Mean-Field Theory for the Spin-Triplet Exciton Liquid in Quantum Wells

Using a mean-field theory, we study the possible existence of a spin-triplet intersubband exciton liquid ground state in semiconductor quantum well systems as a function of the electronic density and the strength of the intersubband Coulomb interaction matrix element at low temperatures. We find the excitonic phase to be stable over a large region of parameter space, and our calculated critical temperatures are attainable experimentally. In addition, we find that the transition to the excitonic phase can be either first- or second-order at zero temperature.Comment: 4 pages, REVTEX with psfig macros; 4 PostScript figures in uufiles forma

The Geology and Geophysics of the United Arab Emirates. Volume 6, Geology of the western and central United Arab Emirates

This volume forms part of the product of a multidisciplinary study by the British Geological Survey (BGS), commissioned by the UAE Federal Government, Ministry of Energy, to produce 1:100 000 scale geological maps of the bedrock and superficial geology of the central and western part of the UAE. 1:50 000 scale maps were produced of selected areas near Abu Dhabi and for seven emergent salt domes (mainly on offshore islands). This document therefore follows on from the previous volume (Styles et al., 2006) on the geology of the northern Emirates. The present volume similarly contains information about the findings of the geological mapping and associated specialist research. Much of the central and western part of the UAE is blanketed by Quaternary and recent dune sands, fluvial sediments and sabkhas. The only significant areas of exposed older rocks occur along the coast between Abu Dhabi and As Sila and on the various salt islands. Previous geological maps were made more than 20 years ago and were based largely on air photo interpretation with limited ground-truthing. The rapid economic development in the intervening period has seen a tremendous expansion of the national infrastructure and this has greatly increased the demand for high quality, field-based geological maps. The area was mapped at a scale of 1:50 000 and maps produced at 1:100 000, with the exception of the salt dome islands which were mapped at 1:25 000 scale. An area of the coast around Abu Dhabi is illustrated in two additional maps produced at 1:50 000 scale. Each 1:100 000 scale map is accompanied by a Sheet Explanation that describes the rock sequences in the area covered by that particular map. This report describes the broader features of the main rock groups on a regional basis and includes the results of the specialist laboratory studies that were used to define and interpret the geology of the project area. The field mapping was undertaken in the winter months between October 2008 and March 2011. The mapping was carried out by A R Farrant, R A Ellison, R J Thomas, J W Merritt, S J Price, A J Newell, J Merritt, J R Lee, A B Leslie, H F Burke, R A Smith, K M Goodenough, A Finlayson, C J Jordan and S L B Arkley. The laboratory studies were mostly carried out at the BGS. The petrographic study of the Miocene and Quaternary rocks and sediments was carried out by E R Phillips, whilst the igneous petrology of the Hormuz Complex rocks was undertaken by members of the mapping team. I P Wilkinson undertook micropalaeontologial determinations of both Miocene and recent sediments. The macropalaeontology of the basal Baynunah Formation is based largely on published information provided by Dr Mark Beech, Professor Andrew Hill and Dr Faisal Bibi. Some additional data on the Fars Group was provided by M A Woods. R Knox did the heavy mineral analyses, whilst D Wagner and S Kemp worked on the XRD analysis. The U-Pb zircon and carbonate geochronology was undertaken by M Horstwood, N Roberts and R Parrish at the NERC Isotope Geoscience Laboratories at the BGS, Keyworth. The Optically Stimulated Luminescence (OSL) dating was carried out by Professor G Duller and Dr H Roberts in the Aberystwyth Luminescence Research Laboratory at the Institute of Geography and Earth Sciences, Aberystwyth University. P Turner and C Simpson were responsible for the GIS systems and map layouts. H Holbrook and S Ward drew the majority of the illustrations. W Masterson and A Hill formatted this Memoir and the Sheet Explanations. This volume was compiled by A R Farrant and edited by R J Thomas

Fine structure of excitons in Cu2_2O

Three experimental observations on 1s-excitons in Cu$_2$O are not consistent with the picture of the exciton as a simple hydrogenic bound state: the energies of the 1s-excitons deviate from the Rydberg formula, the total exciton mass exceeds the sum of the electron and hole effective masses, and the triplet-state excitons lie above the singlet. Incorporating the band structure of the material, we calculate the corrections to this simple picture arising from the fact that the exciton Bohr radius is comparable to the lattice constant. By means of a self-consistent variational calculation of the total exciton mass as well as the ground-state energy of the singlet and the triplet-state excitons, we find excellent agreement with experiment.Comment: Revised abstract; 10 pages, revtex, 3 figures available from G. Kavoulakis, Physics Department, University of Illinois, Urban

Polarized interacting exciton gas in quantum wells and bulk semiconductors

We develop a theory to calculate exciton binding energies of both two- and three-dimensional spin polarized exciton gases within a mean field approach. Our method allows the analysis of recent experiments showing the importance of the polarization and intensity of the excitation light on the exciton luminescence of GaAs quantum wells. We study the breaking of the spin degeneracy observed at high exciton density $(5 \ \ 10^{10} cm ^2)$. Energy level splitting betwen spin +1 and spin -1 is shown to be due to many-body inter-excitonic exchange while the spin relaxation time is controlled by intra-exciton exchange.Comment: Revtex, 4 figures sent by fax upon request by e-mai

