Muscle Co-activation: Definitions, Mechanisms, and Functions.

PubMed

Latash, Mark L

2018-03-28

The phenomenon of agonist-antagonist muscle co-activation is discussed with respect to its consequences for movement mechanics (such as increasing joint apparent stiffness, facilitating faster movements, and effects on action stability), implication for movement optimization, and involvement of different neurophysiological structures. Effects of co-activation on movement stability are ambiguous and depend on the effector representing a kinematic chain with a fixed origin or free origin. Further, co-activation is discussed within the framework of the equilibrium-point hypothesis and the idea of hierarchical control with spatial referent coordinates. Relations of muscle co-activation to changes in one of the basic commands, the c-command, are discussed and illustrated. A hypothesis is suggested that agonist-antagonist co-activation reflects a deliberate neural control strategy to preserve effector-level control and avoid making it degenerate and facing the necessity to control at the level of signals to individual muscles. This strategy, in particular, allows stabilizing motor actions by co-varied adjustments in spaces of control variables. This hypothesis is able to account for higher levels of co-activation in young healthy persons performing challenging tasks and across various populations with movement impairments.

A mirror control mechanism for space telescope

NASA Astrophysics Data System (ADS)

Cadiergues, L.; Bourdit, C.; Trouchet, D.; Larcher, V.; Sugranes, P.; Leletty, R.; Barillot, F.

2003-09-01

The high resolution optical instruments require more and more stability on the relative position between their different mirrors. The use of a mirror control mechanism (MCM) allows to correct in flight the position of the mirror (in particular the focusing and the 2 tilts). The mechanism described hereafter is designed for a Cassegrain telescope secondary mirror. The selected concept is based on 3 vertical actuators which produce the focusing and tilts movements, and three horizontal actuators which produce the transverse movements. This architecture offers 5 degrees of freedom which guarantee the absence of rejection for any kind of correction. After the design phase, a demonstrator was manufactured and characterised by functional and mechanical tests. This mechanism is able to control any type of axisymmetric mirror within 5 degrees of freedom. The mass of the model presented is 3.5kg with overall dimensions ø280mm/H77mm (except electronics). This concept can be adapted to smaller versions of mirror requiring an active control, and in a more general way to equipments for which the pointing precision is a key requirement.

Mechanical control of Renilla luciferase.

PubMed

Tseng, Chiao-Yu; Zocchi, Giovanni

2013-08-14

We report experiments where the activity of the enzyme luciferase from Renilla reniformis is controlled through a DNA spring attached to the enzyme. In the wake of previous work on kinases, these results establish that mechanical stress applied through the DNA springs is indeed a general method for the artificial control of enzymes, and for the quantitative study of mechano-chemical coupling in these molecules. We also show proof of concept of the luciferase construct as a sensitive molecular probe, detecting a specific DNA target sequence in an easy, one-step, homogeneous assay, as well as SNP detection without melting curve analysis.

Recombinant activated factor VII: its mechanism of action and role in the control of hemorrhage.

PubMed

Allen, Geoffrey A; Hoffman, Maureane; Roberts, Harold R; Monroe, Dougald M

2002-12-01

Recombinant activated factor VII (rFVIIa) has proven both safe and efficacious in the treatment of bleeding episodes in patients with hemophilia A or B who have developed inhibitors. More recently, a growing number of reports suggests that rFVIIa may also have indications for the treatment of bleeding in patients with other hemostatic disorders, including qualitative and quantitative platelet defects, factor deficiencies other than hemophilia, and in otherwise healthy patients with uncontrollable hemorrhage following surgery or trauma. We have attempted to reconcile the various proposed mechanisms of action of rFVIIa with its apparent efficacy in such diverse clinical settings. A review of the literature was performed to determine those clinical scenarios in which rFVIIa appears to have been effective in controlling associated hemorrhage. Findings from our group and others have demonstrated that rFVIIa is able to directly activate factor X and increase thrombin production on the surface of activated platelets in the absence of factor VIII or IX, as well as to improve thrombin generation in thrombocytopenia, and to yield a fibrin dot more resistant to fibrinolysis in vitro. Through these primary mechanisms, we believe that rFVIIa may be able to compensate for a variety of defects in hemostasis and merits further investigation as a general therapeutic for uncontrollable hemorrhage.

System and method of active vibration control for an electro-mechanically cooled device

DOEpatents

Lavietes, Anthony D.; Mauger, Joseph; Anderson, Eric H.

2000-01-01

A system and method of active vibration control of an electro-mechanically cooled device is disclosed. A cryogenic cooling system is located within an environment. The cooling system is characterized by a vibration transfer function, which requires vibration transfer function coefficients. A vibration controller generates the vibration transfer function coefficients in response to various triggering events. The environments may differ by mounting apparatus, by proximity to vibration generating devices, or by temperature. The triggering event may be powering on the cooling system, reaching an operating temperature, or a reset action. A counterbalance responds to a drive signal generated by the vibration controller, based on the vibration signal and the vibration transfer function, which adjusts vibrations. The method first places a cryogenic cooling system within a first environment and then generates a first set of vibration transfer function coefficients, for a vibration transfer function of the cooling system. Next, the cryogenic cooling system is placed within a second environment and a second set of vibration transfer function coefficients are generated. Then, a counterbalance is driven, based on the vibration transfer function, to reduce vibrations received by a vibration sensitive element.

Modeling and control of active twist aircraft

NASA Astrophysics Data System (ADS)

Cramer, Nicholas Bryan

The Wright Brothers marked the beginning of powered flight in 1903 using an active twist mechanism as their means of controlling roll. As time passed due to advances in other technologies that transformed aviation the active twist mechanism was no longer used. With the recent advances in material science and manufacturability, the possibility of the practical use of active twist technologies has emerged. In this dissertation, the advantages and disadvantages of active twist techniques are investigated through the development of an aeroelastic modeling method intended for informing the designs of such technologies and wind tunnel testing to confirm the capabilities of the active twist technologies and validate the model. Control principles for the enabling structural technologies are also proposed while the potential gains of dynamic, active twist are analyzed.

Macro-mechanics controls quantum mechanics: mechanically controllable quantum conductance switching of an electrochemically fabricated atomic-scale point contact.

PubMed

Staiger, Torben; Wertz, Florian; Xie, Fangqing; Heinze, Marcel; Schmieder, Philipp; Lutzweiler, Christian; Schimmel, Thomas

2018-01-12

Here, we present a silver atomic-scale device fabricated and operated by a combined technique of electrochemical control (EC) and mechanically controllable break junction (MCBJ). With this EC-MCBJ technique, we can perform mechanically controllable bistable quantum conductance switching of a silver quantum point contact (QPC) in an electrochemical environment at room temperature. Furthermore, the silver QPC of the device can be controlled both mechanically and electrochemically, and the operating mode can be changed from 'electrochemical' to 'mechanical', which expands the operating mode for controlling QPCs. These experimental results offer the perspective that a silver QPC may be used as a contact for a nanoelectromechanical relay.

Active Flow Control Activities at NASA Langley

NASA Technical Reports Server (NTRS)

Anders, Scott G.; Sellers, William L., III; Washburn, Anthony E.

2004-01-01

NASA Langley continues to aggressively investigate the potential advantages of active flow control over more traditional aerodynamic techniques. This paper provides an update to a previous paper and describes both the progress in the various research areas and the significant changes in the NASA research programs. The goals of the topics presented are focused on advancing the state of knowledge and understanding of controllable fundamental mechanisms in fluids as well as to address engineering challenges. An organizational view of current research activities at NASA Langley in active flow control as supported by several projects is presented. On-center research as well as NASA Langley funded contracts and grants are discussed at a relatively high level. The products of this research are to be demonstrated either in bench-top experiments, wind-tunnel investigations, or in flight as part of the fundamental NASA R&D program and then transferred to more applied research programs within NASA, DOD, and U.S. industry.

Reduction of Helicopter Blade-Vortex Interaction Noise by Active Rotor Control Technology

NASA Technical Reports Server (NTRS)

Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean

1997-01-01

Helicopter blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade vortex interaction noise reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations, Published by Elsevier Science Ltd.

Characterization of active hair-bundle motility by a mechanical-load clamp

NASA Astrophysics Data System (ADS)

Salvi, Joshua D.; Maoiléidigh, Dáibhid Ó.; Fabella, Brian A.; Tobin, Mélanie; Hudspeth, A. J.

2015-12-01

Active hair-bundle motility endows hair cells with several traits that augment auditory stimuli. The activity of a hair bundle might be controlled by adjusting its mechanical properties. Indeed, the mechanical properties of bundles vary between different organisms and along the tonotopic axis of a single auditory organ. Motivated by these biological differences and a dynamical model of hair-bundle motility, we explore how adjusting the mass, drag, stiffness, and offset force applied to a bundle control its dynamics and response to external perturbations. Utilizing a mechanical-load clamp, we systematically mapped the two-dimensional state diagram of a hair bundle. The clamp system used a real-time processor to tightly control each of the virtual mechanical elements. Increasing the stiffness of a hair bundle advances its operating point from a spontaneously oscillating regime into a quiescent regime. As predicted by a dynamical model of hair-bundle mechanics, this boundary constitutes a Hopf bifurcation.

Optimal integral force feedback for active vibration control

NASA Astrophysics Data System (ADS)

Teo, Yik R.; Fleming, Andrew J.

2015-11-01

This paper proposes an improvement to Integral Force Feedback (IFF), which is a popular method for active vibration control of structures and mechanical systems. Benefits of IFF include robustness, guaranteed stability and simplicity. However, the maximum damping performance is dependent on the stiffness of the system; hence, some systems cannot be adequately controlled. In this paper, an improvement to the classical force feedback control scheme is proposed. The improved method achieves arbitrary damping for any mechanical system by introducing a feed-through term. The proposed improvement is experimentally demonstrated by actively damping an objective lens assembly for a high-speed confocal microscope.

A glycosyltransferase with a length-controlling activity as a mechanism to regulate the size of polysaccharides

PubMed Central

Ciocchini, Andrés E.; Guidolin, L. Soledad; Casabuono, Adriana C.; Couto, Alicia S.; Iñón de Iannino, Nora; Ugalde, Rodolfo A.

2007-01-01

Cyclic β-1,2-glucans (CβG) are osmolyte homopolysaccharides with a cyclic β-1,2-backbone of 17–25 glucose residues present in the periplasmic space of several bacteria. Initiation, elongation, and cyclization, the three distinctive reactions required for building the cyclic structure, are catalyzed by the same protein, the CβG synthase. The initiation activity catalyzes the transference of the first glucose from UDP-glucose to a yet-unidentified amino acid residue in the same protein. Elongation proceeds by the successive addition of glucose residues from UDP-glucose to the nonreducing end of the protein-linked β-1,2-oligosaccharide intermediate. Finally, the protein-linked intermediate is cyclized, and the cyclic glucan is released from the protein. These reactions do not explain, however, the mechanism by which the number of glucose residues in the cyclic structure is controlled. We now report that control of the degree of polymerization (DP) is carried out by a β-1,2-glucan phosphorylase present at the CβG synthase C-terminal domain. This last activity catalyzes the phosphorolysis of the β-1,2-glucosidic bond at the nonreducing end of the linear protein-linked intermediate, releasing glucose 1-phosphate. The DP is thus regulated by this “length-controlling” phosphorylase activity. To our knowledge, this is the first description of a control of the DP of homopolysaccharides. PMID:17921247

Macro-mechanics controls quantum mechanics: mechanically controllable quantum conductance switching of an electrochemically fabricated atomic-scale point contact

NASA Astrophysics Data System (ADS)

Staiger, Torben; Wertz, Florian; Xie, Fangqing; Heinze, Marcel; Schmieder, Philipp; Lutzweiler, Christian; Schimmel, Thomas

2018-01-01

Here, we present a silver atomic-scale device fabricated and operated by a combined technique of electrochemical control (EC) and mechanically controllable break junction (MCBJ). With this EC-MCBJ technique, we can perform mechanically controllable bistable quantum conductance switching of a silver quantum point contact (QPC) in an electrochemical environment at room temperature. Furthermore, the silver QPC of the device can be controlled both mechanically and electrochemically, and the operating mode can be changed from ‘electrochemical’ to ‘mechanical’, which expands the operating mode for controlling QPCs. These experimental results offer the perspective that a silver QPC may be used as a contact for a nanoelectromechanical relay.

Regulatory T cells control HIV replication in activated T cells through a cAMP-dependent mechanism

PubMed Central

Moreno-Fernandez, Maria E.; Rueda, Cesar Mauricio; Rusie, Laura K.

2011-01-01

We hypothesized that regulatory T cells (Tregs) could play a beneficial role during HIV infection by controlling HIV replication in conventional T cells (Tcons). Purified Tregs and Tcons from healthy donors were activated separately. Tcons were infected with the X4 or R5 HIV strains and cultured with or without autologous Tregs. Coculture of Tcons and Tregs resulted in a dose-dependent inhibition of Tcon infection, which was significant when a 1:1 Treg:Tcon ratio was used. Treg suppression of HIV infection was largely mediated by contact-dependent mechanisms. Blockage of cytotoxic T-lymphocyte–associated antigen-4 did not significantly reduce Treg function. In contrast, Tregs acted through cAMP-dependent mechanisms, because the decrease of cAMP levels in Tregs, the blockade of gap junction formation between Tregs and Tcons, the blockage of CD39 activity, and the blockage of protein kinase A in Tcons all abolished Treg-mediated suppression of HIV replication. Our data suggest a complex role for Tregs during HIV infection. Although Tregs inhibit specific immune responses, their inhibition of HIV replication in Tcons may play a beneficial role, particularly during early HIV infection, when the effector immune cells are not yet activated. Such a protective role of Tregs could have a profound impact on infection outcome. PMID:21436067

Investigation of air gasification of micronized coal, mechanically activated using the plasma control of the process

NASA Astrophysics Data System (ADS)

Butakov, Evgenii; Burdukov, Anatoly; Chernetskiy, Mikhail; Kuznetsov, Victor

2017-10-01

Combination of the processes of coal combustion and gasification into a single technology of mechano-chemical and plasma-chemical activation is of a considerable scientific and technological interest. Enhancement of coal reactivity at their grinding with mechanical activation is associated with an increase in the reaction rate of carbon material, and at plasma-chemical effect, the main is an increase in reactivity of the oxidizing agent caused by the high plasma temperatures of atomic oxygen. The process of gasification was studied on the 1-MW setup with tangential scroll supply of pulverized coal-air mixture and cylindrical reaction chamber. Coal ground by the standard boiler mill is fed to the disintegrator, then, it is sent to the scroll inlet of the burner-reactor with the transport air. Pulverized coal is ignited by the plasmatron of 10-kW power. In experiments on air gasification of micronized coal, carried out at the temperature in the reaction chamber of 1000-1200°C and air excess α = 0.3-1, the data on CO concentration of 11% and H2 concentration of up to 6% were obtained. Air and air-steam gasification of mechanically-activated micronized coals with plasma control was calculated using SigmaFlow software package.

Activating catalysts with mechanical force.

PubMed

Piermattei, Alessio; Karthikeyan, S; Sijbesma, Rint P

2009-05-01

Homogeneously catalysed reactions can be 'switched on' by activating latent catalysts. Usually, activation is brought about by heat or an external chemical agent. However, activation of homogeneous catalysts with a mechanical trigger has not been demonstrated. Here, we introduce a general method to activate latent catalysts by mechanically breaking bonds between a metal and one of its ligands. We have found that silver(I) complexes of polymer-functionalized N-heterocyclic carbenes, which are latent organocatalysts, catalyse a transesterification reaction when exposed to ultrasound in solution. Furthermore, ultrasonic activation of a ruthenium biscarbene complex with appended polymer chains results in catalysis of olefin metathesis reactions. In each case, the catalytic activity results from ligand dissociation, brought about by transfer of mechanical forces from the polymeric substituents to the coordination bond. Mechanochemical catalyst activation has potential applications in transduction and amplification of mechanical signals, and mechanically initiated polymerizations hold promise as a novel repair mechanism in self-healing materials.

Potential Mechanisms of Cancer Prevention by Weight Control

NASA Astrophysics Data System (ADS)

Jiang, Yu; Wang, Weiqun

Weight control via dietary caloric restriction and/or physical activity has been demonstrated in animal models for cancer prevention. However, the underlying mechanisms are not fully understood. Body weight loss due to negative energy balance significantly reduces some metabolic growth factors and endocrinal hormones such as IGF-1, leptin, and adiponectin, but enhances glucocorticoids, that may be associated with anti-cancer mechanisms. In this review, we summarized the recent studies related to weight control and growth factors. The potential molecular targets focused on those growth factors- and hormones-dependent cellular signaling pathways are further discussed. It appears that multiple factors and multiple signaling cascades, especially for Ras-MAPK-proliferation and PI3K-Akt-anti-apoptosis, could be involved in response to weight change by dietary calorie restriction and/or exercise training. Considering prevalence of obesity or overweight that becomes apparent over the world, understanding the underlying mechanisms among weight control, endocrine change and cancer risk is critically important. Future studies using "-omics" technologies will be warrant for a broader and deeper mechanistic information regarding cancer prevention by weight control.

REACTOR CONTROL MECHANISM

DOEpatents

Lane, J.A.; Engberg, R.E.; Welch, J.M.

1959-05-12

A quick-releasing mechanism is described which may be used to rapidiy drop a device supported from beneath during normal use, such as a safety rod in a nuclear reactor. In accordance with this invention an electrical control signal, such as may be provided by radiation detection or other alarm condition sensing devices, is delivered to an electromagnetic solenoid, the armature of which is coupled to an actuating mechanism. The solenoid is energized when the mechanism is in its upper or cocked position. In such position, the mechanism engages a plurality of retaining balls, forcing them outward into engagement with a shoulder or recess in a corresponding section of a tubular extension on the upheld device. When the control signal to the solenoid suddenly ceases, the armature drops out, allowing the actuating mechanism to move slightly but rapidly under the force of a compressed spring. The weight of the device will urge the balls inward against a beveled portion of the actuating mechanism and away from the engaging section on the tubular extension, thus allowing the upheld device to fall freely under the influence of gravity.

Glycolytic control of vacuolar-type ATPase activity: A mechanism to regulate influenza viral infection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohio, Hinissan P.; Adamson, Amy L., E-mail: aladamso@uncg.edu

As new influenza virus strains emerge, finding new mechanisms to control infection is imperative. In this study, we found that we could control influenza infection of mammalian cells by altering the level of glucose given to cells. Higher glucose concentrations induced a dose-specific increase in influenza infection. Linking influenza virus infection with glycolysis, we found that viral replication was significantly reduced after cells were treated with glycolytic inhibitors. Addition of extracellular ATP after glycolytic inhibition restored influenza infection. We also determined that higher levels of glucose promoted the assembly of the vacuolar-type ATPase within cells, and increased vacuolar-type ATPase proton-transportmore » activity. The increase of viral infection via high glucose levels could be reversed by inhibition of the proton pump, linking glucose metabolism, vacuolar-type ATPase activity, and influenza viral infection. Taken together, we propose that altering glucose metabolism may be a potential new approach to inhibit influenza viral infection. - Highlights: • Increased glucose levels increase Influenza A viral infection of MDCK cells. • Inhibition of the glycolytic enzyme hexokinase inhibited Influenza A viral infection. • Inhibition of hexokinase induced disassembly the V-ATPase. • Disassembly of the V-ATPase and Influenza A infection was bypassed with ATP. • The state of V-ATPase assembly correlated with Influenza A infection of cells.« less

Mechanics of human voice production and control

PubMed Central

Zhang, Zhaoyan

2016-01-01

As the primary means of communication, voice plays an important role in daily life. Voice also conveys personal information such as social status, personal traits, and the emotional state of the speaker. Mechanically, voice production involves complex fluid-structure interaction within the glottis and its control by laryngeal muscle activation. An important goal of voice research is to establish a causal theory linking voice physiology and biomechanics to how speakers use and control voice to communicate meaning and personal information. Establishing such a causal theory has important implications for clinical voice management, voice training, and many speech technology applications. This paper provides a review of voice physiology and biomechanics, the physics of vocal fold vibration and sound production, and laryngeal muscular control of the fundamental frequency of voice, vocal intensity, and voice quality. Current efforts to develop mechanical and computational models of voice production are also critically reviewed. Finally, issues and future challenges in developing a causal theory of voice production and perception are discussed. PMID:27794319

Mechanics of human voice production and control.

PubMed

Zhang, Zhaoyan

2016-10-01

As the primary means of communication, voice plays an important role in daily life. Voice also conveys personal information such as social status, personal traits, and the emotional state of the speaker. Mechanically, voice production involves complex fluid-structure interaction within the glottis and its control by laryngeal muscle activation. An important goal of voice research is to establish a causal theory linking voice physiology and biomechanics to how speakers use and control voice to communicate meaning and personal information. Establishing such a causal theory has important implications for clinical voice management, voice training, and many speech technology applications. This paper provides a review of voice physiology and biomechanics, the physics of vocal fold vibration and sound production, and laryngeal muscular control of the fundamental frequency of voice, vocal intensity, and voice quality. Current efforts to develop mechanical and computational models of voice production are also critically reviewed. Finally, issues and future challenges in developing a causal theory of voice production and perception are discussed.

Wnt signalling controls the response to mechanical loading during zebrafish joint development

PubMed Central

Brunt, Lucy H.; Begg, Katie; Kague, Erika; Cross, Stephen

2017-01-01

Joint morphogenesis requires mechanical activity during development. Loss of mechanical strain causes abnormal joint development, which can impact long-term joint health. Although cell orientation and proliferation are known to shape the joint, dynamic imaging of developing joints in vivo has not been possible in other species. Using genetic labelling techniques in zebrafish we were able, for the first time, to dynamically track cell behaviours in intact moving joints. We identify that proliferation and migration, which contribute to joint morphogenesis, are mechanically controlled and are significantly reduced in immobilised larvae. By comparison with strain maps of the developing skeleton, we identify canonical Wnt signalling as a candidate for transducing mechanical forces into joint cell behaviours. We show that, in the jaw, Wnt signalling is reduced specifically in regions of high strain in response to loss of muscle activity. By pharmacological manipulation of canonical Wnt signalling, we demonstrate that Wnt acts downstream of mechanical activity and is required for joint patterning and chondrocyte maturation. Wnt16, which is also downstream of muscle activity, controls proliferation and migration, but plays no role in chondrocyte intercalation. PMID:28684625

Adaptive mechanism-based congestion control for networked systems

NASA Astrophysics Data System (ADS)

Liu, Zhi; Zhang, Yun; Chen, C. L. Philip

2013-03-01

In order to assure the communication quality in network systems with heavy traffic and limited bandwidth, a new ATRED (adaptive thresholds random early detection) congestion control algorithm is proposed for the congestion avoidance and resource management of network systems. Different to the traditional AQM (active queue management) algorithms, the control parameters of ATRED are not configured statically, but dynamically adjusted by the adaptive mechanism. By integrating with the adaptive strategy, ATRED alleviates the tuning difficulty of RED (random early detection) and shows a better control on the queue management, and achieve a more robust performance than RED under varying network conditions. Furthermore, a dynamic transmission control protocol-AQM control system using ATRED controller is introduced for the systematic analysis. It is proved that the stability of the network system can be guaranteed when the adaptive mechanism is finely designed. Simulation studies show the proposed ATRED algorithm achieves a good performance in varying network environments, which is superior to the RED and Gentle-RED algorithm, and providing more reliable service under varying network conditions.

Mechanically activated artificial cell by using microfluidics

NASA Astrophysics Data System (ADS)

Ho, Kenneth K. Y.; Lee, Lap Man; Liu, Allen P.

2016-09-01

All living organisms sense mechanical forces. Engineering mechanosensitive artificial cell through bottom-up in vitro reconstitution offers a way to understand how mixtures of macromolecules assemble and organize into a complex system that responds to forces. We use stable double emulsion droplets (aqueous/oil/aqueous) to prototype mechanosensitive artificial cells. In order to demonstrate mechanosensation in artificial cells, we develop a novel microfluidic device that is capable of trapping double emulsions into designated chambers, followed by compression and aspiration in a parallel manner. The microfluidic device is fabricated using multilayer soft lithography technology, and consists of a control layer and a deformable flow channel. Deflections of the PDMS membrane above the main microfluidic flow channels and trapping chamber array are independently regulated pneumatically by two sets of integrated microfluidic valves. We successfully compress and aspirate the double emulsions, which result in transient increase and permanent decrease in oil thickness, respectively. Finally, we demonstrate the influx of calcium ions as a response of our mechanically activated artificial cell through thinning of oil. The development of a microfluidic device to mechanically activate artificial cells creates new opportunities in force-activated synthetic biology.

Active control of bearing preload using piezoelectric translators

NASA Technical Reports Server (NTRS)

Nye, Ted W.

1990-01-01

In many spacecraft applications, mechanisms are required to perform precision pointing operations or to sometimes dither about or track a moving object. These mechanisms perform in a predictable and repeatable manner in benign temperature environments. Severe thermal gradients experienced in actual space applications however, cause assemblies to expand and contract around their bearings. This results in unpredictable changes in bearing preload, and hence bearing friction. This becomes a limitation for servos controlling pointing accuracy. Likewise, uncontrollable vibrations may couple into fixed preload (hence, fixed stiffness) mechanisms and limit pointing accuracy. Consequently, a complex problem faced today is how to design mechanisms that remain insensitive to changing thermal and vibrational spacecraft environments. Research presented involves the simplified modeling and test results of an actuator module that used piezoelectrically preload controlled bearings. The feasibility of actively controlling bearing preload was demonstrated. Because bearing friction is related to preload, a thermally active system designed with aluminum components and a 440 C bearing, was friction tested at temperatures ranging from 0 to 70 C (32 to 158 F). Effectiveness of the translators were demonstrated by mapping a controllable friction range throughout tested temperatures. It was learned that constant preload for this system could be maintained over an approximate 44 C (79 F) temperature span. From testing, it was also discovered that at the more deviate temperatures, expansions were so large that radial clearances were taken up and the duplex bearing became radially preloaded. Thus, active control of bearing preload is feasible but may be limited by inherent geometry constraints and materials used in the system.

Active cell mechanics: Measurement and theory.

PubMed

Ahmed, Wylie W; Fodor, Étienne; Betz, Timo

2015-11-01

Living cells are active mechanical systems that are able to generate forces. Their structure and shape are primarily determined by biopolymer filaments and molecular motors that form the cytoskeleton. Active force generation requires constant consumption of energy to maintain the nonequilibrium activity to drive organization and transport processes necessary for their function. To understand this activity it is necessary to develop new approaches to probe the underlying physical processes. Active cell mechanics incorporates active molecular-scale force generation into the traditional framework of mechanics of materials. This review highlights recent experimental and theoretical developments towards understanding active cell mechanics. We focus primarily on intracellular mechanical measurements and theoretical advances utilizing the Langevin framework. These developing approaches allow a quantitative understanding of nonequilibrium mechanical activity in living cells. This article is part of a Special Issue entitled: Mechanobiology. Copyright © 2015. Published by Elsevier B.V.

Design and control of active vision based mechanisms for intelligent robots

NASA Technical Reports Server (NTRS)

Wu, Liwei; Marefat, Michael M.

1994-01-01

In this paper, we propose a design of an active vision system for intelligent robot application purposes. The system has the degrees of freedom of pan, tilt, vergence, camera height adjustment, and baseline adjustment with a hierarchical control system structure. Based on this vision system, we discuss two problems involved in the binocular gaze stabilization process: fixation point selection and vergence disparity extraction. A hierarchical approach to determining point of fixation from potential gaze targets using evaluation function representing human visual behavior to outside stimuli is suggested. We also characterize different visual tasks in two cameras for vergence control purposes, and a phase-based method based on binarized images to extract vergence disparity for vergence control is presented. A control algorithm for vergence control is discussed.

Efficacy and possible mechanisms of perillaldehyde in control of Aspergillus niger causing grape decay.

PubMed

Tian, Jun; Wang, Yanzhen; Zeng, Hong; Li, Zongyun; Zhang, Peng; Tessema, Akalate; Peng, Xue

2015-06-02

A variety of plant products have been recognized for their antifungal activity and recently have attracted food industry attention for their efficacy in controlling postharvest fungal decay of fruits. The antifungal activity of perillaldehyde (PAE) was evaluated against Aspergillus niger, a known cause of grape spoilage, and possible mechanisms were explored. PAE showed notable antifungal activity against A. niger, with a minimum inhibitory concentration (MIC) and a minimum fungicidal concentration (MFC) of 0.25 and 1 μl/ml, respectively. The accumulation of mycelial biomass was also inhibited by PAE in a dose-dependent manner, completely inhibiting mycelial growth at 1 μl/ml. In vivo data confirmed that the vapour treatment of grapes with various concentrations of PAE markedly improved control of A. niger and suppressed natural decay. Concentrations of PAE of 0.075 μl/ml air showed the greatest inhibition of fungal growth compared to the controls. Further experiments indicated that PAE activated a membrane-active mechanism that inhibits ergosterol synthesis, increases membrane permeability (as evidenced by extracellular pH and conductivity measurements), and disrupts membrane integrity, leading to cell death. Our findings suggest that this membrane-active mechanism makes PAE a promising potential antifungal agent for postharvest control of grape spoilage. Copyright © 2015 Elsevier B.V. All rights reserved.

Autoregulatory mechanisms controlling the Microprocessor.

PubMed

Triboulet, Robinson; Gregory, Richard I

2010-01-01

The Microprocessor, comprising the ribonuclease Drosha and its essential cofactor, the double-stranded RNA-binding protein, DGCR8, is essential for the first step of the miRNA biogenesis pathway. It specifically cleaves double-stranded RNA within stem-loop structures of primary miRNA transcripts (pri-miRNAs) to generate precursor (pre-miRNA) intermediates. Pre-miRNAs are subsequently processed by Dicer to their mature 22 nt form. Thus, Microprocessor is essential for miRNA maturation, and pri-miRNA cleavage by this complex defines one end of the mature miRNA. Moreover, it is emerging that dysregulation of the Microprocessor is associated with various human diseases. It is therefore important to understand the mechanisms by which the expression of the subunits of the Microprocessor is regulated. Recent findings have uncovered a post-transcriptional mechanism that maintains the integrity of the Microprocessor. These studies revealed that the Microprocessor is involved in the processing of the messenger RNA (mRNA) that encodes DGCR8. This regulatory feedback loop, along with the reported role played by DGCR8 in the stabilization of Drosha protein, is part ofa newly identified regulatory mechanism controlling Microprocessor activity.

Autoregulatory mechanisms controlling the microprocessor.

PubMed

Triboulet, Robinson; Gregory, Richard I

2011-01-01

The Microprocessor, comprising the ribonuclease Drosha and its essential cofactor, the double-stranded RNA-binding protein, DGCR8, is essential for the first step of the miRNA biogenesis pathway. It specifically cleaves double-stranded RNA within stem-loop structures of primary miRNA transcripts (pri-miRNAs) to generate precursor (pre-miRNA) intermediates. Pre-miRNAs are subsequently processed by Dicer to their mature ∼22 nt form. Thus, Microprocessor is essential for miRNA maturation, and pri-miRNA cleavage by this complex defines one end of the mature miRNA. Moreover, it is emerging that dysregulation of the Microprocessor is associated with various human diseases. It is therefore important to understand the mechanisms by which the expression of the subunits of the Microprocessor is regulated. Recent findings have uncovered a post-transcriptional mechanism that maintains the integrity of the Microprocessor. These studies revealed that the Microprocessor is involved in the processing of the messenger RNA (mRNA) that encodes DGCR8. This regulatory feedback loop, along with the reported role played by DGCR8 in the stabilization of Drosha protein, is part of a newly identified regulatory mechanism controlling Microprocessor activity.

14 CFR 27.691 - Autorotation control mechanism.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Design and Construction Control Systems § 27.691 Autorotation control mechanism. Each main rotor blade pitch control mechanism must allow rapid... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Autorotation control mechanism. 27.691...

14 CFR 29.691 - Autorotation control mechanism.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Design and Construction Control Systems § 29.691 Autorotation control mechanism. Each main rotor blade pitch control mechanism must allow rapid... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Autorotation control mechanism. 29.691...

Active porous transition towards spatiotemporal control of molecular flow in a crystal membrane

NASA Astrophysics Data System (ADS)

Takasaki, Yuichi; Takamizawa, Satoshi

2015-11-01

Fluidic control is an essential technology widely found in processes such as flood control in land irrigation and cell metabolism in biological tissues. In any fluidic control system, valve function is the key mechanism used to actively regulate flow and miniaturization of fluidic regulation with precise workability will be particularly vital in the development of microfluidic control. The concept of crystal engineering is alternative to processing technology in microstructure construction, as the ultimate microfluidic devices must provide molecular level control. Consequently, microporous crystals can instantly be converted to microfluidic devices if introduced in an active transformability of porous structure and geometry. Here we show that the introduction of a stress-induced martensitic transition mechanism converts a microporous molecular crystal into an active fluidic device with spatiotemporal molecular flow controllability through mechanical reorientation of subnanometre channels.

Tethered satellite control mechanism

NASA Technical Reports Server (NTRS)

Kyrias, G. M.

1983-01-01

The tethered satellite control mechanisms consist of four major subsystems. The reel drive mechanism stores the tether. It is motor driven and includes a level wind to uniformly feed the tether to the reel. The lower boom mechanism serves two primary functions: (1) it measures tether length and velocity as the tether runs through the mechanism, and (2) it reads the tether tension at the reel. It also provides change the direction for the tether from the reel to the upper boom mechanism. The deployment boom positions the upper boom mechanism with satellite out of the cargo bay. The deployment function places the 500-kg satellite 20 m away from the Space Shuttle (producing a small natural gravity gradient force), impacts an initial velocity to the satellite for deployment, and allows for satellite docking at a safe distance from the body of the Space Shuttle. The upper boom mechanism (UBM) services three functions: (1) it provides tether control to the satellite as the satellite swings in and out of plane; (2) it reads tether tension in the low range during the early deployment and final retrieval parts of the mission; and (3) it produces additional tether tension at the reel when tether tension to the satellite is in the low range.

Rock mechanics. Superplastic nanofibrous slip zones control seismogenic fault friction.

PubMed

Verberne, Berend A; Plümper, Oliver; de Winter, D A Matthijs; Spiers, Christopher J

2014-12-12

Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis. Copyright © 2014, American Association for the Advancement of Science.

Snapshot of Active Flow Control Research at NASA Langley

NASA Technical Reports Server (NTRS)

Washburn, A. E.; Gorton, S. Althoff; Anders, S. G.

2002-01-01

NASA Langley is aggressively investigating the potential advantages of active flow control as opposed to more traditional aerodynamic techniques. Many of these techniques will be blended with advanced materials and structures to further enhance payoff. Therefore a multi-disciplinary approach to technology development is being attempted that includes researchers from the more historical disciplines of fluid mechanics. acoustics, material science, structural mechanics, and control theory. The overall goals of the topics presented are focused on advancing the state of knowledge and understanding of controllable fundamental mechanisms in fluids rather than on specific engineering problems. An organizational view of current research activities at NASA Langley in active flow control as supported by several programs such as the Morphing Project under Breakthrough Vehicle Technologies Program (BVT). the Ultra-Efficient Engine Technology Program (UEET), and the 21st Century Aircraft Technology Program (TCAT) is presented. On-center research as well as NASA Langley funded contracts and grants are discussed at a relatively high level. The products of this research, as part of the fundamental NASA R and D (research and development) program. will be demonstrated as either bench-top experiments, wind-tunnel investigations, or in flight tests. Later they will be transferred to more applied research programs within NASA, DOD (Department of Defense), and U.S. industry.

Mechanics of active surfaces

NASA Astrophysics Data System (ADS)

Salbreux, Guillaume; Jülicher, Frank

2017-09-01

We derive a fully covariant theory of the mechanics of active surfaces. This theory provides a framework for the study of active biological or chemical processes at surfaces, such as the cell cortex, the mechanics of epithelial tissues, or reconstituted active systems on surfaces. We introduce forces and torques acting on a surface, and derive the associated force balance conditions. We show that surfaces with in-plane rotational symmetry can have broken up-down, chiral, or planar-chiral symmetry. We discuss the rate of entropy production in the surface and write linear constitutive relations that satisfy the Onsager relations. We show that the bending modulus, the spontaneous curvature, and the surface tension of a passive surface are renormalized by active terms. Finally, we identify active terms which are not found in a passive theory and discuss examples of shape instabilities that are related to active processes in the surface.

Topographical differences of frontal-midline theta activity reflect functional differences in cognitive control abilities.

PubMed

Eschmann, Kathrin C J; Bader, Regine; Mecklinger, Axel

2018-06-01

Electrophysiological oscillations are assumed to be the core mechanism for large-scale network communication. The specific role of frontal-midline theta oscillations as cognitive control mechanism is under debate. According to the dual mechanisms of control framework, cognitive control processes can be divided into proactive and reactive control. The present study aimed at investigating the role of frontal-midline theta activity by assessing oscillations in two tasks varying in the type of cognitive control needed. More specifically, a delayed match to sample (DMTS) task requiring proactive control and a color Stroop task recruiting reactive control processes were conducted within the same group of participants. Moreover, both tasks contained conditions with low and high need for cognitive control. As expected larger frontal-midline theta activity was found in conditions with high need for cognitive control. However, theta activity was focally activated at frontal sites in the DMTS task whereas it had a broader topographical distribution in the Stroop task, indicating that both proactive and reactive control are reflected in frontal-midline theta activity but reactive control is additionally characterized by a broader theta activation. These findings support the conclusion that frontal-midline theta acts functionally different depending on task requirements. Copyright © 2018 Elsevier Inc. All rights reserved.

Active control of jet flowfields

NASA Astrophysics Data System (ADS)

Kibens, Valdis; Wlezien, Richard W.

1987-06-01

Passive and active control of jet shear layer development were investigated as mechanisms for modifying the global characteristics of jet flowfields. Slanted and stepped indeterminate origin (I.O.) nozzles were used as passive, geometry-based control devices which modified the flow origins. Active control techniques were also investigated, in which periodic acoustic excitation signals were injected into the I.O. nozzle shear layers. Flow visualization techniques based on a pulsed copper-vapor laser were used in a phase-conditioned image acquisition mode to assemble optically averaged sets of images acquired at known times throughout the repetition cycle of the basic flow oscillation period. Hot wire data were used to verify the effect of the control techniques on the mean and fluctuating flow properties. The flow visualization images were digitally enhanced and processed to show locations of prominent vorticity concentrations. Three-dimensional vortex interaction patterns were assembled in a format suitable for movie mode on a graphic display workstation, showing the evolution of three-dimensional vortex system in time.

The control of the controller: molecular mechanisms for robust perfect adaptation and temperature compensation.

PubMed

Ni, Xiao Yu; Drengstig, Tormod; Ruoff, Peter

2009-09-02

Organisms have the property to adapt to a changing environment and keep certain components within a cell regulated at the same level (homeostasis). "Perfect adaptation" describes an organism's response to an external stepwise perturbation by regulating some of its variables/components precisely to their original preperturbation values. Numerous examples of perfect adaptation/homeostasis have been found, as for example, in bacterial chemotaxis, photoreceptor responses, MAP kinase activities, or in metal-ion homeostasis. Two concepts have evolved to explain how perfect adaptation may be understood: In one approach (robust perfect adaptation), the adaptation is a network property, which is mostly, but not entirely, independent of rate constant values; in the other approach (nonrobust perfect adaptation), a fine-tuning of rate constant values is needed. Here we identify two classes of robust molecular homeostatic mechanisms, which compensate for environmental variations in a controlled variable's inflow or outflow fluxes, and allow for the presence of robust temperature compensation. These two classes of homeostatic mechanisms arise due to the fact that concentrations must have positive values. We show that the concept of integral control (or integral feedback), which leads to robust homeostasis, is associated with a control species that has to work under zero-order flux conditions and does not necessarily require the presence of a physico-chemical feedback structure. There are interesting links between the two identified classes of homeostatic mechanisms and molecular mechanisms found in mammalian iron and calcium homeostasis, indicating that homeostatic mechanisms may underlie similar molecular control structures.

Thermal Noise Reduction of Mechanical Oscillators by Actively Controlled External Dissipative Forces

NASA Technical Reports Server (NTRS)

Liang, Shoudan; Medich, David; Czajkowsky, Daniel M.; Sheng, Sitong; Yuan, Jian-Yang; Shao, Zhifeng

1999-01-01

We show that the thermal fluctuations of very soft mechanical oscillators, such as the cantilever in an atomic force microscope (AFM), can be reduced without changing the stiffness of the spring or having to lower the environment temperature. We derive a theoretical relationship between the thermal fluctuations of an oscillator and an actively external-dissipative force. This relationship is verified by experiments with an AFM cantilever where the external active force is coupled through a magnetic field. With simple instrumentation, we have reduced the thermal noise amplitude of the cantilever by a factor of 3.4, achieving an apparent temperature of 25 K with the environment at 295K. This active noise reduction approach can significantly improve the accuracy of static position or static force measurements in a number of practical applications.

Neural mechanisms of interference control in working memory: effects of interference expectancy and fluid intelligence.

PubMed

Burgess, Gregory C; Braver, Todd S

2010-09-20

A critical aspect of executive control is the ability to limit the adverse effects of interference. Previous studies have shown activation of left ventrolateral prefrontal cortex after the onset of interference, suggesting that interference may be resolved in a reactive manner. However, we suggest that interference control may also operate in a proactive manner to prevent effects of interference. The current study investigated the temporal dynamics of interference control by varying two factors - interference expectancy and fluid intelligence (gF) - that could influence whether interference control operates proactively versus reactively. A modified version of the recent negatives task was utilized. Interference expectancy was manipulated across task blocks by changing the proportion of recent negative (interference) trials versus recent positive (facilitation) trials. Furthermore, we explored whether gF affected the tendency to utilize specific interference control mechanisms. When interference expectancy was low, activity in lateral prefrontal cortex replicated prior results showing a reactive control pattern (i.e., interference-sensitivity during probe period). In contrast, when interference expectancy was high, bilateral prefrontal cortex activation was more indicative of proactive control mechanisms (interference-related effects prior to the probe period). Additional results suggested that the proactive control pattern was more evident in high gF individuals, whereas the reactive control pattern was more evident in low gF individuals. The results suggest the presence of two neural mechanisms of interference control, with the differential expression of these mechanisms modulated by both experimental (e.g., expectancy effects) and individual difference (e.g., gF) factors.

Mechanism(s) of action involved in the gastroprotective activity of Muntingia calabura.

PubMed

Zakaria, Zainul Amiruddin; Balan, Tavamani; Suppaiah, Velan; Ahmad, Syahida; Jamaludin, Fadzureena

2014-02-12

Muntingia calabura L. (Muntingiaceae) is locally known as kerukup siam. Its leaves, flowers, barks and roots have been used traditionally in East Asia and South America to treat various diseases including ulcer-related diseases. The present study aimed to investigate the mechanism(s) of gastroprotective effect of methanol extract of Muntingia calabura leaves (MEMC) using the pylorus ligation induced gastric ulceration in rats. Five groups of rats (n=6) were administered orally once daily for 7 days with 8% Tween 80 (negative control), 100 mg/kg ranitidine (positive control), or MEMC (100, 250 or 500 mg/kg), followed by the ulcer induction via ligation of the pyloric part of the rat's stomach. This was followed by the macroscopic analysis of the stomach, evaluation of gastric content parameters, and quantification of mucus content. The antioxidant (measured using the superoxide anion and 2,2-diphenyl-1-picrylhydrazyl (DPPH)-radical scavenging, oxygen radical absorbance capacity (ORAC) and total phenolic content (TPC) assays), anti-inflammatory (evaluated using the in vitro lipoxygenase and xanthine oxidase assays), phytoconstituents and HPLC analysis of MEMC were also carried out. The MEMC significantly (p<0.05) reduced gastric lesion in this model. Furthermore, the extract also significantly (p<0.01) reduced the volume of gastric content whereas the total acidity was significantly (p<0.05) reduced in the doses of 100 and 500 mg/kg MEMC. Moreover, the mucus content increased significantly (p<0.01) in MEMC-treated rats. The extract also showed high antioxidant and anti-inflammatory activities in all assays tested, and demonstrated the presence of high tannins and saponins followed by flavonoids. The MEMC exerted gastroprotective effect via several mechanisms including the anti-secretory, antioxidant and anti-inflammatory activities. These activities could be attributed to the presence of tannins, saponins and flavonoids (e.g. rutin, quercitrin, fisetin and

Neural Mechanisms of Interference Control Underlie the Relationship Between Fluid Intelligence and Working Memory Span

PubMed Central

Burgess, Gregory C.; Gray, Jeremy R.; Conway, Andrew R. A.; Braver, Todd S.

2014-01-01

Fluid intelligence (gF) and working memory (WM) span predict success in demanding cognitive situations. Recent studies show that much of the variance in gF and WM span is shared, suggesting common neural mechanisms. This study provides a direct investigation of the degree to which shared variance in gF and WM span can be explained by neural mechanisms of interference control. We measured performance and fMRI activity in 102 participants during the n-back WM task, focusing on the selective activation effects associated with high-interference lure trials. Brain activity on these trials was correlated with gF, WM span, and task performance in core brain regions linked to WM and executive control, including bilateral dorsolateral PFC (middle frontal gyrus, BA9) and parietal cortex (inferior parietal cortex; BA 40/7). Interference-related performance and interference-related activity accounted for a significant proportion of the shared variance in gF and WM span. Path analyses indicate that interference control activity may affect gF through a common set of processes that also influence WM span. These results suggest that individual differences in interference control mechanisms are important for understanding the relationship between gF and WM span. PMID:21787103

Edge Mechanisms for Power Excursion Control in Burning Plasmas

NASA Astrophysics Data System (ADS)

Hill, M. D.; Stacey, W. M.

2017-10-01

ITER must have active and preferably also passive control mechanisms that will limit inadvertent plasma power excursions which could trigger runaway fusion heating. We are identifying and investigating the potential of ion-orbit loss, impurity seeding, and various divertor ``choking'' phenomena to control or limit sudden increases in plasma density or temperature by reducing energy confinement, increasing radiation loss, etc., with the idea that such mechanisms could be tested on DIII-D and other existing tokamaks. We are assembling an edge-divertor code (GTEDGE-2) with a neutral transport model and a burn dynamics code, for this purpose. One potential control mechanism is the enhanced ion orbit loss from the thermalized ion distribution that would result from heating of the thermalized plasma ion distribution. Another possibility is impurity seeding with ions whose emissivity would increase sharply if the edge temperature increased. Enhanced radiative losses should also reduce the thermal energy flux across the separatrix, perhaps dropping the plasma into the poorer L-mode confinement regime. We will present some initial calculations to quantify these ideas. Work supported by US DOE under DE-FC02-04ER54698.

Control of mechanically activated polymersome fusion: Factors affecting fusion

DOE PAGES

Henderson, Ian M.; Paxton, Walter F.

2014-12-15

Previously we have studied the mechanically-activated fusion of extruded (200 nm) polymer vesicles into giant polymersomes using agitation in the presence of salt. In this study we have investigated several factors contributing to this phenomenon, including the effects of (i) polymer vesicle concentration, (ii) agitation speed and duration, and iii) variation of the salt and its concentration. It was found that increasing the concentration of the polymer dramatically increases the production of giant vesicles through the increased collisions of polymersomes. Our investigations also found that increasing the frequency of agitation increased the efficiency of fusion, though ultimately limited the sizemore » of vesicle which could be produced due to the high shear involved. Finally it was determined that salt-mediation of the fusion process was not limited to NaCl, but is instead a general effect facilitated by the presence of solvated ionic compounds, albeit with different salts initiating fusion at different concentration.« less

A locomotion mechanism with external magnetic guidance for active capsule endoscope.

PubMed

Wang, Xiaona; Meng, Max Q H; Chen, Xijun

2010-01-01

Gastrointestinal (GI) disorder is one of the most common diseases in human body. The swallowable wireless capsule endoscopy has been proved to be a convenient, painless and effective way to examine the whole GI tract. However, lack of motion control makes the movement of the capsule substantially random, resulting in missing diagnosis. In this paper, a locomotion mechanism is developed for the next-generation active capsule endoscope. An internal actuator integrated on-board the capsule is designed to provide driving force and improve the dexterity. A small permanent magnet enclosed inside the capsule interacts with an external magnetic field to control the capsule's orientation and offer extra driving force. This mechanism avoids sophisticated and bulky control system and reduces power consumption inside the capsule. Ex-vivo experimental results showed that it can make a controllable movement inside the porcine large intestine. The mechanism also has the potential to be a platform for further development, such as devices of operations, spraying medicine, biopsy etc.

New modeling method and mechanism analyses for active control of interior noise in an irregular enclosure using piezoelectric actuators.

