Mixing between overflows and ambient water masses is a crucial problem of deep-water formation in the down-welling branch of the meridional overturning circulation of the ocean. In this dissertation work, performance of second-order turbulence closures in reproducing mixing of overflows is investigated within both hydrostatic and non-hydrostatic models. First, a 2D non-hydrostatic model is developed to simulate the Red Sea overflow in the northern channel. The model results are compared to the Red Sea Outflow Experiment. It is found that the experiments without sub-grid scale models cannot reproduce the basic structure of the overflow. The k-ε model yields unrealistically thick bottom layer (BL) and interfacial layer (IL). A new technique so-called very large eddy simulation (VLES) which allows the use of k-ε model in non-hydrostatic models is also employed. It is found that VLES results the most realistic reproduction of the observations. Furthermore, the non-hydrostatic model is improved by introducing laterally average terms, so the model can simulate the constrictions not only in the z-direction but also in the y-direction. Observational data from the Bosphorus Strait is employed to test the spatially average 2D non-hydrostatic model (SAM) in a realistic application. The simulations from SAM with a simple Smagorinsky type closure appear to be excessively diffusive and noisy. We show that SAM can benefit significantly from VLES turbulence closures. Second, the performance of different second-order turbulence closures is extensively tested in a hydrostatic model. Four different two-equation turbulence closures (k-&epsilon, k-&omega, Mellor-Yamada 2.5 (MY2.5) and a modified version of k- &epsilon) and K-Profile Parameterization (KPP) are selected for the comparison of 3D numerical simulations of the Red Sea overflow. All two-equation turbulence models are able to capture the vertical structure of the Red Sea overflow consisting of the BL and IL. MY2.5 with Galperin stability functions produce the largest salinity deviations from the observations along two sections across the overflow and the modified k-&epsilon exhibits the smallest deviations. The rest of the closures fall in between, showing deviations similar to one another. Four different closures (k- &epsilon, k-&omega, MY2.5KC and KPP) are also employed to simulate the Mediterranean outflow. The numerical results are compared with observational data obtained in the 1988 Gulf of Cadiz Expedition. The simulations with two-equation closures reproduce the observed properties of the overflow quite well, especially the evolution of temperature and salinity profiles. The vertically integrated turbulent salt flux displays that the overflow goes under significant mixing outside the west edge of the Strait of Gibraltar. The volume transport and water properties of the outflow are modified significantly in the first 50 km after the overflow exits the strait. The k-&epsilon and k-&omega cases show the best agreement with the observations. Finally, the interaction between the Red Sea overflow and Gulf of Aden (GOA) eddies has been investigated. It is found that the overflow is mainly transported by the undercurrent at the west side of the gulf. The transport of the overflow is episodic depending strength and location of GOA eddies. The most crucial finding is that the Red Sea overflow leaves the Gulf of Aden in patches rather than one steady current. Multiple GOA eddies induce lateral stirring, thus diapycnal mixing of the Red Sea outflow.

As the development of software applications and Internet, the security issues that come with get more serious. Buffer Overflow is an unavoidable problem while software programming. According to the advisories of each year, they show that many security vulnerabilities are from Buffer Overflow. Buffer Overflow is also the cause of intrusion made by hackers. The users of software applications usually depend on the software updates released by software venders to prevent the attacks caused by Buffer Overflow. So before applying software updates, that how to avoid attacks to software and prolong the save period of software is an important issue to prevent Buffer Overflow. By collecting and analyzing the exploit codes used by hackers, we can build the overall pattern of Buffer Overflow attacks, and we can take this pattern as the basis for preventing future Buffer Overflow attacks. Association rules can find the relations of unknown things, so it can help to build the common pattern between Buffer Overflow attacks. So this work applies association rules to build the pattern of Buffer Overflow attacks, and to find out the relations of system calls inside the exploit codes. We experiment and build a group of system call rules that can differentiate the attack behavior and the normal behavior. These rules can detect the Buffer Overflow attacks exactly and perform well in false positives. And then they can help to do further defenses after detecting attacks and alleviate the seriousness of Buffer Overflow attacks to computer systems.

No description available.

The main objective of this study was to describe the overflow of freshwater onto the sea ice surface in the Mackenzie Delta and to investigate the hydraulic behaviour of the upwelling and strudel events. This study was performed from the analysis of data collected during field investigations, from satellite images and from experimental laboratory studies. A forecasting method using the water level in the Mackenzie River was formulated to predict the overflow initiation about five days before its occurrence. The physical modelling of a strudel flow through a circular hole established a relation between the overflow depth and the discharge coefficient. Velocity measurements of the free-surface vortex using an Acoustic Doppler Velocimeter found that velocities at the vortexs core were influenced by its vorticity. Finally, predictions of maximum strudel scour, which are of great importance for the determination of burial depth of pipelines, were predicted from published impinging jet experiments. / Water Resources Engineering

Stack Overflow is the most popular Q&A website among software developers. As a platform for knowledge sharing and acquisition, the questions posted in Stack Over- flow usually contain a code snippet. Stack Overflow relies on users to properly tag the programming language of a question and assumes that the programming language of the snippets inside a question is the same as the tag of the question itself. In this the- sis, a classifier is proposed to predict the programming language of questions posted in Stack Overflow using Natural Language Processing (NLP) and Machine Learning (ML). The classifier achieves an accuracy of 91.1% in predicting the 24 most popular programming languages by combining features from the title, body and code snippets of the question. We also propose a classifier that only uses the title and body of the question and has an accuracy of 81.1%. Finally, we propose a classifier of code snip- pets only that achieves an accuracy of 77.7%.Thus, deploying ML techniques on the combination of text and code snippets of a question provides the best performance. These results demonstrate that it is possible to identify the programming language of a snippet of only a few lines of source code. We visualize the feature space of two programming languages Java and SQL in order to identify some properties of the information inside the questions corresponding to these languages. / Graduate

