Radiometric Active Indoor Imaging in the W-Band

Millimeter wave passive imaging systems constitute a good compromise between resolution and penetration depth for a variety of imaging applications. In an outdoor scenario, the cold sky radiation, interacting with the reflectivity characteristics of the targets, constitutes the main source of contrast in the acquired images. In indoor applications such a source is not available, and higher thermal sensitivity is required. Alternatively, one has to provide an artificial illumination to the scene in order to increase its dynamic range. The implementation of an active source for a passive radiometer can, under certain conditions, increase the contrast of the images acquired and add extra information to the measurement. With such a setup, outdoor systems can be used for indoor observations (the absence of cold sky radiation is compensated with active illumination). The subject of our study is to better understand which kind of source and which setup can provide a diffuse illumination over the targets. This topic was investigated by conducting observations of various indoor scenes with two radiometers in the W-Band, using noise and continuous wave (CW) sources as illumination. In this paper we present the results achieved and our conclusions in order to provide an efficient illumination for indoor environment

Quantum Interference of Coulomb Interaction and Disorder: Phase Shift of Friedel Oscillations and an Instability of the Fermi Sea

We investigate the influence of interference between Coulomb interaction and impurity scattering on the static electronic response $\chi (0,q)$ in disordered metals to leading order in the effective Coulomb interaction. When the transport relaxation time $\tau _{tr}$ is much shorter than the quasiparticle life time, we find a \mbox{sgn}(2p_F-q)/\sqrt{|2p_F-q|} divergence of the polarization function at the Fermi surface ($q=2p_F$). It causes a phase shift of the Friedel oscillations as well as an enhancement of their amplitude. Our results are consistent with experiments and may be relevant for understanding the stability of the amorphous state of certain alloys against crystallization.Comment: 11 pages, 4 PostScript figures appended as a self-extracting tar archive; includes output instruction

Artic-North Atlantic interactions and multidecadal variability of the thermohaline circulation

Analyses of a 500-yr control integration with the non-flux-adjusted coupled atmosphere–sea ice–ocean model ECHAM5/Max-Planck-Institute Ocean Model (MPI-OM) show pronounced multidecadal fluctuations of the Atlantic overturning circulation and the associated meridional heat transport. The period of the oscillations is about 70–80 yr. The low-frequency variability of the meridional overturning circulation (MOC) contributes substantially to sea surface temperature and sea ice fluctuations in the North Atlantic. The strength of the overturning circulation is related to the convective activity in the deep-water formation regions, most notably the Labrador Sea, and the time-varying control on the freshwater export from the Arctic to the convection sites modulates the overturning circulation. The variability is sustained by an interplay between the storage and release of freshwater from the central Arctic and circulation changes in the Nordic Seas that are caused by variations in the Atlantic heat and salt transport. The relatively high resolution in the deep-water formation region and the Arctic Ocean suggests that a better representation of convective and frontal processes not only leads to an improvement in the mean state but also introduces new mechanisms determining multidecadal variability in large-scale ocean circulation

[Klopstock, Friedrich Gottlieb]

http://tartu.ester.ee/record=b1824172~S1*es

Disorder-Enhanced Electron Correlations Near the Crystalline-Amorphous Transition

l--like correlations. This is evidenced by a pronounced peak in the structure factor S(q) at a wave number q = q o = 2=a, where a is the spacing between shells of ions formed around an arbitrary central ion. Remarkably, the wave length F = =kF of the Friedel oscillations of the electron density ae(r) coincides with a at the CAT [1]. This has led several authors [1, 2, 3] to conjecture that the CAT is triggered by the ions being bound in the minima of the Friedel potential. The experimental results [1] then require that, at the CAT, the Friedel oscillations are phase shifted by ' = =2 w.r.t. a clean electron sea, and that their amplitude is enhanced in order to dominate the thermal energies at the typical experimental temperature of T =<F10.3

Les derniers Adieux de Louis XVI, Roi de France et de Navarre à sa Famille...

Référence bibliographique : De Vinck, 5114Référence bibliographique : Vidéodisque, 5877-5879Appartient à l’ensemble documentaire : Est18Rev

Radiometric Active Indoor Imaging in the W-Band

Millimeter wave passive imaging systems constitute a good compromise between resolution and penetration depth for a variety of imaging applications. In an outdoor scenario, the cold sky radiation, interacting with the reflectivity characteristics of the targets, constitutes the main source of contrast in the acquired images. In indoor applications such a source is not available, and higher thermal sensitivity is required. Alternatively, one has to provide an artificial illumination to the scene in order to increase its dynamic range. The implementation of an active source for a passive radiometer can, under certain conditions, increase the contrast of the images acquired and add extra information to the measurement. With such a setup, outdoor systems can be used for indoor observations (the absence of cold sky radiation is compensated with active illumination). The subject of our study is to better understand which kind of source and which setup can provide a diffuse illumination over the targets. This topic was investigated by conducting observations of various indoor scenes with two radiometers in the W-Band, using noise and continuous wave (CW) sources as illumination. In this paper we present the results achieved and our conclusions in order to provide an efficient illumination for indoor environment

Water splitting mediated by an electrocatalytically driven cyclic process involving iron oxide species

For a good reason, water splitting is the most pioneering energy storage technology. However, particularly water electrolysis still has a shadow existence compared to currently used methods for mass production of hydrogen. All known materials currently exploited as anodes for electrocatalytically initiated water-splitting suffer from high overpotentials and substantial mass loss during long term operation in acidic media. Low electrode stability affects operating and maintenance costs and together with high overpotentials directly lowers the overall efficiency of electrocatalytically driven splitting of water. In circumventing these problems, scientists and engineers are currently modifying electrode materials. We chose a completely different path and modified the electrolyte. An electrolysis set up, that consists of a Ni42 stainless steel anode and of hematite which is suspended in high concentration in sulfuric acid and acts as the electrolyte, exhibits oxygen evolution electrocatalysis at extremely low potential (1.26 V vs. RHE; 0.5 M H2SO4, j = 30 mA cm−2). If implemented in a suitable electrolyzer, an ultralow cell voltage of 1.6 V and an almost quantitative charge to oxygen + hydrogen conversion rate can be achieved. Remarkably, the negligible mass loss of the anode which consists exclusively of non-platinum group metals (non-PGM) during 100 h of operation. Experiments aimed at clarifying the mechanism suggest that Fe2O3 is converted to a Fe(II)/Fe(III) oxide species on the cathode which is then reconverted to Fe2O3 upon release of molecular oxygen when touching the anode. As a result, the oxygen-evolving centers are likely to be on the oxide particles rather than on the electrode. This proposed mechanism would explain the low potential of the OER electrode (+1.26 V vs. RHE at j = 30 mA cm−2) that could not be explained convincingly by an assumed direct oxidation of water molecules