Two major types of terrain that formed at or near the bed of Pleistocene continental ice sheets are widespread throughout the prairie region of Canada and the United States. These are (1) glacial-thrust blocks and source depressions and (2) streamlined terrain.

Glacial-thrust terrain formed where the glacier was frozen to the substrate and where elevated pore-water pressure decreased the shear strength of the substrate to a value less than that applied by the glacier. The marginal zone of ice sheets consisted of a frozen-bed zone, no more than 2 to 3 km wide in places, within which glacial-thrust blocks are large and angular. Up-glacier from this zone the thrust blocks are generally smaller and smoothed. Streamlined terrain begins 2 to 3 km behind known ice-margin positions and extends tens of kilometres up-glacier. Streamlined terrain formed in two ways: (1) erosion of the substrate as a consequence of basal sliding in the sub-marginal thawed-bed zone and (2) erosional smoothing accompanied by emplacement of till in the lee of thrust blocks where they were deposited and subsequently exposed to thawed-bed conditions as a result of further advance of the glacier.

This paper has been accepted for publication in full in a future issue of the Journal of Glaciology.

The nature and origin of the hundreds of ionized knots, with cometary tails, in the Helix planetary nebula are both being unravelled by recent observations. Healey and Huggins (1990, AJ, 100, 511), Meaburn et al (1992, MNRAS, 255, 177) and Walsh and Meaburn (1993, ESO Messenger, 73, 35) all showed, in various ways, that these knots have dense (106 cm–3), dusty, molecular cores with ionized arcs of gas on the surfaces pointing towards the ionizing star. This structure is confirmed in detail by the HST imagery of O'Dell and Handron (1996, ApJ, in press).

We used the Wisconsin Ultraviolet Photo-Polarimeter Experiment during the Astro-2 mission aboard the Space Shuttle Endeavour, to obtain ultraviolet spectropolarimetry of three classical novae that had recently gone into outburst. All three novae appear to have intrinsic polarization, with polarization changes across emission lines. This result indicates that, geometrically, the ejecta were quite aspherical.

The literature indicates increasing evidence showing the benefits of classroom-based, universal preventive interventions for mental health and the link between social and emotional learning and academic performance. The FRIENDS program has been extensively tested and has showed promising results not only for preventing childhood anxiety, but also for improving students’ self-concept, social skills and coping skills. However, when it comes to communities in disadvantage, the results are mixed, with some studies reporting the need to include enhancements to the context in which the program is implemented to better support communities at risk. A combined intervention aiming to promote students’ social-emotional skills was piloted in a school located in a low socio-economic status area. Teachers received training to teach social and emotional skills for students and a resilience program for themselves. Students’ social-emotional outcomes were assessed at pre, post, 3 and 6 months following the intervention. Results showed that the intervention helped students to decrease their anxiety, and the intervention was well accepted by participants.

Silicon wafers have been implanted with H+ (90 keV) to doses of 5.0E15/ cm2 and 2.OE16/cm2. The wafers were annealed in nitrogen at temperatures between 450 and 700°C for times between 10 and 60 min. The electrically active carrier profiles were measured by capacitance voltage and spreading resistance techniques. The residual damage was measured by TEM and RBS. The electrical measurements were essentially the same in both FZ and CZ silicon implying that oxygen is not playing a role in the donor formation which was observed. The donor concentration peaks near the projected range of the hydrogen after annealing at temperatures between 450–500°C. As reported previously 1000 H+ ions generate 1 donor in the implant peak. In addition, the donor concentration between the surface and Rp has increased more than a factor of 10 above the background concentration after a 450°C 10 min anneal. Anneals of 550°C for 30 min or more annihilates essentially all of the donors. The RBS results show small amounts of damage for the 5.0E15/cm2 implant dose but considerable crystal damage with a dose of 2.0E16/cm2, even after a 500°C, 30 min anneal. Cross-sectional TEM analysis of 500°C annealed samples showed a large number of small loops at depths corresonding to the depth of the peak electrical carrier concentration. The donors are directly correlated to the implant damage and resultant defects. SIMS data shows little diffusion for anneals of 500°C or less but after 550°C, 30 min the peak H concentration decreases by approximately a factor of 10.

