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Sample records for channel stabilization

  1. Stream Channel Stability. Appendix E. Geomorphic Controls of Channel Stability,

    DTIC Science & Technology

    1981-04-01

    Erosion and Channels Research Unit, USDA Sedimentation Laboratory, Oxford, MS. 1,"<Xi i .. i,,< .;,i,<..7 PREFACE This process -oriented study was...organized to investigate three complementary aspects of channel stability including (a) the nature of channel failure processes ; (b) the influences of...valley-fill depositional units on these processes and (c) the properties and distributions of the valley-fill units. The study was process oriented to

  2. Stream Channel Stability.

    DTIC Science & Technology

    1981-04-01

    geometry of the stilling basin and appurtenances for optimum energy dissipation. The hydraulic design, based on a 100-year return period design storm...cases the only viable alternative based on present technology is to let the channel seek its oa equilibrium, but attempt to minimize total losses by...are degrading, resulting in bank caving, land loss , and damage to highway bridges. Many streams have enlarged to the extent that 50 to 100-year runoff

  3. Channel entrance flow and its linear stability

    NASA Astrophysics Data System (ADS)

    Hifdi, Ahmed; Ouazzani Touhami, Mohammed; Khalid Naciri, Jaâfar

    2004-06-01

    In this work, we present a temporal linear stability analysis of developing channel flow. For the main flow, the considered solution is analytic. It is based on the hypothesis of small disturbances from fully developed flow and it is valid for intermediate Reynolds numbers. The disturbances are separated into symmetric and anti-symmetric eigenmodes of the velocity. We deal subsequently with the linear stability of this main flow, taking into account the nearly parallel flow assumption. The stability problem formulation leads to the Orr-Sommerfeld equation. This equation is then resolved using the Chebyshev spectral collocation method. The stability results depend essentially on the shape and amplitude of the velocity profiles imposed at the channel entry.

  4. Application of Channel Stability Methods - Case Studies

    DTIC Science & Technology

    1994-09-01

    Application for Design Using SAM ...................... 25 Conclusions ..................................... 26 3-Case Study, Puerco River...Stability curves for project design ................. 25 Figure 13. Puerco River study reach ....................... 28 Figure 14. Upstream view of the rock...mile 5.5 31 Figure 18. Realigned channel reach showing sheet pile drop structure - river mile 6.6 ...................... 35 Figure 19. Puerco River

  5. ASSESSMENT OF CHANNEL STABILITY AT BRIDGE SITES.

    USGS Publications Warehouse

    Brice, James C.; ,

    1984-01-01

    Assessment of channel stability from field study and the comparison of time-sequential aerial photographs provides information that is needed in site selection, bridge design, and countermeasure placement. Channel instability is indicated by bank erosion, progressive degradation (or aggradation) of the streambed, or natural scour and fill of the streambed. Bank erosion rates are related to stream type and are proportional to stream size. Predictions of future rates are based on past rates, as measured on time-sequential photographs or mps, and on the typical behavior of meander loops.

  6. Channel stability of Turkey Creek, Nebraska

    USGS Publications Warehouse

    Rus, David L.; Soenksen, Philip J.

    1998-01-01

    Channelization on Turkey Creek and its receiving stream, the South Fork Big Nemaha River, has disturbed the equilibrium of Turkey Creek and has led to channel-stability problems, such as degradation and channel widening, which pose a threat to bridges and land adjacent to the stream. As part of a multiagency study, the U.S. Geological Survey assessed channel stability at two bridge sites on upper and middle portions of Turkey Creek by analyzing streambed-elevation data for gradation changes, comparing recent cross-section surveys and historic accounts, identifying bank-failure blocks, and analyzing tree-ring samples. These results were compared to gradation data and trend results for a U.S. Geological Survey streamflow-gaging station near the mouth of Turkey Creek from a previous study. Examination of data on streambed elevations reveals that degradation has occurred. The streambed elevation declined 0.5 m at the upper site from 1967-97. The streambed elevation declined by 3.2 m at the middle site from 1948-97 and exposed 2 m of the pilings of the Nebraska Highway 8 bridge. Channel widening could not be verified at the two sites from 1967-97, but a historic account indicates widening at the middle site to be two to three times that of the 1949 channel width. Small bank failures were evident at the upper site and a 4-m-wide bank failure occurred at the middle site in 1987 according to tree ring analyses. Examination of streambed-elevation data from a previous study at the lower site reveals a statistically significant aggrading trend from 1958-93. Further examination of these data suggests minor degradation occurred until 1975, followed by aggradation.

  7. Opportunistic Channel Scheduling for Ad Hoc Networks with Queue Stability

    NASA Astrophysics Data System (ADS)

    Dong, Lei; Wang, Yongchao

    2015-03-01

    In this paper, a distributed opportunistic channel access strategy in ad hoc network is proposed. We consider the multiple sources contend for the transmission opportunity, the winner source decides to transmit or restart contention based on the current channel condition. Owing to real data assumption at all links, the decision still needs to consider the stability of the queues. We formulate the channel opportunistic scheduling as a constrained optimization problem which maximizes the system average throughput with the constraints that the queues of all links are stable. The proposed optimization model is solved by Lyapunov stability in queueing theory. The successive channel access problem is decoupled into single optimal stopping problem at every frame and solved with Lyapunov algorithm. The threshold for every frame is different, and it is derived based on the instantaneous queue information. Finally, computer simulations are conducted to demonstrate the validity of the proposed strategy.

  8. Stability of gas discharge channels for final beam transport

    NASA Astrophysics Data System (ADS)

    Tauschwitz, A.; Birkner, R.; Knobloch, R.; Neff, S.; Niemann, C.; Penache, D.; Presura, R.; Ponce, D.; Yu, S.

    2002-07-01

    Discharge plasma channels have been investigated in recent years at Gesellschaft für Schwerionenforschung Darmstadt (GSI) and at the Lawrence Berkeley National Laboratory in Berkeley, California, in a number of experiments. A short summary of the experimental work at Berkeley and GSI is given. Different initiation mechanisms for gas discharges of up to 60 kA were studied and compared. In the Berkeley experiments, laser ionization of organic vapors in a buffer gas was used to initiate and direct the discharge while at GSI, laser gas heating and ion-beam-induced gas ionization were tested as initiation mechanisms. These three initiation techniques are compared and the stability of the resulting discharge channels is discussed. A discharge current of 50 kA, a channel diameter well below 1 cm, a pointing stability better than 200 [mu]m, and MHD stability of more than 10 [mu]s have been demonstrated simultaneously in the recent experiments. These parameters are sufficient or close to the requirements of a reactor application depending on the details of the target design. The experimental results show that transport channels work with sufficient stability, reproducibility, and ion optical properties for a wide pressure range of discharge gases and pressures.

  9. Stability Analysis of a Uniformly Heated Channel with Supercritical Water

    SciTech Connect

    Ortega Gomez, T.; Class, A.; Schulenberg, T.; Lahey, R.T. Jr.

    2006-07-01

    The thermal-hydraulic stability of a uniformly heated channel at supercritical water pressure has been investigated to help understand the system instability phenomena which may occur in Supercritical Water Nuclear Reactors (SCWR). We have extended the modeling approach often used for Boiling Water Nuclear Reactor (BWR) stability analysis to supercritical pressure operation conditions. We have shown that Ledinegg excursive instabilities and pressure-drop oscillations (PDO) will not occur in supercritical water systems. The linear stability characteristics of a typical uniformly heated channel were computed by evaluating the eigenvalues of the model. An analysis of non-linear instability phenomena was also performed in the time domain and the dynamic bifurcations were evaluated. (authors)

  10. Bank stability and channel width adjustment, East Fork River, Wyoming.

    USGS Publications Warehouse

    Andrews, E.D.

    1982-01-01

    Frequent surveys of eight cross sections located in self-formed reaches of the East Fork River, Wyoming, during the 1974 snowmelt flood showed a close relation between channel morphology and scour and fill. Those cross sections narrower than the mean reach width filled at discharges less than bankfull and scoured at discharges greater than bankfull. Those cross sections wider than the mean reach width scoured at discharges less than bankfull and filled at discharges greater than bankfull. Bank stability, and to some extent the adjustment of stream channel width, in the East Fork River study reach appears to be controlled by the processes of scour and fill. -from Author

  11. Plasma Channel Transport for Heavy Ion Fusion: Investigation of Beam Transport, Channel Initiation and Stability

    NASA Astrophysics Data System (ADS)

    Tauschwitz, Andreas; Niemann, Christoph; Penache, Dan; Birkner, Richard; Hoffmann, Dieter H. H.; Kobloch, Renate; Neff, Stefan; Presura, Radu; Ponce, Dave; Rosmej, Frank; Yu, Simon

    2002-12-01

    For final beam transport in an IFE reactor three alternatives are mainly discussed. These are neutralized ballistic transport, self-pinched transport, and plasma channel transport. Discharge plasma channels were investigated in the recent years at GSI Darmstadt and at LBNL Berkeley in a number of experiments. Different initiation mechanisms for gas discharges of up to 60 kA were studied and compared. In the Berkeley experiments laser ionization of organic vapors in a buffer gas was used to initiate and direct the discharge while at GSI laser gas heating and ion beam induced gas ionization were tested as initiation mechanisms. Measurements of temperature, electron density, gas density, and magnetic field distribution in the channels are compared with results of beam transport experiments at the GSI UNILAC accelerator and with MHD simulations of the 1D-fluidcode CYCLOPS, which was developed in Berkeley. Good agreement between plasma diagnostics results, measured ion optical properties and MHD simulations was found. Parameters that are required for a reactor application are a discharge current of 50 kA, a channel diameter below 1 cm, a pointing stability better than 500 μm, and MHD stability for more than 10 μs. These parameters have been demonstrated in the recent experiments. The results imply that transport channels work with sufficient stability, reproducibility and ion optical properties in a wide pressure range and for various discharge gases.

  12. Protonation of the Human PIEZO1 Ion Channel Stabilizes Inactivation*

    PubMed Central

    Bae, Chilman; Sachs, Frederick; Gottlieb, Philip A.

    2015-01-01

    PIEZO1 is a recently cloned eukaryotic cation-selective channel that opens with mechanical force. We found that extracellular protonation inhibits channel activation by ≈90% by increased occupancy in the closed or the inactivated state. Titration between pH 6.3 and 8.3 exhibited a pK of ≈6.9. The steepness of the titration data suggests positive cooperativity, implying the involvement of at least two protonation sites. Whole-cell recordings yielded results similar to patches, and pH 6.5 reduced whole-cell currents by >80%. The effects were reversible. To assess whether pH acts on the open or the inactivated state, we tested a double-mutant PIEZO1 that does not inactivate. Cell-attached patches and whole-cell currents from this mutant channel were pH-insensitive. Thus, protonation appears to be associated with domain(s) of the channel involved with inactivation. pH also did not affect mutant channels with point mutations at position 2456 that are known to exhibit slow inactivation. To determine whether the physical properties of the membrane are altered by pH and thereby affect channel gating, we measured patch capacitance during mechanical stimuli at pH 6.5 and 7.3. The rate constants for changes in patch capacitance were independent of pH, suggesting that bilayer mechanics are not involved. In summary, low pH stabilizes the inactivated state. This effect may be important when channels are activated under pathological conditions in which the pH is reduced, such as during ischemia. PMID:25561736

  13. Linear stability analysis of flows in a grooved channel

    NASA Astrophysics Data System (ADS)

    Mohammadi, Alireza; Floryan, Jerzy Maciej

    2015-11-01

    It is known that longitudinal grooves which are parallel to the flow direction may either stabilize or destabilize the travelling wave instability in a pressure-gradient-driven channel flow depending on the groove wave number. These waves reduce to the classical Tollmien-Schlichting (TS) waves in the smooth channel limit. It is shown that another class of travelling wave instability exists if grooves with sufficiently high amplitude and proper wavelengths are used. It is demonstrated that the new instability is driven by inviscid mechanisms, with the disturbance motion having the form of a wave propagating in the streamwise direction with the phase speed approximately four times larger than the TS wave speed and with its streamwise wavelength being approximately twice the spanwise groove wavelength. The instability motion is concentrated mostly in the middle of the channel and has a primarily planar character, i.e. the dominant velocity components are parallel to the walls. A significant reduction of the corresponding critical Reynolds number can be achieved by increasing the groove amplitude. This mode reduces to the highly attenuated Squire mode in the smooth channel limit. This work has been carried out with support from the Natural Sciences and Engineering Research Council (NSERC) of Canada.

  14. Stability of a droplet pinned in a channel under gravity

    NASA Astrophysics Data System (ADS)

    Hekiri, Haider

    The stability of a two-dimensional, incompressible water droplet, with two cylindrical-caps that is pinned in a channel, is investigated through the development of an analytical model based on Yong-Laplace relationship. The center of mass of the droplet is derived analytically by assuming a perfectly 2-D circular shape of the droplet cap. The derived analytical expressions are validated through the use of CFD. In the simulations, FLUENT with a 2-D pressure based solver is utilized, and Gambit with 2-D rectangular mesh is used to generate the grid. The pinned droplet states are measured by the location of the center of mass. The stability of the droplet states without gravity is evaluated by the growth rate sigmaH of the Hamiltonian of the system computed by CFD for various drop sizes. When a droplet is suspended on the straight channel and under no gravity conditions, it is proven analytically and through the use of CFD that there is a critical droplet volume, Vcr, where asymmetric droplet states appear in addition to the basic symmetric states when the drop volume V >V cr. It is demonstrated that when VVcr and the growth rate sigmaH is positive, the symmetric states become unstable and the asymmetric states become stable. The bifurcation of asymmetric states at Vcr has a pitchfork nature, and the growth rate sigmaH increases with the volume size. When the channel holding the droplet is contracted, the pitchfork bifurcation diagram of the droplet system changes into two separate branches of equilibrium states. The analytical expression of those stability branches has been developed for various contraction ratios. The primary branch describes a gradual and stable change of the droplet from a nearly symmetric to asymmetric state as the droplet volume, V, is increased. The secondary branch appears at a modified critical volume, Vmcr, and describes two

  15. Stability of stratified two-phase flows in inclined channels

    NASA Astrophysics Data System (ADS)

    Barmak, I.; Gelfgat, A. Yu.; Ullmann, A.; Brauner, N.

    2016-08-01

    Linear stability of the stratified gas-liquid and liquid-liquid plane-parallel flows in the inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of the non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of the steady state solutions are presented on the flow pattern map and are accompanied by the critical wavenumbers and the spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by the streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of two stable stratified flow configurations in a region of low flow rates in the countercurrent liquid-liquid flows. These configurations become unstable with respect to the shear mode of instability. It was revealed that in slightly upward inclined flows the lower and middle solutions for the holdup are stable in the part of the triple solution region, while the upper solution is always unstable. In the case of downward flows, in the triple solution region, none of the solutions are stable with respect to the short-wave perturbations. These flows are stable only in the single solution region at low flow rates of the heavy phase, and the long-wave perturbations are the most unstable ones.

  16. Enhanced stability of hillslopes and channel beds to mass failure

    NASA Astrophysics Data System (ADS)

    Prancevic, Jeff; Lamb, Michael; Palucis, Marisa; Venditti, Jeremy

    2016-04-01

    The stability of inclined, unconsolidated sediments subjected to groundwater flow on hillslopes and steep channel beds is important for both landscape evolution and natural hazards. Force-balance models have been used for seven decades to predict the stability of slopes, but they generally underpredict the degree of saturation required to destabilize the sediment. Researchers often appeal to heightened stabilizing forces from root and mineral cohesion, and friction acting on the margins of the failure to explain this underprediction. Surprisingly, infinite-slope stability models in their simplest form have never been tested under controlled laboratory conditions. To address this gap in data, we perform a set of controlled laboratory experiments with slope-parallel seepage in the simplest possible configuration. We performed 47 experiments in a 5 m laboratory flume with 4 grain sizes (D50 = 0.7, 2, 5, and 15 mm) and a wide range in bed angles (20° to 43°), spanning both Darcian and turbulent subsurface flow regimes. Our experiments show that granular slopes were more stable than predicted by simple force balance models in experiments that lack root or mineral cohesion. Despite the smooth plastic walls and the long aspect ratio of our flume, we calculate wall and toe friction to be important. Including these additional resistance terms in the model reduces the model misfit with our experimental results. However, there is considerable remaining misfit (up to 50% underestimation of the saturation level required for failure). We investigate two explanations of this heightened stability: 1) standard frictional resistance terms are underestimated, and 2) seepage stresses are overestimated. Both explanations require that we modify the models used to predict slope stability.

  17. The stability of a flexible cantilever in viscous channel flow

    NASA Astrophysics Data System (ADS)

    Cisonni, Julien; Lucey, Anthony D.; Elliott, Novak S. J.; Heil, Matthias

    2017-05-01

    Most studies of the flow-induced flutter instability of a flexible cantilever have assumed inviscid flow because of the high flow speeds and the large scale of the structures encountered in the wide range of applications of this fluid-structure interaction (FSI) system. However, for instance, in the fields of energy harvesting and biomechanics, low flow speeds and small- and micro-scale systems can give relatively low Reynolds numbers so that fluid viscosity needs to be explicitly accounted for to provide reliable predictions of channel-immersed-cantilever stability. In this study, we employ a numerical model coupling the Navier-Stokes equations and a one-dimensional elastic beam model. We conduct a parametric investigation to determine the conditions leading to flutter instability of a slender flexible cantilever immersed in two-dimensional viscous channel flow for Reynolds numbers lower than 1000. The large set of numerical simulations carried out allows predictions of the influence of decreasing Reynolds numbers and of the cantilever confinement on the single-mode neutral stability of the FSI system and on the pre- and post-critical cantilever motion. This model's predictions are also compared to those of a FSI model containing a two-dimensional solid model in order to assess, primarily, the effect of the cantilever slenderness in the simulations. Results show that an increasing contribution of viscosity to the hydrodynamic forces significantly alters the instability boundaries. In general, a decrease in Reynolds number is predicted to produce a stabilisation of the FSI system, which is more pronounced for high fluid-to-solid mass ratios. For particular fluid-to-solid mass ratios, viscous effects can lower the critical velocity and lead to a change in the first unstable structural mode. However, at constant Reynolds number, the effects of viscosity on the system stability are diminished by the confinement of the cantilever, which strengthens the importance of

  18. Canonical map approach to channeling stability in crystals. II

    NASA Astrophysics Data System (ADS)

    Sáenz, A. W.

    1987-11-01

    A nonrelativistic and a relativistic classical Hamiltonian model of two degrees of freedom are considered describing the plane motion of a particle in a potential V(x1,x2)[(x1,x2) =Cartesian coordinates]. Suppose V(x1,x2) is real analytic in its arguments in a neighborhood of the line x2=0, one-periodic in x1 there, and such that the average value of ∂V(x1,0)/∂x2 vanishes. It is proved that, under these conditions and provided that the particle energy E is sufficiently large, there exist for all time two distinguished solutions, one satisfying the equations of motion of the nonrelativistic model and the other those of the relativistic model, whose corresponding configuration-space orbits are one-periodic in x1 and approach the line x2=0 as E→∞. The main theorem is that these solutions are (future) orbitally stable at large enough E if V satisfies the above conditions, as well as natural requirements of linear and nonlinear stability. To prove their existence, one uses a well-known theorem, for which a new and simpler proof is provided, and properties of certain natural canonical maps appropriate to these respective models. It is shown that such solutions are orbitally stable by reducing the maps in question to Birkhoff canonical form and then applying a version of the Moser twist theorem. The approach used here greatly lightens the labor of deriving key estimates for the above maps, these estimates being needed to effect this reduction. The present stability theorem is physically interesting because it is the first rigorous statement on the orbital stability of certain channeling motions of fast charged particles in rigid two-dimensional lattices, within the context of models of the stated degree of generality.

  19. Metastable dissociation of metallocarbohedrenes. Reaction channels and cluster stabilities

    SciTech Connect

    Wei, S.; Guo, B.C.; Purnell, J.; Buzza, S.A.; Castleman, A.W. Jr. )

    1993-09-23

    An investigation of the metastable unimolecular dissociation channels and decay fractions of Ti[sub m]C[sub n][sup +] was made using a reflection time-of-flight mass spectrometer, coupled with a laser vaporization source in conjunction with multiphoton ionization. The measurements of the decay fractions show that TigC[sub 12][sup +] is a very stable species in accordance with expectation for a closed cagelike structure and, most importantly, provide the first available data on the relative stabilities for different cluster ions involved in the formation of metallocarbohedrenes (Met-Cars). Furthermore, the results reveal that the Ti[sub 8]C[sub n][sup +] mainly lose carbon species for n [ge] 14, while Ti[sub m]C[sub 12][sup +] loses only Ti for m [ge] 6 and both Ti and C[sub 3] for m = 4 and 5; C[sub 2] is never a product of decomposition for this range of Met-Car related species. The present findings are valuable in providing qualitative information for assessing theoretical calculations of structures and properties of metallocarbohedrenes and their building blocks. 32 refs., 2 figs., 1 tab.

  20. Gamma-channel stabilization mechanism in Ni-base superalloys

    NASA Astrophysics Data System (ADS)

    Goerler, Johannes V.; Brinckmann, Steffen; Shchyglo, Oleg; Steinbach, Ingo

    2015-11-01

    A mechanism is presented which opposes coalescence of ?-precipitates in Ni-base superalloys. The mechanism is based on the non-linear behaviour of the elastic energy in ?-channels, caused by the misfit strain between matrix and precipitate, as a function of the channel width. Variation of the channel width causes a disjoining pressure dependent on the density of misfit dislocations.

  1. Channel stability downstream from a dam assessed using aerial photographs and stream-gage information

    USGS Publications Warehouse

    Juracek, K.E.

    2000-01-01

    The stability of the Neosho River channel downstream from John Redmond Dam, in southeast Kansas, was investigated using multiple-date aerial photographs and stream-gage information. Bankfull channel width was used as the primary indicator variable to assess pre- and post-dam channel change. Five six-mile river reaches and four stream gages were used in the analysis. Results indicated that, aside from some localized channel widening, the overall channel change has been minor with little post-dam change in bankfull channel width. The lack of a pronounced postdam channel change may be attributed to a substantial reduction in the magnitude of the post-dam annual peak discharges in combination with the resistance to erosion of the bed and bank materials. Also, the channel may have been overwidened by a series of large floods that predated construction of the dam, including one with an estimated 500-year recurrence interval.

  2. Interference stabilization and UV lasing in a plasma channel formed in gas by intense RF field

    NASA Astrophysics Data System (ADS)

    Bogatskaya, A. V.; Popov, A. M.

    2015-04-01

    The effect of interference stabilization of Rydberg atoms in a high-intensity IR laser field is proposed to create a plasma channel with population inversion for conversion of the input laser energy into the VUV and XUV frequency band.

  3. Hydraulic and Environmental Effects of Channel Stabilization, Twentymile Creek, Mississippi

    DTIC Science & Technology

    1990-12-01

    square kilomitres tons (2,000 pounds, mass) 907.1847 kilograms To obtain Celsius (C) temperi!ure readings from Fahrenheit (F) readings , use the followirg...fr!nula: C 1 (/9)(F - 32). To obtain kelvin (K) read - ings use: K = (5/9)(F - 32) - 27’.l!. 6 HYDRAULIC AND ENVIRONMENTAL EFFECTS OF CHANNEL...1981) method with the existing channel geometry and bed material gradation, an aver- age Manning roughness coefficient (n value) of 0.018 was

  4. Channelized bottom melting and stability of floating ice shelves

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Steffen, K.

    2008-01-01

    The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1-2 km wide, 200-400 m deep, sub-ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea level, confirms the presence of ice-shelf melt water in the channel. These deep incisions in ice-shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously.

  5. Biomimetic Transmembrane Channels with High Stability and Transporting Efficiency from Helically Folded Macromolecules.

    PubMed

    Lang, Chao; Li, Wenfang; Dong, Zeyuan; Zhang, Xin; Yang, Feihu; Yang, Bing; Deng, Xiaoli; Zhang, Chenyang; Xu, Jiayun; Liu, Junqiu

    2016-08-08

    Membrane channels span the cellular lipid bilayers to transport ions and molecules into cells with sophisticated properties including high efficiency and selectivity. It is of particular biological importance in developing biomimetic transmembrane channels with unique functions by means of chemically synthetic strategies. An artificial unimolecular transmembrane channel using pore-containing helical macromolecules is reported. The self-folding, shape-persistent, pore-containing helical macromolecules are able to span the lipid bilayer, and thus result in extraordinary channel stability and high transporting efficiency for protons and cations. The lifetime of this artificial unimolecular channel in the lipid bilayer membrane is impressively long, rivaling those of natural protein channels. Natural channel mimics designed by helically folded polymeric scaffolds will display robust and versatile transport-related properties at single-molecule level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Stability theorem of depolarizing channels for the minimal output quantum Rényi entropies

    NASA Astrophysics Data System (ADS)

    Bae, Eunok; Gour, Gilad; Lee, Soojoon; Park, Jeonghoon; Sanders, Barry C.

    2016-03-01

    The stability theorem of the depolarizing channel states that if a state is close to achieving the minimal/maximal output value of a certain quantity through the channel, then it must be close to an input state giving the minimal/maximal value. We show that the stability theorem of the depolarizing channel holds for the output quantum p-Rényi entropy for p≥slant 2 or p = 1, which is an extension of the known case p = 2. As an application, we present a protocol in which Bob determines whether Alice prepares a pure quantum state close to a product state. In the protocol, Alice transmits to Bob multiple copies of a pure state through a depolarizing channel, and Bob estimates its output quantum p-Rényi entropy. By using our stability theorem, we show that Bob can determine whether her preparation is appropriate.

  7. Ray stability in weakly range-dependent sound channels.

    PubMed

    Beron-Vera, F J; Brown, M G

    2003-07-01

    Ray stability is investigated in environments consisting of a range-independent background sound-speed profile on which a range-dependent perturbation is superimposed. Theoretical arguments suggest and numerical results confirm that ray stability is strongly influenced by the background sound speed profile. Ray instability is shown to increase with increasing magnitude of alpha(I)=(I/omega)d omega/dI, where 2pi/omega(I) is the range of a ray double loop and I is the ray action variable. This behavior is illustrated using internal-wave-induced scattering in deep ocean environments and rough surface scattering in upward refracting environments.

  8. Quality control and quality assurance plan for bridge channel-stability assessments in Massachusetts

    USGS Publications Warehouse

    Parker, Gene W.; Pinson, Harlow

    1993-01-01

    A quality control and quality assurance plan has been implemented as part of the Massachusetts bridge scour and channel-stability assessment program. This program is being conducted by the U.S. Geological Survey, Massachusetts-Rhode Island District, in cooperation with the Massachusetts Highway Department. Project personnel training, data-integrity verification, and new data-management technologies are being utilized in the channel-stability assessment process to improve current data-collection and management techniques. An automated data-collection procedure has been implemented to standardize channel-stability assessments on a regular basis within the State. An object-oriented data structure and new image management tools are used to produce a data base enabling management of multiple data object classes. Data will be reviewed by assessors and data base managers before being merged into a master bridge-scour data base, which includes automated data-verification routines.

  9. Delay-Independent L2 Stability of Four-Channel Bilateral Teleoperators with Damping Injection

    NASA Astrophysics Data System (ADS)

    Tumerdem, Ugur; Ohnishi, Kouhei

    This paper presents an augmented four channel teleoperation architecture with local damping injection, which renders the teleoperation system L2 stable independent of time delay. It is well known that four channel teleoperation architecture, which is based on the transmission of force and position measurements of both the master and the slave robots, provides perfect transparency, when there is no time delay between the robots. In the presence of delay, four channel systems are not stable and they can not provide transparency. With damping injection, stability is guaranteed independent of the size of the delay, as long as it is constant, and furthermore better transparency with high frequency force feedback can be realized. This is an improvement over conventional methods. As transparency and stability are two conflicting goals, there is a tradeoff that a constant damping is felt in free motion. In this paper stability and transparency analyses are presented and the validity of the method is also confirmed with experiments.

  10. Stability of linear dynamic systems over the packet erasure channel: a co-design approach

    NASA Astrophysics Data System (ADS)

    Farhadi, Alireza

    2015-12-01

    This paper is concerned with the stability of linear time-invariant dynamic systems over the packet erasure channel subject to minimum bit rate constraint when an encoder and a decoder are unaware of the control signal. This assumption results in co-designing the encoder, decoder and controller. The encoder, decoder, controller and conditions relating transmission rate to packet erasure probability and eigenvalues of the system matrix A are presented for almost sure asymptotic stability of linear time-invariant dynamic systems over the packet erasure channel with feedback acknowledgment. When the eigenvalues of the system matrix A are real valued, it is shown that the obtained condition for stability is tight. Simulation result illustrates the satisfactory performance of the proposed encoder, decoder and controller for almost sure asymptotic stability.

  11. Effects of an emergent vegetation patch on channel reach bathymetry and stability during repeated unsteady flows

    NASA Astrophysics Data System (ADS)

    Waters, Kevin A.; Crowe Curran, Joanna

    2016-11-01

    While research into the interaction between in-channel vegetation, flow, and bed sediment has increased in recent years, there is still a need to understand how unsteady flows affect these processes, particularly in terms of channel bed adjustments. In this study, flume experiments tested two flood hydrograph sizes run over sand/gravel and sand/silt beds to evaluate reach scale impacts of a midchannel vegetation patch of variable stem density on channel bathymetry and stability. Alternating flood hydrographs with periods of low, steady flow created flow sequences reflective of an extended unsteady flow regime, thereby simulating time scales consisting of multiple flood events. Digital elevation models provided detailed measurements of channel change following each flood event to enable analysis over each unsteady flow sequence. The vegetation patch created characteristic channel bathymetries dependent on sediment mixture and patch density that in all cases resulted in a more variable bed structure than channels without a patch. Reach scale stability, quantified based on net volumetric bed change, only occurred with a sparse patch in the low flood sequence, corresponding with little variation in surface composition and structure. In most other cases, scour measured at the patch prevented stability at the reach scale, especially in the finer substrate. Overall, findings show that a channel may only adjust to a stable bathymetry upon addition of a midchannel vegetation patch within a limited range of flow regimes and patch stem densities, and that for the experimental conditions tested here, in-stream patches generally did not enhance reach scale bed stability.

  12. Metal-Assisted Channel Stabilization: Disposition of a Single Histidine on the N-terminus of Alamethicin Yields Channels with Extraordinarily Long Lifetimes

    PubMed Central

    Noshiro, Daisuke; Asami, Koji; Futaki, Shiroh

    2010-01-01

    Abstract Alamethicin, a member of the peptaibol family of antibiotics, is a typical channel-forming peptide with a helical structure. The self-assembly of the peptide in the membranes yields voltage-dependent channels. In this study, three alamethicin analogs possessing a charged residue (His, Lys, or Glu) on their N-termini were designed with the expectation of stabilizing the transmembrane structure. A slight elongation of channel lifetime was observed for the Lys and Glu analogs. On the other hand, extensive stabilization of certain channel open states was observed for the His analog. This stabilization was predominantly observed in the presence of metal ions such as Zn2+, suggesting that metal coordination with His facilitates the formation of a supramolecular assembly in the membranes. Channel stability was greatly diminished by acetylation of the N-terminal amino group, indicating that the N-terminal amino group also plays an important role in metal coordination. PMID:20441743

  13. WHIRLIN INCREASES TRPV1 CHANNEL EXPRESSION AND CELLULAR STABILITY

    PubMed Central

    Ciardo, Maria Grazia; Andrés-Bordería, Amparo; Cuesta, Natalia; Valente, Pierluigi; Camprubí-Robles, María; Yang, Jun; Planells-Cases, Rosa; Ferrer-Montiel, Antonio

    2017-01-01

    The expression and function of TRPV1 is influenced by its interaction with cellular proteins. Here, we identify whirlin, a cytoskeletal PDZ-scaffold protein implicated in hearing, vision and mechanosensory transduction, as an interacting partner of TRPV1. Whirlin associates with TRPV1 in cell lines and in primary cultures of rat nociceptors. Whirlin is expressed in 55% of mouse sensory C-fibers, including peptidergic and non-peptidergic nociceptors, and co-localizes with TRPV1 in 70% of them. Heterologous expression of Whirlin increased TRPV1 protein expression and trafficking to the plasma membrane, and promoted receptor clustering. Silencing Whirlin expression with siRNA or blocking protein translation resulted in a concomitant degradation of TRPV1 that could be prevented by inhibiting the proteasome. The degradation kinetics of TRPV1 upon arresting protein translation mirrored that of Whirlin in cells co-expressing both proteins, suggesting a parallel degradation mechanism. Noteworthy, Whirlin expression significantly reduced TRPV1 degradation induced by prolonged exposure to capsaicin. Thus, our findings indicate that Whirlin and TRPV1 are associated in a subset of nociceptors and that TRPV1 protein stability is increased through the interaction with the cytoskeletal scaffold protein. Our results suggest that the Whirlin-TRPV1 complex may represent a novel molecular target and its pharmacological disruption might be a therapeutic strategy for the treatment of peripheral TRPV1-mediated disorders. PMID:26516054

  14. Defect structure and mechanical stability of microcrystalline titanium produced by equal channel angular pressing

    NASA Astrophysics Data System (ADS)

    Betekhtin, V. I.; Kadomtsev, A. G.; Narykova, M. V.; Amosova, O. V.; Sklenicka, V.

    2017-01-01

    It is established that increases in nanoporosity and the proportion of high-angle grain boundaries in the process of equal-channel angular pressing are the main structural factors leading to reduction in mechanical stability (durability) of microcrystalline titanium during long-term tests under creeping conditions.

  15. Lateral movement and stability of channel banks near four highway crossings in southwestern Mississippi

    USGS Publications Warehouse

    Turnipseed, D. Phil

    1994-01-01

    Channel meandering in alluvial streams has caused localized channel instability that has resulted in bridge failure and loss of human life in Mississippi. The U.S. Geological Survey, in coopera- tion with the Mississippi Department of Transpor- tation, conducted a study to develop a better methodology for defining and estimating channel meandering. For this report, river reaches near four bridge sites with current lateral movement of channel banks were selected for study. The lateral movement of channel banks was studied by mapping meanders from aerial photographs taken at various times, evaluating available discharge measurements, and measuring existing channel geometry and soil strength properties at these sites. Rapid, unre- stricted meander cuts and sandy banks are charac- teristic of the sites. Lateral movement was signi- ficant upstream from all four sites, and only one bridge site did not have significant lateral channel-bank movement during the study period. The development of cutbanks and localized channel-bank erosion have caused unstable conditions at three of the sites. Maps of tops of channel indicate significant lateral movement of channel banks upstream and downstream of all four sites and near the bridges at three of four sites. No significant movement occurred at the U.S. Highway 98 crossing of the Bogue Chitto near Tylertown from 1941 to 1991 despite large floods in 1983 and 1990. Slope stability analyses indicated this site to be marginally stable. The maximum lateral movement indicated from maps of tops of channel banks was 680 feet of northward movement of the right (north) bank of the Homochitto River near the State Highway 33 crossing at Rosetta from 1941 to 1983.

  16. flowVS: channel-specific variance stabilization in flow cytometry.

    PubMed

    Azad, Ariful; Rajwa, Bartek; Pothen, Alex

    2016-07-28

    Comparing phenotypes of heterogeneous cell populations from multiple biological conditions is at the heart of scientific discovery based on flow cytometry (FC). When the biological signal is measured by the average expression of a biomarker, standard statistical methods require that variance be approximately stabilized in populations to be compared. Since the mean and variance of a cell population are often correlated in fluorescence-based FC measurements, a preprocessing step is needed to stabilize the within-population variances. We present a variance-stabilization algorithm, called flowVS, that removes the mean-variance correlations from cell populations identified in each fluorescence channel. flowVS transforms each channel from all samples of a data set by the inverse hyperbolic sine (asinh) transformation. For each channel, the parameters of the transformation are optimally selected by Bartlett's likelihood-ratio test so that the populations attain homogeneous variances. The optimum parameters are then used to transform the corresponding channels in every sample. flowVS is therefore an explicit variance-stabilization method that stabilizes within-population variances in each channel by evaluating the homoskedasticity of clusters with a likelihood-ratio test. With two publicly available datasets, we show that flowVS removes the mean-variance dependence from raw FC data and makes the within-population variance relatively homogeneous. We demonstrate that alternative transformation techniques such as flowTrans, flowScape, logicle, and FCSTrans might not stabilize variance. Besides flow cytometry, flowVS can also be applied to stabilize variance in microarray data. With a publicly available data set we demonstrate that flowVS performs as well as the VSN software, a state-of-the-art approach developed for microarrays. The homogeneity of variance in cell populations across FC samples is desirable when extracting features uniformly and comparing cell populations with

  17. Stabilization of the conductive conformation of a voltage-gated K+ (Kv) channel: the lid mechanism.

    PubMed

    Santos, Jose S; Syeda, Ruhma; Montal, Mauricio

    2013-06-07

    Voltage-gated K(+) (Kv) channels are molecular switches that sense membrane potential and in response open to allow K(+) ions to diffuse out of the cell. In these proteins, sensor and pore belong to two distinct structural modules. We previously showed that the pore module alone is a robust yet dynamic structural unit in lipid membranes and that it senses potential and gates open to conduct K(+) with unchanged fidelity. The implication is that the voltage sensitivity of K(+) channels is not solely encoded in the sensor. Given that the coupling between sensor and pore remains elusive, we asked whether it is then possible to convert a pore module characterized by brief openings into a conductor with a prolonged lifetime in the open state. The strategy involves selected probes targeted to the filter gate of the channel aiming to modulate the probability of the channel being open assayed by single channel recordings from the sensorless pore module reconstituted in lipid bilayers. Here we show that the premature closing of the pore is bypassed by association of the filter gate with two novel open conformation stabilizers: an antidepressant and a peptide toxin known to act selectively on Kv channels. Such stabilization of the conductive conformation of the channel is faithfully mimicked by the covalent attachment of fluorescein at a cysteine residue selectively introduced near the filter gate. This modulation prolongs the occupancy of permeant ions at the gate. It is this longer embrace between ion and gate that we conjecture underlies the observed stabilization of the conductive conformation. This study provides a new way of thinking about gating.

  18. Direct laser writing of thermally stabilized channel waveguides with Bragg gratings.

    PubMed

    Nishiyama, Hiroaki; Miyamoto, Isamu; Matsumoto, Shin-Ichi; Saito, Mitsunori; Kintaka, Kenji; Nishii, Junji

    2004-09-20

    Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600 degrees C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500 degrees C, whereas the conventional photo-induced grating decayed even at 200 degrees C.

  19. Direct laser writing of thermally stabilized channel waveguides with Bragg gratings

    NASA Astrophysics Data System (ADS)

    Nishiyama, Hiroaki; Miyamoto, Isamu; Matsumoto, Shin-Ichi; Saito, Mitsunori; Kintaka, Kenji; Nishii, Junji

    2004-09-01

    Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600°C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500°C, whereas the conventional photo-induced grating decayed even at 200°C.

  20. Structural stability of ultra-fine grained magnesium alloys processed by equal channel angular pressing

    NASA Astrophysics Data System (ADS)

    Janeček, M.; Krajňák, T.; Minárik, P.; Čížek, J.; Stráská, J.; Stráský, J.

    2017-05-01

    Structural stability of two magnesium alloys AZ31 (MgAlZn) and AX41 (MgAlCa) processed by equal channel angular pressing is investigated. The mechanical properties, microstructure evolution and dislocation density were studied by microhardness, electron back scatter diffraction and positron annihilation spectroscopy, respectively. The loss of microstructure stability at high temperatures and the coarsening of the ultrafine-grained structure as a result of isochronal annealing is accompanied by the sharp decrease of microhardness and the decrease of dislocation density. The differences in thermal stability of both alloys are related to different conditions of ECAP pressing and the phase stability, namely the presence of stable Al2Ca precipitates in AX41 alloy. Microscopic mechanisms controlling the structure stability of both alloys are discussed.

  1. Stabilized finite element methods to simulate the conductances of ion channels

    NASA Astrophysics Data System (ADS)

    Tu, Bin; Xie, Yan; Zhang, Linbo; Lu, Benzhuo

    2015-03-01

    We have previously developed a finite element simulator, ichannel, to simulate ion transport through three-dimensional ion channel systems via solving the Poisson-Nernst-Planck equations (PNP) and Size-modified Poisson-Nernst-Planck equations (SMPNP), and succeeded in simulating some ion channel systems. However, the iterative solution between the coupled Poisson equation and the Nernst-Planck equations has difficulty converging for some large systems. One reason we found is that the NP equations are advection-dominated diffusion equations, which causes troubles in the usual FE solution. The stabilized schemes have been applied to compute fluids flow in various research fields. However, they have not been studied in the simulation of ion transport through three-dimensional models based on experimentally determined ion channel structures. In this paper, two stabilized techniques, the SUPG and the Pseudo Residual-Free Bubble function (PRFB) are introduced to enhance the numerical robustness and convergence performance of the finite element algorithm in ichannel. The conductances of the voltage dependent anion channel (VDAC) and the anthrax toxin protective antigen pore (PA) are simulated to validate the stabilization techniques. Those two stabilized schemes give reasonable results for the two proteins, with decent agreement with both experimental data and Brownian dynamics (BD) simulations. For a variety of numerical tests, it is found that the simulator effectively avoids previous numerical instability after introducing the stabilization methods. Comparison based on our test data set between the two stabilized schemes indicates both SUPG and PRFB have similar performance (the latter is slightly more accurate and stable), while SUPG is relatively more convenient to implement.

  2. Relation of channel stability to scour at highway bridges over waterways in Maryland

    USGS Publications Warehouse

    Doheny, Edward J.; ,

    1993-01-01

    Data from assessments of channel stability and observed-scour conditions at 876 highway bridges over Maryland waterways were entered into a database. Relations were found to exist among specific, deterministic variables and observed-scour and debris conditions. Relations were investigated between (1) high-flow angle of attack and pier- and abutment-footing exposure, (2)abutment location and abutment-footing exposure, (3) type of bed material and pier-footing exposure, (4) tree cover on channel banks and mass wasting of the channel banks, and (5) land use near the bridge and the presence of debris blockage at the bridge opening. The results of the investigation indicate the following: (1) The number of pier and abutment-footing exposures increased for increasing high-flow angles of attack, (2) the number of abutment-footing exposures increased for abutments that protrude into the channel, (3) pier-footing exposures were most common for bridges over streams with channel beds of gravel, (4) mass wasting of channel banks with tree cover of 50 percent or greater near the bridge was less than mass wasting of channel banks with tree cover of less than 50 percent near the bridge, and (5) bridges blockage than bridge in row crop and swamp basins.

  3. L-type calcium channels regulate filopodia stability and cancer cell invasion downstream of integrin signalling

    PubMed Central

    Jacquemet, Guillaume; Baghirov, Habib; Georgiadou, Maria; Sihto, Harri; Peuhu, Emilia; Cettour-Janet, Pierre; He, Tao; Perälä, Merja; Kronqvist, Pauliina; Joensuu, Heikki; Ivaska, Johanna

    2016-01-01

    Mounting in vitro, in vivo and clinical evidence suggest an important role for filopodia in driving cancer cell invasion. Using a high-throughput microscopic-based drug screen, we identify FDA-approved calcium channel blockers (CCBs) as potent inhibitors of filopodia formation in cancer cells. Unexpectedly, we discover that L-type calcium channels are functional and frequently expressed in cancer cells suggesting a previously unappreciated role for these channels during tumorigenesis. We further demonstrate that, at filopodia, L-type calcium channels are activated by integrin inside-out signalling, integrin activation and Src. Moreover, L-type calcium channels promote filopodia stability and maturation into talin-rich adhesions through the spatially restricted regulation of calcium entry and subsequent activation of the protease calpain-1. Altogether we uncover a novel and clinically relevant signalling pathway that regulates filopodia formation in cancer cells and propose that cycles of filopodia stabilization, followed by maturation into focal adhesions, directs cancer cell migration and invasion. PMID:27910855

  4. Retigabine holds KV7 channels open and stabilizes the resting potential

    PubMed Central

    Corbin-Leftwich, Aaron; Mossadeq, Sayeed M.; Ha, Junghoon; Ruchala, Iwona; Le, Audrey Han Ngoc

    2016-01-01

    The anticonvulsant Retigabine is a KV7 channel agonist used to treat hyperexcitability disorders in humans. Retigabine shifts the voltage dependence for activation of the heteromeric KV7.2/KV7.3 channel to more negative potentials, thus facilitating activation. Although the molecular mechanism underlying Retigabine’s action remains unknown, previous studies have identified the pore region of KV7 channels as the drug’s target. This suggested that the Retigabine-induced shift in voltage dependence likely derives from the stabilization of the pore domain in an open (conducting) conformation. Testing this idea, we show that the heteromeric KV7.2/KV7.3 channel has at least two open states, which we named O1 and O2, with O2 being more stable. The O1 state was reached after short membrane depolarizations, whereas O2 was reached after prolonged depolarization or during steady state at the typical neuronal resting potentials. We also found that activation and deactivation seem to follow distinct pathways, suggesting that the KV7.2/KV7.3 channel activity displays hysteresis. As for the action of Retigabine, we discovered that this agonist discriminates between open states, preferentially acting on the O2 state and further stabilizing it. Based on these findings, we proposed a novel mechanism for the therapeutic effect of Retigabine whereby this drug reduces excitability by enhancing the resting potential open state stability of KV7.2/KV7.3 channels. To address this hypothesis, we used a model for action potential (AP) in Xenopus laevis oocytes and found that the resting membrane potential became more negative as a function of Retigabine concentration, whereas the threshold potential for AP firing remained unaltered. PMID:26880756

  5. Protons stabilize the closed conformation of gain-of-function mutants of the TRPV1 channel.

    PubMed

    Boukalova, Stepana; Teisinger, Jan; Vlachova, Viktorie

    2013-03-01

    The vanilloid transient receptor potential channel TRPV1 is a molecular integrator of noxious stimuli, including capsaicin, heat and protons. Despite clear similarities between the overall architecture of TRPV1 and voltage-dependent potassium (Kv) channels, the extent of conservation in the molecular logic for gating is unknown. In Kv channels, a small contact surface between S1 and the pore-helix is required for channel functioning. To explore the function of S1 in TRPV1, we used tryptophan-scanning mutagenesis and characterized the responses to capsaicin and protons. Wild-type-like currents were generated in 9 out of 17 mutants; three mutants (M445W, A452W, R455W) were non-functional. The conservative mutation R455K in the extracellular extent of S1 slowed down capsaicin-induced activation and prevented normal channel closure. This mutant was neither activated nor potentiated by protons, on the contrary, protons promoted a rapid deactivation of its currents. Similar phenotypes were found in two other gain-of-function mutants and also in the pore-helix mutant T633A, known to uncouple proton activation. We propose that the S1 domain contains a functionally important region that may be specifically involved in TRPV1 channel gating, and thus be important for the energetic coupling between S1-S4 sensor activation and gate opening. Analogous to Kv channels, the S1-pore interface might serve to stabilize conformations associated with TRPV1 channel gating. Copyright © 2012 Elsevier B.V. All rights reserved.

  6. Double-diffusive two-fluid flow in a slippery channel: A linear stability analysis

    NASA Astrophysics Data System (ADS)

    Ghosh, Sukhendu; Usha, R.; Sahu, Kirti Chandra

    2014-12-01

    The effect of velocity slip at the walls on the linear stability characteristics of two-fluid three-layer channel flow (the equivalent core-annular configuration in case of pipe) is investigated in the presence of double diffusive (DD) phenomenon. The fluids are miscible and consist of two solute species having different rates of diffusion. The fluids are assumed to be of the same density, but varying viscosity, which depends on the concentration of the solute species. It is found that the flow stabilizes when the less viscous fluid is present in the region adjacent to the slippery channel walls in the single-component (SC) system but becomes unstable at low Reynolds numbers in the presence of DD effect. As the mixed region of the fluids moves towards the channel walls, a new unstable mode (DD mode), distinct from the Tollman Schlichting (TS) mode, arises at Reynolds numbers smaller than the critical Reynolds number for the TS mode. We also found that this mode becomes more prominent when the mixed layer overlaps with the critical layer. It is shown that the slip parameter has nonmonotonic effect on the stability characteristics in this system. Through energy budget analysis, the dual role of slip is explained. The effect of slip is influenced by the location of mixed layer, the log-mobility ratio of the faster diffusing scalar, diffusivity, and the ratio of diffusion coefficients of the two species. Increasing the value of the slip parameter delays the first occurrence of the DD-mode. It is possible to achieve stabilization or destabilization by controlling the various physical parameters in the flow system. In the present study, we suggest an effective and realistic way to control three-layer miscible channel flow with viscosity stratification.

  7. Enhanced stability of steep channel beds to mass failure and debris flow initiation

    NASA Astrophysics Data System (ADS)

    Prancevic, J.; Lamb, M. P.; Ayoub, F.; Venditti, J. G.

    2015-12-01

    Debris flows dominate bedrock erosion and sediment transport in very steep mountain channels, and are often initiated from failure of channel-bed alluvium during storms. While several theoretical models exist to predict mass failures, few have been tested because observations of in-channel bed failures are extremely limited. To fill this gap in our understanding, we performed laboratory flume experiments to identify the conditions necessary to initiate bed failures in non-cohesive sediment of different sizes (D = 0.7 mm to 15 mm) on steep channel-bed slopes (S = 0.45 to 0.93) and in the presence of water flow. In beds composed of sand, failures occurred under sub-saturated conditions on steep bed slopes (S > 0.5) and under super-saturated conditions at lower slopes. In beds of gravel, however, failures occurred only under super-saturated conditions at all tested slopes, even those approaching the dry angle of repose. Consistent with theoretical models, mass failures under super-saturated conditions initiated along a failure plane approximately one grain-diameter below the bed surface, whereas the failure plane was located near the base of the bed under sub-saturated conditions. However, all experimental beds were more stable than predicted by 1-D infinite-slope stability models. In partially saturated sand, enhanced stability appears to result from suction stress. Enhanced stability in gravel may result from turbulent energy losses in pores or increased granular friction for failures that are shallow with respect to grain size. These grain-size dependent effects are not currently included in stability models for non-cohesive sediment, and they may help to explain better the timing and location of debris flow occurrence.

  8. A piecewise linear mean flow model for studying stability in a lined channel

    NASA Astrophysics Data System (ADS)

    Marx, David

    2012-07-01

    Acoustic liners are used to reduce sound emission by turbofan engines. Under grazing flow they may sustain hydrodynamic instabilities and these are studied using a stability analysis, based on a simplified model: the liner is a mass-spring-damper system, the base channel flow is piecewise linear, and the inviscid, incompressible Rayleigh equation is used. The model is an extension to the channel case of a boundary layer model by Rienstra and Darau. The piecewise linear profile introduces a finite boundary layer thickness which ensures well-posedness, allowing an initial value problem to be conducted to investigate absolute stability. For typical values in aeronautics the flow above the liner is unstable. Absolute instability is obtained for somewhat extreme values of the mean flow (tiny boundary layer thickness), and under realistic conditions the flow is convectively unstable. The effect of finite channel height is investigated in both cases. In particular, for large boundary layer thicknesses associated with convective instability the channel height has little effect on the unstable mode. Favorable outcomes and failures of the model are shown by comparison to a published experimental work.

  9. Stability analysis in a ROADM-based multi-channel quasi-ring optical network

    NASA Astrophysics Data System (ADS)

    Tsai, Jimmy; Wang, Zheng; Pan, Yan; Kilper, Daniel C.; Pavel, Lacra

    2015-01-01

    Future networks require dynamic physical layer capabilities to enable rapid and on-demand reconfiguration, while ensuring stability. This paper addresses stability analysis of a ROADM-based quasi-ring optical network. A ROADM-based quasi-ring is the simplest configuration in which channel power excursions can self-propagate indefinitely and be unstable. This network configuration is composed of two reconfigurable optical add-drop multiplexers (ROADMs) each equipped with a constant gain optical amplifier and a wavelength selective switch. Over the amplified spans, two sets of lightpaths (added/dropped by opposite ROADMs) are transmitted in mirror image of each other and form an overlapping ring. Sufficient stability conditions for the quasi-ring as well as an L2 bound for the channel power excursions are derived based on Lyapunov analysis and the small gain theorem. These conditions are functions of the amplifier gain coupling quantified by its Lipschitz constant. Numerical results that verify and compare the theoretical results are provided. The platform used is Bell Lab's A Transparent Optical Mesh (ATOM) simulator, set up for dynamic network loading and input channel disturbance scenarios.

  10. Bed-material, channel stability, and regional gravel production dynamics in Oregon coastal rivers

    NASA Astrophysics Data System (ADS)

    Jones, K. L.; O'Connor, J. E.; Wallick, R.; Anderson, S.; Keith, M. K.; Mangano, J. F.

    2010-12-01

    Along the Oregon coast, gravel-bed rivers of various basin sizes and network topologies carve their way to the Pacific Ocean through a suite of geologic formations and land-use activities. To date, we have initiated assessments of bed-material condition and channel stability for seven coastal Oregon rivers (from north to south: Nehalem, Tillamook, Umpqua, Coquille, Rogue, Hunter, and Chetco). These river channels are of interest, in part, due to historic and on-going removal of gravels for commercial aggregate. Gravel extraction alone or in conjunction with the effects of other land uses may initiate a variety of channel changes, leading to channel instability. For each river, we synthesize multiple lines of evidence (including field observations, particle measurements, GIS analyses, specific gage analyses, and previous studies) to determine if the river channels are in equilibrium, degrading, or aggrading and if bed-material transport is likely limited by transport capacity or sediment supply. Initial field observations include the presence of reaches with some channel instability (mainly aggradation and channel widening) in the Hunter, Rogue, and Coquille basins. Our preliminary specific gage analyses indicate changes in the stage-discharge relationships at several gages, including a long-term gage on Rogue River near Grants Pass, where the channel has either incised or widened, resulting in a lowering of stage over time and different discharges. Building on our preliminary findings and review of the literature, we postulate that gravel production in coastal Oregon rivers is a function of the surrounding geology, basin slope, annual precipitation rates, channel bed elevation patterns (e.g., the length of the channel bed at sea level), and network structure. Bed-material supply tends to be greatest for rivers draining the Klamath terrane. Preliminary statistical analyses also show that the product of basin slope and mean annual precipitation describes 57% of the

  11. Stability of gas channels in a dense suspension in the presence of obstacles

    NASA Astrophysics Data System (ADS)

    Poryles, Raphaël; Varas, Germán; Vidal, Valérie

    2017-06-01

    We investigate experimentally the influence of a fixed obstacle on gas rising in a dense suspension. Air is injected at a constant flow rate by a single nozzle at the bottom center of a Hele-Shaw cell. Without obstacles, previous works have shown that a fluidized zone is formed with a parabolic shape, with a central air channel and two granular convection rolls on its sides. Here, we quantify the influence of the obstacle's shape, size, and height on the location and dynamics of the central air channel. Different regimes are reported: the air channel can simply deviate (stable), or it can switch sides over time (unstable), leading to two signatures not only above the obstacle, but sometimes also below it. This feedback also influences the channel deviation when bypassing the obstacle. A wake of less or no motion is reported above the largest obstacles as well as the maximum probability of gas location, which can be interesting for practical applications. The existence of a critical height hc≃7 cm is discussed and compared with the existence of an air finger that develops from the injection nozzle and is stable in time. A dimensionless number describing the transition between air fingering and fracturing makes it possible to predict the channel's stability.

  12. Sampling surface particle size distributions and stability analysis of deep channel in the Pearl River Estuary

    NASA Astrophysics Data System (ADS)

    Feng, Hao-chuan; Zhang, Wei; Zhu, Yu-liang; Lei, Zhi-yi; Ji, Xiao-mei

    2017-06-01

    Particle size distributions (PSDs) of bottom sediments in a coastal zone are generally multimodal due to the complexity of the dynamic environment. In this paper, bottom sediments along the deep channel of the Pearl River Estuary (PRE) are used to understand the multimodal PSDs' characteristics and the corresponding depositional environment. The results of curve-fitting analysis indicate that the near-bottom sediments in the deep channel generally have a bimodal distribution with a fine component and a relatively coarse component. The particle size distribution of bimodal sediment samples can be expressed as the sum of two lognormal functions and the parameters for each component can be determined. At each station of the PRE, the fine component makes up less volume of the sediments and is relatively poorly sorted. The relatively coarse component, which is the major component of the sediments, is even more poorly sorted. The interrelations between the dynamics and particle size of the bottom sediment in the deep channel of the PRE have also been investigated by the field measurement and simulated data. The critical shear velocity and the shear velocity are calculated to study the stability of the deep channel. The results indicate that the critical shear velocity has a similar distribution over large part of the deep channel due to the similar particle size distribution of sediments. Based on a comparison between the critical shear velocities derived from sedimentary parameters and the shear velocities obtained by tidal currents, it is likely that the depositional area is mainly distributed in the northern part of the channel, while the southern part of the deep channel has to face higher erosion risk.

  13. Robust Stability of Scaled-Four-Channel Teleoperation with Internet Time-Varying Delays

    PubMed Central

    Delgado, Emma; Barreiro, Antonio; Falcón, Pablo; Díaz-Cacho, Miguel

    2016-01-01

    We describe the application of a generic stability framework for a teleoperation system under time-varying delay conditions, as addressed in a previous work, to a scaled-four-channel (γ-4C) control scheme. Described is how varying delays are dealt with by means of dynamic encapsulation, giving rise to mu-test conditions for robust stability and offering an appealing frequency technique to deal with the stability robustness of the architecture. We discuss ideal transparency problems and we adapt classical solutions so that controllers are proper, without single or double differentiators, and thus avoid the negative effects of noise. The control scheme was fine-tuned and tested for complete stability to zero of the whole state, while seeking a practical solution to the trade-off between stability and transparency in the Internet-based teleoperation. These ideas were tested on an Internet-based application with two Omni devices at remote laboratory locations via simulations and real remote experiments that achieved robust stability, while performing well in terms of position synchronization and force transparency. PMID:27128914

  14. Controlling the position of a stabilized detonation wave in a supersonic gas mixture flow in a plane channel

    NASA Astrophysics Data System (ADS)

    Levin, V. A.; Zhuravskaya, T. A.

    2017-03-01

    Stabilization of a detonation wave in a stoichiometric hydrogen-air mixture flowing at a supersonic velocity into a plane symmetric channel with constriction has been studied in the framework of a detailed kinetic mechanism of the chemical interaction. Conditions ensuring the formation of a thrust-producing f low with a stabilized detonation wave in the channel are determined. The inf luence of the inf low Mach number, dustiness of the combustible gas mixture supplied to the channel, and output cross-section size on the position of a stabilized detonation wave in the f low has been analyzed with a view to increasing the efficiency of detonation combustion of the gas mixture. It is established that thrust-producing flow with a stabilized detonation wave can be formed in the channel without any energy consumption.

  15. Remote and reversible inhibition of neurons and circuits by small molecule induced potassium channel stabilization

    PubMed Central

    Auffenberg, Eva; Jurik, Angela; Mattusch, Corinna; Stoffel, Rainer; Genewsky, Andreas; Namendorf, Christian; Schmid, Roland M.; Rammes, Gerhard; Biel, Martin; Uhr, Manfred; Moosmang, Sven; Michalakis, Stylianos; Wotjak, Carsten T.; Thoeringer, Christoph K.

    2016-01-01

    Manipulating the function of neurons and circuits that translate electrical and chemical signals into behavior represents a major challenges in neuroscience. In addition to optogenetic methods using light-activatable channels, pharmacogenetic methods with ligand induced modulation of cell signaling and excitability have been developed. However, they are largely based on ectopic expression of exogenous or chimera proteins. Now, we describe the remote and reversible expression of a Kir2.1 type potassium channel using the chemogenetic technique of small molecule induced protein stabilization. Based on shield1-mediated shedding of a destabilizing domain fused to a protein of interest and inhibition of protein degradation, this principle has been adopted for biomedicine, but not in neuroscience so far. Here, we apply this chemogenetic approach in brain research for the first time in order to control a potassium channel in a remote and reversible manner. We could show that shield1-mediated ectopic Kir2.1 stabilization induces neuronal silencing in vitro and in vivo in the mouse brain. We also validated this novel pharmacogenetic method in different neurobehavioral paradigms.The DD-Kir2.1 may complement the existing portfolio of pharmaco- and optogenetic techniques for specific neuron manipulation, but it may also provide an example for future applications of this principle in neuroscience research. PMID:26757616

  16. Stability analysis of two phase stratified flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Bhagavatula, Dinesh; S, Pushpavanam

    2015-11-01

    Two phase stratified flows arise in extraction operations in microfluidic systems. It is well established that stratified flows in between two infinite plates is always unstable. However such flows are experimentally observed in micro channels. To understand this paradox we perform a linear stability analysis of stratified two phase Poiseuille flow in a rectangular duct. A two-dimensional fully developed flow through the rectangular channel is considered. The linearized equations along with the boundary conditions in primitive variable formulation are numerically solved using Chebyshev collocation method. All the primitive variables, which are the velocity and pressure fields, are retained in the linearised governing equations. Since boundary conditions for disturbance pressure do not exist, the corresponding compatibility conditions derived from the Navier-Stokes equations are collocated both at the walls and the interface. The resulting eigen-value problem is solved using a shift and invert Arnoldi algorithm. The role of different parameters such as Aspect ratio, density ratio, viscosity ratio on the stability characteristics is analyzed. The stability results are validated in the limit of large Aspect Ratios. The flow fields are sought as a combination of Chebyshev polynomials in both y and z directions. Ministry of Human Resource and Development (MHDR).

  17. The initial instability and finite-amplitude stability of alternate bars in straight channels

    USGS Publications Warehouse

    Nelson, J.M.

    1990-01-01

    The initial instability and fully developed stability of alternate bars in straight channels are investigated using linearized and nonlinear analyses. The fundamental instability leading to these features is identified through a linear stability analysis of the equations governing the flow and sediment transport fields. This instability is explained in terms of topographically induced steering of the flow and the associated pattern of erosion and deposition on the bed. While the linear theory is useful for examining the instability mechanism, this approach is shown to yield relatively little information about well-developed alternate bars and, specifically, the linear analysis is shown to yield poor predictions of the fully developed bar wavelength. A fully nonlinear approach is presented that permits computation of the evolution of these bed features from an initial perturbation to their fully developed morphology. This analysis indicates that there is typically substantial elongation of the bar wavelength during the evolution process, a result that is consistent with observations of bar development in flumes and natural channels. The nonlinear approach demonstrates that the eventual stability of these features is a result of the interplay between topographic steering effects, secondary flow production as a result of streamline curvature, and gravitationally induced modifications of sediment fluxes over a sloping bed. ?? 1990.

  18. Stability assessment of QKD procedures in commercial quantum cryptography systems versus quality of dark channel

    NASA Astrophysics Data System (ADS)

    Jacak, Monika; Melniczuk, Damian; Jacak, Janusz; Jóźwiak, Ireneusz; Gruber, Jacek; Jóźwiak, Piotr

    2015-02-01

    In order to assess the susceptibility of the quantum key distribution (QKD) systems to the hacking attack including simultaneous and frequent system self-decalibrations, we analyze the stability of the QKD transmission organized in two commercially available systems. The first one employs non-entangled photons as flying qubits in the dark quantum channel for communication whereas the second one utilizes the entangled photon pairs to secretly share the cryptographic key. Applying standard methods of the statistical data analysis to the characteristic indicators of the quality of the QKD communication (the raw key exchange rate [RKER] and the quantum bit error rate [QBER]), we have estimated the pace of the self-decalibration of both systems and the repeatability rate in the case of controlled worsening of the dark channel quality.

  19. Machine-Learning Based Channel Quality and Stability Estimation for Stream-Based Multichannel Wireless Sensor Networks.

    PubMed

    Rehan, Waqas; Fischer, Stefan; Rehan, Maaz

    2016-09-12

    Wireless sensor networks (WSNs) have become more and more diversified and are today able to also support high data rate applications, such as multimedia. In this case, per-packet channel handshaking/switching may result in inducing additional overheads, such as energy consumption, delays and, therefore, data loss. One of the solutions is to perform stream-based channel allocation where channel handshaking is performed once before transmitting the whole data stream. Deciding stream-based channel allocation is more critical in case of multichannel WSNs where channels of different quality/stability are available and the wish for high performance requires sensor nodes to switch to the best among the available channels. In this work, we will focus on devising mechanisms that perform channel quality/stability estimation in order to improve the accommodation of stream-based communication in multichannel wireless sensor networks. For performing channel quality assessment, we have formulated a composite metric, which we call channel rank measurement (CRM), that can demarcate channels into good, intermediate and bad quality on the basis of the standard deviation of the received signal strength indicator (RSSI) and the average of the link quality indicator (LQI) of the received packets. CRM is then used to generate a data set for training a supervised machine learning-based algorithm (which we call Normal Equation based Channel quality prediction (NEC) algorithm) in such a way that it may perform instantaneous channel rank estimation of any channel. Subsequently, two robust extensions of the NEC algorithm are proposed (which we call Normal Equation based Weighted Moving Average Channel quality prediction (NEWMAC) algorithm and Normal Equation based Aggregate Maturity Criteria with Beta Tracking based Channel weight prediction (NEAMCBTC) algorithm), that can perform channel quality estimation on the basis of both current and past values of channel rank estimation. In the end

  20. Machine-Learning Based Channel Quality and Stability Estimation for Stream-Based Multichannel Wireless Sensor Networks

    PubMed Central

    Rehan, Waqas; Fischer, Stefan; Rehan, Maaz

    2016-01-01

    Wireless sensor networks (WSNs) have become more and more diversified and are today able to also support high data rate applications, such as multimedia. In this case, per-packet channel handshaking/switching may result in inducing additional overheads, such as energy consumption, delays and, therefore, data loss. One of the solutions is to perform stream-based channel allocation where channel handshaking is performed once before transmitting the whole data stream. Deciding stream-based channel allocation is more critical in case of multichannel WSNs where channels of different quality/stability are available and the wish for high performance requires sensor nodes to switch to the best among the available channels. In this work, we will focus on devising mechanisms that perform channel quality/stability estimation in order to improve the accommodation of stream-based communication in multichannel wireless sensor networks. For performing channel quality assessment, we have formulated a composite metric, which we call channel rank measurement (CRM), that can demarcate channels into good, intermediate and bad quality on the basis of the standard deviation of the received signal strength indicator (RSSI) and the average of the link quality indicator (LQI) of the received packets. CRM is then used to generate a data set for training a supervised machine learning-based algorithm (which we call Normal Equation based Channel quality prediction (NEC) algorithm) in such a way that it may perform instantaneous channel rank estimation of any channel. Subsequently, two robust extensions of the NEC algorithm are proposed (which we call Normal Equation based Weighted Moving Average Channel quality prediction (NEWMAC) algorithm and Normal Equation based Aggregate Maturity Criteria with Beta Tracking based Channel weight prediction (NEAMCBTC) algorithm), that can perform channel quality estimation on the basis of both current and past values of channel rank estimation. In the end

  1. Stabilization of inactive braid channels by vegetation as a mechanism for suppressing braiding and reinforcing the dominant channels in a braided network

    NASA Astrophysics Data System (ADS)

    Egozi, R.; Tal, M.

