Dissertations / Theses on the topic 'SIGNATURE FILES'

This thesis studies document signatures, which are small representations of documents and other objects that can be stored compactly and compared for similarity. This research finds that document signatures can be effectively and efficiently used to both search and understand relationships between documents in large collections, scalable enough to search a billion documents in a fraction of a second. Deliverables arising from the research include an investigation of the representational capacity of document signatures, the publication of an open-source signature search platform and an approach for scaling signature retrieval to operate efficiently on collections containing hundreds of millions of documents.

The Internet was originally designed to be a next-generation phone system that could withstand a Soviet attack. Today, we ask the Internet to perform tasks that no longer resemble phone calls in the face of threats that no longer resemble Soviet bombardment. However, we have come to rely on names that can be subverted at every level of the stack or simply be allowed to rot by their original creators. It is possible for us to build networks of content that serve the content distribution needs of today while withstanding the hostile environment that all modern systems face. This dissertation presents the Cryptographically Curated File System (CCFS), which offers five properties that we feel a modern content distribution system should provide. The first property is Strong Links, which maintains that only the owner of a link can change the content to which it points. The second property, Permissionless Distribution, allows anyone to become a curator without dependence on a naming or numbering authority. Third, Independent Validation arises from the fact that the object seeking affirmation need not choose the source of trust. Connectivity, the fourth property, allows any curator to delegate and curate the right to alter links. Each curator can delegate the control of a link and that designee can do the same, leaving a chain of trust from the original curator to the one who assigned the content. Lastly, with the property of Collective Confidence, trust does not need to come from a single source, but can instead be an aggregate affirmation. Since CCFS embodies all five of these properties, it can serve as the foundational technology for a more robust Web. CCFS can serve as the base of a web that performs the tasks of today’s Web, but also may outperform it. In the third chapter, we present a number of scenarios that demonstrate the capacity and potential of CCFS. The system can be used as a publication platform that has been re-optimized within the constraints of the modern Internet, but not the constraints of decades past. The curated links can still be organized into a hierarchical namespace (e.g., a Domain Naming System (DNS)) and de jure verifications (e.g., a Certificate Authority (CA) system), but also support social, professional, and reputational graphs. This data can be distributed, versioned, and archived more efficiently. Although communication systems were not designed for such a content-centric system, the combination of broadcasts and point-to-point communications are perfectly suited for scaling the distribution, while allowing communities to share the burdens of hosting and maintenance. CCFS even supports the privacy of friend-to-friend networks without sacrificing the ability to interoperate with the wider world. Finally, CCFS does all of this without damaging the ability to operate search engines or alert systems, providing a discovery mechanism, which is vital to a usable, useful web. To demonstrate the viability of this model, we built a research prototype. The results of these tests demonstrate that while the CCFS prototype is not ready to be used as a drop-in replacement for all file system use cases, the system is feasible. CCFS is fast enough to be usable and can be used to publish, version, archive, and search data. Even in this crude form, CCFS already demonstrates advantages over previous state-of-the-art systems. When the Internet was designed, there were relatively fewer computers that were far weaker than the computers we have now. They were largely connected to each other over reliable connections. When the Internet was first created, computing was expensive and propagation delay was negligible. Since then, the propagation delay has not improved on a Moore’s Law Curve. Now, latency has come to dominate all other costs of retrieving content; specifically, the propagation time has come to dominate the latency. In order to improve the latency, we are paying more for storage, processing, and bandwidth. The only way to improve propagation delay is to move the content closer to the destination. In order to have the content close to the demand, we store multiple copies and search multiple locations, thus trading off storage, bandwidth, and processing for lower propagation delay. The computing world should re-evaluate these trade-offs because the situation has changed. We need an Internet that is designed for the technologies used today, rather than the tools of the 20th century. CCFS, which regards the trade-off for lower propagation delay, will be better suited for 21st-century technologies. Although CCFS is not preferable in all situations, it can still offer tremendous value. Better robustness, performance, and democracy make CCFS a contribution to the field. Robustness comes from the cryptographic assurances provided by the five properties of CCFS. Performance comes from the locality of content. Democracy arises from the lack of a centralized authority that may grant the right of Free Speech only to those who espouse rhetoric compatible with their ideals. Combined, this model for a cryptographically secure, content-centric system provides a novel contribution to the state of communications technology and information security.

