bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacteria push the limits of chemotactic precision to navigate dynamic chemical gradients
Authors: Brumley Douglas R. , Carrara Francesco , Hein Andrew M. , Yawata Yutaka , Levin Simon A. , Stocker Roman
Published: May 2019

Significance

The limited precision of sensory organs places fundamental constraints on organismal performance. An open question, however, is whether organisms are routinely pushed to these limits and how limits might influence interactions between populations of organisms and their environment. By combining a method to generate dynamic, replicable resource landscapes, high-speed tracking of freely moving bacteria, a mathematical theory, and agent-based simulations, we show that sensory noise ultimately limits when and where bacteria can detect and climb chemical gradients. Our results suggest that the typical chemical landscapes bacteria inhabit are dominated by noise that masks shallow gradients and that the spatiotemporal dynamics of bacterial aggregations can be predicted by mapping the region where gradient signal rises above noise.
Systematic evasion of the restriction-modification barrier in bacteria
Authors: Johnston Christopher D. , Cotton Sean L. , Rittling Susan R. , Starr Jacqueline R. , Borisy Gary G. , Dewhirst Floyd E. , Lemon Katherine P.
Published: May 2019

Bacteria that are recalcitrant to genetic manipulation using modern in vitro techniques are termed genetically intractable. Genetic intractability is a fundamental barrier to progress that hinders basic, synthetic, and translational microbiology research and development beyond a few model organisms. The most common underlying causes of genetic intractability are restriction-modification (RM) systems, ubiquitous defense mechanisms against xenogeneic DNA that hinder the use of genetic approaches in the vast majority of bacteria and exhibit strain-level variation. Here, we describe a systematic approach to overcome RM systems. Our approach was inspired by a simple hypothesis: if a synthetic piece of DNA lacks the highly specific target recognition motifs for a host’s RM systems, then it is invisible to these systems and will not be degraded during artificial transformation. Accordingly, in this process, we determine the genome and methylome of an individual bacterial strain and use this information to define the bacterium’s RM target motifs. We then synonymously eliminate RM targets from the nucleotide sequence of a genetic tool in silico, synthesize an RM-silent “SyngenicDNA” tool, and propagate the tool as minicircle plasmids, termed SyMPL (SyngenicDNA Minicircle Plasmid) tools, before transformation. In a proof-of-principle of our approach, we demonstrate a profound improvement (five orders of magnitude) in the transformation of a clinically relevant USA300 strain of
Staphylococcus aureus
. This stealth-by-engineering SyngenicDNA approach is effective, flexible, and we expect in future applications could enable microbial genetics free of the restraints of restriction-modification barriers.
Long-term neurocognitive benefits of FLASH radiotherapy driven by reduced reactive oxygen species
Authors: Montay-Gruel Pierre , Acharya Munjal M. , Petersson Kristoffer , Alikhani Leila , Yakkala Chakradhar , Allen Barrett D. , Ollivier Jonathan , Petit Benoit , Jorge Patrik Gonçalves , Syage Amber R. , Nguyen Thuan A. , Baddour Al Anoud D. , Lu Celine , Singh Paramvir , Moeckli Raphael , Bochud François , Germond Jean-François , Froidevaux Pascal , Bailat Claude , Bourhis Jean , Vozenin Marie-Catherine , Limoli Charles L.
Published: May 2019

Significance

Ultra-high dose-rate (≥100 Gy⋅s
−1
) irradiation, termed FLASH radiotherapy, affords some remarkable (if not unexpected) normal tissue sparing in the irradiated brain when compared with conventional dose rates (0.07–0.1 Gy⋅s
−1
) used in clinical practice. Radiation-induced neurocognitive deficits, persistent neuroinflammation, and the structural degradation of mature neurons, typical of conventional dose-rate exposures, were resolved significantly in a preclinical mouse model exposed to FLASH radiotherapy. These benefits persisted over a 6-mon postirradiation interval and were caused, in part, by a mechanism involving reduced reactive oxygen species. Since normal tissue injury during and following radiotherapy dictates the maximum tolerated dose, the capability to ameliorate these adverse side effects holds significant promise for improving therapeutic outcome for cancer survivors worldwide.
Crossing the bridge from molecular catalysis to a heterogenous electrode in electrocatalytic water oxidation
Authors: Wu Lei , Nayak Animesh , Shao Jing , Meyer Thomas J.
Published: May 2019

Significance

Artificial photosynthesis by the preparation of solar fuels is a promising strategy for our energy future. An inhibiting factor in artificial photosynthesis is the half-reaction for water oxidation, which, because of its slow kinetics, makes catalysis indispensable. Advances in molecular water oxidation catalysis from detailed mechanistic investigations have provided insight into how this reaction occurs, but in practical applications, including electrolytic cells and dye-sensitized photoelectrosynthesis cells, it must be applied on conductive substrates. We describe here an efficient strategy that combines silane surface functionalization and reductive electropolymerization to bind a molecular catalyst on conductive substrates for sustained catalytic water oxidation.
Human nonvisual opsin 3 regulates pigmentation of epidermal melanocytes through functional interaction with melanocortin 1 receptor
Authors: Ozdeslik Rana N. , Olinski Lauren E. , Trieu Melissa M. , Oprian Daniel D. , Oancea Elena
Published: May 2019

