Magnesium alloys are used in aircraft because of their light weight. However, for these alloys to be applied in electronic devices, high thermal conductivities are required. Several high-potential ...compositions of Mg–Zn–Y–Zr alloys were selected by phase composition and their freezing ranges calculated using Thermo-Calc software. The alloys were prepared, and their fluidity, hot tearing susceptibility, mechanical properties, and thermal conductivity were obtained and compared. The alloy composed of Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr was selected for further investigation, because of its high thermal conductivity and satisfactory mechanical properties. The Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr alloy's fluidity and hot tearing susceptibility were similar to those of the widespread AZ91 commercial casting magnesium alloy. The influence of a heat treatment regime on the microstructure, thermal conductivity, and mechanical properties of the developed alloy was also investigated. It was established that the room temperature thermal conductivity of the Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr alloy after aging at 300 °C for 5 h was 105 W/mK. Additionally, the following tensile test results were obtained in aged condition: 120 MPa yield strength, 200 MPa ultimate tensile strength, and 4% elongation. The utilization of solid solution heat treatment at 520 °C for 8 h prior to aging can promote up to 9% increase in elongation. The Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr casting alloy can be used as a high thermal conductivity material with industrial applications.
Details about molecular membrane dynamics in living cells, such as lipid-protein interactions, are often hidden from the observer because of the limited spatial resolution of conventional far-field ...optical microscopy. The superior spatial resolution of stimulated emission depletion (STED) nanoscopy can provide new insights into this process. The application of fluorescence correlation spectroscopy (FCS) in focal spots continuously tuned down to 30 nm in diameter distinguishes between free and anomalous molecular diffusion due to, for example, transient binding of lipids to other membrane constituents, such as lipids and proteins. We compared STED-FCS data recorded on various fluorescent lipid analogs in the plasma membrane of living mammalian cells. Our results demonstrate details about the observed transient formation of molecular complexes. The diffusion characteristics of phosphoglycerolipids without hydroxyl-containing headgroups revealed weak interactions. The strongest interactions were observed with sphingolipid analogs, which showed cholesterol-assisted and cytoskeleton-dependent binding. The hydroxyl-containing headgroup of gangliosides, galactosylceramide, and phosphoinositol assisted binding, but in a much less cholesterol- and cytoskeleton-dependent manner. The observed anomalous diffusion indicates lipid-specific transient hydrogen bonding to other membrane molecules, such as proteins, and points to a distinct connectivity of the various lipids to other membrane constituents. This strong interaction is different from that responsible for forming cholesterol-dependent, liquid-ordered domains in model membranes.
Fibroblast growth factors (FGFs) signal in a paracrine or endocrine fashion to mediate a myriad of biological activities, ranging from issuing developmental cues, maintaining tissue homeostasis, and ...regulating metabolic processes. FGFs carry out their diverse functions by binding and dimerizing FGF receptors (FGFRs) in a heparan sulfate (HS) cofactor- or Klotho coreceptor-assisted manner. The accumulated wealth of structural and biophysical data in the past decade has transformed our understanding of the mechanism of FGF signaling in human health and development, and has provided novel concepts in receptor tyrosine kinase (RTK) signaling. Among these contributions are the elucidation of HS-assisted receptor dimerization, delineation of the molecular determinants of ligand-receptor specificity, tyrosine kinase regulation, receptor cis-autoinhibition, and tyrosine trans-autophosphorylation. These structural studies have also revealed how disease-associated mutations highjack the physiological mechanisms of FGFR regulation to contribute to human diseases. In this paper, we will discuss the structurally and biophysically derived mechanisms of FGF signaling, and how the insights gained may guide the development of therapies for treatment of a diverse array of human diseases.
Energies of the ground and excited states of excitons in GaAs/AlGaAs and InGaAs/GaAs finite square quantum wells (QWs) of various widths are calculated. This is achieved by studying the ...three-dimensional Schrödinger equation for the exciton in a QW and, in particular, by determining the lower energy boundary of the continuous spectrum of the corresponding differential operator. The eigenvalue problem for the Schrödinger equation is solved numerically by the finite-difference method properly taking into account discontinuities of the material parameters at the interfaces of the QW. The calculated bound states of electron-hole pairs are classified based on the types of their dominant in-plane and quantum-confinement one-dimensional functions of the wave function factorized form. A dependence of energy levels on a QW width as a parameter is thoroughly studied for widths up to 100 nm. The accurate radiative decay rates for calculated s-like exciton states are also obtained. Calculated energy spectra are confronted with the experimental reflectance spectra measured for high-quality InGaAs/GaAs heterostructures with QWs. The ground and, at least, a few excited states of the heavy-hole exciton in QW are identified in the experimental spectra.
