125Te NMR for structural investigations in phase change materials: Optimization of experimental conditions coupled to NMR shift prediction.

Phase Change Materials as those of the Ge-Sb-Te ternary system are of great interest for technological applications. Properties of these compounds are strongly related to presence of vacancies and structural investigations remain challenging. In this paper we evidence that 125Te NMR in natural abundance and using commercial systems at intermediate field (14.1 â€‹T) together with NMR parameters prediction can contribute to improve understanding of electronic structure of such systems. GeTe is a typical phase change material, whose structure contains germanium vacancies, even in its stoichiometric form, giving it metallic properties. Here, we use nominal Ge50Te50 and Ge48Te52 crystalline samples as an example to optimize the WURST-CPMG technique, a powerful technique to record wide NMR spectra which has not yet been used on 125Te. The goal was to minimize the time devoted to experiments as well as maximize the signal-to-noise ratio in order to detect small intensity signals directly linked to vacancies. Virtual Crystal Approximation (VCA) calculations performed with WIEN2K helped to interpret the NMR spectra. For Te-based crystalline conducting samples the best experimental results were obtained using 3.2 â€‹mm thin wall rotors with diluted samples 40 â€‹vol% GeTe-60 â€‹vol% SiO2. In addition to the WURST-CPMG technique, high resolution spectra using MAS as implemented in the pj-MAT technique allowed us to identify the distributions of chemical shift parameters in the high intensity contribution of the 1D spectra. The NMR spectra recorded on the samples showed that an addition of Tellurium in the stoichiometric Ge50Te50 sample leads to an important broadening of the spectrum together with a shift of the lines. According to VCA calculations it could be attributed to a distribution of concentrations of germanium vacancies in the sample and it would appear that Knight Shift but also Chemical Shift could contribute in similar proportion to the NMR line position when metavalent bonding is invoked.

NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations.

We present a benchmark of the density functional linear response calculation of NMR shieldings within the gauge-including projector-augmented-wave method against all-electron augmented-plane-wave+local-orbital and uncontracted Gaussian basis set results for NMR shieldings in molecular and solid state systems. In general, excellent agreement between the aforementioned methods is obtained. Scalar relativistic effects are shown to be quite large for nuclei in molecules in the deshielded limit. The small component makes up a substantial part of the relativistic corrections.

Transition from Reconstruction toward Thin Film on the (110) Surface of Strontium Titanate.

The surfaces of metal oxides often are reconstructed with a geometry and composition that is considerably different from a simple termination of the bulk. Such structures can also be viewed as ultrathin films, epitaxed on a substrate. Here, the reconstructions of the SrTiO3 (110) surface are studied combining scanning tunneling microscopy (STM), transmission electron diffraction, and X-ray absorption spectroscopy (XAS), and analyzed with density functional theory calculations. Whereas SrTiO3 (110) invariably terminates with an overlayer of titania, with increasing density its structure switches from n × 1 to 2 × n. At the same time the coordination of the Ti atoms changes from a network of corner-sharing tetrahedra to a double layer of edge-shared octahedra with bridging units of octahedrally coordinated strontium. This transition from the n × 1 to 2 × n reconstructions is a transition from a pseudomorphically stabilized tetrahedral network toward an octahedral titania thin film with stress-relief from octahedral strontia units at the surface.

Fermi Surface of Three-Dimensional La(1-x)Sr(x)MnO3 Explored by Soft-X-Ray ARPES: Rhombohedral Lattice Distortion and its Effect on Magnetoresistance.

Electronic structure of the three-dimensional colossal magnetoresistive perovskite La(1-x)Sr(x)MnO3 has been established using soft-x-ray angle-resolved photoemission spectroscopy with its intrinsically sharp definition of three-dimensional electron momentum. The experimental results show much weaker polaronic coupling compared to the bilayer manganites and are consistent with the theoretical band structure including the empirical Hubbard parameter U. The experimental Fermi surface unveils the canonical topology of alternating three-dimensional electron spheres and hole cubes, with their shadow contours manifesting the rhombohedral lattice distortion. This picture has been confirmed by one-step photoemission calculations including displacement of the apical oxygen atoms. The rhombohedral distortion is neutral to the Jahn-Teller effect and thus polaronic coupling, but affects the double-exchange electron hopping and thus the colossal magnetoresistance effect.

Density functional theory simulations of B K and N K NEXAFS spectra of h-BN/transition metal(111) interfaces.

