Properties of atoms under pressure: bonded interactions of the atoms in three perovskites.

The crystal structures for the three perovskites, CaSnO(3), YAlO(3), and LaAlO(3), were geometry optimized at the density functional theory level for a wide range of simulated isotropic pressures up to 80 GPa. The connections between the geometry optimized bond lengths, R(M-O), the values of the electron density, ρ(r(c)), the local kinetic, G(r(c)), potential, V(r(c)), energy densities, H(r(c)), and the Laplacian, ∇(2)(r(c)), at the bond critical points, r(c), for the M-O nonequivalent bonded interactions were examined. With increasing pressure, ρ(r(c)) increases along four distinct trends when plotted in terms of the Al-O, Ca-O, Sn-O, Y-O, and La-O bond lengths, but when the bond lengths were plotted in terms of ρ(r(c))/r where r is the periodic table row number of the M atoms, the data scatter along a single trend modeled by the power law regression expression R(M-O) = 1.41(ρ(r(c))/r)(-0.21), an expression that is comparable with that obtained for the bonded interactions for a large number of silicate and oxides crystals, R(M-O) = 1.46(ρ(r(c))/r)(-0.19) and that obtained for a relatively large number of hydroxyacid molecules R(M-O) = 1.39(s/r)(-0.22) where s is the Pauling bond strength of a bonded interaction. The similarity of the expressions determined for the perovskites, silicate and oxides crystals, and hydroxyacid molecules suggest that the bonded interactions in molecules and crystal are not only similar and comparable. The close correspondence of the expressions for the perovskites, the silicate and oxide crystals, and the molecules indicates that Pauling bond strength and ρ(r(c)) are comparable measures of the bonded interactions, the larger the accumulation of the electron density between the bonded atoms the larger the value of s, the shorter the bond lengths. It also indicates that the bonded interactions that govern the bond length variations behave as if largely short ranged. Like ρ(r(c))/r, the values of G(r(c))/r, V(r(c))/r, ∇(2)(r(c))/r likewise correlate in terms of R(M-O) in a single trend. With increasing pressure, the value of V(r(c)) decreases at a faster rate than G(r(c)) increases consistent with the observation that ρ(r(c)) increases with increasing pressure thereby stabilizing the structures at high pressures. As evinced by the well-developed power law trends between R(M-O) and the bond critical point properties, the bulk of the bonded interactions for the perovskites are concluded to change progressively from closed-shell to intermediate polar covalent interactions with increasing pressure. A well-developed trend between the ratios ∣V(r(c))∣ /G(r(c)) and H(r(c))/ρ(r(c)) is consistent with this conclusion. The employment of a positive value for the Laplacian alone in distinguishing between closed shell and polar covalent bonded interactions is unsatisfactory when 2G(r(c)) > ∣V(r(c))∣ > G(r(c)).

High-pressure powder neutron diffraction study on lead scandium niobate.

The structural evolution of PbSc(0.5)Nb(0.5)O(3) (PSN) under pressure has been studied by in situ powder neutron diffraction. Rietveld refinements to the data show that the continuous phase transition detected by x-ray diffraction at p(c) = 4.1 GPa (Maier et al 2010 Phys. Rev. B 81 174116) is associated with long-range ordering of antiphase octahedral tilts and local ordering of ferroic Pb displacements. Similar to PbSc(0.5)Ta(0.5)O(3) (PST) (Maier et al 2010 Acta Crystallogr. 66 280-91), antiphase octahedral tilting even exists below the critical pressure in a regime in which the structure retains a cubic metric. In contrast to PST, in which the Pb atomic displacement parameters (DPs) form ellipsoids elongated along the cubic {111} directions, the atomic DPs of Pb in PSN form flattened discs parallel to the cubic {111}-planes. This indicates that in PST the Pb displacements are along the cubic {111} directions, whereas in PSN the local Pb displacements are randomly distributed along the cubic {110} directions. The latter can be explained by the abundance of underbonded oxygen atoms associated with the chemical B-site disorder.

Lower-extremity functioning in older Mexican Americans and its association with medical problems.

