The analysis and behavior of thin-steel hyperbolic paraboloid shells

An extensive experimental and analytical investigation of thin-steel hyperbolic paraboloid (hypar) structures was carried out to provide design information. As a result of this work, empirical data is provided regarding the behavior of such structures and computer programs are presented for the analysis of thin steel hypar structures. Hyperbolic paraboloid structures possess a unique combination of structural and architectural properties; some of them are the following: 1) Due to the double curvature of the surface the internal stresses in the deck are generally low and the deflections are small. 2) Since a hypar surface can be generated by straight lines, thin-steel or light-gage panels may be used to form the shell; furthermore such panels are well suited to carry the in-plane shear forces in hypar shells. 3) Basic hypar units can be combined in a large variety of ways to produce attractive roofs (Fig. 1-2, page 212). 4) The dead load to live load ratio is very low in the case of thin-steel shell structures. A hypar unit is a warped surface bounded by straight lines (Fig. 1-1, page 211). The equation of the surface is z = Cxy/AB. According to the simple membrane theory, a uniform load p produces pure shear forces Nxy = ABF/2C. This membrane shear transmits uniform eccentric axial forces to the edge members. The following are the major problems associated with the design of thin-steel hypar structures: 1) The deflections, i stresses, and the stability of hypars depends greatly on the shear rigidity of the thin-steel deck. This property must be evaluated experimentally for each combination of decking, connections to edge members, and seam connections. Furthermore, in the case of hypars the deck is warped and thus the shear rigidity may be different from that of an equivalent flat diaphragm. 2) The deck may buckle due to the shear stresses~ and the buckling load must be evaluated for highly orthotropic shells. 3) The design of thin-steel hypar structures is generally governed by stiffness (deflections or buckling) requirements. The evaluation of the deflections is a very complex matter because it depends on the deck rigidity, the edge member axial and bending stiffnesses, and on the eccentricity of the deck-to-edge member connection. 4) If the curvature (or riseto- span ratio) of a hypar is small, the deflections may be large and a considerable portion of the load is carried by bending rather than by membrane shear. 5) Partial or concentrated loads may cause large local deflections, especially if singlelayer decks are used. The present investigation studied all the above-mentioned factors. The experimental and the analytical studies are summarized briefly in the following paragraphs. The ~~perimental investigatio~ consisted of four types of tests: a) Four medium-scale (12 ft by 12 ft in plan) inverted umbrella tests to study the stresses, deflections, and the deck buckling; b) Test on a small-scale (2 ft by 2 ft) inverted umbrella structure to study scaling effects and the overall i1 buckling of hypars; c) Sixteen flat shear tests to determine the shear rigidity of the decks used in the hypar tests; d) Twelve saddle-s~aped hypar tests (S ft by S ft in plan) with various rise-to-span ratios to evaluate the effect of rise or warping on the shear rigidity and to study other factors such as partial loading and single versus double layered decks. Photos of the various types of tests are shown in Figs. 7.1 to 7.S. The experimental program is described in detail in Chapter VII. Prior to the main test program, several small-scale (2 ft by 2 ft) four-quadrant tests and medium-scale single-quadrant tests were also conducted. These tests were however discontinued because of the severe scaling effects in the case of the small-scale models and the violation of the symmetry conditions in the case of single-quadrant experiments where the neighboring quadrants were missing. Nevertheless, these tests produced useful qualitative information and experience with manufacturing and testing thin-steel hypar structures. The edge members of the umbrella-type specimens were made of tubular members since this afforded easy connection of the warped surface to the straight edges. The decking consisted of single or double layers of standard corrugated panels. One layer was connected to the edge ~enbers with sheet metal screws at various spacings. The seam connections between the panels were also made by means of sheet metal screws. In the case of shells with two layers, the top layer was connected to the bottom layer in a similar manner. iii The medium-scale umbrella models were loaded using air bags under each of the four quadrants. The saddle-shaped hypars were loaded with sand, whereas the small-scale models were loaded through loading pads and suspended weights. The following are the principal conclusions of the experimental part of this investigation: The effective shear stiffness of the cold-formed deck and the rise (or curvature) of the structure are the most important factors influencing the behavior of hypars. For low shear stiffnesses and for small rise-to-span ratios the deflections may be large, the bending stresses tend to increase relative to the membrane stresses, and the possibility of deck buckling increases. As in the case of flat shear diaphragms, the shear stiffness depends strongly on the seam and edge connections. The increase in shear stiffness due to the addition of a second layer of deck was found to be only about 1/3 if the second layer was connected only to the first layer and not directly to the edge members. Similarly, the deflections of a double-layered shell are more than half of those of a corresponding single shell. If the two layers are interconnected with sheet metal screws (on an 8 in. grid in the present saddleshaped hypar tests), the deflections are further reduced by about 10 to 20%, depending on the rise ratio. A particular problem of certain types of hypar structures is the deflection of unsupported outside corners (see Fig. 1-2, page 212). The membrane shear cannot carry the load over such flat corners and thus considerable bending and deflections may develop. The tests showed that the bending stiffness of the iv edge members has a great effect on the corner deflections, in fact, they indicate that the design of the edge members in hypars with flat corners