[en] Magnetorheological fluid (MR fluid), a kind of smart material, has been used as a new pressure-carrying medium in magnetorheological pressure forming (MRPF). The mechanical property of MR fluid under the pressure significantly affects the sheet formability. However, there is little knowledge on the deformation behavior of MR fluid under three-dimensional stress states. In this paper, a new procedure via a combination of extrusion test and FEM simulation has been proposed to determine the flow stress of MR fluids. The experimental device for extrusion test of MR fluids was designed. The flow stresses of a MR fluid (MRF-J01T) under four different magnetic fields were determined through the proposed procedure. In addition, the obtained flow stresses were used in the following FEM simulations to verify the accuracy by comparing with the experimental results. The simulation results were in good agreement with the experimental data, which supports the correctness and practicability of the proposed method. - Highlights: • An effective procedure is proposed to determine the flow stress of MR fluids. • The rheological behaviour of a MR fluid during extrusion tests is studied. • Flow stress curves of a MR fluid under different magnetic fields are obtained.

[en] Objective: To reveal the transmiting discipline of parameters and define time window for therapy of ischemia penumbra by continuous detection of diffusion tensor imaging (DTI), and evaluate the relations between cortical spinal tracts (CST) and myodynamia by diffusion tensor tract (DTT). Methods: 71 patients of cerebral infarction with different timing were imaged with conventional MRI, DWI and DTI, measuring DCavg, FA, RA, 1-VR of different ROI and performing DTT in ten patients. Results: DCavg of lesions in different phases were [(0.275 ± 0.022 ), (0.349 ±0.019), (0.465 ± 0.023 ), (0.538 ± 0.035)] x 10^-3 mm²/s, respectively. DCavg value showed tendency of reducing obviously, elevating gradually and false-normalizing (P<0.001). FA /RA /1-VR of lesions elevated in hyperacute stroke and showed tendency of unrecovered decline afterwards. Difference of DCavg, FA, RA, 1-VR between central and peripheral parts of lesions were significant in hyperacute and acute stroke (P<0.001). CST showed not compressed, compressed but not disrupted and disrupted, whose myodnamia was normal, recovered after therapy and not recovered. Conclusion: There is characteristic discipline in changes of DCavg, FA, RA and 1-VR. The peripheral parts of lesions in hyperacute and acute stroke maybe ischemic penumbra, and its time window for therapy could extend to 24 hours. DTT has important value to clinical management and prognosis. (authors)

[en] Objective: To evaluate the MR findings and pathological features, differential diagnosis of atypical anorectal malignant melanoma. Methods: A case of anorectal malignant melanoma proved by histology was retrospectively analysed, and related literatures were reviewed. Results MRI scan revealed a round-like solid mass in the anorectal junction area which showed slightly long T₁ and long T₂ signal intensity, well-defined and relatively homogenous. The size of the mass was about 3.3 cm × 4.2 cm × 4.3 cm. Some nodules and masses were found in the mesorectal area and outside fascia, and the largest one was about 3.2 cm × 2.5 cm × 3.8 cm. Intraoperative observation showed that the tumor was solid, the boundary was clear, and the surface was smooth. Pathological diagnosis: malignant melanoma tumor. Immunohistochemistry showed HMB45 and Melan-A were positive, suggesting melanoma tumor. Conclusion: Anorectal malignant melanoma is rare and usually does not have specific clinical and imaging manifestation. Accurate diagnosis depends on the pathological and immunohistochemical examination. (authors)

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[en] Objective: To study the CT perfusion features of various lymph nodes in the neck. Methods: Dynamic perfusion CT scanning was performed in 83 neck lymph nodes proved by pathology, including tuberculosis lymph nodes, lymphoma and metastatic lymph nodes. The shapes, blood flow modes, and perfusion parameters of these lymph nodes were compared among 3 groups. Statistical analysis of L/T and CT perfusion parameters was performed by one-way ANOVA and LSD test. Results: The values of MTT of tuberculosis lymph nodes, lymphoma and metastatic lymph nodes were (28.13±5.08), (31.08±5.82), and (11.24±5.31) s, respectively. The MTT of metastatic lymph nodes was statistically lower than that of tuberculosis lymph nodes and lymphoma (P<0.05). Their frequencies of marginal blood flow were 5/9, 4/19, and 39/55 (70.9%), respectively. The frequency of marginal blood flow in the tuberculosis lymph nodes and metastatic lymph nodes was statistically higher than that of lymphoma (P<0.05). Their frequencies of central blood flow were 2/9, 11/19, and 9/55 (16.4%), respectively. The frequency of central blood flow in the lymphoma was statistically higher than that of tuberculosis lymph nodes and metastatic lymph nodes (P<0.05). Their values of L/T were 1.82±0.32, 1.80±0.39, and 1.84±0.36, respectively. The values of BF were (34.23±5.96), (34.00±6.88), and (35.62±10.84) ml. min^-1 · 100 g^-1, respectively. The values of BV were (24.68±2.84), (25.30±3.16), and (25.15± 8.81) ml·100 g^-1 respectively. The values of TTP were (40.90±8.85), (40.67±6.45), and (40.98±6.62) s, respectively. There were no significant differences in L/T, BF, BV and TTP among tuberculosis lymph nodes, lymphoma and metastatic lymph nodes (P>0.05). Conclusion: CT perfusion, especially combination functional imaging with perfusion images may be helpful in judging the nature of neck lymph nodes. (authors)

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[en] The effects of extrusion temperature on the microstructure, texture and mechanical properties of a Mg–5 wt%Bi alloy prepared through extrusion were systematically investigated. With the increase of extrusion temperature from 573 to 723 K, the average grain size of the extruded bars gradually increased from 10.2 to 17.4 μm, and the amount of Mg₃Bi₂ precipitates that dynamically formed during the extrusion apparently decreased while their size remarkably increased. Moreover, the basal texture intensity of the extruded bars increased with increasing the extrusion temperature. This may be attributed to the combined effect of the decreased amount of Mg₃Bi₂ precipitates, enhanced activity of the prismatic slip and growth of dynamically recrystallized grains. With increasing extrusion temperature, yield strength first decreased but then increased, whereas elongation to fracture first increased but then decreased. (paper)

[en] Objective: To detect position and morphous as well as coursing of the alar ligament, and to further investigate the sectional anatomy and CT and MRI imaging of the alar ligament. Methods: Twelve formalin fixed specimens including head and neck utilized, three of the twelve were observed in gross anatomy, nine of them were dissectioned. Fifty- one healthy volunteers from each group were selected to perform CT and MRI examination respectively. By combining gross and sectional anatomy. CT and MRI manifestations of the alar ligament were analyzed, the alar ligament width was measured. Results: Location and shape, as well as coursing of the alar ligament could be demonstrated clearly in gross and sectional anatomy. The transverse plane across the upper dens and the coronal plane by the middle dens were the optimal planes for demonstrating the alar ligament. The display ratio of the alar ligament was even 100% (51/51) in both images of CT and MRI. MRI had better advantages than CT in respect of demonstrating the alar ligament, PDWI (proton density weighted imaging, PDWI) is the most optimal sequence for the alar ligament. There were no significant differences of the alar ligament width between male and female and between the right and the left side (P>0.05). Conclusion: In combination with gross and sectional anatomy. CT and MRI could both provide an imageo-anatomic basis for diagnosis of the alar ligament trauma and malformation as well as infection. (authors)