Structural stability of W2B5 under high pressure

High-pressure structural stability studies have been carried out on tungsten boride W₂B₅ up to maximum pressure of 36 GPa using a Mao-Bell diamond-anvil cell at beamline BR-12 of the ELETTRA synchrotron facility (λ = 0.68881 Å). The hexagonal phase (S.G:P6₃/mmc) of W₂B₅ is stable up to the maximum pressure studied. The bulk modulus is estimated to be ~347 GPa using the Birch–Murnaghan equation of state. The variation of lattice parameters and bond lengths B–B and W–B have been studied and the c-axis is seen to be marginally more compressible than the a-axis.     

Microstructure evolution and hardness variation of pack-rolled nanocrystalline nickel

The microstructure evolution and hardness of nanocrystalline nickel during pack rolling at room temperature have been investigated. It was found that the roll-bonding side (R) and non-roll-bonding side (NR) behaved quite differently. The hardness of side R is higher than that of side NR. No obvious work softening was observed in either side R or side NR until the strain reached ~ 0.611. Quantitative X-ray diffraction analysis indicated that the grain size in side NR increases faster than that in side R, a result confirmed by transmission electron microscopy. Texture analysis showed that (2 0 0) preferred orientation first strengthens but then weakens in both sides NR and R, while a strong (2 2 0) preferred orientation emerges, particularly in side R. Further texture analysis suggests that dislocation slip is responsible for the texture discrepancy between side NR and side R. The dislocation activity, grain rotation and grain growth are discussed based on the experimental results.     

Pre‐frontal‐insular‐cerebellar modifications correlate with disgust feeling blunting after subthalamic stimulation: A positron emission tomography study in Parkinson's disease

Subthalamic nucleus (STN) deep brain stimulation (DBS) has recently advanced our understanding of the major role played by this basal ganglion in human emotion. Research indicates that STN DBS can induce modifications in all components of emotion, and neuroimaging studies have shown that the metabolic modifications correlated with these emotional disturbances following surgery are both task‐ and sensory input‐dependent. Nevertheless, to date, these modifications have not been confirmed for all emotional components, notably subjective emotional experience, or feelings. To identify the neural network underlying the modification of feelings following STN DBS, we assessed 16 patients with Parkinson's disease before and after surgery, using both subjective assessments of emotional experience and ¹⁸[F]fluorodeoxyglucose positron emission tomography (¹⁸FDG‐PET). The patients viewed six film excerpts intended to elicit happy, angry, fearful, sad, disgusted, and neutral feelings, and they self‐rated the intensity of these feelings. After DBS, there was a significant reduction in the intensity of the disgust feeling. Correlations were observed between decreased disgust experience and cerebral glucose metabolism (FDG uptake) in the bilateral pre‐frontal cortices (orbitofrontal, dorsolateral, and inferior frontal gyri), bilateral insula, and right cerebellum. We suggest that the STN contributes to the synchronization process underlying the emergence of feelings.     

Cognitive abnormalities and cerebral perfusion defects in a community-dwelling cohort of elderly men with MMSE within the normal range

Objectives: Mini Mental State Examination’s (MMSE’s) sensitivity in its upper level is questioned, hence we investigated cognitive abnormalities and defects in regional cerebral blood flow (rCBF) in elderly with MMSE scores ≥24.

Methods: One hundred and four men at age 81 with MMSE scores ≥24 (mean 28.4 ± 1.7), no dementia or stroke, were examined with neuropsychological test battery, and their rCBF was estimated using ^99mTc-HMPAO SPECT.

Results: MMSE was very sparsely correlated with rCBF. Instead, visuo-spatial tests were correlated with rCBF in parietal and occipital lobe, verbal tests with rCBF in frontal and temporal-parietal lobes, and most of all between Digit Symbol and all rCBF regions, especially in subcortical gray and white matter. In a cluster of low achievers, test of Synonyms, followed by Digit Symbol and Benton test, had highest discriminatory importance. Low achievers had generalized rCBF changes especially in subcortical areas. Only lower scores on two MMSE items, figure drawing and calculation, could discriminate the clusters.

Conclusion: A substantial number of octogenarian men with MMSE ≥ 24p have widespread rCBF changes corresponding to a decreased speeded performance and verbal capacity.     

