Microscopic structure of the polymer-induced liquid precursor for calcium carbonate

Many biomineral crystals form complex non-equilibrium shapes, often via transient amorphous precursors. Also in vitro crystals can be grown with non-equilibrium morphologies, such as thin films or nanorods. In many cases this involves charged polymeric additives that form a polymer-induced liquid precursor (PILP). Here, we investigate the CaCO3 based PILP process with a variety of techniques including cryoTEM and NMR. The initial products are 30–50 nm amorphous calcium carbonate (ACC) nanoparticles with ~2 nm nanoparticulate texture. We show the polymers strongly interact with ACC in the early stages, and become excluded during crystallization, with no liquid–liquid phase separation detected during the process. Our results suggest that “PILP” is actually a polymer-driven assembly of ACC clusters, and that its liquid-like behavior at the macroscopic level is due to the small size and surface properties of the assemblies. We propose that a similar biopolymer-stabilized nanogranular phase may be active in biomineralization

Effects of Vocal Training on Students’ Voices in a Professional Drama School

Objective The purpose of this study was to investigate the effect of vocal training on acoustic and aerodynamic characteristics of student actors’ voices. Study Design Prospective cohort study. Setting Tertiary medical facility speech and swallow center. Subjects and Methods Acoustic, aerodynamic, and Voice Handicap Index–10 measures were collected from 14 first-year graduate-level drama students before and after a standard vocal training program and analyzed for changes over time. Results Among the aerodynamic measures that were collected, mean expiratory airflow was significantly reduced after vocal training. Among the acoustic measures that were collected, mean fundamental frequency was significantly increased after vocal training. On average, Voice Handicap Index–10 scores were unchanged after vocal training. Conclusion The cohort of drama students undergoing vocal training demonstrated improvements in voice aerodynamics, which indicate enhanced glottal efficiency after training. The present study also found an increased average fundamental frequency among the actors during sustained voicing and no changes in jitter and shimmer despite frequent performance

Growth of organic crystals via attachment and transformation of nanoscopic precursors

A key requirement for the understanding of crystal growth is to detect how new layers form and grow at the nanoscale. Multistage crystallization pathways involving liquid-like, amorphous or metastable crystalline precursors have been predicted by theoretical work and have been observed experimentally. Nevertheless, there is no clear evidence that any of these precursors can also be relevant for the growth of crystals of organic compounds. Herein, we present a new growth mode for crystals of DL-glutamic acid monohydrate that proceeds through the attachment of preformed nanoscopic species from solution, their subsequent decrease in height at the surface and final transformation into crystalline 2D nuclei that eventually build new molecular layers by further monomer incorporation. This alternative mechanism provides a direct proof for the existence of multistage pathways in the crystallization of molecular compounds and the relevance of precursor units larger than the monomeric constituents in the actual stage of growth.publishe