    2009-12-01

    A defining feature of braided rivers is their pattern of multiple interweaving channels. A set of laboratory experiments on braiding kinematics demonstrated that only a subset of the total apparent channels at any given time is actually transporting bed material and actively involved in channel morphodynamics. The number of active channels versus the total number of channels was found to vary independently with changes in discharge and each stabilized around an average value when the discharge was remained constant for a sufficiently long time. The results suggest that a ratio of the number of active braids (ABI) to the total number of braids (TBI) and the time-variation of this ratio is a more accurate way to characterize a network of braided channels than the standard braiding index. At any given time, the non-active channels in the network had typically been active earlier and were likely to be reactivated later at the expense of the currently active ones. The implication is that bed activity shifts from one channel to another without obliterating the previous channel. A separate series of laboratory experiments demonstrated that riparian vegetation can cause a braided channel to self-organize to a single-thread channel. The initial condition for the experiments was steady-state braiding in noncohesive sand under uniform discharge. From here, an experiment consisted of repeated cycles alternating a short duration high flow with a long duration low flow, and uniform dispersal of alfalfa seeds over the bed at the end of each high flow. Plants established on freshly deposited bars and areas of braid plain that were unoccupied during low flow. The presence of the plants had the effect of progressively focusing the high flow so that a single dominant channel developed. The unvegetated braided state was typically comprised of one dominant braid channel and several secondary channels. The dominant channel was able to readily switch its location while previously active

  2. Stabilizing effects on 2D channel flow due to longitudinal wall oscillation

    NASA Astrophysics Data System (ADS)

    Atobe, Takashi

    2017-01-01

    Stabilizing effect of longitudinal wall oscillation on two dimensional channel flow is analytically investigated. Model flow considered here is constituted of a superposition of the plane Poiseuille flow and the Stokes layer. The two walls are periodically oscillated in phase. Since the present system has a periodicity, the Floquet method is employed for the stability analysis. For this, a partial difference equation with a periodic function is derived from the time dependent version of the Orr-Sommerfeld equation using the Chebyshev spectral collocation method. The parameters governing the present system are the Reynolds number Re, the period Ω and amplitude Uw of the wall oscillation. Depending on the parameters, it is found that the 2D Tollmein-Shlichtin (TS) modes can be stabilized by the wall oscillation. Furthermore there are some case that 2D TS modes are more stabilized than the oblique TS mode. These results suggest that the oblique TS mode can appear earlier than the TS mode contrary to the Squire's Theorem.

  3. Control of trap density in channel layer for the higher stability of oxide thin film transistors under gate bias stress

    NASA Astrophysics Data System (ADS)

    Moon, Y. K.; Kim, W. S.; Kim, K. T.; Han, D. S.; Shin, S. Y.; Park, J. W.

    2011-12-01

    In this study, we investigated turn-on voltage (VON) stability of oxide-based TFTs under constant voltage stress for the TFTs including intrinsic ZnO, Hf-doped ZnO, and Hf-Zn-Sn-O channel layer. Also, to verify the effects of interfacial trap density on the TFTs stability, we employed SiNX and SiO2/SiNX as gate insulator, respectively. We found that the low trap density of the TFTs, including the interfacial trap density between channel and gate insulator, and oxide semiconductor bulk trap density is intimately related to excellent gate bias and temperature stability.

  4. On the Stability of Wave Disturbances in Non-Pressure Round-Cylindrical Channels

    NASA Astrophysics Data System (ADS)

    Gagoshidze, Shalva

    2015-04-01

    In hydraulic engineering practice, is well know of and take into account the fact that for a nearly fully filled gravity-flow tunnel with a circular cross section the water flows with shocks, i.e. unstable. Such a phenomenon also occurs when emptying a bottle, but no mathematical confirmation has so far been found for it. In the paper, the estimate of the flow stability is obtained for two limiting cases: - when the channel of circular cross-section is nearly fully filled with water and when it is nearly empty, i.e. the water flow in the channel has a small depth as compared with the radius of the water conduit. Wave equations written in a cylindrical system of coordinates x,r,θ where the x- axis coincides with the axis of the channel; r is the radius vector, θ is the angle counted off from the equatorial plane of the channel upward (with sign "+') and downward (with sign "-') are simplified by neglecting the change of the polar angle (π 2 -θ)in limit of a small width of the free surface of the flow. As a result of this simplification the Helmholtz equation for the wave potential reduces to a Bessel equation with respect to the function ψ(r) not depending on the angle θ and its asymptotic solution will be expressed by the relation ° -- R0 ψ(r) = C -r-cosh k(R0 - r). (1) Dispersion relations will take the form σ = kU0 ± i°gk-tanh-k(R0--h) (2) - for channels with nearly full filling, and ° -------- σ = kU0 ± gktanhk(R0 - h) (3) - for round-cylindrical channels with a small water depth. In these relations, R0 is the radius of the channel, U0 is the stationary water flow velocity, i is the imaginary unit, h is the distance between the horizontal axis and the water level in the channel, σ is the wave disturbance frequency, k is the wave number, C is an arbitrary constant. In the first case, the relation (2) indicates the occurrence of Helmholtz instability of wave disturbances independently of a velocity value of stationary water flow. This result fully

  5. Channels

    NASA Image and Video Library

    2014-04-29

    Two channels are visible in this image from NASA 2001 Mars Odyssey spacecraft . The smaller one near the bottom did not carve as deeply as the larger channel at the top. The channel near the top of the image is near the origin of Mamers Valles.

  6. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow

    NASA Astrophysics Data System (ADS)

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  7. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow.

    PubMed

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  8. A novel tarantula toxin stabilizes the deactivated voltage sensor of bacterial sodium channel.

    PubMed

    Tang, Cheng; Zhou, Xi; Nguyen, Phuong Tran; Zhang, Yunxiao; Hu, Zhaotun; Zhang, Changxin; Yarov-Yarovoy, Vladimir; DeCaen, Paul G; Liang, Songping; Liu, Zhonghua

    2017-07-01

    Voltage-gated sodium channels (NaVs) are activated by transiting the voltage sensor from the deactivated to the activated state. The crystal structures of several bacterial NaVs have captured the voltage sensor module (VSM) in an activated state, but structure of the deactivated voltage sensor remains elusive. In this study, we sought to identify peptide toxins stabilizing the deactivated VSM of bacterial NaVs. We screened fractions from several venoms and characterized a cystine knot toxin called JZTx-27 from the venom of tarantula Chilobrachys jingzhao as a high-affinity antagonist of the prokaryotic NaVs NsVBa (nonselective voltage-gated Bacillus alcalophilus) and NaChBac (bacterial sodium channel from Bacillus halodurans) (IC50 = 112 nM and 30 nM, respectively). JZTx-27 was more efficacious at weaker depolarizing voltages and significantly slowed the activation but accelerated the deactivation of NsVBa, whereas the local anesthetic drug lidocaine was shown to antagonize NsVBa without affecting channel gating. Mutation analysis confirmed that JZTx-27 bound to S3-4 linker of NsVBa, with F98 being the critical residue in determining toxin affinity. All electrophysiological data and in silico analysis suggested that JZTx-27 trapped VSM of NsVBa in one of the deactivated states. In mammalian NaVs, JZTx-27 preferably inhibited the inactivation of NaV1.5 by targeting the fourth transmembrane domain. To our knowledge, this is the first report of peptide antagonist for prokaryotic NaVs. More important, we proposed that JZTx-27 stabilized the NsVBa VSM in the deactivated state and may be used as a probe to determine the structure of the deactivated VSM of NaVs.-Tang, C., Zhou, X., Nguyen, P. T., Zhang, Y., Hu, Z., Zhang, C., Yarov-Yarovoy, V., DeCaen, P. G., Liang, S., Liu, Z. A novel tarantula toxin stabilizes the deactivated voltage sensor of bacterial sodium channel. © FASEB.

  9. Beam dynamics and stability analysis of an intense beam in a continuously twisted quadrupole focusing channel

    NASA Astrophysics Data System (ADS)

    Goswami, A.; Sing Babu, P.; Pandit, V. S.

    2016-11-01

    This paper describes the dynamics of a space-charge-dominated beam through a continuously twisted quadrupole magnet using ten independent first-order differential equations of the beam matrix elements under the assumption of linear space-charge force. Various beam optical properties of the magnet and the evolution of the emittance that results from the coupling between the two transverse planes are studied. The perturbed equations of motion around the matched beam envelopes have been derived and utilized to analyze the stability properties of the intense beam transport by calculating the eigenvalues of the transfer map over one lattice period. Detailed analysis shows the presence of instability due to parametric resonances in a twisted quadrupole channel which generally does not appear in the FODO quadrupole channel. A 2D particle-in-cell simulation code has been developed and utilized to verify the analytical results and to examine the behavior of the intense beam with Gaussian (GA) distribution in the twisted quadrupole channel.

  10. Barbiturates Bind in the GLIC Ion Channel Pore and Cause Inhibition by Stabilizing a Closed State.

    PubMed

    Fourati, Zaineb; Ruza, Reinis Reinholds; Laverty, Duncan; Drège, Emmanuelle; Delarue-Cochin, Sandrine; Joseph, Delphine; Koehl, Patrice; Smart, Trevor; Delarue, Marc

    2017-02-03

    Barbiturates induce anesthesia by modulating the activity of anionic and cationic pentameric ligand-gated ion channels (pLGICs). Despite more than a century of use in clinical practice, the prototypic binding site for this class of drugs within pLGICs is yet to be described. In this study, we present the first X-ray structures of barbiturates bound to GLIC, a cationic prokaryotic pLGIC with excellent structural homology to other relevant channels sensitive to general anesthetics and, as shown here, to barbiturates, at clinically relevant concentrations. Several derivatives of barbiturates containing anomalous scatterers were synthesized, and these derivatives helped us unambiguously identify a unique barbiturate binding site within the central ion channel pore in a closed conformation. In addition, docking calculations around the observed binding site for all three states of the receptor, including a model of the desensitized state, showed that barbiturates preferentially stabilize the closed state. The identification of this pore binding site sheds light on the mechanism of barbiturate inhibition of cationic pLGICs and allows the rationalization of several structural and functional features previously observed for barbiturates. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

  11. Weakly nonlinear stability analysis of non-isothermal Poiseuille flow in a vertical channel

    NASA Astrophysics Data System (ADS)

    Khandelwal, Manish K.; Bera, P.

    2015-06-01

    A weakly nonlinear stability theory in terms of Landau equation is developed to analyze the nonlinear saturation of stably stratified non-isothermal Poiseuille flow in a vertical channel. The results are presented with respect to fluids: mercury, gases, liquids, and heavy oils. The weakly nonlinear stability results predict only the supercritical instability, in agreement with the published result [Y. C. Chen and J. N. Chung, "A direct numerical simulation of K and H-type flow transition in heated vertical channel," Comput. Fluids 32, 795-822 (2003)] based on direct numerical simulation. Apart from this, the influence of nonlinear interaction among different superimposed waves on the heat transfer rate, real part of wavespeed, and friction coefficient on the wall is also investigated. A substantial enhancement (reduction) in heat transfer rate (friction coefficient) is found for liquids and heavy oils from the basic state beyond the critical Rayleigh number. The amplitude analysis indicates that the equilibrium amplitude decreases on increasing the value of Reynolds number. However, in the case of mercury, influence of nonlinear interaction on the variation of equilibrium amplitude, heat transfer rate, wavespeed, as well as friction coefficient is complex and subtle. The analysis of the nonlinear energy spectra for the disturbance also supports the supercritical instability at and beyond the critical point. Finally, the effect of superimposed waves on the pattern of secondary flow, based on linear stability theory, is also studied. It has been found that the impact of nonlinear interaction of waves on the pattern of secondary flow for mercury is weak compared to gases, which is the consequence of negligible modification in the buoyant production of disturbance kinetic energy of the mercury.

  12. Inferring tidal wetland stability from channel sediment fluxes: observations and a conceptual model

    USGS Publications Warehouse

    Ganju, Neil K.; Nidzieko, Nicholas J.; Kirwan, Matthew L.

    2013-01-01

    Anthropogenic and climatic forces have modified the geomorphology of tidal wetlands over a range of timescales. Changes in land use, sediment supply, river flow, storminess, and sea level alter the layout of tidal channels, intertidal flats, and marsh plains; these elements define wetland complexes. Diagnostically, measurements of net sediment fluxes through tidal channels are high-temporal resolution, spatially integrated quantities that indicate (1) whether a complex is stable over seasonal timescales and (2) what mechanisms are leading to that state. We estimated sediment fluxes through tidal channels draining wetland complexes on the Blackwater and Transquaking Rivers, Maryland, USA. While the Blackwater complex has experienced decades of degradation and been largely converted to open water, the Transquaking complex has persisted as an expansive, vegetated marsh. The measured net export at the Blackwater complex (1.0 kg/s or 0.56 kg/m2/yr over the landward marsh area) was caused by northwesterly winds, which exported water and sediment on the subtidal timescale; tidally forced net fluxes were weak and precluded landward transport of suspended sediment from potential seaward sources. Though wind forcing also exported sediment at the Transquaking complex, strong tidal forcing and proximity to a turbidity maximum led to an import of sediment (0.031 kg/s or 0.70 kg/m2/yr). This resulted in a spatially averaged accretion of 3.9 mm/yr, equaling the regional relative sea level rise. Our results suggest that in areas where seaward sediment supply is dominant, seaward wetlands may be more capable of withstanding sea level rise over the short term than landward wetlands. We propose a conceptual model to determine a complex's tendency toward stability or instability based on sediment source, wetland channel location, and transport mechanisms. Wetlands with a reliable portfolio of sources and transport mechanisms appear better suited to offset natural and

  13. Functional stabilization of weakened thalamic pacemaker channel regulation in rat absence epilepsy

    PubMed Central

    Kuisle, Mira; Wanaverbecq, Nicolas; Brewster, Amy L; Frère, Samuel G A; Pinault, Didier; Baram, Tallie Z; Lüthi, Anita

    2006-01-01

    Aberrant function of pacemaker currents (Ih), carried by hyperpolarization-activated cation non-selective (HCN) channels, affects neuronal excitability and accompanies epilepsy, but its distinct roles in epileptogenesis and chronic epilepsy are unclear. We probed Ih function and subunit composition during both pre- and chronically epileptic stages in thalamocortical (TC) neurones of the Genetic Absence Epilepsy Rat from Strasbourg (GAERS). Voltage gating of Ih was unaltered in mature somatosensory TC cells, both in vivo and in vitro. However, the enhancement of Ih by phasic, near-physiological, cAMP pulses was diminished by ∼40% and the half-maximal cAMP concentration increased by ∼5-fold. This decreased responsiveness of Ih to its major cellular modulator preceded epilepsy onset in GAERS, persisted throughout the chronic state, and was accompanied by an enhanced expression of the cAMP-insensitive HCN1 channel mRNA (> 50%), without changes in the mRNA levels of HCN2 and HCN4. To assess for alterations in TC cell excitability, we monitored the slow up-regulation of Ih that is induced by Ca2+-triggered cAMP synthesis and important for terminating in vitro synchronized oscillations. Remarkably, repetitive rebound Ca2+ spikes evoked normal slow Ih up-regulation in mature GAERS neurones; that sufficed to attenuate spontaneous rhythmic burst discharges. These adaptive mechanisms occurred upstream of cAMP turnover and involved enhanced intracellular Ca2+ accumulation upon repetitive low-threshold Ca2+ discharges. Therefore, HCN channels appear to play a dual role in epilepsy. Weakened cAMP binding to HCN channels precedes, and likely promotes, epileptogenesis in GAERS, whereas compensatory mechanisms stabilizing Ih function contribute to the termination of spike-and-wave discharges in chronic epilepsy. PMID:16728450

  14. Polycystin-1 Is a Cardiomyocyte Mechanosensor That Governs L-Type Ca2+ Channel Protein Stability.

    PubMed

    Pedrozo, Zully; Criollo, Alfredo; Battiprolu, Pavan K; Morales, Cyndi R; Contreras-Ferrat, Ariel; Fernández, Carolina; Jiang, Nan; Luo, Xiang; Caplan, Michael J; Somlo, Stefan; Rothermel, Beverly A; Gillette, Thomas G; Lavandero, Sergio; Hill, Joseph A

    2015-06-16

    L-type calcium channel activity is critical to afterload-induced hypertrophic growth of the heart. However, the mechanisms governing mechanical stress-induced activation of L-type calcium channel activity are obscure. Polycystin-1 (PC-1) is a G protein-coupled receptor-like protein that functions as a mechanosensor in a variety of cell types and is present in cardiomyocytes. We subjected neonatal rat ventricular myocytes to mechanical stretch by exposing them to hypo-osmotic medium or cyclic mechanical stretch, triggering cell growth in a manner dependent on L-type calcium channel activity. RNAi-dependent knockdown of PC-1 blocked this hypertrophy. Overexpression of a C-terminal fragment of PC-1 was sufficient to trigger neonatal rat ventricular myocyte hypertrophy. Exposing neonatal rat ventricular myocytes to hypo-osmotic medium resulted in an increase in α1C protein levels, a response that was prevented by PC-1 knockdown. MG132, a proteasomal inhibitor, rescued PC-1 knockdown-dependent declines in α1C protein. To test this in vivo, we engineered mice harboring conditional silencing of PC-1 selectively in cardiomyocytes (PC-1 knockout) and subjected them to mechanical stress in vivo (transverse aortic constriction). At baseline, PC-1 knockout mice manifested decreased cardiac function relative to littermate controls, and α1C L-type calcium channel protein levels were significantly lower in PC-1 knockout hearts. Whereas control mice manifested robust transverse aortic constriction-induced increases in cardiac mass, PC-1 knockout mice showed no significant growth. Likewise, transverse aortic constriction-elicited increases in hypertrophic markers and interstitial fibrosis were blunted in the knockout animals PC-1 is a cardiomyocyte mechanosensor that is required for cardiac hypertrophy through a mechanism that involves stabilization of α1C protein. © 2015 American Heart Association, Inc.

  15. Stability of optimal streaks in the buffer layer of a turbulent channel flow with variable viscosity

    NASA Astrophysics Data System (ADS)

    Patel, Ashish; Rinaldi, Enrico; Pecnik, Rene; Schlatter, Philipp; Bagheri, Shervin

    2016-11-01

    Direct Numerical Simulations (DNS) of turbulent channel flows with variable viscosity (Patel et al., 2015, PoF) show that low speed streaks in the buffer layer strengthen and are stabilized for increasing viscosity away from the wall, as they do not lift and tilt as intensely as in a constant property flow. The opposite holds for cases where viscosity decreases away from the wall. In this work, we investigate the above observation by studying the linear stability of the mean turbulent velocity profile obtained from DNS of variable viscosity flows. Examples of such studies for constant property turbulent flows include work of del Alamo & Jiménez, 2006, JFM and Pujals et al., 2009, PoF. The calculated optimal buffer layer streaks show larger transient energy growth for a case where the viscosity increases away from the wall. We further study the stability of the saturated optimal streaks by imposing a secondary sinuous perturbation and by following the nonlinear evolution of the structures in time. The present investigation will improve the understanding of the near-wall turbulence cycle for wall-bounded turbulent flows with viscosity gradients.

  16. Protein interactions central to stabilizing the K+ channel selectivity filter in a four-sited configuration for selective K+ permeation

    PubMed Central

    Sauer, David B.; Zeng, Weizhong; Raghunathan, Srinivasan; Jiang, Youxing

    2011-01-01

    The structural and functional conversion of the nonselective NaK channel to a K+ selective channel (NaK2K) allows us to identify two key residues, Tyr and Asp in the filter sequence of TVGYGD, that participate in interactions central to stabilizing the K+ channel selectivity filter. By using protein crystallography and channel electrophysiology, we demonstrate that the K+ channel filter exists as an energetically strained structure and requires these key protein interactions working in concert to hold the filter in the precisely defined four-sited configuration that is essential for selective K+ permeation. Disruption of either interaction, as tested on both the NaK2K and eukaryotic Kv1.6 channels, can reduce or completely abolish K+ selectivity and in some cases may also lead to channel inactivation due to conformational changes at the filter. Additionally, on the scaffold of NaK we recapitulate the protein interactions found in the filter of the Kir channel family, which uses a distinct interaction network to achieve similar stabilization of the filter. PMID:21933962

  17. Self-assembled two-dimensional nanofluidic proton channels with high thermal stability

    NASA Astrophysics Data System (ADS)

    Shao, Jiao-Jing; Raidongia, Kalyan; Koltonow, Andrew R.; Huang, Jiaxing

    2015-07-01

    Exfoliated two-dimensional (2D) sheets can readily stack to form flexible, free-standing films with lamellar microstructure. The interlayer spaces in such lamellar films form a percolated network of molecularly sized, 2D nanochannels that could be used to regulate molecular transport. Here we report self-assembled clay-based 2D nanofluidic channels with surface charge-governed proton conductivity. Proton conductivity of these 2D channels exceeds that of acid solution for concentrations up to 0.1 M, and remains stable as the reservoir concentration is varied by orders of magnitude. Proton transport occurs through a Grotthuss mechanism, with activation energy and mobility of 0.19 eV and 1.2 × 10-3 cm2 V-1 s-1, respectively. Vermiculite nanochannels exhibit extraordinary thermal stability, maintaining their proton conduction functions even after annealing at 500 °C in air. The ease of constructing massive arrays of stable 2D nanochannels without lithography should prove useful to the study of confined ionic transport, and will enable new ionic device designs.

  18. Erythromelalgia mutation Q875E Stabilizes the activated state of sodium channel Nav1.7.

    PubMed

    Stadler, Theresa; O'Reilly, Andrias O; Lampert, Angelika

    2015-03-06

    The human voltage-gated sodium channel Nav1.7 plays a crucial role in transmission of noxious stimuli. The inherited pain disorder erythromelalgia (IEM) has been linked to Nav1.7 gain-of-function mutations. Here we show that the IEM-associated Q875E mutation located on the pore module of Nav1.7 produces a large hyperpolarizing shift (-18 mV) in the voltage dependence of activation. Three-dimensional homology modeling indicates that the side chains of Gln-875 and the gating charge Arg-214 of the domain I voltage sensor are spatially close in the activated conformation of the channel. We verified this proximity by using an engineered disulfide bridge approach. The Q875E mutation introduces a negative charge that may modify the local electrical field experienced by the voltage sensor and, upon activation, interact directly via a salt bridge with the Arg-214 gating charge residue. Together these processes could promote transition to, and stabilization of, the domain I voltage sensor in the activated conformation and thus produce the observed gain of function. In support of this hypothesis, an increase in the extracellular concentration of Ca(2+) or Mg(2+) reverted the voltage dependence of activation of the IEM mutant to near WT values, suggesting a cation-mediated electrostatic screening of the proposed interaction between Q875E and Arg-214. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  19. Erythromelalgia Mutation Q875E Stabilizes the Activated State of Sodium Channel Nav1.7*

    PubMed Central

    Stadler, Theresa; O'Reilly, Andrias O.; Lampert, Angelika

    2015-01-01

    The human voltage-gated sodium channel Nav1.7 plays a crucial role in transmission of noxious stimuli. The inherited pain disorder erythromelalgia (IEM) has been linked to Nav1.7 gain-of-function mutations. Here we show that the IEM-associated Q875E mutation located on the pore module of Nav1.7 produces a large hyperpolarizing shift (−18 mV) in the voltage dependence of activation. Three-dimensional homology modeling indicates that the side chains of Gln-875 and the gating charge Arg-214 of the domain I voltage sensor are spatially close in the activated conformation of the channel. We verified this proximity by using an engineered disulfide bridge approach. The Q875E mutation introduces a negative charge that may modify the local electrical field experienced by the voltage sensor and, upon activation, interact directly via a salt bridge with the Arg-214 gating charge residue. Together these processes could promote transition to, and stabilization of, the domain I voltage sensor in the activated conformation and thus produce the observed gain of function. In support of this hypothesis, an increase in the extracellular concentration of Ca2+ or Mg2+ reverted the voltage dependence of activation of the IEM mutant to near WT values, suggesting a cation-mediated electrostatic screening of the proposed interaction between Q875E and Arg-214. PMID:25575597

  20. A disulfide tether stabilizes the block of sodium channels by the conotoxin μO§-GVIIJ.

    PubMed

    Gajewiak, Joanna; Azam, Layla; Imperial, Julita; Walewska, Aleksandra; Green, Brad R; Bandyopadhyay, Pradip K; Raghuraman, Shrinivasan; Ueberheide, Beatrix; Bern, Marshall; Zhou, H Mimi; Minassian, Natali A; Hagan, Rebecca H; Flinspach, Mack; Liu, Yi; Bulaj, Grzegorz; Wickenden, Alan D; Olivera, Baldomero M; Yoshikami, Doju; Zhang, Min-Min

    2014-02-18

    A cone snail venom peptide, μO§-conotoxin GVIIJ from Conus geographus, has a unique posttranslational modification, S-cysteinylated cysteine, which makes possible formation of a covalent tether of peptide to its target Na channels at a distinct ligand-binding site. μO§-conotoxin GVIIJ is a 35-aa peptide, with 7 cysteine residues; six of the cysteines form 3 disulfide cross-links, and one (Cys24) is S-cysteinylated. Due to limited availability of native GVIIJ, we primarily used a synthetic analog whose Cys24 was S-glutathionylated (abbreviated GVIIJSSG). The peptide-channel complex is stabilized by a disulfide tether between Cys24 of the peptide and Cys910 of rat (r) NaV1.2. A mutant channel of rNaV1.2 lacking a cysteine near the pore loop of domain II (C910L), was >10(3)-fold less sensitive to GVIIJSSG than was wild-type rNaV1.2. In contrast, although rNaV1.5 was >10(4)-fold less sensitive to GVIIJSSG than NaV1.2, an rNaV1.5 mutant with a cysteine in the homologous location, rNaV1.5[L869C], was >10(3)-fold more sensitive than wild-type rNaV1.5. The susceptibility of rNaV1.2 to GVIIJSSG was significantly altered by treating the channels with thiol-oxidizing or disulfide-reducing agents. Furthermore, coexpression of rNaVβ2 or rNaVβ4, but not that of rNaVβ1 or rNaVβ3, protected rNaV1.1 to -1.7 (excluding NaV1.5) against block by GVIIJSSG. Thus, GVIIJ-related peptides may serve as probes for both the redox state of extracellular cysteines and for assessing which NaVβ- and NaVα-subunits are present in native neurons.

  1. A disulfide tether stabilizes the block of sodium channels by the conotoxin μO§-GVIIJ

    PubMed Central

    Gajewiak, Joanna; Azam, Layla; Imperial, Julita; Walewska, Aleksandra; Green, Brad R.; Bandyopadhyay, Pradip K.; Raghuraman, Shrinivasan; Ueberheide, Beatrix; Bern, Marshall; Zhou, H. Mimi; Minassian, Natali A.; Hagan, Rebecca H.; Flinspach, Mack; Liu, Yi; Bulaj, Grzegorz; Wickenden, Alan D.; Olivera, Baldomero M.; Yoshikami, Doju

    2014-01-01

    A cone snail venom peptide, μO§-conotoxin GVIIJ from Conus geographus, has a unique posttranslational modification, S-cysteinylated cysteine, which makes possible formation of a covalent tether of peptide to its target Na channels at a distinct ligand-binding site. μO§-conotoxin GVIIJ is a 35-aa peptide, with 7 cysteine residues; six of the cysteines form 3 disulfide cross-links, and one (Cys24) is S-cysteinylated. Due to limited availability of native GVIIJ, we primarily used a synthetic analog whose Cys24 was S-glutathionylated (abbreviated GVIIJSSG). The peptide-channel complex is stabilized by a disulfide tether between Cys24 of the peptide and Cys910 of rat (r) NaV1.2. A mutant channel of rNaV1.2 lacking a cysteine near the pore loop of domain II (C910L), was >103-fold less sensitive to GVIIJSSG than was wild-type rNaV1.2. In contrast, although rNaV1.5 was >104-fold less sensitive to GVIIJSSG than NaV1.2, an rNaV1.5 mutant with a cysteine in the homologous location, rNaV1.5[L869C], was >103-fold more sensitive than wild-type rNaV1.5. The susceptibility of rNaV1.2 to GVIIJSSG was significantly altered by treating the channels with thiol-oxidizing or disulfide-reducing agents. Furthermore, coexpression of rNaVβ2 or rNaVβ4, but not that of rNaVβ1 or rNaVβ3, protected rNaV1.1 to -1.7 (excluding NaV1.5) against block by GVIIJSSG. Thus, GVIIJ-related peptides may serve as probes for both the redox state of extracellular cysteines and for assessing which NaVβ- and NaVα-subunits are present in native neurons. PMID:24497506

  2. Benchmarking and qualification of the NUFREQ-NPW code for best estimate prediction of multi-channel core stability margins

    SciTech Connect

    Taleyarkhan, R.; Lahey, R.T. Jr.; McFarlane, A.F.; Podowski, M.Z.

    1988-01-01

    The NUFREQ-NPW code was modified and set up at Westinghouse, USA for mixed fuel type multi-channel core-wide stability analysis. The resulting code, NUFREQ-NPW, allows for variable axial power profiles between channel groups and can handle mixed fuel types. Various models incorporated into NUFREQ-NPW were systematically compared against the Westinghouse channel stability analysis code MAZDA-NF, for which the mathematical model was developed, in an entirely different manner. Excellent agreement was obtained which verified the thermal-hydraulic modeling and coding aspects. Detailed comparisons were also performed against nuclear-coupled reactor core stability data. All thirteen Peach Bottom-2 EOC-2/3 low flow stability tests were simulated. A key aspect for code qualification involved the development of a physically based empirical algorithm to correct for the effect of core inlet flow development on subcooled boiling. Various other modeling assumptions were tested and sensitivity studies performed. Good agreement was obtained between NUFREQ-NPW predictions and data. Moreover, predictions were generally on the conservative side. The results of detailed direct comparisons with experimental data using the NUFREQ-NPW code; have demonstrated that BWR core stability margins are conservatively predicted, and all data trends are captured with good accuracy. The methodology is thus suitable for BWR design and licensing purposes. 11 refs., 12 figs., 2 tabs.

  3. Channels

    NASA Image and Video Library

    2015-11-20

    Today's VIS image shows a number of unnamed channels located on the northeastern margin of Terra Sabaea. Orbit Number: 61049 Latitude: 33.5036 Longitude: 58.6967 Instrument: VIS Captured: 2015-09-18 12:54 http://photojournal.jpl.nasa.gov/catalog/PIA20097

  4. Stream Channel Stability. Appendix D. Bank Stability and Bank Material Properties in the Bluffline Streams of Northwest Mississippi,

    DTIC Science & Technology

    1981-04-01

    2.5 Pulling Assembly, Base Plate and Gas Control Console ....... . 197 2.6 Pulling force is applied by cranking the handle at a rate of two turns per...last fifty years. This degradation is the result of changes in land use, channel straightening and lowering of effective base level by trunk stream... overfall . This headcut forms where the channel bed breaks through resistant substrata of ironstone or clay. The streams lack any bedrock control and are

  5. Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

    NASA Astrophysics Data System (ADS)

    Satheesh Kumar, S. S.; Raghu, T.

    2015-02-01

    Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

  6. The role of phosphatidic acid and cardiolipin in stability of the tetrameric assembly of potassium channel KcsA.

    PubMed

    Raja, Mobeen

    2010-04-01

    In this study, the roles of two anionic phospholipids-phosphatidic acid (PA), which is an important signaling molecule, and cardiolipin (CL), which plays a crucial role in the bioenergetics of the cell-in stabilizing the oligomeric structure of potassium channel KcsA were determined. The stability of KcsA was drastically increased as a function of PA or CL content (mol%) in phosphatidylcholine (PC) bilayers. Deletion of the membrane-associated N terminus significantly reduced channel stability at high levels of PA content; however, the intrinsic stability of this protein was marginally affected in the presence of CL. These studies indicate that the electrostatic-hydrogen bond switch between PA and N terminus, involving basic residues, is much stronger than the stabilizing effect of CL. Furthermore, the unique properties of the PA headgroup alter protein assembly and folding properties differently from the CL headgroup, and both lipids stabilize the tetrameric assembly via their specific interaction on the extra- or the intracellular side of KcsA.

  7. Effect of sub-cooling channel in an ITER 13 T-40 kA Nb 3Sn coil (CS insert) on stability

    NASA Astrophysics Data System (ADS)

    Inaguchi, T.; Hasegawa, M.

    2005-04-01

    This paper analyzes the stability of a center solenoid (CS) insert and describes the effects a sub-cooling channel (central channel) at the center cross section of a cable-in-conduit (CIC) conductor has on stability. First, the calculation results are compared with test results in a center solenoid (CS) insert, and the effectiveness of the calculation is verified. Next, the effects of central channel on stability are examined by comparing the energy margin between a case in which perforations exist between the bundle region and the central channel, such as a CS insert, to allow the fluid to migrate and a case in which perforations are blocked to prevent the coolant from migrating. The following points are clarified: (1) if most of the thermal disturbance is applied to the jacket, the case with perforations is more stable than the case without perforations, thus the central channel contributes to the improvement of stability; (2) if thermal disturbance is applied only to the cable and is produced for about 20 ms, the central channel hardly has any effect on the stability. If the thermal disturbance is produced for about 400 ms, the central channel contributes to the stability; (3) the effect of cooling the bundle region by means of heat conduction through the central channel wall is very small, and it hardly affects the stability at all.

  8. Regulation of high-voltage-activated Ca(2+) channel function, trafficking, and membrane stability by auxiliary subunits.

    PubMed

    Felix, Ricardo; Calderón-Rivera, Aida; Andrade, Arturo

    2013-09-01

    Voltage-gated Ca(2+) (CaV) channels mediate Ca(2+) ions influx into cells in response to depolarization of the plasma membrane. They are responsible for initiation of excitation-contraction and excitation-secretion coupling, and the Ca(2+) that enters cells through this pathway is also important in the regulation of protein phosphorylation, gene transcription, and many other intracellular events. Initial electrophysiological studies divided CaV channels into low-voltage-activated (LVA) and high-voltage-activated (HVA) channels. The HVA CaV channels were further subdivided into L, N, P/Q, and R-types which are oligomeric protein complexes composed of an ion-conducting CaVα1 subunit and auxiliary CaVα2δ, CaVβ, and CaVγ subunits. The functional consequences of the auxiliary subunits include altered functional and pharmacological properties of the channels as well as increased current densities. The latter observation suggests an important role of the auxiliary subunits in membrane trafficking of the CaVα1 subunit. This includes the mechanisms by which CaV channels are targeted to the plasma membrane and to appropriate regions within a given cell. Likewise, the auxiliary subunits seem to participate in the mechanisms that remove CaV channels from the plasma membrane for recycling and/or degradation. Diverse studies have provided important clues to the molecular mechanisms involved in the regulation of CaV channels by the auxiliary subunits, and the roles that these proteins could possibly play in channel targeting and membrane Stabilization.

  9. MTSET modification of D4S6 cysteines stabilize the fast inactivated state of Nav1.5 sodium channels.

    PubMed

    O'Leary, Michael E; Chahine, Mohamed

    2015-01-01

    The transmembrane S6 segments of Na(+) sodium channels form the cytoplasmic entrance of the channel and line the internal aspects of the aqueous pore. This region of the channel has been implicated in Na(+) channel permeation, gating, and pharmacology. In this study we utilized cysteine substitutions and methanethiosulfonate reagent (MTSET) to investigate the role of the S6 segment of homologous domain 4 (D4S6) in the gating of the cardiac (Nav1.5) channel. D4S6 cysteine mutants were heterologously expressed in tsA201 cells and currents recorded using whole-cell patch clamp. Internal MTSET reduced the peak Na(+) currents, induced hyperpolarizing shifts in steady-state inactivation and slowed the recovery of mutant channels with cysteines inserted near the middle (F1760C, V1763C) and C-terminus (Y1767C) of the D4S6. These findings suggested a link between the MTSET inhibition and fast inactivation. This was confirmed by expressing the V1763C and Y1767C mutations in non-inactivating Nav1.5 channels. Removing inactivation abolished the MTSET inhibition of the V1763C and Y1767C mutants. The data indicate that the MTSET-induced reduction in current primarily results from slower recovery from inactivation that produces hyperpolarizing shifts in fast inactivation and decreases the steady-state availability of the channels. This contrasted with a cysteine inserted near the C-terminus of the D4S6 (I1770C) where MTSET increased the persistent Na(+) current at depolarized voltages consistent with impaired fast inactivation. Covalent modification of D4S6 cysteines with MTSET adduct appears to reduce the mobility of the D4S6 segment and stabilize the channels in the fast inactivated state. These findings indicate that residues located near the middle and C-terminus of the D4S6 play an important role in fast inactivation.

  10. The influence of a membrane environment on the structure and stability of a prokaryotic potassium channel, KcsA.

    PubMed

    Encinar, J A; Molina, M L; Poveda, J A; Barrera, F N; Renart, M L; Fernández, A M; González-Ros, J M

    2005-09-26

    The lack of a membrane environment in membrane protein crystals is considered one of the major limiting factors to fully imply X-ray structural data to explain functional properties of ion channels [Gulbis, J.M. and Doyle, D. (2004) Curr. Opin. Struct. Biol. 14, 440-446]. Here, we provide infrared spectroscopic evidence that the structure and stability of the potassium channel KcsA and its chymotryptic derivative 1-125 KcsA reconstituted into native-like membranes differ from those exhibited by these proteins in detergent solution, the latter taken as an approximation of the mixed detergent-protein crystal conditions.

  11. Stabilization of the Activated hERG Channel Voltage Sensor by Depolarization Involves the S4-S5 Linker.

    PubMed

    Thouta, Samrat; Hull, Christina M; Shi, Yu Patrick; Sergeev, Valentine; Young, James; Cheng, Yen M; Claydon, Thomas W

    2017-01-24

    Slow deactivation of hERG channels is critical for preventing cardiac arrhythmia yet the mechanistic basis for the slow gating transition is unclear. Here, we characterized the temporal sequence of events leading to voltage sensor stabilization upon membrane depolarization. Progressive increase in step depolarization duration slowed voltage-sensor return in a biphasic manner (τfast = 34 ms, τslow = 2.5 s). The faster phase of voltage-sensor return slowing correlated with the kinetics of pore opening. The slower component occurred over durations that exceeded channel activation and was consistent with voltage sensor relaxation. The S4-S5 linker mutation, G546L, impeded the faster phase of voltage sensor stabilization without attenuating the slower phase, suggesting that the S4-S5 linker is important for communications between the pore gate and the voltage sensor during deactivation. These data also demonstrate that the mechanisms of pore gate-opening-induced and relaxation-induced voltage-sensor stabilization are separable. Deletion of the distal N-terminus (Δ2-135) accelerated off-gating current, but did not influence the relative contribution of either mechanism of stabilization of the voltage sensor. Lastly, we characterized mode-shift behavior in hERG channels, which results from stabilization of activated channel states. The apparent mode-shift depended greatly on recording conditions. By measuring slow activation and deactivation at steady state we found the "true" mode-shift to be ∼15 mV. Interestingly, the "true" mode-shift of gating currents was ∼40 mV, much greater than that of the pore gate. This demonstrates that voltage sensor return is less energetically favorable upon repolarization than pore gate closure. We interpret this to indicate that stabilization of the activated voltage sensor limits the return of hERG channels to rest. The data suggest that this stabilization occurs as a result of reconfiguration of the pore gate upon opening by

  12. Phosphatidic acid plays a special role in stabilizing and folding of the tetrameric potassium channel KcsA.

    PubMed

    Raja, Mobeen; Spelbrink, Robin E J; de Kruijff, Ben; Killian, J Antoinette

    2007-12-11

    In this study, we investigated how the presence of anionic lipids influenced the stability and folding properties of the potassium channel KcsA. By using a combination of gel electrophoresis, tryptophan fluorescence and acrylamide quenching experiments, we found that the presence of the anionic lipid phosphatidylglycerol (PG) in a phosphatidylcholine (PC) bilayer slightly stabilized the tetramer and protected it from trifluoroethanol-induced dissociation. Surprisingly, the presence of phosphatidic acid (PA) had a much larger effect on the stability of KcsA and this lipid, in addition, significantly influenced the folding properties of the protein. The data indicate that PA creates some specificity over PG, and that it most likely stabilizes the tetramer via both electrostatic and hydrogen bond interactions.

  13. Modelling of ion permeation in K+ channels by nonequilibrium molecular dynamics simulations: I. Permeation energetics and structure stability.

    PubMed

    Neamţu, A; Suciu, Daniela

    2004-01-01

    Because of the great importance of physiological and pathophysiological processes in which ion channels are involved and because their operation is described by physicochemical laws, there have been many attempts to develop physical models able to describe the membrane permeability and also the structural and functional properties of the channel protein structures. In this study (in two parts) we present a series of simulations on a K+ channel model (KcsA) using Nonequilibrium Molecular Dynamics simulations (NEMD), in order to follow structure stability, permeation energetics and the possibility of obtaining quantitative information about the permeation process using the Linear Response Theory (LRT). On K+ ions were applied external forces to determine them to pass through the channel in a relatively small amount of time, accessible computationally. We ascertained a high resistance of the protein to deformation even in conditions when great forces were applied on ions (the system was far from equilibrium). The estimation of energy profiles in the course of ions passage through the channel demonstrates that these proteins create a conductivity pathway with no energetic barriers for ions movement across the channel (which could be present due to ions dehydration). The dynamic model used demonstrates (as proposed before in the literature after the examination of the static KcsA structure obtained by X-Ray crystallography) that this is due to the interaction of ions with the negatively charged carbonyl oxygens of the main polypeptide chain in the selectivity filter region.

  14. Polycystin-1 is a Cardiomyocyte Mechanosensor That Governs L-type Ca2+ Channel Protein Stability

    PubMed Central

    Pedrozo, Zully; Criollo, Alfredo; Battiprolu, Pavan K.; Morales, Cyndi R.; Contreras, Ariel; Fernández, Carolina; Jiang, Nan; Luo, Xiang; Caplan, Michael J.; Somlo, Stefan; Rothermel, Beverly A.; Gillette, Thomas G.; Lavandero, Sergio; Hill, Joseph A.

    2015-01-01

    Background L-type calcium channel (LTCC) activity is critical to afterload-induced hypertrophic growth of the heart. However, mechanisms governing mechanical stress-induced activation of LTCC activity are obscure. Polycystin-1 (PC-1) is a G-protein-coupled receptor-like protein that functions as a mechanosensor in a variety of cell types and is present in cardiomyocytes. Methods and Results We subjected neonatal rat ventricular myocytes (NRVMs) to mechanical stretch by exposing them to hypo-osmotic (HS) medium or cyclic mechanical stretch, triggering cell growth in a manner dependent on LTCC activity. RNAi-dependent knockdown of PC-1 blocked this hypertrophy. Over-expression of a C-terminal fragment of PC-1 was sufficient to trigger NRVM hypertrophy. Exposing NRVMs to HS medium resulted in an increase in α1C protein levels, a response that was prevented by PC-1 knockdown. MG132, a proteasomal inhibitor, rescued PC-1 knockdown-dependent declines in α1C protein. To test this in vivo, we engineered mice harboring conditional silencing of PC-1 selectively in cardiomyocytes (PC-1 KO) and subjected them to mechanical stress in vivo (transverse aortic constriction, TAC). At baseline, PC-1 KO mice manifested decreased cardiac function relative to littermate controls, and α1C LTCC protein levels were significantly lower in PC-1 KO hearts. Whereas control mice manifested robust TAC-induced increases in cardiac mass, PC-1 KO mice showed no significant growth. Likewise, TAC-elicited increases in hypertrophic markers and interstitial fibrosis were blunted in the knockout animals Conclusions PC-1 is a cardiomyocyte mechanosensor and is required for cardiac hypertrophy through a mechanism that involves stabilization of α1C protein. PMID:25888683

  15. Effect of conductive screens on the stabilization of plasma channels with currents of hundreds kAmps

    NASA Astrophysics Data System (ADS)

    Bochkov, V. D.; Bochkov, D. V.; Krivosheev, S. I.; Adamian, Yu. E.

    2016-12-01

    Based on experimental data, we analyzed the results of the influence of external conductive shield on stabilization of plasma channels in high-power pseudospark switches—thyratrons TDI-type. Both no-ferrous and ferrous shields are tested. The research is a part of a work on improvement of switching capabilities of thyratrons capable of transferring currents up to hundreds kA with switching energy more than 50 kJ.

  16. Vegetative impacts upon bedload transport capacity and channel stability for differing alluvial planforms in the Yellow River source zone

    NASA Astrophysics Data System (ADS)

    Li, Zhi Wei; Yu, Guo An; Brierley, Gary; Wang, Zhao Yin

    2016-07-01

    The influence of vegetation upon bedload transport and channel morphodynamics is examined along a channel stability gradient ranging from meandering to anabranching to anabranching-braided to fully braided planform conditions along trunk and tributary reaches of the Upper Yellow River in western China. Although the regional geology and climate are relatively consistent across the study area, there is a distinct gradient in the presence and abundance of riparian vegetation for these reaches atop the Qinghai-Tibet Plateau (elevations in the study area range from 2800 to 3400 m a.s.l.). To date, the influence of vegetative impacts upon channel planform and bedload transport capacity of alluvial reaches of the Upper Yellow River remains unclear because of a lack of hydrological and field data. In this region, the types and pattern of riparian vegetation vary with planform type as follows: trees exert the strongest influence in the anabranching reach, the meandering reach flows through meadow vegetation, the anabranching-braided reach has a grass, herb, and sparse shrub cover, and the braided reach has no riparian vegetation. A non-linear relation between vegetative cover on the valley floor and bedload transport capacity is evident, wherein bedload transport capacity is the highest for the anabranching reach, roughly followed by the anabranching-braided, braided, and meandering reaches. The relationship between the bedload transport capacity of a reach and sediment supply from upstream exerts a significant influence upon channel stability. Bedload transport capacity during the flood season (June-September) in the braided reach is much less than the rate of sediment supply, inducing bed aggradation and dynamic channel adjustments. Rates of channel adjustment are less pronounced for the anabranching-braided and anabranching reaches, while the meandering reach is relatively stable (i.e., this is a passive meandering reach).

  17. Archaerhodopsin Voltage Imaging: Synaptic Calcium and BK Channels Stabilize Action Potential Repolarization at the Drosophila Neuromuscular Junction

    PubMed Central

    Ford, Kevin J.

    2014-01-01

    The strength and dynamics of synaptic transmission are determined, in part, by the presynaptic action potential (AP) waveform at the nerve terminal. The ion channels that shape the synaptic AP waveform remain essentially unknown for all but a few large synapses amenable to electrophysiological interrogation. The Drosophila neuromuscular junction (NMJ) is a powerful system for studying synaptic biology, but it is not amenable to presynaptic electrophysiology. Here, we demonstrate that Archaerhodopsin can be used to quantitatively image AP waveforms at the Drosophila NMJ without disrupting baseline synaptic transmission or neuromuscular development. It is established that Shaker mutations cause a dramatic increase in neurotransmitter release, suggesting that Shaker is predominantly responsible for AP repolarization. Here we demonstrate that this effect is caused by a concomitant loss of both Shaker and slowpoke (slo) channel activity because of the low extracellular calcium concentrations (0.2–0.5 mm) used typically to assess synaptic transmission in Shaker. In contrast, at physiological extracellular calcium (1.5 mm), the role of Shaker during AP repolarization is limited. We then provide evidence that calcium influx through synaptic CaV2.1 channels and subsequent recruitment of Slo channel activity is important, in concert with Shaker, to ensure proper AP repolarization. Finally, we show that Slo assumes a dominant repolarizing role during repetitive nerve stimulation. During repetitive stimulation, Slo effectively compensates for Shaker channel inactivation, stabilizing AP repolarization and limiting neurotransmitter release. Thus, we have defined an essential role for Slo channels during synaptic AP repolarization and have revised our understanding of Shaker channels at this model synapse. PMID:25355206

  18. Archaerhodopsin voltage imaging: synaptic calcium and BK channels stabilize action potential repolarization at the Drosophila neuromuscular junction.

    PubMed

    Ford, Kevin J; Davis, Graeme W

    2014-10-29

    The strength and dynamics of synaptic transmission are determined, in part, by the presynaptic action potential (AP) waveform at the nerve terminal. The ion channels that shape the synaptic AP waveform remain essentially unknown for all but a few large synapses amenable to electrophysiological interrogation. The Drosophila neuromuscular junction (NMJ) is a powerful system for studying synaptic biology, but it is not amenable to presynaptic electrophysiology. Here, we demonstrate that Archaerhodopsin can be used to quantitatively image AP waveforms at the Drosophila NMJ without disrupting baseline synaptic transmission or neuromuscular development. It is established that Shaker mutations cause a dramatic increase in neurotransmitter release, suggesting that Shaker is predominantly responsible for AP repolarization. Here we demonstrate that this effect is caused by a concomitant loss of both Shaker and slowpoke (slo) channel activity because of the low extracellular calcium concentrations (0.2-0.5 mM) used typically to assess synaptic transmission in Shaker. In contrast, at physiological extracellular calcium (1.5 mM), the role of Shaker during AP repolarization is limited. We then provide evidence that calcium influx through synaptic CaV2.1 channels and subsequent recruitment of Slo channel activity is important, in concert with Shaker, to ensure proper AP repolarization. Finally, we show that Slo assumes a dominant repolarizing role during repetitive nerve stimulation. During repetitive stimulation, Slo effectively compensates for Shaker channel inactivation, stabilizing AP repolarization and limiting neurotransmitter release. Thus, we have defined an essential role for Slo channels during synaptic AP repolarization and have revised our understanding of Shaker channels at this model synapse.

  19. Geomorphic Assessment Approach to Evaluate Stream Channel Stability for Regions of Illinois, Case Study: Southern Illinois Region

    NASA Astrophysics Data System (ADS)

    Keefer, L. L.

    2004-12-01

    An array of different geomorphic assessment approaches for evaluating stream-channel stability is being utilized throughout the country to meet the demands of resource managers interested in stream channel restoration and management to reduce erosion and improve stream habitat. Over the last century, most of the Illinois landscape has experienced intensive land use changes which have contributed to stream channel instability. Stream channels in Illinois have adjusted to these changes either by increasing lateral rates of migration, downstream translation of meanders, widening, or development of headward retreat of knickpoints, depending on the region of the state. Illinois can be divided into at least four regions based on prevailing physiographic features and style of channel adjustment. Also, channel response in most of these regions tend to be more subtle than the dramatic response characteristics of streams in the Coastal Plains, mountain environments, and the desert southwest for which other geomorphic approaches have been developed. The observed magnitude and type of channel response are related to topography of the bedrock surface and extent and morphology of several glacial periods, which carry local significance for stream management. Given that geomorphic assessments for stream restoration require non-trivial professional, time, and financial resources, the development of approaches for Illinois regional conditions are more beneficial. A geomorphic assessment approach is being developed by adapting methods from existing process-based approaches utilized around the United States. A case-study was performed in the Big Creek watershed of the Cache River Basin for the southern Illinois region. This region was selected first because it exhibited dramatic channel responses to disturbances and had an extensive hydrologic, sediment, and land management record. This adapted approach includes systematic data collection protocols for characterization leading to an

  20. Impacts of warm water on Antarctic ice shelf stability through basal channel formation

    NASA Astrophysics Data System (ADS)

    Alley, Karen E.; Scambos, Ted A.; Siegfried, Matthew R.; Fricker, Helen Amanda

    2016-04-01

    Antarctica's ice shelves provide resistance to the flow of grounded ice towards the ocean. If this resistance is decreased as a result of ice shelf thinning or disintegration, acceleration of grounded ice can occur, increasing rates of sea-level rise. Loss of ice shelf mass is accelerating, especially in West Antarctica, where warm seawater is reaching ocean cavities beneath ice shelves. Here we use satellite imagery, airborne ice-penetrating radar and satellite laser altimetry spanning the period from 2002 to 2014 to map extensive basal channels in the ice shelves surrounding Antarctica. The highest density of basal channels is found in West Antarctic ice shelves. Within the channels, warm water flows northwards, eroding the ice shelf base and driving channel evolution on annual to decadal timescales. Our observations show that basal channels are associated with the development of new zones of crevassing, suggesting that these channels may cause ice fracture. We conclude that basal channels can form and grow quickly as a result of warm ocean water intrusion, and that they can structurally weaken ice shelves, potentially leading to rapid ice shelf loss in some areas.

  1. Quantifying noise-induced stability of a cortical fast-spiking cell model with Kv3-channel-like current.

    PubMed

    Tateno, T; Robinson, H P C

    2007-01-01

    Population oscillations in neural activity in the gamma (>30 Hz) and higher frequency ranges are found over wide areas of the mammalian cortex. Recently, in the somatosensory cortex, the details of neural connections formed by several types of GABAergic interneurons have become apparent, and they are believed to play a significant role in generating these oscillations through synaptic and gap-junctional interactions. However, little is known about the mechanism of how such oscillations are maintained stably by particular interneurons and by their local networks, in a noisy environment with abundant synaptic inputs. To obtain more insight into this, we studied a fast-spiking (FS)-cell model including Kv3-channel-like current, which is a distinctive feature of these cells, from the viewpoint of nonlinear dynamical systems. To examine the specific role of the Kv3-channel in determining oscillation properties, we analyzed basic properties of the FS-cell model, such as the bifurcation structure and phase resetting curves (PRCs). Furthermore, to quantitatively characterize the oscillation stability under noisy fluctuations mimicking small fast synaptic inputs, we applied a recently developed method from random dynamical system theory to estimate Lyapunov exponents, both for the original four-dimensional dynamics and for a reduced one-dimensional phase-equation on the circle. The results indicated that the presence of the Kv3-channel-like current helps to regulate the stability of noisy neural oscillations and a transient-period length to stochastic attractors.

  2. Stability of the Shab K+ channel conductance in 0 K+ solutions: the role of the membrane potential.

    PubMed

    Gómez-Lagunas, Froylán

    2007-12-15

    Shab channels are fairly stable with K(+) present on only one side of the membrane. However, on exposure to 0 K(+) solutions on both sides of the membrane, the Shab K(+) conductance (G(K)) irreversibly drops while the channels are maintained undisturbed at the holding potential. Herein it is reported that the drop of G(K) follows first-order kinetics, with a voltage-dependent decay rate r. Hyperpolarized potentials drastically inhibit the drop of G(K). The G(K) drop at negative potentials cannot be explained by a shift in the voltage dependence of activation. At depolarized potentials, where the channels undergo a slow inactivation process, G(K) drops in 0 K(+) with rates slower than those predicted based on the behavior of r at negative potentials, endowing the r-V(m) relationship with a maximum. Regardless of voltage, r is very small compared with the rate of ion permeation. Observations support the hypothesized presence of a stabilizing K(+) site (or sites) located either within the pore itself or in its external vestibule, at an inactivation-sensitive location. It is argued that part of the G(K) stabilization achieved at hyperpolarized potentials could be the result of a conformational change in the pore itself.

  3. Modulating secretory pathway pH by proton channel co-expression can increase recombinant protein stability in plants.

    PubMed

    Jutras, Philippe V; D'Aoust, Marc-André; Couture, Manon M-J; Vézina, Louis-Philippe; Goulet, Marie-Claire; Michaud, Dominique; Sainsbury, Frank

    2015-09-01

    Eukaryotic expression systems are used for the production of complex secreted proteins. However, recombinant proteins face considerable biochemical challenges along the secretory pathway, including proteolysis and pH variation between organelles. As the use of synthetic biology matures into solutions for protein production, various host-cell engineering approaches are being developed to ameliorate host-cell factors that can limit recombinant protein quality and yield. We report the potential of the influenza M2 ion channel as a novel tool to neutralize the pH in acidic subcellular compartments. Using transient expression in the plant host, Nicotiana benthamiana, we show that ion channel expression can significantly raise pH in the Golgi apparatus and that this can have a strong stabilizing effect on a fusion protein separated by an acid-susceptible linker peptide. We exemplify the utility of this effect in recombinant protein production using influenza hemagglutinin subtypes differentially stable at low pH; the expression of hemagglutinins prone to conformational change in mildly acidic conditions is considerably enhanced by M2 co-expression. The co-expression of a heterologous ion channel to stabilize acid-labile proteins and peptides represents a novel approach to increasing the yield and quality of secreted recombinant proteins in plants and, possibly, in other eukaryotic expression hosts. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Designing calcium release channel inhibitors with enhanced electron donor properties: stabilizing the closed state of ryanodine receptor type 1.

    PubMed

    Ye, Yanping; Yaeger, Daniel; Owen, Laura J; Escobedo, Jorge O; Wang, Jialu; Singer, Jeffrey D; Strongin, Robert M; Abramson, Jonathan J

    2012-01-01

    New drugs with enhanced electron donor properties that target the ryanodine receptor from skeletal muscle sarcoplasmic reticulum (RyR1) are shown to be potent inhibitors of single-channel activity. In this article, we synthesize derivatives of the channel activator 4-chloro-3-methyl phenol (4-CmC) and the 1,4-benzothiazepine channel inhibitor 4-[-3{1-(4-benzyl) piperidinyl}propionyl]-7-methoxy-2,3,4,5-tetrahydro-1,4-benzothiazepine (K201, JTV519) with enhanced electron donor properties. Instead of activating channel activity (~100 μM), the 4-methoxy analog of 4-CmC [4-methoxy-3-methyl phenol (4-MmC)] inhibits channel activity at submicromolar concentrations (IC(50) = 0.34 ± 0.08 μM). Increasing the electron donor characteristics of K201 by synthesizing its dioxole congener results in an approximately 16 times more potent RyR1 inhibitor (IC(50) = 0.24 ± 0.05 μM) compared with K201 (IC(50) = 3.98 ± 0.79 μM). Inhibition is not caused by an increased closed time of the channel but seems to be caused by an open state block of RyR1. These alterations to chemical structure do not influence the ability of these drugs to affect Ca(2+)-dependent ATPase activity of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase type 1. Moreover, the FKBP12 protein, which stabilizes RyR1 in a closed configuration, is shown to be a strong electron donor. It seems as if FKBP12, K201, its dioxole derivative, and 4-MmC inhibit RyR1 channel activity by virtue of their electron donor characteristics. These results embody strong evidence that designing new drugs to target RyR1 with enhanced electron donor characteristics results in more potent channel inhibitors. This is a novel approach to the design of new, more potent drugs with the aim of functionally modifying RyR1 single-channel activity.

  5. Effect of net spinning caddisfly (Trichoptera: Stenopsyche marmorata) on channel bed stability in a small stream, northern Japan

    NASA Astrophysics Data System (ADS)

    Nunokawa, M.; Gomi, T.; Negishi, J.; Nakahara, O.; Kasahara, T.

    2008-12-01

    The effects of net spinning caddisfly (Trichoptera: Stenopsyche marmorata) on stability of channel beds were assessed based on in situ field experiment and field observation in a gravel bed stream in northern Japan. Stenopsyche larvae were released in experimental cages placed on channel beds where they built nests. Strength of the nests in each cage was measured by applying vertical lifting forces until a cobble, with a diameter ranging from 5 to10 cm, came off the nest. Compared to the cages without the nests, the cages with the nests required stronger force, four-fold on average, for a cobble to come off. In natural riffle, we measured drug force (applied parallel to bed surface pulling toward downstream direction) required for entrainment of bed materials with a diameter of 10 to20cm. Other physical variables, such as weight, size, percentage burial, ambient water velocity, and substrate coarseness around the cobble, and biological characteristics, such as density of Stenopsyche marmorata below and around cobble were also measured in the riffle. Standard regression coefficient of multiple regression analysis with stepwise variable selection procedure showed that density of larvae was the strongest explanatory variable for the drug force required for bed material entrainments. Our results showed that Stenopsyche larvae significantly enhanced the stability of streambed by binding gravels and cobbles using their silky nets.Key words: net spinning caddisfly (Trichoptera: Stenopsyche marmorata), bed stability, physical and biological interaction, gravel-bed stream

  6. A semisynthetic fusicoccane stabilizes a protein-protein interaction and enhances the expression of K+ channels at the cell surface.

    PubMed

    Anders, Carolin; Higuchi, Yusuke; Koschinsky, Kristin; Bartel, Maria; Schumacher, Benjamin; Thiel, Philipp; Nitta, Hajime; Preisig-Müller, Regina; Schlichthörl, Günter; Renigunta, Vijay; Ohkanda, Junko; Daut, Jürgen; Kato, Nobuo; Ottmann, Christian

    2013-04-18

    Small-molecule stabilization of protein-protein interactions is an emerging field in chemical biology. We show how fusicoccanes, originally identified as fungal toxins acting on plants, promote the interaction of 14-3-3 proteins with the human potassium channel TASK-3 and present a semisynthetic fusicoccane derivative (FC-THF) that targets the 14-3-3 recognition motif (mode 3) in TASK-3. In the presence of FC-THF, the binding of 14-3-3 proteins to TASK-3 was increased 19-fold and protein crystallography provided the atomic details of the effects of FC-THF on this interaction. We also tested the functional effects of FC-THF on TASK channels heterologously expressed in Xenopus oocytes. Incubation with 10 μM FC-THF was found to promote the transport of TASK channels to the cell membrane, leading to a significantly higher density of channels at the surface membrane and increased potassium current. Copyright © 2013 Elsevier Ltd. All rights reserved.

  7. Influence of channel subunit composition on L-type Ca2+ current kinetics and cardiac wave stability.

    PubMed

    Gudzenko, Vadim; Shiferaw, Yohannes; Savalli, Nicoletta; Vyas, Roshni; Weiss, James N; Olcese, Riccardo

    2007-09-01

    Previous studies have demonstrated that the slope of the function relating the action potential duration (APD) and the diastolic interval, known as the APD restitution curve, plays an important role in the initiation and maintenance of ventricular fibrillation. Since the APD restitution slope critically depends on the kinetics of the L-type Ca(2+) current, we hypothesized that manipulation of the subunit composition of these channels may represent a powerful strategy to control cardiac arrhythmias. We studied the kinetic properties of the human L-type Ca(2+) channel (Ca(v)1.2) coexpressed with the alpha(2)delta-subunit alone (alpha(1C) + alpha(2)delta) or in combination with beta(2a), beta(2b), or beta(3) subunits (alpha(1C) + alpha(2)delta + beta), using Ca(2+) as the charge carrier. We then incorporated the kinetic properties observed experimentally into the L-type Ca(2+) current mathematical model of the cardiac action potential to demonstrate that the APD restitution slope can be selectively controlled by altering the subunit composition of the Ca(2+) channel. Assuming that beta(2b) most closely resembles the native cardiac L-type Ca(2+) current, the absence of beta, as well as the coexpression of beta(2a), was found to flatten restitution slope and stabilize spiral waves. These results imply that subunit modification of L-type Ca(2+) channels can potentially be used as an antifibrillatory strategy.

  8. Alcohols potentiate the function of 5-HT3 receptor–channels on NCB-20 neuroblastoma cells by favouring and stabilizing the open channel state

    PubMed Central

    Zhou, Qing; Verdoorn, Todd A; Lovinger, David M

    1998-01-01

    5-HT3 receptor-mediated ion current was recorded from NCB-20 neuroblastoma cells using the whole-cell patch-clamp technique. Rapid drug superfusion was used to study the mechanism of alcohol potentiation of 5-HT3 receptor function and to analyse effects of alcohols on receptor-channel kinetics in detail.Trichloroethanol (TCEt) increased in a dose-dependent way the initial slope, 20–80 % rise time and measured desensitization rate of the current induced by low concentrations (1–2 μm) of 5-HT. Ethanol (EtOH) and butanol (ButOH) had similar effects on the 5-HT3 receptor-induced current.TCEt and ButOH decreased the measured desensitization rate of current induced by 10 μm 5-HT, a maximally effective concentration of agonist. These alcohols also increased the relative amplitude of steady state to peak current induced by 2 or 10 μm 5-HT, indicating a possible decrease in the intrinsic rate of desensitization.TCEt also decreased the deactivation rate of the current activated by 2 μm 5-HT after a short pulse of agonist application.Current sweeps generated by 1 μm 5-HT in the presence or absence of 10 mm TCEt or 100 mm EtOH were well fitted using a modified standard kinetic model derived from the nicotinic acetylcholine receptor. This analysis indicated that potentiation by alcohols could be accounted for by increases in the association rate constant coupled with decreases in the dissociation and desensitization rate constants.This study suggests that alcohols potentiate 5-HT3 receptor-mediated current by both increasing the rate of channel activation and stabilizing the open state by decreasing the rates of channel deactivation and desensitization. PMID:9518697

  9. Deconvolution of u channel magnetometer data: Experimental study of accuracy, resolution, and stability of different inversion methods

    NASA Astrophysics Data System (ADS)

    Jackson, Mike; Bowles, Julie A.; Lascu, Ioan; Solheid, Peat

    2010-07-01

    We explore the effects of sampling density, signal/noise ratios, and position-dependent measurement errors on deconvolution calculations for u channel magnetometer data, using a combination of experimental and numerical approaches. Experiments involve a synthetic sample set made by setting hydraulic cement in a 30-cm u channel and slicing the hardened material into ˜2-cm lengths, and a natural lake sediment u channel sample. The cement segments can be magnetized and measured individually, and reassembled for continuous u channel measurement and deconvolution; the lake sediment channel was first measured continuously and then sliced into discrete samples for individual measurement. Each continuous data set was deconvolved using the ABIC minimization code of Oda and Shibuya (1996) and two new approaches that we have developed, using singular-value decomposition and regularized least squares. These involve somewhat different methods to stabilize the inverse calculations and different criteria for identifying the optimum solution, but we find in all of our experiments that the three methods converge to essentially identical solutions. Repeat scans in several experiments show that measurement errors are not distributed with position-independent variance; errors in setting/determining the u channel position (standard deviation ˜0.2 mm) translate in regions of strong gradients into measurement uncertainties much larger than those due to instrument noise and drift. When we incorporate these depth-dependent measurement uncertainties into the deconvolution calculations, the resulting models show decreased stability and accuracy compared to inversions assuming depth-independent measurement errors. The cement experiments involved varying directions and uniform intensities downcore, and very good accuracy was obtained using all of the methods when the signal/noise ratio was greater than a few hundred and the sampling interval no larger than half the length scale of

  10. Using CEOS reference standard test sites to track the calibration stability of NOAA-19 AVHRR reflective solar channels

    NASA Astrophysics Data System (ADS)

    Wu, Aisheng; Angal, Amit; Xiong, Jack; Cao, Changyong

    2010-10-01

    In recent years, there is an increasing interest to establish a global integrated network of calibration sites for the purpose of tracking sensor performance, conducting cross-sensor comparison and assessing data quality and consistency. Based on such a need, the Committee on Earth Observation Satellites (CEOS) proposed eight instrumented sites for which surface measurements can be acquired through field campaigns and five pseudo-invariant desert sites typically consisting of sand dunes. In this study, we select one site from each category to study the calibration stability of reflective solar channels of NOAA- 19 Advanced Very High Resolution Radiometer (AVHRR) (launched on February 6, 2009). Since AVHRR does not have an onboard calibrator for the reflective solar channels and vicarious calibration often needs long-term observations to derive reliable trends, this study will provide an early assessment of sensor on-orbit calibration performance and establish a preliminary trend to examine its calibration consistency with other sensors. The Antarctic Dome C site is selected primarily to monitor the on-orbit calibration performance whereas Libya 4 test site is used to evaluate the cross-calibration consistency of AVHRR with other sensors. A site-specific Bi-directional Reflectance Distribution Function (BRDF) model developed based on observations made by Moderate Resolution Imaging Spectroradiometer (MODIS) is used to normalize AVHRR observed Top-of-Atmosphere (TOA) reflectances. Impact due to calibration applied to NOAA-19 AVHRR L1B is assessed separately using a constant detector response. Results show that for NOAA-19 AVHRR solar channels 1 and 2, variations in reflectance during the first year after launch are still around 6% and more than 10%, respectively, either due to sensor change or improper adjustment of calibration coefficients. While two sites provide consistent trends for the visible channel, the Dome C site is more suitable for the near

  11. Variable responses of fish assemblages, habitat, and stability to natural-channel-design restoration in Catskill Mountain streams

    USGS Publications Warehouse

    Baldigo, Barry P.; Ernst, Anne G.; Warren, Dana R.; Miller, Sarah J.

