29,452 research outputs found
Spectral properties of photon pairs generated by spontaneous four wave mixing in inhomogeneous photonic crystal fibers
The photonic crystal fiber (PCF) is one of the excellent media for generating
photon pairs via spontaneous four wave mixing. Here we study how the
inhomogeneity of PCFs affect the spectral properties of photon pairs from both
the theoretical and experimental aspects. The theoretical model shows that the
photon pairs born in different place of the inhomogeneous PCF are coherently
superposed, and a modulation in the broadened spectrum of phase matching
function will appear, which prevents the realization of spectral factorable
photon pairs. In particular, the inhomogeneity induced modulation can be
examined by measuring the spectrum of individual signal or idler field when the
asymmetric group velocity matching is approximately fulfilled. Our experiments
are performed by tailoring the spectrum of pulsed pump to satisfy the specified
phase matching condition. The observed spectra of individual signal photons,
which are produced from different segments of the 1.9 m inhomogeneous PCF,
agree with the theoretical predictions. The investigations are not only useful
for fiber based quantum state engineering, but also provide a dependable method
to test the homogeneity of PCF.Comment: to appear in Phys. Rev.
Superconducting properties of ultrathin Bi2Sr2CaCu2O8+x single crystals
We use Ar-ion milling to thin Bi2212 single crystals down to a few nanometers
or one-to-two (CuO2)2 layers. With decreasing the thickness, superconducting
transition temperature gradually decreases to zero and the in-plane resistivity
increases to large values indicating the existence of a
superconductor-insulator transition in ultrathin Bi2212 single crystals.Comment: 17 pages, 6 figures, to appear in J. Appl. Phys. 98(3) 200
A distinct sortase SrtB anchors and processes a streptococcal adhesin AbpA with a novel structural property.
Surface display of proteins by sortases in Gram-positive bacteria is crucial for bacterial fitness and virulence. We found a unique gene locus encoding an amylase-binding adhesin AbpA and a sortase B in oral streptococci. AbpA possesses a new distinct C-terminal cell wall sorting signal. We demonstrated that this C-terminal motif is required for anchoring AbpA to cell wall. In vitro and in vivo studies revealed that SrtB has dual functions, anchoring AbpA to the cell wall and processing AbpA into a ladder profile. Solution structure of AbpA determined by NMR reveals a novel structure comprising a small globular α/β domain and an extended coiled-coil heliacal domain. Structural and biochemical studies identified key residues that are crucial for amylase binding. Taken together, our studies document a unique sortase/adhesion substrate system in streptococci adapted to the oral environment rich in salivary amylase
A single intrinsic Josephson junction with double-sided fabrication technique
We make stacks of intrinsic Josephson junctions (IJJs) imbedded in the bulk
of very thin (~nm) single crystals.
By precisely controlling the etching depth during the double-sided fabrication
process, the stacks can be reproducibly tailor-made to be of any microscopic
height (), i.e. enclosing a specified number of IJJ (0-6),
including the important case of a single junction. We discuss reproducible
gap-like features in the current-voltage characteristics of the samples at high
bias.Comment: 3 pages, 4 figures, to be published in APL May. 2
High-efficiency collimation of airborne sound through a single deep-subwavelength aperture in an ultra-thin planar plate
© 2019 The Japan Society of Applied Physics. We propose a mechanism for high-efficiency collimation of airborne sound through an ultra-thin planar structure perforated with a single deep-subwavelength aperture by combining a zigzag-shaped structure with arrays of subwavelength resonators to increase the equivalent refractive index and eliminate high-order diffractive waves simultaneously. Numerical simulations demonstrate that the proposed mechanism enables remarkably enhanced transmission and strong collimation of the transmitted wave, which propagates for a strikingly long distance exceeding 125 wavelengths. Due to its capabilities and flexibility, the proposed design opens up possibilities for novel compact acoustic-steering devices and may have far-reaching impacts in diverse applications such as acoustic communications and loudspeaker design
Enhanced ethanol production from stalk juice of sweet sorghum by response surface methodology
