Electromagnetic topology: Characterization of internal electromagnetic coupling

The main principles are presented of a method dealing with the resolution of electromagnetic internal problems: Electromagnetic Topology. A very interesting way is to generalize the multiconductor transmission line network theory to the basic equation of the Electromagnetic Topology: the BLT equation. This generalization is illustrated by the treatment of an aperture as a four port junction. Analytical and experimental derivations of the scattering parameters are presented. These concepts are used to study the electromagnetic coupling in a scale model of an aircraft, and can be seen as a convenient means to test internal electromagnetic interference

A search for clusters and groups of galaxies on the line of sight towards 8 lensed quasars

In this paper we present new ESO/VLT FORS1 and ISAAC images of the fields around eight gravitationally lensed quasars: CTQ414, HE0230-2130, LBQS1009-0252, B1030+074, HE1104-1805, B1359+154, H1413+117 and HE2149-2745. When available and deep enough, HST/WFPC2 data were also used to infer the photometric redshifts of the galaxies around the quasars. The search of galaxy overdensities in space and redshift, as well as a weak-shear analysis and a mass reconstruction are presented in this paper. We find that there are most probably galaxy groups towards CTQ414, HE0230-2130, B1359+154, H1413+117 and HE2149-2745, with a mass ~ 4x10^14 M_sol h^-1. Considering its photometric redshift, the galaxy group discovered in the field around HE1104-1805 is associated with the quasar rather than with the lensing potential.Comment: 14 pages, 11 figures(.jpg

Mechanics of continental extension from Quaternary strain fields in the Italian Apennines

