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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. Application of Channel Stability Methods - Case Studies

    DTIC Science & Technology

    1994-09-01

    to stabilize the banks (Figure 18). The Hogback , a rock ridge at about mile 8.0 that dips under the Puerco River channel, pro- vides grade control and...the grade control at the Hogback . Reach I was established as the supply reach for the stability analysis (Figure 20). Channel geometry in this reach...was defined by 5-ft contour topographic maps. Reach 2 extends from the Hogback to the upstream end of channel realigned by the highway department. Two

  4. 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.

  5. 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.

  6. 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.

  7. 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)

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  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. 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

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. High-stability transparent amorphous oxide TFT with a silicon-doped back-channel layer

    NASA Astrophysics Data System (ADS)

    Lee, Hyoung-Rae; Park, Jea-Gun

    2014-10-01

    We significantly reduced various electrical instabilities of amorphous indium gallium zinc oxide thin-film transistors (TFTs) by using the co-deposition of silicon on an a-IGZO back channel. This process showed improved stability of the threshold voltage ( V th ) under high temperature and humidity and negative gate-bias illumination stress (NBIS) without any reduction of IDS. The enhanced stability was achieved with silicon, which has higher metal-oxide bonding strengths than gallium does. Additionally, SiO X distributed on the a-IGZO surface reduced the adsorption and the desorption of H2O and O2. This process is applicable to the TFT manufacturing process with a variable sputtering target.

  18. 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.

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. Methacrylate Polymer Scaffolding Enhances the Stability of Suspended Lipid Bilayers for Ion Channel Recordings and Biosensor Development

    PubMed Central

    Bright, Leonard K.; Baker, Christopher A.; Bränström, Robert; Saavedra, S. Scott; Aspinwall, Craig A.

    2016-01-01

    Black lipid membranes (BLMs) provide a synthetic environment that facilitates measurement of ion channel activity in diverse analytical platforms. The limited electrical, mechanical and temporal stabilities of BLMs pose a significant challenge to development of highly stable measurement platforms. Here, ethylene glycol dimethacrylate (EGDMA) and butyl methacrylate (BMA) were partitioned into BLMs and photopolymerized to create a cross-linked polymer scaffold in the bilayer lamella that dramatically improved BLM stability. The commercially available methacrylate monomers provide a simple, low cost, and broadly accessible approach for preparing highly stabilized BLMs useful for ion channel analytical platforms. When prepared on silane-modified glass microapertures, the resulting polymer scaffold-stabilized (PSS)-BLMs exhibited significantly improved lifetimes of 23 ± 9 to 40 ± 14 h and > 10-fold increase in mechanical stability, with breakdown potentials > 2000 mV attainable, depending on surface modification and polymer cross-link density. Additionally, the polymer scaffold exerted minimal perturbations to membrane electrical integrity as indicated by mean conductance measurements. When gramicidin A and α-hemolysin were reconstituted into PSS-BLMs, the ion channels retained function comparable to conventional BLMs. This approach is a key advance in the formation of stabilized BLMs and should be amenable to a wide range of receptor and ion channel functionalized platforms. PMID:26925461

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. 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).

  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. 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

  20. 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

  1. 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.

  2. 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.

  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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. Stability Thresholds and Performance Standards for Flexible Lining Materials in Channel and Slope Restoration Applications

    DTIC Science & Technology

    2012-07-01

    riprap, concrete ), soft or light armoring (e.g., erosion control blankets, ECBs, an early type of so-called rolled erosion control product, reinforced ...slope stabilization. In some applications, reinforced vegetative covers can be used in lieu of rock riprap, concrete paving, or articulated block or...produced in a roll, natural or synthetic, degradable or non-degradable, short- or long-term USEPA, ASTM, ECTC Turf reinforcement mat TRM A type of

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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:

  16. 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.

  17. 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

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  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. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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...

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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

  1. Channel catfish

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  2. 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.

  3. 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).

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. 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).

  13. 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.

  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. 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.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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…

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. 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

  4. 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)

  5. 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.

  6. 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.

  7. Ion channels in asthma.

    PubMed

    Valverde, Miguel A; Cantero-Recasens, Gerard; Garcia-Elias, Anna; Jung, Carole; Carreras-Sureda, Amado; Vicente, Rubén

    2011-09-23

    Ion channels are specialized transmembrane proteins that permit the passive flow of ions following their electrochemical gradients. In the airways, ion channels participate in the production of epithelium-based hydroelectrolytic secretions and in the control of intracellular Ca(2+) levels that will ultimately activate almost all lung cells, either resident or circulating. Thus, ion channels have been the center of many studies aiming to understand asthma pathophysiological mechanisms or to identify therapeutic targets for better control of the disease. In this minireview, we focus on molecular, genetic, and animal model studies associating ion channels with asthma.

  8. 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

  9. 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.

  10. 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).

  11. 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.

  12. 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.

  13. Ion channels in toxicology.

    PubMed

    Restrepo-Angulo, Iván; De Vizcaya-Ruiz, Andrea; Camacho, Javier

    2010-08-01

    Ion channels play essential roles in human physiology and toxicology. Cardiac contraction, neural transmission, temperature sensing, insulin release, regulation of apoptosis, cellular pH and oxidative stress, as well as detection of active compounds from chilli, are some of the processes in which ion channels have an important role. Regulation of ion channels by several chemicals including those found in air, water and soil represents an interesting potential link between environmental pollution and human diseases; for instance, de novo expression of ion channels in response to exposure to carcinogens is being considered as a potential tool for cancer diagnosis and therapy. Non-specific binding of several drugs to ion channels is responsible for a huge number of undesirable side-effects, and testing guidelines for several drugs now require ion channel screening for pharmaceutical safety. Animal toxins targeting human ion channels have serious effects on the population and have also provided a remarkable tool to study the molecular structure and function of ion channels. In this review, we will summarize the participation of ion channels in biological processes extensively used in toxicological studies, including cardiac function, apoptosis and cell proliferation. Major findings on the adverse effects of drugs on ion channels as well as the regulation of these proteins by different chemicals, including some pesticides, are also reviewed. Association of ion channels and toxicology in several biological processes strongly suggests these proteins to be excellent candidates to follow the toxic effects of xenobiotics, and as potential early indicators of life-threatening situations including chronic degenerative diseases.

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Cooperative gating between ion channels.

    PubMed

    Choi, Kee-Hyun

    2014-01-01

    Cooperative gating between ion channels, i.e. the gating of one channel directly coupled to the gating of neighboring channels, has been observed in diverse channel types at the single-channel level. Positively coupled gating could enhance channel-mediated signaling while negative coupling may effectively reduce channel gating noise. Indeed, the physiological significance of cooperative channel gating in signal transduction has been recognized in several in vivo studies. Moreover, coupled gating of ion channels was reported to be associated with some human disease states. In this review, physiological roles for channel cooperativity and channel clustering observed in vitro and in vivo are introduced, and stimulation-induced channel clustering and direct channel cross linking are suggested as the physical mechanisms of channel assembly. Along with physical clustering, several molecular mechanisms proposed as the molecular basis for functional coupling of neighboring channels are covered: permeant ions as a channel coupling mediator, concerted channel activation through the membrane, and allosteric mechanisms. Also, single-channel analysis methods for cooperative gating such as the binomial analysis, the variance analysis, the conditional dwell time density analysis, and the maximum likelihood fitting analysis are reviewed and discussed.

  7. 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.

  8. 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.

  9. 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.

  10. 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)

  11. 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

  12. Calcium Channel Blockers

    MedlinePlus

    ... such as high blood pressure, chest pain and Raynaud's disease. Find out more about this class of medication. ... Irregular heartbeats (arrhythmia) Some circulatory conditions, such as Raynaud's disease For black people and older people, calcium channel ...

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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).

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

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

    DTIC Science & Technology

    1981-04-01

    8217 &’DURING CURRENT TIME BLOCK’/) S06 FORMAT( SX ,’TIME BLOCK’,12,3X,’TIME STEP’,14, SX .,IOF8.3) 509 FORMAT(//15X,’T-OTAL MEASURED SEDIMENT YIELD =’,F20.S,’ LBS...C) WD1H ’WIDTW(IC) [:PR=CPER (IC) EPR=EPER ( I(’) CDP =CDEP (IC) FUP - EDEP (C EXP=1 S BE T= i 0/E XP KIN=CHE-ZY*L..P**) .5 AE= (Q /K I N) **BET IF

  4. 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.

  5. 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.

  6. 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.

  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. 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…

  9. 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.

  10. 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.

  11. 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…

  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. 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.

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  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. 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.

  8. ``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.

  9. 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.

  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. 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

  12. Umbellulone modulates TRP channels.

    PubMed

    Zhong, Jian; Minassi, Alberto; Prenen, Jean; Taglialatela-Scafati, Orazio; Appendino, Giovanni; Nilius, Bernd

    2011-12-01

    Inhalation of umbellulone (UMB), the offensive principle of the so-called "headache tree" (California bay laurel, Umbellularia californica Nutt.), causes a painful cold sensation. We therefore studied the action of UMB and some derivatives devoid of thiol-trapping properties on the "cold" transient receptor potential cation channels TRPA1 and TRPM8. UMB activated TRPA1 in a dose-dependent manner that was attenuated by cysteine-to-serine isosteric mutation in TRPA1 (C622S), while channel block was observed at higher concentration. However, although activation by mustard oil was completely prevented in these mutants, UMB still retained activating properties, indicating that it acts on TRPA1 only as a partial electrophilic agonist. UMB also activated TRPM8, but to a lower extent than TRPA1. Removing Michael acceptor properties of UMB (reduction or nucleophilic trapping) was detrimental for the activation of TRPA1, but increased the blocking potency. This was, however, attenuated by acetylation of the hydroxylated analogs. All UMB derivatives, except the acetylated derivatives, were also TRPM8 activators. They acted, however, in a bimodal manner, inhibiting the channel more potently than UMB, and with tetrahydro-UMB being the most potent TRPM8 activator. In conclusion, UMB is a bimodal activator of TRPA1 and a weak activator of TRPM8. Non-electrophilic derivatives of UMB are better TRPM8 activators than the natural product and also potent blockers of this channel as well as of TRPA1. The lack of effects of the acetylated UMB derivatives suggests that steric hindrance may prevent access to the recognition site for the bicyclic monoterpene pharmacophore on TRPA1 and TRPM8.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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).

  5. 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

  6. 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.

  7. 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.

  8. The stretch-dependent potassium channel TREK-1 and its function in murine myometrium.

    PubMed

    Monaghan, Kevin; Baker, Salah A; Dwyer, Laura; Hatton, William C; Sik Park, Kyung; Sanders, Kenton M; Koh, Sang Don

    2011-03-01

    Smooth muscle of the uterus stays remarkably quiescent during normal pregnancy to allow sufficient time for development of the fetus. At present the mechanisms leading to uterine quiescence during pregnancy and how the suppression of activity is relieved at term are poorly understood. Myometrial excitability is governed by ion channels, and a major hypothesis regarding the regulation of contractility during pregnancy has been that expression of certain channels is regulated by hormonal influences. We have explored the expression and function of stretch-dependent K+ (SDK) channels, which are likely to be due to TREK channels, in murine myometrial tissues and myocytes using PCR, Western blots, patch clamp, intracellular microelectrode and isometric force measurements. TREK-1 is more highly expressed than TREK-2 in myometrium, and there was no detectable expression of TRAAK. Expression of TREK-1 transcripts and protein was regulated during pregnancy and delivery. SDK channels were activated in response to negative pressure applied to patches. SDK channels were insensitive to a broad-spectrum of K+ channel blockers, including tetraethylammonium and 4-aminopyridine, and insensitive to intracellular Ca2+. SDK channels were activated by stretch and arachidonic acid and inhibited by reagents that block TREK-1 channels, l-methionine and/or methioninol. Our data suggest that uterine excitability and contractility during pregnancy is regulated by the expression of SDK/TREK-1 channels. Up-regulation of these channels stabilizes membrane potential and controls contraction during pregnancy and down-regulation of these channels induces the onset of delivery.

  9. 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

  10. Ion Channels in Neurological Disorders.

    PubMed

    Kumar, Pravir; Kumar, Dhiraj; Jha, Saurabh Kumar; Jha, Niraj Kumar; Ambasta, Rashmi K

    2016-01-01

    The convergent endeavors of the neuroscientist to establish a link between clinical neurology, genetics, loss of function of an important protein, and channelopathies behind neurological disorders are quite intriguing. Growing evidence reveals the impact of ion channels dysfunctioning in neurodegenerative disorders (NDDs). Many neurological/neuromuscular disorders, viz, Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, amyotrophic lateral sclerosis, and age-related disorders are caused due to altered function or mutation in ion channels. To maintain cell homeostasis, ion channels are playing a crucial role which is a large transmembrane protein. Further, these channels are important as it determines the membrane potential and playing critically in the secretion of neurotransmitter. Behind NDDs, losses of pathological proteins and defective ion channels have been reported and are found to aggravate the disease symptoms. Moreover, ion channel dysfunctions are eliciting a range of symptoms, including memory loss, movement disabilities, neuromuscular sprains, and strokes. Since the possible mechanistic role played by aberrant ion channels, their receptor and associated factors in neurodegeneration remained elusive; therefore, it is a challenging task for the neuroscientist to implement the therapeutics for targeting NDDs. This chapter reviews the potential role of the ion channels in membrane physiology and brain homeostasis, where ion channels and their associated factors have been characterized with their functional consequences in neurological diseases. Moreover, mechanistic role of perturbed ion channels has been identified in various NDDs, and finally, ion channel modulators have been investigated for their therapeutic intervention in treating common NDDs.

  11. 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.

  12. 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 .

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  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. 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

  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. 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.

  5. 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.

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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).

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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)

  8. 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

  9. 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

  10. 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

  11. 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.)

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Effects of spanwise rotation on the structure of two-dimensional fully developed turbulent channel flow.

    NASA Technical Reports Server (NTRS)

    Johnston, J. P.; Halleen, R. M.; Lezius, D. K.

    1972-01-01

    Experiments on fully developed turbulent flow in a channel which is rotating at a steady rate about a spanwise axis are described. The Coriolis force components in the region of two-dimensional mean flow affect both local and global stability. Three stability-related phenomena were observed or inferred: (1) the reduction (increase) of the rate of wall-layer streak bursting in locally stabilized (destabilized) wall layers; (2) the total suppression of transition to turbulence in a stabilized layer; (3) the development of large-scale roll cells on the destabilized side of the channel by growth of a Taylor-Gortler vortex instability. Local effects of rotational stabilization, such as reduction of the turbulent stress in wall layers, can be related to the local Richardson number in a simple way. This paper not only investigates this effect, but also, by methods of flow visualization, exposes some of the underlying structure changes caused by rotation.-

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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....

  15. 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....

  16. Jamming in Microfluidic Channels

    NASA Astrophysics Data System (ADS)

    Ortiz, Carlos; Daniels, Karen; Riehn, Robert

    2009-11-01

    We experimentally investigate the flow of a colloid through a microfluidic device. The glass microfluidic device consists of a wide channel with spatially periodic funnels manufactured with photolithographic methods. The device was etched to a depth of about 1 micron that restricts the solid phase of the colloid, fluorescent polystyrene spheres with sub-micron radii, to quasi-2D motion. The liquid phase of the colloid is an aqueous solution with trace amounts of a non-ionic surfactant and with a pH about 2 units above the pKa of the surface groups on the polystyrene spheres to maintain a stable colloid at concentrations high enough to produce jamming. The flow rate of the colloid is controlled by a computer interfaced syringe pump with two controllable modes of operation: a continuous, steady mode that provides a plug-like velocity profile and a discrete, jerky mode that sends compressional waves of specifiable sizes through the colloid. Using fluorescence microscopy, we observe the interactions between the colloid and the glass funnels and investigate how the interaction depends on the funnel geometry. In particular, we investigate the jamming transition from a liquid-like flowing state to a solid-like stationary state.

  17. 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

  18. 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

  19. ATP release through pannexon channels

    PubMed Central

    Dahl, Gerhard

    2015-01-01

    Extracellular adenosine triphosphate (ATP) serves as a signal for diverse physiological functions, including spread of calcium waves between astrocytes, control of vascular oxygen supply and control of ciliary beat in the airways. ATP can be released from cells by various mechanisms. This review focuses on channel-mediated ATP release and its main enabler, Pannexin1 (Panx1). Six subunits of Panx1 form a plasma membrane channel termed ‘pannexon’. Depending on the mode of stimulation, the pannexon has large conductance (500 pS) and unselective permeability to molecules less than 1.5 kD or is a small (50 pS), chloride-selective channel. Most physiological and pathological stimuli induce the large channel conformation, whereas the small conformation so far has only been observed with exclusive voltage activation of the channel. The interaction between pannexons and ATP is intimate. The pannexon is not only the conduit for ATP, permitting ATP efflux from cells down its concentration gradient, but the pannexon is also modulated by ATP. The channel can be activated by ATP through both ionotropic P2X as well as metabotropic P2Y purinergic receptors. In the absence of a control mechanism, this positive feedback loop would lead to cell death owing to the linkage of purinergic receptors with apoptotic processes. A control mechanism preventing excessive activation of the purinergic receptors is provided by ATP binding (with low affinity) to the Panx1 protein and gating the channel shut. PMID:26009770

  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

  1. Microbial Senses and Ion Channels

    NASA Astrophysics Data System (ADS)

    Kung, Ching; Zhou, Xin-Liang; Su, Zhen-Wei; Haynes, W. John; Loukin, Sephan H.; Saimi, Yoshiro

    The complexity of animals and plants is due largely to cellular arrangement. The structures and activities of macromolecules had, however, evolved in early microbes long before the appearance of this complexity. Among such molecules are those that sense light, heat, force, water, and ligands. Though historically and didactically associated with the nervous system, ion channels also have deep evolutionary roots. For example, force sensing with channels, which likely began as water sensing through membrane stretch generated by osmotic pressure, must be ancient and is universal in extant species. Extant microbial species, such as the model bacterium Escherichia coli and yeast Saccharomyces cerevisiae, are equipped with stretch-activated channels. The ion channel proteins MscL and MscS show clearly that these bacterial channels receive stretch forces from the lipid bilayer. TRPY1, the mechanosensitive channel in yeast, is being developed towards a similar basic understanding of channels of the TRP (transientreceptor- potential) superfamily. TRPY1 resides in the vacuolar membrane and releases Ca2+ from the vacuole to the cytoplasm upon hyperosmotic shock. Unlike in most TRP preparations from animals, the mechanosensitivity of TRPY1 can be examined directly under patch clamp in either whole-vacuole mode or excised patch mode. The combination of direct biophysical examination in vitro with powerful microbial genetics in vivo should complement the study of mechanosensations of complex animals and plants.

  2. 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.

  3. IA channels: diverse regulatory mechanisms.

    PubMed

    Carrasquillo, Yarimar; Nerbonne, Jeanne M

    2014-04-01

    In many peripheral and central neurons, A-type K(+) currents, IA, have been identified and shown to be key determinants in shaping action potential waveforms and repetitive firing properties, as well as in the regulation of synaptic transmission and synaptic plasticity. The functional properties and physiological roles of native neuronal IA, however, have been shown to be quite diverse in different types of neurons. Accumulating evidence suggests that this functional diversity is generated by multiple mechanisms, including the expression and subcellular distributions of IA channels encoded by different voltage-gated K(+) (Kv) channel pore-forming (α) subunits, interactions of Kv α subunits with cytosolic and/or transmembrane accessory subunits and regulatory proteins and post-translational modifications of channel subunits. Several recent reports further suggest that local protein translation in the dendrites of neurons and interactions between IA channels with other types of voltage-gated ion channels further expands the functional diversity of native neuronal IA channels. Here, we review the diverse molecular mechanisms that have been shown or proposed to underlie the functional diversity of native neuronal IA channels.

  4. Substrate channeling in proline metabolism

    PubMed Central

    Arentson, Benjamin W.; Sanyal, Nikhilesh; Becker, Donald F.

    2012-01-01

    Proline metabolism is an important pathway that has relevance in several cellular functions such as redox balance, apoptosis, and cell survival. Results from different groups have indicated that substrate channeling of proline metabolic intermediates may be a critical mechanism. One intermediate is pyrroline-5-carboxylate (P5C), which upon hydrolysis opens to glutamic semialdehyde (GSA). Recent structural and kinetic evidence indicate substrate channeling of P5C/GSA occurs in the proline catabolic pathway between the proline dehydrogenase and P5C dehydrogenase active sites of bifunctional proline utilization A (PutA). Substrate channeling in PutA is proposed to facilitate the hydrolysis of P5C to GSA which is unfavorable at physiological pH. The second intermediate, gamma-glutamyl phosphate, is part of the proline biosynthetic pathway and is extremely labile. Substrate channeling of gamma-glutamyl phosphate is thought to be necessary to protect it from bulk solvent. Because of the unfavorable equilibrium of P5C/GSA and the reactivity of gamma-glutamyl phosphate, substrate channeling likely improves the efficiency of proline metabolism. Here, we outline general strategies for testing substrate channeling and review the evidence for channeling in proline metabolism. PMID:22201749

  5. 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.

