Microstructural characterization and high-temperature strength of hot-pressed silicon nitride ceramics with Lu2O3 additives

The microstructures of two hot-pressed Si₃N₄ ceramics, with 3.33 and 12.51 wt% Lu₂O₃ additive, have been characterized using transmission electron microscopy. The microstructures of both samples consisted of elongated β-Si₃N₄ grains and a secondary phase, contained in pockets surrounded by the grains, with a crystalline or amorphous form. In the 3.33 wt% Lu₂O₃-containing Si₃N₄ ceramic, all the multiple-grain junctions were completely crystalline while, in the 12.51 wt% Lu₂O₃-containing Si₃N₄ ceramic, approximately half the junctions were devitrified. A thin intergranular amorphous film present between the two-grain boundary was common; however, a film-free grain boundary was observed in the 12.51 wt% Lu₂O₃ sample. The film-free grain boundary was determined to be approximately 35%. Both ceramics fractured in four-point flexure between 1200 and 1600°C. Their high-temperature strength is closely associated with the nature of the grain-boundary phase formed during the sintering process.     

Formation of ductile Al-based metallic glasses without rare-earth elements

Al₇₅Cu₁₇Mg₈ is a eutectic composition according to the ternary phase diagram, which can be quenched into a fully amorphous phase by adding 2-8at.% Ni, but the addition of a similar percentage of Gd failed to form the amorphous phase. The amorphous alloys obtained exhibit two broad diffuse peaks in the X-ray diffraction curves and, correspondingly, two halo rings in the electron diffraction patterns, implying that two types of local atom configuration exist. Thermal analysis of the amorphous alloys indicates that the primary crystallization peak shifts to higher temperatures with increasing Ni content. The occurrence of a nucleation and crystal growth peak during isothermal crystallization reveals the amorphous nature of the quenched ribbon alloys. The quenched amorphous ribbons do not break after bending by 180°. Mechanical testing yielded a tensile strength of 810MPa for (Al₇₅Cu₁₇Mg₈)₉₅Ni₅, and a vein structure, characteristic of amorphous fracture, is apparent in scanning electron micrographs. The different effects of Ni and Gd on the glass formation indicate that the large atomic size of Gd is not critical to the glass formation.     

Cooling-rate-dependent microstructure and mechanical properties of a CuZrAlAg alloy

A Cu₃₆Zr₄₈Al₈Ag₈ alloy rod with a diameter of 10 mm was fabricated using a copper-mould suction casting method. Structural characterization revealed that the rod has different microstructures along the casting direction, including a complete amorphous structure and an amorphous/crystalline composite structure with different amount of B2 CuZr phase. Nanoindentation tests showed that the hardness and the elastic modulus of the crystalline phase are lower than those of the amorphous matrix. The hardness and the elastic modulus of the amorphous matrix decrease with decreasing crystalline proportion of the alloy, while the Vickers hardness of the alloy increases with a reduction in the crystalline proportion.     

An explanation for the low-temperature H evolution peak in hydrogenated amorphous silicon films deposited 'on the edge of crystallinity'

The puzzling existence of a sharp low-temperature (T = 400°C) H evolution peak in compact hydrogenated amorphous silicon (a-Si : H) films deposited 'on the edge of crystallinity' is examined. From infrared absorption and X-ray diffraction (XRD) measurements, we show that none of the standard methods used to explain the existence of this peak in a-Si : H materials is applicable to the present films. From the Si-H wag-mode peak frequency, we postulate the existence of very small Si crystallites contained within the amorphous matrix. While the crystallite volume fraction is too small to be detected by XRD in the as-grown films, crystallization is observed for this material at anneal temperatures as low as 500°C. It is proposed that these crystallites catalyse the crystallization of the remainder of the amorphous matrix upon moderate annealing, enabling H surface desorption and H₂ out-diffusion to the sample surface along newly formed grain boundaries at low anneal temperatures.     

TEM observation of oxide scale formed on a Ti–Al–Zr alloy oxidized at 360°C in alkaline steam

Ti–Al–Zr alloy has been oxidized at 360°C in alkaline steam at a pressure of 10.3?±?0.7?MPa. Cross-sectional transmission electron microscopy (TEM) observations indicated that the oxide scale of Ti–Al–Zr alloy was composed of outer and inner subscales, in which the outer layer consists of anatase-TiO₂ and the inner layer a mixture of TiO and Ti₂O. The thickness of the Ti₂O, TiO and anatase-TiO₂ were approximately 50, 100 and 400?nm, respectively. These results were confirmed by X-ray energy dispersive spectrometry (EDS) measurements. The enhanced corrosion of titanium alloys in LiOH solution is attributed to a high hexagonal Ti₂O to tetragonal TiO₂ phase transformation rate induced by the substitution of Li⁺ for Ti⁴⁺ in the oxide layer.     

