Strong enhancement of Jc in binary and alloyed in-situ MgB2 wires by a new approach: Cold high pressure densification

Cold high pressure densification (CHPD) is presented as a new way to substantially enhance the critical current density of in situ MgB2 wires at 4.2 and 20 K at fields between 5 and 14 T. The results on two binary MgB2 wires and an alloyed wire with 10 wt.% B4C are presented The strongest enhancement was measured at 20K, where cold densification at 1.85 GPa on a binary Fe/MgB2 wire raised both Jcpara and Jcperp by more than 300% at 5T, while Birr was enhanced by 0.7 T. At 4.2K, the enhancement of Jc was smaller, but still reached 53% at 10 T. After applying pressures up to 6.5 GPa, the mass density dm of the unreacted (B+Mg) mixture inside the filaments reached 96% of the theoretical density. After reaction under atmospheric pressure, this corresponds to a highest mass density df in the MgB2 filaments of 73%. After reaction, the electrical resistance of wires submitted to cold densification was found to decrease, reflecting an improved connectivity. A quantitative correlation between filament mass density and the physical properties was established. Monofilamentary rectangular wires with aspect ratios a/b < 1.25 based on low energy ball milled powders exhibited very low anisotropy ratios, Gamma = Jcpara/Jcperp being < 1.4 at 4.2 K and 10T. The present results can be generalized to alloyed MgB2 wires, as demonstrated on a wire with B4C additives. Based on the present data, it follows that cold densification has the potential of further improving the highest Jcpara and Jcperp values reported so far for in situ MgB2 tapes and wires with SiC and C additives. Investigations are under work in our laboratory to determine whether the densification method CHPD can be applied to longer wire or tape lengths.Comment: Submitted to Superconductors Science and Technolog

Obesity and Hypertension in Students of Jahangirnagar University: Alarming Issues

The prevalence of obesity and hypertension (HTN) in university students of Bangladesh has not reported yet. Considering the proper health maintenance of this population in mind, the study was aimed to determine the prevalence of obesity and HTN as well as relationship among them in the students of a residential university of Bangladesh, Jahangirnagar University. This descriptive cross sectional study included 500 randomly selected students (250 males and 250 females). Participants completed a questionnaire on physical activity, sedentary behaviour, dietary factors, smoking and family history of obesity, HTN, and coronary artery disease. Blood pressure and anthropometric parameters such as height, weight, waist and hip circumferences were measured following standard procedure. The Statistical analyses were performed using the software SPSS.The prevalence of overweight was 25% (31.1% males, 15.6% females) and obesity 7.2% (9.4% males, 4% females). Pre-HTN was found at 27.1% (38% males, 11.2% females) and HTN at 2.2% (3.3% males, 0.4% females). A high rate of smoking, sedentary behavior, physical inactivity, excessive consumption of unhealthy food, and caffeine-rich drinks was also observed. Significant correlation was found between parameters of obesity and HTN. High prevalence of pre-HTN in males and central obesity in females were found which is immediately needed to control for better health maintenance of this population