribution which comes from the simple elastic effect of solid helium coupled to the TO is essentially responsible for the entire response. The magnitude of the period drop is linearly proportional to f2, indicating that the responses observed in this TO are mostly caused by the overshoot of "soft" solid helium against the wall of the torus. Dissipation of the rigid TO is vastly suppressed compared to that of nonrigid TOs.

  3. Frequency Dependence of Short Period Seismic Noise from Two Decades of Observations at Warramunga Seismic Array (WRA), Australia

    NASA Astrophysics Data System (ADS)

    Gal, M.; Reading, A. M.; Ellingsen, S. P.; Koper, K. D.; Tkalcic, H.; Hemer, M. A.

    2014-12-01

    The analysis of the seismic ambient noise field has recently received increased attention owing to its success in mapping the Earth's shallow and deep structures. The origin of the passive seismic wavefield is associated with deep ocean and coastal regions where ocean waves, under certain conditions, can excite seismic waves (microseisms) that propagate as surface and body waves. Previous seismological studies mainly focused on the observation of the strongest microseisms that are associated with the frequency range 0.1-0.3Hz. In our study, we focus on short period microseisms (0.325-0.725Hz) and examine the frequency dependant wave field and temporal variations over two decades. We use data recorded over two decades (1991-2012) from the Warramunga array (WRA) in central Australia. The analysis is carried out using IAS Capon beamforming that shows robust estimates of slowness and backazimuth, and is able to resolve multiple wave arrivals. Continuous data records are divided into one hour long recordings and evaluated for multiple arrivals in 8 separate frequency bands. We find multiple surface and body wave sources, which display seasonality and frequency dependence and remain stationary for two decades. We observe, for surface waves, that Rayleigh waves dominate for low frequencies while higher frequencies show a transition to leaky Rayleigh waves. The strong stationarity of the signal over multiple years, supports the suggestion that bathymetry and other site effects, such as coast line geometry, create favourable conditions for the generation of ocean induced surface waves. For body waves, source locations are identified in deep ocean regions for low frequencies and in shallow waters for higher frequencies. We further discuss correlation between arrivals and a WAVEWATCH III ocean wave hindcast for strong events. Fig 1: a) Shows the slowness of strongest incoming arrivals for 1 hour of WRA data over two decades. b) Displays the surface waves paths of incoming

  4. ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow

    NASA Astrophysics Data System (ADS)

    Brinkerink, Christiaan D.; Falcke, Heino; Law, Casey J.; Barkats, Denis; Bower, Geoffrey C.; Brunthaler, Andreas; Gammie, Charles; Impellizzeri, C. M. Violette; Markoff, Sera; Menten, Karl M.; Moscibrodzka, Monika; Peck, Alison; Rushton, Anthony P.; Schaaf, Reinhold; Wright, Melvyn

    2015-04-01

    Context. Radio and mm-wavelength observations of Sagittarius A* (Sgr A*), the radio source associated with the supermassive black hole at the center of our Galaxy, show that it behaves as a partially self-absorbed synchrotron-emitting source. The measured size of Sgr A* shows that the mm-wavelength emission comes from a small region and consists of the inner accretion flow and a possible collimated outflow. Existing observations of Sgr A* have revealed a time lag between light curves at 43 GHz and 22 GHz, which is consistent with a rapidly expanding plasma flow and supports the presence of a collimated outflow from the environment of an accreting black hole. Aims: Here we wish to measure simultaneous frequency-dependent time lags in the light curves of Sgr A* across a broad frequency range to constrain direction and speed of the radio-emitting plasma in the vicinity of the black hole. Methods: Light curves of Sgr A* were taken in May 2012 using ALMA at 100 GHz using the VLA at 48, 39, 37, 27, 25.5, and 19 GHz. As a result of elevation limits and the longitude difference between the stations, the usable overlap in the light curves is approximately four hours. Although Sgr A* was in a relatively quiet phase, the high sensitivity of ALMA and the VLA allowed us to detect and fit maxima of an observed minor flare where flux density varied by ~10%. Results: The fitted times of flux density maxima at frequencies from 100 GHz to 19 GHz, as well as a cross-correlation analysis, reveal a simple frequency-dependent time lag relation where maxima at higher frequencies lead those at lower frequencies. Taking the observed size-frequency relation of Sgr A* into account, these time lags suggest a moderately relativistic (lower estimates: 0.5c for two-sided, 0.77c for one-sided) collimated outflow.

  5. Frequency-dependent conductivity contrast for tissue characterization using a dual-frequency range conductivity mapping magnetic resonance method.

    PubMed

    Kim, Dong-Hyun; Chauhan, Munish; Kim, Min-Oh; Jeong, Woo Chul; Kim, Hyung Joong; Sersa, Igor; Kwon, Oh In; Woo, Eung Je

    2015-02-01

    Electrical conductivities of biological tissues show frequency-dependent behaviors, and these values at different frequencies may provide clinically useful diagnostic information. MR-based tissue property mapping techniques such as magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance electrical property tomography (MREPT) are widely used and provide unique conductivity contrast information over different frequency ranges. Recently, a new method for data acquisition and reconstruction for low- and high-frequency conductivity images from a single MR scan was proposed. In this study, we applied this simultaneous dual-frequency range conductivity mapping MR method to evaluate its utility in a designed phantom and two in vivo animal disease models. Magnetic flux density and B(1)(+) phase map for dual-frequency conductivity images were acquired using a modified spin-echo pulse sequence. Low-frequency conductivity was reconstructed from MREIT data by the projected current density method, while high-frequency conductivity was reconstructed from MREPT data by B(1)(+) mapping. Two different conductivity phantoms comprising varying ion concentrations separated by insulating films with or without holes were used to study the contrast mechanism of the frequency-dependent conductivities related to ion concentration and mobility. Canine brain abscess and ischemia were used as in vivo models to evaluate the capability of the proposed method to identify new electrical properties-based contrast at two different frequencies. The simultaneous dual-frequency range conductivity mapping MR method provides unique contrast information related to the concentration and mobility of ions inside tissues. This method has potential to monitor dynamic changes of the state of disease.

  6. Modulation of epileptic activity by deep brain stimulation: a model-based study of frequency-dependent effects.

    PubMed

    Mina, Faten; Benquet, Pascal; Pasnicu, Anca; Biraben, Arnaud; Wendling, Fabrice

    2013-01-01

    A number of studies showed that deep brain stimulation (DBS) can modulate the activity in the epileptic brain and that a decrease of seizures can be achieved in "responding" patients. In most of these studies, the choice of stimulation parameters is critical to obtain desired clinical effects. In particular, the stimulation frequency is a key parameter that is difficult to tune. A reason is that our knowledge about the frequency-dependant mechanisms according to which DBS indirectly impacts the dynamics of pathological neuronal systems located in the neocortex is still limited. We address this issue using both computational modeling and intracerebral EEG (iEEG) data. We developed a macroscopic (neural mass) model of the thalamocortical network. In line with already-existing models, it includes interconnected neocortical pyramidal cells and interneurons, thalamocortical cells and reticular neurons. The novelty was to introduce, in the thalamic compartment, the biophysical effects of direct stimulation. Regarding clinical data, we used a quite unique data set recorded in a patient (drug-resistant epilepsy) with a focal cortical dysplasia (FCD). In this patient, DBS strongly reduced the sustained epileptic activity of the FCD for low-frequency (LFS, < 2 Hz) and high-frequency stimulation (HFS, > 70 Hz) while intermediate-frequency stimulation (IFS, around 50 Hz) had no effect. Signal processing, clustering, and optimization techniques allowed us to identify the necessary conditions for reproducing, in the model, the observed frequency-dependent stimulation effects. Key elements which explain the suppression of epileptic activity in the FCD include: (a) feed-forward inhibition and synaptic short-term depression of thalamocortical connections at LFS, and (b) inhibition of the thalamic output at HFS. Conversely, modeling results indicate that IFS favors thalamic oscillations and entrains epileptic dynamics.

  7. In Vivo and In Silico Investigation Into Mechanisms of Frequency Dependence of Repolarization Alternans in Human Ventricular Cardiomyocytes

    PubMed Central

    Zhou, Xin; Bueno-Orovio, Alfonso; Orini, Michele; Hanson, Ben; Hayward, Martin; Taggart, Peter; Lambiase, Pier D.; Burrage, Kevin

    2016-01-01

    Rationale: Repolarization alternans (RA) are associated with arrhythmogenesis. Animal studies have revealed potential mechanisms, but human-focused studies are needed. RA generation and frequency dependence may be determined by cell-to-cell variability in protein expression, which is regulated by genetic and external factors. Objective: To characterize in vivo RA in human and to investigate in silico using human models, the ionic mechanisms underlying the frequency-dependent differences in RA behavior identified in vivo. Methods and Results: In vivo electrograms were acquired at 240 sites covering the epicardium of 41 patients at 6 cycle lengths (600–350 ms). In silico investigations were conducted using a population of biophysically detailed human models incorporating variability in protein expression and calibrated using in vivo recordings. Both in silico and in vivo, 2 types of RA were identified, with Fork- and Eye-type restitution curves, based on RA persistence or disappearance, respectively, at fast pacing rates. In silico simulations show that RA are strongly correlated with fluctuations in sarcoplasmic reticulum calcium, because of strong release and weak reuptake. Large L-type calcium current conductance is responsible for RA disappearance at fast frequencies in Eye-type (30% larger in Eye-type versus Fork-type; P<0.01), because of sarcoplasmic reticulum Ca2+ ATPase pump potentiation caused by frequency-induced increase in intracellular calcium. Large Na+/Ca2+ exchanger current is the main driver in translating Ca2+ fluctuations into RA. Conclusions: In human in vivo and in silico, 2 types of RA are identified, with RA persistence/disappearance as frequency increases. In silico, L-type calcium current and Na+/Ca2+ exchanger current determine RA human cell-to-cell differences through intracellular and sarcoplasmic reticulum calcium regulation. PMID:26602864

  8. Black Beans, Fiber, and Antioxidant Capacity Pilot Study: Examination of Whole Foods vs. Functional Components on Postprandial Metabolic, Oxidative Stress, and Inflammation in Adults with Metabolic Syndrome.

    PubMed

    Reverri, Elizabeth J; Randolph, Jody M; Steinberg, Francene M; Kappagoda, C Tissa; Edirisinghe, Indika; Burton-Freeman, Britt M

    2015-08-01

    Beans (Phaseolus vulgaris) contain bioactive components with functional properties that may modify cardiovascular risk. The aims of this pilot study were to evaluate the ability of black beans to attenuate postprandial metabolic, oxidative stress, and inflammatory responses and determine relative contribution of dietary fiber and antioxidant capacity of beans to the overall effect. In this randomized, controlled, crossover trial, 12 adults with metabolic syndrome (MetS) consumed one of three meals (black bean (BB), fiber matched (FM), and antioxidant capacity matched (AM)) on three occasions that included blood collection before (fasting) and five hours postprandially. Insulin was lower after the BB meal, compared to the FM or AM meals (p < 0.0001). A significant meal × time interaction was observed for plasma antioxidant capacity (p = 0.002) revealing differences over time: AM > BB > FM. Oxidized LDL (oxLDL) was not different by meal, although a trend for declining oxLDL was observed after the BB and AM meals at five hours compared to the FM meal. Triglycerides and interleukin-6 (IL-6) increased in response to meals (p < 0.0001). Inclusion of black beans with a typical Western-style meal attenuates postprandial insulin and moderately enhances postprandial antioxidant endpoints in adults with MetS, which could only be partly explained by fiber content and properties of antioxidant capacity. PMID:26225995

  9. Black Beans, Fiber, and Antioxidant Capacity Pilot Study: Examination of Whole Foods vs. Functional Components on Postprandial Metabolic, Oxidative Stress, and Inflammation in Adults with Metabolic Syndrome

    PubMed Central

    Reverri, Elizabeth J.; Randolph, Jody M.; Steinberg, Francene M.; Kappagoda, C. Tissa; Edirisinghe, Indika; Burton-Freeman, Britt M.

    2015-01-01

    Beans (Phaseolus vulgaris) contain bioactive components with functional properties that may modify cardiovascular risk. The aims of this pilot study were to evaluate the ability of black beans to attenuate postprandial metabolic, oxidative stress, and inflammatory responses and determine relative contribution of dietary fiber and antioxidant capacity of beans to the overall effect. In this randomized, controlled, crossover trial, 12 adults with metabolic syndrome (MetS) consumed one of three meals (black bean (BB), fiber matched (FM), and antioxidant capacity matched (AM)) on three occasions that included blood collection before (fasting) and five hours postprandially. Insulin was lower after the BB meal, compared to the FM or AM meals (p < 0.0001). A significant meal × time interaction was observed for plasma antioxidant capacity (p = 0.002) revealing differences over time: AM > BB > FM. Oxidized LDL (oxLDL) was not different by meal, although a trend for declining oxLDL was observed after the BB and AM meals at five hours compared to the FM meal. Triglycerides and interleukin-6 (IL-6) increased in response to meals (p < 0.0001). Inclusion of black beans with a typical Western-style meal attenuates postprandial insulin and moderately enhances postprandial antioxidant endpoints in adults with MetS, which could only be partly explained by fiber content and properties of antioxidant capacity. PMID:26225995

  10. Black Beans, Fiber, and Antioxidant Capacity Pilot Study: Examination of Whole Foods vs. Functional Components on Postprandial Metabolic, Oxidative Stress, and Inflammation in Adults with Metabolic Syndrome.

    PubMed

    Reverri, Elizabeth J; Randolph, Jody M; Steinberg, Francene M; Kappagoda, C Tissa; Edirisinghe, Indika; Burton-Freeman, Britt M

    2015-07-27

    Beans (Phaseolus vulgaris) contain bioactive components with functional properties that may modify cardiovascular risk. The aims of this pilot study were to evaluate the ability of black beans to attenuate postprandial metabolic, oxidative stress, and inflammatory responses and determine relative contribution of dietary fiber and antioxidant capacity of beans to the overall effect. In this randomized, controlled, crossover trial, 12 adults with metabolic syndrome (MetS) consumed one of three meals (black bean (BB), fiber matched (FM), and antioxidant capacity matched (AM)) on three occasions that included blood collection before (fasting) and five hours postprandially. Insulin was lower after the BB meal, compared to the FM or AM meals (p < 0.0001). A significant meal × time interaction was observed for plasma antioxidant capacity (p = 0.002) revealing differences over time: AM > BB > FM. Oxidized LDL (oxLDL) was not different by meal, although a trend for declining oxLDL was observed after the BB and AM meals at five hours compared to the FM meal. Triglycerides and interleukin-6 (IL-6) increased in response to meals (p < 0.0001). Inclusion of black beans with a typical Western-style meal attenuates postprandial insulin and moderately enhances postprandial antioxidant endpoints in adults with MetS, which could only be partly explained by fiber content and properties of antioxidant capacity.

