Detailed simulations of bubble-cluster dynamics

The violent collapse of bubble clusters can be an important mechanism of damage to adjacent material surfaces in both engineering and biomedical applications. Because of their complexity, past theoretical studies have generally been restricted to significantly simplified models, such as homogenized continuum models based upon volume averages or arrays of strictly spherical bubbles, which neglect detailed bubble dynamics. However, the details of the bubble-scale dynamics are potentially important locally. For example, wall or tissue damage is expected to depend upon peak pressures rather than the average pressure that might be computed with a homogeneous model. Here, we simulate the expansion and subsequent collapse of hemispherical clusters of 50 bubbles adjacent to a planar rigid wall and viscous fluids as models for soft tissues in therapeutic ultrasound using a computationally efficient diffuse-interface numerical scheme for compressible multiphase flows. It represents in detail the coupled asymmetric dynamics of each bubble within the cluster. The development of this scheme and its application to simulate detailed bubble-cloud collapse are the principal contributions of this dissertation. The numerical scheme represents multi-fluid interfaces using field variables (interface functions) with associated transport equations. In our formulation, these are augmented, with respect to an established formulation, to enforce a selected interface thickness. The resulting interface region can be set just thick enough to be resolved by the underlying mesh and numerical method, yet thin enough to provide an efficient model for dynamics of well-resolved scales. A key advance in our method is that the interface regularization is asymptotically compatible with the thermodynamic laws of the mixture model upon which it is constructed. It incorporates first-order pressure and velocity non-equilibrium effects while preserving interface conditions for equilibrium flows, even within the thin diffused mixture region. The finite-volume numerical solver is also integrated in a multi-resolution Adaptive Mesh Refinement (AMR) framework that allows efficient resolution of individual bubbles of the cluster in a sufficiently large domain. We first quantify the improved convergence of this formulation in an air-helium shock-tube problem and an air-water bubble-collapse problem, then show that it enables fundamentally better simulations of single-bubble dynamics. Demonstrations include both a spherical-bubble collapse, which facilitates comparison with a semi-analytic solution, and a jetting-bubble collapse adjacent a wall. For the spherical collapse, we show agreement with the semi-analytic solution, and the preservation of symmetry despite the Cartesian mesh. Comparisons for the near-wall case show that without the new formulation the re-entrant jet is suppressed by numerical diffusion leading to qualitatively incorrect results. Next, the method is applied to simulate cluster dynamics adjacent to material surfaces. Simulations near the rigid wall show that collapse propagates inward, and a geometrical pressure focusing occurs, which generates impulsive pressures near the focus. The peak pressures depend strongly on the arrangement of the bubbles, particularly those near the focus. The initial acceleration of the bubbles that drives their expansion is identified as an important parameter governing the bubble interactions, and hence the pressure focusing. The simplified models we compare with provide good agreement for the gross cluster behavior, for example gas volume history, but fail to predict the same peak pressures seen in the detailed simulations during the collapse. Replacing the rigid wall with a viscous fluid, as a crude model for tissue, shows significantly different dynamics compared to the rigid wall. Simulations show weaker pressure focusing with substantially lower peak pressures

A Model of Heat Exchangers and Automotive AC System with Refrigerant-Oil Mixtures

We present the method to simulate refrigerant-oil mixtures (Thome 1995) via a one-dimensional (1D) transient multi-physics system-level simulation tool, GT-SUITE. The impact of oil on bubble point and evaporation enthalpy is first validated, followed by the comparison of the predicted heat transfer coefficient and friction factor with the data by Zurcher et al. (1997). A system model of an automobile air-conditioning (AC) system is developed and validated using experimental data by Liu and Hrnjak (2016). The predicted evaporator capacity and system coefficient of performance (COP) matches very well with the data (both have an average error of 1.4% and the largest error of 4.2%). The simulation provides the detailed state of the refrigerant-oil mixture and the oil concentration along the refrigerant path. The local heat transfer rate from the simulation gives insights into the effectiveness of the evaporator area for engineering design

