arXiv subjects

Peng Li

Publications and source records attributed to Peng Li.

At least 505 records · Page 28Linked to original sources

arXiv2015

Statistical analysis of motion contrast in optical coherence tomography angiography

Optical coherence tomography angiography (Angio-OCT), mainly based on the temporal dynamics of OCT scattering signals, has found a range of potential applications in clinical and scientific research. Based on the model of random phasor sums, temporal statistics of the complex-valued OCT signals are mathematically described. Statistical distributions of the amplitude differential and complex differential Angio-OCT signals are derived. The theories are validated through the flow phantom and live animal experiments. Using the model developed, the origin of the motion contrast in Angio-OCT is mathematically explained, and the implications in the improvement of motion contrast are further discussed, including threshold determination and its residual classification error, averaging method, and scanning protocol. The proposed mathematical model of Angio-OCT signals can aid in the optimal design of the system and associated algorithms.

physics.bio-ph↗

arXiv2015

Overcoming Bifurcation Instability in High-Repetition-Rate Ho:YLF Regenerative Amplifiers

We demonstrate a Ho:YLF regenerative amplifier (RA) overcoming bifurcation instability and consequently achieving high extraction energies of 6.9 mJ at a repetition rate of 1 kHz with pulse-to-pulse fluctuations of 1.1%. Measurements of the output pulse energy, corroborated by numerical simulations, identify an operation point that allows high-energy pulse extraction at a minimum noise level. Complete suppression of the onset of bifurcation was achieved by gain saturation after each pumping cycle in the Ho:YLF crystal via lowering the repetition rate and cooling the crystal. Even for moderate cooling, a significant temperature dependence of the Ho:YLF RA performance was observed.

physics.optics↗

arXiv2015

Low Noise, tunable Ho:fiber Soliton Oscillator for Ho:YLF Amplifier Seeding

We present a passively mode-locked, tunable soliton Ho:fiber ring oscillator, optimized for seeding of Ho:YLF amplifiers. The oscillator is independently tunable in central wavelength and spectral width from 2040 nm to 2070 nm and from 5 nm to 10 nm, respectively. At all settings the pulse energy within the soliton is around 800 pJ. The soliton oscillator was optimized to fully meets the spectral requirements for seeding Ho:YLF amplifiers. Its Kelly sidebands are located outside the amplifier gain spectrum, resulting in a train of about 1 ps long pedestal-free pulses with relative intensity noise (RIN) of only 0.13 % RMS when integrated from 1 Hz to Nyquist frequency.

physics.optics↗

arXiv2015

Concept for a Future Super Proton-Proton Collider

Following the discovery of the Higgs boson at LHC, new large colliders are being studied by the international high-energy community to explore Higgs physics in detail and new physics beyond the Standard Model. In China, a two-stage circular collider project CEPC-SPPC is proposed, with the first stage CEPC (Circular Electron Positron Collier, a so-called Higgs factory) focused on Higgs physics, and the second stage SPPC (Super Proton-Proton Collider) focused on new physics beyond the Standard Model. This paper discusses this second stage.

physics.acc-ph↗

arXiv2015

Determining phase-space properties of the IHEP RFQ output beam using the RMS beam widths from wire-scanners

A beam line is built after the IHEP RFQ for halo study. To determine transverse emittance and ellipse parameters of the RFQ output beam, beam size data obtained from the first two of 14 wire scanners are employed. By using the transfer matrix method and the least square method, a set of linear equations were set up and solved. The solutions were then applied as initial beam parameters in multi-particle simulations to check the method of calculation. It is shown that difference between the simulated RMS beam size and the measured one at the measurement location is less than 7%, which is acceptable in our experiments.

physics.acc-ph↗

arXiv2015

Efficient Approximation Algorithms for Computing \emph{k} Disjoint Restricted Shortest Paths