  11. The stress-strain relationships in wood and fiber-reinforced plastic laminae of reinforced glued-laminated wood beams

    NASA Astrophysics Data System (ADS)

    Tingley, Daniel Arthur

    The reinforcement of wood and wood composite structural products to improve their mechanical properties has been in practice for many years. Recently, the use of high-strength fiber-reinforced plastic (FRP) as a reinforcement in such applications has been commercialized. The reinforcement is manufactured using a standard pultrusion process or alternatively a sheet-forming process commonly referred to as "pulforming". The high-modulus fibers are predominately unidirectional, although off-axis fibers are often used to enhance off-axis properties. The fibers used are either of a single type or multiple types, which are called "hybrids". Unidirectional, single, and hybrid fiber FRP physical properties and characteristics were compared to wood. Full-scale reinforced glulams were tested. Aramid-reinforced plastics (ARP) used as tensile reinforcements were found to be superior in strength applications to other types of FRP made with fiber, such as carbon and fiberglass. Carbon/aramid-reinforced plastic (CARP) was shown to be superior in both modulus and strength design situations. Fiberglass was shown to be suitable only in hybrid situations with another fiber such as aramid or carbon and only in limited use situations where modulus was a design criteria. The testing and analysis showed that the global response of reinforced glulam beams is controlled by localized strength variations in the wood such as slope of grain, knots, finger joints, etc. in the tensile zone. The elemental tensile strains in the extreme wood tensile laminae, due to global applied loads, were found to be well below the strain at failure in clear wood samples recovered from the failure area. Two areas affecting the relationship between the wood and the FRP were investigated: compatibility of the wood and FRP materials and interface characteristics between the wood and FRP. The optimum strain value at yield point for an FRP was assessed to be slightly higher than the clear wood value in tension for a

  12. Digging for answers: contributions of density- and frequency-dependent factors on ectoparasite burden in a social mammal.

    PubMed

    Archer, Elizabeth K; Bennett, Nigel C; Faulkes, Chris G; Lutermann, Heike

    2016-02-01

    Due to the density-dependent nature of parasite transmission parasites are generally assumed to constrain the evolution of sociality. However, evidence for a correlation between group size and parasite burden is equivocal, particularly for mammals. Host contact rates may be modified by mobility of the host and parasite as well as social barriers. In the current study, we used the common mole-rat (Cryptomys hottentotus hottentotus), a social subterranean rodent, as a model system to investigate the effect of host density and frequency of contact rates on ectoparasite burdens. To address these factors we used a study species that naturally varies in population densities and intergroup contact rates across its geographic range. We found that ectoparasite prevalence, abundance and species richness decreased with increasing host density at a regional scale. At the same time, measures of parasite burden increased with intergroup contact rates. Ectoparasite burdens decreased with colony size at the group level possibly as a result of increased grooming rates. Equating group size with population density might be too simplistic an approach when assessing parasite distributions in social mammals. Our data suggest that frequency-dependent mechanisms may play a much greater role at a population level than density-dependent mechanisms in determining parasite distributions in social species. We suggest that future studies should explicitly consider behavioural mechanisms that may affect parasite distribution.

  13. Determination of the magnetocrystalline anisotropy constant from the frequency dependence of the specific absorption rate in a frozen ferrofluid

    NASA Astrophysics Data System (ADS)

    Mosher, Nathaniel; Perkins-Harbin, Emily; Aho, Brandon; Wang, Lihua; Kumon, Ronald; Rablau, Corneliu; Vaishnava, Prem; Tackett, Ronald; Therapeutic Biomaterials Group Team

    2015-03-01

    Colloidal suspensions of superparamagnetic nanoparticles, known as ferrofluids, are promising candidates for the mediation of magnetic fluid hyperthermia (MFH). In such materials, the dissipation of heat occurs as a result of the relaxation of the particles in an applied ac magnetic field via the Brownian and Neel mechanisms. In order to isolate and study the role of the Neel mechanism in this process, the sample can be frozen, using liquid nitrogen, in order to suppress the Brownian relaxation. In this experiment, dextran-coated Fe3O4 nanoparticles synthesized via co-precipitation and characterized via transmission electron microscopy and dc magnetization are used as MFH mediators over the temperature range between -70 °C to -10 °C (Brownian-suppressed state). Heating the nanoparticles using ac magnetic field (amplitude ~300 Oe), the frequency dependence of the specific absorption rate (SAR) is calculated between 150 kHz and 350 kHz and used to determine the magnetocrystalline anisotropy of the sample. We would like to thank Fluxtrol, Inc. for their help with this project

  14. A DTI-based model for TMS using the independent impedance method with frequency-dependent tissue parameters

    NASA Astrophysics Data System (ADS)

    De Geeter, N.; Crevecoeur, G.; Dupré, L.; Van Hecke, W.; Leemans, A.

    2012-04-01

    Accurate simulations on detailed realistic head models are necessary to gain a better understanding of the response to transcranial magnetic stimulation (TMS). Hitherto, head models with simplified geometries and constant isotropic material properties are often used, whereas some biological tissues have anisotropic characteristics which vary naturally with frequency. Moreover, most computational methods do not take the tissue permittivity into account. Therefore, we calculate the electromagnetic behaviour due to TMS in a head model with realistic geometry and where realistic dispersive anisotropic tissue properties are incorporated, based on T1-weighted and diffusion-weighted magnetic resonance images. This paper studies the impact of tissue anisotropy, permittivity and frequency dependence, using the anisotropic independent impedance method. The results show that anisotropy yields differences up to 32% and 19% of the maximum induced currents and electric field, respectively. Neglecting the permittivity values leads to a decrease of about 72% and 24% of the maximum currents and field, respectively. Implementing the dispersive effects of biological tissues results in a difference of 6% of the maximum currents. The cerebral voxels show limited sensitivity of the induced electric field to changes in conductivity and permittivity, whereas the field varies approximately linearly with frequency. These findings illustrate the importance of including each of the above parameters in the model and confirm the need for accuracy in the applied patient-specific method, which can be used in computer-assisted TMS.

  15. Frequency dependence of Néel temperature in CaMnO3-δ ceramics: Synthesized by two different methods

    NASA Astrophysics Data System (ADS)

    Kompany, A.; Ghorbani-Moghadam, T.; Kafash, S.; Ebrahimizadeh Abrishami, M.

    2014-01-01

    Calcium manganese oxide CaMnO3-δ (δ=0.02) nanopowders were synthesized by two different methods; sol-gel and solid-state reaction. X-ray diffraction patterns indicated that both types of the prepared powders have orthorhombic symmetry structures at room temperature. Further characterizations of the samples were preformed employing SEM and TEM techniques. At low magnetic fields, the phase transition temperature from antiferromagnetic to paramagnetic was found to be slightly higher in the sintered O-ring shape specimens made from powders synthesized by sol-gel method. This result can be described in relation to Mn3+-O-Mn4+ double-exchange interaction and also electron hopping mechanism which occur more in these specimens than those made from solid-state reaction powders. The frequency dependence of Néel temperature and the shape of the hysteresis loops, observed in both types of the prepared ceramics specimens, can be attributed to the reduction of relaxation time which occurs with increasing the frequency.

  16. Time-domain response of a metal detector to a target buried in soil with frequency-dependent magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Das, Y.

    2006-05-01

    The work reported in this paper is a part of on-going studies to clarify how and to what extent soil electromagnetic properties affect the performance of induction metal detectors widely used in humanitarian demining. This paper studies the specific case of the time-domain response of a small metallic sphere buried in a non-conducting soil half-space with frequency-dependent complex magnetic susceptibility. The sphere is chosen as a simple prototype for the small metal parts in low-metal landmines, while soil with dispersive magnetic susceptibility is a good model for some soils that are known to adversely affect the performance of metal detectors. The included analysis and computations extend previous work which has been done mostly in the frequency domain. Approximate theoretical expressions for weakly magnetic soils are found to fit the experimental data very well, which allowed the estimation of soil model parameters, albeit in an ad hoc manner. Soil signal is found to exceed target signal (due to an aluminum sphere of radius 0.0127 m) in many cases, even for the weakly magnetic Cambodian laterite used in the experiments. How deep a buried target is detected depends on many other factors in addition to the relative strength of soil and target signals. A general statement cannot thus be made regarding detectability of a target in soil based on the presented results. However, computational results complemented with experimental data extend the understanding of the effect that soil has on metal detectors.

  17. The sound insulation of single leaf finite size rectangular plywood panels with orthotropic frequency dependent bending stiffness.

    PubMed

    Wareing, Robin R; Davy, John L; Pearse, John R

    2016-01-01

    Current theories for predicting the sound insulation of orthotropic materials are limited to a small range of infinite panels. This paper presents a method that allows for the prediction of the sound insulation of a finite size orthotropic panel. This method uses an equation for the forced radiation impedance of a finite size rectangular panel. This approach produces an equation that has three nested integrals. The long numerical calculation times were reduced by using approximate formulas for the azimuthally averaged forced radiation impedance. This reduced the number of nested integrals from three to two. The resulting predictions are compared to results measured using two sample sizes of four different thicknesses of plywood and one sample size of another three different thicknesses of plywood. Plywood was used for all the tests because it is somewhat orthotropic. It was found during testing that the Young's moduli of the plywood were dependent on the frequency of excitation. The influence of the frequency dependent Young's moduli was then included in the prediction method. The experimental results were also compared with a simple isotropic prediction method. PMID:26827045

  18. The sound insulation of single leaf finite size rectangular plywood panels with orthotropic frequency dependent bending stiffness.

    PubMed

    Wareing, Robin R; Davy, John L; Pearse, John R

    2016-01-01

    Current theories for predicting the sound insulation of orthotropic materials are limited to a small range of infinite panels. This paper presents a method that allows for the prediction of the sound insulation of a finite size orthotropic panel. This method uses an equation for the forced radiation impedance of a finite size rectangular panel. This approach produces an equation that has three nested integrals. The long numerical calculation times were reduced by using approximate formulas for the azimuthally averaged forced radiation impedance. This reduced the number of nested integrals from three to two. The resulting predictions are compared to results measured using two sample sizes of four different thicknesses of plywood and one sample size of another three different thicknesses of plywood. Plywood was used for all the tests because it is somewhat orthotropic. It was found during testing that the Young's moduli of the plywood were dependent on the frequency of excitation. The influence of the frequency dependent Young's moduli was then included in the prediction method. The experimental results were also compared with a simple isotropic prediction method.

  19. Distinct frequency dependent effects of whole-body vibration on non-fractured bone and fracture healing in mice.

    PubMed

    Wehrle, Esther; Wehner, Tim; Heilmann, Aline; Bindl, Ronny; Claes, Lutz; Jakob, Franz; Amling, Michael; Ignatius, Anita

    2014-08-01

    Low-magnitude high-frequency vibration (LMHFV) provokes anabolic effects in non-fractured bone; however, in fracture healing, inconsistent results were reported and optimum vibration conditions remain unidentified. Here, we investigated frequency dependent effects of LMHFV on fracture healing. Twelve-week-old, female C57BL/6 mice received a femur osteotomy stabilized using an external fixator. The mice received whole-body vibrations (20 min/day) with 0.3g peak-to-peak acceleration and a frequency of either 35 or 45 Hz. After 10 and 21 days, the osteotomized femurs and intact bones (contra-lateral femurs, lumbar spine) were evaluated using bending-testing, µ-computed tomography, and histomorphometry. In non-fractured trabecular bone, vibration with 35 Hz significantly increased the relative amount of bone (+28%) and the trabecular number (+29%), whereas cortical bone was not influenced. LMHFV with 45 Hz failed to provoke anabolic effects in trabecular or cortical bone. Fracture healing was not significantly influenced by whole-body vibration with 35 Hz, whereas 45 Hz significantly reduced bone formation (-64%) and flexural rigidity (-34%) of the callus. Although the exact mechanisms remain open, our results suggest that small vibration setting changes could considerably influence LMHFV effects on bone formation in remodeling and repair, and even disrupt fracture healing, implicating caution when treating patients with impaired fracture healing.

  20. A frequency-dependent log-quadratic Pn spreading model in the Northeast China and Korean peninsula

    NASA Astrophysics Data System (ADS)

    Hao, J.; Zhao, L.; Xie, X. B.; Yao, Z.

    2015-12-01

    In 9 October 2006, 25 May 2009, and 12 February 2013, North Korea conducted three successive nuclear tests near the China-Korea border. Based on 297 broadband stations distributed in East China, South Korea, and Japan, the digital seismograms from these nuclear tests are collected to investigate the geometric spreading and attenuation of seismic Pn waves in Northeast China and Korean Peninsula. A highly accurate broadband Pn-wave data set generated by North Korean nuclear tests is used to constrain parameters of a frequency-dependent log-quadratic geometric spreading function and a power-law Pn Q model. The geometric spreading function and apparent Pn wave Q is obtained for the studied area between 2.0 and 10.0 Hz. By taking the two-station amplitude ratios of the Pn spectra, followed by correcting it for the known spreading function, we can strip the effects of source and crust legs from the apparent Pn Q, and retrieve the P-wave attenuation information along the pure upper mantle path. We then use a tomographic approach to obtain the upper mantle P-wave attenuation in Northeast China and Korean Peninsula. The Pn wave spectra observed in China are compared with those recorded in Japan, and the result reveals that the high-frequency Pn signal across the oceanic path attenuated faster than those through the continental path. This work was supported by the National Natural Science Foundation of China (grants 41174048 and 41374065).

  1. Asymmetric and frequency-dependent pollinator-mediated interactions may influence competitive displacement in two vernal pool plants.