  6. Pharmacology of cardiac potassium channels.

    PubMed

    Tamargo, Juan; Caballero, Ricardo; Gómez, Ricardo; Valenzuela, Carmen; Delpón, Eva

    2004-04-01

    Cardiac K+ channels are membrane-spanning proteins that allow the passive movement of K+ ions across the cell membrane along its electrochemical gradient. They regulate the resting membrane potential, the frequency of pacemaker cells and the shape and duration of the cardiac action potential. Additionally, they have been recognized as potential targets for the actions of neurotransmitters and hormones and class III antiarrhythmic drugs that prolong the action potential duration (APD) and refractoriness and have been found effective to prevent/suppress cardiac arrhythmias. In the human heart, K+ channels include voltage-gated channels, such as the rapidly activating and inactivating transient outward current (Ito1), the ultrarapid (IKur), rapid (IKr) and slow (IKs) components of the delayed rectifier current and the inward rectifier current (IK1), the ligand-gated channels, including the adenosine triphosphate-sensitive (IKATP) and the acetylcholine-activated (IKAch) currents and the leak channels. Changes in the expression of K+ channels explain the regional variations in the morphology and duration of the cardiac action potential among different cardiac regions and are influenced by heart rate, intracellular signalling pathways, drugs and cardiovascular disorders. A progressive number of cardiac and noncardiac drugs block cardiac K+ channels and can cause a marked prolongation of the action potential duration (i.e. an acquired long QT syndrome, LQTS) and a distinct polymorphic ventricular tachycardia termed torsades de pointes. In addition, mutations in the genes encoding IKr (KCNH2/KCNE2) and IKs (KCNQ1/KCNE1) channels have been identified in some types of the congenital long QT syndrome. This review concentrates on the function, molecular determinants, regulation and, particularly, on the mechanism of action of drugs modulating the K+ channels present in the sarcolemma of human cardiac myocytes that contribute to the different phases of the cardiac action

  7. Marine Toxins Targeting Ion Channels

    PubMed Central

    Arias, Hugo R.

    2006-01-01

    This introductory minireview points out the importance of ion channels for cell communication. The basic concepts on the structure and function of ion channels triggered by membrane voltage changes, the so-called voltage-gated ion channels (VGICs), as well as those activated by neurotransmitters, the so-called ligand-gated ion channel (LGICs), are introduced. Among the most important VGIC superfamiles, we can name the voltage-gated Na+ (NaV), Ca2+ (CaV), and K+ (KV) channels. Among the most important LGIC super families, we can include the Cys-loop or nicotinicoid, the glutamate-activated (GluR), and the ATP-activated (P2XnR) receptor superfamilies. Ion channels are transmembrane proteins that allow the passage of different ions in a specific or unspecific manner. For instance, the activation of NaV, CaV, or KV channels opens a pore that is specific for Na+, Ca2+, or K+, respectively. On the other hand, the activation of certain LGICs such as nicotinic acetylcholine receptors, GluRs, and P2XnRs allows the passage of cations (e.g., Na+, K+, and/or Ca2+), whereas the activation of other LGICs such as type A γ-butyric acid and glycine receptors allows the passage of anions (e.g., Cl− and/or HCO3−). In this regard, the activation of NaV and CaV as well as ligand-gated cation channels produce membrane depolarization, which finally leads to stimulatory effects in the cell, whereas the activation of KV as well as ligand-gated anion channels induce membrane hyperpolarization that finally leads to inhibitory effects in the cell. The importance of these ion channel superfamilies is emphasized by considering their physiological functions throughout the body as well as their pathophysiological implicance in several neuronal diseases. In this regard, natural molecules, and especially marine toxins, can be potentially used as modulators (e.g., inhibitors or prolongers) of ion channel functions to treat or to alleviate a specific ion channel-linked disease (e

  8. DPPX potassium channel antibody

    PubMed Central

    Tobin, William Oliver; Lennon, Vanda A.; Komorowski, Lars; Probst, Christian; Clardy, Stacey Lynn; Aksamit, Allen J.; Appendino, Juan Pablo; Lucchinetti, Claudia F.; Matsumoto, Joseph Y.; Pittock, Sean J.; Sandroni, Paola; Tippmann-Peikert, Maja; Wirrell, Elaine C.

    2014-01-01

    Objective: To describe the detection frequency and clinical associations of immunoglobulin G (IgG) targeting dipeptidyl-peptidase-like protein-6 (DPPX), a regulatory subunit of neuronal Kv4.2 potassium channels. Methods: Specimens from 20 patients evaluated on a service basis by tissue-based immunofluorescence yielded a synaptic immunostaining pattern consistent with DPPX-IgG (serum, 20; CSF, all 7 available). Transfected HEK293 cell-based assay confirmed DPPX specificity in all specimens. Sixty-nine patients with stiff-person syndrome and related disorders were also evaluated by DPPX-IgG cell-based assay. Results: Of 20 seropositive patients, 12 were men; median symptom onset age was 53 years (range, 13–75). Symptom onset was insidious in 15 and subacute in 5. Twelve patients reported prodromal weight loss. Neurologic disorders were multifocal. All had one or more brain or brainstem manifestations: amnesia (16), delirium (8), psychosis (4), depression (4), seizures (2), and brainstem disorders (15; eye movement disturbances [8], ataxia [7], dysphagia [6], dysarthria [4], respiratory failure [3]). Nine patients reported sleep disturbance. Manifestations of central hyperexcitability included myoclonus (8), exaggerated startle (6), diffuse rigidity (6), and hyperreflexia (6). Dysautonomia involved the gastrointestinal tract (9; diarrhea [6], gastroparesis, and constipation [3]), bladder (7), cardiac conduction system (3), and thermoregulation (1). Two patients had B-cell neoplasms: gastrointestinal lymphoma (1), and chronic lymphocytic leukemia (1). Substantial neurologic improvements followed immunotherapy in 7 of 11 patients with available treatment data. DPPX-IgG was not detected in any of the stiff-person syndrome patients. Conclusions: DPPX-IgG is a biomarker for an immunotherapy-responsive multifocal neurologic disorder of the central and autonomic nervous systems. PMID:25320100

  9. Stability of holographic superconductors

    SciTech Connect

    Kanno, Sugumi; Soda, Jiro

    2010-10-15

    We study the dynamical stability of holographic superconductors. We first classify perturbations around black hole background solutions into vector and scalar sectors by means of a 2-dimensional rotational symmetry. We prove the stability of the vector sector by explicitly constructing the positive definite Hamiltonian. To reveal a mechanism for the stabilization of a superconducting phase, we construct a quadratic action for the scalar sector. From the action, we see the stability of black holes near a critical point is determined by the equation of motion for a charged scalar field. We show the effective mass of the charged scalar field in hairy black holes is always above the Breitenlohner-Freedman bound near the critical point due to the backreaction of a gauge field. It implies the stability of the superconducting phase. We also argue that the stability continues away from the critical point.

  10. Stability of holographic superconductors

    NASA Astrophysics Data System (ADS)

    Kanno, Sugumi; Soda, Jiro

    2010-10-01

    We study the dynamical stability of holographic superconductors. We first classify perturbations around black hole background solutions into vector and scalar sectors by means of a 2-dimensional rotational symmetry. We prove the stability of the vector sector by explicitly constructing the positive definite Hamiltonian. To reveal a mechanism for the stabilization of a superconducting phase, we construct a quadratic action for the scalar sector. From the action, we see the stability of black holes near a critical point is determined by the equation of motion for a charged scalar field. We show the effective mass of the charged scalar field in hairy black holes is always above the Breitenlohner-Freedman bound near the critical point due to the backreaction of a gauge field. It implies the stability of the superconducting phase. We also argue that the stability continues away from the critical point.

  11. Infinitely many kinds of quantum channels

    SciTech Connect

    Hastings, Matthew B

    2008-01-01

    We define the ability of a quantum channel to simulate another by means of suitable encoding and decoding operations. While classical channels have only two equivalence classes under simulation (channels with non-vanishing capacity and those with vanishing capacity), we show that there are an uncountable infinity of different equivalence classes of quantum channels using the example of the quantum erasure channel. Our results also imply a kind of 'Matthew principle' for error correction on certain channels.

  12. Stabilized Laser Gravimeter

    DTIC Science & Technology

    1976-11-01

    McMullen, "Stabilized Laser Gravim- eter," Proceedings of the 20th International Instrumentations Symposium, Albuquerque, New Mexico , May 1974. N.D...and N.D. McMullen, "Stabilized Laser Gravimeter," Proceedings of the 20th International Instrumentations Symposium, Albuquerque, New Mexico , May 1974...International Instrumentations *i, Albuquerque, New Mexico , May 1974. 3. J. Levine and J.L. Hall, "Design and Operation of a Methane Absorp- tion Stabilized

  13. Impact of channel incision on the hydraulics of flood flows: Examples from Polish Carpathian rivers

    NASA Astrophysics Data System (ADS)

    Wyżga, Bartłomiej; Zawiejska, Joanna; Radecki-Pawlik, Artur

    2016-11-01

    Channel deepening may result from channel incision or river metamorphosis changing a wide and shallow channel to a narrow and deep one. As only the first type of channel change leads to increased flow capacity of the channel, a lowering of water stage associated with a given discharge rather than a lowering of river bed should be used to identify channel incision. A lowering of minimum annual stage at gauging stations is typically used to assess the relative importance of channel incision along a river or within a particular region. Rivers of the Polish Carpathians incised by 0.5-3.8 m over the twentieth century, with the amount of incision being greater in their lower and middle courses than in the upper ones. Variability in the hydraulic importance of channel incision with increasing river size is analysed by comparing changes in the frequency of valley floor inundation at gauging stations located along the seventh-order Dunajec River. Despite a lower absolute amount of channel incision in the upper river course, here incision has increased channel conveyance and reduced the frequency of valley floor inundation considerably more than in the lower course. Hydraulic effects of channel incision depend also on lateral stability of an incising river. Low-energy rivers from the eastern part of the Polish Carpathians remained laterally stable during channel incision. This has resulted in substantial lowering of stages for low flood discharges and markedly smaller one for high-magnitude floods, whereas velocity of the flows conveyed over the highly elevated floodplains has decreased considerably. In high-energy rivers from the western part of the Polish Carpathians, alternation of incision and lateral channel migration has led to the formation of incised meander belts, with substantially lowered stages for all flood discharges and increased velocity of the flows conveyed over the newly-formed, low-lying floodplains.

  14. GlialCAM, a CLC-2 Cl(-) channel subunit, activates the slow gate of CLC chloride channels.

    PubMed

    Jeworutzki, Elena; Lagostena, Laura; Elorza-Vidal, Xabier; López-Hernández, Tania; Estévez, Raúl; Pusch, Michael

    2014-09-02

    GlialCAM, a glial cell adhesion molecule mutated in megalencephalic leukoencephalopathy with subcortical cysts, targets the CLC-2 Cl(-) channel to cell contacts in glia and activates CLC-2 currents in vitro and in vivo. We found that GlialCAM clusters all CLC channels at cell contacts in vitro and thus studied GlialCAM interaction with CLC channels to investigate the mechanism of functional activation. GlialCAM slowed deactivation kinetics of CLC-Ka/barttin channels and increased CLC-0 currents opening the common gate and slowing its deactivation. No functional effect was seen for common gate deficient CLC-0 mutants. Similarly, GlialCAM targets the common gate deficient CLC-2 mutant E211V/H816A to cell contacts, without altering its function. Thus, GlialCAM is able to interact with all CLC channels tested, targeting them to cell junctions and activating them by stabilizing the open configuration of the common gate. These results are important to better understand the physiological role of GlialCAM/CLC-2 interaction.

  15. Highly stable thin film transistors using multilayer channel structure

    NASA Astrophysics Data System (ADS)

    Nayak, Pradipta K.; Wang, Zhenwei; Anjum, D. H.; Hedhili, M. N.; Alshareef, H. N.

    2015-03-01

    We report highly stable gate-bias stress performance of thin film transistors (TFTs) using zinc oxide (ZnO)/hafnium oxide (HfO2) multilayer structure as the channel layer. Positive and negative gate-bias stress stability of the TFTs was measured at room temperature and at 60 °C. A tremendous improvement in gate-bias stress stability was obtained in case of the TFT with multiple layers of ZnO embedded between HfO2 layers compared to the TFT with a single layer of ZnO as the semiconductor. The ultra-thin HfO2 layers act as passivation layers, which prevent the adsorption of oxygen and water molecules in the ZnO layer and hence significantly improve the gate-bias stress stability of ZnO TFTs.

  16. Highly stable thin film transistors using multilayer channel structure

    SciTech Connect

    Nayak, Pradipta K.; Wang, Zhenwei; Anjum, D. H.; Hedhili, M. N.; Alshareef, H. N.

    2015-03-09

    We report highly stable gate-bias stress performance of thin film transistors (TFTs) using zinc oxide (ZnO)/hafnium oxide (HfO{sub 2}) multilayer structure as the channel layer. Positive and negative gate-bias stress stability of the TFTs was measured at room temperature and at 60 °C. A tremendous improvement in gate-bias stress stability was obtained in case of the TFT with multiple layers of ZnO embedded between HfO{sub 2} layers compared to the TFT with a single layer of ZnO as the semiconductor. The ultra-thin HfO{sub 2} layers act as passivation layers, which prevent the adsorption of oxygen and water molecules in the ZnO layer and hence significantly improve the gate-bias stress stability of ZnO TFTs.

  17. Internet Addiction: Stability and Change

    ERIC Educational Resources Information Center

    Huang, Chiungjung

    2010-01-01

    This longitudinal study examined five indices of stability and change in Internet addiction: structural stability, mean-level stability, differential stability, individual-level stability, and ipsative stability. The study sample was 351 undergraduate students from end of freshman year to end of junior year. Convergent findings revealed stability…

  18. Stabilizing Grout Compatibility Study

    SciTech Connect

    HARBOUR, JOHNR.

    2004-05-19

    This report provides data that will be used to formulate the stabilizing grout and includes experimental results for Tc-99 stabilization by two reagents, (1) ground granulated blast furnace slag (GGBFS) and (2) surface treated hydroxyapatite (HA). One or both of these reagents are being considered by CH2M HILL for incorporation in the binder portion (matrix portion without sand) of the stabilizing grout. The technical basis for identifying the grout ingredient(s) for stabilizing technetium (Tc-99) will be provided by researchers at the Savannah River Technology Center (SRTC) in a subsequent report.

  19. A universal set of qubit quantum channels

    NASA Astrophysics Data System (ADS)

    Braun, Daniel; Giraud, Olivier; Nechita, Ion; Pellegrini, Clément; Žnidarič, Marko

    2014-04-01

    We investigate the set of quantum channels acting on a single qubit. We provide an alternative, compact generalization of the Fujiwara-Algoet conditions for complete positivity to non-unital qubit channels, which we then use to characterize the possible geometric forms of the pure output of the channel. We provide universal sets of quantum channels for all unital qubit channels as well as for all extremal (not necessarily unital) qubit channels, in the sense that all qubit channels in these sets can be obtained by concatenation of channels in the corresponding universal set. We also show that our universal sets are essentially minimal.

  20. Catalytic reaction in confined flow channel

    DOEpatents

    Van Hassel, Bart A.

    2016-03-29

    A chemical reactor comprises a flow channel, a source, and a destination. The flow channel is configured to house at least one catalytic reaction converting at least a portion of a first nanofluid entering the channel into a second nanofluid exiting the channel. The flow channel includes at least one turbulating flow channel element disposed axially along at least a portion of the flow channel. A plurality of catalytic nanoparticles is dispersed in the first nanofluid and configured to catalytically react the at least one first chemical reactant into the at least one second chemical reaction product in the flow channel.

  1. FAITH Water Channel Flow Visualization

    NASA Video Gallery

    Water channel flow visualization experiments are performed on a three dimensional model of a small hill. This experiment was part of a series of measurements of the complex fluid flow around the hi...

  2. TRP channels in the skin.

    PubMed

    Tóth, Balázs I; Oláh, Attila; Szöllősi, Attila Gábor; Bíró, Tamás

    2014-05-01

    Emerging evidence suggests that transient receptor potential (TRP) ion channels not only act as 'polymodal cellular sensors' on sensory neurons but are also functionally expressed by a multitude of non-neuronal cell types. This is especially true in the skin, one of the largest organs of the body, where they appear to be critically involved in regulating various cutaneous functions both under physiological and pathophysiological conditions. In this review, we focus on introducing the roles of several cutaneous TRP channels in the regulation of the skin barrier, skin cell proliferation and differentiation, and immune functions. Moreover, we also describe the putative involvement of several TRP channels in the development of certain skin diseases and identify future TRP channel-targeted therapeutic opportunities.

  3. Potassium Channels in Neurofbromatosis-1

    DTIC Science & Technology

    2006-01-01

    Neurofibromatosis-1 (NF-1) is an autosomal dominant genetic disorder commonly associated with cognitive impairments, including low IQ, learning ... disabilities , behavioral difficulties, executive dysfunction and language-based deficits. Despite the growing recognition of the importance of SK channels

  4. B-52 stability augmentation system reliability

    NASA Technical Reports Server (NTRS)

    Bowling, T. C.; Key, L. W.

    1976-01-01

    The B-52 SAS (Stability Augmentation System) was developed and retrofitted to nearly 300 aircraft. It actively controls B-52 structural bending, provides improved yaw and pitch damping through sensors and electronic control channels, and puts complete reliance on hydraulic control power for rudder and elevators. The system has experienced over 300,000 flight hours and has exhibited service reliability comparable to the results of the reliability test program. Development experience points out numerous lessons with potential application in the mechanization and development of advanced technology control systems of high reliability.

  5. Co-Channel Speaker Separation

    DTIC Science & Technology

    1992-09-01

    Segment Classification .................... 2-8 2.3.3 Comb Filtering. . I. 2-0 2.4 Co-Channel Speaker Separation Algorithms ........... 2-9 i11 Page...4-7 4.4 Test Results ........ ......................... 4-8 4.4.1 Pitch Deviation Method of Assigning Separated Segments ...developed that if given that a segment of co-channel speech is separated into a "stronger" and "weaker" segment , the corrxt assignment of these separated

  6. Ionic Channels as Natural Nanodevices

    DTIC Science & Technology

    2006-05-01

    modeling ion transport in biological channels: Self-consistent particle-based simulations. Journal of Computational Electronics, 2: 239-243. 6. Boda ...dielectric boundary: application to calcium channel selectivity. Molecular Simulation, 30: 89-96. 17 7. Boda , D., Gillespie, D., Nonner, W., Henderson...systems. Phys Rev E, 69, 046702. 8. van der Straaten, T., Kathawala, G., Kuang, Z., Boda , D., Chen, D.P., Ravaioli, U., Eisenberg, R.S., and D

  7. Therapeutic targeting of two-pore-domain potassium (K(2P)) channels in the cardiovascular system.

    PubMed

    Wiedmann, Felix; Schmidt, Constanze; Lugenbiel, Patrick; Staudacher, Ingo; Rahm, Ann-Kathrin; Seyler, Claudia; Schweizer, Patrick A; Katus, Hugo A; Thomas, Dierk

    2016-05-01

    The improvement of treatment strategies in cardiovascular medicine is an ongoing process that requires constant optimization. The ability of a therapeutic intervention to prevent cardiovascular pathology largely depends on its capacity to suppress the underlying mechanisms. Attenuation or reversal of disease-specific pathways has emerged as a promising paradigm, providing a mechanistic rationale for patient-tailored therapy. Two-pore-domain K(+) (K(2P)) channels conduct outward K(+) currents that stabilize the resting membrane potential and facilitate action potential repolarization. K(2P) expression in the cardiovascular system and polymodal K2P current regulation suggest functional significance and potential therapeutic roles of the channels. Recent work has focused primarily on K(2P)1.1 [tandem of pore domains in a weak inwardly rectifying K(+) channel (TWIK)-1], K(2P)2.1 [TWIK-related K(+) channel (TREK)-1], and K(2P)3.1 [TWIK-related acid-sensitive K(+) channel (TASK)-1] channels and their role in heart and vessels. K(2P) currents have been implicated in atrial and ventricular arrhythmogenesis and in setting the vascular tone. Furthermore, the association of genetic alterations in K(2P)3.1 channels with atrial fibrillation, cardiac conduction disorders and pulmonary arterial hypertension demonstrates the relevance of the channels in cardiovascular disease. The function, regulation and clinical significance of cardiovascular K(2P) channels are summarized in the present review, and therapeutic options are emphasized.

  8. β-Scorpion Toxin Modifies Gating Transitions in All Four Voltage Sensors of the Sodium Channel

    PubMed Central

    Campos, Fabiana V.; Chanda, Baron; Beirão, Paulo S.L.; Bezanilla, Francisco

    2007-01-01

    Several naturally occurring polypeptide neurotoxins target specific sites on the voltage-gated sodium channels. Of these, the gating modifier toxins alter the behavior of the sodium channels by stabilizing transient intermediate states in the channel gating pathway. Here we have used an integrated approach that combines electrophysiological and spectroscopic measurements to determine the structural rearrangements modified by the β-scorpion toxin Ts1. Our data indicate that toxin binding to the channel is restricted to a single binding site on domain II voltage sensor. Analysis of Cole-Moore shifts suggests that the number of closed states in the activation sequence prior to channel opening is reduced in the presence of toxin. Measurements of charge–voltage relationships show that a fraction of the gating charge is immobilized in Ts1-modified channels. Interestingly, the charge–voltage relationship also shows an additional component at hyperpolarized potentials. Site-specific fluorescence measurements indicate that in presence of the toxin the voltage sensor of domain II remains trapped in the activated state. Furthermore, the binding of the toxin potentiates the activation of the other three voltage sensors of the sodium channel to more hyperpolarized potentials. These findings reveal how the binding of β-scorpion toxin modifies channel function and provides insight into early gating transitions of sodium channels. PMID:17698594

  9. Design of step composition gradient thin film transistor channel layers grown by atomic layer deposition

    SciTech Connect

    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 cm{sup 2}/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.

