AIP Advances

The time-resolved analysis of periodically excited luminescence decays by the phasor method in the presence of time-gating or binning is revisited. Analytical expressions for discrete configurations of square gates are derived, and the locus of the phasors of such modified periodic single-exponential decays is compared to the canonical universal semicircle. The effects of instrument response function offset, decay truncation, and gate shape are also discussed. Finally, modified expressions for the phase and modulus lifetimes are provided for some simple cases...

This work introduces a method for co-localized multi-modal imaging of sub- μ m features in an additively manufactured (AM) titanium alloy. Ti-6Al-4V parts manufactured by electron beam melting powder bed fusion were subjected to hot isostatic pressing to seal internal porosity and machined to remove contour-hatch interfaces. Electron microscopy and atomic force microscopy-based techniques (electron backscatter diffraction and scanning Kelvin probe force microscopy) were used to measure and categorize the effects of crystallographic texture, misorientation, and phase content on the relative differences in the Volta potential of α -Ti and β -Ti phases...

Telecentric beam scanning using f- θ lenses offers nearly uniform spot size, linear beam displacement, and normal incidence angle over a planar surface. These unique properties allow for the minimization of imaging distortion over a wide field-of-view. In this article, we present a numerical method for designing custom f- θ lenses in the THz regime. We fabricated three lenses made from different commonly used polymer materials in the THz optics. We demonstrated their optical performance metrics compared to a conventional plano-convex lens over the broadband 0...

The Susceptible-Exposed-Infectious-Recovered (SEIR) model is an established and appropriate approach in many countries to ascertain the spread of the coronavirus disease 2019 (COVID-19) epidemic. We wished to create a new COVID-19 model to be suitable for patients in any country. In this work, a modified SEIR model was constructed. We used the real data of COVID-19 spread in Saudi Arabia for statistical analyses and complex analyses. The reproduction number and detailed review of stability demonstrated the complexities of our proposed SEIR model...

The covid-19 infection rates for a large number of infections collected from a large number of different sites are well defined with a negligible scatter. The simplest invertible iterated map, exponential growth and decay, emerges from country-wide histograms whenever Tchebychev's inequality is satisfied to within several decimal places. This is one point. Another is that failed covid-19 pandemic model predictions have been reported repeatedly by the news media. Model predictions fail because the observed infection rates are beyond modeling: any model that uses fixed rates or uses memory or averages of past rates cannot reproduce the data on active infections...

The unique activation signal of phase-change contrast agents (PCCAs or droplets) can be separated from the tissue signal and localized to generate super-resolution (SR) ultrasound (US) images. Lipid-shelled, perfluorocarbon PCCAs can be stochastically vaporized (activated) by a plane wave US transmission thereby enabling them to be used as separable targets for ultrasound localization microscopy. The unique signature of droplet vaporization imaging and the transient inherent nature of this signature increases signal contrast and therefore localization confidence, while the poor resolution of the low-frequency vaporization signal is overcome by the super-resolution result...

Heating and ventilation air conditioning systems in hospitals (cleanroom HVAC systems) are used to control the transmission/spreading of airborne diseases such as COVID-19. Air exiting from these systems may contribute to the spreading of coronavirus droplets outside of hospitals. Some research studies indicate that the shortest time of survival of SARS-CoV-2 in aerosol form (as droplets in the air) is four hours and the virus becomes inactive above 60 °C air temperature. Therefore, SARS-CoV-2 droplets cannot exit from the exhaust duct if the temperature is above 60 °C...

The surface tension of biological fluids is an important parameter because the mechanical properties of fluids are closely linked with hematological diseases and other pathophysiologies. Capillary waves are associated with fluid mechanical properties. Here, we propose a method that utilizes the acoustic radiation force (ARF) to generate propagating waves and optical coherence tomography (OCT) to measure the wave motion. This ARF-OCT method is capable of evaluating the surface tension of fluids, water and porcine whole blood in this study, based on the dispersion relation of capillary waves...

While the fundamental steps outlining myofibril formation share a similar scheme for different cell and species types, various granular details involved in the development of a functional contractile muscle are not well understood. Many studies of myofibrillogenesis focus on the protein interactions that are involved in myofibril maturation with the assumption that there is a fully formed premyofibril at the start of the process. However, there is little known regarding how the premyofibril is initially constructed...

Due to their ability to provide efficient mixing at small scales, confined impinging jet mixers (CIJMs) are employed widely in nanoparticle assembly processes such as flash nanoprecipitation and flash nanocomplexation, which require rapid mixing. In this mixing device, two jets from opposite directions impinge directly on each other forming a thin shear layer that breaks down rapidly into small flow structures. This enables effective mixing of the species transported by each jet by drastically reducing the diffusion distance...