Significance

This study expands understanding of opsin 3 (OPN3) function and of skin pigmentation. The findings presented here reveal that the nonvisual OPN3 modulates the pigmentation of human epidermal melanocytes—the melanin-producing cells of the skin—by controlling the activity of the main pigmentation receptor, melanocortin 1 receptor (MC1R). The study identifies an OPN3 function in regulating human skin pigmentation via a unique molecular mechanism; it also reveals a regulatory mechanism for MC1R in melanocytes. These results advance our understanding of nonvisual opsins and their extraocular role; they also represent a paradigm for OPN3 function via modulation of MC1R’s activity. These findings set the stage for future investigations of OPN3 function in other tissues.
TrxR1, Gsr, and oxidative stress determine hepatocellular carcinoma malignancy
Authors: McLoughlin Michael R. , Orlicky David J. , Prigge Justin R. , Krishna Pushya , Talago Emily A. , Cavigli Ian R. , Eriksson Sofi , Miller Colin G. , Kundert Jean A. , Sayin Volkan I. , Sabol Rachel A. , Heinemann Joshua , Brandenberger Luke O. , Iverson Sonya V. , Bothner Brian , Papagiannakopoulos Thales , Shearn Colin T. , Arnér Elias S. J. , Schmidt Edward E.
Published: May 2019

Thioredoxin reductase-1 (TrxR1)-, glutathione reductase (Gsr)-, and Nrf2 transcription factor-driven antioxidant systems form an integrated network that combats potentially carcinogenic oxidative damage yet also protects cancer cells from oxidative death. Here we show that although unchallenged wild-type (WT), TrxR1-null, or Gsr-null mouse livers exhibited similarly low DNA damage indices, these were 100-fold higher in unchallenged TrxR1/Gsr–double-null livers. Notwithstanding, spontaneous cancer rates remained surprisingly low in TrxR1/Gsr-null livers. All genotypes, including TrxR1/Gsr-null, were susceptible to
N
-diethylnitrosamine (DEN)-induced liver cancer, indicating that loss of these antioxidant systems did not prevent cancer cell survival. Interestingly, however, following DEN treatment, TrxR1-null livers developed threefold fewer tumors compared with WT livers. Disruption of TrxR1 in a marked subset of DEN-initiated cancer cells had no effect on their subsequent contributions to tumors, suggesting that TrxR1-disruption does not affect cancer progression under normal care, but does decrease the frequency of DEN-induced cancer initiation. Consistent with this idea, TrxR1-null livers showed altered basal and DEN-exposed metabolomic profiles compared with WT livers. To examine how oxidative stress influenced cancer progression, we compared DEN-induced cancer malignancy under chronically low oxidative stress (TrxR1-null, standard care) vs. elevated oxidative stress (TrxR1/Gsr-null livers, standard care or phenobarbital-exposed TrxR1-null livers). In both cases, elevated oxidative stress was correlated with significantly increased malignancy. Finally, although TrxR1-null and TrxR1/Gsr-null livers showed strong Nrf2 activity in noncancerous hepatocytes, there was no correlation between malignancy and Nrf2 expression within tumors across genotypes. We conclude that TrxR1, Gsr, Nrf2, and oxidative stress are major determinants of liver cancer but in a complex, context-dependent manner.
A critical assessment of the wicked problem concept: relevance and usefulness for policy science and practice
Authors: Termeer Catrien J A M , Dewulf Art , Biesbroek Robbert
Published: May 2019

The concept of wicked problems has served as an inspiration for research in a variety of research fields but has also contributed to conceptual confusion through the various ways in which it has been defined and used. In this special issue, a number of ontological, theoretical and methodological issues are discussed. First, while its use as a buzzword has undermined precise conceptual definition, recent work goes beyond the wicked versus tame dichotomy and conceptualizes wickedness as a matter of degree, differentiates between dimensions of wickedness and emphasizes the relational character of problem definitions. Second, new and existing governance approaches have often been unproblematically proposed as ways to solve wicked problems, while only imperfect solutions, partial solutions or small wins are achievable in practice. Third, the concept of wicked problems has had little direct impact on policy theories, and while some argue that the analysis of wicked problems should be mainstreamed in public policy thinking, others propose to reject the concept and rely on existing policy theories. Fourth, as a concept used in policy practice, wicked problems tend to provoke either paralysis or an overestimation of what policy can do about wicked problems. Possible ways forward include (1) leaving the concept behind; (2) using the wicked problems literature as knowledge base to understand when and why policy and governance approaches fail; and (3) developing dimensions of wicked problems (i.e. conflict, complexity and uncertainty) into more analytically precise research tools and linking them with more closely with contemporary policy science developments.
Long-Time Asymptotics for the Nonlocal MKdV Equation*
Authors: He Feng-Jing , Fan En-Gui , Xu Jian
Published: May 2019

