Electronic structure and Jahn-Teller effect in GaN:Mn and ZnS:Cr

We present an ab-initio and analytical study of the Jahn-Teller effect in two diluted magnetic semiconductors (DMS) with d4 impurities, namely Mn-doped GaN and Cr-doped ZnS. We show that only the combined treatment of Jahn-Teller distortion and strong electron correlation in the 3d shell may lead to the correct insulating electronic structure. Using the LSDA+U approach we obtain the Jahn-Teller energy gain in reasonable agreement with the available experimental data. The ab-initio results are completed by a more phenomenological ligand field theory.Comment: 15 pages, 5 figure

Crystal Distortion and the Two-Channel Kondo Effect

We study a simple model of the two-channel Kondo effect in a distorted crystal. This model is then used to investigate the interplay of the Kondo and Jahn-Teller effects, and also the Kondo effect in an impure crystal. We find that the Jahn-Teller interaction modifies the characteristic energy scale of the system below which non-Fermi-liquid properties of the model become apparent. The modified energy scale tends to zero as the limit of a purely static Jahn-Teller effect is approached. We find also that the non-Fermi-liquid properties of the quadrupolar Kondo effect are not stable against crystal distortion caused by impurities.Comment: 11 page

The null energy condition and instability

We extend previous work showing that violation of the null energy condition implies instability in a broad class of models, including gauge theories with scalar and fermionic matter as well as any perfect fluid. Simple examples are given to illustrate these results. The role of causality in our results is discussed. Finally, we extend the fluid results to more general systems in thermal equilibrium. When applied to the dark energy, our results imply that w is unlikely to be less than -1.Comment: 11 pages, 5 figures, Revte

The Journal of the Friends' Historical Society vol. 2 No. 3

1. Notices. 2. Notes and Queries. 3. The First Publishers of Truth III. 4. Edmund Peckover, ex-soldier and Quaker. 5. County Tipperary Friends' Records II. 6. Bevan and Naish Library, Birmingham. 7. Decline Literature II. 8. The Price of Candles. 9. Friends on the Atlantic I. 10. Extracts from the Bishop of Chester's Visitation, 1665 I. 11. Meetings in Yorkshire, 1668 III. 12. The Will of Margaret Fox. 13. William Keynell, of Dorsetshire. 14. William Miller at the King's Gardens I. 15. Springett Penn to James Logan. 16. Occurrences for the Progress of Truth I. 17. Friends' in Current Literature. 18. Friends' Reference Library, Devonshire House. 19. Sixth List of Members. 20. Editors' Notes

A 18F radiolabelled Zn(ii) sensing fluorescent probe

A selective fluorescent probe for Zn(ii), AQA-F, has been synthesized. AQA-F exhibits a ratiometric shift in emission of up to 80 nm upon binding Zn(ii) ([AQA-F] = 0.1 mM, [Zn(ii)Cl 2 ] = 0-300 μM). An enhancement of quantum yield from Φ = 4.2% to Φ = 35% is also observed. AQA-F has a binding constant, K d = 15.2 μM with Zn(ii). This probe has been shown to respond to endogenous Zn(ii) levels in vitro in prostate and prostate cancer cell lines. [ 18 F]AQA-F has been synthesized with a radiochemical yield of 8.6% and a radiochemical purity of 97% in 88 minutes. AQA-F shows the potential for a dual modal PET/fluorescence imaging probe for Zn(ii)

Preparation and Use of "Authentic English" Web Materials at The University of Tokushima (Tokushima, Japan)

This paper outlines a pilot project funded by The President’s Fund of the University of Tokushima that was designed to create English educational material to motivate students to acquire “Authentic English.” Recording was at sites in Honolulu (Hawaii, USA), Storrs (Connecticut, USA), Montreal (Canada) and Brisbane (Australia). Material was designed for use in teaching EFL students at our university who are taking general English courses. Section One of this paper refers to the aims and process of making English educational material for the Web. Sections Two, Three, and Four refer to how the materials were created. Section Five introduces technical aspects of the Web application. Sections Six and Seven discuss merits and problems related to the “Authentic English” material and its production

Ultrahigh Bandwidth Spin Noise Spectroscopy: Detection of Large g-Factor Fluctuations in Highly n-Doped GaAs

We advance all optical spin noise spectroscopy (SNS) in semiconductors to detection bandwidths of several hundred gigahertz by employing an ingenious scheme of pulse trains from ultrafast laser oscillators as an optical probe. The ultrafast SNS technique avoids the need for optical pumping and enables nearly perturbation free measurements of extremely short spin dephasing times. We employ the technique to highly n-doped bulk GaAs where magnetic field dependent measurements show unexpected large g-factor fluctuations. Calculations suggest that such large g-factor fluctuations do not necessarily result from extrinsic sample variations but are intrinsically present in every doped semiconductor due to the stochastic nature of the dopant distribution.Comment: 5 pages, 3 figure

Evidence for charge localization in the ferromagnetic phase of La_(1-x)Ca_(x)MnO_3 from High real-space-resolution x-ray diffraction

High real-space-resolution atomic pair distribution functions of La_(1-x)Ca_(x)MnO_3 (x=0.12, 0.25 and 0.33) have been measured using high-energy x-ray powder diffraction to study the size and shape of the MnO_6 octahedron as a function of temperature and doping. In the paramagnetic insulating phase we find evidence for three distinct bond-lengths (~ 1.88, 1.95 and 2.15A) which we ascribe to Mn^{4+}-O, Mn^{3+}-O short and Mn^{3+}-O long bonds respectively. In the ferromagnetic metallic (FM) phase, for x=0.33 and T=20K, we find a single Mn-O bond-length; however, as the metal-insulator transition is approached either by increasing T or decreasing x, intensity progressively appears around r=2.15 and in the region 1.8 - 1.9A suggesting the appearance of Mn^{3+}-O long bonds and short Mn^{4+}-O bonds. This is strong evidence that charge localized and delocalized phases coexist close to the metal-insulator transition in the FM phase.Comment: 8 pages, 8 postscript figures, submitted to Phys. Rev.