[en] Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) are employed to investigate the crystallization behavior in metallic Zr₇₀Cu₂₀Ni₁₀ glass during continuous heating. It is found that the DSC curves of metallic Zr₇₀Cu₂₀Ni₁₀ glass exhibit two exothermic peaks, indicating that the crystallization process proceeds via a double stage mode. TEM microstructural analysis confirms that the first exothermic reaction in the DSC traces of metallic Zr₇₀Cu₂₀Ni₁₀ glass mainly corresponds to the precipitation of the Zr₂Cu phase, while the second one corresponds to the formation of nano-scale Zr₂Ni particles. Ni plays an important role in the stability of the nanocrystals, and its effect is also discussed

[en] Employing the X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques, the effect of Ni content on crystallization behavior of metallic Zr₇₀Cu_30-xNi_x (x=5, 10 and 15) glasses has been investigated. It is found that all the DSC traces of metallic Zr₇₀Cu_30-xNi_x (x=5, 10 and 15) glasses display two exothermic peaks, indicating that the crystallization processes of metallic Zr₇₀Cu_30-xNi_x (x=5, 10 and 15) glasses proceed via a double stage mode. It is observed that the two exothermic peaks in the DSC scans of metallic Zr₇₀Cu₂₅Ni₅ and Zr₇₀Cu₁₅Ni₁₅ glasses overlap, implying that the crystallization processes of these two metallic glasses proceed through the almost simultaneous precipitation of crystalline phases. As for the metallic Zr₇₀Cu₂₀Ni₁₀ glass, the exothermic peaks in the DSC curves are more separated than those of the metallic Zr₇₀Cu₂₅Ni₅ and Zr₇₀Cu₁₅Ni₁₅ glasses, indicating that the crystallization products of metallic Zr₇₀Cu₂₀Ni₁₀ glass precipitate in sequence. To explain these experimental results, a micromechanism for crystallization of metallic Zr₇₀Cu_30-xNi_x (x=5, 10 and 15) glasses is suggested. In addition, the origin of the high stability of the f.c.c.-Zr₂Ni phase is also interpreted from the viewpoint of local activation energy for crystallization

[en] X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to investigate the effect of cooling rate on crystallization behavior of metallic Zr₇₀Cu₂₀Ni₁₀ glass. It is found that all DSC traces of the metallic Zr₇₀Cu₂₀Ni₁₀ glasses under different cooling rates exhibit two exothermic peaks, indicating that the crystallization of metallic Zr₇₀Cu₂₀Ni₁₀ glass proceeds through a double-stage mode. In our previous studies, we have concluded that the first exothermic reaction mainly corresponds to the precipitation of the Zr₂Cu phase, and the second one is mainly due to the formation of nanoscale Zr₂Ni particles. It is observed that there exists a close relationship between the cooling rate and thermodynamic parameters of metallic Zr₇₀Cu₂₀Ni₁₀ glass, such as the onset crystallization temperature T_x, the first peak temperature T_p1 and the second one T_p2. The above three thermodynamic parameters reach a maximum when the surface velocity is 30 m/s. This effect is just similar to that of the Ni concentration, which has been discussed in our previous works. The activation energy for crystallization and the local Avrami exponent of metallic Zr-Cu-Ni glass under isothermal annealing conditions also exhibit a similar tendency with the cooling rate

[en] The technique of maximum entropy image restoration is applied to the problem of deconvolving the point spread function from a deep, high-quality V band image of the optical jet of 3C 273. The resulting maximum entropy image has an approximate spatial resolution of 0.6 arcsec and has been used to study the morphology of the optical jet. Four regularly-spaced optical knots are clearly evident in the data, together with an optical extension at each end of the optical jet. The jet oscillates around its center of gravity, and the spatial scale of the oscillations is very similar to the spacing between the optical knots. The jet is marginally resolved in the transverse direction and has an asymmetric profile perpendicular to the jet axis. The distribution of V band flux along the length of the jet, and accurate astrometry of the optical knot positions are presented. 34 refs

[en] Employing differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM), the micromechanism for crystallization of Zr₇₀Cu₂₀Ni₁₀ metallic glass under isothermal annealing conditions has been investigated. It is found that the relationship between the annealing temperature and the peak position, incubation time and ending time in the isothermal annealing DSC traces of Zr₇₀Cu₂₀Ni₁₀ metallic glass obeys a first-order exponential function. However, the time-temperature transformation curves of Zr₇₀Cu₂₀Ni₁₀ metallic glass at different crystallized volume fractions can be well fitted by a second-order exponential function. It is observed that at the initial crystallization stage some ordered atomic clusters precipitate first, acting as nucleation sites and facilitating the subsequent crystallization process, and the crystal growth process mainly proceeds through the atomic depositing on the previously formed crystals. This behavior confirms that the new micromechanism for crystallization of amorphous alloys proposed by Lu and Wang can also be applied to the new series of zirconium based amorphous alloys