In this paper, we study the Cauchy problem with decaying initial data for the nonlocal modified Korteweg-de Vries equation (nonlocal mKdV) qt(x, t) + qxxx(x,t) −6q(x, t)q(−x, −t)qx (x, t) = 0, which can be viewed as a generalization of the local classical mKdV equation. We first formulate the Riemann-Hilbert problem associated with the Cauchy problem of the nonlocal mKdV equation. Then we apply the Deift-Zhou nonlinear steepest-descent method to analyze the long-time asymptotics for the solution of the nonlocal mKdV equation. In contrast with the classical mKdV equation, we find some new and different results on long-time asymptotics for the nonlocal mKdV equation and some additional assumptions about the scattering data are made in our main results.
Residual Symmetry of the Alice-Bob Modified Korteweg-de Vries Equation*
Authors: Hu Ya-Hong , Ma Zheng-Yi , Chen Li
Published: May 2019

Starting from the truncated Painlevé expansion, the residual symmetry of the Alice-Bob modified Korteweg-de Vries (AB-mKdV) equation is derived. The residual symmetry is localized and the AB-mKdV equation is transformed into an enlarged system by introducing one new variable. Based on Lie’s first theorem, the finite transformation is obtained from the localized residual symmetry. Further, considering the linear superposition of multiple residual symmetries gives rises to N-th Bäcklund transformation in the form of the determinant. Moreover, the
Ps

Td

(the shifted parity and delayed time reversal) symmetric exact solutions (including invariant solution, breaking solution and breaking interaction solution) of AB-mKdV equation are presented and two classes of interaction solutions are depicted by using the particular functions with numerical simulation.
Numerical Simulation of MHD Peristaltic Flow with Variable Electrical Conductivity and Joule Dissipation Using Generalized Differential Quadrature Method
Authors: Qasim Muhammad , Ali Zafar , Wakif Abderrahim , Boulahia Zoubair
Published: May 2019

In this paper, the MHD peristaltic flow inside wavy walls of an asymmetric channel is investigated, where the walls of the channel are moving with peristaltic wave velocity along the channel length. During this investigation, the electrical conductivity both in Lorentz force and Joule heating is taken to be temperature dependent. Also, the long wavelength and low Reynolds number assumptions are utilized to reduce the governing partial differential equations into a set of coupled nonlinear ordinary differential equations. The new set of obtained equations is then numerically solved using the generalized differential quadrature method (GDQM). This is the first attempt to solve the nonlinear equations arising in the peristaltic flows using this method in combination with the Newton-Raphson technique. Moreover, in order to check the accuracy of the proposed numerical method, our results are compared with the results of built-in Mathematica command NDSolve. Taking Joule heating and viscous dissipation into account, the effects of various parameters appearing in the problem are used to discuss the fluid flow characteristics and heat transfer in the electrically conducting fluids graphically. In presence of variable electrical conductivity, velocity and temperature profiles are highly decreasing in nature when the intensity of the electrical conductivity parameter is strengthened.
A Universal Construction of Calogero-Moser System with Two Types Spins Interaction
Authors: Dai Jia-Liang
Published: May 2019

We present universal construction for the Calogero-Moser system with two types spins interaction of trigonometric potential based on the root system of semi-simple Lie algebra. In this formalism, we successfully build up the correct Lax pair as well as the R-matrix for this generalized Calogero-Moser models. Moreover using the property of root system, we make a concise explanation that in the quantized model, the R-matrix takes the same form as the classical one, which is the main new result of this paper.
Tighter Constraints of Multiqubit Entanglement*
Authors: Yang Long-Mei , Chen Bin , Fei Shao-Ming , Wang Zhi-Xi
Published: May 2019

Monogamy and polygamy relations characterize the distributions of entanglement in multipartite systems. We provide classes of monogamy and polygamy inequalities of multiqubit entanglement in terms of concurrence, entanglement of formation, negativity, Tsallis-q entanglement, and Rényi-α entanglement, respectively. We show that these inequalities are tighter than the existing ones for some classes of quantum states.
Dynamics of Quantum Coherence in Bell-Diagonal States under Markovian Channels*
Authors: Wang Yao-Kun , Fei Shao-Ming , Wang Zhi-Xi
Published: May 2019

We study the curves of coherence for the Bell-diagonal states including l1-norm of coherence and relative entropy of coherence under the Markovian channels in the first subsystem once. For a special Bell-diagonal state under bit-phase ip channel, we find frozen coherence under l1 norm occurs, but relative entropy of coherence decrease. It illustrates that the occurrence of frozen coherence depends on the type of the measure of coherence. Also, we study the coherence evolution of Bell-diagonal states under Markovian channels in the first subsystem n times and find that coherence under depolarizing channel decreases initially then increases for small n and tends to zero for large n. The dynamics of coherence of the Bell-diagonal state under two independent same type local Markovian channels is discussed.
General way to define tunneling time*
Authors: Shu Zheng , Hao Xiaolei , Li Weidong , Chen Jing
Published: May 2019

With the development of attosecond science, tunneling time can now be measured experimentally with the attoclock technique. However, there are many different theoretical definitions of tunneling time and no consensus has been achieved. Here, we bridge the relationship between different definitions of tunneling time based on a quantum travel time in one-dimensional rectangular barrier tunneling problem. We find that the real quantum travel time t
Re is equal to the Bohmian time t
Bohmian, which is related to the resonance lifetime of a bound state. The total quantum travel time τ
t can perfectly retrieve the transversal time t

x
and the Büttiker–Landauer time τ
BL in two opposite limits, regardless of the particle energy.
Dynamics of two levitated nanospheres nonlinearly coupling with non-Markovian environment*
Authors: Li Xun , Xiong Biao , Chao Shilei , Jin Jiasen , Zhou Ling
Published: May 2019

