Elucidation and Identification of Double-Tip Effects in Atomic Force Microscopy Studies of Biological Structures

While atomic force microscopy (AFM) has been increasingly applied to life science, artifactual measurements or images can occur during nanoscale analyses of cell components and biomolecules. Tip-sample convolution effect is the most common mechanism responsible for causing artifacts. Some deconvolution-based methods or algorithms have been developed to reconstruct the specimen surface or the tip geometry. Double-tip or double-probe effect can also induce artifactual images by a different mechanism from that of convolution effect. However, an objective method for identifying the double-tip/probe-induced artifactual images is still absent. To fill this important gap, we made use of our expertise of AFM to analyze artifactual double-tip images of cell structures and biomolecules, such as linear DNA, during AFM scanning and imaging. Mathematical models were then generated to elucidate the artifactual double-tip effects and images develop during AFM imaging of cell structures and biomolecules. Based on these models, computational formulas were created to measure and identify potential double-tip AFM images. Such formulas proved to be useful for identification of double-tip images of cell structures and DNA molecules. The present studies provide a useful methodology to evaluate double-tip effects and images. Our results can serve as a foundation to design computer-based automatic detection of double-tip AFM images during nanoscale measuring and imaging of biomolecules and even non-biological materials or structures, and then personal experience is not needed any longer to evaluate artifactual images induced by the double-tip/probe effect.

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap （MOT） system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of - 1 × 10^-6 Pa to the ultra-high-vacuum （UHV） MOT with a pressure of - 8 × 10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is - 2 × 10^7 atoms/s. About 5 × 10^6 caesium atoms are recaptured in the UHV MOT.

Non-sequential double ionization of helium-like atom

In this paper, author investigated the effect of the Coulomb potential of the core of atomic helium on the rescattering processes. Through the calculation author concluded that the Coulomb potential effect may not play an important role in causing the discrepancy between the experimental data and theoretical results of Kuchievs model, and the NS ionization is dependent on the frequency of the laser field. Furthermore, it is concluded that the strength of the laser field and the charge number of the core affect the frequency regime corresponding to the peak value of the NS ionization rate.

Analysis of Cr atom focusing deposition properties in the double half Gaussian standing wave field

The use of the dipole force on atoms is a new technology that is used to build nanostructures. In this way, a high quality standard nano-grating can be obtained. Based on the semi-classical model, the motion equation is investigated and the trajectories of atoms in double half Gaussian standing wave field are simulated. Compared with the Gaussian standing wave field, the double half Gaussian standing wave can well focus the Cr atoms. In order to obtain this kind of beam, a prism is designed and the experimental result shows that the beam is well generated.

Laser-assisted XUV double ionization of helium atoms:Intensity dependence of joint angular distributions

We investigate the intensity effect of ultrashort assisting infrared laser pulse on the single-XUV-photon double ionization of helium atoms by solving full six-dimensional time-dependent Schrodinger equation with implement of finite element discrete variable representation.The studies of joint energy distributions and joint angular distributions of the two photoelectrons reveal the competition for ionized probabilities between the photoelectrons with odd parity and photoelectrons with even parity in single-XUV-photon double ionization process in the presence of weak infrared laser field,and such a competition can be modulated by changing the intensity of the weak assisting-IR laser pulses.The emission angles of the two photoelectrons can be adjusted by changing the laser parameters as well.We depict how the assisting-IR laser field enhances and/or enables the back-to-back and side-by-side emission of photoelectrons created in double ionization process.

Experimental Study on Double Resonance Optical Pumping Spectroscopy in a Ladder-Type System of ^(87)Rb Atoms

Double resonance optical pumping spectroscopy has an outstanding advantage of high signal-to-noise ratio, thus having potential applications in precision measurement. With the counter propagated 780nm and 776nm laser beams acting on a rubidium vapor cell, the high resolution spectrum of 5S1/2 - 5P3/2 - 5D5/2 ladder-type transition of ST Rb atoms is obtained by monitoring the population of the 5S1/2 ground state. The dependence of the spectroscopy lineshape on the probe and coupling fields are comprehensively studied in theory and experiment. This research is helpful for measurement of fundamental physical constants by high resolution spectroscopy.