Quantum Dot Based Nano-Biosensors for Detection of Circulating Cell Free miRNAs in Lung Carcinogenesis: From Biology to Clinical Translation

Lung cancer is the most frequently occurring malignancy and the leading cause of cancer-related death for men in our country. The only recommended screening method is clinic based low-dose computed tomography (also called a low-dose CT scan, or LDCT). However, the effect of LDCT on overall mortality observed in lung cancer patients is not statistically significant. Over-diagnosis, excessive cost, risks associated with radiation exposure, false positive results and delay in the commencement of the treatment procedure questions the use of LDCT as a reliable technique for population-based screening. Therefore, identification of minimal-invasive biomarkers able to detect malignancies at an early stage might be useful to reduce the disease burden. Circulating nucleic acids are emerging as important source of information for several chronic pathologies including lung cancer. Of these, circulating cell free miRNAs are reported to be closely associated with the clinical outcome of lung cancer patients. Smaller size, sequence homology between species, low concentration and stability are some of the major challenges involved in characterization and specific detection of miRNAs. To circumvent these problems, synthesis of a quantum dot based nano-biosensor might assist in sensitive, specific and cost-effective detection of differentially regulated miRNAs. The wide excitation and narrow emission spectra of these nanoparticles result in excellent fluorescent quantum yields with a broader color spectrum which make them ideal bio-entities for fluorescence resonance energy transfer (FRET) based detection for sequential or simultaneous study of multiple targets. In addition, photo-resistance and higher stability of these nanoparticles allows extensive exposure and offer state-of-the art sensitivity for miRNA targeting. A major obstacle for integrating QDs into clinical application is the QD-associated toxicity. However, the use of non-toxic shells along with surface modification not only overcomes the toxicity issues, but also increases the ability of QDs to quickly detect circulating cell free miRNAs in a non-invasive mode. The present review illustrates the importance of circulating miRNAs in lung cancer diagnosis and highlights the translational prospects of developing QD-based nano-biosensor for rapid early disease detection

Molecular surveillance of dengue virus in field-collected Aedes mosquitoes from Bhopal, central India: evidence of circulation of a new lineage of serotype 2

IntroductionDengue fever is hyperendemic in several Southeast and South Asian countries, including India, with all four serotypes (DENV 1–4) circulating at different periods and in different locations. Sustainable and improved virological and entomological surveillance is the only tool to prevent dengue and other vector-borne diseases.ObjectivesThe present study has been carried out to detect and characterize the circulating dengue virus (DENV) in field-collected Aedes mosquitoes in Bhopal, Central India.MethodsAedes mosquitoes were collected from 29 localities within Bhopal city during October 2020 to September 2022. DENV infection was assessed in the individual head and thorax regions of Aedes mosquitoes using reverse transcriptase PCR. Positive samples were sequenced, and the circulating serotypes and genotypes were determined using phylogenetic analysis.ResultsDENV RNA was detected in 7 Aedes aegypti and 1 Aedes albopictus, with infection rates of 0.59 and 0.14%, respectively. Phylogenetic analysis revealed all the isolates belonged to DENV serotype 2 and distinctly clustered with the non-Indian lineage (cosmopolitan genotype 4a), which was not recorded from the study area earlier. The time to most common recent ancestor (TMRCA) of these sequences was 7.4 years old, with the highest posterior density (HPD) of 3.5–12.2 years, indicating that this new lineage emerged during the year 2014. This is the first report on the DENV incrimination in both Ae. aegypti and Ae. albopictus mosquitoes collected from Bhopal, Central India.ConclusionThe observed emergence of the non-Indian lineage of DENV-2 in Bhopal, which again is a first report from the area, coincides with the gradual increase in DENV cases in Bhopal since 2014. This study emphasizes the importance of DENV surveillance and risk assessment in this strategically important part of the country to decipher its outbreak and severe disease-causing potential