PubMed

Geng, Hou C; Rao, Zhu S; Han, Zu S

2003-03-01

A new modeling method is developed in this paper for the active minimization of noise within a three-dimensional irregular enclosure using distributed lead zirconate titanate piezoelectric (PZT) actuators, and the control mechanisms for irregular enclosure are analyzed. The irregular enclosure is modeled with four rigid walls and two simply supported flexible panels, and PZT actuators are bound to one of the flexible panels. The process of the new modeling method is as follows. First, the modal coupling method is used to establish the motion equations, which contain important coefficients such as modal masses and modal coupling coefficients, etc., of acoustic-structural-piezoelectric coupling system. Then, the acoustic modes and the modal masses of irregular enclosure are calculated by numerical methods. Last, the modal coupling coefficients in motion equations are calculated according to the numerical results of the acoustic modes of irregular enclosure and the modes of two panels. The validity of this modeling method is verified by a regular hexahedron enclosure. Two cost functions are applied to this model. With the two cost functions, good results are obtained in minimizing the sound-pressure level (SPL) within irregular enclosure according to numerical investigations. By comparing the results obtained under controlled and uncontrolled states, the control mechanisms of the system are discussed. It is found that the control mechanisms vary with disturbance frequencies. At most disturbance frequencies, the SPL within enclosure is reduced by restructuring the modes of two panels simultaneously. When the disturbance frequency comes close to one of the natural frequencies of panel a, the dominant mode of panel a is suppressed, while the modes of panel b are reconstructed. While the disturbance frequency is near one of the natural frequencies of panel b, the modes of two panels are restructured at the same time.

Investigating the antifungal activity and mechanism(s) of geraniol against Candida albicans strains.

PubMed

Leite, Maria Clerya Alvino; de Brito Bezerra, André Parente; de Sousa, Janiere Pereira; de Oliveira Lima, Edeltrudes

2015-04-01

Candida albicans can be a yeast that is a commensal on the human body but can cause opportunistic or pathogenic infections. Candida infections may create serious health problems and as a result has initiated a search for new drugs with an antifungal action. Geraniol is an acyclic monoterpene alcohol with known pharmacological properties, including antimicrobial activity. The aim of this work was to evaluate the antifungal activity and mechanism(s) of geraniol against C. albicans strains. The minimum inhibitory concentration (MIC) was determined through broth microdilution techniques. We investigated possible geraniol activity on the fungal cell wall (sorbitol protect effect), cell membrane (geraniol to ergosterol binding), the time-kill curve, and its biological activity on the yeast's morphology. Amphotericin B was used as control, and all tests were performed in duplicate. The MIC of geraniol was 16 μg/ml (for 90% of isolates) but its probable mechanism of action did not involve the cell wall and ergosterol binding. In the morphological interference assay, we observed that the product inhibited pseudohyphae and chlamydoconidia formation. Time-dependent kill curve assay demonstrated that the fungicidal activity for MIC × 2 started at 2 h for the ATCC 76485 strain, and at 4 h for the LM-70 strain. Geraniol showed in vitro antifungal potential against strains of C. albicans but did not involve action on the cell wall or ergosterol. This study contributes to the development of new antifungal drugs, especially against Candida spp. © The Author 2014. Published by Oxford University Press on behalf of The International Society for Human and Animal Mycology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Coherent active polarization control without loss

NASA Astrophysics Data System (ADS)

Ye, Yuqian; Hay, Darrick; Shi, Zhimin

2017-11-01

We propose a lossless active polarization control mechanism utilizing an anisotropic dielectric medium with two coherent inputs. Using scattering matrix analysis, we derive analytically the required optical properties of the anisotropic medium that can behave as a switchable polarizing beam splitter. We also show that such a designed anisotropic medium can produce linearly polarized light at any azimuthal direction through coherent control of two inputs with a specific polarization state. Furthermore, we present a straightforward design-on-demand procedure of a subwavelength-thick metastructure that can possess the desired optical anisotropy at a flexible working wavelength. Our lossless coherent polarization control technique may lead to fast, broadband and integrated polarization control elements for applications in imaging, spectroscopy, and telecommunication.

Neuromuscular Control Mechanisms During Single-Leg Jump Landing in Subacute Ankle Sprain Patients: A Case Control Study.

PubMed

Allet, Lara; Zumstein, Franziska; Eichelberger, Patric; Armand, Stéphane; Punt, Ilona M

2017-03-01

Optimal neuromuscular control mechanisms are essential for preparing, maintaining, and restoring functional joint stability during jump landing and to prevent ankle injuries. In subacute ankle sprain patients, neither muscle activity nor kinematics during jump landing has previously been assessed. To compare neuromuscular control mechanisms and kinematics between subacute ankle sprain patients and healthy persons before and during the initial contact phase of a 25-cm single-leg jump. Case-control study. University hospital. Fifteen patients with grade I or II acute ankle sprains were followed up after 4 weeks of conservative management not involving physical therapy. Subjects performed alternately 3 single-leg forward jumps of 25 cm (toe-to-heel distance) barefoot. Their results were compared with the data of 15 healthy subjects. Electromyographic (EMG) activity of the musculus (m.) gastrocnemius lateralis, m. tibialis anterior, and m. peroneus longus as well as kinematics for ankle, knee, and hip joint were recorded for pre-initial contact (IC) phase, post-initial contact phase, and reflex-induced phase. The results showed that EMG activity of the 3 muscles did not differ between ankle sprain patients (n = 15) and healthy persons (n = 15) for any of the analyzed time intervals (all P > .05). However, during the pre-IC phase, ankle sprain patients presented less plantar flexion, as well as during the post-IC phase after jump landing, compared to healthy persons (P < .05). Taken together, these kinematic alterations of the ankle joint can lead to neuromuscular control mechanism disturbances through which functional instability might arise. III. Copyright © 2017 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.

Force feedback controls motor activity and mechanical properties of self-assembling branched actin networks

PubMed Central

Bieling, Peter; Li, Tai-De; Weichsel, Julian; McGorty, Ryan; Jreij, Pamela; Huang, Bo; Fletcher, Daniel A.; Mullins, R. Dyche

2016-01-01

Branched actin networks–created by the Arp2/3 complex, capping protein, and a nucleation promoting factor– generate and transmit forces required for many cellular processes, but their response to force is poorly understood. To address this, we assembled branched actin networks in vitro from purified components and used simultaneous fluorescence and atomic force microscopy to quantify their molecular composition and material properties under various forces. Remarkably, mechanical loading of these self-assembling materials increases their density, power, and efficiency. Microscopically, increased density reflects increased filament number and altered geometry, but no change in average length. Macroscopically, increased density enhances network stiffness and resistance to mechanical failure beyond those of isotropic actin networks. These effects endow branched actin networks with memory of their mechanical history that shapes their material properties and motor activity. This work reveals intrinsic force feedback mechanisms by which mechanical resistance makes self-assembling actin networks stiffer, stronger, and more powerful. PMID:26771487

Universal Controller for Spacecraft Mechanisms

NASA Technical Reports Server (NTRS)

Levanas, Greg; McCarthy, Thomas; Hunter, Don; Buchanan, Christine; Johnson, Michael; Cozy, Raymond; Morgan, Albert; Tran, Hung

2006-01-01

An electronic control unit has been fabricated and tested that can be replicated as a universal interface between the electronic infrastructure of a spacecraft and a brushless-motor (or other electromechanical actuator) driven mechanism that performs a specific mechanical function within the overall spacecraft system. The unit includes interfaces to a variety of spacecraft sensors, power outputs, and has selectable actuator control parameters making the assembly a mechanism controller. Several control topologies are selectable and reconfigurable at any time. This allows the same actuator to perform different functions during the mission life of the spacecraft. The unit includes complementary metal oxide/semiconductor electronic components on a circuit board of a type called rigid flex (signifying flexible printed wiring along with a rigid substrate). The rigid flex board is folded to make the unit fit into a housing on the back of a motor. The assembly has redundant critical interfaces, allowing the controller to perform time-critical operations when no human interface with the hardware is possible. The controller is designed to function over a wide temperature range without the need for thermal control, including withstanding significant thermal cycling, making it usable in nearly all environments that spacecraft or landers will endure. A prototype has withstood 1,500 thermal cycles between 120 and +85 C without significant deterioration of its packaging or electronic function. Because there is no need for thermal control and the unit is addressed through a serial bus interface, the cabling and other system hardware are substantially reduced in quantity and complexity, with corresponding reductions in overall spacecraft mass and cost.

Advanced electrodynamic mechanisms for the nanoscale control of light by light

NASA Astrophysics Data System (ADS)

Andrews, David L.; Leeder, Jamie M.; Bradshaw, David S.

2015-08-01

A wide range of mechanisms is available for achieving rapid optical responsivity in material components. Amongst them, some of the most promising for potential device applications are those associated with an ultrafast response and a short cycle time. These twin criteria for photoresponsive action substantially favor optical, over most other, forms of response such as those fundamentally associated with photothermal, photochemical or optomechanical processes. The engagement of nonlinear mechanisms to actively control the characteristics of optical materials is not new. Indeed, it has been known for over fifty years that polarization effects of this nature occur in the optical Kerr effect - although in fluid media the involvement of a molecular reorientation mechanism leads to a significant response time. It has more recently emerged that there are other, less familiar forms of optical nonlinearity that can provide a means for one beam of light to instantly influence another. In particular, major material properties such as absorptivity or emissivity can be subjected to instant and highly localized control by the transmission of light with an off-resonant wavelength. This presentation introduces and compares the key electrodynamic mechanisms, discussing the features that suggest the most attractive possibilities for exploitation. The most significant of such mechanistic features include the off-resonant activation of optical emission, the control of excited-state lifetimes, the access of dark states, the inhibition or re-direction of exciton migration, and a coupling of stimulated emission with coherent scattering. It is shown that these offer a variety of new possibilities for ultrafast optical switching and transistor action, ultimately providing all-optical control with nanoscale precision.

Development of safe mechanism for surgical robots using equilibrium point control method.

PubMed

Park, Shinsuk; Lim, Hokjin; Kim, Byeong-sang; Song, Jae-bok

2006-01-01

This paper introduces a novel mechanism for surgical robotic systems to generate human arm-like compliant motion. The mechanism is based on the idea of the equilibrium point control hypothesis which claims that multi-joint limb movements are achieved by shifting the limbs' equilibrium positions defined by neuromuscular activity. The equilibrium point control can be implemented on a robot manipulator by installing two actuators at each joint of the manipulator, one to control the joint position, and the other to control the joint stiffness. This double-actuator mechanism allows us to arbitrarily manipulate the stiffness (or impedance) of a robotic manipulator as well as its position. Also, the force at the end-effector can be estimated based on joint stiffness and joint angle changes without using force transducers. A two-link manipulator and a three-link manipulator with the double-actuator units have been developed, and experiments and simulation results show the potential of the proposed approach. By creating the human arm-like behavior, this mechanism can improve the performance of robot manipulators to execute stable and safe movement in surgical environments by using a simple control scheme.

The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects

PubMed Central

Dehkhoda, Farhad; Lee, Christine M. M.; Medina, Johan; Brooks, Andrew J.

2018-01-01

The growth hormone receptor (GHR), although most well known for regulating growth, has many other important biological functions including regulating metabolism and controlling physiological processes related to the hepatobiliary, cardiovascular, renal, gastrointestinal, and reproductive systems. In addition, growth hormone signaling is an important regulator of aging and plays a significant role in cancer development. Growth hormone activates the Janus kinase (JAK)–signal transducer and activator of transcription (STAT) signaling pathway, and recent studies have provided a new understanding of the mechanism of JAK2 activation by growth hormone binding to its receptor. JAK2 activation is required for growth hormone-mediated activation of STAT1, STAT3, and STAT5, and the negative regulation of JAK–STAT signaling comprises an important step in the control of this signaling pathway. The GHR also activates the Src family kinase signaling pathway independent of JAK2. This review covers the molecular mechanisms of GHR activation and signal transduction as well as the physiological consequences of growth hormone signaling. PMID:29487568

Overview of Active Flow Control at NASA Langley Research Center

NASA Technical Reports Server (NTRS)

Pack, L. G.; Joslin, R. D.

1998-01-01

The paper summarizes Active Flow Control projects currently underway at the NASA Langley Research Center. Technology development is being pursued within a multidisciplinary, cooperative approach, involving the classical disciplines of fluid mechanics, structural mechanics, material science, acoustics, and stability and control theory. Complementing the companion papers in this session, the present paper will focus on projects that have the goal of extending the state-of-the-art in the measurement, prediction, and control of unsteady, nonlinear aerodynamics. Toward this goal, innovative actuators, micro and macro sensors, and control strategies are considered for high payoff flow control applications. The target payoffs are outlined within each section below. Validation of the approaches range from bench-top experiments to wind-tunnel experiments to flight tests. Obtaining correlations for future actuator and sensor designs are implicit in the discussion. The products of the demonstration projects and design tool development from the fundamental NASA R&D level technology will then be transferred to the Applied Research components within NASA, DOD, and US Industry. Keywords: active flow control, separation control, MEMS, review

Potential fluid mechanic pathways of platelet activation.

PubMed

Shadden, Shawn C; Hendabadi, Sahar

2013-06-01

Platelet activation is a precursor for blood clotting, which plays leading roles in many vascular complications and causes of death. Platelets can be activated by chemical or mechanical stimuli. Mechanically, platelet activation has been shown to be a function of elevated shear stress and exposure time. These contributions can be combined by considering the cumulative stress or strain on a platelet as it is transported. Here, we develop a framework for computing a hemodynamic-based activation potential that is derived from a Lagrangian integral of strain rate magnitude. We demonstrate that such a measure is generally maximized along, and near to, distinguished material surfaces in the flow. The connections between activation potential and these structures are illustrated through stenotic flow computations. We uncover two distinct structures that may explain observed thrombus formation at the apex and downstream of stenoses. More broadly, these findings suggest fundamental relationships may exist between potential fluid mechanic pathways for mechanical platelet activation and the mechanisms governing their transport.

Potential fluid mechanic pathways of platelet activation

PubMed Central

Shadden, Shawn C.; Hendabadi, Sahar

2012-01-01

Platelet activation is a precursor for blood clotting, which plays leading roles in many vascular complications and causes of death. Platelets can be activated by chemical or mechanical stimuli. Mechanically, platelet activation has been shown to be a function of elevated shear stress and exposure time. These contributions can be combined by considering the cumulative stress or strain on a platelet as it is transported. Here we develop a framework for computing a hemodynamic-based activation potential that is derived from a Lagrangian integral of strain rate magnitude. We demonstrate that such a measure is generally maximized along, and near to, distinguished material surfaces in the flow. The connections between activation potential and these structures are illustrated through stenotic flow computations. We uncover two distinct structures that may explain observed thrombus formation at the apex and downstream of stenoses. More broadly, these findings suggest fundamental relationships may exist between potential fluid mechanic pathways for mechanical platelet activation and the mechanisms governing their transport. PMID:22782543

An active balance board system with real-time control of stiffness and time-delay to assess mechanisms of postural stability.

PubMed

Cruise, Denise R; Chagdes, James R; Liddy, Joshua J; Rietdyk, Shirley; Haddad, Jeffrey M; Zelaznik, Howard N; Raman, Arvind

2017-07-26

Increased time-delay in the neuromuscular system caused by neurological disorders, concussions, or advancing age is an important factor contributing to balance loss (Chagdes et al., 2013, 2016a,b). We present the design and fabrication of an active balance board system that allows for a systematic study of stiffness and time-delay induced instabilities in standing posture. Although current commercial balance boards allow for variable stiffness, they do not allow for manipulation of time-delay. Having two controllable parameters can more accurately determine the cause of balance deficiencies, and allows us to induce instabilities even in healthy populations. An inverted pendulum model of human posture on such an active balance board predicts that reduced board rotational stiffness destabilizes upright posture through board tipping, and limit cycle oscillations about the upright position emerge as feedback time-delay is increased. We validate these two mechanisms of instability on the designed balance board, showing that rotational stiffness and board time-delay induced the predicted postural instabilities in healthy, young adults. Although current commercial balance boards utilize control of rotational stiffness, real-time control of both stiffness and time-delay on an active balance board is a novel and innovative manipulation to reveal balance deficiencies and potentially improve individualized balance training by targeting multiple dimensions contributing to standing balance. Copyright © 2017 Elsevier Ltd. All rights reserved.

Closed-loop control of epileptiform activities in a neural population model using a proportional-derivative controller

NASA Astrophysics Data System (ADS)

Wang, Jun-Song; Wang, Mei-Li; Li, Xiao-Li; Ernst, Niebur

2015-03-01

Epilepsy is believed to be caused by a lack of balance between excitation and inhibitation in the brain. A promising strategy for the control of the disease is closed-loop brain stimulation. How to determine the stimulation control parameters for effective and safe treatment protocols remains, however, an unsolved question. To constrain the complex dynamics of the biological brain, we use a neural population model (NPM). We propose that a proportional-derivative (PD) type closed-loop control can successfully suppress epileptiform activities. First, we determine the stability of root loci, which reveals that the dynamical mechanism underlying epilepsy in the NPM is the loss of homeostatic control caused by the lack of balance between excitation and inhibition. Then, we design a PD type closed-loop controller to stabilize the unstable NPM such that the homeostatic equilibriums are maintained; we show that epileptiform activities are successfully suppressed. A graphical approach is employed to determine the stabilizing region of the PD controller in the parameter space, providing a theoretical guideline for the selection of the PD control parameters. Furthermore, we establish the relationship between the control parameters and the model parameters in the form of stabilizing regions to help understand the mechanism of suppressing epileptiform activities in the NPM. Simulations show that the PD-type closed-loop control strategy can effectively suppress epileptiform activities in the NPM. Project supported by the National Natural Science Foundation of China (Grant Nos. 61473208, 61025019, and 91132722), ONR MURI N000141010278, and NIH grant R01EY016281.

Geometric control of capillary architecture via cell-matrix mechanical interactions.

PubMed

Sun, Jian; Jamilpour, Nima; Wang, Fei-Yue; Wong, Pak Kin

2014-03-01

Capillary morphogenesis is a multistage, multicellular activity that plays a pivotal role in various developmental and pathological situations. In-depth understanding of the regulatory mechanism along with the capability of controlling the morphogenic process will have direct implications on tissue engineering and therapeutic angiogenesis. Extensive research has been devoted to elucidate the biochemical factors that regulate capillary morphogenesis. The roles of geometric confinement and cell-matrix mechanical interactions on the capillary architecture, nevertheless, remain largely unknown. Here, we show geometric control of endothelial network topology by creating physical confinements with microfabricated fences and wells. Decreasing the thickness of the matrix also results in comparable modulation of the network architecture, supporting the boundary effect is mediated mechanically. The regulatory role of cell-matrix mechanical interaction on the network topology is further supported by alternating the matrix stiffness by a cell-inert PEG-dextran hydrogel. Furthermore, reducing the cell traction force with a Rho-associated protein kinase inhibitor diminishes the boundary effect. Computational biomechanical analysis delineates the relationship between geometric confinement and cell-matrix mechanical interaction. Collectively, these results reveal a mechanoregulation scheme of endothelial cells to regulate the capillary network architecture via cell-matrix mechanical interactions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Control of cardiac alternans by mechanical and electrical feedback.

PubMed

Yapari, Felicia; Deshpande, Dipen; Belhamadia, Youssef; Dubljevic, Stevan

2014-07-01

A persistent alternation in the cardiac action potential duration has been linked to the onset of ventricular arrhythmia, which may lead to sudden cardiac death. A coupling between these cardiac alternans and the intracellular calcium dynamics has also been identified in previous studies. In this paper, the system of PDEs describing the small amplitude of alternans and the alternation of peak intracellular Ca(2+) are stabilized by optimal boundary and spatially distributed actuation. A simulation study demonstrating the successful annihilation of both alternans on a one-dimensional cable of cardiac cells by utilizing the full-state feedback controller is presented. Complimentary to these studies, a three variable Nash-Panfilov model is used to investigate alternans annihilation via mechanical (or stretch) perturbations. The coupled model includes the active stress which defines the mechanical properties of the tissue and is utilized in the feedback algorithm as an independent input from the pacing based controller realization in alternans annihilation. Simulation studies of both control methods demonstrate that the proposed methods can successfully annihilate alternans in cables that are significantly longer than 1 cm, thus overcoming the limitations of earlier control efforts.

The concept of the mechanically active guideway as a novel approach to maglev

NASA Technical Reports Server (NTRS)

Horwath, T. G.

1992-01-01

A maglev system that is suitable for operation in the United States will have to meet unique requirements which determine the major systems characteristics. Maglev configurations presently developed in Germany and Japan are based on conventional maglev concepts and as such do not meet all of the requirements. A novel maglev guideway concept is introduced as a solution. This concept, the mechanically active guideway, is articulated in three degrees of freedom and assumes system functions which normally reside in the maglev vehicle. The mechanically active guideway contains spatially distributed actuators which are energized under computer control at the time of vehicle passage to achieve bank angle adjustment and ride quality control. A typical realization of the concept is outlined.

Temporally Dissociable Mechanisms of Self-Control: Early Attentional Filtering Versus Late Value Modulation

PubMed Central

Hare, Todd; Rangel, Antonio

2013-01-01

Optimal decision-making often requires exercising self-control. A growing fMRI literature has implicated the dorsolateral prefrontal cortex (dlPFC) in successful self-control, but due to the limitations inherent in BOLD measures of brain activity, the neurocomputational role of this region has not been resolved. Here we exploit the high temporal resolution and whole-brain coverage of event-related potentials (ERPs) to test the hypothesis that dlPFC affects dietary self-control through two different mechanisms: attentional filtering and value modulation. Whereas attentional filtering of sensory input should occur early in the decision process, value modulation should occur later on, after the computation of stimulus values begins. Hungry human subjects were asked to make food choices while we measured neural activity using ERP in a natural condition, in which they responded freely and did not exhibit a tendency to regulate their diet, and in a self-control condition, in which they were given a financial incentive to lose weight. We then measured various neural markers associated with the attentional filtering and value modulation mechanisms across the decision period to test for changes in neural activity during the exercise of self-control. Consistent with the hypothesis, we found evidence for top-down attentional filtering early on in the decision period (150–200 ms poststimulus onset) as well as evidence for value modulation later in the process (450–650 ms poststimulus onset). We also found evidence that dlPFC plays a role in the deployment of both mechanisms. PMID:24285897

Integrated Application of Active Controls (IAAC) technology to an advanced subsonic transport project. ACT/Control/Guidance System study, volume 1

NASA Technical Reports Server (NTRS)

1982-01-01

The active control technology (ACT) control/guidance system task of the integrated application of active controls (IAAC) technology project within the NASA energy efficient transport program was documented. The air traffic environment of navigation and air traffic control systems and procedures were extrapolated. An approach to listing flight functions which will be performed by systems and crew of an ACT configured airplane of the 1990s, and a determination of function criticalities to safety of flight, are the basis of candidate integrated ACT/Control/Guidance System architecture. The system mechanizes five active control functions: pitch augmented stability, angle of attack limiting, lateral/directional augmented stability, gust load alleviation, and maneuver load control. The scope and requirements of a program for simulating the integrated ACT avionics and flight deck system, with pilot in the loop, are defined, system and crew interface elements are simulated, and mechanization is recommended. Relationships between system design and crew roles and procedures are evaluated.

Myosin filament activation in the heart is tuned to the mechanical task

PubMed Central

Reconditi, Massimo; Caremani, Marco; Pinzauti, Francesca; Powers, Joseph D.; Narayanan, Theyencheri; Stienen, Ger J. M.; Linari, Marco; Lombardi, Vincenzo

2017-01-01

The mammalian heart pumps blood through the vessels, maintaining the dynamic equilibrium in a circulatory system driven by two pumps in series. This vital function is based on the fine-tuning of cardiac performance by the Frank–Starling mechanism that relates the pressure exerted by the contracting ventricle (end systolic pressure) to its volume (end systolic volume). At the level of the sarcomere, the structural unit of the cardiac myocytes, the Frank–Starling mechanism consists of the increase in active force with the increase of sarcomere length (length-dependent activation). We combine sarcomere mechanics and micrometer–nanometer-scale X-ray diffraction from synchrotron light in intact ventricular trabeculae from the rat to measure the axial movement of the myosin motors during the diastole–systole cycle under sarcomere length control. We find that the number of myosin motors leaving the off, ATP hydrolysis-unavailable state characteristic of the diastole is adjusted to the sarcomere length-dependent systolic force. This mechanosensing-based regulation of the thick filament makes the energetic cost of the systole rapidly tuned to the mechanical task, revealing a prime aspect of the Frank–Starling mechanism. The regulation is putatively impaired by cardiomyopathy-causing mutations that affect the intramolecular and intermolecular interactions controlling the off state of the motors. PMID:28265101

A mechanically activated TRPC1-like current in white adipocytes.

PubMed

El Hachmane, Mickaël F; Olofsson, Charlotta S

2018-04-15

Ca 2+ impacts a large array of cellular processes in every known cell type. In the white adipocyte, Ca 2+ is involved in regulation of metabolic processes such as lipolysis, glucose uptake and hormone secretion. Although the importance of Ca 2+ in control of white adipocyte function is clear, knowledge is still lacking regarding the control of dynamic Ca 2+ alterations within adipocytes and mechanisms inducing intracellular Ca 2+ changes remain elusive. Own work has recently demonstrated the existence of store-operated Ca 2+ entry (SOCE) in lipid filled adipocytes. We defined stromal interaction molecule 1 (STIM1) and the calcium release-activated calcium channel protein 1 (ORAI1) as the key players involved in this process and we showed that the transient receptor potential (TRP) channel TRPC1 contributed to SOCE. Here we have aimed to further characterised SOCE in the white adipocyte by use of single cell whole-cell patch clamp recordings. The electrophysiological measurements show the existence of a seemingly constitutively active current that is inhibited by known store-operated Ca 2+ channel (SOCC) blockers. We demonstrate that the mechanical force applied to the plasma membrane upon patching leads to an elevation of the cytoplasmic Ca 2+ concentration and that this elevation can be reversed by SOCC antagonists. We conclude that a mechanically activated current with properties similar to TRPC1 is present in white adipocytes. Activation of TRPC1 by membrane tension/stretch may be specifically important for the function of this cell type, since adipocytes can rapidly increase or decrease in size. Copyright © 2018 Elsevier Inc. All rights reserved.

Neural Mechanisms Underlying Individual Differences in Control-Averse Behavior.

PubMed

Rudorf, Sarah; Schmelz, Katrin; Baumgartner, Thomas; Wiest, Roland; Fischbacher, Urs; Knoch, Daria

2018-05-30

When another person tries to control one's decisions, some people might comply, but many will feel the urge to act against that control. This control aversion can lead to suboptimal decisions and it affects social interactions in many societal domains. To date, however, it has been unclear what drives individual differences in control-averse behavior. Here, we address this issue by measuring brain activity with fMRI while healthy female and male human participants made choices that were either free or controlled by another person, with real consequences to both interaction partners. In addition, we assessed the participants' affects, social cognitions, and motivations via self-reports. Our results indicate that the social cognitions perceived distrust and lack of understanding for the other person play a key role in explaining control aversion at the behavioral level. At the neural level, we find that control-averse behavior can be explained by functional connectivity between the inferior parietal lobule and the dorsolateral prefrontal cortex, brain regions commonly associated with attention reorientation and cognitive control. Further analyses reveal that the individual strength of functional connectivity complements and partially mediates the self-reported social cognitions in explaining individual differences in control-averse behavior. These findings therefore provide valuable contributions to a more comprehensive model of control aversion. SIGNIFICANCE STATEMENT Control aversion is a prevalent phenomenon in our society. When someone tries to control their decisions, many people tend to act against the control. This can lead to suboptimal decisions such as noncompliance to medical treatments or disobeying the law. The degree to which individuals engage in control-averse behavior, however, varies significantly. Understanding the proximal mechanisms that underlie individual differences in control-averse behavior has potential policy implications, for example

Beller Lectureship Talk: Active response of biological cells to mechanical stress

NASA Astrophysics Data System (ADS)

Safran, Samuel

2009-03-01

Forces exerted by and on adherent cells are important for many physiological processes such as wound healing and tissue formation. In addition, recent experiments have shown that stem cell differentiation is controlled, at least in part, by the elasticity of the surrounding matrix. We present a simple and generic theoretical model for the active response of biological cells to mechanical stress. The theory includes cell activity and mechanical forces as well as random forces as factors that determine the polarizability that relates cell orientation to stress. This allows us to explain the puzzling observation of parallel (or sometimes random) alignment of cells for static and quasi-static stresses and of nearly perpendicular alignment for dynamically varying stresses. In addition, we predict the response of the cellular orientation to a sinusoidally varying applied stress as a function of frequency and compare the theory with recent experiments. The dependence of the cell orientation angle on the Poisson ratio of the surrounding material distinguishes cells whose activity is controlled by stress from those controlled by strain. We have extended the theory to generalize the treatment of elastic inclusions in solids to ''living'' inclusions (cells) whose active polarizability, analogous to the polarizability of non-living matter, results in the feedback of cellular forces that develop in response to matrix stresses. We use this to explain recent observations of the non-monotonic dependence of stress-fiber polarization in stem cells on matrix rigidity. These findings provide a mechanical correlate for the existence of an optimal substrate elasticity for cell differentiation and function. [3pt] *In collaboration with R. De (Brown University), Y. Biton (Weizmann Institute), and A. Zemel (Hebrew University) and the experimental groups: Max Planck Institute, Stuttgart: S. Jungbauer, R. Kemkemer, J. Spatz; University of Pennsylvania: A. Brown, D. Discher, F. Rehfeldt.

Robust control of multi-jointed arm with a decentralized autonomous control mechanism

NASA Technical Reports Server (NTRS)

Kimura, Shinichi; Miyazaki, Ken; Suzuki, Yoshiaki

1994-01-01

A decentralized autonomous control mechanism applied to the control of three dimensional manipulators and its robustness to partial damage was assessed by computer simulation. Decentralized control structures are believed to be quite robust to time delay between the operator and the target system. A 10-jointed manipulator based on our control mechanism was able to continue its positioning task in three-dimensional space without revision of the control program, even after some of its joints were damaged. These results suggest that this control mechanism can be effectively applied to space telerobots, which are associated with serious time delay between the operator and the target system, and which cannot be easily repaired after being partially damaged.

Active noise control: a review of the field.

PubMed

Gordon, R T; Vining, W D

1992-11-01

Active noise control (ANC) is the application of the principle of the superposition of waves to noise attenuation problems. Much progress has been made toward applying ANC to narrow-band, low-frequency noise in confined spaces. During this same period, the application of ANC to broad-band noise or noise in three-dimensional spaces has seen little progress because of the recent quantification of serious physical limitations, most importantly, noncausality, stability, spatial mismatch, and the infinite gain controller requirement. ANC employs superposition to induce destructive interference to affect the attenuation of noise. ANC was believed to utilize the mechanism of phase cancellation to achieve the desired attenuation. However, current literature points to other mechanisms that may be operating in ANC. Categories of ANC are one-dimensional field and duct noise, enclosed spaces and interior noise, noise in three-dimensional spaces, and personal hearing protection. Development of active noise control stems from potential advantages in cost, size, and effectiveness. There are two approaches to ANC. In the first, the original sound is processed and injected back into the sound field in antiphase. The second approach is to synthesize a cancelling waveform. ANC of turbulent flow in pipes and ducts is the largest area in the field. Much work into the actual mechanism involved and the causal versus noncausal aspects of system controllers has been done. Fan and propeller noise can be divided into two categories: noise generated directly as the blade passing tones and noise generated as a result of blade tip turbulence inducing vibration in structures. Three-dimensional spaces present a noise environment where physical limitations are magnified and the infinite gain controller requirement is confronted. Personal hearing protection has been shown to be best suited to the control of periodic, low-frequency noise.

Method and apparatus for actively controlling a micro-scale flexural plate wave device

DOEpatents

Dohner, Jeffrey L.

2001-01-01

An actively controlled flexural plate wave device provides a micro-scale pump. A method of actively controlling a flexural plate wave device produces traveling waves in the device by coordinating the interaction of a magnetic field with actively controlled currents. An actively-controlled flexural plate wave device can be placed in a fluid channel and adapted for use as a micro-scale fluid pump to cool or drive micro-scale systems, for example, micro-chips, micro-electrical-mechanical devices, micro-fluid circuits, or micro-scale chemical analysis devices.

Permeation Mechanisms in the TMEM16B Calcium-Activated Chloride Channels

PubMed Central

2017-01-01

TMEM16A and TMEM16B encode for Ca2+-activated Cl− channels (CaCC) and are expressed in many cell types and play a relevant role in many physiological processes. Here, I performed a site-directed mutagenesis study to understand the molecular mechanisms of ion permeation of TMEM16B. I mutated two positive charged residues R573 and K540, respectively located at the entrance and inside the putative channel pore and I measured the properties of wild-type and mutant TMEM16B channels expressed in HEK-293 cells using whole-cell and excised inside-out patch clamp experiments. I found evidence that R573 and K540 control the ion permeability of TMEM16B depending both on which side of the membrane the ion substitution occurs and on the level of channel activation. Moreover, these residues contribute to control blockage or activation by permeant anions. Finally, R573 mutation abolishes the anomalous mole fraction effect observed in the presence of a permeable anion and it alters the apparent Ca2+-sensitivity of the channel. These findings indicate that residues facing the putative channel pore are responsible both for controlling the ion selectivity and the gating of the channel, providing an initial understanding of molecular mechanism of ion permeation in TMEM16B. PMID:28046119

Double-well dynamics of noise-driven control activation in human intermittent control: the case of stick balancing.

PubMed

Zgonnikov, Arkady; Lubashevsky, Ihor

2015-11-01

When facing a task of balancing a dynamic system near an unstable equilibrium, humans often adopt intermittent control strategy: Instead of continuously controlling the system, they repeatedly switch the control on and off. Paradigmatic example of such a task is stick balancing. Despite the simplicity of the task itself, the complexity of human intermittent control dynamics in stick balancing still puzzles researchers in motor control. Here we attempt to model one of the key mechanisms of human intermittent control, control activation, using as an example the task of overdamped stick balancing. In doing so, we focus on the concept of noise-driven activation, a more general alternative to the conventional threshold-driven activation. We describe control activation as a random walk in an energy potential, which changes in response to the state of the controlled system. By way of numerical simulations, we show that the developed model captures the core properties of human control activation observed previously in the experiments on overdamped stick balancing. Our results demonstrate that the double-well potential model provides tractable mathematical description of human control activation at least in the considered task and suggest that the adopted approach can potentially aid in understanding human intermittent control in more complex processes.

Flutter suppression for the Active Flexible Wing - Control system design and experimental validation

NASA Technical Reports Server (NTRS)

Waszak, M. R.; Srinathkumar, S.

1992-01-01

The synthesis and experimental validation of a control law for an active flutter suppression system for the Active Flexible Wing wind-tunnel model is presented. The design was accomplished with traditional root locus and Nyquist methods using interactive computer graphics tools and with extensive use of simulation-based analysis. The design approach relied on a fundamental understanding of the flutter mechanism to formulate understanding of the flutter mechanism to formulate a simple control law structure. Experimentally, the flutter suppression controller succeeded in simultaneous suppression of two flutter modes, significantly increasing the flutter dynamic pressure despite errors in the design model. The flutter suppression controller was also successfully operated in combination with a rolling maneuver controller to perform flutter suppression during rapid rolling maneuvers.

Neural mechanisms of interference control in working memory capacity.

PubMed

Bomyea, Jessica; Taylor, Charles T; Spadoni, Andrea D; Simmons, Alan N

2018-02-01

The extent to which one can use cognitive resources to keep information in working memory is known to rely on (1) active maintenance of target representations and (2) downregulation of interference from irrelevant representations. Neurobiologically, the global capacity of working memory is thought to depend on the prefrontal and parietal cortices; however, the neural mechanisms involved in controlling interference specifically in working memory capacity tasks remain understudied. In this study, 22 healthy participants completed a modified complex working memory capacity task (Reading Span) with trials of varying levels of interference control demands while undergoing functional MRI. Neural activity associated with interference control demands was examined separately during encoding and recall phases of the task. Results suggested a widespread network of regions in the prefrontal, parietal, and occipital cortices, and the cingulate and cerebellum associated with encoding, and parietal and occipital regions associated with recall. Results align with prior findings emphasizing the importance of frontoparietal circuits for working memory performance, including the role of the inferior frontal gyrus, cingulate, occipital cortex, and cerebellum in regulation of interference demands. © 2017 Wiley Periodicals, Inc.

Mechanical loading stimulates ecto-ATPase activity in human tendon cells.

PubMed

Tsuzaki, M; Bynum, D; Almekinders, L; Faber, J; Banes, A J

2005-09-01

Response to external stimuli such as mechanical signals is critical for normal function of cells, especially when subjected to repetitive motion. Tenocytes receive mechanical stimuli from the load-bearing matrix as tension, compression, and shear stress during tendon gliding. Overloading a tendon by high strain, shear, or repetitive motion can cause matrix damage. Injury may induce cytokine expression, matrix metalloproteinase (MMP) expression and activation resulting in loss of biomechanical properties. These changes may result in tendinosis or tendinopathy. Alternatively, an immediate effector molecule may exist that acts in a signal-dampening pathway. Adenosine 5'-triphosphate (ATP) is a candidate signal blocker of mechanical stimuli. ATP suppresses load-inducible inflammatory genes in human tendon cells in vitro. ATP and other extracellular nucleotide signaling are regulated efficiently by two distinct mechanisms: purinoceptors via specific receptor-ligand binding and ecto-nucleotidases via the hydrolysis of specific nucleotide substrates. ATP is released from tendon cells by mechanical loading or by uridine 5'-triphosphate (UTP) stimulation. We hypothesized that mechanical loading might stimulate ecto-ATPase activity. Human tendon cells of surface epitenon (TSC) and internal compartment (TIF) were cyclically stretched (1 Hz, 0.035 strain, 2 h) with or without ATP. Aliquots of the supernatant fluids were collected at various time points, and ATP concentration (ATP) was determined by a luciferin-luciferase bioluminescence assay. Total RNA was isolated from TSC and TIF (three patients) and mRNA expression for ecto-nucleotidase was analyzed by RT-PCR. Human tendon cells secreted ATP in vitro (0.5-1 nM). Exogenous ATP was hydrolyzed within minutes. Mechanical load stimulated ATPase activity. ATP was hydrolyzed in mechanically loaded cultures at a significantly greater rate compared to no load controls. Tenocytes (TSC and TIF) expressed ecto-nucleotidase mRNA (ENTPD

Molecular mechanisms of the antiproliferative activity of somatostatin receptors (SSTRs) in neuroendocrine tumors.

PubMed

Florio, Tullio

2008-01-01

The current treatment of neuroendocrine tumors include the use of somatostatin (SST) agonists. These compounds are able to control most of the symptoms caused by the hypersecretory activity of the tumor cells, and for this reason, they provide a significant improvement in the well-being of the patients. Although, several reports also showed a possible direct antiproliferative activity of SST agonists in different neuroendocrine tumors, the therapeutic potential of an in vivo antiproliferative activity mediated by SST receptors is still debated. In recent years, there has been great insights on understanding the molecular basis of the antitumoral activity of SST that appears to be exerted via both direct and indirect mechanisms. Direct mechanisms require the activation of SST receptors in tumor cells and the induction of cell cycle arrest or apoptosis, mainly through the regulation of phosphotyrosine phosphatase (PTP) and MAP kinase activities. The indirect mechanisms involve the inhibition of tumor angiogenesis and the inhibition of the secretion of factors which are required for tumor growth. Here, we will review the molecular mechanisms which are implicated in the antiproliferative activity of SST. Such an understanding is necessary for improving the antitumoral efficacy of SSTR agonists as well as for the development of novel therapeutic strategies.

Brain Mechanisms of Attentional Control.

ERIC Educational Resources Information Center

Wilke, Thomas

Lack of attentional control--inability to concentrate--has often made the difference between successful and unsuccessful performance on the part of athletes. Attention is controlled neurologically by a very complex interaction of a large portion of the cerebrum and is not localized to any one structure. The mechanism involves a memory retrieval…

The mitogen-activated protein kinase (MAPK) cascade controls phosphatase and tensin homolog (PTEN) expression through multiple mechanisms.

PubMed

Ciuffreda, Ludovica; Di Sanza, Cristina; Cesta Incani, Ursula; Eramo, Adriana; Desideri, Marianna; Biagioni, Francesca; Passeri, Daniela; Falcone, Italia; Sette, Giovanni; Bergamo, Paola; Anichini, Andrea; Sabapathy, Kanaga; McCubrey, James A; Ricciardi, Maria Rosaria; Tafuri, Agostino; Blandino, Giovanni; Orlandi, Augusto; De Maria, Ruggero; Cognetti, Francesco; Del Bufalo, Donatella; Milella, Michele

2012-06-01

The mitogen-activated protein kinase (MAPK) and PI3K pathways are regulated by extensive crosstalk, occurring at different levels. In tumors, transactivation of the alternate pathway is a frequent "escape" mechanism, suggesting that combined inhibition of both pathways may achieve synergistic antitumor activity. Here we show that, in the M14 melanoma model, simultaneous inhibition of both MEK and mammalian target of rapamycin (mTOR) achieves synergistic effects at suboptimal concentrations, but becomes frankly antagonistic in the presence of relatively high concentrations of MEK inhibitors. This observation led to the identification of a novel crosstalk mechanism, by which either pharmacologic or genetic inhibition of constitutive MEK signaling restores phosphatase and tensin homolog (PTEN) expression, both in vitro and in vivo, and inhibits downstream signaling through AKT and mTOR, thus bypassing the need for double pathway blockade. This appears to be a general regulatory mechanism and is mediated by multiple mechanisms, such as MAPK-dependent c-Jun and miR-25 regulation. Finally, PTEN upregulation appears to be a major effector of MEK inhibitors' antitumor activity, as cancer cells in which PTEN is inactivated are consistently more resistant to the growth inhibitory and anti-angiogenic effects of MEK blockade.

Neural mechanisms underlying cognitive control of men with lifelong antisocial behavior.

PubMed

Schiffer, Boris; Pawliczek, Christina; Mu Ller, Bernhard; Forsting, Michael; Gizewski, Elke; Leygraf, Norbert; Hodgins, Sheilagh

2014-04-30

Results of meta-analyses suggested subtle deficits in cognitive control among antisocial individuals. Because almost all studies focused on children with conduct problems or adult psychopaths, however, little is known about cognitive control mechanisms among the majority of persistent violent offenders who present an antisocial personality disorder (ASPD). The present study aimed to determine whether offenders with ASPD, relative to non-offenders, display dysfunction in the neural mechanisms underlying cognitive control and to assess the extent to which these dysfunctions are associated with psychopathic traits and trait impulsivity. Participants comprised 21 violent offenders and 23 non-offenders who underwent event-related functional magnetic resonance imaging while performing a non-verbal Stroop task. The offenders, relative to the non-offenders, exhibited reduced response time interference and a different pattern of conflict- and error-related activity in brain areas involved in cognitive control, attention, language, and emotion processing, that is, the anterior cingulate, dorsolateral prefrontal, superior temporal and postcentral cortices, putamen, thalamus, and amygdala. Moreover, between-group differences in behavioural and neural responses revealed associations with core features of psychopathy and attentional impulsivity. Thus, the results of the present study confirmed the hypothesis that offenders with ASPD display alterations in the neural mechanisms underlying cognitive control and that those alterations relate, at least in part, to personality characteristics. Copyright © 2014. Published by Elsevier Ireland Ltd.

Automatically-Activated Attitudes as Mechanisms for Message Effects: The Case of Alcohol Advertisements.

PubMed

Goodall, Catherine E; Slater, Michael D

2010-10-01

Alcohol advertisements may influence impulsive, risky behaviors indirectly, via automatically-activated attitudes toward alcohol. Results from an experiment in which participants were exposed to either four alcohol advertisements, four control advertisements, or four drunk driving public service advertisements, suggested that alcohol advertisements had more measurable effects on implicit, than on explicit attitude measures. Moreover, there were significant indirect paths from alcohol advertisement exposure through automatically-activated alcohol attitudes on willingness to engage in risky alcohol-related behaviors, notably drinking and driving. A mechanism that may explain how these advertisements activate automatic, non-deliberative alcohol attitudes was investigated. Associative evidence was found supportive of an evaluative conditioning mechanism, in which positive responses to an alcohol advertisement may lead to more positive automatically-activated attitudes toward alcohol itself.

Semi-active control of a cable-stayed bridge under multiple-support excitations.

PubMed

Dai, Ze-Bing; Huang, Jin-Zhi; Wang, Hong-Xia

2004-03-01

This paper presents a semi-active strategy for seismic protection of a benchmark cable-stayed bridge with consideration of multiple-support excitations. In this control strategy, Magnetorheological (MR) dampers are proposed as control devices, a LQG-clipped-optimal control algorithm is employed. An active control strategy, shown in previous researches to perform well at controlling the benchmark bridge when uniform earthquake motion was assumed, is also used in this study to control this benchmark bridge with consideration of multiple-support excitations. The performance of active control system is compared to that of the presented semi-active control strategy. Because the MR fluid damper is a controllable energy- dissipation device that cannot add mechanical energy to the structural system, the proposed control strategy is fail-safe in that bounded-input, bounded-output stability of the controlled structure is guaranteed. The numerical results demonstrated that the performance of the presented control design is nearly the same as that of the active control system; and that the MR dampers can effectively be used to control seismically excited cable-stayed bridges with multiple-support excitations.

Remote controlled vacuum joint closure mechanism

DOEpatents

Doll, David W.; Hager, E. Randolph

1986-01-01

A remotely operable and maintainable vacuum joint closure mechanism for a noncircular aperture is disclosed. The closure mechanism includes an extendible bellows coupled at one end to a noncircular duct and at its other end to a flange assembly having sealed grooves for establishing a high vacuum seal with the abutting surface of a facing flange which includes an aperture forming part of the system to be evacuated. A plurality of generally linear arrangements of pivotally coupled linkages and piston combinations are mounted around the outer surface of the duct and aligned along the length thereof. Each of the piston/linkage assemblies is adapted to engage the flange assembly by means of a respective piston and is further coupled to a remote controlled piston drive shaft to permit each of the linkages positioned on a respective flat outer surface of the duct to simultaneously and uniformly displace a corresponding piston and the flange assembly with which it is in contact along the length of the duct in extending the bellows to provide a high vacuum seal between the movable flange and the facing flange. A plurality of latch mechanisms are also pivotally mounted on the outside of the duct. A first end of each of the latch mechanisms is coupled to a remotely controlled latch control shaft for displacing the latch mechanism about its pivot point. In response to the pivoting displacement of the latch mechanism, a second end thereof is displaced so as to securely engage the facing flange.

Optimisation of active suspension control inputs for improved vehicle handling performance

NASA Astrophysics Data System (ADS)

Čorić, Mirko; Deur, Joško; Kasać, Josip; Tseng, H. Eric; Hrovat, Davor

2016-11-01

Active suspension is commonly considered under the framework of vertical vehicle dynamics control aimed at improvements in ride comfort. This paper uses a collocation-type control variable optimisation tool to investigate to which extent the fully active suspension (FAS) application can be broaden to the task of vehicle handling/cornering control. The optimisation approach is firstly applied to solely FAS actuator configurations and three types of double lane-change manoeuvres. The obtained optimisation results are used to gain insights into different control mechanisms that are used by FAS to improve the handling performance in terms of path following error reduction. For the same manoeuvres the FAS performance is compared with the performance of different active steering and active differential actuators. The optimisation study is finally extended to combined FAS and active front- and/or rear-steering configurations to investigate if they can use their complementary control authorities (over the vertical and lateral vehicle dynamics, respectively) to further improve the handling performance.

Aircraft panel with sensorless active sound power reduction capabilities through virtual mechanical impedances

NASA Astrophysics Data System (ADS)

Boulandet, R.; Michau, M.; Micheau, P.; Berry, A.

2016-01-01

This paper deals with an active structural acoustic control approach to reduce the transmission of tonal noise in aircraft cabins. The focus is on the practical implementation of the virtual mechanical impedances method by using sensoriactuators instead of conventional control units composed of separate sensors and actuators. The experimental setup includes two sensoriactuators developed from the electrodynamic inertial exciter and distributed over an aircraft trim panel which is subject to a time-harmonic diffuse sound field. The target mechanical impedances are first defined by solving a linear optimization problem from sound power measurements before being applied to the test panel using a complex envelope controller. Measured data are compared to results obtained with sensor-actuator pairs consisting of an accelerometer and an inertial exciter, particularly as regards sound power reduction. It is shown that the two types of control unit provide similar performance, and that here virtual impedance control stands apart from conventional active damping. In particular, it is clear from this study that extra vibrational energy must be provided by the actuators for optimal sound power reduction, mainly due to the high structural damping in the aircraft trim panel. Concluding remarks on the benefits of using these electrodynamic sensoriactuators to control tonal disturbances are also provided.

Examination of mechanisms (E-MECHANIC) of exercise-induced weight compensation: study protocol for a randomized controlled trial.

