Frontiers of Physics

ISSN 2095-0462

ISSN 2095-0470(Online)

CN 11-5994/O4

邮发代号 80-965

2018 Impact Factor: 2.483



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The delay time of gravitational wave – gamma-ray burst associations
Bing Zhang
Frontiers of Physics    2019, 14 (6): 64402-null.
摘要   PDF (697KB)

The first gravitational wave (GW) – gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by ~1.7 s with respect to the merger time of the GW signal. We generally discuss the astrophysical origin of the delay time, Δt, of GW-GRB associations within the context of compact binary coalescence (CBC) – short GRB (sGRB) associations and GW burst – long GRB (lGRB) associations. In general, the delay time should include three terms, the time to launch a clean (relativistic) jet, Δtjet; the time for the jet to break out from the surrounding medium, Δtbo; and the time for the jet to reach the energy dissipation and GRB emission site, ΔtGRB. For CBC-sGRB associations, Δtjet and Δtbo are correlated, and the final delay can be from 10 ms to a few seconds. For GWB-lGRB associations, Δtjet and Δtbo are independent. The latter is at least ~10 s, so that Δt of these associations is at least this long. For certain jet launching mechanisms of lGRBs, Δt can be minutes or even hours long due to the extended engine waiting time to launch a jet. We discuss the cases of GW170817/GRB 170817A and GW150914/GW150914-GBM within this theoretical framework and suggest that the delay times of future GW/GRB associations will shed light into the jet launching mechanisms of GRBs.

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12 superconducting qubits for quantum walks
Heng Fan, Xiaobo Zhu
Frontiers of Physics    2019, 14 (6): 61201-null.
摘要   PDF (780KB)
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Investigation of gate-all-around silicon nanowire transistors for ultimately scaled CMOS technology from top–down approach
Ru HUANG (黄如), Run-sheng WANG (王润声)
Frontiers of Physics in China    2010, 5 (4): 414-421.
摘要   HTML   PDF (483KB)

The gate-all-around (GAA) silicon nanowire transistor (SNWT) is considered one of the best candidates for ultimately scaled CMOS devices at the end of the technology roadmap. This paper reviews our recent work on the key issues regarding SNWTs from the top-down approach including process integration, carrier transport, and fluctuation and variability in these unique one-dimensional stronglyconfined nanowire devices. A new process integration scheme for SNWTs is discussed, which features a fully-Si-bulk substrate, an epi-free process, a self-aligned structure and a large source/drain fan-out. The physical characteristics of the fabricated devices with 10-nm-diameter nanowires are further investigated. The carrier transport performance in SNWTs is experimentally estimated, with a modified extraction methodology which takes into account the impact of temperature dependence of parasitic source resistance. SNWTs with sub-40-nm gate lengths exhibit high ballistic efficiency at room temperature, indicating great potential for SNWTs as an alternative device structure for near-ballistic transport. For heat transfer in SNWTs, the self-heating effect is also characterized. However, due to the one-dimensional (1-D) nature of nanowires and increased phonon-boundary scattering in the GAA structure, the self-heating effect in SNWTs based on the bulk substrate is comparable or even a little bit worse than SOI devices, which may limit the ultimate performance of SNWT-based circuits and thus, special design consideration is expected. On the other hand, random variation has become a practical problem at nano-scale. The characteristic variability of SNWTs is experimentally studied in detail. The results of extracted variation sources indicate that, with suppressed random dopant fluctuations in the intrinsic channel, variations in radius and metal-gate work function of SNWTs dominate both the threshold voltage and on-current fluctuations. Comparing with conventional planar MOS devices, SNWT based SRAM cells exhibit better stability due to the superior electrostatic control in SNWTs.

