e performance (especially in translocation speed and polarity) of the models is depend-ing on their intrinsic properties, which are de ned by the model parameters. All the dy-namics in the models is based and optimised on dynamically altering the elastic properties and creating an elasticity gradient. e model’s performance is basically in uenced by the static elasticity of their segments, the bending stiffness of the chains [section 2.2.1] and the adaptation rate responsible for the elasticity gradient [subsection 2.2.3]. e corres-ponding parameters that determine these elastic properties are the elasticity parameterke
3. Simulation results
(a)extended single-chain model
−250 −200 −150 −100 −50 0 50 100 150 200 250
−1
−0.8
−0.6
−0.4
−0.2 0 0.2 0.4 0.6 0.8 1
correlation time
cross−correlation
(b)double-chain model
−25 −20 −15 −10 −5 0 5 10 15 20 25
−1
−0.8
−0.6
−0.4
−0.2 0 0.2 0.4 0.6 0.8 1
correlation time
cross−correlation
Figure 3.11.:The cross-correlation between the smoothed temporal course of translocation speed [Fig-ure 3.2] and mean height [Fig[Fig-ure 3.3] for the extended single-chain model and the double chain model.
The extended single-chain model has its maximum of correlation at a correlation time of ~30 time steps, whereas the double-chain model has a correlation time of zero. Black dotted lines define the confidence interval of correlation.
for the elastic segments [Equation 2.4], the parameter responsible for the strength of the bending stiffness of the chainkm[Equation 2.7] and the raterfor the temporal change of elasticity [Equation 2.13, Equation 2.13, Equation 2.15, Equation 2.16].
A screening of this parameters by decreasing or increasing their value reveals on how these parameters in uence the performance and the movement behaviour. For the screen-ing the translocation speed and polarity are measured over a given constant time interval for each model aer changing the parameter value, which might cause visible uctuations of the data. A measurement over the time of one movement cycle has the disadvantage of varying time intervals, because theses are in uenced by the translocation speed of one movement cycle. For data independent of speed a xed time interval was chosen.
58
(a)extended single-chain model
−250 −200 −150 −100 −50 0 50 100 150 200 250
−1
−0.8
−0.6
−0.4
−0.2 0 0.2 0.4 0.6 0.8 1
correlation time
cross−correlation
(b)double-chain model
−25 −20 −15 −10 −5 0 5 10 15 20 25
−1
−0.8
−0.6
−0.4
−0.2 0 0.2 0.4 0.6 0.8 1
correlation time
cross−correlation
Figure 3.12.:The cross-correlation between the smoothed temporal course of translocation speed [Fig-ure 3.2] and polarity [Fig[Fig-ure 3.5] for the extended single-chain model and the double chain model, de-picting the temporal lag between the two. Black dotted lines define the confidence interval of correlation.
3.2.1. Elasticity
Figure 3.13 presents the parameters screening of the elasticity parameterke in relation to the resulting speed and polarity of each model. Data is shown only for the parameter range, where a model performs a stable persistent locomotion. e single-chain model has only a small parameter range around the optimal value, where it is operating with a persistent locomotion. e extended single-chain model works in a broader range with decreased parameter values. e double-chain model is able to perform in a very broad range. In detail, the in uence ofketo the translocation speed is (as Figure 3.13a shows):
In the double-chain-model a lower value ofkeresults in a lower mean speed. 50% of the initialkevalue results in roughly 74% of the initial mean speed and is slowly converging to an optimum in translocation speed by increasingkebeyond the standard value. Increasing the parameter beyond the maximum of translocation speed results in a faster decrease
3. Simulation results
(a)translocation speed
0.5 0.6 0.7 0.8 0.9 1
0.7 0.8 0.9 1
relative elasticity parameter ke
relative translocation speed
double−chain ext. s.−chain single−chain
(b)polarity
0.5 0.6 0.7 0.8 0.9 1
−0.05 0 0.05 0.1 0.15 0.2
relative elasticity parameter ke
polarity
double−chain ext. s.−chain single−chain
Figure 3.13.: Screening of elasticity parameterke relative to the optimised value used in simulations.s
Translocation speed is relative to the standard mean speed [Figure 3.2]. Data is showing only the range with a stable persistent movement.
of speed: too strong elastic segments is disadvantageous for locomotion. e extended chain has a at optimum at approximately 85% of the standard value. e single-chain model requires an exactly adjusted elasticity parameter with such a small operating range.