Horizontal upper crustal surface strain-rates calculated using slip-vectors from striated faults and offsets of Late Pleistocene-Holocene landforms and sediments are used to investigate the mechanisms responsible for deformation in the Italian Apennines over a variety of length-scales ranging from individual fault segments up to the width of the mountain range. The method used allows strain-rates in any 5km \times 5km grid square or combination of these grid squares to be calculated. This allows comparison of strain-rates from 15 \pm 3 kyrs of slip with those from shorter time periods within polygons that are comparable in size, shape and location with those imposed by geodetic station locations or moment summation calculations. Strain-rates over a time period of 15 \pm 3 kyrs from 5km \times 5km grid squares integrated over an area of 1.28 \times 10^4 km^2 (80km \times 160 km), show the horizontal strain-rate of the Lazio-Abruzzo region of the central Apennines is 1.18^{+0.12} _{-0.04}\times10^{-8}yr^{-1} and -1.83^{+3.80} _{-4.43}\times10^{-10}yr^{-1} parallel and perpendicular to the regional principal strain direction (043^o-223^o \pm 1^o), associated with extension rates of \leq3.1^{+0.7} _{-0.4} mm yr^{-1} if calculated in boxes with a 5km width and 90km length across the Apennines. In Molise-North Campania, the horizontal principal strain-rate calculated over an area of 5\times10^3 km^2 (50km\times100 km) is 2.11^{+1.14} _{-0.16}\times10^{-9} yr^{-1} along the horizontal axis parallel to 039^o - 219^o \pm 3^o, and 0.88^{+2.84}_{-1:30}\times10^{-10} yr^{-1} perpendicular to it, associated with extension rates of \leq0.2^{+0.2} _{-0.1} mm yr^{-1} if calculated in 5km \times 90km transects that cross the Apennines. Within the South Campania-Basilicata region of the southern Apennines of area 8 \pm 103 km2 (50km_160 km), the average horizontal strain-rate over 15 \pm 3 kyrs is 3.70\pm0.26\times10^{-9} yr^{-1} parallel to and 3.65\pm2.05\times10^{-10} mmyr^{-1} perpendicular to the principal strain axis (044^o-224^o\pm2^o), associated with extension rates of \leq0.6\pm0.2mmyr^{-1} if calculated in 5km\times90km transects across the Apennines. The same method is used to calculate strain-rates in Calabria from longerterm offset geological features (\leq 580 ka); the horizontal principal strain-rate calculated over an area of 8\times103 km^2 (40km\times200 km) is 6.71\pm2.13\times10^{-9} yr^{-1} along the horizontal axis parallel to 086^o-226^o\pm3^o, and -8.40\pm5.69\times10^{-10} yr^{-1} perpendicular to it. Strain-rates calculated over 15\pm3 kyrs within 5km\times5km grid squares vary from zero up to 2.34\pm0.54\times10^{-7} yr^{-1}, 3.69\pm1.33\times10^{-8} yr^{-1}, and 1.20\pm0.41\times10^{-7} yr^{-1} in the central Apennines, the Molise-North Campania region, and the southern Apennines, respectively. These strain-rates resolve variations in strain orientations and magnitudes along the strike of individual faults and are used to produce a fault specific earthquake recurrence interval map. In order to study the existence of possible deficits or surpluses of geodetic and earthquake strain in the Apennines, these 15 \pm 3 kyrs multi seismic cycle strain-rates have been compared to short-term strain-rates calculated using geodesy (over 126 yrs, 11 yrs and 5 yrs) and seismic moment summation (over 700 yrs). Regional strain-rates calculated from geodesy and historical earthquakes are greater than those calculated from offset 15 \pm 3 ka landforms and sediments. In detail, 10^{1-2} yr strain-rates are higher than 10^4 yr strain-rates in some small areas (\approx2000 km^2, corresponding to polygons defined by geodesy campaigns and seismic moment summations) with the opposite situation in other areas where seismic moment release rates in large (Ms>6.0) magnitude historical earthquakes have been reported to be as low as zero. This demonstrates (1) the importance of comparing the exact same areas, and (2) that strain-rates vary spatially on the length-scale of individual faults and on a timescale between 10^{1-2} yrs and 10^4 yrs in the Apennines. The results are used to discuss temporal earthquake clustering and the natural variability of the seismic cycle. Spatial variations in upper crustal strain-rate measured across exposed fault scarps since 15\pm3 ka are also used to discuss the regional deformation related to plate boundary and sub-crustal forces, specifically, whether mantle upwelling and uplift contribute to forces associated with the active extension in the Italian Apennines. Strain-rates calculated in 5km \times 90km boxes across the Apennines are compared with data on cumulative upper-crustal strain, topography, free-air gravity and SKS splitting delay times that are a proxy for strain in the mantle. High extension-rates across the Apennines since 15 \pm 3 ka (0.4-3.1mm yr^{-1}) occur in the southern Apennines and central Apennines where values for finite extensional strains that have developed since 2-3Ma are highest (2-7km cumulative throw), and where mean topography from SRTM data (Shuttle Radar Topography Mission) is > 600m; the intervening area of Molise-North Campania with < 600m topography has extension-rates < 0.4mm yr^{-1} and lower values for finite extensional strains (< 2km cumulative throw). These two areas with high upper-crustal extension-rates overlie mantle that has relatively-long spatially-interpolated SKS delay times (1.2-1.8 seconds) and relatively-high free-air gravity values of 140-160 mGals; the intervening area of lower extension-rates has relatively-low spatially-interpolated SKS delay times of 0.8-1.2 seconds and relatively-low free-air gravity values of 120 mGals. These correlations suggest that at the regional length-scale, a sub-crustal process, that is, dynamic support of the topography by mantle upwelling, controls the present-day upper-crustal strain-rate field in the Apennines and the geography of seismic hazard in the region. At a smaller length-scale, in order to investigate the relationship between the throws and 3D orientation of breaching faults crossing relay zones, kinematic data, throw-rates and total throws have been measured for an active normal fault in the Italian Apennines that displays a relay zone at its centre. The c.0.8km long breaching fault, investigated in detail, dips at 67^o\pm5^o and strikes obliquely to c.2-3km long faults outside the relay zone which dip at 61^o\pm5^o.Total throws of pre-rift limestone define a throw profile with a double maximum (370\pm50 m; 360\pm50 m) separated by an area of lower throw (100\pm50 m) where the breaching fault is growing. Throw-rates implied by offsets across bedrock scarps of Late Pleistocene-Holocene landforms (15 \pm 3 ka) are higher across the breaching fault (0.67\pm0.13mm yr^{-1}) than for locations of throw maxima on the neighbouring faults (0.38\pm0.07mm yr^{-1}; 0.55\pm0.11mm yr^{-1}). The deficit in total throw will be removed in 0.68-1.0 Myrs if these deformation rates continue. To investigate why the highest throw-rates occur in the location with lowest total throw, horizontal strain-rate tensors were calculated in 1km \times 2km boxes. It is shown that the oblique strike and relatively-high dip of the breaching fault mean that it must have a relatively-high throw-rate in order for it to have a horizontal strain-rate concomitant with its position at the centre of the overall fault. It is shown that whether throw minima at locations of fault linkage are preserved during progressive fault slip depends on the 3D orientation of the breaching fault. The above is used to discuss the longevity of throw deficits and multiple throw maxima along faults in relation to seismic hazard and landscape evolution. Overall, this thesis shows that calculation of horizontal strain-rates using the method developed herein, supported by collection of field data from active faults, can provide new insights into regional mechanisms of continental extension, seismic hazard, the seismic cycle, and fault growth; it provides a test of the hypothesis that earthquake recurrence is spatially random, providing evidence that instead, earthquake recurrence shows a spatial pattern that is controlled by fault evolution and sub-crustal processes