•The energy spectrum of the exciton in the GaAs-based quantum well is theoretically obtained.•A dependence of energy levels on a quantum well width as a parameter is studied for widths up to 100 nm.•The anticrossings of energy levels with the same symmetry of the quantum-confinement wave function components are observed.•The ground and a few excited states of the heavy-hole exciton in the quantum well are identified in experimental spectra.
Magnesium alloys are commonly used to produce lightweight parts. While most magnesium alloys exhibit low thermal conductivities, high thermal conductivities are needed for electronic devices. In this ...study, we attempted to develop new magnesium casting alloys with high thermal conductivities. The MgZnSiCa alloy compositions were chosen using CALPHAD (CALculation of PHAse Diagrams) calculations, and alloy samples were prepared. The fluidity and hot-tearing resistance were measured. The results indicated that these properties were similar to those of AZ91 alloy. Tensile tests showed that high-pressure die casting could produce MgZnSiCa alloys possessing mechanical properties 1.5–3 times higher than those produced via sand casting. The alloy thermal conductivity was 126 W/mK at room temperature. The corrosion rates of the as-cast samples in NaCl/water solutions were two times higher than that of AZ91. Keywords: Magnesium alloy, Thermal conductivity, Phase composition, Corrosion rate, Sand casting, High-pressure die casting
The high human cost of Zika virus infections and the rapid establishment of virus circulation in novel areas, including the United States, present an urgent need for countermeasures against this ...emerging threat. The development of an effective vaccine against Zika virus may be problematic because of the cross reactivity of the antibodies with other flaviviruses leading to antibody-dependent enhancement of infection. Moreover, rapidly replicating positive strand RNA viruses, including Zika virus, generate large spectrum of mutant genomes (quasi species) every replication round, allowing rapid selection of variants resistant to drugs targeting virus-specific proteins. On the other hand, viruses are ultimate cellular parasites and rely on the host metabolism for every step of their life cycle, thus presenting an opportunity to manipulate host processes as an alternative approach to suppress virus replication and spread. Zika and other flaviviruses critically depend on the cellular secretory pathway, which transfers proteins and membranes from the ER through the Golgi to the plasma membrane, for virion assembly, maturation and release. In this review, we summarize the current knowledge of interactions of Zika and similar arthropod-borne flaviviruses with the cellular secretory machinery with a special emphasis on virus-specific changes of the secretory pathway. Identification of the regulatory networks and effector proteins required to accommodate the trafficking of virions, which represent a highly unusual cargo for the secretory pathway, may open an attractive and virtually untapped reservoir of alternative targets for the development of superior anti-viral drugs.
The objective of this review is the analysis and comment of recent publication results (from July 2010 until February 2017) obtained for selective ethylene oligomerization toward 1-hexene and ...1-octene catalyzed by chromium-based catalytic systems. Both the scientific and patent literature was taken into the consideration. The catalytic systems for ethylene oligomerization are classified on the basis of the ligand type employed. The activities and selectivities of the catalysts are provided throughout the text. Despite a big success in the field, there is still rather limited choice of catalysts affording simultaneously high activity, selectivity and low polymer proportion. This is especially true for ethylene to 1-octene tetramerization reaction. The results of the studies concerning oligomerization mechanisms obtained over the recent years are also included in this review.
Topological phase transitions in condensed matter systems give rise to exotic states of matter such as topological insulators, superconductors, and superfluids. Photonic topological systems open a ...whole new realm of research and technological opportunities, exhibiting a number of important distinctions from their condensed matter counterparts. Photonic modes can leak into free space, which makes it possible to probe topological photonic phases by spectroscopic means via Fano resonances. Based on this idea, we develop a technique to retrieve the topological properties of all-dielectric metasurfaces from the measured far-field scattering characteristics. Collected angle-resolved spectra provide the momentum-dependent frequencies and lifetimes of the photonic modes that enable the retrieval of the effective Hamiltonian and extraction of the topological invariant. Our results demonstrate how the topological states of open non-Hermitian systems can be explored via far-field measurements, thus paving a way to the design of metasurfaces with unique scattering characteristics controlled via topological effects.
Polymerase chain reaction (PCR) and DNA melting methods are run on nucleic acid analyzers. We propose a method for recording melting signals using analyzers of the ANK series that decreases errors in ...determining the main parameter – the DNA melting temperature T
m
. We propose a method for assessing the width of the melting interval ΔT as an additional specificity criterion for PCR products. Measurement errors have been evaluated: standard deviation (RMS) for T
m
, ≤0.11°C; for ΔT, ≤0.06°C.
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