1,802 research outputs found
Flow behavior in liquid molding
The liquid molding (LM) process for manufacturing polymer composites with structural properties has the potential to significantly lower fabrication costs and increase production rates. LM includes both resin transfer molding and structural reaction injection molding. To achieve this potential, however, the underlying science base must be improved to facilitate effective process optimization and implementation of on-line process control. The National Institute of Standards and Technology (NIST) has a major program in LM that includes materials characterization, process simulation models, on-line process monitoring and control, and the fabrication of test specimens. The results of this program are applied to real parts through cooperative projects with industry. The key feature in the effort is a comprehensive and integrated approach to the processing science aspects of LM. This paper briefly outlines the NIST program and uses several examples to illustrate the work
Emergence of foams from the breakdown of the phase field crystal model
The phase field crystal (PFC) model captures the elastic and topological
properties of crystals with a single scalar field at small undercooling. At
large undercooling, new foam-like behavior emerges. We characterize this foam
phase of the PFC equation and propose a modified PFC equation that may be used
for the simulation of foam dynamics. This minimal model reproduces von
Neumann's rule for two-dimensional dry foams, and Lifshitz-Slyozov coarsening
for wet foams. We also measure the coordination number distribution and find
that its second moment is larger than previously-reported experimental and
theoretical studies of soap froths, a finding that we attribute to the wetness
of the foam increasing with time.Comment: 4 pages, 4 figure
Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS using multiphoton microscopy
We report second- and third-harmonic generation in monolayer MoS
as a tool for imaging and accurately characterizing the material's nonlinear
optical properties under 1560 nm excitation. Using a surface nonlinear optics
treatment, we derive expressions relating experimental measurements to second-
and third-order nonlinear sheet susceptibility magnitudes, obtaining values of
m V and for the first time for
monolayer MoS, m V.
These sheet susceptibilities correspond to effective bulk nonlinear
susceptibility values of m V and
m V, accounting for the sheet
thickness. Experimental comparisons between MoS and graphene are
also performed, demonstrating 3.4 times stronger third-order sheet
nonlinearity in monolayer MoS, highlighting the material's
potential for nonlinear photonics in the telecommunications C band.Comment: Accepted by 2D Materials, 28th Oct 201
Nano-magnetic droplets and implications to orbital ordering in La1-xSrxCoO3
Inelastic cold neutron scattering on LaCoO3 provided evidence for a distinct
low energy excitation at 0.6 meV coincident with the thermally induced magnetic
transition. Coexisting strong ferromagnetic (FM) and weaker antiferromagnetic
(AFM) correlations that are dynamic follow the activation to the excited state,
identified as the intermediate S=1 spin triplet. This is indicative of
dynamical orbital ordering favoring the observed magnetic interactions. With
hole doping as in La1-xSrxCoO3, the FM correlations between Co spins become
static and isotropically distributed due to the formation of FM droplets. The
correlation length and condensation temperature of these droplets increase
rapidly with metallicity due to the double exchange mechanism.Comment: To appear in Phys. Rev. Let
Field-dependent heat transport in the Kondo insulator SmB6 : phonons scattered by magnetic impurities
The thermal conductivity of the Kondo insulator SmB was measured
at low temperature, down to 70 mK, in magnetic fields up to 15 T, on single
crystals grown using both the floating-zone and the flux methods. The residual
linear term at is found to be zero in all samples, for
all magnetic fields, in agreement with previous studies. There is therefore no
clear evidence of fermionic heat carriers. In contrast to some prior data, we
observe a large enhancement of with increasing field. The effect of
field is anisotropic, depending on the relative orientation of field and heat
current (parallel or perpendicular), and with respect to the cubic crystal
structure. We interpret our data in terms of heat transport predominantly by
phonons, which are scattered by magnetic impurities.Comment: publish versio
Effect of negative chemical pressure on the prototypical itinerant magnet MnSi
The evolution of the magnetic and charge transport properties of the itinerant magnetic metal MnSi with the substitution of Al and Ga on the Si site is investigated. We observe an increase in unit cell volume indicating that both Al and Ga substitutions create negative chemical pressure. There are substantial increases in the Curie temperature and the ordered moment demonstrating that the substitutions give the magnetism a stronger itinerant character. The substitutions also increase the range of temperature and field where the skyrmion phase is stable due to a change in the character of the magnetism. In contrast to the behavior of pure MnSi and expectations for the intrinsic anomalous Hall effect, we find a significant temperature dependence to the magnitude and sign of anomalous Hall conductivity constant in Al or Ga substituted samples. This temperature dependence likely reflects changes in the spin-orbit coupling strength with temperature, which may have significant consequences on the helical and skyrmion states. Overall, we observe a continuous evolution of magnetic and charge transport properties through positive to negative pressure
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