The dynamics of two nanospheres nonlinearly coupling with non-Markovian reservoir is investigated. A master equation of the two nanospheres is derived by employing quantum state diffusion method. It is shown that the nonlinear coupling can improve the non-Markovianity. Due to the sharing of the common non-Markovian environment, the state transfer between the two nanospheres can be realized. The entanglement and the squeezing of the individual mode, as well as the jointed two-mode are analyzed. The present system can be realized by trapping two nanospheres in a wideband cavity, which might provide a method to study adjustable non-Markovian dynamics of mechanical motion.
Unifying quantum heat transfer and superradiant signature in a nonequilibrium collective-qubit system: A polaron-transformed Redfield approach*
Authors: Chen Xu-Min , Wang Chen
Published: May 2019

We investigate full counting statistics of quantum heat transfer in a collective-qubit system constructed by multi-qubits interacting with two thermal baths. The nonequilibrium polaron-transformed Redfield approach embedded with an auxiliary counting field is applied to obtain the steady state heat current and fluctuations, which enables us to study the impact of the qubit–bath interaction in a wide regime. The heat current, current noise, and skewness are all found to clearly unify the limiting results in the weak and strong couplings. Moreover, the superradiant heat transfer is clarified as a system-size-dependent effect, and large number of qubits dramatically suppress the nonequilibrium superradiant signature.
Isotope effect and Coriolis coupling effect for the Li + H(D)Cl

→

LiCl + H(D) reaction*
Authors: Zhai Hongsheng , Liang Guanglei , Ding Junxia , Liu Yufang
Published: May 2019

A time-dependent quantum wave packet method is used to investigate the dynamics of the Li+ H(D)Cl reaction based on a new potential energy surface (J. Chem. Phys.
146 164305 (2017)). The reaction probabilities of the Coriolis coupled (CC) and centrifugal sudden (CS) calculations, the integral cross sections, the reaction rate constants are obtained. The rate constants of the Li+ HCl reaction are within the error bounds at low temperature. A comparison of the CC and CS results reveals that the Coriolis coupling plays an important role in the Li+ H(D)Cl reaction. The CC cross sections are larger than the CS results within the entire energy range, demonstrating that the Coriolis coupling effect can more effectively promote the Li+ DCl reaction than the Li+ HCl reaction. It is found that the isotope effect has a great influence on the title reaction.
Generation of high-energy-resolved NH3 molecular beam by a Stark decelerator with 179 stages*
Authors: Wei Bin , Hou Shunyong , Guo Hengjiao , Ji Yabing , Li Shengqiang , Yin Jianping
Published: May 2019

We demonstrate the production of cold, slow NH3 molecules from a supersonic NH3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH3 molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH3 molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH3 molecular beam from 333 m/s to 18 m/s, with a final temperature of 29.2 mK. The second is the deceleration-bunch mode, which allows us to decelerate the supersonic NH3 beam from 333 m/s to 24 m/s, with a final temperature of 2.9 mK. It is clear that the second mode promises to produce colder (high-energy-resolution) molecular samples than the normal mode. Three-dimensional Monte Carlo simulations are also performed for the experiments and they show a good agreement with the observed results. The deceleration-bunch operation mode presented here can find applications in the fields of cold collisions, high-resolution spectroscopy, and precision measurements.
Loss induced negative refraction and super-prism effect at highly absorptive interface*
Authors: Wu Jian , Wang Tao , Hou Tianyue , Kan Xuefen , Yin Cheng , Zhou Pu , Cao Zhuangqi
Published: May 2019

It is well-established that waves are inhomogeneous in a lossy isotropic medium, and the validation of the classical Snell's law is still questionable for light refraction at the dissipative and dispersive interface. With high absorption, direct experimental investigation is rather difficult due to the extremely short penetration depth; i.e., the skin depth. In this paper, a simple and unified description of this issue is proposed, which can be applied to both materials with anomalous dispersion and in the Drude region. The gradient

∇

k

ω

is found to be incident angle θ
i-dependent, and the direction of the group velocity may deviate significantly from the phase velocity due to the loss induced permittivity structure. The physics behind the negative refraction effect is explained, and a novel loss induced super-prism effect is also predicted.
High power diode-pumped passively mode-locked Nd:YVO4 laser at repetition rate of 3.2 GHz*
Authors: Cheng Meng-Yao , Wang Zhao-Hua , Cao Yan-Fang , Meng Xiang-Hao , Zhu Jiang-Feng , Wang Jun-Li , Wei Zhi-Yi
Published: May 2019

