Accidental suppression of Landau damping of the transverse breathing mode in elongated Bose-Einstein condensates

We study transverse radial oscillations of an elongated Bose-Einstein condensate using finite temperature simulations, in the context of a recent experiment at ENS. We demonstrate the existence of a mode corresponding to an in-phase collective oscillation of both the condensate and thermal cloud. Excitation of this mode accounts for the very small damping rate observed experimentally, and we find excellent quantitative agreement between experiment and theory. In contrast to other condensate modes, interatomic collisions are found to be the dominant damping mechanism in this case.Comment: 4 pages, 3 figure

Explicit Actions for Electromagnetism with Two Gauge Fields with Only one Electric and one Magnetic Physical Fields

We extend the work of Mello et al. based in Cabbibo and Ferrari concerning the description of electromagnetism with two gauge fields from a variational principle, i.e. an action. We provide a systematic independent derivation of the allowed actions which have only one magnetic and one electric physical fields and are invariant under the discrete symmetries $P$ and $T$. We conclude that neither the Lagrangian, nor the Hamiltonian, are invariant under the electromagnetic duality rotations. This agrees with the weak-strong coupling mixing characteristic of the duality due to the Dirac quantization condition providing a natural way to differentiate dual theories related by the duality rotations (the energy is not invariant). Also the standard electromagnetic duality rotations considered in this work violate both $P$ and $T$ by inducing Hopf terms (theta terms) for each sector and a mixed Maxwell term. The canonical structure of the theory is briefly addressed and the 'magnetic' gauge sector is interpreted as a ghost sector.Comment: v2: 12 pages; References added, discussion concerning degrees of freedom corrected; v3: is now used the standard normalization of 1/4 in the actions; the possibility of theta being a pseudo-scalar implied a title changing; eq (23) added; signs corrected in equations (39,45-47); references adde

Imaging X-ray spectrometer

An X-ray spectrometer for providing imaging and energy resolution of an X-ray source is described. This spectrometer is comprised of a thick silicon wafer having an embedded matrix or grid of aluminum completely through the wafer fabricated, for example, by thermal migration. The aluminum matrix defines the walls of a rectangular array of silicon X-ray detector cells or pixels. A thermally diffused aluminum electrode is also formed centrally through each of the silicon cells with biasing means being connected to the aluminum cell walls and causes lateral charge carrier depletion between the cell walls so that incident X-ray energy causes a photoelectric reaction within the silicon producing collectible charge carriers in the form of electrons which are collected and used for imaging

Orthogonality relations for triple modes at dielectric boundary surfaces

We work out the orthogonality relations for the set of Carniglia-Mandel triple modes which provide a set of normal modes for the source-free electromagnetic field in a background consisting of a passive dielectric half-space and the vacuum, respectively. Due to the inherent computational complexity of the problem, an efficient strategy to accomplish this task is desirable, which is presented in the paper. Furthermore, we provide all main steps for the various proofs pertaining to different combinations of triple modes in the orthogonality integral.Comment: 15 page

Folded RF-excited CO₂ waveguide lasers

This thesis describes theoretical and experimental work on RF excited CO₂ waveguide lasers and amplifiers.The mode coupling losses at a bend in a folded waveguide have been evaluated as a function of the selectable parameters to determine the low-loss folding geometries. A direct comparison is made between three types of optical arrangement used for folding in a compact, sealed-off, Z-fold CO₂ waveguide laser excited by a transverse RF discharge. In particular, the measured laser output power as a function of discharge conditions and mirror alignment for plane and curved mirror, and partial waveguide folded resonators are compared.The Z-fold laser output power is predicted by incorporating the known and estimated laser parameters into a Rigrod-type analysis. A simultaneous solution of the Rigrod equations predicting the laser powers for different intra-cavity gain lengths is used with the experimental data to derive the discharge and resonator parameters. Experimental results are in good agreement with the theoretical predictions, and suggest that a M% power loss per fold has been achieved with partial waveguide folding. Also, the preliminary theoretical results of a multi-mode resonator model predicting the laser output power as a function of the angular mis-alignment of one of the Z-fold laser folding mirrors are in qualitative agreement with the experimental determinations.Experiments related to laser efficiency and frequency stability are discussed briefly. These include an investigation into an automatic impedance matching scheme for dynamic optimisation of the power transfer efficiency between RF generator and the laser head; the Opto-Hertzian effect (RF equivalent to the opto-Galvanic effect) for laser frequency stabilisation; a novel parallel-resonant distributed inductance excitation technique using a multi-start solenoid; and finally, identification of hooting laser resonator modes responsible for impeding heterodyne measurements Mien a clean RF spectrum is required.In addition, theoretical and experimental studies of laser amplification are presented. The suitability of folded waveguide and non-waveguide structures for power amplification or pre-amplification is assessed to determine their applicability to coherent LiDAR. Optical amplification of wideband transmitter and/or receiver signals is considered a favourable way of improving the discrimination of range and velocity determinations.Finally, as a result of this work, up to 53.4 Watts output power in a high quality fundamental Gaussian beam has been obtained from a compact, sealed-off, Z-fold CO₂ waveguide laser with a 115 cm discharge length, which implies a specific power performance of 0.46 W/cm. Efficiencies (laser output power/RF input power) of up to 9.2% have also been observed