PubMed

Myers, Candice A; Johnson, William D; Earnest, Conrad P; Rood, Jennifer C; Tudor-Locke, Catrine; Johannsen, Neil M; Cocreham, Shannon; Harris, Melissa; Church, Timothy S; Martin, Corby K

2014-06-07

Weight loss induced only by exercise is frequently less than expected, possibly because of compensatory changes in energy intake and/or energy expenditure. The purpose of the Examination of Mechanisms (E-MECHANIC) of Exercise-Induced Weight Compensation trial is to examine whether increased energy intake and/or reduced spontaneous activity or energy expenditure (outside of structured exercise) account for the less than expected, exercise-associated weight loss. E-MECHANIC is a three-arm, 6-month randomized (1:1:1) controlled trial. The two intervention arms are exercise doses that reflect current recommendations for (1) general health (8 kcal/kg body weight per week (8 KKW), about 900 kcal/wk) and (2) weight loss (20 KKW, about 2,250 kcal/wk). The third arm, a nonexercise control group, will receive health information only. The sample will include a combined total of 198sedentary, overweight or obese (body mass index: ≥25 kg/m² to ≤45 kg/m²) men and women ages 18 to 65 years. The exercise dose will be supervised and tightly controlled in an exercise training laboratory. The primary outcome variables are energy intake, which will be measured using doubly labeled water (adjusted for change in energy stores) and laboratory-based food intake tests, and the discrepancy between expected weight loss and observed weight loss. Secondary outcomes include changes in resting metabolic rate (adjusted for change in body mass), activity levels (excluding structured exercise) and body composition. In an effort to guide the development of future interventions, the participants will be behaviorally phenotyped and defined as those who do compensate (that is, fail to lose the amount of weight expected) or do not compensate (that is, lose the amount of weight expected or more). In this study, we will attempt to identify underlying mechanisms to explain why exercise elicits less weight loss than expected. This information will guide the development of interventions to increase

Mechanisms controlling nucleic acid-sensing Toll-like receptors.

PubMed

Miyake, Kensuke; Shibata, Takuma; Ohto, Umeharu; Shimizu, Toshiyuki; Saitoh, Shin-Ichiroh; Fukui, Ryutaro; Murakami, Yusuke

2018-03-08

Nucleic acid (NA)-sensing Toll-like receptors (TLRs) respond to DNA/RNA derived from pathogens and dead cells. Structural studies have revealed a variety of molecular mechanisms by which TLRs sense NAs. Double-stranded RNA and single-stranded DNA directly bind to TLR3 and TLR9, respectively, whereas TLR7 and TLR8 bind to nucleosides and oligoribonucleotides derived from RNAs. Activation of ligand-bound TLRs is influenced by the functional status of TLRs. Proteolytic cleavage of NA-sensing TLRs enables ligand-dependent TLR dimerization. Trafficking of ligand-activated TLRs in endosomal and lysosomal compartments is requisite for production of type I interferons. Activation of NA-sensing TLRs is required for the control of viruses such as herpes simplex virus and endogenous retroviruses. On the other hand, excessive activation of NA-sensing TLRs drives disease progression in a variety of inflammatory diseases including systemic lupus erythematosus, heart failure, arthritis and non-alcoholic steatohepatitis. NA-sensing TLRs are targets for therapeutic intervention in these diseases. We here focus on our recent progresses in our understanding of NA-sensing TLRs.

Mechanical Control of Tissue Morphogenesis

PubMed Central

Patwari, Parth; Lee, Richard T.

2008-01-01

Mechanical forces participate in morphogenesis from the level of individual cells to whole organism patterning. This manuscript reviews recent research that has identified specific roles for mechanical forces in important developmental events. One well-defined example is that dynein-driven cilia create fluid flow that determines left-right patterning in the early mammalian embryo. Fluid flow is also important for vasculogenesis, and evidence suggests that fluid shear stress rather than fluid transport is primarily required for remodeling the early vasculature. Contraction of the actin cytoskeleton, driven by nonmuscle myosins and regulated by the Rho family GTPases, is a recurring mechanism for controlling morphogenesis throughout development, from gastrulation to cardiogenesis. Finally, novel experimental approaches suggest critical roles for the actin cytoskeleton and the mechanical environment in determining differentiation of mesenchymal stem cells. Insights into the mechanisms linking mechanical forces to cell and tissue differentiation pathways are important for understanding many congenital diseases and for developing regenerative medicine strategies. PMID:18669930

Automatically-Activated Attitudes as Mechanisms for Message Effects: The Case of Alcohol Advertisements

PubMed Central

Goodall, Catherine E.; Slater, Michael D.

2010-01-01

Alcohol advertisements may influence impulsive, risky behaviors indirectly, via automatically-activated attitudes toward alcohol. Results from an experiment in which participants were exposed to either four alcohol advertisements, four control advertisements, or four drunk driving public service advertisements, suggested that alcohol advertisements had more measurable effects on implicit, than on explicit attitude measures. Moreover, there were significant indirect paths from alcohol advertisement exposure through automatically-activated alcohol attitudes on willingness to engage in risky alcohol-related behaviors, notably drinking and driving. A mechanism that may explain how these advertisements activate automatic, non-deliberative alcohol attitudes was investigated. Associative evidence was found supportive of an evaluative conditioning mechanism, in which positive responses to an alcohol advertisement may lead to more positive automatically-activated attitudes toward alcohol itself. PMID:21258609

Neural, Cellular and Molecular Mechanisms of Active Forgetting

PubMed Central

Medina, Jorge H.

2018-01-01

The neurobiology of memory formation attracts much attention in the last five decades. Conversely, the rules that govern and the mechanisms underlying forgetting are less understood. In addition to retroactive interference, retrieval-induced forgetting and passive decay of time, it has been recently demonstrated that the nervous system has a diversity of active and inherent processes involved in forgetting. In Drosophila, some operate mainly at an early stage of memory formation and involves dopamine (DA) neurons, specific postsynaptic DA receptor subtypes, Rac1 activation and induces rapid active forgetting. In mammals, others regulate forgetting and persistence of seemingly consolidated memories and implicate the activity of DA receptor subtypes and AMPA receptors in the hippocampus (HP) and related structures to activate parallel signaling pathways controlling active time-dependent forgetting. Most of them may involve plastic changes in synaptic and extrasynaptic receptors including specific removal of GluA2 AMPA receptors. Forgetting at longer timescales might also include changes in adult neurogenesis in the dentate gyrus (DG) of the HP. Therefore, based on relevance or value considerations neuronal circuits may regulate in a time-dependent manner what is formed, stored, and maintained and what is forgotten. PMID:29467630

Remote controlled vacuum joint closure mechanism

DOEpatents

Doll, D.W.; Hager, E.R.

1984-02-22

A remotely operable and maintainable vacuum joint closure mechanism for a noncircular aperture is disclosed. The closure mechanism includes an extendible bellows coupled at one end to a noncircular duct and at its other end to a flange assembly having sealed grooves for establishing a high vacuum seal with the abutting surface of a facing flange which includes an aperture forming part of the system to be evacuated. A plurality of generally linear arrangements of pivotally coupled linkages and piston combinations are mounted around the outer surface of the duct and aligned along the length thereof. Each of the piston/linkage assemblies is adapted to engage the flange assembly by means of a respective piston and is further coupled to a remote controlled piston drive shaft to permit each of the linkages positioned on a respective flat outer surface of the duct to simultaneously and uniformly displace a corresponding piston and the flange assembly with which it is in contact along the length of the duct in extending the bellows to provide a high vacuum seal between the movable flange and the facing flange. A plurality of latch mechanisms are also pivotally mounted on the outside of the duct. A first end of each of the latch mechanisms is coupled to a remotely controlled latch control shaft for displacing the latch mechanism about its pivot point. In response to the pivoting displacement of the latch mechanism, a second end thereof is displaced so as to securely engage the facing flange and maintain the high vacuum seal established by the displacement of the flange assembly and extension of the bellows without displacing the entire duct.

Introducing a novel mechanism to control heart rate in the ancestral Pacific hagfish.

PubMed

Wilson, Christopher M; Roa, Jinae N; Cox, Georgina K; Tresguerres, Martin; Farrell, Anthony P

2016-10-15

Although neural modulation of heart rate is well established among chordate animals, the Pacific hagfish (Eptatretus stoutii) lacks any cardiac innervation, yet it can increase its heart rate from the steady, depressed heart rate seen in prolonged anoxia to almost double its normal normoxic heart rate, an almost fourfold overall change during the 1-h recovery from anoxia. The present study sought mechanistic explanations for these regulatory changes in heart rate. We provide evidence for a bicarbonate-activated, soluble adenylyl cyclase (sAC)-dependent mechanism to control heart rate, a mechanism never previously implicated in chordate cardiac control. © 2016. Published by The Company of Biologists Ltd.

Mechanization and Control Concepts for Biologically Inspired Micro Aerial Vehicles

NASA Technical Reports Server (NTRS)

Raney, David L.; Slominski, Eric C.

2003-01-01

It is possible that MAV designs of the future will exploit flapping flight in order to perform missions that require extreme agility, such as rapid flight beneath a forest canopy or within the confines of a building. Many of nature's most agile flyers generate flapping motions through resonant excitation of an aeroelastically tailored structure: muscle tissue is used to excite a vibratory mode of their flexible wing structure that creates propulsion and lift. A number of MAV concepts have been proposed that would operate in a similar fashion. This paper describes an ongoing research activity in which mechanization and control concepts with application to resonant flapping MAVs are being explored. Structural approaches, mechanical design, sensing and wingbeat control concepts inspired by hummingbirds, bats and insects are examined. Experimental results from a testbed capable of generating vibratory wingbeat patterns that approximately match those exhibited by hummingbirds in hover, cruise, and reverse flight are presented.

Integrated Application of Active Controls (IAAC) technology to an advanced subsonic transport project: Current and advanced act control system definition study

NASA Technical Reports Server (NTRS)

1982-01-01

The Current and Advanced Technology ACT control system definition tasks of the Integrated Application of Active Controls (IAAC) Technology project within the Energy Efficient Transport Program are summarized. The systems mechanize six active control functions: (1) pitch augmented stability; (2) angle of attack limiting; (3) lateral/directional augmented stability; (4) gust load alleviation; (5) maneuver load control; and (6) flutter mode control. The redundant digital control systems meet all function requirements with required reliability and declining weight and cost as advanced technology is introduced.

Compensatory mechanisms activated with intermittent energy restriction: A randomized control trial.

PubMed

Coutinho, Sílvia Ribeiro; Halset, Eline Holli; Gåsbakk, Sigrid; Rehfeld, Jens F; Kulseng, Bård; Truby, Helen; Martins, Cátia

2018-06-01

the compensatory mechanisms activated by weight loss. NCT02169778 (the study was registered in clinicaltrial.gov). Copyright © 2017 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.

The Controllable Ball Joint Mechanism

NASA Astrophysics Data System (ADS)

Tung, Yung Cheng; Chieng, Wei-Hua; Ho, Shrwai

A controllable ball joint mechanism with three rotational degrees of freedom is proposed in this paper. The mechanism is composed of three bevel gears, one of which rotates with respect to a fixed frame and the others rotate with respect to individual floating frames. The output is the resultant motion of the differential motions by the motors that rotates the bevel gears at the fixed frame and the floating frames. The mechanism is capable of a large rotation, and the structure is potentially compact. The necessary inverse and forward kinematic analyses as well as the derivation of kinematic singularity are provided according to the kinematical equivalent structure described in this paper.

Consideration of Optimal Input on Semi-Active Shock Control System

NASA Astrophysics Data System (ADS)

Kawashima, Takeshi

In press working, unidirectional transmission of mechanical energy is expected in order to maximize the life of the dies. To realize this transmission, the author has developed a shock control system based on the sliding mode control technique. The controller makes a collision-receiving object effectively deform plastically by adjusting the force of the actuator inserted between the colliding objects, while the deformation of the colliding object is held at the necessity minimum. However, the actuator has to generate a large force corresponding to the impulsive force. Therefore, development of such an actuator is a formidable challenge. The author has proposed a semi-active shock control system in which the impulsive force is adjusted by a brake mechanism, although the system exhibits inferior performance. Thus, the author has also designed an actuator using a friction device for semi-active shock control, and proposed an active seatbelt system as an application. The effectiveness has been confirmed by a numerical simulation and model experiment. In this study, the optimal deformation change of the colliding object is theoretically examined in the case that the collision-receiving object has perfect plasticity and the colliding object has perfect elasticity. As a result, the optimal input condition is obtained so that the ratio of the maximum deformation of the collision-receiving object to the maximum deformation of the colliding object becomes the maximum. Additionally, the energy balance is examined.

Flow-induced phase separation of active particles is controlled by boundary conditions.

PubMed

Thutupalli, Shashi; Geyer, Delphine; Singh, Rajesh; Adhikari, Ronojoy; Stone, Howard A

2018-05-22

Active particles, including swimming microorganisms, autophoretic colloids, and droplets, are known to self-organize into ordered structures at fluid-solid boundaries. The entrainment of particles in the attractive parts of their spontaneous flows has been postulated as a possible mechanism underlying this phenomenon. Here, combining experiments, theory, and numerical simulations, we demonstrate the validity of this flow-induced ordering mechanism in a suspension of active emulsion droplets. We show that the mechanism can be controlled, with a variety of resultant ordered structures, by simply altering hydrodynamic boundary conditions. Thus, for flow in Hele-Shaw cells, metastable lines or stable traveling bands can be obtained by varying the cell height. Similarly, for flow bounded by a plane, dynamic crystallites are formed. At a no-slip wall, the crystallites are characterized by a continuous out-of-plane flux of particles that circulate and re-enter at the crystallite edges, thereby stabilizing them. At an interface where the tangential stress vanishes, the crystallites are strictly 2D, with no out-of-plane flux. We rationalize these experimental results by calculating, in each case, the slow viscous flow produced by the droplets and the long-ranged, many-body active forces and torques between them. The results of numerical simulations of motion under the action of the active forces and torques are in excellent agreement with experiments. Our work elucidates the mechanism of flow-induced phase separation in active fluids, particularly active colloidal suspensions, and demonstrates its control by boundaries, suggesting routes to geometric and topological phenomena in an active matter.

Computational Study of Inlet Active Flow Control

DTIC Science & Technology

2007-05-01

AFRL-VA-WP-TR-2007-3077 COMPUTATIONAL STUDY OF INLET ACTIVE FLOW CONTROL Delivery Order 0005 Dr. Sonya T. Smith Howard University Department...NUMBER A0A2 5e. TASK NUMBER 6. AUTHOR(S) Dr. Sonya T. Smith ( Howard University ) Dr. Angela Scribben and Matthew Goettke (AFRL/VAAI) 5f...WORK UNIT NUMBER 0B 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION Howard University Department of Mechanical

Reduction of interior sound fields in flexible cylinders by active vibration control

NASA Technical Reports Server (NTRS)

Jones, J. D.; Fuller, C. R.

1988-01-01

The mechanisms of interior sound reduction through active control of a thin flexible shell's vibrational response are presently evaluated in view of an analytical model. The noise source is a single exterior acoustic monopole. The active control model is evaluated for harmonic excitation; the results obtained indicate spatially-averaged noise reductions in excess of 20 dB over the source plane, for acoustic resonant conditions inside the cavity.

Design and test of three active flutter suppression controllers

NASA Technical Reports Server (NTRS)

Christhilf, David M.; Waszak, Martin R.; Adams, William M.; Srinathkumar, S.; Mukhopadhyay, Vivek

1991-01-01

Three flutter suppression control law design techniques are presented. Each uses multiple control surfaces and/or sensors. The first uses linear combinations of several accelerometer signals together with dynamic compensation to synthesize the modal rate of the critical mode for feedback to distributed control surfaces. The second uses traditional tools (pole/zero loci and Nyquist diagrams) to develop a good understanding of the flutter mechanism and produce a controller with minimal complexity and good robustness to plant uncertainty. The third starts with a minimum energy Linear Quadratic Gaussian controller, applies controller order reduction, and then modifies weight and noise covariance matrices to improve multi-variable robustness. The resulting designs were implemented digitally and tested subsonically on the Active Flexible Wing (AFW) wind tunnel model. Test results presented here include plant characteristics, maximum attained closed-loop dynamic pressure, and Root Mean Square control surface activity. A key result is that simultaneous symmetric and antisymmetric flutter suppression was achieved by the second control law, with a 24 percent increase in attainable dynamic pressure.

Gamma Band Activity in the RAS-intracellular mechanisms

PubMed Central

Garcia-Rill, E.; Kezunovic, N.; D’Onofrio, S.; Luster, B.; Hyde, J.; Bisagno, V.; Urbano, F.J.

2014-01-01

Gamma band activity participates in sensory perception, problem solving, and memory. This review considers recent evidence showing that cells in the reticular activating system (RAS) exhibit gamma band activity, and describes the intrinsic membrane properties behind such manifestation. Specifically, we discuss how cells in the mesopontine pedunculopontine nucleus (PPN), intralaminar parafascicular nucleus (Pf), and pontine Subcoeruleus nucleus dorsalis (SubCD) all fire in the gamma band range when maximally activated, but no higher. The mechanisms involve high threshold, voltage-dependent P/Q-type calcium channels or sodium-dependent subthreshold oscillations. Rather than participating in the temporal binding of sensory events as in the cortex, gamma band activity in the RAS may participate in the processes of preconscious awareness, and provide the essential stream of information for the formulation of many of our actions. We address three necessary next steps resulting from these discoveries, an intracellular mechanism responsible for maintaining gamma band activity based on persistent G-protein activation, separate intracellular pathways that differentiate between gamma band activity during waking vs during REM sleep, and an intracellular mechanism responsible for the dysregulation in gamma band activity in schizophrenia. These findings open several promising research avenues that have not been thoroughly explored. What are the effects of sleep or REM sleep deprivation on these RAS mechanisms? Are these mechanisms involved in memory processing during waking and/or during REM sleep? Does gamma band processing differ during waking vs REM sleep after sleep or REM sleep deprivation? PMID:24309750

Gamma band activity in the RAS-intracellular mechanisms.

PubMed

Garcia-Rill, E; Kezunovic, N; D'Onofrio, S; Luster, B; Hyde, J; Bisagno, V; Urbano, F J

2014-05-01

Gamma band activity participates in sensory perception, problem solving, and memory. This review considers recent evidence showing that cells in the reticular activating system (RAS) exhibit gamma band activity, and describes the intrinsic membrane properties behind such manifestation. Specifically, we discuss how cells in the mesopontine pedunculopontine nucleus, intralaminar parafascicular nucleus, and pontine SubCoeruleus nucleus dorsalis all fire in the gamma band range when maximally activated, but no higher. The mechanisms involve high-threshold, voltage-dependent P/Q-type calcium channels, or sodium-dependent subthreshold oscillations. Rather than participating in the temporal binding of sensory events as in the cortex, gamma band activity in the RAS may participate in the processes of preconscious awareness and provide the essential stream of information for the formulation of many of our actions. We address three necessary next steps resulting from these discoveries: an intracellular mechanism responsible for maintaining gamma band activity based on persistent G-protein activation, separate intracellular pathways that differentiate between gamma band activity during waking versus during REM sleep, and an intracellular mechanism responsible for the dysregulation in gamma band activity in schizophrenia. These findings open several promising research avenues that have not been thoroughly explored. What are the effects of sleep or REM sleep deprivation on these RAS mechanisms? Are these mechanisms involved in memory processing during waking and/or during REM sleep? Does gamma band processing differ during waking versus REM sleep after sleep or REM sleep deprivation?

Mechanically activated fly ash as a high performance binder for civil engineering

NASA Astrophysics Data System (ADS)

Rieger, D.; Kullová, L.; Čekalová, M.; Novotný, P.; Pola, M.

2017-01-01

This study is aimed for investigation of fly ash binder with suitable properties for civil engineering needs. The fly ash from Czech brown coal power plant Prunerov II was used and mechanically activated to achieve suitable particle size for alkaline activation of hardening process. This process is driven by dissolution of aluminosilicate content of fly ash and by subsequent development of inorganic polymeric network called geopolymer. Hardening kinetics at 25 and 30 °C were measured by strain controlled small amplitude oscillatory rheometry with strain of 0.01 % and microstructure of hardened binder was evaluated by scanning electron microscopy. Strength development of hardened binder was investigated according to compressional and flexural strength for a period of 180 days. Our investigation finds out, that mechanically activated fly ash can be comparable to metakaolin geopolymers, according to setting time and mechanical parameters even at room temperature curing. Moreover, on the bases of long time strength development, achieved compressional strength of 134.5 after 180 days is comparable to performance of high grade Portland cement concretes.

The effects of spaceflight on open-loop and closed-loop postural control mechanisms: human neurovestibular studies on SLS-2

NASA Technical Reports Server (NTRS)

Collins, J. J.; De Luca, C. J.; Pavlik, A. E.; Roy, S. H.; Emley, M. S.; Young, L. R. (Principal Investigator)

1995-01-01

Stabilogram-diffusion analysis was used to examine how prolonged periods in microgravity affect the open-loop and closed-loop postural control mechanisms. It was hypothesized that following spaceflight: (1) the effective stochastic activity of the open-loop postural control schemes in astronauts is increased; (2) the effective stochastic activity and uncorrelated behavior, respectively, of the closed-loop postural control mechanisms in astronauts are increased; and (3) astronauts utilized open-loop postural controls schemes for shorter time intervals and smaller displacements. Four crew members and two alternates from the 14-day Spacelab Life Sciences 2 Mission were included in the study. Each subject was tested under eyes-open, quiet-standing conditions on multiple preflight and postflight days. The subjects' center-of-pressure trajectories were measured with a force platform and analyzed according to stabilogram-diffusion analysis. It was found that the effective stochastic activity of the open-loop postural control schemes in three of the four crew members was increased following spaceflight. This result is interpreted as an indication that there may be in-flight adaptations to higher-level descending postural control pathways, e.g., a postflight increase in the tonic activation of postural muscles. This change may also be the consequence of a compensatory (e.g., "stiffening") postural control strategy that is adopted by astronauts to account for general feeling of postflight unsteadiness. The crew members, as a group, did not exhibit any consistent preflight/postflight differences in the steady-state behavior of their closed-loop postural control mechanisms or in the functional interaction of their open-loop and closed-loop postural control mechanisms. These results are interpreted as indications that although there may be in-flight adaptations to the vestibular system and/or proprioceptive system, input from the visual system can compensate for such changes

Active Cellular Mechanics and its Consequences for Animal Development

NASA Astrophysics Data System (ADS)

Noll, Nicholas B.

A central goal of developmental biology is to understand how an organism shapes itself, a process referred to as morphogenesis. While the molecular components critical to determining the initial body plan have been well characterized, the control of the subsequent dynamics of cellular rearrangements which ultimately shape the organism are far less understood. A major roadblock to a more complete picture of morphogenesis is the inability to measure tissue-scale mechanics throughout development and thus answer fundamental questions: How is the mechanical state of the cell regulated by local protein expression and global pattering? In what way does stress feedback onto the larger developmental program? In this dissertation, we begin to approach these questions through the introduction and analysis of a multi-scale model of epithelial mechanics which explicitly connects cytoskeletal protein activity to tissue-level stress. In Chapter 2, we introduce the discrete Active Tension Network (ATN) model of cellular mechanics. ATNs are tissues that satisfy two primary assumptions: that the mechanical balance of cells is dominated by cortical tension and that myosin actively remodels the actin cytoskeleton in a stress-dependent manner. Remarkably, the interplay of these features allows for angle-preserving, i.e. 'isogonal', dilations or contractions of local cell geometry that do not generate stress. Asymptotically this model is stabilized provided there is mechanical feedback on expression of myosin within the cell; we take this to be a strong prediction to be tested. The ATN model exposes a fundamental connection between equilibrium cell geometry and its underlying force network. In Chapter 3, we relax the tension-net approximation and demonstrate that at equilibrium, epithelial tissues with non-uniform pressure have non-trivial geometric constraints that imply the network is described by a weighted `dual' triangulation. We show that the dual triangulation encodes all

Salicylic acid potentiates an agonist-dependent gain control that amplifies pathogen signals in the activation of defense mechanisms.

PubMed

Shirasu, K; Nakajima, H; Rajasekhar, V K; Dixon, R A; Lamb, C

1997-02-01

The phenylpropanoid-derived natural product salicylic acid (SA) plays a key role in disease resistance. However, SA administered in the absence of a pathogen is a paradoxically weak inductive signal, often requiring concentrations of 0.5 to 5 mM to induce acquired resistance or related defense mechanisms or to precondition signal systems. In contrast, endogenous SA accumulates to concentrations of < 70 microM at the site of attempted infection. Here, we show that although 10 to 100 microM SA had negligible effects when administered to soybean cell suspensions in the absence of a pathogen, physiological concentrations of SA markedly enhanced the induction of defense gene transcripts, H2O2 accumulation, and hypersensitive cell death by an avirulent strain of Pseudomonas syringae pv glycinea, with optimal effects being at approximately 50 microM. SA also synergistically enhanced H2O2 accumulation in response to the protein phosphatase type 2A inhibitor cantharidin in the absence of a pathogen. The synergistic effect of SA was potent, rapid, and insensitive to the protein synthesis inhibitor cycloheximide, and we conclude that SA stimulates an agonist-dependent gain control operating at an early step in the signal pathway for induction of the hypersensitive response. This fine control mechanism differs from previously described time-dependent, inductive coarse control mechanisms for SA action in the absence of a pathogen. Induction of H2O2 accumulation and hypersensitive cell death by avirulent P. s. glycinea was blocked by the phenylpropanoid synthesis inhibitor alpha-aminooxy-beta-phenylpropionic acid, and these responses could be rescued by exogenous SA. Because the agonist-dependent gain control operates at physiological levels of SA, we propose that rapid fine control signal amplification makes an important contribution to SA function in the induction of disease resistance mechanisms.

Active Control of Jets in Cross-Flow for Film Cooling Applications

NASA Technical Reports Server (NTRS)

Nikitopoulos, Dimitris E.

2003-01-01

Jets in cross-flow have applications in film cooling of gas turbine vanes, blades and combustor liners. Their cooling effectiveness depends on the extent to which the cool jet-fluid adheres to the cooled component surface. Lift-off of the cooling jet flow or other mechanisms promoting mixing, cause loss of cooling effectiveness as they allow the hot "free-stream" fluid to come in contact with the component surface. The premise of this project is that cooling effectiveness can be improved by actively controlling (e.9. forcing, pulsing) the jet flow. Active control can be applied to prevent/delay lift-off and suppress mixing. Furthermore, an actively controlled film-cooling system coupled with appropriate sensory input (e.g. temperature or heat flux) can adapt to spatial and temporal variations of the hot-gas path. Thus, it is conceivable that the efficiency of film-cooling systems can be improved, resulting in coolant fluid economy. It is envisioned that Micro Electro-Mechanical Systems (MEMS) will play a role in the realization of such systems. As a first step, a feasibility study will be conducted to evaluate the concept, identify actuation and sensory elements and develop a control strategy. Part of this study will be the design of a proof-of-concept experiment and collection of necessary data.

Control mechanism of double-rotator-structure ternary optical computer

NASA Astrophysics Data System (ADS)

Kai, SONG; Liping, YAN

2017-03-01

Double-rotator-structure ternary optical processor (DRSTOP) has two characteristics, namely, giant data-bits parallel computing and reconfigurable processor, which can handle thousands of data bits in parallel, and can run much faster than computers and other optical computer systems so far. In order to put DRSTOP into practical application, this paper established a series of methods, namely, task classification method, data-bits allocation method, control information generation method, control information formatting and sending method, and decoded results obtaining method and so on. These methods form the control mechanism of DRSTOP. This control mechanism makes DRSTOP become an automated computing platform. Compared with the traditional calculation tools, DRSTOP computing platform can ease the contradiction between high energy consumption and big data computing due to greatly reducing the cost of communications and I/O. Finally, the paper designed a set of experiments for DRSTOP control mechanism to verify its feasibility and correctness. Experimental results showed that the control mechanism is correct, feasible and efficient.

Bio-inspired passive actuator simulating an abalone shell mechanism for structural control

NASA Astrophysics Data System (ADS)

Yang, Henry T. Y.; Lin, Chun-Hung; Bridges, Daniel; Randall, Connor J.; Hansma, Paul K.

2010-10-01

An energy dispersion mechanism called 'sacrificial bonds and hidden length', which is found in some biological systems, such as abalone shells and bones, is the inspiration for new strategies for structural control. Sacrificial bonds and hidden length can substantially increase the stiffness and enhance energy dissipation in the constituent molecules of abalone shells and bone. Having been inspired by the usefulness and effectiveness of such a mechanism, which has evolved over millions of years and countless cycles of evolutions, the authors employ the conceptual underpinnings of this mechanism to develop a bio-inspired passive actuator. This paper presents a fundamental method for optimally designing such bio-inspired passive actuators for structural control. To optimize the bio-inspired passive actuator, a simple method utilizing the force-displacement-velocity (FDV) plots based on LQR control is proposed. A linear regression approach is adopted in this research to find the initial values of the desired parameters for the bio-inspired passive actuator. The illustrative examples, conducted by numerical simulation with experimental validation, suggest that the bio-inspired passive actuator based on sacrificial bonds and hidden length may be comparable in performance to state-of-the-art semi-active actuators.

Brain mechanisms that control sleep and waking

NASA Astrophysics Data System (ADS)

Siegel, Jerome

This review paper presents a brief historical survey of the technological and early research that laid the groundwork for recent advances in sleep-waking research. A major advance in this field occurred shortly after the end of World War II with the discovery of the ascending reticular activating system (ARAS) as the neural source in the brain stem of the waking state. Subsequent research showed that the brain stem activating system produced cortical arousal via two pathways: a dorsal route through the thalamus and a ventral route through the hypothalamus and basal forebrain. The nuclei, pathways, and neurotransmitters that comprise the multiple components of these arousal systems are described. Sleep is now recognized as being composed of two very different states: rapid eye movements (REMs) sleep and non-REM sleep. The major findings on the neural mechanisms that control these two sleep states are presented. This review ends with a discussion of two current views on the function of sleep: to maintain the integrity of the immune system and to enhance memory consolidation.

Active damping using a control structure interaction approach

NASA Astrophysics Data System (ADS)

Umland, Jeffrey W.

1991-12-01

The vibration control of flexible structures using electromagnetic actuators is investigated. A model of an electromagnetic voice coil actuator is developed from elementary theory, and the required parameters are measured. Given a constant magnetic field, the force output of the voice coil varies linearly with the current flowing through the coil. The primary damping mechanism of the actuator used is found to be Coulomb friction. It is seen that Coulomb friction inhibits the response of the actuator to low levels of excitation. It is also seen that the actuator displayed a nonlinear relationship between force and current indicating that the applied magnetic field was not constant. This nonlinearity leads to a closed loop instability. Several design improvements are considered. Four different feedback control laws are developed to add active damping to a structure. The actuator is used as both a point force source and as a link in a mechanism that applies bending moments at two places on the structure. The actuator is used as both a point force source and as a link in a mechanism that applies bending moments at two places on the structure. The first control law uses the actuator as a traditional passive vibration absorber. The second control law is direct structural velocity feedback plus direct proof mass position feedback. The third control strategy is also direct structural velocity feedback but using compensated feedback of the proof mass position. The compensator is designed according to an H infinity optimization technique. The fourth control law uses the actuator as an equivalent mechanical viscous damper connected to two points on the structure. The results show that using direct structural velocity feedback provides improved vibration suppression in comparison to a traditional vibration absorber. Furthermore, the tuning criteria is only restricted to maintaining the actuator's single degree of freedom natural frequency below those of the structure to which

Mechanically activated synthesis of PZT and its electromechanical properties

NASA Astrophysics Data System (ADS)

Liu, X.; Akdogan, E. K.; Safari, A.; Riman, R. E.

2005-08-01

Mechanical activation was successfully used to synthesize nanostructured phase-pure Pb(Zr0.7Ti0.3)O3 (PZT) powders. Lead zirconium titanium (PbZrTi) hydrous oxide precursor, synthesized from chemical co-precipitation, was mechanically activated in a NaCl matrix. The synthesized PZT particles were characterized by using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, laser-light diffraction, and nitrogen adsorption. Thermogravimetric analysis and differential thermal analysis were used to monitor dehydration and phase transformation of PbZrTi hydrous oxide precursor during mechanical activation. The best mechanical activation conditions corresponded to mechanically activating PbZrTi hydrous oxide precursor in a NaCl matrix with a NaCl/precursor weight ratio of 4:1 for 8 h. These conditions resulted in a dispersible phase-pure PZT powder with a median secondary-particle size of ˜110 nm. The properties of PZT 70/30 from mechanically activated powder, as measured on discs sintered at 1150 °C for 2 h, were found to be in close conformity to those obtained by a conventional mixed oxide solid state reaction route.

Whisking mechanics and active sensing

PubMed Central

Bush, Nicholas E; Solla, Sara A

2017-01-01

We describe recent advances in quantifying the three-dimensional (3D) geometry and mechanics of whisking. Careful delineation of relevant 3D reference frames reveals important geometric and mechanical distinctions between the localization problem (‘where’ is an object) and the feature extraction problem (‘what’ is an object). Head-centered and resting-whisker reference frames lend themselves to quantifying temporal and kinematic cues used for object localization. The whisking-centered reference frame lends itself to quantifying the contact mechanics likely associated with feature extraction. We offer the ‘windowed sampling’ hypothesis for active sensing: that rats can estimate an object’s spatial features by integrating mechanical information across whiskers during brief (25–60 ms) windows of ‘haptic enclosure’ with the whiskers, a motion that resembles a hand grasp. PMID:27632212

Whisking mechanics and active sensing.

PubMed

Bush, Nicholas E; Solla, Sara A; Hartmann, Mitra Jz

2016-10-01

We describe recent advances in quantifying the three-dimensional (3D) geometry and mechanics of whisking. Careful delineation of relevant 3D reference frames reveals important geometric and mechanical distinctions between the localization problem ('where' is an object) and the feature extraction problem ('what' is an object). Head-centered and resting-whisker reference frames lend themselves to quantifying temporal and kinematic cues used for object localization. The whisking-centered reference frame lends itself to quantifying the contact mechanics likely associated with feature extraction. We offer the 'windowed sampling' hypothesis for active sensing: that rats can estimate an object's spatial features by integrating mechanical information across whiskers during brief (25-60ms) windows of 'haptic enclosure' with the whiskers, a motion that resembles a hand grasp. Copyright © 2016. Published by Elsevier Ltd.

Computational modeling of the EGFR network elucidates control mechanisms regulating signal dynamics

PubMed Central

2009-01-01

Background The epidermal growth factor receptor (EGFR) signaling pathway plays a key role in regulation of cellular growth and development. While highly studied, it is still not fully understood how the signal is orchestrated. One of the reasons for the complexity of this pathway is the extensive network of inter-connected components involved in the signaling. In the aim of identifying critical mechanisms controlling signal transduction we have performed extensive analysis of an executable model of the EGFR pathway using the stochastic pi-calculus as a modeling language. Results Our analysis, done through simulation of various perturbations, suggests that the EGFR pathway contains regions of functional redundancy in the upstream parts; in the event of low EGF stimulus or partial system failure, this redundancy helps to maintain functional robustness. Downstream parts, like the parts controlling Ras and ERK, have fewer redundancies, and more than 50% inhibition of specific reactions in those parts greatly attenuates signal response. In addition, we suggest an abstract model that captures the main control mechanisms in the pathway. Simulation of this abstract model suggests that without redundancies in the upstream modules, signal transduction through the entire pathway could be attenuated. In terms of specific control mechanisms, we have identified positive feedback loops whose role is to prolong the active state of key components (e.g., MEK-PP, Ras-GTP), and negative feedback loops that help promote signal adaptation and stabilization. Conclusions The insights gained from simulating this executable model facilitate the formulation of specific hypotheses regarding the control mechanisms of the EGFR signaling, and further substantiate the benefit to construct abstract executable models of large complex biological networks. PMID:20028552

Mechanisms of disease: inflammasome activation and the development of type 2 diabetes

PubMed Central

Grant, Ryan W.; Dixit, Vishwa D.

2013-01-01

Over the recent past, the importance of aberrant immune cell activation as one of the contributing mechanisms to the development of insulin-resistance and type 2 diabetes (T2D) has been recognized. Among the panoply of pro-inflammatory cytokines that are linked to chronic metabolic diseases, new data suggests that interleukin-1β (IL-1β) may play an important role in initiating and sustaining inflammation-induced organ dysfunction in T2D. Therefore, factors that control secretion of bioactive IL-1β have therapeutic implications. In this regard, the identification of multiprotein scaffolding complexes, “inflammasomes,” has been a great advance in our understanding of this process. The secretion of bioactive IL-1β is predominantly controlled by activation of caspase-1 through assembly of a multiprotein scaffold, “inflammasome” that is composed of NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) ASC (apoptosis associated speck-like protein containing a CARD) and procaspase-1. The NLRP3 inflammasome appears to be an important sensor of metabolic dysregulation and controls obesity-associated insulin resistance and pancreatic beta cell dysfunction. Initial clinical “proof of concept” studies suggest that blocking IL-1β may favorably modulate factors related to development and treatment of T2D. However, this potential therapeutic approach remains to be fully substantiated through phase-II clinical studies. Here, we outline the new immunological mechanisms that link metabolic dysfunction to the emergence of chronic inflammation and discuss the opportunities and challenges of future therapeutic approaches to dampen NLRP3 inflammasome activation or IL-1β signaling for controlling type 2 diabetes. PMID:23483669

Effects of adult attachment and emotional distractors on brain mechanisms of cognitive control.

PubMed

Warren, Stacie L; Bost, Kelly K; Roisman, Glenn I; Silton, Rebecca Levin; Spielberg, Jeffrey M; Engels, Anna S; Choi, Eunsil; Sutton, Bradley P; Miller, Gregory A; Heller, Wendy

2010-12-01

Using data from 34 participants who completed an emotion-word Stroop task during functional magnetic resonance imaging, we examined the effects of adult attachment on neural activity associated with top-down cognitive control in the presence of emotional distractors. Individuals with lower levels of secure-base-script knowledge--reflected in an adult's inability to generate narratives in which attachment-related threats are recognized, competent help is provided, and the problem is resolved--demonstrated more activity in prefrontal cortical regions associated with emotion regulation (e.g., right orbitofrontal cortex) and with top-down cognitive control (left dorsolateral prefrontal cortex, anterior cingulate cortex, and superior frontal gyrus). Less efficient performance and related increases in brain activity suggest that insecure attachment involves a vulnerability to distraction by attachment-relevant emotional information and that greater cognitive control is required to attend to task-relevant, nonemotional information. These results contribute to the understanding of mechanisms through which attachment-related experiences may influence developmental adaptation.

Effects of Adult Attachment and Emotional Distractors on Brain Mechanisms of Cognitive Control

PubMed Central

Warren, Stacie L.; Bost, Kelly K.; Roisman, Glenn I.; Silton, Rebecca Levin; Spielberg, Jeffrey M.; Engels, Anna S.; Choi, Eunsil; Sutton, Bradley P.; Miller, Gregory A.; Heller, Wendy

2011-01-01

Using data from 34 participants who completed an emotion-word Stroop task during functional magnetic resonance imaging, we examined the effects of adult attachment on neural activity associated with top-down cognitive control in the presence of emotional distractors. Individuals with lower levels of secure-base-script knowledge—reflected in an adult’s inability to generate narratives in which attachment-related threats are recognized, competent help is provided, and the problem is resolved—demonstrated more activity in prefrontal cortical regions associated with emotion regulation (e.g., right orbitofrontal cortex) and with top-down cognitive control (left dorsolateral prefrontal cortex, anterior cingulate cortex, and superior frontal gyrus). Less efficient performance and related increases in brain activity suggest that insecure attachment involves a vulnerability to distraction by attachment-relevant emotional information and that greater cognitive control is required to attend to task-relevant, nonemotional information. These results contribute to the understanding of mechanisms through which attachment-related experiences may influence developmental adaptation. PMID:21098213

A Nodal-independent and tissue-intrinsic mechanism controls heart-looping chirality

NASA Astrophysics Data System (ADS)

Noël, Emily S.; Verhoeven, Manon; Lagendijk, Anne Karine; Tessadori, Federico; Smith, Kelly; Choorapoikayil, Suma; den Hertog, Jeroen; Bakkers, Jeroen

2013-11-01

Breaking left-right symmetry in bilateria is a major event during embryo development that is required for asymmetric organ position, directional organ looping and lateralized organ function in the adult. Asymmetric expression of Nodal-related genes is hypothesized to be the driving force behind regulation of organ laterality. Here we identify a Nodal-independent mechanism that drives asymmetric heart looping in zebrafish embryos. In a unique mutant defective for the Nodal-related southpaw gene, preferential dextral looping in the heart is maintained, whereas gut and brain asymmetries are randomized. As genetic and pharmacological inhibition of Nodal signalling does not abolish heart asymmetry, a yet undiscovered mechanism controls heart chirality. This mechanism is tissue intrinsic, as explanted hearts maintain ex vivo retain chiral looping behaviour and require actin polymerization and myosin II activity. We find that Nodal signalling regulates actin gene expression, supporting a model in which Nodal signalling amplifies this tissue-intrinsic mechanism of heart looping.

Burn Control Mechanisms in Tokamaks

NASA Astrophysics Data System (ADS)

Hill, M. A.; Stacey, W. M.

2015-11-01

Burn control and passive safety in accident scenarios will be an important design consideration in future tokamak reactors, in particular fusion-fission hybrid reactors, e.g. the Subcritical Advanced Burner Reactor. We are developing a burning plasma dynamics code to explore various aspects of burn control, with the intent to identify feedback mechanisms that would prevent power excursions. This code solves the coupled set of global density and temperature equations, using scaling relations from experimental fits. Predictions of densities and temperatures have been benchmarked against DIII-D data. We are examining several potential feedback mechanisms to limit power excursions: i) ion-orbit loss, ii) thermal instability density limits, iii) MHD instability limits, iv) the degradation of alpha-particle confinement, v) modifications to the radial current profile, vi) ``divertor choking'' and vii) Type 1 ELMs. Work supported by the US DOE under DE-FG02-00ER54538, DE-FC02-04ER54698.

Complete unconscious control: Using (in)action primes to demonstrate completely unconscious activation of inhibitory control mechanisms

PubMed Central

Hepler, Justin; Albarracin, Dolores

2018-01-01

Although robust evidence indicates that action initiation can occur unconsciously and unintentionally, the literature on action inhibition suggests that inhibition requires both conscious thought and intentionality. In prior research demonstrating automatic inhibition in response to unconsciously processed stimuli, the unconscious stimuli had previously been consciously associated with an inhibitory response within the context of the experiment, and participants had consciously formed a goal to activate inhibition processes when presented with the stimuli (because task instructions required participants to engage in inhibition when the stimuli occurred). Therefore, prior work suggests that some amount of conscious thought and intentionality are required for inhibitory control. In the present research, we recorded event-related potentials during two go/no-go experiments in which participants were subliminally primed with general action/inaction concepts that had never been consciously associated with task-specific responses. We provide the first demonstration that inhibitory control processes can be modulated completely unconsciously and unintentionally. PMID:23747649

From Concept-to-Flight: An Active Active Fluid Loop Based Thermal Control System for Mars Science Laboratory Rover

NASA Technical Reports Server (NTRS)

Birur, Gajanana C.; Bhandari, Pradeep; Bame, David; Karlmann, Paul; Mastropietro, A. J.; Liu, Yuanming; Miller, Jennifer; Pauken, Michael; Lyra, Jacqueline

2012-01-01

The Mars Science Laboratory (MSL) rover, Curiosity, which was launched on November 26, 2011, incorporates a novel active thermal control system to keep the sensitive electronics and science instruments at safe operating and survival temperatures. While the diurnal temperature variations on the Mars surface range from -120 C to +30 C, the sensitive equipment are kept within -40 C to +50 C. The active thermal control system is based on a single-phase mechanically pumped fluid loop (MPFL) system which removes or recovers excess waste heat and manages it to maintain the sensitive equipment inside the rover at safe temperatures. This paper will describe the entire process of developing this active thermal control system for the MSL rover from concept to flight implementation. The development of the rover thermal control system during its architecture, design, fabrication, integration, testing, and launch is described.

Efficient control-channel multifailure management mechanism in GMPLS-based optical networks

NASA Astrophysics Data System (ADS)

Muñoz, Raül; Martínez, Ricardo; Junyent, Gabriel

2006-12-01

In generalized multiprotocol label switching (GMPLS) architecture, the control channels between each pair of optical nodes are not forced to use the same physical link as the data/transport channels. The problem arises when, due to the fact of allowing the control channels to be physically diverse from the associated data links, there may not be any active control channels available while data channels are still in use. Control-channel faults should not have a service impact on the existing connections; that is, a link that is carrying data traffic must not be torn down because the control channel is no longer available. But, due to the lack of the control channel, the active traffic that is using the data link may no longer be guaranteed with the same level of recovery service (protection or restoration). Under these circumstances the link must be considered to be in a degraded state. This means that routing and signaling should be notified that new connections are not accepted and the link is advertised with no unreserved resources. For this purpose, here we propose a control-channel multifailure management mechanism involving routing, signaling, and link management with extended GMPLS-based protocol extensions to keep the same level of service (in terms of provisioning and recovery) when a link is in the degraded state.

Mechanisms of diminished natural killer cell activity in pregnant women and neonates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baley, J.E.; Schacter, B.Z.

1985-05-01

Because alterations in natural killer (NK) activity in the perinatal period may be important in the maintenance of a healthy pregnancy, the mechanisms by which these alterations are mediated in neonates and in pregnant and postpartum women was examined. NK activity, as measured in a 4-hr /sup 51/Cr-release assay and compared with adult controls, is significantly diminished in all three trimesters of pregnancy and in immediately postpartum women. In postpartum women, NK activity appears to be higher than in pregnant women, although this does not reach statistical significance. Pregnant and postpartum women have normal numbers of large granular lymphocytes andmore » normal target cell binding in an agarose single cell assay but decreased lysis of the bound target cells. NK activity of mononuclear cells from postpartum women, in addition, demonstrate a shift in distribution to higher levels of resistance to gamma-irradiation. Further, sera from postpartum women cause a similar shift to increased radioresistance in mononuclear cells from adult controls. Because radioresistance is a property of interleukin 2-stimulated NK, the shift to radioresistance may represent lymphokine-mediated stimulation occurring during parturition. In contrast, cord blood cells have a more profound decrease in NK activity as determined by /sup 51/Cr-release assay and decreases in both binding and lysis of bound target cells in the single cell assay. The resistance of NK activity in cord cells to gamma-irradiation is also increased, as seen in postpartum women. Cord blood serum, however, did not alter radioresistance or inhibit NK activity. The results suggest that the observed diminished NK activity in pregnant women and neonates arise by different mechanisms: an absence of mature NK cells in the neonate and an alteration of the NK cell in pregnancy leading to decreased killing.« less

Active noise control using a steerable parametric array loudspeaker.

PubMed

Tanaka, Nobuo; Tanaka, Motoki

2010-06-01

Arguably active noise control enables the sound suppression at the designated control points, while the sound pressure except the targeted locations is likely to augment. The reason is clear; a control source normally radiates the sound omnidirectionally. To cope with this problem, this paper introduces a parametric array loudspeaker (PAL) which produces a spatially focused sound beam due to the attribute of ultrasound used for carrier waves, thereby allowing one to suppress the sound pressure at the designated point without causing spillover in the whole sound field. First the fundamental characteristics of PAL are overviewed. The scattered pressure in the near field contributed by source strength of PAL is then described, which is needed for the design of an active noise control system. Furthermore, the optimal control law for minimizing the sound pressure at control points is derived, the control effect being investigated analytically and experimentally. With a view to tracking a moving target point, a steerable PAL based upon a phased array scheme is presented, with the result that the generation of a moving zone of quiet becomes possible without mechanically rotating the PAL. An experiment is finally conducted, demonstrating the validity of the proposed method.

Control plasma renin activity and changes in sympathetic tone as determinants of minoxidil-induced increase in plasma renin activity.

PubMed Central

O'Malley, K; Velasco, M; Wells, J; McNay, J L

1975-01-01

A study was made of the possible mechanism(s) underlying minoxidil-induced increase in plasma renin activity (PRA). 10 patients with essential hypertension were treated with minoxidil and subsequently with a combination of minoxidil plus propranolol. Minoxidil lowered mean arterial pressure 31.6 plus or minus 3.3 mm Hg, mean plus or minus SEM. There was an associated increase in both PRA, 6.26 plus or minus 2.43 NG/ML/H, and heart rate, 21.4 plus or minus 2.7 beats/min. The changes in PRA and heart rate were positively correlated, r, 0.79. Addition of propranolol reduced mean arterial pressure by a further 10.1 plus or minus 1.5 mm Hg and returned heart rate to control levels. Propranolol reduced PRA significantly but not to control levels. Control PRA positively correlated with PRA on minoxidil, r, 0.97, and with PRA on minoxidil plus propranolol, r, 0.98. We conclude that control PRA is a major determinant of change in PRA with minoxidil. Minoxidil increased PRA by at least two mechanisms: (a) an adrenergic mechanism closely related to change in heart rate and blocked by propranolol, and (b) a mechanism(s) not sensitive to propranolol and possibly related to decrease in renal perfusion pressure. PMID:1127099

Mechanical properties, biological activity and protein controlled release by poly(vinyl alcohol)-bioglass/chitosan-collagen composite scaffolds: a bone tissue engineering applications.