A compact high power diode-pumped passively mode-locked Nd:YVO4 laser with high repetition rate is realized. Using an Nd:YVO4 crystal and a semiconductor saturable absorber mirror (SESAM) in the oscillator, the picosecond pulse output with an average power of 1.38 W, a repetition rate of 3.24 GHz, and a pulse duration of 11.4 ps is achieved. After one stage of amplification, the final output power reaches 11.34 W, corresponding to a total optical-to-optical efficiency of about 32%. The root mean square (RMS) value of power fluctuation is demonstrated to be less than 0.6% in 24 hours, showing a superior stability with the compact configuration.
Crystalline order and disorder in dusty plasmas investigated by nonequilibrium molecular dynamics simulations*
Authors: Shahzad Aamir , He Maogang , Ghani Sheeba , Kashif Muhammad , Munir Tariq , Yang Fang
Published: May 2019

The particle structure of a complex system has been explored through a unique Evans's homogenous nonequilibrium molecular dynamics (HNEMD) simulation technique. The crystalline order–disorder structures (OD-structures) and the corresponding energies of three-dimensional (3D) nonideal complex systems (NICSs) have been measured over a wide range of plasma states (Γ, κ) for a body-centered cubic (BCC) structure. The projected technique provides accurate OD-structures with fast convergence and applicable to very small size effect for different temperatures (

≡

1 /

Γ
)

and constant force field (

F

*

)

values. The OD-structure obtained through HNEMD approach is found to be reasonable agreement and more reliable than those earlier identified by simulation approaches and experimental data of NICSs. New simulations of OD-structures show that dusty plasma remains in crystalline (strongly coupled) state at lower temperature and constant

F

*

values, for the whole simulation runs. Our investigations show that the crystalline structure is changed and the particle structure switches from intermediate to disorder (nonideal gaseous) state with an increase of the system's temperature. It has been shown that the long range order shifts toward lower temperature with increasing *

κ

. The presented technique exhibits that the potential energy has a maximum value when the dusty plasma remains in crystalline states (low temperatures), which confirms earlier 3D simulation results.
Crystal structures and decomposing of B–P compounds under pressure*
Authors: Zhang Die , Jin Xilian , Zhuang Quan , Li Ying , Yang Shuhan , Song Liying , Liu Bingbing , Cui Tian
Published: May 2019

We have systematically studied the structures, electronic properties, and lattice dynamics of B–P compounds at high pressures. BP and B6P are found to be thermodynamically stable below 100 GPa, and other stoichiometries are decomposable under pressure. The predicted structures of F-43m BP and R-3m B6P are in good agreement with the experimental results by comparing the powder diffraction file (PDF) standard cards with our simulated x-ray diffractions. The bonding properties of BP and B6P have also been analyzed by electronic localization functions, charge density difference, and Bader charge analysis. Our results show that BP and B6P decompose into B and P under high pressure, which is proven to be dominated by the volumes of them. Furthermore, the infrared and Raman spectra of F-43m and R-3m are investigated at selected pressures and will provide useful information for future experimental studies about B–P compounds.
Low temperature Pmmm and C2/m phases in Sr2CuO3+δ high temperature superconductor*
Authors: Wang Hai-Bo , Luo Zhen-Lin , Yang Yuan-Jun , Liu Qing-Qing , Hu Si-Xia , Yang Meng-Meng , Jin Chang-Qing , Gao Chen
Published: May 2019

A new low temperature Pmmm (120 K) phase was found in high temperature superconductor Sr2CuO3+δ
, which was indicated as a pure electronic phase by resonant x-ray diffraction at Cu K-edge. As shown by x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) at Cu K-edge, the strong charge density redistribution and local lattice fluctuations around Cu site at the onset of phase transition were due to the occurrence of superconductive coherence, the redistribution and fluctuation finished at T
c. Finally, the electron–lattice interaction was mainly elaborated to understand the superconductivity of Sr2CuO3+δ
.
Structural and electrical properties of Ga–Te systems under high pressure*
Authors: Wang Youchun , Tian Fubo , Li Da , Duan Defang , Xie Hui , Liu Bingbing , Zhou Qiang , Cui Tian
Published: May 2019

First-principles evolutionary calculation was performed to search for all probable stable Ga–Te compounds at extreme pressure. In addition to the well-known structures of P63/mmc and Fm-3m GaTe and I4/m Ga2Te5, several new structures were uncovered at high pressure, namely, orthorhombic I4/mmm GaTe2 and monoclinic C2/m GaTe3, and all the Ga–Te structures stabilize up to a maximum pressure of 80 GPa. The calculation of the electronic energy band indicated that the high-pressure phases of the Ga–Te system are metallic, whereas the low-pressure phases are semiconductors. The electronic localization functions (ELFs) of the Ga–Te system were also calculated to explore the bond characteristics. The results showed that a covalent bond is formed at low pressure, however, this bond disappears at high pressure, and an ionic bond is formed at extreme pressure.
Surface stabilized cubic phase of CsPbI3 and CsPbBr3 at room temperature*
Authors: Yang Feng , Wang Cong , Pan Yuhao , Zhou Xieyu , Kong Xianghua , Ji Wei
Published: May 2019

