Identification of line-source transfer mobility and force density by ground acceleration measurements

Ground-borne vibration caused by railway traffic has been a research concern due to its possible side effects on nearby residences. The force density and line-source mobility can effectively characterize the generation and transmission of train-induced vibrations, respectively. This research proposed a frequency-domain method for identifying the line-source transfer mobility and force density using measured vibrations at the ground surface, which was on the basis of the least-square method. The proposed method was applied to a case study at Shenzhen Metro in China, where a total of seven fixed-point hammer impacts with 3.3 m equal intervals were used to represent the train vibration excitations. Line-source transfer mobility of the site and force density levels of the metro train were identified, respectively. Causes for different dominant frequencies can be traced by separating the dynamic characteristics of vibration excitation and transmission. It was found in the case study that at a location 3 m away from the track, the peak at 50 Hz was caused by excitations, while that at 63 Hz was attributed to transmission efficiency related to the soil properties. Subsequently, numerical validations of the fixed-point loads' assumption and identified force density levels were carried out. Good comparisons between numerically predicted and experimentally identified force density levels indicated the feasibility of the proposed method. At last, the identified line-source transfer mobility and force density levels were applied to the forward problem, i.e., making predictions of train-induced vibrations. The predicted ground and structural vibrations at different locations were compared to corresponding measurements, with good agreement, which experimentally validated the identification method. The identification results of the case study can be employed by similar railway systems as a good reference.

[Predictive value of sonographic features in preoperative evaluation of medullary thyroid carcinoma]

OBJECTIVE

To summarize ultrasound features associated with medullary thyroid carcinoma (MTC) and investigate the predictive value of ultrasonography in preoperative diagnosis of MTC.

METHODS

The sonographic and clinical data were studied in a series of nodules histologically proven as MTC collected from January 1993 to January 2013.

RESULTS

A total of 86 patients (92 nodules proven as MTC) were enrolled in the study with an average age of (47±12) years.Among the MTCs, 21.7%(20/92) were excluded because of missing data and the remained 78.3%(72/92) had complete data with the average diameter of (2.1±1.3) cm.The common US findings for MTC were solid, hypoechogenicity, regular sharp, well-defined margin, AP/ TR<1 and calcification (mostly microcalcification). Calcification and vascularization were more common in MTC nodules(48.6% vs 5.6%, P=0.001). Nodules with enlargement of cervical lymph node tended to be undergone FNAB(76.0% vs 55.3%, P=0.084), and ill-defined margin was more common in MTC nodules with cervical lymph node metastasis(36.4% vs 12.8%, P=0.009).

CONCLUSION

Despite having a few US features closely linked to the malignant nodules such as solid, hypoechogenicity and with microcalcification, the MTC nodules also have specific US imaging characteristics as regular sharp, well-defined margin and AP/ TR<1.

Effect of Zn impurity in K0.8Fe(2-δ-x)Zn(x)Se2

A series of K(0.8)Fe(2-δ-x)Zn(x)Se(2) single-crystal samples with nominal compositions 0 ≤ x ≤ 0.05 were grown and their physical properties were measured in order to study the effect of Zn impurity. It is found that the Zn impurity (x ≤ 0.02) does not affect the superconducting transition temperature T(c) significantly. Meanwhile the hump in resistivity which corresponds to the transition from the insulating to metallic phase quickly shifts towards low temperatures. The results imply that there should be a phase separation in this system and Zn impurity causes the enhancement of the insulating phase. The negligible effect of Zn impurity on T(c) suggests an s-wave pairing in the superconducting phase. Meanwhile there is a possibility that the Zn impurity may selectively enter into the insulting phase.

Molecular structure and absolute configuration of the diterpene lactone, praelolide

Praelolide is a new compound which was isolated out from the gorgonian, Menella praelonga (Ridley), collected from the South Sea of China at Zhanjiang, Guangdong. The molecular formula is C28H35O12Cl. The research result by X-ray diffraction method on the crystal structure is presented. The compound is orthorhombic with space group P2(1)2(1)2, cell dimensions a = 16.936, b = 16.709, c = 10.333 A, and Z = 4. The structure has been solved by direct method and refined to R = 0.055 for 2257 unique observable reflexions by least-squares. The molecule is composed of the major conformational isomer in which the three main rings (a six-membered ring, an eight-membered ring, a six-membered ring) take separately the form of chair-chairboat-chair, a five-membered actone ring, a C1 substitution, 4 acetate groups, and a three-membered epoxide ring. The absolute configuration of the molecule has also been determined by statistics (R factor ratio R = 1.012) and Bijvoet pairs observation. For 30 pairs of the greatest anomalous contributions the residuals are R'(+) = 0.057 for the first enantiomorph and R'(-) = 0.005 for the second one, so the latter should unambiguously correspond to the absolute configuration of the molecule.