443 research outputs found
Simultaneous Conversion of Polarization and Frequency via Time‐Division‐Multiplexing Metasurfaces
AbstractMetasurfaces are artificially engineered two‐dimensional materials composed of sub‐wavelength meta‐atoms, which have shown unprecedented capabilities in manipulating the amplitude, phase, frequency, and polarization states of electromagnetic waves. Specifically, polarization control can be attained via suitable anisotropic, linear, and time‐invariant designs, while frequency conversion is realized via nonlinear or time‐varying platforms. Simultaneous manipulations of polarization and frequency would be of considerable practical interest in many application scenarios, but remain unattainable with current approaches. Here, a time‐division‐multiplexing metasurface is proposed to realize the simultaneous conversion of polarization and frequency. The platform relies on time‐modulated polarization switches and, by varying the duty cycle and time delays of the polarization channels, can arbitrarily rotate the polarization at the central frequency of operation, and synthesize various polarization states at selected harmonic frequencies. Theoretical predictions are validated via measurements on a prototype operating at microwave frequencies, providing the first experimental evidence of simultaneous polarization and frequency conversions via time‐division‐multiplexing metasurfaces. The outcomes open a new pathway in manipulating the electromagnetic waves via time‐varying metasurfaces, and may be of interest for a broad variety of applications in scenarios ranging from polarization imaging to quantum optics
Thermodynamic Origins of Structural Metastability in Two-Dimensional Black Arsenic
Two-dimensional (2D) materials have aroused considerable research interests
owing to their potential applications in nanoelectronics and optoelectronics.
Thermodynamic stability of 2D structures inevitably affects the performance and
power consumption of the fabricated nanodevices. Black arsenic (b-As), as a
cousin of black phosphorus, has presented the extremely high anisotropy in
physical properties. However, the systematic research on structural stability
of b-As is still lack. Herein, we demonstrated the detailed analysis on
structural metastability of the natural b-As, and determined its existence
conditions in terms of two essential thermodynamic variables as hydrostatic
pressure and temperature. Our results confirmed that b-As can only survive
below 0.7 GPa, and then irreversibly transform to gray arsenic, in consistent
with our theoretical calculations. Furthermore, thermal annealing strategy was
developed to precisely control the thickness of b-As flake, and it sublimates
at 300 oC. These results could pave the way for 2D b-As in many promising
applications.Comment: 28 pages, 4 figure
On the fairness of the main galaxy sample of SDSS
Flux-limited and volume-limited galaxy samples are constructed from SDSS data
releases DR4, DR6 and DR7 for statistical analysis. The two-point correlation
functions , monopole of three-point correlation functions ,
projected two-point correlation function and pairwise velocity dispersion
are measured to test if galaxy samples are fair for these
statistics. We find that with increment of sky coverage of SDSS, of
flux-limited sample is extremely robust and insensitive to local structures at
low redshift. But for volume-limited samples fainter than at large scales
s>\sim 10\hmpc, deviation of and of DR7 to those of DR4
and DR6 increases with larger absolute magnitude. In the weakly nonlinear
regime, there is no agreement between of different data releases in
all luminosity bins. Furthermore, of volume-limited samples of DR7 in
luminosity bins fainter than are significantly larger,
and of the two faintest volume-limited samples of DR7 display
very different scale dependence than results of DR4 and DR6. Our findings call
for cautions in understanding clustering analysis results of SDSS faint galaxy
samples, and higher order statistics of SDSS volume-limited samples in the
weakly nonlinear regime. The first zero-crossing points of of
volume-limited samples are also investigated and discussed.Comment: 16 pages, 12 figures, accepte
CRISPR/Cas9‐mediated restoration of Tamyb10 to create pre‐harvest sprouting‐resistant red wheat
Protective efficacy of commercial inactivated Newcastle disease virus vaccines in chickens against a recent Korean epizootic strain
Despite the intensive vaccination policy that has been put in place to control Newcastle disease virus (NDV), the recent emergence of NDV genotype VII strains in Korea has led to significant economic losses in the poultry industry. We assessed the ability of inactivated, oil-emulsion vaccines derived from La Sota or Ulster 2C NDV strains to protect chickens from challenge with Kr-005/00, which is a recently isolated Korean epizootic genotype VII strain. Six-week-old SPF chickens were vaccinated once and challenged three weeks later via the eye drop/intranasal route. All vaccinated birds were fully protected from disease, regardless of the vaccine strains used. All vaccinated and challenged groups showed significant sero-conversion 14 days after challenge. However, some vaccinated birds, despite being protected from disease, shed the challenge virus from their oro-pharynx and cloaca, albeit at significantly lower titers than the unvaccinated challenged control birds. The virological, serological, and epidemiological significance of our observations with regard to NDV disease eradication is discussed
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