This thesis covers the master diploma work conducted at Hohai University, Nanjing, People's Republic of China. An overflow spillway section fitted for the Longtan Dam was designed and the loads acting on it was identified after an iterative flood routing calculation. The section was then evaluated, both theoretically and numerically using FEM with a linear-elastic isotropic constitutive model, with regards to the stability against compressive and tensile failure. Also, a numerical analysis of the seepage through and around the structure was conducted. The results show that, for a given design of the section, the structure can handle the compressive stresses that arises. However, the numerical analysis indicates a possible tensile failure at the dam heel, which is inconsistent with the theoretical stability analysis. The seepage analysis show that the maximum seepage occurs at the dam heel, the dam toe, and at grout curtains beneath the structure. A simple convergence analysis was done which showed stress singularities at the dam heel and dam toe. These were discussed and connected to the St Venant's principle, and these singularities shows the risk of blindly trusting numerical results.

Os vertedores são estruturas hidráulicas construídas para controlar o nível d’água do reservatório, permitindo a passagem das vazões escoadas com a máxima eficiência possível sem provocar problemas à estrutura. Para atingir este objetivo, as condições de aproximação do escoamento à estrutura e a forma geométrica do perfil vertente são muito importantes. O controle da soleira por comportas provoca uma mudança significativa nas condições de escoamento sobre o perfil vertente. O posicionamento e a forma da comporta tem forte influência no comportamento do coeficiente de vazão e nas pressões sobre a soleira. A formação de vórtice é um fenômeno indesejável que pode ocorrer quando a operação da comporta é parcial, prejudicando a capacidade de vazão e provocando vibrações na estrutura. Este trabalho apresenta uma abordagem teórica sobre o assunto vertedor de superfície e escoamento sob comportas, apresentando resultados de diferentes estudos para melhor compreensão do funcionamento do vertedor. / Spillways are hydraulic structures constructed to control the water level of the reservoir, allowing the overflows with the maximum possible efficiency without provoking problems to the structure. The approach flow pattern to the structure and the geometric form of the spillway profile are basic importance. The control of the spillway by the floodgates modifies the draining conditions. The positioning and the form of the gate have strong influence in the behavior of the discharge coefficient and the pressures on the surface profile. A vortex formation is an undesirable phenomenon that it can occur when the operation of the floodgate is partial, reducing the discharge coefficient and produce vibrations in structure. This work presents a theoretical approach about flow over spillway and under of the partial opening of the floodgate, presenting results of different studies for better understanding the function of the spillway.

The successful crowdsourcing model and gamification design of Stack Overflow (SO) Q&A platform have attracted many programmers to ask and answer technical questions, regardless of their level of expertise. Researchers have recently found evidence of security vulnerable code snippets being possibly copied from SO to production software. This inspired us to study how reliable is SO in providing secure coding suggestions. In this project, we automatically extracted answer posts related to Java security APIs from the entire SO site. Then based on the known misuses of these APIs, we manually labeled each extracted code snippets as secure or insecure. In total, we extracted 953 groups of code snippets in terms of their similarity detected by clone detection tools, which corresponds to 785 secure answer posts and 644 insecure answer posts. Compared with secure answers, counter-intuitively, insecure answers has higher view counts (36,508 vs. 18,713), higher score (14 vs. 5), more duplicates (3.8 vs. 3.0) on average. We also found that 34% of answers provided by the so-called trusted users who have administrative privileges are insecure. Our finding reveals that there are comparable numbers of secure and insecure answers. Users cannot rely on community feedback to differentiate secure answers from insecure answers either. Therefore, solutions need to be developed beyond the current mechanism of SO or on the utilization of SO in security-sensitive software development. / Master of Science / Stack Overflow (SO), the most popular question and answer platform for programmers today, has accumulated and continues accumulating tremendous question and answer posts since its launch a decade ago. Contributed by numerous users all over the world, these posts are a type of crowdsourced knowledge. In the past few years, they have been the main reference source for software developers. Studies have shown that code snippets in answer posts are copied into production software. This is a dangerous sign because the code snippets contributed by SO users are not guaranteed to be secure implementations of critical functions, such as transferring sensitive information on the internet. In this project, we conducted a comprehensive study on answer posts related to Java security APIs. By labeling code snippets as secure or insecure, contrasting their distributions over associated attributes such as post score and user reputation, we found that there are a significant number of insecure answers (644 insecure vs 785 secure in our study) on Stack Overflow. Our statistical analysis also revealed the infeasibility of differentiating between secure and insecure posts leveraging the current community feedback system (eg. voting) of Stack Overflow.

No description available.

As the functionality that current computer network can provide is becoming complicated, a traditional router with application-specific integrated circuit (ASIC) implementation can't satisfy the flexibility requirements. Instead, a programmable packet forward system based on a general-purpose processor could provide the flexibility. While this system provides flexibility, a new potential security issue arises. Usually, software is involved as the packet forward system is programmable. The software's potential vulnerability, especially as to the remote exploits, becomes an issue of network security. In this thesis work, we proposed a software stack overflow vulnerability on click modular router and show how a disastrous denial-of-service attack on click modular router could be triggered by a single packet. In our research work, click modular router runs on Linux operating system based on general-purpose hardware. We actually showed that even a software router run within a modern operating system's protection is vulnerable by elaborate attack. And we checked the possible stack protection mechanisms on modern OS based on general-purpose hardware and proposed a possible stack protection mechanism for embedded OS.