    2010-01-01

    Natural-channel-design (NCD) restorations were recently implemented within large segments of five first- and second-order streams in the Catskill Mountains of New York in an attempt to increase channel stability, reduce bed and bank erosion, and sustain water quality. In conjunction with these efforts, 54 fish and habitat surveys were done from 1999 to 2007 at six restored reaches and five stable control reaches to evaluate the effects of NCD restoration on fish assemblages, habitat, and bank stability. A before–after–control–impact study design and two-factor analysis of variance were used to quantify the net changes in habitat and fish population and community indices at treatment reaches relative to those at unaltered control reaches. The density and biomass of fish communities were often dominated by one or two small prey species and no or few predator species before restoration and by one or more trout (Salmonidae) species after restoration. Significant increases in community richness (30%), diversity (40%), species or biomass equitability (32%), and total biomass (up to 52%) in at least four of the six restored reaches demonstrate that NCD restorations can improve the health and sustainability of fish communities in geomorphically unstable Catskill Mountain streams over the short to marginally long term. Bank stability, stream habitat, and trout habitat suitability indices (HSIs) generally improved significantly at the restored reaches, but key habitat features and trout HSIs did not change or decreased at two of them. Fish communities and trout populations at these two reaches were not positively affected by NCD restorations. Though NCD restorations often had a positive effect on habitat and fish communities, our results show that the initial habitat conditions limit the relative improvements than can be achieved, habitat quality and stability do not necessarily respond in unison, and biotic and abiotic responses cannot always be generalized.

  12. Temperature-induced opening of TRPV1 ion channel is stabilized by the pore domain

    PubMed Central

    Grandl, Jörg; Kim, Sung Eun; Uzzell, Valerie; Bursulaya, Badry; Petrus, Matt; Bandell, Michael; Patapoutian, Ardem

    2010-01-01

    Summary TRPV1 is the founding and best-studied member of the family of temperature-activated transient receptor potential ion channels (thermoTRPs). Voltage, chemicals, and heat amongst other agonists allosterically gate TRPV1. Molecular determinants for TRPV1 activation by capsaicin, allicin, acid, ammonia, and voltage have been identified. However, the structures and mechanisms mediating its pronounced temperature-sensitivity remain unclear. Recent studies of the related channel TRPV3 identified residues within the pore region required for heat activation. Here we use both random and targeted mutagenesis screens of TRPV1 and identify point mutations in the outer pore region that specifically impair temperature-activation. Single channel analysis shows that TRPV1 mutations disrupt heat-sensitivity by ablating long channel openings, that are part of the temperature-gating pathway. We propose that sequential occupancy of short and long open states upon activation provides a mechanism to enhance temperature-sensitivity. Our study suggests that the outer pore plays a general role in heat-sensitivity of thermoTRPs. PMID:20414199

  13. Effects of a Regional Channel Stabilization Project on Suspended Sediment Yield

    USDA-ARS?s Scientific Manuscript database

    Under legislation passed in 1984, three federal agencies constructed more than $300 million worth of channel erosion control measures in 16 watersheds in northern Mississippi between 1985 and 2003. Most work was completed between 1985 and 1995, and was confined to six larger watersheds. Flows of w...

  14. Stabilization of a gravel channel by large streamside obstructions and bedrock bends, Jacoby Creek, northwestern California

    Treesearch

    Thomas E. Lisle

    1996-01-01

    Abstract - Jacoby Creek (bed width =12 m; bankfull discharge = 32.6 m 3 /s) contains stationary gravel bars that have forms and positions controlled by numerous large streamside obstructions (bedrock outcrops, large woody debris, and rooted bank projections) and bedrock bends. Bank-projection width and bar volume measured in 104 channel segments 1 bed-width long are...

  15. flowVS: channel-specific variance stabilization in flow cytometry

    DOE PAGES

    Azad, Ariful; Rajwa, Bartek; Pothen, Alex

    2016-07-28

    Comparing phenotypes of heterogeneous cell populations from multiple biological conditions is at the heart of scientific discovery based on flow cytometry (FC). When the biological signal is measured by the average expression of a biomarker, standard statistical methods require that variance be approximately stabilized in populations to be compared. Since the mean and variance of a cell population are often correlated in fluorescence-based FC measurements, a preprocessing step is needed to stabilize the within-population variances.

  16. Supplement Analysis for the Watershed Management Program EIS (DOE/EIS-0265/SA-161) - Grave Creek Channel Stabilization Project – Phase II

    SciTech Connect

    Keller, Carl J.

    2004-07-22

    BPA proposes to fund MFWP to accomplish Phase II of channel stabilization along Graves Creek. The current proposal is very much the same as for Phase I (as per our Oct. 15, 2002 Memo.): stabilize about 4,800 feet of the creek by realigning and shaping the channel; install log and rock vanes, and root wads; install debris jams and cobble patches, and planting native vegetation along the riparian corridor to stabilize the banks. The Phase II work is immediately adjacent and downstream from that the Phase I work that was accomplished in 2002. The purpose of the project is to stabilize that channel, provide for floodplain function, improve rearing and adult holding habitat for westslope cutthroat trout and bull trout.

  17. Barbiturates Bind in the GLIC Ion Channel Pore and Cause Inhibition by Stabilizing a Closed State*♦

    PubMed Central

    Fourati, Zaineb; Ruza, Reinis Reinholds; Laverty, Duncan; Drège, Emmanuelle; Delarue-Cochin, Sandrine; Joseph, Delphine; Koehl, Patrice; Smart, Trevor; Delarue, Marc

    2017-01-01

    Barbiturates induce anesthesia by modulating the activity of anionic and cationic pentameric ligand-gated ion channels (pLGICs). Despite more than a century of use in clinical practice, the prototypic binding site for this class of drugs within pLGICs is yet to be described. In this study, we present the first X-ray structures of barbiturates bound to GLIC, a cationic prokaryotic pLGIC with excellent structural homology to other relevant channels sensitive to general anesthetics and, as shown here, to barbiturates, at clinically relevant concentrations. Several derivatives of barbiturates containing anomalous scatterers were synthesized, and these derivatives helped us unambiguously identify a unique barbiturate binding site within the central ion channel pore in a closed conformation. In addition, docking calculations around the observed binding site for all three states of the receptor, including a model of the desensitized state, showed that barbiturates preferentially stabilize the closed state. The identification of this pore binding site sheds light on the mechanism of barbiturate inhibition of cationic pLGICs and allows the rationalization of several structural and functional features previously observed for barbiturates. PMID:27986812

  18. Supplement Analysis for the Watershed Management Program EIS (DOE/EIS-0265/SA-95) - Libby Creek Channel Stabilization Project

    SciTech Connect

    Keller, Carl J.

    2002-10-21

    BPA proposes to fund MFWP to construct a channel stabilization project, which would restore the dimension, pattern, and profile of 3,200 feet of Libby Creek. The project calls for shaping cut banks to a 2:1 slope, installing root wads and tree revetments; and planting and restoring native grasses and riparian shrubs along the margin of the channel. Cross vanes (constructed from rock) and trees will also be established to control channel gradient within the project area. This project is one restoration phase on Libby Creek, and was identified as important by the Libby Area Conservation District, MFWP, U.S. Forest Service, and U.S. Army Corps of Engineers. Libby Creek is also the focus of restoration efforts based, in part, on the finding of the Montana Governor’s Bull Trout Restoration Technical Committee. This Committee identified Libby Creek as critical spawning and migratory habitat for the threatened bull trout. This project reach of Libby Creek is also rearing habitat for resident redband trout and resident and fluvial bull trout migrating from the Kootenai River.

  19. Ion binding properties and structure stability of the NaK channel.

    PubMed

    Shen, Rong; Guo, Wanlin

    2009-05-01

    Ion distribution in the selectivity filter and ion-water and ion-protein interactions of NaK channel are systematically investigated by all-atom molecular dynamics simulations, with the tetramer channel protein being embedded in a solvated phospholipid bilayer. Analysis of the simulation results indicates that K(+) ions prefer to bind within the sites formed by two adjacent planes of oxygen atoms from the selectivity filter, while Na(+) ions are inclined to bind to a single plane of four oxygen atoms. At the same time, both K(+) and Na(+) ions can diffuse in the vestibule, accompanying with movements of the water molecules confined in a complex formed by the vestibule together with four small grottos connecting to it. As a result, K(+) ions show a wide range of coordination numbers (6-8), while Na(+) ions display a constant coordination number of approximately 6 in the selectivity filter, which may result in the loss of selectivity of NaK. It is also found that a Ca(2+) can bind at the extracellular site as reported in the crystal structure in a partially hydrated state, or at a higher site in a full hydration state. Furthermore, the carbonyl group of Asp66 can reorient to point towards the center pore when an ion exists in the vestibule, while that of Gly65 always aligns tangentially to the channel axis, as in the crystallographic structures.

  20. Structure and Stability of Individual DNA or RNA Hairpin Molecules Captured in an Ion Channel

    NASA Astrophysics Data System (ADS)

    Akeson, Mark

    2002-03-01

    Nanoscale pores can be used to analyze individual DNA or RNA molecules. For example, a prototype device based on the alpha-hemolysin protein permits serial examination of hundreds to thousands of molecules per minute. It is routinely used to identify individual polynucleotide homopolymers, and to read segments within single DNA or RNA block copolymers as they thread through a narrow, trans-membrane pore formed by the protein (1.5 nm limiting aperture). In recent reports, we have shown that this device can also be used to examine structural details of individual DNA or RNA hairpins at single base-pair precision. This is achieved by capturing each hairpin in a vestibule of the channel leading to the trans-membrane pore. Under a 120 mV applied voltage, ionic current through the channel is gated by the RNA or DNA hairpin as it is perched in the vestibule, resulting in a dynamic current pattern that is exquisitely sensitive to sequence identity. In this presentation, I will explain the ion channel device and then describe structural details of the hairpin molecules that can be resolved by the instrument. These include: i) Watson-Crick base-pair identity at the hairpin stem terminus; ii) duplex fraying caused by single base pair mismatches internal to the hairpin stem; and iii) A form (RNA) versus B form (DNA) helix conformation. I will then discuss alternative mechanisms that can account for the discrete gating patterns that underlie the analysis.

  1. Modernized scheme of thermal ignition and flame stabilization at flow supersonic speeds in channel

    NASA Astrophysics Data System (ADS)

    Goldfeld, M. A.; Nalivaychenko, D. G.; Starov, A. V.; Timofeev, K. Yu.

    2016-10-01

    For providing fuel ignition at the high supersonic flow velocity original device was developed. Main element of this device in the form of wall slotted channel has to provide the high flow temperature in the area of mixture. Numerical simulation has been performed based on solving the full averaged Navier-Stokes equations, supplemented k-ɛ turbulence model. The experiments were carried out in the hotshot wind tunnel IT-302M at the mode of the attached pipe. The flow parameters at the model entrance were following: M = 2 - 5.8, p0 = 12 - 390bar, T0 = 1170 - 2930K at equivalence ratio of hydrogen from 0.6 to 1.1. Self-ignition of the hydrogen in the slotted channel has occurred at total flow temperature of 2250K at the combustor entrance. The combustion process is extended to the entire channel of the combustor. When the facility worked with decreasing parameters of the flow, combustion continued until drop of the static temperature of about 230K at the entrance of the combustor.

  2. Preliminary assessment of channel stability and bed-material transport along Hunter Creek, southwestern Oregon

    USGS Publications Warehouse

    Jones, Krista L.; Wallick, J. Rose; O'Connor, Jim E.; Keith, Mackenzie K.; Mangano, Joseph F.; Risley, John C.

    2011-01-01

    This preliminary assessment of (1) bed-material transport in the Hunter Creek basin, (2) historical changes in channel condition, and (3) supplementary data needed to inform permitting decisions regarding instream gravel extraction revealed the following: Along the lower 12.4 km (kilometers) of Hunter Creek from its confluence with the Little South Fork Hunter Creek to its mouth, the river has confined and unconfined segments and is predominately alluvial in its lowermost 11 km. This 12.4-km stretch of river can be divided into two geomorphically distinct study reaches based primarily on valley physiography. In the Upper Study Reach (river kilometer [RKM] 12.4-6), the active channel comprises a mixed bed of bedrock, boulders, and smaller grains. The stream is confined in the upper 1.4 km of the reach by a bedrock canyon and in the lower 2.4 km by its valley. In the Lower Study Reach (RKM 6-0), where the area of gravel bars historically was largest, the stream flows over bed material that is predominately alluvial sediments. The channel alternates between confined and unconfined segments. The primary human activities that likely have affected bed-material transport and the extent and area of gravel bars are (1) historical and ongoing aggregate extraction from gravel bars in the study area and (2) timber harvest and associated road construction throughout the basin. These anthropogenic activities likely have varying effects on sediment transport and deposition throughout the study area and over time. Although assessing the relative effects of these anthropogenic activities on sediment dynamics would be challenging, the Hunter Creek basin may serve as a case study for such an assessment because it is mostly free of other alterations to hydrologic and geomorphic processes such as flow regulation, dredging, and other navigation improvements that are common in many Oregon coastal basins. Several datasets are available that may support a more detailed physical assessment

  3. Channel Stability and Water Quality of the Alagnak River, Southwestern Alaska

    USGS Publications Warehouse

    Curran, Janet H.

    2003-01-01

    The Alagnak River, a National Wild River located in southwestern Alaska, drains an area of 3,600 square kilometers and is used for recreational and subsistence activities, primarily angling, camping, rafting, and hunting by visitors and seasonal residents, and for commercial guiding by several lodges. Increases in visitor use in the 1990s included an increase in the use of high-horsepower motorboats on the river, primarily for angling, and raised concerns regarding human impacts on water quality. Downstream from its confluence with the Nonvianuk River at river kilometer (RK) 93, the Alagnak River is formed in glacial drift and outwash with a single, low bedrock outcrop. Analysis of aerial photography from 1951, 1982, and 2001 shows that the river's multiple channels from RK 57 to 93 have been relatively stable. In contrast, long reaches of multiple channels from RK 35 to 57 changed substantially between 1951 and 1982, creating a new complex of channels. Downstream from RK 35, channel changes in the past 50 years consist largely of minor meander migration. Analysis of water samples collected during this study at RK 21, 46, and 93 and in the Alagnak and Nonvianuk Rivers at the outlets of the lakes that form their source shows that the Alagnak River is a nutrient-poor, calcium-bicarbonate water with low suspended-sediment concentrations. Water chemistry changes little over time or in a downstream direction. Weak patterns over time include high late May/early June concentrations of some nutrients, carbon, and iron. Weak patterns over distance include downstream increases in iron, manganese, and phosphorous. No pervasive human impacts on Alagnak River water chemistry were detected. Local effects that could be diluted within a kilometer downstream of the source were not detectable by this study. Data collected at three continuously recording wake gaging stations at RK 21, 46, and 93 showed that 1999-2000 motorboat use was heaviest in the lower reaches of the river

  4. Protein interactions central to stabilizing the K[superscript +] channel selectivity filter in a four-sited configuration for selective K[superscript +] permeation

    SciTech Connect

    Sauer, David B.; Zeng, Weizhong; Raghunathan, Srinivasan; Jiang, Youxing

    2011-11-18

    The structural and functional conversion of the nonselective NaK channel to a K{sup +} selective channel (NaK2K) allows us to identify two key residues, Tyr and Asp in the filter sequence of TVGYGD, that participate in interactions central to stabilizing the K{sup +} channel selectivity filter. By using protein crystallography and channel electrophysiology, we demonstrate that the K{sup +} channel filter exists as an energetically strained structure and requires these key protein interactions working in concert to hold the filter in the precisely defined four-sited configuration that is essential for selective K{sup +} permeation. Disruption of either interaction, as tested on both the NaK2K and eukaryotic K{sub v}1.6 channels, can reduce or completely abolish K{sup +} selectivity and in some cases may also lead to channel inactivation due to conformational changes at the filter. Additionally, on the scaffold of NaK we recapitulate the protein interactions found in the filter of the Kir channel family, which uses a distinct interaction network to achieve similar stabilization of the filter.

  5. Stability of high-dose insulin in normal saline bags for treatment of calcium channel blocker and beta blocker overdose.

    PubMed

    Laskey, Dayne; Vadlapatla, Rajesh; Hart, Katherine

    2016-11-01

    High-dose insulin has become a first-line therapy for treating severe calcium channel blocker and beta blocker toxicity. Insulin infusions used to treat other conditions (e.g., diabetic ketoacidosis) may be used, but this may lead to pulmonary compromise due to fluid volume overload. An obvious solution would be to use a more concentrated insulin infusion; however, data describing the stability of insulin in polyvinyl chloride bags at concentrations >1 unit/mL are not readily available. To determine the stability of insulin at 16 units/mL in 0.9% saline solution. Eight-hundred units of regular insulin (8 mL from a stock vial containing 100 units/mL) were added to 42 mL of 0.9% saline solution in a polyvinyl chloride bag to make a final concentration of 16 units/mL. Two bags were stored at 4 °C (refrigerated) and two at 25 °C (room temperature). Samples were withdrawn and tested for insulin concentration periodically over 14 days. Concentrated regular insulin in a polyvinyl chloride bag remained within 90% of equilibrium concentration at all time points, indicating the 16 units/mL concentration was sufficiently stable both refrigerated and at room temperature for 14 days. Administration of high-dose insulin can cause fluid volume overload when using traditional insulin formulations. The 16 units/mL concentration allows for the treatment of a patient with severe calcium channel blocker or beta blocker toxicity for a reasonable period of time without administering excessive fluid. Insulin at a concentration of 16 units/mL is stable for 14 days, the maximum timeframe currently allowed under US Pharmacopeia rules for compounding of sterile preparations. This stability data will allow institutions to issue beyond-use dating for intravenous fluids containing concentrated insulin and used for treating beta blocker and calcium channel blocker toxicity.

  6. Long-term improvements to photoluminescence and dispersion stability by flowing SDS-SWNT suspensions through microfluidic channels.

    PubMed

    Silvera-Batista, Carlos A; Weinberg, Philip; Butler, Jason E; Ziegler, Kirk J

    2009-09-09

    Shearing single-walled carbon nanotubes (SWNTs) coated with sodium dodecyl sulfate in microfluidic channels significantly increases the photoluminescence (PL) intensity and dispersion stability of SWNTs. The PL quantum yield (QY) of SWNTs improves by a factor of 3 for initially bright suspensions; on the other hand, SWNT QYs in a "poor" suspension improve by 2 orders of magnitude. In both cases, the QYs of the sheared suspensions are approximately 1%. The increases in PL intensity persist for months and are most prominent in larger diameter SWNTs. These improvements are attributed to surfactant reorganization rather than disaggregation of SWNTs bundles or shear-induced alignment. The results also highlight potential opportunities to eliminate discrepancies in the PL intensity of different suspensions and further improve the PL of SWNTs by tailoring the surfactant structure around SWNTs.

  7. Linear stability of optimal streaks in the log-layer of turbulent channel flows

    NASA Astrophysics Data System (ADS)

    Alizard, Frédéric

    2015-10-01

    The importance of secondary instability of streaks for the generation of vortical structures attached to the wall in the logarithmic region of turbulent channels is studied. The streaks and their linear instability are computed by solving equations associated with the organized motion that include an eddy-viscosity modeling the effect of incoherent fluctuations. Three friction Reynolds numbers, Reτ = 2000, 3000, and 5000, are investigated. For all flow cases, optimal streamwise vortices (i.e., having the highest potential for linear transient energy amplification) are used as initial conditions. Due to the lift-up mechanism, these optimal perturbations lead to the nonlinear growth of streaks. Based on a Floquet theory along the spanwise direction, we observe the onset of streak secondary instability for a wide range of spanwise wavelengths when the streak amplitude exceeds a critical value. Under neutral conditions, it is shown that streak instability modes have their energy mainly concentrated in the overlap layer and propagate with a phase velocity equal to the mean streamwise velocity of the log-layer. These neutral log-layer modes exhibit a sinuous pattern and have characteristic sizes that are proportional to the wall distance in both streamwise and spanwise directions, in agreement with the Townsend's attached eddy hypothesis (A. Townsend, the structure of turbulent shear flow, Cambridge university press, 1976 2nd edition). In particular, for a distance from the wall varying from y+ ≈ 100 (in wall units) to y ≈ 0.3h, where h is half the height of the channel, the neutral log-layer modes are self-similar with a spanwise width of λz ≈ y/0.3 and a streamwise length of λx ≈ 3λz, independently of the Reynolds number. Based on this observation, it is suggested that compact vortical structures attached to the wall can be ascribed to streak secondary instabilities. In addition, spatial distributions of fluctuating vorticity components show that the onset

  8. Linear stability of buoyant convective flow in a vertical channel with internal heat sources and a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Hudoba, A.; Molokov, S.

    2016-11-01

    Linear stability of buoyant convective flow of an electrically conducting fluid in a vertical channel owing to internal heat sources has been studied. The flow takes place in a transverse, horizontal magnetic field. The results show that up to four different local minima may be present in the neural stability curve. Up to two of these modes may be the most unstable depending, critically, on the value of the Hartmann number. Over a wide range of moderate to high Hartmann numbers, thermal waves dominate the instability. As the Hartmann number increases, however, this mode is strongly damped. Then the so-called Hartmann mode takes over, which involves the characteristic Hartmann layers at the walls appearing due to modification of the basic velocity profile by the magnetic field. Overall, for liquid metals at high magnetic fields, the basic flow is very stable. Variation of the Prandtl number in a wide range has also been performed as, depending on the type of an electrically conducting fluid (liquid metal or various kinds of electrolytes), the Prandtl number varies over several orders of magnitude. As may be expected, the increase of the Prandtl number lowers the instability threshold for the thermal waves.

  9. Formation of a compound flux rope by the merging of two filament channels, the associated dynamics, and its stability

    SciTech Connect

    Joshi, Navin Chandra; Inoue, Satoshi; Magara, Tetsuya E-mail: njoshi98@gmail.com

    2014-11-01

    We present observations of compound flux rope formation, which occurred on 2014 January 1, via merging of two nearby filament channels, the associated dynamics, and its stability using multiwavelength data. We also discuss the dynamics of cool and hot plasma moving along the newly formed compound flux rope. The merging started after the interaction between the southern leg of the northward filament and the northern leg of the southward filament at ≈01:21 UT and continued until a compound flux rope formed at ≈01:33 UT. During the merging, the cool filament plasma heated up and started to move along both sides of the compound flux rope, i.e., toward the north (≈265 km s{sup –1}) and south (≈118 km s{sup –1}) from the point of merging. After traveling a distance of ≈150 Mm toward the north, the plasma cooled down and started to return back to the south (≈14 km s{sup –1}) after ≈02:00 UT. The observations provide a clear example of compound flux rope formation via merging of two different flux ropes and the occurrence of a flare through tether cutting reconnection. However, the compound flux rope remained stable in the corona and had a confined eruption. The coronal magnetic field decay index measurements revealed that both the filaments and the compound flux rope axis lie within the stability domain (decay index <1.5), which may be the possible cause for their stability. The present study also deals with the relationship between the filament's chirality (sinistral) and the helicity (positive) of the surrounding flux rope.

  10. Suspended-sediment loads, reservoir sediment trap efficiency, and upstream and downstream channel stability for Kanopolis and Tuttle Creek Lakes, Kansas, 2008-10

    USGS Publications Warehouse

    Juracek, Kyle E.

    2011-01-01

    Continuous streamflow and turbidity data collected from October 1, 2008, to September 30, 2010, at streamgage sites upstream and downstream from Kanopolis and Tuttle Creek Lakes, Kansas, were used to compute the total suspended-sediment load delivered to and released from each reservoir as well as the sediment trap efficiency for each reservoir. Ongoing sedimentation is decreasing the ability of the reservoirs to serve several purposes including flood control, water supply, and recreation. River channel stability upstream and downstream from the reservoirs was assessed using historical streamgage information. For Kanopolis Lake, the total 2-year inflow suspended-sediment load was computed to be 600 million pounds. Most of the suspended-sediment load was delivered during short-term, high-discharge periods. The total 2-year outflow suspended-sediment load was computed to be 31 million pounds. Sediment trap efficiency for the reservoir was estimated to be 95 percent. The mean annual suspended-sediment yield from the upstream basin was estimated to be 129,000 pounds per square mile per year. No pronounced changes in channel width were evident at five streamgage sites located upstream from the reservoir. At the Ellsworth streamgage site, located upstream from the reservoir, long-term channel-bed aggradation was followed by a period of stability. Current (2010) conditions at five streamgages located upstream from the reservoir were typified by channel-bed stability. At the Langley streamgage site, located immediately downstream from the reservoir, the channel bed degraded 6.15 feet from 1948 to 2010. For Tuttle Creek Lake, the total 2-year inflow suspended-sediment load was computed to be 13.3 billion pounds. Most of the suspended-sediment load was delivered during short-term, high-discharge periods. The total 2-year outflow suspended-sediment load was computed to be 327 million pounds. Sediment trap efficiency for the reservoir was estimated to be 98 percent. The mean

  11. Channel widening due to urbanization and a major flood can alter bed particle organization and bed stability in an urban boulder-bed channel

    NASA Astrophysics Data System (ADS)

    Prestegaard, K. L.; Behrns, K.; Blanchet, Z.; Hankin, E.

    2007-12-01

    The Anacostia River is a tributary of the Potomac River north of Washington D.C. that has become progressively more urbanized in the past 50 years. Bankfull discharge and bankfull width in the Anacostia have increased by 3- 4x in the past 50 years. Nearby watersheds of similar size and geology, but without significant urbanization, contain threshold gravel-bed streams. The Anacostia, however, is not a threshold channel; it exhibits break-up of boulder-bed channels in upstream reaches and significant gravel bar formation in downstream reaches. These gravel bars have grown and migrated considerably in the past 10-15 years, contributing significantly to local channel widening that can be twice that of adjacent reaches. The purpose of this study is to determine bedload transport rates and grain size distributions and their relationship to discharge, bed organization and sediment supply. Bed mobility data come from both bedload transport measurements and measurements of channel bed changes. Channel bed changes were obtained from a) repeated channel cross section surveys, b) surface and subsurface size distributions, and c) bed particle organization measurements (measurements of location of particles within reaches). These measurements were made prior to and after the floods of 2006, which equalled the largest floods on record for most parts of the Anacostia River. In some boulder bed reaches, boulders were removed from the center of the channel and deposited along and on the channel banks. The mid-channel boulders were replaced by sheets of gravel and cobbles, significantly altering the bed mobility of the channels.

  12. Improving electrical performance and bias stability of HfInZnO-TFT with optimizing the channel thickness

    SciTech Connect

    Li, Jun; Zhang, Zhi-Lin; Ding, Xing-Wei; Jiang, Xue-Yin; Zhang, Jian-Hua; Zhang, Hao

    2013-10-15

    RF magnetron sputtered HfInZnO film and atomic layer deposition (ALD) Al{sub 2}O{sub 3} film were employed for thin film transistors (TFTs) as channel layer and gate insulator, respectively. To achieve HfInZnO-TFT with high performance and good bias stability, the thickness of HfInZnO active layer was optimized. The performance of HfInZnO-TFTs was found to be thickness dependent. As the HfInZnO active layer got thicker, the leakage current greatly increased from 1.73 × 10{sup −12} to 2.54 × 10{sup −8} A, the threshold voltage decreased from 7.4 to −4.7 V, while the subthreshold swing varied from 0.41 to 1.07 V/decade. Overall, the HfInZnO film showed superior performance, such as saturation mobility of 6.4 cm{sup 2}/V s, threshold voltage of 4.2 V, subthreshold swing of 0.43 V/decade, on/off current ratio of 3 × 10{sup 7} and V{sub th} shift of 3.6 V under V{sub GS}= 10 V for 7200 s. The results demonstrate the possibility of fabricating TFTs using HfInZnO film as active layer and using ALD Al{sub 2}O{sub 3} as gate insulator.

  13. Post-transcriptional regulation of BK channel splice variant stability by miR-9 underlies neuroadaptation to alcohol

    PubMed Central

    Pietrzykowski, Andrzej Z.; Friesen, Ryan M.; Martin, Gilles E.; Puig, Sylvie I.; Nowak, Cheryl L.; Wynne, Patricia M.; Siegelmann, Hava T.; Treistman, Steven N.

    2008-01-01

    Summary Tolerance represents a critical component of addiction. The large conductance calcium-and voltage-activated potassium channel (BK) is a well-established alcohol target, and an important element in behavioral and molecular alcohol tolerance. We tested whether microRNA, a newly-discovered class of gene expression regulators, plays a role in the development of tolerance. We show that in adult mammalian brain alcohol upregulates microRNA (miR-9) and mediates post-transcriptional reorganization in BK mRNA splice variants by miR-9-dependent destabilization of BK mRNAs containing 3’UTRs with a miR-9 Recognition Element (MRE). Different splice variants encode BK isoforms with different alcohol sensitivities. Computational modeling indicates that this miR-9 dependent mechanism contributes to alcohol tolerance. Moreover, this mechanism can be extended to regulation of additional miR-9 targets relevant to alcohol abuse. Our results describe a novel mechanism of multiplex regulation of stability of alternatively spliced mRNA by miRNA in drug adaptation and neuronal plasticity. PMID:18667155

  14. The interactions with solvent, heat stability, and 13C-labelling of alamethicin, an ion-channel-forming peptide.

    PubMed

    Yee, A A; Marat, K; O'Neil, J D

    1997-01-15

    The peptide alamethicin was labelled with 13C and 15N by growing the fungus Trichoderma viride in a medium containing [U-13C] glucose and K15NO3. Spin-echo difference spectroscopy showed that 13C was incorporated to a level of about 50% and 15N to about 98%. Incorporation of 13C into the peptide provided residue-specific probes of the interactions with solvent and heat stability of this ion-channel-forming peptide. All of the carbonyl carbons and the alpha-carbons of the alpha-aminoisobutyric acid [Ala(Me)] residues of alamethicin in methanol were assigned using two-dimensional and three-dimensional heteronuclear correlation experiments. Measurements of 1JC'N revealed hydrogen bonding with solvent at residues 1 and 19 at the ends of the peptide and at Gly11 in the middle. The data also support the thesis [see Juranic, N., Ilich, P. K. & Macara, S. (1995) J. Am. Chem. Soc. 117, 405-410 that intramolecular hydrogen bonds in proteins and peptides are weaker than hydrogen bonds to solvent. The sensitivity of alamethicin carbonyl and proton chemical shifts to perturbation by dimethyl sulfoxide correlates well with the calculated solvent accessibilities of the carbonyls in the crystal structures and reveals residues in the middle of the peptide and at the C-terminus which interact with solvent. Taken together with the 1JC'N measurements, the data support a model in which hydrogen bonding to solvent at the Gly11/Leu12 amide could provide a site of hydration in the interior of the alamethicin channel structure. The temperature dependencies of the carbonyl chemical shifts support the suggestion that the peptide is flexible in the regions where solvent interacts with the backbone of the peptide. The linear temperature dependence of the carbonyl chemical shifts and molar ellipticity indicate that, due to steric constraints at the Ala(Me) residues, the peptide folding/unfolding transition is non-cooperative and that the peptide is remarkably heat stable.

  15. Sedimentation, sediment quality, and upstream channel stability, John Redmond Reservoir, east-central Kansas, 1964-2009

    USGS Publications Warehouse

    Juracek, Kyle E.

    2010-01-01

    A combination of available bathymetric-survey information, bottom-sediment coring, and historical streamgage information was used to investigate sedimentation, sediment quality, and upstream channel stability for John Redmond Reservoir, east-central Kansas. Ongoing sedimentation is reducing the ability of the reservoir to serve several purposes including flood control, water supply, and recreation. The total estimated volume and mass of bottom sediment deposited between 1964 and 2009 in the conservation pool of the reservoir was 1.46 billion cubic feet and 55.8 billion pounds, respectively. The estimated sediment volume occupied about 41 percent of the conservation-pool, water-storage capacity of the reservoir. Water-storage capacity in the conservation pool has been lost to sedimentation at a rate of about 1 percent annually. Mean annual net sediment deposition since 1964 in the conservation pool of the reservoir was estimated to be 1.24 billion pounds per year. Mean annual net sediment yield from the reservoir basin was estimated to be 411,000 pounds per square mile per year Information from sediment cores shows that throughout the history of John Redmond Reservoir, total nitrogen concentrations in the deposited sediment generally were uniform indicating consistent nitrogen inputs to the reservoir. Total phosphorus concentrations in the deposited sediment were more variable than total nitrogen indicating the possibility of changing phosphorus inputs to the reservoir. As the principal limiting factor for primary production in most freshwater environments, phosphorus is of particular importance because increased inputs can contribute to accelerated reservoir eutrophication and the production of algal toxins and taste-and-odor compounds. The mean annual net loads of total nitrogen and total phosphorus deposited in the bottom sediment of the reservoir were estimated to be 2,350,000 pounds per year and 1,030,000 pounds per year, respectively. The estimated mean annual

  16. Regulation of Postsynaptic Stability by the L-type Calcium Channel CaV1.3 and its Interaction with PDZ Proteins

    PubMed Central

    Stanika, Ruslan I.; Flucher, Bernhard E.; Obermair, Gerald J.

    2015-01-01

    Alterations in dendritic spine morphology and postsynaptic structure are a hallmark of neurological disorders. Particularly spine pruning of striatal medium spiny neurons and aberrant rewiring of corticostriatal synapses have been associated with the pathology of Parkinson’s disease and L-DOPA induced dyskinesia, respectively. Owing to its low activation threshold the neuronal L-type calcium channel CaV1.3 is particularly critical in the control of neuronal excitability and thus in the calcium-dependent regulation of neuronal functions. CaV1.3 channels are located in dendritic spines and contain a C-terminal class 1 PDZ domain-binding sequence. Until today the postsynaptic PDZ domain proteins shank, densin-180, and erbin have been shown to interact with CaV1.3 channels and to modulate their current properties. Interestingly experimental evidence suggests an involvement of all three PDZ proteins as well as CaV1.3 itself in regulating dendritic and postsynaptic morphology. Here we briefly review the importance of CaV1.3 and its proposed interactions with PDZ proteins for the stability of dendritic spines. With a special focus on the pathology associated with Parkinson’s disease, we discuss the hypothesis that CaV1.3 L-type calcium channels may be critical modulators of dendritic spine stability. PMID:25966696

  17. A room temperature strategy towards enhanced performance and bias stability of oxide thin film transistor with a sandwich structure channel layer

    NASA Astrophysics Data System (ADS)

    Zeng, Yong; Ning, Honglong; Zheng, Zeke; Zhang, Hongke; Fang, Zhiqiang; Yao, Rihui; Xu, Miao; Wang, Lei; Lan, Linfeng; Peng, Junbiao; Lu, Xubing

    2017-04-01

    Thermal annealing is a conventional and effective way to improve the bias stress stability of oxide thin film transistors (TFT) on solid substrates. However, it is still a challenge for enhancing the bias stress stability of oxide TFTs on flexible substrates by high-temperature post-treatment due to the thermal sensitivity of flexible substrates. Here, a room temperature strategy is presented towards enhanced performance and bias stability of oxide TFTs by intentionally engineering a sandwich structure channel layer consisting of a superlattice with aluminum doped zinc oxide (AZO) and Al2O3 thin films. The Al2O3/AZO/Al2O3-TFTs not only exhibit a saturation mobility of 9.27 cm2 V-1 s-1 and a linear mobility of 11.38 cm2 V-1 s-1 but also demonstrate a better bias stress stability than AZO/Al2O3-TFT. Moreover, the underlying mechanism of this enhanced electrical performance of TFTs with a sandwich structure channel layer is that the bottom Al2O3 thin films can obviously improve the crystalline phase of AZO films while decreasing electrical trapping centers and adsorption sites for undesirable molecules such as water and oxygen.

  18. Highly Conserved Salt Bridge Stabilizes Rigid Signal Patch at Extracellular Loop Critical for Surface Expression of Acid-sensing Ion Channels*

    PubMed Central

    Yang, Yang; Yu, Ye; Cheng, Jin; Liu, Yan; Liu, Di-Shi; Wang, Jin; Zhu, Michael X.; Wang, Rui; Xu, Tian-Le

    2012-01-01

    Acid-sensing ion channels (ASICs) are non-selective cation channels activated by extracellular acidosis associated with many physiological and pathological conditions. A detailed understanding of the mechanisms that govern cell surface expression of ASICs, therefore, is critical for better understanding of the cell signaling under acidosis conditions. In this study, we examined the role of a highly conserved salt bridge residing at the extracellular loop of rat ASIC3 (Asp107-Arg153) and human ASIC1a (Asp107-Arg160) channels. Comprehensive mutagenesis and electrophysiological recordings revealed that the salt bridge is essential for functional expression of ASICs in a pH sensing-independent manner. Surface biotinylation and immunolabeling of an extracellular epitope indicated that mutations, including even minor alterations, at the salt bridge impaired cell surface expression of ASICs. Molecular dynamics simulations, normal mode analysis, and further mutagenesis studies suggested a high stability and structural constrain of the salt bridge, which serves to separate an adjacent structurally rigid signal patch, important for surface expression, from a flexible gating domain. Thus, we provide the first evidence of structural requirement that involves a stabilizing salt bridge and an exposed rigid signal patch at the destined extracellular loop for normal surface expression of ASICs. These findings will allow evaluation of new strategies aimed at preventing excessive excitability and neuronal injury associated with tissue acidosis and ASIC activation. PMID:22399291

  19. A Polybasic Plasma Membrane Binding Motif in the I-II Linker Stabilizes Voltage-gated CaV1.2 Calcium Channel Function.

    PubMed

    Kaur, Gurjot; Pinggera, Alexandra; Ortner, Nadine J; Lieb, Andreas; Sinnegger-Brauns, Martina J; Yarov-Yarovoy, Vladimir; Obermair, Gerald J; Flucher, Bernhard E; Striessnig, Jörg

    2015-08-21

    L-type voltage-gated Ca(2+) channels (LTCCs) regulate many physiological functions like muscle contraction, hormone secretion, gene expression, and neuronal excitability. Their activity is strictly controlled by various molecular mechanisms. The pore-forming α1-subunit comprises four repeated domains (I-IV), each connected via an intracellular linker. Here we identified a polybasic plasma membrane binding motif, consisting of four arginines, within the I-II linker of all LTCCs. The primary structure of this motif is similar to polybasic clusters known to interact with polyphosphoinositides identified in other ion channels. We used de novo molecular modeling to predict the conformation of this polybasic motif, immunofluorescence microscopy and live cell imaging to investigate the interaction with the plasma membrane, and electrophysiology to study its role for Cav1.2 channel function. According to our models, this polybasic motif of the I-II linker forms a straight α-helix, with the positive charges facing the lipid phosphates of the inner leaflet of the plasma membrane. Membrane binding of the I-II linker could be reversed after phospholipase C activation, causing polyphosphoinositide breakdown, and was accelerated by elevated intracellular Ca(2+) levels. This indicates the involvement of negatively charged phospholipids in the plasma membrane targeting of the linker. Neutralization of four arginine residues eliminated plasma membrane binding. Patch clamp recordings revealed facilitated opening of Cav1.2 channels containing these mutations, weaker inhibition by phospholipase C activation, and reduced expression of channels (as quantified by ON-gating charge) at the plasma membrane. Our data provide new evidence for a membrane binding motif within the I-II linker of LTCC α1-subunits essential for stabilizing normal Ca(2+) channel function. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  20. Specific inhibition of HCN channels slows rhythm differently in atria, ventricle and outflow tract and stabilizes conduction in the anoxic-reoxygenated embryonic heart model.

    PubMed

    Sarre, Alexandre; Pedretti, Sarah; Gardier, Stephany; Raddatz, Eric

    2010-01-01

    The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed in pacemaker cells very early during cardiogenesis. This work aimed at determining to what extent these channels are implicated in the electromechanical disturbances induced by a transient oxygen lack which may occur in utero. Spontaneously beating hearts or isolated ventricles and outflow tracts dissected from 4-day-old chick embryos were exposed to a selective inhibitor of HCN channels (ivabradine 0.1-10microM) to establish a dose-response relationship. The effects of ivabradine on electrocardiogram, excitation-contraction coupling and contractility of hearts submitted to anoxia (30min) and reoxygenation (60min) were also determined. The distribution of the predominant channel isoform, HCN4, was established in atria, ventricle and outflow tract by immunoblotting. Intrinsic beating rate of atria, ventricle and outflow tract was 164+/-22 (n=10), 78+/-24 (n=8) and 40+/-12bpm (n=23, mean+/-SD), respectively. In the whole heart, ivabradine (0.3microM) slowed the firing rate of atria by 16% and stabilized PR interval. These effects persisted throughout anoxia-reoxygenation, whereas the variations of QT duration, excitation-contraction coupling and contractility, as well as the types and duration of arrhythmias were not altered. Ivabradine (10microM) reduced the intrinsic rate of atria and isolated ventricle by 27% and 52%, respectively, whereas it abolished activity of the isolated outflow tract. Protein expression of HCN4 channels was higher in atria and ventricle than in the outflow tract. Thus, HCN channels are specifically distributed and control finely atrial, ventricular and outflow tract pacemakers as well as conduction in the embryonic heart under normoxia and throughout anoxia-reoxygenation.

  1. Structural modeling and patch-clamp analysis of pain-related mutation TRPA1-N855S reveal inter-subunit salt bridges stabilizing the channel open state.

    PubMed

    Zíma, Vlastimil; Witschas, Katja; Hynkova, Anna; Zímová, Lucie; Barvík, Ivan; Vlachova, Viktorie

    2015-06-01

    The ankyrin transient receptor potential channel TRPA1 is a polymodal sensor for noxious stimuli, and hence a promising target for treating chronic pain. This tetrameric six-transmembrane segment (S1-S6) channel can be activated by various pungent chemicals, such as allyl isothiocyanate or cinnamaldehyde, but also by intracellular Ca(2+) or depolarizing voltages. Within the S4-S5 linker of human TRPA1, a gain-of-function mutation, N855S, was recently found to underlie familial episodic pain syndrome, manifested by bouts of severe upper body pain, triggered by physical stress, fasting, or cold. To clarify the structural basis for this channelopathy, we derive a structural model of TRPA1 by combining homology modeling, molecular dynamics simulations, point mutagenesis and electrophysiology. In the vicinity of N855, the model reveals inter-subunit salt bridges between E854 and K868. Using the heterologous expression of recombinant wild-type and mutant TRPA1 channels in HEK293T cells, we indeed found that the charge-reversal mutants E854R and K868E exhibited dramatically reduced responses to chemical and voltage stimuli, whereas the charge-swapping mutation E854R/K868E substantially rescued their functionalities. Moreover, mutation analysis of highly conserved charged residues within the S4-S5 region revealed a gain-of-function phenotype for R852E with an increased basal channel activity, a loss of Ca(2+)-induced potentiation and an accelerated Ca(2+)-dependent inactivation. Based on the model and on a comparison with the recently revealed atomic-level structure of the related channel TRPV1, we propose that inter-subunit salt bridges between adjacent S4-S5 regions are crucial for stabilizing the conformations associated with chemically and voltage-induced gating of the TRPA1 ion channel.

  2. Benchmarking the stability of human detergent-solubilised voltage-gated sodium channels for structural studies using eel as a reference

    PubMed Central

    Slowik, Daria; Henderson, Richard

    2015-01-01

    With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3 > hNaV1.2 > hNaV1.1 > hNaV1.6 > hNaV1.3 > hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel. PMID:25838126

  3. Benchmarking the stability of human detergent-solubilised voltage-gated sodium channels for structural studies using eel as a reference.

    PubMed

    Slowik, Daria; Henderson, Richard

    2015-07-01

    With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3>hNaV1.2>hNaV1.1>hNaV1.6>hNaV1.3>hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel. Copyright © 2015. Published by Elsevier B.V.

  4. Mutation of Light-dependent Phosphorylation Sites of the Drosophila Transient Receptor Potential-like (TRPL) Ion Channel Affects Its Subcellular Localization and Stability*

    PubMed Central

    Cerny, Alexander C.; Oberacker, Tina; Pfannstiel, Jens; Weigold, Sebastian; Will, Carina; Huber, Armin

    2013-01-01

    The Drosophila phototransduction cascade terminates in the opening of the ion channel transient receptor potential (TRP) and TRP-like (TRPL). Contrary to TRP, TRPL undergoes light-dependent subcellular trafficking between rhabdomeric photoreceptor membranes and an intracellular storage compartment, resulting in long term light adaptation. Here, we identified in vivo phosphorylation sites of TRPL that affect TRPL stability and localization. Quantitative mass spectrometry revealed a light-dependent change in the TRPL phosphorylation pattern. Mutation of eight C-terminal phosphorylation sites neither affected multimerization of the channels nor the electrophysiological response of flies expressing the mutated channels. However, these mutations resulted in mislocalization and enhanced degradation of TRPL after prolonged dark-adaptation. Mutation of subsets of the eight C-terminal phosphorylation sites also led to a reduction of TRPL content and partial mislocalization in the dark. This suggests that a light-dependent switch in the phosphorylation pattern of the TRPL channel mediates stable expression of TRPL in the rhabdomeres upon prolonged dark-adaptation. PMID:23592784

  5. Amplification and lasing in a plasma channel formed in gases by an intense femtosecond laser pulse in the regime of interference stabilization

    NASA Astrophysics Data System (ADS)

    Bogatskaya, A. V.; Volkova, E. A.; Popov, A. M.

    2016-01-01

    The effect of the interference stabilization of Rydberg atoms in a high-intensity laser field is proposed to create a plasma channel with population inversion between a set of Rydberg states and the low-lying excited and ground state for the conversion of the input laser energy into the visible or VUV and XUV frequency band. Furthermore, there is a possibility of creating population inversion between high-lying Rydberg states that can be used for lasing and amplification in the IR, mid-IR, and terahertz frequency band.

  6. A light stabilizer (Tinuvin 770) that elutes from polypropylene plastic tubes is a potent L-type Ca(2+)-channel blocker.

    PubMed Central

    Glossmann, H; Hering, S; Savchenko, A; Berger, W; Friedrich, K; Garcia, M L; Goetz, M A; Liesch, J M; Zink, D L; Kaczorowski, G J

    1993-01-01

    A pharmacologically active agent was easily extracted by aqueous or organic solvents from laboratory plastic tubes (Falcon Blue Max) and has been chemically identified as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate. This compound (approximately 12 micrograms per tube approximately 25 nmol) blocked 1,4-dihydropyridine-sensitive 45Ca2+ uptake into GH3 cells with an IC50 value of 3.6 microM, inhibited Sr2+ currents through L-type Ca2+ channels in A7r5 smooth-muscle cells in whole-cell patch-clamp experiments after extracellular application, and affected the high-affinity binding of Ca2+ entry-blocker ligands to a variety of preparations. Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate is a highly potent (IC50 values < 10 nM) inhibitor at the phenylalkylamine- and benzothiazepine-selective drug-binding domains of the alpha 1 subunit of L-type Ca2+ channels. This compound behaves as a heterotropic allosteric regulator for the 1,4-dihydropyridine-selective domain in purified Ca(2+)-channel preparations from rabbit skeletal muscle. (+)-Tetrandrine stimulation of 1,4-dihydropyridine binding to the membrane-bound L-type Ca2+ channel is inhibited by the compound in a competitive manner (Ki value = 6.8 nM). Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate is therefore classified as the prototype of another class of L-type Ca(2+)-channel blockers that binds to the alpha 1 subunit at the drug-binding domains selective for (+)-tetrandrine or (+)-cis-diltiazem. This compound is identical to Tinuvin 770, which is used worldwide as a light stabilizer for polyolefins. PMID:8415734

  7. Preliminary assessment of channel stability and bed-material transport in the Coquille River basin, southwestern Oregon

    USGS Publications Warehouse

    Jones, Krista L.; O'Connor, Jim E.; Keith, Mackenzie K.; Mangano, Joseph F.; Wallick, J. Rose

    2012-01-01

    This report summarizes a preliminary study of bed-material transport, vertical and lateral channel changes, and existing datasets for the Coquille River basin, which encompasses 2,745 km2 (square kilometers) of the southwestern Oregon coast. This study, conducted to inform permitting decisions regarding instream gravel mining, revealed that:

  8. A defined heteromeric KV1 channel stabilizes the intrinsic pacemaking and regulates the output of deep cerebellar nuclear neurons to thalamic targets.

    PubMed

    Ovsepian, Saak V; Steuber, Volker; Le Berre, Marie; O'Hara, Liam; O'Leary, Valerie B; Dolly, J Oliver

    2013-04-01

    The output of the cerebellum to the motor axis of the central nervous system is orchestrated mainly by synaptic inputs and intrinsic pacemaker activity of deep cerebellar nuclear (DCN) projection neurons. Herein, we demonstrate that the soma of these cells is enriched with K(V)1 channels produced by mandatory multi-merization of K(V)1.1, 1.2 α and KV β2 subunits. Being constitutively active, the K(+) current (IK(V)1) mediated by these channels stabilizes the rate and regulates the temporal precision of self-sustained firing of these neurons. Placed strategically, IK(V)1 provides a powerful counter-balance to prolonged depolarizing inputs, attenuates the rebound excitation, and dampens the membrane potential bi-stability. Somatic location with low activation threshold render IK(V)1 instrumental in voltage-dependent de-coupling of the axon initial segment from the cell body of projection neurons, impeding invasion of back-propagating action potentials into the somato-dendritic compartment. The latter is also demonstrated to secure the dominance of clock-like somatic pacemaking in driving the regenerative firing activity of these neurons, to encode time variant inputs with high fidelity. Through the use of multi-compartmental modelling and retro-axonal labelling, the physiological significance of the described functions for processing and communication of information from the lateral DCN to thalamic relay nuclei is established.

  9. A defined heteromeric KV1 channel stabilizes the intrinsic pacemaking and regulates the output of deep cerebellar nuclear neurons to thalamic targets

    PubMed Central

    Ovsepian, Saak V; Steuber, Volker; Le Berre, Marie; O’Hara, Liam; O’Leary, Valerie B; Dolly, J Oliver

    2013-01-01

    The output of the cerebellum to the motor axis of the central nervous system is orchestrated mainly by synaptic inputs and intrinsic pacemaker activity of deep cerebellar nuclear (DCN) projection neurons. Herein, we demonstrate that the soma of these cells is enriched with KV1 channels produced by mandatory multi-merization of KV1.1, 1.2 α and KVβ2 subunits. Being constitutively active, the K+ current (IKV1) mediated by these channels stabilizes the rate and regulates the temporal precision of self-sustained firing of these neurons. Placed strategically, IKV1 provides a powerful counter-balance to prolonged depolarizing inputs, attenuates the rebound excitation, and dampens the membrane potential bi-stability. Somatic location with low activation threshold render IKV1 instrumental in voltage-dependent de-coupling of the axon initial segment from the cell body of projection neurons, impeding invasion of back-propagating action potentials into the somato-dendritic compartment. The latter is also demonstrated to secure the dominance of clock-like somatic pacemaking in driving the regenerative firing activity of these neurons, to encode time variant inputs with high fidelity. Through the use of multi-compartmental modelling and retro-axonal labelling, the physiological significance of the described functions for processing and communication of information from the lateral DCN to thalamic relay nuclei is established. PMID:23318870

  10. Geometries, stabilities and fragmental channels of neutral and charged sulfur clusters: Sn(Q) (n = 3-20, Q = 0, ±1).

    PubMed

    Jin, Yuanyuan; Maroulis, George; Kuang, Xiaoyu; Ding, Liping; Lu, Cheng; Wang, Jingjing; Lv, Jian; Zhang, Chuanzhao; Ju, Meng

    2015-05-28

    We have performed unbiased searches for the global minimum structures of neutral and charged sulfur clusters Sn(Q) (n = 3-20, Q = 0, ±1) relying on the CALYPSO structure searching method combined with density functional theory geometric optimization. Very accurate ab initio calculations are used to determine relative stabilities and energy ranking among competing low-lying isomers of the neutral and charged sulfur clusters obtained from the structure search. The harmonic vibrational analysis is also undertaken to assure that the optimized geometries are the true minima. It is shown that the most equilibrium geometries of sulfur clusters are closed three-dimensional (3D) helical rings, which is in agreement with the experimental observations. The binding energies, second-order energy differences, and highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of the considered species are calculated and analyzed systematically. Additionally, the fragmentation channels are determined and the results indicate that the Sn(Q) → S2 + Sn-2(Q) channel is a route that the small clusters (n = 3-10) favor, while the larger species (n = 13-20) prefer the Sn(Q) → S8 + Sn-8(Q) channel.

  11. Short channel amorphous In-Ga-Zn-O thin-film transistor arrays for ultra-high definition active matrix liquid crystal displays: Electrical properties and stability

    NASA Astrophysics Data System (ADS)

    Kim, Soo Chang; Kim, Young Sun; Yu, Eric Kai-Hsiang; Kanicki, Jerzy

    2015-09-01

    The electrical properties and stability of ultra-high definition (UHD) amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) arrays with short channel (width/length = 12/3 μm) were examined. A-IGZO TFT arrays have a mobility of ∼6 cm2/V s, subthreshold swing (S.S.) of 0.34 V/decade, threshold voltage of 3.32 V, and drain current (Id) on/off ratio of <109 with Ioff below 10-13 A. Overall these devices showed slightly different electrical characteristics as compared to the long channel devices; non-saturation of output curve at high drain-to-source voltage (Vds), negative shift of threshold voltage with increasing Vds, and the mobility reduction at high gate voltage (Vgs) were observed. The second derivative method adopting Tikhonov's regularization theory is suggested for the robust threshold voltage extraction. The temperature dependency of γ-value was established after taking into consideration the impact of source/drain contact resistances. The AC bias-temperature stress was used to simulate the actual operation of active matrix liquid crystal displays (AM-LCDs). The threshold voltage shift had a dependency on the magnitude of drain bias stress, frequency, and duty cycle due to the impact ionization accelerated at high temperature. This study demonstrates that the short channel effects, source/drain contact resistances and impact ionization have to be taken into account during optimization of UHD AM-LCDs.

  12. Modelling Temporal Stability of EPI Time Series Using Magnitude Images Acquired with Multi-Channel Receiver Coils

    PubMed Central

    Hutton, Chloe; Balteau, Evelyne; Lutti, Antoine; Josephs, Oliver; Weiskopf, Nikolaus

    2012-01-01

    In 2001, Krueger and Glover introduced a model describing the temporal SNR (tSNR) of an EPI time series as a function of image SNR (SNR0). This model has been used to study physiological noise in fMRI, to optimize fMRI acquisition parameters, and to estimate maximum attainable tSNR for a given set of MR image acquisition and processing parameters. In its current form, this noise model requires the accurate estimation of image SNR. For multi-channel receiver coils, this is not straightforward because it requires export and reconstruction of large amounts of k-space raw data and detailed, custom-made image reconstruction methods. Here we present a simple extension to the model that allows characterization of the temporal noise properties of EPI time series acquired with multi-channel receiver coils, and reconstructed with standard root-sum-of-squares combination, without the need for raw data or custom-made image reconstruction. The proposed extended model includes an additional parameter κ which reflects the impact of noise correlations between receiver channels on the data and scales an apparent image SNR (SNR′0) measured directly from root-sum-of-squares reconstructed magnitude images so that κ = SNR′0/SNR0 (under the condition of SNR0>50 and number of channels ≤32). Using Monte Carlo simulations we show that the extended model parameters can be estimated with high accuracy. The estimation of the parameter κ was validated using an independent measure of the actual SNR0 for non-accelerated phantom data acquired at 3T with a 32-channel receiver coil. We also demonstrate that compared to the original model the extended model results in an improved fit to human task-free non-accelerated fMRI data acquired at 7T with a 24-channel receiver coil. In particular, the extended model improves the prediction of low to medium tSNR values and so can play an important role in the optimization of high-resolution fMRI experiments at lower SNR levels. PMID:23284874

  13. Preliminary assessment of channel stability and bed-material transport in the Rogue River basin, southwestern Oregon

    USGS Publications Warehouse

    Jones, Krista L.; O'Connor, Jim E.; Keith, Mackenzie K.; Mangano, Joseph F.; Wallick, J. Rose

    2012-01-01

    This report summarizes a preliminary assessment of bed-material transport, vertical and lateral channel changes, and existing datasets for the Rogue River basin, which encompasses 13,390 square kilometers (km2) along the southwestern Oregon coast. This study, conducted to inform permitting decisions regarding instream gravel mining, revealed that: * The Rogue River in its lowermost 178.5 kilometers (km) alternates between confined and unconfined segments, and is predominately alluvial along its lowermost 44 km. The study area on the mainstem Rogue River can be divided into five reaches based on topography, hydrology, and tidal influence. The largely confined, active channel flows over bedrock and coarse bed material composed chiefly of boulders and cobbles in the Grants Pass (river kilometers [RKM] 178.5-152.8), Merlin (RKM 152.8-132.7), and Galice Reaches (RKM 132.7-43.9). Within these confined reaches, the channel contains few bars and has stable planforms except for locally wider segments such as the Brushy Chutes area in the Merlin Reach. Conversely, the active channel flows over predominately alluvial material and contains nearly continuous gravel bars in the Lobster Creek Reach (RKM 43.9-6.7). The channel in the Tidal Reach (RKM 6.7-0) is also alluvial, but tidally affected and unconfined until RKM 2. The Lobster Creek and Tidal Reaches contain some of the most extensive bar deposits within the Rogue River study area. * For the 56.6-km-long segment of the Applegate River included in this study, the river was divided into two reaches based on topography. In the Upper Applegate River Reach (RKM 56.6-41.6), the confined, active channel flows over alluvium and bedrock and has few bars. In the Lower Applegate River Reach (RKM 41.6-0), the active channel alternates between confined and unconfined segments, flows predominantly over alluvium, shifts laterally in unconfined sections, and contains more numerous and larger bars. * The 6.5-km segment of the lower

  14. Helicity, membrane incorporation, orientation and thermal stability of the large conductance mechanosensitive ion channel from E. coli

    NASA Technical Reports Server (NTRS)

    Arkin, I. T.; Sukharev, S. I.; Blount, P.; Kung, C.; Brunger, A. T.

    1998-01-01

    In this report, we present structural studies on the large conductance mechanosensitive ion channel (MscL) from E. coli in detergent micelles and lipid vesicles. Both transmission Fourier transform infrared spectroscopy and circular dichroism (CD) spectra indicate that the protein is highly helical in detergents as well as liposomes. The secondary structure of the proteins was shown to be highly resistant towards denaturation (25-95 degrees C) based on an ellipticity thermal profile. Amide H+/D+ exchange was shown to be extensive (ca. 66%), implying that two thirds of the protein are water accessible. MscL, reconstituted in oriented lipid bilayers, was shown to possess a net bilayer orientation using dichroic ratios measured by attenuated total-reflection Fourier transform infrared spectroscopy. Here, we present and discuss this initial set of structural data on this new family of ion-channel proteins.

  15. Evaluation of the Earth Radiation Budget Experiment (ERBE) shortwave channel's stability using in-flight calibration sources

    NASA Technical Reports Server (NTRS)

    Gibson, Michael A.; Lee, Robert B., III; Thomas, Susan

    1992-01-01

    The Earth Radiation Budget Experiment (ERBE) radiometers were designed to make absolute measurements of the incoming solar, earth-reflected solar, and earth-emitted fluxes for investigations of the earth's climate system. Thermistor bolometers were the sensors used for the ERBE scanning radiometric package. Each thermistor bolometer package consisted of three narrow field of view broadband radiometric channels measuring shortwave, longwave, and total (0.2 micron to 50 microns) radiation. The in-flight calibration facilities include Mirror Attenuator Mosaics, shortwave internal calibration source, and internal blackbody sources to monitor the long-term responsivity of the radiometers. This paper describes the in-flight calibration facilities, the calibration data reduction techniques, and the results from the in-flight shortwave channel calibrations. The results indicate that the ERBE shortwave detectors were stable to within +/- 1 percent for up to five years of flight operation.

  16. Helicity, membrane incorporation, orientation and thermal stability of the large conductance mechanosensitive ion channel from E. coli

    NASA Technical Reports Server (NTRS)

    Arkin, I. T.; Sukharev, S. I.; Blount, P.; Kung, C.; Brunger, A. T.

    1998-01-01

    In this report, we present structural studies on the large conductance mechanosensitive ion channel (MscL) from E. coli in detergent micelles and lipid vesicles. Both transmission Fourier transform infrared spectroscopy and circular dichroism (CD) spectra indicate that the protein is highly helical in detergents as well as liposomes. The secondary structure of the proteins was shown to be highly resistant towards denaturation (25-95 degrees C) based on an ellipticity thermal profile. Amide H+/D+ exchange was shown to be extensive (ca. 66%), implying that two thirds of the protein are water accessible. MscL, reconstituted in oriented lipid bilayers, was shown to possess a net bilayer orientation using dichroic ratios measured by attenuated total-reflection Fourier transform infrared spectroscopy. Here, we present and discuss this initial set of structural data on this new family of ion-channel proteins.

  17. Evaluation of the Earth Radiation Budget Experiment (ERBE) shortwave channel's stability using in-flight calibration sources

    NASA Technical Reports Server (NTRS)

    Gibson, Michael A.; Lee, Robert B., III; Thomas, Susan

    1992-01-01

    The Earth Radiation Budget Experiment (ERBE) radiometers were designed to make absolute measurements of the incoming solar, earth-reflected solar, and earth-emitted fluxes for investigations of the earth's climate system. Thermistor bolometers were the sensors used for the ERBE scanning radiometric package. Each thermistor bolometer package consisted of three narrow field of view broadband radiometric channels measuring shortwave, longwave, and total (0.2 micron to 50 microns) radiation. The in-flight calibration facilities include Mirror Attenuator Mosaics, shortwave internal calibration source, and internal blackbody sources to monitor the long-term responsivity of the radiometers. This paper describes the in-flight calibration facilities, the calibration data reduction techniques, and the results from the in-flight shortwave channel calibrations. The results indicate that the ERBE shortwave detectors were stable to within +/- 1 percent for up to five years of flight operation.

  18. Rufinamide attenuates mechanical allodynia in a model of neuropathic pain in the mouse and stabilizes voltage-gated sodium channel inactivated state.

    PubMed

    Suter, Marc R; Kirschmann, Guylène; Laedermann, Cedric J; Abriel, Hugues; Decosterd, Isabelle

    2013-01-01

    Voltage-gated sodium channels dysregulation is important for hyperexcitability leading to pain persistence. Sodium channel blockers currently used to treat neuropathic pain are poorly tolerated. Getting new molecules to clinical use is laborious. We here propose a drug already marketed as anticonvulsant, rufinamide. We compared the behavioral effect of rufinamide to amitriptyline using the Spared Nerve Injury neuropathic pain model in mice. We compared the effect of rufinamide on sodium currents using in vitro patch clamp in cells expressing the voltage-gated sodium channel Nav1.7 isoform and on dissociated dorsal root ganglion neurons to amitriptyline and mexiletine. In naive mice, amitriptyline (20 mg/kg) increased withdrawal threshold to mechanical stimulation from 1.3 (0.6-1.9) (median [95% CI]) to 2.3 g (2.2-2.5) and latency of withdrawal to heat stimulation from 13.1 (10.4-15.5) to 30.0 s (21.8-31.9), whereas rufinamide had no effect. Rufinamide and amitriptyline alleviated injury-induced mechanical allodynia for 4 h (maximal effect: 0.10 ± 0.03 g (mean ± SD) to 1.99 ± 0.26 g for rufinamide and 0.25 ± 0.22 g to 1.92 ± 0.85 g for amitriptyline). All drugs reduced peak current and stabilized the inactivated state of voltage-gated sodium channel Nav1.7, with similar effects in dorsal root ganglion neurons. At doses alleviating neuropathic pain, amitriptyline showed alteration of behavioral response possibly related to either alteration of basal pain sensitivity or sedative effect or both. Side-effects and drug tolerance/compliance are major problems with drugs such as amitriptyline. Rufinamide seems to have a better tolerability profile and could be a new alternative to explore for the treatment of neuropathic pain.

  19. High-performance staggered top-gate thin-film transistors with hybrid-phase microstructural ITO-stabilized ZnO channels

    NASA Astrophysics Data System (ADS)

    Deng, Sunbin; Chen, Rongsheng; Li, Guijun; Xia, Zhihe; Zhang, Meng; Zhou, Wei; Wong, Man; Kwok, Hoi-Sing

    2016-10-01

    In this paper, the ITO-stabilized ZnO thin films with a hybrid-phase microstructure were introduced, where a number of nanocrystals were embedded in an amorphous matrix. The microstructural and optical properties of thin films were investigated. It was found that the grain boundary and native defect issues in the pristine polycrystalline ZnO could be well suppressed. Meanwhile, such thin films also possessed relatively smooth surface and high transmittance in the visible range. Afterwards, the corresponding staggered top-gate thin-film transistors (TFTs) were fabricated at a temperature of 300 °C and exhibited fairly high electrical characteristics, especially with a field-effect mobility of nearly 20 cm2 V-1 s-1 and a subthreshold swing as low as 0.115 V/decade. In addition, the electrical uniformity and the stability of devices were also examined to be excellent. It is expected that the staggered top-gate TFTs with hybrid-phase microstructural ITO-stabilized ZnO channels are promising in the next-generation active-matrix flat panel displays.