Nanoporous gold obtained from a metallic glass precursor used as substrate for surface-enhanced Raman scattering

Nanoporous gold (NPG) has been synthesized by electrochemical de-alloying a new precursor, amorphous Au₃₀Cu₃₈Ag₇Pd₅Si₂₀ (at.%), starting from melt-spun ribbons. Ligaments ranging from 75 to 210 nm depending on the de-alloying time were obtained. Analytical and electrochemical evidence showed the ligaments contain residual Cu, Ag and Pd. Surface-enhanced Raman scattering from the NPG was investigated using pyridine and 4,4′-bi-pyridine as probe molecules. It was found that the activity is at maximum when the ribbon is fully de-alloyed although the ligaments then have a larger size. The enhancement is attributed to the small size of crystals in the ligaments, to their morphology and to trapped atoms.     

Ni-based fully amorphous metallic coating with high corrosion resistance

A Ni₅₃Nb₂₀Ti₁₀Zr₈Co₆Cu₃ fully amorphous metallic coating has been deposited by means of kinetic metallization (KM) using gas atomized powders. As the thickness of the amorphous metallic coating is increased to 400?µm, it attains the excellent corrosion resistance of the amorphous alloy, as indicated by the extremely low passive current density and wide passive region in 1?kmol/m³ HCl aqueous solution. The corrosion rate is as low as 10^–3?mm/year in the extremely corrosive environment of 6?kmol/m³ HCl aqueous solution.     

Observation of Cu nanometre scale clusters formed in Fe85Si2B8P4Cu1 nanocrystalline soft magnetic alloy by a spherical aberration-corrected TEM/STEM

Microstructure of a nanocrystalline soft magnetic Fe₈₅Si₂B₈P₄Cu₁ alloy (NANOMET^®) was investigated by the state of the art spherical aberration-corrected TEM/STEM. Observation by TEM shows that the microstructure of NANOMET^® heat treated at 738 K for 600 s which exhibits the optimum soft magnetic properties has homogeneously distributed bcc-Fe nanocrystallites with the average grain size of 30 nm embedded in an amorphous matrix. Elemental mappings indicate that P is excluded from bcc-Fe grains and enriched outside the grains, which causes to retard the grain growth of bcc-Fe crystallites. The aberration-corrected STEM-EDS analysis with the ultrafine electron probe successfully proved that Cu atoms form nanometre scale clusters inside and/or outside the bcc-Fe nanocrystallites.     

Cascade effects on the irradiation stability of amorphous SiOC

We studied the heavy ion radiation tolerance of amorphous silicon oxycarbide (SiOC) alloys by in situ Kr ion irradiation within a transmission electron microscopy. The amorphous SiOC thin films were grown via co-sputtering from SiO₂ and SiC targets on a surface-oxidized Si (100) substrate. These films were irradiated by 1 MeV Kr ions at both room temperature and 300 °C with damage levels up to 5 displacements per atom (dpa). TEM characterization shows no sign of crystallization, void formation or segregation in all irradiated samples. Our findings suggest that SiOC alloys are a class of promising radiation tolerant materials.     

Dendrite growth velocity in the undercooled melt of glass forming Ni50Zr50 compound

Glass-forming Ni₅₀Zr₅₀ intermetallic compound is containerless undercooled and solidified using electrostatic levitation. Large undercoolings up to ?T = 300 K are achieved. The dendrite growth velocity of the congruently melting alloy is measured as a function of undercooling using a high-speed camera technique. The experimental data is analysed within a sharp interface theory. It is found that the driving force of crystallisation is controlling the growth kinetics at ?T < 250 K but at larger undercoolings the growth kinetics is progressively controlled by atomic diffusion. This leads to a slowing down of the growth velocity. The maximum velocity and the temperature at which the maximum occurs (T_max) are inferred from the dendrite growth velocity – undercooling relation. The relation of the temperature T_max and the glass temperature fits into a general classification scheme for glass-forming systems. The kinetic and thermal undercooling terms are calculated within dendrite growth theory as a function of the total undercooling. At ?T > 126 K, the kinetic undercooling dominates and increases rapidly with the undercooling ?T. The maximum prefactor of the kinetic undercooling is plotted vs. the reciprocal temperature. Its temperature dependence is discussed.     

