1,043 research outputs found
Holographic impurities and Kondo effect
No full textMagnetic impurities are responsible for many interesting phenomena in condensed matter systems, notably the Kondo effect and quantum phase transitions. Here we present a holographic model of a magnetic impurity that captures the main physical properties of the large-spin Kondo effect. We estimate the screening length of the Kondo cloud that forms around the impurity from a calculation of entanglement entropy and show that our results are consistent with the g-theorem
Sensor horn: creating an electronically augmented trumpet
No full text© 2010 Andrew McNaughtonThis thesis documents the design, construction and evaluation of an original, electronically augmented trumpet: the Sensor Horn. Relevant existing alternate controllers and augmented trumpets are examined, together with the essential elements of an augmented instrument: gesture and data acquisition, sensors and controllers, analog‐to‐digital interfaces, and appropriate software. Following the construction of the Sensor Horn and the mapping of its hardware to various parameters in a specifically designed Max/MSP patch, the instrument is evaluated for its suitability as a performance instrument for the author in a solo improvisational setting. Finally, a number of hardware and ergonomic improvements are proposed together with recommendations for further software explorations
T-duality of singular spacetime compactifications in an H-flux
No full textWe begin by presenting a symmetric version of the circle equivariant T-duality result in a joint work of the second author with Siye Wu, thereby generalizing the results there. We then initiate the study of twisted equivariant Courant algebroids and equivariant generalized geometry and apply it to our context. As before, T-duality exchanges type II role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative; \u3eIIA and type II role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative; \u3eIIB string theories. In our theory, both spacetime and the T-dual spacetime can be singular spaces when the fixed point set is non-empty; the singularities correspond to Kaluza–Klein monopoles. We propose that the Ramond–Ramond charges of type II role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative; \u3eII string theories on the singular spaces are classified by twisted equivariant cohomology groups, consistent with the previous work of Mathai and Wu, and prove that they are naturally isomorphic. We also establish the corresponding isomorphism of twisted equivariant Courant algebroids
Swords Reluctant: Max Pemberton’s roman-à-clef about the early twentieth century peace movement (1912)
No full textThe article offers an analysis of the historical novel War and the Woman (London: Cassell &
Co., 1912, 21914), published in the United States as Swords Reluctant (New York: G. W.
Dillingham, 1912), by Sir Max Pemberton (1863—1950), which doubles up as a roman-àclef for the early 20th century peace movement. Dedicated to the Scottish-American
industrialist, philanthropist and pacifist Andrew Carnegie and thanking Sir Max Waechter
and Sir Francis Trippel, two Anglo-Germans who were the main drivers behind the European
Unity League, one of the first campaign groups for European Federation as a means to
prevent War on the continent, in the foreword, it is an extraordinary artefact, in which the
prolific and popular adventure and mystery genre author takes Waechter’s real endeavours as
background for a fictional storyline that reflects two discourses: the American gunmaker
Hudson Maxim’s campaign against Pacifism, directed against his fellow industrial Andrew
Carnegie and other anti-war activists, on one side of the Atlantic, and the European Unity
League’s attempt at federating the states of Europe together, on the other. Apart from
modifying the often read assessment of Pemberton as a “literary opportunist”, the novel helps
uncover more about the European Unity League’s organisational history and establish the full
extent of its reach and impact on British society as well as across the Atlantic
Numerical Investigation into Size Effect on Prestressed Concrete Beam Resistance to Shear Tension Cracking
No full textIn the past, many researches on the topic of size effect on concrete structures were mainly focused on the phenomenon of size effect in flexural cracking. The result of those studies can be found today in the concrete structure design specifications of well-known building codes, such as the Eurocode. Nevertheless, the inclusions of the results of those studies into the design specifications are still minimum and therefore, it is necessary to conduct more studies on size effect, especially on other types of cracking. In this thesis, an investigation focused on the size effect in shear tension cracking at prestressed concrete beams was conducted. The model used for investigating the size effect is a prediction that a shear tension crack will occur when the principal tensile stress at a certain location on the web of a beam is equal to the concrete mean uniaxial tensile strength (σ1 = fctm). The