[en] We present a fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios. Utilizing the high flux of the X-rays generated from the third-generation synchrotron source, we can complete a high-resolution tomography scan within a short period of time, after which the three-dimensional (3D) packing structure can be obtained for the subsequent structural analysis. The image phase-retrieval procedure has been implemented to enhance the image contrast. We systematically investigated the effects of particle shape and aspect ratio on the structural properties including packing density and contact number. It turns out that large aspect ratio rod packings will have wider distributions of free volume fraction and larger mean contact numbers. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

[en] Purpose: Database dose predictions and a commercial autoplanning engine both improve treatment plan quality in different but complimentary ways. The combination of these planning techniques is hypothesized to further improve plan quality. Methods: Four treatment plans were generated for each of 10 head and neck (HN) and 10 prostate cancer patients, including Plan-A: traditional IMRT optimization using clinically relevant default objectives; Plan-B: traditional IMRT optimization using database dose predictions; Plan-C: autoplanning using default objectives; and Plan-D: autoplanning using database dose predictions. One optimization was used for each planning method. Dose distributions were normalized to 95% of the planning target volume (prostate: 8000 cGy; HN: 7000 cGy). Objectives used in plan optimization and analysis were the larynx (25%, 50%, 90%), left and right parotid glands (50%, 85%), spinal cord (0%, 50%), rectum and bladder (0%, 20%, 50%, 80%), and left and right femoral heads (0%, 70%). Results: All objectives except larynx 25% and 50% resulted in statistically significant differences between plans (Friedman’s χ"2 ≥ 11.2; p ≤ 0.011). Maximum dose to the rectum (Plans A-D: 8328, 8395, 8489, 8537 cGy) and bladder (Plans A-D: 8403, 8448, 8527, 8569 cGy) were significantly increased. All other significant differences reflected a decrease in dose. Plans B-D were significantly different from Plan-A for 3, 17, and 19 objectives, respectively. Plans C-D were also significantly different from Plan-B for 8 and 13 objectives, respectively. In one case (cord 50%), Plan-D provided significantly lower dose than plan C (p = 0.003). Conclusion: Combining database dose predictions with a commercial autoplanning engine resulted in significant plan quality differences for the greatest number of objectives. This translated to plan quality improvements in most cases, although special care may be needed for maximum dose constraints. Further evaluation is warranted in a larger cohort across HN, prostate, and other treatment sites. This work is supported by Philips Radiation Oncology Systems.

[en] Using a ring-strip resistive anode and a pair of integrated spectroscopy amplifiers, a circular radius-sensitive microchannel plate (MCP) detector is developed for future studies of ion-atom collisions. The detector is tested by a ⁵⁵Fe X-ray source and a radial resolution of 0.2 mm is achieved.

[en] A novel n-body potential for an Zr–Nb system was developed in the framework of the embedded-atom method. All the parameters of the constructed potential have been systematically evaluated by fitting to the ground state properties obtained from experimental measurements and first-principles calculations for pure elements and some alloys. It is shown that most of the static thermodynamics properties for Zr and Nb can be well reproduced by using the present potential. Some calculation results based on the present model are even closer to the experimental data than those based on previous potential models. The ground state properties of hypothetical Zr–Nb alloys were also calculated and found to be in agreement with first-principles calculations. Furthermore, the formation energies of random solid solutions of Zr–Nb with lattices of body centered cubic (bcc) and hexagonal close packed (hcp) type were calculated by fitting the energy–volume relations to Rose’s equation of state. These values were compared with those obtained by first-principles calculations based on special quasirandom structure models and the Miedema-ZSL-07 model (the improved Miedema model proposed by Zhang, Sheng and Liu in 2007). It is indicated that our n-body constructed potential for a Zr–Nb alloy provides an effective description for the interaction between the dissimilar ion interactions for hcp–bcc systems. (paper)

[en] Gd_56-xDy_xAl₂₄Co₂₀ (x = 16, 20 and 22) bulk metallic glasses (BMGs) alloys with a diameter of 2, 3 and 3 mm, respectively, were prepared by using copper mold casting. These alloys exhibit higher values of the glass transition temperature, crystallization temperature, and activation energy of the glass transition and crystallization, compared with those of other known rare-earth-based BMGs. A maximum magnetic entropy changes of 15.78 J/(kg K) is obtained in Gd₄₀Dy₁₆Al₂₄Co₂₀, which is the maximal among all the bulk metallic glasses, and is much larger than those of the known crystalline magnetic refrigerant compound Gd₅Si₂Ge_1.9Fe_0.1 and pure Gd metal. All the three BMG alloys have a broader temperature range of the entropy change peak, resulting in larger refrigerate capacities (RC) than those of conventional crystalline materials. The excellent magnetocaloric properties combining with high thermal stability make them an attractive candidate for magnetic refrigerants in the temperature range of 20-100 K