is usually governed by deflection limitations. The measured bending strains in flat saddle shells (riseto- span ratio of 1.8), was much greater than the bending in hypars with greater curvature (rise ratio of 1/3). The membrane theory is insufficient for the design of flat hypar structures. However, the design of the connections (seam or edge) may be based on the shear forces obtained from the simple membrane theory. Several single and double layered saddle-shaped models were tested under partial loading. Since such loads must be carried mainly by bending of beam strips along the deformations of single decks, relatively large deflections were noted. The deflections under the 8 in. by 8 in. loaded area were about three times greater in the single decks than on the doublelayered structures. Since the effective shear rigidity of the deck is of paramount importance, the effect of curvature (warping) on it is an important question. The effective shear rigidity of various deck, edge member, and connection configurations are determined by tests on flat diaphragms. The comparison of the measured deflections for saddle hypars with various rise-span ratios and the evaluation of the effective shear rigidities backwards from the measured deflections indicated that the shear rigidity is reduced by about 20% due to the warping effect. The buckling of the deck is one of the design factors. For small rise-span ratios and for low deck shear rigidities the deck may buckle. As an example, a 12 ft by 12 ft model v having a single layer 24 gage corrugated sheet deck buckled at a uniform load of 70 psf (see Fig. 6.14). This model had relatively stiff edge members (3 in. dia. tubular sections). The corner deflections remained linear with increasing load beyond the buckling load. The buckling load of double-layered structures is much larger than that for single deck shells. A model, similar to the above but with two layers of 28 gage standard corrugated decks, did not buckle up to a load of 145 psf, when the test was discontinued. The major part of the ~~lytical investigation consisted of two finite element approaches for the calculation of deflections, stresses, and instability. In addition, two simple methods were developed for estimating the deck buckling load and the buckling of the compression edge members, which would suffice in preliminary designs. Two types of finite elements were used: curved shallow shell elements and flat elements. The details of the analysis are described in Chapter III. Both approaches were verified by comparisons with existing experimental and analytical results. The stiffness of the eccentric edge members were properly accounted for in the mathematical representation of the structure. The connection of the decks to the edge members may allow rotation about the axis of the edge members and movement normal to the edges dUe to slip at the connections. These possibilities were also considered in the analysis. The instability of the decks was studied with the help of the incremental stiffness matrix approach. The effective stiffvi ness of the system is reduced due to the in-plane forces in the deck. The in-plane forces depend on the deflections of the shell and to obtain the buckling load, the eigenvalues of a large order system need to be evaluated. In the present study the load increment at ion method was used instead. The effect of the in-plane forces was evaluated iteratively at successive load increwents. The buckling load is obtained from the nonlinear load-deflection curve, (Fig. 6-6, Page 276). The comparison of the results of the flat element and the curved element approaches reveals that both give good results for shells supported around the perimeter. However, the flat element method gave better results in the neighborhood of unsupported flat corners. The analysis of the structures tested in this and in other studies confirmed the conclusions of the experimental part of the investigation. The stresses in most types of hypars are low and the design is usually controlled by deflection or buckling linitations. The relative stiffness of the deck and the edge members is an important factor. For stiff edge members the deck tends to bend between opposite edges, whereas in the case of flexible cantilevered edge members the shell partially supports the edge members. Analysis of a structure including the weight of the edge members indicated that this effect may have to be considered in the design of hypar structures. The analysis of buckling of hypar decks showed that the buckling load of double-layered shells is three to four times vii greater than that of single decks. The predicted buckling loads compared well with experimental or previous analytical evidence. The buckling load does not depend much on pre-buckling deflections, however it depends on the axial stiffness of the edge members. The finite element analysis was also used to calculate the deflection of an unsymmetrically loaded inverted umbrella structure. The results, which compared well with experimental data, showed that these deflections are about four times greater than those due to symmetric loading. This increase of deflections obviously depends on the type of structure; in this case much of the flexibility was due to the bending of the central column of the umbrella structure. Since the instability a~alysis of hypars by the finite element method involves considerable amount of computer capacity and expense, approximate methods were developed for the calculation of buckling loads. The buckling of the compression edge members was studied by isolating them from the structure. The instability of columns loaded by tangential axial forces that remain parallel to the member during deflection was evaluated. The results are tabulated in Fig. 6-13, page 284. The buckling of hypar decks was also investigated by the energy method (Section VI-7. The resulting equation has to be minimized to get the critical load; this can easily be done with the help of a computer. This approach is much simpler than the finite element instability analysis and is preferable in preliminary designs. viii A few buckling analyses of cold-formed hypar shells showed that the critical load for double-layers is about three to four times greater than a shell with a single deck. The finite element analysis computer program will be made available to designers by the A~erican Iron and Steel Institute