  10. Differential distribution of the sodium-activated potassium channels slick and slack in mouse brain.

    PubMed

    Rizzi, Sandra; Knaus, Hans-Günther; Schwarzer, Christoph

    2016-07-01

    The sodium-activated potassium channels Slick (Slo2.1, KCNT2) and Slack (Slo2.2, KCNT1) are high-conductance potassium channels of the Slo family. In neurons, Slick and Slack channels are involved in the generation of slow afterhyperpolarization, in the regulation of firing patterns, and in setting and stabilizing the resting membrane potential. The distribution and subcellular localization of Slick and Slack channels in the mouse brain have not yet been established in detail. The present study addresses this issue through in situ hybridization and immunohistochemistry. Both channels were widely distributed and exhibited distinct distribution patterns. However, in some brain regions, their expression overlapped. Intense Slick channel immunoreactivity was observed in processes, varicosities, and neuronal cell bodies of the olfactory bulb, granular zones of cortical regions, hippocampus, amygdala, lateral septal nuclei, certain hypothalamic and midbrain nuclei, and several regions of the brainstem. The Slack channel showed primarily a diffuse immunostaining pattern, and labeling of cell somata and processes was observed only occasionally. The highest Slack channel expression was detected in the olfactory bulb, lateral septal nuclei, basal ganglia, and distinct areas of the midbrain, brainstem, and cerebellar cortex. In addition, comparing our data obtained from mouse brain with a previously published study on rat brain revealed some differences in the expression and distribution of Slick and Slack channels in these species. J. Comp. Neurol. 524:2093-2116, 2016. © 2015 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc.

  11. Differential distribution of the sodium‐activated potassium channels slick and slack in mouse brain

    PubMed Central

    Knaus, Hans‐Günther; Schwarzer, Christoph

    2015-01-01

    ABSTRACT The sodium‐activated potassium channels Slick (Slo2.1, KCNT2) and Slack (Slo2.2, KCNT1) are high‐conductance potassium channels of the Slo family. In neurons, Slick and Slack channels are involved in the generation of slow afterhyperpolarization, in the regulation of firing patterns, and in setting and stabilizing the resting membrane potential. The distribution and subcellular localization of Slick and Slack channels in the mouse brain have not yet been established in detail. The present study addresses this issue through in situ hybridization and immunohistochemistry. Both channels were widely distributed and exhibited distinct distribution patterns. However, in some brain regions, their expression overlapped. Intense Slick channel immunoreactivity was observed in processes, varicosities, and neuronal cell bodies of the olfactory bulb, granular zones of cortical regions, hippocampus, amygdala, lateral septal nuclei, certain hypothalamic and midbrain nuclei, and several regions of the brainstem. The Slack channel showed primarily a diffuse immunostaining pattern, and labeling of cell somata and processes was observed only occasionally. The highest Slack channel expression was detected in the olfactory bulb, lateral septal nuclei, basal ganglia, and distinct areas of the midbrain, brainstem, and cerebellar cortex. In addition, comparing our data obtained from mouse brain with a previously published study on rat brain revealed some differences in the expression and distribution of Slick and Slack channels in these species. J. Comp. Neurol. 524:2093–2116, 2016. © 2015 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc. PMID:26587966

  12. A three channel telemetry system

    NASA Technical Reports Server (NTRS)

    Lesho, Jeffery C.; Eaton, Harry A. C.

    1993-01-01

    A three channel telemetry system intended for biomedical applications is described. The transmitter is implemented in a single chip using a 2 micron BiCMOS processes. The operation of the system and the test results from the latest chip are discussed. One channel is always dedicated to temperature measurement while the other two channels are generic. The generic channels carry information from transducers that are interfaced to the system through on-chip general purpose operational amplifiers. The generic channels have different bandwidths: one from dc to 250 Hz and the other from dc to 1300 Hz. Each generic channel modulates a current controlled oscillator to produce a frequency modulated signal. The two frequency modulated signals are summed and used to amplitude modulate the temperature signal which acts as a carrier. A near-field inductive link telemeters the combined signals over a short distance. The chip operates on a supply voltage anywhere from 2.5 to 3.6 Volts and draws less than 1 mA when transmitting a signal. The chip can be incorporated into ingestible, implantable and other configurations. The device can free the patient from tethered data collection systems and reduces the possibility of infection from subcutaneous leads. Data telemetry can increase patient comfort leading to a greater acceptance of monitoring.

  13. Mechanical properties of lipid bilayers and regulation of mechanosensitive function: from biological to biomimetic channels.

    PubMed

    Balleza, Daniel

    2012-01-01

    Material properties of lipid bilayers, including thickness, intrinsic curvature and compressibility regulate the function of mechanosensitive (MS) channels. This regulation is dependent on phospholipid composition, lateral packing and organization within the membrane. Therefore, a more complete framework to understand the functioning of MS channels requires insights into bilayer structure, thermodynamics and phospholipid structure, as well as lipid-protein interactions. Phospholipids and MS channels interact with each other mainly through electrostatic forces and hydrophobic matching, which are also crucial for antimicrobial peptides. They are excellent models for studying the formation and stabilization of membrane pores. Importantly, they perform equivalent responses as MS channels: (1) tilting in response to tension and (2) dissipation of osmotic gradients. Lessons learned from pore forming peptides could enrich our knowledge of mechanisms of action and evolution of these channels. Here, the current state of the art is presented and general principles of membrane regulation of mechanosensitive function are discussed.

  14. High basal melting forming a channel at the grounding line of Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Marsh, Oliver J.; Fricker, Helen A.; Siegfried, Matthew R.; Christianson, Knut; Nicholls, Keith W.; Corr, Hugh F. J.; Catania, Ginny

    2016-01-01

    Antarctica's ice shelves are thinning at an increasing rate, affecting their buttressing ability. Channels in the ice shelf base unevenly distribute melting, and their evolution provides insight into changing subglacial and oceanic conditions. Here we used phase-sensitive radar measurements to estimate basal melt rates in a channel beneath the currently stable Ross Ice Shelf. Melt rates of 22.2 ± 0.2 m a-1 (>2500% the overall background rate) were observed 1.7 km seaward of Mercer/Whillans Ice Stream grounding line, close to where subglacial water discharge is expected. Laser altimetry shows a corresponding, steadily deepening surface channel. Two relict channels to the north suggest recent subglacial drainage reorganization beneath Whillans Ice Stream approximately coincident with the shutdown of Kamb Ice Stream. This rapid channel formation implies that shifts in subglacial hydrology may impact ice shelf stability.

  15. [Molecular dynamics simulations of migration of ions and molecules through the acetylcholine receptor channel].

    PubMed

    Shaĭtan, K V; Li, A; Tershkina, K B; Kirpichnikov, M P

    2007-01-01

    A dynamic model of the channel of an acetylcholine receptor in a closed state has been proposed. The channel is formed by five a-helices of subunit M2 and stabilized by the cyclic hydrocarbon (CH2)105. The migration of charged and unchanged van der Waals particles with a diameter of 7.72 A equivalent to the diameter of a hydrated sodium ion has been studied. The migration occurred by the action of external force applied to the complex along the channel axis. In the closed state, the inhibition of ions is due to two components: electrostatic interaction and steric constraints. The van der Waals channel gate is formed by residues 13'-A-Val255, B-Val261, C-Val269, D-Val255, and E-Ile264, and the negatively changed residues occurring in the upper part of the channel have a great effect on ion selectivity.

  16. Ca-α1T, a fly T-type Ca2+ channel, negatively modulates sleep

    PubMed Central

    Jeong, Kyunghwa; Lee, Soyoung; Seo, Haengsoo; Oh, Yangkyun; Jang, Donghoon; Choe, Joonho; Kim, Daesoo; Lee, Jung-Ha; Jones, Walton D.

    2015-01-01

    Mammalian T-type Ca2+ channels are encoded by three separate genes (Cav3.1, 3.2, 3.3). These channels are reported to be sleep stabilizers important in the generation of the delta rhythms of deep sleep, but controversy remains. The identification of precise physiological functions for the T-type channels has been hindered, at least in part, by the potential for compensation between the products of these three genes and a lack of specific pharmacological inhibitors. Invertebrates have only one T-type channel gene, but its functions are even less well-studied. We cloned Ca-α1T, the only Cav3 channel gene in Drosophila melanogaster, expressed it in Xenopus oocytes and HEK-293 cells, and confirmed it passes typical T-type currents. Voltage-clamp analysis revealed the biophysical properties of Ca-α1T show mixed similarity, sometimes falling closer to Cav3.1, sometimes to Cav3.2, and sometimes to Cav3.3. We found Ca-α1T is broadly expressed across the adult fly brain in a pattern vaguely reminiscent of mammalian T-type channels. In addition, flies lacking Ca-α1T show an abnormal increase in sleep duration most pronounced during subjective day under continuous dark conditions despite normal oscillations of the circadian clock. Thus, our study suggests invertebrate T-type Ca2+ channels promote wakefulness rather than stabilizing sleep. PMID:26647714

  17. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, Henry D.; Fugitt, Jock A.; Howard, Donald R.

    1984-01-01

    A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

  18. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

    1984-12-25

    Disclosed is a long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator. 5 figs.

  19. Electrode stabilizing materials

    DOEpatents

    Amine, Khalil; Abouimrane, Ali; Moore, Jeffrey S.; Odom, Susan A.

    2015-11-03

    An electrolyte includes a polar aprotic solvent; an alkali metal salt; and an electrode stabilizing compound that is a monomer, which when polymerized forms an electrically conductive polymer. The electrode stabilizing compound is a thiophene, a imidazole, a anilines, a benzene, a azulene, a carbazole, or a thiol. Electrochemical devices may incorporate such electrolytes.

  20. Interfacial bonding stability

    NASA Technical Reports Server (NTRS)

    Boerio, J.

    1984-01-01

    Interfacial bonding stability by in situ ellipsometry was investigated. It is found that: (1) gamma MPS is an effective primer for bonding ethylene vinyl acetate (EVA) to aluminum; (2) ellipsometry is an effective in situ technique for monitoring the stability of polymer/metal interfaces; (3) the aluminized back surface of silicon wafers contain significant amounts of silicon and may have glass like properties.

  1. Stabilization of Kepler's problem

    NASA Technical Reports Server (NTRS)

    Stokes, A.

    1977-01-01

    A regularization of Kepler's problem due to Moser (1970) is used to stabilize the equations of motion. In other words, a particular solution of Kepler's problem is imbedded in a Liapunov stable system. Perturbations can be introduced into the stabilized equations.

  2. Basic principles of stability.

    PubMed

    Egan, William; Schofield, Timothy

    2009-11-01

    An understanding of the principles of degradation, as well as the statistical tools for measuring product stability, is essential to management of product quality. Key to this is management of vaccine potency. Vaccine shelf life is best managed through determination of a minimum potency release requirement, which helps assure adequate potency throughout expiry. Use of statistical tools such a least squares regression analysis should be employed to model potency decay. The use of such tools provides incentive to properly design vaccine stability studies, while holding stability measurements to specification presents a disincentive for collecting valuable data. The laws of kinetics such as Arrhenius behavior help practitioners design effective accelerated stability programs, which can be utilized to manage stability after a process change. Design of stability studies should be carefully considered, with an eye to minimizing the variability of the stability parameter. In the case of measuring the degradation rate, testing at the beginning and the end of the study improves the precision of this estimate. Additional design considerations such as bracketing and matrixing improve the efficiency of stability evaluation of vaccines.

  3. Rotorcraft aeroelastic stability

    NASA Technical Reports Server (NTRS)

    Ormiston, Robert A.; Warmbrodt, William G.; Hodges, Dewey H.; Peters, David A.

    1988-01-01

    Theoretical and experimental developments in the aeroelastic and aeromechanical stability of helicopters and tilt-rotor aircraft are addressed. Included are the underlying nonlinear structural mechanics of slender rotating beams, necessary for accurate modeling of elastic cantilever rotor blades, and the development of dynamic inflow, an unsteady aerodynamic theory for low-frequency aeroelastic stability applications. Analytical treatment of isolated rotor stability in hover and forward flight, coupled rotor-fuselage stability in hover and forward flight, and analysis of tilt-rotor dynamic stability are considered. Results of parametric investigations of system behavior are presented, and correlation between theoretical results and experimental data from small and large scale wind tunnel and flight testing are discussed.

  4. Ephemeral channel recharge and near-channel evapotranspiration

    NASA Astrophysics Data System (ADS)

    Goodrich, D.; Williams, D.; Scott, R.; Unkrich, C.; Hultine, K.

    2003-04-01

    Ephemeral channel transmission losses play an important role in ground water/surface water dynamics in arid and semi-arid basins in the Southwest. However, identification of the processes driving these dynamics is difficult. Specifically, data on the proportion of runoff transmission losses that escape from near-channel evapotranspiration (ET) and wetted channel evaporation to become deep ground water recharge are difficult to obtain. Quantifying recharge with greater certainty is a critical need required to manage basins whose primary source of water supply is derived from groundwater. This paper addresses two principal objectives: 1) Assess the magnitude and seasonality of ephemeral channel recharge to the regional aquifer and a perched aquifer occluded from the regional aquifer; and, 2) Monitor the dynamics of ET and water movement between Flume 6, Flume 2, and Flume 1 of the USDA-ARS Walnut Gulch Experimental Watershed (WGEW). Groundwater, surface water, chemical, isotopic, tree sap flux and micrometeorological techniques were used to independently estimate ephemeral channel recharge. It was found that during the 1999 and 2000 monsoon seasons a substantial amount of water recharged into the regional aquifer in the 7 km reach between flume 2 and flume 1 of the WGEW. In 2001 and 2002 no recharge was detected.

  5. Stability of Flow around a Cylinder in Plane Poiseuille Flow

    NASA Astrophysics Data System (ADS)

    Dou, Hua-Shu; Ben, An-Qing; Fluid Mechanics Research Team

    2013-11-01

    Simulation of Navier-Stokes equations is carried out to study the stability of flow around a cylinder in plane Poiseuille flow. The energy gradient method is employed to analyze the mechanism of instability of cylinder wake. The ratio of the channel width to the cylinder diameter is 30, and the Reynolds number based on the cylinder diameter and incoming centerline velocity is 26 and 100, respectively. The incoming flow is given as being laminar. It is found that the instability of the cylinder wake, starting near the front stagnation point upstream. The recirculation zone behind the cylinder has no effect on the stability of the wake. In the wake behind the recirculation zone, the flow stability is controlled by the energy gradient in the shear layer along the two sides of the wake. At high Re, the energy gradient of averaged flow in the channel interacts with the wake vortex, strengthening the wake vortex structure. Due to the large ratio of the channel width to the cylinder diameter, the disturbance caused by the cylinder mainly occurs in the vicinity of the centerline and has little effect on the flow near the wall. The velocity profile on the two sides of the cylinder wake in the downstream channel remains laminar (parabolic profile). Professor in Fluid Mechanics; AIAA Associate Fellow.

  6. Electroosmotic Flow in Nanofluidic Channels

    PubMed Central

    2015-01-01

    We report the measurement of electroosmotic mobilities in nanofluidic channels with rectangular cross sections and compare our results with theory. Nanofluidic channels were milled directly into borosilicate glass between two closely spaced microchannels with a focused ion beam instrument, and the nanochannels had half-depths (h) of 27, 54, and 108 nm and the same half-width of 265 nm. We measured electroosmotic mobilities in NaCl solutions from 0.1 to 500 mM that have Debye lengths (κ–1) from 30 to 0.4 nm, respectively. The experimental electroosmotic mobilities compare quantitatively to mobilities calculated from a nonlinear solution of the Poisson–Boltzmann equation for channels with a parallel-plate geometry. For the calculations, ζ-potentials measured in a microchannel with a half-depth of 2.5 μm are used and range from −6 to −73 mV for 500 to 0.1 mM NaCl, respectively. For κh > 50, the Smoluchowski equation accurately predicts electroosmotic mobilities in the nanochannels. However, for κh < 10, the electrical double layer extends into the nanochannels, and due to confinement within the channels, the average electroosmotic mobilities decrease. At κh ≈ 4, the electroosmotic mobilities in the 27, 54, and 108 nm channels exhibit maxima, and at 0.1 mM NaCl, the electroosmotic mobility in the 27 nm channel (κh = 1) is 5-fold lower than the electroosmotic mobility in the 2.5 μm channel (κh = 100). PMID:25365680

  7. Specific stabilization of CFTR by phosphatidylserine.

    PubMed

    Hildebrandt, Ellen; Khazanov, Netaly; Kappes, John C; Dai, Qun; Senderowitz, Hanoch; Urbatsch, Ina L

    2017-02-01

    The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR, ABCC7) is a plasma membrane chloride ion channel in the ABC transporter superfamily. CFTR is a key target for cystic fibrosis drug development, and its structural elucidation would advance those efforts. However, the limited in vivo and in vitro stability of the protein, particularly its nucleotide binding domains, has made structural studies challenging. Here we demonstrate that phosphatidylserine uniquely stimulates and thermally stabilizes the ATP hydrolysis function of purified human CFTR. Among several lipids tested, the greatest stabilization was observed with brain phosphatidylserine, which shifted the Tm for ATPase activity from 22.7±0.8°C to 35.0±0.2°C in wild-type CFTR, and from 26.6±0.7°C to 42.1±0.2°C in a more stable mutant CFTR having deleted regulatory insertion and S492P/A534P/I539T mutations. When ATPase activity was measured at 37°C in the presence of brain phosphatidylserine, Vmax for wild-type CFTR was 240±60nmol/min/mg, a rate higher than previously reported and consistent with rates for other purified ABC transporters. The significant thermal stabilization of CFTR by phosphatidylserine may be advantageous in future structural and biophysical studies of CFTR.

  8. CARMENES-NIR channel spectrograph cooling system AIV: thermo-mechanical performance of the instrument

    NASA Astrophysics Data System (ADS)

    Becerril, S.; Mirabet, E.; Lizon, J. L.; Abril, M.; Cárdenas, C.; Ferro, I.; Morales, R.; Pérez, D.; Ramón, A.; Sánchez-Carrasco, M. A.; Quirrenbach, A.; Amado, P.; Ribas, I.; Reiners, A.; Caballero, J. A.; Seifert, W.; Herranz, J.

    2016-07-01

    CARMENES is the new high-resolution high-stability spectrograph built for the 3.5m telescope at the Calar Alto Observatory (CAHA, Almería, Spain) by a consortium formed by German and Spanish institutions. This instrument is composed by two separated spectrographs: VIS channel (550-1050 nm) and NIR channel (950- 1700 nm). The NIR-channel spectrograph's responsible is the Instituto de Astrofísica de Andalucía (IAACSIC). It has been manufactured, assembled, integrated and verified in the last two years, delivered in fall 2015 and commissioned in December 2015. One of the most challenging systems in this cryogenic channel involves the Cooling System. Due to the highly demanding requirements applicable in terms of stability, this system arises as one of the core systems to provide outstanding stability to the channel. Really at the edge of the state-of-the-art, the Cooling System is able to provide to the cold mass ( 1 Ton) better thermal stability than few hundredths of degree within 24 hours (goal: 0.01K/day). The present paper describes the Assembly, Integration and Verification phase (AIV) of the CARMENES-NIR channel Cooling System implemented at IAA-CSIC and later installation at CAHA 3.5m Telescope, thus the most relevant highlights being shown in terms of thermal performance. The CARMENES NIR-channel Cooling System has been implemented by the IAA-CSIC through very fruitful collaboration and involvement of the ESO (European Southern Observatory) cryo-vacuum department with Jean-Louis Lizon as its head and main collaborator. The present work sets an important trend in terms of cryogenic systems for future E-ELT (European Extremely Large Telescope) large-dimensioned instrumentation in astrophysics.

  9. Vegetation control of gravel-bed channel morphology and adjustment: the case of Carex nudata

    NASA Astrophysics Data System (ADS)

    McDowell, P. F.

    2010-12-01

    In the high energy, gravel- to cobble-bed Middle Fork John Day River of eastern Oregon, C. nudata (torrent sedge) germinates on gravel bars and forms tussocks 0.5 m across by 0.3m high or larger, with dense, tough root masses that are very resistant to erosion. Tussocks may be uprooted during floods (probably >Q-5yr), travel as boulder-sized masses, and may re-root where deposited. Individual tussocks, however, commonly persist for more than a decade in one position. When established, these tussocks behave more like channel obstructions than typical stream side sedges. Lines of C. nudata tussocks form on the stream side margin of former bare gravel bars, creating a secondary flow path and an eroding bank on their landward side. C. nudata also forms small mid-channel islets with bed scour at their base and occasional lee depositional zones. Chains of mid-channel islets can anchor pool boundaries. Observations in the field and from aerial photo time sequences suggest the following evolutionary model for channels with C. nudata. C. nudata establishes on a bare gravel bar, and can stabilize the bar surface or create erosional forms as described above. C. nudata fosters weaker sedges and other species that help extend stabilization of the bar surface. Mid-channel islets form through selective uprooting of tussocks. Observations of a reach where cattle grazing was eliminated in 2000 show that C. nudata has expanded. It has stabilized some formerly active bar surfaces but is now causing bank erosion and channel widening in some locations. In this case, C. nudata mediated the potentially stabilizing effects of management change by increasing channel instability in some respects.

  10. 18 CFR 1304.303 - Channel excavation.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 18 Conservation of Power and Water Resources 2 2012-04-01 2012-04-01 false Channel excavation... Activities on TVA Flowage Easement Shoreland § 1304.303 Channel excavation. (a) Channel excavation of... encourage owners of flowage easement property to adopt the standards for channel excavation applicable...

  11. 18 CFR 1304.303 - Channel excavation.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 18 Conservation of Power and Water Resources 2 2014-04-01 2014-04-01 false Channel excavation... Activities on TVA Flowage Easement Shoreland § 1304.303 Channel excavation. (a) Channel excavation of... encourage owners of flowage easement property to adopt the standards for channel excavation applicable...

  12. 18 CFR 1304.303 - Channel excavation.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 18 Conservation of Power and Water Resources 2 2011-04-01 2011-04-01 false Channel excavation... Activities on TVA Flowage Easement Shoreland § 1304.303 Channel excavation. (a) Channel excavation of... encourage owners of flowage easement property to adopt the standards for channel excavation applicable...