investigation was conducted by studying premature shear tension cracking on a group of several I-profile prestressed reinforced concrete beams, called the trusted specimens, which were experimented by Hanson (1964), Choulli (2005), and Elzanaty (1986) under four-point bending tests. These tested beams were numerically investigated using linear elastic finite element analysis (LEFEA) with an aim to find the nearly realistic principal tensile stresses that caused the shear tension crack to initiate below the designated tensile strength of the beams. To study the size effect, the obtained principal tensile stress distributions were analyzed using two new approaches proposed by the author, namely the σ1 area approach and the ratio-of-distances approach. The σ1 area method is a technique for detecting a structural size dependency of the uniaxial tensile strength by comparing rectangles which areas represents a group of σ1 values that have a higher likelihood in achieving the deviated values of fctm and initiate shear tension cracking on the web of the trusted specimens. In contrast, the ratio-of-distances approach investigates the size dependency of the uniaxial tensile strength by observing the locations of σ1max where a shear tension crack initiated in the web of each trusted specimen under an assumption that a shear tension crack is more likely to originate from near the beam neutral axis instead of near the web-flange junction due to the change of thickness at that interface. In conclusion, the result of the investigation was presented. The σ1 area approach confirmed the presence of size effect in shear tension cracking at the trusted specimens by giving a relation that showed a tendency for the smaller specimens to have a higher resistance towards principal tensile stresses compared to the larger specimens. The ratio-of-distances result, on the other hand, implied that the approach has failed to detect the presence of size effect. In that result, the shear cracks from the smaller specimens and the shear cracks from the larger specimens had similar starting points locations, at which the σ1max was located. In addition, several recommendations are provided for future studies on size effect in shear tension cracking. It was recommended to do research this topic on different physical problems and shear tension cracking with the presence of flexural cracks.Civil Engineering | Structural Engineerin
A Distributed Algorithm for Max-min Bandwidth Sharing: The Asynchronous Case Abstract
No full textspeed switches, and high speed routers are giving rise to networks with plentiful bandwidth in the core. In such networks, bottlenecks and congestion are concentrated at the edge and at end nodes. We consider how end nodes should efficiently and fairly manage capacity across multiple sessions with finite and unknown demands in such lambda networks. We present a novel distributed rate allocation algorithm which is the heart of the Group Transport Protocol (GTP) [45,46]. GTP controls each source and sink independently with local information, adaptively allocating its capacity to candidate sessions. This algorithm is given no knowledge of the desired session rates, but rather discovers them. We prove that our distributed algorithm converges the unique global max-min fair rate allocation. Simulations confirm this behavior, and further show that convergence is in practice fast in networks of 64 to 1024 nodes. We also compare GTP with a modified end point only version of XCP [33] which moves the XCP router functions into end nodes (endpointXCP), and two variants of TCP (New Reno and Highspeed TCP [20]). We investigate their convergence, efficiency, stability, and fairness behavior in lambda networks with high capacity, various round-trip times, and various traffic demands. Our results show that within the first 100 round-trip time, the TCP variants do not deliver the available network capacity. In addition, both GTP and endpointXCP deliver high throughput, endpointXCP fails to deliver the full max-min allocation to large users in some cases. In contrast, GTP supports high speed flows, leading to max-min fair allocation to all flows.
Assisting reading and analysis of text documents by visualization
No full textThe research reported here examined the use of computer generated graphics as a means to assist humans to analyse text documents which have not been subject to markup. The approach taken was to survey available visualization techniques in a broad selection of disciplines including applications to text documents, group those techniques using a taxonomy proposed in this research, then develop a selection of techniques that assist the text analysis objective. Development of the selected techniques from their fundamental basis, through their visualization, to their demonstration in application, comprises most of the body of this research. A scientific orientation employing measurements, combined with visual depiction and explanation of the technique with limited mathematics, is used as opposed to fully utilising any one of those resulting techniques for performing complete text document analysis.
