Math Problem Statement

The following excerpt is taken from Multiscale modeling of red blood cell mechanics and blood flow in malaria. Bruce Caswell et al. PLoS Computational Biology. 7.12 (Dec. 2011).

Membrane macroscopic properties Extension of the linear analysis of [19] for a regular hexagonal network allows us to uniquely relate the model parameters and the network macroscopic elastic properties (shear, area-compression, and Young's moduli), see [13, 17] for details. The derived shear modulus of the membrane is given by

μ0  =    √ 3 KBT 4plmx0  (  x0 2(1 − x0)3   −   1 4(1 − x0)2   +   1 4  )  +   √ 3 kp(n + 1) (4l0m+1)  (7)

where l0 is the equilibrium spring length and x0  =  l0/lm. The area-compression K and Young's moduli are equal to 2μ0 + ka + kd  and  4Kμ0/(K + μ0), respectively.

Reading further, you learn that all quantities involved are positive. Assume that x0  =  1/2 and kp  =  0.

Which of the following statements are always true?

(i) The graph of μ0 as a function of T is linear. (ii) Viewing μ0 as a function of p, we can say that μ0 is proportional to T. (iii) The graph of μ0 as a function of T has a slope of   5 √ 3 KB 8plm  .

Solution

Let's break down the equation for the shear modulus μ0\mu_0 and analyze each statement step by step.

The given formula for μ0\mu_0 is:

μ0=3kBT4plmx0(x02(1x0)314(1x0)2+14)+3kp(n+1)4l0m+1\mu_0 = \frac{\sqrt{3} k_B T}{4 p l_m x_0} \left( \frac{x_0^2}{(1 - x_0)^3} - \frac{1}{4(1 - x_0)^2} + \frac{1}{4} \right) + \frac{\sqrt{3} k_p (n+1)}{4 l_0^{m+1}}

We are told to assume:

  • x0=12x_0 = \frac{1}{2},
  • kp=0k_p = 0.

Step 1: Substitution of x0=1/2x_0 = 1/2

When x0=12x_0 = \frac{1}{2}, let's simplify the term inside the parentheses:

x02(1x0)3=(12)2(112)3=1418=2\frac{x_0^2}{(1 - x_0)^3} = \frac{\left(\frac{1}{2}\right)^2}{\left(1 - \frac{1}{2}\right)^3} = \frac{\frac{1}{4}}{\frac{1}{8}} = 2 14(1x0)2=14(112)2=14×14=1\frac{1}{4(1 - x_0)^2} = \frac{1}{4\left(1 - \frac{1}{2}\right)^2} = \frac{1}{4 \times \frac{1}{4}} = 1 14=0.25\frac{1}{4} = 0.25

Substituting these into the equation for μ0\mu_0, we get:

μ0=3kBT4plm×12(21+0.25)\mu_0 = \frac{\sqrt{3} k_B T}{4 p l_m \times \frac{1}{2}} \left( 2 - 1 + 0.25 \right) μ0=3kBT2plm×1.25\mu_0 = \frac{\sqrt{3} k_B T}{2 p l_m} \times 1.25 μ0=53kBT8plm\mu_0 = \frac{5 \sqrt{3} k_B T}{8 p l_m}

Step 2: Analyze the statements

(i) The graph of μ0\mu_0 as a function of TT is linear.

From the simplified formula, μ0=53kBT8plm\mu_0 = \frac{5 \sqrt{3} k_B T}{8 p l_m}, it is clear that μ0\mu_0 is directly proportional to TT. Since this is a linear equation in TT, statement (i) is true.

(ii) Viewing μ0\mu_0 as a function of pp, we can say that μ0\mu_0 is proportional to TT.

In the equation, μ0=53kBT8plm\mu_0 = \frac{5 \sqrt{3} k_B T}{8 p l_m}, μ0\mu_0 is proportional to TT and inversely proportional to pp. Therefore, statement (ii) is true.

(iii) The graph of μ0\mu_0 as a function of TT has a slope of 53kB8plm\frac{5 \sqrt{3} k_B}{8 p l_m}.

The equation for μ0\mu_0 is μ0=53kBT8plm\mu_0 = \frac{5 \sqrt{3} k_B T}{8 p l_m}, which is in the form of μ0=mT\mu_0 = mT, where the slope m=53kB8plmm = \frac{5 \sqrt{3} k_B}{8 p l_m}. This matches the slope given in the statement, so statement (iii) is true.

Conclusion:

All three statements (i), (ii), and (iii) are true.


Would you like further details on any part of this explanation?

Here are some related questions to deepen your understanding:

  1. What is the physical significance of the shear modulus μ0\mu_0 in this context?
  2. How would the expression for μ0\mu_0 change if x0x_0 were different from 12\frac{1}{2}?
  3. What impact does the parameter (

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Math Problem Analysis

Mathematical Concepts

Elasticity
Shear Modulus
Proportional Relationships
Linear Equations

Formulas

μ0 = √3 KBT / (4plm x0) (x0^2 / (1 - x0)^3 - 1 / (4(1 - x0)^2) + 1/4)
μ0 = 5√3 KBT / (8plm)

Theorems

Proportionality of linear functions

Suitable Grade Level

College Level