The quantum mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs and of sufficient intensity to interact with their target with high probability.Probing these dynamics with atomic-site specificity requires the extension of sub-femtosecond pulses to the soft X-ray spectral region. Here we report the generation of isolated GW-scale soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energy that is six orders of magnitude larger than any other source of isolated attosecond pulses in the soft X-ray spectral region, with a peak power in the tens of gigawatts. This unique combination of high intensity, high photon energy and short pulse duration enables the investigation of electron dynamics with X-ray non-linear spectroscopy and single-particle imaging.their assistance in designing, constructing and installing the XLEAP wiggler. We also acknowledge the SLAC Accelerator Operations group, and the Mechanical and Electrical engineering divisions of the SLAC Accelerator Directorate, especially

This paper contributes to cross-lingual image annotation and retrieval in terms of data and baseline methods. We propose COCO-CN, a novel dataset enriching MS-COCO with manually written Chinese sentences and tags. For more effective annotation acquisition, we develop a recommendationassisted collective annotation system, automatically providing an annotator with several tags and sentences deemed to be relevant with respect to the pictorial content. Having 20,342 images annotated with 27,218 Chinese sentences and 70,993 tags, COCO-CN is currently the largest Chinese-English dataset that provides a unified and challenging platform for cross-lingual image tagging, captioning and retrieval. We develop conceptually simple yet effective methods per task for learning from crosslingual resources. Extensive experiments on the three tasks justify the viability of the proposed dataset and methods. Data and code are publicly available at https://github.com/li-xirong/coco-cn.

W 18 O 49 nanowires were synthesized by a high-temperature physical evaporation technique. The structure, morphology, and composition of the nanowires were characterized by SEM, EMPA, XRD, XPS, and HRTEM techniques. The intrinsic Raman spectrum of W 18 O 49 nanowires was obtained, and the effect of laser power on the change of their structure was also studied. W 18 O 49 nanowires were first oxidized to tungsten trioxide nanowires under irradiation of a certain laser power, and then the tungsten trioxide nanowires underwent a phase transition from monoclinic to orthorhombic with increasing laser power; this phase transition was reversible on turning down the laser power.

Precise fabrication of subtle nanogaps amid individual nanoparticles or between adjacent ones to obtain the highest SERS enhancement is still a challenge. Here, we reported a novel approach for fabricating core-shell-satellite 3D magnetic microspheres (CSSM), that easily form a porous 1.5 nm PEI interlayer to accommodate molecules and create sufficient hotspots between the inner Fe3O4@Ag core and outer assembled Au@Ag satellites. Experiments and finite-difference time-domain (FDTD) simulation demonstrated that the enhancement factor (EF) was about 2.03 × 10(8) and 6.25 × 10(6), respectively. In addition, the micro-scale magnetic core endowed the CSSM with a superior magnetic nature, which enabled easy separation and further enhanced Raman signals due to enrichment of targeted analytes and abundant interparticle hotspots created by magnetism-induced aggregation. Our results further demonstrated that the CSSM is expected to be a versatile SERS substrate, which has been verified by the detection of the adsorbed pesticide thiram and the non-adsorbed pesticide paraquat with a detection limit as low as 5 × 10(-12) M and 1 × 10(-10) M, respectively. The novel CSSM can overcome the long-standing limitations of SERS for the trace characterization of various analytes in different solutions and promises to transform SERS into a practical analytical technique.