Soft and hard tissue assessment of immediate implant placement: a case series

Objectives : The aim of this prospective study was to evaluate clinically and radiographically the success and esthetic result of immediate implant placement at the time of extraction. Material and methods : Twelve patients with 14 titanium screw-shaped implants (13–16 mm length and 4.3 or 5 mm diameters) were placed in the extraction sockets. Defects after implant placement were recorded, and then filled up with deproteinized bovine bone mineral, bioabsorbable collagen membrane, and absorbable pins. The defect was again re-evaluated at second-stage surgery. Clinical and radiographic parameters of the peri-implant conditions were assessed at the moment of prosthesis placement and at 1-year follow-up. Results : The cumulative implant survival and success rate was 100% after a 1-year observation period. Analysis of the esthetic result showed that the mean pink esthetic score (PES) was 11.1 (SD 1.35) at 1-year follow-up. At 1 year, 64.3% papillae had a score of 2 and the remaining 35.7% score 3 according to the Jemt (1997) papillary index. Optimal value of width of the keratinized mucosa was recorded in 13 (92.9%) implant cases in both periods of follow-up. At 1-year follow-up, the linear distance between implant-shoulder to the bone peaks remains stable with a mean of 2.62±0.2 mm at the mesial and 2.9±0.58 mm at the distal aspect. Conclusion : Careful evaluation of potential extraction sites before immediate implant installation promotes optimal implant esthetics. To cite this article: Juodzbalys G, Wang H-L. Soft and hard tissue assessment of immediate implant placement: a case series. Clin. Oral Impl. Res. 18 , 2007; 237–243 doi:10.1111/j.1600-0501.2006.01312.xPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74957/1/j.1600-0501.2006.01312.x.pd

Probing Gravitation, Dark Energy, and Acceleration

The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the properties of the dark energy or gravity through cosmological observations and compare and distinguish between them. In fact, close consistencies exist between a dark energy equation of state function w(z) and changes to the framework of the Friedmann cosmological equations as well as direct spacetime geometry quantities involving the acceleration, such as ``geometric dark energy'' from the Ricci scalar. We investigate these interrelationships, including for the case of superacceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.Comment: 12 pages, 8 figure

Limits on the gravity wave contribution to microwave anisotropies

We present limits on the fraction of large angle microwave anisotropies which could come from tensor perturbations. We use the COBE results as well as smaller scale CMB observations, measurements of galaxy correlations, abundances of galaxy clusters, and Lyman alpha absorption cloud statistics. Our aim is to provide conservative limits on the tensor-to-scalar ratio for standard inflationary models. For power-law inflation, for example, we find T/S<0.52 at 95% confidence, with a similar constraint for phi^p potentials. However, for models with tensor amplitude unrelated to the scalar spectral index it is still currently possible to have T/S>1.Comment: 23 pages, 7 figures, accepted for publication in Phys. Rev. D. Calculations extended to blue spectral index, Fig. 6 added, discussion of results expande

Measurement of νˉμ\bar{\nu}_{\mu} and νμ\nu_{\mu} charged current inclusive cross sections and their ratio with the T2K off-axis near detector

We report a measurement of cross section $\sigma(\nu_{\mu}+{\rm nucleus}\rightarrow\mu^{-}+X)$ and the first measurements of the cross section $\sigma(\bar{\nu}_{\mu}+{\rm nucleus}\rightarrow\mu^{+}+X)$ and their ratio $R(\frac{\sigma(\bar \nu)}{\sigma(\nu)})$ at (anti-)neutrino energies below 1.5 GeV. We determine the single momentum bin cross section measurements, averaged over the T2K $\bar{\nu}/\nu$-flux, for the detector target material (mainly Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory frame kinematics of $\theta_{\mu}$500 MeV/c. The results are $\sigma(\bar{\nu})=\left( 0.900\pm0.029{\rm (stat.)}\pm0.088{\rm (syst.)}\right)\times10^{-39}$ and $\sigma(\nu)=\left( 2.41\ \pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}$in units of cm$^{2}$/nucleon and$R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)= 0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure

Planck intermediate results. VIII. Filaments between interacting clusters

About half of the baryons of the Universe are expected to be in the form of filaments of hot and low density intergalactic medium. Most of these baryons remain undetected even by the most advanced X-ray observatories which are limited in sensitivity to the diffuse low density medium. The Planck satellite has provided hundreds of detections of the hot gas in clusters of galaxies via the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for studying extended low density media through the tSZ effect. In this paper we use the Planck data to search for signatures of a fraction of these missing baryons between pairs of galaxy clusters. Cluster pairs are good candidates for searching for the hotter and denser phase of the intergalactic medium (which is more easily observed through the SZ effect). Using an X-ray catalogue of clusters and the Planck data, we select physical pairs of clusters as candidates. Using the Planck data we construct a local map of the tSZ effect centered on each pair of galaxy clusters. ROSAT data is used to construct X-ray maps of these pairs. After having modelled and subtracted the tSZ effect and X-ray emission for each cluster in the pair we study the residuals on both the SZ and X-ray maps. For the merging cluster pair A399-A401 we observe a significant tSZ effect signal in the intercluster region beyond the virial radii of the clusters. A joint X-ray SZ analysis allows us to constrain the temperature and density of this intercluster medium. We obtain a temperature of kT = 7.1 +- 0.9, keV (consistent with previous estimates) and a baryon density of (3.7 +- 0.2)x10^-4, cm^-3. The Planck satellite mission has provided the first SZ detection of the hot and diffuse intercluster gas.Comment: Accepted by A&

Potential for comparative public opinion research in public administration

The public administration and public services have always taken a marginal place in the political scientists’ behavioural research. Public administration students on the other hand tend to focus on political and administrative elites and institutions, and largely ignored citizens in comparative research. In this article we make a plea for international comparative research on citizens’ attitudes towards the public administration from an interdisciplinary perspective. Available international survey material is discussed, and main trends in empirical practice and theoretical approaches are outlined, especially those with a potential impact on public sector reform