n-point amplitudes with a single negative-helicity graviton

An expression for the n-point one-loop graviton scattering amplitude with a singlenegative helicity external leg is constructed using an augmented recursion technique. We analyse the soft-limits ofthese amplitudes and demonstrate that they have soft behaviour beyond the conjectured universalbehaviour

New Trade Models, Same Old Gains?

Micro-level data have had a profound influence on research in international trade over the last ten years. In many regards, this research agenda has been very successful. New stylized facts have been uncovered and new trade models have been developed to explain these facts. In this paper we investigate to what extent answers to new micro-level questions have affected answers to an old and central question in the field: how large are the welfare gains from trade? A crude summary of our results is: "So far, not much." (JEL F11, F12)

Decomposition of halogenated nucleobases by surface plasmon resonance excitation of gold nanoparticles

Halogenated uracil derivatives are of great interest in modern cancer therapy, either as chemotherapeutics or radiosensitisers depending on their halogen atom. This work applies UV-Vis spectroscopy to study the radiation damage of uracil, 5-bromouracil and 5-fluorouracil dissolved in water in the presence of gold nanoparticles upon irradiation with an Nd:YAG ns-pulsed laser operating at 532 nm at different fluences. Gold nanoparticles absorb light efficiently by their surface plasmon resonance and can significantly damage DNA in their vicinity by an increase of temperature and the generation of reactive secondary species, notably radical fragments and low energy electrons. A recent study using the same experimental approach characterized the efficient laser-induced decomposition of the pyrimidine ring structure of 5-bromouracil mediated by the surface plasmon resonance of gold nanoparticles. The present results show that the presence of irradiated gold nanoparticles decomposes the ring structure of uracil and its halogenated derivatives with similar efficiency. In addition to the fragmentation of the pyrimidine ring, for 5-bromouracil the cleavage of the carbon-halogen bond could be observed, whereas for 5-fluorouracil this reaction channel was inhibited. Locally-released halogen atoms can react with molecular groups within DNA, hence this result indicates a specific mechanism by which doping with 5-bromouracil can enhance DNA damage in the proximity of laser irradiated gold nanoparticles. Graphical abstract

Kinetics of molecular decomposition under irradiation of gold nanoparticles with nanosecond laser pulses—A 5-Bromouracil case study

Laser illuminated gold nanoparticles (AuNPs) efficiently absorb light and heat up the surrounding medium, leading to versatile applications ranging from plasmonic catalysis to cancer photothermal therapy. Therefore, an in-depth understanding of the thermal, optical, and electron induced reaction pathways is required. Here, the electrophilic DNA nucleobase analog 5-Bromouracil (BrU) has been used as a model compound to study its decomposition in the vicinity of AuNPs illuminated with intense ns laser pulses under various conditions. The plasmonic response of the AuNPs and the concentration of BrU and resulting photoproducts have been tracked by ultraviolet and visible (UV–Vis) spectroscopy as a function of the irradiation time. A kinetic model has been developed to determine the reaction rates of two parallel fragmentation pathways of BrU, and their dependency on laser fluence and adsorption on the AuNP have been evaluated. In addition, the size and the electric field enhancement of the decomposed AuNPs have been determined by atomic force microscopy and finite domain time difference calculations, respectively. A minor influence of the direct photoreaction and a strong effect of the heating of the AuNPs have been revealed. However, due to the size reduction of the irradiated AuNPs, a trade-off between laser fluence and plasmonic response of the AuNPs has been observed. Hence, the decomposition of the AuNPs might be limiting the achievable temperatures under irradiation with several laser pulses. These findings need to be considered for an efficient design of catalytic plasmonic systems

Demonstrating predictive wavefront control with the Keck II near-infrared pyramid wavefront sensor

The success of ground-based instruments for high contrast exoplanet imaging depends on the degree to which adaptive optics (AO) systems can mitigate atmospheric turbulence. While modern AO systems typically suffer from millisecond time lags between wavefront measurement and control, predictive wavefront control (pWFC) is a means of compensating for those time lags using previous wavefront measurements, thereby improving the raw contrast in the post-coronagraphic science focal plane. A method of predictive control based on Empirical Orthogonal Functions (EOF) has previously been proposed and demonstrated on Subaru/SCExAO. In this paper we present initial tests of this method for application to the near-infrared pyramid wavefront sensor (PYWFS) recently installed in the Keck II AO system. We demonstrate the expected root-mean-square (RMS) wavefront error and contrast benefits of pWFC based on simulations, applying pWFC to on-sky telemetry data saved during commissioning of the PYWFS. We discuss how the performance varies as different temporal and spatial scales are included in the computation of the predictive filter. We further describe the implementation of EOF pWFC within the PYWFS dedicated real-time controller (RTC), and, via daytime testing at the observatory, we demonstrate the performance of pWFC in real time when pre-computed phase screens are applied to the deformable mirror (DM)