    PubMed

    Runquist, Ryan Briscoe; Stanton, Maureen L

    2013-02-01

    A plant species immigrating into a community may experience a rarity disadvantage due to competition for the services of pollinators. These negative reproductive interactions have the potential to lead to competitive displacement or exclusion of a species from a site. In this study, we used one- and two-species arrays of potted plants to test for density and frequency dependence in pollinator-mediated and above-ground intraspecific and interspecific competition between two species of Limnanthes that have overlapping ranges, but rarely occur in close sympatry. There were asymmetric competitive effects; the species responded differently to their frequency within 16-plant replacement series arrays. Limnanthes douglasii rosea experienced stronger reductions in lifetime and per-flower fertility, likely due to pollinator-mediated competition with Limnanthes alba. This effect may be linked to asymmetrical competition through heterospecific pollen transfer. This study demonstrates that pollinator-mediated competition may discourage establishment of L. d. rosea in sites already occupied by its congener. PMID:23134452

  2. Scanning Acoustic Microscopy Investigation of Frequency-Dependent Reflectance of Acid-Etched Human Dentin Using Homotopic Measurements

    PubMed Central

    Marangos, Orestes; Misra, Anil; Spencer, Paulette; Katz, J. Lawrence

    2013-01-01

    Composite restorations in modern restorative dentistry rely on the bond formed in the adhesive-infiltrated acid-etched dentin. The physical characteristics of etched dentin are, therefore, of paramount interest. However, characterization of the acid-etched zone in its natural state is fraught with problems stemming from a variety of sources including its narrow size, the presence of water, heterogeneity, and spatial scale dependency. We have developed a novel homotopic (same location) measurement methodology utilizing scanning acoustic microscopy (SAM). Homotopic measurements with SAM overcome the problems encountered by other characterization/ imaging methods. These measurements provide us with acoustic reflectance at the same location of both the pre- and post-etched dentin in its natural state. We have applied this methodology for in vitro measurements on dentin samples. Fourier spectra from acid-etched dentin showed amplitude reduction and shifts of the central frequency that were location dependent. Through calibration, the acoustic reflectance of acid-etched dentin was found to have complex and non-monotonic frequency dependence. These data suggest that acid-etching of dentin results in a near-surface graded layer of varying thickness and property gradations. The measurement methodology described in this paper can be applied to systematically characterize mechanical properties of heterogeneous soft layers and interfaces in biological materials. PMID:21429849

  3. Habitat assessment ability of bumble-bees implies frequency-dependent selection on floral rewards and display size

    PubMed Central

    Biernaskie, Jay M; Gegear, Robert J

    2007-01-01

    Foraging pollinators could visit hundreds of flowers in succession on mass-flowering plants, yet they often visit only a small number—potentially saving the plant from much self-pollination among its own flowers (geitonogamy). This study tests the hypothesis that bumble-bee (Bombus impatiens) residence on a particular plant depends on an assessment of that plant's reward value relative to the overall quality experienced in the habitat. In a controlled environment, naive bees were given experience in a particular habitat (all plants having equal nectar quality or number of rewarding flowers), and we tested whether they learn about and adaptively exploit a new habitat type. Bees' residence on a plant (number of flowers probed per visit) was eventually invariant to a doubling of absolute nectar quality and increased only slightly with a doubling of absolute flower number in the habitat. These results help to explain why pollinators are quick to leave highly rewarding plants and suggest that the fitness of rewarding plant traits will often be frequency dependent. One implication is that geitonogamy may be a less significant constraint on the evolution of rewarding traits than generally supposed. PMID:17711839

  4. The frequency-dependent electrooptic response of the electroclinic effect in deVries SmA materials

    NASA Astrophysics Data System (ADS)

    Jones, Christopher D.; Dawin, Ute; Giesselmann, Frank; Clark, Noel; Rudquist, Per

    2007-03-01

    It is well established that electroclinic switching in standard SmA* materials relates to a reorientation of the molecules in a plane normal to the layers, and thus there is no corresponding change in birefringence due to reorientation about a cone, as is the case in the SmC* phase. When the electrooptic response is then analyzed via lock-in amplifier, the signal at the driving frequency is strong, while the second harmonic response, is non-existent [1]. Using this method we have investigated deVries materials W530 and TSiKN65, and show that there is a frequency-dependent second order response -- implying an electroclinic switching that corresponds to a change in birefringence, suggesting a reorientation of the molecule about a cone. We will present our findings and a model for the type of electroclinic switching that occurs in these two materials. Work supported by NSF MRSEC Grant DMR-0213918 and The Swedish Foundation for Strategic Research 2002/0388. [1] W. Kuczynski, et. al., Ferroelectics, 244, [491]/191, (2000)

  5. Frequency-dependent assistance as a way out of competitive exclusion between two strains of an emerging virus.

    PubMed

    Péréfarres, Frédéric; Thébaud, Gaël; Lefeuvre, Pierre; Chiroleu, Frédéric; Rimbaud, Loup; Hoareau, Murielle; Reynaud, Bernard; Lett, Jean-Michel

    2014-04-22

    Biological invasions are the main causes of emerging viral diseases and they favour the co-occurrence of multiple species or strains in the same environment. Depending on the nature of the interaction, co-occurrence can lead to competitive exclusion or coexistence. The successive fortuitous introductions of two strains of Tomato yellow leaf curl virus (TYLCV-Mld and TYLCV-IL) in Réunion Island provided an ideal opportunity to study the invasion of, and competition between, these worldwide emerging pathogens. During a 7-year field survey, we observed a displacement of the resident TYLCV-Mld by the newcomer TYLCV-IL, with TYLCV-Mld remaining mostly in co-infected plants. To understand the factors associated with this partial displacement, biological traits related to fitness were measured. The better ecological aptitude of TYLCV-IL in single infections was demonstrated, which explains its rapid spread. However, we demonstrate that the relative fitness of virus strains can drastically change between single infections and co-infections. An epidemiological model parametrized with our experimental data predicts that the two strains will coexist in the long run through assistance by the fitter strain. This rare case of unilateral facilitation between two pathogens leads to frequency-dependent selection and maintenance of the less fit strain. PMID:24598426

  6. Dynamic linear electro-optic frequency dependence in PMN-32%PT and PZN-8%PT for RF microwave photonics

    NASA Astrophysics Data System (ADS)

    Johnson, Shikik T.

    The electrooptic effect (at lambda = 633nm) in both PMN-32%PT and PZN-8%PT relaxor ferroelectric single crystals was investigated as a function of small signal modulation frequencies. Piezo-resonance measurements were also conducted to examine piezooptic coupling in these materials for selected resonance modes to observe the influence of piezoelectric activity on the electro-optic behavior. The electrooptic rC coefficient in PMN-32PT and PZN-8%PT crystals were found to have strong frequency dependence at frequencies below 100s Hz apparently due to space charge effects. Anomalous electrooptic properties near piezoelectric resonance frequencies are reported to be attributed to a synchronization of the low frequency piezoelectric resonance and high frequency transverse lattice vibrations near 4th harmonics. Also reported is enhanced electrooptic properties near piezoelectric resonant frequencies that may be attributed to synchronization of the low frequency fundamental modes and up to their 5th order harmonics accompanied by nonlinear extrinsic activity in the form of lateral domain region motion. A constructive interaction with overlapping high order piezoelectric and electrooptic resonances can be engineered, using PMN-32%PT rhombohedral and PZN-8%PT crystals as an example, so that a small signal (.25V/mm) amplified electro-optic detector in the RF frequency region may be envisaged.

  7. On the thermally-induced residual stresses in thick fiber-thermoplastic matrix (PEEK) cross-ply laminated plates

    NASA Technical Reports Server (NTRS)

    Hu, Shoufeng; Nairn, John A.

    1992-01-01

    An analytical method for calculating thermally-induced residual stresses in laminated plates is applied to cross-ply PEEK laminates. We considered three cooling procedures: slow cooling (uniform temperature distribution); convective and radiative cooling; and rapid cooling by quenching (constant surface temperature). Some of the calculated stresses are of sufficient magnitude to effect failure properties such as matrix microcracking.

  8. On the thermally-induced residual stresses in thick fiber-thermoplastic matrix (PEEK) cross-ply laminated plates

    SciTech Connect

    Hu, S.; Nairn, J.A.

    1992-09-01

    An analytical method for calculating thermally-induced residual stresses in laminated plates is applied to cross-ply PEEK laminates. The authors considered three cooling procedures: slow cooling (uniform temperature distribution); convective and radiative cooling; and rapid cooling by quenching (constant surface temperature). Some of the calculated stresses are of sufficient magnitude to effect failure properties such as matrix microcracking.

  9. Learning to be different: Acquired skills, social learning, frequency dependence, and environmental variation can cause behaviourally mediated foraging specializations

    USGS Publications Warehouse

    Tinker, M.T.; Mangel, M.; Estes, J.A.

    2009-01-01

    ) Offspring can learn foraging skills from their mothers (matrilineal social learning). (6) Food abundance is limited, such that average individual energy reserves are low Additionally, the following factors increase the likelihood of alternative specializations co-occurring in a predator population: (1) The predator exerts effective top-down control of prey abundance, resulting in frequency-dependent dynamics. (2) There is stochastic Variation in prey population dynamics, but this Variation is neither too extreme in magnitude nor too 'slow' with respect to the time required for an individual forager to learn new foraging skills. For a given predator population, we deduce that the degree of specialization will be highest for those prey types requiring complex capture or handling skills, while prey species that are both profitable and easy to capture and handle will be included in the diet of all individuals. Frequency-dependent benefits of selecting alternative prey types, combined with the ability of foragers to improve their foraging skills by learning, and transmit learned skills to offspring, can result in behaviourally mediated foraging specialization, and also lead to the co-existence of alternative specializations. The extent of such specialization is predicted to be a variable trait, increasing in locations or years when intra-specific competition is high relative to inter-specific competition. ?? 2009 M. Tim Tinker.

  10. Use of frequency-dependent multi-offset phase analysis of surface waves for a riparian zone characterization

    NASA Astrophysics Data System (ADS)

    Vignoli, Giulio; Gervasio, Isabella; Brancatelli, Giuseppe; Boaga, Jacopo; Della Vedova, Bruno; Cassiani, Giorgio

    2015-04-01

    Multi-offset phase analysis (MOPA) of seismic surface waves has been developed as an alternative technique for the lateral variation sensitive extraction of dispersion curves. One of the goals of MOPA is to increase the lateral resolution with respect of the more traditional surface wave methods, and, consequently, to allow a more detailed investigation of the subsurface in terms of 2D shear wave velocity distribution. However, in the published literature, there are still few examples of field applications of this promising technique. The standard MOPA makes possible to calculate, frequency-by-frequency, the derivative of the phase (retrieved by the seismogram) with respect to offset and, by doing that, to extract the information concerning the Rayleigh wave velocity as a function of frequency (i.e., the dispersion curve) with a lateral resolution that depends on the length of the window used to calculate the derivative. Here, we describe a novel MOPA implementation characterized by a moving window with a frequency-dependent width. The window's length is in fact chosen to be smaller for higher frequencies (investigating the shallower layers) and increasingly larger at lower frequencies (where the longer wavelengths supply information about the deeper formations). This approach is clearly in accordance with the physics of the method (the smaller footprint of the shorter wavelengths provides spatially detailed information, while larger wavelengths inevitably average, to some degree, the soil spatial variations). Hence, this frequency-dependent MOPA maximizes the lateral resolution at high frequencies, while assuring stability at the lower frequencies. In this way, we can retrieve the shallow lateral variability with high accuracy and, and the same time, obtain a robust surface wave velocity measurement at depth. The extracted dispersion curves (one for each receiver location) can be then inverted providing an S-wave velocity section. Here we discuss the application

  11. Calmodulin regulates current density and frequency-dependent inhibition of sodium channel Nav1.8 in DRG neurons.

    PubMed

    Choi, Jin-Sung; Hudmon, Andy; Waxman, Stephen G; Dib-Hajj, Sulayman D

    2006-07-01

    Sodium channel Nav1.8 produces a slowly inactivating, tetrodotoxin-resistant current, characterized by recovery from inactivation with fast and slow components, and contributes a substantial fraction of the current underlying the depolarizing phase of the action potential of dorsal root ganglion (DRG) neurons. Nav1.8 C-terminus carries a conserved calmodulin-binding isoleucine-glutamine (IQ) motif. We show here that calmodulin coimmunoprecipitates with endogenous Nav1.8 channels from native DRG, suggesting that the two proteins can interact in vivo. Treatment of native DRG neurons with a calmodulin-binding peptide (CBP) reduced the current density of Nav1.8 by nearly 65%, without changing voltage dependency of activation or steady-state inactivation. To investigate the functional role of CaM binding to the IQ motif in the Nav1.8 C-terminus, the IQ dipeptide was substituted by DE; we show that this impairs the binding of CaM to the IQ motif. Mutant Nav1.8IQ/DE channels produce currents with roughly 50% amplitude, but with unchanged voltage dependency of activation and inactivation when expressed in DRG neurons from Nav1.8-null mice. We also show that blocking the interaction of CaM and Nav1.8 using CBP or the IQ/DE substitution causes a buildup of inactivated channels and, in the case of the IQ/DE mutation, stimulation even at a low frequency of 0.1 Hz significantly enhances the frequency-dependent inhibition of the Nav1.8 current. This study presents, for the first time, evidence that calmodulin associates with a sodium channel, Nav1.8, in native neurons, and demonstrates a regulation of Nav1.8 currents that can significantly affect electrogenesis of DRG neurons in which Nav1.8 is normally expressed. PMID:16598065

  12. The frequency dependence and locations of short-period microseisms generated in the Southern Ocean and West Pacific

    NASA Astrophysics Data System (ADS)

    Gal, M.; Reading, A. M.; Ellingsen, S. P.; Gualtieri, L.; Koper, K. D.; Burlacu, R.; Tkalčić, H.; Hemer, M. A.

    2015-08-01

    The origin of the microseismic wavefield is associated with deep ocean and coastal regions where, under certain conditions, ocean waves can excite seismic waves that propagate as surface and body waves. Given that the characteristics of seismic signals generally vary with frequency, here we explore the frequency- and azimuth-dependent properties of microseisms recorded at a medium aperture (25 km) array in Australia. We examine the frequency-dependent properties of the wavefield, and its temporal variation, over two decades (1991-2012), with a focus on relatively high-frequency microseisms (0.325-0.725 Hz) recorded at the Warramunga Array, which has good slowness resolution capabilities in this frequency range. The analysis is carried out using the incoherently averaged signal Capon beamforming, which gives robust estimates of slowness and back azimuth and is able to resolve multiple wave arrivals within a single time window. For surface waves, we find that fundamental mode Rayleigh waves (Rg) dominate for lower frequencies (<0.55 Hz) while higher frequencies (>0.55 Hz) show a transition to higher mode surface waves (Lg). For body waves, source locations are identified in deep ocean regions for lower frequencies and in shallow waters for higher frequencies. We further examine the association between surface wave arrivals and a WAVEWATCH III ocean wave hindcast. Correlations with the ocean wave hindcast show that secondary microseisms in the lower-frequency band are generated mainly by ocean swell, while higher-frequency bands are generated by the wind sea, i.e., local wind conditions.

  13. Frequency-dependent interference by magnetic fields of nerve growth factor-induced neurite outgrowth in PC-12 cells

    SciTech Connect

    Blackman, C.F.; Benane, S.G.; House, D.E.

    1995-12-31

    The authors have shown that 50 Hz sinusoidal magnetic fields within the 5--10 microTesla ({micro}T) rms range cause an intensity-dependent reduction in nerve growth factor (NGF) stimulation of neurite outgrowth (NO) in PC12- cells. Here they report on the frequency dependence of this response over the 15--70 Hz range at 5 Hz intervals. Primed PC-12 cells were plated in collagen-coated, 60 mm plastic petri dishes with or without 5 ng/ml NGF and were exposed to sinusoidal magnetic fields for 22 h in a CO{sub 2} incubator at 37 C. One 1,000-turn coil, 20 cm in diameter, generated vertically oriented magnetic fields. The dishes were stacked on the center axis of the coil to provide a range of intensities between 3.5 and 9.0 {micro}T rms. The flux density of the ambient DC magnetic field was 37 {micro}T vertical and 29 {micro}T horizontal. The assay consisted of counting over 100 cells in the central portion (radius {le}0.3 cm) of each dish and scoring cells positive for NO. Sham exposure of cells treated identically with NGF demonstrated no difference in the percentage of cells with NO between exposed and magnetically shielded locations within the incubator. Analysis of variance demonstrated flux density-dependent reductions in NGF-stimulated NO over the 35--70 Hz frequency range, whereas frequencies between 15 Hz and 30 Hz produced no obvious reduction. The results also demonstrated a relative maximal sensitivity of cells at 40 Hz with a possible additional sensitivity region at or above 70 Hz. These findings suggest a biological influence of perpendicular AC/DC magnetic fields different from those identified by the ion parametric resonance model, which uses strictly parallel AC/DC fields.

