In this thesis, detailed studies of three different types of binary central stars withinplanetary nebulae (bCSPNe) are presented, with the aim of investigating the effectssuch a range of binary systems has on the morphology and kinematics of the surroundingnebulae, as well as discussing what the implication is for the interaction betweenthe stars themselves. A close binary, an intermediate period binary, and a compactbinary system are examined. The close binary PN HaTr 4 is the first system to be studied via detailed spatiokinematicalanalysis and modelling, and it is one of few known to contain a postcommonenvelope (CE) central star system. CE evolution is believed to play an importantrole in the shaping of PNe, but the exact nature of this role is yet to be understood. High spatial and spectral resolution spectroscopy is presented alongside deep narrowbandimagery to derive the three-dimensional morphology of HaTr 4. The nebula isfound to display an extended ovoid morphology with an enhanced equatorial regionconsistent with a toroidal waist - a feature believed to be typical amongst PNe withpost-CE central stars. The nebular symmetry axis is found to lie perpendicular to theorbital plane of the central binary, concordant with the idea that the formation andevolution of HaTr 4 has been strongly influenced by its central binary. Next, PN LoTr 1 is studied using a combination of spectra and photometry, andis thought to contain an intermediate-period binary central star system (P = 100–1500d). Here, we confirm the binary nature of the central star of LoTr 1, consisting of aK1 III star and a hot white dwarf (WD). The nebula of LoTr 1 presents a very differentmorphology than that of other seemingly similar bCSPNe possessing barium stars,A70 and WeBo 1 (included in this study for direct comparison), which may be anindication of a difference in their mass-transfer episodes. There is no evidence ofbarium enhancement in the K1 III companion, but it is shown to have a rotation periodof 6.4 d which is most likely a sign of mass accretion. Such a system represents arare opportunity to further the investigation into the formation of barium stars andintermediate period, post-asymptotic giant branch (AGB) systems. Finally, the first analysis of an object from the new POPIPlaN catalogue of PNe ispresented. Photometry of the central star system of PN G033.8+01.5 showed it to bea compact binary of P = 0.1268 d, consisting of a cool M2 V main sequence star anda hot WD surrounded by a very asymmetric PN. The very short orbital period leadsto the possibility of PN G033.8+01.5 being a cataclysmic variable candidate, which inturn leads to the question of whether the visible nebulous material is that of a true PNor if it is the remnant of an outburst.

M.Sc. (Mathematics) / Please refer to full text to view abstract

Ransomware, a type of malware that extorts payment from a victim by encrypting her data, is a growing threat that is becoming more sophisticated with each generation. Attackers have shifted from targeting individuals to entire organizations, raising extortions from hundreds of dollars to hundreds of thousands of dollars. In this work, we analyze a variety of ransomware and benign software binaries in order to identify indicators that may be used to detect ransomware. We find that several combinations of strings, cryptographic constants, and a large number loops are key indicators useful for detecting ransomware.

A Reduced Ordered Binary Decision Diagram (BDD) is a symbolic data structure introduced to the model checking community by Bryant in 1986 to help verify properties of systems with very large state spaces. Recently, BDDs have been used in heuristic search algorithms as an approach to representing and solving search problems with very large state spaces. However, these algorithms are still not memory efficient. This thesis presents a symbolic heuristic search algorithm that uses BDDs in a memory efficient way by performing bidirectional breadthirst heuristic search. The approach is evaluated empirically against existing symbolic methods and is shown to provide a significant improvement in performance.

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The fork-join framework project is one of the more challenging programming assignments in the computer science curriculum at Virginia Tech. Students in Computer Systems must manage a pool of threads to facilitate the shared execution of dynamically created tasks. This project is difficult because students must overcome the challenges of concurrent programming and conform to the project's specific semantic requirements. When working on the project, many students received inconsistent test results and were left confused when debugging. The suggested debugging tool, Helgrind, is a general-purpose thread error detector. It is limited in its ability to help fix bugs because it lacks knowledge of the specific semantic requirements of the fork-join framework. Thus, there is a need for a special-purpose tool tailored for this project. We implemented Willgrind, a debugging tool that checks the behavior of fork-join frameworks implemented by students through dynamic program analysis. Using the Valgrind framework for instrumentation, checking statements are inserted into the code to detect deadlock, ordering violations, and semantic violations at run-time. Additionally, we extended Willgrind with happens-before based checking in WillgrindPlus. This tool checks for ordering violations that do not manifest themselves in a given execution but could in others. In a user study, we provided the tools to 85 students in the Spring 2017 semester and collected over 2,000 submissions. The results indicate that the tools are effective at identifying bugs and useful for fixing bugs. This research makes multithreaded programming easier for students and demonstrates that special-purpose debugging tools can be beneficial in computer science education. / Master of Science

