Magnetization and spin-spin energy diffusion in the XY model: a diagrammatic approach

It is shown that the diagrammatic cluster expansion technique for equilibrium averages of spin operators may be straightforwardly extended to the calculation of time-dependent correlation functions of spin operators. We use this technique to calculate exactly the first two non-vanishing moments of the spin-spin and energy-energy correlation functions of the XY model with arbitrary couplings, in the long-wavelength, infinite temperature limit appropriate for spin diffusion. These moments are then used to estimate the magnetization and spin-spin energy diffusion coefficients of the model using a phenomenological theory of Redfield. Qualitative agreement is obtained with recent experiments measuring diffusion of dipolar energy in calcium fluoride.Comment: 28 pages, 15 embedded .eps figures, Elsevier preprint forma

Call for Standardization in Patent Claim Drafting

Call for Standardization in Patent Claim Draftin

Quantum spin transport in paramagnetic systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 87-90).We have studied the transport of magnetization and energy in systems of spins 1/2 on a lattice at high temperature. This work was motivated by recent experiments which observed "spin diffusion" among the dipolar coupled nuclear spins of the insulator calcium fluoride, under conditions where it was appropriate to neglect the coupling to any heat reservoir. The dynamics under these conditions is coherent and reversible, yet signatures of irreversibility (i.e. diffusion) are typically observed. This state of affairs poses a formidable conceptual puzzle. In this thesis we present both phenomenological and microscopic models of spin diffusion, retaining the important aspects of statistical approaches to transport while incorporating relevant quantum effects. These methods allow an efficient calculation of energy diffusion for a long- range interaction, which has largely been an intractable problem. We study transport in two different limits, that where the XY term of the spin Hamiltonian is dominant, and that where it can be treated as a perturbation compared to the Ising term. In the case of dipolar couping, both limits are found to show slightly more rapid diffusion of inter spin energy than magnetization, in qualitative agreement with experiments.by Daniel Greenbaum.Ph.D

An investigation of the mismatch hypothesis for the Boston metropolitan area.

Massachusetts Institute of Technology. Dept. of Urban Studies and Planning. Thesis. 1973. B.S.Bibliography: leaves 59-60.B.S

Planning in its political context : developing organizational strategies for the planning agency.

Thesis. 1975. M.C.P.--Massachusetts Institute of Technology. Dept. of Urban Studies and Planning.Bibliography: leaves 178-180.M.C.P

Efficient quantum circuits for diagonal unitaries without ancillas

The accurate evaluation of diagonal unitary operators is often the most resource-intensive element of quantum algorithms such as real-space quantum simulation and Grover search. Efficient circuits have been demonstrated in some cases but generally require ancilla registers, which can dominate the qubit resources. In this paper, we point out a correspondence between Walsh functions and basis for diagonal operators that gives a simple way to construct efficient circuits for diagonal unitaries without ancillas. This correspondence reduces the problem of constructing the minimal-depth circuit within a given error tolerance, for an arbitrary diagonal unitary eif(ˆx) in the |xi basis, to that of finding the minimal-length Walsh-series approximation to the function f(x). We apply this approach to the quantum simulation of the classical Eckart barrier problem of quantum chemistry, demonstrating that high-fidelity quantum simulations can be achieved with few qubits and low depth.Chemistry and Chemical BiologyPhysic

Nonlinear Quantum Dynamics

The vast majority of the literature dealing with quantum dynamics is concerned with linear evolution of the wave function or the density matrix. A complete dynamical description requires a full understanding of the evolution of measured quantum systems, necessary to explain actual experimental results. The dynamics of such systems is intrinsically nonlinear even at the level of distribution functions, both classically as well as quantum mechanically. Aside from being physically more complete, this treatment reveals the existence of dynamical regimes, such as chaos, that have no counterpart in the linear case. Here, we present a short introductory review of some of these aspects, with a few illustrative results and examples.Comment: 13 pages, 3 figures, invited talk at the NATO Advanced Workshop, "Nonlinear Dynamics and Fundamental Interactions," (October, 2004, Tashkent