  13. 18 CFR 1304.303 - Channel excavation.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 18 Conservation of Power and Water Resources 2 2013-04-01 2012-04-01 true Channel excavation. 1304... Flowage Easement Shoreland § 1304.303 Channel excavation. (a) Channel excavation of privately-owned... encourage owners of flowage easement property to adopt the standards for channel excavation applicable...

  14. 33 CFR 117.966 - Galveston Channel.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... DRAWBRIDGE OPERATION REGULATIONS Specific Requirements Texas § 117.966 Galveston Channel. The drawspan for the Pelican Island Causeway Drawbridge across Galveston Channel, mile 4.5 of the Galveston Channel... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Galveston Channel....

  15. 33 CFR 117.966 - Galveston Channel.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... DRAWBRIDGE OPERATION REGULATIONS Specific Requirements Texas § 117.966 Galveston Channel. The drawspan for the Pelican Island Causeway Drawbridge across Galveston Channel, mile 4.5 of the Galveston Channel... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false Galveston Channel....

  16. 33 CFR 117.966 - Galveston Channel.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... DRAWBRIDGE OPERATION REGULATIONS Specific Requirements Texas § 117.966 Galveston Channel. The drawspan for the Pelican Island Causeway Drawbridge across Galveston Channel, mile 4.5 of the Galveston Channel... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false Galveston Channel....

  17. 47 CFR 95.29 - Channels available.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Channels available. 95.29 Section 95.29... SERVICES General Mobile Radio Service (GMRS) § 95.29 Channels available. (a) For a base station, fixed... transmission of another GMRS station on a different channel or channels), the licensee of the GMRS system...

  18. 47 CFR 95.29 - Channels available.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Channels available. 95.29 Section 95.29... SERVICES General Mobile Radio Service (GMRS) § 95.29 Channels available. (a) For a base station, fixed... transmission of another GMRS station on a different channel or channels), the licensee of the GMRS system...

  19. 47 CFR 73.6006 - Channel assignments.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Channel assignments. 73.6006 Section 73.6006... Class A Television Broadcast Stations § 73.6006 Channel assignments. Class A TV stations will not be authorized on UHF TV channels 52 through 69, or on channels unavailable for TV broadcast station use...

  20. 47 CFR 73.6006 - Channel assignments.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 4 2011-10-01 2011-10-01 false Channel assignments. 73.6006 Section 73.6006... Class A Television Broadcast Stations § 73.6006 Channel assignments. Class A TV stations will not be authorized on UHF TV channels 52 through 69, or on channels unavailable for TV broadcast station use...

  1. SiGe channel deposition by batch epitaxy

    NASA Astrophysics Data System (ADS)

    Reichel, Carsten; Schoenekess, Joerg; Dietel, Andreas; Wasyluk, Joanna; Chow, Yew Tuck; Kammler, Thorsten

    2015-08-01

    Batch epitaxy has been introduced for high volume manufacturing of SiGe channels in order to reduce the cost for this epitaxial process by a factor of 3. Beside cost, SiGe channel deposition by batch epitaxy offers many benefits for manufacturing. The stability of the process and the reduced variability of the SiGe thickness greatly improve the variation of VT. The batch epitaxy process does not show a pattern loading effect for SiGe thickness reducing the complexity for manufacturing significantly. However, since the tool concept is very different to that of the widely used single wafer tools, there are some tool specific issues that need to be managed. The wafer backside is critical for batch epitaxy. A nitride backside facing the front side of the wafer results in a clear degradation of the uniformity and a change of the morphology of the SiGe channel compared to that facing a Si backside. The thermal rounding is more pronounced for the channels deposited in a batch tool for both large and narrow width devices. The device parameters of the large width device are not affected by thermal rounding but the performance of the narrow width device is clearly degraded. The thin SiGe layer at the edge of the channel driven by thermal rounding affects the VT and thus the effective device width. An in-situ etching before SiGe deposition to avoid thermal rounding was not feasible due to defects issues which were induced by the wafer backside. Finally a thermal rounding of the Si by an aggressive H2 bake before SiGe deposition improves the SiGe channel uniformity and recovers the performance degradation of the narrow width device partly.

  2. The pharmacology of TRP channels

    PubMed Central

    Holzer, Peter; Izzo, Angelo A

    2014-01-01

    This themed issue of the British Journal of Pharmacology contains review and research articles on recent advances in transient receptor potential (TRP) channel pharmacology. The review articles, written by a panel of distinguished experts, address the rapid progress in TRP channel research in fields as diverse as oncology, urology, dermatology, migraine, inflammation and pain. These reviews are complemented by original research reports focusing, among others, on the emerging roles of TRPV1 in osteoporosis and cystitis and on evodiamine as a lead structure for the development of potent TRPV1 agonists/desensitizers. Other papers highlight the differences in TRPV3 pharmacology between recombinant and native systems, the mechanisms of TRPM3 activation/inhibition and TRPP2 as a target of naringenin, a dietary flavonoid with anticancer actions. New therapeutic opportunities in pain may arise from the strategy to combine TRP channel and cell membrane impermeant sodium channel blockers to inhibit sensory nerve activity. LINKED ARTICLES This article is part of a themed section on the pharmacology of TRP channels. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-10 PMID:24773265

  3. Generic theory for channel sinuosity.

    PubMed

    Lazarus, Eli D; Constantine, José Antonio

    2013-05-21

    Sinuous patterns traced by fluid flows are a ubiquitous feature of physical landscapes on Earth, Mars, the volcanic floodplains of the Moon and Venus, and other planetary bodies. Typically discussed as a consequence of migration processes in meandering rivers, sinuosity is also expressed in channel types that show little or no indication of meandering. Sinuosity is sometimes described as "inherited" from a preexisting morphology, which still does not explain where the inherited sinuosity came from. For a phenomenon so universal as sinuosity, existing models of channelized flows do not explain the occurrence of sinuosity in the full variety of settings in which it manifests, or how sinuosity may originate. Here we present a generic theory for sinuous flow patterns in landscapes. Using observations from nature and a numerical model of flow routing, we propose that flow resistance (representing landscape roughness attributable to topography or vegetation density) relative to surface slope exerts a fundamental control on channel sinuosity that is effectively independent of internal flow dynamics. Resistance-dominated surfaces produce channels with higher sinuosity than those of slope-dominated surfaces because increased resistance impedes downslope flow. Not limited to rivers, the hypothesis we explore pertains to sinuosity as a geomorphic pattern. The explanation we propose is inclusive enough to account for a wide variety of sinuous channel types in nature, and can serve as an analytical tool for determining the sinuosity a landscape might support.

  4. River meanders and channel size

    USGS Publications Warehouse

    Williams, G.P.

    1986-01-01

    This study uses an enlarged data set to (1) compare measured meander geometry to that predicted by the Langbein and Leopold (1966) theory, (2) examine the frequency distribution of the ratio radius of curvature/channel width, and (3) derive 40 empirical equations (31 of which are original) involving meander and channel size features. The data set, part of which comes from publications by other authors, consists of 194 sites from a large variety of physiographic environments in various countries. The Langbein-Leopold sine-generated-curve theory for predicting radius of curvature agrees very well with the field data (78 sites). The ratio radius of curvature/channel width has a modal value in the range of 2 to 3, in accordance with earlier work; about one third of the 79 values is less than 2.0. The 40 empirical relations, most of which include only two variables, involve channel cross-section dimensions (bankfull area, width, and mean depth) and meander features (wavelength, bend length, radius of curvature, and belt width). These relations have very high correlation coefficients, most being in the range of 0.95-0.99. Although channel width traditionally has served as a scale indicator, bankfull cross-sectional area and mean depth also can be used for this purpose. ?? 1986.

  5. TRP channels in the skin

    PubMed Central

    Tóth, Balázs I; Oláh, Attila; Szöllősi, Attila Gábor; Bíró, Tamás

    2014-01-01

    Emerging evidence suggests that transient receptor potential (TRP) ion channels not only act as ‘polymodal cellular sensors’ on sensory neurons but are also functionally expressed by a multitude of non-neuronal cell types. This is especially true in the skin, one of the largest organs of the body, where they appear to be critically involved in regulating various cutaneous functions both under physiological and pathophysiological conditions. In this review, we focus on introducing the roles of several cutaneous TRP channels in the regulation of the skin barrier, skin cell proliferation and differentiation, and immune functions. Moreover, we also describe the putative involvement of several TRP channels in the development of certain skin diseases and identify future TRP channel-targeted therapeutic opportunities. Linked Articles This article is part of a themed section on the pharmacology of TRP channels. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-10 PMID:24372189

  6. Generic theory for channel sinuosity

    PubMed Central

    Lazarus, Eli D.; Constantine, José Antonio

    2013-01-01

    Sinuous patterns traced by fluid flows are a ubiquitous feature of physical landscapes on Earth, Mars, the volcanic floodplains of the Moon and Venus, and other planetary bodies. Typically discussed as a consequence of migration processes in meandering rivers, sinuosity is also expressed in channel types that show little or no indication of meandering. Sinuosity is sometimes described as “inherited” from a preexisting morphology, which still does not explain where the inherited sinuosity came from. For a phenomenon so universal as sinuosity, existing models of channelized flows do not explain the occurrence of sinuosity in the full variety of settings in which it manifests, or how sinuosity may originate. Here we present a generic theory for sinuous flow patterns in landscapes. Using observations from nature and a numerical model of flow routing, we propose that flow resistance (representing landscape roughness attributable to topography or vegetation density) relative to surface slope exerts a fundamental control on channel sinuosity that is effectively independent of internal flow dynamics. Resistance-dominated surfaces produce channels with higher sinuosity than those of slope-dominated surfaces because increased resistance impedes downslope flow. Not limited to rivers, the hypothesis we explore pertains to sinuosity as a geomorphic pattern. The explanation we propose is inclusive enough to account for a wide variety of sinuous channel types in nature, and can serve as an analytical tool for determining the sinuosity a landscape might support. PMID:23610390

  7. Conformational heterogeneity in closed and open states of the KcsA potassium channel in lipid bicelles

    PubMed Central

    Kim, Dorothy M.; Dikiy, Igor; Upadhyay, Vikrant; Posson, David J.

    2016-01-01

    The process of ion channel gating—opening and closing—involves local and global structural changes in the channel in response to external stimuli. Conformational changes depend on the energetic landscape that underlies the transition between closed and open states, which plays a key role in ion channel gating. For the prokaryotic, pH-gated potassium channel KcsA, closed and open states have been extensively studied using structural and functional methods, but the dynamics within each of these functional states as well as the transition between them is not as well understood. In this study, we used solution nuclear magnetic resonance (NMR) spectroscopy to investigate the conformational transitions within specific functional states of KcsA. We incorporated KcsA channels into lipid bicelles and stabilized them into a closed state by using either phosphatidylcholine lipids, known to favor the closed channel, or mutations designed to trap the channel shut by disulfide cross-linking. A distinct state, consistent with an open channel, was uncovered by the addition of cardiolipin lipids. Using selective amino acid labeling at locations within the channel that are known to move during gating, we observed at least two different slowly interconverting conformational states for both closed and open channels. The pH dependence of these conformations and the predictable disruptions to this dependence observed in mutant channels with altered pH sensing highlight the importance of conformational heterogeneity for KcsA gating. PMID:27432996

  8. Pulse stabilization by high-order dispersion management

    NASA Astrophysics Data System (ADS)

    Moeser, J.; Gabitov, I.; Jones, C. K. R. T.

    2002-12-01

    The stabilizing effects of dispersion management (DM) at second and third order are studied for both single-channel and wavelength-division multiplexed (WDM) systems. We first derive a model for the slow evolution of a pulse in an optical fiber with high-order dispersion management (HODM). For single-channel systems, in contrast with conventional DM with constant third-order dispersion, this equation possesses a stable solution, the ground state for its associated Hamiltonian, which propagates nearly periodically under direct numerical simulation. Improved performance for WDM systems is also observed, as complicated pulse interactions, which can lead to undesirable effects such as frequency shift, are prevented by HODM.

  9. Free-surface stability criterion as affected by velocity distribution

    USGS Publications Warehouse

    Cheng-Lung, Chen

    1995-01-01

    This paper examines how the velocity distribution of flow in open channels affects the kinematic and dynamic wave velocities, from which the various forms of the Vedernikov number V can be formulated. When V >1, disturbances created in open-channel flow will amplify in the form of roll waves; when V <1, some (though not all) disturbances will attenuate. A study of the Vedernikov stability criterion reveals that it can be readily deduced within the framework of the kinematic and dynamic wave theories by comparing the kinematic wave velocity to the corresponding dynamic wave velocity. -from Author

  10. Charged and Neutral Particles Channeling Phenomena Channeling 2008

    NASA Astrophysics Data System (ADS)

    Dabagov, Sultan B.; Palumbo, Luigi

    2010-04-01

    On the discovery of coherent Bremsstrahlung in a single crystal at the Frascati National Laboratories / C. Barbiellini, G. P. Murtas and S. B. Dabagov -- Advances in coherent Bremsstrahlung and LPM-effect studies (to the lOOth anniversary from the birth of L. D. Landau) / N. F. Shul'ga -- Spectra of radiation and created particles at intermediate energy in oriented crystal taking into account energy loss / V. N. Baier and V. M. Katkov -- The coherent Bremsstrahlung beam at MAX-lab facility / K. Fissum ... [et al.] -- Radiation from thin, structured targets (CERN NA63) / A. Dizdar -- Hard incoherent radiation in thick crystals / N. F. Shul'ga, V. V. Syshchenko and A. I. Tarnovsky -- Coherent Bremsstrahlung in periodically deformed crystals with a complex base / A. R. Mkrtchyan, A. A. Saharian and V. V. Parazian -- Induction of coherent x-ray Bremsstrahlung in crystals under the influence of acoustic waves / A. R. Mkrtchyan and V. V. Parazian -- Coherent processes in bent single crystals / V. A. Maisheev -- Experimental and theoretical investigation of complete transfer phenomenon for media with various heat exchange coefficients / A. R. Mkrtchyan, A. E. Movsisyan and V. R. Kocharyan -- Coherent pair production in crystals / A. R. Mkrtchyan, A. A. Saharian and V. V. Parazian -- Negative particle planar and axial channeling and channeling collimation / R. A. Carrigan, Jr. -- CERN crystal-based collimation in modern hadron colliders / W. Scandale -- Studies and application of bent crystals for beam steering at 70 GeV IHEP accelerator / A. G. Afonin ... [et al.] -- Crystal collimation studies at the Tevatron (T-980) / N. V. Mokhov ... [et al.] -- Fabrication of crystals for channeling of particles in accellerators / A. Mazzolari ... [et al.] -- New possibilities to facilitate collimation of both positively and negatively charged particle beams by crystals / V. Guidi, A. Mazzolari and V. V. Tikhomirov -- Increase of probability of particle capture into the channeling

  11. Surface controlled blade stabilizer

    DOEpatents

    Russell, Larry R.

    1983-01-01

    Drill string stabilizer apparatus, controllable to expand and retract entirely from the surface by control of drill string pressure, wherein increase of drill string pressure from the surface closes a valve to create a piston means which is moved down by drill string pressure to expand the stabilizer blades, said valve being opened and the piston moving upward upon reduction of drill string pressure to retract the stabilizer blades. Upward and downward movements of the piston and an actuator sleeve therebelow are controlled by a barrel cam acting between the housing and the actuator sleeve.

  12. Life raft stabilizer

    NASA Technical Reports Server (NTRS)

    Radnofsky, M. I.; Barnett, J. H., Jr.; Harrison, F. L.; Marak, R. J. (Inventor)

    1973-01-01

    An improved life raft stabilizer for reducing rocking and substantially precluding capsizing is discussed. The stabilizer may be removably attached to the raft and is defined by flexible side walls which extend a considerable depth downwardly to one another in the water. The side walls, in conjunction with the floor of the raft, form a ballast enclosure. A weight is placed in the bottom of the enclosure and water port means are provided in the walls. Placement of the stabilizer in the water allows the weighted bottom to sink, producing submerged deployment thereof and permitting water to enter the enclosure through the port means, thus forming a ballast for the raft.

  13. Stabililty and laminarisation of turbulent rotating channel flow

    NASA Astrophysics Data System (ADS)

    Wallin, S.; Grundestam, O.; Johansson, A. V.

    The influence of moderate rotation rate on turbulent channel flow is that the turbulence is suppressed on the stable side and augmented on the unstable side because of the Coriolis force. With increasing rotation rate the turbulent region becomes restricted to a decreasing zone near the unstable wall. For the rotation number, Ro > 3 (normalized by bulk velocity and channel height) inviscid linear theory yields a stable laminar flow [1] and a recent DNS study [2] indicates that the turbulent flow laminarizes for Ro below 3. The critical Ro has been identified by a standard text-book linear stability analysis of rotating laminar channel flow including the viscous effects. The Reynolds number, Re = 10800 based on the bulk velocity and channel half height, is the same as in the recent DNS [2]. The most unstable mode consists of tilted slightly oblique streamwise vortices with a critical rotation number of Ro c = 2.805 and streamwise and spanwise wave numbers of α = 2.7 and β = 19 respectivelly. Steady streamwise roll-cells are slightly more stable.

  14. Restoring the sinuosity of artificially straightened stream channels

    SciTech Connect

    Brookes, A. )

    1987-01-01

    Restoration of Danish stream channels is encouraged by the Watercourse Act of 1982 and has been undertaken partly because of the adverse physical and biological effects caused by artificial straightening. A new technique for restoring morphologic and hydrologic diversity to stream channels has been developed, exemplifying the concept of working with nature rather than against it. This relies on re-creating the former sinuosity, cross-sectional dimensions, slope and substrate of a stream channel. Natural fluvial features are restored to a channel, and because slope is decreased stability is probable. In turn, this could be beneficial to the flora and fauna of a watercourse and to aesthetic qualities. The technique was applied successfully to a small stream in southern Jutland, Denmark, in 1984/5. Additional methods of bank and bed protection were required to limit subsequent minor adjustments along the new course. Further applications of the technique need to be treated individually because of varying local hydrologic and sedimentologic conditions. On-site supervision during construction and planned maintenance are vital components of restoration.

  15. Experimental investigation of electrohydrodynamic instabilities in micro channels

    NASA Astrophysics Data System (ADS)

    Eribol, P.; Uguz, A. K.

    2015-03-01

    An electric field is applied to destabilize the interface between two Newtonian and immiscible liquids flowing in a rectangular micro channel. The liquids are pumped into the micro channel with a syringe pump and a DC electric field is applied either parallel or normal to the flat interface between these liquids. The two liquids used in the experiments are a combination of ethylene glycol, different viscosity silicone oils, castor oil, and olive oil. The onset of electrohydrodynamic instability is investigated for various parameters, including the ratios of the flow rates, and viscosities of the liquids, the width of the micro channel, and the direction of the applied electric field. The order of the voltage applied to destabilize the interface is in the range 95 and 1190 V. The results of the experiments show that an increase in the viscosity ratio and the flow rate ratio of silicone oil to ethylene glycol have a stabilizing effect. It is also found that the important parameter to determine the critical voltage is the flow rate ratio, not the individual flow rates of the liquids. Also, as the width of the micro channel increases, the critical voltage increases. Lastly, for the liquid combinations used in the experiments, the interface could not be destabilized under the influence of a parallel electric field.

  16. Laser Triggered Electron Injection into a Channel Guided Wakefield Accelerator

    NASA Astrophysics Data System (ADS)

    Nakamura, K.; Filip, C.

    2005-10-01

    Laser-plasma accelerators have demonstrated the generation of narrow energy spread (˜ few %) electron beams with considerable amount of charge (>100 pC). Stability of laser-plasma accelerators, as in the conventional accelerators, requires highly synchronized injection of electrons into the structured accelerating field. The Colliding Pulse Method[1] with pre-formed plasma channel guiding [2] can result in jitter-free injection in a dark-current-free accelerating structure. We report on experimental progress of laser triggered injection of electrons into a laser wakefield, where an intense laser pulse is guided by a pre-formed plasma channel. The experiments use the multi-beam, multi-terawatt Ti:Al2O3 laser at LOASIS facility of LBNL. The ignitor-heater method is used to first produce a pre-formed plasma channel in a hydrogen gas jet. Two counter propagating beams (wakefield driver:100-500mJ-50fs, injector:50-300mJ-50fs) then are focused onto the entrance of the channel. Preliminary results indicate that electron beam properties are affected by the second beam. Details of the experiment will be presented. [1]G.Fubiani, et al, Phys. Rev. E 70, 016402 (2004). [2]C.G.R. Geddes et al, Nature 431, 538 (2004). This work is supported by DoE under contract DE-AC02-05CH11231.

  17. Hysteresis of KcsA potassium channel's activation- deactivation gating is caused by structural changes at the channel's selectivity filter.

    PubMed

    Tilegenova, Cholpon; Cortes, D Marien; Cuello, Luis G

    2017-03-21

    Mode-shift or hysteresis has been reported in ion channels. Voltage-shift for gating currents is well documented for voltage-gated cation channels (VGCC), and it is considered a voltage-sensing domain's (VSD) intrinsic property. However, uncoupling the Shaker K(+) channel's pore domain (PD) from the VSD prevented the mode-shift of the gating currents. Consequently, it was proposed that an open-state stabilization of the PD imposes a mechanical load on the VSD, which causes its mode-shift. Furthermore, the mode-shift displayed by hyperpolarization-gated cation channels is likely caused by structural changes at the channel's PD similar to those underlying C-type inactivation. To demonstrate that the PD of VGCC undergoes hysteresis, it is imperative to study its gating process in the absence of the VSD. A back-door strategy is to use KcsA (a K(+) channel from the bacteria Streptomyces lividans) as a surrogate because it lacks a VSD and exhibits an activation coupled to C-type inactivation. By directly measuring KcsA's activation gate opening and closing in conditions that promote or halt C-type inactivation, we have found (i) that KcsA undergoes mode-shift of gating when having K(+) as the permeant ion; (ii) that Cs(+) or Rb(+), known to halt C-inactivation, prevented mode-shift of gating; and (iii) that, in the total absence of C-type inactivation, KcsA's mode-shift was prevented. Finally, our results demonstrate that an allosteric communication causes KcsA's activation gate to "remember" the conformation of the selectivity filter, and hence KcsA requires a different amount of energy for opening than for closing.

