3,128 research outputs found
Unconventional Superconducting Symmetry in a Checkerboard Antiferromagnet
We use a renormalized mean field theory to study the Gutzwiller projected BCS
states of the extended Hubbard model in the large limit, or the
--- model on a two-dimensional checkerboard lattice. At small
, the frustration due to the diagonal terms of and does not
alter the -wave pairing symmetry, and the negative (positive)
enhances (suppresses) the pairing order parameter. At large , the
ground state has an extended s-wave symmetry. At the intermediate , the
ground state is or -wave with time reversal symmetry broken.Comment: 6 pages, 6 figure
Low-Complexity Channel Estimation for Extremely Large-Scale MIMO in Near Field
The extremely large-scale massive multiple-input multiple-output (XL-MIMO)
has the potential to achieve boosted spectral efficiency and refined spatial
resolution for future wireless networks. However, channel estimation for
XL-MIMO is challenging since the large number of antennas results in high
computational complexity with the near-field effect. In this letter, we propose
a low-complexity sequential angle-distance channel estimation (SADCE) method
for near-field XL-MIMO systems equipped with uniformly planar arrays (UPA).
Specifically, we first successfully decouple the angle and distance parameters,
which allows us to devise a two-dimensional discrete Fourier transform (2D-DFT)
method for angle parameters estimation. Then, a low-complexity distance
estimation method is proposed with a closed-form solution. Compared with
existing methods, the proposed method achieves significant performance gain
with noticeably reduced computational complexity.Numerical results verify the
superiority of the proposed near-field channel estimation algorithm
Optical pumping effects on the Rydberg EIT spectrum
We provide a universal discussion of the interplay between Rydberg-state
electromagnetically induced transparency (EIT) and optical pumping (OP) in a
thermal Rb87 medium. By pumping the population to one single Hyperfine/Zeeman
state, we can enhance the interaction strength and, in principle, amplify the
EIT peak. According to our measurements, the EIT peak height can be improved by
a factor of two or reduced by one order of magnitude, and linewidth was
slightly narrowed by the pumping effect. Similar behavior is also seen by
increasing the optical density (OD) of the medium. The EIT feature is predicted
quantitatively using a Doppler-free non-perturbation numerical calculation.
With and without the optical pumping field, the EIT peak heights collapse onto
the same theoretical curve, showing that OP and varying OD have the same
effect. In both simulations and measurements, Rydberg EIT enhancement through
OP is dependent on the intensity of the probe field and the OD. Our work
clarifies the underlying mechanisms of optical pumping and advances
Rydberg-atom research.Comment: 4 pages, 4 figure
A polymer tandem solar cell with 10.6% power conversion efficiency.
An effective way to improve polymer solar cell efficiency is to use a tandem structure, as a broader part of the spectrum of solar radiation is used and the thermalization loss of photon energy is minimized. In the past, the lack of high-performance low-bandgap polymers was the major limiting factor for achieving high-performance tandem solar cell. Here we report the development of a high-performance low bandgap polymer (bandgap <1.4 eV), poly[2,7-(5,5-bis-(3,7-dimethyloctyl)-5H-dithieno[3,2-b:2',3'-d]pyran)-alt-4,7-(5,6-difluoro-2,1,3-benzothia diazole)] with a bandgap of 1.38 eV, high mobility, deep highest occupied molecular orbital. As a result, a single-junction device shows high external quantum efficiency of >60% and spectral response that extends to 900 nm, with a power conversion efficiency of 7.9%. The polymer enables a solution processed tandem solar cell with certified 10.6% power conversion efficiency under standard reporting conditions (25 °C, 1,000 Wm(-2), IEC 60904-3 global), which is the first certified polymer solar cell efficiency over 10%
Strongly enhanced light-matter interaction in a hybrid photonic-plasmonic resonator
We propose a hybrid photonic-plasmonic resonant structure which consists of a
metal nanoparticle (MNP) and a whispering gallery mode (WGM) microcavity. It is
found that the hybrid mode enables a strong interaction between the light and
matter, and the single-atom cooperativity is enhanced by more than two orders
of magnitude compared to that in a bare WGM microcavity. This remarkable
improvement originates from two aspects: (1) the MNP offers a highly enhanced
local field in the vicinity of an emitter, and (2), surprisingly, the
high-\textit{Q} property of WGMs can be maintained in the presence of the MNP.
Thus the present system has great advantages over a single microcavity or a
single MNP, and holds great potential in quantum optics, nonlinear optics and
highly sensitive biosening.Comment: 5 pages, 4 figure
Mixed methods evaluation of a randomized control pilot trial targeting sugar-sweetened beverage behaviors
This is the publisher's version, also available electronically from http://www.scirp.org/journal/ojpm/.This Excessive sugar-sweetened beverage (SSB) consumption and low health literacy skills have emerged as two public health concerns in the United States (US); however, there is limited research on how to effectively address these issues among adults. As guided by health literacy concepts and the Theory of Planned Behavior (TPB), this randomized controlled pilot trial applied the RE-AIM framework and a mixed methods approach to examine a sugar-sweetened beverage (SSB) intervention (SipSmartER), as compared to a matched-contact control intervention targeting physical activity (Move-More). Both 5-week interventions included two interactive group sessions and three support telephone calls. Executing a patient-centered developmental process, the primary aim of this paper was to evaluate patient feedback on intervention content and structure. The secondary aim was to understand the potential reach (i.e., proportion enrolled, representativeness) and effectiveness (i.e. health behaviors, theorized mediating variables, quality of life) of SipS- martER. Twenty-five participants were randomized to SipSmartER (n = 14) or MoveMore (n = 11). Participants’ intervention feedback was positive, ranging from 4.2 - 5.0 on a 5-point scale. Qualitative assessments reavealed several opportuneties to improve clarity of learning materials, enhance instructions and communication, and refine research protocols. Although SSB consumption decreased more among the SipS-martER participants (?256.9 ± 622.6 kcals), there were no significant group differences when compared to control participants (?199.7 ± 404.6 kcals). Across both groups, there were significant improvements for SSB attitudes, SSB behavioral intentions, and two media literacy constructs. The value of using a patient-centered approach in the developmental phases of this intervention was apparent, and pilot findings suggest decreased SSB may be achieved through targeted health literacy and TPB strategies. Future efforts are needed to examine the potential public health impact of a large-scale trial to address health literacy and reduce SSB
- …