  14. Complex anisotropy beneath the Peruvian flat slab from frequency-dependent, multiple-phase shear wave splitting analysis

    NASA Astrophysics Data System (ADS)

    Eakin, Caroline M.; Long, Maureen D.

    2013-09-01

    Flat or shallow subduction is a relatively widespread global occurrence, but the dynamics remain poorly understood. In particular, the interaction between flat slabs and the surrounding mantle flow has yet to be studied in detail. Here we present measurements of seismic anisotropy to investigate mantle flow beneath the Peruvian flat-slab segment, the largest present-day region of flat subduction. We conduct a detailed shear wave splitting analysis at a long-running seismic station (NNA) located near Lima, Peru. We present measurements of apparent splitting parameters (fast direction φ and delay time δt) for SKS, ScS, and local S phases from 80 events. We observe well-defined frequency dependence and backazimuthal variability, indicating the likely presence of complex anisotropy. Forward modeling the observations with two or three layers of anisotropy reveals a likely layer with a trench-normal fast direction underlying a layer with a more trench-oblique (to trench-subparallel) fast direction. In order to further constrain the anisotropic geometry, we analyzed the source-side splitting from events originating within the slab measured at distant stations. Beneath the flat-slab segment, we found trench-normal fast splitting directions in the subslab mantle, while within the dipping portion of the slab further to the east, likely trench-subparallel anisotropy within the slab itself. This subslab pattern contradicts observations from elsewhere in South America for "normal" (i.e., more steeply dipping) slab conditions. It is similar, however, to inferences from other shallowly dipping subduction zones around the world. While there is an apparent link between slab dip and the surrounding mantle flow, at least beneath Peru, the precise nature of the relationship remains to be clarified.

  15. Complex anisotropy beneath the Peruvian flat-slab from frequency-dependent, multiple-phase shear wave splitting analysis

    NASA Astrophysics Data System (ADS)

    Eakin, C. M.; Long, M. D.

    2013-05-01

    Flat or shallow subduction is a relatively widespread global occurrence but the dynamics remain poorly understood. In particular, the interaction between flat-slabs and the surrounding mantle flow has yet to be studied in detail. In this study measurements of seismic anisotropy are utilized to investigate mantle flow beneath the Peruvian flat-slab segment, the largest present-day region of flat-subduction. A detailed shear wave splitting analysis is conducted at a long-running seismic station (NNA) located near Lima, Peru. Measurements of apparent splitting parameters (fast direction φ and delay time δt) for SKS, ScS and local S phases from 86 events were obtained. Well defined frequency dependence and back-azimuthal variability is observed, indicating the likely presence of complex anisotropy. Forward modeling the observations with two or three layers of anisotropy reveals a likely layer with a trench-parallel fast axis overlying a layer(s) with a more trench-normal fast geometry. In order to further constrain the anisotropic geometry, source-side splitting from events originating within the slab measured at distant stations have been analyzed. Beneath the flat-slab segment, trench-normal fast splitting directions in the sub-slab mantle were found and likely trench-parallel anisotropy within the slab itself. This sub-slab pattern contradicts observations from elsewhere in South America for 'normal' (i.e. more steeply dipping) slab conditions. It is similar, however, to inferences from other shallowly dipping subduction zones around the world. While there is an apparent link between slab dip and the surrounding mantle flow, at least beneath Peru, the precise nature of the relationship requires further investigation.

  16. Numerical calculations for effects of structure of skeletal muscle on frequency-dependence of its electrical admittance and impedance

    NASA Astrophysics Data System (ADS)

    Sekine, Katsuhisa; Yamada, Ayumi; Kageyama, Hitomi; Igarashi, Takahiro; Yamamoto, Nana; Asami, Koji

    2015-06-01

    Numerical calculations were carried out by the finite difference method using three-dimensional models to examine effects of the structure of skeletal muscle on the frequency-dependence of its electrical admittance Y and impedance Z in transversal and longitudinal directions. In the models, the muscle cell was represented by a rectangular solid surrounded by a smooth surface membrane, and the cells were assumed to be distributed periodically. The width of the cross section of the cell, thickness of the intercellular medium, and the relative permittivities and the conductivities of the cell interior, the intercellular medium and the surface membrane were changed. Based on the results of the calculations, reported changes in Y and Z of the muscles from 1 kHz to 1 MHz were analyzed. The analyses revealed that a decreased cell radius was reasonable to explain the Y and Z of the muscles of immature rats, rats subjected to sciatic nerve crush at chronic stage and the amyotrophic lateral sclerosis (ALS) mice. Changes in Y and Z due to the sciatic nerve crush at acute stage were attributable to the decreased cell radius, the increased space between the cells, the increased permittivity of the surface membrane and the increased conductivity of the cell interior. The changes in Z due to contraction were explained by the changes in the cell radius, and the conductivities of the cell interior and the intercellular medium. The changes in Z of meat due to aging were compared with the effects of the increase in the conductivity of the surface membrane.

  17. Frequency-dependent streaming potential of porous media: Experimental measurement of Ottawa sand, Lochaline sand and quartz glass beads

    NASA Astrophysics Data System (ADS)

    Glover, Paul; Walker, Emilie; Ruel, Jean; Yagout, Fuad

    2013-04-01

    High quality frequency-dependent streaming potential coefficient measurements have been made upon Ottawa sand, Lochaline sand and glass bead packs using a new apparatus that is based on an electro-magnetic drive. The apparatus operates in the range 1 Hz to 1 kHz with samples of 25.4mm diameter up to 150 mm long. The results have been analysed using theoretical models that are either (i) based upon vibrational mechanics, (ii) treat the geological material as a bundle of capillary tubes, or (iii) treat the material as a porous medium. In each case we have considered the real and imaginary parts of the complex streaming potential coefficient as well as its magnitude. It is clear from the results that the complex streaming potential coefficient does not follow a Debye-type behaviour, differing from the Debye-type behaviour most markedly for frequencies above the transition frequency. The best fit to all the data was provided by the Pride (1994) model and its simplification by Walker and Glover (2010), which is satisfying as this model was conceived for porous media rather than capillary tube bundles. Theory predicts that the transition frequency is related to the inverse square of the effective pore radius. Values for the transition frequency were derived from each of the models for each sample and were found to be in good agreement with those expected from the independently measured effective pore radius of each material. The fit to the Pride model for all four samples was also found to be consistent with the independently measured steady-state permeability, while the value of the streaming potential coefficient in the low-frequency limit was found to be in good agreement with steady-state streaming potential coefficient data measured using a steady-state streaming potential rig as well as the corpus of steady-state determinations for quartz-based samples existing in the literature.

  18. The influence of genetic drift on the formation and stability of polymorphisms arising from negative frequency-dependent selection.

    PubMed

    Zhao, Lei; Waxman, David

    2016-02-21

    We consider the simplest form of negative frequency-dependent selection in a biallelic haploid population, where the selection coefficient of a mutant allele is a linear function of the allele's frequency, and changes from positive to negative as the frequency is increased. In an effectively infinite population this behaviour leads to a stable polymorphism. We present a theoretical investigation of what occurs in a finite population, where a long-lived polymorphism may be formed, but which fluctuates and ultimately disappears due to random genetic drift. We model the dynamics as a branching process and explicitly take into account differences between the census population size and the effective population size, which play different roles in the dynamics. We characterise the behaviour of the population in terms of three distinct timescales associated with: (i) early loss of mutant alleles, (ii) achievement of the long-lived polymorphism, (iii) disappearance of the polymorphism. Timescales (i) and (iii) depend on the effective population size and are, as a consequence, affected by random genetic drift, while timescale (ii) depends primarily on the census size and is relatively insensitive to genetic drift. Analysis and simulations of the branching process clarify the different influences of the census and effective population sizes. One substantial quantitative difference, between populations where the effective and census population sizes coincide and where they differ, lies in the number of mutant alleles in the long-lived polymorphism. This number is approximately proportional to the census size. Thus assuming the census size equals a much smaller effective population size predicts a much smaller number of mutants in the long-lived polymorphism.

  19. Frequency-Dependent Modulation of Regional Synchrony in the Human Brain by Eyes Open and Eyes Closed Resting-States.

    PubMed

    Song, Xiaopeng; Zhou, Shuqin; Zhang, Yi; Liu, Yijun; Zhu, Huaiqiu; Gao, Jia-Hong

    2015-01-01

    The eyes-open (EO) and eyes-closed (EC) states have differential effects on BOLD-fMRI signal dynamics, affecting both the BOLD oscillation frequency of a single voxel and the regional homogeneity (ReHo) of several neighboring voxels. To explore how the two resting-states modulate the local synchrony through different frequency bands, we decomposed the time series of each voxel into several components that fell into distinct frequency bands. The ReHo in each of the bands was calculated and compared between the EO and EC conditions. The cross-voxel correlations between the mean frequency and the overall ReHo of each voxel's original BOLD series in different brain areas were also calculated and compared between the two states. Compared with the EC state, ReHo decreased with EO in a wide frequency band of 0.01-0.25 Hz in the bilateral thalamus, sensorimotor network, and superior temporal gyrus, while ReHo increased significantly in the band of 0-0.01 Hz in the primary visual cortex, and in a higher frequency band of 0.02-0.1 Hz in the higher order visual areas. The cross-voxel correlations between the frequency and overall ReHo were negative in all the brain areas but varied from region to region. These correlations were stronger with EO in the visual network and the default mode network. Our results suggested that different frequency bands of ReHo showed different sensitivity to the modulation of EO-EC states. The better spatial consistency between the frequency and overall ReHo maps indicated that the brain might adopt a stricter frequency-dependent configuration with EO than with EC. PMID:26545233

  20. Frequency-Dependent Modulation of Regional Synchrony in the Human Brain by Eyes Open and Eyes Closed Resting-States

    PubMed Central

    Song, Xiaopeng; Zhou, Shuqin; Zhang, Yi; Liu, Yijun; Zhu, Huaiqiu; Gao, Jia-Hong

    2015-01-01

    The eyes-open (EO) and eyes-closed (EC) states have differential effects on BOLD-fMRI signal dynamics, affecting both the BOLD oscillation frequency of a single voxel and the regional homogeneity (ReHo) of several neighboring voxels. To explore how the two resting-states modulate the local synchrony through different frequency bands, we decomposed the time series of each voxel into several components that fell into distinct frequency bands. The ReHo in each of the bands was calculated and compared between the EO and EC conditions. The cross-voxel correlations between the mean frequency and the overall ReHo of each voxel’s original BOLD series in different brain areas were also calculated and compared between the two states. Compared with the EC state, ReHo decreased with EO in a wide frequency band of 0.01–0.25 Hz in the bilateral thalamus, sensorimotor network, and superior temporal gyrus, while ReHo increased significantly in the band of 0–0.01 Hz in the primary visual cortex, and in a higher frequency band of 0.02–0.1 Hz in the higher order visual areas. The cross-voxel correlations between the frequency and overall ReHo were negative in all the brain areas but varied from region to region. These correlations were stronger with EO in the visual network and the default mode network. Our results suggested that different frequency bands of ReHo showed different sensitivity to the modulation of EO-EC states. The better spatial consistency between the frequency and overall ReHo maps indicated that the brain might adopt a stricter frequency-dependent configuration with EO than with EC. PMID:26545233

  1. Stress

    MedlinePlus

    ... hurt or killed. Examples include a major accident, war, assault, or a natural disaster. This type of ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  2. Intruder localization and identification in fiber optic systems

    NASA Astrophysics Data System (ADS)

    Zyczkowski, M.

    2008-10-01

    The ultimate goal in all fiber optic systems is to extract information about the mechanical perturbations. For example, this information may be the frequency dependent index of perturbation. For security systems we desire to detect and differentiate between different intruders based on the mechanical response. This article shows experimental investigation of ideal intruder classifier. We considered demodulation, denoising, deconvolution and normalisation. We present additionally possible configuration of fiber optic sensor to localizing perturbation place.

  3. Frequency dependence of delayed and instantaneous triggering on laboratory and simulated faults governed by rate-state friction

    NASA Astrophysics Data System (ADS)

    Elst, Nicholas J.; Savage, Heather M.

    2015-05-01

    Earthquake triggering by transient stresses is commonly observed; however, some aspects remain unexplained. The first is the often-observed delay between the triggered earthquakes and the triggering waves, and the second is the unexpected effectiveness of transient stressing in the seismic frequency band. Previous theoretical and laboratory studies have suggested that seismic transients should have little impact on faults if the duration of the transient is smaller than the timescale for nucleation of slip. We reexamine the dynamics of stress triggering during stick-slip sliding on a laboratory fault and make three important observations that pertain to earthquake triggering. (1) Delayed triggering (clock advance) occurs for both bare granite surfaces and granular gouge prior to the onset of instantaneous triggering. (2) Triggering occurs much earlier in the stick-slip cycle than expected for a simple Coulomb stress threshold. (3) Shorter-period (higher stressing rate) pulses are more effective at triggering than longer-period pulses of the same stress amplitude. We use numerical simulations to show that rate-state friction can explain each of the observed features but not all three simultaneously. Only the Ruina slip law for state evolution, in which faults must slip to heal, can reproduce early-onset and stressing rate-dependent triggering. The laboratory and numerical experiments show that faults can remain relatively weak over much of the seismic cycle and that the triggered response depends on a competition between healing and weakening during triggered slip. Transient stressing at seismic frequencies may be more effective at triggering earthquakes than previously recognized.

  4. Lapse time and frequency-dependent attenuation of coda waves in the Zagros continental collision zone in Southwestern Iran

    NASA Astrophysics Data System (ADS)

    Rahimi, H.; Hamzehloo, H.

    2008-06-01

    The coda Q, Qc, were estimated for the Zagros continental collision zone in southwestern Iran by analyzing the coda waves of 51 local earthquakes recorded on the three stations of the Iranian National Seismic Network (INSN) with magnitudes of between 3.1 and 4.9 recorded in the region during March and April 2006. Most of the analyzed events are foreshocks and aftershocks of the Darb-e-Astane earthquake which occurred on 31 March 2006 with a magnitude of 6.1 (IIEES). The earthquakes had an epicentral distance of between 120 and 200 km and a focal depth of about 18 km. The Qc values were computed at nine central frequencies of 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12.0, 16.0 and 20.0 Hz through eight lapse time windows from 25 to 60 s starting at double the time of the primary S-wave from the origin time using the time-domain coda-decay method of a single backscattering model. In this study the collected data were compared between the events that occurred before and after the main event (foreshocks and aftershocks). The analysis showed a significant variation in the value of coda, Q, for the study region in different lapse times and frequencies. The variation of the quality factor, Qc, before and after the main event was estimated at different lapse time windows to observe its effect with depth. The estimated average frequency-dependent relation of Qc for foreshocks varies from Qc = (144 ± 24)f(0.42 ± 0.23) at 25 s to Qc = (85 ± 10)f(0.92 ± 0.11) at 60 s lapse window time length, respectively. For aftershocks, it varies from Qc = (121 ± 55)f(0.97 ± 0.26) at 25 s to Qc = (212 ± 59)f(0.82 ± 0.15) at 60 s. The averages of Qc in all stations and lapse times window are obtained as Qc = 99f0.84 and Qc = 178f0.86 for foreshocks and aftershocks, respectively. The Q frequency relationship for foreshocks is similar to that for the South Carolina, Koyna, western Anatolia and Aleutian earthquakes, whereas for aftershocks it is similar to the Kumaun, NW Himalaya and Parkfield

  5. Lifetime-applied stress response in air of a SiC-based Nicalon-fiber-reinforced composite with a carbon interfacial layer: Effects of temperature (300 to 1150 C)

    SciTech Connect

    Becher, P.F.; Lin, Hua-Tay; More, K.L.

