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Notes: We report the temperature-dependent characteristics of photoluminescence emission in modulation δ-doped AlxGa1−xAs/InyGa1−yAs/GaAs structures. Transition energies are analyzed using a self-consistent solution of the coupled k⋅P Hamiltonian–Poisson equation. At low temperatures, dominant emissions are due to the transitions from the first electron subband to the first heavy-hole subband and from the second electron subband to the first heavy-hole subband irrespective of the location of modulation doping. The second hole subband related transitions associated with the first electron subband or the second electron subband emerges with increasing temperature depending on the location of doping. The relative intensities of the transitions from the first and second electron subbands to the first heavy-hole subband transitions are analyzed as a function of the Fermi energy position. An excellent agreement is found between the measurements and calculations. © 1994 American Institute of Physics.

Notes: Objective— To identify those congenital fetal anomalies, previously identified by ultrasound scanning, in which fast-scan magnetic resonance imaging (F-SMRI) would give additional information for the perinatal management of the infants.Design— Observational clinical study.Setting— Hospital Department of Obstetrics and Gynaecology/Resonance Research Centre.Subjects— Seven women carrying eight fetuses in whom congenital abnormal-ities had been identified using ultrasound scans. The duration of the pregnancies was 28 to 39 weeks gestation.Interventions— Fast-scan magnetic resonance imaging at between 28 and 39 weeks gestation.Main outcome measures— Identification of fetal abnormalities.Results and conclusions— F-SMRI was of limited value in the diagnosis of further assessment of fetuses with abnormalities of accumulation of tissue fluid. Renal anomalies were poorly identified unless associated with cystic formation of the kidney. Further study is required in the imaging of fetal central nervous system anomalies. Until echoplanar imaging is more widely available, MRI does not contribute to the diagnosis of cardiac anomalies. F-SMRI appears to be most useful in the diagnosis and management of soft tissue gastro intestinal abnormalities.

Notes: We present preliminary results of a study of defects in GaAs-AlGaAs superlattices using deep-level transient spectroscopy (DLTS). A dramatic difference is observed between the DLTS spectra of two superlattices when the superlattice period is doubled. This is explained by the presence of miniband conduction in the case of the smaller period and its absence in the case of the larger, and by the consequent difference in the distribution of electrons in the superlattice. Observed activation energies must be reinterpreted for comparisons to bulk material.

Notes: The electrical and optical properties of AlGaAs grown by metalorganic molecular-beam epitaxy using triethylaluminum, tri-isobutylaluminum, and trimethylamine-alane are compared. It is found that tri-isobutylaluminum yields the lowest residual carbon incorporation in the layers (Na − Nd = 4 × 1015 cm−3) and the highest electron and hole mobilities. Photoluminescence spectra for the higher-quality AlGaAs, grown using TiBAl, show excitonic luminescence. However, this luminescence appears to be defect related.

Notes: The thin strained superlattice (TSSL) concept is introduced as a means for extending the practical range of application for pseudomorphic Inx Ga1−x As on GaAs. Growth and characterization results are presented for pseudomorphic high electron mobility transistor structures with GaAs-In0.3 Ga0.7 As TSSL active layers grown by molecular beam epitaxy. The TSSLs are composed of three periods of GaAs(15 A(ring))- In0.3 Ga0.7 As(h2 ), where h2 ranges from 30 to 52 A(ring). Modulation doping of the TSSLs is provided by atomic planar-doped Al0.3 Ga0.7 As overlayers with 45 A(ring) undoped spacers. 77 K Hall effect and transmission electron microscopy reveal that relatively thick TSSLs can be grown with high electronic and structural quality, comparable to much thinner In0.3 Ga0.7 As single quantum wells. Results are compared with a model for critical layer thickness and discussed in light of in situ reflection high-energy electron diffraction measurements.

Notes: We report the temperature dependent characteristics of photoluminescence linewidth in terms of two-dimensional electron gas sheet concentration for modulation δ-doped AlxGa1−xAs/InyGa1−yAs/GaAs structures. The electron concentration is obtained using a self-consistent solution of the coupled k⋅P Hamiltonian–Poisson equation. We find that only the full width at half maximum of the n=2 electron-subband-to-n=1 hole subband transition is useful for characterizing high electron density at T=2–300 K. The importance of hole localization for correlating the electron density with photoluminescence linewidth is discussed. © 1994 American Institute of Physics.