Word-based compression in full-text retrieval systems

Ankara : Department of Industrial Engineering and the Institute of Engineering and Sciences of Bilkent University, 1995.Thesis (Master's) -- Bilkent University, 1995.Includes bibliographical references leaves 44-49.Large space requirement of a full-text retrieval system can be reduced significantly by data compression. In this study, the problem of compressing the main text of a full-text retrieval system is addressed and performance of several coding techniques for compressing the text database is compared. Experiments show that statistical techniques, such as arithmetic coding and Huffman coding, give the best compression among the implemented; and using a semi-static word-based model, the space needed to store English text is less than one third of the original requirement.Selçuk, Ali AydınM.S

The analysis and behavior of thin-steel hyperbolic paraboloid shells

An extensive experimental and analytical investigation of thin-steel hyperbolic paraboloid (hypar) structures was carried out to provide design information. As a result of this work, empirical data is provided regarding the behavior of such structures and computer programs are presented for the analysis of thin steel hypar structures. Hyperbolic paraboloid structures possess a unique combination of structural and architectural properties, some of them are the following 1) Due to the double curvature of the surface the internal stresses in the deck are generally low and the deflections are small. 2) Since a hyper surface can be generated by straight lines, thin-steel or light-gage panels may be used to form the shell; furthermore such panels are well suited to carry the in-plane shear forces in hyper shells. 3) Basic hyper units can be combined in a large variety of ways to produce attractive roofs (Fig. 1-2, page 216). 4) The dead load to live load ratio is very low in the case of thin-steel shell structures. A hypar unit is a warped surface bounded by straight lines (Fig. I-I, page 215). The equation of the surface is z = cxy/ab. According to the simple membrane theory, a uniform load p produces pure shear forces N XY = abp/2c. This membrane shear transmits uniform eccentric axial forces to the edge members. The following are the major problems associated with the design of thin-steel hypar structures: 1) The deflections, stresses and the stability of hypars depends greatly on the shear rigidity of the thin-steel deck. This property must be evaluated experimentally for each combination of decking, connections to edge members, and seam connections. Furthermore, in the case of hypars the deck is warped and thus the shear rigidity may be different from that of an equivalent flat diaphragm. 2) The deck may buckle due to the shear stresses, and the buckling load must be evaluated for highly orthotropic shells. 3) The design of thin-steel hypar structures is generally governed by stiffness (deflections or buckling) requirements. The evaluation of the deflections is a very complex matter because it depends on the deck rigidity, the edge member axial and bending stiffnesses, and on the eccentricity of the deck-to-edge me.ber connection. 4) If the curvature (or rise-to-span ratio) of a hypar is small, the deflections may be very large and a considerable portion of the load is carried by bending nather than by membrane shear. 5) Partial or concentrated loads may cause large local deflections, especially if single-layer decks are used. The present investigation studied all the above mentioned factors. The experimental and the analytical studies are summarized briefly in the following paragraphs. The experimental investigation consisted of four types of tests: a) Four medium-scale (12 ft by 12 ft in plan) inverted umbrella tests to study the stresses, deflections, and the deck buckling, b) Test on a small-scale (2 ft by 2 ft) inverted umbrella structure to study scaling effects and the overall buckling of hypars, c) Sixteen flat shear tests to determine the shear rigidity of the decks used in the hyper tests, d) Twelve saddle-shaped hypar tests (5 ft by 5 ft in plan) with various rise-to-span ratios to evaluate the effect of rise or warping on the shear rigidity and to study other factors such as partial loading and single versus double layered decks. Photos of the various types of tests are shown in Figs. 7.1 to 7.5. The experimental program is described in detail in Chapter VII. Prior to the main test program, several small scale (2 ft by 2 ft) four-quadrant