6,645 research outputs found
Generic model for tunable colloidal aggregation in multidirectional fields
Based on Brownian Dynamics computer simulations in two dimensions we
investigate aggregation scenarios of colloidal particles with directional
interactions induced by multiple external fields. To this end we propose a
model which allows continuous change in the particle interactions from
point-dipole-like to patchy-like (with four patches). We show that, as a result
of this change, the non-equilibrium aggregation occurring at low densities and
temperatures transforms from conventional diffusion-limited cluster aggregation
(DLCA) to slippery DLCA involving rotating bonds; this is accompanied by a
pronounced change of the underlying lattice structure of the aggregates from
square-like to hexagonal ordering. Increasing the temperature we find a
transformation to a fluid phase, consistent with results of a simple mean-field
density functional theory
Ionic liquid-assisted hydrothermal synthesis of a biocompatible filler for photo-curable dental composite : from theory to experiment
Nanostructured hydroxyapatite (HA) is a new class of biocompatible fillers which has been recently utilized in bio hybrid materials by virtue of its excellent tissue bioactivity and biocompatibility. However, the need for higher thermal stability, solubility, surface bioactivity, radiopacity, and remineralization ability suggests a divalent cation substitution of HA for use in light curable dental restorative composites. In this work, structural and optical properties of Sr-doped hydroxyapatite were studied using first-principle calculations based on density functional theory (DFT). Next, Sr-doped hydroxyapatite (HA) was prepared via a new ionic liquid-assisted hydrothermal (ILH) route. Samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), Brunauer-Emmett-Teller (BET) surface area analysis, and cell viability. The obtained experimental data showed that the nucleation and crystal growth process controlled by [BMIM]Br molecules results in uniform products with small and regular particles and high specific surface areas. Finally, cytotoxicity tests showed that the as-prepared Sr-doped HA nanoparticles have good biocompatibility (â¥91%), confirming their potential for use in photo-curable dental restorative composites
Omniscopes: Large Area Telescope Arrays with only N log N Computational Cost
We show that the class of antenna layouts for telescope arrays allowing cheap
analysis hardware (with correlator cost scaling as N log N rather than N^2 with
the number of antennas N) is encouragingly large, including not only previously
discussed rectangular grids but also arbitrary hierarchies of such grids, with
arbitrary rotations and shears at each level. We show that all correlations for
such a 2D array with an n-level hierarchy can be efficiently computed via a
Fast Fourier Transform in not 2 but 2n dimensions. This can allow major
correlator cost reductions for science applications requiring exquisite
sensitivity at widely separated angular scales, for example 21cm tomography
(where short baselines are needed to probe the cosmological signal and long
baselines are needed for point source removal), helping enable future 21cm
experiments with thousands or millions of cheap dipole-like antennas. Such
hierarchical grids combine the angular resolution advantage of traditional
array layouts with the cost advantage of a rectangular Fast Fourier Transform
Telescope. We also describe an algorithm for how a subclass of hierarchical
arrays can efficiently use rotation synthesis to produce global sky maps with
minimal noise and a well-characterized synthesized beam.Comment: Replaced to match accepted PRD version. 10 pages, 9 fig
Intertwined chiral charge orders and topological stabilization of the light-induced state of a prototypical transition metal dichalcogenide
The fundamental idea that the constituents of interacting many body systems
in complex quantum materials may self-organise into long range order under
highly non-equilibrium conditions leads to the notion that entirely new and
unexpected functionalities might be artificially created. However,
demonstrating new emergent order in highly non-equilibrium transitions has
proven surprisingly difficult. In spite of huge recent advances in experimental
ultrafast time-resolved techniques, methods that average over successive
transition outcomes have so far proved incapable of elucidating the emerging
spatial structure. Here, using scanning tunneling microscopy, we report for the
first time the charge order emerging after a single transition outcome in a
prototypical two-dimensional dichalcogenide 1T-TaS initiated by a single
optical pulse. By mapping the vector field of charge displacements of the
emergent state, we find surprisingly intricate, long-range, topologically
non-trivial charge order in which chiral domain tiling is intertwined with
unique unpaired dislocations which play a crucial role in enhancing the
emergent states remarkable stability. The discovery of the principles that lead
to metastability in charge-ordered systems open the way to designing novel
emergent functionalities, particularly ultrafast all-electronic non-volatile
cryo-memories.Comment: preprint version of the paper published in npj Quantum Material
Multiple scattering theory for polycrystalline materials with strong grain anisotropy: theoretical fundamentals and applications
