224 research outputs found
A direct optical method for the study of grain boundary melting
The structure and evolution of grain boundaries underlies the nature of
polycrystalline materials. Here we describe an experimental apparatus and light
reflection technique for measuring disorder at grain boundaries in optically
clear material, in thermodynamic equilibrium. The approach is demonstrated on
ice bicrystals. Crystallographic orientation is measured for each ice sample.
The type and concentration of impurity in the liquid can be controlled and the
temperature can be continuously recorded and controlled over a range near the
melting point. The general methodology is appropriate for a wide variety of
materials.Comment: 8 pages, 8 figures, updated with minor changes made to published
versio
Liquid-Liquid Phase Separation in an Elastic Network
Living and engineered systems rely on the stable coexistence of two
interspersed liquid phases. Yet surface tension drives their complete
separation. Here we show that stable droplets of uniform and tuneable size can
be produced through arrested phase separation in an elastic matrix. Starting
with an elastic polymer network swollen by a solvent mixture, we change the
temperature or composition to drive demixing. Droplets nucleate and grow to a
stable size that is tuneable by the network cross-linking density, the cooling
rate, and the composition of the solvent mixture. We discuss thermodynamic and
mechanical constraints on the process. In particular, we show that the
threshold for macroscopic phase separation is altered by the elasticity of the
polymer network, and we highlight the role of internuclear correlations in
determining the droplet size and polydispersity. This phenomenon has potential
applications ranging from colloid synthesis and structural colour to phase
separation in biological cells.Comment: 6 figure
Competitive Inhibition of Abscisic Acid-Regulated Gene Expression by Stereoisomeric Acetylenic Analogs of Abscisic Acid
Cyclotron resonance of correlated electrons in semiconductor heterostructures
The cyclotron resonance absorption of two-dimensional electrons in
semiconductor heterostructures in high magnetic fields is investigated. It is
assumed that the ionized impurity potential is a dominant scattering mechanism,
and the theory explicitly takes the Coulomb correlation effect into account
through the Wigner phonons. The cyclotron resonance linewidth is in
quantitative agreement with the experiment in the Wigner crystal regime at
T=4.2K. Similar to the cyclotron resonance theory of the charge density waves
pinned by short-range impurities, the present results for the long-range
scattering also show the doubling of the resonance peaks. However, unlike the
case of the charge density waves, our theory gives the pinning mode independent
of the bulk compressibility of the substrate materials.Comment: 6 pages, 5 figure
Effects of Abscisic Acid Metabolites and Analogs on Freezing Tolerance and Gene Expression in Bromegrass (Bromus inermis Leyss) Cell Cultures
Transmitted/Founder and Chronic Subtype C HIV-1 Use CD4 and CCR5 Receptors with Equal Efficiency and Are Not Inhibited by Blocking the Integrin α4β7
Sexual transmission of human immunodeficiency virus type 1 (HIV-1) most often results from productive infection by a single transmitted/founder (T/F) virus, indicating a stringent mucosal bottleneck. Understanding the viral traits that overcome this bottleneck could have important implications for HIV-1 vaccine design and other prevention strategies. Most T/F viruses use CCR5 to infect target cells and some encode envelope glycoproteins (Envs) that contain fewer potential N-linked glycosylation sites and shorter V1/V2 variable loops than Envs from chronic viruses. Moreover, it has been reported that the gp120 subunits of certain transmitted Envs bind to the gut-homing integrin α4β7, possibly enhancing virus entry and cell-to-cell spread. Here we sought to determine whether subtype C T/F viruses, which are responsible for the majority of new HIV-1 infections worldwide, share biological properties that increase their transmission fitness, including preferential α4β7 engagement. Using single genome amplification, we generated panels of both T/F (n = 20) and chronic (n = 20) Env constructs as well as full-length T/F (n = 6) and chronic (n = 4) infectious molecular clones (IMCs). We found that T/F and chronic control Envs were indistinguishable in the efficiency with which they used CD4 and CCR5. Both groups of Envs also exhibited the same CD4+ T cell subset tropism and showed similar sensitivity to neutralization by CD4 binding site (CD4bs) antibodies. Finally, saturating concentrations of anti-α4β7 antibodies failed to inhibit infection and replication of T/F as well as chronic control viruses, although the growth of the tissue culture-adapted strain SF162 was modestly impaired. These results indicate that the population bottleneck associated with mucosal HIV-1 acquisition is not due to the selection of T/F viruses that use α4β7, CD4 or CCR5 more efficiently
Single-cell longitudinal analysis of SARS-CoV-2 infection in human airway epithelium identifies target cells, alterations in gene expression, and cell state changes.
There are currently limited Food and Drug Administration (FDA)-approved drugs and vaccines for the treatment or prevention of Coronavirus Disease 2019 (COVID-19). Enhanced understanding of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and pathogenesis is critical for the development of therapeutics. To provide insight into viral replication, cell tropism, and host-viral interactions of SARS-CoV-2, we performed single-cell (sc) RNA sequencing (RNA-seq) of experimentally infected human bronchial epithelial cells (HBECs) in air-liquid interface (ALI) cultures over a time course. This revealed novel polyadenylated viral transcripts and highlighted ciliated cells as a major target at the onset of infection, which we confirmed by electron and immunofluorescence microscopy. Over the course of infection, the cell tropism of SARS-CoV-2 expands to other epithelial cell types including basal and club cells. Infection induces cell-intrinsic expression of type I and type III interferons (IFNs) and interleukin (IL)-6 but not IL-1. This results in expression of interferon-stimulated genes (ISGs) in both infected and bystander cells. This provides a detailed characterization of genes, cell types, and cell state changes associated with SARS-CoV-2 infection in the human airway
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