The coronavirus 2019 (COVID-19) pandemic was caused by a positive sense single-stranded RNA (ssRNA) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, other human coronaviruses (hCoVs) exist. Historical pandemics include smallpox and influenza, with efficacious therapeutics utilized to reduce overall disease burden through effectively targeting a competent host immune system response. The immune system is composed of primary/secondary lymphoid structures with initially eight types of immune cell types, and many other subtypes, traversing cell membranes utilizing cell signaling cascades that contribute towards clearance of pathogenic proteins. Other proteins discussed include cluster of differentiation (CD) markers, major histocompatibility complexes (MHC), pleiotropic interleukins (IL), and chemokines (CXC). The historical concepts of host immunity are the innate and adaptive immune systems. The adaptive immune system is represented by T cells, B cells, and antibodies. The innate immune system is represented by macrophages, neutrophils, dendritic cells, and the complement system. Other viruses can affect and regulate cell cycle progression for example, in cancers that include human papillomavirus (HPV: cervical carcinoma), Epstein–Barr virus (EBV: lymphoma), Hepatitis B and C (HB/HC: hepatocellular carcinoma) and human T cell Leukemia Virus-1 (T cell leukemia). Bacterial infections also increase the risk of developing cancer (e.g., Helicobacter pylori). Viral and bacterial factors can cause both morbidity and mortality alongside being transmitted within clinical and community settings through affecting a host immune response. Therefore, it is appropriate to contextualize advances in single cell sequencing in conjunction with other laboratory techniques allowing insights into immune cell characterization. These developments offer improved clarity and understanding that overlap with autoimmune conditions that could be affected by innate B cells (B1⁺ or marginal zone cells) or adaptive T cell responses to SARS-CoV-2 infection and other pathologies. Thus, this review starts with an introduction into host respiratory infection before examining invaluable cellular messenger proteins and then individual immune cell markers.

The impact of the residual strain induced by the thermal strain on the dielectric tunability was systematically studied for rf sputtered (100)-one-axis-oriented polycrystalline $\left({\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{0.5}\right)\mathrm{Ti}{\mathrm{O}}_3$ films. These films were grown on various substrates with different thermal expansion coefficients $\left[{\alpha }_{\left(\mathrm{sub}\right)}\right]$ covered with a stack of ${\left(100\right)}_c\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3∕{\left(100\right)}_c\mathrm{La}\mathrm{Ni}{\mathrm{O}}_3∕\left(111\right)\mathrm{Pt}$ layers. The residual strain was ascertained to linearly increase with the increase in ${\alpha }_{\left(\mathrm{sub}\right)}$ by enhancement of the surface-normal lattice spacing of $\left({\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{0.5}\right)\mathrm{Ti}{\mathrm{O}}_3$ and Pt. Dielectric tunability of the films also linearly increased with the increase in ${\alpha }_{\left(\mathrm{sub}\right)}$ . These results clearly demonstrate that dielectric tunability tailoring of the $\left({\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{0.5}\right)\mathrm{Ti}{\mathrm{O}}_3$ films can be achieved by using residual thermal strain.

The dependences of electrical properties on (111) and (100) orientations were investigated for (Ba_0.5Sr_0.5)TiO₃ films with in-plane random (one-axis-oriented films) and aligned orientations (epitaxial films) prepared by RF magnetron sputtering. Epitaxial films with (100) and (111) orientations were grown on (100)_cSrRuO₃∥(100)SrTiO₃ and (111)_cSrRuO₃∥(111)SrTiO₃ substrates, while one-axis-oriented films were grown on (100) _c SrRuO₃/(100)_cLaNiO₃/(111)Pt/TiO₂/SiO₂/Al₂O₃ and (111) _c SrRuO₃/(111)Pt/TiO₂/SiO₂/Al₂O₃ substrates, respectively. Films with the (111) orientation had larger relative dielectric constants, ε _r, measured at an oscillation of 20 mV and 100 kHz under an applied dc bias electric field of 0 kV/cm and a larger tunability against the dc bias electric field than (100)-oriented films for both epitaxial and one-axis orientations. These data show the dependences of ε _r and tunability on orientation were existed, irrespective of the in-plane orientation and the thermal strain caused in the film by the substrates.

In this paper we present the results of the characterization of parallel-plate thin-film (Ba_1-x ,Sr _x )TiO₃ (BST) capacitors, to demonstrate their suitability for use as decoupling capacitors (a capacitance as high as 0.34 µF and a capacitance density of up to 70 fF/µm²) and as tunable RF components (a small capacitance from 0.5 pF to 16 pF, a high tunability of 4.22:1 at 10 V and a capacitance density of up to 34 fF/µm²). BST films of different compositions, (Ba_0.7Sr_0.3)TiO₃ and (Ba_0.5Sr_0.5)TiO₃, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering on Pt/TiO _x /SiO₂/Al₂O₃ ceramic substrates. For large capacitors (2.25 mm²), capacitance and tan δ were measured at low frequencies (1 kHz) using an LCR meter. Smaller capacitors (16 µm² to 961 µm²) were characterized in the frequency range of 0.01–20 GHz. Capacitance, tan δ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationships between dielectric loss, tunability and commutation quality factor (CQF) vs BST composition and deposition conditions were outlined.