The electronic structure and the corresponding B K and N K near-edge x-ray fine structure (NEXAFS) spectra of epitaxially grown h-BN on Ni(111), Pt(111), and Rh(111) surfaces are investigated by density functional theory. The calculations are carried out using the WIEN2k program package applying the augmented-plane-wave+local orbitals (APW+lo) method. The NEXAFS spectra are simulated using a 3 × 3 × 1 super cell and considering the final state rule by means of a (partial) core hole for the corresponding atom. The influence of a full or partial core hole is shown for the h-BN/Ni(111) system, for which the best agreement with the experimental spectra is found when half a core hole is assumed. All characteristic features of the experimental spectra are well reproduced by theory, including the angular dependences. The bonding effects are investigated by comparing the spectra of bulk h-BN with those of the h-BN/Ni(111) system. An analysis of both the density of states and charge densities reveals strong N-p(z)-Ni-d(z(2)) bonding/antibonding interactions. In the case of Pt(111) and Rh(111) surfaces, we discuss the effects of the nanomesh structures in terms of simple 1 × 1 commensurate models.

Breast cancer chemoprevention - a vision not yet realized.

Despite recent advances in the surgical and medical treatment of breast cancer, the number of patients dying from the disease is still high. In addition to improvements of early diagnosis and treatment, the overall mortality of breast cancer could be reduced by means of preventive intervention in both women with particularly normal and with high risk. Preventing the potentially deadly disease is presumably more effective than treatment, for life quality issues as well as for the economic perspective. Chemoprevention though is still a research field with results from large prevention trials being discussed controversially. For women with a defined increased risk for breast cancer, tamoxifen may be a choice for chemoprevention, balancing carefully benefits against risks. With promising results in adjuvant settings, aromatase inhibitors may deliver better prevention treatment options in the future, nevertheless, more research is needed to reliably predict risk on an individual basis in the future.

Murine mobilized peripheral blood stem cells have a lower capacity than bone marrow to induce mixed chimerism and tolerance.

Allogeneic bone marrow transplantation (BMT) under costimulation blockade allows induction of mixed chimerism and tolerance without global T-cell depletion (TCD). The mildest such protocols without recipient cytoreduction, however, require clinically impracticable bone marrow (BM) doses. The successful use of mobilized peripheral blood stem cells (PBSC) instead of BM in such regimens would provide a substantial advance, allowing transplantation of higher doses of hematopoietic donor cells. We thus transplanted fully allogeneic murine granulocyte colony-stimulating factor (G-CSF) mobilized PBSC under costimulation blockade (anti-CD40L and CTLA4Ig). Unexpectedly, PBSC did not engraft, even when very high cell doses together with nonmyeloablative total body irradiation (TBI) were used. We show that, paradoxically, T cells contained in the donor PBSC triggered rejection of the transplanted donor cells. Rejection of donor BM was also triggered by the cotransplantation of unmanipulated donor T cells isolated from naïve (nonmobilized) donors. Donor-specific transfusion and transient immunosuppression prevented PBSC-triggered rejection and mixed chimerism and tolerance were achieved, but graft-versus-host disease (GVHD) occurred. The combination of in vivo TCD with costimulation blockade prevented rejection and GVHD. Thus, if allogeneic PBSC are transplanted instead of BM, costimulation blockade alone does not induce chimerism and tolerance without unacceptable GVHD-toxicity, and the addition of TCD is required for success.

Unraveling the structure of the h-BN/Rh(111) nanomesh with ab initio calculations.

The properties of a single layer of h-BN on top of a Rh(111) surface are discussed in terms of an ab initio generated force field approach as well as by direct ab initio density-functional theory (DFT) calculations. A single-layer model for the h-BN/Rh(111) nanomesh, in contrast to a previously considered (incomplete) double-layer model of h-BN, can explain the experimental data. The main focus of this work is to compare a force field approach described earlier in (Laskowski et al 2007 Phys. Rev. Lett. 98 106802) with direct ab initio calculations. The calculated geometry of the h-BN layer is very similar to the structure predicted by the force field approach. The ab initio calculated density of states projected on N-p(x,y) of BN corresponding to 'low' and 'high' regions with respect to the Rh surface shows a 1 eV splitting and thus explains the observed σ-band splitting. Moreover, we find good agreement between calculated and experimental scanning tunneling microscope (STM) images of this system.

Long-term changes in body weight, BMI, and adiposity rebound among children and adolescents in the Czech Republic.

