Precision-controlled ultrafast electron microscope platforms. A case study: Multiple-order coherent phonon dynamics in 1T-TaSe2 probed at 50 fs-10 fm scales.

We report on the first detailed beam tests attesting the fundamental principle behind the development of high-current-efficiency ultrafast electron microscope systems where a radio frequency (RF) cavity is incorporated as a condenser lens in the beam delivery system. To allow for the experiment to be carried out with a sufficient resolution to probe the performance at the emittance floor, a new cascade loop RF controller system is developed to reduce the RF noise floor. Temporal resolution at 50 fs in full-width-at-half-maximum and detection sensitivity better than 1% are demonstrated on exfoliated 1T-TaSe2 system under a moderate repetition rate. To benchmark the performance, multi-terahertz edge-mode coherent phonon excitation is employed as the standard candle. The high temporal resolution and the significant visibility to very low dynamical contrast in diffraction signals via high-precision phase-space manipulation give strong support to the working principle for the new high-brightness femtosecond electron microscope systems.

Nonequilibrium dynamics of spontaneous symmetry breaking into a hidden state of charge-density wave.

Nonequilibrium phase transitions play a pivotal role in broad physical contexts, from condensed matter to cosmology. Tracking the formation of nonequilibrium phases in condensed matter requires a resolution of the long-range cooperativity on ultra-short timescales. Here, we study the spontaneous transformation of a charge-density wave in CeTe3 from a stripe order into a bi-directional state inaccessible thermodynamically but is induced by intense laser pulses. With ≈100 fs resolution coherent electron diffraction, we capture the entire course of this transformation and show self-organization that defines a nonthermal critical point, unveiling the nonequilibrium energy landscape. We discuss the generation of instabilities by a swift interaction quench that changes the system symmetry preference, and the phase ordering dynamics orchestrated over a nonadiabatic timescale to allow new order parameter fluctuations to gain long-range correlations. Remarkably, the subsequent thermalization locks the remnants of the transient order into longer-lived topological defects for more than 2 ns.

Direct imaging of plasma waves using ultrafast electron microscopy.

A femtosecond plasma imaging modality based on a new development of ultrafast electron microscope is introduced. We investigated the laser-induced formation of high-temperature electron microplasmas and their subsequent non-equilibrium evolution. Based on a straightforward field imaging principle, we directly retrieve detailed information about the plasma dynamics, including plasma wave structures, particle densities, and temperatures. We discover that directly subjected to a strong magnetic field, the photo-generated microplasmas manifest in novel transient cyclotron echoes and form new wave states across a broad range of field strengths and different laser fluences. Intriguingly, the transient cyclotron waves morph into a higher frequency upper-hybrid wave mode with the dephasing of local cyclotron dynamics. The quantitative real-space characterizations of the non-equilibrium plasma systems demonstrate the feasibilities of a new microscope system in studying the plasma dynamics or transient electric fields with high spatiotemporal resolutions.

Proteomic analysis of Tianzhu White Yak (Bos grunniens) testis at different sexual developmental stages.

To explore the protein expression profiles of white yak (Bos grunniens) testis at different sexual developmental stages. The protein profiles of yak testis were determined using two-dimensional electrophoresis and the expression levels of 298 protein spots were analyzed. Mass spectrometry was performed to identify those significantly differential expressed proteins; Western blotting was used to confirm the results. During the developmental stages, 29 protein spots showed more than twofold differences (p < 0.05) at ≥1 time point and were successfully identified. Two proteins were upregulated with age (category 1), five proteins (17.2%) were downregulated with age (category 2), four proteins were upregulated before 4 years of age and downregulated thereafter (category 3), fifteen proteins were upregulated before 2 years of age and downregulated thereafter (category 4), and three proteins fluctuated with age (category 5). The expression patterns of regucalcin and heat shock 60 kDa protein in category 2 were confirmed. The 29 differentially expressed proteins from yak testes (some had more than one function) were categorized into binding (n = 15), catalytic activity (n = 13), molecular function regulator (n = 4), antioxidant (n = 4), molecular transducer (n = 2), transporter (n = 1), and structural molecule (n = 1). The identification and analysis of these testis proteins may assist in understanding the developmental biology of reproduction system in male yak.

