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Search Results: 1 - 10 of 231391 matches for " Brian R. Morrison "
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Self-Directed Learning Modules for Independent Learning: IELTS Exam Preparation
Brian R. Morrison
Studies in Self-Access Learning Journal , 2011,
Abstract: Learners studying for exams sometimes show a lack of awareness in their abilities as tested through the framework of that exam. Instead, such learners focus on the score obtained in exams, and exam preparation includes using textbooks, online materials and timed use of past papers. The purpose of exam-focused flexible self-directed learning modules (FSDLMs) at Kanda University of International Studies have been designed to address this by developing learners’ ability to identify their strengths and weaknesses, to make informed decisions about their own learning, and to improve their test-taking skills. Each FSDLM has at its core a diagnostic for learners to use for self-evaluation, often with guidance from a learning advisor. This process leads to the setting of clear goals and the development and implementation of an individual learning plan through a variety of dialogues. Learners have the potential to transfer this skill beyond examination preparation to other areas of learning. In other words, learners’ awareness of needs analysis, planning, implementation and evaluation is fostered with a view to developing their language learning ability within and beyond this module.
Orbifold Resolution by D-Branes
Michael R. Douglas,Brian R. Greene,David R. Morrison
Physics , 1997, DOI: 10.1016/S0550-3213(97)00517-8
Abstract: We study topological properties of the D-brane resolution of three-dimensional orbifold singularities, C^3/Gamma, for finite abelian groups Gamma. The D-brane vacuum moduli space is shown to fill out the background spacetime with Fayet--Iliopoulos parameters controlling the size of the blow-ups. This D-brane vacuum moduli space can be classically described by a gauged linear sigma model, which is shown to be non-generic in a manner that projects out non-geometric regions in its phase diagram, as anticipated from a number of perspectives.
Multiple Mirror Manifolds and Topology Change in String Theory
Paul S. Aspinwall,Brian R. Greene,David R. Morrison
Physics , 1993, DOI: 10.1016/0370-2693(93)91428-P
Abstract: We use mirror symmetry to establish the first concrete arena of spacetime topology change in string theory. In particular, we establish that the {\it quantum theories} based on certain nonlinear sigma models with topologically distinct target spaces can be smoothly connected even though classically a physical singularity would be encountered. We accomplish this by rephrasing the description of these nonlinear sigma models in terms of their mirror manifold partners--a description in which the full quantum theory can be described exactly using lowest order geometrical methods. We establish that, for the known class of mirror manifolds, the moduli space of the corresponding conformal field theory requires not just two but {\it numerous} topologically distinct Calabi-Yau manifolds for its geometric interpretation. A {\it single} family of continuously connected conformal theories thereby probes a host of topologically distinct geometrical spaces giving rise to {\it multiple mirror manifolds}.
The Monomial-Divisor Mirror Map
Paul S. Aspinwall,Brian R. Greene,David R. Morrison
Physics , 1993,
Abstract: For each family of Calabi-Yau hypersurfaces in toric varieties, Batyrev has proposed a possible mirror partner (which is also a family of Calabi-Yau hypersurfaces). We explain a natural construction of the isomorphism between certain Hodge groups of these hypersurfaces, as predicted by mirror symmetry, which we call the monomial-divisor mirror map. We indicate how this map can be interpreted as the differential of the expected mirror isomorphism between the moduli spaces of the two Calabi-Yau manifolds. We formulate a very precise conjecture about the form of that mirror isomorphism, which when combined with some earlier conjectures of the third author would completely specify it. We then conclude that the moduli spaces of the nonlinear sigma models whose targets are the different birational models of a Calabi-Yau space should be connected by analytic continuation, and that further analytic continuation should lead to moduli spaces of other kinds of conformal field theories. (This last conclusion was first drawn by Witten.)
Measuring Small Distances in N=2 Sigma Models
Paul S. Aspinwall,Brian R. Greene,David R. Morrison
Physics , 1993, DOI: 10.1016/0550-3213(94)90379-4
Abstract: We analyze global aspects of the moduli space of K\"ahler forms for $N$=(2,2) conformal $\sigma$-models. Using algebraic methods and mirror symmetry we study extensions of the mathematical notion of length (as specified by a K\"ahler structure) to conformal field theory and calculate the way in which lengths change as the moduli fields are varied along distinguished paths in the moduli space. We find strong evidence supporting the notion that, in the robust setting of quantum Calabi-Yau moduli space, string theory restricts the set of possible K\"ahler forms by enforcing ``minimal length'' scales, provided that topology change is properly taken into account. Some lengths, however, may shrink to zero. We also compare stringy geometry to classical general relativity in this context.
Black Hole Condensation and the Unification of String Vacua
Brian R. Greene,David R. Morrison,Andrew Strominger
Physics , 1995, DOI: 10.1016/0550-3213(95)00371-X
Abstract: It is argued that black hole condensation can occur at conifold singularities in the moduli space of type II Calabi--Yau string vacua. The condensate signals a smooth transition to a new Calabi--Yau space with different Euler characteristic and Hodge numbers. In this manner string theory unifies the moduli spaces of many or possibly all Calabi--Yau vacua. Elementary string states and black holes are smoothly interchanged under the transitions, and therefore cannot be invariantly distinguished. Furthermore, the transitions establish the existence of mirror symmetry for many or possibly all Calabi--Yau manifolds.
