3,606 research outputs found
Determinant Representation of Correlation Functions for the Free Fermion Model
With the help of the factorizing -matrix, the scalar products of the
free fermion model are represented by determinants. By means of
these results, we obtain the determinant representations of correlation
functions of the model.Comment: Latex File, 20 pages, V.3: some discussions are added, V.4 Reference
update, this version will appear in J. Math. Phy
Channel Acquisition for Massive MIMO-OFDM with Adjustable Phase Shift Pilots
We propose adjustable phase shift pilots (APSPs) for channel acquisition in
wideband massive multiple-input multiple-output (MIMO) systems employing
orthogonal frequency division multiplexing (OFDM) to reduce the pilot overhead.
Based on a physically motivated channel model, we first establish a
relationship between channel space-frequency correlations and the channel power
angle-delay spectrum in the massive antenna array regime, which reveals the
channel sparsity in massive MIMO-OFDM. With this channel model, we then
investigate channel acquisition, including channel estimation and channel
prediction, for massive MIMO-OFDM with APSPs. We show that channel acquisition
performance in terms of sum mean square error can be minimized if the user
terminals' channel power distributions in the angle-delay domain can be made
non-overlapping with proper phase shift scheduling. A simplified pilot phase
shift scheduling algorithm is developed based on this optimal channel
acquisition condition. The performance of APSPs is investigated for both one
symbol and multiple symbol data models. Simulations demonstrate that the
proposed APSP approach can provide substantial performance gains in terms of
achievable spectral efficiency over the conventional phase shift orthogonal
pilot approach in typical mobility scenarios.Comment: 15 pages, 4 figures, accepted for publication in the IEEE
Transactions on Signal Processin
Drinfeld twists and algebraic Bethe ansatz of the supersymmetric model associated with
We construct the Drinfeld twists (or factorizing -matrices) of the
supersymmetric model associated with quantum superalgebra , and
obtain the completely symmetric representations of the creation operators of
the model in the -basis provided by the -matrix. As an application of our
general results, we present the explicit expressions of the Bethe vectors in
the -basis for the -model (the quantum t-J model).Comment: Latex file, 33 pages; V2: minor typos corrected;V3: Reference update,
the new version will appear in Commun. Maths. Phys;V4: misprints correcte
Pancreaticobiliary Maljunction Is Associated with Common Bile Duct Carcinoma: A Meta-Analysis
Objective. Pancreaticobiliary maljunction (PBM) has been reported to be associated with an increased risk of gallbladder carcinoma. However, the relationship between PBM and common bile duct carcinoma (CBDC) remains unclear. We aimed to conduct a meta-analysis to determine the available evidence on the association between PBM and CBDC. Methods. The pooled odds ratio (OR) and standard mean differences (SMD) with 95% confidence interval (95% CI) were used to estimate the effects. Results. A total of eight case-control studies and two cohort studies were identified. The incidence of PBM was higher in CBDC patients than in controls (OR=1.45; 95% CI, 1.19–1.76). Compared with patients without PBM, CBDC patients with PBM were younger at the diagnosis age (SMD=−0.46; 95% CI, −0.64 to −0.28). A difference in the incidence of associated CDC was found between CBDC patients with or without PBM (OR=2.14; 95% CI, 1.60–2.87). Conclusions. Compared with benign biliary tract diseases, the incidence of PBM was higher in CBDC patients, especially in relatively young patients. We also found that the incidence of CDC was higher in CBDC patients with PBM. These findings showed positive association between PBM and CBDC, which may help in identifying high-risk individuals
A new volumetric strain-based method for determining the crack initiation threshold of rocks under compression
The crack initiation stress threshold ( ci) is an essential parameter in the brittle failure process of rocks. In this paper, a volumetric strain response method (VSRM) is proposed to determine the σci based on two new concepts, i.e., the dilatancy resistance state index ( ci) and the maximum value of the dilatancy resistance state index difference (| ci|), which represent the state of dilatancy resistance of the rock and the shear sliding resistance capacity of the crack-like pores during the compressive period, respectively. The deviatoric stress corresponding to the maximum | ci| is taken as the ci . We then examine the feasibility and validity of the VSRM using the experimental results. The results from the VSRM are also compared with those calculated by other strain-based methods, including the volumetric strain method (VSM), crack volumetric strain method (CVSM), lateral strain method (LSM) and lateral strain response method (LSRM). Compared with the other methods, the VSRM is effective and reduces subjectivity when determining the ci . Finally, with the help of the proposed VSRM, influences from chemical corrosion and confining stress on the ci and ci of the carbonate rock are analyzed. This study provides a subjective and practical method for determining σci . Moreover, it sheds light on the effects of confinement and chemical corrosion on σci
- …