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[en] We conduct a comparative study on various kinoform lenses (KLs) for x-ray nanofocusing by using the geometrical theory, the dynamical diffraction theory, and the beam propagation method. This study shows that the geometrical theory becomes invalid to describe the performance of a KL for nanofocusing. The strong edge diffraction effect from individual lens element, which distorts the desired wave field, leads to a reduction in the effective numerical aperture and imposes a limit on how small a focus a KL can achieve. Because this effect is associated with a finite thickness of a lens, larger lens thickness depicts a stronger distortion. We find that a short KL where all lens elements are folded back to a single plane shows an illumination preference: if the illuminating geometry is in favor of the Bragg diffraction for a focusing order, its performance is enhanced and vice versa. We also find that a short KL usually outperforms its long version where all lens elements do not lie in a single plane because the short one suffers less the wave field distortion due to the edge diffraction. Simulation results suggest that for a long KL, an adaptive lens design is needed to correct the wave field distortion in order to achieve a better performance.
[en] The authors have found the correlation between nanoscopic phase separation in the copper-oxygen planes of YBCO and TlBCCO and the transport and magnetic properties of these materials in the a-b planes such as: the temperature dependence of the critical current density Jc(T), the temperature dependence of the superfluid density ns(T) ∝ 1/λ2(T) at low temperatures, the temperature dependence of the normalized logarithmic relaxation rate S(T), and the dependence of the effective energy barrier against vortex motion on the current density Ueff(J). These properties are controlled by the ratio of the amount of an underdoped filamentary phase to that of an optimally doped one
[en] Hard x-ray point focusing by two crossed multilayer Laue lenses is studied using a full-wave modeling approach. This study shows that for a small numerical aperture, the two consecutive diffraction processes can be decoupled into two independent ones in respective directions. Using this theoretical tool, we investigated adverse effects of various misalignments on the 2D focus profile and discussed the tolerance to them. We also derived simple expressions that described the required alignment accuracy
[en] Low temperature sintering of 0.5 wt.% MnO2-added Pb((Zn1/3Nb2/3)0.20 (Zr0.50Ti0.50)0.80)O3 ceramics (PZNT) was investigated using CuO as sintering aids. It was found that the addition of CuO significantly improved the sinterability of PZNT ceramics, resulting in a reduction of sintering temperature from 1050 to 900 deg. C. The CuO addition also influences in a pronounced way both the crystal structure and microstructure of the low temperature sintered PZNT materials. The materials are transformed from the tetragonal to the rhombohedral structure, and the grain sizes are decreased when CuO are added. The distortion of crystal structure for PZNT samples with CuO addition can be explained with Jahn-Teller effect for electron state d9 of Cu2+ ion. On the other hand, with the increasing of CuO addition, kp, d33 were slightly decreased, but Qm and tan δ were optimized at 1.5 wt.% CuO
[en] Highlights: • The 2D lattice physics code WIMS-AECL was compared against MCNP using ENDF/B-VII.0. • Fuels containing mixtures of PuO_2, NUO_2, LEUO_2, ThO_2 and "2"3"3UO_2 were modelled. • 37-Element and 35-element bundle geometries for PT-HWR were considered. • k-inf, LER and CVR agree well for NUO_2, biases appear for (PuO_2/ThO_2),(LEUO_2/ThO_2). • 89-Group fluxes were calculated and overall show a growing discrepancy with burnup. - Abstract: Code-to-code comparisons of lattice physics calculations were made for a series of fuels that could potentially be used in a conventional 700-MWe class pressure tube heavy water reactor to improve the sustainability of the fuel cycle. Studies were performed for natural uranium, slightly enriched uranium and thorium-based fuels containing low enriched uranium, reactor grade plutonium, or "2"3"3UO_2 as the initial fissile driver. The collision probabilities lattice code WIMS-AECL was compared to the stochastic code MCNP using the ENDF/B-VII.0 nuclear data library. Specific parameters that were studied between models include k-infinity, coolant void reactivity, 89-group cell averaged fluence, and ring-by-ring linear element ratings. The calculations performed have demonstrated that physics parameters estimated by WIMS-AECL are consistent with MCNP, especially for fuel where the main fissile component is uranium-based.