Notes: The 9–0 and 9–1 transitions of the A 1Πu–X 1Σ+g system of N2+2 have been observed by fast ion beam photofragment spectroscopy. Multireference configuration interaction ab initio calculations predict v'=8 to be the highest bound level which seemed to be supported by experimental evidence. The dominant predissociation mechanism for the v'=9 level appears to be through tunneling, unlike the v'=6, 7, and 8 levels, which show an e/f symmetry-dependent electronic predissociation. Calculated tunneling lifetimes from our own modified A 1Πu state potential gives good agreement with the experimental lifetimes. In addition to the 9–1 and 9–0 bands, we have also measured the previously unobserved 7–0 and 8–0 rovibronic transitions thus extending Cosby, Müller, and Helm's study to the blue [Phys. Rev. A 28, 766 (1983)]. Molecular constants have been determined for the v=0 of the X 1Σ+g state and v=7, 8, and 9 of the A 1Πu state.

Notes: Four silages were prepared from grass treated with additives designed to produce different extents of fermentation in the silo. The additive treatments were: formic acid at 5 l t−1; a bacterial inoculant (Ecosyl, ICI plc); the inoculant plus molasses at 20 kg t−1; and a noadditive control. All silages were well preserved. Formic acid severely restricted the extent of fermentation, the concentration of lactic acid being only 50% of that seen for the other treatments, all of which were similar in lactic acid concentrations.The silages were offered ad libitum, either as the sole component of the diet or together with three supplement treatments to 16 British Friesian cows, in four 4 treatment × 4 period Latin squares with periods of 28 d duration. The supplements were: a barley-based mixture at 5 kg d−1 (B); a high-fat, high-protein product at 2 kg d−1 (FPI) and at 3 kg d −1 (FP2); both FP treatments were given with 1 kg d−1 of molassed sugarbeet pulp. A preliminary experiment, using three lactating, rumen-cannulated cows in a 3×3 Latin square design with 28-d periods, provided information on rumen digestion when the supplements were given with a separate, non-experimental silage.In the preliminary experiment, neither of the FP treatments influenced the molar proportion of the major rumen volatile fatty acids compared with treatment B; nor were there any depressive effects of the FP treatments on silage intake compared with treatment B.In the main experiment, the intake of silage with the inoculant treatment was less than that with the other treatments, the effect being generally significant (at least P〈0·05) for all three supplements. When the silages were given unsupplemented, there were differences in the concentration (P〈0·001) and yield (P〈0·01) of milk fat, both of which were lowest for the no-additive control and highest for the formic acid silage. When supplement B was given, the concentration and yield of milk fat were lowest for the no-additive control and the concentration and yield of milk protein were highest for the formic acid silage. For all silages both FP treatments tended to depress silage intake and reduce the concentration of fat and protein in milk compared with treatment B.Although there were clear indications of differences in nutritional characteristics between the silages, there was little evidence that the differences between silages influenced the responses to changes in the composition of the supplements.

Notes: Abstract Most orchards in British Columbia, Canada and the northwestern United States received substantial applications of DDT in the mid-1940s through the early 1970s. Bird eggs were collected from orchard and non-orchard areas in the Okanagan Valley fruit-growing region of central British Columbia during 1990 and 1991 to determine levels of DDT, DDE, and other organochlorines. American robin (Turdus migratorius) eggs from orchard areas contained extremely high levels of both DDE (up to 103 mg/kg) and DDT (up to 26 mg/kg). For robins, tree swallows (Tachycineta bicolor), and house wrens (Troglodytes aedon), levels of DDT and DDE in eggs were significantly higher in orchard habitats than in non-orchard habitats. These data suggest that Okanagan Valley birds were acquiring DDT and DDE burdens locally, and not on their Latin American wintering grounds, as has been previously hypothesized. Ratios of DDE to DDT in robin eggs were quite low (〈10), implying that DDT is not breaking down readily in orchard soils and/or that orchards have been receiving recent illicit applications of DDT. There was no evidence of lower reproductive success among tree swallows, house wrens, and bluebirds that nested in orchard versus non-orchard habitats, so the levels of DDT and DDE contained in their eggs (⩽0.1 and ⩽5 mg/kg, respectively) were probably not deleterious. There was no difference in reproductive success of robins nesting in conventional versus organic orchards. Although we did not have a sufficient sample of non-orchard robin nests, comparisons with data on reproductive success in the literature indicates that despite exceedingly high DDT and DDE concentrations, reproduction was not affected. Levels of other organochlorines (dieldrin, heptachlor epoxide, PCBs) in eggs were low, and usually below the minimum detectable threshold. The high DDE concentrations in these eggs from the Okanagan valley indicate that DDE body burdens of passerines nesting there would probably present a considerable toxic hazard to predators, particularly birds of prey.

Notes: Abstract The Gibbs states of binary lattice systems can be characterized by their stability with respect to certain microscopic transitions which have a simple physical interpretation. A detailed analysis is provided for the case of a one-dimensional lattice gas with nearest-neighbor interactions.