The Czech Republic has undergone rapid political, social, and economic transformation since the late 1980s. While obesity rates among children and adolescents in the Czech Republic have been previously relatively low, this has changed in recent years. Across the past 50 years, body weight, body mass index (BMI)-for-age, and adiposity rebound (AR) (the time when a child reaches the lowest BMI before their BMI gradually begins to increase until adulthood) occurs earlier. The most dramatic changes have been observed among school-aged children, where BMI values have increased at the 50th, 90th, and 97th percentiles. In contrast, adolescent girls appear to be thinner than in the past. The analyses of weight-for-height percentiles indicated that the 50th percentile of the body weight among boys and girls remained similar in nearly all age categories across the past 50 years. Although the growth pattern of children at the 50th percentile has not changed, the 10th and 90th percentiles have expanded. Our findings suggest that the secular trend of increased height, accelerated growth, and earlier maturation is responsible for Czech children experiencing adiposity rebound at earlier ages compared to the past.

Weight, body composition and fat distribution of Czech women in relation with reproductive phase: a cross-sectional study.

A sample of 213 healthy Czech women was classified into four groups according to their reproductive phase: fully reproductive, premenopausal, menopausal and postmenopausal women. Changes in body weight, body composition and fat distribution were studied in those four groups using the classical anthropometric method. Body weight rises till the menopause with no further increase. A decrease in relative contribution of muscle and bone mass was observed. The progressive increase in fat mass with age was clearly demonstrated, both the fat mass weight (r = 0.38, p < 0.001) and its percentage contribution (Matiegka r = 0.40, p < 0.001, Parízkovi r = 0.42, p < 0.001). There is a stronger correlation of central fat indices as WHR (r = 0.57, p < 0.001), abdominal (r=0.56, p < 0.001) and waist circumference (r = 0.50, p < 0.001) than for hip circumference (r = 0.27, p < 0.001) to the age. WHR and waist increase most when fully reproductive and premenopausal women were compared (p < 0.001); less when premenopausal to menopausal women are compared (NS) and the least when menopausal to postmenopausal women were compared (NS). The mean values of 14 skinfolds thickness are shown, the skinfold at the abdomen shows the strongest correlation to the age (r = 0.49, p < 0.001). The results are consistent with the hypothesis of progressive fat centralisation.

Two centuries of growth among Czech children and youth.

The trend of increasing height can be interpreted as a reflection of the unfolding progress of civilization. Height changes among children and adolescents are good markers of this trend. We analyze the secular trend in the heights of children and adolescents in the Czech Republic on the basis of data from anthropological surveys. The earliest height data pertain to Czech youths who attended the Military Schools in Austria in 1800-1809. Data also exist for 1895 and continue in 1951 and at 10-year intervals thereafter. Growth curves were obtained for separate age groups by fitting mean values via third-order polynomial smoothing splines. Between 1951 and 2001, the mean heights of boys and girls aged 2.5 years increased by 2.7 and 3 cm, respectively. Since 1895, the mean height of 13-year-old boys has increased by 19.4 cm, and the mean height of girls has increased by 18.3 cm.

Structure, Chemical Bonding, and Nuclear Quadrupole Interactions of beta-Cd(OH)(2): Experiment and First Principles Calculations.

The structure of Cd(OH)(2) was determined by X-ray diffraction on powder crystals and by calculations using the full-potential linearized augmented plane wave method. Good agreement between the two results was found. The chemical bonding is characterized by the interactions of the OH(-) group with Cd(2+) which is not only electrostatic but shows some polarization or covalent admixtures and by the covalent bond in the OH(-) group. The electric field gradient (EFG) was calculated and compared with an experimental determination of the nuclear quadrupole interaction using perturbed angular correlation of gamma-rays. The calculated EFG agrees well with the EFG derived from experiment. The total electric field gradient was decomposed into contributions from different orbitals and energy regions showing that both the Cd 5p and 4d wave functions contribute significantly. Finally, the influence of spin-orbit coupling on the electric field gradient was investigated and found to be of little importance.

Electron-density distribution in stishovite, SiO2: a new high-energy synchrotron-radiation study.