The IRAM-30m line survey of the Horsehead PDR: III. High abundance of complex (iso-)nitrile molecules in UV-illuminated gas

Complex (iso-)nitrile molecules, such as CH3CN and HC3N, are relatively easily detected in our Galaxy and in other galaxies. We constrain their chemistry through observations of two positions in the Horsehead edge: the photo-dissociation region (PDR) and the dense, cold, and UV-shielded core just behind it. We systematically searched for lines of CH3CN, HC3N, C3N, and some of their isomers in our sensitive unbiased line survey at 3, 2, and 1mm. We derived column densities and abundances through Bayesian analysis using a large velocity gradient radiative transfer model. We report the first clear detection of CH3NC at millimeter wavelength. We detected 17 lines of CH3CN at the PDR and 6 at the dense core position, and we resolved its hyperfine structure for 3 lines. We detected 4 lines of HC3N, and C3N is clearly detected at the PDR position. We computed new electron collisional rate coefficients for CH3CN, and we found that including electron excitation reduces the derived column density by 40% at the PDR position. While CH3CN is 30 times more abundant in the PDR than in the dense core, HC3N has similar abundance at both positions. The isomeric ratio CH3NC/CH3CN is 0.15+-0.02. In the case of CH3CN, pure gas phase chemistry cannot reproduce the amount of CH3CN observed in the UV-illuminated gas. We propose that CH3CN gas phase abundance is enhanced when ice mantles of grains are destroyed through photo-desorption or thermal-evaporation in PDRs, and through sputtering in shocks. (abridged)Comment: Accepted for publication in Astronomy & Astrophysic

Laser-induced electron emission from a tungsten nanotip: identifying above threshold photoemission using energy-resolved laser power dependencies

We present an experiment studying the interaction of a strongly focused 25 fs laser pulse with a tungsten nanotip, investigating the different regimes of laser-induced electron emission. We study the dependence of the electron yield with respect to the static electric field applied to the tip. Photoelectron spectra are recorded using a retarding field spectrometer and peaks separated by the photon energy are observed with a 45 % contrast. They are a clear signature of above threshold photoemission (ATP), and are confirmed by extensive spectrally resolved studies of the laser power dependence. Understanding these mechanisms opens the route to control experiment in the strong-field regime on nanoscale objects.Comment: 9 pages, 6 figure

Topological properties of quantum periodic Hamiltonians

We consider periodic quantum Hamiltonians on the torus phase space (Harper-like Hamiltonians). We calculate the topological Chern index which characterizes each spectral band in the generic case. This calculation is made by a semi-classical approach with use of quasi-modes. As a result, the Chern index is equal to the homotopy of the path of these quasi-modes on phase space as the Floquet parameter (\theta) of the band is varied. It is quite interesting that the Chern indices, defined as topological quantum numbers, can be expressed from simple properties of the classical trajectories.Comment: 27 pages, 14 figure

Collisional excitation of water by hydrogen atoms

We present quantum dynamical calculations that describe the rotational excitation of H$_2$O due to collisions with H atoms. We used a recent, high accuracy potential energy surface, and solved the collisional dynamics with the close-coupling formalism, for total energies up to 12 000 cm$^{-1}$. From these calculations, we obtained collisional rate coefficients for the first 45 energy levels of both ortho- and para-H$_2$O and for temperatures in the range T = 5-1500 K. These rate coefficients are subsequently compared to the values previously published for the H$_2$O / He and H$_2$O / H$_2$ collisional systems. It is shown that no simple relation exists between the three systems and that specific calculations are thus mandatory