PubMed

Pon-On, Weeraphat; Charoenphandhu, Narattaphol; Teerapornpuntakit, Jarinthorn; Thongbunchoo, Jirawan; Krishnamra, Nateetip; Tang, I-Ming

2014-05-01

In the present study, composite scaffolds made with different weight ratios (0.5:1, 1:1 and 2:1) of bioactive glass (15Ca:80Si:5P) (BG)/polyvinyl alcohol (PVA) (PVABG) and chitosan (Chi)/collagen (Col) (ChiCol) were prepared by three mechanical freeze-thaw followed by freeze-drying to obtain the porous scaffolds. The mechanical properties and the in vitro biocompatibility of the composite scaffolds to simulated body fluid (SBF) and to rat osteoblast-like UMR-106 cells were investigated. The results from the studies indicated that the porosity and compressive strength were controlled by the weight ratio of PVABG:ChiCol. The highest compressive modulus of the composites made was 214.64 MPa which was for the 1:1 weight ratio PVABG:ChiCol. Mineralization study in SBF showed the formation of apatite crystals on the PVABG:ChiCol surface after 7 days of incubation. In vitro cell availability and proliferation tests confirmed the osteoblast attachment and growth on the PVABG:ChiCol surface. MTT and ALP tests on the 1:1 weight ratio PVABG:ChiCol composite indicated that the UMR-106 cells were viable. Alkaline phosphatase activity was found to increase with increasing culturing time. In addition, we showed the potential of PVABG:ChiCol drug delivery through PBS solution studies. 81.14% of BSA loading had been achieved and controlled release for over four weeks was observed. Our results indicated that the PVABG:ChiCol composites, especially the 1:1 weight ratio composite exhibited significantly improved mechanical, mineral deposition, biological properties and controlled release. This made them potential candidates for bone tissue engineering applications. Copyright © 2014 Elsevier B.V. All rights reserved.

Parallel language activation and inhibitory control in bimodal bilinguals.

PubMed

Giezen, Marcel R; Blumenfeld, Henrike K; Shook, Anthony; Marian, Viorica; Emmorey, Karen

2015-08-01

Findings from recent studies suggest that spoken-language bilinguals engage nonlinguistic inhibitory control mechanisms to resolve cross-linguistic competition during auditory word recognition. Bilingual advantages in inhibitory control might stem from the need to resolve perceptual competition between similar-sounding words both within and between their two languages. If so, these advantages should be lessened or eliminated when there is no perceptual competition between two languages. The present study investigated the extent of inhibitory control recruitment during bilingual language comprehension by examining associations between language co-activation and nonlinguistic inhibitory control abilities in bimodal bilinguals, whose two languages do not perceptually compete. Cross-linguistic distractor activation was identified in the visual world paradigm, and correlated significantly with performance on a nonlinguistic spatial Stroop task within a group of 27 hearing ASL-English bilinguals. Smaller Stroop effects (indexing more efficient inhibition) were associated with reduced co-activation of ASL signs during the early stages of auditory word recognition. These results suggest that inhibitory control in auditory word recognition is not limited to resolving perceptual linguistic competition in phonological input, but is also used to moderate competition that originates at the lexico-semantic level. Copyright © 2015 Elsevier B.V. All rights reserved.

Access control mechanism of wireless gateway based on open flow

NASA Astrophysics Data System (ADS)

Peng, Rong; Ding, Lei

2017-08-01

In order to realize the access control of wireless gateway and improve the access control of wireless gateway devices, an access control mechanism of SDN architecture which is based on Open vSwitch is proposed. The mechanism utilizes the features of the controller--centralized control and programmable. Controller send access control flow table based on the business logic. Open vSwitch helps achieve a specific access control strategy based on the flow table.

Matrix mechanics controls FHL2 movement to the nucleus to activate p21 expression

PubMed Central

Nakazawa, Naotaka; Sathe, Aneesh R.; Shivashankar, G. V.; Sheetz, Michael P.

2016-01-01

Substrate rigidity affects many physiological processes through mechanochemical signals from focal adhesion (FA) complexes that subsequently modulate gene expression. We find that shuttling of the LIM domain (domain discovered in the proteins, Lin11, Isl-1, and Mec-3) protein four-and-a-half LIM domains 2 (FHL2) between FAs and the nucleus depends on matrix mechanics. In particular, on soft surfaces or after the loss of force, FHL2 moves from FAs into the nucleus and concentrates at RNA polymerase (Pol) II sites, where it acts as a transcriptional cofactor, causing an increase in p21 gene expression that will inhibit growth on soft surfaces. At the molecular level, shuttling requires a specific tyrosine in FHL2, as well as phosphorylation by active FA kinase (FAK). Thus, we suggest that FHL2 phosphorylation by FAK is a critical, mechanically dependent step in signaling from soft matrices to the nucleus to inhibit cell proliferation by increasing p21 expression. PMID:27742790

Turing mechanism for homeostatic control of synaptic density during C. elegans growth

NASA Astrophysics Data System (ADS)

Brooks, Heather A.; Bressloff, Paul C.

2017-07-01

We propose a mechanism for the homeostatic control of synapses along the ventral cord of Caenorhabditis elegans during development, based on a form of Turing pattern formation on a growing domain. C. elegans is an important animal model for understanding cellular mechanisms underlying learning and memory. Our mathematical model consists of two interacting chemical species, where one is passively diffusing and the other is actively trafficked by molecular motors, which switch between forward and backward moving states (bidirectional transport). This differs significantly from the standard mechanism for Turing pattern formation based on the interaction between fast and slow diffusing species. We derive evolution equations for the chemical concentrations on a slowly growing one-dimensional domain, and use numerical simulations to demonstrate the insertion of new concentration peaks as the length increases. Taking the passive component to be the protein kinase CaMKII and the active component to be the glutamate receptor GLR-1, we interpret the concentration peaks as sites of new synapses along the length of C. elegans, and thus show how the density of synaptic sites can be maintained.

Control mechanisms in the third-generation planning. Case study: Control to realize sustainable cities

NASA Astrophysics Data System (ADS)

Wicaksono, A. D.

2017-06-01

Since the last few years, Indonesia has experienced important events that bring significant changes to the social, political and economic life. The changes directly or indirectly impact the field of planning. With the challenging condition which grows fast and is more complex ahead, and the greater demands on the role of planning, it is required that planning should have higher quality. This paper seeks to answer some questions as follows: (i) How are changes in paradigm and also the development of planning model for the current transition era?, (ii) What is the best way to improve the quality of planning control on the last generation planning model to realize sustainable city?. Analysis steps that will be used to achieve the paper objectives are: (i) Review of planning and sustainable cities theory, (ii) Pattern recognition, (iii) Identifying control mechanisms and sustainable urban forms, (iv) conceptualization. Based on discussion about sustainable cities and control mechanism, some conclusions can be generated as follows: (i) The third generation planning model is based on the theory of expanded system, emphasizing on the constraint of capacity and the ability of planners within the context of larger environment, (ii) There are various theoretical studies that recommend prescriptive model or solution for sustainable urban form and structure. The concepts of Sustainable Cities can be grouped in Neotraditional Development, Urban Containment, Compact City and The Eco-City. The four models above have criteria, namely (i) high density; (ii) a high level of diversity; (iii) mixed land use; (iv) compactness; (5) sustainable transport; (6) passive solar design; (7) Greening Ecological Design. The three main activities in control mechanisms are: Monitoring and Recommendation; a comparative review of the facts (conditions that exist or are developing) with the purpose (expected conditions, set out in urban planning) and recommendations; Evaluation, a review on the

Understanding The Neural Mechanisms Involved In Sensory Control Of Voice Production

PubMed Central

Parkinson, Amy L.; Flagmeier, Sabina G.; Manes, Jordan L.; Larson, Charles R.; Rogers, Bill; Robin, Donald A.

2012-01-01

Auditory feedback is important for the control of voice fundamental frequency (F0). In the present study we used neuroimaging to identify regions of the brain responsible for sensory control of the voice. We used a pitch-shift paradigm where subjects respond to an alteration, or shift, of voice pitch auditory feedback with a reflexive change in F0. To determine the neural substrates involved in these audio-vocal responses, subjects underwent fMRI scanning while vocalizing with or without pitch-shifted feedback. The comparison of shifted and unshifted vocalization revealed activation bilaterally in the superior temporal gyrus (STG) in response to the pitch shifted feedback. We hypothesize that the STG activity is related to error detection by auditory error cells located in the superior temporal cortex and efference copy mechanisms whereby this region is responsible for the coding of a mismatch between actual and predicted voice F0. PMID:22406500

Semi Active Control of Civil Structures, Analytical and Numerical Studies

NASA Astrophysics Data System (ADS)

Kerboua, M.; Benguediab, M.; Megnounif, A.; Benrahou, K. H.; Kaoulala, F.

Structural control for civil structures was born out of a need to provide safer and more efficient designs with the reality of limited resources. The purpose of structural control is to absorb and to reflect the energy introduced by dynamic loads such as winds, waves, earthquakes, and traffic. Today, the protection of civil structures from severe dynamic loading is typically achieved by allowing the structures to be damaged. Semi-active control devices, also called "smart" control devices, assume the positive aspects of both the passive and active control devices. A semi-active control strategy is similar to the active control strategy. Only here, the control actuator does not directly apply force to the structure, but instead it is used to control the properties of a passive energy device, a controllable passive damper. Semi-active control strategies can be used in many of the same civil applications as passive and active control. One method of operating smart cable dampers is in a purely passive capacity, supplying the dampers with constant optimal voltage. The advantages to this strategy are the relative simplicity of implementing the control strategy as compared to a smart or active control strategy and that the dampers are more easily optimally tuned in- place, eliminating the need to have passive dampers with unique optimal damping coefficients. This research investigated semi-active control of civil structures for natural hazard mitigation. The research has two components, the seismic protection of buildings and the mitigation of wind-induced vibration in structures. An ideal semi-active motion equation of a composite beam that consists of a cantilever beam bonded with a PZT patch using Hamilton's principle and Galerkin's method was treated. A series R-L and a parallel R-L shunt circuits are coupled into the motion equation respectively by means of the constitutive relation of piezoelectric material and Kirchhoff's law to control the beam vibration. A

Test Rig for Evaluating Active Turbine Blade Tip Clearance Control Concepts

NASA Technical Reports Server (NTRS)

Lattime, Scott B.; Steinetz, Bruce M.; Robbie, Malcolm G.

2003-01-01

Improved blade tip sealing in the high pressure compressor and high pressure turbine can provide dramatic improvements in specific fuel consumption, time-on-wing, compressor stall margin and engine efficiency as well as increased payload and mission range capabilities of both military and commercial gas turbine engines. The preliminary design of a mechanically actuated active clearance control (ACC) system for turbine blade tip clearance management is presented along with the design of a bench top test rig in which the system is to be evaluated. The ACC system utilizes mechanically actuated seal carrier segments and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. The purpose of this active clearance control system is to improve upon current case cooling methods. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, re-burst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). The active turbine blade tip clearance control system design presented herein will be evaluated to ensure that proper response and positional accuracy is achievable under simulated high-pressure turbine conditions. The test rig will simulate proper seal carrier pressure and temperature loading as well as the magnitudes and rates of blade tip clearance changes of an actual gas turbine engine. The results of these evaluations will be presented in future works.

A dual closed-loop control system for mechanical ventilation.

PubMed

Tehrani, Fleur; Rogers, Mark; Lo, Takkin; Malinowski, Thomas; Afuwape, Samuel; Lum, Michael; Grundl, Brett; Terry, Michael

2004-04-01

Closed-loop mechanical ventilation has the potential to provide more effective ventilatory support to patients with less complexity than conventional ventilation. The purpose of this study was to investigate the effectiveness of an automatic technique for mechanical ventilation. Two closed-loop control systems for mechanical ventilation are combined in this study. In one of the control systems several physiological data are used to automatically adjust the frequency and tidal volume of breaths of a patient. This method, which is patented under US Patent number 4986268, uses the criterion of minimal respiratory work rate to provide the patient with a natural pattern of breathing. The inputs to the system include data representing CO2 and O2 levels of the patient as well as respiratory compliance and airway resistance. The I:E ratio is adjusted on the basis of the respiratory time constant to allow for effective emptying of the lungs in expiration and to avoid intrinsic positive end expiratory pressure (PEEP). This system is combined with another closed-loop control system for automatic adjustment of the inspired fraction of oxygen of the patient. This controller uses the feedback of arterial oxygen saturation of the patient and combines a rapid stepwise control procedure with a proportional-integral-derivative (PID) control algorithm to automatically adjust the oxygen concentration in the patient's inspired gas. The dual closed-loop control system has been examined by using mechanical lung studies, computer simulations and animal experiments. In the mechanical lung studies, the ventilation controller adjusted the breathing frequency and tidal volume in a clinically appropriate manner in response to changes in respiratory mechanics. The results of computer simulations and animal studies under induced disturbances showed that blood gases were returned to the normal physiologic range in less than 25 s by the control system. In the animal experiments understeady

Design and control of a prosthetic leg for above-knee amputees operated in semi-active and active modes

NASA Astrophysics Data System (ADS)

Park, Jinhyuk; Yoon, Gun-Ha; Kang, Je-Won; Choi, Seung-Bok

2016-08-01

This paper proposes a new prosthesis operated in two different modes; the semi-active and active modes. The semi-active mode is achieved from a flow mode magneto-rheological (MR) damper, while the active mode is obtained from an electronically commutated (EC) motor. The knee joint part of the above knee prosthesis is equipped with the MR damper and EC motor. The MR damper generates reaction force by controlling the field-dependent yield stress of the MR fluid, while the EC motor actively controls the knee joint angle during gait cycle. In this work, the MR damper is designed as a two-end type flow mode mechanism without air chamber for compact size. On other hand, in order to predict desired knee joint angle to be controlled by EC motor, a polynomial prediction function using a statistical method is used. A nonlinear proportional-derivative controller integrated with the computed torque method is then designed and applied to both MR damper and EC motor to control the knee joint angle. It is demonstrated that the desired knee joint angle is well achieved in different walking velocities on the ground ground.

Optimisation of active suspension control inputs for improved performance of active safety systems

NASA Astrophysics Data System (ADS)

Čorić, Mirko; Deur, Joško; Xu, Li; Tseng, H. Eric; Hrovat, Davor

2018-01-01

A collocation-type control variable optimisation method is used to investigate the extent to which the fully active suspension (FAS) can be applied to improve the vehicle electronic stability control (ESC) performance and reduce the braking distance. First, the optimisation approach is applied to the scenario of vehicle stabilisation during the sine-with-dwell manoeuvre. The results are used to provide insights into different FAS control mechanisms for vehicle performance improvements related to responsiveness and yaw rate error reduction indices. The FAS control performance is compared to performances of the standard ESC system, optimal active brake system and combined FAS and ESC configuration. Second, the optimisation approach is employed to the task of FAS-based braking distance reduction for straight-line vehicle motion. Here, the scenarios of uniform and longitudinally or laterally non-uniform tyre-road friction coefficient are considered. The influences of limited anti-lock braking system (ABS) actuator bandwidth and limit-cycle ABS behaviour are also analysed. The optimisation results indicate that the FAS can provide competitive stabilisation performance and improved agility when compared to the ESC system, and that it can reduce the braking distance by up to 5% for distinctively non-uniform friction conditions.

Mechanisms of action of fluoride for caries control.

PubMed

Buzalaf, Marília Afonso Rabelo; Pessan, Juliano Pelim; Honório, Heitor Marques; ten Cate, Jacob Martien

2011-01-01

Fluoride was introduced into dentistry over 70 years ago, and it is now recognized as the main factor responsible for the dramatic decline in caries prevalence that has been observed worldwide. However, excessive fluoride intake during the period of tooth development can cause dental fluorosis. In order that the maximum benefits of fluoride for caries control can be achieved with the minimum risk of side effects, it is necessary to have a profound understanding of the mechanisms by which fluoride promotes caries control. In the 1980s, it was established that fluoride controls caries mainly through its topical effect. Fluoride present in low, sustained concentrations (sub-ppm range) in the oral fluids during an acidic challenge is able to absorb to the surface of the apatite crystals, inhibiting demineralization. When the pH is re-established, traces of fluoride in solution will make it highly supersaturated with respect to fluorhydroxyapatite, which will speed up the process of remineralization. The mineral formed under the nucleating action of the partially dissolved minerals will then preferentially include fluoride and exclude carbonate, rendering the enamel more resistant to future acidic challenges. Topical fluoride can also provide antimicrobial action. Fluoride concentrations as found in dental plaque have biological activity on critical virulence factors of S. mutans in vitro, such as acid production and glucan synthesis, but the in vivo implications of this are still not clear. Evidence also supports fluoride's systemic mechanism of caries inhibition in pit and fissure surfaces of permanent first molars when it is incorporated into these teeth pre-eruptively. Copyright © 2011 S. Karger AG, Basel.

Evaluation of an Active Clearance Control System Concept

NASA Technical Reports Server (NTRS)

Steinetz, Bruce M.; Lattime, Scott B.; DeCastro, Jonathan A.; Oswald, Jay; Melcher, Kevin J.

2005-01-01

Reducing blade tip clearances through active tip clearance control in the high pressure turbine can lead to significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life. Current engines employ scheduled cooling of the outer case flanges to reduce high pressure turbine tip clearances during cruise conditions. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, reburst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). In an effort to improve upon current thermal methods, a first generation mechanically-actuated active clearance control (ACC) system has been designed and fabricated. The system utilizes independent actuators, a segmented shroud structure, and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. Ambient temperature performance tests of this first generation ACC system assessed individual seal component leakage rates and both static and dynamic overall system leakage rates. The ability of the nine electric stepper motors to control the position of the seal carriers in both open- and closed-loop control modes for single and multiple cycles was investigated. The ability of the system to follow simulated engine clearance transients in closed-loop mode showed the system was able to track clearances to within a tight tolerance (0.001 in. error).

Evaluation of an Active Clearance Control System Concept

NASA Technical Reports Server (NTRS)

Steinetz, Bruce M.; Lattime, Scott B.; Taylor, Shawn; DeCastro, Jonathan A.; Oswald, Jay; Melcher, Kevin J.

2005-01-01

Reducing blade tip clearances through active tip clearance control in the high pressure turbine can lead to significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life. Current engines employ scheduled cooling of the outer case flanges to reduce high pressure turbine tip clearances during cruise conditions. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, reburst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). In an effort to improve upon current thermal methods, a first generation mechanically-actuated active clearance control (ACC) system has been designed and fabricated. The system utilizes independent actuators, a segmented shroud structure, and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. Ambient temperature performance tests of this first generation ACC system assessed individual seal component leakage rates and both static and dynamic overall system leakage rates. The ability of the nine electric stepper motors to control the position of the seal carriers in both open- and closed-loop control modes for single and multiple cycles was investigated. The ability of the system to follow simulated engine clearance transients in closed-loop mode showed the system was able to track clearances to within a tight tolerance ( 0.001 in. error).

Understanding Cytokine and Growth Factor Receptor Activation Mechanisms

PubMed Central

Atanasova, Mariya; Whitty, Adrian

2012-01-01

Our understanding of the detailed mechanism of action of cytokine and growth factor receptors – and particularly our quantitative understanding of the link between structure, mechanism and function – lags significantly behind our knowledge of comparable functional protein classes such as enzymes, G protein-coupled receptors, and ion channels. In particular, it remains controversial whether such receptors are activated by a mechanism of ligand-induced oligomerization, versus a mechanism in which the ligand binds to a pre-associated receptor dimer or oligomer that becomes activated through subsequent conformational rearrangement. A major limitation to progress has been the relative paucity of methods for performing quantitative mechanistic experiments on unmodified receptors expressed at endogenous levels on live cells. In this article we review the current state of knowledge on the activation mechanisms of cytokine and growth factor receptors, critically evaluate the evidence for and against the different proposed mechanisms, and highlight other key questions that remain unanswered. New approaches and techniques have led to rapid recent progress in this area, and the field is poised for major advances in the coming years, which promises to revolutionize our understanding of this large and biologically and medically important class of receptors. PMID:23046381

Fully Mechanically Controlled Automated Electron Microscopic Tomography

DOE PAGES

Liu, Jinxin; Li, Hongchang; Zhang, Lei; ...

2016-07-11

Knowledge of three-dimensional (3D) structures of each individual particles of asymmetric and flexible proteins is essential in understanding those proteins' functions; but their structures are difficult to determine. Electron tomography (ET) provides a tool for imaging a single and unique biological object from a series of tilted angles, but it is challenging to image a single protein for three-dimensional (3D) reconstruction due to the imperfect mechanical control capability of the specimen goniometer under both a medium to high magnification (approximately 50,000-160,000×) and an optimized beam coherence condition. Here, we report a fully mechanical control method for automating ET data acquisitionmore » without using beam tilt/shift processes. This method could reduce the accumulation of beam tilt/shift that used to compensate the error from the mechanical control, but downgraded the beam coherence. Our method was developed by minimizing the error of the target object center during the tilting process through a closed-loop proportional-integral (PI) control algorithm. The validations by both negative staining (NS) and cryo-electron microscopy (cryo-EM) suggest that this method has a comparable capability to other ET methods in tracking target proteins while maintaining optimized beam coherence conditions for imaging.« less

Age Related Decline in Postural Control Mechanisms.

ERIC Educational Resources Information Center

Stelmach, George E.; And Others

1989-01-01

Studied voluntary and reflexive mechanisms of postural control of young (N=8) and elderly (N=8) adults through measurement of reflexive reactions to large-fast and small-slow ankle rotation postural disturbances. Found reflexive mechanisms relatively intact for both groups although elderly appeared more disadvantaged when posture was under the…

Distinct promoter activation mechanisms modulate noise-driven HIV gene expression

NASA Astrophysics Data System (ADS)

Chavali, Arvind K.; Wong, Victor C.; Miller-Jensen, Kathryn

2015-12-01

Latent human immunodeficiency virus (HIV) infections occur when the virus occupies a transcriptionally silent but reversible state, presenting a major obstacle to cure. There is experimental evidence that random fluctuations in gene expression, when coupled to the strong positive feedback encoded by the HIV genetic circuit, act as a ‘molecular switch’ controlling cell fate, i.e., viral replication versus latency. Here, we implemented a stochastic computational modeling approach to explore how different promoter activation mechanisms in the presence of positive feedback would affect noise-driven activation from latency. We modeled the HIV promoter as existing in one, two, or three states that are representative of increasingly complex mechanisms of promoter repression underlying latency. We demonstrate that two-state and three-state models are associated with greater variability in noisy activation behaviors, and we find that Fano factor (defined as variance over mean) proves to be a useful noise metric to compare variability across model structures and parameter values. Finally, we show how three-state promoter models can be used to qualitatively describe complex reactivation phenotypes in response to therapeutic perturbations that we observe experimentally. Ultimately, our analysis suggests that multi-state models more accurately reflect observed heterogeneous reactivation and may be better suited to evaluate how noise affects viral clearance.

Long term mechanical properties of alkali activated slag

NASA Astrophysics Data System (ADS)

Zhu, J.; Zheng, W. Z.; Xu, Z. Z.; Leng, Y. F.; Qin, C. Z.

2018-01-01

This article reports a study on the microstructural and long-term mechanical properties of the alkali activated slag up to 180 days, and cement paste is studied as the comparison. The mechanical properties including compressive strength, flexural strength, axis tensile strength and splitting tensile strength are analyzed. The results showed that the alkali activated slag had higher compressive and tensile strength, Slag is activated by potassium silicate (K2SiO3) and sodium hydroxide (NaOH) solutions for attaining silicate modulus of 1 using 12 potassium silicate and 5.35% sodium hydroxide. The volume dosage of water is 35% and 42%. The results indicate that alkali activated slag is a kind of rapid hardening and early strength cementitious material with excellent long-term mechanical properties. Single row of holes block compressive strength, single-hole block compressive strength and standard solid brick compressive strength basically meet engineering requirements. The microstructures of alkali activated slag are studied by X-ray diffraction (XRD). The hydration products of alkali-activated slag are assured as hydrated calcium silicate and hydrated calcium aluminate.

Microalloying of transition metal silicides by mechanical activation and field-activated reaction

DOEpatents

Munir, Zuhair A [Davis, CA; Woolman, Joseph N [Davis, CA; Petrovic, John J [Los Alamos, NM

2003-09-02

Alloys of transition metal suicides that contain one or more alloying elements are fabricated by a two-stage process involving mechanical activation as the first stage and densification and field-activated reaction as the second stage. Mechanical activation, preferably performed by high-energy planetary milling, results in the incorporation of atoms of the alloying element(s) into the crystal lattice of the transition metal, while the densification and field-activated reaction, preferably performed by spark plasma sintering, result in the formation of the alloyed transition metal silicide. Among the many advantages of the process are its ability to accommodate materials that are incompatible in other alloying methods.

Molecular mechanism of APC/C activation by mitotic phosphorylation

PubMed Central

Alfieri, Claudio; Zhang, Ziguo; Yang, Jing; Maslen, Sarah; Skehel, Mark; Barford, David

2016-01-01

In eukaryotes, the anaphase-promoting complex/cyclosome (APC/C) regulates the ubiquitin-dependent proteolysis of specific cell cycle proteins to coordinate chromosome segregation in mitosis and entry into G1 (refs 1,2). The APC/C’s catalytic activity and ability to specify the destruction of particular proteins at different phases of the cell cycle are controlled by its interaction with two structurally related coactivator subunits (Cdc20 and Cdh1). Coactivators recognize substrate degrons3, and enhance the APC/C’s affinity for its cognate E2 (refs 4–6). During mitosis, cyclin-dependent kinase and polo kinase control Cdc20 and Cdh1-mediated activation of the APC/C. Hyper-phosphorylation of APC/C subunits, notably Apc1 and Apc3, is required for Cdc20 to activate the APC/C7–12, whereas phosphorylation of Cdh1 prevents its association with the APC/C9,13,14. Since both coactivators associate with the APC/C through their common C box15 and IR (Ile-Arg) tail motifs16,17, the mechanism underlying this differential regulation is unclear, as is the role of specific APC/C phosphorylation sites. Here, using cryo-electron microscopy (cryo-EM) and biochemical analysis, we define the molecular basis of how APC/C phosphorylation allows for its control by Cdc20. An auto-inhibitory (AI) segment of Apc1 acts as a molecular switch that in apo unphosphorylated APC/C interacts with the C-box binding site and obstructs engagement of Cdc20. Phosphorylation of the AI segment displaces it from the C-box binding site. Efficient phosphorylation of the AI segment, and thus relief of auto-inhibition, requires the recruitment of Cdk-cyclin-Cks to a hyper-phosphorylated loop of Apc3. We also find that the small molecule inhibitor, tosyl-L-arginine methyl ester (TAME), preferentially suppresses APC/CCdc20 rather than APC/CCdh1, and interacts with both the C-box and IR-tail binding sites. Our results reveal the mechanism for the regulation of mitotic APC/C by phosphorylation and provide a

Molecular mechanism of APC/C activation by mitotic phosphorylation.

PubMed

Zhang, Suyang; Chang, Leifu; Alfieri, Claudio; Zhang, Ziguo; Yang, Jing; Maslen, Sarah; Skehel, Mark; Barford, David

2016-05-12

In eukaryotes, the anaphase-promoting complex (APC/C, also known as the cyclosome) regulates the ubiquitin-dependent proteolysis of specific cell-cycle proteins to coordinate chromosome segregation in mitosis and entry into the G1 phase. The catalytic activity of the APC/C and its ability to specify the destruction of particular proteins at different phases of the cell cycle are controlled by its interaction with two structurally related coactivator subunits, Cdc20 and Cdh1. Coactivators recognize substrate degrons, and enhance the affinity of the APC/C for its cognate E2 (refs 4-6). During mitosis, cyclin-dependent kinase (Cdk) and polo-like kinase (Plk) control Cdc20- and Cdh1-mediated activation of the APC/C. Hyperphosphorylation of APC/C subunits, notably Apc1 and Apc3, is required for Cdc20 to activate the APC/C, whereas phosphorylation of Cdh1 prevents its association with the APC/C. Since both coactivators associate with the APC/C through their common C-box and Ile-Arg tail motifs, the mechanism underlying this differential regulation is unclear, as is the role of specific APC/C phosphorylation sites. Here, using cryo-electron microscopy and biochemical analysis, we define the molecular basis of how phosphorylation of human APC/C allows for its control by Cdc20. An auto-inhibitory segment of Apc1 acts as a molecular switch that in apo unphosphorylated APC/C interacts with the C-box binding site and obstructs engagement of Cdc20. Phosphorylation of the auto-inhibitory segment displaces it from the C-box-binding site. Efficient phosphorylation of the auto-inhibitory segment, and thus relief of auto-inhibition, requires the recruitment of Cdk-cyclin in complex with a Cdk regulatory subunit (Cks) to a hyperphosphorylated loop of Apc3. We also find that the small-molecule inhibitor, tosyl-l-arginine methyl ester, preferentially suppresses APC/C(Cdc20) rather than APC/C(Cdh1), and interacts with the binding sites of both the C-box and Ile-Arg tail motifs. Our

Gait asymmetry of transfemoral amputees using mechanical and microprocessor-controlled prosthetic knees.

PubMed

Kaufman, Kenton R; Frittoli, Serena; Frigo, Carlo A

2012-06-01

Amputees walk with an asymmetrical gait, which may lead to future musculoskeletal degenerative changes. The purpose of this study was to compare the gait asymmetry of active transfemoral amputees while using a passive mechanical knee joint or a microprocessor-controlled knee joint. Objective 3D gait measurements were obtained in 15 subjects (12 men and 3 women; age 42, range 26-57). Research participants were longtime users of a mechanical prosthesis (mean 20 years, range 3-36 years). Joint symmetry was calculated using a novel method that includes the entire waveform throughout the gait cycle. There was no significant difference in hip, knee and ankle kinematics symmetry when using the different knee prostheses. In contrast, the results demonstrated a significant improvement in lower extremity joint kinetics symmetry when using the microprocessor-controlled knee. Use of the microprocessor-controlled knee joint resulted in improved gait symmetry. These improvements may lead to a reduction in the degenerative musculoskeletal changes often experienced by amputees. Copyright © 2011 Elsevier Ltd. All rights reserved.

Homeostatic and non-homeostatic appetite control along the spectrum of physical activity levels: An updated perspective.

PubMed

Beaulieu, Kristine; Hopkins, Mark; Blundell, John; Finlayson, Graham

2017-12-28

The current obesogenic environment promotes physical inactivity and food consumption in excess of energy requirements, two important modifiable risk factors influencing energy balance. Habitual physical activity has been shown to impact not only energy expenditure, but also energy intake through mechanisms of appetite control. This review summarizes recent theory and evidence underpinning the role of physical activity in the homeostatic and non-homeostatic mechanisms controlling appetite. Energy intake along the spectrum of physical activity levels (inactive to highly active) appears to be J-shaped, with low levels of physical activity leading to dysregulated appetite and a mismatch between energy intake and expenditure. At higher levels, habitual physical activity influences homeostatic appetite control in a dual-process action by increasing the drive to eat through greater energy expenditure, but also by enhancing post-meal satiety, allowing energy intake to better match energy expenditure in response to hunger and satiety signals. There is clear presumptive evidence that physical activity energy expenditure can act as a drive (determinant) of energy intake. The influence of physical activity level on non-homeostatic appetite control is less clear, but low levels of physical activity may amplify hedonic states and behavioural traits favouring overconsumption indirectly through increased body fat. More evidence is required to understand the interaction between physical activity, appetite control and diet composition on passive overconsumption and energy balance. Furthermore, potential moderators of appetite control along the spectrum of physical activity, such as body composition, sex, and type, intensity and timing of physical activity, remain to be fully understood. Copyright © 2018 Elsevier Inc. All rights reserved.

In Situ Microstructural Control and Mechanical Testing Inside the Transmission Electron Microscope at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Wang, Baoming; Haque, M. A.

2015-08-01

With atomic-scale imaging and analytical capabilities such as electron diffraction and energy-loss spectroscopy, the transmission electron microscope has allowed access to the internal microstructure of materials like no other microscopy. It has been mostly a passive or post-mortem analysis tool, but that trend is changing with in situ straining, heating and electrical biasing. In this study, we design and demonstrate a multi-functional microchip that integrates actuators, sensors, heaters and electrodes with freestanding electron transparent specimens. In addition to mechanical testing at elevated temperatures, the chip can actively control microstructures (grain growth and phase change) of the specimen material. Using nano-crystalline aluminum, nickel and zirconium as specimen materials, we demonstrate these novel capabilities inside the microscope. Our approach of active microstructural control and quantitative testing with real-time visualization can influence mechanistic modeling by providing direct and accurate evidence of the fundamental mechanisms behind materials behavior.

Two Mechanisms to Avoid Control Conflicts Resulting from Uncoordinated Intent

NASA Technical Reports Server (NTRS)

Mishkin, Andrew H.; Dvorak, Daniel L.; Wagner, David A.; Bennett, Matthew B.

2013-01-01

This software implements a real-time access control protocol that is intended to make all connected users aware of the presence of other connected users, and which of them is currently in control of the system. Here, "in control" means that a single user is authorized and enabled to issue instructions to the system. The software The software also implements a goal scheduling mechanism that can detect situations where plans for the operation of a target system proposed by different users overlap and interact in conflicting ways. In such situations, the system can either simply report the conflict (rejecting one goal or the entire plan), or reschedule the goals in a way that does not conflict. The access control mechanism (and associated control protocol) is unique. Other access control mechanisms are generally intended to authenticate users, or exclude unauthorized access. This software does neither, and would likely depend on having some other mechanism to support those requirements.

An Active Micro Vibration Isolator with Zero-Power Controlled Magnetic Suspension Technology

NASA Astrophysics Data System (ADS)

Hoque, Md. Emdadul; Takasaki, Masaya; Ishino, Yuji; Suzuki, Hirohisa; Mizuno, Takeshi

In this paper, a three-degree-of-freedom vibration isolation system using active zero-power controlled magnetic suspension is presented in order to isolate vibrations transmitted from the ground and to attenuate the effect of direct disturbances on the table. The zero-compliance of the isolator for direct disturbances was realized by connecting a conventional mechanical spring in series with a negative spring produced by an active magnetic suspension mechanism. In this work, each degree-of-freedom-of-motion of the vibration isolator is treated analytically and it is shown that the developed system is capable to generate infinite stiffness in each mode. Experimental studies have been conducted as well to measure the effectiveness of the isolator under both types of disturbances. Further improvements for the developed system as well as the control techniques are also discussed.

14 CFR 27.923 - Rotor drive system and control mechanism tests.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Rotor drive system and control mechanism....923 Rotor drive system and control mechanism tests. (a) Each part tested as prescribed in this section... affect test results may be conducted. (b) Each rotor drive system and control mechanism must be tested...

14 CFR 27.923 - Rotor drive system and control mechanism tests.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Rotor drive system and control mechanism....923 Rotor drive system and control mechanism tests. (a) Each part tested as prescribed in this section... affect test results may be conducted. (b) Each rotor drive system and control mechanism must be tested...

Subjective Significance Shapes Arousal Effects on Modified Stroop Task Performance: A Duality of Activation Mechanisms Account.

PubMed

Imbir, Kamil K

2016-01-01

Activation mechanisms such as arousal are known to be responsible for slowdown observed in the Emotional Stroop and modified Stroop tasks. Using the duality of mind perspective, we may conclude that both ways of processing information (automatic or controlled) should have their own mechanisms of activation, namely, arousal for an experiential mind, and subjective significance for a rational mind. To investigate the consequences of both, factorial manipulation was prepared. Other factors that influence Stroop task processing such as valence, concreteness, frequency, and word length were controlled. Subjective significance was expected to influence arousal effects. In the first study, the task was to name the color of font for activation charged words. In the second study, activation charged words were, at the same time, combined with an incongruent condition of the classical Stroop task around a fixation point. The task was to indicate the font color for color-meaning words. In both studies, subjective significance was found to shape the arousal impact on performance in terms of the slowdown reduction for words charged with subjective significance.

The Mechanisms of Alcohol Control

PubMed Central

Carpenter, Christopher S.; Dobkin, Carlos; Warman, Casey

2015-01-01

A substantial economics literature documents that tighter alcohol controls reduce alcohol-related harms, but far less is known about mechanisms. We use the universe of Canadian mortality records to document that Canada’s Minimum Legal Drinking Age (MLDA) significantly reduces mortality rates of young men but has much smaller effects on women. Using drinking data that are far more detailed than in prior work, we document that the MLDA substantially reduces ‘extreme’ drinking among men but not women. Our results suggest that alcohol control efforts targeting young adults should focus on reducing extreme drinking behavior. PMID:27127308

Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration

PubMed Central

Tan, Quanyin; Deng, Chao; Li, Jinhui

2016-01-01

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation and leaching processes for REEs, and explored the feasibility of the method from both theoretical and practical standpoints. Results showed physicochemical changes of structural destruction and particle size reduction after mechanical activation, leading to the easy dissolution of REEs in the activated samples. Under optimal conditions, dissolution yields of 89.4%, 93.1% and 94.6% for Tb, Eu and Y, respectively, were achieved from activated waste phosphors using hydrochloric acid as the dissolution agent. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol. This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency. PMID:26819083

Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration.

PubMed

Tan, Quanyin; Deng, Chao; Li, Jinhui

2016-01-28

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation and leaching processes for REEs, and explored the feasibility of the method from both theoretical and practical standpoints. Results showed physicochemical changes of structural destruction and particle size reduction after mechanical activation, leading to the easy dissolution of REEs in the activated samples. Under optimal conditions, dissolution yields of 89.4%, 93.1% and 94.6% for Tb, Eu and Y, respectively, were achieved from activated waste phosphors using hydrochloric acid as the dissolution agent. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol. This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency.

Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration

NASA Astrophysics Data System (ADS)

Tan, Quanyin; Deng, Chao; Li, Jinhui

2016-01-01

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation and leaching processes for REEs, and explored the feasibility of the method from both theoretical and practical standpoints. Results showed physicochemical changes of structural destruction and particle size reduction after mechanical activation, leading to the easy dissolution of REEs in the activated samples. Under optimal conditions, dissolution yields of 89.4%, 93.1% and 94.6% for Tb, Eu and Y, respectively, were achieved from activated waste phosphors using hydrochloric acid as the dissolution agent. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol. This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency.

Mutational Analysis of Rab3 Function for Controlling Active Zone Protein Composition at the Drosophila Neuromuscular Junction

PubMed Central

Roche, John P.; Alsharif, Peter; Graf, Ethan R.

2015-01-01

At synapses, the release of neurotransmitter is regulated by molecular machinery that aggregates at specialized presynaptic release sites termed active zones. The complement of active zone proteins at each site is a determinant of release efficacy and can be remodeled to alter synapse function. The small GTPase Rab3 was previously identified as playing a novel role that controls the distribution of active zone proteins to individual release sites at the Drosophila neuromuscular junction. Rab3 has been extensively studied for its role in the synaptic vesicle cycle; however, the mechanism by which Rab3 controls active zone development remains unknown. To explore this mechanism, we conducted a mutational analysis to determine the molecular and structural requirements of Rab3 function at Drosophila synapses. We find that GTP-binding is required for Rab3 to traffick to synapses and distribute active zone components across release sites. Conversely, the hydrolytic activity of Rab3 is unnecessary for this function. Through a structure-function analysis we identify specific residues within the effector-binding switch regions that are required for Rab3 function and determine that membrane attachment is essential. Our findings suggest that Rab3 controls the distribution of active zone components via a vesicle docking mechanism that is consistent with standard Rab protein function. PMID:26317909

Linear and non-linear systems identification for adaptive control in mechanical applications vibration suppression

NASA Astrophysics Data System (ADS)

Cazzulani, Gabriele; Resta, Ferruccio; Ripamonti, Francesco

2012-04-01

During the last years, more and more mechanical applications saw the introduction of active control strategies. In particular, the need of improving the performances and/or the system health is very often associated to vibration suppression. This goal can be achieved considering both passive and active solutions. In this sense, many active control strategies have been developed, such as the Independent Modal Space Control (IMSC) or the resonant controllers (PPF, IRC, . . .). In all these cases, in order to tune and optimize the control strategy, the knowledge of the system dynamic behaviour is very important and it can be achieved both considering a numerical model of the system or through an experimental identification process. Anyway, dealing with non-linear or time-varying systems, a tool able to online identify the system parameters becomes a key-point for the control logic synthesis. The aim of the present work is the definition of a real-time technique, based on ARMAX models, that estimates the system parameters starting from the measurements of piezoelectric sensors. These parameters are returned to the control logic, that automatically adapts itself to the system dynamics. The problem is numerically investigated considering a carbon-fiber plate model forced through a piezoelectric patch.

Frequent Activation Delay-Induced Mechanical Dyssynchrony and Dysfunction in the Systemic Right Ventricle.

PubMed

Forsha, Daniel; Risum, Niels; Smith, P Brian; Kanter, Ronald J; Samad, Zainab; Barker, Piers; Kisslo, Joseph

2016-11-01

Patients with systemic right ventricles frequently experience progressive heart failure and conduction abnormalities leading to abnormal ventricular activation. Activation delay-induced mechanical dyssynchrony can contribute to ventricular failure and is identified by a classic strain pattern of paradoxical opposing wall motion that is an excellent predictor of response to cardiac resynchronization therapy in adults with left bundle branch block. The specific aims of this study were to compare right ventricular (RV) mechanics in an adult systemic right ventricle population versus control subjects, evaluate the feasibility of this RV strain pattern analysis, and determine the frequency of the classic pattern. Young adults (n = 25) with d-transposition of the great arteries, status post Mustard or Senning palliation (TGA-MS), were ambispectively enrolled and compared with healthy young adults (n = 30) who were prospectively enrolled. All subjects were imaged using novel three-apical view (18-segment) RV longitudinal speckle-tracking strain analysis (EchoPAC) and electrocardiographic data. Patients with TGA-MS had diminished RV global peak systolic strain compared with control subjects (-12.0 ± 4.0% vs -23.3 ± 2.3%, P < .001). Most patients with TGA-MS had intrinsic or left ventricular paced right bundle branch block. A classic pattern was present in 11 of 25 subjects (44%), but this pattern would have been missed in four of 11 based only on the RV four-chamber (six-segment) model. Only three subjects underwent cardiac resynchronization therapy. Both subjects who had the classic pattern responded to cardiac resynchronization therapy, whereas the one nonresponder did not have the classic pattern. Systemic right ventricles demonstrated decreased function and increased mechanical dyssynchrony. The classic pattern of activation delay-induced mechanical dyssynchrony was frequently seen in this TGA-MS population and associated with activation delays. This

Unconventional mechanisms control cyclic respiratory gas release in flying Drosophila.

PubMed

Lehmann, Fritz-Olaf; Heymann, Nicole

2005-10-01

The high power output of flight muscles places special demands on the respiratory gas exchange system in insects. In small insects, respiration relies on diffusion, and for elevated locomotor performance such as flight, instantaneous gas exchange rates typically co-vary with the animal's metabolic activity. By contrast, under certain conditions, instantaneous release rate of carbon dioxide from the fruit fly Drosophila flying in a virtual-reality flight arena may oscillate distinctly at low frequency (0.37+/-0.055 Hz), even though flight muscle mechanical power output requires constant metabolic activity. Cross-correlation analysis suggests that this uncoupling between respiratory and metabolic rate is not driven by conventional types of convective flow reinforcement such as abdominal pumping, but might result from two unusual mechanisms for tracheal breathing. Simplified analytical modeling of diffusive tracheal gas exchange suggests that cyclic release patterns in the insect occur as a consequence of the stochastically synchronized control of spiracle opening area by the four large thoracic spiracles. Alternatively, in-flight motion analysis of the abdomen and proboscis using infra-red video imaging suggests utilization of the proboscis extension reflex (PER) for tracheal convection. Although the respiratory benefit of synchronized spiracle opening activity in the fruit fly is unclear, proboscis-induced tracheal convection might potentially help to balance the local oxygen supply between different body compartments of the flying animal.

Coupling Active Hair Bundle Mechanics, Fast Adaptation, and Somatic Motility in a Cochlear Model

PubMed Central

Meaud, Julien; Grosh, Karl

2011-01-01

One of the central questions in the biophysics of the mammalian cochlea is determining the contributions of the two active processes, prestin-based somatic motility and hair bundle (HB) motility, to cochlear amplification. HB force generation is linked to fast adaptation of the transduction current via a calcium-dependent process and somatic force generation is driven by the depolarization caused by the transduction current. In this article, we construct a global mechanical-electrical-acoustical mathematical model of the cochlea based on a three-dimensional fluid representation. The global cochlear model is coupled to linearizations of nonlinear somatic motility and HB activity as well as to the micromechanics of the passive structural and electrical elements of the cochlea. We find that the active HB force alone is not sufficient to power high frequency cochlear amplification. However, somatic motility can overcome resistor-capacitor filtering by the basolateral membrane and deliver sufficient mechanical energy for amplification at basal locations. The results suggest a new theory for high frequency active cochlear mechanics, in which fast adaptation controls the transduction channel sensitivity and thereby the magnitude of the energy delivered by somatic motility. PMID:21641302

Laser metrology and optic active control system for GAIA

NASA Astrophysics Data System (ADS)

D'Angelo, F.; Bonino, L.; Cesare, S.; Castorina, G.; Mottini, S.; Bertinetto, F.; Bisi, M.; Canuto, E.; Musso, F.

2017-11-01

The Laser Metrology and Optic Active Control (LM&OAC) program has been carried out under ESA contract with the purpose to design and validate a laser metrology system and an actuation mechanism to monitor and control at microarcsec level the stability of the Basic Angle (angle between the lines of sight of the two telescopes) of GAIA satellite. As part of the program, a breadboard (including some EQM elements) of the laser metrology and control system has been built and submitted to functional, performance and environmental tests. In the followings we describe the mission requirements, the system architecture, the breadboard design, and finally the performed validation tests. Conclusion and appraisals from this experience are also reported.

Controlling Hydrogel Mechanics via Bio-Inspired Polymer-Nanoparticle Bond Dynamics.

PubMed

Li, Qiaochu; Barrett, Devin G; Messersmith, Phillip B; Holten-Andersen, Niels

2016-01-26

Interactions between polymer molecules and inorganic nanoparticles can play a dominant role in nanocomposite material mechanics, yet control of such interfacial interaction dynamics remains a significant challenge particularly in water. This study presents insights on how to engineer hydrogel material mechanics via nanoparticle interface-controlled cross-link dynamics. Inspired by the adhesive chemistry in mussel threads, we have incorporated iron oxide nanoparticles (Fe3O4 NPs) into a catechol-modified polymer network to obtain hydrogels cross-linked via reversible metal-coordination bonds at Fe3O4 NP surfaces. Unique material mechanics result from the supra-molecular cross-link structure dynamics in the gels; in contrast to the previously reported fluid-like dynamics of transient catechol-Fe(3+) cross-links, the catechol-Fe3O4 NP structures provide solid-like yet reversible hydrogel mechanics. The structurally controlled hierarchical mechanics presented here suggest how to develop hydrogels with remote-controlled self-healing dynamics.

Actively controlled shaft seals for aerospace applications

NASA Astrophysics Data System (ADS)

Salant, Richard F.

The objective of years 4 and 5 of this project (1992 and 1993) is to determine experimentally the behavior and operating characteristics of a controllable mechanical seal, and to identify potential problem areas. A controllable mechanical seal is one in which the thickness of the lubricating film separating the sealing surfaces is adjustable, and can be controlled by an electronic control system, based on information supplied by sensors that monitor the condition of the film. This work builds upon work done during years 1-3, in which a controllable mechanical seal was designed, analyzed, and fabricated. At the beginning of year 4, the mechanical seal and test rig was assembled, and preliminary testing begun. The five major tasks of years 4 and 5 encompass instrumentation, configuration changes of the mechanical seal to optimize its performance, systematic steady state tests, systematic transient tests, and a final report. During this reporting period, significant progress was made on instrumenting the test rig and modifying the design to optimize the seal's performance. Initial steady state tests were also performed.

Growth Control and Disease Mechanisms in Computational Embryogeny

NASA Technical Reports Server (NTRS)

Shapiro, Andrew A.; Yogev, Or; Antonsson, Erik K.