Penalized Orthogonal Iteration for Sparse Estimation of Generalized Eigenvalue Problem

We propose a new algorithm for sparse estimation of eigenvectors in generalized eigenvalue problems (GEP). The GEP arises in a number of modern data-analytic situations and statistical methods, including principal component analysis (PCA), multiclass linear discriminant analysis (LDA), canonical correlation analysis (CCA), sufficient dimension reduction (SDR) and invariant co-ordinate selection. We propose to modify the standard generalized orthogonal iteration with a sparsity-inducing penalty for the eigenvectors. To achieve this goal, we generalize the equation-solving step of orthogonal iteration to a penalized convex optimization problem. The resulting algorithm, called penalized orthogonal iteration, provides accurate estimation of the true eigenspace, when it is sparse. Also proposed is a computationally more efficient alternative, which works well for PCA and LDA problems. Numerical studies reveal that the proposed algorithms are competitive, and that our tuning procedure works well. We demonstrate applications of the proposed algorithm to obtain sparse estimates for PCA, multiclass LDA, CCA and SDR. Supplementary materials are available online

Identification and Characterization of an Activating F229V Substitution in the V2 Vasopressin Receptor in an Infant with NSIAD

Gain-of-function mutations in the gene encoding the V2 vasopressin receptor (V2R) cause nephrogenic syndrome of inappropriate antidiuresis. To date, reported mutations lead to the substitution of arginine 137 by either a cysteine or leucine (R137C/L). Here, we describe a 3-month-old hyponatremic infant found to have a phenylalanine 229 to valine (F229V) substitution in V2R. Characterization of this substitution in vitro revealed that it leads to high constitutive activity of the receptor, compatible with spontaneous antidiuresis. In contrast to R137C/L mutant receptors, F229V receptors do not undergo spontaneous desensitization, which results in sustained, high basal activity. Notably, the V2R-selective inverse agonists tolvaptan and satavaptan completely silenced the constitutive signaling activity of the F229V mutant receptor, indicating that this substitution does not lock the receptor in an irreversible active state. Thus, inverse agonists might prove to be effective therapies for treating patients with this or other spontaneously activating mutations that do not lock the V2R in its active state. These results emphasize the importance of genetic testing and the functional characterization of mutant receptors for patients with nephrogenic syndrome of inappropriate antidiuresis because the results might inform treatment decisions

Analysis of transcript and protein overlap in a human osteosarcoma cell line

<p>Abstract</p> <p>Background</p> <p>An interesting field of research in genomics and proteomics is to compare the overlap between the transcriptome and the proteome. Recently, the tools to analyse gene and protein expression on a whole-genome scale have been improved, including the availability of the new generation sequencing instruments and high-throughput antibody-based methods to analyze the presence and localization of proteins. In this study, we used massive transcriptome sequencing (RNA-seq) to investigate the transcriptome of a human osteosarcoma cell line and compared the expression levels with <it>in situ </it>protein data obtained in-situ from antibody-based immunohistochemistry (IHC) and immunofluorescence microscopy (IF).</p> <p>Results</p> <p>A large-scale analysis based on 2749 genes was performed, corresponding to approximately 13% of the protein coding genes in the human genome. We found the presence of both RNA and proteins to a large fraction of the analyzed genes with 60% of the analyzed human genes detected by all three methods. Only 34 genes (1.2%) were not detected on the transcriptional or protein level with any method. Our data suggest that the majority of the human genes are expressed at detectable transcript or protein levels in this cell line. Since the reliability of antibodies depends on possible cross-reactivity, we compared the RNA and protein data using antibodies with different reliability scores based on various criteria, including Western blot analysis. Gene products detected in all three platforms generally have good antibody validation scores, while those detected only by antibodies, but not by RNA sequencing, generally consist of more low-scoring antibodies.</p> <p>Conclusion</p> <p>This suggests that some antibodies are staining the cells in an unspecific manner, and that assessment of transcript presence by RNA-seq can provide guidance for validation of the corresponding antibodies.</p