26 research outputs found
Threshold Resummation for Dark-Matter Production at the LHC
We derive precision predictions for the production of dark-matter particles
recoiling against a jet with large transverse momentum at the LHC. The
dark-matter fermions are described within a simplified model and couple to the
Standard Model via a vector mediator. Our predictions for the mono-jet
signature include the resummation of the leading and next-to-leading threshold
logarithms. The corresponding matching coefficient is evaluated at NLO. The
resummed result is matched to the fixed-order NLO cross section obtained from
the MadGraph framework. We discuss numerical results for several benchmark
scenarios at the LHC.Comment: 19 pages, 3 figure
A Bigraph Relational Model
In this paper, we present a model based on relations for bigraphical reactive
systems [Milner09]. Its defining characteristics are that validity and reaction
relations are captured as traces in a multi-set rewriting system. The
relational model is derived from Milner's graphical definition and directly
amenable to implementation.Comment: In Proceedings LFMTP 2011, arXiv:1110.668
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
Electroluminescence of copper-nitride nanocrystals
Nanocrystals can behave as quantum boxes with confined electronic states
governing their optoelectronic properties. The formation of nanometer-size
crystals of copper nitride (Cu3N) grown by nitrogen sputtering of a Cu(110)
surface is reported. Scanning tunneling spectroscopy shows that the
nanocrystals exhibit a series of well-defined sharp electronic resonances,
which correspond to confined free-electron-like states. We observe that
electrons from a scanning tunneling microscope tip induce the emission of
light with a larger efficiency than on the bare metal surface. The spectral
analysis of the emitted photons reveals various radiative inelastic pathways
enabled by the confined states, which explain the enhanced light emission.
Thus, the Cu3N nanocrystals can be employed as nanometer-size light sources
Poly(ionic liquid) nanovesicles via polymerization induced self-assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction
Herein, we report a straightforward, scalable synthetic route towards poly(ionic liquid) (PIL) homopolymer nanovesicles (NVs) with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one-step free radical polymerization induced self-assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs’ internal morphology is studied in detail by coarse-grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra-small (1 ∼ 3 nm in size) copper nanoparticles (CuNPs) and employed as electrocatalysts for CO2 electroreduction. The composite electrocatalysts exhibit a 2.5-fold enhancement in selectivity towards C1 products (e.g., CH4), compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO2 conversion to C1 products
Poly(ionic liquid) nanovesicles via polymerization induced self-assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction
Herein, we report a straightforward, scalable synthetic route towards poly(ionic liquid) (PIL) homopolymer nanovesicles (NVs) with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one-step free radical polymerization induced self-assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs’ internal morphology is studied in detail by coarse-grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra-small (1 ∼ 3 nm in size) copper nanoparticles (CuNPs) and employed as electrocatalysts for CO2 electroreduction. The composite electrocatalysts exhibit a 2.5-fold enhancement in selectivity towards C1 products (e.g., CH4), compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO2 conversion to C1 products
26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017
This work was produced as part of the activities of FAPESP Research,\ud
Disseminations and Innovation Center for Neuromathematics (grant\ud
2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud
FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud
supported by a CNPq fellowship (grant 306251/2014-0)
Photon Fragmentation in the Antenna Subtraction Formalism
The theoretical description of photon production at particle colliders
combines direct photon radiation and fragmentation processes, which can not be
separated from each other for definitions of photon isolation used in
experimental measurements. The theoretical description of these processes must
account for collinear parton-photon configurations, retaining the dependence on
the photon momentum fraction, and includes the parton-to-photon fragmentation
functions. We extend the antenna subtraction method to include photon
fragmentation processes up to next-to-next-to-leading order (NNLO) in QCD.
Collinear photon radiation is handled using newly introduced fragmentation
antenna functions and associated phase space mappings. We derive the integrated
forms of the fragmentation antenna functions and describe their interplay with
the mass factorisation of the photon fragmentation functions. The construction
principles of antenna subtraction terms up to NNLO for identified photons are
outlined, thereby enabling the application of the method to different photon
production processes at colliders.Comment: 47 pages, 1 figure, 1 table, two ancillary files with the expressions
for the NNLO fragmentation antenna functions enclosed, typos corrected,
journal versio