Relationships among pain intensity,pain-related distress,and psychological distress in pre-surgical total knee arthroplasty patients: a secondary analysis

The current study aimed to examine the relationships between movement and resting pain intensity, pain-related distress, and psychological distress in participants scheduled for total knee arthroplasty (TKA). This study examined the impact of anxiety, depression, and pain catastrophizing on the relationship between pain intensity and pain-related distress. Data analyzed for the current study (N = 346) were collected at baseline as part of a larger Randomized Controlled Trial investigating the efficacy of TENS for TKA (TANK Study). Participants provided demographic information, pain intensity and pain-related distress, and completed validated measures of depression, anxiety, and pain catastrophizing. Only 58% of the sample reported resting pain >0 while 92% of the sample reported movement pain >0. Both movement and resting pain intensity correlated significantly with distress (r_s = .86, p < .01 and .79, p < .01, respectively). About three quarters to two thirds of the sample (78% for resting pain and 65% for movement pain) reported different pain intensity and pain-related distress. Both pain intensity and pain-related distress demonstrated significant relationships with anxiety, depression, and catastrophizing. Of participants reporting pain, those reporting higher anxiety reported higher levels of distress compared to pain intensity. These findings suggest that anxious patients may be particularly distressed by movement pain preceding TKA. Future research is needed to investigate the utility of brief psychological interventions for pre-surgical TKA patients.     

Asthma in children of Caribbean descent living in the inner-city: comparing Puerto Rican and Afro-Caribbean children

Ethnic minority children bear a disproportionate amount of the US asthma burden. We compared asthma morbidity and pulmonary function (%FEV₁) in two Caribbean groups living in the Bronx, NY: Puerto Rican and Afro-Caribbean children. Caregiver-child dyads (Puerto Rican: n = 113, M age = 9.89 ± 2.05; Afro-Caribbean: n = 47, Mage = 10.35 ± 2.08) responded to sociodemographic and asthma-related questions, and children’s %FEV₁ was measured. Puerto Rican children had significantly greater (past year) asthma morbidity, yet there were no significant differences in %FEV₁. This discrepancy between objective pulmonary function and asthma morbidity suggests the importance of considering sociocultural factors in pediatric asthma care.     

The relation between emotional intelligence and subjective well-being: A meta-analytic investigation

This meta-analysis includes studies concerning the relationships between emotional intelligence (EI) and subjective well-being (SWB). A total of 25 studies with 77 effect sizes and a combined sample of 8520 participants were found. The results provided evidence of a positive significant relationship between EI and SWB (? = 0.32). This relationship was found to be higher in studies using self-report mixed EI instruments (? = 0.38), than with in studies using self-report ability EI instruments (? = 0.32) and performance-based ability EI instruments (? = 0.22). When examining EI measures, there was a larger association between EI and the cognitive component of SWB (? = 0.35) than with the affective component (? = 0.29). There is a need for further research with other evaluation methods to achieve a better understanding of the relationship between EI and SWB.     

Children’s judgements of the obligation to help: The role of relationships

ABSTRACT

Children at ages 7 (N = 24, M _age = 6.96, SD _age =.20), 9 (N = 29, M _age = 8.76, SD _age =.44), and 11 (N = 25, M _age = 10.76, SD _age =.66), and adults (N = 30) made judgements about the obligation to help when it conflicts with a personal desire. Across ages, the obligation to help was judged to be strongest when there were positive or neutral past interactions with the person in need of help, compared to mean past interactions. Expectation of a future friendship predicted the obligation to help, even after controlling for age and sex. However, we found no effect of children helping gender in-group members more. Evidence for altruism was not found: expected positive emotions did not predict the obligation to help. We conclude that an expectation of future relationship is the strongest predictor of helping obligation.     

Effect of electron concentration on the Laves phase stability of NbCr2–Ni produced by powder metallurgy

The powder metallurgy technology of mechanical alloying followed by hot-pressing consolidation has been used to obtain NbCr₂–Ni Laves phases. High-purity Nb, Cr, and Ni crystalline powders were milled for periods up to 35 h. These powders were vacuum sintered at 1250°C for 0.5 h under 45 MPa. The phase transformations of NbCr₂–Ni Laves phases have been investigated by X-ray diffraction. The grain size decreases and the microstrain increases with increased Ni content. Different phase transformations were observed from NbCr₂–Ni intermetallics. It is found that the electron concentration and phase stability correlation is obeyed in the Nb–Cr–Ni systems. However, the electron concentration corresponding to the C15/C14 phase transition is found to move to a higher value (i.e. 6.103) than the predicted one (i.e. 5.88) in the literature.     

Dynamics of upconversion photoluminescence in Ge–Ga–S: Er3+: application of quadrature frequency resolved spectroscopy

Quadrature frequency resolved spectroscopy (QFRS) on green (~550 nm) upconversion photoluminescence (UCPL) of Ge–Ga–S: Er³⁺ glasses pumped at 975 nm revealed double-peaked spectra with long lifetime τ₁ ranging from 0.2 to 2 ms and short lifetime τ₂ ≈ several tens of μs. The results are analysed in terms of the transfer function derived by linearizing rate equations for a three-level model. The τ₁ component is attributed to the relaxation at the intermediate level ⁴I_11/2 of Er³⁺ ions and the τ₂ component, to that at the upper ⁴S_3/2 manifold. The dominance of energy transfer upconversion over excited state absorption in the UCPL manifest itself as a greater dependence of τ₁ on the pump power and a lower ratio of the components of τ₂ to τ₁ in the QFRS spectra of a heavily Er-doped sample.     

