Motor loop

Fig. 13.3 Conceptual model summary of the main connections of the motor loop of the BG. VL=Ventrolateral Thalamus, PPN=PedonculoPontine Nucleus. In the classic model, Dopamine net effect is to reduce the output of the BG and to disinhibit...

Other structures have recently been stimulated including the motor cortex [52], the pedunculopontine nucleus in the brain stem [54] and the zona incerta (a structure adjacent to the STN) [55]. This indicates that the stimulation of various structures along the motor loop can lead to improvement of parkinsonian signs but spreading to other adjacent structures cannot be excluded. In the present chapter we focus on DBS of the STN. 

The effects of DBS on the cortex-basal-ganglia-thalamus-cortex motor loop appear to be more complex than initially believed. The paradox of DBS is that electrical stimulation of brain tissue (which presumably induces brain activation), has a similar effect as that of a surgical lesion of that same structure (which effectively destroys brain tissue). These two realities are hard to reconcile. As indicated by [64] the ultimate elucidation of this paradox depends on the nature of the complex and interactive neural connections in the brain that communicate through electrical and chemical processes. There is an emerging view that DBS has both excitatory and inhibitory effects on how brain circuits communicate with one another depending on the distance from the electrode, the cell structures activated and the direction of the activation (ortho- versus anti-dromic). The effect appears to modulate the activity of a network as well as neural firing patterns. Long term effects on neurotransmitters and receptor systems cannot be excluded [64]. 

The cerebral cortex of the brain is an approximately continuous, homogenous neural medium, which is molded (or rutted ) into preferred tracks of neural transmission by imprinting and by repeated activity (i.e., behavioral learning). Within this system, there exists a relatively discrete series of dimensions ("levels ) within which recurrent circular operations stabilize existing patterns (1) the sensory-motor loop, representing interaction with the physical/behavioral space outside, and (2) an internal behavior loop, which operates even in isolation from the... 

Fig. 1. Integrative aspects of cognitive and motor loops. Disturbances in cognitive loops predominate in AD, and motor loops are predominantly affected in PD. Abbreviations nc, nucleus ext pall, external pallidum int pall, internal pallidum nc paranigr, nucleus paranigralis nc subthal, nucleus subthalamicus pont gray, pontine gray. Modified from Alexander et al., 1986 Gerlach et al., 1991b Nieuwenhuys et al., 1991 Braak and Braak, 1993.

Lesions in different anatomical sites of the structures that make up the motor loop can be used to create models of movement disorders (Fig. 1). When the subthalamic nucleus is lesioned, a disruption of the indirect pathway results the decline of glutamatergic stimulation of internal globus pallidus/substantia nigra zona reticulata (SNR) neurons via subthalamico-pallidonigral pathways reveals diminished inhibition of the excitatory thalamocortical pathways. The clinical consequence of this lesion is a proximal ballistic movement of the limbs. 

In view of the interaction of glutamate and DA of the motor loop in physiological and pathological conditions, glutamate-receptor blockade may offer another avenue for PD treatment (Riederer et al.,... 

Several parameters come into the relation between density and equivalence ratio. Generally, the variations act in the following sense a too-dense motor fuel results in too lean a mixture causing a potential unstable operation a motor fuel that is too light causes a rich mixture that generates greater pollution from unburned material. These problems are usually minimized by the widespread use of closed loop fuel-air ratio control systems installed on new vehicles with catalytic converters. 

The principle of operation of the hydraulic reciprocating pump is similar to the beam pump, with a piston-like sub-surface pump action. The energy to drive the pump, however, is delivered through a hydraulic medium, the power fluid, commonly oil or water. The power fluid drives a downhole hydraulic motor which in turn drives the pump. A separate surface pump delivers the hydraulic power. The power fluid system can be of the closed loop or of the open type. In the latter case, the power fluids are mixed with the produced fluid stream. The performance of the hydraulic pump is primarily monitored by measuring the discharge pressures of both surface and sub-surface pumps. 

With this technology it is now possible to achieve extremely accurate speed control of the order of 0.01 % to 0.001 %. To achieve such high accuracy in speed control, closed-loop feedback control systems and microprocessor-based control logistics can be introduced into the inverter control scheme to sense, monitor and control the variable parameters of the motor to very precise limits. 

With the use of statie drives for speed eontrol of induetion motors, through open or elosed-loop feedbaek eontrol... 

To follow through with the open-loop approaeh, there must first be a signal that warns the speed eontrol funetion of load loss (or breaker opening) and impending speed inerease. This is provided by a digital eontaet that indieates motor/generator breaker status. Next, a load loss estimate is needed. This is provided by a kilowatt transdueer on the motor/generator. 

One of the critical measurements is torque or shaft power. A variety of methods is recognized direct methods such as torque meters or reaction mounted drivers (dynamometers) and indirect methods such as electrical power input to drive motors, heat balance, or heat input to a loop cooler. See Part 7, Measurement of Shaft Power, PTC 19.7 1961 [3] for additional information. 

If HjS is continuously present in the flare gas or if the flare seal drum also functions as a sour water disengaging drum, then the effluent seal water must be routed to a sour water stripper, desalter, or other safe means of disposal. Withdrawal from the drum is by pump in place of the normal loop seal arrangement. Two pumps are provided one motor driven for normal use, and the other having a steam turbine drive with low pressure cut-in. The seal drum level is controlled by LIC with high and low alarm lights plus an independent high level alarm. 

Mixing by agitation of liquids normally involves the transfer of momentum from an impeller to the liquid. In some cases, mixing is achieved by gas injection or circulation via a pump loop. An impeller, which is mounted on a shaft driven by an electric motor, is divided into two operation categories ... 

The RCS illustrated in Figure 6.1-3 has two cold legs and one hot-leg for each of the two loops. Two canned-motor pumps are welded to the bottom of steam generator. A large pressurizer is attached to one of the hot legs. 

The fault tree (Figure 7.4-1) has "Pre.ssure Tank Rupture" as the top event (gate G1). This may result from random failure of the tank under load (BEl), OR the gate G2, "Tank ruptures due to overpressure" which is made of BE6 "Relief valve fails to open" AND G3, "Pump motor operates too long." This is made of BE2, "Timer contacts fail to open," AND G4, "Negative feedback loop inactive" which is composed of BE3, "Pressure gauge stuck," OR BE4, "Operator fails to open switch," OR "BE5, "Switch fails to open,"... 

If the wire is formed into a loop or coil, the coil is placed around or in a steel core and voltage is applied to the coil, current will flow through the wire and produce magnetic flux. This is what happens in the stationary part of the induction motor. 

Rawdon used flat specimens that were subjected to repeated flexure while they were being immersed periodically in the corrosive solution. Kenyon used a rotating wire specimen in the form of a loop, the upper part of which was attached to the motor whilst the lower part of the loop passed through the corrodent, and a somewhat similar device was developed by Haigh-Robertson and used in several studiesGough and Sopwith used this machine in their studies, the corrodent being applied as a spray. 

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