OBJECTIVE: To describe lower-extremity functioning in community-dwelling older Mexican Americans and to examine its relationship with medical problems. DESIGN: Cross-sectional analyses of survey and performance-based data obtained in a population-based study employing area probability sampling. SETTING: Households within selected census tracts of five Southwestern states: Arizona, California, Colorado, New Mexico, and Texas. PARTICIPANTS: A total of 2873 Mexican Americans aged 65 years and older. MEASUREMENTS: A multidimensional questionnaire assessing demographic, sociocultural, and health variables. Standardized tests of lower-extremity physical functioning included measures of standing balance, repeated chair stands, walking, and an overall summary measure. RESULTS: Regression analyses revealed that being more than age 75 and female, having arthritis diabetes, visual impairments, or being obese or underweight were all significantly associated with performance on both individual and summary tests of lower-extremity functioning. In separate regression analyses, the total number of medical conditions was also associated with performance. CONCLUSIONS: The likelihood of predicting performance or inability to complete tests of lower-extremity functioning was greatest for those aged 80 and older, those with arthritis or diabetes, and those with three or more medical conditions. Because of the high prevalence of diabetes in Mexican Americans, documentation of the association of diabetes with performance-based tests of lower-extremity functioning may help guide early interventions targeted to prevent progression to more severe limitations or disability.

Lower body function and mortality in Mexican American elderly people.

BACKGROUND: The purpose of this analysis was to examine the differential impact of performance-based and self-reported lower body measures on 2-year mortality in Mexican American elderly persons. METHODS: Data employed are from the Hispanic Established Population for Epidemiological Studies of the Elderly, a probability survey of 3050 community-dwelling Mexican Americans aged 65 and older from the five Southwestern states interviewed in 1993 and 1994. Of the baseline sample with complete data, 198 persons were confirmed deceased 2 years later. A three-task, performance-based, lower body function measure consisting of a short walk, balance, and repeated chair stands tests was used. Self-reported lower body function was measured by a 4-item Activities of Daily Living (ADL) measure involving the lower body. RESULTS: The three-task, lower body function measure was a significant predictor of 2-year mortality. The short walk alone was as predictive as the summary measure. The predictive ability of both measures was minimally reduced by the inclusion of the self-reported ADL measure and life-threatening medical conditions. Finally, the ADL measure was not a significant predictor of mortality with all the other variables in the analysis. CONCLUSION: Objective measures of lower body function were significant predicators of mortality in Mexican American elderly persons, as found in the general population. Unlike previous studies, the ADL measure was not an independent predictor of mortality after controlling for the objective measure and other risk factors. Additional research is needed to address why objective measures of function are such strong predictors of death.

The extent of private and public health insurance coverage among adult Hispanics.

Data from the Health and Retirement Survey reveal extremely low levels of health insurance coverage among Hispanics and, especially, among Mexican Americans. The data reveal that this lack of insurance is associated with lower rates of employer-based and privately purchased coverage. Even after controlling for a large number of insurance-related factors, Hispanics have rates of health insurance coverage that are lower than those of either non-Hispanic blacks or whites. This serious lack of health insurance coverage among preretirement-age Hispanics has serious implications both for health, because the lack of insurance represents a major barrier to health care, and for the adequacy of retirement coverage, because private insurance represents an important supplement to Medicare.

Nativity, declining health, and preferences in living arrangements among elderly Mexican Americans: implications for long-term care.

This study employs data from the 1993-94 Hispanic Established Population for Epidemiological Studies of the Elderly (H-EPESE) to assess the impact of nativity on preferences in living arrangements for a sample of 3,046 Mexican American individuals over the age of 65. Our results reveal great differences between the native and foreign-born in their desire to live with their children. A larger fraction of the foreign-born than native-born currently live with their children and state that they would care to continue living with their children in the event that they could no longer care for themselves. The data also reveal that the foreign-born face more serious economic constraints than the native-born and suggest that living with children may be motivated in part by economic need. We end by speculating on the implications of these findings for community-based care for elderly Mexican Americans.

Age at migration and family dependency among older Mexican immigrants: recent evidence from the Mexican American EPESE.