Tensile properties of precracked tempered martensitic steel specimens tested at ultralow strain rates in high-pressure hydrogen atmosphere

Tensile tests were performed on precracked Cr–Mo martensitic steel (C: 0.38, Si: 0.22, Mn: 0.84, P: 0.024, S: 0.021, Ni: 0.08, Cr: 1.11, Mo: 0.15, Cu: 0.12, Fe: bal. (wt%)) specimens at various strain rates (ranging from 6.5 × 10^?8 s^?1 to 1.0 × 10^?4 s^?1) in high-pressure (95 MPa) hydrogen and helium atmospheres. Irrespective of the strain rate, the tensile strength in the helium atmosphere was 1400 MPa. In the hydrogen atmosphere, the tensile strength decreased to less than 600 MPa at a strain rate of 2.0 × 10^?5 s^?1. However, the tensile strength increased to 900 MPa when the strain rate was decreased to 6.5 × 10^?8 s^?1. This recovery of the tensile strength was because of the decrease in the local stress in the vicinity of the precrack because of hydrogen.     

Retention and thermal desorption of helium in pure tungsten

Tungsten (W) is cited as a candidate first-wall material in fusion reactors owing to its outstanding thermal properties and erosion resistance. An important issue is that the energetic isotopes of hydrogen, tritium (T) and deuterium (D) and helium (He) particles damage the surface of W in fusion reactors. He particles cause more notable damage than D or T because the binding energy of defects and He is larger than that of defects and D or T. In this study, well-annealed W specimens were implanted with 5 keV He ions at room temperature and irradiation dosages of 1.0 × 10²⁰ and 2.5 × 10²¹ ions/m². Then, thermal desorption spectroscopy analysis was performed by heating the samples to 1973 K at a ramping rate of 0.5 K/s. Thermal desorption of He in the sample irradiated with a low dosage occurred at 1400 and 1960 K, whereas that in the sample irradiated with a high dosage occurred at 740, 1050 and 1500 K. According to the microstructures observed using transmission electron microscopy, both peaks in the former case were attributed to He de-trapping from irradiation to nduced helium-vacancy clusters of different sizes, whereas the peaks in the latter case were attributed to He de-trapping from surface defects, irradiation-induced dislocation loops and tiny helium-vacancy clusters, respectively.     

Neural representations of faces and limbs neighbor in human high-level visual cortex: evidence for a new organization principle

Neurophysiology and optical imaging studies in monkeys and functional magnetic resonance imaging (fMRI) studies in both monkeys and humans have localized clustered neural responses in inferotemporal cortex selective for images of biologically relevant categories, such as faces and limbs. Using higher resolution (1.5 mm voxels) fMRI scanning methods than past studies (3–5 mm voxels), we recently reported a network of multiple face- and limb-selective regions that neighbor one another in human ventral temporal cortex (Weiner and Grill-Spector, Neuroimage, 52(4):1559–1573, 2010) and lateral occipitotemporal cortex (Weiner and Grill-Spector, Neuroimage, 56(4):2183–2199, 2011). Here, we expand on three basic organization principles of high-level visual cortex revealed by these findings: (1) consistency in the anatomical location of functional regions, (2) preserved spatial relationship among functional regions, and (3) a topographic organization of face- and limb-selective regions in adjacent and alternating clusters. We highlight the implications of this structure in comparing functional brain organization between typical and atypical populations. We conclude with a new model of high-level visual cortex consisting of ventral, lateral, and dorsal components, where multimodal processing related to vision, action, haptics, and language converges in the lateral pathway.     

Children's appraisal of their relationship with the teacher: Preliminary evidence for construct validity

Teacher–child relationships are increasingly considered as contexts for children's development. While teacher reports are mostly used to study the developmental consequences of the three attachment-based dimensions of closeness, conflict and dependency, children's perceptions are important too. This study evaluated the construct validity of the newly developed Child Appraisal of Relationship with Teacher Scale (CARTS). To this end, data from a special education sample of children with emotional and behavioural disorders (N = 82; M_age = 8.75) and from a general education sample (N = 145; M_age = 8.15) were used. Results supported the reliability and construct validity of the CARTS scales and showed that children's relationship perceptions as assessed with the CARTS were uniquely associated with their feelings about their teacher as measured with the Feelings About School. In addition, child-perceived closeness and conflict converged in expected directions with teacher-perceived closeness and especially conflict in the relationship, as measured with a questionnaire and a diary.