The risk of missed abortion associated with the levels of tobacco, heavy metals and phthalate in hair of pregnant woman: A case control study in Chinese women.

To assess the association between exposure to the tobacco, heavy metals and phthalate on early pregnancy and missed abortion.42 women with missed abortion and 57 matched controls (women with normal pregnancies) were recruited between March and May 2012, from the Department of Gynecology and Obstetrics, First Affiliated Hospital of Guangxi Medical University and the People Hospital of Guangxi Zhuang Autonomous Region. The questionnaire survey was carried on to learn about the basic conditions, as well as smoking history of all participants. The levels of tobacco, heavy metal, and phthalate exposure were compared between the 2 groups by measuring nicotine, cocaine, cadmium (Cd), manganese (Mn), plumbum (Pb) and dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), di-2-ethyl hexyl phthalate (DEHP) in the hair samples.Out results showed that significant differences in age (P = .042), premarital examination (P = .041), passive smoking (P = .021), and heavy metal exposure (P = .022) were found in the case group compared to the control. In addition, the concentration of nicotine (P = .037), cotinine (P = .018), Cd (P = .01), Pb (P = .038) and DEHP (P = .001) in the hair were significantly higher in the case group. Furthermore, logistic analysis revealed that age [Odds Ratio (OR) 1.172, 95% confidence interval (CI) 1.036-1.327], Cd (OR 8.931, 95% CI 2.003-39.811), Cotinine (OR 4.376, 95% CI 1.159-16.531), DEHP (OR 1.863, 95% CI 1.103-3.146) were important factors contributing to the missed abortion (P < .05).It was demonstrated that high gestational age, passive smoking, heavy metals, and the phthalate exposure were the risk factors for missed abortion, while the premarital health examination was a protective factor. Avoiding these harmful substances before getting pregnant and during the early stages of pregnancy, might help prevent missed abortions.

The nature of photoinduced phase transition and metastable states in vanadium dioxide.

Photoinduced threshold switching processes that lead to bistability and the formation of metastable phases in photoinduced phase transition of VO2 are elucidated through ultrafast electron diffraction and diffusive scattering techniques with varying excitation wavelengths. We uncover two distinct regimes of the dynamical phase change: a nearly instantaneous crossover into an intermediate state and its decay led by lattice instabilities over 10 ps timescales. The structure of this intermediate state is identified to be monoclinic, but more akin to M2 rather than M1 based on structure refinements. The extinction of all major monoclinic features within just a few picoseconds at the above-threshold-level (~20%) photoexcitations and the distinct dynamics in diffusive scattering that represents medium-range atomic fluctuations at two photon wavelengths strongly suggest a density-driven and nonthermal pathway for the initial process of the photoinduced phase transition. These results highlight the critical roles of electron correlations and lattice instabilities in driving and controlling phase transformations far from equilibrium.

[Mechanisms of Phosphorus Removal by Modified Zeolites Substrates Coated with Zn-LDHs in Laboratory-scale Vertical-flow Constructed Wetlands].

Zn-Layered double hydroxides (LDHs) were selected to carry out the experiment in present work based on the previous research results. According to the co-precipitation method, three kinds of different Zn-LDHs (FeZn-LDHs, CoZn-LDHs and AlZn-LDHs) were synthesized by ZnCl2, FeCl3, AlCl3, and CoCl3 solution in alkaline conditions and Zn-LDHs were in-situ coated on the surface of natural zeolites. With the filling of the natural and three kinds of Zn-LDHs modified zeolites in the columns, test experiments were conducted to study the removal performance of phosphorus in vertical-flow constructed wetlands. The results showed that: compared with the natural zeolites, the removal rates of phosphorus by the three kinds of Zn-modified zeolites were greatly improved, especially for FeZn-LDHs. Moreover, the maximum adsorption capacity and the desorbed performance of phosphate were enhanced by the Zn-LDHs coated modification. The adsorption type of phosphate was converted from physical adsorption to chemical adsorption. Through reasonable selection of the type of zeolite and the method of modification, Zn-LDHs modified zeolites could be used to enhance the removal of nitrogen and phosphorus for the eutrophic water.

Exploration of metastability and hidden phases in correlated electron crystals visualized by femtosecond optical doping and electron crystallography.