Considering the in uence on shape, Figure 3.13b shows thatkehas no direct impact on polarity. Except of some uctuations, the polarity stays more or less on the same level in the operating parameter range. A small decrease in polarity is only visible for the single-chain model.
60
(a)translocation speed
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
0.7 0.8 0.9 1
relative bending stiffness parameter kM
relative translocation speed
double−chain ext. s.−chain single−chain
(b)polarity
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
−0.05 0 0.05 0.1 0.15 0.2
relative bending stiffness parameter kM
polarity
double−chain ext. s.−chain single−chain
Figure 3.14.:Screening of parameterkmdefining the bending stiffness of the chain relative to the optimised value used in simulations. Translocation speed is relative to the standard mean speed [Figure 3.2]. Data is showing only the range with a stable persistent movement.
3.2.2. Bending stiffness
e model’s dependency of the strength of the bending stiffness is shown in Figure 3.14.
e single-chain model has only a small range forkmwith a persistent locomotion, whereas the extended single-chain model is also operational with lower values ofkm. e double-chain performs on low and high values with a very broad translocation speed optimum at approximately 105% of the standard value [Figure 3.14a]. e speed graph of the double-chain model demonstrates an asymptotic convergence to its optimum, increasing asymp-totic from the lower parameter range and decreasing aer the optimum. e transloca-tion speed of the extended single-chain model is also increasing from lower parameter values with a slight asymptotic curvature, but it becomes unstable with highkm values.
e simple single-chain model also performs an increase in speed with increase in the bending stiffness strength in its narrow operating range.
3. Simulation results
(a)translocation speed
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
0.5 0.6 0.7 0.8 0.9 1 1.1
relative adaptation rate r
relative translocation speed
double−chain ext. s.−chain single−chain
(b)polarity
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
−0.05 0 0.05 0.1 0.15 0.2
relative adaptation rate r
polarity
double−chain ext. s.−chain single−chain
Figure 3.15.:Screening of the adaptation raterdefining the temporal elasticity change of the chain relative to the optimised value used in simulations. Translocation speed is relative to the standard mean speed [Figure 3.2]. Data is showing only the range with a stable persistent movement.
e bending stiffness parameterkmhas an impact on shape, respectively the polarity of the models [Figure 3.14b]. All three models show an increase in polarity with increasing km(more precisely for the double-chain model: the negative polarity value is getting closer to zero). e extended single-chain model has the steepest slope of increase.
In summary, the strength of the bending stiffness of the chains has an impact on polarity, a stronger bending stiffness is increasing the polarity. is is expectable, since the bending stiffness is de ning how rigid the chain behaves on its deformations.
3.2.3. Elasticity adaptation
e temporal elasticity gradient is the motorisation of the models. is gradient is de-termined by the adaptation rates r for the adherent and non-adherent status
[subsec-62
tion 2.2.3]. ese rates should have an impact on translocation speed. Figure 3.15 clearly depicts this. e three models substantially perform slower with lower adaptation rates [Figure 3.15a]. Both single-chain models show a linear increase in translocation speed with an increase inr, but they are limited to approximately 105% (single-chain model) and 107% (extended single-chain model) value of the standard rate before unstable beha-viour occurs, which breaks the persistent movement. e double-chain model shows an slightly asymptotic increase in translocation speed and has still some room for improve-ment with much higher adaptation rates.
In case of polarity, the adaptation rate has no impact on polarity of the double-chain model, but the polarity of the single-chain models increase with increasing adaptation rates. At lower values the simple single-chain model is more polarised than the extended single-chain model, aer around 80% of the standard rates they change their positions and the extended one becomes the most polarised model.