Anisotropic diffusion creep in postperovskite provides a new model for deformation at the core-mantle boundary.

The lowermost portion of Earth's mantle (D″) above the core-mantle boundary shows anomalous seismic features, such as strong seismic anisotropy, related to the properties of the main mineral MgSiO3 postperovskite. But, after over a decade of investigations, the seismic observations still cannot be explained simply by flow models which assume dislocation creep in postperovskite. We have investigated the chemical diffusivity of perovskite and postperovskite phases by experiment and ab initio simulation, and derive equations for the observed anisotropic diffusion creep. There is excellent agreement between experiments and simulations for both phases in all of the chemical systems studied. Single-crystal diffusivity in postperovskite displays at least 3 orders of magnitude of anisotropy by experiment and simulation (Da = 1,000 Db; Db ≈ Dc) in zinc fluoride, and an even more extreme anisotropy is predicted (Da = 10,000 Dc; Dc = 10,000 Db) in the natural MgSiO3 system. Anisotropic chemical diffusivity results in anisotropic diffusion creep, texture generation, and a strain-weakening rheology. The results for MgSiO3 postperovskite strongly imply that regions within the D″ region of Earth dominated by postperovskite will 1) be substantially weaker than regions dominated by perovskite and 2) develop a strain-induced crystallographic-preferred orientation with strain-weakening rheology. This leads to strain localization and the possibility to bring regions with significantly varying textures into close proximity by strain on narrow shear zones. Anisotropic diffusion creep therefore provides an attractive alternative explanation for the complexity in observed seismic anisotropy and the rapid lateral changes in seismic velocities in D″.

The phase diagrams of KCaF3 and NaMgF3 by ab initio simulations.

ABF3 compounds have been found to make valuable low-pressure analogues for high-pressure silicate phases that are present in the Earth's deep interior and that may also occur in the interiors of exoplanets. The phase diagrams of two of these materials, KCaF3 and NaMgF3, have been investigated in detail by static ab initio computer simulations based on density functional theory. Six ABF3 polymorphs were considered, as follows: the orthorhombic perovskite structure (GdFeO3-type; space group Pbnm); the orthorhombic CaIrO3 structure (Cmcm; commonly referred to as the "post-perovskite" structure); the orthorhombic Sb2S3 and La2S3 structures (both Pmcn); the hexagonal structure previously suggested in computer simulations of NaMgF3 (P63/mmc); the monoclinic structure found to be intermediate between the perovskite and CaIrO3 structures in CaRhO3 (P21/m). Volumetric and axial equations of state of all phases considered are presented. For KCaF3, as expected, the perovskite phase is shown to be the most thermodynamically stable at atmospheric pressure. With increasing pressure, the relative stability of the KCaF3 phases then follows the sequence: perovskite â†’ La2S3 structure â†’ Sb2S3 structure â†’ P63/mmc structure; the CaIrO3 structure is never the most stable form. Above about 2.6 GPa, however, none of the KCaF3 polymorphs are stable with respect to dissociation into KF and CaF2. The possibility that high-pressure KCaF3 polymorphs might exist metastably at 300 K, or might be stabilised by chemical substitution so as to occur within the standard operating range of a multi-anvil press, is briefly discussed. For NaMgF3, the transitions to the high-pressure phases occur at pressures outside the normal range of a multi-anvil press. Two different sequences of transitions had previously been suggested from computer simulations. With increasing pressure, we find that the relative stability of the NaMgF3 phases follows the sequence: perovskite â†’ CaIrO3 structure â†’ Sb2S3 structure â†’ P63/mmc structure. However, only the perovskite and CaIrO3 structures are stable with respect to dissociation into NaF and MgF2.

Cognitive Enhancement Treatment for People With Mental Illness Who Do Not Respond to Supported Employment: A Randomized Controlled Trial.

OBJECTIVE: Cognitive impairment presents a serious and common obstacle to competitive employment for people with severe mental illness, including those who receive supported employment. This study evaluated a cognitive enhancement program to improve cognition and competitive employment in people with mental illness who had not responded to supported employment. METHOD: In a randomized controlled trial, 107 people with severe mental illness (46% with schizophrenia or schizoaffective disorder) who had not obtained or kept competitive work despite receiving high-fidelity supported employment were assigned to receive either enhanced supported employment (with specialized cognitive training of employment specialists) or enhanced supported employment plus the Thinking Skills for Work program, a standardized cognitive enhancement program that includes practice of computer cognitive exercises, strategy coaching, and teaching of coping and compensatory strategies. Research assistants tracked competitive employment weekly for 2 years, and assessors blind to treatment assignment evaluated cognitive functioning at baseline, at the end of cognitive enhancement training, and 12 and 24 months after baseline. RESULTS: Participants in the Thinking Skills for Work group improved more than those in the enhanced supported employment only group on measures of cognitive functioning and had consistently better competitive employment outcomes during the follow-up period, including in jobs obtained (60% compared with 36%), weeks worked (23.9 compared with 9.2), and wages earned ($3,421 compared with $1,728). CONCLUSIONS: The findings suggest that cognitive enhancement interventions can reduce cognitive impairments that are obstacles to work, thereby increasing the number of people who can benefit from supported employment and competitive work.