tests and medium-scale single-quadrant tests were also conducted. These tests were however discontinued because of the severe scaling effects in the case of the small-scale models and the violation of the symmetry conditions in the case of single-quadrant experiments where the neighboring quadrants were missing. Nevertheless, these tests produced useful qualitative information and experience with manuafacturing and testing thin-steel hypar structures. The edge members of the umbrella-type specimens were made of tubular members since this afforded easy connection of the warped surface to the straight edges. The decking consisted of single or double layers of standard corrugated panels. One layer was connected to the edge members with sheet metal screws at various spacings. The seam connection between the panels was also by means of sheet metal screws. In the case of shells with two layers, the top layer was connected to the bottom layer in a similar manner. The medium-scale umbrella models were loaded using air bags under each of the four quadrants. The saddle-shaped hypars were loaded with sand, whereas the small-scale models were loaded through loading pads and suspended weights. The following are the principal conclusions of the experimental part of this investigation. The effective shear stiffness of the cold-formed deck and the rise (or curvature) of the structure are the most important factors influencing the behavior of hypars. For low shear stiffnesses and for small rise-to-span ratioa the deflections may be large, the bending stresses tend to increase relative to the membrane stresses, and the possibility of deck buckling increases. As in the case of flat shear diaphragms, the shear stiffness depends strongly on the seam and edge connections. The increase in shear stiffness due to the addition of a second layer of deck was found to be only about 1/3 if the second layer was connected only to the first layer and not directly to the edge members. Similarly, the deflections of a double-layered shell are more than half of those of a corresponding single shell. If the two layers are interconnected with sheet metal screws (on an 8 in. grid in the present saddle-shaped hypar tests), the deflections are further reduced by about 10 to 20%, depending on the rise ratio. A particular problem of certain types of hypar structures is the deflection of unsupported outside corners (see Fig. 1-2, page 216). The membrane shear cannot carry the load over such flat corners and thus considerable bending and deflections may develop. The tests showed that the bending stiffness of the edge members has a great effect on the corner deflections, in fact, they indicate that the design of the edge members in hypars with flat corners is probably governed by deflection limitations. The measured bending strains in flat saddle shells (rise-to-span ratio of 1/8) was much greater than the bending in hypers with greater curvature (rise ratio of 1/3). The membrane theory is insufficient for the design of flat hypar structures. However, the design of the connections (seam or edge) may be based on the shear forces obtained from the simple membrane theory. Several single and double layered saddle-shaped models were tested under partial loading. Since such loads must be carried mainly by bending of beam strips along the deformations of single decks, relatively large deflections were noted. The deflections under the 8 in. by 8 in. loaded area were about three times greater in the single decks than on the double-layered structures. Since the effective shear rigidity of the deck is of paramount importance, the effect of curvature (warping) on it is an important question. The effective shear rigidity of various deck, edge member and connection configurations are determined by tests on flat diaphragms. The comparison of the measured deflections for saddle hypars with various rise-span ratios and the evaluation of the effective shear rigidities backwards from the measured deflections indicated that the shear rigidity is reduced by about 20% due to the warping effect. The buckling of the deck is one of the design factors. For small rise-span ratios and for low deck shear rigidities the deck may buckle. As an example, a 12 ft by 12 ft model having a single layer 24 gage corrugated sheet deck buckled at a uniform load of 70 psf (see Fig. ). This model had relatively stiff edge members (3 in. dia. tubular sections). The corner deflections remained linear with increasing load beyond the buckling