  18. MHD channel development, part 4

    NASA Astrophysics Data System (ADS)

    1989-12-01

    This is the final report of work performed by Avco Research Laboratory, Inc. for the U.S. Department of Energy, Pittsburgh Energy Technology Center. The overall objectives of this program were: to contribute, by appropriate systematic experimental and analytical investigations, to the engineering data base necessary for the design and construction of MHD generators at the 50 MW(sub th) and ultimately at commercial sizes; and to design and fabricate specific hardware items to be tested at a site to be specified by DOE. The program consisted of a series of related tasks, which are described in subsequent sections of this report. Section 4.0, MHD Channel Construction and Lifetime, reports experimental investigations related to MHD channel reliability and lifetime, where the principal aim is to improve the constructability, maintainability, and reliability of coal-fired, long-duration MHD channels.

  19. Resolvability of positron decay channels

    SciTech Connect

    Fluss, M.J.; Howell, R.H.; Rosenberg, I.J.; Meyer, P.

    1985-03-07

    Many data analysis treatments of positron experiments attempt to resolve two or more positron decay or exist channels which may be open simultaneously. Examples of the need to employ such treatments of the experimental results can be found in the resolution of the constituents of a defect ensemble, or in the analysis of the complex spectra which arise from the interaction of slow positrons at or near the surfaces of solids. Experimental one- and two-dimensional angular correlation of annihilation radiation experiments in Al single crystals have shown that two defect species (mono- and divacancies) can be resolved under suitable conditions. Recent experiments at LLNL indicate that there are a variety of complex exit channels open to positrons interacting at surfaces, and ultimely these decay channels must also be suitably resolved from one another. 6 refs., 4 figs.

  20. Continuous equal channel angular pressing

    DOEpatents

    Zhu, Yuntian T.; Lowe, Terry C.; Valiev, Ruslan Z.; Raab, Georgy J.

    2006-12-26

    An apparatus that continuously processes a metal workpiece without substantially altering its cross section includes a wheel member having an endless circumferential groove, and a stationary constraint die that surrounds the wheel member, covers most of the length of the groove, and forms a passageway with the groove. The passageway has a rectangular shaped cross section. An abutment member projects from the die into the groove and blocks one end of the passageway. The wheel member rotates relative to the die in the direction toward the abutment member. An output channel in the die adjacent the abutment member has substantially the same cross section as the passageway. A metal workpiece is fed through an input channel into the passageway and carried in the groove by frictional drag in the direction towards the abutment member, and is extruded through the output channel without any substantial change in cross section.

  1. Sodium Channel Inhibiting Marine Toxins

    NASA Astrophysics Data System (ADS)

    Llewellyn, Lyndon E.

    Saxitoxin (STX), tetrodotoxin (TTX) and their many chemical relatives are part of our daily lives. From killing people who eat seafood containing these toxins, to being valuable research tools unveiling the invisible structures of their pharmacological receptor, their global impact is beyond measure. The pharmacological receptor for these toxins is the voltage-gated sodium channel which transports Na ions between the exterior to the interior of cells. The two structurally divergent families of STX and TTX analogues bind at the same location on these Na channels to stop the flow of ions. This can affect nerves, muscles and biological senses of most animals. It is through these and other toxins that we have developed much of our fundamental understanding of the Na channel and its part in generating action potentials in excitable cells.

  2. Evaluate interference in digital channels

    NASA Technical Reports Server (NTRS)

    Davarian, F.; Sumida, J.

    1985-01-01

    Any future mobile satellite service (MSS) which is to provide simultaneous mobile communications for a large number of users will have to make very efficient use of the spectrum. As the spectrum available for an MSS is limited, the system's channels should be packed as closely together as possible, with minimum-width guard bands. In addition the employment of frequency reuse schemes is an important factor. Difficulties regarding these solutions are related to the introduction of interference in the link. A balance must be achieved between the competing aims of spectrum conservation and low interference. While the interference phenomenon in narrowband FM voice channels is reasonably well understood, very little effort, however, has been devoted to the problem in digital radios. Attention is given to work, which illuminates the effects of cochannel and adjacent channel interference on digital FM (FSK) radios.

  3. Thin-channel electrospray emitter

    DOEpatents

    Van Berkel, Gary J.

    2004-08-31

    An electrospray device includes a high voltage electrode chamber. The high voltage electrode chamber includes an inlet for receiving a fluid to be ionized and for directing the fluid into the chamber and at least one electrode having an exposed surface within the chamber. A flow channel directs fluid over a surface of the electrode and out of the chamber. The length of the flow channel over the electrode is greater than the height of the flow channel over the electrode, thereby producing enhanced mass transport to the working electrode resulting in improved electrolysis efficiency. An outlet is provided for transmitting the fluid out from the electrode chamber. A method of creating charged droplets includes flowing a fluid over an electrode where the length over the electrode is greater than the height of the fluid flowing over the electrode.

  4. Dual Regulation of Voltage-Sensitive Ion Channels by PIP(2).

    PubMed

    Rodríguez-Menchaca, Aldo A; Adney, Scott K; Zhou, Lei; Logothetis, Diomedes E

    2012-01-01

    Over the past 16 years, there has been an impressive number of ion channels shown to be sensitive to the major phosphoinositide in the plasma membrane, phosphatidylinositol 4,5-bisphosphate (PIP(2)). Among them are voltage-gated channels, which are crucial for both neuronal and cardiac excitability. Voltage-gated calcium (Cav) channels were shown to be regulated bidirectionally by PIP(2). On one hand, PIP(2) stabilized their activity by reducing current rundown but on the other hand it produced a voltage-dependent inhibition by shifting the activation curve to more positive voltages. For voltage-gated potassium (Kv) channels PIP(2) was first shown to prevent N-type inactivation regardless of whether the fast inactivation gate was part of the pore-forming α subunit or of an accessory β subunit. Careful examination of the effects of PIP(2) on the activation mechanism of Kv1.2 has shown a similar bidirectional regulation as in the Cav channels. The two effects could be distinguished kinetically, in terms of their sensitivities to PIP(2) and by distinct molecular determinants. The rightward shift of the Kv1.2 voltage dependence implicated basic residues in the S4-S5 linker and was consistent with stabilization of the inactive state of the voltage sensor. A third type of a voltage-gated ion channel modulated by PIP(2) is the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel. PIP(2) has been shown to enhance the opening of HCN channels by shifting their voltage-dependent activation toward depolarized potentials. The sea urchin HCN channel, SpIH, showed again a PIP(2)-mediated bidirectional effect but in reverse order than the depolarization-activated Cav and Kv channels: a voltage-dependent potentiation, like the mammalian HCN channels, but also an inhibition of the cGMP-induced current activation. Just like the Kv1.2 channels, distinct molecular determinants underlied the PIP(2) dual effects on SpIH, with the proximal C-terminus implicated in the

  5. 2D IR spectroscopy reveals the role of water in the binding of channel-blocking drugs to the influenza M2 channel

    NASA Astrophysics Data System (ADS)

    Ghosh, Ayanjeet; Wang, Jun; Moroz, Yurii S.; Korendovych, Ivan V.; Zanni, Martin; DeGrado, William F.; Gai, Feng; Hochstrasser, Robin M.

    2014-06-01

    Water is an integral part of the homotetrameric M2 proton channel of the influenza A virus, which not only assists proton conduction but could also play an important role in stabilizing channel-blocking drugs. Herein, we employ two dimensional infrared (2D IR) spectroscopy and site-specific IR probes, i.e., the amide I bands arising from isotopically labeled Ala30 and Gly34 residues, to probe how binding of either rimantadine or 7,7-spiran amine affects the water dynamics inside the M2 channel. Our results show, at neutral pH where the channel is non-conducting, that drug binding leads to a significant increase in the mobility of the channel water. A similar trend is also observed at pH 5.0 although the difference becomes smaller. Taken together, these results indicate that the channel water facilitates drug binding by increasing its entropy. Furthermore, the 2D IR spectral signatures obtained for both probes under different conditions collectively support a binding mechanism whereby amantadine-like drugs dock in the channel with their ammonium moiety pointing toward the histidine residues and interacting with a nearby water cluster, as predicted by molecular dynamics simulations. We believe these findings have important implications for designing new anti-influenza drugs.

  6. 2D IR spectroscopy reveals the role of water in the binding of channel-blocking drugs to the influenza M2 channel

    SciTech Connect

    Ghosh, Ayanjeet E-mail: gai@sas.upenn.edu; Gai, Feng E-mail: gai@sas.upenn.edu; Hochstrasser, Robin M.; Wang, Jun; DeGrado, William F.; Moroz, Yurii S.; Korendovych, Ivan V.; Zanni, Martin

    2014-06-21

    Water is an integral part of the homotetrameric M2 proton channel of the influenza A virus, which not only assists proton conduction but could also play an important role in stabilizing channel-blocking drugs. Herein, we employ two dimensional infrared (2D IR) spectroscopy and site-specific IR probes, i.e., the amide I bands arising from isotopically labeled Ala30 and Gly34 residues, to probe how binding of either rimantadine or 7,7-spiran amine affects the water dynamics inside the M2 channel. Our results show, at neutral pH where the channel is non-conducting, that drug binding leads to a significant increase in the mobility of the channel water. A similar trend is also observed at pH 5.0 although the difference becomes smaller. Taken together, these results indicate that the channel water facilitates drug binding by increasing its entropy. Furthermore, the 2D IR spectral signatures obtained for both probes under different conditions collectively support a binding mechanism whereby amantadine-like drugs dock in the channel with their ammonium moiety pointing toward the histidine residues and interacting with a nearby water cluster, as predicted by molecular dynamics simulations. We believe these findings have important implications for designing new anti-influenza drugs.

  7. Effects of Mechano-Electric Feedback on Scroll Wave Stability in Human Ventricular Fibrillation

    PubMed Central

    Hu, Yuxuan; Gurev, Viatcheslav; Constantino, Jason; Bayer, Jason D.; Trayanova, Natalia A.

    2013-01-01

    Recruitment of stretch-activated channels, one of the mechanisms of mechano-electric feedback, has been shown to influence the stability of scroll waves, the waves that underlie reentrant arrhythmias. However, a comprehensive study to examine the effects of recruitment of stretch-activated channels with different reversal potentials and conductances on scroll wave stability has not been undertaken; the mechanisms by which stretch-activated channel opening alters scroll wave stability are also not well understood. The goals of this study were to test the hypothesis that recruitment of stretch-activated channels affects scroll wave stability differently depending on stretch-activated channel reversal potential and channel conductance, and to uncover the relevant mechanisms underlying the observed behaviors. We developed a strongly-coupled model of human ventricular electromechanics that incorporated human ventricular geometry and fiber and sheet orientation reconstructed from MR and diffusion tensor MR images. Since a wide variety of reversal potentials and channel conductances have been reported for stretch-activated channels, two reversal potentials, −60 mV and −10 mV, and a range of channel conductances (0 to 0.07 mS/µF) were implemented. Opening of stretch-activated channels with a reversal potential of −60 mV diminished scroll wave breakup for all values of conductances by flattening heterogeneously the action potential duration restitution curve. Opening of stretch-activated channels with a reversal potential of −10 mV inhibited partially scroll wave breakup at low conductance values (from 0.02 to 0.04 mS/µF) by flattening heterogeneously the conduction velocity restitution relation. For large conductance values (>0.05 mS/µF), recruitment of stretch-activated channels with a reversal potential of −10 mV did not reduce the likelihood of scroll wave breakup because Na channel inactivation in regions of large stretch led to conduction block, which

  8. Ferritin Protein Nanocage Ion Channels

    PubMed Central

    Tosha, Takehiko; Behera, Rabindra K.; Ng, Ho-Leung; Bhattasali, Onita; Alber, Tom; Theil, Elizabeth C.

    2012-01-01

    Ferritin protein nanocages, self-assembled from four-α-helix bundle subunits, use Fe2+ and oxygen to synthesize encapsulated, ferric oxide minerals. Ferritin minerals are iron concentrates stored for cell growth. Ferritins are also antioxidants, scavenging Fenton chemistry reactants. Channels for iron entry and exit consist of helical hairpin segments surrounding the 3-fold symmetry axes of the ferritin nanocages. We now report structural differences caused by amino acid substitutions in the Fe2+ ion entry and exit channels and at the cytoplasmic pores, from high resolution (1.3–1.8 Å) protein crystal structures of the eukaryotic model ferritin, frog M. Mutations that eliminate conserved ionic or hydrophobic interactions between Arg-72 and Asp-122 and between Leu-110 and Leu-134 increase flexibility in the ion channels, cytoplasmic pores, and/or the N-terminal extensions of the helix bundles. Decreased ion binding in the channels and changes in ordered water are also observed. Protein structural changes coincide with increased Fe2+ exit from dissolved, ferric minerals inside ferritin protein cages; Fe2+ exit from ferritin cages depends on a complex, surface-limited process to reduce and dissolve the ferric mineral. High concentrations of bovine serum albumin or lysozyme (protein crowders) to mimic the cytoplasm restored Fe2+ exit in the variants to wild type. The data suggest that fluctuations in pore structure control gating. The newly identified role of the ferritin subunit N-terminal extensions in gating Fe2+ exit from the cytoplasmic pores strengthens the structural and functional analogies between ferritin ion channels in the water-soluble protein assembly and membrane protein ion channels gated by cytoplasmic N-terminal peptides. PMID:22362775

  9. Evolutionary stability on graphs

    PubMed Central

    Ohtsuki, Hisashi; Nowak, Martin A.

    2008-01-01

    Evolutionary stability is a fundamental concept in evolutionary game theory. A strategy is called an evolutionarily stable strategy (ESS), if its monomorphic population rejects the invasion of any other mutant strategy. Recent studies have revealed that population structure can considerably affect evolutionary dynamics. Here we derive the conditions of evolutionary stability for games on graphs. We obtain analytical conditions for regular graphs of degree k > 2. Those theoretical predictions are compared with computer simulations for random regular graphs and for lattices. We study three different update rules: birth-death (BD), death-birth (DB), and imitation (IM) updating. Evolutionary stability on sparse graphs does not imply evolutionary stability in a well-mixed population, nor vice versa. We provide a geometrical interpretation of the ESS condition on graphs. PMID:18295801

  10. Stability and Retention.

    PubMed

    Will, Leslie A

    2016-01-01

    Stability of tooth position in the broader sense considers all the forces that may act on the tooth. Reitan reported that significant forces remained in the periodontium after tooth movement, and he carried out research that demonstrated residual stretching of the crestal periodontal fibers more than 7 months after tooth movement. Brain demonstrated that severing the fibers reduced the relapse in tooth position in dogs. Edwards published a series of papers exploring the effects of surgical transection of the gingival fibers on tooth stability, recommending that circumferential fiberotomy be performed in order to increase posttreatment tooth stability. Other researchers have suggested ways to increase the stability of the incisors, which are typically most prone to relapse. Peck and Peck recommended that interproximal reduction be done to broaden the contact point. Boese also recommended interproximal reduction as part of a four-pronged approach to retention.

  11. Thermal Stabilization Blend Plan

    SciTech Connect

    RISENMAY, H.R.

    2000-05-02

    This Blend Plan documents the feed material items that are stored in 2736-2 vaults, the 2736-ZB 638 cage, the 192C vault, and the 225 vault that will be processed through the thermal stabilization furnaces. The purpose of thermal stabilization is to heat the material to 1000 degrees Celsius to drive off all water and leave the plutonium and/or uranium as oxides. The stabilized material will be sampled to determine the Loss On Ignition (LOI) or percent water. The stabilized material must meet water content or LOI of less than 0.5% to be acceptable for storage under DOE-STD-3013-99 specifications. Out of specification material will be recycled through the furnaces until the water or LOI limits are met.

  12. Spacecraft stability and control

    NASA Technical Reports Server (NTRS)

    Barret, Chris

    1992-01-01

    The Earth's first artificial satellite, Sputnik 1, slowly tumbled in orbit. The first U.S. satellite, Explorer 1, also tumbled out of control. Today, satellite stability and control has become a higher priority. For a satellite design that is to have a life expectancy of 14 years, appropriate spacecraft flight control systems will be reviewed, stability requirements investigated, and an appropriate flight control system recommended in order to see the design process. Disturbance torques, including aerodynamic, magnetic, gravity gradient, solar, micrometeorite, debris, collision, and internal torques, will be assessed to quantify the disturbance environment so that the required compensating torques can be determined. The control torques, including passive versus active, momentum control, bias momentum, spin stabilization, dual spin, gravity gradient, magnetic, reaction wheels, control moment gyros, inertia augmentation techniques, three-axis control, and reaction control systems (RCSs), will be considered. Conditions for stability will also be considered.

  13. Metallic alloy stability studies

    NASA Technical Reports Server (NTRS)

    Firth, G. C.

    1983-01-01

    The dimensional stability of candidate cryogenic wind tunnel model materials was investigated. Flat specimens of candidate materials were fabricated and cryo-cycled to assess relative dimensional stability. Existing 2-dimensional airfoil models as well as models in various stages of manufacture were also cryo-cycled. The tests indicate that 18 Ni maraging steel offers the greatest dimensional stability and that PH 13-8 Mo stainless steel is the most stable of the stainless steels. Dimensional stability is influenced primarily by metallurgical transformations (austenitic to martensitic) and manufacturing-induced stresses. These factors can be minimized by utilization of stable alloys, refinement of existing manufacturing techniques, and incorporation of new manufacturing technologies.

  14. Multi-ion occupancy alters gating in high-conductance, Ca(2+)-activated K+ channels

    PubMed Central

    1991-01-01

    In this study, single-channel recordings of high-conductance Ca(2+)- activated K+ channels from rat skeletal muscle inserted into planar lipid bilayer were used to analyze the effects of two ionic blockers, Ba2+ and Na+, on the channel's gating reactions. The gating equilibrium of the Ba(2+)-blocked channel was investigated through the kinetics of the discrete blockade induced by Ba2+ ions. Gating properties of Na(+)- blocked channels could be directly characterized due to the very high rates of Na+ blocking/unblocking reactions. While in the presence of K+ (5 mM) in the external solution Ba2+ is known to stabilize the open state of the blocked channel (Miller, C., R. Latorre, and I. Reisin. 1987. J. Gen. Physiol. 90:427-449), we show that the divalent blocker stabilizes the closed-blocked state if permeant ions are removed from the external solution (K+ less than 10 microM). Ionic substitutions in the outer solution induce changes in the gating equilibrium of the Ba(2+)-blocked channel that are tightly correlated to the inhibition of Ba2+ dissociation by external monovalent cations. In permeant ion-free external solutions, blockade of the channel by internal Na+ induces a shift (around 15 mV) in the open probability--voltage curve toward more depolarized potentials, indicating that Na+ induces a stabilization of the closed-blocked state, as does Ba2+ under the same conditions. A kinetic analysis of the Na(+)-blocked channel indicates that the closed- blocked state is favored mainly by a decrease in opening rate. Addition of 1 mM external K+ completely inhibits the shift in the activation curve without affecting the Na(+)-induced reduction in the apparent single-channel amplitude. The results suggest that in the absence of external permeant ions internal blockers regulate the permeant ion occupancy of a site near the outer end of the channel. Occupancy of this site appears to modulate gating primarily by speeding the rate of channel opening. PMID:2056305

  15. Tidal dynamics in channels: 2. Complex channel networks

    NASA Astrophysics Data System (ADS)

    Hill, A. E.; Souza, A. J.

    2006-11-01

    Intricate networks of tidal channels such as those found in fjordic, barrier island, and branching estuarine systems are often at risk from contaminant inputs and can be important as spawning grounds or migration pathways for marine organisms. These intricate systems are rarely spatially resolved in regional-scale numerical tidal models, and setting up a specific detailed numerical model for the purpose of rapidly assessing the likely tidal behavior of such geometrically complex systems carries a high overhead. Here we describe a straightforward algorithm (implemented in MATLAB) which permits rapid assessment of the linear tidal dynamics in an arbitrarily complex network of tidal channels. The method needs only a minimum of input data, namely, (1) the forcing tidal elevation amplitude and phase at the entrances of those channels directly exposed to the open sea and (2) the length, width, and depth of each channel. The performance of the method is tested against results from the finite element regional-scale numerical model of Foreman et al. (1993) in the fjordic region of western Canada.

  16. MHD channel development, part 3

    NASA Astrophysics Data System (ADS)

    1989-12-01

    This is the final report of work performed by Avco Research Laboratory, Inc. for the U.S. Department of Energy, Pittsburgh Energy Technology Center. The overall objectives of this program were: to contribute, by appropriate systematic experimental and analytical investigations, to the engineering data base necessary for the design and construction of MHD generators at the 50 MW(sub th) and ultimately at commercial sizes; and to design and fabricate specific hardware items to be tested at a site to be specified by DOE. Section 3.0, MHD Channel Design and Performance, reports experimental and analytical investigations related to MHD channel design and performance.

  17. Quantum teleportation without classical channel

    NASA Astrophysics Data System (ADS)

    Al Amri, M.; Li, Zheng-Hong; Zubairy, M. Suhail

    2016-11-01

    For the first time, we show how quantum teleportation can be achieved without the assistance of classical channels. Our protocol does not need any pre-established entangled photon pairs beforehand. Just by utilizing quantum Zeno effect and couterfactual communication idea, we can achieve two goals; entangling a photon and an atom and also disentangling them by non-local interaction. Information is completely transferred from atom to photon with controllable disentanglement processes. More importantly, there is no need to confirm teleportation results via classical channels.

