Magnetization reversal in mesoscopic Ni80Fe20 wires: A magnetic domain launching device

The magnetization reversal process in mesoscopic permalloy (Ni80Fe20) wire structures has been investigated using scanning Kerr microscopy, magnetic force microscopy (MFM) and micromagnetic calculations. We find that the junction offers a site for reversed domain wall nucleation in the narrow part of the wires. As a consequence, the switching field is dominated by the domain nucleation field and the junction region initiates reversal by the wall motion following the nucleation of domains. Our results suggest the possibility of designing structures that can be used to “launch” reverse domains in narrow wires within a controlled field rang

Bingham sealing and application in vacuum clamping

Vacuum clamping is extensively used in shell machining. In this paper a Bingham Sealing (BS) is presented and formulized based on Bingham plastic performance. The sealing capability of BS is evaluated in various cases. A new Bingham plastic is developed and the yield stress is measured. The performances of "O"ring sealing and BS with the developed Bingham plastic are compared to the static experiment. In this experiment the same vacuum is achieved and the distortion of the blade with BS is better than that with "O" ring sealing

Impacts of large quantities of wind energy on the electric power system

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 146-149).Wind energy has been surging on a global scale. Significant penetration of wind energy is expected to take place in the power system, bringing new challenges because of the variability and uncertainty of this renewable resource. Therefore, the understanding of how wind energy could affect a power system is of great significance to system operators, regulators, investors and policy makers. This thesis explores both the long-term and the short-term potential impacts of large quantities of wind energy on power systems. Two computer based models and an analytical model are used or developed as the primary tools for this thesis. Among the models, the ReEDS model is used to project the power system capacity expansion for the ERCOT case and the contiguous US case, under different C02 policy scenarios, for the long-term analysis. The Memphis model is used to simulate in high resolution the operation of a well adapted system for both the ERCOT case and the Spanish case, for the short-term analysis. Sensitivity analyses are also performed to investigate the responses of a power system to different penetration levels of wind energy, as well as to operating reserve requirements. Further, the representation at the operation level in ReEDS is assessed by benchmarking with Memphis. It is concluded in the thesis that in the long term, wind energy is less likely to grow without C02 emission restrictions. The power system could experience significant transition to one that is sufficiently reliable to accommodate a strong penetration of wind energy. Sufficient investment in flexible generation capacity will be necessary to back wind energy. In the short term, an increase of wind energy will displace the marginal technology. Different operating reserve requirements also affect the decision of generators between producing and being idle to provide reserves. Therefore, for system security and reliability, adequate regulatory and policy measures should be adopted to orient investment and operation decisions. Last, the benchmarking results show that ReEDS provides fair representations of the power system at the operational level.by Yuan Yao.S.M.in Technology and Polic

Artistic tactics and attitudes for operations of architecture in the expanded field

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 249-252).Historically the study of architecture has experienced reiterative marriage and divorce with the arts. Some avant-garde architects once tried to flirt with the arts in the late of twentieth century by artwork analysis and philosophical exploration, but the result unwillingly belies the architects' reluctant surrender - artists seem constantly capable of bringing about innovative pieces with sharp insight and inspiration, while architects strive to question the world but only come up with mimicry form. What is more is that the influence of this incompetence has directly or indirectly led to the current common ignorance of art in the architectural world. My thesis interrogates the traditional perspective considering architecture served as a vehicle of art and proposes a new equality between the identity of art and that of architecture. The thesis argues that the "technical support" coined by Rosalind Krauss in the post-medium condition of art is also a support that confirms or modifies the perceptual and mental process of intellectual creation of architecture. It is not about the "brilliant" idea architecture has to convey but the meditation about the mechanism and "supports" permitting them to act on an idea - the rudiments of a language that express their attitude towards the world. The thesis uses my observations and understandings on diverse examples from contemporary art and architecture practice not as models to imitate but illustrations of what specific "technical support" might signify. Then it employs semiotic square as the generative diagram to compare and distinguish these mechanism and hence to look for a more open, flexible "support" for an architectural practice that is confident in its own modes of operation and intrinsic disciplinary knowledge. The narrative of this thesis is in a form of but not only limited in 'know-how' report for practice but also present a process to communicate my intellectual adventures of what I think of what I have already seen and what I still have not seen, so that the reader can learn by the same process and rely on the explosive power of the semiotic square to search for a continual source of innovation and change.by Yao Zhang.S.M

Text localization in natural images through effective re identification of the MSER