The electrical properties of pyrolyzed polymers have been studied recently.1,2 It has been shown that organic, polymeric3 and non-polymeric4 films can be made conductive (ρ ~ 10−3Ωcm) by ion beam irradiation. Common to all of the films was the presence of carbon as a constituent element and both pyrolysis and ion beam irradiation3 was shown to increase the relative carbon content of the films. The ion beam irradiated organic films 3,4 exhibited a temperature dependence of their resistivity of the form ρ(T) = ρ∞e−(TЛ)*, where ρ is the ion-induced resistivity, ρ∞ and T0 are constants and T is the temperature. At very high doses of irradiation (1017cm−2Ar+@ 2MeV) the film resistivity was temperature independent. Very similar transport properties were observed in the pyrolyzed polymers1 as well, though the lowest resistivities achieved were higher than the resistivity values observed in the ion irradiated3 polymer films. In both the pyrolysis and ion-irradiation experiments the temperature dependence has been explained by a model due to Sheng and Abeles,5 which involves charge transport by hopping between conducting islands embedded in an insulating matrix. Such striking similarities between two distinctly different modes of energy deposition in the films, prompted us to compare the effects of pyrolysis and ion irradiation in different carbon containing films. We compared both a polymer (HPR-204°) and a film of electron beam evaporated carbon film. While in the former case one would observe chemical degradation as well as structural modification, by studying pure carbon films the physical nature of the processes could be clarified. We report metallic carrier densities in both films and evidence for significant structural rearrangement. We conclude that pyrolysis and ion beam irradiation have similar effects on both polymer and carbon films.

The effects of N-ion implantation on the corrosive-wear properties of Ti-6Al-4V, an alloy used for construction of the femoral component of artificial hip joints in humans, were tested. In corrosive-wear tests designed to simulate pertinent hip-joint parameters, electrochemical corrosion currents were measured for cylindrical samples in saline electrolyte in an arrangement which allowed the samples to be rotated between loaded polyethylene pads simultaneously with the current measurement. To further quantify material removal, Zr markers were ion-implanted into some samples so that, by use of Rutherford backscattering, material removal could be detected by changes in position of the marker relative to the surface. Corrosion currents were greatly reduced by implantation of approximately 20 at. % N, but even implantation of the Zr markers also reduced corrosion currents. The marker experiments confirmed the low rate of material removal for the implanted samples.

Alterations to the structure and properties of ceramics are complex due to the range of bonding types encountered and the necessity for maintaining local charge balance. Ion damage can occur as a result of ionizing effects as well as displacement collisions. Ion species, implantation temperature, implantation energy, and the specific bonding characteristics of the host are important parameters in determining the structure and properties of implanted ceramics. Some of these effects will be illustrated for Al2O3 implanted with chromium or zirconium and silicon carbide implanted with chromium.

Implantation of nitrogen into steels is known to affect surface sensitive mechanical properties. Tensile properties of thin foils implanted with either nitrogen or helium at 300 K have been measured. Fluences greater than 1 × 1016 ions/cm2 raise the yield stress and fracture stress and reduce the plastic strain to failure. Both nitrogen and helium give comparable stress-strain responses for equal average concentrations of implanted ions. The mechanical response is discussed in terms of plastic flow of laminated structures and hardening mechanisms. Initial results of atom probe field ion microscopy examinations of nitrogen implanted Fe-15 wt.% Cr-12 wt.% Ni alloy are described.

Commercial aluminum bronze (Cu-Al-Fe) alloys have been laser quenched with both continuous and pulsed CO2 laser sources. Metastable near surface regions of approximately 10 μm thickness have been produced. The quenched surfaces have been characterized by optical microscopy, SEM, EDX, AES and glancing angle XRD. The behavior of both laser quenched and “as received” conventional surfaces have been tested in both cavitation erosion and corrosion environments. In some cases significant differences are observed and can be rationalized from the microstructural changes accompanying the self quenching.