  18. Alpha Channeling in Mirror Machines

    SciTech Connect

    Fisch, Nathaniel J.

    2014-07-16

    This Final Report for DE-FG02-06ER54851, Alpha Channeling in Mirror Machines, was in fact submitted on April 9, 2010. Some confusion arose because it was submitted as an initial progress report on a related grant, Alpha Channeling in Open- System Magnetic Devices. The original text is reproduced below, except that the publication record is undated. Note that the articles published in 2009 and 2010 reflect work in fact done under DE-FG02-06ER54851.

  19. The ion-channel laser

    SciTech Connect

    Whittum, D.H.; Sessler, A.M. ); Dawson, J.M. . Dept. of Physics)

    1990-01-01

    A relativistic electron beam propagating through a plasma in the ion-focused regime exhibits an electromagnetic instability at a resonant frequency {omega} {approximately} 2{gamma}{sup 2} {omega}{sub {beta}}. Growth is enhanced by optical guiding in the ion channel, which acts as dielectric waveguide, with fiber parameter V {approximately} 2 (I/I{sub A}){sup 1/2}. A 1-D theory for such an ion-channel laser'' is formulated, scaling laws are derived and numerical examples are given. Possible experimental evidence is noted. 23 refs., 1 fig., 1 tab.

  20. Channel incision and water quality

    NASA Astrophysics Data System (ADS)

    Shields, F. D.

    2009-12-01

    Watershed development often triggers channel incision that leads to radical changes in channel morphology. Although morphologic evolution due to channel incision has been documented and modeled by others, ecological effects, particularly water quality effects, are less well understood. Furthermore, environmental regulatory frameworks for streams frequently focus on stream water quality and underemphasize hydrologic and geomorphic issues. Discharge, basic physical parameters, solids, nutrients (nitrogen and phosphorus), chlorophyll and bacteria were monitored for five years at two sites along a stream in a mixed cover watershed characterized by rapid incision of the entire channel network. Concurrent data were collected from two sites on a nearby stream draining a watershed of similar size and cultivation intensity, but without widespread incision. Data sets describing physical aquatic habitat and fish fauna of each stream were available from other studies. The second stream was impacted by watershed urbanization, but was not incised, so normal channel-floodplain interaction maintained a buffer zone of floodplain wetlands between the study reach and the urban development upstream. The incised stream had mean channel depth and width that were 1.8 and 3.5 times as large as for the nonincised stream, and was characterized by flashier hydrology. The median rise rate for the incised stream was 6.4 times as great as for the nonincised stream. Correlation analyses showed that hydrologic perturbations were associated with water quality degradation, and the incised stream had levels of turbidity and solids that were two to three times higher than the nonincised, urbanizing stream. Total phosphorus, total Kjeldahl N, and chlorophyll a concentrations were significantly higher in the incised stream, while nitrate was significantly greater in the nonincised, urbanizing stream (p < 0.02). Physical aquatic habitat and fish populations in the nonincised urbanizing stream were

  1. Eight-Channel Continuous Timer

    NASA Technical Reports Server (NTRS)

    Cole, Steven

    2004-01-01

    A custom laboratory electronic timer circuit measures the durations of successive cycles of nominally highly stable input clock signals in as many as eight channels, for the purpose of statistically quantifying the small instabilities of these signals. The measurement data generated by this timer are sent to a personal computer running software that integrates the measurements to form a phase residual for each channel and uses the phase residuals to compute Allan variances for each channel. (The Allan variance is a standard statistical measure of instability of a clock signal.) Like other laboratory clock-cycle-measuring circuits, this timer utilizes an externally generated reference clock signal having a known frequency (100 MHz) much higher than the frequencies of the input clock signals (between 100 and 120 Hz). It counts the number of reference-clock cycles that occur between successive rising edges of each input clock signal of interest, thereby affording a measurement of the input clock-signal period to within the duration (10 ns) of one reference clock cycle. Unlike typical prior laboratory clock-cycle-measuring circuits, this timer does not skip some cycles of the input clock signals. The non-cycle-skipping feature is an important advantage because in applications that involve integration of measurements over long times for characterizing nominally highly stable clock signals, skipping cycles can degrade accuracy. The timer includes a field-programmable gate array that functions as a 20-bit counter running at the reference clock rate of 100 MHz. The timer also includes eight 20-bit latching circuits - one for each channel - at the output terminals of the counter. Each transition of an input signal from low to high causes the corresponding latching circuit to latch the count at that instant. Each such transition also sets a status flip-flop circuit to indicate the presence of the latched count. A microcontroller reads the values of all eight status flipflops

  2. Lubiprostone: a chloride channel activator.

    PubMed

    Lacy, Brian E; Levy, L Campbell

    2007-04-01

    In January 2006 the Food and Drug Administration approved lubiprostone for the treatment of chronic constipation in men and women aged 18 and over. Lubiprostone is categorized as a prostone, a bicyclic fatty acid metabolite of prostaglandin E1. Lubiprostone activates a specific chloride channel (ClC-2) in the gastrointestinal (GI) tract to enhance intestinal fluid secretion, which increases GI transit and improves symptoms of constipation. This article reviews the role of chloride channels in the GI tract, describes the structure, function, and pharmacokinetics of lubiprostone, and discusses clinically important data on this new medication.

  3. The role of MscL amphipathic N terminus indicates a blueprint for bilayer-mediated gating of mechanosensitive channels

    PubMed Central

    Bavi, Navid; Cortes, D. Marien; Cox, Charles D.; Rohde, Paul R.; Liu, Weihong; Deitmer, Joachim W.; Bavi, Omid; Strop, Pavel; Hill, Adam P.; Rees, Douglas; Corry, Ben; Perozo, Eduardo; Martinac, Boris

    2016-01-01

    The bacterial mechanosensitive channel MscL gates in response to membrane tension as a result of mechanical force transmitted directly to the channel from the lipid bilayer. MscL represents an excellent model system to study the basic biophysical principles of mechanosensory transduction. However, understanding of the essential structural components that transduce bilayer tension into channel gating remains incomplete. Here using multiple experimental and computational approaches, we demonstrate that the amphipathic N-terminal helix of MscL acts as a crucial structural element during tension-induced gating, both stabilizing the closed state and coupling the channel to the membrane. We propose that this may also represent a common principle in the gating cycle of unrelated mechanosensitive ion channels, allowing the coupling of channel conformation to membrane dynamics. PMID:27329693

  4. The role of MscL amphipathic N terminus indicates a blueprint for bilayer-mediated gating of mechanosensitive channels.

    PubMed

    Bavi, Navid; Cortes, D Marien; Cox, Charles D; Rohde, Paul R; Liu, Weihong; Deitmer, Joachim W; Bavi, Omid; Strop, Pavel; Hill, Adam P; Rees, Douglas; Corry, Ben; Perozo, Eduardo; Martinac, Boris

    2016-06-22

    The bacterial mechanosensitive channel MscL gates in response to membrane tension as a result of mechanical force transmitted directly to the channel from the lipid bilayer. MscL represents an excellent model system to study the basic biophysical principles of mechanosensory transduction. However, understanding of the essential structural components that transduce bilayer tension into channel gating remains incomplete. Here using multiple experimental and computational approaches, we demonstrate that the amphipathic N-terminal helix of MscL acts as a crucial structural element during tension-induced gating, both stabilizing the closed state and coupling the channel to the membrane. We propose that this may also represent a common principle in the gating cycle of unrelated mechanosensitive ion channels, allowing the coupling of channel conformation to membrane dynamics.

  5. The role of MscL amphipathic N terminus indicates a blueprint for bilayer-mediated gating of mechanosensitive channels

    NASA Astrophysics Data System (ADS)

    Bavi, Navid; Cortes, D. Marien; Cox, Charles D.; Rohde, Paul R.; Liu, Weihong; Deitmer, Joachim W.; Bavi, Omid; Strop, Pavel; Hill, Adam P.; Rees, Douglas; Corry, Ben; Perozo, Eduardo; Martinac, Boris

    2016-06-01

    The bacterial mechanosensitive channel MscL gates in response to membrane tension as a result of mechanical force transmitted directly to the channel from the lipid bilayer. MscL represents an excellent model system to study the basic biophysical principles of mechanosensory transduction. However, understanding of the essential structural components that transduce bilayer tension into channel gating remains incomplete. Here using multiple experimental and computational approaches, we demonstrate that the amphipathic N-terminal helix of MscL acts as a crucial structural element during tension-induced gating, both stabilizing the closed state and coupling the channel to the membrane. We propose that this may also represent a common principle in the gating cycle of unrelated mechanosensitive ion channels, allowing the coupling of channel conformation to membrane dynamics.

  6. METHOD FOR STABILIZING KLYSTRONS

    DOEpatents

    Magnuson, D.W.; Smith, D.F.

    1959-04-14

    High-frequency oscillators for the generation of microwaves, particularly a system for stabilizing frequency-modulated klystron oscillators of the reflex type, are described. The system takos advantage of the fact that a change in oscillator frequency will alter the normal phase displacement between the cavity and its modulator, creating an error voltage which is utilized to regulate the frequency of the oscillator and stabilize it.

  7. Factors Influencing Carboxyhemoglobin Stability.

    DTIC Science & Technology

    1985-03-26

    Medical Center, St. Louis, MO. 11. Dennis, R.C., and C.R. Valeri, 1980. Measuring Percent Oxygen Saturation of Hemoglobin, Percent Carboxyhemoglobin and... Carboxyhemoglobin Stability Technical Report 1983 - 1984 6. PERFORMING ORG. REPORT NUMBER 7. AUTNOR(e) S. CONTRACT OR GRANT NUMBER(a) George M. Goldstein...identify by block number) Carboxyhemoglobin Temperature Stability Co-Oxcimieter Heparin Ethylene diamine tetraacetic acid G. 0 ABSTRACT (Ctlze

  8. Food Fortification Stability Study

    NASA Technical Reports Server (NTRS)

    Sirmons, T. A.; Cooper, M. R.; Douglas, G. L.

    2016-01-01

    This study aims to assess the stability of vitamin content, sensory acceptability and color variation in fortified spaceflight foods over a period of 2 years. Findings will identify optimal formulation, processing, and storage conditions to maintain stability and acceptability of commercially available fortification nutrients. Changes in food quality are being monitored to indicate whether fortification affects quality over time (compared to the unfortified control), thus indicating their potential for use on long-duration missions.

  9. Food Fortification Stability Study

    NASA Technical Reports Server (NTRS)

    Sirmons, T. A.; Cooper, M. R.; Douglas, G. L.

    2017-01-01

    This study aimed to assess the stability of vitamin content, sensory acceptability and color variation in fortified spaceflight foods over a period of two years. Findings will help to identify optimal formulation, processing, and storage conditions to maintain stability and acceptability of commercially available fortification nutrients. Changes in food quality were monitored to indicate whether fortification affects quality over time (compared to the unfortified control), thus indicating their potential for use on long-duration missions.

  10. Shearing stability of lubricants

    NASA Technical Reports Server (NTRS)

    Shiba, Y.; Gijyutsu, G.

    1984-01-01

    Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.

  11. Automated RSO Stability Analysis

    NASA Astrophysics Data System (ADS)

    Johnson, T.

    2016-09-01

    A methodology for assessing the attitude stability of a Resident Space Object (RSO) using visual magnitude data is presented and then scaled to run in an automated fashion across the entire satellite catalog. Results obtained by applying the methodology to the Commercial Space Operations Center (COMSpOC) catalog are presented and summarized, identifying objects that have changed stability. We also examine the timeline for detecting the transition from stable to unstable attitude

  12. Tetraphenylborate Solids Stability Tests

    SciTech Connect

    Walker, D.D.

    1997-06-25

    Tetraphenylborate solids are a potentially large source of benzene in the slurries produced in the In-Tank Precipitation (ITP) process. The stability of the solids is an important consideration in the safety analysis of the process and we desire an understanding of the factors that influence the rate of conversion of the solids to benzene. This report discusses current testing of the stability of tetraphenylborate solids.

  13. Stability of Detached Solidification

    NASA Technical Reports Server (NTRS)

    Mazuruk, K.; Volz, M. P.; Croell, A.

    2009-01-01

    Bridgman crystal growth can be conducted in the so-called "detached" solidification regime, where the growing crystal is detached from the crucible wall. A small gap between the growing crystal and the crucible wall, of the order of 100 micrometers or less, can be maintained during the process. A meniscus is formed at the bottom of the melt between the crystal and crucible wall. Under proper conditions, growth can proceed without collapsing the meniscus. The meniscus shape plays a key role in stabilizing the process. Thermal and other process parameters can also affect the geometrical steady-state stability conditions of solidification. The dynamic stability theory of the shaped crystal growth process has been developed by Tatarchenko. It consists of finding a simplified autonomous set of differential equations for the radius, height, and possibly other process parameters. The problem then reduces to analyzing a system of first order linear differential equations for stability. Here we apply a modified version of this theory for a particular case of detached solidification. Approximate analytical formulas as well as accurate numerical values for the capillary stability coefficients are presented. They display an unexpected singularity as a function of pressure differential. A novel approach to study the thermal field effects on the crystal shape stability has been proposed. In essence, it rectifies the unphysical assumption of the model that utilizes a perturbation of the crystal radius along the axis as being instantaneous. It consists of introducing time delay effects into the mathematical description and leads, in general, to stability over a broader parameter range. We believe that this novel treatment can be advantageously implemented in stability analyses of other crystal growth techniques such as Czochralski and float zone methods.

  14. Self-mixing differential vibrometer based on electronic channel subtraction.

    PubMed

    Donati, Silvano; Norgia, Michele; Giuliani, Guido

    2006-10-01

    An instrument for noncontact measurement of differential vibrations is developed, based on the self-mixing interferometer. As no reference arm is available in the self-mixing configuration, the differential mode is obtained by electronic subtraction of signals from two (nominally equal) vibrometer channels, taking advantage that channels are servo stabilized and thus insensitive to speckle and other sources of amplitude fluctuation. We show that electronic subtraction is nearly as effective as field superposition. Common-mode suppression is 25-30 dB, the dynamic range (amplitude) is in excess of 100 microm, and the minimum measurable (differential) amplitude is 20 nm on a B = 10 kHz bandwidth. The instrument has been used to measure vibrations of two metal samples kept in contact, revealing the hysteresis cycle in the microslip and gross-slip regimes, which are of interest in the study of friction induced vibration damping of gas turbine blades for aircraft applications.

  15. The screw-helical voltage gating of ion channels.

    PubMed Central

    Keynes, R D; Elinder, F

    1999-01-01

    In the voltage-gated ion channels of every animal, whether they are selective for K+, Na+ or Ca2+, the voltage sensors are the S4 transmembrane segments carrying four to eight positive charges always separated by two uncharged residues. It is proposed that they move across the membrane in a screw-helical fashion in a series of three or more steps that each transfer a single electronic charge. The unit steps are stabilized by ion pairing between the mobile positive charges and fixed negative charges, of which there are invariably two located near the inner ends of segments S2 and S3 and a third near the outer end of either S2 or S3. Opening of the channel involves three such steps in each domain. PMID:10343407

  16. Instruments at the Lowell Observatory Discovery Channel Telescope (DCT)

    NASA Astrophysics Data System (ADS)

    Jacoby, George H.; Bida, Thomas A.; Fischer, Debra; Horch, Elliott; Kutyrev, Alexander; Mace, Gregory N.; Massey, Philip; Roe, Henry G.; Prato, Lisa A.

    2017-01-01

    The Lowell Observatory Discovery Channel Telescope (DCT) has been in full science operation for 2 years (2015 and 2016). Five instruments have been commissioned during that period, and two additional instruments are planned for 2017. These include:+ Large Monolithic Imager (LMI) - a CCD imager (12.6 arcmin FoV)+ DeVeny - a general purpose optical spectrograph (2 arcmin slit length, 10 grating choices)+ NIHTS - a low resolution (R=160) YJHK spectrograph (1.3 arcmin slit)+ DSSI - a two-channel optical speckle imager (5 arcsec FoV)+ IGRINS - a high resolution (45,000) HK spectrograph, on loan from the University of Texas.In the upcoming year, instruments will be delivered from the University of Maryland (RIMAS - a YJHK imager/spectrograph) and from Yale University (EXPRES - a very high resolution stabilized optical echelle for PRV).Each of these instruments will be described, along with their primary science goals.

  17. 48-channel coincidence counting system for multiphoton experiment

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Li, Wei; Hu, Yi; Yang, Tao; Jin, Ge; Jiang, Xiao

    2016-11-01

    In this paper, we demonstrate a coincidence counting system with 48 input channels which is aimed to count all coincidence events, up to 531 441 kinds, in a multiphoton experiment. Using the dynamic delay adjusting inside the Field Programmable Gate Array, the alignment of photon signals of 48 channels is achieved. After the alignment, clock phase shifting is used to sample signal pulses. Logic constraints are used to stabilize the pulse width. The coincidence counting data stored in a 1G bit external random access memory will be sent to the computer to analyze the amount of 2-, 3-, 4-, 5-, and 6-fold coincidence events. This system is designed for multiphoton entanglement experiments with multiple degrees of freedom of photons.

  18. Structure parameters in rotating Couette-Poiseuille channel flow

    NASA Technical Reports Server (NTRS)

    Knightly, George H.; Sather, D.

    1986-01-01

    It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.

  19. Two-phase flow instabilities in a vertical annular channel

    SciTech Connect

    Babelli, I.; Nair, S.; Ishii, M.

    1995-09-01

    An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.

  20. Physical principles underlying the transduction of bilayer deformation forces during mechanosensitive channel gating.

    PubMed

    Perozo, Eduardo; Kloda, Anna; Cortes, D Marien; Martinac, Boris

    2002-09-01

    In mechanosensitive (MS) channels, gating is initiated by changes in intra-bilayer pressure profiles originating from bilayer deformation. Here we evaluated two physical mechanisms as triggers of MS channel gating: the energetic cost of protein-bilayer hydrophobic mismatches and the geometric consequences of bilayer intrinsic curvature. Structural changes in the Escherichia coli large MS channel (MscL) were studied under nominally zero transbilayer pressures using both patch clamp and EPR spectroscopic approaches. Changes in membrane intrinsic curvature induced by the external addition of lysophosphatidylcholine (LPC) generated massive spectroscopic changes in the narrow constriction that forms the channel 'gate', trapping the channel in the fully open state. Hydrophobic mismatch alone was unable to open the channel, but decreasing bilayer thickness lowered MscL activation energy, stabilizing a structurally distinct closed channel intermediate. We propose that the mechanism of mechanotransduction in MS channels is defined by both local and global asymmetries in the transbilayer pressure profile at the lipid-protein interface.

  1. The role of vegetation and bed-level fluctuations in the process of channel narrowing

    USGS Publications Warehouse

    Friedman, J.M.; Osterkamp, W.R.; Lewis, W.M.

    1996-01-01

    A catastrophic flood in 1965 on Plum Creek, a perennial sandbed stream in the western Great Plains, removed most of the bottomland vegetation and transformed the single-thalweg stream into a wider, braided channel. Following eight years of further widening associated with minor high flows, a process of channel narrowing began in 1973; narrowing continues today. The history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5-km reach of Plum Creek near Louviers, Colorado. Sixty-three of these plants were excavated in order to determine the age and elevation of the germination point. The reconstructed record of channel change was verified from historical aerial photographs, and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach. Channel narrowing at Plum Creek occurs in two ways. First, during periods of high flow, sand and fine gravel are delivered to the channel, temporarily raising the general bed-level. Subsequently, several years of uninterrupted low flows incise a narrower channel. Second, during years of low flow, vegetation becomes established on the subaerial part of the present channel bed. In both cases, surfaces stabilize as a result of vegetation growth and vertical accretion of sediment.

  2. Hydrodynamics and morphodynamics of shallow tidal channels and intertidal flats. Doctoral thesis

    SciTech Connect

    Friedrichs, C.T.

    1993-02-01

    In this thesis, mechanisms which control morphodynamics of shallow tidal embayments are investigated analytically. In the process of exploring these mechanisms (specifically asymmetries in bottom stress), Tau, basis momentum and mass balances which govern flow in these systems are clarified. Temporal asymmetries in Tau are investigated via a new perturbation scheme which quantifies nonlinear processes and combines geometric controls on asymmetry into a single non-dimensional parameter. Implications of spatial asymmetries in Tau are investigated through stability criteria based on a uniform distribution of Tau. Morphologic observations of both tidal channels and intertidal flats are consistent with a uniform distribution of Tau at equilibrium. Investigation of morphodynamic mechanisms leads to scalings of momentum and continuity which diverge from classical models. Scalings for prismatic channels with strong tidal asymmetries indicate friction often dominates acceleration in the momentum equation. The resulting zero-inertia balance gives a time-varying diffusion equation which requires along-channel amplitude to decay. Uniform Tau justifies a new scaling of continuity for exponentially-shaped channels. In such channels, along-channel gradients in tidal velocity are small and are often dominated by gradients in cross-sectional area. The resulting first-order wave equation allows only amplitude, forward propagating waveforms which are independent of channel length. Tidal channels Hydrodynamics, Tidal flats.

  3. Stability in dynamical astronomy*

    PubMed Central

    Szebehely, Victor

    1978-01-01

    Hill's concept of stability is generalized and its relation to bifurcation theory is shown. A quantitative measure of stability is introduced that allows the comparison of the stability of different astronomical systems. Theoretical stability limits for triple stellar systems, for planetary systems, and for satellite systems are established. The measure of stability is evaluated for several known triple stellar systems as well as for the planets and for the natural satellites of the solar system. The model of the restricted problem of three bodies and values of the Jacobian constant are used to study planetary and satellite systems. The model of the general problem of three bodies is used to establish criteria for triple stellar systems. In general, the results show a hierarchy of stability: the existing triple systems are more stable than the planetary orbits of the solar system. The satellites of the solar system are least stable; in fact, some of the satellites are close to the line of instability (the Earth's Moon) and some are actually unstable (the four outermost satellites of Jupiter). PMID:16592589

  4. Local slope stability analysis

    NASA Astrophysics Data System (ADS)

    Hattendorf, I.; Hergarten, St.; Neugebauer, H. J.