2008-01-01

This paper presents novel approach to applying growth control and diseases mechanisms in computational embryogeny. Our method, which mimics fundamental processes from biology, enables individuals to reach maturity in a controlled process through a stochastic environment. Three different mechanisms were implemented; disease mechanisms, gene suppression, and thermodynamic balancing. This approach was integrated as part of a structural evolutionary model. The model evolved continuum 3-D structures which support an external load. By using these mechanisms we were able to evolve individuals that reached a fixed size limit through the growth process. The growth process was an integral part of the complete development process. The size of the individuals was determined purely by the evolutionary process where different individuals matured to different sizes. Individuals which evolved with these characteristics have been found to be very robust for supporting a wide range of external loads.

Macrophages Exhibit a Large Repertoire of Activation States via Multiple Mechanisms of Macrophage-activating Factors.

PubMed

Sumiya, Y U; Inoue, Takahiro; Ishikawa, Mami; Inui, Toshio; Kuchiike, Daisuke; Kubo, Kentaro; Uto, Yoshihiro; Nishikata, Takahito

2016-07-01

Macrophages are important components of human defense systems and consequently key to antitumor immunity. Human-serum macrophage activation factor (serum MAF) can activate macrophages, making it a promising reagent for anticancer therapy. We established four different macrophage subtypes through introduction of different culture conditions to THP-1- and U937-derived macrophages. We assessed phagocytic activity to understand subtype responses to typical macrophage activation factors (MAFs) and the activation mechanisms of serum MAF. All four macrophage subtypes differed in their response to all MAFs. Moreover, serum MAF had two different activation mechanisms: N-acetylgalactosamine (GalNAc)-dependent and GalNAc-independent. Macrophage activation states and mechanisms are heterogeneous. Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.

Photoelectrocyclization as an activation mechanism for organelle-specific live-cell imaging probes.

PubMed

Tran, Mai N; Chenoweth, David M

2015-05-26

Photoactivatable fluorophores are useful tools in live-cell imaging owing to their potential for precise spatial and temporal control. In this report, a new photoactivatable organelle-specific live-cell imaging probe based on a 6π electrocyclization/oxidation mechanism is described. It is shown that this new probe is water-soluble, non-cytotoxic, cell-permeable, and useful for mitochondrial imaging. The probe displays large Stokes shifts in both pre-activated and activated forms, allowing simultaneous use with common dyes and fluorescent proteins. Sequential single-cell activation experiments in dense cellular environments demonstrate high spatial precision and utility in single- or multi-cell labeling experiments. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Seal Investigations of an Active Clearance Control System Concept

NASA Technical Reports Server (NTRS)

Steinetz, Bruce M.; Taylor, Shawn; Oswald, Jay; DeCastro, Jonathan A.

2006-01-01

In an effort to improve upon current thermal active clearance control methods, a first generation, fast-acting mechanically actuated, active clearance control system has been designed and installed into a non-rotating test rig. In order to harvest the benefit of tighter blade tip clearances, low-leakage seals are required for the actuated carrier segments of the seal shroud to prevent excessive leakage of compressor discharge (P3) cooling air. The test rig was designed and fabricated to facilitate the evaluation of these types of seals, identify seal leakage sources, and test other active clearance control system concepts. The objective of this paper is to present both experimental and analytical investigations into the nature of the face-seal to seal-carrier interface. Finite element analyses were used to examine face seal contact pressures and edge-loading under multiple loading conditions, varied E-seal positions and two new face seal heights. The analyses indicated that moving the E-seal inward radially and reducing face seal height would lead to more uniform contact conditions between the face seal and the carriers. Lab testing confirmed that moving the balance diameter inward radially caused a decrease in overall system leakage.

Sedimentation as a Control for Large Submarine Landslides: Mechanical Modeling and Analysis of the Santa Barbara Basin

NASA Astrophysics Data System (ADS)

Stoecklin, A.; Friedli, B.; Puzrin, A. M.

2017-11-01

The volume of submarine landslides is a key controlling factor for their damage potential. Particularly large landslides are found in active sedimentary regions. However, the mechanism controlling their volume, and in particular their thickness, remains unclear. Here we present a mechanism that explains how rapid sedimentation can lead to localized slope failure at a preferential depth and set the conditions for the emergence of large-scale slope-parallel landslides. We account for the contractive shearing behavior of the sediments, which locally accelerates the development of overpressures in the pore fluid, even on very mild slopes. When applied to the Santa Barbara basin, the mechanism offers an explanation for the regional variation in landslide thickness and their sedimentation-controlled recurrence. Although earthquakes are the most likely trigger for these mass movements, our results suggest that the sedimentation process controls the geometry of their source region. The mechanism introduced here is generally applicable and can provide initial conditions for subsequent landslide triggering, runout, and tsunami-source analyses in sedimentary regions.

Mechanical Backup For Fly-By-Wire Control System

NASA Technical Reports Server (NTRS)

Stewart, Eric C.

1992-01-01

Mechanical device eliminates need for redundant fly-by-wire subsystems. Main components are two linkages. One connected to control column in conventional, reversible control system. Other slides inside first linkage and connected to pilot's control wheel. In addition to aircraft applications, design used in control systems in which computer control desirable but safety backup systems required; for example, in boat rudders, engine controls in boats and automobiles, and controls in construction equipment.

Can mechanics control pattern formation in plants?

PubMed

Dumais, Jacques

2007-02-01

Development of the plant body entails many pattern forming events at scales ranging from the cellular level to the whole plant. Recent evidence suggests that mechanical forces play a role in establishing some of these patterns. The development of cellular configurations in glandular trichomes and the rippling of leaf surfaces are discussed in depth to illustrate how intricate patterns can emerge from simple and well-established molecular and cellular processes. The ability of plants to sense and transduce mechanical signals suggests that complex interactions between mechanics and chemistry are possible during plant development. The inclusion of mechanics alongside traditional molecular controls offers a more comprehensive view of developmental processes.

Top-Down Control of Visual Alpha Oscillations: Sources of Control Signals and Their Mechanisms of Action

PubMed Central

Wang, Chao; Rajagovindan, Rajasimhan; Han, Sahng-Min; Ding, Mingzhou

2016-01-01

Alpha oscillations (8–12 Hz) are thought to inversely correlate with cortical excitability. Goal-oriented modulation of alpha has been studied extensively. In visual spatial attention, alpha over the region of visual cortex corresponding to the attended location decreases, signifying increased excitability to facilitate the processing of impending stimuli. In contrast, in retention of verbal working memory, alpha over visual cortex increases, signifying decreased excitability to gate out stimulus input to protect the information held online from sensory interference. According to the prevailing model, this goal-oriented biasing of sensory cortex is effected by top-down control signals from frontal and parietal cortices. The present study tests and substantiates this hypothesis by (a) identifying the signals that mediate the top-down biasing influence, (b) examining whether the cortical areas issuing these signals are task-specific or task-independent, and (c) establishing the possible mechanism of the biasing action. High-density human EEG data were recorded in two experimental paradigms: a trial-by-trial cued visual spatial attention task and a modified Sternberg working memory task. Applying Granger causality to both sensor-level and source-level data we report the following findings. In covert visual spatial attention, the regions exerting top-down control over visual activity are lateralized to the right hemisphere, with the dipoles located at the right frontal eye field (FEF) and the right inferior frontal gyrus (IFG) being the main sources of top-down influences. During retention of verbal working memory, the regions exerting top-down control over visual activity are lateralized to the left hemisphere, with the dipoles located at the left middle frontal gyrus (MFG) being the main source of top-down influences. In both experiments, top-down influences are mediated by alpha oscillations, and the biasing effect is likely achieved via an inhibition

Immediate effects on neck pain and active range of motion after a single cervical high-velocity low-amplitude manipulation in subjects presenting with mechanical neck pain: a randomized controlled trial.

PubMed

Martínez-Segura, Raquel; Fernández-de-las-Peñas, César; Ruiz-Sáez, Mariana; López-Jiménez, Cristina; Rodríguez-Blanco, Cleofás

2006-09-01

The objective of this study is to analyze the immediate effects on neck pain and active cervical range of motion after a single cervical high-velocity low-amplitude (HVLA) manipulation or a control mobilization procedure in mechanical neck pain subjects. In addition, we assessed the possible correlation between neck pain and neck mobility. Seventy patients with mechanical neck pain (25 males and 45 females, aged 20-55 years) participated in this study. The lateral gliding test was used to establish the presence of an intervertebral joint dysfunction at the C3 through C4 or C4 through C5 levels. Subjects were divided randomly into either an experimental group, which received an HVLA thrust, or a control group, which received a manual mobilization procedure. The outcome measures were active cervical range of motion and neck pain at rest assessed pretreatment and 5 minutes posttreatment by an assessor blinded to the treatment allocation of the patient. Intragroup and intergroup comparisons were made with parametric tests. Within-group effect sizes were calculated using Cohen's d coefficient. Within-group changes showed a significant improvement in neck pain at rest and mobility after application of the manipulation (P < .001). The control group also showed a significant improvement in neck pain at rest (P < .01), flexion (P < .01), extension (P < .05), and both lateral flexions (P < .01), but not in rotation. Pre-post effect sizes were large for all the outcomes in the experimental group (d > 1), but were small to medium in the control mobilization group (0.2 < d < 0.6). The intergroup comparison showed that the experimental group obtained a greater improvement than the control group in all the outcome measures (P < .001). Decreased neck pain and increased range of motion were negatively associated for all cervical motions: the greater the increase in neck mobility, the less the pain at rest. Our results suggest that a single cervical HVLA manipulation was more

A methodology for identification and control of electro-mechanical actuators

PubMed Central

Tutunji, Tarek A.; Saleem, Ashraf

2015-01-01

Mechatronic systems are fully-integrated engineering systems that are composed of mechanical, electronic, and computer control sub-systems. These integrated systems use electro-mechanical actuators to cause the required motion. Therefore, the design of appropriate controllers for these actuators are an essential step in mechatronic system design. In this paper, a three-stage methodology for real-time identification and control of electro-mechanical actuator plants is presented, tested, and validated. First, identification models are constructed from experimental data to approximate the plants’ response. Second, the identified model is used in a simulation environment for the purpose of designing a suitable controller. Finally, the designed controller is applied and tested on the real plant through Hardware-in-the-Loop (HIL) environment. The described three-stage methodology provides the following practical contributions: • Establishes an easy-to-follow methodology for controller design of electro-mechanical actuators. • Combines off-line and on-line controller design for practical performance. • Modifies the HIL concept by using physical plants with computer control (rather than virtual plants with physical controllers). Simulated and experimental results for two case studies, induction motor and vehicle drive system, are presented in order to validate the proposed methodology. These results showed that electromechanical actuators can be identified and controlled using an easy-to-duplicate and flexible procedure. PMID:26150992

A methodology for identification and control of electro-mechanical actuators.

PubMed

Tutunji, Tarek A; Saleem, Ashraf

2015-01-01

Mechatronic systems are fully-integrated engineering systems that are composed of mechanical, electronic, and computer control sub-systems. These integrated systems use electro-mechanical actuators to cause the required motion. Therefore, the design of appropriate controllers for these actuators are an essential step in mechatronic system design. In this paper, a three-stage methodology for real-time identification and control of electro-mechanical actuator plants is presented, tested, and validated. First, identification models are constructed from experimental data to approximate the plants' response. Second, the identified model is used in a simulation environment for the purpose of designing a suitable controller. Finally, the designed controller is applied and tested on the real plant through Hardware-in-the-Loop (HIL) environment. The described three-stage methodology provides the following practical contributions: •Establishes an easy-to-follow methodology for controller design of electro-mechanical actuators.•Combines off-line and on-line controller design for practical performance.•Modifies the HIL concept by using physical plants with computer control (rather than virtual plants with physical controllers). Simulated and experimental results for two case studies, induction motor and vehicle drive system, are presented in order to validate the proposed methodology. These results showed that electromechanical actuators can be identified and controlled using an easy-to-duplicate and flexible procedure.

Acquisition of Dynamic Mechanical Analyzer and Stress-Controlled Rheometer for the Mechanical Characterization of Advanced Materials

DTIC Science & Technology

2017-06-27

Distribution Unlimited UU UU UU UU 27-06-2017 1-May-2016 30-Apr-2017 Final Report: Acquisition of Dynamic Mechanical Analyzer and Stress -ControlledRheometer...and Stress -Controlled Rheometer for the Mechanical Characterization of Advanced Materials ARO Grant # W911NF-16-1-0205 K. Wagener (PI) Chemistry

Molecular mechanism of the Syk activation switch.

PubMed

Tsang, Emily; Giannetti, Anthony M; Shaw, David; Dinh, Marie; Tse, Joyce K Y; Gandhi, Shaan; Ho, Hoangdung; Wang, Sandra; Papp, Eva; Bradshaw, J Michael

2008-11-21

Many immune signaling pathways require activation of the Syk tyrosine kinase to link ligation of surface receptors to changes in gene expression. Despite the central role of Syk in these pathways, the Syk activation process remains poorly understood. In this work we quantitatively characterized the molecular mechanism of Syk activation in vitro using a real time fluorescence kinase assay, mutagenesis, and other biochemical techniques. We found that dephosphorylated full-length Syk demonstrates a low initial rate of substrate phosphorylation that increases during the kinase reaction due to autophosphorylation. The initial rate of Syk activity was strongly increased by either pre-autophosphorylation or binding of phosphorylated immune tyrosine activation motif peptides, and each of these factors independently fully activated Syk. Deletion mutagenesis was used to identify regions of Syk important for regulation, and residues 340-356 of the SH2 kinase linker region were identified to be important for suppression of activity before activation. Comparison of the activation processes of Syk and Zap-70 revealed that Syk is more readily activated by autophosphorylation than Zap-70, although both kinases are rapidly activated by Src family kinases. We also studied Syk activity in B cell lysates and found endogenous Syk is also activated by phosphorylation and immune tyrosine activation motif binding. Together these experiments show that Syk functions as an "OR-gate" type of molecular switch. This mechanism of switch-like activation helps explain how Syk is both rapidly activated after receptor binding but also sustains activity over time to facilitate longer term changes in gene expression.

Spectrum and mechanisms of inflammasome activation by chitosan.

PubMed

Bueter, Chelsea L; Lee, Chrono K; Wang, Jennifer P; Ostroff, Gary R; Specht, Charles A; Levitz, Stuart M

2014-06-15

Chitosan, the deacetylated derivative of chitin, can be found in the cell wall of some fungi and is used in translational applications. We have shown that highly purified preparations of chitosan, but not chitin, activate the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in primed mouse bone marrow-derived macrophages (BMMΦ), inducing a robust IL-1β response. In this article, we further define specific cell types that are activated and delineate mechanisms of activation. BMMΦ differentiated to promote a classically activated (M1) phenotype released more IL-1β in response to chitosan than intermediate or alternatively activated macrophages (M2). Chitosan, but not chitin, induced a robust IL-1β response in mouse dendritic cells, peritoneal macrophages, and human PBMCs. Three mechanisms for NLRP3 inflammasome activation may contribute: K(+) efflux, reactive oxygen species, and lysosomal destabilization. The contributions of these mechanisms were tested using a K(+) efflux inhibitor, high extracellular potassium, a mitochondrial reactive oxygen species inhibitor, lysosomal acidification inhibitors, and a cathepsin B inhibitor. These studies revealed that each of these pathways participated in optimal NLRP3 inflammasome activation by chitosan. Finally, neither chitosan nor chitin stimulated significant release from unprimed BMMΦ of any of 22 cytokines and chemokines assayed. This study has the following conclusions: 1) chitosan, but not chitin, stimulates IL-1β release from multiple murine and human cell types; 2) multiple nonredundant mechanisms appear to participate in inflammasome activation by chitosan; and 3) chitin and chitosan are relatively weak stimulators of inflammatory mediators from unprimed BMMΦ. These data have implications for understanding the nature of the immune response to microbes and biomaterials that contain chitin and chitosan. Copyright © 2014 by The American Association of Immunologists, Inc.

Endoscope shaft-rigidity control mechanism: "FORGUIDE".

PubMed

Loeve, Arjo J; Plettenburg, Dick H; Breedveld, Paul; Dankelman, Jenny

2012-02-01

Recent developments in flexible endoscopy and other fields of medical technology have raised the need for compact slender shafts that can be made rigid and compliant at will. A novel compact mechanism, named FORGUIDE, with this functionality was developed. The FORGUIDE shaft rigidifies due to friction between a ring of cables situated between a spring and an inflated tube. A mathematical model for the FORGUIDE mechanism working principle was made and used to obtain understanding of this mechanism, predict the maximum rigidity of a FORGUIDE shaft design, and tune its design variables. The mathematical model gave suggestions for significant performance improvement by fine-tuning the design. A prototype FORGUIDE shaft was built and put to a series of bench tests. These tests showed that the FORGUIDE mechanism provides a reliable and simple way to control the rigidity of a flexible shaft. © 2011 IEEE

Temperature-Controlled Clamping and Releasing Mechanism

NASA Technical Reports Server (NTRS)

Rosing, David; Ford, Virginia

2005-01-01

A report describes the development of a mechanism that automatically clamps upon warming and releases upon cooling between temperature limits of approx. =180 K and approx. =293 K. The mechanism satisfied a need specific to a program that involved repeated excursions of a spectrometer between a room-temperature atmospheric environment and a cryogenic vacuum testing environment. The mechanism was also to be utilized in the intended application of the spectrometer, in which the spectrometer would be clamped for protection during launch of a spacecraft and released in the cold of outer space to allow it to assume its nominal configuration for scientific observations. The mechanism is passive in the sense that its operation does not depend on a control system and does not require any power other than that incidental to heating and cooling. The clamping and releasing action is effected by bolt-preloaded stacks of shape-memory-alloy (SMA) cylinders. In designing this mechanism, as in designing other, similar SMA mechanisms, it was necessary to account for the complex interplay among thermal expansion, elastic and inelastic deformation under load, and SMA thermomechanical properties.

Active twist control methodology for vibration reduction of a helicopter with dissimilar rotor system

NASA Astrophysics Data System (ADS)

Pawar, Prashant M.; Jung, Sung Nam

2009-03-01

In this work, an active vibration reduction of hingeless composite rotor blades with dissimilarity is investigated using the active twist concept and the optimal control theory. The induced shear strain on the actuation mechanism by the piezoelectric constant d15 from the PZN-8% PT-based single-crystal material is used to achieve more active twisting to suppress the extra vibrations. The optimal control algorithm is based on the minimization of an objective function comprised of quadratic functions of vibratory hub loads and voltage control harmonics. The blade-to-blade dissimilarity is modeled using the stiffness degradation of composite blades. The optimal controller is applied to various possible dissimilarities arising from different damage patterns of composite blades. The governing equations of motion are derived using Hamilton's principle. The effects of composite materials and smart actuators are incorporated into the comprehensive aeroelastic analysis system. Numerical results showing the impact of addressing the blade dissimilarities on hub vibrations and voltage inputs required to suppress the vibrations are demonstrated. It is observed that all vibratory shear forces are reduced considerably and the major harmonics of moments are reduced significantly. However, the controller needs further improvement to suppress 1/rev moment loads. A mechanism to achieve vibration reduction for the dissimilar rotor system has also been identified.

Helicopter Pitch-Control Mechanism Reduces Vibration

NASA Technical Reports Server (NTRS)

Lemont, H.

1986-01-01

Large forces accommodated without increasing weight of helicopter structure. New mechanism yields stiffer control and improves accuracy of pitch changes under load. As result, heavy casting not for gearbox, nor extra reinforcing members needed for fuselage bulkheads, stringers, skin, and other parts. In new mechanism, reaction forces developed in rotor hub. Long load paths to gearbox and fuselage elminated. Reaction member rigidly attached to hub and rotates with it. At lower end of reaction member, bearing forms bridge to fuselage through stationary beam and antirotation link. Beam connected to reaction plate through rods.

The mediator subunit Med23 contributes to controlling T-cell activation and prevents autoimmunity.

PubMed

Sun, Yang; Zhu, Xiaoyan; Chen, Xufeng; Liu, Haifeng; Xu, Yu; Chu, Yajing; Wang, Gang; Liu, Xiaolong

2014-10-10

T-cell activation is critical for successful immune responses and is controlled at multiple levels. Although many changes of T-cell receptor-associated signalling molecules affect T-cell activation, the transcriptional mechanisms that control this process remain largely unknown. Here we find that T cell-specific deletion of the mediator subunit Med23 leads to hyperactivation of T cells and aged Med23-deficient mice exhibit an autoimmune syndrome. Med23 specifically and consistently promotes the transcription of multiple negative regulators of T-cell activation. In the absence of Med23, the T-cell activation threshold is lower, which results in enhanced antitumour T-cell function. Cumulatively, our data suggest that Med23 contributes to controlling T-cell activation at the transcriptional level and prevents the development of autoimmunity.

Advance of Mechanically Controllable Break Junction for Molecular Electronics.

PubMed

Wang, Lu; Wang, Ling; Zhang, Lei; Xiang, Dong

2017-06-01

Molecular electronics stands for the ultimate size of functional elements, keeping up with an unstoppable trend over the past few decades. As a vital component of molecular electronics, single molecular junctions have attracted significant attention from research groups all over the world. Due to its pronounced superiority, the mechanically controllable break junctions (MCBJ) technique has been widely applied to characterize the dynamic performance of single molecular junctions. This review presents a system analysis for single-molecule junctions and offers an overview of four test-beds for single-molecule junctions, thus offering more insight into the mechanisms of electron transport. We mainly focus on the development of state-of-the-art mechanically controlled break junctions. The three-terminal gated MCBJ approaches are introduced to manipulate the electron transport of molecules, and MCBJs are combined with characterization techniques. Additionally, applications of MCBJs and remarkable properties of single molecules are addressed. Finally, the challenges and perspective for the mechanically controllable break junctions technique are provided.

Multivariable Dynamic Ankle Mechanical Impedance With Active Muscles

PubMed Central

Lee, Hyunglae; Krebs, Hermano Igo; Hogan, Neville

2015-01-01

Multivariable dynamic ankle mechanical impedance in two coupled degrees-of-freedom (DOFs) was quantified when muscles were active. Measurements were performed at five different target activation levels of tibialis anterior and soleus, from 10% to 30% of maximum voluntary contraction (MVC) with increments of 5% MVC. Interestingly, several ankle behaviors characterized in our previous study of the relaxed ankle were observed with muscles active: ankle mechanical impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness; stiffness was greater in the sagittal plane than in the frontal plane at all activation conditions for all subjects; and the coupling between dorsiflexion–plantarflexion and inversion–eversion was small—the two DOF measurements were well explained by a strictly diagonal impedance matrix. In general, ankle stiffness increased linearly with muscle activation in all directions in the 2-D space formed by the sagittal and frontal planes, but more in the sagittal than in the frontal plane, resulting in an accentuated “peanut shape.” This characterization of young healthy subjects’ ankle mechanical impedance with active muscles will serve as a baseline to investigate pathophysiological ankle behaviors of biomechanically and/or neurologically impaired patients. PMID:25203497

Topological mechanics: from metamaterials to active matter

NASA Astrophysics Data System (ADS)

Vitelli, Vincenzo

2015-03-01

Mechanical metamaterials are artificial structures with unusual properties, such as negative Poisson ratio, bistability or tunable acoustic response, which originate in the geometry of their unit cell. At the heart of such unusual behavior is often a mechanism: a motion that does not significantly stretch or compress the links between constituent elements. When activated by motors or external fields, these soft motions become the building blocks of robots and smart materials. In this talk, we discuss topological mechanisms that possess two key properties: (i) their existence cannot be traced to a local imbalance between degrees of freedom and constraints (ii) they are robust against a wide range of structural deformations or changes in material parameters. The continuum elasticity of these mechanical structures is captured by non-linear field theories with a topological boundary term similar to topological insulators and quantum Hall systems. We present several applications of these concepts to the design and experimental realization of 2D and 3D topological structures based on linkages, origami, buckling meta-materials and lastly active media that break time-reversal symmetry.

Logical Access Control Mechanisms in Computer Systems.

ERIC Educational Resources Information Center

Hsiao, David K.

The subject of access control mechanisms in computer systems is concerned with effective means to protect the anonymity of private information on the one hand, and to regulate the access to shareable information on the other hand. Effective means for access control may be considered on three levels: memory, process and logical. This report is a…

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

Mechanism of Growth Enhancement of Plants Induced by Active Species in Plasmas

NASA Astrophysics Data System (ADS)

Watanabe, Satoshi; Ono, Reoto; Hayashi, Nobuya

2015-09-01

Plant growth enhances when seeds are irradiated by plasma. However the mechanism of the growth enhancement by plasma has not been clarified. In this study, growth enhancement of plants using various active species and variation of plant cells are investigated. RF plasma is generated under conditions where pressure is 60 Pa and input electrical power is 60 W. Irradiation period varies from 0 (control) to 75 min. Air plasma shows maximum growth of plants with irradiation period of 60 min on the other hand, oxygen plasma shows the maximum growth with irradiation period of 15 min. From change of gaseous species and pressure dependence, growth enhancing factor is expected to be active oxygen species produced in plasma. According to gene expression analysis of Arabidopsis, there are two speculated mechanism of plant growth enhancement. The first is acceleration of cell cycle by gene expressions of photosynthesis and glycolytic pathway, and the second is increase of cell size via plant hormone production.

Controlling self-sustained spiking activity by adding or removing one network link

NASA Astrophysics Data System (ADS)

Xu, Kesheng; Huang, Wenwen; Li, Baowen; Dhamala, Mukesh; Liu, Zonghua

2013-06-01

Being able to control the neuronal spiking activity in specific brain regions is central to a treatment scheme in several brain disorders such as epileptic seizures, mental depression, and Parkinson's diseases. Here, we present an approach for controlling self-sustained oscillations by adding or removing one directed network link in coupled neuronal oscillators, in contrast to previous approaches of adding stimuli or noise. We find that such networks can exhibit a variety of activity patterns such as on-off switch, sustained spikes, and short-term spikes. We derive the condition for a specific link to be the controller of the on-off effect. A qualitative analysis is provided to facilitate the understanding of the mechanism for spiking activity by adding one link. Our findings represent the first report on generating spike activity with the addition of only one directed link to a network and provide a deeper understanding of the microscopic roots of self-sustained spiking.

An active locking mechanism for assembling 3D micro structures

NASA Astrophysics Data System (ADS)

Zhang, Ping; Mayyas, Mohammad; Lee, Woo Ho; Popa, Dan; Shiakolas, Panos; Stephanou, Harry; Chiao, J. C.

2007-01-01

Microassembly is an enabling technology to build 3D microsystems consisting of microparts made of different materials and processes. Multiple microparts can be connected together to construct complicated in-plane and out-of-plane microsystems by using compliant mechanical structures such as micro hinges and snap fasteners. This paper presents design, fabrication, and assembly of an active locking mechanism that provides mechanical and electrical interconnections between mating microparts. The active locking mechanism is composed of thermally actuated Chevron beams and sockets. Assembly by means of an active locking mechanism offers more flexibility in designing microgrippers as it reduces or minimizes mating force, which is one of the main reasons causing fractures in a microgripper during microassembly operation. Microgrippers, microparts, and active locking mechanisms were fabricated on a silicon substrate using the deep reactive ion etching (DRIE) processes with 100-um thick silicon on insulator (SOI) wafers. A precision robotic assembly platform with a dual microscope vision system was used to automate the manipulation and assembly processes of microparts. The assembly sequence includes (1) tether breaking and picking up of a micropart by using an electrothermally actuated microgripper, (2) opening of a socket area for zero-force insertion, (3) a series of translation and rotation of a mating micropart to align it onto the socket, (4) insertion of a micropart into the socket, and (5) deactivation and releasing of locking fingers. As a result, the micropart was held vertically to the substrate and locked by the compliance of Chevron beams. Microparts were successfully assembled using the active locking mechanism and the measured normal angle was 89.2°. This active locking mechanism provides mechanical and electrical interconnections, and it can potentially be used to implement a reconfigurable microrobot that requires complex assembly of multiple links and

Mechanism by which BMI influences leisure-time physical activity behavior.

PubMed

Godin, Gaston; Bélanger-Gravel, Ariane; Nolin, Bertrand

2008-06-01

The objective of this prospective study was to clarify the mechanism by which BMI influences leisure-time physical activity. This was achieved in accordance with the assumptions underlying the Theory of Planned Behavior (TPB), considered as one of the most useful theories to predict behavior adoption. At baseline, a sample of 1,530 respondents completed a short questionnaire to measure intention and perceived behavioral control (PBC), the two proximal determinants of behavior of TPB. Past behavior, sociodemographic variables, and weight and height were also assessed. The dependent variable, leisure-time physical activity was assessed 3 months later. Hierarchical multiple regression analyses revealed that BMI is a direct predictor of future leisure-time physical activity, not mediated by the variables of TPB. Additional hierarchical analyses indicated that BMI was not a moderator of the intention-behavior and PBC-behavior relationships. The results of this study suggest that high BMI is a significant negative determinant of leisure-time physical activity. This observation reinforces the importance of preventing weight gain as a health promotion strategy for avoiding a sedentary lifestyle.

Active Flow Control in an Aggressive Transonic Diffuser

NASA Astrophysics Data System (ADS)

Skinner, Ryan W.; Jansen, Kenneth E.

2017-11-01

A diffuser exchanges upstream kinetic energy for higher downstream static pressure by increasing duct cross-sectional area. The resulting stream-wise and span-wise pressure gradients promote extensive separation in many diffuser configurations. The present computational work evaluates active flow control strategies for separation control in an asymmetric, aggressive diffuser of rectangular cross-section at inlet Mach 0.7 and Re 2.19M. Corner suction is used to suppress secondary flows, and steady/unsteady tangential blowing controls separation on both the single ramped face and the opposite flat face. We explore results from both Spalart-Allmaras RANS and DDES turbulence modeling frameworks; the former is found to miss key physics of the flow control mechanisms. Simulated baseline, steady, and unsteady blowing performance is validated against experimental data. Funding was provided by Northrop Grumman Corporation, and this research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357.

A balance of activity in brain control and reward systems predicts self-regulatory outcomes

PubMed Central

Chen, Pin-Hao A.; Huckins, Jeremy F.; Hofmann, Wilhelm; Kelley, William M.; Heatherton, Todd F.

2017-01-01

Abstract Previous neuroimaging work has shown that increased reward-related activity following exposure to food cues is predictive of self-control failure. The balance model suggests that self-regulation failures result from an imbalance in reward and executive control mechanisms. However, an open question is whether the relative balance of activity in brain systems associated with executive control (vs reward) supports self-regulatory outcomes when people encounter tempting cues in daily life. Sixty-nine chronic dieters, a population known for frequent lapses in self-control, completed a food cue-reactivity task during an fMRI scanning session, followed by a weeklong sampling of daily eating behaviors via ecological momentary assessment. We related participants’ food cue activity in brain systems associated with executive control and reward to real-world eating patterns. Specifically, a balance score representing the amount of activity in brain regions associated with self-regulatory control, relative to automatic reward-related activity, predicted dieters’ control over their eating behavior during the following week. This balance measure may reflect individual self-control capacity and be useful for examining self-regulation success in other domains and populations. PMID:28158874

A balance of activity in brain control and reward systems predicts self-regulatory outcomes.

PubMed

Lopez, Richard B; Chen, Pin-Hao A; Huckins, Jeremy F; Hofmann, Wilhelm; Kelley, William M; Heatherton, Todd F

2017-05-01

Previous neuroimaging work has shown that increased reward-related activity following exposure to food cues is predictive of self-control failure. The balance model suggests that self-regulation failures result from an imbalance in reward and executive control mechanisms. However, an open question is whether the relative balance of activity in brain systems associated with executive control (vs reward) supports self-regulatory outcomes when people encounter tempting cues in daily life. Sixty-nine chronic dieters, a population known for frequent lapses in self-control, completed a food cue-reactivity task during an fMRI scanning session, followed by a weeklong sampling of daily eating behaviors via ecological momentary assessment. We related participants' food cue activity in brain systems associated with executive control and reward to real-world eating patterns. Specifically, a balance score representing the amount of activity in brain regions associated with self-regulatory control, relative to automatic reward-related activity, predicted dieters' control over their eating behavior during the following week. This balance measure may reflect individual self-control capacity and be useful for examining self-regulation success in other domains and populations. © The Author (2017). Published by Oxford University Press.

Incentive-Rewarding Mechanism for User-position Control in Mobile Services

NASA Astrophysics Data System (ADS)

Yoshino, Makoto; Sato, Kenichiro; Shinkuma, Ryoichi; Takahashi, Tatsuro

When the number of users in a service area increases in mobile multimedia services, no individual user can obtain satisfactory radio resources such as bandwidth and signal power because the resources are limited and shared. A solution for such a problem is user-position control. In the user-position control, the operator informs users of better communication areas (or spots) and navigates them to these positions. However, because of subjective costs caused by subjects moving from their original to a new position, they do not always attempt to move. To motivate users to contribute their resources in network services that require resource contributions for users, incentive-rewarding mechanisms have been proposed. However, there are no mechanisms that distribute rewards appropriately according to various subjective factors involving users. Furthermore, since the conventional mechanisms limit how rewards are paid, they are applicable only for the network service they targeted. In this paper, we propose a novel incentive-rewarding mechanism to solve these problems, using an external evaluator and interactive learning agents. We also investigated ways of appropriately controlling rewards based on user contributions and system service quality. We applied the proposed mechanism and reward control to the user-position control, and demonstrated its validity.

Applying Workspace Limitations in a Velocity-Controlled Robotic Mechanism

NASA Technical Reports Server (NTRS)

Abdallah, Muhammad E. (Inventor); Hargrave, Brian (Inventor); Platt, Robert J., Jr. (Inventor)

2014-01-01

A robotic system includes a robotic mechanism responsive to velocity control signals, and a permissible workspace defined by a convex-polygon boundary. A host machine determines a position of a reference point on the mechanism with respect to the boundary, and includes an algorithm for enforcing the boundary by automatically shaping the velocity control signals as a function of the position, thereby providing smooth and unperturbed operation of the mechanism along the edges and corners of the boundary. The algorithm is suited for application with higher speeds and/or external forces. A host machine includes an algorithm for enforcing the boundary by shaping the velocity control signals as a function of the reference point position, and a hardware module for executing the algorithm. A method for enforcing the convex-polygon boundary is also provided that shapes a velocity control signal via a host machine as a function of the reference point position.

Tractor Mechanics: Learning Activity Packages 1-19.

ERIC Educational Resources Information Center

Clemson Univ., SC. Vocational Education Media Center.

Learning activity packages are presented for teaching tractor mechanics. The first of two sections deals with miscellaneous tasks and contains learning activity packages on cleaning the tractor and receiving new tractor parts. Section 2 is concerned with maintaining and servicing the electrical system, and it includes the following learning…

Active control: an investigation method for combustion instabilities

NASA Astrophysics Data System (ADS)

Poinsot, T.; Yip, B.; Veynante, D.; Trouvé, A.; Samaniego, J. M.; Candel, S.

1992-07-01

Closed-loop active control methods and their application to combustion instabilities are discussed. In these methods the instability development is impeded with a feedback control loop: the signal provided by a sensor monitoring the flame or pressure oscillations is processed and sent back to actuators mounted on the combustor or on the feeding system. Different active control systems tested on a non-premixed multiple-flame turbulent combustor are described. These systems can suppress all unstable plane modes of oscillation (i.e. low frequency modes). The active instability control (AIC) also constitutes an original and powerful technique for studies of mechanisms leading to instability or resulting from the instability. Two basic applications of this kind are described. In the first case the flame is initially controlled with AIC, the feedback loop is then switched off and the growth of the instability is analysed through high speed Schlieren cinematography and simultaneous sound pressure and reaction rate measurements. Three phases are identified during th growth of the oscillations: (1) a linear phase where acoustic waves induce a flapping motion of the flame sheets without interaction between sheets, (2) a modulation phase, where flame sheets interact randomly and (3) a nonlinear phase where the flame sheets are broken and a limit cycle is reached. In the second case we investigate different types of flame extinctions associated with combustion instability. It is shown that pressure oscillations may lead to partial or total extinctions. Extinctions occur in various forms but usually follow a rapid growth of pressure oscillations. The flame is extinguished during the modulation phase observed in the initiation experiments. In these studies devoted to transient instability phenomena, the control system constitutes a unique investigation tool because it is difficult to obtain the same information by other means. Implications for modelling and prediction of

Simple size-controlled synthesis of Au nanoparticles and their size-dependent catalytic activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suchomel, Petr; Kvitek, Libor; Prucek, Robert

The controlled preparation of Au nanoparticles (NPs) in the size range of 6 to 22 nm is explored in this study. The Au NPs were prepared by the reduction of tetrachloroauric acid using maltose in the presence of nonionic surfactant Tween 80 at various concentrations to control the size of the resulting Au NPs. With increasing concentration of Tween 80 a decrease in the size of produced Au NPs was observed, along with a significant decrease in their size distribution. The size-dependent catalytic activity of the synthesized Au NPs was tested in the reduction of 4-nitrophenol with sodium borohydride, resultingmore » in increasing catalytic activity with decreasing size of the prepared nanoparticles. Eley-Rideal catalytic mechanism emerges as the more probable, in contrary to the Langmuir-Hinshelwood mechanism reported for other noble metal nanocatalysts.« less

Simple size-controlled synthesis of Au nanoparticles and their size-dependent catalytic activity

DOE PAGES

Suchomel, Petr; Kvitek, Libor; Prucek, Robert; ...

2018-03-15

The controlled preparation of Au nanoparticles (NPs) in the size range of 6 to 22 nm is explored in this study. The Au NPs were prepared by the reduction of tetrachloroauric acid using maltose in the presence of nonionic surfactant Tween 80 at various concentrations to control the size of the resulting Au NPs. With increasing concentration of Tween 80 a decrease in the size of produced Au NPs was observed, along with a significant decrease in their size distribution. The size-dependent catalytic activity of the synthesized Au NPs was tested in the reduction of 4-nitrophenol with sodium borohydride, resultingmore » in increasing catalytic activity with decreasing size of the prepared nanoparticles. Eley-Rideal catalytic mechanism emerges as the more probable, in contrary to the Langmuir-Hinshelwood mechanism reported for other noble metal nanocatalysts.« less

Controlled membrane translocation provides a mechanism for signal transduction and amplification

NASA Astrophysics Data System (ADS)

Langton, Matthew J.; Keymeulen, Flore; Ciaccia, Maria; Williams, Nicholas H.; Hunter, Christopher A.

2017-05-01

Transmission and amplification of chemical signals across lipid bilayer membranes is of profound significance in many biological processes, from the development of multicellular organisms to information processing in the nervous system. In biology, membrane-spanning proteins are responsible for the transmission of chemical signals across membranes, and signal transduction is often associated with an amplified signalling cascade. The ability to reproduce such processes in artificial systems has potential applications in sensing, controlled drug delivery and communication between compartments in tissue-like constructs of synthetic vesicles. Here we describe a mechanism for transmitting a chemical signal across a membrane based on the controlled translocation of a synthetic molecular transducer from one side of a lipid bilayer membrane to the other. The controlled molecular motion has been coupled to the activation of a catalyst on the inside of a vesicle, which leads to a signal-amplification process analogous to the biological counterpart.

Coupling active hair bundle mechanics, fast adaptation, and somatic motility in a cochlear model.

PubMed

Meaud, Julien; Grosh, Karl

2011-06-08

One of the central questions in the biophysics of the mammalian cochlea is determining the contributions of the two active processes, prestin-based somatic motility and hair bundle (HB) motility, to cochlear amplification. HB force generation is linked to fast adaptation of the transduction current via a calcium-dependent process and somatic force generation is driven by the depolarization caused by the transduction current. In this article, we construct a global mechanical-electrical-acoustical mathematical model of the cochlea based on a three-dimensional fluid representation. The global cochlear model is coupled to linearizations of nonlinear somatic motility and HB activity as well as to the micromechanics of the passive structural and electrical elements of the cochlea. We find that the active HB force alone is not sufficient to power high frequency cochlear amplification. However, somatic motility can overcome resistor-capacitor filtering by the basolateral membrane and deliver sufficient mechanical energy for amplification at basal locations. The results suggest a new theory for high frequency active cochlear mechanics, in which fast adaptation controls the transduction channel sensitivity and thereby the magnitude of the energy delivered by somatic motility. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Mechanism of APC/CCDC20 activation by mitotic phosphorylation.

PubMed

Qiao, Renping; Weissmann, Florian; Yamaguchi, Masaya; Brown, Nicholas G; VanderLinden, Ryan; Imre, Richard; Jarvis, Marc A; Brunner, Michael R; Davidson, Iain F; Litos, Gabriele; Haselbach, David; Mechtler, Karl; Stark, Holger; Schulman, Brenda A; Peters, Jan-Michael

2016-05-10

Chromosome segregation and mitotic exit are initiated by the 1.2-MDa ubiquitin ligase APC/C (anaphase-promoting complex/cyclosome) and its coactivator CDC20 (cell division cycle 20). To avoid chromosome missegregation, APC/C(CDC20) activation is tightly controlled. CDC20 only associates with APC/C in mitosis when APC/C has become phosphorylated and is further inhibited by a mitotic checkpoint complex until all chromosomes are bioriented on the spindle. APC/C contains 14 different types of subunits, most of which are phosphorylated in mitosis on multiple sites. However, it is unknown which of these phospho-sites enable APC/C(CDC20) activation and by which mechanism. Here we have identified 68 evolutionarily conserved mitotic phospho-sites on human APC/C bound to CDC20 and have used the biGBac technique to generate 47 APC/C mutants in which either all 68 sites or subsets of them were replaced by nonphosphorylatable or phospho-mimicking residues. The characterization of these complexes in substrate ubiquitination and degradation assays indicates that phosphorylation of an N-terminal loop region in APC1 is sufficient for binding and activation of APC/C by CDC20. Deletion of the N-terminal APC1 loop enables APC/C(CDC20) activation in the absence of mitotic phosphorylation or phospho-mimicking mutations. These results indicate that binding of CDC20 to APC/C is normally prevented by an autoinhibitory loop in APC1 and that its mitotic phosphorylation relieves this inhibition. The predicted location of the N-terminal APC1 loop implies that this loop controls interactions between the N-terminal domain of CDC20 and APC1 and APC8. These results reveal how APC/C phosphorylation enables CDC20 to bind and activate the APC/C in mitosis.

Mechanism of APC/CCDC20 activation by mitotic phosphorylation

PubMed Central

Qiao, Renping; Weissmann, Florian; Yamaguchi, Masaya; Brown, Nicholas G.; VanderLinden, Ryan; Imre, Richard; Jarvis, Marc A.; Brunner, Michael R.; Davidson, Iain F.; Litos, Gabriele; Haselbach, David; Mechtler, Karl; Stark, Holger; Schulman, Brenda A.; Peters, Jan-Michael

2016-01-01

Chromosome segregation and mitotic exit are initiated by the 1.2-MDa ubiquitin ligase APC/C (anaphase-promoting complex/cyclosome) and its coactivator CDC20 (cell division cycle 20). To avoid chromosome missegregation, APC/CCDC20 activation is tightly controlled. CDC20 only associates with APC/C in mitosis when APC/C has become phosphorylated and is further inhibited by a mitotic checkpoint complex until all chromosomes are bioriented on the spindle. APC/C contains 14 different types of subunits, most of which are phosphorylated in mitosis on multiple sites. However, it is unknown which of these phospho-sites enable APC/CCDC20 activation and by which mechanism. Here we have identified 68 evolutionarily conserved mitotic phospho-sites on human APC/C bound to CDC20 and have used the biGBac technique to generate 47 APC/C mutants in which either all 68 sites or subsets of them were replaced by nonphosphorylatable or phospho-mimicking residues. The characterization of these complexes in substrate ubiquitination and degradation assays indicates that phosphorylation of an N-terminal loop region in APC1 is sufficient for binding and activation of APC/C by CDC20. Deletion of the N-terminal APC1 loop enables APC/CCDC20 activation in the absence of mitotic phosphorylation or phospho-mimicking mutations. These results indicate that binding of CDC20 to APC/C is normally prevented by an autoinhibitory loop in APC1 and that its mitotic phosphorylation relieves this inhibition. The predicted location of the N-terminal APC1 loop implies that this loop controls interactions between the N-terminal domain of CDC20 and APC1 and APC8. These results reveal how APC/C phosphorylation enables CDC20 to bind and activate the APC/C in mitosis. PMID:27114510

Damper mechanism for nuclear reactor control elements

DOEpatents

Taft, William Elwood

1976-01-01

A damper mechanism which provides a nuclear reactor control element decelerating function at the end of the scram stroke. The total damping function is produced by the combination of two assemblies, which operate in sequence. First, a tapered dashram assembly decelerates the control element to a lower velocity, after which a spring hydraulic damper assembly takes over to complete the final damping.

Mechanical Overstimulation of Hair Bundles: Suppression and Recovery of Active Motility

PubMed Central

Kao, Albert; Meenderink, Sebastiaan W. F.; Bozovic, Dolores

2013-01-01

We explore the effects of high-amplitude mechanical stimuli on hair bundles of the bullfrog sacculus. Under in vitro conditions, these bundles exhibit spontaneous limit cycle oscillations. Prolonged deflection exerted two effects. First, it induced an offset in the position of the bundle. Recovery to the original position displayed two distinct time scales, suggesting the existence of two adaptive mechanisms. Second, the stimulus suppressed spontaneous oscillations, indicating a change in the hair bundle’s dynamic state. After cessation of the stimulus, active bundle motility recovered with time. Both effects were dependent on the duration of the imposed stimulus. External calcium concentration also affected the recovery to the oscillatory state. Our results indicate that both offset in the bundle position and calcium concentration control the dynamic state of the bundle. PMID:23505461

Design and experimental validation of a flutter suppression controller for the active flexible wing

NASA Technical Reports Server (NTRS)

Waszak, Martin R.; Srinathkumar, S.

1992-01-01

The synthesis and experimental validation of an active flutter suppression controller for the Active Flexible Wing wind tunnel model is presented. The design is accomplished with traditional root locus and Nyquist methods using interactive computer graphics tools and extensive simulation based analysis. The design approach uses a fundamental understanding of the flutter mechanism to formulate a simple controller structure to meet stringent design specifications. Experimentally, the flutter suppression controller succeeded in simultaneous suppression of two flutter modes, significantly increasing the flutter dynamic pressure despite modeling errors in predicted flutter dynamic pressure and flutter frequency. The flutter suppression controller was also successfully operated in combination with another controller to perform flutter suppression during rapid rolling maneuvers.

Decentralized control mechanism underlying interlimb coordination of millipedes.

PubMed

Kano, Takeshi; Sakai, Kazuhiko; Yasui, Kotaro; Owaki, Dai; Ishiguro, Akio

2017-04-04

Legged animals exhibit adaptive and resilient locomotion through interlimb coordination. The long-term goal of this study is to clarify the relationship between the number of legs and the inherent decentralized control mechanism for interlimb coordination. As a preliminary step, the study focuses on millipedes as they represent the species with the greatest number of legs among various animal species. A decentralized control mechanism involving local force feedback was proposed based on the qualitative findings of behavioural experiments in which responses to the removal of part of the terrain and leg amputation were observed. The proposed mechanism was implemented in a developed millipede-like robot to demonstrate that the robot can adapt to the removal of the part of the terrain and leg amputation in a manner similar to that in behavioural experiments.

Manual, mechanical, and cultural control methds and tools

Treesearch

Steven Manning; James Miller

2011-01-01

There are many land management scenarios where chemicals are not the ideal choice for controlling invasive plants. More often than not, the best approach is the use of integrated pest management involving a variety of control methods. Maximizing the value of mechanical, manual, and cultural control methods with the added benefit of selective herbicides can offer the...

Antenna Mechanism of Length Control of Actin Cables.

PubMed

Mohapatra, Lishibanya; Goode, Bruce L; Kondev, Jane

2015-06-01

Actin cables are linear cytoskeletal structures that serve as tracks for myosin-based intracellular transport of vesicles and organelles in both yeast and mammalian cells. In a yeast cell undergoing budding, cables are in constant dynamic turnover yet some cables grow from the bud neck toward the back of the mother cell until their length roughly equals the diameter of the mother cell. This raises the question: how is the length of these cables controlled? Here we describe a novel molecular mechanism for cable length control inspired by recent experimental observations in cells. This "antenna mechanism" involves three key proteins: formins, which polymerize actin, Smy1 proteins, which bind formins and inhibit actin polymerization, and myosin motors, which deliver Smy1 to formins, leading to a length-dependent actin polymerization rate. We compute the probability distribution of cable lengths as a function of several experimentally tuneable parameters such as the formin-binding affinity of Smy1 and the concentration of myosin motors delivering Smy1. These results provide testable predictions of the antenna mechanism of actin-cable length control.

Crack-free polydimethylsiloxane-bioactive glass-poly(ethylene glycol) hybrid monoliths with controlled biomineralization activity and mechanical property for bone tissue regeneration.