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In situ analysis of magnesium alloy using a standoff and double-pulse laser-induced breakdown spectroscopy system
Yong Xin (辛勇),Lan-Xiang Sun (孙兰香),Zhi-Jia Yang (杨志家),Peng Zeng (曾鹏),Zhi-Bo Cong (丛智博),Li-Feng Qi (齐立峰)
Frontiers of Physics    2016, 11 (5): 115207-.
摘要   PDF (4190KB)

To monitor the components of molten magnesium alloy during the smelting process in real time and online, we designed a standoff double-pulse laser-induced breakdown spectroscopy (LIBS) analysis system that can perform focusing, collecting and imaging of long-range samples. First, we tested the system on solid standard magnesium alloy samples in the laboratory to establish a basis for the online monitoring of the components of molten magnesium alloy in the future. The experimental results show that the diameters of the focus spots are approximately 1 mm at a range of 3 m, the ablation depth of the double-pulse mode is much deeper than that of the single-pulse mode, the optimum interpulse delay of the double pulse is inconsistent at different ranges, and the spectral intensity decays rapidly as the range increases. In addition, the enhancement effect of the double pulse at 1.89 m is greater than that at 2.97 m, the maximum enhancement is 7.1-fold for the Y(I)550.35-nm line at 1.89 m, and the calibration results at 1.89 m are better than those at 2.97 m. At 1.89 m, the determination coefficients (R2) of the calibration curves are approximately 99% for Y, Pr, and Zr; the relative standard deviations (RSDs) are less than 10% for Y, Pr, and Zr; the root mean square errors (RMSEs) are less than 0.037% for Pr and Zr; the limits of detection (LODs) are less than 1000 ppm for Y, Pr, and Zr; and the LODs of Y, Pr, and Zr at 2.97 m are higher than those at 1.89 m. Additionally, we tested the system on molten magnesium alloy in a magnesium alloy plant. The calibration results of the liquid magnesium alloy are not as favorable as those of the sampling solid magnesium alloys. In particular, the RSDs of the liquid magnesium alloy are approximately 20% for Pr and La. However, with future improvements in the experimental conditions, the developed system is promising for the in situ analysis of molten magnesium alloy.

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Laser-induced breakdown spectroscopy in Asia
Zhen-Zhen Wang (王珍珍),Yoshihiro Deguchi (出口祥啓),Zhen-Zhen Zhang (张臻臻),Zhe Wang (王哲),Xiao-Yan Zeng (曾晓雁),Jun-Jie Yan (严俊杰)
Frontiers of Physics    2016, 11 (6): 114213-.
摘要   PDF (5652KB)

Laser-induced breakdown spectroscopy (LIBS) is an analytical detection technique based on atomic emission spectroscopy to measure the elemental composition. LIBS has been extensively studied and developed due to the non-contact, fast response, high sensitivity, real-time and multi-elemental detection features. The development and applications of LIBS technique in Asia are summarized and discussed in this review paper. The researchers in Asia work on different aspects of the LIBS study in fundamentals, data processing and modeling, applications and instrumentations. According to the current research status, the challenges, opportunities and further development of LIBS technique in Asia are also evaluated to promote LIBS research and its applications.

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Review of borophene and its potential applications
Zhi-Qiang Wang, Tie-Yu Lü, Hui-Qiong Wang, Yuan Ping Feng, Jin-Cheng Zheng
Frontiers of Physics    2019, 14 (3): 33403-null.
摘要   PDF (16562KB)

Since two-dimensional boron sheet (borophene) synthesized on Ag substrates in 2015, research on borophene has grown fast in the fields of condensed matter physics, chemistry, material science, and nanotechnology. Due to the unique physical and chemical properties, borophene has various potential applications. In this review, we summarize the progress on borophene with a particular emphasis on the recent advances. First, we introduce the phases of borophene by experimental synthesis and theoretical predictions. Then, the physical and chemical properties, such as mechanical, thermal, electronic, optical and superconducting properties are summarized. We also discuss in detail the utilization of the borophene for wide ranges of potential application among the alkali metal ion batteries, Li-S batteries, hydrogen storage, supercapacitor, sensor and catalytic in hydrogen evolution, oxygen reduction, oxygen evolution, and CO2 electroreduction reaction. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

