Thermodynamics of the Mg-B system: Implications for the deposition of MgB2 thin films

We have studied thermodynamics of the Mg-B system with the modeling technique CALPHAD using a computerized optimization procedure. Temperature-composition, pressure-composition, and pressure-temperature phase diagrams under different conditions are obtained. The results provide helpful insights into appropriate processing conditions for thin films of the superconducting phase, MgB2, including the identification of the pressure/temperature region for adsorption-controlled growth. Due to the high volatility of Mg, MgB2 is thermodynamically stable only under fairly high Mg overpressures for likely growth temperatures. This constraint places severe temperature constraints on deposition techniques employing high vacuum conditions

Floquet Majorana fermions in driven hexagonal lattice systems

We propose Floquet chiral topological superconducting systems hosting Floquet Majorana fermions, which consist of hexagonal lattices in proximity to superconductors with shining circularly polarized light. Specially for bilayer graphene system, we demonstrate that there exist three topological phases determined by certain parameters, namely, the amplitude and frequency of the induced light. The number of chiral Floquet Majorana edge states is confirmed by calculating Chern number analytically and energy spectrum in ribbon geometry. Moreover, this proposal is generalized to other hexagonal lattice systems, such as monolayer graphene and silicene. Notably, the parameter range of induced light to achieve the chiral Floquet Majorana edge states is experimentally feasible, and the corresponding Floquet Majorana fermions can be probed based on differential conductance using scanning tunneling spectroscopy.Comment: 9 pages, 8 figure

Measuring TGF-β Ligand Dynamics in Culture Medium

TGF-β plays an important role in a myriad of cell activities including differentiation, proliferation, and growth arrest. These effects are influenced by the concentration of TGF-β in the surrounding milieu, which is interpreted by mammalian cells and subsequently translated into meaningful signals that guide their proliferation, survival, or death. To predict cellular responses to TGF-ß signaling based on molecular mechanisms, it is important to consider how cells respond to different ligand doses and how variations in ligand exposure impact Smad signaling dynamics and subsequent gene expression. Here we describe methods to measure TGF-β concentration in the environment and approaches to perturb cellular TGF-β exposure to gain a quantitative understanding of signaling dynamics of this pathway

Programmable Extracellular Vesicles for Macromolecule Delivery and Genome Modifications

Getting large macromolecules through the plasma membrane and endosomal barriers remains a major challenge. Here, we report a generalizable method of delivering proteins and ribonucleoproteins (RNPs) to cells in vitro and mouse liver tissue in vivo with engineered ectosomes. These ectosomes, referred to as “Gectosomes,” are designed to co-encapsulate vesicular stomatitis virus G protein (VSV-G) with bioactive macromolecules via split GFP complementation. We found that this method enables active cargo loading, improves the specific activity of cargo delivery, and facilitates Gectosome purification. Experimental and mathematical modeling analyses suggest that active cargo loading reduces non-specific encapsulation of cellular proteins, particularly nucleic-acid-binding proteins. Using Gectosomes that encapsulate Cre, Ago2, and SaCas9, we demonstrate their ability to execute designed modifications of endogenous genes in cell lines in vitro and mouse liver tissue in vivo, paving the way toward applications of this technology for the treatment of a wide range of human diseases

Lattice QCD calculation of ππ\pi\pi scattering length

We study s-wave pion-pion ($\pi\pi$) scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered fermion formulation, we calculate the $\pi\pi$ four-point functions for isospin I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results. Extrapolating to the physical pion mass gives the scattering lengths as $m_\pi a_0^{I=2} = -0.0416(2)$ and $m_\pi a_0^{I=0} = 0.186(2)$ for isospin I=2 and 0 channels, respectively. Our lattice simulation for $\pi\pi$ scattering length in the I=0 channel is an exploratory study, where we include the disconnected contribution, and our preliminary result is near to its experimental value. These simulations are performed with MILC 2+1 flavor gauge configurations at lattice spacing $a \approx 0.15$ fm.Comment: Remove some typo

Superconducting properties of nanocrystalline MgB2_2 thin films made by an in situ annealing process

We have studied the structural and superconducting properties of MgB$_2$ thin films made by pulsed laser deposition followed by in situ annealing. The cross-sectional transmission electron microscopy reveals a nanocrystalline mixture of textured MgO and MgB$_2$ with very small grain sizes. A zero-resistance transition temperature ($T_{c0}$) of 34 K and a zero-field critical current density ($J_c$) of $1.3 \times 10^6$ A/cm$^2$ were obtained. The irreversibility field was $\sim$ 8 T at low temperatures, although severe pinning instability was observed. These bulk-like superconducting properties show that the in situ deposition process can be a viable candidate for MgB$_2$ Josephson junction technologies

Bridgeness: A Local Index on Edge Significance in Maintaining Global Connectivity

Edges in a network can be divided into two kinds according to their different roles: some enhance the locality like the ones inside a cluster while others contribute to the global connectivity like the ones connecting two clusters. A recent study by Onnela et al uncovered the weak ties effects in mobile communication. In this article, we provide complementary results on document networks, that is, the edges connecting less similar nodes in content are more significant in maintaining the global connectivity. We propose an index named bridgeness to quantify the edge significance in maintaining connectivity, which only depends on local information of network topology. We compare the bridgeness with content similarity and some other structural indices according to an edge percolation process. Experimental results on document networks show that the bridgeness outperforms content similarity in characterizing the edge significance. Furthermore, extensive numerical results on disparate networks indicate that the bridgeness is also better than some well-known indices on edge significance, including the Jaccard coefficient, degree product and betweenness centrality.Comment: 10 pages, 4 figures, 1 tabl

Single nonmagnetic impurity resonance in FeSe-based 122-type superconductors as a probe for pairing symmetry

We study the effect of a single non-magnetic impurity in A$_{y}$Fe$_{2-x}$Se$_{2}$ (A=K, Rb, or Cs) superconductors by considering various pairing states based on a three-orbital model consistent with the photoemission experiments. The local density of states on and near the impurity site has been calculated by solving the Bogoliubov-de Gennes equations self-consistently. The impurity-induced in-gap bound states are found only for attractive impurity scattering potential, as in the cases of doping of Co or Ni, which is characterized by the strong particle-hole asymmetry, in the nodeless $d_{x^2-y^2}$ wave pairing state. This property may be used to probe the pairing symmetry of FeSe-based 122-type superconductors.Comment: 7 pages, 7 figure