In order to determine the suitability of diamond-like carbon (DLC) as a material for storing ultracold neutrons to use in neutron electric-dipole moment (EDM) experiments, a number of tests on DLC coatings have been performed. Thin DLC layers deposited on quartz and aluminium substrates by chemical vapour deposition have been characterised by neutron transmission, neutron reflectometry, electron microscopy and neutron and mercury storage and depolarisation lifetime measurements. Two types of DLC have been compared; DLC made by chemical vapour deposition from natural methane and DLC made by chemical vapour deposition from deuterated methane. With these samples we determined the density, hydrogen concentration and Fermi potential of the coatings. DLC coatings made from deuterated methane are now succesfully being used in an experiment to measure the EDM of the neutron.
The latest neutron electric dipole moment (EDM) experiment has been collecting data at the Institut Laue-Langevin (ILL), Grenoble, since 1996. It uses an atomic-mercury magnetometer to compensate for the magnetic field fluctuations that were the principal source of systematic errors in previous experiments. The first results, in combination with the previous ILL measurement, yield a possible range of values of (-7.0 < d(n) < 5.0) x 10(-26)e cm (90% C.L.). This may be interpreted as an upper limit on the absolute value of the neutron EDM of \d(n)\ < 6.3 x 10(-26)e cm (90% C.L.).
Long ago, Bohr, Pauli, and Mott argued that it is not, in principle, possible to measure the spin components of a free electron. One can try to use a Stern-Gerlach type of device, but the finite size of the beam results in an uncertainty of the splitting force that is comparable with the gradient force. The result is that no definite spin measurement can be made. Recently there has been a revival of interest in this problem, and we will present our own analysis and quantum-mechanical wave-packet calculations which suggest that a spin measurement is possible for a careful choice of initial conditions.
For an optically dilute solid sphere of radius a and dielectric constant independent of frequency, the Casimir energy is evaluated to second order in , subject to an exponential cut-off on wavenumbers, using only standard perturbation theory and elementary mathematics. It is hoped that this can serve to elucidate other far more elaborate methods that aim to determine exactly by summing zero-point energies. For the electromagnetic field, the perturbative result reads
http://ej.iop.org/images/0305-4470/32/3/008/img6.gif
with V the volume and S the surface area. The term of order is related in a simple way to the Casimir-Polder (retarded) potential between polarizable bodies. This relation also yields some insight into the net pressure on a thin spherical shell.
We have observed dramatic line intensity variations in the saturation spectrum of Rb85 and Rb87 due to magnetic fields of magnitude on the order of 100 nT. These variations are detected by rotation of the plane of polarisation of the pump beam and probe beam relative to the magnetic field axis. A modified rate equation model is proposed which accounts for all experimentally observed features. Our results may explain some discrepancies between theory and experiment observed by other authors. Furthermore, our study should lead to a better understanding of the processes involved in saturation spectroscopy.
We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor dominate over vector and tensor components. This result has far reaching consequences. We find that cosmic strings exhibit a single Doppler peak of acceptable height at high . They also seem to have a less severe bias problem than global defects, although the CDM power spectrum in the standard cosmology is the wrong shape to fit large scale structure data.
We report the first large scale numerical study of the dynamics of a second order phase transition caused by a gradual decrease of temperature in a U(1) λφ4 theory in three spatial dimensions. We present a detailed account of the dynamics of the fields and focus on vortex string formation as a function of the quench rate. The results are found in good agreement with the theory of defect formation proposed by Kibble and Zurek.
Internal_Co_Author2 = YV Bogdanova
We study the luminosity function and clustering properties of subsamples of local galaxies selected from the Stromlo¿APM Survey by the rest-frame equivalent widths of their H and [O ii] emission lines. The bJ luminosity function of star-forming galaxies has a significantly steeper faint-end slope than that for quiescent galaxies: the majority of sub-L* galaxies are currently undergoing significant star formation. Emission-line galaxies are less strongly clustered, both amongst themselves and with the general galaxy population, than are quiescent galaxies. Thus as well as being less luminous, star-forming galaxies also inhabit lower density regions of the Universe than quiescent galaxies.
We present high- and medium-resolution phase-resolved far-red spectra of the magnetic cataclysmic variable QQ Vul. The spectra show the Na i doublet absorption features near λ 8190 Å from the cool secondary star, and the lines of He ii, O i, Mg ii, C i, N i, Ca ii and Paschen in emission. Using a Doppler imaging technique, we find that the H i, He ii, C i and O i lines have a narrow component originating near the L1 point and a strong component from the stream, while the Mg ii and Ca ii emission arises solely from the illuminated hemisphere of the red dwarf. We carry out an exhaustive analysis of the emission- and absorption-line velocities and fluxes seen in the QQ Vul spectrum. By simultaneously fitting the radial velocity and flux information we are able to produce surface maps of each line on the secondary star using a technique analogous to the one employed by Davey. The Na i and Mg ii maps show an asymmetric distribution akin to that seen in AM Her. Although the observed velocity semi-amplitudes (K2) of the lines can potentially be corrected for the effects of irradiation, we find that time-dependent changes in the degree of heating on the secondary can lead to large discrepancies in the results, significant enough to give inconsistent values from data taken at different epochs. We discuss the limitations of the surface mapping method as a means of correcting the observed K2. Our results also suggest that the emission features from the red dwarf are likely to be formed at quite high levels of the stellar chromosphere, in some cases probably even beyond the L1 point and inside the Roche lobe of the white dwarf, with the different lines possibly forming at different depths. Using the Na i absorption doublet, we find a velocity semi-amplitude for the secondary star of K2=219±6 km s−1 and a projected rotational velocity of vrot sin i=110±15 km s−1. Thus we estimate the mass ratio to be q=0.54±0.14. Based on the results of the best-fitting surface maps on all the lines, and the nature of the phase-dependent variations of the continuum and lines, we infer a binary inclination of i=65°±7°, and obtain a complete set of binary parameters for QQ Vul. We classify the secondary star as M4V from the TiO band ratios.
Fluctuating electrostrictive forces inside a dielectric lead to the radiation of photons if the dielectric is deformed or displaced by external forces. This is a generalization of the effect of radiation from moving minors to physically realistic systems.
An attractive method of obtaining an effective cosmological constant at the present epoch is through the potential energy of a scalar field. Considering models with a perfect fluid and a scalar field, we classify all potentials for which the scalar field energy density scales as a power law of the scale factor when the perfect fluid density dominates. There are three possibilities. The first two are well known; the much-investigated exponential potentials have the scalar field mimicking the evolution of the perfect fluid, while for negative power laws, introduced by Ratra and Peebles, the scalar field density grows relative to that of the fluid. The third possibility is a new one, where the potential is a positive power law and the scalar field energy density decays relative to the perfect fluid. We provide a complete analysis of exact solutions and their stability properties, and investigate a range of possible cosmological applications.