Atomistic studies of transformation pathways and energetics in plutonium

One of the most challenging problems in understanding the structural phase transformations in Pu is to determine the energetically favored, continuous atomic pathways from one crystal symmetry to another. This problem involves enumerating candidate pathways and studying their energetics to garner insight into instabilities and energy barriers. The purpose of this work is to investigate the energetics of two transformation pathways for the delta to alpha' transformation in Pu that were recently proposed [Lookman et al., Phys. Rev. Lett. 100:145504, 2008] on the basis of symmetry. These pathways require the presence of either an intermediate hexagonal closed-packed (hcp) structure or a simple hexagonal (sh) structure. A subgroup of the parent fcc and the intermediate hexagonal structure, which has trigonal symmetry, facilitates the transformation to the intermediate hcp or sh structure. Phonons then break the translational symmetry from the intermediate hcp or sh structure to the final monoclinic symmetry of the alpha' structure. We perform simulations using the modified embedded atom method (MEAM) for Pu to investigate these candidate pathways. Our main conclusion is that the path via hcp is energetically favored and the volume change for both pathways essentially occurs in the second step of the transformation, i.e. from the intermediate sh or hcp to the monoclinic structure. Our work also highlights the deficiency of the current state-of-the-art MEAM potential in capturing the anisotropy associated with the lower symmetry monoclinic structure.Comment: 12 pages, 5 figures, accepted for publication in Philos. Ma

Environmental protection of titanium alloys in centrifugal compressors at 500°C in saline atmosphere

The use of the titanium alloy Ti-6246 (Ti–6Al–2Sn–4Zr–6Mo, wt-%) for gas turbine compressors allows an increase in working temperature and stress level. Under severe service conditions, the material experiences combined high temperature and high mechanical stress and, in saline atmospheres, stress corrosion cracking (SCC) can occur, leading to catastrophic mechanical failure. The present study was performed to evaluate the potential of several surface treatments to protect Ti-6246 alloy, after salt deposit, from hot salt SCC at temperatures ?500°C and 500 MPa static mechanical stress conditions. Shot peening, thermal oxidation and metal–ceramic coatings were investigated. Experimental results confirm the existence of brittle stress corrosion phenomena marked by a low residual elongation of test samples and the presence of oxides on the fracture surfaces. Both shot peening and metal–ceramic coatings increase the hot salt SCC resistance of the alloy. Times to rupture were improved by a factor of 3 for shot peening and by a factor of 10 for metal–ceramic coatings. Inversely, the time to rupture of preoxidised alloys has been halved compared with uncoated alloys. As well as these interesting quantitative results, structural studies of metal–ceramic coatings showed that they are mechanically and chemically compatible with the titanium alloy substructure and should work under severe thermomechanical stresses and aggressive atmospheres

The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2CO and CH3OH

Aims. We investigate the dominant formation mechanism of H2CO and CH3OH in the Horsehead PDR and its associated dense core. Methods. We performed deep integrations of several H2CO and CH3OH lines at two positions in the Horsehead, namely the PDR and dense core, with the IRAM-30m telescope. In addition, we observed one H2CO higher frequency line with the CSO telescope at both positions. We determine the H2CO and CH3OH column densities and abundances from the single-dish observations complemented with IRAM-PdBI high-angular resolution maps (6") of both species. We compare the observed abundances with PDR models including either pure gas-phase chemistry or both gas-phase and grain surface chemistry. Results. We derive CH3OH abundances relative to total number of hydrogen atoms of ~1.2e-10 and ~2.3e-10 in the PDR and dense core positions, respectively. These abundances are similar to the inferred H2CO abundance in both positions (~2e-10). We find an abundance ratio H2CO/CH3OH of ~2 in the PDR and ~1 in the dense core. Pure gas-phase models cannot reproduce the observed abundances of either H2CO or CH3OH at the PDR position. Both species are therefore formed on the surface of dust grains and are subsequently photodesorbed into the gas-phase at this position. At the dense core, on the other hand, photodesorption of ices is needed to explain the observed abundance of CH3OH, while a pure gas-phase model can reproduce the observed H2CO abundance. The high-resolution observations show that CH3OH is depleted onto grains at the dense core. CH3OH is thus present in an envelope around this position, while H2CO is present in both the envelope and the dense core itself. Conclusions. Photodesorption is an efficient mechanism to release complex molecules in low FUV-illuminated PDRs, where thermal desorption of ice mantles is ineffective.Comment: 12 pages, 5 tables, 7 figures; Accepted for publication in A&