Synthesis of Ni-B Compounds by High-Pressure and High-Temperature Method.

Nickel borides are promising multifunctional materials for high hardness and excellent properties in catalysis and magnetism. However, it is still a blank of intrinsic properties in Ni-B compounds, because crystallization of the single phases of Ni-B compounds with micro-size is a challenge. In this work, single phases of Ni2B (I4/mcm), α-Ni4B3 (Pnma), ß-Ni4B3 (C2/c), and NiB (Cmcm) are synthesized by high pressure and high temperature (HPHT). The results indicate that synthesizing α-Ni4B3 and ß-Ni4B3 requires more energy than Ni2B and NiB. The growth process of Ni-B compounds is that Ni covers B to form Ni-B compounds under HPHT, which also makes the slight excess of B necessary. So, generating homogeneous distribution of starting materials and increasing the interdiffusion between Ni and B are two keys to synthesize well crystallized and purer samples by HPHT. This work uncovers the growth process of Ni-B compounds, which is significant to guide the synthesis of highly crystalline transition metal borides (TMBs) in the future.

Prevalence and risk factors for Helicobacter pylori infection in Chinese populations.

BACKGROUND: The prevalence of Helicobacter pylori is higher in developing countries. The aim of this study was to investigate the prevalence and risk factors of H. pylori infection in areas with high prevalence of gastric cancer in Jiangsu Province, China. METHODS: A prospective epidemiologic survey of H. pylori infection was accomplished in a natural population of 1457 individuals in Xiangshui and Gaoyou counties, Jiangsu Province, China. Questionnaires and laboratory tests for H. pylori infection ((13)C-urea breath test and serum IgG antibodies to H. pylori) were used and performed, respectively. RESULT: Among 1371 subjects who completed questionnaires and H. pylori detection, 851 (62%) were H. pylori positive. The prevalence reached a peak at the age of 30-40 years (67%). There was no sex difference. The annual family income level was shown to be positively correlated with the risk of H. pylori infection. The prevalence of H. pylori infection was also associated with family size, education level, and several diet-related factors, such as the number of times cooked rice and potatoes eaten per week, and a family history of stomach diseases. Compared to nonsymptomatic individuals, people with dyspeptic symptoms (nausea, vomiting, and belching) presented a low prevalence of H. pylori infection. No association between H. pylori prevalence and smoking or drinking was found. Using multivariate logistic regression analysis, annual family income and education level were the independent predictors for H. pylori infection. CONCLUSION: High prevalence of H. pylori infection was found in areas with a high risk of gastric cancer and was related to several risk factors. The underlying mechanisms need to be further investigated.