PubMed

Chen, Jing; Du, Yuzhang; Que, Wenxiu; Xing, Yonglei; Chen, Xiaofeng; Lei, Bo

2015-12-01

Crack-free organic-inorganic hybrid monoliths with controlled biomineralization activity and mechanical property have an important role for highly efficient bone tissue regeneration. Here, biomimetic and crack-free polydimethylsiloxane (PDMS)-modified bioactive glass (BG)-poly(ethylene glycol) (PEG) (PDMS-BG-PEG) hybrids monoliths were prepared by a facile sol-gel technique. Results indicate that under the assist of co-solvents, BG sol and PDMS and PEG could be hybridized at a molecular level, and effects of the PEG molecular weight on the structure, biomineralization activity, and mechanical property of the as-prepared hybrid monoliths were also investigated in detail. It is found that an addition of low molecular weight PEG can significantly prevent the formation of cracks and speed up the gelation of the hybrid monoliths, and the surface microstructure of the hybrid monoliths can be changed from the porous to the smooth as the PEG molecular weight increases. Additionally, the hybrid monoliths with low molecular weight PEG show the high formation of the biological apatite layer, while the hybrids with high molecular weight PEG exhibit negligible biomineralization ability in simulated body fluid (SBF). Furthermore, the PDMS-BG-PEG 600 hybrid monolith has significantly high compressive strength (32 ± 3 MPa) and modulus (153 ± 11 MPa), as well as good cell biocompatibility by supporting osteoblast (MC3T3-E1) attachment and proliferation. These results indicate that the as-prepared PDMS-BG-PEG hybrid monoliths may have promising applications for bone tissue regeneration. Copyright © 2015 Elsevier B.V. All rights reserved.

Dynamics and Control of a Quadrotor with Active Geometric Morphing

NASA Astrophysics Data System (ADS)

Wallace, Dustin A.

Quadrotors are manufactured in a wide variety of shapes, sizes, and performance levels to fulfill a multitude of roles. Robodub Inc. has patented a morphing quadrotor which will allow active reconfiguration between various shapes for performance optimization across a wider spectrum of roles. The dynamics of the system are studied and modeled using Newtonian Mechanics. Controls are developed and simulated using both Linear Quadratic and Numerical Nonlinear Optimal control for a symmetric simplificiation of the system dynamics. Various unique vehicle capabilities are investigated, including novel single-throttle flight control using symmetric geometric morphing, as well as recovery from motor loss by reconfiguring into a trirotor configuration. The system dynamics were found to be complex and highly nonlinear. All attempted control strategies resulted in controllability, suggesting further research into each may lead to multiple viable control strategies for a physical prototype.

Recovery of rhythmic activity in a central pattern generator: analysis of the role of neuromodulator and activity-dependent mechanisms.

PubMed

Zhang, Yili; Golowasch, Jorge

2011-11-01

The pyloric network of decapods crustaceans can undergo dramatic rhythmic activity changes. Under normal conditions the network generates low frequency rhythmic activity that depends obligatorily on the presence of neuromodulatory input from the central nervous system. When this input is removed (decentralization) the rhythmic activity ceases. In the continued absence of this input, periodic activity resumes after a few hours in the form of episodic bursting across the entire network that later turns into stable rhythmic activity that is nearly indistinguishable from control (recovery). It has been proposed that an activity-dependent modification of ionic conductance levels in the pyloric pacemaker neuron drives the process of recovery of activity. Previous modeling attempts have captured some aspects of the temporal changes observed experimentally, but key features could not be reproduced. Here we examined a model in which slow activity-dependent regulation of ionic conductances and slower neuromodulator-dependent regulation of intracellular Ca(2+) concentration reproduce all the temporal features of this recovery. Key aspects of these two regulatory mechanisms are their independence and their different kinetics. We also examined the role of variability (noise) in the activity-dependent regulation pathway and observe that it can help to reduce unrealistic constraints that were otherwise required on the neuromodulator-dependent pathway. We conclude that small variations in intracellular Ca(2+) concentration, a Ca(2+) uptake regulation mechanism that is directly targeted by neuromodulator-activated signaling pathways, and variability in the Ca(2+) concentration sensing signaling pathway can account for the observed changes in neuronal activity. Our conclusions are all amenable to experimental analysis.

Mechanisms and neuronal networks involved in reactive and proactive cognitive control of interference in working memory.

PubMed

Irlbacher, Kerstin; Kraft, Antje; Kehrer, Stefanie; Brandt, Stephan A

2014-10-01

Cognitive control can be reactive or proactive in nature. Reactive control mechanisms, which support the resolution of interference, start after its onset. Conversely, proactive control involves the anticipation and prevention of interference prior to its occurrence. The interrelation of both types of cognitive control is currently under debate: Are they mediated by different neuronal networks? Or are there neuronal structures that have the potential to act in a proactive as well as in a reactive manner? This review illustrates the way in which integrating knowledge gathered from behavioral studies, functional imaging, and human electroencephalography proves useful in answering these questions. We focus on studies that investigate interference resolution at the level of working memory representations. In summary, different mechanisms are instrumental in supporting reactive and proactive control. Distinct neuronal networks are involved, though some brain regions, especially pre-SMA, possess functions that are relevant to both control modes. Therefore, activation of these brain areas could be observed in reactive, as well as proactive control, but at different times during information processing. Copyright © 2014 Elsevier Ltd. All rights reserved.

Active control of spectral detail radiated by an air-loaded impacted membrane

NASA Astrophysics Data System (ADS)

Rollow, J. Douglas, IV

An active control system is developed to independently operate on the vibration of individual modes of an air-loaded drum head, resulting in changes in the acoustic field radiated from the structure. The timbre of the system is investigated, and techniques for changing the characteristic frequencies by means of the control system are proposed. A feedforward control system is constructed for empirical investigation of this approach, creating a musical instrument which can produce a variety of sounds not available with strictly mechanical systems. The work is motivated by applications for actively controlled structures, active control of sound quality, and musical acoustics. The instrument consists of a Mylar timpano head stretched over an enclosure which has been outfitted with electroacoustic drivers. Sensors are arranged on the surface of the drum head and combined to measure modal vibration, and the array of drivers allows independent control of these modes. A signal processor is used to form modal control filters which can modify the loading of each mode, changing the time-dependent and spectral characteristics, and therefore the timbre, of the radiated sound. A theoretical formulation of active control of structural vibration by means of fluid-coupled actuators is expressed, and computational solutions show the effects of fluid loading and the radiated field. Experimental results with the new instrument are shown, with implementations of the control system providing a demonstrated degree of control, and illustrating several limitations of such systems.

Education as a Social Control Mechanism.

ERIC Educational Resources Information Center

Bacchus, M. K.

1979-01-01

With the abolition of slavery, most West Indian planters dramatically changed their attitudes toward education for Blacks, suddenly favoring it. This paper examines reasons behind the attitudinal changes, the planters' perceptions on the role of education for Blacks, and the use of education as a mechanism for social control. (DS)

Mitotic Transcriptional Activation: Clearance of Actively Engaged Pol II via Transcriptional Elongation Control in Mitosis.

PubMed

Liang, Kaiwei; Woodfin, Ashley R; Slaughter, Brian D; Unruh, Jay R; Box, Andrew C; Rickels, Ryan A; Gao, Xin; Haug, Jeffrey S; Jaspersen, Sue L; Shilatifard, Ali

2015-11-05

Although it is established that some general transcription factors are inactivated at mitosis, many details of mitotic transcription inhibition (MTI) and its underlying mechanisms are largely unknown. We have identified mitotic transcriptional activation (MTA) as a key regulatory step to control transcription in mitosis for genes with transcriptionally engaged RNA polymerase II (Pol II) to activate and transcribe until the end of the gene to clear Pol II from mitotic chromatin, followed by global impairment of transcription reinitiation through MTI. Global nascent RNA sequencing and RNA fluorescence in situ hybridization demonstrate the existence of transcriptionally engaged Pol II in early mitosis. Both genetic and chemical inhibition of P-TEFb in mitosis lead to delays in the progression of cell division. Together, our study reveals a mechanism for MTA and MTI whereby transcriptionally engaged Pol II can progress into productive elongation and finish transcription to allow proper cellular division. Copyright © 2015 Elsevier Inc. All rights reserved.

Kinesin-dependent mechanism for controlling triglyceride secretion from the liver.

PubMed

Rai, Priyanka; Kumar, Mukesh; Sharma, Geetika; Barak, Pradeep; Das, Saumitra; Kamat, Siddhesh S; Mallik, Roop

2017-12-05

Despite massive fluctuations in its internal triglyceride content, the liver secretes triglyceride under tight homeostatic control. This buffering function is most visible after fasting, when liver triglyceride increases manyfold but circulating serum triglyceride barely fluctuates. How the liver controls triglyceride secretion is unknown, but is fundamentally important for lipid and energy homeostasis in animals. Here we find an unexpected cellular and molecular mechanism behind such control. We show that kinesin motors are recruited to triglyceride-rich lipid droplets (LDs) in the liver by the GTPase ARF1, which is a key activator of lipolysis. This recruitment is activated by an insulin-dependent pathway and therefore responds to fed/fasted states of the animal. In fed state, ARF1 and kinesin appear on LDs, consequently transporting LDs to the periphery of hepatocytes where the smooth endoplasmic reticulum (sER) is present. Because the lipases that catabolize LDs in hepatocytes reside on the sER, LDs can now be catabolized efficiently to provide triglyceride for lipoprotein assembly and secretion from the sER. Upon fasting, insulin is lowered to remove ARF1 and kinesin from LDs, thus down-regulating LD transport and sER-LD contacts. This tempers triglyceride availabiity for very low density lipoprotein assembly and allows homeostatic control of serum triglyceride in a fasted state. We further show that kinesin knockdown inhibits hepatitis-C virus replication in hepatocytes, likely because translated viral proteins are unable to transfer from the ER to LDs. Copyright © 2017 the Author(s). Published by PNAS.

Mechanism And Control Of The Quadruped Walking Robot

NASA Astrophysics Data System (ADS)

Adachi, Hironori; Nakano, Eiji; Koyachi, Noriho

1987-10-01

This paper provides a description of the quadruped walking robot "TURTLE-1". A new link mechanism named ASTBALLEM is used for the legs of this robot. With this mechanism highly rigid and easily controllable legs are constructed. Each leg has two degrees of freedom and is driven by two DC servo motors. The motion of the legs is controlled by a micro computer and various gaits are generated. Static stability is maintained as the robot walks. Moreover, its walk is quasi-dynamic; that is, it has a manner of walking that has a two legged supporting period.

Self-efficacy, action control, and social support explain physical activity changes among Costa Rican older adults.

PubMed

Reyes Fernández, Benjamin; Montenegro Montenegro, Esteban; Knoll, Nina; Schwarzer, Ralf

2014-11-01

Self-efficacy, action control, and social support are considered to influence changes in physical activity levels in older adults. This study examines the relationship among these variables and explores the putative mediating and moderating mechanisms that might account for activity changes. A longitudinal study with 54 older adults (≥ 50 years of age) was carried out in Costa Rica. In a moderated mediation analysis, action control was specified as a mediator between self-efficacy and physical activity, whereas social support was specified as a moderator between self-efficacy and action control. Baseline physical activity, age, and sex were specified as covariates. Action control mediated between self-efficacy and physical activity. An interaction between social support and self-efficacy on action control pointed to a synergistic effect at the first stage of the mediating process. The effect of self-efficacy on physical activity was partly explained by action control, providing evidence of action control as a proximal mediator of physical activity. Moreover, the moderator role of social support was confirmed: high social support appeared to compensate for low levels of self-efficacy.

Mechanism and regulation of NLRP3 inflammasome activation

PubMed Central

He, Yuan; Hara, Hideki; Núñez, Gabriel

2016-01-01

Members of the nucleotide-binding domain and leucine-rich repeat containing (NLR) family and the pyrin and HIN-domain (PYHIN) family can form multiprotein complexes termed “inflammasomes”. The biochemical function of inflammasomes is to activate caspase-1, which leads to the maturation of interleukin 1β (IL-1β) and IL-18 and induction of pyroptosis, a form of cell death. Unlike other inflammasomes, the NLRP3 inflammasome can be activated by diverse stimuli. The importance of the NLRP3 inflammasome in immunity and human diseases has been well documented, but the mechanism and regulation of NLRP3 inflammasome activation remains unclear. In this review we summarize current understanding of the mechanism and regulation of NLRP3 inflammasome activation, as well as recent advances in the non-canonical and alternative inflammasome pathways. PMID:27669650

Velocity & displacement-dependent damper: A novel passive shock absorber inspired by the semi-active control

NASA Astrophysics Data System (ADS)

Nie, Shida; Zhuang, Ye; Wang, Yong; Guo, Konghui

2018-01-01

The performance of velocity & displacement-dependent damper (VDD), inspired by the semi-active control, is analyzed. The main differences among passive, displacement-dependent and semi-active dampers are compared on their damping properties. Valve assemblies of VDD are modelled to get an insight into its working principle. The mechanical structure composed by four valve assemblies helps to enable VDD to approach the performance by those semi-active control dampers. The valve structure parameters are determined by the suggested two-step process. Hydraulic model of the damper is built with AMEsim. Simulation result of F-V curves, which is similar to those of semi-active control damper, demonstrates that VDD could achieve the similar performance of semi-active control damper. The performance of a quarter vehicle model employing VDD is analyzed and compared with semi-active suspension. Simulation results show that VDD could perform as good as a semi-active control damper. In addition, no add-on hardware or energy consumption is needed for VDD to achieve the remarkable performance.

Chronic sciatic neuropathy in rat reduces voluntary wheel running activity with concurrent chronic mechanical allodynia

PubMed Central

Whitehead, RA; Lam, NL; Sun, MS; Sanchez, JJ; Noor, S; Vanderwall, AG; Petersen, TR; Martin, HB

2016-01-01

hrs) of either the (1) inactive (n=8/gp) or (2) active (n = 8/gp) phase of the diurnal cycle. An additional group of CCI-treated rats (n = 8/gp) were exposed to a locked running wheel to control for the potential effects of wheel running exercise on allodynia. The 1-hr running wheel trial period was further examined at discrete 20-min intervals to identify possible pattern differences in activity during the first, middle and last portion of the 1-hr trial. The effect of neuropathy on activity levels were assessed by measuring the change from their respective BLs to distance traveled in the running wheels. RESULTS While wheel running distances between groups were not different at BL from rats examined during either the inactive phase of the diurnal cycle or active phase of the diurnal cycle, sciatic nerve CCI reduced running wheel activity levels compared to sham-operated controls during the inactive phase. Additionally, compared to sham controls, bilateral low threshold mechanical allodynia was observed at all time-points after surgical induction of neuropathy in rats with free-wheel and locked-wheel access. Allodynia in CCI compared to shams was replicated in rats whose running wheel activity was examined during the active phase of the diurnal cycle. Conversely, no significant reduction in wheel running activity was observed in CCI-treated rats compared to sham controls at any timepoint when activity levels were examined during the active diurnal phase. Lastly, running wheel activity patterns within the 1 hr trial period during the inactive phase of the diurnal cycle were relatively consistent throughout each 20 min phase. CONCLUSIONS Compared to non-neuropathic sham controls, a profound and stable reduction of running wheel activity was observed in CCI rats during the inactive phase of the diurnal cycle. A concurrent robust allodynia persisted in all rats regardless of when wheel running activity was examined or whether they ran on wheels, suggesting that acute

A possible role of actin in the mechanical control of the cell cycle.

PubMed

Tripathi, S C

1989-01-01

Sail-sheet Cultures (SSC) are those in which the cells are i) grown within the meshes of inert grids ii) exposed to nutrients from most sides iii) attached to one another only at the edges like sail of a yacht (hence, the name 'sail-sheet') and iv) have the advantage of three-dimensional structure similar to an in vivo situation. We grew fibroblasts from chicken heart explants as SSC and studied the effect of mechanical stretching on the F-actin content of these cells. This study was designed to investigate the hypothesis that the effect of tension on the cell cycle may be channeled through the microfilaments. Data from this preliminary study suggested that short-term mechanical stretching of sail-sheets, using low frequency tension (1.0 Hz), diminishes F-actin. Thus, it may be possible to relate the decrease in the F-actin content of these cells to the slowing down of their locomotory activity, possible rounding up, and division. This study might contribute to the understanding of the mechanical control of the cell cycle and be of relevance in the phenomena such as healing of wounds and control of the cell division in tumors.

Overview: Mechanism and Control of a Prosthetic Arm.

PubMed

Kulkarni, Tushar; Uddanwadiker, Rashmi

2015-09-01

Continuous growth in industrialization and lack of awareness in safety parameters the cases of amputations are growing. The search of safer, simpler and automated prosthetic arms for managing upper limbs is expected. Continuous efforts have been made to design and develop prosthetic arms ranging from simple harness actuated to automated mechanisms with various control options. However due the cost constraints, the automated prosthetic arms are still out of the reach of needy people. Recent data have shown that there is a wide scope to develop a low cost and light weight upper limb prosthesis. This review summarizes the various designs methodologies, mechanisms and control system developed by the researchers and the advances therein. Educating the patient to develop acceptability to prosthesis and using the same for the most basic desired functions of human hand, post amputation care and to improve patient's independent life is equally important. In conclusion it can be interpreted that there is a wide scope in design in an adaptive mechanism for opening and closing of the fingers using other methods of path and position synthesis. Simple mechanisms and less parts may optimize the cost factor. Reduction in the weight of the prosthesis may be achieved using polymers used for engineering applications. Control system will remain never ending challenge for the researchers, but it is essential to maintain the simplicity from the patients perspective.

Cognitive Behavioral Therapy Is Associated With Enhanced Cognitive Control Network Activity in Major Depression and Posttraumatic Stress Disorder

PubMed Central

Yang, Zhen; Oathes, Desmond J.; Linn, Kristin A.; Bruce, Steven E.; Satterthwaite, Theodore D.; Cook, Philip A.; Satchell, Emma K.; Shou, Haochang; Sheline, Yvette I.

2018-01-01

BACKGROUND Both major depressive disorder (MDD) and posttraumatic stress disorder (PTSD) are characterized by depressive symptoms, abnormalities in brain regions important for cognitive control, and response to cognitive behavioral therapy (CBT). However, whether a common neural mechanism underlies CBT response across diagnoses is unknown. METHODS Brain activity during a cognitive control task was measured using functional magnetic resonance imaging in 104 participants: 28 patients with MDD, 53 patients with PTSD, and 23 healthy control subjects; depression and anxiety symptoms were determined on the same day. A patient subset (n = 31) entered manualized CBT and, along with controls (n = 19), was rescanned at 12 weeks. Linear mixed effects models assessed the relationship between depression and anxiety symptoms and brain activity before and after CBT. RESULTS At baseline, activation of the left dorsolateral prefrontal cortex was negatively correlated with Montgomery–Åsberg Depression Rating Scale scores across all participants; this brain–symptom association did not differ between MDD and PTSD. Following CBT treatment of patients, regions within the cognitive control network, including ventrolateral prefrontal cortex and dorsolateral prefrontal cortex, showed a significant increase in activity. CONCLUSIONS Our results suggest that dimensional abnormalities in the activation of cognitive control regions were associated primarily with symptoms of depression (with or without controlling for anxious arousal). Furthermore, following treatment with CBT, activation of cognitive control regions was similarly increased in both MDD and PTSD. These results accord with the Research Domain Criteria conceptualization of mental disorders and implicate improved cognitive control activation as a transdiagnostic mechanism for CBT treatment outcome. PMID:29628063

Electromagnetic energy coupling mechanism with matrix architecture control

NASA Technical Reports Server (NTRS)

Hughes, Eli (Inventor); Knowles, Gareth (Inventor)

2006-01-01

The present invention relates generally to reconfigurable, solid-state matrix arrays comprising multiple rows and columns of reconfigurable secondary mechanisms that are independently tuned. Specifically, the invention relates to reconfigurable devices comprising multiple, solid-state mechanisms characterized by at least one voltage-varied parameter disposed within a flexible, multi-laminate film, which are suitable for use as magnetic conductors, ground surfaces, antennas, varactors, ferrotunable substrates, or other active or passive electronic mechanisms.

A novel auto-tuning PID control mechanism for nonlinear systems.

PubMed

Cetin, Meric; Iplikci, Serdar

2015-09-01

In this paper, a novel Runge-Kutta (RK) discretization-based model-predictive auto-tuning proportional-integral-derivative controller (RK-PID) is introduced for the control of continuous-time nonlinear systems. The parameters of the PID controller are tuned using RK model of the system through prediction error-square minimization where the predicted information of tracking error provides an enhanced tuning of the parameters. Based on the model-predictive control (MPC) approach, the proposed mechanism provides necessary PID parameter adaptations while generating additive correction terms to assist the initially inadequate PID controller. Efficiency of the proposed mechanism has been tested on two experimental real-time systems: an unstable single-input single-output (SISO) nonlinear magnetic-levitation system and a nonlinear multi-input multi-output (MIMO) liquid-level system. RK-PID has been compared to standard PID, standard nonlinear MPC (NMPC), RK-MPC and conventional sliding-mode control (SMC) methods in terms of control performance, robustness, computational complexity and design issue. The proposed mechanism exhibits acceptable tuning and control performance with very small steady-state tracking errors, and provides very short settling time for parameter convergence. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Evaluation of function, performance, and preference as transfemoral amputees transition from mechanical to microprocessor control of the prosthetic knee.

PubMed

Hafner, Brian J; Willingham, Laura L; Buell, Noelle C; Allyn, Katheryn J; Smith, Douglas G

2007-02-01

To evaluate differences in function, performance, and preference between mechanical and microprocessor prosthetic knee control technologies. A-B-A-B reversal design. Home, community, and laboratory environments. Twenty-one unilateral, transfemoral amputees. Mechanical control prosthetic knee versus microprocessor control prosthetic knee (Otto Bock C-Leg). Stair rating, hill rating and time, obstacle course time, divided attention task accuracy and time, Amputee Mobility Predictor score, step activity, Prosthesis Evaluation Questionnaire score, Medical Outcomes Study 36-Item Short-Form Health Survey score, self-reported frequency of stumbles and falls, and self-reported concentration required for ambulation. Stair descent score, hill descent time, and hill sound-side step length showed significant (P<.01) improvement with the C-Leg. Users reported a significant (P<.05) decrease in frequency of stumbles and falls, frustration with falling, and difficulty in multitasking while using the microprocessor knee. Subject satisfaction with the C-Leg was significantly (P<.001) greater than the mechanical control prosthesis. The study population showed improved performance when negotiating stairs and hills, reduced frequency of stumbling and falling, and a preference for the microprocessor control C-Leg as compared with the mechanical control prosthetic knee.

Understanding disease mechanisms with models of signaling pathway activities.

PubMed

Sebastian-Leon, Patricia; Vidal, Enrique; Minguez, Pablo; Conesa, Ana; Tarazona, Sonia; Amadoz, Alicia; Armero, Carmen; Salavert, Francisco; Vidal-Puig, Antonio; Montaner, David; Dopazo, Joaquín

2014-10-25

Understanding the aspects of the cell functionality that account for disease or drug action mechanisms is one of the main challenges in the analysis of genomic data and is on the basis of the future implementation of precision medicine. Here we propose a simple probabilistic model in which signaling pathways are separated into elementary sub-pathways or signal transmission circuits (which ultimately trigger cell functions) and then transforms gene expression measurements into probabilities of activation of such signal transmission circuits. Using this model, differential activation of such circuits between biological conditions can be estimated. Thus, circuit activation statuses can be interpreted as biomarkers that discriminate among the compared conditions. This type of mechanism-based biomarkers accounts for cell functional activities and can easily be associated to disease or drug action mechanisms. The accuracy of the proposed model is demonstrated with simulations and real datasets. The proposed model provides detailed information that enables the interpretation disease mechanisms as a consequence of the complex combinations of altered gene expression values. Moreover, it offers a framework for suggesting possible ways of therapeutic intervention in a pathologically perturbed system.

Adsorption mechanisms and impact factors of oxytetracycline on activated sludge

NASA Astrophysics Data System (ADS)

Xiancai, Song; Dongfang, Liu; Lejun, Zhao

2017-03-01

The adsorption mechanisms and the effect of Oxytetracycline (OTC) onto activated sludge were studied. The results show that the adsorption of Oxytetracycline (OTC) onto activated sludge was coincident with the Pseudo-second-order kinetic model which suggested that chemical adsorption mechanism was dominant. The influences including pH and metal ions on the OTC were examined. It was demonstrated that the adsorption process was highly pH-dependant, which indicate that cationic exchange mechanisms may play an important role in the adsorption process. Na+, K+, Ca2+, Mg2+ and Cd2+ ions more or less inhibited the adsorption of OTC on activated sludge while Cu2+ enhanced the adsorption ability. The phenomenon may reflect the result that a surface complexation mechanism could involved in the adsorption.

Differences in feedforward trunk muscle activity in subgroups of patients with mechanical low back pain.

PubMed

Silfies, Sheri P; Mehta, Rupal; Smith, Sue S; Karduna, Andrew R

2009-07-01

To investigate alterations in trunk muscle timing patterns in subgroups of patients with mechanical low back pain (MLBP). Our hypothesis was that subjects with MLBP would demonstrate delayed muscle onset and have fewer muscles functioning in a feedforward manner than the control group. We further hypothesized that we would find differences between subgroups of our patients with MLBP, grouped according to diagnosis (segmental instability and noninstability). Case-control. Laboratory. Forty-three patients with chronic MLBP (25 instability, 18 noninstability) and 39 asymptomatic controls. Not applicable. Surface electromyography was used to measure onset time of 10 trunk muscles during a self-perturbation task. Trunk muscle onset latency relative to the anterior deltoid was calculated and the number of muscles functioning in feedforward determined. Activation timing patterns (P<.01; eta=.50; 1-beta=.99) and number of muscles functioning in feedforward (P=.02; eta=.30; 1-beta=.83) were statistically different between patients with MLBP and controls. The control group activated the external oblique, lumbar multifidus, and erector spinae muscles in a feedforward manner. The heterogeneous MLBP group did not activate the trunk musculature in feedforward, but responded with significantly delayed activations. MLBP subgroups demonstrated significantly different timing patterns. The noninstability MLBP subgroup activated trunk extensors in a feedforward manner, similar to the control group, but significantly earlier than the instability subgroup. Lack of feedforward activation of selected trunk musculature in patients with MLBP may result in a period of inefficient muscular stabilization. Activation timing was more impaired in the instability than the noninstability MLBP subgroup. Training specifically for recruitment timing may be an important component of the rehabilitation program.

Quasi-modal vibration control by means of active control bearings

NASA Technical Reports Server (NTRS)

Nonami, K.; Fleming, D. P.

1986-01-01

This paper investigates a design method of an active control bearing system with only velocity feedback. The study provides a new quasi-modal control method for a control system design of an active control bearing system in which feedback coefficients are determined on the basis of a modal analysis. Although the number of sensors and actuators is small, this quasi-modal control method produces a control effect close to an ideal modal control.

Switching control of sympathetic activity from forebrain to hindbrain in chronic dehydration

PubMed Central

Colombari, Débora S A; Colombari, Eduardo; Freiria-Oliveira, Andre H; Antunes, Vagner R; Yao, Song T; Hindmarch, Charles; Ferguson, Alastair V; Fry, Mark; Murphy, David; Paton, Julian F R

2011-01-01

Abstract We investigated the mechanisms responsible for increased blood pressure and sympathetic nerve activity (SNA) caused by 2–3 days dehydration (DH) both in vivo and in situ preparations. In euhydrated (EH) rats, systemic application of the AT1 receptor antagonist Losartan and subsequent pre-collicular transection (to remove the hypothalamus) significantly reduced thoracic (t)SNA. In contrast, in DH rats, Losartan, followed by pre-collicular and pontine transections, failed to reduce tSNA, whereas transection at the medulla–spinal cord junction massively reduced tSNA. In DH but not EH rats, selective inhibition of the commissural nucleus tractus solitarii (cNTS) significantly reduced tSNA. Comparable data were obtained in both in situ and in vivo (anaesthetized/conscious) rats and suggest that following chronic dehydration, the control of tSNA transfers from supra-brainstem structures (e.g. hypothalamus) to the medulla oblongata, particularly the cNTS. As microarray analysis revealed up-regulation of AP1 transcription factor JunD in the dehydrated cNTS, we tested the hypothesis that AP1 transcription factor activity is responsible for dehydration-induced functional plasticity. When AP1 activity was blocked in the cNTS using a viral vector expressing a dominant negative FosB, cNTS inactivation was ineffective. However, tSNA was decreased after pre-collicular transection, a response similar to that seen in EH rats. Thus, the dehydration-induced switch in control of tSNA from hypothalamus to cNTS seems to be mediated via activation of AP1 transcription factors in the cNTS. If AP1 activity is blocked in the cNTS during dehydration, sympathetic activity control reverts back to forebrain regions. This unique reciprocating neural structure-switching plasticity between brain centres emphasizes the multiple mechanisms available for the adaptive response to dehydration. PMID:21708906

Active Motion Control of Tetrahymena pyriformis by Galvanotaxis and Geotaxis

NASA Astrophysics Data System (ADS)

Kim, Jihoon; Byun, Doyoung; Kim, Min Jun

2013-11-01

Recently, there has been increasing interest in the swimming behavior of microorganisms and biologically inspired micro-robots. These microorganisms naturally accompanied by complex motions. Therefore it is important to understand the flow characteristics as well as control mechanisms. One of eukaryotic cells, the protozoa are a diverse group of unicellular organisms, many of which are motile cilia. Motile cilia are cover on the surface of cell in large numbers and beat in oriented waves. Sequential beating motions of a single cilium form metachronal strokes, producing a propagation wave, and therefore the body is achieved propulsion force. So preliminary studies are achieved to understand the flow induced by swimming microorganisms. Based on hydrodynamic results, the follow study of a few micro-scale protozoa cell, such as the Tetrahymena pyriformis, has provided active or passive control into several external stimuli. In typical control methods, the galvanotaxis and geotaxis were adopted active and passive control, respectively. The validation of galvanotaxis is used DC and AC voltage. In terms of geotaxis, corrugated microstructures were used to control in the microchannel. This research was supported by the Ministry of Education, Science and Technology (MEST, 2011-0016461), National Science Foundation (NSF) CMMI Control Systems Program (#1000255) and Army Research Office (W911NF-11-1-0490).

Motivation by potential gains and losses affects control processes via different mechanisms in the attentional network.

PubMed

Paschke, Lena M; Walter, Henrik; Steimke, Rosa; Ludwig, Vera U; Gaschler, Robert; Schubert, Torsten; Stelzel, Christine

2015-05-01

Attentional control in demanding cognitive tasks can be improved by manipulating the motivational state. Motivation to obtain gains and motivation to avoid losses both usually result in faster reaction times and stronger activation in relevant brain areas such as the prefrontal cortex, but little is known about differences in the underlying neurocognitive mechanisms of these types of motivation in an attentional control context. In the present functional magnetic resonance imaging (fMRI) study, we tested whether potential gain and loss as motivating incentives lead to overlapping or distinct neural effects in the attentional network, and whether one of these conditions is more effective than the other. A Flanker task with word stimuli as targets and distracters was performed by 115 healthy participants. Using a mixed blocked and event-related design allowed us to investigate transient and sustained motivation-related effects. Participants could either gain money (potential gain) or avoid losing money (potential loss) in different task blocks. Participants showed a congruency effect with increased reaction times for incongruent compared to congruent trials. Potential gain led to generally faster responses compared to the neutral condition and to stronger improvements than potential loss. Potential loss also led to shorter response times compared to the neutral condition, but participants improved mainly during incongruent and not during congruent trials. The event-related fMRI data revealed a main effect of congruency with increased activity in the left inferior frontal gyrus (IFG) and inferior frontal junction area (IFJ), the pre-supplementary motor area (pre-SMA), bilateral insula, intraparietal sulcus (IPS) and visual word form area (VWFA). While potential gain led to increased activity in a cluster of the IFJ and the VWFA only during incongruent trials, potential loss was linked to activity increases in these regions during incongruent and congruent trials. The

Integrated Application of Active Controls (IAAC) technology to an advanced subsonic transport project. ACT/Control/Guidance System study. Volume 2: Appendices

NASA Technical Reports Server (NTRS)

1982-01-01

The integrated application of active controls (IAAC) technology to an advanced subsonic transport is reported. Supplementary technical data on the following topics are included: (1) 1990's avionics technology assessment; (2) function criticality assessment; (3) flight deck system for total control and functional features list; (4) criticality and reliability assessment of units; (5) crew procedural function task analysis; and (6) recommendations for simulation mechanization.

Electrical Coupling: Novel Mechanism for Sleep-Wake Control

PubMed Central

Garcia-Rill, Edgar; Heister, David S.; Ye, Meijun; Charlesworth, Amanda; Hayar, Abdallah

2007-01-01

Study Objectives: Recent evidence suggests that certain anesthetic agents decrease electrical coupling, whereas the stimulant modafinil appears to increase electrical coupling. We investigated the potential role of electrical coupling in 2 reticular activating system sites, the subcoeruleus nucleus and in the pedunculopontine nucleus, which has been implicated in the modulation of arousal via ascending cholinergic activation of intralaminar thalamus and descending activation of the subcoeruleus nucleus to generate some of the signs of rapid eye movement sleep. Design: We used 6- to 30-day-old rat pups to obtain brainstem slices to perform whole-cell patch-clamp recordings. Measurements and Results: Recordings from single cells revealed the presence of spikelets, manifestations of action potentials in coupled cells, and of dye coupling of neurons in the pedunculopontine nucleus. Recordings in pairs of pedunculopontine nucleus and subcoeruleus nucleus neurons revealed that some of these were electrically coupled with coupling coefficients of approximately 2%. After blockade of fast synaptic transmission, the cholinergic agonist carbachol was found to induce rhythmic activity in pedunculopontine nucleus and subcoeruleus nucleus neurons, an effect eliminated by the gap junction blockers carbenoxolone or mefloquine. The stimulant modafinil was found to decrease resistance in neurons in the pedunculopontine nucleus and subcoeruleus nucleus after fast synaptic blockade, indicating that the effect may be due to increased coupling. Conclusions: The finding of electrical coupling in specific reticular activating system cell groups supports the concept that this underlying process behind specific neurotransmitter interactions modulates ensemble activity across cell populations to promote changes in sleep-wake state. Citation: Garcia-Rill E; Heister DS; Ye M; Charlesworth A; Hayar A. Electrical coupling: novel mechanism for sleep-wake control. SLEEP 2007;30(11):1405-1414. PMID

[Algal control ability of allelopathically active submerged macrophytes: a review].

PubMed

Xiao, Xi; Lou, Li-ping; Li, Hua; Chen, Ying-xu

2009-03-01

The inhibitory effect of allelochemicals released by submerged macrophytes on phytoplankton is considered as one of the mechanisms that contribute to the stabilization of clear-water status in shallow lakes. This paper reviewed the research progress in the allelopathy of submerged macrophytes on algae from the aspects of the occurrence frequency and coverage of allelopathically active submerged macrophytes in lakes, and the kinds and allelopathical effects of the allelochemicals released from the macrophytes. The previous researches indicated that allelopathically active submerged macrophyte species such as Myriophyllum, Ceratophyllum, and Elodea were efficient to control phytoplankton, especially when their biomass was high enough, and the dominant algae were sensitive species. The allelochemicals such as hydroxybenzene released by the submerged macrophytes could inhibit the growth of algae. Different phytoplankton species exhibited different sensitivity against allelochemicals, e.g., cyanobacteria and diatom were more sensitive than green algae, while epiphytic species were less sensitive than phytoplankton. Environmental factors such as light, temperature, and nutrients could significantly affect the allelopathical effect of submerged macrophytes. The research of the allelopathy of submerged macrophytes is still at its beginning, and further researches are needed on the effects of environmental factors on the allelopathy, extraction and identification of allelochemicals, selective algal control mechanisms, and metabolism of the allelochmicals.

Active flow control for a blunt trailing edge profiled body

NASA Astrophysics Data System (ADS)

Naghib Lahouti, Arash

Flow in the wake of nominally two-dimensional bluff bodies is dominated by vortex shedding, beyond a very small threshold Reynolds number. Vortex shedding poses challenges in the design of structures, due to its adverse effects such as cyclic aerodynamic loads and fatigue. The wake vortices are often accompanied by large- and small-scale secondary instabilities, which manifest as dislocations in the primary wake vortices, and/or pairs of counter-rotating streamwise vortices, depending on the dominant instability mode(s), which in turn depends on the profile geometry and Reynolds number. The secondary instabilities interact with the wake vortices through several mechanisms. Therefore, manipulation of the secondary instabilities can be used as a means to alter the wake vortices, in order to reduce their adverse effects. In the present study, flow in the wake of a blunt trailing edge profiled body, composed of an elliptical leading edge and a rectangular trailing edge, has been studied at Reynolds numbers ranging from Re(d) = 500 to 2150 where d is thickness of the body, to identify the secondary instabilities. Various tools, including numerical simulations, Laser Induced Fluorescence (LIF), and Particle Image Velocimetry (PIV) have been used for this study. Proper Orthogonal Decomposition (POD) has been applied to analyze the velocity field data. The results indicate the existence of small-scale instabilities with a spanwise wavelength of 2.0d to 2.5d in the near wake. The mechanism of the instability is similar to the Mode-A instability of a circular cylinder; however, it displays features that are specific to the blunt trailing edge profiled body. An active three-dimensional flow control mechanism based on the small-scale instabilities has been designed and evaluated. The mechanism comprises a series of trailing edge injection ports, with a spanwise spacing equal to the wavelength of the small-scale instabilities. Following preliminary evaluation of the control

Active Control Of Structure-Borne Noise

NASA Astrophysics Data System (ADS)

Elliott, S. J.

1994-11-01

The successful practical application of active noise control requires an understanding of both its acoustic limitations and the limitations of the electrical control strategy used. This paper is concerned with the active control of sound in enclosures. First, a review is presented of the fundamental physical limitations of using loudspeakers to achieve either global or local control. Both approaches are seen to have a high frequency limit, due to either the acoustic modal overlap, or the spatial correlation function of the pressure field. These physical performance limits could, in principle, be achieved with either a feedback or a feedforward control strategy. These strategies are reviewed and the use of adaptive digital filters is discussed for both approaches. The application of adaptive feedforward control in the control of engine and road noise in cars is described. Finally, an indirect approach to the active control of sound is discussed, in which the vibration is suppressed in the structural paths connecting the source of vibration to the enclosure. Two specific examples of this strategy are described, using an active automotive engine mount and the incorporation of actuators into helicopter struts to control gear-meshing tones. In both cases good passive design can minimize the complexity of the active controller.

Analysis technique for controlling system wavefront error with active/adaptive optics

NASA Astrophysics Data System (ADS)

Genberg, Victor L.; Michels, Gregory J.

2017-08-01

The ultimate goal of an active mirror system is to control system level wavefront error (WFE). In the past, the use of this technique was limited by the difficulty of obtaining a linear optics model. In this paper, an automated method for controlling system level WFE using a linear optics model is presented. An error estimate is included in the analysis output for both surface error disturbance fitting and actuator influence function fitting. To control adaptive optics, the technique has been extended to write system WFE in state space matrix form. The technique is demonstrated by example with SigFit, a commercially available tool integrating mechanical analysis with optical analysis.

High precision active nutation control for a flexible momentum biased spacecraft

NASA Technical Reports Server (NTRS)

Laskin, R. A.; Kopf, E. H.

1984-01-01

The controller design for the Solar Dynamics Observatory (SDO) is presented. SDO is a momentum biased spacecraft with three flexible appendages. Its primary scientific instrument, the solar oscillations imager (SOI), is rigidly attached to the spacecraft bus and has arc-second pointing requirements. Meeting these requirements necessitates the use of an active nutation controller (ANC) which is here mechanized with a small reaction wheel oriented along a bus transverse axis. The ANC does its job by orchestrating the transfer of angular momentum out of the bus transverse axes and into the momentum wheel. A simulation study verifies that the controller provides quick, stable, and accurate response.

The Application of LOGO! in Control System of a Transmission and Sorting Mechanism

NASA Astrophysics Data System (ADS)

Liu, Jian; Lv, Yuan-Jun

Logic programming of general logic control module LOGO! has been recommended the application in transmission and sorting mechanism. First, the structure and operating principle of the mechanism had been introduced. Then the pneumatic loop of the mechanism had been plotted in the software of FluidSIM-P. At last, pneumatic loop and motors had been control by LOGO!, which makes the control process simple and clear instead of the complicated control of ordinary relay. LOGO! can achieve the complicated interlock control composed of inter relays and time relays. In the control process, the logic control function of LOGO! is fully used to logic programming so that the system realizes the control of air cylinder and motor. It is reliable and adjustable mechanism after application.

Rejection Triggers Liver Transplant Tolerance: Involvements of Mesenchyme-Mediated Immune Control Mechanisms

PubMed Central

Morita, Miwa; Joyce, Daniel; Miller, Charles; Fung, John J.; Lu, Lina; Qian, Shiguang

2015-01-01

Liver tolerance was initially recognized by the spontaneous acceptance of liver allograft in many species. The underlying mechanisms are not completely understood. We have been inspired by an unexpected phenomenon that the liver transplant tolerance absolutely requires interferon (IFN)-γ, a rejection-associated inflammatory cytokine. In this study, we investigate the rejection of liver allografts deficient in IFN-γ receptor and reveal that the liver graft is equipped with machineries capable of counterattacking the host immune response through a mesenchyme-mediated immune control (MMIC) mechanism. MMIC is triggered by T effectors (Tef) cell-derived IFN-γ to drive the expression of B7-H1 on graft mesenchymal cells leading to Tef cell apoptosis. We describe the negative feedback loop between graft mesenchymal and Tef cells that ultimately results in liver transplant tolerance. Comparable elevations of T regulatory cells and myeloid-derived suppressor cells are seen in both rejection and tolerance groups, and are not dependent on IFN-γ stimulation, suggesting a critical role of Tef cell elimination in tolerance induction. We identify potent MMIC activity in hepatic stellate cells and liver sinusoidal endothelial cells. MMIC is unlikely exclusive to the liver, as spontaneous acceptance of kidney allografts has been reported, although less commonly, probably reflecting variance in MMIC activity. MMCI may represent an important homeostatic mechanism that supports peripheral tolerance, and could be a target for the prevention and treatment of transplant rejection. This study highlights that the graft is actively participant in the equipoise between tolerance and rejection and warrants more attention in the search for tolerance biomarkers. PMID:25998530

Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics

PubMed Central

Grindy, Scott C.; Learsch, Robert; Mozhdehi, Davoud; Cheng, Jing; Barrett, Devin G.; Guan, Zhibin; Messersmith, Phillip B.; Holten-Andersen, Niels

2015-01-01

In conventional polymer materials, mechanical performance is traditionally engineered via material structure, using motifs such as polymer molecular weight, polymer branching, or copolymer-block design1. Here, by means of a model system of 4-arm poly(ethylene glycol) hydrogels crosslinked with multiple, kinetically distinct dynamic metal-ligand coordinate complexes, we show that polymer materials with decoupled spatial structure and mechanical performance can be designed. By tuning the relative concentration of two types of metal-ligand crosslinks, we demonstrate control over the material’s mechanical hierarchy of energy-dissipating modes under dynamic mechanical loading, and therefore the ability to engineer a priori the viscoelastic properties of these materials by controlling the types of crosslinks rather than by modifying the polymer itself. This strategy to decouple material mechanics from structure may inform the design of soft materials for use in complex mechanical environments. PMID:26322715

PPARγ controls pregnancy outcome through activation of EG-VEGF: new insights into the mechanism of placental development.

PubMed

Garnier, Vanessa; Traboulsi, Wael; Salomon, Aude; Brouillet, Sophie; Fournier, Thierry; Winkler, Carine; Desvergne, Beatrice; Hoffmann, Pascale; Zhou, Qun-Yong; Congiu, Cenzo; Onnis, Valentina; Benharouga, Mohamed; Feige, Jean-Jacques; Alfaidy, Nadia

2015-08-15

PPARγ-deficient mice die at E9.5 due to placental abnormalities. The mechanism by which this occurs is unknown. We demonstrated that the new endocrine factor EG-VEGF controls the same processes as those described for PPARγ, suggesting potential regulation of EG-VEGF by PPARγ. EG-VEGF exerts its functions via prokineticin receptor 1 (PROKR1) and 2 (PROKR2). This study sought to investigate whether EG-VEGF mediates part of PPARγ effects on placental development. Three approaches were used: 1) in vitro, using human primary isolated cytotrophoblasts and the extravillous trophoblast cell line (HTR-8/SVneo); 2) ex vivo, using human placental explants (n = 46 placentas); and 3) in vivo, using gravid wild-type PPARγ(+/-) and PPARγ(-/-) mice. Major processes of placental development that are known to be controlled by PPARγ, such as trophoblast proliferation, migration, and invasion, were assessed in the absence or presence of PROKR1 and PROKR2 antagonists. In both human trophoblast cell and placental explants, we demonstrated that rosiglitazone, a PPARγ agonist, 1) increased EG-VEGF secretion, 2) increased EG-VEGF and its receptors mRNA and protein expression, 3) increased placental vascularization via PROKR1 and PROKR2, and 4) inhibited trophoblast migration and invasion via PROKR2. In the PPARγ(-/-) mouse placentas, EG-VEGF levels were significantly decreased, supporting an in vivo control of EG-VEGF/PROKRs system during pregnancy. The present data reveal EG-VEGF as a new mediator of PPARγ effects during pregnancy and bring new insights into the fine mechanism of trophoblast invasion. Copyright © 2015 the American Physiological Society.

Cognitive Control Mechanisms, Emotion & Memory: A neural perspective with implications for psychopathology

PubMed Central

Banich, Marie T.; Mackiewicz, Kristen L.; Depue, Brendan E.; Whitmer, Anson; Miller, Gregory A.; Heller, Wendy

2009-01-01

In this paper we provide a focused review of the literature examining neural mechanisms involved in cognitive control over memory processes that can influence, and in turn are influenced, by emotional processes. The review is divided into two parts, the first focusing on working memory and the second on long-term memory. With regard to working memory, we discuss the neural bases of 1) control mechanisms that can select against distracting emotional information, 2) mechanisms that can regulate emotional reactions or responses, 3) how mood state influences cognitive control, and 4) individual differences in control mechanisms. For long-term memory, we briefly review 1) the neural substrates of emotional memory, 2) the cognitive and neural mechanisms that are involved in controlling emotional memories and 3) how these systems are altered in post-traumatic stress disorder. Finally, we consider tentative generalizations that can be drawn from this relatively unexplored conjunction of research endeavors. PMID:18948135

Control of articulated snake robot under dynamic active constraints.

PubMed

Kwok, Ka-Wai; Vitiello, Valentina; Yang, Guang-Zhong

2010-01-01

Flexible, ergonomically enhanced surgical robots have important applications to transluminal endoscopic surgery, for which path-following and dynamic shape conformance are essential. In this paper, kinematic control of a snake robot for motion stabilisation under dynamic active constraints is addressed. The main objective is to enable the robot to track the visual target accurately and steadily on deforming tissue whilst conforming to pre-defined anatomical constraints. The motion tracking can also be augmented with manual control. By taking into account the physical limits in terms of maximum frequency response of the system (manifested as a delay between the input of the manipulator and the movement of the end-effector), we show the importance of visual-motor synchronisation for performing accurate smooth pursuit movements. Detailed user experiments are performed to demonstrate the practical value of the proposed control mechanism.

An Analytical Dynamics Approach to the Control of Mechanical Systems

NASA Astrophysics Data System (ADS)

Mylapilli, Harshavardhan

A new and novel approach to the control of nonlinear mechanical systems is presented in this study. The approach is inspired by recent results in analytical dynamics that deal with the theory of constrained motion. The control requirements on the dynamical system are viewed from an analytical dynamics perspective and the theory of constrained motion is used to recast these control requirements as constraints on the dynamical system. Explicit closed form expressions for the generalized nonlinear control forces are obtained by using the fundamental equation of mechanics. The control so obtained is optimal at each instant of time and causes the constraints to be exactly satisfied. No linearizations and/or approximations of the nonlinear dynamical system are made, and no a priori structure is imposed on the nature of nonlinear controller. Three examples dealing with highly nonlinear complex dynamical systems that are chosen from diverse areas of discrete and continuum mechanics are presented to demonstrate the control approach. The first example deals with the energy control of underactuated inhomogeneous nonlinear lattices (or chains), the second example deals with the synchronization of the motion of multiple coupled slave gyros with that of a master gyro, and the final example deals with the control of incompressible hyperelastic rubber-like thin cantilever beams. Numerical simulations accompanying these examples show the ease, simplicity and the efficacy with which the control methodology can be applied and the accuracy with which the desired control objectives can be met.

A double-panel active segmented partition module using decoupled analog feedback controllers: numerical model.