Visualization techniques which apply directly to the text and those which exploit measurements produced by associated techniques are considered. Both approaches employ visualization to assist the human viewer to discover patterns which are then used in the analysis of the document. In the measurement case, this requires consideration of data with dimensions greater than three, which imposes a visualization difficulty. Several techniques for overcoming this problem are proposed. Word frequencies, Zipf considerations, parallel coordinates, colour maps, Cusum plots, and fractal dimensions are some of the techniques considered.
One direct application of visualization to text documents is to assist reading of that document by de-emphasising selected words by fading them on the display from which they are read. Three word selection techniques are proposed for the automatic selection of which words to use.
An experiment is reported which used such word fading techniques. It indicated that some readers do have improved reading speed under such conditions, but others do not. The experimental design enabled the separation of that group which did decrease reading times from the remaining readers who did not. Measurement of comprehension errors made under different types of word fading were shown not to increase beyond that obtained under normal reading conditions.
A visualization based on categorising the words in a text document is proposed which contrasts to visualization of measurements based on counts. The result is a visual impression of the word composition, and the evolution of that composition within that document.
The text documents used to demonstrates these techniques include English novels and short stories, emails, and a series of eighteenth century newspaper articles known as the Federalist Papers. This range of documents was needed because all analysis techniques are not applicable to all types of documents. This research proposes that an interactive use of the techniques on hand in a non-prescribed order can yield useful results in a document analysis. An example of this is in author attribution, i.e. assigning authorship of documents via patterns characteristic of an individual's writing style. Different visual techniques can be used to explore the patterns of writing in given text documents.
A software toolkit as a platform for implementing the proposed interactive analysis of text documents is described. How the techniques could be integrated into such a toolkit is outlined. A prototype of software to implement such a toolkit is included in this research. Issues relating to implementation of each technique used are also outlined
Quantum money and scalable 21-cm cosmology
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 165-170).This thesis covers two unrelated topics. The first part of my thesis is about quantum money, a cryptographic protocol in which a mint can generate a quantum state that no one can copy. In public-key quantum money, anyone can verify that a given quantum state came from the mint, and in collision-free quantum money, even the mint cannot generate two valid quantum bills with the same serial number. I present quantum state restoration, a new quantum computing technique that can be used to counterfeit several designs for quantum money. I describe a few other approaches to quantum money, one of which is published, that do not work. I then present a technique that seems to be secure based on a new mathematical object called a component mixer, and I give evidence money using this technique is hard to counterfeit. I describe a way to implement a component mixer and the corresponding quantum money using techniques from knot theory. The second part of my thesis is about 21-cm cosmology and the Fast Fourier transform telescope. With the FFT telescope group at MIT, I worked on a design for a radio telescope that operates between 120 and 200 MHz and will scale to an extremely large number of antennas N. We use an aperture synthesis technique based on Fast Fourier transforms with computational costs proportional toN logN instead of N2. This eliminates the cost of computers as the main limit on the size of a radio interferometer. In this type of telescope, the cost of each antenna matters regardless of how large the telescope becomes, so we focus on reducing the cost of each antenna as much as possible. I discuss the FFT aperture synthesis technique and its equivalence to standard techniques on an evenly spaced grid. I describe analog designs that can reduce the cost per antenna. I give algorithms to analyze raw data from our telescope to help debug and calibrate its components, with particular emphasis on cross-talk between channels and I/Q imbalance. Finally, I present a scalable design for a computer network that can solve the corner-turning problem.by Andrew Lutomirski.Ph.D
Evaluating strut-and-tie models for concrete elements by nonlinear finite element analysis