    Mass movements under the influence of gravity occur as result of diverse disturbing and destabilizing processes, for example of climatic or anthropological origin. The stability of slopes is mainly determined by the geometry of the land-surface and designated slip-horizon. Further contributions are supplied by the pore water pressure, cohesion and friction. All relevant factors have to be integrated in a slope stability model, either by measurements and estimations (like phenomenological laws) or derived from physical equations. As result of stability calculations, it's suitable to introduce an expectation value, the factor-of-safety, for the slip-risk. Here, we present a model based on coupled physical equations to simulate hardly measurable phenomenons, like lateral forces and fluid flow. For the displacements of the soil-matrix we use a modified poroelasticity-equation with a Biot-coupling (Biot 1941) for the water pressure. Latter is described by a generalized Boussinesq equation for saturated-unsaturated porous media (Blendinger 1998). One aim of the calculations is to improve the knowledge about stability-distributions and their temporal variations. This requires the introduction of a local factor-of-safety which is the main difference to common stability models with global stability estimations. The reduction of immediate danger is still the emergent task of the most slope and landslide investigations, but this model is also useful with respect to understand the governing processes of landform evolution.

  5. Molecular pharmacology of the calcium channel: evidence for subtypes, multiple drug-receptor sites, channel subunits, and the development of a radioiodinated 1,4-dihydropyridine calcium channel label, (/sup 125/I)iodipine

    SciTech Connect

    Glossmann, H.; Ferry, D.R.; Goll, A.; Rombusch, M.

    1984-01-01

    Radiolabeled Ca2+ antagonists (1,4-dihydropyridines, verapamil, and D-cis-diltiazem) were used to study voltage-operated Ca2+ channels in different excitable tissues. The concept of three subtypes of Ca2+ channels, represented by brain, heart, and skeletal-muscle isoreceptors for 1,4-dihydropyridines, is developed. The three subtypes are characterized by a variety of criteria. Despite the biochemical differences between the subtypes, they have the same Mr in situ by target-size analysis (Mr approximately equal to 180,000, when evaluated by (/sub 3/H)nimodipine). The concept of the metalloprotein nature of the channel and the interaction of channel drugs with the Me2+ binding sites of the ionic pore is demonstrated. Distinct but interacting drug-receptor sites of the Ca2+ channel are found by direct labeling as well as indirectly by drug competition studies. The authors distinguish between the 1,4-dihydropyridine site, the verapamil site, and the D-cis-diltiazem site. Each receptor site can exist in high and low-affinity state; the distribution of receptor sites in these states is regulated by temperature, ions, and drugs. The concept of intrinsic activity of drugs to stabilize the high-affinity state is exemplified for the 1,4-dihydropyridines. A change in the channel architecture is induced by binding of D-cis-diltiazem to its drug receptor site. This is proven by target-size analysis of the channel in situ. Partially purified t-tubule membranes from skeletal muscle are an extremely rich source of Ca2+ channel drug-receptor sites. The stoichiometry was determined in this preparation and found to be four verapamil:two 1,4-dihydropyridine:one D-cis-diltiazem site. A novel Ca2+ channel probe, (/sup 125/I)iodipine (2,200 Ci/mmol), was synthetized, and the properties of this ligand are presented.

  6. Linear time-invariant controller design for two-channel decentralized control systems

    NASA Technical Reports Server (NTRS)

    Desoer, Charles A.; Gundes, A. Nazli

    1987-01-01

    This paper analyzes a linear time-invariant two-channel decentralized control system with a 2 x 2 strictly proper plant. It presents an algorithm for the algebraic design of a class of decentralized compensators which stabilize the given plant.

  7. A MULTIPLE GRID ALGORITHM FOR ONE-DIMENSIONAL TRANSIENT OPEN CHANNEL FLOWS. (R825200)

    EPA Science Inventory

    Numerical modeling of open channel flows with shocks using explicit finite difference schemes is constrained by the choice of time step, which is limited by the CFL stability criteria. To overcome this limitation, in this work we introduce the application of a multiple grid al...

  8. A MULTIPLE GRID APPROACH FOR OPEN CHANNEL FLOWS WITH STRONG SHOCKS. (R825200)

    EPA Science Inventory

    Abstract

    Explicit finite difference schemes are being widely used for modeling open channel flows accompanied with shocks. A characteristic feature of explicit schemes is the small time step, which is limited by the CFL stability condition. To overcome this limitation,...

  9. Tight coupling of rubidium conductance and inactivation in human KCNQ1 potassium channels.

    PubMed

    Seebohm, Guiscard; Sanguinetti, Michael C; Pusch, Michael

    2003-10-15

    KCNQ1 K+ channels in humans are important for repolarization of cardiac action potentials and for K+ secretion in the inner ear. The pore-forming channel subunits form heteromeric complexes with small regulatory subunits of the KCNE family, in particular with KCNE1 to form channels that conduct a slow delayed rectifier K+ current, IKs. This association leads to alteration of biophysical properties, including a slowing of activation, a suppression of inactivation and an increase of the apparent single-channel conductance. In addition, inward Rb+ currents conducted by homomeric KCNQ1 channels are about threefold larger than K+ currents, whereas heteromeric KCNQ1-KCNE1 channels have smaller inward Rb+ currents compared to K+ currents. We determined inactivation properties and compared K+ vs. Rb+ inward currents for channels formed by co-assembly of KCNQ1 with KCNE1, KCNE3 and KCNE5, and for homomeric KCNQ1 channels with point mutations in the pore helix S5 or S6 transmembrane domains. Several of the channels with point mutations eliminated the apparent inactivation of KCNQ1, as described previously (Seebohm et al. 2001). We found that the extent of inactivation and the ratio of Rb+/K+ currents were positively correlated. Since the effect of Rb+ on the current size has been shown previously to be related to a fast 'flickery' process, our results suggest that inactivation of KCNQ1 channels is related to a fast flicker of the open channel. A kinetic model incorporating two open states, no explicit inactivated state and a fast flicker that is different for the two open states is able to account for the apparent inactivation and the correlation of inactivation and large Rb+ currents. We conclude that an association between KCNQ1 and KCNE subunits or removal of inactivation by mutation of KCNQ1 stabilizes the open conformation of the pore principally by altering an interaction between the pore helix and the selectivity filter and with S5/S6 domains.

  10. Stabilization precision control methods of photoelectric aim-stabilized system

    NASA Astrophysics Data System (ADS)

    Song, Xiaoru; Chen, Hua; Xue, Yonggang

    2015-09-01

    To solve the question that photoelectric aim-stabilized system can be controlled with high precision and stability, this paper researches a new photoelectric aim-stabilized control algorithm, analyzes the photoelectric aim-stabilized system architecture, sets up stability control system mathematical model, designs the stability of the photoelectric aim-stabilized LSSVM identification and control system, discusses uncertain factors and calculates the LSSVM parameters by the Chaos theory, gives the predictive controller model by the LSSVM and designs new photoelectric aim-stabilized system. Through the simulation calculation and experimental analysis, new photoelectric aim-stabilized control algorithm was verified; the results show the new photoelectric aim-stabilized control method can meet the demand of high precision control in photoelectric aim-stabilized system.

  11. Channel function reconstitution and re-animation: a single-channel strategy in the postcrystal age.

    PubMed

    Oiki, Shigetoshi

    2015-06-15

    The most essential properties of ion channels for their physiologically relevant functions are ion-selective permeation and gating. Among the channel species, the potassium channel is primordial and the most ubiquitous in the biological world, and knowledge of this channel underlies the understanding of features of other ion channels. The strategy applied to studying channels changed dramatically after the crystal structure of the potassium channel was resolved. Given the abundant structural information available, we exploited the bacterial KcsA potassium channel as a simple model channel. In the postcrystal age, there are two effective frameworks with which to decipher the functional codes present in the channel structure, namely reconstitution and re-animation. Complex channel proteins are decomposed into essential functional components, and well-examined parts are rebuilt for integrating channel function in the membrane (reconstitution). Permeation and gating are dynamic operations, and one imagines the active channel by breathing life into the 'frozen' crystal (re-animation). Capturing the motion of channels at the single-molecule level is necessary to characterize the behaviour of functioning channels. Advanced techniques, including diffracted X-ray tracking, lipid bilayer methods and high-speed atomic force microscopy, have been used. Here, I present dynamic pictures of the KcsA potassium channel from the submolecular conformational changes to the supramolecular collective behaviour of channels in the membrane. These results form an integrated picture of the active channel and offer insights into the processes underlying the physiological function of the channel in the cell membrane.

  12. Groundwater controls on biogeomorphic succession and river channel morphodynamics

    NASA Astrophysics Data System (ADS)

    Bätz, N.; Colombini, P.; Cherubini, P.; Lane, S. N.

    2016-10-01

    Biogeomorphic succession describes feedbacks between vegetation succession and fluvial processes that, at the decadal timescale, lead to a transition from bare river-deposited sediment to fully developed riparian forest. Where the rate of stabilization by biogeomorphic succession is greater than the rate of ecological disturbance by fluvial processes, a river is likely to evolve into less dynamic states. While river research has frequently considered the physical dimensions of morphodynamics, less is known about physical controls on succession rates, and how these impact stream morphodynamics. Here we test the hypothesis that groundwater dynamics influence morphodynamics via the rate of biogeomorphic succession. We applied historic imagery analysis in combination with dendroecological methods for willows growing on young gravelly fluvial landforms along a steep groundwater-depth gradient. We determined the following: floodplain morphodynamics and plant encroachment at the decadal scale, pioneer willow growth rates, and their relationships to hydrological variables. Willow growth rates were correlated with moisture availability (groundwater, discharge, and precipitation variability) in the downwelling reach, while little correlation was found in the upwelling reach. After a reduction in ecological disturbance frequency, data suggest that where groundwater is upwelling, biogeomorphic succession is fast, the engineering effect of vegetation is quickly established, and hence channel stability increased and active channel width reduces. Where groundwater is downwelling, deeper and more variable, biogeomorphic succession is slower, the engineering effect is reduced, and a wider active width is maintained. Thus, groundwater is an important control on biogeomorphic feedbacks intensity and, through the stabilizing effect of vegetation, may drive long-term river channel morphodynamics.

  13. Cation channels in the Arabidopsis plasma membrane.

    PubMed

    Véry, Anne Aliénor; Sentenac, Hervé

    2002-04-01

    In vivo analyses have identified different functional types of ion channels in various plant tissues and cells. The Arabidopsis genome contains approximately 70 genes for ion channels, of which 57 might be cation-selective channels (K(+), Ca(2+) or poorly discriminating channels). Here, we describe the different families of (putative) cation channels: the Shakers, the two-P-domain and Kir K(+) channels (encoded by the KCO genes), the cyclic-nucleotide-gated channels, the glutamate receptors, and the Ca(2+) channel TPC1. We also compare molecular data with the data obtained in planta, which should lead to a better understanding of the identity of these channels and provide clues about their roles in plant nutrition and cell signalling.

  14. Ion channels in development and cancer.

    PubMed

    Bates, Emily

    2015-01-01

    Ion channels have emerged as regulators of developmental processes. In model organisms and in people with mutations in ion channels, disruption of ion channel function can affect cell proliferation, cell migration, and craniofacial and limb patterning. Alterations of ion channel function affect morphogenesis in fish, frogs, mammals, and flies, demonstrating that ion channels have conserved roles in developmental processes. One model suggests that ion channels affect proliferation and migration through changes in cell volume. However, ion channels have not explicitly been placed in canonical developmental signaling cascades until recently. This review gives examples of ion channels that influence developmental processes, offers a potential underlying molecular mechanism involving bone morphogenetic protein (BMP) signaling, and finally explores exciting possibilities for manipulating ion channels to influence cell fate for regenerative medicine and to impact disease.

  15. Time domain passivity controller for 4-channel time-delay bilateral teleoperation.

    PubMed

    Rebelo, Joao; Schiele, Andre

    2015-01-01

    This paper presents an extension of the time-domain passivity control approach to a four-channel bilateral controller under the effects of time delays. Time-domain passivity control has been used successfully to stabilize teleoperation systems with position-force and position-position controllers; however, the performance with such control architectures is sub-optimal both with and without time delays. This work extends the network representation of the time-domain passivity controller to the four-channel architecture, which provides perfect transparency to the user without time delay. The proposed architecture is based on modelling the controllers as dependent voltage sources and using only series passivity controllers. The obtained results are shown on a one degree-of-freedom setup and illustrate the stabilization behaviour of the proposed controller when time delay is present in the communication channel.

  16. Molecular Diversity and Functional Evolution of Scorpion Potassium Channel Toxins*

    PubMed Central

    Zhu, Shunyi; Peigneur, Steve; Gao, Bin; Luo, Lan; Jin, Di; Zhao, Yong; Tytgat, Jan

    2011-01-01

    Scorpion toxins affecting K+ channels (KTxs) represent important pharmacological tools and potential drug candidates. Here, we report molecular characterization of seven new KTxs in the scorpion Mesobuthus eupeus by cDNA cloning combined with biochemical approaches. Comparative modeling supports that all these KTxs share a conserved cysteine-stabilized α-helix/β-sheet structural motif despite the differences in protein sequence and size. We investigated functional diversification of two orthologous α-KTxs (MeuTXKα1 from M. eupeus and BmP01 from Mesobuthus martensii) by comparing their K+ channel-blocking activities. Pharmacologically, MeuTXKα1 selectively blocked Kv1.3 channel with nanomolar affinity (IC50, 2.36 ± 0.9 nm), whereas only 35% of Kv1.1 currents were inhibited at 3 μm concentration, showing more than 1271-fold selectivity for Kv1.3 over Kv1.1. This peptide displayed a weak effect on Drosophila Shaker channel and no activity on Kv1.2, Kv1.4, Kv1.5, Kv1.6, and human ether-a-go-go-related gene (hERG) K+ channels. Although BmB01 and MeuTXKα1 have a similar channel spectrum, their affinity and selectivity for these channels largely varies. In comparison with MeuTXKα1, BmP01 only exhibits a submicromolar affinity (IC50, 133.72 ± 10.98 nm) for Kv1.3, showing 57-fold less activity than MeuTXKα1. Moreover, it lacks the ability to distinguish between Kv1.1 and Kv1.3. We also found that MeuTXKα1 inhibited the proliferation of activated T cells induced by phorbol myristate acetate and ionomycin at micromolar concentrations. Our results demonstrate that accelerated evolution drives affinity variations of orthologous α-KTxs on Kv channels and indicate that MeuTXKα1 is a promising candidate to develop an immune modulation agent for human autoimmune diseases. PMID:20889474

  17. Curtain Wall Creates Ventilation Channel

    NASA Technical Reports Server (NTRS)

    Lewis, E. V.

    1985-01-01

    Curtain-wall structure proposed for removing methane and airborne coal dust from hydrojet-jaw mining machines. Channel between curtain wall and mine wall forms closed exhaust passage. Through it, gas and dust continuously removed so high concentrations of these explosive materials not build up.

  18. Driven tracers in narrow channels

    NASA Astrophysics Data System (ADS)

    Cividini, J.; Mukamel, D.; Posch, H. A.

    2017-01-01

    Steady-state properties of a driven tracer moving in a narrow two-dimensional (2D) channel of quiescent medium are studied. The tracer drives the system out of equilibrium, perturbs the density and pressure fields, and gives the bath particles a nonzero average velocity, creating a current in the channel. Three models in which the confining effect of the channel is probed are analyzed and compared in this study: the first is the simple symmetric exclusion process (SSEP), for which the stationary density profile and the pressure on the walls in the frame of the tracer are computed. We show that the tracer acts like a dipolar source in an average velocity field. The spatial structure of this 2D strip is then simplified to a one-dimensional (1D) SSEP, in which exchanges of position between the tracer and the bath particles are allowed. Using a combination of mean-field theory and exact solution in the limit where no exchange is allowed gives good predictions of the velocity of the tracer and the density field. Finally, we show that results obtained for the 1D SSEP with exchanges also apply to a gas of overdamped hard disks in a narrow channel. The correspondence between the parameters of the SSEP and of the gas of hard disks is systematic and follows from simple intuitive arguments. Our analytical results are checked numerically.

  19. Store-Operated Calcium Channels.

    PubMed

    Prakriya, Murali; Lewis, Richard S

    2015-10-01

    Store-operated calcium channels (SOCs) are a major pathway for calcium signaling in virtually all metozoan cells and serve a wide variety of functions ranging from gene expression, motility, and secretion to tissue and organ development and the immune response. SOCs are activated by the depletion of Ca(2+) from the endoplasmic reticulum (ER), triggered physiologically through stimulation of a diverse set of surface receptors. Over 15 years after the first characterization of SOCs through electrophysiology, the identification of the STIM proteins as ER Ca(2+) sensors and the Orai proteins as store-operated channels has enabled rapid progress in understanding the unique mechanism of store-operate calcium entry (SOCE). Depletion of Ca(2+) from the ER causes STIM to accumulate at ER-plasma membrane (PM) junctions where it traps and activates Orai channels diffusing in the closely apposed PM. Mutagenesis studies combined with recent structural insights about STIM and Orai proteins are now beginning to reveal the molecular underpinnings of these choreographic events. This review describes the major experimental advances underlying our current understanding of how ER Ca(2+) depletion is coupled to the activation of SOCs. Particular emphasis is placed on the molecular mechanisms of STIM and Orai activation, Orai channel properties, modulation of STIM and Orai function, pharmacological inhibitors of SOCE, and the functions of STIM and Orai in physiology and disease.

  20. EPICS: Channel Access security design

    SciTech Connect

    Kraimer, M.; Hill, J.

    1994-05-01

    This document presents the design for implementing the requirements specified in: EPICS -- Channel Access Security -- functional requirements, Ned. D. Arnold, 03/09/92. Use of the access security system is described along with a summary of the functional requirements. The programmer`s interface is given. Security protocol is described and finally aids for reading the access security code are provided.

  1. Improved Ion-Channel Biosensors

    NASA Technical Reports Server (NTRS)

    Nadeau, Jay; White, Victor; Dougherty, Dennis; Maurer, Joshua

    2004-01-01

    An effort is underway to develop improved biosensors of a type based on ion channels in biomimetic membranes. These sensors are microfabricated from silicon and other materials compatible with silicon. As described, these sensors offer a number of advantages over prior sensors of this type.

  2. Lowell Observatory's Discovery Channel Telescope

    NASA Astrophysics Data System (ADS)

    Hall, Jeffrey C.

    2017-01-01

    Lowell Observatory broke ground on its 4.3-meter Discovery Channel Telescope (DCT) in July 2005 and celebrated first light for the telescope in July 2012. In this overview to this special session, I will discuss the origin and development of the project, the telescope's general specifications and performance, its current operating status, and the initial instrument suite.

  3. Ion channels in analgesia research.

    PubMed

    Rosenbaum, Tamara; Simon, Sidney A; Islas, Leon D

    2010-01-01

    Several recent techniques have allowed us to pinpoint the receptors responsible for the detection of nociceptive stimuli. Among these receptors, ion channels play a fundamental role in the recognition and transduction of stimuli that can cause pain. During the last decade, compelling evidence has been gathered on the role of the TRPV1 channel in inflammatory and neuropathic states. Activation of TRPV1 in nociceptive neurons results in the release of neuropeptides and transmitters, leading to the generation of action potentials that will be sent to higher CNS areas, where they will often be perceived as pain. Its activation will also evoke the peripheral release of pro-inflammatory compounds that may sensitize other neurons to physical, thermal, or chemical stimuli. For these reasons, and because its continuous activation causes analgesia, TRPV1 is now considered a viable drug target for clinical use in the management of pain. Using the TRPV1 channel as an example, here we describe some basic biophysical approaches used to study the properties of ion channels involved in pain and in analgesia.

  4. Channeled partial Mueller matrix polarimetry

    NASA Astrophysics Data System (ADS)

    Alenin, Andrey S.; Tyo, J. S.

    2015-09-01

    In prior work,1,2 we introduced methods to treat channeled systems in a way that is similar to Data Reduction Method (DRM), by focusing attention on the Fourier content of the measurement conditions. Introduction of Q enabled us to more readily extract the performance of the system and thereby optimize it to obtain reconstruction with the least noise. The analysis tools developed for that exercise can be expanded to be applicable to partial Mueller Matrix Polarimeters (pMMPs), which were a topic of prior discussion as well. In this treatment, we combine the principles involved in both of those research trajectories and identify a set of channeled pMMP families. As a result, the measurement structure of such systems is completely known and the design of a channeled pMMP intended for any given task becomes a search over a finite set of possibilities, with the additional channel rotation allowing for a more desirable Mueller element mixing.

  5. Store-Operated Calcium Channels

    PubMed Central

    Lewis, Richard S.