Diamond, a highly radiation-resistant material, is considered a nearly ideal material for radiation detection, particularly in high-energy physics. In this study, radiation damage from high-energy proton beams was induced in diamond crystals to determine exposure lifetime in detectors made from this material; the effects were investigated using non-destructive x-ray techniques and through the FLUKA simulation package. Two diamond detectors were irradiated by an 800 MeV proton beam at different fluence rates, and the real-time current response was recorded to observe degradation in the signal over time...

Van der Waals (vdw) interaction is an important force between atoms and molecules. Many potential functions have been proposed to model vdw interaction such as the Lennard-Jones (L-J) potential. To overcome certain drawbacks of existing function forms, this work proposes a double exponential (DE) potential that contains a repulsive exponential term and an attractive exponential term. This potential decays faster than the L-J potential and has a soft core. The DE potential is very flexible and its two exponential parameters can be adjusted continuously to mimic many potential functions...

We have implemented a rapid scanning technique into THz time-domain spectrometers using an oscillating frictionless delay line, especially adapted for nonlinear THz experiments. Thereby we were able to increase the dynamic range of THz measurements in the frequency range from 40 to 200 cm-1 by up to 24 dB and reduce the scanning time by up to a factor of 200. We report here test measurements on TDS-setups at repetition rates of 80 MHz and 5 kHz. The dynamic range exceeds 64 dB, which allows to record even small changes in the THz absorption upon optical excitation by a THz probe, covering the frequency range of the intermolecular modes and the phonon bands...

Localized application of exogenous forces on soft biomaterials and cells is often essential for the study of their response to external mechanical stimuli. Magnetic means of applying forces, particularly those based on permanent magnets and magnetic beads coupled to substrates or cells provide an accessible means of exerting forces of appropriate magnitude. The amount of force exerted, however, is often inferred from calibration performed ex situ , with typically similar but different magnetic beads. Here, we construct a simple magnetic tweezer by coupling a pencil-shaped stainless-steel probe to permanent neodymium magnets using a 3D printed adapter...

In this paper, micromagnetic analysis of an array of long magnetic nanowires (NWs) embedded in a nonmagnetic matrix is performed. It is found that for NWs with diameters on the order of a hundred nanometers, the anisotropy and exchange energies are negligible, so the total free energy is a sum of the Zeeman and magnetostatic energies. The minimum magnetostatic energy corresponds to the maximum Zeeman energy, whereby half of the NWs are magnetized parallel to the external field, while the rest of the NWs are magnetized antiparallel to the external fields...

The transport properties of hydrogels largely affect their performance in biomedical applications ranging from cell culture scaffolds to drug delivery systems. Solutes can move through the polymer mesh as a result of concentration gradients in the interstitial fluid or pressure gradients that move the fluid and solutes simultaneously. The relationship between the two modalities of transport in hydrogels can provide insight for the design of materials that can function effectively in the dynamic conditions experienced in vitro and in vivo , yet this correlation has not been previously elucidated...

Cylindrical or rod-like particles are promising materials for the applications of fillers in nanocomposite materials and additives to control rheological properties of colloidal suspensions. Recent advances in particle synthesis allows for cylinders to be manufactured with short-ranged attractions to study the gelation as a function of packing fraction, aspect ratio and attraction strength. In order to aid in the analysis of small-angle scattering experiments of rod-like particles, computer simulation methods were used to model these particles with specialized Monte Carlo algorithms and tabular superquadric potentials...

A whispering gallery mode resonator based magnetometer using chip-scale glass microspherical shells is described. A neodynium micro-magnet is elastically coupled and integrated on top of the microspherical shell structure that enables transduction of the magnetic force experienced by the magnet in external magnetic fields into an optical resonance frequency shift. High quality factor optical microspherical shell resonators with ultra-smooth surfaces have been successfully fabricated and integrated with magnets to achieve Q-factors of greater than 1...

Magnetic nanostructures of different size, shape, and composition possess a great potential to improve current technologies like data storage and electromagnetic sensing. In thin ferromagnetic nanowires, their magnetization behavior is dominated by the competition between magnetocrystalline anisotropy (related to the crystalline structure) and shape anisotropy. In this way electron diffraction methods like precession electron diffraction (PED) can be used to link the magnetic behavior observed by Electron Holography (EH) with its crystallinity...

The hydrodynamic mechanisms associated with the formation of femtosecond laser induced ripples on copper for two angles of incidence are reported. Laser pulse length used for this work is 35 fs. A revised two-temperature model is presented that comprises transient changes of optical characteristics during the irradiation with femtosecond pulses to model relaxation processes and thermal response in bulk copper. The theoretical model takes into account the fluid flow dynamics that result in ripple periods shorter than the wavelength of the surface plasmon polaritons...