Boosting the precision of virtual call integrity protection with partial pointer analysis for C++

© 2017 Association for Computing Machinery. We present, Vip, an approach to boosting the precision of Virtual call Integrity Protection for large-scale real-world C++ programs (e.g., Chrome) by using pointer analysis for the first time. Vip introduces two new techniques: (1) a sound and scalable partial pointer analysis for discovering statically the sets of legitimate targets at virtual callsites from separately compiled C++ modules and (2) a lightweight instrumentation technique for performing (virtual call) integrity checks at runtime. Vip raises the bar against vtable hijacking attacks by providing stronger security guarantees than the CHA-based approach with comparable performance overhead. Vip is implemented in LLVM-3.8.0 and evaluated using SPEC programs and Chrome. Statically, Vip protects virtual calls more effectively than CHA by significantly reducing the sets of legitimate targets permitted at 20.3% of the virtual callsites per program, on average. Dynamically, Vip incurs an average (maximum) instrumentation overhead of 0.7% (3.3%), making it practically deployable as part of a compiler tool chain

An improved calcium chloride method preparation and transformation of competent cells

Transformation is one of the fundamental and essential molecular cloning techniques. In this paper, we have reported a modified method for preparation and transformation of competent cells. This modifiedmethod, improved from a classical protocol, has made some modifications on the concentration of calcium chloride and competent bacteria solution, rotation speed in centrifugation and centrifugationtime. It was found that the optimal transformation efficiency were obtained when the concentration of CaCl2 was 75 mmol/l, OD600 of the culture meets 0.35 to 0.45, the temperature of rotation was 4°C , rotation speed was 1000 g and rotation time was 5 min. Even more, we also found out that the transformation efficiency would increase about 10 to 30 times when adding 15% glycerine into CaCl2 solution. The transformation efficiency, using our new method, reaches 108cf u/μg and higher than ultra-competent Escherichia coli method. This method will improve the efficiency in the molecular cloning and the construction of gene library.Keywords: Competent cells, CaCl2, improved method, transformation, glycerine, transformation efficienc

Failure Assessment for the High-Strength Pipelines with Constant-Depth Circumferential Surface Cracks

In the oil and gas transportation system over long distance, application of high-strength pipeline steels can efficiently reduce construction and operation cost by increasing operational pressure and reducing the pipe wall thickness. Failure assessment is an important issue in the design, construction, and maintenance of the pipelines. The small circumferential surface cracks with constant depth in the welded pipelines are of practical interest. This work provides an engineering estimation procedure based upon the GE/EPRI method to determine the J-integral for the thin-walled pipelines with small constant-depth circumferential surface cracks subject to tension and bending loads. The values of elastic influence functions for stress intensity factor and plastic influence functions for fully plastic J-integral estimation are derived in tabulated forms through a series of three-dimensional finite element calculations for different crack geometries and material properties. To check confidence of the J-estimation solution in practical application, J-integral values obtained from detailed finite element (FE) analyses are compared with those estimated from the new influence functions. Excellent agreement of FE results with the proposed J-estimation solutions for both tension and bending loads indicates that the new solutions can be applied for accurate structural integrity assessment of high-strength pipelines with constant-depth circumferential surface cracks

Acoustic phonon recycling for photocarrier generation in graphene-WS_{2} heterostructures

Electron-phonon scattering is the key process limiting the efficiency of modern nanoelectronic and optoelectronic devices, in which most of the incident energy is converted to lattice heat and finally dissipates into the environment. Here, we report an acoustic phonon recycling process in graphene-WS_{2} heterostructures, which couples the heat generated in graphene back into the carrier distribution in WS_{2}. This recycling process is experimentally recorded by spectrally resolved transient absorption microscopy under a wide range of pumping energies from 1.77 to 0.48 eV and is also theoretically described using an interfacial thermal transport model. The acoustic phonon recycling process has a relatively slow characteristic time (>100 ps), which is beneficial for carrier extraction and distinct from the commonly found ultrafast hot carrier transfer (~1 ps) in graphene-WS_{2} heterostructures. The combination of phonon recycling and carrier transfer makes graphene-based heterostructures highly attractive for broadband high-efficiency electronic and optoelectronic applications

Optimization Design on Ventilation Openings of Super Large Circular Coal Storage Dome

