Effort variability

Compaction effort variables of 0.1 and 1.0 indicate compaction efforts of 2 and 75 blows per face, respectively. 

There are two basic kinds of variables that describe the action of a physical system. Effort variables are those things that cause an action to occur. Flow variables are the responses to effort variables, usually involving movement but not always (Table 2.1.1). For the simple case of a running animal, the effort variable is the force required to propel the animal the flow variable is the velocity of movement. Heat loss from that same animal, which is the flow variable, occurs in response to a... 

Resistance describes the limit of the flow variable for any given effort variable amount. Without resistance, the amount of flow that resulted from even a small amount of effort would be limitless. Resistance is what limits the spread of disease, the speed of a nerve action potential, and the speed of a bicyclist, just to name a few (Figure 2.1.1). 

FIGURE 2.1.1 Two cases of effort and flow variables. In the top case, the differences of pressures between the two water tanks canse finid to flow between them. In the bottom case, molecular concentrations are different between the two chambers, and thns molecules move left to right through a membrane. Flow is limited by the resistances of the pipe and membrane, respectively. The amount of water stored in the tanks and the number of molecules in the chambers represents capacity. When the heights of the liquids in the two tanks are the same, and when molecular concentrations in the two chambers are the same, capacities in the two will be eqnal and there will not be any effort variable differences. Net flow will then cease, although movement from one chamber to another can still continue as long as it is equal in both directions. 

Capacity is the ability to accumulate, or store, flow over time. Capacity is given mathematically as the accumulated flow divided by the effort variable value ... 

Wanting to drive from one place to another is the effort variable. The movement of the automobile is the flow variable. 

However, we will see in the next section that effort variables cannot accumulate. Therefore, Equation 2.1.9 is meaningless. 

A desire to graduate (effort variable) acts ou college studeuts, produciug academic work (flow variable), while they must overcome the difficulty of the work (the resistauce). 

Balances written for effort variables are somewhat different from balances written for flow variables. Flow variables can nsnally accumulate, or become stored, in some volume of interest. Thus, heat can accnmnlate, and stored heat makes sense electrical current can accumulate as charge sodium ions can accnmulate, and so can cholesterol. 

Effort variables, on the other hand, cannot accumulate. Pressure, voltage, and temperature, all effort variables, are not stored their corresponding flow variables, flnid, cnrrent, and heat are the entities stored. Thns, an effort variable balance lacks the rate of stnff stored term in Equation 2.2.1. Since this term represents past activity of the system, flow variable balances exhibit memory whereas effort variable balances are always immediate. 

Also, effort variable values are not usually considered to be generated like flow variable values are. Heat, a flow variable, can be generated from frictional work or from metabolism of carbohydrate temperature is not generated from either, in the same way, but instead appears as a manifestation of the presence of heat. Although we may talk of force generation, force is usually considered to be applied rather than generated, and the generation of... term in the effort variable balance equation is usually omitted. 

Without the storage term in effort variable balances, one may use either rate of... or actual amount for effort balances. Thus, a force balance on an object can be either... 

Sometimes balances given for effort variables and flow variables look somewhat similar, but have an inverted appearance. For instance, using the definitions for resistance, capacity, and inertia already given, an effort balance would be... 

Why is this so It was explained in a previous section on effort and flow variables (Section 2.1) that flow always occurs from points of higher effort to lower, never the other way around. Perhaps that explanation is sufficient. We usually have enough experience with real effort variables (pressure, gravity, temperature, etc.) to expect that the impossible just won t happen. And it doesn t. 

The consequence of the fact that a flow can never spontaneously occur against an effort variable gradient is very profound for biological systems. Any biological system, from the subcellular to the biomic levels, represents an ordered system. That is, particular structures are maintained, particular activities are maintained, and particular relationships are maintained. Without these, living systems are unsustainable. 

The fact that a flow can only occur spontaneously from a higher to lower effort variable value means that... 

On a smaller scale, diffusion is the chief mechanism for mass movement. Diffusion causes materials to move when a concentration difference exists between any two points. In terms of effort and flow variables, concentration difference is the effort variable, and the mass rate of flow is the flow variable. 

Considering that resistance is the ratio of effort variable to flow variable, diffusion resistance is... 

From our effort and flow variable perspective, there are two effort variables that act in concert, either adding or subtracting. These are concentration (or osmotic) pressure and hydrostatic pressure (see Section 2.9). Either one can canse the flow of water through the semipermeable membrane (Figure 2.8.4). 

FIGURE 2.8.4 Systems diagram for the apparatus in Figure 2.8.3. The flow variable is the flow of water, and the effort variable is pressure. Two pressure sources appear in series on both sides of the membrane. One pressure source of each pair is osmotic pressure (Ji) and the other is mechanically applied hydrostatic pressure (p). In all cases n > and, therefore, to stop the flow requires that > p . The membrane resistance limits the flow rate when pressures on the two sides are unbalanced. 