load. The buckling load of double-layered structures is much larger than that for single deck shells. A model, similar to the above but with two layers of 28 gage standard corrugated decks, did not buckle up to a load of 145 psf, when the test was discontinued. The major part of the analytical investigation consisted of two finite element approaches for the calculation of deflections, stresses, and instability. In addition, two simple methods were developed for estimating the deck buckling load and the buckling of the compression edge members, which would suffice in preliminary designs. Two types of finite elements were used: curved shallow shell elements and flat elements. The details of the analysis are described in Chapter Ill. Both approaches were verified by comparisons with existing experimental and analytical results. The stiffness of the eccentric edge members were properly accounted for in the mathematical representation of the structure. The connection of the decks to the edge members may allow rotation about the axis of the edge members and movement normal to the edges due to slip at the connections. These possibilities were also considered in the analysis. The instability of the decks was studied with the help of the incremental stiffness matrix approach. The effective stiffness of the system is reduced due to the in-plane forces in the deck. The in-plane forces depend on the deflections of the shell and to obtain the buckling load, the eigenvalues of a large- order system needs to be evaluated. In the present study the load incrementation method was used instead. The effect of the in-plane forces was evaluated iteratively at successive load increments. The buckling load is obtained from the non-linear load deflection curve,(Fig. 6-6, Page 280). The comparison of the results of the flat-element and the curved-element approaches reveals that both give good results for shells supported around the perimetry. However, the flat element method gave better results in the neighborhood of unsupported flat corners. The analysis of the structures tested in this and in other studies confirmed the conclusions of the experimental part of the investigation. The stresses in most types of hypars are low and the design is usually controlled by deflection or buckling limitations. The relative stiffness of the deck and the edge members is an important factor. For stiff edge members the deck tends to bend between opposite edges, whereas in the case of flexible cantilevered edge members the shell partially supports the edge members. Analysis of a structure including the weight of the edge members indicated that this effect may have to be considered in the design of hyper structures. The analysis of buckling of hypar decks showed that the buckling load of double-layered shells is three to four times greater than that of single decks. The predicted buckling loads compared well with experimental or previous analytical evidence. The buckling load does not depend much on pre-buckling deflections, however it depends on the axial stiffness of the edge members. The finite element analysis was also used to calculate the deflection of an unsymmetrically loaded inverted umbrella structure. The results, which compared well with experimental data, showed that these deflections are about four times greater than those due to symmetric loading. This increase of deflections obviously depends on the type of structure. in this case much of the flexibility was due to the bending of the central column of the umbrella structure, Since the instability analysis of hypars by the finite element method involves considerable amount of computer capacity and expense, approximate methods were developed for the calculation of buckling loads. The buckling of the compression edge members was studied by isolating them from the structure. The instability of columns loaded by tangential axial forces that to the member remain parallel during deflection was evaluated. The results are tabulated in Fig. 6-13, page 287. The buckling of hypar decks was also investigated by the energy method (Section VI-7). The resulting equation has to be minimized to get the critical load. this can easily be done with the help of a computer. This approach is much simpler than the finite element instability analysis and is preferable in preliminary designs. A few buckling analyses of cold-formed hypar shells showed that the critical load for double-layers is about three to four times greater than a shell with a single deck

