Spectral artifacts from non-uniform samples analyzed by terahertz time-domain spectroscopy.

We report the impact of the spatial coherence distortion on the measured absorption spectra and the identification of materials analyzed by terahertz time-domain spectroscopy. It is shown that the deformation of the terahertz beam wave front can result into the overestimation of the electromagnetic absorption, the generation of artificial absorption peaks and even to the disappearance of characteristic absorption peaks. Obtaining clear absorption spectra without artifacts is crucial for applications based on terahertz imaging and spectroscopy.

Cloud System Evolution in the Trades-CSET: Following the Evolution of Boundary Layer Cloud Systems with the NSF/NCAR GV.

The Cloud System Evolution in the Trades (CSET) study was designed to describe and explain the evolution of the boundary layer aerosol, cloud, and thermodynamic structures along trajectories within the north-Pacific trade-winds. The study centered on 7 round-trips of the NSF NCAR Gulfstream V (GV) between Sacramento, CA and Kona, Hawaii between 1 July and 15 August 2015. The CSET observing strategy was to sample aerosol, cloud, and boundary layer properties upwind from the transition zone over the North Pacific and to resample these areas two days later. GFS forecast trajectories were used to plan the outbound flight to Hawaii with updated forecast trajectories setting the return flight plan two days later. Two key elements of the CSET observing system were the newly developed HIAPER Cloud Radar (HCR) and the High Spectral Resolution Lidar (HSRL). Together they provided unprecedented characterizations of aerosol, cloud and precipitation structures that were combined with in situ measurements of aerosol, cloud, precipitation, and turbulence properties. The cloud systems sampled included solid stratocumulus infused with smoke from Canadian wildfires, mesoscale cloud-precipitation complexes, and patches of shallow cumuli in very clean environments. Ultra-clean layers observed frequently near the top of the boundary layer were often associated with shallow, optically thin, layered veil clouds. The extensive aerosol, cloud, drizzle and boundary layer sampling made over open areas of the Northeast Pacific along 2-day trajectories during CSET is unprecedented and will enable modeling studies of boundary layer cloud system evolution and the role of different processes in that evolution.

A DFT theoretical study of heats of formation and detonation properties of nitrogen-rich explosives.

We present density-functional theory predictions and analysis of some properties of synthesized high-nitrogen compounds 3,6-diazido-1,2,4,5-tetrazine (DiAT) and N-oxides of 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO) together with 3,6-di(hydrazino)-1,2,4,5-tetrazine (DHT) and 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAAT) for which experimental data are available. In this work the reference molecules DHT and DAAT have been studied in order to validate the theoretical approach and facilitate further progress developments for the molecules of interest such as DiAT and DAATO. Geometries of all compounds have been optimized employing the B3LYP density-functional method in conjunction with 6-311++G(3d,3p) basis sets. The energy content of the molecules in the gas phase is evaluated by calculating standard enthalpies of formation, using isodesmic reaction paths. We also include estimates of the condensed-phase heats of formation and heats of sublimation in the framework of the Politzer approach. The obtained results show that DiAT compound has the highest heat of formation (231 kcal/mol) in comparison with those of DHT, DAAT and DAATO molecules. The detonation velocity and pressure have also been estimated for these molecules using the Stine method.

Nanoscale high energetic materials: a polymeric nitrogen chain N(8) confined inside a carbon nanotube.

We present a theoretical study of a new hybrid material, nanostructured polymeric nitrogen, where a polymeric nitrogen chain is encapsulated in a carbon nanotube. The electronic and structural properties of the new system are studied by means of ab initio electronic structure and molecular dynamics calculations. Finite temperature simulations demonstrate the stability of this nitrogen phase at ambient pressure and room temperature using carbon nanotube confinement. This nanostructured confinement may open a new path towards stabilizing polynitrogen or polymeric nitrogen at ambient conditions.