    1998-07-01

    The lifetimes in air as a function of applied flexure stress and temperature (300--1,150 C) are described for a Si-O-C based (Nicalon) fiber plain-weave cloth reinforced SiC-matrix composite ({approximately}7% closed porosity) with an {approximately}0.3 {micro}m thick carbon interfacial layer. The measured lifetimes of both samples with and without an external SiC seal coating were similar and decreased with applied flexural stress (for stresses greater than {approximately}90 MPa) and with temperature. At temperatures of {ge}600 C, the external CVD SiC coating had negligible effect on the lifetimes; however, at 425 C, a detectable improvement in the lifetime was observed with an external SiC coating. When the applied stress was decreased below an apparent threshold stress (e.g., {approximately}90 MPa) for tests conducted at temperatures {le}950 C, no failures were observed for times of {ge}1,000 H. Electron microscopy observations show that the interfacial carbon layer is progressively removed during tests at 425 and 600 C. In these cases, failure is associated with fiber failure and pull-out. At 950 and 1,150 C, the carbon interface layer is eliminated and replaced by a thick silica layer due to the oxidation of the Nicalon fiber and the SiC matrix. This results in embrittling the composite.

  6. A dynamic model of the frequency-dependent rupture process of the 2011 Tohoku-Oki earthquake

    NASA Astrophysics Data System (ADS)

    Huang, Yihe; Meng, Lingsen; Ampuero, Jean-Paul

    2012-12-01

    We present a 2D dynamic rupture model that provides a physical interpretation of the key features of the 2011 Tohoku-Oki earthquake rupture. This minimalistic model assumes linear slip-weakening friction, the presence of deep asperities and depth-dependent initial stresses. It reproduces the first-order observations of the along-dip rupture process during its initial 100 s, such as large static slip and low-frequency radiation up-dip from the hypocenter, and slow rupture punctuated by high-frequency radiation in deeper regions. We also derive quantitative constraints on the ratio of shallow versus deep radiation from teleseismic back-projection source imaging. This ratio is explained in our model by the rupture of deep asperities surrounded by low stress drop regions, and by the decrease of initial stresses towards the trench.

  7. Stress distribution on dentin-cement-post interface varying root canal and glass fiber post diameters. A three-dimensional finite element analysis based on micro-CT data

    PubMed Central

    LAZARI, Priscilla Cardoso; de OLIVEIRA, Rodrigo Caldeira Nunes; ANCHIETA, Rodolfo Bruniera; de ALMEIDA, Erika Oliveira; FREITAS JUNIOR, Amilcar Chagas; KINA, Sidney; ROCHA, Eduardo Passos

    2013-01-01

    Objective The aim of the present study was to analyze the influence of root canal and glass fiber post diameters on the biomechanical behavior of the dentin/cement/post interface of a root-filled tooth using 3D finite element analysis. Material and Methods Six models were built using micro-CT imaging data and SolidWorks 2007 software, varying the root canal (C) and the glass fiber post (P) diameters: C1P1-C=1 mm and P=1 mm; C2P1-C=2 mm and P=1 mm; C2P2-C=2 mm and P=2 mm; C3P1-C=3 mm and P=1 mm; C3P2-C=3 mm and P=2 mm; and C3P3-C=3 mm and P=3 mm. The numerical analysis was conducted with ANSYS Workbench 10.0. An oblique force (180 N at 45º) was applied to the palatal surface of the central incisor. The periodontal ligament surface was constrained on the three axes (x=y=z=0). Maximum principal stress (σmax) values were evaluated for the root dentin, cement layer, and glass fiber post. Results: The most evident stress was observed in the glass fiber post at C3P1 (323 MPa), and the maximum stress in the cement layer occurred at C1P1 (43.2 MPa). The stress on the root dentin was almost constant in all models with a peak in tension at C2P1 (64.5 MPa). Conclusion The greatest discrepancy between root canal and post diameters is favorable for stress concentration at the post surface. The dentin remaining after the various root canal preparations did not increase the stress levels on the root. PMID:24473716

  8. The optimal fiber volume fraction and fiber-matrix property compatibility in fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Pan, Ning

    1992-01-01

    Although the question of minimum or critical fiber volume fraction beyond which a composite can then be strengthened due to addition of fibers has been dealt with by several investigators for both continuous and short fiber composites, a study of maximum or optimal fiber volume fraction at which the composite reaches its highest strength has not been reported yet. The present analysis has investigated this issue for short fiber case based on the well-known shear lag (the elastic stress transfer) theory as the first step. Using the relationships obtained, the minimum spacing between fibers is determined upon which the maximum fiber volume fraction can be calculated, depending on the fiber packing forms within the composites. The effects on the value of this maximum fiber volume fraction due to such factors as fiber and matrix properties, fiber aspect ratio and fiber packing forms are discussed. Furthermore, combined with the previous analysis on the minimum fiber volume fraction, this maximum fiber volume fraction can be used to examine the property compatibility of fiber and matrix in forming a composite. This is deemed to be useful for composite design. Finally some examples are provided to illustrate the results.

  9. In vivo monitoring of oxidative burst on aloe under salinity stress using hemoglobin and single-walled carbon nanotubes modified carbon fiber ultramicroelectrode.

    PubMed

    Ren, Qiong-Qiong; Yuan, Xiao-Jun; Huang, Xiao-Rong; Wen, Wei; Zhao, Yuan-Di; Chen, Wei

    2013-12-15

    Single-walled carbon nanotubes (SWCNTs) and hemoglobin (Hb) modified carbon fiber ultramicroelectrode (CFUME) were employed to construct a direct electron transfer based in vivo H2O2 sensor. At the low working potential of -0.1 V, Hb/SWCNTs/CFUME showed a dynamic range up to 0.405 mM with a low detection limit of 4 μM (S/N=3) and a high sensitivity of 1.07 log(A) log(M)(-1) cm(-2). The apparent Michaelis-Menten constant (Km, app) was estimated to be as low as 1.35 mM. Due to the extremely small dimension and low working potential, Hb/SWCNTs/CFUME could give directly amperometric in vivo monitoring of H2O2 in aloe leaves with salt stress for 19.5h without the requirement of complex data processing and extra surface coatings to avoid interferences. The sharp increase of H2O2 level in aloe leaves with salt stress was clearly observed using Hb/SWCNTs/CFUME from 12.5 h, while in the aloe without salt stress, H2O2 level remained stable in the whole measurement. For further confirming the in vivo response of Hb/SWCNTs/CFUME, catalase (CAT) was injected into the spot adjacent to the sensor and caused rapid current decrease, which suggests the scavenging of H2O2. These results indicate that Hb/SWCNTs/CFUME can be a powerful tool for in vivo investigation of ROS.

  10. Safety, Tolerance, and Enhanced Efficacy of a Bioavailable Formulation of Curcumin With Fenugreek Dietary Fiber on Occupational Stress: A Randomized, Double-Blind, Placebo-Controlled Pilot Study.

    PubMed

    Pandaran Sudheeran, Subash; Jacob, Della; Natinga Mulakal, Johannah; Gopinathan Nair, Gopakumar; Maliakel, Abhilash; Maliakel, Balu; Kuttan, Ramadasan; Im, Krishnakumar

    2016-06-01

    Drug delivery systems capable of delivering free (unconjugated) curcuminoids is of great therapeutic significance, since the absorption of bioactive and permeable form plays a key factor in mediating the efficacy of a substance which undergoes rapid biotransformation. Considering the recent understanding on the relatively high bioactivities and blood-brain-barrier permeability of free curcuminoids over their conjugated metabolites, the present human study investigated the safety, antioxidant efficacy, and bioavailability of CurQfen (curcumagalactomannoside [CGM]), a food-grade formulation of natural curcumin with fenugreek dietary fiber that has shown to possess improved blood-brain-barrier permeability and tissue distribution in rats. In this randomized double-blinded and placebo-controlled trial, 60 subjects experiencing occupational stress-related anxiety and fatigue were randomized to receive CGM, standard curcumin, and placebo for 30 days (500 mg twice daily). The study demonstrated the safety, tolerance, and enhanced efficacy of CGM in comparison with unformulated standard curcumin. A significant improvement in the quality of life (P < 0.05) with considerable reduction in stress (P < 0.001), anxiety (P < 0.001), and fatigue (P < 0.001) was observed among CGM-treated subjects as compared with the standard curcumin group, when monitored by SF-36, Perceived Stress Scale with 14 items, and Beck Anxiety Inventory scores. Improvement in the quality of life was further correlated with the significant enhancement in endogenous antioxidant markers (P < 0.01) and reduction in lipid peroxidation (P < 0.001). Further comparison of the free curcuminoids bioavailability after a single-dose (500 mg once per day) and repeated-dose (500 mg twice daily for 30 days) oral administration revealed enhanced absorption and improved pharmacokinetics of CGM upon both single- (30.7-fold) and repeated-dose (39.1-fold) administrations. PMID:27043120

  11. Estimation of the frequency-dependent site amplification factors of Japan based on the coda normalization method

    NASA Astrophysics Data System (ADS)

    Takemoto, T.; Furumura, T.; Saito, T.; Maeda, T.; Noguchi, S.

    2011-12-01

    We estimated the frequency dependent properties of the site amplification factors at each station of the K-NET and KiK-net strong motion network across Japan based on the coda normalization method. Using a large number of waveform data of 3,004 acceleration record from 48 earthquakes and waveform record from 1800 strong motion stations, we estimated the site amplification factors at each frequency band from f=0.5-1 Hz, 1-2 Hz, 2-4 Hz, to 4-8 Hz. In this study we assumed a rock-site station (Tashiro at Kyushu) as a reference of the site amplification estimates. The estimated site amplification factors show strong variations in the low frequency band (0.5-1 Hz) as compare with that of the high frequency band (4-8 Hz). Large site amplification factor in the low-frequency band is found in major populated cities such as Tokyo, Osaka, and Nagoya with varying amplification factors between 10 to 20 dB relative to the reference rock-site station. Such distribution of the site amplification factors in the low-frequency (0.5-1 Hz) band is in good corresponding to the depth distribution of a basement rocks with S-wave speed greater than 2.9 km/s. On the other hand the site-amplification factors in high-frequency (4-8 Hz) band are rather small (5 to 10 dB) as compared with that of the low-frequency band and spatial distribution is almost randomly distributed irrespective to surface geology. In order to examine the reliability of our estimates of the site amplification factors based on the coda-normalization method and to examine how the site amplification modify the distribution of seismic intensity distributions for large earthquakes, we reproduced intensity distributions of recent Japanese M7 earthquakes such as the 2004 Niigata Chuetsu (M6.8), the 2005 Western Fukuoka (M7.0), and the 2008 Coast of Iwate (M6.8) earthquakes by removing the site amplification factors of each frequency band from the acceleration waveform record at each K-NET and the KiK-net station. The site

  12. Information content in frequency-dependent, multi-offset GPR data for layered media reconstruction using full-wave inversion

    NASA Astrophysics Data System (ADS)

    De Coster, Albéric; Phuong Tran, Anh; Lambot, Sébastien

    2014-05-01

    Water lost through leaks can represent high percentages of the total production in water supply systems and constitutes an important issue. Leak detection can be tackled with various techniques such as the ground-penetrating radar (GPR). Based on this technology, various procedures have been elaborated to characterize a leak and its evolution. In this study, we focus on a new full-wave radar modelling approach for near-field conditions, which takes into account the antenna effects as well as the interactions between the antenna(s) and the medium through frequency-dependent global transmission and reflection coefficients. This approach is applied to layered media for which 3-D Green's functions can be calculated. The model allows for a quantitative estimation of the properties of multilayered media by using full-wave inversion. This method, however, proves to be limited to provide users with an on-demand assessment as it is generally computationally demanding and time consuming, depending on the medium configuration as well as the number of unknown parameters to retrieve. In that respect, we propose two leads in order to enhance the parameter retrieval step. The first one consists in analyzing the impact of the reduction of the number of frequencies on the information content. For both numerical and laboratory experiments, this operation has been achieved by investigating the response surface topography of objective functions arising from the comparison between measured and modelled data. The second one involves the numerical implementation of multistatic antenna configurations with constant and variable offsets in the model. These two kinds of analyses are then combined in numerical experiments to observe the conjugated effect of the number of frequencies and the offset configuration. To perform the numerical analyses, synthetic Green's functions were simulated for different multilayered medium configurations. The results show that an antenna offset increase leads

  13. Biomechanical analysis of a new carbon fiber/flax/epoxy bone fracture plate shows less stress shielding compared to a standard clinical metal plate.

    PubMed

    Bagheri, Zahra S; Tavakkoli Avval, Pouria; Bougherara, Habiba; Aziz, Mina S R; Schemitsch, Emil H; Zdero, Radovan

    2014-09-01

    Femur fracture at the tip of a total hip replacement (THR), commonly known as Vancouver B1 fracture, is mainly treated using rigid metallic bone plates which may result in "stress shielding" leading to bone resorption and implant loosening. To minimize stress shielding, a new carbon fiber (CF)/Flax/Epoxy composite plate has been developed and biomechanically compared to a standard clinical metal plate. For fatigue tests, experiments were done using six artificial femurs cyclically loaded through the femoral head in axial compression for four stages: Stage 1 (intact), stage 2 (after THR insertion), stage 3 (after plate fixation of a simulated Vancouver B1 femoral midshaft fracture gap), and stage 4 (after fracture gap healing). For fracture fixation, one group was fitted with the new CF/Flax/Epoxy plate (n = 3), whereas another group was repaired with a standard clinical metal plate (Zimmer, Warsaw, IN) (n = 3). In addition to axial stiffness measurements, infrared thermography technique was used to capture the femur and plate surface stresses during the testing. Moreover, finite element analysis (FEA) was performed to evaluate the composite plate's axial stiffness and surface stress field. Experimental results showed that the CF/Flax/Epoxy plated femur had comparable axial stiffness (fractured = 645 ± 67 N/mm; healed = 1731 ± 109 N/mm) to the metal-plated femur (fractured = 658 ± 69 N/mm; healed = 1751 ± 39 N/mm) (p = 1.00). However, the bone beneath the CF/Flax/Epoxy plate was the only area that had a significantly higher average surface stress (fractured = 2.10 ± 0.66 MPa; healed = 1.89 ± 0.39 MPa) compared to bone beneath the metal plate (fractured = 1.18 ± 0.93 MPa; healed = 0.71 ± 0.24 MPa) (p < 0.05). FEA bone surface stresses yielded peak of 13 MPa at distal epiphysis (stage 1), 16 MPa at distal epiphysis (stage 2), 85 MPa for composite and 129

  14. Biomechanical analysis of a new carbon fiber/flax/epoxy bone fracture plate shows less stress shielding compared to a standard clinical metal plate.