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Semiclassical dynamics and nonlinear charge current
Yang Gao
Frontiers of Physics    2019, 14 (3): 33404-null.
摘要   PDF (1755KB)

Electron conductivity is an important material property that can provide a wealth of information about the underlying system. Especially, the response of the conductivity with respect to electromagnetic fields corresponds to various nonlinear charge currents, which have distinct symmetry requirements and hence can be used as efficient probes of different systems. To help the band-structure engineering of such nonlinear currents, a universal treatment of electron dynamics up to second order expressed in the basis of the unperturbed states are highly useful. In this work, we review the general semiclassical framework of the nonlinear charge currents.

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Recent advances in MXene: Preparation, properties, and applications
Lei Jin-Cheng(雷进程), Zhang Xu(张旭), Zhou Zhen(周震)
Frontiers of Physics    2015, 10 (3): 107303-null.
摘要   PDF (677KB)

Owing to the exceptional properties of graphene, intensive studies have been carried out on novel two-dimensional (2D) materials. In the past several years, an elegant exfoliation approach has been used to successfully create a new family of 2D transition metal carbides, nitrides, and carbonitrides, termed MXene, from layered MAX phases. More recently, some unique properties of MXene have been discovered leading to proposals of potential applications. In this review, we summarize the latest progress in development of MXene from both a theoretical and experimental view, with emphasis on the possible applications.

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Novel transition and Bellerophon state in coupled Stuart–Landau oscillators
Jia-Meng Zhang, Xue Li, Yong Zou, Shu-Guang Guan
Frontiers of Physics    2019, 14 (3): 33603-null.
摘要   PDF (4286KB)

We study synchronization in a system of Stuart–Landau oscillators with frequency-weighted coupling. For three typical unimodal frequency distributions, namely, the Lorentzian, the triangle, and the uniform, we found that the first-order transition occurs when the frequency distribution is relatively compact, while the synchronization transition is continuous when it is relatively wide. In both cases, there is a regime of Bellerophon state between the incoherent state and the synchronized state. Remarkably, we revealed novel transition behavior for such coupled oscillators with amplitudes, i.e., the regime of Bellerophon state actually contains two stages. In the first stage, the oscillators achieve chaotic phase synchronization; while in the second stage, oscillators form periodical phase synchronization. Our results suggest that Bellerophon state also exists in coupled oscillators with amplitude dynamics.

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Quantum transport in topological semimetals under magnetic fields (II)
Hai-Peng Sun, Hai-Zhou Lu
Frontiers of Physics    2019, 14 (3): 33405-null.
摘要   PDF (4045KB)

We review our recent works on the quantum transport, mainly in topological semimetals and also in topological insulators, organized according to the strength of the magnetic field. At weak magnetic fields, we explain the negative magnetoresistance in topological semimetals and topological insulators by using the semiclassical equations of motion with the nontrivial Berry curvature. We show that the negative magnetoresistance can exist without the chiral anomaly. At strong magnetic fields, we establish theories for the quantum oscillations in topological Weyl, Dirac, and nodal-line semimetals. We propose a new mechanism of 3D quantum Hall effect, via the “wormhole” tunneling through the Weyl orbit formed by the Fermi arcs and Weyl nodes in topological semimetals. In the quantum limit at extremely strong magnetic fields, we find that an unexpected Hall resistance reversal can be understood in terms of the Weyl fermion annihilation. Additionally, in parallel magnetic fields, longitudinal resistance dips in the quantum limit can serve as signatures for topological insulators.