A Geometric Realization of Confinement
Brian R. Greene,David R. Morrison,Cumrun Vafa
Physics , 1996, DOI: 10.1016/S0550-3213(96)00465-8
Abstract: We study the geometric realization of the Higgs phenomenon in type II string compactifications on Calabi--Yau manifolds. The string description is most directly phrased in terms of confinement of magnetic flux, with magnetic charged states arising from D-branes wrapped around chains as opposed to cycles. The rest of the closed cycle of the D-brane worldvolume is manifested as a confining flux tube emanating from the magnetic charges, in the uncompactified space. We also study corrections to hypermultiplet moduli for type II compactifications, in particular for type IIA near the conifold point.
Mirror Manifolds in Higher Dimension
Brian R. Greene,David R. Morrison,M. Ronen Plesser
Physics , 1994, DOI: 10.1007/BF02101657
Abstract: We describe mirror manifolds in dimensions different from the familiar case of complex threefolds. We emphasize the simplifying features of dimension three and supply more robust methods that do not rely on such special characteristics and hence naturally generalize to other dimensions. The moduli spaces for Calabi--Yau $d$-folds are somewhat different from the ``special K\"ahler manifolds'' which had occurred for $d=3$, and we indicate the new geometrical structures which arise. We formulate and apply procedures which allow for the construction of mirror maps and the calculation of order-by-order instanton corrections to Yukawa couplings. Mathematically, these corrections are expected to correspond to calculating Chern classes of various parameter spaces (Hilbert schemes) for rational curves on Calabi--Yau manifolds. Our results agree with those obtained by more traditional mathematical methods in the limited number of cases for which the latter analysis can be carried out. Finally, we make explicit some striking relations between instanton corrections for various Yukawa couplings, derived from the associativity of the operator product algebra.
Breast cancer stem cells: implications for therapy of breast cancer
Brian J Morrison, Chris W Schmidt, Sunil R Lakhani, Brent A Reynolds, J Alejandro Lopez
Breast Cancer Research , 2008, DOI: 10.1186/bcr2111
Abstract: The past decades have seen advances in the diagnosis and treatment of breast cancer. Despite this progress, breast cancer is still a leading cause of cancer-related deaths among women, with as many as 40% relapsing with metastatic disease [1]. Breast cancer survival rates have been shown to plateau after 7 to 10 years, whereas most cancer survival curves take between 2 and 5 years to plateau [2]. The length of time for the survival rate to plateau in breast cancer might indicate the involvement of a cell type capable of disease recurrence which is able to withstand primary treatment and reside in the body, often undetected, for prolonged periods. Interestingly, it has been shown that, of the 40% of patients with lymph node involvement who did not undergo surgical removal, only 15% had recurrence of disease [3]. This raises the point that immune system surveillance of tumours or other protective mechanisms of the body might be capable of controlling breast cancer relapses.Prominent in the breast cancer field has been the notion of the existence of a transformed population of cells with many of the properties of stem cells that may be responsible for the origin and maintenance of tumours. These stem cell-like cells, designated as cancer stem cells, represent a minor subset of cells in the tumour and are distinct from the more differentiated tumour cells. It is thought that these cancer stem cells may play an important role in cancer establishment, progression, and resistance to current treatments. Traditional cancer therapies are effective at debulking some tumours but often fail to produce long-term clinical remissions, possibly due to their inability to eradicate the cancer stem cell population. Therefore, novel treatments aimed at targeting the cancer stem cell population could find use in treating both primary and metastatic tumours.Therapies aimed at targeting cancer stem cells may prove clinically relevant in inducing long-term clinical remission of cancer. A va
Payoffs, Not Tradeoffs, in the Adaptation of a Virus to Ostensibly Conflicting Selective Pressures
Lindsey W. McGee,Erick W. Aitchison,S. Brian Caudle,Anneliese J. Morrison,Lianqing Zheng,Wei Yang,Darin R. Rokyta
PLOS Genetics , 2014, DOI: doi/10.1371/journal.pgen.1004611
Abstract: The genetic architecture of many phenotypic traits is such that genes often contribute to multiple traits, and mutations in these genes can therefore affect multiple phenotypes. These pleiotropic interactions often manifest as tradeoffs between traits where improvement in one property entails a cost in another. The life cycles of many pathogens include periods of growth within a host punctuated with transmission events, such as passage through a digestive tract or a passive stage of exposure in the environment. Populations exposed to such fluctuating selective pressures are expected to acquire mutations showing tradeoffs between reproduction within and survival outside of a host. We selected for individual mutations under fluctuating selective pressures for a ssDNA microvirid bacteriophage by alternating selection for increased growth rate with selection on biophysical properties of the phage capsid in high-temperature or low-pH conditions. Surprisingly, none of the seven unique mutations identified showed a pleiotropic cost; they all improved both growth rate and pH or temperature stability, suggesting that single mutations even in a simple genetic system can simultaneously improve two distinct traits. Selection on growth rate alone revealed tradeoffs, but some mutations still benefited both traits. Tradeoffs were therefore prevalent when selection acted on a single trait, but payoffs resulted when multiple traits were selected for simultaneously. We employed a molecular-dynamics simulation method to determine the mechanisms underlying beneficial effects for three heat-shock mutations. All three mutations significantly enhanced the affinities of protein-protein interfacial bindings, thereby improving capsid stability. The ancestral residues at the mutation sites did not contribute to protein-protein interfacial binding, indicating that these sites acquired a new function. Computational models, such as those used here, may be used in future work not only as predictive tools for mutational effects on protein stability but, ultimately, for evolution.
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