    PubMed

    Bagheri, Zahra S; Tavakkoli Avval, Pouria; Bougherara, Habiba; Aziz, Mina S R; Schemitsch, Emil H; Zdero, Radovan

    2014-09-01

    Femur fracture at the tip of a total hip replacement (THR), commonly known as Vancouver B1 fracture, is mainly treated using rigid metallic bone plates which may result in "stress shielding" leading to bone resorption and implant loosening. To minimize stress shielding, a new carbon fiber (CF)/Flax/Epoxy composite plate has been developed and biomechanically compared to a standard clinical metal plate. For fatigue tests, experiments were done using six artificial femurs cyclically loaded through the femoral head in axial compression for four stages: Stage 1 (intact), stage 2 (after THR insertion), stage 3 (after plate fixation of a simulated Vancouver B1 femoral midshaft fracture gap), and stage 4 (after fracture gap healing). For fracture fixation, one group was fitted with the new CF/Flax/Epoxy plate (n = 3), whereas another group was repaired with a standard clinical metal plate (Zimmer, Warsaw, IN) (n = 3). In addition to axial stiffness measurements, infrared thermography technique was used to capture the femur and plate surface stresses during the testing. Moreover, finite element analysis (FEA) was performed to evaluate the composite plate's axial stiffness and surface stress field. Experimental results showed that the CF/Flax/Epoxy plated femur had comparable axial stiffness (fractured = 645 ± 67 N/mm; healed = 1731 ± 109 N/mm) to the metal-plated femur (fractured = 658 ± 69 N/mm; healed = 1751 ± 39 N/mm) (p = 1.00). However, the bone beneath the CF/Flax/Epoxy plate was the only area that had a significantly higher average surface stress (fractured = 2.10 ± 0.66 MPa; healed = 1.89 ± 0.39 MPa) compared to bone beneath the metal plate (fractured = 1.18 ± 0.93 MPa; healed = 0.71 ± 0.24 MPa) (p < 0.05). FEA bone surface stresses yielded peak of 13 MPa at distal epiphysis (stage 1), 16 MPa at distal epiphysis (stage 2), 85 MPa for composite and 129

  15. Semi-analytical solution to the frequency-dependent Boltzmann transport equation for cross-plane heat conduction in thin films

    SciTech Connect

    Hua, Chengyun; Minnich, Austin J.

    2015-05-07

    Cross-plane heat transport in thin films with thicknesses comparable to the phonon mean free paths is of both fundamental and practical interest for applications such as light-emitting diodes and quantum well lasers. However, physical insight is difficult to obtain for the cross-plane geometry due to the challenge of solving the Boltzmann equation in a finite domain. Here, we present a semi-analytical series expansion method to solve the transient, frequency-dependent Boltzmann transport equation that is valid from the diffusive to ballistic transport regimes and rigorously includes the frequency-dependence of phonon properties. Further, our method is more than three orders of magnitude faster than prior numerical methods and provides a simple analytical expression for the thermal conductivity as a function of film thickness. Our result enables a straightforward physical understanding of cross-plane heat conduction in thin films.

  16. Implementation of the CCSD-PCM linear response function for frequency dependent properties in solution: Application to polarizability and specific rotation

    NASA Astrophysics Data System (ADS)

    Caricato, Marco

    2013-09-01

    This work reports the first implementation of the frequency dependent linear response (LR) function for the coupled cluster singles and doubles method (CCSD) combined with the polarizable continuum model of solvation for the calculation of frequency dependent properties in solution. In particular, values of static and dynamic polarizability as well as specific rotation are presented for various test molecules. Model calculations of polarizability show that a common approximation used in the definition of the LR function with solvation models recovers over 70% of the full response while maintaining a computational cost comparable to gas phase LR-CCSD. Calculations of specific rotation for three compounds for which gas phase methods predict the wrong sign of the rotation show that accounting for the electronic response of the solvent may be essential to assign the correct absolute configuration of chiral molecules.

  17. Simultaneous measurement of thermal conductivity and heat capacity of bulk and thin film materials using frequency-dependent transient thermoreflectance method.

    PubMed

    Liu, Jun; Zhu, Jie; Tian, Miao; Gu, Xiaokun; Schmidt, Aaron; Yang, Ronggui

    2013-03-01

    The increasing interest in the extraordinary thermal properties of nanostructures has led to the development of various measurement techniques. Transient thermoreflectance method has emerged as a reliable measurement technique for thermal conductivity of thin films. In this method, the determination of thermal conductivity usually relies much on the accuracy of heat capacity input. For new nanoscale materials with unknown or less-understood thermal properties, it is either questionable to assume bulk heat capacity for nanostructures or difficult to obtain the bulk form of those materials for a conventional heat capacity measurement. In this paper, we describe a technique for simultaneous measurement of thermal conductivity κ and volumetric heat capacity C of both bulk and thin film materials using frequency-dependent time-domain thermoreflectance (TDTR) signals. The heat transfer model is analyzed first to find how different combinations of κ and C determine the frequency-dependent TDTR signals. Simultaneous measurement of thermal conductivity and volumetric heat capacity is then demonstrated with bulk Si and thin film SiO2 samples using frequency-dependent TDTR measurement. This method is further testified by measuring both thermal conductivity and volumetric heat capacity of novel hybrid organic-inorganic thin films fabricated using the atomic∕molecular layer deposition. Simultaneous measurement of thermal conductivity and heat capacity can significantly shorten the development∕discovery cycle of novel materials.

  18. Simultaneous measurement of thermal conductivity and heat capacity of bulk and thin film materials using frequency-dependent transient thermoreflectance method

    NASA Astrophysics Data System (ADS)

    Liu, Jun; Zhu, Jie; Tian, Miao; Gu, Xiaokun; Schmidt, Aaron; Yang, Ronggui

    2013-03-01

    The increasing interest in the extraordinary thermal properties of nanostructures has led to the development of various measurement techniques. Transient thermoreflectance method has emerged as a reliable measurement technique for thermal conductivity of thin films. In this method, the determination of thermal conductivity usually relies much on the accuracy of heat capacity input. For new nanoscale materials with unknown or less-understood thermal properties, it is either questionable to assume bulk heat capacity for nanostructures or difficult to obtain the bulk form of those materials for a conventional heat capacity measurement. In this paper, we describe a technique for simultaneous measurement of thermal conductivity κ and volumetric heat capacity C of both bulk and thin film materials using frequency-dependent time-domain thermoreflectance (TDTR) signals. The heat transfer model is analyzed first to find how different combinations of κ and C determine the frequency-dependent TDTR signals. Simultaneous measurement of thermal conductivity and volumetric heat capacity is then demonstrated with bulk Si and thin film SiO2 samples using frequency-dependent TDTR measurement. This method is further testified by measuring both thermal conductivity and volumetric heat capacity of novel hybrid organic-inorganic thin films fabricated using the atomic/molecular layer deposition. Simultaneous measurement of thermal conductivity and heat capacity can significantly shorten the development/discovery cycle of novel materials.

  19. The relation between temperature distribution for lung RFA and electromagnetic wave frequency dependence of electrical conductivity with changing a lung's internal air volumes.

    PubMed

    Yamazaki, Nozomu; Watanabe, Hiroki; Lu, Xiaowei; Isobe, Yosuke; Kobayashi, Yo; Miyashita, Tomoyuki; Fujie, Masakatsu G

    2013-01-01

    Radio frequency ablation (RFA) for lung cancer has increasingly been used over the past few years because it is a minimally invasive treatment. As a feature of RFA for lung cancer, lung contains air during operation. Air is low thermal and electrical conductivity. Therefore, RFA for this cancer has the advantage that only the cancer is coagulated, and it is difficult for operators to control the precise formation of coagulation lesion. In order to overcome this limitation, we previously proposed a model-based robotic ablation system using finite element method. Creating an accurate thermo physical model and constructing thermal control method were a challenging problem because the thermal properties of the organ are complex. In this study, we measured electromagnetic wave frequency dependence of lung's electrical conductivity that was based on lung's internal air volumes dependence with in vitro experiment. In addition, we validated the electromagnetic wave frequency dependence of lung's electrical conductivity using temperature distribution simulator. From the results of this study, it is confirmed that the electromagnetic wave frequency dependence of lung's electrical conductivity effects on heat generation of RFA.

  20. The Drosophila FHOD1-like formin Knittrig acts through Rok to promote stress fiber formation and directed macrophage migration during the cellular immune response.

    PubMed

    Lammel, Uwe; Bechtold, Meike; Risse, Benjamin; Berh, Dimitri; Fleige, Astrid; Bunse, Ingrid; Jiang, Xiaoyi; Klämbt, Christian; Bogdan, Sven

    2014-03-01

    A tight spatiotemporal control of actin polymerization is important for many cellular processes that shape cells into a multicellular organism. The formation of unbranched F-actin is induced by several members of the formin family. Drosophila encodes six formin genes, representing six of the seven known mammalian subclasses. Knittrig, the Drosophila homolog of mammalian FHOD1, is specifically expressed in the developing central nervous system midline glia, the trachea, the wing and in macrophages. knittrig mutants exhibit mild tracheal defects but survive until late pupal stages and mainly die as pharate adult flies. knittrig mutant macrophages are smaller and show reduced cell spreading and cell migration in in vivo wounding experiments. Rescue experiments further demonstrate a cell-autonomous function of Knittrig in regulating actin dynamics and cell migration. Knittrig localizes at the rear of migrating macrophages in vivo, suggesting a cellular requirement of Knittrig in the retraction of the trailing edge. Supporting this notion, we found that Knittrig is a target of the Rho-dependent kinase Rok. Co-expression with Rok or expression of an activated form of Knittrig induces actin stress fibers in macrophages and in epithelial tissues. Thus, we propose a model in which Rok-induced phosphorylation of residues within the basic region mediates the activation of Knittrig in controlling macrophage migration. PMID:24553290

  1. PKCδ Influences p190 Phosphorylation and Activity: Events Independent of PKCδ-Mediated Regulation of Endothelial Cell Stress Fiber and Focal Adhesion Formation and Barrier Function

    PubMed Central

    Fordjour, Akua K.; Harrington, Elizabeth O.

    2009-01-01

    Background We have shown that protein kinase Cδ (PKCδ) inhibition results in increased endothelial cell (EC) permeability and decreased RhoA activity; which correlated with diminished stress fibers (SF) and focal adhesions (FA). We have also shown co-precipitation of p190RhoGAP (p190) with PKCδ. Here, we investigated if PKCδ regulates p190 and whether PKCδ-mediated changes in SF and FA or permeability were dependent upon p190. Methods Protein-protein interaction and activity analyses were performed using co-precipitation assays. Analysis of p190 phosphorylation was performed using in vitro kinase assays. SF and FA were analyzed by immunofluorescence analyses. EC monolayer permeability was measured using electrical cell impedance sensor (ECIS) technique. Results Inhibition of PKCδ increased p190 activity, while PKCδ overexpression diminished p190 activity. PKCδ bound to and phosphorylated both p190FF and p190GTPase domains. p190 protein overexpression diminished SF and FA formation and RhoA activity. Disruption of SF and FA or increased permeability induced upon PKCδ inhibition, were not attenuated in EC in which the p190 isoforms were suppressed individually or concurrently. Conclusion and General Significance Our findings suggest that while PKCδ can regulate p190 activity, possibly at the FF and/ or GTPase domains, the effect of PKCδ inhibition on SF and FA and barrier dysfunction occurs through a pathway independent of p190. PMID:19632305

  2. Some properties of an advanced boron fiber

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1979-01-01

    An advanced coreless boron fiber has exhibited tensile strengths which are more than twice that of the normal CVD B/W fibers. The coreless fiber is made by the chemical removal of the tungsten boride core exposed by splitting the as-grown fiber. The easily splittable fiber is made by the chemical vapor deposition of boron on a larger than usual tungsten substrate. It is expected that the ease of splitting is related to residual stresses in these fibers. Measurements of the axial residual stresses in both the normal and the splittable fibers are presented and the results compared. Differences in these stresses are discussed in connection with the ease of splitting in the splittable fibers.

  3. Dynamic Modulus and Damping of Boron, Silicon Carbide, and Alumina Fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.; Williams, W.

    1980-01-01

    The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide coated boron fibers were measured from-190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamics fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron based fibers are strongly anelastic, displaying frequency dependent moduli and very high microstructural damping. Ths single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

  4. Dynamic modulus and damping of boron, silicon carbide, and alumina fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.; Williams, W.

    1980-01-01

    The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide-coated boron fibers were measured from -190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature-dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamic fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron-based fibers are strongly anelastic, displaying frequency-dependent moduli and very high microstructural damping. The single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

  5. Fiber Sagnac interferometer temperature sensor

    SciTech Connect

    Starodumov, A.N.; Zenteno, L.A.; Monzon, D.; De La Rosa, E.

    1997-01-01

    A modified Sagnac interferometer-based fiber temperature sensor is proposed. Polarization independent operation and high temperature sensitivity of this class of sensors make them cost effective instruments for temperature measurements. A comparison of the proposed sensor with Bragg grating and long-period grating fiber sensors is derived. A temperature-induced spectral displacement of 0.99 nm/K is demonstrated for an internal stress birefringent fiber-based Sagnac interferometer. {copyright} {ital 1997 American Institute of Physics.}

  6. Stiffness of sphere-plate contacts at MHz frequencies: dependence on normal load, oscillation amplitude, and ambient medium.

    PubMed

    Vlachová, Jana; König, Rebekka; Johannsmann, Diethelm

    2015-01-01

    The stiffness of micron-sized sphere-plate contacts was studied by employing high frequency, tangential excitation of variable amplitude (0-20 nm). The contacts were established between glass spheres and the surface of a quartz crystal microbalance (QCM), where the resonator surface had been coated with either sputtered SiO2 or a spin-cast layer of poly(methyl methacrylate) (PMMA). The results from experiments undertaken in the dry state and in water are compared. Building on the shifts in the resonance frequency and resonance bandwidth, the instrument determines the real and the imaginary part of the contact stiffness, where the imaginary part quantifies dissipative processes. The method is closely analogous to related procedures in AFM-based metrology. The real part of the contact stiffness as a function of normal load can be fitted with the Johnson-Kendall-Roberts (JKR) model. The contact stiffness was found to increase in the presence of liquid water. This finding is tentatively explained by the rocking motion of the spheres, which couples to a squeeze flow of the water close to the contact. The loss tangent of the contact stiffness is on the order of 0.1, where the energy losses are associated with interfacial processes. At high amplitudes partial slip was found to occur. The apparent contact stiffness at large amplitude depends linearly on the amplitude, as predicted by the Cattaneo-Mindlin model. This finding is remarkable insofar, as the Cattaneo-Mindlin model assumes Coulomb friction inside the sliding region. Coulomb friction is typically viewed as a macroscopic concept, related to surface roughness. An alternative model (formulated by Savkoor), which assumes a constant frictional stress in the sliding zone independent of the normal pressure, is inconsistent with the experimental data. The apparent friction coefficients slightly increase with normal force, which can be explained by nanoroughness. In other words, contact splitting (i.e., a transport of

  7. Fiber biology

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cotton fiber cells arising from seed epidermis is the most important agricultural textile commodity in the world. To produce fully mature fibers, approximately two months of fiber developmental process are required. The timing of four distinctive fiber development stages consisting of initiation, ...