Fluids move (the flow variable) due to a difference in pressure (the effort variable). The rate of flow is limited by the resistance located in the flow path. The amount of this resistance depends on whether the flow is laminar or turbulent. Laminar flow is smooth, and flow occurs in streamlines. There is little mixing between layers of fluid motion in laminar flow (Figure 2.9.1). 

Force is the effort variable and velocity is the flow variable in the field of mechanics. Within that context, force balances are very important to determine the mechanical state of an object. 

Because force is the effort variable and acceleration is the time rate of change of the flow variable, mass can be seen to be the inertia (or inertance) of the object. 

Can you think of additional physical principles that relate to biology If so, list them. Describe the behavior of a biological organism. In this description identify the effort and flow variables. Remember that effort variables don t describe things that move that is what flow variables do. 

In terms of effort and flow variables, electron affinity represents one effort variable, electron removal energy represents a second effort variable, and combination energy represents a third effort variable. The flow variable is liberated heat. If the sum of the three effort variables is positive, heat is liberated if the sum is negative, then heat is absorbed. Resistance, or the ratio of effort to flow variables, is proportional to the spontaneity of the chanical reaction. 

Hypothesis i.i the universal strategy to augment effort (try harder) does not improve performance. Regression analyses yield only one significant prediction of performance (variability of speed in scenario 2) by the uiuversal strategy to augment effort Variability of speed is diminished with increased effort. The majority of the analyses confirms hypothesis 1.3 (indicated by framed boxes in Table 4.2). 

Storage nodes All ports of a storage node are storage ports, which means that one of the port variables has to be integrated with respect to time before it plays a role in the constitutive relation of the node or obtained by differentiation with respect to time from a result of the constitutive relation. If the flow variable is integrated with respect to time into a so-called g-type state variable or if the flow variable is obtained by differentiation with respect to time of the constitutive relation, that is, a function of the effort, the port is called a C-type port (or -type port). If the effort variable is integrated with respect to time into a so-called p-type state variable or the effort is obtained by differentiation with respect to time of the con-... 

The graphic trick to represent bicausality in a bond graph breaks the causal stroke into two half strokes each dedicated to the assignment of one of the two conjugate power variables (here the flow variable is on the half arrow side and the effort variable on the opposite side). The assignment rule remains in agreement with the one of causality since a flow is imposed on the subsystem far from the flow-dedicated half stroke while an effort is imposed on the subsystem closed to the effort-dedicated half stroke [18] (Fig. 6.6). 

Some of the entries in Table 7.1 are crossed-out. The crossed-out terms in item numbers 18 and 26 mean that the stored fluid mass does not influence the steady-state temperature of the stored fluid. Likewise, in item numbers 20 and 33, the crossed-out entries indicate that the enthalpy flow rates out of the tanks do not influence the temperatures of the fluid (measurable quantity) although in reality, they do influence the total enthalpy of the fluid stored in the tank. Here, the enthalpy flow rates are treated as temperature-generating quantities. The true meaning of enthalpy (and its flow rate) is not used. Because of steady-state assumption, the mass flow rates are taken to be constant in the thermal domain which means the flow variable is proportional to temperature, i.e., there is a loss of distinction between temperature as the effort variable and a temperature proportional flow variable. 

Therefore, the energy storage in the gas mixture can be represented as a four-port C-field as shown in Fig. 10.2. This C-field has four power ports the flow and effort variables for the mechanical port are V and p, respectively those for the thermal port are S and T, respectively and those for the material ports are m s and p. s, respectively. 

Equations (10.9), (10.11), (10.14) and (10.15) are the constitutive relations of the four-port C-field as they give the effort variables (mi, M2, P and T) in terms of the four state variables mi, m2, V and S), which are obtained by integrating the flow variables in the bonds of the four-port C-field. 

From the causal analysis, this sub-model receives six effort variables and computes six fiow variables without the use of integration and/or differentiation. Therefore, this sub-model can be represented as an encapsulated R-field (a six-port element MR in Fig. 10.3). From the continuity equation, the mass fiow rate of a particular gas is the same for the inlet and the outlet side. This reduces the total number of independent fiow variables to four (see Fig. 10.3). Then the eonstitutive relation of the non-linear resistive field element is given as... 

The effort variables of the mechanical section represent the forces and the effort variables of the piezoelectric transformation represent the relation between the forces, which the sensor is subjected to and the voltage produced because of the piezoelectric effect. These variables in the electrical section represent the distinct voltages at any node in the circuit. Respectively, the flow variables represent the velocities and the currents involved. This approach considers the system as a whole so that the state matrix involves all three sections of the sensor, a mechanical section, a piezoelectric, and an electrical, a complete mechatronics system. CAMPG can obtain the desired transfer functions using the computer-generated state matrices derived in symbolic form. The Laplace transform is applied to the state space form and the transfer functions are obtained in symbolic and also in numeric form for... 

Energy store this can store either flow or effort. The accumulation of either flow or effort variables gives the system its state. The consequence is that the system s reaction to a certain input is dependent on the system s previous behaviour... 

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