83,273 research outputs found
Tunable mechanical and thermal properties of ZnS/CdS core/shell nanowires
Using all atom molecular dynamics (MD) simulations, we have studied the
mechanical properties of ZnS/CdS core/shell nanowires. Our results show that
the coating of a few atomic layer CdS shell on the ZnS nanowire leads to a
significant change in the stiffness of the core/shell nanowires compared to the
stiffness of pure ZnS nanowires. The binding energy between the core and shell
region decreases due to the lattice mismatch at the core-shell interface. This
reduction in binding energy plays an important role in determining the
stiffness of a core/shell nanowire. We have also investigated the effects of
the shell on the thermal conductivity and melting behavior of the nanowires
Advances in the ab initio description of nuclear three-cluster systems
We introduce the extension of the ab initio no-core shell model with
continuum to describe three-body cluster systems. We present results for the
ground state of 6He and show improvements with respect to the description
obtained within the no-core shell model and the no-core shell model/resonating
group methods.Comment: Proceedings of the 21st International Conference on Few-Body Problems
in Physics. May 18-22, 2015. Chicago, Illinois, US
Core-shell structures in single flexible-semiflexible block copolymers: Finding the free energy minimum for the folding transition
We investigate the folding transition of a single diblock copolymer
consisting of a semiflexible and a flexible block. We obtain a {\it
Saturn-shaped} core-shell conformation in the folded state, in which the
flexible block forms a core and the semiflexible block wraps around it. We
demonstrate two distinctive features of the core-shell structures: (i) The
kinetics of the folding transition in the copolymer are significantly more
efficient than those of a semiflexible homopolymer. (ii) The core-shell
structure does not depend on the transition pathway
Hypernuclear No-Core Shell Model
We extend the No-Core Shell Model (NCSM) methodology to incorporate
strangeness degrees of freedom and apply it to single- hypernuclei.
After discussing the transformation of the hyperon-nucleon (YN) interaction
into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group
transformation applied to it to improve model-space convergence, we present two
complementary formulations of the NCSM, one that uses relative Jacobi
coordinates and symmetry-adapted basis states to fully exploit the symmetries
of the hypernuclear Hamiltonian, and one working in a Slater determinant basis
of HO states where antisymmetrization and computation of matrix elements is
simple and to which an importance-truncation scheme can be applied. For the
Jacobi-coordinate formulation, we give an iterative procedure for the
construction of the antisymmetric basis for arbitrary particle number and
present the formulae used to embed two- and three-baryon interactions into the
many-body space. For the Slater-determinant formulation, we discuss the
conversion of the YN interaction matrix elements from relative to
single-particle coordinates, the importance-truncation scheme that tailors the
model space to the description of the low-lying spectrum, and the role of the
redundant center-of-mass degrees of freedom. We conclude with a validation of
both formulations in the four-body system, giving converged ground-state
energies for a chiral Hamiltonian, and present a short survey of the
hyper-helium isotopes.Comment: 17 pages, 8 figures; accepted versio
Sub-20 nm Core-Shell-Shell Nanoparticles for Bright Upconversion and Enhanced Förster Resonant Energy Transfer.
Upconverting nanoparticles provide valuable benefits as optical probes for bioimaging and Förster resonant energy transfer (FRET) due to their high signal-to-noise ratio, photostability, and biocompatibility; yet, making nanoparticles small yields a significant decay in brightness due to increased surface quenching. Approaches to improve the brightness of UCNPs exist but often require increased nanoparticle size. Here we present a unique core-shell-shell nanoparticle architecture for small (sub-20 nm), bright upconversion with several key features: (1) maximal sensitizer concentration in the core for high near-infrared absorption, (2) efficient energy transfer between core and interior shell for strong emission, and (3) emitter localization near the nanoparticle surface for efficient FRET. This architecture consists of β-NaYbF4 (core) @NaY0.8-xErxGd0.2F4 (interior shell) @NaY0.8Gd0.2F4 (exterior shell), where sensitizer and emitter ions are partitioned into core and interior shell, respectively. Emitter concentration is varied (x = 1, 2, 5, 10, 20, 50, and 80%) to investigate influence on single particle brightness, upconversion quantum yield, decay lifetimes, and FRET coupling. We compare these seven samples with the field-standard core-shell architecture of β-NaY0.58Gd0.2Yb0.2Er0.02F4 (core) @NaY0.8Gd0.2F4 (shell), with sensitizer and emitter ions codoped in the core. At a single particle level, the core-shell-shell design was up to 2-fold brighter than the standard core-shell design. Further, by coupling a fluorescent dye to the surface of the two different architectures, we demonstrated up to 8-fold improved emission enhancement with the core-shell-shell compared to the core-shell design. We show how, given proper consideration for emitter concentration, we can design a unique nanoparticle architecture to yield comparable or improved brightness and FRET coupling within a small volume
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The effect of core-shell engineering on the energy product of magnetic nanometals.
Solution-based growth of magnetic FePt-FeCo (core-shell) nanoparticles with a controllable shell thickness has been demonstrated. The transition from spin canting to exchange coupling of FePt-FeCo core-shell nanostructures leads to a 28% increase in the coercivity (12.8 KOe) and a two-fold enhancement in the energy product (9.11 MGOe)
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