Sweet sorghum (sugar sorghum, Sorghum bicolor) is one kind of non-grain energy crops. As a novel green regenerated high-energy crop with high utility value, high yield of biomass, the sweet sorghum is widely used and developed in China. Stalk juice of sweet sorghum was used as the main substrate for ethanol production by a Saccharomyces cerevisiae strain because of the high content of sugar. Effects of different medium compositions, including urea, KH2PO4 and MgSO4, on ethanol production were studied by response surface methodology in this paper. A second-order model that related the concentration of ethanol was developed and thus the optimal medium composition was obtained, which was 4.75 g l-1 urea, 3.58 g l-1 KH2PO4, and 0.98 g l-1 MgSO4. Under this condition, the highest ethanol concentration reached 86.2 g l-1.Key words: Ethanol, sweet sorghum, stalk juice, medium composition, response surface methodology
Comparing the Host Galaxies of Type Ia, Type II and Type Ibc Supernovae
We compare the host galaxies of 902 supernovae, including SNe Ia, SNe II and
SNe Ibc, which are selected by cross-matching the Asiago Supernova Catalog with
the SDSS Data Release 7. We further selected 213 galaxies by requiring the
light fraction of spectral observations 15%, which could represent well the
global properties of the galaxies. Among them, 135 galaxies appear on the
Baldwin-Phillips-Terlevich diagram, which allows us to compare the hosts in
terms of star-forming, AGNs (including composites, LINERs and Seyfert 2s) and
"Absorp" (their related emission-lines are weak or non-existence) galaxies. The
diagrams related to parameters D(4000), H, stellar masses, SFRs
and specific SFRs for the SNe hosts show that almost all SNe II and most of SNe
Ibc occur in SF galaxies, which have a wide range of stellar mass and low
D(4000). The SNe Ia hosts as SF galaxies follow similar trends. A
significant fraction of SNe Ia occurs in AGNs and Absorp galaxies, which are
massive and have high D(4000). The stellar population analysis from
spectral synthesis fitting shows that the hosts of SNe II have a younger
stellar population than hosts of SNe Ia. These results are compared with those
of the 689 comparison galaxies where the SDSS fiber captures less than 15% of
the total light. These comparison galaxies appear biased towards higher
12+log(O/H) (0.1dex) at a given stellar mass. Therefore, we believe the
aperture effect should be kept in mind when the properties of the hosts for
different types of SNe are discussed.Comment: 15 pages, 9 figure
Global polarization of QGP in non-central heavy ion collisions at high energies
Due to the presence of a large orbital angular momentum of the parton system
produced at the early stage of non-central heavy-ion collisions, quarks and
anti-quarks are shown to be polarized in the direction opposite to the reaction
plane which is determined by the impact-parameter and the beam momentum. The
global quark polarization via elastic scattering was first calculated in an
effective static potential model, then using QCD at finite temperature with the
hard-thermal-loop re-summed gluon propagator. The measurable consequences are
discussed. Global hyperon polarization from the hadronization of polarized
quarks are predicted independent of the hadronization scenarios. It has also
been shown that the global polarization of quarks and anti-quarks leads also to
spin alignment of vector mesons. Dedicated measurements at RHIC are underway
and some of the preliminary results are obtained. In this presentation, the
basic idea and main results of global quark polarization are presented. The
direct consequences such as global hyperon polarization and spin alignment are
summarized.Comment: plenary talk at the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions (QM2006), Shanghai, China,
November 14-20, 200
X-Ray Flares of Gamma-Ray Bursts: Quakes of Solid Quark Stars?
We propose a star-quake model to understand X-ray flares of both long and
short Gamma-ray bursts (GRBs) in a solid quark star regime. Two kinds of
central engines for GRBs are available if pulsar-like stars are actually
(solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found
that a quark star could be solidified about 10^3 to 10^6 s later after its
birth if the critical temperature of phase transition is a few MeV, and then a
new source of free energy (i.e., elastic and gravitational ones, rather than
rotational or magnetic energy) could be possible to power GRB X-ray flares.Comment: 8 pages, latex file. 2 figures. To appear in Science in China Series
Hertz-level Measurement of the 40Ca+ 4s 2S1/2-3d 2D5/2 Clock Transition Frequency With Respect to the SI Second through GPS
We report a frequency measurement of the clock transition of a single ^40Ca^+
ion trapped and laser cooled in a miniature ring Paul trap with 10^-15 level
uncertainty. In the measurement, we used an optical frequency comb referenced
to a Hydrogen maser, which was calibrated to the SI second through the Global
Positioning System (GPS). Two rounds of measurements were taken in May and June
2011, respectively. The frequency was measured to be 411 042 129 776 393.0(1.6)
Hz with a fractional uncertainty of 3.9{\times}10^-15 in a total averaging time
of > 2{\times}10^6 s within 32 days
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