This study employs new data on Mexican-origin individuals aged 65 and older in the Southwestern United States to examine the impact of the age at which an individual immigrated to the United States on his or her sources of income and living arrangements. The data reveal that, in general, those who immigrated after the age of 50 are more dependent on their families than the native born or those who immigrated earlier in life. Although our findings must be interpreted cautiously because of small cell sizes, those who immigrated later in life are found to be less likely than the native born or those who immigrated earlier to have private pensions and Social Security income. They are also more likely to be living with their children and to be receiving money from them. We discuss the implications of recent restrictions on the eligibility of even legal immigrants for Supplemental Security Income on intergenerational relations and on the potential burden placed on the older immigrant's family, many of which may be seriously strained in hard economic times.

Physical comorbidity and medical care use in children with emotional problems.

As family disruption, violence, and the decline of community become more common, an ever-growing number of children are exposed to psychological and social stressors that can lead to serious emotional problems. For many children emotional problems can interfere with normal psychological and social development and can have serious long-term effects. In this study data from a large national survey are used to examine patterns of emotional and physical comorbidity and the uses of general medical and mental health services by children ages 4 to 11. Results indicate that emotional problems are common among children with physical illnesses and that emotional problems increase general medical care use. Emotional problems are clearly exacerbated by factors associated with poverty. The data also show that a larger proportion of children in single-parent than in two-parent families experience emotional problems and use mental health services. We discuss the implications of these findings for general pediatric practice.

Poverty and health: older minority women and the rise of the female-headed household.

This analysis uses the 1984 Survey on Aging (SOA) supplement to the National Health Interview Survey (NHIS) to compare the relative impacts of poverty and health on the propensity of unmarried older black, Hispanic, and non-Hispanic white women to live with family. The results reveal that for blacks and Hispanics, economics are more significant than health in determining whether a woman lives with her children. Our findings also show that black unmarried elderly females are more likely than similar non-Hispanic white women to head their households. The literature and our findings suggest that black and Hispanic older women have fewer options in living arrangements than non-Hispanic older women in the event of diminished health.

Age at migration, social connections, and well-being among elderly Hispanics.

This study employs data from the 1988 National Survey of Hispanic Elderly People to examine the impact of age at migration and social contacts on the self-assessed health, functional disability, and life satisfaction of elderly Cuban Americans, Mexican Americans, and Puerto Ricans in the United States. The results indicate that the difficulties associated with immigration late in life undermine an older person's morale and interfere with the ability to perform basic activities of daily living. Although children are important sources of social support for all Hispanic groups, our findings also reveal important group differences in the use of other community social resources and their impact on health. Older Cuban Americans, in particular, appear to benefit from residence in ethnic enclaves in which they have largely duplicated their culture of origin.

Chemically induced renormalization phenomena in Pb-based relaxor ferroelectrics under high pressure.

The pressure-induced phase transition sequence in PbSc(0.5)Ta(0.5)O(3) (PST) and PbSc(0.5)Nb(0.5)O(3) (PSN) heavily doped with homo- and heterovalent cations on the A- or B-site of the perovskite-type structure (ABO(3)) was analysed by in situ synchrotron x-ray diffraction and Raman spectroscopy up to pressures of 25 GPa. We focused on the structural phenomena occurring above the first pressure-induced phase transition at p(c1) from a relaxor state to a non-polar rhombohedral phase with antiphase tilting of the BO(6) octahedra. The samples studied were PST doped with Nb(5+) and Sn(4+) on the B-site, PST doped with Ba(2+) and La(3+) on the A-site and PSN doped with Sr(2+) and La(3+) on the A-site. All of them exhibit a second pressure-induced phase transition at p(c2), similar to pure PST and PSN. The second transition involves the development of either order of antiparallel Pb(2+) displacements and complementary a(+)b(-)b(-) octahedral tilts, or a(-)b(-)b(-) (0 ≤ a < b) tilting alone. As in pure PST and PSN, the second phase transition is preceded by the occurrence of unequal octahedral tilts on the local scale. The substitution of Nb(5+) for Ta(5+) as well as the coupled substitution of Sn(4+) for Sc(3+) + Ta(5+) on the octahedral B sites increases the second critical pressure. The doping by Nb(5+) also reduces the length of coherence of antipolar Pb(2+) order developed at p(c2). The isovalent substitution of the larger Ba(2+) for Pb(2+) on the A-site suppresses the antipolar Pb(2+) order due to the induced local elastic stresses and thus significantly increases p(c2). The substitution of smaller cations for Pb(2+) on the A-site generally favours the development of long-range order of antiparallel Pb(2+) displacements because of the chemically enhanced a(-)a(-)a(-) octahedral tilts. However, this ordering is less when the dopant is aliovalent, due to the charge imbalance on the A-site. For all of the relaxors studied here, the dynamic compressibility estimated from the pressure derivative of the wavenumber of the soft mode associated with the first phase transition is larger in the pressure interval between p(c1) and p(c2) than above p(c2). The dynamic compressibility of the phase above p(c2) decreases if the antipolar Pb(2+) order is disturbed.

