Appl. Sci.2014, 4(3), 318-330; doi:10.3390/app4030318 - published online 1 July 2014 Show/Hide Abstract
Abstract: We investigatefour-wave mixing in hydrogen gas using a gas cell and a hollow fiber for the generation of high-energy, multicolor femtosecond (fs) optical pulses. Both a hydrogen-filled gas cell and hollow fiber lead to the generation of multicolor fs pulses in a broad spectral range from the deep ultraviolet to the near infrared. However, there is a difference in the energy distribution of the multicolor emission between the gas cell and the hollow fiber. The hydrogen-filled gas cell generates visible pulses with higher energies than the pulses created by the hollow fiber. We have generated visible pulses with energies of several tens of microjoules. The hydrogen-filled hollow fiber, on the other hand, generates ultraviolet pulses with energies of a few microjoules, which are higher than the energies of the ultraviolet pulses generated in the gas cell. In both schemes, the spectral width of each emission line supports a transform-limited pulse duration shorter than 15 fs. Four-wave mixing in hydrogen gas therefore can be used for the development of a light source that emits sub-20 fs multicolor pulses in a wavelength region from the deep ultraviolet to the near infrared with microjoule pulse energies.
Appl. Sci.2014, 4(2), 305-317; doi:10.3390/app4020305 - published online 30 May 2014 Show/Hide Abstract
Abstract: A semi-classical electrodynamical model is derived to describe the electrical transport along graphene, based on the modified Boltzmann transport equation. The model is derived in the typical operating conditions predicted for future integrated circuits nano-interconnects, i.e., a low bias condition and an operating frequency up to 1 THz. A generalized non-local dispersive Ohm’s law is derived, which can be regarded as the constitutive equation for the material. The behavior of the electrical conductivity is studied with reference to a 2D case (the infinite graphene layer) and a 1D case (the graphene nanoribbons). The modulation effects of the nanoribbons’ size and chirality are highlighted, as well as the spatial dispersion introduced in the 2D case by the dyadic nature of the conductivity.
Appl. Sci.2014, 4(2), 282-304; doi:10.3390/app4020282 - published online 16 May 2014 Show/Hide Abstract
Abstract: Graphene is an ultimate membrane that mixes both flexibility and mechanical strength, together with many other remarkable properties. A good knowledge of the elastic properties of graphene is prerequisite to any practical application of it in nanoscopic devices. Although this two-dimensional material is only one atom thick, continuous-medium elasticity can be applied as long as the deformations vary slowly on the atomic scale and provided suitable parameters are used. The present paper aims to be a critical review on this topic that does not assume a specific pre-knowledge of graphene physics. The basis for the paper is the classical Kirchhoff-Love plate theory. It demands a few parameters that can be addressed from many points of view and fitted to independent experimental data. The parameters can also be estimated by electronic structure calculations. Although coming from diverse backgrounds, most of the available data provide a rather coherent picture that gives a good degree of confidence in the classical description of graphene elasticity. The theory can than be used to estimate, e.g., the buckling limit of graphene bound to a substrate. It can also predict the size above which a scrolled graphene sheet will never spontaneously unroll in free space.
Appl. Sci.2014, 4(2), 265-281; doi:10.3390/app4020265 - published online 16 May 2014 Show/Hide Abstract
Abstract: About 50% of the 1.4 GeV CERN (European Organization for Nuclear Research, www.cern.ch) protons are sent onto targets to produce radioactive beams by online mass separation at the Isotope Separator Online Device (ISOLDE) facility, for a wide range of studies in fundamental and applied physics. CERN-MEDICIS is a spin-off dedicated to R&D in life sciences and medical applications. It is located in an extension of the Class A building presently under construction. It will comprise laboratories to receive the irradiated targets from a new station located at the dump position behind the ISOLDE production targets. An increasing range of innovative isotopes will thus progressively become accessible from the start-up of the facility in 2015 onward; for fundamental studies in cancer research, for new imaging and therapy protocols in cell and animal models and for pre-clinical trials, possibly extended to specific early phase clinical studies up to Phase I trials. Five hundred megabecquerel isotope batches purified by electromagnetic mass separation combined with chemical methods will be collected on a weekly basis. A possible future upgrade with gigabecquerel pharmaceutical-grade i.e., current good manufacturing practices (cGMP) batch production capabilities is finally presented.
Appl. Sci.2014, 4(2), 255-264; doi:10.3390/app4020255 - published online 15 May 2014 Show/Hide Abstract
Abstract: We studied electromagnetic properties of pyrolytic carbon (PyC) films with thicknesses from 9 nm to 110 nm. The PyC films consisted of randomly oriented and intertwined graphene flakes with a typical size of a few nanometers were synthesized by chemical vapor deposition (CVD) at 1100 °C on a quartz substrate. The reflectance and transmittance of these films in Ka-band, 26–37 GHz, were studied both experimentally and theoretically. The discovered remarkably high absorption loss of up to 50% of incident power, along with chemical stability, makes PyC films attractive for electromagnetic (EM) interference shielding in space and airspace communication systems, as well as in portable electronic devices occupying this frequency slot. Since, in practical applications, the PyC film should be employed for coating of dielectric surfaces, two important issues to be addressed are: (i) which side (front or back) of the substrate should be covered to ensure maximum absorption losses; and (ii) the frequency dependence of absorbance/transmittance/reflectance of binary PyC/quartz structures in the Ka-band.
Appl. Sci.2014, 4(2), 240-254; doi:10.3390/app4020240 - published online 12 May 2014 Show/Hide Abstract
Abstract: Active and abandoned mines may present health risks, especially to children, from environmental exposure to airborne chemical elements, such as Pb, As, and Mn. X-ray fluorescence analysis of tailings at the Three Kids Mine show they contain high levels of: Pb (15,300 mg/kg), As (3690 mg/kg), and Mn (153,000 mg/kg). Soil was sampled along eight transects, radiating from the dried tailings ponds. Concentrations of Mn and Pb to the NE are at background concentrations at 4.8 km, and, As and Sr at 3.2 km from the mine. Going SW to the City of Henderson, all elements are at background at 1.6 cm, with the closest houses at 1.8 km. The United States Environmental Protection Agency (USEPA) Regional Screening Levels (RSLs) are exceeded for Pb, As and Mn at 0.8 km on all transects except one. The RSLs are exceeded for Pb, As and Mn on the NE transects at 1.6 km. Future home sites are on a NE transect between 0.4 km and 2.3 km downwind from the tailings ponds, in an area highly impacted by tailings which exceed the USEPA RSLs. This research demonstrates that there has been the farthest transport of tailings offsite by the prevailing winds to the NE; the closest currently-built homes have not received measurable tailings dust because they are upwind; and that precautions must be taken during the proposed remediation of the mine to restrict dust-transport of Pb, As, and Mn to avoid human exposure and ecological damage.