TEMPERATURE DEPENDENCE OF POSITRON ANNIHILATION PARAMETERS IN HIGH Tc SUPERCONDUCTOR YBa_(2)Cu_(3)O_(7-x)

The temperature dependences of the positron annihilation lifetime and the Doppler broadening shape parameters have been measured in high Tc superconductors YBa_(2)Cu_(3)O_(7-x)=between 77.2 and 300K.The measured parameters show an abrupt change across the range of superconducting transition temperature,indicating a change of the electronic structure.The structural instabilities have also been observed in three higher temperature ranges of115-135,150-210 and 250-280K.This suggests that higher Tc superconductors might be found in these temperature ranges.

Epidemiological characteristics of thyroid nodules and risk factors for malignant nodules： a retrospective study from 6 304 surgical cases

Background The prevalence of thyroid nodules （TN） is increasing rapidly.This study analyzed the epidemiological and clinical characteristics of TN in surgically treated patients and identified the risk factors for malignant nodules （MN） to provide more understanding of the differential diagnosis of TN.Methods A total of 6 304 TN cases who underwent thyroid surgery were included in this retrospective study.The clinical data were collected to evaluate the clinical and epidemiological characteristics and related risk factors for MN.The nature of TN （benign nodules （BN） or MN）,medical records,laboratory data,and imaging data were analyzed.The risk factors for MN were screened using Spearman＇s rank correlation analysis and nonconditional binary Logistic regression analysis.Results The number of surgically treated TN cases increased yearly.A total of 34.33％ of cases were MN and 65.67％ were BN.Up to 56.74％ of these cases underwent unnecessary surgery.Among the MN cases,papillary thyroid carcinoma accounted for 94％,in which 46.71％ coexisted with benign thyroid disease and 32.28％ with multiple foci.Single-related factor analysis showed that age,employment,disease duration,history of breast nodules and/or hypertension,the levels of serum thyroid-stimulating hormone （TSH）,thyroglobulin antibody （TgAb）,and thyroid peroxidase antibody （TPoAb）,and ultrasound features of TN were related to MN.Stepwise nonconditional binary Logistic regression analysis showed that 13 factors may be the independent risk factors for MN,including ＜40 years old,previous history of breast nodules and/or hypertension,disease duration ＜1 month,employment,hypoechoic nodule,irregular nodules,nodule calcification,solid echo nodule,fuzzy boundary,rich blood flow within nodules,abnormal lymph nodes around the neck,nodule diameter ＜1 cm,and abnormally high TgAb.Conclusions Our results demonstrate a rapid increase in surgically treated TN cases and ratio of MN and indicate unnecessary surgeries in some cases.This study also suggest that age,duration of thyroid disease,history of breast disease and/or hypertension,the levels of serum TSH,TgAb,and TPoAb,and ultrasound features of TN are related to MN,and some of these factors may be the risk factors for MN.