  20. A Highly Conserved Salt Bridge Stabilizes the Kinked Conformation of β2,3-Sheet Essential for Channel Function of P2X4 Receptors.

    PubMed

    Zhao, Wen-Shan; Sun, Meng-Yang; Sun, Liang-Fei; Liu, Yan; Yang, Yang; Huang, Li-Dong; Fan, Ying-Zhe; Cheng, Xiao-Yang; Cao, Peng; Hu, You-Min; Li, Lingyong; Tian, Yun; Wang, Rui; Yu, Ye

    2016-04-08

    Significant progress has been made in understanding the roles of crucial residues/motifs in the channel function of P2X receptors during the pre-structure era. The recent structural determination of P2X receptors allows us to reevaluate the role of those residues/motifs. Residues Arg-309 and Asp-85 (rat P2X4 numbering) are highly conserved throughout the P2X family and were involved in loss-of-function polymorphism in human P2X receptors. Previous studies proposed that they participated in direct ATP binding. However, the crystal structure of P2X demonstrated that those two residues form an intersubunit salt bridge located far away from the ATP-binding site. Therefore, it is necessary to reevaluate the role of this salt bridge in P2X receptors. Here, we suggest the crucial role of this structural element both in protein stability and in channel gating rather than direct ATP interaction and channel assembly. Combining mutagenesis, charge swap, and disulfide cross-linking, we revealed the stringent requirement of this salt bridge in normal P2X4 channel function. This salt bridge may contribute to stabilizing the bending conformation of the β2,3-sheet that is structurally coupled with this salt bridge and the α2-helix. Strongly kinked β2,3 is essential for domain-domain interactions between head domain, dorsal fin domain, right flipper domain, and loop β7,8 in P2X4 receptors. Disulfide cross-linking with directions opposing or along the bending angle of the β2,3-sheet toward the α2-helix led to loss-of-function and gain-of-function of P2X4 receptors, respectively. Further insertion of amino acids with bulky side chains into the linker between the β2,3-sheet or the conformational change of the α2-helix, interfering with the kinked conformation of β2,3, led to loss-of-function of P2X4 receptors. All these findings provided new insights in understanding the contribution of the salt bridge between Asp-85 and Arg-309 and its structurally coupled β2,3-sheet to the

  1. Streak instability and generation of hairpin-vortices by a slotted jet in channel crossflow: Experiments and linear stability analysis

    NASA Astrophysics Data System (ADS)

    Philip, Jimmy; Karp, Michael; Cohen, Jacob

    2016-01-01

    Streaks and hairpin-vortices are experimentally generated in a laminar plane Poiseuille crossflow by injecting a continuous jet through a streamwise slot normal to the crossflow, with air as the working media. Small disturbances form stable streaks, however, higher disturbances cause the formation of streaks which undergo instability leading to the generation of hairpin vortices. Particular emphasis is placed on the flow conditions close to the generation of hairpin-vortices. Measurements are carried out in the cases of natural and phase-locked disturbance employing smoke visualisation, particle image velocimetry, and hot-wire anemometry, which include, the dominant frequency, wavelength, and the disturbance shape (or eigenfunctions) associated with the coherent part of the velocity field. A linear stability analysis for both one- and two-dimensional base-flows is carried out to understand the mechanism of instability and good agreement of wavelength and eigenfunctions are obtained when compared to the experimental data, and a slight under-prediction of the growth-rates by the linear stability analysis consistent with the final nonlinear stages in transitional flows. Furthermore, an energy analysis for both the temporal and spatial stability analysis revels the dominance of the symmetric varicose mode, again, in agreement with the experiments, which is found to be governed by the balance of the wallnormal shear and dissipative effects rather than the spanwise shear. In all cases the anti-symmetric sinuous modes governed by the spanwise shear are found to be damped both in analysis and in our experiments.

  2. The relationship between vegetation, slope stability and channel processes leading to the recruitment and mobilization of large woody debris

    NASA Astrophysics Data System (ADS)

    Gasser, Eric; Dorren, Luuk; Hübl, Johannes; Schwarz, Massimiliano

    2017-04-01

    Large woody debris fulfills important ecological functions in river systems, but it also increases the risk of damage during flood events in populated regions or along traffic routes. The mobilization and recruitment of "fresh" large woody debris has often been documented to be an important component of the total amount of wood transported during flood events in mountainous catchments. Therefore, research interest on recruitment, transport and deposition of large woody debris has arisen during the last decades. Although the main contributing processes are generally acknowledged and several modeling approaches have been proposed, less is known about the precise mechanisms behind recruitment and mobilization in mountainous catchments. Additionally, the role of vegetation in influencing the magnitude and the frequency of these mechanisms is often neglected or not considered in detail. Root reinforcement is particularly recognized to play an important role on bank erosion, bank failure and shallow landslides, but remains particularly difficult to quantify and implement in numerical models. This work presents a new modeling framework for simulating the effect of the spatio-temporal distribution of root reinforcement on bank erosion and slope stability in small mountainous catchments. The main objective of the work is to couple an existing shallow landslide model (SlideforMAP) with a bank erosion module to improve the prediction of large woody debris recruitment at mountainous catchment scales. Therefore the spatial structure of forest and its effect on root reinforcement, as obtained by remote sensing data, will be explicitly accounted for. Based on a first case study, we present results that help to quantify the effect of vegetation on the recruitment of „fresh" large woody debris and allow to detect potential contributing areas in small mountainous catchments. Further, suggestions on where forest management could improve overall slope and bank stability will be made

  3. Rapid antidepressants stimulate the decoupling of GABA(B) receptors from GIRK/Kir3 channels through increased protein stability of 14-3-3η.

    PubMed

    Workman, E R; Haddick, P C G; Bush, K; Dilly, G A; Niere, F; Zemelman, B V; Raab-Graham, K F

    2015-03-01

    A single injection of N-methyl-D-aspartate receptor (NMDAR) antagonists produces a rapid antidepressant response. Lasting changes in the synapse structure and composition underlie the effectiveness of these drugs. We recently discovered that rapid antidepressants cause a shift in the γ-aminobutyric acid receptor (GABABR) signaling pathway, such that GABABR activation shifts from opening inwardly rectifiying potassium channels (Kir/GIRK) to increasing resting dendritic calcium signal and mammalian Target of Rapamycin activity. However, little is known about the molecular and biochemical mechanisms that initiate this shift. Herein, we show that GABABR signaling to Kir3 (GIRK) channels decreases with NMDAR blockade. Blocking NMDAR signaling stabilizes the adaptor protein 14-3-3η, which decouples GABABR signaling from Kir3 and is required for the rapid antidepressant efficacy. Consistent with these results, we find that key proteins involved in GABABR signaling bidirectionally change in a depression model and with rapid antidepressants. In socially defeated rodents, a model for depression, GABABR and 14-3-3η levels decrease in the hippocampus. The NMDAR antagonists AP5 and Ro-25-6981, acting as rapid antidepressants, increase GABABR and 14-3-3η expression and decrease Kir3.2. Taken together, these data suggest that the shift in GABABR function requires a loss of GABABR-Kir3 channel activity mediated by 14-3-3η. Our findings support a central role for 14-3-3η in the efficacy of rapid antidepressants and define a critical molecular mechanism for activity-dependent alterations in GABABR signaling.

  4. Conformation-dependent stability of junctophilin 1 (JP1) and ryanodine receptor type 1 (RyR1) channel complex is mediated by their hyper-reactive thiols.

    PubMed

    Phimister, Andrew J; Lango, Jozsef; Lee, Eun Hui; Ernst-Russell, Michael A; Takeshima, Hiroshi; Ma, Jianjie; Allen, Paul D; Pessah, Isaac N

    2007-03-23

    Junctophilin 1 (JP1), a 72-kDa protein localized at the skeletal muscle triad, is essential for stabilizing the close apposition of T-tubule and sarcoplasmic reticulum membranes to form junctions. In this study we report that rapid and selective labeling of hyper-reactive thiols found in both JP1 and ryanodine receptor type 1 (RyR1) with 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin, a fluorescent thiol-reactive probe, proceeded 12-fold faster under conditions that minimize RyR1 gating (e.g. 10 mM Mg2+) compared with conditions that promote high channel activity (e.g. 100 microM Ca2+, 10 mM caffeine, 5 mM ATP). The reactivity of these thiol groups was very sensitive to oxidation by naphthoquinone, H2O2, NO, or O2, all known modulators of the RyR1 channel complex. Using preparative SDS-PAGE, in-gel tryptic digestion, high pressure liquid chromatography, and mass spectrometry-based peptide sequencing, we identified 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin-thioether adducts on three cysteine residues of JP1 (101, 402, and 627); the remaining five cysteines of JP1 were unlabeled. Co-immunoprecipitation experiments demonstrated a physical interaction between JP1 and RyR1 that, like thiol reactivity, was sensitive to RyR1 conformation and chemical status of the hyper-reactive cysteines of JP1 and RyR1. These findings support a model in which JP1 interacts with the RyR1 channel complex in a conformationally sensitive manner and may contribute integral redox-sensing properties through reactive sulfhydryl chemistry.

  5. Transcriptional activation of the anchoring protein SAP97 by heat shock factor (HSF)-1 stabilizes Kv1.5 channels in HL-1 cells

    PubMed Central

    Ting, YK; Morikawa, K; Kurata, Y; Li, P; Bahrudin, U; Mizuta, E; Kato, M; Miake, J; Yamamoto, Y; Yoshida, A; Murata, M; Inoue, T; Nakai, A; Shiota, G; Higaki, K; Nanba, E; Ninomiya, H; Shirayoshi, Y; Hisatome, I

    2011-01-01

    BACKGROUND AND PURPOSE The expression of voltage-dependent K+ channels (Kv) 1.5 is regulated by members of the heat shock protein (Hsp) family. We examined whether the heat shock transcription factor 1 (HSF-1) and its inducer geranylgeranylacetone (GGA) could affect the expression of Kv1.5 channels and its anchoring protein, synapse associated protein 97 (SAP97). EXPERIMENTAL APPROACH Transfected mouse atrial cardiomyocytes (HL-1 cells) and COS7 cells were subjected to luciferase reporter gene assay and whole-cell patch clamp. Protein and mRNA extracts were subjected to Western blot and quantitative real-time polymerase chain reaction. KEY RESULTS Heat shock of HL-1 cells induced expression of Hsp70, HSF-1, SAP97 and Kv1.5 proteins. These effects were reproduced by wild-type HSF-1. Both heat shock and expression of HSF-1, but not the R71G mutant, increased the SAP97 mRNA level. Small interfering RNA (siRNA) against SAP97 abolished HSF-1-induced increase of Kv1.5 and SAP97 proteins. A luciferase reporter gene assay revealed that the SAP97 promoter region (from −919 to −740) that contains heat shock elements (HSEs) was required for this induction. Suppression of SIRT1 function either by nicotinamide or siRNA decreased the level of SAP97 mRNA. SIRT1 activation by resveratrol had opposing effects. A treatment of the cells with GGA increased the level of SAP97 mRNA, Kv1.5 proteins and IKur current, which could be modified with either resveratrol or nicotinamide. CONCLUSIONS AND IMPLICATIONS HSF-1 induced transcription of SAP97 through SIRT1-dependent interaction with HSEs; the increase in SAP97 resulted in stabilization of Kv1.5 channels. These effects were mimicked by GGA. PMID:21232033

  6. On the transition between distributed and isolated surface roughness and its effect on the stability of channel flow

    NASA Astrophysics Data System (ADS)

    Floryan, J. M.; Asai, M.

    2011-10-01

    The question of whether a system of roughness elements has to be viewed either as a distributed roughness or a set of individual, hydrodynamically independent roughness elements has been considered. The answer has been given in the context of definition of hydraulic smoothness proposed by Floryan [Eur. J. Mech. B/Fluids 26, 305 (2007)] where a roughness system that cannot destabilize the flow is viewed as hydraulically inactive. Linear stability characteristics have been traced from the distributed to the isolated roughness limits. It has been shown that an increase of distance between roughness elements very quickly stabilizes disturbances in the form of streamwise vortices; however, roughness elements placed quite far apart are able to affect evolution of disturbances in the form of traveling waves. Transition from the distributed to the isolated roughness limit is achieved much faster in the case of roughness elements in the form of "trenches" forming depressions below the reference surface than in the case of roughness elements in the form of "ridges" protruding above the reference surface.

  7. Changes in vegetation and biological soil crust communities on sand dunes stabilizing after a century of grazing on San Miguel Island, Channel Island National Park, California

    USGS Publications Warehouse

    Zellman, Kristine L.

    2014-01-01

    San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or

  8. Stabilization of the skeletal muscle ryanodine receptor ion channel-FKBP12 complex by the 1,4-benzothiazepine derivative S107.

    PubMed

    Mei, Yingwu; Xu, Le; Kramer, Henning F; Tomberlin, Ginger H; Townsend, Claire; Meissner, Gerhard

    2013-01-01

    Activation of the skeletal muscle ryanodine receptor (RyR1) complex results in the rapid release of Ca(2+) from the sarcoplasmic reticulum and muscle contraction. Dissociation of the small FK506 binding protein 12 subunit (FKBP12) increases RyR1 activity and impairs muscle function. The 1,4-benzothiazepine derivative JTV519, and the more specific derivative S107 (2,3,4,5,-tetrahydro-7-methoxy-4-methyl-1,4-benzothiazepine), are thought to improve skeletal muscle function by stabilizing the RyR1-FKBP12 complex. Here, we report a high degree of nonspecific and specific low affinity [(3)H]S107 binding to SR vesicles. SR vesicles enriched in RyR1 bound ∼48 [(3)H]S107 per RyR1 tetramer with EC(50) ∼52 µM and Hillslope ∼2. The effects of S107 and FKBP12 on RyR1 were examined under conditions that altered the redox state of RyR1. S107 increased FKBP12 binding to RyR1 in SR vesicles in the presence of reduced glutathione and the NO-donor NOC12, with no effect in the presence of oxidized glutathione. Addition of 0.15 µM FKBP12 to SR vesicles prevented FKBP12 dissociation; however, in the presence of oxidized glutathione and NOC12, FKBP12 dissociation was observed in skeletal muscle homogenates that contained 0.43 µM myoplasmic FKBP12 and was attenuated by S107. In single channel measurements with FKBP12-depleted RyR1s, in the absence and presence of NOC12, S107 augmented the FKBP12-mediated decrease in channel activity. The data suggest that S107 can reverse the harmful effects of redox active species on SR Ca(2+) release in skeletal muscle by binding to RyR1 low affinity sites.

  9. Characterization of Jupiter's Deep Circulation and Static Stability through Wide Channel Numerical Simulations of the Dynamics and Interactions of Southern Midlatitudes Vortices

    NASA Astrophysics Data System (ADS)

    Morales-Juberias, Raul; Dowling, T. E.

    2012-10-01

    Previous studies have shown that the observed features and dynamics of Jovian vortices are sensitive to the underlying environmental structure of Jupiter’s atmosphere, in particular to the vertical wind shear and the static stability, and that forward modeling techniques can be successfully used to eliminate a large range of possibilities in a self-consistent manner and hence constrain the atmospheric structure below the cloud regions (Youseff and Marcus 2003, Morales-Juberias et al. 2005). However, these studies have generally been done on a narrow latitude-band basis (˜15°). Here we present wide channel simulations (˜40°) of two major meteorological events observed in the southern atmosphere of Jupiter involving the interaction of the Great Red Spot (GRS) with other nearby vortices. Namely, the spots associated with the recirculation of the South Tropical Disturbance of 1979 (Smith et al. 1979) and the White Ovals (WOS) in 2000 when ovals BE and FA merged to form BA (Sanchez-Lavega et al. 2001). By studying these two events using wide channel simulations, not unlike the strategy used in terrestrial synoptic meteorology, we show that we can gain new insights into the patterns governing Jupiter's global circulations, drawing a coherent picture of the vertical structure of the atmosphere for the whole southern mid-latitudinal regions of Jupiter over time. In particular, we find that the model output best captures the dynamics of the individual vortices and the morphology of their interactions when the deformation length in this region is like that derived by Read et al. 2006 and the deep winds vary following a dependence like that derived by Dowling 1995 in which the westward jets remain constant with depth but the eastward jets increase with depth. Computational resources were provided by the New Mexico Computing Applications Center and NMT. This work was supported by PATM grants NNX08AE91G and NNX08AE64G.

  10. Preliminary assessment of channel stability and bed-material transport in the Tillamook Bay tributaries and Nehalem River basin, northwestern Oregon

    USGS Publications Warehouse

    Jones, Krista L.; Keith, Mackenzie K.; O'Connor, Jim E.; Mangano, Joseph F.; Wallick, J. Rose

    2012-01-01

    subject to incision and aggradation as well as lateral shifts in thalweg position and bank deposition and erosion. * In fluvial reaches, unit bar area declined a net 5.3-83.6 percent from 1939 to 2009. The documented reduction in bar area may be attributable to several factors, including vegetation establishment and stabilization of formerly active bar surfaces, lateral channel changes and resulting alterations in sediment deposition and erosion patterns, and streamflow and/or tide differences between photographs. Other factors that may be associated with the observed reduction in bar area but not assessed in this reconnaissance level study include changes in the sediment and hydrology regimes of these rivers over the analysis period. * In tidal reaches, unit bar area increased on the Tillamook and Nehalem Rivers (98.0 and 14.7 percent, respectively), but declined a net 24.2 to 83.1 percent in the other four tidal reaches. Net increases in bar area in the Tidal Tillamook and Nehalem Reaches were possibly attributable to tidal differences between the photographs as well as sediment deposition behind log booms and pile structures on the Tillamook River between 1939 and 1967. * The armoring ratio (ratio of the median grain sizes of a bar's surface and subsurface layers) was 1.6 at Lower Waldron Bar on the Miami River, tentatively indicating a relative balance between transport capacity and sediment supply at this location. Armoring ratios, however, ranged from 2.4 to 5.5 at sites on the Trask, Wilson, Kilchis, and Nehalem Rivers; these coarse armor layers probably reflect limited bed-material supply at these sites. * On the basis of mapping results, measured armoring ratios, and channel cross section surveys, preliminary conclusions are that the fluvial reaches on the Tillamook, Trask, Kilchis, and Nehalem Rivers are currently sediment supply-limited in terms of bed material - that is, the transport capacity of the channel generally exceeds the supply of bed material. The

  11. Medium timescale stability of tidal mudflats in Bridgwater Bay, Bristol Channel, UK: Influence of tides, waves and climate

    NASA Astrophysics Data System (ADS)

    Kirby, Jason R.; Kirby, Robert

    2008-11-01

    This paper presents the results of an 11-year study into mudflat elevation changes within the intertidal zone at Stert Flats in Bridgwater Bay, Somerset. This site is located in the outer Severn Estuary/inner Bristol Channel which is a macro-hypertidal regime dominated by physical processes, characterized by strong tidal currents, high turbidity and a significant degree of exposure to wind generated waves. Two transects of stakes were installed perpendicular to the coast, extending seawards 300 m from the edge of the saltmarsh onto the mudflats, against which variations in accretion or erosion could be measured. The mudflats themselves consisted of an underlying consolidated clay of Holocene age and a surface veneer of fluid mud and/or mobile sand patches which varied both spatially and temporally. Mudflat development was recorded over both short-term (monthly/seasonal) and medium-term (inter-annual) timescales. The results display a significant degree of scatter over all timescales. Such variability in response may be expected in such a dynamic system where noise can be attributed to a combination of factors such as the mobility of surface fluid mud and sand patches and the migration of the underlying ridge-runnel drainage network. Despite this, the expected short-term variations related to neap-spring tidal conditions and seasonal influences were observed at a number of locations on the transects although these were weakly expressed. The over-riding feature of the profiles is a consistent long-term trend of erosion which appears to be masking shorter term trends within the dataset. Viewed over the 11-year period, the changes in mudflat elevation closely match the pattern of the index of the North Atlantic Oscillation (NAO) during the 1990s, suggesting a strong climatic control over mudflat development on a medium-term/decadal scale. Most profiles display a strong erosional trend during the early 1990s when the NAO index was positive. The erosional trend peaked in

  12. Microstructure stability of ultra-fine grained magnesium alloy AZ31 processed by extrusion and equal-channel angular pressing (EX–ECAP)

    SciTech Connect

    Stráská, Jitka; Janeček, Miloš; Čížek, Jakub; Stráský, Josef; Hadzima, Branislav

    2014-08-15

    Thermal stability of the ultra-fine grained (UFG) microstructure of magnesium AZ31 alloy was investigated. UFG microstructure was achieved by a combined two-step severe plastic deformation process: the extrusion (EX) and subsequent equal-channel angular pressing (ECAP). This combined process leads to refined microstructure and enhanced microhardness. Specimens with UFG microstructure were annealed isochronally at temperatures 150–500 °C for 1 h. The evolution of microstructure, mechanical properties and dislocation density was studied by electron backscatter diffraction (EBSD), microhardness measurements and positron annihilation spectroscopy (PAS). The coarsening of the fine-grained structure at higher temperatures was accompanied by a gradual decrease of the microhardness and decrease of dislocation density. Mechanism of grain growth was studied by general equation for grain growth and Arrhenius equation. Activation energies for grain growth were calculated to be 115, 33 and 164 kJ/mol in temperature ranges of 170–210 °C, 210–400 °C and 400–500 °C (443–483 K, 483–673 K and 673–773 K), respectively. - Highlights: • Microhardness of UFG AZ31 alloy decreases with increasing annealing temperature. • This fact has two reasons: dislocation annihilations and/or grain growth. • The activation energies for grain growth were calculated for all temperature ranges.

  13. Arizona Canal Diversion Channel Selection of Roughness Coefficients for Designing the Concrete-Lined Channel.

    DTIC Science & Technology

    1985-09-01

    CHANNEL STABILIZATION Technical Report Title Date 1 Symposium on Channel Stabilization Problems Volume 1 Sep 1983 Volume 2 May 1964 Volume 3 Jun 1965...Volume 4 Feb 1966 2 Review of Research on Channel Stabilization of the Sep 1963 Mississippi River, 1931-1962 3 Effect of Water Temperature on... Effects on Stage-Discharge Relations Sep 1969 * in Large Alluvial Rivers 7 State of Knowledge of Channel Stabilization in Major Oct 1969 Alluvial

  14. REACH SPECIFIC CHANNEL STABILIZATION BASED ON COMPREHENSIVE EVALUATION OF VALLEY FILL HISTORY, ALLUVIAL ARCHITECTURE AND GROUNDWATER HYDROLOGY IN A MOUNTAIN STREAM IN THE CENTRAL GREAT BASIN, NEVADA

    EPA Science Inventory

    Kingston meadow, located in the Toiyabe Range, is one of many wet meadow complexes threatened by rapid channel incision in the mountain ranges of the central Great Basin. Channel incision can lower the baselevel for groundwater discharge and de-water meadow complexes resulting in...

  15. REACH SPECIFIC CHANNEL STABILIZATION BASED ON COMPREHENSIVE EVALUATION OF VALLEY FILL HISTORY, ALLUVIAL ARCHITECTURE AND GROUNDWATER HYDROLOGY IN A MOUNTAIN STREAM IN THE CENTRAL GREAT BASIN, NEVADA

    EPA Science Inventory

    Kingston meadow, located in the Toiyabe Range, is one of many wet meadow complexes threatened by rapid channel incision in the mountain ranges of the central Great Basin. Channel incision can lower the baselevel for groundwater discharge and de-water meadow complexes resulting in...

  16. Switchable topological phonon channels

    NASA Astrophysics Data System (ADS)

    Süsstrunk, Roman; Zimmermann, Philipp; Huber, Sebastian D.

    2017-01-01

    Guiding energy deliberately is one of the central elements in engineering and information processing. It is often achieved by designing specific transport channels in a suitable material. Topological metamaterials offer a way to construct stable and efficient channels of unprecedented versatility. However, due to their stability it can be tricky to terminate them or to temporarily shut them off without changing the material properties massively. While a lot of effort was put into realizing mechanical topological metamaterials, almost no works deal with manipulating their edge channels in sight of applications. Here, we take a step in this direction, by taking advantage of local symmetry breaking potentials to build a switchable topological phonon channel.

  17. The C-terminal coiled-coil of the bacterial voltage-gated sodium channel NaChBac is not essential for tetramer formation, but stabilizes subunit-to-subunit interactions.

    PubMed

    Mio, Kazuhiro; Mio, Muneyo; Arisaka, Fumio; Sato, Masahiko; Sato, Chikara

    2010-09-01

    The NaChBac is a prokaryotic homologue of the voltage-gated sodium channel found in the genome of the alkalophilic bacterium Bacillus halodurans C-125. Like a repeating cassette of mammalian sodium channel, the NaChBac possesses hydrophobic domains corresponding to six putative transmembrane segments and a pore loop, and exerts channel function by forming a tetramer although detailed mechanisms of subunit assembly remain unclear. We generated truncated mutants from NaChBac, and investigated their ability to form tetramers in relation to their channel functions. A mutant that deletes almost all of the C-terminal coiled-coil structure lost its voltage-dependent ion permeability, although it was properly translocated to the cell surface. The mutant protein was purified as a tetramer using a reduced concentration of detergent, but the association between the subunits was shown to be much weaker than the wild type. The chemical cross-linking, blue native PAGE, sedimentation velocity experiments, size exclusion chromatography, immunoprecipitation, and electron microscopy all supported its tetrameric assembly. We further purified the C-terminal cytoplasmic domain alone and confirmed its self-oligomerization. These data suggest that the C-terminal coiled-coil structure stabilizes subunit-to-subunit interactions of NaChBac, but is not critical for their tetramer formation. 2010 Elsevier Ltd. All rights reserved.

  18. Substitutions at the opening of the Rubisco central solvent channel affect holoenzyme stability and CO2/O 2 specificity but not activation by Rubisco activase.

    PubMed

    Esquivel, M Gloria; Genkov, Todor; Nogueira, Ana S; Salvucci, Michael E; Spreitzer, Robert J

    2013-12-01

    Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the initial step of carbon metabolism in photosynthesis. The holoenzyme comprises eight large subunits, arranged as a tetramer of dimers around a central solvent channel that defines a fourfold axis of symmetry, and eight small subunits, arranged as two tetramers at the poles of the axis. The phylogenetically divergent small-subunit loops between β-strands A and B form the entrance to the solvent channel. In the green alga Chlamydomonas reinhardtii, Ile-58 from each of the four small-subunit βA-βB loops defines the minimal diameter of the channel opening. To understand the role of the central solvent channel in Rubisco function, directed mutagenesis and transformation of Chlamydomonas were employed to replace Ile-58 with Ala, Lys, Glu, Trp, or three Trp residues (I58W3) to close the entrance to the channel. The I58E, I58K, and I58W substitutions caused only small decreases in photosynthetic growth at 25 and 35 °C, whereas I58W3 had a substantial effect at both temperatures. The mutant enzymes had decreased carboxylation rates, but the I58W3 enzyme had decreases in both carboxylation and CO2/O2 specificity. The I58E, I58W, and I58W3 enzymes were inactivated at lower temperatures than wild-type Rubisco, and were degraded at slower rates under oxidative stress. However, these mutant enzymes were activated by Rubisco activase at normal rates, indicating that the structural transition required for carboxylation is not affected by altering the solvent channel opening. Structural dynamics alone may not be responsible for these distant effects on the Rubisco active site.

  19. Athermalized channeled spectropolarimeter enhancement.

    SciTech Connect

    Jones, Julia Craven; Way, Brandyn Michael; Mercier, Jeffrey Alan; Hunt, Jeffery P.

    2013-09-01

    Channeled spectropolarimetry can measure the complete polarization state of light as a function of wavelength. Typically, a channeled spectropolarimeter uses high order retarders made of uniaxial crystal to amplitude modulate the measured spectrum with the spectrally-dependent Stokes polarization information. A primary limitation of conventional channeled spectropolarimeters is related to the thermal variability of the retarders. Thermal variation often forces frequent system recalibration, particularly for field deployed systems. However, implementing thermally stable retarders, made of biaxial crystal, results in an athermal channeled spectropolarimeter that relieves the need for frequent recalibration. This report presents experimental results for an anthermalized channeled spectropolarimeter prototype produced using potassium titanyl phosphate. The results of this prototype are compared to the current thermal stabilization state of the art. Finally, the application of the technique to the thermal infrared is studied, and the athermalization concept is applied to an infrared imaging spectropolarimeter design.

  20. Analysis of trafficking, stability and function of human connexin 26 gap junction channels with deafness-causing mutations in the fourth transmembrane helix.

    PubMed

    Ambrosi, Cinzia; Walker, Amy E; Depriest, Adam D; Cone, Angela C; Lu, Connie; Badger, John; Skerrett, I Martha; Sosinsky, Gina E

    2013-01-01

    Human Connexin26 gene mutations cause hearing loss. These hereditary mutations are the leading cause of childhood deafness worldwide. Mutations in gap junction proteins (connexins) can impair intercellular communication by eliminating protein synthesis, mis-trafficking, or inducing channels that fail to dock or have aberrant function. We previously identified a new class of mutants that form non-functional gap junction channels and hemichannels (connexons) by disrupting packing and inter-helix interactions. Here we analyzed fourteen point mutations in the fourth transmembrane helix of connexin26 (Cx26) that cause non-syndromic hearing loss. Eight mutations caused mis-trafficking (K188R, F191L, V198M, S199F, G200R, I203K, L205P, T208P). Of the remaining six that formed gap junctions in mammalian cells, M195T and A197S formed stable hemichannels after isolation with a baculovirus/Sf9 protein purification system, while C202F, I203T, L205V and N206S formed hemichannels with varying degrees of instability. The function of all six gap junction-forming mutants was further assessed through measurement of dye coupling in mammalian cells and junctional conductance in paired Xenopus oocytes. Dye coupling between cell pairs was reduced by varying degrees for all six mutants. In homotypic oocyte pairings, only A197S induced measurable conductance. In heterotypic pairings with wild-type Cx26, five of the six mutants formed functional gap junction channels, albeit with reduced efficiency. None of the mutants displayed significant alterations in sensitivity to transjunctional voltage or induced conductive hemichannels in single oocytes. Intra-hemichannel interactions between mutant and wild-type proteins were assessed in rescue experiments using baculovirus expression in Sf9 insect cells. Of the four unstable mutations (C202F, I203T, L205V, N206S) only C202F and N206S formed stable hemichannels when co-expressed with wild-type Cx26. Stable M195T hemichannels displayed an increased

  1. Analysis of Trafficking, Stability and Function of Human Connexin 26 Gap Junction Channels with Deafness-Causing Mutations in the Fourth Transmembrane Helix

    PubMed Central

    Ambrosi, Cinzia; Walker, Amy E.; DePriest, Adam D.; Cone, Angela C.; Lu, Connie; Badger, John; Skerrett, I. Martha; Sosinsky, Gina E.

    2013-01-01

    Human Connexin26 gene mutations cause hearing loss. These hereditary mutations are the leading cause of childhood deafness worldwide. Mutations in gap junction proteins (connexins) can impair intercellular communication by eliminating protein synthesis, mis-trafficking, or inducing channels that fail to dock or have aberrant function. We previously identified a new class of mutants that form non-functional gap junction channels and hemichannels (connexons) by disrupting packing and inter-helix interactions. Here we analyzed fourteen point mutations in the fourth transmembrane helix of connexin26 (Cx26) that cause non-syndromic hearing loss. Eight mutations caused mis-trafficking (K188R, F191L, V198M, S199F, G200R, I203K, L205P, T208P). Of the remaining six that formed gap junctions in mammalian cells, M195T and A197S formed stable hemichannels after isolation with a baculovirus/Sf9 protein purification system, while C202F, I203T, L205V and N206S formed hemichannels with varying degrees of instability. The function of all six gap junction-forming mutants was further assessed through measurement of dye coupling in mammalian cells and junctional conductance in paired Xenopus oocytes. Dye coupling between cell pairs was reduced by varying degrees for all six mutants. In homotypic oocyte pairings, only A197S induced measurable conductance. In heterotypic pairings with wild-type Cx26, five of the six mutants formed functional gap junction channels, albeit with reduced efficiency. None of the mutants displayed significant alterations in sensitivity to transjunctional voltage or induced conductive hemichannels in single oocytes. Intra-hemichannel interactions between mutant and wild-type proteins were assessed in rescue experiments using baculovirus expression in Sf9 insect cells. Of the four unstable mutations (C202F, I203T, L205V, N206S) only C202F and N206S formed stable hemichannels when co-expressed with wild-type Cx26. Stable M195T hemichannels displayed an increased

  2. Loading characteristics and chemical stability of headgroup-functionalized poly(ethylene glycol)-lipid ligand tethers on polypropylene capillary-channeled polymer fibers.

    PubMed

    Schadock-Hewitt, Abby J; Marcus, R Kenneth

    2014-12-01

    Polypropylene capillary-channeled polymer fibers have been modified by adsorption of headgroup-functionalized poly(ethylene glycol)-lipids to generate a species-specific stationary phase. In order to study ligand binding characteristics, a fluorescein-labeled poly(ethylene glycol)-lipid was used as a model system. Breakthrough curves and frontal analysis were employed to characterize the surface loading characteristics across a range of lipid concentrations and mobile phase flow rates. Efficient mass transfer and fluid transport yield a linear adsorption isotherm up to the maximum loading concentration of 3 mg/mL, at a linear velocity of 57.1 mm/s. Under these conditions, the dynamic binding capacity was found to be 1.52 mg/g of fiber support. Variation of the linear velocity from 8.6 to 57.1 mm/s showed only small changes in breakthrough volume. The maximum capacity of 1.8 mg/g is found under conditions of a load velocity of 34.2 mm/s and a concentration of 3 mg/mL lipid. Exposure of the lipid modified fibers to several challenge solvents reveals a chemically robust system, with only 50% acetonitrile and hexanes able to disrupt the lipid adsorption. The straightforward capillary-channeled polymer fiber surface modification with headgroup-functionalized lipids provides both a diverse yet practically robust ligand tethering system. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Lava Channels

    NASA Image and Video Library

    2013-12-03

    The channels and linear depression in this image captured by NASA 2001 Mars Odyssey spacecraft are located on the western margin of the Elysium Volcanic complex. The channels were created by lava flow.

  4. Biphasic DC measurement approach for enhanced measurement stability and multi-channel sampling of self-sensing multi-functional structural materials doped with carbon-based additives

    NASA Astrophysics Data System (ADS)

    Downey, Austin; D'Alessandro, Antonella; Ubertini, Filippo; Laflamme, Simon; Geiger, Randall

    2017-06-01

    Investigation of multi-functional carbon-based self-sensing structural materials for structural health monitoring applications is a topic of growing interest. These materials are self-sensing in the sense that they can provide measurable electrical outputs corresponding to physical changes such as strain or induced damage. Nevertheless, the development of an appropriate measurement technique for such materials is yet to be achieved, as many results in the literature suggest that these materials exhibit a drift in their output when measured with direct current (DC) methods. In most of the cases, the electrical output is a resistance and the reported drift is an increase in resistance from the time the measurement starts due to material polarization. Alternating current methods seem more appropriate at eliminating the time drift. However, published results show they are not immune to drift. Moreover, the use of multiple impedance measurement devices (LCR meters) does not allow for the simultaneous multi-channel sampling of multi-sectioned self-sensing materials due to signal crosstalk. The capability to simultaneously monitor multiple sections of self-sensing structural materials is needed to deploy these multi-functional materials for structural health monitoring. Here, a biphasic DC measurement approach with a periodic measure/discharge cycle in the form of a square wave sensing current is used to provide consistent, stable resistance measurements for self-sensing structural materials. DC measurements are made during the measurement region of the square wave while material depolarization is obtained during the discharge region of the periodic signal. The proposed technique is experimentally shown to remove the signal drift in a carbon-based self-sensing cementitious material while providing simultaneous multi-channel measurements of a multi-sectioned self-sensing material. The application of the proposed electrical measurement technique appears promising for real

  5. TRP Channels

    PubMed Central

    Venkatachalam, Kartik; Montell, Craig

    2011-01-01

    The TRP (Transient Receptor Potential) superfamily of cation channels is remarkable in that it displays greater diversity in activation mechanisms and selectivities than any other group of ion channels. The domain organizations of some TRP proteins are also unusual, as they consist of linked channel and enzyme domains. A unifying theme in this group is that TRP proteins play critical roles in sensory physiology, which include contributions to vision, taste, olfaction, hearing, touch, and thermo- and osmosensation. In addition, TRP channels enable individual cells to sense changes in their local environment. Many TRP channels are activated by a variety of different stimuli and function as signal integrators. The TRP superfamily is divided into seven subfamilies: the five group 1 TRPs (TRPC, TRPV, TRPM, TRPN, and TRPA) and two group 2 subfamilies (TRPP and TRPML). TRP channels are important for human health as mutations in at least four TRP channels underlie disease. PMID:17579562

  6. Inspired and stabilized by nature: ribosomal synthesis of the human voltage gated ion channel (VDAC) into 2D-protein-tethered lipid interfaces.

    PubMed

    Damiati, Samar; Zayni, Sonja; Schrems, Angelika; Kiene, Elisabeth; Sleytr, Uwe B; Chopineau, Joël; Schuster, Bernhard; Sinner, Eva-Kathrin

    2015-10-15

    We present an elegant synthesis and reconstitution approach for functional studies of voltage responsive membrane proteins. For such studies, we propose a planar architecture of an S-layer-supported lipid membrane as a suitable matrix for presenting unmodified membrane protein species, and here we focus on the voltage-dependent anion channel (VDAC) from human mitochondria. The presented cell-free strategy, in which VDAC proteins are synthesized in bacterial cell lysate, into a membrane structure, offers a great advantage in the study of such subtle membrane proteins over the conventional, cell-based synthesis approach in terms of reproducibility. The material-assay combination is superior over cell-culture related synthesis and purification approaches as here we bypass by a one-step synthesis procedure the complex cell culture, and expression and purification endeavours, and, moreover, the protein of interest never has to be detergent solubilized and had been synthesized de novo. We provide here a detailed description from the all over procedure and our first results, describing in detail the cell-free synthesis and robustness of such a material-assay combination: functional VDAC protein species embedded in a planar membrane architecture and ready for electrochemical characterization.

  7. TRP Channels

    NASA Astrophysics Data System (ADS)

    Voets, Thomas; Owsianik, Grzegorz; Nilius, Bernd

    The TRP superfamily represents a highly diverse group of cation-permeable ion channels related to the product of the Drosophila trp (transient receptor potential) gene. The cloning and characterization of members of this cation channel family has experienced a remarkable growth during the last decade, uncovering a wealth of information concerning the role of TRP channels in a variety of cell types, tissues, and species. Initially, TRP channels were mainly considered as phospholipase C (PLC)-dependent and/or store-operated Ca2+-permeable cation channels. More recent research has highlighted the sensitivity of TRP channels to a broad array of chemical and physical stimuli, allowing them to function as dedicated biological sensors involved in processes ranging from vision to taste, tactile sensation, and hearing. Moreover, the tailored selectivity of certain TRP channels enables them to play key roles in the cellular uptake and/or transepithelial transport of Ca2+, Mg2+, and trace metal ions. In this chapter we give a brief overview of the TRP channel superfamily followed by a survey of current knowledge concerning their structure and activation mechanisms.

  8. Rippley Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    18 September 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a narrow channel on the upper east flank of the martian volcano, Hadriaca Patera. Because it is located on a volcano, most likely this channel was formed by lava, perhaps as a lava tube at which the thin roof later collapsed. Large ripples of windblown sediment now occur on the channel floor; their crests are generally perpendicular to the channel walls, suggesting that winds blow up and down through this channel.

    Location near: 30.5oS, 266.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  9. Rippley Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    18 September 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a narrow channel on the upper east flank of the martian volcano, Hadriaca Patera. Because it is located on a volcano, most likely this channel was formed by lava, perhaps as a lava tube at which the thin roof later collapsed. Large ripples of windblown sediment now occur on the channel floor; their crests are generally perpendicular to the channel walls, suggesting that winds blow up and down through this channel.

    Location near: 30.5oS, 266.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  10. AVHRR channel selection for land cover classification

    USGS Publications Warehouse

    Maxwell, S.K.; Hoffer, R.M.; Chapman, P.L.

    2002-01-01

    Mapping land cover of large regions often requires processing of satellite images collected from several time periods at many spectral wavelength channels. However, manipulating and processing large amounts of image data increases the complexity and time, and hence the cost, that it takes to produce a land cover map. Very few studies have evaluated the importance of individual Advanced Very High Resolution Radiometer (AVHRR) channels for discriminating cover types, especially the thermal channels (channels 3, 4 and 5). Studies rarely perform a multi-year analysis to determine the impact of inter-annual variability on the classification results. We evaluated 5 years of AVHRR data using combinations of the original AVHRR spectral channels (1-5) to determine which channels are most important for cover type discrimination, yet stabilize inter-annual variability. Particular attention was placed on the channels in the thermal portion of the spectrum. Fourteen cover types over the entire state of Colorado were evaluated using a supervised classification approach on all two-, three-, four- and five-channel combinations for seven AVHRR biweekly composite datasets covering the entire growing season for each of 5 years. Results show that all three of the major portions of the electromagnetic spectrum represented by the AVHRR sensor are required to discriminate cover types effectively and stabilize inter-annual variability. Of the two-channel combinations, channels 1 (red visible) and 2 (near-infrared) had, by far, the highest average overall accuracy (72.2%), yet the inter-annual classification accuracies were highly variable. Including a thermal channel (channel 4) significantly increased the average overall classification accuracy by 5.5% and stabilized interannual variability. Each of the thermal channels gave similar classification accuracies; however, because of the problems in consistently interpreting channel 3 data, either channel 4 or 5 was found to be a more

  11. Mechanosensitive Channels

    NASA Astrophysics Data System (ADS)

    Martinac, Boris

    Living cells are exposed to a variety of mechanical stimuli acting throughout the biosphere. The range of the stimuli extends from thermal molecular agitation to potentially destructive cell swelling caused by osmotic pressure gradients. Cellular membranes present a major target for these stimuli. To detect mechanical forces acting upon them cell membranes are equipped with mechanosensitive (MS) ion channels. Functioning as molecular mechanoelectrical transducers of mechanical forces into electrical and/or chemical intracellular signals these channels play a critical role in the physiology of mechanotransduction. Studies of prokaryotic MS channels and recent work on MS channels of eukaryotes have significantly increased our understanding of their gating mechanism, physiological functions, and evolutionary origins as well as their role in the pathology of disease.

  12. Channel catfish

    USDA-ARS?s Scientific Manuscript database

    This book chapter provides a comprehensive overview of channel catfish aquaculture. Sections include fish biology; commercial culture; culture facilities; production practices; water quality management; nutrition, feeding and feed formulation; infectious diseases; harvesting and processing; and the...

  13. Post Falls Dam stabilization

    SciTech Connect

    Gorny, R.H.; Gibson, J.Z.

    1995-12-31

    The stability of Washington Water Power`s (WWP) Middle Channel and South Channel Dams at Post Falls, Idaho, were evaluated as required by the Federal Energy Regulatory Commission (FERC) and did not meet guideline stability criteria under Probable Maximum Flood (PMF) loading. This paper describes the stability analysis, stabilization design, design parameters, construction of the anchors, and compares the design and as-built conditions. Value engineering was used to select the optimal stabilization measure. Constructibility, cost, and schedule were major considerations. The value engineering study evaluated 41 potential stabilization alternatives, selected post tensioning, and used scheduling criteria to optimize the design. Access considerations required the installation of five 47 strand, 7400 kN (1645{sup k}) anchors in the Middle Dam, and installation of six anchors with different capacities anchors in the South Channel Dam. The Washington Water Power - Black & Veatch team used value engineering, contractor prequalification, resident engineering services provided by the engineer, and strong construction support provided by the Owner to successfully complete the project on a very tight schedule.

  14. CHANNEL EVOLUTION IN MODIFIED ALLUVIAL STREAMS.

    USGS Publications Warehouse

    Simon, Andrew; Hupp, Cliff R.

    1987-01-01

    This study (a) assesses the channel changes and network trends of bed level response after modifications between 1959 and 1972 of alluvial channels in western Tennessee and (b) develops a conceptual model of bank slope development to qualitatively assess bank stability and potential channel widening. A six-step, semiquantitative model of channel evolution in disturbed channels was developed by quantifying bed level trends and recognizing qualitative stages of bank slope development. Development of the bank profile is defined in terms of three dynamic and observable surfaces: (a) vertical face (70 to 90 degrees), (b) upper bank (25 to 50 degrees), and (c) slough line (20 to 25 degrees).

  15. Matagorda Ship Channel, Texas: Jetty Stability Study

    DTIC Science & Technology

    2006-08-01

    U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, 4 p. plus two tables and three plates. Dolan, R., Fenster, M. S., and Holme , S...Publication 10-1, U.S. Department of Commerce, Coast and Geodetic Survey, Washington, DC, 749 p. Smith, J. M., Sherlock , A. R., and Resio, D. T. (2001

  16. English Channel

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The cloud covered earthscape of Northern Europe demonstrates the difficulty of photographing this elusive subject from space. The English Channel (51.0N, 1.5E) separating the British Islands from Europe is in the center of the scene. The white cliffs of Dover on the SE coast of the UK, the Thames River estuary and a partial view of the city of London can be seen on the north side of the Channel while the Normandy coast of France is to the south.

  17. English Channel

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The cloud covered earthscape of Northern Europe demonstrates the difficulty of photographing this elusive subject from space. The English Channel (51.0N, 1.5E) separating the British Islands from Europe is in the center of the scene. The white cliffs of Dover on the SE coast of the UK, the Thames River estuary and a partial view of the city of London can be seen on the north side of the Channel while the Normandy coast of France is to the south.

  18. Stabilization of Ca1-dFe2-xMnxO4 (0.44 lt x lt 2) with CaFe2O4-type Structure and Ca2plus Defects in 1D Channels

    SciTech Connect

    T Yang; M Croft; A Ignatov; I Nowik; R Cong; M Greenblatt

    2011-12-31

    Solid solutions of Ca{sub 1-{delta}}Fe{sub 2-x}Mn{sub x}O{sub 4} (0.45 {<=} x {<=} 2) were synthesized from CaCl{sub 2} as flux at 850 C in air. The entire series, even with x = 2, crystallizes in the CaFe{sub 2}O{sub 4}-type structure (Pnma), rather than in the CaMn{sub 2}O{sub 4}-type structure (Pbcm). Rietveld refinements confirmed mixed-valency Mn{sup 3+}/Mn{sup 4+} and a substantial level of Ca{sup 2+} deficiency ({delta} {approx} 0.25) at high x. With increasing x, the unit-cell dimensions a and b decrease, while that of c increases. Detailed structural analyses, together with Mn K-edge X-ray absorption and {sup 57}Fe Moessbauer spectroscopy studies, revealed that the stabilization of CaFe{sub 2}O{sub 4}-type structure, even at high values of x, is due to the existence of non-Jahn-Teller active Mn{sup 4+} (and Fe{sup 3+}), which is compensated by the formation of the Ca{sup 2+} deficiencies in the one-dimensional (1D) channels of Ca{sub 1-{delta}}Fe{sub 2-x}Mn{sub x}O{sub 4} during the flux synthesis. Antiferromagnetic (AFM) long-range ordering is achieved for all compounds at low temperature, because of strong AFM interactions between Mn{sup 3+}/Mn{sup 4+} and Fe{sup 3+}. In addition, a spin (or cluster) glass component was also observed, as expected, because of the extensive Mn/Fe structural and Mn{sup 3+}/Mn{sup 4+} charge disordering.

  19. Stabilization of diastolic calcium signal via calcium pump regulation of complex local calcium releases and transient decay in a computational model of cardiac pacemaker cell with individual release channels

    PubMed Central

    Maltsev, Alexander V.; Maltsev, Victor A.; Stern, Michael D.

    2017-01-01

    Intracellular Local Ca releases (LCRs) from sarcoplasmic reticulum (SR) regulate cardiac pacemaker cell function by activation of electrogenic Na/Ca exchanger (NCX) during diastole. Prior studies demonstrated the existence of powerful compensatory mechanisms of LCR regulation via a complex local cross-talk of Ca pump, release and NCX. One major obstacle to study these mechanisms is that LCR exhibit complex Ca release propagation patterns (including merges and separations) that have not been characterized. Here we developed new terminology, classification, and computer algorithms for automatic detection of numerically simulated LCRs and examined LCR regulation by SR Ca pumping rate (Pup) that provides a major contribution to fight-or-flight response. In our simulations the faster SR Ca pumping accelerates action potential-induced Ca transient decay and quickly clears Ca under the cell membrane in diastole, preventing premature releases. Then the SR generates an earlier, more synchronized, and stronger diastolic LCR signal activating an earlier and larger inward NCX current. LCRs at higher Pup exhibit larger amplitudes and faster propagation with more collisions to each other. The LCRs overlap with Ca transient decay, causing an elevation of the average diastolic [Ca] nadir to ~200 nM (at Pup = 24 mM/s). Background Ca (in locations lacking LCRs) quickly decays to resting Ca levels (<100 nM) at high Pup, but remained elevated during slower decay at low Pup. Release propagation is facilitated at higher Pup by a larger LCR amplitude, whereas at low Pup by higher background Ca. While at low Pup LCRs show smaller amplitudes, their larger durations and sizes combined with longer transient decay stabilize integrals of diastolic Ca and NCX current signals. Thus, the local interplay of SR Ca pump and release channels regulates LCRs and Ca transient decay to insure fail-safe pacemaker cell operation within a wide range of rates. PMID:28792496

  20. Stabilization of diastolic calcium signal via calcium pump regulation of complex local calcium releases and transient decay in a computational model of cardiac pacemaker cell with individual release channels.

    PubMed

    Maltsev, Alexander V; Maltsev, Victor A; Stern, Michael D

    2017-08-01

    Intracellular Local Ca releases (LCRs) from sarcoplasmic reticulum (SR) regulate cardiac pacemaker cell function by activation of electrogenic Na/Ca exchanger (NCX) during diastole. Prior studies demonstrated the existence of powerful compensatory mechanisms of LCR regulation via a complex local cross-talk of Ca pump, release and NCX. One major obstacle to study these mechanisms is that LCR exhibit complex Ca release propagation patterns (including merges and separations) that have not been characterized. Here we developed new terminology, classification, and computer algorithms for automatic detection of numerically simulated LCRs and examined LCR regulation by SR Ca pumping rate (Pup) that provides a major contribution to fight-or-flight response. In our simulations the faster SR Ca pumping accelerates action potential-induced Ca transient decay and quickly clears Ca under the cell membrane in diastole, preventing premature releases. Then the SR generates an earlier, more synchronized, and stronger diastolic LCR signal activating an earlier and larger inward NCX current. LCRs at higher Pup exhibit larger amplitudes and faster propagation with more collisions to each other. The LCRs overlap with Ca transient decay, causing an elevation of the average diastolic [Ca] nadir to ~200 nM (at Pup = 24 mM/s). Background Ca (in locations lacking LCRs) quickly decays to resting Ca levels (<100 nM) at high Pup, but remained elevated during slower decay at low Pup. Release propagation is facilitated at higher Pup by a larger LCR amplitude, whereas at low Pup by higher background Ca. While at low Pup LCRs show smaller amplitudes, their larger durations and sizes combined with longer transient decay stabilize integrals of diastolic Ca and NCX current signals. Thus, the local interplay of SR Ca pump and release channels regulates LCRs and Ca transient decay to insure fail-safe pacemaker cell operation within a wide range of rates.

  1. Intra-membrane molecular interactions of K+ channel proteins :

    SciTech Connect

    Moczydlowski, Edward G.

    2013-07-01

    Ion channel proteins regulate complex patterns of cellular electrical activity and ionic signaling. Certain K+ channels play an important role in immunological biodefense mechanisms of adaptive and innate immunity. Most ion channel proteins are oligomeric complexes with the conductive pore located at the central subunit interface. The long-term activity of many K+ channel proteins is dependent on the concentration of extracellular K+; however, the mechanism is unclear. Thus, this project focused on mechanisms underlying structural stability of tetrameric K+ channels. Using KcsA of Streptomyces lividans as a model K+ channel of known structure, the molecular basis of tetramer stability was investigated by: 1. Bioinformatic analysis of the tetramer interface. 2. Effect of two local anesthetics (lidocaine, tetracaine) on tetramer stability. 3. Molecular simulation of drug docking to the ion conduction pore. The results provide new insights regarding the structural stability of K+ channels and its possible role in cell physiology.

  2. Alluvial channel hydraulics

    NASA Astrophysics Data System (ADS)

    Ackers, Peter

    1988-07-01

    The development and utilisation of water resources for irrigation, hydropower and public supply can be severely affected by sediment. Where there is a mature and well vegetated landscape, sediment problems may be relatively minor; but where slopes are steep and vegetation sparse, the yield of sediment from the catchment gives high concentrations in the rivers. In utilising these resources, for whatever purpose, an understanding of the hydraulics of alluvial channels is vital. The regime of any conveyance channel in alluvium depends on the interrelationships of sediment transport, channel resistance and bank stability. The regime concept was originally based on empirical relations obtained from observations from canal systems in the Indian subcontinent, and for many years was surrounded by a certain degree of mystique and much scepticism from academics. In more recent years the unabashed empiricism of the original method has been replaced by process-based methods, which have also served as broad confirmation of the classic regime formulae, including their extension to natural channels and meandering channels. The empirical approach to the hydraulics of alluvial channels has thus been updated by physically based formulae for sediment transport and resistance, though there remains some uncertainty about the third function to complete the definition of slope and geometry. Latest thoughts in this respect are that the channel seeks a natural optimum state. Physical modelling using scaled down representations of rivers and estuaries has been used for almost a century, but it requires the correct simulation of the relevant processes. The coming of a better understanding of the physics of sediment transport and the complexity of alluvial channel roughness leads to the conclusion that only in very restricted circumstances can scale models simulate closely the full-size condition. However, the quantification of these processes has been instrumental in the development of

  3. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, Victor R.

    1988-01-01

    The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.

  4. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, Victor R.

    1988-01-01

    The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.

  5. Inverted Channels

    NASA Technical Reports Server (NTRS)

    2006-01-01

    23 June 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows sinuous ridges and other landforms exposed by erosion in the Aeolis region of Mars. The ridges in this scene indicate the locations of ancient channels in a fan of sediment deposited in this region. Over time, wind erosion has removed surrounding materials and left the channels, which had been filled by sediment, standing as ridges.

    Location near: 4.5oS, 205.2oW Image width: 2 km (1.2 mi) Illumination from: upper left Season: Southern Autumn

  6. Starburst Channels

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    Translucent carbon dioxide ice covers the polar regions of Mars seasonally. It is warmed and sublimates (evaporates) from below, and escaping gas carves a numerous channel morphologies.

    In this example (figure 1) the channels form a 'starburst' pattern, radiating out into feathery extensions. The center of the pattern is being buried with dust and new darker dust fans ring the outer edges. This may be an example of an expanding morphology, where new channels are formed as the older ones fill and are no longer efficiently channeling the subliming gas out.

    Observation Geometry Image PSP_003443_0980 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 21-Apr-2007. The complete image is centered at -81.8 degrees latitude, 76.2 degrees East longitude. The range to the target site was 247.1 km (154.4 miles). At this distance the image scale is 24.7 cm/pixel (with 1 x 1 binning) so objects 74 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 04:52 PM and the scene is illuminated from the west with a solar incidence angle of 71 degrees, thus the sun was about 19 degrees above the horizon. At a solar longitude of 223.4 degrees, the season on Mars is Northern Autumn.

  7. Starburst Channels

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    Translucent carbon dioxide ice covers the polar regions of Mars seasonally. It is warmed and sublimates (evaporates) from below, and escaping gas carves a numerous channel morphologies.

    In this example (figure 1) the channels form a 'starburst' pattern, radiating out into feathery extensions. The center of the pattern is being buried with dust and new darker dust fans ring the outer edges. This may be an example of an expanding morphology, where new channels are formed as the older ones fill and are no longer efficiently channeling the subliming gas out.

    Observation Geometry Image PSP_003443_0980 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 21-Apr-2007. The complete image is centered at -81.8 degrees latitude, 76.2 degrees East longitude. The range to the target site was 247.1 km (154.4 miles). At this distance the image scale is 24.7 cm/pixel (with 1 x 1 binning) so objects 74 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 04:52 PM and the scene is illuminated from the west with a solar incidence angle of 71 degrees, thus the sun was about 19 degrees above the horizon. At a solar longitude of 223.4 degrees, the season on Mars is Northern Autumn.

  8. Quartz Channel Fabrication for Electrokinetically Driven Separations

    SciTech Connect

    Arnold, D.W.; Ashby, C.I.H.; Bailey, C.G.; Kravitz, S.H., Warren, M.E.; Matzke, C.M.

    1998-12-01

    For well resolved electrokinetic separation, we L tilize crystalline quartz to micromachine a uniformly packe Q&iKLmnel. Packing features are posts 5 Vm on a side with:} pm spacing and etched 42 Vm deep. In addition to anisotropic wet etch characteristics for micromachining, quartz propmties are compatible with chemical soiutioits, ekctrokinetic high voltage operation, and stationary phase film depositions. To seal these channels, we employ a room temperature silicon-oxynhride deposition to forma membrane, that is subsequently coated for mechanical stability. Using this technique, particulate issues and global warp, that make large area wafer bon ding methods difficult, are avoided, and a room temperature process, in contrast to high temperature bonding techniques, accommodate preprocessing of metal films for electrical interconnect. After sealing channels, a number of macro-assembly steps are required to attach a micro-optical detection system and fluid interconnects. Keywords: microcharmel, integrated channel, micromachined channel, packed channel, electrokinetic channel, eleetrophoretic channel

  9. Information geometry of Gaussian channels

    SciTech Connect

    Monras, Alex; Illuminati, Fabrizio

    2010-06-15

    We define a local Riemannian metric tensor in the manifold of Gaussian channels and the distance that it induces. We adopt an information-geometric approach and define a metric derived from the Bures-Fisher metric for quantum states. The resulting metric inherits several desirable properties from the Bures-Fisher metric and is operationally motivated by distinguishability considerations: It serves as an upper bound to the attainable quantum Fisher information for the channel parameters using Gaussian states, under generic constraints on the physically available resources. Our approach naturally includes the use of entangled Gaussian probe states. We prove that the metric enjoys some desirable properties like stability and covariance. As a by-product, we also obtain some general results in Gaussian channel estimation that are the continuous-variable analogs of previously known results in finite dimensions. We prove that optimal probe states are always pure and bounded in the number of ancillary modes, even in the presence of constraints on the reduced state input in the channel. This has experimental and computational implications. It limits the complexity of optimal experimental setups for channel estimation and reduces the computational requirements for the evaluation of the metric: Indeed, we construct a converging algorithm for its computation. We provide explicit formulas for computing the multiparametric quantum Fisher information for dissipative channels probed with arbitrary Gaussian states and provide the optimal observables for the estimation of the channel parameters (e.g., bath couplings, squeezing, and temperature).

  10. Nonlinear channelizer.

    PubMed

    In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D; Leung, Daniel; Liu, Norman; Meadows, Brian K; Gordon, Frank; Bulsara, Adi R; Palacios, Antonio

    2012-12-01

    The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.

  11. Nonlinear channelizer

    NASA Astrophysics Data System (ADS)

    In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D.; Leung, Daniel; Liu, Norman; Meadows, Brian K.; Gordon, Frank; Bulsara, Adi R.; Palacios, Antonio

    2012-12-01

    The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.

  12. Opening the Shaker K+ channel with hanatoxin

    PubMed Central

    Milescu, Mirela; Lee, Hwa C.; Bae, Chan Hyung; Kim, Jae Il

    2013-01-01

    Voltage-activated ion channels open and close in response to changes in membrane voltage, a property that is fundamental to the roles of these channels in electrical signaling. Protein toxins from venomous organisms commonly target the S1–S4 voltage-sensing domains in these channels and modify their gating properties. Studies on the interaction of hanatoxin with the Kv2.1 channel show that this tarantula toxin interacts with the S1–S4 domain and inhibits opening by stabilizing a closed state. Here we investigated the interaction of hanatoxin with the Shaker Kv channel, a voltage-activated channel that has been extensively studied with biophysical approaches. In contrast to what is observed in the Kv2.1 channel, we find that hanatoxin shifts the conductance–voltage relation to negative voltages, making it easier to open the channel with membrane depolarization. Although these actions of the toxin are subtle in the wild-type channel, strengthening the toxin–channel interaction with mutations in the S3b helix of the S1-S4 domain enhances toxin affinity and causes large shifts in the conductance–voltage relationship. Using a range of previously characterized mutants of the Shaker Kv channel, we find that hanatoxin stabilizes an activated conformation of the voltage sensors, in addition to promoting opening through an effect on the final opening transition. Chimeras in which S3b–S4 paddle motifs are transferred between Kv2.1 and Shaker Kv channels, as well as experiments with the related tarantula toxin GxTx-1E, lead us to conclude that the actions of tarantula toxins are not simply a product of where they bind to the channel, but that fine structural details of the toxin–channel interface determine whether a toxin is an inhibitor or opener. PMID:23359283

  13. Enhanced fast-inactivated state stability of cardiac sodium channels by a novel voltage sensor SCN5A mutation, R1632C, as a cause of atypical Brugada syndrome.

    PubMed

    Nakajima, Tadashi; Kaneko, Yoshiaki; Saito, Akihiro; Ota, Masaki; Iijima, Takafumi; Kurabayashi, Masahiko

    2015-11-01

    Mutations in SCN5A, which encodes the cardiac voltage-gated sodium channels, can be associated with multiple electrophysiological phenotypes. A novel SCN5A R1632C mutation, located in the domain IV-segment 4 voltage sensor, was identified in a young male patient who had a syncopal episode during exercise and presented with atrial tachycardia, sinus node dysfunction, and Brugada syndrome. We sought to elucidate the functional consequences of the R1632C mutation. The wild-type (WT) or R1632C SCN5A mutation was coexpressed with β1 subunit in tsA201 cells, and whole-cell sodium currents (INa) were recorded using patch-clamp methods. INa density, measured at -20 mV from a holding potential of -120 mV, for R1632C was significantly lower than that for WT (R1632C: -433 ± 52 pA/pF, n = 14; WT: -672 ± 90 pA/pF, n = 15; P < .05); however, no significant changes were observed in the steady-state activation and fast inactivation rate. The steady-state inactivation curve for R1632C was remarkably shifted to hyperpolarizing potentials compared with that for WT (R1632C: V1/2 = -110.7 ± 0.8 mV, n = 16; WT: V1/2 = -85.9 ± 2.5 mV, n = 17; P < .01). The steady-state fast inactivation curve for R1632C was also shifted to the same degree. Recovery from fast inactivation after a 20-ms depolarizing pulse for R1632C was remarkably delayed compared with that for WT (R1632C: τ = 246.7 ± 14.3 ms, n = 8; WT: τ = 3.7 ± 0.3 ms, n = 8; P < .01). Repetitive depolarizing pulses at various cycle lengths greatly attenuated INa for R1632C than that for WT. R1632C showed a loss of function of INa by an enhanced fast-inactivated state stability because of a pronounced impairment of recovery from fast inactivation, which may explain the phenotypic manifestation observed in our patient. Copyright © 2015 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

  14. Dynamic Channel Allocation

    DTIC Science & Technology

    2003-09-01

    7 1 . Fixed Channel Allocation (FCA) ........................................................7 2. Dynamic Channel ...19 7. CSMA/CD-Based Multiple Network Lines .....................................20 8. Hybrid Channel Allocation in Wireless Networks...28 1 . Channel Allocation

  15. Sediment transport and channel morphology of small, forested streams.

    Treesearch

    Marwan A. Hassan; Michael Church; Thomas E. Lisle; Francesco Brardinoni; Lee Benda; Gordon E. Grant

    2005-01-01

    This paper reviews sediment transport and channel morphology in small, forested streams in the Pacific Northwest region of North America to assess current knowledge of channel stability and morphology relevant to riparian management practices around small streams. Small channels are defined as ones in which morphology and hydraulics may be significantly influenced by...

  16. Eukaryotic mechanosensitive channels.

    PubMed

    Arnadóttir, Jóhanna; Chalfie, Martin

    2010-01-01

    Mechanosensitive ion channels are gated directly by physical stimuli and transduce these stimuli into electrical signals. Several criteria must apply for a channel to be considered mechanically gated. Mechanosensitive channels from bacterial systems have met these criteria, but few eukaryotic channels have been confirmed by the same standards. Recent work has suggested or confirmed that diverse types of channels, including TRP channels, K(2P) channels, MscS-like proteins, and DEG/ENaC channels, are mechanically gated. Several studies point to the importance of the plasma membrane for channel gating, but intracellular and/or extracellular structures may also be required.

  17. CERAMIDE CHANNELS: INFLUENCE OF MOLECULAR STRUCTURE ON CHANNEL FORMATION IN MEMBRANES

    PubMed Central

    Perera, Meenu N.; Ganesan, Vidyaramanan; Siskind, Leah J.; Szulc, Zdzislaw M.; Bielawski, Jacek; Bielawska, Alicja; Bittman, Robert; Colombini, Marco

    2012-01-01

    The sphingolipid, ceramide, self-assembles in the mitochondrial outer membrane (MOM), forming large channels capable of translocating proteins. These channels are believed to be involved in protein release from mitochondria, a key decision-making step. Synthetic analogs of ceramide, bearing modifications in each of the major structural features of ceramide were used to probe the molecular basis for the stability of ceramide channels. Channel stability and mitochondrial permeabilization were disrupted by methylation of the C1-hydroxyl group whereas modifications of the C3 allylic hydroxyl group were well tolerated. A change in chirality at C2 that would influence the orientation of the C1-hydroxyl group resulted in a strong reduction of channel-forming ability. Similarly, methylation of the amide nitrogen is also detrimental to channel formation. Many changes in the degree, location and nature of the unsaturation of ceramide had little effect on mitochondrial permeabilization. Competition experiments between ceramide and analogs resulted in synergy with structures compatible with the ceramide channel model and antagonism with incompatible structures. The results are consistent with ceramide channels being highly organized structures, stabilized by specific inter-molecular interactions, similar to the interactions responsible for protein folding. PMID:22365970

  18. A physically-based channel-modeling framework integrating HEC-RAS sediment transport capabilities and the USDA-ARS bank-stability and toe-erosion model (BSTEM)

    USDA-ARS?s Scientific Manuscript database

    Classical, one-dimensional, mobile bed, sediment-transport models simulate vertical channel adjustment, raising or lowering cross-section node elevations to simulate erosion or deposition. This approach does not account for bank erosion processes including toe scour and mass failure. In many systems...

