Closed-Flux Solutions to the Constraints for Plane Gravity Waves

The metric for plane gravitational waves is quantized within the Hamiltonian framework, using a Dirac constraint quantization and the self-dual field variables proposed by Ashtekar. The z axis (direction of travel of the waves) is taken to be the entire real line rather than the torus (manifold coordinatized by (z,t) is RxR rather than $S_1$ x R). Solutions to the constraints proposed in a previous paper involve open-ended flux lines running along the entire z axis, rather than closed loops of flux; consequently, these solutions are annihilated by the Gauss constraint at interior points of the z axis, but not at the two boundary points. The solutions studied in the present paper are based on closed flux loops and satisfy the Gauss constraint for all z.Comment: 18 pages; LaTe

Array concepts for solid-state and vacuum microelectronics millimeter-wave generation

The authors have proposed that the increasing demand for contact watt-level coherent sources in the millimeter- and submillimeter-wave region can be satisfied by fabricating two-dimensional grids loaded with oscillators and multipliers for quasi-optical coherent spatial combining of the outputs of large numbers of low-power devices. This was first demonstrated through the successful fabrication of monolithic arrays with 2000 Schottky diodes. Watt-level power outputs were obtained in doubling to 66 GHz. In addition, a simple transmission-line model was verified with a quasi-optical reflectometer that measured the array impedance. This multiplier array work is being extended to novel tripler configurations using blocking barrier devices. The technique has also been extended to oscillator configurations where the grid structure is loaded with negative-resistance devices. This was first demonstrated using Gunn devices. More recently, a 25-element MESFET grid oscillating at 10 GHz exhibited power combining and self-locking. Currently, this approach is being extended to a 100-element monolithic array of Gunn diodes. This same approach should be applicable to planar vacuum electron devices such as the submillimeter-wave BWO (backward wave oscillator) and vacuum FET

Energy and directional signatures for plane quantized gravity waves

Solutions are constructed to the quantum constraints for planar gravity (fields dependent on z and t only) in the Ashtekar complex connection formalism. A number of operators are constructed and applied to the solutions. These include the familiar ADM energy and area operators, as well as new operators sensitive to directionality (z+ct vs. z-ct dependence). The directionality operators are quantum analogs of the classical constraints proposed for unidirectional plane waves by Bondi, Pirani, and Robinson (BPR). It is argued that the quantum BPR constraints will predict unidirectionality reliably only for solutions which are semiclassical in a certain sense. The ADM energy and area operators are likely to have imaginary eigenvalues, unless one either shifts to a real connection, or allows the connection to occur other than in a holonomy. In classical theory, the area can evolve to zero. A quantum mechanical mechanism is proposed which would prevent this collapse.Comment: 54 pages; LaTe

Oxygen Diffusion Layer on Ti–6Al–4V Alloy: Scratch and Dry Wear Resistance

Ti–6Al–4V has prominent physical and mechanical properties, which nominate it for various engineering applications. A drawback of the alloy, however, is low scratch and wear resistance, which can be improved by a diffusion treatment. Oxygen diffusion layer (ODL) was produced on Ti–6Al–4V by thermal oxidation at a temperature of 850 °C for 3 and 6 h. Hardness of the samples was measured using a nano-indentation tester. Micro-scratch tests were performed under progressive and constant normal loads of 0–50 N. Dry wear behavior of the samples was studied using a ball-on-disk tribometer. The wear tests were carried out under various normal loads of 7.5, 15 and 30 N for sliding distances of 50, 100, 200 and 300 m using alumina balls as the counterface. The wear and scratch tracks were examined by scanning electron microscope and surface profilometer. The ODL samples showed higher hardness and lower plastic deformation as compared with Ti–6Al–4V. The brittle behavior of the ODL samples caused the formation of cracks and the development of large acoustic signals during scratching under normal loads of 40 and 50 N. The results also showed a higher scratch and wear resistance of the ODL samples compared with Ti–6Al–4V. However, the oxygen diffusion layer formed after 3 h of oxidation showed a sharp increase in the wear rate of the alloy under a normal load of 30 N and a sliding distance of 100 m

