Mathematical modeling of viral kinetics can be used to gain further insight into the viral replication cycle and virus-host interactions. However, many of the virus dynamics models do not incorporate the cell-to-cell heterogeneity of virus yield or the time-dependent factor of virus replication. A recent study of vesicular stomatitis virus (VSV) kinetics in single BHK cells determined that both virus production rate and yield of virus particles varies widely between individual cells of the same cell population. Here we use the results of the previously mentioned study to determine the distribution that best describes the time course of viral production within the single cells. We determined a list of eight potential distributions that are commonly used in viral kinetics models to fit to each data set by minimizing the sum of squared residuals. The model of best fit for each individual cell was determined using Akaike’s Information Criterion (AICC ). Results of this study show that the distribution that best describes viral production varies from cell to cell. This finding could have further reaching implications for incorporating time-dependent viral production into a standard model of virus kinetics in order to better reproduce the diversity of viral replication that occurs over time within a population of cells.

This report presents a novel approach to increase the detection sensitivity of trace amounts of DNA in a sample by employing Förster Resonance Energy Transfer (FRET) between intercalating dyes. Two intercalators that present efficient FRET were used to enhance sensitivity and improve specificity in detecting minute amounts of DNA. Comparison of steady-state acceptor emission spectra with and without the donor allows for simple and specific detection of DNA (acceptor bound to DNA) down to 100 pg/ul. When utilizing as an acceptor a dye with a significantly longer lifetime (e.g., Ethidium Bromide bound to DNA), multi-pulse pumping and time-gated detection enable imaging/visualization of picograms of DNA present in a microliter of an unprocessed sample or DNA collected on a swab or other substrate materials.

We studied room temperature phosphorescence of tryptophan (TRP) embedded in poly (vinyl alcohol) [PVA] films. With UV (285 nm) excitation, the phosphorescence spectrum of TRP appears at about 460 nm. We also observed the TRP phosphorescence with blue light excitation at 410 nm, well outside of the S0→S1 absorption. This excitation reaches the triplet state of TRP directly without the involvement of the singlet excited state. The phosphorescence lifetime of TRP is in the sub-millisecond range. The long-wavelength direct excitation to the triplet state results in high phosphorescence anisotropy which can be useful in macromolecule dynamics study via time-resolved phosphorescence.

The first stars in the Universe, Pop III stars, formed out of the primordial hydrogen and helium sometime during the first billion years of cosmic time. Their formation ended the Cosmic Dark Ages. Despite their critical role in kick starting the formation of all “metals,” (ie. the carbon in our bodies and the oxygen we breathe), we do not know how massive these first stars were, and when and how the era of the first stars ended. While Pop III stars are too faint for a direct detection, their deaths are potentially visible by James Webb Space Telescope (JWST). A subset of Pop III stars end their lives as Pair Instability Supernova (PISN), explosions 100 times more powerful than a typical supernova. However, determining the astrophysics of the first stars will require combining the detection of PISN with theoretical work on the mass distribution of Pop III stars. In this theoretical work, we need to fully explore the range of mass distribution of Pop III stars to determine how dependent the PISN rate is on the masses of Pop III stars. In this work, we present results from a new model which explores the distribution of Population III masses with a set free parameters. We find an order magnitude difference in the PISN rates for various Pop III mass distribution. In addition, we find that PISN rates may provide one of the first independent probes of the maximum mass of Pop III stars.

It has been well established that ZnO is a versatile material with multiple existing and potential applications owing to its numerous and unique properties. ZnO in the nano- and microscale forms has been a focus of attention in recent years due to demonstrated utilities in pharmaceutics, bioengineering and medical diagnostics. Of particular interest is the utilization of ZnO as an antibacterial agent. With growth inhibition observed for both gram-positive and gram-negative bacteria as well as antibiotic strains, the antibacterial action of ZnO is well documented. Yet, there exists much debate over the fundamental mechanisms underlying the antibacterial action of ZnO. Commonly proposed mechanisms include the generation of various reactive oxygen species, release of Zn ions, surface-to-surface interactions, etc. In this work, we investigate the surface and near-surface optoelectronic properties of ZnO microcrystals as they relate to the antibacterial figures of merit. As microscale ZnO particles exhibit comparable antibacterial action to those at the nanoscale, while minimizing effects related to internalization, they are well-suited to serve as a platform to investigate the role of the crystalline free surfaces in this behavior. A bottom-up hydrothermal growth method was employed to synthesize ZnO microcrystals with tunable morphology and a well-controlled relative abundance of polar and non-polar surfaces. The quality of the crystalline lattice and free surfaces as well as the predominant morphology of these samples were confirmed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface photovoltage spectroscopy. The antibacterial efficacy of these particles was characterized via minimum inhibitory concentration assays, performed using Staphylococcus Aureus in a Mueller Hinton broth media. We performed a series of optoelectronic experiments including temperature dependent photoluminescence spectroscopy as well as spectroscopic and transient surface photovoltage as a means to observe changes occurring at the ZnO surface during these assays. We detected significant spectral changes due to interactions with bacteria and growth media. In particular, we showed that interactions with s.aureus resulted in considerable modifications of the excitonic luminescence.