  19. TS - Dean interactions in curved channel flow

    NASA Technical Reports Server (NTRS)

    Singer, Bart A.; Zang, Thomas A.; Erlebacher, Gordon

    1990-01-01

    A weakly nonlinear theory is developed to study the interaction of TS waves and Dean vortices in curved channel flow. The prediction obtained from the theory agree well with results obtained from direct numerical simulations of curved channel flow, especially for low amplitude disturbances. At low Reynolds numbers the wave interaction is generally stabilizing to both disturbances, though as the Reynolds number increases, many linearly unstable TS waves are further destabilized by the presence of Dean vortices.

  20. Voltage-gated sodium channels

    PubMed Central

    Abdelsayed, Mena; Sokolov, Stanislav

    2013-01-01

    Epilepsy is a brain disorder characterized by seizures and convulsions. The basis of epilepsy is an increase in neuronal excitability that, in some cases, may be caused by functional defects in neuronal voltage gated sodium channels, Nav1.1 and Nav1.2. The effects of antiepileptic drugs (AEDs) as effective therapies for epilepsy have been characterized by extensive research. Most of the classic AEDs targeting Nav share a common mechanism of action by stabilizing the channel’s fast-inactivated state. In contrast, novel AEDs, such as lacosamide, stabilize the slow-inactivated state in neuronal Nav1.1 and Nav1.7 isoforms. This paper reviews the different mechanisms by which this stabilization occurs to determine new methods for treatment. PMID:23531742

  1. River channel adjustments in Southern Italy over the past 150 years and implications for channel recovery

    NASA Astrophysics Data System (ADS)

    Scorpio, Vittoria; Aucelli, Pietro P. C.; Giano, Salvatore I.; Pisano, Luca; Robustelli, Gaetano; Rosskopf, Carmen M.; Schiattarella, Marcello

    2015-12-01

    Multi-temporal GIS analysis of topographic maps and aerial photographs along with topographic and geomorphological surveys are used to assess evolutionary trends and key control factors of channel adjustments for five major rivers in southern Italy (the Trigno, Biferno, Volturno, Sinni and Crati rivers) to support assessment of channel recovery and river restoration. Three distinct phases of channel adjustment are identified over the past 150 years primarily driven by human disturbances. Firstly, slight channel widening dominated from the last decades of the nineteenth century to the 1950s. Secondly, from the 1950s to the end of the 1990s, altered sediment fluxes induced by in-channel mining and channel works brought about moderate to very intense incision (up to 6-7 m) accompanied by strong channel narrowing (up to 96%) and changes in channel configuration from multi-threaded to single-threaded patterns. Thirdly, the period from around 2000 to 2015 has been characterized by channel stabilization and local widening. Evolutionary trajectories of the rivers studied are quite similar to those reconstructed for other Italian rivers, particularly regarding the second phase of channel adjustments and ongoing transitions towards channel recovery in some reaches. Analyses of river dynamics, recovery potential and connectivity with sediment sources of the study reaches, framed in their catchment context, can be used as part of a wider interdisciplinary approach that views effective river restoration alongside sustainable and risk-reduced river management.

  2. The inherent instability of leveed seafloor channels

    NASA Astrophysics Data System (ADS)

    Dorrell, Robert M.; Burns, Alan D.; McCaffrey, William D.

    2015-05-01

    New analytical models demonstrate that under aggradational flow conditions, seafloor channel-levee systems are inherently unstable; both channel area and stability necessarily decrease at long timescales. In time such systems must avulse purely through internal (autogenic) forcing. Although autogenic instabilities likely arise over long enough time for additional allogenic forcing to be expected, channel-levee sensitivity to variations in flow character depends on the prior degree of system evolution. Recalibrated modern Amazon Fan avulsion timings are consistent with this model, challenging accepted interpretations of avulsion triggering.

  3. Channel Responses and Hydromodification in Southern California

    NASA Astrophysics Data System (ADS)

    Hawley, R. J.; Dust, D. W.; Bledsoe, B. P.

    2007-12-01

    Hydromodification (changes in watershed hydrologic characteristics, and the resulting hydraulics and channel forms due to urbanization) is ubiquitous in Southern California. In this region, the effects of hydromodification are driven and compounded by the arid/semiarid climate, high relief, erodible soils, high urbanization rates, and relatively low frequency of retention/detention. We conducted a preliminary survey of over 50 stream reaches along a gradient from least disturbed to fully urbanized. All stages of the Channel Evolution Model (CEM) of Schumm et al. (1984) were observed, from stable to degrading, widening, aggrading, and quasi-equilibrium channels. Several sites have CEM stages II through V in close proximity due to headcutting, hardpoints, and infrastructure. We also observed channels in undeveloped watersheds impacted by downstream urbanization via headcutting. A range of intervention measures was observed, with the frequent evolutionary endpoint as a concrete engineered flood control channel. We also observed multiple channel evolution sequences that deviate from the CEM for single-thread, incising channels. An alternative channel response, particularly on smaller urbanized streams is a stabilized, vegetation encroached low-flow channel with regular baseflow supplied by residential irrigation runoff. The limited cases of unimpacted streams that remain tend to be high gradient, high energy systems that are naturally proximate to the transition between braided and meandering form for a given sediment size.

  4. Impacts of salt marsh plants on tidal channel initiation and inheritance

    NASA Astrophysics Data System (ADS)

    Schwarz, C.; Ye, Q. H.; Wal, D.; Zhang, L. Q.; Bouma, T.; Ysebaert, T.; Herman, P. M. J.

    2014-02-01

    At the transition between mudflat and salt marsh, vegetation is traditionally regarded as a sustaining factor for previously incised mudflat channels, able to conserve the channel network via bank stabilization following plant colonization (i.e., vegetation-stabilized channel inheritance). This is in contrast to recent studies revealing vegetation as the main driver of tidal channel emergence through vegetation-induced channel erosion. We present a coupled hydrodynamic morphodynamic plant growth model to simulate plant expansion and channel formation by our model species (Spartina alterniflora) during a mudflat-salt marsh transition with various initial bathymetries (flat, shoal dense, shoal sparse, and deep dense channels). This simulated landscape development is then compared to remote sensing images of the Yangtze estuary, China, and the Scheldt estuary in Netherlands. Our results propose the existence of a threshold in preexisting mudflat channel depth, which favors either vegetation-stabilized channel inheritance or vegetation-induced channel erosion processes. The increase in depth of preexisting mudflat channels favors flow routing through them, consequently leaving less flow and momentum remaining for vegetation-induced channel erosion processes. This threshold channel depth will be influenced by field specific parameters such as hydrodynamics (tidal range and flow), sediment characteristics, and plant species. Hence, our study shows that the balance between vegetation-stabilized channel inheritance and vegetation-induced channel erosion depends on ecosystem properties.

  5. The Psychology of Channeling.

    ERIC Educational Resources Information Center

    Corey, Michael A.

    1988-01-01

    Theoretically analyzes phenomenon of channeling from perspective of C. G. Jung's analytic psychology. Hypothesizes that contact with otherworldly spiritual beings claimed by channelers is actually projected contact with contents of channeler's own unconscious mind. Suggests that channelers seek more constructive ways of contacting their…

  6. Channel nut tool

    DOEpatents

    Olson, Marvin

    2016-01-12

    A method, system, and apparatus for installing channel nuts includes a shank, a handle formed on a first end of a shank, and an end piece with a threaded shaft configured to receive a channel nut formed on the second end of the shaft. The tool can be used to insert or remove a channel nut in a channel framing system and then removed from the channel nut.

  7. Stability of Hartree-Fock solutions and potential-energy surfaces in a reaction involving inversion of the filled and vacant MO of reagent and product. Part 1. Two degenerate reaction channels for the isomerization of CO/sub 2/

    SciTech Connect

    Glukhovtsev, M.N.; Simkin, B.Ya.; Minkin, V.I.

    1987-03-01

    There may be a region in the potential-energy surface (PES) a reaction forbidden by symmetry in the ground electronic state but occurring with inversion of the filled and vacant MO of the reagent and product in which the corresponding solutions obtained in the restricted Hartree-Fock approximation are singlet-unstable. There are then singlet-stable solutions with lower energies, but which correspond to configurations of lower symmetry. As a result, the PES may have reaction channels of reduced symmetry. An example is considered of the cyclization of a linear D/sub infinity h/ structure for CO/sub 2/ to the C/sub 2V/ structure forbidden by symmetry for the ground electronic state. MINDO/3 calculations show that a curve with two wells applies for the region in the PES of the ground singlet state for which the RHF solutions are singlet-unstable, where the section of the minimum-energy path along the distortion coordinate leads to a geometrical configuration of lower symmetry, i.e., there are two degenerate reaction channels in this region of the PES, which correspond to geometrical configurations of symmetry C/sub 1/.

  8. Microfluidic channel fabrication method

    DOEpatents

    Arnold, Don W.; Schoeniger, Joseph S.; Cardinale, Gregory F.

    2001-01-01

    A new channel structure for microfluidic systems and process for fabricating this structure. In contrast to the conventional practice of fabricating fluid channels as trenches or grooves in a substrate, fluid channels are fabricated as thin walled raised structures on a substrate. Microfluidic devices produced in accordance with the invention are a hybrid assembly generally consisting of three layers: 1) a substrate that can or cannot be an electrical insulator; 2) a middle layer, that is an electrically conducting material and preferably silicon, forms the channel walls whose height defines the channel height, joined to and extending from the substrate; and 3) a top layer, joined to the top of the channels, that forms a cover for the channels. The channels can be defined by photolithographic techniques and are produced by etching away the material around the channel walls.

  9. Thermodynamic stability considerations for isostructural dehydrates.

    PubMed

    Murphy, Brendan J; Casteel, Melissa J; Samas, Brian; Krzyzaniak, Joseph F

    2012-04-01

    Nonstoichiometric channel hydrates are a class of crystalline hydrates that can incorporate a range of water levels as a function of temperature and relative humidity (RH). When a nonstoichiometric channel hydrate can dehydrate to yield a physically stable isostructural crystalline lattice, it may become challenging to accurately evaluate the thermodynamic stability relationship associated with a polymorphic system using traditional methods. This work demonstrates application of a eutectic-melting method to determine the stability relationship between a nonstoichiometric channel dehydrate and an anhydrous form. A transition temperature (122°C) between the isostructural dehydrate of the nonstoichiometric channel hydrate and the anhydrous polymorph was identified, with the nonstoichiometric channel hydrate being the thermodynamically stable anhydrous form at room temperature (RT). Solid-state storage at a range of RH conditions demonstrated that the nonstoichiometric channel hydrate is also the stable form at RT above an RH of 94%. These results demonstrate that the nonstoichiometric channel hydrate is the stable form at low temperatures, independent of its hydration state. It has been demonstrated that the eutectic-melting method is applicable to the study of thermodynamic stability relationships between anhydrous forms and dehydrated channel hydrates.

  10. Evaporation from flowing channels ( mass-transfer formulas).

    USGS Publications Warehouse

    Fulford, J.M.; Sturm, T.W.

    1984-01-01

    Stability-dependent and Dalton-type mass transfer formulas are determined from experimental evaporation data in ambient and heated channels and are shown to have similar performance in prediction of evaporation. The formulas developed are compared with those proposed by other investigators for lakes and flowing channels. -from ASCE Publications Information

  11. Experimental quantum channel simulation

    NASA Astrophysics Data System (ADS)

    Lu, He; Liu, Chang; Wang, Dong-Sheng; Chen, Luo-Kan; Li, Zheng-Da; Yao, Xing-Can; Li, Li; Liu, Nai-Le; Peng, Cheng-Zhi; Sanders, Barry C.; Chen, Yu-Ao; Pan, Jian-Wei

    2017-04-01

    Quantum simulation is of great importance in quantum information science. Here, we report an experimental quantum channel simulator imbued with an algorithm for imitating the behavior of a general class of quantum systems. The reported quantum channel simulator consists of four single-qubit gates and one controlled-not gate. All types of quantum channels can be decomposed by the algorithm and implemented on this device. We deploy our system to simulate various quantum channels, such as quantum-noise channels and weak quantum measurement. Our results advance experimental quantum channel simulation, which is integral to the goal of quantum information processing.

  12. Two-Channel Transparency-Optimized Control Architectures in Bilateral Teleoperation With Time Delay.

    PubMed

    Kim, Jonghyun; Chang, Pyung Hun; Park, Hyung-Soon

    2013-01-01

    This paper introduces transparency-optimized control architectures (TOCAs) using two communication channels. Two classes of two-channel TOCAs are found, thereby showing that two channels are sufficient to achieve transparency. These TOCAs achieve a greater level of transparency but poorer stability than three-channel TOCAs and four-channel TOCAs. Stability of the two-channel TOCAs has been enhanced while minimizing transparency degradation by adding a filter; and a combined use of the two classes of two-channel TOCAs is proposed for both free space and constrained motion, which involve switching between two TOCAs for transition between free space and constrained motions. The stability condition of the switched teleoperation system is derived for practical applications. Through the one degree-of-freedom (DOF) experiment, the proposed two-channel TOCAs were shown to operate stably, while achieving better transparency under time delay than the other TOCAs.

  13. Two-Channel Transparency-Optimized Control Architectures in Bilateral Teleoperation With Time Delay

    PubMed Central

    Kim, Jonghyun; Chang, Pyung Hun; Park, Hyung-Soon

    2013-01-01

    This paper introduces transparency-optimized control architectures (TOCAs) using two communication channels. Two classes of two-channel TOCAs are found, thereby showing that two channels are sufficient to achieve transparency. These TOCAs achieve a greater level of transparency but poorer stability than three-channel TOCAs and four-channel TOCAs. Stability of the two-channel TOCAs has been enhanced while minimizing transparency degradation by adding a filter; and a combined use of the two classes of two-channel TOCAs is proposed for both free space and constrained motion, which involve switching between two TOCAs for transition between free space and constrained motions. The stability condition of the switched teleoperation system is derived for practical applications. Through the one degree-of-freedom (DOF) experiment, the proposed two-channel TOCAs were shown to operate stably, while achieving better transparency under time delay than the other TOCAs. PMID:23833548

  14. Membrane stabilizer

    DOEpatents

    Mingenbach, William A.

    1988-01-01

    A device is provided for stabilizing a flexible membrane secured within a frame, wherein a plurality of elongated arms are disposed radially from a central hub which penetrates the membrane, said arms imposing alternately against opposite sides of the membrane, thus warping and tensioning the membrane into a condition of improved stability. The membrane may be an opaque or translucent sheet or other material.

  15. Cholesterol and Ion Channels

    PubMed Central

    Levitan, Irena; Fang, Yun; Rosenhouse-Dantsker, Avia; Romanenko, Victor

    2010-01-01

    A variety of ion channels, including members of all major ion channel families, have been shown to be regulated by changes in the level of membrane cholesterol and partition into cholesterol-rich membrane domains. In general, several types of cholesterol effects have been described. The most common effect is suppression of channel activity by an increase in membrane cholesterol, an effect that was described for several types of inwardly-rectifying K+ channels, voltage-gated K+ channels, Ca+2 sensitive K+ channels, voltage-gated Na+ channels, N-type voltage-gated Ca+2 channels and volume-regulated anion channels. In contrast, several types of ion channels, such as epithelial amiloride-sensitive Na+ channels and Transient Receptor Potential channels, as well as some of the types of inwardly-rectifying and voltage-gated K+ channels were shown to be inhibited by cholesterol depletion. Cholesterol was also shown to alter the kinetic properties and current-voltage dependence of several voltage-gated channels. Finally, maintaining membrane cholesterol level is required for coupling ion channels to signalling cascades. In terms of the mechanisms, three general mechanisms have been proposed: (i) specific interactions between cholesterol and the channel protein, (ii) changes in the physical properties of the membrane bilayer and (iii) maintaining the scaffolds for protein-protein interactions. The goal of this review is to describe systematically the role of cholesterol in regulation of the major types of ion channels and to discuss these effects in the context of the models proposed. PMID:20213557

  16. A Micromechanical RF Channelizer

    NASA Astrophysics Data System (ADS)

    Akgul, Mehmet

    applications that must be stable against environmental perturbations, such as acceleration or power supply variations. Measurements on fabricated devices in fact confirm predictions by the new model of up to 4x improvement in frequency stability against DC-bias voltage variations for contour-mode disk resonators as the resistance loading their ports increases. By enhancing circuit visualization, this circuit model makes more obvious the circuit design procedures and topologies most beneficial for certain mechanical circuits, e.g., filters and oscillators. The second method enables simultaneous low motional resistance ( Rx 70,000) at 61 MHz using an improved ALD-partial electrode-to-resonator gap filling technique that reduces the Q-limiting surface losses of previous renditions by adding an alumina pre-coating before ALD of the gap-filling high-k dielectric. This effort increases the Q over the ˜10,000 of previous renditions by more than 6x towards demonstration of the first VHF micromechanical resonators in any material, piezoelectric or not, to meet the simultaneous high Q (>50,000) and low motional resistance Rx (< 200O) specs highly desired for front-end frequency channelizer requirements in cognitive and software-defined radio architectures. The methods presented in this chapter finally overcome the high impedance bottleneck that has plagued capacitively transduced micro-mechanical resonators over the past decade. The third method introduces a capacitively transduced micromechanical resonator constructed in hot filament CVD boron-doped microcrystalline diamond (MCD) structural material that posts a measured Q of 146,580 at 232.441 kHz, which is 3x higher than the previous high for conductive polydiamond. Moreover, radial-contour mode disk resonators fabricated in the same MCD film and using material mismatched stems exhibit a Q of 71,400 at 299.86 MHz. The material used here further exhibits an acoustic velocity of 18,516 m/s, which is now the highest to date among

  17. Hadamard quantum broadcast channels

    NASA Astrophysics Data System (ADS)

    Wang, Qingle; Das, Siddhartha; Wilde, Mark M.

    2017-10-01

    We consider three different communication tasks for quantum broadcast channels, and we determine the capacity region of a Hadamard broadcast channel for these various tasks. We define a Hadamard broadcast channel to be such that the channel from the sender to one of the receivers is entanglement-breaking and the channel from the sender to the other receiver is complementary to this one. As such, this channel is a quantum generalization of a degraded broadcast channel, which is well known in classical information theory. The first communication task we consider is classical communication to both receivers, the second is quantum communication to the stronger receiver and classical communication to other, and the third is entanglement-assisted classical communication to the stronger receiver and unassisted classical communication to the other. The structure of a Hadamard broadcast channel plays a critical role in our analysis: The channel to the weaker receiver can be simulated by performing a measurement channel on the stronger receiver's system, followed by a preparation channel. As such, we can incorporate the classical output of the measurement channel as an auxiliary variable and solve all three of the above capacities for Hadamard broadcast channels, in this way avoiding known difficulties associated with quantum auxiliary variables.

  18. Fading channel simulator

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.

    1991-12-31

    This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  19. Quantum channel construction with circuit quantum electrodynamics

    NASA Astrophysics Data System (ADS)

    Shen, Chao; Noh, Kyungjoo; Albert, Victor V.; Krastanov, Stefan; Devoret, M. H.; Schoelkopf, R. J.; Girvin, S. M.; Jiang, Liang

    2017-04-01

    Quantum channels can describe all transformations allowed by quantum mechanics. We adapt two existing works [S. Lloyd and L. Viola, Phys. Rev. A 65, 010101 (2001), 10.1103/PhysRevA.65.010101 and E. Andersson and D. K. L. Oi, Phys. Rev. A 77, 052104 (2008), 10.1103/PhysRevA.77.052104] to superconducting circuits, featuring a single qubit ancilla with quantum nondemolition readout and adaptive control. This construction is efficient in both ancilla dimension and circuit depth. We point out various applications of quantum channel construction, including system stabilization and quantum error correction, Markovian and exotic channel simulation, implementation of generalized quantum measurements, and more general quantum instruments. Efficient construction of arbitrary quantum channels opens up exciting new possibilities for quantum control, quantum sensing, and information processing tasks.

  20. The Channel Tunnel

    NASA Image and Video Library

    2006-08-11

    The Channel Tunnel is a 50.5 km-long rail tunnel beneath the English Channel at the Straits of Dover. It connects Dover, Kent in England with Calais, northern France. This image was acquired by NASA Terra spacecraft.

  1. Bayesian sparse channel estimation

    NASA Astrophysics Data System (ADS)

    Chen, Chulong; Zoltowski, Michael D.

    2012-05-01

    In Orthogonal Frequency Division Multiplexing (OFDM) systems, the technique used to estimate and track the time-varying multipath channel is critical to ensure reliable, high data rate communications. It is recognized that wireless channels often exhibit a sparse structure, especially for wideband and ultra-wideband systems. In order to exploit this sparse structure to reduce the number of pilot tones and increase the channel estimation quality, the application of compressed sensing to channel estimation is proposed. In this article, to make the compressed channel estimation more feasible for practical applications, it is investigated from a perspective of Bayesian learning. Under the Bayesian learning framework, the large-scale compressed sensing problem, as well as large time delay for the estimation of the doubly selective channel over multiple consecutive OFDM symbols, can be avoided. Simulation studies show a significant improvement in channel estimation MSE and less computing time compared to the conventional compressed channel estimation techniques.

  2. Quasi-Anonymous Channels

    DTIC Science & Technology

    2003-01-01

    QUASI- ANONYMOUS CHANNELS Ira S. Moskowitz Center for High Assurance Computer Systems - Code 5540 Naval Research Laboratory, Washington, DC...Assurance Computer Systems - Code 5540 Naval Research Laboratory, Washington, DC 20375, USA Abstract Although both anonymity and covert...channels are part of the larger topic of information hiding, there also exists an intrinsic linkage between anonymity and covert channels. This linkage

  3. Channel morphology [Chapter 5

    Treesearch

    Jonathan W. Long; Alvin L. Medina; Daniel G. Neary

    2012-01-01

    Channel morphology has become an increasingly important subject for analyzing the health of rivers and associated fish populations, particularly since the popularization of channel classification and assessment methods. Morphological data can help to evaluate the flows of sediment and water that influence aquatic and riparian habitat. Channel classification systems,...

  4. On 1-qubit channels

    NASA Astrophysics Data System (ADS)

    Uhlmann, Armin

    2001-09-01

    The entropy HT (ρ) of a state with respect to a channel T and the Holevo capacity of the channel require the solution of difficult variational problems. For a class of 1-qubit channels, which contains all the extremal ones, the problem can be significantly simplified by attaching a unique Hermitian antilinear operator ϑ to every channel of the considered class. The channel's concurrence CT can be expressed by ϑ and turns out to be a flat roof. This allows to write down an explicit expression for HT. Its maximum would give the Holevo (one-shot) capacity.

  5. Incompatibility of quantum channels

    NASA Astrophysics Data System (ADS)

    Heinosaari, Teiko; Miyadera, Takayuki

    2017-03-01

    Two quantum channels are called compatible if they can be obtained as marginals from a single broadcasting channel; otherwise they are incompatible. We derive a characterization of the compatibility relation in terms of concatenation and conjugation, and we show that all pairs of sufficiently noisy quantum channels are compatible. The complement relation of incompatibility can be seen as a unifying aspect for several important quantum features, such as impossibility of universal broadcasting and unavoidable measurement disturbance. We show that the concepts of entanglement breaking channel and antidegradable channel can be completely characterized in terms compatibility.

  6. Cardiac ion channels

    PubMed Central

    Priest, Birgit T; McDermott, Jeff S

    2015-01-01

    Ion channels are critical for all aspects of cardiac function, including rhythmicity and contractility. Consequently, ion channels are key targets for therapeutics aimed at cardiac pathophysiologies such as atrial fibrillation or angina. At the same time, off-target interactions of drugs with cardiac ion channels can be the cause of unwanted side effects. This manuscript aims to review the physiology and pharmacology of key cardiac ion channels. The intent is to highlight recent developments for therapeutic development, as well as elucidate potential mechanisms for drug-induced cardiac side effects, rather than present an in-depth review of each channel subtype. PMID:26556552

  7. Ion channels in plants

    PubMed Central

    Baluška, František; Mancuso, Stefano

    2013-01-01

    In his recent opus magnum review paper published in the October issue of Physiology Reviews, Rainer Hedrich summarized the field of plant ion channels.1 He started from the earliest electric recordings initiated by Charles Darwin of carnivorous Dionaea muscipula,1,2 known as Venus flytrap, and covered the topic extensively up to the most recent discoveries on Shaker-type potassium channels, anion channels of SLAC/SLAH families, and ligand-activated channels of glutamate receptor-like type (GLR) and cyclic nucleotide-gated channels (CNGC).1 PMID:23221742

  8. Membrane stabilizer

    DOEpatents

    Mingenbach, W.A.

    1988-02-09

    A device is provided for stabilizing a flexible membrane secured within a frame, wherein a plurality of elongated arms are disposed radially from a central hub which penetrates the membrane, said arms imposing alternately against opposite sides of the membrane, thus warping and tensioning the membrane into a condition of improved stability. The membrane may be an opaque or translucent sheet or other material. 10 figs.

  9. Nested Channels near Hellas

    NASA Image and Video Library

    2015-09-30

    This image from NASA Mars Reconnaissance Orbiter spacecraft shows a channel system flowing to the southwest toward the huge Hellas impact basin. We're not sure if this channel-inside-a-channel was carved by flowing water or lava. Flowing water erodes channels, and flowing lava both erodes and melts surrounding rock to form channels. It's not clear whether a huge surge of water or lava first formed the wide channel and then subsided into a trickle to form this narrow, inner channel, or if a trickle formed the inner channel and a subsequent surge formed the wider one. Detailed analysis of the shape could reveal which scenario is most likely, as well as whether water or lava is responsible. Relevant observations for such a determination would include, for example, the facts that the channels lack levees (ridges along the banks) and that the inner channel diverts around a mound, which at one time was an island. This channel system flowed to the southwest toward the huge Hellas impact basin.

  10. Mechanically Activated Ion Channels.

    PubMed

    Ranade, Sanjeev S; Syeda, Ruhma; Patapoutian, Ardem

    2015-09-23

    Mechanotransduction, the conversion of physical forces into biochemical signals, is essential for various physiological processes such as the conscious sensations of touch and hearing, and the unconscious sensation of blood flow. Mechanically activated (MA) ion channels have been proposed as sensors of physical force, but the identity of these channels and an understanding of how mechanical force is transduced has remained elusive. A number of recent studies on previously known ion channels along with the identification of novel MA ion channels have greatly transformed our understanding of touch and hearing in both vertebrates and invertebrates. Here, we present an updated review of eukaryotic ion channel families that have been implicated in mechanotransduction processes and evaluate the qualifications of the candidate genes according to specified criteria. We then discuss the proposed gating models for MA ion channels and highlight recent structural studies of mechanosensitive potassium channels.

  11. Mechanically Activated Ion Channels

    PubMed Central

    Ranade, Sanjeev S.; Syeda, Ruhma; Patapoutian, Ardem

    2015-01-01

    Mechanotransduction, the conversion of physical forces into biochemical signals, is an essential component of numerous physiological processes including not only conscious senses of touch and hearing, but also unconscious senses such as blood pressure regulation. Mechanically activated (MA) ion channels have been proposed as sensors of physical force, but the identity of these channels and an understanding of how mechanical force is transduced has remained elusive. A number of recent studies on previously known ion channels along with the identification of novel MA ion channels have greatly transformed our understanding of touch and hearing in both vertebrates and invertebrates. Here, we present an updated review of eukaryotic ion channel families that have been implicated in mechanotransduction processes and evaluate the qualifications of the candidate genes according to specified criteria. We then discuss the proposed gating models for MA ion channels and highlight recent structural studies of mechanosensitive potassium channels. PMID:26402601

  12. Graph-state basis for Pauli channels

    SciTech Connect

    Chen Xiaoyu; Jiang Lizhen

    2011-05-15

    Quantum capacities of Pauli channels are not additive, a degenerate quantum code may improve the hashing bound of the capacity. The difficulty in approaching the capacity is how to calculate the coherent information of a generic degenerate quantum code. Using graph state basis, we greatly reduce the problem for the input of quantum error-correcting code. We show that for a graph diagonal state passing through a Pauli channel the output state is diagonalizable and the joint output state of the system and ancilla is block diagonalizable. When the input state is an equal probable mixture of codewords of a stabilizer code, the coherent information can be analytically obtained.

  13. Fading channel simulator

    DOEpatents

    Argo, Paul E.; Fitzgerald, T. Joseph

    1993-01-01

    Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  14. Cholesterol and Kir channels

    PubMed Central

    Levitan, Irena

    2009-01-01

    To date, most of the major types of Kir channels, Kir2s, Kir3s, Kir4s and Kir6s, have been found to partition into cholesterol-rich membrane domains and/or to be regulated by changes in the level of membrane cholesterol. Surprisingly, however, in spite of the structural similarities between different Kirs, effects of cholesterol on different types of Kir channels vary from cholesterol-induced decrease in the current density (Kir2 channels) to the loss of channel activity by cholesterol depletion (Kir4 channels) and loss of channel coupling by different mediators (Kir3 and Kir6 channels). Recently, we have gained initial insights into the mechanisms responsible for cholesterol-induced suppression Kir2 channels, but mechanisms underlying cholesterol sensitivity of other Kir channels are mostly unknown. The goal of this review is to present a summary of the current knowledge of the distinct effects of cholesterol on different types of Kir channels in vitro and in vivo. PMID:19548316

  15. Parallel information processing channels created in the retina

    PubMed Central

    Schiller, Peter H.

    2010-01-01

    In the retina, several parallel channels originate that extract different attributes from the visual scene. This review describes how these channels arise and what their functions are. Following the introduction four sections deal with these channels. The first discusses the “ON” and “OFF” channels that have arisen for the purpose of rapidly processing images in the visual scene that become visible by virtue of either light increment or light decrement; the ON channel processes images that become visible by virtue of light increment and the OFF channel processes images that become visible by virtue of light decrement. The second section examines the midget and parasol channels. The midget channel processes fine detail, wavelength information, and stereoscopic depth cues; the parasol channel plays a central role in processing motion and flicker as well as motion parallax cues for depth perception. Both these channels have ON and OFF subdivisions. The third section describes the accessory optic system that receives input from the retinal ganglion cells of Dogiel; these cells play a central role, in concert with the vestibular system, in stabilizing images on the retina to prevent the blurring of images that would otherwise occur when an organism is in motion. The last section provides a brief overview of several additional channels that originate in the retina. PMID:20876118

  16. Flow Instability in Baffled Channel Flow

    NASA Astrophysics Data System (ADS)

    Kang, Changwoo; Yang, Kyung-Soo; Lee, Kyongjun

    2010-11-01

    Flow instability of baffled channel flow, where thin baffles are mounted on both channel walls periodically in the direction of the main flow, has been numerically investigated. Flow in a baffled channel is regarded as a simple model for flow in finned heat exchangers, including micro channels. In baffled channel flow, flow characteristics are significantly affected by geometrical configuration of the baffles. Two key parameters were considered, namely baffle interval (L) and Reynolds number (Re) of the main flow. The baffle height is fixed as one quarter of the channel height (H). By using a parametric study, we elucidate dependency of the primary instability, a Hopf bifurcation from steady to a time-periodic flow, on L. It turned out that the most unstable flow is obtained with L/H=3. Transition of two-dimensional (2D) time-periodic flow to three-dimensional (3D) flow is initiated by a secondary instability (SI). Floquet stability analysis was performed to identify the critical Reynolds number of SI for some selected baffle intervals. Several distinct modes were identified, and dependency of SI on L was elucidated. A 3D simulation was finally carried out to confirm the Floquet analysis. The current results shed light on understanding flow characteristics of a finned heat exchanger.

  17. R type anion channel

    PubMed Central

    Diatloff, Eugene; Peyronnet, Rémi; Colcombet, Jean; Thomine, Sébastien; Barbier-Brygoo, Hélène

    2010-01-01

    Plant genomes code for channels involved in the transport of cations, anions and uncharged molecules through membranes. Although the molecular identity of channels for cations and uncharged molecules has progressed rapidly in the recent years, the molecular identity of anion channels has lagged behind. Electrophysiological studies have identified S-type (slow) and R-type (rapid) anion channels. In this brief review, we summarize the proposed functions of the R-type anion channels which, like the S-type, were first characterized by electrophysiology over 20 years ago, but unlike the S-type, have still yet to be cloned. We show that the R-type channel can play multiple roles. PMID:21051946

  18. Introduction to sodium channels.

    PubMed

    Peters, Colin H; Ruben, Peter C

    2014-01-01

    Voltage-gated sodium channels (VGSCs) are present in many tissue types within the human body including both cardiac and neuronal tissues. Like other channels, VGSCs activate, deactivate, and inactivate in response to changes in membrane potential. VGSCs also have a similar structure to other channels: 24 transmembrane segments arranged into four domains that surround a central pore. The structure and electrical activity of these channels allows them to create and respond to electrical signals in the body. Because of their distribution throughout the body, VGSCs are implicated in a variety of diseases including epilepsy, cardiac arrhythmias, and neuropathic pain. As such the study of these channels is essential. This brief review will introduce sodium channel structure, physiology, and pathophysiology.

  19. Laser Stabilization

    SciTech Connect

    Hall, John L.; Taubman, Matthew S.; Ye, Jun

    2010-01-01

    This book chapter covers the basics of the field of stabilizing lasers to optical frequency references such as optical cavities and molecular transitions via the application of servo control systems. These discussions are given with reference to the real-life frequency metrology experienced in Hall-Labs (now Ye-Labs), JILA, University of Colorado. The subjects covered include: the basics of control system stability, a discussion of both the theoretical and experimental limitations, an outline of optical cavity susceptibility to environmental noise, and a brief introduction to the use and limitations of molecular transitions as frequency references.

  20. HIPPI and Fibre Channel

    SciTech Connect

    Tolmie, D.E.

    1992-01-01

    The High-Performance Parallel Interface (HIPPI) and Fibre Channel are near-gigabit per second data communications interfaces being developed in ANSI standards Task Group X3T9.3. HIPPI is the current interface of choice in the high-end and supercomputer arena, and Fibre Channel is a follow-on effort. HIPPI came from a local area network background, and Fibre Channel came from a mainframe to peripheral interface background.

  1. Man-induced channel adjustment in Tennessee streams

    USGS Publications Warehouse

    Robbins, C.H.; Simon, Andrew

    1983-01-01

    Channel modifications in Tennessee, particularly in the western part, have led to large-scale instabilities in the channelized rivers and may have contributed to several bridge failures. These modifications, together with land-use practices, led to downcutting, headward erosion, downstream aggradation, accelerated scour, and bank instabilities. Changes in gradient by channel straightening caused more severe channel response than did dredging or clearing. Large-scale changes continue to occur in all the channelized rivers: the Obion River, its forks, and the South Fork Forked Deer River. However, the non-channelized Hatchie River in west Tennessee not only withstood the natural stresses imposed by the wet years of 1973 to 1975 but continues to exhibit characteristics of stability. Water-surface slope, the primary dependent variable, proved to be a sensitive and descriptive parameter useful in determining channel adjustment. Adjustments to man-induced increases in channel-slope are described by inverse exponential functions of the basic form S=ae(-b(t)); where ' S ' is some function describing channel-slope, ' t ' is the number of years since completion of channel work, and ' a ' and ' b ' are coefficients. Response times for the attainment of ' equilibrium ' channel slopes are a function of the magnitude and extent of the imposed modifications. The adjusted profile gradients attained by the streams following channelization are similar to the predisturbed profile gradients, where no alteration to channel length was made. Where the channels were straightened by constructing cut-offs, thus shortening channel length, then slope adjustments (reduction) proceed past the predisturbed profile gradients, to new profiles with lower gradients. (USGS)

  2. Calcium Channel Blockers

    MedlinePlus

    ... calcium channel blockers interact with grapefruit products. References Kaplan NM, et al. Treatment of hypertension: Drug therapy. In: Kaplan's Clinical Hypertension. 11th ed. Philadelphia, Pa.: Wolters Kluwer ...

  3. Selfcomplementary Quantum Channels

    NASA Astrophysics Data System (ADS)

    Smaczyński, Marek; Roga, Wojciech; Życzkowski, Karol

    2016-10-01

    Selfcomplementary quantum channels are characterized by such an interaction between the principal quantum system and the environment that leads to the same output states of both interacting systems. These maps can describe approximate quantum copy machines, as perfect copying of an unknown quantum state is not possible due to the celebrated no-cloning theorem. We provide here a parametrization of a large class of selfcomplementary channels and analyze their properties. Selfcomplementary channels preserve some residual coherences and residual entanglement. Investigating some measures of non-Markovianity, we show that time evolution under selfcomplementary channels is highly non-Markovian.

  4. Robustness of channel-adapted quantum error correction

    SciTech Connect

    Ballo, Gabor; Gurin, Peter

    2009-07-15

    A quantum channel models the interaction between the system we are interested in and its environment. Such a model can capture the main features of the interaction, but, because of the complexity of the environment, we cannot assume that it is fully accurate. We study the robustness of quantum error correction operations against completely unexpected and subsequently undetermined type of channel uncertainties. We find that a channel-adapted optimal error correction operation does not only give the best possible channel fidelity but it is more robust against channel alterations than any other error correction operation. Our results are valid for Pauli channels and stabilizer codes, but based on some numerical results, we believe that very similar conclusions can be drawn also in the general case.

  5. Riparian vegetation recovery patterns following stream channelization: a geomorphic perspective

    USGS Publications Warehouse

    Hupp, C.R.

    1992-01-01

    Hundreds of kilometres of West Tennessee streams have been channelized since the turn of the century. After a stream is straightened, dredged, or cleared, basin-wide ecologic, hydrologic, and geomorphic processes bring about an integrated, characteristic recovery sequence. The rapid pace of channel responses to channelization provides an opportunity to document and interpret vegetation recovery patterns relative to otherwise long-term, concomitant evolution of river geomorphology. The linkage of channel bed aggradation, woody vegetation establishment, and bank accretion all lead to recovery of the channel. Pioneer species are hardy and fast growing, and can tolerate moderate amounts of slope instability and sediment deposition; these species include river birch (Betula nigra), black willow (Salix nigra), boxelder (Acer negundo), and silver maple (Acer saccharinum). High stem densities and root-mass development appear to enhance bank stability. Tree-ring analyses suggest that on average 65 yr may be required for recovery after channelization. -from Author

  6. Fully converged iterative method for coupled channel problems

    NASA Astrophysics Data System (ADS)

    Shu, Di; Simbotin, I.; Côté, R.

    2016-05-01

    We implemented a numerical method using a distorted-wave perturbative approach for coupled-channel scattering problems. Our new method provides a way to avoid costly computations for the propagation of the full solutions in coupled-channel problems to large distances for slowly vanishing couplings. Thus, instead of dealing with large matrices, all computations are performed in a channel by channel fashion. The distorted wavefunction for each channel is initialized with the appropriate solution (which includes the diagonal element of the coupling potential matrix). We then solve single-channel inhomogeneous radial equations which contain the (off-diagonal) couplings as a perturbation, and we iterate until desired accuracy is achieved. We tested for stability by continuing to iterate even after convergence has been achieved, e.g., for a total of 75 iterations. Partial support from the US Army Research Office (ARO-MURI W911NF-14-1-0378), and from NSF (Grant No. PHY-1415560).

  7. Effects of microgravity on liposome-reconstituted cardiac gap junction channeling activity

    NASA Technical Reports Server (NTRS)

    Claassen, D. E.; Spooner, B. S.

    1989-01-01

    Effects of microgravity on cardiac gap junction channeling activity were investigated aboard NASA zero-gravity aircraft. Liposome-reconstituted gap junctions were assayed for channel function during free-fall, and the data were compared with channeling at 1 g. Control experiments tested for 0 g effects on the structural stability of liposomes, and on the enzyme-substrate signalling system of the assay. The results demonstrate that short periods of microgravity do not perturb reconstituted cardiac gap junction channeling activity.

  8. Effects of microgravity on liposome-reconstituted cardiac gap junction channeling activity

    NASA Technical Reports Server (NTRS)

    Claassen, D. E.; Spooner, B. S.

    1989-01-01

    Effects of microgravity on cardiac gap junction channeling activity were investigated aboard NASA zero-gravity aircraft. Liposome-reconstituted gap junctions were assayed for channel function during free-fall, and the data were compared with channeling at 1 g. Control experiments tested for 0 g effects on the structural stability of liposomes, and on the enzyme-substrate signalling system of the assay. The results demonstrate that short periods of microgravity do not perturb reconstituted cardiac gap junction channeling activity.

  9. Stabilizing population.

    PubMed

    Brown, L; Mitchell, J

    1998-04-01

    This article is a reprint of the Worldwatch Institute's "State of the World Report," Chapter 10: "Building a New Economy." 16 countries reached zero population growth by 1997. 33 countries have stabilized population, which amounts to 14% of world population. It is estimated that by 2050 population will include an additional 3.6 billion people beyond the present 6 billion. About 60% of the added population will be in Asia, an increase from 3.4 billion in 1995 to 5.4 billion in 2050. China's current population of 1.2 billion will reach 1.5 billion. India's population is expected to rapidly rise from 930 million to 1.53 billion. Populations in the Middle East and North Africa are expected to double in size. Sub-Saharan population is expected to triple in size. By 2050, Nigeria will have 339 million people, which was the entire population of Africa in 1960. There is a great need to stabilize population in a number of currently unstabilized countries. In 1971, Bangladesh and Pakistan had the same population; however, by 2050, Pakistan, without a strong commitment to reducing population growth, will have 70 million more people than Bangladesh. Population stabilization will depend on removal of physical and social barriers that prevent women from using family planning services and thereby help them control their own unwanted fertility. Stabilization will require poverty alleviation and removal of the need for large families. Family size is reduced with lower infant and child mortality risk, increased education, a higher legal age of marriage, and investment in stabilization programs. Solutions to global population growth cannot wait for health reform and budget deficit reductions.

  10. A linearization of quantum channels

    NASA Astrophysics Data System (ADS)

    Crowder, Tanner

    2015-06-01

    Because the quantum channels form a compact, convex set, we can express any quantum channel as a convex combination of extremal channels. We give a Euclidean representation for the channels whose inverses are also valid channels; these are a subset of the extreme points. They form a compact, connected Lie group, and we calculate its Lie algebra. Lastly, we calculate a maximal torus for the group and provide a constructive approach to decomposing any invertible channel into a product of elementary channels.

  11. Basaltic Lava Channels

    NASA Astrophysics Data System (ADS)

    Cashman, K. V.; Griffiths, R. W.; Kerr, R. C.

    2004-12-01

    In Hawaii, the mode of lava transport - through open channels or through insulating lava tubes - determines the thermal, rheological, and emplacement history of a lava flow. Most Hawaiian lavas are erupted at near-liquidus temperatures and are therefore crystal-poor; lava transport through open channels allows rapid cooling and consequent rapid increases in lava crystallinity. Solidified aa flows resulting from channelized flow are typically fine-grained throughout their thickness, indicating cooling of the entire flow thickness during transport. In contrast, transport of lava through insulating tubes permits flow over long distances with little cooling. Flows emerging from such tubes typically have pahoehoe flow surfaces with glassy crusts. Groundmass textures that coarsen from the flow rind to the interior reflect rates of post-emplacement, rather than syn-emplacement, cooling. To distinguish eruption conditions that result in lava channels from those that allow formation of lava tubes, we have performed a series of laboratory experiments involving injection of PEG 600 (a wax with a Newtonian rheology and freezing temperature of 19ºC) into cold water through both uniform and non-uniform sloping channels. In uniform channels, tube formation can be distinguished from open channel flow using a dimensionless parameter based on a solidification time scale, an advection time scale, and a Rayleigh number that describes convection by heat loss from crust-free shear zones. Theoretical analysis predicts that in the open channel regime, the width of the crust (dc) will vary with the channel width (W) as dc = W5/3. Crustal coverage of non-uniform channels in both laboratory experiments and field examples from Kilauea Volcano, Hawaii, is consistent with this prediction. However, experiments in non-uniform channels illustrate additional controls on the surface coverage of lava channels. Most important is crustal extension resulting from flow acceleration through constrictions

  12. Ion channels in microbes

    PubMed Central

    Martinac, Boris; Saimi, Yoshiro; Kung, Ching

    2008-01-01

    Summary Studies of ion channels have for long been dominated by the animalcentric, if not anthropocentric view of physiology. The structures and activities of ion channels had, however, evolved long before the appearance of complex multicellular organisms on Earth. The diversity of ion channels existing in cellular membranes of prokaryotes is a good example. Though at first it may appear as a paradox that most of what we know about the structure of eukaryotic ion channels is based on the structure of bacterial channels, this should not be surprising given the evolutionary relatedness of all living organisms and suitability of microbial cells for structural studies of biological macromolecules in a laboratory environment. Genome sequences of the human as well as various microbial, plant and animal organisms unambiguously established the evolutionary links, whereas crystallographic studies of the structures of major types of ion channels published over the last decade clearly demonstrated the advantage of using microbes as experimental organisms. The purpose of this review is not only to provide an account of acquired knowledge on microbial ion channels but also to show that the study of microbes and their ion channels may also hold a key to solving unresolved molecular mysteries in the future. PMID:18923187

  13. Ion channels in microbes.

    PubMed

    Martinac, Boris; Saimi, Yoshiro; Kung, Ching

    2008-10-01

    Studies of ion channels have for long been dominated by the animalcentric, if not anthropocentric, view of physiology. The structures and activities of ion channels had, however, evolved long before the appearance of complex multicellular organisms on earth. The diversity of ion channels existing in cellular membranes of prokaryotes is a good example. Although at first it may appear as a paradox that most of what we know about the structure of eukaryotic ion channels is based on the structure of bacterial channels, this should not be surprising given the evolutionary relatedness of all living organisms and suitability of microbial cells for structural studies of biological macromolecules in a laboratory environment. Genome sequences of the human as well as various microbial, plant, and animal organisms unambiguously established the evolutionary links, whereas crystallographic studies of the structures of major types of ion channels published over the last decade clearly demonstrated the advantage of using microbes as experimental organisms. The purpose of this review is not only to provide an account of acquired knowledge on microbial ion channels but also to show that the study of microbes and their ion channels may also hold a key to solving unresolved molecular mysteries in the future.

  14. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1982-01-01

    Early observations of Mars conducted by means of telescopes are considered. Secchi introduced the Italian word 'canale' ('channel') in 1869 to describe apparent lines on the planet's surface. Between 1877 and 1888 Schiaparelli mapped a profusion of 'canali'. Schiaparelli's work led to famous controversies about Mars. This book attempts to investigate the puzzle posed by the Martian channels, taking into account also the results of the studies conducted with the aid of the two orbiting Viking spacecraft which have produced a total number of nearly 60,000 pictures. The channel types are discussed along with questions regarding the distribution, the ages, and the proposed origins of the channels. Attention is given to the geomorphology of Mars, the patterns and networks of Martian valleys, ice and the Martian surface, the outflow channels, catastrophic flood processes, questions of analogy between terrestrial and Martian geographic features, and Martian phenomena associated with water liquid or water ice.

  15. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1982-01-01

    Early observations of Mars conducted by means of telescopes are considered. Secchi introduced the Italian word 'canale' ('channel') in 1869 to describe apparent lines on the planet's surface. Between 1877 and 1888 Schiaparelli mapped a profusion of 'canali'. Schiaparelli's work led to famous controversies about Mars. This book attempts to investigate the puzzle posed by the Martian channels, taking into account also the results of the studies conducted with the aid of the two orbiting Viking spacecraft which have produced a total number of nearly 60,000 pictures. The channel types are discussed along with questions regarding the distribution, the ages, and the proposed origins of the channels. Attention is given to the geomorphology of Mars, the patterns and networks of Martian valleys, ice and the Martian surface, the outflow channels, catastrophic flood processes, questions of analogy between terrestrial and Martian geographic features, and Martian phenomena associated with water liquid or water ice.

  16. Salt marsh vegetation promotes efficient tidal channel networks

    NASA Astrophysics Data System (ADS)

    Kearney, W. S.; Fagherazzi, S.

    2014-12-01

    Tidal channel networks mediate the exchange of water, nutrients and sediment between an estuary and marshes and mudflats. Biology feeds back into channel morphodynamics through vegetation's influence on the cohesive strength of channel banks. Understanding the morphology of a tidal channel network is thus essential to understanding both the biological functioning of intertidal ecosystems and the topographic signature of life. A critical measure of the morphology of a channel network is the unchanneled path length, which is characteristic of the efficiency with which a network dissects the marsh platform. However, the processes which control the formation and maintenance of an efficient tidal channel network remain unclear. Here we show that an unvegetated marsh platform (Estero La Ramada, Baja California, Mexico) is dissected by a less efficient channel network than a vegetated one (Barnstable, Massachusetts, United States). The difference in geometric efficiency reflects a difference in the branching and meandering characteristics of the network, characteristics controlled by the density of vegetation on the channel banks. Our results suggest a feedback between network geometry and vegetation, mediated by fluxes of nutrients and salinity through the channel network, maintains the observed network geometries. An efficient network can support a denser vegetation community which stabilizes channel banks, leading to an efficient meandering geometry.

  17. Conductive Channel for Energy Transmission

    SciTech Connect

    Apollonov, Victor V.

    2011-11-10

    For many years the attempts to create conductive channels of big length were taken in order to study the upper atmosphere and to settle special tasks, related to energy transmission. There upon the program of creation of 'Impulsar' represents a great interest, as this program in a combination with high-voltage high repetition rate electrical source can be useful to solve the above mentioned problems (N. Tesla ideas for the days of high power lasers). The principle of conductive channel production can be shortly described as follows. The 'Impulsar' - laser jet engine vehicle - propulsion take place under the influence of powerful high repetition rate pulse-periodic laser radiation. In the experiments the CO{sub 2}-laser and solid state Nd:YAG laser systems had been used. Active impulse appears thanks to air breakdown (<30 km) or to the breakdown of ablated material on the board (>30 km), placed in the vicinity of the focusing mirror-acceptor of the breakdown waves. With each pulse of powerful laser the device rises up, leaving a bright and dense trace of products with high degree of ionization and metallization by conductive nano-particles due to ablation. Conductive dust plasma properties investigation in our experiments was produced by two very effective approaches: high power laser controlled ablation and by explosion of wire. Experimental and theoretical results of conductive canal modeling will be presented. The estimations show that with already experimentally demonstrated figures of specific thrust impulse the lower layers of the Ionosphere can be reached in several ten seconds that is enough to keep the high level of channel conductivity and stability with the help of high repetition rate high voltage generator. Some possible applications for new technology are highlighted.

  18. Conductive Channel for Energy Transmission

    NASA Astrophysics Data System (ADS)

    Apollonov, Victor V.

    2011-11-01

    For many years the attempts to create conductive channels of big length were taken in order to study the upper atmosphere and to settle special tasks, related to energy transmission. There upon the program of creation of "Impulsar" represents a great interest, as this program in a combination with high-voltage high repetition rate electrical source can be useful to solve the above mentioned problems (N. Tesla ideas for the days of high power lasers). The principle of conductive channel production can be shortly described as follows. The "Impulsar"—laser jet engine vehicle—propulsion take place under the influence of powerful high repetition rate pulse-periodic laser radiation. In the experiments the CO2—laser and solid state Nd:YAG laser systems had been used. Active impulse appears thanks to air breakdown (<30 km) or to the breakdown of ablated material on the board (>30 km), placed in the vicinity of the focusing mirror-acceptor of the breakdown waves. With each pulse of powerful laser the device rises up, leaving a bright and dense trace of products with high degree of ionization and metallization by conductive nano-particles due to ablation. Conductive dust plasma properties investigation in our experiments was produced by two very effective approaches: high power laser controlled ablation and by explosion of wire. Experimental and theoretical results of conductive canal modeling will be presented. The estimations show that with already experimentally demonstrated figures of specific thrust impulse the lower layers of the Ionosphere can be reached in several ten seconds that is enough to keep the high level of channel conductivity and stability with the help of high repetition rate high voltage generator. Some possible applications for new technology are highlighted.

  19. Fine Channel Networks

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A color image of fine channel networks on Mars; north toward top. The scene shows heavily cratered highlands dissected by dendritic open channel networks that dissect steep slopes of impact crater walls. This image is a composite of Viking high-resolution images in black and white and low-resolution images in color. The image extends from latitude 9 degrees S. to 5 degrees S. and from longitude 312 degrees to 320 degrees; Mercator projection. The dendritic pattern of the fine channels and their location on steep slopes leads to the interpretation that these are runoff channels. The restriction of these types of channels to ancient highland rocks suggests that these channels are old and date from a time on Mars when conditions existed for precipitation to actively erode rocks. After the channels reach a low plain, they appear to end. Termination may have resulted from burial by younger deposits or perhaps the flows percolated into the surface materials and continued underground.

  20. Fine Channel Networks

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A color image of fine channel networks on Mars; north toward top. The scene shows heavily cratered highlands dissected by dendritic open channel networks that dissect steep slopes of impact crater walls. This image is a composite of Viking high-resolution images in black and white and low-resolution images in color. The image extends from latitude 9 degrees S. to 5 degrees S. and from longitude 312 degrees to 320 degrees; Mercator projection. The dendritic pattern of the fine channels and their location on steep slopes leads to the interpretation that these are runoff channels. The restriction of these types of channels to ancient highland rocks suggests that these channels are old and date from a time on Mars when conditions existed for precipitation to actively erode rocks. After the channels reach a low plain, they appear to end. Termination may have resulted from burial by younger deposits or perhaps the flows percolated into the surface materials and continued underground.

  1. Assay for calcium channels

    SciTech Connect

    Glossmann, H.; Ferry, D.R.

    1985-01-01

    This chapter focuses on biochemical assays for Ca/sup 2 +/-selective channels in electrically excitable membranes which are blocked in electrophysiological and pharmacological experiments by verapamil, 1,4-dihydropyridines, diltiazen (and various other drugs), as well as inorganic di- or trivalent cations. The strategy employed is to use radiolabeled 1,4-dihydropyridine derivatives which block calcium channels with ED/sub 50/ values in the nanomolar range. Although tritiated d-cis-diltiazem and verapamil can be used to label calcium channels, the 1,4-dihydropyridines offer numerous advantages. The various sections cover tissue specificity of channel labeling, the complex interactions of divalent cations with the (/sup 3/H)nimodipine-labeled calcium channels, and the allosteric regulation of (/sup 3/H)nimodipine binding by the optically pure enantiomers of phenylalkylamine and benzothiazepine calcium channel blockers. A comparison of the properties of different tritiated 1,4-dihydropyridine radioligands and the iodinated channel probe (/sup 125/I)iodipine is given.

  2. Groundwater controls on river channel pattern

    NASA Astrophysics Data System (ADS)

    Bätz, Nico; Colombini, Pauline; Cherubini, Paolo; Lane, Stuart N.

    2017-04-01

    Braided rivers are characterized by high rates of morphological change. However, despite the potential for frequent disturbance, vegetated patches may develop within this system and influence long-term channel dynamics and channel patterns through the "engineering effects" of vegetation. The stabilizing effect of developing vegetation on morphological change has been widely shown by flume experiments and (historic) aerial pictures analysis. Thus, there is a balance between disturbance and stabilization, mediated through vegetation, that may determine the long-term geomorphic and biogeomorphic evolution of the river. It follows that with a change in disturbance frequency relative to the rate of vegetation establishment, a systematic geomorphological shift could occur. Research has addressed how changes in disturbance frequency affect river channel pattern, but has rarely addressed the way in which the stabilizing effects of biogeomorphic succession interact with disturbance frequency to maintain a river in a more dynamic or a less dynamic state. Here, we quantify how the interplay between groundwater access, disturbance frequency and vegetation succession, drive changes in channel pattern. We studied this complex interplay on a transitional gravel-bed river system (braided, wandering, meandering) close to Geneva (Switzerland) - the Allondon River. Dendroecological analysis demonstrate that vegetation growth is driven by groundwater access. Groundwater access conditions the rate of vegetation stabilization at the sub-reach scale and, due to a reduction in flood-related disturbance frequency over the last 50 years, drives a change in channel pattern. Where groundwater is shallower, vegetation encroachment rates were high and as flood-related disturbance decreased, the river has shifted towards a meandering state. Where groundwater was deeper, vegetation growth was limited by water-access and thus vegetation encroachment rates were low. Even though there was a

  3. Reconfigurable virtual electrowetting channels.

    PubMed

    Banerjee, Ananda; Kreit, Eric; Liu, Yuguang; Heikenfeld, Jason; Papautsky, Ian

    2012-02-21

    Lab-on-a-chip systems rely on several microfluidic paradigms. The first uses a fixed layout of continuous microfluidic channels. Such lab-on-a-chip systems are almost always application specific and far from a true "laboratory." The second involves electrowetting droplet movement (digital microfluidics), and allows two-dimensional computer control of fluidic transport and mixing. The merging of the two paradigms in the form of programmable electrowetting channels takes advantage of both the "continuous" functionality of rigid channels based on which a large number of applications have been developed to date and the "programmable" functionality of digital microfluidics that permits electrical control of on-chip functions. In this work, we demonstrate for the first time programmable formation of virtual microfluidic channels and their continuous operation with pressure driven flows using an electrowetting platform. Experimental, theoretical, and numerical analyses of virtual channel formation with biologically relevant electrolyte solutions and electrically-programmable reconfiguration are presented. We demonstrate that the "wall-less" virtual channels can be formed reliably and rapidly, with propagation rates of 3.5-3.8 mm s(-1). Pressure driven transport in these virtual channels at flow rates up to 100 μL min(-1) is achievable without distortion of the channel shape. We further demonstrate that these virtual channels can be switched on-demand between multiple inputs and outputs. Ultimately, we envision a platform that would provide rapid prototyping of microfluidic concepts and would be capable of a vast library of functions and benefitting applications from clinical diagnostics in resource-limited environments to rapid system prototyping to high throughput pharmaceutical applications.

  4. Experiments with a Supersonic Multi-Channel Radial Diffuser.

    DTIC Science & Technology

    1980-09-01

    unlimited. 17 . DISTRIBUTION STATEMENT (o the *bsta~c entered nRItok 20, it dffttt Iton, Report) IS. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue o...Improvements 17 VI SIGNIFICANT TEST RESULTS 20 1. General Considerations 20 2. Typical Radial Diffuser Performance 20 3. Flow Stability Experiments 22 VIII...Adjustments Indicated 39 16 Comparison of the Single Channel Performances for Two Extreme Channel Geometries 40 17 Typical Radial Diffuser Performance

  5. Channel Access in Erlang

    SciTech Connect

    Nicklaus, Dennis J.

    2013-10-13

    We have developed an Erlang language implementation of the Channel Access protocol. Included are low-level functions for encoding and decoding Channel Access protocol network packets as well as higher level functions for monitoring or setting EPICS process variables. This provides access to EPICS process variables for the Fermilab Acnet control system via our Erlang-based front-end architecture without having to interface to C/C++ programs and libraries. Erlang is a functional programming language originally developed for real-time telecommunications applications. Its network programming features and list management functions make it particularly well-suited for the task of managing multiple Channel Access circuits and PV monitors.

  6. ARQ on fading channels

    NASA Astrophysics Data System (ADS)

    Beirouti, Patrick; Leib, Harry; Morgera, Salvatore D.

    A recursive procedure for obtaining a (2 to the power n)-state extended Gilbert-Elliott fading channel model suitable for n-bit block codes is described. The extended model may be used for numerical assessment of the throughput of a variety of popular automatic repeat-request schemes used over fading channels such as those encountered in mobile communications systems. Computationally efficient lower and upper performance bounds are also developed for low memory fading channels. It is found that the throughput of the stop-and-wait protocol exhibits a maximum; therefore, there exists an optimum codeword length for this automatic repeat-request scheme.

  7. Fractional channel multichannel analyzer

    DOEpatents

    Brackenbush, Larry W.; Anderson, Gordon A.

    1994-01-01

    A multichannel analyzer incorporating the features of the present invention obtains the effect of fractional channels thus greatly reducing the number of actual channels necessary to record complex line spectra. This is accomplished by using an analog-to-digital converter in the asynscronous mode, i.e., the gate pulse from the pulse height-to-pulse width converter is not synchronized with the signal from a clock oscillator. This saves power and reduces the number of components required on the board to achieve the effect of radically expanding the number of channels without changing the circuit board.

  8. Fractional channel multichannel analyzer

    DOEpatents

    Brackenbush, L.W.; Anderson, G.A.

    1994-08-23

    A multichannel analyzer incorporating the features of the present invention obtains the effect of fractional channels thus greatly reducing the number of actual channels necessary to record complex line spectra. This is accomplished by using an analog-to-digital converter in the asynchronous mode, i.e., the gate pulse from the pulse height-to-pulse width converter is not synchronized with the signal from a clock oscillator. This saves power and reduces the number of components required on the board to achieve the effect of radically expanding the number of channels without changing the circuit board. 9 figs.

  9. Inverse coupling in leak and voltage-activated K+ channel gates underlies distinct roles in electrical signaling.

    PubMed

    Ben-Abu, Yuval; Zhou, Yufeng; Zilberberg, Noam; Yifrach, Ofer

    2009-01-01

    Voltage-activated (Kv) and leak (K(2P)) K(+) channels have key, yet distinct, roles in electrical signaling in the nervous system. Here we examine how differences in the operation of the activation and slow inactivation pore gates of Kv and K(2P) channels underlie their unique roles in electrical signaling. We report that (i) leak K(+) channels possess a lower activation gate, (ii) the activation gate is an important determinant controlling the conformational stability of the K(+) channel pore, (iii) the lower activation and upper slow inactivation gates of leak channels cross-talk and (iv) unlike Kv channels, where the two gates are negatively coupled, these two gates are positively coupled in K(2P) channels. Our results demonstrate how basic thermodynamic properties of the K(+) channel pore, particularly conformational stability and coupling between gates, underlie the specialized roles of Kv and K(2P) channel families in electrical signaling.

  10. Ion Channels in Epithelial Cells

    NASA Astrophysics Data System (ADS)

    Palmer, Lawrence G.

    Ion channels in epithelial cells serve to move ions, and in some cases fluid, between compartments of the body. This function of the transfer of material is fundamentally different from that of the transfer of information, which is the main job of most channels in excitable cells. Nevertheless the basic construction of the channels is similar in many respects in the two tissue types. This chapter reviews the nature of channels in epithelia and discusses how their functions have evolved to accomplish the basic tasks for which they are responsible. I will focus on three channel types: epithelial Na+ channels, inward-rectifier K+ channels, and CFTR Cl- channels.

  11. 28-Channel rotary transformer

    NASA Technical Reports Server (NTRS)

    Mclyman, W. T.

    1981-01-01

    Transformer transmits power and digital data across rotating interface. Array has many parallel data channels, each with potential l megabaud data rate. Ferrite-cored transformers are spaced along rotor; airgap between them reduces crosstalk.

  12. A Simple Water Channel

    ERIC Educational Resources Information Center

    White, A. S.

    1976-01-01

    Describes a simple water channel, for use with an overhead projector. It is run from a water tap and may be used for flow visualization experiments, including the effect of streamlining and elementary building aerodynamics. (MLH)

  13. Chondrocyte channel transcriptomics

    PubMed Central

    Lewis, Rebecca; May, Hannah; Mobasheri, Ali; Barrett-Jolley, Richard

    2013-01-01

    To date, a range of ion channels have been identified in chondrocytes using a number of different techniques, predominantly electrophysiological and/or biomolecular; each of these has its advantages and disadvantages. Here we aim to compare and contrast the data available from biophysical and microarray experiments. This letter analyses recent transcriptomics datasets from chondrocytes, accessible from the European Bioinformatics Institute (EBI). We discuss whether such bioinformatic analysis of microarray datasets can potentially accelerate identification and discovery of ion channels in chondrocytes. The ion channels which appear most frequently across these microarray datasets are discussed, along with their possible functions. We discuss whether functional or protein data exist which support the microarray data. A microarray experiment comparing gene expression in osteoarthritis and healthy cartilage is also discussed and we verify the differential expression of 2 of these genes, namely the genes encoding large calcium-activated potassium (BK) and aquaporin channels. PMID:23995703

  14. Fractures and Channels

    NASA Image and Video Library

    2013-01-22

    This image from NASA 2001 Mars Odyssey spacecraft of the Claritas Fossae region illustrates how fractures affect other features. In this instance, the fractures control the path of several channels from upper right towards lower left.

  15. A Simple Water Channel

    ERIC Educational Resources Information Center

    White, A. S.

    1976-01-01

    Describes a simple water channel, for use with an overhead projector. It is run from a water tap and may be used for flow visualization experiments, including the effect of streamlining and elementary building aerodynamics. (MLH)

  16. Proton channel models

    PubMed Central

    Pupo, Amaury; Baez-Nieto, David; Martínez, Agustín; Latorre, Ramón; González, Carlos

    2014-01-01

    Voltage-gated proton channels are integral membrane proteins with the capacity to permeate elementary particles in a voltage and pH dependent manner. These proteins have been found in several species and are involved in various physiological processes. Although their primary topology is known, lack of details regarding their structures in the open conformation has limited analyses toward a deeper understanding of the molecular determinants of their function and regulation. Consequently, the function-structure relationships have been inferred based on homology models. In the present work, we review the existing proton channel models, their assumptions, predictions and the experimental facts that support them. Modeling proton channels is not a trivial task due to the lack of a close homolog template. Hence, there are important differences between published models. This work attempts to critically review existing proton channel models toward the aim of contributing to a better understanding of the structural features of these proteins. PMID:24755912

  17. Experimental and Numerical Investigation of Flows in Expanding Channels

    SciTech Connect

    Vorobieff, Peter; Putkaradze, Vakhtang

    2008-10-24

    We present an experimental realization of the classical Jeffery-Hamel flows inside a wedge-shaped channel. We compare the measured velocity fields with the predictions of Jeffery-Hamel theory. A detailed experimental study of bifurcation diagrams for the solutions reveals the absolute stability of the pure outflow solution and an interesting hysteretic structure for bifurcations. We also observe a multiple vortex flow regime predicted earlier numerically and analytically. Experimental studies of the stability of the flow to perturbations at the channel exit are also conducted.