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Topological gapless matters in three-dimensional ultracold atomic gases
Yong Xu
Frontiers of Physics    2019, 14 (4): 43402-null.
摘要   PDF (10266KB)

Three-dimensional topological gapless matters with gapless degeneracies protected by a topological invariant defined over a closed manifold in momentum space have attracted considerable interest in various fields ranging from condensed matter materials to ultracold atomic gases. As a highly controllable and disorder free system, ultracold atomic gases provide a versatile platform to simulate topological gapless matters. Here, the current progress in studies of topological gapless phenomena in three-dimensional cold atom systems is summarized in the review. It is mainly focused on Weyl points, structured (type-II) Weyl points, Dirac points, nodal rings and Weyl exceptional rings in cold atoms. Since interactions in cold atoms can be controlled via Feshbach resonances, the progress in both superfluids for attractive interactions and non-interacting cold atom gases is reviewed.

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Dynamical characteristic of measurement uncertainty under Heisenberg spin models with Dzyaloshinskii–Moriya interactions
Ying-Yue Yang, Wen-Yang Sun, Wei-Nan Shi, Fei Ming, Dong Wang, Liu Ye
Frontiers of Physics    2019, 14 (3): 31601-null.
摘要   PDF (2112KB)

The dynamics of measurement’s uncertainty via entropy for a one-dimensional Heisenberg XY Z mode is examined in the presence of an inhomogeneous magnetic field and Dzyaloshinskii–Moriya (DM) interaction. It shows that the uncertainty of interest is intensively in connection with the filed’s temperature, the direction-oriented coupling strengths and the magnetic field. It turns out that the stronger coupling strengths and the smaller magnetic field would induce the smaller measurement’s uncertainty of interest within the current spin model. Interestingly, we reveal that the evolution of the uncertainty exhibits quite different dynamical behaviors in antiferromagnetic (Ji>0) and ferromagnetic (Ji<0) frames. Besides, an analytical solution related to the systematic entanglement (i.e., concurrence) is also derived in such a scenario. Furthermore, it is found that the DM-interaction is desirably working to diminish the magnitude of the measurement’s uncertainty in the region of high-temperature. Finally, we remarkably offer a resultful strategy to govern the entropy-based uncertainty through utilizing quantum weak measurements, being of fundamentally importance to quantum measurement estimation in the context of solid-state-based quantum information processing and computation.

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Effective models for nearly ideal Dirac semimetals
Feng Tang, Xiangang Wan
Frontiers of Physics    2019, 14 (4): 43603-null.
摘要   PDF (3214KB)

Topological materials (TMs) have gained intensive attention due to their novel behaviors compared with topologically trivial materials. Among various TMs, Dirac semimetal (DSM) has been studied extensively. Although several DSMs have been proposed and verified experimentally, the suitable DSM for realistic applications is still lacking. Thus finding ideal DSMs and providing detailed analyses to them are of both fundamental and technological importance. Here, we sort out 8 (nearly) ideal DSMs from thousands of topological semimetals in Nature 566(7745), 486 (2019). We show the concrete positions of the Dirac points in the Brillouin zone for these materials and clarify the symmetryprotection mechanism for these Dirac points as well as their low-energy effective models. Our results provide a useful starting point for future study such as topological phase transition under strain and transport study based on these effective models. These DSMs with high mobilities are expected to be applied in fabrication of functional electronic devices.

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Studies on the electronic structures of three-dimensional topological insulators by angle resolved photoemission spectroscopy
Yulin Chen
Frontiers of Physics    2012, 7 (2): 175-192.
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Three-dimensional (3D) topological insulators represent a new state of quantum matter with a bulk gap and odd number of relativistic Dirac fermions on the surface. The unusual surface states of topological insulators rise from the nontrivial topology of their electronic structures as a result of strong spin–orbital coupling. In this review, we will briefly introduce the concept of topological insulators and the experimental method that can directly probe their unique electronic structure: angle resolved photoemission spectroscopy (ARPES). A few examples are then presented to demonstrate the unique band structures of different families of topological insulators and the unusual properties of the topological surface states. Finally, we will briefly discuss the future development of topological quantum materials.

