Does the Principle of Equivalence Prohibit Trapped Surfaces from Forming in the General Relativistic Collapse Process?

It has recently been shown that time-like spherical collapse of a physical fluid in General Relativity does not permit formation of trapped surfaces. This result followed from the fact that the formation of a trapped surface in a physical fluid would cause the time-like world lines of the collapsing fluid to become null at the would-be trapped surface, thus violating the Principle of Equivalence in General Theory of Relativity (GTR). For the case of the spherical collapse of a physical fluid, the no trapped surface condition 2GM(r, t)/R(r, t) c ²<1 was found to be required to be satisfied in all regions of spacetime, where R(r, t) is the invariant circumference variable, r is a co-moving radial coordinate and M(r, t) is the gravitational mass confined within the radius r. The above result was obtained by treating the problem from the viewpoint of an internal co-moving observer at radius r. The boundary of the fluid at r _s=R _s(r _s, t) must also behave in a similar manner, and an external stationary observer should be able to obtain a similar no trapped surface relationship. Accordingly, we generalize this analysis by studying the problem of a time-like collapsing radiating plasma from the point of view of the exterior stationary observer. We find the Principle of Equivalence implies that the physical surface surrounding the plasma must obey 1/(1+z _s)>0, where z _s is the surface red shift seen by a zero-angular momentum observer. When this condition is applied to the first integral of the time-time component of the Einstein equation, it leads to the no trapped surface condition 2GM(r _s, t)/R(r _s, t) c ²<1 consistent with the condition obtained above for the interior co-moving metric. The Principle of Equivalence enforces the no trapped surface condition by constraining the physics of the general relativistic radiation transfer process in a manner that requires it to establish and maintain an Eddington limited secular equilibrium on the dynamics of the collapsing radiating surface so as to always keep the physical surface of the collapsing object outside of its Schwarzschild radius. The important physical implication of the no trapped surface condition is that galactic black hole candidates GBHC do not possess event horizons and hence do possess intrinsic magnetic fields. In this context the spectral characteristics of galactic black hole candidates offer strong evidence that their central nuclei are highly red-shifted Magnetospheric Eternally Collapsing Objects (MECO) within the framework of General Relativity.     

A comparison of potential molecular wires as components for molecular electronics

The field of electronics using single-molecule components has recently received much attention as a possible new design concept for the continued miniturisation of electronics. Molecular wires are the conceptually simplest components of such electronic systems and several different compound types have been used to produce molecular wires. Examples of some of the most promising families of molecular wires are presented, namely conjugated hydrocarbons, carbon nanotubes, porphyrin oligomers and DNA. Discussion centres around their potential use in functioning electronic architectures in terms of their electronic properties, ease and controllability of synthesis and potential for self-assembly.     

Cross-correlation analysis of Ge(Li) spectra

A sensitive technique is proposed for activation analysis using cross-correlation and improved spectral orthogonality achieved through use of a rectangular zero area digital filter.     

Crystal deformation during the growth of kink bands in oriented polyethylene

When oriented polyethylene is sheared at an angle to the orientation axis, kink bands often develop and grow, with a resulting change of the crystalline orientation. Beside the crystalline reorientation, the following changes within the kink bands have been observed with wide-angle x-rays: (a) partial transformation to a monoclinic from the normal orthorhombic unit cell; (b) partial alignment of the orthorhombic b axes; (c) rotation of the orthorhombic c axes of a fraction of the crystals around the kinks by an extra 40 to 60° beyond that of the fibrils; and (d) misalignment of the orthorhombic (hk0) planes by a few degrees. These results are suggested to arise, at least in part, from crystal flattening and from crystal twinning or pseudotwinning on planes intersecting the molecular axes.     

Formation of fluoro-meisenheimer complexes using homogeneous and heterogeneous fluoride ion sources

1-Chloro-2,4-dinitrobenzene, 1-fluoro-2,4-dinitrobenzene and 1,3-dinitrobenzene form Meisenheimer complexes with tetra-n-butylammonium fluoride and alumina supported alkali metal fluorides. Both kinetically controlled and thermodynamically controlled complexes are observed.     

Fluorescence detection of exafs: Sensitivity enhancement for dilute species and thin films

The fluorescence intensity is used to measure the X-ray absorption cross-section and is found to yield essentially the same results as a more conventional transmission experiment. However, the fluorescence method is shown to extend the sensitivity of the EXAFS technique by two or more orders of magnitude, and thus nake feasible the study of extremely dilute species.     

The structure of amorphous GeSe and GeTe

We present the results of electronic structure calculations on model 3:3 and 4:2 co-ordinated networks of amorphous GeSe and GeTe. The calculations show that a- GeTe has a predominantly 4:2 chemically ordered structure and suggest that GeSe may be 3:3 co-ordinated. They emphasize how it is often easier to discriminate between different models on the basis of electronic structure rather than other information.     

Semi-chaotic pulse effects in self-modulating Gunn oscillators

Self-modulation behaviour has been observed in GaAs Gunn oscillators operating at W-band, leading to nanosecond pulses of relatively high peak power. Pulse repetition rates and pulse-widths can be varied reproducibly as a function of bias voltage and bias line termination, and there is evidence for semi-chaotic behaviour in certain regimes.