No full textThe strut-and-tie method (STM) has been acknowledged as one of the most reliable tools for designing discontinuity regions in structural concrete. It is capable of producing safe designs consistently since it was developed as an extension of the lower-bound theorem of plasticity theory. However, to aptly address a physical problem of a concrete element, STM often relies heavily on engineering experience and intuition. It is because the current STM has an inability to be transparent in informing the nonlinear consequences of choosing a certain ST model design, which make the method to be troublesome in more complicated design tasks. In this thesis, a supplementary evaluation technique that employs nonlinear finite element analysis (NLFEA) is proposed as a solution. It is advantageous to incorporate NLFEA because it can provide nonlinear behavior of a structural concrete as objective insights for making a more informed decision in determining a suitable ST model. To incorporate NLFEA to STM, the concept of 'ties-as-extended-rebars' or TER model is introduced. A TER model is a numerical model used to assess the influence of a certain ST model design toward the nonlinear behavior of a concrete element. Through a TER model, an ST model is nonlinearly evaluated as a concrete element with embedded reinforcements. Additionally, to allow the TER model to generate a representative failure, the rebars in the TER model are extended with straight anchorage length. Then, the information generated by the model, i.e. failure mode and ultimate capacity, can be utilized as additional information to find a fitting ST model. To assess its ability, the proposed technique was implemented on six ST models generated for two complex concrete beam elements. The implementation provided the TER model versions of the ST models. At the same time, the experimental results of the ST models were also validated using NLFEA. The validation attempt generated six numerical validation (NV) results, which were then compared with the TER model results. The result of the comparison indicated that five out of six TER models were able to suggest failure mode and ultimate capacity (RTER) that are comparable with the failure mode and ultimate capacity (RNV) from the NV results. In more detail, RNV to RTER ratio of models with similar failure mode has an average of 1.04 and a coefficient of variation of 11.1%, which suggests that the proposed technique can provide representative ultimate capacity value with relatively low variability.Civil Engineering | Structural Engineerin
Transient extreme ultraviolet spectroscopy of semiconductors
No full textTransient extreme ultraviolet (XUV) spectroscopy is used to investigate ultrafast photophysics in lead iodide (PbI2) and methylammonium lead iodide perovskite (MAPbI3). Sub-30 fs pulses of XUV light are produced to use as a probe in a tabletop instrument using high-harmonic generation. PbI2 and MAPbI3 both absorb XUV radiation at the iodine N4,5 edge, which arises from transitions from the core I 4d orbitals to the valence and conduction bands of the semiconductor materials. Static measurements at this edge probe the iodine partial density of states of the conduction band, showing good agreement with spectra predicted using density functional theory (DFT). Excitation in the visible promotes electrons from the valence bands to the conduction bands, resulting in photogenerated charge carriers (holes and electrons). The XUV valence band region shows new transitions from the core states into the unoccupied holes, providing a tool for understanding hole dynamics in semiconductor materials. The transient signals in the XUV conduction band region result from a combination of state-blocking (band-filling) and band-gap renormalization. This can be disentangled but will require further theoretical modeling to fully extract electron dynamics. XUV and optical transient absorption (OTA) together reveal unequal cooling in MAPbI3, with the initial excitation giving more excess energy to the hole distribution than the electron distribution. The distributions show rapid cooling by carrier-phonon coupling in the first few hundred fs followed by slow cooling due to the hot-phonon bottleneck effect for tens to hundreds of ps. The cooling dynamics differ, indicating that the electron-phonon and hole-phonon coupling pathways are independent. Additional modeling and DFT prediction are used to better understand fitting OTA data to extract carrier distributions with unequal energy in each band. It is shown that OTA is more sensitive to the lower energy carrier, or to the lighter carrier for unequal effective masses.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-08-01The student, Max Verkamp, accepted the attached license on 2019-07-05 at 13:27.The student, Max Verkamp, submitted this Dissertation for approval on 2019-07-05 at 13:47.This Dissertation was approved for publication on 2019-07-08 at 11:25.DSpace SAF Submission Ingestion Package generated from Vireo submission #14177 on 2019-11-26 at 13:04:31Made available in DSpace on 2019-11-26T20:49:21Z (GMT). No. of bitstreams: 2
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