Network applications, such as multimedia streaming and video conferencing, impose growing requirements over Quality of Service (QoS), including bandwidth, delay, jitter, etc. Meanwhile, networks are expected to be load-balanced, energy-efficient, and resilient to some degree of failures. It is observed that the above requirements could be better met with multiple disjoint QoS paths than a single one. Let $G=(V,\, E)$ be a digraph with nonnegative integral cost and delay on every edge, $s,\, t\in V$ be two specified vertices, and $D\in\mathbb{Z}_{0}^{+}$ be a delay bound (or some other constraint), the \emph{$k$ Disjoint Restricted Shortest Path} ($k$\emph{RSP})\emph{ Problem} is computing $k$ disjoint paths between $s$ and $t$ with total cost minimized and total delay bounded by $D$. Few efficient algorithms have been developed because of the hardness of the problem. In this paper, we propose efficient algorithms with provable performance guarantees for the $k$RSP problem. We first present a pseudo-polynomial-time approximation algorithm with a bifactor approximation ratio of $(1,\,2)$, then improve the algorithm to polynomial time with a bifactor ratio of $(1+ε,\,2+ε)$ for any fixed $ε>0$, which is better than the current best approximation ratio $(O(1+γ),\, O(1+\frac{1}γ)\})$ for any fixed $γ>0$ \cite{orda2004efficient}. To the best of our knowledge, this is the first constant-factor algorithm that almost strictly obeys the constraint for the $k$RSP problem.

cs.DM↗

arXiv2014

The simulation of loss of U ions due to charge changing processes in the CSRm ring

Significant beam loss caused by the charge exchange processes and ions impact induced outgassing play a crucial role in the limitation of the maximum number of accumulated heavy ions during the high intensity operation in the accelerators. With the aim to control beam loss due to charge exchange processes and to confine the generated desorption gas, the tracking of the loss positions and installing the absorber blocks with low-desorption rate material at appropriate locations in the CSRm ring will be taken. The loss simulation of U ions having lost an electron will be presented in this report and the calculation of the collimation efficiency of the CSRm ring will be continued in the future.

physics.acc-ph↗

arXiv2014

Leveraging local identity-by-descent increases the power of case/control GWAS with related individuals

Large case/control Genome-Wide Association Studies (GWAS) often include groups of related individuals with known relationships. When testing for associations at a given locus, current methods incorporate only the familial relationships between individuals. Here, we introduce the chromosome-based Quasi Likelihood Score (cQLS) statistic that incorporates local Identity-By-Descent (IBD) to increase the power to detect associations. In studies robust to population stratification, such as those with case/control sibling pairs, simulations show that the study power can be increased by over 50%. In our example, a GWAS examining late-onset Alzheimer's disease, the $p$-values among the most strongly associated SNPs in the APOE gene tend to decrease, with the smallest $p$-value decreasing from $1.23\times10^{-8}$ to $7.70\times 10^{-9}$. Furthermore, as a part of our simulations, we reevaluate our expectations about the use of families in GWAS. We show that, although adding only half as many unique chromosomes, genotyping affected siblings is more efficient than genotyping randomly ascertained cases. We also show that genotyping cases with a family history of disease will be less beneficial when searching for SNPs with smaller effect sizes.

stat.AP↗

arXiv2014

Distributed Iterative Detection Based on Reduced Message Passing for Networked MIMO Cellular Systems

This paper considers base station cooperation (BSC) strategies for the uplink of a multi-user multi-cell high frequency reuse scenario where distributed iterative detection (DID) schemes with soft/hard interference cancellation algorithms are studied. The conventional distributed detection scheme exchanges {soft symbol estimates} with all cooperating BSs. Since a large amount of information needs to be shared via the backhaul, the exchange of hard bit information is preferred, however a performance degradation is experienced. In this paper, we consider a reduced message passing (RMP) technique in which each BS generates a detection list with the probabilities for the desired symbol that are sorted according to the calculated probability. The network then selects the best {detection candidates} from the lists and conveys the index of the constellation symbols (instead of double-precision values) among the cooperating cells. The proposed DID-RMP achieves an inter-cell-interference (ICI) suppression with low backhaul traffic overhead compared with {the conventional soft bit exchange} and outperforms the previously reported hard/soft information exchange algorithms.

