No abstract

: Acrylonitrile is a key precursor to the production of a wide range of products in the chemical industries. The major products of acrylonitrile include Acrylonitrile butadiene styrene resin, acrylic fibers, adiponitrile. The demand for production of acrylonitrile is affected by global economy but the development of life standards, the demand for producing acrylonitrile and its derivations is significantly increasing. So that in 2016, China alone produced 32% of world acrylonitrile and acrylonitrile production is expected to have 55% increase in 2021. Acrylonitrile and its derivations have wide application in different industries of car manufacturing, electronics, aerospace and textile. Considering the importance of acrylonitrile precursor in the current world, in this study we discuss and investigate its production processes, copolymers obtained from acrylonitrile, poly acrylonitrile production and its application in the carbon fibers and compare it with other carbon fibers precursors such as mesophase pitch and cellulose. Also we investigation marketing in the world.

Background. C# maintains type safety and security by not allowing direct dangerous pointer arithmetic. To improve performance for special cases, pointer arithmetic is provided via an unsafe context. Programmers can use the C# unsafe keyword to encapsulate a code block, which can use pointer arithmetic. In the Common Language Runtime (CLR), unsafe code is referred to as unverifiable code. It then becomes the responsibility of the programmer to ensure the encapsulated code snippet is not dangerous. Naturally, this raises concern on whether such trust is misused by programmers when they promote the use of C# unsafe context. Aim. We aim to analyze the prevalence and vulnerabilities of share code examples using C# unsafe keyword in Stack Overflow (SO) code sharing platform. Method. By using some regular expressions and manual checks, we extracted C# unsafe code relevant posts from SO and categorized them into some software development scenarios. Results. In the entire SO data dump of September 2018, we find 2,283 C# snippets with the unsafe keyword. Among those posts, 27% of posts are about Image processing, where unsafe codes are mainly used for performance reasons. The second most popular category by 21% of the codes in the posts is used for 'Interoperability' reasons. That is 'unsafe' is used to enable 'Interoperability' between C# managed codes and unmanaged codes. The 'stackalloc' operator is the third category with 9% of unsafe code posts. The stackalloc operator allocates a block of memory on the stack. Since C# 7.2, Microsoft recommends against using 'stackalloc'in unsafe context whenever possible. Manual inspection shows 67 code snippets with dangerous functions that can introduce vulnerability if not used with caution (e.g., buffer overflow). Finally, 35% of 'Interoperability' posts have 'P/Invoke' tag were used outside NativeMethods class, which is in contrast to Microsoft design suggestion. Conclusion. Our study leads to 7 main findings, and these findings show the importance of cautiously using this feature.