It is desirable to modify the spectral signature of a surface, particularly in the infrared (IR) region of the electromagnetic spectrum. To alter the surface signature in the IR, two methods are investigated: thin film application and antenna array application. The former approach is a common and straightforward incorporation of optically-thin film coatings on the surface designated for signature modification. The latter technique requires the complex design of a periodic array of passive microantenna elements to cover the surface in order to modify its signature. This technology is known as frequency selective surface (FSS) technology and is established in the millimeter-wave spectral regime, but is a challenging technology to scale for IR application. Incorporation of thin films and FSS antenna elements on a surface permits the signature of a surface to be changed in a deterministic manner. In the seminal application of this work, both technologies are integrated to comprise a circuit-analog absorbing IR FSS. The design and modeling of surface treatments are accomplished using commercially-available electromagnetic simulation software. Fabrication of microstructured antenna arrays is accomplished via microlithographic technology, particularly using an industrial direct-write electron-beam lithography system. Comprehensive measurement methods are utilized to study the patterned surfaces, including infrared spectral radiometry and Fourier-transform infrared spectrometry. These systems allow for direct and complementary spectral signature measurements--the radiometer measures the absorption or emission of the surface, and the spectrometer measures its transmission and reflection. For the circuit-analog absorbing square-loop IR FSS, the spectral modulation in emission is measured to be greater than 85% at resonance. Other desirable modifications of surface signature are also explored; these include the ability to filter radiation based on its polarization orientation and the ability to dynamically tune the surface signature. An array of spiral FSS elements allows for circular polarization conditioning. Three techniques for tuning the IR FSS signature via voltage application are explored, including the incorporation of a pn junction substrate, a piezoelectric substrate and a liquid crystal superstrate. These studies will ignite future explorations of IR FSS technology, enabling various unique applications.
Ph.D.
Other
Optics and Photonics
Optics

Estimates of fire emissions remain uncertain due to limited constraints on the variations in fire characteristics. Here we demonstrate the utility of space-based observations of smoke constituents in addressing this limitation. We introduce a satellite-derived smoke index (SI) as an indicator of the dominant phase of large-scale fires. This index is calculated as the ratio of the geometric mean of observed fractional enhancements (due to fire) in carbon monoxide and aerosol optical depth to that of nitrogen dioxide. We assess the usefulness of this index on fires in the Amazon. We analyze the seasonal, regional, and interannual joint distribution of SI and fire radiative power (FRP) in relation to fire hotspots, land cover, Drought Severity Index, and deforestation rate estimates. We also compare this index with an analogous quantity derived from field data or emission inventories. Our results show that SI changes from low (more flaming) to high (more smoldering) during the course of a fire season, which is consistent with the changes in observed maximum FRPs from high to low. We also find that flaming combustion is more dominant in areas where deforestation fires dominate, while smoldering combustion has a larger influence during drought years when understory fires are more likely enhanced. Lastly, we find that the spatiotemporal variation in SI is inconsistent with current emission inventories. Although we recognize some limitations of this approach, our results point to the utility of SI as a proxy for overall combustion efficiency in the parameterization of fire emission models.

This thesis is focused on the evaluation of rotor dynamics of the induction machine, which can be used as a basis for online diagnosis of driven load in the future. It describes the problem of time varying loading torque at its impact to electromagnetic variables in induction machine. Followed by the possible ways of monitoring and diagnostic of loading torque using Fourier analysis on supply current.

