The structure of epitaxial V2O3 films and their surfaces: A medium energy ion scattering study

Medium energy ion scattering, using 100 keV H⁺ incident ions, has been used to investigate the growth of epitaxial films, up to thicknesses of ~ 200 Å, of V₂O₃ on both Pd(111) and Au(111). Scattered-ion energy spectra provide a measure of the average film thickness and the variations in this thickness, and show that, with suitable annealing, the crystalline quality is good. Plots of the scattering yield as a function of scattering angle, so-called blocking curves, have been measured for two different incidence directions and have been used to determine the surface structure. Specifically, scattering simulations for a range of different model structures show poor agreement with experiment for half-metal (….V′O₃V) and vanadyl (….V′O₃V=O) terminations, with and without surface interlayer relaxations. However, good agreement with experiment is found for the modified oxygen-termination structure, first proposed by Kresse et al., in which a subsurface V half-metal layer is moved up into the outermost V buckled metal layer to produce a VO₂ overlayer on the underlying V₂O₃, with an associated layer structure of ….O₃VV′′V ′O₃. This result is consistent with the predictions of thermodynamic equilibrium at the surface under the surface preparation conditions, but is at variance with the conclusions of earlier studies of this system that have favoured the vanadyl termination. The results of these previous studies are re-evaluated in the light of the new result.     

Magnetic properties of crystalline and amorphous DyAg from μSR measurements

Muon spin relaxation in crystalline and amorphous DyAg has been studied in the paramagnetic and magnetically ordered regimes. In cr-DyAg the critical slowing down of the Dy³⁺ spin fluctuation is seen on approaching T_N = 60 K. In the ordered state we observe a Lorentzian field distribution. The muon spin relaxation in am-DyAg approaches at lower temperatures a root exponential law usually encountered in spin glasses.     

In Vivo and In Vitro Photodynamic Studies with Benzochlorin Iminium Salts Delivered by a Lipid Emulsion

Benzochlorin iminium salts (Bis) are hydrophobic photosensitizers based on an octaethylbenzochlorin nucleus that absorb in the near-IR region of the visible spectrum. In these studies the photodynamic activities of the zinc, copper and metal-free BI derivatives were compared in vivo in C3H-HeJ mice bearing a mammary adenocarcinoma tumor line. In vitro studies were also performed with the radiation-induced fibrosarcoma tumor line. An argon-pumped Ti-sapphire laser tuned to deliver light between 710 and 800 nm or an Oriel arc-lamp filtered to deliver broadband light above 590 nm were used as light source. A lipid emulsion was used as the delivery system for sensitizers in all studies. A pronounced solvent dependence was observed for the Q band for each of all iminium salts examined. As an example, the metal-free (BI) derivative had an absorption maximum at 798 nm in dichloromethane and at 727 nm in serum. The action spectra showed a greater PDT response at blue-shifted wavelengths for each of the three iminium salts both in vivo and in vitro. Among the three derivatives, the zinc analog (ZnBI) produced the greatest tumor regression at the low drug/light dose of 0.7 (μ mole/kg and 200 J/cm². These results indicate that iminium salts have characteristics that may make them promising third-generation photosensitizers.     

Site of the positive muon in YBa2Cu3O7

A combination of μSR and¹⁷O nuclear quadrupolar μLCR has been used to obtain detailed information on the muon site in YBa₂Cu₃O₇. The rms magnitude of the nuclear dipolar fields in YBa₂Cu₃O₇ enriched with 38%¹⁷O is about twice that in the natural¹⁶O sample. In addition the¹⁷O μLCR spectrum shows that the electric field gradient tensor at the oxygen closest to the muon is almost equal to that measured by NMR for the CuO₂ plane sites O(2,3). These results suggest that the muon in fully oxygenated YBa₂Cu₃O₇ is located at a single site 1.0 Å from an oxygen ion, probably O(2,3).     

A high resolution 4π alpha spectrometer with silicon surface barrier detectors

An alpha counting system has been designed which gives counting geometry of nearly 4π with resolution capabilities of 25 keV or better. The alpha source is electro-deposited onto a thin gold foil which is sandwiched between two silicon surface barrier detectors. Alpha pulses from the two detectors are amplified, normalized and summed as a single pulse height spectrum. The techniques for the electrodeposition of the alpha activity onto the thin gold foil are described.     

Magnetic features of the Kondo system CeTSn (T=Ni,Pd, Pt) probed by positive muons

Zero-, longitudinal and transverseSR measurements are reported on CeNiSn, CePdSn and CePtSn. Below 1 K CeNiSn exhibits strong magnetic correlations, up to possible short range order, but a magnetic phase transition did not occur down to 0.033 K. CePdSn and CePtSn signal their transition into the ordered antiferromagnetic phase by a spontaneous spin precession signal. The second magnetic phase transition in CePtSn reveals itself by the onset of a more complex spin precession pattern. Most unusual is the formation of a paramagnetic state with frozen random spin structure in CePtSn about one Kelvin aboveT _N.This work was supported by the German Federal Minister for Research and Technology (Bundesminister für Forschung und Technologie [BMFT]) under Contract Nr. 03KA2-TUM-4.     

N-halogeno-compounds. Part II [1]. N.M.R. data for polyfluorocyclohexadienylideneamines obtained via N- chlorination of polyfluoroarylamines

N.m.r. parameters for nine (I-IX) $\text{N}$-chloropolyfluorocyclohexa-2,5-dienylideneamines are reported and discussed; the magnitudes of the FF-coupling constants fall into the following ranges:

$\text{J}$₁₂ 0-2.8; $\text{J}$₁₃, $\text{J}$₃₅ 6.0-6.8; $\text{J}$₁₄ <1; $\text{J}$₁₅ 0-2.6; $\text{J}$₂₃, $\text{J}$₃₄ 25.5-27.2; $\text{J}$₂₄ 0-6.0; $\text{J}$₂₅ 0-1.2; $\text{J}$₄₅ 5.4-9.8 Hz (I) X = Y = Z = F; (II) X = OMe, Y = Z = F; (III) X - CF₃, Y = Z = F; (IV) X = Ph, Y = Z = F; (V) X = Cl, Y = Z = F; (VI) X = Br, Y = Z = F; (VII) X = Y = F, Z = Cl; (VIII) X = Y = F, Z = Br; (IX) X = Z = F, Y = H. The spectra of $\text{N}$-methyl-4-chloropentafluorocyclohexa-2,5-dienyldeneamine have also been analysed. All the imines examined are configurationally stable at the nitrogen atom.     

Matching Stochastic Algorithms to Objective Function Landscapes

Large scale optimisation problems are frequently solved using stochastic methods. Such methods often generate points randomly in a search region in a neighbourhood of the current point, backtrack to get past barriers and employ a local optimiser. The aim of this paper is to explore how these algorithmic components should be used, given a particular objective function landscape. In a nutshell, we begin to provide rules for efficient travel, if we have some knowledge of the large or small scale geometry.     

A TIME SERIES APPROACH TO STOCK-RECRUITMENT ANALYSIS: TRANSFER FUNCTION NOISE MODELLING

Perceived relationships between stock size and recruitment have long been a corner-stone of fisheries management. These relationships are often used to design harvest strategies for ensuring that sufficient spawning stock exists to generate desired levels of recruitment in subsequent years. However, existing models fail to recognize and exploit the autocorrelation structure of both the recruitment and stock time series. The time series approach to modelling stock and recruitment presented in this paper takes this autocorrelation structure into account. The performance of the time series model is compared to existing stock-recruitment models using North Sea herring and Pacific halibut data.