function xprime = sys_ndRad(t,x,D)

xprime = zeros(2,1);

% Parameters that are fixed

N = 10^9; % Sachs

lambda = 0.40; % Sachs

r = 0.8175; % Fitting , sachs

K = 20; % Sachs       

d = D/K; 

tau = 0.02;   % radiation time- 30 minutes = 0.02 days

alpha = 0.25*(d/tau); % Fitting , sachs

gamma = 10^(-9)*(d/tau); % Fitting , sachs

    if(t<=K+tau)

        t-floor(t);

        if (t-floor(t)<=tau)

            t;

            xprime(1) = lambda*x(1)*(1-x(1)) - alpha*x(1) - gamma*x(1);

            xprime(2) = r*lambda*x(2)*(1-x(1)) - alpha*x(2) + gamma*N*x(1);

        else

            xprime(1) = lambda*x(1)*(1-x(1));

            xprime(2) = r*lambda*x(2)*(1-x(1));

        end

    else

        xprime(1) = lambda*x(1)*(1-x(1));

        xprime(2) = r*lambda*x(2)*(1-x(1));

    end