The fabrication of an ideal noble metal modified magnetic microsphere as high performance SERS substrate that possesses good dispersibility, strong magnetic responsiveness, and high sensitivity is still a challenge. Herein, we reported a novel route to fabricating Ag-coated magnetic core-shell microspheres (Fe 3 O 4 @PEI@Ag) with most of the desired advantages by using polyethyleneimine (PEI) as an interlayer. The size and coverage level of the Ag-NPs shell on Fe 3 O 4 @PEI@Ag microspheres were easily controlled by varying the amount of AgNO 3 .Meanwhile, the magnetic core endowed the Fe 3 O 4 @PEI@Ag microspheres with superior magnetic nature, which enabled convenient separation and further enhanced Raman signals due to enrichment of targeted analytes and abundant interparticle hotspots created by magnetism-induced aggregation. Considering these features, the Fe 3 O 4 @PEI@Ag is expected to be a versatile SERS substrate, which was verified by the detection of adsorbed PATP molecules and human IgG with a detection limit as low as 10 -11 M and 10 -14 g/mL, respectively. Therefore, the novel Fe 3 O 4 @PEI@Ag microsphere has an enormous potential for practical SERS detection applications, especially in the target protein quantitative detection field.Surface-enhanced Raman scattering (SERS) is a powerful fingerprint vibrational spectroscopy with high sensitivity, and it is widely used in biochemical detection, analytical chemistry, environment monitoring and biological sensing. 1-3 All these applications are based on proper utilization of "free-electron-like" metal materials, such as Au, Ag, and Cu, and only these noble metal structures with rough surface can provide obvious SERS effect. 4 Therefore, the key of its prominent application lies in fabricating high performance SERS substrates. So far, researchers have fabricated many SERS substrates, among which metal film over periodic nanostructure and Au/Ag colloids in suspension are extensively utilized. 5 The periodic nanostructure can achieve well sensitivity and high reproducibility, but has disadvantages of high cost and difficult to be further chemically modified. Au/Ag colloidal nanoparticles are more efficient with flexible control over individual geometry, easy to mass fabricate, and have good biocompatibility. 6 However, the drawbacks of Au/Ag colloid substrates are their limited enhancement ability and poor stability. 7 Therefore, a reliable and practical SERS substrate with high sensitivity is still a challenge. It should be noted that, up to now, the main problem of SERS detection is that it is difficult to conduct quantitative analysis and hard to apply in the complex system only depend on the noble metal SERS substrate itself.Magnetic microspheres have been extensively investigated for various applications. 8 Due to their excellent magnetic responsiveness, magnetic microspheres can assist in convenient recycling of novel metals, magnetic enrichment of analytes and rapid separation from reaction system. 9, 10 Recently, noble metal modified magnetic micro...

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Experiments using a THz pump and an X-ray probe at an X-ray free-electron laser (XFEL) facility like the Linac Coherent Light Source II (LCLS II) require frequency-tunable (3 to 20 THz), narrow bandwidth (∼10%), carrier-envelope-phase-stable THz pulses that produce high fields (>1 MV cm−1) at the repetition rate of the X-rays and are well synchronized with them. In this paper, a two-bunch scheme to generate THz radiation at LCLS II is studied: the first bunch produces THz radiation in an electromagnet wiggler immediately following the LCLS II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in THz transport. The two-bunch beam dynamics, the THz wiggler and radiation are described, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.

A method for grafting ethylenediamine to a magnetic graphene oxide composite (EDA-GO@Fe3O4) was developed for Cr(VI) decontamination. The physicochemical properties of EDA-GO@Fe3O4 were characterized using HRTEM, EDS, FT-IR, TG-DSC, and XPS. The effects of pH, sorbent dose, foreign anions, time, Cr(VI) concentration, and temperature on decontamination process were studied. The solution pH can largely affect the decontamination process. The pseudo-second-order model is suitable for being applied to fit the adsorption processes of Cr(VI) with GO@Fe3O4 and EDA-GO@Fe3O4. The intra-particle diffusion is not the rate-controlling step. Isotherm experimental data can be described using the Freundlich model. The effects of multiple factors on the Cr(VI) decontamination was investigated by a 25−1 fractional factorial design (FFD). The adsorption process can significantly be affected by the main effects of A (pH), B (Cr(VI) concentration), and E (Adsorbent dose). The combined factors of AB (pH × Cr(VI) concentration), AE (pH × Adsorbent dose), and BC (Cr(VI) concentration × Temperature) had larger effects than other factors on Cr(VI) removal. These results indicated that EDA-GO@Fe3O4 is a potential and suitable candidate for treatment of heavy metal wastewater.