Deformation T-Cup: a new multi-anvil apparatus for controlled strain-rate deformation experiments at pressures above 18 GPa.

A new multi-anvil deformation apparatus, based on the widely used 6-8 split-cylinder, geometry, has been developed which is capable of deformation experiments at pressures in excess of 18 GPa at room temperature. In 6-8 (Kawai-type) devices eight cubic anvils are used to compress the sample assembly. In our new apparatus two of the eight cubes which sit along the split-cylinder axis have been replaced by hexagonal cross section anvils. Combining these anvils hexagonal-anvils with secondary differential actuators incorporated into the load frame, for the first time, enables the 6-8 multi-anvil apparatus to be used for controlled strain-rate deformation experiments to high strains. Testing of the design, both with and without synchrotron-X-rays, has demonstrated the Deformation T-Cup (DT-Cup) is capable of deforming 1-2 mm long samples to over 55% strain at high temperatures and pressures. To date the apparatus has been calibrated to, and deformed at, 18.8 GPa and deformation experiments performed in conjunction with synchrotron X-rays at confining pressures up to 10 GPa at 800 °C .

High-pressure and -temperature ion exchange of aluminosilicate and gallosilicate natrolite.

The simultaneous application of high pressure and high temperature has been used to achieve direct ion exchange of large cesium cations for the small sodium cations found in the zeolite natrolite by putting it into a superhydrated state with increased pore size. The larger cations remain trapped upon pressure release, and thus, this method is a means of producing new cationic forms of zeolites.

Rapid acquisition of Gigapascal-high-pressure resistance by Escherichia coli.

Pressure and temperature are important environmental variables that influence living systems. However, while they vary over a considerable range on Earth and other planets, it has hardly been addressed how straightforwardly and to what extent cellular life can acquire resistance to extremes of these parameters within a defined genomic context and a limited number of generations. Nevertheless, this is a very pertinent question with respect to the penetration of life in allegedly inhospitable environments. In this study, directed evolution was used to reveal the potential of the nonsporulating and mesophilic model bacterium Escherichia coli to develop the ability to survive exposure to high temperature or pressure. While heat resistance could only marginally be increased, our data show that piezoresistance could readily and reproducibly be extended into the GPa range, thereby greatly exceeding the currently recognized maximum for growth or survival.

Mechanical Properties of Titanium Nitride Nanocomposites Produced by Chemical Precursor Synthesis Followed by High-P,T Treatment.

We investigated the high-P,T annealing and mechanical properties of nanocomposite materials with a highly nitrided bulk composition close to Ti3N4. Amorphous solids were precipitated from solution by ammonolysis of metal dialkylamide precursors followed by heating at 400-700 °C in flowing NH3 to produce reddish-brown amorphous/nanocrystalline materials. The precursors were then densified at 2 GPa and 200-700 °C to form monolithic ceramics. There was no evidence for N2 loss during the high-P,T treatment. Micro- and nanoindentation experiments indicate hardness values between 4-20 GPa for loads ranging between 0.005-3 N. Young's modulus values were measured to lie in the range 200-650 GPa. Palmqvist cracks determined from microindentation experiments indicate fracture toughness values between 2-4 MPa·m1/2 similar to Si3N4, SiC and Al2O3. Significant variations in the hardness may be associated with the distribution of amorphous/crystalline regions and the very fine grained nature (~3 nm grain sizes) of the crystalline component in these materials.

Long-term employment trajectories among participants with severe mental illness in supported employment.

OBJECTIVE: The long-term trajectories of participants in supported employment have not been clear. This exploratory study presents eight- to 12-year employment trajectories among adults with psychiatric disabilities who participated in supported employment. METHODS: We reinterviewed 38 of 78 participants (49%) with severe mental illness eight to 12 years after they enrolled in supported employment studies in a small urban mental health center in New England. Data were analyzed by using quantitative and qualitative methods. RESULTS: All 38 participants worked during the follow-up period, a great majority (82%) in competitive jobs, and 71% worked for more than half of the follow-up years. Participants reported numerous benefits related to employment, including enhancements to self-esteem, relationships, and illness management. Psychiatric illness was the major barrier to work; part-time employment and long-term supports were the major facilitators. Three overlapping themes emerged from the qualitative analysis as significant perceived influences on participants' work-related behavior. First, the successful management of symptoms and the deployment of appropriate coping skills appeared to play an important role in finding and maintaining work. Second, participants generally preferred to work part-time because of the lesser demands of this type of job and because it was perceived to allow for the maintenance of Social Security and health care entitlements. Third, participants saw the importance of ongoing individual placement and support services. Participants stated that this was imperative in making successful transitions between jobs or from unemployment to employment and in helping negotiate pay raises or changes in conditions. CONCLUSIONS: The long-term trajectories of participants in supported employment programs, both vocational and nonvocational, appear to be positive.