Characterizing and understanding the emergence of multiple macroscopically ordered electronic phases through subtle tuning of temperature, pressure, and chemical doping has been a long-standing central issue for complex materials research. We report the first comprehensive studies of optical doping-induced emergence of stable phases and metastable hidden phases visualized in situ by femtosecond electron crystallography. The electronic phase transitions are triggered by femtosecond infrared pulses, and a temperature-optical density phase diagram is constructed and substantiated with the dynamics of metastable states, highlighting the cooperation and competition through which the macroscopic quantum orders emerge. These results elucidate key pathways of femtosecond electronic switching phenomena and provide an important new avenue to comprehensively investigate optical doping-induced transition states and phase diagrams of complex materials with wide-ranging applications.

Microwave-assisted extraction coupled with countercurrent chromatography for the rapid preparation of flavonoids from Scutellaria barbata D. Don.

As a famous Chinese herb having good inhibitory effects on numerous human cancers both in vitro and in vivo, Scutellaria barbata D. Don attracts extensive attention worldwide. In this work, four flavonoids named scutellarin, baicalin, luteolin, and apigenin were simply and rapidly prepared from S. barbata by microwave-assisted extraction coupled to countercurrent chromatography. Extraction conditions including irradiation time, extraction temperature, liquid/solid ratio, and microwave power were optimized using an orthogonal array design method. The extract of S. barbata was separated and purified with a two-phase solvent system composed of hexane/ethyl acetate/methanol/acetic acid/water (1:5:1.5:1:4, v/v/v/v/v) and 4.5 mg of scutellarin, 4.6 mg of baicalin, 1.1 mg of luteolin, 2.1 mg of apigenin were obtained from 2.0 g original sample in a single run. The purities of scutellarin, baicalin, luteolin, and apigenin determined by HPLC were 93.6, 97.3, 97.6, and 98.4%, respectively. The targeted compounds were identified by LC with MS and (1) H NMR spectroscopy. The total time including extraction, separation, and purification was <300 min. Compared to traditional methods, microwave-assisted extraction coupled to countercurrent chromatography method is more simple and rapid for the extraction, separation, and purification of flavonoid compounds from natural products.

Decoupling of structural and electronic phase transitions in VO2.

Using optical, TEM, and ultrafast electron diffraction experiments we find that single crystal VO(2) microbeams gently placed on insulating substrates or metal grids exhibit different behaviors, with structural and metal-insulator transitions occurring at the same temperature for insulating substrates, while for metal substrates a new monoclinic metal phase lies between the insulating monoclinic phase and the metallic rutile phase. The structural and electronic phase transitions in these experiments are strongly first order and we discuss their origins in the context of current understanding of multiorbital splitting, strong correlation effects, and structural distortions that act cooperatively in this system.

Electronically driven fragmentation of silver nanocrystals revealed by ultrafast electron crystallography.

We report an ultrafast electron diffraction study of silver nanocrystals under surface plasmon resonance excitation, leading to a concerted fragmentation. By examining simultaneously transient structural, thermal, and Coulombic signatures of the prefragmented state, an electronically driven nonthermal fragmentation scenario is proposed.

The development and applications of ultrafast electron nanocrystallography.

We review the development of ultrafast electron nanocrystallography as a method for investigating structural dynamics for nanoscale materials and interfaces. Its sensitivity and resolution are demonstrated in the studies of surface melting of gold nanocrystals, nonequilibrium transformation of graphite into reversible diamond-like intermediates, and molecular scale charge dynamics, showing a versatility for not only determining the structures, but also the charge and energy redistribution at interfaces. A quantitative scheme for 3D retrieval of atomic structures is demonstrated with few-particle (<1,000) sensitivity, establishing this nanocrystallographic method as a tool for directly visualizing dynamics within isolated nanomaterials with atomic scale spatio-temporal resolution.

Direct observation of optically induced transient structures in graphite using ultrafast electron crystallography.

We use ultrafast electron crystallography to study structural changes induced in graphite by a femtosecond laser pulse. At moderate fluences of < or =21 mJ/cm2, lattice vibrations are observed to thermalize on a time scale of approximately 8 ps. At higher fluences approaching the damage threshold, lattice vibration amplitudes saturate. Following a marked initial contraction, graphite is driven nonthermally into a transient state with sp3-like character, forming interlayer bonds. Using ab initio density functional calculations, we trace the governing mechanism back to electronic structure changes following the photoexcitation.