Inorganic halide perovskites CsPbX
3 (X = I, Br) have attracted tremendous attention in solar cell applications. However, the bulk form of the cubic phase CsPbX
3, which offers moderate direct bandgaps, is metastable at room temperature and tends to transform into a tetragonal or orthorhombic phase. Here, our density functional theory calculation results found that the surface energies of the cubic phase are smaller than those of the orthorhombic phase, although the bulk counterpart of the cubic phase is less stable than that of the orthorhombic phase. These results suggest a surface stabilization strategy to maintain the stability of the cubic phase at room temperature that an enlarged portion of surfaces shall change the relative stability of the two phases in nanostructured CsPbX
3. This strategy, which may potentially solve the long-standing stability issue of cubic CsPbX
3, was demonstrated to be feasible by our calculations in zero-, one-, and two-dimensional nanostructures. In particular, confined sizes from few to tens of nanometers could keep the cubic phase as the most thermally favored form at room temperature. Our predicted values in particular cases, such as the zero-dimensional form of CsPbI3, are highly consistent with experimental values, suggesting that our model is reasonable and our results are reliable. These predicted critical sizes give the upper and lower limits of the confined sizes, which may guide experimentalists to synthesize these nanostructures and promote likely practical applications such as solar cells and flexible displays using CsPbX
3 nanostructures.
Spatiotemporal Bloch states of a spin–orbit coupled Bose–Einstein condensate in an optical lattice*
Authors: Wei Ya-Wen , Kong Chao , Hai Wen-Hua
Published: May 2019

We study the spatiotemporal Bloch states of a high-frequency driven two-component Bose–Einstein condensate (BEC) with spin–orbit coupling (SOC) in an optical lattice. By adopting the rotating-wave approximation (RWA) and applying an exact trial-solution to the corresponding quasistationary system, we establish a different method for tuning SOC via external field such that the existence conditions of the exact particular solutions are fitted. Several novel features related to the exact states are demonstrated; for example, SOC leads to spin–motion entanglement for the spatiotemporal Bloch states, SOC increases the population imbalance of the two-component BEC, and SOC can be applied to manipulate the stable atomic flow which is conducive to control quantum transport of the BEC for different application purposes.
Epitaxial fabrication of two-dimensional TiTe2 monolayer on Au(111) substrate with Te as buffer layer*
Authors: Song Zhipeng , Lei Bao , Cao Yun , Qi Jing , Peng Hao , Wang Qin , Huang Li , Lu Hongliang , Lin Xiao , Wang Ye-Liang , Du Shixuan , Gao Hong-Jun
Published: May 2019

Two-dimensional (2D) materials provide a platform to exploit the novel physical properties of functional nanodevices. Here, we report on the formation of a new 2D layered material, a well-ordered monolayer TiTe2, on a Au(111) surface by molecular beam epitaxy (MBE). Low-energy electron diffraction (LEED) measurements of the samples indicate that the TiTe2 film forms

(

3

×

7

)

superlattice with respect to the Au(111) substrate, which has three different orientations. Scanning tunneling microscopy (STM) measurements clearly show three ordered domains consistent with the LEED patterns. Density functional theory (DFT) calculations further confirm the formation of 2H-TiTe2 monolayer on the Au(111) surface with Te as buffer layer. The fabrication of this 2D layered heterostructure expands 2D material database, which may bring new physical properties for future applications.
Mechanism of free electron concentration saturation phenomenon in Te-GaSb single crystal*
Authors: Yu Ding , Shen Guiying , Xie Hui , Liu Jingming , Sun Jing , Zhao Youwen
Published: May 2019

Te-doped GaSb single crystal grown by the liquid encapsulated Czochralski (LEC) method exhibits a lag of compensating progress and a maximum carrier concentration around 8×1017 cm−3. The reason for this phenomenon has been investigated by a quantity concentration evaluation of the Te donor and native acceptor. The results of glow discharge mass spectrometry (GDMS) and Hall measurement suggest that the acceptor concentration increases with the increase of Te doping concentration, resulting in the enhancement of electrical compensation and free electron concentration reduction. The acceptor concentration variation is further demonstrated by photoluminescence spectra and explained by the principle of Fermi level dependent defect formation energy.
Effects of interface bound states on the shot noise in normal metal–low-dimensional Rashba semiconductor tunnel junctions with induced s-wave pairing potential
Authors: Chen Wen-Xiang , Wang Rui-Qiang , Hu Liang-Bin
Published: May 2019

We consider the effects of interface bound states on the electrical shot noise in tunnel junctions formed between normal metals and one-dimensional (1D) or two-dimensional (2D) Rashba semiconductors with proximity-induced s-wave pairing potential. We investigate how the shot noise properties vary as the interface bound state is evolved from a non-zero energy bound state to a zero-energy bound state. We show that in both 1D and 2D tunnel junctions, the ratio of the noise power to the charge current in the vicinity of zero bias voltage may be enhanced significantly due to the induction of the midgap interface bound state. But as the interface bound state evolves from a non-zero energy bound state to a zero-energy bound state, this ratio tends to vanish completely at zero bias voltage in 1D tunnel junctions, while in 2D tunnel junctions it decreases smoothly to the usual classical Schottky value for the normal state. Some other important aspects of the shot noise properties in such tunnel junctions are also clarified.
Tunable superconductivity in parent cuprate Pr2CuO4±δ thin films*
Authors: Wei Xinjian , He Ge , Hu Wei , Zhang Xu , Qin Mingyang , Yuan Jie , Zhu Beiyi , Lin Yuan , Jin Kui
Published: May 2019