双源 CT 低剂量 Flash 螺旋模式在全身大血管成像中的应用

评价双源 CT 低剂量 Flash 螺旋模式全身大血管成像的图像质量和辐射剂量,探讨其应用价值。收集我院行双源CT 低剂量 Flash 螺旋扫描全身大血管患者69例（全身大血管 CTA 组）,行相同扫描范围的平扫患者69例（对照 A 组）,行回顾性心电门控螺旋扫描冠状动脉患者69例（对照 B 组）。比较全身大血管 CTA 组与对照 B 组的图像噪声及全身大血管 CTA 组与对照 A 组、B 组的辐射剂量。结果发现,全身大血管 CTA 组颈总动脉、颈内动脉、肾动脉、腹主动脉的图像质量均可满足诊断要求,图像噪声与对照 B 组比较,差异无统计学意义（Z＝-0．42,P＞0．05）。全身大血管 CTA 组有效剂量低于对照 A 组、B 组（Z＝-10．14;Z＝-8．76,P 均＜0．001）。全身大血管 CTA 组平均扫描长度短于对照 A 组（Z＝-8．86,P＜0．001）。故本研究认为,双源 CT 低剂量 Flash 螺旋模式安全、无创、快捷,图像质量高,大范围 CTA 成像的辐射剂量低,是一种适合全身大血管检查的影像技术。     

Effects of annealing temperature on structural,optical, and electrical properties of antimony-doped tin oxide thin films

Antimony-doped tin oxide (ATO) films, approximately 320 nm in thickness, have been prepared by electron beam evaporation onto glass substrates. The films were annealed at temperatures between 400°C and 550°C in air and their structure and surface morphologies were observed by X-ray diffraction (XRD) and atomic force microscopy (AFM) after the different annealing treatments. XRD patterns of the ATO thin films as-deposited and annealed at 400°C showed that they were amorphous, but annealing beyond 400°C caused the films to become polycrystalline with tetragonal structure and orientated in the (1 1 0) direction. The grain size in the annealed films, obtained from the XRD analysis, was in the range 146–256 Å and this increased with the annealing temperature. The dislocation density, cell volume and strain were found to decrease gradually with increasing annealing temperature. Photoluminescence spectra revealed an intensive blue/violet peak at 420 nm, which increased gradually in height with annealing. It is suggested that an increase in the population of Sb⁺⁵ ions might be the reason for the enhancement of the blue/violet emission. The optical properties of the films were also investigated in the UV-visible-NIR region (300–1000 nm). The optical constants, namely the refractive index n and the extinction coefficient k in the visible region were calculated. The optical energy band gap, as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths, was found to increase from 3.59 to 3.76 eV with annealing temperature.     

Antiferromagnetic order and the structural order–disorder transition in the Cd6Ho quasicrystal approximant

It has generally been accepted that the orientational ordering of the Cd₄ tetrahedron within the Cd₆ R quasicrystal approximants is kinetically inhibited for R?=?Ho, Er, Tm and Lu by steric constraints. Our high-resolution X-ray scattering measurements of the Cd₆Ho quasicrystal approximant, however, reveal an abrupt (first-order) transition to a monoclinic structure below T _S?=?178?K for samples that have ‘aged’ at room temperature for approximately one year, reopening this question. Using X-ray resonant magnetic scattering at the Ho L ₃-edge we have elucidated the nature of the antiferromagnetic ordering below T _N?=?8.5?K in Cd₆Ho. The magnetic Bragg peaks are found at the charge forbidden H?+?K?+?L?=?2n?+?1 positions, referenced to the high-temperature body-centred cubic structure. In general terms, this corresponds to antiferromagnetic arrangements of the Ho moments on adjacent clusters in the unit cell as previously found for Cd₆Tb.     

On the structural unit model of grain boundary structure

Abstract

A critique of the structural unit model is presented. It is shown that the predictive capacity of the model is severely limited when it is applied to boundaries with relatively-high-index rotation axes. Recent computer simulations suggest that ‘high index’ means 〈221〉 and above. A new approach to grain boundary structure is needed for mixed tilt and twist boundaries.