cs.IT↗

arXiv2013

Dimer XXZ Spin Ladders: Phase diagram and a Non-Trivial Antiferromagnetic Phase

We study the dimer $XXZ$ spin model on two-leg ladders with isotropic Heisenberg interactions on the rung and anisotropic $XXZ$ interactions along the rail in an external field. Combining both analytical and numerical methods, we set up the ground state phase diagram and investigate the quantum phase transitions and the properties of rich phases, including the full polarized, singlet dimer, Luttinger liquid, triplon solid, and a non-trivial antiferromagnetic phases with gap. The analytical analyses based on solvable effective Hamiltonians are presented for clear view of the phases and transitions. Quantum Monte Carlo and exact diagonalization methods are employed on finite system to verify the exact nature of the phases and transitions. Of all the phases, we pay a special attention to the gapped antiferromagnetic phase, which is disclosed to be a non-trivial one that exhibits the time-reversal symmetry. We also discuss how our findings could be detected in experiment in the light of ultracold atoms technology advances.

cond-mat.quant-gas↗

arXiv2013

Iterative Detection and Decoding for MIMO Systems with Knowledge-Aided Message Passing Algorithms

In this paper, we consider the problem of iterative detection and decoding (IDD) for multi-antenna systems using low-density parity-check (LDPC) codes. The proposed IDD system consists of a soft-input soft-output parallel interference (PIC) cancellation scheme with linear minimum mean-square error (MMSE) receive filters and two novel belief propagation (BP) decoding algorithms. The proposed BP algorithms exploit the knowledge of short cycles in the graph structure and the reweighting factors derived from the hypergraph's expansion. Simulation results show that when used to perform IDD for multi-antenna systems both proposed BP decoding algorithms can consistently outperform existing BP techniques with a small number of decoding iterations.

cs.IT↗

arXiv2013

Adaptive Iterative Decision Feedback Detection Algorithms for Multi-User MIMO Systems

An adaptive iterative decision multi-feedback detection algorithm with constellation constraints is proposed for multiuser multi-antenna systems. An enhanced detection and interference cancellation is performed by introducing multiple constellation points as decision candidates. A complexity reduction strategy is developed to avoid redundant processing with reliable decisions along with an adaptive recursive least squares algorithm for time-varying channels. An iterative detection and decoding scheme is also considered with the proposed detection algorithm. Simulations show that the proposed technique has a complexity as low as the conventional decision feedback detector while it obtains a performance close to the maximum likelihood detector.

cs.IT↗

arXiv2013

Multi-Feedback Successive Interference Cancellation for Multiuser MIMO Systems

In this paper, a low-complexity multiple feedback successive interference cancellation (MF-SIC) strategy is proposed for the uplink of multiuser multiple-input multiple-output (MU-MIMO) systems. In the proposed MF-SIC {algorithm with shadow area constraints (SAC)}, an enhanced interference cancellation is achieved by introducing {constellation points as the candidates} to combat the error propagation in decision feedback loops. We also combine the MF-SIC with multi-branch (MB) processing, which achieves a higher detection diversity order. For coded systems, a low-complexity soft-input soft-output (SISO) iterative (turbo) detector is proposed based on the MF and the MB-MF interference suppression techniques. The computational complexity of the MF-SIC is {comparable to} the conventional SIC algorithm {since very little additional complexity is required}. {Simulation} results show that the algorithms significantly outperform the conventional SIC scheme and {approach} the optimal detector.

cs.IT↗

arXiv2013

Adaptive Decision Feedback Detection with Parallel Interference Cancellation and Constellation Constraints for Multi-Antenna Systems