[en] Thermally-induced stresses in a reactor pressure vessel wall, as a result of high-pressure safety injection, are an essential component of integrated risk analyses of pressurized thermal shock transients. Limiting cooldowns arise when this injection occurs under stagnated loop conditions which, in turn, correspond to a rather narrow range (in size) of small-break loss-of-coolant accidents. Moreover, at these conditions, the flow is thermally stratified, and in addition to the global cooldown, one must be concerned about the additional cooling potential due to the downcomer plumes formed by the cold streams pouring out of the cold legs. In the Nuclear Regulatory Commission's Integrated Pressurized Thermal Shock (IPTS) study, this stratification was calculated with the codes REMIX/NEWMIX. A comprehensive comparison with all available experimental data has currently been compiled. The stress analysis using this input was carried out at Oak Ridge National Laboratory using a one-dimensional approximation with the intent to conservatively bound the magnitude of thermal stresses
[en] The mechanism of modulated microwave absorption (MMA) is suggested from the modulation (Hm) dependence in granular YBa2Cu3Ox superconductor under high-field sweep. It is proposed that the MMA signal S be decomposed into three shape factors to interpret the experimental result. The VN factor arises from the difference in the number of vortices between the add (A) mode and the subtract (S) mode corresponding to the alternating field. The CT factor arises from the appearance of the transition region of the shielding current in the S-mode where the absorption is less. The SS factor arises from the difference in the surface slope of the flux distribution between the two modes. With increasing Hm, the positive VN increases linearly. The positive CT increases initially and then decreases. The slope for the A-mode is very gentle, so that SS is negative, and it initially increases rapidly and then saturates. These factors can reproduce the complex behavior of the Hm dependence of S fairly well
[en] The thermal field in a reactor vessel downcomer and resulting thermal/stress response in the adjacent reactor vessel wall during high-pressure safety injection are examined, especially with regard to departures from one-dimensional behavior. Similarity solutions for the stratification (in the cold leg) that creates the downcomer plumes, and scaling considerations for the thermal conduction and stress fields in the vessel wall are developed to provide generalized criteria for the adequacy of the one-dimensional treatment
[en] Purpose: To assure that tumor motion is within the radiation field during high-dose and high-precision radiosurgery, real-time imaging and surrogate monitoring are employed. These methods are useful in providing real-time tumor/surrogate motion but no future information is available. In order to anticipate future tumor/surrogate motion and track target location precisely, an algorithm is developed and investigated for estimating surrogate motion multiple-steps ahead. Methods: The study utilized a one-dimensional surrogate motion signal divided into three components: (a) training component containing the primary data including the first frame to the beginning of the input subsequence; (b) input subsequence component of the surrogate signal used as input to the prediction algorithm: (c) output subsequence component is the remaining signal used as the known output of the prediction algorithm for validation. The prediction algorithm consists of three major steps: (1) extracting subsequences from training component which best-match the input subsequence according to given criterion; (2) calculating weighting factors from these best-matched subsequence; (3) collecting the proceeding parts of the subsequences and combining them together with assigned weighting factors to form output. The prediction algorithm was examined for several patients, and its performance is assessed based on the correlation between prediction and known output. Results: Respiratory motion data was collected for 20 patients using the RPM system. The output subsequence is the last 50 samples (∼2 seconds) of a surrogate signal, and the input subsequence was 100 (∼3 seconds) frames prior to the output subsequence. Based on the analysis of correlation coefficient between predicted and known output subsequence, the average correlation is 0.9644±0.0394 and 0.9789±0.0239 for equal-weighting and relative-weighting strategies, respectively. Conclusion: Preliminary results indicate that the prediction algorithm is effective in estimating surrogate motion multiple-steps in advance. Relative-weighting method shows better prediction accuracy than equal-weighting method. More parameters of this algorithm are under investigation
[en] The effects of PbO atmosphere on structure and electrical properties of Mn-modified Pb((Zn1/3Nb2/3)0.20(Zr0.50Ti0.50)0.80)O3 ceramics were investigated. Specimens were prepared with and without a PbZrO3 protective ambient, by columbite two-stage process in a temperature region from 1050 to 1200 deg. C. The results indicated that PbZrO3 powder is favored to the liquid-state sintering process of specimens in PbO vapor pressure equilibrium. The specimens sintered with PbZrO3 powder showed the homogenous and intergranular microstructure; whereas, the specimens sintered without PbZrO3 powder demonstrated the inhomogenous and transgranular microstructure. Without protective PbZrO3 powder, the flow of PbO from the compact to the exterior resulted in the formation of amorphous phase in grain boundaries, which deteriorated the electric properties seriously. By the use of PbO protective atmosphere, the excellent piezoelectric and dielectric properties (Qm = 1160, tan δ = 0.004, Kp=0.54) were obtained at 1100 deg. C for 2 h