Atmospheric Attenuation Analysis in Indoor THz Communication Channels

In this paper, we study the terahertz (THz) transmission channels from 100 GHz (0.1 THz) to 1000 GHz (1 THz) by including the effects of frequency-dependent atmospheric attenuation and diffuse reflection (non-specular scattering) due to surface roughness for short-range indoor wireless communications. First and foremost, the ITU-R Rec. P. 676-8 model has been used for this study to compute the effects of water-vapor content in the atmosphere by demonstrating the multipath channel transfer function (CTF) dynamics for line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios in a simple realistic office environment. Then, the indoor multipath propagation and its impact considering rough surfaces has been investigated employing the classical Beckmann-Kirchhoff (B-K) model by using our self-developed ray tracing algorithm (RTA). Finally, the relative received power and contribution of the diffusely scattered power at 300 GHz has been illustrated at each scenario point with different surface roughness to predict the achievable signal-to-noise ratio

Topography of (exo)planets

Current technology is not able to map the topography of rocky exoplanets, simply because the objects are too faint and far away to resolve them. Nevertheless, indirect effect of topography should be soon observable thanks to photometry techniques, and the possibility of detecting specular reflections. In addition, topography may have a strong effect on Earth-like exoplanet climates because oceans and mountains affect the distribution of clouds \citep{Houze2012}. Also topography is critical for evaluating surface habitability \citep{Dohm2015}. We propose here a general statistical theory to describe and generate realistic synthetic topographies of rocky exoplanetary bodies. In the solar system, we have examined the best-known bodies: the Earth, Moon, Mars and Mercury. It turns out that despite their differences, they all can be described by multifractral statistics, although with different parameters. Assuming that this property is universal, we propose here a model to simulate 2D spherical random field that mimics a rocky planetary body in a stellar system. We also propose to apply this model to estimate the statistics of oceans and continents to help to better assess the habitability of distant worlds

Using natural means to reduce surface transport noise during propagation outdoors

This paper reviews ways of reducing surface transport noise by natural means. The noise abatement solutions of interest can be easily (visually) incorporated in the landscape or help with greening the (sub)urban environment. They include vegetated surfaces (applied to faces or tops of noise walls and on building façades and roofs ), caged piles of stones (gabions), vegetation belts (tree belts, shrub zones and hedges), earth berms and various ways of exploiting ground-surface-related effects. The ideas presented in this overview have been tested in the laboratory and/or numerically evaluated in order to assess or enhance the noise abatement they could provide. Some in-situ experiments are discussed as well. When well-designed, such natural devices have the potential to abate surface transport noise, possibly by complementing and sometimes improving common (non-green) noise reducing devices or measures. Their applicability strongly depends on the available space reserved for the noise abatement and the receiver position

Airborne sound propagation over sea during offshore wind farm piling

Offshore piling for wind farm construction has attracted a lot of attention in recent years due to the extremely high noise emission levels associated with such operations. While underwater noise levels were shown to be harmful for the marine biology, the propagation of airborne piling noise over sea has not been studied in detail before. In this study, detailed numerical calculations have been performed with the Green's Function Parabolic Equation (GFPE) method to estimate noise levels up to a distance of 10 km. Measured noise emission levels during piling of pinpiles for a jacket-foundation wind turbine were assessed and used together with combinations of the sea surface state and idealized vertical sound speed profiles (downwind sound propagation). Effective impedances were found and used to represent non-flat sea surfaces at low-wind sea states 2, 3, and 4. Calculations show that scattering by a rough sea surface, which decreases sound pressure levels, exceeds refractive effects, which increase sound pressure levels under downwind conditions. This suggests that the presence of wind, even when blowing downwind to potential receivers, is beneficial to increase the attenuation of piling sound over the sea. A fully flat sea surface therefore represents a worst-case scenario

Realistic Surface Scattering and Surface Bound State Formation in the High T_c Superconductor YBa_2Cu_3O_{6+x}

Surface Umklapp scattering of quasiparticles, and surface roughness are shown to play essential roles in the formation of the surface bound states in realistic models for YBa_2Cu_3O_{6+x}. The results account for the shape, the impurity dependence of the height, and for a proposed universal width of the zero bias conductance peak.Comment: 4 pages, 1 figur

Calculation of Cu/Ta interface electron transmission and effect on conductivity in nanoscale interconnect technology

Resistivity augmentation in nanoscale metal interconnects is a performance limiting factor in integrated circuits. Here we present calculations of electron scattering and transmission at the interface between Cu interconnects and their barrier layers, in this case Ta. We also present a semiclassical model to predict the technological impact of this scattering and find that a barrier layer can significantly decrease conductivity, consistent with previously published measurements.Comment: To appear in Appl. Phys. Lett., Nov. 2009. Replaced with version accepted for publication, clarifies discussion of semiclassical model. Conclusions unchange

Solid deuterium surface degradation at ultracold neutron sources

Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease.Comment: 15 pages, 22 figures, accepted by EPJ-

Phonon-mediated thermal conductance of mesoscopic wires with rough edges

We present an analysis of acoustic phonon propagation through long, free-standing, insulating wires with rough surfaces. Due to a crossover from ballistic propagation of the lowest-frequency phonon mode at $\omega <\omega _{1}=\pi c/W$ to a diffusive (or even localized) behavior upon the increase of phonon frequency, followed by re-entrance into the quasi-ballistic regime, the heat conductance of a wire acquires an intermediate tendency to saturate within the temperature range $T\sim \hbar \omega_{1}/k_{B}$.Comment: 4 pages, 3 figures included; minor changes and corrections, figures 1 and 2 replaced by better versions; to appear in PRB Brief Report