© 2017 Association for Computing Machinery. Text detection and recognition from images have numerous applications for document analysis and information retrieval tasks. An accurate and robust method for detecting texts in natural scene images is proposed in this paper. Text-region candidates are detected using maximally stable extremal regions (MSER) and a machine learning based method is then applied to refine and validate the initial detection. The effectiveness of features based on aspect ratio, GLSM, LBP, HOG descriptors are investigated. Text-region classifiers of MLP, SVM and RF are trained using selections of these features and their combination. A publicly available multilingual dataset ICDAR 2003,2011 has been used to evaluate the method. The proposed method achieved excellent performance on both databases and the improvements are significant in terms of Precision, Recall, and F-measure. The results show that using a suitable feature combination and selection approach can can significantly increase the accuracy of the algorithms

A learning approach for prioritized handoff channel allocation in mobile multimedia networks

An efficient channel allocation policy that prioritizes handoffs is an indispensable ingredient in future cellular networks in order to support multimedia traffic while ensuring quality of service requirements (QoS). In this paper we study the application of a reinforcement-learning algorithm to develop an alternative channel allocation scheme in mobile cellular networks that supports multiple heterogeneous traffic classes. The proposed scheme prioritizes handoff call requests over new calls and provides differentiated services for different traffic classes with diverse characteristics and quality of service requirements. Furthermore, it is asymptotically optimal, computationally inexpensive, model-free, and can adapt to changing traffic conditions. Simulations are provided to compare the effectiveness of the proposed algorithm with other known resource-sharing policies such as complete sharing and reservation policies

A learning approach for prioritized handoff channel allocation in mobile multimedia networks

An efficient channel allocation policy that prioritizes handoffs is an indispensable ingredient in future cellular networks in order to support multimedia traffic while ensuring quality of service requirements (QoS). In this paper we study the application of a reinforcement-learning algorithm to develop an alternative channel allocation scheme in mobile cellular networks that supports multiple heterogeneous traffic classes. The proposed scheme prioritizes handoff call requests over new calls and provides differentiated services for different traffic classes with diverse characteristics and quality of service requirements. Furthermore, it is asymptotically optimal, computationally inexpensive, model-free, and can adapt to changing traffic conditions. Simulations are provided to compare the effectiveness of the proposed algorithm with other known resource-sharing policies such as complete sharing and reservation policies

Resonant thermal transport in semiconductor barrier structures

I report that thermal single-barrier (TSB) and thermal double-barrier (TDB) structures (formed, for example, by inserting one or two regions of a few Ge monolayers in Si) provide both a suppression of the phonon transport as well as a resonant-thermal-transport effect. I show that high-frequency phonons can experience a traditional double-barrier resonant tunneling in the TDB structures while the formation of Fabry-Perot resonances (at lower frequencies) causes quantum oscillations in the temperature variation of both the TSB and TDB thermal conductances $\sigma_{\text{TSB}}$ and $\sigma_{\text{TDB}}$.Comment: 4 pages. 4 figure.

T violation and the unidirectionality of time

An increasing number of experiments at the Belle, BNL, CERN, DA{\Phi}NE and SLAC accelerators are confirming the violation of time reversal invariance (T). The violation signifies a fundamental asymmetry between the past and future and calls for a major shift in the way we think about time. Here we show that processes which violate T symmetry induce destructive interference between different paths that the universe can take through time. The interference eliminates all paths except for two that represent continuously forwards and continuously backwards time evolution. Evidence from the accelerator experiments indicates which path the universe is effectively following. This work may provide fresh insight into the long-standing problem of modeling the dynamics of T violation processes. It suggests that T violation has previously unknown, large-scale physical effects and that these effects underlie the origin of the unidirectionality of time. It may have implications for the Wheeler-DeWitt equation of canonical quantum gravity. Finally it provides a view of the quantum nature of time itself.Comment: 24 pages, 5 figures. Final version accepted for publishing in Foundations of Physics. The final publication is available at http://www.springerlink.com/content/y3h4174jw2w78322

Bounds and optimisation of orbital angular momentum bandwidths within parametric down-conversion systems

The measurement of high-dimensional entangled states of orbital angular momentum prepared by spontaneous parametric down-conversion can be considered in two separate stages: a generation stage and a detection stage. Given a certain number of generated modes, the number of measured modes is determined by the measurement apparatus. We derive a simple relationship between the generation and detection parameters and the number of measured entangled modes.Comment: 6 pages, 4 figure