A Generic Description Model for the Structure of Atomic Nucleus with New Interpretation of the Strong Forces

The present investigation is motivated by finding and developing an easily understandable solution in the context of unified quantum and gravitational theories. Model-based methods are applied, with emphasis on structural descriptions by introducing some strong hypotheses. A subset of the introduced hypotheses led to a surprising understanding of the internal structure and construction of quarks, neutrons, protons and more complex atomic nuclei. The research work therefore focused mainly on the model-based interpretation of subatomic processes. The results obtained so far and presented in this paper are new. They consist of a generic description model for the structure of atomic nuclei. This model contains two important structural links that originate from the initial phase of the cosmological big bang. They hold atomic parts together and are involved in many known nuclear fusion and fission processes. Modifications of them, including the electron-positron annihilation process, are necessary and will be described. A new interpretation of the strong forces from the Standard Model is possible and will be given. In addition, the formation processes for electron and positron particles are considered. Based on the structural relationships, a deeper understanding of matter transformations (transmutations), early cosmological processes and dark matter has been achieved. All challenges of this work are the logical conclusions from the used hypotheses on two structural links. They need to be further investigated and verified by theoretical and experimental works. The postulated particle in this paper, as accompanying product in the electron-positron annihilation, will play a major role for the future investigations.

Engineering single atomic ruthenium on defective nickel vanadium layered double hydroxide for highly efficient hydrogen evolution

Fabricating single-atom catalysts(SACs)with high catalytic activity as well as great stability is a big challenge.Herein,we propose a precise synthesis strategy to stabilize single atomic ruthenium through regulating vanadium defects of nickel vanadium layered double hydroxides(NiV-LDH)ultrathin nanoribbons support.Correspondingly,the isolated atomically Ru doped NiV-LDH ultrathin nanoribbons(NiVRu-R)were successfully fabricated with a super-high Ru load of 12.8 wt.%.X-ray absorption spectrum(XAS)characterization further confirmed atomic dispersion of Ru.As catalysts for electrocatalytic hydrogen evolution reaction(HER)in alkaline media,the NiVRu-R demonstrated superior catalytic properties to the commercial Pt/C.Moreover,it maintained exceptional stability even after 5,000 cyclic voltammetry cycles.In-situ XAS and density functional theory(DFT)calculations prove that the Ru atomic sites are stabilized on supports through forming the Ru-O-V structure,which also help promote the catalytic properties through reducing the energy barrier on atomic Ru catalytic sites.

Comparison of Entanglement Sudden Death and Revival Between Independent and Coherent Double Pathways

Starting from famous Schrodinger equation within the framework of semi-classical theory of light-matter interaction,we firstly obtain the analytical non-resonant solutions of the driven bipartite system’s entanglement dynamics in independent and coherent double pathways.Numerical simulations show that under non-resonant condition, entanglement sudden death and revival between these transition patterns behave quite differently,indicating the utmost importance of transition pathways’ interference.Furthermore,the laser pulse’s area and detuning exert significant but quite distinct influences on the entanglement dynamics.Our analyses are helpful in manipulating entanglement in current experimental technology.

单原子催化剂催化生物质衍生物选择性加氢的研究进展

生物质是以碳源形式存在的可再生资源,其平台化合物及衍生物的升级利用可得到能源和精细化工产品。多相催化剂在生物质资源的转化中起到重要作用,其中不乏纳米催化剂和单原子催化剂的参与。由于木质纤维素的含氧量较高,不能直接作为工业应用原料,因此需要还原反应来降低其含氧量。加氢反应是降低木质纤维素衍生分子中O C比、提高H C比的重要方法。本研究将综合讨论单原子催化剂在呋喃类、α,β-不饱和醛酮和木质素类平台化合物选择性加氢中的应用。

铯原子钟电子倍增器可调高压电源设计

电子倍增器用来放大并输出铯原子的跃迁信号。倍增器电源是其重要组成部分,针对电子倍增器在增益变化及衰减情况下的供电需求,提出了一种基于分流调整电路结合倍压整流电路的高压电源设计方案,该方案在低压部分采用分流调整技术实现了电源输出电压控制;采用变压器结合多级倍压整流电路对电压放大输出,实现了电源可调电压范围在-306~-3 150 V和低输出纹波,电源的遥测电路实现了输出电压遥测。星载铯原子钟经过长期在轨测试,测试结果表明,本设计的电源在控制范围内实现了宽范围电压输出和遥测,低于3.23 V的电源纹波,保证了铯原子钟稳定度指标。