Pressure-induced phase transition in PbSc0.5Ta0.5O3 as a model Pb-based perovksite-type relaxor ferroelectric.

We report pressure-induced structural changes in PbSc(0.5)Ta(0.5)O3 studied by single-crystal x-ray diffraction and Raman scattering. The appearance of a soft mode, a change in the volume compressibility, broadening of the diffraction peaks, and suppression of the x-ray diffuse scattering show that a phase transition occurs near pc approximately 1.9 GPa. The critical pressure is associated with a decoupling of the displacements of the B site and Pb cations in the existing polar nanoregions, leading to the suppression of B-cation off-center shifts and enhancement of the ferroic distortion in the Pb-O system.

Estimation of polyhedral compressibilities and structural evolution of GdFeO3-type perovskites at high pressures.

A new approach based on the bond-valence matching relation is developed to predict the detailed structural evolution of GdFeO(3)-type perovskites at high pressure from knowledge of the room-pressure structure and the high-pressure unit-cell parameters alone. The evolution of perovskite structures estimated in this way is in good agreement with the structure refinements available from high-pressure single-crystal diffraction measurements of a number of perovskites. The method is then extended to predict the structure of MgSiO(3) perovskite at pressures for which no single-crystal structural data are available and the results are compared to ab initio quantum calculations of MgSiO(3) perovskite up to 120 GPa.

General rules for predicting phase transitions in perovskites due to octahedral tilting.

Recent experiments on several oxide perovskites reveal that they undergo tilt phase transitions to higher-symmetry phases on increasing pressure and that dTc/dP<0, contrary to a general rule previously proposed for such zone-boundary transitions. We show that the negative slope of the phase boundary is a consequence of the octahedra in these perovskites being more compressible than the extra-framework cation sites. Conversely, when the octahedra are stiffer than the extra-framework cation sites, the phase transition temperatures increase with increasing pressure, dTc/dP>0.

Self-rated health and mortality in the NHANES-I Epidemiologic Follow-up Study.

The ability of self-rated health status to predict mortality was tested with data from the National Health and Nutrition Examination Survey (NHANES-I) Epidemiologic Follow-Up Study (NHEFS), conducted from 1971-84. The sample consists of adult NHANES-I respondents ages 25-74 years (N = 6,440) for whom data from a comprehensive physical examination at the initial interview and survival status at follow-up are available. Self-rated health consists of the response to the single item, "Would you say your health in general is excellent, very good, good, fair, or poor?" Proportional hazards analyses indicated that, net of its association with medical diagnoses given in the physical examination, demographic factors, and health related behaviors, self-rated health at Time 1 is associated with mortality over the 12-year follow-up period among middle-aged males, but not among elderly males or females of any age.

Functional capacity and living arrangements of unmarried elderly persons.

This analysis employed the 1986 Longitudinal Study of Aging (LSOA) to examine the impact of functional capacity, gender, race and ethnicity, and various socioeconomic characteristics on changes in living arrangements among unmarried elderly persons over a two-year period. The results reveal that a decline in functional capacity greatly increases the likelihood that an elderly person will move in with others or become institutionalized. Nonetheless, even when they experience significant declines in health, most single elderly persons who were living alone at the initial interview continued to live alone two years later. Multivariate analyses show that women who suffer declines in functional capacity are somewhat less likely than men who experience declines to live alone at Time two. In contrast, Blacks who suffer declines are more likely than Whites who experience declines to continue living alone at follow-up.