PubMed

Sagers, Jason D; Leishman, Timothy W; Blotter, Jonathan D

2009-06-01

Low-frequency sound transmission has long plagued the sound isolation performance of lightweight partitions. Over the past 2 decades, researchers have investigated actively controlled structures to prevent sound transmission from a source space into a receiving space. An approach using active segmented partitions (ASPs) seeks to improve low-frequency sound isolation capabilities. An ASP is a partition which has been mechanically and acoustically segmented into a number of small individually controlled modules. This paper provides a theoretical and numerical development of a single ASP module configuration, wherein each panel of the double-panel structure is independently actuated and controlled by an analog feedback controller. A numerical model is developed to estimate frequency response functions for the purpose of controller design, to understand the effects of acoustic coupling between the panels, to predict the transmission loss of the module in both passive and active states, and to demonstrate that the proposed ASP module will produce bidirectional sound isolation.

Mechanisms of Gain Control by Voltage-Gated Channels in Intrinsically-Firing Neurons

PubMed Central

Patel, Ameera X.; Burdakov, Denis

2015-01-01

Gain modulation is a key feature of neural information processing, but underlying mechanisms remain unclear. In single neurons, gain can be measured as the slope of the current-frequency (input-output) relationship over any given range of inputs. While much work has focused on the control of basal firing rates and spike rate adaptation, gain control has been relatively unstudied. Of the limited studies on gain control, some have examined the roles of synaptic noise and passive somatic currents, but the roles of voltage-gated channels present ubiquitously in neurons have been less explored. Here, we systematically examined the relationship between gain and voltage-gated ion channels in a conductance-based, tonically-active, model neuron. Changes in expression (conductance density) of voltage-gated channels increased (Ca2+ channel), reduced (K+ channels), or produced little effect (h-type channel) on gain. We found that the gain-controlling ability of channels increased exponentially with the steepness of their activation within the dynamic voltage window (voltage range associated with firing). For depolarization-activated channels, this produced a greater channel current per action potential at higher firing rates. This allowed these channels to modulate gain by contributing to firing preferentially at states of higher excitation. A finer analysis of the current-voltage relationship during tonic firing identified narrow voltage windows at which the gain-modulating channels exerted their effects. As a proof of concept, we show that h-type channels can be tuned to modulate gain by changing the steepness of their activation within the dynamic voltage window. These results show how the impact of an ion channel on gain can be predicted from the relationship between channel kinetics and the membrane potential during firing. This is potentially relevant to understanding input-output scaling in a wide class of neurons found throughout the brain and other nervous systems

[Mechanism of action and control in the digestion of proteins and peptides in humans].

PubMed

Frenhani, P B; Burini, R C

1999-01-01

This review aims to report the major control mechanisms of protein and peptides digestion of special interest in human patients. Regarding protein assimilation its digestive process begins at the stomach with some not so indispensable actions comparatively to those of duodenal/jejunal lumen. However even the intestine processes are partially under gastric secretion control. Proteolytic enzyme activities are related to protein structure and amino acid constituents, tertiary and quartenary structures need HCl denaturation prior to enzymatic hydrolysis. Thereafter the exopeptidases are guided by either NH2 (aminopeptidases) or COOH (carboxypeptidases) terminals of the molecule while endopeptidases are oriented by the specific amino acids constituents of the peptide. Both dietary and luminal secreted proteins and polypeptides undergo to either limited or complete proteolysis resulting basic or neutral free-amino acids (40%) or dioctapeptides. The brush border peptidases continue to degrade oligopeptide to di-tripeptides and neutral free-amino acids. Some peptides are uptaked by the enterocytes whose cytosolic peptidases complete the hydrolysis. Hence the digestive products flowing in the portal vein are mainly free-amino acids from either luminal or cytosolic hydrolysis and some di-tripeptides intactly absorbed. Both mechanical and chemical processes of digestion are under neural (vagal), neuroendocrinal (acetilcholine), endocrinal (gastrin, secretin and cholecystokinin) or paracrinal (histamine) controls. The gastric phase (hydrochloric acid and pepsinogen secretions) is activated by gastrin, histamine and acetilcholine which respond to both dietary-amino acids (tryptophan and phenylalanine) and mechanic distention of stomach. The pancreatic secretion is stimulated by either cephalic or gastric phases and has influence on the intestinal phase of digestion. The intestinal types of cells S and I release secretin and cholecystokinin respectively in response of acid quimo

Molecular Mechanism of Active Zone Organization at Vertebrate Neuromuscular Junctions

PubMed Central

Nishimune, Hiroshi

2013-01-01

Organization of presynaptic active zones is essential for development, plasticity, and pathology of the nervous system. Recent studies indicate a trans-synaptic molecular mechanism that organizes the active zones by connecting the pre- and the postsynaptic specialization. The presynaptic component of this trans-synaptic mechanism is comprised of cytosolic active zone proteins bound to the cytosolic domains of voltage-dependent calcium channels (P/Q-, N-, and L-type) on the presynaptic membrane. The postsynaptic component of this mechanism is the synapse organizer (laminin β2) that is expressed by the postsynaptic cell and accumulates specifically on top of the postsynaptic specialization. The pre- and the postsynaptic components interact directly between the extracellular domains of calcium channels and laminin β2 to anchor the presynaptic protein complex in front of the postsynaptic specialization. Hence, the presynaptic calcium channel functions as a scaffolding protein for active zone organization and as an ion-conducting channel for synaptic transmission. In contrast to the requirement of calcium influx for synaptic transmission, the formation of the active zone does not require the calcium influx through the calcium channels. Importantly, the active zones of adult synapses are not stable structures and require maintenance for their integrity. Furthermore, aging or diseases of the central and peripheral nervous system impair the active zones. This review will focus on the molecular mechanisms that organize the presynaptic active zones and summarize recent findings at the neuromuscular junctions and other synapses. PMID:22135013

Demonstration of Active Combustion Control

NASA Technical Reports Server (NTRS)

Lovett, Jeffrey A.; Teerlinck, Karen A.; Cohen, Jeffrey M.

2008-01-01

The primary objective of this effort was to demonstrate active control of combustion instabilities in a direct-injection gas turbine combustor that accurately simulates engine operating conditions and reproduces an engine-type instability. This report documents the second phase of a two-phase effort. The first phase involved the analysis of an instability observed in a developmental aeroengine and the design of a single-nozzle test rig to replicate that phenomenon. This was successfully completed in 2001 and is documented in the Phase I report. This second phase was directed toward demonstration of active control strategies to mitigate this instability and thereby demonstrate the viability of active control for aircraft engine combustors. This involved development of high-speed actuator technology, testing and analysis of how the actuation system was integrated with the combustion system, control algorithm development, and demonstration testing in the single-nozzle test rig. A 30 percent reduction in the amplitude of the high-frequency (570 Hz) instability was achieved using actuation systems and control algorithms developed within this effort. Even larger reductions were shown with a low-frequency (270 Hz) instability. This represents a unique achievement in the development and practical demonstration of active combustion control systems for gas turbine applications.

Rule-based mechanisms of learning for intelligent adaptive flight control

NASA Technical Reports Server (NTRS)

Handelman, David A.; Stengel, Robert F.

1990-01-01

How certain aspects of human learning can be used to characterize learning in intelligent adaptive control systems is investigated. Reflexive and declarative memory and learning are described. It is shown that model-based systems-theoretic adaptive control methods exhibit attributes of reflexive learning, whereas the problem-solving capabilities of knowledge-based systems of artificial intelligence are naturally suited for implementing declarative learning. Issues related to learning in knowledge-based control systems are addressed, with particular attention given to rule-based systems. A mechanism for real-time rule-based knowledge acquisition is suggested, and utilization of this mechanism within the context of failure diagnosis for fault-tolerant flight control is demonstrated.

40 CFR 194.41 - Active institutional controls.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 25 2011-07-01 2011-07-01 false Active institutional controls. 194.41... Assurance Requirements § 194.41 Active institutional controls. (a) Any compliance application shall include detailed descriptions of proposed active institutional controls, the controls' location, and the period of...

40 CFR 194.41 - Active institutional controls.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 25 2014-07-01 2014-07-01 false Active institutional controls. 194.41... Assurance Requirements § 194.41 Active institutional controls. (a) Any compliance application shall include detailed descriptions of proposed active institutional controls, the controls' location, and the period of...

40 CFR 194.41 - Active institutional controls.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Active institutional controls. 194.41... Assurance Requirements § 194.41 Active institutional controls. (a) Any compliance application shall include detailed descriptions of proposed active institutional controls, the controls' location, and the period of...

40 CFR 194.41 - Active institutional controls.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 26 2012-07-01 2011-07-01 true Active institutional controls. 194.41... Assurance Requirements § 194.41 Active institutional controls. (a) Any compliance application shall include detailed descriptions of proposed active institutional controls, the controls' location, and the period of...

40 CFR 194.41 - Active institutional controls.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 26 2013-07-01 2013-07-01 false Active institutional controls. 194.41... Assurance Requirements § 194.41 Active institutional controls. (a) Any compliance application shall include detailed descriptions of proposed active institutional controls, the controls' location, and the period of...

Fixed and flexible formularies as cost-control mechanisms.

PubMed

Dewa, Carolyn S; Hoch, Jeffrey S

2003-06-01

The purpose of this review is to consider the prevalent types of fixed and flexible formularies, the general economic principles on which they are based and the evidence for their effectiveness in controlling rising drug expenditures. The principal-agent relationship and economic model underlying the various types of formularies are described. The principal-agent model describes a relationship where there is an asymmetry of information between two parties involved in a particular task. As a result of this asymmetry of information, the party with less information (the principal) allows the party with more information (the agent) to make decisions about that task or activity for them. In the case of formularies and cost-control, the principal is the payer. Depending on the incentives offered by the formulary, the agent can alternately be the prescriber, dispenser or patient. The success of a formulary type to control costs is dependent on two main factors. First, the payer (the principal) must identify the agent for whom it is reasonable to create incentives that incorporate the financial risks associated with use of the drugs. Second, the payer must develop a structure that best aligns the principal and agent objectives. The principal-agent framework serves as the vehicle through which the authors examine five major types of formularies (i.e., closed, best available price, reference-based pricing, tiered and open formularies) and their inherent incentives and limitations. The evidence for their effectiveness as cost-control mechanisms is reviewed and the system factors that can affect formulary success will be discussed. Finally, the authors' observations are summarized and interpreted, and suggested implications for future use of formularies in controlling the costs of pharmaceutical use are offered.

Satellite Dynamic Damping via Active Force Control Augmentation

NASA Astrophysics Data System (ADS)

Varatharajoo, Renuganth

2012-07-01

An approach that incorporates the Active Force Control (AFC) technique into a conventional Proportional-Derivative (PD) controller is proposed for a satellite active dynamic damping towards a full attitude control. The AFC method has been established to facilitate a robust motion control of dynamical systems in the presence of disturbances, parametric uncertainties and changes that are commonly prevalent in the real-world environment. The usefulness of the method can be extended by introducing intelligent mechanisms to approximate the mass or inertia matrix of the dynamic system to trigger the compensation effect of the controller. AFC is a technique that relies on the appropriate estimation of the inertial or mass parameters of the dynamic system and the measurements of the acceleration and force signals induced by the system if practical implementation is ever considered. In AFC, it is shown that the system subjected to a number of disturbances remains stable and robust via the compensating action of the control strategy. We demonstrate that it is possible to design a spacecraft attitude feedback controller that will ensure the system dynamics set point remains unchanged even in the presence of the disturbances provided that the actual disturbances can be modeled effectively. In order to further facilitate this analysis, a combined energy and attitude control system (CEACS) is proposed as a model satellite attitude control actuator. All the governing equations are established and the proposed satellite attitude control architecture is made amenable to numerical treatments. The results show that the PD-AFC attitude damping performances are superiorly better than that of the solely PD type. It is also shown that the tunings of the AFC system gains are crucial to ensure a better attitude damping performance and this process is mandatory for AFC systems. Finally, the results demonstrate an important satellite dynamic damping enhancement capability using the AFC

Impulsive personality and the ability to resist immediate reward: an fMRI study examining interindividual differences in the neural mechanisms underlying self-control.

PubMed

Diekhof, Esther Kristina; Nerenberg, Lesly; Falkai, Peter; Dechent, Peter; Baudewig, Jürgen; Gruber, Oliver

2012-12-01

The ability to resist immediate rewards is crucial for lifetime success and individual well-being. Using functional magnetic resonance imaging, we assessed the association between trait impulsivity and the neural underpinnings of the ability to control immediate reward desiring. Low and high extreme impulsivity groups were compared with regard to their behavioral performance and brain activation in situations, in which they had to forego immediate rewards with varying value to achieve a superordinate long-term goal. We found that highly impulsive (HI) individuals, who successfully compensated for their lack in behavioral self-control, engaged two complementary brain mechanisms when choosing actions in favor of a long-term goal, but at the expense of an immediate reward. First, self-controlled decisions led to a general attenuation of reward-related activation in the nucleus accumbens, which was accompanied by an increased inverse connectivity with the anteroventral prefrontal cortex. Second, HI subjects controlled their desire for increasingly valuable, but suboptimal rewards through a linear reduction of activation in the ventromedial prefrontal cortex (VMPFC). This was achieved by an increased inverse coupling between the VMPFC and the ventral striatum. Importantly, the neural mechanisms observed in the HI group differed from those in extremely controlled individuals, despite similar behavioral performance. Collectively, these results suggest trait-specific neural mechanisms that allow HI individuals to control their desire for immediate reward. Copyright © 2011 Wiley Periodicals, Inc.

Design and control of a high precision drive mechanism

NASA Astrophysics Data System (ADS)

Pan, Bo; He, Yongqiang; Wang, Haowei; Zhang, Shuyang; Zhang, Donghua; Wei, Xiaorong; Jiang, Zhihong

2017-01-01

This paper summarizes the development of a high precision drive mechanism (HPDM) for space application, such as the directional antenna, the laser communication device, the mobile camera and other pointing mechanisms. In view of the great practical significance of high precision drive system, control technology for permanent magnet synchronous motor (PMSM) servo system is also studied and a PMSM servo controller is designed in this paper. And the software alignment was applied to the controller to eliminate the steady error of the optical encoder, which helps to realize the 1 arcsec (1σ) control precision. To assess its capabilities, the qualification environment testing including the thermal vacuum cycling testing, and the sinusoidal and random vibration were carried out. The testing results show that the performance of the HPDM is almost the same between the former and the end of each testing.

Memory-induced mechanism for self-sustaining activity in networks

NASA Astrophysics Data System (ADS)

Allahverdyan, A. E.; Steeg, G. Ver; Galstyan, A.

2015-12-01

We study a mechanism of activity sustaining on networks inspired by a well-known model of neuronal dynamics. Our primary focus is the emergence of self-sustaining collective activity patterns, where no single node can stay active by itself, but the activity provided initially is sustained within the collective of interacting agents. In contrast to existing models of self-sustaining activity that are caused by (long) loops present in the network, here we focus on treelike structures and examine activation mechanisms that are due to temporal memory of the nodes. This approach is motivated by applications in social media, where long network loops are rare or absent. Our results suggest that under a weak behavioral noise, the nodes robustly split into several clusters, with partial synchronization of nodes within each cluster. We also study the randomly weighted version of the models where the nodes are allowed to change their connection strength (this can model attention redistribution) and show that it does facilitate the self-sustained activity.

Further Characterization of an Active Clearance Control Concept

NASA Technical Reports Server (NTRS)

Taylor, Shawn C.; Steinetz, Bruce M.; Oswald, Jay J.

2007-01-01

A new test chamber and precision hydraulic actuation system were incorporated into an active clearance control (ACC) test rig at NASA Glenn Research Center. Using the improved system, a fast-acting, mechanically-actuated, ACC concept was evaluated at engine simulated temperatures and pressure differentials up to 1140 F and 120 psig, on the basis of secondary seal leakage and kinematic controllability. During testing, the ACC concept tracked a simulated flight clearance transient profile at 1140 F, 120 psig, with a maximum error of only 0.0012 in. Comparison of average dynamic leakage of the system with average static leakage did not show significant differences between the two operating conditions. Calculated effective clearance values for the rig were approximately 0.0002 in. at 120 psig, well below the industry specified effective clearance threshold of 0.001 in.

Mechanisms of CaMKII Activation in the Heart.

PubMed

Erickson, Jeffrey R

2014-01-01

Calcium/calmodulin (Ca(2+)/CaM) dependent protein kinase II (CaMKII) has emerged as a key nodal protein in the regulation of cardiac physiology and pathology. Due to the particularly elegant relationship between the structure and function of the kinase, CaMKII is able to translate a diverse set of signaling events into downstream physiological effects. While CaMKII is typically autoinhibited at basal conditions, prolonged rapid Ca(2+) cycling can activate the kinase and allow post-translational modifications that depend critically on the biochemical environment of the heart. These modifications result in sustained, autonomous CaMKII activation and have been associated with pathological cardiac signaling. Indeed, improved understanding of CaMKII activation mechanisms could potentially lead to new clinical therapies for the treatment or prevention of cardiovascular disease. Here we review the known mechanisms of CaMKII activation and discuss some of the pathological signaling pathways in which they play a role.

Capture and quality control mechanisms for ATP binding

PubMed Central

Li, Li; Martinis, Susan A.

2013-01-01

The catalytic events in members of the nucleotidylyl transferase superfamily are initiated by a millisecond binding of ATP in the active site. Through metadynamics simulations on a class I aminoacyl-tRNA synthetase (aaRSs), the largest group in the superfamily, we calculate the free energy landscape of ATP selection and binding. Mutagenesis studies and fluorescence spectroscopy validated the identification of the most populated intermediate states. The rapid first binding step involves formation of encounter complexes captured through a fly-casting mechanism that acts up on the triphosphate moiety of ATP. In the slower nucleoside binding step, a conserved histidine in the HxxH motif orients the incoming ATP through base-stacking interactions resulting in a deep minimum in the free energy surface. Mutation of this histidine significantly decreases the binding affinity measured experimentally and computationally. The metadynamics simulations further reveal an intermediate quality control state that the synthetases and most likely other members of the superfamily use to select ATP over other nucleoside triphosphates. PMID:23276298

COAXIAL CONTROL ROD DRIVE MECHANISM FOR NEUTRONIC REACTORS

DOEpatents

Fox, R.J.; Oakes, L.C.

1959-04-14

A drive mechanism is presented for the control rod or a nuclear reactor. In this device the control rod is coupled to a drive shaft which extends coaxially through the rotor of an electric motor for relative rotation with respect thereto. A gear reduction mehanism is coupled between the rotor and the drive shaft to convert the rotary motion of the motor into linear motion of the shaft with a comparatively great reduction in speed, thereby providing relatively glow linear movement of the shaft and control rod for control purposes.

Controlling mechanisms over the internet

NASA Astrophysics Data System (ADS)

Lumia, Ronald

1997-01-01

The internet, widely available throughout the world, can be used to control robots, machine tools, and other mechanisms. This paper will describe a low-cost virtual collaborative environment (VCE) which will connect users with distant equipment. The system is based on PC technology, and incorporates off-line-programming with on-line execution. A remote user programs the systems graphically and simulates the motions and actions of the mechanism until satisfied with the functionality of the program. The program is then transferred from the remote site to the local site where the real equipment exists. At the local site, the simulation is run again to check the program from a safety standpoint. Then, the local user runs the program on the real equipment. During execution, a camera in the real workspace provides an image back to the remote user through a teleconferencing system. The system costs approximately 12,500 dollars and represents a low-cost alternative to the Sandia National Laboratories VCE.

Attempting to control mite allergens with mechanical ventilation and dehumidification in British houses.

PubMed

Niven, R; Fletcher, A M; Pickering, A C; Custovic, A; Sivour, J B; Preece, A R; Oldham, L A; Francis, H C

1999-05-01

Allergen avoidance is of considerable interest in the treatment and even prevention of asthma. Attempts to control house dust mites have included environmental manipulation in homes in an attempt to reduce humidity below a level that favors mite survival. This appears to have some benefit in Scandinavia, but a previous attempt with mechanical ventilation heat pump recovery (MVHR) units in the UK failed to achieve the desired results. We report a study using an additional central dehumidification modification of the MVHR (MVHRcd) in an attempt to reduce allergen levels in houses of asthmatic subjects. Ten houses of asthmatic patients allergic to dust mites and 10 architectural control houses were studied. The active houses were fitted with an MVHRcd unit in November/December 1994 and activated in January 1995. The active and control houses were monitored continuously for internal temperature and humidity by using digital sensors in the asthmatic and control bedrooms. Dust samples were collected to determine allergen levels at baseline (January 1994) and 3, 6, 9, and 15 months after switching on the units. The winter seasonal average humidity fell from 50% relative humidity (RH) in control bedrooms to 37% RH in asthmatic bedrooms compared with 72% RH in the ambient air as measured on the intake of the MVHRcd systems. There was no corresponding change in seasonal mean temperature within the houses. Although the temperature and humidity weekly and seasonal means remained below the study target of 45% RH or 7 g/kg absolute humidity at 21 degrees C, there were transient rises in humidity detected by the sensors in the houses with MVHRcd systems. Allergen levels fell both in active and control houses during the study period, but there was no significant advantage gained from the installation of MVHRcd systems. The MVHRcd system failed to confer a benefit in terms of mite allergen reduction despite apparently adequate control of temperature and humidity.

Modulation of bone remodeling via mechanically activated ion channels

NASA Technical Reports Server (NTRS)

Duncan, Randall L. (Principal Investigator)

1996-01-01

A critical factor in the maintenance of bone mass is the physical forces imposed upon the skeleton. Removal of these forces, such as in a weightless environment, results in a rapid loss of bone, whereas application of exogenous mechanical strain has been shown to increase bone formation. Numerous flight and ground-based experiments indicate that the osteoblast is the key bone cell influenced by mechanical stimulation. Aside from early transient fluctuations in response to unloading, osteoclast number and activity seem unaffected by removal of strain. However, bone formation is drastically reduced in weightlessness and osteoblasts respond to mechanical strain with an increase in the activity of a number of second messenger pathways resulting in increased anabolic activity. Unfortunately, the mechanism by which the osteoblast converts physical stimuli into a biochemical message, a process we have termed biochemical coupling, remains elusive. Prior to the application of this grant, we had characterized a mechanosensitive, cation nonselective channel (SA-cat) in osteoblast-like osteosarcoma cells that we proposed is the initial signalling mechanism for mechanotransduction. During the execution of this grant, we have made considerable progress to further characterize this channel as well as to determine its role in the osteoblastic response to mechanical strain. To achieve these goals, we combined electrophysiologic techniques with cellular and molecular biology methods to examine the role of these channels in the normal function of the osteoblast in vitro.

Substantia nigra activity level predicts trial-to-trial adjustments in cognitive control

PubMed Central

Boehler, C.N.; Bunzeck, N.; Krebs, R.M.; Noesselt, T.; Schoenfeld, M.A.; Heinze, H.-J.; Münte, T.F.; Woldorff, M.G.; Hopf, J.-M.

2011-01-01

Effective adaptation to the demands of a changing environment requires flexible cognitive control. The medial and lateral frontal cortices are involved in such control processes, putatively in close interplay with the basal ganglia. In particular, dopaminergic projections from the midbrain (i.e., from the substantia nigra (SN) and the ventral tegmental area (VTA)) have been proposed to play a pivotal role in modulating the activity in these areas for cognitive control purposes. In that dopaminergic involvement has been strongly implicated in reinforcement learning, these ideas suggest functional links between reinforcement learning, where the outcome of actions shapes behavior over time, and cognitive control in a more general context, where no direct reward is involved. Here, we provide evidence from functional MRI in humans that activity in the SN predicts systematic subsequent trial-to-trial response time (RT) prolongations that are thought to reflect cognitive control in a Stop-signal paradigm. In particular, variations in the activity level of the SN in one trial predicted the degree of RT prolongation on the subsequent trial, consistent with a modulating output signal from the SN being involved in enhancing cognitive control. This link between SN activity and subsequent behavioral adjustments lends support to theoretical accounts that propose dopaminergic control signals that shape behavior both in the presence and absence of direct reward. This SN-based modulatory mechanism is presumably mediated via a wider network that determines response speed in this task, including frontal and parietal control regions, along with the basal ganglia and the associated subthalamic nucleus. PMID:20465358

Pivotal role of tissue plasminogen activator in the mechanism of action of electroconvulsive therapy.

PubMed

Hoirisch-Clapauch, Silvia; Mezzasalma, Marco A U; Nardi, Antonio E

2014-02-01

Electroconvulsive therapy is an important treatment option for major depressive disorders, acute mania, mood disorders with psychotic features, and catatonia. Several hypotheses have been proposed as electroconvulsive therapy's mechanism of action. Our hypothesis involves many converging pathways facilitated by increased synthesis and release of tissue-plasminogen activator. Human and animal experiments have shown that tissue-plasminogen activator participates in many mechanisms of action of electroconvulsive therapy or its animal variant, electroconvulsive stimulus, including improved N-methyl-D-aspartate receptor-mediated signaling, activation of both brain-derived neurotrophic factor and vascular endothelial growth factor, increased bioavailability of zinc, purinergic release, and increased mobility of dendritic spines. As a result, tissue-plasminogen activator helps promote neurogenesis in limbic structures, modulates synaptic transmission and plasticity, improves cognitive function, and mediates antidepressant effects. Notably, electroconvulsive therapy seems to influence tissue-plasminogen activator metabolism. For example, electroconvulsive stimulus increases the expression of glutamate decarboxylase 65 isoform in γ-aminobutyric acid-releasing neurons, which enhances the release of tissue-plasminogen activator, and the expression of p11, a protein involved in plasminogen and tissue-plasminogen activator assembling. This paper reviews how electroconvulsive therapy correlates with tissue-plasminogen activator. We suggest that interventions aiming at increasing tissue-plasminogen activator levels or its bioavailability - such as daily aerobic exercises together with a carbohydrate-restricted diet, or normalization of homocysteine levels - be evaluated in controlled studies assessing response and remission duration in patients who undergo electroconvulsive therapy.

An intelligent active force control algorithm to control an upper extremity exoskeleton for motor recovery

NASA Astrophysics Data System (ADS)

Hasbullah Mohd Isa, Wan; Taha, Zahari; Mohd Khairuddin, Ismail; Majeed, Anwar P. P. Abdul; Fikri Muhammad, Khairul; Abdo Hashem, Mohammed; Mahmud, Jamaluddin; Mohamed, Zulkifli

2016-02-01

This paper presents the modelling and control of a two degree of freedom upper extremity exoskeleton by means of an intelligent active force control (AFC) mechanism. The Newton-Euler formulation was used in deriving the dynamic modelling of both the anthropometry based human upper extremity as well as the exoskeleton that consists of the upper arm and the forearm. A proportional-derivative (PD) architecture is employed in this study to investigate its efficacy performing joint-space control objectives. An intelligent AFC algorithm is also incorporated into the PD to investigate the effectiveness of this hybrid system in compensating disturbances. The Mamdani Fuzzy based rule is employed to approximate the estimated inertial properties of the system to ensure the AFC loop responds efficiently. It is found that the IAFC-PD performed well against the disturbances introduced into the system as compared to the conventional PD control architecture in performing the desired trajectory tracking.

Abiotic and Biotic Mechanisms Controlling In Situ Remediation of NDMA

DTIC Science & Technology

2009-05-01

FINAL REPORT Abiotic and Biotic Mechanisms Controlling In Situ Remediation of NDMA SERDP Project ER-1421 MAY 2009 James E. Szecsody...00-2009 4. TITLE AND SUBTITLE Abiotic and Biotic Mechanisms Controlling In Situ Remediation of NDMA 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c...investigate whether in situ coupled abiotic/biotic degradation of N-nitrosodimethylamine ( NDMA , an emerging contaminant) could be used as a permeable

Size-controlled growth and antibacterial mechanism for Cu:C nanocomposite thin films.

PubMed

Javid, Amjed; Kumar, Manish; Yoon, Seokyoung; Lee, Jung Heon; Han, Jeon Geon

2016-12-21

The interdependence of 'size' and 'volume-fraction' hinders the identification of their individual role in the interface properties of metal nanoparticles (NPs) embedded in a matrix. Here, the case of Cu NPs embedded in a C matrix is presented for their profound antibacterial activity. Cu:C nanocomposite thin films with fixed Cu content (≈12 atomic%) are prepared using a plasma process where plasma energy controls the size of Cu NPs (from 9 nm to 16 nm). An inverse relationship between the size-effect on antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria is established through the real time monitoring of an aliquot by inductively coupled plasma mass spectrometry, which confirmed the inverse relationship of Cu ion release from the nanocomposite with varied Cu NP sizes. It was found that enhancing the total power density increases the plasma density as well as effective kinetic energy of the plasma species, which in turn creates a large number of nucleation sites and restricts the island kind of growth of Cu NPs. The mechanism of NP size-control is illustrated on the basis of ion density and nucleation and the growth regime of plasma species. This physical approach to NP size reduction anticipates a contamination-free competitive recipe of size-control to capping based chemical methods.

Mechanisms of mTORC1 activation by RHEB and inhibition by PRAS40.

PubMed

Yang, Haijuan; Jiang, Xiaolu; Li, Buren; Yang, Hyo J; Miller, Meredith; Yang, Angela; Dhar, Ankita; Pavletich, Nikola P

2017-12-21

The mechanistic target of rapamycin complex 1 (mTORC1) controls cell growth and metabolism in response to nutrients, energy levels, and growth factors. It contains the atypical kinase mTOR and the RAPTOR subunit that binds to the Tor signalling sequence (TOS) motif of substrates and regulators. mTORC1 is activated by the small GTPase RHEB (Ras homologue enriched in brain) and inhibited by PRAS40. Here we present the 3.0 ångström cryo-electron microscopy structure of mTORC1 and the 3.4 ångström structure of activated RHEB-mTORC1. RHEB binds to mTOR distally from the kinase active site, yet causes a global conformational change that allosterically realigns active-site residues, accelerating catalysis. Cancer-associated hyperactivating mutations map to structural elements that maintain the inactive state, and we provide biochemical evidence that they mimic RHEB relieving auto-inhibition. We also present crystal structures of RAPTOR-TOS motif complexes that define the determinants of TOS recognition, of an mTOR FKBP12-rapamycin-binding (FRB) domain-substrate complex that establishes a second substrate-recruitment mechanism, and of a truncated mTOR-PRAS40 complex that reveals PRAS40 inhibits both substrate-recruitment sites. These findings help explain how mTORC1 selects its substrates, how its kinase activity is controlled, and how it is activated by cancer-associated mutations.

Demo of Active Resonators on the Active Noise Control Fan

NASA Image and Video Library

1998-10-01

NASA has been involved in several projects to reduce aircraft engine noise. In the 1990s Active Noise Control was investigated as a potential method to reduce aircraft engine noise. A description and demonstration of Active Resonators on the Active Noise Control Fan is shown in this video.

Mechanism for the activation of glutamate receptors

Cancer.gov

Scientists at the NIH have used a technique called cryo-electron microscopy to determine a molecular mechanism for the activation and desensitization of ionotropic glutamate receptors, a prominent class of neurotransmitter receptors in the brain and spina

Selected advanced aerodynamics and active controls technology concepts development on a derivative B-747

NASA Technical Reports Server (NTRS)

1980-01-01

The feasibility of applying wing tip extensions, winglets, and active control wing load alleviation to the Boeing 747 is investigated. Winglet aerodynamic design methods and high speed wind tunnel test results of winglets and of symmetrically deflected ailerons are presented. Structural resizing analyses to determine weight and aeroelastic twist increments for all the concepts and flutter model test results for the wing with winglets are included. Control law development, system mechanization/reliability studies, and aileron balance tab trade studies for active wing load alleviation systems are discussed. Results are presented in the form of incremental effects on L/D, structural weight, block fuel savings, stability and control, airplane price, and airline operating economics.

Automatized alignment control of wing mechanization in aerodynamic contour of aircraft

NASA Astrophysics Data System (ADS)

Odnokurtsev, K. A.

2018-05-01

The method of automatized control of accuracy of an aircraft aerodynamic contour when mounting wing mechanization elements is described in the article. A control device in the stand of the wing assembling, equipped with the distance sensors, is suggested to be used. The measurement of control points’ inaccuracies is made automatically in a special computer program. Two kinds of sensor calibration are made in advance in order to increase the accuracy of measurements. As a result, the duration of control and adjustment of mechanization elements is reduced.

The anabolic activity of bone tissue, suppressed by disuse, is normalized by brief exposure to extremely low-magnitude mechanical stimuli

NASA Technical Reports Server (NTRS)

Rubin, C.; Xu, G.; Judex, S.

2001-01-01

It is generally believed that mechanical signals must be large in order to be anabolic to bone tissue. Recent evidence indicates, however, that extremely low-magnitude (<10 microstrain) mechanical signals readily stimulate bone formation if induced at a high frequency. We examined the ability of extremely low-magnitude, high-frequency mechanical signals to restore anabolic bone cell activity inhibited by disuse. Adult female rats were randomly assigned to six groups: baseline control, age-matched control, mechanically stimulated for 10 min/day, disuse (hind limb suspension), disuse interrupted by 10 min/day of weight bearing, and disuse interrupted by 10 min/day of mechanical stimulation. After a 28 day protocol, bone formation rates (BFR) in the proximal tibia of mechanically stimulated rats increased compared with age-matched control (+97%). Disuse alone reduced BFR (-92%), a suppression only slightly curbed when disuse was interrupted by 10 min of weight bearing (-61%). In contrast, disuse interrupted by 10 min per day of low-level mechanical intervention normalized BFR to values seen in age-matched controls. This work indicates that this noninvasive, extremely low-level stimulus may provide an effective biomechanical intervention for the bone loss that plagues long-term space flight, bed rest, or immobilization caused by paralysis.

Mechanical Activation of a Multimeric Adhesive Protein Through Domain Conformational Change

NASA Astrophysics Data System (ADS)

Wijeratne, Sithara S.; Botello, Eric; Yeh, Hui-Chun; Zhou, Zhou; Bergeron, Angela L.; Frey, Eric W.; Patel, Jay M.; Nolasco, Leticia; Turner, Nancy A.; Moake, Joel L.; Dong, Jing-fei; Kiang, Ching-Hwa

2013-03-01

The mechanical force-induced activation of the adhesive protein von Willebrand factor (VWF), which experiences high hydrodynamic forces, is essential in initiating platelet adhesion. The importance of the mechanical force-induced functional change is manifested in the multimeric VWF’s crucial role in blood coagulation, when high fluid shear stress activates plasma VWF (PVWF) multimers to bind platelets. Here, we showed that a pathological level of high shear stress exposure of PVWF multimers results in domain conformational changes, and the subsequent shifts in the unfolding force allow us to use force as a marker to track the dynamic states of the multimeric VWF. We found that shear-activated PVWF multimers are more resistant to mechanical unfolding than nonsheared PVWF multimers, as indicated in the higher peak unfolding force. These results provide insight into the mechanism of shear-induced activation of PVWF multimers.

14 CFR 27.923 - Rotor drive system and control mechanism tests.

Code of Federal Regulations, 2010 CFR

2010-01-01

... the position that will give maximum longitudinal cyclic pitch change to simulate forward flight. The... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Rotor drive system and control mechanism....923 Rotor drive system and control mechanism tests. (a) Each part tested as prescribed in this section...

Integrated Application of Active Controls (IAAC) technology to an advanced subsonic transpot project-demonstration act system definition

NASA Technical Reports Server (NTRS)

Hanks, G. W.; Shomber, H. A.; Crumb, C. B.; Flora, C. C.; Macdonald, K. A. B.; Smith, R. D.; Sassi, A. P.; Dorwart, R. J.

1982-01-01

The 1985 ACT airplane is the Final Active Controls Technology (ACT) Airplane with the addition of three-axis fly by wire. Thus it retains all the efficiency features of the full ACT system plus the weight and cost savings accruing from deletion of the mechanical control system. The control system implements the full IAAC spectrum of active controls except flutter-mode control, judged essentially nonbeneficial, and incorporates new control surfaces called flaperons to make the most of wing-load alleviation. This redundant electronic system is conservatively designed to preserve the extreme reliability required of crucial short-period pitch augmentation, which provides more than half of the fuel savings.

Control of mechanical systems with rolling constraints: Application to dynamic control of mobile robots

NASA Technical Reports Server (NTRS)

Sarkar, Nilanjan; Yun, Xiaoping; Kumar, Vijay

1994-01-01

There are many examples of mechanical systems that require rolling contacts between two or more rigid bodies. Rolling contacts engender nonholonomic constraints in an otherwise holonomic system. In this article, we develop a unified approach to the control of mechanical systems subject to both holonomic and nonholonomic constraints. We first present a state space realization of a constrained system. We then discuss the input-output linearization and zero dynamics of the system. This approach is applied to the dynamic control of mobile robots. Two types of control algorithms for mobile robots are investigated: trajectory tracking and path following. In each case, a smooth nonlinear feedback is obtained to achieve asymptotic input-output stability and Lagrange stability of the overall system. Simulation results are presented to demonstrate the effectiveness of the control algorithms and to compare the performane of trajectory-tracking and path-following algorithms.

Redox Control of Leukemia: From Molecular Mechanisms to Therapeutic Opportunities

PubMed Central

Irwin, Mary E.; Rivera-Del Valle, Nilsa

2013-01-01

Abstract Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability—some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients. Antioxid. Redox Signal. 18, 1349–1383. PMID:22900756

Sensory gain control (amplification) as a mechanism of selective attention: electrophysiological and neuroimaging evidence.

PubMed Central

Hillyard, S A; Vogel, E K; Luck, S J

1998-01-01

Both physiological and behavioral studies have suggested that stimulus-driven neural activity in the sensory pathways can be modulated in amplitude during selective attention. Recordings of event-related brain potentials indicate that such sensory gain control or amplification processes play an important role in visual-spatial attention. Combined event-related brain potential and neuroimaging experiments provide strong evidence that attentional gain control operates at an early stage of visual processing in extrastriate cortical areas. These data support early selection theories of attention and provide a basis for distinguishing between separate mechanisms of attentional suppression (of unattended inputs) and attentional facilitation (of attended inputs). PMID:9770220

Controlling the dual mechanisms of oxide interface doping

NASA Astrophysics Data System (ADS)

Dai, Weitao; Cen, Cheng

The formation of two dimensional electron gas (2DEG) at LaAlO3/SrTiO3 interfaces involves multiple electronic and structural causes. The interplay between them makes the investigation of individual mechanism very challenging. Here we demonstrate the nanoscale selective control of two interface doping pathways: charge transfers from surface adsorbed protons and oxygen vacancies created in LaAlO3 layers. The selective control is achieved by combining intensive electric field generated by conducting AFM probe which controls both the creation/migration of oxygen vacancies and the surface proton density, with plasma assisted surface hydroxylation and solvent based proton solvation that act mainly on surface adsorbates. Robust nanoscale reversible metal-insulator transition was achieved at the interfaces with the LaAlO3 layer thicker than the critic thickness. Different combinations of the experimental methods and doping mechanisms enable highly flexible tuning of the 2DEG's carrier density, mobility and sensitivity to ambient environments. The reversible and independent controls of surface states and vacancies add to the fundamental material research capabilities and can benefit future exploration of designed 2DEG nanoelectronics.

A new active variable stiffness suspension system using a nonlinear energy sink-based controller

NASA Astrophysics Data System (ADS)

Anubi, Olugbenga Moses; Crane, Carl D.

2013-10-01

This paper presents the active case of a variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism which consists of a horizontal control strut and a vertical strut. The horizontal strut is used to vary the load transfer ratio by actively controlling the location of the point of attachment of the vertical strut to the car body. The control algorithm, effected by a hydraulic actuator, uses the concept of nonlinear energy sink (NES) to effectively transfer the vibrational energy in the sprung mass to a control mass, thereby reducing the transfer of energy from road disturbance to the car body at a relatively lower cost compared to the traditional active suspension using the skyhook concept. The analyses and simulation results show that a better performance can be achieved by subjecting the point of attachment of a suspension system, to the chassis, to the influence of a horizontal NES system.

Smurf1 inhibits integrin activation by controlling Kindlin-2 ubiquitination and degradation

PubMed Central

Wei, Xiaofan; Wang, Xiang; Zhan, Jun; Chen, Yuhan; Fang, Weigang; Zhang, Lingqiang

2017-01-01

Integrin activation is an indispensable step for various integrin-mediated biological functions. Kindlin-2 is known to coactivate integrins with Talin; however, molecules that restrict integrin activation are elusive. Here, we demonstrate that the E3 ubiquitin ligase Smurf1 controls the amount of Kindlin-2 protein in cells and hinders integrin activation. Smurf1 interacts with and promotes Kindlin-2 ubiquitination and degradation. Smurf1 selectively mediates degradation of Kindlin-2 but not Talin, leading to inhibition of αIIbβ3 integrin activation in Chinese hamster ovary cells and β1 integrin activation in fibroblasts. Enhanced activation of β1 integrin was found in Smurf1-knockout mouse embryonic fibroblasts, which correlates with an increase in Kindlin-2 protein levels. Similarly, a reciprocal relationship between Smurf1 and Kindlin-2 protein levels is found in tissues from colon cancer patients, suggesting that Smurf1 mediates Kindlin-2 degradation in vivo. Collectively, we demonstrate that Smurf1 acts as a brake for integrin activation by controlling Kindlin-2 protein levels, a new mechanism that permits precise modulation of integrin-mediated cellular functions. PMID:28408404

The Neural Mechanism Exploration of Adaptive Motor Control: Dynamical Economic Cell Allocation in the Primary Motor Cortex.

PubMed

Li, Wei; Guo, Yangyang; Fan, Jing; Ma, Chaolin; Ma, Xuan; Chen, Xi; He, Jiping

2017-05-01

Adaptive flexibility is of significance for the smooth and efficient movements in goal attainment. However, the underlying work mechanism of the cerebral cortex in adaptive motor control still remains unclear. How does the cerebral cortex organize and coordinate the activity of a large population of cells in the implementation of various motor strategies? To explore this issue, single-unit activities from the M1 region and kinematic data were recorded simultaneously in monkeys performing 3D reach-to-grasp tasks with different perturbations. Varying motor control strategies were employed and achieved in different perturbed tasks, via the dynamic allocation of cells to modulate specific movement parameters. An economic principle was proposed for the first time to describe a basic rule for cell allocation in the primary motor cortex. This principle, defined as the Dynamic Economic Cell Allocation Mechanism (DECAM), guarantees benefit maximization in cell allocation under limited neuronal resources, and avoids committing resources to uneconomic investments for unreliable factors with no or little revenue. That is to say, the cells recruited are always preferentially allocated to those factors with reliable return; otherwise, the cells are dispatched to respond to other factors about task. The findings of this study might partially reveal the working mechanisms underlying the role of the cerebral cortex in adaptive motor control, wherein is also of significance for the design of future intelligent brain-machine interfaces and rehabilitation device.

The SH2 domain of Abl kinases regulates kinase autophosphorylation by controlling activation loop accessibility.

PubMed

Lamontanara, Allan Joaquim; Georgeon, Sandrine; Tria, Giancarlo; Svergun, Dmitri I; Hantschel, Oliver

2014-11-17

The activity of protein kinases is regulated by multiple molecular mechanisms, and their disruption is a common driver of oncogenesis. A central and almost universal control element of protein kinase activity is the activation loop that utilizes both conformation and phosphorylation status to determine substrate access. In this study, we use recombinant Abl tyrosine kinases and conformation-specific kinase inhibitors to quantitatively analyse structural changes that occur after Abl activation. Allosteric SH2-kinase domain interactions were previously shown to be essential for the leukemogenesis caused by the Bcr-Abl oncoprotein. We find that these allosteric interactions switch the Abl activation loop from a closed to a fully open conformation. This enables the trans-autophosphorylation of the activation loop and requires prior phosphorylation of the SH2-kinase linker. Disruption of the SH2-kinase interaction abolishes activation loop phosphorylation. Our analysis provides a molecular mechanism for the SH2 domain-dependent activation of Abl that may also regulate other tyrosine kinases.

The SH2 domain of Abl kinases regulates kinase autophosphorylation by controlling activation loop accessibility

NASA Astrophysics Data System (ADS)

Lamontanara, Allan Joaquim; Georgeon, Sandrine; Tria, Giancarlo; Svergun, Dmitri I.; Hantschel, Oliver

2014-11-01

The activity of protein kinases is regulated by multiple molecular mechanisms, and their disruption is a common driver of oncogenesis. A central and almost universal control element of protein kinase activity is the activation loop that utilizes both conformation and phosphorylation status to determine substrate access. In this study, we use recombinant Abl tyrosine kinases and conformation-specific kinase inhibitors to quantitatively analyse structural changes that occur after Abl activation. Allosteric SH2-kinase domain interactions were previously shown to be essential for the leukemogenesis caused by the Bcr-Abl oncoprotein. We find that these allosteric interactions switch the Abl activation loop from a closed to a fully open conformation. This enables the trans-autophosphorylation of the activation loop and requires prior phosphorylation of the SH2-kinase linker. Disruption of the SH2-kinase interaction abolishes activation loop phosphorylation. Our analysis provides a molecular mechanism for the SH2 domain-dependent activation of Abl that may also regulate other tyrosine kinases.

Chronic baroreflex activation restores spontaneous baroreflex control and variability of heart rate in obesity-induced hypertension

PubMed Central

Iliescu, Radu; Tudorancea, Ionut; Irwin, Eric D.

2013-01-01

The sensitivity of baroreflex control of heart rate is depressed in subjects with obesity hypertension, which increases the risk for cardiac arrhythmias. The mechanisms are not fully known, and there are no therapies to improve this dysfunction. To determine the cardiovascular dynamic effects of progressive increases in body weight leading to obesity and hypertension in dogs fed a high-fat diet, 24-h continuous recordings of spontaneous fluctuations in blood pressure and heart rate were analyzed in the time and frequency domains. Furthermore, we investigated whether autonomic mechanisms stimulated by chronic baroreflex activation and renal denervation—current therapies in patients with resistant hypertension, who are commonly obese—restore cardiovascular dynamic control. Increases in body weight to ∼150% of control led to a gradual increase in mean arterial pressure to 17 ± 3 mmHg above control (100 ± 2 mmHg) after 4 wk on the high-fat diet. In contrast to the gradual increase in arterial pressure, tachycardia, attenuated chronotropic baroreflex responses, and reduced heart rate variability were manifest within 1–4 days on high-fat intake, reaching 130 ± 4 beats per minute (bpm) (control = 86 ± 3 bpm) and ∼45% and <20%, respectively, of control levels. Subsequently, both baroreflex activation and renal denervation abolished the hypertension. However, only baroreflex activation effectively attenuated the tachycardia and restored cardiac baroreflex sensitivity and heart rate variability. These findings suggest that baroreflex activation therapy may reduce the risk factors for cardiac arrhythmias as well as lower arterial pressure. PMID:23913707

High efficiency and simple technique for controlling mechanisms by EMG signals

NASA Astrophysics Data System (ADS)

Dugarte, N.; Álvarez, A.; Balacco, J.; Mercado, G.; Gonzalez, A.; Dugarte, E.; Javier, F.; Ceballos, G.; Olivares, A.

2016-04-01

This article reports the development of a simple and efficient system that allows control of mechanisms through electromyography (EMG) signals. The novelty about this instrument is focused on individual control of each motion vector mechanism through independent electronic circuits. Each of electronic circuit does positions a motor according to intensity of EMG signal captured. This action defines movement in one mechanical axis considered from an initial point, based on increased muscle tension. The final displacement of mechanism depends on individual’s ability to handle the levels of muscle tension at different body parts. This is the design of a robotic arm where each degree of freedom is handled with a specific microcontroller that responds to signals taken from a defined muscle. The biophysical interaction between the person and the final positioning of the robotic arm is used as feedback. Preliminary tests showed that the control operates with minimal positioning error margins. The constant use of system with the same operator showed that the person adapts and progressively improves at control technique.

Mechanisms of morphine enhancement of spontaneous seizure activity.

PubMed

Saboory, Ehsan; Derchansky, Miron; Ismaili, Mohammed; Jahromi, Shokrollah S; Brull, Richard; Carlen, Peter L; El Beheiry, Hossam

2007-12-01

High-dose opioid therapy can precipitate seizures; however, the mechanism of such a dangerous adverse effect remains poorly understood. The aim of our study was to determine whether the neuroexcitatory activity of high-dose morphine is mediated by selective stimulation of opioid receptors. Mice hippocampi were resected intact and bathed in low magnesium artificial cerebrospinal fluid to induce spontaneous seizure-like events recorded from CA1 neurons. Application of morphine had a biphasic effect on the recorded spontaneous seizure-like events. In a low concentration (10 microM), morphine depressed electrographic seizure activity. Higher morphine concentrations (30 and 100 microM) enhanced seizure activity in an apparent dose-dependent manner. Naloxone, a nonselective opiate antagonist blocked the proconvulsant action of morphine. Selective mu and kappa opiate receptor agonists and antagonists enhanced and suppressed the spontaneous seizure activity, respectively. On the contrary, delta opioid receptor ligands did not have an effect. The proseizure effect of morphine is mediated through selective stimulation of mu and kappa opiate receptors but not the activation of the delta receptor system. The observed dose-dependent mechanism of morphine neuroexcitation underscores careful adjustment and individualized opioid dosing in the clinical setting.

