Ultra-low Threshold Titanium doped sapphire Whispering-gallery Laser

Titanium doped sapphire (Ti:sapphire) is a laser gain material with broad gain bandwidth benefiting from the material stability of sapphire. These favorable characteristics of Ti:sapphire have given rise to femtosecond lasers and optical frequency combs. Shaping a single Ti:sapphire crystal into a millimeter sized high quality whispering gallery mode resonator ($Q\sim10^8$) reduces the lasing threshold to 14.2 mW and increases the laser slope efficiency to 34%. The observed lasing can be both multi-mode and single-mode. This is the first demonstration of a Ti:sapphire whispering-gallery laser. Furthermore, a novel method of evaluating the gain in Ti:sapphire in the near infrared region is demonstrated by introducing a probe laser with a central wavelength of 795 nm. This method results in decreasing linewidth of the modes excited with the probe laser, consequently increasing their $Q$. These findings open avenues for the usage of whispering gallery mode resonators as cavities for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire can also be utilized as an amplifier inside its gain bandwidth by implementing a pump-probe configuration.Comment: Main text (13 pages, 7 figures) Supplemental document (11 pages, 9 figures

Observing hyperfine interactions of NV centers in diamond in an advanced quantum teaching lab

The negatively charged nitrogen-vacancy (NV$^-$) center in diamond is a model quantum system for university teaching labs due to its room-temperature compatibility and cost-effective operation. Based on the low-cost experimental setup that we have developed and described for the coherent control of the electronic spin (Sewani et al.), we introduce and explain here a number of more advanced experiments that probe the electron-nuclear interaction between the \nv electronic and the \NN~and \CC~nuclear spins. Optically-detected magnetic resonance (ODMR), Rabi oscillations, Ramsey fringe experiments, and Hahn echo sequences are implemented to demonstrate how the nuclear spins interact with the electron spins. Most experiments only require 15 minutes of measurement time and can, therefore, be completed within one teaching lab.Comment: Extension of the teaching lab experiments described in Sewani et al., Coherent control of NV centers in diamond in a quantum teaching lab. American Journal of Physics 88, 1156 (2020). https://doi.org/10.1119/10.000190

Synthesis and applications of protein/peptide-polymer conjugates

Recent advances in synthetic methodologies have brought us closer than ever to the precision conferred by nature. For example, the control possible in reversible deactivation radical polymerization enables us to design and synthesize macromolecules with unprecedented control over not only the polymer chain ends, but also the side chain functionality. Furthermore, this functionality can be exploited to afford chemical modification of peptides and proteins, with ever-improving site-specificity, yielding a range of well-defined protein/peptide-hybrid materials. Such materials benefit from the amalgamation of the properties of proteins/peptides with those of the synthetic (macro)molecules in question. Here, the latest developments in the synthesis of functional polymers and their use for preparation of well-defined protein/peptide-polymer conjugates will be discussed, with particular attention focused on modulating the stability, efficacy and/or administration of therapeutic peptides

Toward halogen-free flame resistant polyethylene extrusion coated paper facings

Wire and cable coverings are potentially a major cause of fire in buildings and other installations. As they need to breach fire walls and are frequently located in vertical ducting, they have significant potential to increase the fire hazard. It is therefore important to understand the ignition and burning characteristics of cables by developing a model capable of predicting their burning behaviour for a range of scenarios. The fire performance of electrical cables is usually dominated by the fire performance of the sheathing materials. The complexity of the problem increases when cable sheathing incorporates fire retardants. One-dimensional pyrolysis models have been constructed for cable sheathing materials, based on milligram-scale and bench-scale test data by comparing the performance of three different software tools (ThermaKin, Comsol Multiphysics and FDS, version 6.0.1). Thermogravimetric analysis and differential scanning calorimetry were conducted on powdered cable coatings to determine the thermal degradation mechanism, the enthalpy of decomposition reactions, and the heat capacities of all apparent species. The emissivity and the in-depth absorption coefficient were determined using reflectance and transmittance measurements, with dispersive and non-dispersive spectrometers and integrating spheres. Bench-scale tests were conducted with a mass loss calorimeter flushed with nitrogen on samples in a horizontal orientation, for comparison with the pyrolysis model of non-flaming decomposition at an external heat flux of 50 kW m-2. The parameters determined through analysis of the milligram-scale data were used to construct a pyrolysis model that predicted the total mass loss from calorimeter tests in anaerobic conditions. A condensed phase pyrolysis model that accurately predicts in-depth temperature profiles of a solid fuel, and the mass flux of volatiles evolved during degradation of the fuel, is an essential component of a comprehensive fire model, which when coupled to a computational fluid dynamics code can be used to predict the burning processes in a fire scenario. Pyrolysis models vary considerably in complexity based on the assumptions incorporated into the development of the model

Inversion symmetry and bulk Rashba effect in methylammonium lead iodide perovskite single crystals

Methylammonium lead iodide perovskite (MAPbI_3) exhibits long charge carrier lifetimes that are linked to its high efficiency in solar cells. Yet, the mechanisms governing these unusual carrier dynamics are not completely understood. A leading hypothesis—disproved in this work—is that a large, static bulk Rashba effect slows down carrier recombination. Here, using second harmonic generation rotational anisotropy measurements on MAPbI_3 crystals, we demonstrate that the bulk structure of tetragonal MAPbI_3 is centrosymmetric with I4/mcmspace group. Our calculations show that a significant Rashba splitting in the bandstructure requires a non-centrosymmetric lead iodide framework, and that incorrect structural relaxations are responsible for the previously predicted large Rashba effect. The small Rashba splitting allows us to compute effective masses in excellent agreement with experiment. Our findings rule out the presence of a large static Rashba effect in bulk MAPbI_3, and our measurements find no evidence of dynamic Rashba effects

THE PROBLEM OF THE TERM "EARLY NOMADS".

<p>Isarov Umidulla Isar ugli Termez State University, PhD student https://doi.org/10.5281/zenodo.10032500 Annotation. This article examines the concept of "early nomads" and its social and economic aspects. The article describes the causes of nomadism and changes in the economic, political and cultural life of society during this period, the factors of nomadism and the analysis of these processes in the scientific literature. </p&gt

Theoretical and Practical Issues of Technical Terminology

The article analyzes the current theoretical and practical issues of terminology, in particular, technical terminology. A diachronic study was conducted on the creation and study of technical terminology. The views of terminologists have been studied from an analytical-critical point of vie