Correlates of using mental health services: implications of using alternative definitions.

BACKGROUND: Studies using varying definitions of mental health visits result in widely divergent estimates. This analysis examines the stability of a predictive model using three varying definitions based on provider type, diagnosis, psychotherapy, and psychotropic medication use. METHODS: Interview and questionnaire data and claims records from the RAND Health Insurance Experiment are used to test these models among 3138 enrollees. RESULTS: Estimates of visits, and factors associated with them, are highly sensitive to definitions. Depression was the only symptom/life situation variable, and education the only sociodemographic measure, predictive across all three models. Risk indicators such as suicide thoughts and drinking problems were only significant for the traditional (mental health specialty) model. While patients within the traditional model definition were significantly younger than other enrollees, those within the model using the most expansive definition were significantly older. Varying the definition also led to different results in respect to experimental manipulations, geographic sites and some specific types of comorbidity. CONCLUSIONS: A reasonable definition, consistent with medical standards, requires, at least, a mental health diagnostic judgment and some form of psychotherapeutic or drug treatment. Studies of the content of mental health care are needed.

New view of the high-pressure behaviour of GdFeO(3)-type perovskites.

Recent determinations of the structures of several GdFeO(3)-type orthorhombic perovskites (ABO(3)) show that the octahedra in some become more tilted with increasing pressure. In others the octahedra become less tilted and the structure evolves towards a higher-symmetry configuration. This variety of behaviour can be explained in terms of the relative compressibilities of the octahedral and dodecahedral cation sites in the perovskite structure. If the BO(6) octahedra are less compressible than the AO(12) sites then the perovskite will become more distorted with pressure, but the perovskite will become less distorted if the BO(6) site is more compressible than the AO(12) site. In this contribution we use the bond-valence concept to develop a model that predicts the relative compressibilities of the cation sites in oxide perovskites. We introduce the site parameter M(i) defined in terms of the coordination number N(i), average bond length at room pressure R(i), and the bond-valence parameters R(0) and B,M(i) = ([R(i)N(i)/B)exp](R(0) - R(i))/B].M(i) represents the variation in the bond-valence sum at the central cation in a polyhedral site because of the change of the average bond distance. Experimental data suggest that the pressure-induced changes in the bond-valence sums at the two cation sites within any given perovskite are equal. With this condition we show that the ratio of cation-site compressibilities is given by betaB/beta(A) = M(A)/M(B). This model, based only upon room-pressure bond lengths and bond-valence parameters, correctly predicts the structural behaviour and some physical properties of the oxide perovskites that have been measured at high pressure.

Local and long-range order in ferroelastic lead phosphate at high pressure.

Pure lead phosphate, Pb(3)(PO(4))(2), undergoes a phase transition from C2/c to R(-)3m symmetry at a pressure of approximately 1.8 GPa and room temperature. Single-crystal X-ray diffraction measurements of the unit-cell parameters of a sample doped with 1.6% Ba(2+) for the Pb(2+) indicates that the doping reduces the transition pressure by approximately 0.1 GPa. The structural evolution of both samples through the phase transition has been determined by Rietveld refinement of neutron powder diffraction data collected to pressures of 6.3 and 3.3 GPa, respectively. There is no evidence for any significant change in the local structure at the phase transition at high pressures; the structure of the R(-)3m phase at pressures just above the phase transition includes disordered positions for several atoms. The observation of diffuse scattering from the R(-)3m phase at high pressure by single-crystal X-ray diffraction suggests that the disorder is static and arises from the presence of several orientations of the ordered microdomains of the monoclinic local structure. The macroscopic transition from monoclinic to trigonal symmetry therefore appears to correspond to the pressure at which the coherency strains between the locally monoclinic microdomains are sufficient to create a dimensionally trigonal lattice within which local displacements of atoms are still significant. A further pressure increase then decreases the magnitude of these displacements until at 3.5 GPa or higher they are not detectable by our current experimental probes, and the structure appears to have true local and global trigonal symmetry.