Hypersonic Vehicle Propulsion System Control Model Development Roadmap and Activities

The NASA Fundamental Aeronautics Program Hypersonic project is directed towards fundamental research for two classes of hypersonic vehicles: highly reliable reusable launch systems (HRRLS) and high-mass Mars entry systems (HMMES). The objective of the hypersonic guidance, navigation, and control (GN&C) discipline team is to develop advanced guidance and control algorithms to enable efficient and effective operation of these challenging vehicles. The ongoing work at the NASA Glenn Research Center supports the hypersonic GN&C effort in developing tools to aid the design of advanced control algorithms that specifically address the propulsion system of the HRRLSclass vehicles. These tools are being developed in conjunction with complementary research and development activities in hypersonic propulsion at Glenn and elsewhere. This report is focused on obtaining control-relevant dynamic models of an HRRLS-type hypersonic vehicle propulsion system

Fatigue Life Prediction of Edge-Welded Metal Bellows Using Neural Networks and Multiple Linear Regression

Edge-welded metal bellows present an ongoing challenge: the prediction of an accurate cycle life. Current methods rely on physical leak detection to determine a bellow\u27s cycle life to failure. It is known, however, that crack initiation begins many cycles before a leak path is present. Bellows manufacturers require a method for detection of fatigue cracks when they initiate but before they result in leak rates large enough to contaminate a process. Acoustic emission (AE) testing is one method which can meet this need and is a proven, reliable technique for detecting crack initiation and monitoring fatigue crack growth. Four sets of metal bellows samples were fatigue tested and AE parameter data recorded. The data sets were analyzed and the determination made that amplitude, duration, and time of occurrence were the AE data variables required for separation of the various failure mechanisms. For two of the four materials, an expanded set of tests were performed. Fourteen tests were used to train and test a back-propagation neural network for prediction of bellows cycle life. The input data consisted of a material identifier, AE parameter data consisting of the amplitude distribution (50-100 dB) of the first 250 hits, and the final cycle life. The network was structured with an input layer consisting of the identifier and amplitude data, two hidden layers for mapping failure mechanisms, and an output layer for predicting cycle life. The network required training on four samples for the Inconel 718 and five samples for the 350 stainless steel. Once trained the network was able to predict cycle life with a worst case error of-4.45 percent and 2.66 percent for the Inconel 718 and 350 stainless steel, respectively. Finally, through the use of multiple linear regression, a statistical analysis was made to develop a model capable of accurate prediction. Applying a natural log transformation to the independent variables of amplitude and energy resulted in a model capable of explaining 95 percent of the variability in cycle life prediction

Signature file access methodologies for text retrieval: a literature review with additional test cases

Signature files are extremely compressed versions of text files which can be used as access or index files to facilitate searching documents for text strings. These access files, or signatures, are generated by storing hashed codes for individual words. Given the possible generation of similar codes in the hashing or storing process, the primary concern in researching signature files is to determine the accuracy of retrieving information. Inaccuracy is always represented by the false signaling of the presence of a text string. Two suggested ways to alter false drop rates are: 1) to determine if either of the two methologies for storing hashed codes, by superimposing them or by concatenating them, is more efficient; and 2) to determine if a particular hashing algorithm has any impact. To assess these issues, the history of suprimposed coding is traced from its development as a tool for compressing information onto punched cards in the 1950s to its incorporation into proposed signature file methodologies in the mid-1980\u27 s. Likewise, the concept of compressing individual words by various algorithms, or by hashing them is traced through the research literature. Following this literature review, benchmark trials are performed using both superimposed and concatenated methodologies while varying hashing algorithms. It is determined that while one combination of hashing algorithm and storage methodology is better, all signature file mehods can be considered viable

A Preliminary Study of the Effect of the Chirped Rotating Wall on a Positron Cloud

The density of the positron cloud is a crucial parameter in many applications ofaccumulated positrons. Previous work has shown that adjusting the frequency ofthe rotating wall potential following positron accumulation can be used to controlthe density of positron clouds. In this work, positron clouds were studied afterbeing compressed using a linear rotating wall frequency sweep under a selection ofrotating wall drive amplitudes and cooling gas pressures following an initial staticfrequency compression. This was performed for SF6, CF4, and briefly for CO. Theeffect of changing the cooling gas appears congruent to that shown by the staticfrequency case. The results are in qualitative agreement with previous work byDeller et al., and compare briefly but favourably to a simplistic numerical model