  18. Chloride channels in stroke

    PubMed Central

    Zhang, Ya-ping; Zhang, Hao; Duan, Dayue Darrel

    2013-01-01

    Vascular remodeling of cerebral arterioles, including proliferation, migration, and apoptosis of vascular smooth muscle cells (VSMCs), is the major cause of changes in the cross-sectional area and diameter of the arteries and sudden interruption of blood flow or hemorrhage in the brain, ie, stroke. Accumulating evidence strongly supports an important role for chloride (Cl−) channels in vascular remodeling and stroke. At least three Cl− channel genes are expressed in VSMCs: 1) the TMEM16A (or Ano1), which may encode the calcium-activated Cl− channels (CACCs); 2) the CLC-3 Cl− channel and Cl−/H+ antiporter, which is closely related to the volume-regulated Cl− channels (VRCCs); and 3) the cystic fibrosis transmembrane conductance regulator (CFTR), which encodes the PKA- and PKC-activated Cl− channels. Activation of the CACCs by agonist-induced increase in intracellular Ca2+ causes membrane depolarization, vasoconstriction, and inhibition of VSMC proliferation. Activation of VRCCs by cell volume increase or membrane stretch promotes the production of reactive oxygen species, induces proliferation and inhibits apoptosis of VSMCs. Activation of CFTR inhibits oxidative stress and may prevent the development of hypertension. In addition, Cl− current mediated by gamma-aminobutyric acid (GABA) receptor has also been implicated a role in ischemic neuron death. This review focuses on the functional roles of Cl− channels in the development of stroke and provides a perspective on the future directions for research and the potential to develop Cl− channels as new targets for the prevention and treatment of stroke. PMID:23103617

  19. Cl(-) channels in apoptosis.

    PubMed

    Wanitchakool, Podchanart; Ousingsawat, Jiraporn; Sirianant, Lalida; MacAulay, Nanna; Schreiber, Rainer; Kunzelmann, Karl

    2016-10-01

    A remarkable feature of apoptosis is the initial massive cell shrinkage, which requires opening of ion channels to allow release of K(+), Cl(-), and organic osmolytes to drive osmotic water movement and cell shrinkage. This article focuses on the role of the Cl(-) channels LRRC8, TMEM16/anoctamin, and cystic fibrosis transmembrane conductance regulator (CFTR) in cellular apoptosis. LRRC8A-E has been identified as a volume-regulated anion channel expressed in many cell types. It was shown to be required for regulatory and apoptotic volume decrease (RVD, AVD) in cultured cell lines. Its presence also determines sensitivity towards cytostatic drugs such as cisplatin. Recent data point to a molecular and functional relationship of LRRC8A and anoctamins (ANOs). ANO6, 9, and 10 (TMEM16F, J, and K) augment apoptotic Cl(-) currents and AVD, but it remains unclear whether these anoctamins operate as Cl(-) channels or as regulators of other apoptotic Cl(-) channels, such as LRRC8. CFTR has been known for its proapoptotic effects for some time, and this effect may be based on glutathione release from the cell and increase in cytosolic reactive oxygen species (ROS). Although we find that CFTR is activated by cell swelling, it is possible that CFTR serves RVD/AVD through accumulation of ROS and activation of independent membrane channels such as ANO6. Thus activation of ANO6 will support cell shrinkage and induce additional apoptotic events, such as membrane phospholipid scrambling.

  20. Fracture channel waves

    NASA Astrophysics Data System (ADS)

    Nihei, Kurt T.; Yi, Weidong; Myer, Larry R.; Cook, Neville G. W.; Schoenberg, Michael

    1999-03-01

    The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh-Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A0 mode) and demonstrates the ease with which a fracture channel wave can be generated and detected.

  1. Determinants of Water Permeability through Nanoscopic Hydrophilic Channels

    PubMed Central

    Portella, Guillem; de Groot, Bert L.

    2009-01-01

    Naturally occurring pores show a variety of polarities and sizes that are presumably directly linked to their biological function. Many biological channels are selective toward permeants similar or smaller in size than water molecules, and therefore their pores operate in the regime of single-file water pores. Intrinsic factors affecting water permeability through such pores include the channel-membrane match, the structural stability of the channel, the channel geometry and channel-water affinity. We present an extensive molecular dynamics study on the role of the channel geometry and polarity on the water osmotic and diffusive permeability coefficients. We show that the polarity of the naturally occurring peptidic channels is close to optimal for water permeation, and that the water mobility for a wide range of channel polarities is essentially length independent. By systematically varying the geometry and polarity of model hydrophilic pores, based on the fold of gramicidin A, the water density, occupancy, and permeability are studied. Our focus is on the characterization of the transition between different permeation regimes in terms of the structure of water in the pores, the average pore occupancy and the dynamics of the permeating water molecules. We show that a general relationship between osmotic and diffusive water permeability coefficients in the single-file regime accounts for the time averaged pore occupancy, and that the dynamics of the permeating water molecules through narrow non single file channels effectively behaves like independent single-file columns. PMID:19186131

  2. Curved-channel microchannel array plates. [photoelectric detectors

    NASA Technical Reports Server (NTRS)

    Timothy, J. G.

    1981-01-01

    The microchannel array plate (MCP) is a photoelectric detector with an imaging capability comparable to that of a photographic plate. Recently MCPs in which the channels are curved to inhibit ion feedback have become available. These devices represent a major advance in MCP technology, since a single curved-channel MCP can be operated stably at high gain in the pulse-counting mode without any of the problems of stability of response or short lifetime reported for 'chevron' MCP detectors. Attention is given to the mode of operation of channel electron multipliers (CEM) and MCP, curved-channel MCP, test procedures, and performance characteristics. The accumulated test data show that the fundamental operating characteristics of the curved-channel MCP are directly related to those for the CEM.

  3. Long-Term Coastal Inlet Channel Area Stability

    DTIC Science & Technology

    2003-01-01

    scour may occur. Table 1. Examples of “Low Keulegan K” Inlets In the United States* Inlet Keulegan K Value New River , NC 0.08 Barnegat, NJ 0.09...Shinnecock, NY 0.15 Ft. Pierce, FL 0.16 Chincoteague, VA 0.16 St. Johns, FL 0.21 Indian River , DE 0.22 Ponce de Leon, FL 0.25 St. Lucie, FL...0.26 Ocean City, MD 0.29 Beach Haven, NJ 0.31 Jones, NY 0.35 Beaufort, NC 0.41 North Edisto , SC 0.42 Jupiter, FL 0.44 Winyah Bay, SC 0.45 Bakers

  4. Riprap Stability: Studies in Near-Prototype Size Laboratory Channel

    DTIC Science & Technology

    1992-06-01

    34 Prepared under Contract Nonr-2121(26) by the University of Chicago, Chicago, IL , for Office of Naval Research, Arlington, VA. Neill, C. R. 1967...4 -4 Ln r-. tr- r-r-- ý4- 41 W C) E-4 CU 41 0 -4 - E-- Il CIJ 0J4 CN 04C%J C%4 14 04 C%4 CN CN e J (N(NCN (4 .- 4 -4 C14-4 m 000 00 LA 0 000000...E3 Lj La. 0-J > , La - .,Li d. 606 l to - IL L) PLAT 5 M ’p z %LI >p I- m" Lii> W Q-.J -C3- ~ W4 w -0 0 Cu U, Cu > 4.4 CD, L6J cli W) 000~~ 0000 ,0

  5. STABILIZED OSCILLATOR

    DOEpatents

    Jessen, P.L.; Price, H.J.

    1958-03-18

    This patent relates to sine-wave generators and in particular describes a generator with a novel feedback circuit resulting in improved frequency stability. The generator comprises two triodes having a common cathode circuit connected to oscillate at a frequency and amplitude at which the loop galn of the circutt ls unity, and another pair of triodes having a common cathode circuit arranged as a conventional amplifier. A signal is conducted from the osciliator through a frequency selective network to the amplifier and fed back to the osciliator. The unique feature of the feedback circuit is the amplifier operates in the nonlinear portion of its tube characteristics thereby providing a relatively constant feedback voltage to the oscillator irrespective of the amplitude of its input signal.

  6. Stabilizing brokerage

    PubMed Central

    Stovel, Katherine; Golub, Benjamin; Milgrom, Eva M. Meyersson

    2011-01-01

    A variety of social and economic arrangements exist to facilitate the exchange of goods, services, and information over gaps in social structure. Each of these arrangements bears some relationship to the idea of brokerage, but this brokerage is rarely like the pure and formal economic intermediation seen in some modern markets. Indeed, for reasons illuminated by existing sociological and economic models, brokerage is a fragile relationship. In this paper, we review the causes of instability in brokerage and identify three social mechanisms that can stabilize fragile brokerage relationships: social isolation, broker capture, and organizational grafting. Each of these mechanisms rests on the emergence or existence of supporting institutions. We suggest that organizational grafting may be the most stable and effective resolution to the tensions inherent in brokerage, but it is also the most institutionally demanding. PMID:22198763

  7. Optical Communications Channel Combiner

    NASA Technical Reports Server (NTRS)

    Quirk, Kevin J.; Quirk, Kevin J.; Nguyen, Danh H.; Nguyen, Huy

    2012-01-01

    NASA has identified deep-space optical communications links as an integral part of a unified space communication network in order to provide data rates in excess of 100 Mb/s. The distances and limited power inherent in a deep-space optical downlink necessitate the use of photon-counting detectors and a power-efficient modulation such as pulse position modulation (PPM). For the output of each photodetector, whether from a separate telescope or a portion of the detection area, a communication receiver estimates a log-likelihood ratio for each PPM slot. To realize the full effective aperture of these receivers, their outputs must be combined prior to information decoding. A channel combiner was developed to synchronize the log-likelihood ratio (LLR) sequences of multiple receivers, and then combines these into a single LLR sequence for information decoding. The channel combiner synchronizes the LLR sequences of up to three receivers and then combines these into a single LLR sequence for output. The channel combiner has three channel inputs, each of which takes as input a sequence of four-bit LLRs for each PPM slot in a codeword via a XAUI 10 Gb/s quad optical fiber interface. The cross-correlation between the channels LLR time series are calculated and used to synchronize the sequences prior to combining. The output of the channel combiner is a sequence of four-bit LLRs for each PPM slot in a codeword via a XAUI 10 Gb/s quad optical fiber interface. The unit is controlled through a 1 Gb/s Ethernet UDP/IP interface. A deep-space optical communication link has not yet been demonstrated. This ground-station channel combiner was developed to demonstrate this capability and is unique in its ability to process such a signal.

  8. Bimodal regulation of an Elk subfamily K+ channel by phosphatidylinositol 4,5-bisphosphate.

    PubMed

    Li, Xiaofan; Anishkin, Andriy; Liu, Hansi; van Rossum, Damian B; Chintapalli, Sree V; Sassic, Jessica K; Gallegos, David; Pivaroff-Ward, Kendra; Jegla, Timothy

    2015-11-01

    Phosphatidylinositol 4,5-bisphosphate (PIP2) regulates Shaker K+ channels and voltage-gated Ca2+ channels in a bimodal fashion by inhibiting voltage activation while stabilizing open channels. Bimodal regulation is conserved in hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, but voltage activation is enhanced while the open channel state is destabilized. The proposed sites of PIP2 regulation in these channels include the voltage-sensor domain (VSD) and conserved regions of the proximal cytoplasmic C terminus. Relatively little is known about PIP2 regulation of Ether-á-go-go (EAG) channels, a metazoan-specific family of K+ channels that includes three gene subfamilies, Eag (Kv10), Erg (Kv11), and Elk (Kv12). We examined PIP2 regulation of the Elk subfamily potassium channel human Elk1 to determine whether bimodal regulation is conserved within the EAG K+ channel family. Open-state stabilization by PIP2 has been observed in human Erg1, but the proposed site of regulation in the distal C terminus is not conserved among EAG family channels. We show that PIP2 strongly inhibits voltage activation of Elk1 but also stabilizes the open state. This stabilization produces slow deactivation and a mode shift in voltage gating after activation. However, removal of PIP2 has the net effect of enhancing Elk1 activation. R347 in the linker between the VSD and pore (S4-S5 linker) and R479 near the S6 activation gate are required for PIP2 to inhibit voltage activation. The ability of PIP2 to stabilize the open state also requires these residues, suggesting an overlap in sites central to the opposing effects of PIP2 on channel gating. Open-state stabilization in Elk1 requires the N-terminal eag domain (PAS domain + Cap), and PIP2-dependent stabilization is enhanced by a conserved basic residue (K5) in the Cap. Our data shows that PIP2 can bimodally regulate voltage gating in EAG family channels, as has been proposed for Shaker and HCN channels. PIP2 regulation

  9. Entanglement-assisted codeword stabilized quantum codes

    SciTech Connect

    Shin, Jeonghwan; Heo, Jun; Brun, Todd A.

    2011-12-15

    Entangled qubits can increase the capacity of quantum error-correcting codes based on stabilizer codes. In addition, by using entanglement quantum stabilizer codes can be construct from classical linear codes that do not satisfy the dual-containing constraint. We show that it is possible to construct both additive and nonadditive quantum codes using the codeword stabilized quantum code framework. Nonadditive codes may offer improved performance over the more common stabilizer codes. Like other entanglement-assisted codes, the encoding procedure acts only on the qubits on Alice's side, and only these qubits are assumed to pass through the channel. However, errors in the codeword stabilized quantum code framework give rise to effective Z errors on Bob's side. We use this scheme to construct entanglement-assisted nonadditive quantum codes, in particular, ((5,16,2;1)) and ((7,4,5;4)) codes.

  10. Pool spacing in forest channels

    Treesearch

    David R. Montgomery; John M. Buffington; Richard D. Smith; Kevin M. Schmidt; George Pess

    1995-01-01

    Field surveys of stream channels in forested mountain drainage basins in southeast Alaska and Washington reveal that pool spacing depends on large woody debris (LWD) loading and channel type, slope, and width. Mean pool spacing in pool-riffle, plane-bed, and forced pool-riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1...

  11. MEMS in microfluidic channels.

    SciTech Connect

    Ashby, Carol Iris Hill; Okandan, Murat; Michalske, Terry A.; Sounart, Thomas L.; Matzke, Carolyn M.

    2004-03-01

    Microelectromechanical systems (MEMS) comprise a new class of devices that include various forms of sensors and actuators. Recent studies have shown that microscale cantilever structures are able to detect a wide range of chemicals, biomolecules or even single bacterial cells. In this approach, cantilever deflection replaces optical fluorescence detection thereby eliminating complex chemical tagging steps that are difficult to achieve with chip-based architectures. A key challenge to utilizing this new detection scheme is the incorporation of functionalized MEMS structures within complex microfluidic channel architectures. The ability to accomplish this integration is currently limited by the processing approaches used to seal lids on pre-etched microfluidic channels. This report describes Sandia's first construction of MEMS instrumented microfluidic chips, which were fabricated by combining our leading capabilities in MEMS processing with our low-temperature photolithographic method for fabricating microfluidic channels. We have explored in-situ cantilevers and other similar passive MEMS devices as a new approach to directly sense fluid transport, and have successfully monitored local flow rates and viscosities within microfluidic channels. Actuated MEMS structures have also been incorporated into microfluidic channels, and the electrical requirements for actuation in liquids have been quantified with an elegant theory. Electrostatic actuation in water has been accomplished, and a novel technique for monitoring local electrical conductivities has been invented.

  12. Mitochondrial Ion Channels

    PubMed Central

    O’Rourke, Brian

    2009-01-01

    In work spanning more than a century, mitochondria have been recognized for their multifunctional roles in metabolism, energy transduction, ion transport, inheritance, signaling, and cell death. Foremost among these tasks is the continuous production of ATP through oxidative phosphorylation, which requires a large electrochemical driving force for protons across the mitochondrial inner membrane. This process requires a membrane with relatively low permeability to ions to minimize energy dissipation. However, a wealth of evidence now indicates that both selective and nonselective ion channels are present in the mitochondrial inner membrane, along with several known channels on the outer membrane. Some of these channels are active under physiological conditions, and others may be activated under pathophysiological conditions to act as the major determinants of cell life and death. This review summarizes research on mitochondrial ion channels and efforts to identify their molecular correlates. Except in a few cases, our understanding of the structure of mitochondrial ion channels is limited, indicating the need for focused discovery in this area. PMID:17059356

  13. TRP channel gating physiology.

    PubMed

    Nieto-Posadas, Andrés; Jara-Oseguera, Andrés; Rosenbaum, Tamara

    2011-01-01

    Transient Receptor Potential (TRP) cation channels participate in several processes of vital importance in cell and organism physiology, and have been demonstrated to participate in the detection of sensory stimuli. The thermo TRP's reviewed: TRPV1 (vanilloid 1), TRPM8 (melastatin 8) and TRPA1 (ankyrin-like 1) are known to integrate different chemical and physical stimuli such as changes in temperature and sensing different irritant or pungent compounds. However, despite the physiological importance of these channels the mechanisms by which they detect incoming stimuli, how the sensing domains are coupled to channel gating and how these processes are connected to specific structural regions in the channel are not fully understood, but valuable information is available. Many sites involved in agonist detection have been characterized and gating models that describe many features of the channel's behavior have been put forward. In this review we will survey some of the key findings concerning the structural and molecular mechanisms of TRPV1, TRPA1 and TRPM8 activation.

  14. Channel Identification Machines

    PubMed Central

    Lazar, Aurel A.; Slutskiy, Yevgeniy B.

    2012-01-01

    We present a formal methodology for identifying a channel in a system consisting of a communication channel in cascade with an asynchronous sampler. The channel is modeled as a multidimensional filter, while models of asynchronous samplers are taken from neuroscience and communications and include integrate-and-fire neurons, asynchronous sigma/delta modulators and general oscillators in cascade with zero-crossing detectors. We devise channel identification algorithms that recover a projection of the filter(s) onto a space of input signals loss-free for both scalar and vector-valued test signals. The test signals are modeled as elements of a reproducing kernel Hilbert space (RKHS) with a Dirichlet kernel. Under appropriate limiting conditions on the bandwidth and the order of the test signal space, the filter projection converges to the impulse response of the filter. We show that our results hold for a wide class of RKHSs, including the space of finite-energy bandlimited signals. We also extend our channel identification results to noisy circuits. PMID:23227035

  15. TRP Channels and Analgesia

    PubMed Central

    Premkumar, Louis S.; Abooj, Mruvil

    2013-01-01

    Since cloning and characterizing the first nociceptive ion channel Transient Receptor Potential (TRP) Vanilloid 1 (TRPV1), other TRP channels involved in nociception have been cloned and characterized, which include TRP Vanilloid 2 (TRPV2), TRP Vanilloid 3 (TRPV3), TRP Vanilloid 4 (TRPV4), TRP Ankyrin 1 (TRPA1) and TRP Melastatin 8 (TRPM8), more recently TRP Canonical 1, 5, 6 (TRPC1, 5, 6), TRP Melastatin 2 (TRPM2) and TRP Melastatin 3 (TRPM3). These channels are predominantly expressed in C and Aδ nociceptors and transmit noxious thermal, mechanical and chemical sensitivities. TRP channels are modulated by pro-inflammatory mediators, neuropeptides and cytokines. Significant advances have been made targeting these receptors either by antagonists or agonists to treat painful conditions. In this review, we will discuss TRP channels as targets for next generation analgesics and the side effects that may ensue as a result of blocking/activating these receptors, because they are also involved in physiological functions such as release of vasoactive neuropeptides and regulation of vascular tone, maintenance of the body temperature, gastrointestinal motility, urinary bladder control etc. PMID:22910182

  16. Calcium channels and migraine.

    PubMed

    Pietrobon, Daniela

    2013-07-01

    Missense mutations in CACNA1A, the gene that encodes the pore-forming α1 subunit of human voltage-gated Ca(V)2.1 (P/Q-type) calcium channels, cause a rare form of migraine with aura (familial hemiplegic migraine type 1: FHM1). Migraine is a common disabling brain disorder whose key manifestations are recurrent attacks of unilateral headache that may be preceded by transient neurological aura symptoms. This review, first, briefly summarizes current understanding of the pathophysiological mechanisms that are believed to underlie migraine headache, migraine aura and the onset of a migraine attack, and briefly describes the localization and function of neuronal Ca(V)2.1 channels in the brain regions that have been implicated in migraine pathogenesis. Then, the review describes and discusses i) the functional consequences of FHM1 mutations on the biophysical properties of recombinant human Ca(V)2.1 channels and native Ca(V)2.1 channels in neurons of knockin mouse models carrying the mild R192Q or severe S218L mutations in the orthologous gene, and ii) the functional consequences of these mutations on neurophysiological processes in the cerebral cortex and trigeminovascular system thought to be involved in the pathophysiology of migraine, and the insights into migraine mechanisms obtained from the functional analysis of these processes in FHM1 knockin mice. This article is part of a Special Issue entitled: Calcium channels.

  17. Wideband transhorizon channel characterization

    NASA Astrophysics Data System (ADS)

    Ndzi, David; Austin, John; Vilar, Enric

    2001-09-01

    The paper describes a 31.25 MHz bandwidth wideband channel sounder used to characterize a transhorizon path over the English Channel (La Manche) at 11.64 GHz. The measurements were done continuously for a period of 8 months (June 5, 1996, to January 5, 1997), capturing 515 Mb of data each day. A nonlinear regression technique, singular value decomposition prony (SVD-P), was used to estimate the channel impulse response from the measured transfer function. The received signal levels obtained together with their dynamic signatures were used to categorize the mechanisms into three broad groups: ducting, strong enhancements, and troposcatter. The statistical analysis carried out gave strong correlation between signal levels, delay spread, coherence bandwidth, and Doppler spread. The results also help to highlight the limitation of traditional channel characterization parameters such as delay spread. The investigation has also revealed the potential and propagation conditions of an over the sea transhorizon path as a high-data-rate communication channel. The research has qualified and quantified the interference potential in spectrum reuse and the frequency decorrelation probabilities to combat it.

  18. TRP channels and analgesia.

    PubMed

    Premkumar, Louis S; Abooj, Mruvil

    2013-03-19

    Since cloning and characterizing the first nociceptive ion channel Transient Receptor Potential (TRP) Vanilloid 1 (TRPV1), other TRP channels involved in nociception have been cloned and characterized, which include TRP Vanilloid 2 (TRPV2), TRP Vanilloid 3 (TRPV3), TRP Vanilloid 4 (TRPV4), TRP Ankyrin 1 (TRPA1) and TRP Melastatin 8 (TRPM8), more recently TRP Canonical 1, 5, 6 (TRPC1, 5, 6), TRP Melastatin 2 (TRPM2) and TRP Melastatin 3 (TRPM3). These channels are predominantly expressed in C and Aδ nociceptors and transmit noxious thermal, mechanical and chemical sensitivities. TRP channels are modulated by pro-inflammatory mediators, neuropeptides and cytokines. Significant advances have been made targeting these receptors either by antagonists or agonists to treat painful conditions. In this review, we will discuss TRP channels as targets for next generation analgesics and the side effects that may ensue as a result of blocking/activating these receptors, because they are also involved in physiological functions such as release of vasoactive neuropeptides and regulation of vascular tone, maintenance of the body temperature, gastrointestinal motility, urinary bladder control, etc.

  19. Wakefield Propagation in Plasma Channels

    NASA Astrophysics Data System (ADS)

    Geddes, Cameron; Leemans, Wim; Esarey, Eric; Shadwick, Brad; Wurtele, Johnathan

    2000-10-01

    Characteristics of laser wakefields propagating in plasma channels have been studied at the l'OASIS laser facility at LBNL. Plasma channels are formed in gas jets using the ignitor-heater method[1], allowing control of channel geometry and profile. The channels are characterized by longitudinal and transverse interferometry, giving both radial and longitudinal profiles of the channel. High intensity (>5E17 W/cm^2, 50fs) pulses at 800nm are guided in these channels and are used to create plasma wakes in the channel. Laser propagation in the channel is characterized by output mode images and energies, and the wakes are profiled by longitudinal spectral interferometry. Measurements of channel and wake profiles, and studies of wake dependence on channel parameters will be presented. [1]P.Volfbeyn, E.Esarey, W.P. Leemans, Phys Plasmas 6, 2269 (1999)

  20. Bidirectional control of BK channel open probability by CAMKII and PKC in medial vestibular nucleus neurons

    PubMed Central

    van Welie, Ingrid

    2011-01-01

    Large conductance K+ (BK) channels are a key determinant of neuronal excitability. Medial vestibular nucleus (MVN) neurons regulate eye movements to ensure image stabilization during head movement, and changes in their intrinsic excitability may play a critical role in plasticity of the vestibulo-ocular reflex. Plasticity of intrinsic excitability in MVN neurons is mediated by kinases, and BK channels influence excitability, but whether endogenous BK channels are directly modulated by kinases is unknown. Double somatic patch-clamp recordings from MVN neurons revealed large conductance potassium channel openings during spontaneous action potential firing. These channels displayed Ca2+ and voltage dependence in excised patches, identifying them as BK channels. Recording isolated single channel currents at physiological temperature revealed a novel kinase-mediated bidirectional control in the range of voltages over which BK channels are activated. Application of activated Ca2+/calmodulin-dependent kinase II (CAMKII) increased BK channel open probability by shifting the voltage activation range towards more hyperpolarized potentials. An opposite shift in BK channel open probability was revealed by inhibition of phosphatases and was occluded by blockade of protein kinase C (PKC), suggesting that active PKC associated with BK channel complexes in patches was responsible for this effect. Accordingly, direct activation of endogenous PKC by PMA induced a decrease in BK open probability. BK channel activity affects excitability in MVN neurons and bidirectional control of BK channels by CAMKII, and PKC suggests that cellular signaling cascades engaged during plasticity may dynamically control excitability by regulating BK channel open probability. PMID:21307321

  1. Channel plate for DNA sequencing

    DOEpatents

    Douthart, Richard J.; Crowell, Shannon L.

    1998-01-01

    This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface.

  2. Channel plate for DNA sequencing

    DOEpatents

    Douthart, R.J.; Crowell, S.L.

    1998-01-13

    This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface. 15 figs.

  3. CARMENES: the VIS channel spectrograph in operation

    NASA Astrophysics Data System (ADS)

    Seifert, W.; Xu, W.; Stahl, O.; Hagen, H. J.; Sánchez Carrasco, M. A.; Veredas, G.; Caballero, J. A.; Guardia, J.; Helmling, J.; Hernandez, L.; Pérez-Calpena, A.; Tulloch, S.; Kaminski, A.; Zechmeister, M.; Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners, A.; Mandel, H.

    2016-08-01

    CARMENES is a fiber-fed high-resolution Echelle spectrograph for the Calar Alto 3.5m telescope. The instrument is built by a German-Spanish consortium under the lead of the Landessternwarte Heidelberg. The search for planets around M dwarfs with a radial velocity of 1 m/s is the main focus of the planned science. Two channels, one for the visible, another for the near-infrared, will allow observations in the complete wavelength range from 550 to 1700 nm. To ensure the stability, the instrument is working in vacuum in a thermally controlled environment. The VIS channel spectrograph is covering the visible wavelength range from 0.55 to 0.95 μm with a spectral resolution of R=93,400 in a thermally and pressure-wise very stable environment. The VIS channel spectrograph started science operation in January 2016. Here we present the opto-mechanical and system design of the channel with the focus on the (re-)integration phase at the observatory and the measured performance during the testing and commissioning periods, including the lessons learned.

  4. Chaos in quantum channels

    DOE PAGES

    Hosur, Pavan; Qi, Xiao-Liang; Roberts, Daniel A.; ...

    2016-02-01

    For this research, we study chaos and scrambling in unitary channels by considering their entanglement properties as states. Using out-of-time-order correlation functions to diagnose chaos, we characterize the ability of a channel to process quantum information. We show that the generic decay of such correlators implies that any input subsystem must have near vanishing mutual information with almost all partitions of the output. Additionally, we propose the negativity of the tripartite information of the channel as a general diagnostic of scrambling. This measures the delocalization of information and is closely related to the decay of out-of-time-order correlators. We back upmore » our results with numerics in two non-integrable models and analytic results in a perfect tensor network model of chaotic time evolution. In conclusion, these results show that the butterfly effect in quantum systems implies the information-theoretic definition of scrambling.« less

  5. Chaos in quantum channels

    SciTech Connect

    Hosur, Pavan; Qi, Xiao-Liang; Roberts, Daniel A.; Yoshida, Beni

    2016-02-01

    For this research, we study chaos and scrambling in unitary channels by considering their entanglement properties as states. Using out-of-time-order correlation functions to diagnose chaos, we characterize the ability of a channel to process quantum information. We show that the generic decay of such correlators implies that any input subsystem must have near vanishing mutual information with almost all partitions of the output. Additionally, we propose the negativity of the tripartite information of the channel as a general diagnostic of scrambling. This measures the delocalization of information and is closely related to the decay of out-of-time-order correlators. We back up our results with numerics in two non-integrable models and analytic results in a perfect tensor network model of chaotic time evolution. In conclusion, these results show that the butterfly effect in quantum systems implies the information-theoretic definition of scrambling.

  6. Entanglement-saving channels

    SciTech Connect

    Lami, L.; Giovannetti, V.

    2016-03-15

    The set of Entanglement Saving (ES) quantum channels is introduced and characterized. These are completely positive, trace preserving transformations which when acting locally on a bipartite quantum system initially prepared into a maximally entangled configuration, preserve its entanglement even when applied an arbitrary number of times. In other words, a quantum channel ψ is said to be ES if its powers ψ{sup n} are not entanglement-breaking for all integers n. We also characterize the properties of the Asymptotic Entanglement Saving (AES) maps. These form a proper subset of the ES channels that is constituted by those maps that not only preserve entanglement for all finite n but which also sustain an explicitly not null level of entanglement in the asymptotic limit n → ∞. Structure theorems are provided for ES and for AES maps which yield an almost complete characterization of the former and a full characterization of the latter.

  7. TRP channels and pain.

    PubMed

    Julius, David

    2013-01-01

    Nociception is the process whereby primary afferent nerve fibers of the somatosensory system detect noxious stimuli. Pungent irritants from pepper, mint, and mustard plants have served as powerful pharmacological tools for identifying molecules and mechanisms underlying this initial step of pain sensation. These natural products have revealed three members of the transient receptor potential (TRP) ion channel family--TRPV1, TRPM8, and TRPA1--as molecular detectors of thermal and chemical stimuli that activate sensory neurons to produce acute or persistent pain. Analysis of TRP channel function and expression has validated the existence of nociceptors as a specialized group of somatosensory neurons devoted to the detection of noxious stimuli. These studies are also providing insight into the coding logic of nociception and how specification of nociceptor subtypes underlies behavioral discrimination of noxious thermal, chemical, and mechanical stimuli. Biophysical and pharmacological characterization of these channels has provided the intellectual and technical foundation for developing new classes of analgesic drugs.

  8. Cryogenic microwave channelized receiver

    SciTech Connect

    Rauscher, C.; Pond, J.M.; Tait, G.B.

    1996-07-01

    The channelized receiver being presented demonstrates the use of high temperature superconductor technology in a microwave system setting where superconductor, microwave-monolithic-integrated-circuit, and hybrid-integrated-circuit components are united in one package and cooled to liquid-nitrogen temperatures. The receiver consists of a superconducting X-band four-channel demultiplexer with 100-MHz-wide channels, four commercial monolithically integrated mixers, and four custom-designed hybrid-circuit detectors containing heterostructure ramp diodes. The composite receiver unit has been integrated into the payload of the second-phase NRL high temperature superconductor space experiment (HTSSE-II). Prior to payload assembly, the response characteristics of the receiver were measured as functions of frequency, temperature, and drive levels. The article describes the circuitry, discusses the key issues related to design and implementation, and summarizes the experimental results.

  9. Nanoscale Vacuum Channel Transistor.

    PubMed

    Han, Jin-Woo; Moon, Dong-Il; Meyyappan, M

    2017-04-12

    Vacuum tubes that sparked the electronics era had given way to semiconductor transistors. Despite their faster operation and better immunity to noise and radiation compared to the transistors, the vacuum device technology became extinct due to the high power consumption, integration difficulties, and short lifetime of the vacuum tubes. We combine the best of vacuum tubes and modern silicon nanofabrication technology here. The surround gate nanoscale vacuum channel transistor consists of sharp source and drain electrodes separated by sub-50 nm vacuum channel with a source to gate distance of 10 nm. This transistor performs at a low voltage (<5 V) and provides a high drive current (>3 microamperes). The nanoscale vacuum channel transistor can be a possible alternative to semiconductor transistors beyond Moore's law.

  10. Ionic Channels in Thunderclouds

    NASA Astrophysics Data System (ADS)

    Losseva, T. V.; Fomenko, A. S.; Nemtchinov, I. V.

    2007-12-01

    We proceed to study the formation and propagation of ionic channels in thunderclouds in the framework of the model of the corona discharge wave propagation (Fomenko A.S., Losseva T.V., Nemtchinov I.V. The corona discharge waves in thunderclouds and formation of ionic channels // 2004 Fall Meeting. EOS Trans. AGU. 2004. V. 85. ¹ 47. Suppl. Abstract AE23A-0835.). In this model we proposed a hypothesis that the structure of a thundercloud becomes nonuniform due to corona discharge on the drops and ice particles and formation of ionic channels with higher conductivity than the surrounding air. When the onset strength of corona discharge becomes smaller than the electric field strength the corona discharge increases concentrations of ions in a small part of the cloud (a hot spot). An additional charge at opposite ends of the hot spot forms due to polarization process. The increased electric field initiates corona discharge in other parts of the cloud on ice particles and water drops with smaller sizes. The corona discharge front moves as a wave with the velocity of the order of ion drift and formes a highly conductive channel. We model this non-stationary problem with Poisson equation which is solved simultaneously with a simplified set of kinetic equations for ions, small charged particles and electrons (at high electric fields), including ionization due to electronic impact, attachment and formation of positive ions. By applying 3D numerical simulations we obtain the parameters of formed ionic channels with respect to onset electric fields both from large particles (in hot spot) and from small particles (surrounding hot spot), microscopic currents from particles with different sizes and the external electric field in the cloud. The interaction of ionic channels is also investigated. This work was supported by Russian Foundation of Basic Research (Project No 07-05-00998-à).

  11. The neutron channeling phenomenon.

    PubMed

    Khanouchi, A; Sabir, A; Boulkheir, M; Ichaoui, R; Ghassoun, J; Jehouani, A

    1997-01-01

    Shields, used for protection against radiation, are often pierced with vacuum channels for passing cables and other instruments for measurements. The neutron transmission through these shields is an unavoidable phenomenon. In this work we study and discuss the effect of channels on neutron transmission through shields. We consider an infinite homogeneous slab, with a fixed thickness (20 lambda, with lambda the mean free path of the neutron in the slab), which contains a vacuum channel. This slab is irradiated with an infinite source of neutrons on the left side and on the other side (right side) many detectors with windows equal to 2 lambda are placed in order to evaluate the neutron transmission probabilities (Khanouchi, A., Aboubekr, A., Ghassoun, J. and Jehouani, A. (1994) Rencontre Nationale des Jeunes Chercheurs en Physique. Casa Blanca Maroc; Khanouchi, A., Sabir, A., Ghassoun, J. and Jehouani, A. (1995) Premier Congré International des Intéractions Rayonnements Matière. Eljadida Maroc). The neutron history within the slab is simulated by the Monte Carlo method (Booth, T. E. and Hendricks, J. S. (1994) Nuclear Technology 5) and using the exponential biasing technique in order to improve the Monte Carlo calculation (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Aboubker, A. (1994) In Proceedings of the 6th International Symposium on Radiation Physics, Rabat, Morocco). Then different geometries of the vacuum channel have been studied. For each geometry we have determined the detector response and calculated the neutron transmission probability for different detector positions. This neutron transmission probability presents a peak for the detectors placed in front of the vacuum channel. This study allowed us to clearly identify the neutron channeling phenomenon. One application of our study is to detect vacuum defects in materials.

  12. Chryse Outflow Channel

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A color image of the south Chryse basin Valles Marineris outflow channels on Mars; north toward top. The scene shows on the southwest corner the chaotic terrain of the east part of Valles Marineris and two of its related canyons: Eos and Capri Chasmata (south to north). Ganges Chasma lies directly north. The chaos in the southern part of the image gives rise to several outflow channels, Shalbatana, Simud, Tiu, and Ares Valles (left to right), that drained north into the Chryse basin. The mouth of Ares Valles is the site of the Mars Pathfinder lander.

    This image is a composite of Viking medium-resolution images in black and white and low-resolution images in color. The image extends from latitude 20 degrees S. to 20 degrees N. and from longitude 15 degrees to 53 degrees; Mercator projection.

    The south Chryse outflow channels are cut an average of 1 km into the cratered highland terrain. This terrain is about 9 km above datum near Valles Marineris and steadily decreases in elevation to 1 km below datum in the Chryse basin. Shalbatana is relatively narrow (10 km wide) but can reach 3 km in depth. The channel begins at a 2- to 3-km-deep circular depression within a large impact crater, whose floor is partly covered by a chaotic material, and ends in Simud Valles. Tiu and Simud Valles consist of a complex of connected channel floors and chaotic terrain and extend as far south as and connect to eastern Valles Marineris. Ares Vallis originates from discontinuous patches of chaotic terrain within large craters. In the Chryse basin the Ares channel forks; one branch continues northwest into central Chryse Planitia (Latin for plain) and the other extends north into eastern Chryse Planitia.

  13. Chryse Outflow Channel

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A color image of the south Chryse basin Valles Marineris outflow channels on Mars; north toward top. The scene shows on the southwest corner the chaotic terrain of the east part of Valles Marineris and two of its related canyons: Eos and Capri Chasmata (south to north). Ganges Chasma lies directly north. The chaos in the southern part of the image gives rise to several outflow channels, Shalbatana, Simud, Tiu, and Ares Valles (left to right), that drained north into the Chryse basin. The mouth of Ares Valles is the site of the Mars Pathfinder lander.

    This image is a composite of Viking medium-resolution images in black and white and low-resolution images in color. The image extends from latitude 20 degrees S. to 20 degrees N. and from longitude 15 degrees to 53 degrees; Mercator projection.

    The south Chryse outflow channels are cut an average of 1 km into the cratered highland terrain. This terrain is about 9 km above datum near Valles Marineris and steadily decreases in elevation to 1 km below datum in the Chryse basin. Shalbatana is relatively narrow (10 km wide) but can reach 3 km in depth. The channel begins at a 2- to 3-km-deep circular depression within a large impact crater, whose floor is partly covered by a chaotic material, and ends in Simud Valles. Tiu and Simud Valles consist of a complex of connected channel floors and chaotic terrain and extend as far south as and connect to eastern Valles Marineris. Ares Vallis originates from discontinuous patches of chaotic terrain within large craters. In the Chryse basin the Ares channel forks; one branch continues northwest into central Chryse Planitia (Latin for plain) and the other extends north into eastern Chryse Planitia.

  14. Small Ion Channel Linking Molecular Simulations and Electrophysiology

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrzej

    2017-01-01

    Ion channels are pore-forming protein assemblies that mediate the transport of small ions across cell membranes. Otherwise, membrane bilayers would be almost impermeable to ions incapable to traverse the low dielectric constant, hydrophobic membrane core. Ion channels are ubiquitous to all life forms. In humans and other higher organisms they play the central role in conducting nerve impulses, cardiac functions, muscle contraction and apoptosis. On the other extreme of biological complexity, viral ion channels (viroporins) influence many stages of the virus infection cycle either through regulating virus replication, such as entry, assembly and release or modulating the electrochemical balance in the subcellular compartments of host cells. Ion channels were crucial components of protocells. Their emergence facilitated adaptation of nascent life to different environmental conditions. The earliest ion channels must have been much simpler than most of their modern ancestors. Viral channels are among only a few naturally occurring models to study the structure, function and evolution of primordial channels. Experimental studies of these properties are difficult and often unreliable. In principle, computational methods, and molecular dynamics (MD) simulations in particular, can aid in providing information about both the structure and the function of ion channels. However, MD suffers from its own problems, such as inability to access sufficiently long time scales or limited accuracy of force fields. It is, therefore, essential to determine the reliability of MD simulations. We propose to do so on the basis of two criteria. One is channel stability on time scales that extend for several microseconds or longer. The other is the ability to reproduce the measured ionic conductance as a function of applied voltage. If both the stability and the calculated ionic conductance are satisfactory it will greatly increase our confidence that the structure and the function of a

  15. Zeolites: Exploring Molecular Channels

    SciTech Connect

    Arslan, Ilke; Derewinski, Mirek

    2015-05-22

    Synthetic zeolites contain microscopic channels, sort of like a sponge. They have many uses, such as helping laundry detergent lather, absorbing liquid in kitty litter, and as catalysts to produce fuel. Of the hundreds of types of zeolites, only about 15 are used for catalysis. PNNL catalysis scientists Ilke Arslan and Mirek Derewinksi are studying these zeolites to understand what make them special. By exploring the mystery of these microscopic channels, their fundamental findings will help design better catalysts for applications such as biofuel production.

  16. Wide, Branching Channels

    NASA Image and Video Library

    2017-01-11

    Southern spring on Mars brings sublimation of the seasonal dry ice polar cap. Gas trapped under the seasonal ice sheet carves channels on its way to escaping to the atmosphere. At this site, the channels are wider than we see elsewhere on Mars, perhaps meaning that the spider-like (or more scientifically, "araneiform") terrain here is older, or that the surface is more easily eroded. Seasonal fans of eroded surface material, pointed in two different directions, are deposited on the remaining ice. http://photojournal.jpl.nasa.gov/catalog/PIA13151

  17. Zeolites: Exploring Molecular Channels

    ScienceCinema

    Arslan, Ilke; Derewinski, Mirek

    2016-07-12

    Synthetic zeolites contain microscopic channels, sort of like a sponge. They have many uses, such as helping laundry detergent lather, absorbing liquid in kitty litter, and as catalysts to produce fuel. Of the hundreds of types of zeolites, only about 15 are used for catalysis. PNNL catalysis scientists Ilke Arslan and Mirek Derewinksi are studying these zeolites to understand what make them special. By exploring the mystery of these microscopic channels, their fundamental findings will help design better catalysts for applications such as biofuel production.

  18. How Gas Carves Channels

    NASA Image and Video Library

    2017-01-24

    NASA Mars Reconnaissance Orbiter spies a layer of dry ice covering Mars south polar layer. In the spring, gas created from heating of the dry ice escapes through ruptures in the overlying seasonal ice, entraining material from the ground below. The gas erodes channels in the surface, generally exploiting weaker material. The ground likely started as polygonal patterned ground (common in water-ice-rich surfaces), and then escaping gas widened the channels. Fans of dark material are bits of the surface carried onto the top of the seasonal ice layer and deposited in a direction determined by local winds. http://photojournal.jpl.nasa.gov/catalog/PIA11706

  19. Tharsis Grooved Channel

    NASA Image and Video Library

    2002-12-04

    The Tharsis Montes region on Mars is a major center of volcanic and tectonic activity. The channel in this image from NASA Mars Odyssey is west of the relatively small volcano called Biblis Patera although it shows no obvious relationship to that volcano. Instead, it may be related to the more distant, but more massive volcano Olympus Mons to the north. The channel may have hosted flowing lava at one time but now contains a material that has eroded into an impressive ridge-and-groove pattern. These features may be yardangs, landforms produced from the erosion by wind of sedimentary material. http://photojournal.jpl.nasa.gov/catalog/PIA04020

  20. Counter-current flow limitation in thin rectangular channels

    NASA Astrophysics Data System (ADS)

    Cheng, Lap Y.

    The phenomenon of counter-current flow limitation (CCFL) in thin rectangular channels is important in determining the heat removal capability of research reactors which use plate-type fuel elements similar to the MTR design. An analytical expression for predicting CCFL in narrow rectangular channels was derived from the momentum equations for the liquid and gas phase. The model assumes that the liquid downflow is in the form of a film along the narrower side walls of the channel, while the gas flow occupies the wide span of the rectangular channel. The average thickness of liquid film is related to the rate of gas flow through a stability criterion for the liquid film. The CCFL correlation agrees with air/water data taken at relatively high gas velocities. Depending on the magnitude of the dimensionless channel width, the new CCFL correlation approaches zero liquid penetration either in the form of a Wallis correlation or in terms of a Kutateladze number. The new correlation indicates that for a thin rectangular channel, the constant C in the Wallis flooding correlation depends on the aspect ratio of the channel. The approach to the appropriate asymptotic solutions also justifies the use of twice the wide span as the correct length scale for thin rectangular channels.

  1. River channel patterns: Braided, meandering, and straight

    USGS Publications Warehouse

    Leopold, Luna Bergere; Wolman, M. Gordon

    1957-01-01

    Channel pattern is used to describe the plan view of a reach of river as seen from an airplane, and includes meandering, braiding, or relatively straight channels.Natural channels characteristically exhibit alternating pools or deep reaches and riffles or shallow reaches, regardless of the type of pattern. The length of the pool or distance between riffles in a straight channel equals the straight line distance between successive points of inflection in the wave pattern of a meandering river of the same width. The points of inflection are also shallow points and correspond to riffles in the straight channel. This distance, which is half the wavelength of the meander, varies approximately as a linear function of channel width. In the data we analysed the meander wavelength, or twice the distance between successive riffles, is from 7 to 12 times the channel width. It is concluded that the mechanics which may lead to meandering operate in straight channels.River braiding is characterized by channel division around alluvial islands. The growth of an island begins as the deposition of a central bar which results from sorting and deposition of the coarser fractions of the load which locally cannot be transported. The bar grows downstream and in height by continued deposition on its surface, forcing the water into the flanking channels, which, to carry the flow, deepen and cut laterally into the original banks. Such deepening locally lowers the water surface and the central bar emerges as an island which becomes stabilized by vegetation. Braiding was observed in a small river in a laboratory. Measurements of the adjustments of velocity, depth, width, and slope associated with island development lead to the conclusion that braiding is one of the many patterns which can maintain quasi-equilibrium among discharge, load, and transporting ability. Braiding does not necessarily indicate an excess of total load.Channel cross section and pattern are ultimately controlled by the

  2. Stream Channel Stability. Appendix J. Numerical Model for Routing Graded Sediments in Alluvial Channels,

    DTIC Science & Technology

    1981-04-01

    bedload discharge with a Helley - Smith bedload sampler . The bedload discharge past the section B-17 was measured with both a bedload trap and...a Helley - Smith sampler . Leopold and Emmett (1976) and Mahoney et al. (1976) describe in detail the stream, the bedload trap , and the data ,ollected...9 2. Routing of water and sediment characteristic waves............... 14 3. Schematic representation of bed

  3. Ion channels in inflammation.

    PubMed

    Eisenhut, Michael; Wallace, Helen

    2011-04-01

    Most physical illness in vertebrates involves inflammation. Inflammation causes disease by fluid shifts across cell membranes and cell layers, changes in muscle function and generation of pain. These disease processes can be explained by changes in numbers or function of ion channels. Changes in ion channels have been detected in diarrhoeal illnesses, pyelonephritis, allergy, acute lung injury and systemic inflammatory response syndromes involving septic shock. The key role played by changes in ion transport is directly evident in inflammation-induced pain. Expression or function of all major categories of ion channels like sodium, chloride, calcium, potassium, transient receptor potential, purinergic receptor and acid-sensing ion channels can be influenced by cyto- and chemokines, prostaglandins, leukotrienes, histamine, ATP, reactive oxygen species and protons released in inflammation. Key pathways in this interaction are cyclic nucleotide, phosphoinositide and mitogen-activated protein kinase-mediated signalling, direct modification by reactive oxygen species like nitric oxide, ATP or protons and disruption of the cytoskeleton. Therapeutic interventions to modulate the adverse and overlapping effects of the numerous different inflammatory mediators on each ion transport system need to target adversely affected ion transport systems directly and locally.

  4. Learning in Tactile Channels

    ERIC Educational Resources Information Center

    Gescheider, George A.; Wright, John H.

    2012-01-01

    Vibrotactile intensity-discrimination thresholds for sinusoidal stimuli applied to the thenar eminence of the hand declined as a function of practice. However, improvement was confined to the tactile information-processing channel in which learning had occurred. Specifically, improvements in performance with training within the Pacinian-corpuscle…

  5. Developments in relativistic channeling

    SciTech Connect

    Carrigan, R.A. Jr.

    1996-10-01

    The possibility of using channeling as a tool for high energy accelerator applications and particle physics has now been extensively investigated. Bent crystals have been used for accelerator extraction and for particle deflection. Applications as accelerating devices have been discussed but have not yet been tried. 61 refs., 1 fig.

  6. Chemistry in Microfluidic Channels

    ERIC Educational Resources Information Center

    Chia, Matthew C.; Sweeney, Christina M.; Odom, Teri W.

    2011-01-01

    General chemistry introduces principles such as acid-base chemistry, mixing, and precipitation that are usually demonstrated in bulk solutions. In this laboratory experiment, we describe how chemical reactions can be performed in a microfluidic channel to show advanced concepts such as laminar fluid flow and controlled precipitation. Three sets of…

  7. Covert Channels within IRC

    DTIC Science & Technology

    2011-03-24

    Distribution ~NA maintain primary management responsibility and Statement "A" - unclassifed, unlimited distribution ? authority to release all...AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED... DISTRIBUTION UNLIMITED. AFIT/GCE/ENG/11-04 COVERT CHANNELS WITHIN IRC Wayne C. Henry, BSCE Captain, USAF Approved

  8. Channels of Propaganda.

    ERIC Educational Resources Information Center

    Sproule, J. Michael

    Defining propaganda as "efforts by special interests to win over the public covertly by infiltrating messages into various channels of public expression ordinarily viewed as politically neutral," this book argues that propaganda has become pervasive in American life. Pointing out that the 1990s society is inundated with propaganda from…

  9. Sodium channel auxiliary subunits.

    PubMed

    Tseng, Tsai-Tien; McMahon, Allison M; Johnson, Victoria T; Mangubat, Erwin Z; Zahm, Robert J; Pacold, Mary E; Jakobsson, Eric

    2007-01-01

    Voltage-gated ion channels are well known for their functional roles in excitable tissues. Excitable tissues rely on voltage-gated ion channels and their auxiliary subunits to achieve concerted electrical activity in living cells. Auxiliary subunits are also known to provide functional diversity towards the transport and biogenesis properties of the principal subunits. Recent interests in pharmacological properties of these auxiliary subunits have prompted significant amounts of efforts in understanding their physiological roles. Some auxiliary subunits can potentially serve as drug targets for novel analgesics. Three families of sodium channel auxiliary subunits are described here: beta1 and beta3, beta2 and beta4, and temperature-induced paralytic E (TipE). While sodium channel beta-subunits are encoded in many animal genomes, TipE has only been found exclusively in insects. In this review, we present phylogenetic analyses, discuss potential evolutionary origins and functional data available for each of these subunits. For each family, we also correlate the functional specificity with the history of evolution for the individual auxiliary subunits.

  10. Learning in Tactile Channels

    ERIC Educational Resources Information Center

    Gescheider, George A.; Wright, John H.

    2012-01-01

    Vibrotactile intensity-discrimination thresholds for sinusoidal stimuli applied to the thenar eminence of the hand declined as a function of practice. However, improvement was confined to the tactile information-processing channel in which learning had occurred. Specifically, improvements in performance with training within the Pacinian-corpuscle…

  11. Visual Channel Problems.

    ERIC Educational Resources Information Center

    Mann, Philip H.; Suiter, Patricia A.

    This teacher training module classifies visual channel problems into the following four main areas: visual perception, revisualization (memory), visual-motor (eye-hand coordination), and ocular-motor tasks. Specific deficits are listed under these main headings, behaviors are given to help identify the problem, and ways to improve the condition…

  12. Chemistry in Microfluidic Channels

    ERIC Educational Resources Information Center

    Chia, Matthew C.; Sweeney, Christina M.; Odom, Teri W.

    2011-01-01

    General chemistry introduces principles such as acid-base chemistry, mixing, and precipitation that are usually demonstrated in bulk solutions. In this laboratory experiment, we describe how chemical reactions can be performed in a microfluidic channel to show advanced concepts such as laminar fluid flow and controlled precipitation. Three sets of…

  13. Two-channel Kondo effect in a modified single electron transistor.

    PubMed

    Oreg, Yuval; Goldhaber-Gordon, David

    2003-04-04

    We suggest a simple system of two electron droplets which should display two-channel Kondo behavior at experimentally accessible temperatures. Stabilization of the two-channel Kondo fixed point requires fine control of the electrochemical potential in each droplet, which can be achieved by adjusting voltages on nearby gate electrodes. We study the conditions for obtaining this type of two-channel Kondo behavior, discuss the experimentally observable consequences, and explore the generalization to the multichannel Kondo case.

  14. Channeling through Bent Crystals

    SciTech Connect

    Mack, Stephanie; /Ottawa U. /SLAC

    2012-09-07

    Bent crystals have demonstrated potential for use in beam collimation. A process called channeling is when accelerated particle beams are trapped by the nuclear potentials in the atomic planes within a crystal lattice. If the crystal is bent then the particles can follow the bending angle of the crystal. There are several different effects that are observed when particles travel through a bent crystal including dechanneling, volume capture, volume reflection and channeling. With a crystal placed at the edge of a particle beam, part of the fringe of the beam can be deflected away towards a detector or beam dump, thus helping collimate the beam. There is currently FORTRAN code by Igor Yazynin that has been used to model the passage of particles through a bent crystal. Using this code, the effects mentioned were explored for beam energy that would be seen at the Facility for Advanced Accelerator Experimental Tests (FACET) at a range of crystal orientations with respect to the incoming beam. After propagating 5 meters in vacuum space past the crystal the channeled particles were observed to separate from most of the beam with some noise due to dechanneled particles. Progressively smaller bending radii, with corresponding shorter crystal lengths, were compared and it was seen that multiple scattering decreases with the length of the crystal therefore allowing for cleaner detection of the channeled particles. The input beam was then modified and only a portion of the beam sent through the crystal. With the majority of the beam not affected by the crystal, most particles were not deflected and after propagation the channeled particles were seen to be deflected approximately 5mm. After a portion of the beam travels through the crystal, the entire beam was then sent through a quadrupole magnet, which increased the separation of the channeled particles from the remainder of the beam to a distance of around 20mm. A different code, which was developed at SLAC, was used to

  15. Capsule-train stability

    NASA Astrophysics Data System (ADS)

    Bryngelson, Spencer H.; Freund, Jonathan B.

    2016-07-01

    Elastic capsules flowing in small enough tubes, such as red blood cells in capillaries, are well known to line up into regular single-file trains. The stability of such trains in somewhat wider channels, where this organization is not observed, is studied in a two-dimensional model system that includes full coupling between the viscous flow and suspended capsules. A diverse set of linearly amplifying disturbances, both long-time asymptotic (modal) and transient (nonmodal) perturbations, is identified and analyzed. These have a range of amplification rates and their corresponding forms are wavelike, typically dominated by one of five principal perturbation classes: longitudinal and transverse translations, tilts, and symmetric and asymmetric shape distortions. Finite-amplitude transiently amplifying perturbations are shown to provide a mechanism that can bypass slower asymptotic modal linear growth and precipitate the onset of nonlinear effects. Direct numerical simulations are used to verify the linear analysis and track the subsequent transition of the regular capsule trains into an apparently chaotic flow.

  16. Composite stabilizer unit

    SciTech Connect

    Ebaugh, L.R.; Sadler, C.P.; Carter, G.D.

    1990-12-31

    This invention is comprised of an improved fin stabilized projectile including multiple stabilizer fins upon a stabilizer unit situated at the aft end of the projectile is provided, the improvement wherein the stabilizer fins are joined into the stabilizer unit by an injection molded engineering grade polymer.

  17. Composite stabilizer unit

    SciTech Connect

    Ebaugh, L.R.; Sadler, C.P.; Carter, G.D.

    1990-01-01

    This invention is comprised of an improved fin stabilized projectile including multiple stabilizer fins upon a stabilizer unit situated at the aft end of the projectile is provided, the improvement wherein the stabilizer fins are joined into the stabilizer unit by an injection molded engineering grade polymer.

  18. Composite stabilizer unit

    DOEpatents

    Ebaugh, Larry R.; Sadler, Collin P.; Carter, Gary D.

    1992-01-01

    An improved fin stabilized projectile including multiple stabilizer fins upon a stabilizer unit situated at the aft end of the projectile is provided, the improvement wherein the stabilizer fins are joined into the stabillizer unit by an injection molded engineering grade polymer.

  19. Stability of thin liquid films

    SciTech Connect

    Bankoff, S.G.; Davis, S.H.

    1994-12-31

    Two topics are discussed in the present progress report. The first is a study of the stability of the interface between two thin immiscible fluid layers in a two-dimensional channel. The flowrates may be specified, or alternatively the total pressure drop and the flowrate of one fluid. The channel may be horizontal or inclined. A long-wave 3D nonlinear evolution equation is derived for the local layer thickness, whose coefficients are high-order polynomials of the viscosity ratio and the initial volume fraction. With a further restriction to small wave amplitude, as well as many slopes, a Kuramoto-Sivashinsky-type (KS) is derived. In countercurrent flow the {open_quotes}group velocity{close_quotes} of the interface can become very small, possibly signaling the onset of flooding. In this case a cubic nonlinearity becomes significant. The properties of this modified KS equation are explored in considerable detail. The classical Yih-Benjamin linear stability theory for long waves on an unforced thin liquid film down a vertical wall has never been experimentally verified, owing to the sensitivity to small random disturbances. However, by careful balancing and by operating under very quiet conditions, the theoretical predictions were verified for the first time. For pointwise measurements, 25-{mu}m resistivity probes were employed, and for global measurements fluorescent imaging.

  20. The Earliest Ion Channels in Protocellular Membranes

    NASA Technical Reports Server (NTRS)

    Mijajlovic, Milan; Pohorille, Andrew; Wilson, Michael; Wei, Chenyu

    2010-01-01

    Cellular membranes with their hydrophobic interior are virtually impermeable to ions. Bulk of ion transport through them is enabled through ion channels. Ion channels of contemporary cells are complex protein molecules which span the membrane creating a cylindrical pore filled with water. Protocells, which are widely regarded as precursors to modern cells, had similarly impermeable membranes, but the set of proteins in their disposal was much simpler and more limited. We have been, therefore, exploring an idea that the first ion channels in protocellular membranes were formed by much smaller peptide molecules that could spontaneously selfassemble into short-lived cylindrical bundles in a membrane. Earlier studies have shown that a group of peptides known as peptaibols is capable of forming ion channels in lipid bilayers when they are exposed to an electric field. Peptaibols are small, non-genetically encoded peptides produced by some fungi as a part of their system of defense against bacteria. They are usually only 14-20 residues long, which is just enough to span the membrane. Their sequence is characterized by the presence of non-standard amino acids which, interestingly, are also expected to have existed on the early earth. In particular, the presence of 2-aminoisobutyric acid (AIB) gives peptaibols strong helix forming propensities. Association of the helices inside membranes leads to the formation of cylindrical bundles, typically containing 4 to 10 monomers. Although peptaibols are excellent candidates for models of the earliest ion channels their structures, which are stabilized only by van der Waals forces and occasional hydrogen bonds between neighboring helices, are not very stable. Although it might properly reflect protobiological reality, it is also a major obstacle in studying channel behavior. For this reason we focused on two members of the peptaibol family, trichotoxin and antiamoebin, which are characterized by a single conductance level. This

  1. The earliest ion channels in protocellular membranes

    NASA Astrophysics Data System (ADS)

    Mijajlovic, Milan; Pohorille, Andrew; Wilson, Michael; Wei, Chenyu

    Cellular membranes with their hydrophobic interior are virtually impermeable to ions. Bulk of ion transport through them is enabled through ion channels. Ion channels of contemporary cells are complex protein molecules which span the membrane creating a cylindrical pore filled with water. Protocells, which are widely regarded as precursors to modern cells, had similarly impermeable membranes, but the set of proteins in their disposal was much simpler and more limited. We have been, therefore, exploring an idea that the first ion channels in protocellular membranes were formed by much smaller peptide molecules that could spontaneously self-assemble into short-lived cylindrical bundles in a membrane. Earlier studies have shown that a group of peptides known as peptaibols is capable of forming ion channels in lipid bilayers when they are exposed to an electric field. Peptaibols are small, non-genetically encoded peptides produced by some fungi as a part of their system of defense against bacteria. They are usually only 14-20 residues long, which is just enough to span the membrane. Their sequence is characterized by the presence of non-standard amino acids which, interestingly, are also expected to have existed on the early earth. In particular, the presence of 2-aminoisobutyric acid (AIB) gives peptaibols strong helix forming propensities. Association of the helices inside membranes leads to the formation of cylindrical bundles, typically containing 4 to 10 monomers. Although peptaibols are excellent candidates for models of the earliest ion channels their struc-tures, which are stabilized only by van der Waals forces and occasional hydrogen bonds between neighboring helices, are not very stable. Although it might properly reflect protobiological real-ity, it is also a major obstacle in studying channel behavior. For this reason we focused on two members of the peptaibol family, trichotoxin and antiamoebin, which are characterized by a single conductance level. This

  2. Validation of the Radiometric Stability of the Atmospheric Infrared Sounder

    NASA Technical Reports Server (NTRS)

    Aumann, H. H.; Elliott, D.; Strow, L. L.

    2012-01-01

    It has been widely accepted that an infrared sounder in low polar orbit is capable of producing climate quality data, if the spectral brightness temperatures have instrumental trends of less than 10 mK/yr. Achieving measurement stability at this level is not only very demanding of the design of the instrument, it is also pushes the state of art of measuring on orbit what stability is actually achieved. We discuss this using Atmospheric Infrared Sounder (AIRS) L1B data collected between 2002 and 2011. We compare the L1B brightness temperature observed in cloud filtered night tropical ocean spectra (obs) to the brightness temperature calculated based on the known surface emissivity, temperature and water vapor profiles from the ECMWF ReAnalysis (ERA) and the growth rates of CO2, N2O and Ozone. The trend in (obs-calc) is a powerful tool for the evaluation of the stability of the 2378 AIRS channels. We divided the channels into seven classes: All channels which sound in the stratosphere (at pressure levels below 150 hPa), 14 micron CO2 sounding, 4 micron CO2 P-branch sounding, 4 micron CO2 R-branch sounding, water vapor sounding, shortwave surface sounding and longwave surface sounding. The peak in the weighting function at 1050 hPa separates sounding and surface channels. The boundary between shortwave and longwave is 5 microns. Except for the stratosphere sounding channels, the remaining six groups have (obs-calc) trends of less than 20 mK/yr. The longwave surface channels have trends of 2 mK/yr, significantly less than the 8 mK/yr trend seem in the shortwave window channels. Based on the design of the instrument, trends within a group of channels should be the same. While the longwave and shortwave trends are less than the canonical 10 mK/yr, the larger trend in the shortwave channels could be an artifact of using the pre-launch determined calibration coefficients. This is currently under evaluation. The trend in (obs-calc) for the non-surface sounding channels, in

  3. Gating mechanosensitive channels in bacteria with an atomic force microscope

    NASA Astrophysics Data System (ADS)

    Garces, Renata; Miller, Samantha; Schmidt, Christoph F.; Third Institute of Physics Team; School of Medical Sciences Collaboration

    The regulation of growth and integrity of bacteria is critically linked to mechanical stress. Bacteria typically maintain a high difference of osmotic pressure (turgor pressure) with respect to the environment. This pressure difference (on the order of 1 atm) is supported by the cell envelope, a composite of lipid membranes and a rigid cell wall. Turgor pressure is controlled by the ratio of osmolytes inside and outside bacteria and thus, can abruptly increase upon osmotic downshock. For structural integrity bacteria rely on the mechanical stability of the cell wall and on the action of mechanosensitive (MS) channels: membrane proteins that release solutes in response to stress in the cell envelope. We here present experimental data on MS channels gating. We activate channels by indenting living bacteria with the cantilever of an atomic force microscope (AFM). We compare responses of wild-type and mutant bacteria in which some or all MS channels have been eliminated.

  4. Learning Channels and Verbal Behavior

    ERIC Educational Resources Information Center

    Lin, Fan-Yu; Kubina, Richard M., Jr.

    2004-01-01

    This article reviews the basics of learning channels and how specification of stimuli can help enhance verbal behavior. This article will define learning channels and the role of the ability matrix in training verbal behavior.

  5. Channel processes and watershed function

    Treesearch

    Tom Lisle

    1999-01-01

    Purpose of this presentation is to put channel monitoring in context of channel processes and dispel the myth of the learned sage walking up the stream channel observing changes in the channel and extrapolating how these changes came about without looking at the rest of the watershed. The message I want to convey is it is not only O.K.to peek at the rest of the...

  6. Meander properties of Venusian channels

    NASA Technical Reports Server (NTRS)

    Komatsu, G.; Baker, V. R.

    1993-01-01

    Venusian lava channels have meander dimensions that relate to their mode of formation. Their meander properties generally follow terrestrial river trends of wavelength (L) to width (W) ratios, suggesting an equilibrium adjustment of channel form. Slightly higher L/W for many Venusian channels in comparison to terrestrial rivers may relate to nonaqueous flow processes. The unusually low L/W values for some Venusian and lunar sinuous rilles probably indicate modification of original meander patterns by lava-erosional channel widening.

  7. Radar channel balancing with commutation

    SciTech Connect

    Doerry, Armin Walter

    2014-02-01

    When multiple channels are employed in a pulse-Doppler radar, achieving and maintaining balance between the channels is problematic. In some circumstances the channels may be commutated to achieve adequate balance. Commutation is the switching, trading, toggling, or multiplexing of the channels between signal paths. Commutation allows modulating the imbalance energy away from the balanced energy in Doppler, where it can be mitigated with filtering.

  8. Universality of receptor channel responses.

    PubMed

    Kardos, J; Nyikos, L

    2001-12-01

    Rate parameters estimated for neurotransmitter-gated receptor channel opening and receptor desensitization are classified according to their dependence on the temporal resolution of the techniques applied in the measurements. Because allosteric proteins constituting receptor channels impose restrictions on the types of model suitable to describe the dynamic response of channels to neurotransmitters, Markovian, non-linear or fractal dynamic models and their possible extension to receptor channel response in excitable membranes are discussed.

  9. Computer Simulation Studies of Ion Channels at High Temperatures

    NASA Astrophysics Data System (ADS)

    Song, Hyun Deok

    The gramicidin channel is the smallest known biological ion channel, and it exhibits cation selectivity. Recently, Dr. John Cuppoletti's group at the University of Cincinnati showed that the gramicidin channel can function at high temperatures (360 ˜ 380K) with significant currents. This finding may have significant implications for fuel cell technology. In this thesis, we have examined the gramicidin channel at 300K, 330K, and 360K by computer simulation. We have investigated how the temperature affects the current and differences in magnitude of free energy between the two gramicidin forms, the helical dimer (HD) and the double helix (DH). A slight decrease of the free energy barrier inside the gramicidin channel and increased diffusion at high temperatures result in an increase of current. An applied external field of 0.2V/nm along the membrane normal results in directly observable ion transport across the channels at high temperatures for both HD and DH forms. We found that higher temperatures also affect the probability distribution of hydrogen bonds, the bending angle, the distance between dimers, and the size of the pore radius for the helical dimer structure. These findings may be related to the gating of the gramicidin channel. Methanococcus jannaschii (MJ) is a methane-producing thermophile, which was discovered at a depth of 2600m in a Pacific Ocean vent in 1983. It has the ability to thrive at high temperatures and high pressures, which are unfavorable for most life forms. There have been some experiments to study its stability under extreme conditions, but still the origin of the stability of MJ is not exactly known. MJ0305 is the chloride channel protein from the thermophile MJ. After generating a structure of MJ0305 by homology modeling based on the Ecoli ClC templates, we examined the thermal stability, and the network stability from the change of network entropy calculated from the adjacency matrices of the protein. High temperatures increase the

  10. Nanochannels: biological channel analogues.

    PubMed

    Pradeep, H; Rajanikant, G K

    2012-06-01

    The flux of ions across the biological membrane is a central activity to many cellular processes, from conduction of nerve impulse to the apoptosis. Traffic of ions or molecules across the membrane and organelles is governed by natural machines of great precision; ion channels, a special class of proteins, reside in the biological membranes. Recent studies in the field of nanoscience have concentrated on to precisely mimic the physical and chemical properties of these pores that make them increasingly attractive in this field. Synthetic nanoporous materials have a great deal of medical applications, including biosensing, biosorting, immune-isolation and drug delivery. In this review, the authors briefly describe the interesting synthetic channels that are extensively studied, and also attempt to furnish a precise overview of recent advances in this arena.

