Tailored nano-antennas for directional Raman studies of individual carbon nanotubes

We exploit the near field enhancement of nano-antennas to investigate the Raman spectra of otherwise not optically detectable carbon nanotubes (CNTs). We demonstrate that a top-down fabrication approach is particularly promising when applied to CNTs, owing to the sharp dependence of the scattered intensity on the angle between incident light polarization and CNT axis. In contrast to tip enhancement techniques, our method enables us to control the light polarization in the sample plane, locally amplifying and rotating the incident field and hence optimizing the Raman signal. Such promising features are confirmed by numerical simulations presented here. The relative ease of fabrication and alignment makes this technique suitable for the realization of integrated devices that combine scanning probe, optical, and transport characterization

Identification of excitons, trions and biexcitons in single-layer WS2

Single-layer WS$_2$ is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS$_2$, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission.Comment: 6 pages, 5 figure

Sepsis-Induced Immunosuppression in Neonates

Neonates, especially those born preterm, are at increased risk of sepsis and adverse long-term effects associated with infection-related inflammation. Distinct neonatal immune responses and dysregulated inflammation are central to this unique susceptibility. The traditional separation of sepsis into an initial hyper-inflammatory response followed by hypo-inflammation is continually under review with new developments in this area of research. There is evidence to support the association of mortality in the early acute phase of sepsis with an overwhelming hyper-inflammatory immune response. Emerging evidence from adults suggests that hypo- and hyper-inflammation can occur during any phase of sepsis and that sepsis-immunosuppression is associated with increased mortality, morbidity, and risk to subsequent infection. In adults, sepsis-induced immunosuppression (SII) is characterised by alterations of innate and adaptive immune responses, including, but not limited to, a prominent bias toward anti-inflammatory cytokine secretion, diminished antigen presentation to T cells, and reduced activation and proliferation of T cells. It is unclear if sepsis-immunosuppression also plays a role in the adverse outcomes associated with neonatal sepsis. This review will focus on exploring if key characteristics associated with SII in adults are observed in neonates with sepsis

SimStack: An Intuitive Workflow Framework

Establishing a fundamental understanding of the nature of materials via computational simulation approaches requires knowledge from different areas, including physics, materials science, chemistry, mechanical engineering, mathematics, and computer science. Accurate modeling of the characteristics of a particular system usually involves multiple scales and therefore requires the combination of methods from various fields into custom-tailored simulation workflows. The typical approach to developing patch-work solutions on a case-to-case basis requires extensive expertise in scripting, command-line execution, and knowledge of all methods and tools involved for data preparation, data transfer between modules, module execution, and analysis. Therefore multiscale simulations involving state-of-the-art methods suffer from limited scalability, reproducibility, and flexibility. In this work, we present the workflow framework SimStack that enables rapid prototyping of simulation workflows involving modules from various sources. In this platform, multiscale- and multimodule workflows for execution on remote computational resources are crafted via drag and drop, minimizing the required expertise and effort for workflow setup. By hiding the complexity of high-performance computations on remote resources and maximizing reproducibility, SimStack enables users from academia and industry to combine cutting-edge models into custom-tailored, scalable simulation solutions

Closing the global radiocarbon budget 1945-2005

The global radiocarbon cycle of the last 60 years was simulated with the Global RAdioCarbon Exploration Model (GRACE). The total radiocarbon production by atmospheric nuclear bomb tests was determined using available stratospheric and tropospheric radiocarbon (14C) observations as constraints. To estimate the range of uncertainty in the explosive force of atmospheric nuclear bomb tests and their respective 14C yield factor, we applied different published bomb test compilations. Furthermore, to account for a possible small bias in the available stratospheric excess radiocarbon observations, we tested the different bomb test compilations with both uncorrected and corrected stratospheric 14C observations. For each of these scenarios of the total bomb 14C burden, the model simulated the distribution of excess radiocarbon among the stratosphere, troposphere, biosphere, and ocean carbon reservoirs. With a global bomb 14C production of 598—632*10^26 atoms (99-105 kmol) 14C between 1945 and 1980, simulated excess radiocarbon inventories are in good agreement with all available stratospheric and tropospheric radiocarbon observations as well as with the latest estimates of the ocean excess radiocarbon inventories during the GEOSECS and WOCE surveys from Peacock (2004) and Key et al. (2004). For the very first time, our model is thus capable of closing the excess radiocarbon budget on the basis of our current knowledge of exchange rates and reservoir sizes in the global carbon system

Multiscale Simulation of Photoluminescence Quenching in Phosphorescent OLED Materials

Bimolecular exciton-quenching processes such as triplet–triplet annihilation (TTA) and triplet–polaron quenching play a central role in phosphorescent organic light-emitting diode (PhOLED) device performance and are, therefore, an essential component in computational models. However, the experiments necessary to determine microscopic parameters underlying such processes are complex and the interpretation of their results is not straightforward. Here, a multiscale simulation protocol to treat TTA is presented, in which microscopic parameters are computed with ab initio electronic structure methods. With this protocol, virtual photoluminescence experiments are performed on a prototypical PhOLED emission material consisting of 93 wt% of 4,4ʹ,4ʺ-tris(N-carbazolyl)triphenylamine and 7 wt% of the green phosphorescent dye fac-tris(2-phenylpyridine)iridium. A phenomenological TTA quenching rate of 8.5 × 10$^{-12}$ cm$^{3}$ s$^{-1}$, independent of illumination intensity, is obtained. This value is comparable to experimental results in the low-intensity limit but differs from experimental rates at higher intensities. This discrepancy is attributed to the difficulties in accounting for fast bimolecular quenching during exciton generation in the interpretation of experimental data. This protocol may aid in the experimental determination of TTA rates, as well as provide an order-of-magnitude estimate for device models containing materials for which no experimental data are available