In this paper, a novel low-complexity adaptive decision feedback detection with parallel decision feedback and constellation constraints (P-DFCC) is proposed for multiuser MIMO systems. We propose a constrained constellation map which introduces a number of selected points served as the feedback candidates for interference cancellation. By introducing a reliability checking, a higher degree of freedom is introduced to refine the unreliable estimates. The P-DFCC is followed by an adaptive receive filter to estimate the transmitted symbol. In order to reduce the complexity of computing the filters with time-varying MIMO channels, an adaptive recursive least squares (RLS) algorithm is employed in the proposed P-DFCC scheme. An iterative detection and decoding (Turbo) scheme is considered with the proposed P-DFCC algorithm. Simulations show that the proposed technique has a complexity comparable to the conventional parallel decision feedback detector while it obtains a performance close to the maximum likelihood detector at a low to medium SNR range.

cs.IT↗

arXiv2013

Ground-state and finite-temperature properties of spin liquid phase in the J1-J2 honeycomb model

In this paper we analyze the groundstate and finite-temperature properties of a frustrated Heisenberg $J_1-J_2$ model on a honeycomb lattice by employing the Schwinger boson technique. The phase diagram and spin gap as functions of ${J}_{2}/{J}_{1}$ are presented, showing that the exotic spin liquid phase lies in $0.21<{J}_{2}/{J}_{1} <0.43$. The temperature and magnetic-field dependences of specific heat, magnetic susceptibility and Knight shift are also presented. We find the spin liquid state is robust with respect to external magnetic field. These results provide clear information characterizing unusual properties of the exotic spin liquid phase for further experiments.

cond-mat.str-el↗

arXiv2012

Topological edge states in spin 1 bilinear-biquadratic model

The spin 1 bilinear-biquadratic model on square lattice in the region $0<ϕ<π/4$ is studied in a fermion representation with a p-wave pairing BCS type mean-field theory. Our results show there may exist a non-trivial gapped spin liquid with time-reversal symmetry spontaneously breaking. This exotic state manifests its topological nature by forming chiral states at the edges. To show it more clear, we set up and solved a ribbon system. We got a gapless dispersion representing the edge modes beneath the bulk modes. The edge modes with nonzero longitudinal momentum ($k_{x}\neq0$) convect in opposite directions at the two edges, which leads to a two-fold degeneracy. While the zero longitudinal momentum ($k_{x}=0$) modes turn out to be Majorana fermion states. The edge spin correlation functions are found to decay in a power law with the distance increasing. We also calculated the contribution of the edge modes to the specific heat and obtained a linear law at low temperatures.

cond-mat.str-el↗

arXiv2012

Analytical Solution of Cross Polarization Dynamics

Cross polarization (CP) dynamics, which was remained unknown for five decades, has been derived analytically in the zero- and double-quantum spaces. The initial polarization in the double-quantum space is a constant of motion under strong pulse condition ($|ω_{1I}+ω_{1S}|\gg |d(t)|$), while the Hamiltonian in the zero-quantum space reduces to $d(t)σ_{z}^Δ$ under the Hartmann-Hahn match condition ($ω_{1I}=ω_{1S}$). The time dependent Hamilontian ($d(t)σ_{z}^Δ$) in the zero-quantum space can be expressed by average Hamiltonians. Since$[d(t')σ_{z}^Δ, d(t")σ_{z}^Δ]=0$, only zero order average Hamiltonian needs to be calculated, leading to an analytical solution of CP dynamics.

quant-ph↗

arXiv2011

Thermodynamics of Third Order Lovelock-Born-Infeld Black Holes

We here explore black holes in the third order Lovelock gravity coupling with nonlinear Born-Infeld electromagnetic field. Considering special second and third order coefficients ($\hatα_2^2=3\hatα_3=α^2$), we analyze the thermodynamics of third order Lovelock-Born-Infeld black holes and, in 7-dimensional AdS space-time, discuss the stability of black holes in different event horizon structures. We find that the cosmological constant $Λ$ plays an important role in the distribution of stable regions of black holes.

gr-qc↗