1,227 research outputs found
Multiple localization transitions and novel quantum phases induced by staggered on-site potential
We propose an one-dimensional generalized Aubry-Andr{\'e}-Harper (AAH) model
with off-diagonal hopping and staggered on-site potential. We find that the
localization transitions could be multiple reentrant with the increasing of
staggered on-site potential. The multiple localization transitions are verified
by the quantum static and dynamic measurements such as the inversed or
normalized participation ratios, fractal dimension and survival probability.
Based on the finite-size scaling analysis, we also obtain an interesting
intermediate phase where the extended, localized and critical states are
coexistent in certain regime of model parameters. These results are quite
different from those in the generalized AAH model with off-diagonal hopping,
and can help us to find novel quantum phases, new localization phenomena in the
disordered systems
Localization and mobility edges in non-Hermitian disorder-free lattices
The non-Hermitian skin effect (NHSE) is a significant phenomenon observed in
non-Hermitian systems under open boundary conditions, where the extensive bulk
eigenstates tend to accumulate at the lattice edges. In this article, we
investigate how an electric field affects the localization properties in a
non-Hermitian mosaic Stark lattice, exploring the interplay between the Stark
localization, mobility edge (ME), and the NHSE induced by nonreciprocity. We
analytically obtain the Lyapunov exponent and the phase transition points as
well as numerically calculate the density distributions and the spectral
winding number. We reveal that in the nonreciprocal Stark lattice with the
mosaic periodic parameter , there exists a critical electric field
strength that describes the transition of the existence-nonexistence of NHSE
and is inversely proportional to the lattice size. This transition is
consistent with the real-complex transition and topological transition
characterized by spectral winding number under periodic boundary conditions. In
the strong fields, the Wannier-Stark ladder is recovered, and the Stark
localization is sufficient to suppress the NHSE. When the mosaic period
, we show that the system manifests an exact non-Hermitian ME and the
skin states are still existing in the strong fields, in contrast to the
gigantic field can restrain the NHSE in the case. Moreover, we
further study the expansion dynamics of an initially localized state and
dynamically probe the existence of the NHSE and the non-Hermitian ME. These
results could help us to control the NHSE and the non-Hermitian ME by using
electric fields in the disorder-free systems
A tight upper bound on channel capacity for visible light communications
Since the optical wireless channel in visible light communication (VLC) systems is subject to the non-negativity of the signal and the average optical power, the classic Shannon channel capacity formula is not applicable to VLC systems. To derive a simple closed-form upper bound on channel capacity, sphere packing argument method has been applied previously. However, there is an obvious gap between the existing sphere-packing upper bounds and the lower bounds at high optical signal-to-noise-ratios (OSNRs), which is mainly caused by the inaccurate mathematical approximation of the intrinsic volumes of the simplex. In this letter, a tight sphere-packing upper bound is derived with a new approximation method. Numerical results demonstrate that compared to the existing sphere-packing upper bounds, our proposed upper bound is tighter at high OSNRs
An optimal scaling scheme for DCO-OFDM based visible light communications
DC-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) is widely used in visible light communication (VLC) systems to provide high data rate transmission. As intensity modulation with direct detection (IM/DD) is employed to modulate the OFDM signal, scale up the amplitude of the signal can increase the effective transmitted electrical power whereas more signals are likely to be clipped due to the limited dynamic range of LEDs, resulting in severe clipping distortion. Thus, it is crucial to scale the signal to find a tradeoff between the effective electrical power and the clipping distortion. In this paper, an optimal scaling scheme is proposed to maximize the received signal-to-noise-plus-distortion ratio (SNDR) with the constraint of the radiated optical power in a practical scenario where DC bias is fixed for a desired dimming level. Simulation results show that the system with the optimal scaling factor outperforms that with fixed scaling factor under different equivalent noise power in terms of the bit error ratio (BER) performance
Stark many-body localization with long-range interactions
In one-dimensional (1D) disorder-free interacting systems, a sufficiently
strong linear potential can induce localization of the many-body eigenstates, a
phenomenon dubbed as Stark many-body localization (MBL). In this paper, we
investigate the fate of Stark MBL in 1D spinless fermions systems with
long-range interactions, specifically focusing on the role of interaction
strength. We obtain the Stark MBL phase diagrams by computing the mean gap
ratio and many-body inverse participation ratio at half-filling. We show that,
for short-range interactions, there is a qualitative symmetry between the
limits of weak and strong interactions. However, this symmetry is absent in the
case of long-range interactions, where the system is always Stark many-body
localized at strong interactions, regardless of the linear potential strength.