  11. Geysering in boiling channels

    SciTech Connect

    Aritomi, Masanori; Takemoto, Takatoshi; Chiang, Jing-Hsien

    1995-09-01

    A concept of natural circulation BWRs such as the SBWR has been proposed and seems to be promising in that the primary cooling system can be simplified. The authors have been investigating thermo-hydraulic instabilities which may appear during the start-up in natural circulation BWRs. In our previous works, geysering was investigated in parallel boiling channels for both natural and forced circulations, and its driving mechanism and the effect of system pressure on geysering occurrence were made clear. In this paper, geysering is investigated in a vertical column and a U-shaped vertical column heated in the lower parts. It is clarified from the results that the occurrence mechanism of geysering and the dependence of system pressure on geysering occurrence coincide between parallel boiling channels in circulation systems and vertical columns in non-circulation systems.

  12. ``Just Another Distribution Channel?''

    NASA Astrophysics Data System (ADS)

    Lemstra, Wolter; de Leeuw, Gerd-Jan; van de Kar, Els; Brand, Paul

    The telecommunications-centric business model of mobile operators is under attack due to technological convergence in the communication and content industries. This has resulted in a plethora of academic contributions on the design of new business models and service platform architectures. However, a discussion of the challenges that operators are facing in adopting these models is lacking. We assess these challenges by considering the mobile network as part of the value system of the content industry. We will argue that from the perspective of a content provider the mobile network is ‘just another’ distribution channel. Strategic options available for the mobile communication operators are to deliver an excellent distribution channel for content delivery or to move upwards in the value chain by becoming a content aggregator. To become a mobile content aggregator operators will have to develop or acquire complementary resources and capabilities. Whether this strategic option is sustainable remains open.

  13. Chryse Outflow Channel

    NASA Image and Video Library

    1998-06-08

    A color image of the south Chryse basin Valles Marineris outflow channels on Mars; north toward top. The scene shows on the southwest corner the chaotic terrain of the east part of Valles Marineris and two of its related canyons: Eos and Capri Chasmata (south to north). Ganges Chasma lies directly north. The chaos in the southern part of the image gives rise to several outflow channels, Shalbatana, Simud, Tiu, and Ares Valles (left to right), that drained north into the Chryse basin. The mouth of Ares Valles is the site of the Mars Pathfinder lander. This image is a composite of NASA's Viking medium-resolution images in black and white and low-resolution images in color. The image extends from latitude 20 degrees S. to 20 degrees N. and from longitude 15 degrees to 53 degrees; Mercator projection. http://photojournal.jpl.nasa.gov/catalog/PIA00418

  14. Lightning energetics: Estimates of energy dissipation in channels, channel radii, and channel-heating risetimes

    SciTech Connect

    Borovsky, J.E.

    1998-05-01

    In this report, several lightning-channel parameters are calculated with the aid of an electrodynamic model of lightning. The electrodynamic model describes dart leaders and return strokes as electromagnetic waves that are guided along conducting lightning channels. According to the model, electrostatic energy is delivered to the channel by a leader, where it is stored around the outside of the channel; subsequently, the return stroke dissipates this locally stored energy. In this report this lightning-energy-flow scenario is developed further. Then the energy dissipated per unit length in lightning channels is calculated, where this quantity is now related to the linear charge density on the channel, not to the cloud-to-ground electrostatic potential difference. Energy conservation is then used to calculate the radii of lightning channels: their initial radii at the onset of return strokes and their final radii after the channels have pressure expanded. Finally, the risetimes for channel heating during return strokes are calculated by defining an energy-storage radius around the channel and by estimating the radial velocity of energy flow toward the channel during a return stroke. In three appendices, values for the linear charge densities on lightning channels are calculated, estimates of the total length of branch channels are obtained, and values for the cloud-to-ground electrostatic potential difference are estimated. {copyright} 1998 American Geophysical Union

  15. Performance characteristics and output power stability of a multichannel fibre laser

    NASA Astrophysics Data System (ADS)

    Kuzmenkov, A. I.; Lukinykh, S. N.; Nanii, O. E.; Odintsov, A. I.; Smirnov, A. P.; Fedoseev, A. I.; Treshchikov, V. N.

    2016-09-01

    The effect of the density and number of spectral channels on the output power stability in a multichannel cw laser has been studied theoretically and experimentally. In our calculations, we used a model in which the interaction between channels due to gain medium saturation was determined by channel frequency spacingdependent cross-saturation coefficients. The key features of lasing have been analysed and illustrated by the examples of three-, fiveand nine-channel lasers. It has been shown that, at a given excess of the pump power over threshold, the channel powers can be equalised by introducing additional losses into the highest power channels. At a sufficiently high channel density, raising the pump power then leads to termination of lasing in the even channels. As the number of channels increases, the laser system retains its stability, but the time needed for the transition to a steady state increases sharply. In our experiments, we used an erbium-doped fibre laser whose design ensured independent control over the powers of up to 40 spectral channels anchored on the telecommunication frequency grid. Our experimental data are in qualitative agreement with the calculation results. In particular, a long-term relative instability less than 3 dB was only observed at a number of channels less than seven and channel frequency spacings above 400 GHz. Instability was shown to increase with an increase in the number and density of channels.

  16. Athermal channeled spectropolarimeter

    SciTech Connect

    Jones, Julia Craven

    2015-12-08

    A temperature insensitive (athermal) channeled spectropolarimeter (CSP) is described. The athermal CSP includes a crystal retarder formed of a biaxial crystal. The crystal retarder has three crystal axes, wherein each axis has its own distinct index of refraction. The axes are oriented in a particular manner, causing an amplitude modulating carrier frequency induced by the crystal retarder to be thermally invariant. Accordingly, a calibration beam technique can be used over a relatively wide range of ambient temperatures, with a common calibration data set.

  17. Aquaglyceroporins: generalized metalloid channels

    PubMed Central

    Mukhopadhyay, Rita; Bhattacharjee, Hiranmoy; Rosen, Barry P.

    2014-01-01

    Background: Aquaporins (AQPs), members of a superfamily of transmembrane channel proteins, are ubiquitous in all domains of life. They fall into a number of branches that can be functionally categorized into two major sub-groups: i) orthodox aquaporins, which are water-specific channels, and ii) aquaglyceroporins, which allow the transport of water, non-polar solutes, such as urea or glycerol, the reactive oxygen species hydrogen peroxide, and gases such as ammonia, carbon dioxide and nitric oxide and, as described in this review, metalloids. Scope of Review: This review summarizes the key findings that AQP channels conduct bidirectional movement of metalloids into and out of cells. Major Conclusions: As(OH)3 and Sb(OH)3 behave as inorganic molecular mimics of glycerol, a property that allows their passage through AQP channels. Plant AQPs also allow the passage of boron and silicon as their hydroxyacids, boric acid (B(OH)3) and orthosilicic acid (Si(OH)4), respectively. Genetic analysis suggests that germanic acid (GeO2) is also a substrate. While As(III), Sb(III) and Ge(IV) are toxic metalloids, borate (B(III)) and silicate (Si(IV)) are essential elements in higher plants. General Significance: The uptake of environmental metalloids by aquaporins provides an understanding of (i) how toxic elements such as arsenic enter the food chain; (ii) the delivery of arsenic and antimony containing drugs in the treatment of certain forms of leukemia and chemotherapy of diseases caused by pathogenic protozoa; and (iii) the possibility that food plants such as rice could be made safer by genetically modifying them to exclude arsenic while still accumulating boron and silicon. PMID:24291688

  18. Comments on ionization cooling channels

    DOE PAGES

    Neuffer, David

    2017-09-25

    Ionization cooling channels with a wide variety of characteristics and cooling properties are being developed. These channels can produce cooling performances that are largely consistent with the linear ionization cooling theory developed previously. In this study, we review ionization cooling theory, discuss its application to presently developing cooling channels, and discuss criteria for optimizing cooling.

  19. Cascading blockages in channel bundles

    NASA Astrophysics Data System (ADS)

    Barré, C.; Talbot, J.

    2015-11-01

    Flow in channel networks may involve a redistribution of flux following the blockage or failure of an individual link. Here we consider a simplified model consisting of Nc parallel channels conveying a particulate flux. Particles enter these channels according to a homogeneous Poisson process and an individual channel blocks if more than N particles are simultaneously present. The behavior of the composite system depends strongly on how the flux of entering particles is redistributed following a blockage. We consider two cases. In the first, the intensity on each open channel remains constant while in the second the total intensity is evenly redistributed over the open channels. We obtain exact results for arbitrary Nc and N for a system of independent channels and for arbitrary Nc and N =1 for coupled channels. For N >1 we present approximate analytical as well as numerical results. Independent channels block at a decreasing rate due to a simple combinatorial effect, while for coupled channels the interval between successive blockages remains constant for N =1 but decreases for N >1 . This accelerating cascade is due to the nonlinear dependence of the mean blocking time of a single channel on the entering particle flux that more than compensates for the decrease in the number of active channels.

  20. Cascading blockages in channel bundles.

    PubMed

    Barré, C; Talbot, J

    2015-11-01

    Flow in channel networks may involve a redistribution of flux following the blockage or failure of an individual link. Here we consider a simplified model consisting of N(c) parallel channels conveying a particulate flux. Particles enter these channels according to a homogeneous Poisson process and an individual channel blocks if more than N particles are simultaneously present. The behavior of the composite system depends strongly on how the flux of entering particles is redistributed following a blockage. We consider two cases. In the first, the intensity on each open channel remains constant while in the second the total intensity is evenly redistributed over the open channels. We obtain exact results for arbitrary N(c) and N for a system of independent channels and for arbitrary N(c) and N=1 for coupled channels. For N>1 we present approximate analytical as well as numerical results. Independent channels block at a decreasing rate due to a simple combinatorial effect, while for coupled channels the interval between successive blockages remains constant for N=1 but decreases for N>1. This accelerating cascade is due to the nonlinear dependence of the mean blocking time of a single channel on the entering particle flux that more than compensates for the decrease in the number of active channels.

  1. Ion channels in the RPE.

    PubMed

    Wimmers, Sönke; Karl, Mike O; Strauss, Olaf

    2007-05-01

    In close interaction with photoreceptors, the retinal pigment epithelium (RPE) plays an essential role for visual function. The analysis of RPE functions, specifically ion channel functions, provides a basis to understand many degenerative diseases of the retina. The invention of the patch-clamp technique significantly improved the knowledge of ion channel structure and function, which enabled a new understanding of cell physiology and patho-physiology of many diseases. In this review, ion channels identified in the RPE will be described in terms of their specific functional role in RPE physiology. The RPE expresses voltage- and ligand-gated K(+), Cl(-), and Ca(2+)-conducting channels. K(+) and Cl(-) channels are involved in transepithelial ion transport and volume regulation. Voltage-dependent Ca(2+) channels act as regulators of secretory activity, and ligand-gated cation channels contribute to RPE function by providing driving forces for ion transport or by influencing intracellular Ca(2+) homoeostasis. Collectively, activity of these ion channels determines the physiology of the RPE and its interaction with photoreceptors. Furthermore, changes in ion channel function, such as mutations in ion channel genes or a changed regulation of ion channel activity, have been shown to lead to degenerative diseases of the retina. Increasing knowledge about the properties of RPE ion channels has not only provided a new understanding of RPE function but has also provided greater understanding of RPE function in health and disease.

  2. Comments on ionization cooling channels

    NASA Astrophysics Data System (ADS)

    Neuffer, D.

    2017-09-01

    Ionization cooling channels with a wide variety of characteristics and cooling properties are being developed. These channels can produce cooling performances that are largely consistent with the linear ionization cooling theory developed previously. In this paper we review ionization cooling theory, discuss its application to presently developing cooling channels, and discuss criteria for optimizing cooling.

  3. Micro-channel plate detector

    DOEpatents

    Elam, Jeffrey W.; Lee, Seon W.; Wang, Hsien -Hau; Pellin, Michael J.; Byrum, Karen; Frisch, Henry J.

    2015-09-22

    A method and system for providing a micro-channel plate detector. An anodized aluminum oxide membrane is provided and includes a plurality of nanopores which have an Al coating and a thin layer of an emissive oxide material responsive to incident radiation, thereby providing a plurality of radiation sensitive channels for the micro-channel plate detector.

  4. Rapid Fabrication Techniques for Liquid Rocket Channel Wall Nozzles

    NASA Technical Reports Server (NTRS)

    Gradl, Paul R.

    2016-01-01

    The functions of a regeneratively-cooled nozzle are to (1) expand combustion gases to increase exhaust gas velocity while, (2) maintaining adequate wall temperatures to prevent structural failure, and (3) transfer heat from the hot gases to the coolant fluid to promote injector performance and stability. Regeneratively-cooled nozzles are grouped into two categories: tube-wall nozzles and channel wall nozzles. A channel wall nozzle is designed with an internal liner containing a series of integral coolant channels that are closed out with an external jacket. Manifolds are attached at each end of the nozzle to distribute coolant to and away from the channels. A variety of manufacturing techniques have been explored for channel wall nozzles, including state of the art laser-welded closeouts and pressure-assisted braze closeouts. This paper discusses techniques that NASA MSFC is evaluating for rapid fabrication of channel wall nozzles that address liner fabrication, slotting techniques and liner closeout techniques. Techniques being evaluated for liner fabrication include large-scale additive manufacturing of freeform-deposition structures to create the liner blanks. Abrasive water jet milling is being evaluated for cutting the complex coolant channel geometries. Techniques being considered for rapid closeout of the slotted liners include freeform deposition, explosive bonding and Cold Spray. Each of these techniques, development work and results are discussed in further detail in this paper.

  5. Inhibition of Kir4.1 potassium channels by quinacrine.

    PubMed

    Marmolejo-Murillo, Leticia G; Aréchiga-Figueroa, Iván A; Cui, Meng; Moreno-Galindo, Eloy G; Navarro-Polanco, Ricardo A; Sánchez-Chapula, José A; Ferrer, Tania; Rodríguez-Menchaca, Aldo A

    2017-05-15

    Inwardly rectifying potassium (Kir) channels are expressed in many cell types and contribute to a wide range of physiological processes. Particularly, Kir4.1 channels are involved in the astroglial spatial potassium buffering. In this work, we examined the effects of the cationic amphiphilic drug quinacrine on Kir4.1 channels heterologously expressed in HEK293 cells, employing the patch clamp technique. Quinacrine inhibited the currents of Kir4.1 channels in a concentration and voltage dependent manner. In inside-out patches, quinacrine inhibited Kir4.1 channels with an IC50 value of 1.8±0.3μM and with extremely slow blocking and unblocking kinetics. Molecular modeling combined with mutagenesis studies suggested that quinacrine blocks Kir4.1 by plugging the central cavity of the channels, stabilized by the residues E158 and T128. Overall, this study shows that quinacrine blocks Kir4.1 channels, which would be expected to impact the potassium transport in several tissues.

  6. Active integrated filters for RF-photonic channelizers.

    PubMed

    El Nagdi, Amr; Liu, Ke; LaFave, Tim P; Hunt, Louis R; Ramakrishna, Viswanath; Dabkowski, Mieczyslaw; MacFarlane, Duncan L; Christensen, Marc P

    2011-01-01

    A theoretical study of RF-photonic channelizers using four architectures formed by active integrated filters with tunable gains is presented. The integrated filters are enabled by two- and four-port nano-photonic couplers (NPCs). Lossless and three individual manufacturing cases with high transmission, high reflection, and symmetric couplers are assumed in the work. NPCs behavior is dependent upon the phenomenon of frustrated total internal reflection. Experimentally, photonic channelizers are fabricated in one single semiconductor chip on multi-quantum well epitaxial InP wafers using conventional microelectronics processing techniques. A state space modeling approach is used to derive the transfer functions and analyze the stability of these filters. The ability of adapting using the gains is demonstrated. Our simulation results indicate that the characteristic bandpass and notch filter responses of each structure are the basis of channelizer architectures, and optical gain may be used to adjust filter parameters to obtain a desired frequency magnitude response, especially in the range of 1-5 GHz for the chip with a coupler separation of ∼9 mm. Preliminarily, the measurement of spectral response shows enhancement of quality factor by using higher optical gains. The present compact active filters on an InP-based integrated photonic circuit hold the potential for a variety of channelizer applications. Compared to a pure RF channelizer, photonic channelizers may perform both channelization and down-conversion in an optical domain.

  7. Active Integrated Filters for RF-Photonic Channelizers

    PubMed Central

    Nagdi, Amr El; Liu, Ke; LaFave, Tim P.; Hunt, Louis R.; Ramakrishna, Viswanath; Dabkowski, Mieczyslaw; MacFarlane, Duncan L.; Christensen, Marc P.

    2011-01-01

    A theoretical study of RF-photonic channelizers using four architectures formed by active integrated filters with tunable gains is presented. The integrated filters are enabled by two- and four-port nano-photonic couplers (NPCs). Lossless and three individual manufacturing cases with high transmission, high reflection, and symmetric couplers are assumed in the work. NPCs behavior is dependent upon the phenomenon of frustrated total internal reflection. Experimentally, photonic channelizers are fabricated in one single semiconductor chip on multi-quantum well epitaxial InP wafers using conventional microelectronics processing techniques. A state space modeling approach is used to derive the transfer functions and analyze the stability of these filters. The ability of adapting using the gains is demonstrated. Our simulation results indicate that the characteristic bandpass and notch filter responses of each structure are the basis of channelizer architectures, and optical gain may be used to adjust filter parameters to obtain a desired frequency magnitude response, especially in the range of 1–5 GHz for the chip with a coupler separation of ∼9 mm. Preliminarily, the measurement of spectral response shows enhancement of quality factor by using higher optical gains. The present compact active filters on an InP-based integrated photonic circuit hold the potential for a variety of channelizer applications. Compared to a pure RF channelizer, photonic channelizers may perform both channelization and down-conversion in an optical domain. PMID:22319352

  8. Crystal structures of the TRIC trimeric intracellular cation channel orthologues

    PubMed Central

    Kasuya, Go; Hiraizumi, Masahiro; Maturana, Andrés D; Kumazaki, Kaoru; Fujiwara, Yuichiro; Liu, Keihong; Nakada-Nakura, Yoshiko; Iwata, So; Tsukada, Keisuke; Komori, Tomotaka; Uemura, Sotaro; Goto, Yuhei; Nakane, Takanori; Takemoto, Mizuki; Kato, Hideaki E; Yamashita, Keitaro; Wada, Miki; Ito, Koichi; Ishitani, Ryuichiro; Hattori, Motoyuki; Nureki, Osamu

    2016-01-01

    Ca2+ release from the sarcoplasmic reticulum (SR) and endoplasmic reticulum (ER) is crucial for muscle contraction, cell growth, apoptosis, learning and memory. The trimeric intracellular cation (TRIC) channels were recently identified as cation channels balancing the SR and ER membrane potentials, and are implicated in Ca2+ signaling and homeostasis. Here we present the crystal structures of prokaryotic TRIC channels in the closed state and structure-based functional analyses of prokaryotic and eukaryotic TRIC channels. Each trimer subunit consists of seven transmembrane (TM) helices with two inverted repeated regions. The electrophysiological, biochemical and biophysical analyses revealed that TRIC channels possess an ion-conducting pore within each subunit, and that the trimer formation contributes to the stability of the protein. The symmetrically related TM2 and TM5 helices are kinked at the conserved glycine clusters, and these kinks are important for the channel activity. Furthermore, the kinks of the TM2 and TM5 helices generate lateral fenestrations at each subunit interface. Unexpectedly, these lateral fenestrations are occupied with lipid molecules. This study provides the structural and functional framework for the molecular mechanism of this ion channel superfamily. PMID:27909292

  9. Ion channeling revisited

    SciTech Connect

    Doyle, Barney Lee; Corona, Aldo; Nguyen, Anh

    2014-09-01

    A MS Excel program has been written that calculates accidental, or unintentional, ion channeling in cubic bcc, fcc and diamond lattice crystals or polycrystalline materials. This becomes an important issue when simulating the creation by energetic neutrons of point displacement damage and extended defects using beams of ions. All of the tables and graphs in the three Ion Beam Analysis Handbooks that previously had to be manually looked up and read from were programed into Excel in handy lookup tables, or parameterized, for the case of the graphs, using rather simple exponential functions with different powers of the argument. The program then offers an extremely convenient way to calculate axial and planar half-angles and minimum yield or dechanneling probabilities, effects on half-angles of amorphous overlayers, accidental channeling probabilities for randomly oriented crystals or crystallites, and finally a way to automatically generate stereographic projections of axial and planar channeling half-angles. The program can generate these projections and calculate these probabilities for axes and [hkl] planes up to (555).

  10. The alpha channeling effect

    SciTech Connect

    Fisch, N. J.

    2015-12-10

    Alpha particles born through fusion reactions in a tokamak reactor tend to slow down on electrons, but that could take up to hundreds of milliseconds. Before that happens, the energy in these alpha particles can destabilize on collisionless timescales toroidal Alfven modes and other waves, in a way deleterious to energy confinement. However, it has been speculated that this energy might be instead be channeled into useful energy, so as to heat fuel ions or to drive current. Such a channeling needs to be catalyzed by waves Waves can produce diffusion in energy of the alpha particles in a way that is strictly coupled to diffusion in space. If these diffusion paths in energy-position space point from high energy in the center to low energy on the periphery, then alpha particles will be cooled while forced to the periphery. The energy from the alpha particles is absorbed by the wave. The amplified wave can then heat ions or drive current. This process or paradigm for extracting alpha particle energy collisionlessly has been called alpha channeling. While the effect is speculative, the upside potential for economical fusion is immense. The paradigm also operates more generally in other contexts of magnetically confined plasma.

  11. Nonlinear stability analysis of Darcy's flow with viscous heating.

    PubMed

    Celli, Michele; Alves, Leonardo S de B; Barletta, Antonio

    2016-05-01

    The nonlinear stability of a rectangular porous channel saturated by a fluid is here investigated. The aspect ratio of the channel is assumed to be variable. The channel walls are considered impermeable and adiabatic except for the horizontal top which is assumed to be isothermal. The viscous dissipation is acting inside the channel as internal heat generator. A basic throughflow is imposed, and the nonlinear convective stability is investigated by means of the generalized integral transform technique. The neutral stability curve is compared with the one obtained by the linear stability analysis already present in the literature. The growth rate analysis of different unstable modes is performed. The Nusselt number is investigated for several supercritical configurations in order to better understand how the system behaves when conditions far away from neutral stability are considered. The patterns of the neutrally stable convective cells are also reported. Nonlinear simulations support the results obtained by means of the linear stability analysis, confirming that viscous dissipation alone is indeed capable of inducing mixed convection. Low Gebhart or high Péclet numbers lead to a transient overheating of the originally motionless fluid before it settles in its convective steady state.

  12. DC/DC Converter Stability Testing Study

    NASA Technical Reports Server (NTRS)

    Wang, Bright L.

    2008-01-01

    This report presents study results on hybrid DC/DC converter stability testing methods. An input impedance measurement method and a gain/phase margin measurement method were evaluated to be effective to determine front-end oscillation and feedback loop oscillation. In particular, certain channel power levels of converter input noises have been found to have high degree correlation with the gain/phase margins. It becomes a potential new method to evaluate stability levels of all type of DC/DC converters by utilizing the spectral analysis on converter input noises.

  13. The Role of the Dielectric Barrier in Narrow Biological Channels: A Novel Composite Approach to Modeling Single-Channel Currents

    PubMed Central

    Mamonov, Artem B.; Coalson, Rob D.; Nitzan, Abraham; Kurnikova, Maria G.

    2003-01-01

    A composite continuum theory for calculating ion current through a protein channel of known structure is proposed, which incorporates information about the channel dynamics. The approach is utilized to predict current through the Gramicidin A ion channel, a narrow pore in which the applicability of conventional continuum theories is questionable. The proposed approach utilizes a modified version of Poisson-Nernst-Planck (PNP) theory, termed Potential-of-Mean-Force-Poisson-Nernst-Planck theory (PMFPNP), to compute ion currents. As in standard PNP, ion permeation is modeled as a continuum drift-diffusion process in a self-consistent electrostatic potential. In PMFPNP, however, information about the dynamic relaxation of the protein and the surrounding medium is incorporated into the model of ion permeation by including the free energy of inserting a single ion into the channel, i.e., the potential of mean force along the permeation pathway. In this way the dynamic flexibility of the channel environment is approximately accounted for. The PMF profile of the ion along the Gramicidin A channel is obtained by combining an equilibrium molecular dynamics (MD) simulation that samples dynamic protein configurations when an ion resides at a particular location in the channel with a continuum electrostatics calculation of the free energy. The diffusion coefficient of a potassium ion within the channel is also calculated using the MD trajectory. Therefore, except for a reasonable choice of dielectric constants, no direct fitting parameters enter into this model. The results of our study reveal that the channel response to the permeating ion produces significant electrostatic stabilization of the ion inside the channel. The dielectric self-energy of the ion remains essentially unchanged in the course of the MD simulation, indicating that no substantial changes in the protein geometry occur as the ion passes through it. Also, the model accounts for the experimentally observed

  14. Effects of N-glycosylation on hyperpolarization-activated cyclic nucleotide-gated (HCN) channels.

    PubMed

    Li, Mo; Tonggu, Lige; Tang, Lan; Wang, Liguo

    2015-02-15

    Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are activated by membrane hyperpolarization and conduct an inward cation current, which contributes to rhythmic electrical activity of neural and cardiac pacemaker cells. HCN channels have been shown to undergo N-linked glycosylation, and the N-glycosylation has been shown to be required for membrane trafficking and possibly function. In this study, recombinant wild-type (WT) and glycosylation-defective N380Q HCN2 channels were individually or co-expressed in HEK-293 cells. We demonstrate that glycosylation is required for trafficking to the plasma membrane and for the stability of HCN channels in the cell. Interestingly, the heteromeric HCN2 channels of WT and glycosylation-defective N380Q have been observed on cell membranes, indicating that not all four subunits of a tetrameric HCN2 channel need to be glycosylated for HCN2 channels to traffic to plasma membranes. Subsequently, we investigate the effect of N-glycosylation on the function of HCN2 channels. We developed a fluorescence-based flux assay, which makes it possible to establish a negative potential inside liposomes to open HCN2 channels. Using this flux assay, we demonstrate that glycosylation-defective N380Q HCN2 channels reconstituted into liposomes function similarly to WT HCN2 channels. This suggests that N-glycosylation is not required for HCN2 channels to function.

  15. A Leucine Zipper Motif Essential for Gating of Hyperpolarization-activated Channels*

    PubMed Central

    Wemhöner, Konstantin; Silbernagel, Nicole; Marzian, Stefanie; Netter, Michael F.; Rinné, Susanne; Stansfeld, Phillip J.; Decher, Niels

    2012-01-01

    Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are pacemakers in cardiac myocytes and neurons. Although their membrane topology closely resembles that of voltage-gated K+ channels, the mechanism of their unique gating behavior in response to hyperpolarization is still poorly understood. We have identified a highly conserved leucine zipper motif in the S5 segment of HCN family members. In order to study the role of this motif for channel function, the leucine residues of the zipper were individually mutated to alanine, arginine, or glutamine residues. Leucine zipper mutants traffic to the plasma membrane, but the channels lose their sensitivity to open upon hyperpolarization. Thus, our data indicate that the leucine zipper is an important molecular determinant for hyperpolarization-activated channel gating. Residues of the leucine zipper interact with the adjacent S6 segment of the channel. This interaction is essential for voltage-dependent gating of the channel. The lower part of the leucine zipper, at the intracellular mouth of the channel, is important for stabilizing the closed state. Mutations at these sites increase current amplitudes or result in channels with deficient closing and increased min-Po. Our data are further supported by homology models of the open and closed state of the HCN2 channel pore. Thus, we conclude that the leucine zipper of HCN channels is a major determinant for hyperpolarization-activated channel gating. PMID:23048023

  16. A comparison of hydrology and channel hydraulics in headwater streams of the Central Oregon Cascades

    NASA Astrophysics Data System (ADS)

    Hempel, L. A.; Grant, G.; Lewis, S.

    2013-12-01

    Streams with distinctly different flow regimes can be found within close proximity of each other in the Central Oregon Cascades due to the unique hydrogeology of the region. Spring-fed streams with stable discharge regimes tend to have rectangular cross-sections, uniform grain sizes, and frequent channel-spanning wood. In contrast, flashier surface-runoff channels tend to have more variable cross-sections, a wider grain-size distribution, and woody debris accumulations along channel margins. To examine differences in channel hydraulics, we collected high-resolution 3-D maps of 12 channel reaches from tributaries of the McKenzie and Metolius Rivers, OR. Stream channel maps were then used to run a 2-D channel stability model (MD_SWMS). We also compared stream hydrology using 10+ years of stream gage data. We expect bed particles are mobilized more frequently in spring-fed systems, but the opportunity for channel form development-- which occurs when sediment is mobile and when flow reaches or exceeds the active channel flow--is higher in surface-runoff channels. Therefore, each channel-type is characterized by a unique set of hydraulic processes that lead to observed differences in channel form.

  17. Voltage-Gated Calcium Channels

    NASA Astrophysics Data System (ADS)

    Zamponi, Gerald Werner

    Voltage Gated Calcium Channels is the first comprehensive book in the calcium channel field, encompassing over thirty years of progress towards our understanding of calcium channel structure, function, regulation, physiology, pharmacology, and genetics. This book balances contributions from many of the leading authorities in the calcium channel field with fresh perspectives from risings stars in the area, taking into account the most recent literature and concepts. This is the only all-encompassing calcium channel book currently available, and is an essential resource for academic researchers at all levels in the areas neuroscience, biophysics, and cardiovascular sciences, as well as to researchers in the drug discovery area.

  18. Absolutely separating quantum maps and channels

    NASA Astrophysics Data System (ADS)

    Filippov, S. N.; Magadov, K. Yu; Jivulescu, M. A.

    2017-08-01

    Absolutely separable states ϱ remain separable under arbitrary unitary transformations U\\varrho {U}\\dagger . By example of a three qubit system we show that in a multipartite scenario neither full separability implies bipartite absolute separability nor the reverse statement holds. The main goal of the paper is to analyze quantum maps resulting in absolutely separable output states. Such absolutely separating maps affect the states in a way, when no Hamiltonian dynamics can make them entangled afterwards. We study the general properties of absolutely separating maps and channels with respect to bipartitions and multipartitions and show that absolutely separating maps are not necessarily entanglement breaking. We examine the stability of absolutely separating maps under a tensor product and show that {{{Φ }}}\\otimes N is absolutely separating for any N if and only if Φ is the tracing map. Particular results are obtained for families of local unital multiqubit channels, global generalized Pauli channels, and combination of identity, transposition, and tracing maps acting on states of arbitrary dimension. We also study the interplay between local and global noise components in absolutely separating bipartite depolarizing maps and discuss the input states with high resistance to absolute separability.

  19. Evolution and stability of tidal river bifurcations

    NASA Astrophysics Data System (ADS)

    Kleinhans, M. G.

    2011-12-01

    At bifurcations, water and sediment are partitioned, so that long-term evolution of fluvial and deltaic channels is determined by the bifurcation stability. Recent work in fluvial environments showed that bifurcations are commonly unstable so that avulsion results. For tidal rivers it could be argued that the discharge fluctuation enhances transport so that it simply closes of faster than in steady flow, but it could also be argued that tidal phase differences between the bifurcates cause a residual flow that counteracts the closing trend and keeps both bifurcates open. A physics-based numerical model (Delft3D) was used to model fixed-bank fork-shaped bifurcations with and without tides, and with short and long length relative to tidal wavelength. In all cases the bifurcations remained as unstable as without tides and ended invariably in avulsion. Tidal bifurcations unbalanced more rapidly than fluvial bifurcations, because of the increased ebb current and nonlinearity of sediment transport. On the other hand, discharge partitioning at the final bifurcation was much less asymmetrical with tides than without. Tidal wave deformation and production of higher harmonics in the longer channels affected sediment partitioning in the unstable phase but seems to have no effect on equilibrium morphology. Significant phase differences between the bifurcates caused a tidal floss effect, which scoured the bifurcation. In conclusion, symmetrical bifurcations affected by tides are unstable, but their final equilibrium is more symmetrical than without tides unless bifurcates have significant tidal phase differences. Furthermore I modelled growing deltas with self-formed distributary channels with and without cohesive sediment and with and without tides. Here, tides cause the flow to be more focussed in fewer and larger channels, whilst the few bifurcations are relatively stable. Combined fluvial discharge and tidal ebb flow in the channels transports more sediment than in fluvial

  20. Plutonium inventories for stabilization and stabilized materials

    SciTech Connect

    Williams, A.K.

    1996-05-01

    The objective of the breakout session was to identify characteristics of materials containing plutonium, the need to stabilize these materials for storage, and plans to accomplish the stabilization activities. All current stabilization activities are driven by the Defense Nuclear Facilities Safety Board Recommendation 94-1 (May 26, 1994) and by the recently completed Plutonium ES&H Vulnerability Assessment (DOE-EH-0415). The Implementation Plan for accomplishing stabilization of plutonium-bearing residues in response to the Recommendation and the Assessment was published by DOE on February 28, 1995. This Implementation Plan (IP) commits to stabilizing problem materials within 3 years, and stabilizing all other materials within 8 years. The IP identifies approximately 20 metric tons of plutonium requiring stabilization and/or repackaging. A further breakdown shows this material to consist of 8.5 metric tons of plutonium metal and alloys, 5.5 metric tons of plutonium as oxide, and 6 metric tons of plutonium as residues. Stabilization of the metal and oxide categories containing greater than 50 weight percent plutonium is covered by DOE Standard {open_quotes}Criteria for Safe Storage of Plutonium Metals and Oxides{close_quotes} December, 1994 (DOE-STD-3013-94). This standard establishes criteria for safe storage of stabilized plutonium metals and oxides for up to 50 years. Each of the DOE sites and contractors with large plutonium inventories has either started or is preparing to start stabilization activities to meet these criteria.

  1. Roughness characteristics of natural channels

    USGS Publications Warehouse

    Barnes, Harry Hawthorne

    1967-01-01

    Color photographs and descriptive data are presented for 50 stream channels for which roughness coefficients have been determined. All hydraulic computations involving flow in open channels require an evaluation of the roughness characteristics of the channel. In the absence of a satisfactory quantitative procedure this evaluation remains chiefly an art. The ability to evaluate roughness coefficients must be developed through experience. One means of gaining this experience is by examining and becoming acquainted with the appearance of some typical channels whose roughness coefficients are known. The photographs and data contained in this report represent a wide range of channel conditions. Familiarity with the appearance, geometry, and roughness characteristics of these channels will improve the engineer's ability to select roughness coefficients for other channels .

  2. Intersecting Channels near Olympica Fossae

    NASA Image and Video Library

    2016-09-21

    This complicated area contains various types of channels, pits and fractures. We can determine the relative ages of the pits and channels based on which features cross-cut others. Older channels appear smooth-edged and shallow. Younger channels and pits are deeper and more sharp-edged, as well as less sinuous than the shallower channels. What caused this array of various channels and intersecting pits? This region is covered in vast lava flows. The collapse pits here may be collapsed lava tubes or where overlying rock "drained" into voids created by extensional faulting. The older smoother channel that seems to source from this region may have carried an outflow of groundwater. It continues on for over 100 kilometers (62 miles). The orientation and shapes of these features make an interesting geological puzzle. http://photojournal.jpl.nasa.gov/catalog/PIA21066

  3. Chloride channels as drug targets

    PubMed Central

    Verkman, Alan S.; Galietta, Luis J. V.

    2013-01-01

    Chloride channels represent a relatively under-explored target class for drug discovery as elucidation of their identity and physiological roles has lagged behind that of many other drug targets. Chloride channels are involved in a wide range of biological functions, including epithelial fluid secretion, cell-volume regulation, neuroexcitation, smooth-muscle contraction and acidification of intracellular organelles. Mutations in several chloride channels cause human diseases, including cystic fibrosis, macular degeneration, myotonia, kidney stones, renal salt wasting and hyperekplexia. Chloride-channel modulators have potential applications in the treatment of some of these disorders, as well as in secretory diarrhoeas, polycystic kidney disease, osteoporosis and hypertension. Modulators of GABAA (γ-aminobutyric acid A) receptor chloride channels are in clinical use and several small-molecule chloride-channel modulators are in preclinical development and clinical trials. Here, we discuss the broad opportunities that remain in chloride-channel-based drug discovery. PMID:19153558

  4. Position and Trajectrories of helical microswimmers inside circular channels

    NASA Astrophysics Data System (ADS)

    Caldag, Hakan; Yesilyurt, Serhat

    2015-11-01

    This work reports the position and orientation of helical mm-sized microswimmers in circular channels obtained by image processing of recorded images. Microswimmers are biologically inspired structures with huge potential for medical practices such as delivery of potent drugs into tissues. In order to understand the hydrodynamic effects of confinement on the velocity and stability of trajectories of swimmers, we developed helical microswimmers with a magnetic head and a rigid helical tail, similar to those of E. coli bacteria. The experiments are recorded using a digital camera, which is placed above the experimental setup that consists of three Helmholtz pairs, generating a rotating magnetic field. A channel containing the microswimmer is placed along the axis of the innermost coil. Image processing tools based on contrast-enhancement are used to obtain the centroid of the head of the swimmer and orientation of the whole swimmer in the channel. Swimmers that move in the direction of the head, i.e. pushed kinematically by the tail, has helical trajectories, which are more unstable in the presence of Poiesuille flow inside the channel; and the swimmers that are pulled by the tail, have trajectories that stabilize at the centerline of the channel.

  5. Single-channel properties of IKs potassium channels.

    PubMed

    Yang, Y; Sigworth, F J

    1998-12-01

    Expressed in Xenopus oocytes, KvLQT1 channel subunits yield a small, rapidly activating, voltage- dependent potassium conductance. When coexpressed with the minK gene product, a slowly activating and much larger potassium current results. Using fluctuation analysis and single-channel recordings, we have studied the currents formed by human KvLQT1 subunits alone and in conjunction with human or rat minK subunits. With low external K+, the single-channel conductances of these three channel types are estimated to be 0.7, 4.5, and 6.5 pS, respectively, based on noise analysis at 20 kHz bandwidth of currents at +50 mV. Power spectra computed over the range 0.1 Hz-20 kHz show a weak frequency dependence, consistent with current interruptions occurring on a broad range of time scales. The broad spectrum causes the apparent single-channel current value to depend on the bandwidth of the recording, and is mirrored in very "flickery" single-channel events of the channels from coexpressed KvLQT1 and human minK subunits. The increase in macroscopic current due to the presence of the minK subunit is accounted for by the increased apparent single-channel conductance it confers on the expressed channels. The rat minK subunit also confers the property that the outward single-channel current is increased by external potassium ions.

  6. Feedback channel in linear noiseless dynamic systems controlled over the packet erasure network

    NASA Astrophysics Data System (ADS)

    Farhadi, Alireza

    2015-08-01

    This paper is concerned with tracking state trajectory at remote controller, stability and performance of linear time-invariant noiseless dynamic systems with multiple observations over the packet erasure network subject to random packet dropout and transmission delay that does not necessarily use feedback channel full time. Three cases are considered in this paper: (1) without feedback channel, (2) with feedback channel intermittently and (3) with full time availability of feedback channel. For all three cases, coding strategies that result in reliable tracking of state trajectory at remote controller with asymptotically zero mean absolute estimation error are presented. Asymptotic mean absolute stability of the controlled system equipped with each of these coding strategies is shown; trade-offs between duty cycle for feedback channel use, transmission delay and performance, which is defined in terms of the settling time, are studied.

  7. Channel to Nowhere

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 22 May 2003

    A channel-like feature roughly halfway between the Isidis Basin and Elysium Mons shows no connection to either a source region or terminal basin. It may be that this feature is not a channel at all and has instead arisen from the erosion of a once continuous layer of material into remnants that mimic a channel.

    Image information: VIS instrument. Latitude 20.9, Longitude 105 East (255) meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  8. Channels and Erosion

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 20 June 2003

    The dissected and eroded channel observed in this THEMIS image taken of plains materials southwest of the volcano Elysium Mons shows typical erosional islands and depositional features. The interesting thing about this channel is that it appears to start out of nowhere. The MOLA context image shows that the channel originates from a fissure within the ground, whose origin is likely volcanic, but may also be related to volatile processes.

    Image information: VIS instrument. Latitude 19.5, Longitude 126.8 East (233.2 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  9. Channels and Erosion

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 20 June 2003

    The dissected and eroded channel observed in this THEMIS image taken of plains materials southwest of the volcano Elysium Mons shows typical erosional islands and depositional features. The interesting thing about this channel is that it appears to start out of nowhere. The MOLA context image shows that the channel originates from a fissure within the ground, whose origin is likely volcanic, but may also be related to volatile processes.

    Image information: VIS instrument. Latitude 19.5, Longitude 126.8 East (233.2 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  10. The Tow Channel

    NASA Image and Video Library

    2016-10-27

    This archival image was released as part of a gallery comparing JPL's past and present, commemorating the 80th anniversary of NASA's Jet Propulsion Laboratory on Oct. 31, 2016. During World War II, the Jet Propulsion Laboratory had a contract with the U.S. Army to develop rocket torpedoes. This picture from August 1944 shows the test facility, known as the "Tow Channel." It was used for storage for many years before being torn out to make space for the Earth and Space Science Laboratory (Building 300) and the Microdevices Laboratory (Building 302). http://photojournal.jpl.nasa.gov/catalog/PIA21124

  11. Cytoskeletal Actin Gates a Cl− Channel in Neocortical Astrocytes

    PubMed Central

    Lascola, Christopher D.; Nelson, Deborah J.; Kraig, Richard P.

    2009-01-01

    Increases in astroglial Cl− conductance accompany changes in cell morphology and disassembly of cytoskeletal actin, but Cl− channels underlying these conductance increases have not been described. We characterize an outwardly rectifying Cl− channel in rodent neocortical cultured astrocytes and describe how cell shape and cytoskeletal actin modulate channel gating. In inside-out patch-clamp recordings from cultured astrocytes, outwardly rectifying Cl− channels either were spontaneously active or inducible in quiescent patches by depolarizing voltage steps. Average single-channel conductance was 36 pS between −60 and −80 mV and was 75 pS between 60 and 80 mV in symmetrical (150 mm NaCl) solutions. The permeability ratio (PNa/PCl) was 0.14 at lower ionic strength but increased at higher salt concentrations. Both ATP and 4,4-diisothiocyanostilbene-2,2′-disulfonic acid produced a flicker block, whereas Zn2+ produced complete inhibition of channel activity. The frequency of observing both spontaneous and inducible Cl− channel activity was markedly higher in stellate than in flat, polygonally shaped astrocytes. In addition, cytoskeletal actin modulated channel open-state probability (PO) and conductance at negative membrane potentials, controlling the degree of outward rectification. Direct application of phalloidin, which stabilizes actin, preserved low PO and promoted lower conductance levels at negative potentials. Lower PO also was induced by direct application of polymerized actin. The actions of phalloidin and actin were reversed by coapplication of gelsolin and cytochalasin D, respectively. These results provide the first report of an outwardly rectifying Cl− channel in neocortical astrocytes and demonstrate how changes in cell shape and cytoskeletal actin may control Cl− conductance in these cells. PMID:9464993

  12. Cytoskeletal actin gates a Cl- channel in neocortical astrocytes.

    PubMed

    Lascola, C D; Nelson, D J; Kraig, R P

    1998-03-01

    Increases in astroglial Cl- conductance accompany changes in cell morphology and disassembly of cytoskeletal actin, but Cl- channels underlying these conductance increases have not been described. We characterize an outwardly rectifying Cl- channel in rodent neocortical cultured astrocytes and describe how cell shape and cytoskeletal actin modulate channel gating. In inside-out patch-clamp recordings from cultured astrocytes, outwardly rectifying Cl- channels either were spontaneously active or inducible in quiescent patches by depolarizing voltage steps. Average single-channel conductance was 36 pS between -60 and -80 mV and was 75 pS between 60 and 80 mV in symmetrical (150 mM NaCl) solutions. The permeability ratio (PNa/PCl) was 0.14 at lower ionic strength but increased at higher salt concentrations. Both ATP and 4, 4-diisothiocyanostilbene-2,2'-disulfonic acid produced a flicker block, whereas Zn2+ produced complete inhibition of channel activity. The frequency of observing both spontaneous and inducible Cl- channel activity was markedly higher in stellate than in flat, polygonally shaped astrocytes. In addition, cytoskeletal actin modulated channel open-state probability (PO) and conductance at negative membrane potentials, controlling the degree of outward rectification. Direct application of phalloidin, which stabilizes actin, preserved low PO and promoted lower conductance levels at negative potentials. Lower PO also was induced by direct application of polymerized actin. The actions of phalloidin and actin were reversed by coapplication of gelsolin and cytochalasin D, respectively. These results provide the first report of an outwardly rectifying Cl- channel in neocortical astrocytes and demonstrate how changes in cell shape and cytoskeletal actin may control Cl- conductance in these cells.

  13. Heat transfer and flow in spiral channels and coils

    NASA Astrophysics Data System (ADS)

    Vilemas, J. V.; Poškas, P. S.

    1993-06-01

    An analysis of the experimental results for heat transfer on convex and concave walls of slotted spiral channels as well as for local heat transfer around the periphery and along the tube of the coils is presented. Great attention is paid to examining surface friction and its pulsations on the hydrodynamic entrance section and under stabilized coil flow conditions. The transition from laminar to turbulent flow on the convex and concave walls of slotted spiral channels and around the periphery of the tube of different-curvature coils is analyzed.

  14. Bacterial sodium channels: models for eukaryotic sodium and calcium channels.

    PubMed

    Scheuer, Todd

    2014-01-01

    Eukaryotic sodium and calcium channels are made up of four linked homologous but different transmembrane domains. Bacteria express sodium channels comprised of four identical subunits, each being analogous to a single homologous domain of their eukaryotic counterparts. Key elements of primary structure are conserved between bacterial and eukaryotic sodium and calcium channels. The simple protein structure of the bacterial channels has allowed extensive structure-function probes of key regions as well as allowing determination of several X-ray crystallographic structures of these channels. The structures have revealed novel features of sodium and calcium channel pores and elucidated the structural importance of many of the conserved features of primary sequence. The structural information has also formed the basis for computational studies probing the basis for sodium and calcium selectivity and gating.

  15. A hybrid method for more efficient channel-by-channel reconstruction with many channels.

    PubMed

    Huang, Feng; Lin, Wei; Duensing, George R; Reykowski, Arne

    2012-03-01

    In MRI, imaging using receiving coil arrays with a large number of elements is an area of growing interest. With increasing channel numbers for parallel acquisition, longer reconstruction times have become a significant concern. Channel reduction techniques have been proposed to reduce the processing time of channel-by-channel reconstruction algorithms. In this article, two schemes are combined to enable faster and more accurate reconstruction than existing channel reduction techniques. One scheme use two stages of channel reduction instead of one. The other scheme is to incorporate all acquired data into the final reconstruction. The combination of these two schemes is called flexible virtual coil. Applications of flexible virtual coil for partially parallel imaging, motion compensation, and compressed sensing are presented as specific examples. Theoretical analysis and experimental results demonstrate that the proposed method has a major impact in reducing computation cost in reconstruction with high-channel count coil elements. Copyright © 2011 Wiley Periodicals, Inc.

  16. Riparian Vegetation: Controls on Channel Planform in Noncohesive Beds

    NASA Astrophysics Data System (ADS)

    Tal, M.; Paola, C.; Gran, K.

    2001-12-01

    Riparian vegetation has strong consequences for the channel planform and dynamics. An understanding of this role is key to accurate modeling of river systems, and may provide answers to fundamental questions concerning stream dynamics as well as bridge the various approaches to modeling channel evolution. Vegetation on the flood plain works to constrain the flow of the river to a single channel by stabilizing banks and offering resistance to overbank flow. These controls were recently established through a set of controlled experiments at the St. Anthony Falls Laboratory. The runs were designed to determine how addition of vegetation affects channel form and flow dynamics. This was achieved by holding water discharge, sediment discharge, grain size, and slope constant, while making vegetation density the only variable between runs. Plants were grown while water discharge was half its channel-forming value. This work showed that as vegetation density increased there was a decrease in braiding intensity, lateral mobility, and width to depth ratios, and an increase in maximum scour hole depth, and channel relief. While producing braiding experimentally has proven simple, no one has yet produced true dynamic meanders (i.e. high-amplitude bends that grow, cut off, and grow again). Present experimental studies at St. Anthony Falls Laboratory aim to investigate the role of vegetation in the development of a meandering river in otherwise insufficiently cohesive sand that would favor a more stable braided river system. The experiments begin with an unseeded bed into which a straight channel has been carved. Each cycle comprises a period of low discharge during which the bed is seeded with alfalfa seeds. The discharge is raised to a higher discharge only after the plants have grown to a height of about 20 mm (approximately 7 days). The duration of the high-flow stage is such that not more than 10-20% of the channel width is eroded. In addition to offering insight as to the

  17. Minio Vallis Channel

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This VIS image is of the southern reach of Minio Vallis, a small fluvial channel located near the larger Mangala Vallis. Both channels are in the Tharsis region, in the area west of Arsia Mons and southeast of Medusae Fossae.

    Image information: VIS instrument. Latitude -8.2, Longitude 208.1 East (151.9 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  18. Channel Wall Landslides

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    The multiple landslides in this VIS image occur along a steep channel wall. Note the large impact crater in the context image. The formation of the crater may have initially weakened that area of the surface prior to channel formation.

    Image information: VIS instrument. Latitude -2.7, Longitude 324.8 East (35.2 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  19. Channel Wall Landslides

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    The multiple landslides in this VIS image occur along a steep channel wall. Note the large impact crater in the context image. The formation of the crater may have initially weakened that area of the surface prior to channel formation.

    Image information: VIS instrument. Latitude -2.7, Longitude 324.8 East (35.2 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. Utrophin suppresses low frequency oscillations and coupled gating of mechanosensitive ion channels in dystrophic skeletal muscle.

    PubMed

    Lansman, Jeffry B

    2015-01-01

    An absence of utrophin in muscle from mdx mice prolongs the open time of single mechanosensitive channels. On a time scale much longer than the duration of individual channel activations, genetic depletion of utrophin produces low frequency oscillations of channel open probability. Oscillatory channel opening occurred in the dystrophin/utrophin mutants, but was absent in wild-type and mdx fibers. By contrast, small conductance channels showed random gating behavior when present in the same patch. Applying a negative pressure to a patch on a DKO fiber produced a burst of mode II activity, but channels subsequently closed and remained silent for tens of seconds during the maintained pressure stimulus. In addition, simultaneous opening of multiple MS channels could be frequently observed in recordings from patches on DKO fibers, but only rarely in wild-type and mdx muscle. A model which accounts for the single-channel data is proposed in which utrophin acts as gating spring which maintains the mechanical stability a caveolar-like compartment. The state of this compartment is suggested to be dynamic; its continuity with the extracellular surface varying over seconds to minutes. Loss of the mechanical stability of this compartment contributes to pathogenic Ca(2+) entry through MS channels in Duchenne dystrophy.

  1. An RF Sensor for Gauging Screen-Channel Liquid Acquisition Devices for Cryogenic Propellants

    NASA Technical Reports Server (NTRS)

    Zimmerli, Gregory A.; Metzger, Scott; Asipauskas, Marius

    2014-01-01

    A key requirement of a low-gravity screen-channel liquid acquisition device (LAD) is the need to retain 100% liquid in the channel in response to propellant outflow and spacecraft maneuvers. The point at which a screen-channel LAD ingests vapor is known as breakdown, and can be measured several different ways such as: visual observation of bubbles in the LAD channel outflow; a sudden change in pressure drop between the propellant tank and LAD sump outlet; or, an indication by wet-dry sensors placed in the LAD channel or outflow stream. Here we describe a new type of sensor for gauging a screen-channel LAD, the Radio Frequency Mass Gauge (RFMG). The RFMG measures the natural electromagnetic modes of the screen-channel LAD, which is very similar to an RF waveguide, to determine the amount of propellant in the channel. By monitoring several of the RF modes, we show that the RFMG acts as a global sensor of the LAD channel propellant fill level, and enables detection of LAD breakdown even in the absence of outflow. This paper presents the theory behind the RFMG-LAD sensor, measurements and simulations of the RF modes of a LAD channel, and RFMG detection of LAD breakdown in a channel using a simulant fluid during inverted outflow and long-term stability tests.

  2. The lysosomal potassium channel TMEM175 adopts a novel tetrameric architecture.

    PubMed

    Lee, Changkeun; Guo, Jiangtao; Zeng, Weizhong; Kim, Sunghoon; She, Ji; Cang, Chunlei; Ren, Dejian; Jiang, Youxing

    2017-07-27

    TMEM175 is a lysosomal K(+) channel that is important for maintaining the membrane potential and pH stability in lysosomes. It contains two homologous copies of a six-transmembrane-helix (6-TM) domain, which has no sequence homology to the canonical tetrameric K(+) channels and lacks the TVGYG selectivity filter motif found in these channels. The prokaryotic TMEM175 channel, which is present in a subset of bacteria and archaea, contains only a single 6-TM domain and functions as a tetramer. Here, we present the crystal structure of a prokaryotic TMEM175 channel from Chamaesiphon minutus, CmTMEM175, the architecture of which represents a completely different fold from that of canonical K(+) channels. All six transmembrane helices of CmTMEM175 are tightly packed within each subunit without undergoing domain swapping. The highly conserved TM1 helix acts as the pore-lining inner helix, creating an hourglass-shaped ion permeation pathway in the channel tetramer. Three layers of hydrophobic residues on the carboxy-terminal half of the TM1 helices form a bottleneck along the ion conduction pathway and serve as the selectivity filter of the channel. Mutagenesis analysis suggests that the first layer of the highly conserved isoleucine residues in the filter is primarily responsible for channel selectivity. Thus, the structure of CmTMEM175 represents a novel architecture of a tetrameric cation channel whose ion selectivity mechanism appears to be distinct from that of the classical K(+) channel family.

  3. A Beacon Transmission Power Control Algorithm Based on Wireless Channel Load Forecasting in VANETs.

    PubMed

    Mo, Yuanfu; Yu, Dexin; Song, Jun; Zheng, Kun; Guo, Yajuan

    2015-01-01

    In a vehicular ad hoc network (VANET), the periodic exchange of single-hop status information broadcasts (beacon frames) produces channel loading, which causes channel congestion and induces information conflict problems. To guarantee fairness in beacon transmissions from each node and maximum network connectivity, adjustment of the beacon transmission power is an effective method for reducing and preventing channel congestion. In this study, the primary factors that influence wireless channel loading are selected to construct the KF-BCLF, which is a channel load forecasting algorithm based on a recursive Kalman filter and employs multiple regression equation. By pre-adjusting the transmission power based on the forecasted channel load, the channel load was kept within a predefined range; therefore, channel congestion was prevented. Based on this method, the CLF-BTPC, which is a transmission power control algorithm, is proposed. To verify KF-BCLF algorithm, a traffic survey method that involved the collection of floating car data along a major traffic road in Changchun City is employed. By comparing this forecast with the measured channel loads, the proposed KF-BCLF algorithm was proven to be effective. In addition, the CLF-BTPC algorithm is verified by simulating a section of eight-lane highway and a signal-controlled urban intersection. The results of the two verification process indicate that this distributed CLF-BTPC algorithm can effectively control channel load, prevent channel congestion, and enhance the stability and robustness of wireless beacon transmission in a vehicular network.

  4. A Beacon Transmission Power Control Algorithm Based on Wireless Channel Load Forecasting in VANETs

    PubMed Central

    Mo, Yuanfu; Yu, Dexin; Song, Jun; Zheng, Kun; Guo, Yajuan

    2015-01-01

    In a vehicular ad hoc network (VANET), the periodic exchange of single-hop status information broadcasts (beacon frames) produces channel loading, which causes channel congestion and induces information conflict problems. To guarantee fairness in beacon transmissions from each node and maximum network connectivity, adjustment of the beacon transmission power is an effective method for reducing and preventing channel congestion. In this study, the primary factors that influence wireless channel loading are selected to construct the KF-BCLF, which is a channel load forecasting algorithm based on a recursive Kalman filter and employs multiple regression equation. By pre-adjusting the transmission power based on the forecasted channel load, the channel load was kept within a predefined range; therefore, channel congestion was prevented. Based on this method, the CLF-BTPC, which is a transmission power control algorithm, is proposed. To verify KF-BCLF algorithm, a traffic survey method that involved the collection of floating car data along a major traffic road in Changchun City is employed. By comparing this forecast with the measured channel loads, the proposed KF-BCLF algorithm was proven to be effective. In addition, the CLF-BTPC algorithm is verified by simulating a section of eight-lane highway and a signal-controlled urban intersection. The results of the two verification process indicate that this distributed CLF-BTPC algorithm can effectively control channel load, prevent channel congestion, and enhance the stability and robustness of wireless beacon transmission in a vehicular network. PMID:26571042

  5. Mechanism of tetrodotoxin block and resistance in sodium channels.

    PubMed

    Chen, Rong; Chung, Shin-Ho

    2014-03-28

    Tetrodotoxin (TTX) has been used for many decades to characterize the structure and function of biological ion channels. Yet, the precise mechanism by which TTX blocks voltage-gated sodium (NaV) channels is not fully understood. Here molecular dynamics simulations are used to elucidate how TTX blocks mammalian voltage-gated sodium (Nav) channels and why it fails to be effective for the bacterial sodium channel, NaVAb. We find that, in NaVAb, a sodium ion competes with TTX for the binding site at the extracellular end of the filter, thus reducing the blocking efficacy of TTX. Using a model of the skeletal muscle channel, NaV1.4, we show that the conduction properties of the channel observed experimentally are faithfully reproduced. We find that TTX occludes the entrance of NaV1.4 by forming a network of hydrogen-bonds at the outer lumen of the selectivity filter. The guanidine group of TTX adopts a lateral orientation, rather than pointing into the filter as proposed previously. The acidic residues just above the selectivity filter are important in stabilizing the hydrogen-bond network between TTX and NaV1.4. The effect of two single mutations of a critical tyrosine residue in the filter of NaV1.4 on TTX binding observed experimentally is reproduced using computational mutagenesis. Copyright © 2014 Elsevier Inc. All rights reserved.

  6. Bond paths as privileged exchange channels.

    PubMed

    Pendás, A Martín; Francisco, Evelio; Blanco, Miguel A; Gatti, Carlo

    2007-01-01

    Evidence that the bond paths of the quantum theory of atoms-in-molecules (QTAIM) signal preferred quantum-mechanical exchange channels is presented. We show how bond paths between an atom A and the atoms B in its environment appear to be determined by competition among the A-B exchange-correlation energies that always contribute to stabilize the A-B interactions. These pairwise additive stabilizations depend neither on the attractive or repulsive nature of the classical electrostatic interaction between the atoms' charge densities, nor on the change in the self energies of the atoms involved. These other terms may well cause an overall molecular-energy increase in spite of a possibly large A-B exchange-correlation stabilization. After our proposal, bond paths, both at and out of equilibrium geometries, are endowed with a specific energetic meaning that should contribute to reconcile the orthodox QTAIM interpretation with other widely accepted views, and to settle recent controversies questioning the meaning of hydrogen-hydrogen bonding and the nature of the so-called "steric interactions", the role of bond paths in endohedral complexes, and the generality of the results provided by the QTAIM. Implications for the nature of more general closed-shell interactions are also briefly discussed.

  7. Tissue channel morphology in Octopus.

    PubMed

    Browning, J; Casley-Smith, J R

    1981-01-01

    The morphology of tissue channels in muscle and neural tissues of Octopus was investigated, at the ultrastructural level, with a technique involving the precipitation of ferrocyanide ions. The numbers, sizes and conductivities of the channels were estimated from quantitative data. No evidence was gained to indicate that the low microvascular density in Octopus is coupled to an especially extensive network of extravascular channels. The tissue channel system in Octopus appears to be broadly comparable with the mammalian system; a lack of information prevents more appropriate comparisons with marine fishes. Probable functions of tissue channels in Octopus and mammals, and reasons for apparent similarities and differences in the channel organization of these divergent groups, are discussed.

  8. Ion channel therapeutics for pain

    PubMed Central

    Skerratt, Sarah E; West, Christopher W

    2015-01-01

    Pain is a complex disease which can progress into a debilitating condition. The effective treatment of pain remains a challenge as current therapies often lack the desired level of efficacy or tolerability. One therapeutic avenue, the modulation of ion channel signaling by small molecules, has shown the ability to treat pain. However, of the 215 ion channels that exist in the human genome, with 85 ion channels having a strong literature link to pain, only a small number of these channels have been successfully drugged for pain. The focus of future research will be to fully explore the possibilities surrounding these unexplored ion channels. Toward this end, a greater understanding of ion channel modulation will be the greatest tool we have in developing the next generation of drugs for the treatment of pain. PMID:26218246

  9. Multiplicative properties of quantum channels

    NASA Astrophysics Data System (ADS)

    Rahaman, Mizanur

    2017-08-01

    In this paper, we study the multiplicative behaviour of quantum channels, mathematically described by trace preserving, completely positive maps on matrix algebras. It turns out that the multiplicative domain of a unital quantum channel has a close connection to its spectral properties. A structure theorem (theorem 2.5), which reveals the automorphic property of an arbitrary unital quantum channel on a subalgebra, is presented. Various classes of quantum channels (irreducible, primitive, etc) are then analysed in terms of this stabilising subalgebra. The notion of the multiplicative index of a unital quantum channel is introduced, which measures the number of times a unital channel needs to be composed with itself for the multiplicative algebra to stabilise. We show that the maps that have trivial multiplicative domains are dense in completely bounded norm topology in the set of all unital completely positive maps. Some applications in quantum information theory are discussed.

  10. Wakefield Generation in Plasma Channels

    NASA Astrophysics Data System (ADS)

    Volfbeyn, P.; Leemans, W. P.; Brussaard, G. J. H.; Esarey, E.; Wurtele, J. S.

    1999-11-01

    Laser wakefield generation in plasma channels is experimentally studied. Plasma channels, produced using the ignitor-heater method [1] in hydrogen and nitrogen, have been used to guide intense (> 5 x 10^17 W/cm^2), short (<70 fs) infrared (800 nm) laser pulses. Laser pulses injected into these channels produce a plasma wake with a phase velocity close to the speed of light. The transverse density profile of the channel determines the properties of the laser mode as well as of the plasma wave mode. The longitudinally integrated properties of the channel are measured with a Mach-Zehnder interferometer using 400 nm radiation. The probe and reference beam are combined directly on a CCD camera to provide two-dimensional interferograms and also through a spectrometer to allow Fourier domain interferometry. Progress on measuring the transverse channel profile and wakefield amplitudes will be presented. [1] P. Volfbeyn, E. Esarey and W.P. Leemans, Phys. Plasmas 6, 2269 (1999).

  11. Sensing pressure with ion channels.

    PubMed

    Nilius, Bernd; Honoré, Eric

    2012-08-01

    Opening of stretch-activated ion channels (SACs) is the earliest event occurring in mechanosensory transduction. The molecular identity of mammalian SACs has long remained a mystery. Only very recently, Piezo1 and Piezo2 have been shown to be essential components of distinct SACs and moreover, purified Piezo1 forms cationic channels when reconstituted into artificial bilayers. In line with these findings, dPiezo was demonstrated to act in the Drosophila mechanical nociception pathway. Finally, the 3D structure of the two-pore domain potassium channel (K(2P)), TRAAK [weakly inward rectifying K⁺ channel (TWIK)-related arachidonic acid stimulated K⁺ channel], has recently been solved, providing valuable information about pharmacology, selectivity and gating mechanisms of stretch-activated K⁺ channels (SAKs). These recent findings allow a better understanding of the molecular basis of molecular and cellular mechanotransduction. Copyright © 2012 Elsevier Ltd. All rights reserved.

  12. Workshop on Feedback Stabilization of MHD Stabilities

    SciTech Connect

    McGuire, K.; Kugel, H.; La Haye, R.; Mauel, M.; Nevins, W.; Prager, S.

    1996-12-31

    The feedback stabilization of MHD instabilities is an area of research that is critical for improving the performance and economic attractiveness of magnetic confinement devices. A Workshop dedicated to feedback stabilization of MHD instabilities was held from December 11-13, 1996 at the Princeton Plasma Physics Laboratory, Princeton NJ, USA. The resulting presentations, conclusions, and recommendations are summarized.

  13. Covert Channels and Anonymizing Networks

    DTIC Science & Technology

    2003-10-30

    Covert Channels and Anonymizing Networks Ira S. Moskowitz Center for High Assurance Computer Systems Naval Research Laboratory Washington, DC 20375...ABSTRACT There have long been threads of investigation into covert channels, and threads of investigation into anonymity , but these two closely related...channel capacity and anonymity , and poses more questions than it answers. Even this preliminary work has proven difficult, but in this investigation lies

  14. Agonist-activated ion channels

    PubMed Central

    Colquhoun, David

    2006-01-01

    This paper looks at ion channels as an example of the pharmacologist's stock in trade, the action of an agonist on a receptor to produce a response. Looked at in this way, ion channels have been helpful because they are still the only system which is simple enough for quantitative investigation of transduction mechanisms. A short history is given of attempts to elucidate what happens between the time when agonist first binds, and the time when the channel opens. PMID:16402101

  15. A leucine zipper motif essential for gating of hyperpolarization-activated channels.

    PubMed

    Wemhöner, Konstantin; Silbernagel, Nicole; Marzian, Stefanie; Netter, Michael F; Rinné, Susanne; Stansfeld, Phillip J; Decher, Niels

    2012-11-23

    It is poorly understood how hyperpolarization-activated cyclic nucleotide-gated channels (HCNs) function. We have identified a leucine zipper in the S5 segment of HCNs, regulating hyperpolarization-activated and instantaneous current components. The leucine zipper is essential for HCN channel gating. The identification and functional characterization of the leucine zipper is an important step toward the understanding of HCN channel function. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are pacemakers in cardiac myocytes and neurons. Although their membrane topology closely resembles that of voltage-gated K(+) channels, the mechanism of their unique gating behavior in response to hyperpolarization is still poorly understood. We have identified a highly conserved leucine zipper motif in the S5 segment of HCN family members. In order to study the role of this motif for channel function, the leucine residues of the zipper were individually mutated to alanine, arginine, or glutamine residues. Leucine zipper mutants traffic to the plasma membrane, but the channels lose their sensitivity to open upon hyperpolarization. Thus, our data indicate that the leucine zipper is an important molecular determinant for hyperpolarization-activated channel gating. Residues of the leucine zipper interact with the adjacent S6 segment of the channel. This interaction is essential for voltage-dependent gating of the channel. The lower part of the leucine zipper, at the intracellular mouth of the channel, is important for stabilizing the closed state. Mutations at these sites increase current amplitudes or result in channels with deficient closing and increased min-P(o). Our data are further supported by homology models of the open and closed state of the HCN2 channel pore. Thus, we conclude that the leucine zipper of HCN channels is a major determinant for hyperpolarization-activated channel gating.