  8. Capacitively Coupled Resistivity measurements to determine frequency-dependent electrical parameters in periglacial environment—theoretical considerations and first field tests

    NASA Astrophysics Data System (ADS)

    Przyklenk, A.; Hördt, A.; Radić, T.

    2016-08-01

    Capacitively Coupled Resistivity (CCR) is conventionally used to emulate DC resistivity measurements and may provide important information about the ice content of material in periglacial areas. The application of CCR theoretically enables the determination of both electrical parameters, that is, the resistivity and the electrical permittivity, by analysing magnitude and phase shift spectra. The electrical permittivity may dominate the impedance, especially in periglacial areas or regions of hydrogeological interest. However, previous theoretical work suggested that the phase shift may strongly depend on electrode height above ground, implying that electrode height must be known with great accuracy to determine electrical permittivity. Here, we demonstrate with laboratory test measurements, theoretical modelling and by analysing the Jacobian matrix of the inversion that the sensitivity towards electrode height is drastically reduced if the electrical permittivity is frequency dependent in a way that is typical for ice. For the first time, we used a novel broad-band CCR device `Chameleon' for a field test located in one of the ridge galleries beneath the crest of Mount Zugspitze. A permanently ice covered bottom of a tunnel was examined. For the inversion of the measured spectra, the frequency dependence of the electrical parameters was parametrized in three different ways: A Debye Model for pure ices, a Cole-Cole Model for pure ices and a dual Cole-Cole Model including interfacial water additionally. The frequency-dependent resistivity and permittivity spectra obtained from the inversion, including low- and high-frequency limits, agree reasonably well with laboratory and field measurements reported in the literature.

  9. The Frequency-Dependence of the NMR Longitudinal Relaxation Rate, T(1)(-1), of Water in Cysts of the Brine Shrimp

    NASA Astrophysics Data System (ADS)

    Egan, Thomas F.

    The NMR spin-lattice relaxation rate, T(,1)(' -1), of water is independent of the Larmor frequency, (omega)/2(pi), in the normal rf range. However, T(,1)('-1) of intracellular water in biological systems, which accounts for as much as 80% of the cell mass, is frequency-dependent. This indicates that the NMR properties of water in the cellular environment are influenced by long-correlation time processes due to the interaction of water with proteins and other macromolecular constituents of the cell. In this research, the relaxation rate T(,1)(' -1) of water in the Artemia (brine shrimp) cyst is examined as a function of: (1) the proton NMR Larmor frequency for .01 <= (omega)/2(pi) <= 500 MHz, (2) different cyst hydration levels from 0.12 to 1.25 grams water/gram dry solid, (3) temperatures of 22C and 5C. The frequency-dependence of T(,1)('-1) is interpreted in terms of a two-phase exchange model. One water phase is similar to pure water and contributes a small constant relaxation rate. The second phase is water closely associated with the surfaces of large molecules and termed "hydration water". A polymer-dynamics relaxation mechanism, which treats fluctuations of long-chain molecules in aqueous solution, has been proposed by Rorschach and Hazlewood to explain the relaxation in this second water phase. In one limit, this mechanism predicts a frequency-dependent relaxation rate proportional to (omega)('- 1/2). This particular dependence has previously been observed in other NMR studies on biological systems and is also observed in this study for Artemia cysts between 10 and 500 MHz. At lower Larmor frequencies, below 1 MHz, the relaxation rates of water in brine shrimp cysts are influenced by additional relexation mechanisms; translational diffusion of hydration water is one possibility.

  10. Admittance–voltage profiling of Al{sub x}Ga{sub 1−x}N/GaN heterostructures: Frequency dependence of capacitance and conductance

    SciTech Connect

    Köhler, K.; Pletschen, W.; Godejohann, B.; Müller, S.; Menner, H. P.; Ambacher, O.

    2015-11-28

    Admittance–voltage profiling of Al{sub x}Ga{sub 1−x}N/GaN heterostructures was used to determine the frequency dependent capacitance and conductance of FET devices in the frequency range from 50 Hz to 1 MHz. The nominally undoped low pressure metal-organic vapor-phase epitaxy structures were grown with an Al-content of 30%. An additional 1 nm thick AlN interlayer was placed in one structure before the Al{sub 0.3}Ga{sub 0.7}N layer growth. For frequencies below 10{sup 8} Hz it is convenient to use equivalent circuits to represent electric or dielectric properties of a material, a method widely used, for example, in impedance spectroscopy. We want to emphasize the relation between frequency dependent admittance–voltage profiling and the corresponding equivalent circuits to the complex dielectric function. Debye and Drude models are used for the description of the frequency dependent admittance profiles in a range of depletion onset of the two-dimensional electron gas. Capacitance- and conductance-frequency profiles are fitted in the entire measured range by combining both models. Based on our results, we see contributions to the two-dimensional electron gas for our samples from surface states (80%) as well as from background doping in the Al{sub 0.3}Ga{sub 0.7}N barriers (20%). The specific resistance of the layers below the gate is above 10{sup 5} Ω cm for both samples and increases with increasing negative bias, i.e., the layers below the gate are essentially depleted. We propose that the resistance due to free charge carriers, determined by the Drude model, is located between gate and drain and, because of the AlN interlayer, the resistance is lowered by a factor of about 30 if compared to the sample without an AlN layer.

  11. Trap States in Al2O3 InAlN/GaN Metal-Oxide-Semiconductor Structures by Frequency-Dependent Conductance Analysis

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Zhao, Sheng-Lei; Xue, Jun-Shuai; Zhang, Kai; Ma, Xiao-Hua; Zhang, Jin-Cheng; Hao, Yue

    2014-03-01

    We present a detailed analysis of the trap states in atomic layer deposition Al2O3/InAlN/GaN high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. Trap densities, trap energies and time constants are determined by frequency-dependent conductance measurements. A high trap density of up to 1.6 × 1014 cm-2eV-1 is observed, which may be due to the lack of the cap layer causing the vulnerability to the subsequent high temperature annealing process.

  12. [Classification and the composition of food fibers].

    PubMed

    Bezhanidze, I Z; Alasaniia, N Sh; Kontselidze, L A; Kharazi, N A; Bezhanidze, N V

    2009-06-01

    Fiber promotes the contractions that keep food moving through the intestine. Also, high-fiber foods expand the inside walls of the colon and eases the passage of waste. The food and fiber research was conducted. In the article, the classification and the composition of food fibers are presented. Multifunctional properties of food fiber in the process of digestion are discussed. The physiological value of food fibers for the human organism is stressed. Diets high in fiber during the entire life are recommended. If a person can't consume enough fiber in diet alone, certain stool softening and bulking agents are recommended. They can be very useful in preventing and treating digestive tract disorders. The analysis of high fiber food sources and world production and consumption of food fiber is also presented. PMID:19578217

  13. Beyond orchids and dandelions: Testing the 5HTT “risky” allele for evidence of phenotypic capacitance and frequency dependent selection

    PubMed Central

    Conley, Dalton; Rauscher, Emily; Siegal, Mark L.

    2013-01-01

    The persistence of behaviorally deleterious genes in the human population poses an interesting question for population genetics: If certain alleles at these loci are deleterious, why have they survived in the population? We consider evidence for phenotypic capacitance and/or frequency dependent selection for an allele that has been putatively shown to have negative associations with human behaviors (the “short” 5-HTT promoter region allele) yet which has persisted in human and non-human primate populations. Using National Longitudinal Study of Adolescent Health data, we compare sibling and twin variation in depression by 5-HTT genotype (specified in several ways) and investigate sibship-level cross-person gene-gene interactions. In support of the “orchid / dandelion” hypothesis, we find evidence that the short allele increases variation in phenotypes in response to environmental (or genetic) differences (i.e. acts as a perturbation of a phenotypic capacitor). Further, we also find some evidence that the effects of allelic variation at this locus are moderated by the genetic environment of the sibship unit (i.e. may be susceptible to frequency dependent selection). We discuss implications of these findings for genetic models in general, specifically with respect to stable unit treatment value assumption violations (i.e. non-independence of units of analysis). PMID:23701535

  14. Heating-frequency-dependent thermal conductivity: An analytical solution from diffusive to ballistic regime and its relevance to phonon scattering measurements

    NASA Astrophysics Data System (ADS)

    Yang, Fan; Dames, Chris

    2015-04-01

    The heating-frequency dependence of the apparent thermal conductivity in a semi-infinite body with periodic planar surface heating is explained by an analytical solution to the Boltzmann transport equation. This solution is obtained using a two-flux model and gray mean free time approximation and verified numerically with a lattice Boltzmann method and numerical results from the literature. Extending the gray solution to the nongray regime leads to an integral transform and accumulation-function representation of the phonon scattering spectrum, where the natural variable is mean free time rather than mean free path, as often used in previous work. The derivation leads to an approximate cutoff conduction similar in spirit to that of Koh and Cahill [Phys. Rev. B 76, 075207 (2007), 10.1103/PhysRevB.76.075207] except that the most appropriate criterion involves the heater frequency rather than thermal diffusion length. The nongray calculations are consistent with Koh and Cahill's experimental observation that the apparent thermal conductivity shows a stronger heater-frequency dependence in a SiGe alloy than in natural Si. Finally these results are demonstrated using a virtual experiment, which fits the phase lag between surface temperature and heat flux to obtain the apparent thermal conductivity and accumulation function.

  15. Complex frequency-dependent polarizability through the π → π* excitation energy of azobenzene molecules by a combined charge-transfer and point-dipole interaction model.

    PubMed

    Haghdani, Shokouh; Davari, Nazanin; Sandnes, Runar; Åstrand, Per-Olof

    2014-11-26

    The complex frequency-dependent polarizability and π → π* excitation energy of azobenzene compounds are investigated by a combined charge-transfer and point-dipole interaction (CT/PDI) model. To parametrize the model, we adopted time-dependent density functional theory (TDDFT) calculations of the frequency-dependent polarizability extended with excited-state lifetimes to include also its imaginary part. The results of the CT/PDI model are compared with the TDDFT calculations and experimental data demonstrating that the CT/PDI model is fully capable to reproduce the static polarizability as well as the π → π* excitation energy for these compounds. In particular, azobenzene molecules with different functional groups in the para-position have been included serving as a severe test of the model. The π → π* excitation is to a large extent localized to the azo bond, and substituting with electron-donating or electron-attracting groups on the phenyl rings results in charge-transfer effects and a shift in the excitation energy giving rise to azobenzene compounds with a range of different colors. In the CT/PDI model, the π → π* excitation in azobenzenes is manifested as drastically increasing atomic induced dipole moments in the azo group as well as in the adjacent carbon atoms, whereas the shifts in the excitation energies are due to charge-transfer effects.

  16. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  17. Some properties of an advanced boron fiber. [high strength, splittable fibers

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1979-01-01

    An advanced coreless boron fiber exhibits tensile strengths which are more than twice that of the normal CVD B/W fibers. The coreless fiber is made by the chemical removal of the tungsten boride core exposed by splitting the as-grown fiber. The easily splittable fiber is made by the chemical vapor deposition of boron on a larger than usual tungsten substrate. It is expected that the ease of splitting is related to residual stresses in these fibers. Measurements of the axial residual stresses in both the normal and the splittable fibers are presented and the results compared. Differences in these stresses are discussed in connection with the ease of splitting in the splittable fibers.

  18. Homogenization of long fiber reinforced composites including fiber bending effects

    NASA Astrophysics Data System (ADS)

    Poulios, Konstantinos; Niordson, Christian F.

    2016-09-01

    This paper presents a homogenization method, which accounts for intrinsic size effects related to the fiber diameter in long fiber reinforced composite materials with two independent constitutive models for the matrix and fiber materials. A new choice of internal kinematic variables allows to maintain the kinematics of the two material phases independent from the assumed constitutive models, so that stress-deformation relationships, can be expressed in the framework of hyper-elasticity and hyper-elastoplasticity for the fiber and the matrix materials respectively. The bending stiffness of the reinforcing fibers is captured by higher order strain terms, resulting in an accurate representation of the micro-mechanical behavior of the composite. Numerical examples show that the accuracy of the proposed model is very close to a non-homogenized finite-element model with an explicit discretization of the matrix and the fibers.

  19. Multichannel laser-fiber vibrometer

    NASA Astrophysics Data System (ADS)

    Dudzik, Grzegorz; Waz, Adam; Kaczmarek, Pawel; Antonczak, Arkadiusz; Sotor, Jaroslaw; Krzempek, Karol; Sobon, Grzegorz; Abramski, Krzysztof M.

    2013-01-01

    For the last few years we were elaborating the laser-fiber vibrometer working at 1550 nm. Our main stress was directed towards different aspects of research: analysis of scattered light, efficient photodetection, optimization of the fiber-free space interfaces and signal processing. As a consequence we proposed the idea of a multichannel fiber vibrometer based on well developed telecommunication technique - Wavelength Division Multiplexing (WDM). One of the most important parts of a fiber-laser vibrometer is demodulation electronic section. The distortion, nonlinearity, offset and added noise of measured signal come from electronic circuits and they have direct influence on finale measuring results. We present the results of finished project "Developing novel laser-fiber monitoring technologies to prevent environmental hazards from vibrating objects" where we have constructed a 4-channel WDM laser-fiber vibrometer.

  20. Specialty fiber optic applications for harsh and high radiation environments

    NASA Astrophysics Data System (ADS)

    Risch, Brian G.

    2015-05-01

    Since the first commercial introduction in the 1980s, optical fiber technology has undergone an almost exponential growth. Currently over 2 billion fiber kilometers are deployed globally with 2014 global optical fiber production exceeding 300 million fiber kilometers. 1 Along with the staggering growth in optical fiber production and deployment, an increase in optical fiber technologies and applications has also followed. Although the main use of optical fibers by far has been for traditional data transmission and communications, numerous new applications are introduced each year. Initially the practical application of optical fibers was limited by cost and sensitivity of the optical fibers to stress, radiation, and other environmental factors. Tremendous advances have taken place in optical fiber design and materials allowing optical fibers to be deployed in increasingly harsh environments with exposure to increased mechanical and environmental stresses while maintaining high reliability. With the increased reliability, lower cost, and greatly expanded range of optical fiber types now available, new optical fiber deployments in harsh and high radiation environments is seeing a tremendous increase for data, communications, and sensing applications. An overview of key optical fiber applications in data, communications, and sensing for harsh environments in industrial, energy exploration, energy generation, energy transmission, and high radiation applications will be presented. Specific recent advances in new radiation resistant optical fiber types, other specialty optical fibers, optical fiber coatings, and optical fiber cable materials will be discussed to illustrate long term reliability for deployment of optical fibers in harsh and high radiation environments.