The electron-density distribution of the high-pressure polymorph of SiO2, stishovite [a = 4.177 (1), c = 2.6655 (5) A, space group P4(2)/mnm, Z = 2], has been redetermined by single-crystal diffractometry using synchrotron radiation of 100.42 and 30.99 keV, respectively, in order to obtain essentially absorption- and extinction-free data. Room-temperature diffraction experiments on two samples of irregular shape were carried out on two different diffractometers installed at HASYLAB/DESY, Hamburg, Germany. The structure refinement on the high-energy data converged at R(F) = 0.0047, wR(F) = 0.0038, GoF = 0.78, for a multipole model with neutral atoms and multipole expansions up to seventh order. For each atom, the radial expansion coefficients of the multipole orders (l > 0) were constrained to a common value. The absence of extinction was indicated by a refined correction parameter equalling zero within error limit. The excellent quality of the data is also illustrated by a high-order (HO) refinement (s > 0.7 A(-1)) yielding R(F) = 0.0060, wR(F) = 0.0048, GoF = 0.85. Both static deformation electron-density distribution and structure amplitudes compare well with corresponding results obtained from band-structure calculations using the linearized-augmented-plane-wave (LAPW) method. Ensuing topological analysis of the total model electron density distribution revealed bond critical point properties for the two unique Si--O bonds, indicating a predominantly closed-shell interaction mixed with a significant shared interaction contribution that decreases with increasing interatomic distance. Calculation of atomic basins yielded charges of +3.39 e and -1.69 e for Si and O, respectively, in good agreement with the theoretically calculated values of +3.30 e and -1.65 e. The volumina of the Si and O basins are 2.32 and 10.48 A3, corresponding to spheres with radii of 0.82 and 1.36 A, respectively. The results also conform well with correlations between bond length and bond critical point properties reported in the literature for geometry-optimized hydroxyacid molecules. Estimates of the Si cation electronegativity indicate that the change of Si coordination by oxygen from 4 to 6 is accompanied by an increase of the ionicity of the Si--O bond of about 7%.

Recovering experimental and theoretical electron densities in corundum using the multipolar model: IUCr Multipole Refinement Project.

This electron-density study on corundum (alpha-Al2O3) is part of the Multipole Refinement Project supported by the IUCr Commission on Charge, Spin and Momentum Densities. For this purpose, eight different data sets (two experimental and six theoretical) were chosen from which the electron density was derived by multipolar refinement (using the MOLLY program). The two experimental data sets were collected on a conventional CAD4 and at ESRF, ID11 with a CCD detector, respectively. The theoretical data sets consist of static, dynamic, static noisy and dynamic noisy moduli of structure factors calculated at the Hartree-Fock (HF) and density functional theory (DFT) levels. Comparisons of deformation and residual densities show that the multipolar analysis works satisfactorily but also indicate some drawbacks in the refinement. Some solutions and improvements during the refinements are proposed like contraction or expansion of the inner atomic shells or increasing the order of the spherical harmonic expansion.

Growth of the Czech child population 0-18 years compared to the World Health Organization growth reference.

Nationwide anthropological surveys of 0-18-year-old children were carried out in the Czech Republic (former Czech regions of Czechoslovakia) five times during the last 40 years, at 10-year intervals. The measurements provide reference data for the growth of the Czech child population and at the same time ample material for comparison with other populations. A comparison of the results of such nationwide anthropometric surveys with the World Health Organization (WHO) growth reference implies that the growth trend of Czech children is comparable with the WHO reference. The greatest similarity in the shape of the WHO height curves and the results obtained in Czechoslovakia was in 1971. The results obtained in the nationwide surveys also imply that the secular trend still exerts its effect. In the case of height, this finding is consistent during the whole period of 40 years. Concerning weight in higher age categories, especially in girls, the trend slowed down or stopped. Furthermore, there is no problem of malnutrition in the Czech child population. Similarly, as in any other developed nations, the prevalence of overweight and obesity is the problem that merits attention. Am. J. Hum. Biol. 9:459-468, 1997. © 1997 Wiley-Liss, Inc.

Leptin levels in obese children: effects of gender, weight reduction and androgens.

Obesity in children is accompanied by increased circulating leptin concentrations. Girls have higher leptin concentrations than boys. The aim of our study was to compare serum leptin levels before and after a five-week weight reduction program and to study the relationship of leptin levels, serum total cholesterol, and androgens (testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulphate) in 33 obese boys (age: 12.7+/-1.97 years, BMI: 30.46+/-4.54) and 66 obese girls (age: 12.7+/-2.51 years, BMI: 29.31+/-4.62). We found that serum leptin concentrations in obese children were significantly decreased after a weight reduction program (before 20.79+/-9.61 ng/ml, after 13.50+/-8.65 ng/ml in girls; before 12.25+/-10.09 ng/ml and after 5.18+/-3.56 ng/ml in boys, p<0.0001 in both genders). Leptin levels correlated positively with the body mass index before and after weight reduction. There was a positive association in obese boys and a negative one in obese girls between leptin levels and the WHR (waist to hip circumference ratio). Serum leptin also shows a strong relationship to fat distribution (p=0.02 in boys, p<0.0001 in girls). No significant correlation was found between leptin concentrations and total cholesterol or androgens. We confirmed that leptin is a sensitive parameter of body composition and weight reduction in obese children.

Social inequality and obesity in Czech school children.

