The nodal loads of each film element are the work balance of the body forces F in volume V, the surface tractions �� on surface S, the strain ��0, and the initial stressg����. The element load vector is:re=��[N]TFdV+��[N]T��dS+��[B]TE��0dV?��[B]Tg����dV(5)where [N], [B], and E are the shape function matrix, the strain-displacement matrix, and the material property matrix, respectively [21].In general, the SAM orientations on the gold surface are complex and induced surface stresses from the SAM adsorption are anisotropic [22�C24]. Here, we assume that SAM domains are randomly dispersed on the surface (as shown in Figure 3a) and oriented according to an arbitrary angle (as shown in Figure
The transfer of oxygen from the lungs to the tissue cells is largely carried out by the hemoglobin molecules in the red blood cells and only 2% of the total oxygen content is dissolved in the plasma.

Oxygen saturation in the blood is the ratio of oxygenated hemoglobin concentration to total hemoglobin concentration in the blood, and its value in the arterial blood, SaO2, is of great clinical and physiological significance since it reflects the adequacy of oxygen delivery and respiratory function. Normal values of SaO2 are 94%�C98% at sea level but the values may decline somewhat beyond the age of 70 years [1].SaO2 can be assessed in vitro, in extracted arterial blood, either directly by means of co-oximetry or by measuring oxygen partial pressure and using the oxygen-hemoglobin dissociation curve.

Estimation of SaO2 can also be obtained non-invasively Anacetrapib by pulse oximetry [2�C4], which is based on the different light absorption spectra for oxygenated and de-oxygenated hemoglobin (Figure 1). In order to assess SaO2, the contribution of the arterial blood to the light absorption must be isolated from that of the venous blood, and in pulse oximetry it is achieved by photoplethysmography (PPG)�Cthe measurement of light absorption changes due to the cardiac-induced blood volume changes. The PPG probe consists of a light source emitting light into the tissue and a detector measuring the intensity of light transmitted through the tissue, which decreases during systole because of the systolic increase in the arterial blood volume (Figure 2). Since the PPG pulse represents light absorption in arterial blood, PPG signals at two wavelengths enable the assessment of oxygen saturation in the arterial blood [2]. As will be explained below, there is still a discrepancy between the value of arterial oxygen saturation obtained by pulse oximetry and that obtained by direct measurements in blood extracted from the arteries, and it is therefore customary to designate the former by SpO2 while the latter retains the name SaO2. [4�C6].Figure 1.