Time-Resolved Single-Particle X-ray Scattering Reveals Electron-Density Gradients As Coherent Plasmonic-Nanoparticle-Oscillation Source.

Dynamics of optically excited plasmonic nanoparticles are presently understood as a series of scattering events involving the initiation of nanoparticle breathing oscillations. According to established models, these are caused by statistical heat transfer from thermalized electrons to the lattice. An additional contribution by hot-electron pressure accounts for phase mismatches between theory and experimental observations. However, direct experimental studies resolving the breathing-oscillation excitation are still missing. We used optical transient-absorption spectroscopy and time-resolved single-particle X-ray diffractive imaging to access the electron system and lattice. The time-resolved single-particle imaging data provided structural information directly on the onset of the breathing oscillation and confirmed the need for an additional excitation mechanism for thermal expansion. We developed a new model that reproduces all of our experimental observations. We identified optically induced electron density gradients as the initial driving source.

Three-dimensional femtosecond snapshots of isolated faceted nanostructures.

The structure and dynamics of isolated nanosamples in free flight can be directly visualized via single-shot coherent diffractive imaging using the intense and short pulses of x-ray free-electron lasers. Wide-angle scattering images encode three-dimensional (3D) morphological information of the samples, but its retrieval remains a challenge. Up to now, effective 3D morphology reconstructions from single shots were only achieved via fitting with highly constrained models, requiring a priori knowledge about possible geometries. Here, we present a much more generic imaging approach. Relying on a model that allows for any sample morphology described by a convex polyhedron, we reconstruct wide-angle diffraction patterns from individual silver nanoparticles. In addition to known structural motives with high symmetries, we retrieve imperfect shapes and agglomerates that were not previously accessible. Our results open unexplored routes toward true 3D structure determination of single nanoparticles and, ultimately, 3D movies of ultrafast nanoscale dynamics.

Single-shot ptychography at a soft X-ray free-electron laser.

In this work, single-shot ptychography was adapted to the XUV range and, as a proof of concept, performed at the free-electron laser FLASH at DESY to obtain a high-resolution reconstruction of a test sample. Ptychography is a coherent diffraction imaging technique capable of imaging extended samples with diffraction-limited resolution. However, its scanning nature makes ptychography time-consuming and also prevents its application for mapping of dynamical processes. Single-shot ptychography can be realized by collecting the diffraction patterns of multiple overlapping beams in one shot and, in recent years, several concepts based on two con-focal lenses were employed in the visible regime. Unfortunately, this approach cannot be extended straightforwardly to X-ray wavelengths due to the use of refractive optics. Here, a novel single-shot ptychography setup utilizes a combination of X-ray focusing optics with a two-dimensional beam-splitting diffraction grating. It facilitates single-shot imaging of extended samples at X-ray wavelengths.

Characterization of the Percival detector with soft X-rays.

In this paper the back-side-illuminated Percival 2-Megapixel (P2M) detector is presented, along with its characterization by means of optical and X-ray photons. For the first time, the response of the system to soft X-rays (250 eV to 1 keV) is presented. The main performance parameters of the first detector are measured, assessing the capabilities in terms of noise, dynamic range and single-photon discrimination capability. Present limitations and coming improvements are discussed.

Relativistic and resonant effects in the ionization of heavy atoms by ultra-intense hard X-rays.

An accurate description of the interaction of intense hard X-ray pulses with heavy atoms, which is crucial for many applications of free-electron lasers, represents a hitherto unresolved challenge for theory because of the enormous number of electronic configurations and relativistic effects, which need to be taken into account. Here we report results on multiple ionization of xenon atoms by ultra-intense (about 1019 W/cm2) femtosecond X-ray pulses at photon energies from 5.5 to 8.3 keV and present a theoretical model capable of reproducing the experimental data in the entire energy range. Our analysis shows that the interplay of resonant and relativistic effects results in strongly structured charge state distributions, which reflect resonant positions of relativistically shifted electronic levels of highly charged ions created during the X-ray pulse. The theoretical approach described here provides a basis for accurate modeling of radiation damage in hard X-ray imaging experiments on targets with high-Z constituents.

Rapid sample delivery for megahertz serial crystallography at X-ray FELs.

