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

Tunneling Currents in Zinc Oxide

An examination of the current-voltage characteristics of gold and palladium surface barriers on degenerate zinc oxide has been made. Both chemically prepared and cleaved surfaces were studied. The current conduction mode is shown to be thermionic-field emission at room temperature and to be pure field emission at liquid-nitrogen temperatures. The voltage dependence of the current is in good agreement with theory. The observed current magnitudes in both current modes were approximately one-tenth that calculated by simple theory

Surface Barriers on Zinc Oxide

The surface barrier systems consisting of gold and palladium on chemically prepared zinc oxide have been investigated in detail. Surface barrier energies have been determined by photoresponse, forward current versus voltage, thermal activation energy, and capacitance-voltage methods. Agreement in barrier energies obtained by the four methods is excellent. The barrier energy for gold is 0.66 eV and for palladium is 0.60 eV. Forward current-voltage characteristics were in quantitative agreement with simple Bethe diode theory as modified by the presence of image force lowering. The reverse current-voltage characteristic is in quantitative agreement with that expected from the simple image force lowering of the barrier, over a bias range of from 0.1 to 3 V. Carrier concentration derived from resistivity and Hall measurements agreed with that obtained from capacitance-voltage measurements. We believe this represents the first comprehensive study where such quantitative consistency has been demonstrated on a compound semiconductor barrier system. Existence of a deep level trap is indicated via the effects on capacitance measurements

Surface barrier energies on strontium titanate

The metal-semiconductor surface-barrier systems consisting of the metals gold, palladium, copper, or indium on chemically prepared or cleaved strontium titanate surfaces have been investigated in detail. Surface-barrier energies have been studied by photoresponse, forward current versus voltage, and thermal activation energy techniques yielding values in excellent agreement with each other. Forward current-voltage characteristics ~ere in quantitative agreement with simple diode thermionic theory as modified by the inclusion of image force lowering. The reverse current-voltage characteristic of these stable barriers also is in agreement with that expected from thermionic theory including simple image force lowering over a bias range from -0.1 to -4 V

Permittivity of Strontium Titanate

The permittivity of single‐crystal single‐domain strontiumtitanate has been measured in detail in the [001], [011], and [111] directions, as a function of temperature (from 4.2 to 300 °K), electric field (from −23 000 to +23 000 V/cm, and frequency (from 1 kHz to 50 MHz). The free energy of the crystal is determined as a function of polarization with temperature as a parameter. The Curie‐Weiss law is satisfied in the temperature range 60–300 °K, giving a Curie temperature of 30 ± 2 °K for the three crystal orientations. The Lyddane‐Sachs‐Teller (LST) relation is satisfied for temperatures between 30 and 300 °K and for electric fields between 0 and 12 000 V/cm. A generalized LST relation is used to calculate the permittivity of strontiumtitanate from zero to optic frequencies. Two active optic modes are important. The lower‐frequency mode is attributed mainly to motion of the strontium ions with respect to the rest of the lattice, while the higher‐frequency active mode is attributed to motion of the titanium ions with respect to the oxygen lattice. The restoring forces that act on the Ti ions begin to "harden" when these ions are displaced approximately 0.002 Å from their equilibrium positions

3D tribo-nanoprinting using triboreactive materials

Tribology: the science of friction, wear and lubrication has never been associated in a positive way with the ability to manufacture at the nanoscale. Triboreactivity, when the contact between two surfaces promotes a chemical reaction, has been harnessed in this study to create highly tenacious nano-features. The reported 3D tribo-nanoprinting methodology has been demonstrated for organic and inorganic fluids on steel and silicon substrates and is adaptable through the interface tribology. The growth rate, composition and shape of the printed features were all found to be dependent on the nature of the printing liquid and shearing interfaces in addition to the applied temperature and contact force. The reported methodology in this study opens unprecedented future possibilities to utilize the nanoprinted films for the expanding fields of microelectronics, medical devices, flexible electronics and sensor technologies

Anomalous resonance of strontium titanate

An anomalous resonance exhibited by perovskite strontium titanate crystals are obtained by cooling the samples with an applied electric field. A plausible mechanism involves a mechanical oscillation with a frequency determined by the domain boundary spacing. which is coupled to the electric field through the piezoelectric strain constant

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

Imaging Polarimeter Arrays for Near-Millimeter Waves

An integrated-circuit antenna array has been developed that images both polarization and intensity. The array consists of a row of antennas that lean alternately left and right, creating two interlaced sub-arrays that respond to different polarizations. The arrays and the bismuth bolometer detectors are made by a photoresist shadowing technique that requires only one photolithographic mask. The array has measured polarization at a wavelength of 800 µm with an absolute accuracy of 0.8° and a relative precision of 7 arc min. and has demonstrated nearly diffraction-Iimited resolutiort of a 20° step in polarization

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.