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Ratchet motion and current reversal of coupled Brownian motors in pulsating symmetric potentials
Chen-Pu Li,Hong-Bin Chen,Zhi-Gang Zheng
Frontiers of Physics    2017, 12 (4): 120502-.
摘要   PDF (1034KB)

In this study, we investigate the collective directed transport of coupled Brownian particles in spatially symmetric periodic potentials under time-periodic pulsating modulations. We find that the coupling between two particles can induce symmetry breaking and consequently collective directed motion. Moreover, the direction of motion can be reversed under certain conditions. The dependence of directed current on various parameters is systematically studied. reverse motion can be achieved by modulating the coupling free length and the phase shift of the pulsating potential. The dynamical mechanism of these transport properties is understood in terms of the effective-potential theory and the space-time transformation invariance. The directed transport of coupled Brownian motors can be manipulated and optimized by adjusting the coupling strength, pulsating frequency, or noise intensity.

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The rise of two-dimensional MoS2 for catalysis
Jun Mao (毛军), Yong Wang (王勇), Zhilong Zheng (郑智龙), Dehui Deng (邓德会)
Frontiers of Physics    2018, 13 (4): 138118-.
摘要   PDF (56346KB)

Two-dimensional (2D) MoS2 is used as a catalyst or support and has received increased research interest because of its superior structural and electronic properties compared with those of bulk structures. In this article, we illustrate the active sites of 2D MoS2 and various strategies for enhancing its intrinsic catalytic activity. The recent advances in the use of 2D MoS2-based materials for applications such as thermocatalysis, electrocatalysis, and photocatalysis are discussed. We also discuss the future opportunities and challenges for 2D MoS2-based materials, in both fundamental research and industrial applications.

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Local electrical characterization of two-dimensional materials with functional atomic force microscopy
Sabir Hussain, Kunqi Xu, Shili Ye, Le Lei, Xinmeng Liu, Rui Xu, Liming Xie, Zhihai Cheng
Frontiers of Physics    2019, 14 (3): 33401-null.
摘要   PDF (15049KB)

Research about two-dimensional (2D) materials is growing exponentially across various scientific and engineering disciplines due to the wealth of unusual physical phenomena that occur when charge transport is confined to a plane. The applications of 2D materials are highly affected by the electrical properties of these materials, including current distribution, surface potential, dielectric response, conductivity, permittivity, and piezoelectric response. Hence, it is very crucial to characterize these properties at the nanoscale. The Atomic Force Microscopy (AFM)-based techniques are powerful tools that can simultaneously characterize morphology and electrical properties of 2D materials with high spatial resolution, thus being more and more extensively used in this research field. Here, the principles of these AFM techniques are reviewed in detail. After that, their representative applications are further demonstrated in the local characterization of various 2D materials’ electrical properties.

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Possible phase transition of anisotropic frustrated Heisenberg model at finite temperature
Ai-Yuan Hu, Lin Wen, Guo-Pin Qin, Zhi-Min Wu, Peng Yu, Yu-Ting Cui
Frontiers of Physics    2019, 14 (5): 53601-null.
摘要   PDF (1645KB)

The frustrated spin-1/2 J1aJ1bJ2 antiferromagnet with anisotropy on the two-dimensional square lattice was investigated, where the parameters J1aand J1b represent the nearest neighbor exchanges and along the x and y directions, respectively. J2 represents the next-nearest neighbor exchange. The anisotropy includes the spatial and exchange anisotropies. Using the double-time Green’s function method, the effects of the interplay of exchanges and anisotropy on the possible phase transition of the Néel state and stripe state were discussed. Our results indicated that, in the case of anisotropic parameter 0≤η<1, the Néel and stripe states can exist and have the same critical temperature as long as J2 = J1b/2. Under such parameters, a first-order phase transformation between the Néel and stripe states can occur below the critical point. For J2J1b/2, our results indicate that the Néel and stripe states can also exist, while their critical temperatures differ. When J2>J1b/2, a first-order phase transformation between the two states may also occur. However, for J2<J1b/2, the Néel state is always more stable than the stripe state.