Layered double hydroxides with atomic-scale defects for superior electrocatalysis

Atomic composition tuning and defect engineering are effective strategies to enhance the catalytic performance of multicomponent catalysts by improving the synergetic effect; however, it remains challenging to dramatically tune the active sites on mulficomponent materials through simultaneous defect engineering at the atomic scale because of the similarities of the local environment. Herein, using the oxygen evolution reaction （OER） as a probe reaction, we deliberately introduced base-soluble Zn（II） or AI（III） sites into NiFe layered double hydroxides （LDHs）, which are one of the best OER catalysts. Then, the Zn（II） or AI（III） sites were selectively etched to create atomic M（I0/M（IIo defects, which dramatically enhanced the OER activity. At a current density of 20 mA.cm-2, only 200 mV overpotential was required to generate M（II） defect-rich NiFe LDHs, which is the best NiFe-based OER catalyst reported to date. Density functional theory （DFT） calculations revealed that the creation of dangling Ni-Fe sites （i.e., unsaturated coordinated Ni-Fe sites） by defect engineering of a Ni-O-Fe site at the atomic scale efficiently lowers the Gibbs free energy of the oxygen evolution process. This defect engineering strategy provides new insights into catalysts at the atomic scale and should be beneficial for the design of a variety of catalysts.

Emission spectrum of a harmonically trapped Λ-type three-level atom

We theoretically investigate the emission spectrum for a A-type three-level atom trapped in the node of a standing wave. We show that the atomic center-of-mass motion not only directly affects the peak number, peak position, and peak height in the atomic emission spectrum, but also influences the effects of the cavity field and the atomic initial state on atomic emission spectrum.

Probabilistic teleportation of an arbitrary pure state of two atoms

In the context of microwave cavity QED, this paper proposes a new scheme for teleportation of an arbitrary pure state of two atoms. The scheme is very different from the previous ones which achieve the integrated state measurement, it deals in a probabilistic but simplified way. In the scheme, no additional atoms are involved and thus only two atoms are required to be detected. The scheme can also be used for the teleportation of arbitrary pure states of many atoms or two-mode cavities.

氢原子钟双选态束光学系统仿真分析

氢原子钟利用氢原子基态超精细能级跃迁信号进行精确计时,具有中短期频率稳定度优异、频率漂移率低的特点.氢原子钟需要通过磁选态将高能态原子选出,目前广泛应用的磁选态方案中,既有原子钟跃迁所需要的|F=1,m_(F)=0>态,还有钟跃迁所不需要的|F=1,m_(F)=1>态氢原子,这使得氢原子钟的中长期频率稳定性难以进一步提高.为了进一步提高氢原子钟原子跃迁谱线质量和整机性能,通过计算和仿真,构建了基于Majorana跃迁的氢原子钟双选态束光学系统,优化了一级选态区、态反转区、二级选态区等关键部件的参数,进一步排除了|F=1,m_(F)=1>态原子.选态后的|F=1,m_(F)=0>态原子纯度达到99%,利用率为58%,工程应用较为理想.有效地提升了进入原子储存泡内|F=1,m_(F)=0>态氢原子的占比,同时原子的利用率处于可控范围.通过实验对该方案的有效性进行了验证,通过开启双选态系统,可以观察到氢原子钟信号的增强;通过调整双选态系统的线圈电流,可以观察到信号随线圈电流的变化,这验证了双选态系统的有效性.

少光周期的中红外激光脉冲驱动的Xe原子非次序双电离

利用经典系综模型,系统研究了不同载波包络相位(Carrier-envelopphase,CEP)下少光周期的中红外激光脉冲驱动的Xe原子非次序双电离,并比较了近红外激光脉冲的情况。结果表明,中红外激光脉冲下,随CEP的增加,关联电子沿激光偏振方向的动量谱由分布在第一、二、四象限的弧形结构转变到主要分布在第一、三象限的弧形结构。而近红外激光脉冲下,关联电子动量谱由主要分布在第一、三象限的V型结构转变到主要分布在第一象限的V型结构。反演分析发现,中红外激光脉冲下,NSDI主要以直接碰撞电离机制主导,碰撞时间主要由位于激光场峰值附近的P1峰和位于激光场零点附近的P2峰贡献,P1峰导致关联电子动量谱在第一、二、四象限的弧形结构,P2峰导致关联电子动量谱在第一、三象限的弧形结构。进一步研究发现,对于中红外激光脉冲,根据双电离与碰撞之间的时间延迟进一步把NSDI事件分开,发现即使对于直接碰撞电离机制,不同的时间延迟范围内,电子关联特性仍呈现出不同的行为。