<p>Adversarial text attack research is crucial for evaluating NLP model robustness and addressing privacy concerns. However, the increasing complexity of transformer and pretrained</p> <p>language models has led to significant time and resource requirements for training and testing. This challenge is particularly pronounced in black-box attacks, where hundreds</p> <p>or thousands of queries may be needed to identify critical words leveraged by the target model. To overcome this, we introduce BinarySelect, a novel method combining binary search</p> <p>with adversarial attack techniques to reduce query numbers significantly while maintaining attack effectiveness. Our experiments show that BinarySelect requires far fewer queries than traditional methods, making adversarial attack research more accessible to researchers with limited resources. We demonstrate the efficacy of BinarySelect across multiple datasets and classifiers, showcasing its potential for efficient adversarial attack exploration and addressing related black-box challenges.</p>

A physico-chemical approach (theory of dissociation and reaction) is developed, which can be used in binary diffusion couple to determine diffusion parameters of the product phases with wide homogeneity range, as well as phases with narrow homogeneity range. It is demonstrated that this approach is basically equivalent to the diffusion based treatment. However, physico-chemical approach pedagogically sheds light on the chemical reactions occurring during interdiffusion at the interphase interfaces and morphology develops in the interdiffusion zone. This theory can be used in any binary systems for any end-member condition to explain single phase or multiphase diffusion controlled growth. Ni-Al and Ag-Zn systems are considered here to calculate diffusion parameters following physico-chemical approach. It is evident from our theoretical analysis and experimental evidence that in the presence of a stable Kirkendall marker plane one should expect duplex grain morphology in a particular phase layer. On the other hand, there is another model which is used rather frequently, is the theory of partitioning of flux. Although, the theory of partitioning of flux is used several times, we found that this theory does not count the mobility of both the species and therefore is not suitable to use in most of the interdiffusion systems. We have first modified this theory to take into account the mobility of both the species and then further extended to develop the relations for the integrated diffusion coefficient and the ratio of diffusivities of the species. The versatility of these two different models (that is the theory dissociation and reaction and the partitioning of flux) is examined in the Co-Si system with respect to different end-member compositions. From our analysis, we found that the applicability of the theory of partitioning of flux is rather limited but the theory of dissociation and reaction can be used in any binary systems. The theory of dissociation and reaction is then used to elucidate this behaviour in a single phase of β-NiAl and to calculate the diffusion parameter at the Kirkendall marker planes in the interdiffusion zone. To apply the physico-chemical approach, Ni-and Al-rich part of the phase is treated as two different phases and the plane corresponding to eqiatomic composition is considered as virtual interface between them. Possible dissociation and reaction equations are considered to combine with the flux equations to derive the relation for diffusion coefficient. Further experiments are conducted in the Cu-Sn, Au-Sn and Ni-Sn systems, which are important for flip chip bonding related to micro electronics industry. Different diffusion parameters, such as integrated diffusion coefficient, tracer diffusion coefficient of elements and the ratio of diffusivities are determined, which shed lights on the atomic mechanism of diffusion. Subsequently, the theory of dissociation and reaction is used when possible to explain the growth of the phases in the interdiffusion zone.

C++ and Microsoft's Component Object Model (COM) are examples of a high- level lan- guage and development framework that were built on top of the lower-level, primitive lan- guage, C. C was never designed to support concepts like object orientation, type enforcement, and language independence. Further, these languages and frameworks are designed to com- pile and run directly on the processor where these concepts are also not supported. Other high-level languages that do support these concepts make use of a runtime or virtual machine to create a computing model to suit their needs. By forcing these high-level concepts into a primitive computing model, many security issues have been introduced. Existing binary- level security analysis tools and runtime enforcement frameworks operate at the lowest level of context. As such, they struggle to detect and remedy higher-level security issues. In this dissertation, a framework for elevating the context of binary code is presented. By bringing the context for analysis closer to where these security issues are introduced, this framework allows for higher-level analyses and enforcement frameworks to be developed.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper focuses on the transceiver design using BOC signal in the telemetry field, including the transmitter and receiver. The transmitter is similar as that using BPSK except from the sub-carrier modulation. But the receiver design is totally different because the BOC signal has different performance. The acquisition methods of BOC signal have been discussed such as the single-side BPSK-like, double-sides BPSK-like and hybrid processing methods, which can restrain side-peak and eliminate ambiguities. The three acquisition process principles and their performances include arithmetic complexity are described, compared and simulated using MATLAB.