Direct Observation and simulation of ladle pouring behaviour in die casting sleeve

The ladle pouring process is one part of die casting which has the advantages of high speed, good quality and mass production. The molten metal is quickly poured into the sleeve by tilting the ladle, and immediately injected into the die cavity with high speed and high pressure by advancing the plunger. Since the entrapment of air and the generation of solidified layer in the ladle pouring may cause the defects of cast products, it is necessary to simulate the ladle pouring behavior. In the present study, the pouring experiment into the sleeve using water and die casting aluminum alloy JIS-ADC12 are carried out to observe the flow behavior by tilting the ladle. The temperature of the dissolved metal is measured using a thermocouple to investigate heat transfer behavior. The flow behaviors in ladle pouring of water and molten aluminum alloy are simulated using ParticleworksTM of MPS software. The simulation results, when using water are almost the same actual wave behavior. It is difficult to simulate the wave behavior of molten aluminum alloy because there is a difference in wave behavior between water and molten aluminum alloy. On the other hands, it is clear that the molten aluminum alloy is not solidified during wave behavior in the early stage of pouring by the experiments. Therefore, we try to adjust the kinematic viscosity of molten metal and the thermal conductivity of sleeve die. As the result, the wave behavior and temperature of molten aluminum alloy after adjusting the parameters are almost agreed with the actual phenomena. Flow and heat transfer simulation using the MPS method is effective method that ladle pouring of molten aluminum alloy with free surface flow can be simulated accurately

Metal-insulator transition and the Pr3+^{3+}/Pr4+^{4+} valence shift in (Pr1−y_{1-y}Yy_{y})0.7_{0.7}Ca0.3_{0.3}CoO3_3

The magnetic, electric and thermal properties of the ($Ln_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ perovskites ($Ln$~=~Pr, Nd) were investigated down to very low temperatures. The main attention was given to a peculiar metal-insulator transition, which is observed in the praseodymium based samples with $y=0.075$ and 0.15 at $T_{M-I}=64$ and 132~K, respectively. The study suggests that the transition, reported originally in Pr$_{0.5}$Ca$_{0.5}$CoO$_3$, is not due to a mere change of cobalt ions from the intermediate- to the low-spin states, but is associated also with a significant electron transfer between Pr$^{3+}$ and Co$^{3+}$/Co$^{4+}$ sites, so that the praseodymium ions occur below $T_{M-I}$ in a mixed Pr$^{3+}$/Pr$^{4+}$ valence. The presence of Pr$^{4+}$ ions in the insulating phase of the yttrium doped samples (Pr$_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ is evidenced by Schottky peak originating in Zeeman splitting of the ground state Kramers doublet. The peak is absent in pure Pr$_{0.7}$Ca$_{0.3}$CoO$_3$ in which metallic phase, based solely on non-Kramers Pr$^{3+}$ ions, is retained down to the lowest temperature.Comment: 10 figure

The Retroperitoneum Protects Prosthetic Graft Material from Intraperitoneal Contamination: An Experimental Study

AbstractObjectivesTo evaluate the ability of the retroperitoneum to serve as a barrier, against bacterial contamination, between the peritoneal cavity to the retroperitoneal space.MethodsSeventy rats had a small piece of knitted Dacron graft placed in the retroperitoneal space and 106–109 colony forming unit (cfu) Enterococcus faecalis was injected into the peritoneal cavity. In half the retroperitoneal (RP) group, the retroperitoneum was preserved and in the remainder, the open peritoneal (OP) group, needle holes were created. Grafts were harvested after 1, 4, or 7 days and cultured for E. faecalis. A blood sample was collected from three rats in each group for culture before the graft was harvested.ResultsGraft infection did not develop in any rat injected with 106 or 107 cfu in the RP group, while seven out of the 10 graft cultures of the OP group grew E. faecalis (P=0.003). In rats injected with 108 or 109 cfu, five out of the 10 graft cultures in the RP group and eight out of 10 in the OP group grew E. faecalis. All blood cultures were negative when the injected bacterial count was 107 cfu or less. One out of the three blood cultures was positive at 108 cfu, and all were positive at 109 cfu.ConclusionsThese results suggest that an intact retroperitroneum acts as a protective barrier against intraperitoneal bacterial contamination, particularly when blood cultures are negative