We studied the role of oxygen in Pr2CuO4±δ
thin films fabricated by the polymer assisted deposition method. The magnetoresistance and Hall resistivity of Pr2CuO4±δ
samples were systematically investigated. It was found that with decreasing oxygen content, the low-temperature Hall coefficient (R
H) and magnetoresistance changed from negative to positive, similar to those with the increase of Ce-doped concentration in

R

2
−
x

Ce
x
CuO4 (R=La, Nd, Pr, Sm, Eu). In addition, we observed that the dependence of the superconducting critical temperature T
c with R
H for the Pr2−x
Ce
x
CuO4 perfectly overlapped with that of Pr2CuO4±δ
. These findings point to the fact that the doped electrons induced by the oxygen removal are responsible for the superconductivity of the

T

′

-phase parent compounds.
Particle–hole fluctuations and possible superconductivity in doped α-RuCl3*
Authors: Wang Bin-Bin , Wang Wei , Yu Shun-Li , Li Jian-Xin
Published: May 2019

We study various particle–hole excitations and possible superconducting pairings mediated by these fluctuations in doped α-RuCl3 by using multi-band Hubbard model with all t2g orbitals. By performing a random-phase-approximation (RPA) analysis, we find that among all particle–hole excitations, the j
eff = 1/2 pseudospin fluctuations are dominant, suggesting the robustness of j
eff = 1/2 picture even in the doped systems. We also find that the most favorable superconducting state has a d-wave pairing symmetry.
Enhanced soft magnetic properties of iron powders through coating MnZn ferrite by one-step sol–gel synthesis*
Authors: Liu Dong , Gao Shanmin , Jin Rencheng , Wang Feng , Chu Xiaoxiao , Gao Taiping , Wang Yubao
Published: May 2019

The MnZn ferrite coating formed on the surface of iron-based soft magnetic powders via facile and modified sol–gel process has been fabricated to obtain better magnetic performance due to its higher permeability compared with traditional nonmagnetic insulation coatings. The influence of the MnZn ferrite contents on the magnetic performance of the soft magnetic composites (SMCs) has been studied. As the MnZn insulation content increases, the core loss first experiences a decreasing trend that is followed by progressive increase, while the permeability follows an increasing trend and subsequently degrades. The optimized magnetic performance is achieved with 2.0 wt% MnZn ferrite, which results from the decrement of inter-particle eddy current losses based on loss separation. A uniform and compact coating layer composed of MnZn ferrite and oxides with an average thickness of

0.38
±
0.08

μ
m

is obtained by utilizing ion beam technology, and the interface between the powders and the coating shows satisfied adhesiveness compared with the sample directly prepared by mechanical mixing. The evolution of the coating layers during the calcination process has been presented based on careful analysis of the composition and microstructure.
Influence of additives on the magnetic damping constant of CoIr soft magnetic thin films with negative magnetocrystalline anisotropy*
Authors: Ma Tianyong , Luo Zhi , Li Zhiwei , Qiao Liang , Wang Tao , Li Fashen
Published: May 2019

The oriented

(
CoIr
)

100
−
x

P

x

(P=B, Ni, and SiO2) soft magnetic films are prepared. Their morphology is measured using transmission electron microscopy (TEM), and reveals that these films exhibit good crystallinity and high degree of the c-axis orientation. The magnetic properties are thoroughly investigated as a function of doping x. Our results show that all of these films possess negative magnetocrystalline anisotropy as required by possible applications. Both the intrinsic and extrinsic contributions are considered to interpret the broadening of the ferromagnetic resonance spectral linewidth. The intrinsic Gilbert damping is identified as the main cause of the linewidth broadening, while the extrinsic part originating from inhomogeneities only plays a minor role. More interestingly, our results show that the damping constant can be controlled by using the doping method.
The c-axis complex permittivity and electrical impedance in BaFe2As2: Experimental examination on transformation validity*
Authors: Li Yongqiang , Du Xinzhe , Gong Dongliang , Yang Qirui , Zhang Wenliang , Xie Tao , Feng Bo , Chen Kai , Luo Huiqian , Liu Junming , Zhu Jinsong
Published: May 2019

Complex permittivity and electrical impedance have been measured along the c-axis in single crystals BaFe2As2, which are the conductors known as the parent compound of 122-type iron superconductor. The resultant relative errors defined in the study indicate the existence of the transformation between complex permittivity and electrical impedance in the conductors, and these two physics quantities possibly reveal different aspects of the consistent superconductivity-relevant physics picture.
Temperature and excitation dependence of stimulated emission and spontaneous emission in InGaN epilayer*
Authors: An Xuee , Shang Zhengjun , Ma Chuanhe , Zheng Xinhe , Zhang Cuiling , Sun Lin , Yue Fangyu , Li Bo , Chen Ye
Published: May 2019