Los títulos de crédito son secuencias que cumplen con una función estructural del relato fílmico siendo, a su vez, parte representante del hecho cinematográfico. Su carácter de firma autoral e identificador general integra a todo el equipo de producción así como indica rasgos estéticos y narrativos concretos a través del uso del lenguaje gráfico-audiovisual. Son dispositivos delimitados y limitadores que sitúan el texto en el tiempo y en el espacio, determinan y señalan la relación entre el filme y el espectador e implican un carácter de apertura y clausura. Esta tesis plantea que estas secuencias adoptan la función de marco de la obra fílmica; se propone, así, una redefinición de los títulos de crédito a través de la catalogación de los mismos como el marco de los cuadros, el de las ventanas y el de los espejos. Para ello se integrarán diversos aspectos teóricos relacionados con el borde pictórico, el frame teatral o el paratexto literario entre otros. La investigación se aplica sobre el cine del periodo 1958-1969.
Film titles are sequences that fulfill a structural function on the narration of the film. They are at the same time a representative part of the film context. Its character as authorial signature and general identifier integrates the entire production unit and indicates specific aesthetic and narrative features through the use of graphic-visual language. They are delimited and limiting devices that place the text in time and space, they determine and indicate the relationship between the film and the viewer and they involve an opening and closing nature. This thesis dissertation suggests that these sequences take on the role of the film frame; thus, it proposes a redefinition of the credits through their cataloguing as the frame of the paintings, of the windows and of the mirrors. For this purpose various theoretical aspects will be integrated such as the pictorial border, the theatrical frame, or the literary paratext, among others. This research is applied to the films of the period from 1958 to 1969.

Wong Chi Yin.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1998.
Includes bibliographical references (leaves 107-114).
Abstract also in Chinese.
Abstract --- p.ii
Acknowledgements --- p.vi
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Introduction to Chinese IR --- p.1
Chapter 1.2 --- Contributions --- p.3
Chapter 1.3 --- Organization of this Thesis --- p.5
Chapter 2 --- Background --- p.6
Chapter 2.1 --- Indexing methods --- p.6
Chapter 2.1.1 --- Full-text scanning --- p.7
Chapter 2.1.2 --- Inverted files --- p.7
Chapter 2.1.3 --- Signature files --- p.9
Chapter 2.1.4 --- Clustering --- p.10
Chapter 2.2 --- Information Retrieval Models --- p.10
Chapter 2.2.1 --- Boolean model --- p.11
Chapter 2.2.2 --- Vector space model --- p.11
Chapter 2.2.3 --- Probabilistic model --- p.13
Chapter 2.2.4 --- Logical model --- p.14
Chapter 3 --- Investigation of Segmentation on the Vector Space Retrieval Model --- p.15
Chapter 3.1 --- Segmentation of Chinese Texts --- p.16
Chapter 3.1.1 --- Character-based segmentation --- p.16
Chapter 3.1.2 --- Word-based segmentation --- p.18
Chapter 3.1.3 --- N-Gram segmentation --- p.21
Chapter 3.2 --- Performance Evaluation of Three Segmentation Approaches --- p.23
Chapter 3.2.1 --- Experimental Setup --- p.23
Chapter 3.2.2 --- Experimental Results --- p.24
Chapter 3.2.3 --- Discussion --- p.29
Chapter 4 --- Signature File Background --- p.32
Chapter 4.1 --- Superimposed coding --- p.34
Chapter 4.2 --- False drop probability --- p.36
Chapter 5 --- Partitioned Signature File Based On Chinese Word Length --- p.39
Chapter 5.1 --- Fixed Weight Block (FWB) Signature File --- p.41
Chapter 5.2 --- Overview of PSFC --- p.45
Chapter 5.3 --- Design Considerations --- p.50
Chapter 6 --- New Hashing Techniques for Partitioned Signature Files --- p.59
Chapter 6.1 --- Direct Division Method --- p.61
Chapter 6.2 --- Random Number Assisted Division Method --- p.62
Chapter 6.3 --- Frequency-based hashing method --- p.64
Chapter 6.4 --- Chinese character-based hashing method --- p.68
Chapter 7 --- Experiments and Results --- p.72
Chapter 7.1 --- Performance evaluation of partitioned signature file based on Chi- nese word length --- p.74
Chapter 7.1.1 --- Retrieval Performance --- p.75
Chapter 7.1.2 --- Signature Reduction Ratio --- p.77
Chapter 7.1.3 --- Storage Requirement --- p.79
Chapter 7.1.4 --- Discussion --- p.81
Chapter 7.2 --- Performance evaluation of different dynamic signature generation methods --- p.82
Chapter 7.2.1 --- Collision --- p.84
Chapter 7.2.2 --- Retrieval Performance --- p.86
Chapter 7.2.3 --- Discussion --- p.89
Chapter 8 --- Conclusions and Future Work --- p.91
Chapter 8.1 --- Conclusions --- p.91
Chapter 8.2 --- Future work --- p.95
Chapter A --- Notations of Signature Files --- p.96
Chapter B --- False Drop Probability --- p.98
Chapter C --- Experimental Results --- p.103
Bibliography --- p.107