层状金属氢氧化物中铁位点辅助分散铂纳米颗粒用于高效甲醇氧化

高活性和耐用性的甲醇氧化电催化剂对于直接甲醇燃料电池的商业可行性至关重要,然而,目前的甲醇氧化电催化剂与预期相去甚远,存在贵金属用量过多、活性平庸、衰减快等问题。在这里,我们报告了锚定在镍铁层状金属氢氧化物(NiFe-LDHs)表面Pt纳米颗粒复合材料,用于在碱性介质中稳定电催化甲醇氧化。基于Pt纳米颗粒的高固有甲醇氧化活性,与商业Pt/C催化剂相比,基底材料NiFe-LDHs在200,000 s循环测试后进一步增强了Pt的抗中毒能力和稳定性。NiFe-LDHs层板上单原子分散的Fe作为锚定位点将Pt纳米颗粒均匀分散在其表面,进一步充分利用了层状金属氢氧化物表面丰富的OH基团,促进邻近Pt位点上毒化中间体的氧化去除。这项工作突出了NiFeLDH在提高甲醇氧化反应整体效率方面的特殊性,为其他甲醇氧化电催化的设计和应用提供了指导。

Double transition metal atoms anchored on Graphdiyne as promising catalyst for electrochemical nitrogen reduction reaction

Ammonia synthesis by electrochemical nitrogen reduction technique is an attractive alternative to traditional Haber-Bosch process.Currently,development of an efficient and effective electrocatalyst is one of the remaining key challenges.In this work,density functional theory(DFT)computations were systematically employed on double transition metal atoms(Fe,Co,Ni,Cu and Mo)anchored Graphdiyne(GDY)for nitrogen reduction reaction(NRR).The Co-Ni heteronuclear complex and Mo-Mo homonuclear complex showed the highest NRR activity while demonstrating synergistic effect of double atomic catalytic sites towards the promising NRR activity.

Controllable coating NiAl-layered double hydroxides on carbon nanofibers as anticorrosive microwave absorbers

For harsh real-world service settings,it is essential to build corrosion-resistant,diverse,and effective microwave absorbers.Herein,we successfully prepared a 3D NiAl-layered double hydroxide/carbon nanofibers(NiAl-LDH/CNFs)composite material as an anticorrosive microwave absorber assisted by an atomic layer deposition(ALD)method.The size,coating thickness,and content of NiAl-LDH can be readily adjusted by changing the ALD cycling numbers.The optimized NiAl-LDH/CNFs demonstrates prominent microwave absorbing properties including the strongest reflection loss of–55.65 dB and the widest effective absorption bandwidth of 4.80 GHz with only 15 wt%loading.The reasons for performance improvement are the cooperative effect of interfacial polarization loss,conduction loss,and three-dimensional porous structure.Moreover,due to the synergistic effects between the excellent impermeability of CNFs and the trapping ability of NiAl-LDH for chloride ions,NiAl-LDH/CNFs exhibits strong corrosion resistances under acidic,neutral,and alkaline conditions.NiAl-LDH/CNFs should be a potential candidate to simultaneously use for microwave absorption and corrosion resistance,and this work provides a certain guiding significance for designing microwave absorbers that satisfy the corrosion resistance.

顺风流动下单双层喷嘴雾化特性的数值模拟研究

为研究顺风流动下单双层喷嘴的雾化特性,采用Fluent中离散相模型对顺风流动下单、双层喷嘴的雾化特性进行数值模拟,先将雾滴平均粒径的模拟值与实验值进行对比分析,验证模型的可靠性,再分析不同工况下单、双层喷嘴喷射出的雾滴群平均粒径及速度变化规律。结果表明:同一扰动风速及供水压力条件下,单层喷嘴比双层喷嘴喷射出的雾滴群平均粒径小;随扰动风速、供水压力的增大,单、双层喷嘴喷射出的雾滴群平均粒径均逐渐减小;扰动风速显著影响雾滴群的速度分布,扰动风速越大,单、双层喷嘴喷射出的雾滴群速度越大且雾滴群射程越远,整体呈现出大粒径雾滴先于小粒径雾滴沉降的趋势。