140 research outputs found
Experimental Observation of Large Chern numbers in Photonic Crystals
Despite great interest in the quantum anomalous Hall phase and its analogs,
all experimental studies in electronic and bosonic systems have been limited to
a Chern number of one. Here, we perform microwave transmission measurements in
the bulk and at the edge of ferrimagnetic photonic crystals. Bandgaps with
large Chern numbers of 2, 3, and 4 are present in the experimental results
which show excellent agreement with theory. We measure the mode profiles and
Fourier transform them to produce dispersion relations of the edge modes, whose
number and direction match our Chern number calculations.Comment: This experimental work was accepted to PRL on Oct. 13, 2015. Our
theoretical work from PRL http://dx.doi.org/10.1103/PhysRevLett.113.11390
Hydrocode modeling of the spallation process during hypervelocity impacts: Implications for the ejection of Martian meteorites
Hypervelocity ejection of material by impact spallation is considered a
plausible mechanism for material exchange between two planetary bodies. We have
modeled the spallation process during vertical impacts over a range of impact
velocities from 6 to 21 km/s using both grid- and particle-based hydrocode
models. The Tillotson equations of state, which are able to treat the nonlinear
dependence of density on pressure and thermal pressure in the strongly shocked
matter, were used to study the hydrodynamic and thermodynamic response after
impacts. The effects of material strength and gravitational acceleration were
not considered. A two-dimensional time-dependent pressure field within a
1.5-fold projectile radius from the impact point was investigated in
cylindrical coordinates to address the generation of spalled material. A
resolution test was also performed to reject ejected materials with peak
pressures that were too low due to artificial viscosity. The relationship
between ejection velocity veject and peak pressure Ppeak was also derived. Our
approach shows that late stage acceleration in an ejecta curtain occurs due to
the compressible nature of the ejecta, resulting in an ejection velocity that
can be higher than the ideal maximum of the resultant particle velocity after
passage of a shock wave. We also calculate the ejecta mass that can escape from
a planet like Mars (i.e., veject higher than 5 km/s) that matches the
petrographic constraints from Martian meteorites, and which occurs when Ppeak
from 30-50 GPa. Although the mass of such ejecta is limited to from 0.1-1
percent of the projectile mass in vertical impacts, this is sufficient for
spallation to have been a plausible mechanism for the ejection of Martian
meteorites. Finally, we propose that impact spallation is a plausible mechanism
for the generation of tektites.Comment: 67 pages, 28 figures, accepted for publication in Icaru
Assessing the impact of curcumin on dualâspecies biofilms formed by Streptococcus mutans and Candida albicans
Streptococcus mutans and Candida albicans are often isolated from plaques associated with early childhood caries. However, there are limited studies examining how these microorganisms interact with one another and how best to manage them. Recent studies have shown that curcumin (CUR), a natural compound, has the potential to independently control both of these microorganisms. The purpose of this study was to investigate how S. mutans and C. albicans respond in monoâ and dualâspecies biofilms challenged with CUR. Quantitative biofilm biomass and viability were first evaluated and supported by liveâdead PCR to assess biofilm composition. Confocal laser scanning microscopy (CLSM) was used to evaluate the exopolysaccharide (EPS) content and thickness of the biofilms, and the structure of the biofilms and morphology of the cells were observed by scanning electron microscopy (SEM). Quantitative realâtime PCR (qRTâPCR) was applied to assess relative gene expression. The 50% minimum biofilm eradication concentration (MBEC50) of CUR against S. mutans and C. albicans was 0.5 mM. The biomass and viability decreased after treatment with CUR both in dualâspecies biofilms and in monoâspecies biofilm. CUR inhibited S. mutans and C. albicans in both monoâ and dualâspecies biofilms. Streptococcus mutans was more sensitive to CUR in dualâspecies biofilm than in monoâspecies biofilms, whereas C. albicans was less sensitive in dualâspecies biofilms. EPS production was decreased by CUR in both monoâ and dualâspecies biofilms, which coincided with the downregulation of glucosyltransferase and quorum sensingârelated gene expression of S. mutans. In C. albicans, the agglutininâlike sequence family of C. albicans was also downregulated in dualâspecies biofilms. Collectively, these data show the potential benefit of using a natural antimicrobial, CUR, to control cariesârelated dualâspecies plaque biofilms
Experimental Realization of an Extreme-Parameter Omnidirectional Cloak
An ideal transformation-based omnidirectional cloak always relies on metamaterials with extreme parameters, which were previously thought to be too difficult to realize. For such a reason, in previous experimental proposals of invisibility cloaks, the extreme parameters requirements are usually abandoned, leading to inherent scattering. Here, we report on the first experimental demonstration of an omnidirectional cloak that satisfies the extreme parameters requirement, which can hide objects in a homogenous background. Instead of using resonant metamaterials that usually involve unavoidable absorptive loss, the extreme parameters are achieved using a nonresonant metamaterial comprising arrays of subwavelength metallic channels manufactured with 3D metal printing technology. A high level transmission of electromagnetic wave propagating through the present omnidirectional cloak, as well as significant reduction of scattering field, is demonstrated both numerically and experimentally. Our work may also inspire experimental realizations of the other full-parameter omnidirectional optical devices such as concentrator, rotators, and optical illusion apparatuses
Long-range adiabatic quantum state transfer through a linear array of quantum dots
We introduce an adiabatic long-range quantum communication proposal based on
a quantum dot array. By adiabatically varying the external gate voltage applied
on the system, the quantum information encoded in the electron can be
transported from one end dot to another. We numerically solve the Schr\"odinger
equation for a system with a given number of quantum dots. It is shown that
this scheme is a simple and efficient protocol to coherently manipulate the
population transfer under suitable gate pulses. The dependence of the energy
gap and the transfer time on system parameters is analyzed and shown
numerically. We also investigate the adiabatic passage in a more realistic
system in the presence of inevitable fabrication imperfections. This method
provides guidance for future realizations of adiabatic quantum state transfer
in experiments.Comment: 7 pages, 7 figure
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