Dynamics of size-selected gold nanoparticles studied by ultrafast electron nanocrystallography.

We report the studies of ultrafast electron nanocrystallography on size-selected Au nanoparticles (2-20 nm) supported on a molecular interface. Reversible surface melting, melting, and recrystallization were investigated with dynamical full-profile radial distribution functions determined with subpicosecond and picometer accuracies. In an ultrafast photoinduced melting, the nanoparticles are driven to a nonequilibrium transformation, characterized by the initial lattice deformations, nonequilibrium electron-phonon coupling, and, upon melting, the collective bonding and debonding, transforming nanocrystals into shelled nanoliquids. The displasive structural excitation at premelting and the coherent transformation with crystal/liquid coexistence during photomelting differ from the reciprocal behavior of recrystallization, where a hot lattice forms from liquid and then thermally contracts. The degree of structural change and the thermodynamics of melting are found to depend on the size of nanoparticle.

Attention deficit and hyperactivity disorder tendency and unintentional injury among adolescents in China.

This study aims to investigate the association between ADD tendency, with or without hyperactivity, and all types of unintentional injuries among adolescents. This study was a population-based health survey utilising a two-stage random cluster sampling design. The study was conducted among high school students in Nanning, the capital city of the Guangxi Province, China. Subjects were recruited from the total population of adolescents who attended high school years 1, 2, and 3 with ages ranging from 13 to 17 years. Information on ADD was collected by trained health professional via personal interviews. Other information, including unintentional injury was collected via a self-report health survey questionnaire. One thousand and twenty-nine (n = 1429) students were recruited with 115 (7.9%) identified as having a high ADD tendency, and 340 (22.6%) reported as having experienced an injury in the last 3 months. After adjusting for other potential confounding factors, results from the logistic regression analyses indicated that adolescents who scored high on the ADD tendency had an increased risk of injury by about 70% as compared to those who scored low (OR = 1.68, 95%CI = 1.18-2.40). ADD tendency has been identified as a potential risk factor of injury among adolescents. Screening for risk factors can be considered as a potential preventive strategy.

Structures and dynamics of self-assembled surface monolayers observed by ultrafast electron crystallography.

In this communication, we report our first study of self-assembled adsorbates on metal surfaces. Specifically, we studied single-crystal clean surfaces of Au(111) with and without a monolayer of reaction involving the assembly of 2-mercaptoacetic acid from 2,2'-dithiodiacetic acid. We also studied monolayers of iron hemes. With ultrafast electron crystallography, we are able to observe and isolate structural dynamics of the substrate (gold) and adsorbate(s) following an ultrafast temperature jump.

Ultrafast electron crystallography of interfacial water.

We report direct determination of the structures and dynamics of interfacial water on a hydrophilic surface with atomic-scale resolution using ultrafast electron crystallography. On the nanometer scale, we observed the coexistence of ordered surface water and crystallite-like ice structures, evident in the superposition of Bragg spots and Debye-Scherrer rings. The structures were determined to be dominantly cubic, but each undergoes different dynamics after the ultrafast substrate temperature jump. From changes in local bond distances (OH.O and O.O) with time, we elucidated the structural changes in the far-from-equilibrium regime at short times and near-equilibration at long times.

Ultrafast electron crystallography: transient structures of molecules, surfaces, and phase transitions.

The static structure of macromolecular assemblies can be mapped out with atomic-scale resolution by using electron diffraction and microscopy of crystals. For transient nonequilibrium structures, which are critical to the understanding of dynamics and mechanisms, both spatial and temporal resolutions are required; the shortest scales of length (0.1-1 nm) and time (10(-13) to 10(-12) s) represent the quantum limit, the nonstatistical regime of rates. Here, we report the development of ultrafast electron crystallography for direct determination of structures with submonolayer sensitivity. In these experiments, we use crystalline silicon as a template for different adsorbates: hydrogen, chlorine, and trifluoroiodomethane. We observe the coherent restructuring of the surface layers with subangstrom displacement of atoms after the ultrafast heat impulse. This nonequilibrium dynamics, which is monitored in steps of 2 ps (total change