Index compression for information retrielval systems

[Abstract] Given the increasing amount of information that is available today, there is a clear need for Information Retrieval (IR) systems that can process this information in an efficient and effective way. Efficient processing means minimising the amount of time and space required to process data, whereas effective processing means identifying accurately which information is relevant to the user and which is not. Traditionally, efficiency and effectiveness are at opposite ends (what is beneficial to efficiency is usually harmful to effectiveness, and vice versa), so the challenge of IR systems is to find a compromise between efficient and effective data processing. This thesis investigates the efficiency of IR systems. It suggests several novel strategies that can render IR systems more efficient by reducing the index size of IR systems, referred to as index compression. The index is the data structure that stores the information handled in the retrieval process. Two different approaches are proposed for index compression, namely document reordering and static index pruning. Both of these approaches exploit document collection characteristics in order to reduce the size of indexes, either by reassigning the document identifiers in the collection in the index, or by selectively discarding information that is less relevant to the retrieval process by pruning the index. The index compression strategies proposed in this thesis can be grouped into two categories: (i) Strategies which extend state of the art in the field of efficiency methods in novel ways. (ii) Strategies which are derived from properties pertaining to the effectiveness of IR systems; these are novel strategies, because they are derived from effectiveness as opposed to efficiency principles, and also because they show that efficiency and effectiveness can be successfully combined for retrieval. The main contributions of this work are in indicating principled extensions of state of the art in index compression, and also in suggesting novel theoretically-driven index compression techniques which are derived from principles of IR effectiveness. All these techniques are evaluated extensively, in thorough experiments involving established datasets and baselines, which allow for a straight-forward comparison with state of the art. Moreover, the optimality of the proposed approaches is addressed from a theoretical perspective.[Resumen] Dada la creciente cantidad de información disponible hoy en día, existe una clara necesidad de sistemas de Recuperación de Información (RI) que sean capaces de procesar esa información de una manera efectiva y eficiente. En este contexto, eficiente significa cantidad de tiempo y espacio requeridos para procesar datos, mientras que efectivo significa identificar de una manera precisa qué información es relevante para el usuario y cual no lo es. Tradicionalmente, eficiencia y efectividad se encuentran en polos opuestos - lo que es beneficioso para la eficiencia, normalmente perjudica la efectividad y viceversa - así que un reto para los sistemas de RI es encontrar un compromiso adecuado entre el procesamiento efectivo y eficiente de los datos. Esta tesis investiga el problema de la eficiencia de los sistemas de RI. Sugiere diferentes estrategias novedosas que pueden permitir la reducción de los índices de los sistemas de RI, enmarcadas dentro da las técnicas conocidas como compresión de índices. El índice es la estructura de datos que almacena la información utilizada en el proceso de recuperación. Se presentan dos aproximaciones diferentes para la compresión de los índices, referidas como reordenación de documentos y pruneado estático del índice. Ambas aproximaciones explotan características de colecciones de documentos para reducir el tamaño final de los índices, mediante la reasignación de los identificadores de los documentos de la colección o bien descartando selectivamente la información que es "menos relevante" para el proceso de recuperación. Las estrategias de compresión propuestas en este tesis se pueden agrupar en dos categorías: (i) estrategias que extienden el estado del arte en la eficiencia de una manera novedosa y (ii) estrategias derivadas de propiedades relacionadas con los principios de la efectividad en los sistemas de RI; estas estrategias son novedosas porque son derivadas desde principios de la efectividad como contraposición a los de la eficiencia, e porque revelan como la eficiencia y la efectividad pueden ser combinadas de una manera efectiva para la recuperación de información. Las contribuciones de esta tesis abarcan la elaboración de técnicas del estado del arte en compresión de índices y también en la derivación de técnicas de compresión basadas en fundamentos teóricos derivados de los principios de la efectividad de los sistemas de RI. Todas estas técnicas han sido evaluadas extensamente con numerosos experimentos que involucran conjuntos de datos y técnicas de referencia bien establecidas en el campo, las cuales permiten una comparación directa con el estado del arte. Finalmente, la optimalidad de las aproximaciones presentadas es tratada desde una perspectiva teórica

Towards Machine Musicians Who Have Listened to More Music Than Us: Audio Database-led Algorithmic Criticism for Automatic Composition and Live Concert Systems

Databases of audio can form the basis for new algorithmic critic systems, applying techniques from the growing field of music information retrieval to meta-creation in algorithmic composition and interactive music systems. In this article, case studies are described where critics are derived from larger audio corpora. In the first scenario, the target music is electronic art music, and two corpuses are used to train model parameters and then compared with each other and against further controls in assessing novel electronic music composed by a separate program. In the second scenario, a “real-world” application is described, where a “jury” of three deliberately and individually biased algorithmic music critics judged the winner of a dubstep remix competition. The third scenario is a live tool for automated in-concert criticism, based on the limited situation of comparing an improvising pianists' playing to that of Keith Jarrett; the technology overlaps that described in the other systems, though now deployed in real time. Alongside description and analysis of these systems, the wider possibilities and implications are discussed