  1. Frequency-Dependent Social Transmission and the Interethnic Transfer of Female Genital Modification in the African Diaspora and Indigenous Populations of Colombia.

    PubMed

    Ross, Cody T; Campiño, Patricia Joyas; Winterhalder, Bruce

    2015-12-01

    We present a quantitative account based on ethnographic and documentary research of the prevalence of female genital modification (FGMo) in the African diaspora and indigenous populations of Colombia. We use these data to test hypotheses concerning the cultural evolutionary drivers of costly trait persistence, attenuation, and intergroup transmission. The uptake of FGMo by indigenous populations in Colombia is consistent with frequency-dependent hypotheses for the social transmission of the FGMo trait from the African diaspora population in the period following the era of slavery in Colombia. The prevalence and severity of practices related to FGMo decline with level of sociocultural integration into mainstream Colombian culture. Our results provide empirical support for the cultural evolutionary models proposed by Ross et al. (2015) to describe the transmission dynamics of FGMo and other costly traits. Analysis of costly trait dynamics contributes knowledge useful to applied anthropology and may be of interest in policy design and human rights monitoring in Colombia and elsewhere. PMID:26471377

  2. Interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

    NASA Astrophysics Data System (ADS)

    Liao, Xue-Yang; Zhang, Kai; Zeng, Chang; Zheng, Xue-Feng; En, Yun-Fei; Lai, Ping; Hao, Yue

    2014-05-01

    Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) structures. Two types of device structures, namely, the recessed gate structure (RGS) and the normal gate structure (NGS), are studied in the experiment. Interface trap parameters including trap density Dit, trap time constant τit, and trap state energy ET in both devices have been determined. Furthermore, the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching (RIE).

  3. Cumulative frequency-dependent selective episodes allow for rapid morph cycles and rock-paper-scissors dynamics in species with overlapping generations

    PubMed Central

    San-Jose, Luis M.; Peñalver-Alcázar, Miguel; Milá, Borja; Gonzalez-Jimena, Virginia; Fitze, Patrick S.

    2014-01-01

    Rock-paper-scissors (RPS) dynamics, which maintain genetic polymorphisms over time through negative frequency-dependent (FD) selection, can evolve in short-lived species with no generational overlap, where they produce rapid morph frequency cycles. However, most species have overlapping generations and thus, rapid RPS dynamics are thought to require stronger FD selection, the existence of which yet needs to be proved. Here, we experimentally demonstrate that two cumulative selective episodes, FD sexual selection reinforced by FD selection on offspring survival, generate sufficiently strong selection to generate rapid morph frequency cycles in the European common lizard Zootoca vivipara, a multi-annual species with major generational overlap. These findings show that the conditions required for the evolution of RPS games are fulfilled by almost all species exhibiting genetic polymorphisms and suggest that RPS games may be responsible for the maintenance of genetic diversity in a wide range of species. PMID:24943372

  4. Frequency dependent negative capacitance effect and dielectric properties of swift heavy ion irradiated Ni/oxide/n-GaAs Schottky diode

    NASA Astrophysics Data System (ADS)

    Bobby, A.; Shiwakoti, N.; Verma, S.; Asokan, K.; Antony, B. K.

    2016-05-01

    The Ni/n-GaAs Schottky barrier diode having thin interfacial oxide layer was subjected to 25 MeV C4+ ion irradiation at selected fluences. The in-situ capacitance and dielectric properties were investigated in the 1 KHz to 5 MHz frequency range. The results show a decrease in capacitance with increase in ion fluence at low frequencies. Interestingly, a negative capacitance effect was also observed in this frequency range in all the samples. As a consequence, changes were observed in parameters like series resistance, conductance, dielectric loss, dielectric constant, loss tangent and ac electrical conductivity. At high frequencies, the capacitance reaches the geometric value 'C0'. The results were interpreted in terms of the generation of irradiation induced traps, carrier capture and emission from deep and shallow states and its frequency dependent saturation effects.

  5. Synthesis and frequency-dependent dielectric properties of epitaxial La1.875Sr0.125NiO4 thin films

    SciTech Connect

    Podpirka, Adrian; Tselev, Alexander; Ramanathan, Shriram

    2012-01-01

    Epitaxial thin films of La{sub 1.875}Sr{sub 0.125}NiO{sub 4} (lanthanum strontium nickelate, LSNO) have been synthesized by sputtering onto single crystal oxide substrates and their structural and dielectric properties are reported. High dielectric constants on the order of 10{sup 7} have been measured up to 1 MHz in interdigitated capacitors with a frequency dependence that correlates with substrate imposed strain and texture. The observation of a high dielectric constant albeit with moderate loss tangent at high frequencies motivates further explorations of charge ordering phenomena in such complex oxides and serves to examine size effects on dielectric response by comparison with studies on bulk single crystal LSNO.

  6. HLA class I-mediated stress fiber formation requires ERK1/2 activation in the absence of an increase in intracellular Ca2+ in human aortic endothelial cells.

    PubMed

    Ziegler, Mary E; Jin, Yi-Ping; Young, Steven H; Rozengurt, Enrique; Reed, Elaine F

    2012-10-15

    Following transplantation, HLA class I antibodies targeting donor endothelium stimulate cell proliferation and migration, which contribute to the development of transplant vasculopathy and chronic allograft rejection. Dynamic remodeling of the actin cytoskeleton regulates cell proliferation and migration in endothelial cells (ECs), but the mechanism(s) involved remain incompletely understood. We explored anti-HLA class I antibody-mediated alterations of the cytoskeleton in human aortic ECs (HAECs) and contrasted these findings to thrombin-induced cytoskeleton remodeling. Our results identify two different signaling pathways leading to myosin light chain (MLC) phosphorylation in HAECs. Stimulation of HAECs with thrombin at 1 U/ml induced a robust elevation of intracellular Ca(2+) concentration, increased MLC phosphorylation, and promoted stress fiber formation via MLC kinase (MLCK) and Rho kinase (ROK) in an ERK-independent manner. In contrast, HAECs stimulated with HLA class I antibodies did not promote any detectable change in intracellular Ca(2+) concentration but instead induced MLC phosphorylation and stress fiber assembly via MLCK and ROK in an ERK1/2-dependent manner. Stimulation of HAECs with low-dose thrombin (1 mU/ml) induced signaling cascades that were similar to stimulation with HLA class I antibodies. HLA class I antibodies also stimulated the translocation of mammalian target of rapamycin complex 2 (mTORC2) and ERK1/2 from the cytoplasm to the plasma membrane independently of stress fiber assembly. These findings identify novel roles for HLA class I signaling in ECs and provide new insights into the role of ERK1/2 and mTORC2 in cytoskeleton regulation, which may be important in promoting transplant vasculopathy, tumor angiogenesis, and atherosclerosis. PMID:22914643

  7. Frequency-Dependent Brain Regional Homogeneity Alterations in Patients with Mild Cognitive Impairment during Working Memory State Relative to Resting State.

    PubMed

    Wang, Pengyun; Li, Rui; Yu, Jing; Huang, Zirui; Li, Juan

    2016-01-01

    Several studies have reported working memory deficits in patients with mild cognitive impairment (MCI). However, previous studies investigating the neural mechanisms of MCI have primarily focused on brain activity alterations during working memory tasks. No study to date has compared brain network alterations in the working memory state between MCI patients and normal control (NC) subjects. Therefore, using the index of regional homogeneity (ReHo), we explored brain network impairments in MCI patients during a working memory task relative to the resting state, and identified frequency-dependent effects in separate frequency bands.Our results indicate that, in MCI patients, ReHo is altered in the posterior cingulate cortex (PCC) in the slow-3 band (0.073-0.198 Hz), and in the bottom of the right occipital lobe and part of the right cerebellum, the right thalamus, a diffusing region in the bilateral prefrontal cortex (PFC), the left and right parietal-occipital regions, and the right angular gyrus in the slow-5 band (0.01-0.027 Hz). Furthermore, in NCs, the value of ReHo in clusters belonging to the default mode network (DMN) decreased, while the value of ReHo in clusters belonging to the attentional network increased during the task state. However, this pattern was reversed in MCI patients, and was associated with decreased working memory performance. In addition, we identified altered functional connectivity of the abovementioned regions with other parts of the brain in MCI patients. This is the first study to compare frequency-dependent alterations of ReHo in MCI patients between resting and working memory states. The results provide a new perspective regarding the neural mechanisms of working memory deficits in MCI patients, and extend our knowledge of altered brain patterns in resting and task-evoked states. PMID:27047375

  8. On the profile of frequency dependent interface states and series resistance in Au/p-InP SBDs prepared with photolithography technique

    NASA Astrophysics Data System (ADS)

    Korucu, D.; Turut, A.; Turan, R.; Altindal, Ş.

    2012-09-01

    The frequency dependent of the forward and reverse bias capacitance-voltage ( C- V) and conductance-voltage ( G/ w- V) characteristics of Au/p-InP SBDs have been investigated in the frequency range of 20 kHz-10 MHz and voltage range of -5 - 5 V at room temperature. The effects of surface states ( N ss) and series resistance ( R s) on C- V and G/ w- V characteristics have been investigated in detail. The frequency dependent N ss and R s profiles were obtained for various applied bias voltages. The experimental results show that the main electrical parameters of Au/p-InP SBD such as barrier height (ΦB), the density of acceptor concentration ( N A), N ss and R s were found strongly frequency and voltage dependent. The values of C and G/ w decrease with increasing frequency due to a continuous distribution of N ss localized at the metal/semiconductor (M/S) interface. The effect of R s on C and G is found considerably high especially at high frequencies. Therefore, the high frequencies of the values of C and G were corrected for the effect of R s in the whole measured bias range to obtain the real diode capacitance C c and conductance G c using the Nicollian and Goetzberger technique. The distribution profile of R s- V gives a peak depending on the frequency especially at low frequencies and disappears with increasing frequencies due to the existence of N ss at the M/S interface.

  9. Frequency-Dependent Brain Regional Homogeneity Alterations in Patients with Mild Cognitive Impairment during Working Memory State Relative to Resting State

    PubMed Central

    Wang, Pengyun; Li, Rui; Yu, Jing; Huang, Zirui; Li, Juan

    2016-01-01

    Several studies have reported working memory deficits in patients with mild cognitive impairment (MCI). However, previous studies investigating the neural mechanisms of MCI have primarily focused on brain activity alterations during working memory tasks. No study to date has compared brain network alterations in the working memory state between MCI patients and normal control (NC) subjects. Therefore, using the index of regional homogeneity (ReHo), we explored brain network impairments in MCI patients during a working memory task relative to the resting state, and identified frequency-dependent effects in separate frequency bands.Our results indicate that, in MCI patients, ReHo is altered in the posterior cingulate cortex (PCC) in the slow-3 band (0.073–0.198 Hz), and in the bottom of the right occipital lobe and part of the right cerebellum, the right thalamus, a diffusing region in the bilateral prefrontal cortex (PFC), the left and right parietal-occipital regions, and the right angular gyrus in the slow-5 band (0.01–0.027 Hz). Furthermore, in NCs, the value of ReHo in clusters belonging to the default mode network (DMN) decreased, while the value of ReHo in clusters belonging to the attentional network increased during the task state. However, this pattern was reversed in MCI patients, and was associated with decreased working memory performance. In addition, we identified altered functional connectivity of the abovementioned regions with other parts of the brain in MCI patients. This is the first study to compare frequency-dependent alterations of ReHo in MCI patients between resting and working memory states. The results provide a new perspective regarding the neural mechanisms of working memory deficits in MCI patients, and extend our knowledge of altered brain patterns in resting and task-evoked states. PMID:27047375

  10. Mitigating artifacts in back-projection source imaging with implications for frequency-dependent properties of the Tohoku-Oki earthquake

    NASA Astrophysics Data System (ADS)

    Meng, Lingsen; Ampuero, Jean-Paul; Luo, Yingdi; Wu, Wenbo; Ni, Sidao

    2012-12-01

    Comparing teleseismic array back-projection source images of the 2011 Tohoku-Oki earthquake with results from static and kinematic finite source inversions has revealed little overlap between the regions of high- and low-frequency slip. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies, down to about 0.1 Hz, have suggested that a progressive transition of rupture properties as a function of frequency is observable. Here, by adapting the concept of array response function to non-stationary signals, we demonstrate that the "swimming artifact", a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We introduce a "reference window strategy" into the multitaper-MUSIC back-projection technique and significantly mitigate the "swimming artifact" at high frequencies (1 s to 4 s). At lower frequencies, this modification yields notable, but significantly smaller, artifacts than time-domain stacking. We perform extensive synthetic tests that include a 3D regional velocity model for Japan. We analyze the recordings of the Tohoku-Oki earthquake at the USArray and at the European array at periods from 1 s to 16 s. The migration of the source location as a function of period, regardless of the back-projection methods, has characteristics that are consistent with the expected effect of the "swimming artifact". In particular, the apparent up-dip migration as a function of frequency obtained with the USArray can be explained by the "swimming artifact". This indicates that the most substantial frequency-dependence of the Tohoku-Oki earthquake source occurs at periods longer than 16 s. Thus, low-frequency back-projection needs to be further tested and validated in order to contribute to the characterization of frequency-dependent rupture properties.

  11. Two-dimensional diffusion in Li0.7NbS2 as directly probed by frequency-dependent 7Li NMR.

    PubMed

    Epp, V; Nakhal, S; Lerch, M; Wilkening, M

    2013-05-15

    Li ion diffusion in layer-structured Li0.7NbS2 has been complementary investigated by nuclear magnetic resonance (NMR) spectroscopy from an atomic scale point of view. In the present case, (7)Li NMR spin-lattice relaxation (SLR) rates R1ρ probed in the rotating frame of reference proved very informative in characterizing the Li self-diffusion process in the van der Waals gap between the NbS2 layers. While temperature-variable SLRρ measurements were used to determine dynamic parameters such as jump rates (τ(-1)) and the activation energy (Ea), frequency-dependent measurements were used to specify the dimensionality of the diffusion process. In particular, the effect of annealing, i.e., the distribution of Li ions between the layers, on overall Li dynamics has been studied. When plotted in an Arrhenius diagram, the R1ρ rates of an annealed sample, which were recorded at a locking frequency of 20 kHz, pass through a diffusion-induced relaxation peak whose maximum shows up at 320 K. Employing an appropriate diffusion model and appropriately accounting for a non-diffusive background relaxation, a Li jump rate τ(-1)(300 K) ≈ 1.3 × 10(5) s(-1) and an activation energy Ea of 0.43(2) eV can be deduced. Most importantly, in the high-T limit of the diffusion-induced rate peak, i.e., when ω1τ < 1 holds, the rates follow a logarithmic frequency dependence. This points to a diffusion process of low dimensionality and is in good agreement with predictions of relaxation models developed for 2D diffusion.

  12. Spectral characteristics of draw-tower step-chirped