## 8 Physical Parameters  
The microenvironments of the circulatory system vary considerably in size, flow rates, and other physical properties. Chemicals in the blood can present distinct diffusion coefficients, and like in any other surgical, prognosis, or integrated pharmacokinetic system, there is a range of plausible designs for the nanorobots depending on customized requirements [5]. In defining the nanorobot application, physical parameters is the key point to determining the architecture prototype [1], sensor based actuation [102], and strategies to increase the medical instrumentation efficiency [18].  
Small vessels have diameters of up to several tens of microns, and lengths of about a millimeter. Notwithstanding our control actuation can be set with different parameters, such as adjusting detection thresholds, we adopted typical values for these properties. The workspace used in the simulator comprised an environment consisting of a segment of the vessel with length \(L=60\mu m\) and diameter \(K\) = \(30\mu m\). The model has also a small group of hostage cells, as the medical target on the vessel wall (Fig. 5), releasing alpha-NAGA proteins into the fluid. Cells and nanorobots continually enter one end of the workspace along with the fluid flow. We treat nanorobots not responding while within the workspace as if they did not detect any signal, so they flow with the fluid as it leaves the workspace. Thus, we choose the workspace length sufficient to include the region where the chemical from the target is significantly above the background level. The cells occupy about 1/5-th of the workspace volume, a typical _hematocrit_ value for small blood vessels.  
The nanorobot morphology is based on microbiology, presenting a cylinder's shape with \(2\mu m\) in length and \(0.5\mu m\) in diameter, which allows free operation inside the body [103]. Therefore, the nanorobot's customized design is useful for health monitoring, but it also enables the nanorobot to cross the blood brain barrier for other biomedical applications, such as required for intracranial therapies. This prototyping allows the nanorobot to have a complete kinematic motion control in regard to Brownian motion events inside microenvironments at low Reynolds number.  
The simulator comprises a real time 3D environment, including nanorobots and chemical signal parameters. Most of the cells are red blood cells, with \(6\mu m\) diameter. The number densities of platelets and white blood cells are about 1/20-th and 1/1000-th that of the red cells, respectively. As specific example, we consider alpha-NAGA protein signal, produced in response to the influenza, having molecular weight of 52 kDa (kilodaltons), with concentration near the hostage cells at \(\approx\)_30 ng/ml_ and background concentration in the bloodstream about 300 times smaller. This choice provides an interesting nanorobot task, though we could equally well study tasks involving chemicals with different concentrations relevant for other similar biomedical problems, such as for new drug target to fight HCV (hepatitis C virus) or HIV (human immunodeficiency virus) [1, 16, 46, 90]. In our study, the chemical signal was taken to be produced uniformly throughout vessel once the person was infected by influenza at the rate Q. This rate changes in proportion to the disease progression.