Agentic misfit: an empirical demonstration of non-matching human agency amid complexity

Alignment of organizations with external imperatives is seen as a sine qua non of proper organizing and strategizing by many fit and complexity scholars. Any deviation from this management mantra engenders organizational decline and, ultimately, mortality. We put this axiomatic principle under empirical scrutiny and use the law of requisite variety as our organizing principle to do so. The law is an iconic cornerstone of this matching contingency logic and it has served to legitimize a wide range of fit decisions in e.g., leadership, organizational learning or corporate governance. Inspired by organizational vignettes inhabiting antithetical complexity regimes, we introduce a novel concept, which we label as ‘agentic misfit’. In this way, we deconstruct deterministic assumptions related to environmental fittingness, we challenge teleological orientations in the fit literature and, we flesh out the viability of non-matching human agency amid complexity

A multi-frequency measurement of thermal microwave emission from soils: The effects of soil texture and surface roughness

An experiment on remote sensing of soil moisture content was conducted over bare fields with microwave radiometers at the frequencies of 1.4 GHz, 5 GHz, and 10.7 GHz during July - September of 1981. Three bare fields with different surface roughnesses and soil textures were prepared for the experiment. Ground truth acquisition of soil temperatures and moisture contents for 5 layers down to the depths of 15 cm was made concurrently with radiometric measurements. The experimental results show that the effect of surface roughness is to increase the soils' brightness temperature and to reduce the slope of regression between brightness temperature and moisture content. The slopes of regression for soils with different textures are found to be comparable, and the effect of soil texture is reflected in the difference of regression line intercepts at brightness temperature axis. The result is consistent with laboratory measurement of soils' dielectric permittivity. Measurements on wet smooth bare fields give lower brightness temperatures at 5 GHz than at 1.4 GHz

SAFT-γ force field for the simulation of molecular fluids: 8. hetero-group coarse-grained models of perfluoroalkylalkanes assessed with new vapour-liquid interfacial tension data

The air-liquid interfacial behaviour of linear perfluoroalkylalkanes (PFAAs) is reported through a combined experimental and computer simulation study. The surface tensions of seven liquid PFAAs (perfluorobutylethane, F4H2; perfluorobutylpentane, F4H5; perfluorobutylhexane, F4H6, perfluorobutyloctane, F4H8; perfluorohexylethane, F6H2; perfluorohexylhexane, F6H6; and perfluorohexyloctane, F6H8) are experimentally determined over a wide temperature range (276 to 350 K). The corresponding surface thermodynamic properties and the critical temperatures of the studied compounds are estimated from the temperature dependence of the surface tension. Experimental density and vapour pressure data are employed to parameterize a generic heteronuclear coarse-grained intermolecular potential of the SAFT- γ family for PFAAs. The resulting force field is used in direct molecular dynamics simulations to predict with quantitative agreement the experimental tensions and to explore the conformations of the molecules in the interfacial region revealing a preferential alignment of the PFAA molecules towards the interface and an enrichment of the perfluoro-groups at the outer interface region

Energy radiated from a fluctuating selfdual string

We compute the energy that is radiated from a fluctuating selfdual string in the large $N$ limit of $A_{N-1}$ theory using the AdS-CFT correspondence. We find that the radiated energy is given by a non-local expression integrated over the string world-sheet. We also make the corresponding computation for a charged string in six-dimensional classical electrodynamics, thereby generalizing the Larmor formula for the radiated energy from an accelerated point particle.Comment: 12 page

Religious education in the experience of young people from mixed-faith families

On the basis of recent ethnographic study at the University of Warwick of the religious identity formation of young people in ‘mixed-faith’ families, this article focuses on their (and their parents’) experiences and perceptions of religious education (RE) and of religious nurture in the community. The young people’s experience of RE differed between primary and secondary school and only a few were engaged in supplementary classes. We highlight the complementarity between school and home in young people’s religious learning and draw out implications for RE