Liquid microjets are a common means of delivering protein crystals to the focus of X-ray free-electron lasers (FELs) for serial femtosecond crystallography measurements. The high X-ray intensity in the focus initiates an explosion of the microjet and sample. With the advent of X-ray FELs with megahertz rates, the typical velocities of these jets must be increased significantly in order to replenish the damaged material in time for the subsequent measurement with the next X-ray pulse. This work reports the results of a megahertz serial diffraction experiment at the FLASH FEL facility using 4.3 nm radiation. The operation of gas-dynamic nozzles that produce liquid microjets with velocities greater than 80 m s-1 was demonstrated. Furthermore, this article provides optical images of X-ray-induced explosions together with Bragg diffraction from protein microcrystals exposed to trains of X-ray pulses repeating at rates of up to 4.5 MHz. The results indicate the feasibility for megahertz serial crystallography measurements with hard X-rays and give guidance for the design of such experiments.

CAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump-probe experiments at the FLASH free-electron laser.

The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump-probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning.

Spatial patterns of Anchoveta (Engraulis ringens) eggs and larvae in relation to pCO2 in the Peruvian upwelling system.

Large and productive fisheries occur in regions experiencing or projected to experience ocean acidification. Anchoveta (Engraulis ringens) constitute the world's largest single-species fishery and live in one of the ocean's highest pCO2 regions. We investigated the relationship of the distribution and abundance of Anchoveta eggs and larvae to natural gradients in pCO2 in the Peruvian upwelling system. Eggs and larvae, zooplankton, and data on temperature, salinity, chlorophyll a and pCO2 were collected during a cruise off Peru in 2013. pCO2 ranged from 167-1392 µatm and explained variability in egg presence, an index of spawning habitat. Zooplankton abundance explained variability in the abundance of small larvae. Within the main spawning and larva habitats (6-10°S), eggs were found in cool, low-salinity, and both extremely low (less than 200 µatm) and high (more than 900 µatm) pCO2 waters, and larvae were collected in warmer, higher salinity, and moderate (400-600 µatm) pCO2 waters. Our data support the hypothesis that Anchoveta preferentially spawned at high pCO2 and these eggs had lower survival. Enhanced understanding of the influence of pCO2 on Anchoveta spawning and larva mortality, together with pCO2 measurements, may enable predictions of ocean acidification effects on Anchoveta and inform adaptive fisheries management.

Satisfação no Trabalho dos Policiais Militares do Rio Grande do Sul: um Estudo Quantitativo / Job Satisfaction of the Rio Grande do Sul Military Policemen: a Quantitative Study / Satisfacción en el Trabajo de los Policías Militares de Rio Grande do Sul: un Estudio Cuantitativo

Resumo Satisfação no Trabalho pode ser entendida como o vínculo afetivo do indivíduo com seu ambiente laboral. A profissão de policial militar é considerada de alto risco, pois ele lida constantemente com a violência, a brutalidade e a morte. Frente a este contexto, esse estudo foi desenvolvido visando identificar o grau de Satisfação no Trabalho dos policiais militares do Rio Grande do Sul. Realizou-se uma pesquisa descritiva, do tipo survey, com abordagem quantitativa. Os participantes do estudo totalizaram 519 policiais militares pertencentes a quartéis de cidades localizadas no estado do Rio Grande do Sul. A Escala de Satisfação no Trabalho (EST) foi utilizada como instrumento de pesquisa. No geral, identificou-se que os policiais tendem a sinalizar insatisfação em relação ao trabalho. Dentre as dimensões que compõe a EST, tendem a sinalizar insatisfação em relação ao salário (média: 2,79) e com as promoções (média: 3,03); indiferença (nem satisfeitos e nem insatisfeitos) em relação à chefia (média: 4,42) e à natureza do trabalho (média: 4,37); e, por fim, sinalizam tendência à satisfação em relação aos colegas (média: 5,00). Espera-se com essas evidências contribuir para as futuras decisões organizacionais que impliquem na saúde dos policiais militares e consequente qualidade de vida, da equipe e seus familiares....(AU)

Abstract Job Satisfaction can be understood as the emotional bond of individuals with their work environment (Siqueira, 2008). The military police profession is considered a high risk one because military policemen constantly deal with violence, brutality and death (Costa, Accioly, Oliveira & Maia, 2007). Given this context, this study was developed to identify Rio Grande do Sul military policemen’s degree of satisfaction in their work. We conducted a descriptive research, survey type, with a quantitative approach. 519 military police belonging to cities barracks located in the state of Rio Grande do Sul participated. Siqueira’s (2008) Satisfaction Scale at Work (EST) was used as a research tool. Overall, it was identified that policemen tend to signal dissatisfaction with work. Among the dimensions that make up the EST, they tend to signal dissatisfaction with salary (mean: 2.79) and promotions (mean: 3.03); indifference (neither satisfied nor dissatisfied) in relation to leadership (mean: 4.42) and the nature of work (mean: 4.37); and finally, they tend to signal satisfaction with colleagues (mean: 5.00). We hope that this evidence contributes to future organizational decisions involving a better health of the military policemen and, subsequently, a better quality of life, for both the team and their families....(AU)

