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

Experiments with a fully instrumented split Stirling cryocooler

A practical model that can be used to accurately size and optimally split stirling cryocoolers is discussed. A practical model that could be used to extrapolate existing designs to meet different specifications was developed. However, to do this detailed knowledge of the dynamic operating parameters of this type of cryocooler is required. The first stage is to fully instrument a refrigerator so that various dynamic parameters can be measured. The second stage involves the application of these measurements to the design and optimization of a range of coolers

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

Opinion: Is the repo a derivative?

An explanation of a derivative instrument (forward, future, swap, option, etc) generally encompasses that the instrument is derived from, i.e. is based on, certain, or aspects of certain, financial market instruments, and takes its value largely from these or other instruments or markets. Explanations also refer to the underlying instrument. No textbooks regard the repurchase agreement (repo) as a derivative instrument. This article argues that the repo is derived from an existing financial market instrument (the underlying instrument) and takes its value from another segment of the financial market. As such, it should be regarded as a derivative instrument. In addition, the use of the word repo is often misrepresented, and the mathematics involved in repos is not readily available in the literature. This article endeavours to address these issues

Quasi-classical rate coefficient calculations for the rotational (de)excitation of H2O by H2

The interpretation of water line emission from existing observations and future HIFI/Herschel data requires a detailed knowledge of collisional rate coefficients. Among all relevant collisional mechanisms, the rotational (de)excitation of H2O by H2 molecules is the process of most interest in interstellar space. To determine rate coefficients for rotational de-excitation among the lowest 45 para and 45 ortho rotational levels of H2O colliding with both para and ortho-H2 in the temperature range 20-2000 K. Rate coefficients are calculated on a recent high-accuracy H2O-H2 potential energy surface using quasi-classical trajectory calculations. Trajectories are sampled by a canonical Monte-Carlo procedure. H2 molecules are assumed to be rotationally thermalized at the kinetic temperature. By comparison with quantum calculations available for low lying levels, classical rates are found to be accurate within a factor of 1-3 for the dominant transitions, that is those with rates larger than a few 10^{-12}cm^{3}s^{-1}. Large velocity gradient modelling shows that the new rates have a significant impact on emission line fluxes and that they should be adopted in any detailed population model of water in warm and hot environments.Comment: 8 pages, 2 figures, 1 table (the online material (4 tables) can be obtained upon request to [email protected]

Rotational Excitation of HC_3N by H_2 and He at low temperatures

Rates for rotational excitation of HC3N by collisions with He atoms and H2 molecules are computed for kinetic temperatures in the range 5-20K and 5-100K, respectively. These rates are obtained from extensive quantum and quasi-classical calculations using new accurate potential energy surfaces (PES)

Collisional excitation of singly deuterated ammonia NH2_2D by H2_2

The availability of collisional rate coefficients with H$_2$ is a pre-requisite for interpretation of observations of molecules whose energy levels are populated under non local thermodynamical equilibrium conditions. In the current study, we present collisional rate coefficients for the NH$_2$D / para--H$_2$($J_2 = 0,2$) collisional system, for energy levels up to $J_\tau = 7_7$ ($E_u$$\sim$735 K) and for gas temperatures in the range $T = 5-300$K. The cross sections are obtained using the essentially exact close--coupling (CC) formalism at low energy and at the highest energies, we used the coupled--states (CS) approximation. For the energy levels up to $J_\tau = 4_2$ ($E_u$$\sim$215 K), the cross sections obtained through the CS formalism are scaled according to a few CC reference points. These reference points are subsequently used to estimate the accuracy of the rate coefficients for higher levels, which is mainly limited by the use of the CS formalism. Considering the current potential energy surface, the rate coefficients are thus expected to be accurate to within 5\% for the levels below $J_\tau = 4_2$, while we estimate an accuracy of 30\% for higher levels

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

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

Internal relaxation time in immersed particulate materials

We study the dynamics of the solid to liquid transition for a model material made of elastic particles immersed in a viscous fluid. The interaction between particle surfaces includes their viscous lubrication, a sharp repulsion when they get closer than a tuned steric length and their elastic deflection induced by those two forces. We use Soft Dynamics to simulate the dynamics of this material when it experiences a step increase in the shear stress and a constant normal stress. We observe a long creep phase before a substantial flow eventually establishes. We find that the typical creep time relies on an internal relaxation process, namely the separation of two particles driven by the applied stress and resisted by the viscous friction. This mechanism should be relevant for granular pastes, living cells, emulsions and wet foams