We report on intersubband transitions in In x Ga1-x As/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown In x Ga1-x As/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded In x Ga1-x As buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in In x Ga1-x As wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.

Ion beam assisted deposition (IBAD) has been used to deposit chromium nitride coatings using 1200 eV nitrogen ions from an RF-type ion source and thermally evaporated chromium. The ion/atom arrival ratio R was varied from 0 to 8 to modify the coating composition, microstructure, growth rate and stress state in order to optimize the properties of the material for use as a possible substitute for electroplated chromium in a number of anti-corrosion and tribological applications. The coatings were examined using Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy, and contained up to 44 at % nitrogen in a mixture of bcc Cr-N, Cr2N, and CrN. The microstructure of the coatings was examined by scanning electron microscopy, and the tribological behavior of the coatings was examined using an automated scratch testing and nanoindentation. XPS examination of the coatings indicates that nitrogen near the surface was bound to the metal as CrN and Cr2N in most of the coatings studied by XPS, which is expected to significantly affect their corrosion behavior. The high R values needed to form large amounts of the CrN phase in the bulk of the coating causes significant sputtering during deposition. This study indicates that it is not possible to form a coating consisting solely of cubic CrN by IBAD under these experimental conditions (room temperature substrate and partial pressure of nitrogen of 1.8 × 10−2 Pa). Nevertheless, the IBAD coatings produced were hard, in a compressive stress state, and highly adherent, all properties that make them candidates for use in selected Army applications.

African trypanosomes have emerged as promising unicellular model organisms for the next generation of systems biology. They offer unique advantages, due to their relative simplicity, the availability of all standard genomics techniques and a long history of quantitative research. Reproducible cultivation methods exist for morphologically and physiologically distinct life-cycle stages. The genome has been sequenced, and microarrays, RNA-interference and high-accuracy metabolomics are available. Furthermore, the availability of extensive kinetic data on all glycolytic enzymes has led to the early development of a complete, experiment-based dynamic model of an important biochemical pathway. Here we describe the achievements of trypanosome systems biology so far and outline the necessary steps towards the ambitious aim of creating a ‘Silicon Trypanosome’, a comprehensive, experiment-based, multi-scale mathematical model of trypanosome physiology. We expect that, in the long run, the quantitative modelling enabled by the Silicon Trypanosome will play a key role in selecting the most suitable targets for developing new anti-parasite drugs.

The ocular cataracts produced by the dominant CatFr gene in the mouse, Mus musculus, are associated with quantitative changes in the lens proteins (crystallins). The three classes of crystallin are affected differentially in homozygotes. Heterozygotes show a smaller effect. The quantitative levels of crystallin subunits are also affected and these changes are different for each subunit. The overall loss in protein is not readily explicable hi terms of a generalised leakage or a general tendency to insolubilisation. Possible mechanisms for the action of the gene are suggested.

The genetically unrelated chick strains Hy-1 and Hy-2, which have been strongly selected for growth rate, both exhibit hyperplasia of the lens epithelium. These two strains and a control strain N, not selected for growth rate, were compared with respect to incorporation of 3H-thymidine and 14C-uridine by freshly excised lenses in culture at different times throughout a 24-h period. The levels of incorporation of label into the lens cells were found to vary according to the time of day. The pattern of diurnal variation in both thymidine and uridine incorporation was found to be strain specific. Hy-1 and Hy-2 showed a greater degree of synchrony than did normal (N) lenses, and the frequency of the peaks of incorporation was also higher. Autoradiography confirmed that only lens epithelium incorporates thymidine during culture and that the number of labelled nuclei depends on the time of day when the lenses were explanted. These data point to genetic control of the cell cycle.

Two strains of poultry selected for high growth-rate were found to have an anomalous lens morphology indicating a failure of the normal process of growth regulation. The implications for lens fibre differentiation are discussed, as are the implications for genetic selection for growth-rate.