  16. The Channel Tunnel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    The Channel Tunnel is a 50.5 km-long rail tunnel beneath the English Channel at the Straits of Dover. It connects Dover, Kent in England with Calais, northern France. The undersea section of the tunnel is unsurpassed in length in the world. A proposal for a Channel tunnel was first put forward by a French engineer in 1802. In 1881, a first attempt was made at boring a tunnel from the English side; the work was halted after 800 m. Again in 1922, English workers started boring a tunnel, and advanced 120 m before it too was halted for political reasons. The most recent attempt was begun in 1987, and the tunnel was officially opened in 1994. At completion it was estimated that the project cost around $18 billion. It has been operating at a significant loss since its opening, despite trips by over 7 million passengers per year on the Eurostar train, and over 3 million vehicles per year.

    With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet.

    ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products.

    The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping, and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring

  17. Channel Forming Discharges and Scaling Relationships in Small Streams

    NASA Astrophysics Data System (ADS)

    Brayshaw, D. D.

    2008-12-01

    One of the major challenges in predicting or mitigating the impacts of disturbance on hydrologic systems is to link changes in hydrology to changes in sediment delivery and transport. Because of the complexity of modelling, usually only one system is considered in isolation, with any potential changes in the corresponding system inferred. For instance, a study of a small watershed might consider changes to peak flows or to sediment delivery to the channel, but not alteration in channel pattern caused by those changes. Linking our understanding of expected changes in hydrology and sediment transport is therefore important for improving land use management. In order to improve this understanding, the development of models and concepts linking hydrologic change to geomorphic change, and vice versa, is necessary. Channel and reach parameters (such as width, depth, slope, and channel pattern) reflect the adjustment of the stream channel to inputs of water, wood and sediment from upstream and upslope. Therefore, channel parameters can be used as indicators which synthesize the hydrologic and geomorphic processes occurring in a watershed (Goodwin et al, 1998). Two parameters which are particularly relevant are the bankfull discharge and the effective discharge. Bankfull discharge (Wolman and Leopold, 1957) is defined as the discharge at which the stream channel is full to the top of its banks, but not flooding over the bank. Effective discharge (Wolman and Miller, 1960) is defined as the discharge that, averaged over time, transports the most sediment. Estimating the frequency, magnitude, and duration of bankfull and effective discharge in a single stream reach provides an indication of the stream channel's stability and the frequency with which geomorphically effective events occur in the watershed upstream. Determining the bankfull and effective discharge for multiple streams across a region enables regionalization, consideration of scaling relationships, and evaluation

  18. Ultrasound modulates ion channel currents

    PubMed Central

    Kubanek, Jan; Shi, Jingyi; Marsh, Jon; Chen, Di; Deng, Cheri; Cui, Jianmin

    2016-01-01

    Transcranial focused ultrasound (US) has been demonstrated to stimulate neurons in animals and humans, but the mechanism of this effect is unknown. It has been hypothesized that US, a mechanical stimulus, may mediate cellular discharge by activating mechanosensitive ion channels embedded within cellular membranes. To test this hypothesis, we expressed potassium and sodium mechanosensitive ion channels (channels of the two-pore-domain potassium family (K2P) including TREK-1, TREK-2, TRAAK; NaV1.5) in the Xenopus oocyte system. Focused US (10 MHz, 0.3–4.9 W/cm2) modulated the currents flowing through the ion channels on average by up to 23%, depending on channel and stimulus intensity. The effects were reversible upon repeated stimulation and were abolished when a channel blocker (ranolazine to block NaV1.5, BaCl2 to block K2P channels) was applied to the solution. These data reveal at the single cell level that focused US modulates the activity of specific ion channels to mediate transmembrane currents. These findings open doors to investigations of the effects of  US on ion channels expressed in neurons, retinal cells, or cardiac cells, which may lead to important medical applications. The findings may also pave the way to the development of sonogenetics: a non-invasive, US-based analogue of optogenetics. PMID:27112990

  19. Capacities of quantum amplifier channels

    NASA Astrophysics Data System (ADS)

    Qi, Haoyu; Wilde, Mark M.

    2017-01-01

    Quantum amplifier channels are at the core of several physical processes. Not only do they model the optical process of spontaneous parametric down-conversion, but the transformation corresponding to an amplifier channel also describes the physics of the dynamical Casimir effect in superconducting circuits, the Unruh effect, and Hawking radiation. Here we study the communication capabilities of quantum amplifier channels. Invoking a recently established minimum output-entropy theorem for single-mode phase-insensitive Gaussian channels, we determine capacities of quantum-limited amplifier channels in three different scenarios. First, we establish the capacities of quantum-limited amplifier channels for one of the most general communication tasks, characterized by the trade-off between classical communication, quantum communication, and entanglement generation or consumption. Second, we establish capacities of quantum-limited amplifier channels for the trade-off between public classical communication, private classical communication, and secret key generation. Third, we determine the capacity region for a broadcast channel induced by the quantum-limited amplifier channel, and we also show that a fully quantum strategy outperforms those achieved by classical coherent-detection strategies. In all three scenarios, we find that the capacities significantly outperform communication rates achieved with a naive time-sharing strategy.

  20. Chaotic behavior of channeling particles.

    PubMed

    Chen, Ling; Kaloyeros, Alain E.; Wang, Guang-Hou

    1994-03-01

    Channeling describes the collimated motion of energetic charged particles along the lattice plane or axis in a crystal. The energetic particles are steered through the channels formed by strings of atomic constituents in the lattice. In the case of planar channeling, the motion of a charged particle between the atomic planes can be periodic or quasiperiodic, such as a simple oscillatory motion in the transverse direction. In practice, however, the periodic motion of the channeling particles can be accompanied by an irregular, chaotic behavior. In this paper, the Moliere potential, which is considered as a good analytical approximation for the interaction of channeling particles with the rows of atoms in the lattice, is used to simulate the channeling behavior of positively charged particles in a tungsten (100) crystal plane. By appropriate selection of channeling parameters, such as the projectile energy E(0) and incident angle psi(0), the transition of channeling particles from regular to chaotic motion is demonstrated. It is argued that the fine structures that appear in the angular scan channeling experiments are due to the particles' chaotic motion.

  1. Genetic Control of Potassium Channels.

    PubMed

    Amin, Ahmad S; Wilde, Arthur A M

    2016-06-01

    Approximately 80 genes in the human genome code for pore-forming subunits of potassium (K(+)) channels. Rare variants (mutations) in K(+) channel-encoding genes may cause heritable arrhythmia syndromes. Not all rare variants in K(+) channel-encoding genes are necessarily disease-causing mutations. Common variants in K(+) channel-encoding genes are increasingly recognized as modifiers of phenotype in heritable arrhythmia syndromes and in the general population. Although difficult, distinguishing pathogenic variants from benign variants is of utmost importance to avoid false designations of genetic variants as disease-causing mutations.

  2. TRP channels and psychiatric disorders.

    PubMed

    Chahl, Loris A

    2011-01-01

    Depression and schizophrenia are major psychiatric disorders that cause much human suffering. Current treatments have major limitations and new drug targets are eagerly sought. Study of transient receptor potential (TRP) channels in these disorders is at an early stage and the potential of agents that activate or inhibit these channels remains speculative. The findings that TRPC6 channels promote dendritic growth and are selectively activated by hyperforin, the key constitutent of St John's wort, suggest that TRPC6 channels might prove to be a new target for antidepressant drug development. There is now considerable evidence that TRPV1 antagonists have anxiolytic activity but there is no direct evidence that they have antidepressant activity. There is also no direct evidence that TRP channels play a role in schizophrenia. However, the findings that TRPC channels are involved in neuronal development and fundamental synaptic mechanisms, and that TRPV1 channels play a role in central dopaminergic and cannabinoid mechanisms is suggestive of potential roles of these channels in schizophrenia. Investigation of TRP channels in psychiatric disorders holds the promise of yielding further understanding of the aetiology of psychiatric disorders and the development of new drug treatments.

  3. On funneling of tidal channels

    NASA Astrophysics Data System (ADS)

    Lanzoni, S.; D'Alpaos, A.

    2015-03-01

    Tidal channels dissect the tidal landscape and exert a crucial control on the morphodynamic evolution of these landscapes. Improving our understanding of channel equilibrium morphology is therefore an important issue for both theoretical and practical reasons. We analyze the case of a tidal channel dissecting a relatively short, unvegetated tidal flat characterized by microtidal conditions and a negligible external sediment supply. The three-dimensional equilibrium configuration of the channel is determined on the basis of a hydrodynamic model, describing the cross-sectional distribution of the longitudinal bed shear stresses, coupled with a morphodynamic model retaining the description of the main physical processes shaping the channel and the adjacent intertidal platform. Both channel bed and width are allowed to adapt to the flow field so that an equilibrium altimetric and planimetric configuration is eventually obtained, when erosion becomes negligibly small, and asymptotically constant elevations are reached everywhere within the domain. Model results reproduce several observed channel characteristics of geomorphic relevance, such as the relationship between channel cross-sectional area and the flowing tidal prism, the scaling of the width-to-depth ratio with channel width, and the longitudinal distributions of bed elevations and channel widths. In analogy with empirical evidence from estuaries, tidal channel funneling is usually assumed to be described by an exponential trend. Our theoretical analyses, modeling results, and observational evidence suggest that a linear relationship also provides a good approximation to describe longitudinal variations in channel width for short tidal channels. Longitudinal bed profiles characterized by a strong planform funneling tend to attain an upward concavity, whereas a low degree of convergence implies an almost linear profile. Finally, the model allows one to analyze the influence of environmental conditions (sediment

  4. Demystifying Mechanosensitive Piezo Ion Channels.

    PubMed

    Xu, X Z Shawn

    2016-06-01

    Mechanosensitive channels mediate touch, hearing, proprioception, and blood pressure regulation. Piezo proteins, including Piezo1 and Piezo2, represent a new class of mechanosensitive channels that have been reported to play key roles in most, if not all, of these modalities. The structural architecture and molecular mechanisms by which Piezos act as mechanosensitive channels, however, remain mysterious. Two new studies have now provided critical insights into the atomic structure and molecular basis of the ion permeation and mechano-gating properties of the Piezo1 channel.

  5. Fiber channel services

    NASA Astrophysics Data System (ADS)

    Malavalli, Kumar

    1993-02-01

    There exists an increasing need, in the user environment, for a computer interconnect scheme with higher speed, higher performance and longer reach than the presently available alternatives. There is also a great demand for a multidirectional networking to provide high bandwidth on demand, high distribution capability, random access and high transport flexibility. The users expect low access delay, low transfer delay, high data integrity and a definable quality of service from their networks. All these requirements, however, have to be met with the preservation of the existing software in which a lot of user investment has already been made. In answer to the demands, there has been an emergence of a new network to interconnect heterogeneous systems at very high cost performance ratio. This new network is based on Fiber Channel Standard, blessed by the American National Standards Institute (ANSI).

  6. Turning the tide: estuarine bars and mutually evasive ebb- and flood-dominated channels

    NASA Astrophysics Data System (ADS)

    Kleinhans, M. G.; Leuven, J.; van der Vegt, M.; Baar, A. W.; Braat, L.; Bergsma, L.; Weisscher, S.

    2015-12-01

    Estuaries have perpetually changing and interacting channels and shoals formed by ebb and flood currents, but we lack a descriptive taxonomy and forecasting model. We explore the hypotheses that the great variation of bar and shoal morphologies are explained by similar factors as river bars, namely channel aspect ratio, sediment mobility and limits on bar erosion and chute cutoff caused by cohesive sediment. Here we use remote sensing data and a novel tidal flume setup, the Metronome, to create estuaries or short estuarine reaches from idealized initial conditions, with and without mud supply at the fluvial boundary. Bar width-depth ratios in estuaries are similar to those in braided rivers. In unconfined (cohesionless) experimental estuaries, bar- and channel dynamics increase with increasing river discharge. Ebb- and flood-dominated channels are ubiquitous even in entirely straight sections. The apparent stability of ebb- and flood channels is partly explained by the inherent instability of symmetrical channel bifurcations as in rivers.

  7. Impacts of salt marsh plants on tidal channel initiation and inheritance

    NASA Astrophysics Data System (ADS)

    Schwarz, Christian; Ye, Qinghua; van der Wal, Daphne; Zhang, Liquan; Ysebaert, Tom; Herman, Peter MJ

    2013-04-01

    Tidal channel networks are the most prominent and striking features visible in tidal wetlands. They serve as major pathways for the exchange of water, sediments, nutrients and contaminants between the wetland and the adjacent open water body. Previous studies identified topography guided sheet flows, as the predominate process for tidal channel initiation. Guided through differences in local topography, sheet flows are able to locally exceed bottom shear stress thresholds, initiating scouring and incision of tidal channels, which then further grow through head ward erosion. The fate of these channels after plant colonization is described in literature as being inherited into the salt marsh through vegetation induced bank stabilization (further referred to as vegetation stabilized channel inheritance). In this study we present a combination of flume experiments and modelling simulations elucidating the impact of vegetation on tidal channel initiation. We first studied the impact of plant properties (stiff: Spartina alterniflora versus flexible: Scirpus mariqueter) on local sediment transport utilizing a flume experiment. Then a coupled hydrodynamic morphodynamic plant growth model was set up to simulate plant colonization by these two different species in the pioneer zone at the mudflat - salt marsh transition. Based on the model we investigated the ramifications of interactions between vegetation, sediment and flow on tidal channel initiation. We specifically compared the effect of vegetation properties (such as stiffness, growth velocity and stress tolerance) on emerging channel patterns, hypothesizing that vegetation mediated channel incision (vegetation induced flow routing and differential sedimentation/erosion patterns leading to tidal channel incision) plays an active role in intertidal landscape evolution. We finally extended our model simulation by imposing pre-existing mudflat channels with different maximum depths, to investigate the impact of existing

  8. Flow characteristics on the blade channel vortex in the Francis turbine

    NASA Astrophysics Data System (ADS)

    Guo, P. C.; Wang, Z. N.; Luo, X. Q.; Wang, Y. L.; Zuo, J. L.

    2016-05-01

    Depending on the long-term hydraulic development of Francis turbine, the blade channel vortex phenomenon was investigated systematically from hydraulic design, experimental and numerical computation in this paper. The blade channel vortex difference between the high water head and low water head turbine was also analyzed. Meanwhile, the relationship between the blade channel vortex and the operating stability of hydraulic turbine was also investigated. The results show that the phenomenon of blade channel vortex is an intrinsic property for Francis turbine under small flow rate condition, the turning-point of the blade channel vortex inception curve appears at low unit speed region, and the variation trend of the blade channel vortex inception curve is closely related to the blade inlet edge profile. In addition to, the vortex of the high water head turbine can generally be excluded from the stable operation region, while which is more different for the one of the low water head turbine.

  9. Long-term morphological response to dredging including cut-across-shoal in a tidal channel-shoal system

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Hai; Wang, Chong-Hao; Tang, Li-Qun; Liu, Da-Bin; Guo, Chuan-Sheng; Liu, Chun-Jing; Zhao, Hui-Ming

    2014-12-01

    This study examines long-term channel-shoal stability in the Tieshan Bay, which is located on the southwest coast of China. A large-scale channel-shoal system has historically existed in the outer Tieshan Bay. A navigation waterway is initiated by cutting and dredging a mid-channel shoal to supply coal to a power plant on the middle coast of the Tieshan Bay. Dredging of the access channel to the Tieshan Port was conducted in two stages followed by land reclamation. It is thus of practical meaning to explore how the channel-shoal system will evolve in long term afterwards. This study uses the process-based finite-volume coastal ocean model (FVCOM) to investigate long-term (centennial) morphological evolution of the channel-shoal system. After well calibration of hydrodynamics and sediment transport, the model forecasts morphodynamic evolution in hundred years. The simulations show that continuous erosion in tidal channels and accretion over shoals and intertidal flats occur. However, the cutting and access channels will be subjected to long-term siltation. A secondary channel indicating the reorientation of the access channel will emerge, and a localized channel-ridge system at the junction of the major channels will be formed. The overall erosion/accretion pattern demonstrates the combined effect of bottom friction and advective sediment transport processes to be responsible for the channel-shoal formation. Dredging of the tidal channels will stimulate the stability of the channel-shoal pattern. It suggests that the navigation waterway should be set up following the long-term morphological evolution of the channel-shoal system at a design stage and maintenance dredging volume might thus be minimized.

  10. More About R Channels

    NASA Astrophysics Data System (ADS)

    Clarke, G. K.

    2007-12-01

    Much of our understanding of how subglacial drainage systems operate is based on key papers by Röthlisberger and Shreve that describe the steady-state hydraulics of circular ice-walled water conduits. Subsequent studies have extended these results to include transient conditions---relevant to diurnally- and seasonally-forced drainage systems---and to semi-circular bed-floored channels. In passing from circular to semi-circular conduits it is usual to adopt Nye's creep closure expression for circular tunnels and to assume that creep closure proceeds as it would for a circular ice-walled conduit. This assumption is only valid if ice can slip freely over the subglacial bed and it completely breaks down if free sliding is inhibited. Even for glaciers and ice streams that are sliding at fast rates the frictional resistance to conduit closure can be substantial and it is therefore impossible to maintain a semi-circular channel in a steady-state. The resulting difference between the rate of creep closure at the conduit ceiling and at the sidewalls forces the cross-sectional geometry of the conduit to evolve. At the time of writing it is unclear whether or not non-circular steady-state geometries can exist but either possibility is interesting. If there is no steady-state geometry then subglacial conduits must necessarily operate in an episodic manner. If steady-state geometries do exist then steady-state subglacial conduits must manifest along-path variations in their height-to-width aspect ratio in response to along-path changes in effective pressure and viscous dissipation.

  11. The Discovery Channel Telescope

    NASA Astrophysics Data System (ADS)

    Millis, R. L.; Dunham, E. W.; Sebring, T. A.; Smith, B. W.; de Kock, M.; Wiecha, O.

    2004-11-01

    The Discovery Channel Telescope (DCT) is a 4.2-m telescope to be built at a new site near Happy Jack, Arizona. The DCT features a large prime focus mosaic CCD camera with a 2-degree-diameter field of view especially designed for surveys of KBOs, Centaurs, NEAs and other moving or time-variable targets. The telescope can be switched quickly to a Ritchey-Chretien configuration for optical/IR spectroscopy or near-IR imaging. This flexibility allows timely follow-up physical studies of high priority objects discovered in survey mode. The ULE (ultra-low-expansion) meniscus primary and secondary mirror blanks for the telescope are currently in fabrication by Corning Glass. Goodrich Aerospace, Vertex RSI, M3 Engineering and Technology Corp., and e2v Technologies have recently completed in-depth conceptual design studies of the optics, mount, enclosure, and mosaic focal plane, respectively. The results of these studies were subjected to a formal design review in July, 2004. Site testing at the 7760-ft altitude Happy Jack site began in 2001. Differential image motion observations from 117 nights since January 1, 2003 gave median seeing of 0.84 arcsec FWHM, and the average of the first quartile was 0.62 arcsec. The National Environmental Policy Act (NEPA) process for securing long-term access to this site on the Coconino National Forest is nearing completion and ground breaking is expected in the spring of 2005. The Discovery Channel Telescope is a project of the Lowell Observatory with major financial support from Discovery Communications, Inc. (DCI). DCI plans ongoing television programming featuring the construction of the telescope and the research ultimately undertaken with the DCT. An additional partner can be accommodated in the project. Interested parties should contact the lead author.

  12. ARROYO SECO PARKWAY OVERCROSSING OF ARROYO SECO CHANNEL. CHANNEL IS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    ARROYO SECO PARKWAY OVERCROSSING OF ARROYO SECO CHANNEL. CHANNEL IS BEHIND TREES AND BUSHES AT RIGHT AND LEFT. STONEY DRIVE PASSES UNDER PARKWAY. LOOKING 282°W - Arroyo Seco Parkway, Arroyo Seco Bridge, Spanning Arroyo Seco at milepost 30.10, Los Angeles, Los Angeles County, CA

  13. Engineering of Metabolic Pathways by Artificial Enzyme Channels

    PubMed Central

    Pröschel, Marlene; Detsch, Rainer; Boccaccini, Aldo R.; Sonnewald, Uwe

    2015-01-01

    Application of industrial enzymes for production of valuable chemical compounds has greatly benefited from recent developments in Systems and Synthetic Biology. Both, in vivo and in vitro systems have been established, allowing conversion of simple into complex compounds. Metabolic engineering in living cells needs to be balanced which is achieved by controlling gene expression levels, translation, scaffolding, compartmentation, and flux control. In vitro applications are often hampered by limited protein stability/half-life and insufficient rates of substrate conversion. To improve stability and catalytic activity, proteins are post-translationally modified and arranged in artificial metabolic channels. Within the review article, we will first discuss the supramolecular organization of enzymes in living systems and second summarize current and future approaches to design artificial metabolic channels by additive manufacturing for the efficient production of desired products. PMID:26557643

  14. Dynamics of premixed hydrogen/air flames in mesoscale channels

    SciTech Connect

    Pizza, Gianmarco; Frouzakis, Christos E.; Boulouchos, Konstantinos; Mantzaras, John; Tomboulides, Ananias G.

    2008-10-15

    Direct numerical simulation with detailed chemistry and transport is used to study the stabilization and dynamics of lean ({phi}=0.5) premixed hydrogen/air atmospheric pressure flames in mesoscale planar channels. Channel heights of h=2, 4, and 7 mm, and inflow velocities in the range 0.3{<=}U{sub IN}{<=}1100cm/ s are investigated. Six different burning modes are identified: mild combustion, ignition/extinction, closed steady symmetric flames, open steady symmetric flames, oscillating and, finally, asymmetric flames. Chaotic behavior of cellular flame structures is observed for certain values of U{sub IN}. Stability maps delineating the regions of the different flame types are finally constructed. (author)

  15. Simulating complex ion channel kinetics with IonChannelLab

    PubMed Central

    Covarrubias, Manuel; Sánchez-Rodríguez, Jorge E; Perez-Cornejo, Patricia; Arreola, Jorge

    2010-01-01

    In-silico simulation based on Markov chains is a powerful way to describe and predict the activity of many transport proteins including ion channels. However, modeling and simulation using realistic models of voltage- or ligand-gated ion channels exposed to a wide range of experimental conditions require building complex kinetic schemes and solving complicated differential equations. To circumvent these problems, we developed IonChannelLab a software tool that includes a user-friendly Graphical User Interface and a simulation library. This program supports channels with Ohmic or Goldman-Hodgkin-Katz behavior and can simulate the time-course of ionic and gating currents, single channel behavior and steady-state conditions. The program allows the simulation of experiments where voltage, ligand and ionic concentration are varied independently or simultaneously. PMID:20935453

  16. Mirrored serpentine flow channels for fuel cell

    DOEpatents

    Rock, Jeffrey Allan

    2000-08-08

    A PEM fuel cell having serpentine flow field channels wherein the input/inlet legs of each channel border the input/inlet legs of the next adjacent channels in the same flow field, and the output/exit legs of each channel border the output/exit legs of the next adjacent channels in the same flow field. The serpentine fuel flow channels may be longer, and may contain more medial legs, than the serpentine oxidant flow channels.

  17. Transition in Plane Channel Flow with Spatially Periodic Perturbations.

    NASA Astrophysics Data System (ADS)

    Schatz, Michael Francis

    We studied experimentally the primary and secondary instabilities in a plane channel flow perturbed by a streamwise -periodic array of cylinders. Wall-bounded shear flow in plane channels typically undergoes a direct transition from simple laminar behavior to turbulence with complex spatial and temporal intermittency; such behavior is characteristic of open flows, where fluid can advect through the system. However, the spatially perturbed channel flow displays bifurcations to well-ordered stable states, similar to transition exhibited by closed flows (flows confined in a box). The primary transition is a supercritical Hopf bifurcation arising from convective rather than absolute instability. The critical value of Reynolds number R _1 = 130 for the transition is more than an order of magnitude less than that for the unperturbed flow (R_1 = 5772 from linear stability theory). The stable secondary flow, a two-dimensional travelling-wave, resembles Tollmein-Schlichting waves, the linear modes of plane Poiseuille flow. As in the spatially unperturbed case, intentionally imposed, controlled disturbances are required to reveal transition since the bifurcation arises from convective instability. Numerical simulations are in quantitative agreement with the experimental observations. The secondary flow loses stability at R _2~ 160 to a three-dimensional state with a preferred spanwise periodicity. This tertiary flow demonstrates standing-wave behavior as it evolves along the streamwise direction; equivalent behavior results from differing initial disturbances. The flow structure and the strictly periodic spectra resemble the beginning stages of turbulent breakdown typically displayed by unperturbed plane channel flow; however, we observed no evidence in our experiment that the three-dimensional states continue to evolve toward turbulence. For R _sp {~}{>} 200, power spectra from our experiment have broad subharmonics that are also observed in other wall-bounded shear flows

  18. Littoral steering of deltaic channels

    NASA Astrophysics Data System (ADS)

    Nienhuis, Jaap H.; Ashton, Andrew D.; Giosan, Liviu

    2016-11-01

    The typically single-threaded channels on wave-influenced deltas show striking differences in their orientations, with some channels oriented into the incoming waves (e.g., Ombrone, Krishna), and others oriented away from the waves (e.g., Godavari, Sao Francisco). Understanding the controls on channel orientation is important as the channel location greatly influences deltaic morphology and sedimentology, both subaerially and subaqueously. Here, we explore channel orientation and consequent feedbacks with local shoreline dynamics using a plan-form numerical model of delta evolution. The model treats fluvial sediment delivery to a wave-dominated coast in two ways: 1) channels are assumed to prograde in a direction perpendicular to the local shoreline orientation and 2) a controlled fraction of littoral sediment transport can bypass the river mouth. Model results suggest that channels migrate downdrift when there is a significant net littoral transport and alongshore transport bypassing of the river mouth is limited. In contrast, river channels tend to orient themselves into the waves when fluvial sediment flux is relatively large, causing the shoreline of the downdrift delta flank to attain the orientation of maximum potential sediment transport for the incoming wave climate. Using model results, we develop a framework to estimate channel orientations for wave-influenced deltas that shows good agreement with natural examples. An increase in fluvial sediment input can cause a channel to reorient itself into incoming waves, behavior observed, for example, in the Ombrone delta in Italy. Our results can inform paleoclimate studies by linking channel orientation to fluvial sediment flux and wave energy. In particular, our approach provides a means to quantify past wave directions, which are notoriously difficult to constrain.

  19. Understand spiciness: mechanism of TRPV1 channel activation by capsaicin.

    PubMed

    Yang, Fan; Zheng, Jie

    2017-03-01

    Capsaicin in chili peppers bestows the sensation of spiciness. Since the discovery of its receptor, transient receptor potential vanilloid 1 (TRPV1) ion channel, how capsaicin activates this channel has been under extensive investigation using a variety of experimental techniques including mutagenesis, patch-clamp recording, crystallography, cryo-electron microscopy, computational docking and molecular dynamic simulation. A framework of how capsaicin binds and activates TRPV1 has started to merge: capsaicin binds to a pocket formed by the channel's transmembrane segments, where it takes a "tail-up, head-down" configuration. Binding is mediated by both hydrogen bonds and van der Waals interactions. Upon binding, capsaicin stabilizes the open state of TRPV1 by "pull-and-contact" with the S4-S5 linker. Understanding the ligand-host interaction will greatly facilitate pharmaceutical efforts to develop novel analgesics targeting TRPV1.

  20. A Calcium-Dependent Plasticity Rule for HCN Channels Maintains Activity Homeostasis and Stable Synaptic Learning

    PubMed Central

    Honnuraiah, Suraj; Narayanan, Rishikesh

    2013-01-01

    Theoretical and computational frameworks for synaptic plasticity and learning have a long and cherished history, with few parallels within the well-established literature for plasticity of voltage-gated ion channels. In this study, we derive rules for plasticity in the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, and assess the synergy between synaptic and HCN channel plasticity in establishing stability during synaptic learning. To do this, we employ a conductance-based model for the hippocampal pyramidal neuron, and incorporate synaptic plasticity through the well-established Bienenstock-Cooper-Munro (BCM)-like rule for synaptic plasticity, wherein the direction and strength of the plasticity is dependent on the concentration of calcium influx. Under this framework, we derive a rule for HCN channel plasticity to establish homeostasis in synaptically-driven firing rate, and incorporate such plasticity into our model. In demonstrating that this rule for HCN channel plasticity helps maintain firing rate homeostasis after bidirectional synaptic plasticity, we observe a linear relationship between synaptic plasticity and HCN channel plasticity for maintaining firing rate homeostasis. Motivated by this linear relationship, we derive a calcium-dependent rule for HCN-channel plasticity, and demonstrate that firing rate homeostasis is maintained in the face of synaptic plasticity when moderate and high levels of cytosolic calcium influx induced depression and potentiation of the HCN-channel conductance, respectively. Additionally, we show that such synergy between synaptic and HCN-channel plasticity enhances the stability of synaptic learning through metaplasticity in the BCM-like synaptic plasticity profile. Finally, we demonstrate that the synergistic interaction between synaptic and HCN-channel plasticity preserves robustness of information transfer across the neuron under a rate-coding schema. Our results establish specific physiological roles

  1. Wavefront preserving channel-cut optics for coherent x-ray scattering experiments at the P10 beamline at PETRAIII

    NASA Astrophysics Data System (ADS)

    Zozulya, A. V.; Shabalin, A.; Schulte-Schrepping, H.; Heuer, J.; Spiwek, M.; Sergeev, I.; Besedin, I.; Vartanyants, I. A.; Sprung, M.

    2014-04-01

    We report on the performance of cryogenically cooled monolithic Si(111) channel-cut monochromator optics installed at the coherence beamline P10 of the PETRA III synchrotron source. Our results show that a high quality channel-cut monochromator crystal preserves the beam wavefront and provides excellent beam stability, which offers considerable benefits for coherent x-ray scattering experiments.

  2. Heme Regulates Allosteric Activation of the Slo1 BK Channel

    PubMed Central

    Horrigan, Frank T.; Heinemann, Stefan H.; Hoshi, Toshinori

    2005-01-01

    Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531–535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G–V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G–V simulated by weakening the coupling of both Ca2+ binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca2+- and voltage-dependent gating as well as intrinsic stability of the open state. PMID:15955873

  3. Heme regulates allosteric activation of the Slo1 BK channel.

    PubMed

    Horrigan, Frank T; Heinemann, Stefan H; Hoshi, Toshinori

    2005-07-01

    Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531-535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G-V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G-V simulated by weakening the coupling of both Ca(2+) binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca(2+)- and voltage-dependent gating as well as intrinsic stability of the open state.

  4. Photonic channels for quantum communication

    PubMed

    van Enk SJ; Cirac; Zoller

    1998-01-09

    A general photonic channel for quantum communication is defined. By means of local quantum computing with a few auxiliary atoms, this channel can be reduced to one with effectively less noise. A scheme based on quantum interference is proposed that iteratively improves the fidelity of distant entangled particles.

  5. Modelling Martian surface channel dynamics

    NASA Astrophysics Data System (ADS)

    Coulthard, T. J.; Skinner, C.; Kim, J.; Schumann, G.; Neal, J. C.; Bates, P. D.

    2014-12-01

    Extensive and large surface channel features found at Athabasca and Kasei have previously been attributed to the erosional power of flowing water with palaeoflood discharges being estimated from the surface channel dimensions. However, in order for these channels to be alluvial there are several basic questions to be answered. Are water flows under Martian conditions capable of eroding the amounts of sediment required to leave these channels? Are our present estimates of palaeoflood discharge of correct magnitude to carry out this erosion? And are the channels a product of one or many flood events? Here, we use a numerical model (CAESAR-Lisflood) that links a two-dimensional hydrodynamic flow scheme to a sediment transport model to simulate fluvial morphodynamics in the Athabasca and Kasei regions. CAESAR-Lisflood has been successfully applied to simulating flooding, erosion and deposition on Earth in a number of locations, and allows the development of channels, bars, braids and other fluvial features to be modelled. The numerical scheme of the model was adapted to Martian conditions by adjusting gravity, drag co-efficient, roughness and grainsize terms. Preliminary findings indicate that fluvial erosion and deposition is capable of creating mega channel features found at these sites and that existing palaeflood estimates are commensurate with channel forming discharges for these features.

  6. One channel: open and closed.

    PubMed

    Robertson, Janice L; Roux, Benoît

    2005-10-01

    Structural information about the prokaryotic KirBac3.1 inward rectifier family K(+) channel from Magnetospirillum magnetotacticum is reported. These results from two-dimensional electron cryomicroscopy (EM) shed light on the gating mechanism of members of the Kir channel family.

  7. Basal channels on ice shelves

    NASA Astrophysics Data System (ADS)

    Sergienko, O. V.

    2013-09-01

    Recent surveys of floating ice shelves associated with Pine Island Glacier (Antarctica) and Petermann Glacier (Greenland) indicate that there are channels incised upward into their bottoms that may serve as the conduits of meltwater outflow from the sub-ice-shelf cavity. The formation of the channels, their evolution over time, and their impact on ice-shelf flow are investigated using a fully-coupled ice-shelf/sub-ice-shelf ocean model. The model simulations suggest that channels may form spontaneously in response to meltwater plume flow initiated at the grounding line if there are relatively high melt rates and if there is transverse to ice-flow variability in ice-shelf thickness. Typical channels formed in the simulations have a width of about 1-3 km and a vertical relief of about 100-200 m. Melt rates and sea-water transport in the channels are significantly higher than on the smooth flat ice bottom between the channels. The melt channels develop through melting, deformation, and advection with ice-shelf flow. Simulations suggest that both steady state and cyclic state solutions are possible depending on conditions along the lateral ice-shelf boundaries. This peculiar dynamics of the system has strong implications on the interpretation of observations. The richness of channel morphology and evolution seen in this study suggests that further observations and theoretical analysis are imperative for understanding ice-shelf behavior in warm oceanic conditions.

  8. Channel routing for VLSI layout

    NASA Astrophysics Data System (ADS)

    Schory, Michael

    1988-12-01

    Channel routing for VLSI layout is reviewed and a set of features required of an industrial channel router is defined. A channel router, CAR, was implemented, based on the Greedy and Detour routers. Integrated circuit design is discussed, with attention to the various channel routing problems and models. The major requirements for an industrial channel router to be integrated within general cells and standard cells routing environments are discussed and their fulfillment in CAR is considered. CAR comprises: the Greedy router functionality; the Detour router's obstacle, obstruction and switch box extensions; rectilinear channels; ports located not on standard and immediately surrounding layers; middle ports within the channel; jog on conflict-only to reduce jog use; single layer jogs; and partial pre-routing and dynamic layer optimization. Special features of CAR include: extension of the net definition with a short range tendency; definition of net preferred track; net visibility range in rectilinear channels; an extended area mechanism to deal with obstacles, rectilinear edges, pre-routing and ports on unusual layers; unified jog cost evaluation functions; unified, efficient jog selection; a general evaluation function for track worth; and a net connectivity part to control and handle split nets. Examples are presented of CAR operations.

  9. Single Streptomyces lividans K+ Channels

    PubMed Central

    Heginbotham, Lise; LeMasurier, Meredith; Kolmakova-Partensky, Ludmilla; Miller, Christopher

    1999-01-01

    Basic electrophysiological properties of the KcsA K+ channel were examined in planar lipid bilayer membranes. The channel displays open-state rectification and weakly voltage-dependent gating. Tetraethylammonium blocking affinity depends on the side of the bilayer to which the blocker is added. Addition of Na+ to the trans chamber causes block of open-channel current, while addition to the cis side has no effect. Most striking is the activation of KcsA by protons; channel activity is observed only when the trans bilayer chamber is at low pH. To ascertain which side of the channel faces which chamber, residues with structurally known locations were mapped to defined sides of the bilayer. Mutation of Y82, an external residue, results in changes in tetraethylammonium affinity exclusively from the cis side. Channels with cysteine residues substituted at externally exposed Y82 or internally exposed Q119 are functionally modified by methanethiosulfonate reagents from the cis or trans chambers, respectively. Block by charybdotoxin, known to bind to the channel's external mouth, is observed only when the toxin is added to the cis side of channels mutated to be toxin sensitive. These results demonstrate unambiguously that the protonation sites linked to gating are on the intracellular portion of the KcsA protein. PMID:10498673

  10. Aggravation of north channels' shrinkage and south channels' development in the Yangtze Estuary under dam-induced runoff discharge flattening

    NASA Astrophysics Data System (ADS)

    Zhu, Bo-yuan; Li, Yi-tian; Yue, Yao; Yang, Yun-ping

    2017-03-01

    Construction of dams on rivers has progressively affected the seasonal variability of runoff discharge, which has consequently produced remarkable impacts on the morphology of estuarine channels. This paper considers four-typical-order bifurcations of the Yangtze Estuary and adopts an ebb partition ratio (defined as the diversion ratio of ebb flow in a given branch divided by the total ebb tidal discharge immediately upstream of the river node where the bifurcation occurs) as a measure of water excavating force in the bifurcation channels. Results show that the seasonal variability of runoff discharge at Datong Hydrological Station (Datong) is flattened, being mainly driven by upstream runoff flattening observed at Yichang Hydrological Station (Yichang) and the tributary rivers. Yearly ebb partition ratios of the channels located to the north and south of the islands present decreasing and increasing trends respectively, and as also do the yearly north and south channel volume of the bifurcations. Yearly ebb partition ratio is proved to be an effective index to represent the water excavating force considering the stability of yearly ebb tidal discharge and its relationship with the channel erosion-deposition. River dams are the driving factors behind the runoff flattening at Datong because of their flattening effects on its main contributors (Yichang and tributary rivers). This flattening significantly helps reduce and enlarge the yearly ebb partition ratios of the north and south channels respectively, and then aggravates the shrinkage and development of the north and south channels separately. Yearly ebb partition ratio of the North Passage (NP) must be enlarged in order for the NP to maintain its function as a shipping channel.

  11. District Stability Framework (DSF)

    DTIC Science & Technology

    2010-10-01

    systemic causes for the SOI. • Monitoring and Evaluation . Measure change in the stability environment with respect to specific SOI as well as overall...conditions and operating environments  Better stabilization planning  Better stabilization execution • More effective/thorough Monitoring and Evaluation (IMPACT

  12. Limits to Stability

    ERIC Educational Resources Information Center

    Cottey, Alan

    2012-01-01

    The author reflects briefly on what limited degree of global ecological stability and human cultural stability may be achieved, provided that humanity retains hope and does not give way to despair or hide in denial. These thoughts were triggered by a recent conference on International Stability and Systems Engineering. (Contains 5 notes.)

  13. Limits to Stability

    ERIC Educational Resources Information Center

    Cottey, Alan

    2012-01-01

    The author reflects briefly on what limited degree of global ecological stability and human cultural stability may be achieved, provided that humanity retains hope and does not give way to despair or hide in denial. These thoughts were triggered by a recent conference on International Stability and Systems Engineering. (Contains 5 notes.)

  14. Longitudinal Stability Calculations

    SciTech Connect

    Blaskiewicz,M.

    2009-01-02

    Coupled bunch longitudinal stability in the presence of high frequency impedances is considered. A frequency domain technique is developed and compared with simulations. The frequency domain technique allows for absolute stability tests and is applied to the problem of longitudinal stability in RHIC with the new 56 MHz RF system.

  15. A Drosophila mechanosensory transduction channel.

    PubMed

    Walker, R G; Willingham, A T; Zuker, C S

    2000-03-24

    Mechanosensory transduction underlies a wide range of senses, including proprioception, touch, balance, and hearing. The pivotal element of these senses is a mechanically gated ion channel that transduces sound, pressure, or movement into changes in excitability of specialized sensory cells. Despite the prevalence of mechanosensory systems, little is known about the molecular nature of the transduction channels. To identify such a channel, we analyzed Drosophila melanogaster mechanoreceptive mutants for defects in mechanosensory physiology. Loss-of-function mutations in the no mechanoreceptor potential C (nompC) gene virtually abolished mechanosensory signaling. nompC encodes a new ion channel that is essential for mechanosensory transduction. As expected for a transduction channel, D. melanogaster NOMPC and a Caenorhabditis elegans homolog were selectively expressed in mechanosensory organs.

  16. Continuity of Quantum Channel Capacities

    NASA Astrophysics Data System (ADS)

    Leung, Debbie; Smith, Graeme

    2009-11-01

    We prove that a broad array of capacities of a quantum channel are continuous. That is, two channels that are close with respect to the diamond norm have correspondingly similar communication capabilities. We first show that the classical capacity, quantum capacity, and private classical capacity are continuous, with the variation on arguments {\\varepsilon} apart bounded by a simple function of {\\varepsilon} and the channel’s output dimension. Our main tool is an upper bound of the variation of output entropies of many copies of two nearby channels given the same initial state; the bound is linear in the number of copies. Our second proof is concerned with the quantum capacities in the presence of free backward or two-way public classical communication. These capacities are proved continuous on the interior of the set of non-zero capacity channels by considering mutual simulation between similar channels.

  17. Channelling, a new immunization strategy.

    PubMed

    Gacharna Romero, M G; Silva Pizano, E; Avendano Lamo, J

    1985-01-01

    In 1981, with PAHO/WHO technical assistance, the Ministry of Health, Colombia, designed what is known as the channelling strategy, aimed at improving immunization coverage. This name was given because the strategy is designed to establish communication channels through direct action aimed at promoting health. Health workers and community leaders or guides conduct household visits to identify unvaccinated children or those with incomplete vaccination schedules and "channel" them to health centers or health posts. The channelling strategy developed in Colombia was briefly mentioned in the case study on the Colombian Vaccination Crusade of 1984. It is now being employed for ORT and other PHC components in the Colombian Child Survival and Development Plan, 1985-1987. In the meantime, other countries have adopted the channelling strategy, which is described in this article.

  18. Dual channel self-oscillating optical magnetometer

    SciTech Connect

    Belfi, J.; Bevilacqua, G.; Biancalana, V.; Dancheva, Y.; Khanbekyan, K.; Moi, L.; Cartaleva, S.

    2009-05-15

    We report on a two-channel magnetometer based on nonlinear magneto-optical rotation in a Cs glass cell with buffer gas. The Cs atoms are optically pumped and probed by free running diode lasers tuned to the D{sub 2} line. A wide frequency modulation of the pump laser is used to produce both synchronous Zeeman optical pumping and hyperfine repumping. The magnetometer works in an unshielded environment, and a spurious signal from distant magnetic sources is rejected by means of differential measurement. In this regime the magnetometer simultaneously gives the magnetic field modulus and the field difference. Rejection of the common-mode noise allows for high-resolution magnetometry with a sensitivity of 2 pT/{radical}(Hz). This sensitivity, in conjunction with long-term stability and a large bandwidth, makes it possible to detect water proton magnetization and its free induction decay in a measurement volume of 5 cm{sup 3}.

  19. Channel Aggregation Schemes for Cognitive Radio Networks

    NASA Astrophysics Data System (ADS)

    Lee, Jongheon; So, Jaewoo

    This paper proposed three channel aggregation schemes for cognitive radio networks, a constant channel aggregation scheme, a probability distribution-based variable channel aggregation scheme, and a residual channel-based variable channel aggregation scheme. A cognitive radio network can have a wide bandwidth if unused channels in the primary networks are aggregated. Channel aggregation schemes involve either constant channel aggregation or variable channel aggregation. In this paper, a Markov chain is used to develop an analytical model of channel aggregation schemes; and the performance of the model is evaluated in terms of the average sojourn time, the average throughput, the forced termination probability, and the blocking probability. Simulation results show that channel aggregation schemes can reduce the average sojourn time of cognitive users by increasing the channel occupation rate of unused channels in a primary network.

  20. Seasonal Change in Nearshore and Channel Morphology at Packery Channel, A New Inlet Serving Corpus Christi, Texas

    DTIC Science & Technology

    2011-01-01

    Channel enjoy a variety of activities including fishing, boating, swimming, snorkeling, and kayaking . Consistently strong wind and a weaker longshore...south of Bob Hall Pier. Fish Pass is an artificial inlet that opened in 1978 and began closing naturally soon after construction with complete closure...the Corpus Christi Water Exchange Pass. Rapid natural closure of the Fish Pass created doubt about the stability of the planned inlet at Packery

  1. Channel Floor Yardangs

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 19 July 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth.

    Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms.

    The yardangs in this image are forming in channel floor deposits. The channel itself is funneling the wind to cause the erosion.

    Image information: VIS instrument. Latitude 4.5, Longitude 229.7 East (133.3 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are

  2. Single-Particle Cryo-EM of the Ryanodine Receptor Channel in an Aqueous Environment

    PubMed Central

    Baker, Mariah R.; Fan, Guizhen

    2015-01-01

    Ryanodine receptors (RyRs) are tetrameric ligand-gated Ca2+ release channels that are responsible for the increase of cytosolic Ca2+ concentration leading to muscle contraction. Our current understanding of RyR channel gating and regulation is greatly limited due to the lack of a high-resolution structure of the channel protein. The enormous size and unwieldy shape of Ca2+ release channels make X-ray or NMR methods difficult to apply for high-resolution structural analysis of the full-length functional channel. Single-particle electron cryo-microscopy (cryo-EM) is one of the only effective techniques for the study of such a large integral membrane protein and its molecular interactions. Despite recent developments in cryo-EM technologies and break-through single-particle cryo-EM studies of ion channels, cryospecimen preparation, particularly the presence of detergent in the buffer, remains the main impediment to obtaining atomic-resolution structures of ion channels and a multitude of other integral membrane protein complexes. In this review we will discuss properties of several detergents that have been successfully utilized in cryo-EM studies of ion channels and the emergence of the detergent alternative amphipol to stabilize ion channels for structure-function characterization. Future structural studies of challenging specimen like ion channels are likely to be facilitated by cryo-EM amenable detergents or alternative surfactants. PMID:26913144

  3. Single-particle cryo-EM of the ryanodine receptor channel in an aqueous environment

    PubMed Central

    Baker, Mariah R.; Fan, Guizhen; Serysheva, Irina I.

    2015-01-01

    Ryanodine receptors (RyRs) are tetrameric ligand-gated Ca2+ release channels that are responsible for the increase of cytosolic Ca2+ concentration leading to muscle contraction. Our current understanding of RyR channel gating and regulation is greatly limited due to the lack of a high-resolution structure of the channel protein. The enormous size and unwieldy shape of Ca2+ release channels make X-ray or NMR methods difficult to apply for high-resolution structural analysis of the full-length functional channel. Single-particle electron cryo-microscopy (cryo-EM) is one of the only effective techniques for the study of such a large integral membrane protein and its molecular interactions. Despite recent developments in cryo-EM technologies and break-through single-particle cryo-EM studies of ion channels, cryospecimen preparation, particularly the presence of detergent in the buffer, remains the main impediment to obtaining atomic-resolution structures of ion channels and a multitude of other integral membrane protein complexes. In this review we will discuss properties of several detergents that have been successfully utilized in cryo-EM studies of ion channels and the emergence of the detergent alternative amphipol to stabilize ion channels for structure-function characterization. Future structural studies of challenging specimen like ion channels are likely to be facilitated by cryo-EM amenable detergents or alternative surfactants. PMID:25844145

  4. Utrophin regulates modal gating of mechanosensitive ion channels in dystrophic skeletal muscle

    PubMed Central

    Tan, Nhi; Lansman, Jeffry B

    2014-01-01

    Dystrophin is a large, submembrane cytoskeletal protein, absence of which causes Duchenne muscular dystrophy. Utrophin is a dystrophin homologue found in both muscle and brain whose physiological function is unknown. Recordings of single-channel activity were made from membrane patches on skeletal muscle from mdx, mdx/utrn+/– heterozygotes and mdx/utrn–/– double knockout mice to investigate the role of these cytoskeletal proteins in mechanosensitive (MS) channel gating. We find complex, gene dose-dependent effects of utrophin depletion in dystrophin-deficient mdx muscle: (1) increased MS channel open probability, (2) a shift of MS channel gating to larger pressures, (3) appearance of modal gating of MS channels and small conductance channels and (4) expression of large conductance MS channels. We suggest a physical model in which utrophin acts as a scaffolding protein that stabilizes lipid microdomains and clusters MS channel subunits. Depletion of utrophin disrupts domain composition in a manner that favours open channel area expansion, as well as allowing diffusion and aggregation of additional MS channel subunits. PMID:24879867

  5. The effect of basal channels on oceanic ice-shelf melting

    NASA Astrophysics Data System (ADS)

    Millgate, Thomas; Holland, Paul R.; Jenkins, Adrian; Johnson, Helen L.

    2013-12-01

    The presence of ice-shelf basal channels has been noted in a number of Antarctic and Greenland ice shelves, but their impact on basal melting is not fully understood. Here we use the Massachusetts Institute of Technology general circulation model to investigate the effect of ice-shelf basal channels on oceanic melt rate for an idealized ice shelf resembling the floating tongue of Petermann Glacier in Greenland. The introduction of basal channels prevents the formation of a single geostrophically balanced boundary current; instead the flow is diverted up the right-hand (Coriolis-favored) side of each channel, with a return flow in the opposite direction on the left-hand side. As the prescribed number of basal channels is increased the mean basal melt rate decreases, in agreement with previous studies. For a small number of relatively wide channels the subice flow is found to be a largely geostrophic horizontal circulation. The reduction in melt rate is then caused by an increase in the relative contribution of weakly melting channel crests and keels. For a larger number of relatively narrow channels, the subice flow changes to a vertical overturning circulation. This change in circulation results in a weaker sensitivity of melt rates to channel size. The transition between the two regimes is governed by the Rossby radius of deformation. Our results explain why basal channels play an important role in regulating basal melting, increasing the stability of ice shelves.

  6. Microchannel Technologies for Artificial Lungs: (2) Screen-filled Wide Rectangular Channels

    PubMed Central

    Kung, MC; Lee, JK; Kung, HH; Mockros, LF

    2009-01-01

    Artificial lungs with blood-side channels on a 10 to 40 μm scale would be characterized, similar to the natural lungs, by tens of thousands to hundreds of millions parallel blood channels, short blood paths, low pressure drops, and low blood primes. A major challenge for developing such devices is the requirement that the multitude of channels must be uniform from channel to channel and along each channel. One possible strategy for developing microchannel artificial lungs is to fill broad rectangular channels with micro scale screens that can provide uniform support and stability. The present work explores the effectiveness of 40 μm screen-filled blood-side channels and, as a comparison, 82 μm screen-filled channels. Small concept-devices, consisting of a single 69 mm wide and 3 or 6 mm long channel, were tested using 30% hematocrit blood and oxygen or air on the gas side. The measured oxygen fluxes in the devices were in the range of 4 to 9×10-7 moles/(min·cm2), with the latter close to the theoretical membrane limit. The pressure drop was in the range of 1 to 6 mmHg. Extrapolating the data to a device designed to process 4 L/min suggests a required blood prime of only 35 mL. PMID:18645355

  7. Utrophin regulates modal gating of mechanosensitive ion channels in dystrophic skeletal muscle.

    PubMed

    Tan, Nhi; Lansman, Jeffry B

    2014-08-01

    Dystrophin is a large, submembrane cytoskeletal protein, absence of which causes Duchenne muscular dystrophy. Utrophin is a dystrophin homologue found in both muscle and brain whose physiological function is unknown. Recordings of single-channel activity were made from membrane patches on skeletal muscle from mdx, mdx/utrn(+/-) heterozygotes and mdx/utrn(-/-) double knockout mice to investigate the role of these cytoskeletal proteins in mechanosensitive (MS) channel gating. We find complex, gene dose-dependent effects of utrophin depletion in dystrophin-deficient mdx muscle: (1) increased MS channel open probability, (2) a shift of MS channel gating to larger pressures, (3) appearance of modal gating of MS channels and small conductance channels and (4) expression of large conductance MS channels. We suggest a physical model in which utrophin acts as a scaffolding protein that stabilizes lipid microdomains and clusters MS channel subunits. Depletion of utrophin disrupts domain composition in a manner that favours open channel area expansion, as well as allowing diffusion and aggregation of additional MS channel subunits.

  8. Design of step composition gradient thin film transistor channel layers grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Ahn, Cheol Hyoun; Hee Kim, So; Gu Yun, Myeong; Koun Cho, Hyung

    2014-12-01

    In this study, we proposed the artificially designed channel structure in oxide thin-film transistors (TFTs) called a "step-composition gradient channel." We demonstrated Al step-composition gradient Al-Zn-O (AZO) channel structures consisting of three AZO layers with different Al contents. The effects of stacking sequence in the step-composition gradient channel on performance and electrical stability of bottom-gate TFT devices were investigated with two channels of inverse stacking order (ascending/descending step-composition). The TFT with ascending step-composition channel structure (5 → 10 → 14 at. % Al composition) showed relatively negative threshold voltage (-3.7 V) and good instability characteristics with a reduced threshold voltage shift ( Δ 1.4 V), which was related to the alignment of the conduction band off-set within the channel layer depending on the Al contents. Finally, the reduced Al composition in the initial layer of ascending step-composition channel resulted in the best field effect mobility of 4.5 cm2/V s. We presented a unique active layer of the "step-composition gradient channel" in the oxide TFTs and explained the mechanism of adequate channel design.

  9. Influences of Hardwood Riparian Vegetation on Stream Channel Geometry in Eastern Forested Environments

    NASA Astrophysics Data System (ADS)

    Cohen, L. J.; Furbish, D. J.

    2015-12-01

    Riparian vegetation has been recognized as a controlling factor of stream channel morphology, but specific influences on bed topography and planform geometry are yet to be fully clarified. In temperate environments, hardwood trees serve as prominent bank stabilizers and help create diverse habitats for a variety of aquatic organisms in alluvial channels. This project explores the influence of riparian vegetation on channel geometry in alluvial streams of different sizes. Exposed rootwads increase bank stability and slow channel migration rates, but also cause pool scour that affects thalweg and bedform locations downstream, implying that woody riparian vegetation influences flow conditions and two-dimensional bed geometry in alluvial streams. Field data suggest that the presence of hardwood vegetation modulates channel width, bed topography and planform geometry in low-order streams. In larger channels, rootwads have less influence on planform curvature, but create patchy variations in bed topography that establish thalweg locations and amplify relief of curvature-dominated bedforms. Flume experiments illustrate the genesis of rootwad-induced pool scour and its effect on downstream pool and bar formation. Experimental rootwad pools reflect the relative size and shape of those observed in natural channels. Introduction of riparian obstructions to planar beds also influences thalweg location several channel widths downstream, further supporting the idea of riparian influence on bedform modulation and regulation.

  10. Voltage-gated Proton Channels

    PubMed Central

    DeCoursey, Thomas E.

    2014-01-01

    Voltage-gated proton channels, HV1, have vaulted from the realm of the esoteric into the forefront of a central question facing ion channel biophysicists, namely the mechanism by which voltage-dependent gating occurs. This transformation is the result of several factors. Identification of the gene in 2006 revealed that proton channels are homologues of the voltage-sensing domain of most other voltage-gated ion channels. Unique, or at least eccentric, properties of proton channels include dimeric architecture with dual conduction pathways, perfect proton selectivity, a single-channel conductance ~103 smaller than most ion channels, voltage-dependent gating that is strongly modulated by the pH gradient, ΔpH, and potent inhibition by Zn2+ (in many species) but an absence of other potent inhibitors. The recent identification of HV1 in three unicellular marine plankton species has dramatically expanded the phylogenetic family tree. Interest in proton channels in their own right has increased as important physiological roles have been identified in many cells. Proton channels trigger the bioluminescent flash of dinoflagellates, facilitate calcification by coccolithophores, regulate pH-dependent processes in eggs and sperm during fertilization, secrete acid to control the pH of airway fluids, facilitate histamine secretion by basophils, and play a signaling role in facilitating B-cell receptor mediated responses in B lymphocytes. The most elaborate and best-established functions occur in phagocytes, where proton channels optimize the activity of NADPH oxidase, an important producer of reactive oxygen species. Proton efflux mediated by HV1 balances the charge translocated across the membrane by electrons through NADPH oxidase, minimizes changes in cytoplasmic and phagosomal pH, limits osmotic swelling of the phagosome, and provides substrate H+ for the production of H2O2 and HOCl, reactive oxygen species crucial to killing pathogens. PMID:23798303

  11. 47 CFR 95.7 - Channel sharing.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Channel sharing. 95.7 Section 95.7... SERVICES General Mobile Radio Service (GMRS) § 95.7 Channel sharing. (a) Channels or channel pairs (one 462... and use of channels to reduce interference and to make the most effective use of the facilities....

  12. 47 CFR 95.7 - Channel sharing.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Channel sharing. 95.7 Section 95.7... SERVICES General Mobile Radio Service (GMRS) § 95.7 Channel sharing. (a) Channels or channel pairs (one 462... and use of channels to reduce interference and to make the most effective use of the facilities....

  13. Feedback stabilization initiative

    SciTech Connect

    1997-06-01

    Much progress has been made in attaining high confinement regimes in magnetic confinement devices. These operating modes tend to be transient, however, due to the onset of MHD instabilities, and their stabilization is critical for improved performance at steady state. This report describes the Feedback Stabilization Initiative (FSI), a broad-based, multi-institutional effort to develop and implement methods for raising the achievable plasma betas through active MHD feedback stabilization. A key element in this proposed effort is the Feedback Stabilization Experiment (FSX), a medium-sized, national facility that would be specifically dedicated to demonstrating beta improvement in reactor relevant plasmas by using a variety of MHD feedback stabilization schemes.

  14. Convergence of estuarine channels

    NASA Astrophysics Data System (ADS)

    Dronkers, Job

    2017-07-01

    Tide-dominated coastal plain estuaries have typically up-estuary convergent tidal channels. Analysis of estuarine characteristics indicates a dependence of the convergence length on relative tidal amplitude, relative intertidal area and river flow velocity. In order to explain these relationships we investigate a condition for continuity of net sediment transport throughout the estuary, corresponding to morphodynamic equilibrium. We show, by using an analytical solution of the tidal equations, that this condition is equivalent to a condition on the convergence length. This condition is evaluated for 21 estuaries in different regions of the world. It appears that the convergence length determined in this way can explain observed convergence lengths for the considered set of estuaries. The dependence of the convergence length on different estuarine characteristics is analysed by solving the fully coupled hydro-morphodynamic equations. We show that this dependence limits the range of variation of the tidal velocity amplitude. The analysis provides insight in the morphological response of estuaries to human interventions. The condition can easily be evaluated to yield an estimate of this response.

  15. THERMAL STABILITY OF GLASS PLASTICS.

    DTIC Science & Technology

    COMPOSITE MATERIALS, THERMAL STABILITY), (* GLASS TEXTILES, THERMAL STABILITY), (*LAMINATED PLASTICS , THERMAL STABILITY), HEATING, COOLING, MECHANICAL PROPERTIES, FATIGUE(MECHANICS), FLEXURAL STRENGTH, THERMAL STRESSES, USSR

  16. Geomorphic and vegetative recovery processes along modified stream channels of West Tennessee

    USGS Publications Warehouse

    Simon, Andrew; Hupp, C.R. Tennessee

    1992-01-01

    Hundreds of miles of streams in West Tennessee have been channelized or otherwise modt@ed since the turn of century. After all or parts of a stream are straightened, dredged, or cleared, systematic hydrologic, geomorphic, and ecologic processes collectively begin to reduce energy conditions towards the premodified state. One hundred and five sites along 15 streams were studied in the Obion, Forked Deer, Hatchie, and Wolf River basins. All studied streams, except the Hatchie River, have had major channel modi@cation along all or parts of their courses. Bank material shear-strength properties were determined through drained borehole-shear testing (168 tests) and used to interpret present critical bank conditions and factors of safety, and to estimate future channel-bank stability. Mean values of cohesive strength and angle of internal friction were 1.26 pounds per square inch and 30.1 degrees, respectively. Dendrogeomorphic analyses were made using botanical evidence of channel-bank failures to determine rates of channel widening; buried riparian stems were analyzed to determine rates of bank accretion. Channel bed-level changes through time and space were represented by a power equation. Plant ecological analyses were ma& to infer relative bank stability, to identify indicator species of the stage of bank recovery, and to determine patterns of vegetation development through the course of channel evolution. Quantitative data on morphologic changes were used with previously developed six-stage models of channel evolution and bank-slope development to estimate trends of geomorphic and ecologic processes and forms through time. Immediately after channel modr@cations, a 10- to 1%yearperiod of channel-bed degradation ensues at and upstream from the most recent modifications (area of maximum disturbance). Channel-bed lowering by &gradation was as much as 20 feet along some stream reaches. Downstream from the area of maximum disturbance, the bed was aggraded by the

  17. Ryanodine receptors as leak channels.

    PubMed

    Guerrero-Hernández, Agustín; Ávila, Guillermo; Rueda, Angélica

    2014-09-15

    Ryanodine receptors are Ca(2+) release channels of internal stores. This review focuses on those situations and conditions that transform RyRs from a finely regulated ion channel to an unregulated Ca(2+) leak channel and the pathological consequences of this alteration. In skeletal muscle, mutations in either CaV1.1 channel or RyR1 results in a leaky behavior of the latter. In heart cells, RyR2 functions normally as a Ca(2+) leak channel during diastole within certain limits, the enhancement of this activity leads to arrhythmogenic situations that are tackled with different pharmacological strategies. In smooth muscle, RyRs are involved more in reducing excitability than in stimulating contraction so the leak activity of RyRs in the form of Ca(2+) sparks, locally activates Ca(2+)-dependent potassium channels to reduce excitability. In neurons the enhanced activity of RyRs is associated with the development of different neurodegenerative disorders such as Alzheimer and Huntington diseases. It appears then that the activity of RyRs as leak channels can have both physiological and pathological consequences depending on the cell type and the metabolic condition.

  18. Pharmacology of cardiac potassium channels.

    PubMed

    Li, Gui-Rong; Dong, Ming-Qing

    2010-01-01

    Cardiac K(+) channels are cardiomyocyte membrane proteins that regulate K(+) ion flow across the cell membrane on the electrochemical gradient and determine the resting membrane potential and the cardiac action potential morphology and duration. Several K(+) channels have been well studied in the human heart. They include the transient outward K(+) current I(to1), the ultra-rapidly activating delayed rectifier current I(Kur), the rapidly and slowly activating delayed rectifier currents I(Kr) and I(Ks), the inward rectifier K(+) current I(K1), and ligand-gated K(+) channels, including adenosine-5'-triphosphate (ATP)-sensitive K(+) current (I(KATP)) and acetylcholine-activated current (I(KACh)). Regional differences of K(+) channel expression contribute to the variable morphologies and durations of cardiac action potentials from sinus node and atrial to ventricular myocytes, and different ventricular layers from endocardium and midmyocardium to epicardium. They also show different responses to endogenous regulators and/or pharmacological agents. K(+) channels are well-known targets for developing novel anti-arrhythmic drugs that can effectively prevent/inhibit cardiac arrhythmias. Especially, atrial-specific K(+) channel currents (I(Kur) and I(KACh)) are the targets for developing atrial-selective anti-atrial fibrillation drugs, which has been greatly progressed in recent years. This chapter concentrates on recent advances in intracellular signaling regulation and pharmacology of cardiac K(+) channels under physiological and pathophysiological conditions.

  19. TRPV channels and vascular function

    PubMed Central

    Baylie, R.L.; Brayden, J.E.

    2010-01-01

    Transient receptor potential channels, of the vanilloid subtype (TRPV), act as sensory mediators, being activated by endogenous ligands, heat, mechanical and osmotic stress. Within the vasculature, TRPV channels are expressed in smooth muscle cells, endothelial cells, as well as in peri-vascular nerves. Their varied distribution and polymodal activation properties make them ideally suited to a role in modulating vascular function, perceiving and responding to local environmental changes. In endothelial cells, TRPV1 is activated by endocannabinoids, TRPV3 by dietary agonists, and TRPV4 by shear stress, epoxyeicosatrienoic acids (EETs), and downstream of Gq-coupled receptor activation. Upon activation, these channels contribute to vasodilation via nitric oxide (NO), prostacyclin (PGI2), and intermediate/small conductance potassium channel (IKCa/SKCa) dependent pathways. In smooth muscle, TRPV4 is activated by endothelial derived EETs, leading to large conductance potassium channel (BKCa) activation and smooth muscle hyperpolarization. Conversely, smooth muscle TRPV2 channels contribute to global calcium entry and may aid constriction. TRPV1 and TRPV4 are expressed in sensory nerves and can cause vasodilation through CGRP and substance P release as well as mediating vascular function via the baroreceptor reflex (TRPV1) or via increasing sympathetic outflow during osmotic stress (TRPV4). Thus, TRPV channels play important roles in the regulation of normal and pathological cellular function in the vasculature. PMID:21062421

  20. Ion Channels in Brain Metastasis

    PubMed Central

    Klumpp, Lukas; Sezgin, Efe C.; Eckert, Franziska; Huber, Stephan M.

    2016-01-01

    Breast cancer, lung cancer and melanoma exhibit a high metastatic tropism to the brain. Development of brain metastases severely worsens the prognosis of cancer patients and constrains curative treatment options. Metastasizing to the brain by cancer cells can be dissected in consecutive processes including epithelial–mesenchymal transition, evasion from the primary tumor, intravasation and circulation in the blood, extravasation across the blood–brain barrier, formation of metastatic niches, and colonization in the brain. Ion channels have been demonstrated to be aberrantly expressed in tumor cells where they regulate neoplastic transformation, malignant progression or therapy resistance. Moreover, many ion channel modulators are FDA-approved drugs and in clinical use proposing ion channels as druggable targets for future anti-cancer therapy. The present review article aims to summarize the current knowledge on the function of ion channels in the different processes of brain metastasis. The data suggest that certain channel types involving voltage-gated sodium channels, ATP-release channels, ionotropic neurotransmitter receptors and gap junction-generating connexins interfere with distinct processes of brain metastazation. PMID:27618016