This work is a natural extension of the authors previous work, Multiple
scattering theory for heterogeneous elastic continua with strong property
fluctuation, theoretical fundamentals and applications, which established the
foundation for developing multiple scattering model for strongly scattering
heterogeneous elastic continua. In this work, the corresponding multiple
scattering theory for polycrystalline materials with randomly oriented
anisotropic crystallites is developed. As applications in ultrasonic
nondestructive evaluation, we calculated the dispersion and attenuation
coefficient of one of the most important polycrystalline materials in
aeronautics engineering, high temperature titanium alloys. The effects of grain
symmetry, grain size, and alloying elements on the dispersion and attenuation
behaviors are examined. Key information is obtained which has significant
implications for quantitatively evaluating the average grain size, monitoring
the phase transition, and even estimating gradual change in chemical
composition of titanium components in gas turbine engines. For applications in
seismology, the velocities and Q-factors for both hexagonal and cubic
polycrystalline iron models for the Earth uppermost inner core are obtained in
the whole frequency range. This work provides a universal, quantitative model
for characterization of a large variety of polycrystalline materials. It also
can be extended to incorporate more complicated microstructures, including
ellipsoidal grains with or without textures, and even multiphase
polycrystalline materials. The new model demonstrates great potential of
applications in ultrasonic nondestructive evaluation and inspection of
aerospace and aeronautic structures. It also provides a theoretical framework
for quantitative seismic data explanation and inversion for the material
composition and structural formations of the Earth inner core.Comment: 37 pages, 16 figure
Colloids with key-lock interactions: non-exponential relaxation, aging and anomalous diffusion
The dynamics of particles interacting by key-lock binding of attached
biomolecules are studied theoretically. Experimental realizations of such
systems include colloids grafted with complementary single-stranded DNA
(ssDNA), and particles grafted with antibodies to cell-membrane proteins.
Depending on the coverage of the functional groups, we predict two distinct
regimes. In the low coverage localized regime, there is an exponential
distribution of departure times. As the coverage is increased the system enters
a diffusive regime resulting from the interplay of particle desorption and
diffusion. This interplay leads to much longer bound state lifetimes, a
phenomenon qualitatively similar to aging in glassy systems. The diffusion
behavior is analogous to dispersive transport in disordered semiconductors:
depending on the interaction parameters it may range from a finite
renormalization of the diffusion coefficient to anomalous, subdiffusive
behavior. We make connections to recent experiments and discuss the
implications for future studies.Comment: v2: substantially revised version, new treatment of localized regime,
19 pages, 10 figure
Correlated cryogenic fluorescence microscopy and electron cryo-tomography shows that exogenous TRIM5α can form hexagonal lattices or autophagy aggregates in vivo
Members of the tripartite motif (TRIM) protein family have been shown to assemble into structures in both the nucleus and cytoplasm. One TRIM protein family member, TRIM5α, has been shown to form cytoplasmic bodies involved in restricting retroviruses such as HIV-1. Here we applied cryogenic correlated light and electron microscopy, combined with electron cryo-tomography, to intact mammalian cells expressing YFP-rhTRIM5α and found the presence of hexagonal nets whose arm lengths were similar to those of the hexagonal nets formed by purified TRIM5α in vitro. We also observed YFP-rhTRIM5α within a diversity of structures with characteristics expected for organelles involved in different stages of macroautophagy, including disorganized protein aggregations (sequestosomes), sequestosomes flanked by flat double-membraned vesicles (sequestosome:phagophore complexes), sequestosomes within double-membraned vesicles (autophagosomes), and sequestosomes within multivesicular autophagic vacuoles (amphisomes or autolysosomes). Vaults were also seen in these structures, consistent with their role in autophagy. Our data 1) support recent reports that TRIM5α can form both well-organized signaling complexes and nonsignaling aggregates, 2) offer images of the macroautophagy pathway in a near-native state, and 3) reveal that vaults arrive early in macroautophagy
Characterization methods dedicated to nanometer-thick hBN layers
Hexagonal boron nitride (hBN) regains interest as a strategic component in
graphene engineering and in van der Waals heterostructures built with two
dimensional materials. It is crucial then, to handle reliable characterization
techniques capable to assess the quality of structural and electronic
properties of the hBN material used. We present here characterization
procedures based on optical spectroscopies, namely cathodoluminescence and
Raman, with the additional support of structural analysis conducted by
transmission electron microscopy. We show the capability of optical
spectroscopies to investigate and benchmark the optical and structural
properties of various hBN thin layers sources
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