Temperature and excitation dependent photoluminescence (PL) of InGaN epilayer grown on c-plane GaN/sapphire template by molecular beam epitaxy (MBE) has been systematically investigated. The emission spectra of the sample consisted of strong multiple peaks associated with one stimulated emission (SE) located at 430 nm and two spontaneous emissions (SPE) centered at about 450 nm and 480 nm, indicating the co-existence of shallow and deep localized states. The peak energy of SE exhibiting weak s-shaped variation with increasing temperature revealed the localization effect of excitons. Moreover, an abnormal increase of the SPE intensity with increasing temperature was also observed, which indicated that the carrier transfer between the shallow and deeper localized states exists. Temperature dependent time-resolved PL (TRPL) demonstrated the carrier transfer processes among the localized states. In addition, a slow thermalization of hot carriers was observed in InGaN film by using TRPL and transient differential reflectivity, which is attributed to the phonon bottleneck effect induced by indium aggregation.
Large-scale control of enhancement and quenching of photoluminescence for ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution*
Authors: Yin Shaoyi , Liao Liming , Luo Song , Zhang Zhe , Zhang Xiaoyu , Lu Jian , Chen Zhanghai
Published: May 2019

We investigated the optical properties of hybrid exciton–plasmon coupling ensembles composed of ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution. We modulated their average interval by changing the ratio of quantum dots and Ag nanoparticles. The transition from dramatic PL enhancement to PL quenching state was experimentally observed, according to the continuous decrease of the PL lifetime. The PL enhancement rate exceeded 10, with the Purcell factor of 3.5. Meanwhile, the proportion of fast decay increased from 0.3 to 0.6, corresponding to the proportion of slow decay decreased from 0.7 to 0.4. Our experiment is important for the hybrid exciton–plasmon coupling system to be practicable in optoelectronic application.
Two-step growth of VSe2 films and their photoelectric properties*
Authors: Zeng Yu , Zhang Shengli , Li Xiuling , Ao Jianping , Sun Yun , Liu Wei , Liu Fangfang , Gao Peng , Zhang Yi
Published: May 2019

We put forward a two-step route to synthesize vanadium diselenide (VSe2), a typical transition metal dichalcogenide (TMD). To obtain the VSe2 film, we first prepare a vanadium film by electron beam evaporation and we then perform selenization in a vacuum chamber. This method has the advantages of low temperature, is less time-consuming, has a large area, and has a stable performance. At 400 °C selenization temperature, we successfully prepare VSe2 films on both glass and Mo substrates. The prepared VSe2 has the characteristic of preferential growth along the c-axis, with low transmittance. It is found that the contact between Al and VSe2/Mo is ohmic contact. Compared to Mo substrate, lower square resistance and higher carrier concentration of the VSe2/Mo sample reveal that the VSe2 film may be a potential material for thin film solar cells or other semiconductor devices. The new synthetic strategy that is developed here paves a sustainable way to the application of VSe2 in photovoltaic devices.
Enhanced performance of AlGaN-based ultraviolet light-emitting diodes with linearly graded AlGaN inserting layer in electron blocking layer*
Authors: Li Guang , Wang Lin-Yuan , Song Wei-Dong , Jiang Jian , Luo Xing-Jun , Guo Jia-Qi , He Long-Fei , Zhang Kang , Wu Qi-Bao , Li Shu-Ti
Published: May 2019

The conventional stationary Al content AlGaN electron blocking layer (EBL) in ultraviolet light-emitting diode (UV LED) is optimized by employing a linearly graded AlGaN inserting layer which is 2.0 nm Al0.3Ga0.7N/5.0 nm Al
x
Ga1−x
N/8.0 nm Al0.3Ga0.7N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes, which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition, the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.
Modeling electric field of power metal-oxide-semiconductor field-effect transistor with dielectric trench based on Schwarz–Christoffel transformation*
Authors: Wang Zhi-Gang , Liao Tao , Wang Ya-Nan
Published: May 2019

A power metal-oxide-semiconductor field-effect transistor (MOSFET) with dielectric trench is investigated to enhance the reversed blocking capability. The dielectric trench with a low permittivity to reduce the electric field at reversed blocking state has been studied. To analyze the electric field, the drift region is segmented into four regions, where the conformal mapping method based on Schwarz–Christoffel transformation has been applied. According to the analysis, the improvement in the electric field for using the low permittivity trench is mainly due to the two electric field peaks generated in the drift region around this dielectric trench. The analytical results of the electric field and the potential models are in good agreement with the simulation results.
Photoinduced phase transitions in two-dimensional charge-density-wave 1T-TaS2
*
Authors: Wen Wen , Dang Chunhe , Xie Liming
Published: May 2019

Charge-density-wave (CDW) materials with strongly correlated electrons have broadband light absorption and ultrafast response to light irradiation, and hence hold great potential in photodetection. 1T-TaS2 is a typical CDW material with various thermodynamically CDW ground states at different temperatures and fertile out-of-equilibrium intermediate/hidden states. In particular, the light pulses can trigger melting of CDW ordering and also forms hidden states, which exhibits strikingly different electrical conductivity compared to the ground phase. Here, we review the recent research on phase transitions in 1T-TaS2 and their potential applications in photodetection. We also discuss the ultrafast melting of CDW ordering by ultrafast laser irradiation and the out-of-equilibrium intermediate/hidden states by optical/electrical pulse. For photodetection, demonstrations of photoconductors and bolometers are introduced. Finally, we discuss some of the challenges that remain.