716 research outputs found
Macroscopic Klein tunneling in spin-orbit-coupled Bose-Einstein condensates
We propose an experimental scheme to detect macroscopic Klein tunneling with spin-orbit-coupled Bose-Einstein condensates (BECs). We show that a nonlinear Dirac equation with tunable parameters can be realized with such BECs. Through numerical calculations, we demonstrate that macroscopic Klein tunneling can be clearly detected under realistic conditions. Macroscopic quantum coherence in such relativistic tunneling is clarified and a BEC with a negative energy is shown to be able to transmit transparently through a wide Gaussian potential barrier. © 2012 American Physical Society.published_or_final_versio
Particle-number fractionalization of a one-dimensional atomic Fermi gas with synthetic spin-orbit coupling
published_or_final_versio
Hyperglycemia-induced inhibition of DJ-1 expression compromised the effectiveness of ischemic postconditioning cardioprotection in rats
published_or_final_versio
Demonstration of a self-pulsing photonic crystal Fano laser
Semiconductor lasers in use today rely on mirrors based on the reflection at
a cleaved facet or Bragg reflection from a periodic stack of layers. Here, we
demonstrate an ultra-small laser with a mirror based on the Fano resonance
between a continuum of waveguide modes and the discrete resonance of a
nanocavity. The Fano resonance leads to unique laser characteristics. Since the
Fano mirror is very narrow-band compared to conventional lasers, the laser is
single-mode and in particular, it can be modulated via the mirror. We show,
experimentally and theoretically, that nonlinearities in the mirror may even
promote the generation of a self-sustained train of pulses at gigahertz
frequencies, an effect that was previously only observed in macroscopic lasers.
Such a source is of interest for a number of applications within integrated
photonics
Efficient control of atmospheric sulfate production based on three formation regimes
The formation of sulfate (SO₄²⁻) in the atmosphere is linked chemically to its direct precursor, sulfur dioxide (SO₂), through several key oxidation paths for which nitrogen oxides or NO_x (NO and NO₂) play essential roles. Here we present a coherent description of the dependence of SO₄²⁻ formation on SO₂ and NO_x under haze-fog conditions, in which fog events are accompanied by high aerosol loadings and fog-water pH in the range of 4.7–6.9. Three SO₄²⁻ formation regimes emerge as defined by the role played by NO_x. In the low-NO_x regime, NO_x act as catalyst for HO_x, which is a major oxidant for SO₂, whereas in the high-NO_x regime, NO₂ is a sink for HO_x. Moreover, at highly elevated NO_x levels, a so-called NO₂-oxidant regime exists in which aqueous NO₂ serves as the dominant oxidant of SO₂. This regime also exists under clean fog conditions but is less prominent. Sensitivity calculations using an emission-driven box model show that the reduction of SO₄²⁻ is comparably sensitive to the reduction of SO₂ and NO_x emissions in the NO₂-oxidant regime, suggesting a co-reduction strategy. Formation of SO₄²⁻ is relatively insensitive to NO_x reduction in the low-NO_x regime, whereas reduction of NO_x actually leads to increased SO₄²⁻ production in the intermediate high-NO_x regime
Adaptively Transforming Graph Matching
Recently, many graph matching methods that incorporate pairwise constraint
and that can be formulated as a quadratic assignment problem (QAP) have been
proposed. Although these methods demonstrate promising results for the graph
matching problem, they have high complexity in space or time. In this paper, we
introduce an adaptively transforming graph matching (ATGM) method from the
perspective of functional representation. More precisely, under a
transformation formulation, we aim to match two graphs by minimizing the
discrepancy between the original graph and the transformed graph. With a linear
representation map of the transformation, the pairwise edge attributes of
graphs are explicitly represented by unary node attributes, which enables us to
reduce the space and time complexity significantly. Due to an efficient
Frank-Wolfe method-based optimization strategy, we can handle graphs with
hundreds and thousands of nodes within an acceptable amount of time. Meanwhile,
because transformation map can preserve graph structures, a domain
adaptation-based strategy is proposed to remove the outliers. The experimental
results demonstrate that our proposed method outperforms the state-of-the-art
graph matching algorithms
Electron quantum metamaterials in van der Waals heterostructures
In recent decades, scientists have developed the means to engineer synthetic
periodic arrays with feature sizes below the wavelength of light. When such
features are appropriately structured, electromagnetic radiation can be
manipulated in unusual ways, resulting in optical metamaterials whose function
is directly controlled through nanoscale structure. Nature, too, has adopted
such techniques -- for example in the unique coloring of butterfly wings -- to
manipulate photons as they propagate through nanoscale periodic assemblies. In
this Perspective, we highlight the intriguing potential of designer
sub-electron wavelength (as well as wavelength-scale) structuring of electronic
matter, which affords a new range of synthetic quantum metamaterials with
unconventional responses. Driven by experimental developments in stacking
atomically layered heterostructures -- e.g., mechanical pick-up/transfer
assembly -- atomic scale registrations and structures can be readily tuned over
distances smaller than characteristic electronic length-scales (such as
electron wavelength, screening length, and electron mean free path). Yet
electronic metamaterials promise far richer categories of behavior than those
found in conventional optical metamaterial technologies. This is because unlike
photons that scarcely interact with each other, electrons in subwavelength
structured metamaterials are charged, and strongly interact. As a result, an
enormous variety of emergent phenomena can be expected, and radically new
classes of interacting quantum metamaterials designed
Observation of a ppb mass threshoud enhancement in \psi^\prime\to\pi^+\pi^-J/\psi(J/\psi\to\gamma p\bar{p}) decay
The decay channel
is studied using a sample of events collected
by the BESIII experiment at BEPCII. A strong enhancement at threshold is
observed in the invariant mass spectrum. The enhancement can be fit
with an -wave Breit-Wigner resonance function with a resulting peak mass of
and a
narrow width that is at the 90% confidence level.
These results are consistent with published BESII results. These mass and width
values do not match with those of any known meson resonance.Comment: 5 pages, 3 figures, submitted to Chinese Physics
- …