    2015-01-01

    Store-operated calcium channels (SOCs) are a major pathway for calcium signaling in virtually all metozoan cells and serve a wide variety of functions ranging from gene expression, motility, and secretion to tissue and organ development and the immune response. SOCs are activated by the depletion of Ca2+ from the endoplasmic reticulum (ER), triggered physiologically through stimulation of a diverse set of surface receptors. Over 15 years after the first characterization of SOCs through electrophysiology, the identification of the STIM proteins as ER Ca2+ sensors and the Orai proteins as store-operated channels has enabled rapid progress in understanding the unique mechanism of store-operate calcium entry (SOCE). Depletion of Ca2+ from the ER causes STIM to accumulate at ER-plasma membrane (PM) junctions where it traps and activates Orai channels diffusing in the closely apposed PM. Mutagenesis studies combined with recent structural insights about STIM and Orai proteins are now beginning to reveal the molecular underpinnings of these choreographic events. This review describes the major experimental advances underlying our current understanding of how ER Ca2+ depletion is coupled to the activation of SOCs. Particular emphasis is placed on the molecular mechanisms of STIM and Orai activation, Orai channel properties, modulation of STIM and Orai function, pharmacological inhibitors of SOCE, and the functions of STIM and Orai in physiology and disease. PMID:26400989

  6. Microwave propagation on acupuncture channels.

    PubMed

    Krevsky, Michael A; Zinina, Ekaterina S; Koshurinov, Yuri; Ovechkin, Aleck M; Tkachenko, Yuri A; Han, Wantaek; Lee, Sang-Min; Yoon, Gilwon

    2006-01-01

    Quantitative studies on functional state of acupuncture points and meridians have been done mostly by electrical measurement that requires the contact of the electrode on skin and is subject to pressure, humidity, etc. In this study, a new modality of using microwave was investigated. Microwave energy in the frequency range of 250 approximately 550MHz was irradiated on an acupuncture point. Transmitted microwave energy along the meridian was measured at the next acupuncture point of the same meridian. Diabetic and cancer patients were compared with healthy persons. Normal group consisted of 50 healthy persons. Diabetic group included 50 diabetic patients. Breast cancer group had also 50 patients. All 12 meridians on both right and left hands and feet were measured. For the diabetic group, the microwave energy propagation in this frequency range was 1.417 dB lower along Lung channel and 1.601 dB higher along Spleen channel compared with the normal group regardless of sex and diabetic types. For cancer patients, the propagation was 1.620 dB lower along Liver channel and 1.245 dB higher along Kidney channel compared with the normal group. Microwave energy proved to be a potential diagnostic method.

  7. Ethanol Stabilizes the Open State of Single 5-Hydroxytryptamine3A(QDA) Receptors

    PubMed Central

    Feinberg-Zadek, Paula L.

    2010-01-01

    Ethanol enhancement of 5-hydroxytryptamine (5-HT)3A receptor-mediated responses may have important consequences in the intoxicating and addictive properties of ethanol. Although the exact mechanism is unknown, ethanol-mediated enhancement of 5-HT3 receptor current has been proposed to occur due to stabilization of the open-channel state. It has not been possible to directly measure the open state of the channel due to the extremely low single-channel conductance of 5-HT3A channels. Recently, three arginine residues within the large intracellular loop of the 5-HT3A subunit were substituted by their equivalent residues (glutamine, aspartate, and alanine) of the 5-HT3B subunit to produce a 5-HT3A(QDA) subunit that forms functional homomeric channels exhibiting a measurable single-channel conductance. Using whole-cell rapid-agonist application techniques and the cell-attached single-channel recording configuration, we examined human 5-HT3A(QDA) receptors expressed in human embryonic kidney 293 cells. The agonist sensitivity, macroscopic kinetics, and modulation by ethanol were similar between mutant and wild-type channels, suggesting the substitutions had not altered these channel structure-function properties. The open time histogram for single-channel events mediated by 5-HT3A(QDA) receptors in the presence of maximal 5-HT was best fit by three exponentials, but in the presence of ethanol a fourth open state was evident. In summary, the QDA substitution greatly enhanced single-channel conductance with little effect on 5-HT3A channel's kinetic properties and ethanol enhances agonist action on 5-HT3A receptors by inducing a new, long-lived open-channel state. Furthermore, the 5-HT3A(QDA) receptor appears to be suitable for pharmacological studies of 5-HT3A receptor modulation at a single-channel level. PMID:20200118

  8. Uncertainties in climate stabilization

    SciTech Connect

    Wigley, T. M.; Clarke, Leon E.; Edmonds, James A.; Jacoby, H. D.; Paltsev, S.; Pitcher, Hugh M.; Reilly, J. M.; Richels, Richard G.; Sarofim, M. C.; Smith, Steven J.

    2009-11-01

    We explore the atmospheric composition, temperature and sea level implications of new reference and cost-optimized stabilization emissions scenarios produced using three different Integrated Assessment (IA) models for U.S. Climate Change Science Program (CCSP) Synthesis and Assessment Product 2.1a. We also consider an extension of one of these sets of scenarios out to 2300. Stabilization is defined in terms of radiative forcing targets for the sum of gases potentially controlled under the Kyoto Protocol. For the most stringent stabilization case (“Level 1” with CO2 concentration stabilizing at about 450 ppm), peak CO2 emissions occur close to today, implying a need for immediate CO2 emissions abatement if we wish to stabilize at this level. In the extended reference case, CO2 stabilizes at 1000 ppm in 2200 – but even to achieve this target requires large and rapid CO2 emissions reductions over the 22nd century. Future temperature changes for the Level 1 stabilization case show considerable uncertainty even when a common set of climate model parameters is used (a result of different assumptions for non-Kyoto gases). Uncertainties are about a factor of three when climate sensitivity uncertainties are accounted for. We estimate the probability that warming from pre-industrial times will be less than 2oC to be about 50%. For one of the IA models, warming in the Level 1 case is greater out to 2050 than in the reference case, due to the effect of decreasing SO2 emissions that occur as a side effect of the policy-driven reduction in CO2 emissions. Sea level rise uncertainties for the Level 1 case are very large, with increases ranging from 12 to 100 cm over 2000 to 2300.

  9. Stabilization of compactible waste

    SciTech Connect

    Franz, E.M.; Heiser, J.H. III; Colombo, P.

    1990-09-01

    This report summarizes the results of series of experiments performed to determine the feasibility of stabilizing compacted or compactible waste with polymers. The need for this work arose from problems encountered at disposal sites attributed to the instability of this waste in disposal. These studies are part of an experimental program conducted at Brookhaven National Laboratory (BNL) investigating methods for the improved solidification/stabilization of DOE low-level wastes. The approach taken in this study was to perform a series of survey type experiments using various polymerization systems to find the most economical and practical method for further in-depth studies. Compactible dry bulk waste was stabilized with two different monomer systems: styrene-trimethylolpropane trimethacrylate (TMPTMA) and polyester-styrene, in laboratory-scale experiments. Stabilization was accomplished by wetting or soaking compactible waste (before or after compaction) with monomers, which were subsequently polymerized. Three stabilization methods are described. One involves the in-situ treatment of compacted waste with monomers in which a vacuum technique is used to introduce the binder into the waste. The second method involves the alternate placement and compaction of waste and binder into a disposal container. In the third method, the waste is treated before compaction by wetting the waste with the binder using a spraying technique. A series of samples stabilized at various binder-to-waste ratios were evaluated through water immersion and compression testing. Full-scale studies were conducted by stabilizing two 55-gallon drums of real compacted waste. The results of this preliminary study indicate that the integrity of compacted waste forms can be readily improved to ensure their long-term durability in disposal environments. 9 refs., 10 figs., 2 tabs.

  10. Aquifer stability investigations

    SciTech Connect

    Allen, R.D.; Doherty, T.J.

    1981-09-01

    The study of compressed air energy storage (CAES) in porous rock reservoirs is carried out within the Reservoir Stability Studies Program at Pacific Northwest Laboratory. The goal of the study is to establish criteria for long-term stability of aquifer CAES reservoirs. These criteria are intended to be guidelines and check lists that utilities and architect-engineering firms may use to evaluate reservoir stability at candidate CAES sites. These criteria will be quantitative where possible, qualitative where necessary, and will provide a focal point for CAES relevant geotechnical knowledge, whether developed within this study or available from petroleum, mining or other geotechnical practices using rock materials. The Reservoir Stability Studies Program had four major activities: a state-of-the-art survey to establish preliminary stability criteria and identify areas requiring research and development; numerical modeling; laboratory testing to provide data for use in numerical models and to investigate fundamental rock mechanics, thermal, fluid, and geochemical response of aquifer materials; and field studies to verify the feasibility of air injection and recovery under CAES conditions in an aquifer, to validate and refine the stability criteria, and to evaluate the accuracy and adequacy of the numerical and experimental methodologies developed in previous work. Three phases of study, including preliminary criteria formulation, numerical model development, and experimental assessment of CAES reservoir materials have been completed. Present activity consists of construction and operation of the aquifer field test, and associated numerical and experimental work in support of that activity. Work is presently planned to be complete by 1983 at the end of the field test. At that time the final stability criteria for aquifers will be issued. Attached here also are preliminary criteria for aquifers.

  11. TRPC channels in pheromone sensing.

    PubMed

    Kiselyov, Kirill; van Rossum, Damian B; Patterson, Randen L

    2010-01-01

    Pheromone recognition relies on an amplification cascade that is triggered by pheromone binding to G protein-coupled receptors (GPCR). The first step in translation of GPCR activation by pheromones in the vomeronasal organ and main olfactory epithelium (MOE) into a cellular response is the activation of a transient receptor potential (TRP) family member, TRPC2 [Zufall, F., Ukhanov, K., Lucas, P., Liman, E. R., and Leinders-Zufall, T. (2005). Neurobiology of TRPC2: From gene to behavior. Pflugers Arch.451, 61-71; Yildirim, E., and Birnbaumer, L. (2007). TRPC2: Molecular biology and functional importance. Handb. Exp. Pharmacol. 53-75]. The members of the canonical (TRPC) family of TRP channels mediate membrane permeability, specifically, Ca(2+) influx into the cytoplasm in response to activation of GPCR and tyrosine kinase receptors by hormones, neurotransmitters, and growth factors [Nilius, B. (2007). TRP channels in disease. Biochim. Biophys. Acta1772, 805-812; Venkatachalam, K., and Montell, C. (2007). TRP channels. Annu. Rev. Biochem.76, 387-417]. Mechanisms of their activation have been the focus of intense interest during the last decade. The data obtained from studies of TRPC2 have resulted in a better understanding of ion channel physiology and led to novel paradigms in modern cell biology [Lucas, P., Ukhanov, K., Leinders-Zufall, T., and Zufall, F. (2003). A diacylglycerol-gated cation channel in vomeronasal neuron dendrites is impaired in TRPC2 mutant mice: Mechanism of pheromone transduction. Neuron40, 551-561; Stowers, L., Holy, T. E., Meister, M., Dulac, C., and Koentges, G. (2002). Loss of sex discrimination and male-male aggression in mice deficient for TRP2. Science295, 1493-1500; Leypold, B. G., Yu, C. R., Leinders-Zufall, T., Kim, M. M., Zufall, F., and Axel, R. (2002). Altered sexual and social behaviors in trp2 mutant mice. Proc. Natl. Acad. Sci. USA99, 6376-6381]. Although TRPC2 activation by pheromones presents one of the most straightforward

  12. Electron channeling and EBIC studies of polycrystalline silicon sheets

    SciTech Connect

    Tsuo, Y S; Matson, R J

    1984-05-01

    Electron channeling and EBIC studies have been performed on silicon sheets grown by the edge-supported pulling (ESP) and low-angle silicon sheet (LASS) processes. We have found that the dominant grain structure of the ESP sheets is long, narrow grains with surface normals oriented near (011); grains with this structure tend to have better electronic quality than random grains. We have also studied the twin-stabilized planar growth material of LASS sheets. This material, grown at 200 cm/sup 2//min, is essentially single-crystal.

  13. Quantum channels and memory effects

    NASA Astrophysics Data System (ADS)

    Caruso, Filippo; Giovannetti, Vittorio; Lupo, Cosmo; Mancini, Stefano

    2014-10-01

    Any physical process can be represented as a quantum channel mapping an initial state to a final state. Hence it can be characterized from the point of view of communication theory, i.e., in terms of its ability to transfer information. Quantum information provides a theoretical framework and the proper mathematical tools to accomplish this. In this context the notion of codes and communication capacities have been introduced by generalizing them from the classical Shannon theory of information transmission and error correction. The underlying assumption of this approach is to consider the channel not as acting on a single system, but on sequences of systems, which, when properly initialized allow one to overcome the noisy effects induced by the physical process under consideration. While most of the work produced so far has been focused on the case in which a given channel transformation acts identically and independently on the various elements of the sequence (memoryless configuration in jargon), correlated error models appear to be a more realistic way to approach the problem. A slightly different, yet conceptually related, notion of correlated errors applies to a single quantum system which evolves continuously in time under the influence of an external disturbance which acts on it in a non-Markovian fashion. This leads to the study of memory effects in quantum channels: a fertile ground where interesting novel phenomena emerge at the intersection of quantum information theory and other branches of physics. A survey is taken of the field of quantum channels theory while also embracing these specific and complex settings.

  14. Monitoring the stability of the CMS electromagnetic calorimeter

    NASA Astrophysics Data System (ADS)

    Ferri, Federico

    2011-04-01

    The lead tungstate electromagnetic calorimeter of the CMS experiment has been proved to achieve an excellent energy resolution during the commissioning phase of the detector. The uniformity of the relative response of individual channels and the energy scale for electrons and photons are constrained by the several calibration procedures. The stability of the detector in time is constantly monitored throughout the LHC operation by means of dedicated runs and data taken at 100 Hz in the 3 μs abort gap at the end of each 89 μs beam cycle. A laser monitoring system is used to track the single channel response variations with time, as changes of the crystal transparency caused by irradiation. The stability of crucial detector parameters such as high voltage, temperature and electronic noise and the performance of the operation of the light monitoring system are shown to fulfill the requirements needed to achieve the target resolution of 0.5% at high energies.

  15. Antibody probe study of Ca2+ channel regulation by interdomain interaction within the ryanodine receptor.

    PubMed Central

    Kobayashi, Shigeki; Yamamoto, Takeshi; Parness, Jerome; Ikemoto, Noriaki

    2004-01-01

    N-terminal and central domains of ryanodine receptor 1 (RyR1), where many reported malignant hyperthermia (MH) mutations are localized, represent putative channel regulatory domains. Recent domain peptide (DP) probe studies led us to the hypothesis that these domains interact to stabilize the closed state of channel (zipping), while weakening of domain-domain interactions (unzipping) by mutation de-stabilizes the channel, making it leaky to Ca2+ or sensitive to the agonists of RyR1. As shown previously, DP1 (N-terminal domain peptide) and DP4 (central domain peptide) produced MH-like channel activation/sensitization effects, presumably by peptide binding to sites critical to stabilizing domain-domain interactions and resultant loss of conformational constraints. Here we report that polyclonal anti-DP1 and anti-DP4 antibodies also produce MH-like channel activation and sensitization effects as evidenced by about 4-fold enhancement of high affinity [3H]ryanodine binding to RyR1 and by a significant left-shift of the concentration-dependence of activation of sarcoplasmic reticulum Ca2+ release by polylysine. Fluorescence quenching experiments demonstrate that the accessibility of a DP4-directed, conformationally sensitive fluorescence probe linked to the RyR1 N-terminal domain is increased in the presence of domain-specific antibodies, consistent with the view that these antibodies produce unzipping of interacting domains that are of hindered accessibility to the surrounding aqueous environment. Our results suggest that domain-specific antibody binding induces a conformational change resulting in channel activation, and are consistent with the hypothesis that interacting N-terminal and central domains are intimately involved in the regulation of RyR1 channel function. PMID:15027895

  16. Stream Bank Stability in Eastern Nebraska

    USGS Publications Warehouse

    Soenksen, Phillip J.; Turner, Mary J.; Dietsch, Benjamin J.; Simon, Andrew

    2003-01-01

    Dredged and straightened channels in eastern Nebraska have experienced degradation leading to channel widening by bank failure. Degradation has progressed headward and affected the drainage systems upstream from the modified reaches. This report describes a study that was undertaken to analyze bank stability at selected sites in eastern Nebraska and develop a simplified method for estimating the stability of banks at future study sites. Bank cross sections along straight reaches of channel and geotechnical data were collected at approximately 150 sites in 26 counties of eastern Nebraska. The sites were categorized into three groups based on mapped soil permeability. With increasing permeability of the soil groups, the median cohesion values decreased and the median friction angles increased. Three analytical methods were used to determine if banks were stable (should not fail even when saturated), at risk (should not fail unless saturated), or unstable (should have already failed). The Culmann and Agricultural Research Service methods were based on the Coulomb equation and planar failure; an indirect method was developed that was based on Bishop's simplified method of slices and rotational failure. The maximum angle from horizontal at which the bank would be stable for the given soil and bank height conditions also was computed with the indirect method. Because of few soil shear-strength data, all analyses were based on the assumption of homogeneous banks, which was later shown to be atypical, at least for some banks. Using the Culmann method and assuming no soil tension cracks, 67 percent of all 908 bank sections were identified as stable, 32 percent were at risk, and 1 percent were unstable; when tension cracks were assumed, the results changed to 58 percent stable, 40 percent at risk, and 1 percent unstable. Using the Agricultural Research Service method, 67 percent of all bank sections were identified as stable and 33 percent were at risk. Using the indirect

  17. Targeting BK (big potassium) Channels in Epilepsy

    PubMed Central

    N'Gouemo, Prosper

    2011-01-01

    Introduction Epilepsies are disorders of neuronal excitability characterized by spontaneous and recurrent seizures. Ion channels are critical for regulating neuronal excitability and, therefore, can contribute significantly to epilepsy pathophysiology. In particular, large conductance, Ca2+-activated K+ (BKCa) channels play an important role in seizure etiology. These channels are activated by both membrane depolarization and increased intracellular Ca2+. This unique coupling of Ca2+ signaling to membrane depolarization is important in controlling neuronal hyperexcitability, as outward K+ current through BKCa channels hyperpolarizes neurons. Areas covered This review focuses on BKCa channel structure-function and discusses the role of these channels in epilepsy pathophysiology. Expert opinion Loss-of-function BKCa channels contribute neuronal hyperexcitability that can lead to temporal lobe epilepsy, tonic-clonic seizures and alcohol withdrawal seizures. Similarly, BKCa channel blockade can trigger seizures and status epilepticus. Paradoxically, some mutations in BKCa channel subunit can give rise to the channel gain-of-function that leads to development of idiopathic epilepsy (primarily absence epilepsy). Seizures themselves also enhance BKCa channel currents associated with neuronal hyperexcitability, and blocking BKCa channels suppresses generalized tonic-clonic seizures. Thus, both loss-of-function and gain-of-function BKCa channels might serve as molecular targets for drugs to suppress certain seizure phenotypes including temporal lobe seizures and absence seizures, respectively. PMID:21923633

  18. Analysis and evaluation of channel models: simulations of alamethicin.

    PubMed Central

    Tieleman, D Peter; Hess, Berk; Sansom, Mark S P

    2002-01-01

    Alamethicin is an antimicrobial peptide that forms stable channels with well-defined conductance levels. We have used extended molecular dynamics simulations of alamethicin bundles consisting of 4, 5, 6, 7, and 8 helices in a palmitoyl-oleolyl-phosphatidylcholine bilayer to evaluate and analyze channel models and to link the models to the experimentally measured conductance levels. Our results suggest that four helices do not form a stable water-filled channel and might not even form a stable intermediate. The lowest measurable conductance level is likely to correspond to the pentamer. At higher aggregation numbers the bundles become less symmetrical. Water properties inside the different-sized bundles are similar. The hexamer is the most stable model with a stability comparable with simulations based on crystal structures. The simulation was extended from 4 to 20 ns or several times the mean passage time of an ion. Essential dynamics analyses were used to test the hypothesis that correlated motions of the helical bundles account for high-frequency noise observed in open channel measurements. In a 20-ns simulation of a hexameric alamethicin bundle, the main motions are those of individual helices, not of the bundle as a whole. A detailed comparison of simulations using different methods to treat long-range electrostatic interactions (a twin range cutoff, Particle Mesh Ewald, and a twin range cutoff combined with a reaction field correction) shows that water orientation inside the alamethicin channels is sensitive to the algorithms used. In all cases, water ordering due to the protein structure is strong, although the exact profile changes somewhat. Adding an extra 4-nm layer of water only changes the water ordering slightly in the case of particle mesh Ewald, suggesting that periodicity artifacts for this system are not serious. PMID:12414676

  19. Stability of multiloop LQ regulators with nonlinearities. I - Regions of attraction. II - Regions of ultimate boundedness

    NASA Technical Reports Server (NTRS)

    Joshi, S. M.

    1986-01-01

    An investigation is conducted for the closed loop stability of linear time-invariant systems controlled by linear quadratic (LQ) regulators, in cases where nonlinearities exist in the control channels lying outside the stability sector in regions away from the origin. The estimate of the region of attraction thus obtained furnishes methods for the selection of performance function weights for more robust LQ designs. Attention is then given to the closed loop stability of linear time-invariant systems controlled by the LQ regulators when the nonlinearities in the loops escape the stability sector in a bounded region containing the origin.

  20. Analytical study of magnetohydrodynamic propulsion stability

    NASA Astrophysics Data System (ADS)

    Abdollahzadeh Jamalabadi, M. Y.

    2014-09-01

    In this paper an analytical solution for the stability of the fully developed flow drive in a magneto-hydro-dynamic pump with pulsating transverse Eletro-magnetic fields is presented. To do this, a theoretical model of the flow is developed and the analytical results are obtained for both the cylindrical and Cartesian configurations that are proper to use in the propulsion of marine vessels. The governing parabolic momentum PDEs are transformed into an ordinary differential equation using approximate velocity distribution. The numerical results are obtained and asymptotic analyses are built to discover the mathematical behavior of the solutions. The maximum velocity in a magneto-hydro-dynamic pump versus time for various values of the Stuart number, electro-magnetic interaction number, Reynolds number, aspect ratio, as well as the magnetic and electrical angular frequency and the shift of the phase angle is presented. Results show that for a high Stuart number there is a frequency limit for stability of the fluid flow in a certain direction of the flow. This stability frequency is dependent on the geometric parameters of a channel.