Flip-flop initialization

This dialog box allows us to specify timing and initial conditions for the digital circuits. We are interested in the initial state of the flip-flops. The default initial state for all flip-flops is X (unknown). We wish to set the initial state of all flip-flops to zero. Select an initial state of 0 ... 

As in the previous example, the flip-flops in the 74161 must be initialized at the start of the simulation. Select the Gate-level simulation Options as shown in the right screen capture below. We will run a Transient Analysis for 130 ms. Fill in the Time Domain (Transient) options as shown in the left screen capture below. 

In the previous section we used the Digital Setup to initialize all flip-flops to the zero state. Suppose that instead of clearing the flip-flops, we specify the initial states as unknown (X). We will be using the circuit shown on page 487. Follow the procedure for running the analysis, except fill in the Gate-level Simulation Options as shown below ... 

Note that the initial state of the flip-flop is specified as unknown. Run the simulation and then display the traces V/VOlj, V/VjCLAMPj, V02, V03, and V04 To display traces, select Trace and then Add Trace from the Probe menu bar or press the INSERT key ... 

Suppose we want to initialize all flip-flops to an initial state but do not want to use the initial condition of 0 or 1. The circuit below clears the flip-flop at the beginning of the simulation ... 

We see that the flip-flop is initialized to an initial state of zero. 

S0UIT1DI1 Wire the circuit as shown. A 1 kHz clock is used. Use the capacitor startup circuit on page 495 to preset the first flip-flop to 1 and the remaining flip-flops to 0. Note that the initial condition of the capacitor is set to zero. 

Always preset or clear all flip-flops before running a simulation. Use the digital setup dialog box or a start-up clear circuit to set the initial state of the flip-flops. 

In order to show the performance of the set-reset flip-flop, a series of events were initiated. The reset pin of the flip-flop was first set high, then low. This allows the flip-flop to read and react to a change-of-state event on the set pin. A pulse was then applied to the set pin. When the set pin transitioned from low to high, the output (Q) of the... 

In order to get this circuit to start, the UIC statement must be included in the. TRAN simulation. Flip-flops inside the model need the UIC directive in order to initialize properly. The SPICE engine has a difficult time determining the steady-state operating point of bistable circuit like the flip-flop without the UIC. Also, the ABSTOL OPTIONS parameter for current absolute current error tolerance has been changed from lp to 1/x to aid convergence. 

We observe also flip-flop-processes of mobile molecular segments that restore the thermodynamical equilibrium in cases, where the distribution of the flowing units does not agree with the statistical distribution of the possible conformations. During the initial stage the number of dislocated particles may be zt i.e. after discharge we observe Zj dislocated flowing units (f = t1). 

Even though phospholipids are initially incorporated into the cytosolic leaflet of the ER membrane, various phospholipids are asymmetrically distributed in the two leaflets of the ER membrane and of other cellular membranes (see Table 5-1). However, phospholipids spontaneously flip-flop from one leaflet to the other only very slowly, although they can rapidly diffuse laterally in the plane of the membrane. For the ER membrane to expand (growth of both leaflets) and have asymmetrically distributed phospholipids, its phospholipid components must be able to rapidly and selectively flip-flop from one membrane leaflet to the other. 

The situation is quite different with S-T -type CIDNP because nuclear spins are flipped in that case. Owing to the coupling of nuclear spin motion and electron spin motion, not only the electron spin state oscillates in such a system but also the nuclear spin state. Since, however, one-half of the pairs or biradicals cannot participate in this because their nuclear spin state does not allow an electron-nuclear flip-flop transition, the oscillation is not symmetrical. Its turning points are zero nuclear spin polarization and 100% nuclear spin polarization of one sign only. In contrast, the distribution of nuclear spin polarizations between singlet and triplet members of the ensemble is symmetrical. As an example, consider an ensemble of biradicals, where each biradical contains a single proton. Let the ensemble be created in the state T >, and without initial nuclear spin polarization. Half of the pairs, namely those that have nuclear spin /J>, cannot undergo flip-flop transitions. The others oscillate between T a> and S/3>. When all of those happen to be in S/ >, every nuclear spin of the triplet biradicals and every... 

Mechanism of Proteolioid Vesicle Penetration into Monolayers. The principle conclusion from the penetration studies at the air-water and oil-water interfaces is that intrinsic membrane protein in vesicles greatly facilitates the transfer of material into monolayers. In marked contrast lipid vesicles do not penetrate monolayers to any appreciable extent although some exchange of lipid between a monolayer and the outer lipid layer of a liposome can occur (48.49). It is established that both glycophorin (50) and the anion transporter (51) increase the rate of "flip-flop" when incorporated into bilayers. Thus in the initial encounter between the proteolipid vesicles and the monolayer the protein-enhanced rate of "flip-flop" between the inner and outer halves of the vesicle bilayer would facilitate lipid transfer to the monolayer. The process of redistribution of lipid between vesicle and monolayer would bring the protein into intimate contact with the monolayer leading to penetration. 

A timing chart for the RS flip-flop is presented in Figure 23.12B. Notice that the Q output is initially set at 1 and remains so until the C input goes to a binary... 

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