Quality control mechanisms exclude incorrect polymerases from the eukaryotic replication fork

PubMed Central

Schauer, Grant D.; O’Donnell, Michael E.

2017-01-01

The eukaryotic genome is primarily replicated by two DNA polymerases, Pol ε and Pol δ, that function on the leading and lagging strands, respectively. Previous studies have established recruitment mechanisms whereby Cdc45-Mcm2-7-GINS (CMG) helicase binds Pol ε and tethers it to the leading strand, and PCNA (proliferating cell nuclear antigen) binds tightly to Pol δ and recruits it to the lagging strand. The current report identifies quality control mechanisms that exclude the improper polymerase from a particular strand. We find that the replication factor C (RFC) clamp loader specifically inhibits Pol ε on the lagging strand, and CMG protects Pol ε against RFC inhibition on the leading strand. Previous studies show that Pol δ is slow and distributive with CMG on the leading strand. However, Saccharomyces cerevisiae Pol δ–PCNA is a rapid and processive enzyme, suggesting that CMG may bind and alter Pol δ activity or position it on the lagging strand. Measurements of polymerase binding to CMG demonstrate Pol ε binds CMG with a Kd value of 12 nM, but Pol δ binding CMG is undetectable. Pol δ, like bacterial replicases, undergoes collision release upon completing replication, and we propose Pol δ–PCNA collides with the slower CMG, and in the absence of a stabilizing Pol δ–CMG interaction, the collision release process is triggered, ejecting Pol δ on the leading strand. Hence, by eviction of incorrect polymerases at the fork, the clamp machinery directs quality control on the lagging strand and CMG enforces quality control on the leading strand. PMID:28069954

Test and theory for piezoelectric actuator-active vibration control of rotating machinery

NASA Technical Reports Server (NTRS)

Palazzolo, A. B.; Lin, R. R.; Alexander, R. M.; Kascak, A. F.; Montague, J.

1989-01-01

The application of piezoelectric actuators for active vibration control (AVC) of rotating machinery is examined. Theory is derived and the resulting predictions are shown to agree closely with results of tests performed on an air turbine driven-overhung rotor. The test results show significant reduction in unbalance, transient and sub-synchronous responses. Results from a 30-hour endurance test support the AVD system reliability. Various aspects of the electro-mechanical stability of the control system are also discussed and illustrated. Finally, application of the AVC system to an actual jet engine is discussed.

Towards a statistical mechanical theory of active fluids.

PubMed

Marini Bettolo Marconi, Umberto; Maggi, Claudio

2015-12-07

We present a stochastic description of a model of N mutually interacting active particles in the presence of external fields and characterize its steady state behavior in the absence of currents. To reproduce the effects of the experimentally observed persistence of the trajectories of the active particles we consider a Gaussian force having a non-vanishing correlation time τ, whose finiteness is a measure of the activity of the system. With these ingredients we show that it is possible to develop a statistical mechanical approach similar to the one employed in the study of equilibrium liquids and to obtain the explicit form of the many-particle distribution function by means of the multidimensional unified colored noise approximation. Such a distribution plays a role analogous to the Gibbs distribution in equilibrium statistical mechanics and provides complete information about the microscopic state of the system. From here we develop a method to determine the one- and two-particle distribution functions in the spirit of the Born-Green-Yvon (BGY) equations of equilibrium statistical mechanics. The resulting equations which contain extra-correlations induced by the activity allow us to determine the stationary density profiles in the presence of external fields, the pair correlations and the pressure of active fluids. In the low density regime we obtained the effective pair potential ϕ(r) acting between two isolated particles separated by a distance, r, showing the existence of an effective attraction between them induced by activity. Based on these results, in the second half of the paper we propose a mean field theory as an approach simpler than the BGY hierarchy and use it to derive a van der Waals expression of the equation of state.

Stirling engine control mechanism and method

DOEpatents

Dineen, John J.

1983-01-01

A reciprocating-to-rotating motion conversion and power control device for a Stirling engine includes a hub mounted on an offset portion of the output shaft for rotation relative to the shaft and for sliding motion therealong which causes the hub to tilt relative to the axis of rotation of the shaft. This changes the angle of inclination of the hub relative to the shaft axis and changes the axial stroke of a set of arms connected to the hub and nutating therewith. A hydraulic actuating mechanism is connected to the hub for moving its axial position along the shaft. A balancing wheel is linked to the hub and changes its angle of inclination as the angle of inclination of the hub changes to maintain the mechanism in perfect balance throughout its range of motion.

On the Active and Passive Flow Separation Control Techniques over Airfoils

NASA Astrophysics Data System (ADS)

Moghaddam, Tohid; Banazadeh Neishabouri, Nafiseh

2017-10-01

In the present work, recent advances in the field of the active and passive flow separation control, particularly blowing and suction flow control techniques, applied on the common airfoils are briefly reviewed. This broad research area has remained the point of interest for many years as it is applicable to various applications. The suction and blowing flow control methods, among other methods, are more technically feasible and market ready techniques. It is well established that the uniform and/or oscillatory blowing and suction flow control mechanisms significantly improve the lift-to-drag ratio, and further, postpone the boundary layer separation as well as the stall. The oscillatory blowing and suction flow control, however, is more efficient compared to the uniform one. A wide range of parameters is involved in controlling the behavior of a blowing and/or suction flow control, including the location, length, and angle of the jet slots. The oscillation range of the jet slot is another substantial parameter.

Control mechanisms of circadian rhythms in body composition: Implications for manned spaceflight

NASA Technical Reports Server (NTRS)

Ede, M. C. M.

1975-01-01

The mechanisms that underlie the circadian variations in electrolyte content in body fluid compartments were investigated, and the mechanisms that control the oscillations were studied in order to investigate what effects internal desynchronization in such a system would have during manned space flight. The studies were performed using volunteer human subjects and squirrel monkeys. The intercompartmental distribution of potassium was examined when dietary intake, activity, and posture are held constant throughout each 24-hour day. A net flux of potassium was observed out of the body cell mass during the day and a reverse flux from the extracellular fluid into the body cell mass during the night, counterbalanced by changes in urinary potassium excretion. Experiments with monkeys provided evidence for the synchronization of renal potassium excretion by the rhythm of cortisol secretion with the light-dark cycle. Three models of the circadian timing system were formalized.

Hypoglycaemic activity of culinary Pleurotus ostreatus and P. cystidiosus mushrooms in healthy volunteers and type 2 diabetic patients on diet control and the possible mechanisms of action.

PubMed

Jayasuriya, W J A Banukie N; Wanigatunge, Chandanie A; Fernando, Gita H; Abeytunga, D Thusitha U; Suresh, T Sugandhika

2015-02-01

This study determined the oral hypoglycaemic effect of suspensions of freeze dried and powdered (SFDP) Pleurotus ostreatus (P.o) and Pleurotus cystidiosus (P.c), using healthy human volunteers and Type 2 diabetic patients on diet control at a dose of 50 mg/kg/body weight, followed by a glucose load. The possible hypoglycaemic mechanisms were evaluated using rats, by examining intestinal glucose absorption and serum levels of insulin, glucokinase (GK) and glycogen synthase kinase (GSK). The P.o and P.c showed a significant reduction (P < 0.05) in fasting and postprandial serum glucose levels of healthy volunteers and reduced the postprandial serum glucose levels and increased the serum insulin levels (P < 0.05) of Type 2 diabetic patients. The P.o and P.c increased the intestinal absorption of glucose but simultaneously reduced the serum glucose levels (P < 0.05) in rats. Both mushrooms reduced the serum GSK and promoted insulin secretion while P.c increased serum GK (P < 0.05). The hypoglycaemic activity of P.o and P.c makes mushrooms beneficial functional foods in diabetes mellitus. The mechanism of hypoglycaemic activity of P.o and P.c is possibly by increasing GK activity and promoting insulin secretion and thereby increasing the utilization of glucose by peripheral tissues, inhibiting GSK and promoting glycogen synthesis. Copyright © 2014 John Wiley & Sons, Ltd.

Apparent synergy among defense mechanisms in subterranean termites (Rhinotermitidae) against epizootic events: limits and potential for biological control.

PubMed

Chouvenc, Thomas; Su, Nan-Yao

2010-08-01

The use of entomopathogens for biological control of subterranean termites (Rhinotermitidae) has attracted attention in the past four decades, and several laboratory studies have shown promising results with fungal agents. This approach was based on the concept of classical biological control with the use of a virulent agent that can self-replicate in a termite nest and be transmitted among individuals, resulting in an epizootic to kill the entire colony. However, the absence of positive results in field studies challenged the potential of fungal pathogens as a realistic approach for subterranean termite control, and the relationship between fungi and subterranean termites remains poorly understood. A multimodal approach of the currently identified defense mechanisms allowed us to show that subterranean termites have the ability to prevent an epizootic from occurring. The defense mechanisms involved in such resistance are reviewed and documented. Finally, the interactions among three major defense mechanisms (grooming, cellular encapsulation, and gut antifungal activity) were analyzed, and it is suggested that these mechanisms act synergistically to produce an efficient defense against the infection of the fungus at the individual and group level so as to protect the colony from epizootics.

Status and trends in active control technology

NASA Technical Reports Server (NTRS)

Rediess, H. A.; Szalai, K. J.

1975-01-01

The emergence of highly reliable fly-by-wire flight control systems makes it possible to consider a strong reliance on automatic control systems in the design optimization of future aircraft. This design philosophy has been referred to as the control configured vehicle approach or the application of active control technology. Several studies and flight tests sponsored by the Air Force and NASA have demonstrated the potential benefits of control configured vehicles and active control technology. The present status and trends of active control technology are reviewed and the impact it will have on aircraft designs, design techniques, and the designer is predicted.

Canonical and non-canonical mechanisms of Nrf2 activation.

PubMed

Silva-Islas, Carlos Alfredo; Maldonado, Perla D

2018-06-15

Nuclear Factor Erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates the expression of genes involved in the metabolism, immune response, cellular proliferation, and other processes; however, the attention has been focused on the study of its ability to induce the expression of proteins involved in the antioxidant defense. Nrf2 is mainly regulated by Kelch-like ECH-associated protein 1 (Keap1), an adapter substrate of Cullin 3 (Cul3) ubiquitin E3 ligase complex. Keap1 represses Nrf2 activity in the cytoplasm by its sequestering, ubiquitination and proteosomal degradation. Nrf2 activation, through the canonical mechanism, is carried out by electrophilic compounds and oxidative stress where some cysteine residues in Keap1 are oxidized, resulting in a decrease in Nrf2 ubiquitination and an increase in its nuclear translocation and activation. In the nucleus, Nrf2 induces a variety of genes involved in the antioxidant defense. Recently a new mechanism of Nrf2 activation has been described, called the non-canonical pathway, where proteins such as p62, p21, dipeptidyl peptidase III (DPP3), wilms tumor gene on X chromosome (WTX) and others are able to disrupt the Nrf2-Keap1 complex, by direct interaction with Keap1 decreasing Nrf2 ubiquitination and increasing its nuclear translocation and activation. In this review, the regulatory mechanisms involved in both canonical and non-canonical Nrf2 activation are discussed. Copyright © 2018. Published by Elsevier Ltd.

Activator Protein-1: redox switch controlling structure and DNA-binding.

PubMed

Yin, Zhou; Machius, Mischa; Nestler, Eric J; Rudenko, Gabby

2017-11-02

The transcription factor, activator protein-1 (AP-1), binds to cognate DNA under redox control; yet, the underlying mechanism has remained enigmatic. A series of crystal structures of the AP-1 FosB/JunD bZIP domains reveal ordered DNA-binding regions in both FosB and JunD even in absence DNA. However, while JunD is competent to bind DNA, the FosB bZIP domain must undergo a large conformational rearrangement that is controlled by a 'redox switch' centered on an inter-molecular disulfide bond. Solution studies confirm that FosB/JunD cannot undergo structural transition and bind DNA when the redox-switch is in the 'OFF' state, and show that the mid-point redox potential of the redox switch affords it sensitivity to cellular redox homeostasis. The molecular and structural studies presented here thus reveal the mechanism underlying redox-regulation of AP-1 Fos/Jun transcription factors and provide structural insight for therapeutic interventions targeting AP-1 proteins. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Activator Protein-1: redox switch controlling structure and DNA-binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Zhou; Machius, Mischa; Nestler, Eric J.

The transcription factor, activator protein-1 (AP-1), binds to cognate DNA under redox control; yet, the underlying mechanism has remained enigmatic. A series of crystal structures of the AP-1 FosB/JunD bZIP domains reveal ordered DNA-binding regions in both FosB and JunD even in absence DNA. However, while JunD is competent to bind DNA, the FosB bZIP domain must undergo a large conformational rearrangement that is controlled by a ‘redox switch’ centered on an inter-molecular disulfide bond. Solution studies confirm that FosB/JunD cannot undergo structural transition and bind DNA when the redox-switch is in the ‘OFF’ state, and show that the mid-pointmore » redox potential of the redox switch affords it sensitivity to cellular redox homeostasis. The molecular and structural studies presented here thus reveal the mechanism underlying redox-regulation of AP-1 Fos/Jun transcription factors and provide structural insight for therapeutic interventions targeting AP-1 proteins.« less

Active weld control

NASA Technical Reports Server (NTRS)

Powell, Bradley W.; Burroughs, Ivan A.

1994-01-01

Through the two phases of this contract, sensors for welding applications and parameter extraction algorithms have been developed. These sensors form the foundation of a weld control system which can provide action weld control through the monitoring of the weld pool and keyhole in a VPPA welding process. Systems of this type offer the potential of quality enhancement and cost reduction (minimization of rework on faulty welds) for high-integrity welding applications. Sensors for preweld and postweld inspection, weld pool monitoring, keyhole/weld wire entry monitoring, and seam tracking were developed. Algorithms for signal extraction were also developed and analyzed to determine their application to an adaptive weld control system. The following sections discuss findings for each of the three sensors developed under this contract: (1) weld profiling sensor; (2) weld pool sensor; and (3) stereo seam tracker/keyhole imaging sensor. Hardened versions of these sensors were designed and built under this contract. A control system, described later, was developed on a multiprocessing/multitasking operating system for maximum power and flexibility. Documentation for sensor mechanical and electrical design is also included as appendices in this report.

Experiments on reduction of propeller induced interior noise by active control of cylinder vibration

NASA Technical Reports Server (NTRS)

Fuller, C. R.; Jones, J. D.

1987-01-01

The feasibility of reducing interior noise caused by advanced turbo propellers by controlling the vibration of aircraft fuselages was investigated by performing experiments in an anechoic chamber with an aircraft model test rig and apparatus. It was found that active vibration control provides reasonable global attenuation of interior noise levels for the cases of resonant (at 576 Hz) and forced (at 708 Hz) system response. The controlling mechanism behind the effect is structural-acoustic coupling between the shell and the contained field, termed interface modal filtering.

Reliable and Affordable Control Systems Active Combustor Pattern Factor Control

NASA Technical Reports Server (NTRS)

McCarty, Bob; Tomondi, Chris; McGinley, Ray

2004-01-01

Active, closed-loop control of combustor pattern factor is a cooperative effort between Honeywell (formerly AlliedSignal) Engines and Systems and the NASA Glenn Research Center to reduce emissions and turbine-stator vane temperature variations, thereby enhancing engine performance and life, and reducing direct operating costs. Total fuel flow supplied to the engine is established by the speed/power control, but the distribution to individual atomizers will be controlled by the Active Combustor Pattern Factor Control (ACPFC). This system consist of three major components: multiple, thin-film sensors located on the turbine-stator vanes; fuel-flow modulators for individual atomizers; and control logic and algorithms within the electronic control.

Antenna Mechanism of Length Control of Actin Cables

PubMed Central

Mohapatra, Lishibanya; Goode, Bruce L.; Kondev, Jane

2015-01-01

Actin cables are linear cytoskeletal structures that serve as tracks for myosin-based intracellular transport of vesicles and organelles in both yeast and mammalian cells. In a yeast cell undergoing budding, cables are in constant dynamic turnover yet some cables grow from the bud neck toward the back of the mother cell until their length roughly equals the diameter of the mother cell. This raises the question: how is the length of these cables controlled? Here we describe a novel molecular mechanism for cable length control inspired by recent experimental observations in cells. This “antenna mechanism” involves three key proteins: formins, which polymerize actin, Smy1 proteins, which bind formins and inhibit actin polymerization, and myosin motors, which deliver Smy1 to formins, leading to a length-dependent actin polymerization rate. We compute the probability distribution of cable lengths as a function of several experimentally tuneable parameters such as the formin-binding affinity of Smy1 and the concentration of myosin motors delivering Smy1. These results provide testable predictions of the antenna mechanism of actin-cable length control. PMID:26107518

Benefits of detailed models of muscle activation and mechanics

NASA Technical Reports Server (NTRS)

Lehman, S. L.; Stark, L.

1981-01-01

Recent biophysical and physiological studies identified some of the detailed mechanisms involved in excitation-contraction coupling, muscle contraction, and deactivation. Mathematical models incorporating these mechanisms allow independent estimates of key parameters, direct interplay between basic muscle research and the study of motor control, and realistic model behaviors, some of which are not accessible to previous, simpler, models. The existence of previously unmodeled behaviors has important implications for strategies of motor control and identification of neural signals. New developments in the analysis of differential equations make the more detailed models feasible for simulation in realistic experimental situations.

Monitoring and controlling ovarian activity in elephants.

PubMed

Thitaram, Chatchote; Brown, Janine L

2018-03-15

Both Asian (Elephas maximus) and African (Loxodonta africana) elephants are important keystone, umbrella and flagship species. Paradoxically, world population numbers of both species are declining in many of their natural ranges due mainly to poaching, while over population of elephants in some areas is resulting in serious human-elephant conflict, and modifications of natural habitats that impact biodiversity. Understanding mechanisms of reproductive control is vital to effective population management, and for that reason significant advances have been made in endocrine and ultrasonographic monitoring techniques, particularly in studies of elephants ex situ. However, there remains a need to develop new methods to control ovarian activity, both for enhancing and inhibiting reproduction, to maintain population numbers at levels that ensure species survival and their ability to safely cohabitate with humans and other species. We present an overview of reproductive monitoring methods and how they have contributed to our knowledge of elephant reproductive biology, as well as their application for in situ and ex situ conservation purposes. Copyright © 2017 Elsevier Inc. All rights reserved.

About mechanisms of tetonic activity of the satellites

NASA Astrophysics Data System (ADS)

Barkin, Yu. V.

2003-04-01

ABOUT MECHANISMS OF TECTONIC ACTIVITY OF THE SATELLITES Yu.V. Barkin Sternberg Astronomical Institute, Moscow, Russia, barkin@sai.msu.ru Due to attraction of the central planet and others external bodies satellite is subjected by tidal and non-tidal deformations. Elastic energy is changed in dependence from mutual position and motion of celestial bodies and as result the tensional state of satellite and its tectonic (endogenous) activity also is changed. Satellites of the planets have the definite shell’s structure and due to own rotation these shells are characterized by different oblatenesses. Gravitational interaction of the satellite and its mother planet generates big additional mechanical forces (and moments) between the neighboring non-spherical shells of the satellite (mantle, core and crust). These forces and moments are cyclic functions of time, which are changed in the different time-scales. They generate corresponding cyclic perturbations of the tensional state of the shells, their deformations, small relative transnational displacements and slow rotation of the shells and others. In geological period of time it leads to a fundamental tectonic reconstruction of the body. Definite contribution to discussed phenomena are caused by classical tidal mechanism. of planet-satellite interaction. But in this report we discuss in first the new mechanisms of endogenous activity of celestial bodies. They are connected with differential gravitational attraction of non-spherical satellite shells by the external celestial bodies which leads: 1) to small relative rotation (nutations) of the shells; 2) to small relative translational motions of the shells (displacements of their center of mass); 3) to relative displacements and rotations of the shells due to eccentricity of their center of mass positions; 4) to viscous elastic deformations of the shells and oth. (Barkin, 2001). For higher evaluations of the power of satellite endogenous activities were obtained

Designing Crane Controls with Applied Mechanical and Electrical Safety Features

NASA Technical Reports Server (NTRS)

Lytle, Bradford P.; Walczak, Thomas A.

2002-01-01

The use of overhead traveling bridge cranes in many varied applications is common practice. In particular, the use of cranes in the nuclear, military, commercial, aerospace, and other industries can involve safety critical situations. Considerations for Human Injury or Casualty, Loss of Assets, Endangering the Environment, or Economic Reduction must be addressed. Traditionally, in order to achieve additional safety in these applications, mechanical systems have been augmented with a variety of devices. These devices assure that a mechanical component failure shall reduce the risk of a catastrophic loss of the correct and/or safe load carrying capability. ASME NOG-1-1998, (Rules for Construction of Overhead and Gantry Cranes, Top Running Bridge, and Multiple Girder), provides design standards for cranes in safety critical areas. Over and above the minimum safety requirements of todays design standards, users struggle with obtaining a higher degree of reliability through more precise functional specifications while attempting to provide "smart" safety systems. Electrical control systems also may be equipped with protective devices similar to the mechanical design features. Demands for improvement of the cranes "control system" is often recognized, but difficult to quantify for this traditionally "mechanically" oriented market. Finite details for each operation must be examined and understood. As an example, load drift (or small motions) at close tolerances can be unacceptable (and considered critical). To meet these high functional demands encoders and other devices are independently added to control systems to provide motion and velocity feedback to the control drive. This paper will examine the implementation of Programmable Electronic Systems (PES). PES is a term this paper will use to describe any control system utilizing any programmable electronic device such as Programmable Logic Controllers (PLC), or an Adjustable Frequency Drive (AID) 'smart' programmable

Active control of sound transmission through a double panel partition

NASA Astrophysics Data System (ADS)

Sas, P.; Bao, C.; Augusztinovicz, F.; Desmet, W.

1995-03-01

The feasibility of improving the insertion loss of lightweight double panel partitions by using small loudspeakers as active noise control sources inside the air gap between both panels of the partition is investigated analytically, numerically and experimentally in this paper. A theoretical analysis of the mechanisms of the fluid-structure interaction of double panel structures is presented in order to gain insight into the physical phenomena underlying the behaviour of a coupled vibro-acoustic system controlled by active methods. The analysis, based on modal coupling theory, enables one to derive some qualitative predictions concerning the potentials and limitations of the proposed approach. The theoretical analysis is valid only for geometrically simple structures. For more complex geometries, numerical simulations are required. Therefore the potential use of active noise control inside double panel structures has been analyzed by using coupled finite element and boundary element methods. To verify the conclusions drawn from the theoretical analysis and the numerical calculation and, above all, to demonstrate the potential of the proposed approach, experiments have been conducted with a laboratory set-up. The performance of the proposed approach was evaluated in terms of relative insertion loss measurements. It is shown that a considerable improvement of the insertion loss has been achieved around the lightly damped resonances of the system for the frequency range investigated (60-220 Hz).

Mechanical control of tissue-engineered bone.

PubMed

Hung, Ben P; Hutton, Daphne L; Grayson, Warren L

2013-01-31

Bone is a load-bearing tissue and physical forces play key roles in the development and maintenance of its structure. Mechanical cues can stimulate the expression of an osteogenic phenotype, enhance matrix and mineral deposition, and influence tissue organization to improve the functional outcome of engineered bone grafts. In recent years, a number of studies have investigated the effects of biophysical forces on the bone formation properties of osteoprogenitor cells. The application of physiologically relevant stimuli to tissue-engineered bone may be determined through observation and understanding of forces to which osteoblasts, osteoclasts, and osteocytes are exposed in native bone. Subsequently, these cues may be parameterized and their effects studied in well-defined in vitro systems. The osteo-inductive effects of three specific mechanical cues - shear stress, substrate rigidity, and nanotopography - on cells cultured in monolayer or in three-dimensional biomaterial scaffolds in vitro are reviewed. Additionally, we address the time-dependent effects of mechanical cues on vascular infiltration and de novo bone formation in acellular scaffolds implanted into load-bearing sites in vivo. Recent studies employing cutting-edge advances in biomaterial fabrication and bioreactor design have provided key insights into the role of mechanical cues on cellular fate and tissue properties of engineered bone grafts. By providing mechanistic understanding, future studies may go beyond empirical approaches to rational design of engineering systems to control tissue development.

Predicting and controlling risks from human exposures to vibration and mechanical shock: flag waving and flag weaving.

PubMed

Griffin, Michael J

2015-01-01

At work or in leisure activities, many people are exposed to vibration or mechanical shocks associated with risks of injury or disease. This paper identifies information that can be used to decide whether there may be a risk from exposure to hand-transmitted vibration or whole-body vibration and shock, and suggests actions that can control the risks. The complex and time-varying nature of human exposures to vibration and shock, the complexity of the different disorders and uncertainty as to the mechanisms of injury and the factors influencing injury have prevented the definition of dose-response relationships well proven by scientific study. It is necessary to wave a flag indicating when there is a need to control risks from exposure to vibration and shock while scientific enquiry provides understanding needed to weave a better flag. It is concluded that quantifying exposure severity is often neither necessary nor sufficient to either identify risks or implement measures that control the risks. The identification of risks associated with exposure to vibration and mechanical shock cannot, and need not, rely solely on the quantification of exposure severity. Qualitative methods can provide a sufficient indication of the need for control measures, which should not be restricted to reducing standardised measures of exposure severity.

Activation of context-specific attentional control sets by exogenous allocation of visual attention to the context?

PubMed

Gottschalk, Caroline; Fischer, Rico

2017-03-01

Different contexts with high versus low conflict frequencies require a specific attentional control involvement, i.e., strong attentional control for high conflict contexts and less attentional control for low conflict contexts. While it is assumed that the corresponding control set can be activated upon stimulus presentation at the respective context (e.g., upper versus lower location), the actual features that trigger control set activation are to date not described. Here, we ask whether the perceptual priming of the location context by an abrupt onset of irrelevant stimuli is sufficient in activating the context-specific attentional control set. For example, the mere onset of a stimulus might disambiguate the relevant location context and thus, serve as a low-level perceptual trigger mechanism that activates the context-specific attentional control set. In Experiment 1 and 2, the onsets of task-relevant and task-irrelevant (distracter) stimuli were manipulated at each context location to compete for triggering the activation of the appropriate control set. In Experiment 3, a prior training session enabled distracter stimuli to establish contextual control associations of their own before entering the test session. Results consistently showed that the mere onset of a task-irrelevant stimulus (with or without a context-control association) is not sufficient to activate the context-associated attentional control set by disambiguating the relevant context location. Instead, we argue that the identification of the relevant stimulus at the respective context is a precondition to trigger the activation of the context-associated attentional control set.

[Effects of mechanical transplanting of rice with controlled release bulk blending fertilizer on rice yield and soil fertility].

PubMed

Zhang, Xuan; Ding, Jun-Shan; Liu, Yan-Ling; Gu, Yan; Han, Ke-Feng; Wu, Liang-Huan

2014-03-01

Abstract: A 2-year field experiment with a yellow-clay paddy soil in Zhejiang Province was conducted to study the effects of different planting measures combined with different fertilization practices on rice yield, soil nutrients, microbial biomass C and N and activities of urease, phosphatase, sucrase and hydrogen peroxidase at the maturity stage. Results showed that mechanical transplanting of rice with controlled release bulk blending (BB) fertilizer (BBMT) could achieve a significantly higher mean yield than traditional manual transplanting with traditional fertilizer (TFTM) and direct seeding with controlled release BB fertilizer (BBDS) by 16.3% and 27.0%, respectively. The yield by BBMT was similar to that by traditional manual transplanting with controlled release BB fertilizer (BBTM). Compared with TFTM, BBMT increased the contents of soil total-N, available N, available P and microbial biomass C, and the activities of urease, sucrase and hydrogen peroxidase by 21.5%, 13.6%, 41.2%, 27.1%, 50.0%, 22.5% and 46.2%, respectively. Therefore, BBMT, a simple high-efficiency rice cultivation method with use of a light-weighted mechanical transplanter, should be widely promoted and adopted.

Self-cleavage of human CLCA1 protein by a novel internal metalloprotease domain controls calcium-activated chloride channel activation.

PubMed

Yurtsever, Zeynep; Sala-Rabanal, Monica; Randolph, David T; Scheaffer, Suzanne M; Roswit, William T; Alevy, Yael G; Patel, Anand C; Heier, Richard F; Romero, Arthur G; Nichols, Colin G; Holtzman, Michael J; Brett, Tom J

2012-12-07

The chloride channel calcium-activated (CLCA) family are secreted proteins that regulate both chloride transport and mucin expression, thus controlling the production of mucus in respiratory and other systems. Accordingly, human CLCA1 is a critical mediator of hypersecretory lung diseases, such as asthma, chronic obstructive pulmonary disease, and cystic fibrosis, that manifest mucus obstruction. Despite relevance to homeostasis and disease, the mechanism of CLCA1 function remains largely undefined. We address this void by showing that CLCA proteins contain a consensus proteolytic cleavage site recognized by a novel zincin metalloprotease domain located within the N terminus of CLCA itself. CLCA1 mutations that inhibit self-cleavage prevent activation of calcium-activated chloride channel (CaCC)-mediated chloride transport. CaCC activation requires cleavage to unmask the N-terminal fragment of CLCA1, which can independently gate CaCCs. Gating of CaCCs mediated by CLCA1 does not appear to involve proteolytic cleavage of the channel because a mutant N-terminal fragment deficient in proteolytic activity is able to induce currents comparable with that of the native fragment. These data provide both a mechanistic basis for CLCA1 self-cleavage and a novel mechanism for regulation of chloride channel activity specific to the mucosal interface.

11. LAUNCH CONTROL SUPPORT BUILDING. INTERIOR OF MECHANICAL ROOM. VIEW ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. LAUNCH CONTROL SUPPORT BUILDING. INTERIOR OF MECHANICAL ROOM. VIEW TO SOUTHEAST. - Minuteman III ICBM Launch Control Facility November-1, 1.5 miles North of New Raymer & State Highway 14, New Raymer, Weld County, CO

Evidence from intrinsic activity that asymmetry of the human brain is controlled by multiple factors.

PubMed

Liu, Hesheng; Stufflebeam, Steven M; Sepulcre, Jorge; Hedden, Trey; Buckner, Randy L

2009-12-01

Cerebral lateralization is a fundamental property of the human brain and a marker of successful development. Here we provide evidence that multiple mechanisms control asymmetry for distinct brain systems. Using intrinsic activity to measure asymmetry in 300 adults, we mapped the most strongly lateralized brain regions. Both men and women showed strong asymmetries with a significant, but small, group difference. Factor analysis on the asymmetric regions revealed 4 separate factors that each accounted for significant variation across subjects. The factors were associated with brain systems involved in vision, internal thought (the default network), attention, and language. An independent sample of right- and left-handed individuals showed that hand dominance affects brain asymmetry but differentially across the 4 factors supporting their independence. These findings show the feasibility of measuring brain asymmetry using intrinsic activity fluctuations and suggest that multiple genetic or environmental mechanisms control cerebral lateralization.

Quantum mechanical design of enzyme active sites.

PubMed

Zhang, Xiyun; DeChancie, Jason; Gunaydin, Hakan; Chowdry, Arnab B; Clemente, Fernando R; Smith, Adam J T; Handel, T M; Houk, K N

2008-02-01

The design of active sites has been carried out using quantum mechanical calculations to predict the rate-determining transition state of a desired reaction in presence of the optimal arrangement of catalytic functional groups (theozyme). Eleven versatile reaction targets were chosen, including hydrolysis, dehydration, isomerization, aldol, and Diels-Alder reactions. For each of the targets, the predicted mechanism and the rate-determining transition state (TS) of the uncatalyzed reaction in water is presented. For the rate-determining TS, a catalytic site was designed using naturalistic catalytic units followed by an estimation of the rate acceleration provided by a reoptimization of the catalytic site. Finally, the geometries of the sites were compared to the X-ray structures of related natural enzymes. Recent advances in computational algorithms and power, coupled with successes in computational protein design, have provided a powerful context for undertaking such an endeavor. We propose that theozymes are excellent candidates to serve as the active site models for design processes.

Economic evaluation of infection control activities.

PubMed

Seko, T; Tachi, T; Kawashima, N; Maeda, T; Yasuda, M; Noguchi, Y; Teramachi, H

2017-08-01

Healthcare-associated infections by drug-resistant bacteria affect a patient's prognosis. Infection control activities at medical institutions in Japan are increasingly focused on the threat from these bacteria. To undertake a full cost analysis that included the costs of consumables and labour required for infection control activities. The cost of infection control activities undertaken by the infection control team (ICT) at Nishimino Kosei Hospital in Japan was surveyed from January 2013 to December 2015. The evaluation index of infection control activities used the meticillin-resistant Staphylococcus aureus detection rate. The cost:effectiveness ratio (CER) of each intervention was calculated. Consumables and labour costs increased over time, as did the ratio of labour cost to total cost over time. However, the CER of interventions was found to have decreased, from ¥164,177 in 2014 to ¥57,989 in 2015. There were increases not only in the amount of consumables, but also in ICT time, suggesting the possibility of improvements in the economic efficiency of infection control. Increasing the amount of consumables and the time input of the ICT could help improve the economic efficiency of infection control. Our research suggests the possibility for improvements in the economic efficiency of infection control. Copyright © 2017 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.

Installation of active noise control and active vibration control on a GP40-2 locomotive : final report.

DOT National Transportation Integrated Search

2016-06-01

This project evaluated the performance of active noise control (ANC) and active vibration control (AVC) technologies using a GP40-2 locomotive located at the Transportation Technology Center (TTC) near Pueblo, CO, to determine the applicability of AN...

Active noise control using noise source having adaptive resonant frequency tuning through stiffness variation

NASA Technical Reports Server (NTRS)

Rajiyah, Harindra (Inventor); Hedeen, Robert A. (Inventor); Pla, Frederic G. (Inventor); Renshaw, Anthony A. (Inventor)

1995-01-01

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.

Development of Ti microalloyed high strength steel plate by controlling thermo-mechanical control process schedule

NASA Astrophysics Data System (ADS)

Xia, Jinian; Huo, Xiangdong; Li, Liejun; Peng, Zhengwu; Chen, Songjun

2017-12-01

In this study, the TMCP parameters including non-recrystallization temperature (Tnr) and optimal isothermal temperature were determined by thermal simulation experiments, and a new Ti microalloyed high strength steel plate was developed by controlling thermo-mechanical control process (TMCP) schedule. The effects of TMCP process on microstructural features, precipitation behavior and mechanical properties of Ti microalloyed high strength steel plate were investigated. The results revealed that the double-stage rolling process consist of rolling in the γ recrystallization region and the γ non-recrystallization region was benefical to promoting the mechanical properties of Ti microalloyed steel by achieving grain refinement. It was also found that large amounts of fine TiC (<10 nm) particles were precipitated during the isothermal treatment at 600 °C, which generated a 215 MPa precipitation strengthening effect.

Optical control of antibacterial activity

NASA Astrophysics Data System (ADS)

Velema, Willem A.; van der Berg, Jan Pieter; Hansen, Mickel J.; Szymanski, Wiktor; Driessen, Arnold J. M.; Feringa, Ben L.

2013-11-01

Bacterial resistance is a major problem in the modern world, stemming in part from the build-up of antibiotics in the environment. Novel molecular approaches that enable an externally triggered increase in antibiotic activity with high spatiotemporal resolution and auto-inactivation are highly desirable. Here we report a responsive, broad-spectrum, antibacterial agent that can be temporally activated with light, whereupon it auto-inactivates on the scale of hours. The use of such a ‘smart’ antibiotic might prevent the build-up of active antimicrobial material in the environment. Reversible optical control over active drug concentration enables us to obtain pharmacodynamic information. Precisely localized control of activity is achieved, allowing the growth of bacteria to be confined to defined patterns, which has potential for the development of treatments that avoid interference with the endogenous microbial population in other parts of the organism.

Cell cycle control, checkpoint mechanisms, and genotoxic stress.

PubMed Central

Shackelford, R E; Kaufmann, W K; Paules, R S

1999-01-01

The ability of cells to maintain genomic integrity is vital for cell survival and proliferation. Lack of fidelity in DNA replication and maintenance can result in deleterious mutations leading to cell death or, in multicellular organisms, cancer. The purpose of this review is to discuss the known signal transduction pathways that regulate cell cycle progression and the mechanisms cells employ to insure DNA stability in the face of genotoxic stress. In particular, we focus on mammalian cell cycle checkpoint functions, their role in maintaining DNA stability during the cell cycle following exposure to genotoxic agents, and the gene products that act in checkpoint function signal transduction cascades. Key transitions in the cell cycle are regulated by the activities of various protein kinase complexes composed of cyclin and cyclin-dependent kinase (Cdk) molecules. Surveillance control mechanisms that check to ensure proper completion of early events and cellular integrity before initiation of subsequent events in cell cycle progression are referred to as cell cycle checkpoints and can generate a transient delay that provides the cell more time to repair damage before progressing to the next phase of the cycle. A variety of cellular responses are elicited that function in checkpoint signaling to inhibit cyclin/Cdk activities. These responses include the p53-dependent and p53-independent induction of Cdk inhibitors and the p53-independent inhibitory phosphorylation of Cdk molecules themselves. Eliciting proper G1, S, and G2 checkpoint responses to double-strand DNA breaks requires the function of the Ataxia telangiectasia mutated gene product. Several human heritable cancer-prone syndromes known to alter DNA stability have been found to have defects in checkpoint surveillance pathways. Exposures to several common sources of genotoxic stress, including oxidative stress, ionizing radiation, UV radiation, and the genotoxic compound benzo[a]pyrene, elicit cell cycle

Adaptively Adjusted Event-Triggering Mechanism on Fault Detection for Networked Control Systems.

PubMed

Wang, Yu-Long; Lim, Cheng-Chew; Shi, Peng

2016-12-08

This paper studies the problem of adaptively adjusted event-triggering mechanism-based fault detection for a class of discrete-time networked control system (NCS) with applications to aircraft dynamics. By taking into account the fault occurrence detection progress and the fault occurrence probability, and introducing an adaptively adjusted event-triggering parameter, a novel event-triggering mechanism is proposed to achieve the efficient utilization of the communication network bandwidth. Both the sensor-to-control station and the control station-to-actuator network-induced delays are taken into account. The event-triggered sensor and the event-triggered control station are utilized simultaneously to establish new network-based closed-loop models for the NCS subject to faults. Based on the established models, the event-triggered simultaneous design of fault detection filter (FDF) and controller is presented. A new algorithm for handling the adaptively adjusted event-triggering parameter is proposed. Performance analysis verifies the effectiveness of the adaptively adjusted event-triggering mechanism, and the simultaneous design of FDF and controller.

Antagonist-perturbation mechanism for activation function-2 fixed motifs: active conformation and docking mode of retinoid X receptor antagonists

NASA Astrophysics Data System (ADS)

Tsuji, Motonori

2017-06-01

HX531, which contains a dibenzodiazepine skeleton, is one of the first retinoid X receptor (RXR) antagonists. Functioning via RXR-PPARγ heterodimer, this compound is receiving a lot of attention as a therapeutic drug candidate for diabetic disease controlling differentiation of adipose tissue. However, the active conformation of HX531 for RXRs is not well established. In the present study, quantum mechanics calculations and molecular mechanical docking simulations were carried out to precisely study the docking mode of HX531 with the human RXRα ligand-binding domain, as well as to provide a new approach to drug design using a structure-based perspective. It was suggested that HX531, which has the R configuration for the bent dibenzodiazepine plane together with the equatorial configuration for the N-methyl group attached to the nitrogen atom in the seven-membered diazepine ring, is a typical activation function-2 (AF-2) fixed motif perturbation type antagonist, which destabilizes the formation of AF-2 fixed motifs. On the other hand, the docking simulations supported the experimental result that LG100754 is an RXR homodimer antagonist and an RXR heterodimer agonist.

Self-Healing Nanocomposite Hydrogel with Well-Controlled Dynamic Mechanics

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Mishra, Sumeet; Chen, Pangkuan; Tracy, Joseph; Holten-Andersen, Niels

Network dynamics is a crucial factor that determines the macroscopic self-healing rate and efficiency in polymeric hydrogel materials, yet its controllability is seldom studied in most reported self-healing hydrogel systems. Inspired by mussel's adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we next designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two hierarchical relaxation modes, we are able to finely control the gel's dynamic mechanical behavior from a viscoelastic fluid to a stiff solid, yet preserving its fast self-healing property without the need for external stimuli.

Mechanism and active variety of allelochemicals

USGS Publications Warehouse

Peng, S.-L.; Wen, J.; Guo, Q.-F.

2004-01-01

This article summarizes allelochemicals' active variety, its potential causes and function mechanisms. Allelochemicals' activity varies with temperature, photoperiod, water and soils during natural processes, with its initial concentration, compound structure and mixed degree during functional processes, with plant accessions, tissues and maturity within-species, and with research techniques and operation processes. The prospective developmental aspects of allelopathy studies in the future are discussed. Future research should focus on: (1) to identify and purify allelochemicals more effectively, especially for agriculture, (2) the functions of allelopathy at the molecular structure level, (3) using allelopathy to explain plant species interactions, (4) allelopathy as a driving force of succession, and (5) the significance of allelopathy in the evolutionary processes.

Mechanical stress regulates insulin sensitivity through integrin-dependent control of insulin receptor localization.

PubMed

Kim, Jung; Bilder, David; Neufeld, Thomas P

2018-01-15

Insulin resistance, the failure to activate insulin signaling in the presence of ligand, leads to metabolic diseases, including type 2 diabetes. Physical activity and mechanical stress have been shown to protect against insulin resistance, but the molecular mechanisms remain unclear. Here, we address this relationship in the Drosophila larval fat body, an insulin-sensitive organ analogous to vertebrate adipose tissue and livers. We found that insulin signaling in Drosophila fat body cells is abolished in the absence of physical activity and mechanical stress even when excess insulin is present. Physical movement is required for insulin sensitivity in both intact larvae and fat bodies cultured ex vivo. Interestingly, the insulin receptor and other downstream components are recruited to the plasma membrane in response to mechanical stress, and this membrane localization is rapidly lost upon disruption of larval or tissue movement. Sensing of mechanical stimuli is mediated in part by integrins, whose activation is necessary and sufficient for mechanical stress-dependent insulin signaling. Insulin resistance develops naturally during the transition from the active larval stage to the immotile pupal stage, suggesting that regulation of insulin sensitivity by mechanical stress may help coordinate developmental programming with metabolism. © 2018 Kim et al.; Published by Cold Spring Harbor Laboratory Press.

Development of a Blood Pressure Measurement Instrument with Active Cuff Pressure Control Schemes.

PubMed

Kuo, Chung-Hsien; Wu, Chun-Ju; Chou, Hung-Chyun; Chen, Guan-Ting; Kuo, Yu-Cheng

2017-01-01

This paper presents an oscillometric blood pressure (BP) measurement approach based on the active control schemes of cuff pressure. Compared with conventional electronic BP instruments, the novelty of the proposed BP measurement approach is to utilize a variable volume chamber which actively and stably alters the cuff pressure during inflating or deflating cycles. The variable volume chamber is operated with a closed-loop pressure control scheme, and it is activated by controlling the piston position of a single-acting cylinder driven by a screw motor. Therefore, the variable volume chamber could significantly eliminate the air turbulence disturbance during the air injection stage when compared to an air pump mechanism. Furthermore, the proposed active BP measurement approach is capable of measuring BP characteristics, including systolic blood pressure (SBP) and diastolic blood pressure (DBP), during the inflating cycle. Two modes of air injection measurement (AIM) and accurate dual-way measurement (ADM) were proposed. According to the healthy subject experiment results, AIM reduced 34.21% and ADM reduced 15.78% of the measurement time when compared to a commercial BP monitor. Furthermore, the ADM performed much consistently (i.e., less standard deviation) in the measurements when compared to a commercial BP monitor.

Mechanism-based screen for G1/S checkpoint activators identifies a selective activator of EIF2AK3/PERK signalling.

PubMed

Stockwell, Simon R; Platt, Georgina; Barrie, S Elaine; Zoumpoulidou, Georgia; Te Poele, Robert H; Aherne, G Wynne; Wilson, Stuart C; Sheldrake, Peter; McDonald, Edward; Venet, Mathilde; Soudy, Christelle; Elustondo, Frédéric; Rigoreau, Laurent; Blagg, Julian; Workman, Paul; Garrett, Michelle D; Mittnacht, Sibylle

2012-01-01

Human cancers often contain genetic alterations that disable G1/S checkpoint control and loss of this checkpoint is thought to critically contribute to cancer generation by permitting inappropriate proliferation and distorting fate-driven cell cycle exit. The identification of cell permeable small molecules that activate the G1/S checkpoint may therefore represent a broadly applicable and clinically effective strategy for the treatment of cancer. Here we describe the identification of several novel small molecules that trigger G1/S checkpoint activation and characterise the mechanism of action for one, CCT020312, in detail. Transcriptional profiling by cDNA microarray combined with reverse genetics revealed phosphorylation of the eukaryotic initiation factor 2-alpha (EIF2A) through the eukaryotic translation initiation factor 2-alpha kinase 3 (EIF2AK3/PERK) as the mechanism of action of this compound. While EIF2AK3/PERK activation classically follows endoplasmic reticulum (ER) stress signalling that sets off a range of different cellular responses, CCT020312 does not trigger these other cellular responses but instead selectively elicits EIF2AK3/PERK signalling. Phosphorylation of EIF2A by EIF2A kinases is a known means to block protein translation and hence restriction point transit in G1, but further supports apoptosis in specific contexts. Significantly, EIF2AK3/PERK signalling has previously been linked to the resistance of cancer cells to multiple anticancer chemotherapeutic agents, including drugs that target the ubiquitin/proteasome pathway and taxanes. Consistent with such findings CCT020312 sensitizes cancer cells with defective taxane-induced EIF2A phosphorylation to paclitaxel treatment. Our work therefore identifies CCT020312 as a novel small molecule chemical tool for the selective activation of EIF2A-mediated translation control with utility for proof-of-concept applications in EIF2A-centered therapeutic approaches, and as a chemical starting point for

Oxaliplatin: mechanism of action and antineoplastic activity.

PubMed

Raymond, E; Faivre, S; Woynarowski, J M; Chaney, S G

1998-04-01

Oxaliplatin, a platinum-based chemotherapeutic agent with a 1,2-diaminocyclohexane (DACH) carrier ligand, has shown in vitro and in vivo efficacy against many tumor cell lines, including some that are resistant to cisplatin and carboplatin. The retention of the bulky DACH ring by activated oxaliplatin is thought to result in the formation of platinum-DNA adducts, which appear to be more effective at blocking DNA replication and are more cytotoxic than adducts formed from cisplatin. Studies by the National Cancer Institute (NCI) have suggested that oxaliplatin has a spectrum of activity different from that of either cisplatin or carboplatin, suggesting that it has different molecular targets and/or mechanisms of resistance. Oxaliplatin has been demonstrated to differ in some mechanisms associated with the development of cisplatin resistance. Compared with cisplatin-conditioned cells, deficiencies in mismatch repair (MMR) and increases in replicative bypass, which appear to contribute to cisplatin resistance, have not been shown to induce a similar resistance to oxaliplatin. A decreased likelihood of resistance development makes oxaliplatin a good candidate for first-line therapy. Studies also demonstrate additive and/or synergistic activity with a number of other compounds, however, suggesting the possible use of oxaliplatin in combination therapies.

A Multi-Mode Blade Damping Control using Shunted Piezoelectric Transducers with Active Feedback Structure

NASA Technical Reports Server (NTRS)

Choi, Benjamin; Morrison, Carlos; Min, James

2009-01-01

The Structural Dynamics and. Mechanics branch (RXS) is developing smart adaptive structures to improve fan blade damping at resonances using piezoelectric (PE) transducers. In this presentation, only one shunted PE transducer was used to demonstrate active control of multi-mode blade resonance damping on a titanium alloy (Ti-6A1-4V) flat plate model, regardless of bending, torsion, and 2-stripe modes. This work would have a significant impact on the conventional passive shunt damping world because the standard feedback control design tools can now be used to design and implement electric shunt for vibration control. In other words, the passive shunt circuit components using massive inductors and. resistors for multi-mode resonance control can be replaced with digital codes. Furthermore, this active approach with multi patches can simultaneously control several modes in the engine operating range. Dr. Benjamin Choi presented the analytical and experimental results from this work at the Propulsion-Safety and. Affordable Readiness (P-SAR) Conference in March, 2009.

Passive and Active Control of Space Structures (PACOSS)

NASA Astrophysics Data System (ADS)

Morosow, G.; Harcrow, H.; Rogers, L.

1985-04-01