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Direct growth of graphene on gallium nitride using C2H2 as carbon source
Bing Wang (王兵),Yun Zhao (赵云),Xiao-Yan Yi (伊晓燕),Guo-Hong Wang (王国宏),Zhi-Qiang Liu (刘志强),Rui-Rei Duan (段瑞飞),Peng Huang (黄鹏),Jun-Xi Wang (王军喜),Jin-Min Li (李晋闽)
Frontiers of Physics    2016, 11 (2): 116803-null.
摘要   PDF (343KB)

Growing graphene on gallium nitride (GaN) at temperatures greater than 900°C is a challenge that must be overcome to obtain high quality of GaN epi-layers. We successfully met this challenge using C2H2 as the carbon source. We demonstrated that graphene can be grown both on copper and directly on GaN epi-layers. The Raman spectra indicated that the graphene films were about 4–5 layers thick. Meanwhile, the effects of the growth temperature on the growth of the graphene films were systematically studied, and 830°C was found to be the optimum growth temperature. We successfully grew high-quality graphene films directly on gallium nitride.

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Laser cooling and trapping of ytterbium atoms
Xin-ye XU (徐信业), Wen-li WANG (王文丽), Qing-hong ZHOU (周庆红), Guo-hui LI (李国辉), Hai-ling JIANG (蒋海灵), Lin-fang CHEN (陈林芳), Jie YE (叶捷), Zhi-hong ZHOU (周志红), Yin CAI (蔡寅), Hai-yao TANG (唐海瑶), Min ZHOU (周敏)
Frontiers of Physics in China    2009, 4 (2): 160-164.
摘要   HTML   PDF (393KB)

The experiments on the laser cooling and trapping of ytterbium atoms are reported, including the two-dimensional transversal cooling, longitudinal velocity Zeeman deceleration, and a magneto-optical trap with a broadband transition at a wavelength of 399 nm. The magnetic field distributions along the axis of a Zeeman slower were measured and in a good agreement with the calculated results. Cold ytterbium atoms were produced with a number of about 107 and a temperature of a few milli-Kelvin. In addition, using a 556-nm laser, the excitations of cold ytterbium atoms at 1S0-3P1 transition were observed. The ytterbium atoms will be further cooled in a 556-nm magneto-optical trap and loaded into a three-dimensional optical lattice to make an ytterbium optical clock.

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Quantum transport in topological semimetals under magnetic fields
Hai-Zhou Lu,Shun-Qing Shen
Frontiers of Physics    2017, 12 (3): 127201-.
摘要   PDF (1444KB)

Topological semimetals are three-dimensional topological states of matter, in which the conduction and valence bands touch at a finite number of points, i.e., the Weyl nodes. Topological semimetals host paired monopoles and antimonopoles of Berry curvature at the Weyl nodes and topologically protected Fermi arcs at certain surfaces. We review our recent works on quantum transport in topological semimetals, according to the strength of the magnetic field. At weak magnetic fields, there are competitions between the positive magnetoresistivity induced by the weak anti-localization effect and negative magnetoresistivity related to the nontrivial Berry curvature. We propose a fitting formula for the magnetoconductivity of the weak anti-localization. We expect that the weak localization may be induced by inter-valley effects and interaction effect, and occur in double-Weyl semimetals. For the negative magnetoresistance induced by the nontrivial Berry curvature in topological semimetals, we show the dependence of the negative magnetoresistance on the carrier density. At strong magnetic fields, specifically, in the quantum limit, the magnetoconductivity depends on the type and range of the scattering potential of disorder. The high-field positive magnetoconductivity may not be a compelling signature of the chiral anomaly. For long-range Gaussian scattering potential and half filling, the magnetoconductivity can be linear in the quantum limit. A minimal conductivity is found at the Weyl nodes although the density of states vanishes there.

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