Numerical simulation of a hybrid trapped field magnet lens (HTFML) magnetized by pulsed fields

Abstract: The hybrid trapped field magnet lens (HTFML) is a promising device that is able to concentrate a magnetic field higher than an applied background field continuously, even after removing a background field, which was conceptually proposed by the authors in 2018. We have numerically investigated the HTFML performance, consisting of a REBaCuO cylindrical magnetic lens and REBaCuO trapped field magnet (TFM) cylinder, magnetized by pulsed fields. Single magnetic pulses were applied ranging from B app = 1.5 T to 5.0 T at the operating temperature of T s = 30, 40 and 50 K, and the performance was compared with that of the single REBaCuO TFM cylinder. The HTFML effect was clearly confirmed for the lower B app values. However, for the higher B app values, the trapped field in the magnetic lens bore was nearly equal to or slightly lower than that for the single TFM cylinder because of a weakened lens effect due to magnetic flux penetration into the lens. A temperature rise in the REBaCuO magnetic lens and TFM cylinder was also observed. These results strongly suggest that lowering the temperature of the REBaCuO magnetic lens could enhance the HTFML effect even for higher B app

High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes

We present the results of high precision measurements of the thermal expansion of the sintered SiC, SiC-100, intended for use in cryogenic space-telescopes, in which minimization of thermal deformation of the mirror is critical and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to $\sim$ 10 K. Three samples, #1, #2, and #3 were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using the 8th order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were derived for temperatures between 293 K and 10 K. The average and the dispersion (1 $\sigma$ rms) of these three CTEs are 0.816 and 0.002 ($\times 10^{-6}$/K), respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the obtained CTE dispersion, we performed an finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m diameter cryogenic mirror made of six SiC-100 segments. It was shown that the present CTE measurement has a sufficient accuracy well enough for the design of the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure

Pressure and chemical substitution effects in the local atomic structure of BaFe2As2

The effects of K and Co substitutions and quasi-hydrostatic applied pressure (P<9 GPa) in the local atomic structure of BaFe2As2, Ba(Fe{0.937}Co{0.063})2As2 and Ba{0.85}K{0.15}Fe2As2 superconductors were investigated by extended x-ray absorption fine structure (EXAFS) measurements in the As K absorption edge. The As-Fe bond length is found to be slightly reduced (<~ 0.01 Angstroms) by both Co and K substitutions, without any observable increment in the corresponding Debye Waller factor. Also, this bond is shown to be compressible (k = 3.3(3)x10^{-3} GPa^{-1}). The observed contractions of As-Fe bond under pressure and chemical substitutions are likely related with a reduction of the local Fe magnetic moments, and should be an important tuning parameter in the phase diagrams of the Fe-based superconductors.Comment: 7 pages, 6 figure

Influence of inner diameter and height of ring-shaped REBaCuO bulks on trapped field and mechanical stress during field-cooled magnetization

In this paper, the trapped field, Bz, thermal hoop stress, σθcool, by cooling from 300 to 50 K and electromagnetic hoop stress, σθFCM, during field cooled magnetization (FCM) from Bapp = 6.3 and 9.4 T are investigated numerically for ring-shaped REBaCuO bulks with various inner diameters (I.D.) and heights (H) and reinforced by an Al alloy ring. For simplicity, an identical critical current density, Jc(B), which is a typical value at 50 K, is assumed in the simulation. The Bz value at the center of the ring bulk changes depending on the I.D. and H values of the ring bulk, which results from the different distribution of the superconducting current. As a result, the total hoop stress, σθtotal, (= σθcool + σθFCM) also changes for each ring bulk and for each Bapp due to the variation of the σθcool and σθFCM values. The maximum σθ total value, which affects the bulk fracture at Bapp = 9.4 T, increases with decreasing the height of ring bulk. These results can present guidelines for designing a trapped-field magnet using ring bulks