This study uses logistic regressions to consider the effect of social factors, physical activity, meal frequency and BMI of parents on children's body mass index (BMI) values. Three thousand three hundred and sixty-two children aged 7-11 years were examined in 38 schools in the Czech Republic. Six anthropometric characteristics were assessed in 1999-2000. Most important factors influencing children's BMI values were: obesity of both or at least one of the parents, being an only child, residence in small communities, and irregular breakfasts.

Proposed standard definition for child overweight and obesity.

The prevalence of obesity in child population is becoming a serious problem in all advanced countries. Therefore many authors try to find a definition according to which it would be possible to assess overweight and obesity in examined subjects in a simple manner. The simplest way is to plot the subject's data in a percentile zone of reference data according to his BMI value. The problem is dealt with e.g. by Cole et al. (1) who defined internationally acceptable standards of BMI for children and adolescents from 0-18 years. These standards are, however, based only on six national studies and on the assumption that in the population of 18-year-olds there are 10% subjects with BMI values above 25 and 3% subjects with values above 30. The suggested standards thus raise the level of the 90th and 97th percentile, as compared with BMI reference data of 1991 which are used in the Czech Republic. Therefore the ratio of obese children in the Czech Republic and in many other countries would be very small. Internationally acceptable standards should be therefore based on a broader discussion of the professional public.

Influence of positioning of infants on long-term changes of cephalic dimensions.

The submitted investigation describes long-term changes of 3 main cephalic dimensions (head circumference, maximal length and maximal width of the head) and analyses the possible influence of positioning of infants after birth (prone, supine and side sleeping position) on these changes. Information about children aged 6 months to 3.99 years, where the need of up-to-date data is greatest, were collected as part of an extensive anthropological survey implemented in 1995 to 1997 in the entire Czech Republic. The authors confirmed the trend of debrachycephalization, which is manifested by a statistically significant increase of the maximal length of the head and a statistically significant decrease of the maximal width of the head, as compared with children examined in the anthropological survey in 1956 to 1962 (1). These changes were established in the group of boys (200 boys) as well as in the group of girls (167 girls). The differences of the magnitude of long-term changes between boys and girls were not significant. Evaluation of the long-term changes of the head circumference in the entire group of 366 children aged 0.5-3.99 years (the head circumference of one girl was not measured) revealed a statistically significant increase of this dimension. During the period from 1956/62 till 1996, the influence of positioning on the magnitude of long-term changes of head circumference was not proved. We can say the same about the maximal length of the head of boys and girls and about the maximal width of the head of girls. Only between three differently positioned groups of boys (prone, side, supine) statistically significant differences in the magnitude of long-term changes of the maximal width of the head were found (p < 0.05). Highly significant changes of the maximum width and maximum length of the head occurred as compared with a reference group in all three groups of positioning of infants and in both sexes. The trend of debrachycephalization seems to be thus a more potent factor, which affects long-term changes in the shape of the head, then the predominating sleeping position during the first months after birth. This conclusion is supported by the persisting trend of debrachycephalization, although the supine position is now preferred.

Bodily characteristics and lifestyle of Czech children aged 7.00 to 10.99 years, incidence of childhood obesity.

In 1991-2000 in the Czech Republic a survey of the prevalence of obesity was made. The assessment was made by the transversal method in elementary schools in all regions of the Czech Republic. Children aged 7.00 to 10.99 years were investigated. The survey comprised a total of 3362 children (1668 girls and 1694 boys). A total of 12 anthropometric dimensions were recorded and questionnaires addressed to the children and parents were analyzed. From the results ensued that the ratio of obese children of both sexes in the CR (i.e. children with BMI values about the 97th percentile of the reference population) increased. This zone comprised 6.0% boys and 5.6% girls of the investigated group. An important finding was also the increase of mean values of the abdominal circumference of the children in all age groups in both sexes. The ratio of obese children in different communities is related unequivocally to the size of the community., In smaller communities there are more obese children (according to our data 6.9%) and in large towns the ratio of obese children is 2.3%. In large towns there is also a greater proportion of thin children - 12.1%, in small communities 8.6%. It was found that there is a higher percentage of obese children in families where the mother has elementary education as compared with children of mothers with secondary and university education. Mothers with elementary education have 9.6% obese children while university educated mothers have only 3.6% obese children. Analysis of the dietary questionnaires revealed that only 62.9% children in large towns eat breakfast, the position in villages is similar - 63.9%. In the group of children with excessive body weight fewer children have breakfast (only 54.1%), in the group of children with a low body weigh the majority eat breakfast (75.3%). The majority of children have a mid-morning snack at school which they bring from home. As regards school lunch the majority of children from large towns replied that they have lunch at school. the number of rural children who had school lunch was smaller. An afternoon snack is taken by less than half the children in different groups.