In order to reduce the pollution of the atmospheric environment, the super large coal storage warehouse has gradually become the main coal storage mode of power plants and other enterprises. However, due to the enclosed structural form, volatile coal dust and coal seam volatile combustible gas concentration is too high, which resulting in increased risk of ignition detonation. Therefore, this paper based on ventilation engineering theory and combined with CFD which focus on natural ventilation used in large diameter (D = 100 m) circular coal storage dome. The impact of opening modes, opening positions and opening size of super large circular coal storage dome on ventilated characteristics were also studied. The designed method of ventilated openings for super large circular coal storage dome is further proposed

Static detection of control-flow-related vulnerabilities using graph embedding

© 2019 IEEE. Static vulnerability detection has shown its effectiveness in detecting well-defined low-level memory errors. However, high-level control-flow related (CFR) vulnerabilities, such as insufficient control flow management (CWE-691), business logic errors (CWE-840), and program behavioral problems (CWE-438), which are often caused by a wide variety of bad programming practices, posing a great challenge for existing general static analysis solutions. This paper presents a new deep-learning-based graph embedding approach to accurate detection of CFR vulnerabilities. Our approach makes a new attempt by applying a recent graph convolutional network to embed code fragments in a compact and low-dimensional representation that preserves high-level control-flow information of a vulnerable program. We have conducted our experiments using 8,368 real-world vulnerable programs by comparing our approach with several traditional static vulnerability detectors and state-of-the-art machine-learning-based approaches. The experimental results show the effectiveness of our approach in terms of both accuracy and recall. Our research has shed light on the promising direction of combining program analysis with deep learning techniques to address the general static analysis challenges

Atmospheric reactive nitrogen concentrations at ten sites with contrasting land use in an arid region of central Asia

Atmospheric concentrations of reactive nitrogen (N<sub>r</sub>) species from 2009 to 2011 are reported for ten sites in Xinjiang, China, an arid region of central Asia. Concentrations of NH<sub>3</sub>, NO<sub>2</sub>, particulate ammonium and nitrate (<i>p</i>NH<sub>4</sub><sup>+</sup> and <i>p</i>NO<sub>3</sub><sup>−</sup>) showed large spatial and seasonal variation and averaged 7.71, 9.68, 1.81 and 1.13 μg N m<sup>−3</sup>, and PM<sub>10</sub> concentrations averaged 249.2 μg m<sup>−3</sup> across all sites. Lower NH<sub>3</sub> concentrations and higher NO<sub>2</sub>, <i>p</i>NH<sub>4</sub><sup>+</sup> and <i>p</i>NO<sub>3</sub><sup>−</sup> concentrations were found in winter, reflecting serious air pollution due to domestic heating in winter and other anthropogenic sources such as increased emissions from motor traffic and industry. The increasing order of total concentrations of N<sub>r</sub> species was alpine grassland; desert, desert-oasis ecotone; desert in an oasis; farmland; suburban and urban ecosystems. Lower ratios of secondary particles (NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>−</sup>) were found in the desert and desert-oasis ecotone, while urban and suburban areas had higher ratios, which implied that anthropogenic activities have greatly influenced local air quality and must be controlled

Flow2Vec: Value-flow-based precise code embedding

© 2020 Owner/Author. Code embedding, as an emerging paradigm for source code analysis, has attracted much attention over the past few years. It aims to represent code semantics through distributed vector representations, which can be used to support a variety of program analysis tasks (e.g., code summarization and semantic labeling). However, existing code embedding approaches are intraprocedural, alias-unaware and ignoring the asymmetric transitivity of directed graphs abstracted from source code, thus they are still ineffective in preserving the structural information of code. This paper presents Flow2Vec, a new code embedding approach that precisely preserves interprocedural program dependence (a.k.a value-flows). By approximating the high-order proximity, i.e., the asymmetric transitivity of value-flows, Flow2Vec embeds control-flows and alias-aware data-flows of a program in a low-dimensional vector space. Our value-flow embedding is formulated as matrix multiplication to preserve context-sensitive transitivity through CFL reachability by filtering out infeasible value-flow paths. We have evaluated Flow2Vec using 32 popular open-source projects. Results from our experiments show that Flow2Vec successfully boosts the performance of two recent code embedding approaches codevec and codeseq for two client applications, i.e., code classification and code summarization. For code classification, Flow2Vec improves codevec with an average increase of 21.2%, 20.1% and 20.7% in precision, recall and F1, respectively. For code summarization, Flow2Vec outperforms codeseq by an average of 13.2%, 18.8% and 16.0% in precision, recall and F1, respectively