Resumen La satisfacción en el trabajo puede ser entendida como el vínculo emocional del individuo con su entorno de trabajo (Smith, 2008). La profesión de policía militar se considera de alto riesgo porque tiene que ver constantemente con la violencia, la brutalidad y la muerte (Costa, Accioly, Oliveira & Maia, 2007). Teniendo en cuenta este contexto, el presente estudio fue desarrollado para identificar el grado de satisfacción en el trabajo de los policías militares de Rio Grande do Sul. Se realizó una investigación descriptiva, tipo encuesta, con un enfoque cuantitativo. Los participantes del estudio fueron 519 policías militares pertenecientes a cuarteles de ciudades ubicadas en el estado de Rio Grande do Sul. La Escala de Satisfacción en el Trabajo (EST) de Siqueira (2008) fue utilizada como herramienta de investigación. En general, se identificó que los policías tienden a indicar insatisfacción con el trabajo. Entre las dimensiones que conforman la EST, las que tienden a indicar insatisfacción son el salario (media: 2,79) y los ascensos (media: 3,03); las que tienden a indicar indiferencia (ni satisfecho ni insatisfecho) son la jefatura (media: 4,42) y la naturaleza del trabajo (media: 4,37); y, finalmente, la que tiende a indicar satisfacción es respecto a los colegas (media: 5,00). Se espera que esta evidencia contribuya a futuras decisiones organizacionales que tengan un impacto en la salud de los policías militares y en la consiguiente calidad de vida, del equipo y de sus familiares....(AU)

Detector developments at DESY.

With the increased brilliance of state-of-the-art synchrotron radiation sources and the advent of free-electron lasers (FELs) enabling revolutionary science with EUV to X-ray photons comes an urgent need for suitable photon imaging detectors. Requirements include high frame rates, very large dynamic range, single-photon sensitivity with low probability of false positives and (multi)-megapixels. At DESY, one ongoing development project - in collaboration with RAL/STFC, Elettra Sincrotrone Trieste, Diamond, and Pohang Accelerator Laboratory - is the CMOS-based soft X-ray imager PERCIVAL. PERCIVAL is a monolithic active-pixel sensor back-thinned to access its primary energy range of 250 eV to 1 keV with target efficiencies above 90%. According to preliminary specifications, the roughly 10 cm × 10 cm, 3.5k × 3.7k monolithic sensor will operate at frame rates up to 120 Hz (commensurate with most FELs) and use multiple gains within 27 µm pixels to measure 1 to ∼100000 (500 eV) simultaneously arriving photons. DESY is also leading the development of the AGIPD, a high-speed detector based on hybrid pixel technology intended for use at the European XFEL. This system is being developed in collaboration with PSI, University of Hamburg, and University of Bonn. The AGIPD allows single-pulse imaging at 4.5 MHz frame rate into a 352-frame buffer, with a dynamic range allowing single-photon detection and detection of more than 10000 photons at 12.4 keV in the same image. Modules of 65k pixels each are configured to make up (multi)megapixel cameras. This review describes the AGIPD and the PERCIVAL concepts and systems, including some recent results and a summary of their current status. It also gives a short overview over other FEL-relevant developments where the Photon Science Detector Group at DESY is involved.

Suppressing bacterial interaction with copper surfaces through graphene and hexagonal-boron nitride coatings.

Understanding biological interaction with graphene and hexagonal-boron nitride (h-BN) membranes has become essential for the incorporation of these unique materials in contact with living organisms. Previous reports show contradictions regarding the bacterial interaction with graphene sheets on metals. Here, we present a comprehensive study of the interaction of bacteria with copper substrates coated with single-layer graphene and h-BN. Our results demonstrate that such graphitic coatings substantially suppress interaction between bacteria and underlying Cu substrates, acting as an effective barrier to prevent physical contact. Bacteria do not "feel" the strong antibacterial effect of Cu, and the substrate does not suffer biocorrosion due to bacteria contact. Effectiveness of these systems as barriers can be understood in terms of graphene and h-BN impermeability to transfer Cu(2+) ions, even when graphene and h-BN domain boundary defects are present. Our results seem to indicate that as-grown graphene and h-BN films could successfully protect metals, preventing their corrosion in biological and medical applications.