Furthermore, we study the dynamics of imbalance and entanglement with various
initial states using time-dependent variational principle (TDVP) numerical
methods. We reveal that the dynamical quantities display a strong dependence on
the initial conditions, which suggests that the Hilbert-space fragmentation
precludes thermalization. Our results demonstrate the robustness of Stark MBL
even in the presence of long-range interactions and offer an avenue to explore
MBL in disorder-free systems with long-range interactions
Pathological characteristics and predictive factors of prostate biopsy in patients with serum PSA levels between 0 and 4.0 ng/ml
BackgroundThis study aimed to analyze the pathological characteristics and predictive factors of prostate biopsy in men with PSA levels below 4.0 ng/ml.Patients and methodsWe retrospectively analyzed 158 patients who underwent prostate biopsy with PSA levels below 4.0 ng/ml. Pathological results were statistically analyzed. The logistic regression analysis was used to determine the predictive factors for malignant outcomes. Subgroup analysis was performed on patients who received surgery and the postoperative pathological upgrading was counted.ResultsA total of 143 patients were enrolled. The tumor detection rate was 20.3%. Among these patients, most of them (79.3%) had prostate adenocarcinoma, but rare malignant tumors also accounted for 20.7%. Logistic regression analysis indicated that the only independent predictive factor for a positive prostate biopsy was the PI-RADS score. For prostate adenocarcinoma cases, 95.7% of them were organ localized and 47.8% of cases were clinically significant. Subgroup analysis was performed on 14 patients who received surgical treatment. 28.6% of patients were upgraded to clinically significant prostate cancer, while 64.3% of patients had an upgrade in tumor stage.ConclusionOur study indicated that 20.3% of men with PSA levels between 0 and 4.0 ng/ml were diagnosed with prostate malignancies. Among these patients, most of them (79.3%) were diagnosed with prostate adenocarcinoma, and several uncommon types of malignancies were also detected in 20.7% of patients. The only risk factor for a positive biopsy in patients with a low PSA concentration was the PI-RADS score. It should be emphasized that the invasiveness of PCa patients diagnosed by biopsy may be underestimated as more than half of patients will upgrade their Gleason score or clinical stages after surgery. Thus, clinicians should pay more attention to patients with PSA levels between 0 and 4.0 ng/ml
ResFormer: Scaling ViTs with Multi-Resolution Training
Vision Transformers (ViTs) have achieved overwhelming success, yet they
suffer from vulnerable resolution scalability, i.e., the performance drops
drastically when presented with input resolutions that are unseen during
training. We introduce, ResFormer, a framework that is built upon the seminal
idea of multi-resolution training for improved performance on a wide spectrum
of, mostly unseen, testing resolutions. In particular, ResFormer operates on
replicated images of different resolutions and enforces a scale consistency
loss to engage interactive information across different scales. More
importantly, to alternate among varying resolutions effectively, especially
novel ones in testing, we propose a global-local positional embedding strategy
that changes smoothly conditioned on input sizes. We conduct extensive
experiments for image classification on ImageNet. The results provide strong
quantitative evidence that ResFormer has promising scaling abilities towards a
wide range of resolutions. For instance, ResFormer-B-MR achieves a Top-1
accuracy of 75.86% and 81.72% when evaluated on relatively low and high
resolutions respectively (i.e., 96 and 640), which are 48% and 7.49% better
than DeiT-B. We also demonstrate, moreover, ResFormer is flexible and can be
easily extended to semantic segmentation, object detection and video action
recognition. Code is available at https://github.com/ruitian12/resformer.Comment: CVPR 202
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