碩士
國立交通大學
資訊科學學系
82
Signature file is a popular strategy applied to the text retrieval methods of relational database. Recently, some researches discovered that the characteristic of signature file could deal with some problems of object-oriented database. There are two primary parts in this thesis. Firstly, it proposes a new method of signature file. Secondly, signature file is applied to object - oriented database. Part I : There are two factors that influence the efficiency of the signature file. One is the false drop probability, the other is the cost of searching the signature file. The false drop probability is affected by the signature extraction methods, while the cost of the signature file is decided by searching storage structures. These two factors were considered separately in the literature. In this thesis, the signature extraction methods are integrated with the storage structures to result in several new signature file methods. The new methods take the two factors into considerations at the same time. The new signature file methods designed upon this concept have the capabilities of high filtering and fast searching. Part II: In the past, the index of OODB was designed for special queries. It is inconvenient and not general. In this thesis, a new method based on the signature file approach is proposed to solve the problem of index in OODB.

Ransomware is a type of malware that hijack victims’ computers, by encrypting or locking corresponding files, and demanding the payment of some ransom in cryptocurrency for the restoration of the files. The last few years have witnessed a sudden rise in ransomware attack incidents, causing significant amount of financial loss to individuals, institutions, and businesses. In reaction to that, ransomware detection has become an important topic for research in recent years. Currently, there are three types of ransomware detection techniques available in the wild: static, dynamic and hybrid. Unfortunately, the current static detection techniques can be easily evaded by code-obfuscation and encryption techniques. Furthermore, current dynamic and hybrid techniques face difficulties to detect novel ransomware. In the current thesis, we present an upgraded dynamic ransomware detection model with two new sets of features: grouped registry key operation, and combined file entropy and file signature. We analyze the new feature model by exploring and comparing 3 different linear machine learning techniques: SVM, Logistic Regression and Random Forest. The proposed approach help achieves improved detection accuracy and provides the ability to detect novel ransomware. Furthermore, the proposed approach helps differentiate user-triggered encryption from ransomware-triggered encryption, which allows saving as many files as possible during an attack. To conduct our study, we use a new public ransomware detection dataset collected at the ISOT lab, which consists of 666 ransomware and 103 benign binaries. Our experimental results show that our proposed approach achieves relatively high accuracy in detecting both previously seen and novel ransomware samples.
Graduate

碩士
朝陽科技大學
資訊管理系碩士班
92
Due to the fast development and the great advance of information technology and Internet, it is easy to retrieve and produce digital images. However, the problem concerning fast and accurately retrieving the required images in an image database is worthy being researched further. Generally speaking, most content-based image retrieval techniques usually adopt the following two steps. First of all, a feature vector of each image is computed and then stored in the image database. Secondly, given a query image, the feature vector of the query image is computed and then is taken to be compared with the feature vector of each image stored in the image database. As a result, the images, which are stored in the image database and are most similar to the query image, are retrieved to the users. Therefore, two topics can be found from the above two steps. The first one concerns the accuracy of the query images. The second one concerns the speed that the technique can respond. Obviously, the operation of image retrieval will be speed up if focusing on the promotion of retrieval speed. Nevertheless, it will result in the decreased accuracy of the retrieved images due to the affect of image content, such as the brightness, hue, shift, and rotation variants. With the problems described above, this thesis proposes an image retrieval technique based on signature file and multi-feature dimension. This technique performs essential factor computation on each image with DWT, sorts the factor number of relative frequency band, and changes them into keyword strings. To generate the signature file, all image signatures which are combined by these generated keyword string for each are combined. And qualified images are found by comparing strings on the signature file. Finally, these qualified images are processed. This technique uses multi-feature dimension so as to compare the features, such as brightness, saturation, frequency, and etc., and compute the similarity between these qualified images and the query one. As a result, the images most similar to the query image will be retrieved to the users.