Plane waves in quantum gravity: breakdown of the classical spacetime

Starting with the Hamiltonian formulation for spacetimes with two commuting spacelike Killing vectors, we construct a midisuperspace model for linearly polarized plane waves in vacuum gravity. This model has no constraints and its degrees of freedom can be interpreted as an infinite and continuous set of annihilation and creation like variables. We also consider a simplified version of the model, in which the number of modes is restricted to a discrete set. In both cases, the quantization is achieved by introducing a Fock representation. We find regularized operators to represent the metric and discuss whether the coherent states of the quantum theory are peaked around classical spacetimes. It is shown that, although the expectation value of the metric on Killing orbits coincides with a classical solution, its relative fluctuations become significant when one approaches a region where null geodesics are focused. In that region, the spacetimes described by coherent states fail to admit an approximate classical description. This result applies as well to the vacuum of the theory.Comment: 11 pages, no figures, version accepted for publication in Phys. Rev.

Interatomic scattering in energy dependent photoelectron spectra of Ar clusters

Soft X-ray photoelectron spectra of Ar 2p levels of atomic argon and argon clusters are recorded over an extended range of photon energies. The Ar 2p intensity ratios between atomic argon and clusters’ surface and bulk components reveal oscillations similar to photoelectron extended X-ray absorption fine structure signal (PEXAFS). We demonstrate here that this technique allows us to analyze separately the PEXAFS signals from surface and bulk sites of free-standing, neutral clusters, revealing a bond contraction at the surface

The caries experience of 5 year-old children in Scotland in 2013-2014, and in England and Wales in 2014-2015. Reports of cross-sectional dental surveys using BASCD criteria

Objective: We report the findings from and comment on the surveys of the oral health of 5-year-old children undertaken in Scotland (2013-14), Wales (2014-15) and England (2014-15). This was the fourteenth survey in Scotland since 1988. In England and Wales it is the third survey since 2007 when changes were required in consent arrangements. Method: Representative samples were drawn within Health Boards across Scotland and local authorities across England and Wales. Consent was sought via opt-out parental consent in Scotland and opt-in parental consent in England and Wales. Children examined were those aged five in England and those in Primary 1 (school year aged 5 to 6) in Scotland and Wales. Examinations were conducted in schools by trained and calibrated examiners. Caries was visually diagnosed at the dentinal threshold. Results: There is a continuing decline in d3mft in all three countries. d3mft was 1.27 (opt-out consent) for Scotland, 0.84 for England (opt-in consent) and 1.29 for Wales (opt-in consent). Tooth decay levels remain higher in more deprived areas across Great Britain, with clear inequalities gradients demonstrated across all geographies. Attempts to measure changes in dental health inequalities across the three countries show no conclusive trends. Conclusion: Inter-country comparisons provide further oral health intelligence despite differences in approach and timing. The third surveys in England and Wales using the new consent arrangements have enabled trend analysis. Dental health inequalities gradients were shown across all geographies and all of the indicators of inequalit

Driver behaviour with adaptive cruise control

This paper reports on the evaluation of adaptive cruise control (ACC) from a psychological perspective. It was anticipated that ACC would have an effect upon the psychology of driving, i.e. make the driver feel like they have less control, reduce the level of trust in the vehicle, make drivers less situationally aware, but workload might be reduced and driving might be less stressful. Drivers were asked to drive in a driving simulator under manual and ACC conditions. Analysis of variance techniques were used to determine the effects of workload (i.e. amount of traffic) and feedback (i.e. degree of information from the ACC system) on the psychological variables measured (i.e. locus of control, trust, workload, stress, mental models and situation awareness). The results showed that: locus of control and trust were unaffected by ACC, whereas situation awareness, workload and stress were reduced by ACC. Ways of improving situation awareness could include cues to help the driver predict vehicle trajectory and identify conflicts